Synthesis, Structure and Applications of Hypervalent Organoantimony

0 downloads 0 Views 2MB Size Report
These compounds have shown many applications in organic synthesis. They are useful ... and property of this kind of compounds have been widely investigated both experimen- ... organoantimony compound containing pendant-arm ligand 2- ... der Waals radii (3.74 Å) [48], indicating hypervalent bonding be- tween the Sb ...
Send Orders of Reprints at [email protected] 2462

Current Organic Chemistry, 2012, 16, 2462-2481

Synthesis, Structure and Applications of Hypervalent Organoantimony Compounds Having Intramolecular ESb (E = N, O, S) Coordinations Nianyuan Tan1, 2, Yi Chen1,3, Shuangfeng Yin1,*, Renhua Qiu1, Yongbo Zhou1 and C.T. Au1, 4 1

College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, PR China

2

College of Chemistry and Chemical Engineering, Hunan Institute of Engineering, Xiangtan 411104, PR China

3

School of Basic Medicine, Hunan University of Chinese Medicine, Changsha 410208, PR China

4

Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong, PR China Abstract: The review article covers the hypervalent organoantimony compounds that are with intramolecular N, O, SSb coordinations synthesized in the past 20 years. We describe their structures and the related coordination chemistry, highlighting a number of hypervalent stibines. These compounds have shown many applications in organic synthesis. They are useful reagents for reactions such as crosscoupling and arylation with organic halides, and addition with carbonyl compounds. They can be used as Lewis acid catalysts in organic synthesis. Furthermore, they can be utilized as catalysts or reagents for CO2 chemical fixation. It is envisaged that more hypervalent organoantimony compounds of novel structure will be synthesized and find new applications in the near future.

Keywords: Organoantimony, Hypervalent compounds, Intramolecular coordination, Organic synthesis, Structure, Reagent, Catalyst. 1. INTRODUCTION In 1850, Löwig and Schweizer synthesized triethylantimony and that started the organoantimony chemistry [1]. However, triethylantimony is spontaneously flammable in air, and it is not until 1882 that the development of organoantimony chemistry began when air-stable triphenylantimony was synthesized by Michaelis and Reese [2]. Since then, a large number of organoantimony compounds of trivalent and pentavalent states were synthesized, and used in areas such as medicine [3], catalysis [4-6], organic synthesis [7-10] and ligand chemistry [11-13]. However, wide application is restricted due to the unstable nature of the compounds, a result of being air-sensitive and/or ligand scrambling. Recent development shows that with the avoidance of bulky ligands such as (Me3Si)2CH [14], and 2,6-Mes2C6H3 [15], the use of aryl ligands with one or two pendant arms (e.g. 2-(Me2NCH2)C6H4 [16-19], 2,6(Me2NCH2)2C6H3 [20, 21], and 2,6-(ROCH2)2C6H3 (R = Me, t-Bu [22]), as well as those ortho-substituted with CH2NMe2 [23, 24]) or analogous ligands such as RN(CH2C6H4)2 (R = Me, t-Bu, cyclohexyl, Ph [25]) and S(CH2C6H4)2 [26] is a common strategy to generate stable organoantimony compounds. In all cases, intramolecular N, O, SSb coordinations were observed in solution and/or solid state. With a valence-shell configuration of 5s25p3, antimony commonly displays +3 and +5 oxidation states but +1 is also known. The coordination of the ligands with the antimony center through the carbon atom of the aryl group as well as through the N, O, S atom of the pendant arm would result in high stability. With more than eight valence-shell electrons, these organoantimony compounds are considered to be hypervalent [27, 28]. It was in 1969 that Musher introduced the concept of hypervalent molecules [27]. Since then, hypervalent compounds of main group elements such as silicon, phosphorus, sulfur, and iodine have

been synthesized. The structure, reactivity, and property of this kind of compounds have been widely investigated both experimentally and theoretically [29-33]. The outcome enables us to know more about the nature of hypervalent organoantimony compounds, especially those with intramolecular N, O, SSb coordinations [34-39]. In the monograph edited by Akiba in 1999 on hypervalent compounds, the static and dynamic structures of hypervalent Sb (III) halides were only briefly presented (by Yamada and Okuda) [33]. Since then, we have learnt more about hypervalency, and how is that related to the structural feature and chemical activity of hypervalent compounds. In this review article, we focused on the chemistry of hypervalent organoantimony compounds with intramolecular N, O, SSb coordinations. The objective is to conduct a survey on the synthesis, structural characterization, and applications of this class of compounds. 2. SYNTHESIS AND STRUCTURE OF HYPERVALENT ORGANOANTIMONY COMPOUNDS WITH INTRAMOLECULAR N, O, SSb INTERACTIONS 2.1. Hypervalent Organoantimony Intramolecular NSb Interaction

Compounds

with

Among the hypervalent organoantimony compounds with intramolecular interaction, organoantimony compounds with intramolecular NSb coordinations attracted considerable attention in the past 20 years. Yamamoto et al. reported the first hypervalent organoantimony compound containing pendant-arm ligand 2(Me2NCH2)C6H4 in 1992 [40]. Almost all the hypervalent organoantimony compounds with intramolecular NSb interaction reported so far are trivalent compounds, though a few pentavalent and monovalent compounds have also been reported [37, 41-44]. 2.1.1. Triorganostibines(III)

* Address correspondence to this author at the College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, PR China; Tel: +86-731-88821310; Fax: +86-731-88821310; E-mail: [email protected] 15-8/12 $58.00+.00

The first example of hypervalent homoleptic triorganostibines with intramolecular NSb interaction was reported by Kamepalli et al. in 1996 [45]. The Ar3Sb [Ar = 2-(Me2NCH2)C6H4] (1) was © 2012 Bentham Science Publishers

Synthesis, Structure and Applications of Hypervalent Organoantimony

Current Organic Chemistry, 2012, Vol. 16, No. 20 2463

Scheme 1. Synthesis of the triorganostibines [(Me2NCHR)C 6H4] 3Sb.

H

CH3

N

(R)-4-dimethyl benzylamine

O

Sb H

3

3

CH3

Sb

H

3

N

(R)-2-aminobutan-1ol / CHCl3

HO Sb 3

4

Scheme 2. Synthesis of the hypervalent triorganostibines 3 and 4.

Compounds 5-10

prepared via salt elimination reaction of ArLi with antimony trichloride (Scheme 1). In triorganostibine compounds, antimony is usually in trivalent state, having three covalently bonded substituents and a lone pair of valence electrons to complete the electron octet. However, it is known that the antimony of compound 1 further interacts with the nitrogen atom of pendant amino group, giving a 14-Sb-6 (N-X-L designation: X, central atom; N, valence-shell electrons of X; L, number of ligands [46]) hypervalent organoantimony species with three NSb coordinations. As revealed in single-crystal XRD analysis, compound 1 crystallizes in P21 space group with two independent molecules per asymmetric unit. It is worth noting that compound 1 shows polymorphism, and according to Sharma et al., it crystallizes in P21/n space group [17]. The length of the three intramolecular N–Sb bond in compound 1 ranging from 2.974(4) to 3.022(4) Å, is larger than the sum of the covalent radii (2.11 Å) [47] but slightly shorter than the sum of the van der Waals radii (3.74 Å) [48], indicating hypervalent bonding between the Sb and N atoms. The central antimony-containing part of compound 1 exhibits a structure of distorted octahedron. In the case of hypervalent triorganostibine Ar3Sb [Ar = 2-(Me2NCHMe)C6H4] (2) synthesized by Sharma et al. [17], there are only two intramolecular NSb coordinations [Sb(1)–N(1) 2.988(5) Å and Sb(1)–N(2) 2.920(4) Å], one less in comparison to compound 1. It is understandable because the bulk of 3 methyl groups would hin-

der further NSb coordination, resulting in the 12-Sb-5 hypervalent organoantimony species. The geometry of the antimony centre is that of a  octahedron where one of the vertices is occupied by a lone pair of electrons. In 2007, Sharma et al. reported for the first time examples of antimoniated schiff bases, viz. 1-[2-(bis-{2-[(1-R-ptolylethylimino)methyl]phenyl}stibanyl)benz-E-ilidene]-(1-R-ptolylethyl)amine (3) and tris[(R) -2-benzyliden-2-yl-amino)butan-1ol]stibine (4) containing imino groups at the ortho position of aryl group [49]. Compounds 3 and 4 were obtained by the reaction of tris(o-formylphenyl)stibine with R-4-dimethyl benzyl amine or (R)2-aminobutan-1-ol, respectively (Scheme 2). The molecular structures of compounds 3 and 4 were determined by single-crystal XRD analysis. The three intramolecular NSb interactions in compounds 3 and 4 are nearly equivalent, the average value of N–Sb bond lengths is 2.922 Å for 3 and 2.870 Å for 4. Taking into account the electron lone-pair of antimony and the three intramolecular coordination bonds, the geometry of the antimony centre of compounds 3 and 4 can be described as that of a distorted pentagonal bipyramid. Reacting organoantimony halides with Grignard reagents or organolithium reagents, Breunig and co-workers synthesized six unsymmetric stibines with two or three different organic groups,

2464

Current Organic Chemistry, 2012, Vol. 16, No. 20

Tan et al.

Scheme 3. Synthetic route for the hypervalent triorganostibines 11a-c.

CH3

RMgBr

Sb Ph

p-Tol

CH3

NMe2

Li

Sb

R = a: Ph b: 1-naphthyl c: 9-phenanthryl

s

p-Tol

s

R

Ph

NMe2

Sb

p-Tol

R

Ph

12a-c

O N p-Tol Sb

Ph

O N

Li Sb

1-naphthyl

p-Tol

1-naphthyl 13

Scheme 4. Synthetic route for Sb-chiral organoantimony compounds 12a-c and 13.

i.e. [2-(Me2NCH2)C6H4]nR3-nSb [n = 1, R = Ph (5), Mes (6); n = 2, R = Ph (7), Mes (8), CH2SiMe3 (9)] and [2(Me2NCH2)C6H4]PhMesSb (10) [50, 51]. Compounds 5-10 exhibit chirality and crystallize as racemic mixtures. The molecular structures of compounds 5, 7, 9 and 10 were determined by singlecrystal XRD analysis. For compounds 5 and 10, the N–Sb distances were found to be 2.848(4) and 2.923(9) Å, respectively. In compounds 5 and 10, there is only one intramolecular NSb coordination, giving hypervalent 10-Sb-4 species of distorted pseudotrigonal-bipyramidal structure. There are two intramolecular NSb coordinations in the antimony center of compounds 7 and 9, resulting in hypervalent 12-Sb-5 species. A common feature for compounds 7 and 9 is that the nitrogen atoms of the pendant arm from both organic groups establish intramolecular NSb interactions of different strengths. The N(1) atom coordinates stronger in the trans position to the C atom of the phenyl or CH2SiMe3 group [Sb(1)– N(1) 2.920(3) Å for 7, Sb(1)–N(1) 2.971(3) Å for 9 ], whereas the N(2) atom exhibits a weaker interaction in the trans position to the C atom of the other aromatic substituent [Sb(1)–N(2) 3.042(3) Å for 7, Sb(1)–N(2) 3.189(3) Å for 9]. Taking into account both intramolecular NSb interactions, the overall coordination geometry around antimony in compounds 7 and 9 can be described as distorted square pyramid. In 2000, Kurita and co-workers prepared three 10-Sb-4 hypervalent organoantimony (III) compounds 11a-c bearing a phenyl or naphthyl substituent with NMe2 or CH2NMe2 in the ortho-position [42]. Compounds 11a-c were prepared via the lithium compounds obtained through the reaction of the corresponding amine precursors with n-BuLi, followed by reaction with bromodi(p-tolyl)stibine (Scheme 3). Single-crystal XRD analysis revealed that the N–Sb

distances of these compounds were 2.874(6), 2.831(6) and 2.766(4) Å, respectively, which were 69 to 77% of the sum of the corresponding van der Waals radii, suggesting strong intramolecular NSb interactions. This was also confirmed by the semi-empirical theoretical calculations [42], 1H-13C and 1H-15N heteronuclear multiple bond correlation (HMBC) experiments [52], and cyclic voltammetry [53]. The overall geometry at antimony in compounds 11a-c is that of pseudo-trigonal bipyramidal structure. Kurita and co-workers recently reported the synthesis of Sbchiral triarylstibines (12a-c), having intramolecular NSb coordinations generated by stepwise nucleophilic displacement of the ethynyl groups on diethynylstibanes with Grignard and organolithium reagents (Scheme 4) [19]. Single-crystal XRD analysis of 12b revealed that there is intramolecular interaction between the antimony and nitrogen atom, and the N–Sb distance in 12b is 2.886(5) Å. It is described that the antimony centre is of pseudo-trigonal bipyramidal structure. Subsequently, they prepared enantiomerically pure Sb-chiral organoantimony compounds 13 bearing 4,4dimethyl-2-oxazolinyl substituents on the ortho-position of the phenyl group (Scheme 4) [54]. The molecular structure of 13 is analogous to that of 12b; the N–Sb distance in 13 is 2.813(4) Å. In 2006, Sharma et al. reported the first example of ferrocenylstibines displaying intramolecular NSb interactions [24]. Two ferrocenylstibines containing pendant arm [2-(Me2NCHR)] [R = H (14) or Me (15)] on ferrocenyl ring were prepared via a salt elimination reaction of 2-lithiated (N, N-dimethylamino)methylferrocene or (N,N-dimethylamino)ethylferrocene with Ph2SbCl (Scheme 5). According to single-crystal XRD analysis of 14 and 15, there is no intramolecular NSb interaction in heterobimetallic stibine 14, while stibine 15 is stabilized by NSb intramolecular interaction.

Synthesis, Structure and Applications of Hypervalent Organoantimony

R

Current Organic Chemistry, 2012, Vol. 16, No. 20 2465

NMe2 Li

Me2 N

H3C

NMe2 SbPh2 Ph2SbCl

Fe

SbPh2 or

Fe

Fe

14: R = H

15: R = CH3

Scheme 5. Preparation of ferrocenylstibines 14 and 15 NHR SbPh2 RNH2

NMe3I

NMe2

16a-c

Fe

SbPh2

SbPh2 MeI

K2CO3/CH3CN

NR'2

Fe

Fe

SbPh2 R'2NH

14

17a-c

Fe

O O HN

NH Ph2Sb

SbPh2

NH Ph2Sb

Fe

Fe

Fe

16a

16b

16c

OH

N

N SbPh2 Fe

17a

HO

Br

N

Ph2Sb

OH SbPh2

Fe

Fe

17b

17c

Scheme 6. Synthetic route for ferrocenylstibines 16a-c and 17a-c.

The N–Sb distance in 15 is 3.042(2) Å, which is shorter than the sum of Van der Waals radii, but is much longer than the corresponding covalent bond length. The antimony centre in compound 15 exhibits a pseudo-trigonal bipyramidal structure.

trigonal bipyramidal structure. Furthermore, there is intermolecular hydrogen bonding O–H…O [2.922(4) Å] in ferrocenylstibine 17c, forming a pseudo dimer in solid state.

Subsequently, Sharma and co-workers reported the synthesis of ferrocenylstibines 16a-c and 17a-c, and had them characterized by various physicochemical methods [55]. Shown in Scheme 6 are the synthetic routes for these compounds. According to the results of single-crystal XRD analysis, there is weak hypervalent NSb interaction in stibine 16a [2.989(3) Å], 17a [3.287(3) Å] and 17c [3.59(2) Å], whereas stibine 16b does not show such interaction in solid state. Taking into account the intramolecular NSb interaction, the geometry around antimony in 16a, 17a and 17c is pseudo-

Organoantimony(III) halides are important starting materials for organometallic syntheses. The preparative and structural aspects of them have been studied for a long time. They can be prepared by methods such as redistribution, halogen exchange, and salt elimination of organometallic reagents with antimony trihalides. In 1997, Carmalt et al. reported the syntheses and structures of diarylantimony(III) monochlorides 18, 19 and monoarylantimony dichloride 20 [23]. The compounds (18-20) were prepared via the salt elimination reaction of ArLi (Ar = 2-(Me2NCH2)C6H4, or 8-(Me2N)C10H6)

2.1.2. Organoantimony Halides(III)

2466

Current Organic Chemistry, 2012, Vol. 16, No. 20

Tan et al.

Scheme 7. Synthesis of organoantimony chlorides 18-20.

Scheme 8. The methods for synthesis of organoantimony halides 18, 21-25.

Scheme 9. Synthesis of organoantimony chlorides 26 and 27.

with SbCl3 in 2:1 or 1:1 molar ratio (Scheme 7). The results of single-crystal XRD analysis of compound 18 revealed that the nitrogen atom of one of the pendant amino groups is strongly coordinated to antimony [Sb(1)–N(1) 2.463(2) Å], while the nitrogen atom of the other group exhibits weak intramolecular interaction [Sb(1)–N(2) 3.216(3) Å]. Taking into account of two intramolecular NSb interactions, the geometry of the antimony centre of compound 18 can be described as distorted square pyramidal. The molecular structure of compound 19 resembles that of compound 18, with the corresponding N–Sb distances being 2.519(4) and 2.903(4) Å, respectively. Very recently, Olaru et al. reported that there is intramolecular C-H…Cl hydrogen bonding in compound 18 [56]. In the solid-state structure of compound 20, it is found that there is strong interaction between the amine arm and the antimony centre [Sb(1)–N(1) 2.460(4) Å]. In 2003, Opris et al. reported their investigation on hypervalent antimony halides of the type Ar2SbX [X = Cl (18), Br (21), I (22)] and ArSbX2 [X = Cl (23), Br (24), I (25)] [Ar = 2(Me2NCH2)C6H4] [18]. Shown in scheme 8 are the methods employed for their synthesis. According to the results of single-crystal XRD analysis, compounds 21 and 22 show molecular structures similar to that of compound 18, having the nitrogen atom of a pendant arm strongly coordinated to antimony [Sb(1)–N(1) 2.423(3) Å for 21 and Sb(1)–N(1) 2.417(3) Å for 22], while the nitrogen atom of the other pendant arm only weakly coordinated to antimony [Sb(1)–N(2) 3.276(3) Å for 21 and Sb(1)–N(2) 3.211(3) Å for 22].

It is worth noting that the 1H NMR spectrum of diarylantimony chloride 22 displayed one set of broad signals at ambient temperature, but resolved into two sets of signals at –60 °C. The results confirmed that the two organic ligands are nonequivalent and there are different degrees of intramolecular NSb coordination in diarylantimony chloride 22. The NMR finding is consistent with the results of single-crystal XRD analysis. In the cases of organoantimony halides 23-25, there is strong intramolecular NSb interaction, and the corresponding N–Sb distances are 2.407(5), 2.409(3) and 2.408(4) Å, respectively. The geometry around the antimony atom in compounds 23-25 can be described as pseudo-trigonal bipyramidal structure. Very recently, Dostál et al. reported the formation of organoantimony monochloride 26 and dichloride 27 [57]. These compounds having ketimino pendant arm(s) with a phenyl group were synthesized by salt elimination reaction of in situ-prepared ArLi {Ar = [oC6H4(CH=NC6H3iPr2-2,6)]} and SbCl3 (Scheme 9). The molecular structure of 26 is similar to that of 18, 21 and 22, while the crystal structure of 27 resembles that of dihalides 23, 24 and 25. The two N–Sb distances in compound 26 are 2.416(2) and 2.952(3) Å, while the N–Sb distance in compound 27 is 2.416(2) Å. The 1H NMR results of compounds 26 and 27 also suggested that the ligands are nonequivalent in the structure of 26, and there is a molecular NSb coordination in 27. In 2003, Breunig et al. reported the structure of unsymmetrical organoantimony chloride ArRSbCl (28) [Ar = 2-(Me2NCH2)C6H4,

Synthesis, Structure and Applications of Hypervalent Organoantimony

Current Organic Chemistry, 2012, Vol. 16, No. 20 2467

NMe2

NMe2 SbCl2

2-(Me2NCH2)C6H4Sn(n-Bu)2F

SbF2 NMe2

NMe2 36

37

Scheme 13. Synthesis of organoantimony difluoride 37. Scheme 10. Synthesis of organoantimony halides 29-32.

Scheme 11. Synthesis of hypervalent compounds 33-35.

Scheme 12. Synthesis of organoantimony dichloride 36.

R = (Me3Si)2CH], that was obtained by the reaction of ArLi with RSbCl2 [58]. Single-crystal XRD analysis revealed that 28 crystallizes as racemate, and there is a strong intramolecular coordination of the pendant amino group to the Sb centre. The N–Sb distance of 2.533(7) Å is between the sums of the corresponding covalent and van der Waals radii. The antimony centre in 28 adopts the distorted pseudo-trigonal bipyramidal geometry. In subsequent works of Breunig and co-workers, there was the synthesis of analogous unsymmetrical organoantimony halides 2932 [50]. Synthetic routes of these compounds are shown in scheme 10. According to the results of NMR and single-crystal XRD analyses, there is strong coordination of the nitrogen atom of pendant arm to the Sb atom. The N–Sb distance in 30a, 30b, 31 and 32 is 2.444(4), 2.426(3), 2.468(4) and 2.456(4) Å, respectively. The antimony centre in all four halides adopts a distorted pseudo-trigonal bipyramidal structure. The compounds can be described as hypervalent 10-Sb-4 species. Sharma and co-workers recently reported the syntheses and structures of ferrocenylstibines 33-35 [59, 60]. Ferrocenylstibines 33 and 34 were prepared via salt elimination reaction of 2-lithiated (N,N-dimethylamino)methylferrocene or (N,N-dimethylamino) ethylferrocene in 2:1 molar ratio with SbCl3, and subsequent reaction of 34 with MeI afforded the generation of iodo-(N,Ndimethylaminoethylferrocenyl)(2-vinylferrocenyl)stibine 35

(Scheme 11). The molecular structures of 33, 34 and 35 were confirmed by single-crystal XRD analysis. There are hypervalent N–Sb bonds in the ferrocenylstibines, and the corresponding N–Sb distances for 33, 34 and 35 are 2.553(2), 2.584(5) and 2.646(5) Å, respectively. Despite very weak in strength, there exists another hypervalent N–Sb interaction [3.614(6) Å] in compound 34; the compound shows tetragonal bipyramidal geometry around the antimony atom. The first example of organoantimony compound [2,6(Me2NCH2)2C6H3]SbCl2 (36) containing NCN picer ligand with two amino groups was given by Atwood et al. in 1992 [20]. The compound was prepared by reacting [2,6-(Me2NCH2)2C6H3]Li with SbCl3 (Scheme 12). The structure of 36 was determined by singlecrystal XRD analysis. The two N–Sb distances are 2.491(9) and 2.422(8) Å, which are slightly longer than the sum of the covalent radii (2.11 Å) [47] but much shorter than the sum of the van der Waals radii (3.74 Å) [48], indicating hypervalent bonding between the antimony and each of the two nitrogen atoms. The Cl(l)-SbCl(2) angle (174.0 o) is close to the ideal angle of 180 o, but the N(l)-Sb-N(2) angle is significantly acute (147.3 o). The geometry around the antimony atom can be described as distorted square pyramidal structure. Recently, Dostál et al. prepared and characterized organoantimony difluorides 37 containing pincer ligand [2,6(Me2NCH2)2C6H3] using organoantimony dichloride 36 as precursor [61]. Then difluoride 37 was synthesized by treating dichloride 36 with 2 equiv of 2-(Me2NCH2)C6H4Sn(n-Bu)2F (Scheme 13). This is the first report on monoorgano-derivatives RMF2 containing two metal–fluorine terminal bonds. The N–Sb distances in 37 are 2.560(3) and 2.588(3) Å, longer than those of 36 (2.491(9) and 2.422(8) Å), indicating that the strength of intramolecular NSb interactions in 37 is significantly weaker than that of 36. The geometry around the central antimony atom is that of a strongly distorted square pyramid, and the F(1)–Sb(1)–F(2) angle is 81.20 o. In subsequent work of Dostál and co-workers, it was found that the reaction of dimeric organoantimony(III) oxide (ArSbO)2 [Ar = 2,6(Me2NCH2)2C6H3] with HBF4 also afforded the formation of difluoride 37, but not the desired organoantimony tetrafluoroborate [62]. The reaction mechanism is somewhat ambiguous. Interestingly, compound 37 also shows polymorphism [17], and crystallizes in P21/c [62] and P-1 space groups [61]. In the 1980s, Akiba and co-workers reported the synthesis of 12-chloro-6-methyl-5,6,7,12-tetrahydrodibenzo[c,f][1,5]azastibocine (38) and other 12-substituted derivatives (39, 40 and 41a-d) [43, 63]. The compounds were prepared by the procedure shown in Scheme 14. Chloride 38 was synthesized by dilithiation of tertiary amines with n-BuLi followed by subsequent reaction with SbCl3. Fluoride 39 and iodide 40 were obtained by halogen exchange reactions of chloride 38 with KF or KI. Treatment of halides 38 with appropriate organolithium reagents furnished the corresponding 12substituted derivatives 41a-d. The hypervalent NSb bonding in the organoantimony compounds was confirmed by NMR examina-

2468

Current Organic Chemistry, 2012, Vol. 16, No. 20

Tan et al.

Scheme 14. Synthetic route for organoantimony compounds 38-40, and 41a-d.

Scheme 15. Synthetic route for organoantimony compounds 42-45.

Scheme 16. Synthesis of compounds 46-50.

tion. There was downfield shift of 1H and 13C NMR signals of the methyl group on nitrogen atom of 38-40 and 41a-d caused by the substituents on the antimony atom, and the chemical shift showed linear relationship against the Hammett's m constants of substituents. The results suggest that the hypervalent bonds are flexible and affected by the substituents. All these compounds are regarded as 10-Sb-4 hypervalent. In 2006, Kakusawa et al. reported the synthesis of 12-bromotetrahydrodibenz[c,f][1,5] azastibocines 42a-g and 12-ethynyltetrahydrodibenz[c,f][1,5]azastibocines 43a-g, 44 and 45 [25]. Modifying the method of Akiba and co-workers [43, 63], they derived a route for the synthesis of these compounds. Briefly, reacting dilithiation of tertiary amines (obtained via reaction of primary amines with o-bromobenzylbromide) with n-BuLi followed by subsequent reaction with SbBr3 would afford the generation of bromides 42a-g (Scheme 15). Treatment of the bromides with appropriate lithium acetylides gave ethynyl-1,5-azastibocines 43a-g, 44 and 45. Only the structure of compound 43a was determined by single-crystal XRD analysis. The distance between N and Sb of 43a is 2.538(4) Å, which is slightly larger than the sum of the covalent

radii (2.11 Å) [47] but significantly shorter than the sum of the van der Waals radii (3.74 Å) [48], indicating the existence of strong hypervalent bonding between nitrogen and antimony atoms. Very recently, Yin and co-worker prepared and structurally characterized three 12-chloro-tetrahydrodibenzo[c,f][1,5]azastibocines 46-48 [64-66]. Chlorides 46-48 were synthesized using the method of Akiba and coworkers (Scheme 16). The reaction of chlorides 46 with AgBF4 gave fluoride 49 rather than tetrafluoroborate, whereas analogous reaction of organobismuth chloride with silver tetrafluoroborate would lead to the formation of organobismouth tetrafluoroborate [67]. A similar situation was observed when organoantimony(III) oxide (ArSbO)2 [Ar = 2,6-(Me2NCH2)2C6H3] reacted with HBF4 [62]. The desired organoantimony triflate 50 was obtained when compound 47 reacted with AgOSO2CF3, and it was reported that triflate 50 could be used as a Lewis acid catalyst [64]. Single-crystal XRD analysis of compounds 46-50 showed that there is strong intramolecular NSb interactions in these organoantimony compounds, and the N–Sb distances are 2.466(2) Å for 46, 2.397(3) Å for 47, 2.467(2) Å for 48, 2.522(2) Å for 49 and 2.331(4) Å for 50. The antimony centre of compounds 46-50 exhib-

Synthesis, Structure and Applications of Hypervalent Organoantimony

Current Organic Chemistry, 2012, Vol. 16, No. 20 2469

Scheme 17. Synthetic route for chalcogen derivatives of Sb(III) 51 – 56.

its a pseudo-trigonal bipyramidal geometry. Fig. (1) shows the molecular structure of 49 as determined by single-crystal XRD analysis.

organoantimony(III) species 53, 54, 55 and 56 are very similar. It features two metal centres bridged by a chalcogen atom, and there is strong intramolecular NSb coordination trans to the Sb– halogen bond. The N–Sb distances of these compounds vary from 2.382(4) to 2.660(4) Å.

Fig. (1). A thermal ellipsoid plot (30% probability level) of compound 49.

2.1.3. Chalcogen Derivatives of Sb(III)

Fig. (2). A thermal ellipsoid plot (30% probability level) of compound 51, and hydrogen atoms are omitted for clarity.

The principal organoantimony(III) chalcogen derivatives of Sb(III) bearing intramolecular NSb interactions are compounds of (ArSbE)n types (n = 1, 2, 3), (Ar2Sb)2E, (ArSbX)2E and ArSb(OH)(OR) (E = group 16 element, X = Cl, Br, I). In 2004, Opris et al. synthesized and characterized organoantimony(III) chalcogen derivatives containing the 2-(Me2NCH2)C6H4 group 5156 [68]. Synthetic routes of these compounds are shown in Scheme 17. Single-crystal XRD analysis revealed that the core of crystalline cyclo-[2-(Me2NCH2)C6H4SbO]3 (51) is a distorted boat-shaped 6membered Sb3O3 ring with the Sb(2) and O(3) atom at the apices (Fig. 2), while the core of crystalline trans-[2-(Me2NCH2) C6H4SbS]2 (52) is a 4-membered Sb2S2 planar ring, with the ligands occupying the trans positions (Fig. 3). Compound 52 is the first reported stable cyclo-(RSbS)2 compound. The molecular units of Fig. (3). A thermal ellipsoid plot (30% probability level) of compound 52, and hydrogen atoms are omitted for clarity.

Scheme 18. Synthesis of compounds 57 and 58.

Reduction of monobromide Ar2SbBr [Ar = 2-(Me2NCH2)C6H4] with Mg in THF gave the distibane Ar2Sb–SbAr2, which was converted in situ into (Ar2Sb)2E [E = O (57), S (58)] by air oxidation or treatment with elemental sulfur, respectively (Scheme 18) [51]. Sulfide 58 was also obtained from Ar2SbCl with an excess amount of Na2S in water/toluene. The 57 and 58 crystals show that the ni-

2470

Current Organic Chemistry, 2012, Vol. 16, No. 20

Scheme 19. Synthesis of compounds 59-62.

Scheme 20. Synthesis of ArSbE 63 and 64.

Scheme 21. Synthesis of ArSbE 65 and 66.

trogen atom of one of the pendant arms is strongly coordinated to antimony [Sb(1)–N(1) 2.775(5) Å for 57 and Sb(1)–N(1) 2.855(3) Å for 58], while the nitrogen atom of the other pendant arm exhibits only weak intramolecular interaction [Sb(1)–N(2) 3.240(4) Å for 57 and Sb(1)–N(2) 3.026(3) Å for 58], resulting in a distorted squarepyramidal geometry around the Sb atom in 57 and 58. Dostál et al. recently reported that four-membered heterocycles trans-(ArSbE)2 [Ar = 2,6-(Me2NCH2)2C6H3, R =O (59), S(60)] were formed by reacting ArSbCl2 with KOH or M2S (M = Na or Li) in water/toluene mixture (Scheme 19) [69, 70]. The dimeric oxide 59 reacted with CO2 in a toluene solution to give carbonate ArSbCO3 (61) (Scheme 19). In order to demonstrate that the antimony sulfide (ArSbS)2 (60) dissociates in solution to monomeric species ArSbS with a terminal Sb-S bond, trithiocarbonate ArSbS2C=S (62) was obtained by treating 60 in CH2Cl2 solution with an excess amount of CS2 (Scheme 19) [71]. The molecular structures of all four compounds were determined by single-crystal XRD analysis. It was found that compounds 59 and 60 are in the form of centrosymmetric dimmer with a core of 4-membered Sb2O2 or Sb2S2 ring, and both NCN pincer ligands located mutually in the trans position. The most interesting feature of the molecular structures of 61 and 62 is coordination of the carbonate moiety as a terminal ligand in a fashion of chelating four-membered SbCO2 or SbCS2 ring. All nitrogen donor atoms of the NCN pincer ligands in compounds 59-62 are coordinated to the central Sb through intramolecular interactions [range of Sb–N bond lengths: 2.467(3)-2.800(3) Å].

Scheme 22. Preparation of compounds 67- 69.

Tan et al.

In recent work of Dostál and co-workers, four organoantimony derivatives of the heavier chalcogens of ArSbE types {Ar = 2,6(Me2NCH2)2C6H3, E = S (63) , Se (64) and Ar = 2,6-bis[N-(2',6'dimethylphenyl)ketimino]phenyl, E = S (65) , Se (66)} were synthesized [21, 72]. Compounds 63 and 64 were obtained by the reaction of tetrameric Sb4Ar4 with an excess amount of elemental selenium and tellurium in THF (Scheme 20). Compounds 65 and 66 were formed by elimination of salt from ArSbCl2 and Li2E (Scheme 21). Single-crystal XRD analyses revealed that all four compounds are monomeric. There are no close intermolecular contacts between chalcogen atoms and other atoms in the unit cell, indicating wellisolated and well-preserved Sb-S (65), Sb-Se (63, 66) and Sb-Te (64) terminal bonds. As a consequence of the presence of strong intramolecular SbN interactions [range of Sb–N bond lengths: 2.393(2)-2.526(5) Å], the coordination geometry around the antimony atoms can be described as distorted pseudo-trigonal bipyramid. Dostál and co-workers claimed that organoantimony hydroxides ArSb(OH)(X) [Ar = 2,6-(CH2NMe2)2C6H3, X=CF3CO2 (67),CF3SO3 (68)] could be obtained by treating dimeric organoantimony (III) oxide (ArSbO)2 (59) with trifluoroacetic acid and trifluoromethanesulfonic acid (Scheme 22) [62]. On the other hand, analogous reactions with acetic acid resulted in the formation of ArSb(CH3CO2)2(69), which could also be prepared via the reaction of dichloride ArSbCl2 (36) with silver acetate (Scheme 22) [62, 73]. The molecular structures of compounds 67-69 were determined by single-crystal XRD analysis. Compound 67 crystallizes in P21/c space group but compound 68 was shown to crystallize in either P1 or P21/c space group. The molecular structures of 67 and 68 could be described as an ionic pair consisting of organoantimony cation [ArSb(OH)]+ and CF3CO2- or OTf- anion that are connected through a Sb–OH…O hydrogen bond. The geometry around the central antimony atom Sb in the organoantimony cation is a distorted pseudo-trigonal bipyramid due to the tridentate bonding mode of NCN ligand. In compound 69, both nitrogen atoms coordinated to the central atom via intramolecular interaction, showing N–Sb distances of 2.674(3) and 2.588(3) Å. 2.1.4. Organoantimony Containing Phosphorus and Arsenic There were studies on organophosphinates and organophosphonates of Sb and Bi but reports on isolated and well-defined compounds of this type are few [39, 74, 75]. Recently, Dostál and co-workers [39, 76, 77] reacted oxide (ArSbO)2 (59) [Ar = 2,6-(CH2NMe2)2C6H3] with selected phosphonic acids to give the corresponding phosphates, phosphites or phosphintaes 70-75. The molecular structures of compounds 70b, 70c, 72, 74 and 75 were determined by single-crystal XRD analysis. In 70b, 70c and 72, the central antimony atom is coordinated by the NCN chelating ligand in a tridentate fashion [range of Sb–N bond lengths in 70b, 70c and 72: 2.385(7)–2.464(8) Å]; the geome-

Synthesis, Structure and Applications of Hypervalent Organoantimony

O

O

R P

O

Current Organic Chemistry, 2012, Vol. 16, No. 20 2471

OH

ArSb O

OH

P

R

O

R = Et (a),

P O

O P ArSb O P O

OH H 73

t-Bu

O

P O

O O ArSb

H P

H H Ph

72

71

H OH

P

ArSb

t-Bu(c)

70a-c

O

O

O ArSb

Ph (b),

Ph

O

NMe2

O SbAr

O

P O O H 74

(ArSb)3(PO4)2

Ar =

NMe2 75

Compounds 70-75.

Compounds 76-79.

try around the central Sb atom can be described as a strongly distorted tetragonal pyramid with the ipso carbon atom C1 occupying the apical position. Fig. (4) shows the molecular structure of 72 as determined by single-crystal XRD analysis. Compound 74 has a dinuclear molecular structure with a central boat-shaped eightmembered Sb2P2O4 ring. In compound 74, the NCN ligand is coordinated in a tridenate fashion to the central Sb atom, showing N–Sb distances of 2.613(5) and 2.543(7) Å. In compound 75, there is the bridging of phosphate moieties by ArSb, and the settings are symmetrically arranged around the central girdle (Fig. 5). All of the nitrogen atoms of the pendant arms are coordinated to the central antimony atoms, with Sb–N bond lengths falling within the 2.593(4)-2.647(4) Å range. As a consequence of NSb interaction, the coordination around each antimony atom exhibits geometry of distorted square pyramid with the ipso carbon atom located at the apical position. Treatment of compounds 71 and 74 with selected phosphonic acids gave the compounds containing phosphorus 7679 [39, 76].

Fig. (5). A thermal ellipsoid plot (30% probability level) of compound 75, and hydrogen atoms are omitted for clarity.

Fig. (4). A thermal ellipsoid plot (30% probability level) of compound 72, and hydrogen atoms except those bonded to phosphorus atoms are omitted for clarity.

Recently, Dostál and co-workers reported the preparation of well-defined mixed Sb/As oxido compounds 80 and 81 containing an AsOSb linkage by reacting oxide (ArSbO)2 (59) [Ar = 2,6(CH2NMe2)2C6H3] with As2O5 and As2O3, respectively (Scheme 23) [78]. The result of crystal determination of 80 revealed only disordered structure. The 1H NMR spectrum of 80 exhibited two sets of signals, suggesting that compound 80 formed two conformers in solution, analogous to phosphate compound 75. The molecular structure of compound 81 was determined by single-crystal XRD analysis. The core of central Sb2As2O5 girdle was divided into

2472

Current Organic Chemistry, 2012, Vol. 16, No. 20

Tan et al.

O As2O5 (3:2)

ArSb

O O

O

ArSb O

O

SbAr ArSb O O As

80

As2O3

O

As

O

As

NMe2

O

O

ArSb

(1:1)

NMe2 Ar =

O

SbAr

59

As

O

SbAr

81

O

Scheme 23. Preparation of compounds 80 and 81.

two six-membered rings SbAs2O3 by an AsOAs bridge. Interestingly, whereas one of these rings adopted a chair-like conformation, the other adopted a boat-like configuration (Fig. 6).

Scheme 24. Preparation of diorganoantimony cation 82.

Fig. (6). A thermal ellipsoid plot (30% probability level) of compound 81, and hydrogen atoms are omitted for clarity.

2.1.5. Organoantimony Cations In 1997, Carmalt et al. reported the preparation and structural characterization of a cationic organoantimony complex (82) stabilized by intramolecular NSb coordinations [79]. Compound 82 was prepared by reacting TlPF6 with diarylantimony(III) monochloride 18 at room temperature (Scheme 24). The structure of compound 82 in solid state was determined by single-crystal XRD analysis. Compound 82 comprises [Ar2Sb]+ [Ar = 2(Me2NCH2)C6H4] cation and hexafluorophosphate anions (PF6-). In the cationic part of compound 82, both amine arms of the aryl ligand coordinate strongly to the Sb centre, and the Sb–N bond lengths are 2.412(3) and 2.416(4) Å. The coordination geometry of the central Sb atom is that of a pseudo-trigonal bipyramid. Dostál et al. recently reported the synthesis and structure of two cationic compounds 83 and 84 [73]. The reaction of organoantimony chloride 36 with AgCB11H12 in 2:1 or 1:1 molar ratio gave 83 and 84, respectively. Single-crystal XRD analysis of compound 83 revealed that the cationic part consists of two distorted tetragonal pyramids around the two central antimony atoms Sb(1) and Sb(2)

Scheme 25. Synthesis of monoorganoantimony cations 83 and 84.

Fig. (7). A thermal ellipsoid plot (30% probability level) of compound 83, and hydrogen atoms are omitted for clarity.

that share an apex [Cl(3)] (Fig. 7). A Sb(1)–Cl(3)–Sb(2) bond angle of 165.34(5)o shows that the bridge is not exactly linear. Interestingly, the bond distances between terminal chlorine atoms and the antimony atoms [Sb(1)–Cl(1) 2.4362(14) Å and Sb(2)–Cl(2) 2.4333(14) Å] are close to the sum of covalent radii for single covalent bond (2.45 Å), but the other Cl-Sb bond lengths [Cl(3)–Sb(1) and Cl(3)–Sb(2): 2.9454(14) Å] are significantly longer than the sum of covalent radii. The CB11H12- anion is well separated from the organoantimony cation [ArSbCl]+ cation in compound 84. The NCN pincer ligand strongly coordinated to the Sb atom, and the

Synthesis, Structure and Applications of Hypervalent Organoantimony

Current Organic Chemistry, 2012, Vol. 16, No. 20 2473

Scheme 26. Preparation of distibines 85 and 86.

Scheme 27. Preparation of compounds 90 and 91.

Sb–N bond lengths are 2.379(5) and 2.422(4) Å. The overall geometry around the Sb atom can be described as a distorted pseudotrigonal bipyramid. 2.1.6. Distibines In 2009, Jura et al. reported distibines 85 and 86 having intramolecular NSb interaction [80]. They were prepared by dilithiation of the corresponding precursor with n-BuLi, followed by subsequent reaction with Me2SbCl (Scheme 26), and their application as Sb donor ligand has been reported [38, 80]. 2.1.7. Organoantimony Compounds with Sb–Sb Bonds The known organoantimony compounds with Sb–Sb bonds bearing intramolecular NSb interactions are distibines Ar2SbSbAr2, cyclostibines Ar4Sb4 and polycycles R5Sb3. In 2004, Opris et al. reported the synthesis of four-membered cyclo-Ar4Sb4 (87) [Ar = 2-(Me2NCH2)C6H4] by reacting ArSbCl2 with Mg in THF or with Na in liquid NH3 [68]. The compound is tetrameric in molecular structure, showing a central Sb4 ring. All nitrogen atoms of the pendant amino arm are weakly coordinated to the central antimony atoms, giving N–Sb distances of 3.040(3), 2.996(4), 2.915(3) and 2.958(3) Å. The geometry around the antimony atoms is distorted pseudo-trigonal bipyramid with a neighbouring antimony atom and nitrogen atom located at axial positions. Dostál et al. recently reported the synthesis and structure of cyclo-Ar4Sb4 (88) and distibine Ar2SbSbAr2 [Ar = [oC6H4(CH=NC6H3iPr2-2,6)] (89) [57]. Compound 88 was obtained by reacting chloride ArSbCl2 with K[B(sBu)3H], while compound 89 was generated by the reduction of Ar2SbCl with Mg. The structure of compound 88 is similar to that of compound 87. In compound 89, only three of the four ligand arms are coordinated to antimony atoms [Sb1–N1 3.018(4), Sb1–N2 2.979(4), Sb2–N3 2.877(4) Å] as a result of steric repulsion amidst the four ligands. In 2008 Dostál et al. reported the synthesis and structures of Ar3Sb5 (90), which is the first organoantimony cluster of the general formula R3Sb5, and Ar4Sb4 (91) [Ar = 2,6-(Me2NCH2)2C6H3] [81]. The reaction of ArSbCl2 (36) with K[B(i-Bu)3H] (Scheme 27) gave, depending on the reaction time, a mixture of two products: 90 and tetrameric Sb4Ar4 (91) (10 min), or compound 91 as a sole product (24 h). The molecular structure of 90 was determined by

Fig. (8). A thermal ellipsoid plot (30% probability level) of compound 90, and hydrogen atoms are omitted for clarity.

single-crystal XRD analysis and shows a trigonal-bipyramidal framework of five antimony atoms. The overall geometry of the Sb5 core is very close to D3h symmetry (Fig. 8). Regarding the six SbN intramolecular coordinations, the Sb-N bond distances are in the region 2.826(7)-3.143(6) Å, approaching the limit of weak intramolecular interaction. Compound 91 is formed as a cyclic tetramer and closely resembles the structure of tetrameric N,Cchelated analogue Sb4Ar4 (87). 2.1.8. Monomeric Compounds of RM Type Recently, Dostál and co-worker synthesized and structurally characterized monomeric compound ArSb {Ar = 2,6-bis[N-(2’,6’dimethylphenyl)ketimino]phenyl} (92) [44]. Synthetic route for compound 92 is shown in Scheme 28. The starting ArSbCl2 was prepared by metathesis of ArLi and SbCl3. Subsequent reaction of ArSbCl2 with K[B(i-Bu)3H] resulted in the generation of compound 92. This is the first report on the isolation and structural characterization of monomeric compounds RM type (stibinidenes). The results of single-crystal XRD analysis showed that the two N atoms in compound 92 are intramolecularly coordinated to the Sb center with N–Sb distances of 2.352(3) and 2.346(3) Å.

2474

Current Organic Chemistry, 2012, Vol. 16, No. 20

Tan et al.

2.2. Hypervalent Organoantimony with Intramolecular O, SSb Interactions

sum of their van der Waals radii. The geometry around the antimony atom is distorted pseudo-trigonal bipyramid where the two carbon atoms bound to Sb occupying the equatorial plane. In order to examine the activation of aryl group linked to antimony through intramolecular non-bonding interaction between antimony and oxygen (or sulfur), Kakusawa et al. synthesized 12phenyl-7,12-dihydro-5H-dibenzo[c,f][1,5]oxa- (96) and thiastibocine (97) [26]. The oxastibocine (96) was prepared from bis(2bromobenzyl) ether through treatment with n-BuLi, followed by addition of dibromophenyl-antimony (PhSbBr2) (Scheme 30). A similar method was applied for the preparation of thiastibocine (97) from bis(2-bromobenzyl) sulfide. Very recently, Levason and co-workers reported the synthesis of distibine 98 bearing intramolecular SSb interaction [38]. Compound 98 was obtained by dilithiation of bis(2-bromobenzyl) sulfide with n-BuLi followed by subsequent reaction with Me2SbCl (Scheme 31). Levason and co-workers also reported the application of distibine 98 as Sb donor ligand [38, 80, 83].

2.2.1. Stibines(III)

2.2.2. Halides(III)

In a study by Sharma et al., two organoantimony compounds 94 and 95 containing intramolecular OSb coordinations were synthesized [82]. Synthetic routes for compounds 94 and 95 are shown in Scheme 29. Stibine 93 was obtained by reacting o-lithiated benzaldehyde diethylacetal with SbCl3, and acidic hydrolysis of stibine 93 yielded tris(2-formylphenyl)stibine (94). Subsequently, the reduction of stibine 93 with NaBH4 gave oxastibol (95). The molecular structures of 94 and 95 were confirmed by single-crystal XRD analysis. Compound 94 crystallizes into two different forms: trigonal form with P-3 space group (3a) and rhombohedral form with R3 space group (3b). In both polymorphs, there are three OSb intramolecular coordinations [O–Sb distances: 2.883(3)-2.899(15) Å], and the formyl groups adopt O-cis-exo conformation. In compound 95 (10-Sb-4), the distance between the oxygen atom of OH group and the central antimony is 2.458(3) Å, much shorter than the

Recently, Dostál and co-workers synthesized and structurally characterized monoarylantimony dihalides containing OCO pincer ligands 99a-c, 100a-b and 101a-b [22, 61, 84]. The 99a-c dichlorides were prepared via the lithiation of appropriate OCO pincer ligands with n-BuLi and subsequent reaction with SbCl3 (Scheme 32). The reaction of dichlorides 99a-b with NaI or Me3SnF resulted in the generation of diiodides 100a-b and difluorides 101a-b (Scheme 33). The molecular structures of dihalides 99a-c, 100a-b and 101a-b were determined by single-crystal XRD analysis. Both oxygen donor atoms in all dihalides are coordinated to the central metal through intramolecular interactions, and the O–Sb bond lengths varied from 2.279(2) to 2.343(2) Å. For these compounds, the overall coordination polyhedron around the central Sb atom can be described as a distorted square pyramid.

Scheme 28. Synthetic route for compound 92.

Scheme 29. Synthetic route for compounds 93 – 95.

1) n-BuLi

E Br

2) PhSbBr2

Br

E Sb Ph 96: E = O

97: E = S

Scheme 30. Synthesis of compounds 96 and 97.

S Br

S

1) n-BuLi Br

2) Me2SbCl

Sb

Sb 98

Scheme 31. Synthesis of compound 98.

Synthesis, Structure and Applications of Hypervalent Organoantimony

Scheme 32. Synthesis of compounds 99a-c.

Scheme 33. Synthesis of compounds 100a-b and 101a-b.

Scheme 34. Synthesis of compounds 102a-b.

Scheme 35. Synthesis of compounds 103, 104a-c.

Utilizing the NCO hybrid pincer ligands, Dostál and coworkers extended their study on intramolecularly stabilized organoantimony compounds [85, 86]. The dichlorides 102a-b containing NCO pincer ligands were synthesized through lithiation of the corresponding precursor followed by subsequent reaction with SbCl3 (Scheme 34). The most interesting structural feature of dichlorides 102a-b is the existence of both OSb and NSb interactions between Sb atoms and oxygen/nitrogen within a single

Scheme 36. Synthetic route for compounds 105 and 106a-c.

Current Organic Chemistry, 2012, Vol. 16, No. 20 2475

molecule. The bond distances between donor and the central atoms [Sb1–O1 2.469(4), Sb1–N1 2.315(5) Å for 102a and Sb1–O1 2.485(2), Sb1–N1 2.336(3) Å for 102b] indicate strong intramolecular interactions, very close to those observed in organoantimony compounds containing OCO or NCN ligands [20, 22]. In a recent study of Dostál et al., diorganoantimony chloride Ar2SbCl [Ar = 2,6-(ROCH2)2C6H3] (103) and its derivatives (104ac) were synthesized [87]. Compound 103 was obtained by the reaction of organolithium compound ArLi with SbCl3 in 2:1 molar ratio (Scheme 35). Treatment of compound 103 with selected lithium acetylides resulted in the formation of the corresponding derivatives 104a-c (Scheme 35). The molecular structures of compounds 103, 104a and 104b were determined by single-crystal XRD analysis. Only one of the oxygen atoms of each ligand in compounds 103, 104a and 104b is coordinated to the central Sb atom, with O– Sb distances ranging from 2.6999(15) to 2.980(3) Å. The whole coordination geometry around the Sb atom of all these compounds might be described as a trigonal pyramid. 12-Bromo-7,12-dihydro-5H-dibenzo[c,f][1,5]oxastibocine (105) and other 12-substituted derivatives (106a-c) were first reported by Kakusawa et al. in 2006 [25]. Bromide 105 was prepared by dilithiation of bis(2-bromobenzyl) ether with n-BuLi, followed by subsequent reaction with SbBr3 (Scheme 36). Treatment of bromide 105 with appropriate lithium acetylides gave ethynyl-1,5oxastibocines (106a-c) (Scheme 36). 2.2.3. Organoantimony(III) Suflides, Carboxylates, Triflates and Cations Treatment of the chlorides 99a-c and Na2S in toluene/water resulted in the formation of the corresponding organoantimony(III) sulfides 107a-c (Scheme 37) [84]. The single-crystal XRD analysis of sulfides 107a-c revealed that all three compounds are centrosymmetric dimmers with a planar central 4-membered Sb2S2 ring. All oxygen donor atoms of pendant arms in these compounds are coordinated to the central antimony atom through intramolecular interactions; the O–Sb bond lengths vary from 2.6323(17) to 2.894(3) Å. The geometry around the Sb atom can be described as a bicapped trigonal pyramid. Recently, Dostál and co-workers synthesized intramolecularly coordinated organoantimony(III) carboxylates 108a-c and 109a-c by reacting chlorides 99a-b with silver salts of selected carboxylic acids in 1:2 molar ratio in CH2Cl2 (Scheme 38) [88]. The molecular structures of 109a and 109c were confirmed by single-crystal XRD analysis. Both acetate groups in 109a are coordinated to the central Sb atom in unidenate fashion. With the two intramolecular OSb interactions [Sb(1)–O(1) 2.692(3) and Sb(1)–O(2) 2.596(2) Å] are taken into account, the overall geometry can be described as a strongly distorted square pyramid. While one of the trifluoracetate groups in 109c acts as unidentate ligand, the other appears as a

2476

Current Organic Chemistry, 2012, Vol. 16, No. 20

Tan et al.

Scheme 37. Synthesis of compounds 107a-c.

OR

OR

SbCl2

AgOOCR'

+

CH2Cl2

OR

Sb(OOR')2

108a-c 109a-c

OR

R = Me

108a: R' = CH3

108b: R' = CH2=CH2 108c: R' = CF3

R = t-Bu

109a: R' = CH3

109b: R' = CH2=CH2 109c: R' = CF3

Scheme 38. Synthesis of compounds 108a-c and 109a-c.

bidentate carboxylate. The overall geometry around the antimony atom in 109c can be best described as a pentagonal pyramid.

Scheme 41. Synthesis of organoantimony cations 113.

Scheme 39. Reaction of compounds 99a and AgOTf.

ArSbCl2

+ AgCB11H12

ArSbCl

CB11H12

112a-b OtBu

OMe

3. APPLICATION OF HYPERVALENT ORGANOANTIMONY COMPOUNDS HAVING INTRAMOLECULAR N, O, SSb INTERACTIONS

b: Ar =

a: Ar =

Recently, Dostál et al. observed the formation of an unexpected product (113) during preparation of intramolecularly coordinated antimony compound [2,6-(MeOCH2)2C6H3]SbCl2 (Scheme 41) [90]. The single-crystal structure of 113 revealed that the product is an ionic complex consisting of four organoantimony cations [2,6(MeOCH2)2C6H3]2Sb+ compensated by an unusual [Sb6Cl22]4- anion. The coordination polyhedron around the antimony atom in the organoantimony cations is best described as a distorted pseudotrigonal bipyramid.

OMe

NMe2

Scheme 40. Preparation of organoantimony cations 112a-b.

Treatment of chlorides ArSbCl2 [Ar = 2,6-(MeOCH2)2C6H3)] (99a) with AgOTf gave ArSbCl(OTf) (110) or ArSb(OTf)2 (111), depending on the molar ratio of starting materials: 1:1 or 1:2 (Scheme 39) [89]. Single-crystal XRD analyses of compounds 110 and 111 showed that all donor oxygen of the OCO pincer ligands are strongly coordinated to the central antimony atom, and the overall geometry around the Sb atom can be described as a distorted square pyramid. The reactions of chlorides ArSbCl2 with AgCB11H12 would result in the formation of organoantimony cations [ArSbCl]+ [CB11H12]- [Ar = 2,6-(MeOCH2)2C6H3 (112a), 2-(Me2NCH2)-6-(tBuOCH2)C6H3 (112b)] (Scheme 40) [86, 89]. Compounds 112a-b exist as separated ion pairs consisting of a [ArSbCl(THF)]+ (112a) or [ArSbCl]+ (112b) cation and [CB11H12]- anion. For compound 112a, the polyhedron around the central Sb atom is a distorted square pyramid, while the structure of the cationic part of 112b can be described as a pseudo-trigonal dipyramid.

3.1. Stibine Ligands The chemistry of antimony ligands is a subject of growing interest as a result of their increasing accessibility and the realization that they may display significantly different electronic properties from their lighter analogues, phosphines and arsines [11-13, 38, 80, 83]. Treatment of stibine Ar3Sb [Ar = 2-(Me2NCH2)C6H4] (1) with K2PtCl2 in acetone/water gave a novel platinum complex [PtCl2(SbAr3)] (114) [17]. There is weak NSb intramolecular coordination [N(2)–Sb(1) 3.237(11) Å] in complex 114. The results of single-crystal XRD analysis of 114 [Pt(1)–Sb(1) 2.4949(7) Å and Pt(1)–N(1) 2.126(9) Å] revealed that stibine ligand 1 acts as both bidentate chelating Sb as well as N-type ligand. Stibine 1 was also found to work effectively as a ligand for the rhodium(I)catalyzed hydroformylation reaction of 1-pentene by Sharma et al. [91]. In 2004 Opris et al. prepared complex ArSb[W(CO)5]2 [Ar = 2(Me2NCH2)C6H4] (115) by reacting Ar4Sb4 or (ArSbS)2 with [W(CO)5(THF)] in THF [68]. The molecule comprises two pentacarbonyl tungsten moieties bridged by the antimony atom of a [2(Me2NCH2)C6H4]Sb unit. Treatment of (ArSb)2S [Ar = 2-

Synthesis, Structure and Applications of Hypervalent Organoantimony

Current Organic Chemistry, 2012, Vol. 16, No. 20 2477

The MeN(CH2-2-C6H4SbMe2)2 (85) and S(CH2-2-C6H4SbMe2)2 (98) ligands have three coordination sites, one nitrogen (or sulfur) atom and two antimony atoms. Therefore, there are three possible coordination modes for the complexes: (i) bridging bidentate such as [{CpFe(CO)2}2(85)][BF4]2 (117) (Fig. 9) [38], (ii) chelating bidentate (both Sb2-coordinated) such as [Cu(85)2}][BF4]2 (118), [Mo(CO)4(85)] (119), [PtMe3I(85)] (120), [Cr(CO)4(85)] (121) and [W(CO)4(85)] (122) [80, 83], and (iii) chelating tridentate (Sb2N- or Sb2S-coordinated) such as [Mn(CO)3(85)] (123) (Fig. 10), [Cr(CO)3(98)] (124) and [Mn(CO)3(98)] (125) [80, 83]. 3.2. Cross-Coupling Reactions Fig. (9). A thermal ellipsoid plot (30% probability level) of compound 117, BF4 anion and hydrogen atoms are omitted for clarity.

Transition metal-catalyzed cross-coupling reactions of organometallic or heteroatom-compounds with organic halides is a tremendously versatile synthetic approach [92]. A variety of metaland heteroatom-compounds participate in this reaction, and organoantimony compounds can also be utilized. In 2003, Bonaterra et al. reported the cross-coupling reaction of stannylstibanes with aryl iodides catalyzed by a palladium complex [93]. Kurita and coworkers reported that ethynyl-1,5-azastibocines compounds having intramolecular interaction can also be applied to the palladiumcatalyzed cross-coupling reaction with acyl halides and aryl halides to give the corresponding ethynyl derivatives (Scheme 42) [25, 94]. 3.3. Arylation Reactions

Fig. (10). A thermal ellipsoid plot (30% probability level) of compound 123, and hydrogen atoms are omitted for clarity.

(Me2NCH2)C6H4] (68) with [W(CO)5(THF)] followed by work up of the reaction mixture in open atmosphere resulted in the formation of complex [(Ar2SbOH)W(CO)5] (116) [51]. According to the molecular structure of 116, there is binding between the W(CO)5 moiety and the Sb atom of diorganoantimony (III) hydroxide. Only one nitrogen atom is strongly coordinated to the antimony atom [Sb(1)–N(1) 2.860(9) Å], trans to the oxygen atom of the hydroxy group.

In 2006, Kakusawa and Kurita reported arylation reactions of 12-aryl-1,5-azastibocines compounds with a wide range of acyl chlorides and aryl iodides in the presence of 5 mol% of PdCl2(PPh3) (Scheme 43) [26]. Although this type of arylation is hardly possible with non-activated triarylstibanes, the intramolecular NSb non-bonding interaction in 1,5-azastibocines facilitates transmetallation of the aryl group in the catalytic cycle. 3.4. Addition Reactions Recently, Kurita and co-workers reported the rhodiumcatalyzed addition reaction of 12-aryl-1,5-azastibocines with , -

Scheme 42. Cross-coupling reactions of ethynyl-1,5-azastibocines with organic halides.

Scheme 43. Arylation reactions of 12-aryl-1,5-azastibocines with organic halides.

2478

Current Organic Chemistry, 2012, Vol. 16, No. 20

Tan et al.

Scheme 44. Addition reactions of 12-aryl-1,5-azastibocines with enones and enoates.

Scheme 45. Reaction of 12-phenyl-1,5-azastibocines with various aldehydes.

Scheme 46. Mannich reaction catalyzed by organoantimony compound 50.

unsaturated ketones and esters (Scheme 44) [95, 96]. Exclusive formation of 1,4-conjugate adduct was achieved in aqueous NMP (N-methyl-2-pyrrolidinone) in the presence of 5 mol% of [RhCl(cod)]2, and no formation of Heck adduct was observed under such condition. Reactions with various enones and enoates were also performed to demonstrate the generality of the 1,4-conjugate addition. In subsequent study by Kurita and co-workers, it was observed that 12-phenyl-1,5-azastibocine can act as soft nucleophile. It reacted only with aldehydes showing high functional compatibility (Scheme 45) [97]. This is a simple and efficient method for the addition of a phenyl group to aldehydes for the formation of aryl alcohols. The reaction can be carried out under aerobic conditions, in contrast to the reactions using hard nucleophiles such as organolithium and Grignard reagents.

3.6. CO2-Fixation Reactions Chemical fixation of CO2 has recently attracted considerable attention, and a number of metal compounds are known to react with CO2. They are potentially applicable in the catalytic transformation and separation of CO2 [106-108]. In 1980, Nomura et al. reported that pentavalent organoantimony compounds Ph4SbBr and Ph3SbBr2 were efficient catalysts for the synthesis of cyclic carbonates from carbon dioxide and epoxides [5]. Recently, a hypervalent organoantimony compound with 2,6-(CH2NMe2)2C6H3 groups was found to fix CO2 efficiently [69]. Dostál and co-workers found that the dimeric organoantimony oxide 59 which is stable in air at ambient temperature (tested for at least several weeks) immediately reacts with carbon dioxide in a toluene solution to form air-stable monomeric carbonate 61. In turn, carbon dioxide can be easily eliminated from carbonate 61 through prolonged heating at 130 °C for the recovery of organoantimony oxide 59 (Scheme 47).

3.5. Lewis Acid Catalysis A number of trivalent and pentavalent antimony compounds such as SbCl3, SbBr3, SbF5, Sb(OEt)3, Ph3SbO, and Ph4SbBr were reported as effective Lewis acid catalysts in various organic reactions [98-100]. However, the utilization of organoantimony(III) compounds as Lewis acid catalysts for organic synthesis was rarely reported partly due to the unstable nature of organoantimony compounds. Recently, Yin and co-workers reported a series of air-stable organobismuth(III) with cyclic 5,6,7,12-tetrahydrodibenz[c,f][1,5] heterobismocine framework that are catalytically active toward many organic reactions in aqueous media as well as in various organic solvents [67, 101-105]. In order to develop suitable organoantimony compounds for catalytic utilization, Yin and co-workers synthesized organoantimony with analogous tetrahydrodibenzo[c,f] [1,5]azastibocine framework, and found that organoantimony(III) triflate (50) can efficiently catalyze the direct diastereoselective Mannich reaction in water (Scheme 46), giving anti/syn molar ratio 95/5 [64].

Scheme 47. Reversible fixation of carbon dioxide by 59 to form ArSbCO3 (61).

4. SUMMARY In this review paper, we present the development of organoantimony compounds having intramolecular N, O, SSb coordinations during the past 20 years. It is known that the stability and molecular conformation of the compounds are determined by the nature of intramolecular heteroatom–antimony interactions. We survey the synthesis and structures of this kind of hypervalent compounds, and highlight the application of some novel organoanti-

Synthesis, Structure and Applications of Hypervalent Organoantimony

Current Organic Chemistry, 2012, Vol. 16, No. 20 2479

mony compounds in the field of ligand chemistry. They can be used as Lewis acid catalysts in organic synthesis, and as reagents for reactions such as cross-coupling and arylation with organic halides as well as addition with carbonyl compounds. Furthermore, they can be used for CO2 chemical fixation as catalysts or reagents. With such achievements, it is hoped that enthusiasm would be promoted, and more research works would be done on the chemistry of hypervalent organoantimony compounds.

[19]

CONFLICT OF INTEREST

[21]

[18]

[20]

The author(s) confirm that this article has no conflicts of interest.

[22]

ACKNOWLEDGEMENTS [23]

This work was supported by the Natural Science Foundation of Hunan Province (10JJ1003), Science Research Foundation of Higher Universities of Hunan Province (10A092) the National Natural Science Foundation of China (20973056, 21003040), the program for New Century Excellent Talents in Universities (NCET-10-0371), and the Fundamental Research Funds for the Central Universities. CTA thanks HNU for an adjunct professorship. REFERENCES [1] [2]

[3] [4]

[5]

[6]

[7] [8] [9]

[10]

[11] [12] [13]

[14]

[15]

[16]

[17]

Löwig, C.; Schweizer, E. Ueber Stibäthyl, ein neues antimonhaltiges organisches Radical. Liebigs Ann. Chem., 1850, 75, 315-355. Michaelis, A.; Reese, A. Ueber aromatische Antimonverbindungen und eine neue Bildungsweise aromatischer Arsenverbindungen. Chem. Ber., 1882, 15, 2876-2877. Sharama, P.; Perez, A.; Cabrera, A.; Rosas, N.; Arias, J.L. Perspectives of antimony compounds in oncology. Acta Pharmacol. Sin., 2008, 29, 881-890. Nomura, R.; Nakano, T.; Nishio, Y.; Ogawa, S.; Ninagawa, A.; Matsuda, H. Regioselective cycloaddition of 1,2-disubstituted aziridines to heterocumulenes catalyzed by organoantimony halides. Chem. Ber., 1989, 122, 24072409. Nomura, R.; Ninagawa, A.; Matsuda, H. Synthesis of cyclic carbonates from carbon dioxide and epoxides in the presence of organoantimony compounds as novel catalysts. J. Org. Chem., 1980, 45, 3735-3738. Yasuike, S.; Kishi, Y.; Kawara, S.; Kurita, J. Catalytic action of triarylstibanes: Oxidation of benzoins into benzyls using triarylstibanes under an aerobic condition. Chem. Pharm. Bull., 2005, 53, 425-427. Freedman, L.D.; Doak, G.O. In: The Metal - Carbon Bond; Hartley F.R. Eds.; John Wiley & Sons, Inc.: Chichester, 1989; Vol. 5, pp. 397-433. Huang, Y.Z. Synthetic Applications of organoantimony compounds. Acc. Chem. Res., 1992, 25, 182-187. Qin, W.; Kakusawa, N.; Wu, Y.; Yasuike, S.; Kurita, J. Pentavalent organoantimony compounds as mild N-arylating agents for amines: Cumediated Ullmann-type N-arylation with tetraarylantimony(V) acetates. Chem. Pharm. Bull., 2009, 57, 436-438. Yasuike, S.; Ikoma, M.; Kakusawa, N.; Tsuchiya, T.; Kurita, J. Synthesis and thermal stability of 3-subtituted 3-benzostibepines. Heterocycles, 2009, 79, 659-667. Champness, N.R.; Levason, W. Coordination chemistry of stibine and bismuthine ligands. Coord. Chem. Rev., 1994, 133, 115-217. Levason, W.; Reid, G. Developments in the coordination chemistry of stibine ligands. Coord. Chem. Rev., 2006, 250, 2565-2594. Bojan, V.R.; Fermández, E.J.; Laguna, A.; López-de-Luzuriaga, J.M.; Monge, M.; Olmos, M.E.; Puelles, R.C.; Silvestru, C. Study of the coordination abilities of stibine ligands to gold(I). Inorg. Chem., 2010, 49, 55305541. Balázs, L.; Breunig, H.J.; Ghesner, I.; Lork, E. Syntheses and crystal structures of a covalent tri-alkylantimony hydroxo bromide and related trialkylantimony(V) halides. J. Organometal. Chem., 2002, 648, 33-38 Waterman, R.; Tilley, T.D. Catalytic antimony-antimony bond formation through stibinidene elimination from zirconocene and hafnocene complexes. Angew. Chem. Int. Ed., 2006, 45, 2926-2929 Yamamoto, Y.; Chen, X.; Kojima, S.; Ohdoi, K.; Kitano, M.; Doi, Y.; Akiba, K. Experimental investigation on edge inversion at trivalent bismuth and antimony: Great acceleration by intra- and intermolecular nucleophilic coordination. J. Am. Chem. Soc., 1995, 117, 3922-3932. Sharma, P.; Castillo, D.; Rosas, N.; Cabrera, A.; Gomez, E.; Toscano A.; Lara F.; Hernández S.; Espinosa G. Synthesis and structures of organoanti-

[24]

[25]

[26]

[27] [28] [29] [30] [31] [32]

[33] [34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

mony compounds containing intramolecular N–Sb interactions. J. Organometal. Chem., 2004, 689, 2593-2600. Opris, L.M.; Silvestru, A.; Silvestru, C; Breunig, H.J.; Lork, E. Solid-state structure and solution behaviour of hypervalent organoantimony halides containing 2-(Me2NCH2)C6H4- moieties. Dalton Trans., 2003, 4367-4374. Okajima, S.; Yasuike, S.; Kakusawa, N.; Yamaguchi, K.; Seki, H.; Kurita, J. Synthesis of Sb-chiral organoantimony compounds having intramolecular N…Sb interaction and their separation into optically pure compounds via ortho-palladated benzylamine complexes. J. Organometal. Chem., 2002, 656, 234-242. Atwood, D.A.; Cowley, A.H.; Ruiz, J. Use of the 2,6-bis[(dimethylamino) methyl]phenyl ligand to form some pentacoordinate derivatives of P(III), As(III), Sb(III) and Bi(III). Inorg. Chim. Acta., 1992, 198-200, 271-274. Dostál, L.; Jambor, R.; R ika, A.; Lyka, A.; Brus, J.; Proft F. Synthesis and structure of organoantimony(III) compounds containing antimonyselenium and -tellurium terminal bonds. Organometallics, 2008, 27, 60596062. Dostál, L.; Císa ová, I.; Jambor, R.; R ika, A.; Jirásko, R.; Holeek, J. Structural diversity of organoantimony(III) and organobismuth(III) dihalides containing O,C,O-chelating ligands. Organometallics, 2006, 25, 4366-4373. Carmalt, C.J.; Cowley, A.H.; Culp, R.D.; Jones, R.A.; Kamepalli, S.; Norman, N.C. Synthesis and Structures of Intramolecularly Base-Coordinated Group 15 Aryl Halides. Inorg. Chem., 1997, 36, 2770-2776. Sharma, P.; Lopez, J.G.; Ortega, C.; Rosas, N.; Cabrera, A.; Alvarez, C.; Toscano, A.; Reyes, E. First ferrocenylstibines and their molecular structures. Inorg. Chem. Commun., 2006, 9, 82-85. Kakusawa, N.; Tobiyasu, Y.; Yasuike, S.; Yamaguchi, K.; Seki, H.; Kurita J. Hypervalent organoantimony compounds 12-ethynyltetrahydrodibenz[c,f][1,5]azastibocines: Highly efficient new transmetallating agent for organic halides. J. Organometal. Chem., 2006, 691, 2953-2968. Kakusawa, N.; Kurita, J. Hypervalent organoantimony compound 12-aryltetrahydrodibenz[c,f] [1,5]azastibocines: New transmetallating agent for palladium-catalyzed arylation of organic halides. Heterocycles, 2006, 68, 13351348. Musher, J.I. The chemistry of hypervalent molecule. Angew. Chem. internat. Edit., 1969, 8, 54-68. Akiba, K.Y. In: Chemistry of Hypervalent Compounds; Akiba, K.Y. Eds.; Wiley-VCH: Weinheim, 1999; pp. 1-8. Chemistry of Hypervalent Compounds; Akiba, K.Y. Eds.; Wiley-VCH: Weinheim, 1999. Akiba, K.Y. Studies on Hypervalent compounds and synthetic work using heteroaromatic cations. Heteroatom Chem., 2011, 22, 207-274. Silva, L.F.; Jr. Hypervalent iodine-mediated ring contraction reactions. Molecules, 2006, 11, 421-434. Milov, A.A.; Minyaev, R.M.; Minkin, V.I. Intramolecular hypervalent interaction in the conjugate five-membered rings. J. Phys. Chem. A, 2011, 115, 12973-12982. Yamada, K.; Okuda, T. In: Chemistry of Hypervalent Compounds; Akiba K.Y. Eds.; Wiley-VCH: Weinheim, 1999; pp. 49-80. Schröder, G.; Okinaka, T.; Mimura, Y.; Watanabe, M.; Matsuzaki, T.; Hasuoka, A.; Yamamoto, Y.; Matsukawa, S.; Akiba, K.Y. Syntheses, crystal and solution structures, ligand-exchange, and ligand-coupling reactions of mixed pentaarylantimony compounds. Chem. Eur. J., 2007, 13, 2517-2529. García-Monforte, M. A.; Alonso, P. J.; Ara, I.; Menjón, B.; Romero, P. Solid-state and solution structure of a hypervalent AX5 compound: Sb(C6F5). Angew. Chem. Int. Ed., 2012, 51, 2754-2757. de Oliveira, L.G.; Silva, M.M.; de Paula, F.C.S.; Pereira-Maia, E.C.; Donnici, C.L.; de Simone, C.A.; Frézard, F.; da Silva Júnior, E.N.; Demicheli, C. Antimony(V) and bismuth(V) complexes of lapachol: Synthesis, crystal structure and cytotoxic activity. Molecules, 2011, 16, 10314-10323. Yamamichi, H.; Matsukawa, S.; Kojima, S.; Ando, K.; Yamamoto, Y. Structure and dynamic behavior of neutral hexacoordinate antimony compounds with intramolecular coordination. Heteroatom Chem., 2011, 22, 553-562. Benjamin, S.L.; Karagiannidis, L.; Levason, W.; Reid, G.; Rogers, M.C. Hybrid dibismuthines and distibines: Preparation and properties of antimony and bismuth oxygen, sulfur, and nitrogen donor ligands. Organometallics, 2011, 30, 895-904. Svoboda, T.; Jambor, R.; R ika, A.; Padélková, Z.; Erben, M.; Jirásko, R.; Dostál, L. NCN-chelated organoantimony(III) and organobismuth(III) phosphonates: Syntheses and structures. Eur. J. Inorg. Chem., 2010, 1663-1669. Yamamoto, Y.; Chen, X.; Akiba, K.Y. Synthesis and crystal structure of intramolecularly coordinated organobismuth compounds and edge inversion at trivalent bismuth. J. Am. Chem. Soc., 1992, 114, 7906-7907. Wakisaka, Y.; Yamamoto, Y.; Akiba, K.Y. Synthesis and X-Ray Crystal Structures of Hypervalent Hexacoordinate Antimony Compounds without Halogen Ligands. Heteroatom Chem., 2001, 12, 33-37. Tokunaga, T.; Seki, H.; Yasuike, S.; Ikoma, M.; Kurita, J.; Yamaguchi, K. Confirmation and characterization of the hypervalent NSb bonding recognized in triarylstibanes bearing an amino side chain by X-ray, NMR and theoretical calculations. Tetrahedron, 2000, 56, 8833-8839. Ohkata, K.; Ohnishi, M.; Akiba, K.Y. Transannular bond formation between the antimony and the nitrogen atoms in dibenz[c,f][1,5]azastibocine system: Formation of X–Sb–X and X–N–Sb+ hypervalent bond. Tetrahedron Lett., 1988, 29, 5401-5404.

2480 [44]

[45]

[46]

[47] [48] [49]

[50]

[51]

[52]

[53]

[54]

[55]

[56]

[57]

[58]

[59]

[60]

[61]

[62]

[63]

[64]

[65]

[66] [67]

Current Organic Chemistry, 2012, Vol. 16, No. 20

imon, P.; Proft, F.; Jambor, R.; R ika, A.; Dostál, L. Monomeric organoantimony (I) and organobismuth (I) compounds stabilized by an NCN chelating ligand: Syntheses and structures. Angew. Chem. Int. Ed., 2010, 49, 5468-5471. Kamepalli, S.; Carmalt, C.J.; Culp, R.D.; Cowley, A.H.; Jones, R.A.; Norman, N.C. Synthesis and structures of intramolecularly base-coordinated aryl group 15 compounds. Inorg. Chem., 1996, 35, 6179-6183. Perkins, C.W.; Martin, J.C.; Arduengo, A.J.; Lau, W.; Alegria, A.; Koch, J.K. An electrically neutral a-sulfuranyl radical from the homolysis of a perester with neighboring sulfenyl sulfur: 9-S-3 species. J. Am. Chem. Soc., 1980, 102, 1153-1159. Pyykkö, P.; Atsumi, M. Molecular Single-Bond Covalent Radii for Elements 1-118. Chem. Eur. J., 2009, 15, 186-197. Batsanov, S. S. Van der waals radii of elements. Inorg. Mater., 2001, 37, 871-885. Sharma, P.; Pérez, D.; Vázquez, J.; Toscano, A.; Gutiérrez, R. First example of antimoniated Schiff bases: Hypervalent SbN(sp2) bonds. Inorg. Chem. Commun., 2007, 10, 389-392. Copolovici, D.; Bojan, V.R.; Rat, C.I. Silvestru, A.; Breunig, H.J.; Silvestru, C. New chiral organoantimony(III) compounds containing intramolecular NSb interactions — solution behaviour and solid state structures. Dalton Trans., 2010, 39, 6410-6418. Opris, L.M.; Preda, A.M.; Varga, R.A.; Breunig, H.J.; Silvestru, C. Synthesis and characterization of hypervalent organoantimony(III) compounds containing the [2-(Me2NCH2)C6H 4]2Sb fragment. Eur. J. Inorg. Chem., 2009, 1187– 1193. Tokunaga, T.; Seki, H.; Yasuike, S.; Ikoma, M.; Kurita, J.; Yamaguchi K. Direct detection of intramolecular NSb nonbonded interaction by 1H-13C and 1H-15N heteronuclear multiple bond correlation spectroscopy. Tetrahedron Lett., 2000, 41, 1031-1034. Hoshino, K.; Ogawa, T.; Yasuike, S.; Seki, H.; Kurita, J.; Tokunaga T.; Yamaguchi K. Cyclic voltammetric study of intramolecular and intermolecular hypervalent organoantimony complexes with NSb bonding. J. Phys. Chem. B, 2004, 108, 18698-18704. Yasuike, S.; Kishi, Y.; Kawara, S.; Yamaguchi, K.; Kurita, J. Synthesis of enantiomerically pure Sb-chirogenic organoantimony compounds and their crystal structures. J. Organometal. Chem., 2006, 691, 2213-2220. Ortiz, A.M.; Sharma, P.; Pérez, D.; Rosas, N.; Cabrera, A.; Velasco, L.; Toscano, A.; Hernández S. New 1,2-disubstituted ferrocenyl stibines containing N-heterocyclic pendant arm: N–Sb hypervalent compounds. J. Organometal. Chem., 2009, 694, 2037-2042. Olaru, M.; Rosca, S.; Rat, C.I.; Silvestru, C. Chloridobis{2[(dimethylamino)methyl]phenyl}anti- mony (III) . Acta Cryst., 2009, E65, m1383-m1384. Dostál, L.; Jambor, R.; R ika, A.; imon, P. On the reduction of NC chelated organoantimony (III) chlorides. Eur. J. Inorg. Chem., 2011, 23802386. Breunig, H.J.; Ghesner, I.; Ghesner, M.E.; Lork, E. Syntheses, Structures, and Dynamic Behavior of Chiral Racemic Organoantimony and -bismuth Compounds RR’SbCl, RR’BiCl, and RR’SbM [R = 2-(Me2NCH 2)C6H4 , R’ = CH(Me3Si)2, M = H, Li, Na]. Inorg. Chem., 2003, 42, 1751-1757. Vázquez, J.; Sharma, P.; Cabrera, A.; Toscano, A.; Hernández, S.; Gutiérrez, R. Formation of (vinyl-ferrocenyl)stibines involving -elimination:Hypervalent N–Sb bonding. J. Organometal. Chem., 2007, 692, 3486-3491. Pérez, D.; Sharma, P.; Rosas, N.; Cabrera, A.; Arias, J.L.; del Rio-Portilla, F.; Vázquez, J.; Gutiérrez, R.; Toscano, A. Tris-(1,2-N,N-dimethylaminomethylferrocenyl)stibine and its heterotrimetallic complex. J. Organometal. Chem., 2008, 693, 3357-3362. Dostál, L.; Jambor, R.; R ika, A.; Jirásko, R.; Císaová, I.; Holeek, J. The synthesis of organoantimony(III) difluorides containing Y,C,Y pincer type ligands using organotin(IV) fluorinating agents. J. Fluor. Chem., 2008, 129, 167-172. Fridrichová, A.; Svoboda, T.; Jambor, R.; Padélková, Z.; R ika, A.; Erben, M.; Jirásko, R.; Dostál, L. Synthesis and structural study on organoantimony(III) and organobismuth(III) hydroxides Ccontaining an NCN pincer type ligand. Organometallics, 2009, 28, 5522-5528. Ohkata, K.; Takemot, K.; Ohnishi, M.; Akiba, K.Y. Synthesis and chemical behavior of 12-substituted dibenz[c,f][1,5]azastibocine and dibenz[c,f][1,5] azabismocine derivatives: Evidences of 10-Pn-4 type hypervalent interaction. Tetrahedron Lett., 1989, 30, 4841-4844. Xia, J.; Qiu, R.H.; Yin, S.F; Zhang, X.W.; Luo, Sh.L.; Au, C.T.; Xia, K.; Wong, W.Y. Synthesis and structure of an air-stable organoantimony complex and its use as a catalyst for direct diastereoselective Mannich reactions in water. J. Organometal. Chem., 2010, 695, 1487-1492. Xia, J. Synthesis, Characterization and Catalytic Application of Functional Organoantimony Complex. MD thesis, Hunan University: Changsha, P.R. China, June 2010. Yi, W.G.; Tan, N.Y. 12-Chloro-6-cyclohexyl-5,6,7,12-tetrahydrodibenzo[c,f] [1,5]azastibocine. Acta Cryst., 2011, E67, m917. Zhang, X.W.; Qiu, R.H.; Tan, N.Y.; Yin, S.F.; Xia, J.; Luo, S.L.; Au, C.T. Air-stable hypervalent organobismuth(III) tetrafluoroborate as effective and reusable catalyst for the allylation of aldehyde with tetraallyltin. Tetrahedron Lett., 2010, 51, 153-156.

Tan et al. [68]

[69]

[70]

[71]

[72]

[73]

[74]

[75]

[76]

[77]

[78]

[79]

[80] [81]

[82]

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

Opris, L.M.; Silvestru, A.; Silvestru, C; Breunig, H.J.; Lork E. Syntheses and chemistry of hypervalent cyclo-R4Sb4, cyclo-(RSbE)n [R = 2(Me2NCH2)C6H 4, E = O, S] and precursors. Dalton Trans., 2004, 3575– 3585. Dostál, L.; Jambor, R.; R ika, A.; Erben, M.; Jirásko, R.; erno ková, E.; Holeek, J. Efficient and reversible fixation of carbon dioxide by NCNchelated organoantimony(III) oxide. Organometallics, 2009, 28, 2633-2636. Dostál, L.; Jambor, R.; R ika, A.; Jirásko, R.; Locha, V.; Bene , L.; de Proft, F. Nonconventional behavior of NCN-chelated organoantimony(III) sulfide and isolation of cyclic organoantimony(III) bis(pentasulfide). Inorg. Chem., 2009, 48, 10495-10497. Dostál, L.; Jambor, R.; R ika, A.; Jirásko, R.; erno ková, E.; Bene , L.; de Proft, F. [2+2] Cycloaddition of carbon disulfide to NCN-chelated organoantimony (III) and organobismuth (III) sulfides: Evidence for terminal Sb-S and Bi-S bonds in solution. Organometallics, 2010, 29, 4486-4490.

imon, P.; Jambor, R.; R ika, A.; Lyka A.; de Proft, F.; Dostál, L. Monomeric organoantimony (III) sulphide and selenide with terminal Sb-E bond (E = S, Se): Synthesis, structure and theoretical consideration. Dalton Trans., 2012, 41, 5140-5143. Dostál, L.; Jambor, R.; Jirásko, R.; Padélková Z.; R ika, A.; Holeek, J. Structural study on the organoantimony(III) NCN–chelated compounds [2,6(CH2NMe2)2C6H3]SbX2 – influence of the polar group X. J. Organometal. Chem., 2010, 695, 392-397. Said, M.A.; Swamy, K.C.K.; Babu, S. K.; Aparnab, K.; Nethajib M. Diphenylantimony(v) Oxo/Chloro Carboxylates and Phosphinates: Crystal Structures of {SbPh2Cl [O2P( C6H11)2]}2O and [SbPh2(O2CPh)2]2O. J. Chem. Soc. Dalton Trans., 1995, 2151-2157. Said, M.A.; Swamy, K.C.K.; Poojary, D.M. Clearfield; A.; Veith, M.; Huch, V. Dinuclear and tetranuclear cages of oxodiphenylantimony phosphinates: synthesis and structures. Inorg. Chem., 1996, 35, 3235-3241. Svoboda T.; Jambor, R.; R ika, A.; Padélková Z.; Erben M.; Dostál, L. NCN chelated organoantimony(III) and organobismuth(III) phosphinates and phosphites: Synthesis, structure and reactivity. Eur. J. Inorg. Chem., 2010, 5222–5230. Svoboda T.; Dostál, L.; Jambor, R.; R ika, A.; Jirásko, R.; Lyka, A. NCN-chelated organoantimony(III) and organobismuth(III) phosphates: Synthesis and solid-state and solution structures. Inorg. Chem., 2011, 50, 6411– 6413. Svoboda T.; Jambor, R.; R ika, A.; Jirásko, R.; Lyka, A.; de Proft, F.; Dostál, L. Reactivity of NCN-chelated (NCN = C6H3-2,6-(CH2NMe2)2) antimony(III) and bismuth(III) oxides toward oxides of arsenic. Organometallics, 2012, 31, 1725 1729. Carmalt, C.J.; Walsh, D.; Cowley, A.H.; Norman, N.C. Cationic complexes of antimony(III) and bismuth(III) stabilized by intra- or intermolecular coordination. Organometallics, 1997, 16, 3597-3600. Jura M.; Levason W.; Reid G.; Webster M. Preparation and properties of cyclic and open-chain Sb/N-donor ligands. Dalton Trans., 2009, 7811-7819. Dostál, L.; Jambor, R.; R ika, A.; Holeek, J. Syntheses and Structures of Ar3Sb5 and Ar4Sb4 Compounds [Ar = 2,6-(Me2NCH2)2C6H3] Organometallics, 2008, 27, 2169–2171. Sharma, P.; Pérez, D.; Rosas, N.; Cabrera, A.; Toscano, A. New stibines containing acetal and formyl group: Platinum complex and unexpected oxastibol derivative. J. Organometal. Chem., 2006, 691, 579-584. Benjamin, S.L.; Levason, W.; Reid, G.; Rogers, M.C. Hybrid dibismuthines and distibines as ligands towards transition metal carbonyls. Dalton Trans., 2011, 40, 6565-6574. Chovancová, M.; Jambor, R.; R ika, A.; Jirásko, R.; Císaová, I.; Dostál, L. Synthesis, Structure, and Reactivity of Intramolecularly Coordinated Organoantimony and Organobismuth Sulfides. Organometallics, 2009, 28, 1934-1941. Vrána, J.; Jambor, R.; R ika, A.; Holeek, J.; Dostál, L. NCO-Chelated organoantimony(III) and organobismuth(III) dichlorides: Syntheses and structures. Collect. Czech. Chem. Commun., 2010, 75, 1041-1050. Dostál, L.; Jambor, R.; R ika, A.; Jirásko, R.; Holeek, J.; de Proft, F. OCO and NCO chelated derivatives of heavier group 15 elements. Study on possibility of cyclization reaction via intramolecular ether bond cleavage. Dalton Trans., 2011, 40, 8922-8934. Dostál, L.; Jambor, R.; R ika, A.; Císaová, I.; Holeek, J. Synthesis and structure of SbO intramolecularly coordinated ethynylstibanes. Inorg. Chim. Acta, 2010, 363, 1607-1610. Machua, L.; Dostál, L.; Jambor, R.; Karel Handlırˇ a, Jirásko, R.; R ika, A.; Císaová, I.; Holeek, J. Intramolecularly coordinated organoantimony(III) carboxylates. J. Organometal. Chem., 2007, 692, 3969-3975. Dostál, L.; Novák, P.; Jambor, R.; R ika, A.; Císaová, I.; Jirásko, R.; Holeek, J.Synthesis and Structural Study of Organoantimony(III) and Organobismuth(III) Triflates and Cations Containing O,C,O-Pincer Type Ligands. Organometallics, 2007, 26, 2911-2917. Dostál, L.; Jambor, R.; Císaová, I.; Bene , L.; R ika, A.; Jirásko, R.; Holeek, J. Unexpected product formed by the reaction of [2,6(MeOCH2)2C6H 3]Li with SbCl 3: Structure of Sb–O intramolecularly coordinated organoantimony cation. J. Organometal. Chem., 2007, 692, 23502353.

Synthesis, Structure and Applications of Hypervalent Organoantimony [91]

[92] [93]

[94]

[95]

[96]

[97]

[98] [99]

[100]

[101]

Current Organic Chemistry, 2012, Vol. 16, No. 20 2481

Sharma, P.; Arias, J.L.; Vasquez, J.; Gomez, V.; Guiterrez, R. Modification of rhodium catalyst with stibines for hydroformylation of 1-Pentene. J. Chin. Chem. Soc., 2007, 54, 681-684. Metal-Catalyzed Cross-Coupling Reactions; Diederich, F.; Stang, P.J. Eds.; Wiley-VCH: Weinheim, 2004. Bonaterra, M.; Martín, S.E.; Rossi, R.A. One-pot palladium-catalyzed crosscoupling reaction of aryl iodides with stannylarsanes and stannylstibanes. Org. Lett., 2003, 5, 2731-2734. Kakusawa, N.; Tobiyasu, Y.; Yasuike, S.; Yamaguchi, K.; Seki, H.; Kurita J. Remarkable reactivity enhancement with Sb···N inter-coordination of ethynyl-1,5-azastibocines in Pd-catalyzed cross-coupling reactions with organic halides. Tetrahedron Lett., 2003, 44, 8589-8592. Kakusawa, N.; Kurita J. Rhodium Catalyzed 1,4-Conjugate Addition of 1,5Azastibocines with Electron Deficient Olefins. Chem. Pharm. Bull., 2008, 56, 1502-1504. Kakusawa, N.; Yasuike, S.; Kurita J. Rhodium-catalyzed conjugate addition of Sb-aryl- 1,5-azastibocines to ,-unsaturated carbonyl compounds. Heterocycles, 2009, 77, 1269 - 1283. Kakusawa, N.; Yasuike, S.; Kurita J. Rhodium-catalyzed 1,2-addition of Sbphenyl-1,5-azastibocines to functionalized aldehydes. Heterocycles, 2010, 80, 163 - 168. Ishihara K. In: Lewis Acids in Organic Synthesis; Yamarnoto H. Eds.; Wiley-VCH: Weinheim, 2000; Vol. 2, pp. 523-542. Nomura R.; Miyazaki S.I.; Nakano T.; Matsuda H. Facile esterification promoted by the triphenylstibine oxide-phosphorus sulfide (Ph3SbO/P4S10) system. Appl. Organometal. Chem., 1991, 5, 513-516. Nomura R.; Hasegawa Y.; Ishimoto M.; Toyosaki T.; Matsuda H. Carbonylation of amines by carbon dioxide in the presence of an organoantimony catalyst. J. Org. Chem., 1992, 57, 7339-7342. Zhang, X.W.; Yin, S.F.; Qiu, R.H.; Xia, J.; Dai, W.L.; Yu, Z.Y.; Au, C.T.; Wong, W.Y. Synthesis and structure of an air-stable hypervalent organobismuth(III) perfluorooctanesulfonate and its use as high-efficiency catalyst for

Received: May 08, 2012

[102]

[103]

[104]

[105]

[106] [107]

[108]

Revised: July 11, 2012

Mannich-type reactions in water. J. Organometal. Chem., 2009, 694, 35593564. Qiu, R.H.; Yin, S.F.; Zhang, X.W.; Xia, J.; Xu, X.H.; Luo, S.L. Synthesis and structure of an air-stable cationic organobismuth complex and its use as a highly efficient catalyst for the direct diastereoselective Mannich reaction in water. Chem. Commun., 2009, 4759-4761. Qiu, R.H.; Qiu, Y.M.; Yin, S.F.; Xu, X.H.; Luo, S.L.; Au, C.T.; Wong, W.Y.; Shimada, S. Highly efficient and selective synthesis of (E)-,unsaturated ketones by crossed condensation of ketones and aldehydes catalyzed by an air-stable cationic organobismuth perfluorooctanesulfonate. Adv. Synth. Catal., 2010, 352, 153-162. Qiu, R.H.; Qiu, Y.M.; Yin, S.F.; Song, X.X.; Meng, Z.G.; Xu, X.H.; Zhang, X.W.; Luo, S.L.; Au, C.-T.; Wong, W.-Y. Facile separation catalyst system: Direct diastereoselective synthesis of (E)-,-unsaturated ketones catalyzed by an air-stable Lewis acidic/basic bifunctional organobismuth complex in ionic liquids. Green Chem., 2010, 12, 1767-1771. Tan, N.Y.; Yin, S.F.; Li, Y.F.; Qiu, R.H.; Meng, Z.G.; Song, X.X.; Luo, S.L.; Au, C.-T.; Wong, W.-Y. Synthesis and structure of an air-stable organobismuth triflate complex and its use as a high-efficiency catalyst for the ring opening of epoxides in aqueous media with aromatic amines. J. Organometal. Chem., 2011, 696, 1579-1583. Darensbourg, D.J.; Holtcamp, M.W. Catalysts for the reactions of epoxides and carbon dioxide. Coord. Chem. Rev., 1996, 153, 155-174. Yin, S.F.; Maruyama, J.; Yamashita, T.; Shimada, S. Efficient fixation of carbon dioxide by hypervalent organobismuth oxide, hydroxide, and alkoxide. Angew. Chem. Int. Ed., 2008, 47, 6590-6593. Yin, S.F.; Shimada, S. Synthesis and structure of bismuth compounds bearing a sulfur-bridged bis(phenolato) ligand and their catalytic application to the solvent-free synthesis of propylene carbonate from CO2 and propylene oxide. Chem. Commun., 2009, 1136-1138.

Accepted: August 05, 2012