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The 5-(3,5-di-tert-butyl-4-hydroxyphenyl)dipyrromethane (5) was synthesized by the reaction of 3,5-di-tert-butyl-4-hydroxybenzaldehyde with pyrrole in the ...

Synopsis

Synopsis

SYNOPSIS

Title of Thesis: Synthesis, covalent and non-covalent interactions of selected porphyrinoids and related compounds.

The thesis is divided into five chapters, Chapter I Synthesis of porphyrinogens, hexa porphyrinogen and their interactions with anions Porphyrinogens bearing hydrogen atoms at their meso position are very important as key

intermediates in bio- and Rothemund syntheses of porphyrinoids. Their structures and isomerization are of particular interest in connection not only with biological peripheral isomerism of naturally occurring porphyrinoids, but also with N-C confusion of pyrroles and

formation of higher homologues of porphyrin such as pentaphyrins and hexaphyrins. Porphyrinogens have been, however, treated just as unstable intermediates and readily oxidized to the targeted dyes without isolation in most cases.

The different fully meso-substituted porphyrinogen calix[4]pyrroles have been prepared by

the reaction of pyrrole with different ketones in presence of organic acid and solid acid in organic solvents in varying yields. The structures were confirmed by different spectroscopic techniques.

O N H

1

+ R 1

R2

Solid acid

R1

CH3OH

R2

2

R1

R2

NH

HN

NH

HN

R1

R2

3

2a. R1=R2 = CH3

3a. R1=R2 = CH3

2b. R1=R2 = C2H5

3b. R1=R2 = C2H5

2c R1-R2 = (CH2)5

3c. R1-R2 = (CH2)5

R1 R1 R2

R1 R2

R2 H N

NH

R1

NH

HN

R1

R2

4

R2

4a. R1=R2 = CH3 4b. R1-R2 = (CH2)5

Scheme 1.1: Synthesis of calix[4]pyrroles and N-confused calix[4]pyrroles

336

Synopsis The 5-(3,5-di-tert-butyl-4-hydroxyphenyl)dipyrromethane (5) was synthesized by the reaction of 3,5-di-tert-butyl-4-hydroxybenzaldehyde with pyrrole in the presence of organic acid and

solid acid in organic solvents at room temperature. The reaction of above dipyrromethane

with corresponding ketones form the required oxocalix[4]pyrroles (7) in moderate yields. The raection of dipyrromethne (5) with acetone in presence of TFA in dichloromethane followed by DDQ oxidation gave calix[4]phyrin (9) (Scheme 2.2). R1

OH

NH HN 5

R2

R1 DDQ

DCM, rt

O

R2

+

NH HN 6

NH HN NH HN

O

DCM/CH3SO3H

R3 R4 rt, 30 Min

a. R3 = R4 = CH3 b. R3 = R4 = -(CH2)5

M e D C e to n A c A T F

HO

R3 R4

D Q , D D

OH

C M

DDQ, DCM

8

R1 O R2

NH HN NH HN

R1 O R2

R3 R4 7

7a. R1 = R2 = C(CH3)3, R3 = R4 = CH3 7b. R1 = R2 = C(CH3)3, R3 = R4 = -(CH2)5

HO

NH

N

N HN

OH

9

Scheme 2.2: Synthesis of oxoporphyrinogens (7) and calix[4]phyrin The anion binding studies were examined by UV-Visible spectroscopic titrations in DMSO and CH2Cl2. On the addition of solution of tetrabutylammonium fluoride, the absorption peak bathochromically decreases, and the presence of three isobestic points were observed at 410,

447 and 540 nm. The large red shifts have been attributed to a partial charge transfer resulting

from the anion being bounded to the –NH protons of the pyrrole constituting the chromophore. The isobestic points in UV-Vis spectra indicate that the complex has been formed between host and guest. The cases, binding stoichiometries were 1:1 as determined by Job’s method and the binding constant were calculated by UV-Vis titrations.

337

Synopsis

Chapter II Synthesis of oxo-porphyrinogens, related macrocycles and their non-covalent interactions.

The development of relatively simple donor-acceptor models to mimic the photosynthetic

reaction centres is one of the important area of chemical research. The conversion of solar

energy into chemical energy and their models have been used in the development of optoelectronic and other newer materials. The covalent and non-covalent donor-acceptor

systems have been used as models to mimic the biological electron transfer and energy transfer. Complexation of anionic species by molecules containing an appropriate binding site

is an area of recent substantial interest in supramolecular chemistry. The oxo-porphyrinogens and N-alkylated oxo-porphyrinogens were synthesized by the modification of reported procedures. The covalent and non-covalent models of oxoporphyrinogens have been prepared and their non-covalent interactions have been examined in chapter.

The cyclocondensation of arylaldehydes with pyrrole form the 5, 10, 15, 20-

tetraarylporphyrins (1) in good yields. The reaction of hydroxy porphyrins (1) with potassium

hydroxide and sodium hydride in presence of oxygen form oxoporphyrinogens (2) in different reaction conditions (Scheme 2.1), further the cyclocondensation of two aryl aldehydes

with

pyrrole

forms

the

symmetrical

and

unsymmetrical

5,10,15,20-

tetraarylporphyrins in moderate yields. The structure of (2) has been confirmed by UVVisible, NMR spectra and other spectroscopic data.

Oxoporphyrinogens (2) belong to the calixpyrroles family and contain a cyclic tetrapyrrole

conjugated with quinoid moieties at their meso-positions. The structures of these compounds

in solution are uncertain because they exist as a variety of structures. They have perturbed absorption

spectra,

O2 reduction

systems,

solvochromisms

and

anion

binding.

Oxoporphyrinogens bind a variety of guest molecules at its pyrrolic NHs as well as at the

quinoids C=O groups. The oxoporphyrinogens have a strong absorption in the visible light region due to π-conjugation between tetrapyrrole and quinoid substituents. This conjugation is sensitive to binding of guests to OxPs and these compounds have been reported to behave

as probes for anions or solvents and enantiomeric excess. Hence they are useful substrate for

absorption of visible light. The covalent and non-covalent models for photosynthesis and 338

Synopsis newer materials from meso-5,10,15,20 tetrakis(4-hydroxyphenyl)porphyrins and their

oxidation to corresponding oxoporphyrinogens have been prepared and their non-covalent interactions have been examined in chapter. R3

R1

R2

NH

R3

N

R1

R2

R1

N

R3

HN

R3

O

R2

R2

Acetone, NaH reflux

O

R1

NH HN NH HN

O

O

1f 1a. R1 = R2 = R3 = H 1b. R1 = R2 = H, R3 = OH 1c. R1 = R2 = H, R3 = CH3 1d. R1 = R2 = H, R3 = OCH3 1e. R1 = R2 = H, R3 = C(CH3)3 1f. R1 = R2 = C(CH3)3, R3 = OH 1g. R1 = R2 = (OCH3), R3 = OH

2

Scheme 2.1: Synthesis of 5,10,15,20-tetraaryl porphyrins and oxoporphyrinogen The anion binding studies were examined by UV-Visible spectroscopic titrations in DMSO and CH2Cl2. The UV-visible spectra of oxoporphyrinogen (2) (5 × 10-7M) gave two peaks at 426 and 517 nm. Oxoporphyrinogen bearing C=O group at meso-position favour the binding

with all the tetrabutyl ammonium anions and strong binding was observed with fluoride. On

the addition of the solution of tetrabutylammonium fluoride (5 × 10-7M to 4 × 10-7M), the absorption peak of oxoporphyrinogen was bathochromatically shifted by 100-107 nm with decrease in relative intensity. The large red shifts have been attributed to a partially charge

transfer resulting from the anion being bounded to the –NH protons of the pyrrole constituting the chromophore. The bathochromic shift was also observed with significant broadening. The two isobestic points were observed at 558 nm and 759 nm which indicate the

complex had been formed between host and guest. The cases, binding stoichiometries were

1:1 as determined by Job’s method. The binding constant calculated by UV-Visible titrations were in the range of 106- 107for oxaporphyrinogen. Oxoporphyrinogen were used as chromophoric probes for the detection of trace water in tetrahydrofuran. The oxidative N-alkylation of porphyrin tetraphenols

339

Synopsis The meso-5,10,15,20-tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)porphyrins and NaH

were stirred in acetone at room temperature for 10–15 min followed by the reaction of benzyl bromide gave the mixture of products which were separated by column chromatography (Scheme 2.3).

O

OH

HO

NH N

N HN

OH

acetone, reflux NaH, BrCH2C6H5

O

NR1R2N

O

NR2R1N

O 3a. R1 = R2 = CH2C6H5 3b. R1 = H, R2 = CH2C6H5 3c. R1 = R2 = 4-NO2C6H4CH2 3d. R1 = H, R2 = 4-NO2C6H4CH2

OH 1g

Scheme 2.3: Synthesis of N,N’-dialkyalated oxoporphyrinogens

N,N’-dialkylated oxoporphyrinogen have been synthesized by the minor modification

of literature procedure and characterized by different spectroscopic data. Oxoporphyrinogen not only binds with selective variety of guest molecules (F-, OAc-) at its pyrrolic NH’s as

well as at the quinoid C=O groups but also binds with trace amount of water in THF at ppm level.

UV-Visible spectra of 5,10,15,20-tetrakis -(3,5-di-tert-butyl-4-oxacyclo-hexa-2,5-dienylene)-

N21, N23-tetrabenzylporphyrinogen showed a characteristic absorption maximum at 520 nm.

On addition of fluoride and acetate anions in DMSO (5×10-5) the characteristic absorption peaks

of

5,10,15,20-tetrakis-(3,5-di-tert-butyl-4-oxacyclo-hexa-2,5-dienylene)-N21,

N23-

tetrabenzylporphyrinogen (5×10-6) at 520 nm gradually decrease and two new peaks at 593

and 744nm were observed. At the same time a clear isobestic point at 540 nm was observed

for receptor 5,10,15,20-tetrakis -(3,5-di-tert-butyl-4-oxacyclo-hexa-2,5-dienylene)-N21, N23-

tetrabenzylporphyrinogen which indicates that there is a balance in the solution and the complex had been formed between host and guest.

340

Synopsis

Chapter III

Synthesis of hetero-porphyrinogens in acidic ionic liquids and their Non-covalent interaction Porphyrinogens are meso reduced porphyrins and they have important role in the

synthesis of both natural and artificial porphyrins. The dialkyl, diaryl or alkyl-aryl

substituents at meso sp3 hybridized carbons prevent the oxidative aromatization of

porphyrinogen to porphyrins. The stable form of porphyrinogens is calixpyrroles where all the meso carbon are sp3 hybridized. The other form of porphyrinogen or calixphyrins where

at least one meso carbon is sp2 hybridized. The core-modified porphyrinogens have been

synthesized by replacement of one or more core nitrogen atoms of parent porphyrinogen with chalcogen atoms such as O, S, Se and Te.

The reaction of thiophene with n-butyllithium (2 equiv.) followed by reaction with acetophenone

afforded

the

corresponding

2,5-bis[(1-phenyl-1-

hydroxymethyl)methyl]thiophene which further on reaction with excess pyrrole in the presence of BF3.OEt2 gave thia-tripyrromethane in good yields.

The 5,10,15,20-tetramethyl-5’,10’,15’,20’-tetraphenyl calix[2]thieno[2]pyrrole (3a)

was synthesized by reaction of 2,5-bis[(1-phenyl-1-pyrrolomethyl)methyl]thiophene with

2,5-bis[(1-phenyl-1-hydroxymethyl)methyl]thiophene in presence of methanesulfonic acid (Scheme 3.1). In 1H NMR spectrum of 5,10,15,20-tetramethyl-5’,10’,15’,20-tetraphenyl calix[2]thieno[2]pyrrole the appearance of singlet at 2.05 ppm for twelve methyl protons, two multiplet at 6.03 and 6.55 ppm for eight

β-pyrrolic and β-thiophenic protons, another

multiplet at 7.12 ppm was assigned for twenty aryl protons and finally a broad singlet at 7.79 ppm was assigned for pyrrolic –NH protons of calix[2]thieno[2]pyrrole. The high resolution

mass spectrum (HRMS) showed [M+H]+ peak at m/z 711.2663, is due to C48H42S2N2. The

peaks of all other remaining protons and carbons were also observed in the 1H and 13C NMR spectrum of the molecule. Based on the above spectral data, the structure of the compound was

unambiguously

calix[2]thieno[2]pyrrole.

established

as

5,10,15,20-tetramethyl-5’,10’,15’,20-tetraphenyl

341

Synopsis X

X

H3 C NH

H3 C

CH3

S

OH

1 HN

S

OH

1. DCM, rt 2. CH3SO3 H

CH3

R1

R2

NH

S

S

HN

R1 R2

R2

R1 3 3a. R1 = CH3, R2 = C6H5 3b. R1 = CH3, R2 = C6H5OCH3 3c. R1 = C6H5, R2 = C6H5

2 X

R2

R1

X 2a. X = H 2b. X = OCH3 2c. X = Cl 2d. X = Br 2e. X = NO2

Scheme 3.1: Synthesis of core modified porphyrinogens The cation binding studies were examined by UV-Visible spectroscopic titrations in

DMSO.. The UV-visible spectra of compound 3a (5 × 10-5M) gave a peak at 259 nm and on

the addition of the solution of mercury(II)perchlorate (5 × 10-5M to 4 × 10-5M ), the absorption peak was bathochromatically shifted by 5-6 nm with increase in relative intensity. The red shifts have been attributed to a partial charge transfer resulting from the cation being

bound to the -S- of the thiophene constituting the chromophore. The bathochromic shift was

also observed with significant broadening which indicate that there is a balance in the solution and the complex has been formed between host and guest. The cases, binding stoichiometries were 1:1 as determined by Job’s method and calculated by UV-Visible titrations.

342

binding constant were

Synopsis Chapter IV Synthesis of functional core modified porphyrins in acidic ionic liquids and their noncovalent interactions The core-modified porphyrins have different aromatic character and stabilize the metals in unusual oxidation states than the normal porphyrins. The assembly of such heteroatom

substituted porphyrin (N3S, N3O, N2S2, N2O2, N2SO, etc.) with normal porphyrin (N4 core) or an assembly of two different heteroatom substituted porphyrins would offer unique arrays with unusual electronic structure and interesting properties.

The 21,23-dithiaporphyrins have been prepared by the reaction of diols which were synthesized by the reaction of thiophene and substituted benzaldehyde in presence of

TMEDA and butyl lithium in dry hexane. Further the reaction of diol with excess of pyrrole in presence of task-specific acidic ionic liquids gave the trimer and this trimer reacted with

diol in presence of acidic ionic liquids followed by oxidation with DDQ and molecular

oxygen gave desired products as core modified porphyrins in moderate yields (Scheme 4.1). The structures were confirmed by UV-Visible and NMR spectroscopic methods. R1

R1

R1

S

NH HN 1 HO R1

+ S 2

OH

1. Acidic ILs, DCM 2. DDQ

R1

S

N

N

S

R1

R1 R1 3

3a. R1 = H 3b. R1 = CH3 3c. R1 = C(CH3)3 3d. R1 = OCH3

Scheme 4.1: Synthesis of core modified porphyrins Symmetrical and unsymmetrical core modified porphyrins have been synthesized by the

reaction of diols with substituted benzaldehyde and pyrrole in presence of acidic ionic liquids in DCM followed by the oxidation with oxidising agent like DDQ and molecular oxygen

gave the mixture of three core modified porphyrins (Scheme 4.2). The mixtures of three porphyrins were separated by silica gel column chromatography. 343

Synopsis But

S

HO

+ OH

+

N H

1. acidic ILs 2. DDQ

But

But

But

But

But

CHO

But

NH N

S

But + But

N HN

N

But + But

N HN

But

But

4

5

S

N

N

S

But

But 3c

Scheme 4.2: Synthesis of symmetrical and unsymmetrical core modified porphyrins The

5,10,15,20-tetrakis(4-tertbutylphenyl)porphyrinatozinc

(6)

was

synthesized

by

metallation of 5,10,15,20-tetrakis(4-tert-butylphenyl)porphyrin with zinc acetate by refluxing in DMF and characterized by NMR IR UV-Visible and other spectroscopic data. The core modified porphyrin (7) was synthesized by above method, the reaction of diol, pyridyl 4carboxaldehyde and pyrrole in presence of acidic ionic liquid in dichloromethane followed by

oxidising agent DDQ gave a mixture of three porphyrins which were isolated by column

chromatography. Non-covalent interactions of metalloporphyrin with core modified porphyrin were carried out in dichloromethane by UV-Visible and other spectroscopic data.

Ar N N Ar

Zn

N

6

Ar N

N

N

S

NH

N

Ar

Ar = 4-C(CH3)3C6H4 7

Scheme 4.3: Non-covalent interaction of core modified porphyrin with 5,10,15,20tetrakis(4-tertbutylphenyl)porphyrinatozinc

344

Synopsis Chapter V Synthesis of 5-substituted dipyrromethanes and their applications in the synthesis of expanded porphyrins and core-modified expanded porphyrins

The expanded porphyrins are synthetic analogues of porphyrin and they contain more than 18

π electrons in conjugated pathway either due to an increased number of pyrroles or due to multiple of meso-carbon bridges. The expanded porphyrins bind to various anions and they

are used in materials and medicinal chemistry. The expanded porphyrins coordinate with large cations like lanthanide and actinides, anions complexation and transport magnetic resonance imaging constrast agents, photodynamic therapy sensitizers and building blocks in

nonlinear materials. The important members of expanded porphyrins containing five pyrroles

or heterocycles are pentaphyrin, sapphyrin and smaragdyrin. The synthesis of sapphyrin and

related expanded porphyrins by condensation of dipyrromethanes and tripyrromethane in

presence of different acids and their non-covalent interactions has been reported in the present chapter.

The 5-substituteddipyrromethanes are important precursors for the synthesis of

calix[4]pyrroles, calix[4]phyrins, porphyrins, expanded porphyrins and porphyrin analogues.

The 5-substituteddipyrromethanes were synthesized by the reaction of pyrrole with aromatic aldehydes in presence of different acidic conditions in good to excellent yields at room

temperature. A series of thiophene diols have been synthesized starting from substituted

acetophenones and different substituted benzaldehydes and used as organic acids in the synthesis of 5-substituted dipyrromethanes (scheme 5.1). R' R1 N H 1

R2 O 2

H3C

OH

S

R" OH

CH3

R1

R2

NH

DCM R' = R'' = 4-NO2Ph

HN 3 3a. R1 = H, R2 = C6H5 3b. R1 = H, R2 = p-CH3C6H5 3c. R1 = H, R2 = p-OCH3C6H4 3d. R1 = H, R2 = 3,5-(C(CH3)3)2-p-OH-C6H2 3e. R1 = H, R2 = 3,5-(OCH3)2-p-OH-C6H2 3f. R1 = H, R2 = C6F5

Scheme 5.1: Synthesis of 5-substituted dipyrromethane

345

Synopsis The reaction of 5-aryldipyrromethanes (3) in trifluoroacetic acid in dichloromethane followed

by oxidation with chloranil gave 5,10,15,20-tetraarylporphyrins (5) and 5,10,15,20 sapphyrins (6), while the same reactions gave N-confused porphyrins (4) in presence of ptoluene sulfonic acid (Scheme 5.2). The structures of above products were confirmed by different spectroscopic techniques. R2

R1

NH HN 3

R1

R2

R2

NH

R2

N

R1

R1

R1

R2

HN

+

R1

R1

R1

R2 R1

N

R1 R2

R2

R1

R2 4

R1

R1

R1

N

R2 5

R2

R1

HN

N

R1

R1

N

NH HC

1. equiv, TFA / CH2Cl2 2.chloronil

R1

R1

R1 PTSA, DCM, DDQ

R1

R2

R1

N H H N

H N

N

6

R1

R1

R1

R2

6a. R1 = R2 = H 6b. R1 = H, R2 =OH 6c. R1 = H, R2 = OCH3 6d. R1 = C(CH3)3 R2 = OH 6e. R1 = (OCH3)2, R2 = OH

R1

Scheme 5.2: Synthesis of sapphyrins and N-confused porphyrin Reaction of dipyrromethane with tripyrromethane The reaction of tripyrromethane (7) with dipyrromethane (3) in TFA, followed by oxidation gave core modified smaragdyrin (8) and related compounds (Scheme 5.3)

NH HN 3 + NH

H N

N DCM, TFA, DDQ

HN

HN

NH H N

HN

8

7

Scheme 5.3: Synthesis of samaragdyrin 346

Synopsis Synthesis of 30π and 40π expanded porphyrinoids The reaction of pentafluorobenzaldehyde with furan in dry dichloromethane in presence of

BF3.OEt2 followed by oxidation with FeCl3 gave the mixture of 30π and 40π expanded porphyrinoids which were separated by column chromatography and characterized by different spectroscopic data (Scheme 5.4).

O 8

CHO

F

+

F

F

F F

1. 1 equiv BF3.O(Et)2 CH2Cl2 2. FeCl3

C6F5 C6F5

C6F5

C6F5

O

O

O

O C6F5

C6F5

O

C6F5

C6F5

O C6F5

O O

C6F5

30π

O C6F5

O

C6F5

9

20π

O

C6F5

C6F5

O

O

O

C6F5

O O C6F5

O O 10

C6F5

C6F5

40π

Scheme 5.4: Synthesis of 30π and 40π expanded porphyrinoids The non-covalent interactions with sapphyrins and related expanded porphyrinoids were examined by UV-Visible and NMR spectroscopy

347