Synthesis,Characterization and Properties of Expanded Pyriporphyrins: A New Family of Alkylidenyl Porphyrin Homologues Bearing meso‐Exocyclic Double Bonds

We present the synthesis and characterization of a new family of expanded meso‐alkylidenyl (2,6‐pyri)porphyrinoids bearing multiple exocyclic double bonds at the meso‐positions. The synthesis was accomplished by using mixed pyrrole condensation. Similar to meso‐alkylidenyl porphyrinoids, this study revealed that pyriporphyrinoids do not possess a porphyrin‐like, global‐aromatic character. The synthesized 2,6‐pyripentaphyrin 1 displays selective ratiometric sensing of pyrophosphate anion in organic solvent.     

Synthesis of meso‐Pyrrole‐Substituted 22‐Oxacorroles by a “3+2” Approach

Unsymmetrical 22‐oxacorrole containing two aryl groups and one pyrrole group at the meso position was synthesized by condensing one equivalent of 16‐oxatripyrrane with one equivalent of meso aryl dipyromethane under mild acid‐catalyzed conditions followed by oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ). This [3+2] condensation approach was expected to yield meso‐free 25‐oxasmaragdyrin but unexpectedly afforded unsymmetrical meso‐pyrrole‐substituted 22‐oxacorrole. We demonstrated the versatility of the reaction by synthesizing four new meso‐pyrrole‐substituted 22‐oxacorroles. The reactivity of α‐position of meso‐pyrrole was tested by carrying out various functionalization reactions such as bromination, formylation, and nitration and obtained the functionalized meso‐pyrrole‐substituted 22‐oxacorroles in decent yields. The X‐ray structure obtained for one of the functionalized meso‐pyrrole substituted 22‐oxacorrole revealed that the macrocycle was nearly planar and the meso‐pyrrole was in the perpendicular orientation with respect to the macrocyclic plane. The meso‐pyrrole‐substituted 22‐oxacorroles absorb strongly in 400–700 nm region with one strong Soret band and four weak Q bands. The 22‐oxacorroles are strongly fluorescent and showed emission maxima at ≈650 nm with decent quantum yields and singlet‐state lifetimes. The 22‐oxacorroles are redox‐active and exhibited three irreversible oxidations and one or two reversible reduction(s). A preliminary biological study indicated that meso‐pyrrole corroles are biocompatible.     

Syntheses of Amino Group‐Substituted N‐Confused Porphyrins

Tetraphenyl N‐confused porphyrins (NCTPP) bearing amino substituents were synthesized for the purpose of functionalization toward water‐soluble and biocompatible molecules. The Pd‐catalyzed coupling reaction of 4‐ethynylaniline with the 2‐bromo NCTPP Ag(III) complex yields Pd(II) and Ag(III) coupling products ( 4a and 4b ), at 39% and 55%, respectively. The identities of these products were confirmed by the differences in the isotope patterns of their molecular ion peaks as well as other spectroscopic data. The Ag(III) coupling product, 4b , was demetallated to form the final product, 5 , with a yield of 85%. The meso‐tetrakis(4‐nitrophenyl) N‐confused porphyrin, 6 , was synthesized through a methanesulfonic acid catalyzed condensation of pyrrole with the 4‐nitrobenzaldehyde with a yield of 6.8%. Reduction of the compound to meso tetrakis(4‐aminophenyl) N‐confused porphyrin, 7 , was achieved with a yield of 90%.     

Synthetic polyhydroxypolyamides from galactaric,xylaric, D‐glucaric,and D‐mannaric acids and alkylenediamine monomers—some comparisons

The condensation polymerization in a methanol solution of four different esterified aldaric acids (D ‐glucaric, meso‐xylaric, meso‐galactaric, and D ‐mannaric) with even‐numbered alkylenediamines (C₂–C₁₂) gave polyhydroxypolyamides whose water solubilities and melting points were compared. In general, an increase in the alkylenediamine monomer length resulted in decreased polyamide water solubility. Differences in the polymer melting points and water solubilities were linked primarily to conformational differences of the monomer aldaryl units; for example, polyamides from meso‐galactaric acid with an extended zigzag conformation aldaryl monomer unit had higher melting points and lower water solubilities than those from D ‐glucaric and meso‐xylaric acids. The latter acid monomer units tended toward bent conformations that served to diminish intermolecular attractive forces between polymer chains, affecting polymer solubility and melting characteristics. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 594–603, 2000     

Synthesis of meso‐tetrakis(4‐chlorocoumarin‐3‐yl)porphyrins

meso‐Tetrakis(4‐chlorocoumarin‐3‐yl)porphyrins were prepared by condensation of corresponding 4‐chlorocoumarin‐3‐carboxaldehydes and pyrrole in the presence of trifluoro acetic acid (TFA) in dichloromethane followed by oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ). These porphyrins exhibited the atropisomerism due to ortho substituent of meso aryl groups. The atropisomers of meso‐tetrakis(4‐chloro‐6‐methylcoumarin‐3‐yl)porphyrin were separated and identified by ¹H‐nmr spectra. Zinc complexes of these porphyrins were synthesized and characterized by ms, ¹H nmr, ir and uv‐vis spectra.     

Trimeric and Tetrameric Electron‐Deficient Porphyrin Tapes

New hybrid porphyrin tapes comprising meso‐3,5‐di‐tert‐butylphenyl‐substituted Zn^II‐porphyrins ( D ) and meso‐pentafluorophenyl‐substituted Zn^II‐porphyrins ( A ) were synthesized via cross‐condensation of meso‐formyl porphyrins 1 , 5 , and 9 with oligopyrromethanes 2 and 6 as key steps. These hybrid tapes exhibit improved solubilities and enhanced chemical stability as compared with original Dn porphyrin tapes, and all display remarkably coplanar structures favorable for π‐conjugation. The absorption spectrum of ADDA displays Q‐like bands at 1400 and 1657 nm with a vibronic structure characteristic of porphyrinoids. The cyclic voltammograms exhibited positively shifted oxidation and reduction waves in the order of DDD < DAD < ADA < AAA . Tetrameric tape ADDA displays five reversible waves in a narrow range of 1.13 V. Two‐photon absorption (TPA) measurement confirmed that the π‐conjugation path is extended from 12 to ADDA and the molecular polarizability of ADA is larger than that of AAA .     

Asymmetric Synthesis of All Possible Stereomers of 4‐Aminoglutamic Acid via Michael Condensation of Chiral Ni(II) Complexes of Glycine and Dehydroalanine

A new method for asymmetric synthesis of all possible stereomers of 4‐aminoglutamic acid has been developed. The method is based on asymmetric Michael condensation of the nucleophilic moiety of glycine and electrophilic moiety of dehydroalanine in their chiral Ni(II) complexes of the Schiff's bases with (S)‐ and (R)‐2‐N‐(N′‐benzylprolyl)aminobenzophenones, resulting in the formation of dimeric complexes of 4‐aminoglutamic acid. Stereoselectivity of the asymmetric condensation of the complexes exceeded 94%. The condensation of nucleophilic and electrophilic complexes in four possible combinations has resulted in the formation of dimeric complexes of all the stereomers of 4‐aminoglutamic acid: (2S,4S), (2S,4R)‐meso and (2R,4R). Optically active stereomers of 4‐aminoglutamic acid with high optical purity were isolated after decomposition of the dimeric complexes.     

Porphyrin Analogues of a Trityl Cation and Anion

Porphyrin‐stabilized meso‐ or β‐carbocations were generated upon treatment of the corresponding bis(4‐tert‐butylphenyl)porphyrinylcarbinols with trifluoroacetic acid (TFA). Bis(4‐tert‐butylphenyl)porphyrinylcarbinols were treated with TFA to generate the corresponding carbocations stabilized by a meso‐ or β‐porphyrinyl group. The meso‐porphyrinylmethyl carbocation displayed more effective charge delocalization with decreasing aromaticity compared with the β‐porphyrinylmethyl carbocation. A propeller‐like porphyrin trimer, tris(β‐porphyrinyl)carbinol, was also synthesized and converted to the corresponding cation that displayed a more intensified absorption reaching over the NIR region. meso‐Porphyrinylmethyl carbanion was generated as a stable species upon deprotonation of bis(4‐tert‐butylphenyl)(meso‐porphyrinyl)methane with potassium bis(trimethylsilyl)amide (KHMDS) and [18]crown‐6, whereas β‐porphyrinylmethyl anions were highly unstable.     

meso‐Ester and Carboxylic Acid Substituted BODIPYs with Far‐Red and Near‐Infrared Emission for Bioimaging Applications

A series of meso‐ester‐substituted BODIPY derivatives 1–6 are synthesized and characterized. In particular, dyes functionalized with oligo(ethylene glycol) ether styryl or naphthalene vinylene groups at the α positions of the BODIPY core ( 3 – 6 ) become partially soluble in water, and their absorptions and emissions are located in the far‐red or near‐infrared region. Three synthetic approaches are attempted to access the meso‐carboxylic acid (COOH)‐substituted BODIPYs 7 and 8 from the meso‐ester‐substituted BODIPYs. Two feasible synthetic routes are developed successfully, including one short route with only three steps. The meso‐COOH‐substituted BODIPY 7 is completely soluble in pure water, and its fluorescence maximum reaches around 650 nm with a fluorescence quantum yield of up to 15 %. Time‐dependent density functional theory calculations are conducted to understand the structure–optical properties relationship, and it is revealed that the Stokes shift is dependent mainly on the geometric change from the ground state to the first excited singlet state. Furthermore, cell staining tests demonstrate that the meso‐ester‐substituted BODIPYs ( 1 and 3 – 6 ) and one of the meso‐COOH‐substituted BODIPYs ( 8 ) are very membrane‐permeable. These features make these meso‐ester‐ and meso‐COOH‐substituted BODIPY dyes attractive for bioimaging and biolabeling applications in living cells.     

meso‐Nitro‐ and meso‐Aminosubporphyrinatoboron(III)s and meso‐to‐meso Azosubporphyrinatoboron(III)s

meso‐Nitrosubporphyrinatoboron(III) was synthesized by nitration of meso‐free subporphyrin with AgNO₂/I₂. The subsequent reduction with a combination of NaBH₄ and Pd/C gave meso‐aminosubporphyrinatoboron(III). meso‐Nitro‐ and meso‐amino‐groups significantly influenced the electronic properties of subporphyrin, which has been confirmed by NMR and UV/Vis spectra, electrochemical analysis, and DFT calculations. Oxidation of meso‐aminosubporphyrinatoboron(III)s with PbO₂ cleanly gave meso‐to‐meso azosubporphyrinatoboron(III)s that exhibited almost coplanar conformations and large electronic interaction through the azo‐bridge.     

meso–meso‐Linked Diarylamine‐Fused Porphyrin Dimers

A meso–meso‐linked diphenylamine‐fused porphyrin dimer and its methoxy‐substituted analogue were synthesized from a meso–meso‐linked porphyrin dimer by a reaction sequence involving Ir‐catalyzed β‐selective borylation, iodination, meso‐chlorination, and S_NAr reactions with diarylamines followed by electron‐transfer‐mediated intramolecular double C?H/C?I coupling. While these dimers commonly display characteristic split Soret bands and small oxidation potentials, they produced different products upon oxidation with tris(4‐bromophenyl)aminium hexachloroantimonate. Namely, the diphenylamine‐fused porphyrin dimer was converted into a dicationic closed‐shell quinonoidal dimer, while the methoxy‐substituted dimer gave a meso–meso, β‐β doubly linked porphyrin dimer.     

5,20‐Bis(ethoxycarbonyl)‐Substituted Antiaromatic [28]Hexaphyrin and Its Bis‐NiII and Bis‐CuII Complexes

5,20‐Bis(ethoxycarbonyl)‐[28]hexaphyrin was synthesized by acid catalyzed cross‐condensation of meso‐diaryl‐substituted tripyrrane and ethyl 2‐oxoacetate followed by subsequent oxidation. This hexaphyrin was found to be a stable 28π‐antiaromatic compound with a dumbbell‐like conformation. Upon oxidization with PbO₂, this [28]hexaphyrin was converted into an aromatic [26]hexaphyrin with a rectangular shape bearing two ester groups at the edge side. The [28]hexaphyrin can incorporate two Ni^II or Cu^II metals by using the ester carbonyl groups and three pyrrolic nitrogen atoms to give bis‐Ni^II and bis‐Cu^II complexes with essentially the same dumbbell‐like structure. The antiaromatic properties of the [28]hexaphyrin and its metal complexes have been well characterized.     

An Electron‐Deficient Porphyrin Tape

Hexakis(pentafluorophenyl)‐substituted meso–meso‐linked Zn^II–diporphyrin ( 9 ), which was prepared by the acid‐catalyzed cross‐condensation of 1,1,2,2‐tetrapyrroethane ( 5 ) with dipyrromethane dicarbinol ( 6 ), was converted into meso–meso,β‐β,β‐β triply linked Zn^II–diporphyrin 3 by oxidation with 2,3‐dichloro‐5,6‐dicyanobenzoquinone (DDQ) and Sc(OTf)₃. Beside the red‐shifted absorption spectrum and split first oxidation potential that are common to the triply‐linked Zn^II–diporphyrins, diporphyrin 3 exhibited considerably improved chemical stability owing to a lowered HOMO and good solubility in common organic solvents. The two‐photon absorption (TPA) cross‐section and S₁‐state lifetime of compound 3 were 1700 GM and 3.3 ps, respectively.     

Synthesis,Molecular Structure and Coordination Chemistry of the First 1‐Aza‐3,7‐diphosphacyclooctanes

The first representatives of a novel type of cyclic bis‐phosphines, namely, 1‐aza‐3,7‐diphosphacyclooctanes ( 4 , 5 ), were synthesized by condensation of 1,3‐bis(arylphosphino)propanes ( 2 , 3 ; aryl = phenyl or mesityl), formaldehyde and 5‐aminoisophthalic acid. Only the meso isomers were obtained, in good to satisfactory yield. The cyclic bis‐phosphines readily form P,P chelate complexes ( 6 , 7 ) with [PtCl₂(cod)] (cod = 1,5‐cyclooctadiene). The bisphosphine 4 and the corresponding complex 6 are soluble in water in the presence of two equivalents of alkali metal hydroxide. The molecular structures of 1‐(meta‐dicarboxyphenyl)‐3,7‐dimesityl‐1‐aza‐3,7‐diphosphacyclooctanes ( 5 ) and cis‐{P,P‐1‐(meta‐dicarboxyphenyl)‐3,7‐diphenyl‐1‐aza‐3,7‐diphosphacyclooctane}dichloroplatinum(II) ( 6 ) are reported.     

Dibutylsilylene Derivatives of Tartaric Acid

Crystals of the bis(tert‐butyl)silylene (DTBS) derivatives of the tartaric acids were synthesized from D ‐, L ‐, rac‐, and meso‐tartaric acid and DTBS bis(trifluoromethanesulfonate): two polymorphs of Si₂tBu₄(L ‐Tart1,2;3,4H_–4) (L ‐ 1a and L ‐ 1b ), the mirror image of the denser modification (D ‐ 1b ) as well as the racemate ( 2 ), and the meso analogue Si₂tBu₄(meso‐Tart1,3;2,4H_–4) ( 3 ). The structures were determined by single‐crystal X‐ray diffraction. The threo‐configured D ‐ and L ‐ (and rac‐) tartrates were coordinated by two tBu₂Si units forming five‐membered chelate rings, whereas the erythro‐configured meso‐tartrate formed six‐membered chelate rings. The new compounds were analyzed by NMR techniques, including ²⁹Si NMR spectroscopy, and single‐crystal X‐ray crystallography.     

meso‐Free BIII Subporphyrins with Electron‐donating Groups

meso‐Free B^III 5,10‐bis(p‐dimethylaminophenyl)subporphyrins were synthesized. They display red‐shifted absorption and fluorescence spectra, bathochromic behaviors in polar solvents, a high fluorescence quantum yield (Φ_F=0.57), and a small HOMO–LUMO gap mainly due to destabilized HOMO as compared with meso‐free B^III 5,10‐diphenylsubporphyrin. This subporphyrin serves as a nice precursor of various meso‐substituted B^III subporphyrins such as B^III meso‐nitrosubporphyrin, B^III meso‐aminosubporphyrin, and meso‐meso’ linked B^III azosubporphyrin dimer. Reactions of meso‐free B^III subporphyrins with NBS or bis(2,4,6‐trimethylpyridine)bromonium hexafluorophosphate gave meso‐meso′ linked subporphyrin dimers, often as a major product along with meso‐bromosubporphyrins.     

The meso Helix: Symmetry and Symmetry‐Breaking in Dynamic Oligourea Foldamers with Reversible Hydrogen‐Bond Polarity

Oligoureas (up to n=6) of meso cyclohexane‐1,2‐diamine were synthesized by chain extension with an enzymatically desymmetrized monomer 2 . Despite being achiral, the meso oligomers adopt chiral canonical 2.5‐helical conformations, the equally populated enantiomeric screw‐sense conformers of which are in slow exchange on the NMR timescale, with a barrier to screw‐sense inversion of about 70 kJ mol^?1. Screw‐sense inversion in these helical foldamers is coupled with cyclohexane ring‐flipping, and results in a reversal of the directionality of the hydrogen bonding in the helix. The termini of the meso oligomers are enantiotopic, and desymmetrized analogues of the oligoureas with differentially and enantioselectively protected termini display moderate screw‐sense preferences. A screw‐sense preference may furthermore be induced in the achiral, meso oligoureas by formation of a 1:1 hydrogen‐bonded complex with the carboxylate anion of Boc‐d ‐proline. The meso oligoureas are the first examples of hydrogen‐bonded foldamers with reversible hydrogen‐bond directionality.     

Synthesis and Characterization of Azobenzene–Porphyrins

A new series of novel covalently connected meso‐tetrakis(3‐azophenyl‐4‐hydroxy‐5‐methoxyphenyl)porphyrins were synthesized by linking azobenzene unit at the meta‐position of the meso‐phenyl group. These are characterized by UV–vis, IR, ¹H‐NMR, CHN, and FABMS spectroscopic techniques. All the porphyrin compounds showed a typical high energy Soret band at around 435 nm and azobenzene absorption at around 350 nm in UV–vis spectra. Fluorescence intensity of meso‐tetrakis(3‐(4‐methoxyazophenyl)‐4‐hydroxy‐5‐methoxyphenyl)porphyrin ( 2c ) has been observed to be maximum compared with other azobenzene porphyrins.     

Cross‐Conjugated Hexaphyrins and Their Bis‐Rhodium Complexes

A cross‐conjugated hexaphyrin that carries two meso‐oxacyclohexadienylidenyl (OCH) groups 9 was synthesized from the condensation of 5,10‐bis(pentafluorophenyl)tripyrrane with 3,5‐di‐tert‐butyl‐4‐hydroxybenzaldehyde. The reduction of 9 with NaBH₄ afforded the Möbius aromatic [28]hexaphyrin 10 . Bis‐rhodium complex 11 , prepared from the reaction of 10 with [{RhCl(CO)₂}₂], displays strong Hückel antiaromatic character because of the 28 π electrons that occupy the conjugated circuit on the enforced planar structure. The oxidation of 11 with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) yielded complexes 12 and 13 depending upon the reaction conditions. Both 12 and 13 are planar owing to bis‐rhodium metalation. Although complex 12 bears two meso‐OCH groups at the long sides and is quinonoidal and nonaromatic in nature, complex 13 bears 3,5‐di‐tert‐butyl‐4‐hydroxyphenyl and OCH groups and exhibits a moderate diatropic ring current despite its cross‐conjugated electronic circuit. The diatropic ring current increases upon increasing the solvent polarity, most likely due to an increased contribution of an aromatic zwitterionic resonance hybrid.     

Tetramethyl‐m‐benziporphodimethene and Isomeric α,β‐Unsaturated γ‐Lactam Embedded N‐Confused Tetramethyl‐m‐benziporphodimethenes

The condensation reaction of α,α′‐dihydroxy‐1,3‐diisopropylbenzene, pyrrole, and an aldehyde leads to the formation of tetramethyl‐m‐benziporphodimethene and outer α‐pyrrolic carbon oxygenated N‐confused tetramethyl‐m‐benziporphodimethenes containing a γ‐lactam ring in the macrocycle. Two isomers with the carbonyl group of the lactam ring either close to (O‐Up) or away from (O‐Down) the neighboring sp³ meso carbon were synthesized and characterized. The single crystal X‐ray diffraction analysis on the regular and γ‐lactam containing tetramethyl‐m‐benziporphodimethenes showed highly distorted macrocycles for all compounds. For O‐Up and O‐Down isomers, dimeric structures, assembling by intermolecular hydrogen‐bonding interactions through lactam rings, were observed in the solid state. Fitting the concentration dependent chemical shifts of the outer NH proton using the non‐linear regression method give a maximum association constant of 108.9 M ^?1 for the meso 4‐methylcarboxyphenyl substituted O‐Down isomer. The DFT calculations concluded that the O‐Up isomer is energetically more stable, and the keto form is more stable than the enol form.