Puttaiah Bhyrappa

An improved protocol for the synthesis of antipodal β-tetrabromo-tetraphenylporphyrin and the crystal structure of its Zn(II) complex

This work reports an improved protocol for the regioselective synthesis of 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin (H 2 TPPBr 4 ) and the crystal structure of its Zn(II) complex which shows saddle shaped geometry.

Influence of Mixed Substituents on the Macrocyclic Ring Distortions of Free Base Porphyrins and Their Metal Complexes

Crystal structures of a series of free base porphyrins, 2,3,12,13-tetra(cyano/chloro/bromo)-5,7,8,10,15,17,18,20-octaphenylporphyrin solvates [H(2)(TPP(Ph)(4)(CN)(4)) x 3 (C(2)H(4)Cl(2)), H(2)(TPP(Ph)(4)Cl(4)) x 2 (CH(3)OH), and H(2)(TPP(Ph)(4)Br(4)) x 2 THF x 1.5 (CH(3)OH)], were determined to examine the influence of mixed antipodal beta-pyrrole substitution on the stereochemistry of the porphyrin macrocycle. Nonplanarity of the porphyrin skeleton increases with an increase in size of the X group at the beta-pyrrole positions, and the root-mean-square deviation of the core atoms follows the order CN (0.508 A) < Cl (0.687 A) < Br (0.792 A). The normal-coordinate decomposition analysis of the free-base structures shows dramatic substituent- (X-)dependent out-of-plane distortions featuring saddling combined with a ruffled conformation in H(2)(TPP(Ph)(4)(CN)(4)), while it is predominantly saddled geometry in H(2)(TPP(Ph)(4)X(4)) (X = Cl, Br) structures. For H(2)(TPP(Ph)(4)X(4)) (X = Cl, Br) structures, the core elongation is along the antipodal pyrroles bearing halogen groups, and in the case of the H(2)(TPP(Ph)(4)(CN)(4)) structure, it is along the other antipodal pyrroles with phenyl groups. However, the average core, N...N separation along the transannular pyrrole direction follows the trend H(2)(TPP(Ph)(4)(CN)(4)) (4.134(4) A) < H(2)(TPP(Ph)(4)Cl(4)) (4.184(5) A) < H(2)(TPP(Ph)(4)Br(4)) (4.205(5) A). The bond lengths of the 24-atom core are comparable, but its bond angles showed significant differences along the antipodal direction bearing beta-pyrrole with X groups when compared to the other transannular pyrrole direction. The four-nitrogen porphyrin core (N(4)H(2)) exhibited weak intramolecular hydrogen bonding and also intermolecular interactions. Interestingly, H(2)(TPP(Ph)(4)Cl(4)) x 2 (CH(3)OH) shows an extended chain structure involving hydrogen-bonding interactions between the CH(3)OH...OHCH(3) (O...O) and CH(3)OH...core (N(4)H(2)) interactions. The nonplanar geometry of these free base porphyrin rings suggests a more predominant influence of steric crowding of the peripheral substituents rather than intermolecular interactions. The four-coordinated Ni(TPP(Ph)(4)(CN)(4)) x C(6)H(14) x 0.5 (C(2)H(4)Cl(2)) complex shows an enhanced ruffling of the macrocycle along with the saddled conformation relative to more saddle-shaped H(2)(TPP(Ph)(4)(CN)(4)) x 3 (C(2)H(4)Cl(2)) structure. The crystal structure of the Zn(TPP(Ph)(4)Cl(4))(Py) x (C(2)H(4)Cl(2)) complex features distorted square-pyramidal geometry with the reduction in the nonplanarity of the core in contrast to its free base porphyrin structure. Normal-coordinate-decomposition analysis for the out-of-plane displacement of the core atoms in the Ni(TPP(Ph)(4)(CN)(4)) structure showed enhanced ruffling combined with saddling of the macrocycle while Zn(TPP(Ph)(4)Cl(4))(Py) exhibited mainly saddling when compared to their corresponding free base porphyrin structures. The nonplanar distortion in the Ni(TPP(Ph)(4)(CN)(4)) x (C(6)H(14)) x 0.5 (C(2)H(4)Cl(2)) complex indicates that the contracted porphyrin core and the weak intermolecular interactions are responsible for the nonplanar geometry of the macrocyclic ring.

[5,10,15,20-Tetrakis(2-thienyl)porphyrinato]zinc(II)

In the title complex, [Zn(C(36)H(20)N(4)S(4))], the Zn(II) ion occupies a special position on an inversion centre with four-coordinate geometry. The porphyrin ring shows a wave-like conformation, with the closest interporphyrin plane separation being 3.60 (6) A. The two disordered thienyl groups are inclined with respect to the porphyrin plane at angles of 70 (4) and 67 (2) degrees.

meso-Tetrathienylporphyrins: Steady-state emission and structural properties

Abstractmeso-Tetra (2′- and 3′-thienyl)porphyrins and their Zn(II)-complexes were examined by steady-state fluorescence measurements. These molecules exhibit significant bathochromic shift in their emission bands with decreased quantum yields relative to their correspondingmeso-tetraphenylporphyrin derivatives. The crystal structure of 5,10,15,20-tetrakis(3′-thienyl)porphinato zinc(II) shows planar and nonplanar stereochemical features of the macrocycle. One of the macrocycle shows nearly planar while the other exhibited predominantly saddle-shaped geometry. The extent of displacement of the Β-pyrrole carbons in the nonplanar (saddle) conformation is as high as ± 0·422 Å.

Unusual solvent dependent electronic absorption spectral properties of nickel(II) and copper(II) perhaloporphyrins

Electronic absorption spectra of divalent metal (Ni(II) and Cu(II)) complexes of 2,3,7,8,12,13,17,18-octa(bromo/chloro)-5,10,15,20-tetraphenylporphyrins (MOXTPP; X = Br, Cl) were examined in various solvents. M(II) perhaloporphyrins exhibited dramatic shifts in their optical absorption spectral features relative to the corresponding metallotetraphenylporphyrins, MTPPs. Copper(II) perhaloporphyrins show significant red-shifts of the absorption bands in coordinating solvents relative to that observed for nickel(II) perhaloporphyrins. The large red-shift of the electronic absorption bands and the gain in intensity of the longest wavelength band (Q(0,0)), of Cu(II) perhaloporphyrins in certain coordinating solvents is comparable to that found in meso-tetraphenylporphinatozinc(II), ZnTPP. The solvent dependent spectral features of M(II) perhaloporphyrins are attributed to a coordinative interaction of the solvent with the core metal ion induced by the electron deficient porphyrin macrocycle.

Facile synthesis and supramolecular network of a Zn(II)–octaesterporphyrin

The present work reports the synthesis of an octaester porphyrin and its Zn(II) complex which shows an unusual two-dimensional supramolecular coordination network structure.

Influence of steric hindrance on the solvent-dependent absorption spectral behavior of highly brominated free base porphyrin and its Zn(II) complex

Electronic absorption spectra of highly brominated free base porphyrin, 2,3,7,8,12,13,17,18-octabromo-tetrakis(2′,6′-dibromo-3′,5′-dimethoxyphenyl)porphyrin, H2T(3′,5′-DMP)PBr16 and its Zn(II) complex were examined in various solvents. These derivatives exhibit red-shifted absorption spectral features in polar solvents relative to that observed in less polar or nonpolar solvents. The extent of red shifts observed in highly brominated porphyrins is less than those reported for the corresponding 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin, H2TPPBr8 and its Zn(II) complex. The crystal structure of the H2T(3′,5′-DMP)PBr16 showed saddle-shaped geometry with steric hindrance of the bromo groups on the opposite phenyl rings which provide limited open access to the core. The decreased red shift of the absorption spectral bands of MT(3′,5′-DMP)PBr16 (M = 2H, Zn(II)) derivatives when compared to unhindered MTPPBr8 is possibly due to the steric hindrance offered by the ortho-bromo groups rather than the electronic effects of the porphyrin π-system.

Covalently linked bisporphyrins bearing tetraphenylporphyrin and perbromoporphyrin units: Synthesis and their properties

A series of covalently linked bisporphyrins bearingmeso-tetraphenylporphyrin (TPP) and octabromotetraphenylporphyrin (OBTPP) units have been synthesised and characterised. Electrochemical studies on these bisporphyrins showed an anodic shift (∼ 30–60 mV) of the TPP unit and a cathodic shift (∼40-80 mV) of OBTPP in redox potentials. Further, steady-state fluorescence studies on bisporphyrins indicated dramatic decrease in fluorescence quantum yields of the TPP moiety. Electrochemical redox and fluorescence data seem to suggest the possible existence of intramolecular interactions in these bisporphyrins

(2,3,5,10,12,13,15,20-Octa­phenyl­porphinato)copper(II) 1,1,2,2-tetra­chloro­ethane solvate

The title complex, [Cu(C68H44N4)]·C2H2Cl4, exhibits nearly square-planar geometry around the CuII centre and the macrocyclic ring is almost planar. The porphyrin molecule has an approximate non-crystallographic inversion centre (Ci), and a non-crystallographic twofold rotation axis (C 2) within the CuII–porphyrin ring plane. Further, it has non-crystallographic twofold rotation axis and mirror plane (Cs) symmetry perpendicular to the molecular plane. The molecular packing of the complexes and the solvent molecules shows weak intermolecular C—H⋯π, C—H⋯Cl and C—H⋯N interactions, forming a clathrate-like structure.

2,3,12,13-Tetrabromo-5,10,15,20-tetrakis(4-butoxyphenyl)porphyrin 1,2-dichloroethane solvate.

Nonmesogenic 2,3,12,13-tetrabromo-5,10,15,20-tetrakis(4-butoxyphenyl)porphyrin crystallizes as the title 1,2-dichloroethane solvate, C(60)H(58)Br(4)N(4)O(4) x C(2)H(4)Cl(2). The porphyrin ring shows a nonplanar conformation, with an average mean plane displacement of the beta-pyrrole C atoms from the 24-atom (C(20)N(4)) core of +/-0.50 (3) A. The 1,2-dichloroethane solvent is incorporated between the porphyrin units and induces the formation of one-dimensional chains via interhalogen Cl...Br and butyl-aryl C-H...pi interactions. These chains are oriented along the unit-cell a axis, with the macrocyclic ring planes lying almost parallel to the (010) plane. The chains are arranged in an offset fashion by aligning the butoxy chains approximately above or below the faces of the adjacent porphyrin core, resulting in decreased interporphyrin pi-pi interactions, and they are held together by weak intermolecular (C-Br...pi, C-H...pi and C-H...Br) interactions. The nonplanar geometry of the macrocyclic ring is probably due to the weak interporphyrin interactions induced by the solvent molecule and the peripheral butoxy groups. The nonplanarity of the mesogens could influence the mesogenic behaviour differently relative to planar porphyrin mesogens.