Electrochemistry of nonplanar copper(ii) tetrabutano- and tetrabenzotetraarylporphyrins in nonaqueous media

Abstract

Two series of copper tetraarylporphyrins containing b,b 0 -fused tetrabutano or tetrabenzo groups were synthesized and characterized as to their electrochemistry and spectroelectrochemistry in nonaqueous media. The examined compounds are represented as butano-(TpYPP)Cu II and benzo-(TpYPP)Cu II , where TpYPP is the porphyrin dianion and Y is a CH 3 , H or Cl substituent on the para-position of the four meso-phenyl rings of the compound. Each neutral porphyrin in the two series is ESR active and shows a typical d 9 Cu(II) signal in frozen CH 2 Cl 2 solution. Each Cu(II) porphyrin also undergoes two reversible one-electron reductions and two reversible one-electron oxidations in DMF or CH 2 Cl 2 containing 0.1 M tetra-n-butylammonium perchlorate to give a p-anion radical and dianion upon reduction and a pcation radical and dication upon oxidation. A third one-electron oxidation is also observed for butano-(TpYPP)Cu (Y ¼ CH 3 and H) and benzo-(TPP)Cu in PhCN and this process is assigned to the Cu II /Cu III transition. The reversible half-wave potential for the first oxidation of each compound in both series is shifted negatively by about 500 mV as compared to E 1/2 values for oxidation of the related copper tetraarylporphyrin without the four fused benzo or butano rings while smaller positive shifts of 60 and 300 mV are seen for reduction of the tetrabenzotetraarylporphyrins and tetrabutaotetraarylporphyrins, respectively, as compared to the same redox reactions of the related tetraarylporphyrins. The electrochemically measured HOMO-LUMO gap averages 1.76 AE 0.05 V for benzo-(TpYPP)Cu II , 2.04 AE 0.06 V for butano-(TpYPP)Cu II and 2.33 AE 0.03 for (TpYPP)Cu in CH 2 Cl 2 .

Spectral, Electrochemical, and ESR Characterization of Manganese Tetraarylporphyrins Containing Four β,β′-Pyrrole Fused Butano and Benzo Groups in Nonaqueous Media

“…The benzo­(Ar) 4 PorMnCl complexes 3a – 3c are all characterized by a relatively high intensity Q band, compared to (Ar) 4 PorMnCl 1a – 1c or butano­(Ar) 4 PorMnCl 2a – 2c . Similar porphyrin UV-vis spectra characterized by an intense Q band have been reported for other tetrabenzotetraarylporphyrins containing Co­(II), Ni­(II), Cu­(II), Zn­(II), or Pt­(II) central ions ,− and this is consistent with a significant interaction between the β,β′-fused benzo groups and the macrocycle.…”

“…We previously reported the electrochemical and spectroscopic properties for a series of β,β′-butano and/or β,β′-benzosubstituted iron(III), 35 copper(II), 36 cobalt(II), 37 zinc(II), 38 and platinum(II) 39 porphyrins and we now turn our attention to manganese(III) derivatives with these two types of macrocycles. The newly examined compounds are shown in Chart 1 and are represented as butano(Ar) 4 PorMnCl and benzo(Ar) 4 PorMnCl, where Por is a dianion of the porphyrin and Ar is a p-CH 3 Ph, Ph, or p-ClPh group on each of the four meso-positions of the macrocycle.…”

“…The benzo(Ar) 4 MnCl complexes 3a−3c were synthesized via the route shown in Scheme 1b. Attempts to generate the free-base benzoporphyrins by direct oxidation of the corresponding free-base butanoporphyrins failed, and therefore they were obtained by an initial synthesis of the Cu(II) derivatives as described in the literature, 36 followed by demetalation with acid 40 and then reaction with MnCl 2 • 4H 2 O in DMF to generate the final desired product in yields of 64%−79%.…”

Electrochemistry and spectroelectrochemistry of metallohexaphyrins containing bis-copper or bis-zinc central metal ions

“…In contrast to these values, smaller HOMO-LUMO gaps have been reported for the non-planar copper porphyrins, (OETPP)Cu and (DPP)Cu [50], the copper tetrabenzotetraarylporphyrin [51], the N-confused porphyrins [52][53][54] and the non-planar free-base porphyrins [55], where the separation ranges from 1.5-1.8 V under similar solution conditions.…”

Axial coordination reactions with nitrogenous bases and determination of equilibrium constants for zinc tetraarylporphyrins containing four β,β′-fused butano and benzo groups in nonaqueous media

“…Synthetic zinc porphyrins are one of the most studied metalloporphyrin derivatives, in part because they have wide potential applications in the fields of solar cells [1][2][3][4][5], nanomaterials [6,7] and supramolecular chemistry [8][9][10][11][12][13]. Among the examined compounds are the zinc tetrabenzoporphyrins which possess an extended conjugated system [14][15][16][17][18][19] and have attracted particular attention due to their unique UV-vis spectral and electrochemical properties [20][21][22][23] as compared to the non-b,b′-pyrrole fused derivatives.…”