Synthesis, Reactions, and Electronic Properties of 16 π-Electron Octaisobutyltetraphenylporphyrin

Abstract

The reaction of the doubly oxidized beta-octaisobutyl-meso-tetraphenylporphyrin (OiBTPP, 4), which has a 16 pi-electronic structure at the porphyrin core, with a variety of metal reagents was investigated. The reaction of 4 with SnCl(2) followed by ethanolysis afforded an 18 pi-electron tin complex, (OiBTPP)Sn(OEt)(2) (5), in a redox manner. No reactions were observed using zerovalent metals (Zn, Cu, and Pd). However, the reaction of 16pi [(OiBTPP)Li](+)[BF(4)](-) (6), which was easily derived from 4, with Zn, Cu, and Pd(2)(dba)(3) gave the corresponding 18pi metalloporphyrins (OiBTPP)M (7, M = Zn(EtOH); 8, M = Cu; and 9, M = Pd). One-electron oxidation of the copper complex 8 by AgSbF(6) afforded a 17 pi-electron cation radical complex, [(OiBTPP)Cu](*+)[SbF(6)](-) (10). The UV-visible and electron spin resonance spectra of 10 were quite similar to those of previously reported beta-octaethyl-meso-tetraphenylporphyrin (OETPP) derivatives, [(OETPP)Cu](*+)X(-) (X = ClO(4), I). In contrast to the reaction of 6 with Zn to give the 18pi complex 7, the reaction of 4 with divalent ZnCl(2) enabled us to isolate a new 16pi porphyrin-zinc(II) complex, [(OiBTPP)Zn(Cl)](+)[ZnCl(3)](-) (11), in 92% yield. The solid-state structures of 5 and 7-11 were unambiguously determined by single-crystal X-ray crystallography. The porphyrin cores of 10 (17pi) and 11 (16pi) are much more distorted than those of the 18pi derivatives 5 and 7-9. Furthermore, the bond distances of 10 and 11 clearly showed the presence of bond alternation in contrast to aromatic 18pi species 8 and 7, respectively. Nucleus-independent chemical shift calculations of 4 and some metalated porphyrins indicated that the highly distorted 16pi porphyrins are essentially nonaromatic, with only weak antiaromaticity. Magnetic circular dichroism studies in conjunction with ZINDO/S calculations assisted in identifying the electronic transitions of the UV-vis spectra of key porphyrins. Electrochemical and thin-layer UV-vis spectroelectrochemical experiments on 4 (16pi) and 11 (16pi) indicated that both compounds can be electroreduced to give the 18pi species, with the 16pi/18pi transition being reversible in the case of [(OiBTPP)Zn(Cl)](+)[ZnCl(3)](-) (11).

Electrochemical and spectroscopic studies of poly(diethoxyphosphoryl)porphyrins

“…3b). This similarity between the electrooxidized porphyrin and its protonated product is not specific to the investigated porphyrins [32,33] nor is it specific to the PhCN or CH 2 Cl 2 solvent. The same ''side reaction'' involving conversion of the electrooxidized species to a protonated porphyrin with an unoxidized macrocycle also occurs in CHCl 3 but in this solvent only one major oxidation is observed for 1, 2 and 6.…”

Hydrogen bond controlled formation of trans-dihydroxo porphyrinato platinum(IV) complexes: Synthesis, characterization and catalytic activity in olefin epoxidation

“…The bond lengths for 16 p-electron [50,56,58] and 18 p-electron [46,[51][52][53] porphyrin rings in comparison with those of the Pt-complex obtained from X-ray analysis are listed in Table 4. From this table, it is found that there is much similarity in the values of bond distances of 18 p-electron rings and the Pt-complex reported here.…”

“…In the oxidative environment of the enzyme, porphyrin p-cation radical with 17 p-electron system has been proposed [22,54,55]. Vaid et al and Yamamoto et al have reported anti-aromatic 16 p-electron porphyrins and their Li + and Zn 2+ complexes [56][57][58][59]. All 20 or 16 anti-aromatic porphyrins have similar features, such as (i) alternating C-C bond distances along the 20 carbon periphery of their porphine ring system, (ii) highly saddle or ruffle distortion of the porphine from planarity, (iii) red shift in Soret band for 20 p-elecron system and blue shift for 16 p-electron system to that of normal porphyrin and (iv) strong paratropic shift in NMR for anti-aromatic porphyrins compared to that of diatropic shift normally seen in aromatic porphyrins.…”

The induced current strengths and aromatic pathways of heteroporphyrins and their antiaromatic derivatives

“…Porphyrins and their derivatives have been extensively investigated during the past decades owing to their important roles in coordination chemistry, biology, optical power limiting, and other practical applications . All of these technological applications are obviously related to the aromaticity of porphyrins and porphyrinoids.…”