# Schiff bases of nickel(II), copper(II) prophyrins and dibenzo-18-crown-6-interspersed bis-metal porphyrins. Protonation studies

Maiya, Bhaskar G and Krishnan, V (1987) Schiff bases of nickel(II), copper(II) prophyrins and dibenzo-18-crown-6-interspersed bis-metal porphyrins. Protonation studies. In: Proceedings of Indian Academy of Sciences: Chemical Sciences, 99 (5-6). pp. 283-296.

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Schiff_bases_of_nickel(IlL_copper.pdf - Published Version

Schid-base (SB) derivatives of Ni(II) and Cu(II) porphyrins endowed with various amine functions $(R-NH_2)$, n-butylamine, p-anisidine and m-nitroaniline have been prepared from corresponding formyl porphyrins. Protonation studies of these SB derivatives reveal a marked red shift of the optical absorption bands in the visible region relative to the unprotonated imines. The magnitude of the observed red shifts in the protonated derivatives, $(SBH^+)$ are found to depend on the electron-withdrawing or electron-donating nature of the R group of the amines. The results of the optical absorption, $^1H$ NMR, EPR, and cyclicovoltammetric studics are illustrative of the fact that protonation of the SB deriwatives results in a localized positive charge, $P-C(H) = _N^+$ (H)-R in the periphery of the porphyrin (p) system. The dibenzo-18-crown-6 interspersed bisporphyrin schiff bases have been prepared from trans $4,4^{\prime}$-diamino dibenzo-18-crown-6 and forrnyl porphyrins. The protonation of these SB derivatives is found to proceed in a concerted Cash&. The cation complexation studies by the crown ether entity in the hisporphyrin systems have been investigated using optical absorption, magnetic resonance and electrochemical methods. The redox characteristics of the protonated dimeric SB porphyrins reveal that the first oxidation step involves a two-electron transfer reaction. This is important in view of their possible usage in multielectron transfer reactions of biological and catalytic interest.