SPECTROSCOPIC AND OXIDATION STUDIES OF MESO-TETRAPHENYLTETRABENZOPORPHYRIN CARBONYL-COMPLEXES OF RUTHENIUM(II) - CO AS THE PROBE TO ELUCIDATE THE BONDING CHARACTERISTICS OF PORPHYRINS

The carbonyl complex of o-tetraphenyltetrabenzoporphyrinato)ruthenium( II), Ru(TPTBP)(CO), has been synthesized and characterized by FABMS, U V/vis, H-1 NMR, and IR spectroscopy. Six-coordinate complexes Ru(TPTBP )(CO)(L) with different pi-bonding-capability ligands (L = NEt3, pip, 1-MeIm, py, PBu3) coordinated trans to CO have been studied. The shift s in nu(CO) for this series of complexes are consistent with the exist ence of M --> CO pi-back-bonding. In contrast to what would be expecte d by nitrogen basicity, nu(CO) values for Ru(TPTBP)(CO), Ru(TPP)(CO), and Ru(OEP)(CO) are 1959, 1930, and 1917 cm(-1), respectively. This re sult suggests that TPTBP should be both a better sigma-donor and a bet ter pi-acceptor than normal porphyrin systems (P). Oxidation studies o f Ru(TPTBP)(CO), Ru(TPTBP)(CO)(py), and Ru(TPTBP)(py)(2) have been car ried out both electrochemically and chemically. H-1 NMR, ESR, and elec tronic spectroscopic studies suggest that there are two different type s of oxidation products. The sites of oxidation should both be on the porphyrin ring to give two different types of ruthenium(II) porphyrin pi-cation radicals [Ru-II(TPTBP)(.+)(L)(L')]X of A(1u) and A(2u) chara cter, respectively. In marked contrast to other ruthenium porphyrins r eported in the literature, extraplanar ligands in the Ru(TPTBP) system do not affect the site of oxidation (metal vs ring) but only mediate the level of oxidation on the ring (a(1u) vs a(2u)). These results can be ascribed to the extended pi-system and the ring deformation of the TPTBP porphyrin macrocycle and are also consistent with the fact that TPTBP is a stronger pi-acceptor than other porphyrin systems.