FLASH-PHOTOLYSIS STUDIES OF THE RUTHENIUM(II) PORPHYRINS RU(P)(NO)(ONO) - MULTIPLE PATHWAYS INVOLVING REACTIONS OF INTERMEDIATES WITH NITRIC-OXIDE

Described are the spectra and kinetics of transients formed by laser f lash photolysis of the ruthenium nitrosyl nitrito complexes Ru(P)(NO)( ONO), P = TPP (meso-tetraphenylporphyrin), OEP (octaethylporphyrin), T mTP (tetra(m-tolyl)porphyrin), and FTTP (tetra(m-trifluoromethylphenyl )porphyrin) in benzene solutions. Two transient decay processes are se en on the time frame (<1 ms) of the flash photolysis experiment, and a residual difference spectrum, which decays to baseline on a longer ti me frame, is noted as well. The accumulated evidence points to the for mation of two primary photoproducts, Ru(P)(ONO) (A) formed by NO photo labilization and Ru(P)(NO) (B) formed by NO2 photolabilization. Both d ecay by NO dependent pathways, the reaction of A with NO to re-form Ru (P)(NO)(ONO) being substantially faster (2.4-5.5 x 10(8) M-1 s(-1) in ambient temperature benzene) than the reaction of B with NO (2.4-10 x 10(7) M-1 s(-1)). The product of the latter reaction is apparently the dinitrosyl complex Ru(P)(NO)(2), which undergoes a much slower therma l reaction with excess NO to give again Ru(P)(NO)(ONO). The possibilit y of B being the oxo complex O=Ru(P)(NO) formed by NO loss from coordi nated nitrite was considered but concluded to be a minor pathway at be st. Isotopic exchange reactions using either labeled complex or labele d NO in cyclohexane demonstrate photochemical exchange of NO into both the nitrosyl and nitrito complexes, and time-resolved infrared experi ments are consistent with formation of a long-lived nitrosyl-containin g intermediate. Flash photolysis studies of the respective nitrosyl ch loro complexes Ru(TPP)(NO)Cl and Ru(OEP)(NO)Cl indicate that only a si ngle transient species, presumably Ru(P)Cl, is formed in each case, an d this decays by a single NO dependent pathway back to starting materi al.