Dichotomy in the reactivity of trivalent phosphorus compounds Z3P (Z = Ph, nBu, OR) observed in the photoreaction with a ruthenium complex

Article abstract of DOI:10.1002/cber.19971301122

Solutions of tris(2,2′-bipyridyl)ruthenium(II) dichloride (Ru²⁺) and various types of trivalent phosphorus compounds Z₃P (Z = Ph, nBu, OR; 1) in methanol have been photolyzed with visible light at 20 °C under an argon atmosphere, resulting in the oxidation of I to the corresponding pentavalent oxo compounds Z₃P=O and ligand exchange of Ru²⁺ with 1. The former process takes place via single-electron transfer (SET) from 1 to Ru²⁺ in the photoexcited state, Ru²⁺*, which gene-rates the radical cation intermediate Z₃P*⁺ from 1. The latter results from nucleophilic attack of 1 upon Ru²⁺*. The results show that 1 can act either as an electron donor or as a nucleo-phile toward Ru²⁺*. The rate constants for both processes are estimated. An excellent linear correlation is found between the logarithm of the SET rate and the oxidation potential for both the aromatic and aliphatic trivalent phosphorus compounds examined here; the slope of the plot is much less negative than expected on the basis of Rehm-Weller theory. Such behavior in the SET rates is interpreted by comparison with SET quenching by amines. On the other hand, a dualparameter correlation analysis shows that the ligand exchange is regulated by both steric and electronic factors in 1. WILEY-VCH Verlag GmbH, 1997.