Ligand-to-ligand charge transfer states and photochemical bond homolysis in metal-carbon bonded platinum complexes

摘要

This paper reviews the photochemical Pt-C bond homolysis reactions of metal-carbon bonded platinum compounds. Three types of complexes are considered: [Pt(R)_2(COD)], [Pt(R)_2(α-diimine)] and [Pt(Me)_4(α-diimine)]. This photoreactivity originates in the involvement of the σ-bonded co-ligands in low-lying excited states. This involvement was proved by time-dependent density-functional theory (TD DFT) calculations and resonance Raman (rR) spectroscopy. In the case of the platinum(Ⅱ) complexes, the contribution of the co-ligand to the high-lying filled orbitals increases with increased σ-donor strength of this ligand. Concurrently, the photoreactivity increases dramatically in the case of the [Pt(R)_2(COD)] complexes. The corresponding α-diimine analogues are much less reactive due to the smaller co-ligand participation in high-lying filled orbitals. The platinum(Ⅳ) complexes [Pt(Me)_4(α-diimine)] are very photoreactive, due to the fact that the HOMO has almost exclusively σ(C_(ax)-Pt-C_(ax)) character.