Photochemical Reductive trans-Elimination from trans-Diacidotetracyanoplatinate(IV) Complexes

Abstract

Upon CT excitation the complex ions trans-[Pt(CN)₄N₃X]^2- and trans-[Pt(CN)₄X₂]^2- (X = Cl and Br) undergo a reductive trans-elimination with formation of [Pt(CN)₄]^2- and two ligand radicals in the photoprimary step. The formation of a Pt(III) intermediate is not observed. Due to the stability of [Pt(CN)₄]^2-, recombination reactions regenerating the starting complex are efficient if the ligand radicals are not scavenged. For the azide complexes the high quantum yields for the production of [Pt(CN)₄]^2- are explained by the instability of azide radicals. For trans-[Pt(CN)₄X₂]^2-, the recombination is efficient in aqueous solution, while in ethanol the halogen atoms are scavenged by hydrogen abstraction. The sequence of steps following CT excitation can be explained by a potential energy diagram.