Photoinduced Multielectron Redox Reactions in the (PtC1₆)^2- /Alcohol System: Visible Light Reduction of Platinum Centers

Abstract

Although the photochemistry of octahedral haloplatinum (IV) complexes has been extensively investigated, it has always been viewed in terms of ligand substi- tution processes. However, the preference of platinum for the (II) and (IV) oxidation states, and the previous observation (Cox et al., 1972) that photo- aquation of [PtCl₆]^2- can involve a Pt(III) intermediate suggests that such complexes may be capable of photoinduced multielectron charge transfer. Such a capability has now been demonstrated in the photoinitiated reaction of [PtCl₆]^2- with alcohols. Up to four electrons can be transferred in this pro- cess leading to the formation of platinum metal (Cameron and Bocarsly, 1986) and aldehydes or ketones depending on whether a primary or secondary alcohol is initially employed. Of special interest is the finding that primary alcohols are not overoxidized to the acid. Further aldehyde formation can be carried out catalytically by addition of O₂/CuCl₂ to the reaction mixture as a reoxidant of lower platinum oxidation states back to Pt(IV) (Cameron and Bocarsly, 1985).