Photoreactions of organic halides, alcohols, and olefins with tetrakis(pyrophosphito)diplatinate(II)

The photoreactions of [Pt2(P2O5H2)4] 4- (Pt2) with organic halides (RX), alcohols (RR′CHOH), and olefins have been investigated. The second-order rate constants (kq) for the reactions of 3A2u Pt2 (3Pt2*) with these substrates have been determined by Stern-Volmer quenching experiments. With RX, the kq values increase with decreasing C-X bond strength. Flash-photolysis experiments establish that the primary step of the photoreactions of Pt2 with RX is halogen atom transfer. Broad-band irradiation of RR′CHOH (λ > 300 nm) in the presence of Pt2 leads to the production of an aldehyde or ketone and molecular hydrogen. The kq values for aliphatic and benzylic alcohols range from 104 to 106 M-1 s-1, being highest with benzyl alcohol. Flash-photolysis experiments confirm that the first step in these reactions is H-atom transfer. Photoisomerizations of cis- and trans-stilbenes are sensitized by Pt2.