PHOTOOXIDATION OF DIIMINE DITHIOLATE PLATINIUM(II) COMPLEXES INDUCED BY CHARGE-TRANSFER TO DIIMINE EXCITATION

A photochemical and photophysical investigation was carried out on (tb ubpy)Pt-II(dpdt) and (tbubpy)Pt-II(edt) (1 and 2, respectively, where tbubpy = 4,4'-di-tert-butyl-2,2'-bipyridine, dpdt = meso-1,2-diphenyl- 1,2-ethanedithiolate and edt = 1,2-ethanedithiolate). Luminescence and transient absorption studies reveal that these complexes feature a lo west excited state with Pt(S)(2) --> tbubpy charge transfer to diimine character. Both complexes are photostable in deoxygenated solution; h owever, photolysis into the visible charge transfer band in air-satura ted solution induces moderately efficient photooxidation. Photooxidati on of 1 produces the dehydrogenation product (tbubpy)Pt-II-(1,2-diphen yl-1,2-ethenedithiolate) (4). By contrast, photooxidation of 2 produce s S-oxygenated complexes in which one or both thiolate ligands are con verted to sulfinate (-SO(2)R) ligands. Mechanistic photochemical studi es and transient absorption spectroscopy reveal that photooxidation oc curs by (1) energy transfer from the charge transfer to diimine excite d state of 1 to O-3(2) to produce O-1(2) and (2) reaction between O-1( 2) and the ground state 1. Kinetic data indicates that excited state 1 produces O-1(2) efficiently and that reaction between ground state 1 and O-1(2) occurs with k approximate to 3 x 10(8) M(-1) s(-1).