Atom-Transfer Reactivity of Binuclear d^8 Complexes

The long-lived ^3(dσ^*pσ) state of binuclear d8 complexes undergoes a variety of reactions. One prominent reaction, photooxidative addition of halocarbons, apparently proceeds by halogen atom transfer rather than outersphere electron transfer. Excited-state hydrogen atom transfer occurs in reactions between several binuclear d^8 complexes and a number of organic and organometallic substrates. Specific results for Pt_2(P_2O_5H_2)_4^(4-) and Ir_2(TMB)_4^(2+) (TMB = 2,5-diisocyano-2,5-dimethylhexane) are discussed. Production of a hole in the dσ* orbital is believed to be an important factor in these photochemical atom-transfer reactions. Electrochemical generation of such a hole produces a highly reactive intermediate that can undergo atom abstraction, thereby yielding net oxidation of an organic substrate. The net reaction is electrocatalytic in metal complex.