MIXED CARBONYL-THIOCARBONYL DIRHENIUM(III) COMPLEXES OF THE TYPE [RE-2(MU-S)(MU-X)X(2)(CS)(MU-DPPM)(2)(CO)]PF6 (X=CL OR BR) AND THEIR CONVERSION TO THE ANALOGOUS MU-SULFUR DIOXIDE COMPOUNDS

The reactions of Re-2(mu-S)(mu-X)X(3)CS)(mu-dppm)(2) (X = Cl or Br) with TIPF6 and CO mixtures in CH2Cl2 afford green complexes of the type [Re-2(mu-S)(mu-X)X(2)(CS)(mu-dppm)(2)(CO)]PF6. The treatment of these carbonyl-containing products with NOPF6/O-2 mixtures leads to the formation of the corresponding sulphur dioxide complexes [Re-2(mu-SO2)(mu-X)X(2)(CS)(mu-dppm)(2)(CO)]PF6. The mu-S and mu-SO2 complexes exhibit a rich redox chemistry, which in the case of [Re-2(mu-SO2)(mu-X)X(2)(CS)(mu-dppm)(2)(CO)]PF6 has led to the isolation of the stable one- and two-electron reduction products Re-2(mu-SO2)(mu-X)X(2)(CS)(mu-dppm)(2)(CO) and [n(5)-C5H5)(2)Co][Re-2(mu-SO2)(mu-X)X(2)(CS)(mu-dppm)(2)(CO)]. A comparison of the cyclic voltammetric and IR spectral properties of these carbonyl complexes with those of the previously isolated species Re-2(mu-S)(mu-X)X(3)(CS)(mu-dppm)(2)[Re-2(mu-S)(mu-X)X(2)(CS)(mu dppm)(2)(L)]PF6(L=RCN or RNC) (L = RCN or RNC) and their mu-S0(2) analogues reveals a clear dependence of the potentials of the metal-based redox couples and the frequencies of the tl(CS) mode upon the electron-withdrawing ability of the ancillary ligand (CO, RCN or RNC).