A molecular orbital comparison of molybdenum-sulfur dimers with sulfido ligands bridged by CH2 and FeCp fragments

Abstract

An extensive reactivity with hydrogen and unsaturated molecules has been characterized for the [mu]-sulfide ligands in (CpMo)[sub 2]([mu]-S)[sub 2]S[sub 2]CH[sub 2] (2). However, the bridging disulfide ligand in the heteronuclear cluster [(CpMo)[sub 2]([mu]-S[sub 2])([mu]-S[sub 2]FeCp)][sup +] (3) was not reactive toward hydrogen or olefins. Extended Huckel molecular orbital calculations have been carried out for 2 and for the hypothetical Fe-Mo cluster with bridging sulfides rather than a disulfide ligand [(CpMo)[sub 2]([mu]-S)[sub 2](S[sub 2]FeCp)][sup +] (3[prime]). The electronic structures of complexes 2 and 3[prime] are analyzed in terms of the Cp[sub 2]Mo[sub 2]S[sub 4] and methylene and the FeCp[sup +] fragment orbitals, respectively. This approach leads to a qualitative understanding of the reasons for the structural and reactivity differences between 2 and 3. 23 refs., 2 figs., 1 tab.