ELECTROCHEMISTRY OF DIMOLYBDENUM COMPLEXES CONTAINING OXO, IMIDO, AND SULFIDO MOIETIES - A MEASURE OF THEIR RELATIVE PI-DONOR ABILITIES

The electrochemistry of dimolybdenum complexes [(RC5H4)Mo(X)(mu-X)]2 (X = multiply bonded ligand) has been investigated by cyclic voltammetry. The tetraoxo complex [(MeC5H4)MoO(mu-O)]2 (1) which adopts a cis-puckered geometry shows two reversible one electron reduction waves in THF. The substitution of oxo by imido moieties results in the adoption of a trans-planar geometry which substantially effects the electrochemistry such that complexes show oxidation chemistry. The trisimido-oxo complex [(MeC5H4)2Mo2(NPh)(mu-NPh)2] (2) shows an irreversible oxidation wave at +815 mV which becomes reversible at high scan rates indicative of an EC mechanism. The trisimido-sulphido complex [(MeC5H4)2Mo2S(NPh)(mu-NPh)2] (3) shows a quasi-reversible oxidation at +620 mV and the tetraimido complex [(MeC5H4)Mo(NPh)(mu-NPh)2 (4) shows a reversible one electron oxidation at +525 mV together with a second irreversible oxidation at higher potential. A comparison of the oxidation potentials of 2, 3, and 4 gives a measure of the relative pi-donor abilities of oxo, sulphido, and imido ligands at a Mo(V) centre.