Mixed mu-phosphido or mu-thiolato mu-halo-dimolybdenum(III) compounds [Mo2Cp2(mu-SMe)(2)(mu-X)(mu-Y)] (X = PPh2, Y = Cl; X = SCH3,Y = Br, I): Electrochemical and structural comparisons – The X-ray structure of [{Mo2Cp2Br(mu-O)(mu-SMe)(2)}(2)(mu-MoO4)]

Mixed mu-phosphido or mu-thiolato mu-halo-dimolybdenum(III) compounds [Mo2CP2(mu-SMe)(2)(mu-X)(mu-Y)] (X = PPh2, Y = Cl (1); X = SCH3, Y = Br (3), I(4)) have been studied. Syntheses and X-ray structures of the new bromo and iodo analogues of [Mo2CP2(mu-SMe)(3)(mu-Cl)] (2) are reported. While preparing 3 a side-product 5 was obtained and structurally characterised as the Mo-5 system [{Mo2CP2Br(mu-O)(mu-SMe)(2)}(2)(mu-MoO4)], containing a {Mo-IV-Mo-IV-O-((MoO2)-O-VI)-O-Mo-IV-Mo-IV} unit. The influence of the bridging groups on the structures and electrochemical behaviour of the complexes [Mo2Cp2(mu-SMe)(2)(mu-X)(mu-Y)]1-4 has been investigated. In MeCN-[NBu4][PF6] the first oxidation of [Mo2Cp2(mu-SMe)(2)(mu-PPh2)(mu-Cl)] (1) is quasi-reversible, contrasting with the essentially irreversible first oxidation of the thiolate analogue [Mo2Cp2(mu-SMe)(3)(mu-Cl)] (2) under similar conditions. The effects of lowering the temperature or increasing the scan rate on the oxidation of I were examined: the initial quasi-reversible oxidation at first became irreversible but at still higher scan rates or lower temperatures the oxidation was again quasi-reversible. This suggests that the oxidation of 1 in MeCN is followed by reversible coordination of acetonitrile to afford the species [Mo2CP2(mu-SMe)(2)(mu-PPh2)(Cl)(MeCN)](+) (7(+)). Cyclic voltammetry of [MO2Cp2(mu-SMe)(3)(mu-Y](Y = Br (3) or I (4)) showed two quasi-reversible diffusion-controlled oxidation steps in CH2Cl2-[NBU4][PF6] or thf-[NBu4][PF6]. In acetonitrile, the fast loss of the halide ligands results in the formation of [Mo2Cp2(mu-SMe)(3)-(MeCN)(2)](+) species. (c) 2005 Elsevier B.V. All rights reserved.