Mixed-metal hydrocarbyl complexes involving the Rh Mo and Rh/W metal combinations

Reaction of [RhMo(H)(CO)(4)(dppm)(2)] (dppm = Ph2PCH2PPh2) with a number of alkynes, RC = CR' (R = R' = C(O)OCH3, CF3; R = H, R' = C(O)CH3, C(O)OCH3) yields the alkenyl complexes [RhMo(C(R') = C(H)R)(CO)(4)(dppm)(2)], which i n all cases have an electron-withdrawing substituent on the alpha-carbon. A series of analogous complexes [RhMo(R)(CO)(4)(dppm)(2)] (R = CHCH2, CH3, C H2CHCH2, CH2C6H5, C6H5) are prepared by the reaction of [RhMoCl(CO)(4)(dppm )(2)] and the appropriate Grignard reagent. The analogous Rh/W complex (R = CHCH2) was prepared from [RhWCl(CO)(4)(dppm)(2)] and vinylmagnesium chlori de. In all cases the hydrocarbyl fragment is eta(1)-bound to Rh, with the f our carbonyl ligands primarily bound to the group 6 metal; two carbonyls as sume a semibridging arrangement. The reaction of both vinyl complexes (Rh/M o and Rh/W) with HBF4 at -80 degrees C yields the respective ethylidene pro ducts [RhM( = C(H)CH3)(CO)(4)(dppm)(2)][BF4] by protonation at the beta-car bon of the vinyl group. Upon warming, these carbenes transform to the ethyl ene adducts [RhM(C2H4)(CO)(4)(dppm)(2)][BF4]. Owing to uncertainties concer ning the structure of the halide precursor [RhMoCl(CO)(4)(dppm)(2)], its st ructure was determined by X-ray techniques and the chloro ligand was found to bridge the metals giving a square planar coordination at Rh and an octah edral coordination at Mo. One carbonyl on Mo assumes a weak semibridging in teraction with Rh.