HOMOBIMETALLIC AND HETEROBIMETALLIC, MIXED-VALENCE M(II) M(0) COMPLEXES OF MOLYBDENUM AND TUNGSTEN WITH S2CPR3 LIGANDS - X-RAY STRUCTURE OF[(ETA(3)-C3H5)(CO)2MO(MU-BR)(MU-S2CPCY3)MO(CO)3]/

Addition of S2CPR3 to [(eta3-C3H5)M(CO)2(nitrile)2Br] (M = Mo, W) at r oom temperature readily produces mononuclear complexes [(eta3-C3H6)M(C O)2(S2CPR3)Br] [R = Cy, Pr(i)] which have been isolated as crystalline solids and characterized by analytical and spectroscopic methods. The se mononuclear complexes react with [M(CO)a(nitrile)3] (M = Mo, W), in CH2Cl2 to afford dinuclear complexes of formula [(eta3-C3H5)(CO)2M(II )(mu-Br)(mu-S2CPR3)M0(CO)3] (M(II) = Mo, 4a-d; M(II) = W, 5a-d). An X- ray determination of the derivative with M(II) = MO = Mo and R = Cy [4 a, triclinic, space group P1BAR, a = 10.037(5) angstrom, b 10.669(5) a ngstrom, c = 15.323(6) angstrom, alpha = 84.52(3)degrees, beta = 78.40 (3)degrees, gamma = 82.01(4)degrees, Z = 2, R = 0.042, R(w) = 0.043)] shows the presence of the S2CPCy3 ligand coordinated as a eta2-S,S' ch elate to Mo(II) and as a eta3-S,C,S' pseudoallyl to Mo0. The spectrosc opic properties, particularly the signals of the central carbons of th e S2CPR3 bridge and of the allyl, together with the results of the X-r ay structure determination of 4a, permit an unambiguous assignment of the structures of all the derivatives 4 and 5. For all combinations of metals (Mo(II)/Mo0, Mo(II)/W0, W(II)/Mo0, or W(II)/W0), a bond is for med selectively between the central carbon Of S2CPR3 and the metal ato m in oxidation state zero.