Low-oxidation-state molybdenum and tungsten complexes with bis(eta(5)-cyclopentadienyl) bridges

The paper describes the preparation of new dinuclear Mo and W complexes bridged by Cp(1)Cp[Cp(1)Cp = (C5H4)(2)(SiMe(2))] or Cp(2)Cp[Cp(2)Cp = (C5H3)(2)(SiMe(2))(2)] ligands, [{W(CO)3H)}2(mu-eta(5):eta(5)-Cp(2)Cp)] (5) or K-2[{W(CO)(3))(2)(mu-eta 5:eta 5-Cp(2)Cp)] (6) are obtained by reaction of [W(CO) 3-(NCMe)(3)] with HCp(2)CpH or K-2(Cp(2)Cp), respectively, as a cis-trans mixture of isomers which differ in the stereodisposition of the two metals with respect to the Cp(2)Cp system. cis- and trans-5 have been separated and reacted with CCl4 to give [{W(CO)(3)Cl}2(mu-eta 5:eta 5-Cp(2)Cp)] (cis- or trans-7). Reaction of [(Mo(CO)(3)X}(2)(mu-eta 5:eta(5)-Cp(n)Cp)] (n = 1, X = H (1); Cl (3); n = 2, X = H (2), Cl (4)) with CN(t)Bu gives [{Mo(CO)(2)(CN(t)Bu)}(2)(mu-eta 5:eta(5)-Cp(n)Cp)] (8-11). Reaction of 9 with KH gives K-2[{Mo(CO)(2)(CN(t)Bu)}(2)(mu-eta 5:eta 5-Cp(2)Cp)] (12). The cis isomers of the chloro derivatives 4, 7, or 11 are reduced to the-dinuclear metal-metal-bonded complexes [{M(CO)(2)L}(2)(mu-eta 5:eta(5)-Cp(2)Cp)] (M-M) (L = CO, M = Mo (13), W (15), L = CN(t)Bu, M = Mo (16)) by reaction with MeMgCl, whereas the trans isomer of 4 affords the polymer [(Mo(CO)(3))(2)(mu-eta 5:eta 5-Cp(2)Cp)](n)(Mo-Mo) (17). cis-2 reacts with H2O2 to give a mixture of 13 and [{Mo(CO)(3))(2)(mu-eta(5):eta(5)-(C5H3(SiMe(2)OH)SiMe(2)C(5)H(4))}](Mo-Mo) (14).