Low-Oxidation-State Molybdenum and Tungsten Complexes with Bis(η5-cyclopentadienyl) Bridges

The paper describes the preparation of new dinuclear Mo and W complexes bridged by Cp1Cp[Cp1Cp = (C5H4)2(SiMe2)] or Cp2Cp [Cp2Cp = (C5H3)2(SiMe2)2] ligands. [{W(CO)3H}2(μ-η5:η5-Cp2Cp)] (5) or K2[{W(CO)3}2(μ-η5:η5-Cp2Cp)] (6) are obtained by reaction of [W(CO)3(NCMe)3] with HCp2CpH or K2(Cp2Cp), respectively, as a cis−trans mixture of isomers which differ in the stereodisposition of the two metals with respect to the Cp2Cp system. cis- and trans-5 have been separated and reacted with CCl4 to give [{W(CO)3Cl}2(μ-η5:η5-Cp2Cp)] (cis- or trans-7). Reaction of [{Mo(CO)3X}2(μ-η5:η5-CpnCp)] (n = 1, X = H (1), Cl (3); n = 2, X = H (2), Cl (4)) with CNtBu gives [{Mo(CO)2(CNtBu)X}2(μ-η5:η5-CpnCp)] (8−11). Reaction of 9 with KH gives K2[{Mo(CO)2(CNtBu)}2(μ-η5:η5-Cp2Cp)] (12). The cis isomers of the chloro derivatives 4, 7, or 11 are reduced to the dinuclear metal−metal-bonded complexes [{M(CO)2L}2(μ-η5:η5-Cp2Cp)](MM) (L = CO, M = Mo (13), W (15), L = CNtBu, M = Mo (16)) by reaction with MeMgCl, whereas the trans isom...