Dimetallic Imido Complexes of Molybdenum and Tungsten with Bridged Bis(η5-cyclopentadienyl) Ligands. Molecular Structure of [(MoO)2(μ-NtBu)2{μ-(η5-C5H4)2SiMe2}]

New imido and oxo dimetallic complexes of Mo and W with the monobridged or dibridged bis(cyclopentadienyl) ligands Cp1Cp or Cp2Cp [Cp1Cp = (η5-C5H4)2SiMe2, Cp2Cp = (η5-C5H3)2(SiMe2)2] have been synthesized. The Cp2Cp complexes have been obtained as both cis and trans isomers which differ in the stereodisposition of the two metal fragments with respect to the Cp2Cp system, the stereochemistry being unchanged in all the reactions described. Addition of H2NtBu to [(MCl4)2(μ-CpnCp)] (M = Mo, n = 1, 2a; n = 2, 2b; M = W, n = 2, 2c) affords the imido M(V) complexes [{M(NtBu)Cl2}2(μ-CpnCp)] (4a−c). Complexes 4a,c are oxidized by PCl5 to give [{M(NtBu)Cl3}2(μ-CpnCp)] (5a,c). Both 4a and 5a afford [{MoCl(μ-NtBu)}2(μ-Cp1Cp)] (6) by reduction with sodium amalgam. The differences found between this reaction and the related reductions of the mononuclear Cp analogues are discussed. Reaction of 6 with HgO affords the oxo complex [{MoO(μ-NtBu)}2(μ-Cp1Cp)] (7). [(MoOCl)2(μ-O)(μ-Cp2Cp)] (3) is obtained by reaction of [{Mo(CO)3Cl}2(μ-Cp2Cp)] with CH3NO2 or bubbling air through a THF solution of cis-[(MoCl4)2(μ-Cp2Cp)]. The molecular structure of 7 has been determined by a single-crystal X-ray analysis.