Dimetallic Imido Complexes of Molybdenum and Tungsten with Bridged Bis(η⁵-cyclopentadienyl) Ligands. Molecular Structure of [(MoO)₂(μ-N^tBu)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 H₂N^tBu 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(N^tBu)Cl₂}₂(μ-CpⁿCp)] (4a−c). Complexes 4a,c are oxidized by PCl₅ to give [{M(N^tBu)Cl₃}₂(μ-CpⁿCp)] (5a,c). Both 4a and 5a afford [{MoCl(μ-N^tBu)}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-N^tBu)}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.