Synthesis and structural studies of chromium, molybdenum, and tungsten compounds containing cyclopentadienyl-like ligands. Part 3. Dicarbonylnitrosyl(η-pentamethylcyclopentadienyl) complexes

Abstract

The complexes [M(η-C₅Me₅)(CO)₂(NO)], where M = Cr, Mo, or W, have been synthesized and their i.r. and ¹H n.m.r. spectra are reported. The crystal structures of all three compounds have been determined from three-dimensional X-ray data measured by counter methods. The [Cr(η-C₅Me₅)(CO)₂(NO)] complex crystallizes in the space group P2₁/n with unit-cell dimensions of a= 12.346(5), b= 7.805(4), c= 14.378(5)Å, β= 106.85(3)°, and Z= 4. Full-matrix least-squares refinement has led to a final R value of 0.043 based on 1 802 unique observed reflections. The [M(η-C₅Me₅)(CO)₂(NO)](M = Mo or W) compounds are isostructural and crystallize in the space group P with unit-cell dimensions a= 6.992(4), b= 7.828(4), c= 12.955(5)Å, α= 84.70(3), β= 86.71(3), γ= 75.51(3)°, Z= 2, and a= 6.947(4), b= 7.804(4), c= 12.957(5)Å, α= 84.41(3), β= 86.58(3), γ= 75.48(3)°, Z= 2 respectively. Full-matrix least-squares refinement has led to final R values of 0.035 and 0.073 based on 2 190 and 2 132 unique observed reflections, respectively. The three structures each have disordered M(CO)₂(NO) moieties in which the CO and NO ligands are C- or N-bonded to the metal in a linear fashion. For M = Cr, four of the Cr–C(π) distances are equivalent [average 2.200(5)Å] while the remaining one is longer by 0.031(7)Å(4.4σ). For M = Mo, the equivalent Mo–C(π) distances average 2.346(3)Å while the unique distance is 0.020(6)Å(3.3σ) longer. For M = Cr, Mo, and W the methyl groups are bent away from the metal, out of the plane of the cyclopentadienyl ring.