Silicon-containing carbene complexes. 6. Stable 16-electron carbonyl carbene complexes of tungsten(0), molybdenum(0), and chromium(0)

Article abstract of DOI:10.1021/om00132a031

On warming (CO)₅W=C(NR₂)SiPh₃ (NR₂ = NMe₂, 1a, NC₅H₁₀, 1b) under vacuum, a CO ligand is eliminated and 16-electron carbene complexes (CO)₄W= C(NR₂)SiPh₃ (2a,b) are formed as stable compounds. Analogous chromium and molybdenum complexes (CO)₄M=C(NC₅H₁₀)SiPh₃ (M = Mo, 2c, Cr, 2d) are already formed during the preparation of (CO)₅M=C-(NC₅H₁₀)SiPh₃ (1c,d). The reaction is readily reversed on bubbling CO through solutions of 2. X-ray structure determination of (CO)₄W=C(NC₅H₁₀)SiPh₃ (2b) shows that the vacant coordination site at the metal is capped by a phenyl group of the SiPh₃ substituent. However, the long W-C(phenyl) distances exclude strong bonding interaction. The driving force for the conversion of 1 to give 2 seems to be relaxation of the steric strain within the carbene ligand.