Tungsten carbonyl isocyanide carbene complexes: A structural and spectroscopic study of three types of metal-carbon bonds in the same molecule

Article abstract of DOI:10.1021/om00139a030

The syntheses, spectroscopic characterization, and X-ray structural determinations of (CO)₄W(C-(OCH₃)(C₆H₅))(CNC ₆H₄-p-CH₃) (1) and (CO)₄W(C(OCH₃)(C₆H₅)(CNC(CH ₃)₃) (2) are reported. Data from related complexes are also presented in order to compare differences in metal-carbon bonding in W-CO, W-C_CAR, and W-C_CNR bonds in the complexes. The X-ray crystal structures of both molecules reveal that the carbene ligand is cis to the isocyanide ligand with W-CO distances significantly shorter than the other W-C distances in each complex. Crystal data for 1: space group Pbca (No. 61); Z = 8, a = 21.172 (3) ?, b = 22.463 (3) ?, c = 8.322 (2) ?; V = 3957.9 (9) ?³; R = 0.038, R_w = 0.030. Crystal data for 2: space group P2₁/n (No. 14); Z = 4, a = 16.709 (2) ?, b = 9.425 (2) ?, c = 12.823 (2) ?; β = 111.52 (3)°; V = 1875.8 (5) ?³; R = 0.047, R_w = 0.045. Carbonyl force constants, ¹³CO chemical shifts, tungsten-carbon coupling constants, and metal-carbon bond lengths all indicate that carbon monoxide is as an overwhelming π acid in the molecules. Both isocyanide ligands appear to be much weaker π acceptors, while phenylmethoxycarbene is primarily a σ donor.