Pentagonal-bipyramidal molybdenum- and tungsten-(II) derivatives: crystal and molecular structure of 1–3-η-allyldicarbonylchlorobis-(trimethyl phosphite)molybdenum(II)

Abstract

Compounds of the type [MX(CO)₂(η³-C₃H₄R)L₂][M = Mo or W; X = halide; R = H, L = P(OMe)₃ or P(OEt)₃; R = Me, L = P(OMe)₃] have been prepared. A crystal-structure determination has been carried out on the title compound as a representative member of the series. Crystals are triclinic, space group P, with a= 13.309(11), b= 10.093(10), c= 8.148(7)Å, α= 114.9(8), β= 93.1(7), γ= 100.6(7)°, and Z= 2. A total of 1534 independent reflections above background were collected on a diffractometer and refined to R 0.072. The geometry around the metal atom is best considered in terms of a distorted pentagonal bipyramid with a chlorine atom [Mo–Cl 2.606(6)Å] and a carbonyl group [Mo–C 1.91 (3)Å] in axial positions, and the equatorial girdle occupied by two phosphite ligands [Mo–P 2.432(6), 2.425(6)Å], one carbonyl group [Mo–C 2.03(3)Å], and the allyl ligand which occupies two adjacent sites. The molecule has approximate C_s symmetry with the mirror plane containing the metal atom, both carbonyl groups, and the central carbon atom of the allyl group. The Mo–C(allyl) bond lengths are 2.403(20), 2.347(24), and 2.407(22)Å. Carbon-13 and ¹H n.m.r. data indicate that this geometry is retained in solution below 230 K, but at room temperature the molecule is fluxional. The two cationic complexes [Mo(CO)₂(η³-C₃H₄R){P(OMe)₃}₃][BF₄](R = H or Me) have also been characterised.