Reactions of the bis(alkyne) complexes [Wi2(CO)(NCMe)(η2-RC2R)2](R = Me or Ph) with mono- and bi-dentate phosphine-donor ligands and the X-ray crystal structure of [Wl2(CO){Ph2P(CH2)PPh2}(η2-MeC2Me)]

Abstract

Reaction of the complexes [Wl₂(CO)(NCMe)(η²-RC₂R)₂](R = Me or Ph) either with 2 equivalents of L{L = PMe₃, PEt₃, PBuⁿ₃, PMe₂Ph, PMePh₂, PEt₂Ph, PEtPh₂, PPh₂(CH₂CHCH₂)[(PPh₃) and PPh₂(C₆H₁₁) for R = Me only]} or 1 equivalent of L₂{L₂= Ph₂P(CH₂)_nPPh₂(n= 1,2,3,4, or 6) or [Fe(η⁵-C₅H₄PPh₂)₂] for R = Me only} in CH₂Cl₂, at room temperature affords good yields of the compounds [Wl₂(CO)L₂(η²-RC₂R)](1)–(24) by successive substitutions of acetonitrile and an alkyne ligand. X-Ray crystallographic studies were carried out on the complex [Wi₂(CO){Ph₂P(CH₂)PPh₂}(η²-MeC₂Me)](19). Crystals of (19) are monoclinic, space group P2₁/n with a= 12.208(4), b= 13.395(2), c= 20.820(6)Å, and β= 104.31(2)°. The structure was refined to R= 0.052 (R′= 0.060) for 2 860 reflections with F_o < 3σ(F_o). The tungsten co-ordination may be described in terms of a pseudo-octahedral structure. The bidentate phosphine ligand, but-2-yne, and an iodide ligand occupy the four equatorial sites, and the carbonyl and iodide ligands the two axial sites. The but-2-yne ligand is oriented so that it is approximately coplanar with the axial ligands. Phosphorus-31 n.m.r. and i.r. spectral studies are interpreted to suggest the likely structures for the other [Wl₂(CO)L₂(η²-RC₂R)] complexes. The barrier to but-2-yne rotation of a number of complexes has been determined by variable-temperature ¹H n.m.r. spectroscopy. These results are discussed in terms of the electronic and steric effects of the phosphorus-donor ligands and also the di-iodo complexes are compared with the analogous dibromo and dichloro complexes reported by other workers. The ¹³C n.m.r. chemical shifts of the alkyne contact carbons suggest that the alkyne ligand is acting as a four-electron donor in these complexes.