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)A, and β= 104.31(2)°. The structure was refined to R= 0.052 (R′= 0.060) for 2 860 reflections with Fo < 3σ(Fo). 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.