3,3-Dimethyl-1-butyne complexes of tungsten(II). Crystal structures of [WI2(CO)(NCPh)(η2-HC2But)2] and [WI2(CO){P(OR)3}2(η2-HC2But)] (R=Me and Et)

Reaction of [WI2(CO)3(NCMe)2] with two equivalents of 3,3-dimethyl-1-butyne (HC2But) in CH2Cl2 at room temperature, in the absence of light, afforded the bis(alkyne) complex, [WI2(CO)(NCMe)(η2-HC2But)2], 1, in high yield. Nitrile exchange reactions of 1 with NCR (R=Et, Pri, But, Ph) gave the complexes [WI2(CO)(NCR)(η2-HC2But)2], (2–5). Complex 5 (R=Ph) was structurally characterised by a single crystal X-ray diffraction study and has a pseudo-octahedral geometry, with cis and parallel 3,3-dimethyl-1-butyne ligands, trans to the two mutually cis-iodo ligands, in the equatorial plane. The benzonitrile and carbon monoxide ligands are in the axial sites. The tert-butyl groups on the alkyne ligands are trans to one another. Treatment of 1 with two equivalents of P(OR)3 in Et2O afforded the bis(phosphite) complexes, [WI2(CO){P(OR)3}2(η2-HC2But)] {R=Me, 6; Et 7; Pri8}. The structures of 6 and 7 have been crystallographically determined with both complexes having similar pseudo-octahedral structures. The structures may be represented by two cis phosphite ligands in the equatorial plane with an iodo group and the carbonyl ligand, whilst the second iodo-group and the 3,3-dimethyl-1-butyne ligand are in the axial positions. Reaction of 6–8 with one equivalent of Ag[BF4] in acetonitrile, in the absence of light, yielded the cationic complexes, [WI(CO)(NCMe){P(OR)3}2(η2-HC2But)][BF4] (9–11). Detailed 1H, 13C{1H}, 13C1H and 31P{1H}-NMR studies are described, which gave comprehensive structural information on these complexes in solution.