Bis(1-phenyl-1-propyne) complexes of tungsten(II): crystal structures of [WI2(CO)(NCR)(eta(2)-MeC2Ph)(2)] (R = Me, Et, or Ph)

Reaction of [WI2(CO)(3)(NCMe)(2)] with two equivalents of 1-phenyl-1-propyn e (MeC2Ph) in CH2Cl2, and in the absence of light, gave the bis(1-phenyl-1- propyne) complex [WI2(CO)(NCMe)(eta (2)-MeC2Ph)(2)] (1) in 77% yield. Treat ment of equimolar quantities of 1 and NCR (R = Et, i-Pr, t-Bu, Ph) in CH2Cl 2 afforded the nitrile-exchanged products, [WI2(CO)(NCR)(eta (2)-MeC2Ph)(2) ] (2-5) (R = Et (2), i-Pr (3), t-Bu (4), Ph (5)). Complexes 1, 2, and 5 wer e structurally characterized by X-ray crystallography. All three structures have the same pseudo-octahedral geometry, with the equatorial sites being occupied by cis and parallel alkyne groups, which are trans to the cis-iodo groups. The trans carbon monoxide and acetonitrile ligands occupy the axia l sites. In structures 1 and 2, the methyl and phenyl substituents of the 1 -phenyl-1-propyne ligands are cis to each other, whereas for the bulkier NC Ph complex (5), the methyl and phenyl groups are trans to one another. This is the first time that this arrangement has been observed in the solid sta te in bis(alkyne) complexes of this type.