ACETONITRILE EXCHANGE-REACTIONS OF [WI2(CO)(NCME)(ETA-2-RC2R)2] (R = ME OR PH) AND [WI(CO)(NCME)(PH2P(CH2)PPH2) (ETA-2-MEC2ME)][BF4] WITH THIOPHENE-3-ACETONITRILE - X-RAY CRYSTAL-STRUCTURE OF [WI2(CO)(NCCH2(3-C4H3S)) (ETA-2-MEC2ME)2]

The complexes [WI2(CO)(NCMe)(eta-2-RC2R)2] (R = Me or Ph) and [WI(CO)(NCMe)(Ph2P(CH2)-PPh2)(eta-2-MeC2Me)][BF4] react with equimolar quantities of thiophene-3-acetonitrile (NCCH2(3-C4H3S)) in dichloromethane at room temperature to give the acetonitrile-exchanged products [WI2(CO){NCCH2(3-C4H3S)}(eta-2-RC2R)2] (1 and 2) and [WI(CO){NCCH2(3-C4H3S)}{Ph2P(CH2)PPh2}(eta-2-MeC2Me)][BF4] (3) respectively in good yields. The crystal structure of [WI2(CO){NCCH2(3-C4H3S)}(eta-2-MeC2Me)2] (1) was determined. The coordination geometry about the tungsten may be regarded as octahedral, with the but-2-yne ligands parallel to each other and trans to the iodide ligands. The carbon monoxide and thiophene-3-acetonitrile ligands are mutually trans to each other. C-13 NMR spectroscopy indicates that the alkyne ligands in 1 are donating a total of six electrons to the tungsten, whereas the but-2-yne ligand in 3 is donating four electrons to the tungsten. The barrier to but-2-yne rotation of 3 was calculated to be 51.3 kJ mol-1.