The synthesis and spectral properties of the new bis(but-2-yne) and mono(but-2-yne) complexes [w(co)l(s2CNC4H8)(η2-MeC2Me)2][BPh4] and [W(CO)L2(S2CNC4H8)(η2-MeC2Me)][BPh4] (where = imidazole, 2-methylimidazole and 4-methylimidazole)

Abstract Reactions of the complex [W(CO)(NCMe)(S 2 CNC 4 H 8 )(η 2 -MeC 2 Me) 2 ][BPh 4 ] with one equivalent of L (L = imidazole, 2-methylimidazole or 4-methylimidazole) in the presence of excess but-2-yne at room temperature in CH 2 Cl 2 affords good yields of the bis(but-2-yne) complexes [W(CO)L(S 2 CNC 4 H 8 )(η 2 -MeC 2 Me) 2 ][BPh 4 ] ( 1–3 ). Whereas, reaction of [W(CO)(NCMe)(S 2 CNC 4 H 8 )(η 2 -MeC 2 Me) 2 [BPh 4 ] with two equivalents of L (L = imidazole, 2-methylimidazole or 4-methylimidazole) affords high yields of the new mono(but-2-yne) complexes [W(CO)L 2 (S 2 CNC 4 H 8 )(η 2 -MeC 2 Me)][BPh 4 ] ( 4–6 ). 13 C NMR spectroscopy indicates that the but-2-yne ligands in 1 are donating a total of six electrons to the tungsten, whereas in 4–6 the but-2-yne is donating four electrons to the tungsten. Variable-temperature 1 H NMR studies have been carried out on 4–6 in order to calculate the barrier to but-2-yne rotation.