Synthesis of Tungsten Oxo Alkylidene Complexes

Reaction of W(O)2(CH2-t-Bu)2(bipy) with a mixture of ZnCl2(dioxane), PMe2Ph, and trimethylsilyl chloride in toluene at 100 °C produced the known tungsten oxo alkylidene complex W(O)(CH-t-Bu)Cl2(PMe2Ph)2 (1a) in 45% isolated yield. The neophylidene analogue W(O)(CHCMe2Ph)Cl2(PMe2Ph)2 was prepared similarly in 39% yield. The reaction between 1a and LiOR (LiOR = LiOHIPT, LiOHMT) in benzene at 22 °C led to formation of the off-white W(O)(CH-t-Bu)Cl(OR)(PMe2Ph) complexes 4a (OR = OHMT = 2,6-dimesitylphenoxide) and 4b (OR = OHIPT = 2,6-(2,4,6-triisopropylphenyl)2phenoxide). Compound 4a serves as a starting material for the synthesis of W(O)(CH-t-Bu)(OHMT)(2,6-diphenylpyrrolide) (6), W(O)(CH-t-Bu)[N(C6F5)2](OHMT)(PMe2Ph) (7), W(O)(CH-t-Bu)[OSi(t-Bu)3](OHMT) (8), and W(O)(CH-t-Bu)(OHMT)2 (10). The reaction between 8 and ethylene was found to yield the square-pyramidal metallacyclobutane complex W(O)(C3H6)[OSi(t-Bu)3](OHMT) (9), while the reaction between 10 and ethylene was found to yield the square-pyramidal metallacyclobutane complex W(O)(C3H6)(OHMT)2 (11). Compound 11 loses ethylene to yield isolable W(O)(CH2)(OHMT)2 (12). X-ray structures were determined for 6, 7, 9, and 12.