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 degrees C produced the known tungsten oxo alkylidene complex W(O)(CH-t-Bu)Cl-2(PMe2Ph)(2) (1a) in 45% isolated yield. The neophylidene analogue W(O)(CHCMe2Ph)Cl-2(PMe2Ph)(2) was prepared similarly in 39% yield. The reaction between la and LiOR (LiOR = LiOHIPT, LiOHMT) in benzene at 22 degrees 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)(2)phenoxide). 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.