Reaction of the η2(4e)-donor alkyne complexes [Mo{η2(4e)-R1C2R2}{P(OMe)3}2(η-C5H5)](R1= R2= Ph or Me; R1= Me, R2= Ph) with the Grignard reagents MgR3(X)(R3= Me, Et, CH2Ph, CH2CHCH2 or CHCH2) and CH2(MgI)2

Abstract

Reaction of the complex [Mo{η²(4e)-PhC₂Ph}{P(OMe)₃}₂(η-C₅H₅)][BF₄]1 with MgR(X)(R = Me, Et or PhCH₂) afforded good yields of [Mo{η²(4e)-PhC₂Ph}R{P(OMe)₃}(η-C₅H₅)]. Unexpectedly, reaction of 1 with the 1,1-di-Grignard reagent CH₂(MgI)₂ gave the X-ray crystallographically identified zwitterionic complex [Mo{η²(4e)-PhC₂Ph}{η²-P(OMe)₂OBF₂OP(OMe)₂}(η-C₅H₅)], similar reactions with the but-2-yne and 1-phenylprop-2-yne complexes affording the analogous [Mo{η²(4e)-(RC₂R²){η²-P(OMe)₂OBF₂OP(OMe)₂}(η-C₅H₅)](R = R²= Me; R = Me, R²= Ph). Treatment of the zwitterionic diphenylacetylene- and 1-phenylprop-2-yne-substituted complexes with K[BHBu^s₃] gave the anionic η²(3e)-vinyl complexes K[[graphic omitted]H(Ph)}{η²-P(OMe)₂OBF₂OP(OMe)₂(η-C₅H₅)](R = Ph or Me). Protonation (HBF₄·Et₂O) of the diphenyl-substituted η²(3e)-vinyl complex followed by addition of carbon monoxide, trimethyl phosphite, or diphenylacetylene afforded trans-stilbene and the complexes [Mo(CO)₂{η²-P(OMe)₂OBF₂OP(OMe)₂}(η²-C₅H₅)], [Mo{P(OMe)₃}₂{η²-P(OMe)₂OBF₂OP(OMe)₂}(η-C₅H₅)] and [Mo{η²(4e)-PhC₂Ph}{η²-P(OMe)₂OBF₂OP(OMe)₂}(η-C₅H₅)] respectively. When CH₂CHCH₂MgBr was added to 1 an unstable compound was formed, which on addition of P(OMe)₃ gave [Mo{η³-C(Ph)C(Ph)CH₂CHCH₂}{P(OMe)₃}₂(η-C₅H₅)], the identity of which was confirmed by X-ray crystallography. This reaction is explained in terms of an unusual metalla-3,3-sigmatropic shift process. A similar reaction between 1 and CH₂CHMgBr followed by addition of P(OMe)₃ surprisingly gave the η³-cyclopropenyl complex [Mo(η³-C₃Ph₂Me){P(OMe)₃}₂(η-C₅H₅)]. The complex [Mo{η²(4e)-PhC₂Ph}Me{P(OMe)₃}(η-C₅H₅)] reacted thermally (78 °C) with an excess of PhC₂Ph to give the X-ray crystallographically identified complex [MoH(η⁴-C₅H₂Ph₄){P(OMe)₃}(η-C₅H₅)], which on heating (100 °C) afforded the dihydride [MoH₂(η⁵-C₅HPh₄)(η-C₅H₅)].