Reactions of phosphavinyl Grignard reagents with aldehydes: synthesis, characterisation and further reactivity of β-phosphaallylic alcohols

Abstract

The reactions of the phosphavinyl Grignard reagents, Z-[RPC(Bu^t)MgCl(OEt₂)], R = cyclohexyl (Cy) or cyclopentyl (Cy^p), with benzaldehyde have afforded the β-phosphaallylic alcohols, Z-RPC(Bu^t)C(H)(OH)Ph, after quenching with methanol. This methodology has been successfully applied to a series of other alkyl, aryl and functionalised aldehydes. The β-phosphaallylic alcohol, Z-CyPC(Bu^t)C(H)(OH)Ph, undergoes unusual reactions with ZnEt₂, M{N(SiMe₃)₂} (M = Na or K) and Sn{N(SiMe₃)₂}₂ to give three isomers (Z,Z-, Z,E- and E,E-) of the bis(alkenyl)diphosphine mono-oxide, PhC(H)C(Bu^t)P(Cy)P(O)(Cy)C(Bu^t)C(H)Ph. By contrast its reaction with Ti(OPrⁱ)₄ led to the formation of the secondary phosphine oxide, Z-CyP(H)(O)C(Bu^t)C(H)Ph. A facile synthesis of the phosphaalkenes, E-RPC(H)Bu^t, R = Cy or mesityl (Mes), is also reported, as is an unusual tungsten complex of one of these, [{W(CO)₄[η¹-P,η²-PC–CyPC(H)Bu^t]}₂]. The X-ray crystal structures of seven of the reported complexes are discussed.