Reaction of [WMe(CO)3(η-C5H5)] with LiBHEt3. Formation and reactions of the anionic formyl trans-[W(CHO)Me(CO)2(η-C5H5)]– and the anionic hydrido acyl trans-[WH(COMe)(CO)2(η-C5H5)]–

Abstract

Addition of LiBHEt₃ to [WMe(CO)₃(η-C₅H₅)]5 at –70°C results in the formation of the formyl trans-[W(CHO)Me(CO)₂(η-C₅H₅)]^–7. In solution, this species exists as a mixture of two BEt₃ adducts and a BEt₃-free species. All the formyl species undergo chemical exchange at –50°C. Warming of the reaction mixture to ambient temperature results in solutions containing the anionic hydrido acyl complex trans-[WH(COMe)(CO)₂(η-C₅H₅)]^–6 isolable as a boron-free salt [Li(12-crown-4)₂][WH(COMe)(CO)₂(η-C₅H₅)](12-crown-4 = 1,4,7,10-tetraoxacyclododecane). This moisturesensitive anion gives [W(CO)₃(η-C₅H₅)]^– on exposure to water and undergoes hydride for halide (X) exchange on low-temperature treatment with CCl₄, CBr₄ or CHI₃ forming the reactive anions [WX(COMe)(CO)₂(η-C₅H₅)]^–8–10. The major product of warming these halogenoacyl anions is 5. Addition of [Me₃O][BF₄] to boron-free solutions of [WI(COMe)(CO)₂(η-C₅H₅)]^–10 results in the new carbene trans-[WI{C(OMe)Me}(CO)₂(η-C₅H₅)]11, while treatment with SiMe₃Cl followed by low-temperature filtration through silica gives the hydroxycarbene trans-[Wl{C(OH)Me}(CO)₂(η-C₅H₅)]12.