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Proton Addition to an Anionic Carbene Complex as a Route to Seven-Coordinate Methyl Carbonyl Complexes in Equilibrium with η2-Acyl Complexes

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posted on 30.08.2004, 00:00 by Kenneth C. Stone, Adanna Onwuzurike, Peter S. White, Joseph L. Templeton
Proton addition to the anionic methylene carbene complex [Na][Tp‘(CO)2WCH2] in the presence of a trapping phosphine ligand generates seven-coordinate complexes of the form Tp‘(CO)2(PR3)W(CH3) (PR3 = PMe3, PMe2Ph, PMePh2). The seven-coordinate phosphine complexes are in equilibrium with their CO-insertion products Tp‘(CO)(PR3)W(η2-C(O)Me). The geometry of these complexes allowed us to probe the stereoselectivity of CO insertion into the W−Me bond by means of a C-13 spin-saturation transfer NMR experiment. The ΔG358 value determined for the insertion reaction was 18.5 kcal/mol for the PMe2Ph adduct. Single-crystal structures revealed detailed solid state geometries for Tp‘(CO)2(PMe2Ph)W(CH3), Tp‘(CO)2(PMe3)W(CH3), Tp‘(CO)(PMe3)W(η2-C(O)CH3), and a second isomer of Tp‘(CO)2(PMe3)W(CH3). Trapping of the protonated carbene complex with phenyl acetylene yields an η1-acyl product.