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

Abstract

Proton addition to the anionic methylene carbene complex [Na][Tp'(CO) 2 W=CH 2 ] in the presence of a trapping phosphine ligand generates seven-coordinate complexes of the form Tp'(CO) 2 (PR 3 )W(CH 3 ) (PR 3 = PMe 3 , PMe 2 Ph,PMePh 2 ). The seven-coordinate phosphine complexes are in equilibrium with their CO-insertion products Tp'(CO)(PR 3 )W(η 2 -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 ΔG 3 58 value determined for the insertion reaction was 18.5 kcal/mol for the PMe 2 Ph adduct. Single-crystal structures revealed detailed solid state geometries for Tp'(CO) 2 (PMe 2 Ph)W-(CH 3 ), Tp'(CO) 2 (PMe 3 )W(CH 3 ), Tp'(CO)(PMe 3 )W(η 2 -C(O)CH 3 ), and a second isomer of Tp'-(CO) 2 (PMe 3 )W(CH 3 ). Trapping of the protonated carbene complex with phenyl acetylene yields an η 1 -acyl product.