Evidence for an intramolecular transition metal Arbuzov reaction

Abstract

Reaction of [CpCo(C3F7)(I)(L)], (L = PPh2Me (1a), PPhMe2 (1b), PMe3 (1c), and PPh(OMe)2 (2)), with PPh(OMe)2 affords diastereomeric Co-and P-chiral metallophosphinates CpCo(C3F7)(L)(P(O)Ph(OMe)), 4a,b,c and 6, respectively. The solid state structure and relative configuration of the lower Rf diastereomeric phosphinate CpCo(C3F7)(PPh(OMe)2)(P(O)Ph(OMe)), 6-2, was determined by X-ray diffraction. RR;SS-6-2 crystallizes in the triclinia system with space group [Formula: see text](no. 2), with a = 12.928(4) Å, b = 14.683(4) Å, c = 7.666(2) Å, a = 103.50(2)°, β = 101.31(3)°, γ = 109.50(2)°, V = 1272.8(7) Å3, Z = 2, and R = 0.036 (Rw = 0.030) for 2867 reflections with I > 3.00σ(I). CpCo(C3F7)(I)(PPh(OMe)2), 2, reacts with PPh2Me to yield the same Co-and P-chiral phosphinate products as obtained for the reaction of 1a with PPh(OMe)2, albeit with different optical yields. The product stereochemistry is not accounted for by the established mechanism for transition metal Arbuzov-like dealkylations, which requires formation of a common, ionic intermediate [CpCo(C3F7)(PPh2Me)(PPh(OMe)2)]+, 3, via iodide substitution and subsequent nucleophilic attack at carbon. A parallel intramolecular dealkylation pathway is proposed to account for the results. Key words: stereochemistry, mechanism, Arbuzov, Co(III) complex, chiral metal. X-ray