Evidence for an intramolecular transition metal Arbusov reaction

Article abstract of DOI:10.1139/v96-237

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 R_f 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 triclinic system with space group P1(no. 2), with a = 12.928(4) A, b = 14.683(4) A, c = 7.666(2) A, α = 103.50(2)°, β = 101.31(3)°, γ = 109.50(2)°, V = 1272.8(7) A³, Z = 2, and R = 0.036 (R_w = 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.