Synthesis, structure, and reactions of cationic dimethylmanganese(III) complexes containing 1,2-bis(dimethylphosphino)ethane ligands

Article abstract of DOI:10.1021/om00051a020

A stable dimethylmanganese(III) complex, [MnMe₂(dmpe)₂]⁺AlMe₄^- (1) has been prepared by the reaction of Mn(acac)₃ with trimethylaluminum in the presence of 1,2-bis(dimethylphosphino)ethane in ether. An anion-exchange reaction of 1 stabilizes the dimethylmanganese(III) complex to give [MnMe₂(dmpe)₂]⁺BPh₄^- (2). X-ray structure analysis reveals that 2 has an octahedral trans configuration: triclinic, space group P1, a = 16.587 (4) ?, b = 17.122 (8) ?, c = 16.539 (2) ?, α = 106.86 (2)°, β = 105.76 (2)°, γ = 107.64 (2)°, Z = 4, R = 0.081, R_w = 0.094, respectively, with use of 6956 reflections. The average Mn-P bond distance in 2 is longer than that in the isostructural dimethylmanganese(II) complex and shorter than that in octahedral tetramethyl(1,2-bis(dimethylphosphino)ethane)manganese(IV), reflecting the importance of back-bonding in the M-P bond. Reaction of 2 with carbon monoxide in benzonitrile at 90°C affords [Mn(CO)(PhCN)(dmpe)₂]⁺BPh₄^- (3) with liberation of a quantitative yield of acetone. Octahedral trans configuration of 3 is unequivocally determined by X-ray structure analysis: monoclinic, space group P2₁/n, a = 23.111 (4) ?, b = 14.935 (3) ?, c = 13.602 (3) ?, β = 105.14°, Z = 4, R = 0.059, R_w = 0.053, respectively with use of 3699 reflections. An intermediate unstable purple complex, [Mn(PhCN)(dmpe)₂]⁺BPh₄^- (5) has been obtained when the reaction of 2 with carbon monoxide is carried out at 40°C.