Osmium(II)-Induced Rearrangement of Allenols for Metallafuran Complexes

Osmafuran complexes in the form of cis-[Os­(L∧L)2(C∧O)]+ (L∧L = 1,1-bis­(diphenylphosphino)­methane (dppm) or 2,2′-bipyridine (bpy); C∧O = [C(CH3)­C­(CH3)­CRO]−, coordinating atoms in italics) were prepared from reactions between dichloro-Os­(II) complexes cis-[Os­(L∧L)2Cl2] and allenols H2CCC­(CH3)­(CH­(R)­(OH)) in alcoholic solvents. Rearrangement of allenolates H2CCC­(CH3)­(CH­(R)­(O–)) involving deprotonation of the secondary alcoholic carbon and protonation of the terminal allenic carbon was evident from the X-ray crystal structures of the resulting complexes. Density functional theory (DFT) calculations suggested a rearrangement mechanism involving Os–alkene intermediates cis-[Os­(L∧L)2(H2CCH–C­(CH3)­(C­(R)­(O–)))]+ but not Os–hydride intermediates. Overall, these osmafurans are not directly derived from common metal–allene reaction patterns.