ALKYL, ARYL, HYDRIDO, AND ACETATE COMPLEXES OF (DMPM)2RU [DMPM = BIS(DIMETHYLPHOSPHINO)METHANE] - REDUCTIVE ELIMINATION AND OXIDATIVE ADDITION OF C-H BONDS

Complexes of the general formula (DMPM)(n)Ru(X)(Y) [DMPM = 1,2-bis(dimethylphosphino)methane] were investigated. Addition of excess DMPM to the ruthenium triphenylphosphine compound (PPh3)2Ru(OAc)2 (1) led to formation of the mononuclear tris (DMPM) complex with the formula (eta-1-DMPM)2(eta-2-DMPM)Ru(OAc)2 (2). Addition of 2 equiv of DMPM to 1 gave the dimeric complex (eta-1-DMPM)2(eta-2-DMPM)2Ru2(OAc)4 (3), and thermolysis of 3 led to formation of the monomeric product cis-(eta-2-DMPM)2Ru(OAc)2 (4). Monomeric compound 4 was used as a precursor to the dihydride cis-(eta-2-DMPM)2Ru(H)2 (5) by addition of lithium aluminum hydride, and as a precursor to diaryl and dialkyl complexes cis-(eta-2-DMPM)2Ru(R)2 by addition of aluminum and magnesium alkyl and aryl reagents. Irradiation of the dihydride 5 in benzene solvent led to extrusion of hydrogen and formation of the phenyl hydride complex cis-(eta-2-DMPM)2Ru(Ph)(H) (10). Addition of methanesulfonic acid to 5 formed the hydrido methanesulfonate trans-(eta-2-DMPM)2Ru(H)(OSO2Me) (8), which formed trans-(eta-2-DMPM)2Ru(H)(Me) (11) upon addition of trimethylaluminum at -78-degrees-C. This alkyl hydride was unstable at room temperature, eliminating methane to form phenyl hydride complex 10 in arene solvents. Phenyl hydride 10 undergoes exchange reactions at room temperature with toluene-d8 solvent to form a series of tolyl hydride products. These C-H oxidative additions proceed through the (DMPM)2Ru intermediate, also formed photolytically from dihydride 5, as determined by isotopic labeling studies.