Insertion of CO2 into the Ru-C Bonds of cis- and trans-Ru(dmpe)2Me2 (dmpe = Me2PCH2CH2PMe2)

The reaction of cis-Ru(dmpe)(2)Me-2 (1) and trans-Ru(dmpe)(2)Me-2 (2) [dmpe = 1, 2-bis(dimethylphosphino)ethane] with carbon dioxide was investigated. Addition of 3-4 atm of CO2 at 300 K to trans-Ru(dmpe)(2)Me-2 (2) results in the formation of the expected methyl acetate complex trans-Ru (dmpe)(2)(C)COMe)Me (3) and bis-acetate complex trans-Ru(dmpe)(2)(OCOMe)(2) (5). Addition of 3-4 atm of CO2 at 300 K to cis-Ru(dmpe)(2)Me-2 (1) leads to the formation of the expected methyl acetate complex cis-Ru(dmpe)(2)(OCOMe)Me (4) and to the bis-acetate complex cis-Ru(dmpe)(2)(OCOMe)(2) (6) when the reaction mixture is heated at 333 K. A carbonate byproduct, Ru(dmpe)(2)CO3 (7), is also formed in both reactions. As part of this study, a new ruthenium methyl hydride complex has been synthesized, Ru(dmpe)(2)CH3H (8), and its isomerization properties and reactions with CO2 are reported. At 300 K, addition of CO2 to 8 forms the methyl formate product Ru(dmpe)(2)(O2CH)CH3 (9). The reaction with CO2 is reversible, and on heating, the methyl formate 9 decarboxylates and CO2 insertion into the metal carbon bond eventually forms the hydrido acetate complex Ru(dmpe)(2)(O2CCH3)H (12) as the thermodynamic product. This means that the insertion of CO2 into the Ru-H bond is kinetically favored, but the thermodynamic product results from insertion into the Ru-C bond. All complexes have been characterized by multinuclear NMR spectroscopy, with IR spectroscopy and elemental analyses where complexes were thermally stable. Complexes 5, 7, 8, and 12 have also been characterized by X-ray crystallography.