INSERTION REACTIONS OF CO AND CO2 WITH RUTHENIUM BENZYL, ARYLAMIDO, AND ARYLOXIDE COMPLEXES - A COMPARISON OF THE REACTIVITY OF RUTHENIUM CARBON, RUTHENIUM NITROGEN, AND RUTHENIUM OXYGEN BONDS

An investigation of the mechanism and selectivies of CO and CO2 insertion reactions into four-membered metallacycles containing Ru-O, Ru-N, benzylic Ru-C, and aryl Ru-C bonds was conducted. The reaction of carbon monoxide with (PMe3)4Ru(eta-2-CH2C6H4) (1), (PMe3)4Ru(eta-2-OC6H3Me) (2), and (PMe3)4Ru(eta-2-NHC6H4) (3) provides products resulting from insertion of CO into the metal-aryl bond and replacement of one PMe3 ligand with CO. Reaction of CO2 with (PMe3)4Ru(eta-2-CH2C6H4) (1) or (PMe3)4Ru(eta-2-OC6H3Me) (2) in arene solvent also occurs at the metal-aryl bond, while reaction Of CO2 with (PMe3)4Ru(eta-2-CH2C6H4) (1) in pentane results in insertion into the ruthenium-aryl bond and dissociation of PMe3 to give (PMe3)3Ru(eta-4-CH2C6H4CO2). In contrast to these reactions with the metal-aryl bond, reaction of CO2 with (PMe3)4Ru(eta-2-NHC6H4) (3) results in a formal insertion into the metal-nitrogen bond. Low-temperature NMR experiments demonstrate that reaction of 3 with CO2 occurs by direct attack of the CO2 at the nitrogen atom of the metallacycle, followed by rearrangement to the final product (11). Thermolysis of insertion product 11 at 120-degrees-C for 2 h led to formation of the carboxamide complex (PMe3)4Ru(eta-2-OC(O)NPh) (15), independently prepared during the course of a separate study; no rearrangement to the anthranilic acid dianion complex (PMe3)4Ru(eta-2-NHC6H4C(O)O) (13), the formal insertion product of CO2 into the ruthenium-aryl bond, was observed, The anthranilate complex 13 was independently synthesized to determine if it rearranges to the direct insertion product 11 or is stable to the thermolysis conditions leading to the rearrangement of 11. Thermolysis did not lead to the product of insertion into the metal nitrogen bond or to the carboxamide complex formed from 11 at these temperatures. Instead, it underwent a reversible proton transfer and ring contraction to form the carbon and oxygen bound anthranilate complex (PMe3)4Ru(eta-2-OC(O)C6H3(NH2)) (17).