SYNTHESIS AND CHEMISTRY OF RUTHENIUM HYDRIDO ARYLOXIDES AND ARYLAMIDES - AN INVESTIGATION OF STRUCTURE, N-H AND O-H ELIMINATION PROCESSES, PROTON-CATALYZED EXCHANGE-REACTIONS, AND RELATIVE RU-X BOND STRENGTHS

The synthesis and reactivity of ruthenium complexes containing a hydride and an aryloxide or arylamide ligand are reported. The arylamide complex (PMe3)4Ru(H)(NHC6H5) (1) was prepared by the addition of aniline to the ethylene complex (PMe3)4Ru(C2H4) (3) or to the cyclometalated hydride complex (PMe3)4Ru(CH2PMe2)(H) (4). Monitoring of the reaction showed that the addition of aniline to 3 proceeds by initial conversion of 3 to 4. Moreover, H/D-exchange reactions between a series of arylamines and organic acids showed that this process is catalyzed by trace amounts of water and we believe that the addition of aniline to 4 may also be catalyzed by water or another trace acid, although the rate-determining step is clearly opening of the metallacycle. Addition of p-cresol to 3 or 4 formed the complex (PMe3)4Ru(H)(OC6H4-p-Me) (2). This reaction proceeded faster than exchange of phosphine, indicating that the O-H bond of this substrate reacts directly with the ruthenium center. Addition of CO to 2 led to formation of the CO substitution product (PMe3)3(CO)Ru(H)(OC6H4-p-Me) (5). X-ray structural analysis of 1, 2, and 5 showed that CO substitution has a marked effect on the Ru-O bond length. In addition variable-temperature NMR studies indicated that the ancillary ligands affect the barrier to aryl ring rotation, presumably due to a difference in the double-bond character of the X-Ar bond. Addition of H-2 and CO led to extrusion of p-cresol and aniline. Reaction of CO with 1 formed free aniline and (PMe3)2Ru(CO)3 (7) after 8 h at 85-degrees-C, while reaction of CO with 2 formed free p-cresol and 7 after 4 days at 135-degrees-C. Addition of p-cresol to 1 cleanly formed 2, demonstrating that the Ru-O bond is stronger than the Ru-N bond in these compounds. In separate studies it has been shown that the precursor to these compounds, cyclometalated hydride 4, forms from thermolysis of benzyl hydride (PMe3)4Ru(H)(CH2Ph) (8), and the reaction of hydrogen with 1 and 2 forms dihydride (PMe3)4Ru(H)2. Therefore these Ru-O and Ru-N bonds are stronger than the Ru-C bond in benzyl hydride 8, and the Ru-H bond in dihydride 4 is stronger than either the Ru-O or Ru-N bond. The following trend in Ru-X bond energies results: L4(H)Ru-H > L4(H)Ru-OAr > L4(H)Ru-NHPh > L4(H)Ru-CH2Ph.