C−C Bond Activation of the NHC Ligand of an Osmium−Amido Complex

Treatment of (η6-p-cymene)OsCl2(IPr) (1, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene) with AgBF4 in acetonitrile leads to [(η6-p-cymene)Os(CH3CN)2(IPr)][BF4]2 (2), which reacts with aniline and cyclohexylamine to afford [(η6-p-cymene)Os(dNHR)(IPr)]BF4 (R = Ph (3), Cy (4)). Complexes 3 and 4 have also been prepared by addition of nBuLi to tetrahydrofuran solutions of the amine compounds [(η6-p-cymene)OsCl(NH2R)(IPr)]BF4 (R = Ph (6), Cy (7)). Complex 4 decomposes in tetrahydrofuran at 100 _C and in the presence of H2O to give cyclohexanone, propane, and [η6-p-cymene)Os{CCHCHCHC(iPr)CNCHCHN(C6H3iPr2)C}(NH3)]BF4 (8). In dichloromethane at 50 _C, 4 evolves to [(η6-p-cymene)OsH(NHdCCH2CH2CH2CH2CH2)(IPr)]BF4 (9), which also gives 8 in tetrahydrofuran at 100ºC and in the presence of H2O. On the basis of these transformations, a mechanism for the formation of 8 is proposed.
Financial support from the Spanish MICINN (project number CTQ2008-00810 and Consolider Ingenio 2010 CSD2007-00006), the Diputación General de Aragón (E35), and the European Social Fund is acknowledged.