Preparation of Capped Octahedral OsHC6 Complexes by Sequential Carbon-Directed C–H Bond Activation Reactions

A synthetic procedure based on sequential C-directed C–H bond activation reactions is reported for the preparation of capped octahedral OsHC6 complexes. Reactions of the dimer [OsCl2(η6-p-cymene)]2 (1) with PhMeLAgI (PhMeL = 1-phenyl-3-methyl-1H-benzimidazolyl­idene (PhMeBIm), 1-phenyl-3,5,6-trimethyl-1H-benzimidazolyl­idene (PhMeBIm*)) afford OsCl2(η6-p-cymene)­(PhMeL) (L = BIm (2), BIm* (3)), which undergo cyclization to give OsCl­{κ2-C,C-(MeL-C6H4)}­(η6-p-cymene) (L = BIm (4), BIm* (5)) by stirring in dichloromethane suspensions of Al2O3. Complexes 4 and 5 exchange the anion with AgOTf (OTf = CF3SO3). In acetonitrile, at 75 °C, the resulting OTf derivatives Os­(OTf)­{κ2-C,C-(MeL-C6H4)}­(η6-p-cymene) (L = BIm (6), BIm* (7)) release the arene to yield the tetra­(solvento) compounds [Os­{κ2-C,C-(MeL-C6H4)­(CH3CN)4]­OTf (L = BIm (8), BIm* (9)). Complexes 8 and 9 react with PhMeLAgI to coordinate a second NHC ligand. The generated species Os­{κ2-C,C-(MeL-C6H4)­(PhMeL)­(CH3CN)3]­OTf (L = BIm (10), BIm* (11)), containing a C,C-chelate NHC-C6H4 ligand and a monodentate NHC group, exist as a mixture of mer (a and b) and fac (c) acetonitrile isomers. The X-ray diffraction structure of 10c reveals aromatic–aromatic interactions between the N-phenyl substituent of the monodentate NHC group and aromatic rings of the chelate ligand. The π–π stacking has been analyzed by means of DFT calculations by using the AIM approach. Treatment of 10 and 11 with [PhMeLH]­I, in the presence of an excess of Et3N, leads to the capped octahedral target compounds OsH­{κ2-C,C-(MeL-C6H4)}3 (L = BIm (12), BIm* (13)), as a result of the coordination of a third NHC group and the orthometalation of the N-phenyl substituents of the second and third NHC ligands.