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.