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Hemilabile and Bimetallic Coordination in Rh and Ir Complexes of NCN Pincer Ligands

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journal contribution
posted on 06.10.2014, 00:00 by Giulia Mancano, Michael J. Page, Mohan Bhadbhade, Barbara A. Messerle
Two new pincer ligands have been developed that contain a central N-heterocyclic carbene (NHC) moiety linked to two pendant pyrazole groups by either a methylene (NCNme) or ethylene (NCNet) chain. The coordination of these two ligands to rhodium and iridium resulted in a variety of binding modes. Tridentate coordination of the ligands was observed in the complexes [Rh­(NCNme)­(COD)]­BPh4 (8), [Ir­(NCNme)­(COD)]­BPh4 (10), [Rh­(NCNet)­(CO)2]­BPh4 (13), and [Ir­(NCNme)­(CO)2]­BPh4 (14), and monodentate NHC coordination was observed for [Ir­(NCNme)2(COD)]­BPh4 (11) and [Ir­(NCNet)2(COD)]­BPh4 (12). Both tridentate and bidentate coordination modes were characterized for [Rh­(NCNet)­(COD)]­BPh4 (9) in the solution and solid state, respectively, while an unusual bridging mode was observed for the bimetallic complex [Rh­(μ-NCNme)­(CO)]2(BPh4)2 (15). The impact of this diverse coordination chemistry on the efficiency of the complexes as catalysts for the addition of NH, OH, and SiH bonds to alkynes was explored.