Ruthenium (II) and Iridium (III) Complexes of N-Heterocyclic Carbene and Pyridinol Derived Bidentate Chelates: Synthesis, Characterization, and Reactivity.

We report the synthesis and characterization of new ruthenium(II) and iridium(III) complexes of a new bidentate chelate, NHC-py (OR = OMe, OtBu, OH and R' = Me, Et). Synthesis and characterization studies were done on the following compounds: four ligand precursors (1-4); two silver complexes of these NHC-py ligands (5-7); six ruthenium complexes of the type [η-(p-cymene)Ru(NHC-py)Cl]X with R' = Me, Et and R = Me, tBu, H and X = OTf, PF and POF (8-13); and two iridium complexes, [Cp*Ir(NHC-py)Cl]PF (14) and [Cp*Ir(NHC-py)Cl]POF (15). The complexes are air stable and were isolated in moderate yield. However, for the PF salts, hydrolysis of the PF counter anion to POF during t-butyl ether deprotection was observed. Most of the complexes were characterized by H and C-NMR, MS, IR, and X-ray diffraction. The ruthenium complexes [η-(p-cymene)Ru(NHC-py)Cl]OTf (R = Me (8) and tBu (9)) were tested for their ability to accelerate CO hydrogenation and formic acid dehydrogenation. However, our studies show that the complexes transform during the reaction and these complexes are best thought of as pre-catalysts.