Ir(III) Complexes with Tp ^Me2 (Tris(pyrazolyl)borate) and 2‐Mercapto‐5‐(CF ₃ )pyridine Ligands for Transfer Hydrogenation Catalysis

The synthesis of a series of iridium(III) complexes supported by tris(pyrazolyl)borate (Tp Me2 ) and 2‐mercapto‐5‐(CF 3 )pyridine is reported. The new complexes are obtained via the treatment of the Tp Me2 Ir(C 2 H 4 ) 2 and Tp Me2 Ir[( η 4 ‐CH 2 C(Me)C(Me)CH 2 ] precursors with equimolar amounts of 2‐mercapto‐5‐(CF 3 )pyridine at room temperature. The new heteroleptic complexes display a variety of structural features including four‐ or five‐membered iridacycles (obtained through intramolecular CS and CN bond formation) and different iridium:mercaptopyridine ratios. All new compounds are characterized by means of 1 H and 13 C NMR spectroscopy, elemental analyses, and by X‐ray diffraction analysis. The full series of iridium(III) complexes are tested as catalysts in the transfer hydrogenation of aldehydes and ketones demonstrating good performance under low catalyst loadings (0.05 mol%) and providing good conversions. Mercury poisoning tests suggest that as the temperature of the catalytic procedure increases, the presence of a heterogeneous iridium plays an important role in the reduction process.