61st Annual Report on Research 2016

The goal of this project is to study asymmetric hydrogen transfer processes catalyzed by chiral iridium pincer complexes, such as 1.  To prepare these precursors, we optimized the synthesis of the known phosphine-boranes 2 and 3.  After deprotection of 3, reaction of bis(phosphine) 4 with [Ir(COE)₂Cl]₂ (COE = cyclooctene) gave dinuclear 5, which contains the desired coordinated pincer ligand, but also a bridging bis(phosphine).  In contrast, a similar reaction with Ni(DME)Br₂ (DME = dimethoxyethane) gave the mononuclear nickel-pincer complex 6, which was crystallographically characterized.  We hypothesize that the relatively small size and high nucleophilicity of the dimethylphospholane group precluded the isolation of five-coordinate iridium pincer complexes like 1 (R = Me).  Therefore, we are now investigating second-generation ligands with larger R groups.