B(C₆F₅)₃-Catalyzed Reductive Amination using Hydrosilanes

In contrast to the established dogma that B(C₆F₅)₃ is irreversibly poisoned by excess H₂O/amine (or imine) bases, B(C₆F₅)₃ is actually a water-tolerant catalyst for the reductive amination of primary and secondary arylamines with aldehydes and ketones in "wet solvents" at raised temperatures and using only 1.2 equiv of Me₂PhSiH as reductant. Arylamines/N-arylimines do not result in the irreversible deprotonation of H₂O-B(C₆F₅)₃, allowing sufficient B(C₆F₅)₃ to be evolved at raised temperatures to effect catalytic reductions. Stronger Brønsted basic amines such as ^tBuNH₂ (and derived imines) result in irreversible formation of [HO-B(C₆F₅)₃]^- from H₂O-B(C₆F₅)₃, precluding the formation of B(C₆F₅)₃ at raised temperatures and thus preventing any imine reduction. A substrate scope exploration using 1 mol % nonpurified B(C₆F₅)₃ and "wet solvents" demonstrates that this is an operationally simple and effective methodology for the production of secondary and tertiary arylamines in high yield, with imine reduction proceeding in preference to other possible reactions catalyzed by B(C₆F₅)₃, including the dehydrosilylation of H₂O and the reduction of carbonyl moieties (e.g., esters).