Redox-Noninnocent Ligand-Supported Vanadium Catalysts for the Chemoselective Reduction of C═X (X = O, N) Functionalities.

ABSTRACT

Catalysis is the second largest application for V after its use as an additive to improve steel production. Molecular complexes of vanadium(V) are particularly useful and efficient catalysts for oxidation processes; however, their ability to catalyze reductive transformations has yet to be fully explored. Here we report the first examples of polar organic functionality reduction mediated by V. Open-shell VIII complexes that feature a π-radical monoanionic 2,2'6',2″-terpyridine ligand (Rtpy•)- functionalized at the 4'-position (R = (CH3)3SiCH2, C6H5) catalyze mild and chemoselective hydroboration and hydrosilylation of functionalized ketones, aldehydes, imines, esters, and carboxamides with turnover numbers (TONs) of up to ∼1000 and turnover frequencies (TOFs) of up to ∼500 h-1. Computational evaluation of the precatalyst synthesis and activation has revealed underappreciated complexity associated with the redox-active tpy chelate.