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

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.