Electronically and Sterically Varied Vanadium Aminopyridinate Complexes Applied to the Catalytic Reductive Coupling of Alcohols

Abstract

2-Aminopyridinate complexes of vanadium were synthesized, isolated, and characterized. Comparative reactivity showed that 2-aminopyridinate ligands can be used in the synthesis of monometallic complexes and DFT calculations indicate increased electron donation for the 2-aminopyridinate ligand on vanadium compared to pyridonate ligands. A homoleptic, monometallic tris(N-phenyl-2-aminopyridinate)vanadium(III) complex was used for the catalytic reductive coupling of benzhydrol, and a series of various 2-aminopyridinate ligands were also screened for this transformation. Unsubstituted 2-aminopyridine as the proligand resulted in the highest activity, with the in situ catalytic system demonstrating improved reactivity with benzylic and allylic alcohols compared to previously reported systems. The isolation of the vanadium aminopyridinate complexes, coupled with kinetic investigations, supports monometallic intermediates for the catalytic reductive coupling of alcohols.