Addition of Si–H and B–H Bonds and Redox Reactivity Involving Low-Coordinate Nitrido–Vanadium Complexes

In this study we enumerate the reactivity
for two molecular vanadium nitrido complexes of [(nacnac)­VN­(X)]
formulation [nacnac = (Ar)­NC­(Me)­CHC­(Me)­(Ar)−, Ar
= 2,6-(CHMe2)2C6H3); X– = OAr (1) and N­(4-Me-C6H4)2 (Ntolyl2) (2)]. Density
functional theory calculations and reactivity studies indicate the
nitride motif to have nucleophilic character, but where the nitrogen
atom can serve as a conduit for electron transfer, thus allowing the
reduction of the vanadium­(V) metal ion with concurrent oxidation of
the incoming substrate. Silane, H2SiPh2, readily
converts the nitride ligand in 1 into a primary silyl–amide
functionality with concomitant two-electron reduction at the vanadium
center to form the complex [(nacnac)­V­{N­(H)­SiHPh2}­(OAr)]
(3). Likewise, addition of the B–H bond in pinacolborane
to the nitride moiety in 2 results in formation of the
boryl–amide complex [(nacnac)­V­{N­(H)­B­(pinacol)}­(Ntolyl2)] (4). In addition to spectroscopic data, complexes 3 and 4 were also elucidated structurally by
single-crystal X-ray diffraction analysis. One-electron reduction
of 1 with 0.5% Na/Hg on a preparative scale allowed for
the isolation and structural determination of an asymmetric bimolecular
nitride radical anion complex having formula [Na]2[(nacnac)­V­(N)­(OAr)]2 (5), in addition to room-temperature solution
X-band electron paramagnetic resonance spectroscopic studies.