Dinitrogen Partial Reduction by Formally Zero- and Divalent Vanadium Complexes Supported by the Bis-iminopyridine System

Reduction of the two trivalent 2,6-{[2,6-(i-Pr)2C6H5]NC(CH3)}2(C5H3N)VCl3 and {[2,6-{[2,6-(i-Pr)2C6H3]NC(CH2)}2(C5H3N)]VCl(THF) complexes with excess NaH afforded two corresponding
end-on dinitrogen-bridged complexes [2,6-{[2,6-(i-Pr)2C6H5]NC(CH3)}2(C5H3N)V]2(m-N2)·(hexane) (1) and [{[2,6-{[2,6-(i-Pr)2C6H3]NC(CH2)}2(C5H3N)]V]2(m-N2)·(hexane) (3). Despite their
very close structural similarity, the two species have completely
different natures. The first is paramagnetic and may be regarded
as generated by the two-electron attack of two formally zerovalent
vanadium moieties on the same N2 unit. In the nearly diamagnetic
3 instead, the N2 unit has been reduced by two vanadium atoms,
formally divalent. Structural analysis and DFT calculations have
indicated that partial reduction of the bridging nitrogen occurred
for both complexes while, in the case of 1, substantial metal-to-ligand electron transfer also occurs.