DINITROGENVANADATES(-I) - SYNTHESIS, REACTIONS AND CONDITIONS FOR THEIR STABILITY

Reduction of [VCl3(thf)(3)] by Na or Li (M) in the presence of phosphi nes (L(m)) and N-2 yielded the complexes Na[V(N-2)(n)(PMe(2)Ph)(6-n)] (n = 1 or 2), M[V(N-2)(n)L(4-n)(2)] [n = 1 or 2, L(2) = Me(2)PCH(2)CH( 2)-PMe(2) (dmpe) or Ph(2)PCH(2)CH(2)PPh(2)], Na[V(N-2)(dmpe)L(3)] {L(3 ) = PhP[(CH2)(2)PPh(2)](2), MeP[(CH2)(3)PMe(2)](2) (bdmpm) or MeP[(CH2 )(3)PEt(2)](2)} and Na[V(N-2)(2)L(4)] {L(4) = P[(CH2)(2)PPh(2)](3), P[ (CH2)(3)PMe(2)](3) or P[(CH2)(3)PEt(2)](3)}. Generally, the complexes are labile, with a maximum stability for cis- and trans-M[V(N-2)(2)(dm pe)(2)]. In the presence of CO or CNBu(t), N-2 is replaced by these li gands. The compounds have been characterized by their v(NN) pattern an d by V-51, Na-23 and Li-7 NMR spectroscopy The V-51 NMR spectra exhibi t well resolved multiplets. All spectroscopic data, in particular Li-7 NMR of cis-and trans-[Li(thf)(x)][V(N-2)(2)(dmpe)(2)] in tetrahydrofu ran, are indicative of close contact ion-pair interaction of the kind V-N=N ... M(+). The potassium ion and large cations such as [NEt(4)]() do not provide stable complexes, and complexation of Li+ and Na+ by crown ethers leads to immediate decomposition of the N-2 complexes. Th e reductive protonation of part of the co-ordinated N-2 to NH4+ (plus small amounts of N2H5+) is discussed in terms of similar reactivity fe atures to the analogous complexes, and in the context of these N-2 com plexes as functional models for nitrogenases. The compound [V-2(bdmpm) (2)Cl-3], isolated as an intermediate product of the reduction of VCl3 reacted with LiNHNH2 to yield ammonia.