Vanadium Complexes of the N(CH2CH2S)3 3- and O(CH2CH2S)2 2- Ligands with Coligands Relevant to Nitrogen Fixation Processes

Vanadium(III) and vanadium(V) complexes derived from the tris(2-thiolatoethyl)amine ligand [(NS 3)3-] and the bis(2-thiolatoethyl)ether ligand [(OS 2)2-] have been synthesized with the aim of investigating the potential of these vanadium sites to bind dinitrogen and activate its reduction. Evidence is presented for the transient existence of {V(NS 3)(N2)V(NS 3)}, and a series of mononuclear complexes containing hydrazine, hydrazide, imide, ammine, organic cyanide, and isocyanide ligands has been prepared and the chemistry of these complexes investigated. [V(NS 3)O] (1) reacts with an excess of N2H4 to give, probably via the intermediates {V(NS 3)(NNH2)} (2a) and {V(NS 3)(N2)V(NS 3)} (3), the VIII adduct [V(NS 3)(N2H4)] (4). If 1 is treated with 0.5 mol of N2H4, 0.5 mol of N2 is evolved and green, insoluble [{V(NS 3)} n ] (5) results. Compound 4 is converted by disproportionation to [V(NS 3)(NH3)] (6), but 4 does not act as a catalyst for disproportionation of N2H4 nor does it act as a catalyst for its reduction by Zn/HOC6H3Pri 2-2,6. Compound 1 reacts with NR1 2NR2 2 (R1 = H or SiMe3; R2 2 = Me2, MePh, or HPh) to give the hydrazide complexes [V(NS 3)(NNR2 2)] (R2 2 = Me2, 2b; R2 2 = MePh, 2c; R2 2 = HPh, 2d), which are not protonated by anhydrous HBr nor are they reduced by Zn/HOC6H3Pri 2-2,6. Compound 2b can also be prepared by reaction of [V(NNMe2)(dipp)3] (dipp = OC6H3Pri 2-2,6) with NS 3H3. N2H4 is displaced quantitatively from 4 by anions to give the salts [NR3 4][V(NS 3)X] (X = Cl, R3 = Et, 7a; X = Cl, R3 = Ph, 7b; X = Br, R3 = Et, 7c; X = N3, R3 = Bun, 7d; X = N3, R3 = Et, 7e; X = CN, R3 = Et, 7f). Compound 6 loses NH3 thermally to give 5, which can also be prepared from [VCl3(THF)3] and NS 3H3/LiBun. Displacement of NH3 from 6 by ligands L gives the adducts [V(NS 3)(L)] (L = MeCN, νCN 2264 cm-1, 8a; L = ButNC, νNC 2173 cm-1, 8b; L = C6H11NC, νNC 2173 cm-1, 8c). Reaction of 4 with N3SiMe3 gives [V(NS 3)(NSiMe3)] (9), which is converted to [V(NS 3)(NH)] (10) by hydrolysis and to [V(NS 3)(NCPh3)] (11) by reaction with ClCPh3. Compound 10 is converted into 1 by [NMe4]OH and to [V(NS 3)NLi(THF)2] (12) by LiNPri in THF. A further range of imido complexes [V(NS 3)(NR4)] (R4 = C6H4Y-4, where Y = H (13a), OMe (13b), Me (13c), Cl (13d), Br (13e), NO2 (13f); R4 = C6H4Y-3, where Y = OMe (13g); Cl (13h); R4 = C6H3Y2-3,4, where Y = Me (13i); Cl (13j); R4 = C6H11 (13 k)) has been prepared by reaction of 1 with R4NCO. The precursor complex [V(OS 2)O(dipp)] (14) [O