Vanadium complexes of the N(CH2CH2S)33- and O(CH2CH2S)22- ligands with coligands relevant to nitrogen fixation processes

Vanadium(III) and vanadium(V) complexes derived from the tris(2-thiolatoethyl)amine ligand [(NS3)(3-)] and the bis(2-thiolatoethyl)ether ligand [(OS2)(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(NS3)(N-2)V(NS3)}, 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(NS3)O] (1) reacts with an excess of N2H4 to give, probably via the intermediates {V(NS3)(NNH2)} (2a) and {V(NS3)(N-2)V(NS3)} (3), the V-III adduct [{V(NS3)(N2H4)}] (4). If 1 is treated with 0.5 mol of N2H4, 0.5 mol of N-2 is evolved and green, insoluble [{V(NS3)}(n)] (5) results. Compound 4 is converted by disproportionation to [V(NS3)-(NH3)- (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/HOC6H3Pr2i-2,6. Compound 1 reacts with (NR2NR22)-N-1 (R-1 = H or SiMe3; R-2(2) = Me-2, MePh, or HPh) to give the hydrazide complexes [V(NS3)(NNR22)] (R-2(2) = Me-2, 2b; R-2(2) = MePh, 2c; R-2(2) HPh, 2d), which are not protonated by anhydrous HBr nor are they reduced by Zn/HOC6H3Pri2-2,6. Compound 2b can also be prepared by reaction of [V(NNMe2)(dipp)(3)] (dipp = OC6H3Pr2i-2,6) with NS3H3. N2H4 is displaced quantitatively from 4 by anions to give the salts [NR43][V(NS3)X] (X = Cl, R-3 = Et, 7a; X = Cl. R-3 = Ph, 7b; X = Br, R-3 = Et, 7c; X = N-3, R-3 = Bu-n, 7d; X = N-3, R-3 = Et, 7e; X = CN, R-3 = Et, 7f). Compound 6 loses NH3 thermally to give 5, which can also be prepared from [VCl3(THF)(3)] and NS3H3/LiBun. Displacement of NH3 from 6 by ligands L gives the adducts [V(NS3)(L)] (L = MeCN, nu(CN) 2264 cm(-1), 8a; L = (BuNC)-N-t, nu(NC) 2173 cm(-1), 8b; L = C6H11NC. nu(NC) 2173 cm(-1), 8c). Reaction of 4 with N3SiMe3 gives [V(NS3)(NSiMe3)] (9), which is converted to [V(NS3)(NH)] (10) by hydrolysis and to [V(NS3)(NCPh3)] (11) by reaction with ClCPh3. Compound 10 is converted into 1 by [NMe4]OH and to [V(NS3)NLi(THF)(2)] (12) by LiNPri in THF. A further range of imido complexes [V(NS3)(NR4)] (R-4 = C6H4Y-4, where Y = H (13a), OMe (13b), Me (13c), Cl (13d), Br (13e), NO2 (13f); R-4 = C6H4Y-3, where Y = OMe (13g); Cl (13h); R-4 = C6H3Y2-3,4, where Y = Me (13i); C1(13j); R-4 = C6H11 (13k)) has been prepared by reaction of 1 with (RNCO)-N-4. The precursor complex [V(OS2)O(dipp)] (14) [OS22- = O(CH2CH2S)(2)(2-)] has been prepared from [VO(OPri)(3)], Hdipp, and OS2H2 It reacts with NH2NMe2 to give [V(OS2)(NH2Me2)(dipp)] (15) and with NsSiMe(3) to give [V(OS2)(NSiMe3)(dipp)] (16). A second oxide precursor, formulated as [V(OS2)(1.5)O] (17), has also been obtained, and it reacts with SiMe3NHNMe2 to give [V(OS2)(NNMe2)(OSiMe3)] (18). The X-ray crystal structures of the complexes 2b, 2c, 4, 6, 7a, 8a, 9, ill, 13d, 14, 15, 16, and 18 have been determined, and the V-51 NMR and other spectroscopic parameters of the complexes are discussed in terms of electronic effects.