Dinitrogen complexes vanadium

A further vanadium-dinitrogen complex is represented by [ V(NPr2)3 2(/i-N2)], the molecular structure of which is illustrated in Figure 44.60... 

The compound [V(N2)6] has been obtained by matrix isolation techniques (56), and its UV spectrum analyzed. lODq for this compound is 22,460 cm1 (compared with 28,845 cm-1 for [V(CO)6]) and the charge-transfer bands are principally of the t2M —> tt type. This material is analogous to Ti(N2)6], No other vanadium dinitrogen complexes have been isolated. 

Table 3. Dinitrogen reduction by vanadium(II) complexes with aromatic ligands (L) (room temperature, [V ] = 0.05 M, [L] = 0.5 m).

Shilov s group found that soluble vanadium(Il) complexes with pyro-catechol and other phenols having ortho-hydroxyl groups are able to reduce nitrogen to ammonia in aqueous solutions [49]. The active species is believed to be a three-centered vanadium catecholate complex with a bridging dinitrogen ligand [49],... 

A large amount of work has been carried out, primarily by Shilov, on the chemical fixation of dinitrogen using various vanadium-containing systems. However, no stable dinitrogen complexes of vanadium have been reported or in situ nitrogen fixation observed with phosphines present. 

Ishida Y, Kawaguchi H. Nitrogen atom transfer from a dinitrogen-derived vanadium nitride complex to carbon monoxide and isocyanide. J Am Chem Soc. 2014 136 16990-16993. 

The photoreduction of N2 by irradiation of vanadium chloride in aqueous ethanol with u.v. light has been describedAn unstable dinitrogen divanadium complex has been proposed to be the key intermediate and the reaction products include NH3, N2H4, and H2. A model system for N2 reduction involves the photoreduction of acetylene and this can be achieved with a sacrificial bipysRu /Co " system. 

Apart from the compounds already mentioned, vanadium, manganese, and cobalt chlorides, tetra-alkoxy derivatives of titanium, acetylacetonates of V, Cr, Mo, Mn, and Ni, Cp derivatives of Zr and Nb, and triphenyl phosphine complexes of Ti and Fe were found to be active. Later lanthanide complexes were included in the list of dinitrogen-reducing systems, the most effective being compounds of samarium and yttrium. 

Acetylene is quantitatively reduced by V catecholate to ethylene with cw-di-deuteroethylene formed selectively from C2D2, also similarly to enzymatic reduction of C2D2 by nitrogenase. Distinct from N2 reduction, the pH range for the reduction of acetylene is much broader than for dinitrogen (from ca pH 5 to concentrated alkali solution). Kinetic studies of the oxidation of vanadium(II) catecholate complex by dinitrogen have led to the reaction equation ... 

New important information about the structure of the intermediate complex was obtained from the X-ray studies of V complex with di-ferf-butylcatecholate [18]. The complex, the structure of which is presented in Figure 4, contains four vanadium ions two are divalent and two trivalent, but they are indistinguishable, thus their oxidation state is 2.5 and the complex can be regarded as existing in a semi-reduced state, similar to the s-r state of FeMoco in the presence of dithionite, which is not sufficiently reduced to activate dinitrogen. 

Top row the three components of the Yandulov-Schrock cycle for catalytic dinitrogen reduction. Left the catalyst with the substrate Nj coordinated to Mo (Ar refers to the aryl substituent drawn in detail for one of the nitrogens). Centre the reductant bis(pentamethylcyclopentadienyl)chromium, CpjCr. Right the proton source 2,6-lutidinium borate. Bottom row vanadium complexes with intermediates of nitrogen reduction activated dinitrogen or diazenido(2—) (46a), imide (46b) and ammonia (46c). 

Other dinitrogen vanadium complexes have been introduced in the last two decades, all of which are dinuclear and contain dinitrogen (originally stemming from aerial N2) in the... 

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