Dinitrogen activation reactivity

So far, studies on the reactivity of the divalent complexes mentioned above in Section 2.3 have been very limited. Dinitrogen activation has been observed not only for isolated divalent complexes but also for systems containing divalent species or trivalent rare earths in the presence of reducing agents, thus displaying divalent-like behaviour this important topic will be developed later in Section 2.3.4. 

In solution, the heterometallic clusters display some specific reactivity but no evidence of dinitrogen activation. Reduced bridged double cubanes... 

Crossland JL, Tyler DR. Iron-dinitrogen coordination chemistry dinitrogen activation and reactivity. Coord Chem Rev. 2010 254 1883-1894. 

There are no mechanistic details known from intermediates of copper, like we have seen in the studies on metathesis, where both metal alkylidene complexes and metallacyclobutanes that are active catalysts have been isolated and characterised. The copper catalyst must fulfil two roles, first it must decompose the diazo compound in the carbene and dinitrogen and secondly it must transfer the carbene fragment to an alkene. Copper carbene species, if involved, must be rather unstable, but yet in view of the enantioselective effect of the ligands on copper, clearly the carbene fragment must be coordinated to copper. It is generally believed that the copper carbene complex is rather a copper carbenoid complex, as the highly reactive species has reactivities very similar to free carbenes. It has not the character of a metal-alkylidene complex that we have encountered on the left-hand-side of the periodic table in metathesis (Chapter 16). Carbene-copper species have been observed in situ (in a neutral copper species containing an iminophosphanamide as the anion), but they are still very rare [9],... 

Intramolecular C-N bond coupling in arylazides via C-H bond activation catalyzed by [Ir(COD)(OMe)]2 was recently reported [131]. The intermediate iridium nitrenoid complex (50) formed after the extrusion of dinitrogen is proposed as a reactive species, which can cleave the benzylic C-H bond to yield indoline derivatives (31). 

Reactions other than Lewis acid-base associations/dissociations are frequently observed wit donor molecules, leading notably to solvolysis, oxygen or sulfur abstraction, insertion reaction and carbon-carbon coupling reactions. The tendency to form metal-element multiple bonds i remarkable in this respect the activation of dinitrogen by tantalum or niobium is unique. Th formation and chemistry of constrained reactive metallacycles open another promisin fast-developing area, on the frontier with organometallic chemistry. 

It was discovered recently that 5-morpholino-l,2,3,4-thiatriazole 249 on refluxing in toluene decomposes into dinitrogen, morpholino-cyanamide, and an active form of sulfur that is able to react with thioketones converting them into elusive thiocarbonyl-A-sulfides. With a second mole of thioketone, these reactive thiosulfines combine forming... 

A select number of transition metal compounds are effective as catalysts for carbenoid reactions of diazo compounds (1-3). Their catalytic activity depends on coordination unsaturation at their metal center which allows them to react as electrophiles with diazo compounds. Electrophilic addition to diazo compounds, which is the rate limiting step, causes the loss of dinitrogen and production of a metal stabilized carbene. Transfer of the electrophilic carbene to an electron rich substrate (S ) in a subsequent fast step completes the catalytic cycle (Scheme I). Lewis bases (B ) such as nitriles compete with the diazo compound for the coordinatively unsaturated metal center and are effective inhibitors of catalytic activity. Although carbene complexes with catalytically active transition metal compounds have not been observed as yet, sufficient indirect evidence from reactivity and selectivity correlations with stable metal carbenes (4,5) exist to justify their involvement in catalytic transformations. 

Freshly prepared mixed hydroxide contains vanadium(II) clusters reactive towards dinitrogen. Some indirect evidence indicates that the number of vanadium ions in the clusters activating dinitrogen approaches four or six. For example, introduction of other ions, such as V + inhibits N2 reduction and quantitative analysis of the inhibition effect leads to the conclusion that tetramers are the likely species tetramers are also suggested by analysis of ethane and ethylene formation in the reduction of acetylene. 

Sutton has reported a pentamethylcyclopentadienyl rhenium dinitrogen complex that activates benzene (Eq. 29) [114]. The intermediate involved is similar to that described above in studies by Bergman [92]. In the absence of a reactive solvent, cyclometallation was observed. 

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