Hydrides imido complexes

The niobium imines can also be prepared by reaction of a niobium halo hydride with a nitrile. Thus a niobium reagent prepared from 1 and Bu3SnH reacts with nitriles to form a niobium-imido complex, which is hydrolyzed to a v/c-diamine. 

Mechanistically, the unusual reactivity of the starting tantalum hydrides [(sSiO)2Ta H] and [(=SiO)2Ta (H)3] towards ammonia to yield the amido imido complex [(=SiO)2Ta(=NH)(NH2)] can be fully rationalized in terms of classical molecular organometallic elementary steps. Scheme 2.21 offers an example of a such sequence of elementary steps with the noteworthy close analogy with methane activation by the same hydrides described above. 

In summary, the tantalum hydride system adds to the few previously reported well-defined organometallic complexes capable of cleaving N-H bonds of ammonia to yield either an amido or an imido complex, and achieves unprecedented dinitrogen N=N triple bond cleavage with dihydrogen on isolated tantalum atoms to yield reduction of both N atoms. 

This is analogous to the previously described method (Section II,A,2) for making bridging-dinitrogen complexes. Metal chlorides and hydrides also react with nitriles to yield imido complexes, as shown in reaction (77) (6, 165, 280). 

In aprotic solvents, nitro compounds reacts with [HFe3(CO)n] to give in poor yields an imido complex 6, which, by acidification, leads to the bis-hydride imido derivative 7 (Scheme 10) [64] ... 

Remarkably, both alkyl and aryl C-H activations have been described in the formation of the metallacyclic osmium(iv)-hydride complex 25, generated as the minor component (12%) of a mixture with the deprotonated methylene-amido complex [Os(=N=CH2)Gp(GH2SiMe3)2], from the reaction of the imido complex [Os(=NMe)Cp(CH2SiMe3)2][OTf] with PPhs. ... 

The organometaUic starting reagents are the MCM-41 supported ](=SiO)2TaH] and ](=SiO)2TaH3] described in the previous section. The MCM-41 supported hydrides cleave N-H bonds of ammonia at room temperature to yield the weU-defined imido amido surface complex ](=SiO)2Ta(NH)(NH2)] [9]. Dihydrogen is released in the gas phase during the reaction (Scheme 2.20). 

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