Metal-nitrogen bonds, insertion reactions

Insertion into metal nitrogen bonds is illustrated by the formation of the anion [(C6F5)2Pd(S2CNIIPh)] in the reaction of [Pd2(C6F5)4(p-NHPh)2]2-with carbon disulfide.362... 

Carbon dioxide does not insert into all metal-carbon bonds, as demonstrated by the lack of reaction with [HIr(PMe3)4CH2CN]+ 137). Similarly, benzylchromium complexes failed to insert C02 142), and in the reaction of Me(Me2N)2W=W(NMe2)2Me with C02, the molecule inserts into the metal-nitrogen bonds, but not into the metal-carbon bonds 143). 

An alternative method of amine activation is opened via the oxidative addition of the N-H bond to an appropriate transition metal in a lower oxidation state. After formation of the /ff-aminoalkyl compound by insertion of the olefin into the transition-metal-nitrogen bond, the alkylamine can be generated by reductive elimination (Scheme 2), and with the reformed reduced transition metal complex the catalytic reaction can run again. 

The metal-nitrogen bond in the adducts is often reactive toward protic reagents. The combination MOR/HOR can thus lead to overall formation of a carbamate by insertion of isocyanate into the M—O bond, followed by acidolysis of the adduct, as for the reactions of Bu3SnOMe/HOMe with phenyl isocyanate ... 

Also, multiple insertion reactions may occur leading to the formation of polyimine ligands [equation (12.47)]. Alkyl iodides and Ni(CNBu )4 afford pentaimine complexes (12.48). The metal-nitrogen bond of the polyimine complexes may be broken by the... 

Sobota P, Trzebiantowska J, Janas Z (1976) Insertion of CO2 into the metal-nitrogen bond formed in the reaction with molecular nitrogen. J Oiganomet Chem 118(3) 253-258... 

Experimental evidence for insertion of alkenes into the metal-nitrogen bond was reported recently in the studies of aminopalladation reactions [41,42]. Intramolecular insertion reaction was confirmed to be a yn-addition process and was monitored by NMR spectroscopy of the well-defined palladium(aryl)(amido) complexes (Scheme 11) [41, 43]. The reaction proceeded as insertion into Pd-N bond with complete chemoselectivity and the alternative route of alkene insertion into the Pd-C bond was not observed. The activation enthalpy determined for the insertion step A// = 24.8 zb 0.6 kcal/mol was comparable with the values reported for other insertion reactions, and small activation entropy = 4.6 zb 1.8 eu is consistent with intramolecular transformation [41, 43]. The final product of the reaction was formed after C-C reductive elimination, which is known to be rather fast step if at least one aryl group is involved [44, 45]. The mechanistic study of the alkene insertion into the Pd-N bond has also pointed out on possible reversible nature of such process [46]. 

Facile isocyanide insertion reactions into metal-carbon, -nitrogen, -sulfur, -oxygen, - hydride, and - halide bonds have been found to readily occur. The insertion into metal-hydrides to give stable formimidines is particularly noteworthy since corresponding formyls (—CHO) are exceptionally difficult to synthesize and tend to be very unstable. There is a great deal of interest in carbon monoxide reductions, and the instability of the intermediate reduction products has made a study of the reduction process extremely difficult. Recently, however, the interaction of isocyanides with zirconium hydrides has allowed the isolation of the individual reduction steps of the isocyanide which has provided a model study for carbon monoxide reduction (39). 

The first site of protonation in a dinitrogen complex, based on mechanistic studies of complexes, must be the dinitrogen itself, yielding the diazenido species (N2H). If protonation occurs at the metal then reaction proceeds no further, or results in the loss of coordinated dinitro-gen. The formal insertion of dinitrogen into a metal-hydride bond (a popular proposal in the early chemical nitrogen-fixation literature) is unknown. 

---