Nitrogen-containing insertion products

Table 17 Niobium and Tantalum Nitrogen-containing Insertion Products (Acetamidinato, Acetamide, Thioacetamido...

Tertiary amines have been shown to react with isocyanates in an analogous fashion to form ureas (41—43). Similarly, aziridines (three-membered rings containing nitrogen) are found to react with isocyanates to yield cyclic ureas. Tertiary amines have also been shown to form labile dipolar 1 1 adducts with isocyanates reminiscent of salt formation. In contrast, formaldehyde A/,Ai-acetal aminals form insertion products with sulfonyl isocyanates (44,45). 

Metal rf-inline complexes with various transition metals [1-10] and lanthanides [11,12] are well known in the literature. Early transition metal if-imine complexes have attracted attention as a-amino carbanion equivalents. Zirconium rf-imine complexes, or zirconaaziridines (the names describe different resonance structures), are readily accessible and have been applied in organic synthesis in view of the umpolung [13] of their carbons whereas imines readily react with nucleophiles, zirconaaziridines undergo the insertion of electrophilic reagents. Accessible compounds include heterocycles and nitrogen-containing products such as allylic amines, diamines, amino alcohols, amino amides, amino am-idines, and amino acid esters. Asymmetric syntheses of allylic amines and a-amino acid esters have even been carried out. The mechanism of such transformations has implications not only for imine complexes, but also for the related aldehyde and ketone complexes [14-16]. The synthesis and properties of zirconaaziridines and their applications toward organic transformations will be discussed in this chapter. 

Whereas the catalytic hydrosilylation of alkynes was one of the first methods of controlled reduction and functionalization of alkynes, the ruthenium-catalyzed hydroamination of alkynes has emerged only recently, but represents a potential for the selective access to amines and nitrogen-containing heterocydes. It is also noteworthy that, in parallel, the ruthenium activation of inert C-H bonds allowing alkyne insertion and C-C bond formation also represents innovative aspects that warrant future development. Among catalytic additions to alkynes for the production of useful products, the next decade will clearly witness an increasing role for ruthenium-vinylidenes in activation processes, and also for the development of ruthenium-catalyzed hydroamination and C-H bond activation. 

The hydrides of boron and aluminum insert a wide variety of nitrogen-containing, unsaturated compounds, but in only a few cases are the identities of the primary insertion products known. BjHe reacts with nitriles under mild conditions to give tri-N-sub-stituted borazines Under more forcing conditions, (CH3)3C[(CH3)3N]BH2 undergoes single insertion. ... 

To test our hypothesis that the generation of methyl radicals can enhance the reaction between CH4 and NOx compounds, we first examined NO reduction by CH4 over MgO and Li/MgO, which is the most characterized catalyst system for methane oxidative coupling. This study showed that Li/MgO catalysts as well as pure MgO are indeed active for NO reduction by CH4 and the activity continuously increased with temperature up to 953K. Both N2 and N2O as nitrogen-containing products were observed, and selectivity to N2 increased with temperature. N2 mass balances showed that litde or no NO2 formation occurred. Control experiments demonstrated that there was no reaction of either NO or CH4 in an empty quartz tube reactor with quartz wool inserted. Further experiments in the absence of CH4 showed that there was no direct NO decomposition over these catalysts, which implies that NO reduction can proceed only in the presence of gaseous CH4. 

Thus, Frye and co-workers [47] were able to provide evidence by infrared (IR) spectroscopy [46] and radiochemistry [48] of the insertion of ester groupings from barium, cadmium or zinc-carboxylates into PVC after heat treatment. Tin contents and organic residues of organotin stabilisers in heat-treated PVC are indicated by the same authors [47, 49]. Schlimper [50] and Schroder and co-workers [51] proved the direct reaction between PVC and nitrogen-containing organic stabilisers by elemental analytical examinations and infrared and UV spectrometry. Phenolic antioxidants or their decomposition products in part were re-found in PP after oxidative degradation. With rubber vulcanisates hydrochloric acid-resistant amine-rubber compounds have been reported after thermal oxidation in the presence of aromatic amines [52]. 

These reactions proceed smoothly because the rate of insertion of CO is faster than the rate of insertion of allene into arylpalladium(II) spedes. Starting from the carbonylation products, a series of sulfur- and nitrogen-containing heterolytic compounds have been prepared conveniently (Scheme 11.15). 

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