N-H bond, cleavage

The pyrolysis of pyrrole produces a variety of products hydrogen cyanide, propyne, allene, acetylene, c/ -crotonitrile, and allyl cyanide, among them. Lifshitz et al. hypothesized that pyrrole undergoes 1,2-bond (N—C) cleavage, then an internal H-atom transfer, to yield a radical intermediate that can isomerize to either c/ -crotonitrile or allyl cyanide, or dissociate to HCN and propyne.Bacskay et al. completed quantum chemical comparisons of the isoelectronic pyrrolyl and cyclopentadienyl radicals they hypothesized that pyrrolyl radical is formed via C—H bond scission in the intermediate pyrrolenine (2/f-pyrrole) rather than directly via N—H bond cleavage (Fig. 14). Mackie et al. explained a similar finding, postulating that it was the formation of pyrrolenine that dictated the rate at which pyrrole pyrolysis occurred. 

Usually, the proton acceptor ability of amines (reaction A of Scheme 3) lead to ammonium ion formation, while the N—H bond cleavage (or formation) (reaction B of Scheme 3) is a less common process which may be obtained under drastic experimental conditions or via metal aniline complexes29. 

Treatment of dialkoxoosmium(II) shown in Scheme 3.93 with BuNH2 results in the successive N-H bond cleavages to give imidoosmium(II) complex... 

Thus, N-H bond cleavage in this system provides a foundation for the development of mild catalytic transformation of ammonia as in arene-oxidative amination and olefin hydroamination. 

The anodically induced heterolytic N-H bond cleavage at the aminocarbyne ligand agrees with the expected increase of the acidic caracter of this ligand as a result of the electron removal from the complex, and can also be accounted for by some theoretical studies which indicate [24] the appearance of a positive charge on the N atom upon oxidation of the complex. Related electrode processes have been observed for the nitrile-derived methyleneamide complexes... 

Scheme 15.5 N-H bond cleavage of amine-borane adducts by IfBu to produce imidazolium borate salts (R2NH = ammonia, diphenylamine, aniline Ar = pentafluorophenyl) [95].

At high temperatures and/or low pressures where the N surface coverage is low, the rate is controlled by N H bond cleavage and the reaction becomes first order in ammonia with an almost zero activity energy. 

Intramolecular N-H bond cleavage of ammonia, allqrlamines and aty-lamines by oxidative addition to tricoordinate phosphorus compounds (a -P) (5) leading to pentacoordinated adducts have been reported by Radosevich et al. These reactions proceeded smoothly under mild conditions in homogenous solution giving rise to structurally robust phos-phorane adducts (6) as depicted in Scheme 2. 

Under similar conditions, N-unsubstituted benzamides 89 undergo 1 2 coupling with 2 accompanied by double C—H and double N—H bond cleavages to afford tetracyclic dibenzoquinolizinone derivatives 90 (Scheme 25.43) [20]. 

Under similar conditions, benzophenone imine (102) undergoes endo annulation accompanied by C—H and N—H bond cleavages to give 1,3,4-triphenylisoquinoline (103) (Scheme 25.50) [45],... 

In 2008, Umeda et al. reported that 2-phenylimidazole (117) and 2-phenyl-benzimidazole (118) undergo rhodium-catalyzed coupling with 2c in a 1 1 manner through C—H and N—H bond cleavages to produce tri- and tetracyclic compounds 119 and 120, respectively (Scheme 25.58) [7a]. Li and Zhao reported similar reactions of 5-aryl-1/7-pyrazoles [56]. 

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