Formation of the N-H bond

An N-H bond can be formed by addition or exchange. All the methods coming in question for this purpose are reducing methods. 

---

Whereas within the precursor complex the presence of the base does not influence the covalent state of the radical cation when the C-H bond elongates, the ionic state is highly stabilized by the presence of the base as the C-H distance increases [137]. This model implies that formation of the N-H bond does not interfere to a large extent in the dynamics of the reaction, the deprotonation of the radical cation... 

Irradiation of ethyleneimine (341,342) with light of short wavelength ia the gas phase has been carried out direcdy and with sensitization (343—349). Photolysis products found were hydrogen, nitrogen, ethylene, ammonium, saturated hydrocarbons (methane, ethane, propane, / -butane), and the dimer of the ethyleneimino radical. The nature and the amount of the reaction products is highly dependent on the conditions used. For example, the photoproducts identified ia a fast flow photoreactor iacluded hydrocyanic acid and acetonitrile (345), ia addition to those found ia a steady state system. The reaction of hydrogen radicals with ethyleneimine results ia the formation of hydrocyanic acid ia addition to methane (350). Important processes ia the photolysis of ethyleneimine are nitrene extmsion and homolysis of the N—H bond, as suggested and simulated by ab initio SCF calculations (351). The occurrence of ethyleneimine as an iatermediate ia the photolytic formation of hydrocyanic acid from acetylene and ammonia ia the atmosphere of the planet Jupiter has been postulated (352), but is disputed (353). 

The intramolecular addition of the N-H bond onto the acetylene moiety in ethynylanilines is presumed to lead to the formation of an indolylpalladium complex (c.f Chapter 1.2.). Trapping of this intermediate in subsequent transformations leads to the introduction of a substituent into... 

A combined application of direct calorimetric measurements and thermochemical investigations has made possible to obtain a number of important thermochemical quantities characterizing the interaction of the N—H bond of the amine with the epoxy ring 53). Combustion and evaporation enthalpies of phenylglycidyl ether and its condensation products with aniline and butylamine have been determined. Standard enthalpies of the formation of these compounds, strain energies of the epoxy ring in the phenylglycidyl ether molecule and — AH values for the three-phase states, which are most important for the determination of the true thermodynamic reaction characteristics, have been estimated. 

N-H O and C-H O bonds with three other molecules. The amino group behaves similarly and participates in the formation of the N-H it interaction (Figure 17). 

This entropy decrease for the formation of the eoloured form (12b) may be due to the planarization of the molecule (formation of the N—H N bridge) and the fixation of the di-ctT-form (12b), while in (12a) there is free rotation about the central C—C bond. In protic solvents, the colourless form (12a) is already stabilized by hydrogen bonding and T AS° is small. Therefore, the AG° values are greater in these solvents and AH° is positive [68],... 

Both the intermolecular and intramolecular addition of the N —H bond of secondary amines to phenyl-substituted alkenes8 9,52,53,67 and arenes1013 can be accomplished under UV irradiation through the formation of excited state complexes (exciplexes). An example is given in the following scheme ... 

The analogous primary amine had been earlier studied by Wubbels and gave only the photo-Smiles reaction, but this process was not observed for the present system and the reaction is suggested to proceed by a photo-electron transfer mechanism to yield the radical ion pair. Photoaddition of N-H bonds to aromatic compounds has been known for some years, and the intramolecular process which leads to cyclization products has been reported for the reaction of 9-(aj-anilinolalkyl)phenanthrenes (220). The formation of the spiro-compounds (221) by addition of the N-H bond across the phenan-threne 9,10-positions is suggested to arise from the intramolecular exciplex in... 

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. 

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. 

---