Ammonia hydroamination

The cationic gold complex with CAAC ligand 29 can also catalyze the unprecedented hydroamination reaction of alkynes and allenes using ammonia [59, 60]. It was also demonstrated that it can catalyze the simple hydroamination reaction. It... 

The addition of ammonia and amines to unsaturated hydrocarbons, called hydroa-mination, is a desirable but difficult reaction. Only activated multiple bonds react readily in hydroamination to yield amines in an equilibrium reaction. It is necessary, therefore, to use catalysts in the transformation of nonactivated compounds. 

One possible way to promote hydroamination is to activate the reacting ammonia or amine.288-291 Alkali metals were found to be useful catalysts. Even in the catalyzed addition of ammonia to simple alkenes, however, drastic reaction conditions are... 

The feasibility of acid-catalyzed direct hydroamination has been demonstrated. Acidic zeolites afford, at low conversions, highly selective formation of ethyla-mine,297,298 isopropylamine,298 and ferf-butylamine,298-301 in the reaction of ammonia with ethylene, propylene, and isobutylene, respectively. Amine formation is explained as a reaction of surface carbocation intermediates with adsorbed or... 

Despite the industrial importance of amines and imines, hydroamination, i.e. the direct reaction of alkenes or alkynes with primary or secondary amines, is only used in one commercial process where isobutene and ammonia are converted in the presence of a zeolite catalyst to /-butylaminc. Turnover frequencies are generally very low and consequently, high catalyst loadings are necessary, which in turn demands efficient recycling. 

Preparation of Amines and /V-Hetero-Substitiited Amines by Hydroamination Reactions Involving Cleavage of the N-H Bond of Ammonia, Amines and /V-Hetero-Substituted Amines (RNHX)... 

Addition of ammonia and amines to alkenes (hydroamination) is thermodynamically feasible, but kinetically hindered, hence it requires activation of either of the reactants1,2,51. The intramolecular reaction is generally more easily accomplished than the intermolecular reaction and allows the stereochemistry to be controlled to a certain degree. 

The amides of rubidium or cesium have been proven as the best catalysts for the hydroamination of ethylene with ammonia. In liquid ammonia below the critical temperature (132.5 °C) at 100 °C and an initial pressure of only 11 MPa a turnover number (TON) of about 4 mol C2H4/(mol CSNH2) per h could be reached [6]. 

Water is another ideal, environmentally sound reagent with exciting prospects, but numerous questions are still open. Could water be added to olefins in the anti-Markownikov mode Primary alcohols would thus be cheaply available (eq. (12)). Similarly, what is the appropriate catalyst to add ammonia across a double bond (hydroamination, eq. (13), Section 2.7) to yield organic amines as starting materials for a number of fine chemicals ... 

Aliphatic amines are amongst the most important bulk and fine chemicals in the chemical and pharmaceutical industry [13]. Hydroaminomethylation of alkenes to amines presents an atom-economic, efficient and elegant synthetic pathway towards this class of compounds. In hydroaminomethylation a reaction sequence of hydroformylation of an alkene to an aldehyde with subsequent reductive amina-tion proceeds in a domino reaction (see Eq. 4) [14]. Recently, the highly selective hydroamination of alkenes with ammonia to form linear primary and secondary aliphatic amines with a new Rh/Ir catalytic system (] Rh(cod)Cl 2], ] Ir(cod)Cl 2], aqueous TPPTS solution) has been described (see Scheme 2) [15]. The method is of particular importance for the production of industrially relevant, low molecular weight amines. 

As shown in Scheme 17.9, TAA derivatives can be made by hydrogenation or hydroamination with ammonia, butylamine or hexamethylene diamine leading to intermediates for the most commercial HALS stabilizers as, for example, HMW-HALS-2, HMW-HALS-4, or HMW-HALS-6 [53],... 

Recently, the highly selective hydroamination of olefins with ammonia to form linear primary and secondary aliphatic amines with a new Rh/Ir catalytic system ([ Rh(cod)Cl 2, [ Ir(cod)Cl 2], aqueous TPPTS solution) has been described (Scheme 2) [14], The method is of particular importance for the production of industrially relevant, low molecular weight amines. 

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. 

A computational study unravelled two key factors that account for the efficiency of the gold(I)-catalysed hydroamination of alkynes with ammonia, using MeC=CMe as the model system (i) the excess nucleophile, NH3, which assists the proton transfer, and (ii) an unexpected [Au] migration, which allows a feasible enamine-imine tautomerization. ... 

Computational approaches have also been used to investigate the potential application of Rh and Ir pincer complexes in the hydroamination of ethylene by ammonia [172]. In this case, a NCN-pincer complex of Rh was determined to promote the reaction via ethylene migratory insertion into a Rh-N bond (Figure 15.5). 

Figure 15.5 Gibbs free activation barriers (ACt, in kcal mol ) for key steps of Rh-pincer complex catalyzing the hydroamination of ethylene with ammonia.

Using ammonia as N-feedstock in the hydroamination of C-C multiple bonds is an outstanding challenge in the field that has been targeted for decades. Indeed several zeoHte-based heterogeneous catalysts have been reported for this transformation at... 

Scheme 15.23 Hydroamination of 3-hexyne and ammonia catalyzed by a CAAC-Au complex.

Scheme 15.24 Stoichiometric reactions probing reaction mechanism of hydroamination with ammonia.

Table 15.13 CAAC-Au-complex-catalyzed hydroamination of alkynes or allene with ammonia.

Scheme 15.25 Proposed mechanism for the hydroamination with ammonia catalyzed by CAAC-Au complex.

In gold-catalyzed allene hydroamination, Bertrand has shown that the previously discussed cationic CAAC complexes for Au(I) (Table 15.17) are very important in the hydroamination of allenes with ammonia (Section 15.3.3) [179], and with both primary and secondary amines [235]. Notably, both aryl- and alkylamines can be used, and both 1,1-disubstituted allenes and monosubstituted allenes can be used as substrates to give allylamine products. In the case of monosubstituted allenes, mixtures of the T/Z diastereomers resulted. Depending on the amine substrate... 

In addition to these findings, the most remarkable example of the improvement of the stability of a gold catalyst was reported by Bertrand and coworkers. In their studies of intermolecular hydroamination reactions of allenes and alkynes, which were either conducted with ammonia or hydrazine, they showed that their gold catalysts based on abnormal NHC ligands have amazing thermal stability [38]. Due to the fact that the amines used are capable of coordinating to the open side of the catalytic species and therefore can block the catalyst, these reactions require high reaction temperatures. Therefore, the reactions are carried out at temperatures of 160-200 °C (see Scheme 9.19) [38]. 

The production of tert-hutylamine is interesting for the fact that this amine has been used to demonstrate the technical potential of hydroamination in commercial amine production [route (b) in Topic 5.3.4]. BASF introduced in the early 1990s the first process that operates vith a zeolite catalyst and converts isobutene directly with ammonia. The reaction is carried out by contacting the supercritical reaction mixture with the catalyst at temperatures between 250 and 300 °C and at pressures between 200 and 350 bar. Under equilibrium conversion conditions tert-butylamine forms in 95% selectivity. 

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