Selective Double Addition Reaction of an E‒H Bond (E = Si, B) to a C≡N Triple Bond of Organonitriles

Abstract

The catalytic double hydrometalation such as hydrosilylation and hydroborylation of organonitriles has attracted considerable attention because the obtained products are widely used in organic synthesis and it is thought to be one of the effective methods for reduction of organonitriles. However, the examples of these reactions are quite limited to date. This paper summarizes the development of selective double hydrosilylation, double hydroborylation, and dihydroborylsilylation of organonitriles, including their reaction mechanisms and the role of the metal species in the catalytic cycle.

Efficient Co‐Catalyzed Double Hydroboration of Nitriles: Application to One‐Pot Conversion of Nitriles to Aldimines

“…Conventional methods for preparation of amines, such as N−H alkylation reactions, stoichiometric reduction of imines, amides and nitriles as well as reductive amination of carbonyl compounds with metal hydride reagents often suffer from lack of control and functional group tolerance and lead to formation of large amounts of byproducts . In contrast, catalytic reduction of readily available nitriles to amines by means of hydrogenation, hydrosilylation and hydroboration reactions serves as an attractive alternative to conventional stoichiometric methods. Although direct hydrogenation of nitriles to amines represents the most atom‐economical approach, the reactions usually require precious metal catalysts and harsh conditions and often show poor selectivity, affording mixtures of aldimines and primary, secondary and tertiary amines .…”

“…Although direct hydrogenation of nitriles to amines represents the most atom‐economical approach, the reactions usually require precious metal catalysts and harsh conditions and often show poor selectivity, affording mixtures of aldimines and primary, secondary and tertiary amines . Whereas a number of transition‐metal catalysts, including non‐precious metal systems, have been developed for hydrosilylation of nitriles, the examples of mild and selective hydroboration of nitriles are still scarce . With regard to the reactions catalyzed by earth abundant metals (Fe, Co, Ni), only a handful of systems for selective double addition of hydroboranes (akin to HBPin or HBCat; Pin=pinacol, Cat=catechol) to nitriles have been reported, many of which require elevated temperatures and/or the use of rather sophisticated ligands (Figure )…”

“…In addition, catalytic hydroboration of nitriles results in formation of N,N‐diborylamines, which are thought to possess labile B−N bonds and, therefore, can be used in the synthesis of a variety of N‐containing organic molecules beyond simple protodeborylation . Although synthetic routes to N,N‐diborylamines have been developed only recently and their chemistry is rather underdeveloped, a few examples of applications of N,N‐diborylamines in C−N bond forming reactions have been already demonstrated (Scheme ) . Thus, our previous studies revealed unprecedented reactivity of PhCH 2 N(BCat) 2 with benzaldehyde to afford N ‐benzylidenebenzylamine (Scheme ) .…”

Alkylaluminum Complexes as Precatalysts in Hydroboration of Nitriles and Carbodiimides

“…Dihydroborylsilylation of Nitrile Catalyzed by LAl(n-Bu) 2 . The reaction of PhCN with both HBpin and PhSiH 3 in the presence of LAl(n-Bu) 2 catalyst in a Young NMR tube under solvent-free 60 °C within 10 h. PhCH 2 N(Bpin)(SiH 2 Ph) (5). The crude product can be further purified by washing in hexane.…”

“…The obtained hydroborated compounds are useful high purity products and can be easily converted to the corresponding amines. The latter are used for the production of polyesters, dyes, and as precursors of pharmaceutical as well as agrochemical compounds, − with increasing importance in synthetic industrial chemistry . Moreover, it is well-known that hydroboration of the CN bond is one of the effective strategies to reduce organonitriles. − However, the strong CN bond dissociation energy (750.0 kJ/mol) does not allow these hydrometalations to occur under the typical reaction conditions .…”