Organic aluminum hydrides catalyze nitrile hydroboration

Abstract

The eco-friendly and highly efficient catalytic hydroboration of nitriles has been elucidated by using organic aluminum hydrides.

Catalyst‐Free and Solvent‐Free Facile Hydroboration of Imines

“…Among metal catalyzed processes, transition metal and even rare earth metal complexes have been studied (Scheme ). There is also a recent surge in utilization of s ‐ and p ‐block elements and till date, several research groups have studied the hydroboration of carbonyl and to some extent imine compounds using main‐group element (Ca, Mg, Al,– Si) based systems (Scheme ). Alkali metal based compounds for example, n BuLi and NaOH have also been utilized for the same process .…”

Catalytic Nitrile Hydroboration: A Route to N,N‐Diborylamines and Uses Thereof

“…Finally, efficient transition-metal-free dihydroboration of nitriles has been achieved with main group element catalysts based on Li, [40] Davit Hayrapetyan was born and raised in Armenia. Mg, [41,42] B, [43] Al [44][45][46][47][48] and Zn [49] systems. All these reports are discussed below with an emphasis on advantages and limitations of hydroboration methods, experimental conditions, substrate scope and functional group tolerance.…”

“…[56,57] The majority of main group metal systems developed for hydroboration of nitriles concern aluminum catalysts. [44][45][46][47][48] Thus, the first example of such transformations was reported in 2018 by Cowley and Thomas et al, who employed LiAlH 4 as a precatalyst for a series of hydroborations of alkenes, alkynes and ketones with HBPin. Within the scope of these catalytic trials, the authors also reported hydroboration of 4-trifluoromethylbenzonitrile proceeded with full conversion within 6 h at room temperature using 1 mol% of LiAlH 4 .…”

“…In 2019, the research groups of Ma and Yang [48] and Roesky [44] have almost simultaneously reported hydroboration of nitriles catalyzed by very similar ( EtPh NacNac)AlH 2 (23) and ( Dipp NacNac)Al(Bu) 2 (24) complexes (Scheme 22). Operating under solvent-free conditions, both systems were found to efficiently convert a series of aliphatic and aromatic nitriles to the corresponding N,N-diborylamines with 2 equivalents of HBPin and 3-5 mol% catalyst loadings.…”

“…The proposed mechanisms for both 23 and 24-catalyzed reactions are similar and involve insertion of the nitrile into the AlÀ H bond of the catalytically active species to form the aluminum imide, which reacts with HBPin to give first aluminum N-borylamide and then N,N-diborylamine products. [44,48] Recently, Nembenna and co-workers reported the related Al (III) hydride 25 supported by conjugated bis-guanidine ligand and showed its catalytic activity in hydroboration of aliphatic and aromatic nitriles with HBPin (Scheme 23). [46] Similar to the NacNac system 24, the reactions were performed at 60°C under neat conditions with 3 mol% catalyst loading.…”