Catalytic Hydroboration of Organic Nitriles Promoted by Aluminum Complex

Abstract

We demonstrate an efficient protocol for the chemoselective hydroboration of organic nitriles with pinacolborane (HBpin) and catecholborane (HBcat) using aluminum alkyl complex [k 2 -{2-FÀC 6 H 4 NP(Se)Ph 2 } 2 AlÀ(Me)] as a pre-catalyst to afford diboryl amines under solvent-free and mild conditions (60 8C) in high yield. The aluminum complex was prepared by the reaction of [2-FÀC 6 H 4 NHP(Se)Ph 2 ] and trimethylaluminum in toluene. The solid-state structure of Al complex is established. Nitriles with a wide array of electronwithdrawing and electron-donating functional groups were easily converted to the desired products through the formation of aluminum hydride as an active species. A kinetic study of the catalytic reaction is also reported.

Organoaluminum Compounds as Catalysts for Monohydroboration of Carbodiimides

“…On the basis of these experimental results and several mechanisms previously reported in the literature, the most possible mechanism for the hydroboration of carbodiimide with HBpin catalyzed by aluminum hydride complex is shown in Scheme (left). Taking compound 1 as an example to describe the mechanism, compounds 2 – 4 , belonging to aluminum hydride compounds, have the same catalytic mechanism as that of compound 1 .…”

“…Catalytic aluminum hydride compounds 2, 3,a nd a reported pre-catalyst aluminuma lkyl compound 5 were used for the hydroboration of carbodiimides. Based on the results mentioned above,t oe nsure maximum efficiency and selectivity,1 .1 equivalents of HBpin were used in neat conditions at (2), Al(1)ÀN(2) 1.860(2), Al(1)ÀN(3) 1.863 (2), Al(1)ÀN (4) 2.090(2), N(2)ÀC (6) 1.450(3), N(3)ÀC(24) 1.448 (4);N(2)-Al(1)-N(3)124.35 (11), N(1)-Al(1)-N(4) 171.24(10), N(3)-Al(1)-N(4) 81.40 (8), N(2)-Al(1)-N(1)81.27 (8). Table 1.…”

“…The organoboron compounds derived from hydroboration reactions are crucial organic intermediates in various chemical transformations and material synthesis . In recent years, the ability of organoaluminum complexes to work as efficient catalysts for the hydroboration of unsaturated bonds with C=E (E=O, C, N), and C≡E motifs (E=C, N) was discovered. Intense work was invested in the hydroboration of unsaturated bonds through the use of aluminum‐containing pre‐catalysts.…”

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 .…”