Metal‐Free Catalytic Hydroboration of Unsaturated Compounds: A Greener Strategy for the Synthesis of Organoboranes

Abstract

This review discusses the immense progress made over recent years in metal‐free catalytic hydroboration. Reactions with several unsaturated functional groups, such as alkynes, alkenes, carbonyl compounds, carbon dioxide, carbodiimides, imines, allenes, pyridines, carboxylic acid derivatives etc., have been explored. Although there are significant developments in hydroboration reactions using metal‐based catalysts, metal‐free catalytic strategies are more desirable from a sustainability perspective. Considerable effort has been made by various research groups on metal‐free catalysts in the hydroboration of unsaturated compounds. Lewis acid, Brønsted acid, Lewis acid‐base pairs, and frustrated Lewis pairs were involved as metal‐free sources to catalyze hydroboration reactions in a sustainable manner. Detailed mechanisms of the catalytic pathways of metal‐free hydroboration are also discussed in this review. This discussion will provide an overview of the extent of work carried out as well as indicate scope for future research.

2-Anilidomethylpyridine-Derived Three-Coordinate Zinc Hydride: The Journey Unveils Anilide Backbone’s Reactive Nature

“…The present literature suggests that the carbonyl hydroboration is quite an easy process in terms of catalyst choices . Any Lewis acidic site can potentially catalyze the process, including the HBpin itself without the need of an external catalyst . Bases like NaH, LiOtBu, and MeMgI are also catalytically active.…”

Magnesium halide-catalyzed hydroboration of isocyanates and ketones

“…Under the solvent-free conditions, the hydroboration of acetophenone could also be completed after 2 h even in the presence of 0.1 mol% MgCl 2 (Table 4, entries 10-12). Furthermore, the reaction time was shortened to 0.5 h for the MgI 2 catalyst under similar reaction conditions (Table 4, entries [13][14][15][16][17]. Subsequently, we studied the influence of different amounts of HBpin in the hydroboration of acetophenone again and found that it could be lowered to 1.1 equiv.…”

“…Recently, the hydroboration of unsaturated organic substrates has attracted wide attention and considerable development has been achieved. 11–27 Compared with alkene (CC), alkyne (CC) and nitrile (CN) unsaturated bonds, reports on metal-catalyzed hydroboration of isocyanates are very few. 28–35 In 2021, Nembenna et al .…”

“…Recently, the hydroboration of unsaturated organic substrates has attracted wide attention and considerable development has been achieved. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Compared with alkene (CvC), alkyne (CuC) and nitrile (CuN) unsaturated bonds, reports on metal-catalyzed hydroboration of isocyanates are very few. [28][29][30][31][32][33][34][35] In 2021, Nembenna et al reported that a remarkable conjugated bisguanidinate supported zinc hydride was employed as an efficient catalyst in the hydroboration of a range of aryl and alkyl isocyanates to afford selectively N-boryl formamide, bis (boryl) hemiaminal and N-boryl methyl amine products, respectively.…”

Zinc Catalyzed Hydroelementation (HE; E = B, C, N, and O) of Carbodiimides: Intermediates Isolation and Mechanistic Insights

“…The metal-catalyzed hydroelementation reaction of unsaturated bonds has been an active research area over the past decade . The hydroelementation reaction is used to construct C-heteroatom bonds via hydroboration, hydrosilylation, hydroamination, hydrophosphination, hydrothiolation, hydroalkoxylation, and hydrogenation of alkenes and alkynes. These reactions have been studied using a wide range of transition, lanthanide, actinide, alkali, and alkaline-earth metal catalysts .…”