Hydroboration Reaction and Mechanism of Carboxylic Acids using NaNH₂(BH₃)₂, a Hydroboration Reagent with Reducing Capability between NaBH₄ and LiAlH₄

Abstract

Hydroboration reactions of carboxylic acids using sodium aminodiboranate (NaNH 2 [BH 3 ] 2 , NaADBH) to form primary alcohols were systematically investigated, and the reduction mechanism was elucidated experimentally and computationally. The transfer of hydride ions from B atoms to C atoms, the key step in the mechanism, was theoretically illustrated and supported by experimental results. The intermediates of NH 2 B 2 H 5 , PhCHCHCOOBH 2 NH 2 BH 3 − , PhCHCHCH 2 OBO, and the byproducts of BH 4 − , NH 2 BH 2 , and NH 2 BH 3 − were identified and characterized by 11 B and 1 H NMR. The reducing capacity of NaADBH was found between that of NaBH 4 and LiAlH 4 . We have thus found that NaADBH is a promising reducing agent for hydroboration because of its stability and easy handling. These reactions exhibit excellent yields and good selectivity, therefore providing alternative synthetic approaches for the conversion of carboxylic acids to primary alcohols with a wide range of functional group tolerance.

Catalyst-free reductions of nitriles to amino-boranes using sodium amidoborane and lithium borohydride

“…Due to the possible H/D exchange process, the origin of the hydrogen atom in the products and the synergy effect could not be fully addressed at this moment (see the ESI† for details). However, based on the current results and our recent discoveries, 11,16 it is clear that metal amidoboranes still constantly provide us exciting and sometimes surprising chemistry.…”

Sodium Aminodiboranate, a New Reagent for Chemoselective Reduction of Aldehydes and Ketones to Alcohols

“…To investigate the reduction of NaADBH to aldehydes and ketones, cinnamic aldehyde 25 was selected as the model carbonyl compounds to establish broadly applicable hydroboration conditions (Table 1). Firstly, we examined different solvents and found, similarly to the reactions of NaADBH with carboxylic acids, 15 that the reaction proceeded very smoothly in THF, acetonitrile (CH 3 CN), dioxane, diethyl ether (Et 2 O), and 1,2-dimethoxyethane (DME) (Table 1, entries 1-5). In these solvents, NaADBH reacted with cinnamic aldehyde within 5 minutes and achieved good yields.…”

“…Very recently, we have studied the reaction of NaADBH with carboxylic acid and investigated the reaction mechanism experimentally and theoretically, as well as found that the reducing capability of NaADBH is between that of NaBH 4 and LiAlH 4 . 15 Considering six negatively charged hydrogen atoms involved in NaADBH and its relative high stability in tetrahydrofuran (THF) solution, it is expected that NaADBH will exhibit interesting features in the SYNLETT0 9 3 6 -5 2 1 4 1 4 3 7 -2 0 9 6 Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart 2021, 32, 1104-1108 letter en J. W. et al…”

Structure, preparation and properties of liquid fluoroelastomers with different end groups

“…These reductants exist in the form of complex hydrogen anion salts, which are nucleophiles that can attack the positively charged atoms in unsaturated polar bonds, resulting in a reduction process via hydrogen anion transfer. 15,16 The carboxyl group can be easily converted to a hydroxyl group simultaneously.…”