Reactions of a BICAAC with hydroboranes: propensity for Lewis adduct formation and carbene insertion into the B–H bond

Abstract

A BICAAC interacts differently with different boranes: Lewis adducts were formed with simple hydroboranes and insertion of the carbene carbon into the B–H bond was observed with more hydridic boranes.

A Bis (BICAAC) Palladium(II) Complex: Synthesis and Implementation as Catalyst in Heck-Mizoroki and Suzuki-Miyaura Cross Coupling Reactions

“…To explore the properties of BICAAC, previously we reported its reactivity with different hydroboranes . Very recently, we reported the synthesis of two coordinated complexes of Cu­(I) and Au­(I) with BICAAC ligand .…”

Carbene B−H Insertion Reactions for C−B Bond Formation

“…Bicyclic (alkyl)(amino)carbenes (BICAACs) 24 reacted with 9-borabicyclo[3.3.1]nonane 25 and catecholborane 28 through a similar pathway leading to the formation of organoborane products 26 and 29, as reported in 2019 by Singh and co-workers (Scheme 9). [27] Very recently, Zhu, Zhou and co-workers reported an elegant protocol for alkylidene carbene insertion into BÀ H bonds, enabling the formation of C(sp 2 )À B bonds. [28] This finding provides, for the first time, a bridge between unsaturated carbenes and organoboron chemistry.…”

Bicyclic (alkyl)(amino)carbene (BICAAC) as a metal-free catalyst for reduction of nitriles to amines

“…Two singlets at δ 3.54 and 3.65 ppm were observed in the 1 H NMR spectrum of 1a in C 6 D 6 which suggests the formation of a pair of diastereomers. 11,12 The 11 B NMR spectrum of 1a in C 6 D 6 revealed a broad singlet at δ = 32.0 ppm, which appeared at a deshielded zone compared to free borane ( δ = 27.4 ppm). 12 In this regard, when DBpin was used instead of HBpin, the characteristic signals at δ 3.65 and 3.54 ppm were missing suggesting deuterium incorporation in the product (Fig.…”

“…First, BICAAC 1 reacts with HBPin leading to the BICAAC B–H insertion product 1a , which was spectroscopically characterized and the data were compared with earlier reports. 12 The activation energy barrier for the hydride transfer from HBpin to carbene carbon is 1.9 kcal mol −1 . Therefore, the formation of 1a is highly facile even at room temperature.…”

“…11 In 2019, the reactivity of a BICAAC ligand with various boranes also showed a similar pattern. 12 Such reactivity towards borane is reminiscent of a transition metal undergoing oxidative addition. This motivated us to check the behaviour of the same BICAAC with pinacolborane and we further studied it in metal-free catalytic reduction of nitriles to the corresponding amine hydrochloride salts (Scheme 1).…”