The [(NHC)B(H)C₆F₅]⁺ Cations and Their [B](H)−CO Borane Carbonyls

Abstract

Hydride abstraction from the heterocyclic carbene borane adducts (NHC)BH 2 C 6 F 5 (NHC: IMes or IMe 4) gave the BÀH containing [(NHC)B(H)C 6 F 5 ] + borenium cations. They added carbon monoxide to give the respective [(NHC)B-(H)(C 6 F 5)CO] + boron carbonyl cations. Carbon nucleophiles add to the boron carbonyl to give [B](H) acyls. Hydride reduced the [B]CO cation to hydroxymethylborane derivatives.

Formation and Cycloaddition Reactions of a Reactive Boraalkene Stabilized Internally by N‐Heterocyclic Carbene

“…It was recently shown that hydride removal from the NHC N,N'-bis (2,4,6-trimethylphenyl)imidazolylidene (IMes) borane adduct 6a gave the [IMesB(H)C 6 F 5 ] + cation, [13] which upon heating underwent intramolecular CÀHactivation [14] at aCH 3 group of amesityl substituent with loss of H 2 to give the cyclization product 4a.This was now readily deprotonated at the acidified CH 2 group adjacent to the B-C 6 F 5 moiety to give the neutral product 5a (Scheme 2). Its X-ray crystal structure analysis showed the presence of aB = Cdouble bond (C17-B1: 1.456( 4) ,cf.…”

“…In solution ([D 2 ]dichloromethane,2 99 K) compound 5b shows a 11 BNMR signal at 15.6 (Dd 19 F m,p = 3.7 ppm). The carbon atom of the N1-C1-N2 unit shows an iminium-type 13 CNMR feature at d 166. 5…”

“…In solution ([D 2 ]dichloromethane) compound 19 shows at otal of seven 1 HNMR methyl doublets of the three isopropyl substituents and the 17-CH 3 group.T he 13 We assume that the 18/19 pair of products might be derived from the intermediate 17 formed by a[ 3 + +2] cycloaddition reaction [20] between the boraalkene B=Cf unctionality in 5b and N 2 O. This then apparently undergoes apair of fast competing subsequent reactions,n amely N 2 loss to give the oxaborirane system of 18 and af ragmentation reaction with concomitant H-migration to give the diazoalkane product 19.T he later pathway may be regarded as ar ather unusual reaction.…”

“…Compound 13 CNMR resonance occurs at d 166.4. Compound 12 was characterized by an X-ray crystal structure analysis (for the depicted structure,s ee the Supporting Information).…”

Generation of boryl-nitroxide radicals from a boraalkene via the nitroso ene reaction

“…We had described that the cyclic boraalkene 1 was readily prepared starting from the corresponding [(IMes)(C 6 F 5 )BH] + borenium cation (with [B(C 6 F 5 ) 4 ]anion) 11 by a sequence involving thermally induced intramolecular C-H activation at an ortho-methyl group of a NHC mesityl substituent (with H 2 formation) followed by deprotonation. 12 Compound 1 was now found to rapidly react with nitrosobenzene 13 The X-ray crystal structure analysis of compound 2 showed bond lengths inside the newly formed four-membered heterocycle of 1.505( 4) Å (B1-O1), 1.624( 4) Å (B1-C17), 1.504(3) Å (N3-C17) and 1.475(3) Å (N3-O1).…”