Preparation and reactivity of an isolable N-heterocyclic carbene–borane

Winkler, Andrea; Freytag, Mat­thias; Jones, Peter G.; Tamm, Matthias

doi:10.1016/j.jorganchem.2014.04.037

Cited by 17 publications

(27 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Therefore,t he latter is best described as aboryl-substituted DAC-centered radical. Although slightly upfield from the chemical shifts reported for related compounds, [13,14,43] these resonances fall in the range expected for tricoordinate boron atoms,r evealing that the triflate counterions are not bound to the boron atoms.The formation of separated ion pairs in the solid state was confirmed for 10 a-10 c by single-crystal X-ray diffraction analyses.T he molecular structures are shown in Figure 2f (7) . It is obvious that, to av ariable extent, similar mesomeric structures must also be considered for the radicals 1-7 (vide infra).…”

mentioning

confidence: 56%

N‐Heterocyclic Carbene Stabilized Boryl Radicals

et al. 2016

Self Cite

View full text Add to dashboard Cite

The reaction of the 2-(trimethylsilyl)imidazolium triflate 9 with diarylboron halides (4-R-C H ) BX (R=H, X=Br; R=CH , X=Cl; R=CF , X=Cl) afforded the NHC-stabilized borenium cations 10 a-c. Cyclic voltammetry revealed a linear correlation between the Hammett parameter σ of the para substituent and the half-wave potential. Chemical reduction with decamethylcobaltocene, [(C Me ) Co], furnished the corresponding radicals 11 a-c; their characterization by EPR spectroscopy confirmed the paramagnetic character of 11 a-c, with large hyperfine coupling constants to the boron isotopes B and B, while delocalization of the unpaired electron into the NHC is negligible. DFT calculations of the percentage of spin density distribution between the carbene (NHC) and the boryl fragments (BR ) revealed for 11 a-c a spin density ratio (BR /NHC) of ca. 9:1, which underlines their distinct boryl radical character. The molecular structure of the most stable species 11 c was established by X-ray diffraction analysis.

show abstract

mentioning

confidence: 56%

N‐Heterocyclic Carbene Stabilized Boryl Radicals

et al. 2016

Self Cite

View full text Add to dashboard Cite

show abstract

“…But, such structural combination (NHC─X─BR 2 ) in previously proposed FLP design proved effective (both thermodynamically and kinetically) for dihydrogen activation . Recent synthesis and isolation of NHC‐borane based intramolecular FLPs, proved efficient for CO 2 activation, which encourages us to probe systematic and rational studies of such rarely explored frameworks for the extremely challenging N 2 molecule.…”

Section: Introductionmentioning

confidence: 99%

Dinitrogen Activation by Tricoordinated Boron Species: A Systematic Design

Rouf

Dai

et al. 2020

Advcd Theory and Sims

View full text Add to dashboard Cite

Molecular nitrogen (N2), an abundant component of the atmosphere, is appealing for industrial value‐added products. However, its intrinsic inertness limits its activation to mainly metallic species. Environmental concerns and harsh reaction conditions have resulted in a demand for alternate nonmetallic and nontoxic routes to activate and functionalize N2 at ambient conditions. Comprehensive density functional theory (DFT) calculations are performed on N2 activation by boron species, specifically for the experimentally more accessible tricoordinated boron compounds. Subsequently designed frustrated Lewis pairs (FLPs) combining screened N‐heterocyclic carbene with boron moieties can make N2 activation both kinetically and thermodynamically favorable, displaying high potential for metal‐free N2 activation. The significant thermodynamic stability of the products stabilized by aromaticity and low activation barriers could be a breakthrough for the development of FLP chemistry on metal‐free N2 activation.

show abstract

“…The reaction of 1 with 9‐chloro‐9‐borabicyclo[3.3.1]nonane (BBN‐Cl) in toluene furnished a white precipitate, which slowly re‐dissolved by stirring the reaction mixture at room temperature for 2 d. Evaporation of all volatiles and crystallization of the remaining solid from hexane/dichloromethane solution afforded the abnormal carbene‐borane adduct 5 as a white crystalline solid in 80 % yield. The reaction presumably proceeds via the formation of the kinetically favored normal C2 adduct, followed by rearrangement to the thermodynamically favored abnormal C4 adduct 5 ; this pathway had previously been confirmed for the reaction of 1 with Mes 2 BF . Because of the unsymmetrical substitution pattern, the 1 H and 13 C NMR spectra of 5 display two sets of signals for the tert ‐butyl groups.…”

Section: Resultsmentioning

confidence: 56%

“…Aiming at the isolation of an intramolecular frustrated carbene‐borane Lewis pair related to the iconic para ‐Mes 2 P(C 6 F 4 )B(C 6 F 5 ) 2 system (vide supra), this method was also employed successfully by treatment of 2 with Mes 2 BF (Mes = 2,4,6‐trimethylphenyl), affording 4 after elimination of lithium fluoride (Scheme ). Alternatively, the reaction of 1 with Mes 2 BF afforded the abnormal adduct 3 and subsequently 4 by reaction with potassium bis(trimethylsilyl)amide (potassium hexamethyldisilazide, KHMDS) . 4 can be clearly regarded as a frustrated Lewis pair, since no interaction between the Lewis acid and base was detected in solution or in the solid state.…”

Section: Introductionmentioning

confidence: 99%

“…However, typical FLP reactivity was not observed, and the carbene‐borane 4 behaved in all reactions as a conventional NHC ligand, with the BMes 2 moiety remaining uninvolved. This behavior was ascribed to an over‐stabilization by the sterically demanding substituents at the boron atom, and it was speculated that subtle tuning of the electronic and steric properties might be required to find a compromise between stability and reactivity of such carbene‐borane species …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Isolation and Reactivity of a Frustrated N‐Heterocyclic Carbene‐Borane

Winkler

Freytag

Jones

et al. 2016

Zeitschrift anorg allge chemie

Self Cite

View full text Add to dashboard Cite

The synthesis of the frustrated carbene-borane 4-(9-borabicyclo[3.3.1]nona-9-yl)-1,3-di-tert-butylimidazolin-2-ylidene (6) was accomplished by deprotonation of the N-heterocyclic carbene (NHC) 1,3di-tert-butylimidazolin-2-ylidene (1) at the 4-position with n-butyllithium, followed by addition of 9-chloro-9-borabicyclo[3.3.1]nonane (BBN-Cl). The abnormal carbene-borane adduct 5, with the BBN-Cl moiety at the 4-position, was obtained from the reaction of 1 with BBN-Cl; however, its conversion into 6 by treatment with K[N(SiMe 3 ) 2 ] (potassium hexamethyldisilazide, KHMDS) was not achieved. The reactions of 6 with the rhodium(I) complexes [Rh(COD)Cl] 2 (COD = 1,4-* Prof. Dr. M. Tamm

show abstract

Preparation and reactivity of an isolable N-heterocyclic carbene–borane

Cited by 17 publications

References 54 publications

N‐Heterocyclic Carbene Stabilized Boryl Radicals

N‐Heterocyclic Carbene Stabilized Boryl Radicals

Dinitrogen Activation by Tricoordinated Boron Species: A Systematic Design

Isolation and Reactivity of a Frustrated N‐Heterocyclic Carbene‐Borane

Contact Info

Product

Resources

About