Isolation and Reactivity of a Frustrated <i>N</i>‐Heterocyclic Carbene‐Borane

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

doi:10.1002/zaac.201600290

Cited by 16 publications

(16 citation statements)

References 127 publications

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“…The complexes have been employed in transmetalation reactions, which in turn have been used as hydrogenation catalysts of alkenes in nonpolar solvents . The group also synthesized the Mes 2 B and 9-BBN backbone-substituted free NHCs 42 and 43 by addition of substituted haloboranes to 34c . , …”

Section: Nhc Complexes Of Main Group Elementsmentioning

confidence: 99%

“…123 The group also synthesized the Mes 2 B and 9-BBN backbonesubstituted free NHCs 42 and 43 by addition of substituted haloboranes to 34c. 122,125 Goicoechea et al isolated the potassium analogue 45 of 34a by addition of KO t Bu (vide infra). However, isolation of the free carbanionic species, for example, by addition of the potassium sequestering agent 2,2,2-crypt, failed.…”

Section: Chemical Reviewsmentioning

confidence: 99%

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NHCs in Main Group Chemistry

et al. 2018

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Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds. Significant progress has been achieved in stabilization and isolation of such species as Lewis acid/base adducts with highly tunable NHC ligands. This has allowed investigation of numerous novel types of compounds with unique electronic structures and opened new opportunities in the rational design of novel organic catalysts and materials. This Review gives a general overview of this research, basic synthetic approaches, key features of NHC-main group element adducts, and might be useful for the broad research community.

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Section: Nhc Complexes Of Main Group Elementsmentioning

confidence: 99%

Section: Chemical Reviewsmentioning

confidence: 99%

NHCs in Main Group Chemistry

et al. 2018

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“…[25] But, such structural combination (NHC─X─BR 2 ) in previously proposed FLP design proved effective (both thermodynamically and kinetically) for dihydrogen activation. [26,27] Recent synthesis and isolation of NHC-borane based intramolecular FLPs, [28,29] 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

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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.

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“…Intramolecular systems still remain scars in literature. Tamm et al were the first to report a backbone‐functionalized NHC featuring a borane unit in the NHC backbone ( A , Scheme ) . As reported for most FLP systems, the reactive functional entities are spatially separated to provide “frustration”.…”

Section: Introductionmentioning

confidence: 99%

Imidazolyl Alanes – Synthesis, Structures, and Reactivity Studies

et al. 2020

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Targeting the synthesis of Al/C based ambiphilic molecules, we investigated the dehydrohalogenation of a series of (benz)imidazole alane adducts. Depending on the steric bulk of the heterocycle, different dimeric products with various ring sizes were obtained. Dehydrohalogenation of the adduct of 1mesityl imidazole ( Mes Im) and 0.5 [tBu 2 AlBr] 2 furnished the dimer 2, featuring a "classical" N-heterocyclic carbene (NHC) and a mesoionic or "abnormal" NHC (aNHC) subunit within a single molecule. The dimer is bound loosely enough to allow thermally induced isomerization of 2 into the isomers 2 NHC (all NHC) and 2 aNHC (all aNHC). Dehydrohalogenation of the adduct of 1-mesityl-2-methyl imidazole ( Mes Im Me ) and 0.5 [tBu 2 AlBr] 2 (4) [a] Dr. M. Simon, Dr. M. Radius, Dr.Although several compounds with this architecture were described, [16,17] no reactivity studies for such with small molecules were reported until now. Inspired by our earlier findings on hidden aluminum phosphorus FLPs [19] and related B/C combinations [20] as well as the dimeric FLP C reported by Fontaine et al., [21] we targeted imidazolyl-alanes (D) bearing a highly Lewis acidic aluminum atom in geminal position to the Lewis base. We anticipated that such dimers might show FLP-type reactivity, either as Al/C or Al/N FLP, depending on steric and electronic effects of the substituents. Herein we report our efforts in preparing imidazolyl alanes with various substituent patterns. Results and Discussion Alane-Substituted NHCsThe synthesis of an imidazolyl alane was attempted by dehydrohalogenation of Mes Im·tBu 2 AlBr 1 (see Experimental Section for the synthesis) by Na{N(SiMe 3 ) 2 } in THF at 80°C yielding compound 2 (Scheme 2, Mes Im = 1-mesityl imidazole). The product was isolated after recrystallization from hot toluene in 46 % yield. Interestingly, the deprotonation of the imidazoles selectively took place at two different positions of both heterocycles. Hence, 2 features a "classical" NHC and a mesoionic or "abnormal" [22] NHC subunit within a single molecule as evidenced by two carbene resonances in the 13 C{ 1 H} NMR spectrum (δ = 169.8 ppm for NHC and 150.8 ppm for aNHC, respectively). Additionally, four 15 N NMR chemical shifts and two well-separated sets of 1 H NMR resonances were detected. Scheme 2. Dehydrohalogenation of 1 leading to formation of 2. Blue indicates the NHC subunit, red the aNHC subunit.

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

Cited by 16 publications

References 127 publications

NHCs in Main Group Chemistry

NHCs in Main Group Chemistry

Dinitrogen Activation by Tricoordinated Boron Species: A Systematic Design

Imidazolyl Alanes – Synthesis, Structures, and Reactivity Studies

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