On the Interaction between N-Heterocyclic Carbenes and Organic Acids: Structural Authentication of the First N−H⋅⋅⋅C Hydrogen Bond and Remarkably Short C−H⋅⋅⋅O Interactions

Cowan, John A.; Clyburne, Jason A. C.; Davidson, Matthew G.; Harris, Rebecca; Howard, Judith A. K.; Küpper, Patrick; Leech, Michael A.; Richards, Stephen P.

doi:10.1002/1521-3773(20020415)41:8<1432::aid-anie1432>3.0.co;2-m

Cited by 101 publications

(32 citation statements)

References 18 publications

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“…The planarization of the biphenyl backbone (as quantified by the decrease of the C 2 —C 1 —C 1 —C 1′ —C 2′ dihedral angle from 36° in 1 to 1° in TS 1 → 4 ) allows the carbene center to approach the C 2′ —H bond enough for the insertion to occur. The disrupting C 2′ —H bond is elongated in TS 1 → 4 by 35% compared to that of carbene 1 (1.46 vs 1.08 Å), while the forming C carbene —H bond is elongated in TS 1 → 4 by only 10% compared to that of the insertion product 4 (1.21 vs 1.10 Å), indicating a very advanced proton transfer from C 2′ to the carbene center 18. In parallel, the distance between the two carbon centers C carbene and C 2′ remains long (2.31 Å) and the N—C carbene π-interaction remains strong.…”

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confidence: 96%

Rearrangement of Biaryl Monoaminocarbenes via Concerted Asynchronous Insertion into Aromatic C−H Bonds

et al. 2008

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The biphenyl and binaphthyl diisopropylaminocarbenes were found to be only transient species that spontaneously and quantitatively rearrange into the corresponding aminofluorenes. DFT calculations confirm that these insertion reactions of aminocarbenes into proximal aromatic C-H bonds require only a moderate energy barrier and support a concerted, strongly asynchronous, mechanism dominated by C arom →C carbene proton transfer.Over the past 20 years, spectacular progress has been achieved in carbene chemistry. These divalent six-valence-electron fleeting intermediates have shifted into the realm of isolable compounds, 1 and the availability of a variety of stable singlet carbenes has allowed for considerable synthetic developments in metal-mediated 2 as well as organo-catalyzed transformations. 3 More insight has also been gained into typical carbene reactivity including cyclopropanation, 4 dimerization, 5 1,2-and 1,3-migration, 6 as well as O-H, N-H, 7 and Correspondence to: Karinne Miqueu, karine.miqueu@univ-pau.fr; Didier Bourissou, dbouriss@chimie.upstlse.fr; Guy Bertrand, gbertran@mail.ucr.edu. Supporting Information Available: Experimental procedures, spectroscopic characterizations for all new compounds, computational details, and Z-matrices for all optimized structures. This material is available free of charge via the Internet at http://pubs.acs.org. C sp -and C sp 3-H 8,9 insertion reactions. In addition, unusual transformations such as radical fragmentation 10 and nucleophilic substitution at the carbene center 11 have been evidenced. NIH Public AccessIn this context, our interest for increasing further the structural variety of singlet carbenes prompted us to investigate biaryl monoaminocarbenes, and we recently reported the synthesis and original coordination behavior of the stable biphenyl and binaphthyl representatives I and II (Figure 1). 12 In continuation of this work, we became interested into the corresponding carbenes 1 and 2 free of methoxy groups on the biaryl moieties and report here on the spontaneous rearrangement of these transient carbenes via an unprecedented insertion into C sp 2-H bonds.A one-pot procedure 13 starting from commercially available 2-bromobiphenyl afforded the biphenyl iminium salt 3 in 58% overall yield (Scheme 1). The characteristic CH iminium signals were observed at 8.75 and 173.5 ppm in the respective 1 H and 13 C NMR spectra. In addition, the presence of only seven CH arom signals in the 13 C NMR spectrum indicated free rotation around the biphenyl axis on the NMR time scale. Monitoring the reaction of 3 with LiHMDS in THF by 1 H and 13 C NMR at low temperature indicated that deprotonation immediately and cleanly occurred at −80 °C. However, the characteristic low-field 13 C NMR signal expected for carbene 1 was not observed, and the resulting product was unambiguously identified as the diisopropylaminofluorene isomer 4. The 1 H NMR chemical shift for the central CH (4.96 ppm) is identical to that reported previously, 14 and the presence of only 4 CH a...

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confidence: 96%

Rearrangement of Biaryl Monoaminocarbenes via Concerted Asynchronous Insertion into Aromatic C−H Bonds

et al. 2008

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“…1a), showing these species can be structurally authenticated. 31 Movassaghi and Schmidt also identied a MeOH/IMes adduct in their efforts to catalyze amidation reactions with carbenes, authenticating the adduct both in solid-and solution-state ( Fig. 1a).…”

Section: Introductionmentioning

confidence: 78%

“…33 Previous studies of non-traditional X-H/:C hydrogen bonding (X ¼ N (ref. 31) or O (ref. 32, 47, 48 and 64)) did not quantitate the strengths of interaction.…”

Section: Introductionmentioning

confidence: 99%

Preferential N–H⋯:C hydrogen bonding involving ditopic NH-containing systems and N-heterocyclic carbenes

2020

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“…30 NHCs as strong Lewis bases are readily protonated to imidazolium cations. 31 In this study, we employed 1,3,4,5-tetramethylimidazol-2-ylidene, NHC Me 4 , 32 and 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, NHC i Pr 2 Me 2 , 32 as precursors to N , N ′-dialkylimidazolium counter cations with differing steric bulk at the N centers to directly deprotonate anionic phosphate monoesters. 33 Indeed, the 1:1 reactions of 4 with NHC Me 4 and NHC i Pr 2 Me 2 in dry tetrahydrofuran (THF) afforded compounds 12 and 13 , respectively (Scheme 6).…”

Section: Resultsmentioning

confidence: 99%

Structural Diversity in Supramolecular Organization of Anionic Phosphate Monoesters: Role of Cations

et al. 2019

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Syntheses and structures of anionic arylphosphate monoesters [ArOP(O) 2 (OH)] − (Ar = 2,6-CHPh 2 -4-R-C 6 H 2 ; R = Me/Et/ i Pr/ t Bu) with different counter cations are reported. The counter cations were varied systematically: imidazolium cation, 2-methyl imidazolium cation, N -methyl imidazolium cation, N , N ′-alkyl substituted imidazolium cation, 1,4-diazabicyclo[2.2.2]octan-1-ium cation, 4,4′-bipyridinium dication, and magnesium(II) dication. The objective was to examine if the supramolecular structure of anionic arylphosphate monoesters could be modulated by varying the cation. It was found that an eight-membered P 2 O 4 H 2 -hydrogen-bonded dimeric motif involving intermolecular H-bonding between the [P(O)(OH)] unit of the anionic phosphate monoester along with the counter cation is formed with 2-methyl imidazolium cation, N -methyl imidazolium cation, N , N ′-alkyl substituted imidazolium cation, 1,4-diazabicyclo[2.2.2]octan-1-ium cation, and magnesium(II) dication; both discrete and polymeric H-bonded structures are observed. In the case of imidazolium cations and 1,4-diazabicyclo[2.2.2]octan-1-ium cation, the formation of one-dimensional polymers (single lane/double lane) was observed. On the other hand, two types of phosphate motifs, intermolecular H-bonded dimer and an open-form, were observed in the case of 4,4′-bipyridinium dication.

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On the Interaction between N-Heterocyclic Carbenes and Organic Acids: Structural Authentication of the First N−H⋅⋅⋅C Hydrogen Bond and Remarkably Short C−H⋅⋅⋅O Interactions

Cited by 101 publications

References 18 publications

Rearrangement of Biaryl Monoaminocarbenes via Concerted Asynchronous Insertion into Aromatic C−H Bonds

Rearrangement of Biaryl Monoaminocarbenes via Concerted Asynchronous Insertion into Aromatic C−H Bonds

Preferential N–H⋯:C hydrogen bonding involving ditopic NH-containing systems and N-heterocyclic carbenes

Structural Diversity in Supramolecular Organization of Anionic Phosphate Monoesters: Role of Cations

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