A simple 1H NMR method for determining the σ-donor properties of N-heterocyclic carbenes

Meng, Guangrong; Kakalis, Lazaros T.; Nolan, Steven P.; Szostak, Michal

doi:10.1016/j.tetlet.2018.12.059

Cited by 76 publications

(81 citation statements)

References 60 publications

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“…The phosphonium salt exhibited a signal at 26.1 ppm in the 31 P NMR spectrum and a multiplet at 7.23-7.26 ppm in the 1 H NMR spectrum for the pyrrole hydrogen atom. The 1 J CH coupling constant of 189.2 Hz suggested a slightly stronger σ-donating character of 8 compared to 7 [34]. Treatment of 11 with an equiv.…”

Section: Attempted Synthesis Of Caycs With Trialklyl Onium Groupsmentioning

confidence: 97%

“…The salt 9 exhibited a pseudo triplet in the 1 H NMR spectrum at 7.35 ppm for the NCHCSMe 2 moiety. Recently, Szostak and coworkers showed that the σ-donor strengths of carbenes can easily be estimated by measurement of the 1 J CH coupling constant in the protonated carbene precursors [34]. Measurement of the 1 J CH coupling constant of 9 revealed a value of 194.0 Hz, which suggests that the CAYC 7 is a stronger donor than typical NHCs and of a strength comparable to CAACs.…”

Section: Attempted Synthesis Of Caycs With Trialklyl Onium Groupsmentioning

confidence: 99%

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Towards the Preparation of Stable Cyclic Amino(ylide)Carbenes

et al. 2020

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Cyclic amino(ylide)carbenes (CAYCs) are the ylide-substituted analogues of N-heterocyclic Carbenes (NHCs). Due to the stronger π donation of the ylide compared to an amino moiety they are stronger donors and thus are desirable ligands for catalysis. However, no stable CAYC has been reported until today. Here, we describe experimental and computational studies on the synthesis and stability of CAYCs based on pyrroles with trialkyl onium groups. Attempts to isolate two CAYCs with trialkyl phosphonium and sulfonium ylides resulted in the deprotonation of the alkyl groups instead of the formation of the desired CAYCs. In case of the PCy3-substituted system, the corresponding ylide was isolated, while deprotonation of the SMe2-functionalized compound led to the formation of ethene and the thioether. Detailed computational studies on various trialkyl onium groups showed that both the α- and β-deprotonated compounds were energetically favored over the free carbene. The most stable candidates were revealed to be α-hydrogen-free adamantyl-substituted onium groups, for which β-deprotonation is less favorable at the bridgehead position. Overall, the calculations showed that the isolation of CAYCs should be possible, but careful design is required to exclude decomposition pathways such as deprotonations at the onium group.

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Section: Attempted Synthesis Of Caycs With Trialklyl Onium Groupsmentioning

confidence: 97%

Section: Attempted Synthesis Of Caycs With Trialklyl Onium Groupsmentioning

confidence: 99%

Towards the Preparation of Stable Cyclic Amino(ylide)Carbenes

et al. 2020

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“…Recently, silver complexes containing N-heterocyclic carbenes (NHC) have become a popular subject of research because of their versatility and they may release silver ions slowly under biological conditions. Moreover, NHCs are highly desired owing to their facile synthetic modifications and strong affinity for transition-data reports metal centers, which ensures the delayed release of silver to the biological system over longer periods of time (Herrmann, 2002;Jafarpour et al, 1999;Garrison & Youngs, 2005;Meng et al, 2019). Several silver-NHC complexes have been synthesized and tested against several bacterial strains (gram-positive and gram-negative).…”

Section: Structure Descriptionmentioning

confidence: 99%

Di-μ-acetato-bis{[3-benzyl-1-(2,4,6-trimethylphenyl)imidazol-2-ylidene]silver(I)}

et al. 2019

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The title compound, [Ag2(C2H3O2)2(C19H20N2)2] (2), was readily synthesized by treatment of 3-benzyl-1-(2,4,6-trimethylphenyl)imidazolium chloride with silver acetate. The solution structure of the complex was analyzed by NMR spectroscopy, while the solid-state structure was confirmed by single-crystal X-ray diffraction studies. Compound 2 crystallizes in the triclinic space group P\overline{1}, with a silver-to-carbene bond length (Ag—CNHC) of 2.084 (3) Å. The molecule resides on an inversion center, so that only half of the molecule is crystallographically unique. The planes defined by the two imidazole rings are parallel to each other, but not coplanar [interplanar distance is 0.662 (19) Å]. The dihedral angles between the imidazole ring and the benzyl and mesityl rings are 77.87 (12) and 72.86 (11)°, respectively. The crystal structure features π–π stacking interactions between the benzylic groups of inversion-related (−x + 1, −y + 1, −z + 1) molecules and C—H...π interactions.

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“…An ideal organometallic drug design for therapeutic applications hinges directly on the judicial selection of the metal and the ligand; one such ligand system is N-heterocyclic carbene (NHC). Such developments are attributed to the strong -donating properties of NHCs and the stability of the M-C(carbene) bond (Jacobsen et al, 2009;Meng et al, 2019;Tonner et al, 2007), an important trait that could be exploited to withstand physiological conditions for organometallic therapeutic drugs. Such developments are attributed to the strong -donating properties of NHCs and the stability of the M-C(carbene) bond (Jacobsen et al, 2009;Meng et al, 2019;Tonner et al, 2007), an important trait that could be exploited to withstand physiological conditions for organometallic therapeutic drugs.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and molecular structure of biologically significant bis(1,3-dimesityl-4,5-naphthoquinoimidazol-2-ylidene)gold(I) complexes with chloride and dichloridoaurate counter-ions

et al. 2019

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Diffraction-quality single crystals of two gold(I) complexes, namely bis(1,3-dimesityl-4,5-naphthoquinoimidazol-2-ylidene)gold(I) chloride benzene monosolvate, [Au(C29H26N2O2)2]Cl·C6H6 or [(NQMes)2Au]Cl·C6H6, 2, and bis(1,3-dimesityl-4,5-naphthoquinoimidazol-2-ylidene)gold(I) dichloridoaurate(I) dichloromethane disolvate, [Au(C29H26N2O2)2][AuCl2]·2CH2Cl2 or [(NQMes)2Au][AuCl2]·2CH2Cl2, 4, were isolated and studied with the aid of single-crystal X-ray diffraction analysis. Compound 2 crystallizes in a monoclinic space group C2/c with eight molecules in the unit cell, while compound 4 crystallizes in the triclinic space group P\overline{1} with two molecules in the unit cell. The crystal lattice of compound 2 reveals C—H...Cl− interactions that are present throughout the entire structure representing head-to-tail contacts between the aromatic (C—H) hydrogens of naphthoquinone and Cl− counter-ions. Compound 4 stacks with the aid of short interactions between a naphthoquinone O atom of one molecule and the mesityl methyl group of another molecule along the a axis, leading to a one-dimensional strand that is held together by strong π–η2 interactions between the imidazolium backbone and the [AuCl2]− counter-ion. The bond angles defined by the AuI atom and two carbene C atoms [C(carbene)—Au—C(carbene)] in compounds 2 and 4 are nearly rectilinear, with an average value of ∼174.1 [2]°. Though 2 and 4 share the same cation, they differ in their counter-anion, which alters the crystal lattice of the two compounds. The knowledge gleaned from these studies is expected to be useful in understanding the molecular interactions of 2 and 4 under physiological conditions.

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A simple 1H NMR method for determining the σ-donor properties of N-heterocyclic carbenes

Cited by 76 publications

References 60 publications

Towards the Preparation of Stable Cyclic Amino(ylide)Carbenes

Towards the Preparation of Stable Cyclic Amino(ylide)Carbenes

Di-μ-acetato-bis{[3-benzyl-1-(2,4,6-trimethylphenyl)imidazol-2-ylidene]silver(I)}

Synthesis and molecular structure of biologically significant bis(1,3-dimesityl-4,5-naphthoquinoimidazol-2-ylidene)gold(I) complexes with chloride and dichloridoaurate counter-ions

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