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Isolation of a C5-deprotonated imidazolium, a crystalline "abnormal" N-heterocyclic carbene.

ABSTRACT: The discovery two decades ago of metal-free stable carbenes, especially imidazol-2-ylidenes [N-heterocyclic carbenes (NHCs)], has led to numerous breakthroughs in organic and organometallic catalysis. More recently, a small range of complexes has been prepared in which alternative NHC isomers, namely imidazol-5-ylidenes (also termed abnormal NHCs or aNHCs, because the carbene center is no longer located between the two nitrogens), coordinate to a transition metal. Here we report the synthesis of a metal-free aNHC that is stable at room temperature, both in the solid state and in solution. Calculations show that the aNHC is more basic than its normal NHC isomer. Because the substituent at the carbon next to the carbene center is a nonbulky phenyl group, a variety of substitution patterns should be tolerated without precluding the isolation of the corresponding aNHC.

SUBMITTER: Aldeco-Perez E

PROVIDER: S-EPMC2871154 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Shape-controllable formation of poly-imidazolium salts for stable palladium N-heterocyclic carbene polymers.

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From Imidazole toward Imidazolium Salts and N-Heterocyclic Carbene Ligands: Electronic and Geometrical Redistribution.

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Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr.HCl, IMes.HCl and IXy.HCl.

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Stepwise Synthesis of <i>Tetra</i>-imidazolium Macrocycles and Their <i>N</i>-Heterocyclic Carbene Metal Complexes.

Project description:A modular stepwise synthetic method has been developed for the preperation of tetra-imidazolium macrocycles. Initially a series of three bis(imidazolylmethyl)benzene precursors were alkylated with 1,2-dibromoethane to produce the corresponding bis-bromoethylimidazolium bromide salts. In the second step the bis-bromoethylimidazolium bromide salts were reacted with selected bis(imidazolylmethyl)benzene molecules to produce a series of two symmetrical and three asymmetrical tetra-imidazolium macrocycles. These tetra-imidazolium salts act receptors for anions and 1H-NMR titration studies were used to determine the association constants between two of the macrocycles and the halide anions chloride, bromide and iodide. The tetra-imidazolium salts are precursors for N-heterocyclic carbene (NHC) ligands and the corresponding silver(I), gold(I), and palladium(II) NHC complexes have been prepared. Varied structures were obtained, which depend on the chosen macrocyclic ligand and metal ion and in the case of the coinage metals Ag(I) and Au(I), mono, di, and hexanuclear complexes were formed.

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Synthesis and isolation of a stable, axially-chiral seven-membered N-heterocyclic carbene.

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| S-EPMC4931868 | biostudies-other

A persistent P,N-heterocyclic carbene.

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Actinide tetra-N-heterocyclic carbene 'sandwiches'.

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| S-EPMC8188502 | biostudies-literature

N-Heterocyclic carbene-based gold etchants.

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Aryl radical-mediated N-heterocyclic carbene catalysis.

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| S-EPMC8219674 | biostudies-literature

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