Sulfur-functionalized N-heterocyclic carbenes and their transition metal complexes

Bierenstiel, Matthias; Cross, Edward D.

doi:10.1016/j.ccr.2010.10.040

Cited by 140 publications

(42 citation statements)

References 71 publications

(193 reference statements)

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“…The catalytic activity of these NHC-transition metal complexes can be readily fine-tuned through the structural modification of the NHC ligands. Recent investigations show that donor-functionalized NHC-metal complexes can generate the active catalytic species through the reversible coordination/dissociation process of the donor functions from the metal centers, which accelerate the rapid development of various donor-functionalized NHC ligands, such as N-, P-, O-, S-functionalized NHCs [5][6][7][8][9][10]. In the family of N-functionalized NHCs, pyrazolylfunctionalized NHCs have drawn much attention owing to the coordination versatility of pyrazole-based ligands and the catalytic activity of their complexes [11][12][13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Synthesis and catalytic activity of N-heterocyclic carbene metal carbonyl complexes based on 1-[2-(pyrazol-1-yl)phenyl]imidazole

Cheng

Guo

Cui

et al. 2015

Transition Met Chem

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A series of N-heterocyclic carbene transition metal (molybdenum, tungsten and ruthenium) carbonyl complexes derived from 1-[2-(pyrazol-1-yl)phenyl]-imidazole have been synthesized and characterized by physico-chemical and spectroscopic methods, and the structures of five complexes have been confirmed by X-ray crystal structure analyses. The azaaryl-functionalized N-heterocyclic carbenes act as chelating N,C-bidentate ligands in these five complexes. Preliminary catalytic tests of these NHC-molybdenum (tungsten) carbonyl complexes in the oxidation of styrene have been carried out, showing that benzaldehyde was the main oxidation product when hydrogen peroxide was used as the oxidant, while 2,5-diphenyl-1,4-dioxane was obtained as the exclusive product in the oxidation by tert-butyl hydroperoxide.

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Section: Introductionmentioning

confidence: 99%

Synthesis and catalytic activity of N-heterocyclic carbene metal carbonyl complexes based on 1-[2-(pyrazol-1-yl)phenyl]imidazole

Cheng

Guo

Cui

et al. 2015

Transition Met Chem

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“…While neutral, soft [13] donors stabilize low-valent metal centers, anionic, hard donors in contrast enhance the stability of high-valent and electron-poor metals, and such bonding principles have recently started to emerge also with NHC complexes [14].…”

Section: Introductionmentioning

confidence: 99%

Synthesis of pincer-type N-heterocyclic carbene palladium complexes with a hemilabile ligand and their application in cross-coupling catalysis

Leigh¹,

Ghattas²,

Müeller-Bunz³

et al. 2014

Journal of Organometallic Chemistry

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Benzimidazolium salts containing both a neutral imine and a masked carboxylate functional group for potential metal chelation were prepared. Palladation of the ester-protected ligand afforded a N,C-bidentate carbene complex 4. Subsequent ester hydrolysis preserved the bidentate coordination mode and yielded complex 5 with a pending COOH group exclusively.However, when ester deprotection was carried out prior to metalation, the N,C,O-tridentate pincer-type coordinated palladium complex 7 was obtained. Proton-abstraction of the dangling COOH group in the bidentate ligand of complex 5 by treatment with a base led to the formation of the N,C,O-tridentate coordinated Pd system 7, and inversely, exposure of the tridentate bound Pd complex 7 with acid afforded the N,C-bidentate ligand coordination mode in complex 5, demonstrating hemilability of the oxygen donor site in the pincer ligand. All three palladium(II) complexes 4, 5, and 7 were evaluated in cross-coupling catalysis and revealed distinct activity differences that are dependent on the type of coupling (Suzuki vs.Heck) and the substrate (Ar-Br vs. Ar-Cl). These differences suggest that judicious choice of donor groups in pincer-type complexes is a viable strategy for catalyst optimization.

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“…The presence of a third donor may also encourage the formation of more robust κ 3 complexes, relative to bidentate counterparts. Pd(II) and Ag(I) complexes bearing thioether‐functionalized N‐heterocyclic carbenes have been shown to demonstrate hemilability in the presence of moderate to strong donors such as phosphines . Encouragingly, these species bearing a hemilabile sulfur donor were found to serve as efficient pre‐catalysts for a variety of cross‐coupling applications, suggesting that the traditional view of sulfur as a “catalyst poison” is not applicable in all instances.…”

Section: Introductionmentioning

confidence: 99%

Ruthenium (II) complexes bearing thioether‐appended α‐iminopyridine ligands: Arene precursors permit access to κ²‐N,N and κ³‐N,N,S complexes

Ternes

Morgan

Lanquist

et al. 2020

Applied Organom Chemis

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Herein we report the preparation of a series of Ru(II) complexes featuring α‐iminopyridine ligands bearing thioether functionality (NNSR, where R = Me, CH2Ph, Ph). Metallation using [(p‐cymene)RuCl]2 permits access to Ru complexes with a κ2‐N,N donor set in which the thioether moiety remains uncoordinated. In the presence of a strong field ligand such as acetonitrile or triphenylphosphine, the p‐cymene moiety is displaced, and the ligand adopts a κ3‐N,N,S binding mode. These complexes are characterized using a combination of solution and solid state methods, including the crystal structure of [(NNSMe)Ru (NCMe)2Cl]Cl. The κ2‐N,N‐Ru(II) complexes are shown to serve as efficient precatalysts for the oxidation of sec‐phenethyl alcohol at modest loadings (alcohol: Ru = 20:1), using a variety of external oxidants and solvents. The complex bearing an S‐Ph donor was found to be the most active oxidation catalyst of those surveyed, suggesting that the thioether donor plays an active role in the catalytic cycle.

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Sulfur-functionalized N-heterocyclic carbenes and their transition metal complexes

Cited by 140 publications

References 71 publications

Synthesis and catalytic activity of N-heterocyclic carbene metal carbonyl complexes based on 1-[2-(pyrazol-1-yl)phenyl]imidazole

Synthesis and catalytic activity of N-heterocyclic carbene metal carbonyl complexes based on 1-[2-(pyrazol-1-yl)phenyl]imidazole

Synthesis of pincer-type N-heterocyclic carbene palladium complexes with a hemilabile ligand and their application in cross-coupling catalysis

Ruthenium (II) complexes bearing thioether‐appended α‐iminopyridine ligands: Arene precursors permit access to κ²‐N,N and κ³‐N,N,S complexes

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Sulfur-functionalized N-heterocyclic carbenes and their transition metal complexes

Cited by 140 publications

References 71 publications

Synthesis and catalytic activity of N-heterocyclic carbene metal carbonyl complexes based on 1-[2-(pyrazol-1-yl)phenyl]imidazole

Synthesis and catalytic activity of N-heterocyclic carbene metal carbonyl complexes based on 1-[2-(pyrazol-1-yl)phenyl]imidazole

Synthesis of pincer-type N-heterocyclic carbene palladium complexes with a hemilabile ligand and their application in cross-coupling catalysis

Ruthenium (II) complexes bearing thioether‐appended α‐iminopyridine ligands: Arene precursors permit access to κ2‐N,N and κ3‐N,N,S complexes

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Ruthenium (II) complexes bearing thioether‐appended α‐iminopyridine ligands: Arene precursors permit access to κ²‐N,N and κ³‐N,N,S complexes