Synthesis, Structure, and Solvent‐Induced Spontaneous Homochiral Assembly of Bidentate Bis(<i>N</i>,<i>N′</i>‐diaryl‐N‐heterocyclic carbene)‐Palladium Complexes

“…The isolation and crystallographic characterization of thermally stable N-heterocyclic carbenes (NHCs) by Arduengo et al initiated a considerable amount of research into the organometallic chemistry of these versatile ligands. − Since this discovery, a wide range of different NHC ligands have been prepared, including systems which incorporate NHCs in chelate and pincer scaffolds. − It has been shown that these ligands coordinate to most transition metals and can be utilized in a number of important catalytic reactions, particularly using Pd. − , Surprisingly, given the plethora of research into bidentate chelating NHC ligands for Pd, only a handful are known to coordinate in a trans fashion (NHC−M−NHC close to 180°). − Selected examples are shown in Figure . The first example ( i ) was described in 2000 by RajanBabu et al and contains two dinapthyl groups .…”

Section: Introductionmentioning

confidence: 99%

New Bidentate Trans-Chelating N-Heterocyclic Carbene Ligands for Palladium

et al. 2011

View full text Add to dashboard Cite

A family of imidazolium salts of the type [BnN(CH 2 CH 2 CH 2 R Im) 2 ] 3 2[Cl] (Bn = CH 2 Ph; R Im = 1-methylimidazole (1a), 1-tertbutylimidazole (1b), 1-benzylimidazole (1c), 1-methylbenzimidazole (1d)), which contain a tertiary amine linking two imidazolium groups, has been synthesized. These imidazolium salts can be deprotonated with Ag 2 O to generate the Ag carbene complexes 2d)). In the solid state 2d exists as an unusual tetramer, which consists of an [Ag 2 Cl 4 ] 2À core bridging two Ag(NHC) cations. Subsequent reaction of the Ag complexes with PdCl 2 (MeCN) 2 generates Pd species of the type {BnN(CH 2 CH 2 CH 2 R Im) 2 }PdCl 2 ( R Im = 1-methylimidazole (3a), 1-tert-butylimidazole (3b), 1-benzylimidazole (3c), 1-methylbenzimidazole (3d)), which is a rare example of a family of Pd complexes that contain a bidentate trans-chelating N-heterocyclic carbene ligand. Compounds 3a and 3c were crystallographically characterized by X-ray crystallography and contain unusual 12-membered metallacycles. DFT calculations suggest that the preference for trans binding of the ligand is related to conformational effects of the linker. Compound 3b reacts with excess MeI to form {BnN(CH 2 CH 2 CH 2 tBu Im) 2 }PdI 2 (5b), a reaction in which we believe a Pd(IV) intermediate is generated. Compound 5b was crystallographically characterized. Compounds 3aÀd are all active catalysts for the Heck reaction, and 3a can also catalyze the Suzuki reaction.

show abstract

“…However, only two examples of N ‐Mes, N ′‐Dipp imidazolium salts were described. Since that time, surprisingly a few examples of unequally 1,3‐diaryl‐substituted imidazolium salts have been synthesized by this method and utilized for the preparation of the corresponding metal complexes . In the present work, we for the first time investigated the reaction of the binucleophilic fluorinated arylamine 3 with the mesityl‐substituted oxazolinium salt 4 and synthesized a new type of functionalized NHC precursors.…”

Section: Resultsmentioning

confidence: 99%

Fluorinated Unsymmetrical N,N′‐Diaryl Imidazolium Salts—New Functionalized NHC‐Ligand Precursors

Topchiy

Zotova

Masoud

et al. 2017

Chemistry A European J

View full text Add to dashboard Cite

An efficient and scaled-up synthesis of the imidazol-2-ylidene-based unsymmetrical NHC precursors bearing the sterically demanding hexafluoroisopropylalkoxy group [(CF ) (OR)C-] at the ortho position of the N-aryl substituent was developed. The key step of the method involved the transformation of a Mes-substituted oxazolinium tetrafluoroborate salt through the reaction with the corresponding binucleophilic fluoroalkyl-substituted aniline. The subsequent post-modification of the resulting hydroxyl-containing salt through a simple one-step O-alkylation protocol provided access to a new family of unsymmetrical fluorinated NHC precursors. These compounds were successfully utilized for the preparation of several novel metal complexes. The molecular structures of some NHC precursors and their metal complexes have been unambiguously characterized by single-crystal X-ray diffraction analysis. A preliminary evaluation of the catalytic activity of the palladium complexes was performed on a Buchwald-Hartwig amination reaction. As a result, two PEPPSI-type (PEPPSI=pyridine-enhanced pre-catalyst preparation stabilization and initiation) Pd complexes have demonstrated promising activity in alkane solvents.

show abstract

Synthesis, Structure, and Solvent‐Induced Spontaneous Homochiral Assembly of Bidentate Bis(N,N′‐diaryl‐N‐heterocyclic carbene)‐Palladium Complexes

Cited by 14 publications

References 55 publications

‘Auto-click’ functionalization for diversified copper(i) and gold(i) NHCs

‘Auto-click’ functionalization for diversified copper(i) and gold(i) NHCs

New Bidentate Trans-Chelating N-Heterocyclic Carbene Ligands for Palladium

Fluorinated Unsymmetrical N,N′‐Diaryl Imidazolium Salts—New Functionalized NHC‐Ligand Precursors

Contact Info

Product

Resources

About