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

Abstract

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.

Synthesis, characterization, crystal structure, α‐glycosidase, and acetylcholinesterase inhibitory properties of 1,3‐disubstituted benzimidazolium salts

“…Additionally, fluorinated NHC ligands and their complexes with different metals have been studied in recent decades. [38][39][40][41][42][43][44] Some of the published works in the literature prove that these transition metal complexes containing fluorinated NHC ligand are easy to prepare, require no special handling precautions, and are quite good catalysts in many organic reactions (e.g., hydrosilylation of propargylic alcohols, Mizoroki-Heck arylations, and transfer hydrogenations) giving high yields. [45][46][47][48] These complexes containing fluorinated NHC ligand also possess good biological activities.…”

Ruthenium‐Alkylidene Complexes with Sterically Rigid Fluorinated NHC Ligands

“…Previously we have described the heterocyclic interconversion of mesityl‐substituted oxazolinium salt 1 via the reaction with the binucleophilic fluorinated arylamine 2 mediated by tetrafluoroboric acid to afford a mixture of hydroxyl‐containing imidazolium salt 3 along with unexpected tricyclic by‐product 4 likely arising from additional heterocyclization upon the hydroxyl group under the reaction conditions (Scheme ).…”

“…Purification of allylbenzene and syntheses of 2‐(2‐amino‐3,5‐dimethylphenyl)‐1,1,1,3,3,3‐hexafluoro‐propan‐2‐ol ( 2a ),[16a] 2‐(2‐amino‐5‐methylphenyl)‐1,1,1,3,3,3‐hexafluoro‐propan‐2‐ol ( 2b ), N ‐mesityl‐ N ‐(2‐oxoethyl)formamide ( 5a ), N ‐(2,6‐diisopropylphenyl)‐ N ‐(2‐oxoethyl)formamide ( 5b )[18b] were carried out according to literature procedures.…”

“…Recently we have developed an efficient route to the new family of unsymmetrical N , N ‐diaryl imidazolium and imidazolinium salts with bulky hexafluoroisopropylalkoxy [(CF 3 ) 2 (OR)C‐] group in one of the N ‐aryl substituents and investigated their potential as universal precursors of the corresponding NHC ligands for metal catalysis. Some of ruthenium‐alkylidene complexes bearing these ligands demonstrated a good performance in olefin RCM and cross‐metathesis (CM) .…”

Halogen-containing heteroaromatic carbenes of the 1,2,4-triazole series and their transformations

“…[25][26][27][28][29][30] Fluorinecontaining imidazolylidenes can be generated from the precursors G, H of two types obtained on the basis of 2,4-xylidine and hexauoroacetone (Scheme 2). 31 The formation of a fused carbenoid imidazolinium salt H occurred as a side process.…”