A New Class of Chelating N-Heterocyclic Carbene Ligands and Their Complexes with Palladium

Abstract

N-(Mesityl)-oxanilic acid ethyl ester (1, Ar = Mesityl). 2,4,6-Trimethylaniline (20 mL, 142 mmol, 1.0 equiv.) and triethylamine (20 mL, 143 mmol, 1 equiv.) were dissolved in dry THF (150 mL). This solution was cooled to 0 °C, and ethyl chlorooxoactetate (15.3 mL, 142 mmol, 1.0 equiv.) was added slowly via syringe. Precipitation of a white solid occurred immediately upon addition. It was allowed to stir overnight, warming to room temperature. At this point, the solid was filtered off, and the organic layer was washed with 2 M HCl solution (2x100 mL). The aqueous layer was washed with ethyl acetate, and the combined organic layers were washed with brine (100 mL), and dried over MgSO 4. The solvent was then removed under reduced pressure, leaving a yellowish solid. This was recrystallized from hexanes/EtOAc (9:1), producing a white crystalline solid (30.15 g, 128 mmol, 90% yield).

Palladium Complexes of N‐Heterocyclic Carbenes as Catalysts for Cross‐Coupling Reactions—A Synthetic Chemist's Perspective

“…4,5-Dihydroimidazolium salts are especially well suited for the preparation of multiple analogues because the aryl substituents on the two nitrogen atoms can be varied independently when the mixed oxalamide route is employed, something that is difficult to achieve in the case of the unsaturated ligands (Scheme 3). [53][54][55] The shorter routes via symmetrical oxalamides [56] or diazabutadienes, [57] however, only allow the preparation of symmetrical products (Scheme 4).…”

Copolymerization of cyclohexene oxide with CO2catalyzed by tridentate N-heterocyclic carbene titanium(iv) complexes

“…[110,113]. Other complexes have been developed as the bis(imidazolidene-N-methyl-N'-cyclopentenyl-2-alkoxy)zirconium diamide 31 [111] and the bis-ligated phenolate NHC group 4 compounds 32 [112,114,115]. These bidentate complexes showed to be active catalysts for the polymerization of raclactide [110] and the polymerization of ethylene, styrene and propylene [111,112,115].…”

Aus der Sicht des Synthetikers: Palladiumkomplexe N‐heterocyclischer Carbene als Katalysatoren für Kreuzkupplungen

“…4,5-Dihydroimidazoliumsalze sind hervorragend dazu geeignet, viele verschiedene Analoga aufzubauen, da ausgehend von den gemischten Oxalamiden die Arylsubstituenten an den beiden Stickstoffatomen unabhängig voneinander variiert werden können, was bei ungesättigten Liganden nur sehr schwer möglich ist (Schema 3). [53][54][55] Die kürzeren Routen über symmetrische Oxalamide [56] oder Diazabutadiene [57] führen dagegen zwangsläufig zu symmetrischen Produkten (Schema 4).…”