Acenaphthene-Based N-Heterocyclic Carbene Metal Complexes: Synthesis and Application in Catalysis

Abstract

N-Heterocyclic carbene (NHC) ligands have become a privileged structural motif in modern homogenous and heterogeneous catalysis. The last two decades have brought a plethora of structurally and electronically diversified carbene ligands, enabling the development of cutting-edge transformations, especially in the area of carbon-carbon bond formation. Although most of these were accomplished with common imidazolylidene and imidazolinylidene ligands, the most challenging ones were only accessible with the acenaphthylene-derived N-heterocyclic carbene ligands bearing a π-extended system. Their superior σ-donor capabilities with simultaneous ease of modification of the rigid backbone enhance the catalytic activity and stability of their transition metal complexes, which makes BIAN-NHC (BIAN—bis(imino)acenaphthene) ligands an attractive tool for the development of challenging reactions. The present review summarizes synthetic efforts towards BIAN-NHC metal complexes bearing acenaphthylene subunits and their applications in modern catalysis, with special emphasis put on recently developed enantioselective processes.

Synthesis of Carbene‐Metal‐Amido (CMA) Complexes and Their Use as Precatalysts for the Activator‐Free, Gold‐Catalyzed Addition of Carboxylic Acids to Alkynes

“…Complexes bearing these ligands with metals such as Au, Cu, Pd, Rh and Pt have been reported as potent catalysts in various reactions such as crosscoupling, sulfonation, alkene metathesis, among others. [28] Therefore, the straightforward synthesis of novel metal complexes bearing BIAN-NHC ligands, and investigations of their catalytic activity are needed investigations to gauge their true potential and uses in catalysis. The flexible steric bulk of BIAN-NHC ligands and their enhanced ability to protect the metal center while modulating its catalytic properties, are features which need to be further explored in gold catalysis.…”

“…The ease of scaffold modification and the metal center protection by these ligands have led to improvements in some catalytic processes. Complexes bearing these ligands with metals such as Au, Cu, Pd, Rh and Pt have been reported as potent catalysts in various reactions such as cross‐coupling, sulfonation, alkene metathesis, among others [28] . Therefore, the straightforward synthesis of novel metal complexes bearing BIAN‐NHC ligands, and investigations of their catalytic activity are needed investigations to gauge their true potential and uses in catalysis.…”

Diaza-1,3-butadienes as Useful Intermediate in Heterocycles Synthesis

“…These compounds are important because they are the precursors of N -heterocyclic carbenes (NHCs), which are generated by deprotonation [ 106 ]. The NHCs are interesting structures due to the catalytic activity of their metal complexes and are widely used in organic synthesis [ 107 , 108 ].…”

“…N -Heterocyclic carbene precursors with an acenaphthylene moiety 239 have a perfect combination of electronic and steric characteristics, making them particularly helpful in organic synthesis and have found broad use in the synthesis of different metal complexes. There are several reports on the synthesis of these precursors 239 [ 108 ], but in general, the initial step is the synthesis of the diimine 240 , which is accomplished by condensation of the aniline derivatives with acenaphthoquinone ( 241 ) dissolved in AcOH, in the presence of a Lewis acid, usually ZnCl 2 . Finally, the cyclization reaction, usually performed with chloromethyl methyl ether (MOMCl) or ethyl chloromethyl ether (EOMCl), affords the imidazolium salts 239 with excellent yields ( Scheme 56 ).…”

NHC Polymeric Particles Obtained by Self-Assembly and Click Approach of Calix[4]Arene Amphiphiles as Support for Catalytically Active Pd Nanoclusters

“…During the last few decades, N-heterocyclic carbene (NHC) ligands have attracted considerable attention, owing to their high stability and outstanding applications in homogeneous catalysis [1][2][3]. The advantage of this class of ligands is the ease of their generation through deprotonation of appropriate precursors (most often, imidazolium salts are used) and easily regulated steric/electron donor properties of the ligand by substituents on the heterocyclic precursor core [4][5][6][7]. Amongst N-heterocyclic carbenes, polytopic ligands featuring more than one NHC unit are of high demand, as they impact the stability of the final metal complex, owing to their chelating abilities [8,9].…”