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.
Highlights
N-Heterocyclic carbene ligands (NHC), since first being isolated in a stable form by Arduengo [1] in 1991, have revolutionized the field of modern metal catalysis [2,3,4,5,6,7,8,9], as well as organocatalysis [10,11,12,13,14]
Much research is limited to the classical imidazolium or imidazolinium ligands, further structural tuning of the imidazole core has brought a breakthrough for catalysis [15,16]
Polyfunctional carbene ligands are attractive due to their potential for Polyfunctional carbene ligands are attractive due to their potential for use use in catalysis, as they lead to metal complexes [48] often exhibiting higher catalytic in catalysis, as they lead to metal complexes [48] often exhibiting higher catalytic activity activity compared to their monofunctional analogues [49]
Summary
N-Heterocyclic carbene ligands (NHC), since first being isolated in a stable form by Arduengo [1] in 1991, have revolutionized the field of modern metal catalysis [2,3,4,5,6,7,8,9], as well as organocatalysis [10,11,12,13,14]. Much research is limited to the classical imidazolium or imidazolinium ligands, further structural tuning of the imidazole core has brought a breakthrough for catalysis [15,16] In this respect, NHCBIAN-type ligands [BIAN–bis(imino)acenaphthene] bearing a π-extended system have found tremendous applications in the area of C-C or C-heteroatom bond formation, as well as in enantioselective catalysis in the last decade. The structural electrochemical of the imidazole core has brought a breakthrough for catalysis [15,16] In this respect, studies confirmed that the redox potential is slightly lower The electrochemical studies confirmed that the redox potential is slightly lower
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