O- and S-heterocyclic carbenes (OHCs, SHCs) are stronger π acceptors than N-heterocyclic carbenes (NHCs) and they lack substituents at the heteroatoms (pictured below). This results in different electronic and steric characteristics that make OHCs and SHCs interesting ligands for coordination chemistry.
To enhance the general accessibility of OHCs and SHCs, Koop Lammertsma, Vrije Universiteit Amsterdam, The Netherlands, and colleagues have developed convenient syntheses of new OHC and SHC transition-metal complexes. The team compared the benzannulated derivatives of OHC and SHC to the NMe-substituted NHC derivatives (pictured above). Their iridium(I), iridium(III), and coinage-metal(I) (Cu, Ag, Au) complexes have been accessed in good yields. The team used:
Molecular structures and detailed bonding analyses of these complexes showed their strong π-accepting properties. These can be beneficial in synthetic and catalytic applications. According to the researchers, the applications of the new benzannulated heterocyclic carbenes OHC and SHC are a target for further study.
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