The field of asymmetric catalysis is rapidly developing, and the electron-rich chiral NHC ligands play a key role as stereodirecting ancillary ligands in enantioselective transition-metal catalysis. Several well-defined novel palladium(II), iridium(I)/(III), and rhodium(I)/(III) complexes possessing easily accessible tailor-made chiral NHC ligands for asymmetric catalysis have been described.

The field of asymmetric catalysis is rapidly developing and the chiral ligands play a key role in enantioselective transition-metal catalysis. The electron-rich chiral N-heterocyclic carbenes (NHCs) have established themselves as a popular class of stereodirecting ancillary ligands to catalyze enantioselective organic transformations in more efficient ways. Several novel transition-metal complexes in combination with tailored ligand design have emerged during last few decades in asymmetric catalysis. The tailor-made NHCs can easily be accessed due to the modular synthesis of their parent azolium salt precursors. Their donor capability and the molecular shape can easily be tuned by changing substituent at N-atom or by changing the cyclic backbone framework. This review article aims to describe the recent advances in this rapidly evolving research area of enantioselective catalysis using well-defined transition-metal complexes possessing chiral NHC donor ligands.

Solution and solid-state properties of novel dinuclear and trinuclear Ag(I) and Au(I) complexes based on a di-(N-heterocyclic carbene) ligand are studied.

Abstract

The coordinating properties of the bis(1,4-dimethyl-1,2,4-triazol-5-ylidene) ligand (abbreviated as bitz) towards silver(I) and gold(I) centres have been explored. The bitz behaves as bridging ligand giving both dinuclear [M₂(bitz)₂](PF₆)₂ and trinuclear [M₃(bitz)₃](PF₆)₃ species, whose formation has been supported by X-ray diffraction analysis, NMR spectroscopy and mass spectrometry evidences. The dinuclear and trinuclear gold(I) complexes present very similar luminescence properties, emitting in the blue region, at ~450 nm, when excited at 350 nm. Selected experimental aspects dealing with the synthesis of the dinuclear and trinuclear species, as well as with the absorption properties of the gold(I) complexes, have been investigated also through relativistic DFT calculations.