Iridium(I) complexes with bidentate NHC ligands as catalysts for dehydrogenative directed C-H silylation.

A series of (NHC)(cod)Ir(I) complexes bearing NHC-carboxylate ligands were efficiently synthesized and fully characterized. Their solid-state structures confirmed the bidentate coordination mode of these LX-type NHC ligands. These unprecedented iridium(I) complexes demonstrated efficient catalytic activities in dehydrogenative directed C-H silylation of arenes, and allowed for excellent ortho-selectivity control with aromatic silylating agents.

Ruthenium-NHC complex-catalyzed P(III)-directed C-H borylation of arylphosphines.

(NHC)(arene)Ru(II) complexes with bidentate LX-type NHC-carboxylate ligands were efficiently synthesized and fully characterized including solid-state structures. The strong coordination of the NHC carboxylate ligand and the labile character of the arene ligand are highlighted. These unprecedented Ru(II) complexes demonstrated efficient catalytic activities in the selective P(III)-directed C-H borylation at the ortho position of arylphosphines, representing the first report of the use of a ruthenium-NHC based catalyst in C-H borylation.

Chiral N-Heterocyclic Carbene Ligands Enable Asymmetric C-H Bond Functionalization.

The asymmetric functionalization of C-H bond is a particularly valuable approach for the production of enantioenriched chiral organic compounds. Chiral N-heterocyclic carbene (NHC) ligands have become ubiquitous in enantioselective transition-metal catalysis. Conversely, the use of chiral NHC ligands in metal-catalyzed asymmetric C-H bond functionalization is still at an early stage. This minireview highlights all the developments and the new advances in this rapidly evolving research area.

Visible Light Induced Rhodium(I)-Catalyzed C-H Borylation.

An efficient visible light induced rhodium(I)-catalyzed regioselective borylation of aromatic C-H bonds is reported. The photocatalytic system is based on a single NHC-RhI complex capable of both harvesting visible light and enabling the bond breaking/forming at room temperature. The chelating nature of the NHC-carboxylate ligand was critical to ensure the stability of the RhI complex and to provide excellent photocatalytic activities. Experimental mechanistic studies evidenced a photooxidative ortho C-H bond addition upon irradiation with blue LEDs, leading to a cyclometalated RhIII -hydride intermediate.

Directed ortho C-H borylation catalyzed using Cp*Rh(iii)-NHC complexes.

Cp*Rh(NHC) complexes with bulky chiral bidentate NHC-carboxylate ligands were efficiently synthesized and fully characterized including solid-state structures. These unprecedented rhodium(iii) complexes demonstrated high selectivity in pyridine-directed ortho-C-H borylation of arenes under mild conditions.

Readily Accessible Unsymmetrical Unsaturated 2,6-Diisopropylphenyl N-Heterocyclic Carbene Ligands. Applications in Enantioselective Catalysis.

A new multicomponent procedure was applied to the synthesis of (a)chiral bulky unsymmetrical unsaturated 2,6-diisopropylphenyl N-heterocyclic carbene (NHC) precursors with excellent selectivity (up to 95%) and good yields. This approach offers access to new chiral NHC ligands, which have found successful applications in both copper-catalyzed asymmetric allylic alkylation and copper-catalyzed asymmetric borylation.