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.

Expedient synthesis of conjugated triynes via alkyne metathesis.

The first synthesis of conjugated triynes by molybdenum-catalysed alkyne metathesis is reported. Strategic to the success of this approach is the utilization of sterically-hindered diynes that allowed for the site-selective alkyne metathesis to produce the desired conjugated triyne products. The steric hindrance of the alkyne moiety was found to be crucial in preventing the formation of diyne byproducts. This novel synthetic strategy was amenable to self- and cross-metathesis providing straightforward access to the corresponding symmetrical and dissymmetrical triynes with high selectivity.

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.

A kinetic resolution strategy for the synthesis of chiral octahedral NHC-iridium(iii) catalysts.

The transmetalation reaction of a chiral-bidentate NHC-silver complex to racemic [Ir(µ-Cl)(ppy)2]2 operates with kinetic resolution leading to chiral octahedral NHC-iridium(iii) complexes and enantio-enriched bis-cyclometalated iridium(iii) complexes. The iridium(iii) complexes demonstrated efficient catalytic activities in intermolecular [2+2] photocycloaddition reactions and in asymmetric Friedel-Crafts alkylations, respectively.