A leap forward in iridium-NHC catalysis: new horizons and mechanistic insights.

This review summarises the most recent advances in Ir-NHC catalysis while revisiting all the classical reactions in which this type of catalyst has proved to be active. The influence of the ligand system and, in particular, the impact of the NHC ligand on the activity and selectivity of the reaction have been analysed, accompanied by an examination of the great variety of catalytic cycles hitherto reported. The reaction mechanisms so far proposed are described and commented on for each individual process.

A well-defined NHC-Ir(iii) catalyst for the silylation of aromatic C-H bonds: substrate survey and mechanistic insights.

A well-defined NHC-Ir(iii) catalyst, [Ir(H)(IPr)(py)][BF] (IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene), that provides access to a wide range of aryl- and heteroaryl-silanes by intermolecular dehydrogenative C-H bond silylation has been prepared and fully characterized. The directed and non-directed functionalisation of C-H bonds has been accomplished successfully using an arene as the limiting reagent and a variety of hydrosilanes in excess, including EtSiH, PhMeSiH, PhMeSiH, PhSiH and (EtO)SiH. Examples that show unexpected selectivity patterns that stem from the presence of aromatic substituents in hydrosilanes are also presented.

Efficient preparation of carbamates by Rh-catalysed oxidative carbonylation: unveiling the role of the oxidant.

The synthesis of a wide variety of carbamates from amines, alcohols and carbon monoxide has been achieved by means of a Rh-catalysed oxidative carbonylation reaction that uses Oxone as a stoichiometric oxidant. In-depth studies on the reaction mechanism shed light on the intimate role of Oxone in the catalytic cycle.

N-Heterocyclic olefins as ancillary ligands in catalysis: a study of their behaviour in transfer hydrogenation reactions.

The Ir(i) complexes [Ir(cod)(κP,C,P'-NHO(PPh2))]PF6 and [IrCl(cod)(κC-NHO(OMe))] (cod = 1,5-cyclooctadiene, NHO(PPh2) = 1,3-bis(2-(diphenylphosphanyl)ethyl)-2-methyleneimidazoline) and NHO(OMe) = 1,3-bis(2-(methoxyethyl)-2-methyleneimidazoline), both featuring an N-heterocyclic olefin ligand (NHO), have been tested in the transfer hydrogenation reaction; this representing the first example of the use of NHOs as ancillary ligands in catalysis. The pre-catalyst [Ir(cod)(κP,C,P'-NHO(PPh2))]PF6 has shown excellent activities in the transfer hydrogenation of aldehydes, ketones and imines using (i)PrOH as a hydrogen source, while [IrCl(cod)(κC-NHO(OMe))] decomposes throughout the reaction to give low yields of the hydrogenated product. Addition of one or two equivalents of a phosphine ligand to the latter avoids catalyst decomposition and significantly improves the reaction yields.

Efficient Rhodium-Catalyzed Multicomponent Reaction for the Synthesis of Novel Propargylamines.

[{Rh(μ-Cl)(H)2 (IPr)}2 ] (IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazole-2-ylidene) was found to be an efficient catalyst for the synthesis of novel propargylamines by a one-pot three-component reaction between primary arylamines, aliphatic aldehydes, and triisopropylsilylacetylene. This methodology offers an efficient synthetic pathway for the preparation of secondary propargylamines derived from aliphatic aldehydes. The reactivity of [{Rh(μ-Cl)(H)2 (IPr)}2 ] with amines and aldehydes was studied, leading to the identification of complexes [RhCl(CO)IPr(MesNH2 )] (MesNH2 = 2,4,6-trimethylaniline) and [RhCl(CO)2 IPr].