Chiral cyclometalated iridium complexes for asymmetric reduction reactions.

A series of chiral cyclometalated iridium complexes have been synthesised by cyclometalating chiral 2-aryl-oxazoline and imidazoline ligands with [Cp*IrCl2]2. These iridacycles were studied for asymmetric transfer hydrogenation reactions with formic acid as the hydrogen source and were found to display various activities and enantioselectivities, with the most effective ones affording up to 63% ee in the asymmetric reductive amination of ketones and 77% ee in the reduction of pyridinium ions.

Combined experimental and computational investigations of rhodium-catalysed C - H functionalisation of pyrazoles with alkenes.

Detailed experimental and computational studies have been carried out on the oxidative coupling of the alkenes C2 H3 Y (Y=CO2 Me (a), Ph (b), C(O)Me (c)) with 3-aryl-5-R-pyrazoles (R=Me (1 a), Ph (1 b), CF3 (1 c)) using a [Rh(MeCN)3 Cp*][PF6 ]2 /Cu(OAc)2 ⋅H2 O catalyst system. In the reaction of methyl acrylate with 1 a, up to five products (2 aa-6 aa) were formed, including the trans monovinyl product, either complexed within a novel Cu(I) dimer (2 aa) or as the free species (3 aa), and a divinyl species (6 aa); both 3 aa and 6 aa underwent cyclisation by an aza-Michael reaction to give fused heterocycles 4 aa and 5 aa, respectively. With styrene, only trans mono- and divinylation products were observed, whereas with methyl vinyl ketone, a stronger Michael acceptor, only cyclised oxidative coupling products were formed.

A highly active cyclometallated iridium catalyst for the hydrogenation of imines.

A cyclometallated iridium complex containing an imino ligand has been shown to catalyse the hydrogenation of imines. The catalyst is highly active and selective for imino bonds, with a wide variety of imines being hydrogenated in less than 1 hour at a substrate/catalyst (S/C) ratio of 2000 at 20 bar H2 pressure and 75 °C.

Preparation of single enantiomers of chiral at metal bis-cyclometallated iridium complexes.

Reaction of [Ir(C^N)2Cl]2 with chiral bidentate N⁁OH ligands provides complexes [Ir(C^N)2(N^O)] as a 1 : 1 mixture of diastereomers which can be separated by crystallisation. A pure diastereomer can be converted to [Ir(C^N)2(bipy)][CF3CO2] with complete retention of stereochemistry at the metal.

Hydrogenation of imino bonds with half-sandwich metal catalysts.

Imines can be reduced to afford synthetically important amines via a number of means, of which half-sandwich metal complex-effected reduction has gained particular prominence in the past one decade or so. This Feature Article aims to summarise the progress made with such metal catalysts, placing emphasis on our own work. The article covers transfer hydrogenation and hydrogenation, and finishes with a brief account of catalyst immobilisation and mechanistic understanding.

Bifunctional catalysis: direct reductive amination of aliphatic ketones with an iridium-phosphate catalyst.

Chiral amines are one of the ubiquitous functional groups in fine chemical, pharmaceutical and agrochemical products, and the most convenient, economical, and eco-benign synthetic pathway to these amines is direct asymmetric reductive amination (DARA) of prochiral ketones. This paper shows that a wide range of aliphatic ketones can be directly aminated under hydrogenation conditions, affording chiral amines with good to excellent yields and with enantioselectivities up to 96% ee. The catalysis is effected by the cooperative action of a cationic Cp*Ir(III) complex and its phosphate counteranion.

Metal-Brønsted acid cooperative catalysis for asymmetric reductive amination.

Direct reductive amination of a wide range of ketones has been accomplished by the cooperative catalysis of an Ir(III)-diamine complex and a chiral phosphoric acid or its conjugate base.

Chiral counteranion-aided asymmetric hydrogenation of acyclic imines.

When combined with a chiral phosphate counteranion, a chiral diamine-ligated Ir(III) catalyst displayed excellent enantioselectivities in the asymmetric hydrogenation of a wide range of acyclic imines, affording chiral amines in up to 99% ee.