Synthesis, reactivity, crystal structures and catalytic activity of new chelating bisimidazolium-carbene complexes of Rh

A series of new bridging, chelating and pincer N-heterocyclic carbenes of RhI and RhIII have been obtained under mild conditions. The compounds have been fully characterised and their crystal structures determined. The chelate-pincer coordination of the ligands means that the stability of these compounds is significantly greater than other carbene complexes of Rh. The compounds have been tested in catalytic reactions such as hydrogen transfer from alcohols to ketones, and hydrosilylation of terminal olefins and alkynes; they show a high activity for both processes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Coordination versatility of pyridine-functionalized N-heterocyclic carbenes: a detailed study of the different activation procedures. Characterization of new Rh and Ir compounds and study of their catalytic activity.

Three different reaction procedures for the coordination of N-n-butyl-N'-(2-pyridylmethyl)imidazolium salt have produced new N-heterocyclic complexes of Rh and Ir. The direct reaction of the imidazolium salt with [IrCl(cod)](2) provides a NHC-Ir(III)-H complex, while transmetalation from a silver-NHC complex and deprotonation with NEt(3) give new NHC complexes of M(I) and M(III) when reacting with [MCl(cod)](2) or [MCl(coe)(2)](2) (M = Rh, Ir). The crystal structures of the biscarbene Rh(III) and Ir(III) complexes are described. The catalytic properties of the compounds obtained have been tested in the hydrosilylation of acetylenes, the cyclization of acetylenic carboxylic acids, and hydrog…

A New Rhodium(III) Complex with a Tripodal Bis(imidazolylidene) Ligand. Synthesis and Catalytic Properties

A new bis(imidazolylidene) tripodal ligand has been obtained by a simple method. The coordination of this ligand to Rh provides the first Rh(III) complex with a bis(carbene) ligand in a tripodal coordination, and its catalytic properties toward hydrogen transfer have been examined.

A new pyridine-bis-N-heterocyclic carbene ligand and its coordination to Rh: Synthesis and characterization

Abstract The new bis(imidazolylidene) tripodal ligand precursor (2-pyridine)bis(3-methylimidazolium-1-yl)methane diiodide, [H2PYBIMMe]I2, has been obtained by a simple method. The molecular structure of this new ligand precursor has been determined by means of X-ray diffraction. The coordination of this ligand to Rh, provides a Rh(III) complex with very low solubility in most solvents, which we attributed to the polymeric nature of the species. Solution of this polymer in DMSO provided a biscarbene Rh(III) complex in which the pyridine fragment remained unbound.

An N-heterocyclic carbene/iridium hydride complex from the oxidative addition of a ferrocenyl-bisimidazolium salt: implications for synthesis.

Synthesis and Reactivity of New Complexes of Rhodium and Iridium with Bis(dichloroimidazolylidene) Ligands. Electronic and Catalytic Implications of the Introduction of the Chloro Substituents in the NHC Rings

The preparation of a new bis(dichloroimidazolylidene) ligand has provided chelate-N-heterocyclic complexes of Rh(I) and Ir(I), which have been fully characterized. The crystal structures of three of the new complexes are described. The study of the electronic properties of the new ligands was made on the basis of the ν(CO) stretching frequencies of the carbonyl derivatives, showing that the chloroimidazolylidene ligand is significantly less σ-donating than the related nonchlorinated analogue. This electronic modification of the ligand has important implications for the catalytic properties of the compounds obtained, as observed from enhanced activity shown in catalytic hydrosilylation of te…

Carbene complexes of rhodium and iridium from tripodal N-heterocyclic carbene ligands: synthesis and catalytic properties.

Two tripodal trisimidazolium ligand precursors have been tested in the synthesis of new N-heterocyclic carbene rhodium and iridium complexes. [Tris(3-methylbenzimidazolium-1-yl)]methane sulfate gave products with coordination of the decomposed precursor. [1,1,1-Tris(3-butylimidazolium-1-yl)methyl]ethane trichloride (TIMEH(3)(Bu)) coordinated to the metal in a chelate and bridged-chelate form, depending on the reaction conditions. The crystal structures of two of the products are described. The compounds resulting from the coordination with TIME(Bu) were tested in the catalytic hydrosilylation of terminal alkynes.

Crystalline-Size Dependence of Dual Emission Peak on Hybrid Organic Lead-Iodide Perovskite Films at Low Temperatures

In this work, we have investigated the crystalline-size dependence of optical absorption and photoluminescence emission of CH3NH3PbI3 films, which is necessary to identify the potential practical applications of the gadgets based on perovskite films. This study was carried out at low temperatures to minimize the extra complexity induced by thermal effects. The purpose was to clarify the origin of the dual emission peak previously reported in the literature. We found that the grain size is responsible for the appearance or disappearance of this dual emission on CH3NH3PbI3 at low temperatures, whereas we have inferred that the thickness of the perovskite layer is a much more important factor …

Electrospray Ionization Mass Spectrometry Studies on the Mechanism of Hydrosilylation of Terminal Alkynes Using an N-Heterocyclic Carbene Complex of Iridium, Allow Detection/Characterization of All Reaction Intermediates

A new pyridine-4,5-dichloroimidazol-2-ylidene complex of Ir(I) has been obtained, and its catalytic activity toward hydrosilylation of phenylacetylene and 4-aminophenylacetylene has been studied. T...

Synthesis and Reactivity of New Chelate-N-Heterocyclic Biscarbene Complexes of Ruthenium

The carbene-ligand precursors methylenebis(N-alkylimidazolium) iodide (alkyl = methyl, neo-pentyl) and ethylenebis(N-methylimidazolium) chloride have been used in the preparation of several new Ru(II)-p-cymene complexes where the ligand behaves as mono- and bidentate. The molecular structures of the two biscarbene-complexes are reported. From the data reported, we can conclude that steric reasons (mainly the bisimidazolium linkers, methylene/ethylene) are the main factors determining both reactivity and synthetic difficulties of the products reported.