Christophe Michon

Metalated (η6-arene)tricarbonylchromium complexes in organometallic chemistry

Abstract (η 6 -Arene)Cr(CO) 3 complexes differ from their chromium-free analogs in that they undergo a variety of new transformations as a result of the electron withdrawing effect and the stereocontrol effected by the Cr(CO) 3 moiety. Two classes of application are apparent: (1) those that use the Cr(CO) 3 group as an auxiliary which may eventually be removed upon completion of a sequence of reactions; and (2) those that aim at designing novel molecules incorporating a Cr(CO) 3 moiety and possessing specific stereochemical properties. We present a detailed review of the extensive chemistry of metalated (η 6 -arene)Cr(CO) 3 complexes developed in the past 30 years and illustrate the main methods of preparation as well as the most important structural, physical and chemical properties of this family of compounds.

Stereoselective synthesis of configurationally stable functionalized ethano-bridged Tröger bases

New functionalized ethano-bridged Tröger bases are readily prepared using a simple alkylation/rearrangement sequence which affords configurationally stable derivatives as single stereoisomers (de > 96%).

Efficient hydrosilylation of imines using catalysts based on iridium(III) metallacycles

Ir(III) metallacycles were applied as catalysts for the hydrosilylation of various ketimines and aldimines with sodium tetrakis[(3,5-trifluoromethyl)phenyl]borate, NaBArF24, as an additive. By using a slight excess of the organosilane reagent, the reactions proceeded rapidly and efficiently, at low catalyst loadings and at room temperature. Several examples of cationic Ir(III) catalysts could be synthesised, characterized and tested. In situ-generated catalysts proved to be more active as compared to isolated ones and species with non-coordinating BArF24 counterion gave the highest catalytic activities.

Solid-state NMR investigations of the immobilization of a BF4(-) salt of a palladium(II) complex on silica.

The structure of the silica supported palladium(II) complex [Pd(dppp)(S2C-NEt2)]BF4 (abbreviated as [Pd(dppp)(dtc)]BF4, where dppp is Ph2P(CH2)3PPh2) and interactions between the [Pd(dppp)(dtc)]+ cation, the BF4(-) anion, and the silica surface are studied using solid-state NMR spectroscopy. The unsupported, crystalline form of [Pd(dppp)(dtc)]BF4 is also investigated, both by X-ray diffraction and NMR. The structures of the cation and anion are found to be essentially the same in both unsupported and supported complex. The [Pd(dppp)(dtc)]BF4 loading has been determined by quantitative measurements of 11B, 19F, and 31P intensities, whereas the arrangement of anions and cations on the surface of silica has been established by two-dimensional heteronuclear correlation experiments involving 1H, 11B, 13C, 19F, 29Si, and 31P nuclei. At low coverages, the [Pd(dppp)(dtc)]+ cations are located near the BF4(-) anions, which in turn are immobilized directly on the surface near the Q4 sites. At higher loadings, which in this study corresponded to 0.06-0.15 mmol/g, the complexes stack on top of each other, despite the fact that the directly adsorbed molecules take up less than 10% of the silica surface. The relevance of these findings to heterogeneous catalysis is discussed.

NMR enantiodifferentiation of quaternary ammonium salts of Tröger base

Hexacoordinated phosphorus BINPHAT anion 1 is an efficient NMR chiral solvating agent for quaternary ammonium cations (quats) derived from Tröger base leading to large separations of the proton signals of the enantiomers and even in polar solvent media such as CD(3)CN (Delta Delta delta up to 0.12 ppm). Quite surprisingly, this efficacy in the NMR split efficiency is not translated into a supramolecular stereocontrol (Pfeiffer effect) of the cation configuration by the anion.

Asymmetric Intramolecular Hydroamination of Alkenes in Mild and Wet Conditions—Structure and Reactivity of Cationic Binuclear Gold(I) Catalysts

A selected diphosphine binuclear gold(I) chloride complex was combined with a silver salt to catalyze efficiently, for the first time, the asymmetric intramolecular hydroamination of alkenes with high conversions and enantioselectivities, in mild conditions and in presence of water. Both enantiomers of the products could be obtained by controlling the molecular ion‐pairs through the solvent polarity. The gold(I) cationic active species was characterized unambiguously at the solid state by X‐ray analysis and in solution by DOSY 1H NMR experiments. No contribution of silver chloride was observed on the bonding mode of the catalyst.

Synthesis of (+)2,3-PinDione, a versatile chiral 1,2-diketone

Abstract The preparation of a 1,2-diketone derived from (−)-β-pinene, i.e. (+)-2,3-PinDione, is reported. The latter is shown to be a useful substrate for the Hinzberg-type syntheses of chiral quinoxaline ((−)-6,7-dimethyl-PinQuinox) and pyrazine ((+)-2,3-diphenylPinazine) derivatives as well in the preparation of the bis-hydrazone ((+)- N ′, N ′-diphenyl-2,3-Pinazone).

Pentamethylcyclopentadienyl Iridium(III) Metallacycles Applied to Homogeneous Catalysis for Fine Chemical Synthesis

Pentamethylcyclopentadienyl cyclometallated complexes have been used to catalyse a variety of organic transformations over the last decades. However, the huge potential of pentamethylcyclopentadienyl iridacycles has only been truly recognised in recent years. Indeed, an upsurge of reports on such new half‐sandwich iridium(III) metallacycles has been observed. The application of these organometallic complexes in various homogeneous catalysed organic reactions has led to the development of environmentally and economically beneficial routes towards important and highly functionalised fine chemicals. Studied reactions include hydrogenation, amine alkylation, dehydrogenation, oxidation and hydrofunctionalisation reactions as well as dynamic kinetic resolutions (DKR). This minireview focusses specifically on the recent applications of half‐sandwich iridium(III) metallacycles in such processes.

Selective Hydrosilylation of Esters to Aldehydes Catalysed by Iridium(III) Metallacycles through Trapping of Transient Silyl Cations.

The combination of an iridium(III) metallacycle and 1,3,5-trimethoxybenzene catalyses rapidly and selectively the reduction of esters to aldehydes at room temperature with high yields through hydrosilylation followed by hydrolysis. The ester reduction involves the trapping of transient silyl cations by the 1,3,5-trimethoxybenzene co-catalyst, supposedly by formation of an arenium intermediate whose role was addressed by DFT calculations.

Efficient and Selective Hydrosilylation of Secondary and Tertiary Amides Catalyzed by an Iridium(III) Metallacycle: Development and Mechanistic Investigation

Readily accessible cationic IrIII metallacycles catalyze efficiently the chemoselective hydrosilylation of tertiary and secondary amides to amines. The catalyst described herein operates at low loadings using inexpensive 1,1,3,3‐tetramethyldisiloxane and allows fast reactions with high yields, selectivities, and turnover numbers. A transient iminium intermediate has been observed for the first time by using mass spectrometry, and the activation of the catalyst and the silane reagent have been studied by using DFT calculations. These fundamental insights support the present and future improvements of IrIII metallacycles through proper ligand modifications and enable further broad applications of catalysts based on metallacycles.