International audienceA library of organometallic compounds derived from primary and secondary amines cyclometalated by ruthenium(II), rhodium(III) and iridi- um(III) was tested in the asymmetric transfer hydrogenation of a number of ketones and imines. All compounds displayed high catalytic activity for the reduction of ketones under mild conditions. The most enantioselective catalysts were based on secondary amines containing two asymmetric carbon atoms bound to the nitrogen atom. For the reduction of aryl alkyl ketones [Ar(C[DOUBLE BOND]O)R where R=CH3 or CH2R′] the cyclometalated ruthenium and rhodium derivatives of the (2R,5R)-2,5-diphenylpyrrolidine ligand displayed the best results with respect to activity and selectivity (ees up to 97%). However, for the reduction of aryl tert-alkyl ketones [Ar(C[DOUBLE BOND]O)R′′ in which R′′ is a tertiary alkyl group] the best catalyst was a ruthenium compound derived from bis[(R)-1-phenylethyl]amine, allowing the reduction of isobutyrophenone and cyclohexyl phenyl ketone which were both reduced with high enantioselectivities (ees up to 98%). This shows that the cyclometalated compounds have a high substrate specificity. In addition, acyclic and cyclic imines were reduced with good selectivities by both rhodium(III) and iridium(III) metalacycles built up with (2R,5R)-2,5-diphenylpyrrolidine

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The copper‐catalyzed asymmetric hydrosilylation of ketones is an efficient method for the synthesis of chiral enantiopure secondary alcohols. Herein, we present a detailed computational study (DFT/B3LYP) of the copper(I)‐catalyzed reaction. In particular, the two transition states involved in the catalytic cycle have been determined. The insertion of the ketone into the Cu–H bond was found to have a lower activation barrier than the reaction of the copper alkoxy intermediate with the silane, which regenerates Cu–H along with the silyl ether product. Our findings also reveal the importance of the copper hydride dimer in controlling the reactivity toward the ketone. The conclusions are supported by experimental mechanistic investigations including kinetic studies, kinetic isotope effect, and isotope labeling measurements.

The reaction of (2R,5R)-2,5-diphenylpyrrolidine (L 1 ) with [(η 5 -C 5 Me 5 )MCl 2 ] 2 (M = Rh, Ir) in acetonitrile in the presence of KPF 6 and NaOH at room temperature led to mixtures of two products, [(η 5 -C 5 Me 5 )M(N-C)(NCMe)](PF 6 ) (N-C designating a cyclometalated ligand). These products were cyclometalated complexes of pyrrolidine (

Cyclometalation of (2R,5R)-2,5-diphenylpyrrolidine (1) with [(η5-Cp*)MCl2]2 using NaOAc in CH2Cl2 at room temperature, followed by cationization with KPF6 in CH3CN, cleanly yielded the cationic cyclometalated amines 2a,b (a, M = Ir; b, M = Rh). This constituted an improvement with regard to another cyclometalation pathway, which had led to unwanted oxidation of the ligand to an imine. Compounds 2a,b were characterized by elemental analysis and X-ray diffraction of single crystals; the latter gave evidence of an R configuration of the metal center, and a λ envelope conformation of the five-membered metallacycle. Successful application of the NaOAc/CH2Cl2 methodology to the cycloiridation and cyclorhodation of the imidazolines 3–5 led to the neutral half-sandwich chloro complexes 6–8, which were completely characterized, with yields ranging from 44% to 82%. In these complexes, the labile NH proton was localized in a γ position with regard to the metal. From the enantiopure chiral ligands 4 and 5, both diastereoisomers of the four compounds 7a,b and 8a,b were identified in solution by NMR; they were in equilibrium in solution. Complexes 6b, (S M)-7a,b, and (R M)-8a,b were characterized by radiocrystallography, which showed that the metallacycles were planar. Complexes 6–8 were tested as catalysts for the reduction of acetophenone and imines by hydrogen transfer.

The synthesis of a new Ru(II) complex is reported. Its absorption spectrum when interacting with DNA in water was calculated at the hybrid quantum mechanics molecular mechanics level of theory and compared with experimental data. The vertical transitions were computed using time-dependent density functional theory in the linear response approximation. The complex and its environment were treated at the quantum mechanical and molecular mechanical levels, respectively. The effects of the environment were investigated in detail and conveniently classified into electrostatic and polarization effects. The latter were modeled using the computationally inexpensive "electronic response of the surroundings" method. It was found that the main features of the experimental spectrum are nicely reproduced by the theoretical calculations. Moreover, analysis of the most intense transitions utilizing the natural transition orbital formalism revealed important insights into their nature and their potential role in the irreversible oxidation of DNA, a phenomenon that could be relevant in the field of cancer therapy.

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