New Mechanism for the Intermolecular Hydroamination of Alkynes: Catalysis by Dinuclear Ruthenium Complexes with a Rigid Dicyclopentadienyl Ligand

Aminocarbyne-Alkyne Coupling in Diruthenium Complexes: Exploring the Anticancer Potential of the Resulting Vinyliminium Complexes and Comparison with Diiron Homologues

New diruthenium complexes based on the scaffold Ru2Cp2(CO)2 (Cp = η5-C5H5) and containing a bridging vinyliminium ligand, [2a-d]CF3SO3, were synthesized through regioselective coupling of alkynes with an aminocarbyne precursor (85-90% yields). The reaction involving phenylacetylene proceeded with the formation of a diruthenacyclobutene byproduct, [4]CF3SO3 (10% yield). Complexes [2a-d]+ undergo partial alkyne extrusion in contact with alumina or CDCl3. All products were characterized by elemental analysis, infrared and multinuclear NMR spectroscopy, and single crystal X-ray diffraction in two cases. Complexes [2a-d]+ revealed an outstanding stability in DMEM cell culture medium at 37 °C (<1% degradation over 72 h). These complexes exhibited cytotoxicity in human colon colorectal adenocarcinoma HT-29 cells in the low micromolar range, with lower IC50 values than those obtained with the homologous diiron complexes previously reported. Evaluation of ROS (reactive oxygen species) production and O2 consumption rate (OCR) highlighted the higher potential of Ru2 complexes, compared to the Fe2 counterparts, to impact mitochondrial activity, with the heterometallic Ru2-ferrocenyl complex [2d]+ showing the best performance.

Catalysis and regioselectivity in hydrofunctionalization reactions of unsaturated carbon bonds. Part II. Hydroamination

This review continues consideration of the regioselectivity problem in the catalyzed hydrofunctionalization of unsaturated organic compounds and addresses hydroamination of unsaturated hydrocarbons. Particular parts of the review deal with reactions of alkenes, alkynes, allenes and dienes. It is shown that the selectivity of hydroamination depends on the natures of the reactants and the catalyst. Conditions of the reactions are described; in some cases, reaction mechanisms are discussed. Reactions for which divergent regioselectivity is possible are noted.

The bibliography includes 249 references.

Dedicated to the memory of V.V.Markovnikov.

General zinc-catalyzed intermolecular hydroamination of terminal alkynes

Catalytic hydroaminations are one of the most sustainable C-N bond-forming processes as a result of 100% atom economy and the availability of substrates. Here, it is shown that the intermolecular hydroamination of terminal alkynes with anilines proceeds smoothly in the presence of catalytic amounts of zinc triflate, an easily available and inexpensive zinc salt. Amination and subsequent reduction with NaBH3CN gives a variety of secondary and tertiary amines in up to 99% yield and with over 99% Markovnikov regioselectivity. Moreover, difficult functional groups such as nitro and cyano substituents are tolerated by the homogeneous catalyst.

The catalytic hydroamination of alkynes

Catalytic additions of ammonia or primary and secondary amines to non-activated alkenes and alkynes are called hydroaminations. These reactions of fundamental simplicity represent the most atom efficient processes for the formation of amines, enamines and imines, which are important bulk and fine chemicals or building blocks in organic synthesis. Consequently, the development of corresponding hydroamination reactions has received much attention and great progress has been achieved in the case of catalytic hydroaminations of alkynes over the past four years. To illustrate this progress, this tutorial review will mostly focus on recent developments in the field of intermolecular hydroamination of alkynes that appeared in the literature between the end of 2002 and October 31, 2006.

Highly Selective Hydrogenation of Carbon-Carbon Multiple Bonds Catalyzed by the Cation [(C6Me6)2Ru2(PPh2)H2]+: Molecular Structure of [(C6Me6)2Ru2(PPh2)(CHCHPh)H]+, a Possible Intermediate in the Case of Phenylacetylene Hydrogenation

The dinuclear cation [(C(6)Me(6))(2)Ru(2)(PPh(2))H(2)](+) (1) has been studied as the catalyst for the hydrogenation of carbon-carbon double and triple bonds. In particular, [1][BF(4)] turned out to be a highly selective hydrogenation catalyst for olefin functions in molecules also containing reducible carbonyl functions, such as acrolein, carvone, and methyljasmonate. The hypothesis of molecular catalysis by dinuclear ruthenium complexes is supported by catalyst-poisoning experiments, the absence of an induction period in the kinetics of cyclohexene hydrogenation, and the isolation and single-crystal X-ray structure analysis of the tetrafluoroborate salt of the cation [(C(6)Me(6))(2)Ru(2)(PPh(2))(CHCHPh)H](+) (2), which can be considered as an intermediate in the case of phenylacetylene hydrogenation. On the basis of these findings, a catalytic cycle is proposed which implies that substrate hydrogenation takes place at the intact diruthenium backbone, with the two ruthenium atoms acting cooperatively in the hydrogen-transfer process.