Concurrent tandem catalysis

In this tutorial review recent mechanistic studies on transition metal-catalyzed hydrogen transfer reactions are discussed. A common feature of these reactions is that they involve metal hydrides, which may be monohydrides or dihydrides. An important question is whether the substrate coordinates to the metal (inner-sphere hydrogen transfer) or if there is a direct concerted transfer of hydrogen from the metal to substrate (outer-sphere hydrogen transfer). Both experimental and theoretical studies are reviewed.

Mechanistic aspects of transition metal-catalyzed hydrogen transfer reactions.

Alcohols can be temporarily converted into carbonyl compounds by the metal-catalysed removal of hydrogen. The carbonyl compounds are reactive in a wider range of transformations than the precursor alcohols and can react in situ to give imines, alkenes, and α-functionalised carbonyl compounds. The metal catalyst, which had borrowed the hydrogen, then returns it to the transformed carbonyl compound, leading to an overall process in which alcohols can be converted into amines, compounds containing CC bonds and β-functionalised alcohols.

Borrowing hydrogen in the activation of alcohols

Treatment of a stoichiometric hydroxyapatite (HAP), Ca10(PO4)6(OH)2, with PdCl2(PhCN)2 gives a new type of palladium-grafted hydroxyapatite. Analysis by means of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX), IR, and Pd K-edge X-ray absorption fine structure (XAFS) proves that a monomeric PdCl2 species is chemisorbed on the HAP surface, which is readily transformed into Pd nanoclusters with a narrow size distribution in the presence of alcohol. Nanoclustered Pd0 species can effectively promote the alcohol oxidation under an atmospheric O2 pressure, giving a remarkably high turnover number (TON) of up to 236,000 with an excellent turnover frequency (TOF) of approximately 9800 h(-1) for a 250-mmol-scale oxidation of 1-phenylethanol under solvent-free conditions. In addition to advantages such as a simple workup procedure and the ability to recycle the catalyst, the present Pd catalyst does not require additives to complete the catalytic cycle. The diameters of the generated Pd nanoclusters can be controlled upon acting on the alcohol substrates used. Oxidation of alcohols is proposed to occur primarily on low-coordination sites within a regular arrangement of the Pd nanocluster by performing calculations on the palladium crystallites.

Hydroxyapatite-Supported Palladium Nanoclusters: A Highly Active Heterogeneous Catalyst for Selective Oxidation of Alcohols by Use of Molecular Oxygen

Intellectually, the advantages that flow from the availability of single-site heterogeneous catalysts (SSHC) are many. They facilitate the determination of the kinetics and mechanism of catalytic turnover-both experimentally and computationally-and make accessible the energetics of various intermediates (including short-lived transition states). These facts in turn offer a rational strategic principle for the design of new catalysts and the improvement of existing ones. It is generally possible to prepare soluble molecular fragments that circumscribe the single-site, thus enabling a direct comparison to be made, experimentally, between the catalytic performance of the same active site when functioning as a heterogeneous (continuous solid) as well as a homogeneous (dispersed molecular) catalyst. This approach also makes it possible to modify the immediate atomic environment as well as the central atomic structure of the active site. From the practical standpoint, SSHC exhibit very high selectivities leading to the production of sharply defined molecular products, just as do their homogeneous analogues. Given that mesoporous silicas with very large internal surface areas are ideal supports for SSHC, and that more than a quarter of the elements of the Periodic Table may be grafted as active sites onto such silicas, there is abundant scope for creating new catalytic opportunities.

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Single-site heterogeneous catalysts.

Efficient Ruthenium-Catalyzed Aerobic Oxidation of Alcohols Using a Biomimetic Coupled Catalytic System

Efficient ruthenium-catalyzed aerobic oxidation of alcohols using a biomimetic coupled catalytic system.

Evidence for a ruthenium dihydride species as the active catalyst in the RuCl2(PPh3)-catalyzed hydrogen transfer reaction in the presence of base

New efficient ruthenium catalysts for racemization of alcohols at room temperature

The voltage-gated sodium channel Na(V)1.7 is believed to be a critical mediator of pain sensation based on clinical genetic studies and pharmacological results. Clinical utility of nonselective sod ...

3-Oxoisoindoline-1-carboxamides: potent, state-dependent blockers of voltage-gated sodium channel Na(V)1.7 with efficacy in rat pain models.

A zeolite-encapsulated cobalt salophen catalyst was prepared by the intrazeolite ligand synthesis method This catalyst proved to be active in the ruthenium-catalyzed oxidation of primary and secondary alcohols to aldehydes or ketones Several advantages of the heterogenized catalyst was found in this system compared to the homogeneous counterpart, namely easy handling and better performance (less sensitive to solvent effects, higher specific rates)

Gabor Csjernyik

Papers

Efficient ruthenium-catalyzed aerobic oxidation of alcohols using a biomimetic coupled catalytic system.

Evidence for a ruthenium dihydride species as the active catalyst in the RuCl2(PPh3)-catalyzed hydrogen transfer reaction in the presence of base

New efficient ruthenium catalysts for racemization of alcohols at room temperature

3-Oxoisoindoline-1-carboxamides: potent, state-dependent blockers of voltage-gated sodium channel Na(V)1.7 with efficacy in rat pain models.

Ruthenium-catalyzed aerobic oxidation of alcohols on zeolite-encapsulated cobalt salophen catalyst