Tetraarylphosphonium halides as arylating reagents in Pd-catalyzed Heck and cross-coupling reactions.
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Biomedical subjects
Youngim Na
Publications and source records attributed to Youngim Na.
Cooperative multi-catalyst systems for one-pot organic transformations.
One-pot co-catalyst systems are covered in this tutorial review. It is divided into three sections according to the reaction types: i) one catalyst performs a desired reaction as the second catalyst restores the first catalytic species back into its original state for the next catalytic cycles, ii) two catalysts carry out sequential organic transformations, in which the first step is carried out by one catalyst to afford certain intermediates being to be subjected to the second catalyst for the next step, and iii) cooperative catalytic actions on both substrates by suitable catalysts proceed in a substrate-selective manner followed by the subsequent coupling of the two activated adducts providing the desired products.
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Ruthenium-catalyzed Heck-type olefination and Suzuki coupling reactions: studies on the nature of catalytic species.
Ruthenium-catalyzed Heck olefination and Suzuki cross coupling reactions have been developed. When starting with a ruthenium complex [RuCl(2)(p-cymene)](2) as a homogeneous catalyst precursor, induction periods were observed and ruthenium colloids of zero oxidation state were generated under catalytic conditions. Isolated ruthenium colloids carried out the olefination, implying that active catalytic species are ruthenium nanoclusters. To support this hypothesis, ruthenium nanoparticles stabilized with dodecylamine were independently prepared via a hydride reduction procedure, and their catalytic activity was subsequently examined. Olefination of iodobenzene with ethyl acrylate was efficiently catalyzed by the ruthenium nanoparticles under the same conditions, which could be also reused for the next runs. In poisoning experiments, the conversion of the olefination was completely inhibited in the presence of mercury, thus supporting our assumption on the nature of catalytic species. No residual ruthenium was detected from the filtrate at the end of the reaction. On the basis of the postulation, a heterogeneous catalyst system of ruthenium supported on alumina was consequently developed for the Heck olefination and Suzuki cross coupling reactions for the first time. It turned out that substrate scope and selectivity were significantly improved with the external ligand-free catalyst even under milder reaction conditions when compared to results with the homogeneous precatalyst. It was also observed that the immobilized ruthenium catalyst was recovered and reused up to several runs with consistent efficiency. Especially in the Suzuki couplings, the reactions could be efficiently carried out with as low as 1 mol % of the supported catalyst over a wide range of substrates and were scaled up to a few grams without any practical problems, giving coupled products with high purity by a simple workup procedure.
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Chelation-accelerated sequential decarbonylation of formate and alkoxycarbonylation of aryl halides using a combined Ru and Pd catalyst.
An efficient cooperative catalyst system for the coupling of a wide range of organic electrophiles with chelated formate is reported to afford aryl and alkenyl esters by the simultaneous employment of Ru and Pd catalyst, in which ruthenium first promotes chelation-accelerated decarbonylation of formate to release CO and carbinol that are presumed to be transferred, still chelated to Ru, into Pd catalyst, which catalyzes alkoxycarbonylation of the organic electrophiles.
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[RuCl(2)(p-cymene)](2) on carbon: an efficient, selective, reusable, and environmentally versatile heterogeneous catalyst.
[reaction: see text] A heterogeneous ruthenium catalyst, easily prepared by adsorption of [RuCl(2)(p-cymene)](2) on activated carbon, exhibited a highly efficient and selective catalytic activity in various environmentally attractive transformations such as aerobic oxidation, hydrolytic oxidation, and dehydration processes with excellent recyclability.
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A novel chelation-assisted hydroesterification of alkenes via ruthenium catalysis.
An efficient and catalytic protocol of hydroesterification of alkenes has been developed without a need for CO atmosphere. With the introduction of the 2-pyridyl moiety as a chelating group in formate, Ru3(CO)12-catalyzed activation of the formyl C-H bond of formate and subsequent addition of the intermediate to alkenes proceeded with almost complete suppression of decarbonylation. Stereoselectivity of the produced one-carbon elongated esters was good to excellent for the formation of the linear adduct depending on the bulkiness of the alkenes used. This procedure could be readily applied to a variety of olefins such as terminal, internal, cyclic, bicyclic, vinyl ether, and conjugated enone systems with high efficiency and selectivity. It was also amenable to a solvent-free condition. On the basis of the chelation-driven C-H bond activation of formate, a putative mechanism of the Ru-catalyzed hydroesterification of 2-pyridylmethyl formate has been proposed.
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