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See detailSynthesis and Catalytic Evaluation of Ruthenium-Arene Complexes Bearing Imidazol(in)ium-2-thiocarboxylate Ligands
Hans, Morgan ULg; Willem, Quentin ULg; Wouters, Johan et al

in Organometallics (2011), 30(22), 6133-6142

Five new complexes with the generic formula [RuCl(2)(p-cymene)(SOC.NHC)] (2-6) were isolated in high yields by reacting the [RuCl(2)(p-cymene)](2) dimer with a range of imidazol(in)ium-2-thiocarboxylate ... [more ▼]

Five new complexes with the generic formula [RuCl(2)(p-cymene)(SOC.NHC)] (2-6) were isolated in high yields by reacting the [RuCl(2)(p-cymene)](2) dimer with a range of imidazol(in)ium-2-thiocarboxylate zwitterions bearing cyclohexyl, 2,4,6-trimethylphenyl (mesityl), or 2,6-diisopropylphenyl groups on their nitrogen atoms in CH(2)Cl(2) at -20 degrees C. All the products were fully characterized by IR and NMR spectroscopy, and the molecular structures of [RuCl(2)(p-cymene)(SOC.IMes)] (3) and [RuCl(2)(p-cymene)(SOC.SIMes)] (5) were determined by X-ray diffraction analysis. Coordination of the NHC.COS ligands took place via the sulfur atom. A remarkable shielding of the methine proton on the p-cymene isopropyl group was observed by (1)H NMR spectroscopy for complexes 3-6. It is most likely caused by the aromatic ring current of a neighboring mesityl or 2,6-diisopropylphenyl substituent. The catalytic activity of compounds 2-6 was probed in the ring-opening metathesis polymerization (ROMP) of cyclooctene, in the atom transfer radical polymerization (ATRP) of methyl methacrylate, and in the synthesis of enol esters from 1-hexyne and 4-acetoxybenzoic acid. In all these reactions, the [RuCl(2)(p-cymene)(SOC.NHC)] complexes displayed performances slightly inferior to those exhibited by [RuCl(2)(p-cymene)(NHC)] species that result from the reaction of [RuCl(2)(p-cymene)](2) with NHC.CO(2) inner salts. However, they were significantly better catalyst precursors than the much more robust chelates of the [RuCl(p-cymene)(S(2)C.NHC)PF(6) type obtained by coordination of NHC.CS(2) betaines to the ruthenium dimer. These results suggest that the Ru-(SOC.NHC) motif undergoes a dethiocarboxylation under the experimental conditions adopted for the catalytic tests and leads to the same elusive Ru-NHC active species as the preformed [RuCl(2)(p-cymene)-(NHC)] family of complexes. [less ▲]

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See detailRuthenium-arene complexes bearing imidazol(in)ium-2-dithiocarboxylate ligands: Evaluation of their catalytic activity in the synthesis of enol esters
Willem, Quentin ULg; Nicks, Francois ULg; Sauvage, Xavier et al

in Journal of Organometallic Chemistry (2009), 694(25), 4049-4055

The catalytic activity of four ruthenium imidazol(in)ium-2-dithiocarboxylates was evaluated for the synthesis of vinyl esters through addition of 4-acetoxybenzoic acid to 1-hexyne, and compared to those ... [more ▼]

The catalytic activity of four ruthenium imidazol(in)ium-2-dithiocarboxylates was evaluated for the synthesis of vinyl esters through addition of 4-acetoxybenzoic acid to 1-hexyne, and compared to those of the parent ruthenium-N-heterocyclic carbene complexes and [RuCl2(p-cymene)(PPh3)] (a standard catalyst). It turned out that ruthenium imidazol(in)ium-2-dithiocarboxylates were poorly active and selective. Quantitative yields, indeed, were obtained only after extended reaction times. However, the catalytic activity could be improved significantly under microwave heating or conventional heating in a sealed tube at 160 degrees C, driving the reaction to completion in less than 4 h of reaction. [less ▲]

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