Synthesis and catalytic evaluation of ruthenium-arene complexes bearing imidazol(in)ium-2-thiocarboxylate ligands

Morgan Hans, Quentin Willem, Johan Wouters, Albert Demonceau, Lionel Delaude

Research output: Contribution to journalArticle

Abstract

Five new complexes with the generic formula [RuCl2(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 2Cl2 at -20 °C. All the products were fully characterized by IR and NMR spectroscopy, and the molecular structures of [RuCl2(p-cymene)(SOC·IMes)] (3) and [RuCl2(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 1H 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 [RuCl2(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·CO2 inner salts. However, they were significantly better catalyst precursors than the much more robust chelates of the [RuCl(p-cymene)(S2C·NHC)]PF6 type obtained by coordination of NHC·CS2 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 [RuCl2(p-cymene)(NHC)] family of complexes.

Original languageEnglish
Pages (from-to)6133-6142
Number of pages10
JournalOrganometallics
Volume30
Issue number22
DOIs
Publication statusPublished - 28 Nov 2011

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Bearings (structural)
Ruthenium
imidazoles
ruthenium
polymerization
dimers
Ligands
betaines
nuclear magnetic resonance
ligands
zwitterions
ring currents
evaluation
metathesis
synthesis
chelates
nitrogen atoms
spectroscopy
shielding
atoms

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Hans, Morgan ; Willem, Quentin ; Wouters, Johan ; Demonceau, Albert ; Delaude, Lionel. / Synthesis and catalytic evaluation of ruthenium-arene complexes bearing imidazol(in)ium-2-thiocarboxylate ligands. In: Organometallics. 2011 ; Vol. 30, No. 22. pp. 6133-6142.
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abstract = "Five new complexes with the generic formula [RuCl2(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 2Cl2 at -20 °C. All the products were fully characterized by IR and NMR spectroscopy, and the molecular structures of [RuCl2(p-cymene)(SOC·IMes)] (3) and [RuCl2(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 1H 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 [RuCl2(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·CO2 inner salts. However, they were significantly better catalyst precursors than the much more robust chelates of the [RuCl(p-cymene)(S2C·NHC)]PF6 type obtained by coordination of NHC·CS2 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 [RuCl2(p-cymene)(NHC)] family of complexes.",
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Synthesis and catalytic evaluation of ruthenium-arene complexes bearing imidazol(in)ium-2-thiocarboxylate ligands. / Hans, Morgan; Willem, Quentin; Wouters, Johan; Demonceau, Albert; Delaude, Lionel.

In: Organometallics, Vol. 30, No. 22, 28.11.2011, p. 6133-6142.

Research output: Contribution to journalArticle

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T1 - Synthesis and catalytic evaluation of ruthenium-arene complexes bearing imidazol(in)ium-2-thiocarboxylate ligands

AU - Hans, Morgan

AU - Willem, Quentin

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AU - Demonceau, Albert

AU - Delaude, Lionel

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AB - Five new complexes with the generic formula [RuCl2(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 2Cl2 at -20 °C. All the products were fully characterized by IR and NMR spectroscopy, and the molecular structures of [RuCl2(p-cymene)(SOC·IMes)] (3) and [RuCl2(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 1H 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 [RuCl2(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·CO2 inner salts. However, they were significantly better catalyst precursors than the much more robust chelates of the [RuCl(p-cymene)(S2C·NHC)]PF6 type obtained by coordination of NHC·CS2 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 [RuCl2(p-cymene)(NHC)] family of complexes.

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