Article (Scientific journals)
Homobimetallic ruthenium-N-heterocyclic carbene complexes: Synthesis, characterization, and catalytic applications
Sauvage, Xavier; Borguet, Yannick; Noels, Alfred et al.
2007In Advanced Synthesis and Catalysis, 349 (1-2), p. 255-265
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Keywords :
homogeneous catalysis; metathesis; polymerization; radical reactions; ruthenium; arene ligands
Abstract :
[en] Two new homobimetallic ruthenium-arene complexes [(p-cymene)Ru(mu-Cl)(3)RuCl(eta(2)-C2H4)(L)], where L=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (3a) or 1,3-bis(2,4,6-trimethylphenyl)-4,5-dichloroimidazolin-2-ylidene (3b), were isolated in high yields upon heating a toluene solution of [RuCl2 (p-cymene)](2) with 1 equivalent of carbene ligand under an ethylene atmosphere. They were characterized by NMR and TGA. Their catalytic activity was investigated in the atom transfer radical polymerization of vinyl monomers. In the polymerization of methyl methacrylate, complex 3a displayed faster reaction rates than 3b and the related phosphine-based complex 2a (L=tricyclohexylphosphine), although control was more effective with the latter catalyst. When n-butyl acrylate or styrene served as monomer, a major shift of reactivity was observed between complex 2a that promoted controlled radical polymerization, and complexes 3a or 3b that favored metathetical coupling. Further homocoupling experiments with various styrene derivatives confirmed the outstanding aptitude of complex 3a (and to a lesser extent of 3b) to catalyze olefin metathesis reactions. Contrary to monometallic ruthenium-arene complexes of the [RuCl2(p-cymene)(L)] type, the new homobimetallic species did not require the addition of a diazo compound or visible light illumination to initiate the ring-opening metathesis of norbornene or cyclooctene. When alpha,omega-dienes were exposed to 3a or 3b, a mixture of cycloisomerization and ring-closing metathesis products was obtained in a non-selective way. Addition of a terminal alkyne co-catalyst enhanced the metathetical activity while completely repressing the cycloisomerization process. Thus, quantitative conversions of diethyl 2,2-diallylmalonate and N,N-diallyltosylamide were achieved within 2 h at room temperature using 2 mol % of catalyst precursor 3 a and 6 mol % of phenylacetylene.
Disciplines :
Chemistry
Author, co-author :
Sauvage, Xavier ;  Université de Liège - ULiège > Département de chimie (sciences) > Chimie macromoléculaire et catalyse organique
Borguet, Yannick ;  Université de Liège - ULiège > Département de chimie (sciences) > Chimie macromoléculaire et catalyse organique
Noels, Alfred ;  Université de Liège - ULiège > Services généraux (Faculté des sciences) > Relations académiques et scientifiques (Sciences)
Delaude, Lionel  ;  Université de Liège - ULiège > Département de chimie (sciences) > Chimie macromoléculaire et catalyse organique
Demonceau, Albert ;  Université de Liège - ULiège > Département de chimie (sciences) > Chimie macromoléculaire et catalyse organique
Language :
English
Title :
Homobimetallic ruthenium-N-heterocyclic carbene complexes: Synthesis, characterization, and catalytic applications
Publication date :
2007
Journal title :
Advanced Synthesis and Catalysis
ISSN :
1615-4150
eISSN :
1615-4169
Publisher :
Wiley-VCH Verlag Gmbh, Weinheim, Germany
Volume :
349
Issue :
1-2
Pages :
255-265
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 26 June 2009

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