Reference : Homobimetallic ruthenium-N-heterocyclic carbene complexes: Synthesis, characterizatio...
Scientific journals : Article
Physical, chemical, mathematical & earth Sciences : Chemistry
http://hdl.handle.net/2268/15424
Homobimetallic ruthenium-N-heterocyclic carbene complexes: Synthesis, characterization, and catalytic applications
English
Sauvage, Xavier [Université de Liège - ULg > Département de chimie (sciences) > Chimie macromoléculaire et catalyse organique >]
Borguet, Yannick mailto [Université de Liège - ULg > Département de chimie (sciences) > Chimie macromoléculaire et catalyse organique >]
Noels, Alfred mailto [Université de Liège - ULg > Services généraux (Faculté des sciences) > Relations académiques et scientifiques (Sciences) >]
Delaude, Lionel mailto [Université de Liège - ULg > Département de chimie (sciences) > Chimie macromoléculaire et catalyse organique >]
Demonceau, Albert mailto [Université de Liège - ULg > Département de chimie (sciences) > Chimie macromoléculaire et catalyse organique >]
2007
Advanced Synthesis & Catalysis
Wiley-VCH Verlag Gmbh
349
1-2
255-265
Yes (verified by ORBi)
International
1615-4150
Weinheim
Germany
[en] homogeneous catalysis ; metathesis ; polymerization ; radical reactions ; ruthenium ; arene ligands
[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.
http://hdl.handle.net/2268/15424
10.1002/adsc.200600515

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