Synthesis and Application of New N-Heterocyclic Carbene Ruthenium Complexes in Catalysis: A Case Study

Delaude, Lionel; Demonceau, Albert; Noels, Alfred F.

doi:10.2174/138527206775192924

Cited by 67 publications

(1 citation statement)

References 55 publications

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“…In principle, Ru may be coordinated by a carbene formed from the imidazolium cation. [24] This possibility was investigated by performing a reaction in 1-ethyl-2,3-dimethylimidazolium bromide (Table 3, entry 4). While not all bromide-based ionic liquids are suitable for cellulose dissolution, [6g, 25] the use this particular ionic liquid resulted in a complete dissolution of the cellulose reactant.…”

Section: Resultsmentioning

confidence: 99%

Reductive Splitting of Cellulose in the Ionic Liquid 1‐Butyl‐3‐Methylimidazolium Chloride

et al. 2010

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The depolymerization of cellulose is carried out in the ionic liquid 1-butyl-3-methylimidazolium chloride in the presence of hydrogen gas. First, the ketal 1,1-diethoxycyclohexane and cellobiose were used as model substrates. For the depolymerization of cellulose itself, the combination of a heterogeneous metal catalyst and a homogeneous ruthenium catalyst proved effective. One of the possible roles of the ruthenium compound is to enhance the transfer of hydrogen to the metallic surface. The cellulose is fully converted under relatively mild conditions, with sorbitol as the dominant product in 51-74% yield.

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Section: Resultsmentioning

confidence: 99%

Reductive Splitting of Cellulose in the Ionic Liquid 1‐Butyl‐3‐Methylimidazolium Chloride

et al. 2010

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Simple Ruthenium Precatalyst for the Synthesis of Stilbene Derivatives and Ring‐Closing Metathesis in the Presence of Styrene Initiators

Cariou

Fischmeister

et al. 2007

Adv Synth Catal

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was found to be an efficient precatalyst, with styrene as an initiating species, for the alkene metathesis of various styrenes into symmetrical and unsymmetrical stilbene derivatives and for the ring-closing metathesis reaction of a sterically hindered olefin leading to a tetrasubstituted cycloolefin.Keywords: alkene metathesis; N-heterocyclic carbenes; ring-closing metathesis; ruthenium; stilbenes; styrenes Stilbene derivatives, in particular hydroxy-or alkoxysubtituted ones are gaining importance due to their biological activities for the prevention of cancer or cardiovascular diseases.[1] They are also an important family of building blocks for the design of conjugated materials with optical properties.[2] Wittig or WittigHorner reactions [3] constitute a priviledged approach for the synthesis of stilbene derivatives but they generate stoichiometric amounts of phosphine oxides hence requiring fastidious purification. Catalytic reactions such as Heck or Suzuki couplings can be used as more efficient ways to synthesize stilbene derivatives.[4] More recently catalytic olefin metathesis [5] appeared as a tool of choice for the efficient and stereoselective synthesis of stilbene derivatives thanks to the emergence of very active catalysts for cross-metathesis.[6] In particular, the ruthenium-based second generation Grubbs catalyst has been shown to efficiently promote the self-and cross-metathesis of styrene derivatives. [7] Other complexes based on molybdenum [8] or osmium [9] have also been described as efficient catalysts for this transformation.We recently reported the intramolecular vinyl C À H bond activation of an N-vinyl-N-heterocyclic carbeneruthenium(II) intermediate leading to a bidentate NHC-alkenyl ruthenium complex (Scheme 1). [10] In an attempt to explore the intermolecular version of this transformation, styrene was reacted with the readily available ruthenium complex[11] [IMes = 1,3bis(2,4,6-trimethylphenyl)imidazol-2-ylidene]. This reaction resulted in the stereoselective formation of E-stilbene in very good yield, thus suggesting a self-metathesis reaction. Here we describe several aspects of RuCl 2 A C H T U N G T R E N N U N G (p-cymene)-A C H T U N G T R E N N U N G (IMes) as catalyst precursor for alkene metathesis reactions. In the absence of an alkene metathesis carbene initiator, complex 1 acts as a pre-catalyst for the metathesis transformation of various styrene derivatives into the corresponding stilbenes including unsymmetrical ones. We show the dual ring-closing metathesis (RCM) vs. cycloisomerisation activity of 1 and that, in the presence of styrene as an activator, complex 1 is effective for the RCM of a sterically hindered diene.

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Homobimetallic Ruthenium–N‐Heterocyclic Carbene Complexes: Synthesis, Characterization, and Catalytic Applications

et al. 2007

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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 [RuCl 2 A C H T U N G T R E N N U N G (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 [RuCl 2 A C H T U N G T R E N N U N G (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 a,w-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.

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Synthesis and Application of New N-Heterocyclic Carbene Ruthenium Complexes in Catalysis: A Case Study

Cited by 67 publications

References 55 publications

Reductive Splitting of Cellulose in the Ionic Liquid 1‐Butyl‐3‐Methylimidazolium Chloride

Reductive Splitting of Cellulose in the Ionic Liquid 1‐Butyl‐3‐Methylimidazolium Chloride

Simple Ruthenium Precatalyst for the Synthesis of Stilbene Derivatives and Ring‐Closing Metathesis in the Presence of Styrene Initiators

Homobimetallic Ruthenium–N‐Heterocyclic Carbene Complexes: Synthesis, Characterization, and Catalytic Applications

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