- Effects of NHC-backbone substitution on efficiency in ruthenium-based olefin metathesis
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A series of ruthenium olefin metathesis catalysts bearing N-heterocycliccarbene (NHC) ligands with varying degrees of backbone and N-aryl subst itution have been prepared. These complexes show greater resistance to decomposition through C-H activation of
- Kuhn, Kevin M.,Bourg, Jean-Baptiste,Chung, Cheol K.,Virgil, Scott C.,Grubbs, Robert H.
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supporting information; experimental part
p. 5313 - 5320
(2009/09/30)
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- Scandium(III) catalysis of transimination reactions. Independent and constitutionally coupled reversible processes
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Sc(OTf)3 efficiently catalyzes the self-sufficient transimination reaction between various types of C=N bonds in organic solvents, with turnover frequencies up to 3600 h-1 and rate accelerations up to 6 × 105. The mechanism of the crossover reaction in mixtures of amines and imines is studied, comparing parallel individual reactions with coupled equilibria. The intrinsic kinetic parameters for isolated reactions cannot simply be added up when several components are mixed, and the behavior of the system agrees with the presence of a unique mediator that constitutes the core of a network of competing reactions. In mixed systems, every single amine or imine competes for the same central hub, in accordance with their binding affinity for the catalyst metal ion center. More generally, the study extends the basic principles of constitutional dynamic chemistry to interconnected chemical transformations and provides a step toward dynamic systems of increasing complexity.
- Giuseppone, Nicolas,Schmitt, Jean-Louis,Schwartz, Evan,Lehn, Jean-Marie
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p. 5528 - 5539
(2007/10/03)
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- Synthesis and complexation properties of poly(ethylene glycol)-linked mono- and bis-dioxocyclams
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Both tri- and tetra(ethylene glycol) linked bis-chromium carbene complexes have been synthesized. These carbene complexes were photolyzed with N-protected imidazolines to give protected azapenams. These were transformed into polyether-linked basket dioxocyclams 4a,b and bis-dioxocyclams 5a,b. These compounds have cavities for the complexation of both 'hard' and 'soft' metal ions. The complexes of Ni, Ba, and Gd were synthesized.
- Puntener,Hellman,Kuester,Hegedus
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p. 8301 - 8306
(2007/10/03)
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- A NEW REDUCTIVE PROCEDURE FOR THE PREPARATION OF VICINAL DIAMINES AND MONOAMINES
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Selective reductive procedures for the preparation of vicinal diamines and monoamines from alkyl bromocyanamides are described.
- Jung, Sang-Hun,Kohn, Harold
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p. 399 - 402
(2007/10/02)
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- MODELS OF FOLATE COENZYMES-VII SYNTHESIS AND CARBON TRANSFER REACTIONS OF N5,N10-METHENYL AND N5,N10-METHYLENETETRAHYDROFOLATE MODELS
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Carboxylate esters react with 1,2-diaminoethanes to yield imidazolines, which upon consecutive reaction with acetic anhydride or tosyl chloride and methyl iodide give imidazolinium salts that serve as models of N5,N10-(CH+)-tetrahydrofolate (THF) coenzymes (7a,b and 18a,b).Reduction of the latter salts with sodium borohydride or reaction with anions (R-) give the corresponding 5,10--THF models.Mono- and bifunctional nucleophiles react with 18a,b to yield carbon-transfer products. 6-Alkylamino-1,3-dimethyluracils react with 1-tosyl-3,4,4-trimethylimidazolidine (the reduction product of 18b), in the presence of acetic acid, to form carbon-transfer products via a mechanism which bears close analogy to the mechanism of action of thymidylate synthetase.
- Bieraeugel, H.,Plemp, R.,Hiemstra, H. C.,Pandit, U. K.
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p. 3971 - 3980
(2007/10/02)
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