221110-45-8Relevant articles and documents
Scope and limitations of one-pot multistep reactions with heterogeneous catalysts: The case of alkene epoxidation coupled to epoxide ring-opening
Fraile, José M.,García, Nuria,Herrerías, Clara I.,Mayoral, José A.
experimental part, p. 15 - 20 (2012/07/03)
The combination of two reactions in one-pot multistep system requires the compatibility not only between the catalysts of both reactions, but also between all the reaction components and conditions. In the case of the coupling of alkene epoxidation and epoxide ring opening, it has been possible to synthesize cyanohydrin and azidohydrin derivatives through a simple process that involves a one-pot multistep process by using a mixture of two heterogeneous catalysts, a silica-grafted Ti catalyst and ytterbium chloride, whose efficiency depends on the reactivity of the starting alkene. In addition, in some cases the mixture of catalysts can be recovered and reused in several one-pot multistep cycles. However, this system is not possible with electron-deficient alkenes, as the basic catalyst required for epoxidation has shown to be incompatible with the ring-opening process.
Polyolefin-supported recoverable/reusable Cr(III)-salen catalysts
Bergbreiter, David E.,Hobbs, Christopher,Hongfa, Chayanant
experimental part, p. 523 - 533 (2011/04/17)
The design of functional soluble polyolefins for use as supports for salen ligands and metal complexes is described. Examples and applications that use both polyisobutylene (PIB)-and polyethylene (PEOlig)-bound recoverable/recyclable salen ligands/metal complexes are detailed. In the case of using PIB as a support, the polymer-bound complexes can be recovered through the use of latent biphasic or a thermomorphic mixed solvent systems. In the case of PEOlig-supported complexes, the thermomorphic PE Olig-bound salen species can be dissolved in "hot" solvents and quantitatively recovered as solids upon cooling to room temperature. Both the PIB-and PEOlig-bound salen catalysts were shown to catalyze the ring-opening of epoxides with various nucleophiles. Both sorts of polyolefin-bound catalysts can be recycled and reused with no observed loss in activity. However, limitations of catalyst concentration make chiral versions of these complexes uncompetitive in comparison to conventional chiral salen catalysts that can be used in neat substrate at higher concentration to produce high enantioselectivity in the ring-opening products. The preparation of a PIB-bound "half-salen" catalyst was also briefly examined.
Reversibly addressing an allosteric catalyst in situ: Catalytic molecular tweezers
Gianneschi, Nathan C.,Cho, So-Hye,Nguyen, SonBinh T.,Mirkin, Chad A.
, p. 5503 - 5507 (2007/10/03)
Abiotic allosteric regulation: The design, synthesis, and application of novel, reversible allosteric catalytic molecular tweezers that contain a structural metal, addressable in situ, and two functional catalytic metals are reported (see picture). Kinetic and selectivity data reflect a significant decrease in cooperativity upon opening of the "arms" of the catalyst caused by reactions occurring at the hinge.
A supramolecular approach to an allosteric catalyst
Gianneschi, Nathan C.,Bertin, Paul A.,Nguyen, SonBinh T.,Mirkin, Chad A.,Zakharov, Lev N.,Rheingold, Arnold L.
, p. 10508 - 10509 (2007/10/03)
The design and synthesis of a novel, supramolecular allosteric catalyst system, assembled via the weak-link approach, is presented. The catalyst contains two structural Rh(I) centers in thioether- and phosphine-rich hemilabile pockets, and two functional Cr(III) centers bound within salen-based moieties. The catalytic properties of the supramolecular catalyst are compared to those of a Cr(III)-salen monomeric analogue in the context of the asymmetric ring opening of cyclohexene oxide by TMSN3. Allosteric control is afforded via reactions that occur at distal sites which open the macrocyclic cavity and facilitate the catalytic reaction. Kinetic data show a significant rate increase upon opening of the catalyst's flexible macrocyclic cavity and enhanced selectivity and reactivity with respect to the monomeric Cr(III)-salen analogue. The work presented represents a new approach to the construction of abiotic allosteric catalysts. Copyright
Metal(II) d-Tartarates Catalyzed Asymmetric Ring Opening of Oxiranes with Various Nucleophiles
Yamashita, Hiroyuki
, p. 1213 - 1220 (2007/10/02)
The asymmetric ring opening of meso-2,3-disubstituted oxiranes with thiols, aniline, and trimethylsilyl azide was studied by the use of metal(II) d-tartarates as heterogeneous chiral Lewis acid catalysts.The enantioselectivity varied widely with the combination of oxirane, nucleophile, and metal(II) d-tartarate, and Zn(II) d-tartarate gave the best enantioselectivity in the respective reactions of 1,2-epoxycyclohexane with 1-butanethiol, aniline, and trimethylsilyl azide to afford the corresponding adducts in 85, 58, and 42 percent ee, respectively.Furthermore, the kinetic resolution of racemic oxiranes with thiols catalyzed by Zn(II) d-tatratate was studied.
