Asymmetric Catalysis of Epoxide Ring-Opening Reactions

Jacobsen, Eric N.

doi:10.1021/ar960061v

Cited by 1,185 publications

(702 citation statements)

References 28 publications

Supporting

Mentioning

665

Contrasting

Unclassified

Order By: Relevance

“…32 In addition to diamide ligands, we also explored the use of ferrocene-derived Schiff base metal complexes for the ring-opening polymerization of cyclic esters. 17,[33][34][35][36] Schiff base metal complexes have found numerous uses in coordination chemistry and catalysis, [37][38][39][40][41][42] alkoxide yttrium complexes supported by such ligands being intensely researched as initiators for the ring-opening polymerization of cyclic esters. 17,[35][36][43][44][45][46][47][48][49][50] On the other hand, reports of structurally characterized alkyl or aryl rare earth complexes bearing an imine functionality in the backbone are rare, [51][52] the majority being represented by phosphinimine ligands.…”

Section: Introductionmentioning

confidence: 99%

Yttrium-Alkyl Complexes Supported by a Ferrocene-Based Phosphinimine Ligand

Brosmer

Diaconescu

2015

Organometallics

View full text Add to dashboard Cite

The synthesis and characterization of two yttrium alkyl complexes supported by a bisphosphinimine ferrocene ligand, NP by NMR spectroscopy, electrochemical measurements, and elemental analysis. Reactivity studies were also carried out, however, the lack of prolonged thermal stability at ambient temperature of these molecules led to decomposition before the clean formation of reaction products could be observed.1

show abstract

Section: Introductionmentioning

confidence: 99%

Yttrium-Alkyl Complexes Supported by a Ferrocene-Based Phosphinimine Ligand

Brosmer

Diaconescu

2015

Organometallics

View full text Add to dashboard Cite

show abstract

“…It is of interest in this context that binuclear analogues of many catalysts that rely on bimetallic interactions show enhanced activity when compared to monomeric species, examples include certain Ru and Os diporphyrin H 2 evolving catalysts with cofacial orientation (24,25). In one noteworthy case, Jones and coworkers (26,27) showed that a "bisalen" analogue of Jacobsen's Co-(salen) catalyst for hydrolytic kinetic resolution of racemic epoxides (a reaction that also shows a second-order dependence on catalyst concentration) maintained activity when linked to a solid support, whereas the immobilized monomer was essentially inactive (26)(27)(28). Because one of our goals is construction of a catalytic cobaloxime-modified electrode for water reduction, we have investigated the reactivity of a covalently-linked dicobalt complex.…”

mentioning

confidence: 99%

Catalytic hydrogen evolution from a covalently linked dicobaloxime

Valdez

Dempsey

Brunschwig

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

103

View full text Add to dashboard Cite

A dicobaloxime in which monomeric Co(III) units are linked by an octamethylene bis(glyoxime) catalyzes the reduction of protons from p-toluenesulfonic acid as evidenced by electrocatalytic waves at −0.4 V vs. the saturated calomel electrode (SCE) in acetonitrile solutions. Rates of hydrogen evolution were determined from catalytic current peak heights (k app ¼ 1100 AE 70 M −1 s −1 ). Electrochemical experiments reveal no significant enhancement in the rate of H 2 evolution from that of a monomeric analogue: The experimental rate law is first order in catalyst and acid consistent with previous findings for similar mononuclear cobaloximes. Our work suggests that H 2 evolution likely occurs by protonation of reductively generated Co II H rather than homolysis of two Co III H units.hydrogen evolving catalysts | solar fuel E fficient catalytic reduction of protons to dihydrogen is a requirement for one half of a functional solar water splitting system (1, 2). Progress has been made recently in identifying catalysts capable of producing hydrogen from acidic media using either small molecule mimics of hydrogenase active sites or other synthetic systems (3-11).Our work has focused on difluoroboryl-bridged Co II -diglyoxime complexes that catalyze hydrogen evolution at low overpotentials (12)(13)(14)(15). With these complexes, hydrogen evolution is initiated upon reduction to Co I , which then reacts with a proton donor to form a Co III -hydride (Co III H). The Co III H intermediate can either undergo subsequent protonation to release H 2 and a Co III species that is reduced to regenerate the catalyst (heterolytic route) or react with another Co III H to eliminate H 2 by a homolytic route. Alternatively, Co III H can be reduced further to form Co II H, which can react via similar heterolytic or homolytic routes (16). Digital simulations of electrocatalytic waves performed by Hu et al. (17) indicated that the bimolecular homolytic Co III H route is the dominant pathway for hydrogen evolution. Our analysis of electron transfer rates in the catalytic cycle confirmed that the barriers to H 2 evolution associated with this pathway are more favorable than that for protonation of Co III H (17, 18). Recent work in our group examining the mechanism of hydrogen evolution from a photogenerated hydridocobaloxime suggests that hydrogen evolution via protonation of Co II H is favored under certain conditions (Co III H in low concentrations with reducing equivalents in excess) (16). Computational studies reported by 20) and Muckerman (21) suggest that Co II H protonation is a very favorable reaction pathway and that relative fluxes through the homolytic Co III H and heterolytic Co II H channels depend on experimental conditions (relative concentrations of acid and catalyst).In the low-barrier homolytic mechanism, two Co III H species must diffuse together in solution in order to react and release H 2 . It follows that immobilization onto an electrode surface would disfavor this pathway (7,22,23). It is of interest in this context that...

show abstract

“…It has already been demonstrated that the oligo(salamo) helical complexes show unique physical properties and reactivities [98][99][100][101], and the dynamic helicity control would be useful for switching of the chiroptical properties of the helical structures. The catalytic reactivity of the chiral metallosalen scaffold [84][85][86][87] could also be incorporated into the oligo(salamo) helical structures, which could dynamically switch the enantioselectivity of the catalytic reactions. In this sense, the oligo(salen)-type helical structures are promising to provide an excellent platform that can drive the dynamic switching of various kinds of chiral functions.…”

Section: Discussionmentioning

confidence: 99%

“…In order to control the helicity in a more rational and predictable fashion, we focused on chiral salen derivatives, which have two chiral carbon centers at the ethylene bridge of the salen ligands. It is well known that some chiral salen complexes act as excellent enantioselective catalysts (up to 99% ee) [84][85][86][87] and this indicates that the chiral twist is perfectly controlled in these systems. The chiral twist can be discussed in terms of the N-C-C-N dihedral angles (+60 deg or −60 deg) of the ethylene bridge in the salen ligands.…”

Section: Strategymentioning

confidence: 94%

Dynamic Helicity Control of Oligo(salamo)-Based Metal Helicates

Akine

2018

Inorganics

View full text Add to dashboard Cite

Much attention has recently focused on helical structures that can change their helicity in response to external stimuli. The requirements for the invertible helical structures are a dynamic feature and well-defined structures. In this context, helical metal complexes with a labile coordination sphere have a great advantage. There are several types of dynamic helicity controls, including the responsive helicity inversion. In this review article, dynamic helical structures based on oligo(salamo) metal complexes are described as one of the possible designs. The introduction of chiral carboxylate ions into Zn 3 La tetranuclear structures as an additive is effective to control the P/M ratio of the helix. The dynamic helicity inversion can be achieved by chemical modification, such as protonation/deprotonation or desilylation with fluoride ion. When (S)-2-hydroxypropyl groups are introduced into the oligo(salamo) ligand, the helicity of the resultant complexes is sensitively influenced by the metal ions. The replacement of the metal ions based on the affinity trend resulted in a sequential multistep helicity inversion. Chiral salen derivatives are also effective to bias the helicity; by incorporating the gauche/anti transformation of a 1,2-disubstituted ethylene unit, a fully predictable helicity inversion system was achieved, in which the helicity can be controlled by the molecular lengths of the diammonium guests.

show abstract

Asymmetric Catalysis of Epoxide Ring-Opening Reactions

Cited by 1,185 publications

References 28 publications

Yttrium-Alkyl Complexes Supported by a Ferrocene-Based Phosphinimine Ligand

Yttrium-Alkyl Complexes Supported by a Ferrocene-Based Phosphinimine Ligand

Catalytic hydrogen evolution from a covalently linked dicobaloxime

Dynamic Helicity Control of Oligo(salamo)-Based Metal Helicates

Contact Info

Product

Resources

About