Olefinmetathesis as a tool for multinuclear Co(<scp>iii</scp>)salen catalyst construction: access to cooperative catalysts

Haak, Robert M.; Belmonte, Marta Martínez; Escudero‐Adán, Eduardo C.; Benet‐Buchholz, Jordi; Kleij, Arjan W.

doi:10.1039/b911856j

Cited by 53 publications

(22 citation statements)

References 30 publications

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“…[3] For example, a second-order dependence on the chiral (salen)Co (salen = bis-(salicyliden)-ethylendiaminato) catalyst in the hydrolytic kinetic resolution (HKR) of epoxides [4] led to the development of a number of multinuclear (salen)Co structures connected mainly through a covalent linker; these multinuclear complexes been devised to enforce a cooperative pathway. Thus, dimeric, [5] oligomeric, [6] dendritic, [7] polymeric, [8] colloidal, [9] and encapsulated [10] (salen)Co complexes showed much improved catalytic efficiency in the HKR, whereas requiring lower catalyst loading.…”

Section: Introductionmentioning

confidence: 99%

Self‐Assembly Approach toward Chiral Bimetallic Catalysts: Bis‐Urea‐Functionalized (Salen)Cobalt Complexes for the Hydrolytic Kinetic Resolution of Epoxides

Park

Lang

Abboud

et al. 2011

Chemistry A European J

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A series of novel bis-urea-functionalized (salen)Co complexes has been developed. The complexes were designed to form self-assembled structures in solution through intermolecular urea-urea hydrogen-bonding interactions. These bis-urea (salen)Co catalysts resulted in rate acceleration (up to 13 times) in the hydrolytic kinetic resolution (HKR) of rac-epichlorohydrin in THF by facilitating cooperative activation, compared to the monomeric catalyst. In addition, one of the bis-urea (salen)Co(III) catalyst efficiently resolves various terminal epoxides even under solvent-free conditions by requiring much shorter reaction time at low catalyst loading (0.03-0.05 mol %). A series of kinetic/mechanistic studies demonstrated that the self-association of two (salen)Co units through urea-urea hydrogen bonds was responsible for the observed rate acceleration. The self-assembly study with the bis-urea (salen)Co by FTIR spectroscopy and with the corresponding (salen)Ni complex by (1)H NMR spectroscopy showed that intermolecular hydrogen-bonding interactions exist between the bis-urea scaffolds in THF. This result demonstrates that self-assembly approach by using non-covalent interactions can be an alternative and useful strategy toward the efficient HKR catalysis.

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Section: Introductionmentioning

confidence: 99%

Self‐Assembly Approach toward Chiral Bimetallic Catalysts: Bis‐Urea‐Functionalized (Salen)Cobalt Complexes for the Hydrolytic Kinetic Resolution of Epoxides

Park

Lang

Abboud

et al. 2011

Chemistry A European J

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“…[25,26] The combination of multiple catalytic sites into a single molecule was thus studied as a means to improve the catalytic properties of metallosalens, and in many cases cooperativity was observed. [27][28][29] Multimetallic Schiff-base catalysts exhibit significant potential, enabling the activation of multiple reaction components; however, these catalysts are very sensitive to the distance between the metal centers, the orientation of the catalytic units, and nature of the linker. [22,30] The electronic structure of monometallic bis-ligand radical complexes has been studied by a number of groups, and the electronic structure is dependent on the interaction between the open-shell ligands, and in some cases additional interactions with the paramagnetic transition metal ion.…”

Section: Introductionmentioning

confidence: 99%

Class III Delocalization and Exciton Coupling in a Bimetallic Bis‐ligand Radical Complex

Dunn

Chiang

Ramogida

et al. 2013

Chemistry A European J

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The geometric and electronic structure of an oxidized bimetallic Ni complex incorporating two redox-active Schiff-base ligands connected via a 1,2-phenylene linker has been investigated and compared to a monomeric analogue. Information from UV/Vis/NIR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, electrochemistry, and density functional theory (DFT) calculations provides important information on the locus of oxidation for the bimetallic complex. The neutral bimetallic complex is conformationally dynamic at room temperature, which complicates characterization of the oxidized forms. Comparison to an oxidized monomer analogue 1 provides critical insight into the electronic structure of the oxidized bimetallic complex 2. Oxidation of 1 provides [1˙](+), which is characterized as a fully delocalized ligand radical complex; the spectroscopic signature of this derivative includes an intense NIR band at 4500 cm(-1). Oxidation of 2 to the bis-oxidized form affords a bis-ligand radical species [2˙˙](2+). Variable temperature EPR spectroscopy of [2˙˙](2+) shows no evidence of coupling, and the triplet and broken symmetry solutions afforded by theoretical calculations are essentially isoenergetic. [2˙˙](2+) is thus best described as incorporating two non-interacting ligand radicals. Interestingly, the intense NIR intervalence charge transfer band observed for the delocalized ligand-radical [1˙](+) exhibits exciton splitting in [2˙˙](2+), due to coupling of the monomer transition dipoles in the enforced oblique dimer geometry. Evaluating the splitting of the intense intervalence charge transfer band can thus provide significant geometric and electronic information in less rigid bis-ligand radical systems. Addition of excess pyridine to [2˙˙](2+) results in a shift in the oxidation locus from a bis-ligand radical species to the Ni(III) /Ni(III) derivative [2(py)4](2+), demonstrating that the ligand system can incorporate significant bulk in the axial positions.

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“…[61] Recently, some adaptations of this proven concept have been elaborated on, using supramolecular bowl-shaped structures. [62] The area of "click chemistry", originally defined by Sharpless [63] to include 100 % atom-efficient, thermodynamically favored and very selective coupling reactions between two reactive coupling partners, is dominated by the copper-catalyzed azide-alkyne coupling to generate bioorthogonal triazole fragments. The group of Marks has made elegant contributions using welldesigned dinickel complexes based on dinucleating phenoxyiminato ligands, which were shown to induce cooperative catalysis in both the homopolymerization of ethylene and the copolymerization of ethylene with polar comonomers (norbornadiene and acrylates).…”

Section: Bimetallic Catalysismentioning

confidence: 99%

Cooperative Catalysis with First‐Row Late Transition Metals

2011

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Cooperative catalysis with first-row transition metals holds much promise for future developments regarding sustainable, selective transformations, including e.g. alkenes, dienes and a variety of small molecules such as CO 2 , N 2 and water. This non-exhaustive analysis of the current state-ofthe-art aims to give a comprehensive overview of the various design strategies and applications of first-row transition metal cooperative reactivity and to provide leads for new research initiatives in order to expand this emerging field. The

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Olefinmetathesis as a tool for multinuclear Co(iii)salen catalyst construction: access to cooperative catalysts

Cited by 53 publications

References 30 publications

Self‐Assembly Approach toward Chiral Bimetallic Catalysts: Bis‐Urea‐Functionalized (Salen)Cobalt Complexes for the Hydrolytic Kinetic Resolution of Epoxides

Self‐Assembly Approach toward Chiral Bimetallic Catalysts: Bis‐Urea‐Functionalized (Salen)Cobalt Complexes for the Hydrolytic Kinetic Resolution of Epoxides

Class III Delocalization and Exciton Coupling in a Bimetallic Bis‐ligand Radical Complex

Cooperative Catalysis with First‐Row Late Transition Metals

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