Modular Approach for the Development of Supported, Monofunctionalized, Salen Catalysts

Abstract

We report a modular approach toward polymer-supported, metalated, salen catalysts. This strategy is based on the synthesis of monofunctionalized Mn- and Co-salen complexes attached to a norbornene monomer via a stable phenylene-acetylene linker. The resulting functionalized monomers can be polymerized in a controlled fashion using ring-opening metathesis polymerization. This polymerization method allows for the synthesis of copolymers, resulting in an unprecedented control over the catalyst density and catalytic-site isolation. The obtained polymeric manganese and cobalt complexes were successfully used as supported catalysts for the asymmetric epoxidation of olefins and the hydrolytic kinetic resolution of epoxides. All polymeric catalysts showed outstanding catalytic activities and selectivities comparable to the original catalysts reported by Jacobsen. Moreover, the copolymer-supported catalysts are more active and selective than their homopolymer analogues, providing further proof that catalyst density and site isolation are key toward highly active and selective supported salen catalysts.

Poly(norbornene)‐Supported N‐Heterocyclic Carbenes as Ligands in Catalysis

“…We have observed the same solubility problems with other poly(norbornene)-based catalyst supports. [77] To investigate if any changes of the polymer backbone during or after catalysis are the reason for this reduced solubility, we carried out a series of in situ 1 H and 13 C NMR experiments. The SuzukiMiyaura transformation of phenylboronic acid with chlorotoluene was chosen for the in situ NMR studies.…”

Covalent Heterogenization of a Discrete Mn(II) Bis-Phen Complex by a Metal-Template/Metal-Exchange Method: An Epoxidation Catalyst with Enhanced Reactivity

“…[8][9][10][11][25][26][27] Few of these materials, however, maintain high reactivity with terminal olefins and are even less effective with more electron-deficient olefins such as α,β-unsaturated ketones and esters. The few heterogenized transition metal catalysts that epoxidize electron-deficient olefins, such as a covalently tethered Ru-porphyrin system, 24 have limitations including multiple reaction byproducts and a narrow substrate scope.…”

New strategy for chemically attachment of Schiff base complexes on Multiwalled Carbon Nanotubes surfaces

“…In recent years, the interest of many researchers has been focused on heterogenizing of homogeneous catalysts, and there are a number of successful demonstrations of immobilized homogeneous complexes on supports. Heterogenization of homogeneous catalysts with similar activities affords an appealing methodology to expand the industrial application of homogeneous catalysts; for this purpose, immobilization of metal Schiff base complexes on organic or inorganic supports had been widely reported [27][28][29] . Immobilization via covalent bond on the support is more advantageous and improving the long-term stability of the solid catalyst.…”