Controllable Construction of Bio-nanoreactors for Asymmetric Catalysis in Water
Author:Zhang Yao Yao
Supervisor:yin dong hong tan rong
Water is an attractive cleaning solvent in the field of green chemistry.Native enzymes can catalyze efficiently biomass conversion in an aqueous medium.However,traditional catalysts could not dissolve in water,resulting in low catalytic efficiency.Based on the principle of biomimetic catalysis,the aims of this dissertation is to design and synthesize a series of new water-soluble temperature-sensitive bio-nanoreactors for asymmetric catalysis in water.,the bio-nanoreactors can be self-assembled in water via intramolecular interaction at room temperature,forming aggregations with hydrophilic surface and hydrophobic core.The self-assemblies provide a hydrophobic and confined reaction cavity for the aqueous catalytic reaction to solve limited mass transfer associated with aqueous organic reaction.After the reaction,the catalysts could be precipitated from aqueous solution by heating above their LCST,and could be easily recovered and used.No organic solvents were required for the reaction and separation process.(1)A novel thermoresponsive surfactant-type chiral salen Mn(Ⅲ)catalyst was developed by axially grafting "smart"poly(Nisopropylacrylamide)(PNIPAAm)onto the metal center of a neat chiral salen Mn(Ⅲ)complex.At room temperature,the catalysts dissolved in water and form metallomicellar with size of 9 nm via intermolecular interaction,acted as nanoreactors to carry out asymmetric epoxidation of unfunctionalized olefins in water.Dramatically accelerated the reaction rates by "concentrator effect" and outstanding catalytic efficiency was observed in the nanoreactor system.Quantitative conversion(99%)of styrene with high enantioselectivity(39%)was achieved over 0.8 mol%of the catalyst within 3 min,presenting an unprecedented TOF value(2.48×103 h-1)which was significantly higher than that obtained over previously reported homogeneous or heterogeneous systems.Moreover,the catalyst could be easily recovered by thermocontrolled separation and be reused with high activity for five cycles.(2)Chiral salen Ti(Ⅳ)complex was successfully grafted on the hydrophobic block of the thermoresponsive amphiphilic copolymers of poly(N-isopropylacrylamide-co-N,N-dimethyl acrylamide)(poly(NIPAAM-co-DMAAM))through covalent linkage,resulting in novel chiral salen Ti(Ⅳ)catalysts with thermo-responsive surfactant properties.Characterization results suggested the self-assembly behavior of PNIPAAM-tagged chiral salen Ti(Ⅳ)catalysts with various morphologies in water at room temperature.The self-assembled metallomicelles induced a micellar catalytic approach for the asymmetric sulfoxidation in water,leading to an acceleration of reaction and causing selective effects.Only 0.5 mol%of the novel catalyst was sufficient to give quantitative conversion(>99%)with up to 96%chemoselectivity and 95%enantioselectivity in asymmetric oxidation of methyl phenyl sulfide within 30 min,whereas neat complex was far less efficient(9%conversion with 72%chemoselectivity and 79%enantioselectivity).Besides,the catalysts could be easily recovered by thermocontrolled separation and be reused with high activity for several cycles.(3)A series of bio-inspired catalysts containing chiral salen Ti(Ⅳ)complex in their hydrophobic cavity were constructed from the synthesized amphiphilic copolymers of poly(NIPAAm-co-IL/Ti(salen))(NIPAAm,N-isopropylacrylamide;IL/Ti(salen),vinylimidazolium ionic liquid-modified chiral salen Ti(Ⅳ)complex).At room temperature,catalysts can form single-chain polymeric nanoparticles(SCPNs)with size of 3 nm in water via intramolecular hydrophobic effect.These SCPNs behaved as enzyme-mimetic catalysts due to compartmentalization and site isolation,mediating enantioselective oxidation of various sulfides in water.Only 0.5 mol%of the novel catalyst was sufficient to give quantitative conversion(>99%)with up to 95%chemoselectivity and 98%enantioselectivity in asymmetric oxidation of methyl phenyl sulfide.Moreover,the catalysts could be easily recovered for steady reuse by thermo-controlled separation due to the thermo-responsive property.This work first constructed the titanium-containing biomimetic SCNPs for biocatalysis of enantioselective sulfoxidation in water.(4)Amphiphilic random copolymers of poly(NIPAAm-co-oxazoline)carrying chiral oxazoline side-chains were synthesized by copolymerizing chiral oxazoline with thermo-sensitive NIPAAm via reversible addition-fragmentation chain transfer(RAFT)polymerization techniques.Coordinating titanium(Ⅳ)ions to the chiral oxazoline side groups driven self-folding of the individual copolymer chains through the formation of Ti(oxazoline)complex.The TiⅣ-folded SCPNs with size of 1 nm behaved as biomimetic catalysis characteristic via the intramolecular hydrophobic interaction and metal coordination interactions in water,which provides a hydrophobic,constrained cavity for reaction at the room temperature.Only 0.1 mol%of the chiral catalyst was sufficient for affording extremely high activity(conversion>99%)with up to 95%chemoselectivity and enantioselectivity(>97%)for a wide range of sulfides in water.After reaction,the SCPNs became hydrophobic upon heating above its LCST,and precipitated from aqueous system for recovery.It can be recycled for seven times without significant loss of the activity.This work showed the characteristics of bionic catalysis by combines intramolecular hydrophobic effect and metal coordination to construct a controlled SCNPs nanoreactor.(5)A series of three-block thermo-responsive catalysts CuⅡ-PNxFeyOz containing oxazoline Cu complex were constructed from the synthesized three-block copolymers of poly PNxFeyOz by substep reversible addition-fragmentation chain transfer polymerization(RAFT).The catalyst behaved as biomimetic catalysis characteristic via the intramolecular hydrophobic interaction and metal coordination interactions in water,which provides a hydrophobic,constrained cavity for asymmetric Henry reaction.Only 2.0 mol%of the novel catalyst was sufficient to give quantitative conversion(>95%)with up to 99%chemoselectivity and 99%enantioselectivity in asymmetric Henry reaction between 4-nitrobenzaldehyde and nitromethane within 12 h,After reaction,the catalyst became hydrophobic due to NIPAAm upon heating above its LCST,and precipitated from aqueous system for recovery.This work first constructed the oxazoline Cu biomimetic SCNPs for biocatalysis of asymmetric Henry reaction in water.