Ru–Pd Thermoresponsive Nanocatalyst Based on a Poly(ionic liquid) for Highly Efficient and Selectively Catalyzed Suzuki Coupling and Asymmetric Transfer Hydrogenation in the Aqueous Phase

Abstract

The development of intelligent polymeric materials to precisely control the catalytic sites of heterogeneous catalysts and enable highly efficient catalysis of a cascade reaction is of great significance. Here, the utilization of a polymer ionic liquid (PIL) containing two different anions facilitates the preparation of Ru−Pd catalysts with controllable phase transition temperatures and hydrophilic and hydrophobic surfaces. The combined multifunctionality, synergistic effects, micellar effects, aggregation effects, and temperature responsiveness of the nanocatalyst render it suitable for promoting selectively catalyzed Suzuki coupling and asymmetric transfer hydrogenation in water. Above the lower critical solution temperature (LCST) of the catalyst, it catalyzes only the coupling reaction with a high turnover number (TON) of up to 999.0. Below the LCST, the catalyst catalyzes only the asymmetric transfer hydrogenation with good catalytic activity and enantioselectivity. It is important that the catalyst can be simply and effectively recovered and recycled at least 10 times without significant loss of catalytic activity and enantioselectivity. This study also highlights the superiority of multifunctional heterogeneous catalysts based on PILs, which not only overcome limitations associated with low activity of heterogeneous catalysts but also realize selective reactions according to a temperature change, thereby improving the reactivity and enantioselectivity in multiple organic transformations.

Compartmentalization and Photoregulating Pathways for Incompatible Tandem Catalysis

“…Scientists have developed multicompartmental catalytic systems based on various strategies including the use of sol–gels, Pickering emulsion droplets, supramolecular metal complex architectures, , and polymers. , Catalytic frameworks fabricated from these materials have realized compartmentalization for multiple active catalytic sites, as epitomized by the cell, and enabled multistep nonorthogonal transformations. − ,− Incorporating responsive elements into the support structures has rendered them “smart”, i.e., allowing for reversible alterations of the physical and chemical properties in response to external stimuli such as temperature, , pH, light, , or enzymes. , The properties of the resulting smart materials impart an additional bioinspired control over single-step catalytic transformations. ,− Manipulation of multicatalytic tandem sequences, however, remains challenging and restricted to the regulation of reactivities via temperature actuation. , This limitation significantly affects the choice of catalysts and limits the feasibility of performing one-pot tandem catalysis at arbitrary temperature ranges. To date, no “smart” catalytic system can use or control different switchable states to tune and activate a desired synthetic pathway among many possible ones during a multistep synthesis.…”

“…24,31−35 Manipulation of multicatalytic tandem sequences, however, remains challenging and restricted to the regulation of reactivities via temperature actuation. 36,37 This limitation significantly affects the choice of catalysts and limits the feasibility of performing one-pot tandem catalysis at arbitrary temperature ranges. To date, no "smart" catalytic system can use or control different switchable states to tune and activate a desired synthetic pathway among many possible ones during a multistep synthesis.…”

From a single helix to a helical porous metalloenzyme catalyst based on temperature sensitive polyionic liquids

“…This concept of “biomimetic enzyme catalysis” has been successfully applied to palladium catalyzed reactions in water. 22–29 For example, Weberskirch et al reported that a polymer with an oxazolinyl group supported metal Pd catalyst can effectively catalyze the Suzuki coupling reaction in water by forming micelles. 26 Anderson et al .…”

Self-Assembled Thermoresponsive Molecular Brushes as Nanoreactors for Asymmetric Aldol Addition in Water

“…Polymer-supported catalysts that are functionalized with triggerable units can change their activity and selectivity in response to external stimuli ( e.g., temperature and light). , Poly­( N -isopropylacrylamide) (PNIPAM) is a thermoresponsive polymer with a lower critical solution temperature (LCST) of approximately 32 °C in water. , The solubility differences of PNIPAM as a function of temperature have been used for the recovery of polymer-supported catalysts from reaction mixtures. , Elevating the temperature of PNIPAM above the LCST can form a hydrophobic micellar pocket to enhance substrate uptake and reaction conversion. , Alternatively, it can cause aggregation of the PNIPAM chains, thereby preventing accessibility to catalytic sites and diminishing reactivity. , …”

“…16−19 Polymer-supported catalysts that are functionalized with triggerable units can change their activity and selectivity in response to external stimuli (e.g., temperature and light). 20,21 Poly(N-isopropylacrylamide) (PNIPAM) is a thermoresponsive polymer with a lower critical solution temperature (LCST) of approximately 32 °C in water. 22,23 The solubility differences of PNIPAM as a function of temperature have been used for the recovery of polymer-supported catalysts from reaction mixtures.…”