The design and preparation of a chiral Pt nanocatalyst system possessing thermoregulated phase-separation property and its application in recyclable asymmetric hydrogenation of α-ketoesters are presented.

Thermoregulated phase-separable Rh nanoparticles (abbreviated as TPS-Rhnano) were found to be efficient catalysts for selective hydrogenation of CC bonds in α,β-unsaturated aldehydes and ketones with a selectivity of >99% at >99% conversion. More importantly, the catalyst could be easily separated by simple phase separation and reused directly eight times without evident loss in activity and selectivity.

Reversible phase transfer of noble metal nanoparticles (NMNPs) without the presence of phase transfer agents or supplementary reagents is a big challenge. Through a simple protocol, we demonstrated and expanded an easy, highly efficient, and continuously reversible hydrogen-bond-selective phase transfer directed towards thermoregulated ligand Ph2P(CH2CH2O)22CH3-stabilized noble metal (Pt, Ru, Ir, Pd, and Au) nanoparticles in the aqueous/alcohols biphasic system. When the thermoregulated ligand was integrated onto the NMNP surface, it provided a better switchable surface hydrophobicity/hydrophilicity for the NMNPs. So the critical parameters controlling the phase transfer of NMNPs, such as temperature, gas atmosphere and organic solvent, were studied. With the help of TEM, UV-vis, and ICP-AES, the as-prepared NMNPs (Pt, Ru, Ir, Pd, and Au) not only exhibited a high level of dispersion stability, but also had an almost constant size distribution (excluding Au-NPs) and very high phase transfer efficiency during the multiple reversible phase transfer processes. In addition, a simple mechanism with respect to the reason for the increase of Au nanoparticle size was discussed. Subsequently, the as-prepared Pt-NPs were used as the catalyst for the hydrogenation of diphenylacetylene (DPA). A complete semihydrogenation to stilbene and a better stereoselectivity to cis-stilbene were achieved. Additionally, the as-prepared Pt-NPs can be recycled for 13 times without evident loss in activity and selectivity. Therefore, our investigations supply a fundamental and systematic study of the reversible phase transfer of NMNPs (Pt, Ru, Ir, Pd, and Au), and then also afford an attractive solution to the problem of separating and recycling the NMNP catalysts.

PEG-stabilized rhodium nanoparticles exhibited high activity, selectivity and recyclability for the hydrogenation of quinoline and its derivatives. The selectivity of 1,2,3,4-tetrahydroquinoline was higher than 99%. The catalysts were recycled ten times with a total turnover number of 10592, which is the highest value ever reported for quinoline.

A thermoregulated ionic liquid and organic biphasic system composed of ionic liquid [CH3(OCH2CH2)16N+Et3][CH3SO3−] (ILPEG750) with ILPEG750-stabilized Pd nanoparticles and organic solvents, which allows for not only a highly efficient homogeneous catalytic reaction, but also an easy biphasic separation and reuse of catalyst attributed to the thermoregulated phase-transition property of the system, was employed for Heck reaction. The ILPEG750-stabilized Pd nanoparticle catalyst exhibited high efficiency, more importantly, after reaction the Pd nanoparticle catalyst could be separated from products by simple phase separation and recycled for six times without evident loss of activity.

A thermoregulated ionic liquid and organic biphasic system composed of quaternary ammonium-based ionic liquid N,N-dimethyl-N-(2-(2-methoxyethoxy)ethyl)-N-(2-(2-octyloxyethoxy)ethyl) ammonium methanesulfonate (1) and cyclohexane was first applied for the Rh nanoparticle catalyzed hydroformylation of olefins, which allows for not only a highly efficient homogeneous catalytic reaction, but also an easy separation and reuse of catalyst. Under the optimized conditions, various olefins could be converted completely with ≥98 % selectivity for aldehydes. After reaction, the Rh nanoparticle catalyst could be recovered by simple phase separation and reused for five times without evident loss of activity.

A novel thermoregulated phosphine ligand Ph2P(CH2CH2O)nCH3 (n = 22) was synthesized and used for the Rh-catalyzed hydroformylation of mixed C11–12 olefins in aqueous/organic biphasic system. Under the optimized conditions, pressure = 5 MPa (H2:CO = 1:1), phosphine/Rh = 13 (molar ratio), reaction time = 6 h and temperature = 130 °C, the conversion of C11–12 olefins and the yield of aldehyde are 99% and 94%, respectively. The catalyst retained in aqueous phase can be easily separated from the product-containing organic phase by simple phase separation and the catalytic activity remains almost constant after four consecutive cycles.

Rh nanoparticles stabilized by PEG-substituted triphenyl-phosphine (PETPP, P[C6H4-p-(OCH2CH2)nOH]3) combining double stabilization effects demonstrated high activity and good recyclability in aqueous biphasic hydrogenation of benzene. The value of turnover frequency (TOF) was 3333 h−1. Furthermore, the rhodium nanoparticle catalyst could be easily recycled for five times without loss in activity.

Rh nanoparticle catalyzed hydrogenation of olefins in a biphase system composed of [CH3(OCH2CH2)16N+Et3][CH3SO3−] (ILPEG750) ionic liquid and organic solvent allows for not only a highly efficient homogeneous catalytic reaction, but also an easy separation and reuse of catalyst attributed to the thermoregulated phase-transition property of the ILPEG750 and organic biphase system. Under the optimized conditions, various alkenes could be hydrogenated to the corresponding alkanes as the sole product with 100% conversion. The Rh nanoparticles can be recovered by simple phase separation and reused for nine times without evident loss of activity.We present a new method for the hydrogenation of olefins catalyzed by Rh nanoparticles in a biphase system composed of [CH3(OCH2CH2)16N+Et3][CH3SO3−] (ILPEG750) ionic liquid and organic solvent. The method allows for not only a highly efficient catalytic hydrogenation reaction, but also an easy separation and reuse of catalyst attributed to the thermoregulated phase-transition property of the ILPEG750 and organic biphase system.Download full-size imageHighlights► A thermoregulated ionic liquid/organic biphase system with nano-Rh was developed. ► The system can realize homogeneous reaction coupled with biphase separation. ► Nano-Rh was active and recyclable catalyst for hydrogenation of olefins.

Poly(ethylene glycol) (PEG)-stabilized Rh nanoparticles prepared by simple hydrogen reduction of RhCl3·3H2O in the presence of PEG4000 (PEG with an average molecular weight of 4000 g/mol) were shown to be efficient and recyclable catalysts for hydroformylation of olefins in thermoregulated PEG biphasic system, which allows for not only an efficient homogeneous catalytic reaction, but also an easy biphasic separation and reuse of catalyst. Under the optimized conditions, the conversion of various olefins and the yield of corresponding aldehydes were ≥ 98%. The Rh nanoparticle catalyst could be separated from products by simple phase separation and recycled for twenty times without evident loss of activity.Poly(ethylene glycol) (PEG)-stabilized Rh nanoparticles in thermoregulated PEG biphasic system, which can realize homogeneous reaction under heating coupled with an easy biphasic separation by cooling, were active, stable and recyclable catalysts for hydroformylation of olefins.Download full-size imageHighlights► PEG-stabilized Rh nanoparticles in thermoregulated PEG biphasic system were firstly used for hydroformylation. ► The system can realize a homogeneous reaction coupled with a biphasic separation. ► PEG-stabilized Rh nanoparticles are active, stable and recyclable catalysts for hydroformylation of olefins.

A simple, effective and reversible aqueous/organic phase-transfer method for rhodium nanoparticles was developed on the basis of the cloud point (Cp) of thermoregulated ligand. The rhodium nanoparticles stabilized by thermoregulated ligand Ph2P(CH2CH2O)nCH3 (n = 16) could transfer from aqueous phase to 1-butanol phase and vice versa by means of changing temperature. This thermoregulated phase-transfer rhodium nanoparticle catalyst evaluated in the hydrogenation of olefins in an aqueous/1-butanol biphasic system exhibited high activity and stability.

PEG-stabilized rhodium nanoparticles exhibited high activity, selectivity and recyclability for the hydrogenation of quinoline and its derivatives. The selectivity of 1,2,3,4-tetrahydroquinoline was higher than 99%. The catalysts were recycled ten times with a total turnover number of 10592, which is the highest value ever reported for quinoline.

In the same catalytic system, thermoregulated ligand Ph2P(CH2CH2O)22CH3-stabilized iridium nanoparticles exhibited a totally different orientation for the hydrogenation of unsaturated carbonyl compounds, namely, highly selective hydrogenation of the CO bond for α,β-unsaturated aldehydes and the CC bond for α,β-unsaturated ketones.

The design and preparation of a chiral Pt nanocatalyst system possessing thermoregulated phase-separation property and its application in recyclable asymmetric hydrogenation of α-ketoesters are presented.