Jean-François Blanco

Core–Shell Nanoreactors for Efficient Aqueous Biphasic Catalysis

Water-borne phosphine-functionalized core-cross-linked micelles (CCM) consisting of a hydrophobic core and a hydrophilic shell were obtained as stable latexes by reversible addition-fragmentation chain transfer (RAFT) in water in a one-pot, three-step process. Initial homogeneous aqueous-phase copolymerization of methacrylic acid (MAA) and poly(ethylene oxide) methyl ether methacrylate (PEOMA) is followed by copolymerization of styrene (S) and 4-diphenylphosphinostyrene (DPPS), yielding P(MAA-co-PEOMA)-b-P(S-co-DPPS) amphiphilic block copolymer micelles (M) by polymerization-induced self-assembly (PISA), and final micellar cross-linking with a mixture of S and diethylene glycol dimethacrylate. The CCM were characterized by dynamic light scattering and NMR spectroscopy to evaluate size, dispersity, stability, and the swelling ability of various organic substrates. Coordination of [Rh(acac)(CO)2 ] (acac=acetylacetonate) to the core-confined phosphine groups was rapid and quantitative. The CCM and M latexes were then used, in combination with [Rh(acac)(CO)2 ], to catalyze the aqueous biphasic hydroformylation of 1-octene, in which they showed high activity, recyclability, protection of the activated Rh center by the polymer scaffold, and low Rh leaching. The CCM latex gave slightly lower catalytic activity but significantly less Rh leaching than the M latex. A control experiment conducted in the presence of the sulfoxantphos ligand pointed to the action of the CCM as catalytic nanoreactors with substrate and product transport into and out of the polymer core, rather than as a surfactant in interfacial catalysis.

Preparation of Polymer Supported Phosphine Ligands by Metal Catalyzed Living Radical Copolymerization and Their Application to Hydroformylation Catalysis

A series of well‐defined polystyrene‐supported tertiary phosphine ligands were prepared by copper‐catalyzed atom transfer radical polymerization (ATRP), involving direct copolymerization of styrene and 4‐diphenylphosphinostyrene (or 4‐styryldiphenylphosphine, SDPP). Copolymerization of the two monomers at different molar ratios showed a decreasing level of control as the SDPP molar fraction (fSDPP) increased. A satisfactory level of control was achieved for fSDPP≤0.25 such that there was a constant concentration of growing “living chains”, and linear Mn growth with conversion and low dispersity. Copper‐free polymers with different chain lengths were prepared and tested as polymeric ligands in the rhodium‐catalyzed hydroformylation of 1‐octene. The polymeric ligands yielded higher linear/branched selectivity and lower activity relative to PPh3 at the same P/Rh ratio. The selectivity increased slightly as a function of the polymer chain length.

One-Pot RAFT Synthesis of Triphenylphosphine-Functionalized Amphiphilic Core-Shell Polymers and Application as Catalytic Nanoreactors in Aqueous Biphasic Hydroformylation

Controlled radical polymerization has recently been used to develop polymers engineered for applications as catalytic nanoreactors. In this contribution, we present the joint development, in our laboratories, of core-cross-linked micelles (CCM) for application under aqueous biphasic conditions through the micellar approach, using triphenylphosphine (TPP) as polymer-anchored ligand and rhodium as catalytic metal for the hydroformylation of 1-octene as a model α-olefin. The polymers were synthesized by a one-pot convergent approach using RAFT as controlling method in water, making use of the polymerization-induced self-assembly (PISA) principle. The article will also show the polymer properties in terms of size, polydispersity, swelling, metal coordination and exchange, and interpenetration. It will also illustrate our initial catalytic studies with focus on the effect of the polymer architecture (ligand nature, ligand density, core size, nature of cross-linking) and of the stirring rate on the catalytic performance (turnover frequency) and catalyst leaching.

Synthesis of High-Molecular-Weight Multifunctional Glycerol Polyhydroxyurethanes PHUs.

Glycerol carbonate acrylate is a 5-membered cyclic carbonate synthesized from glycerol that is used as a chemical coupling agent and has proven highly suitable for use in the synthesis of multifunctional polyhydroxyurethanes (PHUs). The multifunctionality of the structure of PHUs is determined by the density of the carbon-amine groups generated by the Aza-Michael reaction and that of the urethane groups and adjacent primary and secondary hydroxyl groups generated by aminolysis. Glycerol carbonate acrylate is polymerized with polyfunctional mono-, di-, tri, and tetra-amines, by type-AB polyaddition, either in bulk or in solution, through stepwise or one-pot reaction strategies in the absence of added catalysts. These approaches result in the generation of linear, interchain, and crosslinked structures, through the polyaddition of linear and branched amines to the ethylene and cyclic carbonate sites of glycerol carbonate acrylate. The resulting collection of organic molecules gives rise to polyethylene amino ester PHUs with a high molar mass, exceeding 20,000 g·mol−1, with uniform dispersity.

Core-Cross-Linked Micelles and Amphiphilic Nanogels as Unimolecular Nanoreactors for Micellar-Type, Metal-Based Aqueous Biphasic Catalysis

Biphasic homogeneous protocols are attractive for catalyzed transformations in industry, especially when conducted with water as the catalyst phase as exemplified by the large-scale Rhone-Poulenc/Ruhrchemie hydroformylation process, but can only be applied when the substrate is sufficiently soluble in the aqueous phase to sustain sufficiently fast mass transport . Different solutions to reduce mass transport limitations include the use of additives to increase the substrate solubility in water or increase the water/organic interface, anchoring the catalyst onto a lower critical solution temperature (LCST) polymer to implement thermomorphic behavior, and anchoring the catalyst to the hydrophobic part of surfactants or amphiphilic block copolymers that self-assemble in the form of micelles in water. The use of catalytic micelles appears as the most attractive approach but is limited by the potential formation of stable emulsions and by loss of free macromolecules during separation. These limitations are removed by cross-linking the macromolecules into a unimolecular nanoreactor. This chapter covers the emerging area of unimolecular catalytic nanoreactors, focusing on transition metal-based catalytic applications. It will also present the synthesis of new types of catalytic unimolecular nanoreactors developed in our laboratories, conceived to function on the basis of the micellar catalysis principle. These nanoreactors consist of either core-cross-linked micelle (CCM) or amphiphilic functionalized nanogels (NG). The proof of principle of their catalytic performance in the aqueous biphasic hydroformylation of 1-octene will also be presented. The catalyst confinement objective which is highlighted in this chapter is process optimization in terms of the catalyst phase recovery and recycling.