Christophe M. Thomas

Synthesis of biodegradable polymers from renewable resources

The vast majority of commodity materials are obtained from fossil fuels. However, many studies predict that all fossil resources will be depleted within a few centuries. Biomass represents an abundant carbon-neutral renewable resource for the production of materials. Using biomass for the production of new polymers can have both economic and environmental benefits. This review focuses on the use of biomass for the synthesis of biodegradable polymers.

Polymerization of enantiopure monomers using syndiospecific catalysts: a new approach to sequence control in polymer synthesis.

The ring-opening polymerization of a mixture of enantiomerically pure but different monomers using an yttrium complex as initiator proceeds readily at room temperature to give the corresponding highly alternating polyester.

Artificial metalloenzymes: proteins as hosts for enantioselective catalysis

Enantioselective catalysis is one of the most efficient ways to synthesize high-added-value enantiomerically pure organic compounds. As the subtle details which govern enantioselection cannot be reliably predicted or computed, catalysis relies more and more on a combinatorial approach. Biocatalysis offers an attractive, and often complementary, alternative for the synthesis of enantiopure products. From a combinatorial perspective, the potential of directed evolution techniques in optimizing an enzymes selectivity is unrivaled. In this review, attention is focused on the construction of artificial metalloenzymes for enantioselective catalytic applications. Such systems are shown to combine properties of both homogeneous and enzymatic kingdoms. This review also includes our recent research results and implications in the development of new semisynthetic metalloproteins for the enantioselective hydrogenation of N-protected dehydro-amino acids.

Direct amination of aryl halides with ammonia

The traditional homogeneous access to aromatic amine derivatives is a nucleophilic aromatic substitution of the corresponding aryl halides. The halogen atom is usually relatively inert to amination reaction unless it is activated by the presence of electron withdrawing groups. Consequently, there has been particular emphasis over the past decade on the synthesis of metal complexes that are active catalysts for the preparation of aromatic amines. This tutorial review focuses on the use of metal-based complexes for the direct amination of aryl halides with ammonia.

Bis(guanidinate) Alkoxide Complexes of Lanthanides : Synthesis, Structures and Use in Immortal and Stereoselective Ring-Opening Polymerization of Cyclic Esters

A series of new bis(guanidinate) alkoxide Group 3 metal complexes [Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) has been synthesized. X-ray structural determinations revealed that bis(guanidinate) tert-butoxides are monomeric complexes. The isopropoxide complex [Y((Me3Si)2NC(NiPr)2)2(OiPr)] undergoes slow decomposition in solution, to afford the unusual dimeric amido complex [(Y((Me3Si)2NC(NiPr)2)2(mu-N(iPr)C triple chemical bond N))2]. Complexes [Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) are active catalysts/initiators for the ROP of rac-lactide and rac-beta-butyrolactone under mild conditions. Most of those polymerizations proceed with a significant degree of control. Bis(guanidinate) alkoxides appear to be well suited for achieving immortal polymerization of lactide, through the introduction of large amounts of isopropanol as a chain-transfer agent. The synthesized complexes are able to promote the stereoselective ROP of rac-beta-butyrolactone to afford syndiotactic poly(hydrobutyrate) through a chain-end control mechanism, while they are surprisingly non-stereoselective for the ROP of lactide under strictly similar conditions.

Tandem synthesis of alternating polyesters from renewable resources

The vast majority of commodity materials are obtained from petrochemical feedstocks. These resources will plausibly be depleted within the next 100 years, and the peak in global oil production is estimated to occur within the next few decades. In this regard, biomass represents an abundant carbon-neutral renewable resource for the production of polymers. Here we report a new strategy, based on tandem catalysis, to obtain renewable materials. Commercially available complexes are found to be efficient catalysts for alternating polyesters from the cyclization of dicarboxylic acids followed by alternating copolymerization of the resulting anhydrides with epoxides. This operationally simple method is an attractive strategy for the production of new biodegradable polyesters.

Controlled ring-opening polymerization of lactide by group 3 metal complexes

In this review, attention is focused on the use of group 3 metal complexes for the ring-opening polymerization (ROP) of lactide to give polylactides (PLAs). Synthesis of PLAs has been studied intensively due to their biocompatible and biodegradable properties and their potential applications in medical and agricultural fields. ROP of lactide, a cyclic diester of lactic acid, provides PLA. This review includes our recent research results and implications in developing new amino-bis(phenolate) group 3 initiators for the synthesis of polyesters.

Precision Synthesis of Biodegradable Polymers

while on the other hand they have to complywith increasingly stringent regulations on sterilization, bio-compatibility, and in vivo clearance. Consequently, therenowadays is a huge gap between promising options reportedin the scientific literature and real bioapplicable systems. Forinstance,theoverallnumberofapprovedpolymersforhumanuse is relatively low. Biodegradable aliphatic polyesters suchas poly(lactic acid) (PLA), poly(glycolic acid) (PGA) andpoly(lactic-co-glycolic acid) (PLGA) are widely used poly-mers in life sciences.

Metal-Catalyzed Synthesis of Alternating Copolymers

The creation of polymers with a high degree of sequence and/or stereocontrol represents an exciting frontier in materials science. In order to obtain alternating polymers, coordination polymerization using well-defined metal complexes has played a leading role in the last two decades. In the following paper, we will describe selected published efforts to achieve these research goals using discrete, structurally well-characterized metal complexes.

Catalytic oxidation of alcohols into aldehydes and ketones by an osmium-copper bifunctional system using molecular oxygen

Abstract The oxidation of allylic and benzylic alcohols to aldehydes can be carried out at room temperature as low as 25°C with molecular oxygen, in the presence of the bifunctional osmium-copper system OsO 4 CuCl acting as the catalyst.