Carbon monoxide/heterocycle copolymerisation: New catalysts and new biodegradable polymers – NewCatNewBioPol

Only a few different catalytic systems have been studied yet and all systems are based on in-situ formed cobalt catalyst, except the work of Jia, based on the use of well-defined single site cobalt catalyst.
Jia demonstrates that the use of small monophosphine ligand could inhibit the polymerisation reaction due to competition for the nucleophilic attack between the phosphine and the aziridine on the acetyl moiety.It was shown also, that the formation of by-product such as beta-lactame, the ring closure product is probably due to catalyst decomposition.
Thus, introduction of chelating and/or bulky ligands instead of the classical monophosphines such as PPh3, P(o-tolyl)3 could lead to the formation of more stable and productive catalysts, decreasing the formation of by-product and avoiding a possible decoordination of the phosphine ligand as well as the possible nucleophilic attack of the phosphine on the acetyl moiety. Hemilabile ligands, i.e. a strong donor atom such as phosphorus and a weak donor atom such as oxygen, nitrogen, sulfur donor function can also be envisaged.
Based on these observations, the use of chelating trans-diphosphines looks very judicious and promising. Beside, this type of ligand is the center of numerous studies in homogeneous catalysis and especially for carbonylation reaction such as hydroformylation, carbonylation of olefins and methanol carbonylation.
The methodology used for this project is based on an iterative approach: Thus, we will drawn structure/activity/selectivity relationships comparing in situ and preformed catatic systems.

During this first period, we synthetized different reported ligands such as wide bite angle diphosphines developed by Suss-Fink or van Leeuwen (SPANPhos). Moreover we prepared other reported diphosphines P-N-N-P and P-NH-NH-P to study the influence of inclusion of other donor atoms in the ligand structure.
We also prepared new polydentates P,N ligands, easily prepared from diphenyphosphinobenzaldehyde and amine, like P-N-P, N2-P2 and NP3.

Study of the coordination chemistry of the ligands.
Starting the ligand testing in the copolymerization carbon monoxide and heterocycles.

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Due to their unique properties, the demand of synthetic biodegradable polymers as alternative environmentally friendly polymers compared to polyolefins, increases regularly. The remaining problem is the cost of such well defined biodegradable polymers such as polyesters or polyamides, especially because of the cost and poor availability of the starting material. The metal-catalysed alternative copolymerisation of heterocycles and carbon monoxide is a synthetic route of choice for the preparation of polyesters and polyamides from cheap and available monomers. Unfortunately, only a few efficient catalysts, based on cobalt and basic ligand systems, have been described yet. The ambition of the project is to study and develop more elaborated and efficient catalyst to develop and promote a cheap, efficient and industrially viable methodology for the preparation of biodegradable polymers. The first objective of the project will be to develop a large family of potential trans-diphosphine ligands, possessing different electronic and steric properties and then to prepare the corresponding complexes of cobalt and iron. Thanks to their unique properties, chelating trans-diphosphines look very judicious and promising to solve the problems encountered during the copolymerisation (i.e.: catalyst stability, decoordination of the ligand, possible side-reactions). Indeed, trans-diphosphine will stabilise and govern the properties of the catalyst giving a more stable productive and selective system. Beside, this type of ligand is the center of numerous studies in carbonylation reaction such as hydroformylation, carbonylation of olefins… Homogeneous polymerisation results in polymer contamination by metal residues and loss of catalyst, thus there is a considerable interest in developing catalyst based on iron, because of its low cost, biocompatibility and low bio-toxicity. In order to achieve efficient control of the catalytic process, the mechanism and kinetics of the reaction will be investigated as well as systematic structure reactivity studies of the ligand system. Then, attention will be paid to the copolymerisation of CO/heterocycles initiated by our cobalt and iron disphosphine complexes. We will first focus on the copolymerisation of known monomers such as epoxide and aziridine and on optimisation of reaction conditions. Another interesting part of the project will be to use our best systems for the copolymerisation of new monomers, to develop and characterize new materials. Stereoselective copolymerisation with chiral complexes will be an extremely motivating and challenging part for the project as well as the development and characterisation of new materials. By using the catalysts prepared in this project, efficient synthetic method and bio(co)polymers with original properties should result and open new avenues for an industrially viable preparation of biodegradable polymers.