Highlight of the results
Work package 2 (Ligand Design)
Ligand design is crucial in molecular catalysis. Therefore, an entire work package is dedicated to the development of new ligands, aiming at the improvement of catalytic activities, stabilities, and especially selectivities (notably enantioselectivity in asymmetric catalysis). This activity is heavily centred on synthesis but also relies on DFT computations for guidance. Particular attention has been devoted to specific objectives, which are declined in four separate tasks as follows (with the implicated ESRs in parentheses): T2.1: NHC Ligands (ESRs 1, 10); T2.2: Chiral Ligands (ESRs 2, 4, 8); T2.3: New Phosphorus Ligands (ESRs 7, 12); T2.4: Ligand modification for immobilization (ESRs 2, 4, 9, 10, 12, 13).
Within the objective to develop a new generation of Z-selective or stereoretentive Ru-based olefin metathesis (OM) catalysts, ESR1 has synthesized modified N-Heterocyclic Carbene (NHC) ligands. The aim of ESR2 is the development of efficient catalytic systems for the synthesis of drugs and/or biologically active molecules via the asymmetric Rh-catalysed hydroaminomethylation of alkenes, notably with several families of diphosphites and phosphite-phosphoramidite ligands. He has initiated the synthesis of a new backbone for subsequent ligand formation. ESR4’s project aims at developing phosphine-type chiral ligands in order to prepare both chiral rhodium complexes and chiral rhodium nanoparticles. Up to now, two ligands have been synthesized and grafted onto carbon nanotubes. ESR7 aims at using light to control the rate and selectivity of chemical reactions through photo-switchable catalysts. For this purpose, she has developed new ligands base on the dithienylethene core, which undergoes an open-closed photoisomerisation process. ESR10 has synthesized new NHC ligand precursors by the incorporation of phenolic/amino tags in the structure, which could provide an anchoring point for Janus-type dendrimers, with the goal of immobilizing Ru catalysts for the implementation of olefin metathesis reactions in green media, such as water or supercritical carbon dioxide (scCO2). ESR12 has synthesized and fully characterized one carboranyl diphosphine equipped with an additional function, suitable for the grafting to dendrimers. ESR13 has synthesize a phenol phosphine for further incorporation on the surface of dendrimers that are further functionalized by perfluoroalkyl chains for compatibilization and catalytic applications in supercritical CO2.
Work package 3 (Precatalyst development)
Pre-catalyst development is an essential phase in preparation for the catalytic studies. Three facets of this work can be distinguished and are separated in different tasks. One of them (T3.1, Precatalysts based on the new ligands; ESRs 1, 2, 7, 8, 10) is the metal coordination of the newly developed ligands for the generation of new complexes similar to others that have already demonstrated activity in the catalysed transformations of interest. The second facet (T3.2, New catalytic systems; ESRs 3, 4, 6, 9, 11, 14, 15) is the development of entirely new systems for the development of new reaction, comprising s-block metal systems, Ge-based ligands and the development of new and better controlled metal nanoparticles. The third one (T3.3, Ligand and precatalyst confinement; ESRs 2, 4, 9, 10, 11, 12, 13) is the ligand modification with functions that do not alter the nature, activity and selectivity of the active site but that allow the catalyst confinement in special media.
ESR1 has synthesized Ru complexes with his ligands developed in WP2.In parallel with a preliminary screening of reaction conditions, ESR2 has prepared [Rh(acac)(L-L)] and [Rh(COD)(L-L)][BF4] catalyst precursors for the hydroaminomethylation reaction. ESR3 has developed alkali metal arylphosphinides with known secondary phosphines, to be used in the catalysed hydrophosphination of unsaturated substrates. ESR4 has used her new ligands to prepare rhodium complexes and has immobilized them onto non-functionalized and functionalized carbon nanotubes. ESR6 has prepared a new Mg hydride dimer complex with a bulky amidinate ligand, for later use in CO2 reduction processes. ESR9 has developed Rh new olefin metathesis catalysts based on his new ligands. ESR11 has used a series of new functionalized ionic liquids for the immobilization of ruthenium metal nanoparticles. ESR13 has grafted phenol bearing perfluoroalkyl chain and the phenol functionalized iminophosphines developed in WP2, affording the expected bifunctional dendrimer. ESR14 has prepared new ruthenium pre-catalysts containing silanes and germanes.
Work package 4 (Reactions and mechanisms)
Catalyst improvement requires a profound understanding of the catalyst mechanism of action, namely the identification of the elementary steps of the catalytic cycle and notably the two key structures delimiting the energy span of the cycle (resting state or rate-determining intermediate and rate-determining transition state) for the catalyst activity (turnover frequency). The improvement of selectivities requires, in addition, knowledge about the mechanism and energy span of the cycle(s) leading to the formation of the by-product(s). This work package also comprises the exploration of new bond activation modes, aiming at the ultimate development of new catalysed reactions, with particular focus on the involvement of C-F bonds and on new processes of hydrophosphination, hydrosilylation and hydrogermylation (P-H, Si-H and Ge-H bond activation). This work package is therefore organized in two separate tasks as follows: T4.1 New bond activation and reactions (ESRs 5, 6, 14, 15); T4.2: Analysis of catalytic mechanisms (ESRs 1, 3, 8).
ESR3 has explore the mechanism of the addition of P-H bonds of phosphine oxides Ar2P(O)H onto alkynes (hydrophosphorylation), which shows a strong dependence on the catalyst alkali metal ion. The work of ESR5 consists in studying novel metal-mediated C–F bond activation and formation processes with the ultimate goal to find new catalytic pathways leading to organic molecules with complex fluorination patterns. She has developed a new process leading to regioselective C–F bond activation/C–C coupling for a fluorinated pyridine scaffold. ESR6 has thoroughly investigated the reactivity of Mg and Ca hydride complexes featuring β-diketiminate (nacnac) ligands with CO2. ESR8 has explored the role of a strong based and the intimate nature of the active catalyst generated from [IrCl(η-1,5-COD)]2 (COD = cyclooctadiene) and bidentate phosphine-thioether ligands, used in asymmetric ketone hydrogenation, using a model dppe ligand system by a combination of experiments and DFT calculations. ESR14 has explore the reactivity of bis-silane Ru complexes towards nitrile and fully elucidated the mechanism of the catalytic generation of iminohydrosilazanes through a combined experimental/computational approach. ESR15 has developed Lewis acid/base pair systems using bulky NHCs and boranes and has explored, using electrochemistry and DFT computations, their propensity for 1e- reduction and spin density localization on the CO2 carbon atom, in order to promote C-C bond formation from CO2. The ultimate goal is to accomplish a photocatalyzed direct carboxylation of aliphatic C-H bonds.
Work package 5 (Catalytic studies)
In this work package, which represents the ultimate goal of the network scientific and training activity, all different types of catalytic implementation are considered, including the application of the new precatalysts to already known catalytic transformations seeking improved performance, the development of new catalysed transformations based on the newly discovered bond activation modes, as well as novel ways to implement known catalysed processes aiming at a facilitated catalyst recovery and recycling (e.g. continuous flow or biphasic implementations, using immobilized versions of known catalytic systems on solid supports, in dendrimers or in polymeric nanoreactors. The task organization is as follows: T5.1, Known catalytic reactions (ESRs 1, 3, 6, 8, 10, 12); T5.2, New catalysed transformations (ESRs 2, 5, 14, 15); T5.3, New implementations of catalysis (ESRs 2, 4, 7, 9, 10, 11, 12, 13).
ESR1 has studied the activity of his new Ru-complexes in different model reactions and using various activation pathways. Quite satisfactorily, one developed catalyst is more active and more stable than the state of the art, validating the initial concept and approach. ESR2 has focused on the synthesis of (R)-Tolterodine, which is a chiral amine-containing drug used in the treatment of urinary incontinence. Moderate enantioselectivites have been obtained and work is ongoing aiming to improve it. ESR3 has obtained phospholes by the double P-H addition of primary phosphines to 1,3-diyines. Studies with respect to the nature of the alkali metal catalyst (size and hardness) as well as to the influence of the bulky aryl group (steric hindrance) are planned. ESR4 first studied the catalytic behaviour of Valmet chiral bases as organocatalysts in the Henry and aldol reactions, and of their copper (II) complexes as homogeneous catalysts for the cyanosilylation reaction. The obtained results were published at ChemCatChem in 2021. Then, the hydrogenation of dimethyl itaconate was studied with the rhodium pre-catalysts described in WP3 under homogeneous and heterogeneous conditions. ESR6 is using Mg and Ca complexes for the selective 4e- reduction of CO2 by hydroboration. While this specific CO2 reduction field has emerged as a powerful tool for very complex transformations of CO2, there is no example of 4e- hydroboration of CO2 catalysed by Mg or Ca complexes. Satisfyingly, CO2 hydroboration occurs under mild conditions. ESR9 has implemented substrate reduction processes with nanoreactor-confined Rh NPs under aqueous biphasic conditions for efficient catalyst recovery by decantation and recycling. ESR11 has successfully implemented ruthenium nanoparticles stabilized by functionalized ionic liquid in catalytic hydrogenations of phenylacetylene and styrene under mild reaction conditions. The conversion of more polar substrates and recycling studies are ongoing. ESR14 has accomplished the catalytic hydrosilylation of nitriles by dihydrosilane, leading to iminohydrosilane, with better activity and perfect selectivity compared with the state of the art.