ICMUB - UMR CNRS 6302

 

Leading Thematic Keywords related to published works 1998-2008:
Group 4 organometallics / carbozirconation / heterocycles / alkyne activation / olefin polymerization / palladium chemistry / C-C and C- N bond forming catalysis (Suzuki, Sonogashira, Heck, Tsuji-Trost reactions) / ligand chemistry / ferrocene / polyphosphines, / "through-space" NMR spin coupling / resin supported systems / low-loading catalysis / aqueous and ionic liquid medium / polymer supported phosphines / sustainable chemistry and recycling/

Our team has a long time experience in organometallic chemistry of group 4 elements (zirconium, hafnium, titane), as well as metallocene chemistry and its applications (ferrocene, zirconocene). Some recent orientations towards palladium catalysis and polyphosphine chemistry are now completed with related sustainable development through various strategy of resources economy (supported systems, high turnover catalysis). Several themes are developed within the framework of this experience:

• Synthesis of novel heterocycles by zirconium-assisted organometallic chemistry

Starting from arynezirconocenes novel heterocycles incorporating either phosphorus, selenium,  arsenic or sulphur have been obtained in the coordination sphere of the metal. This pathway of synthesis allow to form heterocycles virtually inaccessible by other organic or classical methods (Intramolecular coupling of acetylenic groups of bis(alkynyl)phosphanes and silanes mediated by benzynezirconocene: a route to new mono- and tricyclic heterocycles. Tetrahedron (2004), 60, 1317.)

• Novel metallocene/MAO catalytic systems for olefin polymerisation

The stereoselective synthesis of group 4 organometallic complexes based on isodicyclopentadienyl ligand recently allowed to reach high selectivity and activity in olefin polymerisation and co-polymerisation. One interest of these systems is their non-planarity and the opportunity to modify the hindrance around the metal centre (Titanium isodicyclopentadienide hemimetallocenes for ethylene/styrene copolymerization. European Polymer Journal (2004), 40, 2241-2246.)

• Nonmetallocenes complexes stabilized by nitrogen and phosphorus polydentate ligands

Owing to the fact that in complexes new ligand environments might result in novel patterns of reactivity, and with the view to circumvent an excessively patented area of research, the design and synthesis of zirconium and titanium complexes not incorporating cyclopentadienyl rings has been subject of growing interest in the last decade. The purpose of the present subject is an investigation of the classes of "post-metallocene" group 4 complexes available now for molecular chemists, macrocycles and ferrocenylpolyphosphines complexes are particularly targeted (Selective formation of a unique diphosphonium-diphosphine from a tetraphosphine double protonation induced by zirconium salts. Dalton Transaction (2008) in press.)

• Multidentate phosphine ligands design for high turnover palladium-catalysis

High turnover catalysis in C-C and C-N cross-coupling reactions such as Suzuki, Sonogashira, Heck or Tsuji-Trost (efficient tools for modern catalytic synthesis of pharmaceuticals, alkaloids and materials) was accomplished by employing unprecedented ferrocene-based tri- and tetraphosphine selectively obtained either symmetric or dissymmetric. The fundamental properties of the multidentate ligands towards metal at the various formal oxidation states of the catalytic cycles are studied by electrochemistry and by NMR in collaboration with electrochemists from ICMUB-ARECO group  (Ultra-low catalyst loading as a concept in economical and sustainable modern chemistry: the contribution of ferrocenylpolyphosphane ligands. European Journal of Inorganic Chemistry  (2007),   (24),  3767-3780.)

• Nuclear spin-spin transmission "through-space" in constrained ferrocenyl polyphosphines, development of theoretical models for an unusual phenomenon

³¹P³¹P solution phase "through-space" nuclear spin-spin coupling constants from novel organometallic tetraphosphine nickel and palladium complexes were identified. These JPP constants were accurately determined through NMR iterative simulation based on the second order spectra obtained for the compounds. The corresponding solid state X-ray structure of complexes were determined, and the "through-space" PP distances were determined. Due to the blocked conformation of the species in solution, a qualitative and semi-quantitative experimental correlation was obtained, which links the geometric parameters and the intensity of the corresponding PP coupling constant. The lone-pair overlap theory developed for ¹⁹F¹⁹F and ¹⁵N¹⁹F "through-space" couplings in organic compounds (J. Am. Chem. Soc. 1973, 95, 7747) appears to be a reliable foundation to account for our results. As a consequence more elaborated DFT models are currently developed in collaboration with theoretician from Slovakia Academy of Science on this poorly-known ad yet fundamental topic ("Through-Space" Nuclear Spin-Spin JPP Coupling in Tetraphosphine Ferrocenyl Derivatives: A ³¹P NMR and X-ray Structure Correlation Study for Coordination Complexes. Journal of the American Chemical Society  (2004), 126, 11077).

• Heterogeneisation/recycling of palladium/phosphine innovative systems for C-C coupling

We are currently working on the first supported ferrocenylpolyphosphines and their properties in catalysis and for recycling. On the same topic systems immobilized in ionic liquids are developed in collaboration with ICMUB-SYMS group (The first catalytic method for Heck alkynylation of unactivated aryl bromides (copper-free Sonogashira) in an ionic liquid: 1 mol-% palladium/triphenylphosphane/pyrrolidine in [BMIM][BF₄] as a simple, inexpensive and recyclable system. European Journal of Organic Chemistry  (2007), (4),  583-587.)

• Resin supported organic and organometallic chemistry

Solid-phase synthesis and Merrifield resin chemistry are currently developed in the group both from the aspect of organic chemistry and of the design of organometallic supported complexes. Biologically active and anti-tumoral properties from new resveratrol modified-supports are currently investigated in collaboration with LBMN-INSERM U 866 and IUVV-UMR INRA 1088 CNRS in Dijon.

Based on these results various middle term objectives are currently pursued:
1. Innovative reactivity and syntheses from group 4 organometallic and coordination chemistry.
2. Sustainable development and green chemistry from catalysis under ultra-low loading as well as heterogeneisation of catalytic systems and recyclable medium.
3. Fundamental understanding and mechanistic elucidation in chemical bonding (through nonbonded nuclear  spin couplings ) or of the metal-assisted and metal-catalyzed reactions for fine chemicals (such as carbozirconation, palladium cross-couplings).


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