Bob De Clercq

Immobilization of multifunctional Schiff base containing ruthenium complexes on MCM-41

Abstract Two solid catalysts in which a Schiff base containing ruthenium complex has been covalently anchored on MCM-41 have been prepared and characterized. The catalytic behavior of these materials in ring-closing metathesis (RCM), ring-opening metathesis polymerization (ROMP), Kharasch addition, atom transfer radical polymerization (ATRP) and vinylation reactions as well as the recycling characteristics in RCM reactions are presented to exemplify the effectiveness and the multifunctional character of these catalytic systems. For ROMP the influence of the polymerization solvent on the performance of the catalysts was checked. For the RCM reactions both reaction time and reaction temperature were varied in order to determine the influence of these parameters on the RCM activity of our catalysts. The activity of our catalytic systems in radical reactions such as ATRP and the Kharasch addition is promising. Our results demonstrate that the ATRP process of styrene proceeds in a controlled fashion allowing the synthesis of well-defined polymers. Furthermore, we were able to demonstrate that the Kharasch activity of our catalysts shows a pronounced temperature dependence. In addition to all this, we also postulated a mechanism that explains for the observed selectivities in the vinylation experiments. The host–guest interaction of these hybrid catalytic systems is studied by XRD, XRF, ICP/MS, BET, FT-Raman and solid state NMR analysis.

Assessing the scope of the introduction of Schiff bases as co-ligands for monometallic and homobimetallic ruthenium ring-opening metathesis polymerisation and ring-closing metathesis initiators.

A new class of homobimetallic and monometallic Schiff base-substituted ruthenium olefin metathesis catalysts has been prepared, characterised and tested in ring-closing metathesis (RCM) and ring-opening metathesis polymerisation (ROMP) reactions. The results obtained point out that the synergy of Schiff base ligands with coordinatively labile ligands leads to bimetallic catalytic systems that combine very high activity with excellent stability. Furthermore, the catalytic activity of these catalysts is very dependent on the steric and electronic environment of the Schiff base. To conclude, a mechanism that explains the obtained data is postulated.

A new class of ruthenium complexes containing Schiff base ligands as promising catalysts for atom transfer radical polymerization and ring opening metathesis polymerization

A novel series of Schiff base ruthenium complexes that are active catalysts in the field of atom transfer radical polymerization (ATRP), have been prepared. Moreover, when activated with trimethylsilyldiazomethane (TMSD), these species exhibit good catalytic activity in the ring opening metathesis polymerization (ROMP) of norbornene and cyclooctene. The activity for both the ROMP and ATRP reaction is dependent on the steric bulk and electron donating ability of the Schiff base ligand. The control over polymerization in ATRP was verified for the two substrates that exhibit the highest activity, namely MMA and styrene. The results show that the optimal ATRP equilibrium leading to a controlled polymerization, can be established by adjusting the steric and electronic properties of the Schiff base ligand.

Synthesis and evaluation of a new class of ruthenium-based catalytic systems for atom transfer radical addition and enol ester synthesis

Abstract We now report the synthesis and characterization of a new class of N-heterocyclic carbene (NHC) and Schiff base containing ruthenium complexes and their performance as catalysts in atom transfer radical addition and enol ester synthesis reactions. The ruthenium Schiff base complexes 3a – f mediated the atom transfer radical addition (ATRA) of carbon tetrachloride across olefins in excellent yields which markedly depended on the catalyst and the substrate used. Furthermore, dependant on the catalytic system and the reaction conditions used, enol esters or enynes can be obtained in excellent yields with very high selectivities.

Activity of a new class of ruthenium based ring-closing metathesis and ring-opening metathesis polymerization catalysts coordinated with a 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene and a Schiff base ligand

Abstract A new class of ruthenium based catalysts coordinated with a 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene and a Schiff base ligand have been tested in ring-closing metathesis and ring-opening metathesis polymerization reactions. The results obtained point out that the synergy of Schiff base ligands with a strong Lewis basic N-heterocyclic carbene ligand lead to mixed ligand catalytic systems that combine very high activity with excellent stability. Furthermore, the catalytic activity of these catalysts is very dependent on the steric and electronic environment of the Schiff base.

Ring-closing metathesis, Kharasch addition and enol ester synthesis catalysed by a novel class of ruthenium(II) complexes

Abstract Ruthenium Schiff base complexes I – III mediated the Kharasch addition of carbon tetrachloride across olefins with high yields which markedly depended on the catalyst and the substrate used. In addition, ring-closing metathesis of some representative diolefins was carried out. The best catalytic system III is able to form tri- and tetrasubstituted double bond products. Finally, dependent of the catalytic system and the reaction conditions used, these systems can catalyse the stereoselective formation of enol esters or enynes in excellent yields.

Radical reactions catalysed by homobimetallic ruthenium(II) complexes bearing Schiff base ligands: atom transfer radical addition and controlled polymerisation.

Abstract The homobimetallic ruthenium Schiff base complexes Ia–f mediated the atom transfer radical addition (ATRA) of carbon tetrachloride across olefins in excellent yields which markedly depended on the catalyst and the substrate used. The best catalytic system Ic is able to compete with the highest performing ruthenium catalysts reported so far for ATRA reactions. In addition these systems are also capable of performing atom transfer radical polymerisation (ATRP) reactions with styrene in high yields and with good control over molecular weight and molecular weight distribution.

Limitations of short-term experiments designed for identification of activated sludge biodégradation models by fast dynamic phenomena

Abstract Experimental results obtained in a batch reactor are presented showing different fast dynamic phenomena. All measured OUR-profiles show a ‘start-up’ phase upon substrate addition. Neither the response time of the DO-electrode, the mixing characteristics in the reactor or the extracellular transport limitations could explain this behaviour. It is hypothesised that intracellular transport and conversion processes are responsible for the transient response. Second, dynamics induced by regulation processes of the macromolecular cell composition could be observed. Finally, the adaptation of the mixed culture population to changed operating conditions is demonstrated. The implications for modelling activated sludge biodegradation with simple structured models identified from such experiments are discussed.

A new heterogeneous hybrid ruthenium catalyst being an eco-friendly option for the production of polymers and organic intermediates

We succeeded in synthesising and characterising a new heterogeneous hybrid ruthenium catalyst that exhibits excellent stability, reusability and leaching characteristics. The host–guest interaction is studied by XRD, XRF, ICP/MS, BET, FT-Raman and solid state NMR analysis. Moreover, we tested this catalytic system in ring-closing metathesis (RCM), ring-opening metathesis polymerization (ROMP), Kharasch addition, atom transfer radical polymerization (ATRP) and vinylation reactions. The results obtained from these tests show that for ROMP, RCM, Kharasch addition and vinylation reactions the heterogeneous catalyst possesses important advantages in comparison with its homogeneous analogue.