Monika Mayr

Monolithic Materials: New High‐Performance Supports for Permanently Immobilized Metathesis Catalysts

Polymerchemistry and materials sciences have seen the introductionof new trends by metathesis-based techniques, such as ring-opening metathesis polymerization (ROMP) or acyclic dienepolymerization (ADMET). Complementary, cross-metathesisand ring-closing metathesis find ample application in organicchemistry.

Synthesis of a Silica‐Based Heterogeneous Second Generation Grubbs Catalyst

The synthesis of a second generation Grubbs catalyst immobilized onto non-porous silica is described. For this purpose, a polymerizable cationic NHC precursor, 1,3-bis(1-mesityl)-4-{[(bicyclo[2.2.1]hept-5-en-2-ylcarbonyl)oxy]methyl}-4,5-dihydro-1H-imidazol-3-ium tetrafluoroborate (5) was prepared and characterized by X-ray analysis. Oligomers were prepared therefrom using both the well-defined Schrock initiator Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)[OCMe(CF3)2]2 and the first generation Grubbs catalyst Cl2Ru(CHPh)(PCy3)2. Ru-initiated oligomerizations were terminated with ethyl vinyl ether, Mo-initiated oligomerizations were terminated by addition of (EtO)3SiCH2CH2CH2NCO. (EtO)3Si-terminated oligomers obtained by the Wittig-like reaction between the Mo-containing oligomer and the isocyanate were used for the immobilization of the NHC-precursor containing oligomers on non-porous silica. Both oligomerizations were characterized by quantitative consumption of the corresponding initiator. This allowed the controlled synthesis of oligomers via stoichiometry. Using both non-porous and porous silica, degrees of derivatization of 0.04 and 0.02 mmol, respectively, of cationic NHC precursor/g silica were obtained. These precursors were converted into the corresponding NHCs by standard procedures and used for the generation of a heterogeneous second-generation Grubbs catalyst. Ruthenium loadings of 5.3 and 1.3 μmol/g, corresponding to 0.5 and 0.1 weight-% of catalyst were realized. Additionally, coating techniques were applied, where C18-derivatized silica-60 was loaded with oligo-5. Conversion into the corresponding heterogeneous catalyst revealed 4.1 μmol/g, corresponding to 0.4 weight-% of catalyst. All supported catalysts prepared by this approach were successfully used in RCM in slurry type reactions.

Access to silica- and monolithic polymer supported CC-coupling catalysts via ROMP: applications in high-throughput screening, reactor technology and biphasic catalysis

N ,N -Di(pyrid-2-yl)norborn-2-ene-5-ylcarbamide (1) and N ,N -di(pyrid-2-yl)-7-oxanorborn-2-ene-5-ylcarbamide (3) were used for the synthesis of the corresponding dichloropalladium(II) complexes, N -(norborn-2-ene-5-ylcarboxyl)-N ,N -di(pyrid-2-yl)amine dichloropalladium(II) (2) and N -(7-oxanorborn-2-ene-5-ylcarboxyl)-N ,N -di(pyrid-2-yl)amine dichloropalladium(II) (4), respectively. The structures of 3 and 4 were determined by X-ray crystallography. Using Mo(N -2,6-Me2/C6H3)(CHCMe2Ph)(OCMe(CF3)2)2, 1 was surface-grafted onto various silica-based carriers. Poly-1 was additionally used for the coating of silica and ROMP-derived monolithic supports. Heck systems were generated by loading of the corresponding dipyridylamide-functionalized supports with Pd(II). Alternatively, monolithic Pd-loaded supports were synthesized by an in situ grafting of 4 onto a ROMPderived monolithic support. Finally, 4 was copolymerized with 7-oxanorborn-2-ene-5,6-dicarboxylic anhydride to yield a watersoluble Heck coupling-active copolymer suitable for biphasic catalysis. All supports were successfully tested in the coupling of selected aryliodides and arylbromides under various conditions including flow-through systems, cartridges, biphasic catalysis and microwave-assisted synthesis. Selected data including turn-over numbers (TONs) and frequencies (TOFs) are presented. # 2002 Elsevier Science B.V. All rights reserved.

Novel well-defined heterogeneous metathesis catalysts

The synthesis of heterogeneous, N-heterocyclic carbene-based metathesis catalysts is described. Heterogenization based on various grafting approaches was performed on both monolithic and silicious supports. The general principles of heterogenization, the synthetic approach, selected applications as well as advantages and disadvantages of the resulting heterogeneous catalysts are discussed.