Heterocycles catalysts: heterogeneous

For further information see Heterocyclic Chemistry Heterogeneous Catalyst... 

Five- and six-membered oxygen-containing heterocycles include furan, benzofuran, pyran, flavanone, flavonol, and cyclic carbonates, etc. The synthesis of these heterocycles by heterogeneous supported metal catalysts will be discussed here. 

The use of supported (i.e., heterogenized) homogeneous catalysts offers another possibility for easy catalyst separation. New examples include polymer-anchored Schiff-base complexes of Pd(TT),446 PdCl2(PhCN)2 supported on heterocyclic polyamides,447 various Pd complexes supported on crosslinked polymers 448 sol-gel-encapsulated Rh-quatemary ammonium ion-pair catalysts,449 and zwitterionic Rh(T) catalysts immobilized on silica with hydrogen bonding.450... 

Heteroboranes, structure prediction for. 802-807 Heterocatenation. 741-742 Heterocyclic inorganic ring systems, 775-780 Heterogeneous catalysts, 705 Heteronuclear diatomic molecules. molecular orbitals in, 167-175... 

Heterogeneous metal catalysis is the most useful general method for the deuteration and/or tritiation of heterocyclic compounds.57 It involves exchange between the organic substrate and isotopic hydrogen (as water, usually, or gas) in the presence of a Group VIII transition metal catalyst at temperatures up to 180° [Eq. (18)]. 

There has also been continuous interest in the preparation of thermally stable pxjlymers which can be utilized as heterogeneous catalyst supports. Polybenzimidazole (PBI) (32) is a thermally stable heterocyclic polymer." Polybenzimidazole forms a complex with PdCb (33) which can be reduced to PBI-Pd (34). This catalyst is extremely stable yet it can be used to reduce a variety of nitro compounds (Scheme 6). The catalyst may be recycled simply by washing with methanol to remove the reduced substrate from the polymer the recycled catalyst shows no loss of activity or of Pd content after more than 20 cycles. 

Bis(pyrazolyl)borate copper complex 902 has been employed as a catalyst in homogeneous and heterogeneous styrene epoxidation reactions <2000CC1653>. Pyrazole palladacycles 903 have proved to be stable and efficient catalysts for Heck vinylations of aryl iodides <2000CG2053>. A hemilabile pyrazolyl-functionalized N-heterocyclic carbene complex of palladium(ll) such as 904 has been found to be an excellent catalyst for Heck and Suzuki crosscoupling reactions in ionic liquids <2006JOC426>. 

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