Zinc porphyrin-based catalysts

Homopolymerization, epoxides aluminate-Lewis acid catalyst system, 11, 602 via aluminum-porphyrin-Lewis acid catalysts, 11, 599 aluminum-tetradentate ligand catalyst system, 11, 601 anionic polymerization, 11, 598 cationic aluminum catalyst system, 11, 603 cationic polymerization, 11, 598 characteristics, 11, 597 zinc-based catalyst system, 11, 605 Homopolymers, cyclic olefins, 11, 716... 

The use of inorganic supramolecular compounds in catalysis has also been successful in recent years. Hupp etal. incorporated a Mn(IIl)-porphyrm (see Porphyrin) epoxidation catalyst inside a molecular square, a system that shows enhanced catalyst stabihty and substrate selectivity as compared to the free catalyst. In another example, chiral metaUocyclophanes were constructed from Pt(PEt3)2 units and enantiopme atropoisomeric t,t -binapthyl-6,6 -bis-(acetylenes) and used in enantioselective diethyl zinc addition to aldehydes to afford chiral secondary alcohols. The first organometaUic triangle based on Pt(II) and alkyne-di-substituted-binaphfhyl system was reported and found to effect asymmetric catalysis reactions of aldehydes to alcohols with excellent conversion rates and enantiomeric excess/ ... 

Inoue and Takeda reported that the polymerization of propylene oxide at 20 °C with the zinc porphyrin catalyst (Et2Zn/fV-methyl-5,10,15,20-tetraphenylporphyrin, 10) produced syndiotactic poly(propylene oxide) (Af = 31,000, 60% r) (Scheme 24.12). This result was in contrast to those seen for all other zinc-based systems, which afford isotactic poly(propylene oxide). The authors attributed the unexpected syndiotactic microstructure of the polymer to the planar ligand and the isolated nature of the zinc center, which is different than that present in most other zinc aggregate systems." ... 

Aluminium alkoxides (especially aluminium isopropoxide), dialkylalumi-nium alkoxides, yttrium alkoxides, zinc alkoxides, aluminoxanes, zincoxanes, bimetallic -oxoalkoxides, aluminium porphyrins and aluminium Schiff s base complexes are the most representative coordination catalysts, containing multi-nuclear or mononuclear species, for lactone polymerisations (Table 9.5). 

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