Catalysts zirconium

Several examples of catalytic aza Diels-Alder reactions using the chiral zirconium catalyst are shown in Table 5.5 [18]. High chemical yields and good to high... 

The precise structure of the zirconium catalyst was examined by NMR analysis. When Zr(Ot-Bu)4 (1 equiv), 8b (2 equiv), and NMI (3 equiv.) were combined in benzene-dg at 23 °C, two independent species which were assigned to a new zirconium catalyst and free 8b were observed. Although the signals of free 8b were still observed when Zr(Ot-Bu)4 (1 equiv), 8b (1 equiv), and NMI (3 equiv.) were stirred at 23 °C, only the signals assigned to the new zirconium catalyst were detected when the mixture was stirred at 80 °C for 2.5 h. These results indicated the formation of 9b as the new zirconium catalyst. The structure was also supported by an experiment in which Zr(Ot-Bu)4 (0.2 equiv), 8a (0.2 equiv), NMI (0.6 equiv), and MS 3 A were combined in benzene and the mixture was stirred for 2.5 h at 80 °C (formation of 9a). Imine Id (1 equiv.) and 7a (1.2 equiv.) were then added to the catalyst solution, and the mixture was stirred for 48 h at 23 °C. After the same work-up procedures as described above, the desired piperidine derivative was obtained in >98% yield with 89% ee, values comparable with those... 

The first enantioselective aza-Diels-Alder reactions of imino dienophiles on use of a chiral zirconium catalyst [116]... 

Alkenes and alkynes can also add to each other to give cyclic products in other ways (see 15-61 and 15-63). The first exclusive exo-dig carbocyclization was reported using HfCU as a catalyst. Alkynes also add to alkenes for form rings in the presence of a palladium catalyst or a zirconium catalyst. " Carbocyclization of an alkene unit to another alkene unit was reported using an yttrium catalyst and alkenes add to alkynes to give cyclic compounds with titanium catalysts. ... 

The ability to control the polymer from the design of the catalyst, coupled with high catalytic efficiency has led to an explosion of commercial and academic interest in these catalysts. Exxon started up a 30 million lb/5rr ethylene copol3rmer demonstration plant in 1991 using a bis-cyclopentadienyl zirconium catalyst of structure 1. The Dow Chemical Company (Dow) began operating a 125 million Ib/yr ethylene/l-octene copolymer plant in 1993 and has since expanded production capacity to 375 million Ib/yr. This paper will focus on the structure / property relationships of the catalysts used by Dow to produce single-site ethylene a-olefin copolymers. 

A chiral zirconium catalyst generated from Zr(0,-Bu)4 and (R)-3,3 -diiodo-1,1 -binaphthalene-2,2 -diol [(f )-3,3/-l2BINOL] catalyzed... 

All of the reactions described above use anionic alkyl metal complexes as stoichiometric reductants. Cationic zirconium catalyst 58 was shown to re-ductively cyclize a variety of 1,5-dienes to give both mono- and bicyclic silane products when H3SiPh was employed as the stoichiometric reductant (Scheme 10) [32]. Poor yields due to competing polymerization processes were observed when less substituted dienes were employed. It is likely that... 

This catalyst can catalyze a new reaction, called alkane metathesis. By this reaction, alkanes are transformed into higher and lower alkanes.265 Silica-supported zirconium catalysts were also used for the mild oxidation of alkenes by H202 266... 

Kobayashi et al.51 have reported an asymmetric Mannich-type reaction using chiral zirconium catalysts of type 124 (see Section 3.7). This catalyst is also effective for asymmetric aza Diels-Alder reactions. Kobayashi s study showed that the ligand had a profound influence on the yields and enantiose-lectivities of the reaction, and NMI (1-methylimidazole) proved to be the best ligand.51 With an increase in the amount of catalyst, both the chemical yields and enantioselectivities of the product can be enhanced. Scheme 5-39 depicts such aza Diels-Alder reactions, and its table shows that good to excellent enantioselectivity can be obtained for most reactions. 

Table 6.S. Hydrogenation of styrene as a function of the zirconium catalyst precursor.

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