Jacobsen s ligand

Chiral salen ligands are diimines of salicylaldehydes with chiral diamines, usually cyclohexane-1,2-diamine (salen Hgands 1) or 1,2-diphenylethylene-diamine (salen ligands 2). The most widely used salen ligand in homogeneous catalysis is probably Jacobsen s ligand (la. Fig. 2), which is commercially available and hence has been used as reference to compare the results of im-... 

J-acid, 9 402, 403 Jackets, heat-transfer, 16 111—718 Jacobsen s ligand, 20 305 Jacobson-Stockmayer theory, in siloxane polymer manufacture, 22 558 Jacquinot advantage, 14 228 J-aggregation, 9 508 Jahn-Teller distortion, 22 203 Jahn—Teller effect, 6 611 Jai Tire process, 21 476 Jameson cell, 16 653 Jamming phase diagram, 12 18 Jams... 

Fig. 5 General structure of salen ligand 13 and Jacobsen s ligand 14...

The nitrido complexes 16-21, as shown in Section 6.3, which bear various substituents on the para (R1) and/or ortho (R2) positions of a benzene ring of complex 15 were employed in the asymmetric aziridination of styrene (Table 6.2). The reaction of styrene with complex 16 or 17 gave lower product yields and enantioselectivities compared to the reaction with the complex 15. Complex 18 decreased the yield of the aziridination, but the enantioselectivity was not affected however, when complex 19 was employed, the yield and the selectivity were low. In the case of 20, the enantioselectivity was moderate but the yield was very low complex 21, which bears Jacobsen s ligand, showed a similar result with complex 20. Thus far, complex 15 is the best nitrogen source for the asymmetric aziridination of styrene. 

C-H oxidation (150). The Jacobsen s ligand has been used for the modification of the manganese exchanged Al-MCM-41, that is the immobilized catalyst has been investigated in epoxidation of styrene (151). Chiral manganese-Schiff base complexes were immobilized on a glassy carbon electrode surface (152). Enan-tioselective epoxidation reactions were also catalyzed with Mn(III) complexes of chiral porphirines (97,153). 

Figure 12.2 Schreiner s thiourea (3a), Takemoto s bifunctional catalyst (4e), and Jacobsen s ligand (5).

The limitations of the system with regard to substrates and oxidants was attributed to the strong electron-withdrawing character of the perfluorinated chains and the lower steric hindrance in the position adjacent to phenols, in marked contrast to the ferf-butyl groups present in Jacobsen s catalyst, hi view of this, a second generation of fluorinated salen ligands le and If was... 

In one case, the insertion of the whole chiral hgand into a Co-exchanged zeohte by subhmation was described [24], Only small ligands, such as li and 2i, can be efficiently introduced into the micropores of the Y zeohte, whereas the bulkier Jacobsen s hgand la only remains on the external surface of the sohd. Unfortunately, these occluded (salen)Co complexes led to very low enantioselectivities (up to 8% ee) in the reduction of acetophenone with NaBH4. 

In the present work, the Jacobsen s catalyst was immobilized inside highly dealuminated zeolites X and Y, containing mesopores completely surrounded by micropores, and in Al-MCM-41 via ion exchange. Moreover, the complex was immobilized on modified silica MCM-41 via the metal center and through the salen ligand, respectively. cis-Ethyl cinnamate, (-)-a-pinene, styrene, and 1,2-dihydronaphtalene were used as test molecules for asymmetric epoxidation with NaOCl, m-CPBA (m-chloroperoxybenzoic acid), and dimethyldioxirane (DMD) generated in situ as the oxygen sources. 

The obvious choice (at least from the standpoint of availability) to test the role of the salen ligand chelating Co(II) was to buy Jacobsen s cobalt catalyst, 2330 (Scheme 12). This species would introduce several new structural and stereoelectronic factors at the same time (relative to the... 

Many other projects in the past dealt with the immobilization of the famous chelating salen ligand or salen metal complexes, respectively—the Mnm salen Schiff base complex is also known as Jacobsen s catalyst, and it is used, among others, in asymmetric epoxidation of olefinstttt—mainly onto the surface of MCM-41 and SBA-15. 

G. Sager, D. Sandes, A. Besseseb, and S. Jacobsen, Adrenergic ligand binding in human serum, Biochem. Pharmacol., 34 2832 (1985). 

JACOBSEN S SALEN AS A CHIRAL LIGAND FOR THE CHROMIUM-CATALYSED ADDITION OF 3-CHLORO-PROPENYL PTVALATE TO ALDEHYDES A CATALYTIC ASYMMETRIC ENTRY TO SYN-ALK- 1-ENE-3.4-DIOLS... 

Chiral epoxidation with Jacobsen s catalyst. Chiral centres in the ligand and product are marked ( ). 

Meunier has reviewed recent advances in asymmetric oxidation. Jacobsen s asymmetric epoxidation catalysts are some of the most successful. These use Mn(III) in a chiral salen ligand with NaOCl as primary oxidant. The intermediacy of Mn(V) 0x0 species has been proposed as the active species formed after O atom transfer from the hypochlorite. Enantiomeric excesses of 97-98% are seen in the epoxide product on a consistent basis across a wide variety of alkene substrates. 

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