Metallosalen catalyst

Dihydrofuran, metallosalen catalyst, C6H5CI or CH2CI2, rt, 24 h, 81-100% yield. Since this reaction employs a chiral catalyst the derivatization proceeds with 71-86% ee or 40-99% de. ... 

Breslow, R., Brown, A.B., McCullough, R.D. and White, P.W., Substrate selectivity in epoxidation by metal-loporphyrin and metallosalen catalysts carrying binding groups,/. Am. Chem. Soc., 1989, 111, 4517-4518. 

Metallosalen complexes have assumed considerable importance as asymmetric epoxidation catalysts. This catalyst system is widely applicable for... 

Metallosalen complex [salen = N, A-ethylenebis(salicyldeneaminato)] has a structure similar to metalloporphyrin, and these two complexes catalyze the epoxidation of olefins. For example, Kochi et al. have found that metallosalen complexes such as (salen )manganese(III) [25] and (salen)chromium(IIl) complexes [26] (hereafter referred to as Mn- and Cr-salen complexes, respectively) serve as catalysts for the epoxidation of unfunctionalized olefins by using iodosylbenzene [25] or sodium hypochlorite [27], In particular, cationic Mn-salen complex is a good catalyst for epoxidation of unfunctionalized olefins, which proceeds through an oxo(salen)manganese(V) species (Scheme 6B.14) [25,28], The presence of oxo-Mn(V)-salen... 

Inorganic-organic hybrid POMs have attracted much attention because the electron and steric properties of the POMs significantly affect the catalytic properties of a metal center [88-91]. One hybrid catalyst consisted of a metallo-salen complex attached covalently to a lacunary POM [SiWn039]8- via two propyl spacers. In contrast with an usual Mn(III) salen species, the metallosalen complex modified with the POM afforded a more oxidized Mn(IV) salen-POM or Mn(III) salen cation radical-POM compound [89]. 

Many oxene, nitrene and carbene transfer reactions using well-designed chiral first- and second-generation metallosalen complexes as catalysts. 

Cr3+ chelated in planar salen-type ligands is a catalyst for olefin epoxi-dation with single oxygen donors such as PhlO. A Cr(V)=0(salen)+ compound transfers the active oxygen atom to the olefin (69). Cr remains firmly bound by the ligand throughout the catalytic cycle, and this may offer an opportunity to immobilize a Cr epoxidation catalyst. However, in a report on immobilization of such a Cr(salen)+ complex in Al-containing MCM-41, it was stated that the complex is simply physisorbed on the support (70) it is doubtful whether this provides a stable link. Moreover, the relevance of Cr(III)(salen)+ as an oxidation catalyst is limited since other metallosalen complexes are far more effective. 

This past year s literature has shown extraordinary activity in this realm. Perhaps the most firmly entrenched methodology for the preparation of chiral epoxides is the metallosalen mediated epoxidation of unfunctionalized alkenes (the Jacobsen-Katsuki epoxidation), which has been recently reviewed <03SL281 >. It is widely accepted that this reaction proceeds through an 0X0 intermediate, and that the observed enantioselectivities depend upon the electronic stability of this species. For example, Jacobsen found empirically that electron-donating substituents in the 5 and 5 positions of catalyst 1 gave better enantioselectivities <91JA6703>. More recent... 

Katsuki T. Chiral metallosalen complexes structures and catalyst tuning for asymmetric epoxidation and cyclopropanation. Adv. Synth. Catal. 2002 344 131-147. 

Katsuki, T. Asymmetric reactions using metallosalen complexes as catalysts. Recent Research Developments in Pure Applied Chemistry 1997, 1, 35-44. 

A poly(bmaphthyl metallosalen complex) 128 (Scheme 3.36) was prepared and used as a catalyst for the asymmetric epoxidation of alkene [72]. Although enantioselectivities obtained by using the polymeric catalyst were low, this represented a new type of polymeric chiral complex based on the main-chain hehcity. 

Optically active metallosalen complexes as catalysts for atom-efficient asymmetric reactions 05Y478. 

The examples discussed above mainly rely on the intrinsic catalytic activity of the metal connecting points. Nevertheless, a more rational strategy for rationally immobilizing catalytically active OMSs within porous MOFs is to incorporate well-established organometallic catalyst units into the linkers of a framework such as BlNOLate, metallosalen, and metalloporphyrin. 

To incorporate the metallosalen complex into the framework. Hupp and coworkers reported a micro-porous homochiral pillared-layer MOF as an highly effective enantioselective catalyst for olefin epoxidation. A solvothermal reaction between a chiral (salen)Mn complex (R,R)- -)-1,2-cyclohexanediamino-A,M -bis(3-... 

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