Bifunctional molecular catalyst

Oxidative Transformations with Bifunctional Molecular Catalysts. 45... 

In this chapter, I outline our recent progress in asymmetric reductive and oxidative transformations with bifunctional molecular catalysts based on ruthenium, rhodium, and iridium complexes bearing chiral chelating amine ligands. 

Heterolytic cleavage of H2 with bifunctional molecular catalyst... 

Doubly substituted analogues of TS-1 have also been reported. Trong et al. (130) synthesized bifunctional molecular sieves with titanium and various trivalent ions, for example, Ti-MFI that also contained, Al, or Ga. Tin and vanadium have also been incorporated into the titanium silicalite structure (33,131) by a primary synthesis method. The incorporation of a second metal changes the redox properties of the materials as well as their morphology. Incorporation of tin into titanium silicalite improved the epoxidation selectivity of the catalyst compared with that of (mono-substituted) TS-1. 

Ikariya, T., Blacker, A. J. (2007). Asymmetric transfer hydrogenation of ketones with bifunctional transition metal-based molecular catalysts. Accounts of Chemical Research, 40, 1300-1308. http //dx.doi.org/10.1021/ar700134q. 

E-Caprolactam (CL) is a very important monomer for the production of nylon-6, and about 4.2 million tons of CL were manufactured worldwide in 1998 [126]. Most current methods of CL production involve the conversion of cyclohexanone with hydroxylamine sulfate into cyclohexanone oxime followed by Beckmaim rearrangement by the action of oleum and then treatment with ammonia, giving CL. A serious drawback ofthis process is the co-production of a large amount of ammonium sulfate waste [126, 127]. Raja and Thomas reported a method for one-step production of cyclohexanone oxime and CL by the reaction of cyclohexanone with ammonia under high-pressure air (34.5 atm) in the presence of a bifunctional molecular sieve catalyst [128]. Hydrogen peroxide oxidation of cyclohexanone in the presence of NH3 catalyzed by titanium silicate is reported to produce CL [129]. In patent work, on the other hand, the transformation of l,l -peroxydicyclohexylamine (PDHA) to a 1 1 mixture of CL and cyclohexanone by LiBr has been reported [130]. 

A review article by Blumel describes classical and modern solid-state NMR methods that allow to gain insight into catalyst systems where one or two metal complexes are bound to oxide supports via bifunctional phosphine linkers, such as (EtO)3Si(CH2)3PPh2. It has been shown that many aspects of the immobilized molecular catalysts can be elucidated with the corresponding NMR technique. For example, the bulk of the support can be studied, as well as the interface of the support with the ethoxysilane. In addition, electrostatic bonding to the support via phosphonium groups can be proven by solid-state NMR. For the immobilized catalysts, leaching, and even horizontal translational mobility effects, as probed by HR MAS NMR under realistic conditions in the presence of solvents, are described. 

Ikariya, T. Murata, K. Noyori, R. Bifunctional transition metal-based molecular catalysts for asymmetric syntheses. Org. Biomol. Chem. 2006, 4, 393-406. 

Ikariya, T. Blacker, A. J. Asymmetric Transfer Hydrogenation of Ketones with Bifunctional Transition Metal-Based Molecular Catalysts. Acc. Chem. Res. 2007,40,1300-1308. 

Ikariya, T. Gridnev, I. D. Bifunctional Transition Metal-based Molecular Catalysts for Asymmetric C-C and C-N Bond Formation. Chem. Rec. 2009, 9,106-123. 

The iodoaminocyclization of hydrazones proceeded under very mild conditions to generate pyrazolines with high selectivity (Scheme 7.33 and Example 7.13) [56]. The organocataly tic reaction was promoted by the use of a bifunctional thiourea catalyst Using A -iodopyrrolidinone as the source of electrophilic iodine leads to the highest selectivity for the reaction. Control reactions were carried out and the authors noted that strict control of the temperature was needed to prevent a background reaction. Additionally, including molecular sieves in the reaction mixture led to an increase in the selectivity. 

Bifunctional Transition Metal-Based Molecular Catalysts for Asymmetric Syntheses... 

This unique concept of the recently developed bifunctional metal-based molecular catalysts leads to high reaction rates and excellent stereochemical outcome because the reactions proceed through a closed assembly of reactants and catalysts, providing a wide substrate scope and applicability in organic synthetic chemistry. This volume is intended to highlight the recent exciting advances in bifunctional catalysis with well-designed multimetallic systems, dinuclear, mononuclear... 

Nazarov reagents 238, which possess both a nucleophiUc carbon and an electron-deficient C—C double bond, have been employed in the synthesis of enantioenriched spiro[4-cyclohexanone-l,3 -oxindoUne] derivatives 239 by Wei and Gong. The Michael-Michael cascade reaction of 238 and methyleneindolinones 55 proceeded smoothly in the presence of the bifunctional urea catalyst 140 h and 4-A molecular sieves, which afforded structurally diverse spirooxindole derivatives 239 with excellent enantioselectivities (Scheme 2.64) [93],... 

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