An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Rh diphosphine complexes using DuPhos and JosiPhos as chiral ligands have been immobilised by ion exchange into the mesoporous material MCM-41. When used as catalysts for the enantioselective hydrogenation of dimethyl itaconate and methyl-2-acetamidoacrylate, these heterogeneous catalysts give catalytic performance in terms of yield and enantioselection that are comparable to the corresponding homogeneous catalysts. Furthermore, the heterogeneous catalysts can be readily recovered and reused without loss of catalyst performance. A second immobilisation strategy is described in which [Rh(COD)2]+BF4- is initially immobilised by ion exchange and subsequently modified by the chiral diphosphine and this give comparable catalyst performance. This immobilisation strategy opens up the possibility of easy ligand-screening for parallel synthesis and libraries.

A range of crystalline TS-1 samples with different morphologies as well as the corresponding TS-1 precursor structures have been synthesised using hydrothermal crystallisation. The materials have been characterised using powder X-ray diffraction, IR and Raman spectroscopy and electron microscopy. The materials were used as catalysts for the oxidation of crotyl alcohol, phenol and norbornylene and, in particular, the reactivity of the precursor structures was contrasted with crystalline TS-1. The oxidation of crotyl alcohol, selected as a relatively non-reactive substituted alkene, did not require the TS-1 structure for reactivity and TS-1 precursor structures are active, although crystalline TS-1 was found to be more reactive than the precursor structures. In contrast, phenol hydroxylation is only catalysed by crystalline TS-1. The reaction of phenol is observed to occur only on the exterior surface of large TS-1 crystallites. With smaller crystallites of TS-1, i.e. the size range of interest for catalysis, the rapid subsequent reaction of hydroquinone makes it difficult to determine whether reaction occurs solely on the exterior of the crystallites or at sites within the porous structure. Hence it is suggested that this reaction has limited scope as a probe reaction for the reactivity of sites within the crystallites. It is, however, feasible that phenol hydroxylation is a viable probe reaction for TS-1 type structural units. Norbornylene was studied as an example of a reactant too large to enter the internal pore structure of TS-1 and hence only reaction at pore mouths and external surface sites was possible. Larger TS-1 crystallites were more active for this substrate than suggested by surface area considerations. The results are discussed in terms of the selection of model reactions for the study of TS-1 catalysts.

AbstractFor Abstract see ChemInform Abstract in Full Text.

[reaction: see text] The poly(ethylene glycol)-supported ruthenium precatalyst shown above is highly effective for asymmetric transfer hydrogenation of unfunctionalized aromatic ketones by HCOONa in neat water, affording fast rates, good to excellent enantioselectivities, and outstanding reusability.

During the aziridination of styrene using copper bis(oxazoline) complexes the ee increases with conversion due to further reactions of the product.

Effective catalysts have Cu2+-exchange levels of ca. 40-60% of the maximum concentration for electroneutrality and, consequently, Cu-zeolite Y catalysts contain an additional counter-cation (H+, Li+, Na+, K+, Rb+, Cs+) whose effect is explored. With Li+, Na+, K+ counter-cations, the zeolite structure is not markedly affected but, with Rb+ and Cs+, there is some loss of crystallinity. Replacement of H+ by group I cations does not markedly influence the overall ee observed for aziridine indicating that the presence of protons in the Cu-HY catalysts are not detrimental to the reaction. Catalysts containing group I cations typically give decreased leaching of Cu2+ during the reaction. At low nitrene donor to styrene molar ratios (1 : 1), replacement of H+ by group I cations leads to a small enhancement in the ee of aziridine, although the yield of aziridine formed is decreased under all reaction condition. At higher molar ratios of nitrene donor to styrene, the ee is suppressed, particularly with Rb and Cs. The effect of reaction time on aziridine yield reveals a reaction pro. le in which the reaction initially proceeds rapidly, then slows down prior to accelerating again in the latter part of the reaction. This effect is accentuated by increasing the size of the counter-cation. This reaction profile is also observed for the homogeneously catalysed pathway and, consequently, it cannot be due solely to a confinement effect within the zeolite pores. Over addition of reaction by-products (NsNH(2), PhI) accentuates the shape of this reaction profile and the effect is discussed in terms of the interactions of such molecules at the active site.

The copper-catalyzed aziridination of styrene with copper-exchanged zeolite HY (CuHY) and copper(II) triflate (trifluoromethanesulfonate) (Cu(OTf)2) as catalysts is described using N-(p-tolylsulfonyl)imino]phenyliodinane (PhI=NTs) as the nitrene donor. The effects on the ee and yield of the aziridine when the catalyst is modified by the presence of a chiral bis(oxazoline) are investigated in detail. The heterogeneously catalyzed reaction under these conditions shows a slight, but significant, enhancement in ee with increasing conversion at 25 °C. This is not observed in the more rapid homogeneously catalyzed reaction under identical reaction conditions using PhINTs as the nitrene donor. The enhancement in ee is proposed to result from the preferential reaction of the (S)-aziridine with the Cu2+:bis(oxazoline) complex in the presence of PhI=NTs, leading to an enhancement of the (R)-aziridine in the remaining aziridine product.

The copper-catalyzed aziridination of styrene is described using both heterogeneous, copper-exchanged zeolite HY, and homogeneous, copper (II) triflate catalysts using both [N-(p-tolylsulfonyl)imino]phenyliodinane (PhI=NTs) and [N-(p-nosylsulfonyl)imino]phenyliodinane (PhI=NNs) as nitrene donors. The key differences observed for the two catalysts when modified by chiral bis(oxazoline) ligands are discussed in detail. In particular, the heterogeneously catalyzed asymmetric reaction can give much higher enantioselection than the comparable homogeneously catalyzed reaction. The structure of the bis(oxazoline) ligand is the critical factor, and bis(oxazoline) ligands that are ineffective with the homogeneous catalysts are highly effective for the Cu2+ cation constrained within the zeolite micropores. The consequences of this observation for the design of chiral ligands for asymmetric heterogeneous catalysis are discussed. The effect of the degree of styrene conversion on the enantioselectivity is described in detail using PhI=NNs as a nitrene donor. The reaction shows a significant enhancement in ee with conversion at 25°C, and the possible origin of this effect is discussed.

Previous work on the catalytic decomposition of sodium hypochlorite streams has focussed on high levels of destruction (typically >99.99%), with exit concentrations typically in the 1-50 ppm range. This design requires low space velocities and minimisation of forward mixing, and a multi-bed downflow reactor has been successfully utilised in industry. This paper reports on the development of an alternate reactor for lower conversion levels-in the order of 90%. At the space velocities required to achieve this economically, the downflow bed becomes infeasible due to classic hydraulic limitations. The scenario hare differs from those reported in the literature for upflow packed bubble columns; the gas is evolved through the height of the reactor, and the gas flux therefore varies over the height of the catalyst bed, with implications for gas phase hold-up. The gas phase hold-up is expected to exert considerable influence on reactor performance as the as will occupy space thereby reducing the residence time of the liquid phase and by blinding the catalyst surface.The study was based on experimental work in the laboratory, and later on a 0.2 m diameter pilot. In analysing the data, kinetic effects were accounted by the use of intrinsic rate constants from previous work. This allowed decoupling of the kinetic effects from the hydrodynamic effects. The results indicated a strong dependence of the apparent catalyst performance on the liquid and gas superficial velocities, which have been observed in the literature to be the key variables affecting gas phase hold-up in packed bubble columns. The performance data measured on the pilot unit mapped well onto the laboratory data, indicating the process scales simply. (C) 2003 Elsevier Science B.V. All rights reserved.

The formation of dihydropyran from the Diels–Alder reaction between E-ethyl-2-oxo-3-pentenonate and vinyl ethyl ether is investigated using copper (II) bis(oxazoline) as catalyst. The homogeneously and heterogeneously catalyzed reactions are contrasted. Immobilization using mesoporous materials (Cu-MCM-41, Cu-AlSBA-15, Cu-MSU-2) and zeolite Y is found to produce an effective heterogeneous catalyst. Although the level of enantioselection is not high in this initial study, the CuH-zeolite Y/bis(oxazoline) catalyst gives the highest ee (41% ee), which is significantly higher than that observed for the Cu(OTf)2 homogeneous catalyst (20% ee) under comparable conditions. In addition, with the heterogeneously catalyzed reaction, the enantioselection changes from the initial 2R,4S product to the 2S,4R diastereoisomer. This behavior is not observed with the homogeneously catalyzed reaction, which always yields the 2R,4S product. These results are discussed in terms of the confinement of the catalyst complex within the pores of the heterogeneous catalyst.

The copper-catalysed aziridination of styrene with copper-exchanged zeolite Y (CuHY) and copper(II) triflate (Cu(OTf)2) as catalysts is described and discussed. In particular, the effects of reaction conditions on the yield and enantiomeric excess of the aziridine product are described using [N-(p-nitrophenylsulfonyl)imino]phenyliodinane (PhINNs) as nitrene donor. By careful control of the styrene:nitrene donor molar ratio and the solvent, an ee of 95% can be obtained for the heterogeneously catalysed bis(oxazoline)-modified zeolite CuHY. The ee achieved with the zeolite immobilised catalyst is significantly higher than that achieved for the non-immobilised homogeneous catalyst under comparable reaction conditions.

Chloramine-T and [N-(p-tolylsulfonyl)imino]phenyliodinane (PhINTs) are contrasted as nitrene donors for the aziridination of styrene using copper(II) triflate, and copper-exchanged zeolite Y (CuHY) as catalysts. For both catalysts, PhINTs is found to give significantly higher yields of the aziridine both in the presence and absence of a chiral bis(oxazoline) modifier. In addition, chloramine-T is found to induce leaching of most of the Cu from CuHY, and with this nitrene donor CuHY does not function as a heterogeneous catalyst. In contrast, PhINTs causes negligible leaching of Cu from CuHY and, consequently, for the heterogeneous CuHY catalyst, PhINTs is the preferred nitrene donor. With chloramine-T, the beneficial effects observed on addition of copper powder are shown to be due to the copper powder acting as a reservoir for Cu2+ in solution, since Cu2+ in solution is rapidly deactivated by toluenesulfonamide, a degradation product of the nitrene donor.

The stability of the heterogeneous CuHY catalyst for the aziridination of styrene using nitrene donors, with and without the presence of chiral bis(oxazoline) modifiers, is described in detail. Cu2+ is found to leach from the CuHY and the rate of Cu-leaching is dependent on the reaction time, the nature of the nitrene donor, the structure of the bis(oxazoline), the presence of solvent and the breakdown products of the nitrene donor. It is found that between 0.08–6.8% by weight of the Cu present in CuHY can be leached during standard reaction conditions. However, using short reaction times it is shown that the amount of Cu removed can be limited readily to the lower value. Detailed studies show that for this reaction system the leached Cu2+ plays no significant role in the formation of the aziridine, and that the high enantioselectivities observed with CuHY are due to Cu2+ which is electrostatically bound within the pores of the zeolite and modified by a chiral bis(oxazoline) ligand.

Transition-metal-exchanged zeolite Y (Cr, Mn, Fe, Co, Ni, Cu, Zn) are compared as catalysts for the aziridination of styrene using ( N -( p -tolylsulfonyl)imino)phenyliodinane (PhI=NTs) as the nitrene precursor. The Cu-exchanged zeolite shows high levels of aziridine formation, but significant yields of aziridine are also obtained with the Cr-, Mn-, Fe- and Co-exchanged zeolite Y. In contrast, these cations produce much lower yields of aziridine in the corresponding homogeneously catalysed reactions. Addition of a chiral bis-oxazoline ligand leads to a significant decrease in the yield of aziridine for all the ion-exchanged zeolites, with the exception of the Cu-exchanged zeolite Y. Further experiments with ( N -( p -nitrophenylsulfonyl)imino)phenyliodinane (PhI=NNs) as nitrene donor indicate that, in addition to Cu-exchanged zeolite Y, significant yields of the aziridine can be formed for Zn-, Mn-, Fe- and Co-exchanged zeolite Y. The major by-product was benzaldehyde, probably formed by oxidation of styrene. These data confirm that Cu-exchanged zeolite Y is the best aziridination catalyst but it is shown that other metal-exchanged zeolites are also catalytically active.

A comparative study of the oxidation of the crotyl alcohol using hydrogen peroxide and tert-butyl hydroperoxide as oxidants with TS-1, Ti-β, Ti-Alβ, Ti-MCM-41, Ti-Al-MCM-41 and Ti-grafted-MCM-41 as catalysts is described and discussed. With hydrogen peroxide as oxidant, significant Ti-leaching is observed with all the catalysts except TS-1 (Ti-Alβ>Ti-grafted- MCM-41>Ti-MCM-41>Tiβ>Ti-Al-MCM-41⪢TS-1). For Ti-Alβ, Ti-grafted- MCM-41 and Ti-Al-MCM-41, initial heterogeneously catalysed formation of the epoxide was observed. However, the formation of a Ti-species in solution is shown to contribute to competing homogeneously catalysed formation of ether diols and triol. Using tert-butyl hydroperoxide as oxidant the Ti-leaching was minimised and selective epoxide formation was observed with Ti-β, Ti-Alβ and Ti-MCM-41 as heterogeneous catalysts, although, with Ti-Alβ, the ether diols and triol products dominated due to acid catalysed solvolysis of the epoxide.

In the production of aromatic N-oxides using the oxidation of N-containing heterocyclic aromatic substrates with H 2 O 2 as oxidant, the non-catalysed homogeneous oxidation is found to play an important part in the overall reaction. In addition, when TS-1 is used as a catalyst, there are many potential competitive interactions between the catalyst, the reactants and the products, which limit the effectiveness of the catalyst. It is concluded that the use of TS-1 and other microporous catalysts for the heterogeneous N-oxidation of pyridine and substituted pyridines needs to be interpreted with caution.

The immobilisation of enantioselective homogeneous catalysts is described using an approach in which cations are immobilised by ion-exchange within a microporous (zeolite Y) or a mesoporous material (Al-MCM-41). The catalysts are used under nonaqueous conditions so that cation leaching is minimised during the catalytic reaction. The cations can be modified using chiral ligands to form an enantioselective catalyst that is wholly heterogeneous and can be readily reused. Using this approach it is shown that copper-exchanged zeolite Y is a highly active catalyst for the aziridination of alkenes. Modification using bis(oxazolines) leads to the formation of an enantioselective aziridination catalyst. Using a similar approach, manganese-exchanged Al-MCM-41 modified with a chiral salen ligand is found to be an effective enantioselective heterogeneous epoxidation catalyst for cis-stilbene. The approach is also used to show that immobilisation of cobalt-exchanged Al-MCM-41 can also give some activity for the enantio selective epoxidation of cis-stilbene. However, in this case, although only low enantioselection is observed, the immobilised catalyst gives higher enantioselection than the non-immobilised homogeneous catalyst.