1,721,140 research outputs found
Straightforward heterogeneization of Cu(I) complexes of chiral pyridine containing macrocyclic ligands (Pc-L*) and their applications to cyclopropanation reactions
No full textWe have recently reported that copper(I) complexes of the new C1-symmetric pyridine-based 12 membered tetraaza macrocyclic (Pc-L*) ligands are competent catalysts in the enantioselective cyclopropanation of olefins employing ethyl diazoacetate (EDA) as carbene precursor.1 Heterogeneous single site catalysts in many cases show superior performances in terms of activity, selectivity and reciclability coupling together the advantages of heterogeneous and homogeneous systems.2 We report here preliminary results on the heterogeneization of our system. Cu(I) complexes (see fig), based on functionalised pyridine-containing macrocyclic chiral ligands were heterogeneized on mesoporous ordered and non-ordered silicas (Davisil, MCM-41, etc.) by the SHB method.2 Materials obtained were fully characterized for metal content, textural properties, hydrogen bonds between Cu complex and surface silanols by a pool of techniques. Catalysts were tested in enantioselective cyclopropanation of olefins and they showed performances at least comparable to those obtained with the homogeneous counterpart. Tests using both basic and ordered silicas with the aim of exploiting the confinement effect on stereoselectivity are currently in progress.
References
[1] Caselli, A.; Cesana, F.; Gallo, E.; Casati, N.; Macchi, P.; Sisti, M.; Celentano, G.; Cenini, S.. Dalton Trans. 2008, 4202. [2] C. Bianchini, P. Barbaro, V. Dal Santo, R. Gobetto, A. Meli, W. Oberhauser, R. Psaro, F. Vizza, Adv. Synth. Catal., 2001, 343, 41-45
An improved and convenient synthesis of the osmium (II) carbonyl chlorides Os(CO)4Cl2 and [Os(CO)3Cl2]2.
No full textStaightforward heterogeneization of chiral Cu(I) complexes and their applications to Henry and cyclopropanation reactions
No full textHeterogeneous single site catalysts in many cases show superior performances in terms of activity, selectivity and reciclability coupling together the advantages of heterogeneous and homogeneous systems [1]. Cu(I) complexes (see fig. 1), based on functionalised pyridine-containing macrocyclic chiral ligands [2] were heterogeneized on mesoporous ordered and non-ordered silicas (Davisil, MCM-41, etc.) by the SHB method [3] and they were successfully applied to asymmetric cyclopropanation reactions. Materials obtained were fully characterized for metal content, textural properties, hydrogen bonds between Cu complex and surface silanols by a pool of techniques. Catalysts were tested in asymmetric cyclopropanation of olefins employing ethyldiazoacetate (EDA) as carbene precursor and in the Henry or nitro-aldol reaction and they show performances at least comparable to those obtained with the homogeneous counterpart. Tests using both basic and ordered silicas with the aim of exploiting the confinement effect on stereoselectivity are currently in progress.
References
[1] V. Dal Santo, F. Liguori, C. Pirovano and M. Guidotti, Molecules accepted for publication
[2] A. Caselli, F. Cesana, E. Gallo, N. Casati, P. Macchi, M. Sisti, G. Celentano and S. Cenini, Dalton Trans., 2008, 4202–4205.
[3] C. Bianchini, P. Barbaro, V. Dal Santo, R. Gobetto, A. Meli, W. Oberhauser, R. Psaro and F. Vizza, Adv. Synth. Catal., 2001, 343, 41-45.
Aknowledgents
EU through IDECAT Network of Excellence, European Community’s Sixth Framework Programme (contract NMP3-CT-2005-011730) and NANO-HOST “Homogeneous Supported Catalyst Technologies: the sustainable approach to highly-selective, fine chemicals production” Initial Training Network -The People Program Project no. 215193-2, and MIUR through the project “ItalNanoNet” (Rete Nazionale di Ricerca sulle Nanoscienze; prot. no. RBPR05JH2P) are gratefully acknowledged for financial support
ENANTIOSELECTIVE CYCLOPROPANATION REACTIONS CATALYZED BY CU(I) COMPLEXES OF PYRIDINE CONTAINING MACROCYCLIC CHIRAL LIGANDS (PC-L*) SUPPORTED ON SILICAS
No full textWe have reported that copper(I) complexes of the new C1-symmetric pyridine-based 12 membered tetraaza macrocyclic (Pc-L*) ligands are competent catalysts in the enantioselective cyclopropanation of olefins employing ethyl diazoacetate (EDA) as carbene precursor in homogeneous phase[1]. Heterogeneous single site catalysts in many cases show superior performances in terms of activity, selectivity and recyclability coupling together the advantages of heterogeneous and homogeneous systems [2]. Aim of the present work has been to heterogeneize the chiral copper(I) complexes on mesoporous silicas and to test them as catalysts in asymmetric synthesis. Pc-L* Cu(I) complexes were grafted on mesoporous ordered and non-ordered silicas (MCM-41, SBA-15 and Davisil) by the SHB method (Figure).2 SHB (Supported by Hydrogen Bond) is a simple, very mild, rather strong grafting, procedure applicable to a wide range of metal complexes bearing the SO3- moiety as counterion.
Materials obtained were fully characterized for metal content, textural properties, hydrogen bonds between Cu(I) complex and surface silanols by a variety of techniques. Catalysts were tested in enantioselective cyclopropanation reactions of olefins. The results will be presented in terms of chemical yields and stereochemical outcome and compared with those obtained in homogeneous phase. The confinement effects, namely the pore size influence as well as the issue of catalyst separation and recyclability were studied and rationalized.
[1] Caselli, A.; Cesana, F.; Gallo, E.; Casati, N.; Macchi, P.; Sisti, M.; Celentano, G.; Cenini, S. Dalton Trans. 2008, 4202. [2] C. Bianchini, P. Barbaro, V. Dal Santo, R. Gobetto, A. Meli, W. Oberhauser, R. Psaro, F. Vizza, Adv. Synth. Catal., 2001, 343, 41-45
Surface supported metal cluster carbonyls: an investigation of the behaviour of Os3(CO)12 supported on highly decarbonated magnesia.
No full text[Rh(CO)2X]2 (X = Cl, CH3COO) species supported on highly decarbonated magnesium oxide : observation of a strong effect of the chloride ion on the surface organometallic chemistry.
No full textSURFACE ORGANOMETALLIC CHEMISTRY - REDUCTIVE CARBONYLATION OF SILICA-SUPPORTED RUCL3.3H2O
No full textThe reductive carbonylation of silica-supported RuCl3 · 3H2O was investigated. This physisorbed salt reacts with CO at 25-50°C to form the silica-bound species [Ru(CO)2Cl2(HOSi{A figure is presented})2], which is converted into the silica-bound tricarbonyl species [Ru(CO)3 Cl2(HOSi{A figure is presented})] when the temperature is raised to 100°C. The surface species may be extracted with suitable donor solvents at room temperature. With [Ru(CO)3Cl2(HOSi{A figure is presented})], extraction using acetone followed by recrystallization from dichloroethane/ pentane affords [Ru(CO)3Cl2]2 in high yield. The dimer sublimes directly from the surface upon carbonylation at 180°C. Liberated HCl probably inhibits further reduction. However, starting from physisorbed [{Ru(CO)3Cl2}2], the species [Ru2(CO)6Cl 4(H2O)] is formed on the surface in the presence of CO + H2O at 100°C. Only traces of [{Ru(CO)3Cl2}2] and clusters such as [Ru3(CO)10Cl2] and [Ru3(CO)12] sublime under these conditions
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