2,002 research outputs found
Catalytic Applications of Pyridine-Containing Macrocyclic Complexes
No full textPolyazamacrocycles are a common class of macrocyclic compounds, utilized across a number of fields, including, but not limited to, catalysis, selective metal recovery and recycling, therapy and diagnosis, and materials and sensors.1 Worth of note is their ability to form stable complexes with a plethora of both transition, especially late, and lanthanide metal cations.2 Deviation of the macrocycle donor atoms from planarity often leads to rather uncommon oxidation states.3 Both the thermodynamic properties and the complexation kinetics are strongly affected by the introduction of a pyridine moiety into the skeleton of polyazamacrocycles by increasing the conformational rigidity and tuning the basicity.4 Pyridine-containing ligands engender great interest due to various potential field of applications. They have been successfully employed in biology, Magnetic Resonance Imaging, molecular recognition, supramolecular chemistry and self-assembly, molecular machines and mechanically interlocked architectures.5 In this lecture, I will provide a perspective on the catalytic applications of metal complexes of pyridine-containing macrocyclic ligands (Pc-L’s) which have been studied in our group (Figure), with a focus interest on the structural features relevant to catalysis.6 The increased conformational rigidity imposed by the pyridine ring allowed for the isolation and characterization of metal complexes which showed a rich coordination chemistry.7 The very different conformations accessible upon coordination and the easy tuneable synthesis of the macrocyclic ligands have been exploited in stereoselective syntheses.8
References:
1 L. F. Lindoy, G. V. Meehan, I. M. Vasilescu, H. J. Kim, J.-E. Lee, S. S. Lee, Coord. Chem. Rev. 2010, 254, 1713.
2 T. Ren, Chem. Commun. 2016, 52, 3271.
3 A. Casitas, X. Ribas, Chem. Sci. 2013, 4, 2301.
4 K. M. Lincoln, M. E. Offutt, T. D. Hayden, R. E. Saunders, K. N. Green, Inorg. Chem. 2014, 53, 1406.
5 M. Rezaeivala, H. Keypour, Coord. Chem. Rev. 2014, 280, 203.
6 B. Castano, S. Guidone, E. Gallo, F. Ragaini, N. Casati, P. Macchi, M. Sisti, A. Caselli, Dalton Trans. 2013, 42, 2451.
7 a) G. Tseberlidis, M. Dell'Acqua, D. Valcarenghi, E. Gallo, E. Rossi, G. Abbiati, A. Caselli, RSC Adv. 2016, 6, 97404; b) T. Pedrazzini, P. Pirovano, M. Dell'Acqua, F. Ragaini, P. Illiano, P. Macchi, G. Abbiati, A. Caselli, Eur. J. Inorg. Chem. 2015, 2015, 5089.
8 a) M. Dell’Acqua, B. Castano, C. Cecchini, T. Pedrazzini, V. Pirovano, E. Rossi, A. Caselli, G. Abbiati, J. Org. Chem. 2014, 79, 3494; b) M. Trose, M. Dell’Acqua, T. Pedrazzini, V. Pirovano, E. Gallo, E. Rossi, A. Caselli, G. Abbiati, J. Org. Chem. 2014, 79, 7311; c) B. Castano, E. Gallo, D. J. Cole-Hamilton, V. Dal Santo, R. Psaro, A. Caselli, Green Chem. 2014, 16, 3202
Designing new Ligands: Catalytic Applications of Pyridine-Containing Macrocyclic Complexes
No full textThe introduction of a pyridine moiety into the skeleton of a polyazamacrocyclic ligand affects both the thermodynamic properties and the coordination kinetics of the resulting metal complexes. These features have engender a great interest in the scientific community and the applications of pyridine-containing macrocyclic ligands ranges from biology to supramolecular chemistry, encompassing MRI, molecular recognitions, materials and catalysis. In this lecture, I will provide a perspective on the catalytic applications of metal complexes of pyridine-containing macrocyclic ligands (Pc-L’s) which have been studied in our group (Figure 1), with a focus interest on the structural features relevant to catalysis.1 The increased conformational rigidity imposed by the pyridine ring allowed for the isolation and characterization of metal complexes which show a rich coordination chemistry.2 The very different conformations accessible upon coordination and the easy tuneable synthesis of the macrocyclic ligands have been exploited in stereoselective syntheses.3
References
1 B. Castano, S. Guidone, E. Gallo, F. Ragaini, N. Casati, P. Macchi, M. Sisti, A. Caselli, Dalton Trans. 2013, 42, 2451.
2 a) G. Tseberlidis, M. Dell'Acqua, D. Valcarenghi, E. Gallo, E. Rossi, G. Abbiati, A. Caselli, RSC Adv. 2016, 6, 97404; b) T. Pedrazzini, P. Pirovano, M. Dell'Acqua, F. Ragaini, P. Illiano, P. Macchi, G. Abbiati, A. Caselli, Eur. J. Inorg. Chem. 2015, 2015, 5089.
3 a) M. Dell’Acqua, B. Castano, C. Cecchini, T. Pedrazzini, V. Pirovano, E. Rossi, A. Caselli, G. Abbiati, J. Org. Chem. 2014, 79, 3494; b) M. Trose, M. Dell’Acqua, T. Pedrazzini, V. Pirovano, E. Gallo, E. Rossi, A. Caselli, G. Abbiati, J. Org. Chem. 2014, 79, 7311; c) B. Castano, E. Gallo, D. J. Cole-Hamilton, V. Dal Santo, R. Psaro, A. Caselli, Green Chem. 2014, 16, 3202
How structural modifications can tune the asymmetric cyclopropanations catalyzed by Cu(I) complexes of chiral pyridine containing macrocylcic ligands (Pc-L*)
No full textWe have recently reported that copper(I) complexes of the new C1-symmetric pyridine-based 12-membered tetraaza macrocycles, Pyridine Containing Ligands (Pc-L*), are competent catalysts in the asymmetric cyclopropanation.[1] We report here the synthesis of new C1- and C2-symmetric Pc-L* macrocycles and the use of their Cu(I) complexes as catalysts for the title reaction. The synthetic paths, reportedi in Scheme 1, are very simple and they take advantage of commercially available, enantiomerically pure, chiral amino-alcohols and/or primary amines. These last compounds can react either with 2,6-bis(chloromethyl)pyridine(path A) or with the stereochemically pure forms of the alkyl pyridines obtained by the Lipase-catalyzed kinetic acetylation of 2,6-bis(1-hydroxyethyl)pyridine [2] (path B).
Ligands with different structures have been obtained in moderate to good yields (40-80%) and they have been fully characterized. The Cu(I) complexes of those ligands showed good catalytic activities in the cyclopropanation of differently substituted olefins employing ethyl diazoacetate (EDA) as carbene precursor.
In all cases a complete conversion of EDA was observed and, depending on the employed ligand, cyclopropanes were obtained with tunable cis/trans stereoselectivities and e.e. up to 96%.
[1] Caselli, A.; Cesana, F.; Gallo, E.; Casati, N.; Macchi, P.; Sisti, M.; Celentano, G.; Cenini, S. Dalton Trans. 2008, 4202-4205. [2] Uenishi, J.; Aburatani, S.; Takami, V. J. Org. Chem., 2007, 72, 132-138
Selective oxidation of alkenes by H2O2 catalysed by well-defined [Iron(III)(Pyridine-Containing Ligand)] complexes
No full textThe introduction of a pyridine moiety into the skeleton of a polyazamacrocyclic ligand affects both thermodynamic properties and coordination kinetics of the resulting metal complexes (1). These features have engendered a great interest of the scientific community in recent years. The applications of pyridine-containing macrocyclic ligands ranges from biology to supramolecular chemistry, encompassing MRI, molecular recognitions, materials and catalysis. Much of the efforts in the use of macrocyclic pyridine containing ligands have been devoted to the study of catalytic oxidation reactions. We report here the synthesis and characterization of [Fe(III)Pc-L’s)] complexes (Pc-L = Pyiridine-Containing Ligand) and their catalytic applications in alkene epoxidation or cis-dihydroxylation reactions using H2O2 as the terminal oxidant under mild conditions (Figure). Depending on the anion employed for the synthesis of the iron(III) metal complex, we observed a completely reversed selectivity. When X = OTf, a selective cis-dihydroxylation reaction was observed. On the other hand, employing X = Cl, we obtained the epoxide as the major product (traces of aldehyde were observed at very high conversions). It should be pointed out that under otherwise identical reaction conditions, using FeCl3·6H2O as catalyst in the absence of the ligand, no reaction was observed.
References:
1 a) B. Castano, S. Guidone, E. Gallo, F. Ragaini, N. Casati, P. Macchi, M. Sisti, A. Caselli, Dalton Trans. 2013, 42, 2451; b) G. Tseberlidis, M. Dell'Acqua, D. Valcarenghi, E. Gallo, E. Rossi, G. Abbiati, A. Caselli, RSC Adv. 2016, 6, 97404; c) T. Pedrazzini, P. Pirovano, M. Dell'Acqua, F. Ragaini, P. Illiano, P. Macchi, G. Abbiati, A. Caselli, Eur. J. Inorg. Chem. 2015, 2015, 5089
A simple combinatorial proof of a generalization of a result of Polo Author: F. Caselli Representation Theory 8 (2004), 479-486
No full textWe provide a simple combinatorial proof of, and generalize, a theorem
of Polo which asserts that for any polynomial P with nonnegative integer
coefficients such that P(0)=1 there exist two permutations u and v in a
suitable symmetric group such that P is equal to the Kazhdan-Lusztig
polynomial Pu,v
Expectations Anchoring and Inflation Persistence
No full textReplication files for "Expectations Anchoring and Inflation Persistence".
R. Bems, F. Caselli, F. Grigoli, B. Gruss.
JIE 202
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
Synthesis of copper(I) complexes with new chiral nitrogen donor macrocyclic ligands and their use in asymmetric catalysis
No full textCopper complexes play an important role in asymmetric catalysis and a number of different chiral ligands has been reported in the last decades. Among those, chiral C2-symmetric bidentate ligands have enjoyed a remarkable success in copper-catalyzed asymmetric cyclopropanation.1 This can be in part ascribed to the fact that fewer reaction channels are possible for the reaction, which simplifies the prediction of chiral induction. Furthermore, the synthesis of the ligands is often simpler than for C1-symmetric compounds. Only recently, C1-symmetric N,N-ligands have been reported to give moderate results in these reactions.2 We have recently found that copper(I) complexes of the new C1-symmetric pyridine-based 12 membered tetraaza macrocyclic (Pc-L*) ligands are competent asymmetric catalysts in the cyclopropanation of differently substituted olefins employing ethyl diazoacetate (EDA) as carbene precursor.3 We report here the synthesis of new C1- and C2-symmetric Pc-L* macrocycles and their use for the same reaction. The designed synthetic path is very simple and take advantage of commercially available, enantiomerically pure, chiral amino-alcohols and/or primary amines. All the macrocycles could be obtained in moderate to good yields and have been fully characterized. Their copper(I) complexes showed excellent catalytic activities and in all cases a quantitative conversion of the starting EDA was observed to give the desired cyclopropane derivatives. Enantiomeric excesses up to 90% were obtained. Moreover, the obtained results allow for a direct comparison of the stereoselective outcome of the reaction between C1- and C2-symmetric ligands of the same molecular structure.
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References:
1. (a) Pfaltz, A. Acc. Chem. Res.., 1993, 26, 339. (b) Evans, D.A.; Woerpel, K.A.; Hinmann, M.M., Faul, M.M. J. Am. Chem. Soc. 1991, 113, 726. (c) Ito, K.; Katsuki, T. Tetrahedron Lett. 1993, 34, 2661.
2. (a) Teng, P.-F.; Tsang, C.-S.; Yeung, H.-L.; Wong, W.-L.; Kwong, H.-L. J. Organomet. Chem. 2006, 691, 5664. (b) Borriello, C., Cucciolito, M.E.; Panunzi, A.; Ruffo, F. Tetrahedron: Asymm. 2001, 12, 2467.
3. Caselli, A.; Cesana, F.; Gallo, E.; Casati, N.; Macchi, P.; Sisti, M.; Celentano, G.; Cenini, S.. Dalton Trans. 2008, 4202
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