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Catalytic Applications of Pyridine-Containing Macrocyclic Complexes
Full text linkPolyazamacrocycles 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
Full text linkThe 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
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
Amination of C-H Bonds by Metal Porphyrins Catalysed Nitrene Transfer Reaction
No full textThe biological and pharmaceutical activities of organonitrogen compounds prompted the scientific community to develop new methods for the direct and selective C-N bond formation, working within restricted financial parameters and environmentally friendly requirements.In the last few years we have reported on the catalytic activity of metal porphyrin complexes in a wide range of reactions, such as olefin epoxidation,1 hydrocarbon amination and olefin aziridination. For these last reactions arylazides, a versatile class of starting material, was employed as atom-efficient aminating agents.2 ArN3 generate a nitrene functionality “ArN” and the eco-friendly molecular nitrogen is the only side product.
The selective insertion of “ArN” into C–H bonds of benzylic substrates or olefins yields benzylic amines, benzylic imines or allylic amines. To clarify the mechanism of the C-H amination reactions, the ruthenium bis-imido porphyrin complex (1) was isolated and characterised by X-ray analysis.
The role of 1 in catalytic nitrene insertions into C H bonds was studied in the reaction of ArN3 with several hydrocarbons proving that 1 is an active reaction intermediate. It also appears to have equilibrium between stability and reactivity.3 To the best of our knowledge, complex 1 is the first structurally characterized bis-imido porphyrin complex that shows a good catalytic activity in this class of reactions.
References: [1] S. Fantauzzi, E. Gallo, E. Rose, N. Raoul, A. Caselli, S. Issa, F. Ragaini, S. Cenini, Organometallics , 2008, 27, 6143; [2] For a review see: S. Fantauzzi, A. Caselli and E. Gallo, Dalton Trans., 2009, 5434; [3] S. Fantauzzi, E. Gallo, A. Caselli, F. Ragaini, N. Casati, P. Macchi and S. Cenini Chem. Commun., 2009, 3952–395
Pyridine-Containing Macrocyclic Complexes and their catalytic applications
Full text linkPolyazamacrocycles 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. Worth of note is their ability to form stable complexes with a plethora of both transition, especially late, and lanthanide metal cations. Deviation of the macrocycle donor atoms from planarity often leads to rather uncommon oxidation states. 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. 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. 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. The increased conformational rigidity imposed by the pyridine ring allowed for the isolation and characterization of metal complexes which showed a rich coordination chemistry. The very different conformations accessible upon coordination and the easy tuneable synthesis of the macrocyclic ligands have been exploited in stereoselective syntheses
Transition metal complexes of pyridine-containing macrocycles as catalysts for selective oxidations and CO2 valorisation reactions
No full textIron, the most abundant transition metal on earth, and its complexes are knowing an increasing interest in organic synthesis. The field of iron-catalysed oxidation reactions is of great importance not only in synthetic organic chemistry, but also in biochemistry and industrial applications. In order to design catalysts capable of performing high regio- and/or stereo-selective C-OH, C-H or C=C bond oxidations, it is important the choice of critical components of iron coordination sphere, namely the donor atoms and their geometry. In this lecture, I will provide a perspective on the catalytic applications of iron(III) and zinc(II) metal complexes of tetraaza 12-membered pyridine containing macrocyclic ligands.1 I will focus on the selective iron(III) catalysed epoxidation or dihydroxylation of alkenes by using hydrogen peroxide as terminal oxidant.2 Depending on the anion of the iron(III) metal complex employed as catalyst, a completely reversed selectivity was observed (Figure). Our approach towards the selective oxidation of alcohols by using the same catalytic system will also be covered. As for iron, catalytic applications of zinc complexes fall in the scientific community’s effort to develop more eco-friendly chemical processes. CO2 is the principal greenhouse gas, largely recognized as responsible for global warming, but it is also an abundant C1 source. Limiting CO2 emissions can only stem the problem but to solve it a circular economy based on carbon dioxide should be pursued and in this respect, research in the last decade has focussed on the design of systems able to promote the functionalisation of CO2. I will outline our approach towards the synthesis of cyclic carbonates by cycloaddition of CO2 to epoxides by using zinc(II) complexes
SmI2-mediated reactions of diethyl iodomethylphosphonate with esters and lactones: a highly stereoselective synthesis of a precursor of the C-glycosyl analogue of thymidine 5′-(β-l-rhamnosyl)diphosphate
No full textIn the presence of samarium iodide diethyl iodomethylphosphonate reacts with esters to afford beta-ketophosphonates. The protocol has been applied to sugar lactones to afford in fairly good yields intermediates that are useful precursors for a variety of potentially bioactive compounds, such as the C-glycosyl analogue of thymidine 5'-(beta-L-rhamnosyl)diphosphate
Application in asymmetric cyclopropanation of new chiral macrocycles
Full text linkOur group has been focusing for years on the synthesis and on the study of chiral macrocyclic ligand. Their complexes with metal ions – specially copper(I) and silver(I) – are competent catalysts in various organic reactions.
The synthesis of this class of compounds is simple and fast (scheme 1). It does not involve either complex procedures nor expensive reagents, since the macrocycles can be obtained from enantiomerically pure and naturally available aminoacids in good yields (overall 40-50%).
In this presentation, we reported the synthesis of three new chiral ligands bearing different chiral arms on the macrocyclic backbone.
We also report the studies of complexation of these ligands by Ag(I) and Cu(I) ions and the good applicative results of the latter complexes as catalysts for the cyclopropanation reaction of α-methylstyrene
A new entry to β-hydroxyphosphonates: the SmI2-mediated reaction of diethyl iodomethylphosphonate with carbonyl compounds
No full textIn the presence of samarium iodide alpha-halophosphonates react with aliphatic carbonyl compounds (aldehydes and ketones) to afford beta-hydroxyphosphonates in fairly good yields under neutral and mild conditions. Lower yields are obtained with aromatic carbonyl compounds
Controlling selectivity in alkene oxidation and CO2 cycloaddition reactions: fine tuning of Pc-L transition metal complexes
Full text linkSustainable synthesis and green chemistry have become a fundamental tool when planning a new process. In catalysis this means to correctly design since the beginning the properties of the target metal complex. The cost and the availability of the metal ion, as well as its biocompatibility must be taken into account. Despite the fact that their greater reactivity makes more difficult their use, first row transition metals are to be considered as the first choice to plan a new catalytic cycle. In this lecture, I will provide a perspective on the catalytic applications of iron(III) and zinc(II) metal complexes of tetraaza 12-membered pyridine containing macrocyclic ligands.1 I will focus on the selective iron(III) catalysed epoxidation or dihydroxylation of alkenes by using hydrogen peroxide as terminal oxidant.2 Depending on the anion of the iron(III) metal complex employed as catalyst, a completely reversed selectivity was observed (Figure). Our approach towards the selective oxidation of alcohols by using the same catalytic system will also be covered. As for iron, catalytic applications of zinc complexes fall in the scientific community’s effort to develop more eco-friendly chemical processes. CO2 is the principal greenhouse gas, largely recognized as responsible for global warming, but it is also an abundant C1 source. Limiting CO2 emissions can only stem the problem but to solve it a circular economy based on carbon dioxide should be pursued and in this respect, research in the last decade has focussed on the design of systems able to promote the functionalisation of CO2. I will outline our approach towards the synthesis of cyclic carbonates by cycloaddition of CO2 to epoxides by using zinc(II) complexes
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