Configurationally stable molecular propellers: the [corrected] resolution of phosphorus-centered [corrected] residual enantiomers.
Explore the source record for details and available documents.
Journal Article↗
Biomedical subjects
Tullio Pilati
Publications and source records attributed to Tullio Pilati.
Metric engineering of supramolecular Borromean rings.
Two homologues of supramolecular Borromean rings were obtained based on the halogen-bonding-driven self-assembly of iodide ions with telechelic diiodoperfluoroalkanes.
Journal Article↗
A halogen-bonding-based heteroditopic receptor for alkali metal halides.
A new heteroditopic receptor for alkali metal halides has been designed and synthesized. It is comprised of a well-established motif for cation binding and a motif for halogen-bonding-based anion recognition processes. The single-crystal X-ray structure of the complex between the heteroditopic receptor and sodium iodide is reported. Thanks to the cooperativity of metal coordination and the strong I-...I halogen bonding, the ion pair is fully separated. The boosting effect of the binding of the anion through halogen bonding on the coordination of the cation by the receptor has been proved also in solution by NMR experiments. The selectivity of the new heterotopic receptor toward different alkali metal halides has been tested by ESI mass experiments.
Journal Article↗
Steric and electronic tuning of chiral bis(oxazoline) ligands with 3,3'-bithiophene backbone.
[structure: see text] The role played by the electronic properties and the steric features of bis(oxazoline) ligands in the Cu(I)-catalyzed cyclopropanation of styrene effected with ethyl diazoacetate was investigated. Two pairs of new bis(oxazolines) displaying flexible and atropisomeric 3,3'-bithiophene backbones were synthesized and structurally and electronically characterized. For the first time, the electrochemical oxidative potential was used as a reliable index of the electronic density on the nitrogen atom of the chelating groups of new and, for comparative purposes, of already known bis(oxazolines). The Cu(I) complexes of the new ligands were prepared, and their enantioselection ability and catalytic efficiency were tested. This investigation suggests that steric factors and catalyst geometrical features are clearly more important than any consideration of the electronic properties of the chiral ligands.
Journal Article↗
2,5-Dimethyl-3,4-bis[(2R,5R)-2,5-dimethylphospholano]thiophene: first member of the hetero-DuPHOS family.
[reaction: see text] The 2,5-dimethyl-3,4-bis[(2R,5R)-2,5-dimethylphospholano]thiophene (UlluPHOS), a new thiophene-based analogue of (R,R)-1,2-bis(phospholano)benzene (Me-DuPHOS), was synthesized, geometrically and electronically characterized, and employed as ligand of Rh and Ru in some standard hydrogenation reactions of prostereogenic functionalized carbon-carbon and carbon-oxygen double bonds. The synthesis of UlluPHOS is much easier than that provided for Me-DuPHOS. UlluPHOS and Me-DuPHOS display very similar geometries, while the electronic availability of the former is higher than that exhibited by the latter. The Rh and Ru complexes of UlluPHOS produced excellent enantiomeric excesses (98.9-99.5%) in the hydrogenation of N-acetyl-alpha-enamino acids and reaction rates higher than those found when employing the analogous complexes of Me-DuPHOS.
Journal Article↗
Polycyclic compounds from aminopolyols and alpha-dicarbonyls: structure and application in the synthesis of exoditopic ligands.
The structure and stereochemistry of the crystalline 2 : 2 condensation product ("glytham") of glyoxal and tris(hydroxymethyl)aminomethane was conclusively determined by X-ray diffractometric analysis. The singular disposition of the heteroatoms suggests the employment of glytham as starting material for the synthesis of ditopic ligands for metal ions. Some derivatives of glytham were prepared and their binding properties towards alkaline metal ions were preliminarily investigated by ESI-MS and NMR.
Journal Article↗
Spontaneous resolution in a halogen bonded supramolecular architecture.
The halogen bonding driven self-assembly of 1,8-diiodoperfluorooctane and N,N,N',N'-tetramethyl-p-phenylenediamine induces the formation of a chiral and enantiopure co-crystal wherein the fluorinated chains adopt an unusual gauche arrangement.
Journal Article↗
Halogen bonding based recognition processes: a world parallel to hydrogen bonding.
Halogen bonding is the noncovalent interaction between halogen atoms (Lewis acids) and neutral or anionic Lewis bases. The main features of the interaction are given, and the close similarity with the hydrogen bonding will become apparent. Some heuristic principles are presented to develop a rational crystal engineering based on halogen bonding. The focus is on halogen-bonded supramolecular architectures given by halocarbons. The potential of the interaction is shown by useful applications in the field of synthetic chemistry, material science, and bioorganic chemistry.
Journal Article↗
Experimental electron density study of the supramolecular aggregation between 4,4'-dipyridyl-N,N'-dioxide and 1,4-diiodotetrafluorobenzene at 90 K.
The electron density of the halogen-bonded complex of 4,4'-dipyridyl-N,N'-dioxide (bpNO) with 1,4-diiodotetrafluorobenzene (F(4)dIb) at 90 K has been determined by X-ray diffraction and analysed. The nature of the I.O intermolecular bond connecting the bpNO and F(4)dIb molecules into one-dimensional infinite chains, as well as the other non-covalent interactions present in the crystal, such as C-H...O, C-H...F and C-H...I hydrogen bonds and C...C, C...N, C...I and F...F interactions, have been investigated. The integration of electron density over the atomic basins reveals the electrostatic nature of the I...O halogen bond, which is very similar to a previously analysed I...N halogen bond.
Journal Article↗
Metric engineering of perfluorocarbon-hydrocarbon layered solids driven by the halogen bonding.
The halogen bonding driven self-assembly of 1,4-dicyanobutane and 1,6-dicyanohexane with a range of perfluorinated telechelic diiodoalkanes yields layered 1D, infinite chain co-crystals. The structure and metrics of these co-crystals are remarkably predictable.
Journal Article↗
Halogen bonding and pi...pi stacking control reactivity in the solid state.
The halogen bonding and the pi...pi stacking interactions induce the noncovalent self-assembly of modules into photoreactive supramolecular architecture. The pi...pi interaction pre-organizes the template, and the halogen bonding aligns the olefins to conform to the topochemical principle for photoreaction. The UV irradiation of the crystal resulted in a cyclization product with quantitative yield and stereospecificity.
Journal Article↗
N.Br halogen bonding: one-dimensional infinite chains through the self-assembly of dibromotetrafluorobenzenes with dipyridyl derivatives.
The N.Br halogen bonding drives the self-assembly of 1,4-dibromotetrafluorobenzene (1 a) and its 1,3 or 1,2 analogues (1 b,c, respectively) with dipyridyl derivatives 2 a,b. The isomeric supramolecular architectures 3 a-f are obtained as cocrystals that are stable in the air at room temperature. The solid-state features of these 1D infinite chains 3 have been fully characterized by single-crystal X-ray, Raman, and IR analyses. The occurrence of N.Br halogen bonding in solution has been detected with (19)F NMR spectroscopy. The N.Br halogen bonding is highly selective and directional and the geometry of the single strands of noncovalent copolymers 3 is programmed by the geometry of halogen-bonding donor and acceptor sites on the starting modules. The composition and topology of the instructed networks can be predicted with great accuracy. Experiments of competitive cocrystal formation established the strength of the N.Br interaction relative to other halogen bondings and the ability of different modules 1 to be involved in site-selective supramolecular syntheses.
Journal Article↗
3-Formylcyclopent-3-enyl- and 3-carboxycyclopentylglycine derivatives: a new stereocontrolled approach via retro-aldol or retro-Claisen reactions.
A new synthetic approach to diastereomeric cyclopent-3-enylglycines 19/20, functionalized on the ring with a formyl group, and to cyclopentylglycine, substituted with a carboxy group (compounds 21/22), was devised by applying retro-aldol and retro-Claisen reactions, respectively, to diastereomeric 2-amino-3-ethoxycarbonyloxynorbornene-2-carboxylic acid derivatives 5, 6 and to diastereomeric 2-amino-3-oxo-norbornane-2-carboxylic acid derivatives 17, 18. The goal of controlling the cis stereochemistry of the cyclopentyl substituents was reached using compounds 17, 18. A partial control of the stereochemistry of the amino acidic carbon was achieved starting from 17 and using sodium hydrogen carbonate in acetone/DMF. From exo-17, the acid 22 was obtained as the major diastereomer.
Catalysis↗
The experimental electron density distribution in the complex of (E)-1,2-bis(4-pyridyl)ethylene with 1,4-diiodotetrafluorobenzene at 90 K.
The experimental electron density of the donor-acceptor complex of (E)-1,2-bis(4-pyridyl)ethylene (bpe) with 1,4-diiodotetrafluorobenzene (F(4)DIB) at 90 K has been determined with the aspherical atom formalism and analyzed by means of the topological theory of molecular structure. The bpe and F(4)DIB molecules are connected by intermolecular I.N bonds into infinite 1D chains. F.H bonds link these chains together to form the crystal assembly. The topological analysis reveals that the Cbond;I bond is of the "closed shell" type. Its bond-critical properties run parallel to those found in metal-metal and metal-ligand bonds of organometallic compounds. The integrated net charges show that the I.N halogen bond has an essentially electrostatic nature. F.F, F.C, and C.C intermolecular interactions, for which a bond path was found, contribute to reinforce the crystal structure.
Journal Article↗
Atomic displacement parameters for spessartine Mn3Al2Si3O12 and their lattice-dynamical interpretation.
A rigid-ion lattice-dynamical treatment accounts reasonably well for most of the atomic displacement parameters (ADPs) reported in the literature for a synthetic sample of spessartine Mn(3)Al(2)Si(3)O(12); the model accounts less well for the ADPs of the Mn atom. These results are similar to those obtained for the corresponding garnets pyrope Mg(3)Al(2)Si(3)O(12) and almandine Fe(3)Al(2)Si(3)O(12). The results are confirmed by a very good agreement of the lattice-dynamical estimates with the experimental values of the heat capacity that are currently available, as well as those of the Raman and infrared vibrational spectra. The anomalous behaviour of the Mn atom is reflected in the entropy values. As is the case for pyrope and almandine, here the agreement with the experimental results can be markedly improved if the existence of a low-temperature order-disorder transition concerning the Mn atom is considered. The lattice-dynamical estimates for all the atoms presented here do not agree with the corresponding ADPs obtained in a crystal structure refinement of a supposedly 'pure' natural sample from Elba. In turn, these experimental ADPs do not agree with those observed for the synthetic sample, thereby showing a physical difference; such a possibility is in agreement with recent observations by other authors, who found an unexpected fluorine content in several natural specimens of spessartine. Therefore, theoretical estimates of ADPs are reliable enough to point out unexpected situations if disagreement with the observed values occurs.
Journal Article↗
The diastereoisomers methyl 5-(S)-[2-(R)/(S)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate.
The title diastereoisomers, methyl 5-(S)-[2-(S)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate and methyl 5-(S)-[2-(R)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate, both C(19)H(23)N(3)O(5), have been studied in two crystalline forms. The first form, methyl 5-(S)-[2-(S)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate--methyl 5-(S)-[2-(R)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate (1/1), 2(S),5(S)-C(19)H(23)N(3)O(5) x 2(R),5(S)-C(19)H(23)N(3)O(5), contains both S,S and S,R isomers, while the second, methyl 5-(S)-[2-(S)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate, 2(S),5(S)-C(19)H(23)N(3)O(5), is the pure S,S isomer. The S,S isomers in the two structures show very similar geometries, the maximum difference being about 15 on one torsion angle. The differences between the S,S and S,R isomers, apart from those due to the inversion of one chiral centre, are more remarkable, and are partially due to a possible rotational disorder of the 2-(methoxycarbonyl)tetrahydropyrrole group.
Journal Article↗
New Class of Chiral Diphosphine Ligands for Highly Efficient Transition Metal-Catalyzed Stereoselective Reactions: The Bis(diphenylphosphino) Five-membered Biheteroaryls.
The synthesis and application of three examples of a new class of chiral (C(2)) atropisomeric diphosphines characterized by two interconnected five-membered heteroaromatic rings, with hindered rotation around the interanular bond, are described. Optically pure (+)- and (-)-2,2'-bis(diphenylphosphino)-4,4',6,6'-tetramethyl-3,3'-bibenzo[b]thiophene (tetraMe-bitianp) (1a) and the parent unsubstituted system (+)- and (-)-bitianp (1b) were synthesized. They were found to be optically stable at 100 degrees C and were successfully employed as ligands in the Ru(II)-catalyzed hydrogenation of alpha- and beta-oxo esters to the corresponding alpha- and beta-hydroxy esters and in the hydrogenation of olefinic substrates. The optical and chemical yields were comparable with those reported for the same Ru(II)-binap-catalyzed reactions carried out under the same experimental conditions. The 2,2'-bis(diphenylphosphino)-3,3'-bibenzo[b]furan (1c), the oxygenated analogue of bitianp, was found to be configurationally unstable at room temperature. Complete structural X-ray elucidation of the Pd complexes of 1a-c is reported. The advantages of these biheteroaromatic ligands over the classical biaryl systems are discussed.
Journal Article↗