Consiglia Tedesco

Structural Effects of Proline Substitution and Metal Binding on Hexameric Cyclic Peptoids

L-Proline and N-methoxyethyl glycine have been included in novel cyclic hexameric peptoids. Supramolecular coordination with Na(+) triggered the formation of the first 1D metal-organic framework based on peptoids.

Organocatalytic stereoselective epoxidation of trisubstituted acrylonitriles.

The first diastereospecific and enantioselective epoxidation of trans-2-aroyl-3-arylacrylonitriles by means of the commercially available diaryl L-prolinol/tert-butyl hydroperoxide system has been developed. These diversely functionalized epoxides were obtained in excellent yield (up to 99%), complete diastereoselectivity for the trans-isomer, and good enantioselectivity (up to 84% ee). Highly enantioenriched epoxides can be easily obtained after a single crystallization (ee > 90%).

Methane Adsorption in a Supramolecular Organic Zeolite

Gas storage in solids is an increasingly important research area with applications in the field of energy, environment, biology and medicine. Because it concerns the adsorption of methane, the main component of natural gas fuels, the storage target for any solid to be effective in energy applications and compete with the compressed form is approximately 35 wt % or 180 v/v. Several different types of porous materials such as carbon materials, zeolites, silica gels, MOFs and polymers have been recently examined in addition to organic crystalline microporous solids and nonporous ones, but no ideal candidates have emerged so far. In this paper we wish to report on the methane adsorption properties of a new microporous organic zeolite based on 1,2-dimethoxy-p-tert-butylcalix[4]dihydroquinone (Scheme 1), which has been recently characterised by our research group. The crystalline solid has a cubic structure (a= 36.412(4) ) with networked channels and hydrophobic cages. The channels have minimum and maximum diameter of 3.9 and 8.5 , respectively, excluding van der Waals radii, and they are filled with easily removable water molecules. The hydrophobic cages show a gate diameter of 2.2 and can reach a maximum diameter of 11.2 (excluding van der Waals radii), and the estimated cage volume is about 1000 . Interestingly, the supramolecular framework is also preserved after the removal of channel water molecules. Previous studies showed that the BET surface area corresponds to 230 m g 1 (N2 at 77 K) and that carbon dioxide can be absorbed at room temperature inside its nanochannels with high selectivity with respect to H2 gas, [9] encouraging further studies towards methane adsorption. Methane adsorption measurements were performed by using a home-made volumetric system. Sorption isotherms have been carried out at 298, 278 and 203 K. Data have been collected at initial pressures between 0.5 and 3 atm. The adsorption isotherm at 203 K is reported in Figure 1, (see the Supporting Information for adsorption isotherms at 298 and 278 K). At 1 atm and 298 K our compound adsorbs 0.11 methane molecules for each calixarene molecule. For comparison, p-tert-butylcalix[4]arene adsorbs 0.14 methane molecules for each calixarene molecule under the same conditions. Under the mild conditions of ambient pressure and temperature our sample shows an efficiency for methane storage of 0.29 wt %, whereas in the case of CO2 molecules the value was 0.5 wt %. The adsorption isotherm at 203 K is not of type I. The adsorption step at 2 atm could be interpreted by considering that at first the methane molecules enter the channels, interacting with the most favourite sites, and then upon increasing the pressure the channels are progressively filled. Note that there are 90 methane molecules in the unit cell at 3 atm pressure, which approximately corresponds to a 1:2 ratio between calixarene molecules and methane molecules. [a] Dr. C. Tedesco, Dr. L. Erra, Dr. V. Cipolletti, Dr. C. Gaeta, Prof. P. Neri Department of Chemistry and Nano_MATES Research Center University of Salerno, 84084 Fisciano (Italy) Fax: (+39) 089-969603 E-mail : ctedesco@unisa.it neri@unisa.it [b] Dr. M. Brunelli, Prof. A. N. Fitch European Synchrotron Radiation Facility 38043 Grenoble (France) [c] Prof. J. L. Atwood Department of Chemistry University of Missouri-Columbia Columbia, Missouri 65211 (USA) [d] Dr. M. Brunelli Current address: ILL Institut Laue-Langevin BP 156, 38042 Grenoble Cedex 9 (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200903218. Scheme 1. 1,2-Dimethoxy-ptert-butylcalix[4]dihydroquinone.

Interconnected water channels and isolated hydrophobic cavities in a calixarene-based, nanoporous supramolecular architecture

An interesting interplay of H-bond and van der Waals-like interactions in a proximal calix[4]arene dihydroquinone derivative gives rise to a nanoporous supramolecular architecture with the simultaneous existence of water channels and very large hydrophobic cavities.

New Neutral and Cationic Dialkylaluminium Complexes Bearing Imino‐Amide or Imino‐Phenoxide Ligands: Synthesis, Characterization and Reactivity With Olefins

The synthesis and the characterization of some new aluminium complexes carrying bidentate monoanionic imino-amide or imino-phenoxide ligands are described. Reaction of 1-(o,o′-diisopropylphenylamino)-6-(o,o′-diisopropylphenylimino)cyclohexene with AlMe3 proceeded by methane elimination to produce the yellow compound dimethylaluminium N-(o,o′-diisopropylphenyl)-6-[N-(o,o′-diisopropylphenyl)imido]-1-cyclohexen-1-amide (1). In contrast, reaction of the same ligand with AlEt3 under the same experimental conditions involved the 1,4-addition of AlEt3 to the α,β-unsaturated imine, and led to the highly crystalline diethylaluminium N(o,o′-diisopropylphenyl)-2-[(o,o′-diisopropylphenyl)amino]3-ethyl-1-cyclohexen-1-amide (2). The structures of compounds 1 and 2 were determined by single-crystal X-ray diffraction. Thermolysis of 2 gave rise to ethane elimination, and led to the oily bis(amido) monoethyl derivative. Treatment of the salicylaldimine ligands 3-tBu-2-(OH)C6H3CH=N−R with AlMe3 yielded the dimethylaluminium compounds {3-tBu-2-(O)C6H3CH=N−R}AlMe2 [R = C6H5 (3); 2,6-iPr2C6H3 (4); and C6F5 (5)]. Compounds 1, 3, and 5 underwent methyl abstraction reactions with B(C6F5)3; trapping of the cationic species was accomplished in the presence of THF in dichloromethane solution. Preliminary polymerization tests were carried out for the synthesized Al complexes. Toluene solutions of 3, 4, and 5, when activated with 1 equiv. of B(C6F5)3, polymerised ethylene (1 atm) to solid polyethylene with low activity.

Solid state assembly of cyclic α-peptoids

The solid state assembly of free and metal coordinated cyclic α-peptoids has been examined with the aim to find common underlying features and to direct the design of new functional biomimetic materials with desired properties in terms of molecular recognition, drug delivery and catalysis. The lack of the amide proton prevents the formation of NH⋯OC hydrogen bonds and weaker interactions play a key role in the intermolecular recognition and assembly. Inter-annular CH⋯OC hydrogen bonds provide face to face or side by side arrangement of macrocycles in a way that can be considered the peptoid counterpart of β-sheet secondary structure in proteins. The choice of side chains is crucial for the solid state properties of α-cyclic peptoids. Side chains have a strong influence on the solid state assembly of peptoid macrocycles: they may provide competing interactions to CH⋯OC inter-annular hydrogen bonds, leading either to a T-shape or to a tubular arrangement of the peptoid macrocycles. The size of the macrocycle is another important factor influencing the tubular arrangement. In particular, a larger size of the macrocycle promotes side by side with respect to T-shape interactions. Hirshfeld surfaces and their fingerprint analysis allowed the analysis of the contributions of weak intermolecular interactions, such as weak CH⋯OC hydrogen bonds and CH–pi interactions, towards the crystal packing.

Straightforward enantioselective access to γ-butyrolactones bearing an all-carbon β-quaternary stereocenter.

An enantioselective one-pot aldol/lactonization sequence has been developed to access highly challenging γ-butyrolactones bearing an all-carbon quaternary stereocenter at the β-position by reacting acylated succinic esters with aqueous formaldehyde in the presence of 3 mol % loading of a cinchona alkaloid-derived squaramide providing direct access to paraconic acid derivatives in high yield and fairly good level of enantioselectivity (up to 88% ee).

Synthesis of α-diimine V(III) complexes and their role as ethylene polymerisation catalysts

Two novel α-diimine vanadium complexes, [PhNC(Me)–C(Me)NPh]V(THF)Cl3 (1) and {[2,6-(i-Pr)2Ph]NCH–CHN[2,6-(i-Pr)2Ph]}VCl3 (2) were synthesized by ligand exchange reaction of VCl3(THF)3 with the appropriate α-diimine ligand. The chemical structure of 1 was determined by X-ray crystallography and found to consist of a vanadium atom in a distorted octahedral geometry with the oxygen atom of the coordinated THF, two nitrogen atoms of the diimine ligand and one chlorine atom in the same plane. Complexes 1 and 2 were characterized by FT-IR, 1H NMR, elemental analysis and 2 was identified as the THF free V(III) diimine complex. The behavior of 1 and 2 as ethylene polymerisation catalysts was preliminarily explored after activation with MAO or AlEt2Cl and compared with that of {2,6-bis[2,6-(i-Pr)2PhNC(Me)]2(C5H3N)}VCl3 (3) under similar conditions. Upon activation of 1–3 with AlEt2Cl, moderate polymerisation activities were observed at −40 °C whereas the corresponding MAO activated catalysts exhibit lower activity. The molar concentration of the active sites at −40 °C is rather low (found in the range 5–12% of total vanadium) and results from slow alkylation of the complexes followed by reduction of V(III) catalysts to inactive V(II) species. At 50 °C an increase of the ethylene polymerisation activities of the 1–3-AlEt2Cl catalysts was observed and the trend of the productivity values follows the steric hindrance at the metal center. Alkylation of the diimine ligands of the 1–3 catalysts with AlEt2Cl producing deactivation of the active sites is only partially active under polymerisation conditions whereas the reaction of 1 and 2 with MAO produces fast degradation of the active species.

NMR Spectroscopy and X-Ray Characterisation of Cationic N-Heteroaryl-Pyridylamido ZrIV Complexes: A Further Level of Complexity for the Elusive Active Species of Pyridylamido Olefin Polymerisation Catalysts

New [(N(-),N,N(-))ZrR2] dialkyl complexes (N(-),N,N(-)=pyrrolyl-pyridyl-amido or indolyl-pyridyl-amido; R=Me or CH2Ph) have been synthesised and tested as pre-catalysts for ethene and propene polymerisation in combination with different activators, such as B(C6F5)3, [Ph3C][B(C6F5)4], [HNMe2Ph][B(C6F5)4] or solid AlMe3-depleted methylaluminoxane (DMAO). Polyethylene (M(w)>2 MDa and M(w)/M(n)= 1.3-1.6) has been produced if pre-catalysts were activated with 1000 equivalents of DMAO (based on Al) [activity >1000 kg(PE)(mol([Zr]) h mol atm)(-1)] or by using a higher pre-catalyst concentration and a mixture of [HNPhMe2][B(C6F5)4] (1 equiv) and AliBu2H (60 equiv). In the case of propene polymerisation, activity has been observed only if pre-catalysts were treated with an excess of AliBu2H prior to addition of DMAO, which led to highly isotactic polypropylene ([mmmm]>95%). Neutral pre-catalysts and ion pairs derived from their activation have been characterised in solution by using advanced 1D and 2D NMR spectroscopy experiments. The detection and rationalisation of intercationic NOEs clearly showed the formation of dimeric species in which some pyrrolyl or indolyl π-electron density of one unit is engaged in stabilising the metal centre of the other unit, which relegates the counterions in the second coordination sphere. The solid-state structure of the dimeric indolyl-pyridyl-amidomethylzirconium derivative, determined by X-ray diffraction studies, points toward a weak Zr···η(3)-indolyl interaction. It can be hypothesised that the formation of dimeric cationic species hampers monomer coordination (especially of less reactive α-olefins) and that addition of AliBu2H is crucial to split the homodimers.

A solid-state molecular capsule based on p-sulfonatocalix[7]arene and dicationic Diquat guest

An extended framework of molecular capsules based on p-sulfonatocalix[7]arene and a dicationic Diquat guest has been obtained. One Diquat guest molecule is encapsulated inside two trimeric ¾-cone subunits of two different p-sulfonatocalix[7]arene caps. The molecular capsules are sealed electrostatically by means of interactions between anionic sulfonato groups and Ba2+ cations. Interestingly, the extended capsular framework gives rise to cavities hosting water molecules.