Chlorido(η 4-cyclo­octa-1,5-diene)(N,N′-diethyl­thio­urea-κS)rhodium(I)

In the title rhodium(I) complex, [RhCl(C8H12)(C5H12N2S)], N,N′-diethyl­thio­urea acts as a monodenate S-donor ligand. The rhodium(I) coordination sphere is completed by the Cl atom and the COD [= 1,5-cyclo­octa­diene] ligand inter­acting through the π-electrons of the double bonds. If the midpoints of these two bonds are taken into account, the Rh atom exhibits a distorted square-planar coordination. The syn conformation of the N,N′-diethyl­thio­urea ligand with respect to the Cl atom is stabilized by an intra­molecular N—H⋯Cl hydrogen bond. A weak inter­molecular N—H⋯Cl inter­action links mol­ecules along the a axis

The Origin of Selectivity in the Complexation of N-Methyl Amino Acids by Tetraphosphonate Cavitands

We report on the eligibility of tetraphosphonate resorcinarene cavitands for the molecular recognition of amino acids. We determined the crystal structure of 13 complexes of the tetraphosphonate cavitand Tiiii[H, CH3, CH3] with amino acids. 1H NMR and 31P NMR experiments and ITC analysis were performed to probe the binding between cavitand Tiiii[C3H7, CH3, C2H5] or the water-soluble counterpart Tiiii[C3H6Py+Cl-, CH3, C2H5] and a selection of representative amino acids. The reported studies and results allowed us (i) to highlight the noncovalent interactions involved in the binding event in each case; (ii) to investigate the ability of tetraphosphonate cavitand receptors to discriminate between the different amino acids; (iii) to calculate the Ka values of the different complexes formed and evaluate the thermodynamic parameters of the complexation process, dissecting the entropic and enthalpic contributions; and (iv) to determine the solvent influence on the complexation selectivity. By moving from methanol to water, the complexation changed from entropy driven to entropy opposed, leading to a drop of almost three orders in the magnitude of the Ka. However, this reduction in binding affinity is associated with a dramatic increase in selectivity, since in aqueous solutions only N-methylated amino acids are effectively recognized. The thermodynamic profile of the binding does not change in PBS solution. The pivotal role played by cation 12\u3c0 interactions is demonstrated by the linear correlation found between the log\u202fKa in methanol solution and the depth of +N\u2013CH3 cavity inclusion in the molecular structures. These findings are relevant for the potential use of phosphonate cavitands as synthetic receptors for the detection of epigenetic modifications of histones in physiological media

3-[2-(1H-1,3-Benzodiazol-2-yl)eth­yl]-1,3-oxazolidin-2-one

In the title compound, C12H13N3O2, the dihedral angle between the oxazolone ring and the benzimidazole unit is 45.0 (5)°, exhibiting a staggered conformation at the Cα—Cβ bond. In the crystal, a strong N—H⋯N hydrogen bond links the mol­ecules into a C(4) chain along the c axis while a C—H⋯O hydrogen-bonding inter­action generates a C(5) chain along the a axis, i.e. perpendicular to the other chain

Triptycene-Roofed Quinoxaline Cavitands for the Supramolecular Detection of BTEX in Air

Two novel triptycene quinoxaline cavitands (DiTriptyQxCav and MonoTriptyQxCav) have been designed, synthesized, and applied in the supramolecular detection of benzene, toluene, ethylbenzene, and xylenes (BTEX) in air. The complexation properties of the two cavitands towards aromatics in the solid state are strengthened by the presence of the triptycene moieties at the upper rim of the tetraquinoxaline walls, promoting the confinement of the aromatic hydrocarbons within the cavity. The two cavitands were used as fiber coatings for solid-phase microextraction (SPME) BTEX monitoring in air. The best performances in terms of enrichment factors, selectivity, and LOD (limit of detection) values were obtained by using the DiTriptyQxCav coating. The corresponding SPME fiber was successfully tested under real urban monitoring conditions, outperforming the commercial divinylbenzene\u2013Carboxen\u2013polydimethylsiloxane (DVB\u2013CAR\u2013PDMS) fiber in BTEX adsorption

(S)-2-[(2-Hy­droxy­benz­yl)aza­nium­yl]-4-(methyl­sulfan­yl)butano­ate

The zwitterionic title compound, C12H17NO3S, is a reduced Schiff base derived from (S)-N-(2-hy­droxy­benzyl­idene)methio­nine. An intra­molecular inter­action between the N—H and carboxyl­ate groups forms a roughly planar (r.m.s. deviation = 0.1405 Å) five-membered ring containing the H(N), N, Cα, C(carboxyl­ate) and O atoms in a penta­gonal conformation. In the crystal, a supra­molecular triangle-shaped motif is generated by mol­ecules held together by O—H⋯O and N—H⋯O hydrogen bonds

Probing the Structural Determinants of Amino Acid Recognition: X-Ray Studies of Crystalline Ditopic Host-Guest Complexes of the Positively Charged Amino Acids, Arg, Lys, and His with a Cavitand Molecule

Crystallization of tetraphosphonate cavitand Tiiii[H, CH3, CH3] in the presence of positively charged amino acids, namely arginine, lysine, or histidine, afforded host-guest complex structures. The X-ray structure determination revealed that in all three structures, the fully protonated form of the amino acid is ditopically complexed by two tetraphosphonate cavitand molecules. Guanidinium, ammonium, and imidazolium cationic groups of the amino acid side chain are hosted in the cavity of a phosphonate receptor, and are held in place by specific hydrogen bonding interactions with the P=O groups of the cavitand molecule. In all three structures, the positively charged α-ammonium groups form H-bonds with the P=O groups, and with a water molecule hosted in the cavity of a second tetraphosphonate molecule. Furthermore, water-assisted dimerization was observed for the cavitand/histidine ditopic complex. In this 4:2 supramolecular complex, a bridged water molecule is held by two carboxylic acid groups of the dimerized amino acid. The structural information obtained on the geometrical constrains necessary for the possible encapsulation of the amino acids are important for the rational design of devices for analytical and medical applications

Synthesis, coordination properties and application of new N,N-ligands based on bornyl and binaphthylazepine chiral backbones in palladium-catalyzed allylic substitution reactions

The synthesis of new imine-amine and diamine ligands, based on both the atropisomeric (Sa)- or (Ra)-1,1′-binaphthyl and (R)-bornyl backbones, and incorporating an ethylenediamino spacer, are reported. In addition, analogue ligands in which one chiral arm is replaced by the achiral NMe2 group were synthesized. These N,N-ligands when coordinated to a palladium metal centre form highly enantioselective catalysts for the asymmetric allylic alkylation of rac-2-acetoxy-1,3-diphenylpropene by dimethyl malonate. In one case, the synergic effect of the chirality elements in the palladium catalyst afforded the (S) substitution product with an enantiomeric excess (ee) of >99 %. Based on NMR studies of the active species in solution, a reliable explanation for the origin of the enantioselectivity of these palladium catalysts is also provided. New dinitrogen chiral ligands were synthesized and investigated in palladium-catalyzed allylic alkylation reactions. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.This work was supported by Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR), PRIN 2007HMTJWP_005Peer Reviewe

Formation and Structure of a Cobalt(III) Complex Containing a Nonstabilized Pyridinium Ylide Ligand

The reaction of [CoIII(4,4\u2032dmsalen)(CH2Cl)(S)], where 4,4\u2032dmsalen = 4,4\u2032-dimethylsalen and S = solvent, with pyridine led to the formation of [CoIII(4,4\u2032dmsalen)(CH2py)(Cl)], containing a nonstabilized pyridinium ylide as axial ligand. The complex has been unambiguously characterized by single-crystal X-ray diffraction analysis. Time-resolved 1H NMR spectra showed that the formation of [CoIII(4,4\u2032dmsalen)(CH2py)(Cl)] occurs in a two-step process involving a metallacyclized intermediate, cis-\u3b2-[CoIII(4,4\u2032dmsalenCH2)(py)(S)]+. A similar experiment carried out in the presence of different nitrogen bases having higher pKa values (4-Me-py or 4-t-Bu-py) allowed a better separation of the two consecutive reactions. The almost complete conversion of [CoIII(4,4\u2032dmsalen)(CH2Cl)(S)] in the cyclized intermediate before the formation of the ylide indicates that the ylide complex forms exclusively through the nucleophilic attack of the nitrogen base at the 12CH2O\u2013 carbon of the cyclized species, whereas a parallel direct conversion through the displacement of Cl\u2013 from the axial CH2Cl group of [CoIII(4,4\u2032dmsalen)(CH2Cl)(S)] may be ruled out

Mono- and dinuclear uranyl(VI) complexes with chiral Schiff base ligand

Slow evaporation of an equimolar solution containing chiral uranyl-salen-pyrene complex and (L)-phenylalanine tetramethylammonium salt ((L)-Phe-TMA) in toluene/EtOH mixture produced crystals built by anionic mononuclear [(UO2)(L)(L\u2032)]- and dinuclear [(UO 2)2(L)2(\u3bc2-OH)]- (L = salen-pyrene, L\u2032 = pyrenolate) complexes, counterbalanced by tetramethylammonium (TMA) cations. The single-crystal X-ray diffraction analysis shows that in both complexes the salen-pyrene ligand acts as a tetradentate ligand through its nitrogen and oxygen atoms chelating the UO2 2+ ion at the equatorial plane. Uranium centers show a seven-coordinated pentagonal-bipyramidal environment, where the fifth equatorial site is occupied by an oxygen atom from the pyrenolate ligand in the monomer and a \u3bc2-OH bridging group in the dimer. In the dinuclear complex the central \u3bc2-OH bridges two UO2 2+ ions forming a double-stranded helical structure. TMA cations are sandwiched between the anionic uranyl-salen-pyrene complexes through weak hydrogen bonds and cation ef\u3c0 interactions. This produces alternating monomer/TMA/dimer/TMA pillars assembled by van der Waals interactions in the three-dimensional crystal lattice. The chiral uranyl-salen-pyrene receptor and the mixture of mono- and dimeric complexes have been also characterized by ESI-MS, UV-Vis and fluorescence spectroscopy. \ua9 2012 Elsevier B.V. All rights reserve