Mario Sánchez

Macrocyclic Diorganotin Complexes of γ-Amino Acid Dithiocarbamates as Hosts for Ion-Pair Recognition

The dimethyl-, di-n-butyl-, and diphenyltin(IV) dithiocarbamate (dtc) complexes [{R2Sn(L-dtc)}x] 1-7 (1, L = L1, R = Me; 2, L = L1, R = n-Bu; 3, L = L2, R = Me, x = infinity; 4, L = L2, R = n-Bu; 5, L = L3, R = Me, x = 2; 6, L = L3, R = n-Bu, x = 2; 7, L = L3, R = Ph, x = 2) have been prepared from a series of secondary amino acid (AA) homologues as starting materials: N-benzylglycine (alpha-AA derivative = L1), N-benzyl-3-aminopropionic acid (beta-AA derivative = L2), and N-benzyl-4-aminobutyric acid (gamma-AA derivative = L3). The resulting compounds have been characterized by elemental analysis, mass spectrometry, IR and NMR ((1)H, (13)C, and (119)Sn) spectroscopy, thermogravimetric analysis, and X-ray crystallography, showing that in all complexes both functional groups of the heteroleptic ligands are coordinated to the tin atoms. By X-ray diffraction analysis, it could be shown that [{Me2Sn(L2-dtc)}x] (3) is polymeric in the solid state, while the complexes derived from L3 (5-7) have dinuclear 18-membered macrocyclic structures of the composition [{R2Sn(L3-dtc)}2]. For the remaining compounds, it could not be established with certainty whether the structures are macrocyclic or polymeric. A theoretical investigation at the B3LYP/SBKJC(d,p) level of theory indicated that the alpha-AA-dtc complexes might have trinuclear macrocyclic structures. The macrocyclic complexes 5-7 have a double-calix-shaped conformation with two cavities large enough for the inclusion of aliphatic and aromatic guest molecules. They are self-complementary for the formation of supramolecuar synthons that give rise to 1D molecular arrangements in the solid state. Preliminary recognition experiments with tetrabutylammonium acetate have shown that the [{R2Sn(L3-dtc)}2] macrocycles 6 and 7 might interact simultaneously with anions (AcO(-)), which coordinate to the tin atoms, and organic cations (TBA(+)), which accommodate within the hydrophobic cavity (ion-pair recognition).

Facile preparation of [4.4]metacyclophane- and [5.5]paracyclophane-type macrocycles from arylboronic acids and salicylideneaminoaryl alcohols

Four different salicylideneaminoaryl alcohols have been treated with arylboronic acids in order to prepare air-stable cyclophane-type macrocyclic systems. In two cases, this objective could be realized with the high-yield formation of [4.4]metacyclophane and [5.5]paracyclophane derivatives. The skeleton in these macrocycles is held together by two chiral boron atoms. In the other two cases, monomeric boronates or polymeric material were obtained. The title structures were characterized by spectroscopic techniques and X-ray crystallography. They show transannular C-H...O hydrogen bonding, but no intramolecular pi-pi interactions. A synthetic strategy for the preparation of further boron macrocycles is presented.

Planar tetracoordinate carbons in cyclic semisaturated hydrocarbons

A series of planar tetracoordinate carbon molecules in cyclic semisaturated hydrocarbons resulting from the combination of the C5(2-) skeleton with saturated hydrocarbon fragments is reported. The electronic stabilization and the bonding situation are studied through the analyses of molecular orbitals and the electron localization function. The magnetic properties are also revised, giving particular attention to the induced magnetic field. These systems are the first semisaturated cycles containing a planar tetracoordinate carbon stabilized only by electronic factors.

Conformational analysis of cyclic phosphates derived from 5-C′ substituted 1,2-O-isopropylidene-α-d-xylofuranose derivatives

Abstract Twelve 2-phenoxy-2-oxo-1,3,2-dioxaphosphorinanes fused with a 1,2-O-isopropylidene-α- d -xylofuranose moiety in cis orientation and substituted at the C′5 position were prepared in two steps from commercially available diacetone-α- d -glucose. Their conformations, and configurations were determined by 1H and 31P NMR and X-ray crystallographic techniques. Both, chair–twisted–chair and chair–boat equilibria were observed in solution. We observed that the strong anisotropic shielding effect of the benzene ring in the phenoxy group generates an upfield shift of the H1 hydrogen atom, when the cyclic phosphates adopt a boat conformation. This is due to a relative cis-orientation of the P-phenoxy group and the H1 proton of the 1,2-O-isopropylidene-α- d -xylofuranose moiety. Therefore, the configuration of the phosphorus center (SP or RP) can be determined by 1H NMR spectroscopy. Interestingly, the crystal structure of one of the cyclic phosphates exhibits two independent molecules in the asymmetric unit, one with a chair and the other one with a boat conformation.

Salen-supported dinuclear and trinuclear boron compounds

Abstract Six boron compounds have been synthesized through the combination of phenylboronic acid and various Salen ( N , N ′-ethylenebis(2-hydroxy)benzylidenimine) ligands. They contain seven- and eight-membered heterocycles with a bridging oxygen and have the formula: L[(PhB) 2 (μ-O)] (L=Acmen ( 1 ), Salen( t Bu) ( 2 ), Sal(2-OH)pen ( 3 ), Salpen( t Bu) ( 4 ), Acpen ( 5 )) and L[B 2 (μ-O)(O 2 BPh)] (L=Acen ( 6 ), Salmen ( 7 )). Compounds 6 and 7 are interesting trinuclear boron derivatives with two four-coordinate and one three-coordinate boron atoms. The compounds have been characterized by MP, MS, IR, EA and 1 H- and 11 B-NMR, by 11 B-MAS for 6 and 7 and by X-ray crystallography for 2 , 4 – 7 .

Fluorescent Molecular Rotors of Organoboron Compounds from Schiff Bases: Synthesis, Viscosity, Reversible Thermochromism, Cytotoxicity, and Bioimaging Cells

We report the design, synthesis, and characterization of two new fluorescent molecular rotors of boron derived from Schiff bases: (2,4,8,10-tetra-tert-butyl-6-phenyldibenzo[d,h][1,3,6,2]dioxazaboronine (3) and 1,4-bis(2,4,8,10-tetra-tert-butyldibenzo[d,h][1,3,6,2]dioxazaboronin-6-yl)benzene (4), as well as the free ligand 2-[[(3,5-di-tert-butyl-2-hydroxyphenyl)imino]methyl]-4,6-di-tert-butylphenol 1. All compounds were fully characterized by NMR (1H, 11B, and 13C), IR, UV/vis, fluorescence spectroscopy, and high-resolution mass spectrometry. The crystal structures of 3 and 4 showed tetracoordinated boron atoms with semiplanar skeleton ligands. The free rotation of the fluorescent molecular rotor, only observed in the binuclear compound, was decreased with increasing viscosity, while the quantum yield was increased. Interestingly, the property of reversible thermochromism was found in organoboron 4 in the solid state. DFT calculations to determine the both complexes have free rotation around the CPh-B1 bond. The boron compounds 3 and 4 have shown low cytotoxicity activity in cell line A-431 and low green staining in cells.

Pyrene bichromophores composed of polyaminopolycarboxylate interlink: pH response of excimer emission

Fluorescent response to pH has been studied on water-soluble pyrene-based bichromophores, (edtapy)H2 and (dtpapy)H3, in which two pyrenyl groups are linked by an ethylenediaminetetraacetate (EDTA) and a diethylenetriaminepentaacetate (DTPA) unit, respectively, through amide linkages. The excimer emission of the EDTA derivative is strengthened sharply with increasing pH at two steps; the first step is associated with the dissociation of acidic hydrogen from amino nitrogen in partially protonated species (edtapy)H− and the second step is attributable to the amide group. The excitation spectra have evidenced the formation of a static excimer in the ground state of completely deprotonated species (edtapy)2 − . The close contact between pyrenyl groups in (edtapy)2 − has been confirmed by density functional theory, which has also shown that the close contact is broken when amino nitrogen is protonated. The DTPA derivative exhibits a strong excimer emission, which shows an intensity–pH profile of an ‘off–on–off–on’ type. This rare pH response is ascribable to multiple protonation sites in the DTPA chain, as confirmed by 1H NMR. The novel pH-sensing capabilities in specific pH regions are due to the combination of the fluorescent group with the polyaminopolycarboxylate chains whose conformations are reversibly altered by protonation–deprotonation processes.

Penta- and heteropentadienyl ligands coordinated to beryllium

AbstractIn this work we have performed a systematic study of new organometallic complexes containing penta- and heteropentadienyl (CH2CHCHCHX, X = CH2, O, NH, S) ligands coordinated to beryllium. Calculated complexes were studied using the density functional theory (PBE) in combination with the 6-311++G(3d,2p) basis set. The coordination number on the beryllium atom varies according to the type of ligand. Pentadienyl ligand shows hapticities η1 and η5, while heteropentadienyl ligands display η1 and η2 hapticities. A Wiberg bond indices study was performed in order to get information about their bond orders. FigureOrganometallic structures with beryllium and heteropentadienyl ligands

Substituent Effects on 31P NMR Chemical Shifts and 1JP–Se of triarylselenophosphates

The effect of electron-withdrawing (EW) and electron-releasing (ER) substituents on the 31P NMR chemical shifts and the structural parameters of a series of tris-(p-X-aryl)selenophosphates is reported in this article. Similarly to O-aryl phosphates and O-aryl thiophosphates, EW groups attached to aromatic rings induce a shielding effect on the 31P NMR signal. After a detailed experimental and theoretical analysis, we confirmed that the selenium atom is the main part responsible for the charge density transfer toward phosphorus through a back-bonding effect. The obtained 1JP-Se values for the complete series agree with this observation. Supplemental materials are available for this article. Go to the publishers online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Synthesis, Characterization, X-Ray Structure, and Conformation DFT Calculation of a Carbohydrazide Derivative

The synthesis and characterization of a new Carbonic dihydrazide, bis[2-(hydroxyimino)-1-methylpropylidene] is described. The compound was characterized by NMR (1H, 13C), high-resolution mass spectrometry and X-ray diffraction. We observed the ligand with anti-trans conformation in solid state and symmetric (C2) conformer in solution. The relative energies of the conformers were calculated, using the density functional theory (DFT) to determine their relative stability. Both the single-crystal and calculated structures indicate that the asymmetric conformer is the most stable conformer in the absence of solvent.Graphical Abstract