Manuel N. Chaur

Configurational and constitutional information storage: multiple dynamics in systems based on pyridyl and acyl hydrazones.

The C=N group of hydrazones can undergo E/Z isomerization both photochemically and thermally, allowing the generation of a closed process that can be tuned by either of these two physical stimuli. On the other hand, hydrazine-exchange reactions enable a constitutional change in a given hydrazone. The two classes of processes: 1) configurational (physically stimulated) and 2) constitutional (chemically stimulated) give access to short-term and long-term information storage, respectively. Such transformations are reported herein for two hydrazones (bis-pyridyl hydrazone and 2-pyridinecarboxaldehyde phenylhydrazone) that undergo a closed, chemically or physically driven process, and, in addition, can be locked or unlocked at will by metal-ion coordination or removal. These features also extend to acyl hydrazones derived from 2-pyridinecarboxaldehyde. Similarly to the terpydine-like hydrazones, such acyl hydrazones can undergo both constitutional and configurational changes, as well as metal-ion coordination. All these types of hydrazones represent dynamic systems capable of acting as multiple state molecular devices, in which the presence of coordination sites furthermore allows the metal ion-controlled locking and unlocking of the interconversion of the different states.

Preparation and characterization of soluble carbon nano-onions by covalent functionalization, employing a Na–K alloy

Herein we report the preparation of truly soluble CNOs by covalent functionalization with hexadecyl chains. These compounds are prepared in two steps: first, reduction of CNOs with a Na-K alloy in 1,2-DME under vacuum, followed by nucleophilic substitution employing 1-bromohexadecane.

Multiple Dynamics of Hydrazone Based Compounds

Hydrazone derivatives of 2-quinolinecarboxaldehyde and 6-bromo-2-pyridinecarboxaldehyde were synthesized by sequence reactions with hydrazine derivatives. These compounds exhibited E/Z isomerization upon irradiation using a mercury lamp (250 W). The configurational changes were monitored by 1 H nuclear magnetic resonance (NMR), UV-Vis and fluorescence spectroscopy. Data of concentration of the E/Z isomers versus time showed first order kinetics with constants ranging from 0.024 to 0.0799 min−1. The Z isomers were isolated by chromatographic methods and characterized by 1 H NMR, UV-Vis and fluorescence spectroscopy and X-ray diffraction. The Z compounds are stable even in solution for several months. Such stability is due to a thermodynamic stabilization by the formation of an intramolecular hydrogen bond in the Z structure, which is not seen in the E configuration. Furthermore, some of the compounds were used as ligands for various metal centers (Zn2+, Co2+ and Hg2+) and their electronic properties were studied including measurements of cyclic voltammetry. The compounds studied herein allow their use as dynamic systems in dynamic combinatorial chemistry as their properties can be modulated by light, heat and the presence of metal centers. Besides, obtaining a metastable state (Z-isomer) allows the use of these compounds as photo-brakes, and therefore they can be implemented as molecular machines.

Synthesis and Derivatization of Expanded [n]Radialenes (n=3, 4)

Versatile, iterative synthetic protocols to form expanded [n]radialenes have been developed (n=3 and 4), which allow for a variety of groups to be placed around the periphery of the macrocyclic framework. The successful use of the Sonogashira cross-coupling reaction to complete the final ring closure demonstrates the ability of this reaction to tolerate significant ring strain while producing moderate to excellent product yields. The resulting radialenes show good stability under normal laboratory conditions in spite of their strained, cyclic structures. The physical and electronic characteristics of the macrocycles have been documented by UV-visible spectroscopy, electrochemical methods, and X-ray crystallography (four derivatives), and these studies provide insight into the properties of these compounds as a function of pendent substitution in terms of conjugation and donor/acceptor functionalization.

6-Bromo-pyridine-2-carbaldehyde phenyl-hydrazone.

The title compound, C12H10BrN3, is essentially planar (r.m.s. deviation of all non-H atoms = 0.0174 Å), with a dihedral angle of 0.5 (2)° between the two aromatic rings. In the crystal, molecules are linked by weak N—H⋯N interactions, forming a zigzag chain running parallel to [001].

Dichlorido{(E)-4-dimethyl-amino-N'-[(pyri-din-2-yl)methyl-idene-κN]benzo-hydrazide-κO}zinc.

In the mononuclear title complex, [ZnCl2(C15H16N4O)], the ZnII cation is five-coordinated in a strongly distorted square-pyramidal environment by two Cl− anions and a neutral tridentate Schiff base ligand. The ZnII cation is chelated by the carbonyl O atom, the imine N atom and the pyridine N atom, which causes a slight loss of planarity for the ligand; the dihedral angle between the aromatic rings is 4.61 (8)°.

Kinetic Selectivity and Thermodynamic Features of Competitive Imine Formation in Dynamic Covalent Chemistry

The kinetic and thermodynamic selectivities of imine formation have been investigated for several dynamic covalent libraries of aldehydes and amines. Two systems were examined, involving the reaction of different types of primary amino groups (aliphatic amines, alkoxy-amines, hydrazides and hydrazines) with two types of aldehydes, sulfobenzaldehyde and pyridoxal phosphate in aqueous solution at different pD (5.0, 8.5, 11.4) on one hand, 2-pyridinecarboxaldehyde and salicylaldehyde in organic solvents on the other hand. The reactions were performed separately for given amine/aldehyde pairs as well as in competitive conditions between an aldehyde and a mixture of amines. In the latter case, the time evolution of the dynamic covalent libraries generated was followed, taking into consideration the operation of both kinetic and thermodynamic selectivities. The results showed that, in aqueous solution, the imine of the aliphatic amine was not stable, but oxime and hydrazone formed well in a pH dependent way. On the other hand, in organic solvents, the kinetic product was the imine derived from an aliphatic amine and the thermodynamic products were oxime and hydrazone. The insights gained from these experiments provide a basis for the implementation of imine formation in selective derivatization of mono-amines in mixtures as well as of polyfunctional compounds presenting different types of amino groups. They may in principle be extended to other dynamic covalent chemistry systems.

Synthesis and characterization of (6-{[2-(pyridin-2-yl)hydrazinylidene]methyl}pyridin-2-yl)methanol: a supramolecular and topological study.

Hydrazones exhibit a versatile chemistry and are of interest for their potential use as functional molecular systems capable of undergoing reversible changes of configuration, i.e. E/Z isomerization. The title compound, C12H12N4O, has an E configuration with respect to the hydrazone C=N bond. The crystal packing is formed by N-H...N and O-H...N hydrogen bonds that give a two-dimensional layer structure and C-H...C interactions associated with layer stacking to produce the three-dimensional supramolecular structure. These intermolecular interactions were analyzed and quantified by the Hirshfeld surface method and the two-dimensional supramolecular arrangement was topologically simplified as a hcb network.

(E)-5-[1-Hy­droxy-3-(3,4,5-tri­meth­oxy­phen­yl)allyl­idene]-1,3-di­methyl­pyrimidine-2,4,6-trione: crystal structure and Hirshfeld surface analysis

In the title compound, C—H⋯O hydrogen bonds and aromatic π–π stacking combine to generate a three-dimensional network. A Hirshfeld surface analysis is presented.

[4-(Allyloxy)phenyl](phenyl)methanone

The structure of the title compound, C16H14O2, features a dihedral angle of 54.4 (3)° between the aromatic rings. The allyl group is rotated by 37.4 (4)° relative to the adjacent benzene ring. The crystal packing is characterized by numerous C—H⋯O and C—H⋯π interactions. Most of these interactions occur in layers along (011). The layers are linked by C—H⋯π interactions along [100], forming a three-dimensional network.