Competition between Hydrogen Bonding and Proton Transfer during Specific Anion Recognition by Dihomooxacalix[4]arene Bidentate Ureas

Intermolecular hydrogen bonding of alcohols with dinitrobenzene radical anion and dianion: A combined electrochemical and DFT study

Hydrogen bonding is one of the most important inter-molecular interactions in the field of biochemistry and medicinal chemistry. Such non-covalent interactions play a vital role in self-assembly phenomena, chemical structures, material properties and enzymatic catalysis. Herein, we present hydrogen bonding phenomenon in alcohols-dinitrobenzene (DNB) radical anion/dianion systems using electrochemical and computational approaches. First, 1,3-DNB radical anion and dianion were generated through electrochemical method and then hydrogen bonding interactions with aliphatic alcohols in DMSO are studied through cyclic voltammetry (CV). CV results show that the cathodic peak potential of 1,3-Dinitrobenzene in Dimethyl sulfoxide is shifted catholically upon addition of alcohols which represent hydrogen bonding phenomenon. Theoretical investigations are performed to gain deep insight on hydrogen bonding interaction strength in DNB-alcohol systems. H-bonding interaction of all isomers of DNB (1,2-, 1,3-, 1,4-), its corresponding radical anion, and dianion with aliphatic alcohols is studied using density functional calculations. The strength of H-bonding is evaluated both qualitatively and quantitatively using interaction energies, vibrational and electronic spectroscopic analysis. Understanding of these interactions will be helpful in gaining insight into biological systems where these interactions play significant role.

Exploring the Role of H-Bonding in Organic Electrochemistry - From Supramolecular Applications to Mechanistic Investigations

H-bonds can exert a substantial impact on the course of organic electrode reactions due to their ability to stabilize charged intermediates and products formed during these reactions, as well as facilitate proton-coupled electron transfer (PCET) reactions. This has fundamental implications for the mechanism of organic electrode reactions, but also practical impact in supramolecular chemistry and potentially synthetic electrochemistry. My group's main focus has been on the supramolecular applications, using electron transfer to alter the strength of H-bonds to create highly redox-responsive H-bond dimers. Initially we sought to avoid proton transfer because we feared that would lead to irreversible electrochemistry. However, inevitably proton transfer did show up, but, to our surprise, did not lead to irreversible electrochemistry. To explain this, we developed a new mechanism, the "wedge scheme", that shows how H-bonding can facilitate reversible electron and proton transfer. This insight recently led us to a new PCET-based design strategy for the creation of our most highly redox-responsive H-bond dimers yet.

Supramolecular D⋯A-layered structures based on germanium complexes with 2,3-dihydroxynaphthalene and N,N'-bidentate ligands

The concept of using redox-active ligands, which has become extremely widespread in organometallic chemistry, is often considered from 'their effect on the metal center properties' point of view and 'how to modify the ligands'. In this paper, we present the reverse side of this effective approach - a dramatic change of redox properties of ligands under the influence of a redox-inert metal. Germanium derivatives based on 2,3-dihydroxynaphthalene (1) and N,N'-bidentate ligands, namely 2,2'-bipyridine (2) and 1,10-phenanthroline (3), were obtained and characterized by CV, UV-vis spectroscopy, DFT calculations and in the case of 3 X-ray diffraction. It was shown that the HOMO of the complexes is almost completely located on the naphthalene fragment while the LUMO is on the N,N-ligands. At the same time, there are no boundary molecular orbitals on the germanium atom, but it forms the axial part of the molecule holding two opposite motifs together. Moreover, it sharply affects the level of HOMO and LUMO. Derivatives 2 and 3 are more easily oxidized compared to 2,3-dihydroxynaphthalene by 0.31-0.34 V (7-8 kcal mol-1) and are more easily reduced compared to N,N-donors by 1.08-1.15 V (25-26.5 kcal mol-1). All this together makes it possible to form a system with a narrow HOMO/LUMO gap (∼2 eV). The crystal structure of 3 consists of alternating monomolecular easily oxidizing and easily reducing layers formed due to intermolecular interactions, in particular π-stacking. In addition, in contrast to 1 that starts to decompose noticeably at the temperatures from 200 °C, 2 and 3 have an extremely high thermal stability. They remain stable with no signs of decomposition and melting up to 400 °С. We believe that this approach to the formation of the supramolecular structure may present prospects for obtaining new functional materials.

Gold-catalyzed domino cyclization enabling construction of diverse fused azaspiro tetracyclic scaffolds: a cascade catalysis mechanism due to a substrate and counterion

The detailed mechanism and origins of gold-catalyzed domino cyclization to diverse fused azaspiro tetracyclic scaffolds by cooperative dual catalysis and cascade catalysis are systematically studied.

Multi-point interaction-based recognition of fluoride ions by tert-butyldihomooxacalix[4]arenes bearing phenolic hydroxyls and thiourea

A series of p-tert-butyldihomooxacalix[4]arenes bearing phenolic hydroxyls and thiourea moieties were prepared to investigate their anion binding behavior.