Tetrakis(2-hydroxyphenyl)ethene and Derivatives. A Structurally Preorganized Tetradentate Ligand System for Polymetallic Coordination Chemistry and Catalysis

Abstract

A topologically unique, conformationally constrained tetradentate ligand system for polymetallic coordination chemistry has been developed: tetrakis(2-hydroxyphenyl)ethene (1a) and substituted derivatives. The design exploits the planarity of the tetraphenylethylene core to impart rigidity to the roughly square oxygen binding array, while maintaining a degree of conformational mobility associated with rotation about the aryl-ethylene carbon-carbon bonds. Tetrakis(2-hydroxyphenyl)ethene derivatives are designed to promote multiple metal bridging over chelating coordination modes. The ligand is synthesized from anisole or 4-tert-butylanisole in four steps via the 2,2'-dimethoxybenzophenone hydrazones 4a,b. The sterically hindered ortho-substituted tetraphenylethylene core is produced in high yield by acid-catalyzed decomposition of the corresponding diaryl diazomethane prepared in situ by oxidation of the hydrazone using nickel peroxide. Deprotection of the methyl ethers using boron tribromide gives tetrakis(2-hydroxyphenyl)ethene (1a), characterized by X-ray crystallography, and tetrakis(5-tert-butyl-2-hydroxyphenyl)ethene (1b). Sterically isolating substituents in the 3-position can be installed via Claisen rearrangement/hydrogenation, providing tetrakis(3-n-propyl-2-hydroxyphenyl)ethene (6) efficiently. To illustrate potential applications of this unprecedented ligand class, two coordination complexes are reported, including tetrakis(2-diethylaluminoxyphenyl)ethene (8), a structurally robust eight-membered-ring aluminum/oxygen crown complex characterized both in solution and in the solid state.

Crystal structure of 2,2'-[1,2-diethanediyl-bis(thio)]bis(1,3,4-thiadiazole) copper(II) diperchlorate, [Cu(C6H6N4S4)4][ClO4]2

“…In constructing metal-organic frameworks, flexible ligands are usually selected because the flexibility and conformation restrainability offers the new possibilities for the arrangement of diverse frameworks [1][2][3]. Meanwhile, thiadiazoles have attracted increasing attention because of their potential applications in pharmaceutical, agricultural, industrial, coordination and polymer chemistry [4][5][6].…”

Crystal structure of catena-bis[2,2'-(1,3-propanedithio)- bis(1,3,4-thiadiazole)]bis(2,4,6-trinitrophenolate)copper(II), Cu(C7H8N4S4)2(C6H2N3O7)2

“…In recent years, the rational design of coordination polymers based on multitopic or flexible bridging ligands as linkers and metal centers as connectors represents one of the most rapidly developing fields owingtotheir potentialasfunctional materials in,e.g., electronic,magnetic, optical, catalytic applications [1][2][3]. In particular,t he uses of flexible ligands in such studies have attractedremarkableattention becausethe flexibilityand conformation restrainability of such ligands offer the possibility for the construction of diverse frameworks.…”

Crystal structure of tris{2,2′-[1,2-[methylenebis(thio)]-bis[1,3,4-thiadiazole]]}copper(II) tetranitrate — acetonitrile (1:1), Cu2(C5H4N4S4)3(NO3)4 · CH3CN

“…In recent years, the rational design of coordination polymers based on multi-topic or flexible bridging ligands as linkers and metal centers as connectors represents one of the most rapidly developing fields owing to their potential as functional materials in electronic, magnetic, optical, catalytic applications [1][2][3]. In particular, the use of flexible ligands in such studies have attracted remarkable attention because the flexibility and conformation restrainability of such ligands offer the possibility for the construction of diverse frameworks.…”