Synthesis and physico-chemical properties of the first water soluble Cu(ii)@hemicryptophane complex

Abstract

A hemicryptophane ligand soluble in water at neutral pH was obtained thanks to the derivatization of the cyclotribenzylene unit with three carboxylate groups. The corresponding Cu(ii) complex was then synthesized and its spectroscopic and electrochemical properties in water were investigated, showing that water solubilisation retains the geometry of the complex around the metal center but strongly affects its redox properties, compared to previously reported Cu(ii)@hemicryptophane complexes soluble in organic solvents.

Emergence of Hemicryptophanes: From Synthesis to Applications for Recognition, Molecular Machines, and Supramolecular Catalysis

“…Two strategies that address this issue have been reported, where hydrosoluble groups allow solubilization of the host in strong basic aqueous solution 105 or in water at physiological pH. 106 The two strategies that either introduce phenol functions or incorporate carboxylate groups on the CTV units originate from the synthesis of water-soluble cryptophanes. 107−109 The tren-hemicryptophane 123 bearing three phenol functions on the CTV cap was synthesized from hemicryptophane 15a (Scheme 27).…”

“…To overcome this problem the hemicryptophane 125 was synthesized based on the above intermediate 122 (Scheme 28). 106 The first step involves reaction of 122 with tert-butyl-bromoacetate in DMF in the presence of Cs 2 CO 3 to yield the protected triester derivative 124. Deprotection of the amine and the ester functions with trifluoroacetic acid affords quantitatively the desired hemicryptophane 125 bearing three carboxylate groups and soluble in water at physiological pH (pH ≈ 7).…”

“…146 It is important to point out that Cu(II)@125 constitutes the first water-soluble Cu(II)@hemicryptophane complex. 106 Recently, Dutasta et al reported the preparation of Ga(III)@ 101 and Fe(III)@101 hemicryptophane complexes presenting an octahedral coordination site inside the molecular cavity of the host molecule. 71 The complexes were obtained by addition of Ga(acac) 3 or Fe(acac) 3 to a solution of 101 in 1,1,2,2tetrachloroethane and characterized by 1 H, 13 C, and 31 P NMR spectroscopies.…”

Cyanide Docking and Linkage Isomerism in Models for the Artificial [FeFe]-Hydrogenase Maturation Process

“…Both complexes display a pseudoaxial EPR signal ( [1 + ]­PF 6 : g 1 = 1.999, g 2 = 2.130, and g 3 = 2.195; [3 + ]­PF 6 : g 1 = 2.019, g 2 = 2.115, and g 3 = 2.190) with well-resolved hyperfine splitting, resulting in R values, ( g 2 – g 1 )/( g 3 – g 2 ), equal to 2.015 for [1 + ]­PF 6 and 1.28 for [3 + ]­PF 6 . These values, g 1 < 2.04 and R > 1, along with the values of the hyperfine splitting parameters, indicate the population of a d z 2 ground state, a characteristic of trigonal bipyramidal geometries. , Therefore, we assert that the solid state structure, as observed from XRD where the Cu­(II) has a trigonal bipyramidal geometry, is retained in solution for both complexes [ 1 + ]­PF 6 and [3 + ]­PF 6 .…”

“…Table S1 lists the g values and the hyperfine coupling constants, A, obtained by simulation of the EPR spectra. Both complexes display a pseudoaxial EPR signal ([1 + ]PF 6 : 32,33 Therefore, we assert that the solid state structure, as observed from XRD where the Cu(II) has a trigonal bipyramidal geometry, is retained in solution for both complexes [1 + ]PF 6 and [3 + ]PF 6 .…”