Synthesis and Structure of the Bis- and Tris-Polyhedral Hybrid Carboranoclathrochelates with Functionalizing Biorelevant Substituents—The Derivatives of Propargylamine Iron(II) Clathrochelates with Terminal Triple C≡C Bond(s)

Abstract

A synthetic strategy for obtaining structurally flexible hybrid iron(II) carboranoclatrochelates functionalized with biorelevant groups, based on a combination of a 1,3-dipolar cycloaddition reaction with nucleophilic substitution of an appropriate chloroclathrochelate precursor, was developed. In its first stage, a stepwise substitution of the dichloroclathrochelate precursor with amine N-nucleophiles of different natures in various solvents was performed. One of its two chlorine atoms with morpholine or diethylamine in dichloromethane gave reactive monohalogenoclathrochelate complexes functionalized with abiorelevant substituents. Further nucleophilic substitution of their remaining chlorine atoms with propargylamine in DMF led to morpholine- and diethylamine-functionalized monopropargylamine cage complexes, the molecules of which contain the single terminal C≡C bond. Their “click” 1,3-cycloaddition reactions in toluene with ortho-carborane-(1)-methylazide catalyzed by copper(II) acetate gave spacer-containing di- and tritopic iron(II) carboranoclatrochelates formed by a covalent linking between their different polyhedral(cage) fragments. The obtained complexes were characterized using elemental analysis, MALDI-TOF mass, UV-Vis, 1H, 1H{11B}, 11B, 11B{1H}, 19F{1H} and 13C{1H}-NMR spectra, and by a single crystal synchrotron X-ray diffraction experiment for the diethylamine-functionalized iron(II) carboranoclathrochelate. Its encapsulated iron(II) ion is situated almost in the center of the FeN6-coordination polyhedron possessing a geometry intermediate between a trigonal prism and a trigonal antiprism with a distortion angle φ of approximately 28º. Conformation of this hybrid molecule is strongly affected by its intramolecular dihydrogen bonding: a flexibility of the carborane-terminated ribbed substituent allowed the formation of numerous C–H…H–B intramolecular interactions. The H(C) atom of this carborane core also forms the intermolecular C–H…F–B interaction with an adjacent carboranoclathrochelate molecule. The N–H…N intermolecular interaction between the diethylamine group of one hybrid molecule and the heterocyclic five-membered 1Н-[1,2,3]-triazolyl fragment of the second molecule of this type caused formation of H-bonded carboranoclathrochelate dimers in the X-rayed crystal.

Multistep synthesis and X-ray structures of carboxyl-terminated hybrid iron(ii) phthalocyaninatoclathrochelates and their postsynthetic transformation into polytopic carboranyl-containing derivatives

“…19 It gave their (pseudo)cage derivatives with a terminal CC bond. Then we used the well-known 18 easy and convenient approach { i.e. 1,3-dipolar [2 + 3] cycloaddition of an appropriate carborane-based azide to the latter alkyne-terminated (semi)clathrochelate precursors} for obtaining the ditopic carboranosemiclathrochelate and the tritopic carboranyl-terminated phthalocyaninatoclathrochelate complexes, respectively.…”

“…We have recently prepared and structurally characterized 18 spacer-containing carboranoclathrochelates (including those with a functionalizing biorelevant substituent 18 b ), trying to optimize the hydrophilic–hydrophobic balance in these ditopic molecules. Indeed, the latter combines the metal-centered macrobicyclic tris-dioximate framework (as a more polar core) with the carboranyl-terminated substituent (as a more hydrophobic core) in its chelating α-dioximate fragment.…”

“…, clathrochelate, phthalocyaninate and carborane) fragments. The 1,3-dipolar cycloaddition (so-called “click”) reactions 19 were found 18 to be the most prospective pathway for their preparation. Indeed, this copper-catalyzed process easily proceeded under mild reaction conditions, giving the corresponding bis-polyhedral products in moderate or even high yields.…”