Metal-catalyzed cross-coupling reactions of iron(II) cage complexes: New furyl-containing macrobicyclic scaffold, a reactive halogenoclathrochelate precursor and its ribbed-functionalized derivatives

Abstract

Condensation of α-furyldioxime with the macrocyclic iron(II) bis-α-benzyldioximate gave the 2-furyl-containing iron(II) clathrochelate with non-equivalent aromatic chelate fragments. The selective bromination of its furyl ribbed substituents with N-bromosuccinimide afforded the dibromoclathrochelate precursor, Suzuki–Miyaura and Sonogashira reactions of which with 4-carboxyphenylboronic acid and trimethylsilylacetylene in the presence of a generated in situ palladium-containing catalyst gave the target ribbed-functionalized cage complexes with inherent aromatic substituents; aromatic nucleophilic substitution of this precursor with a derivative of piperazine led to the corresponding monofunctionalized iron(II) monobromoclathrochelate. The diamagnetic low-spin iron(II) complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–vis, 1H, 11B, 13C and 19F{1H} NMR spectroscopies, and by X-ray diffraction. The FeN6-coordination polyhedra of X-rayed molecules of clathrochelate scaffold, dibromomacrobicyclic precursor and monofunctionalized iron(II) monobromoclathrochelate possess a similar distorted trigonal prismatic–trigonal antiprismatic geometry with the distortion angles φ of approximately 26°; their heights h and the bite angles α are approximately 2.31Å and 39.0°. So, metal-catalyzed cross-coupling reactions of a dibromine derivative of the new furyl-containing tris-dioximate iron(II) clathrochelate have been successfully used, for the first time, for the synthesis of ribbed-functionalized cage complexes with inherent functionalized aromatic substituent(s). This expands our ability to create clathrochelate complexes of different structures, symmetries and functionalities that meet criteria for practical use as transcription inhibitors, DNA intercalators as well as versatile entities for molecular (photo)electronic devices; the monofunctionalized iron(II) cage complex seems to be a suitable bromoclathrochelate precursor for further functionalization via metal-catalyzed reactions.