C-carboranylation of a quasi-aromatic iron(II) cage complex and its organic aromatic analog by the metal-catalyzed (promoted) cross-coupling reactions

Abstract

One-pot reaction a quasi-aromatic diiodoclathrochelate precursor with the carboranylating agent, generated in situ from equimolar amounts of lithium 1-ortho-carboranyl and trimethoxyborate, in the presence of a palladium catalyst afforded a ribbed-functionalized iron(II) mono-ortho-carboranoclathrochelate. Such a formation of С(carborane)C(clathrochelate) bond is accompanied by hydrodeiodination in a vicinal position and a monomethinemonocarborane macrobicyclic complex was isolated and characterized by the single crystal X-ray diffraction. The geometry of its FeN6-coordination polyhedron is intermediate between a trigonal prism and a trigonal antiprism with the distortion angle φ of 24.9° and the height h of this polyhedron is equal to 2.32Å; FeN distances vary from 1.889(2) to 1.921(2) Å and the average bite angle α is approximately 39.1°. The model reaction of this carboranylating agent with 4-iodobiphenyl, giving the corresponding aryl carborane, proceeds only in vigorous reaction conditions with a palladium catalyst and copper(I) iodide as a promotor. The compounds obtained were characterized using elemental analysis, ESI and EI mass spectrometry, IR, Raman, UV–vis, 1H, 11B, 19F and 13C{1H} NMR spectroscopy. Thus, palladium-catalyzed Suzuki–Miyaura (copper-promoted in the case of an aryl iodide) cross-coupling reactions of a generated in situ derivative of carboranylboronic ester have been successfully used, for the first time, for one-pot synthesis of a quasi-aromatic hybrid carboranoclathrochelate with an inherent polyhedral ribbed substituent and its aromatic analog 4-(1-ortho-carboranyl)biphenyl. The developed strategy has been then found useful in the organic chemistry as a versatile approach towards carborane-based organic compounds.