Perfluorinated 1H-indazoles and hydrotris(indazol-1-yl)borates. Supramolecular organization and a new synthetic procedure to form scorpionate ligands

Abstract

This paper describes the syntheses and full characterization of perfluorinated 1H-indazoles 2–5 and hydrotris(indazolyl)borate thallium complexes 6–9 that contain linear perfluoroalkyl chains varying from two to six carbon atoms in the 3-position. In the solid state, the perfluorinated 1H-indazoles exhibit supramolecular structures that depend on the length of the perfluoroalkyl chain. A catemer of order 3 is observed for the CF₂CF₃ derivative 2 (chiral space group P3₂), catemers of order 2 are observed for the C₃F₇ and C₄F₉ derivatives 3 (chiral space group P2₁2₁2₁, one type of helix in the unit cell) and 4 (space group P2₁/n, two types of helices in the unit cell), respectively, and stacks of dimers are observed for the indazole with the longer C₆F₁₃ chain 5 (space group P2₁/c). The perfluorinated hydrotris(indazolyl)borate thallium complexes 6–9 [TlFn–Tp^4Bo,3Rf] have been obtained by a new reaction based on the reaction of HBBr₂ (generated in situ from BBr₃ and Et₃SiH) with the indazolates of 2–5 followed by cation exchange. The X-ray crystal structure of [TlF₃₃–Tp^{4Bo,3C₃F₇}] 7 shows that, in addition to coordination to the three nitrogens, the thallium is buried in a nest of fluorines with seven short intramolecular Tl⋯F contacts with the pendant perfluoropropyl chains. The potential of these highly fluorinated molecules to act as ligands is highlighted.