Highly fluorinated hydrotris(indazolyl)borate calcium complexes: the structure and reactivity heavily depend on the ligand's electronic properties

Abstract

Two series of highly fluorinated 3-substituted hydrotris(indazolyl)borate (F_n-Tp^4Bo,3R; R = Ph, n = 12; R = CF₃, n = 21) complexes of calcium were synthesized by salt metathesis reactions. CaI₂ reacts with 2 and 1 equiv. of Tl(F₁₂-Tp^4Bo,3Ph) in THF to form the homo- and heteroleptic complexes [Ca(F₁₂-Tp^(4Bo,3Ph)*)₂] (1) and [(F₁₂-Tp^4Bo,3Ph)CaI(THF)] (2), respectively. 1 has C_2h symmetry due to a 1,2-borotropic shift. The reaction of CaI₂ with 2 equiv. of the more electron poor Tl(F₂₁-Tp^4Bo,3CF₃) in THF, on the other hand, leads to the salt [Ca(THF)₆][F₂₁-Tp^4Bo,3CF₃]₂ (3), with [F₂₁-Tp^4Bo,3CF₃] acting as a counter-ion. This emphasizes the tuning ability of F_n-Tp^4Bo,3R ligands and the consequences on their ability to bind hard electrophilic Ca²⁺ centers.