Highly fluorinated hydrotris(indazolyl)borate calcium complexes: the structure and reactivity heavily depend on the ligand's electronic properties
Résumé
Two series of highly fluorinated 3-substituted hydrotris(indazolyl)borate (Fn-Tp4Bo,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-Tp4Bo,3Ph) in THF to form the homo- and heteroleptic complexes [Ca(F12-Tp(4Bo,3Ph)*)2] (1) and [(F12-Tp4Bo,3Ph)CaI(THF)] (2), respectively. 1 has C2h symmetry due to a 1,2-borotropic shift. The reaction of CaI2 with 2 equiv. of the more electron poor Tl(F21-Tp4Bo,3CF3) in THF, on the other hand, leads to the salt [Ca(THF)6][F21-Tp4Bo,3CF3]2 (3), with [F21-Tp4Bo,3CF3] acting as a counter-ion. This emphasizes the tuning ability of Fn-Tp4Bo,3R ligands and the consequences on their ability to bind hard electrophilic Ca2+ centers.