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 (Fn-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 C2h 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 Fn-Tp(4Bo,3R) ligands and the consequences on their ability to bind hard electrophilic Ca(2+) centers.

s‐Block Metal Complexes with Bis‐ and Tris(pyrazolyl)methane and ‐methanide Ligands

“…The tris(pyrazolyl)boranates quickly conquered coordination chemistry due to the ease of synthesis and the stability of their metal complexes. Nevertheless, borotropic shifts have been observed and undesired side products have correspondingly been obtained . Recently, high‐yield protocols have been developed for the isoelectronic tris(pyrazolyl)methanes.…”

“…For the s‐block metals many derivatives have also been described, and these ligands are considered stable anions in the vicinity of metal ions. Nevertheless, borotropic shifts have recently been observed for a calcium complex, with unexpected products being obtained . Substantial use of bis(pyrazolyl)‐ and tris(pyrazolyl)methane, as well as ‐methanide ligands, is only the case for transition‐metal chemistry.…”

Highly Fluorinated Tris(indazolyl)borate Silylamido Complexes of the Heavier Alkaline Earth Metals: Synthesis, Characterization, and Efficient Catalytic Intramolecular Hydroamination

“…2 Ca], even though the latter exhibits one inverted indazolyl ring. [31] Despite this distortion and the low coordination number, complex 1 does not show any agostic-type interaction involving the hexamethyldisilylamido group.…”

“…[30] Two differently substituted ligands, {F n -Tp 4Bo, 3R } À (R = CF 3 , n = 21, and R = Ph, n = 12), have been tested on Ca, the phenyl-based ligand providing the best compromise in terms of steric protection and electron-withdrawing properties (Scheme 2). [31] Earlier reports have shown that sterically encumbered, differently substituted tris(pyrazolyl)borates (Tp') coordinate Ca 2 + with the formation of heteroleptic Tp'CaX complexes. [32] A [33] These amido complexes were shown to catalyze the ring-opening polymerization of lactide, [33] but to our knowledge they have not been tested for hydroamination reactions.…”

Cyclopropylmagnesium Scorpionates: A Missing Member of the Series with Both Staggered and Eclipsed Rotamers in the Crystal

“…For our part, we have been interested in varying the electron‐withdrawing properties of the Tp′ ligand and investigating the consequences in calcium chemistry , . We used magnesium derivatives for benchmarking in the case of hydrocarbyl derivatives .…”