Non-coordinating Anion

Tetrakis(pentafluorophenyl)borate[(C₆F₅)₄B^-] is a weak nucleophilic and an inert non-coordinative anion. Therefore it is employed as a counter anion to unstable cation chemical species, thereby generating the "free" cation that may be used for studies related to reactivity and structure^1,2).

Minoura, et al. have succeeded in synthesizing the first nonclassical onium compound, pentaphenyltelluronium 2, using the agent 1²⁾. X-ray crystallographic analysis provided evidence for the compound 2 to be free hypervalent tellurium cation without any interaction with the counter anion, (C₆F₅)₄B^-, in the crystalline state.

Furthermore, in catalyzed olefin polymerization, a number of catalysts have been reported where the catalytic activity is due to the "free" cation when the anion used was (C₆F₅)₄B^- in place of Ph₄B^{- 3)}.