Towards Weakly Coordinating Anions with the Extremely Electron Withdrawing Perfluoropyridinoxy Ligand -OC5F4N

The extreme electron withdrawing properties of the perfluoropyridinoxy ligand -OC5F4N were used for the preparation of new (weakly) coordinating borate and aluminate anions of the type [E(OC5F4N)(4)](-) (E = B or Al). These new anions are based on the potent parent Lewis acids E(OC5F4N)(3), which possess exceptionally high calculated fluoride ion affinities (FIAs) of 500 and 587 kJ mol(-1) for E = B and Al respectively. For aluminum, this extreme Lewis acidity dominates the chemistry and from mixtures of the neutral polymeric Lewis acid [Al(OC5F4N)(3)](n), the five- and six-coordinate complexes Al(OC5F4N)(3)(OEt2)(2) (1) and [Al(OC5F4N)(2)(mu-OC5F4N) (NCMe)(2)](2) (2) were crystallized upon addition of ether or MeCN. The aluminate salts M[Al(OC5F4N)(4)] (M = Li or K) were prepared from the reaction between the alcohol 4-HO-C5F4N and either LiAlH4 or K[AlEt4] respectively. The aluminate anion [Al(OC5F4N)(4)](-) remains Lewis acidic coordinating small donor molecules forming [Al(OC5F4N)(4)(L)](-) (L = THF or NMe3) and even supports formation and structural characterisation of the aluminum dianion containing salt [Na(OEt2)(2)][Na][Al(OC5F4N)(5)] (8). The from NaBH4 and 4-HO-C5F4N accessible borate salt Na[B(OC5F4N)(4)] shows increased kinetic stability in comparison to the aluminum analogue.