Interactions of Verkade's Superbase with Strong Lewis Acids: From Labile Mono- and Binuclear Lewis Acid-Base Complexes to Phosphenium Cations.

A series of mono- and binuclear Lewis acid-base complexes of the formulas N[CH2CH2N(Pri)]3P→LA [LA = BH3 (8), Ga(C6F5)3 (10), GaCl3 (11)], LA←N[CH2CH2N(Pri)]3P [LA = Al(C6F5)3 (6a), AlMe3 (6b), AlEt3 (6c), AlBui3 (6d), BF3 (13)], and LA←N[CH2CH2N(Pri)]3P→LA [Lewis acid (LA) = Al(C6F5)3 (7a), AlMe3 (7b), AlEt3 (7c), AlBui3 (7d), AlCl3 (7e), BH3 (9)] were generated from reactions of Verkade's base, N[CH2CH2N(Pri)]3P (1), with various boron-, aluminum-, and gallium-containing Lewis acids, and characterized by multinuclear NMR spectroscopy. {N[CH2CH2N(Pri)]3P→C7H7}[BF4] (5) was synthesized via the treatment of 1 with [C7H7][BF4]. The reaction of 1 with B(C6F5)3, followed by the addition of [Ph3C]2[B12Cl12], gave rise to the rearranged borate salt [PN4C9H17(Pri)2][B12Cl12] (3), while treating 1 with [Ph3C]2[B12Cl12] exclusively afforded {N[CH2CH2N(Pri)]3PH}2[B12Cl12] (4). Reactions of 1 with 2 equiv of GaCl3 and BF3, respectively, afforded the novel phosphenium gallate and borate salts 12a, 12b, and 15. The solid-state structures of 1, 3-5, 6b, 7a, 7b, 7e, 8, 10, 11, 12b, 13, and 15 were determined by X-ray crystallography.