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[CH2 CH2 N(Pri )]3 P→LA [LA = BH3 (8), Ga(C6 F5 )3 (10), GaCl3 (11)], LA←N[CH2 CH2 N(Pri )]3 P [LA = Al(C6 F5 )3 (6a), AlMe3 (6b), AlEt3 (6c), AlBui 3 (6d), BF3 (13)], and LA←N[CH2 CH2 N(Pri )]3 P→LA [Lewis acid (LA) = Al(C6 F5 )3 (7a), AlMe3 (7b), AlEt3 (7c), AlBui 3 (7d), AlCl3 (7e), BH3 (9)] were generated from reactions of Verkade's base, N[CH2 CH2 N(Pri )]3 P (1), with various boron-, aluminum-, and gallium-containing Lewis acids, and characterized by multinuclear NMR spectroscopy. {N[CH2 CH2 N(Pri )]3 P→C7 H7 }[BF4 ] (5) was synthesized via the treatment of 1 with [C7 H7 ][BF4 ]. The reaction of 1 with B(C6 F5 )3 , followed by the addition of [Ph3 C]2 [B12 Cl12 ], gave rise to the rearranged borate salt [PN4 C9 H17 (Pri )2 ][B12 Cl12 ] (3), while treating 1 with [Ph3 C]2 [B12 Cl12 ] exclusively afforded {N[CH2 CH2 N(Pri )]3 PH}2 [B12 Cl12 ] (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.