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