An Azophosphine Synthetic Equivalent of Mesitylphosphaazide and Its 1,3-Dipolar Cycloaddition Reactions

Abstract

Dibenzo-7-phosphanorbornadiene-substituted diazene MesN₂P<b>A</b> (<b>1</b>, where Mes = mesityl, <b>A</b> = anthracene, or C₁₄H₁₀), a synthetic equivalent of mesitylphosphaazide (MesN₂P) and anthracene, was synthesized by treatment of [Ph₃BP<b>A</b>][Na(OEt₂)₂] with [MesN₂]OTf (OTf = CF₃SO₃^-) in thawing tetrahydrofuran (14% isolated yield). Treatment of <b>1</b> with unsaturated molecules cyclooctyne, [Na(dioxane)_2.5][OCP] (phosphaethynolate), and Ad-C≡P (Ad = adamantyl) results in the corresponding [3 + 2] phosphaazide-(phospha)alkyne cycloadducts, with concomitant loss of anthracene in 65%, 49%, and 38% isolated yield, respectively. Structural data for the phosphaethynolate cycloadduct ([<b>3</b>][Na(12-crown-4)₂]) were obtained in a single-crystal X-ray diffraction study. A diazatriphosphole was generated by combining <b>1</b> with P₂<b>A</b>₂, a thermally activated anthracene-based molecular precursor to diphosphorus (P₂). Thermolysis (33-65 °C) of <b>1</b> in benzene-<i>d</i>₆ leads to anthracene extrusion. This process has a unimolecular kinetic profile and proceeds with activation parameters of Δ<i>H</i>^⧧ = 21.6 ± 0.3 kcal/mol and Δ<i>S</i>^⧧= -4.9 ± 0.8 cal/(mol K).