Nucleophilic Addition of Stabilized Phosphorus Ylides to Closo-Decaborate Nitrilium Salts: A Synthetic Route to Boron Cluster-Functionalized Iminoacyl Phosphoranes and Their Application in Potentiometric Sensing

This work explores a novel and efficient synthetic approach to a new class of boron cluster derivatives via the nucleophilic addition of stabilized phosphorus ylides, Ph₃P=CHR² (R² = COOEt, CN), to a series of nitrilium salts of the <i>closo</i>-decaborate anion, [2-B₁₀H₉NCR¹]^- (R¹ = Me, Et, <i>ⁿ</i>Pr, <i>ⁱ</i>Pr, Ph). The reaction proceeds regio- and stereospecifically, affording a diverse range of iminoacyl phosphorane derivatives, [2-B₁₀H₉NH=C(R¹)C(PPh₃)R²]^-, in high isolated yields (up to 95%). The obtained compounds (10 examples) were isolated as tetrabutylammonium or tetraphenylphosphonium salts and thoroughly characterized by multinuclear NMR (¹¹B, ¹H, ¹³C, ³¹P), high-resolution mass spectrometry, and single-crystal X-ray diffraction. The reaction feasibility was found to be strongly influenced by the steric hindrance of the R¹ group. Furthermore, the practical utility of these novel hybrids was demonstrated by employing the [2-B₁₀H₉NH=C(CH₃)C(COOC₂H₅)=PPh₃]^- anion as a highly effective membrane-active component in ion-selective electrodes. The developed tetraphenylphosphonium (TPP⁺) sensor exhibited a near-Nernstian response, a low detection limit of 3 × 10^-8 M, and excellent selectivity over a range of common inorganic and organic cations, showcasing the potential of <i>closo</i>-borate-based ionophores in analytical chemistry.