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 closo-decaborate anion, [2-B10H9NCR1]− (R1 = Me, Et, nPr, iPr, 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 closo-borate-based ionophores in analytical chemistry.