A pentacoordinated arsenic(V) dication stabilized by intramolecular donor coordination.

We report the design, synthesis, and comprehensive characterization of a novel intramolecularly pentacoordinated arsenic(V)-centered dication, [Ph(ppy)2As]2+ ([2]2+; ppy = 2-(2-pyridyl)phenyl). The neutral precursor Ph(ppy)2As (2) was prepared from nonvolatile arsenic sources, and subsequent oxidation afforded the dicationic species [2][PF6]2. Single-crystal X-ray diffraction analysis revealed that oxidation strengthens intramolecular As-N coordination, leading to a slightly distorted trigonal-bipyramidal geometry. Despite its dicationic and electrophilic character, [2]2+ exhibits remarkable thermal and hydrolytic stability, attributable to its robust intramolecular chelation. Treatment with NaOH and NaOMe affords hexacoordinated hydroxide and methoxide adducts, respectively, whereas reactions with external neutral Lewis bases are inhibited by steric shielding. Fluoride-ion affinity calculations revealed that the pentacoordinated [2]2+ exhibits consistently higher fluoride affinity than the hexacoordinated analogue [1]2+ in both the gas phase and solvent-corrected calculations. This study demonstrates that intramolecular pentacoordination provides an effective structural platform for balancing the stability and accessible reactivity of arsenic(V) dications.