Polygroup Prepares Phosphorus Polycation

Binary polyatomic cations built from group 15 and group 16 elements aren’t strangers to main-group chemists. But a cation involving phosphorus and a group 16 element hasn’t been made before. All of a sudden, three research groups have independently synthesized the first one—the same phosphorus-selenium cation, [P₃Se₄]⁺—by three different methods. The multinational teams, led by Jan J. Weigand of Dresden University of Technology, in Germany, decided to join forces to report the synthesis and characterization of their cagey molecule in one research paper (Chem. Eur. J. 2015, DOI: 10.1002/chem.201406476). One team prepared the compound by heating red phosphorus, gray selenium, and selenium tetrachloride in the Lewis-acidic ionic liquid [bmimCl][AlCl₃]. Another team observed formation of the cation in an arylation reaction of P₄Se₃ with C₆(CH₃)₅Br in the presence of AlCl₃ in dichloromethane solvent. And the third team synthesized it by adding [(CH₃)₃Si]₂Se to a dichloromethane solution of PCl₃ and MX₃, where M is Al or Ga and X is Cl or Br. The researchers studied various metalate salts of the phosphorus-selenium cation by a combination of single-crystal X-ray diffraction, ³¹P and ⁷⁷Se solid-state and solution NMR spectroscopy, Raman spectroscopy, and quantum chemical calculations.