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Polygroup Prepares Phosphorus Polycation

Main-Group Chemistry: Three teams independently made a phosphorus-selenium cation, then joined forces to report the results

by Stephen K. Ritter
May 25, 2015 | A version of this story appeared in Volume 93, Issue 21

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.

Credit: Adapted from Chem. Eur. J.
Three groups used different reagents to prepare [P3Se4]+.
Schematic showing the reagents needed to make [P3Se4]+ cation via 3 different synthetic pathways.
Credit: Adapted from Chem. Eur. J.
Three groups used different reagents to prepare [P3Se4]+.


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