Arsenic joins the cyanate family

Oxford University chemists who have been exploring the similarities between cyanate, N≤C–O_–, and 2-phosphaethynolate, P≤C–O_–, have now made the first isolable version of the next heaviest group 15 analog, 2-arsaethynolate, As≤C–O_–. Like its nitrogen and phosphorus analogs, 2-arsaethynolate could be a useful reagent in organic synthesis or as a precursor for making electronic materials. Alexander Hinz and Jose M. Goicoechea prepared the arsenic anion by first reacting elemental sodium and arsenic with catalytic amounts of naphthalene to make Na₃As, which they protonated with tert-butyl alcohol to make NaAsH₂. The researchers then treated NaAsH₂ with diethylcarbonate to form As≤C–O_–, isolating it as a crown ether salt (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201602310). The Oxford team found that the arsenic anion readily undergoes [2+2] cycloadditions with ketenes (shown) and carbodiimides to form four-membered arsenic-containing heterocyclic anions. With isocyanates, As≤C–O_– forms five-membered heterocycles. The researchers also discovered that As≤C–O_– is susceptible to decarbonylation to form arsenic clusters, including never-before-seen As_102– and As_124–.