Issue Date: May 2, 2016
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 As102– and As124–.
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