Chromium mediated reductive coupling of isonitrile forms unusual heterocycles.

The quintuply bonded α-diimine chromium dimer [(H)L(iPr)Cr]2 reductively couples cyclohexyl isocyanide to produce various novel nitrogen heterocycles. Tetramerization yielded, inter alia, the aromatic squaramidinate, i.e. [C4(NCy)4](2-), whereas hexamerization produces a substituted 1,4-diaza-bicyclo[3.3.0]octadiene dianion. These unprecedented transformations complement the coupling reactions of isoelectronic CO, and they may prove synthetically useful.