Chromium Mediated Reductive Coupling of lsonitrile Forms Unusual Heterocycles

The quintuply bonded a-diimine chromium dimer [(LCr)-L-H-Cr-iPr](2) reductively couples cyclohexyl isocyanide to produce various novel nitrogen heterocycles. Tetramerization yielded, inter alia, the aromatic squaramidinate, i.e. [C-4(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.