An unexpected pentacarbonyl chromium complexation of a cyano group of the ABC core of cephalotaxine

•Preparation of chromium carbonyl complexes with benzodioxole-containing ligands.•Chromium complexes were characterized using X-ray diffraction.•Safrole chromium tricarbonyl complex has a staggered conformation.•Complexation of a cyano-pyrrolobenzazepine led to a CN → Cr coordination.•Irrespective of the transfer agent, its pentacarbonyl chromium complex is formed.

A new penta-carbonyl chromium(0) complex of the type [Cr(CO)5(L)] (L = tetracyclic pyrrolobenzazepine unit 3) was surprisingly obtained by reacting [Cr(CO)3(naphthalene)] or [Cr(CO)3(tmtach)] with the tetracyclic pyrrolobenzazepine unit 3 in octane-ether/THF-solvent mixtures or acetone under ambient temperature or reflux. The new complex 13 has been characterized by spectral analysis including IR, 1H and 13C NMR data. For comparison purposes, the safrole-tricarbonyl chromium(0) complex 12 was prepared and characterized. X-ray diffraction analyses of both complexes were determined. Based on the above data, an octahedral structure has been assigned to the new complex 13.

Graphical abstractContrary to safrole which reacts with chromium carbonyl to give the expected arene tricarbonyl chromium species, its derivative bearing an enamino-nitrile function leads, in the presence of transfer agents, [Cr(CO)3(naphthalene)] or [Cr(CO)3(tmtach)], to a pentacarbonyl chromium complex at the electron rich nitrile nitrogen atom.Figure optionsDownload full-size imageDownload as PowerPoint slide