Synthesis, X-ray structure, and theoretical studies of novel cationic mono-cyclopentadienyl complexes of Co(III): the orthometalation of trans-azobenzene

New cationic mono-cyclopentadienyl complexes of Co(III) containing mono or bidentate nitrogen donor ligands of general formula [Co(η5-C5H5)(PPh3)L2][BF4]2 (L=NC–CH3,2, and NC–Ph, 3) or [Co(η5-C5H5)(PPh3)(L–L)][BF4]2, [L–L=2,2′-bisimidazole (H2biim) (4) and dipyridylamine [HN(NC5H5)2] (5) have been synthesised by the stoichiometric reaction of the Co(III) complex Co(η5-C5H5)(PPh3)I2 (1), with Ag[BF4] and the appropriate ligand in CH2Cl2. Under the same conditions and using trans-azobenzene as a ligand, an orthometalation reaction took place, giving the new compound [Co(η5-C5H5)(PPh3)(κ-C,κ-N–C6H4NNPh)][BF4] (6) in high yield. The structural characterisation of compounds 4 and 6, and of the starting compound Co(η5-C5H5)(PPh3)I2 (1) was done by single-crystal X-ray diffraction studies. DFT calculations (adf program) were performed in order to understand the orthometallation reaction.