Metal π complexes of benzene derivatives: Part 57. p-Phenylenediamine as a sandwich-complex ligand

Metal-atom ligand-vapor cocondensation affords the sandwich complexes di[1,4-bis(trimethylsilylamino)-η6-benzene]chromium (4) and di[1,4-bis(dimethylamino)-η6-benzene]chromium, (TMPD)2Cr (5). In the crystal 4 adopts an eclipsed structure with intramolecular, interannular NH⋯N hydrogen bonds. 5+radical dotI− in the crystal forms staggered, synclinal cations 5+radical dot (twist angle 31°) featuring boat distortions of the η6-arenes and displacements of the N atoms away from the central metal atoms. This deformation is virtually absent in the structure of 4. According to EPR spectroscopy, in rigid solution the cations 5+radical dot relax to a twist angle of 45°. Cyclic voltammetry performed on 5 points to the oxidation sequence (TMPD)2Cr[(TMPD)2Cr]+radical dot[(TMPD)2Cr]2+→Cr2+(solv)+2 TMPD2 TMPD+radical dot2 TMPD2+, which, in part, can be monitored by EPR spectroscopy (observation of (TMPD)2Cr+radical dot and TMPD+radical dot). The potential E1/2(5+/0) is the most cathodic one ever reported for a bis(arene)metal complex.