METAL-COMPLEXES OF HETEROARENES .6. HEXAKIS-(ETA(1)-PHOSPHININE) CHROMIUM - SYNTHESIS, STRUCTURE AND REDOX BEHAVIOR

Two alternative pathways, metal-atom ligand-vapor cocondensation and ligand substitution at bis(2,4-dimethyl-eta5-pentadienyl)chromium, lead to hexakis(eta1-phosphinine)chromium(0), 10. According to an X-ray crystal structure determination the CrP6 core represents an almost ideal octahedron, the bond lengths d(CT-P) 226.5 pm being particularly short. Whereas the intraligand bond-lengths experience only minor changes upon eta1-coordination of phosphinine, the changes in the H-1-, C-13- and P-31 parameters are substantial. Compared with hexakis(eta1-phenylisocyanide)chromium, the UV/VIS spectrum of 10 displays a bathochromic shift in the MLCT region which attests to a stronger pi-acceptor character of phosphinine. The attendant propensity of this ligand to stabilize the oxidation state Cro manifests itself in the redox potentials for the couples CrL+/0 which are increasingly anodic according to the sequence Cr(bpy)3 < Cr(PhNC)6 < Cr(C5H5P), < Cr(CO)6.