SYNTHESIS AND STRUCTURE OF ISOCYANIDE COMPLEXES OF CHROMIUM IN DIFFERENT OXIDATION STATES. Gabriele Kociok-Köhn, Dirk Wössner, Alexander C. Filippou_*. Fachinstitut für Anorganische Chemie, Humboldt Universität, D-10115 Berlin, Germany

Group VI transition-metal isocyanide complexes have been recently shown to undergo a variety of carbon-carbon bond forming reactions (A. C. Filippou, W. Grünleitner, Z. Naturforschung, 46b (1991) 216). The chromium derivatives display a considerably different redox chemistry than the analogous molybdenum and tungsten compounds. In this context we have synthesized various isocyanide complexes of chromium in the oxidation state 0, I, II and III, in order to study the effect of the oxidation state on the nature of the metal-ligand bonding. We were able to obtain crystal structures of the complexes [CrCl₃(CN^tBu)₃]^.(CH₂Cl₂)₃ 1, [CrI₂(CNiPr)₄][I₃] 2 and [Cr(CNtBu)₆] [PF₆] 3. All three structures feature six coordinated chromium. In complex 1 the three isocyanide ligands adopt a meridional arrangement around the Cr(III) centre (Cr-C: 2.087-2.104(3) Å). The unit-cell contains an extraordinary amount of CH₂Cl₂, which interacts via hydrogen bonds with the chloro ligands of the complex. In complex 2 the two I-ligands are trans-oriented giving rise to a tetragonally distorted octahedron with the four isocyanide ligands in the square plane (Cr-I: 2.649(10), Cr-C: 2.064(9) Å). The six t-butyl isocyanide ligands in complex 3 are bound to a Cr(I) centre, forming a slightly distorted octahedron (Cr-C: 1.977(5) and 1.981(4) Å).