CRYSTAL AND MOLECULAR-STRUCTURE OF (ETA-5-TRIMETHYLSILYLCYCLOPENTADIENYL)-(ETA-4-TETRAPHENYLCYCLOBUTADIENE)COBALT

The structure of (η5-trimethylsilylcyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt, ((CH3)3SiC5H4)Co((C6H5)4C4), has been determined by single crystal X-ray diffraction techniques using three-dimensional data collected on an automatic diffractometer. The crystals are monoclinic, space group P21/c, with lattice parameters a 11.551(1), b 16.352(6), c 18.324(2) », β 122.85(1)° with four molecules in the unit cell. The structure consists of discrete molecules in which a cobalt atom is sandwiched between the η5-cyclopentadienyl (Cp) and the η4-cyclobutadience (Cb) ligands bonded to the metal in the hapto mode. The perpendicular distances Co⋯(Cp) and Co⋯(Cb) of 1.688 and 1.699 », respectively, as well as the dihedral angle of 6.9° between the two rings and the distortions of their side groups, indicate steric interactions within the molecule. The Cb ring is planar within 0.015 » and has a rectangular shape with edges of 1.480(5) and 1.463(3) ». The Cp ring, which is planar to within 0.005 », appears to be highly distorted by the trimethylsilyl group, which induces a lengthening of the C-C distances involving the substituted carbon atom (1.440(7) ») and a narrowing of the corresponding bond angle (105.3(2)°). © 1979.