Crystal and molecular structure of (η5-trimethylsilylcyclopentadienyl)(η4-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)°).