Phil Rudolf

THE CRYSTAL AND MOLECULAR STRUCTURE OF (η5‐CYCLOPENTADIENYL)(η4‐2,4‐DIMESITYL‐3,5‐DIPHENYLCYCLOPENTADIENONE)CO# BALT

Abstract The crystal structure of (η 5 -cyclopentadienyl)(η 4 -2, 4-dimesityl-3, 5-diphenylcyclopentadienone)cobalt, CoC 40 H 37 O, was determined from 3385 unique reflections obtained with a computer automated diffractometer. The unit cell is triclinic with a = 8.401(3), b = 9.339(1), c = 20.343(3) A ; α =95.39(1), β = 92.26(1), γ = 104.93(2)°; ϱ = 1.154 g cm −3 , space group (assumed) P 1 and Z = 2. Refinement of the data by the full matrix least squares procedure with anisotropic temperature factors for all non-hydrogen atoms and calculated positional and thermal parameters for hydrogen atoms resulted in a final R value of 0.044 (R W = 0.0550. The structure consists of two five membered rings π-bonded to cobalt. The cyclopentadienyl ring is planar with all five carbon atoms equidistant from the metal. However, the cyclopentadienone ring is decidedly nonplanar with the C 1 , C 2 , C 3 C 4 fragment making a dihedral angle of 10.9° with the mean plane formed by C 1 , C 5 , O, C 4 . Torsional angles show that the substituent rings are twisted about the cyclopentadienone ring so as to minimize steric interactions. However, the short hydrogen-hydrogen interactions are sufficient to create a sizeable barrier to rotation about the mesityl-cyclopentadienone bonds.