Structural and Spectroscopic Study of Cyclopentadienylcobalt N-Phenyl-o-benzoquinone Dilmines. A Case for Delocalized π Bonding

The compounds (η⁵-C₅H₅)Co(HNC₆X₄NC₆X₅), X = H and F, are produced by photolysis of (η⁵-C₅H₅)Co(C₆X₅N₄C₆X₅). The crystal structure of the complex (η⁵-C₅H₅)Co(HNC₆F₄NC₆F₅) has been determined at −60 °C by single-crystal X-ray diffraction techniques and shown to contain a bidentate α-diimine moiety, bonded through the nitrogen atoms to (η⁵-cyclopentadienyl)cobalt. The metallacycle and perfluorophenylene ring are essentially coplanar. Short Co-N and N-C bond lengths in the former are indicative of delocalized π bonding. An intense π → π* transition of the metallacycle dominates the electronic absorption spectrum. The C₅ portion of the C₅H₅ ring is planar; however, the H atoms are bent out of the plane toward the Co atom by an average of 0.07 Å. The C-C distances in the C₅H₅ ring show a significant distortion from idealized D_5h geometry. Crystals of C₁₇H₆CoF₉N₂ are triclinic, space group C_i¹—P1̄, with two formula units in a unit cell of dimensions at −60 °C of a = 9.832 (3) Å, b = 9.932 (3) Å, c = 8.922 (3) Å, α = 103.88 (1)°, β = 101.19 (1)°, and λ = 74.02 (1)°. Least-squares refinement of 286 variables has led to a final value of the R index on F² of 0.054 for 5673 observations; the conventional R index on F is 0.043 for 4054 observations having F_o² > 3δ(F_o²).