Cobalt metallocycles. Part 10. Preparation and X-ray structures of two isomeric dicyanocobaltacyclopentanes

Abstract

Two isomeric 1,4-dicyanocobaltacyclopentanes, [Co(η-C₅H₅)(C₆H₆N₂)(PPh₃)], have been prepared by the reaction of the acrylonitrile complex [Co(η-C₅H₅)(CH₂CHCN)(PPh₃)](1) with free acrylonitrile and were characterized by single-crystal X-ray analysis. The cis isomer (2) crystallizes in the triclinic space group P with unit-cell dimensions a= 11.464(3), b= 13.782(3), c= 9.277(2)Å, α= 87.48(2), β= 110.23(1), γ= 84.26(2)°, Z= 2, and R= 0.067 for 4 238 independent observations. Crystals of the trans isomer (3) are orthorhombic, space group Fdd2, with a= 12.821 (1), b= 65.833(20), c= 11.470(1)Å, Z= 16, and R= 0.057 for 2 024 independent reflections. The cobaltacyclopentane ring in the cis form has an ‘opened-envelope’ conformation while that in the trans isomer is puckered. Although (2) and (3) are thermally more stable than the unsubstituted analogue, [Co(η-C₅H₅)(C₄H₈)(PPh₃)](4), their Co–C(α) distances are approximately equal to the reported values for (4) while the Co–P distances are distinctly longer.