Isostructural triazenido complexes of first row transition metals. Part 3. Low spin cyclopentadienyl complexes of cobalt(II) (η5-C5H5)(PPh3)(RN3R)Co

Summary Reaction of (PPh₃)₂Cl₂Co^II with TlC₅H₅ gave the new (⁵-C₅H₅)(PPh₃)ClCo^II complex. This complex reacted with Ag(RN₃R) or Cu(RN₃R) (R=p-MeC₆H₄,p-ClC₆H₄ or 3,5-Cl₂C₆H₃) to give the novel compounds (⁵-C₅H₅)(PPh₃)(RN₃R)Co^II, with a spin state of one half, which are representatives of the very small class of paramagnetic monocyclopentadienyl transition metal complexes. The structural conclusions are based on comparison with the isostructural [⁵-C₅H₅)(PPh₃)(RN₃R)Co^III]PF₆ complex, on the i.r. spectra and on the observed redox behaviour. The e.p.r. spectra are reported, but are not well enough resolved for the determination of the hyperfine interactions. The orbital scheme of the new complex is discussed in terms of a distorted octahedral crystal field in relation to the series of isostructural (⁵-C₅H₅)(PPh₃)(RN₃R)M^II (M = Fe, Co or Ni) complexes.