An extensive series of complexes [(cp)Col(L)RF][L = phosphorus donor; RF= CF3, CF2CF3, or CF(CF3)2] and [(cp)CoCO(PPh3)CF2CF3]ClO4(cp =π-cyclopentadienyl), many of them hitherto unreported, have been prepared and characterized. Variable-temperature proton and fluorine n.m.r. spectra of several of the complexes provide evidence for hindered rotation about both metal–carbon and phosphorus–aryl bonds, while the i.r. spectrum of the carbonyl complex suggests the presence of diastereoisomers, the co-ordinated phosphine and the cobalt constituting chiral centres.