Structure and reactivity of paramagnetic cyclopentadienyl cobalt complexes with bulky alkyl substituents

Sodium tetraisopropylcyclopentadienide or lithium tri(tert-butyl)cyclopentadienide reacts with cobalt(II) chloride in THF to give the corresponding dimers [(C5HR4)Co(mu-Cl)](2) (1a: R = CHMe2) or [(C5H2R3)Co(mu-Cl)](2) (1b, R = CMe3) in good yield. The nitrosyl complexes [(C5HR4)Co(mu-NO)](2) (2a), [(C5HR4)Co(mu-Cl)(mu-NO)Co(C5HR4)] (3a), and [(C5HR4)Co(NO)Cl] (4a) (R = CHMe2) or the tri(tert-butyl)cyclopentadienyl derivatives 2b, 3b, and 4b have been obtained from CoCl2, the respective cyclopentadienide, and nitric oxide. From the disproportionation of la or Ib with carbon monoxide, the salt [(C5HR4)Co(mu-Cl)(3)Co(C5HR4)](2)(+)[Cl2Co(mu-Cl)(2)(2-) (5a, R = CHMe2) and the dicarbonyl complex [(C5HR4)Co(CO)(2)] (6a, R = CHMe2) or the tri(tert-butyl)cyclopentadienyl derivatives 5b and 6b have been isolated. Compounds 6a and 6b were converted to the carbonyl-bridged dimers [(C5HR4)Co(mu-CO)](2) (7a, R = CHMe2) or [(C5H2R3)Co(mu-CO)](2) (7b, R = CMe3) by UV irradiation. Compound 1a was cleaved with acetonitrile to yield the novel 17 valence electron cation [(C5HR4)Co(MeCN)(2)](+) (8, R = CHMe2), which in acetonitrile solution could be further oxidized to [(C5HR4)Co(MeCN)(3)](2+) (9, R=CHMe2) by electrochemical means or chemically with ferrocenium hexafluorophosphate. Compound 1a gave the neutral 17 VE complex [(C5HR4)Co(PMe3)Cl] (10, R=CHMe2) with trimethylphosphane, which could be converted to the methyl-substituted odd-electron compound [(C5HR4)Co(PMe3)CH3] (11, R = CHMe2) by treatment with methyllithium. Hydrolysis of complex 11 proceeded with phosphane loss and resulted in formation of the hydroxo-bridged dimer [(C5HR4)Co(mu-OH)](2) (12, R = CHMe2). Crystal structure analyses have been carried out for 1a, 3b, 5a, 7a, 7b, 8, 10, and 12. For growth of single crystals tetraisopropylcyclopentadiene turned out to be a well-suited solvent. (C) 1999 Elsevier Science S.A. All rights reserved.