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(μ-Cl)]2 (1a, R=CHMe2) or [(C5H2R3)Co(μ-Cl)]2 (1b, R=CMe3) in good yield. The nitrosyl complexes [(C5HR4)Co(μ-NO)]2 (2a), [(C5HR4)Co(μ-Cl)(μ-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 1a or 1b with carbon monoxide, the salt [(C5HR4)Co(μ-Cl)3Co(C5HR4)]+2[Cl2Co(μ-Cl)]22− (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(μ-CO)]2 (7a, R=CHMe2) or [(C5H2R3)Co(μ-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(μ-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.