Chromocene, ferrocene, cobaltocene, and nickelocene derivatives with isopropyl and methyl or trimethylsilyl substituents

•Dimethyl-diisopropylcyclopentadienyl ligands confer solubility and crystallinity.•No other high spin chromocenes found among alkylated or silylated derivatives.•Efficient transfer of a C5H5 ligand from nickelocene to a cationic nickel fragment.

From sodium 2,3-diisopropyl-1,4-dimethyl-cyclopentadienide and MBr2(dme) (M = Fe, Co, Ni) the corresponding ferrocene (1), cobaltocene (2) and nickelocene (3) could be obtained as pure, crystalline solids. From an analogous reaction of sodium 2,3,5-triisopropyl-1,4-dimethyl-cyclopentadienide with FeCl2, only the mixed-substituted ferrocene (C23p)(C22p)Fe (4) could be crystallized (C23p = 2,3,5-triisopropyl-1,4-dimethyl-cyclopentadienyl, C22p = 2,3-diisopropyl-1,4-dimethyl-cyclopentadienyl). The trimethylsilyl substituted ferrocene (5) and nickelocene (6) were synthesized from the corresponding metal halides and potassium 2,3-diisopropyl-1,4-dimethyl-5-trimethylsilyl-cyclopentadienide as well as a series of chromocenes with silylated or alkylated cyclopentadienyl ligands (7–10) from chromium(II) acetate. Octaisopropylnickelocene (11) has been obtained and converted to octaisopropylnickelocenium hexafluorophosphate (12). 1,2,3,4-tetraisopropylnickelocenium tetrabromoaluminate (13) was obtained from tetraisopropylcyclopentadienylnickel(II) tetrabromoaluminate and nickelocene. Crystal structures have been obtained for metallocenes 1–5, 7–9, and 11.

Graphical abstractMetallocenes with easily available 1,4-dimethyl-2,3-diisopropylcyclopentadienide or its silylated derivative show good solubility and crystallinity. Chromocenes with trimethylsilyl or tert-butyl substituents are examples for the flexibility of CSi bonds in contrast to CC bonds. Another high spin chromocene was not found among the silylated or alkylated examples.Figure optionsDownload full-size imageDownload as PowerPoint slide