Metallocenylborane III. Darstellung und eigenschaften von ferrocenyl- und cymantrenylboranen

Ferrocene, cymantrene and methylcymantrene react with BI₃, BBr₃, C₆H₅BI₂ and CH₃BI₂ in boiling CS₂ or C₆H₁₂ forming air-sensitive metallocenylhaloboranes. The direct dichloroborylation is only possible with ferrocene. Starting from metallocenyliodoboranes the corresponding substituted metallocenylboranes are obtained by halogen exchange with AsF₃ or AsCl₃, by methylation with Sn(CH₃)₄, by ether cleavage of (C₂H₅)₂O, by redox reaction with (CH₃S)₂ and by reaction with R₂NH. ¹H and ¹³C NMR spectra indicate that in contrast to cymantrenylhaloboranes, in ferrocenylhaloboranes the 3,4-protons are more deshielded than the 2,5-protons. The metallocenylboranes, isoelectronic with α-metallocenylcarbenium ions, are weaker Lewis acids than phenylboranes; they form donor-acceptor compounds with pyridine and dimethylsulfane, respectively.