Ferrocenophanes with interannular boron-phosphorus bridges: Synthesis, structure, and reactivity toward nitrogen bases

Eberhardt Herdtweck, Frieder Jäkle, Matthias Wagner

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Abstract

Starting from readily available diborylferrocenes 1,1′-fc[B(Br)R]2 (fc = (C5H4)Fe(C5H4); R: Br (1a), Me (1b), OEt (1d)), ferrocenophanes 1,1′-fc[B(μ-PPh2)R]2 (R = Br (2a), Me (2b), PPh2 (2d)) and 1,1′-fc[B(μ-PPh2) OEt][B(μ-PPh2)PPh2] (2c) are obtained upon reaction with LiPPh2. In contrast, 1,1′-fc[B(Br)pyr]2 (pyr = pyrrolidinyl, 1e) and 2 equiv of LiPPh2 give an open-chain ferrocene 1,1′-fc[B(PPh2)pyr]2 (2e). The dynamic behavior of the B2P2-bridged species has been investigated using variable-temperature NMR spectroscopy and the Forsén-Huffman spin saturation transfer method. The reaction of 2a with Lipz (pz = pyrazolide) gives the ansa-ferrocene 1,1′-fc[B(μ-PPh2)PPh2][B(μ-pz)Br] (3a), featuring an interannular (BNNBP) heterocyclic bridge. When Lipz* (pz* = 4-bromo-3,5-dimethylpyrazolide) was used rather than Lipz, two products could be isolated: 3b, which is analogous to 3a, and 1,1′-fc[B(μ-PPh2)Br][B(μ-pz)Br] (3c), which bears Br substituents at both bridgehead boron centers. 2d and 3c have been characterized by X-ray crystallography. Treatment of 2a with excess γ-picoline (pic) results in an ansa-bridge opening and bromide substitution with the formation of the ionic species {1,1′-fc[B(PPh2)pic2]2}Br2 (5a). The presence of three-coordinate phosphorus centers in 5a was confirmed by showing their ability to bind Cr(CO)5 fragments, which afforded the trimetallic complex 5b.

Original languageEnglish (US)
Pages (from-to)4737-4745
Number of pages9
JournalOrganometallics
Volume16
Issue number21
DOIs
StatePublished - Oct 14 1997
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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