Synthesis, structure, and dynamic behavior of ansa-ferrocenes with pyrazabole bridges

Frieder Jäkle, Thomas Priermeier, Matthias Wagner

Research output: Contribution to journalArticlepeer-review

48 Scopus citations


A variety of stereorigid ansa-ferrocenes 2 with o-phenylene-type bridges have been obtained by the reaction of 1,1′-diborylferrocenes (1,1′-Fc(BBrR)2; Fc = ferrocenyl; R = CH3, Br, OEt, NC4H8) with selected pyrazole derivatives. Subsequent intramolecular B-N adduct formation establishes the interannular bridges. The synthetic approach is based on the replacement of certain critical carbon-carbon links by the isoelectronic, self-assembling, dative boron-nitrogen bonds and thus follows the principles of noncovalent synthesis. The pyrazabole bridge does not seem to cause any significant distortion of the ferrocene core. Most substituents at boron or pyrazole lead to an ansa-ferrocene structure. However, the presence of both strong electron donors (i.e. pyrrolidine) at boron and strongly electron-withdrawing pyrazole substituents (i.e. ester groups) results in an open chain structure 2i with three-coordinate boron atoms. The tetravalent boron centers in ansa-1,1′-Fc[B(Br)(μ-pz)]2, 2a, show an unusually high tendency to undergo nucleophilic substitution reactions, even though they are located at bridgehead positions. NMR spectroscopy, as well as chemical evidence argue against an unbridged open chain intermediate in the course of these reactions.

Original languageEnglish (US)
Pages (from-to)2033-2040
Number of pages8
Issue number8
StatePublished - Apr 16 1996
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry


Dive into the research topics of 'Synthesis, structure, and dynamic behavior of ansa-ferrocenes with pyrazabole bridges'. Together they form a unique fingerprint.

Cite this