Chiral organoborane Lewis pairs derived from pyridylferrocene

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


In an effort to develop a new class of redox-active chiral Lewis pairs, pyridine and borane moieties with different steric and electronic properties were introduced onto a planar chiral 1,2-disubstituted ferrocene framework. Metathesis of lithiated, stannylated, or mercuriated pyridylferrocenes with boron halides afforded (pR)-2-[bis(pentafluorophenyl)boryl]-1-(3,5- dimethylpyrid-2-yl)ferrocene (4-Pf), (pR)-2-[dimesitylboryl]-1-(3,5- dimethylpyrid-2-yl)ferrocene (4-Mes), (pS)-2-(bis(pentafluorophenyl)boryl)-1-(2- trimethylsilylpyrid-6-yl)ferrocene (5-Pf), or (pS)-2-[dimesitylboryl]-1-(2- trimethylsilylpyrid-6-yl)ferrocene (5-Mes). The borylated products were analyzed by multinuclear NMR spectroscopy, HRMS, and single-crystal X-ray diffraction. Chiral HPLC and optical-rotation measurements were employed to assess the stereoselectivity of the borylation process and to establish the correct stereochemical assignments. The strength of the B-N interactions were investigated in solution and in the solid state. Compounds 4-Pf and 4-Mes formed robust 'closed' B-N heterocyclic systems that proved to be perfectly stable to air and moisture, whereas 5-Pf established a dynamic equilibrium, in which the B-N heterocycle was observed exclusively at room temperature, but opened up at high temperature according to 19F NMR exchange spectroscopy data. As a consequence, 5-Pf reacted readily with a molecule of water to generate a ring-opened pyridinium borate. The combination of bulky borane and bulky pyridyl groups in 5-Mes led to a completely 'open' frustrated Lewis pair system with uncomplexed pyridine and borane groups, even at room temperature. Electrochemical studies were performed and the effect of preparative ferrocene oxidation on the structural features was also explored. Open or closed? Planar chiral Lewis pairs derived from pyridylferrocene were prepared. They form closed, open, or dynamic structures depending on the steric and electronic nature of the Lewis acidic and Lewis basic sites (see scheme; Mes=mesityl). The effect of oxidation on the Lewis acid-base interaction was also explored.

Original languageEnglish (US)
Pages (from-to)9120-9129
Number of pages10
JournalChemistry - A European Journal
Issue number29
StatePublished - Jul 14 2014

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Organic Chemistry


  • Lewis acids
  • boranes
  • ferrocene
  • frustrated Lewis pairs
  • planar chirality


Dive into the research topics of 'Chiral organoborane Lewis pairs derived from pyridylferrocene'. Together they form a unique fingerprint.

Cite this