Iron Precatalysts with Bulky Tri(tert-butyl)cyclopentadienyl Ligands for the Dehydrocoupling of Dimethylamine-Borane

Josh Turner, Nicholas F. Chilton, Amit Kumar, Annie Colebatch, George Whittell, Hazel Sparkes, Andrew Weller, Ian Manners*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

3 Citations (Scopus)
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In an attempt to prepare new Fe catalysts for the dehydrocoupling of amine-boranes and to provide mechanistic insight, the paramagnetic FeII dimeric complex [Cp′FeI]2 (1) (Cp′=η5-((1,2,4-tBu)3C5H2)) was used as a precursor to a series of cyclopentadienyl FeII and FeIII mononuclear species. The complexes prepared were [Cp′Fe(η6-Tol)][Cp′FeI2] (2) (Tol=C6H5Me), [Cp′Fe(η6-Tol)][BArF 4] (3) (BArF 4=[B(C6H3(m-CF3)2)4]), [N(nBu)4][Cp′FeI2] (4), Cp′FeI2 (5), and [Cp′Fe(MeCN)3][BArF 4] (6). The electronic structure of the [Cp′FeI2] anion in 2 and 4 was investigated by SQUID magnetometry, EPR spectroscopy and ab initio Complete Active Space Self Consistent Field-Spin Orbit (CASSCF-SO) calculations, and the studies revealed a strongly anisotropic S=2 ground state. Complexes 1–6 were investigated as catalysts for the dehydrocoupling of Me2NH⋅BH3 (I) in THF at 20 °C to yield the cyclodiborazane product [Me2N-BH2]2 (IV). Complexes 1–4 and 6 were active dehydrocoupling catalysts towards I (5 mol % loading), however 5 was inactive, and ultra-violet (UV) irradiation was required for the reaction mediated by 3. Complex 6 was found to be the most active precatalyst, reaching 80 % conversion to IV after 19 h at 22 °C. Dehydrocoupling of I by 1–4 proceeded via formation of the aminoborane Me2N=BH2 (II) as the major intermediate, whereas for 6 the linear diborazane Me2NH-BH2-NMe2-BH3 (III) could be detected, together with trace amounts of II. Reactions of 1 and 6 with Me3N⋅BH3 were investigated in an attempt to identify Fe-based intermediates in the catalytic reactions. The σ-complex [Cp′Fe(MeCN)(κ2-H2BH⋅NMe2H][BArF 4] was proposed to initially form in dehydrocoupling reactions involving 6 based on ESI-MS (ESI=Electrospray Ionisation Mass Spectroscopy) and NMR spectroscopic evidence. The latter also suggests that these complexes function as precursors to iron hydrides which may be the true catalytic species.

Original languageEnglish
Pages (from-to)14127-14136
Number of pages10
JournalChemistry - A European Journal
Issue number53
Early online date24 Mar 2018
Publication statusPublished - 20 Sep 2018


  • amines
  • boranes
  • catalysis
  • dehydrocoupling
  • iron catalysts


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