Synthesis, electronic structure, and alkene hydrosilylation activity of terpyridine and bis(imino)pyridine iron dialkyl complexes

Aaron M. Tondreau, Crisita Carmen Hojilla Atienza, Jonathan M. Darmon, Carsten Milsmann, Helen M. Hoyt, Keith J. Weller, Susan A. Nye, Kenrick M. Lewis, Julie Boyer, Johannes G.P. Delis, Emil Lobkovsky, Paul J. Chirik

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Abstract

Iron dialkyl complexes, [N 3]Fe(CH 2SiMe 3) 2, with three different classes of tridentate, nitrogen-based "[N 3]" ligands, aryl-substituted bis(imino)pyridines, terpyridine, and pyridine bis(oxazoline), have been synthesized and evaluated in the catalytic hydrosilylation of olefins with tertiary silanes. The 2,2′:6′,2″-terpyridine (terpy) complex, (terpy)Fe(CH 2SiMe 3) 2, was prepared either via alkylation of (terpy)FeCl 2 with LiCH 2SiMe 3 or by pyridine displacement from (pyridine) 2Fe(CH 2SiMe 3) 2 by free terpyridine. The aryl-substituted bis(imino)pyridine compounds, ( RPDI)Fe(CH 2SiMe 3) 2 ( RPDI = 2,6-(2,6-R 2-C 6H 3N=CMe) 2C 5H 3N), with smaller 2,6-dialkyl substituents (R = Et, Me) or a 2- iPr substituent ( 2-iPrPDI)Fe(CH 2SiMe 3) 2 ( 2-iPrPDI = 2,6-(2- iPr-C 6H 4N=CMe) 2C 5H 3N, are effective precursors (0.5 mol %) for the anti-Markovnikov hydrosilylation of 1-octene with (Me 3SiO) 2MeSiH and (EtO) 3SiH over the course of 1 h at 60 °C. No hydrosilylation activity was observed with Et 3SiH. The most hindered member of the series, ( iPrPDI)Fe(CH 2SiMe 3) 2, and the pyridine bis(oxazoline) iron compound, (R,R)-( iPrPybox)Fe(CH 2SiMe 3) 2 ( iPrPybox = 2,6-bis[isopropyl-2-oxazolin-2-yl]pyridine), were inactive for the hydrosilylation of 1-octene with all tertiary silanes studied. By contrast, the terpyridine precursor, (terpy)Fe(CH 2SiMe 3) 2, reached >95% conversion at 60 °C with Et 3SiH and (Me 3SiO) 2MeSiH. In addition, the hydrosilylation of vinylcyclohexene oxide was accomplished in the presence of 1.0 mol % (terpy)Fe(CH 2SiMe 3) 2, demonstrating functional group compatibility unique to this compound that is absent from bis(imino)pyridine iron compounds. The electronic structures of all three classes of iron dialkyl compounds have been evaluated by a combination of X-ray diffraction, magnetochemistry, Mössbauer spectroscopy, and density functional theory calculations. All of the compounds are best described as high-spin iron(III) compounds with antiferromagnetic coupling to chelate radical anions.

Original languageEnglish (US)
Pages (from-to)4886-4893
Number of pages8
JournalOrganometallics
Volume31
Issue number13
DOIs
StatePublished - Jul 9 2012

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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    Tondreau, A. M., Atienza, C. C. H., Darmon, J. M., Milsmann, C., Hoyt, H. M., Weller, K. J., Nye, S. A., Lewis, K. M., Boyer, J., Delis, J. G. P., Lobkovsky, E., & Chirik, P. J. (2012). Synthesis, electronic structure, and alkene hydrosilylation activity of terpyridine and bis(imino)pyridine iron dialkyl complexes. Organometallics, 31(13), 4886-4893. https://doi.org/10.1021/om3004527