Synthesis and electronic structure of cationic, neutral, and anionic bis(imino)pyridine iron alkyl complexes: Evaluation of redox activity in single-component ethylene polymerization catalysts

Aaron M. Tondreau, Carsten Milsmann, Andrew D. Patricks, Helen M. Hoyt, Emil Lobkovsky, Karl Wieghardt, Paul J. Chirik

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118 Scopus citations

Abstract

A family of cationic, neutral, and anionic bis(imino)pyridine iron alkyl complexes has been prepared, and their electronic and molecular structures have been established by a combination of X-ray diffraction, Mössbauer spectroscopy, magnelochemistry, and open-shell density functional theory. For the cationic complexes, [(iPrPDI)Fe-R][BPh4] (iPrPDI = 2, 6-(2,6-iPr2-C6H3N=CMe)2C5H3N; R = CH2SiMe3, CH2CMe3, or CH3), which are known single-component ethylene polymerization catalysts, the data establish high spin ferrous compounds (SFe= 2) with neutral, redox-innocent bis(imino)pyridine chelates. One-electron reduction to the corresponding neutral alkyls, (iPrPDI)Fe(CH2SiMe3) or (iPrPDI)Fe(CH2CMe3), is chelatebased, resulting in a bis(imino)pyridine radical anion (SpDI= V2) antiferromagnetically coupled to a high spin ferrous ion (SFe= 2). The neutral neopentyl derivative was reduced by an additional electron and furnished the corresponding anion, [Li(Et2O)3][(iPrPDI)Fe(CH2CMe3)N2], with concomitant coordination of dinitrogen. The experimental and computational data establish that this S=O compound is best described as a low spin ferrous compound (SFe= O) with a closed-shell singlet bis(imino)pyridine dianion (Sprji = O), demonstrating that the reduction is ligand-based. The change in field strength of the bis(imino)pyridine coupled with the placement of the alkyl ligand into the apical position of the molecule induced a spin state change at the iron center from high to low spin. The relevance of the compounds and their electronic structures to olefin polymerization catalysis is also presented.

Original languageEnglish (US)
Pages (from-to)15046-15049
Number of pages4
JournalJournal of the American Chemical Society
Volume132
Issue number42
DOIs
StatePublished - Oct 27 2010
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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