TY - JOUR
T1 - Synthesis and electronic structure of cationic, neutral, and anionic bis(imino)pyridine iron alkyl complexes
T2 - Evaluation of redox activity in single-component ethylene polymerization catalysts
AU - Tondreau, Aaron M.
AU - Milsmann, Carsten
AU - Patricks, Andrew D.
AU - Hoyt, Helen M.
AU - Lobkovsky, Emil
AU - Wieghardt, Karl
AU - Chirik, Paul J.
PY - 2010/10/27
Y1 - 2010/10/27
N2 - 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.
AB - 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.
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U2 - 10.1021/ja106575b
DO - 10.1021/ja106575b
M3 - Article
C2 - 20882992
AN - SCOPUS:78649742545
SN - 0002-7863
VL - 132
SP - 15046
EP - 15049
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 42
ER -