Reduction chemistry of aryl- and alkyl-substituted bis(imino)pyridine iron dihalide compounds: Molecular and electronic structures of [(PDI)2Fe] derivatives

Bradley M. Wile, Ryan Trovitch, Suzanne C. Bart, Aaron M. Tondreau, Emil Lobkovsky, Carsten Milsmann, Eckhard Bill, Karl Wieghardt, Paul J. Chink

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Abstract

Sodium amalgam reduction of the aryl-substituted bis(imino)pyridine iron dibromide complex, (EtPDI)FeBr2 (EtPDI = 2,6-(2,6-Et2-C6H3N=CMe)2C5H3N), under a dinitrogen atmosphere in pentane furnished the bis(chelate)iron compound, (EtPDI)2Fe. Characterization by X-ray crystallography established a distorted four-coordinate iron center with two K2-bis(imino)pyridine ligands. Reducing the steric demands of the imine substituent to either a less sterically encumbered aryl ring (e.g., C6H4-4-OMe) or an alkyl group (e.g., Cy, Pr, c/s-myrtanyl) also yielded bis(chelate) compounds from sodium amalgam reduction of the corresponding dihalide. Characterization of the compounds with smaller imine substituents by X-ray diffraction established six-coordinate, pseudo-octahedral compounds. In one case, a neutral bis(chelate)iron compound was prepared by reduction of the corresponding iron dication, [(PDI)2Fe]2+, providing chemical confirmation of electrochemically generated species that were previously reported as too reducing to isolate. Magnetic measurements, metrical parameters from X-ray structures, Mossbauer spectroscopy, and open-shell, broken symmetry DFT calculations were used to establish the electronic structure of both types (four- and six-coordinate) of neutral bis(chelate) compounds. The experimentally observed S = 1 compounds are best described as having high-spin ferrous (SFe = 2) centers antiferromagnetically coupled to two bis(imino)pyridine radical anions. Thus, the two-electron reduction of the diamagnetic, low-spin complex [(PDI)2Fe]2+ to [(PDI)2Fe] is ligand-based with a concomitant spin change at iron.

Original languageEnglish
Pages (from-to)4190-4200
Number of pages11
JournalInorganic Chemistry
Volume48
Issue number9
DOIs
Publication statusPublished - May 4 2009

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Iron Compounds
iron compounds
chelates
Molecular structure
Electronic structure
pyridines
molecular structure
Iron
electronic structure
Derivatives
mercury amalgams
Mercury amalgams
iron
Imines
imines
Sodium Compounds
Shells (structures)
sodium
Ligands
dibromides

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

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Reduction chemistry of aryl- and alkyl-substituted bis(imino)pyridine iron dihalide compounds : Molecular and electronic structures of [(PDI)2Fe] derivatives. / Wile, Bradley M.; Trovitch, Ryan; Bart, Suzanne C.; Tondreau, Aaron M.; Lobkovsky, Emil; Milsmann, Carsten; Bill, Eckhard; Wieghardt, Karl; Chink, Paul J.

In: Inorganic Chemistry, Vol. 48, No. 9, 04.05.2009, p. 4190-4200.

Research output: Contribution to journalArticle

Wile, Bradley M. ; Trovitch, Ryan ; Bart, Suzanne C. ; Tondreau, Aaron M. ; Lobkovsky, Emil ; Milsmann, Carsten ; Bill, Eckhard ; Wieghardt, Karl ; Chink, Paul J. / Reduction chemistry of aryl- and alkyl-substituted bis(imino)pyridine iron dihalide compounds : Molecular and electronic structures of [(PDI)2Fe] derivatives. In: Inorganic Chemistry. 2009 ; Vol. 48, No. 9. pp. 4190-4200.
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abstract = "Sodium amalgam reduction of the aryl-substituted bis(imino)pyridine iron dibromide complex, (EtPDI)FeBr2 (EtPDI = 2,6-(2,6-Et2-C6H3N=CMe)2C5H3N), under a dinitrogen atmosphere in pentane furnished the bis(chelate)iron compound, (EtPDI)2Fe. Characterization by X-ray crystallography established a distorted four-coordinate iron center with two K2-bis(imino)pyridine ligands. Reducing the steric demands of the imine substituent to either a less sterically encumbered aryl ring (e.g., C6H4-4-OMe) or an alkyl group (e.g., Cy, Pr, c/s-myrtanyl) also yielded bis(chelate) compounds from sodium amalgam reduction of the corresponding dihalide. Characterization of the compounds with smaller imine substituents by X-ray diffraction established six-coordinate, pseudo-octahedral compounds. In one case, a neutral bis(chelate)iron compound was prepared by reduction of the corresponding iron dication, [(PDI)2Fe]2+, providing chemical confirmation of electrochemically generated species that were previously reported as too reducing to isolate. Magnetic measurements, metrical parameters from X-ray structures, Mossbauer spectroscopy, and open-shell, broken symmetry DFT calculations were used to establish the electronic structure of both types (four- and six-coordinate) of neutral bis(chelate) compounds. The experimentally observed S = 1 compounds are best described as having high-spin ferrous (SFe = 2) centers antiferromagnetically coupled to two bis(imino)pyridine radical anions. Thus, the two-electron reduction of the diamagnetic, low-spin complex [(PDI)2Fe]2+ to [(PDI)2Fe] is ligand-based with a concomitant spin change at iron.",
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AU - Bart, Suzanne C.

AU - Tondreau, Aaron M.

AU - Lobkovsky, Emil

AU - Milsmann, Carsten

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AB - Sodium amalgam reduction of the aryl-substituted bis(imino)pyridine iron dibromide complex, (EtPDI)FeBr2 (EtPDI = 2,6-(2,6-Et2-C6H3N=CMe)2C5H3N), under a dinitrogen atmosphere in pentane furnished the bis(chelate)iron compound, (EtPDI)2Fe. Characterization by X-ray crystallography established a distorted four-coordinate iron center with two K2-bis(imino)pyridine ligands. Reducing the steric demands of the imine substituent to either a less sterically encumbered aryl ring (e.g., C6H4-4-OMe) or an alkyl group (e.g., Cy, Pr, c/s-myrtanyl) also yielded bis(chelate) compounds from sodium amalgam reduction of the corresponding dihalide. Characterization of the compounds with smaller imine substituents by X-ray diffraction established six-coordinate, pseudo-octahedral compounds. In one case, a neutral bis(chelate)iron compound was prepared by reduction of the corresponding iron dication, [(PDI)2Fe]2+, providing chemical confirmation of electrochemically generated species that were previously reported as too reducing to isolate. Magnetic measurements, metrical parameters from X-ray structures, Mossbauer spectroscopy, and open-shell, broken symmetry DFT calculations were used to establish the electronic structure of both types (four- and six-coordinate) of neutral bis(chelate) compounds. The experimentally observed S = 1 compounds are best described as having high-spin ferrous (SFe = 2) centers antiferromagnetically coupled to two bis(imino)pyridine radical anions. Thus, the two-electron reduction of the diamagnetic, low-spin complex [(PDI)2Fe]2+ to [(PDI)2Fe] is ligand-based with a concomitant spin change at iron.

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