Reduction chemistry of aryl- and alkyl-substituted bis(imino)pyridine iron dihalide compounds: molecular and electronic structures of [(PDI)2Fe] derivatives.
Sodium amalgam reduction of the aryl-substituted bis(imino)pyridine iron dibromide complex, ((Et)PDI)FeBr2 ((Et)PDI = 2,6-(2,6-Et2-C6H3N=CMe)2C5H3N), under a dinitrogen atmosphere in pentane furnished the bis(chelate)iron compound, ((Et)PDI)2Fe. Characterization by X-ray crystallography established a distorted four-coordinate iron center with two kappa2-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, iPr, cis-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, Mössbauer 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 (S(Fe) = 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.
Wile
Bradley M
BM
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA.
Trovitch
Ryan J
RJ
Bart
Suzanne C
SC
Tondreau
Aaron M
AM
Lobkovsky
Emil
E
Milsmann
Carsten
C
Bill
Eckhard
E
Wieghardt
Karl
K
Chirik
Paul J
PJ
D001965:Bromides / Q000138:chemical synthesis / Q000737:chemistry; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D007097:Imines / Q000138:chemical synthesis / Q000737:chemistry*; D058085:Iron Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry; D010084:Oxidation-Reduction; D010420:Pentanes / Q000138:chemical synthesis / Q000737:chemistry; D011725:Pyridines / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D015204:Spectroscopy, Mossbauer
D001965:Bromides; D007097:Imines; D058085:Iron Compounds; D010420:Pentanes; D011725:Pyridines; C033353:pentane; D009584:Nitrogen