TY - JOUR
T1 - Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes
T2 - Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis
AU - Kovel, Carli B.
AU - Darmon, Jonathan M.
AU - Stieber, S. Chantal E.
AU - Pombar, Gisselle
AU - Pabst, Tyler P.
AU - Theis, Bastian
AU - Turner, Zoë R.
AU - Üngör, Ökten
AU - Shatruk, Michael
AU - DeBeer, Serena
AU - Chirik, Paul J.
N1 - Funding Information:
This research was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Catalysis Science program, under Award DE-SC0022303. S.D. acknowledges the Max Planck Society for funding. S.C.E.S. thanks NSF GRFP and CAREER (1847926) for funding. Characterization of magnetic properties was performed with support from the National Science Foundation, Award CHE-1955754. The XES data were measured at the Center for High Energy X-ray Sciences (CHEXS), which is supported by the National Science Foundation under award DMR-1829070. We also thank Dr. Grant Marguileux for experimental assistance with X-ray diffraction, Megan Mohadjer Beromi for helpful discussion, and Dr. Istvan Pelczer and Kenneth Conover for guidance with NMR spectroscopy.
Publisher Copyright:
© 2023 American Chemical Society.
PY - 2023/3/8
Y1 - 2023/3/8
N2 - The application of bimolecular reductive elimination to the activation of iron catalysts for alkene-diene cycloaddition is described. Key to this approach was the synthesis, characterization, electronic structure determination, and ultimately solution stability of a family of pyridine(diimine) iron methyl complexes with diverse steric properties and electronic ground states. Both the aryl-substituted, (MePDI)FeCH3 and (EtPDI)FeCH3 (RPDI = 2,6-(2,6-R2-C6H3N═CMe)2C5H3N), and the alkyl-substituted examples, (CyAPDI)FeCH3 (CyAPDI = 2,6-(C6H11N═CMe)2C5H3N), have molecular structures significantly distorted from planarity and S = 3/2 ground states. The related N-arylated derivative bearing 2,6-di-isopropyl aryl substituents, (iPrPDI)FeCH3, has an idealized planar geometry and exhibits spin crossover behavior from S = 1/2 to S = 3/2 states. At 23 °C under an N2 atmosphere, both (MePDI)FeCH3 and (EtPDI)FeCH3 underwent reductive elimination of ethane to form the iron dinitrogen precatalysts, [(MePDI)Fe(N2)]2(μ-N2) and [(EtPDI)Fe(N2)]2(μ-N2), respectively, while (iPrPDI)FeCH3 proved inert to C-C bond formation. By contrast, addition of butadiene to all three iron methyl complexes induced ethane formation and generated the corresponding iron butadiene complexes, (RPDI)Fe(η4-C4H6) (R = Me, Et, iPr), known precatalysts for the [2+2] cycloaddition of olefins and dienes. Kinetic, crossover experiments, and structural studies were combined with magnetic measurements and Mössbauer spectroscopy to elucidate the electronic and steric features of the iron complexes that enable this unusual reductive elimination and precatalyst activation pathway. Transmetalation of methyl groups between iron centers was fast at ambient temperature and independent of steric environment or spin state, while the intermediate dimer underwent the sterically controlled rate-determining reaction with either N2 or butadiene to access a catalytically active iron compound.
AB - The application of bimolecular reductive elimination to the activation of iron catalysts for alkene-diene cycloaddition is described. Key to this approach was the synthesis, characterization, electronic structure determination, and ultimately solution stability of a family of pyridine(diimine) iron methyl complexes with diverse steric properties and electronic ground states. Both the aryl-substituted, (MePDI)FeCH3 and (EtPDI)FeCH3 (RPDI = 2,6-(2,6-R2-C6H3N═CMe)2C5H3N), and the alkyl-substituted examples, (CyAPDI)FeCH3 (CyAPDI = 2,6-(C6H11N═CMe)2C5H3N), have molecular structures significantly distorted from planarity and S = 3/2 ground states. The related N-arylated derivative bearing 2,6-di-isopropyl aryl substituents, (iPrPDI)FeCH3, has an idealized planar geometry and exhibits spin crossover behavior from S = 1/2 to S = 3/2 states. At 23 °C under an N2 atmosphere, both (MePDI)FeCH3 and (EtPDI)FeCH3 underwent reductive elimination of ethane to form the iron dinitrogen precatalysts, [(MePDI)Fe(N2)]2(μ-N2) and [(EtPDI)Fe(N2)]2(μ-N2), respectively, while (iPrPDI)FeCH3 proved inert to C-C bond formation. By contrast, addition of butadiene to all three iron methyl complexes induced ethane formation and generated the corresponding iron butadiene complexes, (RPDI)Fe(η4-C4H6) (R = Me, Et, iPr), known precatalysts for the [2+2] cycloaddition of olefins and dienes. Kinetic, crossover experiments, and structural studies were combined with magnetic measurements and Mössbauer spectroscopy to elucidate the electronic and steric features of the iron complexes that enable this unusual reductive elimination and precatalyst activation pathway. Transmetalation of methyl groups between iron centers was fast at ambient temperature and independent of steric environment or spin state, while the intermediate dimer underwent the sterically controlled rate-determining reaction with either N2 or butadiene to access a catalytically active iron compound.
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U2 - 10.1021/jacs.2c10547
DO - 10.1021/jacs.2c10547
M3 - Article
C2 - 36821524
AN - SCOPUS:85148955050
SN - 0002-7863
VL - 145
SP - 5061
EP - 5073
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 9
ER -