期刊
JACS AU
卷 3, 期 7, 页码 2007-2024出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacsau.3c00229
关键词
iron; metallacycle; ethylene; cycloaddition; hydrovinylation
A series of C-S-symmetric (aryl,alkyl)-substituted pyridine(dimine) iron methyl ((Cy)ARPDI)FeCH3 complexes have been synthesized and used as precatalysts for [2+2] cycloaddition. The chemoselectivity of the reaction is affected by the stability and resting state of the catalyst, leading to the formation of vinylcyclobutane and (Z)-hexa-1,4-diene.
A series of C-S-symmetric (aryl,alkyl)-substituted pyridine(dimine) iron methyl ((Cy)ARPDI)FeCH3 complexes have been prepared, characterized, and evaluated as precatalysts for the [2+2]-cycloaddition of butadiene and ethylene. Mixtures of vinylcyclobutane and (Z)-hexa-1,4-diene were observed in each case. By comparison, C-2v-symmetric, arylated (PDI) iron catalysts are exclusively selective for reversible [2+2]-cycloaddition to yield vinylcyclobutane. The alteration in the chemoselectivity of the catalytic reaction was investigated through a combination of precatalyst stability studies, identification of catalytic resting state(s), and H-2 and C-13 isotopic labeling experiments. While replacement of an aryl-imine substituent with an N-alkyl group decreases the stability of the formally iron(0) dinitrogen and butadiene complexes, two diamagnetic metallacycles were identified as catalyst resting states. Deuterium labeling and NOESY/EXSY NMR experiments support 1,4-hexadiene arising from catalytic hydrovinylation involving reversible oxidative cyclization leading to accessible cis-metallacycle. Cyclobutane formation proceeds by irreversible C(sp(3))-C(sp(3)) bond-forming reductive elimination from a trans-metallacycle. These studies provide key mechanistic understanding into the high selectivity of bis(arylated) pyridine(diimine) iron catalysts for [2+2]-cycloaddition, unique, thus far, to this class of iron catalysts.
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