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Iron‐Catalyzed Olefin Metathesis with Low‐Valent Iron Alkylidenes
Author(s) -
Mauksch Michael,
Tsogoeva Svetlana B.
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201702276
Subject(s) - olefin fiber , cycloaddition , olefin metathesis , catalysis , chemistry , metathesis , cyclopropanation , activation barrier , salt metathesis reaction , stereochemistry , medicinal chemistry , photochemistry , organic chemistry , polymerization , polymer
Inspired by recent reports of low‐valent iron‐complex‐catalyzed formal [2+2] cycloaddition of olefins, we demonstrate computationally that with such low‐valent iron complexes and with “strong” ligands, the olefin metathesis is also preferred over the undesired cyclopropanation side‐reaction, competition already studied by Hoffmann and co‐workers almost 40 years ago ( J. Am. Chem. Soc . 1981 , 103 , 5582). The [2+2] cycloaddition step in metathesis propagation, which gives a Chauvin‐type metallacyclobutane intermediate, is proposed to proceed either via a planar four‐electron Craig–Möbius aromatic [π2 s +π2 s ] transition‐state structure with a low barrier of 4.7 kcal mol −1 or, alternatively, via a twisted Zimmerman–Möbius aromatic [π2 s +π2 a ] transition state with a 5.5 kcal mol −1 activation‐energy barrier, with respect to an “encounter” π‐complex minimum obtained from an Fe II alkylidene and the entering olefin, while the corresponding triplet pathways are all disfavored.