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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
Quinoidal distortion in ferrocenyl- and cymantrenyl-substituted bis(4-CF3-phenyl)anthracenyl methylium ions
Anja Rehse1, Michael Linseis1, Rainer F Winter1
1Department of Chemistry, University of Konstanz, 78464 Konstanz, Germany. rainer.winter@uni-konstanz.de.
Abstract:
We present three new intensely colored ferrocenyl- (Fc-) (Fc = (η5-C5H5)Fe(η5-C5H4), 1+) and cymantrenyl-substituted (CpMn(CO)2(L); Cp = (η5-C5H4), L = CO in 2+, PiPr3 in 3+) triarylmethylium ions, in which a sterically demanding anthryl spacer links the (half-)sandwich donor to an electron-poor diarylmethylium acceptor (4-CF3-C6H4)2C+. Single-crystal X-ray studies as well as NOESY experiments reveal that these dyads exhibit strongly bent fulvene-anthraquinodimethane (AQDM) structures in the crystalline state and in solution, in which the positive charge is efficiently transmitted from the diarylmethylium unit to the (half-)sandwich complex entity. Despite large differences between the redox potentials for metal oxidation and tritylium reduction, EPR spectroscopy detects small amounts of paramagnetic open-shell isomers (valence tautomers) with one unpaired spin at each site. Reduction to neutral monoradicals 1˙-3˙ converts the AQDM to an anthryl linker, resulting in structural transformation from a folded to a twisted form.
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