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Highly Selective Ortho‐Directed Dicarboxylation of Cyclopentadiene by Methylcarbonates and CO 2 or COS – First Insight into Co‐ordination Chemistry of New Ambident Ligands
Author(s) -
Vollgraff Tobias,
Sundermeyer Jörg
Publication year - 2021
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.202100300
Subject(s) - chemistry , cyclopentadiene , carboxylation , medicinal chemistry , lewis acids and bases , intramolecular force , regioselectivity , stereochemistry , delocalized electron , nuclear magnetic resonance spectroscopy , isoprene , organic chemistry , catalysis , copolymer , polymer
Abstract This research presents the highly regioselective syntheses of 1,2‐dicarboxylated cyclopentadienide salts [Cat] 2 [C 5 H 3 (CO 2 ) 2 H] by reaction of a variety of organic cation methylcarbonate salts [Cat]OCO 2 Me (Cat=NR 4 + , PR 4 + , Im + ) with cyclopentadiene (CpH) or by simply reacting organic cation cyclopentadienides Cat[Cp] (Cat=NR 4 + , PR 4 + , Im + ) with CO 2 . One characteristic feature of these dianionic ligands is the acidic proton delocalized in an intramolecular hydrogen bridge (IHB) between the two carboxyl groups, as studied by 1 H NMR spectroscopy and XRD analyses. The reaction cannot be stopped after the first carboxylation. Therefore, we propose a Kolbe‐Schmitt phenol‐carboxylation related mechanism where the acidic proton of the monocarboxylic acid intermediate plays an ortho‐ directing and CO 2 activating role for the second kinetically accelerated CO 2 addition step exclusively in ortho position. The same and related thiocarboxylates [Cat] 2 [C 5 H 3 (COS) 2 H] are obtained by reaction of COS with Cat[Cp] (Cat=NR 4 + , PR 4 + , Im + ). A preliminary study on [Cat] 2 [C 5 H 3 (CO 2 ) 2 H] reveals, that its soft and hard coordination sites can selectively be addressed by soft Lewis acids (Mo 0 , Ru 2+ ) and hard Lewis acids (Al 3+ , La 3+ ).