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Synchronizing Steric and Electronic Effects in {Ru II (NNNN,P)} Complexes: The Catalytic Dehydrative Alkylation of Anilines by Using Alcohols as a Case Study
Author(s) -
Weickmann Daniel,
Frey Wolfgang,
Plietker Bernd
Publication year - 2013
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.201203285
Subject(s) - chemistry , reactivity (psychology) , alkylation , ligand (biochemistry) , phosphine , steric effects , aniline , medicinal chemistry , benzyl alcohol , catalysis , redox , substituent , stereochemistry , photochemistry , organic chemistry , medicine , biochemistry , alternative medicine , receptor , pathology
A series of new hexacoordinated {Ru II (NNNN,P)} complexes was prepared from [RuCl 2 (R 3 P) 3 ]. Their structure was determined by X‐ray crystallography. The catalytic potential of this new class of complexes was tested in the alkylation of aniline with benzyl alcohol. In this test reaction, the influence of the counteranion plus electronic influences at the tetradentate ligand and the phosphine ligand were examined. The electrochemistry of all complexes was studied by cyclic voltammetry. Depending on the substituent at the ligand backbone, the complexes showed a different behavior. For all N ‐benzyl substituted complexes, reversible Ru II/III redox potentials were observed, whereas the N ‐methyl substituted complex possessed an irreversible oxidation event at small scan rates. Furthermore, the electronic influence of different substituents at the ligand scaffold and at the phosphine on the Ru II/III redox potential was investigated. The measured E 0 values were correlated to the theoretically determined HOMO energies of the complexes. In addition, these HOMO energies correlated well with the reactivity of the single complexes in the alkylation of aniline with benzyl alcohol. The exact balance of redox potential and reactivity appears to be crucial for synchronizing the multiple hydrogen‐transfer events. The optimized catalyst structure was applied in a screening on scope and limitation in the catalytic dehydrative alkylation of anilines by using alcohols.