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Atypical and Asymmetric 1,3‐P,N Ligands: Synthesis, Coordination and Catalytic Performance of Cycloiminophosphanes
Author(s) -
Rong Mark K.,
Holtrop Flip,
Bobylev Eduard O.,
Nieger Martin,
Ehlers Andreas W.,
Slootweg J. Chris,
Lammertsma Koop
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.202101921
Subject(s) - chemistry , catalysis , cyclohexanone , benzonitrile , triflic acid , medicinal chemistry , transfer hydrogenation , imine , stereochemistry , polymer chemistry , organic chemistry , ruthenium
Novel seven‐membered cyclic imine‐based 1,3‐P,N ligands were obtained by capturing a Beckmann nitrilium ion intermediate generated in situ from cyclohexanone with benzotriazole, and then displacing it by a secondary phosphane under triflic acid promotion. These “cycloiminophosphanes” possess flexible non‐isomerizable tetrahydroazepine rings with a high basicity; this sets them apart from previously reported iminophophanes. The donor strength of the ligands was investigated by using their P‐κ 1 ‐ and P,N‐κ 2 ‐tungsten(0) carbonyl complexes, by determining the IR frequency of the trans ‐CO ligands. Complexes with [RhCp*Cl 2 ] 2 demonstrated the hemilability of the ligands, giving a dynamic equilibrium of κ 1 and κ 2 species; treatment with AgOTf gives full conversion to the κ 2 complex. The potential for catalysis was shown in the Ru II ‐catalyzed, solvent‐free hydration of benzonitrile and the Ru II ‐ and Ir I ‐catalyzed transfer hydrogenation of cyclohexanone in isopropanol. Finally, to enable access to asymmetric catalysts, chiral cycloiminophosphanes were prepared from l ‐menthone, as well as their P,N‐κ 2 ‐Rh III and a P‐κ 1 ‐Ru II complexes.