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Osmium Complexes Coordinated with Poly(pyridylmethyl)diamine‐Based Hexadentate Ligands
Author(s) -
Sugimoto Hideki,
Kiriyama Kahori,
Itoh Shinobu
Publication year - 2018
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201701173
Subject(s) - osmium , chemistry , ligand (biochemistry) , pyridine , medicinal chemistry , octahedron , ethylenediamine , deprotonation , stereochemistry , crystal structure , crystallography , inorganic chemistry , ion , ruthenium , organic chemistry , biochemistry , receptor , catalysis
Osmium(II) and osmium(III) complexes with a potentially hexadentate ligand [ N , N , N′ , N′ ‐tetrakis(2‐pyridylmethyl)ethylenediamine, (TPEN)] are synthesized. The X‐ray structural analysis of [Os II/III (TPEN)](PF 6 ) 2/3 complexes reveals that the chelating ligand exhibits a hexadentate coordination fashion and induces distortion from a regular octahedron to the osmium centers. Due to this distortion, the osmium(III) center becomes labile toward substitution by chloride and bromide anions. The osmium(III) complex, [Os III (TPEN)](PF 6 ) 3 , reacts with Cl – and Br – to give the anion bound six coordinated osmium(III) complex {[Os III (Cl/Br)(κ 5 ‐TPEN)] 2+ }, in which one of the equatorial pyridine donor groups is dissociated from the osmium(III) center. Kinetic and spectroscopic studies on the reaction with Br – at a low temperature suggest that the ligand substitution involves an associative mechanism via a seven coordinate osmium(III) complex intermediate involving Br – , [Os III Br(κ 6 ‐TPEN)] 2+ . On the other hand, when the propylenediamine analogue [ N , N , N′ , N′ ‐tetrakis(2‐pyridylmethyl)propylenediamine, TPPN] is employed for the preparation of osmium(III) complex, [Os III (TPPN)](PF 6 ) 3 , the osmium(III) center displays a less distorted octahedral structure due to the longer alkylene tether. In contrast to the TPEN system, the osmium(III) complex of TPPN is reduced to the osmium(II) complex, [Os II (TPPN)](PF 6 ) 2 , upon the reaction with Cl – and Br – yielding Cl 2 or Br 2 . In this TPPN ligand system, associative mechanism involving an anion bound seven‐coordinate osmium(III) intermediate with the κ 6 ‐hexadentate ligand is suggested to be operated as in the case of the TPEN ligand system.