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One‐ versus Two‐Electron Oxidation of Complexed Guanidino‐Functionalized Aromatic Compounds
Author(s) -
Trumm Christine,
Hübner Olaf,
Walter Petra,
Leingang Simone,
Wild Ute,
Kaifer Elisabeth,
Eberle Benjamin,
Himmel HansJörg
Publication year - 2014
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.201402840
Subject(s) - chemistry , dication , ligand (biochemistry) , unpaired electron , redox , photochemistry , electron transfer , non innocent ligand , oxidation state , crystallography , inorganic chemistry , radical , molecule , organic chemistry , catalysis , biochemistry , receptor
Herein, we report a rational synthetic access to dinuclear Cu II complexes with radical monocationic guanidine ligands. The starting point was the first directed synthesis of a dinuclear Cu II complex of the redox‐active, neutral guanidino‐functionalized aromatic (GFA) compound 1,2,4,5‐tetrakis(tetramethylguanidino)benzene ( 1 ) as ligand by treatment of 1 with Cu(OAc) 2 . The neutral complex [ 1 {Cu(OAc) 2 } 2 ] was then oxidized with several oxidizing reagents. With I 2 two‐electron oxidation occurred, thus leading to green salts of the dication [ 1 {Cu(OAc) 2 } 2 ] 2+ . In contrast, with AgPF 6 or AgSbF 6 one‐electron oxidation was observed to yield red salts of the monocation [ 1 {Cu(OAc) 2 } 2 ] + , which is a three‐spin system with one unpaired electron at each copper atom and at the ligand unit. Superconducting quantum interference device (SQUID) magnetometric measurements confirm a quartet electronic ground state that arises from strong ferromagnetic copper–ligand coupling. Intense charge‐transfer transitions in the visible region (576 and 536 nm) were observed in the electronic absorption spectra and assigned to strong ligand–ligand ( 1 · + ←OAc) charge‐transfer (LLCT) excitations. These LLCT bands open up the possibility of photoinduced redox reactions with [ 1 {Cu(OAc) 2 } 2 ] + driven by restoration of the aromatic system at the GFA ligand.