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Metal‐Induced Tautomerization of p ‐ to o ‐Quinone Compounds: Experimental Evidence from Cu I and Re I Complexes of Azophenine and DFT Studies
Author(s) -
Frantz Stéphanie,
Rall Jochen,
Hartenbach Ingo,
Schleid Thomas,
Záliš Stanislav,
Kaim Wolfgang
Publication year - 2004
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.200305369
Subject(s) - tautomer , chemistry , ligand (biochemistry) , metal , yield (engineering) , transition metal , proton , hydrogen bond , crystallography , medicinal chemistry , molecule , materials science , organic chemistry , catalysis , biochemistry , receptor , metallurgy , physics , quantum mechanics
Abstract Azophenine (7,8‐diphenyl‐2,5‐bis(phenylamino)‐ p ‐quinonediimine, L p ) reacts with [Cu(PPh 3 ) 4 ](BF 4 ) or [Re(CO) 5 Cl] to yield the (Ph 3 P) 2 Cu + or [(OC) 3 ClRe] complex of the tautomeric form 7,8‐diphenyl‐4,5‐bis(phenylamino)‐ o ‐quinonediimine, L o , as evident from structure determinations and from very intense metal‐to‐ligand charge transfer (MLCT) transitions in the visible region. Time‐dependent DFT (TD‐DFT) calculations on model complexes [(N∩N)Re(CO) 3 Cl] confirm the spectroscopic results, showing considerably higher oscillator strengths of the MLCT transition for the o ‐quinonediimine complexes in comparison to compounds with N∩N=1,4‐dialkyl‐1,4‐diazabutadiene. The complexes are additionally stabilized through hydrogen bonding between two now ortho ‐positioned NHPh substituents and one fluoride of the BF 4 − anion (Cu complex) or the chloride ligand (Re complex). DFT Calculations on the model ligands p ‐quinonediimine or 2,5‐diamino‐ p ‐quinonediimine and their ortho ‐quinonoid forms with and without Li + or Cu + are presented to discuss the relevance for metal‐dependent quinoproteins.