Metal-induced tautomerization of p- to o-quinone compounds: Experimental evidence from CuI and ReI complexes of azophenine and DFT studies

, , , , , und . Chemistry - A European Journal 10 (1): 149--154 (2004)


Azophenine (7,8-diphenyl-2,5-bis(phenylamino)-p-quinonediimine, Lp) reacts with Cu(PPh3)4(BF4) or Re(CO)5Cl to yield the (Ph3P)2Cu+ or (OC)3ClRe complex of the tautomeric form 7,8-diphenyl-4,5-bis(phenylamino)-o-quinonediimine, Lo, as evident from structure detns. and from very intense metal-to-ligand charge transfer (MLCT) transitions in the visible region. Time-dependent DFT (TD-DFT) calcns. on model complexes (N-N)Re(CO)3Cl (e.g., N-N = 1,4-dialkyl-1,4-diazabutadiene) confirm the spectroscopic results, showing considerably higher oscillator strengths of the MLCT transition for the o-quinonediimine complexes in comparison to compds. with N-N = 1,4-dialkyl-1,4-diazabutadiene. The complexes are addnl. stabilized through H 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 Calcns. 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 quino-proteins. on SciFinder(R)

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