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Copper(II) Complexes of 2,2′:6′,2″‐Terpyridine Derivatives for Catalytic Aerobic Alcohol Oxidations – Observation of Mixed‐Valence Cu I Cu II Assembles
Author(s) -
Zhang Guoqi,
Liu E,
Yang Chengxiong,
Li Li,
Golen James A.,
Rheingold Arnold L.
Publication year - 2015
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.201403140
Subject(s) - chemistry , catalysis , copper , valence (chemistry) , supramolecular chemistry , reactivity (psychology) , terpyridine , benzaldehyde , coordination sphere , alcohol oxidation , alcohol , redox , medicinal chemistry , inorganic chemistry , coordination complex , photochemistry , polymer chemistry , metal , crystallography , organic chemistry , crystal structure , medicine , alternative medicine , pathology
The reactions of copper(II) salts with simple terpyridine (tpy) ligands gave mononuclear monoligand complexes 1 – 3 , of which two new structures have been characterized by X‐ray crystallography. These complexes were applied as catalysts for the oxidation of benzylic alcohol to benzaldehyde in air in the presence of the radical 2,2,6,6‐tetramethylpiperidinyl‐1‐oxyl (TEMPO). Copper complexes 1 and 2 are efficient catalysts for the reactions in water at 70 °C with 4‐dimethylaminopyridine (DMAP) as an extra base. The influence of TEMPO on the formation of new reactive intermediates during the catalytic reactions was tentatively investigated by introducing TEMPO into the reaction solutions of tpy derivatives with copper dichloride. Two new complexes with interesting solid‐state structures resulting from these reactions have been isolated and characterized. The coordination reactions in the presence of TEMPO led to new mixed‐valence Cu I Cu II supramolecular assembles ( 4 and 5 ), although they adopt either discrete complex or 1D polymeric structures. Further catalytic studies indicated that the mixed‐valence assembles 4 and 5 displayed higher catalytic activity than those of the mononuclear complexes under milder conditions. The relationship between the molecular structures of diverse copper complexes and their reactivity is discussed on the basis of the results obtained.