Premium
Dioxygen Activation of a Trinuclear Cu I Cu I Cu I Cluster Capable of Mediating Facile Oxidation of Organic Substrates: Competition between O‐Atom Transfer and Abortive Intercomplex Reduction
Author(s) -
Maji Suman,
Lee Jason C.M.,
Lu YuJhang,
Chen ChangLi,
Hung MuCheng,
Chen Peter P.Y.,
Yu Steve S.F.,
Chan Sunney I.
Publication year - 2012
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.201103075
Subject(s) - chemistry , propionitrile , acetonitrile , electron paramagnetic resonance , benzonitrile , photochemistry , absorption spectroscopy , adduct , medicinal chemistry , electron transfer , crystallography , inorganic chemistry , organic chemistry , physics , nuclear magnetic resonance , quantum mechanics
The dioxygen activation of a series of Cu I Cu I Cu I complexes based on the ligands ( L ) 3,3′‐(1,4‐diazepane‐ 1,4‐diyl)bis(1‐{[2‐(dimethylamino)ethyl](methyl)amino}propan‐2‐ol) ( 7‐Me ) or 3,3′‐(1,4‐diazepane‐1,4‐diyl)bis(1‐{[2‐(diethylamino)ethyl](ethyl)amino}propan‐2‐ol) ( 7‐Et ) forms an intermediate capable of mediating facile O‐atom transfer to simple organic substrates at room temperature. To elucidate the dioxygen chemistry, we have examined the reactions of 7‐Me , 7‐Et , and 3,3′‐(1,4‐diazepane‐1,4‐diyl)bis[1‐(4‐methylpiperazin‐1‐yl)propan‐2‐ol] ( 7‐N‐Meppz ) with dioxygen at −80, −55, and −35 °C in propionitrile (EtCN) by UV‐visible, 77 K EPR, and X‐ray absorption spectroscopy, and 7‐N‐Meppz and 7‐Me with dioxygen at room temperature in acetonitrile (MeCN) by diode array spectrophotometry. At both −80 and −55 °C, the mixing of the starting [Cu I Cu I Cu I ( L )] 1+ complex ( 1 ) with O 2 ‐saturated propionitrile (EtCN) led to a bright green solution consisting of two paramagnetic species: the green dioxygen adduct [Cu II Cu II (μ‐η 2 :η 2 ‐peroxo)Cu II ( L )] 2+ ( 2 ) and the blue [Cu II Cu II (μ‐O)Cu II ( L )] 2+ species ( 3 ). These observations are consistent with the initial formation of [Cu II Cu II (μ‐O) 2 Cu III ( L )] 1+ ( 4 ), followed by rapid abortion of this highly reactive species by intercluster electron transfer from a second molecule of complex 1 to give the blue species 3 and subsequent oxygenation of the partially oxidized [Cu II Cu I Cu I ( L )] 2+ ( 5 ) to form the green dioxygen adduct 2 . Assignment of 2 to [Cu II Cu II (μ‐η 2 :η 2 ‐peroxo)Cu II ( L )] 2+ is consistent with its reactivity with water to give H 2 O 2 and the blue species 3 , as well as its propensity to be photoreduced in the X‐ray beam during X‐ray absorption experiments at room temperature. In light of these observations, the development of an oxidation catalyst based on the tricopper system requires consideration of the following design criteria: 1) rapid dioxygen chemistry; 2) facile O‐atom transfer from the activated cluster to substrate; and 3) a suitable reductant to rapidly regenerate complex 1 to accomplish efficient catalytic turnover.