Oxygen Activation by Copper Complexes with an Aromatic Bis(guanidine) Ligand.

Combining the new aromatic bis(guanidine) ligand bis(tetramethylguanidino)toluene (TMG²tol) and different copper salts led to four new complexes. The molecular structures were analysed by X-ray diffraction. Three of the complexes are active in biomimetic activation of oxygen. It is the first time a bis-µ-oxido species of an aromatic guanidine copper complex is analysed by Raman and UV/Vis spectroscopy. The formation and decay of the bis(µ-oxido)dicopper species were investigated at low temperatures up to 273 K by UV/Vis spectroscopy with a stopped-flow setup. The results showed that theCu₂O₂ intermediate of an aromatic guanidine-copper complex decays much faster than most known bis(guanidine) complexes. Moreover, natural bond orbital (NBO) analyses revealed that the aromatic guanidine is the stronger donor compared to the aliphatic one. [ABSTRACT FROM AUTHOR]