Three oxidation states of the bis(3,5-di-tert-butyl-2-phenolato)azanido pincer ligand on chromium(III).

Three monomeric complexes of chromium(III) containing the redox-active ligand derived from bis(3,5-di- tert -butyl-2-phenol)amine, [ONO cat ]H 3 , were prepared and fully characterized. The potassium salt of [ONO q ] 1− reacted with CrCl 3 (THF) 3 to afford [ONO q ]CrCl 2 (THF) ( 1 ); whereas, the trilithium salt of [ONO cat ] 3− reacted with CrCl 3 (THF) 3 in the presence of pyridine to afford [ONO cat ]Cr(py) 3 ( 3 ). The three electron series was completed by reacting 1 with K[bpy ] to afford [ONO sq ]CrCl(bpy) ( 2 ). All three members of the series were characterized by structural, spectroscopic, and electrochemical methods. Attempts to effect the two-electron reduction of 1 resulted in the formation of a bimetallic chromium complex, {[ONO cat ]Cr(py) 2 } 2 ( 4 ), which was also structurally characterized. The reaction of 1 with aryl transfer reagents resulted in a mixture of one- and two-electron reactivity, comprising the expulsion of either phenyl radical or biphenyl from the chromium coordination sphere. [ABSTRACT FROM AUTHOR]