A heterobimetallic superoxide complex formed through O2 activation between chromium(II) and a lithium cation.

The reaction of 1,1,3,3-tetraphenyl-1,3-disiloxandiol (LH2) with n-butyllithium and CrCl2 results in a mononuclear chromium(II) complex (1) that further reacts with O2 at low temperatures to yield a mononuclear chromium(III) superoxide complex [L2CrO2(THF)][Li2(THF)3] (2). The crystal structure revealed that the chromium superoxido entity is stabilized by the coordination to an adjacent lithium cation. Complex 2 thus contains an unprecedented heterobimetallic [Cr(III)(µ-O2)Li(+)] core; beyond this it is the first chromium superoxide for which a temperature-dependent magnetic characterization could be achieved, and the first structurally characterized representative with chromium in an exclusive O-donor environment.

Dioxygen activation by siloxide complexes of chromium(II) and chromium(IV).

The reaction of a tripodal trisilanol with n-butyllithium and CrCl2 results in a dinuclear Cr(II) complex (1), which is capable of cleaving O2 to yield in a unique complex (2) with an asymmetric diamond core composed of two Cr(IV) O units. Magnetic susceptibility data reveal significant exchange coupling of Cr(II) (S=2) in 1 and large zero-field splitting for Cr(IV) (S=1) in 2 owing to strong spin-orbit coupling of the ground state. The Cr(IV) O compound can also be generated using PhIO, and evidence was gathered that although it is the stable product isolated after excessive O2 treatment, it further activates O2 to yield an intermediate species that oxidizes THF or Me-THF. By extensive (18) O labeling studies we were able to show, that in the course of this process (18) O2 exchanges its label with siloxide O atoms of the ligand via terminal oxido ligands.