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.