Dioxygen Activation by Siloxide Complexes of Chromium(II) and Chromium(IV)

The reaction of a tripodal trisilanol with n ‐butyllithium and CrCl 2 results in a dinuclear Cr II complex ( 1 ), which is capable of cleaving O 2 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 O 2 treatment, it further activates O 2 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 O 2 exchanges its label with siloxide O atoms of the ligand via terminal oxido ligands.