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

• Published in: Angewandte Chemie (International ed.) Vol. 53; no. 47; pp. 12741 - 12745
• Main Authors: Schax, Fabian, Bill, Eckhard, Herwig, Christian, Limberg, Christian
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 17.11.2014; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Activation; Asymmetry; chromium; Diamonds; dioxygen activation; Exchange; Ligands; Magnetic permeability; Marking; oxido complexes; scrambling; siloxides; Splitting; Terminals; siloxides; chromium; dioxygen activation; scrambling; oxido complexes
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201406313

The reaction of a tripodal trisilanol with n‐butyllithium and CrCl2 results in a dinuclear CrII complex (1), which is capable of cleaving O2 to yield in a unique complex (2) with an asymmetric diamond core composed of two CrIVO units. Magnetic susceptibility data reveal significant exchange coupling of CrII (S=2) in 1 and large zero‐field splitting for CrIV (S=1) in 2 owing to strong spin–orbit coupling of the ground state. The CrIV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 18O labeling studies we were able to show, that in the course of this process 18O2 exchanges its label with siloxide O atoms of the ligand via terminal oxido ligands. A dinuclear CrII siloxide complex was synthesized that cleaves O2 to yield a unique CrIV complex with an asymmetric core composed of two CrIVO units. Although it is the stable product isolated after excess O2 treatment, it further activates O2 to yield an intermediate species that oxidizes THF or Me‐THF. 18O labeling studies show that 18O2 and PhI18O thereby exchange with siloxide O atoms of the ligand.