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

Abstract

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.

Palanquin-Like Cu4Na4 Silsesquioxane Synthesis (via Oxidation of 1,1-bis(Diphenylphosphino)methane), Structure and Catalytic Activity in Alkane or Alcohol Oxidation with Peroxides

“…It is important to note that the oxidation of dppm to dppmO2 was previously reported in the literature [40]. Moreover, some examples of oxidations during CLMS synthesis were described [33,34,37,[41][42][43][44][45], but to the best of our knowledge, no single example of CLMS synthesis accompanied by dppm oxidation has been reported to date. An additional and intriguing feature of such oxidation that acted favorably in aiding the formation of 1 is the requirement of mild conditions.…”

Cage‐like Copper(II) Silsesquioxanes: Transmetalation Reactions and Structural, Quantum Chemical, and Catalytic Studies

“…To the best of our knowledge,q uantum chemical calculation on CLMSs is the rarest type of such modeling. [20] Possibly,t he realization of such calculations was constrained by the huge size of such clusters. In turn, quantum chemical calculations may be useful to reveal the electronic structure of these compounds.…”

A Heterobimetallic Superoxide Complex formed through O2 Activation between Chromium(II) and a Lithium Cation

“…[11] A dinuclear chromium(II) complex based on a tripodal siloxide ligand, PhSi(OSiPh 2 O À ) 3 , cleaved O 2 forming a complex in which two Cr IV =O units form a unique asymmetric diamond core that is still reactive towards O 2 : It mediates THF oxidation with labelled O 2 and during this process the O 2 exchanges its label, not only with the terminal oxido ligand but also with the O atoms of the siloxide ligand. [11] We reckoned that by decreasing the ligand complexity further information on the formation of the initial O 2 activation steps might be gathered and therefore employed 1,1,3,3-tetraphenyl-1,3-disiloxandiol (LH 2 ) as a ligand precursor, providing [-OSi(Ph) 2 O À ] donor functions, too, but only two per ligand entity. LH 2 dissolved in THF was deprotonated and subsequently 0.5 equivalent of CrCl 2 was added at room temperature (Scheme 2).…”