Activation of Dioxygen at a Lewis Acidic Nickel(II) Complex: Characterization of a Metastable Organoperoxide Complex

Abstract

In metal-mediated O activation, nickel(II) compounds hardly play a role, but recently it has been shown that enzymes can use nickel(II) for O activation. Now a low-coordinate Lewis acidic nickel(II) complex has been synthesized that reacts with O to give a nickel(II) organoperoxide, as proposed for the enzymatic system. Its formation was studied further by UV/Vis absorption spectroscopy, leading to the observation of a short-lived intermediate that proved to be reactive in both oxygen atom transfer and hydrogen abstraction reactions, while the peroxide efficiently transfers O atoms. Both for the enzyme and for the functional model, the key to O activation is proposed to represent a concomitant electron shift from the substrate/co-ligand.

Synthesis and Reactivity of Heteroleptic Ga‐P‐C Allyl Cation Analogues

“…ligand backbone.N ucleophilic bond-forming reactions involving the g-carbon have been previously reported for bdiketiminate stabilized cationic transition metal [32] and Al complexes [33] as well as neutral metal complexes [34] with heteroallenes,t hat is,C O 2 ,C S 2 ,d iphenylketene,i so-(thio)cyanates,a nd other unsaturated substrates including oxygen and ethylene. [35] However,t ot he best of our knowledge,t he formation of at ripodal N,N',N'' ligand as observed in compound 7 was only reported for the reaction between [LMg(n-Bu)] 2 and phenylisothiocyanate, [36] while the CÀC bond forming reaction of LLi with t-BuNCO yielded the isocyanate insertion product [{(MeCN-2,6-i-Pr 2 C 6 H 3 ) 2 C-(CONH(t-Bu))}Li•TMEDA],i nw hich the Li cation is coordinated in an N,O-chelating mode.…”

Activation of Molecular Hydrogen and Oxygen by PSiP Complexes of Cobalt

“…Interestingly, exposure of the siloxane species K to O 2 does not lead to the formation of J . In the case of the Ni example G , O 2 activation involving Ni II is generally not well‐established . Moreover, the observation of multiple unidentified products in this reaction further complicates the mechanistic possibilities .…”

Stabilization of β‐Diketiminato Nickel(I) with Alkaline Metal Halide Entities for Small Molecule Activation

“…The KBr entities are readily released in the presence of donors – as has been observed previously also for LiBr adducts – and the fact that even the rather weak donor N 2 replaces the alkali metal halide moieties shows that the latter represent rather labile leaving groups with low donor strength. They are thus suitable as placeholders in complexes that activate small molecules, and this recently has been exploited in nickel(II) chemistry . Furthermore, the presence of stoichiometric amounts of a Lewis acid – namely potassium ions – may influence the activation process or allow for the trapping of intermediates.…”