[Lithium tert-butylperoxide]12 : Crystal Structure of an Aggregated Oxenoid

Abstract

The X-ray crystal structure of the dodecameric lithium tert-butylperoxide [2]₁₂ is the first of an alkali or alkaline earth peroxide. It shows the lithium ion bridging the two oxygen atoms of the peroxide unit and a slight lenghtening of the O-O bond, in agreement with quantum-chemical calculations. A calculation for the model reaction of MeLi with LiOOH to give MeOLi and LiOH reveals the importance of Li bridging the O-O bond in the transition state of this reaction, as similarly discussed for many oxidation reactions of (transition-) metal peroxides. Preliminary theoretical studies of the O-O bond length (and thus of the oxenoid character) as a function of the aggregation of 2 disclose that increasing aggregation leads to stabilization of the charge at the anionic oxygen atom and thus to a reduction of the O-O bond length (oxenoid character). Related considerations of the effect of aggregation should also be valid for other lithium (organometallic) compounds and their structure and reactivity as well as other properties.

Keywords: aggregates; lithium compounds; oxenoids; peroxides; structure elucidation.