Werner, Daniel, Deacon, Glen B., Junk, Peter C., and Anwander, Reiner (2017) Pyrazolates advance cerium chemistry: a Ce-III/Ce-IV redox equilibrium with benzoquinone. Dalton Transactions, 46 (19). pp. 6265-6277.

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Abstract

Two stable cerium(IV) 3,5-dialkylpyrazolate complexes are presented, namely dimeric [Ce(Me(2)pz)(4)](2) (Me(2)pz = 3,5-dimethylpyrazolate) and monomeric Ce(tBu(2)pz)(4) (tBu(2)pz = 3,5-di-tert-butylpyrazolate) along with their trivalent counterparts [Ce(Me(2)pz)(3)] and [Ce(tBu(2)pz)(3)](2). All complexes were obtained from protonolysis reactions employing the silylamide precursors Ce[N(SiHMe2)(2)](4) and Ce[N(SiMe3)(2)](3). Treatment of homoleptic Ce-IV and Ce-III Me(2)pz complexes with 1,4-hydroquinone (H(2)hq) or 1,4-benzoquinone (bq), respectively, ultimately gave the same trimetallic Ce-III species via a cerium redox equilibrium. The Ce-III complex Ce-3(Me(2)pz)(5)(pchd)(2)(L) (pchd = 1,4-bis(3,5-dimethylpyrazol-1-yl)cyclohex-2,5-diene-1,4-diolato; L = Me(2)pzH or (thf)(2)) results from a di-1,4-pyrazolyl attack on pre-coordinated bq. The reduction of bq by [Ce(Me(2)pz)(3)(thf)](2), and re-oxidation by the resulting Ce-IV species was supported by UV-vis spectroscopic investigations. Comparisons with the redox-innocent complexes [Ln(Me(2)pz)(3)(thf)](2) (Ln = La and Pr) revealed far less selective reactions with bq, giving hexametallic and octametallic rare-earth metal side products containing 2-Me(2)pz substituted hq ligands.

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