Electrochimica Acta 50 (2005) 1383–1390 The positive effect of oxygenated solvents for the synthetic use of electroregenerated ytterbium(II)  Bernardo A. Frontana-Uribe a,∗,1 , R. Daniel Little b a Laboratorio de Electroqu´ ımica y Electros´ ıntesis, Instituto de Qu´ ımica de la Universidad Nacional Aut´ onoma de M´ exico, Circuito Exterior, Ciudad Universitaria, Coyoac´ an 04510, DF, Mexico b Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106-9510, USA Received 17 June 2004; received in revised form 17 August 2004; accepted 21 August 2004 Available online 1 October 2004 Abstract The addition of an oxygen based solvent, THF for example, to classical electrochemical media (DMF or ACN) improved the electrochemical behavior of the Yb(III)/Yb(II) couple. Two highlights of using 2:1 THF–DMF include the diminishing of the passivation at the carbon vitreous electrode when successive cycles are recorded and the almost totally reversible response of the system. The complexing effect of THF positively affects the electron-transfer kinetics of the redox couple, being faster in DMF–THF than in ACN–THF. A similar complexation effect was confirmed using tetraglyme as a cosolvent. The use of 2:1 THF–DMF allowed us to successfully substitute reticulated vitreous carbon in place of mercury as the working electrode for the Yb(II) electrogeneration experiments. Due to the stability of the alcoholate–Yb(III) complex, the recycling of Yb(III) to Yb(II) could not be achieved in the pinacolization reactions that were attempted. © 2004 Elsevier Ltd. All rights reserved. Keywords: Ytterbium; Electrosynthesis; Mediators; Cyclic voltammetry; Electrocatalysis 1. Introduction Electrogenerated reagents have been used in organic chemistry to improve selectivity and reduce costs. Electro- generated redox reagents appear to have particularly promis- ing applications in the field of redox catalysis [1]. Among them, samarium and ytterbium and their low valent salts have frequently been used by organic chemists because of their rich reducing chemistry [2–4]. Because the Yb(III/II) couple has a lower redox potential than Sm(III/II) (E Yb(III/II) = -1.1 versus E Sm(III/II) = -1.55 versus SHE) [5], the selective re- duction of organic compounds can be envisaged. The electro- regeneration of Sm(II) is well established and has been used efficiently in organic chemistry by the Du˜ nach–Perichon re-  Contribution 2472 from Instituto de Qu´ ımica, UNAM. ∗ Corresponding author. Tel.: +52 55 56224507; fax: +52 55 56162217/56162203. E-mail address: bafrontu@servidor.unam.mx (B.A. Frontana-Uribe). 1 ISE Member. search groups during the 1990s [6,7]. In contrast, the elec- troregeneration of Yb(II) has not been developed to satisfac- tion; only recently have studies in the area been published [8,9]. In previous investigations [8,9], the electrogeneration of YbBr 2 was accomplished using acetonitrile or DMF as the solvent with tetrabutylammonium bromide (TBABr) as the supporting electrolyte and mercury as the working electrode. The stoichiometric pinacol coupling of dibenzoylpropane us- ing Yb(OTf) 3 as the Yb(II) source proved to be stereospe- cific under these conditions [8]. In contrast, two problems were detected when attempting to electroregenerate Yb(II) in this reaction: (a) fast passivation occurs using solid elec- trodes, but not with toxic mercury; (b) a strong complex- ation occurs between the two oxygen atoms of the adduct and the Yb(III) cation that is generated after the electron transfer. This complex is so stable that Yb(III) cannot eas- ily be freed to allow its return to Yb(II). Thus a competi- tive reaction is needed to liberate Yb(III) from this complex [9]. 0013-4686/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2004.08.027