Enhancing the value of free metals in the synthesis of lanthanoid formamidinates: is a co-oxidant needed?

Glen B Deacon, Peter C Junk, Daniel Werner

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20 Citations (Scopus)


Treatment of N,N'-bis(aryl)formamidines (ArFormH), N,N'-bis(2,6-difluorophenyl)formamidine (DFFormH) or N,N'-bis(2,6-diisopropylphenyl)formamidine (DippFormH), with europium metal in CH3CN is an efficient synthesis of the divalent complexes: [{Eu(DFForm)2(CH3CN)2}2] (Eu1) or [Eu(DippForm)2(CH3CN)4] (Eu2). The synthetic method was extended to ytterbium, but the metal required activation by addition of Hg0. With DFFormH in CH3CN, [{Yb(DFForm)2(CH3CN)}2] (Yb1) was obtained in good yield, and [Yb(DFForm)2(thf)3] (Yb3) was obtained from a synthesis in CH3CN/THF. Thus, this synthetic method completely circumvents the use of either salt metathesis, or redox transmetallation/protolysis (RTP) protocols to prepare divalent rare-earth formamidinates. Heating Yb1 in PhMe/C6D6 resulted in decomposition to trivalent products, including one from a CH3CN activation process. For a synthetic comparison, divalent ytterbium DFForm and DippForm complexes were synthesised by RTP reactions between Yb0, Hg(R)2 (R=Ph, C6F5), and ArFormH in THF, leading to the isolation of either [Yb(DFForm)2(thf)3] (Yb3), or the first five coordinate rare-earth formamidinate complex [Yb(DippForm)2(thf)] (Yb4 b), and, from adjustment of the stoichiometry, trivalent [Yb(DFForm)3(thf)] (Yb6). Oxidation of Yb3 with benzophenone (bp), or halogenating agents (TiCl4(thf)2, Ph3CCl, C2Cl6) gave [Yb(DFForm)3(bp)] or [Yb(DFForm)2Cl(thf)2], respectively. Furthermore, the structural chemistry of divalent ArForm complexes has been substantially broadened. Not only have the highest and lowest coordination numbers for divalent rare-earth ArForm complexes been achieved in Eu2 and Yb4 b, respectively, but also dimeric Eu1 and Yb1 have highly unusual ArForm bridging coordination modes, either perpendicular μ-1κ(N:N'):2κ(N:N') in Eu1, or the twisted μ-1κ(N:N'):2κ(N':F') DFForm coordination in Yb1, both unprecedented in divalent rare-earth ArForm chemistry and in the wider divalent rare-earth amidinate field.
Original languageEnglish
Pages (from-to)160-173
Number of pages14
JournalChemistry - A European Journal
Issue number1
Publication statusPublished - 2016


  • lanthanides
  • reactivity
  • redox transmetallation
  • synthetic methods
  • X-ray structures

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