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

Deacon, Glen B., Junk, Peter C., and Werner, Daniel (2016) Enhancing the value of free metals in the synthesis of lanthanoid formamidinates: is a co-oxidant needed? Chemistry: a European journal, 22 (1). pp. 160-173.

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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.

Item ID: 43333
Item Type: Article (Refereed Research - C1)
Keywords: lanthanides, reactivity, redox transmetallation, synthetic methods, X-ray structures
ISSN: 1521-3765
Funders: Australian Research Council (ARC)
Projects and Grants: ARC Discovery grant DP130100152
Date Deposited: 24 Feb 2016 07:33
FoR Codes: 03 CHEMICAL SCIENCES > 0302 Inorganic Chemistry > 030202 f-Block Chemistry @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970103 Expanding Knowledge in the Chemical Sciences @ 100%
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