Bulky Ytterbium Formamidinates Stabilise Complexes with Radical Ligands, and Related Samarium “Tetracyclone” Chemistry

Daniel Werner, Xuefei Zhao, Stephen Peter Best, Laurent Maron, Peter C Junk, Glen B. Deacon

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19 Citations (Scopus)

Abstract

Divalent [Yb(DippForm)2(thf)n] (n=2 (1 a), or 1 (1 b), DippForm=N,N′-bis(2,6-diisopropylphenyl)formamidinate) complexes were treated with the ketones: 9-fluorenone (fn), or 2,3,4,5-tetraphenylcyclopentadienone (tpc, tetracyclone), giving ketyl complexes: [Yb(DippForm)2(fn.-O)(thf)] (2), and [Yb(DippForm)2(tpc.-O)] (3), respectively (ketyl=a radical anion containing a C.−O(−) group. By contrast, when perfluorobenzophenone (pfb) was treated with either 1 a or 1 b, transitory ketyl formation was followed by rapid decomposition through a C−F activation pathway, giving [YbF(DippForm)2(thf)] (4 a) and a highly unusual fluoride/oxide-bridged species: [Yb5F6O2(DippForm)5] (4 b). The reduction of diketones: 3,5-di-tert-butyl-1,2-benzoquinone (tbbq), 9,10-phenanthrenequinone (phen), or 1,2-acenaphthenequinone (acen), was also examined giving ketyl complexes: [Yb(DippForm)2(tbbq.-O2)] (5), [Yb(DippForm)2(phen.-O2)] (6), and [Yb(DippForm)2(acen.-O2)(thf)] (7). An unsolvated derivative of 7, namely [Yb(DippForm)2(acen.-O2)] (8), was obtained from PhMe. All ketyl complexes had suitably elongated C.−O bonds, were stable in both polar and non-polar solvents—an uncommon trait for rare-earth ketyl complexes—and, with the exception of 3, showed radical signals in ESR spectra. To investigate the reactivity of the tpc.-O ketyl complex, 3 was treated with oxidants (CS2, Se) and reducing agents (Mg0, KH, or [SmI2(thf)2]). Thus 3 was oxidised to tpc by Se. Treatment of 3 with KH led to a ligand exchange process giving an unusual diketyl species [Yb(DippForm)(tpc.-O)2(thf)2] (10), which has two cisoid tpc.-O ligands in very close proximity. When treated with [SmI2(thf)2], the tpc.-O ketyl was further reduced to a dianion (1-oxido-2,3,4,5-tetraphenylcyclopentadianide2−), ({C5Ph4}-O)2− by [SmI2(thf)2], giving dimeric [{SmI({C5Ph4}-O)(thf)2}2] (Sm11) and monomeric complexes [YbI(DippForm)2(thf)] (11 b) and [YbI2(DippForm)(thf)2] (11 c). Activated Sm metal reduced neutral tetracyclone to the dianion, ({C5Ph4}-O)2−, in THF, giving tetranuclear [{SmII 2({C5Ph4}-O)2(thf)3}2] (Sm13). Treatment of Sm13 with iodine in situ provided access to [{SmI({C5Ph4}-O)(thf)2}2] (Sm11), in good yield.

Original languageEnglish
Pages (from-to)2084-2102
Number of pages19
JournalChemistry - A European Journal
Volume23
Issue number9
DOIs
Publication statusPublished - 10 Feb 2017

Keywords

  • ketyl complexes
  • lanthanides
  • rare earths
  • reactivity
  • synthesis

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