Simple syntheses, structural diversity, and Tishchenko reaction catalysis of neutral homoleptic rare Earth(II or III) 3,5-di-tert-butylpyrazolates -the structures of [Sc(tBu2pz)3], [Ln2(tBu2pz)6] (Ln = La, Nd, Yb, Lu), and [Eu4(tBu2pz)8]

Glen B. Deacon, Alex Gitlits, Peter W. Roesky, Markus R. Bürgstein, Kevin C. Lim, Brian W. Skelton, Allan H. White

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Abstract

The homoleptic rare-earth pyrazolate complexes [Sc(tBu2pz)3], [Ln2(tBu2pz)6] (Ln = La, Nd, Sm, Lu), [Eu4(tBu2pz)8] and the mixed oxidation state species [Yb2(tBu2pz)5] (tBu2pz = 3,5-di-tert-butylpyrazolate) have been prepared by a simple reaction between the corresponding rare-earth metal and 3,5-di-tert-butylpyrazole, in the presence of mercury, at elevated temperatures. In addition, [Yb2(tBu2pz)6] was prepared by redox transmetallation/ligand exchange between ytterbium, diphenyl-mercury(II) and tBu2pzH in toluene, whilst the same reactants in toluene under different conditions or in diethyl ether gave [Yb2(tBu2pz)5]. The complexes of the trivalent lanthanoids display dimeric structures [Ln2(tBu2pz)6] (Ln = La, Nd, Yb, Lu) with chelating η2-terminal and η22-bridging pyrazolate coordination. The considerably smaller Sc3+ ion forms monomeric [Sc(tBu2pz)3] of putative D3h molecular symmetry, with pyrazolate ligands solely η2-bonded. [Eu4(tBu2pz)8] is a structurally remarkable tetranuclear EuII complex with two types of europium centres in a linear array. The outer two are bonded to one terminal and two bridging pyrazolates, and the inner two are coordinated by four bridging ligands. Unprecedented μ-η52 pyrazolate ligation is observed, with each outer Eu2+ sandwiched between two η5-bonded pyrazolate groups, which are also η2-linked to an inner Eu2+. The two inner Eu2+ ions are linked together by two equally occupied components of each of two symmetry related, disordered pyrazolate groups with one component η42 bridging and one η32 bridging. [La2-(tBu2pz)6] has also been shown to be a Tishchenko reaction catalyst with several organic substrates.

Original languageEnglish
Pages (from-to)127-138
Number of pages12
JournalChemistry - A European Journal
Volume7
Issue number1
Publication statusPublished - 5 Jan 2001

Keywords

  • Catalysts
  • Lanthanides
  • N ligands
  • Pyrazolates
  • Rare-earth metals
  • Structure elucidation

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