Simple syntheses, structural diversity, and Tishchenko reaction catalysis of neutral homoleptic rare earth(II or III) 3,5-di-tert-butylpyrazolates--the structures of |
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Authors: | Deacon G B Gitlits A Roesky P W Bürgstein M R Lim K C Skelton B W White A H |
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Institution: | School of Chemistry, Monash University, Victoria, Australia. glen.deacon@sci.monash.edu.au |
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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, diphenylmercury(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 eta2-terminal and eta2:eta2-bridging pyrazolate coordination. The considerably smaller Sc3+ ion forms monomeric Sc(tBu2pz)3] of putative D3h molecular symmetry, with pyrazolate ligands solely eta2-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 mu-eta5:eta2 pyrazolate ligation is observed, with each outer Eu2+ sandwiched between two eta5-bonded pyrazolate groups, which are also eta2-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 eta4:eta2 bridging and one eta3:eta2 bridging. La2(tBu2pz)6] has also been shown to be a Tishchenko reaction catalyst with several organic substrates. |
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