The homoleptic rare-earth pyrazolate complexes [Sc(tBu(2)pz)(3)], [Ln(2)(tBu(2)pz)(6)] (Ln=La, Nd, Sm, Lu), [Eu-4(tBu(2)pz)(8)] and the mixed oxidation state species [Yb-2(tBu(2)pz)(5)] (tBu(2)pz= 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, [Yb-2(tBu(2)pz)(6)] was prepared by redox transmetallation/ligand exchange between ytterbium, diphenyl-mercury(Ir) and tBu(2)pzH in toluene, whilst the same reactants in toluene under different conditions or in diethyl ether gave [Yb-2(tBu(2)pz)(5)]. The complexes of the trivalent lanthanoids display dimeric structures [Ln(2)(tBu(2)pz)(6)] (Ln = La, Nd, Yb, Lu) with chelating eta (2) terminal and eta (2):eta (2)-bridging pyrazolate coordination. The considerably smaller Sc3+ ion forms monomeric [Sc(tBu(2)pz)(3)] of putative D-3h molecular symmetry, with pyrazolate ligands solely eta (2)-bonded. [Eu-4(tBu(2)pz)(8)] is a structurally remarkable tetranuclear Eu-II 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-eta (5):eta (2) pyrazolate ligation is observed, with each outer EU2+ sandwiched between two eta (5)-bonded pyrazolate groups, which are also eta (2)-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 eta (4):eta (2) bridging and one eta (3):eta (2) bridging. [La-2-(tBu(2)pz)(6)] has also been shown to be a Tishchenko reaction catalyst with several organic substrates.
