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]

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 η2‐terminal and η2:η2‐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‐η5:η2 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 η4:η2 bridging and one η3:η2 bridging. [La2(tBu2pz)6] has also been shown to be a Tishchenko reaction catalyst with several organic substrates. Structural variety and novelty, including the new μ‐η5:η2 pyrazolate coordination mode, are exhibited by homoleptic rare‐earth pyrazolates (an example is illustrated here) that have been prepared by the direct reaction of the elements with 3,5‐di‐tert‐butylpyrazole. The [La2(tBu2pz)6] complex works as an effective Tishchenko reaction catalyst.