Simple Syntheses, Structural Diversity, and Tishchenko Reaction Catalysis of Neutral Homoleptic Rare Earth(II orIII) 3,5-Di-tert-butylpyrazolates—The Structures of [Sc(tBu2pz)3], [Ln2(tBu2pz)6] (Ln=La, Nd, Yb, Lu), and [Eu4(tBu2pz)8]

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.

Distortion Pathways of Transition Metal Coordination Polyhedra Induced by Chelating Topology

“…It must be noted that the complexes that appear most twisted toward trigonal prisms are those of metal ions with d 0 , d 1 , d 2 , d 5 , or d 10 electron configurations, which are known to have an electronic preference for the trigonal prismatic geometry . Thus, the most twisted coordination polyhedron with ligands containing the dimethoxyethane skeleton belongs to a Zn­(II) malato complex that has θ < 30°, while with ethylenediamine two Cd­(II) complexes are nearly trigonal prismatic. , Cd­(II) is also present in the most trigonal prismatic dithiocarbamate complexes, − a trigonal prismatic complex with nitrato ligands has Ag­(I) as its central ion, and Fe­(III) and Sc­(III) are present in trigonal prismatic pyrazolato complexes. Even complexes with a large bite angle ligand such as the diketonates can appear in a trigonal prismatic geometry with the appropriate electron configuration, as in Cd­(II) and Y­(III) compounds.…”

Developments in the Coordination Chemistry of Europium(II)

“…Mercury, which activates Eu 0 through amalgamation, was used to prepare the homoleptic and tetranuclear Eu 2+ complex Eu 4 [( t Bu) 2 pz] 8 ( 16 ) in which ( t Bu) 2 pz is 3,5-di- tert -butylpyrazolate (Figure 4). [34] Structural elucidation of linear complex 16 revealed different coordination modes (η 2 , μ-η 5 :η 2 , and μ-η 2 :η 2 ) of the pyrazolate groups to Eu 2+ . The outer Eu 2+ ions are bonded in a η 2 fashion by the two terminal pyrazolate groups; a μ-η 5 :η 2 coordination mode is observed for the four pyrazolate groups that bridge the inner and outer Eu 2+ ions; and a μ-η 2 :η 2 binding mode is exhibited by the two pyrazolate groups that bridge the two inner Eu 2+ centers.…”

“…The outer Eu 2+ ions are bonded in a η 2 fashion by the two terminal pyrazolate groups; a μ-η 5 :η 2 coordination mode is observed for the four pyrazolate groups that bridge the inner and outer Eu 2+ ions; and a μ-η 2 :η 2 binding mode is exhibited by the two pyrazolate groups that bridge the two inner Eu 2+ centers. [34] …”

The AHA Moment: Assessment of the Redox Stability of Ionic Liquids Based on Aromatic Heterocyclic Anions (AHAs) for Nuclear Separations and Electric Energy Storage

“…Such AHAs are as weakly coordinating as the more familiar imide anions (e.g., bistriflimide and dicyanamide) that are widely used to compose IL diluents. Furthermore, this coordination can be exploited rather than avoided (e.g., refs − ; see also ref ), as AHAs have “soft” nitrogen atoms that can covalently interact with 4f and 5f electrons, enabling ion selectivity. In fact, many of the selective extraction agents for separations of minor actinides from lanthanides (which rely on “soft” atom interactions) include the protonated AHAs shown in Schemes and , for example, 6-methyl-2-(2-pyridyl)­benzimidazole, and the closely related triazinylpyridine N -donor ligands (see ref and references therein).…”