Peter W. Roesky

Pentanuclear Dysprosium Hydroxy Cluster Showing Single-Molecule-Magnet Behavior

A pentanuclear dysprosium hydroxy cluster of composition [Dy 5(mu 4-OH)(mu 3-OH) 4(mu-eta (2)-Ph 2acac) 4(eta (2)-Ph 2acac) 6] ( 1; Ph 2acac = dibenzoylmethanide) was prepared starting from [DyCl 3.6H 2O] and dibenzoylmethane. Both static (dc) and dynamic (ac) magnetic properties of 1 have been studied. Below 3 K, the appearance of slow relaxation of the magnetization typical for single-molecule magnets is seen, even if no hysteresis effects on the M vs H data are observed above 1.8 K.

Homoleptic lanthanide amides as homogeneous catalysts for alkyne hydroamination and the Tishchenko reaction.

The homoleptic bis(trimethylsilyl)amides of Group 3 metals and lanthanides of the general type [Ln[N(SiMe3)2]3] (1) (Ln=Y, lanthanide) represent a new class of Tishchenko precatalysts and, to a limited extent, precatalysts for the hydroamination/cyclization of aminoalkynes. It is shown that 1 is the most active catalyst for the Tishchenko reaction. This contribution presents investigations on the scope of the reaction, substrate selectivity, lanthanide-ion size-effect, and kinetic/mechanistic aspects of the Tishchenko reaction catalyzed by 1. The turnover frequency is increased by the use of large-center metals and electron-withdrawing substrates. The reaction rate is second order with respect to the substrate. While donor atoms, such as nitrogen, oxygen, or sulfur, on the substrate decrease the turnover frequency, 1 shows a tolerance for a large number of functional groups. For the hydroamination/cyclization of aminoalkynes, 1 is less active than the well-known metallocene catalysts. On the other hand, 1 is much more readily accessible (one-step synthesis or commercially available), than the metallocenes and might therefore be an attractive alternative catalyst.

Trigonal-Bipyramidal Lewis Base Adducts of Methyltrioxorhenium(VII) and Their Bisperoxo Congeners: Characterization, Application in Catalytic Epoxidation, and Density Functional Mechanistic Study

Pyrazole and pyridine adducts of methyltrioxorhenium(VII) form bisperoxo complexes with excess H2O2 (see picture). Density functional calculations reveal that the increased efficiency of these complexes as catalysts for olefin epoxidation originates from their stability and from the moderate energies of the corresponding transition states. Nonaromatic nitrogen-base ligands reduce the catalytic performance of the adducts, in agreement with the computational results.

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 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.

A new homogeneous zinc complex with increased reactivity for the intramolecular hydroamination of alkenes

The new zinc compound N-cyclohexyl-2-(cyclohexylamino)troponiminate zinc methyl, [(Cy)2ATI]ZnMe, was synthesized and showed a superior reactivity in the intramolecular hydroamination reaction of non-activated alkenes compared to previously reported homogeneous zinc complexes.

HOMOLEPTIC LANTHANIDE AMIDES AS HOMOGENEOUS CATALYSTS FOR THE TISHCHENKO REACTION

Known for about 25 years, the bis(trimethylsilyl)amides of Group 3 metals and lanthanides, M[N(SiMe3 )2 ]3 , are well suited as highly efficient catalysts for the dimerization of aldehydes [Tishchenko reaction, Eq. (1)].

Main-group and transition-metal complexes of bis(phosphinimino)methanides

Bis(phosphinimino)methanides exhibit a wide variety of coordination chemistry with almost all elements in the periodic table. This critical review deals with the chemistry and coordination behavior of bulky monoanionic {CH(PPh(2)NR)(2)}(-) bis(phosphinimino)methanide and dianionic {C(PPh(2)NR)(2)}(2-) bis(phosphinimino)methanediide (R = SiMe(3), aryl) ligands focusing on s- and p-block as well as transition metals (109 references).

Nitrophenolate as a Building Block for Lanthanide Chains and Clusters

Infinite, extended chains or tetradecanuclear lanthanide clusters (see structure) can be formed, depending on conditions, from the reaction of potassium o-nitrophenolate with different lanthanide trichlorides.

Luminescent cell-penetrating pentadecanuclear lanthanide clusters.

A novel pentadecanuclear lanthanide hydroxy cluster [{Ln15(μ3-OH)20(PepCO2)10(DBM)10Cl}Cl4] (Ln = Eu (1), Tb (2)) featuring the first example with peptoids as supporting ligands was prepared and fully characterized. The solid-state structures of 1 and 2 were established via single-crystal X-ray crystallography. ESI-MS experiments revealed the retention of the cluster core in solution. Although OH groups are present, 1 showed intense red fluorescence with 11(1)% absolute quantum yield, whereas the emission intensity and the quantum yield of 2 were significantly weaker. In vitro investigations on 1 and 2 with HeLa tumor cells revealed an accumulation of the clusters in the endosomal-lyosomal system, as confirmed by confocal microscopy in the TRLLM mode. The cytotoxicity of 1 and 2 toward the HeLa cells is moderate.

[Ln(BH4)2(THF)2] (Ln = Eu, Yb)—A Highly Luminescent Material. Synthesis, Properties, Reactivity, and NMR Studies

The divalent lanthanide borohydrides [Ln(BH(4))(2)(THF)(2)] (Ln = Eu, Yb) have been prepared in a straightforward approach. The europium compound shows blue luminescence in the solid state, having a quantum yield of 75%. Nonradiative deactivation of C-H and B-H oscillator groups could be excluded in the perdeuterated complex [Eu(BD(4))(2)(d(8)-THF)(2)], which showed a quantum yield of 93%. The monocationic species [Ln(BH(4))(THF)(5)][BPh(4)] and the bis(phosphinimino)methanides [{(Me(3)SiNPPh(2))(2)CH}Ln(BH(4))(THF)(2)] have been prepared from [Ln(BH(4))(2)(THF)(2)]. They show significantly lower or no luminescence. Using the diamagnetic compound [{(Me(3)SiNPPh(2))(2)CH}Yb(BH(4))(THF)(2)], we performed a 2D (31)P/(171)Yb HMQC experiment.