Showing papers by "Eberhardt Herdtweck published in 2002"

Octahedral bipyridine and bipyrimidine dioxomolybdenum(VI) complexes: characterization, application in catalytic epoxidation, and density functional mechanistic study.

Abstract: Complexes of the general formula [MoO 2 X 2 L 2 ] (X=Cl, Br, Me; L 2 =bipy, bpym) have been prepared and fully characterized, including X-ray crystallographic investigations of all six compounds. Additionally, the highly soluble complex [MoO 2 Cl 2 (4,4'-bis(hexyl)-2,2'-bipyridine)] has been synthesized. The reaction of the complexes with tert-butyl hydroperoxide (TBHP) is an equilibrium reaction, and leads to Mo V I η 1 -alkylperoxo complexes that selectively catalyze the epoxidation of olefins. Neither the Mo-X bonds nor the Mo-N bonds are cleaved during this reaction. These experimental results are supported by theoretical calculations, which show that the attack of TBHP at the Mo center through the X-O-N face is energetically favored and the TBHP hydrogen atom is transferred to a terminal oxygen of the Mo=O moiety. After the attack of the olefin on the Mo-bound peroxo oxygen atom, epoxide and tert-butyl alcohol are formed. The latter compound acts as a competitive inhibitor for the TBHP attack, and leads to a significant reduction in the catalytic activity with increasing reaction time.

Diruthenium σ-alkynyl complexes as potential building blocks for heterometallic molecular rods

Abstract: Diruthenium(III) bis(σ-pyridylacetylide) complexes can be utilized for axially connecting to monometallic organometallic units in order to construct heterobimetallic building blocks for molecular rods; the synthesis and characterization of an exemplary rhenium–diruthenium–rhenium complex is described, which is stable to air, moisture and a broad variety of organic solvents and which displays electron delocalisation along the propagation axis.

Ruthenium(II) alkynyl-hydride and ruthenium(II) bis(σ-pyridylacetylide) as ligands and linkers for metal–metal-bonded complexes

Abstract: The syntheses of new linear π-conjugated building blocks, ruthenium(II) alkynyl-hydride and bis(σ-pyridylacetylide) complexes, and their application to the formation of heterobimetallic units and oligomers incorporating metal–metal-bonded complexes are reported. The structure of a tetrametallic subunit has been determined by X-ray crystallography. Thermogravimetry shows a stabilization of the tetramer and the oligomers in comparison to the least stable starting material. Spectroscopic results and cyclovoltammetry indicate an N–M donor–acceptor interaction, but no extended electron delocalization along the backbone of the tetramer.

O-Benzylated-calix[4]arenes as ancillary ligands in organolanthanide chemistry

Abstract: 25,27-O-Benzylated-calix[4]arenes H2L react with Ln[N(SiHMe2)2]3(thf)x (Ln = Sc (x = 1), Lu (x = 2)) via an extended silylamide route to yield monomeric, heteroleptic calix[4]arene complexes with a N(SiHMe2)2 ligand bonded to the metal centre which is suitable for further ligand exchange reactions

Exocyclic coordination of the η3-fluorenyl, η3-cyclopenta[def]phenanthrenyl and η3-8,9-dihydrocyclopenta[def]phenanthrenyl anions: X-ray crystal structures, NMR fluxionality and theoretical studies

Abstract: The novel complexes IndMo(η3-Flu)(CO)2 (Flu = fluorenyl), (η5-Ind)Mo(η3-cpp)(CO)2 (cpp = cyclopenta[def]phenanthrenyl) and (η5-Ind)Mo(η3-H2cpp)(CO)2 (H2cpp = 8,9-dihydrocyclopenta[def]phenanthrenyl) have been prepared and their molecular structures determined. X-Ray crystallographic studies show an exocyclic η3-coordination for the Flu, cpp and H2cpp ligands, which is also predicted from DFT calculations. 1H NMR spectra, recorded at temperatures between 303 and 318 K, indicated that exchange broadening was taking place for the protons near the η3-coordination site. It was found that ring slippage occurred at lower temperatures for Mo-Flu and Mo-H2cpp than for Mo-cpp. This result is in agreement with the order of the Mo–X bond strengths determined using DFT calculations and the calculated activation energies.