Ligand exchange at tetra-coordinated beryllium centres.

Mono and dinuclear phosphine complexes of beryllium halides [(PMe)BeX], [(PMe)BeX] and [(PCy)BeX] (X = Cl, Br, I) were synthesised and characterised NMR and IR spectroscopy as well as single crystal X-ray diffraction experiments. Dissociation and ligand exchange processes at these complexes were investigated through variable temperature NMR experiments in combination with line shape analysis and complemented by quantum chemical calculations. The PMe dissociation energy is smallest in [(PMe)BeCl], while PMe exchange is similar in energy in all mononuclear [(PMe)BeX] complexes and follows an interchange mechanism.

Dimorpholinoacetylene and Its Use for the Synthesis of Tetraaminocyclobutadiene Species.

The new diaminoacetylene (DAA) dimorpholinoacetylene (3) was prepared from 1,1-dimorpholinoethene (1) by bromination to form the dibromoketene aminal 2, which upon lithiation afforded 3 through a Fritsch-Buttenberg-Wiechell rearrangement. Heating 3 at elevated temperatures resulted in a complete conversion into the dimer 1,1,2,4-tetramorpholino-1-buten-3-yne (4), which was used for the synthesis of four-membered cyclic bent allene (CBA) transition-metal complexes of the type [(CBA)ML ] (5-7; ML =AuCl, RhCl(COD), RhCl(CO) ; CBA=1,3,4,4-tetramorpholino-1,2-cyclobutadiene; COD=1,5-cyclooctadiene). The reaction of 3 with tetraethylammonium bromide gave 1,2,3,4-tetramorpholinocyclobutenylium bromide (8), which reacted with bromine to form 1,2,3,4-tetra(morpholino)cyclobutenediylium bis(tribromide) (9).

Quinol-containing ligands enable high superoxide dismutase activity by modulating coordination number, charge, oxidation states and stability of manganese complexes throughout redox cycling.

Reactivity assays previously suggested that two quinol-containing MRI contrast agent sensors for HO, [Mn()(MeCN)] and [Mn()Br], could also catalytically degrade superoxide. Subsequently, [Zn()(OTf)] was found to use the redox activity of the ligand to catalyze the conversion of O˙ to O and HO, raising the possibility that the organic ligand, rather than the metal, could serve as the redox partner for O˙ in the manganese chemistry. Here, we use stopped-flow kinetics and cryospray-ionization mass spectrometry (CSI-MS) analysis of the direct reactions between the manganese-containing contrast agents and O˙ to confirm the activity and elucidate the catalytic mechanism.

Adaptive Behavior of Dynamic Orthoester Cryptands.

The integration of dynamic covalent bonds into macrocycles has been a tremendously successful strategy for investigating noncovalent interactions and identifying effective host-guest pairs. While numerous studies have focused on the dynamic responses of macrocycles and larger cages to various guests, the corresponding constitutionally dynamic chemistry of cryptands remains unexplored. Reported here is that cryptands based on orthoester bridgeheads offer an elegant entry to experiments in which a metal ion selects its preferred host from a dynamic mixture of competing subcomponents.

A Soft Grip: Magnesium Complexes with a Phosphine-Modified Phosphonium Diylidic Lewis Base.

Simple strategies to obtain magnesium complexes with the soft chelating diylidic ligand [Ph PCHPPh (fluorenylidene)] (dppmflu ) were developed to evaluate the influence of the hard acid (cation) and soft base (anion) mismatch on the stability and reactivity of the formed derivatives. Deprotonation of the precursor Ph PCH PPh (flu) (dppmfluH) by an alkylmagnesium derivative or magnesium amide provided access to [{Mg(dppmflu)(μ-nBu)} ], [Mg(dppmflu){N(SiMe ) }], and [{Mg(dppmflu)(μ-Me)} ], which were used as starting materials for further investigations. The reaction of [{Mg(dppmflu)(μ-nBu)} ] with PhSiH in the presence of THF allowed isolation of the magnesium hydride complex [{Mg(dppmflu)(μ-H)(thf)} ] without a stabilizing nitrogen donor ligand.

Behavior of highly diluted electrolytes in strong electric fields-prevention of alumina deposition on grading electrodes in HVDC transmission modules by CO2-induced pH-control.

Alumina deposition on platinum grading electrodes in high voltage direct current (HVDC) transmission modules is an unsolved problem that has been around for more than three decades. This is due to the unavoidable corrosion of aluminum heat sinks that causes severe damage to electrical power plants and losses in the range of a million Euro range per day in power outage. Simple experiments in a representative HV test setup showed that aluminates at concentrations even below 10(-8) mol L(-1) can deposit on anodes through neutralization by protons produced in de-ionized water (κ≤0.

Why do cationic hydridoiridium(III) complexes with beta-aminophosphane ligands favour the transfer hydrogenation of ketones over the direct "H2-hydrogenation"?--A computational approach.

Density functional theory and ab initio molecular orbital calculations show that the observed inability of cationic hydridoiridium(III) complexes with beta-aminophosphane ligands to catalyse the direct hydrogenation of carbonyl compounds with dihydrogen ("H2-hydrogenation") in contrast to their ruthenium(II) equivalents is due to the inability of H2 to displace a coordinated solvent molecule from an intermediate hydrido complex.

The formation of endo-complexes between calixarenes and amines--a reinvestigation.

The formation of an endo-complex between p-allylcalix[4]arene and t-butylamine was described by Gutsche in 1985. However, for a comparable system, it has been shown using NOE methods that the amine does not reside inside the calix. Instead, an exo-calix complex is formed.