The position of the VO3−4 charge-transfer transition as a function of the VO distance

The lowest singlet excited states of the VO^3?₄ complex are calculated as a function of the VO bond distance using the Hartree-Fock-Slater discrete variational method. The calculated average singlet transition energies ¹ΔE(?₁ → 2e) support assignments made before.     

The unexpected role of pyridine-2-carboxylic acid in manganese based oxidation catalysis with pyridin-2-yl based ligands

A number of manganese-based catalysts employing ligands whose structures incorporate pyridyl groups have been reported previously to achieve both high turnover numbers and selectivity in the oxidation of alkenes and alcohols, using H(2)O(2) as terminal oxidant. Here we report our recent finding that these ligands decompose in situ to pyridine-2-carboxylic acid and its derivatives, in the presence of a manganese source, H(2)O(2) and a base. Importantly, the decomposition occurs prior to the onset of catalysed oxidation of organic substrates. It is found that the pyridine-2-carboxylic acid formed, together with a manganese source, provides for the observed catalytic activity. The degradation of this series of pyridyl ligands to pyridine-2-carboxylic acid under reaction conditions is demonstrated by (1)H NMR spectroscopy. In all cases the activity and selectivity of the manganese/pyridyl containing ligand systems are identical to that observed with the corresponding number of equivalents of pyridine-2-carboxylic acid; except that, when pyridine-2-carboxylic acid is used directly, a lag phase is not observed and the efficiency in terms of the number of equivalents of H(2)O(2) required decreases from 6-8 equiv. with the pyridin-2-yl based ligands to 1-1.5 equiv. with pyridine-2-carboxylic acid.     

On the mechanism of the copper-catalyzed enantioselective 1,4-addition of grignard reagents to alpha,beta-unsaturated carbonyl compounds

The mechanism of the enantioselective 1,4-addition of Grignard reagents to alpha,beta-unsaturated carbonyl compounds promoted by copper complexes of chiral ferrocenyl diphosphines is explored through kinetic, spectroscopic, and electrochemical analysis. On the basis of these studies, a structure of the active catalyst is proposed. The roles of the solvent, copper halide, and the Grignard reagent have been examined. Kinetic studies support a reductive elimination as the rate-limiting step in which the chiral catalyst, the substrate, and the Grignard reagent are involved. The thermodynamic activation parameters were determined from the temperature dependence of the reaction rate. The putative active species and the catalytic cycle of the reaction are discussed.     

Synthesis and reactivity of mono(amidinate) organoiron(II) complexes

The mono(amidinate) iron(ii) ferrate complex [{PhC(NAr)(2)}FeCl(micro-Cl)Li(THF)(3)] (1, Ar = 2,6-iPr(2)C(6)H(3)) was prepared and was found to undergo ligand redistribution in non-coordinating solvents to give the homoleptic [{PhC(NAr)(2)}(2)Fe] (2) as the only isolable product. Reaction of with alkylating agents also induces this redistribution, but the presence of pyridine allows isolation of the four-coordinate 14 VE monoalkyl complex [{PhC(NAr)(2)}FeCH(2)SiMe(3)(py)] (4). Generation of the 12 VE alkyl via pyridine abstraction from 4 by B(C(6)F(5))(3) again induced ligand redistribution. Attempts to trap a 12 VE alkyl species with CO led to the isolation of a dimeric Fe(0)-Li-ferrate complex (3) with a carbamoyl ligand, derived from CO insertion into the iron-amidinate bond.     

Influence of the solvent on the crystal structure of PCBM and the efficiency of MDMO-PPV:PCBM ''plastic'' solar cells

Two crystal structures of PCBM, obtained from different crystallisation solvents, are presented; a proposed link with solvent dependence of the efficiency of MDMO-PPV:PCBM solar cells is described.     

Controlling the speed of rotation in molecular motors. Dramatic acceleration of the rotary motion by structural modification

Substitution of a 6-membered by a 5-membered ring upper half in the light driven second generation molecular motors resulted in a dramatic increase of the speed of rotation.     

cis-Dihydroxylation and epoxidation of alkenes by [Mn(2)O(RCO(2))(2)(tmtacn)(2)]: tailoring the selectivity of a highly H(2)O(2)-efficient catalyst

The carboxylic acid promoted cis-dihydroxylation and epoxidation of alkenes catalyzed by [MnIV2O3(tmtacn)2]2+ 1 employing H2O2 as oxidant is described. The use of carboxylic acids at cocatalytic levels not only is effective in suppressing the inherent catalase activity of 1, but also enables the tuning of the catalyst's selectivity. Spectroscopic studies and X-ray analysis confirm that the control arises from the in situ formation of carboxylate-bridged dinuclear complexes, for example, 2 {[MnIII2O(CCl3CO2)2(tmtacn)2]2+} and 3 {[MnII2(OH)(CCl3CO2)2(tmtacn)2]+}, during catalysis. For the first time, the possibility to tune, through the carboxylate ligands employed, both the selectivity and activity of dinuclear Mn-based catalysts is demonstrated. To our knowledge, the system 1/2,6-dichlorobenzoic acid (up to 2000 turnover numbers for cis-cyclooctanediol) is the most active Os-free cis-dihydroxylation catalyst reported to date.     

A highly efficient titanium-based olefin polymerisation catalyst with a monoanionic iminoimidazolidide pi-donor ancillary ligand

The titanium complex Cp[1,3-(2',6'-Me2C6H3)2(CH2N)2C=N]Ti(CH2Ph)2, with a monoanionic eta 1-iminoimidazolidide ancillary ligand, is shown to be a highly efficient catalyst for olefin polymerisation when activated with the Lewis acid B(C6F5)3.