Homogeneous transition-metal catalysis is a crucial technology for the sustainable preparation of valuable chemicals. The catalyst concentration is usually kept as low as possible, typically at mM or μM levels, and the effect of high catalyst concentration is hardly exploited because of solubility issues and the inherent unfavorable catalyst/substrate ratio. Herein, a self-assembly strategy is reported which leads to local catalyst concentrations ranging from 0.05 M to 1.1 M, inside well-defined nanospheres, whilst the overall catalyst concentration in solution remains at the conventional mM levels. We disclose that only at this high concentration, the gold(I) chloride is reactive and shows high selectivity in intramolecular CO and CC bond-forming cyclization reactions.

Metallamacrocylic tetraruthenium complexes were generated by treatment of 1,4-divinylphenylene-bridged diruthenium complexes with functionalized 1,3-benzene dicarboxylic acids and characterized by HR ESI-MS and multinuclear NMR spectroscopy. Every divinylphenylene diruthenium subunit is oxidized in two consecutive one-electron steps with half-wave potential splittings in the range of 250 to 330 mV. Additional, smaller redox-splittings between the + /2 + and 0/ + and the 3 + /4 + and 2 + /3 + redox processes, corresponding to the first and the second oxidations of every divinylphenylene diruthenium entity, are due to electrostatic effects. The lack of electronic coupling through bond or through space is explained by the nodal properties of the relevant molecular orbitals and the lateral side-by-side arrangement of the divinylphenylene linkers. The polyelectrochromic behavior of the divinylphenylene diruthenium precursors is retained and even amplified in these metallamacrocyclic structures. EPR studies down to T = 4 K indicate that the dications 1-H 2 + and 1-OBu 2 + are paramagnetic. The dications and the tetracation of macrocycle 3-H display intense (dications) or weak (3-H 4 + ) EPR signals. Quantum chemical calculations indicate that the four most stable conformers of the macrocycles are largely devoid of strain. Bond parameters, energies as well as charge and spin density distributions of model macrocycle 5-H Me were calculated for the different charge and spin states.

Homogeneous transition-metal catalysis is a crucial technology for the sustainable preparation of valuable chemicals. The catalyst concentration is usually kept as low as possible, typically at mm or mm levels, and the effect of high catalyst concentration is hardly exploited because of solubility issues and the inherent unfavorable catalyst/substrate ratio. Herein, a self-assembly strategy is reported which leads to local catalyst concentrations ranging from 0.05 m to 1.1m, inside well-defined nanospheres, whilst the overall catalyst concentration in solution remains at the conventional mm levels. We disclose that only at this high concentration, the gold(I) chloride is reactive and shows high selectivity in intramolecular C À O and C À C bond-forming cyclization reactions.Transition-metal catalysis plays an extremely important role in the synthesis of chemicals relevant for pharmacology, biology, agrochemistry, materials science, and petrochemistry.[1] It allows the preparation of valuable molecules from readily available bulk chemicals in an atom-economic and sustainable manner.[2] It also enables the construction of sophisticated molecules in more efficient manners, thus simplifying synthetic routes towards the desired target molecules.[3] In the past decades several tools to control the activity and selectivity of transition-metal catalysts have been developed, and have mostly focused on the ligands which together with the metal form the active complex. [4,5] More recently, enzyme-inspired approaches have been explored, thus providing excellent tools to control the second coordination sphere around the transition-metal complex. [6] Various examples demonstrate that the use of a second coordination sphere can lead to activities and selectivities which are not accessible by traditional approaches. [7] The operational modes of these second spheres are many, including the precise orientation of the substrate at the metal center [8] and controlling the local pH value. [9] What all these catalysts have in common is that they are employed in a limited concentration window, typically between 10 À6 m and 10 À3 m. At these concentrations the catalysts generally dissolve well and a large excess of substrate can be added to achieve high turnover numbers without running into limitations of substrate solubility. From a reactivity point of view, however, it is interesting to also explore extremely high concentrations of catalyst as new reactivity patterns may evolve through, for example, metal cooperativity effects. We realized that if one would like to apply molar concentrations of catalyst, this can only be achieved by devising systems in which the "local catalyst concentration" is high, whereas the overall catalyst concentration in solution is still around the commonly used 10 À3 m (Figure 1), thus still allowing high turnover numbers to be achieved. Fujita et al. have developed appealing strategies to form nanosized molecular spheres (M 12 L 24 ) which form by self-assembly of 24 ditopic nitrogen ligands and...

The redox reaction of superoxide (KO2) with highly charged iron porphyrins (Fe(P4+), Fe(P8+), and Fe(P8-)) has been investigated in the ionic liquids (IL) [EMIM][Tf2N] (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and [EMIM][B(CN)4] (1-ethyl-3-methylimidazolium tetracyanoborate) by using time-resolved UV/vis stopped-flow, electrochemistry, cryospray mass spectrometry, EPR, and XPS measurements. Stable KO2 solutions in [EMIM][Tf2N] can be prepared up to a 15 mM concentration and are characterized by a signal in EPR spectrum at g = 2.0039 and by the 1215 cm(-1) stretching vibration in the resonance Raman spectrum. While the negatively charged iron porphyrin Fe(P8-) does not react with superoxide in IL, Fe(P4+) and Fe(P8+) do react in a two-step process (first a reduction of the Fe(III) to the Fe(II) form, followed by the binding of superoxide to Fe(II)). In the reaction with KO2, Fe(P4+) and Fe(P8+) show similar rate constants (e.g., in the case of Fe(P4+): k1 = 18.6 ± 0.5 M(-1) s(-1) for the first reaction step, and k2 = 2.8 ± 0.1 M(-1) s(-1) for the second reaction step). Notably, these rate constants are four to five orders of magnitude lower in [EMIM][Tf2N] than in conventional solvents such as DMSO. The influence of the ionic liquid is also apparent during electrochemical experiments, where the redox potentials for the corresponding Fe(III)/Fe(II) couples are much more negative in [EMIM][Tf2N] than in DMSO. This modified redox and kinetic behavior of the positively charged iron porphyrins results from their interactions with the anions of the ionic liquid, while the nucleophilicity of the superoxide is reduced by its interactions with the cations of the ionic liquid. A negligible vapor pressure of [EMIM][B(CN)4] and a sufficient enrichment of Fe(P8+) in a close proximity to the surface enabled XPS measurements as a case study for monitoring direct changes in the electronic structure of the metal centers during redox processes in solution and at liquid/solid interfaces.

Keywords: Polyoxometalates / Cluster compounds / Vanadium / Ionic liquids / Hybrid materialsA novel intercluster compound, [(n-C 4 H 9 ) 4 P] 3 [H 3 V 10 O 28 ] (IL01-V 10 ), constructed from the tetrabutylphosphonium cation and decavanadate, has been synthesized and unequivocally characterized by elemental analysis, FTIR spectroscopy, mass spectrometry, X-ray crystallography, and solution 1 H, 13 C, 31 P{ 1 H}, and 51 V NMR spectroscopy. Compound IL01- [a]V 10 was formed by ionic interaction between the phosphonium cation and the decavanadate anion. Cryospray high-resolution mass spectrometry revealed the [H 3 V 10 O 28 ] 3cluster remains intact in solution. Three further phosphonium polyoxovanadates were synthesized and characterized by the same techniques as used for IL01-V 10 .