Light‐driven metallo‐organic catalysis: Intramolecular photoelectron transfer in the heterodinuclear complex 1 facilitates the photocatalytic production of hydrogen and the selective hydrogenation of tolane to give cis‐stilbene. All three well‐coordinated parts of the supramolecular system are essential: the (tbbpy)2Ru fragment as a photoactive unit, the redox‐active bridging ligand as an electron relay and storage site, and the palladium as a catalytically active center.

The reaction of bromo-2,4,6-triphenylbenzene with activated magnesium in THF yielded the Grignard reagent [(thf)(2)Mg(Br)-C(6)H(2)-2,4,6-Ph(3)] (1) with a Mg-C bond length of 214.8(3) pm. A similar reaction of bromo-2,4,6-triphenylbenzene with activated calcium led to an "inverse" sandwich complex [(thf)(3)Ca{mu-C(6)H(3)-1,3,5-Ph(3)}Ca(thf)(3)] (2) with the calcium atoms on opposite sides of the central arene ring showing small Ca-Ca' and Ca-C distances of 427.9(3) and 259.2(3) pm. This extremely air- and moisture-sensitive complex exhibits thermochomic and solvatochromic behavior. It is paramagnetic with spin of S = 1 (triplet) with an ESR resonance at g = 2.0023. Quantum chemical calculations shed light on the bonding situation in this very unusual dinuclear Ca(I) compound.

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Ru-dppz (dppz = dipyrido[3,2-a:2',3,3'-c]phenazine) complexes play an important role as environmentally sensitive luminescence sensors and building blocks for larger supramolecular compounds. Their photophysical properties are known to be highly sensitive to intermolecular solvent-solute interactions and solvent bulk-properties. Here, the synthesis and characterisation of a novel Ru-dppz derivative is reported. The potential of drastically tuning the photophysical properties of such complexes is exemplified, by introducing very simple structural modifications, namely bromine, into the dppz-ligand scaffold. The photophysics i.e. nature of excited states and the excited-state relaxation pathway of the various complexes has been investigated by means of electrochemical measurements, steady-state emission experiments and femtosecond time-resolved spectroscopy. It could be shown that the location of bromine substitution influences the relative energy between a luminescent and a non-luminescent metal-to-ligand charge-transfer state and therefore quenches or facilitates transitions between both. Hence it is illustrated that the luminescent properties and the underlying ultrafast excited-state dynamics of the complexes can be controlled by structural variations, i.e. by intramolecular interactions as opposed to changes in the intermolecular interactions.

Abstract:The complexes [ (P,)Rh(hfacac)] 1 [P, = R,P-(X)-PR,] are introduced as model compounds for the investigation of the intrinsic steric properties of the [(PJRh] fragment. The ligand exchange processes that occur during the syntheses of 1 from [(cod)Rh(hfacac)] and the appropriate chelating diphosphanes 3 were studied by variable-temperature multinuclear NMR spectroscopy. The molecular structures of eight examples of 1 with systematic structural variations in 3 were determined by X-ray crystallography. The steric repulsion of the PR, groups within the chelating fragment was found to significantly influence the coordination geometry of [(P,)Rh], depending on the nature and length of the backbone (X). A linear correlation between the P-Rh-P angles in the solid state and the lo3Rh Keywords: carbon dioxide activation * homogeneous catalysis ligand effects * molecular modeling * rhodium chemical shifts reveals a similar geometric situation in solution. A unique molecular modeling approach was developed to define the accessible molecular surface (AMS) of the rhodium center within the flexible [ (PJRh] fragment. The potential of this model for application in homogeneous catalysis was exemplified by the use of 1 as catalysts in a test reaction, the hydrogenation of CO, to formic acid. Complexes 1 were found to be the most active catalyst precursors for this process in organic solvents known to date.

A systematic series of heteroleptic bis(tridentate)ruthenium(II) complexes of click-derived 1,3-bis(1,2,3-triazol-4-yl)benzene N^C^N-coordinating ligands was synthesized, analyzed by single crystal X-ray diffraction, investigated photophysically and electrochemically, and studied by computational methods. The presented comprehensive characterization allows a more detailed understanding of the radiationless deactivation mechanisms. Furthermore, we provide a fully optimized synthesis and systematic variations towards redox-matched, broadly and intensely absorbing, cyclometalated ruthenium(II) complexes. Most of them show a weak room-temperature emission and a prolonged excited-state lifetime. They display a broad absorption up to 700 nm and high molar extinction coefficients up to 20 000 M(-1)cm(-1) of the metal-to-ligand charge transfer bands, resulting in a black color. Thus, the complexes reveal great potential for dye-sensitized solar-cell applications.

The direct synthesis of activated calcium with aryl halides in tetrahydrofuran (THF) gave the following compounds of the type RCaX in fair to good yields: [MesCaI(THF) 4 ] (1), [(p-tolyl)CaI(THF) 4 ] (2), [PhCaI(THF) 4 ] (3), and [PhCaBr(THF) 4 ] (5). All of these "heavy Grignard reagents" contain a calcium atom in a slightly distorted octahedral environment. They must be handled at low temperatures in order to avoid ether cleavage reactions. The Ca-C bond lengths vary between 2.556(5) Å (3) and 2.583(3) Å ( 5). The thermal stability is enhanced when the coordination number of calcium is increased. The calcium in the seven-coordinate complex [PhCaI(THF)(DME) 2 ] (4) has a distorted-pentagonal-bipyramidical configuration. This complex is thermally more stable and can be handled at 0 °C. The larger coordination number results in a longer Ca-C bond of 2.621(5) Å.

The reaction of a nickelalactone with dppm, resulting in the formation of a stable binuclear Ni(I) complex with an acrylate, a Ph2P- and a dppm bridge, models a key step in the formation of acrylic acid from CO2 and ethylene.