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.

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.

A series of novel regioselective substituted tpphz ligands and two novel mononuclear ruthenium complexes of the type [(tbbpy)(2)Ru(tpphzR(n))](PF(6))(2) (where tbbpy = 4,4'-di-tert.-butyl-2,2'-bipyridine, tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine, with n = 2 and R represents the bromine substituents at different positions) have been synthesized. All compounds were completely characterized by NMR and MS spectroscopy, absorption and steady-state emission spectroscopy as well as emission lifetime and electrochemical measurements. Additionally the solid-state structures of the two isomers [(tbbpy)(2)Ru(Br(2)tpphz)](PF(6))(2) 6 and [(tbbpy)(2)Ru(tpphzBr(2))](PF(6))(2) 7 are presented and compared with the results of density-functional theory calculations (DFT). Furthermore calculated Raman spectra were obtained by means of DFT calculations and used to assign the vibrational modes of the measured off resonance Raman spectra. A clear influence caused by the electronic effects of the different type and position of the substituents of tpphz on the photophysical behavior was observed.

The sequential order of photoinduced charge transfer processes and accompanying structure changes were analyzed by UV-vis and resonance-Raman spectroscopy of intermediates of a Ru(ii) based photocatalytic hydrogen evolving system obtained by electrochemical reduction.

The Grignard reaction offers a straight forward atom-economic synthesis of organomagnesium halides, which undergo redistribution reactions (Schlenk equilibrium) yielding diorganylmagnesium and magnesium dihalides. The homologous organocalcium complexes (heavy Grignard reagents) gained interest only quite recently owing to several reasons. The discrepancy between the inertness of this heavy alkaline earth metal and the enormous reactivity of its organometallics hampered a vast and timely development after the first investigation more than 100 years ago. In this overview the synthesis of organocalcium reagents is described as is the durability in ethereal solvents. Aryl-, alkenyl-, and alkylcalcium halides are prepared by direct synthesis. Characteristic structural features and NMR parameters are discussed. Ligand redistribution reactions can be performed by addition of potassium tert-butanolate to ethereal solutions of arylcalcium iodides yielding soluble diarylcalcium, whereas sparingly soluble potassium iodide and calcium bis(tert-butanolate) precipitate. Furthermore, reactivity studies with respect to metalation and addition to unsaturated organic compounds and metal-based Lewis acids, leading to the formation of heterobimetallic complexes, are presented.

Metalation of N, benzamidine (1a) and -pivalamidine (1b) in tetrahydrofuran (THF) with nbutyllithium and potassium bis(trimethylsilyl)amide gives the corresponding N,NЈ-bis(2,6-diisopropylphenyl)benzamidinates and -pivalamidinates of lithium, [(thf) ). Because metalation of these amidines is not possible with [(thf) 2 Ca{N(SiMe 3 ) 2 } 2 ], a metathetical approach has been [a] 1312 chosen. Hence, the reaction of 3a with calcium iodide in THF yields (tetrahydrofuran)calcium bis[N,NЈ-bis(2,6-diisopropylphenyl)benzamidinate] (4a). For the bulkier N,NЈ-bis(2,6diisopropylphenyl)pivalamidinate, heteroleptic [(thf)Ca-{(Dipp-N) 2 C-tBu}{N(SiMe 3 ) 2 }] (4b) forms. Depending on the softness and charge-to-radius ratio, syn configuration of the amidinate ligands is observed for 2a, 4a, and 4b, whereas the anti configuration is realized in complexes 2b, 3a, and 3b, the latter being stabilized by intramolecular metal-π interactions.

Iodide is a very soft and large anion and as such its extreme ability to be polarized leads to a flat energy surface with respect to the variation of the Ca-I distances in [(L) n CaI 2 ] and [(L) n Ca(R)I]. The influence of the donor strength and the bulkiness of the neutral coligands L on the Ca-I distances is studied. The base adducts of calcium diiodide can be isolated after the addition of L to CaI 2 or from the Schlenk equilibrium after the direct synthesis of calcium powder with aryl iodides. As L the ethers diethyl ether (Et 2 O), tetrahydrofuran (thf), tetrahydropyran (thp), 1,2-dimethoxyethane (dme), 18-crown-6 (18C6), bis(methoxyethyl)ether (diglyme), and amines tetramethylethylenediamine (tmeda), and hexamethyltriethylenetetramine (hmteta) * Prof. Dr. M. Westerhausen

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