Hermann A. Mayer

CHEMISTRY IN INTERPHASES : A NEW APPROACH TO ORGANOMETALLIC SYNTHESES AND CATALYSIS

Combining the advantages of homogeneous and heterogeneous catalysis is still a problem that has not been satisfactorily solved. Chemistry in interphases offers a new approach for overcoming the difficulties, as is described in this article. Owing to the swellable or porous matrix, an interphase represents a state which in the most favorable case is similar to that of a solution. Moreover the proper choice of a mobile hybrid copolymer enables the control of the density and accessibility of the reactive centers, which results in a distinct improvement of the activity of the catalysts (two examples are shown schematically).

Brightly Blue and Green Emitting Cu(I) Dimers for Singlet Harvesting in OLEDs

With the chelating aminophosphane ligands Ph2P-(o-C6H4)-N(CH3)2 (PNMe2) and Ph2P-(o-C6H4)-NC4H8 (PNpy), the four halide (Cl, Br, I)-bridged copper coordination compounds [Cu(μ-Cl)(PNMe2)]2 (1), [Cu(μ-Br)(PNMe2)]2 (2), [Cu(μ-I)(PNMe2)]2 (3), and [Cu(μ-I)(PNpy)]2 (4) were synthesized and structurally characterized. Their photophysical properties were studied in detail. The complexes exhibit strong blue (λmax = 464 (3) and 465 nm (4)) and green (λmax = 506 (1) and 490 nm (2)) luminescence as powders with quantum yields of up to 65% at decay times as short as 4.1 μs. An investigation of the emission decay behavior between 1.3 and 300 K gives insight into the nature of the emitting states. At temperatures below T ≈ 60 K, the decay times of the studied compounds are several hundred microseconds long, which indicates that the emission originates from a triplet state (T1 state). DFT calculations show that this state is of (metal+halide)-to-ligand charge transfer (3)(M+X)LCT character. Investigations at 1.3 K allow us to gain insight into the three triplet substates, in particular, to determine the individual substate decay times being as long as a few milliseconds. The zero-field splittings are smaller than 1 or 2 cm(-1). With an analysis of these data, conclusions about the effectiveness of spin-orbit coupling (SOC) can be drawn. Interestingly, the large differences of SOC constants of the halides are not obviously displayed in the triplet state properties. With a temperature increase from T ≈ 60 to 300 K, a significant decrease of the emission decay time by almost 2 orders of magnitude is observed, and at ambient temperature, the decay times amount only to ∼4-7 μs without a significant reduction of the emission quantum yields. This drastic decrease of the (radiative) decay time is a result of the thermal population of a short-lived singlet state (S1 state) that lies energetically only a few hundred wavenumbers (460-630 cm(-1)) higher than the T1 state. Such an emission mechanism corresponds to a thermally activated delayed fluorescence (TADF). At ambient temperature, almost only a delayed fluorescence (∼98%) is observed. Compounds showing this mechanism are highly attractive for applications in OLEDs or LEECs as, in principle, it is possible to harvest all singlet and triplet excitons for the generation of light in the lowest excited singlet state. This effect represents the singlet harvesting mechanism.

Rhodium pincer complexes of 2,2′-bis(diphenylphosphino)diphenylamine

Abstract The novel pincer ligand 2,2′-bis(diphenylphosphino)diphenylamine (1) has been synthesized by treatment of 2,2′-dibromodiphenylamine with n-butyl lithium and subsequent reaction with diphenylchlorophosphine. When ligand 1 is treated with RhCl3 hydrate the dinuclear complex 1a forms which can be converted into the square planar carbonyl complex 1c upon reduction with Na/Hg in the presence of CO. Depending on the reaction conditions two different complexes were isolated when 1 reacts with [(COE)2RhCl]2. In THF the hydrochloro complex 1b and with n-butyl lithium the COE complex 1d is generated. Interestingly, the formation of 1b represents a rare case of N–H oxidative addition to a late transition metal complex fragment. Compound 1c is observed upon reaction of the COE complex 1d with carbon monoxide. Quantum chemical calculations at different levels of theory are in good agreement with the experimental structure of 1c.

Chemie in Interphasen – ein neuer Weg für die metallorganische Synthese und Katalyse

Wie lassen sich die Vorteile homogener und heterogener Katalyse vereinen? Darauf gibt es noch keine zufriedenstellende Antwort. Ein erfolgversprechender neuer Ansatz wird hier vorgestellt: die Chemie in Interphasen. Die quellbare oder porose Matrix als stationare Phase macht die Interphase zu einem Zustand, der im gunstigsten Fall dem in Losung ahnlich ist. Daruber hinaus last sich uber ein mobiles Hybridcopolymer die Dichte und die Zuganglichkeit der reaktiven Zentren einstellen, was eine gezielte Beeinflussung der Katalysatoraktivitat ermoglicht. Zwei Komplexe, die erfolgreich als Hybridkatalysatoren eingesetzt werden konnten, sind gezeigt.

Stöber silica particles as basis for redox modifications: particle shape, size, polydispersity, and porosity.

The synthesis of Stöber silica particles as basis for redox modifications is optimized for desired properties, in particular diameter in a wide sub-micrometer range, spherical shape, monodispersity, the absence of porosity, and aggregation free isolability for characterization and later covalent modification. The materials are characterized by SEM, DLS, nitrogen sorption isotherms, helium as well as Gay-Lussac (water) pycnometry, and DRIFT spectroscopy. Particles with diameters between approximately 50 and 800 nm are obtained by varying the concentrations of the reagents and reactants, the type of solvent as well as the temperature. The use of high water concentrations and post-synthetic calcination at 600 °C results in silica particles that can be considered as nonporous with respect to the size of the active molecules to be immobilized. The effect of reaction temperature on size distribution is identified. Low polydispersity is achieved by performing the reaction in a temperature range in which a change in temperature has only a weak or no effect on the final particle diameter. Upon optimization of the sol-gel process, the shape of the particles is still spherical. The agreement between experimental and geometric data is within the expected precision of the characterization techniques.

Macrocyclic Gd3+ Chelates Attached to a Silsesquioxane Core as Potential Magnetic Resonance Imaging Contrast Agents: Synthesis, Physicochemical Characterization, and Stability Studies

Two macrocyclic ligands, 1,4,7,10-tetraazacyclododecane-1-glutaric-4,7,10-triacetic acid (H(5)DOTAGA) and the novel 1,4,7,10-tetraazacyclododecane-1-(4-(carboxymethyl)benzoic)-4,7,10-triacetic acid (H(5)DOTABA), were prepared and their lanthanide complexes (Ln = Gd(3+), Y(3+)) attached to an amino-functionalized T(8)-silsesquioxane. The novel compounds Gadoxane G (GG) and Gadoxane B (GB) possess eight monohydrated lanthanide complexes each, as evidenced by multinuclear ((1)H, (13)C, (29)Si) NMR spectroscopy and high resolution mass spectrometry (HR-MS). Pulsed-field gradient spin echo (PGSE) diffusion (1)H NMR measurements revealed hydrodynamic radii of 1.44 nm and global rotational correlation times of about 3.35 ns for both compounds. With regard to potential MRI contrast agent applications, a variable-temperature (17)O NMR and (1)H nuclear magnetic relaxation dispersion (NMRD) study was carried out on aqueous solutions of the gadolinium(III) complexes of the Gadoxanes and the corresponding monomeric ligands to yield relevant physicochemical properties. The water exchange rates of the inner-sphere water molecules are all very similar (k(ex)(298) between (5.3 +/- 0.5) x 10(6) s(-1) and (5.9 +/- 0.3) x 10(6) s(-1)) and only slightly higher than that reported for the gadolinium(III) complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (H(4)DOTA) (k(ex)(298) = 4.1 x 10(6) s(-1)). Despite their almost identical size and their similar water exchange rates, GB shows a significantly higher longitudinal relaxivity than GG over nearly the whole range of magnetic fields (e.g., 17.1 mM(-1) s(-1) for GB and 12.1 mM(-1) s(-1) for GG at 20 MHz and 25 degrees C). This difference arises from their different local rotational correlation times (tau(lR)(298) = 240 +/- 10 ps and 380 +/- 20 ps, respectively), because of the higher rigidity of the phenyl ring of GB as compared to the ethylene spacer of GG. A crucial feature of these novel compounds is the lability of the silsesquioxane core in aqueous media. The hydrolysis of the Si-O-Si moieties was investigated by (29)Si NMR and PGSE diffusion (1)H NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), as well as by relaxivity measurements. Although frozen aqueous solutions (pH 7.0) of GG and GB can be stored at -28 degrees C for at least 10 months without any decomposition, with increasing temperature and pH the hydrolysis of the silsesquioxane core was observed (e.g., t(1/2) = 15 h at pH 7.4 and 55 min at pH 8.1 for GG at 37 degrees C). No change in relaxivity was detected within the first 3 h, since the hydrolysis of the initial Si-O-Si moieties has no influence on the rotational correlation time. However, the further hydrolysis of the silsesquioxane core leads to smaller fragments and therefore to a decrease in relaxivity.

Supported organometallic complexes Part XXXV. Synthesis, characterization, and catalytic application of a new family of diamine(diphosphine)ruthenium(II) complexes

The novel diamine(dppp)ruthenium(II) complexes 3L1 � /3L12 have been obtained by reaction of equimolar amounts of Cl2Ru(dppp)2 (2) with the diamines L1 � /L12 in excellent yields. Within a few minutes one of the diphosphine ligands was quantitatively exchanged by the corresponding diamine. X-ray structural investigations of 3L1, 3L2, and 3L8 show triclinic unit cells with the space groups P/ ¯ 1 (3L1, 3L2) and P 1( 3L8). Whereas in solution all these complexes prefer a trans -RuCl2 configuration, in the solid state cis -(3L1, 3L2) and trans -isomers (3L8) were observed. With the exception of 3L5, 3L6, and 3L12 all mentioned ruthenium complexes are highly catalytically active in the hydrogenation of the a,b-unsaturated ketone trans -4-phenyl-3-butene-2one. In most cases the conversions and selectivities toward the formation of the unsaturated alcohol trans -4-phenyl-3-butene-2-ol were � /99% with high turnover frequencies (TOFs) under mild conditions. # 2002 Elsevier Science B.V. All rights reserved.

Asymmetric hydrogenation of an α,β-unsaturated ketone by diamine(ether–phosphine)ruthenium(II) complexes and lipase-catalyzed kinetic resolution: a consecutive approach

Abstract The RuCl2(η1-Ph2PCH2CH2OCH3)2(diamine) complexes 2L1–2L5 have been prepared in high yields from the reaction of equimolar amounts of RuCl2(η2-Ph2PCH2CH2OCH3)2 1 with various kinds of chelating diamines L1–L5 to form five-membered chelates with ruthenium. These novel ruthenium(II) complexes have been used as catalysts in the asymmetric hydrogenation of the prochiral ketone trans-4-phenyl-3-butene-2-one 3, using 2-propanol and different types of cocatalysts. Whereas complexes with achiral diamines afforded the racemic alcohols, complexes with chiral diamines (R,R or S,S) allowed the formation of the corresponding enantiomerically enriched secondary alcohol (S or R) with ee values of 45%. In order to obtain the secondary alcohol with ee of >99%, the kinetic resolution of enantiomerically enriched trans-4-phenyl-3-butene-2-ol 3 was performed in a consecutive approach using either the lipase-catalyzed enantioselective transesterification of the alcohol with isopropenyl acetate as the acyl donor in toluene or the enantioselective hydrolysis of the corresponding acetate in buffer. The determination of the enantiomeric excess (ee) of the resulting enantiomerically enriched secondary alcohols was performed by gas chromatography using heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as the chiral stationary phase.

Supported organometallic complexes Part 34: synthesis and structures of an array of diamine(ether/phosphine)ruthenium(II) complexes and their application in the catalytic hydrogenation of trans-4-phenyl-3-butene-2-one

The novel diamine/bis(ether/phosphine)ruthenium(II) complexes Cl2Ru(h 1 -Ph2PCH2/CH2OCH3)2(diamine)2(3L1/3L11 )h ave been obtained by reaction of equimolar amounts of Cl2Ru(PS/O)2 (2) with the respective diamines L1/L11 in good yields. X-ray structural investigations of 3L2 and 3L8 show monoclinic unit cells with the space group P 21/c . The octahedrally coordinated ruthenium atoms have each two trans- chlorides and cis -phosphines which is in agreement with NMR studies in solution. With the exception of 3L4 all mentioned ruthenium complexes are highly catalytically active in the hydrogenation of the a,b-unsaturated ketone trans -4-phenyl-3-butene-2-one. In most cases the conversions and selectivities toward the formation of the unsaturated alcohol trans -4-phenyl-3-butene-2-ol were 100% with high turnover frequencies under mild conditions. # 2003 Elsevier Science B.V. All rights reserved.

Über die Koexistenz von tetragonalem und monoklinem CaC2: Strukturelle und spektroskopische Untersuchungen an Erdalkalimetallacetyliden, MC2 (M = Ca, Sr, Ba)

Fur die Erdalkalimetallacetylide CaC2, SrC2 und BaC2 kann die Existenz von jeweils drei polymorphen Strukturen angenommen werden, die monokline Tieftemperaturform, die tetragonale Form und die kubische Hochtemperaturform. Einkristallstrukturanalysen und 13C-MAS-NMR-Messungen ergaben, das die C22–-Ionen in den tetragonalen Strukturen axialsymmetrisch angeordnet sind. Allerdings enthielten die von uns synthetisierten CaC2-Proben stets Anteile von monokliner und tetragonaler Phase. Raman-Spektren von CaC2-Proben zeigten die Prasenz zweier verschiedener C2-Streckschwingungsbanden. Die aus der Koexistenz dieser beiden Phasen resultierende Problematik bei der Interpretation von 13C-MAS-NMR-Spektren wird diskutiert. On the Coexistence of Tetragonal and Monoclinic CaC2: Structural and Spectroscopic Studies on Alkaline Earth Metal Acetylides, MC2 (M = Ca, Sr, Ba) The alkaline earth acetylides CaC2, SrC2 and BaC2 can be considered to occur in three polymorphic structures each. The monoclinic low-temperature form, the tetragonal form, and the cubic high-temperature form. No deviation from axial symmetry is obtained for the C22– ions in the tetragonal structure determinations, as confirmed by X-ray single-crystal structures and 13C MAS NMR studies. The CaC2 samples prepared by us were always a mixture of monoclinic and tetragonal phase. Their Raman spectra exhibited two distinct C2 streching vibrations. Problems arising from the coexistence of these two phases for the interpretation of 13C MAS NMR spectra are discussed.