Marc-Heinrich Prosenc

Molecular Kondo Chain

An important development in recent synthesis strategies is the formation of electronically coupled one and two-dimensional organic systems for potential applications in nanoscale molecule-based devices. Here, we assemble one-dimensional spin chains by covalently linking basic molecular building blocks on a Au(111) surface. Their structural properties are studied by scanning tunneling microscopy and the Kondo effect of the basic molecular blocks inside the chains is probed by scanning tunneling spectroscopy. Tunneling spectroscopic images reveal the existence of separate Kondo regions within the chains while density functional theory calculations unveil antiferromagnetic coupling between the spin centers.

Cyclopenta[l]phenanthrene titanium trichloride derivatives : syntheses, crystal structure and properties as catalysts for styrene polymerization

Abstract Cyclopenta[l]phenanthrene titanium trichloride and its 2-methyl and phenyl derivatives were synthesized; the crystal structure of the 2-methyl-substituted complex was determined by X-ray diffraction analysis. In the presence of methylalurnoxane (MAO), these complexes give highly active catalysis for the syndiotactic polymerization of styrene; the 2-phenyl-substituted complex exceeds all previously described catalysis in its catalytic activity.

ansa-Metallocene derivatives XXXIII. 2-Dimethylamino-substituted bis-indenyl zirconium dichloride complexes with and without a dimethylsilyl bridge: syntheses, crystal structures and properties in propene polymerization catalysis

Abstract Bis(2-N,N-dimethylamino-indenyl) zirconium dichloride, (2-(CH 3 ) 2 N-C 9 H 6 ) 2 ZrCl 2 , and dimethylsilyl-bridged bis(2-N,N-dimethylamino-indenyl) zirconium dichloride, (CH 3 ) 2 Si(2-(CH 3 ) 2 N-C 9 H 5 ) 2 ZrCl 2 , were prepared by reaction of the corresponding ligand lithium salts with ZrCl 4 in toluene. Diffractometric structure determinations reveal C 2 -symmetric complex geometries for both complexes. An increased electron density at the Zr center of the dimethylamino-substituted complexes is indicated by reduction potentials which are 0.3–0.4 V more negative than those of their unsubstituted analogs. When activated with methyl aluminoxane in toluene solution, (CH 3 ) 2 Si(2-(CH 3 ) 2 N-C 9 H 5 ) 2 ZrCl 2 catalyzes the polymerization of propene to polymers with a microstructure comparable with that of polymers produced with other Me 2 Si-bridged bis(indenyl)ZrCl 2 complexes, but with a substantially increased fraction of i-propyl end groups derived from alkyl exchange between Zr-polymer and AlMe species.

ansa-metallocene derivatives XXXIX biphenyl-bridged metallocene complexes of titanium, zirconium, and vanadium : syntheses, crystal structures and enantioseparation

Chiral, biphenyl-bridged metallocene complexes of general type biph(3,4-R 2 C 5 H 2 ) 2 MCl 2 (biph = 1,1′-biphenyldiyl) were synthesized and characterized. For the dimethyl-substituted titanocenes and zirconocenes (R = CH 3 ; M = Ti, Zr), preparations with increased overall yields and an optical resolution method were developed. The bis(2-tetrahydroindenyl) complexes (R,R = (CH 2 ) 4 ; M = Ti, Zr) were obtained by an alternative synthetic route and characterized with regard to their crystal structures. Syntheses of the phenyl-substituted derivatives (R = C 6 H 5 ; M = Ti, Zr) and of a chiral, methyl-substituted vanadocene complex (R = CH 3 ; M = V) are also reported.

Steering Two‐Dimensional Molecular Growth via Dipolar Interaction

The growth of self-organized molecular networks is recognized as a nature-given, potential bottom-up solution for further miniaturization of electronic devices into the nanometer regime. With self-assembling processes being fully parallelized rather than sequential as in conventional top-down approaches as e-beam writing, molecule-based devices gain their potential from a rational design of the fundamental molecular building blocks for controlled bond formation. Relevant aspects are bonding directions and bonding mechanisms. Several different bonding mechanisms are established for network formation as hydrogen bonding, covalent bonding, or even metal–organic coordination. Although the impact of dipole– dipole interaction on network formation is reported the design of molecular dipole fields is so far not further exploited. Here we report for the first time on such an approach and switch by synthetic means between dominating repulsive and attractive forces among metal–organic complexes. The effect is demonstrated for Co(5,5’-X2-Salen) complexes, X=H (1), Me (2), and Cl (3) locally monitored in ultra-high vacuum (UHV) by scanning tunneling microscopy (STM). Salen complexes of transition metals are versatile and easily modified to tailor electronic, magnetic, and structural bulk properties. Salen complexes are present in a variety of applications in material chemistry and catalysis. Moreover, most complexes are volatile in UHV which enable local studies in a well-defined nanoscopic environment. In Salen complexes the metal center is surrounded by two nitrogen and oxygen donor atoms, which can lead to complexes in quite high oxidization states. The hydrogen atoms at the 5,5’-positions can be substituted by CH3, F, Cl, Br, I, NO2, etc. via the respective salicylaldehyde precursor. Here, individual Co-salen complexes adsorbed on a surface are studied for the first time by STM and reveal an insight into the mechanism of intermolecular coupling. The experiments are performed in a variable temperature STM operated at ~25 K. Tips and Cu ACHTUNGTRENNUNG(111) surfaces are prepared by standard procedures with molecules sublimed from homebuilt Knudsen cells. Voltages refer to the potential of the tip relative to the sample. Positive voltages refer to tunneling into unoccupied sample states and negative voltages to tunneling out of occupied sample states. We focus on the analysis of STM images as acquired at 1.4 V, 0.1 V, and +1.4 V which are referred as ‘at large negative bias’, ‘at low bias’, and ‘at elevated positive bias’ throughout the text. Images at these biases show characteristic features as discussed below and are representative for images as acquired within a larger bias interval (~ 0.5 V) with only gradual changes in between. The chemical structures of the complexes used herein are presented in Figure 1 along with corresponding, equally scaled STM images at low bias of isolated molecules adsorbed on a Cu ACHTUNGTRENNUNG(111) surface. For visualization a scaled model of the structure is superimposed. For complex 1 the appearance of the complex in the STM image perfectly fits to the structure. Due to different substituents the apparent size of 2 and 3 varies in the topographic images. We will first focus on the appearance and adsorption of isolated molecules of complex 1, that is, after low temperature preparation which hinders thermally induced mobility and therefore self-assembling on Cu ACHTUNGTRENNUNG(111). Figures 2b–2d show the same isolated molecule of complex 1 but as imaged at different energies. Imaged at low bias (Figure 2c), the molecule nicely fits to the molecular structure and exhibits a maximum in the apparent height at a location between the cobalt center and the top C2H4 bridge. Imaged at a large negative energy a pronounced topographic maximum at the site of the Co ion dominates the overall molecular appearance (Figure 2b). We interpret this as resulting from occupied Co 3d orbitals perpendicular to the molecular plane similar to the case of other metal-organic complexes. A significant change can be observed when tunneling through unoccupied molecular states at elevated positive bias: molecules become asymmetric and the maximum in the apparent height is shifted towards one side of the C2H4 bridge (Figure 2d). A first interpretation is suggested by results of DFT calculations for the free complex. In Figure 2a an optimized structure of complex 1 is depicted. The side view clarifies a C2 symmetry due to a deformation of the C2H4-bridge which implies chirality. STM measurements identified complexes adsorbed in 12 different configurations on the Cu ACHTUNGTRENNUNG(111) surface. Figure 2e shows all 12 configurations as imaged at low bias. The observable asymmetry at elevated positive energies (Figure 2 f) unambiguously reveals two mirror symmetric (R vs L) sets of 6 molecules each rotated in steps of 608. With the exact crystallographic axes determined from atomically resolved images of the bare substrate, two mirror symmetric enantiomers can be attributed to each crystallographic direction. Molecules denoted with R are rotated clockwise by +118 38 relative to the substrate axes and with L anticlockwise by 88 38. This is schematically illustrated in Figure 2 g. [a] S. Kuck, Dr. S.-H. Chang, Dr. G. Hoffmann, Prof. Dr. R. Wiesendanger Institut f r Angewandte Physik Universit t Hamburg, Jungiusstrase 9, Hamburg (Germany) Fax: (+49)40-42838-2944 E-mail : skuck@physnet.uni-hamburg.de [b] J.-P. Klcckner, Prof. Dr. M. H. Prosenc Institut f r Anorganische und Angewandte Chemie Universit t Hamburg, Martin-Luther-King-Platz 6, Hamburg (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.200900281

Displacement of weakly coordinating anions from zirconocene alkyl cations by trialkyl phosphines: A model for olefin coordination in homogeneous Ziegler–Natta catalysis

y w . . q . Displacement of the anion H C-B C F from the zirconocene contact-ion pair C H Zr CH PPP m-H C -

ansa-Metallocene derivatives: XLI. Chiral ansa-Magnesocene complexes–syntheses, crystal structures and structural dynamics in solution

Abstract A series of chiral ansa-magnesocene complexes with dimethylsilanediyl- or ethanediyl-bridged, substituted cyclopentadienyl or indenyl ligands, prepared in form of their THF adducts, has been structurally characterized by diffractometric crystal structure determination and by NMR studies in solution. The hapticities of the ring ligands vary between η 1 and η 5 , depending on the nature of the interanular bridge and the C 5 ring substituents. A racemic configuration is preferred by Mg bis-indenyl complexes with either Me 2 Si- or C 2 H 4 -bridges in the solid state and in solution, while meso isomers predominate for t -butyl-substituted ansa-magnesocenes.

ansa-metallocene derivatives XXXVI. Dimethylsilyl-bridged permethyl chromocene carbonyl complexes : syntheses, crystal structures and interconversion reactions

Abstract The ring-bridged chromocene carbonyl complex Me 2 Si(C 5 Me 4 ) 2 Cr(CO) 1 is obtained by reaction of Me 2 Si(C 5 Me 4 ) 2 Li 2 with CrCl 2 · THF in the presence of CO. Reaction with CO transforms the monocarbonyl complex 1 to a dicarbonyl complex Me 2 Si(C 5 Me 4 )(C 5 ( endo -3-H)(2-CH 2 )Me 3 )Cr(CO) 2 2 ; in this reaction, a hydrogen atom is shifted from one of the α-CH 3 groups to the adjacent β-position of a C 5 ring ligand. The rate of this reaction is first order in complex and CO concentration, with an activation enthalpy of H ≠ = 51 ± 3 kJ mol −1 and an activation entropy of S ≠ = 136 ± 10 J mol −1 K −1 . In toluene solution at 50°C, complex 2 isomerizes to Me 2 Si(C 5 Me 4 )(C 5 ( exo -3-H)(2-CH 2 )Me 3 )Cr(CO) 2 3 , then to Me 2 Si(C 5 Me 4 )(C 5 ( exo -1-H)(2-CH 2 )Me 3 )Cr(CO) 2 4 and further to Me 2 Si(C 5 Me 4 )(C 5 ( endo -5-H)(2-CH 2 )Me 3 )Cr(CO) 2 5 . The kinetics of these isomerizations, which involve hydrogen migrations and ring rotation reactions, indicate monomolecular reactions. Possible reaction paths and transition states are discussed. The structures of complexes 1–5 were determined by 1 H NMR spectroscopy, those of 1, 2, 4 and 5 also by single-crystal X-ray diffraction. Complex 1 : space group P 2 1 / n , a = 13.257(7)A, b = 10.186(5)A, c = 14.739(7) A, β = 90.89(4)°; V = 1990.1(7)A 3 ; Z = 4. Complex 2 : space group Pbca , a = 8.699(3) A, b = 14.713(6) A, c = 32.801(14)A; V = 4198(3)A 3 ; Z = 8. Complex 4 : space group P 2 1 , a = 9.497(2)A, b = 9.895(3) A, c = 11.371(2)A, β = 103.919(8)°; V = 1037.1(4) A 3 ; Z = 2. Complex 5 : space group P 2 1 / c , a = 16.555(4)A, b = 13.036(3)A, c = 10.044(2)A, β = 107.45(1)°; V = 2067.8(8)A 3 ; Z = 4.

Synthesis and Properties of a Novel Series of Organometallic Merocyanines Combining the Potent Electron‐Donating [(CpFeCO)2(μ‐CO)(μ‐C=CH−)] Fragment with Tropylium‐Type Acceptors

The potent electron-donating group [(CpFeCO)2(µ-CO)(µ-C=CH−)] was combined with different tropylium-based acceptors yielding the push-pull complexes [(CpFeCO)2(µ-CO)(µ-C=CH−CH=A)][BF4] where =A represents [=CH−(η7-C7H6)Cr(CO)3]+ (5), [={C10H7}]+ (azulenylium) (7) [={C10H4Me2iPr}]+ (guaiazulenylium) (8). Crystal structures of the precursor complexes [(CpFeCO)2(µ-CO)(µ-C=CH−CH=CH−C7H7)] (3), [(CpFeCO)2(µ-CO){µ-C=CH−CH=CH−(η6-C7H7)Cr(CO)3}] (4) and the push-pull derivative 5 are presented. Whereas complexes 3 and 4 demonstrate localised carbon−carbon double and single bonds in the π-bridge between the diiron moiety and the seven-membered ring a small but distinct π-bond delocalisation can be observed in the π-linker of the cationic derivative 5. From the NMR spectroscopic results a correlation between the 13C NMR shift of the bridging carbon atom µ-C of the diiron unit and the coupling constant J(1H-1H) of the β- and γ-protons of the π-bridge was found. This correlation indicates an increased π-bond delocalisation throughout the conjugated bridge with respect to the electron-accepting capability in the order tricarbonyl(η7-cycloheptatrienylium)chromium < guaiazulenylium < azulenylium implying a predominantly charge-delocalised form in the case of the azulenylium complex 7. Considerably large first hyperpolarisabilities β were determined for 5 and 8 by means of hyper-Rayleigh scattering. Based on the two-level model β0 values were calculated and related to the bond-length alternation in the π-linker. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

ansa-Metallocene derivatives XX. An assignment of 1H- and 13C-NMR signals in ansa-metallocene complexes with 16-electron and 18-electron configuration

Abstract The NMR signals of cyclopentadienyl ring protons and C atoms in ansa -metallocene derivatives of general type (CH 3 ) 4 C 2 (C 5 H 4 ) 2 M(X,L) n , with a 16-electron configuration, i.e. with MX n = TiF 2 , TiCl 2 , TiBr 2 , TiI 2 or Ti(CH 3 ) 2 , and with an 18-electron configuration, i.e. with ML n = Ti(CO) 2 , Ti(P(CH 3 ) 3 ) 2 , Cr(CO) or Fe, have been assigned to the α- and β-ring positions by nuclear Overhauser effect and selective decoupling studies. Whereas the α-proton resonances appear at higher fields than those for the β-protons in all the complexes with the 16-electron configuration, the opposite is the case for the 18-electron ansa -metallocene derivatives studied.