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

Bis(2-N,N-dimethylamino-indenyl) zirconium dichloride, (2-(CH₃)₂N-C₉H₆)₂ZrCl₂, and dimethylsilyl-bridged bis(2-N,N-dimethylamino-indenyl) zirconium dichloride, (CH₃)₂Si(2-(CH₃)₂N-C₉H₅)₂ZrCl₂, were prepared by reaction of the corresponding ligand lithium salts with ZrCl₄ in toluene. Diffractometric structure determinations reveal C₂-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, (CH₃)₂Si(2-(CH₃)₂N-C₉H₅)₂ZrCl₂ catalyzes the polymerization of propene to polymers with a microstructure comparable with that of polymers produced with other Me₂Si-bridged bis(indenyl)ZrCl₂ complexes, but with a substantially increased fraction of i-propyl end groups derived from alkyl exchange between Zr-polymer and Al---Me species.     

Electronic coupling through intramolecular π-π interactions in biscobaltocenes: a structural, spectroscopic, and magnetic study

The paramagnetic dinuclear complexes 1,8-bis(cobaltocenyl)naphthalene (2) and 1,8-bis[(pentamethyl-η(5)-cyclopentadienyl)(η(5)-cyclopentadiendiyl)cobalt(II)]naphthalene (4) were synthesized. The molecular structures were characterized by X-ray structure analysis and consisted of two cobaltocenes linked through a distorted naphthalene clamp. Electronic interactions between the two cobalt atoms were observed by cyclic voltammetric studies. Superconducting quantum interference device (SQUID) measurements of the pure compounds and diluted in their diamagnetic iron derivatives, as well as variable-temperature NMR spectroscopy experiments in solution are presented. Magnetic measurements revealed an antiferromagnetic coupling of the electrons in complexes 2 and 4. From NMR spectroscopy experiments, Curie behavior in the temperature range from -60 to +60 °C can be deduced. The electronic structure and magnetic behavior is supported by results of broken-symmetry DFT and multireference calculations along with UV/Vis spectroscopic data, which revealed an intramolecular through space π-π interaction between the cobaltocene units.     

Computational and structural studies on the complexation of cobalt(II) acetate by water and pyridine

Four different complexes of the cobalt(II) acetate–pyridine–water system were obtained as dominant species by crystallization from a series of dichloromethane and toluene solutions. The complexes were characterized by terms of X-ray crystal structure determination. Factors in solution properties leading to crystallization of certain complexes are discussed. Furthermore, trends in terms of structure and binding energies in a systematic series of mononuclear cobalt(II) complexes were studied using density functional calculations.     

Multi-centre, hydrogen and dihydrogen bonds in lithium closo-hydroborate obtained from liquid ammonia

Charge density analysis reveals multi-centre bonds in the cluster, hydrogen bridges in the ammonia network, and the dihydrogen bond between H(delta-) and H(delta+); all observed in one compound, [Li(NH3)4]2B6H6.2NH3.     

Zur Elektronenstruktur metallorganischer Komplexe der f‐Elemente. 78[1]Ergänzende Informationen von “polarisierten” Raman‐Spektren orientierter Einkristalle und Modellrechnungen auf der Grundlage der Dichtefunktionaltheorie bei der Zuordnung der Schwingungsspektren von Decamethylosmocen

The far and mid infrared (FIR/MIR) spectra of powdered Os(η⁵‐C₅Me₅)₂ (OsCp*₂) as well as the polarized Raman spectra of an oriented single crystal (where the two molecules of D_5h symmetry in the unit cell are uniformly oriented) have been recorded. The latter allow the assignment of the observed Raman lines to irreducible representations (irreps) which agree well with the predictions of a calculation applying density functional theory. This finding suggests additional correlation of the observed (unpolarized) bands in the FIR/MIR spectra with the calculated wavenumbers (and their irreps) of IR active normal modes. Neglecting νCH vibrations an r.m.s. deviation of 15.8 cm^–1 for 40 assignments (Raman and IR) could be achieved. Skeletal and intra‐ligand vibrations could be identified and a number of previous assignments of the latter had to be revised. Because of mixing with skeletal modes some of the low frequency intra‐ligand vibrations display a noticeable dependence on the mass of the central atom which prevents the direct transfer of the identified γCCH₃ and βCCH₃ normal modes from MCp*₂ (M = Fe, Ru, Os) to LnCp*₃ (Ln = La, Ce, Pr, Nd, Sm) complexes.