SUMMARY: Elastomeric poly(propylene) with low percentages of isotactic pentads and high molecular weight was synthesized using unbridged "oscillating" metallocenes. The polymer sample with the highest [mmmm] content (22%) shows a small amount of crystallinity, which is highly influenced by the thermal history, and differs significantly in stress-strain and dynamic mechanical properties from all other samples. Polymers with lower isotacticity index, although lacking crystallinity in thermal analysis, differ in their viscoelastic behaviour from those of atactic poly(propylene). In dynamic mechanical analysis the c relaxation at low temperature shows high sensitivity to low isotactic contents.

The reaction of rac-(ebthi)Zr(η2-Me3SiC2SiMe3) (1) [ebthi = 1,2-ethylene-1,1‘-bis(η5-tetrahydroindenyl)] with an excess of ethylene at room temperature leads to the corresponding zirconacyclopentane 3, which was isolated as stable yellow crystals and characterized by an X-ray crystal structure analysis. At 203 K complex 1 reacts with only 1 equiv of ethylene to form the zirconacyclopentene 2, possibly an intermediate in the reaction from 1 to 3. Upon activation with tris(pentafluorophenyl)borane under an ethylene atmosphere, complex 3 was shown to be an effective catalyst for ethylene polymerization. The reaction of 2 equiv of styrene with the alkyne complex 1 leads to the unsymmetrically substituted zirconacyclopentane 6.

Chiral ansa-zirconocene complexes with a trimethylene link between the Si bridge atom and an a-position of each C s ring ligand were prepared; two representatives, with i-propyl and t-butyl groups as f3-substituents, were structurally characterized. The properties of these complexes with respect to MAO-activated propene polymerization were studied in comparison with those of their Me 2 Si-bridged analogs. The t-butyl-substituted spirosilane complex gives a polymer with relatively high content of 3, I-insertions. These increased regioirregularities appear to be associated with decreased coordination gap aperture and increased lateral extension angles of the spirosilane-bridged zirconocene complexes; this notion is supported by a molecular-mechanics analysis of alternative olefin-insertion transition states.

An easily accessible device for the study of reactions with gases in the liquid phase, consisting of a 10 mm NMR tube with a gas inlet, is presented. This arrangement serves for reaction monitoring and mechanistic studies by acquiring NMR spectra (1H, 13C, 31P) with a resolution that allows one to observe and characterize intermediates that cannot be isolated as pure substances. The quantity of the gas to be consumed is not limited. Examples from organometallic chemistry are presented: the formation of a zirconacyclopentene from a zirconium–alkyne complex and ethylene and investigations on rhodium‐catalysed olefin hydrogenation. The qualitative and quantitative evaluation of the measurements and application to reaction kinetics are discussed. An uptake of 0.1 ml of gas per minute at normal pressure (isobaric) is possible without a marked influence of diffusion (stationary conditions). © 1997 John Wiley & Sons, Ltd.