title: Combination of spectroscopic methods: in situ NMR and UV/Vis measurements to understand the formation of group 4 metallacyclopentanes from the corresponding metallacyclopropenes.
abstract: By reaction of the dichloride rac-(ebthi)HfCl(2) [ebthi = 1,2-ethylene-1,1'-bis(eta(5)-tetrahydroindenyl)] with lithium in the presence of bis(trimethylsilyl)acetylene, the hafnacyclopropene rac-(ebthi)Hf(eta(2)-Me(3)SiC(2)SiMe(3)) (1-Hf) was obtained. The reaction of the blue-green complex 1-Hf with an excess of ethylene at room temperature leads by insertion of the olefin to the yellow-green hafnacyclopentene 2-Hf which is only stable in solution and eliminates the alkyne at 100 degrees C under ethylene to form the corresponding yellow hafnacyclopentane 3-Hf, which was characterized by X-ray crystal structure analysis. The reaction of 1-Hf to give stepwise via 2-Hf the complex 3-Hf was investigated in detail and compared to the formation and stability of the corresponding zirconacyclopropene 1-Zr, zirconacyclopentene 2-Zr, and zirconacyclopentane 3-Zr. Moreover, the reaction of the titanocene alkyne complex 1-Ti with ethylene was studied. For investigating the reaction behavior of the alkyne complexes 1-M, NMR spectroscopy was used and the results were compared with UV/vis spectroscopy, suggesting the existence of a bis-pi-complex prior to the formation of the hafnacyclopentene 2-Hf.
authors.affiliation: Leibniz-Institut fur Katalyse e. V. an der Universitat Rostock, Albert-Einstein-Strasse 29a, D-18059 Rostock, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Beweries
authors.forename: Christian
authors.initials: C
authors.lastname: Fischer
authors.forename: Stephan
authors.initials: S
authors.lastname: Peitz
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Burlakov
authors.forename: Perdita
authors.initials: P
authors.lastname: Arndt
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Baumann
authors.forename: Anke
authors.initials: A
authors.lastname: Spannenberg
authors.forename: Detlef
authors.initials: D
authors.lastname: Heller
authors.forename: Uwe
authors.initials: U
authors.lastname: Rosenthal