The crystal and molecular structures of the C2 symmetric rac-(EBI)ZrCl2 (1r) [monoclinic, space group I2/c, No. 15, a = 11.957(1) Å, b = 10.627(1) Å, c = 13.775(2) Å, β = 106.06(1)°] and of its meso isomer (1m) [monoclinic, space group P21/n, No. 14, a = 11.119(3) Å, b = 10.467(1) Å, c = 14.949(2) Å, β = 100.94(2)°] have been solved. 1r is in the indenyl-forward (Π) conformation, as is the case for most of the chiral ansa ethylene-bridged bisindenyl-type metallocenes. In solution however, already at room temperature there is a rapid (NMR time scale) interconversion between the two Π and Y (indenyl-backward) conformations, as shown by conformational analysis on the proton spectra of the bridge methylenes. This equilibrium is shifted toward the lower energy conformation δ at lower temperatures and is influenced by both the solvent and the σ-ligands. The solid state structure of 1m shows that this meso form is actually in a chiral conformation (C1 symmetry) because of the staggered placement of the two indenyl ligands (Ind∧Ind = 10.0°). In solution this aspecific zirconocene gives a perfectly symmetric 1H NMR spectrum, indicating that, as in the case of the rac-isomer, there is a rapid interconversion between the two equienergetic, mirror-image limit conformations. © 1995 American Chemical Society.
|Titolo:||Crystal structures and solution conformations of the meso and racemic isomers of (ethylenebis(1-indenyl))zirconium dichloride|
|Settore Scientifico Disciplinare:||Settore CHIM/03 - Chimica Generale e Inorganica|
|Data di pubblicazione:||1995|
|Digital Object Identifier (DOI):||10.1021/om00003a028|
|Appare nelle tipologie:||01 - Articolo su periodico|