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.

Crystal structures and solution conformations of the meso and racemic isomers of (ethylenebis(1-indenyl))zirconium dichloride / F. Piemontesi, I. Camurati, L. Resconi, D. Balboni, A. Sironi, M. Moret, R. Zeigler, N. Piccolrovazzi. - In: ORGANOMETALLICS. - ISSN 0276-7333. - 14:3(1995), pp. 1256-1266.

Crystal structures and solution conformations of the meso and racemic isomers of (ethylenebis(1-indenyl))zirconium dichloride

A. Sironi;
1995

Abstract

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.
Settore CHIM/03 - Chimica Generale e Inorganica
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/188237
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