Effects of an Interannular Bridge on Spectral and Electronic Properties of Bis(cyclopentadienyl)- and Bis(indenyl)zirconium(IV) Complexes

Abstract

Interconnection of the indenyl ligands of bis(indenyl)zirconium dichloride complexes by a 1,1‘-positioned Me2Si or (CH2)2 bridge causes pronounced bathochromic shifts of the longest wavelength UV/vis absorption bands by ca. 50 nm, while much smaller shifts are caused by a Me2Si bridge in otherwise analogous bis(cyclopentadienyl) complexes. Extended Hückel MO calculations show that overlap between the empty 4d orbitals of the ZrCl2 2+ fragment and the highest filled π orbitals of the indenyl anions is decreased when a Me2Si bridge forces the indenyl ligands into a lateral orientation. Consequences of this orbital mismatch, e.g. on electron densities at the Zr center, are discussed.

Mechanism of the interaction of components in the metallocene catalytic systems containing titanium and zirconium tetracyclopentadienyls and methylaluminoxane

“…However, a strong bathochromic shift can be combined with the almost unchanged electron density on the Zr atom as it was shown earlier [17].…”

“Bound but Not Gagged”Immobilizing Single-Site α-Olefin Polymerization Catalysts

“…Subsequent UV−vis studies on the supported systems indicated that light irradiation may, however, favor olefin coordination . UV−vis spectroscopy has been used to extensively study the activation of metallocenes in homogeneous solution − and has recently been extended to silica-supported systems in an attempt to elucidate the interactions between the metal center and the monomer 81 or supported cocatalyst …”

An NMR study on the reaction of substituted dimethyl zirconocenes with dimethylanilinium borate

“…Such a different behavior is likely due to a combination of steric and electronic effects since 1e4 are not only less encumbered than 5e6 [26] but they also bear most acidic metal centers [27]. Once the ZreN bond is formed, the CeH activation of one of the NMe groups of the amine leads to the formation of the zirconaziridinium structures 7e10.…”