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 ZrCl22+ 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.