Allyl complexes of chromium and zirconium: molecular structures from DFT and ab initio calculations

The molecular structures of trisallylchromium, tris-2-methylallylchromium, allylchromium dibromide, tetrakisallylzirconium, tetrakis-2-methylallylzirconium and allylzirconium tribromide have been investigated by means of quantum chemical calculations. Restricted Hartree-Fock (HF) geometries show some sigma-character in the allyl bonding to the metal centres, especially for the chromium systems, while the allyl groups coordinate in a purely trihapto fashion at the DFT level. For allylchromium dibromide, test calculations at the unrestricted HF level show problematic SCF convergence and severe spin contamination, indicating strong correlation effects; hence, we place higher confidence in the DFT results. All molecules under study are fluctional. (C) 1998 Elsevier Science S.A. All rights reserved.