ELECTRON DELOCALIZATION IN PARAMAGNETIC METALLOCENES .2. EXTENDED HUCKEL MOLECULAR ORBITAL CALCULATIONS

Self-consistent charge extended Hückel molecular orbital calculations were carried out for vanadocene, methylvanadocene, cobaltocene, methylcobaltocene, nickelocene, and methylnickelocene. For these calculations, Basch, Gray, Viste VOIP's were used for the Hii's and the Wolfsberg-Helmholz approximation was used for the Hij's. The overlap matrices were computed using dementi's SCF atomic functions. The molecular orbital calculation gives a generally good account of the experimental facts for the metallocenes, in particular the nmr contact shifts. It was found that the primary unpaired electron delocalization mechanism for vanadocene and chromo-cene involves ó MO's. This is in agreement with our earlier experimental conclusions. In cobaltocene and nickelocene, unpaired electron delocalization is dominated by the π contribution, but the ó effects are quite large. In all cases the magnitudes and signs of the coupling consta ts are well reproduced. © 1969, American Chemical Society. All rights reserved.