Bonding In Ring Whizzers. I. Photoeiectrom Spectra and Molecular Orbital Calculations for (η⁵-C₆H₇)Mn(CO)₃, (η⁵-C₇H₉)Mn(CO)₃, and (η⁵.C₇H₇)Mn(CO)₃

A series of calculations, checked by reference to photoelectron spectral (PES) data, is used to interpret the electronic structure and elucidate the principal bonding interactions in a series of cyclic pentadienylmanganese tricarbonyl complexes. A linear correlation is obtained between the calculated eigenvalues and the observed ionization potentials. This correlation suggests that deviations from Koopman's theorem are reasonably constant in these complexes and that the PES data can be adequately assigned by the results of the calculations. Two important conclusions result from this study. (1) The principal bonding interaction between the organic ligand and the metal is due to the interaction of the a′(e1″) level of the pentadienyl moiety with the metal dxz orbital; this interaction is considerably more important than the a″(e1″)-dyz interaction. (2) Calculations indicate a low-lying virtual level in C₇H₇Mn(CO)₃, resulting from the interaction of the π* level with a″(e2″) which may play an important role in the fluxional degenerate rearrangement of this molecule.