The Aryl Effect in Disubstituted Dimanganese and Dicobalt Carbonyls

The energies of the intense bands in the near-UV−vis spectra of a number of axially substituted Mn2(CO)8L2 and Co2(CO)6L2 complexes containing non-π-acid phosphine substituents have been measured in solution. When combined with data reported previously, the trends show unambiguously that a major contributor to the energies is Giering and Prock's aryl effect (quantifiable by E ar values that are almost proportional to the number of aryl groups …