Substituent Effects on the Bond-Dissociation Energies of Cationic Arene−Transition-Metal Complexes

The bond-dissociation energies (BDEs) of more than twenty arene−M+ complexes (M = Cr, Fe, Co) have been studied by mass spectrometry, using the kinetic method. With minor exceptions, the same relative order of BDEs is found for the three metals and the series of substituted arenes: electron-donating substituents, like alkyl or amino groups, increase the arene−metal BDE whereas electron-withdrawing substituents, e.g. halogens, lower the BDE compared to the unsubstituted benzene complexes. Interestingly, inverse linear correlations of the arene−M+ BDEs and the arenes′ ionization energies (IEs) exist for particular classes of substituents. The present results may serve as a guide to predict BDEs of similar organometallic complexes based on the IEs of substituted arenes and vice versa.