Effect of M(CO)₃ (M = Cr, Mn⁺) on aromatic C-Cl BDE in (η⁶-ArCl)M(CO)₃ complexes

The coordination of Cr(CO)₃ to chlorobenzenes significantly reduces the C-Cl bond dissociation energy. Treatment of chloroarene-Cr(CO) ₃ complexes with SmI₂/HMPA at room temperature led to complete dechlorination. Reaction of o-allyloxychlorobenzene-Cr(CO)₃ complexes with SmI₂ at room temperature resulted in the corresponding dechlorinative cyclization products in good to excellent yields. Competition experiments indicated the following relative reactivities of dehalogenation by SmI₂: PhI/PhCl-Cr(CO)₃/PhBr/PhCl = 50:1:0.3:<0.001. On the other hand, the coordination of Mn(CO)₃⁺ to chlorobenzene showed a much smaller activation effect. Density functional theory calculations revealed that the spin delocalization effect of the metal center plays an important role in the C-Cl bond activation.