Understanding Heterolytic Bond Cleavage

When considering the fragmentation of a single bond, the attractive singlet and repulsive triplet potential energy curves of the prototype H2 - 2 H dissociation often come to mind. For species in which homolytic bond cleavage is energetically favored, such comparisons are reasonable. For other species where heterolytic cleavage gives lower-energy products, the H2 analogy is inappropriate. This paper offers a qualitative theoretical treatment of the singlet and triplet potential energy curves that arise when a single bond formed by an electron pair is cleaved either homolytically or heterolytically. This analysis is shown to provide insight into several problems involving transition metal systems transition metal carbonyls, metal ion-ligand complexes, and transition metal dimers.