The Role of Bulkiness in Haptotropic Shifts of Metal–Cumulene Complexes

Abstract

In metal–cumulene complexes, the metal easily slides through the double bonds of the chain. A series of late‐transition‐metal–[5]cumulene complexes has been studied by theoretical and experimental methods in order to understand the factors that control such haptotropic shifts. The bulkiness of the cumulene terminal groups plays a central role in the tautomeric preferences. The quantum theory of atoms in molecules and the electron localizability indicator show that the M–C bond closer to the terminal groups is significantly weakened by steric interactions between these groups and the rest of ligands around the metal center. The results emphasize that special attention should be paid to the orientation of both the bulky substituents at the cumulene and other voluminous ligands around the metal, because the orientation of such moieties is important in predicting the direction of the haptotropic equilibrium correctly.

Effect of Spectator Ligands on Haptotropic Rearrangements of Metal‐Azulene Complexes

“…This process involves a rapid migration of the metal atom from one position to another within one face of a π-ligand that has multiple coordination sites. [1][2][3][4] There are several theoretical and experimental studies of these processes with PALs, such as naphthalene, [3,[5][6][7] anthracene, [8][9][10] phenalene, [11][12][13][14] with energy barriers related to this migration between 20-30 kcal/mol. The idea of controlling the metal shift in these complexes by suitable promoters or stopping devices could let us use them as molecular switches.…”