Dispersion stabilizes metal-metal bonds in the 1,8-bis(silylamido)naphthalene ligand environment

Abstract

There is emerging consensus that stabilization of weak bonds using bulky substituents operates not only by steric shielding, but also by boosting the dispersive attraction across the bond. While many studies have explored this concept for hydrocarbon, arene, carbene, and phosphine ligands, it remains minimally explored for amide ligands. Bulky 1,8-bis(silylamido) naphthalenes were recently used to isolate the first example of Sb--Bi σ bonds, which was tentatively ascribed to an unexpectedly-high degree of inter-fragment dispersive stabilization. To understand this finding and study how the interplay between steric repulsion and dispersive attraction alters metal-metal bond strengths more generally, we have computationally examined Sb--Sb, Sb--Bi, and Bi--Bi σ bond enthalpies and energies in 21 compounds within the 1,8-bis(silylamido) naphthalenes ligand framework. The energies have been dissected into base electronic, dispersion, and ligand deformation contributions. The dispersion component has been further deconvoluted to identify the most significant pairwise functional group interactions driving dispersive stabilization. Steric clash has been considered by examining the extent of ligand deformation. The resulting insights will enable the rational evolution of these accessible and tunable ligands in the context of stabilizing weak bonds and may also be transferable to other amide ligands.