Dispersion Stabilizes Metal–Metal Bonds in the 1,8-Bis(silylamido)naphthalene Ligand Environment

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 interfragment 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,
London dispersion, and ligand deformation contributions. The London
dispersion component has been further deconvoluted to identify the
most significant pairwise functional group interactions driving stabilization
from noncovalent interactions. Steric clashes have 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.