Interaction of In(I) and Tl(I) cations with 2,6-diaryl pyridine ligands: Cation encapsulation within a very weakly interacting N/arene host environment

The interaction of 2,6-dimesitylpyridine with Tl(I) and In(I) cations has been investigated with a view to developing tractable molecular M(I) compounds which are soluble in organic media. In stark contrast to isosteric and isoelectronic terphenyl systems, complexes featuring the [(2,6-Mes ₂py)M]⁺ fragment feature very weak metal-ligand interactions in the solid state, as revealed by M-N distances of the order of 2.45 Å (M = In) and 2.64 Å (M = Tl). While additional weak φ interactions are observed with arene solvate molecules in these systems, the related 2:1 complex [(2,6-Mes₂py)₂In][BAr^f ₄] features an In(I) center wholly encapsulated by the bulky Mes ₂py donors, and even longer In-N distances [2.586(6) and 2.662(5) Å]. These contacts are about 0.5 Å greater than the sum of the respective covalent radii (2.13 Å) and provide evidence for an effectively "naked" In(I) cation stabilized to a minor extent by orbital interactions.