Noncovalent Interactions of Metal Cations and Arenes Probed with Thallium(I) Complexes

The
synthesis, characterization, and computational analysis of Tl­(I) complexes
bearing the bis­(imino)­pyridine scaffold, [{ArNCPh}2(NC5H3)]­Tl+(OTf)− (Ar = 2,6-Et2C6H3 3, 2,5-tBu2C6H3, 4), are reported. The cations of these species showed long
Tl–N and Tl–OTf distances indicating only weak or no
ligand coordination. Computational analysis of the interactions between
the Tl cation and the ligands (orbital populations, bond order, and
energy decomposition analysis) point to only minimal covalent interactions
of the cation with the ligands. The weak ligand-to-metal donation
allows for additional interactions between the Tl cation and arene
rings that are either intramolecular, in the case of 3, or intermolecular. From benzene or toluene, 4 crystallizes
with inverted sandwich structures having two [{(2,5-tBu2C6H3)­NCPh}2(NC5H3)]­Tl+ cations bridged by either benzene
or toluene. A density functional computational description of these
Tl-arene contacts required exchange-correlation functionals with long-range
exchange corrections (e.g., CAM-B3LYP or LC-PBE) and show that Tl-arene
contacts are stabilized by noncovalent interactions.