Superphenylphosphines: Nanographene-Based Ligands That Control Coordination Geometry and Drive Supramolecular Assembly

Tertiary
phosphines remain widely utilized in synthesis, most notably
as supporting ligands in metal complexes. A series of triarylphosphines
bearing one to three hexa-peri-hexabenzocoronene
(HBC) substituents has been prepared by an efficient divergent route.
These “superphenylphosphines”, P­{HBC­(t-Bu)5}nPh3‑n (n = 1–3), form the palladium complexes
PdCl2L2 and Pd2Cl4L2 where the isomer distribution in solution is
dependent on the number of HBC substituents. The crystalline structures
of five complexes all show intramolecular π-stacking between
HBC-phosphines to form a supramolecular bidentate-like ligand that
distorts the metal coordination geometry. When n =
2 or 3, the additional HBC substituents engage in intermolecular π-stacking
to assemble the complexes into continuous ribbons or sheets. The phosphines
adopt HBC’s characteristics including strong optical absorption,
green emission, and redox activity.