Small Molecule Regulation of Self-Association and Catalytic Activity in a Supramolecular Coordination Complex

Herein,
we report the synthesis and characterization of the first
weak-link approach (WLA) supramolecular construct that employs the
small molecule regulation of intermolecular hydrogen bonding interactions
for the in situ control of catalytic activity. A biaryl urea group,
prone to self-aggregation, was functionalized with a phosphinoalkyl
thioether (P,S) hemilabile moiety and incorporated into a homoligated
Pt­(II) tweezer WLA complex. This urea-containing construct, which
has been characterized by a single crystal X-ray diffraction study,
can be switched in situ from a rigid fully closed state to a flexible
semiopen state via Cl– induced changes in the coordination
mode at the Pt­(II) structural node. FT-IR and 1H NMR spectroscopy
studies were used to demonstrate that while extensive urea self-association
persists in the flexible semiopen complex, these interactions are
deterred in the rigid, fully closed complex because of geometric and
steric restraints. Consequently, the urea moieties in the fully closed
complex are able to catalyze a Diels-Alder reaction between cyclopentadiene
and methyl vinyl ketone to generate 2-acetyl-5-norbornene. The free
urea ligand and the semiopen complex show no such activity. The successful
incorporation and regulation of a hydrogen bond donating catalyst
in a WLA construct open the doors to a vast and rapidly growing catalogue
of allosteric catalysts for applications in the detection and amplification
of organic analytes.