Coordination-Induced Molecular Tweezing: Ruthenium Clusters Docked at Azuliporphyrinogens

The reaction of [Ru3(CO)12] with a series of conformationally flexible
thiaazuliporphyrinogens, namely, dithiadiazuli-, thiatriazuli- and
tetraazuliporphyrinogen, yielded a series of complexes with two azulene
rings coordinated by either Ru2(CO)5 and Ru4(CO)9 or two Ru4(CO)9 clusters.
For dithiadiazuliporphyrinogen, three fundamental arrangements were
detected, with two clusters being located at the same side or different
sides of the meso plane. Coordination altered the electron density
on the rings, allowing for dispersion-promoted interactions between
coordinated azulenes. To create this face-to-face arrangement, the
ligand framework performs a tweezing movement with coordinated azulenes
approaching each other. The tweezer-like arrangement of the coordinated
azulene rings assists the formation of azulene inclusion complexes
as determined by 1H NMR titration.