Four-component nanorotors are prepared by the self-assembly of stator [Cu4(4)](4+) with its four copper(I)-loaded phenanthroline stations and various rotators carrying one, two, or three pyridine terminals. The fourth component, 1,4-diazabicyclo[2.2.2]octane, serves as a connecting axle between rotator and stator. Capitalizing on the heteroleptic pyridyl and phenanthroline metal complexes concept, the rotators pyridine terminals are connected to the copper(I)-loaded phenanthroline stations (N-py -> [Cu(phen)](+)) in the STOP state and disconnected in the transition state of rotation. As the barrier of the thermally activated rotation, measured by variable-temperature 1H NMR, is mainly governed by attractive forces between stator stations and rotator terminals, it increases along the series Ea (monopyridine rotator) < Ea (dipyridine rotator) < Ea (tripyridine rotator). However, there are even distinct differences in rate between rotors with equal number of rotator terminals. The change from the 5,10-dipyridyl (cis) to 5,15-dipyridyl (trans) zinc porphyrin rotator enhances the rotational frequency by almost 1000-fold. Density functional theory computational results suggest that not only coordinative N-py -> [Cu(phen)](+) interactions but also dispersive attraction influence the barrier of rotation.
DABCO as a Dynamic Hinge between Cofacial Porphyrin Panels and Its Tumbling inside a Supramolecular Cavity
作者:Soumen K. Samanta、Debabrata Samanta、Jan W. Bats、Michael Schmittel
DOI:10.1021/jo201252q
日期:2011.9.16
The heteroleptic supramolecular double-decker porphyrin 1 was synthesized with DABCO as a guest between two cofacial porphyrin units as characterized by H-1 NMR and ESI-MS. While DABCO is not seen to tumble inside the cavity, even at higher temperatures (80 degrees C), such motion was triggered upon addition of various coordinating ligands (quinuclidine, 4-bromopyridine, or excess of DABCO). Different stoichiometric amounts were needed depending on the n donor quality of the added ligands to initiate tumbling of the "inside" DABCO. As demonstrated in an example with excess DABCO, the tumbling was stopped by lowering the temperature to -50 degrees C.