Influence of Rotator Design on the Speed of Self-Assembled Four-Component Nanorotors: Coordinative Versus Dispersive Interactions

Abstract

Four-component nanorotors are prepared by the self-assembly of stator [Cu(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 rotator's pyridine terminals are connected to the copper(I)-loaded phenanthroline stations (N → [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 H NMR, is mainly governed by attractive forces between stator stations and rotator terminals, it increases along the series E (monopyridine rotator) < E (dipyridine rotator) < E (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 → [Cu(phen)] interactions but also dispersive attraction influence the barrier of rotation.

Heteroleptic copper phenanthroline complexes in motion: From stand-alone devices to multi-component machinery

“…Rate measurements on five-component rotors with brake stones in their trajectory [62], however, do not allow conclusions to be drawn on the cleavage step. We thus focus our report on four-component rotors where the exchange rate has been varied by using rotators with one, two, or three pyridyl terminals [63]. By increasing the number of pyridyl terminals the activation energy for rotation increases and thus the rotational speed decreases as anticipated by thermodynamic considerations (Fig.…”

“…For instance, in most examples, acetonitrile is present, usually due to the use of [Cu(MeCN) 4 ] + as a source for copper. In those cases, rigorous removal of acetonitrile changed the rates significantly [63]. As such the kinetic data can be influenced by number of contributors.…”

Dynamic Functional Molecular Systems: From Supramolecular Structures to Multi‐Component Machinery and to Molecular Cybernetics

“…If both stations of the stator and both terminals of the rotator are identical as in 15 , then rotation cannot be evaluated by VT 1 H NMR ,. As a result, a variety of stators (with two or four phenanthroline stations) and desymmetrized rotators was probed . In all cases, the four‐component assemblies formed in a clean manner as they are held together by one or even several N py →[Cu(phenAr 2 )] + (log K =3.2) as well as two N DABCO →ZnPor (log K =5.4) interactions.…”

“…Surprisingly, even minor alterations at the station of the stator and the terminals of the rotators lead to quite distinct rotational rates (from 0.1 to ca. 100000 Hz at 298 K) ,,. Several factors influence the rotational exchange, such as differential strain, dative solvent(s), dispersive attractions, and the number of terminals in the rotator.…”

“…100000 Hz at 298 K). [31,32,34] Several factors influence the rotational exchange, such as differential strain, dative solvent(s), dispersive attractions, and the number of terminals in the rotator. Moreover, the effect of conformational slippage has been addressed.…”