Metallocene: multi-layered molecular rotors

Besides a negligible rotation barrier, the reasonable rotational period associated with the ultra-soft rotation mode is a critical point for the observability of dynamical behavior in multi-layered molecular rotors.

Palladium-Catalysed Coupling Reactions En Route to Molecular Machines: Sterically Hindered Indenyl and Ferrocenyl Anthracenes and Triptycenes, and Biindenyls

Pd-catalysed Stille and Suzuki cross-couplings were used to prepare 9-(3-indenyl)-, 6, and 9-(2-indenyl)-anthracene, 7; addition of benzyne led to the 9-Indenyl-triptycenes, 8 and 9. In 6, [4 + 2] addition also occurred to the indenyl substituent. Reaction of 6 through 9 with Cr(CO)6 or Re2(CO)10 gave their M(CO)3 derivatives, where the Cr or Re was complexed to a six- or five-membered ring, respectively. In the 9-(2-indenyl)triptycene complexes, slowed rotation of the paddlewheel on the NMR time-scale was apparent in the η5-Re(CO)3 case and, when the η6-Cr(CO)3 was deprotonated, the resulting haptotropic shift of the metal tripod onto the five-membered ring also blocked paddlewheel rotation, thus functioning as an organometallic molecular brake. Suzuki coupling of ferrocenylboronic acid to mono- or dibromoanthracene yielded the ferrocenyl anthracenes en route to the corresponding triptycenes in which stepwise hindered rotations of the ferrocenyl groups behaved like molecular dials. CuCl2-mediated coupling of methyl- and phenyl-indenes yielded their rac and meso 2,2′-biindenyls; surprisingly, however, the apparently sterically crowded rac 2,2′-Bis(9-triptycyl)biindenyl functioned as a freely rotating set of molecular gears. The predicted high rotation barrier in 9-phenylanthracene was experimentally validated via the Pd-catalysed syntheses of di(3-fluorophenyl)anthracene and 9-(1-naphthyl)-10-phenylanthracene.

Starting a subnanoscale tank tread: dynamic fluxionality of boron-based B10Ca alloy cluster

Alloying a B10 cluster with Ca lowers the rotation barrier by one order of magnitude (down to 1 kcal mol−1), leading to a fluxional B10Ca tank tread at the subnanoscale.

Effect of magnetic fields on the methyl rotation in a paramagnetic cobalt(ii) complex. Quasielastic neutron scattering studies

Methyl rotation in a paramagnetic Co(II) complex is slowed down by magnetic field with an increased rotation barrier.