Formation of Diruthenium(II) Complexes Containing 2,2′;6′,2′′-Terpyridine Domains Possessing Rotationally Restricted Connectivity: The Influence of Shape-Persistence

The synthesis and characterization of a structurally related series of bis-terpyridine diruthenium(II) complexes are described. Two of the complexes (10 and 11) contained elements of rotational immobility around the central axis due to a mesitylene moiety, while two other complexes (12 and 13) were free-to-rotate about the central tolyl moiety. It was found that the complexes that included the mesitylene moiety in the central region showed a unique splitting pattern of the protons associated with the inner bis-terpyridine, while the complexes that lacked the mesitylene showed no such splitting; there was also no unusual splitting observed for the complexes that contained a peripheral mesitylene group. Molecular modeling calculations indicated the rotational barrier around the central axis of the mesitylene moiety to be substantially greater than the rotational barrier of the tolyl group. The X-ray crystal structure of the rotationally frozen ligand is also described.