Light-Induced Geometrical Changes in Acyclic Ruthenium(II) Complexes and Their Ruthena−Macrocyclic Analogues

The two ligands 1 (4‘-(3-anisylphenyl)-2,2‘;6‘,2‘ ‘-terpyridine) and 2 (2-mesityl-8-anisyl-1,10-phenanthroline) (Scheme
) were synthesized and coordinated to ruthenium. The corresponding complexes Ru(1)(2)(L)n+, where L = Cl-,
CH3CN, or C5H5N, have been fully characterized. Notably, the hindering mesityl group of the phenanthroline ligand
was shown to lie opposite to the monodentate ligand L both in solution and in the solid state. Upon irradiation in
acetonitrile or pyridine, quantitative isomerization of the complex occurred, which consisted of a 90° rotation of the
bidentate chelate. In the new isomers the mesityl group was shown to π stack to the coordinated monodentate
ligand with the anisyl group of the phen (1,10-phenanthroline) lying on the other side of the ruthenium atom. The
back reaction was performed by heating the photochemical isomers of the complexes in DMSO and exchanging
the DMSO with chloride anion, acetonitrile, or pyridine. The stability of the ruthenium(II)−pyridine bond was used
in order to inscribe the Ru(terpy)(phen) motif in a molecular ring. Functionalization of the ligands and subsequent
cyclization reaction on the complex were performed on the two isomers of Ru(1)(2)(C5H5N)2+. Four macrocyclic
complexes including the Ru(terpy)(phen)(py)n+ moiety were obtained and characterized. A (CH2)18 alkane chain or
polyethylene glycol chain formed the flexible part of the ruthena−macrocycles. Upon visible light irradiation a dramatic
geometrical changeover of the cyclic complex took place, which could be reversed thermally.