A novel strategy to construct Janus metallamacrocycles with both a Ru-arene face and an imidazolium face

The bottom-up construction of highly functional metallamacrocycles from simple building blocks is a challenge of much current interest. We have used solvothermal reactions of a bifunctional p-bitmb ligand with [Ru(arene)X₂]₂ in CH₂Cl₂ or CH₂Br₂ to generate the novel mononuclear metallamacrocyclic [RuX(arene)L₂CH₂]X₃ complexes 1-3 (1, arene = p-cym, X = Cl; 2, arene = bip, X = Cl; 3, arene = p-cym, X = Br), which were characterized by various techniques. These complexes are "bowl-like" and have two faces: one coordinative Ru centre (arene)Ru(N,N)X bridged by L (L = 1,4-bis(imidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene, p-bitmb) to a dipositive bis-imidazolinium centre. Cl^- or Br^- anions can be trapped inside the cavity of the "bowl-like" structure, forming H-bonds with the backbone. Experimental (NMR and ESI-MS) and computational (DFT calculations) studies show that the source of the bridging -CH₂- group is the dihalogenated solvent (CH₂Cl₂ or CH₂Br₂) that links the two arms of an initially formed non-cyclic complex (arene)RuX₂L₂ by a mechanism of nucleophilic substitution. Optimization of the reaction conditions afforded the macrocyclic complexes in almost quantitative yields. The applications of these complexes as anti-proliferative agents towards cancer cells and for selective anion sensing have been explored.