Stepwise Formation of Molecular Rectangles of Half-Sandwich Rhodium and Ruthenium Complexes Containing Bridging Chloranilate Ligands

Binuclear complexes [Cp*2Rh2(μ-CA)Cl2] (2a) and [(p-cymene)2Ru2(μ-CA)Cl2] (2b) (CA = chloranilate) were obtained by the reactions of [Cp*RhCl(μ-Cl)]2 (1a) or [(p-cymene)RuCl(μ-Cl)]2 (1b) with H2CA in the presence of base, respectively. Treatment of 2a or 2b with bidentate ligands (L) such as pyrazine, 4,4′-dipyridine (bpy), 2,5-bis(4-pyridyl)-1,3,5-oxadiazole (bpo), and E-1,2-bis(4-pyridyl)ethene (bpe) in the presence of AgOTf (OTf = CF3SO3) in CH3OH gave the corresponding tetranuclear complexes, with the general formulas [Cp*4Rh4(μ-CA)2(μ-L)2](OTf)4 (3a−d) and [(p-cymene)4Ru4(μ-CA)2(μ-L)2](OTf)4 (4a−d), respectively. The molecular structures of [Cp*4Rh4(μ-CA)2(μ-bpy)2](OTf)4 (3b), [(p-cymene)4Ru4(μ-CA)2(μ-bpy)2](OTf)4 (4b), and [(p-cymene)4Ru4(μ-CA)2(μ-bpe)2](OTf)4 (4d) have been determined by single-crystal X-ray analysis and revealed that the metal centers were connected by pyridyl ligands and bis-bidentate chloranilate (CA) ligands to construct a rectangular cavity with different dimensions and strong π interactions between independent molecules to form rectangle channels in the solid state.