Synthesis and characterization of molecular rectangles of half-sandwich p-cymene ruthenium complexes bearing oxamidato ligands.

A series of binuclear half-sandwich p-cymene ruthenium complexes bearing oxamidato ligands [(p-cymene)(2)Ru(2)(mu-N,N'-bis(aryl)oxamidato)Cl(2)] (1-3) was synthesized by the reactions of the lithium salts of oxamide with [(p-cymene)RuCl(2)](2), respectively. Treatment of the binuclear complexes (1-3) with bidentate ligands such as 4,4'-bipyridine (4,4'-bpy) and trans-1,2-bis(4-pyridyl)ethylene (bpe) in the presence of AgOTf (OTf = CF(3)SO(3)) gave the corresponding tetranuclear complexes generally formulated as [(p-cymene)(4)Ru(4)(mu-N,N'- bis(aryl)oxamidato)(2)(mu-4,4'-bpy)(2)](OTf)(4) (4a-c) and [(p-cymene)(4)Ru(4)(mu-N,N'-bis(aryl)oxamidato)(2)(mu-bpe)(2)](OTf)(4) (5a-c) in high yields. All compounds (1-3, 4a-5c) have been characterized by NMR and IR spectra and elemental analyses. The molecular structures of , and have been determined by single-crystal X-ray analyses. The molecular structures of tetranuclear complexes and showed that two binuclear fragments as building blocks were connected by 4,4'-bpy or bpe to construct a rectangular cavity with the dimensions 5.57 x 11.28 A (4a) and 5.56 x 13.65 A (5a).