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

Abstract

A series of binuclear half-sandwich p-cymene ruthenium complexes bearing oxamidato ligands [(p-cymene)₂Ru₂(μ-N,N′-bis(aryl)oxamidato)Cl₂] (1–3) was synthesized by the reactions of the lithium salts of oxamide with [(p-cymene)RuCl₂]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 = CF₃SO₃) gave the corresponding tetranuclear complexes generally formulated as [(p-cymene)₄Ru₄(μ-N,N′- bis(aryl)oxamidato)₂(μ-4,4′-bpy)₂](OTf)₄ (4a–c) and [(p-cymene)₄Ru₄(μ-N,N′-bis(aryl)oxamidato)₂(μ-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 1, 4a and 5a have been determined by single-crystal X-ray analyses. The molecular structures of tetranuclear complexes 4a and 5a 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 × 11.28 Å (4a) and 5.56 × 13.65 Å (5a).