P-Quinquephenyl diamine, C 6H 5– p-C 6H 4– p-C 6H 2(2,3-NH 2)– p-C 6H 4–C 6H 5, and its corresponding diimine–Ru(II) complex: Crystal structure and electrochemical and optical properties

Abstract

The molecular structure of an o-phenylenediamine unit-containing oligophenylene ( 1), Ph–Ph′–Ph′(2,3-NH 2)–Ph′–Ph (Ph = phenyl; Ph′ = p-phenylene; Ph′(2,3-NH 2) = 2,3-diamino- p-phenylene), was determined by X-ray crystallography. 1 has a twisted structure, and forms an intermolecular C–H⋯π interaction network. The –NH 2 group of 1 was air-oxidized to an imine, NH, group in the presence of [RuCl 2(bpy) 2] (bpy = 2,2′-bipyridyl) and gave a ruthenium(II)–benzoquinone diimine complex [Ru( 2)(bpy) 2](PF 6) 2 ( 2: Ph–Ph′–Ph′(2,3-imine)–Ph′–Ph). The molecular structure of [Ru( 2)(bpy) 2](PF 6) 2 was confirmed by X-ray crystallography. [Ru( 2)(bpy) 2](PF 6) 2 underwent two-step electrochemical reduction with E 1/2 = −0.889 V and −1.531 V versus Fc +/Fc. The E 1/2’s were located at higher potentials by 91 mV and 117 mV, respectively, than those of reported [Ru(bqdi)(bpy) 2](PF 6) 2 (bqdi = benzoquinone diimine). Electrochemical oxidation of [Ru( 2)(bpy) 2](PF 6) 2 occurred at a lower potential by 180 mV than that of [Ru(bqdi)(bpy) 2](PF 6) 2. Occurrence of the easier reduction and oxidation of [Ru( 2)(bpy) 2](PF 6) 2 than those of [Ru(bqdi)(bpy) 2](PF 6) 2 is ascribed to the presence of a large π-conjugation system in 2.