[Ru(bpy)2(bqdiBr2)](PF6)2 bearing a 3,6-dibromo-1,2-benzoquinone diimine ligand (bqdiBr2 = Br-C6H2(NH)2-Br): Synthesis and its cross coupling reactions with organostannanes and organoboronic acids

•A new Ru complex having 3,6-dibrominated benzoquinone diimine (bqdi) were prepared.•Cross-coupling reactions of the Ru complex with Ar-SnBu3 and Ar-B(OH)2 were studied.•Redox potentials of the Ru complex can be regulated by introduction of the Ar groups.•The Ru-bqdi complex-containing π-conjugated polymer was prepared by cross-coupling.

[Ru(bpy)2(bqdiBr2)](PF6)2 ([1](PF6)2, bpy = 2,2′-bipyridyl, bqdiBr2 = 3,6-dibromo-1,2-benzoquinone diimine) was synthesized by the reaction of 3,6-dibromo-1,2-phenylenediamine with [RuCl2(bpy)2] in air, and the reactivity of [1](PF6)2 in Pd-catalyzed cross-coupling reactions with metalated thiophene and benzene was investigated. The structure of [1](PF6)2 was determined using X-ray crystallography. The Migita–Kosugi–Stille cross-coupling of [1](PF6)2 with 2 equiv of Th-SnBu3 (Th = 2-thienyl; Bu = butyl) afforded a 3,6-di(2-thienyl)-1,2-benzoquinone diimine (Th-C6H2(NH)2-Th)-coordinated Ru(II) complex [2](PF6)2. Similarly, the Suzuki–Miyaura cross-coupling of [1](PF6)2 with 2 equiv of CH3OC6H4-B(OH)2-p proceeded smoothly to afford a p-CH3OC6H4-C6H2(NH)2-C6H4OCH3-p-coodinated Ru(II) complex, [3](PF6)2. The optical and electrochemical properties of these complexes were evaluated based on the presence of the extended π-conjugated diimine ligand in the diimine moiety. The Stille cross-coupling of [1](PF6)2 with 1 equiv of Me3Sn-C4H2S-SnMe3 (C4H2S: thiophene-2,5-diyl) afforded a π-conjugated polymer consisting of the [Ru(bpy)2(bqdi)]2+ units.

Graphical abstractNew Ru(II) complexes bearing 1,2-benzoquinone diimine (bqdi) as a ligand, [1](PF6)2, was synthesized, and the reactivity of [1](PF6)2 in Pd-catalyzed cross-coupling reactions with metalated thiophene and benzene was investigated. [1](PF6)2 can be converted to a π-conjugation extended Ru-bqdi complex by the cross-coupling reactions.Figure optionsDownload full-size imageDownload as PowerPoint slide