2,3-Di(2-pyridyl)-5-phenylpyrazine: A NN-CNN-Type Bridging Ligand for Dinuclear Transition-Metal Complexes

• Published in: Chemistry, an Asian journal an Asian journal, 2013-07, Vol.8 (7), p.1504-1513
• Main Authors: Wu, Si-Hai, Zhong, Yu-Wu, Yao, Jiannian
• Format: Article
• Language: English
• Subjects: Atoms & subatomic particles; bridging ligands; Chemistry; coordination modes; cyclometalated complexes; Ligands; platinum; ruthenium
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201300327

A new bridging ligand, 2,3‐di(2‐pyridyl)‐5‐phenylpyrazine (dpppzH), has been synthesized. This ligand was designed so that it could bind two metals through a NN‐CNN‐type coordination mode. The reaction of dpppzH with cis‐[(bpy)2RuCl2] (bpy=2,2′‐bipyridine) affords monoruthenium complex [(bpy)2Ru(dpppzH)]2+ (12+) in 64 % yield, in which dpppzH behaves as a NN bidentate ligand. The asymmetric biruthenium complex [(bpy)2Ru(dpppz)Ru(Mebip)]3+ (23+) was prepared from complex 12+ and [(Mebip)RuCl3] (Mebip=bis(N‐methylbenzimidazolyl)pyridine), in which one hydrogen atom on the phenyl ring of dpppzH is lost and the bridging ligand binds to the second ruthenium atom in a CNN tridentate fashion. In addition, the RuPt heterobimetallic complex [(bpy)2Ru(dpppz)Pt(CCPh)]2+ (42+) has been prepared from complex 12+, in which the bridging ligand binds to the platinum atom through a CNN binding mode. The electronic properties of these complexes have been probed by using electrochemical and spectroscopic techniques and studied by theoretical calculations. Complex 12+ is emissive at room temperature, with an emission λmax=695 nm. No emission was detected for complex 23+ at room temperature in MeCN, whereas complex 42+ displayed an emission at about 750 nm. The emission properties of these complexes are compared to those of previously reported Ru and RuPt bimetallic complexes with a related ligand, 2,3‐di(2‐pyridyl)‐5,6‐diphenylpyrazine. NN‐CNN breaking news: 2,3‐Di(2‐pyridyl)‐5‐phenylpyrazine, which is able to bind two metals through a NN‐CNN‐type coordination mode, has been designed and synthesized. A RuPt heterobimetallic complex with this bridging ligand shows near‐infrared emission at 750 nm, with a quantum yield of 0.41 % and an excited‐state lifetime of 170 ns.