Synthesis and Characterization of Azidobipyridyl Ruthenium Complexes and Their “Click” Chemistry Derivatives

The ligand 4‐azido‐2,2′‐bipyridyl ( 1 ) has been used to prepare 1,2,3‐triazole‐substituted ligands through copper‐catalyzed alkyne/azide cycloaddition (CuAAC or “click” chemistry) with phenylacetylene, ethynylferrocene and 2‐ethynylpyridine to yield 4‐(4‐phenyl‐1,2,3‐triazol‐1‐yl)‐2,2′‐bipyridyl ( 2a ), 4‐(4‐ferrocenyl‐1,2,3‐triazol‐1‐yl)‐2,2′‐bipyridyl ( 2b ) and 4‐[4‐(pyridyl‐2‐yl)‐1,2,3‐triazol‐1‐yl]‐2,2′‐bipyridyl ( 2c ). Complexes of the form [Ru( p ‐cymene)(Cl)(L)]PF 6 ( 3 , L = 1 ; 4a , L = 2a ; 4b , L = 2b ) were then prepared and characterized. We also report the synthesis of the complex of the analogous ligand 4,4′‐bisazido‐2,2′‐bipyridyl ( 1′ ), [Ru( p ‐cymene)(Cl)( 1′ )]PF 6 ( 3′ ). Complexes 4a and 4b were also prepared by an alternative route, whereby 3 undergoes CuAAC coupling with phenylacetylene and ethynylferrocene respectively. Complexes prepared with ligands that are pre‐assembled or “clicked” at the metal show identical 1 H NMR spectra. CuAAC coupling of 3 and 2‐ethynylpyridine results in the formation of the complex [Ru( p ‐cymene)(Cl)( 2c )]PF 6 ( 4c ), which contains a coordinatively vacant pyridyltriazole moiety. The reaction of [Ru( p ‐cymene)(Cl) 2 ] 2 with pre‐assembled 2c results in the formation of the dinuclear complex [{Ru( p ‐cymene)(Cl)} 2 ( 2c )] · 2PF 6 ( 5 ), which incorporates ruthenium atoms at both bipyridyl and pyridyltriazole binding domains. The 1 H NMR spectrum of the complex shows two signals for the triazole ring proton as well as duplicate signals for other protons of the bridging ligand, which indicates that 5 is produced as a mixture of diastereoisomers. The complex [{Ru( p ‐cymene)Cl} 2 {di‐4‐([1‐{2,2′‐bipyrid‐4‐yl}triazol‐4‐yl]methyl)ether}][PF 6 ] 2 ( 7 ) was also prepared through the coupling of 3 with dipropargyl ether.