Novel pyridazine, pyrimidine, and pyrazine bridging ligands: Synthesis and coordination chemistry with ruthenium(II)

A double Friedländer condensation of 2-aminobenzaldehyde (87) or 2-aminonicotinaldehyde (90) with either 2,5-diacetylpyrazine (91) or 4,6-diacetylpyrimidine (95 ) led to the series of bis-bidentate bridging ligands 4,6-di(2 ′-quinolyl)pyrimidine (81), 4,6-di(2′ -[1′,8′]naphthyridyl)pyrimidine (82), 2,5-di(2′-quinolyl)pyrazine ( 83), and 2,5-di(2′-[1′,8 ′]-naphhyridyl)pyrazine (84). The analogous 3,6-di(2 ′-quinolyl)pyridazine (85) was synthesized in three steps from 2-cyanoquinoline (95).; Ligands 81–84 were treated with [Ru(bpy)₂Cl ₂] to afford both the mono- [Ru(81–84)(bpy) ₂]2+ and dinuclear [(bpy)₂Ru(81–84 )Ru(bpy)₂]4+ complexes, whose photo- and electrochemical properties were evaluated.; The double Friedländer condensation of 8-amino-7-quinolinecarbaldehyde (102) with either 91 or 95 gave the bis-tridentate bridging ligands 4,6-di(2′-[1′ ,10′]-phenanthrolinyl)pyrimidine (99) and 2,5-di(2′-[1′,10′ ]-phenanthrolinyl)pyrazine (100). The analogous bridging ligand 3,6-di(2′-[1′,10′ ]-phenanthrolinyl)pyridazine (101) was synthesized in a manner similar to 85.; Ligands 99–101 were treated with [Ru(tpy- d₁₁)Cl₃] to afford both the mono- [Ru( 99–101)(tpy-d₁₁)]2+ and dinuclear [(tpy-d₁₁)Ru(99, 100)Ru(tpy- d₁₁)]4+complexes, whose photo- and electrochemical properties were evaluated.; The bidentate chelators 2-(2′-quinolyl)pyrazine (123), 2-(2′-[1′,8 ′]-naphthyridyl)pyridine (124) and 2-(2 ′-[1′,8′]-naphthyridyl)pyrazine (125) as well as the tridentate chelators 2-(2′ -[1′,10′]-phenanthrolinyl)pyridine (126), 2-(2′-[1′,10 ′]-phenanthrolinyl)pyrimidine (127), and 2-(2 ′-[1′,10′]-phenanthrolinyl)pyrazine (128) were synthesized by a Friedländer condensation of the appropriate aminoaldehyde with either 2-acetylpyrazine, 2-acetylpyridine, or 2-acetylpyrimidine.; The mononuclear Ru(II) complexes of 123–128 were synthesized and compared with the mononuclear Ru(II) complexes of the corresponding bridging ligands.; Finally, the coordination chemistry of metals other than Ru(II) was investigated. The dirhodium complexes [Rh₂(124, 125)(OAc)₃ ]1+ were synthesized and their photo- and electrochemical properties were evaluated. Mass spectrometry indicates that the dinuclear Pt(II) complexes [(Cl)Pt(99, 101)Pt(Cl)]2+ were synthesized and characterization by X-ray crystallography is anticipated.