85698-56-2Relevant articles and documents
Ruthenium(II)–Pyridylimidazole Complexes as Photoreductants and PCET Reagents
Pannwitz, Andrea,Prescimone, Alessandro,Wenger, Oliver S.
supporting information, p. 609 - 615 (2017/02/05)
Complexes of the type [Ru(bpy)2pyimH]2+[bpy = 2,2′-bipyridine; pyimH = 2-(2-pyridyl)imidazole] with various substituents on the bpy ligands can act as photoreductants. Their reducing power in the ground state and in the long-lived3MLCT excited state is increased significantly upon deprotonation, and they can undergo proton-coupled electron transfer (PCET) in the ground and excited state. PCET with both the proton and electron originating from a single donor resembles hydrogen atom transfer (HAT) and can be described thermodynamically by formal bond dissociation free energies (BDFEs). Whereas the class of complexes studied herein has long been known, their N–H BDFEs have not been determined even though this is important in view of assessing their reactivity. Our study demonstrates that the N–H BDFEs in the3MLCT excited states are between 34 and 52 kcal mol–1depending on the chemical substituents at the bpy spectator ligands. Specifically, we report on the electrochemistry and PCET thermochemistry of three heteroleptic complexes in 1:1 (v/v) CH3CN/H2O with CF3, tBu, and NMe2substituents on the bpy ligands.
Dehydrogenative Coupling of 4-Substituted Pyridines Catalyzed by a Trinuclear Complex of Ruthenium and Cobalt
Nagaoka, Masahiro,Kawashima, Takashi,Suzuki, Hiroharu,Takao, Toshiro
, p. 2348 - 2360 (2016/08/02)
The dehydrogenative coupling of 4-substituted pyridines catalyzed by a heterometallic trinuclear complex composed of Ru and Co, (Cp?Ru)2(Cp?Co)(μ-H)3(μ3-H) (1, Cp? = η5-C5Me5), was investigated. When the pyridine substrate contains an electron-donating group at the 4-position, complex 1 showed a high catalytic activity compared to di- and triruthenium complexes (Cp?Ru)2(μ-H)4 (4) and (Cp?Ru)3(μ-H)3(μ3-H)2 (5). The catalytic activity of 1 was also remarkably higher than the congeners of other group 9 metals, Ru2Rh (2) and Ru2Ir analogues (3). The distinctive reactivity of 1 was attributed to a paramagnetic intermediate, (Cp?Ru)2{(dmbpy)Co}(μ-H)(μ3-H)2 (12, dmbpy = 4,4′-dimethyl-2,2′-bipyridine), which was formed by the reaction of 1 with 4-picoline accompanied by the dissociation of the Cp? at the Co atom. The reaction of 12 with unsubstituted pyridine resulted in the elimination of 4,4′-dimethyl-2,2′-bipyridine, indicating that the Co atom in 12 acts as a dissociation site. In contrast to the reaction of 1 with 4-picoline, the reaction of 2 and 3 with 4-picoline afforded the corresponding μ3-pyridyl complexes (Cp?Ru)2(Cp?M)(μ-H)3(μ3-η2(||)-C5H3NCH3) (15, M = Rh; 16, M = Ir). 4-(Trifluoromethyl)pyridine was not dimerized by 1; however, a similar μ3-pyridyl complex, (Cp?Ru)2(Cp?Co)(μ-H)3(μ3-η2(||)-C5H3NCF3) (13), was obtained. The stability of the μ3-pyridyl complex is probably one of the reasons for the low catalytic activity of 2 and 3 in the coupling reaction.
Strongly blue luminescent cationic iridium(III) complexes with an electron-rich ancillary ligand: Evaluation of their optoelectronic and electrochemiluminescence properties
Ladouceur, Sebastien,Swanick, Kalen N.,Gallagher-Duval, Shawn,Ding, Zhifeng,Zysman-Colman, Eli
, p. 5329 - 5343 (2013/11/06)
Two strongly blue luminescent cationic heteroleptic iridium complexes 1b and 2b bearing a 4,4′-bis(dimethylamino)-2,2′-bipyridine (dmabpy) ancillary ligand and either 1-benzyl-4-(2,4-difluorophenyl)-1H-1,2,3-triazole (dFphtl) or 2-(2,4-difluorophenyl)-5-methylpyridine (dFMeppyH), respectively, have been synthesized and fully characterized. In comparison with other analogues, the interplay of the triazole unit with the dmabpy unit and methylation of the pyridine ring are discussed with respect to the photophysical, electrochemical, and electrochemiluminescent (ECL) properties of the complexes. The two complexes, 1b and 2b, are blue emitters with λmax = 495 and 494 nm, respectively. The nature of the excited states was established by various photophysical and photochemical experiments as well as DFT calculations. Both complexes emit from a ligand-centered state, however, the emission of 1b possesses significant charge-transfer character, which is absent in 2b. The presence of the methyl group on the cyclometalating ligand leads only to a modest increase in the radiative rate constant, k r, but otherwise does not appreciably influence the optoelectronic properties of the complex compared with the non-methylated analogue. In contrast, the efficacy of the ECL emission when scanning to 2.50 V is strongly influenced by the presence of the methyl group. ECL emission is also enhanced in complexes bearing dmabpy ancillary ligands compared with those containing dtBubpy ligands. The two complexes exhibit similar electrochemical behavior. Incorporation of the dmabpy ligand shifts both the oxidation and reduction cathodically. The combination of the dmabpy and dFphtl groups increases the redox potential difference and thus the HOMO-LUMO gap but the emission is not further blueshifted. Thus, the structural modification of the cyclometalating ligand, although only modestly tuning the emission energy, modulates the nature of the excited state and the efficiency of the ECL process. The synthesis, photophysical, electrochemical, and electrochemiluminescent properties of two highly emissive cationic blue-emitting Ir complexes are reported. Variation of the ligand results in a change in the nature of the emission. The decoration on both the cyclometalating and ancillary ligands strongly influences the ECL efficiencies. A detailed DFT/TDDFT study corroborates experiment. Copyright
