17217-57-1Relevant articles and documents
Zinc oxide nanocrystal quenching of emission from electron-rich ruthenium-bipyridine complexes
Hue, Ryan J.,Vatassery, Rajan,Mann, Kent R.,Gladfelter, Wayne L.
, p. 4630 - 4639 (2015)
A series of heteroleptic bipyridine ruthenium complexes were prepared using known synthetic methods. Each compound incorporated one electron withdrawing 4,4′-dicarboxylic acid-2,2′-bipyridine and two bipyridines each of which had electron donating dialkylamine substituents in the 4 and 4′ positions. The electronic absorption spectra exhibited absorptions that moved to lower energy as the donor ability of the amine substituent increased. Density functional calculations established that the HOMO was delocalized over the metal and two pyridine groups located trans to the pyridines of the dicarboxylic acid bipyridine. The LUMO was delocalized over the dicarboxylic acid bipyridine. Cyclic voltammetry of the deprotonated compounds exhibit one quasi-reversible oxidation and three reductions. Coupled with the emission data, the excited state reduction potentials were estimated to range from -0.93 to -1.03 V vs. NHE. Monodispersed 3.2 nm diameter nanocrystals (NCs) of zinc oxide were found to quench partially the excited state of the dyes via a static quenching electron transfer process involving the formation of a dyad of the complex and the NC. The magnitude of the partial quenching of complexed dyes was correlated to the distribution of band gaps for the NCs, which is an inverse function of diameter. Dyes attached to the NCs on the small end of the particle size distribution had electron transfer rates that were uncompetitive with radiative and nonradiative decay mechanisms. This journal is
Structural and Synthetic Insights into Pyridine Homocouplings Mediated by a β-Diketiminato Magnesium Amide Complex
Davin, Laia,Clegg, William,Kennedy, Alan R.,Probert, Michael R.,McLellan, Ross,Hevia, Eva
supporting information, p. 14830 - 14835 (2018/09/25)
The reaction of [(DippNacnac)Mg(TMP)] (1) with 4-subtituted pyridines proceeds via sequential regioselective metallation and 1,2-addition to furnish a range of symmetric 4,4′-R2-2,2′-bipyridines in good yield, representing a new entry into bipyridine synthesis. Interestingly, the reaction of 1 with 2-OMe-pyridine led to formation of asymmetric bipyridine 6, resulting from the C6-magnesiation of the heterocycle followed by a C?C coupling step by addition to the C2 position of a second, non-metallated molecule, and subsequent elimination of [DippNacnacMgOMe]2 (7). Synthesis combined with spectroscopic and structural analysis help rationalise the underlying processes resulting in the observed reactivity, and elucidate the key role that the sterically encumbered β-diketiminate ligand plays in determining regioselectivity.
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.
