A practical approach to the direct α-methylation of 1,8-naphthyridines under mild reaction conditions has been developed using simple and readily available DMSO as a convenient and environmentally friendly carbon source.
Understanding C–H Bond Activation on a Diruthenium(I) Platform
作者:Arup Sinha、Moumita Majumdar、Mithun Sarkar、Tapas Ghatak、Jitendra K. Bera
DOI:10.1021/om301228h
日期:2013.1.14
Activation of the C-H bond at the axial site of a [Ru-I-Ru-I] platform has been achieved. Room-temperature treatment of 2-(R-phenyl)-1,8-naphthyridine (R = H, F, OMe) with [Ru-2(CO)(4)(CH3CN)(6)][BF4](2) in CH2Cl2 affords the corresponding diruthenium(I) complexes, which carry two ligands, one of which is orthometalated and the second ligand engages an axial site via a Ru center dot center dot center dot C-H interaction. Reaction with 2-(2-N-methylpyrrolyl)-1,8-naphthyridine under identical conditions affords another orthometalated/nonmetalated (om/nm) complex. At low temperature (4 degrees C), however, a nonmetalated complex is isolated that reveals axial Ru center dot center dot center dot C-H interactions involving both ligands at sites trans to the Ru-Ru bond. A nonmetalated (nm/nm) complex was characterized for 2-pyrrolyl-1,8-naphthyridine at room temperature. Orthometalation of both ligands on a single [Ru-Ru] platform could not be accomplished even at elevated temperature. X-ray metrical parameters clearly distinguish between the orthometalated and nonmetalated ligands. NMR investigation reveals the identity of each proton and sheds light on the nature of [Ru-Ru]center dot center dot center dot C-H interactions (preagostic/agostic). An electrophilic mechanism is proposed for C-H bond cleavage that involves a C(p(pi))-H -> sigma* [Ru-Ru] interaction, resulting in a Wheland-type intermediate. The heteroatom stabilization is credited to the isolation of nonmetalated complexes for pyrrolyl C-H, whereas lack of such stabilization for phenyl C-H causes rapid proton elimination, giving rise to orthometalation. NPA charge analysis suggests that the first orthometalation makes the [Ru-Ru] core sufficiently electron rich, which does not allow significant interaction with the other axial C-H bond, making the second metalation very difficult.
Catalytic activity in transfer hydrogenation using ruthenium (II) carbonyl complexes containing two 1,8-naphthyridine as N-monodentate ligands
作者:Juana Gajardo、Juan C. Araya、Andrés Ibáñez、Véronique Guerchais、Hubert Le Bozec、Sergio A. Moya、Pedro Aguirre
DOI:10.1016/j.ica.2018.10.037
日期:2019.2
N-monodentate fashion. The ruthenium(II) complexes have been studied as catalysts in the transfer hydrogenation of acetophenone. We found that complexes show moderate activities and a 100% selectivity. The best turnover frequency (390 h−1) is found for cis-[RuCl2(CO)2(2-(4′-methoxyphenyl)-1,8-naphthyridine-κN8)2] when the substrate/catalysis ratio was 1000/1. The catalytic conditions were optimized
Selective synthesis of nitrogen bi-heteroarenes by a hydrogen transfer-mediated direct α,β-coupling reaction
作者:Xiu-Wen Chen、He Zhao、Biao Xiong、Huan-Feng Jiang、Pierre. H. Dixneuf、Min Zhang
DOI:10.1039/c7ob01434a
日期:——
By an external hydrogen transfer-mediated activation mode, we herein demonstrate a new palladium-catalyzed direct α,β-coupling of different types of N-heteroarenes. Such a selective couplingreaction proceeds with the advantages of operational simplicity, high atom-economical efficiency, and use of safe and abundant i-propanol as the activating agent, offering a practical way to access nitrogen bi-heteroarenes