Half-Sandwich Ruthenium Complexes for One-Pot Synthesis of Quinolines and Tetrahydroquinolines: Diverse Catalytic Activity in the Coupled Cyclization and Hydrogenation Process

Abstract

Four types of half-sandwich ruthenium complexes with an N,O-coordinate mode based on hydroxyindanone-imine ligands have been prepared in good yields. These stable ruthenium complexes exhibited high activity in the catalytic synthesis of quinolines from the reactions of amino alcohols with different types of ketones or secondary alcohols under very mild conditions. Moreover, the methodology for the direct one-pot synthesis of tetrahydroquinoline derivatives from amino alcohols and ketones has been also developed on the basis of the continuous catalytic activity of this ruthenium catalyst in the selective hydrogenation of the obtained quinoline derivatives with a low catalyst loading. The corresponding products, quinolines and tetrahydroquinoline derivatives, were afforded in good to excellent yields. The efficient and diverse catalytic activity of these ruthenium complexes suggested their potential large-scale application. All of the ruthenium complexes were characterized by various spectroscopies to confirm their structures.

Half-Sandwich Ru(II) Complexes with N,O-Chelate Ligands: Diverse Catalytic Activity for Amine Synthesis in Water

“…The ruthenium complex crystallized in the monoclinic space group P 2 1 c (Figure ). Geometric data are listed in the Supporting Information (Table S1), and the characteristic bond lengths and angles which are consistent with the reported values are summarized in the footnote of Figure . The ruthenium center of this complex displayed a typical three-legged piano-stool conformation.…”

“…The half-sandwich moiety has emerged as a important building block in organometallic complexes synthesis and catalysis due to their high stability, good solubility, easy modification, and excellent catalytic activity. − The detailed advantages of the half-sandwich moiety are as follows: (i) the dichloro-bridged metal precursor can be easily prepared in good yields through inorganic metal salts; (ii) the metal center was protected by the half-sandwich structure which avoided the side reactions; (iii) the electron and steric effects can be tuned conveniently by choosing different substituents. Among these types of complexes, half-sandwich Ru­(II) complexes were frequently employed as the building blocks in the preparation of diverse compounds which showed particular activity in catalysis, coordination-driven self-assembly, and biochemistry. − Recent study indicated that the half-sandwich Ru­(II) complexes with nitrogen-containing ligands showed good catalytic efficiency in diverse organic reactions. , However, there are limited studies of RA reactions using half-sandwich Ru­(II) complexes.…”

Borrowing Hydrogen and Acceptorless Dehydrogenative Coupling in the Multicomponent Synthesis of N‐Heterocycles: A Comparison between Base and Noble Metal Catalysis

“…[24] Another approach to synthesize 1,2,3,4-tetrahydroquinolines 2 was pursued with the N,O-chelate half-sandwich ruthenium complex Ru-5 starting from 2-aminobenzyl alcohols and ketones. [25] The cyclization to form the corresponding quinoline and its hydrogenation were combined in a one-pot synthesis. Thus, usage of hydrogen pressure, low catalyst loading (0.1 mol%) and a stoichiometric amount of base produced the desired 1,2,3,4-tetrahydroquinolines 2 in good yields.…”

A simple continuous reaction for the synthesis of quinoline compounds

“…Yao and coworkers reported the synthesis of quinoline derivatives starting from amino alcohols and ketones as well as secondary alcohols catalyzed by half-sandwich N,O-chelate ruthenium complexes. 14 Yang's group reported the synthesis of quinolines via acceptorless dehydrogenative coupling of o-aminobenzyl alcohols with ketones in the presence of carbonate salt with the 2,2′-bibenzimidazole ligand [( p-cymene)Ru(BiBzImH 2 )Cl][Cl]. 15 The reaction doesn't require the addition of strong inorganic bases to carry out acceptor-free dehydrogenation.…”