Arene diruthenium(II)‐mediated synthesis of imines from alcohols and amines under aerobic condition

Abstract

The utility and selectivity of the newly synthesized dinuclear arene Ru(II) complex were demonstrated towards the synthesis of imines from coupling of alcohols and amines in the aerobic condition. Analytical and various spectral methods have been used to establish the unprecedented formation of the new thiolato‐bridged dinuclear ruthenium complex. The molecular structure of the titled complex was evidenced with aid of X‐ray crystallographic technique. A wide range of imines were obtained in good‐to‐excellent yields up to 98% and water as the by‐product through an acceptorless dehydrogenative coupling of alcohols with amines. The catalytic reaction operated a concise atom economical without any oxidant with 1 mol% of the catalyst load. Further, the role of base, solvent and catalyst loading of the coupling reaction has been investigated. A plausible mechanism has been described and was found to proceed via the formation of an aldehyde intermediate. Short synthesis of antibacterial drug N‐(salicylidene)‐2‐hydroxyaniline illustrated the utility of the present protocol.

Pincer Nickel‐Catalyzed Olefination of Alcohols with Benzylphosphine Oxides

“…It has been reported that pincer transition metal complexes such as pincer Ru, Ni, and Mn complexes can catalyze acceptorless dehydrogenative coupling of alcohols with appropriate nucleophilic species [5d–g,6a,b,7,8,9a,b,g,h,10] . In our previous studies we synthesized N,N,P‐pincer nickel complex [Ni1] (Figure 1) and studied its catalysis in activating C−X (X=F, N, O) bonds [14] .…”

Catálise de Mn para a Formação Sustentável e Eficiente de Iminas: um Passo Rumo a uma Via Bimetálica One-pot para a Síntese de N-Heterociclos

“…Ao longo dos anos, várias adaptações foram sendo realizadas, introduzindo-se ácidos de Lewis para facilitar a reação ou trocando as montagens complexas de destilação por procedimentos mais simples, nomeadamente de adsorção, envolvendo agentes exsicantes, como peneiros moleculares [17][18][19]. Mesmo assim, a maioria destas metodologias continuava a apresentar limitações, sendo razoavelmente eficientes apenas para substratos específicos, apresentando tempos de reação longos e/ou requerendo condições vigorosas [20][21][22].…”

“…Neste contexto, metodologias sintéticas alternativas foram sendo desenvolvidas, envolvendo a reação aza-Wittig [23] ou métodos oxidativos, como a oxidação de aminas secundárias [24], a condensação oxidativa de aminas primárias [25] ou o acoplamento de álcoois e aminas na presença de um oxidante [26] (Esquema 3). No entanto, o uso de reagentes tóxicos e a obtenção de uma baixa economia atómica, bem como uma baixa seletividade são frequentemente observados nestes protocolos [19,21,27].…”

Open Air Direct Oxidative Coupling of Alcohols and Amines to Imines Catalyzed by Ruthenium Nanoclusters Supported on a Mesoporous Carbon (CMK-8) in/on Water

“…In recent years, various homogeneous and heterogeneous noble − and non-noble − metal catalysts have been explored for the direct coupling of alcohols and amines to imine. Ruthenium-based catalysts are among the most active and effective metal-based catalysts in this field, catalyzing this dehydrogenative condensation reaction either with an oxidant (typically, O 2 or air) − or even in the absence of any oxidants under an inert atmosphere. − While the latter could largely avoid overoxidation of alcohols to carboxylic acids, it might also be faced with a significant decrease in reaction selectivity caused by the formation of amine byproducts as a result of the reaction of imine products with the hydride species generated during the dehydrogenation process. , Moreover, some of the catalytic systems presented for the coupling of alcohols with amines under inert conditions have drawbacks such as using large amounts of poorly accessible, expensive, complex, and yet nonrecyclable homogeneous catalysts, using additives, requiring high reaction temperatures, and needing to conduct the reactions under an Ar/N 2 atmosphere. − Therefore, it seems that the aerobic oxidative coupling of alcohols and amines, especially by employing heterogeneous and recoverable catalytic systems, is still an active and preferable approach to the synthesis of imines. However, while the utilization of various Ru catalysts, either in the form of homogeneous or heterogeneous catalytic systems, has been extensively established in the aerobic oxidation of alcohols and/or amines, − the use of Ru-based catalytic systems in the one-pot tandem synthesis of imines through the selective oxidative coupling of alcohols and amines is a multifaceted and relatively less explored process.…”