Catalytic dehydrogenation of cyclic amines, in particular partially saturated N-heterocycles to N-heterocyclic arenes, with the removal of molecular hydrogen as the sole byproduct in water is ...reported. This dehydrogenation reaction proceeds smoothly under very mild and benign conditions and operates at room temperature. This distinctive reactivity has been achieved under dual catalytic conditions by merging the visible-light active Ru(bpy)32+ as the photoredox catalyst and a newly synthesized cobalt complex as the proton-reduction catalyst. A detailed mechanistic study (control experiments, electrochemical studies, UV-visible experiments) is presented for the present dual catalysis.
The oxidation of alcohols to carboxylic acids is an important industrial reaction used in the synthesis of bulk and fine chemicals. Most current processes are performed by making use of either ...stoichiometric amounts of toxic oxidizing agents or the use of pressurized dioxygen. Here, we describe an alternative dehydrogenative pathway effected by water and base with the concomitant generation of hydrogen gas. A homogeneous ruthenium complex catalyses the transformation of primary alcohols to carboxylic acid salts at low catalyst loadings (0.2 mol%) in basic aqueous solution. A consequence of this finding could be a safer and cleaner process for the synthesis of carboxylic acids and their derivatives at both laboratory and industrial scales.
The ability of hydrogen‐transfer transition‐metal catalysts, which enable increasingly rapid access to important structural scaffolds from simple starting materials, has led to a plethora of research ...efforts on the construction of heterocyclic scaffolds. Transition‐metal‐catalyzed hydrogen‐transfer annulations are environmentally benign and highly atom‐economical as they release of water and hydrogen as by‐product and utilize renewable feedstock alcohols as starting materials. Recent advances in this field with respect to the annulations of alcohols with various nucleophilic partners, thus leading to the formation of heterocyclic scaffolds, are highlighted herein.
Pass it along: Transition‐metal‐catalyzed hydrogen‐transfer annulation strategies have received significant attention for the construction of a variety of heterocyclic scaffolds. They are environmentally benign and highly atom‐economical as they utilize renewable feedstock alcohols as the starting materials and generate hydrogen gas and water as the by‐products. Described are recent advances in the development of such annulations.
Sustainable chemical production requires fundamentally new types of catalysts and catalytic technologies. The development of coherent and robust catalytic systems based on earth-abundant transition ...metals is essential, but highly challenging. Herein, we systematically explored a general hydrogenative cleavage/N-alkylation tandem of cyclic and acyclic diazo (N=N) compounds to value-added amines under manganese catalysis. The reaction is catalyzed by a single-site molecular manganese complex and proceeds via tandem dehydrogenation, transfer hydrogenation, and borrowing hydrogenation strategies. Interestingly, the reaction involves abundantly available renewable feedstocks, such as alcohols, that can act as (transfer)hydrogenating and alkylating agents. The synthetic application of our approach in large-scale pharmaceutical synthesis and easy access to highly demanding N-CH3/CD3 derivatives are also demonstrated. Kinetic studies show that the reaction rate depends on the concentration of alcohol and Mn-catalyst and follows fractional orders. Several selective bond activation/formation reactions occur sequentially via amine-amide metal-ligand cooperation.
In recent times, earth-abundant 3d-transition-metal catalysts have attracted much attention in contemporary catalysis. They have been widely employed as suitable alternatives to their counterparts ...noble metals. In particular, nickel catalysts provide distinctive redox properties; thus, their efficiency in sustainable organic transformations is manifold. In this review article, recent advances in nickel-catalyzed hydrogen auto-transfer (HA) and acceptorless dehydrogenative coupling (ADC) reactions for the construction of C-C and C-N bonds have been discussed.
In recent times, the transition metal-catalyzed borrowing hydrogen (BH) and interrupted borrowing hydrogen (IBH) strategies have attracted much attention and represent atom- and step-economic ...processes to access diverse building blocks
via
various C-C and C-heteroatom bond-forming reactions. The advantages of these approaches include (i) use of feedstock chemicals, (ii) high atom economy, (iii) no pre-activation of the substrates, and (iv) producing water as the only by-product. In this context, several synthetic strategies have been developed in this regime for the past few decades. To the best of our knowledge, no review article describes the important concepts of interrupted borrowing hydrogen (IBH) reaction. This review article highlights the recent advances in the IBH strategy and its application in sustainable chemical synthesis, particularly C-C bond formation using methanol as a C1 source, synthesis of 3,3′-bisindolylmethanes (3,3′-BIMs), α-branched ketones/diketones, and regioselective alkylation of N-heterocycles.
This review article highlights the recent advances of transition-metal-catalyzed interrupted borrowing hydrogen (IBH) catalysis and its applications in the sustainable and affordable chemical synthesis using alcohols as C1 feedstocks.
Herein, an air‐stable, molecularly defined NNN−Mn(II) pincer complex catalyzed acceptorless dehydrogenative coupling of alcohols with indoles is reported. A wide variety of symmetrical and ...unsymmetrical bis(indolyl)methane derivatives as well as some structurally important products such as Vibrindole A, Turbomycin B alkaloid, Antileukemic, and Anticancer agents were synthesized. Mechanistic studies illustrate the importance of the NH moiety in the complex and the crucial role of metal‐ligand cooperation during catalysis.
Electron-rich PNP- and PNN-type ruthenium(II) hydrido borohydride pincer complexes, RuH(BH4)( t Bu-PNP) (tBu-PNP = (2,6-bis(di-tert-butylphosphinomethyl)pyridine) (5) and RuH(BH4)( t Bu-PNN) ( t ...Bu-PNN = 2-di-tert-butylphosphinomethyl-6-diethylaminomethylpyridine) (6), were prepared from their corresponding N2-bridged dinuclear Ru(II) complexes ( t Bu-PNP)RuCl22(μ-N2) (3) and ( t Bu-PNN)RuCl22(μ-N2) (4), respectively. The X-ray structure of 5 reveals a BH4 – anion η2 coordinated to ruthenium through two bridging hydrides. A variable-temperature 1H NMR study of 6 exhibits interesting fluxional behavior of the BH4 – ligand. Similarly, the Ru(II) hydrido borohydride complex 9, in which the BH4 – moiety is coordinated in a η1 bonding mode, was obtained by reaction of RuCl2(PPh3)( i Pr-PNP) ( i Pr-PNP = 2,6-bis(diisopropylphosphinomethyl)pyridine) (8) with two equivalents of NaBH4 at room temperature. The hydrido borohydride pincer complexes 5, 6, and 9 catalyze the acceptorless dehydrogenative coupling of primary alcohols to esters and the dehydrogenation of secondary alcohols to the corresponding ketones, accompanied by evolution of hydrogen gas. The reactivity follows the order 6 > 9 > 5. With the hydrido borohydride complex 6 as catalyst, high yields (up to 98%) and high turnover numbers (TON ∼1000) were obtained in the dehydrogenation of primary alcohols under mild and neutral conditions. In addition, 6 effectively catalyzes the hydrogenation of nonactivated aromatic and aliphatic esters to the corresponding alcohols with TON ∼200 under a relatively mild pressure of dihydrogen and neutral and homogeneous conditions. Thus, an efficient homogeneous catalytic system for the dehydrogenation–hydrogenation reactions of alcohols is developed, which is relevant to the current interest in hydrogen storage.
Visible light-mediated photocatalytic organic transformation has drawn significant attention as an alternative process for replacing thermal reactions. Although precious metal/organic dyes based ...homogeneous photocatalysts have been developed, their toxic and nonreusable nature makes them inappropriate for large-scale production. Therefore, we have synthesized a triazine and a keto functionalized nonmetal based covalent organic framework (TpTt) for heterogeneous photocatalysis. As the catalyst shows significant absorption of visible light, it has been applied for the photocatalytic uphill conversion of trans-stilbene to cis-stilbene in the presence of blue light-emitting diodes with broad substrate scope via an energy transfer process.
Here, the first example is reported of a new, molecularly defined SNS-cobalt(ii) catalyst for the acceptorless dehydrogenative coupling (ADC) of unprotected amino alcohols with secondary alcohols ...leading to pyrrole and pyridine derivatives.
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