Dehydrogenative Coupling Of Primary Alcohols Research Articles

Formation of Tertiary Amides and Dihydrogen by Dehydrogenative Coupling of Primary Alcohols with Secondary Amines Catalyzed by Ruthenium Bipyridine‐Based Pincer Complexes

AbstractDehydrogenative coupling of primary alcohols with secondary amines to form tertiary amides and dihydrogen (H2) is efficiently catalyzed by bipyridyl‐based ruthenium pincer complexes (0.2–1 mol%) under neutral conditions (in case of the dearomatized complexes), or with added catalytic amount of base. The reaction is sensitive to steric hindrance; in the case of amidation of bulky secondary amines a less sterically hindered complex is more efficient. Selective acylation of primary amines in the presence of secondary amines was also demonstrated.magnified image

Dehydrogenative Coupling of Primary Alcohols To Form Esters Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex

The ruthenium complex [RuCl2(IiPr)(p-cymene)] catalyzes the direct condensation of primary alcohols into esters and lactones with the release of hydrogen gas. The reaction is most effective with linear aliphatic alcohols and 1,4-diols and is believed to proceed with a ruthenium dihydride as the catalytically active species.

Insights into Dehydrogenative Coupling of Alcohols and Amines Catalyzed by a (PNN)–Ru(II) Hydride Complex: Unusual Metal–Ligand Cooperation

Density functional theory calculations were performed to elucidate the mechanism of dehydrogenative coupling of primary alcohols and amines mediated by a PNN-Ru(II) hydride complex (PNN = (2-(di-tert-butylphosphinomethyl)-6-(diethylaminomethyl)pyridine)). A plausible reaction pathway was proposed which contains three stages: (1) The alcohol dehydrogenation reaction to generate the aldehyde and H(2); (2) The aldehyde-amine condensation reaction to form the hemiaminal intermediate; (3) The dehydrogenation process of the hemiaminal intermediate to yield the final amide product with the liberation of H(2). The first and third stages occur via a similar pathway: (a) Proton transfer from the substrate to the PNN ligand; (b) Intramolecular rearrangement of the deprotonated substrate to form an anagostic complex; (c) Hydride transfer from the deprotonated substrate to the Ru center to yield the trans-dihydride intermediate and the aldehyde (or amide); (d) Benzylic proton migration from the PNN ligand to the metal center forming a dihydrogen complex and subsequent H(2) liberation to regenerate the catalyst. In all these steps, the metal-ligand cooperation plays an essential role. In proton transfer steps (a) and (d), the metal-ligand cooperation is achieved through the aromatization/dearomatization processes of the PNN ligand. While in steps (b) and (c), their collaboration are demonstrated by the formation of an anagostic interaction between Ru and the C-H bond and two ionic hydrogen bonds supported by the PNN ligand.

PNP pincer osmium polyhydrides for catalytic dehydrogenation of primary alcohols

This paper reports the synthesis, structure, and properties of a series of PNP pincer complexes of osmium OsH(3)Cl[HN(C(2)H(4)P(i)Pr(2))(2)] (1), OsH(3)[N(C(2)H(4)P(i)Pr(2))(2)] (2), OsH(4)[HN(C(2)H(4)P(i)Pr(2))(2)] (3), and OsH(2)(PMe(3))[HN(C(2)H(4)P(i)Pr(2))(2)] (4). The tetrahydride 3 operates as an efficient catalyst at 0.1 mol% loading for the reactions of amination and dehydrogenative coupling of primary alcohols, producing secondary amines and symmetrical esters, respectively. The catalyst 3 is distinguished by outstanding stability, and it can be used in an aqueous environment at temperatures as high as 200 °C.

Catalytic Aerobic Dehydrogenative Coupling of Primary Alcohols and Water to Acids Promoted by a Rhodium(I) Amido N‐Heterocyclic Carbene Complex

AbstractThe amino diolefin complex [Rh(trop2NH)(TMIY)]+(OTf)− (OTf−=CF3SO3−; trop=5‐H‐dibenzo[a,d]cyclohepten‐5yl), incorporating N‐heterocyclic carbene ligand 1,3,4,5‐tetramethylimidazole‐2‐ylidene (TMIY), has been prepared. The structure is determined by single‐crystal X‐ray diffraction, which shows a butterfly structure with the NH and TMIY groups in the apical and the two olefinic binding sites in the equatorial position of a trigonal bipyramid with one vacant site in the equatorial plane. This complex can be deprotonated to give the amide [Rh(trop2N)(TMIY)], which cleaves H2 heterolytically across the RhN bond to give the amino hydride [RhH(trop2NH)(TMIY)]. In dimethylsulfoxide (DMSO), both the amide and amino hydride complexes are active as catalysts in the dehydrogenative coupling (DHC) of various primary alcohols with water to give the corresponding acids under aerobic conditions. O2 serves as hydrogen acceptor. One O atom is converted into water while the other is transferred to DMSO as oxygen acceptor, to yield Me2SO2. Hence, the net reaction RCH2OH+2 O2+2 DMSO→RCOOH+2 Me2SO2+H2O is catalyzed by the butterfly‐shaped rhodium amide complexes.

Discovery of Environmentally Benign Catalytic Reactions of Alcohols Catalyzed by Pyridine-Based Pincer Ru Complexes, Based on Metal–Ligand Cooperation

We have developed a new mode of metal–ligand cooperation, based on aromatization–dearomatization of pyridine-based pincer-type ligands, and have demonstrated it in the activation of H2 and C–H bonds by PNP Ir complexes. This type of metal–ligand cooperation plays a key role in the recently discovered environmentally benign reactions of alcohols, catalyzed by PNP and PNN pincer complexes of ruthenium, including (a) dehydrogenation of secondary alcohols to ketones (b) dehydrogenative coupling of primary alcohols to form esters and H2 (c) hydrogenation of esters to alcohols under mild conditions (d) unprecedented amide synthesis: catalytic coupling of amines with alcohols, with liberation of H2. Ligand modification in the latter reaction has led to unprecedented synthesis of imines with H2 liberation. These reactions are very efficient, proceed under neutral conditions and produce no waste.

ChemInform Abstract: Catalyzed Dehydrogenative Coupling of Primary Alcohols with Water, Methanol, or Amines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Catalyzed Dehydrogenative Coupling of Primary Alcohols with Water, Methanol, or Amines

A working partnership: Metal–ligand cooperativity is responsible for the high activity of the rhodium amido complex 1 in the dehydrogenative coupling of primary alcohols with water, methanol, or amines, including ammonia (see scheme), to give carboxylic acids, methyl carboxylates, or amides, respectively. The catalysis proceeds under mild reaction conditions in the presence of a recyclable hydrogen acceptor A. The multistep mechanism was elucidated by computational methods.

Catalyzed Dehydrogenative Coupling of Primary Alcohols with Water, Methanol, or Amines

Gute Zusammenarbeit von Metallzentrum und Liganden ist der Schlüssel zur hohen Aktivität des Rhodiumamidokomplexes 1 in den dehydrierenden Kupplungen primärer Alkohole mit Wasser, Methanol oder Aminen (einschließlich Ammoniak) zu Carbonsäuren, Methylestern bzw. Amiden. Der katalytische Prozess verläuft unter milden Bedingungen in der Gegenwart des zurückgewinnbaren Wasserstoffakzeptors A, und der vielstufige Mechanismus wurde durch Rechnungen aufgeklärt.