Terpyridine Ruthenium-Catalyzed One-Pot Conversion of Aldehydes into Amides

Rearrangement of aldoximes to amides in water under air atmosphere catalyzed by water-soluble iridium complex [Cp*Ir(H2O)3][OTf]2

R = aryl or aliphatic group phosphorous ligand-free low catalytic loading under air atmosphere up to 93% yield; 37 examples.

Transamidation of primary amides with amines catalyzed by zirconocene dichloride

Zirconocene dichloride (Cp(2)ZrCl(2)) has been shown to be an effective catalyst for the transamidation of primary amides with amines in cyclohexane at 80 °C in 5-24 hours. For favourable substrates, the reaction can be performed at temperatures as low as 30 °C.

Metal-catalysed approaches to amide bond formation

Amongst the many ways of constructing the amide bond, there has been a growing interest in the use of metal-catalysed methods for preparing this important functional group. In this tutorial review, highlights of the recent literature have been presented covering the key areas where metal catalysts have been used in amide bond formation. Acids and esters have been used in coupling reactions with amines, but aldehydes and alcohols have also been used in oxidative couplings. The use of nitriles and oximes as starting materials for amide formation are also emerging areas of interest. The use of carbon monoxide in the transition metal catalysed coupling of amines has led to a powerful methodology for amide bond formation and this is complemented by the addition of an aryl or alkenyl group to an amide typically using palladium or copper catalysts.

Catalytic acylation of amines with aldehydes or aldoximes

The simple nickel salt NiCl(2)·6H(2)O catalyzes the coupling of aldoximes with amines to give secondary or tertiary amide products. The aldoxime can be prepared in situ from the corresponding aldehyde. The use of (18)O-labeled oximes has allowed insight into the mechanism of this reaction.

Amide synthesis from alcohols and amines catalyzed by ruthenium N-heterocyclic carbene complexes

The direct synthesis of amides from alcohols and amines is described with the simultaneous liberation of dihydrogen. The reaction does not require any stoichiometric additives or hydrogen acceptors and is catalyzed by ruthenium N-heterocyclic carbene complexes. Three different catalyst systems are presented that all employ 1,3-diisopropylimidazol-2-ylidene (IiPr) as the carbene ligand. In addition, potassium tert-butoxide and a tricycloalkylphosphine are required for the amidation to proceed. In the first system, the active catalyst is generated in situ from [RuCl(2)(cod)] (cod=1,5-cyclooctadiene), 1,3-diisopropylimidazolium chloride, tricyclopentylphosphonium tetrafluoroborate, and base. The second system uses the complex [RuCl(2)(IiPr)(p-cymene)] together with tricyclohexylphosphine and base, whereas the third system employs the Hoveyda-Grubbs 1st-generation metathesis catalyst together with 1,3-diisopropylimidazolium chloride and base. A range of different primary alcohols and amines have been coupled in the presence of the three catalyst systems to afford the corresponding amides in moderate to excellent yields. The best results are obtained with sterically unhindered alcohols and amines. The three catalyst systems do not show any significant differences in reactivity, which indicates that the same catalytically active species is operating. The reaction is believed to proceed by initial dehydrogenation of the primary alcohol to the aldehyde that stays coordinated to ruthenium and is not released into the reaction mixture. Addition of the amine forms the hemiaminal that undergoes dehydrogenation to the amide. A catalytic cycle is proposed with the {(IiPr)Ru(II)} species as the catalytically active components.

Direct amide synthesis from either alcohols or aldehydes with amines: activity of Ru(II) hydride and Ru(0) complexes

An in situ generated catalyst from readily available RuH(2)(PPh(3))(4), an N-heterocyclic carbene (NHC) precursor, NaH, and acetonitrile was developed. The catalyst showed high activity for the amide synthesis directly from either alcohols or aldehydes with amines. When a mixture of an alcohol and an aldehyde was reacted with an amine, both of the corresponding amides were obtained with good yields. Homogeneous Ru(0) complexes such as (eta(4)-1,5-cyclooctadiene)(eta(6)-1,3,5-cyclooctatriene)ruthenium [Ru(cod)(cot)] and Ru(3)(CO)(12) were also active in the amidation of an alcohol or an aldehyde with the help of an in situ generated NHC ligand.