Ruthenium catalysis amidation

Diisopropenyl oxalate results from the addition of oxalic acid to propyne. The ester condenses with all types of amines under ruthenium catalysis to yield the corresponding ester amides or oxamides, depending on the amounts of amines used (equation 104)327. 

Here we describe a new route to the synthesis of N,N-dimethylform-amide using synthesis gas and ammonia as the only chemical building blocks (eq. 26). Once again this involves an adaption of ruthenium melt catalysis (13). At about the time this work was published, Marsella and Fez of Air Products, disclosed a similar synthesis using solvent-solubilized ruthenium catalysis (79). 

Crochet P, Cadierno V (2014) Ruthenium-catalyzed amide-bond formation. In Dixneuf HP, Bmneau C (eds) Ruthenium in catalysis. Springer, Cham, pp 81-118... 

Chen C, Verpoort F, Wu Q (2016) Atom-eeonomie dehydrogenative amide synthesis via ruthenium catalysis. RSC Adv 6(60) 55599-55607... 

The unique transformation of formamides to ureas was reported by Watanabe and coworkers [85]. In place of carbon monoxide, formamide derivatives are used as a carbonyl source. The reaction of formanilide with aniline was conducted in the presence of a catalytic amount of RuCl2(PPh3)3 in refluxing mesitylene, leading to N,AT-diphenylurea in 92% yield (Eq. 56) [85]. They proposed that the catalysis starts with the oxidative addition of the formyl C-H bond to the active ruthenium center. In the case of the reaction of formamide, HCONH2, with amines, two molecules of the amine react with the amide to afford the symmetrically substituted ureas in good yields. This reaction evolves one molecule of NH3 and one molecule of H2. 

Isomerization reactions of 2-ynoic acids [59] and P-allenic amides [60] also provide suitable methodologies for the preparation of conjugated amides. The former compounds are isomerized by catalysis with ruthenium or iridium complexes and allow the synthesis of pellitorine (1), Achillea amide (4) and trichonine (13) (Scheme 15). 

A related iridium complex has been used for the decarbo)grlative radical allylation of aminoacids and phenylacetic acids that occurs smoothly at room temperature in the presence of Pd(PPh3)4, irradiating by white LEDs. The proposed scheme (Scheme 6) is based on dual catalysis. Ruthenium tris(phenanthroline) dichloride has been used for visible light catalysis of the mild amidation of ketoacids by ort/zo-substituted anilines using ozygen as terminal oxidant (Scheme 7) ... 

In continuation of our research on design of novel catalysts for selective organic transformations, we have synthesized more flexible, expanded PNN-type pincer ruthenium complexes (18-20). However, only modest catalytic activity and selectivity was observed with these bridged-bipyridine-based PNN-Ru(II) complexes in amide hydrogenation (25-65% yields) and other reactions [70]. This is likely a result of cyclometalation of the active species 21 and 22, which is detrimental to the catalysis (Scheme 8 Fig. 10). The low stability of the expected dearomatized complex (20a) formed by deprotonation of 20 was also detrimental to catalysis. 

Keywords Alcohols Amides Amines Carbon dioxide Catalysis Dehydrogenative coupling Esters Hydrogen Imines Iridium Metal-ligand cooperation O-H activation Pincer complexes PNN PNP Ruthenium... 

MacMillan described a photoredox catalysis approach whereby photo-excited ruthenium(ii) species generate a trifluoromethyl radical which is then trapped by a silylenolether (Scheme 15.106). The reaction displays broad utility in terms of applicable substrates and extends to enol silanes of ketones, esters or amides. °... 

---