Ruthenium pincer compound

For example, 6-(4 -methylphenyl)-2-pyridylmethylamine ruthenium pincer compounds 8.110 are highly efficient catalysts in transfer hydrogenation involving 2-propanol to perform the reduction of ketone quantitatively with very low loading and in a short time, as shown in Eq. (8.30) [151]. 

It was not until 1997 that the first study involving a direct reaction of carbon monoxide with a ruthenium pincer compound was reported. Jia and coworkers reported [47] the synthesis of (PCP)Ru(II) (118) and examined its reactivity toward carbon monoxide. They found that the reaction of (118) with CO gas leads to the replacement of the PPh3 ligand, giving place to the white compound (PCP)RuCl(CO)2 (119) (Scheme 2.53). 

Pincer organometallic compounds are reported mainly with regard to two types of compounds, PCP and NCN transition metal complexes [28, 34]. However, ruthenium pincer CNN compounds have also been applied to hydrogen-transfer reductions of ketones. 

The direct conversimi of esters into amides is a synthetically useful transformation. However, most of the methodologies developed till now usually require harsh reaction conditions, are poorly compatible with sensitive substrates, and present a low atom economy [136, and references cited therein]. Very recently, MUstein and co-workers demonstrated that esters can be selectively converted into amides generating molecular hydrogen as the only by-product (Scheme 31) [137]. The catalytic reactions were carried out with 2 equiv. of amine per ester in toluene or benzene at reflux in the presence of 0.1 mol% of the dearomatized PNN-pincer ruthenium complex [RuH(CO)(PNN)] (28) (see Scheme 21). Strikingly, both the acyl and the aUcoxo units of the starting ester are involved in the amide production. Hence, to avoid mixtures of products, the process was only applied to symmetrical esters. The catalytic protocol was effective for both primary and secondary cyclic amines. In addition, the coupling of piperazine and butylbutyrate provided compound 46, which results from the bis-acylation of the diamine (Scheme 31). 

Dehydrogenation of alcohols to aldehyde or ketone allows subsequent bond construction steps which would not be possible for the parent alcohols. Hence, a variety of iridium, rhodium or ruthenium phosphine, pincer and related complexes, that are efficient catalysts for the dehydrogenation of alcohols, can potentially be appHed for the related hydrogen-transfer reactions, thus leading to new added-value compounds. The hydrogen atoms transfer to a sacrificial hydrogen acceptor, such as a carbonyl compound or an olefin which is reduced to the corresponding alcohol or alkane. 

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