Ruthenium reactions with substrate complexes

Reactions with Other Substrate Complexes. The ruthenium analog of 45, coordinatively unsaturated RuCl(NO)(PPh3)2, also yields methylene and ethylidene complexes on treatment with diazomethane and diazoethane (39,85). 

Introduction of mesityl groups at the porphyrin ring can prevent the formation of the dimeric products and the reaction with dioxygen now leads to ruthenium(VI)-dioxo complexes of TMP (tetramesitylporphyrin) [35], The tram-Ru(VI)02-TM P species can catalyse the epoxidation of alkenes as well as whole range of other oxidation reactions. After transfer of one oxygen atom to an organic substrate Ru(IV)0-TMP is formed, which disproportionates to an equilibrium of Ru02 and llu ). 

The CM of olefins bearing electron-withdrawing functionalities, such as a,/ -unsaturated aldehydes, ketones, amides, and esters, allows for the direct installment of olefin functionality, which can either be retained or utilized as a synthetic handle for further elaboration. The poor nucleophilicity of electron-deficient olefins makes them challenging substrates for olefin CM. As a result, these substrates must generally be paired with more electron-rich crosspartners to proceed. In one of the initial reports in this area, Crowe and Goldberg found that acrylonitrile could participate in CM reactions with various terminal olefins using catalyst 1 (Equation (2))." Acrylonitrile was found not to be active in secondary metathesis isomerization, and no homodimer formation was observed, making it a type III olefin. In addition, as mentioned in Section 11.06.3.2, this reaction represents one of the few examples of Z-selectivity in CM. Subsequent to this report, ruthenium complexes 6 and 7a were also observed to function as competent catalysts for acrylonitrile... 

Compound (Z)-30. A solution of diene 29 (68.4 mg, 0.231 mmol) and the ruthenium complex 5 (19.5 mg, 0.023 mmol) in CH2C12 (100 mL) is refluxed for 8 h until TLC shows complete conversion of the substrate. After quenching the reaction with ethyl vinyl ether (0.5 mL), all volatiles are removed in vacuo and the residue is purified by flash chromatography (pentane/Et20, 10 1) to afford... 

Rhodium and ruthenium complexes of CHIRAPHOS are also useful for the asymmetric hydrogenation of p-keto esters. Dynamic kinetic resolution of racemic 2-acylamino-3-oxobutyrates was performed by hydrogenation using ((5,5)-CHIRAPHOS)RuBr2 (eq 3). The product yields and enantiomeric excesses were dependent upon solvent, ligand, and the ratio of substrate to catalyst. Under optimum conditions a 97 3 mixture of syn and anti p-hydroxy esters was formed, which was converted to o-threonine (85% ee) and D-allothreonine (99% ee) by hydrolysis and reaction with propylene oxide. 

Highly efficient oxygenation reactions with ruthenium porphyrin complexes and aromatic 7V-oxides in the presence of strong mineral acids have been described by Hirobe et al. [4], We have recently reported that electron deficient perhalogenated ruthenium porphyrins catalyze the oxygenation of a variety of even unreactive substrates under mild conditions (40 - 65 C) in the presence of 2,6-dichloropyridine A -oxide in aprotic media [5]. Unusually high rates and turnover numbers (TO) were obtained. 

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