Ruthenium complexes hydroxy

ASYMMETRIC HYDROGENATION OF 3-OXO CARBOXYLATES USING BINAP-RUTHENIUM COMPLEXES (R)-(-)-METHYL 3-HYDROXYBUTANOATE (Butanoic acid, 3-hydroxy-, methyl ester, (R)-)... 

Increase in the ruthenium concentration increases the stoichiometric factor, n in Eq. (2), from about 6 up to about 20, and in these more concentrated solutions rates of ruthenium(III) reduction are no longer first order in ruthenium(III). Under these conditions reaction products depend on the hydroxide concentration and include hydroxy-aromatic ligands [cf. Eq. (3)], carbonate, and trace amounts of dioxygen. Ruthenium complexes of ligands in which one pyridine ring had been completely oxidized were also characterized (2). This accounts for the carbonate, and the minor dioxygen yields could originate from complexes oxidized to ruthenium(IV) (8). Unlike the iron(III) system, neither free 2,2 -bipyridine nor the N-oxide was detected. 

Complex 3c, a catalytic precursor for addition reactions to alkynes (65), reacts at room temperature with a variety of terminal alkynes in alcohols to produce stable alkoxyl alkyl carbene ruthenium(II) derivatives 109 in good yields (Scheme 7). Reaction of 3c (L = PMe3), with trimethylsilyacetylene in methanol gives the carbene ruthenium complex 110, by protonolysis of the C—Si bond, whereas with 4-hydroxy-l-butyne in methanol the cyclic carbene complex 111 is obtained (65,66). 

A dinuclear ruthenium complex with both ruthenium in 2+ oxidation states catalyzes the oxidation of adamantane to hydroxy adamantane and alkene to epoxide by dioxygen. Suggest a possible mechanism. 

A number of derivatives of ruthenium(II) have the potential to oxidize a primary alcohol in the presence of a secondary alcohol the original report of Sharpless et al has been followed by a number of modifications. The ruthenium complex can be used as a catalyst in conjunction with a cooxidant, which in the original work was A -methylmorpholine A -oxide. In general benzylic and allylic alcohols react more readily than their saturated counterparts, and primary alcohols react more readily than secondary alcohols. Alkenes can interfere with this oxidation, probably by binding to the metal and inhibiting the catalytic process. The stoichiometric use of tris(triphenylphosphine)ruthenium(II) chloride will oxidize a primary/secondary diol to the corresponding hydroxy aldehyde in excellent yield (equation 13). ... 

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. 

Another ion exchange procedure involves the interaction of a metal acetylacetonate (acac) with an oxide support. Virtually all acetylacetonate complexes, except those of rhodium and ruthenium, react with the coordinatively unsaturated surface sites of 7 alumina to produce stable catalyst precursors. On thermal treatment and reduction these give alumina supported metal catalysts having relatively high dispersions. 38 Acetylacetonate complexes which are stable in the presence of acid or base such as Pd(acac)2, Pt(acac)2 and Co(acac)3, react only with the Lewis acid, Al" 3 sites, on the alumina. Complexes which decompose in base but not in acid react not only with the Al 3 sites but also with the surface hydroxy groups. Complexes that are sensitive to acid but not to base react only slightly, if at all, with the hydroxy groups on the surface. It appears that this is the reason the rhodium and ruthenium complexes fail to adsorb on an alumina surface. 38... 

The importance of hydroxycarbonyl intermediates is well illustrated in a recent study of the stepwise oxidation of CO to CO2 by binuclear ruthenium complexes". Deprotonation of a diruthenium(I) aquo species yields a hydroxy intermediate which rearranges to an isolable hydroxycarbonyl complex, equation (h). Deprotonation of the hydroxycarbonyl with NEts in dichloromethane results in a formally diruthenium(O) ii-CO complex, equation (i). 

Among the other reduced prochiral substrates, methylene succinic acid was hydrogenated with ee values up to 59 and 50% using respectively the catalysts Rh-3 [3] and Ru-BINAP (9) [21]. The hydrogenation of the /hketo ester 21 was also performed in water in the presence of ruthenium complexes associated with ligands 13 and 14 (Eq. 4) [24, 25] the hydroxy ester 22 was obtained with enantioselectivi-ties up to 94%. 

Like the 2-hydroxy-2,2-di-methylethyl radical, C02 can add to the reduced 2,2 -bipyridyl ligand in the ruthenium complex (reaction 33). In contrast to the electron-transfer reaction, the addition reaction is nearly diffusion controlled. Rates of many of the electron-transfer reactions of C02 are sufficiently below... 

Jt-Complex activation was the method of choice for the construction of a cyclic peptide model related to the antibiotic teicoplanin, where ring closure of the ruthenium complex of the corresponding open-chain hydroxy-chloroarene was effected by sodium... 

A ruthenium complex (268), formed in situ by [Ru(p-cymene)Cl2] and the amino acid hydroxy-amide ligand (269), catalysed the asymmetric reduction of aryl alkyl ketones to secondary alcohols in moderate to good yields and with up to 97% ee... 

A widely-reported method for the DKR of secondary alcohols and a- and p-hydroxy acid esters involves ruthenium catalysed hydrogenation. No additional base is required as a cocatalyst (and consequently base-catalysed transesterification can be avoided) because one of the ligand s oxygen atoms can act as a basic centre. A robust ruthenium complex (named Shvo s catalyst) along with a p-chlorophenylacetate was developed by the BackvaU group. The metal catalyst must be used in combination with thermostable enzymes because it is activated by heat (Scheme 4.26). This system (with CALB) has been successfully used for the DKR of many secondary alcohols and diols (Scheme 4.27) [52, 63, 64]. 

Ruthenium complexes have found limited use as reagents for the oxidation of 3p-hydroxy-A -steroids, since these rather unpredictable reactions occur with very low conversions of the substrates. The optimized procedure described below illustrates the successful sonochemical oxidation of the 5-en-3p-ol homo-allylic system with tetra-n-propylammonium perruthenate (TPAP) used in association with 4-methylmorpholine N-oxide (NMO). The present procedure is based on the reaction conditions used for primary, secondary, and... 

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