Ruthenium complexes primary alcohols

The conversion of primary alcohols and aldehydes into carboxylic acids is generally possible with all strong oxidants. Silver(II) oxide in THF/water is particularly useful as a neutral oxidant (E.J. Corey, 1968 A). The direct conversion of primary alcohols into carboxylic esters is achieved with MnOj in the presence of hydrogen cyanide and alcohols (E.J. Corey, 1968 A,D). The remarkably smooth oxidation of ethers to esters by ruthenium tetroxide has been employed quite often (D.G. Lee, 1973). Dibutyl ether affords butyl butanoate, and tetra-hydrofuran yields butyrolactone almost quantitatively. More complex educts also give acceptable yields (M.E. Wolff, 1963). 

ATH with Ruthenium Complexes of Amino Alcohol Complexes Linked to the Primary Face of P-Cyclodextrin 48... 

To improve the rate of reduction the amino alcohol ligand of the ruthenium complexes was exchanged for monotosylated 1,2-diamine ligands. For exploratory experiments AT-tosylethane-1,2-diamine was prepared hy monotosylation of ethane-1,2-diamine and attached to the primary face of P-CD yielding 80. With P-CD as the only chiral unit the ruthenium complex of 80 could reduce aromatic and aliphatic standard ketones 63 and 69 in 91% 5deld, 25% ee (S) and 68% 5deld, 58% ee, respectively, within only 4h under standard conditions (Fig. 24). 

Selective oxidation of alcohols. Primary alcohols are oxidized by this RuCL complex about 50 times as rapidly as secondary alcohols. Use of benzene as solvent is critical lor this high selectivity. Little or no reaction occurs in CH3CN, THF, or DMF. Most oxidants, if they show any selectivity, oxidize secondary alcohols more rapidly than primary ones. However, ruthenium-catalyzed oxidations with N-mcthylmorpholine N-nxide and oxidations with PCC4 proceed about three times as rapidly with primary alcohols as with secondary ones. 

Although, in separate experiments, secondary alcohols are oxidized faster than primary ones, in competition experiments the ruthenium/TEMPO system displayed a preference for primary over secondary alcohols. This can be explained by assuming that initial complex formation between the alcohol and the ruthenium precedes rate-limiting hydrogen transfer and determines substrate specificity, i.e. complex formation with a primary alcohol is favoured over a secondary one. 

Other ruthenium-based catalysts for the aerobic oxidation of alcohols have been described where it is not clear if they involve oxidative dehydrogenation by low-valent ruthenium, to give hydridoruthenium intermediates, or by high-valent oxoruthenium. Masutani et al. [107] described (nitrosyl)Ru(salen) complexes, which can be activated by illumination to release the NO ligand. These complexes demonstrated selectivity for oxidation of the alcoholic group versus epoxidation, which was regarded as evidence for the intermediacy of Ru-oxo moieties. Their excellent alcohol coordination properties led to a good enantiomer differentation in the aerobic oxidation of racemic secondary alcohols (Fig. 19) and to a selective oxidation of primary alcohols in the presence of secondary alcohols [108]. 

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). ... 

A high-valent ruthenium complex is also reported to cleave the sp C-H bond. RuCl3 -3H20 catalyzes the transformation of cyclic alkanes to the corresponding ketones in the presence of peracetic acid, where oxoruthenium species is considered to act as the active species. Alcohol, as a primary product in this oxidation reaction, is obtained as an intermediate in the presence of trifluoroacetic acid (Scheme 14.11) [25]. 

Bis(trimethylsilyl) peroxide, (CH3)3SiOOSi(CH3)3, is prepared from trimethylsilyl chloride, l,4-diaza[2,2,2]bicyclooctane, and Dabco s complex with 2 mol of hydrogen peroxide [127]. It is used alone [228] or in the presence of catalysts such as pyridinium dichromate [236] trimethylsilyl trifluoromethanesulfonate, CF3S03Si(CH3)3 [228, 237] or tris-(triphenylphosphine)ruthenium dichloride, [(C6H5)3P]3RuCl2 [236]. This reagent oxidizes primary alcohols to aldehydes (in preference to the oxidation of secondary alcohols to ketones [236]), ketones to esters or lactones Baeyer-Villiger reaction) [238], and nucleoside phosphites to phosphates [228]. All these oxidations require anhydrous conditions. 

As mentioned in the Introduction, we can distinguish simple FT catalysts, producing hydrocarbons exclusively with ruthenium as the outstanding example, and complex FT catalysts, such as promoted iron, wherein the steady-state metallic, oxidic, and carbidic phases can coexist. With the latter catalysts the product is a cocktail containing various oxygenates, in particular primary alcohols, as well as hydrocarbons. 

Divalent ruthenium complexes are efficient catalysts for A -alkylation of amines by a primary alcohol. RuCl2(PPh3)3 or RuCl3-3H20/P(0Bu)3 effectively catalyze the A -alkylation of aromatic amines (eq (38)) [133-134]. On the other hand, yV-alkylation of aliphatic amines with a primary alcohol is carried out in high yield by the use of RuH2(PPh3>4as catalyst [135]. 

Ruthenium complexes catalyze the reaction of primary alcohols with o-phenylenediamine. The catalyst apparently has dual roles in promotion of cyclization and oxidation of the alcohol to aldehyde <91CL1275>. A novel palladium-catalyzed carbonylation of iodobenzene has been linked to base-induced coupling and cyclization with o-phenylenediamine to give 2-arylbenzimidazoles without having to use an arylcarboxylic acid (Scheme 152) <93JOC7016>. 

Reduction. Under hydrogenation conditions the title ruthenium complex reduces an ester to a primary alcohol without affecting a double bond. 

Oxidation of Primary Alcohols with fert-Butylhydroperoxide in the Presence of Ruthenium Complexes... 

We present here some results obtained for the selective oxidation of a primary alcohol, with t-BuOOH catalyzed by some commercially available ruthenium complexes. In addition, the effect of some free radical scavengers on the reaction selectivity is also described as well as the use of other transition metal complexes as oxidizing agents. 

Ruthenium An amido ruthenium(II) complex catalyzes the addition of primary and secondary alcohols to acrylonitrile, crotononitrile, methacrylonitrile, and other unsaturated nitriles at ambient temperature and a low catalyst loading of 0.1 mol% (Scheme 16) [89]. NMR experiments indicate that the basic amido ligand at ruthenium deprotonates the alcohol to give a cationic amido complex [(MeCONH2) RuH(CO)(PCy3)2(5)] (S - nitrile substrate). The authors assume that the nitrile substrate is activated by coordination to ruthenium via the nitrile unit and then attacked by external alkoxide [89]. 

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