Ruthenium complexes alcohol oxidation

Ruthenium complexes alcohol oxidation, 788-9 alkene/alkyne vicinal dihydroxylation, 556 dioxetane decomposition, 1189-90... 

A number of mechanistic pathways have been identified for the oxidation, such as O-atom transfer to sulfides, electrophilic attack on phenols, hydride transfer from alcohols, and proton-coupled electron transfer from hydroquinone. Some kinetic studies indicate that the rate-determining step involves preassociation of the substrate with the catalyst.507,508 The electrocatalytic properties of polypyridyl oxo-ruthenium complexes have been also applied with success to DNA cleavage509,5 and sugar oxidation.511... 

The enantioselective oxidative coupling of 2-naphthol itself was achieved by the aerobic oxidative reaction catalyzed by the photoactivated chiral ruthenium(II)-salen complex 73. 2 it reported that the (/ ,/ )-chloronitrosyl(salen)ruthenium complex [(/ ,/ )-(NO)Ru(II)salen complex] effectively catalyzed the aerobic oxidation of racemic secondary alcohols in a kinetic resolution manner under visible-light irradiation. The reaction mechanism is not fully understood although the electron transfer process should be involved. The solution of 2-naphthol was stirred in air under irradiation by a halogen lamp at 25°C for 24 h to afford BINOL 66 as the sole product. The screening of various chiral diamines and binaphthyl chirality revealed that the binaphthyl unit influences the enantioselection in this coupling reaction. The combination of (/f,f )-cyclohexanediamine and the (R)-binaphthyl unit was found to construct the most matched hgand to obtain the optically active BINOL 66 in 65% ee. 

Benzyl alcohol, oxidation, by ruthenium oxo complexes, 39 287-289 Benzylazide, NMR of, 4 263 Benzylidene diacetate, nitration of, 6 114 Berkelium... 

C6H5I(OAc)2 is used. Oxidation of unsaturated alcohols can be complex. With the exception of Ru02, almost any ruthenium complex is effective.1... 

In the synthesis of alkylidenecyclobutenes from propargyl alcohols, stoichiometric experiments show that the first step involves [2+2] oxidative head-to-head coupling of the alkynes, leading to an isolable cyclobutadiene-ruthenium complex. Addition of acid generates a cyclobutenyl metal intermediate which undergoes carboxylate addition on the less substituted allylic carbon atom (Scheme 7). 

Iron-containing cytochrome P-450 constitutes the most famous example of a selective C-H bond oxidizer. Although the exact nature of the mechanism remains controversial, the reaction most likely proceeds through radical intermediates [2]. The hydroxylation of activated C-H bonds has also been carried out in the presence of synthetic porphyrin complexes. In these biomimetic processes, ruthenium plays a relatively minor role when compared with iron. Zhang et al. [50], however, recently reported the enantioselective hydroxylation of benzylic C-H bonds using ruthenium complexes supported by a D4-sym-metric porphyrin bearing a crafted chiral cavity. Thus, complex 23 reacts in a stoichiometric manner with ethylbenzene to give phenethyl alcohol with a... 

Ruthenium compounds are widely used as catalysts for hydrogen-transfer reactions. These systems can be readily adapted to the aerobic oxidation of alcohols by employing dioxygen, in combination with a hydrogen acceptor as a cocatalyst, in a multistep process. For example, Backvall and coworkers [85] used low-valent ruthenium complexes in combination with a benzoquinone and a cobalt Schiff s base complex. The proposed mechanism is shown in Fig. 14. A low-valent ruthenium complex reacts with the alcohol to afford the aldehyde or ketone product and a ruthenium dihydride. The latter undergoes hydrogen transfer to the benzoquinone to give hydroquinone with concomitant... 

Fig. 19 Ruthenium salen type complexes active as catalysts in alcohol oxidation under illumination...

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). ... 

The present hydrogen transfer reaction is extended to the aerobic oxidation of alcohols. Thus, the oxidation of alcohols can be carried out with a catalytic amount of hydrogen acceptor under an O2 atmosphere by a multistep electron-transfer process. As shown in Scheme 3.4, the ruthenium dihydrides formed during the hydrogen transfer can be regenerated by a multistep electron-transfer process including hydroquinone, ruthenium complex, and molecular oxygen. 

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