Oxoruthenium

Reaction of [Ru2(CH2SiMe3)6] in hexane at —30°C with O2 produces the unusual metal-metal bridged oxoruthenium(V) species, [Ru202(CH2SiMe3)g], as a red crystalline solid.This... 

This complex shows an exceptionally high Ru=0 stretching frequency of 845crn . The stronger Ru=0 bond is also consistent with the measured Ru=0 distance of 1.739 A, " the shortest one ever reported for oxoruthenium(IV) complexes. The difference in the... 

As shown by their redox potentials oxoruthenium(IV) species containing polypyridyl ligands are strong oxidants and they oxidize a variety of substrates. The complex [Ru(0)(bpy)2(py)] has also been used electrocatalytically for the oxidation of alcohols, aldehydes, alkenes, and aromatics." Electrocatalytic oxidation has also been performed on this complex that has been incorporated into poly-4-vinylpyridine. ... 

Ru(Cl)2(PPh3)3] catalyzes the oxidation of alkanes and alkylaromatics with t-butylhydroper-oxides and peracetic acid, and an oxoruthenium(IV) active intermediate has been proposed. ... 

Metal salts and complexes have also often been used as redox catalysts for the indirect electrochemical oxidation of alcohols. Particularly, the transformation of benzylic alcohols to benzaldehydes has been studies. For this purpose oxoruthe-nium(IV) and oxoruthenium(V) complexes have been applied as redox catalysts. In a similar way, certain benzyl ethers can be cleaved to yield benzaldehydes and the corresponding alcohols using a di-oxo-bridged binuclear manganese complex Electrogenerated 02(804)3 was used to generated 1-naphthaldehyde from 1-naphthylmethanol... 

Aliphatic alcohols can be oxidized to ketones, aldehydes, or carboxylic acids using oxoruthenium(IV)complexes as redox catalyst or clectrogenerated ruthenium tetroxide In the latter case, a double mediator system is used in which an electrochemically generated active chlorine species (Cl or CP ) oxidizes RuO to RUO4 (Eq. (29)). 

Transition metal ions in their high oxidation state have also been used to oxidize DNA components. These reactions may involve one-electron oxidation steps, i.e., free-radicals may also play a role. Oxoruthenium(IV) complexes oxidize GMP an order of magnitude faster (k = 6.1 -15 dm3 mol-1 s-1) at the base moiety than dCMP (0.24 - 0.47 dm3 mol-1 s-1), where the sugar moiety is attacked (Far-rer and Thorp 2000). 

Farrer BT, Thorp HH (2000) Redox pathways in DNA oxidation kinetic studies of guanine and sugar oxidation by para-substituted derivatives of oxoruthenium(IV). Inorg Chem 39 44-49 Fasman GD (1975) Handbook of biochemistry and molecular biology. Nucleic acids. CRC Press, Cleveland... 

The C(l )-radical does not give rise to frank SSB as such, at least not in remarkable yields (see above), but cationic polyamines and divalent metal cations (Roginskaya et al. 2005) as well as transition metal ions such as 1,10-phenanth-roline-copper ion are capable of catalyzing p-elimination processes from 2-dRL that lead to an SSB and eventually to 5-MF. These reactions are discussed in some detail below (Sect. 12.9.4). 5-MF is also produced by desferal-copper ion (Joshi et al. 1994) or oxoruthenium(IV) (Neyhart et al. 1995 Cheng et al. 1995). 

Neyhart GA, Cheng C-C, Thorp HH (1995) Kinetics and mechanism of the oxidation of sugars and nucleotides by oxoruthenium(IV) model studies for predicting cleavage patterns in polymeric DNA and RNA. J Am Chem Soc 117 1463-1471... 

Autoxidadon of Bare ruthenium( II) and osmium(II) porphyrins - A resonance Raman study of the intermediates formed during the reaction of Ru(TPP) (which was obtained according Scheme 1, paths — f, — j, — k) in toluene [258] proved the anticipated [205] reaction scheme of the inner-sphere autoxidation, the first step of which is the formation of a p-peroxobis[porphyrinato-ruthenium(III)] complex which is split into two oxoruthenium (IV) fragments. These species precede the formation of /r-oxobisruthenium(IV) porphyrins (reaction 16) for P = TPP, OEP for P = TMP, a disproportionation (17) is indicated, the resulting Ru(P) itself is further autoxidized. 

One example which deserves special mention is the use of a percarboxylic acid such as peracetic acid, generated in situ by autoxidation of the corresponding aldehyde, developed by Murahashi and coworkers, see Eq. (1) [25-27]. These reactions are generally considered to involve high-valent oxoruthenium complexes, generated by reaction of the percarboxylic acid with the ruthenium catalyst, as the active oxidant. 

More detailed mechanistic studies are obviously necessary in order to elucidate the details of this fascinating reaction. It is worth noting, in this context, that the reaction of TPAP with 2-propanol was found to be autocatalytic, possibly owing to the formation of colloidal Ru02 [105]. Another possible alternative is one involving the initial formation of oxoruthenium( VI), followed by cycling between ruthenium( VI), ruthenium(IV) and possibly ruthenium(II). 

The oxoruthenium( VI) complex was prepared by exposing a benzene solution of trans-Ru11 (tmp)(MeCN)2 to air at 20°C. Addition of 2-propanol to the resulting solution, in the absence of air, afforded the dialkoxyruthenium(IV) complex, in quantitative yield, within 24 hours. In the presence of air, benzene... 

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]. 

Work in our laboratory has shown that oxoruthenium(IV) and hy-droxoruthenium(III) complexes are capable of DNA cleavage (7). These reagents can be generated by oxidation of complexes based on Ru(tpy)(bpy)OH22+, either chemically or electrochemically ... 

Ruthenium oxo compounds catalyze the oxidation of amides, e.g. -lactams, at the position a to the nitrogen, using peracetic acid as the oxidant, presumably via oxoruthenium intermediates [264]. 

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]. 

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