Ruthenium-catalyzed water oxidation

In addition to the reactions discussed above, there are still other alkyne reactions carried out in aqueous media. Examples include the Pseudomonas cepacia lipase-catalyzed hydrolysis of propargylic acetate in an acetone-water solvent system,137 the ruthenium-catalyzed cycloisomerization-oxidation of propargyl alcohols in DMF-water,138 an intramolecular allylindination of terminal alkyne in THF-water,139 and alkyne polymerization catalyzed by late-transition metals.140... 

Tseng HW, Zong R, Muckerman JT, Thummel R. Mononuclear ruthenium(II) complexes that catalyze water oxidation. Inorg Chem. 2008 47 11763-11773. 

Hurst JK. Water oxidation catalyzed by dimeric ja-oxo bridged ruthenium diimine complexes. Coord Chem Rev 2005 249 313-28. 

Besides ruthenium tetroxide, other ruthenium salts, such as ruthenium trichloride hydrate, may be used for oxidation of carbon-carbon double bonds. Addition of acetonitrile as a cosolvent to the carbon tetrachloride-water biphase system markedly improves the effectiveness and reliability of ruthenium-catalyzed oxidations. For example, RuCl3 H20 in conjunction with NaI04 in acetonitrile-CCl4-H20 oxidizes (Ej-S-decene to pentanoic acid in 88% yield. Ruthenium salts may also be employed for oxidations of primary alcohols to carboxylic acids, secondary alcohols to ketones, and 1,2-diols to carboxylic acids under mild conditions at room temperature, as exemplified below. However, in the absence of such readily oxidized functional groups, even aromatic rings are oxidized. 

This conversion is catalyzed by [Ru(Hedta)(H20)] (Hedta = trianion of eth-ylenediaminetetraacetic acid) at 30 °C and 10 Pa in the presence of a solid semiconductor mixture (CdS/Pt/RuO,). The photocatalytic production of ammonia is initiated by absorption of visible light (505 nm) by the CdS semiconductor (Fig. 13.12). Presumably, the incoming photons promote electrons from the valence band (VB) of CdS to its conducting band (CB), a process that leaves holes in the valence band. Water is photooxidized by RuOi, releasing electrons which are trapped by holes in the valence band of CdS. The electrons in the conducting band are transferred to the nithenium complex via platinum metal. Protons from the water oxidation are attracted to the reduced ruthenium complex, interact with coordinated N, in some unknown fashion, and are expelled as NH3. The cycle is complete when the coordination site left by NH3 becomes occupied once again by HjO. It remains to be seen whether proposed cycles such as this one measure up to their promise. 

It is interesting to include in this eategory of interphase systems, the use of highly water-soluble proteetive agents, like polymers, surfactants, or ionic species, to stabilize colloidal metallic particles finely dispersed in water. Larpent and Patin have developed this original approach [72]. Ruthenium eolloids ean efficiently catalyze the oxidation, under room eonditions, of cyclo-octane by t-butylhydroperoxide [73]. Recent results show that... 

Alternatively, a ruthenium catalyst could be applied in phthalide preparation. In 2011, Ackermann s group developed a ruthenium-catalyzed cross-dehydrogenative C-H bond alkenylation reaction. The methodology used water as a solvent, benzoic acids and terminal alkenes as substrates good yields of the desired phthalides were isolated (Scheme 2.164). The reaction sequence consisted of cross-dehydrogenative alkenylation and a subsequent intramolecular oxa-Michael reaction. Mechanistic studies provided strong evidence that the oxidative alkenylation proceeds by an irreversible C-H bond metalation via acetate assistance. 

If one could trap the intermediate 5 with external nucleophiles, such as water, a new type of catalytic oxidation of alkenes could be performed. Indeed, a transformation of alkenes into a-ketols was discovered to proceed highly effldently. Thus, the low-valent ruthenium-catalyzed oxidation of alkenes with peracetic acid in an aqueous solution under mild conditions gives the corresponding a-ketols, which are important key structures of various biologically active compounds (Eq. (7.21)) [60]. 

After the seminal work reported by Satoh and Miura in early 2011 on ruthenium-catalyzed oxidative vinylation of heteroarene carboxylic acids with alkenes [17], Ackermann demonstrated a ruthenium(ll)-catalyzed cross-dehydrogenative C-H bond alkenylations of benzoic acid derivatives with acrylonitrile or alkyl acrylates. Following the oxidative C—H bond alkenylation reaction, subsequent intramolecular oxa-Michael reaction occurred leading to phthalides in good yields (Eq. (7.12)) [18]. The reactions took place with water as an environmentally benign medium under mild conditions. 

Recently, Dong et al. reported a multicatalytic cascade reaction combining Pd, acid, and Ru catalysis [11]. By coupling palladium-catalyzed oxidation, acid-catalyzed hydrolysis, and ruthenium-catalyzed reduction, the elusive anti-Markovnikov olefin hydration was formally achieved, affording primary alcohols from waters and aryl-substituted terminal alkenes (Scheme 9.8). 

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