Ruthenium polyoxometalate

Orlandi M, Argazzi R, Sartorel A, Carraro M, Scorrano G, Bonchio M, Seandola F (2010) Ruthenium polyoxometalate water splitting catalyst very fast hole scavenging fiorn photogenerated oxidants. Chem Commun 46 3152-3154... 

An example of a system for photocatalytic water oxidation with a molecular catalyst based on abundant metals is shown in Fig. Id. The Cobalt polyoxometalate catalyst is oxidized with Ru —trisbipyridine that is generated by quenching of the photo-excited Ru —trisbipyridine sensitizer with peroxodisulfate as sacrificial electron acceptor. The system operates at pH 8 and exhibits a high (30 %) photon-to-02 yield while the stability of the catalyst allowed for turnover numbers >220 that were limited by depletion of electron acceptor only [7]. This performance of the abundant-metal-based catalyst is superior to that of an analogue ruthenium polyoxometalate water oxidation catalyst. 

Chen et al. recently reported the stable ruthenium-oxo-oxalato cluster Na7[Ru4(p3-0)4(C204)g] (2) (Fig. lc) as a particularly potent inhibitor of HIV-1 reverse transcriptase (RT) with an IC50 value of 1.9 nM [17], Apparently, the polyanionic cluster mimics poly anionic nucleic acid in its binding to HIV-1 RT through electrostatic interactions. The cluster shows promising anti-HIV-1 activity without being cytotoxic. In contrast to many polyoxometallates, this cluster has been demonstrated to be stable under physiological conditions. 

Few examples involve the use of dioxygen alone as the primary oxidant. The use of a Ru(III) ethylenediaminetetraacetate complex has been described [28] but this almost certainly involves a free-radical autoxidation pathway and offers no advantages. Following the initial report by Neumann et al. [29] on the use of [WZnRu2(0H)(H20)(ZnW9034)2]11 attention has been focused on the use of ruthenium-containing polyoxometalates (POMs) as catalysts for the aerobic... 

Table 6 Ruthenium-substituted polyoxometalates as catalysts for the oxidation of alcohols...

Very few methods have been reported for direct aerobic oxidation of alkanes using a perfluorinated ruthenium catalyst [Ru30(0C0CF2CF2CF3)6(Et20)3] [120c] and a ruthenium-substituted polyoxometalate [WZnRu2(0H)(H20)(ZnW9034)2] (Eqs. 3.102 and 3.103) [159, 160[. 

An alternative strategy for the functionalization of polyoxometalates relies on self-assembly processes. Up to now we failed to introduced a Schrock-type alkylidyne in the lacunar undodecaphosphotungstate. As the current trend in olefin metathesis reaction now favours ruthenium catalysts, such as the Grubbs s ones, we turn to ruthenium precursors and to more stable Lappert-type carbene fragments, stabilized in the a-position by nitrogen atoms. The reaction of [PWii039p- with the carbene precursor... 

R. Neumann and M. Dahan, A Ruthenium-Substituted Polyoxometalate as an Inorganic Dioxygenase for... 

Khenkm AM, Elfemenko I, Weiner L et al (2010) Photochemical reduction of carbon dioxide catalyzed by a ruthenium substituted polyoxometalate. Chem A Eur J 16 1356-1364... 

Beyond the two mechanistic themes presented above, that is, autooxidation and redox-type reactions involving electron transfer, a ruthenium-substituted sandwich -type polyoxometalate was shown to be a catalyst for oxidation by a dioxygenase -type mechanism as outlined in Scheme 9.13 [125]. 

Polyoxometalates are able to act as ligands for different redox-active transition metals (M ) such as iron, manganese, cobalt and ruthenium or d metals (such as zirconium, hafnium, titanium). The coordination of a heterometal by a polyoxometalate framework takes place either through the superficial coordination of a metal cation by electrostatic interaction, or by incorporation of the transition metal within the POM structure resulting in the formation of transition metals substituted polyoxometalates (TMSPs), which generally exhibit a higher stability. 

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