Ru VII Complexes

Just as Ru(VIII) chemistry is dominated by RuO, Ru(VII) chemistry is dominated by salts of the perruthenate ion, [RuO ] , particularly TPAP, ( Pr N)[RuO ]. Another similarity between RuO and [RuO ] in solution is their reluctance to expand their coordination spheres beyond tetrahedral. The principal salts are listed first. There are few Ru(VII) complexes apart from [RuO ] . 

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Practical Cr -catalyzed oxidations of alcohols have not been adopted widely, but Pr4N+ Ru04 (TPAP, tetrapropylammonium perruthenate) catalyzes the oxidation of alcohols to aldehydes by a stoichiometric oxidant such as NMO, H2O2, or O2 itself. The Ru(VII) complex oxidizes alcohols by the same mechanism described earlier for stoichiometric Cr species. The stoichiometric oxidant then reoxidizes the Ru(V) by-product back to Ru(VII). 

Modern variations include the in situ, and thus catalytic, use of this high-valent selective reagent, not only for alcohols but also for ethers (see later). Ru(VII) (perruthenate) in the compounds tetra-n-butylammonium perruthenate (TBAP) and tetra-n-propylammonium perruthenate (TPAP) has found wide application in alcohol oxidation. Ru-oxo complexes with valence states of IV to VI are key intermediates in, for example, the selective oxygen transfer to alkenes, leading to epoxides. On the other hand 16-electron Ru(II) complexes can be used to catalyse hydrogen transfer thus these are excellent catalysts for oxidative dehydrogenation of alcohols. A separate section is included to describe the different mechanisms in more detail. 

Metal complexes can be attached to membranes. For example, Ru BINAP complexes (cf. Scheme 22-VII) and a Brpnsted acid attached to a polydimethyl-siloxane membrane act as effective heterogenized catalysts for asymmetric hydrogenations.172... 

VII. Reaction of Ru" -pac Complexes with Biologically Important Oxidants... 

Ru-catalyzed AROM/CM sequences served as a key step in the total synthesis of baconipyrone C (163, Scheme 24.42), a marine polyketide isolated from Siphonaria baconi The employed Ru carbene [Ru]-VI is generated in situ by treatment of the achiral Ru-PCya complex with Ag-based V-heterocyclic carbene (NHC) and Nal. And then, the [Ru]-VI-catalyzed AROM/RCM of oxabicycle 161 with styrene (8 equiv) afforded the fully substituted pyran 162 in 62% yield and in 88% ee. The additional transformations led to 163 in good overall yield. Although this application of AROM/CM process to 161 was the first and rare example of Ru-catalyzed enantioselective olefin metathesis process, very recently, an application of enantioselective RCM reaction catalyzed by [Ru]-VII to the synthesis of (—)-5-e/>/-citreoviral has been reported by Funk. ... 

First synthetic attempts with compound 11 using catalyst [Ru]-VII [17] delivered the undesired bicyclic structure 12, which results from the initial attack of the ruthenium carbene complex at the terminal olefin via intermediate 13 (Scheme 11.5). To direct the initiation of the catalytic cycle into the other double bond, through intermediate 14, Honda et al. decided to introduce steric hindrance using a disub-stituted olefin in the alkyl chain. Their results showed, however, that the resulting compound was not reactive enough to undergo metathesis under the chosen reaction conditions. With the use of a more electron-rich allyl ether moiety such as in 15, it was possible to isolate the desired product in 74% yield and successfully complete the synthesis of securinine. Ruthenium complexes [Ru]-I and [Ru]-II were... 

The simple oxidative addition product Ru(CF3)(CdCF3)(CO)2(PPh3)2 is a likely intermediate in this reaction. Several stable, zero-valent CF2 complexes have been isolated using Cd(CF3)2, and they are included in Table VII (see Section V,C,2,b). 

Recendy, we found that A -allyl-o-vii rlaniline 44 gave 1,2-dihydroquinoline 45 by normal RCM and developed silyl enol ether-ene metathesis for the novel synthesis of 4-siloxy-1,2-dihydroquinoline and demonstrated a convenient entry to quinolines and 1,2,3,4-tetrahydroquinoline [13], We also have found a novel selective isomerization of terminal olefin to give the corresponding enamide 46 using rathenium carbene catalyst [Ru] and silyl enol ether [14], which represented a new synthetic route to a series of substituted indoles 47 [12], We also succeeded an unambiguous characterization of mthenium hydride complex [RuH] with ACheterocyclic carbene... 

Ruthenium(ii).—Group VII Donors. Halide donor ligands. A study has shown that the blue complexes obtained by electrolytic reduction of H2[RuCl5H20] in acidic solution are further examples of mixed Ru"-Ru " complexes. They were previously assumed to contain only Ru . Dimers of the type Ru2Ch3Vi," (n = 0,1, or 2) were separated and isolated using ion-exchange chromatography. 

Ruthenium(m).—Group VII Donors. The consecutive stability constants Ky—Kj of chloro-complexes of Ru have been determined in aqueous and aqueous-alcoholic 1N-HC104. Other Russian workers have compared the... 

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