Ru VIII 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 ] . 

In work reported elsewhere (31) we have shown that the oxidation of styrene under mild conditions is promoted by many group VIII metal complexes. The product profile depends on the nature of the metal center and often differs from that observed when radical initiators are used (Table IX). Substantial quantities of styrene oxide are found in some cases but not in others (31). The epoxide which is formed, however, seems to arise via the co-oxidation of styrene and formaldehyde which is formed by oxidative cleavage of the double bond. Formaldehyde may be oxidized to performic acid or formylperoxy radicals which are efficient epoxidizing agents. Reactions of styrene with oxygen in the presence of group VIII complexes exhibit induction periods and are severely retarded by radical inhibitors (31). Thus, the initial step in the oxidation of styrene in the presence of the Ir(I),Rh(I), Ru(II), and Os(II) com-... 

The reactions of butane-2,3-diol by HCF in alkaline medium using Ru(III) and Ru(VI) compounds as catalysts leads to similar experimental rate equations for both the reactions. The mechanism involves the formation of a catalyst-substrate complex that yields a carbocation for Ru( VI) or a radical for Ru(III) oxidation. The role of HCF is in catalyst regeneration. The rate constants of complex decomposition and catalyst regeneration have been determined.89 A probable mechanism invoving formation of an intermediate complex has been proposed for the iridium(III)-catalysed oxidation of propane- 1,2-diol and of pentane-1,5-diol, butane-2,3-diol, and 2-methylpentane-2,4-diol with HCF.90-92 The Ru(VIII)-catalyzed oxidation some a-hydroxy acids with HCF proceeds with the formation of an intermediate complex between the hydroxy acid and Ru(VIII), which then decomposes in the rate-determining step. HCF regenerates the spent catalyst.93... 

No imido complexes of Ru(VIII) have yet been reported. 

Second-order rate constants for the oxidation of Ru and complexes obtained under steady-state at [H2O2] optimal for catalysis (when the oxidation by Compound II is rate-limiting), are summarized in Table VIII. They are in the range 10" 10 s for the majority of... 

The following two examples from our recent work also illustrate the limitations of our systematic approach to Lewis acid promoted alkylations of aliphatic tt systems. The reaction of cumyl chloride 26 with tetramethyl-ethylene in presence of various Lewis acids gave complex mixtures of products, probably because of the strain generated during the formation of the regular addition product. Titanium tetrachloride, however, induces a rapid consecutive cyclization, and the TiCl catalyzed reaction of 26 with tetramethylethylene yields hexamethylindan in 72% yield. Since the aromatic ring can be oxidized under Ru(VIII) catalysis, the reaction sequence shown in Figure 16 allows the construction of acyclic compounds with adjacent quaternary carbon atoms. 

The formation of TMM complex from Group VIII transition metal such as Ir, Ru, and Os from precursors derived from (1) has been reported M.D. Jones, R. D.W. Kemmitt,/. Chem. Soc., Chem. Commun., 1985, 811-812. 

The most important metals for catalysis are those of the groups VIII and I-B of the periodic system. Three crystal structures are important, face-centered cubic (fee Ni, Cu, Rh, Pd, Ag, Ir, Pt, Au), hexagonally dose-packed (hep Co, Ru, Os) and body-centered cubic (bcc Fe). Figure 5.1 shows the unit cell for each of these structures. Note that the unit cells contain 4, 2, and 6 atoms for the fee, bcc, and hep structure, respectively. Many other structures, however, exist when considering more complex materials such as oxides, sulfides etc, which we shall not treat here. Before discussing the surfaces that the metals expose, we mention a few general properties. 

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