Ruthenium reactivity order

Kinetic studies have shown that electrophilicity in the iron triad is strongly metal dependent with Fe Ru, Os, and the nucleophilic reactivity order is PPh3 > P(0-tBu)3. Adducts 237 (PR3 = phosphites) react with water to give the cyclohexadienyl phosphonate complexes 239. Complex 235 is a effective catalyst for the conversion of phosphites to HP(0)(0R)2 (99,146,147) [Eq. (29)]. In a similar fashion, benzene ruthenium dications... 

In summary, the order of reactivity for the most commonly used ruthenium-based metathesis catalysts was found to be 56d>56c>9=7. This order of reactivity is based on IR thermography [39], determination of relative rate constants for the test reaction 58—>59 (Eq. 8) [40], and determination of turnover numbers for the self metathesis of methyl-10-undecenoate [43]. 

Methane is a stable molecule and therefore hard to activate. As a result the sticking probability for dissociative chemisorption is small, of the order of 10 only, and ruthenium is more reactive than nickel. However, a stretched overlayer of nickel is significantly more active than nickel in its common form, in agreement with expectation. 

Many late transition metals such as Pd, Pt, Ru, Rh, and Ir can be used as catalysts for steam reforming, but nickel-based catalysts are, economically, the most feasible. More reactive metals such as iron and cobalt are in principle active but they oxidize easily under process conditions. Ruthenium, rhodium and other noble metals are more active than nickel, but are less attractive due to their costs. A typical catalyst consists of relatively large Ni particles dispersed on an AI2O3 or an AlMg04 spinel. The active metal area is relatively low, of the order of only a few m g . ... 

The coordination of ligands at the surface of metal nanoparticles has to influence the reactivity of these particles. However, only a few examples of asymmetric heterogeneous catalysis have been reported, the most popular ones using a platinum cinchonidine system [65,66]. In order to demonstrate the directing effect of asymmetric ligands, we have studied their coordination on ruthenium, palladium, and platinum nanoparticles and the influence of their presence on selected catalytic transformations. 

The dicyclopentadienyl metal compounds undergo Friedel-Crafts alkylation and acylation, sulfonation, metalation, arylation, and formyla-tion in the case of ferrocene, dicyclopentadienyl ruthenium, and dicyclopentadienyl osmium, whereas the others are unstable to such reactions ( ). Competition experiments (128) gave the order of electrophilic reactivity as ferrocene > ruthenocene > osmocene and the reverse for nucleophilic substitution of the first two by n-butyl lithium. A similar rate sequence applies to the acid-catalysed cleavage of the cyclopentadienyl silicon bonds in trimethylsilylferrocene and related compounds (129), a process known to occur by electrophilic substitution for aryl-silicon bonds (130). 

A second-order dependence on crotonic acid has been observed in its Os(VIII)-catalysed oxidation with CAT in alkaline solution. The reaction rate varied linearly with the concentration of Os(VIII). A mechanism has been proposed.140 The kinetics of the ruthenium(III)-catalysed oxidation of the secondary amines with CAT in acidic medium have been obtained and mechanisms have been postulated.141 Uncatalysed and Ru(III)-catalysed oxidation of ethylenediamine, diethylenetriamine, triethylenete-tramine, aminoethylpiperazine, and isophoronediamine with CAT in HC1 solution showed a fractional dependence on the amine, hydrogen ions, and Ru(III), and it is independent of CAT concentration. TSNH2CI has been postulated as the reactive species and a mechanism has been suggested.142... 

In order to investigate this point more fully, the rates of reaction of the two complexes with ethyl vinyl ether (EVE) were studied. This alkene was chosen as it is rather reactive towards ruthenium alkylidene complexes and forms an inert alkoxyalkylidene product in an essentially irreversible manner. This alkene, therefore, should rapidly capture any nascent complex from which a Cy3P ligand has dissociated (27 and 30 in Scheme 12.21). The two complexes displayed very different kinetics. The rate of reaction of the first generation pro-catalyst complex 24c with EVE was found to be dependent on EVE concentration (over a range of 30-120 equivalents of EVE) and did not reach pseudo-first-order conditions... 

The ruthenium-catalyzed oxidation of aldoses by NBS under acidic46 and basic47 conditions have been investigated. The order of reactivity of some pentoses and hexoses has been determined for their oxidation by NBS in aqueous acidic media containing Hg(II) acetate. A mechanism for the reaction has been suggested on the basis of kinetic measurements.48... 

A particularly promising feature of the Ru(terpy)(phen)(L)2+ series, in relation to future molecular machine and motors, is related to the pronounced effect of steric factors on the photochemical reactivity of the complexes [84]. When the bulkiness of the spectator phenanthroline moiety was increased, the steric congestion of the coordination sphere of the ruthenium complex also increased. This increased congestion was qualitatively correlated to the enhanced photoreactivities of these complexes (Fig. 14). More specifically, changing phen for dmp increased by one to two orders of magnitude the quantum yield of the photosubstitution reaction of L by pyridine with L = dimethylsulfide or 2,6-dimethoxybenzonitrile. 

These -oxo-bridged Ru(V)=0 complexes were generated by electrochemical or chemical oxidations of the corresponding ruthenium(III) aqua precursors in aqueous solutions and are very reactive with high E° values. The rate of oxidation of water to oxygen by [(bpy)2(0)Ruv 0Ruv(0)(bpy)2]4+ has been estimated to be a first-order process with rate = /zobs Ru(V)—Ru(V)], where kobs is 0.01 s-1 at 298 K (p = 0.1 Af) (63). 

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