Ruthenium isomerization activity

None of the ruthenium complexes gave greater than trace amounts of disproportionation. Both of the nitrosyl-containing ruthenium derivatives showed some double-bond isomerization activity with 1-2% 1-pen-tene being observed. 

This thesis was demonstrated (1) in the selective hydrogenation of the pairs of olefins shown in Table I, over ruthenium-on-carbon, a catalyst with relatively low isomerization activity. The experiments were carried out by partial hydrogenation of a mixture of 1 mole of each olefin, and the reaction was interrupted and analyzed after absorption of 1 mole of hydrogen. Those compounds underlined in Table I were reduced with high selectivity in preference to the other member of the pair. This high degree of selectivity was limited to those pairs of olefins... 

Selectivity of the type found with ruthenium was not possible when palladium catalysts were used. For instance, hydrogenation of a mixture of 1- and 2-octene was completely nonselective over palladium catalysts. This lack of selectivity resulted from the high isomerization activity of palladium when the reaction was stopped at only one-tenth of completion, all 1-octene had disappeared by migration of the terminal double bond inward. 

A comparison of Rh and Ru catalysts in the hydroformylation of linear butenes [110] or 3,3,3-trifluoropropene allowed the conclusion that the latter are less active [111]. Moreover, in the hydroformylation of propene, inferior regioselectiv-ity was observed [112]. Apparently, ruthenium catalysts can exhibit pronounced isomerization activity, which is supported by heteroatoms in the substrate (e.g., allyl alcohols, allylamines) [113]. 

Conventionally, organometallic chemistry and transition-metal catalysis are carried out under an inert gas atmosphere and the exclusion of moisture has been essential. In contrast, the catalytic actions of transition metals under ambient conditions of air and water have played a key role in various enzymatic reactions, which is in sharp contrast to most transition-metal-catalyzed reactions commonly used in the laboratory. Quasi-nature catalysis has now been developed using late transition metals in air and water, for instance copper-, palladium- and rhodium-catalyzed C-C bond formation, and ruthenium-catalyzed olefin isomerization, metathesis and C-H activation. Even a Grignard-type reaction could be realized in water using a bimetallic ruthenium-indium catalytic system [67]. 

The CM of olefins bearing electron-withdrawing functionalities, such as a,/ -unsaturated aldehydes, ketones, amides, and esters, allows for the direct installment of olefin functionality, which can either be retained or utilized as a synthetic handle for further elaboration. The poor nucleophilicity of electron-deficient olefins makes them challenging substrates for olefin CM. As a result, these substrates must generally be paired with more electron-rich crosspartners to proceed. In one of the initial reports in this area, Crowe and Goldberg found that acrylonitrile could participate in CM reactions with various terminal olefins using catalyst 1 (Equation (2))." Acrylonitrile was found not to be active in secondary metathesis isomerization, and no homodimer formation was observed, making it a type III olefin. In addition, as mentioned in Section 11.06.3.2, this reaction represents one of the few examples of Z-selectivity in CM. Subsequent to this report, ruthenium complexes 6 and 7a were also observed to function as competent catalysts for acrylonitrile... 

Metals differ in their ability to catalyze isomerizations. Both the relative rates of isomerization of individual alkenes and the initial isomer distribution vary with the metal. The rates of isomerization of the three n-butenes on ruthenium and osmium, for example, are cis-2- > trans-2- > 1-butene,175 whereas on platinum and iridium they are cis-2- > 1- > trans-2-butene.176 These observations are in accordance with the fact that the rates of formation of the 1- and 2-butyl intermediates are different on the different metals. The order of decreasing activity of platinum metals in catalyzing the isomerization of dimethylcyclohexenes was found to be Pd Rh,... 

Complexes 98 [L = PPh3, P(Ph-p-F)3, P(Ph-p-Me)3] react with methyl-lithium to give, after methanolysis, the orthometallated complexes 99 (Scheme 5). Complex 98 (L = PPh3) also leads to 99 by reaction with phenyllithium or Red-Al 54). The formation of 99 suggests that the initial reduction of 98 leads to a 16-electron ruthenium (0) intermediate followed by C—H bond activation as for the transformations of 90 and 91. Treatment of complex 98 (L = P-i-Pr3) with methyllithium produces the cyclo-metallated diastereoisomers 100. Complexes 101 and 102 are obtained by treatment of 98 (L = PPh2-f-Bu) with methyllithium at -78°C and at +70°C, respectively. Complex 101 isomerizes to 102 by a first-order process (k 0.2 hour-1 in C6D6 at 50°C) when L is PPh2-i-Pr 98 leads to 103 which isomerizes to the orthometallated complex 104 54). 

We have already alluded to the diversity of oxidation states, the dominance of oxo chemistry and the cluster carbonyls. Brief mention should be made too of the tendency of osmium (shared also by ruthenium and, to some extent, rhodium and iridium) to form polymeric species, often with oxo, nitrido or carboxylato bridges. Although it does have some activity in homogeneous catalysis (e.g. of m-hydroxylation, hydroxyamination or animation of alkenes, see p. 558, and occasionally for isomerization or hydrogenation of alkenes, see p. 571), osmium complexes are perhaps too substitution-inert for homogeneous catalysis to become a major feature of the chemistry of the element. The spectroscopic properties of some of the substituted heterocyclic nitrogen-donor complexes may yet make osmium an important element for photodissociation energy research. 

Mixed metal clusters (clusters containing two different metals) have considerable potential for mechanistic studies. Three separate studies on iron mthenium clusters show the possibilities. Reactions of FeRu2(CO)i2 and Fe2Ru(CO)i2 in comparison to Fe3(CO)i2 and Ru3(CO)i2 show a very interesting activation of the iron center towards CO dissociation by ruthenium centers in the mixed metal-cluster system. Such an activation of the iron center by ruthenium has also been demonstrated for (/r-H)FeRu2(/(r-COMe)(CO)io. The presence of different metal centers for H2FeRu3(CO)i2 allowed unusually detailed interpretation of the isomerization, substitution, and CO exchange reactions. ... 

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