Ruthenium complexes acyclic

Several calixarenes 17-20 bridged on the lower rim with ruthenium(II) and rhenium(I) bipyridyl complexes have been prepared and studied for anion recognition [19]. When compared to acyclic receptor 21 having a similar active structure (ruthenium complex), all receptors show significantly better complexation of AcO" and chloride in DMSO-d6. Thus, calixarene 17 exhibits an almost 30 times higher association constant for AcO (Kl7=9,990 M 1 vs K21=... 

This procedure was first used to prepare ruthenocene and other ruthenium complexes of cyclic olefin (136). The acyclic ruthenocenes are pale yellow, air-stable materials, soluble in organic solvents and readily sublimed. One representative compound of the lanthanides, NdPl 3 (137), and one of the actinides, UP1 3 (138), have also been described. 

Thanks to the development of the Grubbs benzylidene catalyst (2) and other related ruthenium complexes, olefin metathesis has experienced spectacular advances over the past 10 years. The various incarnations of the reaction (acyclic diene metathesis, ring-closing metathesis, ring-opening metathesis polymerization, etc.) have now acquired first rank importance in synthesis. Clearly, the emergence of a similar, generic, efficient catalytic system for con-... 

Among the unimolecular cyclizations, the synthesis yielding a single product with excellent yields was the cyclization of allyloxy alcohols brought about by a ruthenium complex. The other unimolecular processes exhibited very low yields and/or mixture of products. The most popular synthesis of 1,3-dioxocins involved the cyclization of 1,5-alcohols with the insertion of a carbon unit. Such acetalization of both acyclic dialcohols or hydroxyl groups bound to rings is particularly efficient and the cyclization of methane-diphenols or dihydroxybenzophenones with dihalomethanes was of wide applications. Palladium-promoted cyclization of chloromercurio compounds showed to be certainly less effective even if it presented some cases in reasonable yields. The sole example synthesis of 1,3-dioxocins by transformation of another ring has no preparative interest. 

Apart from rhodium, ruthenium complexes are known to effect catalytic cyclopropanation reactions. In the presence of Grubbs ruthenium catalyst, acyclic en)mes would react with dimethyl di-azomalonate under an ethylene atmosphere to give vinyl cyclopropanes in good yields (eq 45) This transformation presumably occurs via a ring-closing en)me metathesis, followed by a selective cyclopropanation of the resulting diene. 

Acyclic diene molecules are capable of undergoing intramolecular and intermolec-ular reactions in the presence of certain transition metal catalysts molybdenum alkylidene and ruthenium carbene complexes, for example [50, 51]. The intramolecular reaction, called ring-closing olefin metathesis (RCM), affords cyclic compounds, while the intermolecular reaction, called acyclic diene metathesis (ADMET) polymerization, provides oligomers and polymers. Alteration of the dilution of the reaction mixture can to some extent control the intrinsic competition between RCM and ADMET. 

X(A1C13) = 0.5) to immobilize a ruthenium carbene complex for biphasic ADMET polymerization of an acyclic diene ester (Figure 7.4-2). The reaction is an equilibrium processes, and so removal of ethylene drives the equilibrium towards the products. The reaction proceeds readily at ambient temperatures, producing mostly polymeric materials but also 10 % dimeric material. 

Numerous studies aimed at the understanding of the mechanism of these processes rapidly appeared. In this context, Murai examined the behavior of acyclic linear dienyne systems in order to trap any carbenoid intermediate by a pendant olefin (Scheme 82).302 A remarkable tetracyclic assembly took place and gave the unprecedented tetracyclo[6.4.0.0]-undecane derivatives as single diastereomer, such as 321 in Scheme 82. This transformation proved to be relatively general as shown by the variation of the starting materials. The reaction can be catalyzed by different organometallic complexes of the group 8-10 elements (ruthenium, rhodium, iridium, and platinum). Formally, this reaction involves two cyclopropanations as if both carbon atoms of the alkyne moiety have acted as carbenes, which results in the formation of four carbon-carbon bonds. 

Abstract This review gives an insight into the growing field of transition metal-catalyzed cascades. More particularly, we have focused on the construction of complex molecules from acyclic precursors. Several approaches have been devised. We have not covered palladium-mediated cyclizations, multiple Heck reactions, or ruthenium-catalyzed metathesis reactions because they are discussed in others chapters of this book. This manuscript is composed of two main parts. In the first part, we emphasize cascade sequences involving cycloaddition, cycloisomerization, or ene-type reactions. Most of these reaction sequences involve a transition metal-catalyzed step that is either followed by another reaction promoted by the same catalyst or by a purely thermal reaction. A simple change in the temperature of the reaction mixture is often the only technical requirement to go from one step to another. The second part covers the cascades relying on transition metalo carbenoid intermediates, which have recently undergone tremendous... 

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