Transition metal catalysts with ruthenium

Transition metals can display selectivities for either carbonyls or olefins (Table 20.3). RuCl2(PPh3)3 (24) catalyzes reduction of the C-C double bond function in the presence of a ketone function (Table 20.3, entries 1-3). With this catalyst, reaction rates of the reduction of alkenes are usually higher than for ketones. This is also the case with various iridium catalysts (entries 6-14) and a ruthenium catalyst (entry 15). One of the few transition-metal catalysts that shows good selectivity towards the ketone or aldehyde function is the nickel catalyst (entries 4 and 5). Many other catalysts have never been tested for their selectivity for one particular functional group. 

From the results presented here, one could get the impression that such allenes with hydroxyl groups in the substituents will always form heterocydes in the presence of transition metal catalysts, but in the presence of other substrates even allenylcarbinols can react to give different products. Examples are the rhodium-catalyzed reaction of allenylcarbinol 78 and phenylacetylene 79 to 80 [42], the palladium-catalyzed reaction of 81 and pyrrolidine 82 to 83 [43] and the ruthenium-catalyzed reaction of 78 and 79 to 84, an isomer of the rhodium-catalyzed reaction of the same substrates mentioned above [44] (Scheme 15.19). 

More synthetic interest is generated by the potentially very useful hydration of dienes. As shown on Scheme 9.6, methylethylketone (MEK) can be produced from the relatively cheap and easily available 1,3-butadiene with combined catalysis by an acid and a transition metal catalyst. Ruthenium complexes of several N-N chelating Hgands (mostly of the phenanthroline and bipyridine type) were found active for this transformation in the presence of Bronsted acids with weakly coordinating anions, typically p-toluenesulfonic acid, TsOH [18,19]. In favourable cases 90 % yield of MEK, based on butadiene, could be obtained. 

Inter-ring metal migrations, dynamic NMR studies, 1, 412 Intracyclic germanium-carbon bond formation large rings, 3, 706 small rings, 3, 703 Intramolecular Alder-ene reactions with metals, 10, 576 with palladium, 10, 568 with rhodium, 10, 575 with ruthenium, 10, 572 with transition metal catalysts, 10, 568 Intramolecular allylations, in cyclizations, with indium compounds, 9, 679... 

Cyclic sulfates provide a useful alternative to epoxides now that it is viable to produce a chiral diol from an alkene. These cyclic compounds are prepared by reaction of the diol with thionyl chloride, followed by ruthenium-catalyzed oxidation of the sulfur (Scheme 9.26).166 This oxidation has the advantage over previous procedures because it only uses a small amount of the transition metal catalyst.167168... 

An example where a transition metal catalyst is used in combination with an enzyme has been described (Scheme 19.26).207 The racemic alcohol 50 was converted to the (A1)-acetate 51, using a ruthenium catalyst along with Novozym 435 (immobilized Lipase B from Candida antarctica), 3 equivalents of p-chlorophenylacetate in t-BuOH, and 1 equivalent of 1-indanone. The reaction yield was 81% with an optical purity of >99.5% ee. 

Only one example of an NHC-containing olefin metathesis catalyst containing a transition metal other than ruthenium has been reported in the literature. The NHC-osmium complexes 53a and 53b (Scheme 2) are synthesized from the dichloro(i]6-p-cymene)osmium dimer by addition of the NHC prepared in situ and abstraction of the chloride, followed by introduction of the ben-zylidene moiety with phenyl diazomethane. 

Abstract Metathesis-based polymerizations of 1-alkynes and cyclopolymerizations of 1,6-heptadiynes using late transition metal catalysts are reviewed. Results obtained with both binary, ternary, and quaternary catalytic systems and well-defined molybdenum- and ruthenium-based catalysts are presented. Special consideration is given to advancements in catalyst design and mechanistic understanding that have been made in this area over the last few years advancements that have facilitated tailor-made syntheses of poly(ene)s. In addition, the first supported ruthenium-based cyclopolymerization-active systems are summarized. Finally, selected structure-dependent properties will be outlined where applicable. 

Catalytic hydroboration is a new methodology of great synthetic potential. The reaction is usually carried out with catecholborane in the presence of rhodium, palladium, iridium and ruthenium compounds.2 In contrast to olefins, very little is known on catalytic hydroboration of conjugated dienes and enynes. Our earlier studies on the uncatalyzed monohydroboration of conjugated dienes,6 reports on the hydroboration of 1-decene with catecholborane catalyzed by lanthanide iodides,7 and monohydroboration of 1,3-enynes in the presence of palladium compounds,8 prompted us to search for other transition metal catalysts for monohydroboration of conjugated dienes and enynes 9 10... 

In comparison with classic Lewis acids derived from main group halides (e.g., B, Al, Sn), f-elements, and early transition metal halides, late transition metal Lewis acids often are more inert to ubiquitous impurities such as water, offer higher stability, tunable properties by ligand modification, and a well-defined structure and coordination chemistry, thus allowing detailed studies of reaction mechanisms, and a rational basis for catalyst optimization. Among this new class of late transition metal Lewis acids, ruthenium complexes - the subject of this chapter - display remarkable properties... 

The reductive carbonylation of nitroarenes with transition metal catalysts is a very important process in industry, as the development of a phosgene-free method for preparing isocyanate is required. Ruthenium, rhodium, and palladium complex catalysts have all been well studied, and ruthenium catalysts have been shown to be both highly active and attractive. The reduction of nitroarene with CO in the presence of alcohol and amine gives urethanes and ureas [95], respectively, both of which can be easily converted into isocyanates [3,96]. 

Polymer-supported benzenesulfonyl azides have been developed as a safe diazotransfer reagent. ° These compounds, including CH2N2 and other diazoalkanes, react with metals or metal salts (copper, paUadium, and rhodium are most commonly used) to give the carbene complexes that add CRR to double bonds. Diazoketones and diazoesters with alkenes to give the cyclopropane derivative, usually with a transition-metal catalyst, such as a copper complex. The ruthenium catalyst reaction of diazoesters with an alkyne give a cyclopropene. An X-ray structure of an osmium catalyst intermediate has been determined. Electron-rich alkenes react faster than simple alkenes. ... 

The copper and palladium transition metal catalysts noted in Table 18 proved to be superior to nickel, ruthenium and rhodium catalysts. The nature of the reacting species has not been unequivocally defined, but the following experimental observations may provide some insight (i) tetrahydrofuran solvent is essential for the palladium-mediated reactions, since complex reaction mixtures (presumably containing carbinols) were observed when the reactions were performed in either benzene or methylene chloride (ii) the reaction is truly catalytic with respect to palladium (2 mmol alkylaluminum, 0.05 mmol of Pd(PPh3)4), whereas the copper catdyst is stoichiometric and (iii) in the case where a direct comparison may be made (entries 1-8, Table 18), the copper-based system is superior to palladium catalysis with regard to overall yield. 

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