Ruthenium, isomerization studies

Histidine residues are, however, generally regarded as major possible binding sites for ruthenium-arene complexes in proteins. To model this interaction, we also studied the reaction of [RuCl(en)(rj6-bip)]+ (10) with L-histidine at 310 K in aqueous solution (91). The reaction was quite sluggish and did not reach equilibrium until 24 h at 310 K, by which time only about 22% of the complex had reacted. Two isomeric imidazole-bound histidine adducts could be discerned, with more or less equal binding of Ne... 

In an extensive study of the isomerization of hexenes and heptenes by platinum, palladium, and ruthenium, Harrod and Chalk (65) found that in many cases the equilibrium mixture of isomerized olefins was obtained. Isomerizations were achieved with Pt(II) (as 1,3-bisethylene-2,4-dichloro-fi-dichlorodiplatinum(II) with alcohol as cocatalyst), Pd(II)... 

Gompared with vinylidene complexes, allenylidne complexes are not well studied theoretically. In this chapter, theoretical calculations of an allenylidene-vinylvinyli-dene equilibrium and the Z/E isomeric interconversion of aminoallenylidene ruthenium complexes were summarized. 

Detailed mechanistic studies with respect to the application of Speier s catalyst on the hydrosilylation of ethylene showed that the process proceeds according to the Chalk-Harrod mechanism and the rate-determining step is the isomerization of Pt(silyl)(alkyl) complex formed by the ethylene insertion into the Pt—H bond.613 In contrast to the platinum-catalyzed hydrosilylation, the complexes of the iron and cobalt triads (iron, ruthenium, osmium and cobalt, rhodium, iridium, respectively) catalyze dehydrogenative silylation competitively with hydrosilylation. Dehydrogenative silylation occurs via the formation of a complex with cr-alkyl and a-silylalkyl ligands ... 

Asymmetric catalysis undertook a quantum leap with the discovery of ruthenium and rhodium catalysts based on the atropisomeric bisphosphine, BINAP (3a). These catalysts have displayed remarkable versatility and enantioselectivity in the asymmetric reduction and isomerization of a,P- and y-keto esters functionalized ketones allylic alcohols and amines oc,P-unsaturated carboxylic acids and enamides. Asymmetric transformation with these catalysts has been extensively studied and reviewed.81315 3536 The key feature of BINAP is the rigidity of the ligand during coordination on a transition metal center, which is critical during enantiofacial selection of the substrate by the catalyst. Several industrial processes currently use these technologies, whereas a number of other opportunities show potential for scale up. 

Isomerization of allylic alcohol to ketone has been extensively studied [13], and two different pathways have been established, including tt-allyl metal hydride and the metal hydride addition-elimination mechanisms [5,14]. McGrath and Grubbs [ 15] investigated the ruthenium-catalyzed isomerization of allyl alcohol in water and proposed a modified metal hydride addition-elimination mechanism through an oxygen-functionality-directed Markovnikov addition to the double bond. 

The control of alkene geometry in RCM reactions has been an area of intense research and interest since the process was first developed. While a general solution to this challenge has not yet been developed, intriguing observations of E Z control in macrocyclizations continue to be reported. For example, in the course of their studies on the synthesis of herbarumin I and II, Fiirstner and co-workers reported the selective formation of either of the two isomeric alkene products 16 or 17 via RCM of diene 15 <02JA7061> (Scheme 8). The diene 15 was transformed into the -alkene 17 using the ruthenium indenylidene catalyst (Fiirstner Metathesis Catalyst FMC, <01MI4811>) while use of the MC2 led to clean formation of the Z-isomer 16. 

Complexes of 82 have also been formed by the reaction of 2,6-diacetylpyridine and Af.Af-hwQ-aminopropyOamine in the presence of nickel(II) chloride and copper(II) chloride50). Other metals that have been used include copper(II) 63,64), nickel64165), cobalt(II) 66), manganese(II)73>, cobalt(I)69), eobalt(III)68,70-72), zinc(II)73>, and ruthenium(II)74). Kam and Busch 51 have reported the catalytic hydrogenation of the nickel(II) perchlorate complex of 82 to afford two nickel(II) complexes of 83 a yellow minor component and a red major component which preliminary studies indicate to be the meso form (84). The isomeric ligands can be displaced from the respective reduced complexes by cyanide ion. Ligand 84 has also been isolated and characterized as the cobalt(III) 67), iron(II)61,62), iron(III) 62>, and copper(II) complex 75,76). Dehydro — 82 has also been synthesized and complexed with nickel(II) 65,65a), and nickel(III)65 a. ... 

Propenyl Ethers and Unsaturated Cyclic Ethers Propenyl ethers (CH3—CH=CH—OR R = ethyl, isobutyl, etc. cis- and trans-isomers) and 3,4-dihydrofuran are linear and cyclic a,/3-unsaturated ethers, that can be regarded as / -substituted vinyl ether derivatives. For these monomers a few controlled/living cationic polymerizations have been reported. The HI/I2 system is generally effective for both linear and cyclic monomers [181,182,183], whereas a recent study by Nuyken indicates that the IBVE-HI adduct coupled with nBu4NC104 is suited for 3,4-dihydrofuran (see Section V.A.4) [184]. A variety of mono- and bifunctional propenyl ethers can readily be prepared by the ruthenium complex-catalyzed isomerization of corresponding allyl ethers [185]. 

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. ... 

Platinum and palladium complexes of thietane and 3,3-dimethylthietane have been prepared as illustrated for 90. The platinum complexes exist in cis and trans configurations, but no cis-trans isomerization of the palladium complexes in the solid state was observed. Stability constants of thietane with Mn(ll), Co(II), and Ni(II) chelates have been determined. Proton nmr studies show that the absorption of the a-methylene protons, which are syn to the metal, is shifted downfield (about 0.7 ppm) more than the absorption of the protons anti to the metal (about 0.4 ppm downfield). Energies of activation for pyramidal inversion were determined. Bis-ruthenium complexes of di-, tri- and tetraspirothietanes (e.g., 90a) show rapid electron transfer between the ruthenium ions long-range electron tunneling was proposed. ... 

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