Ruthenium complexes experimental

Allyl methylcarbonate reacts with norbornene following a ruthenium-catalyzed carbonylative cyclization under carbon monoxide pressure to give cyclopentenone derivatives 12 (Scheme 4).32 Catalyst loading, amine and CO pressure have been optimized to give the cyclopentenone compound in 80% yield and a total control of the stereoselectivity (exo 100%). Aromatic or bidentate amines inhibit the reaction certainly by a too strong interaction with ruthenium. A plausible mechanism is proposed. Stereoselective CM-carboruthenation of norbornene with allyl-ruthenium complex 13 followed by carbon monoxide insertion generates an acylruthenium intermediate 15. Intramolecular carboruthenation and /3-hydride elimination of 16 afford the -olefin 17. Isomerization of the double bond under experimental conditions allows formation of the cyclopentenone derivative 12. 

The systems that we investigated in collaboration with others involved intermolecular and intramolecular electron-transfer reactions between ruthenium complexes and cytochrome c. We also studied a series of intermolecular reactions between chelated cobalt complexes and cytochrome c. A variety of high-pressure experimental techniques, including stopped-flow, flash-photolysis, pulse-radiolysis, and voltammetry, were employed in these investigations. As the following presentation shows, a remarkably good agreement was found between the volume data obtained with the aid of these different techniques, which clearly demonstrates the complementarity of these methods for the study of electron-transfer processes. 

In 2002, Kiindig et al. [23, 24] developed catalytic DCR between diaryl nitrones and a,(3-unsaturated aldehydes in the presence of Binop-F iron and ruthenium complexes as chiral Lewis-acid catalysts (Scheme 6). The corresponding cycloadducts were obtained in good yields with complete endo selectivity and up to 94% ee. The isoxazolidine products were obtained as a mixture of regioi-somers in molar ratios varying from 96 4 to 15 85. Experimental and computational data show that the regioselectivity correlates directly with the electronic properties of the nitrone. 

Another focus of this chapter is the alkynol cycloisomerization mediated by Group 6 metal complexes. Experimental and theoretical studies showed that both exo- and endo- cycloisomerization are feasible. The cycloisomerization involves not only alkyne-to-vinylidene tautomerization but alo proton transfer steps. Therefore, the theoretical studies demonstrated that the solvent effect played a crucial role in determining the regioselectivity of cycloisomerization products. [2 + 2] cycloaddition of the metal vinylidene C=C bond in a ruthenium complex with the C=C bond of a vinyl group, together with the implication in metathesis reactions, was discussed. In addition, [2 + 2] cycloaddition of titanocene vinylidene with different unsaturated molecules was also briefly discussed. 

Good agreement between the CNDO/S semiempirical HAB calculation and the experimental k j for the Ru/Ru-DNA duplex is found. Of course, this comparison requires use of Eq. (4) and a specified value of (0.9 eV) in addition to the measured driving force of 0.7 eV. Combining these data yields a calculated kB1 = 7.1 x 106 s 1 compared to the experimental k j = 1.6 x 106 s 1. Extensive use of the same ruthenium complexes as D/A groups in protein studies means that there is not much uncertainty in X (ca. 0.2 eV). 

The monosubstituted vinylidene complexes are readily deprotonated with a variety of mild bases (e.g., MeO-, C032 ), and this reaction constitutes the most convenient route to ruthenium acetylide complexes. Experimentally the deprotonation is most easily achieved by passing the vinylidene complex through basic alumina. Addition of a noncomplexing acid (e.g., HPF6) to the acetylide results in the reformation of the vinylidene complex [Eq. (66)]. Reaction of 1 and terminal alkynes such as phenylacetylene in methanol followed by the addition of an excess of... 

Fig. 9a,b. Plot of the ratio jS/j rnonomer function of the numher of ruthenium complex building blocks N. experimental data continuous lines display the N or dependence of... 

These ruthenium complexes react rapidly and quantitatively with ethyl vinyl ether to form a Fischer carbene that is only weakly metathesis active at elevated temperatures [86, 87]. This property can be employed to end-cap ROMP and ADMET polymers and to ensure that there are no polymeric ruthenium alkyhdenes present. Since ruthenium alkylidenes are relatively robust complexes they could survive workup procedures, although experimental evidence has yet to confirm this notion. Treatment of an ADMET polymer with ethyl vinyl ether gives the polymer well-defined terminal olefinic endgroups and should prevent backbiting metathesis upon dilution of the polymer (Scheme 6.22). 

In more elaborate studies, Kubiak and coworkers have established experimentally the existence of dynamic equilibrium mixtures containing charge-transfer isomers of mixed-valence ruthenium complexes within [ Ru3(p-0)-(p-CH3C00)6(12c1 0)(L ) ](p-BL)[ Ru3(p-0)(p-CH3C00)6( C 0)(L") ] by monitoring the v(CO) vibrations in the infrared (p-BL = unsymmetrical pyr-azine derivatives). The mixed-valence charge-transfer isomers differ in the... 

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