Cyclometalations, ruthenium

Thus, the [Ru(phpy)(phen)2]+ ruthenacycle is a strikingly reactive electron donor for HRR High rate constants for other complexes are summarized in Table IX. Plant peroxidases from sources other than horseradish also show a high reactivity to cyclometalated ruthenium(II) complexes listed in Table IX (234). 

Binuclear [RuX2(arene)]2 (1) and mononuclear RuX2(L) (arene) (3) derivatives have been shown to be useful precursors for access to alkyl-or hydrido(arene)ruthenium complexes. The latter are key compounds for the formation of arene ruthenium(O) intermediates capable of C—H bond activation leading to new hydrido and cyclometallated ruthenium arene derivatives. Arene ruthenium carboxylates appear to be useful derivatives of alkyl-ruthenium as precursors of hydrido-ruthenium complexes their access is examined first. 

The OLED applications in Sect. 9.2 are used mainly for cyclometalated iridium compounds. However, in the case of dye-sensitized solar cells, the cyclometalated ruthenium compounds are used mainly for these cells. This is because iridium compounds are not usually considered to be strong absorbers, which is of key importance to the device efficiency provided by dye-sensitized solar cells [6]. Some representative cyclometalated dye-sensitized solar cells are shown in Fig. 9.7. 

Although the cyclometallated ruthenium complexes were formerly claimed to be configurationally stable at the stereogenic metal, Brunner and co-workers have shown that they are indeed configurationally labile. Revisiting previous NMR spectroscopic data, variable-temperature NMR studies (—80 to 21 °G) were carried out, and showed that epimerization processes take place. This has also been assessed by the isolation of cyclometallated ruthenium and osmium derivatives which have been synthesized through transmetallation reactions of [ MGl(p-Gl)(77 -y>-cymene) 2] (M = Ru, Os) with the enantiomerically pure mercurated (3 )-(-h)-iV,iV-dimethyl(l-phenyl)ethyl-amine. In both cases, two diastereoisomers (i M c) ( m c) were obtained, which undergo epimerization in... 

Cyclometalated Ruthenium Alkylidene Complexes A Powerful Family of... 3... 

Accordingly, considerable effort has been dedicated to the development of olefin metathesis catalysts exhibiting kinetic selectivity. As a result, a number of Z-selective tungsten-, molybdenum-, and ruthenium-based olefin metathesis catalysts have been recently developed (For Mo- and W-based Z-selective catalysts [24-41], For Ru-based Z-selective catalysts [42-45], For cyclometalated Ru-based Z-selective catalysts [46-58]). Many of these systems exhibit consistently high levels of activity and selectivity across a broad range of substrates. Herein, we will focus specifically on the cyclometalated ruthenium-based catalysts developed in our laboratory [46-58]. This chapter is intended to provide a comprehensive summary of the evolution of these cyclometalated ruthenium catalysts, from their initial serendipitous discovery to their recent applications in Z-selective olefin metathesis transformations. Current mechanistic hypotheses and limitations, as well as future directions, will also be discussed. 

Model for Z-Selectivity of Cyclometalated Ruthenium-Based Catalysts... 

Cyclometalated Ruthenium Alkylidene Complexes A Powerful Family of. 

The abovementioned cyclometalated ruthenium catalysts have been applied in a number of Z-selective olefin metathesis reactions [46-58]. Of these catalysts, 10 remains the state of the art with respect to a general Z-selective catalyst for CM (Sect. 3.1) and mRCM (Sect. 3.3). The potential of 10 remains to be fully evaluated in more specialized transformations such as AROCM (Sect. 3.2), Z-selective ethenolysis (Sect. 3.5), or ROMP (Sect. 3.4). 

Our extensive studies in the realm of Z-selective ethenolysis reactions have important mechanistic implications for CM and mRCM reactions catalyzed by cyclometalated ruthenium alkylidene complexes. For example, it was observed that the CM of two internal double bonds only proceeded in the presence of ethylene, and when both olefins were of the Z-configuration [53]. When an equimolar mixture of an E-olefin and a Z-olefin was reacted in the presence of ethylene, no crossover products were observed. This suggests that all internal olefins must undergo ethenolysis before they can form CM products, and that productive CM reactions only proceed through terminal olefins. 

Taketoshi A, Beh XN, Kuwabara J, Koizumi T, Kanbara T. Aerobic oxidative dehydrogenation of benzyl alcohols to benzaldehydes by using a cyclometalated ruthenium catalyst. Tetrahedron Lett. 2012 53 3573-3576. 

Zhang Y-M, Shao J-Y, Yao C-J, Zhong Y-W. Cyclometalated ruthenium(II) complexes with a bis-carbene CCC-pincer ligand. Dalton Trans. 2012 41 9280-9282. 

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