2-phenylpyridine moieties

Ruthenium-catalyzed arylation seems to favor the proton abstraction mechanism. We studied the coupling of an aryl group to a phenylpyridine moiety [64]. The first step consists of cleavage of a C- H bond to form a Ru-C bond. The two mechanisms, oxidative addition on the ruthenium or H-abstraction, were evaluated. As for palladium, the oxidation of Ru(II) to Ru(IV) is energetically disfavored with a barrier of 133 kJ/mol. The H-abstraction possesses a much lower barrier, 35 kJ/mol with HCOs" as proton abstractor (Fig. 11.13). The barrier of H-abstraction is sensitive to the nature of the base it is only of 22 kJ/mol with acetate. 

Cationic complexes of cyclometallated Ir (ppy)2 (ppy = 2-phenylpyridine) with chelated diimine ligands, such as bipyridines (bipy) and phenan-throlines (phen), have interesting phosphorescent properties with potential applications in electroluminescent devices. Such compounds show at rather high energy MLCT transitions (2,nax = 340-380 nm) from the [Ir° (ppy)2]-based HOMOs to the LUMOs based on the n -orbitals of the phen (or bipy) ligands. Thus, these complexes can be considered as push-pull molecules in which the Ir° (ppy)2 moiety acts as the donor and the diimine as the acceptor part. 

Chiral catalysts are usually bulky chiral moieties, such as pincer-type compounds, naphthalenes, biaryl compounds such as 2-phenylpyridines, pentaphenyl-ferrocenes, and bicyclic compounds, or oxazolines. 

Photoswitching of the electronic communication between two metal centers using the photochromic diarylethene bridging ligand with both thiophene moieties substituted with two cyclometallated phenylpyridines (Figure 23a) was first reported by Coudret and Launay. Although the comproportionation constants (Kc) for the dinuclear mixed-valence ruthenium complexes in both the open and closed forms were similar, the intervalence charge-transfer (IVCT) transitions were observed only in the closed... 

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