Bipyridine based complexes

T. Hasegawa, T. Yonemura, K. Matsuura, and K. Kobayashi, Tris-bipyridine ruthenium complex-based glyco-clusters Amplified luminescence and enhanced lectin affinities, Tetrahedron Lett., 42 (2001) 3989-3992. 

Recently, Angelescu et a/.[92] have studied the activity and selectivity for dimerization of ethylene of various catalysts based on Ni(4,4-bipyridine)Cl2 complex coactivated with A1C1(C2H5)2 and supported on different molecular sieves such as zeolites (Y, L, Mordenite), mesoporous MCM-41 and on amorphous silica alumina. They found that this type of catalyst is active and selective for ethylene dimerization to n-butenes under mild reaction conditions (298 K and 12 atm). The complex supported on zeolites and MCM-41 favours the formation of higher amounts of n-butenes than the complex supported on silica alumina, which is more favourable for the formation of oligomers. It was also found that the concentration in 1-butene and cw-2-butene in the n-butene fraction obtained with the complex supported on zeolites and MCM-41, is higher compared with the corresponding values at thermodynamic equilibrium. 

Hue I, Krische MJ, Funeriu DP, Lehn JM, Dynamic combinatorial chemistry Substrate H-bonding directed assembly of receptors based on bipyridine-metal complexes, Eur. J. Inorg. Chem., 1415-1420, 1999. 

Photocatalytic enantioselective oxidative arylic coupling reactions have been investigated by two different groups. Both studies involved the use of ruthenium-based photocatalysts [142, 143]. In 1993, Hamada and co-workers introduced a photostable chiral ruthenium tris(bipyridine)-type complex (A-[Ru(menbpy)3]2+) 210 possessing high redox ability [143]. The catalytic cycle also employed Co(acac)3 211 to assist in the generation of the active (A-[Ru(menbpy)3]3+) species 212. The authors suggested that the enantioselection observed upon binaphthol formation was the result of a faster formation of the (R)-enantiomer from the intermediate 213 (second oxidation and/or proton loss), albeit only to a rather low extent (ee 16 %) (Scheme 54). 

Several ruthenium complexes bearing chiral Schiff s base ligands have been published. RuL(PPh3)(H20)2], complex C (Fig. 11), with PhIO produced (S)-styrene oxide in 80% ee [61]. Chiral Schiff s base complex D was examined using molecular oxygen with aldehyde, with or without 2,6-dichloropyridine N-oxide as an axial ligand. Styrene oxide was produced in up to 24% ee[62]. A chiral bis(oxazolinyl)pyridine ruthenium complex E with iodosylbenzene diacetate PhI(OAc)2 produced (lS,2S)-fra s-stilbene oxide in 74% ee [63]. Similarly, chiral ruthenium bis(bipyridine) sulfoxide complex F [64] was effective in combination with PhI(OAc)2 as an oxidant and resulted in in 33% ee for (R,R) trans-stilbene oxide and 94% ee for (R,R) trans-/i-Me-styrene (after 75 h at 25 °C). 

Recently, an alternative to the catalytic system described above was reported [204]. The new catalytic procedure for the selective aerobic oxidation of primary alcohols to aldehydes was based on a CunBr2(Bpy)-TEMPO system (Bpy=2,2 -bipyridine). The reactions were carried out under air at room temperature and were catalyzed by a [copper11 (bipyridine ligand)] complex and TEMPO and base (KOtBu) as co-catalysts (Fig. 4.70). 

We have developed an extensive background over a period of years with a type of chemical system—polypyridyl complexes of ruthenium—which appear to have all of the desired characteristics. As examples consider the following 1) Ru111/11 couples based on the bis-2,2 -bipyridine (bpy) complexes RuII(bpy>2L2 + (L = Cl-,... 

Deprotonation of a pyridinylmethylenic proton of pyridine- and bipyridine-based pincer complexes can lead to dearomatization. The dearomatized complexes can then activate a chemical bond (H-Y, Y = H, OH, OR, NH2, NR2, C) by cooperation between the metal and the ligand, thereby regaining aromatization (Figure 1.1). The overall process does not involve a change in the metal s oxidation state [6-8]. In this chapter, we describe the novel, environmentally benign catalytic synthesis of esters, amides, and peptides that operate via this new metal-ligand cooperation based on aromatization-dearomatization processes. 

Scandium trifiate was found to be an effective catalyst for the aldol reactions of silyl enol ethers with aldehydes in aqueous solvent/micellar systems (205). While the reactions proceeded sluggishly in water, remarkable enhancement of the reactivity was observed in the presence of a small amount of a surfactant (206). In related asymmetric version, scandium trifiate (Sc(OTf)3) catalyzed asymmetric aldol of formaldehyde (hydroxymethylation) could be conducted with highly enantioselectively in the presence of chiral bipyridine based ligand (Scheme 53) (207). A significant progress was also made by Feng and co-workers recently a C-2-symmetric iV,iV -dioxide-Sc(III) complex has been developed to asymmetric catalytic aldol reaction of a-ketoesters and diazoacetate... 

Exemplary CV studies on translation in rotaxane Rot-(Figure 18) make use of the thermodynamic effect of a sterically small and flexible 2,2 -bipyridine-based spacer (colored purple). In the first account, three stations are used instead of the normal two such that the 2,2 -bipyridine unit was envisioned as an intermediate station. The evidence for this role (and perhaps the initial inspiration) involves model complexes C-1+, C-2+, and C-S" " (Figure 18), used in the same manner that models were used with rotaxane Rot-l" + (Figure 14) and catenate " Cat-1+ (Figure 15). The CV of rotaxane Rot-4+ was recorded using scan rates that allow almost complete conversion to occur. The published CV shows peaks at two very different locations corresponding to oxidation of the four-coordinate state at about +0.4 V and reduction of the five-coordinate state at about —0.05 V. Model complexes corresponding to the three possible translational isomers were also characterized by CV where the Cu(ll/1) peak potential for the 2,2 -bipyridine system C-2+ sits at an intermediate potential... 

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