Bipyridine-based ligands

Three main parameters were used to evaluate the efficiency of the polymerization, namely monomer conversion (Cmma), initiation efficiency of the reaction (/ = Mn theo/3 n,SEc), and polydispcrsity index (PDI). These results are depicted in Fig. 2. It is obvious that the Cu(I)-catalyzed systems are more effective than the Fe(II)-catalyzed systems under the studied conditions. It was concluded that a bipyridine based ligand with a critical length of the substituted alkyl group (e.g., dHbpy) shows the best performance in Cu(I)-mediated systems. Besides, Cu(I) halide-mediated ATRP with 4,5 -Mbpy as the ligand and TsCl as the initiator was better controlled than that with dMbpy as the ligand, and polymers with much lower PDI values were obtained in the former case. 

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... 

Magenau, A.J.D., Kwak, Y., Schroder, K., Mat5qaszewski, K. Highly active bipyridine-based ligands for atom transfer radical polymerization. ACS Macro. Lett. 1(4), 508-512... 

Pyridine-based ligands which have been used for dendrimers are 2,2-bipyridine (bpy) 17,2,3-bis(2-pyridyl)pyrazine (2,3-dpp) 18 and its monomethylated salt 19, and 2,2 6, 2"-terpyridine 20. Their transition metal complexes possessing dendritic structures were first reported in the collaborative work of Denti, Campagne, and Balzani whose divergent synthetic strategy has led to systems containing 22 ruthenium centers. - The core unit is [Ru(2,3-dpp)3] 21 which contains three... 

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). 

The one-stage condensation of tren with 5,5 -diformyl-2,2 -bipyridine made it possible to also obtain the macrobicyclic Schiff base, whose hydrogenation on the palladium catalyst yielded the clathrochelate tris-bipyridine tranbpy ligand 1 (Scheme 91) [195]. 

A Cu(II) complex with a bipyridine-type ligand (Cu-4) is effective in the controlled polymerization of styrene and acrylates in the presence of Al(0-i-Pr)3, which most probably serves as a reducing agent of Cu(II) into Cu(I).93-94 A fluoroalkyl-substituted bipyridine ligand (L-7) was also employed in supercritical carbon dioxide for the polymerization of fluorinated acrylates and methacrylates.95 Similar pyridine-based bidentate ligands, 1,10-phenanthroline and its... 

Diamine compounds such as L-15 coordinate to copper species, but their use for MA, MMA, and styrene results in slower polymerizations and broader MWDs (MJMn = 1.3—2.5) than those with bipyridine-based bidentate ligands.81108 An increase of the number of amine linkages and bulkier substituents further broadened the MWDs.81 Sparteine (L-16), a bicyclic diamine, was found to be an efficient ligand for homogeneous living radical polymerization of styrene and MMA with CuBr and CuCl, respectively, to give better-controlled polymers (MJMn = 1.1 —... 

FIGURE 12.5 Asymmetric CO stretches for Ti02 anchored Ru(II) sensitizers based on the 4,4 -(COOH)2-2,2 -bipyridine (deb) ligand have been observed at 1730 and 1600cm 1. The former has only been reported on acidified surfaces. The latter is by far the most commonly observed, although the nature and number of Ti02 sites involved in the carboxylate binding remain speculative. 

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