Terpyridine-based ligands

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... 

Fluorescent redox switches based on compounds with electron acceptors and fluorophores have been also reported. For instance, by making use of the quinone/ hydroquinone redox couple a redox-responsive fluorescence switch can be established with molecule 19 containing a ruthenium tris(bpy) (bpy = 2,2 -bipyridine) complex.29 Within molecule 19, the excited state of the ruthenium center, that is, the triplet metal-to-ligand charge transfer (MLCT) state, is effectively quenched by electron transfer to the quinone group. When the quinone is reduced to the hydroquinone either chemically or electrochemically, luminescence is emitted from the ruthenium center in molecule 19. Similarly, molecule 20, a ruthenium (II) complex withhydroquinone-functionalized 2,2 6, 2"-terpyridine (tpy) and (4 -phenylethynyl-2,2 6, 2"- terpyridine) as ligands, also works as a redox fluorescence switch.30... 

Tridentate nitrogen ligands form 1 1 uncharged complexes with copper, in contrast to bidentate ligands that form tetrahedral ionic complexes.81 Well-controlled polymers of styrene and MA are obtained with a substituted terpyridine (L-18), whereas the unsubstituted derivative induced a heterogeneous and uncontrolled polymerization.111 A similar controlled polymerization of styrene was reported for a substituted terpyridine-based complex of Cu(II) (Cu-5) coupled with Al(O i-Pr)3.112 A tridentate ligand with two pyridines and one amine (L-19) gave narrow MWDs for styrene, MA, and MMA (MJMn = 1.1 —... 

Photoactive molecular wires based on metal complexes with 2,2 -bipyridine, phenathroline, and 2,2, 6,2-terpyridine as ligands 00CSR1. 

A new class of bleach catalysts is based on the 2, 2 6, 2" terpyridine (terpy) ligands [43]. Whereas nonsubstituted Mn(II)-terpy complexes show only poor activity, the incorporation of electron-donating substituents in the 4-position significantly improves performance in solution and surface bleaching [44]. 

Fig. 5 Examples of quenching enantioselective sensors involving metal ions (a) JV.W -dioxide of the 1,8-diacridylnaphtalene units which can form a scandium(m) complex (b) high enantioselective quenching obtained by the scandium complex of 11 for 2-aminopropanol (reprinted with permission from [64]. Copyright 2008 American Chemical Society) (c) triamino-diamido copper (II) complex (12) (d) Zn (II) complex with terpyridine based chiral ligand (13) (e) chiral oxazoline containing maleimido polymers (14)...

Pyridine-based N-containing ligands have been tested in order to extend the scope of the copper-catalyzed cyclopropanation reaction of olefins. Chelucci et al. [33] have carefully examined and reviewed [34] the efficiency of a number of chiral pyridine derivatives as bidentate Hgands (mainly 2,2 -bipyridines, 2,2 6, 2 -terpyridines, phenanthrolines and aminopyridine) in the copper-catalyzed cyclopropanation of styrene by ethyl diazoacetate. The corresponding copper complexes proved to be only moderately active and enantios-elective (ee up to 32% for a C2-symmetric bipyridine). The same authors prepared other chiral ligands with nitrogen donors such as 2,2 -bipyridines 21, 5,6-dihydro-1,10-phenanthrolines 22, and 1,10-phenanthrolines 23 (see Scheme 14) [35]. 

For instance, some time ago Newkome et al. reported the synthesis of ruthenium based dendrimers [170]. A dendrimer (80) with twelve peripheral terpyridine ligands was built around a central quaternary carbon-based core. In the final step complexation between the terminal ligand of the dendrimer and a terpyridinyl ruthenium chloride building block afforded the dodecaruthenium cascade molecule 80 (Fig. 35). Thus, preconstructed cores and dendritic fragments were linked by Ru2+ as the connecting unit and this mode of connectivity could be denoted by [—(Ru)—]. 

Terpyridine moieties have been introduced as a terminal unit of macromolecules. In a subsequent procedure the two-step self-assembly process based on Rum/Run chemistry was used for polymers end-capped with the 2,2/ 6/,2 -terpyridine ligand. More precisely, the terpyridine-functionalized polymers were complexed with RUCI3 to selectively form a mono-complex. In a further step, this mono-complex was reacted under reducing conditions with other uncomplexed 2,2/ 6/,2/-terpyridine-terminated polymer blocks in order to form an asymmetrical AB ruthenium(II) frzs-complex. 

The photoelectrochemical performances given by the mononuclear complex [Ru(dcbH2)2(NCS)2] have been surpassed by an analogous species based on the terpyridine ligand.8... 

It has long been known that, when bound to cobalt(II), the pyridine-based chelate ligands 2,2 -bipyridine (bipy), 1,10-phenanthroline (phen), and 2,2 6, 2"-terpyridine (terpy) form complexes that react with dioxygen in aqueous solution (32-34). The mixed-ligand complexes [Co(terpy)(bipy)]2+ and [Co(terpy)(phen)]2+ can act as oxygen carriers in aqueous solutions at pH values as low as 3.0 (34b), and the superoxo species thus formed are apparently dinuclear. In addition, the dinuclear bipyridine complex [(bipy)2Coin(/ 2-0 )(/ 2-02 )CoIn(bipy)2 ]3+ has been shown to catalyze the oxidation of 2,6-di-ter -butylphenol to the feri-butyl-substituted diphenoquinone and quinone (35). 

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