Terpyridine monomers

As a continued effort to prepared hexameric systems based on the self-assembly of directed bw-terpyridine monomers, several interesting in families, e.g. 43, of iron and ruthenium connectivity have appeared <06DMP413, 06DT3518>. But in the assembly process, the creation of a three-step procedure to the novel first nondendritic fractal 44 entitled the "Sierpinski hexagonal gasket" was reported <06MI1782>. 

Ru(II) based terpyridine polymers were prepared by Houston et al. in 2003.21 The polymers were prepared by reacting /h.v-terpyridine monomers with Ru(DMSO)4Cl2 in hot ethanol (Fig. 3). To improve the solubility of the coordination polymers, pinene moieties are attached to the monomers. The degree of polymerization of the polymers was studied by elemental analyses, gel permeation chromatography, vapor phase osmometry, STM and electrospray ionization mass spectrometry. However, no precise result was obtained, and the size of the polymers was estimated to be between 40 and 60 repeating units. 

Assemble a second-generation library by creating a second collection of terpyridine monomers with modifications of the initial lead, and repeat from step 1. 

While the use of one terpyridine monomer results in only one dimeric complex, the use of more than one monomer leads to a mixture of complexes. Two monomers (X and Y) will lead to 25% dimeric X X, 25% dimeric Y Y, and 50% mixed complex X Y determined by high-pressure liquid chromatography (HPLC) of reaction products. Complexes (X Y) and (Y X) are degenerate and only one need be considered. Each bis(terpyridine) metal complex exists as a pair of stereoisomers due to the two possible arrangements around the metal center, and no attempt was made to distinguish or separate these stereogenic pairs. The total number of components of these combinatorial libraries must include both symmetric and asymmetric complexes. If n terpyridine monomers are combined, the same number of symmetric complexes (X X) are formed. The number of asymmetric complexes (X Y) formed is /[( -2) 2 ] or better represented as n(n-l)/2. Thus the total number of dimeric complexes is the sum of n and ( -l)/2, which is n(n+l)/2. For example, a library with 5 monomers will form 15 dimers, 10 monomers will produce 55 dimers, and 20 monomers will produce 210 dimers. 

Substituted terpyridine, 4,4, 4"-tris(5-nonyl)-2,2 <5, 2"-terpyridine (tNtpy), is a planar tridentate ligand that was successfully used in homogeneous ATRP of methyl acrylate and styrene [79]. Polymerization of both monomers was controlled and the resulting polymers had relatively low polydispersities (MJMn < 1.2). Similarly to PMDETA, the typical ligand to copper halide ratio used in the polymerization was 1 1. Terpyridine and its derivatives are expected to form tetra-coordinated complexes with copper in which the fourth coordination sphere is occupied by a monodentate ligand (Br-, Cl , solvent, monomer, etc.). Although,... 

Briefly, norbornene-derivatized silica was first reacted with Mo(N-2,6-i-Pr2-C6H3)(CHCMe2Ph)(OCMe(CF3)2)2, followed by (4 -(norbom-2-en-5-ylmethylen-oxy)terpyridine). Loading with Cu (I) afforded the desired ATRP support [18, 22-24], Typical metal loadings were in the range of 15 mmolg. Polystyrene (PS) obtained with these supports under ATRP-conditions showed comparably low poly-dispersities (PDI = 1.55-1.77). The ATRP system consisted of a metal center with one terpyridyl and presumably three acetonitrile ligands, which were at least in part substituted by monomer. Consequently, in contrast to standard systems [25], the equilibrium in this type of reaction did not require conformational... 

In 1995, Constable proposed that coordination polymers can be obtained on addition of metal ions to terpyridine functionalized monomers.8 Terpyr-idine based coordination polymers containing Fe2+, Ru2+, and Zn2+ template ions were subsequently synthesized by El-Ghayoury,9 Constable,10 and Wiirthner,11 respectively. These polymers are soluble, emissive, and exhibit charge transporting properties, rendering them to have potential application in optoelectronic devices such as polymer light-emitting devices (PLEDs). 

The synthesis of 2,2 6, 2"-terpyridine was first described by Morgan and Burstall in 1931.19 Subsequently, metal-terpyridine complexes have become an area of active research. In 1995, Constable proposed a concept of using terpyridine functionalized monomer to give coordination polymers upon addition of metal ions (Fig. I).8... 

In 2003, we first used self-assembled zinc(II) terpyridine polymers in the fabrication of PLEDs.22 We synthesized a series of monomers containing two terpyridine as chelating units, which are at opposite ends and separated by a spacer group (R) (Fig. 5). The self-assembled zinc(II) coordination polymers were easily prepared by the addition of Zn(OAc)2 into solution of monomers. The product yields were up to 80%, and the inherent viscosities of the polymers were in the range of 0.48 to 1.21 dL/g, as determined using an Ubbelohde viscometer in NMP at 30 0.1 °C. 

Spectroscopic data of la—li, monomers of la—li, and model compound 1 (zinc(II) fe(V-phenyl salicylaldiminato) are listed in Table 2. The absorption spectra of these zinc(II) terpyridine polymers are similar, with absorption maxima at 286—290 and 320—391 nm. PL of these polymers span violet, blue, green, and yellow color. The PL quantum yields ( I>PL) range from 25% for lb and le to 77% for If in DM Ac. The PL values of the polymer thin films were determined using integrating sphere,23 which were found to vary from 0.15 to 0.55 0.05 (Table 2). 

Scheme 8.5. Newkome et al.[20J have modified aminotriols and hydroxytribenzyl ether monomers to afford terpyridine-based building blocks. Synthesis of a dodecaruthenium cascade (15) was thus easily effected.

Fig. 7 Predicted average number of monomers per chain (< >) as a function of concentration for different mixing ratios y for the Fe(II)-l coordination systems (one benzenyl ring as the spacer). Here, the stability constants of Fe(II) and terpyridine are used (log[ 2] log[ i]). Adapted from [8]. Reprinted with permission from the Royal Chemistry Society...

Figure 18 Schematic representation of the formation of supramolecular coordination polymers of main-chain or side-chain type from iigands containing bidentate and/or tridentate complexation subunits (such as bipyridine and terpyridine) binding metal ions of tetra-, penta-, or hexa-coordination, and of the constituting subunits. Dynamic diversity may be generated by scrambling of different ligand monomers.

This metal-templated self-assembly approach to combinatorial receptors is presented below, starting from functionalized terpyridine derivatives. Methods include the creation of monomers, dimerization with several metals to form dimeric receptors, and several procedures used to gauge association strength and catalytic activity of library components. 

Figure 4.11 Schematic representation of a seif-heaiing supramoiecuair poiymer network (a) containing coordinated terpyridine-Ru-pincer compiex (b), and formation of aqueous miceiie (c) by copoiymerization with monomers [48].

Terpyridines provide a versatile metal-binding substructure for the development of new monomers for the preparation of coordination polymers and oligomers. The ligands are easily prepared, and the metal complexes are readily characterised. Structurally developed ligands allow the control of metal-centred properties, and allow a variety of coimectivities to be defined by the ligand whilst the metal is constrained to a connectivity of two. This provides a useM complement to related 2,2 -bipyridine ligands. 

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