Poly macroligands

Scheme 6.3 Amphiphilic poly(2-oxazoline) block copolymers bearing triphenylphosphine and bipyridine moieties respectively as polymeric macroligands for micellar catalysis.

Scheme 6.5 Hydroformylation of 1 -octene as a model reaction for micellar catalysis using tri-phenylphosphine-functionalized poly(2-oxazoline)s as macroligands.

Much research has already been devoted in the past couple of years to (i) the immobilization of ATRP active metal catalysts on various supports to allow for catalyst separation and reycycling and (ii) ATRP experiments in pure water as the solvent of choice [62]. A strategy to combine these two demands with an amphiphilic block polymer has recently been presented. Two types of polymeric macroligands where the ligand was covalently linked to the amphiphilic poly(2-oxazo-line)s were prepared. In the case of ruthenium, the triphenylphosphine-functiona-lized poly(2-oxazoline)s described in section 6.2.3.2 were used, whereas in the case of copper as metal, 2,2 -bipyridine functionalized block copolymers were prepared via living cationic polymerization [63] of 2-methyl-2-oxazoline and a bipyridine-functionalized monomer as shown in Scheme 6.8. 

The binding of functionalized chiral ligands to water-soluble polymers has also been shown a (diphenylphosphino)pyrrolidine derivative reacts with poly(acrylic acid) to form a macroligand that is useful in biphasic reduction (35). 

The application of such techniques to high-molecular weight compound chemistry is complicated by problems involved in the synthesis of the corresponding macroligands. Among the examples which are few in number is the production of binuclear Co (II) and Ni(II) chelates based on PE-g-poly (iV-salicyloylacryl-amide) [15, 22d] ... 

It should be noted that PCMU based on cross-linked macroligands possess a relatively high chemical and thermal stability. The stability of poly(enol-ketonate) chelates obtained by oxidation of thin polyvinylacetate films increases in the series of mono-, di- and trivalent ions [122], the oxidation promoting the penetration of the metal ions into the deep film layers. The weight loss of Co and Mn polychelates based on the condensation products of stoichiometric amounts of 5,5 -methylene-bis-salicylaldehyde and 4,4 -diaminophenyl ether at 300, 500, and 600 °C is 2.1, and 0.5 8.0 and 9.8 25.0 and 27.5%, respectively [14b]. The stability, in the range between 275 and 640 °C, of chelates formed by the transition metals and condensation products of p-hydroxybenzoic acid, urea and formaldehyde follow the series [123] Fe(III)>Co(II)>Cu(II)>Ni(II)>V02(II)> Zn(II) Mn(II) > CML. 

Recently, it has been shown that coupling the chiral ligand PPM with a water-soluble poly(acrylic acid) gave a macroligand 9, the rhodium complex of which allowed the reduction of amino acid precursors in water or water/ethyl acetate as the solvents with enantioselectivity up to 56 and 74%, respectively [41]. 

Carboxylate groups were used in many cases to achieve water-solubilization of simple achiral phosphines. With the synthesis of the water-soluble polymer shown in Eq. (2) this methodology was extended into the field of chiral ligands [28a]. Acylation of the diphosphine (2S,4S)-4-diphenylphosphino-2-diphenylphosphinome-thylpyrrolidone (PPM) with poly(acrylic acid) (PPA) yields the hydrophilic macroligand PAA-PMM [28a,b] and PAA-pyrphos [28c]. 

This approach was used to estimate the constants of conplex formation for CXi(2+) and Ni(2+), the conplexes incorporating with polyethylene (PE)-grafted - poly (acrylic) acid (12, 13). For cross-linked polymers K is one-two orders of magnitude hi er than that for soluble macroligands. However, the rate of metal complex formation is markedly lower than that of linear polymers and is controlled by the... 

Consistent with the chain effect, which can be added to the neighboring group effect, the Avc=o V tie is strongly affected by the molecular weight of a macroligand. For example, for C0CI2 complexes with poly(vinylpyrrolidone) with polymerization degrees of n = 100, 200, 360, and 6300 and Avc=o values of 54, 49, 48, and 43 cm , respectively, were found. ... 

There is still no resolution on the effect of macroligand stereochemistry on complex formation. A particular case is the formation of a complex between P2ViPy and MCI2 (M = Co, Ni, Cu, Zn). In that case, the order of reactivity is as follows atactic > isotactic > crosslinked. However, the rate of complex formation for isotactic poly(acrylic acid) (PAAc) with Cu is 1.5 times greater than for the syndiotactic form, and the E for these reactions is 6.0 and T.Okcal moP, respectively. 

Figure 3.3. Reaction scheme for the synthesis of an oligomeric poly-N-isopropylacrylamide based affinity macroligands through chain transfer polymerization, followed by conjugation of the affinity ligand 2-iminobiotin (reproduced with permission from reference 25).

In one of the earliest studies [39], we carried out the purification of A5 4 3-oxosteroid isomerase from a crude extract of Pseudomonas testosteroni by affinity pardoning in a poly(ethylene glycol)/dextran system. The macroligand was prepared by covalent coupling on poly(ethylene glycol) (PEG) of the same steroid derivative as previously described in Fig. 14.2. The resulting macroligand PEG-E,i had an inhibition constant Ki around 5 pM towards the isomerization of A5-androstene-3,17-dione, by isomerase. 

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