Phosphonic acids arenes

The original reaction procedures have steadily been extended and improved, and an overwhelming number of catalyst systems are now known. Besides aryl halides, many additional substrates, for example aryl triflates, diazonium salts, sulfonyl and aroyl halides, carboxylic and phosphonic acids, and even arenes have been used as... 

Derivatives of Phosphonic Acids. A very noteworthy method for the production of arylpho iionic dichlorides starting from arene dichlorophosphines and phosphorus pentoxide leads, in the most prominent case, to phenylphosphonic dichloride. Hereby, according to Figure 11, the mixture of dichloro phenylphosphine and phosphorus pentoxide is chlorinated at 130-150 C (17). 

Recently, Garska et al. took an interest in the preparation of methacrylated calix[4]arene PAs (Scheme 8.5). Moszner et al. had previously demonstrated that the incorporation of modified calix[4]arenes into dental materials results in a significant decrease of the polymerization shrinkage. As an extension of this work, the phosphonic acid PA-7 and the diphosphonic acid PA-8 were prepared in three steps, starting from j-tert-butylcalix[4]arene. To evaluate their adhesive properties, those two monomers were... 

Fig. 37.16 Chemical structure of the p -phosphonic acid calix[8]arene and graphical illustration of the synthesis of calix[8]arene capped Ru, Pt and Pd nanoparticles by hydrogen bubbling (Reproduced with permission from Ref. [105], Copyright 2014, The Royal Society of Chemistry)...

Several reports in the literature show that calixarene derivatives play a crucial role in controlling the size and stability of MNPs [106-108]. For example, Raston reported on the synthesis of p-phosphonic acid calix[8]arene-modified Ru, Pt and Pd nanoparticles in aqueous solution (Fig. 37.16) [109]. The macrocycle was demonstrated to exert a control over the shape and size of the produced nanoparticles by acting as stabilizing agent. Molecular modeling revealed that 12 molecules of the macrocycle surround 2-nm Ru particles, where a H-bonding network among calix[8]arenes contribute to the interfacial self-assembly. 

In addition, there are several investigations on proton exchange polymers, whose phosphonic acid sites are linked to aromatic ring directly or by means of alkylene spacers. These polymers can be prepared by polycondensation of phosphonic acid functionalized monomers or phosphorylation of existing aromatic condensation polymers. There are several methods reported for the preparation of arene phosphonates from aryl bromides [38-40]. The classical Arbuzow reaction [41,42] is commoifly used, in which triethylphos-phite and nickel dichloride are employed as catalysts. The reaction often requires harsh conditions (160 °C) and suffers from low yields. Alternative paUadiiun-catalyzed reaction [43-45] useful for phosphonation proceeds more smoothly. 

The use of RTF allowed encapsulation a guest organic molecule by dimeric para-phosphonic acid-containing calix[5]arene capsule 382 [50]. This hydrogen-bonded capsule binds carboplatin... 

Martin AD, Boulos RA, Hubble LJ, HartUeb KJ, Raston CL (2011) Multifunctional water-soluble molecular capsules based on p-phosphonic acid calix[5]arene. Chem Commun 47 7353-7355... 

A 1 1 complex of para-phosphonic acid-beared calix[5]arene-based caging ligand 382 (Scheme 6.8) with an encapsulated carboplatin molecule releases this guest in aqueous solutions, so the ligand can be used for delivery of these drug molecules [14], A similar approach, devel-... 

The action of phosphonic acid substituted calix[4]arenes (701)-(704) on solvent-containing planar bilayer membranes made of cholesterol and egg phosphatidylcholine (egg PC) or synthetic 18-carbon-tail phospholipid DOPC have been investigated in a voltage-clamp mode. A steady-state voltage-dependent transmembrane current has been achieved only after addition of the compound (702) from the side of the membrane the positive potential has been applied to. This current exhibited anion selectivity passing more chloride at negative potentials applied from the side of the membrane to which calix[4]arene (702) has been introduced. The kinetics and temperature-dependence determined for calix[4]arene (702)-mediated ionic transport suggested a carrier mode of facilitated diffusion. 

More and more, solid catalysts like zeolites, clays or resins are used instead of traditional catalysts. Thus, zeolites are good catalysts for the acylation of non-heterocyclic aromatic compounds, both in the gas phase [2] and in the liquid phase [3]. The acylation of thiophene and of furan can also be carried out in the gas phase with M-5 catalysts [4]. Lasdo and co-woikers have shown that modified clays like montmorillonite doped with ZnCl2 can catalyse the reactioi of arenes with substituted benzoyle chlorides in good yields [5] (70 to 100%). Delmas and co-workers have reported the acylation of furan by carboxylic acids with nafion-H [6] (sulfonic resin) and duolite [7] (ion exchanged phosphonic resin). One of the advantages of these catalysts is the safety of environment. Actually, the use of homogeneous catalysts causes problems of corrosion, waste and troublesome workups [8,9]. 

Unfortunately, TEMPO is not the ideal nitroxide, and reactions give poor yields of polymer with several by-products that contaminate the product and are difficult to remove. Improvements can be achieved by using TEMPO-hke struetures, such as di-tert-butyl nitroxides, and additives, such as acetic acid, that improve the rate of polymerization. More important has been the development of new alkoxyamine structures such as phosphonate (1) and arene (2) nitroxides... 

Palladium-catalyzed dehydrogenative cis double phosphorylation of 1-octyne with the /7-phosphonate (88) leading to (Z)-l,2-bisphosphoryl-octene (89) has been sueeessfully carried out by Han et al (Scheme 28). p-Aryl-p-ketophosphonates (90) have been efficiently prepared in good yields using the TBAA/H3P04-mediated acylation of electron-rich arenes with phosphonoacetic acids. The conditions enabled preparation of (90) without use of strong bases, cryogenics or anhydrous and inert atmosphere. 

Hydrophobic residues in dipeptides like alanine, glycine, and tyrosine (Fig. 23.10) were recognized by a diphosphorylated calix[4]arene, 5. Thermodynamic data showed that 5 recognized and included the protonated N-terminus of the small peptides [12]. More favourable binding energies exist for dipeptides relative to the amino acids, as the charge-charge repulsion between the phosphonates and carboxylates decreased, as their mutual separation distance increased (Table 23.3). 

Fig. 37.8 Chemical structure of the p-phosphonato-calix[4]arene (a) and suggested binding mode of the p-phosphonate-calix[4]arene embedded in a stearic acid monolayer with arginine residues of basic proteins dissolved in the aqueous subphase (b) (Reproduced with permission from Ref. [53], Copyright 2005, American Chemical Society)...

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