2,6-pyridine dicarboxylate ligands

The mechanism of substitution reactions of trans-[MnN(H20)(CN)4] with pyridine dicarboxylate ligands has been explored (H. J. van der Westhuizen, R. Meijboom, M. Schutte, A. Roodt, Inorg. Chem., 2010, 49, 9599). The rate determining step is the second one, resulting in chelation and loss of cyanide. Attachment of the carboxylate oxygen to the Mn(V) center of trans-[MnN(H20)(CN)4] is extremely fast. 

A related geometry results from the use217 of 2,6-pyridine dicarboxylate in Ph2SnC7H3N04-H20. The two phenyl groups are at normal distances and trans (CSnC = 172°). The tridentate ligand occupies three sites in the equatorial plane and the coordinated... 

Finally, Beller and coworkers introduced a new approach towards the optimisation of activity and selectivity in Ru-catalyzed asymmetric epoxidations. Their catalysts contained pyridine dicarboxylate (pydic) as the second ligand. Although excellent results (e.g., 85% yield and 59% ee for styrene) were obtained using 5 mol% of catalyst, the authors reported that a similar level of efficiency could be achieved with only 0.5 mol% of catalyst (Scheme 21)." ... 

The first metal-ligand alternative base pair to be incorporated in DNA duplexes was of [3 -f-1] type and was reported by Meggers et al. in 2000 (96). This pair was based on tridentate pyridine-2,6-dicarboxylate (Dipic) and monodentate pyridine (py) ligands, which were introduced in complementary positions in the middle of a DNA duplex (Entry 14, Table V). The same group reported the incorporation in DNA duplexes of three other tridentate ligands that bear structural similarity to Dipic, namely, pyridine-2,6-dicarboxamide (Di-pam) (Entry 15, Table V) (120), pyridine-2,6-(N-methyl-)dicarboxamide (Me-Dipam) (120), and 2,6-bis(ethylthiomethyl)pyridine (SPy) (Entry 16, Table V) (106). In the absence of a metal ion, incorporation in DNA duplexes of any of the four tridentate ligands opposite a pyridine had a destabilization effect similar to that of a mismatch or completely prevented the formation of a duplex. 

The luminescence intensity and decay time of EuCls in carboxymethyl cellulose membranes is decreased in presence of heavy metal ions like Cu" or Cu ", but also Cr " and Fe " exert a distinct quenching effect [111]. It is not likely that a sensor with high specificity can be prepared on the basis of LLCs that is free of interferences from other metal ions. However, an adequate choice of the ligand system may help to improve the selectivity of the response. Another approach uses a sol-gel technique to embed a complex of Eu " and silanized 2,6-pyridine-dicarboxylic acid as antenna in a silica network. This luminescent material can sense copper ion concentrations in water down to 50 pg but the sensor was not evaluated with respect to interferences of other metal ions or in environmental samples [112]. 

Scheme 23.9. Asymmetric epoxidation of stilbenes with H2O2 catalyzed by Fe(III) complexes bearing the chiral bidentate sulfonamide ligand and pyridine dicarboxylate as the achiral tridentate ligand.

Zhao Y-H, Su Z-M, Fu Y-M, Shao K-Z, Li P, Wang Y, et al. Syntheses and characterizations of four metal coordination polymers constructed by the pyridine-3,5-dicarboxylate ligand. Polyhedron 2008 27 583-92. 

Optically active namral and unnamral amino acids as well as various cyclic amino alcohols have been utilized in the synthesis of a wide variety of bis(oxazo-line) ligands. As previously mentioned, the first bis(oxazoline) ligands, py-box la-d, were synthesized by Nishiyama and co-workers in 1989. The common material for their syntheses was pyridine 2,6-dicarboxylic acid 19. Conversion of 19 to the acid chloride was achieved by treatment with thionyl chloride, as illustrated in Figure 9.4. This was followed by condensation with (5)-valinol in the presence of triethylamine. Conversion of the resulting bis(amidodiol) 20 to py-box-ip lb was achieved by sequential treatment of 20 with thionyl chloride at 50 °C followed by cyclization with aqueous sodium hydroxide in methanol to afford py-box-/p lb in 60% overall yield. The same synthetic scheme can be used to obtain the other... 

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