Pyridyl donor sites

Regeneration of carbonyl compounds from 5-(2-pyridyl)-l,3-dioxanes [75] can be effected by A-methylation and treatment with a mild base. The picolyl carbon is a donor site, and the loss of a proton from that position is facile. 

As an oligo(a-pyridyl)amido ligand has an odd number of donor sites, the corresponding metal string molecule has the same number of metal atoms. 

Abstract The metal-driven construction of multi-porphyrin assemblies, which exploits the formation of coordination bonds between exocyclic donor site(s) on the porphyrins and metal centers, has recently allowed the design and preparation of sophisticated supra-molecular architectures whose complexity and function begin to approach the properties of naturally occurring systems. Within this framework, meso-pyridyl/phenyl porphyrins (PyPs), or strictly related chromophores, can provide geometrically well-defined connections to as many as four metal centers by coordination of the pyridyl peripheral groups. Several discrete assemblies of various nuclearities, in which the pyridylporphyrins are connected through external coordination compounds, have been constructed in recent years. In this review, we summarize recent work in this field from our and other laboratories. The photophysical properties of some ruthenium-mediated assemblies of porphyrins prepared by our group are also described. 

A new photoactive monoclinic polymorph of 6-(2, 4 -dinitrobenzyl)-2,2 -bipyri-dine was obtained from an acetone/methanol solution, and the structure compared to the previously known photoactive orthorhombic and photoinactive monoclinic forms [94]. Correlation of these structures with those of related nitrobenzylpyridines was used to understand the relationships existing between structure and photochro-mism. The comparison of the reaction cavities around the reactive pyridyl-benzyl-nitro fragment indicated that photochromic activity required rotational freedom of the ortho-nitro group in the crystal and its accessibility from the proton-donor and proton-acceptor sites. 

Grant et al. described an investigation of the ternary complex of ATP and bis(2-pyridyl)amine (MgATP/BPA), using advanced solid-state NMR methods such as Mg REDOR and Mg MQMAS in Mg-isotopically enriched samples. In the 3QMAS spectrum, the authors detected the presence of two Mg sites with close Mg quadrupole parameters. With help of a REDOR experiment, the assignment of these two sets of parameters to Mg ions either coordinated to water molecules or to phosphate oxygen donors was then possible. 

The most substantial difference between the blends CPS/BVPy and PS(t-OH)/BVPy lies in the ability to form complexes. The proton donor in PS(t-OH) is much weaker than that in CPS, so that much higher interaction site concentrations are required for complexation. For example, BVPy with pyridyl less than 40 mol% does not complex with PS(t-OH), no matter how high the hydroxyl content is. However, BVPy with a pyridyl content of only 10 mol% may complex with CPS containing carboxyl more than 11 mol%. 

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