Terminal donor group

In later work, Vogtle and his coworkers prepared analogs of both crown ethers and cryptands. These molecules are designed to have a terminal donor group which is capable of offering a complexed cation additional binding sites. Numerous... 

Compounds om.4 and om.5 have the same metal center as om.l, but longer conjugated linkers, which also incorporate fluorene units, and they have terminal donor groups. 2PA spectra of these molecules are characterized by... 

Generation of xanthyl cation from 2-(9-xanthyl)ethanol [87] is an extended Grob fragmentation. The intervening chain of separating the terminal donor groups may also incorporate heteroatoms, as shown in the deconvolution of a decalindione monoxime tosylate [88]. 

Many polypodands having terminal donor groups are also available, e.g. (39)-(41).33 These also exhibit cation complexation and phase transfer properties. KMn04 and aqueous alkali metal picrates are much more readily taken into organic phases in the presence of these podands than with dibenzo-18-crown-6.239 The KSCN complex of (39) exhibits a novel coordination geometry as all 10 donor atoms participate in coordination of the metal cation, and in order to do this the three arms wrap around the cation in a propeller-like fashion.240... 

The cyclization reactions discussed here either involve the intramolecular reaction of a donor group D with an acceptor group A or a cyclizing dimerization of two molecules with two terminal acceptors and two donors. A polymerization reaction will always compete with cyclization. For macrolides see p. 146 and p. 319 — 329. 

Unsymmetric compartmental ligands that allow for the controlled synthesis of unsymmetric Ni2 or heterobimetallic NiM complexes have received particular attention.1876,1892 A wide range of such ligands derived particularly from 2-hydroxy-3-hydroxymethyl-5-methylbenzaldehyde and 2-hydroxy-3-hydroxymethyl-bromo-benzaldehyde has now been prepared and used for Ni com-plexation. These ligands have monopodal iminic pendent arms and either mono- or dipodal aminic pendent arms and the terminal donors of the pendent arms can be provided by pyridine, imidazole, and tertiary amino groups.1893-1897 Complexes are usually prepared by reaction of the requisite Ni11 salts with the preformed ligand. 

Appending different terminal groups to the ji-conjugated ends, the cyanine-like molecules may have the following molecular structures D-ji-D, D-ji-A, and A-ji-A. Additionally, electron acceptor/donor groups may be included into the main Ji-conjugation chain to form D-7i-A-ji-D or A-ji-D-ji-A quadrupolar structures. These basic structures are shown schematically in Fig. 4 and discussed in detail in Sect. 3. 

Cyanine dyes fall within the more general category of polymethine dyes, in which a chain of methine groups is terminated with a donor group and an acceptor group respectively [82]. 

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