Ligand systems, exploration

In the course of the quest for new Fe(III) spin crossover compounds, systems related to N,N-disubstituted-dithiocarbamates have been explored. This section deals with oxygen and selenium derivatives of this parent ligand system, as displayed in Fig. 2. 

It is understandable, therefore, that since its introduction in 1966 this ligand system has been explored to a considerable extent, and by 1984 poly(l-pyrazolyl)borate derivatives of most transition metals (except for Sc, Hf and Os) up to Np have been described and a few brief reviews of this subject matter have appeared Since... 

Successful examples of chelate assisted activation of aromatic C-F bonds provided the foundation for further exploration of the organometallic chemistry of fluorocarbons. While early examples were limited to perfluorinated aromatic systems, the scope of this process is now fully defined using W(CO)3 and PtMe2 metal fragments [44, 29]. In addition to these amine, imine based ligand systems, several new examples of C-F activation have been achieved using a variety of later transition metals. 

One of the most studied polymerization systems employs alkyllithium initiators that are modified by chiral amine ligands for the polymerization of sterically bulky methacrylates [8,38,39,40,41], acrylates [42],crotonates [43], and acrylamides [44]. A primary example is the reaction of triphenylmethyl methacrylate with an initiator derived from 9-fluorenyllithium and (-)-sparteine (3) at -78 °C (Scheme 4). The resultant isotactic polymer is optically active, and is postulated to adopt a right-handed helix as it departs from the polymerization site. This polymer has been particularly successful as a chiral stationary phase for the chromatographic resolution of atropisomers [8]. Many modifications of the or-ganolithium initiator/chiral ligand system have been explored. Recently, Okamo-to has applied enantiopure radical initiators for the enantioselective polymerization of bulky methacrylate monomers [45]. 

The chemistry of organolanthanides has been dominated by complexes with metallocene and half-sandwich ligand systems because of the rigidity, steric bulk, thermal and chemical stability of the cyclopentadienyl ligands. However, driven by the desire to explore novel structural... 

And then there is finally - besides the artificial evolutions of selecting functional nucleic acids for specific interactions with cooperative mates, high-affinic recognitions, and catalytic activities fiom random pools - the evolution of an individual scientific life s work [50], which itself follows decisive stages of the grand process the exploration of early chemical requirements, the development of prebiotic ligand systems, the fixation into the ordered structures of informational inorganic matrix patterns... 

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