Metal ions, extraction using ligand materials

The standard synthesis for cyclam was developed by Barefield and Wagner in 1976.29 They used similar starting materials to the van Alphen procedure but the cyclisation yield is improved through the use of a nickel (II) template. Glyoxal completes the macrocycle by a Schiff base condensation reaction. The resulting imine functionalities are reduced with sodium borohydride to leave the complexed macrocycle. The metal ion is then removed by reaction with cyanide and the free ligand extracted with chloroform (Scheme 3.19). Yields are typically in the region of 60%. 

Carboranes - polyhedral boranes containing carbon in the framework - have been known for over 35 years, and their intrinsic stability, versatility, structural variety, and electronic properties have been put to use in a number of diverse areas, [1] for example in the synthesis of extraordinarily heat-stable polymers, in BNCT (boron neutron capture therapy), as ligands in metallacarborane catalysts, as com-plexing agents for extraction of metal ions, as precursors to ceramics, conducting polymers, and nonlinear optical materials, as anticancer... 

For grafted pol5mier materials, pollutant sorption results were foimd to be a function of the degree of attachment of the polyfunctional groups. In the case of chitosan, the best method of achieving selective extraction is to use a metal specific ligand, but it has proved impossible to find specific ligands for each metal ion. 

---