Tris ligands, complexes magnesium

The successful utilization of alkoxo Zn- and Mg-tris(pyrazolyl) borate initiators in the lactide polymerization inspired the synthesis of sterically bulky B-diketiminates (BDls) (Fig. 5) and their zinc and magnesium derivatives [60-62]. Replacing the ancillary ligands resulted in the production of several mono- and dinuclear complexes of Mg" and Zn" 24-39 (Fig. 6), which demonstrated excellent catalytic activity for the polymerization of l- and rac-lactide [62-66]. 

Intramolecular aromatic substitution in transition metal complexes is an area of research where there is considerable current interest, and tri(phenyl-ds)-phosphine is a ligand often used in such investigations. This phosphine can be prepared from phenyl-ds-magnesium bromide by its reaction with PCI3 in diethylether, as described below. 

Several macrobicyclic ruthenium, nickel, zinc, manganese, copper, chromium, magnesium, and lithium complexes, as well as two free macrobicyclic tris-dioximate ligands, have also been synthesized. 

The reactions usually proceeded to approximately 90% completion over a period of days, at which point the authors believe the redistribution reached equilibrium. However, substitution of the tris(3,5-dimethylpyrazolyl)hydroborato (>/ -HB(3,5-Me2pz)3) by the more sterically demanding tris(t-butylpyrazoyl)hydroborato ligand ( -HB(3- -Bupz)3) in magnesium complexes 13 prevents ligand redistribution after 7 days at 120°C. 

A series of commercial styrene-divinylbenzene copolymers called Amberlite XAD (Rohm and Haas Co., Philadelphia) has been used as a base to immobilize a variety of complexing agents (269). On XAD-2, tri-/i-octylamine (270), several ferroin-type chromogens (277), and phenylarsonic acid (272) have been used to concentrate and separate several trace species from seawater and fresh water. An EDTA ligand (273) and phenylarsonic acid on XAD-4 can also extract trace metals such as Cr(III), Pb(II), Hg(II), U(VI), Zr(IV), and Zn(II) at the sub-parts-per-billion levels, even in the presence of excess calcium and magnesium if the pH is less than 3.0. 

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