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Titanium, zirconium, and hafnium tetradentate Schiff-base monomers and analogous polymers
Abstract
The study of transition metal complexes involving high denticity ligands has achieved importance in recent decades. This type of ligand can coordinate with metal centers and give products with unusual geometries and coordination numbers. Because group-4 complexes have many special properties and applications, group-4 tetradentate Schiff-base monomers have been synthesized and further applied to polymer chemistry. Several monomers have been synthesized successfully including dichloro (N,N$\sp\prime$-ethylenedisalicylidene-1,2-phenylenediaminato) titanium(IV), Ti(salen)Cl$\sb2$; bis(N,N$\sp \prime$-disalicylidene-1,2-phenylenediaminato)titanium(IV), Ti(dsp)$\sb2$; bis(4-amino-N,N$\sp\prime$-disalicylidene-1,2-phenylenediaminato)zirconium(IV), Zr(adsp)$\sb2$; bis(N,N$\sp \prime$-disalicylidene-1,2-phenylenediaminato)-hafnium(IV), Hf(dsp)$\sb2$; bis(4-amino-N,N$\sp\prime$-disalicylidene-1,2-phenylenediaminato)hafnium(IV), Hf(adsp)$\sb2.$ Among them, the first X-ray structure of the hafnium-tetradentate complex, Hf(dsp)$\sb2,$ has been solved. It has a dodecahedral geometry which is very similar to Zr(dsp)$\sb2.$ The metal center is bridged by two tetradentate organic Schiff-base ligands, and this causes the metal to have a completely chelated coordination sphere. These metal-containing Schiff-base monomers can be further used as the basic structures for making linear alternating A-B type copolymers. These polymers have been characterized by IR, NMR, elemental analysis, TGA and DSC, and have shown interesting properties. Moreover, Zr(adsp) and Hf(dsp)$\sb2$ have also been used as initiators in the polymerization of $\beta$-butyrolactone and $\varepsilon$-caprolactone. It is found in the studies that not only the amine ends but also the cleaved metal-oxygen bonds serve as nucleophiles when compared with the results of other organic amines.
Subject Area
Chemistry
Recommended Citation
Tan, Uan-Kang, "Titanium, zirconium, and hafnium tetradentate Schiff-base monomers and analogous polymers" (1996). Doctoral Dissertations Available from Proquest. AAI9639036.
https://scholarworks.umass.edu/dissertations/AAI9639036