Solid state and mechanistic study on pyrone based complexes of early, middle and platinum group transition metal elements

Abstract

3-Hydroxypyrones and their corresponding analogues 3-hydroxypyridinones are a versatile class of chelators. The commercially available pyrones: 3-hydroxy-2-methylpyran-4-one (1) and 3- hydroxy-2-ethylpyran-4-one (2) were functionalised to yield the respective 3-hydroxy-2- methylpyrid-4-one (3) and 3-hydroxy-2-ethylpyrid-4-one (4) derivatives. These ligands were coordinated to an array of metals, divided broadly into three groups: early, middle and platinum group transition metals, to form the corresponding metal complexes. A total of eight bidentate ligands with different electronic and steric properties were used in this study. These ligands and the corresponding complexes are explored as models for: (i) the potential beneficiation of hafnium and zirconium for the nuclear industry, (ii) the application as model complexes for diagnostic and therapeutic radiopharmaceuticals in studies using the fac-[ReI(CO)3]+ core and (iii) rhodium(I) homogeneous catalysts for oxidative addition reactions. In all of the respective sub-sections of this study, the structural characterisation of crystalline products of the above mentioned compounds were extensively evaluated by means of single crystal X-Ray Diffraction (XRD). This study therefore covers a detailed structural discussion of the analysis and comparison with similar Zr(IV), Hf(IV), Re(I) and Rh(I) compounds which could yield valuable insights into physical and/or chemical state differences to be exploited for purification/separation techniques, diagnostic and therapeutic endeavours and catalytic processes respectively. Finally, structure/ reactivity relationships were attempted to assist in the future prediction of relevant characteristics of these compounds. A kinetic evaluation on fac-[ReI(O,O’-bid)(CO)3(Y)] (O,O’- bid = O,O’-bidentate ligand and Y = monodentate ligand) substitution reactions with monodentate chelators in methanol, indicated a possible dissociative activated methanol substitution mechanism in these types of complexes and that these substitutions are solvolytic in nature.