Soluble ring-unsubstituted d0 early-transition metallophthalocyanines: Synthesis, structural characterization and reactivity studies

Early-transition metallophthalocyanine (PcM) chemistry, an underdeveloped area in the field of phthalocyanines, is explored in this thesis with a focus on synthesis, coordination chemistry and reactivity studies, while improving solubility. A series of soluble ring-unsubstituted d0 early-transition metal PcM alkoxides, notably with zirconium(IV) and niobium(V), were prepared via salt metathesis with the PcM chlorides, and structurally characterized. Given their larger ionic size, the unusual structural feature of the metal centre protruding out of the Pc cavity is observed, engendering cis-axial ligation, which drastically improved solubility. The effect of the axial alkoxide ligands of various degree of steric bulk (–OMe, –OEt, –OiPr, –OtBu) on the coordination chemistry and solubility was investigated, in addition to a comparative study between d0 PcZr(IV) and PcNb(V); systems with anionic "ate" species were favoured for Zr(IV) over neutral PcNb(V) complexes with the targeted alkoxide groups. The exposed coordination sphere of these larger Lewis-acidic d0 metals makes these PcM complexes attractive catalysts. The catalytic activity of PcZr(IV) and PcNb(V) alkoxides was probed towards the ring-opening polymerization (ROP) of rac-lactide, with PcZr(OiPr)¬3Li(THF) being the most active catalyst. A comparative structure-reactivity study between the Zr(IV) and Nb(V) systems, and the evaluation of the performance of PcZr(OiPr)¬3Li(THF) versus other reported benchmark catalysts for ROP of rac-lactide, were also examined. Reaction of PcSc(III)Cl with LiOiPr and NaOtBu instead yielded the hydroxides, (PcSc)2(μ3-OH)4Li2(THF)(DME) and (PcSc)2(μ-OH)2(THF), obtained from the hydrolysis of the putative PcSc-alkoxide intermediate. These two soluble PcSc(III) hydroxides have a tilted "butterfly" shape structure. The direct hydrolysis of PcSc(III)Cl and the analogous PcZr(IV) and PcNb(V) systems were also probed. Their reactivity towards the displacement reaction with fluoride ions were also investigated. Access to soluble PcM(III) alkoxides with Al(III) and In(III) centres, which have similar complexation chemistry to Sc(III), was investigated. Isolation of mono-axially functionalized ring-unsubstituted PcM(III)OR complexes via salt metathesis were more challenging due to low solubility compared to cis-axial ligated PcM complexes. Preliminary work towards improving solubility by targeting the anionic PcM(III) complex and accessing a neutral Pc(-2)M(III) via a soluble Pc(-4)M(III) intermediate, are described.