Browsing by Author "Genjang, Nevil Nuvala"

The thesis is written on the catalytic activation of carbon dioxide. It includes a literature part and an experimental part. In the literature part, a review on metal (salen) complexes in relation to their electronic and geometric properties is presented. Salicylidene-aminates are included considering similarity to the salens. Also included from literature is a selective review focusing on the mechanistic aspects in the carboxylation of epoxides by metal (salen) complexes. Some applications of iron (salen) complexes as catalyst are mentioned. In the experimental part, the bis(phenoxyiminato) chlorido iron(III)complexes are synthesized, characterized and applied on carbon dioxide/epoxide coupling reactions. Characterization is done by UV-vis, infra-red, nuclear magnetic resonance and electron impact mass spectroscopy and elemental analysis for C, H, and N. Thermogravimetric analysis for the complexes, DFT calculation for the most active species (L11)2Fe(III)Cl and X-ray for (L6)2Fe(III)Cl are also presented. X-ray crystallography reveals the space group of (L6)2Fe(III)Cl to be orthorhombic, Pbcn; a = 29.0038(14) Å, b = 8.6123(8) Å, c = 10.7843(9) Å; α = β = γ = 90 o. The ML2Cl complexes are observed to have M-O and M-N bonds involving the phenolic oxygen and azomethine nitrogen. Correlation study between spin state and the Fe-N bond length indicates a high-spin state for Fe(III) nucleus. The geometry around the metal nucleus is distorted square pyramidal. Reaction conditions for catalytic activity were fine-tuned envisaging the exclusive production of cyclic carbonates. Propylene and styrene oxides show high reactivity. The ketiminato complexes show better activity over the aldiminato complexes. Optimal result is obtained in dimethyl formamide at a temperature of 145 oC and carbon dioxide pressure of 10 bars in the presence of tetrabutylphosphonium bromide as co-catalyst. A TOF of 572/h is observed for propylene oxide. Three reaction mechanisms are proposed. Comparatively the Co(III) analogues are more active, and iodide as a halogen ligand produces a more active complex than chloride. Improving nucleophilicity of Fe(III), elimination of intramolecular H-bond and improving on solubility could yield a more active complex. Iron is a cheap and environmentally benign metal. The use of iron complexes is an attractive alternative to other transition metals which are expensive and/or toxic. The complexes are robust and show high thermal stability. Surprisingly, oligomers of styrene carbonate were noticed at the reaction temperature and pressure known to favor exclusive production of cyclic carbonates. These observations suggest the complexes for a promising study and application in future research for copolymerization. Such copolymers may have useful charateristics for diverse applications.