Development Of Ruthenium/terpyridine Complexes For Water Oxidation

DEVELOPMENT OF RUTHENIUM/TERPYRIDINE COMPLEXES FORWATER OXIDATIONbyDAKSHIKA C. WANNIARACHCHIMay 2014Advisor: Prof. Cláudio VeraniMajor: Chemistry (Physical)Degree: Doctor of PhilosophyThe work presented in the dissertation is focused on developing catalysts forwater oxidation. In this regard, a series of unsysmmetrical ruthenium complexes of type[Ru(terpy-R)(phen-X)Cl]PF6 where terpy-R= 4’-(4-methylmercaptophenyl)-2,2’:6’2”-terpyridine and phen-X=H (1), X= 5-nitro (2), X=5,6-dimethyl (3), and X= 3,4,7,8-tretramethyl (4) was synthesized as precursors for self-assembled monolayers. Water oxidation properties of these complexes were evaluated in the presence of(NH4)2[Ce(NO3)6] as the sacrificial oxidant by measuring catalytic turnover number(TON) after 24 h of reaction time and rate of dioxygen evolution in solution during early stages of catalysis. The results revealed that all complexes 1 – 4 are catalytic towardswater oxidation. However, the presence of electron-withdrawing nitro substituent on phenanthroline dramatically decreased the water oxidation activity (TON 60, rate of dioxygen evolution 2.40 × 10-4 μmol O2/s) compared to the complex 1 (TON 410, rate 8.19 × 10-4 μmol O2/s). In contrast, complex 4 with electron-donating methyl substituents on phenanthroline indicated enhanced rate of dioxygen evolution (27.3 × 10-4 μmol O2/s)in solution than complex 1. Furthermore, reactivity of complexes 1 4 towards