Catalytic oxidation of water and organic substrates by iron, nickel, manganese and ruthenium complexes

Abstract

The thesis is made of four parts. The first part describes chemical and visible light-driven water oxidation using simple iron salts as precatalysts. The second part discloses chemical-driven water oxidation using simple nickel salts as precatalysts. The third part is about the oxygenation of organic substrates driven by visible-light using a manganese nitrido complex as catalyst. The fourth part concerns the activation of ruthenium-oxo complexes by Lewis acids towards alkane oxidation. In part one, simple iron salts are used as precatalysts for water oxidation. Both chemical and visible light-driven water oxidation are highly efficient in borate buffer at pH 7.5 - 8.5. For chemical water oxidation using Ru(bpy)3(ClO4)3 as oxidant, turnover number of up to 394 was obtained. Under visible light irradiation in the presence of Ru(bpy)3Cl2 as photosensitizer and Na2S2O8 as sacrificial oxidant, oxygen evolved at turnover number up to 1115. Fe2O3 nanoparticles are found to be formed during water oxidation, which are the actual catalyst. In part two, simple nickel salts are used as precatalysts for water oxidation. Using Ru(bpy)3(ClO4)3 as oxidant, oxygen evolution catalysed by nickel processed smoothly in borate buffer at pH 7.5 - 8.5 with a maximum turnover number of 170. Large particles (0.3 mm to 2 mm) were observed during chemical-driven water oxidation through dynamic light scattering (DLS) measurement. In part three, the manganese(V) nitrido complex, (PPh4)2[Mn(N)(CN)4] is found to be an efficient catalyst for the visible-light driven oxygenation of organic substrates in water using [RuII(bpy)3]2+ as a photosensitizer and [CoIII(NH3)5Cl]2+ as the sacrificial oxidant. Alkenes are oxidized to epoxides and alcohols are oxidized to carbonyl compounds with turnover numbers high up to 117 and 137, respectively. 18O-isotopic labeling study for epoxidation of styrene confirmed that the oxygen atoms incorporated into styrene came from water. In part four, the high-valent ruthenium-oxo complexes, [RuVIIO4]- and [RuVIO2Cl3]- were activated by Lewis acids, such as FeCl3, BF3, or Sc(OTf)3, to oxidize alkanes to the corresponding alcohols and ketones. Oxidation occurs rapidly under argon atmosphere, and excellent yields up to 46% were achieved in the oxidation of cyclohexane to cyclohexanone with [RuVIO2Cl3]-/BF3 in acetonitrile at 296 K. The accelerating effect of BF3 on the oxidation of methane by [RuVIIO4]- and [RuVIO2Cl3]- have also been studied computationally by the Density Functional Theory (DFT) method. A significant decrease in the reaction barrier resulting from BF3 coordination to ruthenium-oxo complexes was observed.

Date of Award	3 Oct 2012
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	T C LAU (Supervisor)