AbstractsChemistry

This thesis is divided into two parts. Part I is concerned with catalytic oxidation of alkenes by (salen)ruthenium(III) complexes, Part II describes BF3-activated oxidation of hydrocarbons by permanganate. In Part I , a series of (salen)ruthenium(III) solvento species, [RuIII(L)(S)2]+ (L = N,N’-bis(salicylidiene)-o-cyclohexyldiamine dianion) and its derivatives (S = solvent, e.g. H2O,CH3OH, CH3CH2OH) have been prepared either by N…N coupling of [RuVI(N)(L)(MeOH)]+ in refluxing acetone/water or by direct reaction of [NnBu4][RuVI(N)Cl4] with the salen ligand in methanol followed by the addition of thallium(I) hexafluorophosphate. These complexes have been characterized by IR, electrospray ionization mass spectrometry (ESI-MS) and CHN elemental analysis. The structure of [RuIV(3,3’,5,5’-tBu4salchda)Cl2] has been determined by X-ray crystallography. These (salen)ruthenium(III) solvento complexes are effective catalysts for the oxidation of alkenes in the presence of various oxygen donors such as iodosylbenzene and 2,6-dichloropyridine-N-oxide. It was found that catalysts with electron withdrawing groups give better yields. A reaction scheme involving the formation of a ruthenium(V) oxo species as the active intermediate is proposed. A series of chiral (salen)ruthenium(III) solvento species (R,R’)-[RuIII(L)(S)2]+ and its derivatives have also been synthesized by similar methods. These complexes have also been characterized by IR, electrospray mass spectrometry (ESI-MS) and CHN elemental analysis. These chiral (salen)ruthenium(III) complexes catalyze the asymmetric epoxidation of alkenes with moderate to good enantioselectivity. The asymmetric epoxidation of styrene and trans-β-methylstyrene catalyzed by (R,R’)-[RuIII(3,3’,5,5’-Br4salchda)(EtOH)2]+ proceeds with 73 % and 62 % ee respectively. In Part II, the effects of BF3 on the oxidation of hydrocarbons have been investigated. It was found that the oxidizing power of MnO4- could be greatly enhanced by just adding a few equivalents of BF3. The BF3/MnO4- system is able to oxidize various alkanes and alkyl aromatics. A mechanism involving the formation of an adduct between the permanganate and BF3 is proposed. This adduct is proposed to be the active species, as the electron withdrawing effect by BF3 would enhance the oxidizing power of permanganate. CityU Call Number: QD305.H7 L44 2005 xix, 136 leaves : ill. ; 30 cm.