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Synthesis and reactivity of metal complexes supported by Kläui's oxygen tripodal ligand

Authors Ip, Ho Fai
Issue Date 2010
Summary Irradiation of LOEtRuCl2(NO) (LOEt- = [CpCo{P(O)(OEt)2}3]- where Cp = η5-C5H5) with UV light in CH2Cl2/CH3CN afforded the Ru(III) solvato complex LOEtRuCl2(CH3CN). Similarly, photolysis of LOEtRuCl2(NO) in tetrahydrofuran (THF)/H2O, followed by silica gel chromatography yielded [LOEtRuCl]2(μ-Cl)2. Refluxing LOEtRuCl2(CH3CN) with RNH2 in THF afforded LOEtRuCl2(NH2R) (R = t-Bu, p-tol and Ph). Reaction of RuCl3(N^N)(NO) with AgLOEt and AgOTf (OTf- = triflate) afforded [LOEtRu(N^N)(NO)][OTf]2 where N^N = 4,4’-di-tert-butyl-2,2’-bipyridyl (dtbpy), 2,2’-bipyridyl (bpy) and N,N,N',N'-tetramethylethylenediamine (tmeda). Photolysis of [LOEtRu(dtbpy)(NO)][OTf]2 in CH2Cl2/CH3CN afforded [LOEtRu(dtbpy)CH3CN][OTf]2. Treatment of [LOEtRu(bpy)(NO)][BF4]2 with benzyl amine led to formation of [{LOEtRu(bpy)}2(μ-N2)][BF4]2 that exhibited ν(N≡N) at ca. 2009 cm-1 in the Raman spectrum. Oxidation of [{LOEtRu(bpy)}2(μ-N2)][BF4]2 with [Cp2Fe][BF4] afforded the Ru(III)/Ru(II) mixed valence complex [{LOEtRu(bpy)}2(μ-N2)][BF4]3 that showed an intervalence charge transfer band at 1893 nm. The reduction potentials of the above Ru-LOEt complexes have been determined by cyclic voltammetry. Reduction of [LOEtRuCl]2(μ-Cl)2 with zinc granule in CH3CN, followed by treatment with NH4PF6 gave [LOEtRu(CH3CN)3][PF6]. Reduction of [LOEtRuCl]2(μ-Cl)2 with zinc granule in CH3OH under nitrogen afforded a Ru(II) terminal dinitrogen complex, which was converted to the heterometallic Ru(II)/Zn(II) methoxide cluster (LOEtRu)2Zn2(μ2-OCH3)4(μ3-OCH3)2(CH3OH)2 upon recrystallization from acetone in air. This Ru(II) dinitrogen complex can catalyze the C=C double bond isomerization of terminal olefins such as hex-1-ene, hex-5-en-1-ol and allyl phenyl ether. Reaction of LOEtRu(N)Cl2 with PCy3 afforded LOEtRuCl2(NPCy3) (Cy = cyclohexyl), which can be oxidized by tris(4-bromophenyl)aminium hexachloroantimonate to give cationic [LOEtRuCl2(NPCy3)][SbCl6]. Chlorination of [LOEtRuCl]2(μ-Cl)2 with PhICl2 yielded the Ru(IV) complex LOEtRuCl3. Refluxing [LOEtRuCl]2(μ-Cl)2 with 1-azidoadamantane in toluene afforded the Ru(IV) metallacyclic LOEtRuCl[κ2-N,C-(AdNCHC6H4)], possibly via double C-H activation of toluene by a Ru(IV) adamantylimido intermediate. Treatment of [LOEtRuCl]2(μ-Cl)2 with p-nitrophenyl azide gave the Ru(III) amine complex LOEtRuCl2(NH2C6H4NO2-4). Treatment of [Ir(COE)2]2(μ-Cl)2 (COE = cis-cyclooctene) with AgLOEt resulted in the formation of LOEtIrCl2(COE) that reacted with AgNO3, dtbpy and NH4PF6 to afford [LOEtIr(dtbpy)(COE)][PF6]2. Oxidation of LOEtIrCl2(COE) with ozone in CH2Cl2 led to formation of the Ir(IV) complex LOEtIrCl3. Alternatively, reaction of LOEtIrCl2(COE) with PhICl2 also gave LOEtIrCl3 that exhibited the Ir(IV/III) potential at ca. 0 V vs. Cp2Fe+/0. Reaction of [Rh(COE)2]2(μ-Cl)2 with AgLOEt gave [LOEtRhCl]2(μ-Cl)2. Heating [LOEtRhCl]2(μ-Cl)2 with excess t-BuNH2 in THF afforded LOEtRhCl(NH2-t-Bu)2Cl. Treatment of Rh(N^N)Cl3(DMF) (DMF = N,N-dimethylformamide), AgLOEt and AgOTf in acetone gave [LOEtRh(N^N)Cl]OTf (N^N = dtbpy and bpy). Reaction of [LOEtRh(bpy)Cl]OTf with AgOTf in acetone resulted the formation of water-soluble [LOEtRh(bpy)(acetone)][OTf]2. Reaction of (LOEt)2Zr(NO3)2 with KMnO4 gave (LOEt)2Zr(MnO4)2. Reaction of (LOEt)2Ce(NO3)2 with K2[Os(O)2(OH)4] afforded a grey precipitate which was slowly converted to the dinuclear Ce(IV) oxalate complex [(LOEt)2Ce]2(μ-C2O4) upon recrystallization from methanol in air. (LOEt)2Ce(MnO4)2 can oxidize alkylbenzenes such as toluene, ethylbenzene, and cumene to give the corresponding alcohol and/or aldehyde/ketone products. By contrast, (LOEt)2Zr(MnO4)2 is incapable of alkylbenzene oxidation. The kinetics of stoichiometric oxidation of ethylbenzene with (LOEt)2Ce(MnO4)2 has been studied. At room temperature, the oxidation of neat ethylbenzene with (LOEt)2Ce(MnO4)2 was found to follow pseudo-first-order kinetics with an observed rate constat of kobs = (3.3 ± 0.3) × 10-4 s-1. The kinetic isotope effect (kH/kD) for the oxidation of ethylbenzene was determined to be 6.0 ± 0.5, suggesting that a hydrogen atom transfer mechanism is involved in the C-H oxidation. (LOEt)2Ce(MnO4)2 is capable of catalyzing aerobic oxidation of ethylbenzene at room temperature with a turnover number (TON) of about 9. Ce(III) and -(IV) LOEt complexes were found to be active catalysts for aerobic oxidation of cumene at 100 ℃. For example, aerobic oxidation of neat cumene in the presence of a catalytic amount of [(LOEt)2Ce(H2O)2]Cl (1.0 mM) at 100 ℃ resulted in the formation of a mixture of cumyl alcohol, cumyl hydroperoxide and acetophenone with a total conversion of 95% and total turnover of 6810 in 20 h. It is believed that the LOEtCe-catalyzed aerobic oxidation of cumene at high temperature proceeds via a free radical mechanism.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2010
Language English
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