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UBC Theses and Dissertations

Synthesis and characteristic chemistry of sixteen-electron group 6 hydrocarbyl-containing nitrosyl complexes Veltheer, John E.

Abstract

This thesis addresses the non-generality of the previous method used to prepare CpW(NO)(alkyl)2 complexes from their diiodide precursors. The three most significant problems inherent to the original synthetic method were: (a) the reagents being used (i.e. transition-metal dihalide, alkylating agent and solvent), (b) excessive hydrolysis during workup, and (c) thermal decomposition. This work presents a rationalization for, and utilization of, a new general methodology for the preparation of Cp'M(NO)R2 [Cp' = Cp (i5-05H5), Cp* (i5-05Me5); M = Mo, W; R = alkyl, aryl] complexes. Reactions of Cp*M(NO)C12 with (ary1)2Mg•X(dioxane) [aryl = Ph, p-tolyl, o-tolyl] in THE provide Cp*M(NO)(aryl)2 complexes. These 16-electron diaryl complexes irreversibly form 1:1metal-centered adducts with PMe3. CpW(NO)(o-tolyl)2 is the only isolable diaryl complex of this type that does not incorporate a Cp* ligand. Electrochemical and IR studies indicate that the sediaryl complexes are more potent Lewis acids than their Cp'M(NO)(alkyl)2 congeners. X-raycrystallographic analyses indicate that these diaryl complexes have more sterically accessible metal centers than related dialkyl complexes. The thermal stability of Cp'M (NO)R2 complexes is Cp* >Cp, W > Mo and alkyl > aryl. The relative Lewis acidities of this family of nitrosyl complexes mirrors the thermal stability trend. Reactions of Cp*Mo(NO)C12 with (alky1)2Mg•X(dioxane) [alkyl = CH2CMe3, CH2CMe2Ph,CH2SiMe3] in THE provide previously inaccessible Cp*Mo(NO)(alkyl)C! and Cp*Mo(N0)(alky1)2 complexes in a stepwise fashion. Cp*Mo(NO)(alkyl)Cl species are comparable in Lewis acidity to related Cp*Mo(N0)(ary1)2 complexes. Cp*Mo(NO)(CH2CMe3)Cl reacts with PMe3 and pyridine to afford metal-centered 18-electronadducts while CO and CNCMe3 readily insert into its Mo-neopentyl bond. The chloride ligand inCp*Mo(NO)(CH2CMe3)Cl is easily abstracted by Ag+ in NCMe to form[Cp*Mo(NO)(CH2CMe3)(NCMe)]BF4. The phosphine complex, Cp*Mo(N0)(CH2CMe3)(PMe3)C1, is readily dehydrohalogenated by LDA in THE to afford the novel cyclometallated dialkyl complex (15,111-05Me4CH2)Mo(N0)(CH2CMe3)(PMe3). Reactions of Cp*Mo(NO)R2 complexes with water afford bimetallic complexes of the type,[Cp*Mo(NO)R]2-(11-0), and free hydrocarbon. A kinetic analysis of the reaction between H2Oand Cp*Mo(N0)(CH2SiMe3)2 implicates Cp*Mo(NO)(CH2SiMe3)(OH) as a key intermediate in the formation of [Cp*Mo(N0)(CH2SiMe3)]2-(A-0). Cp'W(NO)(alkyl)2 complexes are hydrolytically stable, whereas Cp'W(NO)(aryl)2 complexes react vigorously with water providing Cp'W(0)2(aryl) complexes. CpMo(NO)(CH2CMe3)2 thermally decomposes via a first-order intramolecular extrusion of neopentane yielding the 16-electron alkylidene complex, CpMo(NO)(=CHCMe3). A mechanistic analysis of the above-mentioned thermal reaction shows little solvent dependence and suggests a highly ordered transition state. CpMo(NO)(=CHCMe3) cannot be isolated, but it can be trapped with phosphines or pyridine (L) yielding CpMo(NO)(=CHCMe3)L complexes. Primary amines and alcohols add their heteroatom-hydrogen bonds across the Mo=C double bond of CpMo(NO)(=CHCMe3) stereoselectively to give alkyl amide and alkyl alkoxide complexes. CpMo(NO)(=CHCMe3) reacts with CpMo(NO)(CH2CMe3)2 to give [CpMo(NO)](12-11 1:112-N0)(A-CHCMe3)[CpMo(=CHCMe3)], which contains the first g-111:12-nitrosyl ligand.

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