ORGANOMETALLIC CHEMISTRY OF TANTALUM SUPPORTED BY 2,6-DI-ALKYLPHENOXIDES

LINDA RAE CHAMBERLAIN, Purdue University

Abstract

The treatment of hydrocarbon solutions of TaCl(,5) and NbCl(,5) with lithium 2,6-di-alkylphenoxides produces mixed chloro-aryloxide complexes. The degree of substitution is dependent on the steric bulk of the aryloxide ligand, which ranges from 2,6-di-methyl to 2,6- di-tert-butylphenoxide. Subsequent alkylation of the mixed chloro-aryloxide complexes with lithium alkyls results in a variety of product formation, the most interesting developments occurring on alkylation of Ta(OC(,6)H(,3)Bu('t)(,2)-2,6)(,2)Cl(,3). Reaction of Ta(OC(,6)H(,3)Bu('t)(,2)-2,6)(,2)Cl(,3) with LiMe leads to the expected substitution of the chlorine atoms to yield Ta(OC(,6)H(,3)Bu('t)(,2)-2,6)(,2)Me(,3). Reaction with LiCH(,2)SiMe(,3) provides an alkylidene compound, Ta(OC(,6)H(,3)Bu('t)(,2)-2,6)(,2)(=CHSiMe(,3))(CH(,2)SiMe(,3)). Reaction with LiPh leads to the formation of ta(O-CH(,2))(OC(,6)H(,3)Bu('t)(,2)-2,6)Ph(,2) O-CH(,2)=Ta-OC(,6)H(,3)Bu('t)-CMe(,2)CH(,2) ,(' )whereby one of the aryloxide tert-butyl groups has undergone CH bond activation, producing a monocyclometallated compound. Mild thermolysis of Ta(OC(,6)H(,3)Bu('t)(,2)-2,6)(,2)Me(,3), Ta(OC(,6)H(,3)Bu('t)(,2)-2,6)(,2) (=CHSiMe(,3))(CH(,2)SiMe(,3)) and Ta(O-CH(,2))(OC(,6)H(,3)Bu('t)(,2)-2,6)Ph(,2) provides biscyclometallated compounds, Ta(O-CH(,2))R, R = Me, CH(,2)SiMe(,3), Ph , in which the second aryloxide ligand has undergone aliphatic CH bond activation. Kinetic and labelling studies of this reaction show the ring closures to follow first order kinetics, and conclusively prove the mechanism of activation in the d('o)-metal systems follows a multicenter pathway. At elevated temperatures the compounds Ta(O-CH(,2))(,2)(C(,2)D(,5)) and Ta(O-CH(,2))(,2)(tolyl-x) x = ortho, meta, para produce benzyne intermediates which are detected by aryl isomerization of the tolyl groups and H/D exchange in the labelled phenyl complex. The photochemical reactivity of the tantalum alkyl-aryloxides was also explored. It is found that photolysis of Ta(OC(,6)H(,3)Bu('t)(,2)-2,6)(,2)Me(,3) generates a methylidene complex, Ta(OC(,6)H(,3)Bu('t)(,2)-2,6)(,2)(=CH(,2))(CH(,3)), citing one of the first examples of photochemically induced (alpha)-hydride abstraction. This process also occurs for Ta(OC(,6)H(,3)Pr('i)(,2)-2,6)(,2)- (CH(,2)SiMe(,3))(,3) generating the alkylidene complex, Ta(OC(,6)H(,3)Pr('i)(,2)-2,6)(,2)(=CHSiMe(,3))(CH(,2)SiMe(,3)). In related compounds the migratory insertion of aryl-isocyanides into tantalum-alkyl bonds has been observed. Compounds of the formulation, Ta(OC(,6)H(,3)Me(,2)-2,6)(,2)(C(R)=NAr)(,2)R Ar = 2,6 di-methyl/ 2,6 diisopropylphenyl isocyanide; R = Me, Benzyl are readily synthesized and characterized. When thermolyzed the isocyanide complexes intramolecularly react, producing an interesting array of imide, amide, and enediamide compounds.

Degree

Ph.D.

Subject Area

Chemistry

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