The reaction of [U(NN3 )I] [NN -N(CH2CH2NSiMe2But)3] with Group 1 and 2 metal alkyls gives, via metalation of a methylsilyl group, a highly strained metallacycle [U(bit-NN )] in high yield. The molecular structure of this compound shows that it has an unusually long U-C bond (ca. 2.75 A, ) and additional C-H···M agostic interactions. On exposure of the complex in solution to 2H2 the methylsilyl groups and the metallacyclic UCH2Si group are deuterated, leaving the tert-butyl and methylene groups intact. The analogous thorium metallacycle is prepared from the reactions of [Th(NN3 )Cl], or by attempted reduction of [Th(NN3 )I] with potassium metal in pentane. Attempted reduction of [U(NN3 )I] in a similar manner in toluene gave a high yield of a fascinating dimeric metallacyclic anion {[K(eta6-C6H5Me)][U(bit-NN3 )]}2, which was characterised by X-ray crystallography. The authenticity of this compound as U(III) is established by near-IR spectroscopy, and also by its production from the reaction of the neutral uranacycle [U(bit-NN3 )] with potassium. A mechanism for the formation of the anion is postulated. Its reaction with benzyl chloride led to oxidation to the parent uranacycle. Oxidation of [U(bit-NN3 )] with air or oxide sources leads to formation of an oxo-bridged dimer with intermonomer metalated methylsilyl groups and pentavalent uranium centres. Reactions of [U(bit-NN3 )] with a range of acids HX occur rapidly, reprotonating the previously metalated methylsilyl group and forming complexes [U(NN3 )X]. For example, lutidinium hydrochloride, diethylamine and tert-butanol gave [(NN3 )UCl], [(NN3)U(NEt2)] and [(NN3 )U(OBut)], respectively. Reactions with carbon acids were also successful. For example, b-hydropyridines gave h2-dehydropyridyl complexes. One of these, [U(NN3 )(eta2-NC5H4)], is shown in the first X-ray crystallographic study of such an actinide complex to contain an essentially planar U(eta2-NC5H4) unit. Monosubstituted alkynes react with the uranacycle in a similar manner to give eta1-alkynyls. The molecular structure of one example shows that the U-C≡C unit is bent (156°) in contrast to other structurally characterised non-bridging alkynyls of the f-elements.

Synthesis of a highly strained uranacycle: molecular structures of organometallic products arising from reduction, oxidation and protonolysis

BOARETTO, Rita;
1999

Abstract

The reaction of [U(NN3 )I] [NN -N(CH2CH2NSiMe2But)3] with Group 1 and 2 metal alkyls gives, via metalation of a methylsilyl group, a highly strained metallacycle [U(bit-NN )] in high yield. The molecular structure of this compound shows that it has an unusually long U-C bond (ca. 2.75 A, ) and additional C-H···M agostic interactions. On exposure of the complex in solution to 2H2 the methylsilyl groups and the metallacyclic UCH2Si group are deuterated, leaving the tert-butyl and methylene groups intact. The analogous thorium metallacycle is prepared from the reactions of [Th(NN3 )Cl], or by attempted reduction of [Th(NN3 )I] with potassium metal in pentane. Attempted reduction of [U(NN3 )I] in a similar manner in toluene gave a high yield of a fascinating dimeric metallacyclic anion {[K(eta6-C6H5Me)][U(bit-NN3 )]}2, which was characterised by X-ray crystallography. The authenticity of this compound as U(III) is established by near-IR spectroscopy, and also by its production from the reaction of the neutral uranacycle [U(bit-NN3 )] with potassium. A mechanism for the formation of the anion is postulated. Its reaction with benzyl chloride led to oxidation to the parent uranacycle. Oxidation of [U(bit-NN3 )] with air or oxide sources leads to formation of an oxo-bridged dimer with intermonomer metalated methylsilyl groups and pentavalent uranium centres. Reactions of [U(bit-NN3 )] with a range of acids HX occur rapidly, reprotonating the previously metalated methylsilyl group and forming complexes [U(NN3 )X]. For example, lutidinium hydrochloride, diethylamine and tert-butanol gave [(NN3 )UCl], [(NN3)U(NEt2)] and [(NN3 )U(OBut)], respectively. Reactions with carbon acids were also successful. For example, b-hydropyridines gave h2-dehydropyridyl complexes. One of these, [U(NN3 )(eta2-NC5H4)], is shown in the first X-ray crystallographic study of such an actinide complex to contain an essentially planar U(eta2-NC5H4) unit. Monosubstituted alkynes react with the uranacycle in a similar manner to give eta1-alkynyls. The molecular structure of one example shows that the U-C≡C unit is bent (156°) in contrast to other structurally characterised non-bridging alkynyls of the f-elements.
1999
Boaretto, Rita; P., Roussel; N. W., Alcock; A. J., Kingsley; I. J., Munslow; C. J., Sanders; P., Scott
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/522744
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