Exploring the auxiliary co-ordination sphere of tripodal amino(triamido) actinide complexes

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Abstract
High-yield syntheses of the soluble, volatile complexes [{ML(Cl)}2][M = U or Th, L = N(CH2CH2-NSiMe3)3] have been achieved. The molecular structure of the uranium complex shows it to be a dimer bridged by long U–(µ-Cl) bonds. These compounds are shown to be versatile starting materials for exploration of the chemistry of the amino(triamido) actinide fragment. Their reactions with Na[C5R5](R = H or Me) gave high yields of the monomeric complexes [ML(C5R5)] for which analogous non-chelate compounds are unknown. These species are fluxional and display apparent three-fold symmetry on the NMR time-scale in solution at room temperature, although an exchange process via a trigonal-bipyramidal transition state is postulated on the basis of variable-temperature NMR studies for the compound M = Th, R = Me. The molecular structure of the compound M = U, R = Me has been determined by X-Ray diffraction. Reaction of the chloro complexes with lithium tetrahydroborate in tetrahydrofuran (thf) gave high yields of [ML(H3BH)(thf)]. The uranium derivative has been structurally characterised and has distorted-octahedral geometry. Sublimation of these compounds in vacuo led cleanly to the base-free complexes [{ML(H3BH)}2]. The volatile dimeric alkoxide derivatives [{ML(OBut)}2] have been prepared similarly.

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