Reactivity of (C₅Me₅)₂UMe₂ and (C₅Me₅)₂UMeCl toward Group 13 Alkyls

Abstract

The reactions of group 13 alkyl reagents (AlMe₃, AlEt₃, GaMe₃, InMe₃) with the uranium metallocene complexes Cp*₂UCl₂, Cp*₂UMe₂, and Cp*₂UClMe (Cp* = C₅Me₅) were studied, and similarities to pertinent group 4 and lanthanide chemistry were considered. The methyl derivative Cp*₂UMe₂ exhibits high reactivity toward the alkylaluminum reagents involving C−H bond activation, in contrast to Cp*₂UCl₂, which did not react under similar conditions. The orange-red C−H bond activation product of the AlMe₃ reaction, Cp*₂MeU(μ-Me)AlMe₂(μ₃-CH₂)Al₂(μ-Me)Me₄, was identified by X-ray crystallography. It contains a trinuclear aluminum−methyl−methylene moiety, [Al₃Me₈(CH₂)]⁻, linked to [Cp*₂UMe]⁺ via a bridging methyl group. The reaction of triethylaluminum with the orange-red chloro-methyl derivative Cp*₂UClMe gives reduction to the dark green uranium(III) complex Cp*₂U[(μ-CH₂CH₃)AlEt₂(μ-Cl)]₂UCp*₂ as evidenced by an X-ray structural analysis. Reactions of the less Lewis acidic gallium and indium alkyls were not observable by NMR spectroscopy, but the heterobimetallic complex Cp*₂U[(μ-Me)(InMe₃)]₂ was obtained by crystallization of a 1:2 mixture of Cp*₂UMe₂ and InMe₃ from hexane. As indicated by a rather long (U−CH₃)···In distances in the range of 2.846−2.922 Å, the InMe₃ molecules interact only weakly with the dimethyl metallocene unit (no tetramethylindate coordination), which is further substantiated by facile removal of the group 13 alkyl under vacuum.