Reactivity of (C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>UMe<sub>2</sub> and (C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>UMeCl toward Group 13 Alkyls
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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.
