Novel Ruthenium(II) Aluminate Anions: Building Blocks of Unique Cage Structures

Abstract

New anionic ruthenium(II) aluminohydrides were synthesized from [Cp*RuCl]4, LiAlH4, and lithium alkyls. The reaction of [Cp*RuCl]4 with 8 equiv of LiAlH4 afforded the lithium salt [Li(DME)3][Cp*2Ru2(μ-H)(μ-AlH4)2] (1) in 65% isolated yield. Reactions of [Cp*RuCl]4, LiAlH4, and RLi (R = Me, Et, iPr, nBu) in THF yielded the new compounds [Li5(THF)2Cp*6Ru6Al4Me4H19] (2) and [Li2(THF)2Cp*RuAl2R2H7)]2 (3–5, R = Et, iPr, tBu). The compounds were characterized by single-crystal X-ray crystallography, multinuclear liquid and solid-state NMR spectroscopy, IR spectroscopy, and microanalysis. The molecular structures of 1–5 display novel anionic ruthenium(II) aluminate frameworks. In the case of 2–5, these anions associate into unusual cage structures via Li–H interactions in the solid state. Variable-temperature 1H and 7Li NMR studies on the fluxional complex 5 in deuterated toluene show that the cage structure of this compound is retained at low temperature in solution.