Reaction of a Potassium Aluminyl with Sn[N(SiMe₃)₂]₂ - Isolation of a Stable, Trimetallic Sn(I) Radical Anion

The reaction of the potassium aluminyl K[Al(NON)] ([NON]^2-=[O(SiMe₂NDipp)₂]^2-, Dipp=2,6-iPr₂C₆H₃) with the stannylene Sn[N(SiMe₃)₂]₂ in benzene afforded K₃[(Sn₄){Al(NON)}₂{N(SiMe₃)₂}], containing a distorted tetrahedral Sn₄-cluster. Computational analysis indicates that four of the edges in this unit are composed of Sn-Sn bonds, with the remaining two that are spanned by aluminium involved in three centre two electron (3c2e) Sn-Al-Sn bonds. The formation of Al(II) species during this reaction is indicated by the isolation of the dialuminated cyclohexadiene 1,4-[Al(NON)]₂(μ-C₆H₆). Repeating the reaction in methylcyclohexane generated a thermally stable, trimetallic Sn(I) radical anion in K[Sn{Al(NON)}₂]. Compared to all other reported Sn(I) radicals, its EPR spectrum is unique; the main turning points of its spectrum appear at g values above 2 and the Sn hyperfine coupling is substantially smaller in magnitude. These data, together with ENDOR measurements and DFT calculations show that the SOMO is entirely localised in an unhybridised 5p orbital, such that spin-orbit contributions to the g and Sn hyperfine tensors are quenched.