Isolation and Reactivity of Stannylenoids Stabilized by Amido/Imino Ligands

The reaction of the lithium aryl(silyl)amide Dipp(ⁱ Pr₃ Si)NLi (Dipp=2,6-ⁱ Pr₂ C₆ H₃ ) with one equivalent of SnCl₂ in THF gave a novel stannylenoid Dipp(ⁱ Pr₃ Si)NSnCl⋅LiCl(THF)₂ . Heating the solution of amidostannylenoid in toluene to 80 °C resulted in dimeric amido(chloro)stannylene [Dipp(ⁱ Pr₃ Si)NSnCl]₂ , which can be converted to bis(amido)stannylene Sn[N(Dipp)(ⁱ Pr₃ Si)]₂ and amido(imino)stannylene Sn[N(Dipp)(ⁱ Pr₃ Si)][IPrN] (IPrN=bis(2,6-diisopropylphenyl)imidazolin-2-imino). Treatment of bis(imino)stannylenoid [IPrN]₂ Sn(Cl)Li with N₂ O resulted in the dimeric complex [IPrNSn(Cl)OLi]₂ . All compounds were characterized by NMR, elementary analysis, and X-ray structural determination.

A Stable Cyclic (R2 SnAu)3 Anion Having In-Plane σ-Möbius Aromaticity

A cyclic (R₂ SnAu)₃ anion (3^- , R₂ Sn=2,2,5,5-tetrakis(trimethylsilyl)-1-stannacyclopentane-1,1-diyl) has been synthesized as a stable blue salt with K⁺ (THF)₆ through the reaction of stable dialkylstannylene 1 with R'₃ PAuCl (R'=Et, Ph) followed by the reduction with KC₈ . Crystallographic and NMR analysis shows that the six-membered (SnAu)₃ ring of 3^- is planar and highly symmetric with an equal distance of six Au-Sn bonds. A UV/Vis spectrum of 3^- in hexane reveals an intense absorption maximum at 598 nm. While cyclic Au₃ ^- with four valence electrons is known as unstable anti-aromatic anion, 3^- with three divalent tin ligands is stable σ aromatic anion with an unprecedented Möbius orbital array as predicted by the perturbation MO and CCSD analysis of 3^- .

Cation-Triggered Stannate(II)/Stannylenoid/Stannylene Conversion

The reaction of dipotassio-tetrasilan-1,4-diide (4) with anhydrous SnCl₂ at low temperature results in the formation of a five-membered cyclic potassio chlorostannate(II) ([(18-C-6)K](1)). By careful cation exchange reactions, it was transformed into the sodium chlorostannylenoid 2 (by using Na₂ [B₁₂ Cl₁₂ ]) or into the non-stabilized cyclic bissilylstannylene 3 (through applying Li[Al(OC(CF₃ )₃ )₄ ]). The increasing Lewis basicity of the bissilylstannylene 3 was analyzed by combined methods of DFT calculations and NMR spectroscopy and substantiated by the synthesis of the corresponding iron carbonyl complexes 7 and 8 from the chlorostannate 1 and the stannylene 3, respectively.