Synthesis and Structures of Sterically Encumbered Group 14 Monolithio Compounds and Unexpected Differences in Their Reactivity

Synthesis, isolation and characterization of a stable lithium stannenolate. A keto or an enol tautomer?

A stable lithium stannenolate 7 was synthesized and isolated by the reaction of acylstannane 6 with LDA or tBu₂MeSiLi in THF. 7 was characterized by X-ray crystallography and by NMR and UV-Vis spectroscopy. Spectroscopic and structural features, in combination with DFT quantum-mechanical calculations, indicate that 7 is best described as an acyl-substituted stannyl anion, adopting the stannenolate keto tautomeric structure.

Deprotonation of Organogermanium and Organotin Trihydrides

Terphenyltin and terphenylgermanium trihydrides were deprotonated in reaction with strong bases, such as LiMe, LDA, or KBn. In the solid state, the Li salts of the germate anion 4 and 4a exhibit a Li-Ge contact. In the Li salt of the dihydridostannate anion 6a, the Li cation is not coordinated at the tin atom instead an interaction of the Li cation with the hydride substituents was found. Evidenced by ¹H-⁷Li-HOESY NMR spectroscopy the Li-salt of the deprotonated tin hydride 6a exhibits in toluene solution a contact between Li cation and hydride substituents, whereas in the ¹H-⁷Li-HOESY NMR spectrum of the homologous germate salt 4a, no crosspeak between hydride and Li signals was found. The organodihydridogermate and -stannate react as nucleophiles with low-valent Group 14 electrophiles. Thus, three compounds were synthesized: Ar-Ë'-EH₂-Ar (E', E = Sn, Ge; Pb, Ge; Pb, Sn; Ar = Ar', Ar*). Following an alternative synthesis Ar'SnH₂PbAr* was synthesized in reaction between [(Ar*PbH)₂] and [(Ar'SnH)₄] generated in situ. In reaction between low-valent organotin hydride [(Ar*SnH)₂] and organdihydridostannate [Ar*SnH₂]^- formation of distannate [Ar*₂Sn₂H₃]^- was found.