Synthesis, Isolation and Crystal Structures of the Metalated Ylides [Cy3P-C-SO2Tol]M (M = Li, Na, K)

Abstract

The preparation and isolation of the metalated ylides [Cy₃PCSO₂Tol]M ( ^Cy1-M) (with M = Li, Na, K) are reported. In contrast to its triphenylphosphonium analogue the synthesis of ^Cy1-M revealed to be less straight forward. Synthetic routes to the phosphonium salt precursor ^Cy1-H₂ via different methods revealed to be unsuccessful or low-yielding. However, nucleophilic attack of the ylide Cy₃P = CH₂ at toluenesulfonyl fluoride under basic conditions proved to be a high-yielding method directly leading to the ylide ^Cy1-H. Metalation to the yldiides was finally achieved with strong bases such as nBuLi, NaNH₂, or BnK. In the solid state, the lithium compound forms a tetrameric structure consisting of a (C-S-O-Li)₄ macrocycle, which incorporates an additional molecule of lithium iodide. The potassium compound forms a C ₄-symmetric structure with a (K₄O₄)₂ octahedral prism as central structural motif. Upon deprotonation the P-C-S linkage undergoes a remarkable contraction typical for metalated ylides.

Keywords: Alkali metals; Carbanions; Phosphorus ligands; Structure elucidation; Ylides.