Allyl strontium compounds: synthesis, molecular structure and properties

Abstract

The synthesis and attempted isolation of neutral bis(allyl)strontium [Sr(C₃H₅)₂] (1) resulted in the isolation of potassium tris(allyl)strontiate K[Sr(C₃H₅)₃] (2). In situ generated 1 shows a pronounced Brønsted basicity, inducing polymerisation of THF. Ate complex 2 crystallises as [K(THF)₂{Sr(C₃H₅)₃}(THF)]_∞ (2·(THF)₃). The salt-like solid state structure of 2·(THF)₃ comprises a two-dimensional network of (μ₂-η³:η³-C₃H₅)⁻ bridged potassium and strontium centres. Synthesis of allyl complexes 1 and 2 utilised SrI₂, [Sr(TMDS)₂] (3) (TMDS = tetramethyldisilazanide), and [Sr(HMDS)₂] (HMDS = hexamethyldisilazanide) as strontium precursors. The solid state structure of previously reported [Sr(TMDS)₂] (3) was established by X-ray single crystal analysis as a dissymmetric dimer of [Sr₂(TMDS)₄(THF)₃] (3·(THF)₃) with multiple Si–H⋯Sr agostic interactions. The presence of ether ligands (THF, 18-crown-6) influenced the Si–H⋯Sr resonances in the NMR spectra of the amido complex 3.