Structural variation in silver acetylide complexes: Syntheses and X-ray structure determinations of [Ph₃PAgC≡CPh]⁴·3.5THF and [Me₃PAgC≡CSiMe₃]_∞

[Ph₃PAgC≡CPh]₄·3.5THF (2) can be prepared by the reaction of CpAgPPh₃ (1) with lithium phenylacetylide (1:1 equiv). Similarly [Me₃PAgC≡CSiMe₃]_∞ (4) can be prepared by the reaction of CpAgPMe₃ (3) and lithium (trimethylsilyl)acetylide (1:1 equiv). Both complexes have been characterized by elemental analyses, solid-state IR spectroscopy, ¹H and ³¹P NMR spectroscopy, and low-temperature X-ray diffraction studies. The structure of 2 consists of a tetranuclear "flat-butterfly" core, with the two "hinge" silver atoms σ-bonded to two acetylide fragments, which then π-complex the apical Ag(PPh₃)₂ fragments. In 4, the smaller steric bulk of the phosphine employed allows this complex to crystallize as a polymer. Rather than being constructed from simple [R₃PAg(acetylide)] units, both 2 and 4 are formed by the aggregation of (acetylide)₂Ag^- and Ag(PR₃)₂⁺ fragments. The preparation of complexes 2 and 4 demonstrates the synthetic utility of nucleophilic substitution of CpAgPR₃ in the synthesis of Ag organometallics. The different structural alternatives adopted by 2 and 4 point to the steric bulk of the phosphine ligands being the major influence on the structure of Ag acetylide complexes.