Phosphonium fullerides: isolable zwitterionic adducts of a phosphine with C₆₀

Although fullerene derivatization has been extensively studied for decades, zwitterionic adducts with neutral Lewis bases are rare, and those with tertiary phosphines remain elusive. This work presents a combined experimental and computational study on the first isolable zwitterionic phosphonium fullerides. The reaction of tris(tetramethylguanidinyl)phosphine ((tmg)₃P) with C₆₀ results in the formation of the zwitterionic adducts (tmg)₃PC₆₀ and (tmg)₃PC₆₀P(tmg)₃ in quantitative yield. Stoichiometric studies demonstrate that up to two (tmg)₃P molecules can reversibly bind to C₆₀, forming bisphosphine adducts as regioisomeric mixtures with reduced P-C bond stability. Spectroscopic, crystallographic, and computational analyses reveal the presence of σ-type dative P-C bonds and significant charge redistribution within the fullerene cage. Furthermore, functionalizations of the phosphonium fullerides with electrophiles yield ionic derivatives, highlighting their reactivity and potential for further modification.