Silylimidazolium Hexafluorophosphate Salts as Synthetic Precursors to N-Heterocyclic Carbene Pentafluorophosphorus Adducts.

N-Heterocyclic carbene pentafluorophosphorus (NHC-PF5) adducts are six-coordinate phosphorus(v) compounds with emerging applications but poor synthetic accessibility. We have developed a simple and high yielding protocol for synthesizing imidazolylidene NHC-PF5 adducts from silylimidazolium hexafluorophosphate salts. Using this methodology, we have prepared a series of NHC-PF5 adducts in high yields, including new NHC-PF5 building blocks amenable to subsequent synthetic diversification. We also demonstrate that a similar approach enables access to analogous, synthetically elusive NHC-BF3 and NHC-SbF5 adducts.