Biphenylene Ring Expansion by a (H₃C)₂Si Link from Silicone Grease As Proven by the Crystal Structures of [(Sodium⁺[2.2.1]cryptand)(9,9-dimethylsilafluorene•-)] as Well as [Sodium⁺(triglyme)₂(biphenylene•-)] and by Total-Reflection X-ray Fluorescence Spectrometry (TXRF)¹

Sodium metal mirror reduction of biphenylene in aprotic THF solution containing [2.2.1]cryptand yields as a structurally characterized product the 9,9-dimethylsilafluorene radical anion salt containing a (H 3 C) 2 Si expanded cyclobutadiene ring. In addition, the Si content can be detected by total reflection X-ray (TXRF) analysis. When the use of any silicon grease was avoided for all glass fittings, the solvent-separated biphenylene radical anion contact pair crystallized from an aprotic diglyme solution.