Synthesis and characterization of heavily cyanated boron clusters

Compounds based on polyhedral boron clusters, such as [B₁₂H₁₂]²⁻, have a wide array of potential applications ranging from new drugs to advanced electronics. Computational and experimental studies suggest that heavily cyanated boron cluster derivatives are amongst the most electronically stable anions known and could function as excellent weakly coordinating anions (WCAs) or as superior electrolytes in metal-ion batteries. Current methods for the derivatization of these boron clusters are limited, and the synthesis and isolation of any percyanated boron clusters has not previously been reported. The percyanated closo-dodecaborate anion, [B₁₂(CN)₁₂]²⁻, has been prepared by a microwave-promoted palladium-catalyzed cyanation reaction and isolated for the first time. Characterization of[B₁₂(CN)₁₂]²⁻ by NMR (¹¹B, ¹H, and ¹³C), liquid chromatography-mass spectrometry (LC-MS), high-resolution mass spectrometry (HRMS), and infrared spectroscopy (IR), is reported along with the single-crystal X-ray structures of (CH₃CN)₃Cu[μ-B₁₂(CN)₁₂]Cu(NCCH₃)₃ and [Et₄N]₂[B₁₂(CN)₁₂]. The exhaustive acid-catalyzed hydrolysis of [B₁₂(CN)₁₂]²⁻ was attempted, but only the hydrolysis of up to two of the cluster’s CN ligands was observed by MS. Preliminary studies suggest that heavily cyanated derivatives of [CB₁₁H₁₂]⁻ and [B₁₀H₁₀]²⁻ can also be prepared by microwave-promoted palladium-catalyzed cyanation reactions. In addition, the electronic stability of functionalized derivatives of [B₁₀H₁₀]²⁻ has been explored computationally using density functional theory (DFT).