Silylium ion-mediated cage-opening functionalization of closo-B₁₀H₁₀^2- salts

The cage-opening functionalization of stable closo-B₁₀H₁₀^2- salts is a great way to get various boron clusters. However, the known methods to mediate cage-opening functionalization rely on the use of strong acids, which suffer from low efficiency and narrow substrate scope. Herein, an efficient method to synthesize 6-substituted decaboranyl ethers and sulfides has been developed. The reaction was mediated by trimethylsilyl trifluoromethanesulfonate (TMSOTf) and occurred at room temperature. Six 6-substituted ethers were obtained in 65-92% yields and five 6-substituted sulfides were prepared in 38-58% yields. The reaction had excellent regioselectivity, affording the single B(6) regioisomer in all cases. The interaction between the B-H bonds of the boron cage and the silylium ion was believed to be the key factor in the reaction.