Unexpected Formation of the Highly Symmetric Borate Ion [B(SiCl3)4]−

Abstract

AbstractDisproportionation reactions of chlorosilane compounds in the presence of boron trichloride yield the compound H[B(SiCl3)4]. Spectroscopic analyses of the yellow‐whitish solid with IR‐, Raman‐, and NMR‐spectroscopy (29Si, 11B) show the presence of a highly symmetric anion containing boron, which is fourfold coordinated with silicon. Due to the high symmetry 1J(11B,29Si) and even 1J (10B, 29Si) couplings can be observed in the NMR spectra of the dissolved compound. The crystal structure analysis with a crystal obtained from toluene solution proves the existence of a highly symmetric borate anion, which is stabilized by four trichlorosilyl groups. The molecular structure consists of a para‐protonated toluene cation and the weakly coordinating borate anion [B(SiCl3)4]−. Quantum chemical analysis of the tetrakis(trichlorosilyl)borate ion shows a negatively charged boron atom and the presence of polar Si−Cl and Si−B bonds. Highly reactive compounds [E(SiCl3)n]− which are stabilized solely by trichlorosilyl groups have been prepared with E=C, Si, Ge, P, S in recent years. The superacid H[B(SiCl3)4] represents a new member in this elusive compound family.