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

Abstract

Disproportionation reactions of chlorosilane compounds in the presence of boron trichloride yield the compound H[B(SiCl 3 ) 4 ]. Spectroscopic analyses of the yellow-whitish solid with IR-, Raman-, and NMR-spectroscopy ( 29 Si, 11 B) show the presence of a highly symmetric anion containing boron, which is fourfold coordinated with silicon. Due to the high symmetry 1 J( 11 B, 29 Si) and even 1 J ( 10 B, 29 Si) 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(SiCl 3 ) 4 ] À . Quantum chemical analysis of the tetrakis(trichlorosilyl)borate ion shows a negatively charged boron atom and the presence of polar SiÀ Cl and SiÀ B bonds. Highly reactive compounds [E(SiCl 3 ) n ] À which are stabilized solely by trichlorosilyl groups have been prepared with E=C, Si, Ge, P, S in recent years. The superacid H[B(SiCl 3 ) 4 ] represents a new member in this elusive compound family.

Trichlorosilyl Anions of p‐Block Elements – New Applications for Simple Molecules

“…The structures of the anions have been elucidated by single crystal structure analyses. [B(SiCl 3 ) 4 ] − features a tetrahedral coordination geometry of the boron atom [41] . Structural differences are observed between the group 14 derivatives.…”

“…H[B(SiCl 3 ) 4 ] has been recently prepared by the reaction of BCl 3 with an excess of HSi 2 Cl 5 under pressure and temperatures up to 100 °C [41] . A mechanism for the formation of the compound has been proposed (see Scheme 1).…”

“…Quantum chemical calculations show a wide distribution of charges at the central atoms (see Table 2). There are high negative charges on the second period elements boron, carbon, nitrogen, and oxygen [41,51,101] . Third period elements have far smaller negative charges as one would expect according to the decrease of electronegativity [102] .…”

Main Group Catalysis: Cationic Si(II) and Ge(II) Compounds as Catalysts in Organosilicon Chemistry

“…The perfluorinated phenylboranate and aluminate anions are well established as WCAs. Recently, however, a novel fluorine-free WCA, the tetrakis(trichlorosilyl) boranate anion, B(SiCl3)4 − , was successfully introduced for the first time by reacting the tetrelocenes 3 and 4 with H + B(SiCl3)4 − , Bochmann's acid [30,36] (Table 1, entries 2, 3 and 5).…”

“…The perfluorinated phenylboranate and aluminate anions are well established as WCAs. Recently, however, a novel fluorine-free WCA, the tetrakis(trichlorosilyl) boranate anion, B(SiCl 3 ) 4 − , was successfully introduced for the first time by reacting the tetrelocenes 3 and 4 with H + B(SiCl 3 ) 4 − , Bochmann's acid [30,36] (Table 1, entries 2, 3 and 5). For Me 5 Cp-ligands, an attractive alternative to the protonation reaction is the hydride abstraction from one of the methyl groups using an electrophilic tritylium salt, Ph 3 C + [WCA] − (Equations (2a) and (2b), Table 2) [37].…”