Fourier Transform Ion Cyclotron Resonance Spectrometric Studies of Lewis Acid-Base Chemistry in Monochlorosilane

Abstract

Fourier transform ion cyclotron resonance spectrometry is used to determine reaction pathways and rate constants for the reactions of the Lewis acids, SiH_nCl_(3-n)^+ (n = 1-3), with SiH_3Cl. SiH_2Cl^+ is observed to participate in both an H^- transfer reaction and a disproportionation reaction with SiH_3Cl. The ions SiH_3^+ and SiHCl_2^+ are observed to participate in only H^- transfer reactions with SiH_3Cl. The H^- affinity of SiH_2-Cl^+ is determined to be 1.4 ± 0.3 kcal mol^(-1) greater than that of SiHCl_2^+. Within experimental uncertainty, the values of the H^- affinities of the chlorosilyl ions lie within 1.7 kcal mol^(-1) of each other and decrease in the order SiH_2Cl^+ ≈ SiCl_3^+ > SiHCl_2^+. The disilylchloronium ion, (SiH_3)_2Cl^+, is proposed to be an intermediate complex in the reaction of SiH_3^+ with SiH_3Cl. Here, (SiH_3)_2Cl^- is formed through the reaction of protonated SiH_3Cl with SiH_3Cl. It is stable at room temperature at least on the order of tenths of seconds. By use of previously reported thermochemical data, the ionization potential of SiH_2Cl and the hydride affinity of SiH_2Cl^+ are derived to be 7.66 ± 0.23 eV and 251.2 ± 5.1 kcal mol^(-1), respectively.