Pentacoordinated silicon anions: synthesis and reactivity

Abstract

Scholarship, and we are indebted to the Center for Information Science (University of Auckland) and to IBM New Zealand Ltd. for providing large amounts of computer time.Supplementary Material Available: Tables of thermal parameters and all bond lengths and angles for 2a (5 pages); a table of observed and calculated structure factors (15 pages). Ordering information is given on any current masthead page.

Nucleophilic displacement versus electron transfer in the reactions of alkyl chlorosilanes with electrogenerated aromatic anion radicals

“…Indeed, the reduction of the majority of chlorosilanes is usually observed at -3.2…-2.4 V vs. SCE [9], whereas the E 1/2 of the couple Ph 3 Si  /Ph 3 Si -, estimated by photomodulated voltammetry, is -1.39 V vs SCE [17];…”

“…Admitting steady-state for [R 3 Si  ] in the ET scheme implies that k 1 is rate-limiting, i.e. k 1 << (k dim + k 3 + k 4 ), and the concentration of silyl radicals is manly determined by the competition between k 1 and their consumption in reactions 8-10.…”

“…PE profiles, plotted at zero driving force, are shown in figure 5. Although electrochemistry of hyper-coordinate silicon species is still to be developed, some idea on relative electrophilicity of silicon in DMF-coordinated Me 3 SiCl with respect to its non-coordinated form can be obtained from NPA charges and from the relative LUMO levels in these species (scheme 1). In spite of smaller partial positive charge on Si (1.608 vs. 1.721), LUMO level in DMFassociated penta-coordinated chlorosilane is 0.408 eV lower than in the non-associated form rendering the electron uptake easier.…”

“…1). The intermediacy of silyl radicals and radical pathway of formation of disilanes were ruled out already in earlier works: the addition of PhOH during the electroreduction of Ph 3 SiCl lead to the quantitative protonation of triorganosilyl anion and no disilane products were formed under these conditions [5], eq. (2).…”

“…With all importance of the chemistry of introduction and removal of silyl groups, it is surprising that relatively few quantitative studies on the fundamentals of reactivity of chlorosilanes are available [2]. Corriu evoked the possibility of both single electron transfer (ET) and a pure nucleophilic pathway in nucleophilic reactions of chlorosilanes [3]. The first one involves one-electron transfer from an electron-rich nucleophile to an electrophilic chlorosilane, supposedly with the intermediacy of an anion radical of the chlorosilane [4].…”