Gas-Phase Characterization of Unhindered Silanimines by Photoelectron Spectroscopy:  Experimental and Theoretical Study of the SiN Double Bond¹

Abstract

The coupling of flash vacuum thermolysis reactions (retro [2+2] cleavages) with photoelectron spectroscopy allowed the first direct characterization of several highly reactive N-alkylated silanimines. For the trimethylsilanimine 1b, the IPs corresponding to the ejection of an electron from the nitrogen lone pair (n(N)) and the pi(Si)(=)(N) orbital are observed at 7.9 and 8.3 eV, respectively. In the case of the N-isopropylated and N-tert-butylated analogues 1c,d, these characteristic ionizations are energetically closed (7.8 and 7.4 eV). These unexpected attributions have been corroborated by the ab initiocalculations of the ionization energies using 6-31G(d) and LANL1DZ basis sets and MP2 level. Our results have been completed by the determination of the structural and electronic characteristics of these silanimines.

The SiF32+ Dication: Chemistry Counts!

“…Natural bond analysis reveals s-bonding with negligible double-bond character. [13][14][15] The alternative structure with a SiN 2 three-membered ring could not be localized.…”

Flash Vacuum Thermolysis Synthesis of New Reactive Compounds Containing a Silicon−Heteroatom Double Bond

“…[29] Compound 19 was thus prepared and cleanly yielded the corresponding silanimine 5 (not directly obtained from 2), characterized by PES and as its cyclic dimer 20 (Scheme 4). [30] Scheme 4…”

“…Its intermediacy was also confirmed, in the presence of tertbutyl alcohol, by the formation of compound 15. [23,30] N-Alkylcyclo-1,3-disila-2,4-diazanes 25, 20 and 24 are known, stable and easily prepared compounds. [31] Upon FVT in conjunction with PES, 25 and 20 proved to be excellent precursors for the corresponding silanimines, undergoing as their only reactions equilibria with monomeric species 26 and 5, respectively (Scheme 5).…”

“…These results reveal, for these silanimines, a destabilization of the π system and of the nitrogen lone pair, resulting in an enhanced nucleophilicity (see later, photoelectron spectrometry). [30] Scheme 5…”

“…[30] The relatively stable N-isopropenylcyclo-1,3-disila-2,4-diazanes 27 and 28, resulting from the demethylation of 24, were also characterized, by HRMS and NMR, in the thermolysis products. [32] Phosphasilenes (R 2 Si‫؍‬PRЈ) FVT of the previously described phosphasilacyclobutane 29 [33] and cyclo-1,3-diphospha-2,4-disiletane 30 [34] was investigated in a similar manner.…”