Application of photoelectron spectroscopy to molecular properties. Part 61. First gas-phase generation of a cis chloroiminoarsane ClAs=NSiMe3 and a cis chloroiminophosphane ClP=(NSiMe2Bu)-Bu-t. Characterization by photoelectron spectroscopy

摘要

Photoelectron spectroscopy-flash vacuum thermolysis in the gas phase allowed us to synthesize, for the first time, the cis forms of two weakly hindered, low-coordinate arsenic and phosphorus compounds (ClPn=NSiR3; Pn=P, As), as well as to characterize them by their ionization energies. In order to assign the different bands in the PE spectra and to estimate the effect of the substituents SiMe3 and Cl on the electronic and structural properties of these compounds, we performed calculations using density functional theory (hybrid functional B3LYP) with the basis set 6-311G(d,p). The thermodynamic stabilization of these halogenated systems appears in the important antiperiplanar interactions between the nitrogen lone pair n(N) and the sigma (AsCl)* (or sigma (PCl)*) orbital. For these two compounds, in spite of a poor 2p pi (N)-3p pi (P)/4p pi (As) overlap, it was observed that the substitution of a chlorine atom on the pnictogen (As, P) and a silyl group on nitrogen (negative hyperconjugation) leads to a relatively high ionization energy for the pi (PnJN) orbital [IE(pi (PnJN))approximate to 10 eV]. [References: 46]