Bond Strengths in ChCl₃^-and ChOCl₃^-(Ch = S, Se, Te):  Experiment and Theory

Abstract

The strengths of the SeCl2−Cl-, SeOCl2−Cl-, SeBr2−Br-, and TeCl2−Cl- bonds have been measured to be 133 ± 9, 150 ± 10, 110 ± 6, and 170 ± 7 kJ mol-1, respectively, by determining thresholds for collision-induced dissociation in a flowing afterglow-tandem mass spectrometer. These values are stronger than the previously measured D(SCl2−Cl-) and D(SOCl2−Cl-), both 85 ± 8 kJ mol-1. Bond energies and other properties for these molecules and TeOCl3 - have also been computed by several high-level computational techniques, including B3LYP/aug-cc-pVTZ. There is excellent agreement between the experimental and computational energetics for SeCl3 -, SeOCl3 -, and TeCl3 -. The bond strengths increase in the order S < Se < Te.

Nucleophilic Attack at Selenium in Diselenides and Selenosulfides. A Computational Study

“…Selenium can therefore more easily accommodate a third ligand than can sulfur, an idea that can be rationalized by the larger size of the selenium atom, the energetically closer orbitals of selenium, and its ability to participate in four electron-three-center bonding. 37 The larger 28 Se-Cl bond energy in SeCl 3over the S-Cl bond in SCl 3 is consistent with the preference of selenium attack described here.…”

“…9-INT sits in a very asymmetric well: the barrier toward reactant is about 11 kcal mol -1 , but the barrier forward is about 0.5 kcal mol -1 . The large barrier toward reactant is reminiscent of the deep wells seen in the reactions such as Cl - + SCl 2 , − where the transition state in fact disappears. The low barrier for exiting the intermediate reflects the very early nature of 9-TSx ; reaction 9 is the least endothermic of the three reactions in going from intermediate to product, consistent with the Hammond Postulate.…”

“…This concept has recently been extended to seleniumthe gas-phase reaction of chloride and SeCl 2 produces stable SeCl 3 -. 28 DFT computations of this reaction (and also the reaction of chloride with SeOCl 2 ) indicate a potential energy surface devoid of all features except the stable, hypercoordinate intermediate; the reagents combine together without a barrier. This suggests an addition-elimination mechanism for nucleophilic substitution at selenium.…”

“…We have also demonstrated that electron-withdrawing substituents on sulfur will stabilize the hypercoordinate intermediate; for the reaction of chloride with SCl 2 or SOCl 2 , the hypercoordinate intermediate is readily identifiable in the gas phase. This concept has recently been extended to selenium − the gas-phase reaction of chloride and SeCl 2 produces stable SeCl 3 - . DFT computations of this reaction (and also the reaction of chloride with SeOCl 2 ) indicate a potential energy surface devoid of all features except the stable, hypercoordinate intermediate; the reagents combine together without a barrier.…”

Theoretical Study of Nucleophilic Substitution at Sulfur in Sulfinyl Derivatives

“…Altogether, these results suggest that reaction 1a proceeds without a barrier to produce INT-1a with the PES shown in Scheme a. We have observed this type of PES before in the reaction of thionyl chloride with chloride . The geometry of the intermediate is trigonal bipyramidal, but strongly distorted from trigonal symmetry, with the angle between apical chlorine atoms only ∼150° (Figure a).…”