The Mechanism of CX (X=F, Cl, Br, and I) Bond Activation in CX₄ by a Stabilized Dialkylsilylene

Abstract

The potential-energy surfaces for the abstraction and insertion reactions of dialkylsilylene with carbon tetrahalides (CX4) have been characterized in detail using density functional theory (B3LYP), including zero-point corrections. Four CX4 species, CF4, CCl(4), CBr4, and CI(4), were chosen as model reactants. The theoretical investigations described herein suggest that of the three possible reaction paths, the one-halogen-atom abstraction (X abstraction), the one-CX3-group abstraction (CX3 abstraction), and the insertion reaction, the X-abstraction reaction is the most favorable, with a very low activation energy. However, the insertion reaction can lead to the thermodynamically stable products. Moreover, for a given stable dialkylsilylene, the chemical reactivity has been found to increase in the order CF4<<CCl(4)<CBr4<CI(4), that is, the heavier the halogen atom (X), the more facile is its reaction with a stable dialkylsilylene. In particular, halogen abstraction is always predicted to be much more favorable than abstraction of a CX3 group from both energetic and kinetic viewpoints. In brief, electronic as well as steric factors play a crucial role in determining the chemical reactivity of the haloalkane species, kinetically as well as thermodynamically. Our conclusions based on the results of our theoretical investigations are in accordance with available experimental observations. Furthermore, a configuration-mixing model based on the work of Pross and Shaik has been used to rationalize the computational results. The results obtained allow a number of predictions to be made.

Adsorption of Titanium Halides on Nitride and Oxide Surfaces during Atomic Layer Deposition: A DFT Study

“…Coatings 2020, 10, x FOR PEER REVIEW 7 of 11 [46,48]. Our results are consistent with these findings, and the above theory suggests a comparative analysis among the different titanium halide precursors.…”

“…The Ti-X bond dissociation energy (BDE) calculated at the current DFT level of theory are 413, 359, and 304 kJ/mol for TiCl 4 , TiBr 4 , and TiI 4 , respectively, confirming such hypothesis. In previous studies, the relative reactivities of the compounds containing halogen ligands were compared experimentally, and a similar reactivity hierarchy was reported (I > Br > Cl) [46,48]. Our results are consistent with these findings, and the above theory suggests a comparative analysis among the different titanium halide precursors.…”

“…The reactivity between the precursor and the surface varied with the size and electronegativity of the halogen element [46]. The higher the electronegativity of the halogen element is (Cl, Br, and I: 2.88, 2.75, and 2.6, respectively [47]), and the shorter the Ti-X bond length is (TiCl 4 , TiBr 4 , and TiI 4 : 2.18, 2.34, and 2.57 Å, respectively), the stronger the Ti-X bond would become [48]. The Ti-X bond dissociation energy (BDE) calculated at the current DFT level of theory are 413, 359, and 304 kJ/mol for TiCl 4 , TiBr 4 , and TiI 4 , respectively, confirming such hypothesis.…”

Kinetic and mechanistic studies of the reactions of diarylgermylenes and tetraaryldigermenes with carbon tetrachloride

“…Ando et al 26 reported the spectroscopic detection of the complexes of various germylenes (including GePh 2 ) with chlorohexane and chlorobenzene in hydrocarbon glasses at 77 K, prompting the later proposal by Neumann 16 for their involvement in the reactions of GeMe 2 with halocarbons; computational evidence for the intermediacy of analogous complexes in the reactions of some stable silylenes with CCl 4 has been reported by Su and co-workers. [81][82][83] If a reactive complex is involved as a discrete intermediate in the reaction of GePh 2 with CCl 4 , we are unable to detect it even at 80-90 K, so the free energy barrier for its further transformation must be relatively small. The low-temperature experiments with CDCl 3 as substrate are consistent with the formation of a complex in this case, judging from the similarity of the spectrum to those of the complexes of GePh 2 with the chlorocarbons reported by Ando et al 26 The rate constant for reaction of GePh 2 with CHCl 3 in hexanes at 25 8C is at least 50 times smaller than that with CCl 4 , 20 consistent with a significantly higher barrier for the second step of the reaction with CHCl 3 , whose C-Cl bond is ca.…”

Carbenes and Nitrenes

“…124 Halogen abstraction was shown to be the favoured path, and the CX 4 reactivity increased with the size of the halogen.…”