β-Hydrogen Elimination Mechanism in the Absence of Low-Lying Acceptor Orbitals in EH₂(t-C₄H₉) (E = N–Bi)

Abstract

The β-hydrogen elimination reactions of group 15 alkyl compounds at the example of EH2(t-C4H9) (element E = N-Bi) were investigated and compared to the group 13 example of GaH2(t-C4H9). With the aid of extensive density functional theory based analysis of atomic and electronic structures at the transition state, we can derive three distinct reaction classes. The gallium compound follows the well-known β-hydride route with participation of an empty p orbital at the metal in a concerted, synchronous fashion, exhibiting a low barrier. For compounds with group 15 elements, we find highly nonsynchronous reactions with high reaction barriers. In the case of nitrogen, a proton-like H atom is transferred via attack of the nitrogen nonbonding electron pair. For the heavier homologues (P-Bi), E-Cα bond breaking occurs first and the H atom does not carry charge at the transition state. The reaction barrier in group 15 homologues is thus determined by the E-Cα bond strength down the group. The results enable a rationale for ligand design for precursors involved in chemical vapor-phase deposition processes because a good ligand needs to stabilize the positive charge at Cα.

An experimental approach for real time mass spectrometric CVD gas phase investigations

“…reported that there are two decomposition pathways, first a free radical process producing isobutane and second a β-H-elimination process, that generates isobutene as a side product 30 , 31 . Hence, the observations made in these experiments as well confirm β-H-elimination as the main decomposition mechanism at temperatures above 390 °C 32 , 33 .…”

Complementary Base Lowers the Barrier in SuFEx Click Chemistry for Primary Amine Nucleophiles

“…[31,32] It thus allows to characterize the nature of transition states and provides a microscopic picture on the crucial changes in the molecule along the minimum energy path with the largest influence on the reaction barrier. [33] The first finding is an asymmetric profile of the transition region (grey area). The TS is positioned rather close to the product and the minimum of the force constant curve (green) does not coincide with the maximum of the energy (black circles).…”

“…Those characteristics are indicative of a non-concerted reaction where bond-breaking and bond-making do not happen simultaneously along the reaction path as has been found before for the -H elimination of group 15 alkyls. [33] An analysis of the bond lengths along the reaction path ( Fig. 2) confirms that the S-F bond is only slightly elongated at the beginning of the transition region (deviation from value in 2, ∆d(SF) = +0.227 Å) while the S-N bond is already close to its value at the TS (deviation from value at TS: ∆d(SN) = +0.190 Å, see also the animated IRC in the supporting information).…”

Gas phase chemical vapor deposition chemistry of triethylboron probed by boron–carbon thin film deposition and quantum chemical calculations

“…8(a)) and without ( Fig. 37,38 From Table 1, it is found that b-hydride eliminations exhibit moderately high electronic barriers, which increase only slightly with increasing temperature. This simulates the growth in H 2 and Ar atmospheres since in the latter case, reactions with H 2 is not possible.…”