DFT Study on the Mechanism of PtCl₂-Catalyzed Rearrangement of Cyclopropenes to Allenes

Abstract

The mechanisms of PtCl 2 -catalyzed rearrangement of cyclopropenes to allenes have been investigated using density functional theory calculations carried out at the B3LYP/6-31G(d,p) (LANL2TZ(f) for Pt) level of theory. The solvent effect was taken into account by B3LYP/6-311++G(d,p) (LANL2TZ(f) for Pt) single-point calculations with the integral equation formalism polarizable continuum model (IEFPCM) in dichloromethane. The radii and nonelectrostatic terms were taken from Truhlar and co-workers' universal solvation model (SMD). Three pathways which lead to the formation of allene via a [1,2]-C−C bond migration (regioselectivity) and C−Si bond migration were performed. Our calculations suggest the following. (1) The major pathway of the cycle involves an initial [1,2]-silyl shift leading to a platinum intermediate. A subsequent [1,2]-C−C bond shift of this intermediate then provides the corresponding allenes. ( 2) Due to the consequence of an interaction between the Lewis acidic platinum and the allene, the rearrangement of α-alkoxy-substituted cyclopropenes does not give the allene as the final product. (3) The calculations suggest that the electronic effect of a silyl substituent on the cyclopropene is essential for this reaction. Furthermore, the silyl groups provide not only the β-cation-stabilizing effect but also a facile migration group for the whole reaction.

Manifestation of the β-Silicon Effect in the Reactions of Unsaturated Systems Involving a 1,2-Silyl Shift

“…Then, the reaction goes directly through 1,2-silyl shift to give intermediate 175 that, after rearrangement and Pt elimination, yields the desired product 173. 74…”

C–C Bond Cleavages of Cyclopropenes: Operating for Selective Ring-Opening Reactions

“…In any case, further studies will be required to support these or different mechanisms. In this sense, two subsequent computational studies did not agree about a possible mechanism, 246,247 indicating the complexity of this molecular rearrangement.…”

“…The origins of metalation reactions of cyclopropenes with subsequent ring-opening go back to the 70s, when various groups described this reactivity. Nesmeyanova and co-workers reported the allylboration of 1-methylcyclopropene (247) with triallylborane (248) to yield, after methanolysis, cyclopropane 249 along with noticeable amounts of acyclic product 250 via C2−C3 bond cleavage in the cyclopropene (Scheme 38A). 179 The same group described the reaction with trialkylboranes 251.…”

Theoretical investigation on the mechanism of FeCl3-catalysed cross-coupling reaction of alcohols with alkenes

“…This kind of basis set is denoted as B1. It is widely applied in the mechanistic studies of transition-metal-and non-transition-metal-catalysed reactions [45][46][47][48][49]. The vibrational frequencies were also calculated at the same level to ensure the stationary points to be transition state or minimum.…”