DFT and ONIOM study on the alkylation of the lithium enolate in solution: microsolvation cluster models for CH2=CHOLi + CH3Cl + (THF)0–6

摘要

DFT computational study on the alkylation of the lithium enolate derived from acetaldehyde with MeCl was performed. The reaction of the free enolate CH2=CHO? with MeCl has an early transition state with low barrier, and the reaction of its lithium enolate gave a cyclic transition structure with high activation energy; neither of them is a good model for reaction in solution. In the presence of 1–6 THF molecule(s), a typical SN2 transition structures were obtained with reasonable activation energies after the PCM correction. Especially, the reaction in the presence of three THF molecules completed the tetra-coordination of the lithium cation, and structurally and energetically, this is an optimal model for the reaction in the solution. The transition structures were also located at the ONIOM level (high = B3LYP/6–31(+)G*: low = RHF/3–21 G*). The results are favorably compared with the full DFT results.