Mechanistic investigation of the reaction between triphenylphosphine with Dimethylacetylenedicarboxylate in the presence of 2-indolinone as NH-acid

Stable phosphorus ylids are usually synthesized as a mixture of two E- and Z- isomeric forms with different percentages. Experimental methods and techniques cannot find a reason for the presence of these products in different proportions. Therefore, in this project, we are trying to find evidence for the preference of one of the E- and Z-structural isomers. For this purpose, the mechanism of the reaction between triphenylphosphine R1 and dimethyl acetylenedicarboxylate R2 was investigated in the presence of 2-indolinone as NH-acid, based on quantum mechanical calculations. Theoretical studies were performed to evaluate the energy levels of all structures participating in the mechanism. All structures optimized at the B3LYP/6-311++g(d,p) levels. The first step of the reaction was recognized as a rate-determining step in the reaction mechanism. To investigate the solvent effect on the energy level of structures, condensed phase calculations in dichloromethane carried out with the polarizable continuum model (PCM). Finally, the natural bond orbital (NBO) method applied for a better understanding of molecular interaction.