A mechanistic DFT study of Z-selective ring-opening metathesis polymerization by MAP catalysts

Abstract

Herein we present a detailed mechanistic investigation of Z-selective ROMP of norbornadiene (NBD) with MAP-based catalyst 3a-b by DFT (M06) calculations. The studied catalytic reaction mechanism include the initiation, interconversion, and propagation stages with anti and syn NBD olefin attacks. In the initiation, we found the inversion of the metal center from the (R) configuration in the initial reactant to the (S). Further, we found that the olefin attack anti is kinetically more favorable than syn. Following this, we found that the stabilization order of the ring-opening species (ROS) is vital for the Z-selectivity due to the 3a-b-anti-1/2-cis/trans producing cis-polymers, and 3a-b-syn-1/2-trans produces trans-polymers. Furthermore, the 3a-anti-2-cis+syn pathways form cis-syndiotactic polymers that must overcome 30.8 kcal mol−1, respectively, during the propagation stage. Finally, the [2+2] cycloaddition of the propagation stages determines the reaction rate, which is essential for producing stereoregular polymers.