Mechanistic Study on Copper- and Silver-Catalyzed Hydroboration of Internal Alkynes: A DFT Study.

The present study employs DFT calculations and the independent gradient model (IGM) approach to investigate a mechanism study of the hydroboration reaction of internal alkynes catalyzed by Ag-(I)-IMes and Cu-(I)-IMes complexes. A detailed analysis of the mechanism's steps revealed that Cu-(I)-IMes exhibits superior efficiency, showing a more favorable energy pathway than Ag-(I)-IMes. The IGM method was crucial for quantifying molecular interactions, highlighting essential differences in binding forces between catalysts and substrates throughout the catalytic steps. For Cu-(I)-IMes, the migratory insertion step (TS1) demonstrated a barrier 2.5 times lower than its Ag-(I)-IMes counterpart. Additionally, the protonation step (TS2) exhibited lower energy for Cu-(I)-IMes compared to Ag-(I)-IMes, indicating a more efficient formation of the desired β-product. The results also suggest that Cu-(I)-IMes operates on a more efficient pathway, with lower energy for the catalytic cycle. These findings, coupled with detailed analyses of molecular interactions using the IGM method, provide an enhanced understanding of the reaction mechanism, highlighting the promising efficacy of Cu-(I)-IMes as a catalyst in hydroboration reactions.