Highly efficient hydroboration of alkynes catalyzed by porous copper-organic framework under mild conditions

Abstract

The hydroboration of alkynes is crucial due to the wide applications in organic synthesis, while such reaction is often completed with low turnover frequency (TOF) value and long reaction time. Therefore, it is very important and necessary that the hydroboration of alkynes is performed with high TOF value, however the corresponding investigations have been never reported hitherto. Herein, a new Cu-organic framework 1 with mixed-valence Cu(I) and Cu(II) blocks was successfully synthesized and employed for the hydroboration of alkynes with bis(pinacolato)diboron (B2Pin2). 1 displays good thermostability and excellent solvent stability. Catalytic explorations reveal that 1 can serve as a high efficient heterogeneous catalyst for this reaction with a record TOF value of 310 h−1 under mild conditions, and 1 as catalysts which can be recycled at least five times without adding any cocatalysts. Mechanism investigations suggest that the Cu(I) and Cu(II) clusters in the framework of 1 have a synergistic catalytic effect in the hydroboration of alkynes, which can effectively activate the alkyne to react with B2Pin2. The density functional theory (DFT) calculations explicitly elucidate the reaction pathways, and the results indicate that the Cu(I) and Cu(II) clusters in 1 as the catalytic sites can greatly reduce the Gibbs free energy of the hydroboration of alkyne indifferentdegree, which accounts for the high catalytic activity of 1.