Magnesium and Calcium Bisguanidinates: Catalytic Activity in the Hydroboration of Unsaturated Molecules

The role of ligands in catalytically active metal complexes can be crucial. Herein, we present a study on the synthesis and catalytic behavior of alkaline earth bisguanidinato complexes. The reactivity of trisubstituted guanidines, specifically (iPrHN)₂CNR (R=Ph, 2‐Ph₂PC₆H₄, 2‐MeSC₆H₄), towards magnesium and calcium alkyls or amides was explored. All the compounds were found to be very active in the hydroboration of acetophenone with pinacolborane. Notably, a calcium‐based complex was especially effective in the hydroboration of carbonyl compounds, demonstrating significant chemoselectivity against other reactive functional groups. This complex was also particularly effective in the double hydroboration of nitriles and moderately active in the hydroborative dearomatization of pyridine. Our experimental and DFT studies allow us to propose a mechanism in which the participation of the guanidinato ligands, along with the metal, is key to the activation of both the unsaturated species and borane.