Cobalt as an Anchor: Acetate and Nontrigonal Phosphorus Ligand-Assisted Hydroboration

Abstract Replacing precious metals with earth-abundant alternatives remains a vital challenge in sustainable catalytic systems. Herein, the synthesis and catalytic application of a cobalt(II) acetate complex with a tridentate, dianionic urea-based ligand bearing a nontrigonal phosphorus center are reported. The Co(II) complex was fully characterized, including by single-crystal X-ray diffraction to confirm the direct coordination of the Co(II) center to the nontrigonal phosphorus. Catalytic studies reveal that this complex promotes the hydroboration of aldehydes, ketones, styrene, and phenylacetylene using pinacolborane under mild conditions. The system operates with catalyst loadings as low as 0.1 mol % for aldehydes and 0.5 mol % for ketones at room temperature and displays high selectivity toward aldehydes. Experimental and computational mechanistic studies indicate that the Co(II) center does not serve as the locus of B–H bond activation, with no evidence for catalytically active boryl or hydride species. Instead, density functional theory suggests that the strongly coordinated acetate ligand serves to activate pinacolborane during catalysis, positioning the BH group near the electrophilic phosphorus center. These findings demonstrate the potential role of ligand-centered chemistry in first-row transition-metal catalysis and open new directions for the design of cooperative ligand platforms beyond traditional metal-centered pathways.