Design, Synthesis, Application, and DFT Investigation of Suzuki−Miyaura Reactions of a Dicobalt Carbonyl-Containing Phosphine Ligand

The preparation and characterization of a novel dicobalt-containing monophosphine ligand, 4a, is presented. Palladium-catalyzed Suzuki−Miyuara reactions employing 4a /Pd(OAc) 2 were pursued. The optimized reaction conditions were found to start with 1 molar equiv of arylhalides, 1.5-fold of phenylbronic acid, 3-fold of KF in 1 mL of THF, and 1 mol % of 4a /Pd(OAc) 2 as catalytic precursor. The 31 P NMR studies reveal moderate reductive capacity of 4a toward Pd(OAc) 2 . The unique bonding mode of 4a toward Pd ensures that the ratio of 4a /Pd is equal to 1:1. Two plausible active species, I and [ I - OAc ] -, were proposed as the catalytically active species in the Suzuki−Miyaura cross-coupling reaction. The validity of this assumption was examined by 31 P NMR spectra and density functional theory (DFT) means. In addition, we have demonstrated theoretically that the dicobalt moiety of 4a acts as an effective auxiliary in stabilizing the Pd(0) center during catalytic reaction.