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 31P 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 31P 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.