Synthesis of cobalt-containing monodentate phosphine ligand and application toward Suzuki cross-coupling reactions

A bulky, dicobalt complexed, mono-dentate phosphine, [(μ-PPh2CH2PPh2)Co2(CO)4](μ,η-PhCtriple bond; length of mdashCPCy2) (4), was prepared from the reactions of the bis(diphenylphosphino)methylene (dppm)-bridged dicobalt complex Co2(CO)6(μ-Ph2PCH2PPh2) (2) with PhCtriple bond; length of mdashCPCy2 (3). Combination of 4 and Pd(OAc)2 (1:1) gave an active catalyst for the palladium-catalyzed Suzuki coupling of aryl bromides with phenylboronic acid; the catalytic reactions can be performed even under low catalyst loadings (0.1–0.001 mol% 4/Pd(OAc)2). Compound 4 has been proved to be an authentic and effective mono-dentate phosphine ligand. Crucial factors such as 4/Pd(OAc)2 ratio, base being used, solvent volume, temperature, and electronic variation of the aryl bromides in reactions were also investigated and results are reported.