Amination and Suzuki coupling reactions catalyzed by palladium complexes coordinated by cobalt-containing monodentate phosphine ligands with bis-trifluoromethyl substituents on bridged arylethynyl: Observation of some unusual metal-containing compounds

Two cobalt-containing bulky monodentate phosphines {[(μ-PPh2CH2PPh2)Co2(CO)4][(μ,η-(tBu)2PCCAr]} (4cm: Ar = 3-CF3C6H4; 4cmm: Ar = 3,5-(CF3)2C6H3) were prepared from the reaction of Co2(CO)6(μ-PPh2CH2PPh2) (3) with each corresponding alkynes (tBu)2PCCAr. Both compounds were converted to their oxidized forms {[(μ-PPh2CH2PPh2)Co2(CO)4][(μ,η-(tBu)2P(O)CCAr]} (4cmO: Ar = 3-CF3C6H3; 4cmmO: Ar = 3,5-(CF3)2C6H3) in the presence of oxide. Further reactions of 4cm and 4cmm with Pd(OAc)2 gave palladium complexes {[(μ-PPh2CH2PPh2)Co2(CO)4][(μ,η-(tBu)2PCC(Ar)-κC1)]Pd(μ-OAc)} 5cm (Ar = 3-CF3C6H3) and 5cmm (Ar = 3,5-(CF3)2C6H2), respectively. By contrast, reactions of 4cm and 4cmm with Pd(COD)Cl2 gave products, [{μ-P,P-PPh2CH2PPh2}Co2(CO)3(μ-CO){μ,η-(tBu)2PCCAr}]-PdCl2] 8cm and 8cmm, respectively, with unique bonding modes. Several crystallines of [(4cm)2Pd3(μ-Cl)(μ-CO)2)(μ-Cl)]2 (9) were obtained along with crystallines of 8cm during the crystallization process. The crystal structures of all three compounds, 4cmmO, 8cmm and 9 were determined by single-crystal X-ray diffraction methods. Fair to excellent efficiencies were observed for employing 4cmm/palladium salt as catalytic precursor in amination as well as in Suzuki coupling reactions.

Graphical abstractA cobalt-containing bulky monodentate phosphine 4cmm was prepared from the reaction of 3 with corresponding alkyne 2cmm. Its capacity as phosphine ligand in the amination as well as Suzuki coupling reactions in the presence of palladium salt was evaluated.Figure optionsDownload full-size imageDownload as PowerPoint slide