Preparation and characterization of cobalt-containing P,N-ligands and an unusual palladium complex ion pair: their applications in amination reactions

Several cobalt-containing P,N-ligands, alkyne-bridged dicobalt phosphines [(μ-PPh2CH2PPh2)Co2(CO)4(μ,η-Me2NCH2Ctriple bond; length of mdashCPR2)] (4a: R=tBu; 4b: R=Ph; 4c: R=Cy), were prepared from the reactions of corresponding alkynylphosphines Me2NCH2Ctriple bond; length of mdashCPR2 (2a: R=tBu; 2b: R=Ph; 2c: R=Cy) with a dppm-bridged dicobalt complex [Co2(CO)6(μ-P,P-PPh2CH2PPh2)] 3. A unique palladium complex ion pair [(μ-PPh2CH2PPh2)Co2(CO)4(μ,η-Me2NCH2Ctriple bond; length of mdashCP (tBu)2)Pd(η3-C3H5)]+[(η3-C3H5)PdCl2]− 7a was obtained from the reaction of 4a with [(η3-C3H5)PdCl]2. Compounds 4a, 4b, and 4c are authentic cobalt-containing P,N-bidentate ligands and can be used for ligation of palladium from various sources such as Pd(OAc)2 or [(η3-C3H5)PdCl]2. Satisfactory efficiencies were observed for the amination reactions of aryl bromides with morpholine employing either a 4a-chelated palladium complex formed in situ or pre-formed 7a as the catalytic precursor.