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-Me₂NCH₂CCPR₂)] (4a: R=^tBu; 4b: R=Ph; 4c: R=Cy), were prepared from the reactions of corresponding alkynylphosphines Me₂NCH₂CCPR₂ (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-Me₂NCH₂CCP (^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.