Allenylphosphine Oxides As Starting Materials for the Synthesis of Conjugated Enynes: Boosting the Catalytic Performance by MOF Encapsulated Palladium Nanoparticles

A direct coupling of allenylphosphine oxides and alkynes is disclosed here mediated by MOF encapsulated palladium nanocatalysts. The methodology using alpha-allenyl ethers as starting materials provides a heterogeneous approach to generate tri-conjugated enynes with medium to excellent yields. The reaction tolerates a variety of functional groups to afford a range of structurally diverse substituted conjugated enynes. MOF served as support plays a significant role in dispersing and stabilizing the Pd nanoparticles. When compared with the homogeneous system, the advantage is also witnessed exhibiting a steady and high TOF value as well as the efficient reusability. A remarkable pore-control effect of the MOF catalysts was also revealed, depending on the dimension of MOF, molecular size of allenylphosphine oxides, alkynes and enynes respectively. Benefitting from the heterogeneous manner, successful recycling of the MOF catalyst was further achieved with high reaction efficiency maintained.