Dynamic Pdᴵᴵ/Cuᴵ Multimetallic Assemblies as Molecular Models to Study Metal-Metal Cooperation in Sonogashira Coupling
2019-12-23T20:42:44Z (GMT) by
Cooperation between two different metals plays a crucial role in many synergistic catalytic reactions such as the Sonogashira C-C cross-coupling reaction, where an interaction between the organometallic Pd and Cu centers is proposed in the transmetalation step. Although several heterobimetallic Pd/Cu complexes were proposed as structural models of the active species in Sonogashira coupling, the detailed understanding of the metal-metal cooperation in both transmetalation and C-C elimination steps is still lacking in current systems. In this work, we report a stepwise and systematic approach to building heteromultimetallic Pd/Cu assemblies as a tool to study metal-metal cooperativity in catalysis. We obtained fully characterized Pd/Cu multimetallic assemblies that show reactivity in alkyne activation, formation of catalytically relevant aryl/acetylide species, and C-C elimination, serving as functional models for Sonogashira reaction intermediates. The combined experimental and DFT studies highlight the importance of ligand-controlled coordination geometry, metal-metal distances and dynamics of the multimetallic assembly for transmetalation step. The phosphine ligand was shown to promote facile C-C elimination explained through NMR and DFT studies.