Click Heterogenization of Phosphines Furnishes Recyclable Hydroformylation Catalysts that Reproduce Homogeneous Performance

Abstract

Heterogeneous catalysts confer notable practical advantages for large-scale reactions, while homogeneous catalysts permit targeted performance optimization. A rapid and general method for the heterogenization of molecular transition-metal catalysts without loss of performance would thus permit facile translation of optimized homogeneous catalysts into practical heterogeneous catalysts. Here, we show how a wide variety of phosphines carrying anionic substituents can be charge-tethered to the walls of the spacious supercages of a metal–organic framework (MOF) to provide an adaptable heterogeneous ligand set in a single synthetic step. The addition of Co2(CO)8to MOF-heterogenized phosphine ligands provides recyclable, heterogeneous hydroformylation catalysts that faithfully reproduce the performance of the molecular analogues in both activity and selectivity. Key to the solution-like reactivity of the click heterogenized phosphines is their high degree of mobility, which was directly demonstrated by31P NMR analysis and which enables them to effectively accommodate cobalt complexes with three distinct oxidation states and coordination geometries. While the lack of directionality of the ionic interaction between the ligand and the host permits the phosphines to effectively reproduce homogeneous catalytic cycles, the strength of the ionic interaction ensures that phosphine leaching remains below 0.05 ppm.