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

Heterogeneous catalysts confer notable practical advantages for large-scale reactions, while homogenous 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 super-cages of a metal-organic-framework (MOF) to provide an adaptable heterogeneous ligand set in a single synthetic step. The addition of Co2(CO)8 to 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 the high degree of mobility of the heterogenized phosphines, which could be directly demonstrated by 31P 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 homogenous catalytic cycles, the strength of the ionic interaction ensures that phosphine leaching remains below 0.05 ppm.