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Abstract

Pd-catalyzed carbonylation has attracted considerable interest since it affords easy access to carbonyl compounds in industrial applications. Transition metal diphosphine complexes are commonly utilized as homogeneous catalysts in Pd-catalyzed carbonylation reactions. However, the difficulty of recycling the precious transition metal complexes hampers the use of homogeneous catalysis. An effective strategy to solve the issue is the immobilization of the transition metal complexes on a solid support. Minimizing the leaching of the complexes into the solution is crucial to reduce the loss of the complexes. Thus, the task in this project is to heterogenize Pd-diphosphine complexes by affixing them to the pores of the metal-organic framework NU-1000 by robust carbon−carbon bonds and investigate their catalytic performance.
Protection of 1,2-DTBPMB with BH₃ was carried out to produce a borane-phosphorous adduct. A borylated borane-phosphorous adduct was obtained by sterically controlled Ir-catalyzed C−H borylation. Post-synthetic bromination of linkers in NU-1000 showed bromine was evenly dispersed across well-defined rod-shaped crystals MOFs crystals, and the PXRD pattern remained unchanged. Suzuki-Miyaura coupling of the brominated NU-1000 and the borylated 1,2-DTBPMB gave rise to phosphine-modified MOFs. The phosphine-modified MOF derived from a toluene/H₂O solvent system demonstrated a combination of the phosphine oxide and the borane-protected phosphine. The expected change in sorption behaviour of the MOF was observed with a decrease in mesopore size that was attributed to the functionalization of MOF mesopores with the phosphine. PXRD analysis indicated that the MOF crystallinity remained intact. Further removal of borane and coordination to Pd(acac)₂ furnished the heterogeneous phosphine based Pd catalysts. Solid-state ³¹P NMR spectrum showed that the majority is phosphine oxide. Partially damaged crystals of the heterogeneous catalyst were observed based on SEM images of the catalysts.
Methoxycarbonylation of ethylene catalyzed by the heterogeneous catalysts was investigated and showed that none of the desired products was found. The result might be attributed to the presence of inactive phosphine oxide, accounting for the majority of the catalyst, which is not a competent ligand for Pd-catalyzed methoxycarbonylation.