Immobilization systems Suzuki cross-coupling

There has been considerable interest in hydrogenation and Pd-mediated C—C bond formation reactions in supercritical CO2 (scC02) [40]. Lee et al. [36] applied polyurea as a suitable encapsulation matrix to ligate and retain metal species such as Pd(OAc)2. The microcapsules were prepared by an in situ interfadal polymerization approach. A standard HPLC capillary was packed with immobilized catalyst. The combination of microencapsulated Pd(OAc)2 and nBu4NX (X = OMe and OH) was an efficient and economical catalytic system for Suzuki cross couplings at low temperatures in both organic solvents and SCCO2. 

A different example of triphasic catalysis for the Heck, Stille and Suzuki reactions relied on a three-phase microemulsion/sol-gel transport system. Gelation of an z-octyl(triethoxy)silane, tetramethoxysilane and Pd(OAc)2 mixture in a H2O/CH2CI2 system led to a hydrophobicitized sol-gel matrix that entrapped a phosphine-free Pd(ii) precatalyst. The immobilized precatalyst was added to a preformed microemulsion obtained by mixing the hydrophobic components of a cross coupling reaction with water, sodium dodecyl sulfate and a co-surfactant, typically zz-propanol or butanol. This immobilized palladium catalyst was leach proof and easily recyclable. 

The nature of ligands, such as Boxs, phosphines, and N-heterocyclic carbenes (NHC), bound to a transition metal center usually afiects the selectivities and reaction rates in the organic reactions. Styring et al. described the preparation of a Pd (Il)-salen complex immobilized on Merrifield resin (42). The polymer catalyst facilitated the Suzuki-Miyaura cross-coupling reaction in a continuous-flow system (Scheme 7.32) [130]. The reactor continuously afforded biaryl adducts (43) from aryl... 

---