Abstract
The immobilization of 2-phenyl-2-((3(tryethoxysicyl)propyl)imino)ethanol (HL1) and 4-methyl-2-(((3(triethoxysilyl)propyl)imino)methyl)phenol (HL2) on MCM-41 afforded the respective ligands HL1-MCM-41 (HL3) and HL2-MCM-41 (HL4). The treatment of complexes Pd(L1)2 and Pd(L2)2 with MCM-41 afforded the immobilized complexes (Pd(L1)2)-MCM-41 (1) and (Pd(L2)2)-MCM-41 (2) respectively. Separately, the reactions of HL3 and HL4 with Pd(NCMe)2Cl2 produced the immobilized complexes Pd(HL3)Cl2 (3) and Pd(HL4)Cl2 (4) respectively. The immobilized compounds were characterized by FT-IR, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), energy-dispersive X-ray (EDX), Thermogravimetric Analysis (TGA) and X-ray Powder Diffraction (XRD). All the complexes (1–4) formed active catalysts in the methoxycarbonylation of 1-hexene to give linear and branched esters. The catalysts were recycled four times without the loss of catalytic activity. Hot filtration experiments established the absence of leaching, and the heterogeneous nature of the active species was derived from mercury drop experiments.
Highlights
Homogeneous catalysts have been used in a number of industrial processes largely due to their high selectivity and ease of understanding of the reaction kinetics and mechanisms [1]
We report the application of palladium complexes immobilized on MCM-41 as recyclable catalysts in the methoxycarbonylation of 1-hexene
We have successfully synthesized and characterized four palladium complexes ofimine ligands immobilized on mesoporous MCM-41 silica
Summary
Homogeneous catalysts have been used in a number of industrial processes largely due to their high selectivity and ease of understanding of the reaction kinetics and mechanisms [1]. Heterogeneous catalysts, on the other hand, are recoverable, but they too have several drawbacks, mainly associated with low catalytic activities and poor selectivity [2]. This has necessitated a search for catalyst systems that can exploit the advantages and limit the disadvantages of both homogeneous and heterogeneous catalysts [3,4]. A number of methods of heterogenizing homogeneous catalysts have been adopted. These include the immobilization of homogeneous catalysts on insoluble solid supports such as silica [7], polymer [8], magnetic nanoparticles [9] as well as biphasic catalysis [10]
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