Structures and Mechanism of MOF-505 and Cu-ZSM-5 Promoted Mukaiyama Aldol Reaction: An ONIOM study
S. Yadnum, S. Choomwattana, P. Khongpracha, J. Limtrakul
Kasetsart University, TH
Keywords: nanoporous MOF-505, Cu-ZSM-5 zeolite, Mukaiyam Aldol Reaction, nano confinement effects, metal-organic framework (MOF-505), ONIOM
Abstract:The reaction mechanism of Metal organic framework (MOF-505) and Cu-exchange ZSM-5 zeolite promoted Mukaiyama Aldol reaction is studied theoretically. Density-functional theory (B3LYP/6-31G(d,p)) and ONIOM (B3LYP/6-31G(d,p):UFF) have been employed to investigate the reaction of Mukaiyama aldol reaction and compare the catalytic efficiency between Metal-Organic Framework (MOF-505) and Cu-exchanged zeolite (Cu-ZSM-5). The Mukaiyama aldol reaction of encapsulated formaldehyde and silyl enol ether was studied on three model systems: (1) a bare model: O=CH2/H3SiOHC=CH2; (2) Cu-exchanged zeolite: Cu-zeolite/ O=CH2/H3SiOHC=CH2; and (3) MOF-505/O=CH2/H3SiOHC=CH2. The Mukaiyama aldol reaction of silyl enol ether with formaldehyde takes place in single concerted reaction step. It is found that both catalysts make the carbon atom in formaldehyde more electrophillic which leads to a lower energy barrier of the reaction as compared to the bare model system. For the comparison of the catalytic efficiency, it is found that Cu-ZSM-5 reduces the activation energy (6.31 kcal/mol) to be lower than MOF-505 (12.0 kcal/mol).