Jacobsen’s Catalyst Interaction with Polydimethylsiloxane/Tetraethoxysilane Network and Solvent Molecules: Theoretical Design of a New Polymeric Membrane Josefredo R. Pliego Jr.* ,† and Marco A. Schiavon Departamento de Cie ˆncias Naturais, UniVersidade Federal de Sa ˜o Joa ˜o del-Rei, 36301-160, Sa ˜o Joa ˜o del-Rei, MG, Brazil ReceiVed: May 13, 2008; ReVised Manuscript ReceiVed: July 1, 2008 Theoretical calculations were used for understanding the occlusion of the Jacobsen’s catalyst inside a polydimethylsiloxane/tetraethoxysilane (PDMS/TEOS) polymeric membrane. Our analysis indicates there is a partition equilibrium of the catalyst between the solvent and the swelled membrane. Density functional theory calculations at the B3LYP level predict interaction energies of the Jacobsen’s catalyst with benzene, chlorobenzene, dichloromethane, tetrahydrofuran, and acetone and with a model of PDMS chain in the range of 6-8 kcal mol -1 . For methanol, the hydrogen bonding involving the coordinated chloride atom reaches 14 kcal mol -1 . These findings were used for designing a new membrane, where a diol structure was added to the side of the polymeric chain. The modified membrane should present improved retention properties. Introduction Many organometallic compounds are useful homogeneous catalysts. An example is Jacobsen’s catalyst (Figure 1), an organometallic used for stereoselective olefin epoxidation. 1 However, it is known that catalysis on homogeneous conditions have some problems, mainly related to recovery of the catalyst. 2 Trying to overcome these problems, many studies on heterog- enization of homogeneous catalysts has been reported. 2-7 One procedure is the occlusion of the catalyst inside a polymeric membrane. In the occlusion process, the catalyst stay inside the membrane either through chemical bond 7,8 or physical interac- tions. 4-6 In the latter case, polydimethylsiloxane (PDMS) 5,6 and composite membranes (PDMS/TEOS) 3,9 have been used as supporting membranes (Figure 1). The PDMS is a linear polymer, whereas in the PDMS/TEOS network, the tetraethox- ysilane (TEOS) is used to generate a silica cluster, which cross- links the PDMS linear chains, generating a three-dimensional structure. The occlusion of the Jacobsen’s catalyst has been experi- mentally investigated in a recent paper using a PDMS/TEOS polymeric membrane. 3 This heterogenization process is interest- ing, because it enable the exclusive recovery of the hydrophobic oxidation product in the organic phase. However, a very common problem in such system is the leaching of the catalyst out of the membrane, which is accentuated by the use of solvents with a high affinity for the catalyst and able to cause swelling of the membrane. Therefore, understanding the mechanism of the catalyst’s interaction with the membrane wall and with solvent molecules is a fundamental problem and may be important in the rational design of new membrane/solvent combinations. The aim of this paper is to provide molecular level insights on the interaction of the catalyst with a model PDMS/TEOS membrane and with some solvent molecules such as C 6 H 6 , PhCl, CH 2 Cl 2 , THF, CH 3 COCH 3 , and CH 3 OH. On the basis of these insights, we have designed a new polymeric membrane that should be able to form a complex with the catalyst without loss of catalytic activity and have improved retention properties. Membrane Model In the study of the Jacobsen’s catalyst interaction with the PDMS/TEOS membrane wall, it is important to have a view of * Corresponding author e-mail: pliego@unifesp.br. † Present address: Departamento de Cie ˆncias Exatas e da Terra, Univer- sidade Federal de Sa ˜o Paulo, 09972-270, Diadema, SP, Brazil. Figure 1. Jacobsen’s catalyst and polymeric membranes. J. Phys. Chem. C 2008, 112, 14830–14834 14830 10.1021/jp804245f CCC: $40.75  2008 American Chemical Society Published on Web 08/27/2008