Département de chimie moléculaire

We report herein a mol. dynamics study of the main species involved in the hydroformylation of higher olefins promoted by cyclodextrins in 1-decene/water biphasic systems at a temp. of 350 K. The two liqs. form a well-defined sharp interface of approx. 7 {\AA} width in the absence of solute; the decene mols. are generally oriented "parallel" to the interface where they display transient contacts with water. We first focused on rhodium complexes bearing water-sol. TPPTS3- ligands (where TPPTS3- represents tris(m-sulfonatophenyl)phosphine) involved in the early steps of the reaction. The most important finding concerned the surface activity of the "active" form of the catalyst [RhH(CO)(TPPTS)2]6-, the [RhH(CO)2(TPPTS)2]6- complex, and the key reaction intermediate [RhH(CO)(TPPTS)2(decene)]6- (with the olefin $π$-coordinated to the metal center) which are adsorbed at the water side of the interface in spite of their -6 charge. The free TPPTS3- ligands themselves are also surface-active, whereas the -9 charged catalyst precursor [RhH(CO)(TPPTS)3]9- prefers to be solubilized in water. The role of cyclodextrins was then investigated by performing simulations on 2,6-dimethyl-$\beta$-cyclodextrin ("CD") and its inclusion complexes with the reactant (1-decene), a reaction product (undecanal), and the corresponding key reaction intermediate [RhH(CO)(TPPTS)2-(decene)]6- as guests; they were all shown to be surface-active and prefer the interface over the bulk aq. phase. These results suggest that the biphasic hydroformylation of higher olefins takes place "right" al the interface and that the CDs promote the "meeting" of the olefin and the catalyst in this peculiar region of the soln. by forming inclusion complexes "preorganized" for the reaction. Our results thus point to the importance of adsorption at the liq./liq. interface in this important phase-transfer-catalyzed reaction. [on SciFinder(R)]