Catalytic Activity of a Thermoregulated, Phase-Separable Pd(II)-perfluoroalkylphthalocyanine Complex in an Organic/Fluor

  • PDF / 269,751 Bytes
  • 6 Pages / 595.276 x 790.866 pts Page_size
  • 7 Downloads / 150 Views

DOWNLOAD

REPORT


Catalytic Activity of a Thermoregulated, Phase-Separable Pd(II)perfluoroalkylphthalocyanine Complex in an Organic/Fluorous Biphasic System: Hydrogenation of Olefins ¨ zer Æ Ibrahim _ Filiz Yılmaz Æ Metin O Kani Æ ¨ Ozer Bekarog˘lu

Received: 26 January 2009 / Accepted: 26 March 2009 / Published online: 15 April 2009 Ó Springer Science+Business Media, LLC 2009

Abstract A fluoroalkene-soluble tetrakis[heptadecafluorononyl]-substituted Pd(II)-phthalocyanine complex has been studied for olefin (styrene, 1-octene, trans-2-octene and cyclohexene) hydrogenation with molecular hydrogen in an organic/fluorous biphasic system [n-hexane/perfluoromethyl cyclohexane (PFMCH)]. The palladium complex was found to be an active catalyst for styrene (100% conversion, TON = 634) and 1-octene (92%, TON = 596) at 80 °C and 15 bar of H2 after 6 h of reaction time. The catalyst was recycled in nine consecutive reactions for the hydrogenation of styrene without the loss of activity or metal contamination. Keywords Biphasic catalysis  Hydrogenation  Phthalocyanine  Palladium complex  Fluorous solvent

1 Introduction Redox-active d-metal-phthalocyanine (Pc) complexes exhibit very high catalytic activities in different oxidation reactions [1–7]. The major problem with metal-phthalocyanines is low solubility in common organic solvents, which restricts their utility as catalysts. To deal with this

¨ zer M. O Department of Chemistry, Marmara University, 34722 Istanbul, Turkey _ Kani (&) F. Yılmaz  I. Department of Chemistry, Anadolu University, 26470 Eskis¸ ehir, Turkey e-mail: [email protected] ¨ . Bekarog˘lu O Department of Chemistry, Istanbul Technical University, 34469 Istanbul, Turkey

123

problem, one solution is the heterogenization of metalphthalocyanines by encapsulating them in zeolites [8–10], supporting them on polymers or intercalating them in layered solids [11–13]. Another reason to anchor metalphthalocyanines on solid support is to avoid their aggregation in solution, which limits their effectiveness as catalysts. The other solution is to utilize an organic/aqueous phase or organic/fluorous biphasic system. However, a major disadvantage of this approach is the low activity and selectivity resulting from the mass-transfer limitation [14–20]. Fluorous biphasic catalysis, an alternative to aqueous biphasic catalysis, was originally developed by Horva´th and Rabai as a method for facile catalyst recovery [21]. In this approach, the low miscibility of fluorocarbons with most organic solvents allows for the segregation of a catalyst soluble in the fluorocarbon phase from the substrate and products dissolved in the organic phase. One of the unique features of the organic/fluorous phase system, with an appropriate choice of organic and fluorous phases, is that upon warming, the two-phase organic/fluorous biphasic system becomes homogeneous. Consequently, catalysis occurs under genuine homogenous conditions, and after cooling, the two phases are quickly reestablished, allowing facile product/catalyst separation. This proces