Alkene epoxidation with iodosylbenzene catalysed by polyionic manganese porphyrins electrostatically bound to counter-charged supports

Abstract

Manganese() complexes of tetra-anionic and tetra-cationic porphyrins have been immobilised on counter-charged, surface-modified silica supports and on organic ion-exchange resins. The reactions of these supported manganese() porphyrin systems and analogous uncharged homogeneous systems have been examined using cyclooctene and (E)-and (Z)-4-methylpent-2-ene epoxidations, with iodosylbenzene (PhIO) as the oxygen donor.Comparisons using the manganese porphyrin systems as catalysts for the epoxidation of cyclooctene in acetonitrile reveal that, in low turnover reactions (maximum 136 turnovers), they all give an essentially quantitative yield of epoxide although the heterogeneous reactions are significantly slower than the homogeneous analogues. In large scale repeat-use experiments, however, the supported catalysts are clearly superior, giving markedly better yields.The epoxidations of (E)-and (Z)-4-methylpent-2-ene with all the catalysts show a very high stereoretention, with the (Z)-alkene reacting faster than the (E)-isomer. The sterically hindered manganese() 5,10,15,20-tetrakis-(2,6-dichloro-3-sulfonatophenyl)porphyrin (MnTDCSPP) shows the highest selectivity for the (Z)-isomer; by contrast the supported manganese() 5,10,15,20-tetrakis[2,3,5,6-tetrafluoro-4-(trimethylammonio)phenyl]porphyrin on Dowex (MnTF 4 TMAPP-Dowex) reacts with the two alkenes at effectively the same rate.The mechanism of the epoxidations and the influence of the porphyrin ligand and support on the substrate selectivity are discussed.

A cooperative effect between support and the heterogenised metalloporphyrins on electrocatalytic oxygen reduction

“…A useful means to avoid these limitations is by heterogenisation of these transition metal complexes onto robust inorganic supports, due to the stable covalent binding established between catalyst and support and the demonstrated increased stability of the metallic complexes after supporting. Different methods have been used to heterogenise metalloporphyrins, namely, electrostatic binding [2], entrapment [3], polymerisation [4], covalent binding [5] or axial ligation of metal [6], but most of them suffer from a reversible binding under working conditions [2,6] or a fairly low porphyrin contents onto the solid matrix(%0.02 mmol/g) [5]. In order to achieve a stable binding between ligand and support and increased loading of metallic complex we have developed a simple way to synthesise heterogenised porphyrins and metalloporphyrins.…”

A New Mesoporous Hybrid Material: Porphyrin-Doped Aerogel as a Catalyst for the Epoxidation of Olefins

“…The catalyst was presumably deactivated by accumulation of iodoxybenzene PhIO 2 , a by-product formed by catalytic oxidation of iodosylbenzene, around the anchored metalloporphyrin. [6,16] To compare the efficiency of homogeneous and heterogeneous catalysis, the epoxidation of cyclooctene was investigated with porphyrin 1 in homogeneous solution, using the same reaction conditions as for the heterogeneous catalysis by the hybrid aerogel (Fig. 3).…”

“…However, reduced catalytic activity, slower reaction rates, transport limitations, and lack of accessibility of the active sites are commonly encountered problems. A variety of solid supports, mostly microporous, such as silica, [2] molecular sieves, [3] polystyrene, [4] Merrifield peptide resins, [5] counter-charged supports, [6] polydimethylsiloxane membranes, [7] or xerogels [8] have been used in the past for immobilization of porphyrins. We became interested in combining the advantages of efficient homogeneous metalloporphyrin catalysis with the unique properties of mesoporous aerogel materials, mainly the high porosity and high surface area.…”

A convenient preparation of polymer-supported manganese porphyrin and its use as hydrocarbon monooxygenation catalyst

“…On the other hand, immobilization of metalloporphyrin complexes on solid supports can provide catalysts that are easier to handle, and may exhibit improved selectivities and activities because of the support environment. To date, different approaches have been taken in the design of heterogeneous metalloporphyrin catalysts including: (i) electrostatic binding of charged porphyrins to counter-charged supports; (ii) intercalation or entrapment of porphyrin between the layers of clays or within the pores or matrices of solids; (iii) axial ligation to surface-bound ligands; and (iv) covalent binding to the supports [4][5][6][7][8][9][10][11][12]. Polymer covalently-bounded porphyrins are available by polymerization of vinyl group containing porphyrin or by immobilization of suitable porphyrins on reactive polymers [13,14].…”