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Synthesis and Characterization of Various Transition Metal Complexes and the Application in Oxidation, Heck, Suzuki, Sonogashira and Olefin Metathesis

Amini, Mojtaba | 2012

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 43104 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Bagherzadeh, Mojtaba
  7. Abstract:
  8. In nature, catalysis is of vital importance in a wide variety of biochemical processes catalyzed by metalloenzymes. The functions performed by the metalloenzymes and their significance have inspired a range of biomimetic studies, and intense efforts have been concentrated on the synthesis of low molecular weight complexes to model the spectroscopic features of such enzymes. Concomitantly, a challenging frontier in the field of biomimetic chemistry is the development of highly reactive model compounds that are able to effect rapid and selective substrate conversion. Some important catalytic transformations that have gained attention in recent years involve the carbon-carbon coupling, olefin metathesis and oxidation reaction.The first part of this thesis describes the synthesis and characterization of several Mn, V, Fe and Mo complexes containing Schiff base, s-triazine and oxazoline ligands and their reactivities as catalysts in the oxidation of organic compounds like olefins, sulfides, alcohols and alkans, as well. The complexes have been characterized by elemental analysis, Uv-Vis, IR, 1H NMR, molar conductance data, and finally by X-ray structure analysis.In the beginning of experimental section, the catalytic activity of the Schiff base complex of iron, [Fe(L)(acac)(EtOH)] in the oxidation of sulfides with UHP (urea hydrogen peroxide) in mixture of CH2Cl2/CH3OH as solvent system was studied. Using this catalytic system in the oxidation of sulfides, sulfoxides were obtained as the main products, together with variable amounts of sulfones, depending on the nature of the substrate. Our studies on the catalytic properties of newly prepared complexes lead to the designing highly efficient catalytic systems for the oxidation of various alcohols by Mn(II) and V(IV) complexes of [Mn(tptz)(Cl)2(OH2)], {Mn(O2CCH2NH2CH2CO2)2(H2O)2}n and [VO(L)2] (where, L = N-(phenolyl)-benzaldimine), oxone as oxidizing agent and tetra-n-butylammonium bromide as phase transfer agent in biphasic mixture of CH2Cl2/H2O. Full characterization of these complexes were accomplished with elemental analyses, spectroscopic studies (IR and electronic) and X-ray structure analysis for Mn(II) complexes. These complexes were tested as a catalyst for the homogeneous oxidation of alcohols. Easy preparation, mild reaction condition, high yields of the products, short reaction time, no further oxidation, high selectivity and inexpensive system make these catalytic systems a useful method for oxidation of alcohols.Also in these part three new oxo-peroxo Mo(VI) and W(VI) complexes [MO(O2)L(CH3OH)] (M= Mo, W, where, L = salicylidene benzoyl hydrazine) and [MoO(O2)(phox)2] were synthesized and characterized by X-ray structure analysis, elemental analysis, infrared and 1H NMR spectroscopy. In order to study the catalytic potentiality of complexes [MO(O2)L(CH3OH)] and [MoO(O2)(phox)2], the catalysts are respectively used in the oxidation of sulfides, epoxidation of olefins and oxidation of alkanes to their respective oxidation products. The results have shown that these complexes are very efficient catalyst in oxidation reactions with high conversion and selectivity.The second part of this thesis is about Heck, Suzuki-Miyaura and Sonogashira coupling reactions. The first two novel complexes of Pd(II) and Cu(II) with (N,O) oxazine ligand, 2-(2'-hydroxyphenyl)-5,6-dihydro-1,3-oxazine,have been prepared and the molecular structures of these complexes have been confirmed by X-ray structure analysis, NMR, IR and UV-Visible spectroscopy. The catalytic activity in the Heck reaction of these new complexes is compared. This study is the first report of the catalytic activity for a copper(II) complex in the Heck reaction. In general, Pd(II) appears to be more efficient for the Heck reaction of aryl iodide and bromide compared with Cu(II), but their activity is much lower for the coupling of aryl chloride. The procedure is simple and efficient for coupling various aryl halides with olefins and does not involve an induction period.
    Also in this thesis two highly effective, easy to handle and environmentally benign process for palladium/copper-mediated Heck, Suzuki-Miyaura and Sonogashira coupling reactions were developed. The in situ prepared three-component system composed of palladium(II) acetate or CuI, a Halogenated N-Heterocyclic imidazolium chloride or Gluco- Schiff base and a base efficiently catalyzes the Heck, Suzuki-Miyaura and Sonogashira coupling in aqueous solvents.
    The third part of this thesis (Chapter 3) has been devoted to studies of the olefin ring-closing metathesis (RCM) reaction by some novel complexes of ruthenium. The work was performed in Prof. Herbert Plenio’s group at Technische Universität Darmstadt during the sabbatical leave. A NHC ligand, 4,5-dichloro-1,3-dimesitylimidazol-2-ylidene (Cl2-IMes), was readily prepared with a one-step synthesis. Two novel complexes [(Cl2-IMes)(Py)2(Cl)2Ru=CHPh] (2a) and [(Cl2-IMes)2(Cl)2Ru=CHPh] (3a) bearing this ligand have been prepared from [(Cl2-IMes)(PCy3)(Cl)2Ru=CHPh] (1a). These complexes efficiently catalyze the RCM reactions leading to tetrasubstituted olefins at 80 ºC in 3 h. The reaction conditions for the RCM reactions were optimized by varying the amount of the catalyst, reaction temperature and time of reaction. The respective complexes 3a display excellent activities in RCM reactions leading to tetrasubstituted olefins
  9. Keywords:
  10. Palladium ; Olefins Epoxidation ; Sulfide Oxidation ; Alcohols ; Oxone ; Oxazine ; Iron Complexes ; Homogeneous Catalyst ; Oxidation Reactions ; Coupling Reactions ; Olefins Methatesis

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