Browsing by Author "Hamad, Fatma B."
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Item Alkyl Group-Tagged Ruthenium Indenylidene Complexes: Synthesis, Characterization and Metathesis Activity(Elsevier, 2015) Yu, Baoyi; Hamad, Fatma B.; Leus, Karen; Lyapkov, Alex A.; Van Hecke, Kristof; Verpoort, FrancisWe report on the synthesis of ruthenium indenylidene catalysts [RuCl2(3-R-1-indenylidene)(PCy3)2inwhich R is iso-propyl (7a), tert-butyl (7b) or cyclohexyl (7c)]. The obtained alkyl tagged indenylidenecatalysts were analyzed by means of IR, elementa l analysis, NMR and single crystal X-Ray diffractionanalysis. Furthermore, the catalytic performance of these new complexes was examined in dif ferentmetathesis reactions: ring-closing metathesis (RCM), ring-closing ene-yne metathesis (RCEYM), ring-opening metathesis polymerization (ROMP) and cross metathesis (CM), exhibiting a comparable activ-ity in comparison with the commercially available catalyst 3aItem Bidentate Schiff Base Ruthenium Complexes as Precursors of Homogeneous and Immobilized Catalysts(Bentham Science, 2013) Verpoort, Francis; Yu, Baoyi; Hamad, Fatma B.; Velazquez, Heriberto D.; Luo, ZhixiongThe paper presents an overview of the work conducted in our group on the synthesis of a novel class of homogeneous and immobilized Ru-complexes containing Schiff bases as O, N-bidentate ligands benefiting from a versatile, quite general and thoroughly exemplified two-step procedure. The new Ru-complexes with improved stability incorporate a variety of Schiff bases, associated with traditional inorganic and organic ligands such as chloride, phosphanes, arenes, cyclodienes, NHC etc., and different carbenes (alkylidene, vinylidene, allenylidene and indenylidene). By a proper choice of the Schiff base, useful physical and chemical properties of the derived Ru-complexes could be induced resulting in tunable catalytic activity for metathesis and related processes. A pertinent example is the latency of selected Schiff base Ru catalysts which by becoming active only under specific conditions (heat or acid activation) are ideal for industrial applications, e.g. reaction injection molding processes. The synthetic approaches that are critically discussed in this chapter have led to a diversity of Ru-complexes of which several members have risen to the rank of commercial catalysts.Item Effect of the Bulkiness of Indenylidene Moieties on the Catalytic Initiation and Efficiency of Second-Generation Ruthenium-Based Olefin Metathesis Catalysts(2016) Yu, Baoyi; Luo, Zhixiong; Hamad, Fatma B.; Leus, Karen; Van Hecke, Kristof; Verpoort, FrancisWe report on the synthesis and characterization of the second generation of ruthenium catalysts bearing various sized indenylidene ligands, denoted as RuCl2(3-(2,6-xylyl)-1-indenylidene)(SIMes)(PCy3) 5a, RuCl2(4-methyl-3-(o-tolyl)-1- indenylidene)(SIMes)(PCy3) 5b, RuCl2(3-1-naphthyl-1-indenylidene)(SIMes)(PCy3) 5c and RuCl2(3-(p-fluorophenyl)-1- indenylidene)(SIMes)(PCy3) 5d. The obtained complexes were characterized by NMR, IR, HRMS and elemental analysis. Moreover, the configurations of complexes 5a, 5b and 5d were confirmed by single-crystal X-ray diffraction analysis. The catalytic performance of the obtained complexes 5a-d were evaluated in several olefin metathesis reactions: the RCM of substrates 6 and 7, the RCEYM of substrate 8 and the ROMP of COD in comparison with the commercially available catalyst 3a. Careful analysis of the catalysts performance and single-crystal X-ray diffraction data of the obtained complexes reveals that the steric modification on the 3-phenyl group can have an obvious influence on the ligands congestion around the ruthenium center and hence, alters the catalytic activities in metathesis reactions. Additionally, the better performing complex 5a was further investigated in the RCM of substrate 6 in comparison with complex 3c and bench mark complexes 1b, 2 and 3a.Item Novel Ruthenium Indenylidene Catalysts: From Homogeneous to Heterogeneous(2013) Hamad, Fatma B.Nowadays a number of ruthenium metathesis catalysts have been developed owing to their accessibility, remarkable activity and selectivity, connected with good tolerance towards functional groups, air and moisture. Innovative development in the class of ruthenium metathesis catalysts coordinated with NHC has been experienced which mainly directed toward tuning their catalytic activity and selectivity through altering both steric and electronic properties. The unsymmetrical NHC ligands in particular, have been introduced to induce dissymmetry, a key for achieving higher level of selectivity in different reactions. A great number of the ruthenium complexes bearing unsymmetrical NHC ligands have been developed up to this moment. The bis-coordinated ruthenium indenylidene developed in this work showed moderate activity at higher temperature in RCM, ROMP and other kind of reactions such as isomerization of allylic alcohols and isomerization of alkenes. Failure of these catalysts to work at room temperature has been attributed to the lack of labile ligand.This call for further research which will focus on tuning of unsymmetrical NHC ligands to achieve more active and selective ruthenium complexes coordinated with non-labile NHC ligand with the labile one. The research should go in hand with design and synthesis of heterogeneous catalysts that can be recovered from the reaction mixture and be recycled. Although the support materials used in this study proved to be not suitable for metathesis, the obtained results can be considered as a challenge in the journey toward designing stable and active heterogeneous ruthenium indenylidene catalysts. Up to now a number of solid materials have been developed and successfully utilized in the immobilization of ruthenium benzylidene complexes. It is expected that the same materials can act as the suitable supports for ruthenium indenylidene and therefore, a study about development heterogeneous ruthenium indenylidene analogs would be of great interest.Item Olefin Metathesis Ruthenium Catalysts Bearing Unsymmetrical Heterocylic Carbenes(Elsevier, 2013) Hamad, Fatma B.; Sun, Taolei; Xiao, Shengqiang; Verpoort, FrancisCatalytic olefin metathesis has become a powerful tool for carbon–carbon bond formation in organic and polymer chemistry. The Grubbs’ 1st generation catalyst 1 constitutes a highly efficient metathesis catalyst tolerating a wide variety of functional groups. The introduction of N-heterocyclic carbenes (NHCs) as ligands has afforded the more stable and active 2nd generation ruthenium catalyst 2. Several ruthenium metathesis initiators of the 2nd generation type have been prepared from various NHCs. Altering the steric and electronic properties of the ligand can control the activity and selectivity of the NHC coordinated catalysts. One of the reported modifications for the NHC-containing ruthenium metathesis initiators is the application of unsymmetrical NHC ligands. The unsymmetrical nature of these ligands may lead to the selective catalysts in different metathesis reactions. This survey highlights the developments in ruthenium catalysts coordinated with unsymmetrical NHC ligands and their trends in activity and selectivity on olefin metathesis. The discussion includes the description of ruthenium initiators coordinated with N-aryl-N′-alkyl NHCs, N-aryl-N′-aryl NHCs, and those coordinated with two unsymmetrical NHCs. Ruthenium complexes bearing chiral NHCs, cyclic (alkyl) (amino) carbenes (CAACs) as well as thiazol-2-ylidene ligands are also described.Item Ruthenium Indenylidene Complexes Bearing N-Alkyl/N-Mesityl-Substituted N-Heterocyclic Carbene Ligands(2015) Yu, Baoyi; Hamad, Fatma B.; Sels, Bert; Van Hecke, Kristof; Verpoort, FrancisWe report on the synthesis and characterization of second generation ruthenium indenylidene catalysts bearing unsymmetrical N-heterocyclic carbene (NHC) ligands denoted as RuCl2(3-phenyl-1-indenylidene)(1-mesityl-3-R-4,5-dihydroimidazol-2-ylidene)(PCy3), in which R is methyl , octyl or cyclohexyl . The characterization of was performed by NMR spectroscopy, elemental analysis, IR, HRMS and single-crystal X-ray diffraction analysis. In addition, the catalytic activity of the obtained initiators was evaluated in various representative metathesis reactions. The results reveal that the complexes , bearing an N-alkyl side on the NHC, show a faster catalytic initiation than the reference complex . Complex , which performs the best among the investigated indenylidene complexes, exhibits slower initiation but better overall efficiency than its benzylidene analogue , especially in a low catalyst loading.Item Solid Supported Ruthenium Complexes for Olefin Metathesis(2013) Hamad, Fatma B.; Kai, Cheng; Cai, Yuan; Xie, Yu; Lu, Yin; Ding, Fu; Sun, Yaguan; Verpoort, FrancisImmobilization of ruthenium metathesis catalysts on solid supports has attracted much attention in recent years since it opens up the possibility for easy catalyst–product separation and catalyst reuse as well as reduction of the residual ruthenium content in the organic product. The state of the art on immobilization of ruthenium based metathesis initiators on solid supports is surveyed in this review. In addition, a comparison of the performance of the heterogenized catalysts with homogeneous analogues is made.Item Synthesis and Characterization of Non-Chelating Ruthenium–Indenylidene Olefin Metathesis Catalysts Derived From Substituted 1,1-Diphenyl-2-Propyn-1-Ols(2015) Yeates, Baoyi; Xie, Yu; Hamad, Fatma B.; Leus, Karen; Lyapkov, Alex A.; Van Hecke, Kristof; Verpoort, FrancisWe report on the synthesis and characterization of the first generation of modified non-chelating indenylidene ruthenium catalysts denoted as RuCl2(4-methyl-3-(o-tolyl)-1-indenylidene)(PCy3)2 5a, RuCl2(3-(p-fluorophenyl)-1-indenylidene)(PCy3)2 5b, RuCl2(3-(2,6-xylyl)-1-indenylidene)(PCy3)2 5c and RuCl2(3-(1-naphthyl)-1-indenylidene)(PCy3)2 5d. The obtained complexes of 5a–d were characterized by means of NMR spectroscopy and elemental analysis. Moreover the structures of 5a–d were confirmed by single-crystal X-ray diffraction and compared with the standard ruthenium indenylidene complex 3 and the chelating benzylidene complex 2. Additionally, the catalytic performances of the obtained complexes 5a–d were evaluated in various metathesis reactions demonstrating that the ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions revealed a similar catalytic activity in comparison with the reference indenylidene catalyst 3.