Browsing by Author "Luo, Zhixiong"

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    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, Zhixiong
    The 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.
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    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, Francis
    We 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.