Browsing by Author "Valderrama, Mauricio"
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Item New bis(azolylcarbonyl)pyridine chromium(III) complexes as initiators for ethylene polymerization(Inorganica Chimica, 2011) Hurtado, John; Ugarte, Javiera; Rojas, René; Valderrama, Mauricio; Carey, Desmond Mac-Leod; Muñoz-Castro, Alvaro; Arratia-Pérez, Ramiro; Fröhlich, RolandReaction of 2,6-pyridinedicarbonyl dichloride with 3,5-dimethylpyrazole and 1H-indazole, respectively, yield the tridentate ligands 2,6-bis(3,5-dimethylpyrazol-1-ylcarbonyl)pyridine (1) and 2,6-bis(indazol-1-ylcarbonyl)pyridine (2). The molecular structure of the new compound (2) was determined by single-crystal X-ray diffraction. These ligands react with CrCl3(THF)3 in THF to form neutral complexes of general formula [CrCl3{2,6-bis(azolylcarbonyl)pyridine-N,N,N}] (3, 4) which were isolated in high yield as air stable green solids and characterized by elemental analysis, magnetic moment, IR, and mass spectroscopies. Theoretical calculations predict that the thermodynamically preferred structure of the complexes is the fac configuration. After reaction with methylaluminoxane (MAO) the chromium(III) complexes are active for the polymerization of ethylene.Item Synthesis, characterization and reactivity studies in ethylene polymerization of cyclometalated palladium(II) complexes containing terdentate ligands with a N,C,N-donor set(Journal of Coordination Chemistry, 2009) John, Hurtado; Portaluppi, Mariana; Quijada, Raúl; Rojas, René; Valderrama, MauricioThe reaction of [Na2PdCl4] with 3,5-bis(2-pyridoxy)toluene (LpyH) in acetic acid yields the cyclometalated complex [PdCl(Lpy-N, C, N)] (1). Complex 1 can be further converted into neutral species by metathesis reaction exchange of chloride by either iodide or thiocyanate to yield [PdX(Lpy-N, C, N)] (X = I (2), SCN (3)). The chloride can be replaced by neutral ligands like pyridine or acetonitrile in the presence of silver tetrafluoroborate to give the corresponding cationic compounds [PdL(Lpy-N, C, N)]BF4 (L = Py (4), MeCN (5)). In contrast, the reaction of [Na2PdCl4] with 3,5-bis(3, 5-dimethylpyrazol-1-ylmethyl)toluene (LpzH) under analogous conditions yields the neutral complex [PdCl2(LpzH-N, N)](6) with the ligand bidentate N,N-donor. The cyclometalated palladium complex [PdCl(Lpz-N, C, N)] (7) was prepared by the reaction of Pd(OAc)2 with LpzH in acetic acid followed by a metathetic reaction with lithium chloride in acetone/water. Complexes 1, 6, and 7 in the presence of methylaluminoxane (MAO) lead to an active catalyst for the polymerization of ethylene.