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Fluorous biphasic catalysis: synthesis and characterization of copper(I) and copper(II) fluoroponytailed 1,4,7-Rf-TACN and 2,2'-Rf-bipyridine complexes--their catalytic activity in the oxidation of hydrocarbons,olefins, and alcohols,including mechanistic implications
Authors:Contel María  Izuel Cristina  Laguna Mariano  Villuendas Pedro R  Alonso Pablo J  Fish Richard H
Institution:Instituto de Ciencia de Materiales de Aragón Departamento de Química Inorgánica Universidad de Zaragoza-C.S.I.C, 50009 Zaragoza, Spain. mcontel@posta.unizar.es
Abstract:In this contribution on fluorous biphasic catalysis (FBC), we present the synthesis and characterization of new copper complexes, and define their role, as precatalysts, in the FBC oxidation of hydrocarbons, olefins, and alcohols. Thus the previously reported, but poorly characterized, fluoroponytailed ligand, 2,2'-R(f)-bipyridine (R(f)=-(CH(2))(3)C(8)F(17)) 2, as well as the new Cu(II) fluoroponytailed carboxylate synthon complex Cu(C(8)F(17)(CH(2))(2)CO(2))(2)] 3, will be addressed. Moreover, the reaction of previously described ligands, 1,4,7-R(f)-TACN 1, or 2,2'-R(f)-bipyridine 2 with 3 afforded new perfluoroheptane-soluble Cu(II) complexes, Cu(C(8)F(17)(CH(2))(2)CO(2))(2)(R(f)-tacn)] 4 and Cu(C(8)F(17)(CH(2))(2)CO(2))(2)(R(f)-bpy)] 5, respectively. The reaction of 1 with Cu(CH(3)CN)(4)]PF(6) or CuCl] provided new Cu(I) complexes, which could be isolated and fully characterized as Cu(R(f)-tacn)X']X, in which X=PF(6) (6) or X'=Cl (7) (soluble in perfluoroheptane). The Cu(II) and Cu(I) complexes, 4-7, were characterized by elemental analysis, mass spectrometry, and IR, diffuse reflectance UV/Vis, and EPR spectroscopies; complex 7 was also characterized by (1)H and (19)F(1)H] NMR spectroscopy. Complexes 4 and 5, as well as 6 and 7 generated in situ, were evaluated as precatalysts for hydrocarbon and olefin functionalization. The oxidation reactions of these substrates in the presence of the necessary oxidants, tert-butyl hydroperoxide (TBHP) and oxygen gas, proceeded under FBC conditions for 5, 7, and Cu(I) salts with 2. However, the complexes with ligand 2 could not be recycled, owing to significant ligand dissociation. The Cu(II) complex 4, with the ligand 1, provide the oxidation of 4-nitrobenzyl alcohol to 4-nitrobenzaldehyde under single-phase FBC conditions at 90 degrees C with TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy) and O(2); the precatalyst 4, can be utilized for an additional four catalytic cycles without loss of activity. Plausible mechanisms concerning these FBC oxidation reactions will be discussed.
Keywords:biphasic catalysis  copper  mechanisms  N ligands  oxidation
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