Fluorous Biphasic Catalysis: Synthesis and Charactreization of Copper(I) and Copper(II) Fluoroponytailed 1,4,7-R_f-TACN and 2,2'-R_f-Bipyridine Complexes-Their Catalytic Activity in the Oxidation of Hydrocarbons, Olefins, and Alcohols, Including Mech

摘要

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)_3C_8F_17) 2, as well as the new Cu~(II0 fluoroponytailed carboxylate synthon complex [Cu(C_8F_17(CH_23)_2CO_2)_2] 3, will be addressed. Moreover, the rection 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_8F_17(CH_2)_2CO_2)_2(R_f-tacn)] 4 and [Cu(C_8F_17(CH_2)_2CO_2)_2(R_f-bpy)] 5, respectively. The reaction of 1 with [Cu(CH_3CN)_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 spectroscopic; complex 7 was also characterized by ~1H and ~19F{~1H} NMR spectroscopy. Compounds 4 and 4, 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 deg C with TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy) and O_2; the precatalyst 4, ca nbe utilized for an additional four catalytic cycles without loss of activity. Plausible mechanisms concerning these FBC oxidation reactions will be discussed.