An Expedient Synthesis of Perfluorinated Tetraazamacrocycles: New Ligands for Copper‐Catalyzed Oxidation under Fluorous Biphasic Conditions

Abstract

Conjugate additions of cyclam to perfluorohexyl vinyl sulfone and sulfoxide, which act as efficient fluorous Michael acceptors, readily give access to new fluoro-ponytail tetraazamacrocycles in good yields. The solubility of the N-tetrasubstituted macrocycles depends dramatically on the nature of the polar function (SO or SO2): the sulfoxide cyclam derivative is soluble in perfluorodecaline (pfd) and perfluoromethylcyclohexane (pfmc) while the sulfonyl derivative is almost insoluble in organic or fluorous solvents. In agreement with the well known affinity of cyclam for copper(II) ions, stable copper complexes of the fluorous macrocyclic ligands have been isolated and characterized. In chloroform/methanol, complexes with four perfluorinated tails have been obtained from reaction of the tetra-N-perfluorohexylsulfinyl-substituted macrocycle with copper nitrate and copper perfluorocarboxylate. In trifluoroethanol, a selective retro-Michael reaction has been observed and the same reaction specifically gives copper complexes of the tri-N-substituted macrocycle. Complexes with three and four fluorous tails associated with perfluorocarboxylate counteranions are soluble in fluorous solvents (pfd and pfmc). These copper complexes were tested as catalysts for the oxidation of cyclohexene by molecular oxygen in the presence of tert-butyl hydroperoxide (tbhp). The oxidation reactions proceed under fluorous biphasic conditions and the catalyst can be recovered and reused. Quenching experiments indicate that cyclohexenyl hydroperoxide is the main oxidation product of the reaction performed with or without tbhp. Interestingly, these perfluorinated copper complexes are good, recyclable catalysts for the oxidation of cyclohexene by molecular oxygen without tbhp at room temperature and 65 °

New Trends in Oxidative Functionalization of Carbon–Hydrogen Bonds: A Review

“…Consequently, the reaction proceeds without the participation of free radicals, unless it was proposed, for example, for an oxidation with hydrogen peroxide via hydroxyl radicals The so-called Shul'pin method [257][258][259] of analysis of oxygenates discussed above in this section and based on GC and PPh 3 has been used by other authors (selected examples are given in Refs. [260][261][262][263][264][265][266][267][268][269][270][271][272][273][274][275][276][277][278]). Finally, if the GC analysis shows that there is no difference between chromatograms obtained before and after reduction with PPh 3 , it indicates that the samples do not contain alkyl hydroperoxides.…”

Macrocyclic coordination chemistry

“…119 Tetra-N-perfluorohexyl sulfinyl substituted cyclam was synthesised to solubilise cyclam complexes in perfluorinated solvents and to allow formation of copper complexes to act as oxidation catalysts under fluorous biphasic conditions, the copper complex successfully catalysed the oxidation of cyclohexene by molecular oxygen both in the presence and absence of tert-butyl hydroperoxide. 120 Abbreviations [12]…”

Fluorous biphase oxidation of ethyl benzene and benzyl alcohol catalyzed by perfluoroalkyl phthalocyanine complexes

“…This method allows a facile separation of the catalyst from the product as the catalyst is insoluble in the organic solvents. In addition, the high solubility of oxygen in fluorous fluids is beneficial in oxidation reactions 22–26…”