Applications of Macrocyclic Ligands in C-H Activation and Olefin Aziridination Reactions
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The cyclic tridentate ligand [2.1.1]-(2,6)-9,16-dioxapyridinophane (O2-L), in analogy to the previously reported macrocycle [2.1.1]-(2,6)-pyridinophane (L), has been prepared for potential applications in C-H activation/functionalization. Studies of the d8 complex (O2-L)PdCl2 reveals that only two of the three nitrogen atoms in O2-L bind to the metal; the Pd atom migrates quickly between the two nitrogen atoms tethered by the ethylene linkage at room temperature. The complex (O2-L)Cu+ exhibited outstanding performance in promoting direct aziridination reactions, furnishing aziridines from olefins and PhINTs in near-quantitative yields in the absence of bulky substituents attached to the olefin C=C bonds. The complex [LPtIVH2Me]+ was found to cleave CH bonds of disubstituted benzenes with exceptional regioselectivity, as a result of the reaction’s sensitivity to sterics. Mechanistic studies suggest that the dissociation of an alkane or arene molecule from the PtII-alkane/arene σ-complex requires high activation energy and is rate-limiting.