Copper Complexes with N-Alkylated NS2-Macrocyclic Ligands: Synthesis, Characterization, and Capabilities as Aziridination Precatalysts

Abstract

The syntheses of two new ligands containing macrocyclic [10]-aneNS2 (1-aza-4,8-dithiacyclodecane) units are reported, including the N-methylated analogue (LMe) and a dinucleating version that separates two [10]-aneNS2 groups with a m-xylyl spacer (L2). Copper complexes with these new ligands as well as previously reported related complexes have been found to mediate the aziridination of olefins. Thus, isolated copper complexes containing the ethylnaphthyl-appended [10]-aneNS2 macrocyclic ligand (Lnap), including [LnapCu]PF6 (1) and [LnapCu(CH3CN)]PF6 (2), the Cu(I) complex [LMeCu(CH3CN)]PF6 (3), and the Cu(II) complex LMeCuBr2 (4), were compared in their ability to function as aziridination precatalysts. In addition, the aziridination capabilities were probed for complexes generated in situ from copper(I) ion sources and L2, 1,4,7-triazacyclononane, 1,4,7-trithiacyclononane, or 1,4,7-trimethyl-1,4,7-triazacyclononane. The synthesis and characterization of the new complexes 3 and 4 are reported, including X-ray crystal structures. The aziridination reaction using precatalyst 3 was examined for its tolerance to different functional groups near the olefin as well as to the use of other nitrogen group sources and reaction conditions.