Synthesis, Structure, and Highly Efficient Copper‐Catalyzed Aziridination with a Tetraaza‐Bispidine Ligand

Abstract

The distorted trigonal-bipyramidal Cu(II) complex [Cu(L(1))(NCCH(3))](2+) of the novel tetradentate bispidine-derived ligand L(1) with four tertiary amine donors (L(1)=1,5-diphenyl-3-methyl-7-(1,4,6-trimethyl-1,4-diazacycloheptane-6-yl)diazabicyclo[3.3.1]nonane-9-one) is a very efficient catalyst for the aziridination of olefins in the presence of a nitrene source. In agreement with the experimental data (in situ spectroscopy, product distribution, and its dependence on the geometry of the substrate and of the nitrene source), a theoretical analysis based on DFT calculations indicates that the active catalyst has the Cu center in its +II oxidation state, that electron transfer is not involved, and that the conversion of the olefin to an aziridine is a stepwise process involving a radical intermediate. The striking change of efficiency and reaction mechanism between classical copper-bispidine complexes and the novel L(1)-based catalyst is primarily attributed to the structural variation, enforced by the ligand architecture.

Dioxygen Reactivity of New Bispidine-Copper Complexes

“…As expected from the rigid ligand cavity and earlier structural analyses, 16, 25 no isomerism in the ligand binding mode is apparent. 21 The vibrational frequency of the carbonyl group in the IR spectrum of [Cu I (L 2 )(CO)][B(C 6 F 5 ) 4 ] is at 2100 cm −1 , i.e.…”

“…16, 25 Due to the relatively small N-Cu-N angle, enforced by the diazaheptane cycle, the Cu II complexes have a “ d x2-y2 ground state” (i.e., the unpaired electron is in d x2-y2 ; in axial tbp symmetry the unpaired electron instead is in d z2 ), and this is reflected in their EPR spectra. 29 That of [Cu II (L 2 )(OH 2 )] 2+ is very similar to the spectrum of the L 1 -based bispidine Cu II complex (see Table 1).…”

“…L 1 and [Cu II (L 1 )(NCCH 3 )](BF 4 ) 2 were described before. 25 NMR spectra were recorded at 200.13 MHz ( 1 H) and 50.33 MHz ( 13 C) on a Bruker AS-200 or a Bruker DRX-200 instrument with the solvent signals used as reference. IR spectra were recorded with a Perkin Elmer Spectrum 100 FT-IR spectrometer instrument from KBr pellets.…”

Novel RuII Complexes with Bispidine‐Based Bridging Ligands: Luminescence Sensing and Photocatalytic Properties

“…[20,21] Some show outstanding catalytic properties in processes such as the Cu-catalyzed aziridination [22][23][24] and the Cu-and Feinduced oxygen activation. [25][26][27][28] Consequently, we have considered bispidine subunits as prospective building blocks for covalent bonding to a photoactive Ru II -bipyridine site.…”

Optimization of Hexadentate Bispidine Ligands as Chelators for 64CuII PET Imaging

“…Among other reasons, these arise from the rigid adamantane‐derived backbone—preorganized and complementary for tetragonally distorted octahedral geometries—that is well suited and selective for binding Cu II ; it is also for this reason that bispidines have been described as a favorable ligand platform for medicinal applications . In addition to radiopharmaceutical chemistry, applications of Cu–bispidines include aziridination catalysis, and hemocyanine and catecholase biomimetic chemistry …”