The structurally characterized copper complex [(i-Pr3TACN)Cu(O2CCF3)2] (1) mediates nitrene transfer from PhINTs to olefins to form N-tosylaziridines in good to excellent yields, in catalytic amounts (0.5 mol %) 1 order of magnitude less than is required for other copper catalysts, such as [Cu(acac)2]. Nitrene transfer reactivity has also been observed with substituted styrenes, internal and terminal aliphatic olefins, and sulfides, suggesting that 1 may be a general nitrene transfer catalyst for use on organic synthesis.

We have synthesized and characterized, using X-ray crystallographic, spectroscopic, and computational techniques, a six-coordinate diazide Fe 3+ complex, LFe(N 3 ) 2 (where L is the tetradentate ligand 7-diisopropyl-1,4,7-triazacyclononane-1-acetic acid), that serves as a model of the azide adducts of Fe 3+ superoxide dismutase (Fe 3+ SOD). While previous spectroscopic studies revealed that two distinct azide-bound Fe 3+ SOD species can be obtained at cryogenic temperatures depending on protein and azide concentrations, the number of azide ligands coordinated to the Fe 3+ ion in each species has been the subject of some controversy. In the case of LFe(N 3 ) 2 , the electronic absorption and magnetic circular dichroism spectra are dominated by two broad features centered at 21 500 cm −1 (ε ≈ 4000 M −1 cm −1 ) and ~30 300 cm −1 (ε ≈ 7400 M −1 cm −1 ) attributed to N 3 − → Fe 3+ charge transfer (CT) transitions. A normal coordinate analysis of resonance Raman (RR) data obtained for LFe(N 3 ) 2 indicates that the vibrational features at 363 and 403 cm −1 correspond to the Fe-N 3 stretching modes (ν Fe-N3 ) associated with the two different azide ligands and yields Fe-N 3 force constants of 1.170 and 1.275 mdyne/Å, respectively. RR excitation profile data obtained with laser excitation between 16 000 and 22 000 cm −1 reveal that the ν Fe-N3 modes at 363 and 403 cm −1 are preferentially enhanced upon excitation in resonance with the N 3 − → Fe 3+ CT transitions at lower and higher energies, respectively. Consistent with this result, density functional theory electronic structure calculations predict a larger stabilization of the molecular orbitals of the more strongly bound azide due to increased σ-symmetry orbital overlap with the Fe 3d orbitals, thus yielding higher N 3 − → Fe 3+ CT transition energies. Comparison of our data obtained for LFe(N 3 ) 2 with those reported previously for the two azide adducts of Fe 3+ SOD provides compelling evidence that a single azide is coordinated to the Fe 3+ center in each protein species.© 2008 American Chemical Society * Author to whom correspondence should be addressed. brunold@chem.wisc.edu. Supporting Information Available: Cartesian coordinates of crystal-structure and DFT geometry-optimized LFe(N 3 ) 2 models, INDO/S-CI calculated ZFS parameters for all models of LFe(N 3 ) 2 , DFT predicted MO energies and compositions for LFe(N 3 ) 2 models, TD-DFT calculated electronic excitation energies, Abs and MCD data of LFe(N 3 ) 2 collected at 4.5 K, and analysis of VTVH MCD data collected at 20 661 cm −1 . This material is available free of charge via the Internet at