Oxaziridine cleavage with a low-valent nickel complex: competing C–O and C–N fragmentation from oxazanickela(ii)cyclobutanes

Abstract

Reacting the low-valent nickel complex [(dtbpe)Ni](μ-η:η-CH) with oxaziridines was found to form mixtures of imine, amide and aldehyde products. If the N-substituent of the oxaziridine is sufficiently bulky, a short-lived intermediate can be isolated and characterized by X-ray diffraction studies as an oxazanickela(ii)cyclobutane. This is the first well-defined example of N-O oxidative addition of an oxaziridine to a transition metal. Subsequent fragmentation of this oxazanickelacyclobutane forms a complex mixture of products, including a nickel(ii) imido complex, demonstrating that oxaziridines can serve as nitrene precursors. Preliminary mechanistic analysis is consistent with a bimetallic mechanism of fragmentation of the oxazanickelacyclobutane to form the nickel imido and η-aldehyde complexes.

The Importance of Ligand‐Induced Backdonation in the Stabilization of Square Planar d10 Nickel π‐Complexes

“…DFT calculations were performed on each of the species in Table using simplified diphosphine ligands (see Figure SI 07 for details, Supporting Information). Molecular structures derived from B3LYP/def2‐TZVP calculations of the dtbpe complexes, as well as those using a simplified diphosphine ligand (dmpe=1,2‐bis(dimethylphosphino) ethane), yield good agreement with solid‐state molecular structures of 1 – 12 . The effect of decreasing the steric bulk and electron donation in the supporting diphosphine ligand does not affect the general structural trends and conclusions, which are consistent with those observed in the experimental data.…”

“…Molecular structures derived from B3LYP/def2-TZVP calculations of the dtbpe complexes, as well as those using as implified diphosphine ligand (dmpe = 1,2-bis(dimethylphosphino) ethane), 1 yield good agreement with solid-state molecular structures of 1-12. [10,11,22,57,102,103] The effect of decreasing the steric bulk and electron donation in the supporting diphosphine ligand does not affect the generals tructural trendsa nd conclusions, which are consistent with those observed in the experimental data. Furthermore, the spectroscopic features observed in the Ni Kedge XASd ata are well-reproduced using time-dependent (TD) DFT analysis.…”

“…In previous work, we noted that the 31 P{ 1 H} NMR spectroscopic data of a number of (dtbpe)Ni [dtbpe=1,2‐bis(di‐ tert ‐butyl)phosphinoethane] π‐complexes were consistent with typical d 10 Ni 0 complexes (Table ) . In contrast, we also noted that the distorted square planar geometry with significant elongation of the π‐bond was most consistent with a d 8 Ni II formulation, in keeping with the metallaepoxide extreme of the Dewar–Chatt–Duncanson (DCD) model of bonding (Scheme ).…”

“…In previous work, we noted that the 31 P{ 1 H} NMR spectroscopic data of an umber of (dtbpe)Ni [dtbpe = 1,2-bis(di-tertbutyl)phosphinoethane] p-complexes werec onsistent with typical d 10 Ni 0 complexes (Table 1). [10,11,57] In contrast, we also noted that the distorted squarep lanar geometry with significant elongation of the p-bond was mostc onsistentw ith ad 8 Ni II formulation,i nk eeping with the metallaepoxide extreme of the Dewar-Chatt-Duncanson (DCD) model of bonding (Scheme 1). In addition, preliminaryd ensity functional theory (DFT) calculations (vide infra) revealed prohibitively high barriers to rotationo ft he p-ligand (i.e.,8 0-100 kJ mol À1 ), demonstratingt hat these complexes have as trong preference for the square planar geometry despite stericc onstraints.…”

“…Ni(COD) 2 ( 13 ) was purchased from Strem and used as received. Compounds 1 – 2 , 3 , 4 , 5 – 6 , 7 , 8 – 10 , 11 , 12 , 14 , and 15 were prepared according to literature procedures. All other chemicals were purchased from commercial suppliers and used as received.…”