Dataset Information

Direct Comparison of C-H Bond Amination Efficacy through Manipulation of Nitrogen-Valence Centered Redox: Imido versus Iminyl.

ABSTRACT: Reduction of previously reported iminyl radical (ArL)FeCl(•N(C6H4-p-tBu)) (2) with potassium graphite furnished the corresponding high-spin (S = 5/2) imido (ArL)Fe(N(C6H4-p-tBu)) (3) (ArL = 5-mesityl-1,9-(2,4,6-Ph3C6H2)dipyrrin). Oxidation of the three-coordinate imido (ArL)Fe(NAd) (5) with chlorotriphenylmethane afforded (ArL)FeCl(•NAd) (6) with concomitant expulsion of Ph3C(C6H5)CPh2. The respective aryl/alkyl imido/iminyl pairs (3, 2; 5, 6) have been characterized by EPR, zero-field 57Fe Mössbauer, magnetometry, single crystal X-ray diffraction, XAS, and EXAFS for 6. The high-spin (S = 5/2) imidos exhibit characteristically short Fe-N bonds (3: 1.708(4) Å; 5: 1.674(11) Å), whereas the corresponding iminyls exhibit elongated Fe-N bonds (2: 1.768(2) Å; 6: 1.761(6) Å). Comparison of the pre-edge absorption feature (1s ? 3d) in the X-ray absorption spectra reveals that the four imido/iminyl complexes share a common iron oxidation level consistent with a ferric formulation (3: 7111.5 eV, 2: 7111.5 eV; 5: 7112.2 eV, 6: 7112.4 eV) as compared with a ferrous amine adduct (ArL)FeCl(NH2Ad) (7: 7110.3 eV). N K-edge X-ray absorption spectra reveal a common low-energy absorption present only for the iminyl species 2 (394.5 eV) and 6 (394.8 eV) that was assigned as a N 1s promotion into a N-localized, singly occupied iminyl orbital. Kinetic analysis of the reaction between the respective iron imido and iminyl complexes with toluene yielded the following activation parameters: Ea (kcal/mol) 3: 12.1, 2: 9.2; 5: 11.5, 6: 7.1. The attenuation of the Fe-N bond interaction on oxidation from an imido to an iminyl complex leads to a reduced enthalpic barrier [?(?H‡) ? 5 kcal/mol]; the alkyl iminyl 6 has a reduced enthalpic barrier (1.84 kcal/mol) as compared with the aryl iminyl 2 (3.84 kcal/mol), consistent with iminyl radical delocalization into the aryl substituent in 2 as compared with 6.

SUBMITTER: Wilding MJT

PROVIDER: S-EPMC5821126 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Direct Comparison of C-H Bond Amination Efficacy through Manipulation of Nitrogen-Valence Centered Redox: Imido versus Iminyl.

Wilding Matthew J T MJT Iovan Diana A DA Wrobel Alexandra T AT Lukens James T JT MacMillan Samantha N SN Lancaster Kyle M KM Betley Theodore A TA

Journal of the American Chemical Society 20171009 41

Reduction of previously reported iminyl radical (ArL)FeCl(•N(C6H4-p-tBu)) (2) with potassium graphite furnished the corresponding high-spin (S = 5/2) imido (ArL)Fe(N(C6H4-p-tBu)) (3) (ArL = 5-mesityl-1,9-(2,4,6-Ph3C6H2)dipyrrin). Oxidation of the three-coordinate imido (ArL)Fe(NAd) (5) with chlorotriphenylmethane afforded ...[more]

PMID: 28937756

Similar Datasets

Project description:Metalation of the deprotonated dipyrrin (AdFL)Li with NiCl2(py)2 afforded the divalent Ni product (AdFL)NiCl(py)2 (1) (AdFL: 1,9-di(1-adamantyl)-5-perfluorophenyldipyrrin; py: pyridine). To generate a reactive synthon on which to explore oxidative group transfer, we used potassium graphite to reduce 1, affording the monovalent Ni synthon (AdFL)Ni(py) (2) and concomitant production of a stoichiometric equivalent of KCl and pyridine. Slow addition of mesityl- or 1-adamantylazide in benzene to 2 afforded the oxidized Ni complexes (AdFL)Ni(NMes) (3) and (AdFL)Ni(NAd) (4), respectively. Both 3 and 4 were characterized by multinuclear NMR, EPR, magnetometry, single-crystal X-ray crystallography, theoretical calculations, and X-ray absorption spectroscopies to provide a detailed electronic structure picture of the nitrenoid adducts. X-ray absorption near edge spectroscopy (XANES) on the Ni reveals higher energy Ni 1s → 3d transitions (3: 8333.2 eV; 4: 8333.4 eV) than NiI or unambiguous NiII analogues. N K-edge X-ray absorption spectroscopy performed on 3 and 4 reveals a common low-energy absorption present only for 3 and 4 (395.4 eV) that was assigned via TDDFT as an N 1s promotion into a predominantly N-localized, singly occupied orbital, akin to metal-supported iminyl complexes reported for iron. On the continuum of imido (i.e., NR2-) to iminyl (i.e., 2NR-) formulations, the complexes are best described as NiII-bound iminyl species given the N K-edge and TDDFT results. Given the open-shell configuration (S = 1/2) of the iminyl adducts, we then examined their propensity to undergo nitrenoid-group transfer to organic substrates. The adamantyl complex 4 readily consumes 1,4-cyclohexadiene (CHD) via H-atom abstraction to afford the amide (AdFL)Ni(NHAd) (5), whereas no reaction was observed upon treatment of the mesityl variant 3 with excess amount of CHD over 3 hours. Toluene can be functionalized by 4 at room temperature, exclusively affording the N-1-adamantyl-benzylidene (6). Slow addition of the organoazide substrate (4-azidobutyl)benzene (7) with 2 exclusively forms 4-phenylbutanenitrile (8) as opposed to an intramolecular cyclized pyrrolidine, resulting from facile β-H elimination outcompeting H-atom abstraction from the benzylic position, followed by rapid H2-elimination from the intermediate Ni hydride ketimide intermediate.

Dataset Information

Direct Comparison of C-H Bond Amination Efficacy through Manipulation of Nitrogen-Valence Centered Redox: Imido versus Iminyl.

Publications

Direct Comparison of C-H Bond Amination Efficacy through Manipulation of Nitrogen-Valence Centered Redox: Imido versus Iminyl.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure