ESR experiments on an X-irradiated single crystal of enantiomerically pure bis(2,4,6-tri-tert-butylphenyl)phosphinic chloride (Ar,P(O)CI) reveal the formation of the corresponding phosphoryl radical (la, Ar2PO) via a dissociative electron-capture reaction of the PCI bond. At 120 K, this radical exhibits an exclusive and enantioselective stereoinversion in the single-crystal matrix leading to the phosphoryl radical structure lb. This process was monitored in detail using anisotropic ESR spectroscopy combined with X-ray crystallographic data. An analysis of the nonbonded steric interactions demonstrates that the stereoinversion is controlled intramolecularly and occurs in a synchronous reorientation of the PO bond and two methyl groups of the ortho tert-butyl substituents. Besides the stereoinversion, other radical reactions are observed in the crystal matrix. Ab initio quantum chcmical calculations are employed to assess the electronic structure of the phosphoryl radical in more detail. An ROHF/6-31G* gcomctry optimization within C, symmetry constraints yields two equilibrium structures which basically differ by their PO bond length (1.478 and 1.616 A). The two geometries correspond to the canonical valence bond structures: H2P+-O-and HIP-0, respectively. Calculated 3iP hyperfine interactions of the H2P+-O-equilibrium structure are in good agreement with expcrimcnt.( 5 ) Yoshifuji, M.; Shima, 1.; Inamoto, N.; Hirotsu, K.; Higuchi, T.
A convenient methodology has been developed for the solidphase synthesis of a cyclic NGR-functionalized Gd III DTPA complex employing an isocyanate-functionalized DTPA pentaester. This methodology is an alternative strategy for
de, B. F. M. (1991). Radical cations of bis(diphenylphosphino) derivatives (Ph2P-R-PPh2): the formation of localized, cyclic, and dimeric configurations; an ESR and quantum chemical study. Journal of Physical Chemistry, 95(23), 9256-9263. DOI: 10.1021/j100176a042 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Phys. Chem. 1991, 95, 9256-9263 binations and overtones) of a free pseudorotor can become very complicated. ConclusionsWe have carried out calculations to provide a descriptive picture of the energy level patterns expected for the ring-puckering vibrations of spiro compounds. Since the spectra of these molecules are expected to be complicated, it is necessary to have a basic understanding of how these levels will change as a function of the interaction between the two rings (Le., the magnitude of the c coefficient).Since the vapor pressures of most spiro compounds are quite low, it is necessary in most cases to heat the samples in order to record their vapor-phase far-infrared spectra. We have constructed a special sample cell to do this and are initiating this work. 5600 MB Eindhoven, The Netherlands (Received: March 19, 1991) A matrix ESR study on radiogenic radical cations of Ph2P-R-PPh, derivatives with various linkers (R) is presented. The experiments show that in a frozen dichloromethane solution the radical cations can adopt localized (Ph2PR+), cyclic (Ph2P-R-PPh2'+), and dimeric (Ph2RP:PRPh2+) configurations, depending on the nature of the linker. The cyclic and dimeric products are formed in the reaction of a localized cation with a second free-electron pair, resulting in an intra-or intermolecular three-electron PLP u* bond, respectively. The formation of the cyclic structure, with a strongly bent PLP u* bond, requires a specific proximate position of the two phosphine moieties in the precursor molecule. The mutual orientation of the two free-electron pairs of the precursors is assessed by NMR via the nJpp spin-spin coupling constant. Ab initio UHF quantum chemical calculations at the 3-21G*/SCF level support the assignments. Acknowledgment
Molecular mechanics calculations, using the AMBER program (version 3.0), are presented on the radiogenic electron‐capture radical formation in the crystalline chiral organophosphorus compounds (2R,4S,5R) and (2S,4S,5R) 2‐chloro‐3,4‐dimethyl‐5‐phenylphospholidine 2‐sulfide (respectively 1 and 2). Geometry optimization of the corresponding radical anion structures and their respective crystal surroundings reveals an increase of the Van der Waals interactions, which is significantly larger in compound 2 than in 1. This is in good agreement with previous single‐crystal ESR experiments and molecular interactions calculations without geometry optimization [1].
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