No abstract

Site-selective chlorination of benzylic C–H bonds is achieved using a CuICl/bis­(oxazoline) catalyst with N-fluorobenzenesulfonimide as the oxidant and KCl as a chloride source. This method exhibits higher benzylic selectivity, relative to established chlorination protocols, and is compatible with diverse alkyl arenes. Sequential benzylic C–H chlorination/nucleophilic substitution affords C–O, C–S, and C–N coupling products with oxidatively sensitive coupling partners.

the latter surrounded by six oxygen atoms arranged at the vertices of a distorted octahedron. One of the six 0 atoms is an atom from the bromite anion (see Figure l ) , and the remainder are water molecules. The stoichiometry requires that some of the water molecules be associated with more than one octahedron, and zigzag chains of edge-linked octahedra are present in the solid. The compound is isomorphous with the corresponding chlorine compound,22 and Br-0 distances of 1.731 (2) and 1.702 (2) A may be compared with CI-0 distances of 1.564 (1) and 1.557 (1) A.The anion, as expected, is a bent species with a bond angle (0-Br-0 = 105.3 (1)O) comparable with the 0-(21-0 angle (108.23 (6)') in NaC102.3H20.22 The Br-0 distances in the oxoanions decrease with increasing bromine oxidation state, and the present values can be compared with the Br-0 distances in NaBr0323(1.648 (4) A) and KBr0424 (1.59 (1)-1.62 (1) A).Bromine K-edge EXAFS data were obtained for solid NaBr-O2.3H20 diluted with boron nitride and for saturated aqueous solutions. The k3 weighted data obtained after background subtraction were used for curve fitting without smoothing or Fourier filtering, and the background-subtracted data and the corresponding Fourier transform for solid NaBr02.3H20 are shown in Figure 2. The fitting employed the single scattering curved wave theory as contained in the EXCURVE program and utilized ab initio phase shifts calculated in the usual manner.'* Analysis of the data from solid-state samples gave an average Br-O distance of 1.75 A,25 and no further shells arising from other neighboring atoms are statistically significant. In solution, a Br-O bond length of 1.72 A25 was obtained. Both values compare well with the bond lengths obtained from the X-ray study and suggest that EXAFS results for related compounds of uncertain structure may be viewed with confidence. Acknowledgment.(25) Systematic errors in data collection and analysis give rise to errors of ca. f0.02-0.03 A in the first shell distances. NaBr02+3H20: 2u2 = 0.013 A, FI = 0.04, R = 11.9. NaBr02 aqueous solution ' 2u2 = 0.009 A, FI = x 100. 0.20, R = 11.4. FI = xi (x: -xi k )k?. R = [Ilx4'-xElk' dk/.fIXEl dk]Abstract: We present the application of molecular mechanics/dynamics and free energy perturbation computational techniques to simulation of iron(I1) porphyrin systems. Force field parameters were developed by modeling the geometry of four systems whose crystal structure is known. This force field was then used in molecular dynamics/free energy perturbation calculations, at 300 K in vacuo, on a separate set of four iron(I1) porphyrin systems including models of 5,Spyridine cyclophane heme( 1,5-DCI) (I), picket fence heme(2-MeIm) (11), monochelated heme (111), and 7,7-durene cyclophane heme( 1,5-DCI) (IV). The perturbation calculations reproduced reasonably well the trend in the partition coefficient, M value, of this set. Our simplified model indicates that the electrostatic component of both I and I1 favors the binding of O2 over CO, whereas the electrostatic...

We report the synthesis and reactivity of Zr complexes supported by a 9,10-anthracenediyl-linked bisphenoxide ligand, L. ZrIVLBn2 (1) undergoes facile photolytic reduction with concomitant formation of bibenzyl and ZrIVL­(THF)3 (2), which displays a two-electron reduced anthracene moiety. Leveraging ligand-stored reducing equivalents, 2 promotes the oxidative coupling of internal and terminal alkynes to isolable zirconacyclopentadiene complexes, demonstrating the reversible utilization of anthracene as a redox reservoir. With diphenylacetylene under CO, cyclopentadienone is formed stoichiometrically. 2 is competent for the catalytic formation of pyrimidines from alkynes and nitriles. Mechanistic studies suggest that selectivity for pyrimidine originates from preferred formation of an azazirconacyclopentadiene intermediate, which reacts preferentially with nitriles over alkynes.

The protein contribution to the relative binding affinity of the ligands CO and O2 toward myoglobin (Mb) has been simulated using free energy perturbation calculations. The tautomers of the His E7 residue are different for the oxymyoglobin (MbO2) and carboxymyoglobin (MbCO) systems. This was modeled by performing two‐step calculations that mutate the ligand and mutate the His E7 tautomers in separate steps. Differences in hydrogen bonding to the O2 and CO ligands were incorporated into the model. The O2 complex was calculated to be 2–3 kcal/mol more stable than the corresponding CO complex when compared to the same difference in an isolated heme control. This value agrees well with the experimental value of 2.0 kcal/mol. In qualitative agreement with experiments, the Fe‐C‐O bond is found to be bent (θ = 159.8°) with a small tilt (ϕ = 6.2°). The contributions made by each of the 29 residues — within the 9.0‐Å radius of the iron atom — to the free energy difference are separated into van der Waals and electrostatic contributions; the latter contributions are dominant. Aside from the proximal histidine and the heme group, the residues having the largest difference in free energy in mutating MbO2 → MbCO are His E7, Phe CD1, Phe CD4, Val E11, and Thr E10.