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Articles
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methods
Full experimental procedures, computational details and experimental data are
provided in the Supplementary Information.
General. DFT calculations of the 1,2- and 1,4-boryl migration pathways were
conducted in dichloromethane and acetonitrile, respectively, at the IEFPCM29/
B3LYP/6-311+G(d,p) level of theory using Gaussian 0930, and the output
was visualized with Gauss View v5.0.8. The structures resulting from these
calculations were confirmed to be minima by the presence of only real vibrational
frequencies, whereas all transition states had only one imaginary frequency.
Thermochemical quantities were evaluated at 298.15 K (1,2-boryl migration) and
328.15 K (1.4-boryl migration) and the intrinsic reaction coordinate methodology
was used to obtain the minima on either side of each transition state. Natural
bond orbital analysis (NBO Version 3.144 as implemented in Gaussian 09) was
used to quantify the electronic donor−acceptor interactions as second-order
perturbation energies (ENBO).
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Kinetics of 1,4-MIDA boronate migration in acetonitrile. Five-millimetre
precision NMR tubes (Aldrich ColorSpec NMR tubes, 8 in. length x 5 mm
diameter, 0.38 mm wall, precision, 800 MHz, code red) and sealed capillary
tubes (Corning 9530-3 PYREX 90 mm, wall range of 0.2 mm) were used for
NMR experiments. All NMR experiments were conducted on a Varian 600 MHz
spectrometer (probe: OneNMR600). A known amount of α-MIDA boryl
nitrone was dissolved in 0.6 ml of CD3CN and transferred into a 5 mm NMR
tube containing a sealed capillary tube ([1,3,5-trimethylbenzene] = 9.3 mM in
CD3CN, V = 0.075 ml). 1H NMR arrayed kinetics data sets were processed using
the NMR Reaction Monitoring program by MestReNova (v12.0.1-20560). The
Data Analysis module was then used to generate concentration versus time
graphs for the disappearance of starting material with respect to the internal
reference signal. Concentration versus time data were exported into Excel and
processed using reaction progress kinetic analysis. All curve fitting parameters
and concentration versus time data are provided in the Supplementary
Information. First-order rate constants were determined by linear regression of
the graphical rate equations between α-MIDA boryl nitrone concentrations of
2.5 and 12.5 mM. The only exception to this is 12f, where rate constants were
obtained from the following concentrations ranges: 2.5–6.5 mM, 2.5–7 mM and
0.32–3.7 mM. For Hammett experiments, each rate constant was determined
from the average of three repeat experiments, with the variability represented by
the standard deviation.
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one automated process. Science 347, 1221–1226 (2015).
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Data availability. The data that support the findings of this study are available
from the corresponding authors upon request. Separate documents that contain
kinetic data processing and fitting are supplied as Excel data sets. Raw coordinate
files for the computational studies are also available.
Received: 10 April 2017; Accepted: 29 May 2018;
Published: xx xx xxxx
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