10.1002/ejic.201900847
European Journal of Inorganic Chemistry
FULL PAPER
population analysis (NPA) was based on the geometry from the single
crystal X-ray diffraction analysis of ADB and ADB-Me.
We have investigated the reactions between B-substituted
amine boranes (NH3BH2R) and THFBH3. It was found that when
R is Me, an electron-donating group, the major product of the
reaction is THFBH(Me)(-NH2)BH3. When R is Ph, a weak
electron-donating group, the reaction mainly tends to undergo
the intermolecular NH3-THF exchange to produce AB and
THFBH2Ph. The reversible intermolecular Cl-H exchange
reaction occurs when the R group is Cl, an electron-withdrawing
group. The R group on the B atom affects the nucleophilicity of
the B-H bond. The strong electron-donating ability of the R
group reinforces the hydricity of H on the B atom and increases
the nucleophilicity of the B-H bond, which probably are the
reasons for the different reactions of NH3BH2R (R = Me, Ph, and
Cl) and THFBH3.
Acknowledgments
This work was supported by the National Natural Science
Foundation of China (Grant Numbers, 21771057, U1804253,
21773214, and 21571052).
Keywords: B-substituted aminodiborane • B-substituted amine
boranes •THF·BH3 • mechanism
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General remarks
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Reaction of NH3BH2Me with THFBH3 at low temperature
NH3BH2Me (0.031 g, 0.68 mmol ) was put into a 10 mL flask which was
connected to a Schlenk line and then 5 mL of THF was added. The flask
was cooled in an ice-water bath and THFBH3 (0.68 mL, 1 mol/L) was
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3 h
at this temperature and monitored by 11B NMR
spectroscopy. After NH3BH2Me disappeared completely, the reaction
mixture was condensed to another flask. The collected liquid was
subjected to fractional distillation to remove the excess THFBH3 to further
purify the products. The 11B NMR spectra of the final product are
provided in the Supporting Information (Figure S1h).
Reaction of NH3BH2Ph with THFBH3
At room temperature, NH3BH2Ph (0.104 g,0.97 mmol) was placed in a
10 mL flask which was connected to a Schlenk line. Then 2 mL of THF
and 4 mL of THFBH3 solution (1 mol/L) were added. The mixture was
stirred for 42
h
and monitored by 11B NMR spectroscopy. After
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NH3BH2Ph disappeared completely, the reaction mixture was condensed
to another flask.
Reaction of NH3BH2Cl with THFBH3
NH3BH2Cl (0.065 g, 1 mmol) was put into a 10 mL flask which was
connected to a Schlenk line and then 2 mL of THF was added. After the
flask was cooled in an ice-water bath, 1 mL of THFBH3 solution (1 mol/L)
was added. The reaction mixture was stirred at this temperature and
monitored by 11B NMR spectroscopy until the equilibrium was reached
(52 h). The 11B NMR spectra are provided in the supporting Information
(Figure S3a and b). The reaction was repeated with the NH3BH2Cl to
THFBH3 ratios of 1:2 and 1:3 using the same procedure.
Density Functional Theory (DFT) Calculation
All DFT calculations were carried out by using Gaussian 09.[23] The M06-
2X functional was used with a standard 6-311++G(d,p) basis set and
SMD model in THF solvent to optimize the geometries of all the
structures. The frequency calculations were performed for all stationary
points to confirm the local minima or transition state (TS) structures and
to derive Gibbs free energies (△G, kcalmol-1 at 298K). The natural
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