10.1021/jacs.5b08033.s002
Huizhen Li
Huizhen
Li
Nana Ma
Nana
Ma
Wenjuan Meng
Wenjuan
Meng
Judith Gallucci
Judith
Gallucci
Yongqing Qiu
Yongqing
Qiu
Shujun Li
Shujun
Li
Qianyi Zhao
Qianyi
Zhao
Jie Zhang
Jie
Zhang
Ji-Cheng Zhao
Ji-Cheng
Zhao
Xuenian Chen
Xuenian
Chen
Formation
Mechanisms, Structure, Solution Behavior,
and Reactivity of Aminodiborane
American Chemical Society
2015
form sodium aminodiboronate
ion pair reversibly
THF
room temperature exchange
NH 2BH AoB
2 H NMR
MS
B 2H DB
ion pair
AB
crystal analysis
NH 3BH AaDB
NH 2B ADB
2015-09-30 00:00:00
Dataset
https://acs.figshare.com/articles/dataset/Formation_Mechanisms_Structure_Solution_Behavior_and_Reactivity_of_Aminodiborane/2127382
A facile
synthesis of cyclic aminodiborane (NH<sub>2</sub>B<sub>2</sub>H<sub>5</sub>, ADB) from ammonia borane (NH<sub>3</sub>·BH<sub>3</sub>, AB) and THF·BH<sub>3</sub> has made it possible to
determine its important characteristics. Ammonia diborane (NH<sub>3</sub>BH<sub>2</sub>(μ-H)BH<sub>3</sub>, AaDB) and aminoborane
(NH<sub>2</sub>BH<sub>2</sub>, AoB) were identified as key intermediates
in the formation of ADB. Elimination of molecular hydrogen occurred
from an ion pair, [H<sub>2</sub>B(NH<sub>3</sub>) (THF)]<sup>+</sup>[BH<sub>4</sub>]<sup>−</sup>. Protic-hydridic hydrogen scrambling
was proved on the basis of analysis of the molecular hydrogen products,
ADB and other reagents through <sup>2</sup>H NMR and MS, and it was
proposed that the scrambling occurred as the ion pair reversibly formed
a BH<sub>5</sub>-like intermediate, [(THF)BH<sub>2</sub>NH<sub>2</sub>](η<sup>2</sup>-H<sub>2</sub>)BH<sub>3</sub>. Loss of molecular
hydrogen from the ion pair led to the formation of AoB, most of which
was trapped by BH<sub>3</sub> to form ADB with a small amount oligomerizing
to (NH<sub>2</sub>BH<sub>2</sub>)<sub><i>n</i></sub>. Theoretical
calculations showed the thermodynamic feasibility of the proposed
intermediates and the activation processes. The structure of the ADB·THF
complex was found from X-ray single crystal analysis to be a three-dimensional
array of zigzag chains of ADB and THF, maintained by hydrogen and
dihydrogen bonding. Room temperature exchange of terminal and bridge
hydrogens in ADB was observed in THF solution, while such exchange
was not observed in diethyl ether or toluene. Both experimental and
theoretical results confirm that the B–H–B bridge in
ADB is stronger than that in diborane (B<sub>2</sub>H<sub>6</sub>,
DB). The B–H–B bridge is opened when ADB and NaH react
to form sodium aminodiboronate, Na[NH<sub>2</sub>(BH<sub>3</sub>)<sub>2</sub>]. The structure of the sodium salt as its 18-crown-6 ether
adduct was determined by X-ray single crystal analysis.