Cationic Pd(II) complexes catalyzed the dehydrogenation of ammonia borane in the most efficient manner with the release of 2.0 equiv of H_2 in less than 60 s at 25 °C. Most of the hydrogen atoms were obtained from the boron atom of the ammonia borane. The first step of the dehydrogenation reaction was elaborated using density functional theory calculations

Han, Won-Sik

Hwang, Son-Jong

Kang, Sang Ook

Kim, Sung-Kwan

Kim, Tae-Jin

Kim, Tae-Young

Michalak, Artur

Mitoraj, Mariusz

Nam, Suk Woo

Pieko, Łukasz

English

Sung-Kwan Kim

Won-Sik Han

Tae-Jin Kim

Tae-Young Kim

Suk Woo Nam

Mariusz Mitoraj

Łukasz Piekoś

Artur Michalak

Son-Jong Hwang

Sang Ook Kang

Crossref

Journal of the American Chemical Society

Palladium Catalysts for Dehydrogenation of Ammonia Borane with Preferential B−H Activation

Piękoś, Łukasz

Jagiellonian Univeristy Repository

Palladium catalysts for dehydrogenation of ammonia borane with preferential B-H activation

Caltech Authors - Main

 S1 
Supporting Information for 
 
 
Palladium Catalysts for Dehydrogenation of Ammonia Borane with Preferential 
B-H Activation 
 
Sung-Kwan Kim,
†
 Won-Sik Han,
†
 Tae-Jin Kim,
†
 Tae-Young Kim,
†
 Suk Woo Nam,
‡
 Mariusz Mitoraj,
§
 
Łukasz Piękoś,
 § 
Artur Michalak,
*,§ 
Son-Jong Hwang,
#
 and Sang Ook Kang
*,† 
 
 
†
Department of Chemistry, Korea University, Chung-nam 339-700, Korea. 
‡
Fuel Cell Center, Korea Institute of 
Science and Technology, Hawolgok-dong 39-1, Seongbuk-gu, Seoul 136-791, Korea. 
§
Department of Theoretical 
Chemistry, Faculty of Chemistry, Jagiellonian University, R. Ingardena 3, 30-060 Kraków, Poland. 
#
Division of 
Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA. 
 
 
Contents 
 
General Methods S2 
AB dehydrogenation procedure S4 
SFig-1. 
1
H NMR spectrum of catalyst 2 along with its structure S3 
SFig-2A. Schematic diagram of the experimental apparatus S5 
SFig-2B. H2 release profile of solid AB at 100 °C for the flow rate calibration S5 
SFig-3. Mass spectrum of the volatile compounds from the AB dehydrogenation with 3 S6 
SFig-4. Negative- and positive-ion ESI mass spectra of the tetraglyme solution S6 
SFig-5. Dehydrogenation KIE plots for AB with the deuterated AB derivatives S7 
STable 1. Elemental analysis and formula of spent fuel S7 
SFig-6. Infrared spectra of the spent fuels for N- or B- alkylated ABs S8 
SFig-7. 
11
B MAS and 2D MQMAS NMR spectra of BNHx powder S9 
STable 2. 
11
B peaks from decomposition of MAS NMR spectra S10 
SFig-8. 
11
B MAS NMR spectra of BN
i
PrHx and BNEt2Hx. S10 
Computational Details S11 
References S12 
 
 
 
 S2 
General Methods 
Materials and Methods. All experiments were carried out under a nitrogen atmosphere 
using Schlenk techniques or in a HE-493 dry box (Vacuum Atmosphere Co. Hawthorne, CA, 
USA). The solvents were dried over Na (tetraglyme), Na/benzophenone (THF), and CaCl2 
(nitromethane) distilled under nitrogen, then deoxygenated prior to use. The deuterated 
solvents were dried through trap-to-trap distillation from Na (C6D6) and CaH2 (CDCl3) and 
deoxygenated using three freeze-pump-thaw cycles. A palladium sponge and nitrosonium 
tetrafluoroborate were purchased from Strem Chemicals (Newburyport, MA, USA). Catalysts 
1
1
and 3
2 
were prepared as previously described. NaBH4, BH3SMe2, and all of the alkyl 
amines were used as received from their commercial sources. NH3BH3, R
1
nNH3-nBH3 (n = 1, 
R
1 
= Me, Et, 
i
Pr, Ph; n = 2, R
1 
= Et) were prepared using previously reported methods.
3
 
NH3BRH2 (R = 
i
Pr, Ph) was prepared from LiBRH3
4
 and (NH4)2SO4 in THF with stirring at 
40 °C over night. NaBD4 was used as purchased from Sigma Aldrich (St. Louis, MO, USA). 
The partially- and fully-deuterated ammonia boranes (ABs) were prepared from deuterated 
starting materials as previously reported for NH3BH3.
5
 Deuterated ammonium sulfate was 
prepared as previously reported.
6 
Synthesis of [Pd(allyl)(2,4-hexadiene)][BF4] (2). The di-µ-dichloro-bis(η
3
-allyl)dipalladium 
dimer (1.83 g, 5.0 mmol) and silver tetrafluoroborate (1.95 g, 10.0 mmol) in CH2Cl2 (50 mL) 
were stirred for 15 min. The 2,4-hexadiene (1.9 mL) was added and stirring continued for an 
additional 2 min. The mixture was filtered and the precipitate washed with 10 mL of CH2Cl2. 
Subsequently, Et2O (150 mL) was added to the combined filtrate to produce a white 
precipitate which was filtered and dried. The obtained solid was dissolved in 70 mL of 
CH2Cl2, and that solution was repeatedly filtered through a tightly packed plug of cotton until 
the solution was clear. Et2O (100 mL) was added to the combined mother liquid of CH2Cl2 to 
precipitate the product. After filtration, the product was dried in vacuo to produce an off-
white solid. Yield: 2.3 g (73 %); 
1
H NMR (300.1 MHz, CDCl3): δ 1.93 (d, 6H, CH3), δ 2.60 
(m, 2H, CH3CHCH), δ 3.63 (d, 2H, CH), δ 3.90 (d, 2H, CHCHCH), δ 4.91 (d, 2H, CH), and δ 
6.10 (m, 1H, CH). 
 S3 
 
SFig-1. 
1
H NMR spectrum of catalyst 2 along with its structure. 
 
Analytical Methods. Solution NMR spectra were collected at room temperature using a 
Mercury-300BB spectrometer (Varian Inc., Palo Alto, CA, USA) unless otherwise stated. The 
spectral frequency was 96.3 MHz for 
11
B and the NMR shifts in ppm were reported with 
reference to external standards of BF3·Et2O for the 
11
B nucleus. 
11
B solid state NMR 
experiments were performed using a DSX-500 spectrometer (Bruker AXS, Madison, WI, 
USA) and a boron-free, 4 mm CPMAS probe (Bruker AXS). Experimental details were 
described previously.
7
 The spectral frequency was 160.5 MHz for 
11
B and the NMR shifts in 
ppm were reported with reference to external standards of BF3·Et2O for the 
11
B nucleus. 
Samples were loaded into a 4 mm ZrO2 NMR rotor in Ar atmosphere inside a glove box. Dry 
nitrogen gas was used for sample spinning. The IR spectra were recorded on a Nicolet Avatar 
330 FT-IR spectrometer (Thermo Fisher Scientific, Rochester, NY, USA) with a KBr pellet.                      
Elemental analyses were performed using a Flash EA 1112 Series analyzer (ThermoQuest 
Italia SpA, Milan, Italy). Inductively coupled plasma-atomic emission spectroscopy was 
performed using a Varian 710-ES Model. 
X-ray photoelectron spectroscopy (XPS) was carried out using the 8A1 beam line of the 
Pohang Light Source (PLS; Pohang Accelerator Laboratory, Pohang, Korea) and a 
laboratory-based ESCALAB 250 spectrometer (VG Scientific, Beverly, MA, USA) with a 
photon energy of 1486.6 eV (Al Kα). 
Quadrupole mass spectroscopy (QMS) data were obtained using a SRS (Stanford Research 
Systems, Sunnyvale, CA, USA) RGA200 quadrupole mass spectrometer attached to a glass 
vacuum line system. 
 S4 
A Quattro Micro triple quadrupole mass spectrometer with an electrospray ionization source 
(Waters Corporation, Milford, MA, USA) was used in negative- and positive-ionization 
modes. The sample solution was directly infused at a flow rate of 100 µL/min using a syringe 
pump. The scanning mass range of the mass spectrometer was 5–2000 Da with a 0.5 Da step 
size. The capillary and cone voltages were set at 3200 V and 15–25 V, respectively, with 
nitrogen as the drying gas. The desolvation and cone gas flows were 350 L/h and 70 L/h, 
respectively. The desolvation temperature was 350 °C and the source temperature was 100 °C. 
 
AB Dehydrogenation Procedure 
Apparatus and procedure for Pd(II) catalyzed dehydrogenation. SFig-1 shows the 
experimental apparatus. The reactor consisted of modified 150 mL double jacket glassware. A 
three-way connector was modified to allow the system to be purged with argon gas and to 
allow the hydrogen gas produced during the dehydrogenation reaction to pass through the 
mass flow meter (MFM). The apparatus enabled the catalyst to be injected into the reactor 
without exposing the reactants to air. The reaction temperature was monitored and controlled 
with a thermocouple and an external heater/cooler (chiller), respectively. The experimental 
procedure involved filling the reactor with 2 mL of a tetraglyme solution containing 1.46 
mmol of AB. The reactor was subsequently flushed with argon for at least 30 min to 
minimize the moisture level inside the vessel. After thermal equilibration of the reactor and 
the low temperature trap, 3 mol% of catalyst 3 was dissolved in 0.5 mL nitromethane 
(MeNO2) and injected into the AB solution. Reaction time began at the time when the catalyst 
was introduced into the mixture and ended when H2 evolution ceased. The progress of the 
reaction was monitored by examining the amount of hydrogen generated using a volumetric 
technique that allowed real time tracking of the reaction.
8
 MeNO2 (bp 101 °C) and other 
volatiles including NH3 in the product stream were anticipated because of the large 
exothermy expected under the experimental conditions, even though the reactor temperature 
was controlled at 25 °C. In the apparatus, a −90 °C low temperature bath (liquid N2 with 
CH2Cl2) trapped the volatiles to ensure that the gas volume measured as it passed through the 
MFM system was only due to hydrogen. After dehydrogenation, the solid remaining in the 
reactor was collected through filtration, rinsed with Et2O and dried in vacuo. Because of the 
fast hydrogen release kinetics for catalyst 3, there was the possibility of a heterogeneous 
pathway. That possibility was examined either by the supplemental addition of AB after 
dehydrogenation or through mercury poisoning
9
 as previously described. The H2 release 
 S5 
kinetics was not altered following either of those actions. 
 
 
SFig-2A. Schematic diagram of the experimental apparatus used to determine H2 release 
kinetics. 
 
SFig-2B. H2 release profile for solid AB at 100 °C. That profile was used to calibrate the flow 
rate of the MFM portion of the apparatus. 
 
 
 
 S6 
 
SFig-3. Mass spectrum of the volatile compounds from the AB dehydrogenation with catalyst 
3 recorded at room temperature. Other than the intensity of the Ar carrier gas, the highest 
intensity mass number was m/z = 2.0 (H2). A trace amount of m/z = 17.0 (NH3) was detected. 
 
SFig-4. (a) Negative- and (b) positive-ion ESI mass spectra of a tetraglyme solution of the 
spent fuel acquired using a triple quadrupole mass analyzer. Following dehydrogenation, BF4
-
 
and NO2
-
 were the only chemical substances identified in the tetraglyme solution. 
 S7 
 
SFig-5. (a) Dehydrogenation kinetic isotope effect (KIE) plots for AB and deuterated ABs 
with catalyst 3 at 25 °C and (b) their corresponding logarithmic plots. The straight lines in (b) 
were obtained from linear regression analysis of the data points. 
 
STable 1. Elemental analysis and formula of spent fuel 
Method Spent fuel components 
 B N H Pd Formula of spent fuel 
EA
a
 - 0.95 4.50 - 
ICP
b
 1.00 - - 0.024 
B1.00N0.95H4.50Pd0.024 
XPS
c
 1.00 0.7 - - BN0.7 
a
Elemental analysis, 
b
Inductively coupled plasma-atomic emission spectroscopy, 
c
X-ray 
photoelectron spectroscopy 
 
 S8 
 
SFig-6. Infrared spectra of the spent fuels from a series of alkyl ABs: (a)BNHx, (b) BNMeHx, 
(c) BNEtHx, (d) BN
 i
PrHx, (e) BNPhHx, (f) 
i
PrBNHx and (g) PhBNHx. 
 S9 
 
SFig-7. 1D 
11
B MAS (left) and 2D 
11
B MQMAS (right) NMR spectra of BNHx powder. 
 
First, a two dimension (2D) 
11
B MQMAS NMR spectrum was obtained to sort out the non-
equivalent boron sites that are indistinguishable in a one dimension (1D) MAS spectrum. 
Two groups of peaks were initially identified using this approach. The broad peaks between 
10 and 20 ppm apparently originated from borons in a trigonal geometry (B
3
) while the 
several sharp peaks in the +6~−6 ppm range were due to borons in a tetrahedral coordination. 
These tetrahedral borons (B
4
) are believed to be responsible for the BN4 or BHN3 units in 
diamondoid type structures. Based on the 2D spectrum, the 1D spectrum was decomposed as 
in SFig-7 to 7 different sites. The respective peaks are compiled in STable 2. An additional 
resonance is seen at −10 ppm in the 2D spectrum, but it was ignored due to its negligible 
contribution. The 1D spectrum without 
1
H decoupling allowed us to conclude that nearly all 
boron peaks except for the peaks at −6 ppm and −10 ppm are without direct B-H bonds. 
Moreover, nearly all peaks showed high efficiency in 
1
H-
11
B cross polarization MAS NMR, 
indicating that the borons are in close proximity to either NH or -CHn organic species. Based 
on the spectral decomposition, the ratio of [B]trigonal to [B]tetrahedral, or B
3
:B
4
, was calculated to 
be 2:3, a ratio that helped us to speculate on a possible structure. Lastly, the relatively sharp 
peak at -1.6 ppm is believed to be BF4
-
, although its bounding cation is not known. 
 
 
 
 S10 
STable 2. 
11
B peaks from decomposition of 1D and 2D MAS NMR spectra 
Chemical 
shift (δiso) 
CQ
10 η10 Intensity Relative Intensity ratio 
21.6 2.53 0.1 38.25 0.14 
18.4 2700 0.1 68.48 0.25 
sp
2
: 0.39 
6.1 0.5 1 60.77 0.22 
3.6 0.5 1 62.82 0.23 
1.1 0.5 1 35.61 0.13 
sp
3
: 0.57 
−6.0 0.5 1 11.80 0.04 BHx 
−1.6 - - - <0.02 BF4
- 
 
 
SFig-8. 
11
B MAS NMR spectra of BNHx, BN
i
PrHx and BNEt2Hx. 
 
Other spent fuels of sample entries 4 and 6 (Table 1): The boron sites found in BNHx 
appeared similarly in both cases (see 
11
B MAS NMR spectra in SFig-7) with an exception of 
the boron sites at 21.6 ppm (trigonal B
3
). 
 
 
 
 
 
 
 
 S11 
 
Computational Details 
DFT calculations based on the Becke-Perdew exchange-correlation functional
11-13 
were 
performed using the Amsterdam Density Functional (ADF) program, version 2009.01.
14-18
 
Within the ADF program, a standard double-zeta STO basis with one set of polarization 
functions was applied for the H, C, and N atoms, while a standard triple-zeta basis set was 
employed for the Pd atom. The 1s electrons of B, C, and N, as well as the 1s-3d electrons of 
Pd were treated as a frozen core. Auxiliary s, p, d, f, and g STO functions, centered on all 
nuclei, were used to fit the electron density and obtain accurate Coulomb and exchange 
potentials in each SCF cycle. Relativistic effects were included at the level of ZORA 
approximation as implemented in the ADF program.
19 
The natural orbitals for chemical 
valence (NOCV)
20-22
 analysis, supported by the extended transition state (ETS) Ziegler-Rauk 
bond-energy decomposition scheme,
22,23
 was performed for catalyst (A), to describe the bond 
between the AB molecule and the metal containing fragment. The combined ETS-NOCV 
approach
20
 allowed us to separate the independent components of the differential density, ∆ρ, 
into the electron charge transfer channels that contribute to the bonding between fragments in 
a molecule. That approach provides energetic estimates of the components’ relative 
significance. In particular, in the case of transition metal complexes, the ETS-NOCV 
approach provides estimates of the independent contributions from ligand → metal donation 
and metal → ligand back-bonding. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 S12 
 
Reference 
1. Lai, T. W.; Sen, A. Organometallics 1984, 3, 366 
2. Mathew, J. P.; Reinmuth, A.; Melia, J.; Swords, N.; Risse, W. Macromolecules 1996, 29, 
2755. 
3. Jaska, C. A.; Temple, K.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2003, 125, 9424. 
4. Singaram, B.; Cole, T. E.; Brown, H. C. Organometallics 1984, 3, 774. 
5. Keaton, R. J.; Blacquiere, J. M.; Baker, R. T. J. Am. Chem. Soc. 2007, 129, 1844. 
6. Käß, M., Friedrich A.; Drees, M.; Schneider, S. Angew. Chem. Int. Ed. 2009, 48, 905. 
7. Hwang, S.-J.; Bowman, R. C.; Reiter, J. W.; Rijssenbeek; Soloveichik, G. L.; Zhao, J.-C.; 
Kabbour, H.; Ahn, C. C. J. Phys. Chem. C 2008, 112, 3164. 
8. Kim,S. J; Lee J.; Kong K. Y.; Jung, C. R.; Mina, I.-K.; Lee, S.-Y.; Kim H.-J; Nam S. W.; 
Lim T.-H. Journal of Power Sources 2007, 170, 412. 
9. Jaska, C. A.; Manners, I. J. Am. Chem. Soc. 2004, 126, 9776. 
10. Stowe, A. C.; Shaw, W. J.; Linehan, J. C.; Schmid, B.; Autrey, T. Phys. Chem. Chem. 
Phys. 2007, 9, 1831. 
11. Becke, A. Phys. Rev. A 1988, 38, 3098. 
12. Perdew, J. P. Phys. Rev. B 1986, 33, 8822. 
13. Perdew, J. P. Phys. Rev. B 1986, 34, 7406. 
14. te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; Fonseca Guerra, C.; van Gisbergen, S. J. 
A.; Snijders, J. G.; Ziegler, T. J. Comput. Chem. 2001, 22, 931, and refs therein. 
15. Baerends, E. J.; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2, 41. 
16. Baerends, E. J.; Ros, P. Chem. Phys. 1973, 2, 52. 
17. te Velde, G.; Baerends, E. J. J. Comput. Phys. 1992, 99, 84. 
18. Fonseca Guerra, C. G.; Visser, O.; Snijders, J. G.; te Velde, G.; Baerends, E. J. In 
Methods and Techniques in Computational Chemistry, METECC-95; Clementi, E., 
Corongiu, G., Eds.; STEF; Cagliari, Italy, 1995; p 303. 
19. E. van Lenthe, E.; van Leeuwen, R.; Baerends, E.J.; Snijders, J.G. International Journal 
of Quantum Chemistry 1996, 57, 281. 
20. Mitoraj, M.; Michalak, A; Ziegler, T. J. Chem. Theory Comput. 2009, 5, 962. 
21. Mitoraj, M.; Michalak, A. J. Mol. Model. 2007, 13, 347. 
22. Michalak, A.; Mitoraj, M.; Ziegler, T. J. Phys. Chem. A. 2008, 112, 1933. 
23. Ziegler, T.; Rauk, A. Inorg. Chem. 1979, 18, 1755. 


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Palladium Catalysts for Dehydrogenation of Ammonia Borane with Preferential B−H Activation

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