Journal of Crystallization Process and Technology, 2011, 1, 1-7
doi:10.4236/jcpt.2011.11001 Published Online April 2011 (http://www.SciRP.org/journal/jcpt)
1
A Facile Route to Phosphanylborohydrides:
Synthesis, Crystal Structure and
Spectroscopic Properties of
1,2-Bis(Diphenylphosphinoborane)Ethane
Leyla Tatar Yildirim1, Mehdi Masjedi2, Saim Özkar2
1Department of Engineering Physics, Hacettepe University, Ankara, Turkey;
2Department of Chemistry, Middle East Technical University, Ankara, Turkey
Received February 22nd, 2011; revised March 16th, 2011; accepted March 17th, 2011.
ABSTRACT
A novel and simple synthetic way using NaBH4 in the mixture of H2O-THF was applied to prepare 1,2-bis(diphenyl-
phosphinoborane)ethane, dppe(BH3)2, in high yield and purity. The phosphanylborohydride compound dppe(BH3)2 was
isolated in the form of colorless crystals and characterized by single crystal X-ray diffractio n, 1H, 13C, 31P and 11B NMR
spectroscopy. Prismatic colorless crystals of dppe(BH3)2 were obtained in monoclinic crystal system and space group
P21 with two asymmetric units in the unit cell. Lattice parameters were: a = 11.657(2), b = 17.237(2), c = 12.764(2) Å,
 = 98.735(14)˚, 2535.0 (7) Å3.
Keyword s: Crystal Structure, Synthesis, Phosphinoborane, Sodium Boro h ydride, Phosphanylborohydride,
X-Ray Diffraction
1. Introduction
A recent study [1] has reported the catalytic activity of
ruthenium (III) acetylacetonate in the presence of differ-
ent phosphorus compounds such as 1,2-bis(diphenyl-
phosphino)ethane, dppe, in the hydrolysis of sodium
borohydride. At the end of catalytic reaction, in addition
to the unreacted dppe, unexpectedly we isolated a new
species which contains two BH3 molecules coordinated
to dppe. Obviously, in this catalytic reaction, NaBH4 acts
not only as a substrate to generate hydrogen, but also as a
BH3 supplier in forming phosphanylborohydrides such as
1,2-bis(diphenylphosphinoborane)ethane, dppe(BH3)2. In
literature, phosphanylborohydrides have been prepared
by using the mixture of sodium borohydride and iodine
in monoglyme [2] or using the other borane sources:
dppe(BH3)2 by complexation of dppe with BH3·S(CH3)2
[3], rac/meso-[HP(BH3)(Ph)CH2]2 from the reaction of
BH3.thf [4] or reaction of phosphine oxides with dibo-
rane [5], from the reaction of trialkylphosphines with
bromoboranes or bromochloroboranes [6]. In addition
following phosphanylborohydrides have been reported:
tertiary mono and diphosphine-borane complexes [7-9],
cyclic phosphine-boranes [10], phosphine-carborane
clusters [11], phosphinyl-borane radicals [12] and
phosphine alkylene boranes [13]. It is noteworthy that the
phosphanylborohydride [P(BH3)Ph2]- forms dative bonds
of higher p character and establish more stable σ adducts
towards the acceptor orbital of the Lewis acid in com-
parison with its neutral counterpart P(CH3)Ph2 [14]. A
similar phenomenon was observed in the study of chal-
cogenated phosphanylborohydrides K[EP(BH3)R2] (E: O,
S, Se, Te; R: Ph, t-Bu) with a certain degree of E=P mul-
tiple bond character [15]. Borane complexes of phosphorus
compounds, a very common oxidation free relay for cata-
lytic ligands (phosphines, phosphites or phosphinites) can be
easily deprotected by treatment with polymer- supported
piperazine, N-methylpiperazine [16] or pyrrol derivatives
[3]. Phosphanylborohydrides supported by amines such
as polypyrroles, are very useful for homogeneous cataly-
sis due to more efficient recovery and purification [3].
Despite the known examples given above, the chemistry
of phosphanylborohydrides is still largely undeveloped
[17-22]. Herein we report a new and simple synthetic
way using NaBH4 in an homogeneous aqueous-organic
solution to yield

A Facile Route to Phosphanylborohydrides: Synthesis, Crystal Structure and Spectroscopic
2
Properties of 1,2-Bis(Diphenylphosphinoborane)Ethane
characterization by single crys-
1H, 13C, 31P and 11B NMR spec-
tal
ith ace-
ious rinsing with distilled water
0˚C in oven for a few hours.
P NMR. Posi-
tiv
hydrogen liberated during hy-
, 129.87, 131.85, 137.59. P {H} NMR
R (CD2Cl2, ppm):
BH3) and phenyl rin
drogen’s of the comp
1,2-bis(diphenylphosphinoborane)ethane, dppe(BH3)2,
and its
tal X-ray diffraction,
troscopy.
2. Experimen
2.1. Materials
Sodium borohydride, NaBH4 (98%) and 1,2-bis(di-
phenylphosphino)ethane, dppe, were purchased from
Aldrich. Tetrahydrofuran, THF and dichloromethane,
CH2Cl2 were purchased from Merck. All glassware and
Teflon-coated magnetic stir bars were cleaned w
tone, followed by cop
before drying at 15
2.2. Equipment
All reactions involving air sensitive compounds were
performed under argon or nitrogen atmospheres. 1H, 13C,
31P and 11B NMR spectra were recorded on Bruker
Avance DPX 400 MHz spectrometer (400.1 MHz for 1H;
100.6 MHz for 13C; 161.3 MHz for 31P; 128.2 MHz for
11B). TMS was used as internal reference for 1H and 13C
NMR chemical shifts. BF3·(C2H5)2O was used as external
reference for 11B NMR chemical shifts. H3PO4 (85% in
glass capillary) was used as reference for 31
e ion mass spectrometry data was obtained on a
Bruker Micro TOF-LC/ESI/Ms system.
The experimental setup consists of a 75 mL jacketed
reaction flask containing a Teflon-coated stir bar placed
on a magnetic stirrer (Heidolph MR-301) which can be
thermostated to 25.0˚C by circulating water through its
jacket from a constant temperature bath (RL6 LAUDA
water bath). Note that
drolysis of sodium borohydride was released from the
flask through a bubbler.
2.3. Synthesis of 1,2-Bis(Diphenylphosphinobo-
rane)Ethane, DPPE(BH3)2
For the preparation of 1,2-bis(diphenylphosphinoborane)
ethane, dppe(BH3)2, 140 mg (0.35 mmol) of 1,2-bis(di-
phenylphospino)ethane, dppe, was dissolved in 10 mL of
THF by vigorous stirring. Then, the solution was trans-
ferred into a 75 mL jacketed reaction flask containing 30
mg (0.79 mmol) NaBH4 dissolved in 40 mL water and
thermostated at 25.0˚C. The reaction was started by
turning on the magnetic stirrer (Heidolph MR-301) at
1000 rpm under inert atmosphere (argon or nitrogen).
After 3 h stirring, the mixture was extracted with di-
chloromethane and the combined organic extracts were
cooled in order to precipitate out traces of sodium boro-
hydride or metaborate remaining in organic extracts.
Then, the solution was dried over magnesium sulfate,
filtered and evaporated in vacuum giving 144 mg of pure
dppe(BH3)2 complex (96% yield). Colorless crystals of
dppe(BH3)2 were obtained by crystallization from the
hexane-dichloromethane solution at 0˚C after one week,
which were separated by filtration. [Ph2P(BH3)CH2]2: 1H
NMR (CD2Cl2, ppm): δ 1.99 (t, 6H, JP-H = 4.8 Hz, 2BH3),
2.15 (br d, 2H, JP-H = 6.4 Hz, CH2), 2.38 (br d, JP-H = 2.8
Hz, 2H, CH2), 7.38 (m, 12H, H-m,p), 7.54(m, 4H, H-o),
7.61 (m, 4H, H-o). 13C {1H} NMR (CD2Cl2, ppm): δ
22.93, 127.8131 1
(CD2Cl2, ppm): δ –12.5. 11B {1H} NM
δ –40.06.
3. Crystal Structure Analysis
X-ray diffraction measurements were performed with
MoKα radiation on an Enraf-Nonius CAD4 diffractome-
ter [23] equipped with a graphite monochromator. Inten-
sity data were collected by
 /2  scan mode. The cell
parameters were determined from a least-squares refine-
ment of 18 centered reflections in the range of 10.12˚ 

 18.03˚. Cell refinement was carried out using CAD-4
EXPRESS. Data reduction was carried out using XCAD4
[24]. The structures were solved by Patterson methods
and refined using the program SHELX [25]. A
full-matrix least-squares refinement on F2 was done. For
all non-hydrogen atoms anisotropic displacement pa-
rameters were refined. Borane(g hy-
ound were placed geometrically and
a riding model was used with ()1.5()
iso eq
UH UC and
()1.2()
iso eq
UH UC

, respectively. Methylene hydro-
gen’s were taken from a difference Fourier map and re-
fined. Single crystal X-ray diffraction analysis of the
colorless crystal shows the crystallization in monoclinic
system with space group P21 and two asymmetric units
with a formula of C26H30B2P2 and four molecules per unit
cell. Table 1 shows the crystal data and crystal refine-
ment of dppe(BH3)2. The atomic coordinates and iso-
tropic displacement parameters are listed in Table 2.
Selected bond lengths and angles are given in Table 3.
ORTEP [26] drawing of the dppe(BH3)2 complex with
the atomic numbering scheme is given in Figure 1. The
unit cell of the structure as shown in Figure 2. The con-
formations of molecules and molecular packing geome-
try were analyzed using PLATON [27]. The structure
includes several pi-ring interactions between two asym-
ng interaction geome-metric moieties. Details of the pi-ri
try are given in Table 4.
4. Results and Discussion
When an aqueous solution of sodium borohydride is
dded to a solution of 1,2-bis(diphenylphospino)ethane, a

A Facile Route to Phosphanylborohydrides: Synthesis, Crystal Structure and Spectroscopic
Properties of 1,2-Bis(Diphenylphosphinoborane)Ethane
3
pe, in tetrahydrofurane undeaction occurs, along with the
. Crystal data and structure refinement for dppe
emical Formula C26H30B2P2
dpr vigorous stirring in inert atmosphere at 25.0˚C, a re
Table 1(BH3)2.
Ch
Formula weight [g/mol] 426.06
Crystal colour and shape
system, Space group , P21
6
 l  15
que int= 0.0492]
0.1301
prism, colorless
Crystal size (mm)
erature (K)
0.3 × 0.3 × 0.3
Temp
l
295(2)
Crysta monoclinic
a (Å)
11.657(2)
b (Å)17.237(2)
c (Å) 12.764(2)
4)β (˚)
3
98.735(1
(7)Cell volume (Å)
lated density (g/cm3)
2535.0
11Z, calcu 4, 1.
Absorption coefficient (mm–1) 0.182
F (000) 904
θ-range for data collection (º) 2.21-26.29
 k  21, –15
Limiting indices
Uni
–14  h 0, 0
286 [RReflections collected / 5542/5
Data/restrains/parameters
25286/553/4
Goodness-of-fit on F
Final R indices [I > 2σ(I)]
1.001
R = 0.0558, wR =
1 2
Largest diff. peak and hole (e/Å3) 0.519 and –0.303
Further details on the structural investigation are available on request from the Cambridge Crystallographica Data Centre, quoting the depository number
CCDC 75288
Table 2. Atomic coordinates and equivalotropplacemt paramet (Å2) for dppe(BH3).
Atom x z Ueq Atom x z Ueq
3.
ent isic diseners
y y
Molecule I Molecule II
B1 0.4854(7) 0.1328(6) 0.9091(8) 0.076(3) B1' 0.1375(10)0.3864(7) 0.4564(7) 0.098(4)
B2 0.8379(9) 0.1832(6) 1.2510(7) 0.085(3) B2' 0.6106(9) 0.4078(8) 0.7863(8) 0.102(4)
P1 0.62838(14) 0.08831(10) 0.89049(14) 0.0544(5)P1' 0.19495(15)0.34115(11) 0.58949(14) 0.0597(5)
P2 0 1 00 0
00
00
0
0
.86384(15) 0.22715(10) .12275(14) 0.0534(5)P2' .54049(16).45444(12).65608(15)0.0629(5)
C1 0.6261(6) –0.0166(4) 0.8938(5) .0554(19)C1' 0.1708(6) 0.2379(4) 0.5901(5) .0593(18)
C2 0.6967(6) –0.0625(5) 0.8385(6) 0.071(2) C2' 0.2342(7) 0.1881(5) 0.6624(6) 0.071(2)
C3 0.6936(8) –0.1412(5) 0.8464(7) 0.089(3) C3' 0.2160(7) 0.1088(5) 0.6572(7) 0.081(2)
C4 0.6239(8) –0.1750(5) 0.9098(7) 0.084(3) C4' 0.1320(7) 0.0775(5) 0.5804(7) 0.084(2)
C5 0.5550(7) –0.1319(6) 0.9644(7) 0.083(2) C5' 0.0685(7) 0.1260(5) 0.5095(7) 0.081(2)
C6 0.5572(6) –0.0527(5) 0.9566(6) 0.073(2) C6' 0.0858(6) 0.2057(5) 0.5135(6) 0.071(2)
C7 0.6817(6) 0.1161(4) 0.7718(6) .0621(19)C7' 0.1323(6) 0.3814(4) 0.6979(6) .0596(18)
C8 0.6033(8) 0.1336(5) 0.6817(7) 0.092(3) C8' 0.0241(7) 0.4146(6) 0.6764(8) 0.103(3)
C9 0.6447(15) 0.1521(7) 0.5869(9) 0.131(4) C9' –0.0286(9)0.4421(7) 0.7604(12) 0.127(4)
C10 0.7593(17) 0.1524(8) 0.5842(11) 0.137(5) C10' 0.0270(12)0.4403(7) 0.8622(11) 0.122(4)
C11 0.8375(11) 0.1368(7)
0.6693(10) 0.126(4) C11' 0.1327(11)0.4088(6) 0.8823(8) 0.103(3)
C12 0.7993(7) 0.1182(5) 0.7641(7) 0.087(2) C12' 0.1867(7) 0.3789(5) 0.8012(6) 0.083(2)
C13 0.7410(6) 0.1148(4) 1.0009(6) 0.0588(19)C13' 0.3526(6) 0.3535(5) 0.6246(8) 0.071(2)
C14 0.7504(7) 0.2023(4) 1.0154(7) 0.062(2) C14' 0.3843(6) 0.4399(5) 0.6297(8) 0.074(2)
C15 0.9964(8) 0.1979(6) 1.0806(10) 0.1055(16)C15' 0.5950(6) 0.4217(4) 0.5387(5) .0599(18)
C16 1.0228(8) 0.2233(6) 0.9836(9) 0.1055(16)C16' 0.5452(7) 0.4447(5) 0.4389(6) 0.081(2)
C17 1.1287(8) 0.2001(5) 0.9498(9) 0.1055(16)
0
C17' 0.5935(9) 0.4216(6) 0.3511(7) 0.094(3)
C18 1.2024(8) 0.1564(6) 1.0190(9) .1055(16)C18' 0.6882(9) 0.3766(6) 0.3618(8) 0.094(3)
C19 1.1808(8) 0.1314(5) 1.1106(9) 0.1055(16)C19' 0.7410(8) 0.3524(6) 0.4595(8) 0.093(3)
C20 1.0748(7) 0.1514(5) 1.1433(8) 0.097(3) C20' 0.6922(7) 0.3747(5) 0.5480(7) 0.081(2)
C21 0.8710(5) 0.3316(4) 1.1266(5) .0498(17)C21' 0.5562(6) 0.5580(4) 0.6561(5) 0.062(2)
C22
C23 0.7938(7)
0.8033(7)
0.3779(5)
0.4581(5)
1.0625(6)
1.0697(7)
0.069(2)
0.084(2)
C22'
C23' 0.4858(7)
0.5003(9)
0.6070(5)
0.6864(6)
0.7037(7)
0.7041(8)
0.089(3)
0.107(3)
C24 0.8903(8) 0.4909(5) 1.1428(7) 0.080(2) C24' 0.5826(10)0.7187(6) 0.6564(8) 0.100(3)

A Facile Route to Phosphanylborohydrides: Synthesis, Crystal Structure and Spectroscopic
4
Properties of 1,2-Bis(Diphenylphosphinoborane)Ethane
C25 0.9654( 0.118(4) 7) 0.4449(5) 1.2062(6) 0.081(2) C25' 0.6512(10)0.6726(7) 0.6109(9)
C26 0.9546(6) 0.3663(4)6) 0.069(2) C26' 0.6405(8) 0.6082(7) 0.092(3) 1.1979(0.5929(5)
Tabcted bond length [Å] and angles˚] for tmetric units oH3)2.
Molecule I Molecule II
le 3. Sele [wo asymf dppe(B
B1 – P1 1.882(8) B1' – P1' 1.896(9)
B2 – P2 1.870(9) B2' – P2' 1.914(10)
P1 – C1 1.809(7) P1' – C1' 1.802(8)
P1 – C7 1.788(7) P1' – C7' 1.799(7)
P1 – C13 1.832(7) P1' – C13' 1.837(8)
P2 – C14
P2 – C15
1.805(7)
1.784(9)
P2' – C14'
2' – C15'
1.818(8)
1.805(7) P
P2 – C21 1.803(7) P2' – C21' 1.794(8)
C13 – C14 1.521(9) C13' – C14' 1.533(11)
B1 – P1 – C1 112.8(4) B1' – P1' – C1' 112.1(4)
B1 – P1 – C7 115.3(4) B1'– P1' – C7' 113.6(5)
B1 – P1 – C13 110.2(4) B1' – P1' – C13'
'
112.0(5)
B2 – P2 – C14111.8(5) B2' – P2' – C14112.7(5)
B2 – P2 – C15 114.3(5) B2' – P2' – C15' 115.6(5)
B2 – P2 – C21 113.2(4) B2' – P2' – C21' 112.8(5)
C1 – P1 – C7 107.2(3) C1' – P1' – C7' 107.2(3)
C1 – P1 – C13 104.0(3) C1' – P1' – C13' 105.3(4)
C7 – P1 – C13 106.5(3) C7' – P1' – C13' 106.0(4)
C14 – P2 – C15 105.8(5) C14' – P2' – C15' 105.8(4)
C14 – P2 – C21
C15 – P2 – C21
106.5(3)
104.6(4)
C14' – P2' – C21'
C15' – P2' – C21'
103.7(4)
105.2(3)
P1 – C13 – C14 111.8(5) P1' – C13' – C14' 110.4(5)
P2 – C14 – C13 111.0(5) P2' – C14' – C13' 111.7(5)
Ttural parameters oing interaceometry (e title compound.
CDg
able 4. Strucf pi-rtion gÅ,˚) for th
D  H  Cg DH gH DCg HC
C9 H9Cg4' 0.93 2.81 3.685(14) 158
C11H11Cg1i 0.93 2.79 3.634(12) 151
C25 H25Cg1ii 0.93 2.91 3.662(12) 138
Symmetry codes [i: x, y, 1 + z and ii: 1 – x, ½ + y,1 – z]

A Facile Route to Phosphanylborohydrides: Synthesis, Crystal Structure and Spectroscopic
Properties of 1,2-Bis(Diphenylphosphinoborane)Ethane
5
Figure 1. ORTEP drawing for the dppe(BH3)2 complex with the atomic numbe ring scheme.
ll of dppe(BH3)2.
In the crystal structure of the title compound, the
monoclinic unit cell contains two molecules of [C26H30B2P2]
and four molecules per unit cell. All molecular properties
of two asymmetric units of the molecule I are similar of
the molecule II as given in Table 3.
Figure 2. The un
hydrogen evolution, yielding 1,2-bis(diphenylphosphi-
noborane)ethane, dppe(BH3)2, which can be isolated by
extraction in dichloromethane. Colorless crystals of
dppe(BH3)2 obtained by cr
it ce
ystallization from the hex-
ane-dichloromethane solution were used for the single
crystal diffraction determination.

A Facile Route to Phosphanylborohydrides: Synthesis, Crystal Structure and Spectroscopic
6
Properties of 1,2-Bis(Diphenylphosphinoborane)Ethane
angles around phosphorus atoms are
nyl rings in coordi
Cg1-Cg2 = 76.4(3) Å, Cg3-
le I and Cg5-Cg6 = 71.2(3)
on NMR data of 1,2-bis(dipheny
phosphinoborane are also in good
agreement with tcture. It is note-
1
ns of phenyl rings
ylene groups, or-
ore shielded than corre-
)CH ] complex
facile BH3 source
loro-
ontaining nearly
by the Turkish Academy of
esting Catalytic
tonate in the Pres-
2
The average bond
112.9˚, 113.1˚, 105.8˚, and 105.5˚ for B-P-C, B'-P'-C',
C-P-C and C'-P'-C', respectively. Study of the interac-
tions between P atoms and contact atoms in coordination
sphere with average distances (P-B: 1.876 Å for the
molecule I, 1.905 Å for II and P-C 1.804 Å for I, 1.809
Å for II) reveals that the P atoms are surrounded by four
atoms (one boron and three carbon atoms) in nearly ideal
tetrahedral geometry.
Both molecules in an asymmetric unit have a similar
three-dimensional conformation. Dihedral angles be-
tween the least square planes of phe-
Sc
nation sphere of P atoms are
Cg4 = 88.2(3) Å for molecu
Å, Cg7-Cg8 = 71.5(3) Å for molecule II. Figure 2 shows
the unit cell of dppe(BH3)2.
There is no classic hydrogen bond in the structure but
the compound includes several pi-ring interactions be-
tween two asymmetric moieties. Rings are composed of
atoms Cg1 = C1/C6, Cg2 = C7/C12, Cg3 = C15/C20,
Cg4 = C21/C26, Cg1' = C1'/C6', Cg2' = C7'/C12', Cg3' =
C15'/C20', Cg4' = C21'/C26'. Details of the pi-ring inter-
action geometry are given in Table 4.
The solutil-
en )ethane, dppe(BH3)2,
he single crystal stru
worthy that the H NMR spectrum gives two doublets
at 2.15 and 2.38 ppm for the prochiral methylene
groups [28] while the 13C NMR spectrum exhibits only
one signal at 22.93 ppm for the methylene carbons.
Moreover, two separated multiplets at 7.54 and 7.61
ppm are observed for ortho-hydroge
and similar to hydrogens of meth
tho-hydrogens of phenyl rings are not identical due to
their different positions with respect to borane moie-
ties. 31P NMR spectrum shows a peak at –12.5 ppm
which is about 10 ppm m
sponding peak of meso-[HP(BH3)(Ph)CH2]2 complex
[4], indicating that dppe(BH3)2 complex containing
more phenyl rings has more electron-rich phosphorus
atoms. However, 11B NMR gives a peak at –40.06 ppm
for borane groups comparable to the value of –41.6
ppm reported for meso-[HP(BH3)(Ph 22
[ 4]. MS does not show the molecular ion peak ex-
pected at m/z = 425. Instead, it shows peaks at m/z =
429 or 431 due to oxidation of dppe(BH3)2 during the
sampling/ionization whereby BH3 groups are replaced
by the oxo groups.
5. Conclusions
In conclusion, sodium borohydride is a
in the synthesis of phosphanylborohydride compounds
such as 1,2-bis(diphenylphosphinoborane)ethane, dppe
(BH3)2, in high yield. Sodium borohydride and metabo-
rate are easily separated by extraction with dich
methane, providing an easy separation for the preparation
of phosphanylborohydrides with high purity. The adduct
dppe(BH3)2 crystallizes in monoclinic system with space
group P21 and two asymmetric units c
ideal tetrahedral phosphorus atoms.
6. Acknowledgements
Partial support of this work
iences and the Scientific and Technological Research
Council of Turkey (TUBITAK, Project No.: 105M357) is
gratefully acknowledged. L.T. Yildirim thanks Hacettepe
University Scientific Research Unit (grant No. 04
A602004) for financial support. MM thanks TUBITAK
for awarding a PhD fellowship. We thank Mr. Bunyamin
Cosut from Gebze Institute of Technology for performing
mass analysis.
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