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)
Copyright © 2011 SciRes. JCPT
1
A Facile Route to Phosphanylborohydrides:
Synthesis, Crystal Structure and
Spectroscopic Properties of
1,2-Bis(Diphenylphosphinoborane)Ethane
Leyla Tatar Yildirim
1
, Mehdi Masjedi
2
, Saim Özkar
2
1
Department of Engineering Physics, Hacettepe University, Ankara, Turkey;
2
Department of Chemistry, Middle East Technical University, Ankara, Turkey
E-mail:
1
tatar@hacettepe.edu.tr,
2
mehdimasjedi@yahoo.com,
3
sozkar@metu.edu.tr
Received February 22
nd
, 2011; revised March 16
th
, 2011; accepted March 17
th
, 2011.
ABSTRACT
A novel and simple synthetic way using NaBH
4
in the mixture of H
2
O-THF was applied to prepare 1,2-bis(diphenyl-
phosphinoborane)ethane, dppe(BH
3
)
2
, in high yield and purity. The phosphanylborohydride compound dppe(BH
3
)
2
was
isolated in the form of colorless crystals and characterized by single crystal X-ray diffraction,
1
H,
13
C,
31
P and
11
B NMR
spectroscopy. Prismatic colorless crystals of dppe(BH
3
)
2
were obtained in monoclinic crystal system and space group
P2
1
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) Å
3
.
Keywords: Crystal Structure, Synthesis, Phosphinoborane, Sodium Borohydride, 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 BH
3
molecules coordinated
to dppe. Obviously, in this catalytic reaction, NaBH
4
acts
not only as a substrate to generate hydrogen, but also as a
BH
3
supplier in forming phosphanylborohydrides such as
1,2-bis(diphenylphosphinoborane)ethane, dppe(BH
3
)
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(BH
3
)
2
by complexation of dppe with BH
3
·S(CH
3
)
2
[3], rac/meso-[HP(BH
3
)(Ph)CH
2
]
2
from the reaction of
BH
3
.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(BH
3
)Ph
2
]
-
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(CH
3
)Ph
2
[14]. A
similar phenomenon was observed in the study of chal-
cogenated phosphanylborohydrides K[EP(BH
3
)R
2
] (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 NaBH
4
in an homogeneous aqueous-organic
s o l u t i o n t o y i e l d