Isolation and Structural Characterisation of Monoprotonated 1,2-Bis(diphenylphosphino)benzene in its Tetrabromogallate(III) Salt

Article abstract of DOI:10.1515/znb-1998-1113

Hydrolysis of gallium tribromide complexes of 1,2-bis(diphenylphosphino)benzene in toluene solvent affords crystals of the mono-phosphonium salt [1,2-Ph₂P-(C₆H₄)-PPh₂H]⁺ [GaBr₄]^-

Full text of DOI:10.1515/znb-1998-1113

Isolation and Structural Characterisation of Monoprotonated
1.2-Bis(diphenylphosphino)benzene in its Tetrabromogallate(III) Salt
Marcus Sigl, Annette Schier, Hubert Schmidbaur*
Anorganisch-chemisches Institut der Technischen Universität München,
Lichtenbergstrasse 4, D-85747 Garching, Germany
Z. Naturforsch. 53 b, 1313-1315 (1998); received August 28, 1998
1.2-Bis(diphenylphosphino)benzene, Tertiary Phosphonium Cation, Crystal Structure, Tetra-
bromogallate(III)
Hydrolysis of gallium tribromide complexes of l,2-bis(diphenylphosphino)benzene in
toluene solvent affords crystals of the mono-phosphonium salt [l,2 -Ph2P-(C6H4 )-PPh2H]+
[GaBr4]_ . The structure analysis by single crystal X-ray diffraction allows an internal compar-
ison of Ph2P phosphino and PfbPH phosphonium
functions.
Ph\ /Ph
Introduction
In a recent study of the coordination chemistry of
gallium and indium trihalides with chelating diter-
tiary phosphines a rich series of 1:1 and 1:2 com-
plexes has been isolated and structurally charac-
terised [11. The metals appear in a tetra-, penta- and
hexacoordinated state both in neutral molecules and
in ionic crystals. The compounds are often fluctional
in solution and various sets of isomers have been
discovered [2 ].
Ph Ph
( 1 )
X = Br, I
The tetra&rowogallate crystallizes very well from
chloroform. Its structure has been studied because
the salt provides a unique chance for an internal
comparison of phosphino and phosphonium func-
tions at a common orrßo-phenylene unit.
These compounds show tailored Lewis acid re-
activity depending on the nature of the metal (Ga,
In), the halogen (Cl, Br, I), and the phosphine ligand
[3], They are also sensitive to hydrolysis, and this
is particularly true for the gallium(III) complexes
[41. It therefore was of no surprise that in many
experiments small amounts of the corresponding
hydrolysis products have also been observed even
if moisture was rigorously excluded. A typical ex-
ample has been the title salt, which appeared when-
ever gallium tribromide was reacted with 1,2-bis-
(diphenylphosphino)benzene. After its identity had
been confirmed by standard methods, the compound
was prepared deliberately by controlled hydrolysis
as described below (eq. (1)). Following the same
procedure, but using gallium triiodide, the analo-
gous tetra/odogallate(III) has also been obtained. A
protonation of both phosphorus atoms was never
observed. The formation of a second onium centre
in cis position seems to be hindered by electrostatic
repulsion.
Structural Results
The title compound crystallizes in the monoclinic
space group P2i/n with four formula units in the
unit cell. The lattice is composed of independent
tetrabromogallate anions and P-protonated ligand
cations (Fig. 1).
The anion has a tetrahedral geometry with all
angles close to the 109.48° standard [106.75(5) -
111.96(4)°]. The Ga-Br distances are in the narrow
range 2.3044(2) - 2.3345(11) A. The data compare
well with literature values [1]. The cation shows
no symmetry element, because the P-H bond is
not in the potential mirror plane of the central
phenylene ring. The P-C6H5/C6H4 bond lengths are
significantly different for the protonated and non-
protonated phosphorus atoms PI and P2, respec-
tively. The former bonds:
[Pl-C l, -C lll, -C121 = 1.790(7), 1.783(7),
1.7787(7) A]
are consistently shorter than the corresponding data
of the latter:
* Reprint requests to Prof. Dr. H. Schmidbaur.
für Naturforschung, Tübingen • www.znaturforsch.com
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1314
M. Sigl et al. • M onoprotonated 1,2-Bis(diphenylphosphino)benzene
drous GaBr3 (83 mg, 0.27 mmol) without rigorous exclu-
sion of moisture for 2 h at 20°C. A heavy pale yellow oil
separates, which is taken up with chloroform and layered
with pentane. Colourless crystals (147 mg, 64% yield)
are collected and dried in a vacuum (m.p. 169°C).
C212
V
^ ^ C122
J 1 C 3
* c2 iiN ir
C121
CioffeBrjGaP: (836.81)
Calcd C 43.06, H3.01%,
Found C 42.78, H 2.95%.
C1
cm
C221I
1H NMR (CDCI3, -60°C): 6 9.77, d ['./(PH) = 528 Hz],
1H, PH; 6.94 - 7.82, m, 20H, C6H5/4. 3iP{'H}: 6 17.4, d;
-0.9, d [3/(PP) = 80 Hz], I3C{'H}: 6 131.1, 135.2, 135.6,
136.4, 137.0, 143.1, all m, C6H4; 129.4, s and 131.9, d
[47(PC) = 4 Hz], Cpara-, 133.3, d [27(PC) = 19 Hz] and
133.5, d [27(PC) = 9 Hz], Cortho; 128.7, d [V(PC) = 7 Hz]
and 130.3, d [V(PC) = 13 Hz], Cmeta\ 114.6, dd ['./(PC)
= 8 8 , 47(PC) = 6 Hz] and 121.1, dd ['y(PC) = 91, V(PC)
= 36 Hz], Cipso-
1C112
C 222I
Fig. 1. Molecular structure of [l,2-(diphenylphosphino)-
(diphenylphosphonio)benzene](+)[tetra-bromo-
gallate(III)](-) with atomic numbering (ORTEP drawing,
50% probability ellipsoids, hydrogen atoms of the phenyl
groups omitted for clarity).
The analogous tetraiodogallate(III) was prepared sim-
ilarly, m.p. 164°C, 6 6 % yield.
C3üH25l4GaP2 (1024.81)
Calcd C 35.16, H 2.46%,
Found C 34.69, H 2.33%.
[P2-C2, -C211, -C221 = 1.845(7), 1.8825(7),
1.8840(7) A].
In a similar way all C-P-C angles are smaller for the
PhoP group (P2) as compared to the Ph?PH+ group
(PI):
Crystal structure determination
C1-P1-C111 111.5(3), C1-P1-C121 112.4(3),
Cl 11-P1-C121 109.5(3)°;
C2-P2-C211 102.4(3), C2-P2-C221 102.1(3),
C211-P2-C221 105.9(3)°.
A specimen of suitable quality and size (0.40 x 0.25
x 0 .2 0 mm) was mounted in a glass capillary and used
for measurements of precise cell constants and intensity
data collection. Diffraction measurements were made on
Protonation thus widens the C-P-C angles by an an Enraf-Nonius CAD-4 diffractometer, using graphite-
monochromated Mo-KQ radiation (A = 0.71073 A) with
uj scan mode at -90°C. Lp correction was applied but data
were not corrected for absorption effects. The structure
was solved by Patterson methods and completed by full-
matrix least-squares refinement against F2.
average of 7.3° and shortens the P-C bonds by
0.020 A. There are no significant changes in the
dimensions of the phenyl and phenylene groups.
The conformation of the cation is such that the P I-
H 1bond has a dihedral angle C2-C1-P1-H1 =40.3°
relative to the phenylene plane. It appears that the
vector of the lone pair of electrons at P2 has roughly
the same orientation, i.e. it is directed to the same
side of the phenylene plane. However, the distance
P I— P2 is too long for P1-H1-P2 hydrogen bond-
ing.
C3oH25Br4GaP2, Mr = 836.80, monoclinic,
a =
10.585( 1), b = 23.490(2), c = 12.752( 1) A, ß = 106.25( 1)°,
space group P 2\/n [No. 14],Z = 4, Dcaic = 1.826 gem -3 ,
F(000) = 1624 e, p(Mo-KQ) = 62.8 cm- '. 7189 inten-
sity data were measured up to (sin0/A)max = 0.64 A- ', of
which 5515 independent structure factors were consid-
ered “observed” [F0 > 4<r(F0)] and used for refinement.
All non-H atoms were refined with anisotropic displace-
ment parameters; C-H-atoms were placed in idealized
calculated positions and allowed to ride on their carbon
atoms. The P-H atom was located and refined isotrop-
ically. The function minimized was wR2 = {[Xw(F02-
Fc2)2]/S[w(F02)2]}'/2; w = \/[a2(F02)+(ap)2+bpy, p =
(F02+ 2Fc2)/3; a = 0.1027, b = 0.000. The final R and
Rw values were 0.0590 and 0.1392, respectively, for 338
refined parameters; residual electron densities: +1.196/
-1.767 eA-3 . Important bond lengths and angles are given
Experimental Section
All experiments were carried out using standard equip-
ment. For the preparation of the ligand see Ref. [5].
[ 1 ,2 -(Diphenylphosphino)(diphenylphosphonio)ben-
zene](+)[tetrabromogallate(III)](-)
A solution of 1.2-bis(diphenylphosphino)benzene (122
mg, 0.27 mmol) in 10 ml of toluene is treated with anhy-
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M. Sigl et al. • M onoprotonated l,2-Bis(diphenylphosphino)benzene
Acknowledgement
in the Figure Caption. Further information on the X-
ray structure determination can be obtained from Fach-
informationszentrum Karlsruhe, Gesellschaft für wissen-
schaftlich-technische Information mbH, D-76344 Eggen-
stein-Leopoldshafen, on quoting the depository number
CSD 410067, the names of the authors, and the journal
citation.
This work was generously supported by VW-Stiftung
and Fonds der Chemischen Industrie. The authors are
grateful to Mr. J. Riede for establishing the X-ray data
set.
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