M535-mS37 trans-Bis[1-benzyl-3-(2,3,4,5,6-pentafluorobenzyl)benzimidazol-2- ylidene]-dibrompalladium(II)

Article abstract of DOI:10.1107/S0108270106039527

The title compound, [PdBr₂(C₂₁H₁₃F ₅N₂)₂], crystallizes with two independent centrosymmetric conformational isomers having a square-planar coordination at the Pd atom. The conformational isomers differ by the ligands having a cis or trans orientation of their benzyl and pentafluorobenzyl rings with respect to the benzimidazole ring plane. The benzimidazole rings are rotated with respect to the coordination plane of the metal by 79.1 (2) and 75.2 (1)° for molecules A and B, respectively. The Pd-Br bond lengths are 2.4218 (8) and 2.4407 (10) A for molecules A and B, respectively, and the Pd-C bond lengths are 2.030 (8) and 2.018 (9) A. The crystal structure contains two types of C-H...F and one type of C-H...Br intramolecular contact, as well as C-H...π interactions.

Full text of DOI:10.1107/S0108270106039527

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
Comment
N-Heterocyclic carbenes (NHCs) have been the subject of
intense research in the ®eld of organometallic chemistry
(Herrmann et al., 2001; Crudden & Allen, 2004; Scott & Nolan,
2005), and NHCs and their metal complexes continue to
attract interest as components in homogeneous catalysis
(Herrmann, 2002). NHCs are increasingly used as the major
structural units for many organometallic compounds and
ISSN 0108-2701
trans-Bis[1-benzyl-3-(2,3,4,5,6-penta-
fluorobenzyl)benzimidazol-2-ylidene]-
dibromopalladium(II)
AytacË Gurhan GokcËe,a* Suleyman Gulcemal,b Muhittin
È
È
È
È
Aygun,a Bekir CËetinkayab and Orhan Buyukgungorc
È
È
È È
È
:
aDepartment of Physics, Dokuz Eylul University, 35160 Buca-Izmir, Turkey,
È
:
bDepartment of Chemistry, Ege University, 35100 Bornova-Izmir, Turkey, and
cDepartment of Physics, Ondokuz Mayõs University, 55139 Kurupelit±Samsun,
Turkey
Correspondence e-mail: aytac.gokce@deu.edu.tr
homogeneous catalysts, but little attention has been paid to
the synthesis of NHC derivatives with ¯uorophilic properties.
NHC complexes with ¯uorinated substituents are rare (Xu et
al., 2000; McGrandle & Saunders, 2005; DincËer et al., 2006;
Burling et al., 2006). Prompted by the novel properties of these
carbene ligands, we decided to prepare some supercritical
carbon dioxide (scCO2) soluble derivatives in the hope that
the resulting carbene complexes can be adapted for catalysis
in scCO2, which is an attractive alternative to conventional
organic liquids for clean synthesis. One of the major limita-
tions of scCO2 as a reaction medium for homogeneous cata-
lysis is its rather low solvent strength towards catalysts derived
from common organometallic complexes (Smart et al., 1997;
Kainz et al.,1997; Jessop et al., 1999). In order to accomplish
this goal, we required a ligand that has electronic properties
similar to those of an NHC ligand but allows solubility in
scCO2. To solve this problem, we synthesized ligands with
different numbers of ¯uorine-containing groups. We report
Received 12 September 2006
Accepted 26 September 2006
Online 31 October 2006
The title compound, [PdBr2(C21H13F5N2)2], crystallizes with
two independent centrosymmetric conformational isomers
having a square-planar coordination at the Pd atom. The
conformational isomers differ by the ligands having a cis or
trans orientation of their benzyl and penta¯uorobenzyl rings
with respect to the benzimidazole ring plane. The benzimida-
zole rings are rotated with respect to the coordination plane of
the metal by 79.1 (2) and 75.2 (1)ꢀ for molecules A and B,
respectively. The PdÐBr bond lengths are 2.4218 (8) and
Ê
2.4407 (10) A for molecules A and B, respectively, and the
Ê
PdÐC bond lengths are 2.030 (8) and 2.018 (9) A. The crystal
structure contains two types of CÐHÁ Á ÁF and one type of CÐ
HÁ Á ÁBr intramolecular contact, as well as CÐHÁ Á Áꢀ inter-
actions.
Figure 1
The molecular structures of conformational isomers A (left) and B (right), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the
30% probability level. H atoms have been omitted for clarity. [Symmetry codes: (i) x + 1, y + 1, z + 1; (ii) x + 2, y, z.]
Acta Cryst. (2006). C62, m535±m537
DOI: 10.1107/S0108270106039527
# 2006 International Union of Crystallography m535

metal-organic compounds
here the syntheses of 1-benzyl-3-(2,3,4,5,6-penta¯uorobenzyl)-
benzimidazolium bromide, (I), and the title compound,
[PdBr2(C21H13F5N2)2], (II), and the crystal structure of (II)
(Fig. 1).
Compound (II) crystallizes with two independent centro-
symmetric conformational isomers, molecules A and B. While
one-half of each molecule is crystallographically independent,
the other half is generated by an inversion centre located at
the metal centre of the molecule. The conformational isomers
differ by the orientations of their benzyl and penta¯uoro-
benzyl rings. The benzyl and penta¯uorobenzyl rings within
each ligand of molecule A are located on the same side of the
benzimidazole ring plane, while these rings in molecule B are
located on opposite sides of the benzimidazole ring plane.
The coordination geometries around the Pd atoms are
slightly distorted square planar, formed by the two coordi-
nating C atoms of the benzimidazole rings and two Br atoms in
a trans arrangement. The cis angles deviate by up to 1.1ꢀ from
the ideal value of 90ꢀ. The planes of the benzimidazole rings
make dihedral angles of 79.1 (2) and 75.2 (1)ꢀ with the coor-
dination planes for molecules A and B, respectively.
Figure 3
Part of the crystal structure of (II), showing the formation of a chain
generated by the CÐHÁ Á Áꢀ interaction involving atom C3A. For the sake
of clarity, H atoms not involved in the motif shown have been omitted.
[Symmetry codes: (*) x + 1, y + 1, z + 1; (c) x, y + 1, z + 1; (d) x 1,
y, z.]
Ê
The PdÐBr bond lengths are 2.4218 (8) and 2.4407 (10) A
for molecules A and B. The PdÐC bond distances between
the NHC ligand and the metal atom are 2.030 (8) and
Ê
2.018 (9) A, comparable to those in other palladium(II)±NHC
È
complexes (Magill et al., 2001; Liu et al., 2003; GokcËe et al.,
double-bond character due to partial electron donation by the
È
2004). Although both CÐN bonds in the NHC rings are single
bonds, their distances are different, as found in related
N atoms to the carbene C-atom donor (Frohlich et al., 1997;
Herrmann et al., 2001). A theoretical study also indicates that
the stability of these carbenes is due to electron donation from
the N-atom lone pairs into the formally vacant p(ꢀ) orbital of
the carbene C atom (herein C1A and C1B) (Karabõyõk et al.,
2005).
È
complexes (GokcËe et al., 2004, 2006; Karabõyõk et al., 2006a,b).
The CÐN bond distances involving the carbene C atom
bonded to Pd are shorter than the other CÐN bond distances
(Table 1). This is possibly indicative of a greater partial
There are three short intramolecular contacts in the crystal
structure (Table 2), two of CÐHÁ Á ÁF type for molecule A and
one of CÐHÁ Á ÁBr type for molecule B. As shown in Figs. 2 and
3, atoms C25B and C3A in the molecule at (x, y, z) act as CÐ
HÁ Á Áꢀ hydrogen-bond donors to the C2A±C7A ring in the
molecule at (2 x, y, 1 z) and the C22B±C27B ring in the
molecule at ( 1 + x, y, z), respectively.
Experimental
For the synthesis of (I), a mixture of penta¯uorobenzyl bromide
(2.10 g, 7.96 mmol) and 1-benzylbenzimidazole (1.652 g, 7.94 mmol)
was re¯uxed in toluene (15 ml) for 2 h. The volume of the solution
was reduced to ca 3±4 ml under vacuum. Diethyl ether (10 ml) was
added and the solution was ®ltered. The remaining white precipitate
was dissolved in methanol (4 ml) and diethyl ether was added (15 ml).
The resulting white crystals were ®ltered off and dried under vacuum
(yield 3.4 g, 91%; m.p. 418 K). Analysis calculated for C21H14BrF5N2:
C 53.73, H 2.99, N 5.97%; found: C 53.53, H 2.94, N 5.89%. 1H NMR
(CDCl3): ꢁ 5.89 (s, 2H, CH2C6H5), 6.19 (s, 2H, CH2C6F5), 7.34±7.63
(m, 9H, Ar±H), 11.71 (s, 1H, CH). 13C NMR (CDCl3): ꢁ 39.58
(CH2C6H5), 52.01 (CH2C6F5), 107.01, 114.58, 127.86, 128.56, 129.48,
131.25, 112.75, 132.63, 136.85, 139.31, 141.30, 143.74, 144.51 (Ar±C),
147.08 (CH). 19F NMR (CDCl3): ꢁ 140.75 (2F, Fo), 149.76 (1F, Fp),
159.22 (2F, Fm). For the synthesis of (II), a 50 ml Schlenk tube was
charged with (I) (187.60 mg, 0.4 mmol), Pd(OAc)2 (44.88 mg,
Figure 2
Part of the crystal structure of (II), showing the formation of a chain
generated by the CÐHÁ Á Áꢀ interaction involving atom C25B. For the
sake of clarity, H atoms not involved in the motif shown have been
omitted. [Symmetry codes: (*) x + 2, y, z; (a) x + 2, y, z + 1; (b)
x + 1, y + 1, z.]
ꢁ
m536 GokËce et al. [PdBr2(C21H13F5N2)2]
Acta Cryst. (2006). C62, m535±m537
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metal-organic compounds
0.2 mmol) and tetrahydrofuran (5 ml). The solution was heated under
re¯ux for 24 h, and the colour of the solution changed from orange to
yellow. Upon cooling to room temperature, hexane (10 ml) was
added to the mixture. The solid was ®ltered off and then recrys-
tallized from CH2Cl2/MeOH (1:5 v/v, 12 ml) (yield 160 mg, 77%; m.p.
541±542 K). Analysis calculated for C42H26Br2F10N4Pd: C 48.35, H
2.49, N 5.37%; found: C 47.60, H 1.96, N 5.36%. 1H NMR (CDCl3): ꢁ
5.91 (s, 4H, CH2C6H5), 6.07 (d, 4H, J = 10 Hz, CH2C6F5), 6.99±7.42
(m, 18H, Ar±H). 13C NMR (CDCl3): ꢁ 53.00 (CH2C6H5), 41.30
(CH2C6F5), 110.33 (d, J = 15.3 Hz), 111.96 (d, J = 10.7 Hz), 123.68,
127.40, 127.65, 128.88, 128.81, 134.56, 134.63, 134.76, 134.89, 135.11,
135.49 (Ar±C), 183.06 (CÐPd). 19F NMR (CDCl3): ꢁ 140.82 (2F,
Fo), 150.57 (1F, Fp), 159.44 (2F, Fm).
Table 2
The intra- and intermolecular hydrogen-bond interactions in (I) (A, ).
ꢀ
Ê
Cg1 and Cg2 are the centroids of the C2A±C7A and C22B±C27B rings,
respectively.
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
C21AÐH21AÁ Á Á F1Ai
C11AÐH12AÁ Á ÁF1A
C11BÐH11BÁ Á ÁBr1Bii
C26BÐH26BÁ Á ÁF4Biii
C25BÐH25BÁ Á ÁCg1iv
C3AÐH3AÁ Á ÁCg2v
0.97
0.97
0.97
0.93
0.93
0.93
2.45
2.39
2.89
2.38
2.59
2.78
3.19 (1)
2.80 (1)
3.70 (1)
3.21 (1)
3.41 (1)
3.62 (1)
132
105
142
148
148
150
Symmetry codes: (iii) x ‡ 1; y; z; (iv) x ‡ 2; y; z ‡ 1; (v) x 1; y; z.
Crystal data
The authors acknowledge the Faculty of Arts and Sciences,
Ondokuz Mayõs University, Turkey, for the use of the Stoe
IPDS-II diffractometer (purchased under grant No. F.279 of
È
the University Research Fund) and Dokuz Eylul University
Research Funds (project No. 04.KB.FEN.100).
3
Ê
[PdBr2(C21H13F5N2)2]
Mr = 1042.89
Triclinic, P1
a = 11.6122 (8) A
Ê
b = 12.1401 (9) A
V = 1912.1 (2) A
Z = 2
3
Dx = 1.811 Mg m
Mo Kꢂ radiation
Ê
1
ꢅ = 2.66 mm
T = 293 (2) K
Ê
c = 13.6590 (11) A
ꢂ = 92.589 (6)ꢀ
ꢃ = 95.610 (6)ꢀ
ꢄ = 92.520 (6)ꢀ
Prism, colourless
0.18 Â 0.16 Â 0.09 mm
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GD3050). Services for accessing these data are
described at the back of the journal.
Data collection
Stoe IPDS-II diffractometer
! scans
Absorption correction: integration
(X-RED32; Stoe & Cie, 2002)
Tmin = 0.646, Tmax = 0.796
23746 measured re¯ections
7493 independent re¯ections
3911 re¯ections with I > 2ꢆ(I)
Rint = 0.121
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535 parameters
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91.1 (2)
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È
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Acta Cryst. (2006). C62, m535±m537
GokËce et al. [PdBr2(C21H13F5N2)2] m537
È