New bimetallic complexes supported by a tetrakis(imino)pyracene (TIP) ligand

Article abstract of DOI:10.1039/c1nj20128j

The first examples of palladium dihalide and indium trihalide complexes supported by a tetrakis(imino)pyracene (TIP) ligand have been prepared and structurally characterized.

Full text of DOI:10.1039/c1nj20128j

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PAPER
New bimetallic complexes supported by a tetrakis(imino)pyracene
(TIP) ligandwz
Kalyan V. Vasudevan and Alan H. Cowley*
Received (in Victoria, Australia) 16th February 2011, Accepted 28th March 2011
DOI: 10.1039/c1nj20128j
The first examples of palladium dihalide and indium trihalide complexes supported by a
tetrakis(imino)pyracene (TIP) ligand have been prepared and structurally characterized.
Introduction
Although the first metal complexes supported by the bis(imino)-
acenaphthene (BIAN) ligand were disclosed over four decades
ago,1 it is only much more recently that compounds of this
genre have begun to attract significant attention. Since BIAN
ligands can be regarded as arising from the fusion of a
naphthalene ring to a 1,4-diaza-1,2-butadiene, the rigidity of
the resulting ligand framework has rendered this ligand class
excellent platforms for the support of a wide range of robust
transition metal catalysts that are capable of facilitating a
significant number of important transformations such as the
homopolymerization of alkenes2 and the copolymerization of
carbon monoxide and alkenes.3
Fig. 1 Mono- and difunctional imino ligands.
Given the foregoing, it was anticipated that bifunctional
analogues of the BIAN ligand class might prove to be inter-
esting as e.g. bimetallic catalyst supports, metallopolymers
and molecular wire models. The first two examples of the
so-called tetrakis(imino)pyracene (TIP) ligands were prepared
by two different synthetic routes, each of which employed
tetraketopyracene as the starting material (Fig. 1).4 An initial
objective of this work was to demonstrate the feasibility of
preparing a polymer that incorporated a TIP ligand. This
objective was accomplished by layering two equivalents of
CuBr2 in ethanol on top of the 2,6-diisopropylphenyl-substituted
TIP ligand (dipp-TIP). Crystals of a metallopolymer of overall
composition [BrCu(dipp-TIP)CuBr]n formed slowly from
ethanol/THF solution over a period of 7 days of storage at
ambient temperature (Fig. 2).4 The X-ray crystal structure
comprises a chain of essentially planar Cu(dipp)Cu rhomboids
that are oriented in a close to orthogonal fashion along the
polymer chain. It is clear from the stoichiometry of the
product that CuBr2 is reduced to CuBr in the course of
polymerization. However, the polymer scaffold itself is not
redox active and the Cuꢀ ꢀ ꢀCu distance of 2.718(1) A exceeds
the sum of covalent radii for Cu(I).
Given the importance of palladium-catalyzed cross-
coupling reactions, it is clear that there is a strong interest in
the development of new catalysts that feature this and other
metals. Accordingly, we have turned our attention recently to
the potential usefulness of TIP ligands for the assembly of
stable main-chain polymers that are both tunable and recoverable.
While no such examples incorporating a BIAN ligand have
been reported, an encapsulated pyridyl-substituted BIAN
system which is effective for the copolymerization of carbon
monoxide and 4-tert-butylstyrene5 could potentially be used
for such systems. For the purpose of generating the desired
catalysts, we have recently prepared, structurally characterized
and herein report the requisite palladium monomers of the
type X2Pd(dipp-TIP)PdX2 [X = Cl (1); X = Br (2)] as well as
a series of indium complexes of the form X3In(dipp-TIP)InX3
[X = Cl (3); X = Br (4); X = I (5)].
Department of Chemistry and Biochemistry, 1 University Station,
Austin, TX, USA. E-mail: cowley@mail.utexas.edu;
Tel: +1 512-632-5088
w Dedicated with admiration to Professor Didier Astruc on the
occasion of his 65th birthday.
z CCDC reference numbers 812611–812615. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c1nj20128j
Fig. 2 (CuBr)2TIP polymer.
c
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7.55 (t, 4H, Ar-H); IR (cmꢁ1): 1771s, 1625s, 1601s, 1586, 1458,
Experimental section
1440, 1300, 1187, 1064; mp 299 1C (d).
General considerations
Preparation of (PdBr2)2(dipp-TIP) (2)
Manipulations involving InX3 were performed in a dry and
oxygen-free argon atmosphere by using standard Schlenk or
glove-box techniques. Hexanes and dichloromethane were
dried over Na and CaH2, respectively, and freshly distilled
prior to use. Acetonitrile was used as received from Sigma
Aldrich. The metal halides PdX2 and InX3 were purchased
from Strem Chemicals and used without further purification.
The ligand dipp-TIP4 was synthesized according to the
published procedure.
Acetonitrile (10 mL) was added to a flask charged with dipp-TIP
(0.030 g, 0.034 mmol) following which PdBr2 (0.018 g, 0.068 mmol)
was added and the resulting mixture was stirred at reflux for
45 min. Cooling of the reaction mixture and subsequent
stripping of the reaction solvent afforded a dark red solid
which was washed with deionized water (5 mL) and cold
diethyl ether (2 mL) and dried, resulting in an analytically
pure red powder. The solid was dissolved in a minimal volume
of dichloromethane, filtered and allowed to evaporate slowly
for 3 days, affording a crop of dark red crystalline blocks.
Yield 0.037 g (77%).
Physical measurements
Low-resolution CI mass spectra were collected on a Finnigan
MAT TSQ-700 mass spectrometer. High resolution mass
spectra were acquired on a VG Analytical ZAB-VE sector
instrument. All 1H NMR spectra were recorded at 295 K on a
Varian 300 MHz NMR spectrometer. Deuterated solvents
were obtained from Cambridge Isotopes and stored over 4 A
molecular sieves prior to use. The 1H spectra are reported
relative to tetramethylsilane and referenced to solvent. Melting
points were obtained on a Fisher–Johns apparatus and are
reported uncorrected.
MS (CI+, CH4): m/z 1405 [M + H]+; HRMS (CI+, CH4):
calcd for C62H72N4Pd2Br4 m/z 1405.2332; found, 1405.2326;
1H NMR (CD2Cl2): d 0.86 (d, 24H, CH3), 1.44 (d, 24H, CH3),
3.29 (sept, 8H, -CH), 6.46 (d, 4H, NapC-H), 7.37 (d, 8H, Ar-H),
7.51 (t, 4H, Ar-H); IR (cmꢁ1): 1722s, 1627s, 1603s, 1586s,
1451, 1441s, 1364, 1296, 1187s, 1065s; mp 291 1C (d).
Preparation of [(InCl3)2(dipp-TIP)] (3)
Dichloromethane (20 mL) was added to a flask charged with
dipp-TIP (0.025 g, 0.029 mmol) and InCl3 (0.013 g, 0.059 mmol)
and the resulting orange mixture was stirred for 12 h. The
solvent was stripped and the crude solid was dissolved in a
minimal volume of a 4 : 1 dichloromethane/hexanes solution.
The resulting red solution was filtered and stored at room
temperature for 5 days, affording a crop of red crystals. Yield
0.032 g (84%).
X-Ray crystallography
The X-ray data were collected on a Nonius Kappa CCD
diffractometer equipped with an Oxford Cryostream liquid
nitrogen cooling system. Samples were covered with mineral
oil and mounted on a nylon thread loop prior to data
collection. All data collections were performed at 153(2) K using
graphite-monochromated Mo Ka radiation (l = 0.71069 A).
A correction was applied for Lorentz-polarization in each
case. All structures were solved by direct methods and refined
by full-matrix least squares on F2 using the Siemens SHELXL
PLUS 5.0 (PC) software package.6 All hydrogen atoms were
placed in calculated positions (CH3 = 0.96 A, C–H = 0.98 A,
Ar–H = 0.93 A) and refined using a riding model and a
general isotropic thermal parameter. The program SQUEEZE
was used to remove two disordered dichloromethane molecules
from structures 1 and 3 and one disordered dichloromethane
molecule from structures 4 and 5.
1
MS (CI+, CH4): m/z 1094 (M-InCl3); H NMR (CDCl3):
d 0.69 (d, 24H, CH3), 1.31 (d, 24H, CH3), 2.95 (sept, 8H, -CH),
6.54 (d, 4H, NapC-H), 7.30 (b, 8H, Ar-H), 7.45 (t, 4H, Ar-H);
IR (cmꢁ1): 1727s, 1631s, 1462, 1362s, 1073s, 748s.
Preparation of [(InBr3)2(dipp-TIP)] (4)
Dichloromethane (20 mL) was added to a flask charged
with dipp-TIP (0.025 g, 0.029 mmol) and InBr3 (0.021 g,
0.059 mmol) and the resulting orange mixture was stirred for
12 h. Removal of the reaction solvent in vacuo resulted in the
formation of a solid residue that was subsequently recrystallized
from a saturated 4 : 1 dichloromethane/hexanes solution
stored at room temperature for 5 days. Yield 0.041 g (89%).
Preparation of (PdCl2)2(dipp-TIP) (1)
1
MS (CI+, CH4): m/z 1226 (M-InBr3); H NMR (CDCl3):
Acetonitrile (10 mL) was added to a flask charged with dipp-TIP
(0.030 g, 0.034 mmol) and PdCl2 (0.012 g, 0.068 mmol) and the
resulting mixture was stirred at reflux for 1 h. Cooling of the
reaction mixture and stripping of solvent afforded a red solid.
The crude solid was washed with deionized water (5 mL) and
cold diethyl ether (2 mL) and dried, resulting in an analytically
pure red powder. The solid was dissolved in dichloromethane,
filtered and allowed to evaporate slowly over 3 days thereby
affording a crop of red crystalline blocks. Yield 0.032 g (76%).
MS (CI+, CH4): m/z 1227 [M + H]+; HRMS (CI+, CH4):
calcd for C62H72N4Pd2Cl4 m/z 1227.3122; found, 1227.3130;
1H NMR (CD2Cl2): d 0.90 (d, 24H, CH3), 1.45 (d, 24H, CH3),
3.31 (sept, 8H, -CH), 6.50 (d, 4H, NapC-H), 7.38 (d, 8H, Ar-H),
d 0.75 (d, 24H, CH3), 1.30 (d, 24H, CH3), 2.94 (sept, 8H, -CH),
6.58 (d, 4H, NapC-H), 7.35 (b, 8H, Ar-H), 7.49 (t, 4H, Ar-H);
IR (cmꢁ1): 1655s, 1617s, 1460s, 1360, 1093, 1020, 797s.
Preparation of [(InI3)2(dipp-TIP)] (5)
Dichloromethane (20 mL) was added to a flask charged with
dipp-TIP (0.025 g, 0.029 mmol) and InI3 (0.030 g, 0.060 mmol)
and the resulting orange mixture was stirred for 12 h. Solvent
stripping resulted in the isolation of a red-orange solid.
The crude solid was recrystallized from a saturated 4 : 1
dichloromethane/hexanes solution stored at room temperature
for 5 days. Yield 0.048 g (87%).
c
2044 New J. Chem., 2011, 35, 2043–2046
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MS (CI+, CH4): m/z 1368 (M-InI3); 1H NMR (CDCl3):
d 0.66 (d, 24H, CH3), 1.35 (d, 24H, CH3), 2.95 (sept, 8H, -CH),
6.61 (d, 4H, NapC-H), 7.40 (b, 8H, Ar-H), 7.53 (t, 4H, Ar-H);
IR (cmꢁ1): 1660s, 1611s, 1584, 1459s, 1365, 896, 739s.
Table 2 Selected metrical parameters (A) for (PdCl2)2-TIPꢀ2 CH2Cl2
(1), (PdBr2)2-TIP (2), (InCl3)2-TIPꢀ2 CH2Cl2 (3), (InBr3)2-TIPꢀCH2Cl2
(4) and (InI3)2-TIPꢀCH2Cl2 (5)
Bond
1
2
3
4
5
C(1)–C(5) 1.503(7) 1.506(5)
C(1)–N(1) 1.288(7) 1.281(5)
C(5)–N(2) 1.289(7) 1.290(5)
N(1)–M(1) 2.061(4) 2.050(3)
N(2)–M(1) 2.068(4) 2.051(3)
M(1)–X(1) 2.3889(8) 2.2692(12) 2.3468(13) 2.5047(12) 2.7060(14)
M(1)–X(2) 2.3949(9) 2.2703(13) 2.3864(15) 2.5058(8) 2.7118(11)
M(1)–X(3)
1.542(5)
1.277(4)
1.261(4)
2.309(3)
2.438(3)
1.530(5)
1.275(4)
1.271(5)
2.411(3)
2.381(3)
1.519(9)
1.273(8)
1.267(8)
2.366(5)
2.483(5)
Results and discussion
As detailed above, compounds 1 and 2 were prepared by
treatment of the dipp-TIP ligand with two equivalents of the
appropriate Pd(II) dihalide in hot acetonitrile solution. Both
compounds were structurally authenticated by single crystal
X-ray diffraction, the details of which are presented in Table 1.
A listing of selected metrical parameters for 1 and 2 is
presented in Table 2 and the overall structure of 2 is illustrated
in Fig. 3. Both 1 and 2 are located on an inversion center and,
within experimental error, both molecular frameworks are
planar and the dipp substituents are arranged in an orthogonal
fashion with respect to the rest of the molecule. Akin to the
BIAN ligand, the TIP ligand is redox-active, hence a number
of bonding modes are possible. In the cases of compounds 1
and 2, however, no redox reaction has taken place and the
nitrogen atoms function in a purely donor fashion. Such a
conclusion is evident from the C(1)–N(1) and C(5)–N(2) bond
lengths of 1.281(5) and 1.290(5) A, respectively, for 2 which
correspond to double bonds. Moreover, the C(1)–C(5) separation
of 1.506(5) A is consistent with the presence of a single bond.
As expected, the Pd2+ cation adopts a square planar
coordination environment. The sum of bond angles at this
center is 360.121.
2.3579(12) 2.5041(9) 2.7301(9)
Fig. 3 ORTEP view of 2 with thermal ellipsoids shown at 40%
probability. All hydrogen atoms have been omitted for clarity.
The main group chemistry of the TIP ligand is also proving
to be fruitful. In earlier work, it was found that treatment of
the dipp-TIP ligand with four equivalents of BCl3 resulted in the
formation of [Cl2B(dipp-TIP)BCl2][BCl4]2 which represented
the first example of a dicationic species supported by a TIP
ligand.4 Examination of the X-ray crystal structure of this
compound revealed that the diimine groups are linked to
bonds. No comparable reactions have been explored with the
heavier congeneric Group 13 trihalides with respect to the TIP
ligand. However, it has been demonstrated that the reaction of
the mesityl-substituted BIAN ligand with InCl3 in THF solution
results in the formation of [mes-BIAN-InCl3(THF)] which
possesses a distorted octahedral geometry at the indium center.7
+
BCl2 moieties at either end of the dication by donor–acceptor
Table 1 Selected crystal data, data collection and refinement parameters for (PdCl2)2-TIPꢀ2 CH2Cl2 (1), (PdBr2)2-TIP (2), (InCl3)2-TIPꢀ2 CH2Cl2
(3), (InBr3)2-TIPꢀCH2Cl2 (4) and (InI3)2-TIPꢀCH2Cl2 (5)
1 (812612)
2 (812611)
3 (812614)
4 (812615)
5 (812613)
Empirical formula
M
T/K
Color
Crystal system
Space group
C64H76N4Pd2Cl8
1397.69
153(2)
Red
Orthorhombic
Pbca
C62H72N4Pd2Br4
1405.68
153(2)
Red
Orthorhombic
Pbca
C64H76N4In2Cl10
1485.43
153(2)
Red
Monoclinic
P21/n
C63H74N4In2Br6Cl2
1667.26
153(2)
Orange
Monoclinic
P21/n
C63H74N4In2I6Cl2
1949.20
153(2)
Red-orange
Monoclinic
P21/n
a/A
b/A
19.460(5)
15.257(5)
23.428(5)
90.0
6956(3)
4
1.335
19.605(5)
15.173(5)
23.927(5)
90.0
7117(3)
4
1.312
11.676(5)
17.250(5)
18.117(5)
91.994(5)
3647(2)
10.178(5)
21.687(5)
15.394(5)
92.761(5)
3394(2)
10.370(2)
22.405(5)
15.448(3)
95.681(5)
3572(2)
c/A
b/1
V/A3
Z
2
1.353
2
1.631
2
1.353
Dc/Mg mꢁ3
m/mmꢁ1
0.863
0.25 ꢂ 0.17 ꢂ 0.15
2.785
0.15 ꢂ 0.12 ꢂ 0.10
1.037
0.19 ꢂ 0.14 ꢂ 0.06
4.329
0.17 ꢂ 0.16 ꢂ 0.06
1.037
0.13 ꢂ 0.11 ꢂ 0.05
Crystal size/mm
Reflections collected
Rint
25 734
0.0941
26 799
0.0623
14 713
0.0443
12 781
0.0461
13 664
0.0558
Data/restraints/parameters
R1 [I 4 2 (I)]
wR2 (all data)
Largest peak, hole/e Aꢁ3
7958/0/333
0.0557
0.1456
0.697, ꢁ1.849
8177/0/333
0.0672
0.1906
2.508, ꢁ1.527
8317/0/342
0.0478
0.1377
0.796, ꢁ0.833
7768/0/342
0.0510
0.1049
1.281, ꢁ1.130
8143/0/342
0.0545
0.1168
1.267, ꢁ1.084
c
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Lastly, contrary to the analogous BIAN compounds, the
geometry around each indium center is best described as
distorted trigonal bipyramidal.
Conclusions
In conclusion, we have prepared a series of bimetallic TIP-
supported palladium dihalide and indium trihalide complexes
as precursors for applications such as new catalysts and
novel polymeric materials. All five new complexes exhibit
nitrogen - metal donor–acceptor bonding as evidenced by
single crystal X-ray diffraction studies.
Acknowledgements
We are grateful to the Robert. A. Welch Foundation (Grant
F-0003) for financial support of this work.
Fig. 4 ORTEP view of 5 with thermal ellipsoids shown at 40%
probability. All hydrogen atoms have been omitted for clarity and one
molecule of disordered dichloromethane was removed using
SQUEEZE.
Notes and references
1 M. H. Normant, C. R. Seances Acad. Sci., Ser. C, 1969, 268,
1811–1813; I. Matei and T. Lixandru, Bul. Inst. Politeh. Iasi,
1967, 13, 245–255.
2 B. L. Small, M. Brookhart and M. A. Bennett, J. Am. Chem. Soc.,
1998, 120, 4049–4050; S. D. Ittel, L. K. Johnson and M. Brookhart,
Chem. Rev., 2000, 100, 1169–1203.
3 E. Drent and P. H. M. Budzelaar, Chem. Rev., 1996, 96, 663–681;
C. Bianchini and A. Meli, Chem. Rev., 2002, 225, 35–66.
4 K. V. Vasudevan, M. Findlater and A. H. Cowley, Chem. Commun.,
2008, 1918–1919.
5 J. Flapper and J. N. H. Reek, Angew. Chem., Int. Ed., 2007, 46,
8590–8592.
6 G. M. Sheldrick, SHELL-PC, version 5.03, Siemens Analytical
X-ray Instruments, Inc., Madison, WI, 1994.
7 N. J. Hill, G. Reeske, J. A. Moore and A. H. Cowley, J. Chem. Soc.,
Dalton Trans., 2006, 4838–4844.
8 A. N. Tishkina, A. N. Lukoyanov, A. G. Morozov, G. K. Fukin,
K. A. Lyssenko and I. L. Fedushkin, Russ. Chem. Bull., 2009, 58,
2250–2257.
Interestingly, treatment of the dipp-BIAN ligand with InMe3
in non-coordinating solvents results in the isolation of
(Me–dipp-BIAN–InMe2) which possesses a chiral center at one
of the carbon atoms of the diazabutadiene moiety due to the
attachment of a methyl group.8 We were therefore curious
about the outcome(s) of the reactions of the dipp-TIP ligand
with the heavier congeneric indium trihalides, InX3 (X = Cl (3),
Br (4), and I (5)). However, it was found that 3–5 exhibited
C(1)–C(5) and average C–N bond distances in the ranges of
1.510–1.550 A and 1.260–1.285 A, respectively (Fig. 4). Thus, it is
evident that all three trihalides react with the dipp-TIP ligand in
the same fashion, that is by donor–acceptor bonding between the
dipp-TIP nitrogen atoms and the indium atom. As observed in the
cases of 1 and 2, all three complexes possess an inversion center.
c
2046 New J. Chem., 2011, 35, 2043–2046
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