Palladium carbene complexes derived from imidazolium-linked ortho-cyclophanes

Article abstract of DOI:10.1039/b007293l

Reaction of imidazolium-linked ortho-cyclophanes with nickel(II) and palladium(II) salts in the presence of acetate base led to the formation of complexes where a metal centre is bound by a pair of heterocyclic carbenes which themselves are part of a cyclophane skeleton. These cyclophane-metal complexes have been characterised by NMR spectroscopy and (for five complexes) X-ray diffraction studies. The complexes are highly active as promoters of Heck and Suzuki couplings, with preliminary studies showing Heck reactions with turnover numbers approaching 107. The Royal Society of Chemistry 2001.

Full text of DOI:10.1039/b007293l

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Palladium carbene complexes derived from imidazolium-linked
ortho-cyclophanes
Murray V. Baker,* Brian W. Skelton, Allan H. White and Charlotte C. Williams
Department of Chemistry, The University of Western Australia, Nedlands, WA 6907, Australia
Received 8th September 2000, Accepted 17th November 2000
First published as an Advance Article on the web 21st December 2000
Reaction of imidazolium-linked ortho-cyclophanes with nickel() and palladium() salts in the presence of acetate
base led to the formation of complexes where a metal centre is bound by a pair of heterocyclic carbenes which
themselves are part of a cyclophane skeleton. These cyclophane–metal complexes have been characterised by
NMR spectroscopy and (for five complexes) X-ray diffraction studies. The complexes are highly active as
promoters of Heck and Suzuki couplings, with preliminary studies showing Heck reactions with turnover
7
numbers approaching 10 .
Introduction
C2 carbons of the imidazolium units are positioned within
the cavity between the arene rings, and are thus relatively
inaccessible to attack by approaching reagents. The imid-
azolium-linked ortho-cyclophanes III–V and related benz-
imidazolium-linked counterparts (e.g. VI) can be synthesized
in the same way as the [1,3,5]- and para-cyclophanes. The
ortho-cyclophanes are relatively flexible structures, however,
Heterocyclic carbenes derived from imidazolium ions form com-
1
–5
plexes with many transition metals, particularly palladium
6–10
and nickel.
Reports of carbene complexes include examples
containing unidentate carbene ligands (e.g. 1), chelating di-
carbene ligands (e.g. 2), and even a rhodium–cyclooctadiene
adduct 3 in which a bidentate ligand contains two carbene
18
and their NMR spectra do show signs of fluxionality. For
11
units within a cyclophane structure. Carbene ligands have
some similarities to phosphine ligands, but metal–carbene
complexes are often more stable than similar metal phosphine
example, dynamic behaviour has been noted in the NMR
spectra of solutions containing VI, this behaviour being
interpreted in terms of interconversion between anti and syn
12–14
complexes,
and are thus attracting interest as possible
19
conformations. In ortho-cyclophanes the imidazolium (or
alternatives to transition-metal phosphine complexes for
applications in catalysis. Complexes such as the palladium
di-carbene complexes 1 and 2, for example, have been used
as catalysts for Heck and Suzuki couplings and CO–olefin
benzimidazolium) C2 carbons are not positioned within the
cavity between the benzene rings and so are thus more
accessible to attack by approaching reagents.
In this paper we report the synthesis of a family of transition
metal di-carbene complexes where the di-carbene is formally
obtained by deprotonation at C2 of the imidazolium (or
benzimidazolium) units of the parent ortho-cyclophanes III–
3
,13,15,16
co-polymerisation,
and demonstrate excellent thermal
16
stability.
18
VI. For convenience, throughout this paper we will refer
to the ortho-cyclophanes III–VI as “free” cyclophanes and the
derived metal complexes as “cyclophane complexes”.
The cyclophane skeleton brings interesting structural
possibilities to its complexes. For example, its rigidity may
confer added stability on the metal–carbene structure which
could be a valuable feature if the complexes were to be useful
as catalysts. We have found that the cyclophane complexes are
indeed exceptionally stable and do promote Heck and Suzuki
reactions, some with outstanding turnover numbers. We report
here the findings of our initial studies of the catalytic activity
of a number of these complexes as well as their full charac-
terisation by spectroscopic and X-ray methods.
Results and discussion
Synthesis of cyclophane complexes
The free cyclophanes III–VI were synthesized, as their
dibromide salts III–VIؒ2Br, by reactions of derivatives of
bis(bromomethyl)benzene with appropriate bis(imidazolyl-
methyl)benzene derivatives, using methods developed for
We have recently reported the synthesis of [1,3,5]-cyclophane
cations (e.g. I) and para-cyclophane cations (e.g. II) in which
arene rings are linked by imidazolium units. Molecular
models suggest these cyclophanes to be conformationally quite
rigid structures, a hypothesis supported by their NMR spectra
which show no signs of fluxionality. In these structures the
17
17
[1,3,5]- and para-cyclophanes. Metal complexes were then
formed by reaction of the free cyclophanes with suitable metal
sources in the presence of a mild base (acetate). We did not
attempt to isolate any free cyclophane di-carbenes or generate
DOI: 10.1039/b007293l
J. Chem. Soc., Dalton Trans., 2001, 111–120
This journal is © The Royal Society of Chemistry 2001
111

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9,21
cations. Other workers
report seeing decomposition of the
starting materials during attempts to prepare chelate di-carbene
complexes from bis(imidazolium) precursors where the linkages
between the imidazolium units extend beyond a CH group.
2
The cyclophane skeleton may impose steric and conformational
constraints that disfavour certain side reactions.
Amongst complexes 4–12, the diiodides 5 and 8 were
di-carbenes in situ by treatment of cyclophanes with strong
bases.
The carbene complexes 1 and 2 have been synthesized by the
quite soluble in polar solvents (CH Cl , acetone, dmso) but
2
2
the dibromides 4, 7, 10, and 12 were poorly soluble in all
solvents and could not conveniently be purified by recrystal-
lisation. Nevertheless, these complexes were sufficiently
soluble in dmso to permit their characterisation by NMR
spectroscopy. Solubility was improved by incorporation of
alkyl substituents into the cyclophane skeleton, as in 9, which
was highly soluble in dmso, as well as in less polar solvents such
as acetone.
reaction of Pd(OAc) with the appropriate imidazolium iodides
2
20
in dmso. Following related procedures, we synthesized the
palladium carbene complex 4 by reaction of Pd(OAc) with
2
IIIؒ2Br in dmso at 60–100 ЊC. This method frequently resulted
in formation of black reaction mixtures (presumably a con-
sequence of formation of colloidal Pd) but this problem was
avoided when dmf or CH CN was used as the reaction solvent
Palladium complexes such as 2 are already recognised
3
22
instead of dmso. Appropriate combinations of a metal source,
an acetate source (base), and a free cyclophane salt could be
used to achieve similar results, and were used for the synthesis
of cyclophane complexes 5–10. For example, the palladium
iodide adduct 5 was synthesized by reaction of the salt IIIؒ2PF6
as highly stable. Complexes 4–12 were also found to be
remarkably stable to air and heat. These complexes were
routinely synthesized under an atmosphere of air (albeit
in a sealed Schlenk flask) and could be heated in dmso or
dmf solutions in air to at least 140 ЊC with little or no
decomposition. To compare the stability of a cyclophane metal
complex with that of a similar non-cyclophane complex,
a solution of 2 and 5 in (CD ) SO, with 1,3,5-trioxane as an
with PdI in the presence of two equivalents of NaOAc, or
2
by reaction of IIIؒ2Br with Pd(OAc) in the presence of two
2
equivalents of NaI.
3
2
Variants of the structures exemplified by 4–10 may also be
internal standard for integration of NMR signals, was heated
overnight at 140 ЊC under an atmosphere of air. Examination
of the solution by NMR spectroscopy showed that ca. 60% of
2 had decomposed, whereas only ca. 15% of the cyclophane
complex 5 had decomposed. The enhanced stability of the
cyclophane complexes may result from increased rigidity
of the carbene–metal bonding imposed by the cyclophane
skeleton.
formed. For example, reaction of PdI with two equivalents
2
of the diacetate salt IIIؒ2OAc produced the palladium bis-
cyclophane complex 11. The “open” complex 12, which lacks
the complete cyclophane skeleton, was readily synthesized by
reaction of the salt VIIؒ2Br with Pd(OAc) in dmf.
2
The syntheses of complexes 4–12 were remarkably clean.
We saw no evidence for decomposition of the free cyclophane
1
12
J. Chem. Soc., Dalton Trans., 2001, 111–120

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1
a
Table 1 H NMR data (δ, J/Hz) for complexes 4–12
Imidazolium
H4/H5
Complex
Benzylics
Aromatics
Other
2
4
5
6
7
8
5.10, 6.53 (8H, AX, J 14.2)
7.45 (4H, s)
7.45 (4H, s)
7.41 (4H, s)
7.50 (4H, s)
7.51 (4H, s)
7.39 (4H, s)
7.34–7.39, 7.75–7.80 (8H, m)
7.35–7.40, 7.75–7.80 (8H, m)
7.35–7.40, 7.80–7.85 (8H, m)
7.50–7.55, 7.83–7.88 (8H, m); 8.34 (4H, s)
7.50–7.55, 7.83–7.88 (8H, m); 8.35 (4H, s)
7.61 (4H, s)
HH
2
5.07, 6.44 (8H, AX, J 14.1)
HH
2
5.26, 7.89 (8H, AX, J 14.5)
HH
2
5.25, 6.57 (8H, AX, J 14.4)
HH
2
5.24, 6.54 (8H, AX, J 14.5)
HH
b
2
3
9
5.03, 6.70 (8H, AX, J 14.3)
0.84 (12H, t, JHH 7.0, 4 × CH );
3
HH
1
1
.18–1.40 (32H, m, 16 × CH ); 1.49–
2
.58 (8H, m, 4 × CH ); 2.55–2.66
2
(
8H, m, 4 × CH2)
2
1
0
5.73, 7.05 (8H, AX, J 14.8)
7.39–7.44, 8.09–8.14 (8H, m)
7.35–7.40, 8.14–8.19 (8H, m, benz-
imidazolium C H )
HH
6
4
2
1
1
1
2
5.31, 6.61 (8H, AX, J 14.3)
7.52 (4H, s)
7.42–7.47, 7.84–7.89 (8H, m)
7.38–7.43, 7.83–7.88 (4H, m)
HH
2
5.11, 6.48 (4H, AX, J 14.4)
7.29, 7.62 (4H,
3.91 (6H, s, 2 × CH3)
HH
3
AX, J 1.9)
HH
a
b
Recorded at 500.13 MHz and ambient temperature from solutions in (CD ) SO unless otherwise indicated. From a solution in (CD ) CO.
3
2
3 2
1
H NMR spectra of 4–12 the benzylic protons appear as two
separate doublets. We tentatively assign the more downfield
doublet to the endo benzylic protons (closer to the metal) and
the more upfield doublet to the exo protons. For the palladium
complexes 4, 5, 7–9, 11, and 12 the chemical shifts of these
protons fall into narrow bands (exo, δ 5.0–5.3; endo, δ 6.4–6.7).
Relative to the signals due to the endo hydrogens in the
1
palladium complexes, the H NMR signal attributed to the endo
benzylic protons in the nickel complex 6 occurs at unusually
low field (δ 7.89), perhaps a consequence of a stronger Hendo
–
metal interaction in the nickel case (but see Structural studies,
below). Differences in proximity to the metal centre have been
invoked to account for similarly disparate chemical shifts for
geminal protons in palladium complexes of other heterocyclic
12
1
carbenes. The H NMR signals for the benzylic protons of the
benzimidazolium-derived complex 10 fall outside the ranges
exhibited by these protons in the other palladium complexes,
perhaps a consequence of differences in the interactions
between the arene and benzimidazolium groups that make up
the cyclophane “cone”. Steric repulsion between these groups
may tend to open up the cone and in doing so distort the
conformation around the benzylic centres.
The C NMR spectra for the cyclophane complexes (Table 2)
showed the expected signals. Each complex displayed a signal
due to the carbene carbons in the region δ 159–175, within
the range reported previously for carbene signals of complexes
1
Fig. 1 H NMR spectra [(CD ) SO, 500.1 MHz, ambient temperature]
3
2
for (a) the free cyclophane salt IVؒ2Br and (b) the corresponding cyclo-
phane complex 8.
13
NMR spectroscopic studies
Reactions of the cyclophanes with metal sources were easily
followed by H NMR spectroscopy. All of the cyclophanes were
fluxional on the NMR timescale and exhibited broad spectral
features (e.g. Fig. 1(a)) due to conformational flexibility.
The cyclophane–metal complexes, however, displayed sharp
spectra (e.g. Fig. 1(b)), which we interpret as a consequence
of the cyclophane skeleton being locked into a single con-
formation by co-ordination.
1
having similar metal co-ordination environments to those of
19,23
6,8,25
4
–12.
Structural studies
The results of the single crystal X-ray studies of complexes
Examination of the spectra of complexes 4–9 and 11 indi-
cated that the H4/H5 protons of the co-ordinated imidazolium
units were equivalent and resonated at lower field (ca. δ 7.5,
see Table 1) than the corresponding protons in the free cyclo-
phane precursors (ca. δ 7.1). These results are consistent with
the cyclophane skeletons in the complexes being in the syn
conformation, reminiscent of the cone conformation of calix-
4ؒ2CH CN, 5ؒ0.5CH OH, 6ؒdmso, 11ؒ6CH NO and 12ؒ
3
3
3
2
(CH ) CO are consistent with the stoichiometries, connec-
3
2
tivities, and stereochemistries implied therein (caveat: “4”, see
below), each complex being mononuclear with each cyclo-
phane ligand chelating a pair of obligate cis-co-ordination sites
about the four-co-ordinate (‘square-’) planar metal atom, the
complexes being diversely solvated (Fig. 2).
[
4]arenes. In contrast to the present study, previous studies
For complex 5ؒ0.5CH OH one formula unit devoid of crys-
3
16,20
1
of palladium carbene complexes
signals due to the H4/H5 protons in the complexes occurred at
higher field than the signals due to the corresponding protons
in the precursor imidazolium salts. The more downfield
chemical shift for the H4/H5 protons in the cyclophane com-
plexes may be a consequence of H4 and H5 being held within
the region of deshielding associated with the arene rings,
whereas in the free cyclophanes (which are fluxional on the
NMR timescale) the environments of H4 and H5 are averaged
found that the H NMR
tallographic symmetry comprises the asymmetric unit of the
structure. The solvent moieties have no intimate interaction
with the cones of the substrate molecules, simply occupying
lattice voids about special positions at the origin (etc.),
modelled with the methyl carbon located on the origin (albeit
with high ‘thermal’ motion presumably encompassing disorder
by a small shift to either side), and the oxygen disordered to
either side, contacting the ligand periphery (O ؒ ؒ ؒ H(25) (1 ϩ x,
y, z) 2.5 Å). The approach of a screw-related substrate molecule
towards “inclusion” with the parent may go some way towards
24
23
amongst sites near, and away from, the benzene rings. In the
J. Chem. Soc., Dalton Trans., 2001, 111–120
113

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Fig. 2 Molecular projections, viewed similarly, oblique to the co-ordination plane, and showing any “included” solvents for: (a) 6ؒdmso;
(
b) “4”ؒCH CN; (c) the cation of 11 with included nitromethanes; (d) 12; and (e) the approach of a symmetry related molecule (¹ Ϫ x, ¹ ϩ y,
3
¯
²
¯
²
¹
Ϫ z) to the parent in 5.
¯
²
compensating for the lack of solvation. The co-ordination
geometry including the cyclophane about the palladium is
distorted square planar, the angle between the two carbene
carbons (C–Pd–C) being 82.2(1)Њ, with the angle between
the two iodide atoms (I–Pd–I) 96.53(1)Њ. The lengths of the
Pd–carbene bonds in 5 are similar (2 × 1.984(4) Å) to those
1
14
J. Chem. Soc., Dalton Trans., 2001, 111–120

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13
a
Table 2
C NMR data (δ) for complexes 4–12
Imidazolium
C4/C5
Complex Carbene Benzylics
Aromatics
Other
4
5
6
7
8
9
160.0
162.4
162.1
160.0
162.5
163.1
50.7
50.6
51.2
50.9
50.9
52.1
121.9
122.0
122.3
122.1
122.1
122.3
129.4 (CH), 132.2 (CH), 135.6 (C)
129.4 (CH), 132.2 (CH), 135.5 (C)
129.3 (CH), 131.9 (CH), 136.4 (C)
127.2 (CH), 127.5 (CH), 131.9 (CH), 132.7 (C), 132.9 (C)
127.2 (CH), 127.5 (CH), 131.9 (CH), 132.6 (C), 133.0 (C)
b
c
133.9 (CH and C), 143.0 (C)
14.3 (CH ), 23.3, 29.8, 30.4, 32.0,
3
3
2.5, 32.8 (all CH2)
1
1
1
0
1
2
175.0
166.8
159.9
50.3
51.9
50.2
129.3 (CH), 134.2 (CH), 134.6 (C)
129.5 (CH), 132.2 (CH), 136.0 (C)
129.3 (CH), 131.6 (CH), 135.5 (C)
112.6 (CH), 123.8 (CH), 133.4 (C)
122.9
121.5, 124.2
37.8 (CH3)
a
b
Recorded at 125.8 MHz at ambient temperature from solutions in (CD ) SO unless otherwise indicated. From a solution in (CD ) CO.
3
2
3 2
c
13
The proton-coupled C NMR spectrum showed a broad singlet and a broad doublet (splitting ca. 160 Hz) centred at δ 133.9.
Table 3 Selected substrate parameters
a
Species
6
5
“4”
11 (cation)
12
Distances/Å
M–C(22)
M–C(42)
1.862(2)
1.863(2)
2.2285(6)
2.2208(5)
2.20(3)
1.984(4)
1.984(4)
2.6378(4)
2.6510(4)
2.15
2.13
2.80
1.962(6)
1.970(6)
2.4728(9)
2.4786(9)
2.11
2.09
2.80
2.050(2)
2.052(2)
(2.052(2))
(2.050(2))
2.19(3)
2.23(3)
2.82
1.982(5)
1.989(4)
2.4645(8)
2.4688(7)
2.06
—
2.90
M–X(1)(C(42Ј))
M–X(2)(C(22Ј))
b
H ؒ ؒ ؒ H
2
.16(3)
c
M ؒ ؒ ؒ H(endo)
2.79(2)
Ϫ2.83(2)
Ϫ2.92
Ϫ2.94
Ϫ3.02
Ϫ3.06
Angles/Њ
C(22)–M–C(42)
87.49(8)
82.2(1)
91.9(1)
171.5(1)
172.91(9)
89.3(1)
85.5(2)
89.5(2)
174.1(2)
174.0(2)
89.1(2)
81.35(7)
98.65(7)
180(—)
[180(—)]
[98.65(7)]
[81.35(7)]
89.7(2)
87.5(1)
178.8(1)
176.7(1)
89.1(1)
C(22)–M–X(1)(C(42Ј))
C(22)–M–X(2)(C(22Ј))
C(42)–M–X(1)(C(42Ј))
C(42)–M–X(2)(C(22Ј))
X(1)–M–X(2)
90.35(6)
174.48(7)
177.82(5)
87.22(5)
94.94(2)
96.53(1)
95.71(3)
93.65(3)
Interplanar dihedral angles/Њ
C X /C (1)
27.09(6)
29.74(6)
87.34(6)
88.51(6)
56.82(7)
88.84(9)
69.17(8)
69.02(8)
72.64(8)
69.77(8)
44.7(1)
36.8(1)
87.9(1)
89.3(1)
80.6(1)
70.1(2)
65.6(2)
69.1(2)
74.8(2)
63.3(2)
25.7(2)
—
87.4(2)
87.4(2)
—
87.3(3)
69.8(2)
69.7(2)
—
44.19(7)
23.61(7)
82.05(5)
84.10(8)
67.70(7)
67.16(8)
70.97(7)
75.50(7)
70.43(7)
71.43(7)
—
2
2
6
C X /C (3)
28.2(1)
85.1(2)
79.2(2)
—
86.5(2)
—
—
67.6(2)
57.9(2)
2
2
6
C X /C N (2)
2
2
3
2
C X /C N (4)
2
2
3
2
C (1)/C (3)
6
6
C N (2)/C N (4)
3
2
3
2
C (1)/C N (2)
6
3
2
C (1)/C N (4)
6
3
2
C (3)/C N (2)
6
3
2
C (3)/C N (4)
—
6
3
2
Out-of-plane metal atom deviations δM/Å
C N (2)
0.055(3)
0.181(3)
0.332(7)
0.077(6)
0.04(1)
0.03(1)
0.178(3)
0.324(3)
0.086(9)
0.026(9)
3
2
C N (4)
3
2
Torsion angles/Њ
Ϫ108.1(2)
Ϫ117.9(4)
118.3(4)
114.8(4)
Ϫ111.2(4)
86.3(5)
Ϫ85.1(4)
89.3(5)
Ϫ104.8(6)
105.6(6)
104.2(6)
Ϫ105.4(6)
92.1(7)
Ϫ91.2(7)
93.1(6)
Ϫ109.8(2)
115.8(2)
118.3(2)
Ϫ115.6(2)
87.7(2)
Ϫ89.4(2)
85.7(2)
—
107.1(5)
—
Ϫ109.8(5)
—
—
C(22)–N(21)–C(1)–C(11)
C(22)–N(23)–C(2)–C(32)
C(42)–N(43)–C(4)–C(12)
C(42)–N(41)–C(3)–C(31)
C(12)–C(11)–C(1)–N(21)
C(11)–C(12)–C(4)–N(43)
C(32)–C(31)–C(3)–N(41)
C(31)–C(32)–C(2)–N(23)
1
1
04.0(2)
02.9(2)
Ϫ102.8(2)
1.0(2)
Ϫ92.3(2)
1.6(2)
Ϫ92.9(2)
9
9
93.7(6)
Ϫ91.5(6)
Ϫ83.1(5)
Ϫ91.5(7)
Ϫ89.6(2)
a
b
c
Also: H(1a) ؒ ؒ ؒ H(3aЈ) 2.17(3); H(2a) ؒ ؒ ؒ H(4bЈ) 2.14(4) Å. Contacts between the endo hydrogen pairs on C(2,3), C(1,4) respectively. The range of
the four values (inclusive of the appropriate methyl hydrogens in complex 12).
observed in other palladium carbene complexes such as 2
square planar, but the angle between the two carbene carbons
(C–Ni–C, 87.49(8)Њ) is expanded relative to that for the
palladium complex 5, presumably a consequence of shorter
metal–ligand atom distances in the nickel case (Ni–C 1.862,
1.863(2) Å, cf. the Pd–C bonds in 5 (Table 3)) consistent with the
literature, where, in general, nickel–carbene bonds appear to be
20
(
1.988, 1.989(8) Å).
In complex 6ؒdmso the co-ordination environment about the
nickel is completed by chloride ions, this complex also being
mononuclear with the imidazolium groups bound in a cis
arrangement. The geometry about the nickel is also distorted
J. Chem. Soc., Dalton Trans., 2001, 111–120
115

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6
shorter than palladium–carbene bonds, the present particularly
The conformations of the cyclophane ligand change quite
so. There is little apparent impact on the M ؒ ؒ ؒ CH hydrogen
appreciably across the four complexes 4, 5, 6 and 11. In all
cases, the imidazolium planes are almost normal to the co-
ordination planes, as expected and in keeping with the various
putative symmetries. In the nickel complex 6 these two imid-
azolium planes are effectively normal to each other also, with
metal atom deviations δM rather small, but, in the three
palladium complexes, the interplanar dihedral angles are
considerably reduced with the metal atom deviations increased,
and with rather erratic differences within each pair across
all four complexes. This variability is reflected in the torsions
in the bonds to either side of the benzylic carbon atoms, the
endo-hydrogens of which contact each other pairwise above
and below the co-ordination plane, compounded by additional
inter-ligand contacts in the cation of 11. Changes in pitch are
also evident between the pairs of phenylene planes among the
three complexes, a feature possibly related to the presence or
otherwise of included solvent.
2
estimates (Table 3). One formula unit, 6ؒdmso, devoid of
crystallographic symmetry, comprises the asymmetric unit of
the structure. Methyl C(01) of the dmso projects into the cone
of the ligand, so that the formulation of this compound may
be better represented as [{(CH SOCH )L}NiCl ], a neutral
3
3
2
aggregate. Despite the inclusion of the methyl, the sulfur is
offset towards one side of the cone and its interactions, albeit
long, may be influential in determining the detail of the solvent
disposition (S ؒ ؒ ؒ C(45) 3.760(2) Å), with an equivalent contact
to a nearby symmetry-related molecule (S ؒ ؒ ؒ C(35)( x¯ , y Ϫ ¹,
¯
²
¹
Ϫ z) 3.738(2) Å).
¯
²
A similar parent array is also found in complex “4”ؒ2CH3-
CN, the apparent presence of hydroxide in this material being
rationalised on the basis of the procedure (see Experimental
section) employed to obtain somewhat unsatisfactory (note
R ) crystals. While the detailed derivative geometries should
int
be treated circumspectly, the global view is of interest, the cone
of the ligand in this case including one of the co-crystallised
acetonitrile molecules, quasi-axial in its approach, with the
methyl group nearest the metal.
In the final complex, 12ؒ(CH ) CO, the cyclophane is incom-
3
2
plete, and, devoid of the ring-closure constraint, significant
differences are found between the geometric parameters vis-
à-vis their counterparts in the other palladium complexes.
The “bite” of the ligand is larger than in the other arrays,
interestingly without any diminution in the associated Pd–C
distances, despite the fact that the palladium atoms are more
nearly coplanar with the imidazolium rings in this complex
than in all except “4”. It is interesting that in “4”, despite
the larger X–Pd–X bite and the probable substitution of the
bromides by lighter atoms, Pd–X is longer than in 12. In the
bromide complexes “4” and 12 the interplanar dihedral angles
between the pair of imidazolium planes are markedly larger
than those of the iodide complex 5 and the cation 11. This
result suggests that either the ligand cone is very susceptible to
distortion by rather random lattice or inclusion effects, or that
the latter are rather small, and that, regardless of the changes in
Pd–C distances, the electronic parameters of a second ligand
parallel those of the two iodide donors, seemingly rather
unlikely.
One half of the formula unit 11ؒ6CH NO comprises the
3
2
asymmetric unit of the structure, the palladium atom being
located on a crystallographic inversion centre and the complex
being ionic (solvated). Nitromethane solvent molecule 1 lies
in association with the ligand, so that the overall formulation
of the structure may be best represented as [Pd{L(CH3-
NO )} ]I ؒ4CH NO , the included solvent lying with its
2
2
2
3
2
plane quasi-normal to its N ؒ ؒ ؒ Pd line, and the other two
independent solvent molecules occupying lattice voids, albeit
with long contacts to various neighbouring ligands. This
complex array is more symmetrical, but the geometry at the
palladium centre is still distorted square planar, the angle
between the two carbene carbons on either side of the
palladium (C–Pd–C) being 81.35(7)Њ, smaller than the corre-
sponding angle in 5. The Pd–carbene bond lengths in the
cationic bis(cyclophane) complex 11 are significantly longer
(
2.050(2) (× 2), 2.052(2) Å (× 2)) than those for the single
cyclophane complex 5.
Catalytic properties of palladium–carbene complexes
The metal environments of complexes 4–6 and 11, of
putative mm or mmm symmetry, have precursive immediate
counterparts. In the case of the nickel complex 6, perhaps the
Our initial studies of reactions catalysed by cyclophane
complexes have focussed on the activity of 5, 9, and 12 in
some Heck and Suzuki reactions (eqns. 1 and 2), and results of
6
most closely related comparator is 13, in which Ni–C are
1.871(4), 1.942(4) Å, trans angles to Cl and P being 177.6(2),
155.8(2)Њ respectively, with C–N–C 84.9(2)Њ, and Ni–Cl
2.195(1) Å, rather shorter than in 6, with Ni–C trans slightly
(
1)
longer, in the context of a bidentate ligand of rather similar
20
‘
bite’ (Table 3). Structure 5 has a closer counterpart in 2, in
which Pd–C are 1.989(8), 1.988(7) Å, C–Pd–C 83.2(3)Њ, with
Pd–I 2.6450(9), 2.6573(8) Å, closely resembling the present.
Compared to the situation in 5, the Pd–C distances in the cation
26
1
1 are appreciably lengthened, as is also the case in 14, where
they are grossly (and curiously) different: 2.049(4), 2.137(5) Å,
C–Pd–C (centrosymmetric cation) 81.8(2)Њ (an erratum has
been noted in the Cambridge Data Base entry but only in
respect of the nitrogen atoms). Seemingly, the Pd–C distances
are shorter in “4” relative to those of 5. It appears more
likely that this is a consequence of a different trans effect of the
bromine, rather than the smaller OH (if it be that) component.
(
2)
these studies are summarised in Table 4. While the catalysts
promoted Heck and Suzuki reactions under an atmosphere of
air, results under those conditions were irreproducible; results
reported in Table 4 are for reactions performed under nitrogen
and were reproducible. These results, particularly entries 4–7,
9
, and 10, reveal high catalyst turnover numbers, with the out-
standing catalyst being the cyclophane complex 5. Interestingly,
has consistently superior performance to the non-cyclophane
5
analogue 12. The result may be a consequence of the different
co-ordination geometries about the metal centre (see Structural
studies above) or higher stability of the metal–carbene binding
in the more rigid cyclophane structure 5 compared to that in
the “open” structure in 12. Studies to isolate the factors that
1
16
J. Chem. Soc., Dalton Trans., 2001, 111–120

View Article Online
a
b
Table 4 Heck and Suzuki couplings promoted by palladium–cyclophane complexes
Amount of
catalyst/mol%
Alkene/boronic
acid
c
c
Entry
Catalyst
Aryl halide
Time/h
Yield (%)
TON
Heck couplings
Ϫ4
1
2
3
4
5
6
7
8
9
0
5
9
12
5
5
9
12
5
1.4 × 10
6.3 × 10
3.6 × 10
1.4 × 10
1.4 × 10
6.3 × 10
3.6 × 10
1.4 × 10
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
4-Bromonitrobenzene
4-Bromonitrobenzene
4-Bromonitrobenzene
Methyl acrylate
Methyl acrylate
Methyl acrylate
Butyl acrylate
Butyl acrylate
Butyl acrylate
Butyl acrylate
Methyl acrylate
Butyl acrylate
Butyl acrylate
24
24
24
24
44
44
44
24
40
40
20
52
46
140,000
83,000
Ϫ4
Ϫ4
130,000
710,000
7,100,000
160,000
260,000
150,000
680,000
250,000
Ϫ4
>99
Ϫ4
>99
>99
93
21
95
Ϫ5
Ϫ4
Ϫ4
Ϫ4
5
12
1.4 × 10
3.6 × 10
Ϫ4
1
90
Suzuki couplings
Ϫ3
1
1
1
2
5
12
1.4 × 10
3.6 × 10
4-Bromotoluene
4-Bromotoluene
Phenylboronic acid
Phenylboronic acid
24
40
67
29
48,000
8,100
Ϫ3
a
Reactions were conducted at 140 ЊC using 10 mmol each of the aryl halide, the alkene, and Et N, and the specified amount of catalyst in
3
3
b
dmf (1 cm ). Reactions were conducted at 120 ЊC in dmf containing the specified amount of catalyst along with 10 mmol each of 4-bromotoluene,
phenylboronic acid, and K CO . Yields and turnover numbers (TONs) were determined by H NMR spectroscopy.
c
1
2
3
contribute to the highest catalytic activities in these systems are
in progress.
and, in cases where DEPT spectra gave ambiguous results,
1 13 13
fully H-coupled C NMR spectra and/or C NMR spectra
recorded with selective decoupling of specific protons. Mass
spectra (FAB) were recorded using a VG Autospec mass
spectrometer with a caesium ion source and a m-nitrobenzyl
alcohol matrix. Microanalyses were performed by the Micro-
analytical Laboratory at the Australian National University,
Canberra. Synthesis and isolation of free cyclophanes and
cyclophane complexes were conducted in air. All solvents were
re-distilled (under the laboratory atmosphere) prior to use,
except for N,N-dimethylformamide (APS Finechem, AR grade)
and dimethyl sulfoxide (Ajax Chemicals, AR grade), which
were used as received.
22
Previous researchers
have reported induction periods
for Heck reactions promoted by other palladium–carbene
complexes. It was proposed that during these induction
periods palladium()–carbene complexes were slowly reduced
to catalytically active palladium(0)–carbene complexes, and
it was shown that an induction period could be avoided by
addition of a suitable reducing agent (e.g. hydrazine) or by
22
the use of a palladium(0)–carbene complex as catalyst. In
similar kinetic studies (using 0.05 mol% catalyst) we have
also observed induction periods, with up to 1 h required for
maximum catalytic activity to be achieved. These induction
periods could be avoided by heating a solution of the catalyst
in dmf prior to addition of the other reagents. We note,
however, that the results summarised in Table 4 are for experi-
ments where no attempts were made to avoid any induction
period. Optimisation of reaction conditions (e.g. by addition of
reagents to eliminate the induction period) is expected to lead
to improvements in catalyst turnover number.
Synthesis of the ortho-cyclophanes as their bromide salts
1
,2-Bis(imidazolylmethyl)benzene. A solution of imidazole
(
40.5 g, 0.59 mol) and α,αЈ-dibromo-o-xylene (10.0 g, 0.038
mol) in methanol (300 cm ) was refluxed for 27 h. The mixture
3
was stripped of solvent under reduced pressure, the residue
3
dissolved in an aqueous solution of K CO (1.4 M, 300 cm ),
2
3
and the solution allowed to stand overnight. The white
solid that precipitated was collected and recrystallised from
methanol to give 1,2-bis(imidazolylmethyl)benzene as hygro-
scopic colourless crystals (9.06 g, 44%) (Found: C, 60.24;
H, 6.12; N, 20.13. C H N ؒ2.2H O requires C, 60.50; H,
Conclusion
Di-carbenes derived from imidazolium-linked ortho-cyclo-
phanes form exceptionally stable complexes with nickel and
palladium. The cyclophane skeleton imposes structural con-
straints and some rigidity on the cyclophane–metal bonding.
The palladium–cyclophane complexes show high activity as
catalysts for Heck and Suzuki reactions. The cyclophane
framework is readily amenable to structural variation (e.g. by
incorporation of solubilising alkyl substituents, different arene
units or different heterocyclic bridging groups) and so offers
an interesting structural motif as a platform for synthesis of a
variety of metal–carbene complexes. We are currently extending
our studies to include cyclophane complexes of other metals,
and have already synthesized cyclophane complexes of Hg,
Rh, and Ru, which we will report in due course.
14
14
4
2
6
.67; N, 20.16%); δ [(CD ) SO] 5.33 (4H, s, 2 × CH ), 6.92–7.00
H 3 2 2
(
(
4H, m, 2 × imidazole H4 or H5 and 2 × Ar H), 7.08–7.11
2H, m, 2 × imidazole H4 or H4), 7.25–7.32 (2H, m, 2 × Ar H),
7
.71–7.74 (2H, m, 2 × imidazole H2); δ [(CD ) SO] 46.6 (2C,
C 3 2
2
× CH ), 119.9, 128.1, 128.4 and 128.9 (2C each, 2 × imidazole
2
C4, 2 × imidazole C5, 4 × aromatic CH), 135.3 (2C, 2 ×
aromatic C) and 137.8 (2C, 2 × imidazole C2).
Cyclophane salt IIIؒ2Br. A solution of 1,2-bis(bromo-
3
methyl)benzene (1.107 g, 4.2 mmol) in acetone (100 cm ) was
added dropwise to a solution of 1,2-bis(imidazolylmethyl)-
3
benzene (1.00 g, 4.2 mmol) in acetone (100 cm ) at room
temperature and stirred for 2 days. The cyclophane salt IIIؒ2Br
precipitated as a moderately hygroscopic white powder (1.81 g,
Experimental
8
6%), which was collected by filtration and used without
Nuclear magnetic resonance spectra were recorded on Bruker
further purification (Found: C, 49.24; H, 4.73; N, 10.72.
C H Br N ؒ2H O requires C, 49.09; H, 4.87; N, 10.41%);
δ [(CD ) SO, 66 ЊC, 300.1 MHz] 5.60 (8H, br s, W 40,
H 3 2 h/2
1
13
AM 300 (300.1 MHz for H, 75.5 MHz for C) or ARX 500
22
22
2
4
2
1
13
(
500.13 MHz for H, 125.8 MHz for C) spectrometers at
ambient temperature unless otherwise stated. Chemical shifts
are referenced with respect to solvent signals. Assignments of
C NMR spectra were made with the aid of DEPT spectra
4 × CH ), 7.12 (4H, br s, W 20, 4 × imidazolium H4/H5),
2 h/2
7.64–7.72 (4H, m, 4 × Ar H) and 7.80–7.88 (4H, m, 4 × Ar H)
and 8.60 (2H, br s, Wh/2 90 Hz, 2 × imidazolium H2);
13
J. Chem. Soc., Dalton Trans., 2001, 111–120
117

View Article Online
δ [(CD ) SO, 66 ЊC, 75.5 MHz] 50.3 (CH ), 122.0 (CH), 130.9
Synthesis of carbene complexes
C
3
2
2
(
CH), 132.6 (C), 134.1 (CH), and 135.5 (CH).
Palladium complex 4. The cyclophane salt IIIؒ2Br (76 mg,
0
.15 mmol) and Pd(OAc) (34 mg, 0.15 mmol) were heated in
2
Cyclophane salt IVؒ2Br. This compound was prepared in the
same way as IIIؒ2Br and obtained as a white, mildly hygro-
scopic powder recrystallised from methanol. Yield 84%
dmf for several hours at 60–80 ЊC, in a thick walled flask sealed
with a Young’s tap. Removal of the volatiles under reduced
pressure gave complex 4 as a pale yellow solid (78 mg, 81%)
(Found: C, 41.08; H, 3.37; N, 8.72. C H Br N Pdؒ2H O
(
Found: C, 56.35; H, 5.02; N, 8.57. C H Br N ؒ2H O requires
30 26 2 4 2
22
20
2
4
2
C, 56.44; H, 4.74; N, 8.78%); δ [(CD ) SO, 66 ЊC, 300.1 MHz]
H
3
2
requires C, 41.12; H, 3.76; N, 8.72%); m/z 526.9913 (M Ϫ Br)
79 108
5
.78 (8H, br s, Wh/2 15, 4 × CH ), 7.24 (4H, br s, W 9, 4 ×
2
h/2
(C H N Br Pd requires 526.9910). The poor solubility of
22 20 4
imidazolium H4/H5), 7.69–7.77 (4H, m, 4 × Ar H), 8.03–8.11
4H, m, 4 × Ar H), 8.42 (4H, s, 4 × Ar H) and 8.83 (2H, br s,
Wh/2 45 Hz, 2 × imidazolium H2); δ [(CD ) SO, 66 ЊC, 75.5
this compound in all solvents prevented satisfactory recrystal-
lisation. A sample of the crude product was subjected to
Soxhlet extraction with acetonitrile overnight, and a crystal
which formed in the acetonitrile extract was characterised by
X-ray diffraction.
(
C
3 2
MHz] 50.6 (CH ), 121.9 (CH), 127.7 (2 × CH), 128.7 (C), 132.9
2
(
C), 134.1 (CH), and 135.5 (CH).
Cyclophane salt Vؒ2Br. This compound was made in the
Palladium complex 5. A sample of the cyclophane salt IIIؒ2Br
was converted into the corresponding acetate salt IIIؒ2OAc by
passage through an anion exchange column (Dowex 1 × 8,
same way as IIIؒ2Br, but did not precipitate. Instead, the sol-
vent was removed under reduced pressure and the residue
recrystallised from acetone. Yield 46%. m/z 733.6149 (M Ϫ H;
acetate form). A solution of IIIؒ2OAc (38 mg, 0.09 mmol)
ϩ
3
loss of H from cyclophane dication V) (C H N requires
and PdI (32 mg, 0.09 mmol) in dmso (5 cm ) was heated
50
77
4
2
7
33.6148); δ [(CD ) SO, 66 ЊC, 300.1 MHz] 0.88 (12H, t,
at 60–80 ЊC for 3 h. The solvent was removed under reduced
pressure at ca. 70 ЊC and the residue recrystallised from
dichloromethane–pentane. Complex 5 was obtained as yellow
needles (21 mg, 33%) (Found: C, 37.14; H, 3.05; N, 7.72.
C H I N Pdؒ0.25CH Cl requires C, 37.02; H, 2.86; N,
H
3 2
3
JHH 7.1 Hz, 4 × CH ), 1.22–1.48 (32H, m, 16 × CH ), 1.63
3
2
(
2
5
8H, apparent quintet, splitting 6.6 Hz, 4 × C H CH CH ),
6 2 2 2
.69 (8H, apparent t, splitting 8 Hz, 4 × C H CH CH ),
6 2 2 2
.46 (8H, s, 4 × benzylic CH ), 7.08 (4H, s, 4 × imidazolium
2
22 20
2
4
2
2
106
H4/H5), 7.57 (4H, s, 4 × Ar H) and 8.48 (2H, br s, Wh/2 10 Hz,
× imidazolium H2); δ [(CD ) SO, 25 ЊC, 125.8 MHz] 14.0
7.76%); m/z 572.9789 (M Ϫ I) (C H N I Pd requires
22 20 4
2
(
(
1
572.9767). Crystals of 5 suitable for characterisation by X-ray
diffraction were grown by layering of a solution of the complex
in CH Cl with methanol.
C
3 2
CH ), 22.1 (CH ), 28.5 (CH ), 29.1 (CH ), 30.5 (CH ), 31.2
3 2 2 2 2
CH ), 31.6 (CH ), 50.1 (CH ), 122.0 (CH), 129.9 (C),
2 2 2
2
2
34.7 (CH), 135.5 (CH), and 142.8 (C). Vؒ2Br contained no
impurities that could be detected by NMR spectroscopy but
perhaps because of its surfactant-like properties a satisfactory
microanalysis could not be obtained. An analytically pure
Nickel complex 6. A solution of the cyclophane salt IIIؒ2Br
3
(
1.0 g, 1.99 mmol) in methanol (10 cm ) was added dropwise to
3
a solution of KPF (1.47 g, 7.96 mmol) in methanol (10 cm )
6
sample of V, as its tetraphenylborate salt Vؒ2BPh , was
4
with stirring. The precipitate that formed over several hours
was collected by filtration and recrystallised from acetone to
obtained by addition of a solution of NaBPh (142 mg, 0.415
4
3
mmol) in methanol (5 cm ) to a solution of Vؒ2Br (149 mg,
.166 mmol) in methanol (10 cm ). The resulting precipitate
give the cyclophane salt IIIؒ2PF as colourless crystals (1.24 g,
6
3
0
9
8%) (Found: C, 42.71; H, 3.62; N, 8.17. C H F N P requires
11 11 6 2
was collected, washed with ice-cold methanol and recrystallised
from acetone–water to afford analytically pure product as
colourless crystals (181 mg, 79%) (Found: C, 84.21; H, 8.37;
C, 41.79; H, 3.51; N, 8.86%). A mixture of IIIؒ2PF (72.2 mg,
6
0
.114 mmol), anhydrous NiCl (14.8 mg, 0.114 mmol) and
2
3
NaOAc (19.7 mg, 0.240 mmol) in dmf (6 cm ) was stirred at
90 ЊC for 2 days. After removal of the solvent and recrystallis-
ation of the residue from dichloromethane–acetonitrile com-
plex 6 was isolated as a bright yellow solid (22 mg, 41%)
N, 4.07. C H B N ؒH O requires C, 84.58; H, 8.69; N,
98
118
2
4
2
4
.03%).
Cyclophane salt VIؒ2Br. This compound was made in the
(Found: C, 46.67; H, 4.28; N, 9.19. C22H22Cl N Niؒ1.6CH Cl
2 4 2 2
1
13
same way as Vؒ2Br as a white powder in 28% yield. H and
C
requires C, 46.63; H, 4.18; N, 9.22%). Crystals of 6 suitable for
X-ray diffraction studies were grown by vapour diffusion of
toluene into a nitromethane solution.
NMR data were consistent with those reported by Shi and
19
Thummel. δ [(CD ) SO, 300.1 MHz] 5.6 (4H, br s, W 100,
H
3
2
h/2
4
× benzylic CH), 6.1 (4H, br s, Wh/2 100 Hz, 4 × benzylic
CH), 6.6–8.2 (4H, br m, 4 × Ar H), 7.1 (4H, br s, Wh/2 50,
× Ar H), 7.75 (4H, br s, Wh/2 15, 4 × Ar H), 8.05 (4H, br s,
Palladium complex 7. This complex was prepared by the same
method as for 4 (yield, 92%) (Found: C, 50.08; H, 4.16; N, 8.90.
C H Br N Pdؒ1.25dmf requires C, 50.79; H, 4.14; N, 9.21%).
Poor solubility in all solvents tested prevented satisfactory
recrystallisation.
4
Wh/2 36, 4 × Ar H) and 9.0 (2H, br s, Wh/2 23 Hz, 2 × imid-
azolium H2); δ [(CD ) CO–D O, 75.5 MHz] 49.5 (CH ), 113.3
30
24
2
4
C
3
2
2
2
(
(
CH), 129.1 (CH), 130.6 (C), 131.9 (C), 132.3 (CH) and 135.0
CH).
Palladium complex 8. This complex was prepared by refluxing
a mixture of the cyclophane salt IVؒ2Br (68.5 mg, 0.114 mmol),
3
,3Ј-(o-Phenylenedimethylene)di(1-methylimidazolium)
dibromide VIIؒ2Br. N-Methylimidazole (0.78 g, 0.76 cm ,
.5 mmol) was added to a stirred solution of 1,2-bis(bromo-
3
PdI (40.9 mg, 0.114 mmol) and NaOAc (19.6 mg, 0.24 mmol)
2
3
9
in acetonitrile (25 cm ) for 19 h. The reaction mixture was
filtered through Celite–alumina, and the solvent removed
under reduced pressure. Recrystallisation of the crude product
from chloroform gave 8 as a yellow powder (20 mg, 21%)
3
methyl)benzene (1.0 g, 3.8 mmol) in 1,4-dioxane (13 cm ) and
heated to 100 ЊC for 24 h. The precipitate which formed was
collected, washed with diethyl ether, and air-dried to afford
the cyclophane salt VIIؒ2Br as a white powder (1.55 g, 95%)
Found: C, 43.66; H, 4.81; N, 12.76. C H Br N ؒ0.5H O
requires C, 43.96; H, 4.84; N, 12.82%); δ [(CD ) SO, 300.1
(Found: C, 34.25; H, 2.61; N, 4.58. C30
H I N Pdؒ3CHCl
24 2 4 3
(
requires C, 34.20; H, 2.35; N, 4.83%); m/z 672.0109 (M Ϫ I)
16 20 2 4 2
105
(C30H N I Pd requires 672.0096).
24 4
H
3 2
MHz] 3.87 (6H, s, 2 × CH ), 5.70 (4H, s, 2 × CH ), 7.30–7.39
3
2
(
2H, m, Ar H), 7.44–7.49 (2H, m, Ar H), 7.79 (4H, s, 4 × imid-
Palladium complex 9. This complex was prepared by the same
method as for 4. After removal of volatiles from the reaction
mixture, purification of the product was achieved by chrom-
atography on silica (40–63 µm) by elution with 10% acetone
azolium H4/H5) and 9.30 (2H, br s, 2 × imidazolium H2);
δ [(CD ) SO, 75.5 MHz] 49.0 (CH ), 122.4 (CH), 123.9 (CH),
1
C
3
2
2
29.6 (CH), 129.7 (CH), 132.9 (C) and 136.9 (CH).
1
18 J. Chem. Soc., Dalton Trans., 2001, 111–120

View Article Online
in CH Cl . Yield (after chromatography) 29% (Found: C, 55.49;
measured (2θmax = 58Њ; Bruker AXS instrument, T ca. 153 K
2
2
H, 6.82; N, 5.00. C H Br N Pdؒ1.25CH Cl requires C, 55.68;
(except for complex 4ؒ2CH CN, ca. 300 K); monochromatic
50
76
2
4
2
2
3
ϩ
79
108
H, 7.16; N, 5.07%); m/z 919.4338 (M Ϫ Br) (C H N Br Pd
Mo-Kα radiation, λ = 0.71073 Å) yielding Nt(otal) reflections,
merging to N unique after ‘empirical’/multiscan absorption
correction (proprietary software, Rint quoted), No with
F > 4σ(F ) being considered ‘observed’ and used in the full
matrix least squares refinement (non-hydrogen atom aniso-
tropic thermal parameter refinement, (x, y, z, U ) constrained
50
76
4
requires 919.4292).
Palladium complex 10. This complex was prepared by the
same method as for 4. After removal of volatiles from the reac-
tion mixture, the crude product was extracted into acetonitrile,
removal of which gave 10 as an orange solid (46%) (Found:
C, 49.30; H, 4.18; N, 7.04. C H Br N Pdؒ1.5H O requires C,
iso
H
2
at estimated values). Conventional residuals R, R (w = σ (F ) ϩ
0.0004F ) ) are quoted at convergence. Neutral atom complex
w
2
Ϫ1
30
24
2
4
2
4
9.10; H, 3.71; N, 7.64%).
scattering factors were employed within the context of the
27
XTAL 3.4 program system. Pertinent results are given
below and in the Tables and Figures (50% displacement
ellipsoids for non-hydrogen atoms, hydrogen atoms having
arbitrary radii of 0.1 Å), individual variations, difficulties (etc.)
quoted as “variata”.
Bis(cyclophane) palladium complex 11.
A
solution of
IIIؒ2OAc (60 mg, 0.13 mmol) and PdI (23.5 mg, 0.065 mmol)
in dmf (5 cm ) was heated at 80 ЊC for 2 days in a flask sealed
with a Young’s tap. The volatiles were removed under reduced
pressure and the residue was recrystallised from methanol–
diethyl ether to give the product 11 as colourless crystals
2
3
6ؒ(CH ) SO. C H Cl N NiOS, M = 548.2, monoclinic,
3
2
24 26
5
2
4
(
12 mg, 9%) (Found: C, 48.24; H, 4.23; N, 10.17. C H I N -
space group P2 /c (C , no. 14), a = 12.760(1), b = 8.7243(8),
1 2h
3
44
40
2
8
Pdؒ3H O requires C, 48.26; H, 4.23; N, 10.23%). m/z 912.1485
c = 22.027(2) Å, β = 102.829(1)Њ, V = 2391 Å , D (Z = 4) = 1.52
c 3
Ϫ3 Ϫ1
2
1
05
(
M Ϫ I; cationic complex ϩ iodide) (C H N I Pd requires
g cm , µ = 11.5 cm , specimen 0.12 × 0.11 × 0.07 mm,
44
40
8
Mo
9
12.1471). Crystals of 11 suitable for X-ray diffraction studies
‘T ’min,max = 0.80, 0.93, N = 28196, N = 6081 (R = 0.039), N =
t
int
o
Ϫ3
were grown by vapour diffusion of toluene into a nitromethane
4783, R = 0.031, R = 0.036, |∆ρ | = 0.44(6) e Å . (x, y, z,
w
max
solution.
U ) were refined.
iso H
Palladium complex 12. This compound was prepared in the
same way as for 4 and was purified by recrystallisation from
acetonitrile (yield, 35%) (Found: C, 36.37; H, 3.65; N, 10.66.
C H Br N Pd requires C, 36.09; H, 3.41; N, 10.52%). Crystals
5ؒ0.5CH OH. C H I N O Pd, M = 716.7, monoclinic,
3 22.5 22 2 4 0.5
5
space group P2 /n (C , no. 14 (variant)), a = 10.380(1),
1
2h
3
b = 8.981(1), c = 25.693(3) Å, β = 95.946(2)Њ, V = 2382 Å , D
c
Ϫ3
Ϫ1
(Z = 4) = 1.99 g cm , µ = 34 cm , specimen 0.40 × 0.38 ×
1
6
18
2
4
8
Mo
of 12 suitable for X-ray diffraction studies were grown by
vapour diffusion of acetone into a dmso solution.
0.08 mm, ‘T ’min,max = 0.50, 0.80, N = 26807, N = 5935 (R =
t int
Ϫ3
0.042), N = 5744, R = 0.031, R = 0.044, |∆ρ | = 1.50(3) e Å .
o
w
max
Difference map residues were modelled in terms of a meth-
anol of solvation, disordered about the origin. The similarity of
the cell of this complex with that of the previous does not
appear to translate into any genuine isomorphism.
Catalytic studies
Stock solutions of palladium complexes 5, 9, and 12 were
prepared by dissolving 1.0 mg of the appropriate complex
3
in 10.0 cm of dmf. Solutions containing smaller quantities of
“
4”ؒ2CH CN. C H26.25Br1.75N O0.25Pd (attempts to crystal-
3 26 6
catalysts were prepared by serial 1:10 dilutions of the stock
solutions. These solutions were prepared in air and used as
sources of catalysts for Heck and Suzuki reactions. Procedures
for Heck and Suzuki reactions were modifications of methods
reported by Herrmann et al. Representative examples are
given below.
lise 4 were “successful” only after prolonged boiling in aceto-
nitrile, the material being quite insoluble, and the formulation
suggested by the structure determination is less secure, seem-
ingly in consequence of partial hydrolysis at the bromide site),
20
M = 673.0, monoclinic, space group P2 /n, a = 14.592(2),
1
3
b = 8.6343(9), c = 22.013(2) Å, β = 104.547(2)Њ, V = 2685 Å , D
Z = 4) = 1.66 g cm , µ = 33 cm , specimen 0.3 × 0.3 × 0.08
c
Ϫ3
Ϫ1
(
3
5 Mo
Heck reactions. A 25 cm thick walled flask fitted with a
Young’s tap was charged with iodobenzene (1.10 cm , 10.0
mm, Tmin,max = 0.64, 0.89, N = 29981, N = 6700 (R = 0.09),
3
t
int
Ϫ3
N = 3285, R = 0.043, R = 0.037, |∆ρ | = 0.8(1) e Å .
3
o
w
max
mmol), butyl acrylate (1.43 cm , 10.0 mmol), triethylamine
Refinement with the bromide sites fully occupied as such
converged at R = 0.054, with aberrant displacement parameter
behaviour; site occupancy refinement suggested somewhat
diminished populations, and they were modelled in terms of
partial occupancy by (hydroxide?) oxygens (?), at the same
locations as composites, since they could not meaningfully
be resolved independently, refinement converging with occu-
pancies of the bromides effectively identical (0.868(1), 0.873(1)),
oxygen occupancies as complements. Difference map resi-
dues were modelled as acetonitrile of solvation, one molecule
included, one not, seemingly ordered with methyl hydrogen
atoms resolvable in difference maps and consistent refinement
3
(
1.40 cm , 10.0 mmol), and a solution of complex 5 (1.4 nmol
3
in 1 cm dmf). A small stirrer bar was added and the flask
degassed by three freeze–pump–thaw cycles and back-filled
with nitrogen. The flask was then sealed (Young’s tap) and the
contents were heated with stirring at 140 ЊC. After the required
time had elapsed a small aliquot was removed from the reaction
mixture, dissolved in CDCl , and examined by H NMR
spectroscopy.
1
3
3
Suzuki reactions. A 25 cm thick walled flask fitted with a
Young’s tap was charged with phenylboronic acid (0.67 g,
5
1
.5 mmol), p-bromotoluene (0.85 g, 5.0 mmol), K CO (1.38 g,
2 3
3
behaviour. In common P2 /x settings the present complex dis-
1
0 mmol), dmf (10 cm ), and a solution of complex 5 (0.14
plays considerable similarity in respect of disposition of the
component moieties within the cell to that of the nickel
complex, above, again insufficiently similar to be regarded as
genuinely ‘isomorphous’.
3
µmol) in dmf (1 cm ). A small stirrer bar was added and the
flask degassed by three freeze–pump–thaw cycles and back-
filled with nitrogen. The flask was then sealed (Young’s tap) and
the contents were heated with stirring at 120 ЊC. After the
required time had elapsed a small aliquot was removed from
1
1ؒ6CH NO . C H I N O Pd, M = 1407.3, monoclinic,
3 2 50 58 2 14 12
1
the reaction mixture, dissolved in CDCl , and examined by H
3
space group P2 /c, a = 11.672(2), b = 15.279(2), c = 16.558(2) Å,
β = 102.283(2)Њ, V = 2885 Å , Dc (Z = 4) = 1.620 g cm ,
µMo = 14.6 cm , specimen 0.38 × 0.28 × 0.22 mm, ‘T ’
1
NMR spectroscopy.
3
Ϫ3
Ϫ1
=
min,max
Structure determinations
0
.76, 0.86, N = 33318, N = 7270 (R = 0.018), N = 6555,
t int o
Ϫ3
Full spheres of CCD area detector diffractometer data were
R = 0.023, R = 0.032, |∆ρ | = 0.86(3) e Å .
w
max
J. Chem. Soc., Dalton Trans., 2001, 111–120
119

View Article Online
‘
Thermal motion’ associated with the methyl group of
P. T. Gomes, A. M. Martins and A. A. Danopoulos, Organo-
metallics, 1999, 18, 4584.
V. P. W. Böhm, C. W. K. Gstöttmayr, T. Weskamp and
W. A. Herrmann, J. Organomet. Chem., 2000, 595, 186.
F. E. Hahn and M. Foth, J. Organomet. Chem., 1999, 585, 241.
W. A. Herrmann, J. Schwarz and M. G. Gardiner, Organometallics,
solvent molecule 3 was rather higher than for the remainder
of the structure; (x, y, z, U ) for those atoms were constrained
at estimated values, the remainder being refined.
7
iso
H
8
9
1
999, 18, 4082.
1
2ؒ(CH ) CO. C H Br N OPd, M = 590.7, monoclinic,
3
2
19 24
2
4
1
1
0 M. J. Green, K. J. Cavell, B. W. Skelton and A. H. White,
J. Organomet. Chem., 1998, 554, 175.
1 Z. Shi and R. P. Thummel, Tetrahedron Lett., 1995, 36, 2741.
12 W. A. Herrmann, L. J. Goossen and M. Spiegler, Organometallics,
1998, 17, 2162.
13 D. S. McGuinness, K. J. Cavell, B. W. Skelton and A. H. White,
Organometallics, 1999, 18, 1596.
4 J. Huang and S. P. Nolan, J. Am. Chem. Soc., 1999, 121, 9889.
5 L. Xu, W. Chen and J. Xiao, Organometallics, 2000, 19, 1123.
6 M. G. Gardiner, W. A. Herrmann, C.-P. Reisinger, J. Schwarz and
M. Spiegler, J. Organomet. Chem., 1999, 572, 239.
7 M. V. Baker, M. J. Bosnich, C. C. Williams, B. W. Skelton and
A. H. White, Aust. J. Chem., 1999, 52, 823.
8 Preliminary results have been reported: M. V. Baker, B. W. Skelton,
A. H. White and C. C. Williams, Proceedings of the 11th National
Convention of the Royal Australian Chemical Institute, Organic
Division, Canberra, 2000, P120.
9 Z. Shi and R. P. Thummel, J. Org. Chem., 1995, 60, 5935.
0 W. A. Herrmann, C.-P. Reisinger and M. Spiegler, J. Organomet.
Chem., 1998, 557, 93.
space group P2 /c, a = 11.207(3), b = 13.300(3), c = 15.434(3) Å,
β = 106.661(3)Њ, V = 2204 Å , Dc (Z = 4) = 1.780 g cm ,
µMo = 45 cm , specimen 0.40 × 0.30 × 0.20 mm, ‘T ’
1
3
Ϫ3
Ϫ1
=
min,max
0
.41, 0.80, N = 25643, N = 5589 (R = 0.044), N = 3828,
t int o
Ϫ3
R = 0.039, R = 0.047, |∆ρ | = 1.08(9) e Å .
w
max
CCDC reference number 186/2278.
See http://www.rsc.org/suppdata/dt/b0/b007293l/ for crystal-
lographic files in .cif format.
1
1
1
1
Acknowledgements
1
A grant from the Australian Research Council (to M. V. B.) and
an Australian Postgraduate Research Award (to C. C. W.) are
much appreciated. We thank Dr Anthony Reeder for assistance
with mass spectrometry.
1
2
2
2
1 D. S. Clyne, J. Jin, E. Genest, J. C. Gallucci and T. V. RajanBabu,
Org. Lett., 2000, 2, 1125.
2 W. A. Herrmann, M. Elison, J. Fischer, C. Köcher and
G. R. J. Artus, Angew. Chem., Int. Ed. Engl., 1995, 34, 2371.
References
1
2
3
4
5
6
L. Ackermann, A. Fürstner, T. Weskamp, F. J. Kohl and
W. A. Herrmann, Tetrahedron Lett., 1999, 40, 4787.
A. J. Arduengo, III, H. V. R. Dias, J. C. Calabrese and F. Davidson,
Organometallics, 1993, 12, 3405.
W. A. Herrmann and C. Kocher, Angew. Chem., Int. Ed. Engl., 1997,
23 M. V. Baker, B. W. Skelton, A. H. White and C. C. Williams,
unpublished work.
24 R. M. Claramunt, J. Elguero and T. Meco, J. Heterocycl. Chem.,
1983, 20, 1245.
25 W. A. Herrmann, J. Schwarz, M. G. Gardiner and M. Spiegler,
J. Organomet. Chem., 1999, 575, 80.
26 W. P. Fehlhammer, T. Bliss, U. Kernbach and I. Brüdgam,
J. Organomet. Chem., 1995, 490, 149.
3
6, 2162.
J. C. C. Chen and I. J. B. Lin, J. Chem. Soc., Dalton Trans., 2000,
39.
J. Huang, E. D. Stevens and S. P. Nolan, Organometallics, 2000, 19,
194.
R. E. Douthwaite, D. Haüssinger, M. L. H. Green, P. J. Silcock,
8
1
27 S. R. Hall, G. S. D. King and J. M. Stewart, The XTAL 3.4 User’s
Manual, Lamb, Perth, 1995.
1
20
J. Chem. Soc., Dalton Trans., 2001, 111–120