Tripodal N-heterocyclic carbene complexes of palladium and copper: Syntheses, characterization, and catalytic activity

Article abstract of DOI:10.1021/om100758x

The tris-palladium tripodal N-heterocyclic carbene (NHC) complexes (timteb^tBu){Pd(ICy)I₂}₃ (4a), (timteb ^tBu){Pd(PPh₃)I₂}₃ (5a), and (timteb^dipp){Pd(PPh₃)I₂}₃ (5b) (timteb^tBu = 1,3,5-{tris(tert-butylimidazol-2-ylidene)methyl}-2,4,6- triethylbenzene, 3a; ICy = 1,3-dicyclohexylimidazol-2-ylidene; timteb ^dipp = 1,3,5-{tris({2,6-diisopropylphenyl}imidazol-2-ylidene)methyl}- 2,4,6-triethylbenzene, 3b) were prepared by reaction of Pd(II) precursors with either the free carbenes or imidazolium salts. Treatment of [Cu(NCMe) ₄]X (X = PF₆, BF₄) with 3a or 3b produced the tris-copper(I) bridged complexes [(timteb^R) Cu₃(μ₃-O)]X (R = ^tBu, X = PF₆, 6a; R = dipp, X = BF₄, 6b). Complexes 4a, 5a, and 6a were structurally characterized. The palladium complexes were tested as catalysts for Suzuki-Miyaura and Sonogashira coupling reactions and the copper species also employed for the Sonogashira reaction, as well as for the Ullmann-type arylation of imidazoles and phenols.

Full text of DOI:10.1021/om100758x

Organometallics 2010, 29, 4097–4104 4097
DOI: 10.1021/om100758x
Tripodal N-Heterocyclic Carbene Complexes of Palladium and Copper:
Syntheses, Characterization, and Catalytic Activity
Charles E. Ellul, Graham Reed, Mary F. Mahon, Sofia I. Pascu,* and
Michael K. Whittlesey*
Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
Received August 3, 2010
The tris-palladium tripodal N-heterocyclic carbene (NHC) complexes (timtebtBu){Pd(ICy)I2}3
(4a), (timtebtBu){Pd(PPh3)I2}3 (5a), and (timtebdipp){Pd(PPh3)I2}3 (5b) (timtebtBu = 1,3,5-{tris(tert-
butylimidazol-2-ylidene)methyl}-2,4,6-triethylbenzene, 3a; ICy = 1,3-dicyclohexylimidazol-2-
ylidene; timtebdipp = 1,3,5-{tris({2,6-diisopropylphenyl}imidazol-2-ylidene)methyl}-2,4,6-triethylbenzene,
3b) were prepared by reaction of Pd(II) precursors with either the free carbenes or imidazolium salts.
Treatment of [Cu(NCMe)4]X (X = PF6, BF4) with 3a or 3b produced the tris-copper(I) bridged
complexes [(timtebR)Cu3(μ3-O)]X (R = tBu, X = PF6, 6a; R = dipp, X = BF4, 6b). Complexes 4a,
5a, and 6a were structurally characterized. The palladium complexes were tested as catalysts for
Suzuki-Miyaura and Sonogashira coupling reactions and the copper species also employed for the
Sonogashira reaction, as well as for the Ullmann-type arylation of imidazoles and phenols.
Introduction
3 (abbreviated timtebR)5 restricts the extent to which a single
metal ion can be accommodated between the three carbene
arms to only the very large thallium atom.6,7 As a result, the
chemistry of 3 has largely been overlooked.
Polydentate N-heterocyclic carbene (NHC) ligands repre-
sent a small subset of the vast array of NHCs now present in
the literature.1 Of the tripodal NHCs, ligand 1, reported by
Fehlhammer and Smith,2,3 and 2, prepared by Meyer,4 have
received the most attention (Scheme 1). The presence of a
small central linker atom or group gives 1 and 2 the ability to
bind a selection of single metal atoms, such as Mn, Fe, Co,
Ni, and Cu, within the ligand coordination sphere, whereas
the much larger central arene group in the tris-carbene ligand
An alternative mode of coordination for timtebR involves
the three arms anchoring more than one metal center.8,9 Such
an approach has very recently been reported by Hahn and
co-workers using 3c to afford a supramolecular structure
based on a [Ag3(3c)2]3þ framework.10 We now describe the
use of the tert-butyl and 2, 6-diisopropylphenyl (abbreviated
to dipp)-substituted ligands 3a and 3b to form Pd3 and Cu3
complexes. The catalytic activity of both sets of compounds
for C-C and C-N coupling reactions has been investigated.
*To whom correspondence should be addressed. E-mail: chsmkw@
bath.ac.uk.
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Angew. Chem., Int. Ed. 2005, 44, 3759–3763. (c) Pugh, D.; Danopoulos,
A. A. Coord. Chem. Rev. 2007, 251, 610–641. (d) McKie, R.; Murphy, J. A.;
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Results and Discussion
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timtebdipp Complexes. The reaction of 3a with 3 equiv of the
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2010 American Chemical Society
Published on Web 08/30/2010
pubs.acs.org/Organometallics

4098 Organometallics, Vol. 29, No. 18, 2010
Ellul et al.
mixed NHC-phosphine complex trans-Pd(ICy)(PPh3)I2 (ICy =
1,3-dicyclohexylimidazol-2-ylidene)11 in THF at 70 °C for 4 h
allowed the isolation of the Pd3 complex (timtebtBu){Pd(ICy)I2}3
(4a) as a yellow, air-stable microcrystalline solid in 68% yield
(Scheme 2). The 1H NMR spectrum of 4a provided little in the
way of confirmation for the structure, as only minimal differ-
ences were seen in the chemical shifts of the compound relative to
the free carbene 3a. This was also the case for the 13C{1H}
spectrum, apart from at high frequency, where two new singlets
at δ 167.6 and 164.9 were observed corresponding to the two
types of Pd-CNHC groups.
Scheme 1
The molecular structure of 4a was elucidated by X-ray
crystallography, as shown in Figure 1. The compound adopts
an idealized C3-symmetrical arrangement with the three Pd-
(ICy)I2 fragments pointing out on the opposite side of the
central arene ring to the three ethyl substituents. Each palla-
dium center has a trans-timtebtBu-Pd-ICy geometry with the
dihedral angles between the planes of the imidazole ring pairs
bonded to each palladium ranging from 9.6° to 25.8°. All six
Scheme 2
Figure 1. Molecular structure of 4a. Thermal ellipsoids are represented at 30% probability. Hydrogen atoms and solvent are omitted for
˚
clarity. Selected bond lengths (A) andangles (deg):Pd(1)-C(1) 2.013(9), Pd(1)-C(16) 2.024(8), Pd(2)-C(39) 2.030(8), Pd(2)-C(44) 2.033(8),
Pd(3)-C(60) 2.031(8), Pd(3)-C(67) 2.049(8), C(1)-Pd(1)-C(16) 177.5(3), C(39)-Pd(2)-C(44) 178.0(3), C(60)-Pd(3)-C(67) 175.5(3).

Article
Organometallics, Vol. 29, No. 18, 2010 4099
Figure 2. Molecular structure of 5a. Thermal ellipsoids are represented at 30% probability. All hydrogen atoms are omitted for clarity.
˚
Selected bond lengths (A) and angles (deg): Pd(1)-C(19) 1.994(18), Pd(2)-C(42) 2.050(18), Pd(3)-C(68) 2.037(16), Pd(1)-P(1)
2.309(5), Pd(2)-P(2) 2.319(5), Pd(3)-P(3) 2.324(5), C(19)-Pd(1)-P(1) 169.4(5).
˚
Scheme 3
Pd-CNHC bond lengths range between 2.013(9) and 2.049(8) A
and are unexceptional for PdII-NHC complexes.12
A number of reports have detailed the higher catalytic
activity of NHC-Pd-phosphine complexes relative to their
bis-carbene analogues.13,14 This prompted us to synthesize
the corresponding timtebtBu and timtebdipp palladium phos-
phine species 5a and 5b (Scheme 2). Both compounds were
prepared using a two-step procedure, the first of which
involved reaction of Pd(OAc)2 with the corresponding tris-
imidazolium salt in the presence of NaI and KOtBu. Orange
solids were formed, which we believe to be the bis-timtebR
complexes (timtebR)2{PdI2}3, although the lack of both
definitive NMR information (cf. 4a) and X-ray quality
crystals prevented unambiguous characterization of these
species.15 Nevertheless, reaction of both species with PPh3
in a second step gave the desired products 5a and 5b, which
were isolated in low yields as a yellow-orange air-stable
solids.16 The high-frequency region of the 13C{1H} NMR
spectrum again proved to be most informative in terms of
spectroscopic characterization, showing doublet carbene
resonances at δ 155.0 (5a) and δ 163.2 (5b) with large trans
2JCP couplings of 192 and 196 Hz, respectively.
The molecular structure of 5a was confirmed by X-ray
crystallography, as shown in Figure 2. Crystals of only
moderate quality could be grown (see Experimental Section),
ruling out any detailed comparison of the bond lengths and
angles in 5a versus 4a.
Formation of Tris-Cu(I) Complexes of timtebR. Treatment
of [Cu(NCMe)4]X (X = PF6, BF4) and 0.33 equiv of the
tris-imidazolium salts 1,3,5-{tris(3-tert-butylimidazolium)-
methyl}-2,4,6-triethylbenzene tribromide or 1,3,5-{tris(2,6-
diisopropylphenyl)imidazolium)methyl}-2,4,6-triethylbenzene
tribromide with NaOtBu in thf at room temperature gave,
after workup, pale yellow solids, which upon extraction with
CH2Cl2 afforded the unexpected tris-copper(I) μ3-oxo com-
plexes [(timtebR)Cu3(μ3-O)]X (R = tBu, X = PF6, 6a; R =
dipp, X = BF4, 6b) in good to excellent isolated yields
(Scheme 3).
(11) As reported in the Experimental Section, trans-Pd(ICy)(PPh3)I2
was prepared by addition of PPh3 to the dimer [Pd(ICy)I2]2. The X-ray
crystal structure of the dimer is given in the Supporting Information.
(12) Viciu, M. S.; Navarro, O.; Germaneau, R. F.; Kelly, R. A.;
Sommer, W. J.; Marion, N.; Stevens, E. D.; Cavallo, L.; Nolan, S. P.
Organometallics 2004, 23, 1629–1635.
(13) Herrmann, W. A.; Bohm, V. P. W.; Gstottmayr, C. W. K.;
Grosche, M.; Reisinger, C.-P.; Weskamp, T. J. Organomet. Chem. 2001,
617-618, 616–628.
(14) Liao, C.-Y.; Chan, K.-T.; Tu, C.-Y.; Chang, Y.-W.; Hu, C.-H.;
Lee, H. M. Chem.—Eur. J. 2009, 15, 405–417.
(15) Complexes of this type have been identified by others. (a) Reference
10. (b) Willans, C. E.; Anderson, K. M.; Paterson, M. J.; Junk, P. C.;
Barbour, L. J.; Steed, J. W. Eur. J. Inorg. Chem. 2009, 2835–2843.
(16) The low yields of 5a and 5b result primarily from poor yields of
the intermediate species (timtebR)2{PdI2}3.
€
€
The structure of 6a was established by X-ray crystal-
lography, and the cation is shown in Figure 3. The complex

4100 Organometallics, Vol. 29, No. 18, 2010
Ellul et al.
Table 1. Suzuki-Miyaura and Sonogashira Reactions Catalyzed
by 4a, 5a, and 5b
entry
1a
Ph-X
I
substrate
cat.
T/°C
t/h
% convc
PhB(OH)2
4a
80
120
80
120
80
80
120
80
120
80
120
120
80
120
80
120
80
2
2
2
2
2
2
2
3
2
2
3
3
2
2
2
2
2
2
2
2
73
80
75
100
86
3
48
62
100
70
21
16
2a
I
PhB(OH)2
5a
3a
4a
I
Br
PhB(OH)2
PhB(OH)2
5b
4a
5a
Br
PhB(OH)2
5a
6a
Br
Cl
Cl
I
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhCtCH
5b
5a
5b
4a
7a
8a
10b
20 (3)d
28(3)d
24
11b
12b
I
I
PhCtCH
PhCtCH
5a
5b
54 (3)d
7 (3)d
13 (2)d
4 (3)d
0
120
120
120
13b
14b
Br
Br
PhCtCH
PhCtCH
5a
6a
Figure 3. Molecular structure of one of the cations in the
asymmetric unit of 6a. Thermal ellipsoids are represented at
30% probability. Hydrogen atoms, counterions, and solvent
a 0.5 mmol of aryl halide, 0.75 mmol of phenylboronic acid, 1 mmol of
Cs2CO3, 0.83 mol % 4a or 5a, 1.5 mL of dioxane. b 0.5 mmol of aryl
halide, 0.7 mmol of PhCtCH, 1 mmol of Cs2CO3, 2 mol % CuI, 1.0 mol %
4a or 5a, 1.5 mL of dioxane. c Yields were detemined by GC. d Yields in
parentheses are for the oxidative dimerization product, 1,4-diphenylbu-
tadiyne.
˚
moieties are omitted for clarity. Selected bond lengths (A) and
angles (deg): Cu(1)-C(14) 1.860(3), Cu(2)-C(22) 1.868(3),
Cu(3)-C(30) 1.869(3), Cu(1)-O(1) 1.807(2), Cu(2)-O(1)
1.812(2), Cu(3)-O(1) 1.821(2), O(1)-Cu(1)-C(14) 174.17(13),
Cu(1)-O(1)-Cu(2) 106.93(12).
The oxo ligand appears to originate from both the base
(NaOtBu) and the solvent (thf). Thus, 6a was still formed
when the base was changed to KN(SiMe3)2, but in a lower
yield. Replacing thf by MeCN also afforded a lower yield of
6a, along with a number of other unknown products.
displays pseudo-C3 symmetry with an axis running through
the μ3-O ligand, the center of the plane defined by the three
Cu atoms, and the centroid of the anchoring arene ring.
Catalytic Activity of Pd3 and Cu3 timtebR Complexes. The
activity of 4a, 5a, and 5b in Suzuki-Miyaura and Sonoga-
shira coupling reactions was investigated, and the results are
summarized in Table 1.20,21 As the focus of the study was
essentially to demonstrate the potential of timtebR as sup-
porting ligands, catalytic activities were not optimized. A
comparsion of the Suzuki-Miyaura coupling of PhB(OH)2
with iodo- and bromobenzene (entries 1-6) showed that
mixed timtebR-PPh3 complexes 5a and 5b were more active
than the bis-carbene species 4a. Chlorobenzene proved to be
the most unreactive of the aryl halides (entries 7, 8), even with
the bulkier timtebdipp containing catalyst.22 Sonogashira
coupling was probed in light of the relatively little impact
˚
The bridging oxygen lies 0.8 A above the plane of the three
˚
copper atoms, which themselves are located 3 A above the
˚
arene ring of the carbene. The Cu-O distance of 1.81 A is
comparable to the values found in CuI4(μ4-O) reported by
Hakansson and Meyer.17 The Cu-CNHC bond length in 6a
(1.86 A) is noticeably shorter than found in other Cu(I)-
˚
NHC species,8,18 while the Cu Cu separations range from
3 3 3
˚
2.7557(6) to 2.9078(5) A, outside of the generally accepted
range for d10-d10 interactions.19 In contrast to the structures
of 4a and 5a, in the structure of 6a only two of the ethyl
groups at the tripodal ligand core are directed toward the
same side of the central aryl moiety. This reflects, in part, an
opening of the pocket created by the presence of the Cu3O
scaffold, which can accommodate a twist of the third ethyl
group in the latter structure and is evidenced by the average
of the Caryl-CH2-Nimidazole angles across all three struc-
tures, which register at 112° (4a), 111° (5a), and 116° (6a).
As for the Pd complexes above, the proton NMR spectra of
6a and 6b were similar to the spectra of the free ligands.
However, the 13C{1H} spectra exhibited characteristic high-
frequency carbenic resonances at δ 169.2 (6a) and δ 177.6 (6b).
(20) C-C coupling by Pd-NHC complexes has been the subject of a
number of recent and very comprehensive reviews, which provide an
excellent introduction to this area. (a) Hillier, A. C.; Grasa, G. A.; Viciu,
M.; Lee, H. M.; Yang, C.; Nolan, S. P. J. Organomet. Chem. 2002, 653,
69–82. (b) Reference 21. (c) Scott, N. M.; Nolan, S. P. In N-Heterocyclic
Carbenes in Synthesis; Nolan, S. P., Ed.; Wiley-VCH: Weinheim, 2006; pp
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55-72. (d) Díez-Gonzalez, S.; Nolan, S. P. In N-Heterocyclic Carbenes in
Transition Metal Catalysis; Glorius, F., Ed.; Springer-Verlag: Heidelberg,
2007; Vol. 21, pp 47-82. (e) Kantchev, E. A. B.; O’ Brien, C. J.; Organ,
M. G. Angew. Chem., Int. Ed. 2007, 46, 2768–2813. (f) W€urtz, S.; Glorius,
F. Acc. Chem. Res. 2008, 41, 1523–1533. (g) Marion, N.; Nolan, S. P. Acc.
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(17) (a) Hakansson, M.; Ortendahl, M.; Jagner, S.; Sigalas, M. P.;
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C.; Meyer, F. Chem. Commun. 2008, 1744–1746.
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Chem. Commun. 2001, 2340–2341. (b) Tulloch, A. A. D.; Danopoulos,
A. A.; Kleinhenz, S.; Light, M. E.; Hursthouse, M. B.; Eastham, G.
Organometallics 2001, 20, 2027–2031. (c) Hu, X.; Castro-Rodríguez, I.;
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(21) Herrmann, W. A.; Ofele, K.; van Preysing, D.; Schneider, S. K.
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Organometallics, Vol. 29, No. 18, 2010 4101
Table 2. Sonogashira Coupling of Aryl Halides and PhCtCH
Catalyzed by 6a and 6b
Coupling of imidazole with p-iodotoluene was more challeng-
ing, with 6b proving to be somewhat more active. Biffis also
reported a significant drop in activity on going from
p-iodoacetophenone to p-iodotoluene using [Cu3(1)2]þ bear-
ing N-Me-substituted 1, although they noted that upon
changing to N-benzyl-substituted 1, p-iodotoluene was the
more reactive substrate. Disappointingly, 6a showed no
reactivity toward p-chloroacetophenone, even at higher
temperature and with double the catalyst loading (entries 4
and 5). The o-arylation of phenols was briefly investigated,
and activities were found to be in line with those for the C-N
coupling of imidazole (entries 6-8).
entry
aryl halide
t/h
% conv (6a)a,b
% conv (6b)a,b
1
2
3
p-MeC(O)C6H4I
p-MeC(O)C6H4Br
p-MeC6H4I
24
24
24
96
83
86
86
72
91
a Reaction conditions: 1 mol % catalyst, aryl halide (0.5 mmol),
phenylacetylene (0.6 mmol), Cs2CO3 (1.2 equiv), DMSO (1.5 mL), 120 °C.
b Yields determined by NMR.24
Table 3. Catalytic Arylation of Azoles and Phenols with 6a and 6b
Summary
Tris-palladium and tris-copper complexes of the tripodal
N-heterocyclic carbenes 1,3,5-{tris(tert-butylimidazol-2-
ylidene)methyl}-2,4,6-triethylbenzene (3a) and 1,3,5-{tris-
({2,6-diisopropylphenyl}imidazol-2-ylidene)methyl}-2,4,6-
triethylbenzene (3b) have been prepared, fully characterized,
and employed in C-X (X = C, N, O) coupling reactions.
The palladium(II) compounds show activity for Suzuki-
Miyaura and Sonogashira coupling of aryl iodides and
bromides. As expected, higher levels of conversion are ob-
served with the mixed NHC-phosphine species than with the
bis-carbene complexes. In the case of the copper, the reaction
conditions employed afford copper(I) complexes with an
unusual Cu3(μ-O) motif that proves active in both Sonoga-
shira and Ullmann arylation reactions. Further modifica-
tions to the tripodal NHC substituents may allow higher
levels of catalytic performance to be induced. Similarly, it
will be of interest to see if 3a and 3b can support other metal
centers, thus broadening the scope of these unusual NHC
ligands.
aryl
halide
% conv % conv
(6a)a
entry
phenol
t/h
(6b)a
1
2
3
4
5
6
7
8
R = COMe, X = I
R = COMe, X = Br
R = Me, X = I
R = Me, X = Cl
R = Me, X = Cl
R = MeCO, X = I
R = MeCO, X = Br R0 = Me
24
24
24
48
24
24
24
24
90b
65b
21b
0b
91b
68b
39b
nd
0c
nd
R0 = Me
76d
52d
52d
90d
nd
R = Me, X = I
R0 = Me
nd
a Yields determined by NMR.26 b 1 mol % catalyst, aryl halide (1.0
mmol), azole (1.5 mmol), Cs2CO3 (2 equiv), DMSO (1.5 mL), 100 °C.
c 6 mol % catalyst, 150 °C. d 3 mol % catalyst, aryl halide (1.0 mmol),
phenol (1.5 mmol), Cs2CO3 (2.0 equiv), DMSO (1.5 mL), 100 °C. nd =
not determined.
Experimental Section
that Pd-NHCs have made on this class of coupling
reaction.21,23 Catalytic activity was restricted to the coupling
of PhCtCH with iodobenzene (entries 10-12) and necessi-
tated a temperature of 120 °C in order for even moderate
conversion to be recorded for the most active catalyst 5a.
Biffis and co-workers have recently reported the use of
trinuclear Cu(I) complexes of the borate-carbene ligand 1 in
Sonogashira coupling.3b Employing their same reaction
conditions, we investigated the activity of 6a and 6b for the
coupling of phenylacetylene with aryl iodides and bromides
as summarized in Table 2. Both complexes showed good
activity toward p-iodoacetophenone and p-iodotoluene, as
well as the more challenging p-bromoacetophenone.
The catalytic activity of 6a and 6b was also tested in
Ullmann-type arylation reactions of azoles and phenols
(Table 3).25 Again, the optimum conditions employed by
Biffis and co-workers were used.3 The two complexes
showed equivalent activity for the N-arylation of imidazole
with p-iodo and p-bromoacetophenone (entries 1 and 2).
All manipulations were carried out using standard Schlenk,
high-vacuum, and glovebox techniques using dried and de-
gassed solvents, unless otherwise stated. NMR spectra were
recorded on Bruker Avance 300, 400, and 500 MHz NMR
spectrometers and referenced to residual solvent signals for 1H
and 13C spectra for CDCl3 (δ 7.24, 77.2) and CD2Cl2 (δ 5.32,
54.0). Elemental analyses were performed by Elemental Micro-
analysis Ltd., Okehampton, Devon, UK, or the Elemental
Analysis Service, London Metropolitan University, London,
UK. 1,3,5-Tris(bromomethyl)-2,4,6-triethylbenzene, 1-tert-
butylimidazole, and 2,6-diisopropylphenylimidazole were pre-
pared according to literature methods.27,28
[Pd(ICy)I2]2. The synthesis was based on that for the analo-
gous ItBu dimer.13 Pd(OAc)2 (336 mg, 1.5 mmol), NaI (900 mg,
6.0 mmol), KOtBu (198 mg, 1.8 mmol), and 1,3-dicyclohexyli-
midazolium tetrafluoroborate (459 mg, 1.5 mmol) were sus-
pended in THF (40 mL), and the mixture was stirred at room
temperature for 16 h. The solvent was removed, the products
were separated by column chromatography (silica, Et2O) in air,
and the red-orange fraction was isolated. Evaporation gave the
product as a red microcrystalline powder in 72% yield (628 mg).
1H NMR (CDCl3, 500 MHz): δ 6.99 (s, 4H, NCHdCHN), 5.23
(23) (a) McGuinness, D. S.; Cavell, K. J. Organometallics 2000, 19,
741–748. (b) Loch, J. A.; Albrecht, M.; Peris, E.; Mata, J.; Faller, J. W.;
ꢀ
Crabtree, R. H. Organometallics 2002, 21, 700–706. (c) Mas-Marza, E.;
(26) (a) Cristau, H.-J.; Cellier, P. P.; Spindler, J.-F.; Taillefer, M. Eur.
J. Org. Chem. 2004, 695–709. (b) Ghosh, R.; Samuelson, A. G. New J.
Chem. 2004, 28, 1390–1393. (c) Naidu, A. B.; Jaseer, E. A.; Sekar, G. J. Org.
Chem. 2009, 74, 3675–3679.
Segarra, A. M.; Claver, C.; Peris, E.; Fernandez, E. Tetrahedron Lett. 2003,
44, 6595–6599. (d) Kim, J.-H.; Lee, D.-H.; Jun, B.-H.; Lee, Y.-S. Tetra-
hedron Lett. 2007, 48, 7079–7084.
(24) Deng, C.-L.; Xie, Y.-X.; Yin, D.-L.; Li, J.-H. Synthesis 2006,
3370–3376.
(25) Monnier, F.; Taillefer, M. Angew. Chem., Int. Ed. 2009, 48, 6954–
6971.
(27) Wallace, K. J.; Hanes, R.; Anslyn, E.; Morey, J.; Kilway, K. V.;
Siegel, J. Synthesis 2005, 2080–2083.
(28) Liu, J.; Chen, J.; Zhao, J.; Zhao, Y.; Li, L.; Zhang, H. Synthesis
2003, 2661–2666.

4102 Organometallics, Vol. 29, No. 18, 2010
Ellul et al.
(m, 4H, NCH), 2.30 (m, 8H, CH2), 1.93 (m, 8H, CH2), 1.82 (m,
4H, CH2), 1.63 (m, 8H, CH2), 1.43 (m, 8H, CH2), 1.24 (m, 4H,
CH2). 13C{1H} NMR: δ 148.9 (s, NCN), 119.4 (s, N(CH)2N),
60.7 (s, NCH), 33.4 (s, CH2), 25.7 (s, CH2), 25.6 (s, CH2). Anal.
Found (calcd) for C30H48N4Pd2I4: C, 30.52 (30.40); H, 4.04
(4.08); N, 4.68 (4.73).
118.6 (d, JCP = 6 Hz, NCHdCHN), 60.6 (s, NCH), 33.0 (s,
CH2), 26.0 (s, CH2), 25.6 (s, CH2). Anal. Found (calcd) for
C33H39N2PPdI2 CHCl3: C, 41.68 (41.92); H, 4.07 (4.13); N, 2.96
3
(2.87).
(timtebtBu){Pd(ICy)I2}3 (4a). trans-Pd(ICy)(PPh3)I2 (482 mg,
0.56 mmol) and 1,3,5-{tris(3-tert-butylimidazol-2-ylidene)-
methyl}-2,4,6-triethylbenzene (timtebtBu, 161 mg, 0.28 mmol)
were suspended in THF (30 mL) in an ampule fitted with a J.
Young PTFE valve, and the mixture was stirred at 70 °C for 4 h.
After cooling to room temperature, the solvent was removed
under vacuum and the residue washed with EtOH (1 ꢀ 10 mL)
and hexane (3 ꢀ 10 mL) to afford the product as a pale yellow
solid. Yield: 296 mg (68%). 1H NMR (CDCl3 500 MHz): δ 7.00
(br s, 3H, NCHdCHN), 6.93 (s, 6H, NCHdCHN), 6.14 (br s,
3H, NCHdCHN), 5.94 (br m, 6H, CH2N), 5.08 (m, 6H, NCH),
2.65 (br m, 6H, CH2CH3), 2.40 (m, 24H, CH2), 1.98 (s, 27H,
C(CH3)3), 1.90 (m, 6H, CH2), 1.74 (m, 6H, CH2), 1.70 (m, 12H,
CH2), 1.44 (m, 21H, CH2 þ CH2CH3). 13C{1H} NMR: δ 167.6
(s, NCN), 164.9 (s, NCN), 148.9 (s, C-CH2N or C-CH2CH3),
130.3 (s, C-CH2N or C-CH2CH3), 118.8 (s, NCHdCHN), 117.8
(s, NCHdCN), 60.3 (s, N-CH2N), 60.1 (s, N-CH), 58.4 (s,
NC(CH3)3), 33.4 (s, NC(CH3)3), 33.3 (s, CH2), 26.3 (s, CH2),
25.7 (s, CH2), 25.6 (s, CH2CH3), 17.8 (s, CH2CH3). Anal. Found
1,3,5-{Tris(3-tert-butylimidazolium)methyl}-2,4,6-triethylbenzene
Tribromide. 1,3,5-Tris(bromomethyl)-2,4,6-triethylbenzene (2.00 g,
4.58 mmol) was dissolved in 1,4-dioxane (100 mL) in air in a 250
mL round-bottomed flask. The solution was vigorously stirred and
1-tert-butylimidazole added (1.66 g, 14 mmol), resulting in the
immediate formation of a cloudy suspension. This was stirred for a
further 1 h and then heated at 50 °C for 30 min. After cooling, the
solid was filtered off, washed with Et2O (3 ꢀ 30 mL), and dried
under vacuum to give a white solid. Yield: 2.80 g (76%). 1H NMR
(CDCl3, 500 MHz, 298 K): δ 10.88 (s, 3H, NCHN), 7.53 (s, 3H,
NCHdCHN), 7.13 (s, 3H, NCHdCHN), 5.79 (s, 6H, -CH2N),
2.66 (quart, 6H, JHH = 7.4 Hz, -CH2CH3), 1.72 (s, 27H, NC-
(CH3)3), 1.09 (t, 9H, JHH = 7.4 Hz, -CH2CH3). 13C{1H} NMR: δ
147.0 (s, C-CH2N or C-CH2CH3), 135.9 (s, NCHdCHN), 126.9 (s,
C-CH2CH3 or C-CH2N), 121.8 (s, NCHdCHN), 120.1 (s,
NCHdCHN), 60.9 (s, NC(CH3)3), 47.4 (s, C-CH2N), 30.4 (s,
NC(CH3)3), 26.7 (s, C-CH2CH3), 15.4 (s, C-CH2CH3).
1,3,5-{Tris(3-(2,6-diisopropylphenyl)imidazolium)methyl}-2,4,6-
triethylbenzene Tribromide. The reaction was performed as for
1,3,5-{tris(3-tert-butylimidazolium)methyl}-2,4,6-triethylbenzene
tribromide but using 1,3,5-tris(bromomethyl)-2,4,6-triethylben-
zene (3.00 g, 6.8 mmol) and 2,6-diisopropylphenylimidazole
(4.65 g, 20.4 mmol). The initially formed suspension was stirred
for 24 h at room temperature, then heated at 50 °C for 1 h. The
dioxane was removed under vacuum, and the resulting solid
filtered and washed with Et2O (3 ꢀ 30 mL). Yield: 4.98 g (65%).
1H NMR (CDCl3, 300 MHz, 298 K): δ 10.69 (s, 3 H, NCHN),
8.92 (s, 3 H, NCHdCHN), 7.45 (t, 3H, JHH = 7.65 Hz,
(calcd) for C81H126N12Pd3I6 3C4H8O: C, 43.28 (43.54); H, 5.67
(5.66); N, 6.66 (6.55).
3
(timtebtBu){Pd(PPh3)I2}3 (5a). 1,3,5-{Tris(3-tert-butylimida-
zolium)methyl}-2,4,6-triethylbenzene tribromide (250 mg,
0.307 mmol), Pd(OAc)2 (206 mg, 0.924 mmol), NaI (555 mg,
3.696 mmol), and KOtBu (104 mg, 0.924 mmol) were suspended
in THF (50 mL), and the mixture was stirred at room tempera-
ture for 48 h. The solvent was removed and the products were
separated by column chromatography (silica, THF) in air. The
orange-yellow fraction that eluted was evaporated to give 120
mg of an orange solid. This was redissolved in THF (15 mL) and
stirred with PPh3 (70 mg, 0.267 mmol) for 30 min at room
temperature. The solvent was removed and the residue washed
with hexane (3 ꢀ 10 mL) to afford a pale yellow solid, which was
recrystallized from CH2Cl2/hexane to give 160 mg (19%) of 5a.
1H NMR (CDCl3 500 MHz): δ 7.75 (m, 18H, PPh3), 7.38 (m,
27H, PPh3), 7.00 (br s, 3H, NCHdCHN), 6.21 (br s, 3H,
NCHdCHN), 5.52 (m, 6H, CH2N), 2.61 (m, 6H, CH2CH3),
1.93 (s, 27H, C(CH3)3), 1.16 (m, 9H, CH2CH3). 31P{1H} NMR:
δ 18.0 (s). 13C{1H} NMR: δ 155.0 (d, JCP = 192 Hz, NCN),
147.2 (s, C-CH2N or C-CH2CH3), 147.0 (s, C-CH2N or C-
i
i
C6 Pr2H3), 7.22 (d, 6H, JHH = 7.65 Hz, C6 Pr2H3), 7.07 (s,
3H, NCHdCHN), 6.10 (s, 6H, CH2N), 2.78 (sept, 6H, JHH
=
7.65 Hz, CH(CH3)2), 2.20 (quart, 6H, JHH = 6.90 Hz,
-CH2CH3), 1.13, (d, 18H, JHH = 7.65 Hz, CH(CH3)2), 1.07
(d, 18H, JHH = 7.65 Hz, CH(CH3)2), 0.84 (t, 9H, JHH = 7.53
Hz, -CH2CH3). 13C{1H} NMR: δ 148.9 (s, C-CH2N), 145.1 (s,
i
i
C6 Pr2H3), 137.9 (s, NCHN), 131.9 (s, C6 Pr2H3), 130.4 (s, C-
i
CH2CH3), 128.6 (s, C6 Pr2H3) 125.3 (s, NCHdCHN), 124.7 (s,
i
C6 Pr2H3), 124.4 (s, NCHdCHN), 48.7 (s, -CH2N), 31.1 (s,
NCH(CH3)2), 24.6 (s, NCH(CH3)2), 24.3 (s, -CH2CH3), 24.2 (s,
CH(CH3)2), 15.9 (s, -CH2CH3).
CH2CH3), 135.1 (d, JCP = 11 Hz, PC6H5), 132.9 (d, JCP
=
trans-Pd(ICy)(PPh3)I2. PPh3 (273 mg, 1.04 mmol) was added
to a THF solution (30 mL) of [Pd(ICy)I2]2 (628 mg, 0.52 mmol),
and the mixture stirred rapidly at room temperature for 30 min.
Removal of solvent gave an orange residue, which was washed
with hexane (3 ꢀ 10 mL) and then redissolved in CH2Cl2. Slow
addition of hexane precipitated out cis-Pd(ICy)(PPh3)I2,29 leav-
ing trans-Pd(ICy)(PPh3)I2 in solution. After removal of the solid
by cannula filtration, the filtrate was reduced to dryness to leave
trans-Pd(ICy)(PPh3)I2 as an orange solid, which was recrystal-
lized from CHCl3/hexane. Yield: 482 mg (54%). 1H NMR
(CDCl3, 500 MHz): δ 7.72 (m, 6H, PPh3), 7.39 (m, 9H, PPh3),
6.96 (d, 2H, JHP = 1.52 Hz, NCHdCHN), 4.78 (m, 2H, NCH),
2.38 (m, 4H, CH2), 1.88 (m, 4H, CH2), 1.77 (m, 4H, CH2), 1.42
(m, 4H, CH2), 1.23 (m, 2H, CH2), 1.06 (m, 2H, CH2). 31P{1H}
NMR: δ 17.9 (s). 13C{1H} NMR: δ 152.9 (d, JCP = 191 Hz,
NCN), 135.6 (d, JCP = 11 Hz, PPh3), 133.0 (d, JCP = 44 Hz,
PPh3), 131.0 (d, JCP = 3 Hz, PPh3), 128.0 (d, JCP = 11 Hz, PPh3),
44.4 Hz, PC6H5), 130.2 (s, PC6H5), 128.0 (d, JCP = 10 Hz,
PC6H5), 119.9 (s, NCHdNCH), 119.4 (s, NCHdNCH) 58.8 (s,
NC(CH3)3), 50.5 (s, NCH2), 37.4 (s, C(CH3)3), 27.0 (s,
CH2CH3), 16.0 (s, CH2CH3). Anal. Found (calcd) for
C90H99N6P3Pd3I6: C, 44.63 (44.33); H, 3.88 (4.09); N, 3.80
(3.45).
(timtebdipp){Pd(PPh3)I2}3 (5b). 1,3,5-{Tris(3-(2,6-diisopropyl-
phenyl)imidazolium)methyl}-2,4,6-triethylbenzene tribromide
(334.8 mg, 0.298 mmol), Pd(OAc)2 (200 mg, 0.893 mmol), NaI
(535.7 mg, 3.571 mmol), andKOtBu(100.3mg, 0.894mmol) were
suspended in THF (50 mL), and the mixture was stirred at room
temperature for 48 h. The solvent was removed and the products
were separated by column chromatography (silica, Et2O) in air.
The red fraction that eluted was evaporated to leave 192 mg of a
red solid. Thiswas redissolvedinCH2Cl2 (15mL) andstirred with
PPh3 (80 mg, 0.305 mmol) for 1 h at room temperature. Removal
ofthe solvent gave an orange residue, whichwas washedwithcold
hexane (3 ꢀ 10 mL) and then recrystallized from CH2Cl2/hexane
to afford 153 mg (19% yield) of 5b. 1H NMR (CDCl3, 500 MHz):
1
(29) Spectroscopic data for cis-Pd(ICy)(PPh3)I2. H NMR (CDCl3,
i
500 MHz): δ 7.73 (m, 6H, PC6H5), 7.37 (m, 9H, PC6H5), 6.93 (s, 2H,
NCHdCHN), 5.09 (m, 2H, NCH), 2.40 (m, 4H, CH2), 1.94 (m, 4H,
CH2), 1.79 (m, 2H, CH2), 1.49 (m, 4H, CH2), 1.25 (m, 2H, CH2). 31P{1H}
NMR: δ 24.9 (s). 13C{1H} NMR: δ 165.0 (s, NCN), 135.5 (d, JCP = 11
Hz, PC6H5), 133.0 (d, JCP = 43 Hz, PC6H5), 130.9 (s, PC6H5), 128.6 (d,
JCP = 11 Hz, PC6H5), 117.8 (s, NCHdCHN), 60.1 (s, NCH2), 33.4 (s,
CH2), 25.8 (s, CH2), 25.3 (s, CH2).
δ 7.56-7.27 (m, 54H, C6 Pr2H3 þ PPh3), 6.99 (s, 3H, NCHd
CHN), 6.49 (s, 3H, NCHdCHN), 5.88 (s, 6H, N-CH2), 3.26 (br
m, 6H, CH(CH3)2), 2.92 (br s, 6H, CH2CH3), 1.31 (d, JHH = 5.6
Hz, 18H, CH(CH3)2), 1.14(brs,9H, CH2CH3), 1.02(d, JHH =5.6
Hz, 18H, CH(CH3)2). 31P{1H} NMR:δ16.2 (s). 13C{1H} NMR: δ
163.2 (d, JCP = 196 Hz), 149.2 (s, C-CH2N or C-CH2CH3), 147.6

Article
Organometallics, Vol. 29, No. 18, 2010 4103
Table 4. Crystal Data and Structure Refinement for 4a, 5a, and 6a
4a
5a
6a
empirical formula
fw
cryst syst
C
86.50H129Cl11I6N12Pd3
C93H102Cl9I6N6P3Pd3
2796.37
triclinic
C75.50H115Cl7Cu6F12N12O2P2
2807.57
triclinic
P1
2142.13
triclinic
P1
space group
˚
P1
a/A
15.6880(2)
19.6950(2)
20.6950(3)
64.251(1)
87.499(1)
76.260(1)
5581.55(12)
2
17.1220(3)
18.2790(3)
21.0660(5)
113.781(1)
96.783(1)
108.888(1)
5467.95(18)
2
16.8277(5)
16.9316(6)
17.3903(5)
75.988(3)
89.409(2)
81.522(3)
4753.2(3)
2
˚
b/A
˚
c/A
R/deg
β/deg
γ/deg
3
˚
U/A
Z
Dc/g cm-3
1.671
2.445
1.698
2.489
1.497
1.620
μ/mm-1
F(000)
2750
0.30 ꢀ 0.30 ꢀ 0.25
2712
0.20 ꢀ 0.20 ꢀ 0.02
2198
0.43 ꢀ 0.21 ꢀ 0.04
cryst size/mm
θ min., max. for
data collection
index ranges
3.55, 27.48
3.77, 22.00
3.64, 26.37
-20 e h e 20;
-25 e k e 25;
-26 e l e 26
89 235
-18 e h e 18;
-19 e k e 18;
-22 e l e 22
70 271
-20 e h e 21;
-21 e k e 21;
-21 e l e 17
33 920
reflns collected
indep reflns, Rint
reflns obsd (>2σ)
data completeness
absorp corr
25 391, 0.0515
18 519
0.991
13 290, 0.1294
8376
0.992
19 379, 0.0295
11 896
0.997
analytical (face indexation)
0.748, 0.177
19 379/28/1062
0.904
0.0405, 0.0910
0.0731, 0.0958
0.713, -0.447
multiscan
multiscan
max., min transmn
data/restraints/params
goodness-of-fit on F2
final R1, wR2 [I > 2σ(I)]
final R1, wR2 (all data)
largest diff.
0.659, 0.506
25 391/0/1082
1.085
0.0639, 0.1633
0.0937, 0.1822
2.281, -1.861
0.962, 0.886
13 290/184/1224
1.050
0.0761, 0.1632
0.1314, 0.1986
3.332, -1.877
-3
˚
peak, hole/e A
(s, C-CH(CH3)2), 135.4 (d, JCP = 10 Hz, PC6H5), 134.8 (s, C-
CH2N or C-CH2CH3) 133.3 (d, JCP = 45 Hz, PC6H5), 130.5 (d,
2.79 (quart, JHH = 6.8 Hz, 6H, CH2CH3), 2.36 (sept, JHH = 7.6
Hz, 6H, CH(CH3)2), 1.17 (d, JHH = 7.6 Hz, 18H, CH(CH3)2),
1.09 (d, JHH = 7.6 Hz, 18H, CH(CH3)2), 0.92 (t, JHH = 6.8 Hz,
9H, CH2CH3). 13C{1H} (273 K): δ 177.6 (s, NCN), 148.1 (s, C-
CH2N or C-CH2CH3), 145.7 (s, C(CH(CH3)2), 136.0 (s,
i
CP = 5 Hz, PC6H5),130.1 (s, C6 Pr2H3), 127.2 (d, JCP = 10 Hz,
J
i
PC6H5), 124.8 (s, NCHdCHN), 124.3 (s, C6 Pr2H3), 119.2 (s,
NCHdCHN), 50.7 (s, NCH2), 29.1 (s, CH(CH3)2), 23.6 (s,
CH2CH3), 26.9 (s, CH(CH3)2), 16.8 (s, CH2CH3). Anal. Found
(calcd) for C114H123N6I6P3Pd3: C, 49.77 (49.65); H, 4.51 (4.43);
N, 3.06 (3.15).
i
N-C6 Pr2H3), 130.1 (s, C-CH2N or C-CH2CH3), 129.8 (s, p-
CH), 124.4 (s, NCHdCHN), 124.0 (s, N-C6 Pr2H3), 21.9 (s,
i
NCHdCHN), 48.3 (s, CH2N), 31.3 (s, CH(CH3)2, 28.4 (s,
CH2CH3), 24.3 (s, CH(CH3)2), 15.5 (s, CH2CH3). Anal. Found
(calcd) for C60H78N6OCu3BF4: C, 60.74 (61.24); H, 6.48 (6.68);
N, 6.72 (7.14). MS (FABþ): m/z 1089.4, [M]þ calculated
1089.4.
General Catalytic Procedures. (i). Pd-Catalyzed Suzuki-
Miyaura Coupling. Aryl halide (0.5 mmol), phenylboronic
acid (0.75 mmol), cesium carbonate (1.0 mmol), palladium
complex (1 mol %), and 1,4-dioxane (1.5 mL) were combined
in a J. Young ampule modified to fit a Thermo Scientific
Omnistation reactor and heated at 80 or 120 °C for 2 or 3 h.
After cooling to room temperature, a 30 μL aliquot was
withdrawn and diluted with 1 mL of 1,4-dioxane. A 5 μL
amount of anisole was added as an internal standard and the
mixture analyzed by GC.
[(timtebtBu)Cu3(μ3-O)]PF6 (6a). A suspension of 1,3,5-{tris(3-
tert-butylimidazolium)methyl}-2,4,6-triethylbenzene tribro-
mide (360 mg, 0.45 mmol), [Cu(NCMe)4]PF6 (500 mg, 1.34
mmol), and NaOtBu (129 mg, 1.34 mmol) in thf (20 mL) was
stirred at room temperature for 2 h. The mixture was passed
through a pad of Celite, and the filtrate reduced to dryness.
Extraction with CH2Cl2 gave a yellow solution, which upon
addition of Et2O gave a colorless solution along with a brown
oil. The solution was decanted off and reduced to dryness to
afford a white solid. Yield: 210 mg (51%). 1H NMR (CD2Cl2,
500 MHz, 298 K): δ 7.33 (s, 3H, NCHdCHN), 7.28 (s, 3H,
NCHdCHN), 5.25 (s, 6H, NCH2), 2.53 (quart, JHH = 7.57 Hz,
6H, CH2CH3), 1.72 (s, 27H, NC(CH3)3), 1.17 (br t, 9H,
CH2CH3). 13C{1H} NMR: δ 169.2 (s, NCN), 148.8 (s, C-
CH2N or C-CH2CH3), 131.4 (s, C-CH2N or C-CH2CH3),
121.6 (s, NCHdCHN), 120.1 (s, NCHdCHN), 58.3 (s, NC-
(CH3)3), 49.1 (s, NCH2), 32.3 (s, NC(CH3)3), 24.7 (s, CH2CH3),
14.7 (s, CH2CH3). Anal. Found (calcd) for C36H54N6OCu3PF6:
C, 46.28 (46.87); H, 5.82 (5.90); N, 8.73 (9.11). MS (FABþ): m/z
777.2, [M]þ calculated 777.0.
(ii). Pd-Catalyzed Sonogashira Coupling. As for (i) but with
aryl halide (0.5 mmol), phenylacetylene (0.7 mmol), cesium
carbonate (1.0 mmol), copper iodide (0.01 mmol), palladium
complex (1 mol %), and 1,4-dioxane (1.5 mL).
(iii). Cu-Catalyzed Sonogashira Coupling. Similar to (i) but
with aryl halide (0.5 mmol), phenylacetylene (0.6 mmol), cesium
carbonate (0.6 mmol), copper catalyst (1 mol %), and DMSO
(1.5 mL). The mixture was heated and stirred at 120 °C for 24 h,
after which it was cooled to room temperature, diluted with 10
mL of CH2Cl2, and filtered. The filtrate was washed with water
(3 ꢀ 10 mL) and dried over MgSO4. The solvent was removed
under vacuum to yield the crude product, which was analyzed by
NMR to determine the conversion. The products were identified
by comparison to the literature.
[(timtebdipp)Cu3(μ3-O)]BF4 (6b). The reaction was performed
as for 6a but with 1,3,5-{tris(3-(2,6-diisopropylphenyl)-
imidazolium)methyl}-2,4,6-triethylbenzene tribromide (563
mg, 0.53 mmol), [Cu(NCMe)4]BF4 (500 mg, 1.59 mmol), and
NaOtBu (153 mg, 1.59 mmol) to afford 570 mg (91%) of 6b. 1H
NMR (CD2Cl2, 400 MHz, 273 K): δ 7.59 (t, JHH = 7.6 Hz, 3H,
iPr2C6H3), 7.31 (s, 3H, NCHdCHN), 7.25 (d, JHH = 7.6 Hz,
6H, iPr2C6H3), 6.94 (s, 3H, NCHdCHN), 5.49 (s, 6H, CH2N),

4104 Organometallics, Vol. 29, No. 18, 2010
Ellul et al.
(iv). Cu-Catalyzed Ullmann-Type Arylation Reactions. Simi-
lar to (i) but with aryl halide (1.0 mmol), imidazole or phenol
(1.5 mmol), cesium carbonate (2.0 mmol), copper catalyst (1 mol %),
and DMSO (1.5 mL). The mixture was heated and stirred at
100 °C for 24 h, after which it was cooled to room temperature,
diluted with 10 mL of CH2Cl2, and filtered. The filtrate was
washed with 5% w/w aqueous KHCO3 solution (2 ꢀ 10 mL) and
water (2 ꢀ 10 mL) and finally dried over MgSO4. The solvent
was removed under vacuum to yield the crude product, which
was analyzed by NMRtodetermine the conversion. The products
were identified by comparison to the literature.
X-ray Crystallography. Single crystals of compounds for 4a,
5a, and 6a were studied at 150 K using Mo(KR) radiation. Data
collection for 6a was effected on an Oxford Diffraction Gemini
diffractometer, while 4a and 5a were analyzed on a Nonius
Kappa CCD machine. Details of the data collections, solutions,
and refinements are given in Table 4. The structures were solved
using SHELXS-9730 and refined using full-matrix least-squares
in SHELXL-97.30 Refinements were not entirely straightfor-
ward, and specific points that merit note are as follows.
In 4a, the asymmetric unit was seen to contain 4.5 molecules
of dichloromethane per one molecule of the complex. Residual
electron density is located in the region of the iodides and, as
such, is not chemically significant. The asymmetric unit in 5a
consists of one molecule of the gargantuan complex and four
regions of solvent (chloroform). The solvent based on C93 is
present at full occupancy, while that based on C93 and C94 is
each present 60% of the time. The chloroform moiety based on
C91 equates to 80% of a full molecule, disordered between two
proximate sites in a 60:80 ratio. While the refinement of the
model in 5a provides unambiguous proof of the molecular
structure, the caliber of the data is not as high as the authors
would wish, and we do not wish to make detailed claims based
on the associated metric data. The key issue was that, despite
stringent and copious efforts, this compound crystallized as
plates of mediocre quality. The smallest dimension of the
crystals meant that there was little diffraction at higher Bragg
angles; this is also reflected in the Rint value and the weighting
scheme. Thus, in order to secure a credible refinement, data were
truncated at a 2θmax value of 44°. Refinement was also ham-
pered by some disorder and solvent fragments with partial
occupancy. Within the complex, N1, N2, and C20-25 exhibited
disorder over two sites in a 50:50 ratio. C-Cl and Cl Cl
3 3 3
distance restraints and some ADP restraints were applied to the
fractional atoms in disordered solvent regions in order to assist
convergence. The residual density maxima are at nonchemically
significant distances from I3 and I6, respectively. Efforts to
model the two iodides as being split over two sites proved
unfruitful and, hence, were abandoned. There is also an artifact
of electron density proximate to C57, which resulted in several
restraints being incorporated on behalf of the aromatic ring to
which this carbon belongs. Finally, there was no evidence for
twinning in 5a.
Two cations, two anions, and 3.5 molecules of dichloro-
methane constitute the motif in the structure of 6a. Four of
the fluorines in the anion based on P2 were found to be
disordered in a 50:50 ratio. P-F and F F distances were
3 3 3
restrained in this disordered region. Cl3 was also disordered
over two sites (65:35 ratio in this instance). Hydrogens in this
solvent moiety were included at calculated positions relative to
the major Cl3 fraction. Unfortunately, 1.5 molecules of the
solvent were so badly disordered that modeling was not possible.
Hence, PLATON SQUEEZE was employed, and the results
were consistent with three additional CH2Cl2 entities in the unit
cell (1.5 in the asymmetric unit). The formula presented herein
has been amended to reflect the presence of this extra solvent.
Crystallographic data for compounds 4a, 5a, and 6a, along
with [Pd(ICy)I2]2 (ESI only), have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publications CCDC 785334-785337. Copies of the data can
be obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK [fax: (þ44) 1223 336033,
e-mail: deposit@ccdc.cam.ac.uk].
Acknowledgment. Financial support was provided by
an EPSRC Doctoral Training Award (C.E.E.) and The
Royal Society (S.I.P.). We thank Dr. Andrew Ashley
(Oxford University) for supplying the initial sample of
3a and the EPSRC National Mass Spectrometry Service
(Swansea, UK) for characterization.
Supporting Information Available: CIF files giving X-ray
crystallographic data for 4a, 5a, and 6a. X-ray structure of
[Pd(ICy)I2]2. This material is available free of charge via the
Internet at http://pubs.acs.org.
(30) Sheldrick, G. M. Acta Crystallogr. 1990, 467-473, A46. Shel-
drick, G. M. SHELXL- 97, a computer program for crystal structure
€
refinement; University of Gottingen, 1997.