Palladium, rhodium and platinum complexes of ortho-xylyl-linked bis-N-heterocyclic carbenes: Synthesis, structure and catalytic activity

Article abstract of DOI:10.1016/j.jorganchem.2006.09.037

New Pd(II), Pt(II) and Rh(I) N-heterocyclic carbene (NHC) complexes containing two NHC units linked by an ortho-xylyl group are described and structurally and spectroscopically characterised. The Pt(II) complexes represent the first examples of Pt-bis(NHC) complexes where the NHC units are linked by an ortho-xylyl group. Functionalisation of the bis(NHC) ligands with heptyl groups has been used as a means of enhancing the solubility of the complexes, in order to facilitate spectroscopic characterisation and catalytic studies. The catalytic activity of the palladium(II) complexes in Heck and Suzuki cross-coupling reactions has been examined to investigate any effects of the diverse structural changes, though these appear to be insignificant.

Full text of DOI:10.1016/j.jorganchem.2006.09.037

Journal of Organometallic Chemistry 691 (2006) 5845–5855
www.elsevier.com/locate/jorganchem
Palladium, rhodium and platinum complexes of ortho-xylyl-linked
bis-N-heterocyclic carbenes: Synthesis, structure and catalytic activity
*
Murray V. Baker , David H. Brown, Peter V. Simpson, Brian W. Skelton,
Allan H. White, Charlotte C. Williams
Chemistry M313, School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia,
35 Stirling Highway, Crawley, WA 6009, Australia
Received 1 September 2006; received in revised form 15 September 2006; accepted 15 September 2006
Available online 26 September 2006
Abstract
New Pd(II), Pt(II) and Rh(I) N-heterocyclic carbene (NHC) complexes containing two NHC units linked by an ortho-xylyl group are
described and structurally and spectroscopically characterised. The Pt(II) complexes represent the first examples of Pt-bis(NHC) com-
plexes where the NHC units are linked by an ortho-xylyl group. Functionalisation of the bis(NHC) ligands with heptyl groups has been
used as a means of enhancing the solubility of the complexes, in order to facilitate spectroscopic characterisation and catalytic studies.
The catalytic activity of the palladium(II) complexes in Heck and Suzuki cross-coupling reactions has been examined to investigate any
effects of the diverse structural changes, though these appear to be insignificant.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Heterocyclic carbene complexes; Pd complexes; Pt complexes; Catalysis
1. Introduction
on imidazole, dihydroimidazole (imidazolidine), benzimid-
azole, thiazole, oxazole, oxazoline and benzoxazole frame-
works [5]. Acyclic diaminocarbenes have also been used as
ligands in metal complexes of exceptional catalytic activity
[6]. These recent advances illustrate the considerable cur-
rent interest in exploring the impact of structural changes
in NHC-metal complexes and changes in reaction condi-
tions on catalytic activity.
We have been interested in bidentate NHC ligands based
on azolium-linked cyclophane systems [7,8], in particular
ligands with two imidazol-2-ylidenes linked by two ortho-
xylyl groups. The imidazolium salts that are precursors to
these NHC ligands are readily synthesised and the subse-
quent formation of mononuclear complexes of Pd(II),
Ni(II), Rh(I) and Ir(I), or dinuclear complexes of Ag(I)
and Au(I) has proved facile [9–11]. Once bound to metal
centres, the ligands are rigid and appear to confer significant
stability on the metal complexes. We have previously
reported high activity in the Heck reaction of the Pd(II)
complex 1 containing such a ligand [9]. In some cases,
however, these NHC complexes have very low solubility
The use of N-heterocyclic carbenes (NHCs) as ligands is
now ubiquitous in modern organometallic chemistry and
there are examples of NHC complexes with a large number
of the transition metals [1,2]. Of particular interest is the
catalytic behaviour exhibited by NHC complexes of palla-
dium, ruthenium and rhodium, and more recently nickel,
platinum and iridium [3]. NHC complexes of these metals
catalyse a broad range of reactions including C–C and
C–N coupling, olefin metathesis, polymerisation and
hydrogenation. In addition, the use of chiral NHC-metal
complexes enables asymmetric catalysis [4]. The structural
diversity of NHCs and NHC-metal complexes that is
now synthetically available has facilitated this broad range
of applications. This diversity in NHC ligands encompasses
mono- and poly-dentate NHC ligands and numerous
mixed donor systems. Changes in the NHC ring systems
have also been explored and a range of NHCs exist based
*
Corresponding author. Tel.: +61 8 6488 2576; fax: +61 8 6488 1005.
E-mail address: mvb@chem.uwa.edu.au (M.V. Baker).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.09.037

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M.V. Baker et al. / Journal of Organometallic Chemistry 691 (2006) 5845–5855
and we thus sought variants of the NHC ligands that could
improve the solubility of the complexes. An approach that
we have adopted in this work is to explore the use of ligands
containing two NHCs linked by only one ortho-xylyl group
(e.g. 2), a structural motif that in most cases binds metal cen-
tres in the same rigid cis-bis(NHC) mononuclear arrange-
ment as analogous motifs containing two ortho-xylyl
linkers [9,12,13]. The Pd(II) complex 2 and related Rh(I)
and Ir(III) complexes have exhibited catalytic activity in a
number of reactions [9,12]. The ligand system with only
one ortho-xylyl linker, such as the bis-NHC in 2, allows
for the facile introduction of solubilizing groups as well as
the inclusion of groups that may impose a useful steric effect
around the metal centre. Studies have suggested that manip-
ulation of steric bulk around a metal centre may affect the
efficiency of some of the steps in a catalytic cycle [2,14].
pale beige microcrystalline materials. The complexes hav-
ing alkyl chains (7 and 9) exhibited good solubility in
organic solvents (CH2Cl2, CHCl3, acetone, DMSO) com-
pared to the methyl analogue 2 or the non-alkylated ana-
logue 1, which exhibit low solubility in most common
organic solvents [9]. The increased solubility of 9 allows
it to be readily purified by recrystallisation, much more eas-
ily than its non-alkylated analogue 1. The naphthyl com-
plex 8 is less soluble than 7 and 9 in most common
organic solvents but can be recrystallised from hot CH2Cl2.
2 Br
R
R
N
N
N
N
N
N
N R
N R
2 Br
3.2Br R = n-C7H15
5.2Br R = n-C7H15
6.2Br R = H
4.2Br R = 1-naphthyl
CH3
N
N
N
N
H3C
N
Br
Br
N
N
Br
Br
Pd
Pd
N
N
N
N
N
Br
Br
Br
N
N
2
Pd
Pd
1
Br
N
N
In this paper we report the synthesis of a series of palla-
dium, platinum and rhodium complexes bearing bis(NHC)
ligands that are linked by at least one ortho-xylyl group.
The addition of heptyl or naphthyl groups to the ligand
framework has provided a ready path to the improvement
of solubility or the exploration of steric effects in these sys-
tems. Examples within this series have been structurally
characterised. The platinum complexes reported here are
the first examples of platinum-bis(NHC) complexes where
the NHC ligands are bridged by an ortho-xylyl linker.
The effect of diverse structural changes in a series of palla-
dium complexes on catalytic activity in the Heck and
Suzuki reactions is also examined.
7
8
H15C7
H15C7
PF6
N
N
N
N
N
N
N
N
Br
Rh
Pd
Br
10.PF6
9
2. Results and discussion
N
N
N
2.1. Synthesis of complexes
N
N
Cl
Cl
N
Pt
N
N
Cl
Cl
Pt
The imidazolium cations 3–6 as dibromide salts were
prepared by established procedures [7,9]. The reaction of
excess N-heptylimidazole or N-(naphth-1-ylmethyl)imidaz-
ole with 1,2-bis(bromomethyl)benzene afforded the bis-imi-
dazolium salts 3 Æ 2Br and 4 Æ 2Br respectively, in good
yields. The cyclophane salt 5 Æ 2Br was prepared by the
reaction of 1,2-bis(imidazol-1-ylmethyl)-4,5-diheptylben-
zene with 1,2-bis(bromomethyl)benzene, while the synthe-
sis of 6 Æ 2Br has been reported elsewhere [9]. Methods
used to synthesize complexes 7 to 12 are exemplified in
Scheme 1. The palladium complexes 7–9 were prepared
by treatment of the appropriate imidazolium salts with pal-
ladium acetate in DMF or acetonitrile, and were isolated in
acceptable yields (7: 31%, 8: 47%, 9: 61%) as colourless or
12
11
The rhodium complex 10 was prepared as its hexaflu-
orophosphate salt by the reaction of 3 Æ 2PF6 (formed by
anion exchange of 3 Æ 2Br) with [Rh(cod)Cl]2 and potas-
sium tert-butoxide in DMSO. The salt 10 Æ PF6 was iso-
lated as a bright yellow powder in 36% yield and was
found to be very soluble in common organic solvents
(acetone, CH2Cl2, methanol, acetonitrile). The platinum
complexes 11 and 12 were prepared by the reaction of
[Pt(cod)Cl2] with the acetate salts 3 Æ 2OAc and 6 Æ 2OAc

M.V. Baker et al. / Journal of Organometallic Chemistry 691 (2006) 5845–5855
5847
singlets in the case of 3 and 4 or broad signals in the case
of 5 and 6 (in DMSO-d6 solutions). In the case of 5 and
6, the broadness of the signals in the H NMR spectra is
attributed to the interconversion of different conformations
at a rate comparable to the NMR timescale [7]. The com-
plexity of the signals due to the protons a to nitrogen on
the heptyl chains in 7, 10 and 11 is due to the diastereotopic
nature of these protons.
[Pd(OAc)2]
X = Br
H15C7
N
C7H15
N
7
1
2 X
[Rh(cod)Cl]2, KOtBu
X = PF6
N
N
10.PF6
[Pt(cod)Cl2]
X = OAc
11
3.2X
The 13C NMR spectra for 7–9 each display a single sig-
nal in the range 160–163 ppm, which is attributed to the
carbene carbons bound to the palladium centre. The signal
for the carbene carbon in the 13C NMR spectra for 10 Æ PF6
is a doublet (1JRh,C = 53.5 Hz) at ca. 180 ppm. The signals
corresponding to the carbene carbons in the 13C NMR
spectra for the platinum complexes 11 and 12 appear at
149.5 ppm (acetone-d6) and 147.1 ppm (DMSO-d6)
respectively.
Danopoulos et al. recently characterised the bis(NHC)-
PdCl2 adduct 13 in which the NHC groups were also linked
by an ortho-xylyl unit but were nevertheless mutually trans
[13]. In that case, the bulky 2,6-diisopropylphenyl groups
presumably prevent the NHC units from adopting the
mutually cis arrangement we see in 7, 8, 10 and 11.
Scheme 1. Synthetic pathways for Pd, Pt and Rh complexes derived from
3.
(formed by anion exchange of 3 Æ 2Br and 6 Æ 2Br). The
complexes were isolated in acceptable yields (11: 58%,
12: 44%) as colourless microcrystalline materials. The
complex 12 is readily prepared in CH3CN, but in the case
of 11, improved yields were obtained using DMF as the
solvent. A number of other procedures were attempted
for the preparation of 11, including the reaction of
3 Æ 2Cl with [Pt(cod)Cl2] in the presence of NaOAc. Proce-
dures that used CH3CN as solvent or 3 Æ 2Cl as a starting
material were less successful than the reaction of 3 Æ 2OAc
with [Pt(cod)Cl2] in DMF, and were often slower reac-
tions that afforded lower yields and/or impure materials.
Complex 11 exhibits good solubility in polar and chlori-
nated organic solvents, much higher than 12, which is
sparingly soluble in acetonitrile and chlorinated solvents.
Complexes 11 and 12 represent the first examples of plat-
inum-bis(NHC) complexes where the NHC groups are
bridged by an ortho-xylyl linker.
Various syntheses of [Pt(cod)Cl2] involving a variety of
platinum sources (Pt metal, H2PtCl6 or K2PtCl4), solvent
systems and work-up procedures have been reported [15].
We have found a variant of some of the literature proce-
dures to be particularly convenient. The treatment of an
aqueous solution of potassium tetrachloroplatinate (heated
in a conical flask on a hotplate) with an ethanolic solution
of 1,5-cyclooctadiene affords analytically pure [Pt(cod)Cl2]
in high yield (ca. 80%) within ca. 30 min.
Cl
N
N
N
N
Pd
Cl
Ar
Ar
Ar = 2,6-C6H3Pri2
13
The Pt–Cl bonds in complexes 11 and 12 undergo rapid
1
solvolysis in DMSO at room temperature. The H NMR
spectrum of a solution of 11 in DMSO-d6, recorded within
5 min of the sample being prepared, exhibited signals
expected for 11 but also showed additional signals
(Fig. 1a) consistent with the presence of the solvolysis
product 14. No change in the relative amounts of the
dichloride 11 and the solvolysis product 14 was observed
when the sample was heated at 80 ꢁC for 16 h (Fig. 1b).
These observations suggest that the solvolysis is rapid,
reaching equilibrium within 5 min at room temperature.
A 1H NMR spectrum recorded immediately after the addi-
tion of Et4NCl to the solution (Fig. 1c) showed an increase
in the concentration of the dichloride complex 11 and a
decrease in the concentration of the solvate complex 14.
Subsequent addition of a small amount of water to this
solution did not affect the relative concentrations of 11
and 14, indicating that the solvolysis process involved
DMSO and not adventitious traces of water in the solvent.
In DMSO-d6 solutions, complex 12 shows behaviour simi-
lar to that of 11, but neither complex undergoes solvolysis
in acetonitrile or acetone solutions.
2.2. NMR spectra of complexes
The 1H and 13C NMR spectra of solutions containing 7–
12 exhibit signals that are diagnostic for metal complexes
having mutually cis NHCs linked by an ortho-xylyl spacer
1
[9]. The H NMR signals attributed to the xylyl benzylic
protons (diastereotopic protons, an endo and an exo pro-
ton in each benzylic group) appear as a pair of doublets
in most cases (two pairs in the case of 9), indicative of
the bis(NHC) ligand being locked into a conformation that
1
is rigid on the NMR timescale. In the H NMR spectrum
of 8, there is an additional pairs of signals, due to the dia-
stereotopic benzylic protons associated with the naphthyl
groups. These results are in stark contrast to the appear-
ance of the H NMR signals for the benzylic protons on
the corresponding imidazolium ions 3–6, which are sharp
1

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M.V. Baker et al. / Journal of Organometallic Chemistry 691 (2006) 5845–5855
N
N
N
N
N
N
Cl
N
N
DMSO
Cl -
Pt
Pt
+DMSO
+
Cl
Cl
a
b
a
11
14
b
a
a
b b
b
b
8.0
7.5
7.0
6.5
6.0
5.5
5.0 ppm
Fig. 1. 1H NMR spectra of a sample prepared by dissolution of 11 in DMSO-d6: (a) 5 min after preparation; (b) after 16 h at 80 ꢁC; and (c) immediately
after the addition of NEt4Cl. (For clarity only the downfield region is shown.)
2.3. X-ray studies
try, comprises the asymmetric unit of the structure; in the
case of 9, two similar molecules do so. In all cases, the
metal atom is disposed in a quasi-square planar environ-
ment, comprising the two donors of the carbene ligand
mutually cis, and the two halide donors (or, in the case
of the cation of 10, the two double bonds of the cod ligand)
occupying the other pair of mutually cis sites. The geome-
tries about the metal atoms (Table 1) are sometimes impre-
cise but generally in keeping with expected norms and we
do not discuss them in detail. We comment on the struc-
tures individually as follows, at the level of interest sup-
ported by the data.
In general it proved extremely difficult to grow crystals
of the above complexes suitable for crystallographic stud-
ies. In the case of 7, 9 and 12 the complexes typically crys-
tallised as extremely fine needles. In addition, complexes 11
and 12 produced crystals that rapidly desolvated. Repeated
attempts to crystallise 12 from acetonitrile afforded crystals
of a disolvate that were invariably twinned, but with persis-
tence a very small crystal was obtained from DMSO that
was suitable for X-ray work.
The results of the single crystal X-ray studies are consis-
tent with the stoichiometries and connectivities as indicated
in the above formulations for 8–12, encompassing the
gamut of that range of compounds completely, albeit in a
number of cases with less than desirable precision. In all
cases except 9, one formula unit, with associated solvent
molecules in most cases, devoid of crystallographic symme-
2.3.1. Compound 8
This complex crystallises as an acetone monosolvate, the
acetone well-ordered and the carbonyl unambiguously
defined; the nearest approach of the latter is to its inversion
˚
image C(02)ꢀ ꢀ ꢀO(02) (2 ꢁ x,1 ꢁ y,2 ꢁ z) 3.195(7) A. The
Table 1
Metal atom ambiences in 8 and 10–12
˚
Cpd/M/X
Distance (A)
M–C
Angles (ꢁ)
C–M–C
91.9(2)
C–M–X (trans,cis)
ha
M–X
X–M–X
95.2(2)
8/Pd/Br
1.990(3)
1.978(4)
2.4664(5)
2.470(5)
173.53(10)
171.16(10)
83.83(11)
89.74(10)
81.1(2)
85.7(2)
86.4(11)
86.5(2)
10/Rh/codb
11/Pt/Cl
2.074(5)
2.091(4)
2.126
2.115
89.9(2)
91.2(10)
87.5(2)
86.0
178.4
175.4
92.1
91.7
2.01(2)
1.92(2)
2.389(6)
2.417(7)
90.7(2)
91.81(4)
179.3(7)
175.9(6)
88.3(6)
90.0(8)
12/Pt/Cl
1.943(4)
1.938(4)
2.353(1)
2.362(1)
175.5(1)
179.9(1)
88.2(1)
92.5(1)
a
h is the dihedral angle between the pair of C3N2 planes.
X are the centroids of the two double bonds.
b

M.V. Baker et al. / Journal of Organometallic Chemistry 691 (2006) 5845–5855
5849
naphthyl substituents lie quasi-normal to the coordination
2.3.3. Compound 10 Æ PF6
plane and to each other (Fig. 2), C2Br2/C10 interplanar
dihedral angles 89.14(7)ꢁ, 81.32(8)ꢁ, the C10/C10 angle
being 89.1(1)ꢁ; H(404,405) contact the acetone oxygen
This compound crystallises as a chloroform monosol-
vate (Fig. 3), the chloroform molecule being well-ordered
despite disorder in the anion, the chloroform hydrogen
atom contacting F(1,5) (1 ꢁ x,1 ꢁ y,1 ꢁ z) of the anion
at 2.66, 2.58. The anion is also involved in contacts to
H(13,16) at similar distances. Again the tails aggregate into
a hydrophobic domain, about (x,0,1/2).
˚
(2 ꢁ x,1 ꢁ y,1 ꢁ z) at 2.76 A (·2). Inversion-related naph-
thyl groups 4 stack, obligate parallel, up a. Interesting
interactions occur between the bromine atoms of one mol-
ecule and the aryl hydrogen atoms of the xylyl bridge of an
adjacent molecule: Br(1)ꢀ ꢀ ꢀH(33) (1 ꢁ x,2 ꢁ y,2 ꢁ z) 2.86,
˚
Br(2)ꢀ ꢀ ꢀH(36) (1 ꢁ x,2 ꢁ y,1 ꢁ z) 2.85 A.
2.3.4. Compound 11
This compound is also a chloroform monosolvate, the
chloroform hydrogen atom contacting the chlorine associ-
ated with the shorter of the two Pt–Cl distances
2.3.2. Compound 9
Two independent molecules, differing in the dispositions
of their heptyl ‘tails’, comprise the asymmetric unit of this
unsatisfying determination, the results of which are given
in the associated CCDC deposition (#618567). The mole-
cules pack within the unit cell with their cores disposed
in sheets about z = 0.5, held together by intermolecular
(Ar)Hꢀ ꢀ ꢀBr interactions of the type found in 8 and other
compounds in this paper, with the tails disposed in a
hydrophobic sheet about the ab face of the cell. Even at
the present level of precision, it is evident that C–Pd–C is
less than the value for 8, by virtue of the presence of two
xylyl bridges, rather than one.
˚
(H(02)ꢀ ꢀ ꢀCl(1) (est.) 2.51 A) (Fig. 4). The molecular cores
are disposed about the plane x = 0.5, the hydrophobic tails
about the bc face of the cell. Cl(1) is also associated with
inter-molecular contacts to H(13,14) ð1 ꢁ x; 1 ꢁ y;ꢀzÞ (est.
˚
2.80, 2.75 A).
2.3.5. Compound 12
This compound is a DMSO monosolvate, the solvent
molecule being included in the cup of the ligand (Fig. 5),
notwithstanding that its strongest interactions appear to
be with other neighbouring molecules via the outwardly
C(11)
C(1)
C(31)
C(3)
C(12)
N(21)
C(32)
C(2)
C(4)
C(02)
N(43)
N(41)
C(42)
C(22)
Rh
Br(2)
Pd
C(05)
C(42)
N(41)
C(231)
C(01)
Br(1)
N(43)
C(4)
C(06)
N(21)
C(1)
C(411)
C(101)
C(401)
Fig. 2. Projection of a molecule of 8.
Fig. 3. Projection of a cation of 10 Æ PF6.

5850
M.V. Baker et al. / Journal of Organometallic Chemistry 691 (2006) 5845–5855
directed oxygen atom, there being a notably short contact
to an imidazole hydrogen atom O(101)ꢀ ꢀ ꢀH(45) (2 ꢁ x,
˚
y ꢁ 0.5,1.5 ꢁ z) 2.39 A (est.).
C(11)
C(1)
C(12)
2.4. Catalysis studies
C(4)
We have undertaken preliminary studies to explore the
effect of the diverse structural changes in 7–9 on catalytic
activity. The activities of these complexes were also com-
pared against the catalytic activity of 1 (the non-alkylated
analogue of 9) which we have previously studied and
which exhibits excellent activity [9]. We expected the com-
plexes 1 and 9 to exhibit almost identical activity since
the structural differences are extraneous to the site of
activity. In the case of 8 it was envisaged that steric
effects imposed by the naphthyl group might contribute
to a change in catalytic activity. The complexes were
tested for activity in the Heck and Suzuki reactions.
The Heck reaction focussed on the coupling of iodoben-
zene and butyl acrylate to produce butyl cinnamate while
the Suzuki reaction involved the coupling of 4-bromotol-
uene and phenyl boronic acid to afford 4-methylbiphenyl.
Relatively low TONs (500000 and 83000 for the Heck
reaction and 50000 for the Suzuki reaction) were targeted
to explore the effect of the structural changes in the com-
plexes. The results of these catalysis studies are detailed
in the Sections 4.4.1 and 4.4.2. The results are remarkably
N(21)
Cl(2)
C(22)
Pt
Cl(21)
C(42)
N(23)
Cl(1)
N(41)
C(02)
C(231)
Cl(22)
Cl(23)
C(142)
Fig. 4. Projection of a molecule of 11, showing its association with a
chloroform molecule.
C31
C3
C32
C2
N41
O101
Cl2
C42
Pt1
N23
N21
C101
C22
N43
Cl1
S1
C4
C102
C12
C1
C11
Fig. 5. Projection of a molecule of 12, with included DMSO solvent molecule.

M.V. Baker et al. / Journal of Organometallic Chemistry 691 (2006) 5845–5855
5851
similar for the different complexes. It is possible that the
4.2. Synthesis of compounds
changes we have examined here in the structure of palla-
dium dibromide complexes of bis(NHCs) linked by an
ortho-xylyl group, including the introduction of sterically
demanding groups and the inclusion of a second ortho-
xylyl linker, do not contribute significantly to catalytic
activity, and that activity may be dominated by structural
features common to all of the complexes, such as the
rigidity imposed by an ortho-xylyl linker and a pair of
mutually cis NHC ligands. However, in view of increas-
ing evidence in the literature for these types of reactions
to be catalysed by ill-defined (‘‘colloidal’’) Pd species
[16] it is also possible that the complexes studied here
merely decompose to afford active colloidal Pd species,
particularly given the uniform but otherwise unremark-
able results obtained. Detailed catalytic studies [17] to
elucidate the nature of the active species in these systems
are underway.
4.2.1. Imidazolium salt 3 Æ 2Br
A solution of N-heptylimidazole (3.00 g, 18 mmol) and
1,2-bis(bromomethyl)benzene (1.90 g, 7.2 mmol) in THF
(50 mL) was heated at reflux under argon overnight.
The resulting precipitate was collected under argon to
afford 3 Æ 2Br as a white powder (4.08 g, 76%). H NMR
(300.13 MHz, DMSO-d6): d 0.85 (6H, t, JH,H = 6.7 Hz,
1
3
2 · CH3), 1.10–1.30 (16H, m, 8 · CH2), 1.70–1.85 (4H,
m, 2 · CH2), 4.15 (4H, t, JH,H = 7.2 Hz, 2 · NCH2),
3
5.60 (4H, s, 2 · benzylic CH2), 7.20–7.25 (2H, m, 2 · Ar
H), 7.35–7.40 (2H, m, 2 · Ar H), 7.75 (2H, s, 2 · Im
H4/5), 7.85 (2H, s, 2 · Im H4/5), 9.25 (2H, s, 2 · NCHN).
13C NMR (75.47 MHz, DMSO-d6): d 13.9 (CH3), 22.0,
25.5, 28.0, 29.3, 31.1 (CH2), 49.0 (NCH2), 49.1 (benzylic
CH2), 122.7, 122.8 (Im C4 and C5), 129.6, 129.7 (Ar
CH), 133.0 (Ar C), 136.5 (NCHN). Anal. Calc. for
C28H44N4Br2: C, 56.38; H, 7.43; N, 9.39. Found: C,
56.34; H, 7.45; N, 9.12%.
An initial test of the activity of 10 Æ PF6 and 11 in the
hydrosilylation reaction of 1-octene and triethylsilane in
toluene did not suggest any significant activity of these
complexes in this reaction. Further studies of these com-
plexes are in progress.
4.2.2. Imidazolium salt 3 Æ 2PF6
A solution of 3 Æ 2Br (1.00 g, 1.7 mmol) in water (40 mL)
was added dropwise with heating to a solution of potas-
sium hexafluorophosphate (0.77 g, 4.2 mmol) in water
(40 mL). The resulting cloudy solution was left overnight
and the precipitate that formed was collected and dried
to afford 3 Æ 2PF6 as a white powder (1.13 g, 93%). Anal.
Calc. for C28H44N4P2F12: C, 46.28; H, 6.10; N, 7.71.
Found: C, 46.37; H, 6.00; N, 7.64%.
3. Conclusions
We have reported facile syntheses for a range of new
NHC complexes of palladium, rhodium and platinum.
The complexes each have mutually cis-NHC moieties, the
solubility of the complexes being enhanced by the presence
of alkyl chains on each NHC ligand framework. In the case
of the platinum complexes these are the first examples of
platinum-bis(NHC) complexes where the NHC ligands
are bridged by an ortho-xylyl linker. A number of the com-
plexes have been characterised by single crystal X-ray dif-
fraction studies. The new palladium complexes have
exhibited activity, though unremarkable, in promoting
Heck and Suzuki couplings. The study of the role of these
complexes in catalysis is facilitated by their improved solu-
bility compared to the analogous cyclophane-NHC com-
plexes reported previously [9].
4.2.3. Imidazolium salt 4 Æ 2Br
A solution of N-(naphth-1-ylmethyl)imidazole (1.32 g,
6.4 mmol) and 1,2-bis(bromomethyl)benzene (808 mg,
3.06 mmol) in THF (40 mL) was stirred for 3 d. The
resulting precipitate was collected, washed with THF
(2 · 30 mL) and dried in vacuo to afford a pale brown
powder. The powder was recrystallised from acetonitrile
to afford pale brown crystals (1.26 g, 61%). 1H NMR
(300.13 MHz, DMSO-d6): d 5.62 (4H, s, 2 · xylyl CH2),
5.98 (4H, s, 2 · –CH2C10H7), 7.21–7.28 (2H, AA0 part
of AA0XX0 pattern, xylyl 3-CH and 6-CH), 7.43–7.49
(2H, XX0 part of AA0XX0 pattern, xylyl 4-CH and 5-
CH), 7.55–7.65 (8H, m, 8 · naphthyl-CH), 7.75 (2H, t,
3J = 1.6 Hz, 2 · Im-H4), 7.83 (2H, t, 3J = 1.6 Hz,
2 · Im-H5), 8.03 (4H, m, 4 · naphthyl-CH), 8.14 (2H,
m, 2 · naphthyl-CH), 9.44 (2H, s, 2 · NCHN). 13C
NMR (125.8 MHz, DMSO-d6): d 49.1 (xylyl CH2), 50.1
(–CH2C10H7), 122.86 (Im-C4), 122.88 (naphthyl-CH),
123.1 (Im-C5), 125.6 (naphthyl-CH), 126.4 (naphthyl-
CH), 127.2 (naphthyl-CH), 127.9 (naphthyl-CH), 128.9
(naphthyl-CH), 129.3 (xylyl 3-CH and 6-CH), 129.5 (xylyl
4-CH and 5-CH), 129.7 (naphthyl-CH), 129.9 (naphthyl-
C), 130.4 (naphthyl-C), 132.9 (xylyl 1-C and 2-C), 133.4
(naphthyl-C), 136.8 (NCHN). Anal. Calc. for
C36H32N4Br2 Æ 1.5H2O: C, 61.12; H, 4.99; N, 7.92. Found:
C, 61.15; H, 5.00; N, 7.91%.
4. Experimental
4.1. General
General experimental procedures have been described
previously [10]. 1,2-Bis(bromomethyl)benzene (Aldrich),
palladium(II) acetate and potassium tetrachloroplatinate
(Precious Metals Online) were used as received. 1,2-
Bis(imidazol-1-ylmethyl)-4,5-diheptylbenzene [10], imi-
dazolium salt 6 Æ 2Br [7,9] and palladium complex 1 [9]
and [Rh(cod)Cl]2 [18] were prepared by literature proce-
dures. N-(Naphth-1-ylmethyl)imidazole was prepared from
1-(bromomethyl)naphthalene [19] by the method of Lee
1
et al. [20]. H and 13C NMR spectral assignments were
made with the aid of DEPT, HSQC and HMBC spectra.

5852
M.V. Baker et al. / Journal of Organometallic Chemistry 691 (2006) 5845–5855
4.2.4. Imidazolium salt 5 Æ 2Br
afford colourless crystals (96 mg, 47%). 1H NMR
2
Solutions of 1,2-bis(imidazol-1-ylmethyl)-4,5-diheptyl-
benzene (1.27 g, 2.9 mmol) in acetone (50 mL) and 1,2-
bis(bromomethyl)benzene (0.81 g, 3.1 mmol) in acetone
(50 mL) were added portionwise, simultaneously, to ace-
tone (200 mL) heated at reflux over the course of 6 h.
The mixture was then heated at reflux overnight. The vol-
ume of solvent was concentrated by ca. 200 mL and then
cooled to RT. The resulting precipitate was collected,
washed with acetone and dried to afford 5 Æ 2Br as a white
(500.13 MHz, DMSO-d6): d 5.28 (2H, d, JH,H = 14 Hz,
2
2 · xylyl CHH), 5.38 (2H, d, JH,H = 16 Hz, 2 ·
–CHHC10H7), 6.12 (2H, d, 2JH,H = 16 Hz, 2 ·
–CHHC10H7), 6.67 (2H, br s, 2 · naphthyl-CH) 6.74 (2H,
2
d, JH,H = 14 Hz, 2 · xylyl CHH), 6.91 (2H, s, 2 ·
Im-H5), 7.32 (2H, apparent t, splitting = 7.7 Hz, 2 · naph-
thyl-CH), 7.42 (2H, apparent t, splitting = 7.2 Hz,
2 · naphthyl-CH), 7.48–7.53 (2H, AA0 part of AA0XX0
pattern, xylyl 4-CH and 5-CH), 7.58 (2H, apparent t,
splitting = 7.5 Hz, 2 · naphthyl-CH), 7.63 (2H, br d,
JH,H = 7.6 Hz, 2 · naphthyl-CH), 7.71 (2H, s, 2 · Im-H4),
7.90 (2H, d, JH,H = 8.2 Hz, 2 · naphthyl-CH), 7.96–8.01
(2H, XX0 part of AA0XX0 pattern, xylyl 3-CH and 6-
CH) and (2H, d, JH,H = 8.3 Hz, 2 · naphthyl-CH). 13C
NMR (125.8 MHz, DMSO-d6): d 50.7 (xylyl CH2), 51.0
(–CH2C10H7), 122.3 (Im-C4), 122.7 (Im-C5), 122.9 (naph-
thyl-CH), 125.3 (naphthyl-CH), 125.4 (br, naphthyl-CH),
126.2 (naphthyl-CH), 126.7 (naphthyl-CH), 128.5 (naph-
thyl-CH), 128.6 (naphthyl-CH), 129.5 (xylyl 4-CH and 5-
CH), 130.2 (naphthyl-C), 131.3 (naphthyl-C), 131.9 (xylyl
3-CH and 6-CH), 133.1 (naphthyl-C), 135.6 (xylyl 1-C
1
powder (1.68 g, 83%). H NMR (300.13 MHz, DMSO-d6):
3
d 0.87 (6H, t, JH,H = 6.6 Hz, 2 · CH3), 1.23–1.45 (16H,
m, 8 · CH2), 1.55–1.68 (4H, m, 2 · CH2), 2.67 (4H, t,
3JH,H = 7.8 Hz, 2 · ArCH2CH2), 5.30–5.85 (8H, br s,
4 · benzylic CH2), 7.00–7.35 (4H, br m, 2 · Im H4 and
2 · Im H5), 7.60 (2H, s, 3-CH and 6-CH of diheptyl-
xylyl), 7.66–7.73 (2H, AA0 part of AA0XX0 pattern,
2 · xylyl CH), 7.82–7.87 (2H, XX0 part of AA0XX0 pat-
tern, 2 · xylyl CH), 8.53 (2H, br s, Wh/2 90 Hz,
2 · NCHN). 13C NMR (75.47 MHz, DMSO-d6): d 14.0
(CH3), 22.1, 28.5, 29.1, 30.5, 31.2, 31.6 [(CH2)6CH3],
50.1, 50.3 (benzylic CH2), 121.9, 122.1 (Im C4 and C5),
129.9 (Ar C), 130.9 (Ar CH), 132.8 (Ar C), 134.1, 134.7
(Ar CH), 135.5 (NCHN), 142.8 (Ar C). Anal. Calc. for
C36H50N4Br2 Æ 2H2O: C, 58.86; H, 7.41; N, 7.63. Found:
C, 59.09; H, 7.56; N, 7.42%.
and
2-C),
160.9
(C–Pd).
Anal.
Calc.
for
C36H30N4Br2Pd Æ 0.2CH2Cl2: C, 54.22; H, 3.82; N, 6.99.
Found: C, 54.59; H, 4.03; N, 6.94%. Colourless crystals
of 8, suitable for crystallographic studies were grown from
acetone solutions.
4.2.5. Palladium complex 7
A solution of 3 Æ 2Br (0.36 g, 0.61 mmol) and palla-
dium(II) acetate (0.15 g, 0.68 mmol) in DMF (25 mL)
was heated at 90 ꢁC for 3 d. The mixture was filtered
through Celite and the filtrate was concentrated in vacuo.
The residue was purified by rapid silica gel filtration
(elution with acetone) and recrystallised from CH2Cl2/
hexanes to yield a beige solid (0.13 g, 31%). 1H NMR
4.2.7. Palladium complex 9
A solution of 5 Æ 2Br (591 mg, 0.80 mmol) and palla-
dium(II) acetate (200 mg, 0.89 mmol) in acetonitrile
(50 mL) was heated at reflux for 3 d. The reaction mixture
was hot filtered through a plug of Celite/silica. The filtrate
was concentrated in vacuo and then dissolved in dichloro-
methane/acetone (1:1) and filtered through a plug of silica.
The filtrate was concentrated in vacuo and the residue was
recrystallised from acetonitrile to afford 9 as colourless
3
(300.13 MHz, acetone-d6): d 0.85 (6H, t, JH,H = 6.6 Hz,
2 · CH3), 1.15–1.45 (16H, m, 8 · CH2), 1.70–1.85 (2H,
m, 2 · NCH2CHH), 1.90–2.05 (2H, m, 2 · NCH2CHH),
4.15–4.30 (2H, m, 2 · NCHHCH2), 4.60–4.75 (2H, m,
1
crystals (391 mg, 61%). H NMR (500.13 MHz, CDCl3):
3
d 0.87 (6H, t, JH,H = 7 Hz, 2 · CH3), 1.23–1.39 (16H, m,
2
2 · NCHHCH2), 5.15 (2H, d, JH,H = 14.6 Hz, 2 · ben-
8 · CH2), 1.52 (4H, m, 2 · Ar CH2CH2), 2.56 (4H, m,
2
2
zylic CHH), 6.80 (2H, d, JH,H = 14.6 Hz, 2 · benzylic
2 · ArCH2CH2), 4.86 (2H, d, JH,H = 15 Hz, 2 · diheptyl-
3
2
CHH), 7.26 (2H, d, JH,H = 2.0 Hz, 2 · Im H4/5), 7.45–
xylyl CHHN), 4.95 (2H, d, JH,H = 15 Hz, 2 · xylyl
3
2
7.50 (2H, m, 2 · Ar H), 7.57 (2H, d, JH,H = 2.0 Hz,
CHH), 6.80 (2H, d, JH,H = 15 Hz, 2 · diheptyl-xylyl
2 · Im H4/5), 7.88–7.95 (2H, m, 2 · Ar H). 13C NMR
(75.47 MHz, acetone-d6): d 14.4 (CH3), 23.2, 27.6, 29.7,
30.8, 32.5, 51.9 (CH2), 52.0 (benzylic CH2), 122.3, 122.6
(Im C4 and Im C5), 130.4, 132.8 (Ar CH), 136.7 (Ar
C), 163.0 (C–Pd). Anal. Calc. for C28H42N4Br2Pd: C,
47.98; H, 6.04; N, 7.99. Found: C, 47.46; H, 5.98; N,
7.81%.
CHHN), 6.91 (2H, d, JH,H = 15 Hz, 2 · xylyl CHH),
2
6.92 (2H, br d, 2 · Im-H4 or H5), 6.94 (2H, br d, 2 · Im
H4 or H5), 7.21 (2H, s, 2 · diheptyl-xylyl Ar H), 7.39–
7.43 (2H, AA0 part of AA0XX0 pattern, 2 · xylyl Ar H),
7.51–7.55 (2H, XX0 part of AA0XX0 pattern, 2 · xylyl Ar
H). 13C NMR (125.76 MHz, CDCl3): d 14.1 (CH3), 22.6,
29.1, 29.7, 31.2, 31.8, 32.3 (CH2), 52.3 (diheptyl-xylyl
CH2N), 52.4 (xylyl CH2), 121.0, 121.1 (Im-C4 and Im-
C5), 130.2 (xylyl 4-CH and 5-CH), 132.2 (diheptyl-xylyl
1-C and 2-C), 132.3 (xylyl 3-CH and 6-CH), 132.9 (dihep-
tyl-xylyl 3-CH and 6-CH), 135.3 (xylyl 1-C and 2-C), 143.0
(diheptyl-xylyl 4-C and 5-C), 162.7 (C–Pd). Anal. Calc. for
C36H48N4Br2Pd: C, 53.85; H, 6.02; N, 6.98. Found: C,
53.70; H, 6.25; N, 6.75%.
4.2.6. Palladium complex 8
A solution of 4 Æ 2Br (176 mg, 0.26 mmol) and palla-
dium(II) acetate (68 mg, 0.30 mmol) in acetonitrile
(100 mL) was heated at reflux overnight. The mixture
was filtered and the filtrate was concentrated in vacuo.
The residue was recrystallised from dichloromethane to

M.V. Baker et al. / Journal of Organometallic Chemistry 691 (2006) 5845–5855
5853
4.2.8. Rhodium salt 10 Æ PF6
[Pt(cod)Cl2] (171 mg, 0.46 mmol) and sodium acetate
(10 mg, 0.12 mmol) in DMF (20 mL) was stirred under
reduced pressure (oil pump vacuum) for 10 min. The mix-
ture was then heated under nitrogen at ca. 85 ꢁC for 4 d.
The mixture was cooled and then concentrated in
vacuo.The residue was dissolved in acetonitrile (20 mL)
and the resulting solution was filtered through a very short
plug of silica. The filtrate was concentrated in vacuo and
the residue was recrystallised from dichloromethane-ethyl
acetate solutions to afford 11 as colourless crystals
(186 mg, 58%). 1H NMR (300.13 MHz, acetone-d6): d
A solution of 3 Æ PF6 (0.38 g, 0.53 mmol), [Rh(cod)Cl]2
(0.13 g, 0.26 mmol) and potassium tert-butoxide (0.21 g,
1.85 mmol) in dry DMSO (20 mL) was stirred at room
temperature for 24 h. The solution was poured into water
and the resulting precipitate was collected and purified by
rapid silica gel filtration (elution with 2.5% methanol in
dichloromethane) to afford 10 as a yellow powder (0.15 g,
36%), which was recrystallised from chloroform/hexane.
1H NMR (300.13 MHz, CDCl3): d 0.85 (6H, br t,
3JH,H = 7.0 Hz, 2 · CH3), 1.15–1.55 (16H, m, 8 · CH2),
1.65–1.85 (4H, m, 2 · NCH2CH2), 2.25 (4H, m, cod
CH2), 2.40–2.60 (4H, m, CH2), 3.90–4.00 (2H, m, cod
CH), 4.30–4.35 (2H, m, 2 · NCHHCH2), 4.40–4.55 (2H,
m, cod CH), 4.40–4.55 (2H, m, 2 · NCHHCH2), 5.05
3
0.89 (6H, br t, JH,H = 6.7 Hz, 2 · CH3), 1.27–1.51 (16H,
m, 8 · CH2), 1.72–1.87 (2H, m, 2 · NCH2CHH), 2.00–
2.13 (2H, m, 2 · NCH2CHH), 4.21–4.30 (2H, m,
2 · NCHHCH2), 4.72–4.82 (2H, m, 2 · NCHHCH2), 5.05
2
2
(2H, d, JH,H = 14.2 Hz, 2 · benzylic CHH), 6.60 (2H, d,
(2H, d, JH,H = 14.4 Hz, 2 · benzylic CHH), 6.92 (2H, d,
2JH,H = 14.2 Hz, 2 · benzylic CHH), 6.90 (2H, d,
2JH,H = 14.4 Hz, 2 · benzylic CHH), 7.21 (2H, d,
3JH,H = 2.1 Hz, 2 · Im H4 or H5), 7.45–7.49 (2H, AA0 part
of AA0XX00 pattern, 2 · Ar H), 7.53 (2H, d,
3JH,H = 2.1 Hz, 2 · Im H5 or H4), 7.88–7.92 (2H, XX0 part
of AA0XX00 pattern, 2 · Ar H). 13C NMR (75.47 MHz,
acetone-d6): d 14.4 (CH3), 23.3, 27.6, 29.7, 31.0, 32.5
(CH2) 51.3, 51.5 (NCH2CH2 + benzylic CH2), 121.2,
121.6 (Im C4 and Im C5), 130.2 132.7 (Ar CH), 136.8
(Ar C), 149.5 (C–Pt). Anal. Calc. for C28H42N4Cl2Pt: C,
48.00; H, 6.04; N, 8.00. Found: C, 48.14; H, 5.84; N,
7.94%. Colourless crystals of 11 suitable for diffraction
studies were grown by the diffusion of hexanes vapours into
a solution of the complex in chloroform.
3JH,H = 2.0 Hz, 2 · Im H4/5), 7.25 (2H, d, JH,H = 2.0 Hz,
3
2 · Im H4/5), 7.40–7.45 (2H, m, 2 · Ar H), 7.60–7.65 (2H,
m, 2 · Ar H). 13C NMR (75.47 MHz, CDCl3): d 13.9
(CH3), 22.5, 26.9, 28.9, 30.6, 30.8, 30.9, 31.6 (CH2 from
heptyl chain + cod), 51.0, 51.5 (NCH2CH2 + benzylic
1
CH2), 88.4 (d, JRh,C = 7.7 Hz, cod CH), 88.4 (d,
1JRh,C = 8.5 Hz, cod CH), 120.8, 121.4 (Im C4 and Im
C5), 129.8, 131.8 (Ar CH), 134.8 (Ar C), 179.9 (d, 1JRh,C
=
53.5 Hz, NCN). Anal. Calc. for C36H54N4RhPF6 Æ
0.9CHCl3: C, 49.35; H, 6.16; N, 6.24. Found: C, 49.32;
H, 6.39; N, 5.98%. Yellow plates of 10 Æ PF6 suitable for
crystallographic studies were grown by the diffusion of
hexanes vapours into a solution of the complex in
chloroform.
4.2.11. Platinum complex 12
The bromide salt 6 Æ 2Br was converted into the acetate
salt 6 Æ 2OAc by passage of an aqueous solution of 6 Æ 2Br
(1.0 g, 2 mmol) through an anion exchange column
(Dowex 1 · 8, acetate form), and elution with 1 L of dis-
tilled water. Evaporation of the resulting solution afforded
6 Æ 2OAc as an off-white solid (0.71 g), which was used
without further purification. A solution of 6 Æ 2OAc
(203 mg, 0.44 mmol) and [Pt(cod)Cl2] (165 mg, 0.44 mmol)
in acetonitrile (20 mL) was heated at reflux for 4 d, during
which time a precipitate formed. The solid was collected
and subjected to Soxhlet extraction with acetonitrile for
3 d. The acetonitrile extract was concentrated (not to dry-
ness) and cooled to afford 12 as a white powder (118 mg,
44%). 1H NMR (500.13 MHz, CD3CN): 4.93 (4H, d,
4.2.9. (1,5-Cyclooctadiene)platinum(II) dichloride
A solution of K2PtCl4 (1.0 g, 2.4 mmol) in water
(40 mL) in a conical flask was heated on a hotplate with
stirring. To this solution was added a solution of 1,5-cyclo-
octadiene (1 mL, 8 mmol) in ethanol (40 mL) over the
course of 10 min. Stirring and heating was continued until
the colour of the solution faded (ca. 30 min). The mixture
was then cooled (ice bath). The precipitate was collected,
washed with water (4 · 20 mL) and diethyl ether (4 · 20
mL) and air dried to afford a colourless microcrystalline
1
material (710 mg, 78%). H NMR (500.13 MHz, CDCl3):
d 2.26 (4H, m, CHH), 2.71 (4H, m, CHH), 5.61 (4H,
2
CH, a multiplet with 195Pt satellites JH,Pt = 68 Hz). 13C
2
NMR (125.7 MHz, CDCl3): d 30.9 (CH2), 100.1 (CH; a sin-
2JH,H = 14.2 Hz, 4 · CHH), 6.91 (4H, d, JH,H = 14.2 Hz,
1
glet with 195Pt satellites JC,Pt = 152 Hz). Anal. Calc. for
4 · CHH), 7.09 (4H, s, 2 · Im H4 and 2 · Im H5), 7.35–
7.39 (4H, m, 4 · Ar H), 7.58–7.63 (4H, m, 4 · Ar H). 13C
NMR (125.8 MHz, DMSO-d6): d 50.6 (CH2), 120.7 (Im
C4 and Im C5), 129.3, 132.3 (Ar CH), 135.9 (Ar C),
147.1 (C–Pt). Anal. Calc. for C22H20N4Cl2Pt.CH3CN: C,
44.52; H, 3.58; N, 10.82. Found: C, 44.19; H, 3.70; N,
11.14%. HRMS (FAB): m/z 571.1027 (MꢁCl)
(C22H20N4Cl196Pt requires 571.1026). Colourless crystals
of 12 suitable for diffraction studies were grown by the
diffusion of diethyl ether vapour into a solution of the com-
plex in DMSO.
C8H12Cl2Pt: C, 25.68; H, 3.23. Found: C, 25.67; H, 3.40%.
4.2.10. Platinum complex 11
The bromide salt 3 Æ 2Br was converted into the acetate
salt 3 Æ 2OAc by passage of an aqueous solution of 3 Æ 2Br
(1.3 g, 2.2 mmol) through an anion exchange column
(Dowex 1 · 8, acetate form), and elution with 1 L of
distilled water. Evaporation of the resulting solution affor-
ded 3 Æ 2OAc (0.75 g), which was used without further puri-
fication. A mixture of 3 Æ 2OAc (256 mg, 0.46 mmol),

5854
M.V. Baker et al. / Journal of Organometallic Chemistry 691 (2006) 5845–5855
4.3. Structure determinations
4.3.1.3.
Compound
8. Me2CO”C39H36Br2N4OPd,
ꢀ
M = 843.0. Triclinic, space group P1, a = 10.9860(8), b =
˚
(Some of the determinations are of less than optimal
quality, in consequence of difficulties encountered in
respect of specimen size and quality, solvent (efflorescent
tendencies), disorder and/or high displacement parameters,
etc.)
11.9500(9), c = 13.6870(10) A, a = 87.081(1), b = 81.304(2),
c = 81.392(2)ꢁ, V = 1756 A . Dc (Z = 2) = 1.595 g cmꢁ3
.
3
˚
l
Mo = 2.8 mmꢁ1
‘T’min/max = 0.76. 2hmax = 60ꢁ; Nt = 31628, N = 9594
(Rint = 0.035), No = 7721; R = 0.040, Rw = 0.088
(nw = 12; refinement on F2). T ca. 170 K.
;
specimen = 0.22 · 0.07 · 0.07 mm;
Full spheres of CCD/area-detector diffractometer data
were measured (x-scans; monochromatic MoKa radia-
˚
tion, k = 0.71073 A) yielding Nt(otal) reflections, these
4.3.1.4.
Compound
12. Me2SO”C24H26Cl2N4OPtS,
merging to N unique after ‘empirical’/multiscan absorp-
tion correction (proprietary software), No with F > 4r(F)
being considered ‘observed’ and used in the full matrix
least squares refinements, refining anisotropic displace-
ment parameter forms for the non-hydrogen atoms,
M = 684.5. Monoclinic, space group P21/c, a = 12.660(2),
˚
b = 8.725(1), c = 22.418(5) A, b = 103.04(2)ꢁ, V = 2412
3
A . Dc (Z = 4) = 1.885 g cmꢁ3. lMo = 6.2 mmꢁ1; speci-
˚
men = 0.16 · 0.03 · 0.025 mm; ‘T’min/max = 0.47. Nt =
29086, N = 7501 (Rint = 0.072), No = 4932; R = 0.034,
Rw = 0.046 (nw = 1; refinement on F2). T ca. 100 K.
(x,y,z,Uiso H being included, constrained at estimated
)
values where possible. Conventional residuals R, Rw on
jFj are cited at convergence (reflection weights: (r2(F) +
0.000nwF2)ꢁ1 (refinement on jFj) ((r2(F2) + nwF2)ꢁ1 (refine-
ment on F2))). Neutral atom complex scattering factors
were employed within the context of the XTAL 3.7 program
system [21]. Pertinent results are presented below and in
the tables and figures, the latter displaying 50% probability
amplitude displacement envelopes for the non-hydrogen
4.4. Catalysis studies
Stock solutions of 1 and 7–9 in DMF at 3.55 · 10ꢁ4 M
and 5.69 · 10ꢁ5 M concentrations were prepared by dis-
solving the appropriate mass of each of the complexes in
DMF.
˚
atoms, hydrogen atoms having arbitrary radii of 0.1 A
4.4.1. Heck reactions
(where shown). Individual diversions in procedure are
noted under ‘variata’. Full.cif depositions (excluding struc-
ture factor amplitudes but including compound 9) reside
with the Cambridge Crystallographic Data Base, CCDC
618566–618570.
A 25 mL thick walled flask fitted with a Young’s tap was
equipped with a stirrer bar and charged with iodobenzene
(0.35 mL, 3.1 mmol), butyl acrylate (0.41 mL, 2.8 mmol),
triethylamine (3.9 mmol), DMF (0.5 mL) and a solution
of the appropriate complex (35.5 nmol, 0.0012 mol% or
5.7 nmol, 0.0002 mol% in 100 lL DMF). The solution
was degassed by three freeze–pump–thaw cycles, and the
flask was then back filled with nitrogen, sealed and heated
at 140 ꢁC with stirring for 24 h. After this time, a small ali-
quot was removed and dissolved in CDCl3, and analysed
4.3.1. Crystal/refinement data
4.3.1.1.
M = 939.4. Monoclinic, space group P21/c, a = 15.783(5),
Compound
11. 2CHCl3”C30H44Cl8N4Pt,
˚
b = 14.947(5), c = 17.151(5) A, b = 102.31(1)ꢁ, V = 3953
3
1
A . Dc (Z = 4) = 1.578 g cmꢁ3. lMo = 4.1 mmꢁ1; specimen =
by H NMR spectroscopy. For studies with 0.0002 mol%
˚
0.32 · 0.21 · 0.10 mm; ‘T’min/max = 0.32. 2hmax = 50ꢁ;
Nt = 33532, N = 6654 (Rint = 0.12), No = 3685; R = 0.10,
Rw = 0.13 (nw = 8; refinement on jFj). T ca. 170 K.
Variata. An inferior determination, consequent on
high displacement parameters (isotropic form refinement)
in the ligand ‘tails’ (figure for this determination
displays).
complex (complex, conversion %, TON): 7, 79%, 390000;
8, 84%, 418000; 9, 60%, 300000; 1, 63%, 314000. For stud-
ies with 0.0012 mol% complex (complex, conversion %,
TON): 7, 95%, 75700; 8, 99%, 79400; 9, 92%, 73600; 1,
99%, 79400.
4.4.2. Suzuki reactions
A pencil Schlenk flask equipped with a stirrer bar was
charged with 4-bromotoluene (0.34 g, 2 mmol), phenyl
boronic acid (0.31 g, 2.5 mmol), K2CO3 (3 equiv.), DMF
(4–5 mL) and a solution of catalyst (40 nmol, 0.002 mol%
in 115 lL DMF). The mixture was degassed by three
freeze–pump–thaw cycles and the flask was then back filled
with nitrogen, fitted with a condenser and heated at 120 ꢁC
with stirring. After a period of time, a small aliquot of the
reaction mixture was diluted with CDCl3 and the resulting
4.3.1.2. Compound 10 Æ PF6. CHCl3”C37H55Cl3F6N4PRh,
ꢀ
M = 910.1. Triclinic, space group P1, a = 11.3340(10), b =
˚
14.4170(10), c = 14.621(3) A, a = 82.047(3), b = 68.061(3),
3
c = 82.436(2)ꢁ, V = 2187 A . Dc (Z = 2) = 1.382 g cmꢁ3
.
˚
l
Mo = 0.67 mmꢁ1
;
specimen = 0.40 · 0.38 · 0.05 mm;
‘T’min/max = 0.88. 2hmax = 58ꢁ; Nt = 19027, N = 9901
(Rint = 0.034), No = 7798; R = 0.067, Rw = 0.14 (nw = 15;
refinement on F2). T ca. 160 K.
Variata. The PF6 component was modelled with the
fluorine atoms disordered over two sets of sites (occupan-
cies refining to 0.58(1) and complement), some displace-
ment parameters being very high (also true of the solvent
molecule, for which no disorder was resolved).
1
solution filtered and then analysed by H NMR spectros-
copy. For studies with no additive, after 89 h (complex,
conversion %, TON, TOF): 7, 70%, 34300, 386; 8, 72%,
36000, 406; 9, 45%, 22500, 254; 1, 55%, 27500, 310. For
studies with 10 mol% NBu4Br, after 65 h (complex, conver-

M.V. Baker et al. / Journal of Organometallic Chemistry 691 (2006) 5845–5855
5855
[7] M.V. Baker, M.J. Bosnich, D.H. Brown, L.T. Byrne, B.W. Skelton,
A.H. White, C.C. Williams, J. Org. Chem. 69 (2004) 7640.
[8] For a review, see: M.V. Baker, D.H. Brown, Mini Rev. Org. Chem. 3
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sion %, TON, TOF): 7, 50%, 25000, 385; 8, 32%, 16000,
246; 9, 49%, 24500, 377; 1, 42%, 21000, 322.
Acknowledgements
We thank the Australian Research Council for a Dis-
covery Grant (to M.V.B. and A.H.W.) and The University
of Western Australia for a UWA Research Grant (to
D.H.B.).
[10] M.V. Baker, D.H. Brown, R.A. Haque, B.W. Skelton, A.H. White,
Dalton Trans. (2004) 3756.
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