N-heterocyclic carbene tethered amido complexes of palladium and platinum

Article abstract of DOI:10.1039/c0dt01149e

With a view to applications in bifunctional catalysis, a modular cross-coupling strategy has been used to prepare amine bis(imidazolium) salts (3a and 3b) and an amine mono(imidazolium) salt (6) as precursors to chelating amido-NHC ligands. Treating the p

Full text of DOI:10.1039/c0dt01149e

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PAPER
N-heterocyclic carbene tethered amido complexes of palladium and platinum†
Warren B. Cross,*a Christopher G. Daly,a Rachel L. Ackerman,a Ian R. Georgeb and Kuldip Singha
Received 1st September 2010, Accepted 25th October 2010
DOI: 10.1039/c0dt01149e
With a view to applications in bifunctional catalysis, a modular cross-coupling strategy has been used
to prepare amine bis(imidazolium) salts (3a and 3b) and an amine mono(imidazolium) salt (6) as
precursors to chelating amido-NHC ligands. Treating the pro-ligands 3 with 3 equivalents of the bulky
base KHMDS and Pd(OAc)2 or PtCl2(COD) gave the four amido bis(N-heterocyclic carbene) pincer
complexes [CNC-R]M-I [M = Pd (7) or Pt (8); R = i-Pr (a) or n-Bu (b)], including the first examples of
platinum complexes of a CNC ligand. The reaction of 7a with AgOTf in pyridine gave the cationic
complex {[CNC-i-Pr]Pd-py}OTf (9a). Heating a mixture of amine mono(imidazolium) salt 6 with
PdCl2 or K2PtCl4, K2CO3 and KI in pyridine at 100 ◦C gave the complexes [C,NH]MI2py [M = Pd (10)
or Pt (11)], in which the amine arm of the NHC ligand is not deprotonated and does not coordinate to
the metal. For a solution of 10 in 1,4-dioxane, deprotonation of the amine occurred in a biphasic
reaction with aqueous KOH at 40 ◦C, giving the dimeric amido complex {[C,N]Pd(m-OH)}2 (12). The
more inert Pt analogue 11 was unreactive under the same conditions. Solid-state structures of the
complexes 7a, 7b, 9a, 10, 11 and 12 have been determined by single crystal X-ray diffraction.
also been used to tether the reactive nitrogen to the metal in trans-
Introduction
fer hydrogenation. However, the application of N-heterocyclic
Bifunctional catalysis, in which an electrophilic metal and a
carbene (NHC) donor groups to tether a nucleophilic amido
nucleophilic ligand act in concert to activate a substrate, enables
ligand to an electrophilic metal in bifunctional catalysis has yet
to be fully exploited,24,25 and even simple coordination chemistry
of multidentate amido-NHC ligands is under-explored. Of note,
tridentate bis(amido)-NHC [NCN] pincer complexes of zirconium
and hafnium have been reported,26,27 and amido-bis(NHC) [CNC]
and amido-NHC [C,N] complexes of some early and late transition
metals are also known.28–35 Most closely related to this work,
Douthwaite has described the palladium [CNC] complex A and,
during the course of our research, Luo has reported the Pd
complexes B, Fig. 1.36,37
reactions to take place that are not possible using classical catalytic
transformations that occur only at the metal centre.1–3 Wide-
ranging applications have been found for bifunctional catalysis,
many in asymmetric synthesis, including hydrogenation under
H2,4 transfer hydrogenation,5,6 isomerisation of allylic alcohols,7
alkene hydroamination,8 hydrosilylation,9 Michael addition,10 C–
H activation11–15 and lactide polymerisation.16 The most studied of
these reactions is the asymmetric transfer hydrogenation between
alcohols and carbonyl compounds, catalysed by half-sandwich
complexes of Ru, Ir or Rh with a chiral diamine ligand such as N-
tosyl-1,2-diphenylethylenediamine. The key steps in the catalytic
cycle occur after deprotonation of the primary amine group to give
a metal amido complex: subsequent transfer hydrogenation from i-
PrOH to the M–N bond gives a metal amine-hydride complex that
transfers an acidic and a basic hydrogen to the carbonyl substrate.17
Crucially, the chelating amine ligand makes the catalyst more
resistant to undesirable M–N bond cleavage.18 Other chelating
groups such as aryl,19 phosphine20–22 and thiol/thioether23 have
aDepartment of Chemistry, University of Leicester, University Road, Leices-
ter, UK LE1 7RH. E-mail: wbc2@le.ac.uk; Fax: +44 (0)116 252 3789;
Tel: +44(0)116 252 2126
Fig. 1 Pd [CNC] complexes similar to those reported herein.
bSchool of Chemistry, University of Nottingham, University Park, Notting-
ham, UK NG7 2RD
As part of a research programme exploring new applications in
bifunctional catalysis, we have been investigating late transition
metal complexes containing amido-NHC ligands. Herein, we
report tridentate amido-bis(NHC) [CNC] ligand complexes of
† Electronic supplementary information (ESI) available: 1H and 13C NMR
spectra for all compounds. CCDC reference numbers 791423–791428. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c0dt01149e
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palladium and for the first time platinum. We also report the first
bidentate arylamido-NHC [C,N] ligand complex of palladium.
Results and discussion
The synthesis of the amine bis(imidazolium) pro-ligands
proceeded with
a palladium catalysed amination of 2-
bromoiodobenzene to give bis(2-bromophenyl)amine (1) using a
procedure adapted from the literature (Scheme 1).38 A copper
catalysed Ullman-type reaction39 of imidazole with 1 gave the
coupled product 2 in 90% yield. Subsequent alkylation of 2 with
i-propyliodide or n-butyliodide gave the imidazolium iodide salts
3a and 3b in 89 and 93% yields respectively. As expected, the
alkylation reaction proceeded faster for the primary alkyl halide
than the secondary alkyl halide. Hence, the pro-ligands 3a and 3b
were prepared in three steps in 74–78% yield from commercially
available materials.
Scheme 2 Synthesis of the amine imidazolium pro-ligand 6.a
complex was generated in situ, and subsequent transmetallation
to Pd was successful. For our ligands, however, this strategy also
proved to be unsuccessful.
Luo reported that the preparation of [CNC] pincer complexes
of palladium B by deprotonation of the amine bis(imidazolium)
ligand with an organometallic or amide base were unsuccessful.37
In contrast, we found that treating a DME solution of 3a or 3b
with 3 equivalents of potassium hexamethyldisilazide (KHMDS)
at 0 ◦C in the presence of Pd(OAc)2 gave, after work-up and
purification by column chromatography, the complexes [CNC-
i-Pr]Pd–I (7a) and [CNC-n-Bu]Pd–I (7b) in 33 and 42% yields
respectively, Scheme 3. These moderate yields do not appear to
arise from the purification procedure: the 1H NMR spectrum
recorded for the crude product showed several other species that
could not be identified and repeating the column chromatography
gave complete recovery of analytically pure material. Using
PdCl2(COD) in the reaction instead of Pd(OAc)2 or using THF as
the solvent gave lower yields, and performing the reaction in the
absence of a palladium salt gave an intractable mixture of prod-
ucts. Coordination of the anionic tridentate bis(N-heterocyclic
carbene) ligand to palladium was confirmed by 1H and 13C NMR
Scheme 1 Synthesis of the amine bis(imidazolium) pro-ligands 3a and
3b.a
The same methodology was also applied to prepare an analo-
gous pro-ligand containing only one imidazolium moiety: starting
instead from N-(2-bromophenyl)-2,6-diisopropylaniline (4),40 the
Ullman-type cross coupling with imidazole gave intermediate 5
and subsequent alkylation with i-propyl iodide gave the imida-
zolium pro-ligand 6 (Scheme 2).
A common method for the coordination of N-heterocyclic
carbene ligands to transition metals is to prepare the silver(I)
NHC complex from the reaction of an imidazolium salt and Ag2O;
subsequent transmetallation then gives the required metal-NHC
complex.41,42 Douthwaite et al. have shown that this is a viable
route to the complex A.36 However, treating our more rigid pro-
ligands 3a or 3b with Ag2O in DCM at room temperature gave
an intractable mixture of products. Performing the reaction in
refluxing THF also gave an unidentifiable mixture, as did including
Pd(OAc)2 or PdCl2(COD) in the reaction mixture. Conversely, Luo
et al. have reported that treatment of an amine bis(imidazolium)
salt with Ag2O followed by PdCl2(MeCN)2 gave the corresponding
[CNC]PdCl complexes B, although a silver complex of their
ligands could not be isolated.37 Presumably, a silver(I) NHC
1
spectroscopy: the H NMR spectra for 7a and 7b lack a signal
that could be assigned to the NCHN proton of an imidazolium
cation (these were present as singlet resonances at dH 9.56 and
9.72 ppm respectively in the spectra recorded for 3a and 3b) and the
1
13C{ H} NMR spectra for 7a and 7b contained signals at d 165.3
and 167.0 ppm respectively for the carbene bound to palladium.
1
An unexpected feature of the H NMR spectrum recorded for
7a was the downfield shift observed for the i-Pr CH resonance,
which appeared as an apparent septet at 6.35 ppm. The ligand
completing the fourth coordination site at Pd was confirmed as
iodide by FAB MS and microanalysis.
Crystals of 7a and 7b suitable for single crystal X-ray diffraction
were obtained by the slow evaporation of a C6D6 solution of each;
ORTEP figures for the solid state structures are shown in Fig. 2
and 3 and selected bond lengths are shown in Table 1.
The complexes 7a and 7b both display the expected square
planar geometry around Pd and iodide is confirmed as the ligand
filling the fourth coordination site. The [CNC] ligand is strongly
496 | Dalton Trans., 2011, 40, 495–505
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Scheme 3 Synthesis of palladium and platinum [CNC] complexes.
˚
Table 1 Selected bond lengths (A) for 7a, 7b and 9a
9a
7a
7b
molecule 1
molecule 2
M-N(amide)
M-C(NHC)
2.023(3)
2.024(3)
2.024(3)
—
2.020(4)
2.020(6)
2.019(6)
—
2.022(8)
2.00(1)
2.036(9)
2.054(8)
—
2.016(8)
2.027(11)
2.034(10)
2.072(11)
—
M-N(py)
M-I
2.5887(6)
2.6034(6)
Fig. 3 ORTEP view of 7b (ellipsoids drawn at 50% probability). Hydrogen
atoms have been omitted for clarity.
Atropisomerism has been observed for pyridyl and aryl bridged
NHC pincers and rapid interconversion of the atropisomers is
common.29,43,44 In addition, the [CNC]PdCl complex A and the
related amine complex {[CN(H)C]PdCl}Cl also show intercon-
version of atropisomers at ambient temperature.36,45 Conversely,
1
variable temperature H NMR spectra recorded for 7a in C6D6
up to 344 K showed no coalescence of the diastereotopic methyl
groups or indeed any line broadening consistent with fluxionality.
Hence, these [CNC] palladium complexes appear to possess
greater stereochemical rigidity that could enable new strategies
for the synthesis of non-racemic chiral complexes from achiral
ligands.46
The Pd–N bond lengths in the two complexes 7a and 7b are
typical for a Pd(II)-amide bond and the Pd–C bond lengths are
also typical for two trans NHC ligands bound to square planar
palladium.47 These bond lengths do not differ significantly from
those reported for the complexes B by Luo.37 There is a large
angle (7a: 81.3◦; 7b: 78.3◦) between the planes of the two NHC
ligands. In turn, the plane of each NHC ring lies at an angle of
Fig. 2 ORTEP view of 7a (ellipsoids drawn at 50% probability). Hydrogen
atoms except H(10) have been omitted for clarity.
distorted from planarity: the angle between the square plane
around Pd and the trigonal plane around the amide nitrogen is
53.3◦ in 7a and 57.4◦ in 7b. Hence, the ligand adopts a helical
conformation and two atropisomers arise. Complex 7a crystallizes
in the non-centrosymmetric chiral space group C222(1), and only
one enantiomer is present in the unit cell. Complex 7b, however,
crystallizes in the non-centrosymmetric achiral space group Aba2,
and hence both enantiomers are observed in the unit cell.
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ca. 40◦ to the square plane around Pd (7a: 41.1◦; 7b: 38.7, 41.2◦).
Although two trans NHC ligands will often lie in the same plane
as each other, a large angle between these two planes - either as
forced by the conformation of a pincer ligand or as the result of
steric interactions between bulky NHCs and the cis ligands - is
not uncommon; the torsion angle between the two trans NHC
rings has no correlation with the Pd–C bond length, as would be
expected for a purely s-bonding interaction between palladium
and the carbene.47
˚
In 7a there is a very short H–I contact (2.859 A) between
the methyne hydrogen of the i-propyl substituent and the iodide
ligand. This H-bonding interaction also appears to be present
in solution, as there is a large downfield shift (dH 6.35 ppm) for
1
the signal arising from this proton in the H NMR spectrum for
7a. Similar short H–I distances are observed for 7b (2.789 and
˚
2.917 A).
We found that the coordination chemistry could be extended
from palladium to platinum. Hence, reacting the imidazolium
salts 3a or 3b with PtCl2(COD) and 3 equivalents of KHMDS
gave the analogous platinum pincer complexes [CNC-i-Pr]Pt–
I (8a) or [CNC-n-Bu]Pt–I (8b), although the yields were poor,
Scheme 3. As for 7a and 7b, iodide rather than chloride occupies
the fourth coordination site, as confirmed for both complexes
by mass spectrometry and microanalysis. Coordination of the
tridentate pincer ligand to platinum gave similar NMR spectra to
the Pd complexes: in particular, the 13C NMR spectrum recorded
contained characteristic singlets at 162.5 ppm (8a) and 164.0 ppm
(8b) corresponding to the carbene. Moreover, for 8a the apparent
septet corresponding to the i-Pr CH was shifted downfield to
6.38 ppm, indicating that a H-bonding interaction with the iodide
ligand is also present in the Pt complex. Therefore, although we
have thus far been unable to grow crystals of 8a or 8b suitable for
X-ray crystallography, the data we have obtained indicates that the
complexes have a very similar structure to those of their palladium
analogues. Although several pincer carbene complexes of Pd have
been reported, platinum pincer carbene complexes are surprisingly
rare,48,49 and these are the first reported platinum [CNC] complexes.
We were interested to see if the halide ligand could be replaced
with a neutral donor in a cationic complex. When 7a was dissolved
Fig. 4 ORTEP view of one of the independent cations of 9a (ellipsoids
drawn at 50% probability). Hydrogen atoms have been omitted for clarity.
and the trigonal planar amide nitrogen is 49.9 and 49.4◦ and the
torsion angle between the planes of the two trans NHC ligands is
◦
72.8 and 70.5 . There are no significant differences between the
metal amide and metal carbene bond lengths in the iodide complex
7a or the cation 9a. Our attempts to isolate an analytically pure
sample of 9a on a larger scale were unsuccessful as it was not
possible to completely separate 9a from pyridine.
The strategy described above for the coordination of the
[CNC] ligands to Pd and Pt was also attempted with the amine
mono(imidazolium) pro-ligand 6, but NHC complexes could not
be isolated under these conditions. Alternatively, treating 6 with
K2CO3, PdCl2 and potassium iodide in refluxing pyridine gave
[C,NH]PdI2py (10) as a yellow-orange solid in 89% yield after
column chromatography (Scheme 4). Performing the reaction
with K2PtCl4 instead of PdCl2 gave the platinum analogue
[C,NH]PtI2py (11) as yellow crystals in 47% yield.
The solid-state structures of both 10 and 11 were determined
by single crystal X-ray diffraction (Fig. 5 and 6; selected bond
lengths are given in Table 2). The structure of 10 is very similar to
the structures of trans-(NHC)PdX2py complexes that have been
reported previously.50–53 The NHC-amine ligand in both complexes
is only bound to the metal through the carbene; the amine nitrogen
is not coordinated. The inner coordination sphere is completed by
two trans iodide ligands and a pyridine ligand. In 10, the bond
lengths and angles around the square planar Pd are extremely
similar for the two independent molecules found in the unit cell,
1
in d5-pyridine the H NMR spectrum indicated the presence of
two different complexes. One of these complexes exhibited an
apparent septet attributable to the i-Pr group at 6.40 ppm (which
we assign, by the downfield shift, as 7a) whereas the other exhibited
an apparent septet at 3.68 ppm. The addition of 1.5 equivalents
of silver triflate to this solution gave quantitative conversion to
the latter complex (Scheme 3), which we subsequently identified
as the triflate salt {[CNC-i-Pr]Pd-py}OTf (9a) by single crystal
X-ray diffraction. The solid-state structure of 9a is shown in Fig. 4
and selected bond lengths are shown in Table 1. Unfortunately
the crystal was weakly diffracting and hence the data is weak; the
crystal also contained disordered dichloromethane. Despite this, it
is possible to discuss the prominent structural features of 9a. The
geometry around Pd is square planar, with the tridentate pincer
and a molecule of pyridine bound to the metal. The triflate anion
is not coordinated to Pd, and also shows significant disorder in the
crystal, requiring the splitting of one of the F atoms in one of the
triflate ions. It is apparent that there is still a significant twist in the
[CNC] ligand: in the two independent molecules of 9a present in
the unit cell the angle between the square plane around the metal
˚
Table 2 Selected bond lengths (A) for 10, 11 and 12
10
11
molecule 1 molecule 2 molecule 1 molecule 2 12
M-N(amide)
M-C(NHC) 1.957(7)
M-N(py)
M-I
—
—
1.981(7)
2.086(6)
—
—
1.998(3)
1.965(13) 1.968(11) 1.945(3)
2.094(10) 2.102(8)
2.121(6)
—
—
—
2.5902(18) 2.5889(16) 2.5901(10) 2.5969(11)
2.6063(17) 2.6054(15) 2.6024(10) 2.6060(10)
M-O1
M-O1¢
—
—
—
—
—
—
—
—
2.052(2)
2.086(2)
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Scheme 4 Synthesis of amine-NHC complexes 10 and 11 and the amido-NHC complex 12.
Fig. 6 ORTEP view of one of the independent molecules of 11 (ellipsoids
drawn at 50% probability). Hydrogen atoms except H(1) have been omitted
for clarity.
Fig. 5 ORTEP view of one of the independent molecules of 10 (ellipsoids
drawn at 50% probability). Hydrogen atoms except H(1) have been omitted
for clarity.
sharp signal at 143.6 ppm, rather than one of the broad 4 ◦C signals
at 147.2 and 148.2 ppm (unfortunately 195Pt satellites, which would
have aided the identification of the carbene resonance, could not be
observed). These signals fall into the range previously reported for
carbenes in trans-(NHC)MX2py (M = Pd or Pt) complexes.51,52,54
Pre-catalysts of the type trans-(NHC)PdX2py (PEPPSI cat-
alysts: Pyridine-Enhanced Pre-catalyst Preparation, Stabiliza-
tion and Initiation) deliver excellent activity in cross-coupling
reactions;55–57 complexes with NHC ligands that are function-
alised with carbonyl (amide50–52 and ketone52), alcohol and ether
groups51,53 have also been reported previously, but, to the best of
our knowledge, 10 is the first amine functionalised complex of
this type. Furthermore, the nucleophilic substitution reactions of
alkyl or benzyl halides used to prepare the functionalised NHC
ligands in these previously reported complexes contrast with the
cross-coupling strategy used to synthesise the pro-ligand 6, which
enables efficient access to aryl substituted NHC ligands with
the functional group (amine) also bound to the aromatic ring.
despite the two molecules having very different angles between the
mean plane of the NHC and pyridine ring (14.9 and 40.2◦). The
˚
Pd–C bond lengths (1.957(7) and 1.981(7) A) are shorter than for
the pincer complexes, demonstrating the weaker trans influence of
the pyridine ligand in 10 compared with the NHC in 7a, 7b and
9a. The unit cell for 11 also contains two unique molecules, which
like 10 differ greatly with respect to the angle between the mean
plane of the NHC ring and the pyridine ring (19.8 and 38.7◦).
However, both of the unique molecules show very similar bond
˚
lengths around Pt (e.g. d(Pt–C) are 1.965(13) and 1.968(11) A).
The signals arising from the carbene are difficult to assign in the
13C NMR spectra for 10 and 11. For 10, the signal at 147.3 ppm
is most likely the carbene resonance, as the nearby signals for 4◦
carbons at 146.6 and 148.0 ppm are broad like the signals we can
unambiguously assign as arising from the 2,6-diisopropylphenyl
group. Likewise for 11, the carbene resonance appears to be the
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Platinum analogues of these Pd catalysts have been reported,54 but
these are much less common.
the typical range of ca. -0.25 to -3.5 ppm for cationic and neutral
Pd(m-OH)2 moieties.62,66–69 In the previously reported b-diiminato
complex {[Ph2nacnac]Pd(m-OH)}2 the OH signal was observed
even further upfield at -5.24 ppm, most likely as a consequence
of the shielding effect of the two nearby phenyl groups of the
Ph2nacnac ligands.69 Likewise, the 2,6-diisopropylphenyl group in
12 also appears to shield the bridging hydroxide, which sits ca.
We first attempted to deprotonate the amine group in 10 to yield
an amido-NHC complex using KHMDS as the base. Surprisingly,
the novel dimeric amido complex {[C,N]Pd(m-OH)}2 (12) was
the only compound that could be isolated from this reaction.
Presumably the hydroxide ligand was produced from adventitious
moisture, but the reaction showed poor reproducibility, even when
an excess of water was added to a rigorously dry reaction mixture.
Alternatively, 12 could be isolated in good yield by stirring a
solution of 10 in 1,4-dioxane with aq. KOH, Scheme 4. The IR
spectrum recorded for 12 contains a weak resonance at 3601 cm-1
that is consistent with a bridging hydroxide ligand.
2.54 A above the aromatic ring in the solid state. In the 13C NMR
˚
spectrum for 12, the carbene signal could not be clearly identified
as there are four signals for 4◦ C atoms between d 144–148 ppm.
Palladium complexes of a bidentate amido-NHC ligand have
been reported for an amido donor that is derived from depro-
tonation of an N-acyl group.50 However, to the best of our
knowledge, compound 12 is the first reported Pd complex of either
an arylamido or alkylamido functionalised NHC ligand.
We attempted to prepare the platinum analogue of 12 by also
treating a solution of 11 in 1,4-dioxane with aqueous KOH
at 40 ◦C, but 11 was unreactive under these conditions. This
observation is consistent with a mechanism where hydroxide reacts
at the metal first and follows the common trend that ligand
substitution reactions are slower for Pt than Pd.70–72 Increasing
the temperature of the reaction to 60 ◦C gave complete conversion
of 11 to a mixture of products, but we were unable to isolate a pure
compound from this reaction.
The solid-state structure of 12 was determined by single crystal
X-ray diffraction (Fig. 7; selected bond lengths are given in
Table 2). Two crystallographically equivalent monomer units make
up the dimer in 12, with a non-bonding Pd(1) ◊ ◊ ◊ Pd(1¢) distance of
˚
3.2348(6) A. The Pd2O2 ring is almost planar, with a Pd–O–Pd–O
torsion angle of 4.7◦, but the two Pd–O bond lengths are different,
˚
˚
with the bond trans to the NHC (2.086(2) A) ca. 0.03 A longer
˚
than the bond trans to the amido ligand (2.052(2) A) due to the
stronger trans influence of the carbene. A search of the Cambridge
Structural Database for complexes of the type [L1L2Pd(m-OH)]2
revealed that the Pd–O bond length tends to correlate with the
Lewis basicity of the trans ligand.47 Hence, the shortest Pd–O
˚
distances (2.005(2) to 2.016(3) A) have been observed with a
Conclusions
pyridine or imine donor trans to m-OH;58–61 the database contained
no examples of NHC or amido ligands in complexes of this type,
but the Pd–O bond lengths in 12 are similar to those reported for
complexes with a phosphine trans to the m-OH ligand,62–64 and the
We have prepared precursors to bidentate amido-NHC [C,N]
and tridentate amido-bis(NHC) [CNC] ligands in high yield
using an efficient sequence of two cross-coupling reactions and
an alkylation. Different strategies were required to coordinate
these ligands to Pd and Pt. For the [CNC] ligands, reaction
of the amine bis(imidazolium) salts 3 with KHMDS and either
Pd(OAc)2 or PtCl2(COD) enabled the isolation of the palladium
complexes [CNC-i-Pr]Pd–I (7a) and [CNC-n-Bu]Pd–I (7b) and the
first [CNC] platinum complexes [CNC-i-Pr]Pt–I (8a) and [CNC-
n-Bu]Pt–I (8b); treating 7a with AgOTf in pyridine also gave
the cationic complex [CNC-i-Pr]Pd(py)}OTf 9a with pyridine
bound in the fourth site. For the [C,N] ligand, reaction of the
amine mono(imidazolium) salt 6 with PdCl2 or K2PtCl4, K2CO3
and KI in pyridine at 100 ◦C gave the complexes [C,NH]MI2py
[M = Pd (10) or Pt (11)], in which the amine arm of the
NHC ligand is not deprotonated and does not coordinate to the
metal. The amine group in 10 was deprotonated in a biphasic
˚
longest Pd–O distance (2.126 A) is for m-OH trans to a phenyl
ligand.65
◦
reaction with aqueous KOH at 40 C, giving the dimeric amido
complex {[C,N]Pd(m-OH)}2 (12), the first reported arylamido-
NHC complex of palladium. Under the same conditions, the more
inert Pt analogue 11 was unreactive. We are currently investigating
the reactivity of these ligands and complexes with a view to
applications in bifunctional catalysis.
Fig. 7 ORTEP view of 12 (ellipsoids drawn at 50% probability). Hydrogen
atoms except H(1) have been omitted for clarity.
Experimental
˚
Both the metal-amide (1.998(3) A) and metal-carbene
˚
(1.945(3) A) distances are the shortest for all the complexes that we
All manipulations were performed under dry, oxygen free nitrogen
using standard Schlenk techniques unless otherwise stated. THF
and toluene were dried by passing through a column of activated
alumina and then degassed; DME was pre-dried over sodium
and distilled from Na-benzophenone; anhydrous DMF was
purchased from Sigma-Aldrich and used as supplied; KHMDS
report herein. Unusually for a metal hydroxide, there is an absence
of H-bonding in the solid state, which may be a consequence of the
bulky N-aryl and N-alkyl substituents that surround the hydroxide
ligand. The bridging hydroxide ligand can be clearly identified in
the 1H NMR spectrum for 12 at dH -3.97 ppm, slightly upfield of
500 | Dalton Trans., 2011, 40, 495–505
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was purchased as a solution in toluene and titrated against
N-4-phenylbenzylidene benzylamine.73 Bis(2-bromophenyl)amine
(1),38 N-(2-bromophenyl)-2,6-diisopropylaniline (4)40 and
PtCl2(COD)74 were prepared as reported in the literature. All
other reagents were obtained from Sigma–Aldrich, Johnson
Matthey or Alfa Aesar and used as supplied. NMR spectra were
recorded on a Bruker DPX300, DRX400 or AV500 spectrometer;
chemical shifts have been referenced to the residual protonated
solvent peak and J values are given in Hz. IR spectra were run in
a diamond ATR cell using a Perkin Elmer Spectrum 1 instrument.
ESI mass spectra were recorded on a micromass Quattra LC
spectrometer in MeCN–MeOH with a cone voltage of +50 or
-25 V unless stated; FAB mass spectra were obtained on a
Kratos concept spectrometer using NBA as the matrix. Elemental
analyses were performed at London Metropolitan University.
514.1462, found 514.1465. Anal. Calcd. for C24H29I2N5: C, 44.95;
H, 4.56; N, 10.92. Found C, 45.01; H, 4.27; N, 10.61%.
Bis(2-(3-butyl-1H-imidazolium)phenyl)amine diiodide (3b)
In an identical procedure to that used for 3a, 3b was prepared from
n-butyl iodide (0.940 g, 5.11 mmol) and 2 (0.700 g, 2.33 mmol)
◦
in MeCN (10 mL). The tube was sealed and heated at 90 C for
24 h, giving a red solution. The mixture was allowed to cool to
RT and filtered. The volatiles were removed in vacuo to give 3b as
◦
a light brown solid (1.450 g, 93%) m.p. 56–57 C. dH(400 MHz,
CDCl3) 0.95 (6H, t, J = 7.5, CH3), 1.36 (4H, apparent sext, J =
7.5, CH2), 1.92 (4H, apparent quint, J = 7.5, CH2), 4.40 (4H, t,
J = 7.5, CH2), 7.10 (2H, t, J = 7.6, CH), 7.25 (2H, d, J = 7.6, CH),
7.39 (2H, d, J = 8.2, CH), 7.44 (2H, t, J = 8.2, CH), 7.56 (2H, t,
J = 1.5, NCHCHN), 7.66 (2H, t, J = 1.5, NCHCHN), 9.72 (2H, s,
NCHN); dC(100 MHz, CDCl3) 13.6 CH3, 19.6 CH2, 31.6 CH2, 50.5
CH2, 122.8, 123.6, 123.8, 123.9, 126.1, 127.6, 132.1, 136.7, 137.7
(aromatic C). nmax/cm-1 (solid) 3066 w, 2978 w, 1597 m, 1546 m,
1497 s, 1458 m, 1375 w, 1305 m, 1264 w, 1192 s, 1161 w, 958 w, 875
w, 827 w, 758 vs, 681 w, 650 s. m/z (ESI) 542 (34%, [M-I]+), 414
(100% [M-I-HI]+), 358 (30%, [M-I-HI-Bu]+); HRMS C26H33IN5
calcd. 542.1781, found 542.1770. Anal. Calcd. for C26H33I2N5: C,
46.65; H, 4.97; N, 10.46. Found C, 46.25; H, 4.70; N, 10.13%.
Bis(2-(1H-imidazol-1-yl)phenyl)amine (2)
Compound 1 (2.97 g, 9.10 mmol), imidazole (1.24 g, 18.2 mmol),
Cs2CO3 (11.86 g, 36.40 mmol), CuI (0.346 g, 1.82 mmol) and 8-
hydroxyquinoline (0.264 g, 1.82 mmol) were suspended in DMF
(5 mL) in a pre-dried sealable tube. The tube was sealed and heated
at 125 ◦C for 24 h. The reaction mixture was then allowed to cool
to room temperature and diluted with DCM (50 mL). The mixture
was filtered through a pad of Celite and washed with a solution of
5% LiCl(aq.) (5 ¥ 100 mL) and brine (2 ¥ 50 mL). The solution was
then dried (MgSO4) and the volatiles removed in vacuo to give 2 as
a green solid (2.47 g, 90%) m.p. 80–82 ◦C. dH(500 MHz, CD2Cl2)
5.12 (1H, s, NH), 7.11 (2H, t, J = 7.8, Ar CH), 7.24–7.32 (4H, m,
Ar CH), 7.36 (2H, t, J = 7.8, Ar CH), 7.75 (br, imidazole CH);
dC(67.9 MHz, CDCl3) 119.3, 122.6, 127.6, 129.7, 137.7. nmax/cm-1
(solid) 3116 w, 3096 w, 2914 w, 1593 m, 1510 s, 1500 s, 1482 s, 1459
m, 1312 s, 1278 m, 1236 w, 1108 m, 1088 w, 1059 s, 963 m, 907 m,
821 m, 772 s. m/z (ESI) 302 (100%, M+H+), 324 (21% M+Na+);
HRMS C18H16N5 calcd. 302.1400, found 302.1414. Compound 2
could not be isolated in analytically pure form, but this did not
hinder subsequent steps. Some signals are broad or not apparent
in the NMR spectra; we speculate that this is due to inter- and
intramolecular H-bonding.
N-(2-(1H-imidazol-1-yl)phenyl)-2,6-diisopropylaniline (5)
Compound 4 (2.00 g, 6.01 mmol), imidazole (0.409 g, 6.01 mmol),
Cs2CO3 (3.916 g, 12.02 mmol), CuI (0.114 g, 0.601 mmol) and
8-hydroxyquinoline (0.087 g, 0.60 mmol) were suspended in DMF
(10 mL) in a pre-dried sealable tube. The tube was sealed and
heated at 125 ◦C for 72 h. The reaction mixture was then allowed
to cool to room temperature and diluted with DCM (75 mL).
The mixture was filtered through a pad of Celite and washed
with a solution of 5% LiCl(aq.) (4 ¥ 100 mL) and brine (100 mL).
The solution was then dried (MgSO4) and the volatiles removed
in vacuo to give a green residue that was redissolved in DCM
(30 mL). Hexane (70 mL) was then added and a solid precipitate
removed by filtration. Volatiles were removed in vacuo to give 5 as a
pale yellow powder (1.592 g, 83%) m.p. 142–144 ◦C. dH(300 MHz,
d4-MeOH) 1.11 (12H, d, J = 6.8, CH(CH3)2), 3.11 (2H, sept,
J = 6.8, CH(CH3)2), 5.83 (1H, br s, NH), 6.17 (1H, d, J = 8.2,
ArH), 6.74 (1H, t, J = 7.2, ArH), 7.10–7.32 (m, 6H, ArH), 7.50–
8.40 (2H, br, ArH); dC(75 MHz, CDCl3) 23.0 (CH(CH3)2), 24.4
(CH(CH3)2), 28.4 (CH(CH3)2), 112.7, 117.3, 124.0, 127.2,127.9,
130.1, 133.6, 143.6, 147.4 (aromatic C); nmax/cm-1 (solid) 3205
w, 2961 w, 2868 w, 1603 m, 1586 w, 1511 s, 1493 m, 1465 m,
1453 m, 1310 m, 1057 m. m/z (ESI) 320 (100%, M+H+); HRMS
(FAB) C21H25N3 calcd. 320.21202, found 320.21208. Anal. Calcd.
for C21H25N3: C, 78.96; H, 7.89; N, 13.15. Found C, 79.03; H, 7.48;
N, 13.04%. Some signals are broad or not apparent in the NMR
spectra; we speculate that this is due to inter- and intramolecular
H-bonding.
Bis(2-(3-iso-propyl-1H-imidazolium)phenyl)amine diiodide (3a)
In a sealable tube under an atmosphere of air, i-propyl iodide
(0.36 mL, 3.7 mmol) was added to a green suspension of 2 (0.500 g,
1.66 mmol) in MeCN (10 mL). The tube was sealed and heated at
90 ◦C for 48 h, giving a red solution. The mixture was allowed to
cool to RT and filtered. The volatiles were removed in vacuo to give
3a as an orange solid (0.951 g, 89%) m.p. 81–84 ◦C. dH(300 MHz,
CDCl3) 1.70 (12H, d, J = 6.7, CH(CH3)2), 4.97 (2H, sept, J = 6.7,
3
4
CH(CH3)2), 7.14 (2H, dt, J = 7.8, J = 1.2, CH), 7.30 (2H, dd,
3J = 7.9, 4J = 1.2, CH), 7.36 (2H, dd, 3J = 7.8, 4J = 1.5, CH), 7.46
(2H, dt, 3J = 7.9, 4J = 1.5, CH), 7.53 (2H, t, J = 1.7, NCHCHN),
7.75 (2H, t, J = 1.7, NCHCHN), 9.56 (2H, t, J = 1.7, NCHN);
dC(67.9 MHz, CDCl3) 22.9 (CH(CH3)2), 52.8 (CH(CH3)2), 121.5,
122.9, 123.8, 124.2, 126.1, 127.7, 132.0, 135.6, 137.7 (aromatic C).
N-(2-(3-iso-propyl-1H-imidazolium)phenyl)-2,6-diisopropylaniline
iodide (6)
n
max/cm-1 (solid) 3066 w, 2978 w, 1597 m, 1546 m, 1497 s, 1458
m, 1375 w, 1305 m, 1264 w, 1192 s, 1161 w, 958 w, 875 w, 827
w, 758 vs, 681 w, 650 s. m/z (ESI) 514 (18%, [M-I]+), 386 (100%
[M-I-HI]+), 344 (36%, [M-I-HI-iPr]+); HRMS C24H29I2N5 calcd.
In a sealable tube under an atmosphere of air, i-propyl iodide
(0.35 mL, 3.4 mmol) was added to a green suspension of 5 (1.00 g,
3.14 mmol) in MeCN (10 mL). The tube was sealed and heated at
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90 ◦C for 48 h, giving a red solution. The mixture was allowed
to cool to RT and filtered through Celite. The volatiles were
removed in vacuo to give a brown solid that was purified by
two precipitations from MeOH (5 mL) upon addition of Et2O
(80 mL), giving 6 (1.138 g, 74%) as a white solid m.p. 228–230 ◦C.
dH(300 MHz, CDCl3) 1.11 (6H, d, J = 6.8, CH(CH3)2), 1.21 (6H, d,
J = 6.8, CH(CH3)2), 1.75 (6H, d, J = 6.7, NCH(CH3)2), 3.14 (2H,
sept, J = 6.8, CH(CH3)2), 5.19 (1H, sept, J = 6.7, CH(CH3)2, 6.27
(1H, s, NH), 6.34 (1H, d, J = 8.4, ArH), 6.80 (1H, td, 3J = 7.6, 4J =
1.1, ArH), 7.20 (1H, t, J = 8.4, ArH), 7.21 (2H, d, J = 7.0, ArH),
7.28–7.34 (2H, m, ArH), 7.54 (1H, ap t, J = 1.7, NCHCHN),
7.64 (1H, ap t, J = 1.7, NCHCHN), 9.36 (1H, br s, NCHN);
dC(75 MHz, CDCl3) 22.7 (CH(CH3)2), 23.4 (CH(CH3)2), 24.9
(CH(CH3)2), 28.4 (CH(CH3)2), 54.0 (NCH(CH3)2), 115.3, 118.1,
120.0, 122.0, 123.4, 124.2, 127.4, 127.9, 131.8, 133.4, 135.3, 143.0,
147.3 (aromatic C). nmax/cm-1 (solid) 3215 w, 3070 w, 2962 m, 2867
w, 1608 m, 1563 w, 1549 w, 1505 s, 1463 m, 1432 w, 1303 m, 1199
w, 1120 w, 1048 w, 797 m, 743 vs. m/z (ESI) 362 (100% [M-I]+);
HRMS (FAB) C24H32N3 calcd. 362.25882, found 362.25878. Anal.
Calcd. for C24H32IN3: C, 58.90; H, 6.59; N, 8.59. Found C, 59.07;
H, 6.29; N, 8.69%.
0.90 mL, 0.90 mmol). Purification by flash column chromatogra-
phy (33% EtOAc/pet. ether) gave 7b (0.082 g, 42%) as an orange
◦
solid m.p. 106-108 C, Rf 0.37 (33% EtOAc/pet. ether). Crystals
of 7b suitable for structure determination by X-ray diffraction
were obtained by slow evaporation of a solution of 7b in C6D6.
dH(300 MHz, C6D6) 0.72 (6H, t, J = 7.4, CH3), 0.96–1.24 (4H,
m, NCH2CH2CH2CH3), 1.25–1.43 (2H, m, NCH2CH2CH2CH3),
1.70–1.87 (2H, m, NCH2CH2CH2CH3), 4.12–4.24 (2H, m,
NCH2CH2CH2CH3), 4.61–4.73 (2H, m, NCH2CH2CH2CH3),
6.10 (2H, d, J = 2.0, NCH2CH2N), 6.61 (2H, t, J = 7.6, CH), 6.64
(2H, d, J = 2.0, NCH2CH2N), 6.81 (2H, t, J = 7.6, CH), 7.00 (2H,
d, J = 7.6, CH), 7.03 (2H, d, J = 7.6, CH); dC(75 MHz, C6D6) 14.2
(CH3), 19.9 (NCH2CH2CH2CH3), 33.8 (NCH2CH2CH2CH3), 52.7
(NCH2CH2CH2CH3), 118.0 (NCH2CH2N), 119.2, 121.7, 123.0,
123.2, 127.9, 134.1, 145.2, 167.0 (N2C–Pd); nmax/cm-1 (solid) 2952
w, 2868 w, 1588 w, 1487 s, 1451 m, 1416 m, 1336 m, 1269 m,
1133 w, 1073 w, 1039 w, 952 w, 880 w, 745 s, 724 s, 696 s, 683 s.
m/z (ESI) 518 (20%, [M-I]+), 559 (100%, [M-I+MeCN]+) (FAB)
645 [M]+; HRMS C26H30N5Pd ([M-I]+) calcd. 518.1557, found
518.1517; Anal. Calcd for C26H30IN5Pd: C, 48.35; H, 4.68; N,
10.84. Found C, 48.41; H, 4.68; N, 10.74%.
Palladium bis(2-(3-iso-propylimidazolin-2-yliden-1-
yl)phenyl)amide iodide, [CNC-i-Pr]PdI (7a)
Platinum bis(2-(3-iso-propylimidazolin-2-yliden-1-yl)phenyl)amide
iodide, [CNC-i-Pr]PtI (8a)
A solution of Pd(OAc)2 (0.026 g, 0.12 mmol) and the imidazolium
A solution of PtCl2(cod) (0.292 g, 0.780 mmol) and 3a (0.500 g,
0.780 mmol) in THF (15 mL) was cooled to -78 ◦C and a solution
of 0.55 M KHMDS in toluene (5.00 mL, 2.73 mmol) added
dropwise with stirring. The mixture was stirred for 8 h at -78 ◦C
and then allowed to warm to RT overnight. The crude reaction
mixture was filtered through Celite and the solvent removed under
reduced pressure to give a yellow-orange solid. The solid was
dissolved in DCM (ca. 20 mL) and the solution decanted to remove
insoluble salts. Purification by flash column chromatography (20%
EtOAc–hexane) gave 8a (0.043 g, 9%) as a yellow solid m.p. 287–
salt 3a (0.075 g, 0.12 mmol) in DME (15 mL) was cooled to
0
◦C and a solution of 1 M KHMDS in toluene (0.36 mL,
0.36 mmol) added dropwise with stirring. The mixture was stirred
for 6 h at 0 ◦C and then allowed to warm to RT overnight.
The crude reaction mixture was filtered through Celite and the
solvent removed in vacuo to give a red-brown solid. The solid was
dissolved in DCM (ca. 20 mL) and the solution decanted to remove
insoluble material. Purification by flash column chromatography
(33% EtOAc/pet. ether) gave 7a (0.024 g, 33%) as an orange
◦
◦
solid m.p. 272-275 C, Rf 0.37 (33% EtOAc/pet. ether). Crystals
289 C, Rf 0.26 (20% EtOAc–hexane). dH(300 MHz, C6D6) 0.73
of 7a suitable for structure determination by X-ray diffraction
were obtained by slow evaporation of a solution of 7a in C6D6.
dH(300 MHz, C6D6) 0.71 (6H, d, J = 6.7, CH3), 1.32 (6H, d, J =
6.7, CH3), 6.23 (2H, d, J = 1.8, NCHCHN), 6.35 (2H, apparent
sept, J = 6.7, CH(CH3)2), 6.60 (2H, t, J = 7.8, CH), 6.71 (2H,
d, J = 1.8, NCHCHN), 6.81 (2H, t, J = 7.8, CH), 6.99 (2H,
d, J = 7.8, CH), 7.09 (2H, d, J = 7.8, CH); dC(75 MHz, C6D6)
23.2 (CH(CH3)2), 23.7 (CH(CH3)2), 53.5 (CH(CH3)2), 117.7, 118.9
(NCHCHN), 119.2 (NCHCHN), 121.3, 122.8, 127.4, 133.5, 144.7,
165.3 (N2C–Pd); nmax/cm-1 (solid) 2962w, 2926w, 2870w, 1587w,
1487 s, 1449 m, 1403 m, 1334 s, 1266 m, 1216 m, 1132 m, 1077w,
1039w, 882w, 842w, 743 s, 728 s, 682s. m/z (ESI) 490 (65%, [M-I]+),
531 (100%, [M-I+MeCN]+); (FAB) 617 [M]+; HRMS C24H26N5Pd
([M-I]+) calcd. 490.1227, found 490.1239. Anal. Calcd for
C24H26IN5Pd: C, 46.66, H, 4.24, N, 11.34. Found: C, 46.70, H, 4.22,
N, 11.37%.
(6H, d, J = 6.9, CH3), 1.37 (6H, d, J = 6.9, CH3), 6.19 (2H, d,
J = 2.2, NCHCHN), 6.38 (2H, apparent sept, J = 6.9, CH(CH3)2),
6.60 (2H, t, J = 7.8, CH), 6.68 (2H, d, J = 2.2, NCHCHN), 6.78
(2H, t, J = 7.8, CH), 6.95 (2H, d, J = 7.8, CH), 7.09 (2H, d, J = 7.8,
CH); dC(125 MHz, CD2Cl2) 23.4 (CH(CH3)2), 24.1 (CH(CH3)2),
53.2 (CH(CH3)2), 118.5, 118.8 (NCHCHN), 119.4 (NCHCHN),
121.0, 122.2, 127.1, 133.1, 144.0, 162.5 (N2C–Pt); nmax/cm-1 (solid)
3061 w, 2971 w, 1563 w, 1489 s, 1451 m, 1401 m, 1340 s, 1268 m,
1214 m, 1131 w, 1079 w, 1037 w, 951 w, 889 w, 723 s, 690 s. m/z
(ESI) 620 (25%, [M-I+MeCN]+), 579 (100% [M-I]+); m/z (FAB)
706 [M]+; Anal. Calcd. for C24H26IN5Pt: C, 40.80; H, 3.71; N, 9.91.
Found C, 40.82; H, 3.75; N, 9.91%.
Platinum bis(2-(3-n-butyl-imidazolin-2-yliden-1-yl)phenyl)amide
iodide, [CNC-n-Bu]PtI (8b)
Complex 8b was prepared in an identical procedure to that for 8a,
using PtCl2(cod) (0.280 g, 0.747 mmol), 3b (0.500 g, 0.747 mmol),
THF (15 mL) and a solution of 1 M KHMDS in toluene (2.24 mL,
2.24 mmol). Purification by flash column chromatography (33%
EtOAc/pet. ether) gave 8b (0.057 g, 12%) as a yellow solid
m.p. 169–171 ◦C, Rf 0.25 (33% EtOAc/pet. ether). dH(500 MHz,
CD2Cl2) 0.84 (6H, t, J = 7.4, CH3), 1.27 (4H, m, CH2CH3), 1.74
Palladium bis(2-(3-n-butylimidazolin-2-yliden-1-yl)phenyl)amide
iodide, [CNC-n-Bu]PdI (7b)
Complex 7b was prepared in an identical procedure to that for 7a,
using Pd(OAc)2 (0.067 g, 0.30 mmol), 3b (0.200 g, 0.299 mmol),
DME (15 mL) and a solution of KHMDS in toluene (1 M,
502 | Dalton Trans., 2011, 40, 495–505
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(2H, m, CH2CH2CH3), 1.98 (2H, m, CH2CH2CH3), 4.52 (4H, m,
CH2CH2CH2CH3), 6.76 (2H, t, J = 7.3, CH), 6.92 (4H, m, CH),
7.12 (2H, d, J = 2.0, NCHCHN), 7.37 (2H, d, J = 8.0, CH), 7.45
(2H, d, J = 2.0, NCHCHN); dC(125 MHz, CD2Cl2) 14.0 (CH3),
19.9 (CH2CH3), 33.5 (CH2CH2CH3), 52.5 (CH2CH2CH2CH3),
118.7, 118.8 (NCHCHN), 121.3, 122.4, 123.1 (NCHCHN), 127.4,
133.4, 144.2, 164.0 (N2C–Pt); nmax/cm-1 (solid) 2957 w, 2872
w, 1587 w, 1562 w, 1487 s, 1448 m, 1414 m, 1387 m, 1327 s,
1270 s, 1232 m, 1134 w, 1041 w, 951 m, 888 w, 717 s, 685 s. m/z
(ESI) 735 (10%, [M+H]+), 607 (100%, [M-I]+); Anal. Calcd. for
C26H30IN5Pt: C, 42.51; H, 4.12; N, 9.53. Found C, 42.55; H, 4.17;
N, 9.57%.
754 s, 726 m, 685 s. m/z (ESI) 466 (100% [M-I-HI-py]+); 507 (70%
[M-I-HI-py+MeCN]+). Anal. Calcd. for C29H36I2N4Pd: C, 43.49;
H, 4.53; N, 7.00. Found C, 43.51; H, 4.45; N, 7.12%.
Pyridyl platinum N-(2-(3-iso-propylimidazolin-2-yliden-1-
yl)phenyl)-2,6-diisopropylaniline diiodide, [C,NH]PtI2py (11)
Imidazolium salt 6 (0.400 g, 0.818 mmol), K2PtCl4 (0.309 g,
0.744 mmol), K2CO3 (0.513 g, 3.72 mmol) and KI (0.617 g,
3.72 mmol) were suspended in pyridine (15 mL) and heated at
100 ◦C for 48 h. After cooling to RT, the reaction mixture was di-
luted with DCM (30 mL), filtered through Celite and the volatiles
removed in vacuo. Purification by flash column chromatography
(13% EtOAc/pet. ether) followed by crystallisation from Et2O–
pentane gave 11 (0.313 g, 47%) as yellow crystals m.p. 206–
208 ◦C (dec.), Rf 0.3 (13% EtOAc/pet. ether). Crystals suitable
for structure determination by X-ray diffraction were obtained by
slow evaporation of a saturated DCM solution of 11. dH(300 MHz,
CD2Cl2) 1.11 (12H, d, J = 6.5, CH(CH3)2), 1.60 (6H, d, J = 6.7,
NCH(CH3)2), 3.10 (1H, br, CH(CH3)2), 3.53 (1H, br, CH(CH3)2),
5.99 (1H, sept, J = 6.7, NCH(CH3)2), 6.30 (1H, d, J = 8.2, ArH),
6.90 (1H, t, J = 7.6, ArH), 7.14–7.33 (8H, m, CH), 6.73 (1H, t, J =
7.6, pyH), 8.01 (1H, d, J = 7.9, ArH), 8.90 (2H, d, J = 5.3, pyH);
dC(125.8 MHz, CD2Cl2) 22.4 (NCH(CH3)2), 22.8 (CH(CH3)2),
24.4 (CH(CH3)2), 25.0 (CH(CH3)2), 25.5 (CH(CH3)2), 28.2
(CH(CH3)2), 28.8 (CH(CH3)2), 53.1 (NCH(CH3)2), 115.1, 117.3,
117.9, 124.2, 124.6, 125.2, 126.7, 127.6, 129.9, 131.2, 135.1, 136.7,
137.9 (Ar/py C), 143.6 (N2CPt), 147.2, 148.2 (Ar C), 154.1 (py C).
Pyridyl palladium bis(2-(3-iso-propylimidazolin-2-yliden-1-
yl)phenyl)amide triflate, {[CNC-i-Pr]Pd-(d5-py)}OTf (9a)
Iodide complex 7a (0.012 g, 0.019 mmol) was dissolved in d5-
pyridine and AgOTf added (0.007 g, 0.03 mmol). Crystals of
9a suitable for structure determination by X-ray diffraction were
obtained by diffusion of pentane into this solution. Attempts to
isolate an analytically pure sample of 9a on a larger scale were
unsuccessful as it was not possible to completely separate 9a from
pyridine. dH(400 MHz, d5-pyridine) 0.72 (6H, d, J = 6.7, CH3), 0.90
(6H, d, J = 6.7, CH3), 3.68 (2H, apparent sept, J = 6.7, CH(CH3)2),
6.96 (2H, t, J = 7.9, CH), 7.08 (2H, t, J = 7.9, CH), 7.17 (2H, d,
J = 7.9, CH), 7.64 (2H, d, J = 2.1, NCHCHN), 7.76 (2H, d, J =
7.9, CH), 8.14 (2H, d, J = 2.1, NCHCHN); dC(125 MHz, d5-
pyridine) 21.9 (CH3), 23.8 (CH3), 51.7 (CH(CH3)2), 119.3, 120.2,
120.3, 121.8, 124.6, 128.1, 132.3, 143.8, 163.8 (N2C–Pd); 19F NMR
(282 MHz, d5-pyridine) d -77.2. m/z (ESI) 490 (65%, [M-OTf-
py]+), 531 (100%, [M-OTf-py+MeCN]+).
n
max/cm-1 (solid) 3389 w (NH), 2966 m, 2866 w, 1605 m, 1445 m,
1416 m, 1370 w, 1328 m, 1300 m, 1240, 1210 m, 1117 w, 1071 w,
1043 w, 1022 w, 958 w, 938 w, 883 w, 800 m, 758 s, 730 m, 693 s. m/z
(ESI) 555 (100% [M-I-HI-py]+); 634 (10% [M-I-HI-py+MeCN]+).
Anal. Calcd. for C29H36I2N4Pt: C, 39.16; H, 4.08; N, 6.30. Found
C, 39.27; H, 4.17; N, 6.18%.
Pyridyl palladium N-(2-(3-iso-propylimidazolin-2-yliden-1-
yl)phenyl)-2,6-diisopropylaniline diiodide, [C,NH]PdI2py (10)
Imidazolium salt 6 (0.150 g, 0.307 mmol), PdCl2 (0.050 g,
0.28 mmol), K2CO3 (0.193 g, 1.40 mmol) and KI (0.232 g,
1.40 mmol) were suspended in pyridine (10 mL) and heated
at 100 ◦C for 18 h. After cooling to RT, the reaction mixture
was diluted with DCM (30 mL), filtered through Celite and
the volatiles removed in vacuo. Purification by flash column
chromatography (17% EtOAc/pet. ether) gave 10 as a yellow-
orange solid (0.199 g, 89%) m.p. 122-123 ◦C, Rf 0.18 (17%
EtOAc/pet. ether). Crystals suitable for structure determination
by X-ray diffraction were obtained by diffusion of hexane into a
saturated DCM solution of 10. dH(300 MHz, CD2Cl2) 1.11 (12H,
br d, J = 6.8, CH(CH3)2), 1.62 (6H, d, J = 6.8, NCH(CH3)2),
3.15 (1H, br, CH(CH3)2), 3.48 (1H, br, CH(CH3)2), 5.27 (1H, s,
NH), 5.79 (1H, sept, J = 6.8, NCH(CH3)2), 6.32 (1H, d, J = 8.2,
ArH), 6.94 (1H, t, J = 7.6, ArH), 7.17–7.35 (8H, m), 7.74 (1H, t,
J = 7.6, pyH), 7.16 (1H, d, J = 7.9, ArH), 8.88 (2H, br d, J = 4.9,
pyH); dC(125.8 MHz, C6D6) 21.9 (NCH(CH3)2), 22.3 (CH(CH3)2),
22.7 (CH(CH3)2), 25.0 (CH(CH3)2), 25.5 (CH(CH3)2), 28.5
(CH(CH3)2), 28.7 (CH(CH3)2), 53.9 (NCH(CH3)2), 116.1, 117.7,
118.8, 123.8, 124.2, 124.9, 125.1, 127.0, 127.6, 130.4, 131.5, 135.4,
136.8, 144.0, 146.6 (Ar/py C), 147.3 (N2CPd), 148.0 (Ar C), 154.1
(py CH). nmax/cm-1 (solid) 3386 w (NH), 2965 m, 2865 w, 1603 m,
1506 m, 1444 m, 1430 m, 1362 w, 1326 m, 1300 m, 1240 w, 1210
m, 1111 w, 1070 w, 1045 w, 1020 w, 957 w, 937 w, 880 w, 803 m,
Hydroxy palladium N-(2-(3-iso-propylimidazolin-2-yliden-1-
yl)phenyl)-2,6-diisopropylphenylamide dimer, {[C,N]Pd(l-OH)}2
(12)
A solution of complex 10 (0.100 g, 0.125 mmol) in 1,4-dioxane
(18 mL) was stirred vigorously with a solution of KOH (0.350 g,
6.250 mmol) in H2O (3 mL) at 40 ◦C for 24 h. After cooling
to RT, the volatiles were removed in vacuo. The crude solid
was re-dissolved in DCM (15 mL), dried (MgSO4) and filtered
through Celite. Removing the solvent under reduced pressure gave
12 (0.076 g, 63%) as an orange/red powder m.p. 190 ◦C (dec.).
Crystals suitable for structure determination by X-ray diffraction
were obtained by slow evaporation of an Et2O–pentane solution
of 12. dH(300 MHz, CD2Cl2) -3.97 (2H, s, OH), 0.96 (12H, d,
J = 6.9, CH(CH3)2), 1.11 (12H, d, J = 6.7, NCH(CH3)2), 1.46
(12H, d, J = 6.9, CH(CH3)2), 3.49 (4H, sept, J = 6.9, CH(CH3)2),
5.17 (2H, sept, J = 6.7, NCH(CH3)2), 5.80 (2H, d, J = 8.1, CH),
6.23 (2H, t, J = 7.7, CH), 6.63 (2H, t, J = 8.1, CH), 7.02 (2H,
d, J = 2.2, NCHCHN), 7.08 (6H, br s, 2,6-iPr2C6H3), 7.22 (2H,
d, J = 7.7, CH), 7.50 (2H, d, J = 2.2, NCHCHN); dC(75 MHz,
C6D6) 23.8 (CH(CH3)2), 24.7 (CH(CH3)2), 25.5 (CH(CH3)2), 28.1
(CH(CH3)2), 50.1 (NCH(CH3)2), 110.8, 117.4, 117.7, 117.8, 118.9
(ArCH), 122.9 (ArC), 124.7, 125.2, 126.7 (ArCH), 144.7, 145.7,
147.4, 147.5 (4 ◦C). nmax/cm-1 (solid) 3601 w (OH), 2961 m, 2863
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 495–505 | 503
©

View Article Online
w, 1598 m, 1493 s, 1455 m, 1426 m, 1410 m, 1356 s, 1337 s, 1284
m, 1221 m, 1161 w, 1124 w, 1081 w, 1055 m, 952 w, 850 s, 825 m,
801 m, 767 m, 735 s, 723 s, 713 s, 693 m, 672 s. m/z (ESI, 25 V) 466
(100% [(C,N)Pd]+), 500 (100% [(C,N)Pd(OH)2]-). Anal. Calcd. for
C48H62N6O2Pd2: C, 59.56; H, 6.46; N, 8.68. Found C, 59.47; H,
6.30; N, 8.73%.
Disordered CH2Cl2 was omitted using the SQUEEZE option
3
of PLATON.76 The solvent accessible voids are 207.5 A with
˚
an estimated 124 e/cell to be added. Three solvent CH2Cl2
molecules/unit cell accounting for 126 e were included in the
formula, FWt, (000) and density calculations. The CF3 group of
one of the triflate anions was disordered and one of the F atoms
has been split; attempts to split other atoms failed.
X-ray crystallographic studies
Crystal data for 10·(0.5CH2Cl2)(0.25C6H14). C31H40.50ClI2N4-
Pd, Mw = 864.82 gmol-1, T = 150(2) K, triclinic space group
All single crystal diffraction data were collected using graphite-
monochromated Mo-Ka X-radiation (l = 0.71073 A) on a Bruker
APEX 2000 CCD diffractometer at 150 K. The data were corrected
for Lorentz and polarisation effects and empirical absorption
corrections applied. Structures were solved by Patterson methods
and structures refined by least-squares full-matrix refinement
against F2 employing SHELXTL version 6.10.75 Hydrogen atoms
¯
˚
˚
˚
P1, a = 13.616(9) A, b = 15.293(10) A, c = ◦18.724(13) A, a =
˚
◦
◦
3
˚
73.804(12) , b = 73.014(12) , g = 64.088(12) , V = 3302(4) A ,
Z = 4, rcalcd = 1.740 Mgm-3, m = 2.539 mm-1, F(000) = 1694,
crystal size 0.20 ¥ 0.20 ¥ 0.13 mm3, 25832 reflections collected,
12785 unique [R(int) = 0.0875] (completeness to theta = 26.00◦
98.6%). Empirical absorption correction made, Tmin and Tmax
=
0.831 and 0.455 respectively. GOF = 0.952, final R indices [I>2sI]
R1 = 0.0589, wR2 = 0.1341, R indices (all data) R1 = 0.0825, wR2 =
0.1428. Largest diff. peak and hole 2.244 and -0.858 e A .
˚
were included in calculated positions (d(C–H) = 0.95 to 0.99 A)
riding on the bonded atom with isotropic displacement parameters
set to 1.5 Ueq(C) for methyl H atoms and 1.2 Ueq(C) for all
other C atoms. All non-H atoms were refined with anisotropic
displacement parameters.
-3
˚
Disordered CH2Cl2 and C6H14 were omitted using the
SQUEEZE option of PLATON.76 The solvent accessible voids
3
˚
are 325.1 A with an estimated 144e/cell to be added. Two solvent
Crystal data for 7a·(2C6H6). C36H38IN5Pd, Mw = 774.01
gmol-1, T = 150(2) K, orthorhombic space group C222(1), a ◦=
CH2Cl2 molecules and one C6H14 molecule/unit cell accounting
for 134e were included in the formula, FWt, (000) and density
calculations.
˚
˚
10.8012(19) A, b = 19.746(4), c = 15.230(3) A, a = b = g = 90 ,
3
V = 3248.2(10) A , Z = 4, rcalcd = 1.583 Mgm-3, m = 1.555 mm-1,
˚
F(000) = 1552, crystal size 0.33 ¥ 0.26 ¥ 0.21 mm3, 13040 reflections
collected, 3336 unique [R(int) = 0.0341] which were used in all
calculations. Empirical absorption correction made, Tmin and Tmax
0.831 and 0.646 respectively. GOF = 1.064, final R indices [I>2sI]
R1 = 0.0260, wR2 = 0.0661, R indices (all data) R1 = 0.0277, wR2 =
Crystal data for 11. C29H36I2N4Pt, Mw = 889.51 gmol-1,
¯
˚
T = 150(2) K, triclinic space group P1, a = 13.412(3) A, b =
◦
◦
˚
˚
15.242(3) A, c◦= 18.357(4) A, a = 95.858(4) , b = 104.069(4) ,
g = 114.812(4) , V = 3214.0(12) A , Z = 4, rcalcd = 1.838 Mgm-3,
3
˚
m = 6.309 mm-1, F(000) = 1688, crystal size 0.23 ¥ 0.08 ¥
0.04 mm3, 25327 reflections collected, independent reflections
12490 [R(int) = 0.0920] (completeness to theta = 26.00◦ 98.80%).
Empirical absorption correction made, Tmin and Tmax = 0.831 and
-3
˚
0.0667. Largest diff. peak and hole 0.692 and -0.554 e A .
Disordered C6H6 was omitted using the SQUEEZE option of
3
PLATON.76 The solvent accessible voids are 1128.7 A with an es-
˚
0.518 respectively. GOF = 0.897, final R indices [I>2sI] R1
=
timated 375e/cell to be added. Eight solvent C6H6 molecules/unit
cell accounting for 336e were included in the formula, FWt, (000)
and density calculations.
0.0602, wR2 = 0.1004, R indices (all data) R1 = 0.1104, wR2 =
-3
˚
0.1130. Largest diff. peak and hole 3.255 and -1.506 e.A .
Crystal data for 12·(C5H12). C53H74N6O2Pd2, Mw = 1039.98
Crystal data for 7b·(C6H6). C32H36IN5Pd, Mw = 723.96 gmol-1,
gmol-1, T = 150(2) K, tetragonal space group I4(1)/a, a =
˚
T = 150(2) K, orthorhombic space group Aba2, a = 29.370(5) A, b =
◦
˚
˚
˚
19◦.443(2) A, b = 19.443(2) A, c = 25.426(4) A, a = 90 , b =
◦
3
˚
˚
˚
20.178(3) A, c = 10.3042(17) A, a = b = g = 90 , V = 6106.4(18) A ,
Z = 8, rcalcd = 1.575 Mgm-3, m = 1.648 mm-1, F(000) = 2896,
crystal size = 0.15 ¥ 0.14 ¥ 0.10 mm3, 23246 reflections collected,
5940 unique [R(int) = 0.0843] which were used in all calculations.
Empirical absorption correction made, Tmin and Tmax 0.802 and
◦
90 , g = 90 , V = 9612(2) A , Z = 8, rcalcd = 1.437 Mgm-3, m =
3
˚
0.796 mm-1, F(000) = 4336, crystal size 0.31 ¥ 0.24 ¥ 0.15 mm3,
37121 reflections collected, independent reflections 4713 [R(int) =
0.0767] (completeness to theta = 26.00◦ 100.00%). Empirical
absorption correction made, Tmin and Tmax = 0.802 and 0.634
respectively. GOF = 1.029, final R indices [I>2sI] R1 = 0.0378,
wR2 = 0.0914, R indices (all data) R1 = 0.0497, wR2 = 0.0960.
0.628 respectively. GOF = 0.934, final R indices [I>2sI] R1
=
0.0457, wR2 = 0.0751, R indices (all data) R1 = 0.0594, wR2 =
-3
˚
0.0790. Largest diff. peak and hole 0.894 and -1.009 e A .
-3
˚
Largest diff. peak and hole 0.690 and -0.388 e.A .
Disordered pentane (C5H12) was omitted using the SQUEEZE
Crystal data for 9a·(0.75CH2Cl2). C30.75H32.50Cl1.50F3N6O3PdS,
3
option of PLATON.76 The solvent accessible voids are 1135.0 A
˚
-1
¯
Mw = 782.76 gmol , T = 150(2) K, triclinic space group P1,
˚
˚
˚
with an estimated 332e/cell to be added. Eight solvent C5H12
molecules/unit cell accounting for 336e were included in the
formula, FWt, (000) and density calculations.
a = 10.372◦(4) A, b = 11.◦933(5) A, c = 26.284(11) A, a =
◦
3
˚
101.593(10) , b = 94.150(9) , g = 95.257(10) , V = 3159(2) A ,
Z = 4, rcalcd = 1.646 Mgm-3, m = 0.842 mm-1, F(000) = 1590,
crystal size 0.22 ¥ 0.13 ¥ 0.02 mm3, 25010 reflections collected,
12296 unique [R(int) = 0.2109] (completeness to theta = 26.00◦
Acknowledgements
98.9%). Empirical absorption correction made, Tmin and Tmax
=
0.802 and 0.338 respectively. GOF = 0.795, final R indices [I>2sI]
R1 = 0.0910, wR2 = 0.1639, R indices (all data) R1 = 0.1872, wR2 =
0.1958. Largest diff. peak and hole 1.347 and -2.118 e A .
We thank the Leverhulme Trust (WBC), The Nuffield Foundation
(IRG) and the University of Leicester for financial support and
Johnson Matthey for a loan of palladium salts.
-3
˚
504 | Dalton Trans., 2011, 40, 495–505
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
37 W. Wei, Y. Qin, M. Luo, P. Xia and M. S. Wong, Organometallics, 2008,
27, 2268–2272.
38 M. Uchiyama, Y. Matsumoto, S. Nakamura, T. Ohwada, N. Kobayashi,
N. Yamashita, A. Matsumiya and T. Sakamoto, J. Am. Chem. Soc.,
2004, 126, 8755–8759.
39 L. Liu, M. Frohn, N. Xi, C. Dominguez, R. Hungate and P. J. Reider,
J. Org. Chem., 2005, 70, 10135–10138.
40 A. R. Chianese, P. T. Bremer, C. Wong and R. J. Reynes,
Organometallics, 2009, 28, 5244–5252.
References
1 T. Ikariya, K. Murata and R. Noyori, Org. Biomol. Chem., 2006, 4,
393–406.
2 H. Gru¨tzmacher, Angew. Chem., Int. Ed., 2008, 47, 1814–1818.
3 T. Ikariya and I. D. Gridnev, Chem. Rec., 2009, 9, 106–123.
4 C. A. Sandoval, T. Ohkuma, N. Utsumi, K. Tsutsumi, K. Murata and
R. Noyori, Chem.–Asian J., 2006, 1, 102–110.
5 R. Noyori, M. Yamakawa and S. Hashiguchi, J. Org. Chem., 2001, 66,
7931–7944.
6 T. Ikariya and A. J. Blacker, Acc. Chem. Res., 2007, 40, 1300–
1308.
41 H. M. J. Wang and I. J. B. Lin, Organometallics, 1998, 17, 972–975.
42 J. M. Hayes, M. Viciano, E. Peris, G. Ujaque and A. Lledo´s,
Organometallics, 2007, 26, 6170–6183.
7 M. Ito, S. Kitahara and T. Ikariya, J. Am. Chem. Soc., 2005, 127,
6172–6173.
8 Y. Kashiwame, S. Kuwata and T. Ikariya, Chem. Eur. J., 2010, 16,
766–770.
43 S. Grundemann, M. Albrecht, J. Loch, J. Faller and R. Crabtree,
Organometallics, 2001, 20, 5485–5488.
44 A. Danopoulos, A. Tulloch and S. Winston, Dalton Trans., 2003, 1009–
1015.
9 K. A. Nolin, J. R. Krumper, M. D. Pluth, R. G. Bergman and F. D.
Toste, J. Am. Chem. Soc., 2007, 129, 14684–96.
10 M. K. Samantaray, M. M. Shaikh and P. Ghosh, Organometallics, 2009,
28, 2267–2275.
11 Y. Boutadla, D. L. Davies, S. A. Macgregor and A. I. Poblador-
Bahamonde, Dalton Trans., 2009, 5820–5831.
12 D. L. Davies, S. M. A. Donald and S. A. Macgregor, J. Am. Chem.
Soc., 2005, 127, 13754–5.
45 J. Houghton, G. Dyson, R. E. Douthwaite, A. C. Whitwood and B. M.
Kariuki, Dalton Trans., 2007, 3065–3073.
46 L. Ma, P. M. Imbesi, J. B. Updegraff, A. D. Hunter and J. D.
Protasiewicz, Inorg. Chem., 2007, 46, 5220–5228.
47 Cambridge Structural Database: F. H. Allen, Acta Crystallogr., Sect.
B: Struct. Sci., 2002, 58, 380–388.
48 D. Pugh and A. A. Danopoulos, Coord. Chem. Rev., 2007, 251, 610–
641.
13 T. Koike and T. Ikariya, Organometallics, 2005, 24, 724–730.
14 S. I. Gorelsky, D. Lapointe and K. Fagnou, J. Am. Chem. Soc., 2008,
130, 10848–9.
15 D. Garc´ıa-Cuadrado, A. A. C. Braga, F. Maseras and A. M.
Echavarren, J. Am. Chem. Soc., 2006, 128, 1066–1067.
16 D. Patel, S. T. Liddle, S. A. Mungur, M. Rodden, A. J. Blake and P. L.
Arnold, Chem. Commun., 2006, 1124–1126.
49 N. Manabe, M. Yasui, H. Nishiyama, S. Shimamoto, N. Matsumura
and F. Iwasaki, Bull. Chem. Soc. Jpn., 1996, 69, 2771–2780.
50 C.-Y. Liao, K.-T. Chan, J.-Y. Zeng, C.-H. Hu, C.-Y. Tu and H. M. Lee,
Organometallics, 2007, 26, 1692–1702.
51 L. Ray, M. M. Shaikh and P. Ghosh, Dalton Trans., 2007, 4546–4555.
52 L. Ray, S. Barman, M. M. Shaikh and P. Ghosh, Chem.–Eur. J., 2008,
14, 6646–6655.
17 K.-J. Haack, S. Hashiguchi, A. Fujii, T. Ikariya and R. Noyori, Angew.
Chem., Int. Ed. Engl., 1997, 36, 285–288.
53 L. Ray, M. M. Shaikh and P. Ghosh, Organometallics, 2007, 26, 958–
964.
18 S. Kuwata and T. Ikariya, Dalton Trans., 2010, 39, 2984–2992.
19 S. Arita, T. Koike, Y. Kayaki and T. Ikariya, Organometallics, 2008, 27,
2795–2802.
54 C. Pubill-Ulldemolins, C. Bo, J. A. Mata and E. Ferna´ndez, Chem.–
Asian J., 2010, 5, 261–264.
55 M. G. Organ, S. C¸ alimsiz, M. Sayah, K. H. Hoi and A. J. Lough,
Angew. Chem. Int. Ed., 2009, 48, 2383–2387.
56 C. J. O’Brien, E. A. B. Kantchev, C. Valente, N. Hadei, G. A. Chass, A.
Lough, A. C. Hopkinson and M. G. Organ, Chem.–Eur. J., 2006, 12,
4743–4748.
20 M. Ito, A. Sakaguchi, C. Kobayashi and T. Ikariya, J. Am. Chem. Soc.,
2007, 129, 290–291.
21 M. Ito, M. Hirakawa, A. Osaku and T. Ikariya, Organometallics, 2003,
22, 4190–4192.
22 M. Ito, Pure Appl. Chem., 2008, 80, 1047–1053.
23 M. Ito, Y. Shibata, A. Watanabe and T. Ikariya, Synlett, 2009, 10,
1621–1626.
24 For an examination of Ru(I) amido-NHC complexes as pre-catalysts for
hydrogenation and transfer hydrogenation see: H. Jong, B. O. Patrick
and M. D. Fryzuk, Can. J. Chem., 2008, 86, 803–810.
25 For a Ru(II) amine-NHC pre-catalyst for transfer hydrogenation see:
W. W. N. O, A. J. Lough and R. H. Morris, Organometallics, 2009, 28,
6755–6761.
57 M. G. Organ, S. Avola, I. Dubovyk, N. Hadei, E. A. B. Kantchev, C. J.
O’Brien and G. Valente, Chem.–Eur. J., 2006, 12, 4749–4755.
58 N. R. Conley, L. A. Labios, D. M. Pearson, C. C. L. McCrory and
R. M. Waymouth, Organometallics, 2007, 26, 5447–5453.
59 S. Kannan, A. J. James and P. R. Sharp, Polyhedron, 2000, 19, 155–
163.
60 R.-D. Schnebeck, E. Freisinger and B. Lippert, Eur. J. Inorg. Chem.,
2000, 1193–1200.
61 R. A. Adrian, G. A. Broker, E. R. T. Tiekink and J. A. Walmsley, Inorg.
Chim. Acta, 2008, 361, 1261–1266.
26 L. P. Spencer and M. D. Fryzuk, J. Organomet. Chem., 2005, 690,
5788–5803.
62 A. D. Getty and K. I. Goldberg, Organometallics, 2001, 20, 2545–2551.
63 G. Pieri, M. Pasquali, P. Leoni and U. Englert, J. Organomet. Chem.,
1995, 491, 27–30.
27 L. P. Spencer, S. Winston and M. D. Fryzuk, Organometallics, 2004,
23, 3372–3374.
28 I. S. Edworthy, M. Rodden, S. A. Mungur, K. M. Davis, A. J. Blake,
C. Wilson, M. Schro¨der and P. L. Arnold, J. Organomet. Chem., 2005,
690, 5710–5719.
29 I. S. Edworthy, A. J. Blake, C. Wilson and P. L. Arnold, Organometallics,
2007, 26, 3684–3689.
64 CCDC 239623.
65 V. V. Grushin and H. Alper, Organometallics, 1993, 12, 1890–1901.
66 A. Fujii, E. Hagiwara and M. Sodeoka, J. Am. Chem. Soc., 1999, 121,
5450–5458.
67 L. D´ıez, P. Espinet and J. A. Miguel, J. Chem. Soc., Dalton Trans., 2001,
30 M. Moser, B. Wucher, D. Kunz and F. Rominger, Organometallics,
2007, 26, 1024–1030.
1189–1195.
68 D. Nama, D. Schott, P. S. Pregosin, L. F. Veiros and M. J. Calhorda,
Organometallics, 2006, 25, 4596–4604.
69 A. Hadzovic and D. Song, Inorg. Chem., 2008, 47, 12010–12017.
70 F. Basolo, J. Chatt, H. B. Gray, R. G. Pearson and B. L. Shaw, J. Chem.
Soc., 1961, 2207–2215.
71 A. Peloso, Coord. Chem. Rev., 1973, 10, 123–181.
72 J. J. Pesek and W. R. Mason, Inorg. Chem., 1983, 22, 2958–2959.
73 L. Duhamel and J.-C. Plaquevent, J. Organomet. Chem., 1993, 448, 1–3.
74 H. Clark and L. Manzer, J. Organomet. Chem., 1973, 59, 411–428.
75 G. M. Sheldrick, SHELXTL Version 6.10, Bruker AXS, Madison, WI,
USA, 2000.
31 P. L. Arnold, J. McMaster and S. T. Liddle, Chem. Commun., 2009,
818–820.
32 P. L. Arnold and S. T. Liddle, C. R. Chim., 2008, 11, 603–611.
33 P. L. Arnold, I. S. Edworthy, C. D. Carmichael, A. J. Blake and C.
Wilson, Dalton Trans., 2008, 3739–3746.
34 S. T. Liddle, I. S. Edworthy and P. L. Arnold, Chem. Soc. Rev., 2007,
36, 1732–1744.
35 P. L. Arnold, S. Mungur, A. J. Blake and C. Wilson, Angew. Chem., Int.
Ed., 2003, 42, 5981–5984.
36 R. E. Douthwaite, J. Houghton and B. Kariuki, Chem. Commun., 2004,
698–699.
76 A. L. Spek, Acta Cryst., 1990, A46, C34.
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