Synthesis of N-heterocyclic carbene palladium(II) bis-phosphine complexes and their decomposition in the presence of aryl halides

Article abstract of DOI:10.1039/b706053j

Methylpalladium(ii) carbene complexes of the type [Pd(NHC)Me(P-P)]BF ₄ (NHC = N-heterocyclic carbene, P-P = chelating phosphine) have been synthesised, the complex [Pd(tmiy)Me(dcype)]BF₄ (tmiy = 1,3,4,5-tetramethylimidazol-2-ylidene, dcype = 1,2-bis(dicyclohexylphosphino) ethane) being characterised crystallographically. Complexes bearing the tmiy ligands were shown to decompose in an analogous manner to complexes bearing monodentate phosphine ligands, with the rate of decomposition being nominally linked to the size of the chelate ring. The decomposition of these complexes in the presence of aryl halides - expected to yield Pd(Ar)X(P-P) - was studied and shown instead to yield PdX₂(P-P) and [Pd(tmiy)X(P-P)]BF₄. Additionally, Pd(Me)X(P-P) and Pd(Ar)X(P-P) were observed in some cases. Intermolecular cross-over reactions between the starting complex and Pd(Ar)X(P-P) were found to be the source of these unexpected products. The Royal Society of Chemistry 2007.

Full text of DOI:10.1039/b706053j

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Synthesis of N-heterocyclic carbene palladium(II) bis-phosphine complexes
and their decomposition in the presence of aryl halides†‡
a
Alison M. Magill,§ Brian F. Yates,a Kingsley J. Cavell,*b Brian W. Skeltonc and Allan H. Whitec
Received 26th April 2007, Accepted 31st May 2007
First published as an Advance Article on the web 26th June 2007
DOI: 10.1039/b706053j
Methylpalladium(II) carbene complexes of the type [Pd(NHC)Me(P–P)]BF4 (NHC = N-heterocyclic
carbene, P–P = chelating phosphine) have been synthesised, the complex [Pd(tmiy)Me(dcype)]BF4
(tmiy = 1,3,4,5-tetramethylimidazol-2-ylidene, dcype = 1,2-bis(dicyclohexylphosphino)ethane) being
characterised crystallographically. Complexes bearing the tmiy ligands were shown to decompose in an
analogous manner to complexes bearing monodentate phosphine ligands, with the rate of
decomposition being nominally linked to the size of the chelate ring. The decomposition of these
complexes in the presence of aryl halides—expected to yield Pd(Ar)X(P–P)—was studied and shown
instead to yield PdX2(P–P) and [Pd(tmiy)X(P–P)]BF4. Additionally, Pd(Me)X(P–P) and Pd(Ar)X(P–P)
were observed in some cases. Intermolecular cross-over reactions between the starting complex and
Pd(Ar)X(P–P) were found to be the source of these unexpected products.
Introduction
The reductive elimination of 2-alkylimidazolium salts from alkyl-
palladium carbene complexes is now recognised as a common de-
composition mode for complexes of this type.1–4 Previous studies4,5
of this decomposition reaction in which phosphines are present
as ancillary ligands (i.e. [Pd(carbene)Me(PR3)2]BF4) have been,
in all but one case,4 limited to monodentate phosphines. These
studies have shown that the decomposition yields the expected
products, namely 2-methylimidazolium tetrafluoroborate salts
and palladium(0) phosphine complexes (Pd(PR3)2).
Zero-valent, two-coordinate, bis-phosphine complexes of group
10 metals bearing monodentate phosphines are known to be
less reactive than the analogous compounds bearing chelating
bidentate ligands. Thus, Pt(PCy3)2 is inert to oxidative addition
by non-activated C–H bonds,6 but the chelated platinum frag-
ment Pt(dcype) (dcype = 1,2-bis(dicyclohexylphosphino)ethane,
formed via reductive elimination of neopentane from cis-
[(dcype)hydridoneopentylplatinum(II)]7 reacts with the non-
activated carbon–hydrogen bonds in benzene to yield cis-
[(dcype)hydridophenylplatinum(II)].8,9
This bending has a dramatic effect on both the shape and energy of
the frontier orbitals of the ML2 complex. In the bent complex, the
HOMO is an “in-L–M–L-plane” d-orbital that contains a single
lone pair of electrons10 (in fact these species are isolobal with
methylene).11 The orbital extends into space away from the L–
M–L chelate ring, and is not shielded by the phosphine ligands.10
In contrast, the HOMO of a linear ML2 complex is sheltered
between the two ligands.10 This change in orbital shape was the
original reason given for the higher reactivity.6
There have been several attempts made to synthesise Pd0L2
compounds containing chelating phosphines. The photolysis
of (dcype)Pd(oxalate) gives high yields of the dinuclear palla-
dium compound Pd2(l-dcype)2.12,13 In solution, this compound
readily dissociates to form the reactive monomer Pd(dcype),
and the subsequent reactivity of the system is dominated
by this species, e.g. reaction with PhX (X = Br, I) to
yield the monomeric Pd(Ph)X(dcype),12 and with diphenyldis-
elenide to generate Pd(SePh)2(dcype).13 Similar reactivity has
been reported for the compound Pd2(l-dippe)2 (dippe = 1,2-
bis(diisopropylphosphino)ethane).14
The reductive elimination of RCN (R = CH2Si(CH3)3) from
Pd(dppe)(R)(CN) in the presence of excess dppe yields the complex
Pd0(dppe)2.15 The authors of this study made no attempt to
carry out oxidative addition reactions using the reactive Pd(dppe)
fragment that is presumably generated during the course of the
reaction.
The compound [Pd(dmiy)Me(dppp)]BF4 (dmiy = 1,3-dimethyl-
imidazol-2-ylidene; dppp = 1,3-bis(diphenylphosphino)propane)
is stable at room temperature in solution for prolonged periods,16
and is significantly more stable than analogous compounds
The high reactivity of these complexes is usually attributed to
the fact that the chelate ring dictates a bent P–Pt–P configuration.
aSchool of Chemistry, University of Tasmania, Private Bag 75, Hobart,
Tasmania, Australia 7001. E-mail: Brian.Yates@utas.edu.au
bSchool of Chemistry, Cardiff University, P.O. Box 912, Cardiff, UK CF24
3TB. E-mail: cavellkj@cardiff.ac.uk; Fax: +44 (0)29 2087 5899; Tel: +44
(0)29 2087 5899
cChemistry M313, School of Biomolecular, Biomedical and Chemical
Sciences, University of Western Australia, Crawley, W. A., Australia 6009
† CCDC reference numbers 645468 and 645600. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b706053j
‡ Electronic supplementary information (ESI) available: Detailed syn-
thesis and characterisation of [Pd(tmiy)X(P–P)]BF4, PdX2(P–P) and
Pd(Me)X(P–P) complexes; crystal structure of Pd(dppp)I2. See DOI:
10.1039/b706053j
§ Present address: School of Chemistry, The University of New South
Wales, Sydney, Australia 2052.
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Table 1 Selected NMR data for complexes 1–3a
containing monodentate phosphines which commonly decompose
within several hours at room temperature.4 It would seem reason-
able to assume that the reductive elimination of 2-methylimida-
zolium salts from compounds of the type [Pd(carbene)Me(P–
P)]BF4 (P–P = chelating phosphine) would yield the reactive
fragment Pd(P–P) which could be trapped by further reaction with,
for example, an aryl halide to yield a Pd(Ar)X(P–P) compound.
Herein the synthesis of a number of [Pd(carbene)Me(P–P)]BF4
compounds and their subsequent decomposition in the presence
of several trapping agents is described.
Pd–CH3
Pd–CH3
NCN
Pd–P
1a
1b
2a
2b
3a
3b
3c
3d
0.35
0.35
0.10
−3.46
−3.24
−6.89
−6.64
0.66
175.3
176.3
178.6
181.1
175.3
179.5b
182.4
186.0
50.40
39.93
40.44
61.32
62.33
−0.67
−0.45
−6.12
−9.18
51.07
67.10
67.92
11.96
12.24
13.78
15.08
0.06
0.14
0.12b
0.00
0.70b
9.16
−0.04
8.62
a Spectra recorded in CDCl3 or CD2Cl2. b These shifts are taken from
ref. 16.
Results and discussion
The reaction of the chelating phosphines 1,2-bis(diphenylphos-
phino)ethane (dppe), 1,2-bis(dicyclohexylphosphino)ethane
(dcype) or 1,3-bis(diphenylphosphino)propane (dppp) with
dimeric mono-carbene palladium complexes in the presence of
AgBF4 furnishes the desired complexes in good yield (Scheme 1).
In the case of 1a and 2a a highly coloured by-product is formed
that may be removed by treatment with activated charcoal.
coupled with a large down-field shift for the Pd–CH3 signal in the
1
13C{ H} NMR spectrum (0.66 ppm (3a) cf. 8.62 ppm (3d)).
Crystals of 2a suitable for X-ray structure determination were
grown by solvent diffusion of diethyl ether into a DCM solution.
This analysis (Fig. 1, Table 2) shows that the Pd centre in 2a
exhibits a distorted square planar core geometry, with the Ctmiy
–
Pd–Cmethyl bond angle (84.90(8)◦) being significantly smaller than
the ideal 90◦. Coupled with this is an increase in the P(1)–Pd–Ctmiy
angle (98.02(5)◦). The di-phosphine bite angle (86.17(2)◦) is typical
of palladium complexes bearing the dcype ligand. The distortions
from ideal square planar metal coordination geometry presumably
arise to minimise steric interaction between the cyclohexyl groups
of the phosphine ligand and the methyl groups of the carbene
ligand, in addition to accommodating the acute bite angle of the
di-phosphorus ligand.
Scheme 1 i. 0.5 equiv. Ag2O, DCM, r.t. 1 h. ii. Pd(Me)Cl(COD), 0 ◦C,
1 h. iii. Pd(Me)Cl(COD), THF, 0 ◦C, 20 min. iv. P–P, AgBF4, 0 ◦C, 2 h.
1
1
Complexes 1–3 were characterised by H and 31P{ H} NMR
spectroscopy, mass spectrometry and either microanalysis or high-
resolution mass spectrometry. Compound 2a was also charac-
terised crystallographically. Selected NMR data are shown in
1
Table 1. The 31P{ H} chemical shift of 3b has been previously
reported as d 58.3 and 45.7 ppm.16 A brief survey of the literature
indicates that palladium(II) complexes of dppp typically resonate
1
between 25 and −10 ppm in the 31P{ H} NMR spectrum.17,18 This,
coupled with the similar shifts for complexes 3a–d, suggests that
the previously reported chemical shift of 3b is incorrectly reported.
The chemical shifts for complexes 1a–b and 2a–b are reasonably
consistent within each group. This is not surprising, given the
similarity of the tmiy and dmiy ligands. The chemical shifts within
group 3 show dramatic changes upon moving from the simple
methyl-substituted ligands (tmiy 3a, dmiy 3b) to the much larger
Fig. 1 Molecular projection of 2a normal to the coordination plane
showing the atom labelling scheme. Thermal ellipsoids are shown at the
˚
50% probability level, while hydrogen atoms have arbitrary radii of 0.1 A.
1
aryl-substituted carbenes (IMes 3c, IDipp, 3d). In the 31P{ H}
The Pd–Ctmiy bond distance (2.061(2) A) is within the typical
˚
1,16,19
˚
NMR spectrum, there is a large high-field shift of one phosphorus
range reported for Pd(II) carbene complexes (1.96-2.09 A),
atom upon moving from 3a (−0.67 ppm) to 3d (−9.18 ppm),
albeit towards the higher end of the range. Pd–Ccarbene bond lengths
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Table 2 Selected bond lengths, angles and interplane angles for 2a
both complexes decompose to yield 1,2,3-trimethylimidazolium
tetrafluoroborate and palladium black. The decomposition of 3b
is considerably faster than for 1b, with all resonances attributable
to 3b being essentially absent after 6 h; in contrast large quantities
of 1b remain in the reaction mixture after this time. An increase
in the rate of reductive elimination reactions is known to occur
upon widening of the bite-angle of the P–P chelate.15,31,32 Thus, on
moving from the smaller bite angle of dppe to dppp a qualitatively
dramatic rise in the rate of decomposition is observed.
˚
Bond lengths/A
Pd–C(1)
Pd–P(1)
C(1)–N(2)
2.061(2)
2.3369(5)
1.353(2)
Pd–C(0)
Pd–P(2)
C(1)–N(5)
2.147(2)
2.2864(5)
1.343(3)
Bond angles/◦
C(1)–Pd–P(2)
C(1)–Pd–C(0)
P(1)–Pd–P(2)
175.12(5)
84.90(8)
86.17(2)
P(1)–Pd–C(0) 176.24(7)
C(1)–Pd–P(1)
C(0)–Pd–P(2)
98.02(5)
91.02(6)
It was initially envisaged that, in the presence of excess aryl
halide, complexes 1–3 would decompose via reductive elimination
to give products as shown in Scheme 2.
˚
Planes/A
2
˚
I: P(1,2), C(0,1)
v = 2361, d Pd = 0.007(1) A
2
˚
II: N(2,5), C(1,3,4) v = 18, d Pd = 0.110(3) A
Interplane angles/◦
I/II
80.174(62)
˚
of this magnitude (i.e. > 2.05 A) are most commonly found for
chelating carbene complexes (e.g. Pd(tBuCCeth)Me2, which has Pd–
20
tBuCCeth
=
˚
Ccarbene bond distances of 2.070(3) and 2.089(3) A
(
1,2-ethylene-3,3ꢀ-di-tert-butyldiimidazol-2,2ꢀ-diylidene)).
The plane of the carbene ligand is twisted by 80.17(6)◦ relative to
the plane defined by P(1), P(2), C(1), C(0). This is typical behaviour
for carbene ligands, which adopt a twisted orientation to minimise
steric interactions with other ligands in the metal coordination
sphere.21,22
Scheme 2 Possible mode of decomposition for methylpalladium carbene
complexes of chelating phosphines in the presence of aryl halides. P–P =
dppe, dcype, dppp.
˚
˚
The 0.05 A difference between the Pd–P(1) (2.3369(5) A) and
˚
Pd–P(2) (2.2864(5) A) bond lengths demonstrates that the methyl
ligand exerts a stronger trans influence than the tmiy ligand. This
observation is consistent with the findings of previous studies.23
Both Pd–P bond lengths are comparable to those found in other
The decomposition of 2a in the presence of 4-iodotoluene or 4-
iodoanisole was studied in THF-d8. Complex 2a is soluble in this
solvent only at elevated temperatures. In addition, electrospray
ionisation mass spectroscopy (ESI-MS) and GC-MS analyses of
˚
palladium(II) complexes of dcype, e.g. Pd(dcype)Cl2 (2.233(1) A,
8
24
˚
˚
˚
2.232(1) A), Pd(dcype)(SiHMe2)2 (2.3518(7) A, 2.3614(8) A),
1
the crude reaction mixture was undertaken. By 31P{ H} NMR
25
˚
˚
and Pd(dcype)Cl(C(O)CMe3) (2.366(1) A, 2.254(1) A).
spectroscopy, both the decomposition reactions were found to
yield two phosphorus-containing products, with one identified
as the known, but unexpected, complex PdI2(dcype).12 ESI-MS
showed the presence of the [Pd(tmiy)I(dcype)]+ ion (correct isotope
pattern) in the reaction mixture, thus an independent synthesis of
The Cambridge Crystallographic Database26 suggests that 2a is
the first methylpalladium complex bearing the dcype ligand to be
crystallographically characterised. As such, direct comparison of
Pd–CH3 bond lengths with analogous complexes is not possible,
although palladium–methyl complexes bearing the dppe and dmpe
ligands are known. Based on comparisons with methylpalladium
complexes bearing other chelating phosphines,27 it may be seen
1
[Pd(tmiy)I(dcype)]BF4 was undertaken (Scheme 3). The 31P{ H}
NMR spectrum of this complex was identical with that observed
for the second decomposition product.
˚
that the Pd–CH3 bond length in 2a (2.147(2) A) is quite long (cf.
28
29
˚
˚
Pd(dmpe)Me2 (2.087(4) A), Pd(dmpe)Me(OPh) (2.101(9) A)
30
˚
and [Pd(dmpe)Me(NH3)]PF6 (2.081(4) A). ) This is presumably
due to increased electron density on the metal centre, arising
from donation by the carbene ligand, leading to a decrease in
r-donation from the methyl group. This characteristic has been
observed previously.23
Scheme
3
Synthesis of [Pd(tmiy)I(dcype)]BF4. i. Pd(PhCN)2Cl2.
Decomposition of complexes
ii. AgBF4, dcype. iii. NaI, acetone.
The previous investigation of the decomposition of methylpalla-
dium carbene complexes bearing bidentate phosphines has shown
that these complexes do not decompose at room temperature, even
In addition to the cationic palladium complex, 1,2,3,
4,5-pentamethylimidazolium and 1,3,4,5-tetramethyl-2-phenyl-
imidazolium were observed by ESI-MS, whilst GC-MS revealed
1
after 24 h.4 The decomposition of 1b and 3b was studied by H
◦
NMR spectroscopy in acetonitrile-d3 at 65 C; it was found that
3400 | Dalton Trans., 2007, 3398–3406
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the presence of biaryls (e.g. 4,4ꢀ-bitolyl in the case of 4-
iodotoluene), and confirmed the presence of species arising from
methyl–aryl coupling.
acetylphenyl)PdBr(dppp) in good yields confirmed that our initial
premise of this study, relating to the formation of the reactive
fragment [Pd(P–P)], was sound.
1,2,3,4,5-Pentamethylimidazolium is the expected product of
the initial reductive elimination from 1a. However the presence
of toluene and 1,3,4,5-tetramethyl-2-phenylimidazolium as by-
products is surprising, and suggests one of two possibilities:
firstly, that rather than by the generation of a Pd(0) species and
subsequent oxidative addition of the aryl halide, the reaction
is proceeding via a Pd(IV) intermediate resulting from oxidative
addition of the aryl halide to the initial Pd(II) species followed by
reductive elimination to regenerate Pd(II) species, or, secondly,
that there are intermolecular exchange reactions occurring
(vide infra).
In contrast, the reaction of 3a with 4-bromotoluene yielded
none of the expected (4-methylphenyl)PdBr(dppp); instead, the
major product was identified as [Pd(tmiy)Br(dppp)]BF4, while
Pd(dppp)Br2 and several unidentified species were observed in
minor quantities.
To determine whether the products [Pd(tmiy)X(P–P)]BF4 and
Pd(Me)X(P–P) arise from an intermolecular rearrangement or
possibly from an intermediate Pd(IV) species, the reaction between
compound 1a and Pd(Ph)I(dppe) was studied in the presence
of MAH (maleic anhydride).35 The reaction between a 1 : 1
mixture of 1a and Pd(Ph)I(dppe) was performed in acetone-d6 and
1
The formation of unexpected by-products in the reactions of 3a
with aryl halides prompted further investigation into the generality
of the reaction. The reaction of 3a with phenyl iodide or 5-iodo-
m-xylene in acetone-d6 was studied (Scheme 4). In the former case,
while the reaction gave Pd(Ph)I(dppp)18,31,33 after 4 h at 60 ◦C, the
major phosphorus-containing product after 11 h was Pd(dppp)I2,
followed by 31P{ H} NMR spectroscopy. As the latter complex is
only moderately soluble in acetone-d6 at room temperature, the
mixture was gently warmed to 45 ◦C for 5 min before any spectra
1
were recorded. Surprisingly, the first 31P{ H} NMR spectrum run
after this time showed complete consumption of Pd(Ph)I(dppe),
coupled with the formation of [Pd(tmiy)I(dppe)]+ and Pd(Me)-
I(dppe). No formation of MAH complexes was observed.
This result demonstrates that Pd(II) carbene complexes may
undergo intermolecular rearrangements of the type shown be-
low in Scheme 5. Two different reaction pathways are shown.
Reaction A shows the cross-over reaction which generates the
ionic [Pd(tmiy)I(P–P)]+ complex, together with Pd(Ph)Me(P–
P), by exchange of the methyl and iodide ligands. Complexes
of the latter type (where P–P = dppp) have been shown to
reductively eliminate toluene.31 Reaction B generates Pd(Me)I(P–
P) and [Pd(tmiy)Ph(P–P)]+ by exchange of the methyl and phenyl
ligands. The reductive elimination of arylimidazolium salts from
palladium carbene complexes is a known reaction,1,3,22 while
theoretical calculations suggest this type of decomposition is a
more facile reaction than the elimination of alkyl imidazolium
salts from the analogous complexes.32 In this case, the expected
product of reductive elimination would be the 2-phenyl-1,3,4,5-
tetramethylimidazolium ion.
1
as shown by the presence of a singlet at d 1.76 in the 31P{ H}
NMR spectrum. This final complex was previously unreported in
the literature, and an independent synthesis was undertaken (see
ESI‡ for further details, including crystal structure).
Scheme 4 Product distribution for the reaction of 3a with aryl iodides
(P–P = dppp).
In order to ascertain if this unexpected reactivity was restricted
to aryl iodides, the reaction of 3a with 4-bromoacetophenone was
studied at 65 ◦C in acetonitrile-d3. The reaction was relatively
clean with (4-acetylphenyl)PdBr(dppp) being formed as the major
product, together with minor amounts of other phosphorus-
1
containing products later identified as Pd(dppp)Br2 (31P{ H}
Scheme 5 Intermolecular rearrangements during the reaction of 1a with
Pd(Ph)I(P–P) (P–P = dppe).
NMR: d 9.85 ppm),34 Pd(Me)Br(dppp) (d 26.2, −5.2 ppm) and
[Pd(tmiy)Br(dppp)]BF4 (d 10.67, −4.08 ppm) were also observed
by 31P{ H} NMR spectroscopy. The two latter complexes were
In a similar reaction, the intermolecular rearrangement between
2a and Pd(Ph)I(dppe) was studied. This reaction was found to give
twomajorphosphorus-containingproducts:[Pd(tmiy)I(dcype)]BF4
1
previously unreported in the literature, and independent syntheses
were undertaken to confirm their identities. The formation of (4-
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and Pd(Me)I(dppe), suggesting that the carbene remains tightly
bound to the metal centre and does not participate in the
cross-over reaction. Given this, a proposal for the mechanism of
the reaction of [Pd(carbene)Me(P–P)]+-type complexes with aryl
halides may now be made (Scheme 6).
of which (VII and VIII) are commonly observed during or upon
completion of the reactions. Complex VI would be expected to
reductively eliminate ArMe compounds, while IX would eliminate
2-arylimidazolium salts. These two compounds are also commonly
noted upon completion of the reactions.
The starting complex I decomposes on warming to yield the
reactive palladium(0) fragment II. This then undergoes oxidative
addition with the aryl halide to yield the Pd(Ar)X(P–P) complex
III. An intermolecular exchange between two molecules of III
would then generate complexes IV and V, with complex V
undergoing reductive elimination to yield a biaryl species, and
reforming II.
It may be expected then, that the presence of 2-arylimidazolium
salts would always be coupled with the presence of VIII, but
this is not the case. It is possible that VIII undergoes another
intermolecular exchange reaction with III to generate PdX2(P–
P) and Pd(Ar)Me(P–P). Once again, the latter would undergo
reductive elimination of ArMe, whilst the former compound is
one of the observed reaction products. Similar reactions have
been reported previously.36 Clearly, this cross-over reaction is not
favourable in all cases, particularly when aryl bromides are used.
Compound III also undergoes exchange reactions with I, as was
shown previously. These reactions generate complexes VI–IX, two
Scheme 6 Proposed mechanism for the reaction of [Pd(NHC)Me(P–P)]BF4 with aryl halides. Counter-ions have been omitted for clarity. Shaded
compounds are those that were observed experimentally.
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charcoal, which was removed by filtration with a filter cannula. The
clear, colourless filtrate was concentrated in vacuo to approx. 2 mL,
layered with Et2O and placed at −20◦ for 2 d. The mother-liquor
was decanted and the off-white crystalline product was dried
in vacuo. 1H NMR indicated the presence of ∼0.5 Et2O per product
Conclusion
Methylpalladium(II) complexes bearing N-heterocyclic carbenes
and chelating phosphines have been synthesised in moderate to
excellent yields. Initial studies regarding the stability of these
complexes showed that they decomposed at elevated temperatures
to yield the expected 2-methylimidazolium salts, free phosphine
and Pd(0). The rate of decomposition could be nominally linked
to the size of the phosphine chelate ring.
The chelate complexes could be used to generate reactive
Pd(0) fragments by reductive elimination of 2-methylimidazolium
salts. In the presence of aryl halides, these reactive fragments
undergo oxidative addition to yield Pd(II) complexes of the type
Pd(Ar)X(P–P), however at the elevated temperatures required for
decomposition, these complexes undergo further intermolecular
cross-over reactions.
These cross-over reactions may occur between two molecules of
the arylpalladium species, generating PdX2(P–P) and PdAr2(P–
P), with the latter undergoing reductive elimination to yield
biaryl compounds. Cross-over reactions may also occur between
the arylhalopalladium(II) complexes and the methylpalladium(II)
carbene complexes, which yield a number of products, including
those arising from methyl–aryl coupling. It was shown that the
carbene ligand does not move between metal centres, rather that
the methyl group is transferred, while both the halide and the
aryl group may be transferred from Pd(Ar)X(P–P). The degrees
to which these cross-over reactions occurred appeared highly
dependent on the nature of the aryl halide, with aryl bromides
only occasionally yielding the desired arylhalogenatopalladium(II)
complexes.
1
molecule. Yield: 0.13 g (76%). H NMR (CD2Cl2, 300 MHz): d
7.7–7.2 (m, 20H, ArH), 3.25 (s, 6H, N–CH3), 2.4 (m, 4H, PCH2),
1
2.05 (s, 6H, C–CH3), 0.355 (t, 3H, Pd–CH3, J = 6.6 Hz). 31P{ H}
NMR (CD2Cl2, 121.4 MHz): d 50.40 (d, J = 22.6 Hz), 39.93
1
(d, J = 22.6 Hz). 13C{ H} NMR (CD2Cl2, 75 MHz): d 175.29
(dd, J
= 137.3 Hz, J
= 15.7 Hz) 133.4 (d, J = 11.4 Hz),
CP
CP
132.6 (d, J = 12.0 Hz), 131.9 (d, J = 2.9 Hz), 131.6 (d, J =
1.7 Hz), 131.4 (s), 129.8 (s), 129.6 (d, J = 10.8 Hz), 129.4 (d,
J = 9.7 Hz), 129.2 (s), 126.7 (d, J = 3.4 Hz), 35.03 (s, N–CH3),
27.59 (dd, J
= 29.2 Hz, J
= 20.0 Hz, PCH2), 25.82 (dd, J
CP
CP
= 26.4 Hz, J = 14.3 Hz, PCH2), 9.01 (s, C–CH3), −3.46 (d,
CP
CP
J = 92.5 Hz, Pd–CH3). MS (LSI-MS) m/z (relative intensity): 643
(10; M+), 139 (100; ylidene + CH3). HR-MS for C34H39N2104PdP2:
calc, 641.16288; obsd, 641.16252.
[Pd(dmiy)Me(dppe)]BF4 (1b)
To a −20 ◦C suspension of [Pd(dmiy)Me(l-Cl)]2 (0.1241 g,
0.245 mmol) in DCM (2 mL) was added a solution of dppe
(0.2003 g, 0.5035 mmol) in DCM (3 mL). This mixture was stirred
at −20 ◦C for 30 min, before being transferred into a solution
of AgBF4 (0.110 g, 0.565 mmol) in DCM (3 mL). The resultant
R
mixture was stirred for 3 h before being filtered through Celiteꢀ.
The filtrate was concentrated to dryness in vacuo and the residue
recrystallised from DCM–Et2O (1 mL : 15 mL) to give a pink–
brown oil. The mother-liquor was removed and the oil triturated
with DCM–THF (1 mL : 5 mL) to give a pale pink powder. This
was washed with THF–Et2O and Et2O and dried in vacuo to yield
a very pale pink powder. Yield: 0.26 g (76%). Anal. Calc. for
C32H35N2PdP2BF4: C, 54.69; H, 5.02; N, 3.99. Found: C, 54.66; H,
5.10; N, 4.05. MS (LSI-MS) m/z (relative intensity): 615 (100; M+),
291 (28). 1H NMR (CD2Cl2, 200 MHz): d 7.7–7.2 (m, 20H, ArH),
This study demonstrates that the desired coordinatively unsatu-
rated Pd0(P–P) species is generated. However, for this approach
to be generally useful, cross-over reactions would need to be
controlled or preferably prevented altogether.
Experimental
=
7.03 (s, 2H, HC CH), 3.40 (s, 6H, N–CH3), 2.7–2.2 (m, 4H,
Unless otherwise stated, all reactions were carried out under
an atmosphere of dry dinitrogen or argon using standard
Schlenk techniques. Solvents were purified and dried by the
usual methods.37 [Pd(NHC)Me(l-Cl)]2 complexes were prepared
1
PCH2CH2P), 0.35 (t, 3H, J = 6.5 Hz, Pd–CH3). 13C{ H} NMR
(CD2Cl2, 75 MHz): d 176.34 (dd, J = 135.2, 16.1 Hz) 133.8 (d,
J = 11.4 Hz), 133.2 (d, J = 13.6 Hz), 131.7 (s), 131.2 (s), 130.9 (s),
129.9 (s), 129.6 (d, J = 12.4 Hz), 129.1 (d, J = 9.1 Hz), 128.5 (s),
125.9 (s), 122.4 (s), 36.12 (s, N–CH3), 27.37 (dd, J CP = 28.3 Hz, J
= 18.4 Hz, PCH2), 26.74 (dd, J = 25.1 Hz, J = 13.7 Hz,
1
1
as described previously.5 1H, 13C{ H} and 31P{ H} NMR were run
on Varian Gemini 200, Varian Mercury Plus 300 and Varian Unity
Inova 400 instruments at ambient temperature and referenced
CP
CP
CP
PCH2), −3.24 (d, J = 91.6 Hz, Pd–CH3). 31P{ H} NMR (CDCl3,
1
1
1
1
to residual solvent signals for H and 13C{ H}. 31P{ H} NMR
spectra were referenced to external H3PO4. Elemental analyses
(Carlo Erba EA1108 or ThermoFinnigan Flash 1112 Series EA)
and Liquid Secondary Ion Mass Spectrometry (LSI-MS, Kratos
Concept ISQ) were performed by the Central Science Laboratory,
University of Tasmania.
161.8 MHz): d 51.1 (d, J = 23.6 Hz), 40.4 (d, J = 23.6 Hz).
[Pd(tmiy)Me(dcype)]BF4 (2a)
This was prepared as described for 1a, from [Pd(tmiy)Me(l-Cl)]2
(0.0969 g, 0.172 mmol), dcype (0.1459 g, 0.345 mmol) and AgBF4
1
(0.069 g, 0.354 mmol) in DCM (3 mL). Yield: 0.23 g (88%). H
[Pd(tmiy)Me(dppe)]BF4 (1a)
NMR (CD2Cl2, 300 MHz): d 3.61 (s, 6H, N–CH3), 2.2–2.0 (m, 4H,
PCH2CH2P), 2.18 (s, 6H, C–CH3), 2.0–1.6 (br m, 22H, CyH), 1.4–
1.1 (m, 20H, CyH), 0.8–0.6 (br, 2H, CyH), 0.10 (t, 3H, Pd–CH3,
[Pd(tmiy)Me(l-Cl)]2 (0.0698 g, 0.124 mmol) and dppe (0.0995 g,
0.249 mmol) were taken up in DCM (2.5 mL). This mixture was
cooled to 0 ◦C before being transferred into a cold solution of
AgBF4 (0.050 g, 0.257 mmol) in DCM (2.5 mL). The reaction
mixture was stirred for 50 min before being filtered through
1
J = 5.7 Hz). 31P{ H} NMR (CD2Cl2, 121.4 MHz): d 67.1 (d, J =
16.5 Hz), 61.3 (d, J = 16.5 Hz). MS (ESI) m/z (intensity): 687.1
(15%), 667.0 (100%) [M]+. X-Ray quality crystals were grown by
solvent diffusion of Et2O into a DCM solution of the product.
R
Celiteꢀ. The sepia-coloured filtrate was treated with activated
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 3398–3406 | 3403
©

View Article Online
1
spectrum.16 31P{ H} NMR (CD2Cl2, 121.3 MHz): d 12.24 (d, J =
[Pd(dmiy)Me(dcype)]BF4 (2b)
49 Hz), −0.45 (d, J = 49 Hz).
This was prepared as described for 1b, from [Pd(dmiy)Me(l-Cl)]2
(0.0772 g, 0.153 mmol), dcype (0.1291 g, 0.305 mmol) and AgBF4
(0.062 g, 0.318 mmol) to give an off-white powder. Yield: 0.15 g
(68%). Anal. Calc. for C32H59N2PdP2BF4: C, 52.87; H, 8.18; N,
3.85. Found: C, 52.52; H, 8.33; N, 4.00. MS (ESI) m/z (intensity):
663.2 (15%), 643.0 (30%), 639.0 (100%) [M+], 624.2 (20%), 563.1
(13%), 527.1 (23%), 458.9 (25%), 377.0 (12%). 1H NMR (CDCl3,
[Pd(IMes)Me(dppp)]BF4 (3c)
To a 0 ◦C solution of [Pd(IMes)Me(l-Cl)]2 (0.1096 g, 0.119 mmol)
in DCM (8 mL) was added dppp (0.0984 g, 0.239 mmol) in DCM
(3 mL). The phosphine was rinsed over with DCM (2 mL), and the
reaction mixture stirred at 0 ◦C for 20 min. After this time the clear
solution was transferred into a cold suspension of AgBF4 (0.046 g,
0.236 mmol) in DCM (3 mL). After stirring for 2.5 h, the mixture
was filtered through Celiteꢀ and the volatiles concentrated in vacuo
to approx. 4 mL. Ether (12 mL) was added, and the mixture stored
at −20 ◦C overnight to complete precipitation of the product. The
mother liquor was decanted and the product dried in vacuo to
=
200 MHz): d 7.24 (s, 2H, HC CH), 3.76 (s, 6H, N–CH3), 2.2–1.6
(br m, 28H, PCH2CH2P + CyH), 1.5–1.1 (br m, 18H, CyH), 0.9–
0.6 (br, 2H CyH), 0.057 (t, 3H, J = 5.8 Hz, Pd–CH3). 31P{ H}
1
R
NMR (CDCl3, 161.8 MHz): d 67.9 (d, J = 16.0 Hz), 62.3 (d, J =
1
16.0 Hz). 13C{ H} NMR (CDCl3, 75 MHz): d 181.10 (dd, J =
=
132.0, 13.7 Hz, NCN), 123.86 (d, J = 3.4 Hz, HC CH), 37.89,
34.77, 34.58, 34.47, 34.37, 29.77 (d, J = 2.9 Hz), 29.13, 28.05,
27.4–26.7 (m), 26.18, 24.18–23.61 (m, PCH2CH2P), 20.18–19.73
(m, PCH2CH2P), −6.64 (dd, J = 89.7, 4.0 Hz, Pd–CH3).
1
yield a white powder. Yield: 0.17 g (75%). H NMR (CD2Cl2,
400 MHz): d 7.4–6.8 (m, 26H, ArH + MesH + HC CH), 2.40
(s, 6H, Mes–CH3), 2.32 (m, 2H, PCH2), 2.21 (s, 6H, Mes–CH3),
=
2.03 (m, 2H, PCH2), 1.75 (br m, 2H, PCH2CH2CH2P), 1.74 (s,
1
6H, Mes–CH3), 0.00 (t, 3H, Pd–CH3, J = 6.8 Hz). 31P{ H} NMR
[Pd(tmiy)Me(dppp)]BF4 (3a)
(CDCl3, 161.8 MHz): d 13.8 (J = 51.1 Hz), −6.1 (J = 51.1 Hz).
13C{ H} NMR (CD2Cl2, 75 MHz): d 182.42 (dd, J CP = 132.8 Hz,
1
[Pd(tmiy)Me(l-Cl)]2 (0.0379 g, 0.0674 mmol) and dppp (0.0565 g,
0.137 mmol) were taken up in DCM (2 mL). This mixture was
cooled to 0 ◦C before being transferred into a cold solution of
AgBF4 (0.027 g, 0.138 mmol) in DCM (3 mL). The reaction
mixture was stirred for 90 min before being filtered through
J
= 13.7 Hz, NCN), 139.9 (s), 136.2 (s), 135.9 (s), 135.5 (s),
CP
135.0 (s), 133.9 (s), 133.5 (d, J = 10.3 Hz), 133.3 (d, J = 8.6 Hz),
131.1 (d, J = 18.8 Hz), 130.4 (s), 130.2 (s), 129.6 (d, J = 2.9 Hz),
129.1 (t, J = 10.3 Hz), 125.2 (d, J = 3.4 Hz), 28.26 (d, J =
22.9 Hz), 25.28 (dd, J = 26.4 Hz, J = 9.2 Hz), 21.40 (d, J =
1.2 Hz), 19.80 (s), 19.66 (s), 19.48 (s), 17.48 (s), 9.16 (d, J =
85.3 Hz, Pd–CH3). Anal. Calc. for C49H53N2P2PdBF4: C, 63.62;
H, 5.77; N, 3.03. Found: C, 63.51; H, 5.55; N, 2.92. MS (LSI-MS)
m/z (relative intensity): 837.4 (12, M+), 717.4 (16), 319.2 (100,
ylidene+CH3).
R
Celiteꢀ. Ether (40 mL) was added to the filtrate and the volatiles
concentrated in vacuo to approx. 10 mL. The mother-liquor was
decanted off the resultant white precipitate. This was washed with
Et2O and dried in vacuo to yield a white powder. Yield: 0.08 g
1
(80%). H NMR (CD2Cl2, 300 MHz): d 7.6 (m, 10H, ArH), 7.3
(m, 3H, ArH), 7.1 (m, 7H, ArH), 3.27 (s, 6H, N–CH3), 2.29 (m,
4H, PCH2), 1.90 (s + m, 8H, C–CH3 + PCH2CH2CH2P), 0.14 (t,
3H, J = 6.9 Hz, Pd–CH3). 13C{ H} NMR (CD2Cl2, 75.4 MHz):
1
[Pd(IDipp)Me(dppp)]BF4 (3d)
d 175.33 (dd, J = 135.1 Hz, J = 16.6 Hz, NCN), 134.25 (s),
133.76 (s), 133.42 (d, J = 10.6 Hz), 132.98 (d, J = 11.5 Hz),
131.49 (s), 130.95 (s), 130.81 (s), 130.22 (s), 129.62 (d, J = 9.7 Hz),
128.96 (d, J = 9.2 Hz), 126.57 (d, J = 3.5 Hz), 35.26 (s, N–CH3),
27.8 (m, PCH2), 18.76 (d, J = 3.4 Hz, PCH2CH2CH2P) 9.13 (s,
To
a 0
◦C solution of [Pd(IDipp)Me(l-Cl)]2 (0.0962 g,
0.0882 mmol) in DCM (8 mL) was added dppp (0.0732 g,
0.177 mmol) in DCM (2 mL). The phosphine was rinsed over
◦
with DCM (2 mL), and the reaction mixture stirred at 0 C for
C–CH3), 0.66 (d, J = 91.0 Hz, Pd–CH3). 31P{ H} NMR (CDCl3,
1
25 min. After this time the clear solution was transferred into a
cold suspension of AgBF4 (0.035 g, 0.180 mmol) in DCM (3 mL).
After stirring for 2.5 h, the mixture was filtered through Celiteꢀ
and the volatiles concentrated in vacuo to approx. 1 mL. Ether
(10 mL) was added, and the mixture stored at −20 ◦C overnight
to complete precipitation of the product. The mother liquor was
decanted and the product dried in vacuo to yield a white powder.
Yield: 0.13 g (72%). 1H NMR (CD2Cl2, 200 MHz): d 7.6–7.0 (m,
121.4 MHz): d 11.95 (d, J = 48.0 Hz), −0.67 (d, J = 48.0 Hz). Anal.
Calc. for C35H41N2PdP2BF4: C, 56.43; H, 5.55; N, 3.76. Found: C,
56.26; H, 5.50; N, 3.66. MS (LSI-MS) m/z (relative intensity): 657
(4; M+), 139 (100; ylidene + CH3). HR-MS for C35H41N2104PdP2:
calc, 655.17853; obsd, 655.17740.
R
[Pd(dmiy)Me(dppp)]BF4 (3b)
=
26H, ArH + DippH + HC CH), 3.21 (quintet, 2H, J = 7.7 Hz),
To a solution of [Pd(dmiy)Me(l-Cl)]2 (0.0573 g, 0.113 mmol) in
DCM (5 mL) was added a solution of dppp (0.0933 g, 0.226 mmol)
in DCM (2 mL). This mixture was stirred for 5 min, before being
transferred into a solution of AgBF4 (0.048 g, 0.247 mmol) in
DCM (2 mL). The resultant mixture was stirred for 2.5 h before
2.65 (quintet, 2H, J = 7.7 Hz), 2.40 (q, 2H, J = 6.6 Hz), 2.01 (m,
2H, PCH2), 1.80 (br m, 2H, PCH2CH2CH2P), 1.14 (d, 6H, J =
6.7 Hz, (CH3)2CH), 1.06 (d, 6H, J = 6.7 Hz, (CH3)2CH), 0.95 (d,
6H, J = 6.7 Hz, (CH3)2CH), 0.41 (d, 6H, J = 6.6 Hz, (CH3)2CH),
1
−0.04 (dd, 3H, J = 7.8 Hz, J = 6.5 Hz, Pd–CH3). 31P{ H} NMR
R
being filtered through Celiteꢀ. The solvent was concentrated
(CDCl3, 161.8 MHz): d 15.1 (J = 47.7 Hz), −9.2 (J = 47.7 Hz).
1
in vacuo to approx. 2 mL and 10 mL of Et2O was added to
precipitate the product. The supernatant was decanted, and the
product recrystallised from DCM–Et2O (4 mL : 10 mL), washed
with Et2O (2 × 5 mL) and dried in vacuo to yield a white powder.
13C{ H} NMR (CD2Cl2, 75 MHz): d 186.0 (dd, J = 132.8 Hz, J =
13.2 Hz), 147.5 (s), 145.6 (s), 136.1 (s), 133.7 (s), 133.6 (s), 133.4
(s), 132.3 (s), 131.9 (s), 131.5 (d, J = 9.1 Hz), 131.3 (s), 129.9 (s),
129.5 (d, J = 9.2 Hz), 129.3 (s), 129.1 (d, J = 10.3 Hz), 127.0
(s), 125.4 (s), 124.9 (s), 29.4 (s), 26.77 (d, J = 8.6 Hz), 24.41 (dd,
1
Yield: 0.13 g (83%). The H NMR was identical to the reported
3404 | Dalton Trans., 2007, 3398–3406
This journal is
The Royal Society of Chemistry 2007
©

View Article Online
J = 26.4 Hz, J = 10.0 Hz), 22.58 (s), 21.84 (s), 18.67 (s), 8.62
(d, J = 83.0 Hz, Pd–CH3). Anal. Calc. for C55H65N2P2PdBF4: C,
65.45; H, 6.49; N, 2.76. Found: C, 65.66; H, 6.36; N, 2.83. MS (LSI-
MS) m/z (relative intensity): 921.7 (20, M+), 721.6 (16), 403.4 (100,
ylidene + CH3).
References
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Reaction of 3a with 4-bromoacetophenone
A CD3CN solution of 3a (0.0402 g, 0.0561 mmol) and 4-
bromoacetophenone (0.0552 g, 0.277 mmol) was made up in an
NMR tube fitted with a Young’s tap. This solution was heated
to 65 ◦C overnight. After this time, the reaction mixture was
chromatographed on silica gel using CHCl3–CH3CN (20 : 1)
as eluent. The fractions containing a product with Rf = 0.15
were combined and concentrated in vacuo. The residue was taken
up in CD3CN, which caused large diamond-shaped crystals of
(4-acetylphenyl)PdBr(dppp) to form. These were collected and
1
dried in vacuo. H NMR (CD2Cl2, 300 MHz): d 7.85–7.78 (m,
4H), 7.50–7.48 (m, 6H), 7.36–7.29 (m, 6H), 7.20–7.04 (m, 8H),
2.64–2.55 (m, 2H, PCH2), 2.47–2.40 (m, 2H, PCH2), 2.35 (s,
1
3H, C(O)CH3), 1.95–1.76 (br m, 2H, PCH2CH2CH2P). 31P{ H}
NMR (CD2Cl2, 121.4 MHz): d 15.92 (d, J = 51 Hz), −8.01 (d,
J = 51 Hz). Anal. Calc. for C37H33P2PdBrO: C, 59.90; H, 4.48.
Found: C, 59.71, H, 4.69. MS (LSI-MS) m/z (relative intensity):
13 R. Landtiser, Y. Pan and M. J. Fink, Phosphorus, Sulfur Silicon Relat.
Elem., 1994, 93–94, 393–394.
14 S. M. Reid and M. J. Fink, Organometallics, 2001, 20, 2959–2961.
15 J. E. Marcone and K. G. Moloy, J. Am. Chem. Soc., 1998, 120, 8527–
8528.
719.1 (5, M + H+), 637.2 (25, M+ − Br), 599.0 (33, M+
−
PhC(O)CH3), 518.1 (68, M+ − Br-PhC(O)CH3), 391.3 (100).
HR-MS for C35H34OBr104PdP2 (M + H): calc, 715.03085; obsd,
715.01510.
16 M. J. Green, K. J. Cavell, B. W. Skelton and A. H. White, J. Organomet.
Chem., 1998, 554, 175–179.
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and P. Bru¨ggeller, Polyhedron, 1997, 16, 2827–2835.
Structure determination
Full spheres of CCD area-detector diffractometer data were mea-
˚
18 M. Ludwig, S. Stro¨mberg, M. Svensson and B. Akermark,
sured (Bruker AXS instrument, x-scans, 2hmax = 75◦; monochro-
Organometallics, 1999, 18, 970–975.
19 (a) A. Furstner, G. Seidel, D. Kremzow and C. W. Lehmann,
Organometallics, 2003, 22, 907–909; (b) A. A. D. Tulloch, S. Win-
ston, A. A. Danopoulos, G. Eastham and M. B. Hursthouse, Dal-
ton Trans., 2003, 699–708; (c) W. A. Herrmann, V. P. W. Bo¨hm,
C. W. K. Gsto¨ttmayr, M. Grosche, C.-P. Reisinger and T. Weskamp,
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Herdtweck, M. Spiegler, A. K. Pleier and W. R. Thiel, J. Organomet.
Chem., 2001, 626, 100–105; (e) J. A. Chamizo, J. Morgado, M.
Castro and S. Bernes, Organometallics, 2002, 21, 5428–5432; (f) W. A.
Herrmann, M. Elison, J. Fischer, C. Kocher and G. R. J. Artus, Angew.
Chem., Int. Ed. Engl., 1995, 34, 2371–2374.
˚
matic Mo-Ka radiation, k = 0.71073 A; T ca. 153 K) yielding
Nt(otal) reflections, these merging to N unique (Rint cited) after
‘empirical’/multiscan absorption correction, No with F > 4r(F)
being employed in the full matrix least squares refinements on
|F|; anisotropic displacement parameters were refined for the
non-hydrogen atoms, (x ,y, z, Uiso
)
estimates. Conventional
H
residuals R, Rw on |F| are cited at convergence (reflection weights:
(r2(F) + 0.00nwF)2)−1. Neutral atom complex scattering factors
were employed within the Xtal 3.7 program system.38 Pertinent
results are presented in the tables and figures, the latter showing
50% probability amplitude displacement envelopes for the non-
20 R. E. Douthwaite, M. L. H. Green, P. J. Silcock and P. T. Gomes,
J. Chem. Soc., Dalton Trans., 2002, 1386.
21 (a) W. A. Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1290–1309;
(b) A. M. Magill, D. S. McGuinness, K. J. Cavell, G. J. P. Britovsek, V. C.
Gibson, A. J. P. White, D. J. Williams, A. H. White and B. W. Skelton,
J. Organomet. Chem., 2001, 617–618, 546–560; (c) W. A. Herrmann, M.
Elison, J. Fischer, C. Ko¨cher and G. R. J. Artus, Chem.–Eur. J., 1996,
2, 772–780.
22 D. S. McGuinness, K. J. Cavell, B. W. Skelton and A. H. White,
Organometallics, 1999, 18, 1596–1605.
23 D. S. McGuinness, M. J. Green, K. J. Cavell, B. W. Skelton and A. H.
White, J. Organomet. Chem., 1998, 565, 165–178.
˚
hydrogen atoms, hydrogen atoms having arbitrary radii of 0.1 A.
Crystal/refinement data 2a·Et2O. C38H73BF4OP2Pd, M =
829.3. Monoclinic, space group P21/c (C52h, No 14), a =
◦
˚
11.7468(7), b = 12.3711(8), c = 28.598(2) A, b = 94.917(1) , V =
3
−3
−1
˚
4141 A . Dc (Z = 4) = 1.330 g cm . l(Mo) = 0.57 mm ; specimen:
0.21 × 0.20 × 0.16 mm, Tmin/max = 0.89. Nt = 82 879, N = 21 630
(Rint = 0.045), No = 15400; R = 0.045, Rw = 0.065 (nw = 2); S =
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25 Y. Koide, S. G. Bott and A. R. Barron, Organometallics, 1996, 15,
2213.
−3
˚
1.06. |Dqmax| = 1.1 e A .
26 F. H. Allen, Acta Crystallogr., Sect. B, 2002, 58, 380–388; I. J. Bruno,
J. C. Cole, P. R. Edgington, M. Kessler, C. F. Macrae, P. McCabe,
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397.
Acknowledgements
We are indebted to the Australian Research Council for
funding and providing an Australian Postgraduate Award for
A. M. M. Johnson Matthey is acknowledged for a generous loan
of palladium salts.
27 In the case of Pd(dppe)Cl2 and Pd(dcype)Cl2 complexes Pd–Cl bond
˚
distances are within 0.02 A. See: (a) A. S. Batsanov, J. A. K. Howard,
G. S. Robertson and M. Kilner, Acta Crystallogr., Sect. E, 2001, 57,
m301; (b) W. L. Steffen and G. J. Palenik, Inorg. Chem., 1976, 15, 2432;
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The Royal Society of Chemistry 2007
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(c) S. Ganguly, J. T. Mague and D. M. Roundhill, Acta Crystallogr.,
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between complexes bearing dppe and those bearing dcype may be made.
28 W. de Graaf, J. Boersma, W. J. J. Smeets, A. L. Spek and G. van Koten,
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34 J. M. Vila, J. M. Ortigueira, M. Lo´pez, J. J. Ferna´ndez and A.
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35 The MAH was included to trap any Pd(dppe) that may have formed
during the course of the reaction. A similar approach was used to study
the reaction between PdAr2L2 and Pd(Me)IL2 (Ar = m-tolyl, L =
PEt2Ph) in which the absence of the trapping agent dimethyl maleate
led to rapid decomposition of starting materials catalysed by the Pd0L2
species. See ref. 36(a).
36 (a) F. Ozawa, M. Fujimori, T. Yamamoto and A. Yamamoto,
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Fujimori, T. Hidaka, T. Toyoshima and A. Yamamoto, Organo-
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29 A. L. Seligson, R. L. Cowan and W. C. Trogler, Inorg. Chem., 1991, 30,
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30 A. L. Seligson and W. C. Trogler, J. Am. Chem. Soc., 1991, 113,
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31 J. M. Brown and P. J. Guiry, Inorg. Chim. Acta, 1994, 220, 249–259.
32 D. C. Graham, PhD thesis, University of Tasmania, 2003.
33 K. K. Hii, T. D. W. Claridge, J. M. Brown, A. Smith and R. J. Deeth,
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37 W. L. F. Armarego and D. D. Perrin, Purification of Laboratory
Chemicals, Butterworth-Heinemann, Oxford, 4th edn, 1996.
38 S. R. Hall, D. J. du Boulay and R. Olthof-Hazekamp, The Xtal 3.7
System, University of Western Australia, Perth, 2000.
3406 | Dalton Trans., 2007, 3398–3406
This journal is
The Royal Society of Chemistry 2007
©