A recyclable perfluoroalkylated PCP pincer palladium complex

Article abstract of DOI:10.1039/c0dt01004a

A new fluorous PCP pincer ligand has been coordinated to Ni(ii), Pd(ii) and Pt(ii). The air stable palladium complex, which promotes Heck reactions between methyl acrylate and either aryl bromides or iodides, can be recovered intact by fluorous solid-phase extraction and was reused four times in the Heck reaction between methyl acrylate and 4-bromoacetophenone without loss in catalytic activity. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c0dt01004a

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Cite this: Dalton Trans., 2011, 40, 1998
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PAPER
A recyclable perfluoroalkylated PCP pincer palladium complex†‡
Daniel Duncan, Eric G. Hope, Kuldip Singh and Alison M. Stuart*
Received 12th August 2010, Accepted 30th November 2010
DOI: 10.1039/c0dt01004a
A new fluorous PCP pincer ligand has been coordinated to Ni(II), Pd(II) and Pt(II). The air stable
palladium complex, which promotes Heck reactions between methyl acrylate and either aryl bromides
or iodides, can be recovered intact by fluorous solid-phase extraction and was reused four times in the
Heck reaction between methyl acrylate and 4-bromoacetophenone without loss in catalytic activity.
over conventional palladium catalysts, [Pd(OAc)2/PPh3], because
Introduction
the metal–carbon s-bond is responsible for the high stability
of the pincer complex preventing, at least to a large extent, the
metal dissociating from the ligand (leaching) and giving a high
degree of thermal stability.7 Since much of our early work on
fluorous biphase catalysis had concentrated on the applications of
perfluoroalkylated phosphines,8 we were interested in synthesising
a “light fluorous” pincer PCP ligand and evaluating fluorous
solid-phase extraction as a separation technique for recycling the
palladium complex.
Since Horva´th and Ra´bai’s seminal paper on fluorous biphase
catalysis in 1994, fluorous chemistry has continued to evolve
and offer new approaches for designing recyclable catalysts.1,2
In fluorous biphase catalysis it is essential that the catalysts
contain >60% fluorine by molecular weight in order to give
good liquid/liquid separation between organic and perfluoro-
carbon solvents. On the other hand, “light fluorous” molecules
normally require <50% fluorine by molecular weight and so,
the cost of the fluorous catalyst can be reduced by minimising
the number of fluorous ponytails attached to the catalyst. The
other advantages of the “light fluorous” approach over fluorous
biphase catalysis are that the “light fluorous” catalysts can be
used in conventional organic solvents, thus avoiding the use of
the expensive perfluorocarbon solvents, they can be recovered and
recycled efficiently by solid-phase extraction on fluorous reverse
phase silica gel, and similar, if not better, catalytic activity can
be achieved with the perfluoroalkylated catalyst compared to the
parent, non-fluorinated catalyst. In 2003 we reported the first
example of a “light fluorous” catalyst, which promoted additions
of 1,3-diketones to ethyl cyanoformate in dichloromethane and
the perfluoroalkylated nickel catalyst was recovered by solid-phase
extraction on fluorous reverse phase silica gel.3 Although “light
fluorous” catalysis has been applied successfully to a number of
organic-based catalysts,4 there have been relatively few reports
on the recycling of metal-based catalysts by fluorous solid-phase
extraction.5
There have been a few reports on the synthesis and applications
of pincer complexes incorporating perfluoroalkyl groups (Fig. 1).
In 1998 the first fluorous NCN nickel complexes 1 were tested in
the Kharash addition between carbon tetrachloride and methyl
methacrylate, but they were not sufficiently soluble in perflu-
orocarbon solvents for them to be investigated under fluorous
biphasic conditions.9a In the same study, a ruthenium PCP pincer
complex 2 was synthesised, but there have been no reports of
catalysis with this metal complex.9b More recently, fluorous PCP
complexes containing aliphatic perfluoroalkyl phosphines (3 and
4) were prepared, but again, there have been no reports about the
catalytic applications of these complexes.10 In contrast, Curran
synthesised the fluorous SCS pincer palladium complex 5 which
was used successfully to catalyse a number of Heck reactions
between aromatic iodides or bromides with either methyl acrylate
or styrene in dimethylacetamide under microwave conditions.5c
The light fluorous catalyst was recycled three times by fluorous
solid-phase extraction but only 75–83% of the catalyst was
recovered after each cycle, probably as a result of handling such
small amounts of catalyst (42 mg). Gladysz has also reported
the straightforward syntheses of a family of fluorous SCS pincer
palladium complexes 6 and demonstrated that they can be used
as catalyst precursors for promoting the Heck reaction between
iodobenzene and methyl acrylate.10c Unfortunately, it was not
possible to recycle the fluorous palladium complexes and the
active catalysts were believed to be palladium nanoparticles. In this
paper we report the synthesis of a stable fluorous PCP palladium
complex, which promotes Heck reactions and can be recycled
efficiently by fluorous solid-phase extraction.11
Homogeneous palladium catalysts are one of the most versatile
and useful tools in an organic chemist’s armoury for the synthesis
of carbon–carbon bonds offering a range of versatile reactions.6
Tridentate palladium pincer complexes offer unique advantages
Department of Chemistry, University of Leicester, Leicester, UK LE1 7RH.
E-mail: Alison.Stuart@le.ac.uk
† Electronic supplementary information (ESI) available. CCDC reference
number 788537. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c0dt01004a
‡ This publication is part of the web themed issue on fluorine chemistry.
1998 | Dalton Trans., 2011, 40, 1998–2005
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Fig. 1 Previously reported perfluoroalkylated pincer complexes.
fluorous and non-fluorous metal complexes show only very small
differences in DP, which is the difference in the chemical shift
between the metal complex and the free ligand, between the
fluorous and non-fluorous complexes indicating that there are
negligible differences in the binding properties of the complexes
and that the phosphorus donor atoms are insulated effectively
from the electron-withdrawing effects of the perfluoroalkyl groups.
Crystals of the non-fluorinated nickel complex 12, suitable for
X-ray crystallography, were grown by slow diffusion of hexane
into a dichloromethane solution of 12 and the molecular structure
is shown in Fig. 2. The coordination geometry around the nickel
centre is distorted square planar since the three donor atoms of the
ligand, C(1), P(1) and P(2), are held in two fused five-membered
chelate rings. In fact, the two chelating rings are quite strained
with a small C(1)–Ni(1)–P angle (average 82.5◦) which distorts the
P(1)–Ni(1)–P(2) angle to 164.81◦ (see ESI†).
Results and discussion
Synthesis and coordination chemistry of the fluorous pincer ligand
9
The syntheses of the fluorous and non-fluorous pincer phos-
phine ligands 9 and 10 are shown in Scheme 1. After react-
ing bis(4-1H,1H,2H,2H-perfluorooctylphenyl)phosphine oxide12
with sodium hydride for 1 h, 1,3-bis(bromomethyl)benzene was
added and the reaction mixture was stirred at room temperature
overnight to afford the perfluoroalkylated pincer phosphine oxide
7 in 82% yield. In the second step 7 was reduced by refluxing
with an excess of trichlorosilane in benzotrifluoride for 3 h.13
After removing the excess of trichlorosilane, a basic work-up was
used to isolate the perfluoroalkylated pincer phosphine 9. The
non-fluorinated PCP pincer ligand 10 was also prepared by the
same protocol (overall yield 88%) for direct comparison with the
fluorous ligand 9.
The PCP ligands
9
and 10 were coordinated to
Catalysis and recycling studies of the fluorous palladium pincer
complex 13
nickel, palladium and platinum by refluxing with ei-
ther [NiCl2.6H2O], [PdCl2(CH3CN)2] or [PtCl2(COD)] in 2-
methoxyethanol (Scheme 2).14 All of the complexes were fully
Since there are no reports of the non-fluorinated palladium
pincer complex catalysing a Heck reaction, a Design of Ex-
periment software package was used to optimise the reaction
conditions for the Heck reaction between bromobenzene and
methyl acrylate, and a range of solvents, organic and inorganic
bases were screened (see ESI†). With a 1 mole % catalyst loading
the optimum conditions were N-methyl-2-pyrrolidone (NMP) in
combination with potassium hydrogen carbonate (1 equivalent)
1
characterised by H, 31P and 19F NMR spectroscopy, elemental
analysis, mass spectrometry and infrared spectroscopy. In the
1H NMR spectra of all of the complexes, the benzylic protons
appeared as a virtual triplet at approximately 3.8 ppm, which
collapsed to a singlet in the 1H{ P} NMR spectra and is
31
characteristic of the benzylic protons coupling with 2 phosphorus
atoms held in a trans-arrangement. 31P{ H} NMR data for the
1
Scheme 1 Syntheses of PCP pincer ligands 9 and 10.
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Scheme 2 Coordination chemistry of the PCP pincer ligands 9 and 10.
and acetophenone substrates, but the non-fluorous catalyst 14 was
much superior for the anisoles.
The Heck reaction between 4-bromoacetophenone and methyl
acrylate was investigated in more detail and the catalytic activities
of the two palladium complexes were compared directly by
monitoring the reaction by GC over a 6 h timeframe (Fig. 3).
Under these reaction conditions the perfluoroalkylated palladium
pincer complex 13 was slightly more active with the reaction
complete after 4 h compared to 6 h for the non-fluorinated
palladium complex 14. Unfortunately, neither of the palladium
complexes were able to promote the Heck reaction between
4-chloroacetophenone and methyl acrylate under the reaction
conditions used.
Fig. 2 The molecular structure of [NiCl(PCP)] 12 showing 50% displace-
ment ellipsoids. The hydrogen atoms have been omitted for clarity.
Fig. 3 Rate of formation of Heck product.
and ◦tetra-n-butylammonium bromide (TBAB, 0.2 equivalents) at
120 C. Under these optimum conditions the fluorous and non-
fluorous palladium pincer complexes, 13 and 14, were tested in
a range of Heck reactions to evaluate their versatility towards
different substrates (Table 1). Initially, a series of aryl iodides
and aryl bromides were all reacted successfully. Marginally better
yields were obtained with the fluorous catalyst 13 for the benzene
Only the perfluoroalkylated palladium complex 13 could be
recycled using fluorous solid-phase extraction. After removing
the solvent by Kugelro¨hr distillation, the resulting solid was
dissolved in acetonitrile and loaded onto a short column of
fluorous reverse phase silica gel which had been preconditioned
2000 | Dalton Trans., 2011, 40, 1998–2005
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Table 1 Optimised Heck reaction conditions applied to a range of substrates
Substrate
R
X
Catalyst
Time (h)
Yield (%)a
CH3CO
CH3CO
H
H
CH3O
CH3O
I
I
I
I
I
I
13 [PdCl(Rf6-PCP)]
14 [PdCl(PCP)]
13 [PdCl(Rf6-PCP)]
14 [PdCl(PCP)]
13 [PdCl(Rf6-PCP)]
14 [PdCl(PCP)]
5
5
5
5
5
5
>98
87
91
81
66
>98
CH3CO
CH3CO
H
H
CH3O
CH3O
Br
Br
Br
Br
Br
Br
13 [PdCl(Rf6-PCP)]
14 [PdCl(PCP)]
13 [PdCl(Rf6-PCP)]
14 [PdCl(PCP)]
13 [PdCl(Rf6-PCP)]
14 [PdCl(PCP)]
5
5
24
24
24
24
>98
>98
82
79
57
>98
a Determined by GC.
Table 2 Recycling results of 13 in the Heck reaction
Run
Catalyst used (mg)
Recovered catalyst (mg)a
Yieldb (%)
Accumulative TONc
Pd leaching (%)d
1
50.0
48.2
45.0
40.5
48.2 (96%)
45.0 (93%)
40.5 (90%)
36.4 (90%)
>99
>99
>99
>99
99
0.19
0.06
0.05
0.05
2e
3e
4e
198f
297f
396f
a Weight percent is shown in parenthesis. b Determined by GC using tolyl ether as the internal standard. c TON = mmol of product/mmol of catalyst.
d Determined by ICP-OES. e Catalysis using 13 from the previous run. f Accumulative TON = TON from reaction + TON from previous reaction(s).
with acetonitrile. The column was eluted with acetonitrile to give
the clean organic product, and 96% of the fluorous palladium
complex was recovered by elution with ethyl acetate. The column
was then washed with water in order to remove the TBAB and
inorganics, before preconditioning with acetonitrile to prepare the
column for the next cycle.
The recovered palladium complex was reused in the next run
using the same reaction conditions, except the amount of substrate
was lowered in order to keep the catalyst loading at 1 mole %
throughout the recycling experiments. The recycling results are
summarised in Table 2, whilst Fig. 4 shows the kinetic data for
each of the recycles and demonstrates clearly that there was
Fig. 4 Recycling results of 13 in the Heck reaction.
no loss in catalytic activity over the 4 runs. An accumulative
turnover number (TON) of 396 was achieved and recovery of the
1
1
product. Finally, 1H, 31P{ H} and 19F{ H} NMR spectroscopy of
the recovered fluorous palladium complex confirmed that there
was no sign of decomposition.
fluorous complex was extremely good, ranging from 90–96% of
the palladium complex. ICP-OES analysis of palladium leaching
in to the organic product gave a combined total of 0.35% of the
total palladium for the four runs. The organic fractions were also
There is considerable evidence that palladacycles and pincer
palladium complexes function as precatalysts that release highly
active forms of metallic palladium which then promote the Heck
1
1
analysed by H and 19F{ H} NMR spectroscopy which revealed
that there was no catalyst, ligand or oxidised ligand in the organic
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reaction.15,16 Kinetic studies of these systems normally show an in-
duction period and sigmoidal kinetics.17,18 In contrast, our kinetic
studies on the palladium pincer complexes 13 and 14 in Fig. 3
and 4, have revealed that the Heck reaction occurred without an
induction period. Despite this observation, however, the function
of the fluorinated and non-fluorinated palladium pincer complexes
in these Heck reactions is not known, but they are probably acting
as precursors of ultra-low levels of soluble ligandless palladium
metal. From the reaction optimisation studies with the palladium
complex 14 (see ESI†), it was obvious that the incorporation of
TBAB was essential for high yields in the Heck reaction with
bromobenzene. Although TBAB was used initially as a phase
transfer catalyst to transfer the inorganic salt into the organic
solvent, it may actually be performing a secondary role since it is
well established that tetraalkylammonium halides stabilise nano-
sized transition metal colloids and palladium clusters stabilised
by quaternary ammonium salts have been shown to be active
catalysts in the Heck reaction with aryl bromides.19 In this work,
if the small amount of palladium detected in the product phase
represents the actual catalyst that was released from palladium
complex 13, then these Heck reactions were promoted by about
0.003 mole % palladium. Regardless of its function, however, the
perfluoroalkylated PCP pincer palladium complex 13 is an easy-
to-handle, air stable complex that promotes the Heck reaction, can
be recovered intact by fluorous solid-phase extraction and reused
without loss in catalytic activity.
Preparation of 1,3-bis[methylbis(4-1H,1H,2H,2H-
perfluorooctylphenyl) phosphine oxide] benzene 7
A 250 mL, three-necked round-bottomed flask was charged
with bis(4-1H,1H,2H,2H-perfluorooctylphenyl)phosphine oxide
(3.86 g, 4.31 mmol), sodium hydride (60% on oil, 0.17 g, 4.31
mmol) and dry THF (40 mL). After stirring the reaction mixture
for 1 h under nitrogen, a solution of 1,3-bis(bromomethyl)benzene
(0.55 g, 2.10 mmol) in dry THF (15 mL) was added slowly and
the reaction mixture was then allowed to stir overnight at room
temperature. The reaction was quenched slowly with water (1 mL)
and stirred for 10 min. The organic layer was extracted with CHCl3
(3 ¥ 50 mL), dried (MgSO4) and concentrated to give the crude
product as a brown oil which was washed with hot petroleum
ether (40–60 ◦C) to give 7 as a white powder (3.27 g, 82%). mp
162–164 ◦C (from petroleum ether). (Found C, 40.6; H, 2.1. Calc.
for C64H40F52O2P2: C, 40.65; H, 2.1); 1H NMR (300 MHz, CDCl3)
3
3
dH 7.50 (8 H, dd, JHP = 11.0 Hz, JHH = 8.0 Hz, ArH), 7.14 (8
H, dd, 3JHH = 8.0 Hz, 4JHP = 1.6 Hz, ArH), 7.11 (1 H, br s, ArH-
2
2), 6.91–6.81 (3 H, m, ArH-5 and ArH-4), 3.46 (4 H, d, JHP
=
13.5 Hz, PhCH2), 2.86–2.81 (8 H, m, CH2), 2.34–2.17 (8 H, m,
31
CH2); 1H{ P} NMR (300 MHz, CDCl3) dH 7.50 (8 H, d, 3JHH
=
8.0 Hz, ArH), 7.14 (8 H, d, 3JHH = 8.0 Hz, ArH), 7.11 (1 H, s, ArH-
2), 6.91–6.81 (3 H, m, ArH-5 and ArH-4), 3.46 (4 H, s, PhCH2),
2.86–2.81 (8 H, m, CH2), 2.34–2.17 (8 H, m, CH2); 19F NMR
(282 MHz, CDCl3) dF -81.13 (12 F, t, 4JFF = 9.9 Hz, CF3), -114.82
(8 F, t, 4JFF = 13.8 Hz, a-CF2), -122.12 (8 F, m, CF2), -123.12 (8
F, m, CF2), -123.78 (8 F, m, CF2), -126.43 (8 F, m, CF2); 31P{ H}
1
NMR (121 Hz, CDCl3) dP 29.4 (s); 13C NMR (75 MHz, CDCl3) dC
143.3 (C), 132.3 (t, JCP = JCP¢ = 4.8 Hz, CH), 132.0 (d, JCP = 10.3 Hz,
Conclusions
1
The novel fluorous PCP pincer ligand 9 was synthesised in two
steps from bis(4-1H,1H,2H,2H-perfluorooctylphenyl)phosphine
oxide and it was straightforward to coordinate 9 to nickel,
palladium and platinum. Both the fluorous and non-fluorinated
palladium complexes, 13 and 14, promoted a range of Heck
reactions between methyl acrylate and either aryl iodides or
bromides. Recycling was only possible with the perfluoroalkylated
pincer palladium complex 13, which was recovered and reused
four times in the Heck reaction between methyl acrylate and 4-
bromoacetophenone without loss in catalytic activity.
CH), 131.6 (d, JCP = 9.6 Hz, CH), 130.6 (d, JCP = 100.7 Hz, C),
128.6 (d, JCP = 12.2 Hz, CH), 37.9 (d, 1JCP = 66.6 Hz, CH2), 32.4 (t,
2JCF = 22.1 Hz, CH2), 26.4 (CH2); despite several attempts using
different deuterated solvents and high field NMR spectroscopy,
two peaks are missing in the 13C NMR spectrum for the middle
aromatic ring, maybe due to overlapping of the aryl peaks. m/z
(FAB) 1891 (MH+); nmax/cm-1 (solid) 1604 (w), 1181 (br, s), 1140
(s), 1073 (s).
Preparation of 1,3-bis[methyldiphenylphosphine oxide]benzene 8
The title compound was prepared similarly to
7 using
Experimental
diphenylphosphine oxide (1.19 g, 5.87 mmol), sodium hydride
(60% on oil, 0.24 g, 5.87 mmol) and 1,3-bis(bromomethyl)benzene
(0.191 M solution in THF, 15.4 mL, 2.93 mmol). After quenching
the reaction slowly with water (1 mL), the THF was removed and
the residue was extracted with CHCl3 (3 ¥ 50 mL). The organic
layer was dried (MgSO4) and concentrated to give a white solid
which was washed with hot petroleum ether (40–60 ◦C) to give 8 as
a white solid (1.51 g, 98%). mp 91–93 ◦C (from petroleum ether);
Proton, 19F and 13C NMR spectroscopies were carried out on a
Bruker ARX 300 spectrometer at 300.14, 282.41 and 75.5 MHz
respectively. All chemical shifts are quoted in ppm using the high
frequency positive convention; 1H NMR spectra were referenced
to external SiMe4; 19F NMR spectra to external CFCl3 and
13C NMR spectra to external SiMe4. The highly coupled 13C
signals of the fluorinated carbons are not listed below. Elemental
analyses were performed by the Elemental Analysis Service at
the University of North London. Mass spectra were recorded
on a Kratos Concept 1H mass spectrometer. GC analyses
were performed using a Perkin Elmer Clarus 500 GC using
a Perkin Elmer-Elite Series PE-5 column (30 m ¥ 0.25 mm,
5% diphenyl, 95% dimethyl polysiloxane). Bis(4-1H,1H,2H,2H-
perfluorooctylphenyl)phosphine oxide was prepared by the liter-
3
1H NMR (300 MHz, CDCl3) dH 7.56 (8 H, dd, JHP = 8.1 Hz,
3JHH = 7.3 Hz, ArH), 7.40–7.36 (4 H, m, ArH), 7.31 (8 H, td,
3JHH = 7.3 Hz, 4JHP = 2.4 Hz, ArH), 6.98 (1 H, s, ArH-2), 6.88–6.83
(1 H, m, ArH-5), 6.79 (2 H, d, 3JHH = 6.8 Hz, ArH-4), 3.46 (4 H,
31
d, 2JHP = 13.7 Hz, PhCH2); 1H{ P} NMR (300 MHz, CDCl3) dH
7.56 (8 H, d, 3JHH = 7.3 Hz, ArH), 7.40–7.36 (4 H, m, ArH), 7.31 (8
H, t, 3JHH = 7.3 Hz, ArH), 6.98 (1 H, s, ArH-2), 6.88–6.83 (1 H, m,
ArH-5), 6.79 (2 H, d, 3JHH = 6.8 Hz, ArH-4), 3.46 (4 H, s, PhCH2);
ature method.12 Fluoroflashꢀ silica gel (40 mm) was purchased
R
1
from Fluorous Technologies.
31P{ H} NMR (121 Hz, CDCl3) dP 30.0 (s);13C NMR (75 MHz,
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d6-DMSO) dC 133.42 (d, 1JCP = 96.9 Hz, C), 132.26 (t, JCP = JCP¢
=
C32H29P2 requires 475.17445); nmax/cm-1 (solid) 1673 (m), 1489 (s),
1163 (s), 1101 (s), 892 (m).
4.8 Hz, CH), 131.94 (d, JCP = 9.8 Hz, C), 131.51 (CH), 130.69 (d,
JCP = 9.4 Hz, CH), 128.48 (d, JCP = 11.6 Hz, CH), 128.11 (CH),
127.54 (CH), 36.04 (d, 1JCP = 66.2 Hz, CH2); m/z (FAB) 507.16425
(MH+. C32H29O2P2 requires 507.16428); nmax/cm-1 (solid) 3436 (br,
w), 1680 (m), 1487 (s), 1160 (s), 1118 (s), 695 (s).
Preparation of {2,6-bis[methyl(4-1H,1H,2H,2H-
perfluorooctylphenylphosphino)]phenyl}nickel chloride 11
A 50 mL Schlenk flask was charged with 9 (0.753 g, 0.41 mmol),
NiCl2.6H2O (0.052 g, 0.41 mmol) and 2-methoxyethanol (20 mL).
The colour changed instantly from green to purple. The reaction
mixture was heated to 60 ◦C for 3 h before diisopropylethylamine
(0.063 g, 0.49 mmol) was added carefully and the reaction mixture
was refluxed overnight. Within 5 min the colour had changed
from purple to golden yellow. The solvent was removed and the
product was recrystallised from ethanol to isolate 11 as lime green
Preparation of 1,3-bis[methylbis(4-1H,1H,2H,2H-
perfluorooctylphenyl) phosphine]benzene 9
A flame-dried 200 mL Schlenk flask was charged with 7 (4.35 g,
2.30 mmol) and BTF (20 mL). The reaction mixture was heated
to reflux before trichlorosilane (2.18 g, 1.63 mL, 16.10 mmol) was
added. The reaction mixture was refluxed for 3 h, cooled and
the excess trichlorosilane was removed under vacuum. A solution
of sodium hydroxide (3.22 g, 80.50 mmol) in water (20 mL) was
added and the reaction mixture was stirred for 15 min. The organic
layer was separated and the aqueous layer was extracted with
diethyl ether (2 ¥ 30 mL). The combined organic layers were dried
(MgSO4) and concentrated to give 9 as an orange solid (1.77 g,
41%). mp 80–82 ◦C (from hexane). (Found C, 41.25; H, 2.2. Calc.
◦
crystals (0.55 g, 69%). mp 113–115 C (from EtOH). (Found C,
1
39.4; H, 2.15. Calc. for C64H39F52ClP2Ni: C, 39.4; H, 2.0); H
NMR (300 MHz, CDCl3) dH 7.73 (8 H, dd, 3JHH = 8.2 Hz, 3JHP
=
3
5.1 Hz, ArH), 7.16 (8 H, d, JHH = 8.2 Hz, ArH), 7.07 (2 H, d,
3JHH = 6.7 Hz, ArH-4), 6.89–6.80 (1 H, m, ArH-5), 3.77 (4 H,
vt, JHP = 4.7 Hz, PhCH2), 2.90–2.81 (8 H, m, CH2), 2.40–2.19 (8
1
31
H, m, CH2); H{ P} NMR (300 MHz, CDCl3) dH 7.73 (8 H, d,
3
3JHH = 8.2 Hz, ArH), 7.16 (8 H, d, JHH = 8.2 Hz, ArH), 7.07 (2
1
H, d, 3JHH = 6.7 Hz, ArH-4), 6.89–6.80 (1 H, m, ArH-5), 3.77 (4
for C64H40F52P2: C, 41.35; H, 2.2); H NMR (300 MHz, CDCl3)
3
dH 7.19 (8 H, t, 3JHH = JHP = 7.7 Hz, ArH), 7.04 (8 H, d, 3JHH
=
H, s, PhCH2), 2.90–2.81 (8 H, m, CH2), 2.40–2.19 (8 H, m, CH2);
3
1
31P{ H} NMR (121 Hz, CDCl3) dP 33.9 (s); 19F NMR (282 MHz,
7.7 Hz, ArH), 6.87 (1 H, t, JHH = 7.5 Hz, ArH-5), 6.78 (1 H, s,
ArH-2), 6.68 (2 H, d, 3JHH = 7.5 Hz, ArH-4), 3.18 (4 H, s, PhCH2),
4
CDCl3) dF -80.81 (12 F, t, JFF = 9.4 Hz, CF3), -114.60 (8 F, t,
2.82–2.76 (8 H, m, CH2), 2.33–2.16 (8 H, m, CH2); 1H{ P} NMR
31
4JFF = 14.1 Hz, a-CF2), -121.88 (8 F, m, CF2), -122.87 (8 F, m,
CF2), -123.46 (8 F, m, CF2), -126.15 (8 F, m, CF2); m/z (FAB)
1915 (M–Cl)+; nmax/cm-1 (solid) 1204 (br, s), 1187 (s), 1141 (s),
1119 (s), 697 (m).
(300 MHz, CDCl3) dH 7.19 (8 H, d, 3JHH = 7.7 Hz, ArH), 7.04 (8
3
3
H, d, JHH = 7.7 Hz, ArH), 6.87 (1 H, t, JHH = 7.5 Hz, ArH-5),
6.78 (1 H, s, ArH-2), 6.68 (2 H, d, 3JHH = 7.5 Hz, ArH-4), 3.18 (4
H, s, PhCH2), 2.82–2.76 (8 H, m, CH2), 2.33–2.16 (8 H, m, CH2);
1
31P{ H} NMR (121 Hz, CDCl3) dP -11.5 (s); 19F NMR (282 MHz,
Preparation of {2,6-bis[methyl(diphenylphosphino)]phenyl}nickel
4
CDCl3) dF -81.13 (12 F, t, JFF = 10.0 Hz, CF3), -114.76 (8 F, t,
chloride 12
4JFF = 13.9 Hz, a-CF2), -122.04 (8 F, m, CF2), -123.03 (8 F, m,
CF2), -123.62 (8 F, m, CF2), -126.35 (8 F, m, CF2); 13C NMR
The title compound was prepared similarly to 11, us-
ing 10 (0.890 g, 1.88 mmol), NiCl2.6H2O (0.428 g, 1.80
mmol), diisopropylethylamine (0.291 g, 2.25 mmol) and 2-
methoxyethanol (20 mL). Recrystallisation from ethanol isolated
12 as a dark yellow powder (0.76 g, 75%). Crystals suitable for
X-ray crystallography were grown by slow diffusion of hexane
into a solution of DCM containing 12. mp 280–282 ◦C (from
ethanol). (Found C, 67.6; H, 4.7. Calc. for C32H27ClP2Ni: C, 67.7;
H, 4.8); 1H NMR (300 MHz, CDCl3) dH 7.87–7.73 (8 H, m, ArH),
2
(75 MHz, CDCl3) dC 139.79 (C), 137.27 (d, JCP = 7.5 Hz, C),
1
136.56 (d, JCP = 15.4 Hz, C), 133.28 (d, JCP = 18.5 Hz, CH),
131.65 (t, JCP = JCP¢ = 8.5 Hz, CH), 130.48 (t, JCP = JCP¢ = 6.8 Hz,
CH), 128.34 (d, JCP = 6.5 Hz, CH), 127.06 (d, JCP = 4.0 Hz, CH),
1
2
35.98 (d, JCP = 15.7 Hz, CH2), 32.72 (t, JCF = 22.0 Hz, CH2),
26.21 (CH2); m/z (FAB) 1858 (M+); nmax/cm-1 (solid) 1605 (w),
1194 (br, s), 1146 (s), 1120 (m).
7.42–7.25 (12 H, m, ArH), 6.89 (3 H, s, ArH), 3.78 (4 H, vt, JHP
=
31
3.8 Hz, PhCH2); 1H{ P} NMR (300 MHz, CDCl3) dH 7.78 (8 H, d,
Preparation of 1,3-bis[methyldiphenylphosphine]benzene 10
3JHH = 6.6 Hz, ArH), 7.40–7.25 (12 H, m, ArH), 6.89 (3 H, s, ArH),
The title compound was prepared similarly to 9 using 8 (1.48 g,
2.82 mmol), trichlorosilane (2.68 g, 2.00 mL, 19.67 mmol) and
BTF (20 mL) to give 10 as a colourless oil (1.21 g, 90%). 1H NMR
(300 MHz, CDCl3) dH 7.65–7.58 (8 H, m, ArH), 7.50–7.48 (12 H,
m, ArH), 7.22 (1 H, s, ArH-2), 7.19 (1 H, m, ArH-5), 7.06 (2 H,
1
3.78 (4 H, s, PhCH2); 31P{ H} NMR (121 Hz, CDCl3) dP 34.8 (s);
m/z (FAB) 566.06305 (M+. C32H27ClP2Ni requires 566.06296), 531
(M-Cl)+; nmax/cm-1 (solid) 2929 (w), 1463 (m), 1171 (m), 741 (m).
Crystal data for 12†
3
1
31
d, JHH = 7.8 Hz, ArH-4), 3.56 (4 H, s, PhCH2); H{ P} NMR
(300 MHz, CDCl3) dH 7.65–7.58 (8 H, m, ArH), 7.50–7.48 (12 H,
m, ArH), 7.22 (1 H, s, ArH-2), 7.19 (1 H, m, ArH-5), 7.06 (2 H,
C32H27ClNiP2, M = 567.64, monoclinic, space group P21/n,
◦
˚
˚
˚
a = 10.146(4) A, b = 15.988(7) A, c = 16.899(7) A, a = 90 ,
◦
◦
3
1
3
d, JHH = 7.8 Hz, ArH-4), 3.56 (4 H, s, PhCH2); 31P{ H} NMR
b = 105.768(8) , g = 90 , U = 2638.0(18) A (by least-squares
refinement), T = 150(2) K, graphite-monochromated Mo-Ka
˚
(121 Hz, CDCl3) dP -9.9 (s); 13C NMR (75 MHz, CDCl3) dC 138.47
(d, 1JCP = 15.4 Hz, C), 137.47 (d, 2JCP = 7.7 Hz, C), 133.02 (d, JCP
=
radiation, l = 0.71073 A, Z = 4, Dc = 1.429 mg m , F(000) =
-3
˚
18.4 Hz, CH), 131.90 (CH), 131.32 (d, JCP = 9.0 Hz, CH), 130.61
(t, JCP = JCP¢ = 6.8 Hz, CH), 128.78 (CH), 128.48 (d, JCP = 6.5 Hz,
CH), 36.03 (d, 1JCP = 15.8 Hz, CH2); m/z (FAB) 475.17441 (M+.
1176, dimensions 0.20 mm ¥ 0.16 mm ¥ 0.08 mm, m(Mo-
Ka) = 0.978 mm-1, empirical absorption correction, maximum
and minimum transmission factors of 0.928 and 0.604 respectively,
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Bruker APEX 2000 CCD diffractometer, data collection range
1.79 < q < 26.00◦, -12 £ h £ 12, -19 £ k £ 19, -20 £ l £ 20, no
crystal decay was detected; 20 425 reflections were measured and
5182 were unique (Rint = 0.0789), final R1 = 0.0591, wR2 = 0.1210
(0.0865 and 0.1308 respectively for all the data). The final residual
577.06240); nmax/cm-1 (solid) 1484 (s), 1435 (m), 1102 (m), 1025
(m), 958 (m), 846 (m), 741 (m), 691 (s).
Preparation of {2,6-bis[methyl(4-1H,1H,2H,2H-
perfluorooctylphenylphosphino)]phenyl} platinum chloride 15
-3
˚
Fourier map showed peaks of 0.881 and -0.548 e A .
A 50 mL Schlenk flask was charged with 9 (0.700 g, 0.38 mmol),
[PtCl2(COD)] (0.141 g, 0.38 mmol) and mesitylene (250 mL).
The reaction mixture was refluxed before triethylamine (0.046 g,
0.45 mmol) was added carefully. After refluxing the reaction
mixture overnight, it was cooled to room temperature and filtered
through Celite. The solvent was removed and the residue was
purified by recrystallisation from DCM–hexane to give pure 15 as
Structure solution and refinement
Structure solution by direct methods and structure refinement on
F2 employed SHELXTL version 6.10.20 Hydrogen atoms were
˚
included in calculated positions (C–H = 0.95–099 A) riding on
the bonded atom with isotropic displacement parameters set to
1.2 Ueq(C) for all H atoms. All non-H atoms were refined with
anisotropic displacement parameters. The data were corrected for
Lorentz and polarization effects.
◦
colourless crystals (0.31 g, 40%). mp 128–130 C (from hexane).
(Found C, 36.7; H, 2.0. Calc. for C64H39F52ClP2Pt: C, 36.8; H, 1.9);
1H NMR (300 MHz, CDCl3) dH 7.77 (8 H, m, ArH), 7.20 (8 H, d,
3JHH = 8.0 Hz, ArH), 7.03 (2 H, d, 3JHH = 7.0 Hz, ArH-4), 6.98–6.92
(1 H, m, ArH-5), 3.81 (4 H, vt, JHP = 4.7 Hz, PhCH2), 2.90–2.79 (8
Preparation of {2,6-bis[methyl(4-1H,1H,2H,2H-
31
H, m, CH2), 2.37–2.18 (8 H, m, CH2); 1H{ P} NMR (300 MHz,
perfluorooctylphenylphosphino)]phenyl}palladium chloride 13
CDCl3) dH 7.77 (8 H, d, 3JHH = 8.0 Hz, ArH), 7.20 (8 H, d, 3JHH
8.0 Hz, ArH), 7.03 (2 H, d, JHH = 7.0 Hz, ArH-4), 6.98–6.92 (1
=
3
A 50 mL Schlenk flask was charged with 9 (1.77 g, 0.95 mmol),
[PdCl2(MeCN)2] (0.25 g, 0.95 mmol) and 2-m◦ethoxyethanol (20
mL). The reaction mixture was heated to 130 C for 62 h. After
cooling the reaction mixture to room temperature, the solvent was
removed. The crude material was dissolved in CHCl3, filtered to
remove any palladium metal and the solvent was removed to give
an orange solid which was washed with hexane (3 ¥ 10 mL). The
product 13 was obtained as a yellow/orange powder (1.01 g, 53%).
H, m, ArH-5), 3.81 (4 H, br s, PhCH2), 2.90–2.79 (8 H, m, CH2),
1
2.37–2.18 (8 H, m, CH2); 31P{ H} NMR (121 Hz, CDCl3) dP 32.3
1
(s, JPPt = 2971 Hz); 19F NMR (282 MHz, CDCl3) dF -81.00 (12
F, t, 4JFF = 9.8 Hz, CF3), -114.67 (8 F, t, 4JFF = 13.6 Hz, a-CF2),
-121.95 (8 F, m, CF2), -122.96 (8 F, m, CF2), -123.59 (8 F, m,
CF2), -126.26 (8 F, m, CF2); m/z (FAB) 2087 (M+), 2052 (M–Cl)+;
n
max/cm-1 (solid) 1187 (br, s), 1141 (s), 1119 (s), 8111 (m), 698 (m).
◦
mp 140–142 C (from CHCl3). (Found C, 38.4; H, 2.0. Calc. for
Preparation of
1
C64H39F52ClP2Pd: C, 38.4; H, 2.0); H NMR (300 MHz, CDCl3)
{2,6-bis[methyl(diphenylphosphino)]phenyl}platinum chloride 16
3
3
dH 7.74 (8 H, dd, JHH = 8.0 Hz, JHP = 5.7 Hz, ArH), 7.18 (8
3
3
H, d, JHH = 7.7 Hz, ArH), 7.05 (2 H, d, JHH = 7.5 Hz, ArH-4),
6.98–6.93 (1 H, m, ArH-5), 3.88 (4 H, vt, JHP = 4.7 Hz, PhCH2),
The title compound was prepared similarly to 15, using 10 (0.880 g,
1.85 mmol), [PtCl2(COD)] (0.674 g, 1.80 mmol), triethylamine
(0.225 g, 2.22 mmol) and mesitylene (250 mL). After washing
with ethanol (3 ¥ 20 mL), 16 was obtained as a white powder
(0.863 g, 68%). mp 281–283 ◦C (from ethanol). (Found C, 54.5; H,
3.8. Calc. for C32H27ClP2Pt: C, 54.6; H, 3.9); 1H NMR (300 MHz,
CDCl3) dH 7.89–7.79 (8 H, m, ArH), 7.43–7.30 (12 H, m, ArH),
2.87–2.80 (8 H, m, CH2), 2.36–2.18 (8 H, m, CH2); 1H{ P} NMR
31
(300 MHz, CDCl3) dH 7.74 (8 H, d, 3JHH = 8.0 Hz, ArH), 7.18 (8
3
3
H, d, JHH = 7.7 Hz, ArH), 7.05 (2 H, d, JHH = 7.5 Hz, ArH-4),
6.98–6.93 (1 H, m, ArH-5), 3.88 (4 H, s, PhCH2), 2.87–2.80 (8
1
H, m, CH2), 2.36–2.18 (8 H, m, CH2); 31P{ H} NMR (121 Hz,
CDCl3) dP 32.7 (s); 19F NMR (282 MHz, CDCl3) dF -81.00 (12 F,
3
7.03 (2 H, d, JHH = 7.0 Hz, ArH-4), 6.96–6.92 (1 H, m, ArH-
4
4
t, JFF = 11.3 Hz, CF3), -114.67 (8 F, t, JFF = 14.1 Hz, a-CF2),
-121.94 (8 F, m, CF2), -122.95 (8 F, m, CF2), -123.57 (8 F, m,
CF2), -126.29 (8 F, m, CF2); m/z (FAB) 1963 (M–Cl)+; nmax/cm-1
(solid) 1191 (br, s), 1142 (s), 1086 (m), 1073 (m).
3
1
31
5), 3.89 (4 H, t, JHPt = 25.0 Hz, JHP = 4.7 Hz, PhCH2); H{ P}
NMR (300 MHz, CDCl3) dH 7.89–7.79 (8 H, m, ArH), 7.43–7.30
3
(12 H, m, ArH), 7.03 (2 H, d, JHH = 7.0 Hz, ArH-4), 6.96–6.92
(1 H, m, ArH-5), 3.89 (4 H, s, JHPt = 25.0 Hz, PhCH2); 31P{ H}
3
1
1
NMR (121 Hz, CDCl3) dP 33.1 (s, JPPt = 2969 Hz); m/z (FAB)
702.09054 (M+, C32H27ClP2Pt requires 702.09046), 668 (M–Cl)+;
Preparation of
n
max/cm-1 (solid) 3017 (br, w), 1435 (s), 1217 (s), 1103 (m), 690 (s).
{2,6-bis[methyl(diphenylphosphino)]phenyl}palladium chloride 14
The title compound was prepared similarly to 13, using 10
(0.620 g, 1.31 mmol), [PdCl2(MeCN)2] (0.300 g, 1.16 mmol) and
2-methoxyethanol (20 mL). The product 14 was obtained as a
yellow powder (0.65 g, 91%). mp 250 ◦C (dec.) (from hexane).
(Found C, 62.3; H, 4.5. Calc. for C32H27ClP2Pd: C, 62.5; H, 4.4);
1H NMR (300 MHz, CDCl3) dH 7.83–7.70 (8 H, m, ArH), 7.35–
General procedure for the Heck reaction between aryl halides and
methyl acrylate
Solid aryl halides (0.48 mmol), KHCO3 (0.0505 g, 0.504 mmol),
TBAB (0.0309 g, 0.096 mmol) and [PdCl(Rf-PCP)] 13 or
[PdCl(PCP)] 14 (1 mole %, 0.0048 mmol) were added to a Radley’s
Carousel reaction tube. The tube was evacuated and refilled with
argon (¥3), before liquid aryl halides (0.48 mmol), methyl acrylate
(0.0620 g, 0.0650 mL, 0.72 mmol) and NMP (2.00 mL) were
added. The tube was placed into a preheated oil bath (120 ◦C)
for the reaction time. After cooling to room temperature, the
reaction mixture was poured into a volumetric flask (25 mL) and
3
7.29 (12 H, m, ArH), 7.04 (2 H, d, JHH = 7.3 Hz, ArH-4), 6.95
1
31
(1 H, m, ArH-5), 3.89 (4 H, vt, JHP = 4.7 Hz, PhCH2); H{ P}
NMR (300 MHz, CDCl3) dH 7.83–7.70 (8 H, m, ArH), 7.35–7.29
3
(12 H, m, ArH), 7.04 (2 H, d, JHH = 7.3 Hz, ArH-4), 6.95 (1 H,
1
m, ArH-5), 3.89 (4 H, s, PhCH2); 31P{ H} NMR (121 Hz, CDCl3)
dP 33.5 (s); m/z (FAB) 577.06248 ((M–Cl)+. C32H27P2Pd requires
2004 | Dalton Trans., 2011, 40, 1998–2005
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methanol was added. Samples were taken and analysed by GC.
(200 ◦C for 5 min. Injector: 250 ◦C, detector: 240 ◦C. Rt 2.5 min (4-
iodoacetophenone), 2.2 min (4-bromoacetophenone), 2.0 min (4-
chloroacetophenone), 4.5 min (trans-methyl 4-acetylcinnamate).
Rt 2.1 min (4-iodoanisole), 2.0 min (4-bromoanisole), 3.5 min
(trans-methyl 4-methoxycinnamate).
2 J. A. Gladysz, D. P. Curran and I. T. Horva´th, Handbook of Fluorous
Chemistry, 2004, Wiley-VCH, Weinheim, Germany.
3 B. Croxtall, E. G. Hope and A. M. Stuart, Chem. Commun., 2003,
2430.
4 (a) B. Gourdet, J. A. Vidal and A. M. Stuart, J. Fluorine Chem., 2010,
131, 1133; (b) L. Wang, C. Cai, D. P. Curran and W. Zhang, Synlett,
2010, 433; (c) Y.-B. Huang, W.-B. Yi and C. Cai, J. Fluorine Chem.,
2010, 131, 879; (d) T. Miura, K. Imai, M. Ina, N. Tada, N. Imai and
A. Itoh, Org. Lett., 2010, 12, 1620; (e) G. Pozzi, V. Mihali, F. Foschi,
M. Penso, S. Quici and R. H. Fish, Adv. Synth. Catal., 2009, 351,
3072; (f) J. A. Vidal and A. M. Stuart, J. Org. Chem., 2007, 72, 3166;
(g) Q. Chu, W. Zhang and D. P. Curran, Tetrahedron Lett., 2006, 47,
9287.
5 (a) J. Fawcett, E. G. Hope, A. M. Stuart and A. J. West, Green Chem.,
2005, 7, 316; (b) M. Matsugi and D. P. Curran, J. Org. Chem., 2005, 70,
1636; (c) D. P. Curran, K. Fischer and G. Moura-Letts, Synlett, 2004,
1379.
General recycling procedure for the Heck reaction between
4-bromoacetophenone and methyl acrylate
4-Bromoacetophenone (0.4976 g, 2.500 mmol), KHCO3 (0.2628 g,
2.630 mmol), TBAB (0.1612 g, 0.500 mmol), tolyl ether (0.4957 g,
2.500 mmol) and [PdCl(Rf-PCP)] 13 (50 mg, 1 mole%, 0.025
mmol) were added to a Radley’s Carousel reaction tube. The tube
was evacuated and refilled with argon (¥3), before methyl acrylate
(0.3228 g, 0.338 mL, 3.750 mmol) and NMP (5.00 mL) were added.
6 J. Tsuji, Palladium Reagents and Catalysts: Innovations in Or-
ganic Synthesis, 1995, John Wiley
England.
& Sons Ltd., Chichester,
◦
The tube was placed into a preheated oil bath (120 C), samples
7 (a) J. T. Singleton, Tetrahedron, 2003, 59, 1837; (b) M. E. Van Der Boom
and D. Milstein, Chem. Rev., 2003, 103, 1759.
(0.01 mL) were taken over 4 h and analysed by GC. The reaction
mixture was allowed to cool to room temperature under argon
before the solvent and the remaining volatiles were removed by
8 (a) P. Bhattacharyya, D. Gudmunsen, E. G. Hope, R. D. W. Kemmitt,
D. R. Paige and A. M. Stuart, J. Chem. Soc., Perkin Trans. 1, 1997,
3609; (b) J. Fawcett, E. G. Hope, R. D. W. Kemmitt, D. R. Paige, D. R.
Russell and A. M. Stuart, J. Chem. Soc., Dalton Trans., 1998, 3751;
(c) E. G. Hope, R. D. W. Kemmitt and A. M. Stuart, J. Chem. Soc.,
Dalton Trans., 1998, 3765; (d) D. Sinuo, G. Pozzi, E. G. Hope and A. M.
Stuart, Tetrahedron Lett., 1999, 40, 849; (e) B. Croxtall, J. Fawcett, E. G.
Hope, D. R. Russell and A. M. Stuart, J. Chem. Soc., Dalton Trans.,
2002, 491.
9 (a) H. Kleijn, J. T. B. H. Jastrzebski, R. A. Gossage, H. Kooijman,
A. L. Spek and G. van Koten, Tetrahedron, 1998, 54, 1145; (b) P. Dani,
B. Richter, G. P. M. van Klink and G. van Koten, Eur. J. Inorg. Chem.,
2001, 125.
10 (a) R. Tuba, V. Tesevic, L. V. Dinh, F. Hampel and J. A. Gladysz, Dalton
Trans., 2005, 2275; (b) C. S. Consorti, F. Hampel and J. A. Gladysz,
Inorg. Chim. Acta, 2006, 359, 4874; (c) R. C. da Costa, M. Jurisch and
J. A. Gladysz, Inorg. Chim. Acta, 2008, 361, 3205.
11 D. Duncan, PhD Thesis, University of Leicester, 2007.
12 K. S. Vallin, Q. Zhang, M. Larhed, D. P. Curran and A. Hallberg,
J. Org. Chem., 2003, 68, 6639.
◦
Kugelro¨hr distillation (0.1 mbar, 40 C). The resulting solid was
dissolved in acetonitrile (8 mL) and loaded onto a column of
FRPSG (4 g) which had been preconditioned with acetonitrile.
The flask was washed with dichloromethane (0.5 mL ¥ 2) and
finally with acetonitrile (2 mL). The column was eluted with
acetonitrile (28 mL) to give the organic products and then ethyl
acetate (90 mL) to give the fluorous palladium complex. Both
1
fractions were concentrated and analysed by 1H, 31P{ H} and
1
19F{ H}NMR spectroscopy. The organic compound was also
analysed by ICP-OES for any palladium leaching. The FRPSG
column was washed with water (20 mL) to remove any inorganic
salts and was regenerated with acetonitrile. The organic phase
was analysed by gas chromatography to determine the conversion
to product using tolyl ether as the internal standard (200 ◦C
for 5 min. Injector: 250 ◦C, detector: 240 ◦C. Rt 2.2 min (4-
bromoacetophenone), 3.2 min (tolyl ether), 4.5 min (trans-methyl
4-acetylcinnamate).
13 I. P. Beletskaya, A. V. Chuchuryukin, G. van Koten, H. P. Dijkstra,
G. P. M. van Klink, A. N. Kashin, S. E. Nefedov and I. L. Eremenko,
Russ. J. Org. Chem., 2003, 39, 1268.
14 (a) H. Rimml and L. M. Venanzi, J. Organomet. Chem., 1983, 259, C6;
(b) R. J. Cross, A. R. Kennedy and K. W. Muir, J. Organomet. Chem.,
1995, 487, 227; (c) M. A. Bennett, H. Jin and A. C. Willis, J. Organomet.
Chem., 1993, 451, 249.
Acknowledgements
15 N. T. S. Phan, M. Van Der Sluys and C. W. Jones, Adv. Synth. Catal.,
2006, 348, 609.
We thank the Royal Society (AMS), the EPSRC (DD) and
GlaxoSmithKline (DD) for financial support. Michael Urquhart
and Mark Armitage from GSK are gratefully acknowledged for
their help with the reaction optimisation.
16 (a) J. G. de Vries, Dalton Trans., 2006, 421; (b) M. T. Reetz and J. G. de
Vries, Chem. Commun., 2004, 1559; (c) A. H. M. de Vries, J. M. C. A.
Mulders, J. H. M. Mommers, H. J. W. Henderickx and J. G. de Vries,
Org. Lett., 2003, 5, 3285.
17 M. R. Eberhard, Org. Lett., 2004, 6, 2125.
18 (a) C. Rocaboy and J. A. Gladysz, New J. Chem., 2003, 27, 39; (b) C.
Rocaboy and J. A. Gladysz, Org. Lett., 2002, 4, 1993.
19 M. T. Reetz and E. Westermann, Angew. Chem., Int. Ed., 2000, 39, 165.
20 G. M. Sheldrick, SHELXTL Version 6.10, Bruker AXS, Inc., Maddi-
son, Wisconsin, USA, 2000.
References
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1995.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 1998–2005 | 2005
©