Polystyrene-supported dicyclohexylphenylphosphine adducts of amine- and phosphite-based palladacycles in the Suzuki coupling of aryl chlorides

Article abstract of DOI:10.1039/b415286g

The polystyrene-immobilised palladacyclic complexes [Pd(TFA) (κ²-N,C-C₆H₄CH₂NMe ₂){P(C₆H₄-4-PS)Cy₂}] and [PdCl(κ²-P,C-{P(OC₆H₂-2,4-

Full text of DOI:10.1039/b415286g

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F U L L P A P E R
Polystyrene-supported dicyclohexylphenylphosphine adducts of
amine- and phosphite-based palladacycles in the Suzuki coupling
of aryl chlorides†
Robin B. Bedford,*a Simon J. Coles,b Michael B. Hursthouseb and Ve´ronique J. M. Scordiaa
a Department of Chemistry, University of Exeter, Exeter, UK EX4 4QD.
E-mail: r.bedford@ex.ac.uk; Fax: +44 (0) 1392 263434
b EPSRC National Crystallography Service, Department of Chemistry, University of
Southampton, Highfield Road, Southampton, UK SO17 1BJ
Received 1st October 2004, Accepted 13th January 2005
First published as an Advance Article on the web 7th February 2005
The polystyrene-immobilised palladacyclic complexes [Pd(TFA)(j2-N,C-C6H4CH2NMe2){P(C6H4-4-PS)Cy2}] and
[PdCl(j2-P,C-{P(OC6H2-2,4-tBu2)(OC6H3-2,4-tBu2)2}{P(C6H4-4-PS)Cy2}] (PS = polystyrene) and the homogeneous
analogues [Pd(TFA)(j2-N,C-C6H4CH2NMe2)(PPhCy2)] and PdCl(j2-P,C-{P(OC6H2-2,4-tBu2)(OC6H3-2,4-tBu2)2}-
(PPhCy2)] were synthesised and characterised. The X-ray structure of one of the homogeneous analogues,
[Pd(TFA)(j2-N,C-C6H4CH2NMe2)(PPhCy2)] was determined. All the complexes have been tested and show good
activity in the Suzuki coupling of aryl chloride substrates. While the polystyrene-immobilised complexes are not
recyclable, they are easily extracted and show low levels of palladium leaching.
We have recently prepared a range of di- and trialkylphosphine
Introduction
adducts of N- and P-based palladacycles and shown them
The coupling of aryl halides with aryl boronic acids, the Suzuki
to have good to outstanding activity in the Suzuki coupling
reaction (Scheme 1), is one of the most powerful and versatile
of aryl chlorides.7,8 We wondered whether simple polystyrene-
methods for the synthesis of biaryls.1 The use of aryl chloride
immobilised versions could be synthesised and whether they
substrates in such reactions is attractive because they tend to
would show good activity and recyclability. The results from
be cheaper and more widely available than their bromide or
this study are reported here.
iodide counterparts. Unfortunately the relatively high C–Cl
bond strength retards the rate of oxidative addition and thus
makes their activation more difficult than heavier congeners.2
Results and discussion
Currently there is much interest in the development of catalysts
Synthesis of supported complexes and homogeneous analogues
that facilitate the coupling of aryl chloride substrates,3 and
palladacyclic complexes have played a particularly successful
The reaction of the dimeric precursor complexes 3 and 4
with the commercially available dicyclohexylphenylphosphine
polystyrene, 5, in dichloromethane for 1 h led to the formation
of the supported complexes 6 and 7, respectively (Scheme 2).
For comparison purposes we also synthesised the closely related
homogeneous complexes 8 and 9 using an analogous method.
role in this regard.4
1
The 31P{ H} NMR spectrum of complex 8 shows a singlet
Scheme 1 The Suzuki biaryl coupling reaction.
at d 47.0 ppm in CHCl3 and 46.5 ppm in C6D6 indicating the
presence of only one isomer in solution. This value is within
the range reported for complexes of the formula [Pd(TFA)(j2-
N,C-C6H4CH2NMe2)(PR3)] (PR3 = PCy3, PCy2(o-biphenyl),
The perennial problem of catalyst removal and recycling
has featured less frequently in the Suzuki coupling of aryl
chlorides compared with easier to couple substrates (bromides
and iodides). One of the simplest ways of immobilising pal-
ladium catalysts is by the use of polystyrene-supported phos-
phine ligands. Inada and Miyaura demonstrated that simple
diphenylphosphine-modified polystyrene supports, 1, can be
used to immobilise Pd catalysts capable of coupling chloropy-
ridines and activated (electron-deficient) aryl chlorides.5 Par-
rish and Buchwald showed that the polystyrene-supported
dialkylphosphinobiphenyl ligand 2 gives catalysts that can be
used with non-activated and reasonably sterically encumbered
aryl chloride substrates.6
7b,9
PtBu3, PPh3, P(C6H4OMe)3, P(C6H4CF3)3) implying a similar
structure. This is further indicated by the fact that the 1H NMR
spectrum shows a doublet at 2.70 ppm for the NMe2 groups,
with a 3JPH of 2.3 Hz, which is within the range of the coupling
7b,9
constants reported for the analogous complexes.
The molecular structure of complex 8 has been determined
by single-crystal X-ray analysis and the results are presented
in Fig. 1. As can be seen the molecule is approximately
square planar about the palladium with the P-donor adopting
a trans disposition to the N-atom of the orthometallated
N,N-dimethylbenzylamine ligand. As suggested by the NMR
data, the structure is similar to those reported for a range
of other phosphine adducts of the formula [Pd(X)(j2-N,C-
7b,9
C6H4CH2NMe2)(PR3)]. Comparing 8 with the closely related
2
7b
complexes [Pd(TFA)(j -N,C-C6H4CH2NMe2)(PRCy2)] (11a:
R = Cy, 11b: R = o-biphenyl) it can be seen that there is no
significant difference in the Pd–C or the Pd–N bond lengths
and the Pd–O bond of 8 is only marginally shorter. By contrast
the Pd–P bond length of 8 is significantly shorter, possibly due
to the lower steric profile of the PPhCy2 ligand. Indeed the
† Electronic supplementary information (ESI) available: IR spectra for
complexes 6–9. See http://www.rsc.org/suppdata/dt/b4/b415286g/
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 9 9 1 – 9 9 5
9 9 1
©

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peaks corresponding to the immobilised complex that are very
similar to those of the non-supported analogue 8 (see ESI† for
IR spectra of complexes 6–9). These data are consistent with the
supported complex 6 having a very similar structure to that of
complex 8.
The 31P NMR spectrum of complex 9 (C6D6), shown in
Fig. 2(a), indicates the presence of both possible isomers in
which the P-donor atoms are either cis- (two doublets at 135.1
2
and 23.6 ppm with a JPP of 36.2 Hz) or trans-disposed (two
2
doublets at 128.2 and 32.7 ppm with a JPP of 582.3 Hz), with
the major isomer being that with the P-donors trans. In addition
there are two small peaks around ∼120 ppm which correspond to
the cis and trans isomers of unreacted complex 4. The gel-phase
1
31P{ H} spectrum of the polystyrene-immobilised analogue 7 in
C6D6 is shown in Fig. 2(b). As can be seen there are two very
broad doublets at 128 and 33 ppm with a 2JPP of ∼550 Hz. The
1
31P{ H}-MAS NMR spectrum of 7 shows broad peaks at 129
and 32 ppm. These data imply that the immobilised complex 7 is
very similar to the non-supported analogue 9. It is not possible
to discern whether any of the second possible isomer, with the
P-donors cis, is present. Again, the IR spectrum of 7 shows
peaks corresponding to the immobilised complex that are very
similar to those of the non-supported analogue 9.
Scheme 2 Reagents and conditions: (i) 0.5 equiv. 3, CH2Cl2, r.t. (ii) 0.5
equiv. 4, CH2Cl2, r.t.
1
Fig. 2 (a) The 31P{ H} NMR spectrum of complex 9 (C6D6). (b) The
1
gel-phase 31P{ H} NMR spectrum of supported complex 7 (C6D6).
1
(c) The 31P{ H}-MAS NMR spectrum of supported complex 7.
The palladium loadings of complexes 6 and 7 were determined
by ICP-MS as 0.54 and 0.69 mmol g−1, respectively, compared
with a nominal phosphine loading of 0.96 mmol g−1 for 5.10
This corresponds to 56 and 72% saturation of the phosphine
Fig. 1 The molecular structure of [Pd(TFA)(j2-N,C-C6H4CH2NMe2)-
◦
˚
(PPhCy2)], 8. Selected interatomic lengths (A) and angles ( ): Pd1–C1
1.994(2), Pd1–P1 2.2494(6), Pd1–O1 2.1202(16), Pd1–N1 2.124(2);
C1–Pd1–N1 82.77(9), N1–Pd1–O1 91.27(7), O1–Pd1–P1 87.66(5),
P1–Pd1–C1 98.56(8).
1
residues in 6 and 7, respectively. The gel-phase 31P{ H} NMR
spectrum of the immobilised complex 6 shows the presence of
only a small number of unreacted phosphine residues (2.5 ppm)
along with a peak at 45.5 ppm which presumably corresponds
to the phosphine oxide.
Pd–P bond length is essentially identical to that in a related
complex with a smaller triarylphosphine ligand, [Pd(TFA)(j2-
N,C-C6H4CH2NMe2){P(C6H4-4-CF3)3}].9
Catalytic studies
1
The gel-phase 31P{ H} NMR spectrum of complex 6, the
polystyrene-immobilised analogue of complex 8, shows a broad
The catalysts 6–9 were tested in the Suzuki coupling of phenyl
boronic acid with a range of aryl chloride substrates and the
results are summarised in Table 1. The reaction conditions were
1
singlet at 45.8 ppm in C6D6, while the 31P{ H}-MAS NMR
spectrum shows a singlet at 46 ppm. The IR spectrum of 6 shows
9 9 2
D a l t o n T r a n s . , 2 0 0 5 , 9 9 1 – 9 9 5

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Table 1 Suzuki coupling of aryl chlorides with phenylboronic acid catalysed by catalysts 6–9a
Entry
Aryl chloride
Catalyst (mol% Pd)
Product
Conv.b (%) [TON/mol prod. (mol Pd)−1
]
1
2
3
4
8 (1.0)
6 (0.72)
7 (0.56)
9 (1.0)
85.5 [85.5]
67 [93]
19 [34]
43.5 [43.5]
5
6
7
8
6 (0.72)
8 (1.0)
7 (0.56)
9 (1.0)
73 [101]
95 [95]
53 [94.5]
45.5 [45.5]
9
10
11
12
6 (0.72)
8 (1.0)
7 (0.56)
9 (1.0)
100 [139]
95 [95]
80.5 [144]
46 [46]
13
14
15
16
6 (0.72)
8 (1.0)
7 (0.56)
9 (1.0)
76.5 [106]
97.5 [97.5]
50.5 [90]
46 [46]
a Reagents and conditions: Aryl chloride (5.0 mmol), PhB(OH)2 (7.5 mmol), Cs2CO3 (10.0 mmol), 1,4-dioxane (15 mL), 100 ◦C, 18 h. b Conversion to
coupled product determined by GC (hexadecane internal standard).
not optimised, but rather 1,4-dioxane was used as the solvent
and Cs2CO3 as the base in order to allow comparison with results
obtained previously with related catalyst systems.
The homogeneous N-based palladacyclic catalyst 8 gives a
healthy conversion to coupled product at 1 mol% Pd loading
(entry 1). A similar activity, in terms of TON (turnover number),
is observed with the supported analogue 6 (entry 2). However,
when the loading of 8 is reduced to 0.1 mol% Pd loading or
less, essentially no activity is seen. By contrast, catalysts 11a
and b give TONs of 7100 and 4500, respectively, under similar
7b
conditions. The poorer performance compared with 11a may
well be explained in terms of both lower net electron-donating
ability and steric profile of the ligand PCy2Ph compared with
PCy3. While the phosphine in 11b, PCy2(o-biphenyl), has similar
P-donor properties to PCy2Ph, it also has the potential to
undergo further donor interactions with the palladium centre via
p-complexation of the secondary aromatic ring of the o-biphenyl
function, which can help stabilise catalytic intermediates.11
In comparison with the N-palladacyclic catalysts 6 and 8, both
the supported and non-supported P-palladacyclic complexes, 7
and 9, respectively, show lower activities with the deactivated
substrate, 4-chloroanisole (entries 3 and 4). This is perhaps sur-
Fig. 3 Attempted recycles of catalysts 6 and 7 in the Suzuki couplings
prising given that PCy3 adducts of phosphite-based palladacy-
of phenylboronic acid with 4-chloroanisole and 4-chlorotoluene.
cles give far superior performance compared with amine-based
analogues, even with this electron rich aryl chloride.8 This is pre-
substrate. This marries with the observation that the pale yellow
sumably a function of changing the phosphine. The lower net do-
nation of the aryldicyclohexylphosphines compared with PCy3,
coupled with the p-acidity of the phosphite co-ligand would
render the active Pd(0) species electron-deficient compared with
PCy3-containing analogues and thus would be expected to retard
the rate of oxidative addition with 4-chloroanisole.12
On changing the aryl chloride substrate it can be seen that
the supported N-palladacyclic complex 6 shows slightly higher
TONs than the homogeneous analogue 8. Except with 4-
chloroanisole, the supported P-palladacyclic complex 7 also
gives similar TONs to the supported P-based complex 6. By
contrast the homogeneous analogue 9 shows much lower activity
with all the chloride substrates tested. We are not currently able
to explain why immobilisation appears to have such an effect on
the performance of the P-based palladacyclic system.
catalysts turn black during the first run, indicating substantial
catalyst decomposition. This reduction presumably occurs via
a reductive elimination of the orthometallated ligand with a
phenyl group introduced by the phenylboronic acid.12 The resul-
tant decomposition implies that active Pd(0) complexes formed
during such a process are too labile to be stabilised for prolonged
periods by the phosphine residues of the polystyrene supports,
even in the presence of a p-acidic triaryl phosphite ligand.
The crude product, obtained after removal of solvent, from
run 1 of the coupling of 4-chlorotoluene with phenylboronic acid
catalysed by 6, showed minimal contamination by palladium
(12 ppm, determined by ICP-MS). This demonstrates that while
the catalysts are not recyclable, leaching of catalyst residues into
the product is low.
We next investigated the extractability and potential recycla-
bility of the immobilised catalysts 6 and 7 and the results are
summarised in Fig. 3. As can be seen, both catalysts exhibit
poor recyclability, with essentially no activity observed on the
second runs with either 4-chloroanisole or 4-chlorotoluene as
Conclusions
In summary, we have synthesised two new palladacycle-
based catalysts supported by a polystyrene-immobilised aryl-
dialkylphosphine ligand. In addition homogeneous analogues
D a l t o n T r a n s . , 2 0 0 5 , 9 9 1 – 9 9 5
9 9 3

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were synthesised for comparison purposes. All the catalysts syn-
thesised show good activity in the Suzuki coupling of activated,
non-activated and deactivated aryl chloride substrates. In one
of the cases it was found that immobilisation of the catalyst
on the polystyrene support leads to enhanced performance,
compared with the homogeneous counterpart. Despite the fact
that the supported catalysts are not recyclable, they are easily
extracted; removal of the catalyst by simple filtration leads to low
contamination of the coupled product by palladium residues.
obscured by tBu peaks. Major isomer, P-donors trans, 7.52 (m,
3
4H), 7.41 (m, 5H, Ph), 7.09 (dd, 2H, JHH = 8.5, J = 2.5 Hz),
6.94 (m, br, 1H), 6.55 (m, 1H), 1.52 (s, 18H, tBu), 1.26 (s, 18H,
tBu), 1.14 (s, 9H, tBu), 0.75 (s, 9H, tBu) ppm, Cy signals mostly
t
obscured by Bu peaks. dP (121.5 MHz) minor isomer, 23.3 (d,
2
2JPP = 38.1 Hz), 133.8 (d, JPP = 38.1 Hz). Major isomer, 32.8
(d, 2JPP = 537.5 Hz), 128.2 (d, 2JPP = 537.5 Hz) ppm. See ESI†
for IR spectrum.
X-Ray structure determination of complex 8
Experimental
Data were collected at 120 K on an Nonius KappaCCD area
detector diffractometer located at the window of a Nonius
FR591 rotating anode X-ray generator, equipped with a molyb-
General methods
All reactions and manipulations of air-sensitive materials were
carried out under nitrogen either in a glove-box or using
standard Schlenk techniques. Solvents were dried and freshly
distilled prior to use. All other chemicals were used as received.
˚
denum target (k(Mo-Ka) = 0.71073 A). Structures were solved
and refined using the SHELX-97 suite of programs.13 Data
were corrected for absorption effects by means of comparison
of equivalent reflections using the program SORTAV.14 Non-
hydrogen atoms were refined anisotropically, whilst hydrogen
atoms were generally fixed in idealised positions with their
thermal parameters riding on the values of their parent atoms.
Complexes 3 and 4 were prepared according to literature
7b,8c
methods.
Dicyclohexylphenylphosphine polystyrene, 5, was
purchased from Novabiochem. GC analyses were performed on
a Varian 3800 GC fitted with a 25 m CPSil 5CB column and
data were recorded on a Star workstation.
Crystal data. C29H39F3NO2PPd, monoclinic, P21/n, a =
◦
−1
˚
−3
13.4166(19), b = 11.8901(6), c = 18.106(3) A, b = 108.377(12) ,
Synthesis of catalysts
3
˚
V = 2741.0(5) A , Z = 4, Dc = 1.522 Mg m , l = 0.783 mm ,
34543 measured, 6280 unique (Rint = 0.0482) and 5500 (I >
2r(I)) reflections, R1 (obs) = 0.0328 and wR2 (all data) = 0.0818,
Polystyrene immobilised catalyst 6. A mixture of complex 3
(0.34 g, 0.48 mmol) and the polystyrene-immobilised ligand 5
(1.00 g, 0.96 mmol) were stirred in dichloromethane (50 ml) at
room temperature for 1 h. The pale yellow product was collected
by filtration and washed with dichloromethane (3 × 10 mL) and
then dried in vacuo. The palladium loading was determined as
−3
˚
qmax/qmin = 0.940/−1.281 e A .
CCDC reference number 251869.
See http://www.rsc.org/suppdata/dt/b4/b415286g/ for cry-
stallographic data in CIF or other electronic format.
0.54 mmol g−1 (ICP-MS). NMR: 31P{ H}-MAS, (162 MHz) dP
1
46 (s, br) ppm. dP (121.5 MHz, C6D6, gel-phase) 45.8 (s, br) ppm.
Catalysis
See ESI† for IR spectrum.
Suzuki coupling of aryl chlorides using catalysts 6 and 7
(Table 1). In a three-necked round-bottom flask equipped with
a reflux condenser were placed the appropriate aryl chloride
(5.0 mmol), phenylboronic acid (0.914 g, 7.5 mmol) and Cs2CO3
(3.258 g, 10.0 mmol) and then 1,4-dioxane (15 mL) was added.
The appropriate amount of the required catalyst was added and
the mixture was heated at 100 ◦C for 18 h, cooled, quenched with
HCl (2 M, 20 mL) and extracted with dichloromethane (3 ×
20 mL). The combined organic fraction was dried (MgSO4), the
solvent was removed under reduced pressure, the residue was
redissolved in dichloromethane (6 mL), hexadecane (0.068 M in
CH2Cl2, 1.00 mL) was added as an internal standard and the
conversion to coupled product determined by GC analysis.
Polystyrene immobilised catalyst 7. This was prepared in the
same way as 6 using complex 4 (0.38 g, 0.24 mmol) and ligand 5
(0.50 g, 0.48 mmol). The palladium loading was determined as
1
0.69 mmol g−1 (ICP-MS). NMR: 31P{ H}-MAS, (162 MHz) dP
32 (s, br), 129 (s, br) ppm. dP (C6D6, gel-phase) 33 (d, br, coupling
2
not determined), 128 (d, br, JPP ∼550 Hz) ppm. See ESI† for
IR spectrum.
[Pd(TFA)(j2-N,C-C6H4CH2NMe2)(PPhCy2)], 8.
A solu-
tion of complex 3 (0.38 g, 0.53 mmol) and dicyclohexylphenyl-
phosphine (0.29 g, 1.06 mmol) in dichloromethane (20 mL) was
stirred at room temperature for 30 min. The solvent was removed
on a rotary evaporator and the crude solid was crystallised from
dichloromethane–methanol to give complex 8 as a colourless
solid. Yield 82%. Found: C, 55.4; H, 6.2; N, 2.2. Calc. for
C29H39F3NO2PPd: C, 55.46; H, 6.26; N, 2.23%. NMR (CDCl3):
dH (300 MHz) 7.47 (m, 2H, Ph), 7.40 (m, 1H, Ph), 7.21 (m,
Suzuki coupling of aryl chlorides using catalysts 8 and 9
(Table 1). As above except that the appropriate catalyst was
added as a 1,4-dioxane solution (1.00 mL) made up to the correct
concentration by dilution of a stock solution.
3
4
2H, Ph), 6.92 (dd, 1H, JHH = 7.1, JHH = 1.1 Hz, metallated
aryl), 6.78 (dd, 1H, 3JHH = 7.1, 3JHH = 7.6 Hz, metallated aryl),
6.36 (ddd, 1H, 3JHH = 7.7, 3JHH = 7.6 Hz, metallated aryl), 6.15
Recyclability studies (Fig. 3). The reactions were performed
in a modified 100 mL three-necked flask, in which one of the
necks was fitted with a sintered frit. A mixture of the appropriate
aryl chloride (10.0 mmol), phenyl boronic acid (1.830 g,
15.0 mmol), and Cs2CO3 (6.510 g, 20.0 mmol) in 1,4-dioxane
(30 mL) and the appropriate catalyst (52 mg) was heated at
100 ◦C for 18 h. The reaction was allowed to cool and then the su-
pernatant liquid was removed by filtration through the sintered
frit. The residue was washed with dichloromethane (3 × 20 mL),
water (3 × 20 mL) and then dichloromethane (3 × 20 mL). The
combined organic fraction was dried (MgSO4), the solvent was
removed under reduced pressure, the residue was redissolved
in dichloromethane (6 mL), hexadecane (0.068 M in CH2Cl2,
1.00 mL) was added as an internal standard and the conversion
to coupled product determined by GC analysis. The residue in
the flask was dried in vacuo (3 h), the flask was recharged with
substrates, base and solvent and the reaction repeated.
3
(dd, 1H, JHH = 7.7, J = 4.8 Hz, metallated aryl), 3.95 (s, br,
2H, CH2), 2.70 (d, 6H, 4JPH = 2.3 Hz, CH3), 2.06 (m, 2H, Cy),
1.72 (m, 6H, Cy), 1.66 (m, 8H, Cy), 1,12 (m, 4H, Cy) ppm. dP
(121.5 MHz) 47 (s) ppm. See ESI† for IR spectrum.
cis/trans-[PdCl(j2 -P,C -{P(OC6H2 -2,4-tBu2 )(OC6H3 -2,4-
tBu2)2}(PPhCy2)], 9. As for complex 8, with complex 4
(1.32 g, 0.83 mmol) and dicyclohexylphenylphosphine (0.46 g,
1.67 mmol). Yield 80%. Found: C, 67.05; H, 8.45. Calc. for
C60H89ClO3P2Pd: C, 67.85; H, 8.57%. NMR (CDCl3): dH
(300 MHz) minor isomer, P-donors cis, 8.55 (ddd, 1H, J = 2.2,
3
4
2.1, 7.7 Hz, metallated aryl), 7.61 (dd, 2H, JHH = 8.5, JHH
=
2.8 Hz, non-metallated aryl), 7.57 (m, 1H), 7.47 (m, 1H), 7.33
(m, 5H, Ph), 7.18 (m, br, 1H), 7.00 (dd, 2H, 3JHH = 8.5, 4JHH
=
t
t
2.5, non-metallated aryl), 1.39 (s, 9H, Bu), 1.29 (s, 18H, Bu),
t
t
1.27 (s, 18H, Bu), 0.91 (s, 9H, Bu) ppm, Cy signals mostly
9 9 4
D a l t o n T r a n s . , 2 0 0 5 , 9 9 1 – 9 9 5

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8 For P-based systems see: (a) R. B. Bedford, C. S. J. Cazin and S. L.
Acknowledgements
Hazelwood, Angew. Chem., Int. Ed., 2002, 41, 4120; (b) R. B. Bedford,
S. L. Hazelwood and M. E. Limmert, Chem. Commun., 2002, 2610;
(c) R. B. Bedford, S. L. Hazelwood, M. E. Limmert, D. A. Albisson,
S. M. Draper, P. N. Scully, S. J. Coles and M. B. Hursthouse, Chem.
Eur. J., 2003, 9, 3216; (d) R. B. Bedford, S. L. Hazelwood, P. N.
Horton and M. B. Hursthouse, Dalton Trans., 2003, 4164.
9 R. B. Bedford, C. S. J. Cazin, V. J. M. Scordia, S. J. Coles, M. E. Light
and M. B. Hursthouse, Dalton Trans., 2003, 3350.
We thank the EPSRC and the Institute of Applied Catalysis for
funding and Johnson Matthey for the loan of palladium salts
and for ICP-MS analysis. The solid-state 31P{ H}-MAS NMR
1
were performed by Dr S. Wimperis and N. G. Dowell at the
University of Exeter.
10 Manufacturer’s data.
Notes and references
1 For recent reviews, see: (a) N. Miyaura and A. Suzuki, Chem. Rev.,
1995, 95, 2457; (b) S. P. Stanforth, Tetrahedron, 1998, 54, 263; (c) A.
Suzuki, J. Organomet. Chem., 1999, 576, 147.
2 For a discussion, see: V. V. Grushin and H. Alper, Chem. Rev., 1994,
94, 1047.
3 For recent reviews see: (a) A. F. Littke and G. C. Fu, Angew. Chem.,
Int. Ed., 2002, 41, 4176; (b) R. B. Bedford, C. S. J. Cazin and D.
Holder, Coord. Chem. Rev., 2004, 248, 2283.
11 For examples of Pd–aryl p-interactions, see: (a) S. M. Reid, R. C.
Boyle, J. T. Mague and M. J. Fink, J. Am. Chem. Soc., 2003, 125,
7816; (b) J. Yin, M. P. Rainka, X.-X. Zhang and S. J. Buchwald,
J. Am. Chem. Soc., 2002, 124, 1162; (c) P. Kocovsky´, S. Yyskocil,
I. C´ısarovra´, J. Sejbal, I. Tisˇlerova´, M. Smrcina, G. C. Lloyd-Jones,
S. C. Stephen, C. P. Butts, M. Murray and V. Langer, J. Am. Chem.
Soc., 1999, 121, 7714; (d) T. Hayashi, H. Iwamura, M. Naito, Y.
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4 For a recent review see: R. B. Bedford, Chem. Commun., 2003, 1787.
5 K. Inada and N. Miyaura, Tetrahedron, 2000, 56, 8661.
6 C. A. Parrish and S. L. Buchwald, J. Org. Chem., 2001, 66, 3820.
7 For N-based systems see: (a) R. B. Bedford and C. S. J. Cazin,
Chem. Commun., 2001, 1540; (b) R. B. Bedford, C. S. J. Cazin, S. J.
Coles, T. Gelbrich, P. N. Horton, M. B. Hursthouse and M. E. Light,
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12 We have shown that phosphine adducts of N-, P- and S-based pal-
ladacycles undergo reductive ring-opening processes in the presence
of arylboronic acids to liberate zerovalent palladium species. For an
overview see ref. 4.
13 G. M. Sheldrick, SHELX-97: Programs for structure solution and
refinement, University of Go¨ttingen, Germany, 1997.
14 R. H. Blessing, J. Appl. Crystallogr., 1997, 30, 421.
D a l t o n T r a n s . , 2 0 0 5 , 9 9 1 – 9 9 5
9 9 5