Chiral palladacycles based on resorcinol monophosphite ligands: The role of the meta-hydroxyl in ligand C-H activation and catalysis

Article abstract of DOI:10.1039/c1dt10357a

The reactions of a range of chiral resorcinol monophosphite ligands with [PdCl₂(NCMe)₂] was investigated in order to establish whether the meta-hydroxyl function was involved in the orthometallation processes. These ligands underwent facile orthopalladation at room temperature in the presence of Et₃N, whilst the equivalent hydroxyl-free analogues needed more forcing conditions to induce orthometallation. When the hydroxyl function was replaced by a similar sized methyl group no orthometallation occurred, even on heating. Furthermore the hydroxyl group influences both the structure and isomerism in the resultant palladacycles via hydrogen bonding to adjacent chloride ligands. Similarly, the hydroxyl function leads to higher enantiocontrol in the asymmetric allylation of benzaldehyde with allyl tributyltin. Representative examples of the ligands and the palladium complexes obtained were characterised by single crystal X-ray diffraction. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt10357a

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Cleavage of unreactive bonds with pincer metal complexes
Martin Albrecht and Monika M. Lindner
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CSC-pincer versus pseudo-pincer complexes of palladium(II): a comparative study on
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Dalton Trans., 2011, DOI: 10.1039/C1DT10269A
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PAPER
Chiral palladacycles based on resorcinol monophosphite ligands: the role of
the meta-hydroxyl in ligand C–H activation and catalysis†
Robin B. Bedford,* Yu-Ning Chang, Mairi F. Haddow and Claire L. McMullin
Received 2nd March 2011, Accepted 21st June 2011
DOI: 10.1039/c1dt10357a
The reactions of a range of chiral resorcinol monophosphite ligands with [PdCl2(NCMe)2] was
investigated in order to establish whether the meta-hydroxyl function was involved in the
orthometallation processes. These ligands underwent facile orthopalladation at room temperature in
the presence of Et3N, whilst the equivalent hydroxyl-free analogues needed more forcing conditions to
induce orthometallation. When the hydroxyl function was replaced by a similar sized methyl group no
orthometallation occurred, even on heating. Furthermore the hydroxyl group influences both the
structure and isomerism in the resultant palladacycles via hydrogen bonding to adjacent chloride
ligands. Similarly, the hydroxyl function leads to higher enantiocontrol in the asymmetric allylation of
benzaldehyde with allyl tributyltin. Representative examples of the ligands and the palladium
complexes obtained were characterised by single crystal X-ray diffraction.
acids and arylsiloxanes to enones (Scheme 1),11 as well as the
allylation of aldehydes with allyl tributyltin (Scheme 2).12
Introduction
Despite early reports on the preparation of triarylphosphite-
based palladacycles, 1,1 until about 13 years ago, their catalytic
activity was not examined in detail.2 Since then phosphite-based
palladacycles, 1, and their phosphine and carbene adducts, 2, have
been shown to display excellent catalytic activity in a range of C–
C and C-heteroatom bond-forming reactions.3 This includes their
application to Suzuki,4 Stille,4a,5 Heck6 and Buchwald–Hartwig
Scheme 1 Catalytic arylation of enones.
amination reactions,7 catalytic C–P bond formation,8 the alkoxy-
and amido-carbonylation of aryl halides,9 and the borylation of
aryl halides.10
Scheme 2 Catalytic allylation of aldehydes.
Recently attention has focussed on the development of chiral
versions of triarylphosphite-based palladacycles, not least because
of the relative ease of synthesis of chiral phosphites. In particular,
In most if not all of these cross-coupling reactions, where
the BINOL-based ligand 3a13 has proved to be a particularly useful
the mode of catalyst activation has been studied, the phosphite-
ligand for the facile production of palladacyclic and platinacyclic
palladacycles undergo reductive processes to liberate active pal-
complexes (4a and 5) and their phosphine, phosphite and carbene
ladium (0) species. By contrast Lewis-acid catalysed addition
adducts.14
reactions do not require a reduction of the palladium(II) centre and
These complexes have been found to show good activity but
thus the palladacycles are more likely to remain intact during the
poor enantioselectivity in the conjugate addition of arylboronic
catalytic cycle. Accordingly, the use of catalysts of the types 1 and
acids to enones and the allylation of aldehydes with allyl tin
2 in addition reactions has become the focus of recent research and
reagents (Schemes 1 and 2).14b
they have been exploited in the conjugate addition of arylboronic
In the preceding paper we described the synthesis of
chiral monophosphite ligands 6, derived from 2,4-di-tert-
butylresorcinol, which acted as intermediates in the formation
School of Chemistry, University of Bristol, Cantocks Close, Bristol, UK,
of mixed phosphite-phosphinite pincer ligands.15 These mono-
BS8 1TS. E-mail: r.bedford@bristol.ac.uk
phosphite ligands have the potential for secondary interactions
arising from the meta-hydroxyl function which could play a
† CCDC reference numbers 815807–815810. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt10357a
9042 | Dalton Trans., 2011, 40, 9042–9050
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The Royal Society of Chemistry 2011
©

significant role in both the formation and structure of their
complexes and also in the subsequent exploitation of the resultant
complexes in catalytic reactions. Accordingly, we now turn our
attention to the affect of the proximate hydroxyl function in
both the formation of palladacycles and in asymmetric catalytic
addition reactions.
Scheme 3 Ligand synthesis. Conditions: C6H2-2,4-tBu2-1-(OH)-5-(OLi),
toluene, 0 ◦C–r.t., 18 h. (ii) 2,4-di-tert-butylresorcinol, NEt3, toluene, r.t.,
24 h. (iii) 2,4-di-tert-butylphenol, NEt3, toluene, r.t. 18 h. (For 3c, 90 ◦C
for 5 days). (iv) 2,4-di-tert-butyl-5-methylphenol, NEt3, toluene, r.t. 18 h.
Results and discussion
Ligand synthesis
The lower steric profile monophosphite ligands 6a and b
(R = H and Me respectively) were synthesised from 2,4-di-tert-
butylresorcinol by treating the latter with one equivalent of butyl-
lithium followed by reaction of the resultant phenoxide with the
appropriate S,S-chlorophosphite, 7, in order to prevent formation
of the bis(phosphite) pincer ligands (Scheme 3). By contrast,
the bulkier monophosphite ligands 6c, e and f were prepared as
described in the preceding paper by reacting the resorcinol with
the appropriate chlorophosphite 7 in the presence of triethylamine.
This milder route is effective here because the formation of
the bis(phosphite) ligands with these bulkier substituents is not
possible under these or indeed more forcing conditions.15 This
latter methodology was extended to the synthesis of the 3,3¢-
dimethylphenylsilylated-BINOL derivative 6d. For comparison
purposes, in order to help delineate the role of the hydroxyl
function in complex formation and catalysis, we also prepared the
ligands 3b–e, which lack the hydroxyl residue, and the analogue 8
in which the hydroxyl of 6b was replaced by a similar sized methyl
residue. The single crystal X-ray structure of one of the new ligands
(3b) was determined and the molecule is shown in Fig. 1.
The ligands based on 3,3¢-silylated BINOL phosphites showed
a steady downfield shift in their 31P NMR spectra as methyl groups
were replaced with bulkier phenyl residues on the silicon for both
ligands based on 2,4-di-tert-butylresorcinol, 6c–f (d 139.3 ppm for
SiMe3 to 148.8 ppm for SiPh3) and 2,4-di-tert-butylphenol 3c–e (d
145.3 ppm for SiMe3 to 149.5 ppm for SiMePh2). It is tempting
to conclude that this can be attributed to perturbations in the 7-
membered ring caused by steric interactions with the silyl residues.
However the 31P NMR spectroscopic data for the unsubstituted
ligand 6a (d 144.5 ppm) and the methyl substituted ligands 6b and
Fig. 1 X-ray structure of ligand 3b. Thermal ellipsoids set at 30%
probability.
3b (d 141.0 and 142.9 ppm respectively) are not consistent with
this simple analysis.
1
The H NMR spectra of the ligands 6 showed broad singlets
in the range d 3.62–4.64 ppm for the OH peaks. These values are
consistent with simple phenols in CDCl3 solution.16
Complex synthesis
We previously reported that complex 4a can be readily synthesised
by the heating ligand 3a with [PdCl2(NCMe)2] in toluene at reflux
temperature for 20 h.14b Similar procedures led to the isolation
of the new, bulkier palladacyclic complexes 4b–4d. Complexes
4b–d exist as a mixture of cis and trans isomers in solution as
1
observed by 31P and H NMR spectroscopy, consistent with the
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 9042–9050 | 9043
©

data obtained for 4a14b and indeed most if not all previously
reported triarylphosphite-based palladacycles.
simple dimeric adduct, complex 10 (Scheme 4) as a mixture of
cis and trans isomers. Therefore the role of the hydroxyl group in
facilitating orthometallation is presumably an electronic one. The
reactions are run in the presence of triethylamine as base, so the
oxygen donor is likely to be deprotonated. The phenoxide formed
may help direct C–H activation by coordination of the oxygen to
the palladium centre and the oxygen anion could also act as an
intramolecular base to facilitate the C–H deprotonation.20
In the solid state complex 4c adopts the anticipated trans17
geometry as determined by a single crystal X-ray diffraction study,
the results of which are shown in Fig. 2. The square planar
environments of the two palladium atoms are not co-planar: the
angle a (defined by the two metal and two Cl atoms, Fig. 3) is
19.5(1)◦. Of all 30 published crystal structures of square planar
dimeric palladium and platinum phosphorus-based metallacycles
of the form shown in Fig. 3,18 only those twelve that are in space
groups in which chiral molecules can crystallise have a > 0◦, with
only two exceptions.19 All others adopt a planar conformation
(with a = 0◦), usually imposed by a crystallographic centre
of inversion on the centroid of M ◊ ◊ ◊ M, presumed to be the
lowest energy conformation, but which is obviously unavailable
to enantiomerically pure chiral compounds. Thus it is presumed
that a > 0◦ is a consequence of the chiral nature of the ligands, with
its value broadly dependent on the bulkiness of the substituents.
Fig. 2 X-ray structure of complex 4c. Thermal ellipsoids set at 30%
probability.
Scheme 4 Synthesis of complexes. Conditions: (i) [PdCl2(NCMe)2],
toluene, 80–85 ◦C, 16–48 h. (ii) [PdCl2(NCMe)2], NEt3, DCE, r.t. 18–24 h.
(iii) [PdCl2(NCMe)2], toluene, 80 ◦C, 24 h. (iv) [PdCl2(NCMe)2], NEt3,
DCE, r.t. 24 h.
The 1H NMR spectra of complexes 9 in CDCl3 show a
substantial downfield shift of the hydroxyl protons to d 8.4–
10.0 ppm. This deshielding is consistent with hydrogen bonding to
the phenolic OH.16 Interestingly both 31P and 1H NMR spectra of
complexes 9a–d show only one isomer for the dimer, in contrast to
all other triarphosphite-based palladacycles which, to the best of
our knowledge, all show cis–trans isomerism in solution. The single
crystal X-ray structure of complex 9d (shown in Fig. 4) shows
O ◊ ◊ ◊ Cl separations of 2.974(9) and 2.997(8) A, again consistent
with a hydrogen bond, suggesting that this is the hydrogen bonding
observed in solution.
As seen with complex 4c, there is a deviation away from co-
planarity of the two palladium square planes, although in this
case it is far more pronounced (a = 48.4(1)◦). The hydrogen-
bonding motif may account for observation of only one isomer in
solution for the complexes 9a–d; the trans isomer would maximise
the strength of the hydrogen bonds whereas the cis would lead to
Fig. 3 Angle between square planes (a) in palladacyclic and platinacyclic
dimers, defined by MCl2 planes.
The palladacycles based on the resorcinol monophosphite lig-
ands 6a, b, d–f, complexes 9a–d respectively, were readily formed at
room temperature in 1,2-dichloroethane employing triethylamine
as base. When the same conditions were applied to the reaction
of ligand 3e with [PdCl2(NCMe)2] then a mixture of products
˚
1
was observed by H NMR of which the dimer 4d was a minor
component. This suggests that the incorporation of the hydroxyl
residue aids the orthometallation process. The role played by the
hydroxyl group is unlikely to be due to steric considerations, indeed
the similarly sized methyl-substituted ligand 8 does not undergo
orthopalladation, even under heating, but rather generates the
9044 | Dalton Trans., 2011, 40, 9042–9050
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The Royal Society of Chemistry 2011
©

Fig. 4 X-ray structure of complex 9d. Phenyl groups of SiPh3 and pentane
solvate omitted for clarity. Thermal ellipsoids set at 30% probability.
Fig. 5 X-ray structure of complex 11, Et3NH+ counterion and solvate
omitted for clarity. Thermal ellipsoids set at 30% probability.
for 24 h show small amounts of a second product in their 31P
NMR spectra at d 131.9, 129.5 and 125.8 ppm, consistent with
‘ate’ complex formation.
both hydroxyl residues competing for electron density from the
same chloride.
The attempted synthesis of the palladacycle derived from
ligand 6c did not yield the expected dimeric complex; instead a
monomeric palladacyclic ‘ate’ species with a triethylammonium
counterion, complex 11, was produced. Such palladacyclic ‘ate’
complexes have been prepared previously from dimeric pallada-
cycles and ammonium chloride salts,21 but we cannot account
for why this is the sole instance where this occurs with ligands 6
in spite of the fact that all the palladacycles 9 are produced in
the presence of triethylamine hydrochloride. The X-ray structure
of complex 11 is shown in Fig. 5. Again the O ◊ ◊ ◊ Cl (2.936(8)
Catalysis
We have previously shown that chiral palladium-PCP pincer com-
plexes based on BINOL-derived resorcinol bis(phosphites) show
good activity and moderate enantioselectivity in the allylation of
benzaldehye with allyl tributyltin.22,15 By contrast, whilst com-
plexes 4a and 5 and various examples of their adducts show good
to excellent activity in the same reaction, their stereoselectivity is
poor (maximum 15% e.e.).14b We therefore chose the same reaction
to study here as it would provide a clear indication as to whether
or not the incorporation of a hydroxyl function and/or modified
BINOL residues would improve enantiocontrol and the results
from this study are summarised in Table 1.
˚
A) separation is consistent with a hydrogen bonding interaction,
which is supported by 1H NMR spectroscopy which shows a
downfield shift of the phenolic proton to d 9.32 ppm in CDCl3.
The 31P NMR spectrum of 11 shows a peak at d 130.35 ppm.
Interestingly solutions of complexes 9a–c in CDCl3 left to stand
Table 1 Palladacycle-catalysed allylation of benzaldehydea
entry
palladacycle
K2CO3 (equiv.)
Temp., ◦
C
Time, h
Spec. yield, %b
e.e., %c
1
2
3
4
5
6
7
8
4b
4c
4d
0
0
0
0
24
24
24
24
24
24
24
24
24
24
24
24
70
24
24
17
32
32
93
82
13
71
48
12
54
49
58
15
7
27
11
13
22
24
43
37
24
46
24
48
46
29
25
17
0.1
0.1
0.1
0.1
0.1
0
0.1
0.1
0
0.1
1.0
0
0.1
0.1
R.T.
R.T.
0
R.T.
R.T.
0
R.T.
R.T.
R.T.
0
9b
9c
9
10
11
12
13
14
15
9d
0
R.T.
47
a Conditions: 5 mol% Pd catalyst loading, CH2Cl2. b Determined by 1H NMR spectroscopy (1,3,5-trimethoxybenzene internal standard). c Determined
by chiral HPLC, R-isomer obtained in all cases.
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Dalton Trans., 2011, 40, 9042–9050 | 9045
©

Comparing entries 1 and 2 it can be seen that the addition of
10% K2CO3 to the reaction mixture increases the performance
of palladacycles 4b at the expense of stereoselectivity. Despite
this, base was added to the rest of the reactions catalysed by
complexes 4 (unless otherwise stated) in order to maximise turn-
over. Complex 4c seems to show unusual behaviour in that lower
e.e. is seen at lower temperature (compare entries 3 and 4, Table
1). This may well be as a result of base induced decomposition
of the active catalyst to a more active but less selective species.
Of the simple palladacyclic catalysts tested, complex 4d showed
the highest enantioselectivity, albeit at low conversion (entry 6,
Table 1). With this catalyst, enantioselectivity was less strongly
influenced by base than 4b (entry 7, Table 1).
Comparing the hydroxyl-containing catalyst 9b in the presence
of 10 mol% base with the equivalent hydroxyl-free palladacycle
4b under identical conditions (entries 9 and 2, Table 1) it appears
that the introduction of the hydroxyl function led to a significant
increase in enantioselectivity (from 11 to 46% ee). Unfortunately,
in this case, the yield was lower. Running the reaction at room
temperature led to an increase in yield but a drop in enantiocontrol
(entry 8, Table 1). The best balance of enantioselectivity (46%)
and activity (58%) was achieved using complex 9c with 100 mol%
K2CO3 at room temperature (entry 12, Table 1). Interestingly, when
the reaction was performed in the absence of base then a similar
conversion but a far lower enantioselectivity was observed (entry
10, Table 1). Here, unlike with hydroxyl-free palladacycles 4, it
seems that the addition of base is beneficial. It is possible that
the deprotonated hydroxyl coordinates to the tin centre leading
to greater enantiocontrol. This is an area that we are currently
investigating further.
All NMR spectra were recorded using a Jeol GX270, Jeol GX400,
Jeol ECP300 and Jeol Lambda 300 spectrometers. HPLC analysis
was carried out using a Varian Prostar 210 solvent delivery
module equipped with a Varian 320 UV/Vis detector fitted with a
Chiralcel OD column (0.46 ¥ 25 cm) and using STAR workstation
software (v. 6.41). Compounds 7,24 6c, e, f,15 were prepared
according to literature methods. ESI and EI Mass spectra were
recorded on VG Analytical Quattro and VG Analytical Autospec
spectrometers respectively. Microanalyses were carried out by the
Microanalytical Laboratory of the School of Chemistry at the
University of Bristol.
Preparation of ligand 6a. To a solution of 2,4-di-tert-butyl
resorcinol (0.271 g, 1.22 mmol) in toluene (10 ml) at 0 ◦C was
added n-BuLi (1.5 M in hexane (titrated before use), 0.80 ml,
1.22 mmol) dropwise over 10 min. The resulting suspension was
stirred at room temperature for 1 h then re-cooled to 0 ◦C. After
a further 15 min at 0 ◦C, a solution of (S)-1,1¢-binaphthalene-
2,2¢-dioxychlorophosphonite (0.259 g, 0.683 mmol) in toluene
(10 ml) was added. The reaction mixture was left to warm to room
temperature and stirred for 18 h. The reaction was quenched by
addition of aqueous saturated NH4Cl solution, then extracted into
CH2Cl2. And the organic layer was washed with brine and then
dried over MgSO4, filtered and the solvent removed under reduced
pressure. The product was purified by column chromatography
(silica CH2Cl2 : hexane 3 : 2 eluent) to yield 6a as a white solid.
Yield: 0.246 g (37.5%). Anal. Calcd for C34H33O4P: C, 76.10; H,
1
6.20%. Found: C, 76.48.; H, 7.08%. 31P{ H} NMR (121.5 MHz,
1
CDCl3): d 144.5 (s). H NMR (300 MHz, CDCl3): 1.38 (s, 9,
C(CH3)3), 1.42 (s, 9, C(CH3)3), 4.64 (s, 1, OH), 6.66 (d, 1, ArH),
7.26 (s, 1, ArH), 7.27–7.34 (m, 2, ArH), 7.41–7.50 (m, 5, ArH),
7.59–7.61 (m, 1, ArH), 7.89–7.98 (m, 3, ArH), 8.02–8.04 (m, 1,
ArH). MS (ESI) m/z: 537.22 ([M+H]+), 559.20 (M+Na)+.
Conclusions
In summary we have demonstrated that the meta-hydroxyl
function of chiral mono-phosphites based on 2,4-di-tert-butyl
resorcinol can have a positive role on the ease of formation of
palladacycles. Furthermore the structures of the resultant dimeric
palladacycles feature hydrogen-bonding interactions between the
hydroxyl group and proximate chloride ligands. These interactions
influence both isomerism and the co-planarity of the metal
coordination spheres in the dimers. In one instance a palladacyclic
‘ate’ complex was formed in preference to a dimeric species under
the same reaction conditions, and again the complex contains
a hydrogen-bonding motif between the OH and the adjacent
chloride. Finally it was shown that the hydroxyl function can have
a beneficial role on enantioselectivity in the asymmetric allylation
of benzaldehyde with allyl tributyltin in the presence of base, giving
the highest e.e. yet achieved in this reaction by chiral phosphite-
based palladacycles, an effect that we are currently exploring
further.
Preparation of ligand 6b. As for 6a with 2,4-di-tert-
butyl resorcinol (0.152 mg, 0.683 mmol) and (S)-3,3¢-
dimethyl-1,1¢-binaphthalene-2,2¢-dioxychlorophosphonite
(0.259 g, 0.683 mmol). The product was purified by column
chromatography (silica, CH2Cl2 : hexane 1 : 1 eluent) to yield 6b as
a white solid. Yield: 0.235 g (61.0%). Anal. Calcd for C36H37O4P:
1
C, 76.58; H, 6.60%. Found: C, 73.23; H, 6.64%. 31P{ H} NMR
1
(121.5 MHz, CDCl3): d 141.0 (s). H NMR (300 MHz, CDCl3):
1.29 (s, 9, C(CH3)3), 1.41 (s, 9, C(CH3)3), 2.49 (d, 3, ArMe), 2.60
(d, 3, ArMe), 4.53 (br, s, 1, OH), 6.58 (d, 1, ArH), 7.19–7.24 (m,
3, ArH), 7.30–7.33 (m, 2, ArH), 7.39–7.45 (m, 2, ArH), 7.77 (s, 1,
ArH), 7.84–7.88 (m, 3, ArH). MS (ESI) m/z: 565.25 (M+H)+.
Preparation of ligand 6d. A stirred solution of 2,4-di-tert-
butylresorcinol (0.072 g, 0.32 mmol) and (S)-3,3¢-bis-(dimethyl-
phenylsilanyl)-1,1¢-binaphthalene-2,2¢-dioxychlorophosphonite
(0.200 g, 0.32 mmol) in toluene (10 ml) at room temperature was
treated with NEt3 (0.32 ml, 2.26 mmol) dropwise. The reaction
mixture was stirred for 1 day, the resultant mixture filtered
through Celite and the volatiles removed under reduced pressure.
Purification by column chromatography (silica, CH2Cl2 : hexane
1 : 1 eluent) to afforded 6d as a white solid. Yield: 0.24 g (92.3%).
Anal. Calcd for C50H53O4PSi2: C, 74.59; H, 6.64%. Found: C,
Experimental
General notes
All reactions were carried out under a nitrogen atmosphere in
either a glove box or using standard Schlenk techniques. Dry N2-
saturated solvents were collected from a Grubbs solvent system.23
All other chemicals were used as received unless otherwise stated.
1
73.58; H, 6.89%. 31P{ H NMR (121.5 MHz, CDCl3): d 143.5 (s).
1H NMR (300 MHz, CDCl3): 0.57–0.60 (m, 12, SiMe2Ph), 1.04 (s,
9, C(CH3)3), 1.38 (s, 9, C(CH3)3), 3.95 (s, 1, OH), 5.80 (d, 1, ArH),
9046 | Dalton Trans., 2011, 40, 9042–9050
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The Royal Society of Chemistry 2011
©

7.11–7.24 (m, 7, ArH), 7.29–7.40 (m, 6, ArH), 7.46–7.48 (m, 2,
ArH), 7.54–7.56 (m, 2, ArH), 7.79–7.88 (m, 3, ArH), 8.103 (s, 1,
ArH). HRMS (ESI) m/z: 805.3270 (M+H)+, 827.3080 (M+Na)+.
3, ArH), 7.94 (s, 1, ArH). MS (ESI) m/z: 913.36 (M+H)+, 935.35
(M+Na)+.
Preparation of ligand 8. As for 3b with 2,4-di-tert-butyl-5-
methylphenol (0.20 g, 0.91 mmol) and (S)-3,3¢-dimethyl-1,1¢-
binaphthalene-2,2¢-dioxychlorophosphonite (0.344 g, 0.91 mmol).
White solid. Yield: 0.498 g (97.5%). Anal. Calcd for C37H39O3P: C,
Preparation of ligand 3b. A stirred solution of 2,4-di-tert-
butyl phenol (0.12 g, 0.59 mmol) and (S)-3,3¢-dimethyl-1,1¢-
binaphthalene-2,2¢-dioxychlorophosphonite (0.222 g, 0.59 mmol)
in toluene (20 ml) at room temperature was treated with NEt3
(0.57 ml, 4.1 mmol) dropwise and the reaction mixture was then
stirred for 18 h. Filtration through Celite and removal of the
solvent gave the crude product which was purified by column
chromatography (silica, CH2Cl2 : hexane 1 : 1 eluent) to afford 3b
as a white solid. Yield: 0.22 g (68.5%). Crystals suitable for X-ray
analysis were grown from a concentrated diethyl ether solution.
Anal. Calcd for C36H37O3P: C, 78.81; H, 6.80%. Found: C, 78.97;
1
78.98; H, 6.99%. Found: C, 79.06; H, 7.02%. 31P{ H} NMR (121.5
MHz, CDCl3): d 141.8 (s). 1H NMR (300 MHz, CDCl3): 1.57 (s,
9, C(CH3)3), 1.63 (s, 9, C(CH3)3), 2.64 (s, 3, ArMe), 2.77 (s, 3,
ArMe), 2.81 (s, 3, ArMe), 7.31 (s, 1, ArH), 7.34–7.39 (m, 2, ArH),
7.53–7.59 (m, 4, ArH), 7.61 (s, 1, ArH), 7.95 (s, 1, ArH), 7.96–
8.02 (m, 3, ArH). HRMS (ESI) m/z: 563.2688 (M+H)+, 585.2506
(M+Na)+.
Preparation of complex 4b. A mixture of the ligand 3b (0.100 g,
0.182 mmol) and [PdCl2(NCMe)2] (0.047 g, 0.182 mmol) in toluene
(5 ml) was heated at 80 ◦C for 2 days. The resulting mixture was
filtered through Celite, the solvent was removed under reduced
pressure and the product recrystallised from Et2O to give 4b as a
yellow solid (0.086 g, 68.5%). Crystals suitable for X-ray analysis
were grown by slow evaporation of an Et2O/hexane solution
under air. Anal. Calcd for C72H72Cl2O6P2Pd2: C, 62.71; H, 5.26%.
Found: C, 62.84; H, 5.43%. HRMS (ESI) m/z: 1343.2589 (M-Cl)+,
1
H, 6.99%. 31P{ H} NMR (121.5 MHz, CDCl3): d 142.9 (s).
1H NMR (300 MHz, CDCl3): 1.34 (s, 9, C(CH3)3), 1.36 (s, 9,
C(CH3)3), 2.55 (s, 3, ArMe), 2.61 (s, 3, ArMe), 7.20–7.25 (m, 3,
ArH), 7.31–7.45 (m, 6, ArH), 7.78 (s, 1, ArH), 7.83–7.89 (m, 3,
ArH). MS (ESI) m/z: 549.25 (M+H)+, 571.23 (M+Na)+.
Preparation of ligand 3c. A stirred solution of 2,4-di-tert-butyl
phenol (0.15 g, 0.73 mmol) and (S)-3,3¢-bis(trimethylsilanyl)-1,1¢-
binaphthalene-2,2¢-dioxychlorophosphonite (0.36 g, 0.73 mmol)
in toluene (20 ml) at room temperature was treated dropwise with
NEt3 (0.71 ml, 5.1 mmol). The reaction mixture was heated at
90 ◦C for 5 days. Filtration through Celite and concentration under
reduced pressure a light yellow solid which was purified by column
chromatography (silica, CH2Cl2 : hexane 1 : 1 eluent) to afford 3c as
a white solid. Yield: 0.43 g (89%). Anal. Calcd for C40H49O3PSi2:
1
1401.2158 (M+Na)+. Major isomer: 31P{ H} NMR (121.5 MHz,
1
CDCl3): d 136.4 (s). H NMR (300 MHz, CDCl3): 1.13 (s, 18,
C(CH3)3), 1.23 (s, 18, C(CH3)3), 2.49 (s, 6, ArMe), 2.96 (s, 6,
ArMe), 7.12–7.22 (m, 4, ArH), 7.26–7.36 (m, 8, ArH), 7.46–7.53
1
(m, 4, ArH), 7.85–7.97 (m, 6, ArH). Minor isomer: 31P{ H} NMR
1
(121.5 MHz, CDCl3): d 139.0 (s). H NMR (300 MHz, CDCl3):
1.17 (s, 18, C(CH3)3), 1.40 (s, 18, C(CH3)3), 2.49 (s, 6, ArMe), 2.58
(s, 6, ArMe), all other peaks obscured.
1
C, 72.25; H, 7.43%. Found: C, 72.45; H, 7.65%. 31P{ H} NMR
1
(121.5 MHz, CDCl3): d 145.3 (s). H NMR (300 MHz, CDCl3):
0.36 (s, 9, SiMe3), 0.39 (s, 9, SiMe3), 1.10 (s, 9, C(CH3)3), 1.32 (s,
9, C(CH3)3), 7.09–7.15 (m, 2, ArH), 7.18–7.28 (m, 4, ArH), 7.33
(d, 1, ArH), 7.41–7.4 (m, 2, ArH), 7.93–7.96 (m, 2, ArH), 8.09 (s,
2, ArH). MS (ESI) m/z: 665.28 (M+H)+, 687.26 (M+Na)+.
Preparation of complex 4c. A mixture of the ligand 3d (0.100 g,
0.127 mmol) and [PdCl2(NCMe)2] (0.033 g, 0.127 mmol) in toluene
(5 ml) was heated at 85 ◦C for 18 h. The resulting mixture was
filtered through Celite, the solvent was removed under reduced
pressure and the product recrystallised from Et2O/hexane to give
the 4c as a yellow solid Yield: 0.066 g (56%). Anal. Calcd for
C100H104Cl2O6P2Pd2Si4: C, 64.58; H, 5.64%. Found: C, 64.27; H,
Preparation of ligand 3d. As for 3c using 2,4-di-tert-butyl
phenol (0.077 g, 0.37 mmol) and (S)-3,3¢-bis-(dimethyl-phenyl-
silanyl)-1,1¢-binaphthalene-2,2¢-dioxychlorophosphonite (0.23 g,
0.37 mmol), the product was purified by column chromatography
(silica, CH2Cl2 : hexane 1 : 3 eluent) to afford 3d as a white solid.
Yield: 0.20 g (69.1%). Anal. Calcd for C50H53O3PSi2: C, 76.10; H,
1
5.56%. Major isomer: 31P{ H} NMR (161.8 MHz, CDCl3): d 134.5
(s). 1H NMR (400 MHz, CDCl3): 0.51 (d, 6, SiMe2Ph), 0.90 (s, 3,
SiMe2Ph), 1.06 (s, 3, SiMe2Ph), 1.12 (s, 9, C(CH3)3), 1.16 (s, 9,
C(CH3)3), 7.03–7.09 (m, 3, ArH), 7.14–7.25 (m, 7, ArH), 7.27–
7.30 (m, 2, ArH), 7.39–7.45 (m, 2, ArH), 7.51–7.55 (m, 2, ArH),
7.68–7.71 (m, 2, ArH), 7.83–7.85 (m, 2, ArH), 7.93 (s, 1, ArH), 8.01
1
6.77%. Found: C, 76.14; H, 6.78%. 31P{ H} NMR (161.8 MHz,
CDCl3): d 147.6 (s). 1H NMR (400 MHz, CDCl3): 0.61–0.63 (m,
12, SiMe2Ph), 1.01 (s, 9, C(CH3)3), 1.36 (s, 9, C(CH3)3), 6.92–6.95
(m, 1, ArH), 7.08–7.42 (m, 14, ArH), 7.47–7.49 (m, 2, ArH), 7.56–
7.59 (m, 2, ArH), 7.80–7.90 (m, 3, ArH), 8.04 (s, 1, ArH). HRMS
(ESI) m/z: 789.3347 (M+H)+, 811.3166 (M+Na)+.
1
(s, 1, ArH). Minor isomer: 31P{ H} NMR (161.8 MHz, CDCl3):
1
d 134.8 (s). H NMR (400 MHz, CDCl3): all peaks obscured by
major isomer. MS (ESI) m/z: 1825.20 (M-Cl)+, 1883.15 (M+Na)+.
Preparation of complex 4d. A mixture of the ligand 3e (0.244 g,
Preparation of ligand 3e. As for 3c with 2,4-di-tert-butyl
phenol (0.146 g, 0.71 mmol) and (S)-3,3¢-bis-(diphenylmethyl-
silanyl)-1,1¢-binaphthalene-2,2¢-dioxychlorophosphonite (0.53 g,
0.71 mmol). Purification by column chromatography (silica,
CH2Cl2 : hexane 2 : 3 eluent) gave 3e as a white solid. Yield: 0.50 g
(77.5%). Anal. Calcd for C60H57O3PSi2: C, 78.91; H, 6.29%. Found:
0.267 mmol) and [PdCl2(NCMe)2] (0.069 g, 0.267 mmol) in toluene
(10 ml) was heated at 80 C for 16 h. The resulting mixture was
◦
filtered through Celite, the solvent was removed under reduced
pressure and the product purified by column chromatography
(silica, EtOAc : hexane 1 : 3 eluent) to give 4d as a white solid
(0.23 g, 82%). Anal. Calcd for C120H112Cl2O6P2Pd2Si4: C, 68.37;
H, 5.35%. Found: C, 68.23; H, 5.50%. MS (ESI) m/z: 2073.46
1
C, 78.72; H, 6.35%. 31P{ H} NMR (121.5 MHz, CDCl3): d 149.5
(s). 1H NMR (300 MHz, CDCl3): 0.78 (s, 3, SiMePh2), 0.88 (s, 3,
SiMePh2), 0.88 (s, 9, C(CH3)3), 1.33 (s, 9, C(CH3)3), 6.53 (dd, 1,
ArH), 6.95 (dd, 1, ArH), 7.16–7.52 (m, 27, ArH), 7.73–7.83 (m,
(M-Cl)+, 2132.43(M+Na)+. Major isomer: 31P{ H} NMR (121.5
1
1
MHz, CDCl3): d 135.7 (s). H NMR (300 MHz, CDCl3): 0.83
(d, 3, SiMePh2), 1.19 (s, 9, C(CH3)3), 1.24 (s, 9, C(CH3)3), 1.52
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 9042–9050 | 9047
©

(s, 3, SiMePh2), 7.10–7.16 (m, 4, ArH), 7.21–7.41 (m, 14, ArH),
7.49–7.64 (m, 8, ArH), 7.80 (dd, 2, ArH), 7.91 (dd, 2, ArH), 8.16
(m, 2, ArH), 7.73–7.75 (m, 6, ArH), 7.86–8.06 (m, 2, ArH), 8.18
(s, 1, ArH), 8.41 (s, 1, OH). MS (ESI) m/z: 2352.56 (M-Cl)+.
1
(d, 2, ArH). Minor isomer: 31P{ H} NMR (121.5 MHz, CDCl3):
Preparation of complex 10. A mixture of the ligand 8 (0.200 g,
1
d 136.2 (s). H NMR (300 MHz, CDCl3): all peaks obscured by
0.355 mmol) and [PdCl2(NCMe)2] (0.092 g, 0.255 mmol) in toluene
major isomer.
◦
(8 ml) was heated at 80 C for 1 day. The resulting mixture was
filtered through Celite, the solvent was removed under reduced
pressure and the product purified by column chromatography
(silica, THF : hexane 1 : 2 eluent) followed by recrystallisation from
Et2O/hexane to afford 10 as an orange solid. Yield: 0.201 g,
(76.5%). Anal. Calcd for C74H78Cl4O6P2Pd2: C, 60.05; H, 5.31%.
Found: C, 60.35; H, 5.20%. MS (ESI) m/z: 1445.24 (M-Cl)+,
Preparation of complex 9a. A mixture of the ligand 6a (0.201 g,
0.37 mmol) and [PdCl2(NCMe)2] (0.097 g, 0.37 mmol) in 1,2-
dichloroethane (10 ml) was stirred at room temperature for 1 h
during which time the colour of the mixture changed from yellow
to orange. The mixture was then treated with NEt3 (0.05 ml,
0.354 mmol) and then stirred for 18 h. The resulting mixture was
filtered through Celite, the solvent was removed under reduced
pressure and the product purified by column chromatography
(silica, THF : hexane 1 : 1 eluent) to afford 9a as a yellow solid.
Yield: 0.21 g (83%). Calcd for C68H64Cl2O8P2Pd2: C, 60.28; H,
1
1467.22 (M-Cl+Na)+, 1503.20 (M+Na)+. Major isomer: 31P{ H}
1
NMR (121.5 MHz, CDCl3): d 74.70 (s). H NMR (300 MHz,
CDCl3): 1.19 (s, 18, C(CH3)3), 1.43 (s, 18, C(CH3)3), 2.21 (s, 6,
ArMe), 2.38 (s, 6, ArMe), 3.01 (s, 6, ArMe), 7.10–7.24 (m, 8, ArH),
7.32–7.51 (m, 6, ArH), 7.63 (s, 4, ArH), 7.77 (m, 2, ArH), 7.95 (m,
1
4.76%. Found: C, 60.81; H, 5.06%. 31P{ H} NMR (121.5 MHz,
1
1
2, ArH), 8.01 (s, 2, ArH). Minor isomer: 31P{ H} NMR (121.5
CDCl3): d 140.6 (s). H NMR (300 MHz, CDCl3): 1.13 (s, 9,
MHz, CDCl3): d 76.72 (s). 1H NMR (300 MHz, CDCl3): 1.21 (s,
18, C(CH3)3), 1.46 (s, 18, C(CH3)3), all other peaks obscured.
C(CH3)3), 1.40 (s, 9, C(CH3)3), 7.03–7.04 (m, 1, ArH), 7.14–7.18
(m, 3, ArH), 7.28–7.38 (m, 4, ArH), 7.44–7.54 (m, 4, ArH), 7.97–
8.03 (m, 2,ArH), 9.81 (s, 1, OH). MS (ESI) m/z: 1319.15 (M-Cl)+.
Preparation of complex 11. A solution of ligand 6c (0.200 g,
0.29 mmol) and [PdCl2(NCMe)2] (0.076 g, 0.29 mmol) in 1,2-
dichloroethane (10 ml) at room temperature was treated dropwise
with NEt3 (0.13 ml, 0.88 mmol) and the mixture stirred for 1
day. Filtration through Celite and removal of the solvent under
reduced pressure gave the title compound as a brown solid (0.265 g,
94%). Crystals suitable for X-ray analysis were grown by slow
evaporation of an Et2O/pentane solution under argon. Anal.
Calcd for C46H64Cl2NO4PPdSi2: C, 57.58; H, 6.72%; N, 1.46.
Found: C, 57.91; H, 7.02; N, 1.71%. MS (ESI) m/z: 924.28
Preparation of complex 9b. As for 9a with ligand 6b (0.200 g,
0.354 mmol) and [PdCl2(NCMe)2] (0.092 g, 0.354 mmol) to give
9b as a yellow solid. Yield: 0.222 g (89%). Anal. Calcd for
C72H72Cl2O8P2Pd2: C, 61.29; H, 5.14%. Found: C, 60.97; H, 5.67%.
1
1
31P{ H} NMR (121.5 MHz, CDCl3): d 138.1 (s). H NMR (300
MHz, CDCl3): 1.15 (s, 9, C(CH3)3), 1.49 (s, 9, C(CH3)3), 2.43 (s,
3, ArMe), 2.48 (s, 3, ArMe), 6.90–7.12 (m, 2, ArH), 7.20–7.33 (m,
4, ArH), 7.47–7.60 (m, 2, ArH), 7.67–7.92 (m, 3, ArH), 10.01 (s,
1, OH). MS (ESI) m/z: 1433.18 (M+Na)+, 1397.21 (M+Na-Cl)+,
1375.23 (M-Cl)+.
1
1
(M-Cl)+. 31P{ H} NMR (161.8 MHz, CDCl3): d 130.35 (s). H
NMR (400 MHz, CDCl3): 0.41 (s, 9, SiMe3), 0.48 (s, 9, SiMe3),
0.97 (s, 9, C(CH3)3), 1.28 (t, 9, NCH2Me), 1.40 (s, 9, C(CH3)3),
3.11 (dq, 6, NCH2Me), 6.95 (d, 1, ArH), 7.07–7.24 (m, 4, ArH),
7.37–7.47 (m, 2, ArH), 7.88–7.95 (m, 2, ArH), 8.06 (s, 1, ArH),
8.09 (s, 1, ArH), 9.32 (s, 1, OH), 9.59 (br, s, 1, NH).
Preparation of complex 9c. A solution of ligand 6e (0.400 g,
0.43 mmol) and [PdCl2(NCMe)2] (0.112 g, 0.43 mmol) in 1,2-
dichloroethane (10 ml) at room temperature was treated dropwise
with NEt3 (0.18 ml, 1.29 mmol) and the resultant mixture was
stirred for 1 day. The resulting mixture was filtered through Celite,
the solvent removed under reduced pressure and the product
purified by column chromatography (silica, THF : hexane 3 : 2
eluent) to afford a 9c as a yellow solid. Yield: 0.447 g (97%). Anal.
Calcd for C120H112Cl2O8P2Pd2Si4: C, 67.34; H, 5.27%. Found: C,
68.36; H, 5.77%. 31P{1H} NMR (121.5 MHz, CDCl3): d 132.9
(s). 1H NMR (300 MHz, CDCl3): 0.52 (s, 3, SiMePh2), 1.08 (s, 3,
SiMePh2), 1.08 (s, 9, C(CH3)3), 1.51 (s, 9, C(CH3)3), 6.98–7.27 (m,
16, ArH), 7.34–7.49 (m, 10, ArH), 7.54–7.57 (m, 2, ArH), 7.62
(s, 1, ArH), 7.81–7.84 (m, 1, ArH), 7.99 (s, 1, ArH), 8.80 (s, 1,
OH). MS (ESI) m/z: 2142.43 (M+H)+, 2105.43 (M-Cl)+, 2069.46
(M-2Cl)+.
General method for the allylation of benzaldehyde
To a dried reaction tube, charged with a solution of the appropriate
palladacycle (0.025 mmol Pd) in CH2Cl2 (0.5 ml), were added
benzaldehyde (0.050 ml, 0.053 g, 0.5 mmol) and allyltributyl
tin (0.200 ml, 0.212 g, 0.64 mmol). Additional CH2Cl2 (0.5 ml)
was added to ensure all reagents were washed into the reaction
mixture and the resulting solution was stirred at the appropriate
temperature for 24–70 h (see Table 1 for details). The reaction
mixture was quenched with water (10 ml), the product extracted
with CH2Cl2 (3 ¥ 10 ml), the combined organic phase dried
(MgSO4) and the solvent removed under reduced pressure. 1,3,5-
Trimethoxybenzene (internal standard) was added and the spec-
troscopic yield was determined by 1H NMR spectroscopy (CDCl3,
300 MHz). The product was purified by column chromatography
(silica, EtOAc : hexane 1 : 6 eluent) prior to determining optical
purity by chiral HPLC.
Preparation of complex 9d. As for 9c with ligand 6f (0.250 g,
0.24 mmol) and [PdCl2(NCMe)2] (0.062 g, 0.24 mmol), purified
by column chromatography (silica, THF : hexane = 1 : 1) to afford
9d as yellow solid. Yield: 0.249 g (88%). Crystals suitable for X-
ray analysis were grown by slow evaporation of an Et2O/pentane
solution under air. Anal. Calcd for C140H120Cl2O8P2Pd2Si4: C,
X-ray crystallography
1
70.40; H, 5.06%. Found: C, 70.39; H, 5.31%. 31P{ H} NMR (121.5
MHz, CDCl3): d 128.3 (s). 1H NMR (300 MHz, CDCl3): 0.98 (s, 9,
C(CH3)3), 1.36 (s, 9, C(CH3)3), 6.71–6.85(m, 10, ArH), 7.03(s, 1,
ArH), 7.18–7.27 (m, 11, ArH), 7.33–7.42 (m, 8, ArH), 7.47–7.58
X-ray diffraction experiments on 9d and 11 were carried out at
100 K on a Bruker APEX II diffractometer using Mo-Ka radiation
˚
(l = 0.71073 A). X-ray diffraction experiments on 3b and 4c were
9048 | Dalton Trans., 2011, 40, 9042–9050
This journal is
The Royal Society of Chemistry 2011
©

Table 2 Crystallographic data
Compound
3b
4c
9d·C5H12
11
Colour, habit
Size/mm
Empirical Formula
M
colourless, plate
0.08 ¥ 0.06 ¥ 0.04
C36H37O3P
548.63
colourless, plate
0.05 ¥ 0.03 ¥ 0.02
C100H104Cl2O6P2Pd2Si4
1859.83
yellow, cube
0.07 ¥ 0.05 ¥ 0.05
C145H132Cl2O8P2Pd2Si4
2460.51
brown, shard
0.68 ¥ 0.21 ¥ 0.10
C46H64Cl2NO4PPdSi2
959.43
Crystal system
Space group
Monoclinic
P 21
9.9688(11)
9.1502(10)
16.0481(17)
90.00
99.461(4)
90.00
1443.9(3)
2
Monoclinic
C2
29.464(3)
9.6174(9)
22.049(2)
90.00
132.779(3)
90.00
4585.7(7)
2
Monoclinic
P 21
14.4938(6)
30.6692(13)
14.4991(5)
90.00
106.461(3)
90.00
6180.9(4)
2
Monoclinic
C2
27.1630(4)
14.3800(2)
14.1182(2)
90.00
105.286(1)
90.00
5319.53(13)
4
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
m/mm-1
1.115
100
4.946
100
0.458
100
0.561
100
T/K
qmin,max
2.79,60.85
0.997 to q = 60.85◦
15287/4340
0.0414
0.0310, 0.0783
0.281, -0.205
1.262
2.73,65.11
0.994 to q = 65.11◦
27683/7624
0.0480
0.0287, 0.0665
0.544, -0.443
1.347
2.20,27.58
0.997 to q = 27.58◦
73461/27759
0.1448
0.0919, 0.2009
1.523, -1.143
1.322
1.50,30.60
0.994 to q = 30.60◦
77077/16225
0.0482
0.0321, 0.0745
0.558, -0.281
1.198
Completeness
Reflections: total/independent
Rint
Final R1 and wR2
-3
˚
Largest peak, hole/eA
rc/g cm-3
Flack parameter
0.056(16)
0.007(5)
0.01(3)
-0.013(11)
carried out at 100 K on a Bruker Microstar diffractometer using
J. Coles, M. B. Hursthouse and V. J. M. Scordia, Dalton Trans., 2005,
991; (g) R. B. Bedford, M. Betham, M. E. Blake, R. M. Frost, P. N.
Horton, M. B. Hursthouse and R.-M. Lo´pez-Nicola´s, Dalton Trans.,
2005, 2774.
5 R. B. Bedford, C. S. J. Cazin and S. L. Hazelwood, Chem. Commun.,
2002, 2608.
6 (a) D. A. Albisson, R. B. Bedford and P. N. Scully, Tetrahedron Lett.,
1998, 39, 9793; (b) 12 V. P. W. Bo¨hm and W. A. Herrmann, Chem.–Eur.
J., 2000, 6, 1017.
7 R. B. Bedford and M. E. Blake, Adv. Synth. Catal., 2003, 345, 1107.
8 J. Li, M. Lutz, A. L. Spek, G. P. M. van Klink, G. van Koten and R. J.
M. Klein Gebbink, J. Organomet. Chem., 2010, 695, 2618.
9 I. J. S. Fairlamb, S. Grant, P. McCormack and J. Whittall, Dalton Trans.,
2007, 859.
˚
Cu-Ka radiation (l = 1.54178 A). Data collections were performed
using a CCD area detector from a single crystal mounted on a glass
fibre. Intensities were integrated25 from several series of exposures
measuring 0.5◦ in w or f. Absorption corrections were based on
equivalent reflections using SADABS.26 The structures were solved
2
using SHELXS and refined against all Fo data with hydrogen
atoms riding in calculated positions using SHELXL.27 Crystal
structure and refinement data are given in Table 2.
The difference map of 11 contained residual electron density,
likely to be disordered pentane, which could not be modelled satis-
factorily. The data were modelled using the program SQUEEZE,28
details of which may be found in the CIF.†
10 W. Tang, S. Keshipeddy, Y. Zhang, X. Wei, J. Savoie, N. D. Patel, N. K.
Yee and C. H. Senanayake, Org. Lett., 2011, 13, 1366.
11 (a) R. B. Bedford, M. Betham, J. P. H. Charmant, M. F. Haddow, A.
G. Orpen and L. T. Pilarski, Organometallics, 2007, 26, 6346; (b) P. He,
Y. Lu, C. Guo-Dong and Q.-S. Hu, Org. Lett., 2007, 9, 343; (c) P. He,
Y. Lu and Q.-S. Hu, Tetrahedron Lett., 2007, 48, 5283.
12 R. B. Bedford and L. T. Pilarski, Tetrahedron Lett., 2008, 49, 4216.
13 R. B. Bedford, M. Betham, M. E. Blake, A. Garces, S. L. Millar and S.
Prashar, Tetrahedron, 2005, 61, 9799.
Acknowledgements
We thank and the CCDC for a studentship (CLM) and Johnson
Matthey for the loan of palladium salts.
14 (a) V. V. Dunina, P. A. Zykov, M. V. Livantsov, I. V. Glukhov, K. A.
Kochetkov, I. P. Gloriozov and Y. K Grishin, Organometallics, 2009,
28, 425; (b) R. B. Bedford, H. Dumycz, M. F. Haddow, L. T. Pilarski, A.
G. Orpen, P. G. Pringle and R. L. Wingad, Dalton Trans., 2009, 7796;
(c) J. Li, M. A. Siegler, M. Lutz, A. L. Spek, R. J. M. Klein Gebbink
and G. van Koten, Organometallics, 2009, 28, 5323.
15 R. B. Bedford, Y.-N. Chang, M. F. Haddow and C. L. McMullin, Dalton
Trans. , submitted.
16 R. J. Abraham and M. Mobli, Magn. Reson. Chem., 2007, 45, 865.
17 For a rare example of cis geometry observed in the solid state see: R. B.
Bedford, M. Betham, S. J. Coles, P. N. Horton and M.-J. Lo´pez-Sa´ez,
Polyhedron, 2006, 25, 1003.
Notes and references
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