The addition of bromine and iodine to palladacyclopentadienyl complexes bearing bidentate heteroditopic P-N spectator ligands derived from differently substituted quinolinic frames. the unexpected evolution of the reaction

Article abstract of DOI:10.1039/c5dt01884f

We have synthesized two palladacyclopentadienyl derivatives bearing bidentate ligands heteroditopic 8-(diphenylphosphino)quinoline or 8-(diphenylphosphino)-2-methylquinoline. We have reacted the palladacyclopentadienyl complexes with Br₂ and I₂ to gain clues on the formation mechanism of the corresponding σ-butadienyl derivatives. We were able to obtain the pure σ-butadienyl derivative only in the case of Br₂ reacting with the palladacyclopentadienyl complex bearing the unsubstituted quinoline. However, an equilibrium mixture of the σ-butadienyl and a novel zwitterionic species was obtained when the same complex reacts with I₂. Furthermore, we have obtained exclusively an unprecedented zwitterionic complex when I₂ reacts with the palladacyclopentadienyl complex bearing the substituted quinoline and a different ratio of an equilibrium mixture of σ-butadienyl and the zwitterionic species when the latter derivative reacts with Br₂. The solid state structures of one σ-butadienyl complex and of the two novel zwitterionic derivatives were determined and an interpretation of the observed reactivity based on kinetic data and a computational study has been suggested.

Full text of DOI:10.1039/c5dt01884f

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The addition of bromine and iodine to
palladacyclopentadienyl complexes bearing
bidentate heteroditopic P−N spectator ligands
derived from differently substituted quinolinic
frames. The unexpected evolution of the reaction†
Cite this: DOI: 10.1039/c5dt01884f
a
a
a
a
Luciano Canovese,* Fabiano Visentin, Thomas Scattolin, Claudio Santo and
Valerio Bertolasi
b
We have synthesized two palladacyclopentadienyl derivatives bearing bidentate ligands heteroditopic
8
-(diphenylphosphino)quinoline or 8-(diphenylphosphino)-2-methylquinoline. We have reacted the pallada-
cyclopentadienyl complexes with Br and I to gain clues on the formation mechanism of the corres-
ponding σ-butadienyl derivatives. We were able to obtain the pure σ-butadienyl derivative only in the case
of Br reacting with the palladacyclopentadienyl complex bearing the unsubstituted quinoline. However,
an equilibrium mixture of the σ-butadienyl and a novel zwitterionic species was obtained when the same
complex reacts with I . Furthermore, we have obtained exclusively an unprecedented zwitterionic
complex when I reacts with the palladacyclopentadienyl complex bearing the substituted quinoline and
a different ratio of an equilibrium mixture of σ-butadienyl and the zwitterionic species when the latter
derivative reacts with Br . The solid state structures of one σ-butadienyl complex and of the two novel
2
2
2
2
2
Received 19th May 2015,
Accepted 19th July 2015
2
DOI: 10.1039/c5dt01884f
zwitterionic derivatives were determined and an interpretation of the observed reactivity based on kinetic
data and a computational study has been suggested.
www.rsc.org/dalton
are important compounds contained in many natural and bio-
active products. Therefore, their synthesis is of remarkable
Introduction
A number of catalyzed reactions are based on the stability and importance as testified by the development of catalytic proto-
4
5
6
6b,7
chemical versatility of palladium complexes toward oxidative cols based on cobalt, ruthenium, nickel and palladium.
addition and reductive elimination. In particular, interconver- Particular emphasis has been placed on the reactivity of palla-
1
sion between Pd(0) and Pd(II) derivatives has been widely dacyclopentadienyl derivatives bearing different spectator
2
,3,8
studied since it often represents the keystone for several cross ligands.
We have recently carried out a detailed study on
coupling processes. In contrast, the red–ox reactions involving the oxidative addition of I2 to palladacyclopentadienyl com-
the Pd(II)–Pd(IV)–Pd(II) conversions are comparatively less investi- plexes bearing monodentate isocyanides as spectator ligands.
gated and are often related to addition of halogens or organic We were able to measure the rates of intramolecular conver-
2
3
halides in catalytic or stoichiometric processes yielding con- sion of the intermediate trans-diiodo palladium(IV) into the cis-
jugated dienes as their final products. The conjugated dienes diisocyanide-tetramethyl pallada-1-iodobuta-1,3-diene-1,2,3,4-
tetracarboxylate, its subsequent isomerisation to the trans-
isomer, and support the experimental results with a compu-
9
tational study.
a
Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari, Venice,
We also think that the conversion of the metallacyclopenta-
Italy. E-mail: cano@unive.it
b
Dipartimento di Chimica e Centro di Strutturistica Diffrattometrica, Università di
dienyl complexes into the σ-butadienyl derivatives deserves a
further study since the stereospecific formation of the final
butadienyl fragment is mainly governed by the transition state
and the intermediate structures involved in this first step. We
have therefore synthesized two palladacyclopentadienyl com-
plexes bearing the bidentate heteroditopic ligands 8-(diphenyl-
Ferrara, Ferrara, Italy
†
Electronic supplementary information (ESI) available: Further details of the
structure determination, final coordinates, bond distances and bond angles and
ORTEP representations for 2a, 4b and 5b, NMR spectra, schematic compu-
tational outcomes. CCDC 1053523–1053525. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c5dt01884f
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Scheme 1 Ligands, starting complexes and identified σ-butadienyl
derivatives.
Fig. 1 ORTEP view of complex 2a showing the thermal ellipsoids at the
30% probability level.
phosphino)quinoline (DPPQ) or 8-(diphenylphosphino)-2-methyl
quinoline (DPPQ-Me) which, while avoiding complications
arising from cis–trans isomerization of the spectator ligands,
impart to the palladium derivative properties that could be
different COOCH
3
groups with marked downfield shifts of the
2
1
0
quinoline H (δ ≈ 10.5 ppm clearly indicating its cis position
exploited in insertion reactions,
isomerization of a co-
1
2
1
1
to bromide ) compared to those of the precursor, and the
phosphorus peak (δ = 34.3 ppm) show the course of the
reaction.
ordinated olefin and nucleophilic attack on the allyl frag-
1
2
ment. We have finally studied from the experimental and
theoretical point of view the oxidative addition of the cited
complexes using bromine and iodine.
Due to its stability in solution and in the solid state it was
possible to confirm definitively the structure of 2a as inferred
from NMR, by X-ray diffraction. In Fig. 1 we report the ORTEP
The ligands, the palladacyclopentadienyl and the identified
σ-butadienyl complexes are reported in the following Scheme 1.
16
representation of the solid state structure of complex 2a which
will be discussed later.
Results and discussion
Synthesis of cyclometallated complexes 1a and 1b
Reactivity of complex 1b with Br2
The reaction of complex 1b with bromine under similar experi-
mental conditions gives immediately complex 2b which can be
quantitatively separated from the reaction mixture when pre-
cipitation with diethyl ether is induced soon after the addition
1
3
14
The addition in acetone of the ligands DPPQ or DPPQ-Me
under an inert atmosphere (Ar) to the polymer [PdC (COO-
4
1
5
Me)4]n which was synthesized using published procedures,
yields complexes 1a and 1b which were easily isolated with
good yield. These compounds are characterized by the down-
field shift of the phosphorus (ca. 40 ppm) and of the quinoline
(complex 1b) protons, with respect to
the free ligands in the P NMR and H NMR spectra. There
are also distinct signals related to four different COOCH
groups in the H and C NMR spectra (see ESI Fig. S1†).
Notably, at variance with the pyridylthioether palladacyclo-
of the Br and at low temperature (273 K). The NMR spectra of
2
31
complex 2b are very similar to those of 2a. In particular the
P
singlet of the former is almost isochronous to that of the latter
2
H (complex 1a) or CH
3
(
δ = 34.2 ppm) (see ESI Fig. S3†).
3
1
1
Complex 2b, however, is not stable in solution and in about
3
30 h undergoes a remarkable change which is evident when
1
13
the NMR spectra of the starting and the final derivative are
compared. In fact, the phosphorus peak shifts upfield by
8
g
pentadienyl species,
complexes 1a and 1b display no
tendency for rotation of the spectator ligands (i.e. exchange of
coordination sites between the different donor atoms).
about 20 ppm and the signals ascribable to the four OCH
groups resonate in different positions in the H NMR spec-
trum (see ESI Fig. S4†).
3
1
However, the key contribution for understanding the nature
of the new species (4b) was the determination of its solid state
to give structure which is reported in Fig. 2 (again, the discussion of
Reactivity of complex 1a with Br
2
As can be seen in Scheme 1, complex 1a reacts with Br
2
the expected σ-butadienyl derivative 2a. The formation of 2a is the structure will be dealt with in another section).
1
13
31
13
apparent as can be deduced from the H, C and P NMR
According to the structure of 4b, the C NMR spectrum
spectra in CDCl of the reaction product after precipitation shows a doublet at ca. 42 ppm (JCP ≈ 60 Hz) and a singlet at
3
from the concentrated reaction mixture with diethyl ether (see ca. 31 ppm ascribable to the alkyl carbons bound to the palla-
ESI Fig. S2†). As a matter of fact, the persistence of four dium centre.
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1
Fig. 3 H NMR concentration profiles of 2b (squares) and 4b (circles)
vs. time (s) for the reaction: 2b = 4b in CDCl at 298 K.
3
Fig. 2 ORTEP view of complex 4b showing the thermal ellipsoids at the
30% probability level.
high temperature in CDCl (323 K) a massive decomposition
3
occurred.
The reaction and the suggested mechanism yielding this
Reactivity of complex 1b with I
2
unprecedented complex 4b are shown in eqn (1):
The addition at RT of an equimolecular amount of I to a solu-
2
2 2
tion of 1b in CH Cl gives readily and quantitatively complex
5b as the only reaction product (eqn (2)).
ð1Þ
ð2Þ
The formation of the zwitterionic complex 4b might be
explained as the result of an intramolecular nucleophilic
Complex 5b displays NMR spectra very similar to those of
attack of the phosphorus originally coordinated to the metal complex 4b previously described; in particular, the single
2
31
on the sp carbon of the butadienyl fragment. The overall signal in the P NMR spectrum resonates at 8.9 ppm, whereas
1
3
process is a slow equilibrium reaction and the amount of the C NMR spectrum shows the characteristic peaks of the
complex 2b that remained unreacted was evaluated to be 15% Pd–C–PPh (doublet at ca. 44 ppm, JCP = 61.8 Hz) and Pd–C–I
(singlet at 32.9 ppm) (see ESI Fig. S5†). Again the structure of
Thus, it was possible to calculate k and k independently derivative 5b was definitively resolved by X-ray diffractometry as
2
1
7
of its initial concentration (K ≈ 5.4).
E
f
r
by non-linear regression of the concentration vs. time data reported in the Crystal structure determination section (Fig. 4).
implemented in the SCIENTIST® computing environment
However, when the reaction is carried out at a low tempera-
ture (253 K) it is possible to observe the formation of complex
(Fig. 3).
1
The k
f
and k
r
values were estimated to be (4.93 ± 0.01) × 3b which was identified on the basis of the similarity of its H
1
0− and (8.93 ± 0.02) × 10
5
−6 −1
s , respectively. The equili- and P NMR spectra with those of the parent complex 3a (vide
18
31
brium constant was calculated as K = k /k = 5.52 ± 0.02 which infra). As expected, complex 3b readily reverts to complex 5b at
f
r
is in good agreement with the value determined from the RT (see ESI Fig. S6†).
experimentally detected final concentrations of species 2b and Complex 1a when reacting with I
middle course and an equilibrium mixture of the σ-butadienyl
It is noteworthy that it was not possible to obtain derivative 3a and zwitterionic 5a complexes is detectable in solution. In
2
predictably takes the
4
4
b (K ≈ 5.4) (see also footnote SI 1 in the ESI†).
1
31
a from complex 1a. As a matter of fact, when the reaction of Fig. 5 the H and P NMR spectra of the equilibrium mixture
complex 1a with Br was carried out for a prolonged time at of complexes 3a and 5a taken soon after the addition of I to
2
2
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1
31
equivalents of (n-Bu)
4
NI, in CD
2
Cl
2
at 298 K. The H and
P
NMR spectra of the reaction mixture in CD Cl show that an
2
2
equilibrium reaction between the starting complex 2b and a
new species 2b* is immediately established. Complex 2b* was
−
formed as a consequence of the substitution of the Br co-
ordinated to palladium with iodide. The equilibrium mixture
is slowly converted into a new equilibrium mixture of the zwit-
terions 4b and 4b*, as summarized in Scheme 3. The presence
1
31
of complex 4b was proved by comparison with the H and
P
NMR spectra of an authentic sample of 4b. The structure of
1
4
b* was instead assessed by the comparison with the H and
3
1
P NMR spectra of the complex obtained by reacting complex
4
4b with an excess (2 : 1) of (n-Bu) NI (6c). In the latter case,
only the bromide coordinated to palladium should be substi-
tuted according to the well-established theory of nucleophilic
1
9
substitution on square planar complexes (see Scheme 3 and
ESI Fig. S7a–c†).
As already stated, complex 3b is not stable and immediately
gives zwitterion 5b at RT. In contrast, since the parent complex
Fig. 4 ORTEP view of complex 5b showing the thermal ellipsoids at the
30% probability level.
2
b* reacts slowly to yield zwitterion 4b* it is reasonable to
2
surmise that the halide bound to sp carbon is also a determi-
a are reported. Remarkably, the immediately established con- nant in modulating the reaction rate. In summary, the rate of
1
centration ratio between isomers remains constant over time.
the reaction yielding the zwitterionic complexes seems to be
A summary of the oxidative additions of Br
plexes 1a and 1b is reported in the following Scheme 2 in of the coordinating ring,
2 2
and I on com- due to an interplay of three different factors, i.e. the distortion
1
0a,b,11,20
the trans influence of the
which the complexes within dotted squares (4a, 3b) have not halide trans to quinoline phosphorus, and the charge density
2
been isolated.
on the butadienyl sp carbon (which is clearly influenced by
the electronegativity of the bound halide). Therefore, the best
combination favoring the widening of the coordinated ring
Reactivity of complex 2b with I−
In order to gain some more information about the driving is the presence of the methyl substituted quinoline (and the
force promoting the widening of the coordinative ring, we have consequent induced distortion of the original coordinative
−2
−3
reacted complex 2b ([2b]
≈ 1 × 10 mol dm ) with two ring), the iodide trans to quinoline phosphorus, and the
0
1
31
3
Fig. 5 H and P NMR spectra of the starting complex 1a (bottom) and of the equilibrium mixture of complexes 3a and 5a (top) in CDCl at 298 K.
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Scheme 2 General overview of the reactivity of complexes 1a and 1b towards the addition of Br
2
and I
2
(within the dotted squares the not isolated
products).
2
iodide bound to the butadienyl sp carbon. Conversely, the
other end is represented by the unsubstituted quinoline and
2
the bromides bound to the palladium and to butadienyl sp
carbon.
Computational study
Such experimental observations were not in contrast to a
detailed computational study carried out by the Gaussian 09
2
1
program. To save computing time the carboxymethyl group
COOMe was replaced by the less disordered CN moiety (in the
following discussion the CN derivatives will maintain the
same labels of the original complexes marked with an apex).
Taking into account the limitations due to the errors
−
1
implicit in this sort of calculation (ΔΔG° ≈ ± 2 kcal mol ) and
the replacement of COOMe with CN groups, it was calculated
that:
(
i) complex 4b′ is more stable than complex 2b′ by
−
1
2
5
.3 kcal mol
.
(
ii) complex 5b′ is more stable than complex 3b′ by
−
1
.0 kcal mol
.
(
iii) complex 4a′ is less stable than complex 2a′ by
Scheme 3 Schematic representation of the equilibrium reactions trig-
gered by the addition of (n-Bu) NI to complex 2b in CD Cl at RT.
−
1
4
2
2
0.9 kcal mol .
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(iv) complex 5a′ is less stable than complex 3a′ but the maximum deviations from the mean planes of −0.081(4) for
difference is reduced if compared with the former (ΔG° = C25 and 0.074(3) Å for C26 in complex 4b and −0.072(3) for
.5 kcal mol− ).
1
C25 and 0.058(3) Å for C26 in complex 5b.
0
(See ESI Fig. S8† for a schematic comparison).
The different coordination modes of the buta-1,3-diene
The assessed energy values agree with the experimental ligand in complexes 4b and 5b with respect to that observed in
results and in particular they account for the observed equili- complex 2a give rise to variations both in carbon hybridis-
brium distribution between complexes 2b′ and 4b′ (ΔG° = ations and in C–C bond distances.
−
1
2
.3 kcal mol ) and complexes 3a′ and 5a′ (ΔG° = 0.5 kcal
−
1
mol ). The higher difference in energy between complex 3b′
−
1
and 5b′ (ΔG° = 5.0 kcal mol ) is consistent with the fact that
complex 5b was the only isolated species, but it does not fully
explain the behavior of complexes 2a′ and 4a′. Although the
higher energy of complex 4a′ is clearly apparent, the calculated
ΔΔG° (0.9 kcal mol− ) would be indicative of an equilibrium
distribution.
Conclusions
2 2
The oxidative addition of Br or I to palladacyclopentadienyl
complexes bearing the bidentate DPPQ or DPPQ-Me as spec-
tator ligands yields different derivatives depending on the
nature of the ancillary ligands and halogens. Thus, complex
1
1
a reacts with Br yielding the σ-butadienyl derivative 2a and
However, since no equilibrium is experimentally observed,
we think that this fact might depend on kinetic factors which
are modulated by the interplay between the less destabilizing
nature of bromide toward phosphorus (the trans-influence of
bromide being lower than that of iodide) and the higher stabi-
lity of the undistorted chelating ring of the DPPQ. More
simply, it could just be the intrinsic uncertainty typical of this
sort of calculations.
2
2
complex 1b with I to give the unprecedented zwitterionic
complex 5b, only. The cross reactivity yields in both cases an
equilibrium mixture of the σ-butadienyl and zwitterionic
complexes 2b and 4b (in the case of complex 1b reacting with
Br ) and 3a and 5a (in the case of complex 1a reacting with
2
I2). The experimental results and in particular the reactivity
of the butadienyl derivatives were interpreted taking into
account the different lability of the bidentate ligands
Crystal structure determination
(
DPPQ-Me which is more labile than DPPQ), the higher trans-
−
−
1
6
influence of I compared to Br , and the charge density on
the butadienyl sp carbon which is modulated by the electro-
An ORTEP view of neutral complex 2a is shown in Fig. 1. A
selection of bond distances and angles is given in Table S2.†
The geometry around the Pd centre is a slightly distorted
square planar. The four positions around the central Pd are
2
negativity of the bound halide. In order to give adequate
support to the experimental observations a detailed study
of the solid state structure of complexes 2a, 4b and 5b
together with the determination of the reaction rates charac-
terizing the equilibrium reaction between 2b and 4b were
also carried out.
α
occupied by the carbon C of the 1,2,3,4-tetrakis(methoxy-
carbonyl)buta-1,3-diene-4-Br-1-yl anionic ligand, a Br anion, the
pyridine nitrogen and phosphorus of the 8-diphenylphospha-
nyl-quinoline (DPPQ) ligand. The deviations from the basal
plane are: −0.0004(4) for Br1, 0.016(3) for N1, −0.021(1) for P1
and 0.022(3) Å for C22. Pd1 is situated at 0.0662(3) Å above
this average plane. The C22 = C23–C24 = C25 buta-1,3-diene Experimental
moiety displays an anti-clinal conformation with a torsion
Solvents and reagents
angle of −117.0(4)°.
1
6
All the following distillation processes were carried out under
an inert atmosphere (argon). Acetone and CH Cl were dis-
tilled over 4 Å molecular sieves and CaH respectively. All the
An ORTEP view of the neutral isostructural complexes 4b
2
2
and 5b is shown in Fig. 2 and 4.
2
A selection of bond distances and angles is given in
Table S2.† In both complexes, the geometry around the Pd
centre is square planar distorted towards a tetrahedral arrange-
ment. The four positions around the central Pd are occupied
by halogen atoms, Br in 4b or I in 5b. The pyridine nitrogen
of the 8-diphenylphosphanyl-2-methyl-quinoline (DPPQ-Me)
ligand and the α,δ-carbons of the buta-1,3-diene-4-Br(or I)-1-yl
moiety of the ligand are as in the previous complex 2a. The
deviations of the four atoms from the basal plane are: −0.0053(5)
for Br1, 0.224(3) for N1, −0.273(3) for C23 and 0.285(3) Å
for C26 with the Pd1 atom at 0.0975(3) Å above this average
plane, in complex 4b. For complex 5b they are: −0.0019(3) for
I1, 0.222(3) for N1, −0.333(3) for C23 and 0.289(3) Å for C26
other chemicals were commercially available grade products
and were used as purchased.
Data analysis. Nonlinear analysis of the data related to equi-
librium and kinetics measurements was performed by locally
adapted routines written in the SCIENTIST® environment.
IR and NMR measurements
1
13
31
The IR, H, C and P NMR spectra were recorded on a
Perkin-Elmer Spectrum One spectrophotometer and on a
Bruker 300 Avance spectrometer, respectively.
Computational details
with the Pd1 atom at 0.1228(3) Å above this average plane, in The geometrical optimization of the complexes was carried out
complex 5b. In both complexes the Pd1–C23–C24–C25−C26 without symmetry constraints, using the hyper-GGA functional
2
2,23
palladacyclopentene rings are approximately planar with M06
in combination with polarized triple-ζ-quality basis
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2
4,25
13
1
sets (LAN2TZ(f))
Pd atoms, a polarized double-ζ-quality basis set (LANL2DZdp)
with diffuse functions for the halogen atoms and a polarized (CH, C ), 127.8 (d, CH, JCP = 5.5 Hz, C ), 129.3 (d, C, JCP
and relativistic pseudopotential for the
C{ H}-NMR (CDCl
3 3 3
, T = 298 K, ppm) δ: 50.5 (CH , OCH ),
2
6
50.9 (CH , OCH ), 51.2 (CH , OCH ), 51.3 (CH , OCH ), 122.6
3
3
3
3
3
3
3
6
=
1
0
5
8
double-ζ-quality basis set (6-31G(d,p)) for the other elements.
7.8 Hz, C ), 131.1 (CH, C ), 135.9 (d, C, JCP = 41.7 Hz, C ),
7
4
Solvent effects (dichloromethane, ε = 8.93) were included 136.1 (CH, C ), 139.0 (CH, C ), 143.2 (C, CvC), 150.1
2
7,28
9
2
using CPCM.
(C, CvC), 150.9 (d, C, JCP = 21.6 Hz, C ), 154.9 (CH, C ), 157.2
The “restricted” formalism was applied in all the calcu- (d, C, JCP = 7.5 Hz, CvC), 164.1 (C, CvO), 165.3 (C, CvO),
lations. By means of the stationary points characterized by IR 173.1 (d, C, JCP = 8.0 Hz, CvO), 175.4 (d, C, JCP = 7.4 Hz,
simulation, the zero-point vibrational energies and thermodyn- CvO), 176.7 (C, CvC).
2
9
amic parameters were obtained.
8
Anal. calcd for C33H28NO PPd: C 56.30, H 4.01, N 1.99.
2
1
The software used was Gaussian 09 and all the compu- Found: C 56.41, H 4.18, N 1.87.
tational work was carried out on Intel based × 86 − 64
workstations.
Synthesis of complex 1b
Crystal structure determinations
Complex 1b was obtained following the same procedure as for
complex 1a.
The crystal data of compounds 2a, 4b and 5b were collected at
room temperature using a Nonius Kappa CCD diffractometer
with graphite monochromated Mo-Kα radiation. The data sets
A yellow-orange microcrystalline solid was obtained with a
7
4% yield.
1
3
0
3
H-NMR (300 MHz, CDCl , T = 298 K, ppm) δ: 2.86 (s, 3H,
were integrated with the Denzo-SMN package and corrected
3
1
OCH ), 2.89 (s, 3H, OCH ), 3.39 (s, 3H, quinoline–CH ),
3
3
3
for Lorentz, polarization and absorption effects (SORTAV).
The structures were solved by direct methods using the
3
3
.68 (s, 3H, CH
Hz), 8.18 (d, 1H, H , J = 9 Hz); 7.42 (m, 10H).
3
), 3.64 (s, 3H, OCH
3
), 7.89 (d, 1H, H , J = 9.0
4
3
2
SIR97
system of programs and refined using full-matrix
3
1
1
P{ H}-NMR (CDCl , T = 298 K, ppm) δ: 30.16.
3
least-squares with all non-hydrogen atoms anisotropically and
hydrogens included on calculated positions, riding on their
carrier atoms.
8
Anal. calcd for C34H30NO PPd: C 56.88, H 4.21, N 1.95.
Found: C 56.94, H 4.07, N 1.89.
3
3
All calculations were performed using SHELXL-97
and
3
4
35
PARST implemented in the WINGX system of programs.
The crystal data are given in Table S3.†
Synthesis of complex 2a
In a two necked 50 ml flask, 71.1 mg (0.10 mmol) of com-
pound 1 dissolved in 10 ml of anhydrous CH Cl 17.8 mg
0.111 mmol) of Br dissolved in 5 ml of CH Cl was added
Crystallographic data have been deposited at the Cam-
bridge Crystallographic Data Centre and allocated the depo-
sition numbers CCDC 1053523, 1053524, and 1053525.
2
2
(
2
2
2
under an inert atmosphere (Ar). The reaction mixture immedi-
ately decolorized and after 5 min stirring the solution was
evaporated under vacuum to 3–4 ml. The dropwise addition of
diethyl ether induces the precipitation of the title complex as a
yellow microcrystalline solid. The solid was filtered off on a
gooch filter, washed several times with diethyl ether and
n-pentane and dried under vacuum to obtain 81.7 mg (94%
Synthesis of the ligands and starting complex
1
2
13
The ligands DPPQ, DPPQ-Me and the polymeric complex
1
5
[
PdC (COOMe)4]n
were synthesized according to the pub-
4
lished procedures.
Synthesis of complex 1a
yield) of the complex.
1
In a two necked 100 ml flask 198.0 mg (0.51 mmol) of
3
H-NMR (300 MHz, CDCl , T = 298 K, ppm) δ: 3.41 (s, 3H,
[
PdC (COOMe) ] and 172.2 mg (0.55 mmol) of DPPQ were dis- OCH ), 3.63 (s, 3H, OCH ), 3.72 (s, 3H, OCH ), 3.74 (s, 3H,
4
4 n
3
3
3
3
6
solved in 20 ml of anhydrous acetone under an inert atmos- OCH
phere (Ar). The resulting solution was stirred for 1 h and 7.82–7.98 (m, 4H, H , Ph), 8.05 (d, 1H, J = 8.0 Hz, H ), 8.43
concentrated under vacuum to a reduced volume (2–3 ml). (dt, 1H, J = 8.3, 1.5 Hz, H ), 10.47 (dd, 1H, J = 5.1, 1.5 Hz, H ).
Dropwise addition of diethyl ether (5–10 ml) causes the pre-
3
), 7.37–7.54 (m, 6H, Ph), 7.65–7.70 (m, 2H, H , H ),
7
5
4
2
3
1
1
P{ H}-NMR (CDCl
3
, T = 298 K, ppm) δ: 34.3.
3 3
, T = 298 K, ppm) δ: 51.3 (CH , OCH ),
1
3
1
cipitation of the 309.2 mg (87% yield) of the title complex as a
C{ H}-NMR (CDCl
3
yellow-orange microcrystalline product which was filtered off 52.0 (CH , OCH ), 53.2 (CH , OCH ), 53.3 (CH , OCH ), 120.9
3
3
3
3
3
3
3
6
on a gooch filter, carefully washed with diethyl ether and (C, CvCBr), 123.4 (CH, C ), 127.9 (d, CH, JCP = 6.9 Hz, C ),
1
0
5
n-pentane and dried under vacuum.
129.6 (d, C, JCP = 9.4 Hz, C ), 130.4 (C, CvC), 131.8 (CH, C ),
H-NMR (300 MHz, CDCl , T = 298 K, ppm) δ: 2.77 (s, 3H, 134.4 (d, C, JCP = 44.3 Hz, C ), 137.0 (CH, C ), 139.0 (CH, C ),
), 3.71 (s, 3H, OCH ), 3.73 (s, 3H, 142.7 (C, CvC), 150.2 (d, C, JCP = 20.2 Hz, C ), 156.4 (CH, C ),
3 3
), 7.39–7.61 (m, 8H, H , Ph), 7.64 (ddd, 1H, J = 7.7, 7.2, 161.8 (C, CvO), 162.5 (C, CvC), 162.9 (C, CvO), 166.3
1
8
7
4
3
9
2
OCH
OCH
3
), 3.64 (s, 3H, OCH
3
3
6
5
1
.2 Hz, H ), 7.66–7.77 (m, 4H, H , Ph), 7.98 (d, 1H, J = 7.9 Hz, (C, CvO), 171.4 (d, C, JCP = 2.6 Hz, CvO).
7
4
−1
H ), 8.37 (dt, 1H, J = 8.5, 1.4 Hz, H ), 9.06 (dd, 1H, J = 5.0,
IR (KBr pellets): νCvO 1709 cm
Anal. calcd for C33 28Br NO
Found: C 45.73, H 3.18, N 1.54.
.
2
1
.4 Hz, H ).
H
2
8
PPd: C 45.89, H 3.27, N 1.62.
3
1
1
P{ H}-NMR (CDCl , T = 298 K, ppm) δ: 33.4.
3
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3
1
1
3
1
Synthesis of complex 2b
P{ H}-NMR (CDCl
3
, T = 298 K, ppm) δ: 8.9.
1
C{ H}-NMR (CDCl , T = 298 K, ppm) δ: 32.9 (C, Pd–C–I),
3
Complex 3a was obtained following similar conditions to
complex 2a but the synthesis was carried out at a low tempera-
ture (273 K) and the complex was collected within 10 min.
A pale-yellow microcrystalline solid was obtained with a
3
5
(
1
3.6 (CH
2.1 (CH
3
, quinoline–CH
3
), 43.8 (d, C, JCP = 61.8 Hz, C–PPh
3
),
3
, OCH ), 52.2 (CH
3
3
3
, OCH ), 52.3 (CH , OCH ), 52.4
3
3
3
10
CH , OCH ), 124.7 (CH, C ), 127.9 (d, C, J = 7.0 Hz, C ),
3 3 CP
31.3 (d, C, JCP = 66.8 Hz, C ), 132.4 (CH, C ), 134.2 (CH, C ),
135.5 (C, CvC), 139.2 (CH, C ), 140.8 (d, CH, JCP = 11.0 Hz,
C ), 148.9 (d, C, J = 3.0 Hz, C ), 161.4 (d, C, J = 10.5 Hz,
8
6
5
6
1% yield.
4
1
H-NMR (300 MHz, CDCl , T = 298 K, ppm) δ: 3.32 (s, 3H,
3
7
9
CP
CP
quinoline–CH
3
3 3
), 3.45 (s, 3H, OCH ), 3.60 (s, 3H, OCH ), 3.87
2
3
CvC), 164.4 (CH, C ), 165.0 (C, CvO), 166.2 (C, CvO), 169.5
(
7
1
3 3 2
s, 3H, OCH ), 3.88 (s, 3H, OCH ), 7.34–7.62 (m, 9H, PPh , H ),
5
6
7
(d, C, JCP = 7.2 Hz, CvO), 171.6 (C, CvO).
.76–8.04 (m, 5H, H , H , H , PPh ), 8.14 (dd, 1H, J = 8.5,
2
IR (KBr pellets): νCvO 1718 cm−
1
.
4
.6 Hz, H ).
3
1
1
30 2 8 2 2
Anal. calcd for C34H I NO PPd·CH Cl : C 39.78, H 3.05,
P{ H}-NMR (CDCl , T = 298 K, ppm) δ: 34.3.
3
−
1
N 1.33. Found: C 39.651, H 2.97, N 1.19.
IR (KBr pellets): νCvO 1732, 1716 and 1704 cm
.
Anal. calcd for C33 NO PPd: C 41.38, H 2.95, N 1.46.
H
28
I
2
8
Found: C 41.21, H 2.97, N 1.32.
Notes and references
Synthesis of complex 4b
1
(a) J. Tsuji, in Palladium Reagents and Catalysts: Innovations
in Organic Synthesis, Wiley and Sons, New York, 1995, ch. 4;
Complex 4b was obtained by reacting complex 1b and Br2
under the same experimental conditions described above in
the case of complex 2a. The reaction mixture was stirred for
(
(
(
b) L. S. Hegedus, Coord. Chem. Rev., 1996, 147, 443–545;
c) L. S. Hegedus, Coord. Chem. Rev., 1997, 161, 129–255;
d) I. P. Beletskaya and A. V. Cheprakov, Chem. Rev., 2000,
2
8 h and the reaction product precipitated by addition of
diethyl ether.
100, 3009–3066; (e) C. Amatore and A. Jutand, Acc. Chem.
A yellow microcrystalline solid was obtained with a 78%
Res., 2000, 33, 314–321; (f) R. Zimmer, C. U. Dinesh,
E. Nandanan and F. A. Khan, Chem. Rev., 2000, 100, 3067–
yield.
1
3
H-NMR (300 MHz, CDCl , T = 298 K, ppm) δ: 3.31 (s, 3H,
3125; (g) J. A. Marshall, Chem. Rev., 2000, 100, 3163–3186;
OCH ), 3.42 (s, 3H, OCH ), 3.54 (s, 3H, quinoline–CH ), 3.64
3
3
3
(
h) E.-I. Negishi, in Handbook of Organopalladium Chemistry
3
(
s, 3H, OCH ), 3.71 (s, 3H, OCH ), 7.39–7.62 (m, 9H, PPh , H ,
3 3 2
for Organic Synthesis, ed. E.-I. Negishi and A. de Meijere,
Wiley-Interscience, New York, 2002, ch. I.1, I.2;
7
6
5
2 2
H ), 7.67–7.81 (m, 3H, H , PPh ), 7.95–8.08 (m, 2H, H , PPh ),
4
8
.28 (dd, 1H, J = 8.5, 1.9 Hz, H ).
(
i) K. Tamao, T. Hiyama and E.-I. Niegishi, in 30 Years of
3
1
1
P{ H}-NMR (CDCl , T = 298 K, ppm) δ: 10.7.
3
the Cross-coupling Reaction, Special issue, J. Organomet.
Chem., 2002, 653, 1–303. ( j) L. A. Agrofoglio, I. Gillaizeau
and Y. Saito, Chem. Rev., 2003, 103, 1875–1916;
1
3
1
C{ H}-NMR (CDCl
3
, T = 298 K, ppm) δ: 30.8 (CH
3
, quino-
= 59.9 Hz,
line–CH ), 31.2 (C, Pd–C–Br), 41.7 (d, C, J
3
CP
C–PPh ), 51.9 (CH , OCH ), 52.0 (CH , OCH ), 52.1 (CH ,
3
3
3
3
3
3
(
k) E. Negishi and L. Anastasia, Chem. Rev., 2003, 103,
3
OCH
3
), 52.4 (CH
3
3
, OCH ), 124.9 (CH, C ), 127.4 (d, C, JCP =
1979–2017; (l) G. Zeni and R. C. Larock, Chem. Rev., 2004,
1
0
8
6
7
.0 Hz, C ), 130.5 (d, C, J = 65.9 Hz, C ), 132.4 (CH, C ),
CP
104, 2285–2309; (m) K. C. Nicolaou, P. G. Bulger and
5
4
1
33.9 (CH, C ), 137.7 (C, CvC), 138.6 (CH, C ), 140.4 (d, CH,
D. Sarlah, Angew. Chem., Int. Ed., 2005, 44, 4442–4489;
7
9
JCP = 11.4 Hz, C ), 148.3 (d, C, JCP = 3.0 Hz, C ), 157.9 (d, C,
(
(
n) E.-I. Negishi, Bull. Chem. Soc. Jpn., 2007, 80, 233–257;
o) C. J. Elsevier and M. R. Eberhard, in Comprehensive
2
JCP = 11.5 Hz, CvC), 157.9 (C, CvO), 164.4 (CH, C ), 166.5
C, CvO), 170.3 (d, C, JCP = 7.9 Hz, CvO), 171.4 (C, CvO).
(
Organometallic Chemistry III From Fundamentals to Appli-
cations, ed. A. Canty, ed. in Chief, R. H. C. D. Michael and
P. Mingos, Elsevier, Amsterdam, Boston, 2007, vol. 8, ch.
−
1
IR (KBr pellets): νCvO 1722 cm
.
Anal. calcd for C H Br NO PPd·CH Cl : C 43.66, H 3.35,
3
4
30
2
8
2
2
N 1.45. Found: C 43.51, H 3.23, N 1.32.
8.05, pp. 270–298; (p) M. García-Melchor, X. Solans-
Monfort and G. Ujaque, in CC Bond Formation Comprehen-
sive Inorganic Chemistry II (Second Edition): From Elements to
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S. Qu, J. W. Nelson, H. D. Pham, Z.-X. Wang and X. Wang,
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Synthesis of complex 5b
2
Complex 5b was obtained by reacting complex 1b and I under
the same experimental conditions as described above. The
reaction mixture was stirred for 10 min and the reaction
product precipitated by addition of diethyl ether.
A pale-yellow microcrystalline solid was obtained in 93%
yield.
1
3
H-NMR (300 MHz, CDCl , T = 298 K, ppm) δ: 3.24 (s, 3H,
OCH ), 3.43 (s, 3H, OCH ), 3.61 (s, 3H, quinoline–CH ), 3.63
3
3
3
(
s, 3H, OCH
3
), 3.74 (s, 3H, OCH
3
), 7.39–7.80 (m, 12H, PPh
2
,
3 (a) R. Van Belzen, R. A. Klein, H. Kooijman, N. Veldman,
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3
7
6
H , H , H , PPh
7
2
), 7.98–8.05 (m, 2H, PPh
2
), 8.15 (dt, 1H, J =
5
4
.1, 2.3 Hz, H ), 8.34 (dd, 1H, J = 8.5, 1.9 Hz, H ).
Dalton Trans.
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2
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