Reactivity toward neutral N- and P-donor ligands of eight-membered palladacycles arising from monoinsertion of alkynes into the Pd-C bond of orthopalladated homoveratrylamine and phentermine. A new example of the transphobia effect

Article abstract of DOI:10.1021/om401090b

Eight-membered palladacycles arising from the insertion of one molecule of alkyne into the Pd-C bond of the palladacycles derived from homoveratrylamine and phentermine react with neutral N- and P-donor ligands to give mononuclear or unusual dinuclear complexes, containing a vinylarylethylamino bridge, depending on the size of the ligand and the substituents of the palladacycle. Diffusion-ordered nuclear magnetic resonance spectroscopy experiments are used to measure the diffusion coefficients and propose the nuclearity of these complexes in solution. Density functional theory calculations show that steric and electronic (transphobia) effects are responsible for the unprecedented observed reactivity differences. A mechanism for the formation of the unusual dinuclear complexes is proposed.

Full text of DOI:10.1021/om401090b

Article
pubs.acs.org/Organometallics
Reactivity toward Neutral N- and P‑Donor Ligands of Eight-
Membered Palladacycles Arising from Monoinsertion of Alkynes into
the Pd−C Bond of Orthopalladated Homoveratrylamine and
Phentermine. A New Example of the Transphobia Effect
María-Jose Oliva-Madrid,† Jose-Antonio García-Lopez,† Isabel Saura-Llamas,*,† Delia Bautista,‡
́
́
́
and Jose Vicente*,†
́
†Grupo de Química Organometal
Spain
‡SAI, Universidad de Murcia, Apartado 4021, 30071 Murcia, Spain
́ ́
ica, Departamento de Química Inorganica, Universidad de Murcia, Apartado 4021, 30071 Murcia,
S
* Supporting Information
ABSTRACT: Eight-membered palladacycles arising from the
insertion of one molecule of alkyne into the Pd−C bond of the
palladacycles derived from homoveratrylamine and phenter-
mine react with neutral N- and P-donor ligands to give
mononuclear or unusual dinuclear complexes, containing a
vinylarylethylamino bridge, depending on the size of the ligand
and the substituents of the palladacycle. Diffusion-ordered
nuclear magnetic resonance spectroscopy experiments are used
to measure the diffusion coefficients and propose the
nuclearity of these complexes in solution. Density functional
theory calculations show that steric and electronic (transphobia) effects are responsible for the unprecedented observed reactivity
differences. A mechanism for the formation of the unusual dinuclear complexes is proposed.
membered palladacycles A−E with isocyanides, CO, and
INTRODUCTION
■
tBuOK) has been published separately.3
Dinuclear halogen-bridged palladacycles normally react with
monodentate ligands to afford mononuclear complexes
resulting from the cleavage of the bridge. This behavior is so
common that this type of reaction could be considered as
routine. Nevertheless, we conduct such a reaction sometimes,
especially when the dinuclear palladacycle is scarcely soluble or
is obtained in a contaminated form and its purification is not
possible.1,2 Thus, the reaction with a neutral ligand, as PPh3,
allows us to obtain a soluble and characterizable derivative. This
is the case of complex A (Scheme 1), resulting from the
insertion of one molecule of diphenylacetylene into the Pd−C
bond of the palladacycle derived from homoveratrylamine,
which is insoluble in most common organic solvents. However,
the reaction between this palladacycle and PPh3 does not afford
the expected mononuclear complex, but a new dinuclear one in
which the halogen bridge is replaced by a vinylarylethylamino
bridge, apparently resulting from the cleavage of the Pd−N
bond and formation of a new bond with another Pd atom. This
is surprising taking into account that, in our wide experience in
the chemistry of cyclopalladated derivatives of primary amines,
we have never observed the cleavage of the strong N−Pd bond.
This Article reports the study of the reactions of various eight-
membered palladacycles similar to A with neutral ligands and
includes a proposed mechanism for this unusual behavior. A
closely related work (reporting the reactions of eight-
RESULTS AND DISCUSSION
■
Reactivity of Eight-Membered Palladacycles toward
Neutral Ligands. Trying to obtain a soluble derivative of
complex A (Scheme 1), we reacted it with 2 equiv of PPh3.
However, instead of the expected monomeric complex resulting
from the cleavage of the halogen bridge,1,4−6 we obtained the
d i m e r i c s p e c i e s [ P d { μ - C , N - C ( P h )  C ( P h ) -
C6H2CH2CH2NH2-2-(MeO)2-4,5}Br(PPh3)]2 [1a (Scheme
1)], in which the C,N-ligand was bridging two palladium
atoms. Only a few complexes containing potentially C,N-
chelates acting as bridging ligands have been reported, but they
involve pyridine derivatives that, otherwise, would lead to four-
membered palladacycles.7 Alternatively, some C,N-palladacycles
react with phosphines to undergo metallacycle ring opening
processes, rendering complexes in which the amine acts as a C-
monodentate anionic ligand.5,8
The crystal structure of complex 1a was determined by an X-
ray diffraction study (Figure 1) showing a centrosymmetric
molecule with the palladium atoms in a distorted square-planar
environment [mean deviation of the Pd(1)−N(1)−Br(1)−
Received: November 11, 2013
Published: December 6, 2013
© 2013 American Chemical Society
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observed for the first alkenyl fragment after a second insertion
of an alkyne into the Pd−Caryl bond.6,12
Scheme 1. Reactions of Eight-Membered Palladacycles A−E
with N- and P-Donor Neutral Ligands
To elucidate the influence of the phosphine on the nature of
the formed phosphino complex, we conducted the reaction of
A with PCy3 or PMe3, yielding complex 2a or 3a, respectively.
The crystal structure of complex 3a, containing PMe3, a
phosphine with a Tolman cone angle (118°) smaller than that
of PPh3 (145°),13 was determined by X-ray diffraction (XRD)
studies (Figure 2) showing its monomeric nature. This
Figure 2. Thermal ellipsoid plot (50% probability) of complex 3a
along with the labeling scheme. The hydrogen atoms bonded to
carbon have been omitted for the sake of clarity. Selected bond lengths
(angstroms) and angles (degrees): Pd(1)−Br(1), 2.5237(3); Pd(1)−
N(1), 2.1252(17); Pd(1)−C(8), 2.0091(18); Pd(1)−P(1), 2.2424(5);
C(7)−C(8), 1.348(3); Br(1)−Pd(1)−N(1), 89.37(5); N(1)−Pd(1)−
C(8), 87.01(7); C(8)−Pd(1)−P(1), 91.94(5); P(1)−Pd(1)−Br(1),
91.807(15).
suggested that formation of dimeric complex 1a could be
related to the steric hindrance of PPh3 being greater than that
of PMe3. Unfortunately, we could not grow appropriate single
crystals of 2a to establish its structure in the solid state, which
in the case of being dimeric would support our hypothesis.
Assuming that the nature of vinylarylethylamino ligand could
also affect the nature of the adducts, we reacted complex B, C,
or D with 2 equiv of PPh3 yielding 1b, 1c, or 1d, respectively
(Scheme 1). Similarly, complex E reacts with 4-picoline (4-pic)
to afford 4e. The crystal structures of 1d·2CH2Cl2 (Figure 3)
and 4e·1/2CHCl3 (see the Supporting Information) complexes
were determined by XRD studies. Both complexes are
monomeric, and the palladium atom forms part of an eight-
membered ring, which adopts an almost twist-boat conforma-
tion, although the usual designations of cyclooctane con-
formations are not strictly applicable here.14
Figure 1. Thermal ellipsoid plot (50% probability) of the 1a·2CH2Cl2
complex along with the labeling scheme. The solvent molecules and
the hydrogen atoms bonded to carbon have been omitted for the sake
of clarity. Selected bond lengths (angstroms) and angles (degrees):
Pd(1)−Br(1), 2.5475(5); Pd(1)−N(1), 2.137(3); Pd(1)−C(1),
2.022(4); Pd(1)−P(1), 2.2607(10); C(1)−C(2), 1.346(5); Br(1)−
Pd(1)−N(1), 90.30(8); N(1)−Pd(1)−C(1), 88.28(13); C(1)−
Pd(1)−P(1), 91.38(11); P(1)−Pd(1)−Br(1), 91.74(3).
P(1)−C(1) plane of 0.154 Å]. The phosphino and vinyl ligands
adopted a mutually cis disposition, which was the expected
geometry according to the great transphobia9 between the C-
and P-donor ligands.2,10 The geometry around the double bond
of the vinyl ligand is different from that in the starting
palladacycle A (Scheme 1).11 This isomerization has no
precedent in this type of palladacycle, although it has been
The remaining complexes, the nuclear magnetic resonance
(NMR) spectra and elemental analysis of which were in
agreement with the incorporation of one phosphine ligand per
palladium, could not be characterized by XRD. The 31P NMR
did not allow us to distinguish between monomeric and dimeric
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Organometallics
Article
m2/s) for complex 1a, showing that D does not change
significantly in the range of 10−20 mmol/L. For complex 1d,
the 1H DOSY experiment was followed through the CH2
protons. The value of D for 1d (6.70 m2/s) was significantly
different from that of complex 1a and consistent with that
expected for a less bulky compound. Those for complexes 1b,
1c, and 2a (Table 1) were determined as described for 1a,
suggesting a dimeric structure for complexes 1b and 2a and a
monomeric structure for complex 1c, as depicted in Scheme 1.
This suggests that homoveratrylamine derivatives are more
likely to form dinuclear than mononuclear complexes when the
phosphine is voluminous (PPh3, 1a and 1b; PCy3, 2a).
However, the mononuclear nature of 1c suggests that this
condition is necessary but not sufficient and that the electronic
and/or the steric hindrance of R2 (Me instead of Ph or
CO2Me) also plays an important role.
The singular behavior of the homoveratrylamine derivatives
could be attributed to the strong steric demand of the aryl ring
bearing the two methoxy groups. In fact, in the solid state,
structurally characterized eight-membered palladacycles derived
from arylalkylamines showed an approximately boat or boat-
chair conformation, in which the Pd coordination plane and the
aryl ring formed an angle of 52−67°.11,17 The predicted
monomeric product of the reaction between A and PPh3 could
be a hypothetical complex cis-1a′, the structure of which was
optimized through density functional theory (DFT) calcu-
lations showing one H atom of one phenyl ring attached to P
(HPhP) quite near one C atom bonded to a MeO group [COMe
(Figure 4)]. The shortest H···C distance is 3.05 Å. To prevent
Figure 3. Thermal ellipsoid plot (50% probability) of the 1d·2CH2Cl2
complex along with the labeling scheme. The solvent molecules and
the hydrogen carbon atoms have been omitted for the sake of clarity.
Selected bond lengths (angstroms) and angles (degrees): Pd(1)−
Cl(1), 2.4216(4); Pd(1)−N(1), 2.1167(13); Pd(1)−C(8),
2.0040(15); Pd(1)−P(1), 2.2640(4); C(7)−C(8), 1.346(2); Cl(1)−
Pd(1)−N(1), 90.39(4); N(1)−Pd(1)−C(8), 84.85(5); C(8)−Pd(1)−
P(1), 94.63(4); P(1)−Pd(1)−Cl(1), 90.073(15).
structures, as the chemical shifts of coordinated PPh3 for dimer
1a (δ 26.7), monomer 1d (δ 27.7), and complexes 1b and 1c (δ
27.4 and 27.8, respectively) were quite similar, in spite of the
different structures of 1a and 1d, and comparable to those
found for mononuclear phosphino complexes derived from
eight-membered C,N-palladacycles containing an alkenyl frag-
ment (δ 25.9−29.8).15
The formula weight of a complex is correlated to its volume
and hence to its diffusion in solution.16 Diffusion-ordered NMR
spectroscopy (DOSY) experiments were used to measure the
diffusion coefficients (D) of complexes 1b, 1c, and 2a, to
compare them with the values obtained for the fully
characterized complexes 1a and 1d. The experimental results
are listed in Table 1.
Complex 1a was dissolved in CDCl3 at room temperature,
Figure 4. Optimized structures of hypothetical molecules of cis-1a′
(left) and trans-1a′ (right). Most hydrogen atoms have been omitted
for the sake of clarity.
1
and a H DOSY experiment was conducted. The value of D
(6.28 m2/s) was measured for the protons corresponding to the
OMe groups. An analogous experiment using a double
concentration rendered approximately the same D value (6.26
this steric hindrance,18 the phosphine could coordinate trans to
the Pd−C aryl bond to give trans-1a′; its hypothetical structure
was also optimized through DFT calculations (Figure 4).
However, complex trans-1a′ was 5.4 kcal/mol less stable than
cis-1a, although, in its energy minimum, the HPhP−COMe
distance is 3.84 Å. That is, although there was less steric
hindrance in the trans structure, the cis isomer is more stable.
This electronic effect is a new and quantified example of what
we call the “transphobia effect”9 that, in this case, is greater than
5.4 kcal/mol. In conclusion, to avoid steric hindrance, the most
stable mononuclear complex cis-1a′ transforms into the dimeric
complex 1a (Scheme 1 and Figure 1, HPhP−COMe distance of
Table 1. Diffusion Coefficients (D) for Complexes 1a, 1b, 1c,
1d, and 2a
sample weight
(mg)
C
D
compd
(mmol/L)
(×10−10 m2/s)
structure
c
1a
1a
1d
1b
8.10
16.00
7.30
10.04
19.82
19.98
6.28
6.26
6.70
6.36
dimer
c
dimer
c
monomer
a
d
7.90
20.02
dimer
b
10.01
a
d
1c
2a
7.45
8.25
20.00
6.64
6.36
monomer
b
4.181 Å) because the trans-1a′ isomer, in which the HPhP−
10.00
a
d
COMe repulsion would be weaker, is electronically destabilized
by the transphobia effect.
19.99
dimer
b
10.00
Trying to explain the mechanism of the chelating to bridging
transformation of the vinylarylethylamino ligand, we propose
that the coordination of the bulky phosphine (PPh3 or PCy3) to
the ortho-metalated homoveratrylamine fragment leads to the
a
b
Concentration assuming a monomeric structure. Concentration
c
d
assuming a dimeric structure. Structure in the solid state. Proposed
structure in solution.
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unstable intermediate cis-1a′ (Scheme 2) that evolves through
studies were conducted to propose the factors influencing the
formation the dinuclear complexes.
the decoordination of the amine, relieving the steric congestion.
EXPERIMENTAL SECTION
Scheme 2. Proposed Mechanism for the Formation of the
Dimeric Complexes
■
General Procedures. Infrared spectra, C, H, and N analyses,
conductance measurements, and melting point determinations were
conducted as described previously.20 Unless otherwise stated, NMR
spectra were recorded in CDCl3 via a 300, 400, or 600 MHz
spectrometer. Chemical shifts are referenced to TMS (1H, 13C{1H})
1
or H3PO4 (31P{1H}). Signals in the H and 13C NMR spectra of all
complexes were assigned with the help of APT, HMQC, and HMBC
techniques. Reactions were conducted at room temperature without
special precautions against moisture unless otherwise specified. Chart
1 gives the numbering scheme for the eight-membered palladacycles.
Chart 1. Numbering Scheme for the Eight-Membered
Palladacycles
The palladacycles [Pd{C,N-C(Ph)C(R)C6H2CH2CH2NH2-2-
(OMe)2-4,5}(μ-Br)]2 (R = Ph, A; R = CO2Me, B; R = Me, C) and
[Pd{C,N-C(Ph)C(R)-C6H4CH2CMe2NH2-2}(μ-Cl)]2 (R = Ph, D;
R = Me, E) were prepared as previously reported.11 A PMe3 solution
(1.0 M, toluene), 4-methylpyridine (4-picoline), PPh3, and PCy3 were
used as received.
Synthesis of [Pd{C,N-C(Ph)C(Ph)C6H2CH2CH2NH2-2-
(OMe)2-4,5}Br(PPh3)]2·H2O (1a·H2O). PPh3 (48 mg, 0.183 mmol)
was added to a suspension of palladacycle A (100 mg, 0.092 mmol) in
CH2Cl2 (20 mL), and the resulting solution was stirred for 30 min.
The mixture was filtered through a plug of Celite; the filtrate was
concentrated to ∼1 mL, and Et2O (30 mL) was added. The
suspension was filtered, and the solid was washed with Et2O (2 × 5
mL) and air-dried to afford complex 1a·H2O as a yellow solid. Yield:
231 mg, 0.141 mmol, 77%. Mp: 254 °C. Anal. Calcd for
C84H78Br2N2O4P2Pd2·H2O (1632.165): C, 61.14; H, 5.01; N, 1.70.
Found: C, 61.13; H, 4.66; N, 1.70. IR (cm−1): ν(NH) 3417 br w, 3323
The enhanced electrophilicity of the Pd center promotes the
homolytic splitting of the double bond, giving a diradical I
(Scheme 2), which is stabilized by the delocalization with the
CO2Me or Ph groups (but not for R2 = Me). The cleaved
double bond can rotate to weaken the steric hindrance of the
[PdBr(PPh3)] fragment and the substituted aryl group, giving
intermediate II (Scheme 2), in which R2 and the phenyl group
of the alkenyl moiety are trans. Radical isomerizations of
stilbene derivatives are well-known.19 Re-formation of the
double bond and coordination of the amino group to the
Pd(II) center of an adjacent molecule would afford dimer 1a
(R2 = Ph) or 1b (R2 = CO2Me).
1
br w, 3256 br w. H NMR (300.1 MHz): δ 1.55 (s, 2 H, H2O), 1.64
(m, 1 H, NH2), 2.82 (m, 1 H, CH2Ar), 2.99 (m, 1 H, CH2Ar), 3.16 (s,
3 H, MeO), 3.44−3.53 (m, 3 H, CH2N + 1 H of NH2), 4.05 (s, 3 H,
MeO), 5.47 (s, 1 H, H3), 6.68−6.73 (m, 2 H, o-H, Ph), 6.97 (s, 1 H,
H6), 6.98−7.05 (m, 6 H, 4 H of m-H + 2 H of p-H, Ph), 7.50−7.27
(m, 15 H, m-H + p-H + o-H, PPh3). 13C{1H} NMR (75.45 MHz): δ
34.2 (s, CH2Ar), 47.1 (s, CH2N), 55.5 (s, MeO), 55.9 (s, MeO), 111.5
(s, CH, C3), 112.2 (s, CH, C6), 125.5 (s, CH, Ph), 125.6 (s, CH, Ph),
127.3 (s, CH, Ph), 128.1 (br d, m-CH, PPh3, 3JCP = 10.5 Hz), 128.5 (s,
CH, Ph), 129.5 (s, CH, Ph), 129.7 (s, CH, Ph), 130.2 (br s, CH,
PPh3), 133.5 (s, C, Ph), 137.6 (d, C, JCP = 3.6 Hz), 139.3 (s, C), 140.6
(s, C), 145.4 (s, C), 147.4 (s, C-OMe), 148.5 (s, C-OMe), 158.1 (s,
C). The 13C NMR resonance corresponding to the i-C group of PPh3
was not observed. 31P{1H} NMR (121.5 MHz): δ 26.7 (s). Single
crystals of 1a·2CH2Cl2, suitable for an X-ray diffraction study, were
obtained by slow diffusion of n-pentane into a solution of 1a·H2O in
CH2Cl2.
Synthesis of [Pd{C,N-C(Ph)C(CO2Me)C6H2CH2CH2NH2-2-
(OMe)2-4,5}Br(PPh3)]2 (1b). PPh3 (42 mg, 0.162 mmol) was added
to a suspension of palladacycle B (see next paragraph; 85 mg, 0.080
mmol) in CH2Cl2 (20 mL), and the resulting solution was stirred for
30 min. The mixture was filtered through a plug of Celite; the filtrate
was concentrated to ∼1 mL, and n-pentane (30 mL) was added. The
suspension was filtered, and the solid was washed with n-pentane (2 ×
5 mL) and air-dried to afford 1b as a yellow solid. Yield: 55 mg, 0.072
mmol, 86%. Anal. Calcd for C36H34BrNO4PPd (761.9681): C, 56.75;
The structure of intermediate II (R2 = Ph) was optimized
through DFT calculations (see the Supporting Information).
The C(Ph)−C(Ph) and C(Pd)−Ph distances (1.435 and 1.427
Å, respectively) indicate the delocalization of the electronic
density.
CONCLUSION
■
The reactions of eight-membered palladacycles, derived from
the monoinsertion of internal alkynes into the Pd−C bond of
ortho-metalated homoveratrylamine and phentermine, with
PR3 render surprising results. Steric and electronic factors,
associated with both the palladacycles and the entering ligand,
play a key role in the formation of unusual dimers, in which the
C,N-fragment acts as a bridging ligand. Diffusion-ordered NMR
spectroscopy (DOSY) experiments were used to measure the
diffusion coefficients to elucidate the mononuclear or dinuclear
structure of some of these complexes in solution, and DFT
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H, 4.50; N, 1.84. Found: C, 56.55; H, 4.88; N, 1.88. IR (cm−1): ν(NH)
3305 br w, 3248 br w, 3256 w; ν(CO) 1697 s. 1H NMR (300.1 MHz):
δ 1.85 (br s, 1 H, NH2), 2.76 (m, 1 H, CH2Ar), 2.90 (br d, 1 H,
H, 5.38; N, 1.91. Found: C, 68.83; H, 5.36; N, 2.21. IR (cm−1): ν(NH)
3287 w, 3234 w. 1H NMR (400.91 MHz): δ 1.40 (s, 3 H, Me, CMe2),
1.58 (s, 3 H, Me, CMe2), 1.80 (br dd, 1 H, NH2, 2JHH = 9.6 Hz, 3JPH
=
2
2
3.6 Hz), 2.76 (d, 1 H, CH2Ar, JHH = 14.0 Hz), 3.12 (d, 1 H, CH2Ar,
CH2Ar, JHH = 14.5 Hz), 3.31 (s, 3 H, MeO), 3.40−3.48 (m, partially
2
obscured by the MeO signal, 2 H, CH2N), 3.42 (s, partially obscured
by the CH2N signal, 3 H, MeO), 3.50 (br s, 1 H, NH2), 5.65 (s, 1 H,
H3), 6.91 (s, 1 H, H6), 7.06−7.20 (m, 5 H, Ph), 7.35−7.48 (m, 15 H,
PPh3). 13C{1H} NMR (75.45 MHz): δ 34.1 (s, CH2Ar), 47.1 (s,
CH2N), 51.2 (s, MeO), 55.6 (s, MeO), 60.0 (s, MeO), 111.3 (s, CH,
C3), 112.6 (s, CH, C6), 127.8 (s, CH, Ph), 128.1 (d, m-CH, PPh3, 3JCP
2JHH = 14.0 Hz), 3.29 (br d, 1 H, NH2, JHH = 8.0 Hz), 5.18 (d, 1 H,
3
H3, JHH = 6.8 Hz), 6.66−6.68 (m, 2 H, o-H, Ph), 6.79 (td, 1 H, H4,
3JHH = 6.8 Hz, 4JHH = 0.8 Hz), 6.93−6.99 (m, 3 H, 2 m-H + p-H, Ph),
7.04−7.05 (m, 3 H, 2 m-H + p-H, Ph), 7.15−7.19 (m, 2 H, o-H, Ph),
7.22−7.43 (m, 17 H, H5 + H6 + PPh3). 13C{1H} NMR (100.81
MHz): δ 28.8 (s, Me, CMe2), 36.3 (d, Me, CMe2, 4JCP = 4.2 Hz), 45.0
(s, CH2Ar), 56.5 (s, CMe2), 125.3 (s, p-CH, Ph), 125.5 (s, p-CH, Ph),
125.7 (s, CH, C5), 126.8 (s, CH, C4), 127.2 (s, m-CH, Ph), 128.0 (br
= 12.8 Hz), 130.8 (br s, p-CH, PPh3), 131.2 (d, i-C, PPh3, 1JCP = 49.9
2
Hz), 133.5 (s, C, Ar), 134.5 (s, C, Ar), 134.8 (d, o-CH, PPh3, JCP
=
2
12.7 Hz), 144.8 (d, C, Ph, JCP = 2.6 Hz), 147.4 (s, C-OMe), 149.1 (s,
C-OMe), 166.4 (s, CO), 177.1 (s, C). 31P{1H} NMR (162.3 MHz): δ
27.4 (s).
d, o-CH, PPh3, JCP = 10.4 Hz), 128.7 (s, m-CH, Ph), 128.8 (s, CH,
C3), 129.4 (s, o-CH, Ph), 129.8 (s, o-CH, Ph), 130.2 (br s, p-CH,
PPh3), 131.2 (d, i-C, PPh3, 1JCP = 48.3 Hz), 131.9 (s, CH, C6), 135.0
(br m, m-CH, PPh3), 137.9 (s, C), 138.2 (d, C, JCP = 5.1 Hz), 140.5 (s,
C, Ph), 145.5 (d, C, Ph, JCP = 2.1 Hz), 148.0 (d, C, JCP = 1.9 Hz),
158.3 (d, C, JCP = 2.9 Hz). 31P{1H} NMR (121.5 MHz): δ 27.7 (s,
PPh3). Single crystals of 1d·2CH2Cl2, suitable for an X-ray diffraction
study, were obtained by slow diffusion of n-pentane into a solution of
1d in CH2Cl2.
The starting material is actually a 2.5:1 mixture of palladacycle B and
its regioisomer B′, which differs in the position of the substituents in
the alkenyl moiety.2 Therefore, compound 1b is isolated along with a
small amount of its corresponding regioisomer 1b′ (1b:1b′ ratio of
1
10:1, by H NMR), which arises from the reaction of B′ with PPh3.
1
Selected data for 1b′. H NMR (300.1 MHz): δ 3.26 (s, 3 H, MeO),
3.49 (s, 3 H, MeO), 3.86 (s, 3 H, MeO), 5.49 (s, 1 H, H3), 6.61 (s, 1
H, H6). 13C{1H} NMR (75.45 MHz): δ 51.4 (s, MeO), 55.7 (s,
MeO), 55.8 (s, MeO), 111.1 (s, CH, C3), 112.4 (s, CH, C6). 31P{1H}
NMR (162.3 MHz): δ 28.5 (s).
Synthesis of [Pd{C,N-C(Ph)C(Ph)C6H2CH2CH2NH2-2-
(OMe)2-4,5}Br(PCy3)]2 (2a). PCy3 (51 mg, 0.183 mmol) was added
to a suspension of palladacycle A (100 mg, 0.092 mmol) in dry
CH2Cl2 (20 mL) under a N2 atmosphere, and the resulting solution
was stirred for 1 h. The mixture was filtered through a plug of Celite;
the filtrate was concentrated to ∼1 mL, and n-pentane (30 mL) was
added. The suspension was filtered, and the solid was washed with n-
pentane (2 × 5 mL) and air-dried to afford complex 2a as a yellow
solid. Yield: 121 mg, 0.147 mmol, 80%. Mp: 185 °C. Anal. Calcd for
C42H57BrNO2PPd (825.218): C, 61.13; H, 6.96; N, 1.70. Found: C,
60.72; H, 7.37; N, 1.73. IR (cm−1): ν(NH) 3302 m, 3249 m. 1H NMR
(300.1 MHz): δ 1.10−1.31 (m, 9 H, CH and CH2, Cy), 1.35−1.51 (m,
6 H, CH2, Cy), 1.58−1.80 (m, 13 H, 1 H of NH2 + CH2 of Cy), 1.95−
2.15 (m, 6 H, CH2, Cy), 2.56−2.77 (m, 2 H, CH2Ar), 3.35−3.45 (m, 3
H, CH2N + 1 H of NH2), 3.87 (s, 3 H, MeO), 3.90 (s, 3 H, MeO),
6.77 (s, 1 H, H6), 6.81 (s, 1 H, H3), 6.94−7.98 (m, 8 H, 2 H of p-H +
4 H of m-H + 2 H of o-H Ph), 7.40 (d, 2 H, o-H, Ph, 3JHH = 6.9 Hz).
13C{1H} NMR (75.45 MHz): δ 26.2 (s, CH2, Cy), 27.5 (d, CH2, Cy,
Synthesis of [Pd{C,N-C(Ph)C(Me)C6H2CH2CH2NH2-2,-
(OMe)2-4,5}Br(PPh3)]·H2O (1c·H2O). PPh3 (43 mg, 0.166 mmol)
was added to a suspension of palladacycle C (see next paragraph; 80
mg, 0.083 mmol) in CH2Cl2 (20 mL), and the resulting solution was
stirred for 30 min. The mixture was filtered through a plug of Celite;
the filtrate was concentrated to ∼1 mL, and Et2O (30 mL) was added.
The suspension was filtered, and the solid was washed with Et2O (2 ×
5 mL) and air-dried to afford a first crop of 1c·H2O (20 mg) as a
yellow solid. The filtrate was concentrated to ∼2 mL, and n-pentane
(20 mL) was added. The suspension was filtered, and the solid was
washed with n-pentane (2 × 5 mL) and air-dried to afford a second
crop of 1c·H2O (50 mg) as a yellow solid. Yield: 70 mg, 0.092 mmol,
55%. Anal. Calcd for C37H37BrNO2PPd·H2O (763.001): C, 58.24; H,
5.15; N, 1.83. Found: C, 58.29; H, 4.86; N, 1.69. IR (cm−1): ν(NH)
3325 w, 3263 w. 1H NMR (400.91 MHz): δ 1.67 (s, 2 H, H2O), 1.98
2
3JCP = 10.8 Hz), 30.5 (d, CH2, Cy, JCP = 22.1 Hz), 34.4 (s, CH2Ar),
5
1
(d, 3 H, Me, JPH = 1.2 Hz), 2.60−2.67 (m, 1 H, CH2Ar), 2.82−2.87
36.3 (br d, CH, Cy, JCP = 21.2 Hz), 45.9 (s, CH2N), 55.6 (s, MeO),
(m, 1 H, CH2Ar), 3.32 (s, 3 H, MeO), 3.42−3.51 (m, 4 H, CH2N +
NH2), 4.00 (s, 3 H, MeO), 5.56 (s, 1 H, H3), 6.88 (s, 1 H, H6), 7.11−
7.15 (m, 4 H, 2 H of o-H + 2 H of m-H, Ph), 7.21−7.32 (m, 14 H, 1 H
of Ph + 13 H of PPh3), 7.33−7.42 (m, 4 H, PPh3). 13C{1H} NMR
(100.81 MHz): δ 22.9 (s, Me), 34.0 (s, CH2Ar), 47.0 (s, CH2N), 55.7
(s, MeO), 56.0 (s, MeO), 110.2 (s, CH, C3), 112.7 (s, CH, C6), 125.4
(s, CH, Ph), 127.8 (s, CH, Ph), 127.9 (d, m-CH, PPh, 3JCP = 10.4 Hz),
128.0 (s, CH, Ph), 129.7 (s, CH, Ph), 130.1 (s, CH, Ph), 131.6 (s,
55.8 (s, MeO), 112.9 (s, CH, C6 + C3), 125.4 (s, CH, Ph), 127.5 (s,
CH, Ph), 127.6 (s, CH, Ph), 129.8 (s, CH, Ph), 131.2 (s, CH, Ph),
132.9 (s, C), 138.4 (s, C), 139.8 (s, C), 142.0 (s, C), 146.0 (s, C),
147.0 (s, C-OMe), 148.1 (s, C-OMe), 154.1 (s, C). 31P{1H} NMR
(121.5 MHz): δ 39.2 (s).
Synthesis of [Pd{C,N-C(Ph)C(Ph)C6H2CH2CH2NH2-2-
(OMe)2-4,5}Br(PMe3)]·H2O (3a·H2O). PMe3 (0.0128 mL of a
solution 1.0 M in toluene, 0.128 mmol) was added to a suspension
of palladacycle A (70 mg, 0.064 mmol) in dry CH2Cl2 (20 mL) under
a N2 atmosphere, and the resulting solution was stirred for 1 h. The
mixture was filtered through a plug of Celite; the solvent was removed
from the filtrate, and Et2O (30 mL) was added. The suspension was
filtered, and the solid was washed with Et2O (2 × 5 mL) and air-dried
to afford complex 3a·H2O as a pale yellow solid. Yield: 50 mg, 0.078
mmol, 61%. Mp: 241 °C. Anal. Calcd for C27H33BrNO2PPd·H2O
(638.859): C, 50.76; H, 5.52; N, 2.19. Found: C, 50.41; H, 5.39; N,
2.09. IR (cm−1): ν(NH) 3333 br m, 3272 br w. 1H NMR (300.1 MHz,
CD2Cl2): δ 1.45 (d, 9 H, Me, 2JPH = 10.5 Hz), 1.54 (s, 2 H, H2O), 1.62
(m, partially obscured by the H2O signal, 1 H, NH2), 2.77−2.94 (m, 2
H, CH2Ar), 3.00 (br s, 1 H, NH2), 3.21 (m, 1 H, CH2N), 3.39 (br s, 1
H, CH2N), 3.69 (s, 3 H, MeO), 3.89 (s, 3 H, MeO), 6.44 (s, 1 H, H3),
6.79−6.89 (m, 2 H, o-H, Ph), 6.91 (s, 1 H, H6), 6.99−7.07 (m, 4 H, 1
H of p-H + 3 H of m-H, Ph), 7.40−7.65 (m, 4 H, 2 H of o-H + 1 H of
p-H + 1 H of m-H, Ph). 13C{1H} NMR (75.45 MHz): δ 16.4 (d, Me,
1JCP = 32.5 Hz), 34.1 (s, CH2Ar), 47.1 (s, CH2N), 55.9 (s, MeO), 56.0
1
C1), 131.9 (d, i-C, PPh3, JCP = 43.7 Hz), 132.9 (d, C, JCP = 3.5 Hz),
2
134.8 (d, o-CH, PPh3, JCP = 11.6 Hz), 140.2 (s, C), 144.2 (s, C),
147.4 (s, C-OMe), 148.1 (s, C-OMe), 150.5 (s, C). 31P{1H} NMR
(121.5 MHz): δ 27.8 (s).
The starting material is actually a 5:1 mixture of palladacycle C and its
regioisomer C′, which differs in the position of the substituents in the
alkenyl moiety.2 Therefore, compound 1c·H2O is isolated along with a
small amount of its corresponding regioisomer 1c′·H2O (1c:1c′ ratio
of 5:1, for both crops, by 1H NMR), which arises from the reaction of
1
C′ with PPh3. Selected data for 1c′. H NMR (400.91 MHz): δ 1.98
(d, 3 H, Me, 5JPH = 1.2 Hz), 3.10 (s, 3 H, MeO), 4.01 (s, 3 H, MeO),
5.89 (s, 1 H, H3), 6.92 (s, 1 H, H6). 31P{1H} NMR (121.5 MHz): δ
27.7 (s).
Synthesis of [Pd{C,N-C(Ph)C(Ph)-C6H4CH2CMe2NH2-2}Cl-
(PPh3)] (1d). PPh3 (86 mg, 0.327 mmol) was added to a solution
of palladacycle D (150 mg, 0.160 mmol) in CH2Cl2 (15 mL), and the
resulting solution was stirred for 3 h. The mixture was concentrated to
∼1 mL, and Et2O (20 mL) was added. The suspension was filtered,
and the solid was washed with Et2O (2 × 5 mL) and air-dried to give
complex 1d as a pale yellow solid. Yield: 147 mg, 0.201 mmol, 63%.
Dec pt: 255 °C. Anal. Calcd for C42H39ClNPPd (730.625): C, 69.04;
(s, MeO), 110.7 (s, CH, C3), 112.8 (s, CH, C6), 125.5 (s, CH, Ph),
125.6 (s, CH, Ph), 127.7 (s, CH, Ph), 128.2 (s, CH, Ph), 129.1 (s, CH,
Ph), 129.2 (s, CH, Ph), 129.7 (s, CH, Ph), 129.7 (s, CH, Ph), 133.8
(d, C, JCP = 1.4 Hz), 137.7 (d, C, JCP = 5.6 Hz), 139.8 (d, C, JCP = 2.3
37
dx.doi.org/10.1021/om401090b | Organometallics 2014, 33, 33−39

Organometallics
Article
Hz), 141.1 (s, C), 145.2 (d, C, Ph, 3JCP = 2.7 Hz), 147.0 (s, C-OMe),
complex 4e·1/2CHCl3. This material is available free of charge
2
148.2 (s, C-OMe), 159.4 (d, C, JCP = 2.7 Hz). 31P{1H} NMR (121.5
via the Internet at http://pubs.acs.org.
MHz): δ −7.1 (s). Single crystals of 3a, suitable for an X-ray diffraction
study, were obtained by slow diffusion of Et2O into a solution of 3a·
H2O in CH2Cl2.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: ims@um.es.
*E-mail: jvs1@um.es.
Synthesis of [Pd{C,N-C(Ph)C(Me)-C6H4CH2CMe2NH2-2}Cl-
(NC5H4Me-4)] (4e). 4-Picoline (0.025 mL, 0.257 mmol) was added
to a solution of palladacycle E (90 mg, 0.111 mmol) in CH2Cl2 (10
mL), and the mixture was stirred for 30 min. The solution was
concentrated to ∼1 mL, and Et2O (20 mL) was added. The resulting
suspension was filtered, and the solid was washed with Et2O (2 × 5
mL) and air-dried to afford complex 4e as a pale yellow solid. Yield: 77
mg, 0.154 mmol, 69%. Mp: 161 °C. Anal. Calcd for C25H29ClN2Pd
(499.391): C, 60.12; H, 5.85; N, 5.61. Found: C, 59.86; H, 5.87; N,
5.52. IR (cm−1): ν(NH) 3280 w, 3227 w; ν(CN) 1619 m. 1H NMR
(400.91 MHz): δ 1.46 (s, 3 H, Me, CMe2), 1.51 (s, 3 H, Me, CMe2),
1.91 (s, 3 H, MeC), 2.07 (br d, 1 H, NH2, 2JHH = 7.2 Hz), 3.31 (s, 3
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Ministerio de Educacion
(CTQ2011-24016), and Fundacion
́
y Ciencia (Spain), FEDER
Seneca (04539/GERM/
́
́
06) for financial support. J.-A.G.-L. and M.-J.O.-M. are grateful
to the Fundacion Seneca (CARM, Spain) and Ministerio de
2
4
́
́
H, Me, pic), 2.68 (dd, 1 H, CH2Ar, JHH = 14.0 Hz, JHH = 1.2 Hz),
2
2
2.90 (d, 1 H, CH2Ar, JHH = 14.0 Hz), 3.20 (br d, 1 H, NH2, JHH
=
Educacion
́
y Ciencia (Spain), respectively, for their research
3
́
10.0 Hz), 6.82 (m, 2 H, o-H, Ph), 7.02 (d, 2 H, m-H, pic, JHH = 6.4
Hz), 7.15−7.24 (m, 4 H, H3 + m-H and p-H of Ph), 7.26−7.32 (m,
H4 + H5 + H6), 8.38 (m, 2 H, o-H, pic). 13C{1H} NMR (100.81
MHz): δ 21.0 (s, Me, pic), 22.0 (s, MeC), 27.5 (s, Me, CMe2), 35.6
(s, Me, CMe2), 44.9 (s, CH2Ar), 55.6 (s, CMe2), 125.0 (s, p-CH, Ph),
125.2 (s, CH, m-CH, pic), 125.8 (s, CH, C5), 126.3 (s, CH, C4),
126.8 (s, o-CH, Ph), 127.9 (s, CH, C3), 128.5 (s, m-CH, Ph), 132.9 (s,
CH, C6), 133.2 (s, MeC), 135.4 (s, C1), 144.8 (s, i-C, Ph), 145.4 (s,
C-Pd), 147.0 (s, C2), 148.9 (s, p-C, pic), 152.0 (s, o-CH, pic). Single
crystals of 4e·1/2CHCl3, suitable for an X-ray diffraction study, were
obtained by slow diffusion of n-pentane into a solution of 4e in CHCl3.
Single-Crystal X-ray Structure Determinations. Relevant
crystallographic data and details of the refinements for complexes
1a·2CH2Cl2, 1d·2CH2Cl2, 3a, and 4e·1/2CHCl3 are given in the
Supporting Information.
grants. We thank Dr. Gabriel Aullon
Inorgan
́
(Departament de Quimica
̀
ica of the Universitat de Barcelona) for his valuable
advice about the DFT calculations.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Cartesian coordinates (angstroms), absolute energies (arbitrary
units) of computed structures, crystal data, structure refinement
details, hydrogen bond data, and CIF files for compounds
characterized by XRD and an X-ray thermal ellipsoid plot of
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