Palladium complexes derived from N,N-bidentate NH-iminophosphorane ligands: Synthesis and use as catalysts in the Sonogashira reaction

Article abstract of DOI:10.1039/c2dt31290e

The addition of primary amines to the CC bond of diphenylalkenyl iminophosphoranes yielded a new subtype of N,N-bidentate ligands bearing NP ^V-C-C-NH backbones. These donor ligands reacted with PdCl ₂(COD) to give the corresponding σ

Full text of DOI:10.1039/c2dt31290e

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PAPER
Palladium complexes derived from N,N-bidentate NH-iminophosphorane
ligands: synthesis and use as catalysts in the Sonogashira reaction†
Mateo Alajarin,*a Carmen Lopez-Leonardo,*a Pilar Llamas-Lorente,a Rosalia Raja,a Delia Bautistab and
Raul-Angel Orenesa
Received 15th June 2012, Accepted 27th July 2012
DOI: 10.1039/c2dt31290e
The addition of primary amines to the CvC bond of diphenylalkenyl iminophosphoranes yielded a new
subtype of N,N-bidentate ligands bearing NvPV–C–C–NH backbones. These donor ligands reacted with
PdCl2(COD) to give the corresponding σN,σN-palladium complexes containing secondary amino groups,
bearing an intrinsically chiral nitrogen atom, and iminophosphorane units. These new complexes have
been fully characterized by the use of spectroscopic techniques and X-ray crystallography. The
comparison of the data extracted from their solution NMR spectra with their solid state structures
demonstrated the conformational stability of their six-membered chelate ring and also the configurational
stability of the chiral nitrogen atom, thus ruling out an arm-off racemization process. The addition of the
chiral, racemic α-methylbenzylamine to the prochiral P-alkenyl iminophosphoranes yielded mixtures of
the two expected diasteroisomeric ligands in low diastereoisomeric ratios. One of these mixtures was
resolved into their components, each one in turn giving rise to a pair of diasteromeric palladium
complexes epimeric at the amino nitrogen atom. One selected example of the new complexes efficiently
catalyzes the copper- and amine-free Sonogashira reaction of aryl halides with acetylenes.
a few reports on structurally related complexes where the second
Introduction
N atom is not fully substituted, in other words, is linked to at
Iminophosphoranes R3PvNR′ (λ5-phosphazenes) are versatile
reagents in organic synyhesis.1 The presence of a lone pair on
the N atom of the highly polarized PvN bond allows these
species to behave as good ligands toward transition metals to
give stable complexes.2
Transition metal complexes derived from functionalized imino-
phosphorane-containing bidentate ligands bearing a second
donor site are well known and many of them have been used in
catalytic reactions with varying degrees of success. The most
studied examples are those derived from the homobidentate bis
(iminophosphoranes).3,4 Another widely populated class are
complexes containing phosphino-iminophosphorane ligands.5,6
In contrast, examples of complexes with iminophosphorane
ligands bearing an additional nitrogen atom as a second donor
site are scarce7 and, to the best of our knowledge, there are only
least one H atom.8
While a considerable number of complexes bearing mono and
bidentate iminophosphorane ligands have been prepared, only a
few have been examined for their applicability in catalysis. In
this domain, only some of them have found application in useful
chemical transformations including, for instance, oligomerisa-
tion/polymerisation,2g,4c,7e,j cyclopropanation,3l hydrogenation8d
and C–C coupling reactions.6e
A diphenyliminophosphoranyl unit is known to activate an
olefinic residue for nucleophilic Michael-type additions when
reacted with simple N-nucleophilic species.9 This activating
effect is also shown by other related electron-withdrawing
groups, such as the diphenylphosphinoyl and diphenylthiophos-
phinoyl fragments.10 Within this context, we have previously
demonstrated that the addition of secondary amines to P,P,P-
diphenylvinyliminophosphoranes is a convenient way to prepare
a variety of bidentate N(PvN),N(NR2)-ligands, which were
further used to build the respective σN,σN-palladium complexes.
This methodology has also been extended to the synthesis of
analogous σN,σP- and σN,σS-complexes.6c,8b In the present
work, we did not prepare complexes from ligands containing NH
secondary amino groups (resulting from the utilization of
primary amines in the initial nucleophilic addition). We assumed
that such complexes would be accessible following the same
methodology and wondered if their intrinsically chiral NH nitro-
gen atom would be configurationally stable or not. Given that Pd
aDepartamento de Química Orgánica, Facultad de Química, Regional
Campus of International Excellence “Campus Mare Nostrum”,
Universidad de Murcia, E-30100 Murcia, Spain.
E-mail: alajarin@um.es, melill@um.es
bServicio Universitario de Instrumentación Científica, Edificio SACE,
Universidad de Murcia, Campus de Espinardo, E-30100 Murcia, Spain.
E-mail: dbc@um.es
†Electronic supplementary information (ESI) available: Synthesis and
spectroscopic data for ligands 4–6, 10 and 11. CCDC 881653 (7a),
881654 (u-8b), 881655 (u-9b) and 881656 (u,l-12). For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c2dt31290e
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complexes bearing NH ligands are not very common, we were
also intrigued by the possibility that the relatively acidic NH
proton would be involved in a secondary reaction (acid–base
equilibria or elimination reactions). We herein disclose our
results concerning some of these points: the preparation of a new
class of bidentate N(NvP),N(NH) ligands, their coordination
chemistry with Pd(II) species and the catalytic application of one
of the new Pd-complexes in the Sonogashira reaction.
The chirality of ligands 5 and 6, bearing one stereogenic
carbon atom, is revealed by the magnetic non-equivalence of the
1
diastereotopic protons of the methylene groups in their H NMR
spectra and also by that of the diastereotopic phenyl groups at
1
the Ph2P moiety. For instance, the H NMR spectrum of com-
pound 5 shows two doublets of doublets of doublets (δHa
3
3
2
3.22–3.23, JHH = 4.1–6.2 Hz, JHP = 7.6–8.5 Hz, JHH
=
=
3
3
12.0–12.1 Hz and δHb 3.36–3.42, JHP = 7.6–9.8 Hz, JHH
8.2–9.9 Hz, 2JHH = 12.0–12.1 Hz) due to the CH2–N methylenic
protons, whereas a complex system of two multiplets (δ
1
2.19–2.67) appears in the H NMR spectrum of compound 6 as
result of the CH2–P protons. In the 13C{1H} NMR spectra of
ligands 5 and 6, two differentiated set of signals for the phenyl
rings of the Ph2P groups are observed (see the ESI†).
Results and discussion
The starting iminophosphoranes 1 and 2 were readily prepared
by reacting commercially available diphenylvinylphosphane or
easily prepared diphenyl(1-phenylvinyl)phosphane11 with a
range of aryl azides under the standard conditions of the Staudin-
ger P(III) imination reaction.1,8b,9f Compound 3, with a P-1-pro-
penyl fragment, was obtained by the autocatalytic isomerization
of the corresponding P-allyl iminophosphoranes.12 The Michael-
type additions of primary amines to the CvC bond of com-
pounds 1–3 were carried out by refluxing benzene solutions of
the iminophosphoranes 1–3 containing an excess (10 equiv.) of
volatile amines, such as propylamine (bp 40 °C), isobutylamine
(bp 33–34 °C) or butylamine (bp 78 °C). The products of these
reactions, the respective N,N-ligands 4–6, were isolated in practi-
cally quantitative yields by a simple work-up (Scheme 1 and
Table 1). After removing the solvent and the excess of amine
under reduced pressure, the residue was washed with n-hexane
and the crude products were not subject to further purification
since the NMR analyses showed a high degree of purity. The
success of the addition reaction was evidenced by the disappear-
ance of the signals corresponding to the C(R2)vCH(R3) group
The coordination of compounds 4–6 in a bidentate N,N
manner by means of their iminophosphoranyl and amino nitro-
gen atoms was attempted by reacting them with an equimolar
amount of Pd(COD)Cl2 in dichloromethane at room temperature.
In fact, these reactions afforded the six-membered σN,σN-com-
plexes 7–9 as orange crystalline solids in very good yields
(94–98%) (Scheme 1 and Table 1). Complexes 8 and 9, with
two chiral centers (one methine carbon and the nitrogen atoms),
were isolated as mixtures of two diastereoisomers with high dia-
stereomeric ratios (from 85 : 15 to 90 : 10). The major com-
ponent of these mixtures, the u-diastereoisomer in all cases,
1
present in 1–3 in the H and 13C{1H} NMR spectra of com-
pounds 4–6 and the appearance of signals attributed to the new
ethylenic fragment. Thus, the 1H NMR spectrum of 4 shows two
doublets of triplets, one in the range of δ 2.54–2.76 with a coup-
ling constant with the phosphorus atom (2JHP) of 11.1–11.4 Hz
for the P-methylenic protons, and the other in the δ 2.85–2.89
interval with a coupling constant with the phosphorus atom
(3JHP) of 11.8–12.5 Hz for the N-methylenic protons. These two
types of protons are mutually coupled with a vicinal coupling
(3JHH) of 7.1–7.3 Hz. In general, these coupling constants have
Scheme 1
Table 1 Ligands 4–6 and complexes 7–9
1
been determined with the help of H{31P} NMR experiments.
Ligands 4–6
Yield (%)
Complexes 7–9
Yield (%)
The bidimensional 13C–1H NMR spectrum of compound 4
showed that, as expected, the multiplet in the lower field region
is due to the CH2N group, whereas the multiplet in the higher
field region corresponds to the CH2P group. In the 13C{1H}
NMR spectrum of 4, the signals appearing in the δ 28.48–28.94
interval, with a coupling constant (1JCP) of 71.9–73.5 Hz, and in
the δ 40.46–43.17 interval, with a 2JCP of 0–2.3 Hz, are assigned
to the CH2P and CH2N carbon atoms, respectively. These data
are in agreement with other previously published data showing
that in diverse P(V)-alkyl substituted compounds, the value of
R1
R2
R3
R4
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
4-CH3OC6H4
4-CH3OC6H4
4-BrC6H4
4-CH3C6H4
4-BrC6H4
4-BrC6H4
H
H
H
H
H
H
C6H5
C6H5
C6H5
C6H5
H
H
H
H
H
H
H
H
H
H
H
nPr 4a, 93
7a, 97
iPr
4b, 95
nBu 4c, 98
nPr 4d, 97a
nBu 4e, 97
7b, 97a
7c, 97
7d, 95
8a, 98
8b, 95
8c, 96
8d, 98
9a, 94
9b, 96
9c, 95
9d, 97
iPr
4f, 92
nPr 5a, 95
nPr 5b, 96
iPr
5c, 98
4-BrC6H4
nBu 5d, 97
4-CH3C6H4
4-CH3C6H4
4-CH3OC6H4
4-CH3OC6H4
CH3 nPr 6a, 97
CH3 nBu 6b, 92
CH3 nPr 6c, 93
CH3 nBu 6d, 92
1
the JCP coupling constant is in the range of 60–75 Hz, whereas
H
H
H
2JCP is very small or non-observable.9b,c,10h The amine addition
also provoked the deshielding of the signal corresponding to the
Ph2PvNAr phosphorus atom in the 31P NMR spectra of 4a–f
when compared with that of compounds 1 (Δδ = 4.71–6.57).
a see ref. 8b.
12260 | Dalton Trans., 2012, 41, 12259–12269
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could be isolated in a good yield by successive recrystallizations
from dichloromethane–diethyl ether mixtures.
The 31P{1H} NMR data are particularly useful for assessing
the coordination of the iminophosphoranyl unit to the metal as
the P nucleus has been shown to exhibit large downfield shifts
upon the coordination of the PvN unit to a Lewis acid.13
A
signal is observed in the range of δ 23.97–24.45 for complexes
7, δ 28.18–29.93 for 8 and δ 22.18–23.05 for 9, remarkably
deshielded in comparison to the signals shown by ligands 4 (Δδ
16.28–18.84), 5 (Δδ 18.99–20.81) and 6 (Δδ 16.27–17.87),
respectively.
Complexes 7 were characterized by a combination of NMR
techniques and other analytical data. Additional evidence for its
formulation resulted from the X-ray crystal structure analysis.
Single crystals of complex 7a were obtained by the slow diffu-
sion of diethyl ether into a dichloromethane solution at room
temperature. A view of one molecule of complex 7a is shown in
Fig. 1 and the most significant crystallographic parameters are
given in Table 2.
In complex 7a, the ligand coordinates in a bidentate manner
as a σN,σN-donor, showing a chair conformation for its six-
membered chelate ring with cis geometry around the metal and
an almost perfect square-planar structure, the mean deviation
from the plane of the Pd, N(1), N(2), Cl(1) and Cl(2) atoms is
0.0384 Å. The Pd–Cl bond lengths (2.3077(7) and 2.3053(7))
while chemically distinct are nearly identical, suggesting that the
Fig. 1 Thermal ellipsoid plot (50% probability level) of 7a. Selected
bond lengths (Å) and angles (°): Pd–N(2) 2.062(2), Pd–N(1) 2.053(2),
Pd–Cl(1) 2.3077(7), Pd–Cl(2) 2.3053(7), P–N(2) 1.618(3); N(2)–Pd–
N(1) 89.89(10), N(2)–Pd–Cl(1) 93.27(7), N(1)–Pd–Cl(1) 175.31(7),
N(2)–Pd–Cl(2) 176.88(7), N(1)–Pd–Cl(2) 87.23(7), Cl(1)–Pd–Cl(2),
89.69(3), C(11)–N(2)–P 123.6(2), C(11)–N(2)–Pd 117.55(19), P–N(2)–
Pd 114.07(13), C(3)–N(1)–Pd 110.00(18).
Table 2 Crystallographic data for compounds 7a, u-8b, u-9b and u,l-12
7a·1 CH2Cl2
u-8b
u-9b·1 CH3CN
u,l-12·2 CHCl3
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C25H31Cl4N2PPd
638.69
100(2)
C29H30BrCl2N2PPd
694.73
100(2)
0.71073 Å
Monoclinic
P 21/n
C28H36Cl2N3PPd
622.87
100(2)
0.71073
Monoclinic
P 21/c
C32H35Cl8N2PPd
868.59
173(2)
0.71073
Monoclinic
P 2(1)/c
0.71073
Tetragonal
ˉ
P4 21 c
21.6139(4)
21.6139(4)
11.7959(4)
90
8.5072(4)
20.6152(9)
16.0082(7)
90
18.6505(13)
7.6545(5)
20.4198(14)
90
10.0275(6)
14.4426(16)
25.536(2)
90
b (Å)
c (Å)
α (°)
β (°)
90
90
5510.6(2)
8
1.540
1.136
2592
96.562(2)
90
2789.1(2)
4
1.654
2.369
93.675(2)
90
2909.1(3)
4
1.422
0.898
92.837(6)
90
3693.7(6)
4
1.562
1.150
γ (°)
Volume (Å3)
Z
Density (calculated) (Mg m−3
)
)
Absorption coefficient (mm−1
F(000)
1392
1280
1752
Crystal size (mm)
Theta range for data collection 1.88 to 28.25°
0.24 × 0.19 × 0.16
0.23 × 0.07 × 0.03
1.98 to 28.22°
0.18 × 0.18 × 0.12
2.19 to 28.57°
0.44 × 0.26 × 0.10
3.00 to 25.00°
Index ranges
−28 ≤ h ≤ 27, −28 ≤ k ≤ −11 ≤ h ≤ 11, −27 ≤ k ≤
−24 ≤ h ≤ 24, −10 ≤ k ≤ −11 ≤ h ≤ 11, −17 ≤ k ≤ 1,
28, −15 ≤ l ≤ 15
27, −21 ≤ l ≤ 21
10, −27 ≤ l ≤ 26
0 ≤ l ≤ 30
Reflections collected
Independent reflections
Refinement method
62 664
32 047
33 932
6676
6569 [R(int) = 0.0235]
Full-matrix least-squares
on F2
6497 [R(int) = 0.0439]
Full-matrix-block least-
squares on F2
6497/0/330
6990 [R(int) = 0.0294]
Full-matrix least-squares
on F2
6467 (R(int) = 0.0347)
Full-matrix least-squares on
F2
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]a
R indices (all data)b
6569/2/302
6990/0/324
1.301
6467/38/403
0.937
1.097
1.071
R1 = 0.0304, wR2 = 0.0793 R1 = 0.0351, wR2 = 0.0750 R1 = 0.0411, wR2 = 0.0846 R1 = 0.0362, wR2 = 0.0824
R1 = 0.0310, wR2 = 0.0799 R1 = 0.0434, wR2 = 0.0782 R1 = 0.0433, wR2 = 0.0857 R1 = 0.0562, wR2 = 0.0881
Largest diff. peak and
0.874 and −1.108
0.840 and −0.455
0.723 and −0.774
0.8529 and −0.526
hole (e Å−3
)
Absorption correction
Semi-empirical from
equivalents
Semi-empirical from
equivalents
Semi-empirical from
equivalents
Psi-scans
2
2 2
2 2 0.5
a R1 = Σ||Fo| − |Fc||/Σ|Fo| for reflections with I > 2σ(I). b wR2 = [Σ[w(Fo − Fc ) ]/Σ[w(Fo ) ] for all reflections; w−1 = σ2(F2) + (aP)2 + bP, where
2
P = (2Fc2 + Fo )/3 and a and b are constants set by the program.
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trans influence of the two donor N atoms is very similar. The
natural bite angle of 89.89(10)° for N–Pd–N is very close to the
ideal value of 90°. The Pd-iminophosphoranyl N atom (Pd–
N(2))] bond length (2.062(2)) is in the range of highly polarized
P–N bonds.5j,7e,8b
hindered at 298 K (the habitual temperature of the NMR exper-
iments) as its two Ho protons appear as non-equivalents in its 1H
NMR spectrum. We also recorded variable temperature 1H NMR
spectra but no substantial changes were observed between 298 K
and 376 K. This fact could be reasonably interpreted as the
absence of a dynamic situation in which each proton occupies a
fixed position and, in consequence, we can therefore attribute a
large conformational and configurational stability to complexes 7.
The major component in the mixture of diastereoisomers for
complexes 8 could be, in all cases, obtained in its pure form by
fractional crystallization and, in the case of 8b, was shown to be
the u-stereoisomer by the X-ray analysis of a monocrystal. A
view of one molecule of complex 8b is shown in Fig. 2 and the
most significant metric parameters are given in Table 2.
The chiral complexes 7, with the amino N atom as the only
stereogenic center, shows the magnetic non-equivalence of the
diastereotopic phenyl groups of the Ph2P moiety in its 13C{1H}
NMR spectrum and that of the protons of the PCH2 and NCH2
1
methylene groups in its H NMR spectra (see the Experimental
section and Table 3). Bidimensional 13C–1H HMQC NMR
experiments on compound 7 show that the multiplets centered
near δ 2.76 and δ 3.45 (Δδ = 0.69) in the 1H NMR spectra
are due to the CH2P protons, whereas those at δ 3.00 and δ 3.24
(Δδ = 0.24) correspond to the CH2N protons.
The selected bond lengths and angles around the palladium
atom of 8b are very similar to those measured in 7a, although
the conformations of both species in the solid state are very
different. In the case of 8b, the bidentate N,N ligand coordinates
to Pd forming a twist-boat six-membered chelate ring.
The solution structure of compound 7a could be established
on the basis of the H–H distance constraints, as evidenced by
NOESY two-dimensional experiments. Specifically, the confor-
mation of the chelate six-membered ring is determined by NOE
effects involving the protons of the CH2P, C H 2N and NH
groups. Of special significance are the NOEs between the proton
labeled as Heq from the CH2P group and the Hax proton of the
CH2N group, and those between the Hax of CH2P and the Heq of
CH2N. Furthermore, the NOE effect between the amine proton
and the Hax of the CH2N group is observed. The relative
volumes of the NOESY cross-peaks are consistent with the dis-
tances observed in the crystal structure of 7a, i.e., Heq(CH2P)–
Hax(CH2N): 2.343 Å, Hax(CH2P)–Heq(CH2N): 2.292 Å and
Heq(NH)–Hax(CH2N): 2.369 Å, suggesting that a static chair-
type ring conformation is preserved in solution. In this situation,
the alkyl substituent R4 at the amino N atom shows a clear pre-
ference for the axial position, perhaps in order to avoid steric
interference with the nearby Cl–Pd fragment. Another remark-
1
The room temperature H NMR spectrum of compounds 8 in
solution displays two complex multiplets, assignable to the
protons of the methylene CH2N group, and a well resolved
doublet of doublets for the methine CHP proton of the chelating
ring (Table 4).
Apparently, the methine CHP proton shows very different
3
coupling constants with the two CH2N protons. The observed J
value in the range of 10.6–11.2 Hz corresponds to its coupling
with the downfield CHaxN proton, while the value of the coup-
ling constant with the upfield CHeqN proton seems to be close to
0. These values are in agreement with the expected Karplus-like
3
behaviour for JHH and with the twist-boat chelate ring confor-
mation determined in the solid state. Note that the Hax–C(P)–
C(N)–Hax dihedral angle measured in the X-ray study of complex
8b is −157.80°, which is near to the maximum J value deter-
mined by the Karplus equation, while the measured Hax–C(P)–
C(N)–Heq dihedral angle is 84.40°, close to the minimum J = 0
value. A NOESY experiment for compound 8b displays a strong
NOE effect between the CHP and CHeqN protons, whereas the
1
able fact in the H NMR of complex 7 is the number of signals
assignable to the two Ph groups at the phosphorus atom, adopt-
ing well differentiated positions on the six-membered ring. Five
multiplets are observed for the ten protons of the Ph2P group
centered near δ 7.4 (2 Ho and 2 Hm), δ 7.6 (1 Ho), δ 7.7 (2 Hm),
δ 7.8 (1 Ho) and δ 8.3 (2 Hp). This observation is in accord with
the conformational rigidity of the chelate six-membered ring.
Moreover, the rotation around one P-phenyl bond seems to be
Table 3 Chemical shifts for the CH2P and CH2N hydrogen atoms of
compounds 7
Compound
δ(CHaxP)
δ(CHaxN)
δ(CHeqN)
δ(CHeqP)
Fig. 2 Thermal ellipsoid plot (50% probability level) of u-8b. Selected
bond lengths (Å) and angles (°): Pd–N(1) 2.057(2), Pd–N(2) 2.067(2),
Pd–Cl(1) 2.2999(7), Pd–Cl(2) 2.3035(7), P–N(1) 1.618(2); N(1)–Pd–
N(2) 90.88(9), N(1)–Pd–Cl(1) 90.37(6), N(2)–Pd–Cl(1) 176.68(7),
N(1)–Pd–Cl(2) 175.06(7), N(2)–Pd–Cl(2) 86.48(7), Cl(1)–Pd–Cl(2),
92.49(3), C(11)–N(1)–P 123.95(19), C(11)–N(1)–Pd 119.11(17),
P–N(1)–Pd 115.71(12), C(3)–N(2)–Pd 112.20(17).
7a
7b
7c
7d
3.39
3.43
3.38
3.63
3.17
3.15
3.19
3.46
2.88
3.10
2.92
3.04
2.76
2.74
2.77
2.78
Chemical shifts of centered multiplets in ppm referenced to TMS.
12262 | Dalton Trans., 2012, 41, 12259–12269
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Table 4 Chemical shifts and coupling constants for the CHP and
CH2N hydrogen atoms of compound u-8
Scheme 2
3JHax(CHP)
Hax(CH2N)
2
a
a
Compound δ(CHaxP) JHP
δ(CHaxN)b δ(CHeqN)b
dissociating the amine ligand via Pd–NH bond cleavage and
further reassociation would most probably give rise to the for-
mation of a fraction of the l-diastereoisomer of 9a, epimeric of
the major u-diastereoisomer at the N atom, a fact that was not
observed in these VT-NMR experiments. A similar configura-
tional stability of a chiral N atom has been previously observed
in one of the scarcely reported types of palladium-complexes
bearing N-chiral ligands, those derived from 1,2-diamines.14
In order to investigate the potential facial diastereoselectivity
of the addition reaction of amines to prochiral P-vinyl iminophos-
phoranes, we carried out the thermal treatment of the N-4-tolyl-
P,P-diphenyl-P-alkenyl iminophosphoranes 2 and 3 with an
excess of racemic α-methylbenzylamine by heating at 140 °C in
a sealed tube for 18 hours. Disappointingly, the diastereomeric
excesses obtained in these reactions to give ligands 10 and 11
were practically null (d.e. 0–20%) (Scheme 2). The complete
separation of the two diastereoisomers could only be achieved in
the case of complex 11 by means of column chromatography on
silica gel deactivated by previous treatment with 5% Et3N in
n-hexane.
u-8a
u-8b
u-8c
u-8d
5.47
5.48
5.57
5.44
13.9 11.0
14.6 11.2
15.2 10.9
13.0 10.6
3.18
3.15
3.20
3.19
2.88
2.89
2.72
2.89
3
The values of JHax(CHP)Heq(CH N) are very close to
0 and not
2
included.a Absolute values in Hz. b Chemical shifts of centered
multiplets in ppm referenced to TMS.
We were not able to distinguish between the l and u diastereo-
isomers of compounds 10 and 11 simply by analysing their solu-
tion NMR data. Alternatively, we expected that the formation of
the respective Pd-complexes with the two separated diastereoi-
somers of ligand 11 would allow for the indirect assignment of
the relative configuration between their stereogenic centres, as
far as the X-ray crystal structures of the so formed complexes
could be determined. After the complexation reaction a new
chiral centre, the amino N atom bound to the metal, would then
add to the pre-existing two chiral carbons of the ligands. Thus,
the l-11 diastereoisomer would give rise to a new two-com-
ponent diastereoisomeric mixture of species, for instance the l,u
and u,l species, whereas u-11 would yield a mixture of the other
two conceivable diastereoisomers, l,l and u,u in the same
instance.
Fig. 3 Thermal ellipsoid plot (50% probability level) of u-9a. Selected
bond lengths (Å) and angles (°): Pd–N(1) 2.043(2), Pd–N(2) 2.058(2),
Pd–Cl(1) 2.3111(7), Pd–Cl(2) 2.3066(7), P–N(1) 1.600(2); N(1)–Pd–
N(2) 90.52(9), N(2)–Pd–Cl(2) 88.28(7), N(1)–Pd–Cl(2) 178.70(7),
N(2)–Pd–Cl(1) 178.88(7), N(1)–Pd–Cl(1) 90.08(7), Cl(1)–Pd–Cl(2),
91.12(3), C(11)–N(1)–P 124.52(19), C(11)–N(1)–Pd 119.58(17),
P–N(1)–Pd 115.41(13), C(4)–N(2)–Pd 113.27(17).
effect between CHP and CHaxN is very weak. Furthermore, there
is also a measurable NOE effect between CHaxN and the amino
proton (labelled as NHeq in the structure presented in Table 4).
The u-configuration of the major diastereoisomer of 9 was
determined by X-ray analysis and NOESY experiments. Fig. 3
shows an ORTEP view of 9a with a selection of bond lengths
and bond angles, whereas Table 2 gives the experimental details
of the structure determination. The conformation of 9a is similar
to that of 7a, that is a six-membered chelate ring with a chair
conformation. A NOESY experiment with the Pd complex 9a in
CD2Cl2 solution displays two important NOE effects involving
the methyl protons: one with the proton in the equatorial position
of the endocyclic methylene group (a multiplet centered near
δ 3.3) and another one with the amino proton in the equatorial
position.
In fact, the reaction of the major diastereoisomer of ligand 11
with an equimolar amount of Pd(COD)Cl2 in dichloromethane at
room temperature gave rise to the six-membered σN,σN-complex
12 in a 98% yield as a mixture of two diastereoisomers in a ratio
1
of 3.5 : 1, as determined by the integration of its H NMR spec-
trum (Scheme 3).
X-Ray-quality crystals of the major component were obtained
by successive recrystallizations of the diastereoisomeric mixture
of 12 from chloroform–n-hexane. Its structure is shown to be the
u,l-12 species (Fig. 4).
Solution VT-NMR experiments with 9a, recorded between
243 K and 376 K, showed no significant changes, thus indicating
not only the conformational rigidity of the ring but also the
configurational stability of the chiral nitrogen atom. Any process
In this way, the relative u-configuration of the two chiral
carbon atoms of the major diastereoisomer of ligand 11 (major-
11, as illustrated in Scheme 3) was indirectly established. Note
that u,l-12 and l,u-12 are epimeric at the chiral N atom.
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Table 5 Selected results for the Sonogashira reaction of aryl halides
and terminal acetylenes catalyzed by 7a
Entry Ar
X
R
Time (h) Yield (%)a
1
2
3
4
5
6
7
8
4-CH3COC6H4
I
I
I
I
I
I
C6H5
2-NH2C6H4
C6H5
2-NH2C6H4
HOCH2(CH2)3
CH3(CH2)5
1
5
4
8
6
8
36
98
96
97
90
96
90
85
87
89
79
75
84
4-CNC6H4
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
4-CH3COC6H4 Br 2-NH2C6H4
4-CH3OC6H4
4-CH3OC6H4
4-tBuC6H4
Br HOCH2(CH2)3 32
Br CH3(CH2)5
Br C6H5
Br 2-NH2C6H4
Br HOCH2(CH2)3 24
9
38
32
48
10
11
12
4-tBuC6H4
4-tBuC6H4
a Determined by GC. Conditions: 1.0 equiv. of aryl halide, 1.2 equiv. of
acetylene, 2 equiv. of TBAF, cat. 7a (1 mol%), DMF (5 mL per mmol of
aryl halide), 110 °C, nitrogen atmosphere.
Scheme 3
reactions. In general, the copper- and amine-free procedure sim-
plifies the reaction protocol and is especially useful for the
optimization of the reaction parameters.
Conclusions
In conclusion, herein we have demonstrated that the nucleophilic
addition of primary amines to the CvC bond of diphenylalkenyl
iminophosphoranes occurs efficiently and that the resulting
bidentate N(NvP),N(NH) ligands easily form σN,σN-palladium
complexes, not experiencing undesired secondary reactions
brought about by the NH proton. From this study we can also
conclude that the notorious stability of these complexes in sol-
ution is due to the particularly stable conformations of their six-
membered chelate rings and to the configurational stability of
their intrinsically chiral nitrogen atoms belonging to the NH
groups as the arm-off processes which detach this N atom from
the metal does not occur in the range of temperatures studied.
We hope these new palladium complexes could potentially find
interesting applications in catalysis, as evidenced by the success-
ful Sonogashira coupling reactions shown in this work.
Fig. 4 Thermal ellipsoid plot (50% probability level) of u,l-12.
Selected bond lengths (Å) and angles (°): Pd–N(1) 2.039(3), Pd–N(2)
2.066(3), Pd–Cl(1) 2.3021(10), Pd–Cl(2) 2.3321(10), P–N(1) 1.610(3);
N(1)–Pd–N(2) 89.85(12), N(1)–Pd–Cl(2) 175.89(9), N(2)–Pd–Cl(2)
87.27(10), N(1)–Pd–Cl(1) 91.15(9), N(2)–Pd–Cl(1) 178.98(10), Cl(1)–
Pd–Cl(2), 91.71(4), C(31)–N(1)–P 122.7(2), C(31)–N(1)–Pd 118.1(2),
P–N(1)–Pd 114.27(16), C(3)–N(2)–Pd 118.5(2).
The catalytic activity of complex 7a was investigated in a
copper- and amine-free Sonogashira C–C cross-coupling reac-
tion15 between aryl halides and terminal acetylenes. The prelimi-
nary optimization of the conditions of the reaction16 between
4-iodoacetophenone and phenylacetylene under nitrogen and in
the presence of 1 mol% of complex 7a was established at 110 °C
by a combination of different solvents (toluene, acetonitrile and
dimethylformamide) and additives (TBAA, TBAB and TBAF).
The best results are summarized in Table 5. The reaction times in
this Table are those when the aryl halide conversions were deter-
mined to be higher that 95%.
Experimental
All reactions were carried out under nitrogen in HPLC grade sol-
vents (Scharlab), which were nitrogen saturated, dried and deoxy-
genated using an Innovative Technology Inc. Pure-Solv 400
Solvent Purification System. Diphenylvinylphosphane and
dichloro(1,5-cyclooctadiene)palladium(II) [Pd(COD)Cl2] were
purchased from the Aldrich Chemical Co. and used as received.
Diphenyl(1-phenylvinyl)phosphane11 and iminophosphoranes
1,8b 29f and 312 were prepared as reported. Column chromato-
graphy was performed with the indicated solvent using silica gel
(70–200 μm) as the stationary phase. All melting points were
determined on a Kofler hot-plate melting point apparatus and are
uncorrected. IR spectra were determined as Nujol emulsions or
It should be emphasized that this efficient procedure does not
require the use of either cuprous iodide as a cocatalyst or an
amine as a base,17 habitually needed in common Sonogashira
12264 | Dalton Trans., 2012, 41, 12259–12269
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films on a Nicolet 380 FT-IR spectrophotometer. NMR spectra
7.71–7.82 (m, 3H, Ho + 2Hm), 8.29–8.39 (m, 2H, Hp). 13C{1H}
NMR (100 MHz, CD2Cl2): δ 14.06 (CH3CH2CH2CH2), 20.66
were recorder at 25 °C on a Bruker AC200 (200 MHz), Bruker
1
1
Avance 300 (300 MHz) and Bruker Avance 400 (400 MHz). H
(CH3CH2CH2CH2), 31.03 (d, JCP 83.0, PCH2), 31.12
and 13C chemical shifts were reported in ppm downfield of the
internal tetramethylsilane and 31P chemical shifts were externally
referenced to 85% H3PO4. J values are given in Hz. The mass
spectra were recorded on an Hewlett-Packard 5993C spec-
trometer (EI), on a VG Autospec spectrometer (FAB+) or on an
Agilent VL (ESI) mass spectrometer. Microanalyses were per-
formed on an EA 1108 Carlo Erba instrument. The syntheses
and data for ligands 4–6 are given in the ESI.†
(CH3CH2CH2CH2), 43.73 (d, JCP 7.8, CH2N), 54.87
2
1
(CH3CH2CH2CH2), 55.66 (OCH3), 113.70 (C3), 124.38 (d, JCP
1
3
87.6, Ci), 127.13 (d, JCP 89.5, Ci), 128.10 (d, JCP 10.8, C2),
3
3
129.72 (d, JCP 11.7, Cm), 130.02 (d, JCP 12.6, Cm), 133.13 (d,
2JCP 9.1, Co), 133.84 (d, 4JCP 2.5, Cp), 134.01 (d, 2JCP 10.6, Co),
134.23 (d, JCP 2.9, Cp), 140.82 (C1), 155.34 (C4). 31P{1H}
4
NMR (81 MHz, CD2Cl2): δ 24.45. HRMS (ESI): calcd for
C25H31ClN2OPPd [M − Cl]+, 547.0897; Found, 547.0910.
7d [R1 = 4-BrC6H4, R2 = R3 = H, R4 = (CH3)2CH]. Yield:
0.18 g (95%); mp (decomp) 185–187 °C. IR (Nujol)/cm−1
:
3444, 1481, 1437, 1256, 1109, 999, 997, 722, 691, 659. 1H
Synthesis
3
NMR (400 MHz, CD2Cl2): δ 1.51 [d, 3H, JHH 6.6, (CH3)2CH],
General procedure for the synthesis of complexes 7–9. 1
equiv of Pd(COD)Cl2 (0.09 g, 0.3 mmol) was added to a dry
dichloromethane solution (15 mL) of the corresponding imino-
phosphorane-amine 4–6 (0.3 mmol) under a nitrogen atmos-
phere. The solution was stirred at 25 °C for 0.5 h. The solvent
was removed under vacuum and the residue was treated with dry
diethyl ether to give 7–9 as an orange solid, which was isolated
by filtration and dried under reduced pressure. Analytically pure
samples were obtained by crystallization from CH2Cl2–Et2O. In
the cases where a mixture of diastereoisomers was obtained, the
analytical and spectral data correspond to the major component,
which was purified by successive recrystallizations.
1.69 [d, 3H, 3JHH 6.2, (CH3)2CH], 2.71–2.85 [m, 2H, (CH3)2CH
+ PCHeq], 2.99–3.08 (m, 1H, CHeqN), 3.42–3.50 (m, 1H,
CHaxN), 3.59–3.67 (m, 1H, PCHax), 4.63 (br s, 1H, NH), 7.08
3
3
(d, 2H, JHH 8.7, HAr), 7.17 (d, 2H, JHH 8.7 Hz, HAr),
7.42–7.49 (m, 4H, 2Ho + 2Hm), 7.60–7.65 (m, 1H, Ho),
7.70–7.74 (m, 2H, Hm), 7.79–7.83 (m, 1H, Ho), 8.28–8.33 (m,
2H, Hp). 13C{1H} NMR (100 MHz, CD2Cl2): δ 20.20
1
[(CH3)2CH], 23.36 [(CH3)2CH], 31.27 (d, JCP 83.3, PCH2),
2
38.53 (d, JCP 7.5, CH2N), 53.62 [(CH3)2CH], 114.06 (C4),
1
1
123.46 (d, JCP 87.5, Ci), 125.39 (d, JCP 87.9, Ci), 128.13 (d,
3JCP 12.4, C2), 129.89 (d, JCP 11.8, Cm), 129.96 (d, JCP 12.5,
3
3
Cm), 130.88 (C3), 132.86 (d, 2JCP 9.3, Co), 133.92 (d, JCP 10.5,
2
7a (R1 = 4-CH3C6H4, R2 = R3 = H, R4 = CH3CH2CH2). Yield:
4
4
Co), 134.03 (d, JCP 2.5, Cp), 134.31 (d, JCP 2.1, Cp), 147.69
(C1). 31P{1H} NMR (162 MHz, CD2Cl2): δ 24.05. HRMS
(ESI): calcd for C23H26BrClN2PPd [M − Cl]+, 580.9740;
Found, 580.9731.
0.16 g (97%); mp (decomp) 149–151 °C. IR (Nujol)/cm−1
:
3440, 1503, 1438, 1250, 1111, 734, 727, 694. 1H NMR
3
(400 MHz, CD2Cl2): δ 1.10 (t, 3H, JHH 7.4, CH3CH2CH2),
2.10 (m, 2H, CH3CH2CH2), 2.17 (s, 3H, CH3), 2.70–2.94 (m,
3H, PCHeq + CHeqN + CH3CH2CHAHB), 3.12–3.21 (m, 1H,
CHaxN), 3.31–3.46 (m, 2H, PCHax + CH3CH2CHAHB), 4.45 (br
8a (R1 = 4-CH3C6H4, R2 = C6H5, R3 = H, R4 = CH3CH2CH2).
Yield of the diastereoisomeric mixture: 0.18 g (98%), dr (l : u):
1 : 8.5; u-8a: mp (decomp) 169–171 °C. IR (Nujol)/cm−1: 3463,
1504, 1255, 1107, 780, 747, 701. 1H NMR (400 MHz, CD2Cl2):
3
3
s, 1H, NH), 6.82 (d, 2H, JHH 8.3, HAr), 7.14 (d, 2H, JHH 8.3,
HAr), 7.41–7.44 (m, 4H, 2Ho + 2Hm), 7.56–7.61 (m, 1H, Ho),
7.73–7.78 (m, 2H, Hm), 7.81–7.85 (m, 1H, Ho), 8.28–8.31 (m,
2H, Hp). 13C{1H} NMR (100 MHz, CD2Cl2): δ 11.46
(CH3CH2CH2), 20.74 (CH3), 22.41 (CH3CH2CH2), 31.48 (d,
3
δ 1.07 (t, 3H, JHH 7.3, CH3CH2CH2), 1.94–2.12 (m, 2H,
CH3CH2CH2), 2.17 (s, 3H, CH3), 2.82–2.93 (m, 1H, CHeqN),
3.08–3.27 (m, 2H, CHaxN + CH3CH2CHAHB), 3.48–3.58 (m,
2
1H, CH3CH2CHAHB), 4.96 (br s, 1H, NH), 5.47 (dd, 1H, JHP
2
1JCP 83.6, PCH2), 43.36 (d, JCP 7.8, CH2N), 56.88
3
3
13.9, JHH 11.0, PCH), 6.53 (d, 2H, JHH 7.6, Ho-Ph), 6.82 (d,
1
1
(CH3CH2CH2), 124.29 (d, JCP 87.2, Ci), 126.53 (d, JCP 89.2,
Ci), 126.57 (d, 3JCP 11.5, C2), 128.92 (C3), 129.67 (d, 3JCP 11.9,
Cm), 129.89 (d, 3JCP 12.7, Cm), 131.52 (C4), 132.95 (d, 2JCP 9.3,
3
3
2H, JHH 7.6, Hm-Ar), 7.11 (t, 2H, JHH 7.5, Hm-Ph), 7.26–7.37
(m, 7H, (2Ho + 2Hm)-PPh2 + 2Ho-Ar + Hp-Ph), 7.59–7.66 (m,
3H, (Ho + 2Hm)-PPh2), 7.73–7.76 (m, 1H, Ho-PPh2), 8.19–8.24
(m, 2H, Hp-PPh2). 13C{1H} NMR (100 MHz, CD2Cl2): δ 11.54
(CH3CH2CH2), 20.78 (CH3), 22.43 (CH3CH2CH2), 49.11 (d,
4
2
Co), 133.78 (d, JCP 2.8, Cp), 133.90 (d, JCP 10.6, Co), 134.19
(d, JCP 3.1, Cp), 145.33 (d, JCP 1.4, C1). 31P{1H} NMR
4
2
(162 MHz, CD2Cl2):
δ 23.97. HRMS (ESI): calcd for
1
2JCP 5.0, CH2N), 50.14 (d, JCP 76.9, PCH), 58.18
C24H29ClN2PPd [M − Cl]+, 517.0792; Found, 517.0783.
1
1
(CH3CH2CH2), 120.19 (d, JCP 86.3, Ci), 124.93 (d, JCP 84.6,
7b (R1 = 4-CH3OC6H4, R2 = R3 = H, R4 = CH3CH2CH2). See
3
4
Ci), 126.23 (d, JCP 12.0, C2), 128.79 (d, JCP 2.4, C3′), 128.92
(C3), 129.03 (d, JCP 3.2, C4′) 129.24 (d, JCP 11.5, Cm), 129.48
(d, JCP = 12.1, Cm), 130.75 (d, JCP 5.1, C2′), 131.16 (C4/C1′),
131.85 (C4/C1′), 133.97 (d, JCP 2.8, Cp), 134.07 (d, JCP 2.7,
5
3
ref. 8b.
3
3
7c (R1 = 4-CH3OC6H4, R2 = R3 = H, R4 = CH3CH2CH2CH2).
4
4
Yield: 0.17 g (97%); mp (decomp) 148–150 °C. IR (Nujol)/
1
2
2
cm−1: 3412, 1499, 1440, 1234, 1107, 845, 723, 691. H NMR
Cp), 134.80 (d, JCP 9.5, Co), 135.11 (d, JCP 8.0, Co), 146.37
(C1). 31P{1H} NMR (162 MHz, CD2Cl2): δ 28.18. HRMS
(ESI): calcd for C30H33ClN2PPd [M − Cl]+, 593.1105; Found,
593.1114.
(200 MHz, CD2Cl2): δ 1.06 (t, 3H, 3JHH 7.3, CH3CH2CH2CH2),
3
1.51 (sextet, 2H, JHH 7.3, CH3CH2CH2CH2), 1.98–2.23 (m,
2H, CH3CH2CH2CH2), 2.69–2.99 (m, 3H, PCHeq + CHeqN +
CH3CH2CH2CHAHB), 3.09–3.47 (m, 3H, PCHax + CHaxN +
CH3CH2CH2CHAHB), 3.68 (s, 3H, OCH3), 4.48 (br s, 1H, NH),
8b (R1 = 4-BrC6H4, R2 = C6H5, R3 = H, R4 = CH3CH2CH2).
Yield of the diastereoisomeric mixture: 0.2 g (95%), dr (l : u):
1 : 6.6; u-8b: mp (decomp) 161–163 °C. IR (Nujol)/cm−1: 3450,
1482, 1439, 1253, 1106, 997, 751, 723, 700. 1H NMR
3
3
6.56 (d, 2H, JHH 8.5, HAr), 7.13 (d, 2H, JHH 8.5, HAr),
7.35–7.44 (m, 4H, 2Ho + 2Hm), 7.53–7.63 (m, 1H, Ho),
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3
1
1
3
(400 MHz, CD2Cl2): δ 1.07 (t, 3H, JHH 7.4, CH3CH2CH2),
(d, JCP 85.8, Ci), 123.90 (d, JCP 85.1, Ci), 127.86 (d, JCP
4
5
1.94–1.98 (m, 1H, CH3CHAHBCH2), 2.04–2.07 (m, 1H,
CH3CHAHBCH2), 2.84–2.93 (m, 1H, CHeqN), 3.06–3.24 (m,
12.4, C2), 128.88 (d, JCP 2.6, C3′), 129.23 (d, JCP 3.2, C4′),
3
3
129.46 (d, JCP 11.7, Cm), 129.60 (d, JCP 12.3, Cm), 130.62 (d,
4
2H, CHaxN
+
CH3CHAHBCH2), 3.48–3.55 (m, 1H,
3JCP 5.4, C2′), 131.07 (C3), 131.35 (C1′), 134.27 (d, JCP 3.1,
2
4
2
CH3CHAHBCH2), 4.93 (br s, 1H, NH), 5.48 (dd, 1H, JHP 14.6,
Cp), 134.37 (d, JCP 2.7, Cp), 134.68 (d, JCP 9.4, Co), 134.96
3JHH 12.2, PCH), 6.53 (d, 2H, JHH 7.6, Ho-Ph), 7.01 (d, 2H,
(d, JCP 8.1, Co), 148.41 (C1). 31P{1H} NMR (121 MHz,
3
2
3JHH 8.2), 7.14 (t, 2H, JHH 7.7, Hm-Ph), 7.25–7.30 (m, 5H,
CD2Cl2): δ 29.72. HRMS (ESI): calcd for C30H32BrClN2PPd
3
2Ho-Ph2 + 2Ho-Ar + Hp-Ph), 7.36–7.40 (m, 2H, 2Hm-PPh2),
7.62–7.67 (m, 3H, (1Ho + 2Hm)-PPh2), 7.75–7.78 (m, 1H, 1Ho-
PPh2), 8.17–8.21 (m, 2H, 2Hp-PPh2). 13C{1H} NMR (100 MHz,
CD2Cl2): δ 11.41 (CH3CH2CH2), 22.35 (CH3CH2CH2), 49.09
[M − Cl]+, 671.0210; Found, 671.0202.
9a (R1 = 4-CH3C6H4, R2 = H, R3 = CH3, R4 = CH3CH2CH2).
Yield of the diastereoisomeric mixture: 0.16 g (94%), dr (l : u):
1 : 6; u-9a: mp (decomp) 140–142 °C. IR (Nujol)/cm−1: 3261,
1504, 1438, 1259, 1113, 819, 746, 727, 708, 693. 1H NMR
2
1
(d, JCP 4.9, CH2N), 50.14 (d, JCP 78.0, PCH), 58.11
1
3
(CH3CH2CH2), 114.09 (C4), 119.43 (d, JCP 86.2, Ci), 124.00
(400 MHz, CD2Cl2): δ 1.16 (t, 3H, JHH 7.4, CH3CH2CH2),
1.52 (d, 3H, JHH = 6.6 Hz, CHCH3), 2.14 (s, 3H, CH3),
2.16–2.21 (m, 1H, CH3CHAHBCH2), 2.55–2.63 (m, 1H,
CH3CH2CHAHB),
CH3CHAHBCH2), 2.96–3.06 (m, 1H, CHCH3), 3.25–3.34 (m,
1H, CH3CH2CHAHB), 3.42–3.50 (m, 1H, PCHeq), 4.08 (br s,
1H, NH), 6.78 (d, 2H, JHH 8.1, Hm-Ar), 7.05 (d, 2H, JHH 8.1,
Ho-Ar), 7.41–7.45 (m, 4H, (2Ho + 2Hm)-PPh2), 7.55–7.59 (m,
1H, Ho-PPh2), 7.71–7.76 (m, 2H, Hm-PPh2), 7.78–7.82 (m, 1H,
Ho-PPh2), 8.29–8.34 (m, 2H, Hp-PPh2). 13C{1H} NMR
(50 MHz, CD2Cl2): δ 11.86 (CH3CH2CH2), 20.80 (CH3), 22.58
(d, 3JCP 9.0, CHCH3), 23.31 (CH3CH2CH2), 38.42 (d, 1JCP 82.9,
(d, 1JCP 84.6, Ci), 127.90 (d, 3JCP 12.4, C2), 128.82 (d, 4JCP 2.2,
3
C3′), 129.15 (d, JCP 3.1, C4′), 129.42 (d, 3JCP 11.6, Cm), 129.58
5
(d, 3JCP 12.2, Cm), 130.67 (d, 3JCP 5.5, C2′), 131.03 (C3), 131.44
2.71–2.80
(m,
2H,
PCHax
+
4
4
(C1′), 134.20 (d, JCP 2.4, Cp), 134.32 (d, JCP 2.8, Cp), 134.68
(d, JCP 9.5, Co), 134.95 (d, JCP 8.0, Co), 148.52 (C1). 31P{1H}
NMR (162 MHz, CD2Cl2): δ 29.33. HRMS (ESI): calcd for
C29H30ClN2PPd [M − Cl]+, 657.0053; Found, 657.0055.
2
2
3
3
8c (R1 = 4-BrC6H4, R2 = C6H5, R3 = H, R4 = (CH3)2CH. Yield
of the diastereoisomeric mixture: 0.2 g (96%), dr (l : u): 1 : 7.2;
u-8c: mp (decomp) 165–167 °C. IR (Nujol)/cm−1: 3450 (s),
1
1483, 1440, 1253, 1111, 991, 819, 811, 750, 725, 700, 691. H
NMR (300 MHz, CD2Cl2): δ 1.61 (d, 3H, JHH 6.5, (CH3)2CH),
1.71 (d, 3H, JHH 6.5, (CH3)2CH), 2.65–2.79 (m, 1H, CHeqN),
3.11–3.29 (m, 1H, CHaxN), 3.85 (sept, 1H, JHH 6.5,
(CH3)2CH), 4.84 (br s, 1H, NH), 5.57 (dd, 1H, JHP 15.2, JHH
10.9, PCH), 6.53 (d, 2H, JHH 8.3, Ho-Ph), 7.09 (d, 2H, JHH
8.5, Hm-Ar), 7.14 (t, 2H, JHH 8.3, Hm-Ph), 7.24–7.31 (m, 5H,
3
2
PCH2), 53.69 (d, JCP 7.3, CHCH3), 56.57 (CH3CH2CH2),
3
1
3
123.91 (d, JCP 87.9, Ci), 126.37 (d, JCP 11.7, C2), 127.19 (d,
1JCP 87.6, Ci), 128.99 (C3), 129.80 (d, JCP 12.5, Cm), 130.05
3
3
2
3
3
2
(d, JCP 13.2, Cm), 131.46 (C4), 133.14 (d, JCP 9.3, Co), 133.86
3
3
4
2
4
(d, JCP 3.0, Cp), 133.88 (d, JCP 10.5, Co), 134.21 (d, JCP 2.9,
Cp), 145.35 (C1). 31P{1H} NMR (81 MHz, CD2Cl2): δ 23.05.
HRMS (ESI): calcd for C25H31ClN2PPd [M − Cl]+, 531.0948;
Found, 531.0950.
3
2Ho-PPh2 + Hp-Ph + Ho-Ar), 7.38–7.46 (m, 2H, 2Hm-PPh2),
7.61–7.69 (m, 3H, (1Ho + 2Hm)-PPh2), 7.74–7.80 (m, 1H, 1Ho-
PPh2), 8.16–8.23 (m, 2H, Hp-PPh2). 13C{1H} NMR (75 MHz,
CD2Cl2): δ 20.75 ((CH3)2CH), 23.40 ((CH3)2 CH), 44.31 (d,
9b (R1
= = = =
4-CH3C6H4, R2 H, R3 CH3, R4
CH3CH2CH2CH2). Yield of the diastereoisomeric mixture:
0.17 g (96%), dr (l : u): 1 : 5.8; u-9b: mp (decomp) 137–139 °C.
IR (Nujol)/cm−1: 3187, 1504, 1437, 1259, 1111, 846, 819, 723,
2JCP 4.7, CH2N), 50.07 (d, JCP 76.6, PCH), 55.65 ((CH3)2CH),
1
1
1
113.81 (C4), 118.43 (d, JCP 86.5, Ci), 122.76 (d, JCP 84.2, Ci),
127.25 (d, JCP 13.5, C2), 129.02 (C3′), 129.61 (d, JCP 11.9,
Cm), 130.44 (d, JCP 5.2, C2′), 130.65 (C1′), 131.03 (br s, C3 +
693. 1H NMR (300 MHz, CD2Cl2): δ 1.17 (t, 3H, JHH 7.5,
3
3
3
4
3
CH2CH2CH2CH3), 1.54 (d, 3H, JHH 6.5, CHCH3), 1.56–1.68
(m, 2H, CH3CH2CH2CH2), 2.15 (s, 3H, CH3), 2.17–2.24 (m,
1H, CH3CH2CHAHBCH2), 2.61–2.83 (m, 3H, PCHax +
CH3CH2CHAHBCHAHB), 3.00–3.10 (m, 1H, CHCH3),
3.28–3.39 (m, 1H, CH3CH2CHAHBCHAHB), 3.44–3.55 (m, 1H,
PCHeq), 4.08 (br s, 1H, NH), 6.80 (d, 2H, JHH 8.1, Hm-Ar),
7.08 (d, 2H, JHH 8.1, Ho-Ar), 7.42–7.46 (m, 4H, (2Ho + 2Hm)-
PPh2), 7.56–7.62 (m, 1H, Ho-PPh2), 7.72–7.85 (m, 3H, (Ho +
2Hm)-PPh2), 8.30–8.37 (m, 2H, Hp-PPh2). 13C{1H} NMR
(50 MHz, CD2Cl2): δ 13.99 (CH3CH2CH2CH2), 20.68 (CH3),
20.80 (CH3CH2CH2CH2), 22.49 (d, JCP 8.9, CHCH3), 31.64
(CH3CH2CH2CH2), 38.24 (d, JCP 82.3, PCH2), 53.66 (d, JCP
7.2, CHCH3), 54.48 (CH3CH2CH2CH2), 123.78 (d, JCP 87.9,
Ci), 126.26 (d, JCP 11.6, C2), 127.06 (d, JCP 88.1, Ci), 128.83
(C3), 129.67 (d, JCP 12.5, Cm), 129.93 (d, JCP 13.1, Cm),
131.69 (C4), 133.00 (d, JCP 9.3, Co), 133.75 (d, JCP 2.7, Cp),
2
C4′), 134.32–134.65 (m, 2Co + 2Cp), 147.47 (d, JCP 2.6, C1).
31P{1H} NMR (121 MHz, CD2Cl2): δ 29.93. HRMS (ESI):
calcd for C29H30BrClN2PPd [M − Cl]+, 657.0053; Found,
657.0054.
3
8d (R1 = 4-BrC6H4, R2 = C6H5, R3 = H, R4 = CH3CH2CH2CH2).
Yield of the diastereoisomeric mixture: 0.21 g (98%), dr (l : u):
1 : 6.9; u-8d: mp (decomp) 159–161 °C. IR (Nujol)/cm−1: 3457,
3
1
1482, 1440, 1259, 1103, 997, 727, 699. H NMR (300 MHz,
CD2Cl2): δ 1.04 (t, 3H, JHH 7.4, CH3CH2CH2CH2), 1.47–153
3
3
(m,
CH3CH2CH2CH2), 2.83–2.94 (m, 1H, CHeqN), 3.11–3.26 (m,
2H, NCHax CH3CH2CH2CHAHB), 3.59–3.65 (m, 1H,
CH3CH2CH2CHAHB), 4.72 (br s, 1H, NH), 5.44 (dd, 1H, JHP
2H,
CH3CH2CH2CH2),
1.86–2.00
(m,
2H,
1
2
1
+
2
3
1
3
3
3
3
13.0, JHH 10.6, PCH), 6.53 (d, 2H, JHH 7.0, Ho-Ph), 7.11 (d,
2H, JHH 7.0, Hm-Ar), 7.14 (t, 2H, 2Hm-Ph), 7.23–7.30 (m, 5H,
2Ho-PPh2 + 2Ho-Ar + Hp-Ph), 7.36–7.41 (m, 2H, Hm-PPh2),
7.55–7.68 (m, 3H, (2Hm + 1Ho)-PPh2), 7.38–7.82 (m, 1H, Ho-
PPh2), 8.16–8.21 (m, 2H, Hp-PPh2). 13C{1H} NMR (75 MHz,
CD2Cl2): δ 13.88 (CH3CH2CH2CH2), 20.34 (CH3CH2CH2CH2),
3
2
4
2
4
133.76 (d, JCP 10.5, Co), 134.07 (d, JCP = 2.9, Cp), 145.25
(C1). 31P{1H} NMR (121 MHz, CD2Cl2): δ 23.00. HRMS
(ESI): calcd for C26H33ClN2PPd [M − Cl]+, 545.1105; Found,
545.1129.
2
31.04 (CH3CH2CH2CH2), 49.15 (d, JCP 5.0, CH2N), 50.37 (d,
9c (R1 = 4-CH3OC6H4, R2 = H, R3 = CH3, R4 = CH3CH2CH2).
Yield of the diastereoisomeric mixture: 0.17 g (95%), dr (l : u):
1JCP 77.6, PCH), 56.32 (CH3CH2CH2CH2), 114.14 (C4), 119.33
12266 | Dalton Trans., 2012, 41, 12259–12269
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u,l-12 + l,u-12 (R1 = 4-CH3C6H4). Yield of: 0.18 g (98%), dr
(u,l : l,u): 3.5 : 1; IR (Nujol)/cm−1: 3062, 1503, 1435, 1262,
1 : 6.9; u-9c: mp (decomp) 138–140 °C. IR (Nujol)/cm−1: 3215,
1503, 1438, 1237, 1111, 998, 746, 716, 693. 1H NMR
1
3
1114, 921, 726, 701. H NMR (400 MHz, CD2Cl2): δ 1.23 [dd,
(400 MHz, CD2Cl2): δ 1.07 (t, 3H, JHH 7.0, CH3CH2CH2),
3
4
3
3
3H, JHH 6.5, JHP 2.0, CH3CHCH2P (u,l)], 1.46 [dd, 3H, JHH
1.45 (d, 3H, JHH 6.6, CHCH3), 2.07–2.15 (m, 1H,
4
3
6.0, JHP 2.9, CH3CHCH2P (l,u)], 1.72 [d, 3H, JHH 6.7,
CH3CHAHBCH2), 2.48–2.56 (m, 1H, CH3CHAHBCH2),
2.62–2.74 (m, 2H, PCHax + CH3CH2CHAHB), 2.93–3.00 (m,
1H, CHCH3), 3.21–3.30 (m, 2H, PCHeq + CH3CH2CHAHB),
3
CH3(Ph)CH (u,l)], 2.04 [d, 3H, JHH 6.4, CH3(Ph)CH (l,u)],
2.14 [s, 3H, CH3-Ar (u,l)], 2.21 [s, 3H, CH3-Ar (l,u)], 2.34 [m,
2
2
3
3
1H, CHCH2P (l,u)], 2.64 [ddd, 1H, JHH 16.0, JHP 7.7, JHH
2.3, CHAHBP (u,l)], 2.65 [m, 1H, CHAHBP (l,u)], 3.06 [m, 1H,
3.56 (s, 3H, OCH3), 4.00 (br s, 1H, NH), 6.44 (d, 2H, JHH 8.8,
3
Hm-Ar), 6.95 (d, 2H, JHH 8.8, Ho-Ar), 7.31–7.34 (m, 4H, (2Ho
3
CHCH2P (u,l)], 3.97 [d, JHH 9.2, NH (l,u)], 4.15 [ddd, 1H,
+ 2Hm)-PPh2), 7.44–7.50 (m, 1H, Ho-PPh2), 7.65–7.69 (m, 2H,
Hm-PPh2), 7.71–7.74 (m, 1H, Ho-PPh2), 8.24–8.29 (m, 2H, Hp-
2
3
2JHH 16.0, JHP 11.7, JHH 10.2 Hz, CHAHBP (u,l)], 4.21 [m,
1H, CH3(Ph)CH (l,u)], 4.32–4.50 [m, 2H, CH3(Ph)CH + NH
(u,l)], 4.77 [dt, 1H, 2JHH 15.5, 2JHP = 3JHH 10.4, CHAHBP (l,u)],
PPh2). 13C{1H} NMR (100 MHz, CD2Cl2):
δ
11.88
(CH3CH2CH2), 22.61 (d, 3JCP 8.5, CHCH3), 23.29
3
1
2
6.71 [d, 2H, JHH 8.4, HAr (u,l)], 6.77 [br s, 2H, HAr (l,u)], 6.90
(CH3CH2CH2), 37.76 (d, JCP 82.2, PCH2), 53.92 (d, JCP 7.5,
CHCH3), 55.62 (OCH3), 56.44 (CH3CH2CH2), 113.67 (C3),
3
3
[d, 2H, JHH 8.1, HAr (l,u)], 6.96 [d, 2H, JHH 8.4, HAr (u,l)],
3
3
1
1
7.16 [t, 2H, JHH 7.2, Ph (l,u)], 7.22 [t, 1H, JHH 7.2, Ph (l,u)],
7.35 [d, 2H, JHH 7.2, Ph (l,u)], 7.44–7.80 [m, 21H, 5H-Ph (u,l)
123.92 (d, JCP 88.4, Ci), 127.71 (d, JCP 88.0, Ci), 127.78 (d,
3
3JCP 11.0, C2), 129.74 (d, JCP 11.6, Cm), 130.11 (d, JCP 12.6,
Cm), 133.19 (d, JCP 9.2, Co), 133.88 (d, JCP 2.7, Cp), 133.90
(d, JCP 10.7, Co), 134.19 (d, JCP 3.0, Cp), 140.74 (C1), 155.23
(C4). 31P{1H} NMR (162 MHz, CD2Cl2): δ 22.18. HRMS
(ESI): calcd for C25H31ClN2PPd [M − Cl]+, 547.0897; Found,
547.0912.
3
3
2
4
+ 16H-PPh2 (u,l + l,u)], 8.07–8.12 [m, 2H, PPh2 (l,u)],
8.21–8.26 [m, 2H, PPh2 (u,l)]. 13C{1H} NMR (100 MHz,
2
4
3
CD2Cl2): δ 18.75 [d, JCP 14.0, CH3CHCH2P (l,u)], 19.81
[CH3(Ph)CH (u,l)], 20.57 [CH3 (u,l)], 20.69 [CH3 (l,u)], 23.52
3
[d, JCP 12.9, CH3CHCH2P (u,l)], 25.93 [CH3(Ph)CH (l,u)],
1
1
9d (R1 = 4-CH3OC6H4, R2 = H, R3 = CH3, R4 = CH3CH2
CH2CH2). Yield of the diastereoisomeric mixture: 0.17 g (97%),
dr (l : u): 1 : 6.6; u-9d: mp (decomp) 152–154 °C. IR (Nujol)/
cm−1: 3145, 1501, 1439, 1253, 1237, 1111, 820, 752, 728, 712,
41.31 [d, JCP 79.1, CH2P (l,u)], 42.12 [d, JCP 84.5, CH2P
2
2
(u,l)], 48.65 [d, JCP 7.1, CHCH2P (u,l)], 50.83 [d, JCP 7.7,
CHCH2P (l,u)], 56.74 [CH3(Ph)CH (l,u)], 61.94 [CH3(Ph)CH
(u,l)], 123.13 [d, JCP 87.6, Ci (u,l)], 124.13 [d, JCP 87.6,
1
1
3
3
3
691. 1H NMR (400 MHz, CD2Cl2): δ 1.02 (t, 3H, JHH 7.4,
Ci (l,u)], 124.82 [d, JCP 13.5, C2 (l,u)], 125.49 [d, JCP 13.5,
1
1
3
C2 (u,l)], 126.50 [d, JCP 84.2, Ci (u,l)], 126.69 [d, JCP 85.9,
Ci (l,u)], 128.44 [d, JCP 0.8 Hz, (u,l)], 128.44–129.31 [4 signals
(u,l + l,u)], 129.32 [C3 (u,l)], 129.43, 129.47, 129.91 [d, 3JCP 11.8,
Cm (u,l)], 129.95 [d, JCP 12.4, Cm (u,l)], 130.28 [d, JCP 11.6,
Cm (l,u)], 130.31 [d, JCP 12.7, Cm (l,u)], 130.45 [q, (u,l)],
CH3CH2CH2CH2), 1.46 (d, 3H, JHH 6.6, CHCH3), 1.47–1.55
(m,
2H,
CH3CH2CH2CH2),
2.02–2.12
(m,
1H,
CH3CH2CHAHBCH2), 2.51–2.65 (m, 2H, CH3CH2CHAHB-
CHAHB), 2.70–2.75 (m, 1H, PCHax), 2.91–3.02 (m, 1H,
CHCH3), 3.22–3.31 (m, 2H, PCHeq + CH3CH2CHAHBCHAHB),
3
3
3
2
2
3
131.70 [q, (l,u)], 132.49 [d, JCP 11.0, Co (l,u)], 132.77 [d, JCP
3.56 (s, 3H, OCH3), 4.00 (br s, 1H, NH), 6.43 (d, 2H, JHH 8.5,
9.2, Co (l,u)], 133.11 [d, 2JCP 9.2, Co (u,l)], 133.27 [d, 2JCP 10.4,
3
HAr), 6.95 (d, 2H, JHH 8.5, HAr), 7.30–7.34 (m, 4H, (2Ho +
4
4
Co (u,l)], 133.93 [d, JCP 2.7, Cp (u,l)], 134.03 [d, JCP 3.0,
Cp (u,l)], 134.37 [d, JCP 2.8, 2 Cp (l,u)], 139.48 [C4 (l,u)],
2Hm)-PPh2), 7.45–7.49 (m, 1H, Ho-PPh2), 7.64–7.69 (m, 2H,
Hm-PPh2), 7.70–7.74 (m, 1H, Ho-PPh2), 8.24–8.29 (m, 2H, Hp-
4
140.73 [C4 (u,l)], 144.95 [br s, C1 (u,l + l,u)]. 31P{1H} NMR
(161 MHz, CD2Cl2): δ 23.46 (u,l), 26.44 (l,u). FAB+-MS m/z
(rel. intensity): 630 (M+ + 2, 6), 629 (M+ + 1, 3), 628 (M+, 6),
593 (M+ − Cl, 11), 561 (27), 560 (27), 559 (54), 558 (36), 557
(74), 556 (57), 453 (49), 451 (100), 306 (77).
PPh2). 13C{1H} NMR (75 MHz, CD2Cl2):
(CH3CH2CH2CH2), 20.93 (CH3CH2CH2CH2), 22.64 (d, JCP
δ
14.12
3
1
8.1, CHCH3), 31.73 (CH3CH2CH2CH2), 37.64 (d, JCP 82.1,
2
PCH2), 54.00 (d, JCP 7.2, CHCH3), 54.45 (CH3CH2CH2CH2),
55.61 (OCH3), 113.62 (C3), 123.91 (d, 1JCP 88.4, Ci), 127.72 (d,
3
3
1JCP 87.8, Ci), 127.78 (d, JCP 11.0, C2), 129.73 (d, JCP 11.7,
General procedure for the Sonogashira reaction. All reactions
were performed in a Radley carousel adapted for a rigorous inert
atmosphere. A dry solution containing the appropriate aryl
halide (1 mmol), the corresponding alkyne (1.2 mmol), tetra-
butylammonium fluoride (1.81 g, 2 mmol) and the palladium
catalyst 7a (0.01 g, 1 mol%) in DMF (5 mL) was stirred under
nitrogen at 110 °C until the aryl halide had been consumed (the
reaction was followed by GC). The reaction mixture was diluted
with H2O (10 mL) and extracted with EtOAc (3 × 10 mL). The
organic extracts were dried (MgSO4) and evaporated to afford
the crude product18 which was purified by column
chromatography.
3
2
Cm), 130.10 (d, JCP 12.6, Cm), 131.16 (d, JCP 9.2, Co), 133.89
2
4
4
(d, JCP 10.6, Co), 133.82 (d, JCP 2.5, Cp), 134.17 (d, JCP 2.7,
Cp), 140.76 (C1), 155.18 (C4). 31P{1H} NMR (162 MHz,
CD2Cl2): δ 22.21. HRMS (ESI): calcd for C26H33ClN2PPd
[M − Cl]+, 561.1054; Found, 561.1067.
General procedure for the synthesis of complex 12. 1 equiv of
Pd(COD)Cl2 (0.09 g, 0.3 mmol) was added to a dry dichloro-
methane solution (15 mL) of the corresponding iminophosphor-
ane-amine 11 (0.14 g, 0.3 mmol) under a nitrogen atmosphere.
The solution was stirred at 25 °C for 0.5 h. The solvent was
removed under vacuum and the residue was treated with dry
diethyl ether to give 12 as an orange solid, which was then iso-
lated by filtration and dried under reduced pressure. In the cases
in which a mixture of u,l-12 and l,u-12 was obtained, the major
component (u,l-12) was purified by successive recrystallizations
from dichloromethane–n-hexane.
X-ray structure determinations
X-ray structure determinations of compounds 7a, u-8b and u-9a
were carried out with a Bruker Smart APEX diffractometer.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 12259–12269 | 12267

View Article Online
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4 Selected more recent references: (a) S. Al-Benna, M. J. Sarsfield,
M. Thornton-Pett, D. L. Ormsby, P. J. Maddox, P. Bres and
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Trans., 2008, 1787; (i) A. Buchard, H. Heuclin, A. Auffrant, X. Le Goff
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Compound u,l-12 was measured on a Siemens P4 instrument.
Data were collected with use of monochromated Mo–Kα radi-
ation in a ω-scan mode. The structures were solved by direct
methods and all non-hydrogen atoms refined anisotropically on
F2 using the program SHELXL-97.19 Hydrogen atoms were
refined using a riding model except for the ordered methyl
groups, which were refined using rigid groups, and the NH
hydrogens, which were refined freely.
Special features: compound 7a contains a disordered dichloro-
methane molecule refined isotropically; u-9a contains a molecule
of acetonitrile and u,l-12 contains two molecules of chloroform.
The crystal structures for 7a, u-8b, u-9b and u,l-12 have been
deposited in the Cambridge Crystallographic Data Centre
(CCDC) and allocated the deposition numbers CCDC
881653–881656.
Acknowledgements
This work was supported by MCINN and FEDER (Project
CTQ2008-05827/BQU) and Fundación Séneca-CARM (Project
08661/PI/08). P. L.-L. thanks the Fundación Séneca-CARM for a
fellowship.
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28, 413; (c) K. V. Katti and R. G. Cavell, Inorg. Chem., 1989, 28, 3033;
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