PdII complexes of tridentate PCP N-heterocyclic carbene ligands: Structural aspects and application in asymmetric hydroamination of cyano olefins

Article abstract of DOI:10.1002/ejic.200500612

The synthesis of the ligand precursor 1,3-bis{(R)-1-[(S)-2- (diphenylphosphanyl)ferrocenyl]ethyl}imidazolium iodide ([PCPH]I, 1) was extended to the electronically and sterically modified ligand precursors 1,3-bis{(R)-1-[(S)-2-{[3,5-bis(trifluoromethyl)phenyl]phosphanyl}ferrocenyl] ethyl}imidazolium iodide ([3,5-CF₃-PCPH]I, 6), and 1,3-bis[(R)-1-{(S)-2-[bis(3,5-dimethylphenyl)phosphanyl]ferrocenyl}ethyl] imidazolium iodide ([3,5-Me-PCPH]I, 7). Palladium complexes were prepared starting from [Pd(OAc)₂]₃ in THF to afford [PdI(PCP)]OAc (8), [Pd(OAc)(3,5-CF₃-PCP)]I (9), and [PdI(3,5-Me-PCP)]OAc (10), in excellent yields. The crystal structures of the ligand precursor [3,5-CF ₃-PCPH]I (6), the complex [PdI(3,5-CF₃-PCP)]PF₆ (14), as well as the dicationic complex [Pd(NCCH₃)(PCP)](PF ₆)₂ (11), were determined by X-ray diffraction. Complex 11 and its derivative [Pd(NCCH₃)-(3,5-Me-PCP)](PF₆) ₂ (13) have been tested as catalysts in the asymmetric addition of, for example, thiomorpholine to methacrylonitrile giving selectivities up to 63 and 75 % ee, respectively, at -80°C. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejic.200500612

FULL PAPER
DOI: 10.1002/ejic.200500612
PdII Complexes of Tridentate PCP N-Heterocyclic Carbene Ligands:
Structural Aspects and Application in Asymmetric Hydroamination of Cyano
Olefins
Sebastian Gischig[a] and Antonio Togni*[a]
Keywords: N-heterocyclic carbene ligands / Ferrocenes / Palladium complexes / Asymmetric catalysis / Hydroamination /
Aminonitriles
The synthesis of the ligand precursor 1,3-bis{(R)-1-[(S)-2-
(diphenylphosphanyl)ferrocenyl]ethyl}imidazolium iodide
structures of the ligand precursor [3,5-CF3-PCPH]I (6), the
complex [PdI(3,5-CF3-PCP)]PF6 (14), as well as the dicationic
complex [Pd(NCCH3)(PCP)](PF6)2 (11), were determined by
X-ray diffraction. Complex 11 and its derivative [Pd(NCCH3)-
(3,5-Me-PCP)](PF6)2 (13) have been tested as catalysts in the
asymmetric addition of, for example, thiomorpholine to
methacrylonitrile giving selectivities up to 63 and 75% ee,
respectively, at –80 °C.
([PCPH]I, 1) was extended to the electronically and sterically
modified ligand precursors 1,3-bis{(R)-1-[(S)-2-{[3,5-bis(tri-
fluoromethyl)phenyl]phosphanyl}ferrocenyl]ethyl}imid-
azolium iodide ([3,5-CF3-PCPH]I, 6), and 1,3-bis[(R)-1-{(S)-2-
[bis(3,5-dimethylphenyl)phosphanyl]ferrocenyl}ethyl]imid-
azolium iodide ([3,5-Me-PCPH]I, 7). Palladium complexes
were prepared starting from [Pd(OAc)2]3 in THF to afford
[PdI(PCP)]OAc (8), [Pd(OAc)(3,5-CF3-PCP)]I (9), and
[PdI(3,5-Me-PCP)]OAc (10), in excellent yields. The crystal
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
with the application of these NHC complexes in the cata-
lytic hydroamination reaction of cyano olefins.
Introduction
N-Heterocyclic carbenes (NHCs), their corresponding
metal complexes, and their applications in catalysis have be-
come a well-established area of research in organometallic
chemistry.[1–5] An important step in the development of car-
bene ligands is their chiral modification and many chiral
NHCs acting as monodentate[6–10] as well as bidentate li-
gands[11–15] in asymmetric reactions have been reported.[5]
Our interest in tridentate ligands based on the ferrocene
scaffold derives from the successful application of the tri-
phosphane Pigiphos (see Scheme 1)[16] in, for instance, Ni-
catalyzed hydroamination and hydrophosphanation of cy-
ano olefins.[17,18] The replacement of the central PCy unit
of Pigiphos by an NHC fragment generates a C2-symmetric
ligand. We speculated that this should lead, in the case of
square-planar complexes, to a chiral environment that is
better defined than in Pigiphos. We previously reported the
synthesis of the PCP ligand precursor 1 as well as its com-
plexation with ruthenium and palladium.[19] In this work
we address the modification of the ligand, the complexation
with palladium, and the formation of dicationic complexes.
The X-ray crystal structures of the activated palladium
complex 11, the CF3-modified ligand precursor 6 and the
palladium complex of this ligand (14) are presented, along
Scheme 1. The C1-symmetric triphosphane Pigiphos and a struc-
turally related C2-symmetric PCP ligand.
Results and Discussion
Ligand Synthesis
The introduction of substituents at the 3- and 5-positions
of the phenyl groups in diphenylphosphanyl derivatives is a
common approach in view of modifying both the steric and
electronic properties of such ligands. Modifications of this
kind, as applied to carbene precursor 1 ([PCPH]I), should
lead to altered catalytic properties of the corresponding Pd
complexes. The synthesis of the ligand precursors−via the
amines 2 and 3, as well as the acetates 4 and 5, i.e. the
(diarylphosphanyl)ferrocene derivatives bearing either a di-
methylamino group or an acetate at the stereogenic
center−containing methyl and trifluoromethyl substituents,
[a] Department of Chemistry and Applied Biosciences, Swiss Fed-
eral Institute of Technology,
ETH Hönggerberg, 8093 Zürich, Switzerland
E-mail: togni@inorg.chem.ethz.ch
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S. Gischig, A. Togni
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respectively, has been accomplished analogously to the one azolium salts of 218.7, 222.6, and 218.8 Hz for 1, 6, and 7,
of the unsubstituted derivative 1. The preparation of [3,5- respectively, could be estimated with the help of 2D one-
CF3-PCPH]I (6) and [3,5-Me-PCPH]I (7) from the corre- bond HMQC experiments. Interestingly, the coupling con-
sponding acetate derivatives 4 and 5, respectively, and imid- stant for the more electron-deficient compound 6, contain-
azole was carried out in a mixture of acetonitrile and water ing the CF3 substituents, is larger than for 1 and 7.
in a ratio of 4:1 for 6 and 2:1 for 7. However, for reactions
Table 1. 13C NMR chemical shifts of the free carbenes derived from
1, 6, and 7.
at room temperature as described for 1, no substitution of
the acetate by imidazole was observed. Heating of the reac-
Free carbene of
δ [ppm]
Line width [Hz]
JCP [Hz]
tion mixture at 60 °C followed by ion exchange with NaI in
ethanol yielded 6 in 50% yield after 24 h and 7 in 51% yield
after 32 h, respectively (Scheme 2). The yields are lower
than the one obtained for 1 and could not be improved by
longer reaction times or by using different reaction condi-
tions (temperature, acetonitrile/water mixture).
1
6
7
209.0
209.8
209.5
36
–
25
–
13.3 (t)
–
Synthesis of Palladium Complexes
As already shown for the ligand precursor 1, the method
of choice for the complexation of these carbene ligands to
PdII is to start from [Pd(OAc)2]3 {see the synthesis of
[PdI(PCP)]OAc (8), giving 98% yield}.[19] Analogously, the
reaction of (3,5-CF3-PCPH)I (6) and (3,5-Me-PCPH)I (7)
with [Pd(OAc)2]3 generates the complexes [Pd(OAc)(3,5-
CF3-PCP)]I (9) and [PdI(3,5-Me-PCP)]OAc (10) in 91%
and 95% yield, respectively (Scheme 3).
In order to isolate the complexes containing iodide as a
ligand and acetate as the counterion, an ionic ligand ex-
change reaction is necessary. This ion exchange was studied
by NMR on samples of the 13C-labeled complexes
(Table 2). It is reasonable to expect that iodide and acetate
Scheme 2. Synthesis of the ligand precursors 1, 6, and 7.
Treatment of 1, 6, and 7 with NaOtBu in THF resulted will exert a different influence on the chemical shift of the
in the deprotonation of the imidazolium salts. However, the carbene carbon atom in the trans position. Addition of NaI
attempted isolation of the free carbenes was not successful. to a dichloromethane solution of the palladium complexes
For 13C NMR spectroscopic reasons, these imidazolium 8, 9, and 10 shifts the ion exchange equilibrium towards the
salts were also prepared in the form containing a 13C label iodo complex (Table 2, Entries 1, 3, and 5). Abstraction of
at position 2 of the imidazole.[20] The deprotonation of the the counterion and the fourth ligand with Et3OPF6 (vide
labeled 1, 6, and 7 using an excess of NaOtBu in THF al- infra), followed by the addition of Bu4NOAc leads to the
lowed us to observe broad 13C NMR signals of the free formation of the complexes having acetate as a ligand
carbenes at room temperature (Table 1). While the NMR (Table 2, Entries 2, 4, and 6). These experiments show a
spectroscopic data of the free carbenes confirm the clean slight downfield shift of the 13C carbene signal in going
generation of these reactive species, the significant line from coordinated acetate to coordinated iodide, this effect
widths account for the difficulties in observing the same being more pronounced for [Pd(OAc)(3,5-CF3-PCP)]I (9).
signals for the nonlabeled compounds. Furthermore, solu- We also observed a larger coupling constant JCP between
tions of these species in C6D6 showed the formation of the the carbene carbon atom and the P atoms for the iodo com-
imidazolium ion within minutes, indicating that the acidic plexes. Comparing the chemical shifts and the coupling
sites of the NMR tube glass are sufficient to protonate the constants observed for compounds 8, 9, and 10 we con-
carbenes. The C(2)–H coupling constants (JCH) of the imid- cluded that there is an ion exchange for [PdI(PCP)]OAc (8)
Scheme 3. Synthesis of the palladium complexes 8, 9, and 10.
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PdII Complexes of Tridentate PCP N-Heterocyclic Carbene Ligands
Table 2. 13C NMR spectroscopic data for labeled carbene derivatives.
FULL PAPER
JCP
[Hz]
JCP
[Hz]
Entry Complex
Ligand
δ [ppm] (by ion exchange)
δ [ppm] (by synthesis)
1
2
3
4
5
6
[PdI(PCP)]OAc (8)
I–
–OAc
I–
152.3 (t)
149.8 (t)
151.5 (br)
145.7 (t)
152.5 (t)
149.9 (t)
12.0
14.6
–
13.5
12.4
13.6
151.4 (t)
13.2
[Pd(OAc)(PCP)]PF6
[PdI(3,5-CF3-PCP)]OAc
[Pd(OAc)(3,5-CF3-PCP)]I (9)
[PdI(3,5-Me-PCP)]OAc (10)
[Pd(OAc)(3,5-Me-PCP)]PF6
–OAc
I–
146.8 (t)
151.8 (t)
13.3
12.4
–OAc
and [PdI(3,5-Me-PCP)]OAc (10), resulting in products with Crystal Structures
iodide as the ligand, instead of acetate. This exchange is
quite slow and takes approximately 1 d to reach complete-
Crystals of imidazolium salt 6 suitable for X-ray analysis
ness in dichloromethane. Therefore, for further synthesis could be obtained from a dichloromethane solution over-
the equilibrium mixture was used. However, the clean prod- layered with hexane. An ORTEP representation of the
uct [PdI(3,5-Me-PCP)]OAc (10) could only be obtained by structure is shown in Figure 1 and selected bond lengths
flash chromatography (silica, dichloromethane + 4% meth- and angles are listed in Table 4. The overall structure is only
anol). For the electron-poorer complex [Pd(OAc)(3,5-CF3- approximately C2-symmetric, i.e., the two ferrocenyl units
PCP)]I (9), ion exchange seems to be absent, resulting in a are not symmetry-related. Three CF3 groups with the atoms
complex with acetate as the fourth ligand. Only the ad- C(6), C(12), and C(15) are disordered over two positions, a
dition of an excess of NaI to 9 allowed us to observe the phenomenon which can be observed very often for crystal
iodo complex characterized by a rather broad 13C NMR structures containing CF3 substituents. Iodide was also
signal (Table 2, Entry 3).
found to be disordered over two positions with an occu-
In order to obtain catalytically active species acting as pational ratio of 93:7. One of the most specific structural
chiral Lewis acids, complexes 8 and 10 were converted into features of this compound is that the molecule backbone,
the dicationic derivatives [Pd(NCCH3)(PCP)](PF6)2 (11) i.e., the chain joining the two phosphorus atoms, displays
and [Pd(NCCH3)(3,5-Me-PCP)](PF6)2 (13) in 79% and helical chirality with (P) configuration. This chain approxi-
94% yield, respectively, using Et3OPF6 in acetonitrile mately describes a full screw turn in going from one P atom
(Scheme 4). The acetonitrile complexes 11 and 13 are char- to the other. The distance between the two P atoms is
acterized by higher 31P chemical shifts and significantly 7.353 Å and can be viewed as the screw pitch, the backbone
lower 13C carbene chemical shifts with respect to their cor- being the screw thread. The three donor atoms are already
responding precursors, as summarized in Table 3. Some- positioned in such a way that the coordination to a metal
what surprisingly, the activation of 9 with Et3OPF6 was not center only requires a relatively minor conformational
selective and led to product mixtures from which the dicat- change that can be best viewed as a compression of the
ionic species could not be identified. It is important to note screw pitch of the ligand backbone (vide infra). Two of the
that all complexes described in this section give NMR spec- aryl groups, one of each of the phosphane units, are placed
tra consistent with C2-symmetric structures in solution.
on each side of the imidazole plane indicating a possible
Scheme 4. Synthesis of the dicationic complexes 11 and 13.
Table 3. 31P and 13C NMR chemical shifts of 8, 10, and the dicationic complexes 11 and 13.
Complex
31P δ [ppm] (JCP [Hz])
13C δ [ppm] (JCP [Hz])
[PdI(PCP)]OAc (8)
–1.46 (d, JCP = 12.0)
1.81 (d, JCP = 11.7)
–2.11 (d, JCP = 12.4)
0.93 (d, JCP = 11.6)
152.7 (t, JCP = 12.0)
144.8 (t, JCP = 11.7)
152.5 (t, JCP = 12.4)
144.5 (t, JCP = 11.6)
[Pd(NCCH3)(PCP)](PF6)2 (11)
[PdI(3,5-Me-PCP)]OAc (10)
[Pd(NCCH3)(3,5-Me-PCP)](PF6)2 (13)
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S. Gischig, A. Togni
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weak π-stacking interaction of the aryl groups and the imid-
azole ring (the average distance between the aromatic rings
is 4.02 Å and the interplanar angles are 23.7 and 31.4°).
The orientation of the ferrocenyl moieties can be described
as pseudo-equatorial with respect to the imidazole plane.
Figure 2. ORTEP representation of the cation in [PdI(3,5-CF3-
PCP)]PF6 (14). Hydrogen atoms are omitted for clarity. Thermal
ellipsoids are set to 30% probability.
containing C(29), N(1), C(30), C(31), N(2) and Pd(1), I(1),
P(1), P(2), C(29), respectively, which is 70.8°. This deviation
from the perpendicular situation of the two planes is in-
herently due to the helical conformation of the ligand back-
bone. It has also been found in the previously reported
structure of the complex [PdCl(PCP)]PF6 (15), with the cor-
responding torsion angle of –75.6(7)° and the angle be-
tween the coordination plane and the imidazole plane of
72.9°. As opposed to the case of [PdCl(PCP)]PF6 (15), the
solid-state structure of 14 is almost, but not perfectly C2-
symmetric. Therefore, the aryl groups on each side of the
ligand have very similar orientations. One aryl group at
each phosphorus atom is lying roughly in the coordination
Figure 1. ORTEP representation of (3,5-CF3-PCPH)I (6). Hydro-
gen atoms and the CF3 disorder are omitted for clarity. Thermal
ellipsoids are set to 30% probability.
The N(1)–C(29)–N(2) angle is with 109.3(5)° at the upper plane defined by Pd(1), P(1), P(2) and C(29) pushing the
limit of the range found for derivatives of this kind (usually iodo ligand out of this plane by 0.7468 Å. The other two
107.6–109.7°[21–24]). It is also larger than the values mea- aryl groups assume a pseudo-axial orientation.
sured in the complexes [PdCl(PCP)]PF6 [106.2(7)°],
[Pd(NCCH3)(PCP)](PF6)2 [106.2(7)]°, [PdI(3,5-CF3-PCP)]- of 14 displays helical chirality with (P) configuration. From
PF6 [108.4(10)°], and [RuClI(PCP)] [103.7(19), 104(2)°]. a topological point of view, the essential difference between
As was the case for the precursor 6, the ligand backbone
Although it was not possible to isolate the complex the two compounds is the compression of the screw pitch
[PdI(3,5-CF3-PCP)]PF6 (14) on a preparative scale, we ob- on going from 6 to 14. In fact, the distance between the
tained crystals suitable for X-ray analysis from a chloro- two P atoms decreases from 7.353 Å to 4.601 Å, as a conse-
form solution of the mixture obtained from the activation quence of a conformational change. There are only two
of [Pd(OAc)(3,5-CF3-PCP)]I (9) with Et3OPF6. The struc- pairs of equivalent single bonds potentially susceptible to
ture is represented in Figure 2 and selected bond lengths significant conformational changes, i.e., the linkages joining
and angles are listed in Table 4.
the stereogenic centers to the respective Cp and N atom.
The geometry around the Pd atom is almost square- An inspection of the torsion angles provided in Table 4 re-
planar with a slight tetrahedral distortion, as indicated for veals that a counterclockwise rotation around the two N–C
instance by the C(29)–Pd(1)–I(1) angle of 165.7(4)°. The bonds by ca. 35 and 47°, respectively, mainly accounts for
Pd(1)–C(29) bond of 2.040(12) Å is longer than the re- the observed change of conformation. Indeed, rotation
ported PdII–carbene distances with iodide trans to a car- around the crucial pair of single C–C bonds occurs in a
bene
C
atom [1.984(4),[25] 1.990(3),[26] 1.990(9),[27] clockwise manner, but only to an extent of ca. 19 and 3°,
2.004(3),[27] 1.991(5) Å,[28] 1.994(5),[28] 1.962(8) Å[19] are ex- respectively, in going from 6 to 14.
amples of previously reported distances]. The P(1)–Pd(1)–
It was also possible to obtain X-ray quality crystals of
C(29) and P(2)–Pd(1)–C(29) bite angles are 83.0(4) and the moisture-sensitive complex [Pd(NCCH3)(PCP)](PF6)2
86.3(4)°, which is less than the ideal value of 90°. Contrary (11) by slow diffusion of diethyl ether into an acetonitrile
to what is found for many (carbene)PdII complexes, the imi- solution at –20 °C. The structure is represented in Figure 3
dazole plane is not orthogonal to the coordination plane, and selected bond lengths and angles are collected in
as illustrated by the torsion angle P(2)–Pd(1)–C(29)–N(2) Table 4. This complex shows in the solid state an almost
of –68.2(12)° and the angle between the least-squares planes square-planar geometry. The overall structure is approxi-
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PdII Complexes of Tridentate PCP N-Heterocyclic Carbene Ligands
FULL PAPER
Table 4. Selected bond lengths [Å] angles [°], and torsion angles [°] of the ligand precursor (3,5-CF3-PCPH)I (6) and the complexes
[PdI(3,5-CF3-PCP)]PF6 (14) and [Pd(NCCH3)(PCP)](PF6)2 (11).
(3,5-CF3-PCPH)I (6)
C(29)–N(1)
C(29)–N(2)
N(1)–C(30)
N(2)–C(31)
C(30)–C(31)
N(1)–C(27)
N(2)–C(32)
C(29)–N(1)–C(27)–C(21)
C(17)–C(21)–C(27)–N(1)
C(17)–C(21)–C(27)–C(28)
1.336(8)
1.325(7)
1.394(8)
1.391(7)
1.330(9)
1.481(8)
1.486(8)
133.9(6)
–78.7(7)
161.2(6)
C(29)–N(1)–C(27)
C(29)–N(1)–C(30)
C(30)–N(1)–C(27)
C(29)–N(2)–C(32)
C(29)–N(2)–C(31)
C(31)–N(2)–C(32)
125.1(5)
107.4(5)
127.5(5)
125.4(5)
108.2(5)
126.3(5)
C(29)–N(2)–C(32)–C(34)
N(2)–C(32)–C(34)–C(38)
C(33)–C(32)–C(34)–C(38)
120.7(6)
–69.9(7)
167.8(6)
[PdI(3,5-CF3-PCP)]PF6 (14)
Pd(1)–C(29)
Pd(1)–P(1)
P(1)–Pd(1)–C(29)
2.040(12)
2.324(4)
83.0(4)
Pd(1)–P(2)
Pd(1)–I(1)
P(2)–Pd(1)–C(29)
2.299(4)
2.6142(15)
86.3(4)
I(1)–Pd(1)–C(29)
I(1)–Pd(1)–P(1)
165.7(4)
98.62(10)
–72.8(11)
25(2)
110.9(11)
87.1(16)
-60.0(17)
173.2(14)
P(1)–Pd(1)–P(2)
I(1)–Pd(1)–P(2)
168.76(13)
92.59(10)
108.2(13)
–154.3(9)
–68.2(12)
85.7(15)
P(1)–Pd(1)–C(29)–N(1)
I(1)–Pd(1)–C(29)–N(1)
P(2)–Pd(1)–C(29)–N(1)
C(29)–N(1)–C(27)–C(21)
C(17)–C(21)–C(27)–N(1)
C(17)–C(21)–C(27)–C(28)
P(1)–Pd(1)–C(29)–N(2)
I(1)–Pd(1)–C(29)–N(2)
P(2)–Pd(1)–C(29)–N(2)
C(29)–N(2)–C(32)–C(34)
N(2)–C(32)–C(34)–C(38)
C(33)–C(32)–C(34)–C(38)
–67.2(18)
172.0(14)
[Pd(NCCH3)(PCP)](PF6)2 (11)
Pd(1)–C(25)
Pd(1)–P(1)
N(3)–C(52)
P(1)–Pd(1)–C(25)
N(3)–Pd(1)–C(25)
N(3)–Pd(1)–P(1)
1.993(9)
2.351(3)
1.126(10)
87.3(2)
177.9(4)
92.7(2)
Pd(1)–P(2)
Pd(1)–N(3)
2.334(3)
2.037(8)
P(2)–Pd(1)–C(25)
P(1)–Pd(1)–P(2)
N(3)–Pd(1)–P(2)
83.7(2)
170.56(8)
96.5(2)
P(1)–Pd(1)–C(25)–N(1)
N(3)–Pd(1)–C(25)–N(1)
P(2)–Pd(1)–C(25)–N(1)
C(25)–N(1)–C(23)–C(14)
C(13)–C(14)–C(23)–N(1)
C(13)–C(14)–C(23)–C(24)
–71.7(7)
16(11)
111.0(7)
84.8(8)
–71.1(9)
165.9(7)
P(1)–Pd(1)–C(25)–N(2)
N(3)–Pd(1)–C(25)–N(2)
P(2)–Pd(1)–C(25)–N(2)
C(25)–N(2)–C(28)–C(30)
N(2)–C(28)–C(30)–C(31)
C(29)–C(28)–C(30)–C(31)
107.0(7)
–165(10)
–70.3(7)
86.1(9)
–63.8(9)
170.7(7)
mately C2-symmetric with one pair of phenyl rings located
very close to the coordination plane and the second pair,
together with the ferrocenyl units, in a pseudo-axial posi-
tion. The C(25)–Pd(1)–N(3) angle of 177.9(4)° is much
closer to the ideal value of 180° than the corresponding
angles of the previously discussed complexes [PdI(3,5-CF3-
PCP)]PF6 (14), with 165.7(4)°, and [PdCl(PCP)]PF6 (15),
containing the unsubstituted PCP ligand, with 164.3(3)°.[19]
The Pd(1)–C(25) bond length for 11 is 1.993(9) Å which is
longer than that observed in [PdCl(PCP)]PF6 (15), with a
value of 1.962(8) Å. Lee recently reported crystal structures
of a cationic [PdCl(PCP)]+ complex, as well as of the corre-
sponding dicationic counterpart [Pd(NCCH3)(PCP)]2+
,
containing the tridentate NHC ligand PCP = PPh2–(CH2)2
–NHC–(CH2)2–PPh2, i.e., compounds structurally related
to ours.[29] However, in contrast to our results, Lee found
that the Pd–C distance is longer in the chloro complex than
in the dicationic acetonitrile derivative [1.983(7) vs.
1.961(4) Å]. The bite angles P(1)–Pd(1)–C(25) of 87.3(2)°
and P(2)–Pd(1)–C(25) of 83.7(2)° are slightly larger than
Figure 3. ORTEP representation of the dication in
[Pd(NCCH3)(PCP)](PF6)2 (11). Hydrogen atoms are omitted for
the corresponding values for [PdCl(PCP)]PF6 (15) [86.6(3) clarity. Thermal ellipsoids are set to 30% probability.
Eur. J. Inorg. Chem. 2005, 4745–4754
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4749

S. Gischig, A. Togni
FULL PAPER
and 82.2(3)°]. The imidazole plane is again tilted away from ing always the isolated product of the anti-Markovnikoff
the orientation perpendicular to the coordination plane. addition. The first experiments were carried out with the
The torsion angle P(1)–Pd(1)–C(25)–N(1) has a value of complex [Pd(NCCH3)(PCP)](PF6)2 (11) using methyl meth-
–71.7(7)° and the angle between the least-squares planes acrylate as the activated olefin; however, no activity was
containing C(25), N(1), C(26), C(27), N(2) and Pd(1), P(1), found. The test runs with crotonitrile as the amine acceptor
P(2), N(3), C(25), respectively, is 70.9°. The N(3)–C(52) afforded good to excellent yields (76–98%) but low enantio-
bond length in the acetonitrile ligand is 1.126(10) Å which selectivities (up to 6% ee) in the case of aliphatic amines,
lies within the range of N–C distances found for palladium whereas aniline showed no activity at all. We reasoned that
complexes containing phosphanes (1.114–1.144 Å),[30–34] or aniline is poisoning the catalyst by coordination to the
pincer-type carbene ligands (1.124–1.135 Å)[35–38] trans to active site, but we never succeeded in isolating an aniline
the acetonitrile.
complex. The first promising results could be obtained with
methacrylonitrile, having the methyl group in the α-position
with respect to the electron-withdrawing group. The results
involving methacrylonitrile as the substrate are summarized
in Table 5. While aniline still showed no activity, the prod-
ucts derived from the aliphatic olefins were isolated in good
to excellent yields, but the enantioselectivities were still low
(up to 36% ee for N-methylpiperazine). No improvement
was found by using acetone (no activity), or 1,2-dichloroe-
thane as solvents. In this latter solvent, thiomorpholine
could be added to methacrylonitrile affording 78% yield
and 27% ee. Lowering of the reaction temperature from
room temperature to –20 °C resulted, as expected, in lower
isolated yields after a reaction time of 24 h (Table 5, Entries
5–8). The enantioselectivity could be somewhat improved
for morpholine (38% ee) and thiomorpholine (44% ee).
Surprisingly, for piperidine (23% ee) and N-methylpipera-
zine (33% ee) the enantioselectivity was reproducibly lower
at –20 °C than at room temperature. Lowering of the tem-
perature to –80 °C while using longer reaction times (3 d)
in order to reach complete conversion, resulted in an im-
provement of the selectivity (except for piperidine) up to
63% ee (Table 5, Entries 9–12).
Catalysis
The
acetonitrile
ligand
in
the
complexes
[Pd(NCCH3)(PCP)](PF6)2 (11) and [Pd(NCCH3)(3,5-Me-
PCP)](PF6)2 (13) can be readily replaced by a substrate con-
taining a functional group. This allows an activation of
such substrates with the complex acting as a Lewis acid.
Encouraged by the results achieved in our group[17,18] with
[Ni(PPP)(THF)](ClO4)2 (PPP = Pigiphos, Scheme 1) as a
Lewis acidic catalyst, we also tested our complexes in the
asymmetric hydroamination of cyano olefins (Scheme 5).
Scheme 5. Hydroamination of cyano olefines.
In most experiments we used 5 mol-% of catalyst and the
In view of a possible improvement of the enantio-
typical reaction time was 24 h at room temperature. The selectivity, the ligands bearing 3,5-disubstituted phenyl
amines tested for this reaction were morpholine, thiomor- rings were tested. As mentioned earlier, the activation of
pholine, piperidine, N-methylpiperazine, and aniline afford- the complex [Pd(OAc)(3,5-CF3-PCP)]I (9) with Et3OPF6 re-
Table 5. Asymmetric addition of aliphatic amines to methacrylonitrile (see Scheme 5).
Entry
X
Catalyst [Ar]
T [°C]
t
Yield [%]
ee [%]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
O
S
CH2
NMe
O
11 [Ph]
11 [Ph]
20
20
20
24 h
24 h
24 h
24 h
24 h
24 h
24 h
24 h
3 d
3 d
3 d
3 d
24 h
24 h
24 h
24 h
3 d
3 d
3 d
96
99
60
84
82
83
67
73
94
91
94
98
99
96
99
99
91
83
93
92
32
33
26
36
38
44
23
33
47
63
22
46
54
61
54
51
71
75
56
73
11 [Ph]
11 [Ph]
20
11 [Ph]
–20
–20
–20
–20
–80
–80
–80
–80
20
20
20
20
–80
–80
–80
–80
S
11 [Ph]
CH2
NMe
O
11 [Ph]
11 [Ph]
11 [Ph]
S
11 [Ph]
CH2
NMe
O
11 [Ph]
11 [Ph]
13 [3,5-(CH3)2C6H3]
13 [3,5-(CH3)2C6H3]
13 [3,5-(CH3)2C6H3]
13 [3,5-(CH3)2C6H3]
13 [3,5-(CH3)2C6H3]
13 [3,5-(CH3)2C6H3]
13 [3,5-(CH3)2C6H3]
13 [3,5-(CH3)2C6H3]
S
CH2
NMe
O
S
CH2
NMe
3 d
4750
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2005, 4745–4754

PdII Complexes of Tridentate PCP N-Heterocyclic Carbene Ligands
FULL PAPER
sulted in a mixture from which the active species could not pointingly, it appears that the C2-symmetric PCP ligands
be identified. Using this mixture as the catalyst did not re- described here do not offer any significant advantage when
sult in any activity even after heating the reaction mixture compared to the asymmetric ligand Pigiphos in the Ni/Pd-
at 60 °C. Therefore, the less electron-deficient complex catalyzed addition of amines to methacrylonitrile.
[Pd(NCCH3)(3,5-Me-PCP)](PF6)2 (13) was tested for the
methacrylonitrile system. The activity at room temperature
(Table 5, Entries 13–16) as well as at –80 °C (Table 5, En-
tries 17–20) was found to be in the same range as when
using the unsubstituted ligand. The enantioselectivities,
however, were improved up to 61% ee (thiomorpholine) at
room temperature and finally up to 75% ee (thiomorpho-
line) at –80 °C. Interestingly, the lowering of the reaction
temperature again had no significant influence on the selec-
tivity for piperidine. This indicates that in this system the
additional heteroatom (O, S, NMe) has an influence on the
stereodifferentiating step during the catalysis.
Experimental Section
General Methods: (R)-N,N-Dimethyl-1-ferrocenylethylamine was
generously provided by Solvias AG (Basel) and was recrystallized
as tartrate salt according to the reported procedure.[39] The chloro-
phosphanes [3,5-(CF3)2C6H3]2PCl and [3,5-(CH3)2C6H3]2PCl were
prepared as described.[40] Derivatives 2–5 have been prepared be-
fore in our laboratory.[41] All reactions were performed under an
inert gas and air-sensitive substances were handled in a glove box.
1
NMR: The routine H, 13C, and 31P NMR spectra were measured
in the given solvent with either a Bruker DPX250 or Bruker
DPX300 instrument. The 2D experiments were generally carried
out with a Bruker DPX500 instrument. EI-MS, FAB-MS, MALDI-
MS: Measurements were performed by the MS service of the “La-
boratorium für Organische Chemie der ETHZ”. The signals are
given as m/z. Elemental analyses were performed by the micro ele-
mental analysis service of the “Laboratorium für Organische
Chemie der ETHZ”. Crystallography: X-ray structural measure-
ments were carried out with a Bruker CCD diffractometer (Bruker
SMART PLATFORM, with a CCD detector, graphite monochro-
mator, and Mo-Kα radiation). The program SMART served for
data collection. Integration was performed with SAINT. The struc-
ture solution (direct methods) and refinement on F2 were ac-
complished with SHELXTL-97. Model plots were made with OR-
TEP32. For the structures of 6, 14 (with exceptions), and 11 all
non-hydrogen atoms were refined freely with anisotropic refine-
ment parameters. For 6 a CH2Cl2 molecule was found to be disor-
dered over two sites. The C–Cl bond lengths were restrained to
standard values. Iodide and some of the CF3 groups are disordered
over two sites. The C–F distances were restrained by the use of
a variable and the F···F distances were equalized with the SADI
instruction. In the structure of 14 there are three CHCl3 molecules
present. The carbon atom in one of the CHCl3 molecules is disor-
dered over two positions. The C–Cl bond lengths were restrained
to standard values. For the disordered CF3 groups of C(6) and
C(45) the same procedure was adopted as for 6. Due to the low
data-to-parameter ratio, the atoms C(1), C(10), C(62), C(29), and
N(2) were refined anisotropically in combination with the ISOR
instruction. In the structure of 11 one ethanol and one diethyl ether
molecule are present. C(55) of the ether molecule and C(58) of
ethanol is disordered over two positions. Hydrogen atoms were re-
fined at calculated positions riding on their carrier atoms. Weights
were optimized in the final refinement cycles. Crystallographic data
are given in Table 6. CCDC-240665 (6), -240662 (14), and -240664
(11) contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Conclusions
The three-step synthesis of the ligand precursor [PCPH]-
I (1) was extended to the synthesis of the electronically and
sterically modified ligand precursors (3,5-CF3-PCPH)I (6)
and (3,5-Me-PCPH)I (7), bearing substituents at the 3- and
5-positions of the aryl groups. The reaction of the imid-
azolium salts 1, 6, and 7 with [Pd(OAc)2]3 in THF is the
most efficient route to PdII complexes of the corresponding
carbene
ligands
affording
[PdI(PCP)]OAc
(8),
[Pd(OAc)(3,5-CF3-PCP)]I (9), and [PdI(3,5-Me-PCP)]OAc
(10) in excellent yields. These complexes displayed a dif-
ferent behavior concerning the exchange of the anions ace-
tate and iodide as addressed by NMR studies. Reaction of
these complexes with Et3OPF6 in acetonitrile afforded the
dicationic species [Pd(NCCH3)(PCP)](PF6)2 (11) and
[Pd(NCCH3)(3,5-Me-PCP)](PF6)2 (13) in good to excellent
yields. However, a similar activation of [Pd(OAc)(3,5-CF3-
PCP)]I (9) failed and resulted in a product mixture that was
catalytically not active.
The solid-state structures of the ligand precursor (3,5-
CF3-PCPH)I (6) and its corresponding complex [PdI(3,5-
CF3-PCP)]PF6 (14) show that their common molecule
backbone assumes a helical conformation and that the most
relevant conformational difference between the two com-
pounds is accounted for mainly by a different torsion
around the two N–C single bonds.
The dicationic complexes [Pd(NCCH3)(PCP)](PF6)2 (11)
and [Pd(NCCH3)(3,5-Me-PCP)](PF6)2 (13) are active cata-
lysts for the addition of cyclic aliphatic secondary amines
to cyano olefins. The additions to methacrylonitrile cata-
lyzed by [Pd(NCCH3)(PCP)](PF6)2 (11) showed moderate
enantioselectivities which increased at low temperatures.
The sterically modified complex [Pd(NCCH3)(3,5-Me-
PCP)](PF6)2 (13) showed higher enantioselectivities at room
temperature (up to 61% ee) as well as at –80 °C (up to 75%
ee). Comparing Pd(PCP) and Ni(Pigiphos) catalysts having
the same absolute configuration of the ferrocenyl units, it is
interesting to note that products of opposite absolute con-
1,3-Bis{(R)-1-[(S)-2-{[3,5-bis(trifluoromethyl)phenyl]phosphanyl}-
ferrocenyl]ethyl}imidazolium Iodide (6): A suspension of 4 (1.51 g,
2.07 mmol) and imidazole (77.5 mg, 1.14 mmol, 0.55 equiv.) in a
mixture of acetonitrile (14 mL) and water (3.5 mL) was heated at
60 °C for 24 h. After addition of benzene (9 mL), the organic phase
was separated and concentrated in vacuo. The residue was dis-
solved together with NaI (683 mg, 4.55 mmol, 2 equiv.) in ethanol
(15 mL) and stirred for 3 h. After evaporation of the solvent in
figuration are obtained. Somewhat surprisingly and disap- vacuo, the crude product was filtered through silica (CH2Cl2, then
Eur. J. Inorg. Chem. 2005, 4745–4754
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4751

S. Gischig, A. Togni
Table 6. Crystallographic data for (3,5-CF3-PCPH)I (6), [PdI(3,5-CF3-PCP)]PF6 (14), and [Pd(NCCH3)(PCP)](PF6)2 (11).
FULL PAPER
(3,5-CF3-PCPH)I (6)
[PdI(3,5-CF3-PCP)]PF6 (14)
[Pd(NCCH3)(PCP)](PF6)2 (11)
Color, shape
yellow cube
red cube
yellow needle
Empirical formula
Formula mass
C
59H39F24Fe2N2P2, I, CH2Cl2
C59H38F24Fe2IN2P2Pd, PF6, 3(CHCl3)
2053.28
C53H49Fe2N3P2Pd, 2(PF6), C2H6O, C4H10O
1401.99
1615.37
Temperature [K]
Wavelength [Å]
Crystal system
200
0.71073
monoclinic
P21
200
0.71073
monoclinic
P21
150
0.71073
triclinic
P1
Space group
Unit cell dimensions [Å; °]
a = 8.3762(4); α = 90
a = 10.781(3); α = 90
a = 10.645(9); α = 94.368(17)
b = 33.4516(16); β = 109.0080(10) b = 28.236(8); β = 114.11
b = 11.133(9); β = 107.592(19)
c = 12.4853(6); γ = 90
3307.6(3)
c = 13.194(4); γ = 90
3665.9(17)
c = 13.707(11); γ = 109.542(18)
1431(2)
Volume [Å3]
Z
2
2
1
Calcd. density [g cm–3
]
1.622
1.860
1.627
Absorption coeff. [mm–1
Crystal size [mm]
Reflns. collected, unique
Rint
Refinement method
Data, restraints, params.
Goodness of fit
]
1.141
1.486
1.009
0.94×0.42×0.36
18999, 10593
0.0352
Full-matrix least-squares on F2
10593, 29, 958
1.094
0.32×0.23×0.16
21112, 9648
0.1028
Full-matrix least-squares on F2
9648, 48, 1008
1.021
0.24×0.07×0.04
9837, 7953
0.0287
Full-matrix least-squares on F2
7953, 3, 766
1.000
R, Rw
0.0581, 0.1304
0.006(16)
1.108/–0.369
0.0811, 0.1655
0.06(4)
1.211/–0.941
0.0525, 0.0892
0.02(2)
1.028/–0.753
Abs. structure parameter
Min./max. resd. [e·Å–3
]
CH2Cl2 + 4% MeOH) and chromatographed (silica, hexane/ethyl
acetate, 1:1 + 2% acetic acid). Yield: 793 mg (0.52 mmol, 50%),
orange crystals. TLC (hexane/ethyl acetate, 1:1): Rf = 0.64.
Cp), 4.58 (t, JCHCH = 2.4 Hz, 2 H, Cp), 4.89 (m, 2 H, Cp), 5.38 (q,
JCHMe = 6.9 Hz, 2 H, CHMe), 6.66 (s, 2 H, PAr2), 6.68 (s, 2 H,
PAr2), 7.04 (s, 2 H, PAr2), 7.17 (s, 2 H, PAr2), 7.18 (s, JCHCH
=
C59H39F24Fe2IN2P2 (1532.46): calcd. C 46.24, H 2.57, N 1.83; 1.5 Hz, 2 H, HC=CH Im), 7.26 (s, 2 H, PAr2), 7.29 (s, 2 H, PAr2),
found C 45.95, H 2.83, N 1.97. MS-MALDI: m/z = 669
8.08 (t, JCHCH = 1.6 Hz, 1 H, +CH, Im) ppm. 13C NMR (300 MHz,
CD2Cl2): δ = 20.4 (CH3, CHMe), 21.2 (CH, ArMe), 21.4 (CH,
1
[Ar2PFcEt+]. H NMR (300 MHz, CD2Cl2): δ = 1.21 (d, JCHMe
=
6.9 Hz, 6 H, CHMe), 3.91 (t, JCHCH = 1.2 Hz, 2 H, Cp), 4.08 (s, ArMe), 55.4 (d, JCP = 9.8 Hz, CH, CHMe), 69.7 (CH, Cp), 70.3
10 H, CpЈ), 4.69 (t, JCHCH = 2.6 Hz, 2 H, Cp), 4.79 (m, 2 H, Cp), (CH, CpЈ), 71.0 (CH, Cp), 73.1 (CH, Cp), 75.8 (d, JCP = 9.1 Hz,
6.44 (dq, JCHMe = 6.9 Hz, JPH = 3.0 Hz, 2 H, CHMe), 6.50 (d,
JCHCH = 1.2 Hz, 2 H, HC=CH Im), 7.24 (s, 2 H, PAr2), 7.26 (s, 2
C, Cp), 90.6 (d, JCP = 25.4 Hz, C, Cp), 119.4 (CH, HC=CH Im),
129.7 (d, JCP = 17.8 Hz, CH, PAr2), 130.3 (CH, PAr2), 131.5 (CH,
H, PAr2), 7.79 (s, 2 H, PAr2), 8.06 (s, 4 H, PAr2), 8.09 (s, 2 H, PAr2), PAr2), 132.5 (+CH, Im), 132.8 (d, JCP = 20.8 Hz, CH, PAr2), 135.4
10.65 (s, 1 H, +CH, Im) ppm. 13C NMR (300 MHz, CD2Cl2): δ =
20.6 (CH3, CHMe), 55.1 (d, JCP = 9.8 Hz, CH, CHMe), 70.4 (d,
(C, PAr2), 137.9 (C, PAr2), 138.0 (C, PAr2), 138.9 (d, JCP = 4.5 Hz,
C, PAr2) ppm. 31P NMR (300 MHz, CD2Cl2): δ = –28.36 (PAr2)
JCP = 4.5 Hz, CH, Cp), 70.7 (CH, CpЈ), 72.3 (d, JCP = 4.7 Hz, CH, ppm.
Cp), 72.5 (CH, Cp), 90.3 (d, JCP = 29.7 Hz, C, Cp), 118.1 (CH,
(SP-4)-(1,3-Bis{(R)-1-[(S)-2-{[3,5-bis(trifluoromethyl)phenyl]phos-
phanyl-κP}ferrocenyl]ethyl}imidazol-2-ylidene)(iodo)palladium(II
HC=CH Im), 122.5 (CH, PAr2), 123.0, (dq, JCP = 7.8 Hz, JCF
=
)
273.2 Hz, C, CF3), 124.2 (CH, PAr2), 131.1 (d, JCP = 16.5 Hz, CH,
PAr2), 131.3 (dq, JCP = 4.2 Hz, C, CCF3), 131.8 (dq, JCP = 8.2 Hz,
JCF = 33.5 Hz, C, CCF3), 134.3 (+CH, Im), 135.1 (d, JCP = 4.2 Hz,
C, PAr2), (d, JCP = 22.9 Hz, CH, PAr2), 138.8 (d, JCP = 14.3 Hz, C,
PAr2), 142.4 (d, JCP = 17.2 Hz, C, PAr2) ppm. 31P NMR (300 MHz,
CD2Cl2): δ = –25.32 (PAr2) ppm.
Acetate, [Pd(OAc)(3,5-CF3-PCP)]I (9): [Pd(OAc)2]3 (44 mg,
0.065 mmol) and 6 (300 mg, 0.196 mmol) were dissolved in THF
(6 mL) and heated at 60 °C for 12 h. After evaporation of the sol-
vent in vacuo, the residue was dissolved in CH2Cl2 and the product
precipitated with hexane, filtered off, washed three times with hex-
ane and dried in vacuo. Yield: 313.6 mg (0.272 mmol, 91%), deep
1,3-Bis[(R)-1-{(S)-2-[(3,5-Dimethylphenyl)phosphanyl]ferrocenyl}-
ethyl]imidazolium Iodide (7): A suspension of 5 (300 mg,
0.59 mmol) and imidazole (20.3 mg, 0.30 mmol, 0.51 equiv.) in a
mixture of acetonitrile (8 mL) and water (4 mL) was heated at
60 °C for 32 h. After addition of benzene (5 mL), the organic phase
was separated and concentrated in vacuo. The residue was dis-
solved together with NaI (193 mg, 1.29 mmol, 2 equiv.) in ethanol
(10 mL) and stirred for 3 h. After evaporation of the solvent in
vacuo, the crude product was filtered through silica (CH2Cl2, then
CH2Cl2 + 4% MeOH) and chromatographed (silica, ethyl acetate,
then ethyl acetate + 2 % MeOH). Yield: 163.3 mg (0.15 mmol,
51%), orange crystals. C59H63Fe2IN2P2 (1100.69): calcd. C 64.38,
H 5.77, N 2.55; found C 64.45, H 5.87, N 2.41. MS-MALDI:
m/z = 973 [3,5-Me-PCPH+], 453 [Ar2PFcEt+]. 1H NMR (300 MHz,
CD2Cl2): δ = 1.58 (d, JCHMe = 6.9 Hz, 6 H, CHMe), 2.37 (s, 6 H,
Ar-Me), 2.42 (s, 6 H, Ar-Me), 4.10 (s, 10 H, CpЈ), 4.14 (s, 2 H,
1
red crystals. H NMR (250 MHz, [D6]acetone): δ = 1.16 (d, 6 H,
JCHMe = 7.0 Hz, CHMe), 2.85 (br., 3 H, OAc), 4.08 (m, 2 H, Cp),
4.35 (s, 10 H, CpЈ), 4.66 (t, JCHCH = 2.5 Hz, 2 H, Cp), 4.98 (m, 2
H, Cp), 6.30 (q, JCHMe = 7.0 Hz, 2 H, CHMe), 7.53 (s, 2 H,
HC=CH Im), 7.83 (t, JCHCH = 4.5 Hz, 4 H, PAr2), 8.19 (br., 2 H,
PAr2), 8.35 (br., 2 H, PAr2), 9.41 (t, JCHCH = 5.3 Hz, 4 H, PAr2)
ppm. 13C NMR (250 MHz, [D6]acetone): δ = 14.0 (CH3, CHMe),
52.8 (CH, CHMe), 53.7, 54.14 (CH3, OAc), 70.0 (CH, Cp), 71.0
(CH, Cp), 71.3 (CH, Cp), 71.7 (CH, CpЈ), 73.7 (C, Cp), 93.1 (C,
Cp), 121.3 (CH, HC=CH Im), 120.9, 124.3, 125.2, 125.6, 130.3,
130.7, 131.3, 131.9, 136.2, 136.9 (CH, C, PAr2), 146.8 (br., CPd,
Im) ppm. 31P NMR (250 MHz, [D6]acetone): δ = 1.79 (PAr2) ppm.
(SP-4)-(1,3-Bis{(R)-1-{(S)-2-[(3,5-dimethylphenyl)phosphanyl-κP]-
ferrocenyl}ethyl}imidazol-2-ylidene)(iodo)palladium(II) Acetate,
[PdI(3,5-Me-PCP)]OAc (10): [Pd(OAc)2]3 (165.4 mg, 0.25 mmol)
4752
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2005, 4745–4754

PdII Complexes of Tridentate PCP N-Heterocyclic Carbene Ligands
FULL PAPER
and 7 (811 mg, 0.74 mmol) were dissolved in THF (20 mL) and
heated at 60 °C for 12 h. After evaporation of the solvent in vacuo,
the residue was dissolved in CH2Cl2 and the product precipitated
with hexane, filtered off, washed three times with hexane, and dried
in vacuo. Yield: 883.6 mg (0.70 mmol; 95 %), brown solid.
C61H65Fe2IN2O2P2Pd (1265.14): calcd. C 53.16, H 4.69; found: C
52.00, H 5.30. MS-MALDI: m/z = 1205 [PdI(3,5-Me-PCP)+], 1077
7.27 (br., JCHCH = 7.5 Hz, 2 H, PAr2), 7.40 (m, 6 H, PAr2) ppm.
13C NMR (300 MHz, NCCD3): δ = 0.3 (NCCH3), 14.7 (CH3,
CHMe), 20.4 (CH, ArMe), 20.5 (CH, ArMe), 54.8 (CH, CHMe),
69.3 (t, JCP = 29.1 Hz, C, Cp), 70.6 (t, JCP = 3.0 Hz, CH, Cp), 71.3
(m, CH, Cp), 71.4 (CH, CpЈ), 75.3 (t, JCP = 2.8 Hz, CH, Cp), 90.4
(t, JCP = 6.8 Hz, C, Cp), 118.1 (NCCH3), 119.9 (CH, HC=CH Im),
126.7 (t, JCP = 27.2 Hz, C, PAr2), 128.6 (t, JCP = 6.2 Hz, CH, PAr2),
[Pd(3,5-Me-PCP)+]. 1H NMR (250 MHz, CD2Cl2): δ = 1.27 (d, 130.8 (t, JCP = 27.0 Hz, C, PAr2), 131.8 (t, JCP = 6.4 Hz, CH, PAr2),
JCHMe = 7.0 Hz, 6 H, CHMe), 2.04 (s, 3 H, OAc), 2.30 (s, 6 H, 133.2 (CH, PAr2), 134.0 (CH, PAr2), 138.7 (t, JCP = 5.8 Hz, CMe,
ArMe), 2.40 (s, 6 H, ArMe), 3.65 (m, JCHCH = 1.3 Hz, 2 H, Cp), PAr2), 139.5 (t, JCP = 5.5 Hz, CMe, PAr2), 144.5 (t, JCP = 11.6 Hz,
4.28 (s, 10 H, CpЈ), 4.51 (t, JCHCH = 2.6 Hz, 2 H, Cp), 4.87 (m, 2 CPd, Im) ppm. 31P NMR (300 MHz, NCCD3): δ = –144.47 (sept,
H, Cp), 5.56 (q, JCHCH = 7.2 Hz, 2 H, CHMe), 6.54 (t, JCHCH
=
JPF = 706.6, PF6), 1.01 (PPh2) ppm.
5.5 Hz, 4 H, PAr2), 6.90 (s, 2 H, HC=CH Im), 7.16 (br., 2 H, PAr2),
7.22 (br., 2 H, PAr2), 7.50 (t, JCHCH = 5.8 Hz, 4 H, PAr2) ppm.
13C NMR (250 MHz, CD2Cl2): δ = 15.6 (CH3, CHMe), 21.2 (CH,
ArMe), 53.9 (CH, CHMe), 70.5 (t, JCP = 3.5 Hz, CH, Cp), 71.8 (t,
JCP = 2.8 Hz, CH, Cp), 71.2 (CH, CpЈ), 71.7 (t, C, Cp), 76.0 (t,
JCP = 2.8 Hz, CH, Cp), 90.2 (t, JCP = 6.6 Hz, C, Cp), 118.7 (CH,
General Procedure for the Pd-Catalyzed Hydroamination of Cyano
Olefins: A solution of palladium complex (0.025 mmol; 5 mol-%)
and olefin (1 mmol; 2 equiv.) in THF (3 mL) was stirred at room
temperature for 5 min. The amine (0.5 mmol) was then added and
the reaction mixture was stirred at the required temperature for the
corresponding time. The reaction was stopped by the addition of
hexane. Filtration and evaporation of the solvent yielded the hy-
droamination product. If necessary, the product was purified by
chromatography (silica, hexane/ethyl acetate, 1:1 + 5% NEt3).
Enantioselectivities were determined by GC or HPLC analysis.
HC=CH Im), 128.2 (t, JCP = 27.9 Hz, C, PAr2), 128.4 (t, JCP
=
6.0 Hz, CH, PAr2), 132.5 (CH, PAr2), 133.0 (CH, PAr2), 133.6 (t,
JCP = 24.7 Hz, C, PAr2), 134.1 (t, JCP = 5.5 Hz, CH, PAr2), 136.8
(t, JCP = 5.9 Hz, C–Me, PAr2), 138.8 (t, JCP = 5.3 Hz, CMe, PAr2),
152.7 (t, JCP = 12.4 Hz, CPd, Im) ppm. 31P NMR (250 MHz,
CD2Cl2): δ = –2.11 (PAr2) ppm.
3-(Morpholino)butanenitrile (16): TLC (hexane/ethyl acetate, 1:1 +
1
5% NEt3): Rf = 0.47. H NMR (250 MHz, CDCl3): δ = 1.20 (d, J
(SP-4)-(Acetonitrilo)(1,3-bis{(R)-1-[(S)-2-(Diphenylphosphanyl-κP)-
ferrocenyl]ethyl}imidazol-2-ylidene)palladium(II) Bis(hexafluoro-
phosphate), [PdPCP(NCCH3)](PF6)2 (11): A solution of 8 (253 mg,
0.22 mmol) and Et3OPF6 (136 mg, 0.55 mmol, 2.5 equiv.) in aceto-
nitrile (10 mL) was stirred at room temperature for 10 h. The mix-
ture was concentrated to an amount of 2 mL and the product was
precipitated with diethyl ether, filtered off, washed two times with
= 6.8 Hz, 3 H, CHCH3), 2.38 (dd, J = 7.3 Hz, J = 16.8 Hz, 1 H,
CHHЈCN), 2.52 (t, J = 4.8 Hz, 4 H, CH2N), 2.52 (dd, J = 6.5 Hz,
J = 16.8 Hz, 1 H, CHHЈCN), 2.94 (m, J = 6.0 Hz, 1 H, NCHCH3),
3.70 (t, J = 4.6 Hz, 4 H, CH2O) ppm. 13C(DEPT) NMR (250 MHz,
CDCl3): δ = 15.2 (CHCH3), 21.3 (CHHЈCN), 48.8 (CH2N), 56.3
(NCHCH3), 67.1 (CH2O) ppm. GC (β-dex, 90 °C iso): tr = 267.50,
267.64 min.
diethyl ether and dried in vacuo. Yield: 225 mg (0.17 mmol, 79%),
1
brown solid. H NMR (300 MHz, NCCD3): δ = 1.27 (d, JCHMe
7.2 Hz, 6 H, CHMe), 2.25 (br., 3 H, NCCH3), 3.93 (m, JCHCH
=
=
3-(Thiomorpholino)butanenitrile (17): TLC (hexane/ethyl acetate,
1:1 + 5% NEt3): Rf = 0.60. 1H NMR (250 MHz, CDCl3): δ = 1.14
1.2 Hz, 2 H, Cp), 4.25 (s, 10 H, CpЈ), 4.65 (t, JCHCH = 2.6 Hz, 2 H, (d, J = 6.8 Hz, 3 H, CHCH3), 2.32 (dd, J = 7.3 Hz, J = 16.8 Hz, 1
Cp), 4.89 (d, JCHCH = 1.2 Hz, 2 H, Cp), 5.47 (q, JCHCH = 6.9 Hz, 2
H, CHHЈCN), 2.48 (dd, J = 6.5 Hz, J = 16.8 Hz, 1 H, CHHЈCN),
H, CHMe), 6.90 (s, 2 H, HC=CH Im), 7.10 (q, JCHCH = 6.9 Hz, 4 2.63 (m, 4 H, CH2N), 2.77 (m, 4 H, CH2S), 2.99 (m, J = 7.0 Hz, 1
H, PPh2), 7.53 (t, JCHCH = 7.5 Hz, 4 H, PPh2), 7.61–7.84 (m, 12
H, NCHCH3) ppm. 13C(DEPT) NMR (250 MHz, CDCl3): δ = 15.1
H, PPh2) ppm. 13C NMR (300 MHz, NCCD3): δ = 0.4 (NCCH3), (CHCH3), 21.1 (CHHЈCN), 28.3 (CH2N), 50.8 (CH2S), 57.7
15.1 (CH3, CHMe), 55.0 (CH, CHMe), 68.6 (t, JCP = 29.4 Hz, C, (NCHCH3) ppm. HPLC (OJ, hexane/iPrOH, 95:5, 0.5 mL/ min,
Cp), 70.9 (t, JCP = 3.4 Hz, CH, Cp), 71.5 (t, JCP = 4.2 Hz, CH,
Cp), 71.6 (CH, CpЈ), 75.1 (t, JCP = 3.1 Hz, CH, Cp), 90.6 (t, JCP
= 6.9 Hz, C, Cp), 117.7 (NCCH3), 120.1 (CH, HC=CH Im), 126.9
(t, JCP = 27.7 Hz, CH, PPh2), 128.9 (t, JCP = 5.6 Hz, CH, PPh2),
129.7 (t, JCP = 5.3 Hz, CH, PPh2), 130.8 (t, JCP = 27.2 Hz, CH,
PPh2), 131.3 (t, JCP = 6.3 Hz, CH, PPh2), 131.8 (CH, PPh2), 132.5
25 °C, DAD 210 nm): tr = 38.12, 41.18 min.
3-(Piperidin-1-yl)butanenitrile (18): 1H NMR (250 MHz, CDCl3): δ
= 1.19 (d, J = 6.8 Hz, 3 H, CHCH3), 1.42 (m, 2 H, CH2), 1.56 (m,
J = 5.4 Hz, 4 H, CH2), 2.32 (dd, J = 8.0 Hz, J = 16.8 Hz, 1 H,
CHHЈCN), 2.47 (m, 4 H, CH2N), 2.51 (dd, J = 5.5 Hz, J = 16.8 Hz,
1 H, CHHЈCN), 2.99 (m, 1 H, NCHCH3) ppm. 13C(DEPT) NMR
(250 MHz, CDCl3): δ = 15.5 (CHCH3), 20.6 (CHHЈCN), 24.6
(CH2), 26.2 [(CH2)2], 49.4 (CH2N), 56.8 (NCHCH3) ppm. GC (β-
dex, 80 °C iso): tr = 324.7, 325.2 min.
(CH, PPh2), 134.2 (t, JCP = 6.5 Hz, CH, PPh2), 144.5 (t, JCP
=
11.6 Hz, CPd, Im) ppm. 31P NMR (300 MHz, NCCD3): δ =
–144.45 (sept, JPF = 706.8, PF6), 1.57 (PPh2) ppm.
(SP-4)-(Acetonitrilo)(1,3-bis[(R)-1-{(S)-2-[(3,5-dimethylphenyl)phos-
phanyl-κP]ferrocenyl}ethyl]imidazol-2-ylidene)palladium(II) Bis-
(hexafluorophosphate), [Pd(3,5-Me-PCP)(NCCH3)](PF6)2 (13): A
solution of 10 (81.9 mg, 0.065 mmol) and Et3OPF6 (40.3 mg,
0.16 mmol, 2.5 equiv.) in acetonitrile (4 mL) was stirred at room
temperature for 10 h. The mixture was concentrated to an amount
of 2 mL and the product was precipitated with diethyl ether, filtered
off, washed two times with diethyl ether and dried in vacuo. Yield:
86.2 mg (0.06 mmol, 94%), brown solid. 1H NMR (300 MHz,
NCCD3): δ = 1.26 (d, JCHMe = 7.2 Hz, 6 H, CHMe), 1.99 (s, 3 H,
NCCH3), 2.31 (s, 6 H, ArMe), 2.45 (s, 6 H, ArMe), 3.92 (m, JCHCH
3-(4-Methylpiperazin-1-yl)butanenitrile (19): 1H NMR (CDCl3): δ
= 1.16 (d, J = 6.8 Hz, 3 H, CHCH3), 2.24 (s, 3 H, NCH3), 2.32
(dd, J = 7.5 Hz, J = 16.8 Hz, 1 H, CHHЈCN), 2.40 (br. s, 4 H,
CH2N), 2.49 (dd, J = 5.5 Hz, J = 16.8 Hz, 1 H, CHHЈCN), 2.52
(br. m, 4 H, CH2NCH3), 2.96 (m, 1 H, NCHCH3) ppm. 13C(DEPT)
NMR (CDCl3): δ = 15.4 (CHCH3), 21.1 (CHHЈCN), 45.9 (NCH3),
48.1 (CH2N), 55.2 (CH2NCH3), 56.8 (NCHCH3) ppm. GC (β-dex,
90 °C iso): tr = 352.4, 360.1 min.
2-Methyl-3-(morpholino)propionitrile (20): TLC (hexane/ethyl ace-
1
tate, 1:1 + 5% NEt3): Rf = 0.55. H NMR (250 MHz, CDCl3): δ =
= 1.8 Hz, 2 H, Cp), 4.23 (s, 10 H, CpЈ), 4.63 (t, JCHCH = 2.4 Hz, 2 1.28 (d, J = 7.0 Hz, 3 H, CHCH3), 2.37 (dd, J = 6.3 Hz, J =
H, Cp), 4.86 (m, 2 H, Cp), 5.39 (q, JCHCH = 6.9 Hz, 2 H, CHMe), 12.5 Hz, 1 H, CHHЈ), 2.47 (t, J = 4.6 Hz, 4 H, CH2N), 2.57 (dd,
6.62 (t, JCHCH = 6.3 Hz, 4 H, PAr2), 6.93 (s, 2 H, HC=CH Im), J = 8.3 Hz, J = 12.5 Hz, 1 H, CHHЈ), 2.75 (m, 1 H, CHCH3), 3.67
Eur. J. Inorg. Chem. 2005, 4745–4754
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4753

S. Gischig, A. Togni
FULL PAPER
(t, J = 4.6 Hz, 4 H, CH2O) ppm. 13C(DEPT) NMR (250 MHz,
CDCl3): δ = 15.9 (CHCH3), 24.1 (CHCH3), 53.6 (CH2N), 61.3
(CHHЈ), 66.8 (CH2O) ppm. GC (β-dex, 92 °C iso): tr = 128.1 (R),
130.3 (S) min.
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2-Methyl-3-(thiomorpholino)propionitrile (21): TLC (hexane/ethyl
1
acetate, 1:1 + 5% NEt3): Rf = 0.58. H NMR (250 MHz, CDCl3):
δ = 1.26 (d, J = 7.0 Hz, 3 H, CHCH3), 2.42 (dd, J = 6.3 Hz, J =
12.8 Hz, 1 H, CHHЈ), 2.59 (dd, J = 8.3 Hz, J = 12.8 Hz, 1 H,
CHHЈ), 2.65 (m, 4 H, CH2N), 2.75 (m, 1 H, CHCH3, 4 H, CH2S)
ppm. 13C(DEPT) NMR (250 MHz, CDCl3): δ = 15.9 (CHCH3),
24.5 (CHCH3), 27.9 (CH2N), 55.2 (CH2S), 61.7 (CHHЈ) ppm.
HPLC (OJ, hexane/iPrOH, 95:5, 0.5 mL/ min, 25 °C, DAD
230 nm): tr = 25.52, 28.06 min.
2-Methyl-3-(piperidin-1-yl)propionitrile (22): TLC (hexane/ethyl
1
acetate, 1:1 + 5% NEt3): Rf = 0.8. H NMR (250 MHz, CDCl3): δ
= 1.31 (d, J = 7.0 Hz, 3 H, CHCH3), 1.43 (m, 2 H, CH2), 1.58 (m,
J = 5.3 Hz, 4 H, CH2), 2.37 (dd, J = 6.5 Hz, J = 12.5 Hz, 1 H,
CHHЈ), 2.44 (t, J = 5.5 Hz, 4 H, CH2N), 2.59 (dd, J = 8.0 Hz, J
= 12.5 Hz, 1 H, CHHЈ), 2.76 (m, 1 H, CHCH3) ppm. 13C(DEPT)
NMR (250 MHz, CDCl3): δ = 16.2 (CHCH3), 24.2 (CH2), 24.3
(CHCH3), 25.9 [(CH2)2], 54.7 (CH2N), 61.8 (CHHЈ) ppm. GC (α-
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NCH3), 2.36 (dd, J = 6.3 Hz, J = 2.5 Hz, 1 H, CHHЈ), 2.37 (s br,
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Acknowledgments
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Received: July 11, 2005
Published Online: October 25, 2005
4754
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2005, 4745–4754