Syntheses, characterization and catalytic application of palladacycles containing phosphane or phosphane oxide functionalities

Article abstract of DOI:10.1002/ejic.200800007

The preparation of ligand precursors PhN=C(CMe₂)(NPh)-C= N(CH₂)₂PPh₂ (1) and PhN=C(CMe ₂)(NPh)C=N(CH₂)₂P(O)-Ph₂ (2) are described. Treatment of 1 or 2 with 1 molequiv. Pd(OAc)₂ affords orthometallated palladium(II) complexes [PhN=C(CMe₂)(N- η¹-Ph)C=N(CH₂)₂PPh₂]Pd(OAc) (3) as a mononuclear complex or {[PhN=C(CMe₂)(N-η¹-Ph)C=N- (CH₂)₂P(O)Ph₂]Pd(OAc)}₂ (4) as an acetate-bridged dinuclear complex, respectively. Reaction of 3 with excess LiCl in methanol affords a mononuclear palladium(II) complex [PhN=C(CMe ₂)(N-η¹-Ph)C=N(CH₂)₂PPh ₂]PdCl (5). The crystal and molecular structures are reported for compounds 3-5. Application of these novel palladacyclic complexes to the Suzuki and Heck reactions with aryl halide substrates was examined. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800007

FULL PAPER
DOI: 10.1002/ejic.200800007
Syntheses, Characterization and Catalytic Application of Palladacycles
Containing Phosphane or Phosphane Oxide Functionalities
Kuo-Fu Peng,[a] Ming-Tsz Chen,[a] Chi-An Huang,[a] and Chi-Tien Chen*[a]
Keywords: Palladacyclic complexes / Phosphane / Phosphane oxide / Suzuki reaction / Heck reaction
The preparation of ligand precursors PhN=C(CMe2)(NPh)-
methanol affords a mononuclear palladium(II) complex
C=N(CH2)2PPh2 (1) and PhN=C(CMe2)(NPh)C=N(CH2)2P(O)- [PhN=C(CMe2)(N-η1-Ph)C=N(CH2)2PPh2]PdCl (5). The crys-
Ph2 (2) are described. Treatment of 1 or 2 with 1 molequiv.
Pd(OAc)2 affords orthometallated palladium(II) complexes
[PhN=C(CMe2)(N-η1-Ph)C=N(CH2)2PPh2]Pd(OAc) (3) as a
mononuclear complex or {[PhN=C(CMe2)(N-η1-Ph)C=N-
(CH2)2P(O)Ph2]Pd(OAc)}2 (4) as an acetate-bridged dinuclear
complex, respectively. Reaction of 3 with excess LiCl in
tal and molecular structures are reported for compounds 3–
5. Application of these novel palladacyclic complexes to the
Suzuki and Heck reactions with aryl halide substrates was
examined.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
Results and Discussion
Syntheses and Characterization of Ligand Precursors and
Palladacycles
Among studies on the palladium-catalyzed cross-coup-
ling reactions palladacycles are likely to serve as a source of
highly active but unstable zero-valent palladium species.[1a]
They were considered to function as low-ligated and phos-
phane-free catalysts, which helped toward the evaluation
the real potential of these systems.[1] Recently, enhanced
catalytic activities are observed with new palladium com-
plexes containing electron-rich and bulky ligands such as
phosphanes and carbenes.[1–2] The effectiveness of these sys-
tems was attributed to a combination of electronic and ste-
ric properties of the ligands that favour both the oxidative
addition and reductive elimination steps in the catalytic cy-
cle.
The new ligand precursor 1 was synthesized from the re-
action of PhN=C(CMe2)(NPh)C=N(CH2)2Cl with KPPh2
in thf.[4] Compound 2 was synthesized by the oxidation of
1 with excess H2O2(aq.) in thf.[5] Both compounds were
characterized by NMR spectroscopy and elemental analy-
sis, which indicate four-membered diimine compounds with
different functionalities than those reported previously.[3]
The 31P{1H} NMR spectrum of the phosphorus(V) species
2
shows
a
characteristic upfield-shifted singlet at
+31.9 ppm, whereas the spectrum of the phosphorus(III)
original ligand 1 presents a signal at –18.7 ppm. A sum-
mary of the synthetic route and the proposed structures is
shown in Scheme 1.
In our previous reports,[3] palladacycles bearing four-
membered diimine ligands with pendant functionalities
have exhibited comparable catalytic activities towards Suz-
uki- and Heck-type reactions. Owing to the success in the
application of those palladacycles and the advantages of
phosphanes involved in the cross-coupling reactions, the en-
hancement of the catalytic activity might be expected by
introducing electron-rich and bulky groups, such as phos-
phanes, into our four-membered diimine ligands as the pen-
dant functionalities. Therefore, we report here the syntheses
and characterization of novel palladacycles supported by
four-membered diimine ligands with pendant phosphane or
phosphane oxide functionalities. Their catalytic activity to-
ward the Suzuki- and Heck-type reactions was also investi-
gated.
Treatment of 1 or 2 with 1 molequiv. Pd(OAc)2 in thf at
room temperature or under reflux conditions yielded com-
plexes 3 or 4 as an orange or a greyish solid, respectively.
Both compounds were characterized by NMR spectroscopy
and elemental analysis. Similarly to the results reported pre-
viously, one more tertiary carbon atom is found in the re-
gion of phenyl ring on the basis of the 13C{1H} NMR spec-
trum in each case, which indicates that the metallated car-
bon atom is created during the reaction in both compounds.
The 31P{1H} NMR spectrum of 3 shows one singlet at
+29.5 ppm, which indicates the coordination of the phos-
phorus(III) group to the palladium centre.[6a] However, the
31P{1H} NMR spectrum of 4 shows one singlet at
+29.8 ppm. This indicates that the oxide group is not coor-
dinated to the palladium atom, as a significant downfield
shift is expected to occur on coordination as a result of the
inductive deshielding effect on the phosphorus atom.[7]
[a] Department of Chemistry, National Chung Hsing University,
Taichung 402, Taiwan, Republic of China
Fax: +886-4-22862547
E-mail: ctchen@dragon.nchu.edu.tw
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K.-F. Peng, M.-T. Chen, C.-A. Huang, C.-T. Chen
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Scheme 1.
Suitable crystals of 3 or 4 for structural determination length Pd–OOAc [2.052(7) and 2.085(2) Å disordered] is
were obtained from a thf/hexane solution. The molecular comparable to those found in the literature [2.036(2)–
structures are depicted in Figures 1 and 2. Compound 3 2.0897(19) Å].[3,8a,8b] In compound 4, only one signal corre-
demonstrates a mononuclear form, whereas compound 4 is sponding to the OAc group is observed in the NMR spec-
formed as a dinuclear species with two acetate groups as trum, which indicates the anti conformation.[6a,6b] This con-
bridging ligands. In compound 3, the bond angles around formation matches that in the solid state. The bond angles
Pd metal centre [from 83.39(5) to 92.96(8)°] indicate a com- around each Pd metal centre [from 82. 9(3) to 93.6(5)° for
plex that has a slightly distorted square-planar geometry, in Pd; from 83.1(4) to 93.4(4)° for PdA] indicate a dinuclear
which the palladium metal centre is coordinated to one palladium complex that has a slightly distorted square-
phenyl carbon atom, one imine nitrogen atom, one phos- planar geometry around each Pd metal centre. Each palla-
phorus atom, and one disordered OAc oxygen atom. The dium metal centre is coordinated to one phenyl ring carbon
bite angles Nimine–Pd–Cmetallated [92.96(8)°] and Nimine–Pd– atom, one imine nitrogen atom and two bridging acetate
P [83.39(5)°] are similar to those found in our previous oxygen atoms. The bite angles
Nimine–Pd–Cmetallated
work [93.20(10)°, 93.77(8)°, 94.51(10)° and 93.47(12)° re- [93.6(5)° and 93.4(4)°] and the bond lengths Pd–Cmetallated
sulting from the imino nitrogen and the metallated carbon; [1.997(12) and 2.012(13) Å] and Pd–Nimine [2.015(10) and
79.89(7)°, 80.06(9)°, 81.86(9)° and 84.62(8)° resulting from 2.028(10) Å] are similar to those discussed for 3. The bond
the imino nitrogen and pendant functionalities].[3] The angles OOAc–Pd–OOAc [82.9(3)°and 83.1(4)°] are smaller
bond length Pd–P [2.3129(5) Å] is within the range found than and the bond lengths Pd–OOAc [2.058(9), 2.069(9),
for some phosphane-containing palladacycles [2.2091(5)– 2.141(8) and 2.163(8) Å] are comparable to those found for
2.319(2) Å].[8] The bond length Pd–Cmetallated [2.053(2) Å] is acetate-bridged dinuclear palladacycles [86.5(2)–91.3(1)°
longer than those found for phosphane-containing pallada- and 2.029(2)–2.175(11) Å, respectively].[6] The differing bond
cycles[8] and from our previous reports [1.978(10)– lengths exhibited by the two Pd–OOAc bonds around the
2.025(3) Å].[3] The bond length Pd–Nimine [2.0210(17) Å] same Pd metal centre reflect the higher trans influence of the
falls in the range between those found for some pallada- aryl carbon atom relative to the imine nitrogen atom.[6a–6e]
cycles with a tridentate ligand [1.988(2)–2.000(7) Å][3,8a] and The distance between Pd and PdA [2.8878(4) Å] is within the
those found for some palladium complexes containing a range found for acetate-bridged dinuclear palladacycles of
iminophosphane ligand [2.049(4)–2.224(4) Å].[9] The bond the [C,N] coordination type [2.8502(13)–2.929(2) Å].[6]
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Palladacycles Containing Phosphane or Phosphane Oxide Functionalities
structure similar to 3, but with a Cl atom coordinated to
the metal centre instead of an OAc group. Suitable crystals
of 5 for structural determination were obtained from a
CH2Cl2/hexane solution. The molecular structure is de-
picted in Figure 3. The bond lengths and angles are similar
to those discussed above. The bond length Pd–Cl
[2.3124(6) Å] falls towards the lower end of the range of
those found for palladacycles containing tridentate ligands
[2.3181(8)–2.427(2) Å].[3a,8c–8e] Attempts to synthesize a
palladium chloride complex containing ligand 2 by a sim-
ilar route have been unsuccessful.
Figure 1. Molecular structure of 3. Selected bond lengths [Å] and
bond angles [°]: Pd–N(3), 2.0210(17); Pd–O(1), 2.085(2); Pd–O(1Ј),
2.052(7), Pd–C(31), 2.053(2); Pd–P, 2.3129(5); N(3)–Pd–C(31),
92.96(8); C(31)–Pd–O(1), 92.51(8), N(3)–Pd–P, 83.39(5); O(1)–Pd–
P, 91.29(6); N(3)–Pd–O(1), 168.52(8); C(31)–Pd–P, 176.17(6). Hy-
drogen atoms on carbon atoms omitted for clarity.
Figure 3. Molecular structure of 5. Selected bond lengths [Å] and
bond angles [°]: Pd–N(3), 2.0321(18); Pd–C(27), 2.078(2); Pd–Cl,
2.3124(6); Pd–P, 2.3129(6); N(3)–Pd–C(27), 92.91(8); N(3)–Pd–Cl,
172.32(5); C(27)–Pd–Cl, 94.22(6); N(3)–Pd–P, 83.81(5); C(27)–Pd–
P, 175.95(6); Cl(1)–Pd–P, 89.18(2). Hydrogen atoms on carbon
atoms omitted for clarity.
Catalytic Studies
Because of the success of some phosphane-containing or
CN-type palladacycles in catalyzing cross-coupling reac-
tions,[1] these palladacycles are expected to catalyze carbon–
carbon coupling reactions. For the purpose of comparing
the reactivity with other corresponding palladacycles, Su-
zuki and Heck reactions were chosen to demonstrate the
catalytic activities. Potential candidates 3–5 as catalyst pre-
cursors were introduced in the Suzuki coupling reaction of
4-bromoacetophenone with phenylboronic acid at 50 °C
with a 0.5 mol-% Pd, as shown in Scheme 2. Selected results
are listed in Table 1. The optimum base/solvent mixture for
the reaction was found to be K3PO4/toluene after several
trials with a combination of bases (KF, K3PO4 and
Cs2CO3) and solvents [N,N-dimethylacetamide (dma), thf
and toluene]. A higher reactivity was observed for 4 with a
conversion of up to 99% in 10 min (Entries 1–3). A similar
trend was observed by using electron-rich 4-bromoanisole
as the substrate (Entries 4, 5 and 7). The coupling activities
were higher when KF was used as the base (Entries 6 and
8). Therefore KF/toluene was introduced to examine the
performance of 4 in the coupling reactions involving poor-
coupling partners, at room temperature. The conversion
Figure 2. Molecular structure of one of the crystallographically in-
dependent molecules of 4. Selected bond lengths [Å] and bond
angles [°]: Pd–C(31), 2.012(13); Pd–N(3), 2.015(10); Pd–O(2),
2.069(9); Pd–O(3A), 2.141(8); Pd–PdA, 2.8878(4); PdA–C(31A),
1.997(12); PdA–N(3A), 2.028(10); PdA–O(2A), 2.058(9); PdA–
O(3), 2.163(8); C(31)–Pd–N(3), 93.6(5); C(31)–Pd–O(2), 90.9(5);
N(3)–Pd–O(2), 175.4(4); C(31)–Pd–O(3A), 173.2(5); N(3)–Pd–
O(3A), 92.6(4); O(2)–Pd–O(3A), 82.9(3); C(31A)–PdA–N(3A),
93.4(4); C(31A)–PdA–O(2A), 91.5(4); N(3A)–PdA–O(2A),
175.1(4); C(31A)–PdA–O(3), 173.2(4); N(3A)–PdA–O(3), 92.1(4);
O(2A)–PdA–O(3), 83.1(4). Hydrogen atoms on carbon atoms omit-
ted for clarity.
Reaction of 3 with excess lithium chloride in refluxing was up to 92% over 6 h when 2 mol-% Pd was used (Entries
methanol yields 5 as a dark green solid.[10] The spectro- 10 and 11). Compound 4 also exhibited an excellent conver-
scopic and elemental analysis data are consistent with a sion over 4 h with 4-bromoacetophenone under the opti-
Eur. J. Inorg. Chem. 2008, 2463–2470
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K.-F. Peng, M.-T. Chen, C.-A. Huang, C.-T. Chen
FULL PAPER
mized conditions and at room temperature when 1 mol-% with other CNX-type palladacycles of four-membered di-
Pd was used (Entry 9). Because of the higher activity and imine systems,[3] a higher reactivity was observed for the
solubility of 4, lower catalyst concentrations were investi- palladacycle containing the pendant PPh2 moiety. However,
gated with 4-bromoanisole as the substrate; catalyst/sub- the CN-type palladacycle 4 demonstrates a higher catalytic
strate ratios from 5ϫ10–4 to 5ϫ10–6 were investigated. The activity for the Suzuki reaction (Entries 4, 6, 7, 21 and 22).
reactions gave a conversion of 95% over 2.5 h at 70 °C for
the 5ϫ10–4 ratio, 96% over 1 h at 100 °C for the 5ϫ10–5
ratio and 74% over 48 h at 100 °C for the 5ϫ10–6 ratio
(Entries 12–14). The same conditions were applied to exam-
ine the catalytic activity of 4 with methyl 4-bromobenzoate
Scheme 2. Application of the palladacycles in the Suzuki reaction.
as the substrate with a catalyst/substrate ratio of 5ϫ10–6.
The reaction gave a conversion of 97% over 12 h at 100 °C
(Entry 15). Catalyst productivities were observed with a
turnover of up to 1.4ϫ105 during a 48-h period for the
coupling of the electronically deactivated aryl bromide and
with a turnover of up to 1.9ϫ105 during a 12-h period for
the coupling of the electronically activated aryl bromide.
These values are comparable to those for palladacycles
bearing C,N-type or C,P-type ligands.[11] Complex 4 was
tested with 4-chloroacetophenone and phenylboronic acid,
and 1 mol-% Pd and K3PO4/toluene at 100 °C. The reaction
gave a conversion of 55% over 24 h (Entry 16). Better con-
Scheme 3. The palladacycles with terdentate [C,N,N] or [C,N,S] li-
gands.
versions were found by adding tetra-n-butylamine bromide
Compounds 3–5 were also examined as catalysts in the
(nBu4NBr, TBAB) as cocatalyst (70% conversion for Heck coupling reaction of 4-bromoacetophenone with sty-
20 mol-% TBAB in Entry 17; 99% conversion for 50 mol- rene at 135 °C over a period of 1.5 h with 1 mol-% Pd and
% TBAB in Entry 18).[12] A poor conversion was observed under optimum conditions (KF/dma), as shown in
when 4-chloroanisole was used as the substrate under the Scheme 4. Selected results are listed in Table 2. Excellent
optimum conditions (Entry 19). In order to determine the activities under the optimum conditions (Entries 1–3) were
influence of the pendant functionality on the catalytic ac- obtained. A higher activity was observed for 3 when using
tivity,[3] the OAc-containing palladacycles 3, 6[3a] and 7[3b] a less reactive substrate in the presence of 20 mol-% TBAB
(as shown in Scheme 3) were examined as catalysts with 4- over 12 h (Entries 4–6). The same conditions were applied
bromoanisole as the substrate and 1 mol-% Pd under opti- to examine the other electronically deactivated aryl bro-
mized conditions at 70 °C (Entries 20–22). In comparison mide, however, with lower conversions (Entries 7 and 8).
Table 1. Suzuki coupling reaction catalyzed by new palladium complexes.[a]
Entry
Catalyst
Aryl halide
Base
Solvent
[Pd] [mol-%] T [°C]
t [h]
Conversion [%][b] Yield [%][c]
1
2
3
4
5
6
7
8
3
4
5
3
4
4
5
4
4
4
4
4
4
4
4
4
4
4
4
3
6
7
4-bromoacetophenone
4-bromoacetophenone
4-bromoacetophenone
4-bromoanisole
4-bromoanisole
4-bromoanisole
4-bromoanisole
4-tert-butyl-bromobenzene KF
4-bromoacetophenone
4-bromoanisole
4-bromoanisole
4-bromoanisole
4-bromoanisole
4-bromoanisole
Methyl 4-bromobenzoate
4-chloroacetophenone
4-chloroacetophenone
4-chloroacetophenone
4-chloroanisole
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
KF
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
thf
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1
50
50
50
50
50
50
50
50
1.5
0.16
1.5
6
0.75
0.75
6.5
1.25
4
3
6
2.5
1
48
12
24
24
24
72
1
97
99
98
92
87
93
90
95
99
56
92
95
96
74
97
55
70
99
Ͻ5
96
94
97
95
92
94
85
84
91
86
92
95
–
84
92
94
70
95
–
K3PO4
9
K3PO4
KF
KF
KF
KF
KF
KF
K3PO4
K3PO4
K3PO4
KF
K3PO4
KF
room temp.
room temp.
room temp.
70
100
100
100
100
100
100
100
70
10
11
12
13
14
15
16
17[d]
18[e]
19[e]
20
21
22
1
2
0.05
0.005
0.0005
0.0005
1
1
1
1
1
–
95
–
91
91
90
4-bromoanisole
4-bromoanisole
4-bromoanisole
1
1
70
70
12
4
K3PO4
toluene
1
[a] Reaction conditions: 1.0 mmol aryl halide, 1.5 mmol phenylboronic acid, 2.0 mmol base, 2 mL solvent. [b] Determined by H NMR
spectroscopy. [c] Isolated yield (average of two experiments). [d] Addition of 20 mol-% TBAB. [e] Addition of 50 mol-% TBAB.
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Palladacycles Containing Phosphane or Phosphane Oxide Functionalities
Table 2. Heck coupling reaction catalyzed by new palladium complexes.[a]
Entry
Catalyst
Aryl halide
Base
Solvent
[Pd] [mol-%] T [°C]
t [h]
Conversion [%][b] Yield [%][c]
1
2
3
3
4
5
3
4
5
3
3
3
3
3
3
3
6
7
3
4
5
4
4
4
4
4
4
4
4
4-bromoacetophenone
4-bromoacetophenone
4-bromoacetophenone
4-bromoanisole
4-bromoanisole
4-bromoanisole
KF
KF
KF
KF
KF
KF
KF
KF
KF
KF
KF
KF
KF
KF
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
dma
dma
dma
dma
dma
dma
dma
dma
dma
dma
dma
dma
dma
dma
dmf
thf
thf
thf
thf
thf
thf
thf
thf
thf
1
1
1
1
1
1
1
1
135
135
135
135
135
135
135
135
135
135
135
135
135
135
135
70
70
70
70
70
70
70
70
70
1.5
1.5
1.5
12
12
12
12
12
2.75
8
36
24
36
12
12
1.5
1.5
1.5
12
12
10
12
30
18
24
24
91
94
93
96
80
92
73
68
99
95
97
29
38
80
96
Ͻ5
49
Ͻ5
63
90
97
99
85
90
81
70
84
89
90
91
77
88
–
4[d]
5[d]
6[d]
7[d]
8[d]
9
4-bromotoluene
4-tert-butyl-bromobenzene
4-bromoacetophenone
4-bromoacetophenone
4-bromoacetophenone
4-chloroacetophenone
4-chloroacetophenone
4-bromoanisole
–
0.1
0.01
0.001
1
3
1
1
1
1
1
1
1
1
1
1
1
1
1
92
90
91
–
10
11
12[d]
13[e]
14[d]
15
–
71
91
–
–
–
4-bromoanisole
16
17
18
19
4-bromoacetophenone
4-bromoacetophenone
4-bromoacetophenone
4-bromoacetophenone
4-bromoacetophenone
Methyl 4-bromobenzoate
4-bromobenzaldehyde
4-bromoanisole
–
20[d]
21[d]
22[d]
23[d]
24[e]
25[e]
26[e]
82
92
94
77
84
77
–
4-bromoanisole
4-bromotoluene
4-tert-butyl-bromobenzene
thf
thf
70
70
[a] Reaction conditions: 1.0 mmol aryl halide, 1.3 mmol styrene, 1.5 mmol base, 2 mL solvent. [b] Determined by 1H NMR spectroscopy.
[c] Isolated yield (average of two experiments). [d] Addition of 20 mol-% TBAB. [e] Addition of 50 mol-% TBAB.
Lower catalyst concentrations were loaded with catalyst/ 3). Better conversions were achieved by extending the reac-
substrate ratios of 10–3 to 10–5, which led to conversions tion time or by adding 20 mol-% TBAB (Entries 19 and
above 95% over periods of 2.75 to 36 h (Entries 9–11). Cat- 20). Similar conversions were observed when using methyl
alyst productivity was observed with a turnover of up to 4-bromobenzoate or 4-bromobenzaldehyde as substrates
9.1ϫ104 during a 36-h period for the coupling of the elec- (Entries 21 and 22). Similar conditions were applied when
tronically activated aryl bromide; the TOF is comparable investigating the electronically deactivated aryl bromide,
to those found in the literature.[13] Complex 3 exhibited a with 85% conversion over 30 h (Entry 23). Higher activities
poor activity in the reaction with the electronically activated were observed over 18 h by increasing the loading of TBAB
aryl chloride even with higher catalyst and TBAB loadings up to 50 mol-% (Entry 24). These conditions were applied
(Entries 12 and 13). Compounds 6 and 7 were examined when investigating the other electronically deactivated aryl
under optimized conditions with 4-bromoanisole as the bromides, however, with lower conversions over 24 h (En-
substrate. The catalytic activities fall in the order 3 = 7 Ͼ tries 25 and 26).
6 (Entries 4, 14 and 15). A higher activity was observed
with the palladacycle containing a pendant PPh2 moiety for
the Heck reaction.
Conclusion
Three novel palladacycles bearing phosphane or phos-
phane oxide functionalities have been prepared and their
catalytic activity toward the Suzuki and Heck C–C coupling
reactions has been demonstrated. Under optimized condi-
tions, palladacycle 4 exhibits a comparable activity to those
of existing CN-type palladacyclic systems for both the Su-
Scheme 4. Application of the palladacycles in the Heck reaction.
zuki and Heck coupling reactions. For those CNP-type pal-
The reaction of 4-bromoacetophenone with styrene can ladacycles, the OAc-containing complex 3 exhibits a slightly
also be performed under mild reaction conditions with higher activity than the Cl-containing complex 5 for both
1 mol-% Pd.[14] Compound 4 exhibits a higher activity with coupling reactions. Although complex 3 is more active in
K3PO4/thf when using 3–5 as candidates for the precatalysts catalyzing the Heck reaction with aryl bromides containing
at 70oC (Entries 16–18), whereas compounds 3 and 5 dem- electron-donating groups at higher temperatures, complex 4
onstrate higher activities at high temperature (Entries 1 and seems to be more active in catalyzing both coupling reac-
Eur. J. Inorg. Chem. 2008, 2463–2470
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2467

K.-F. Peng, M.-T. Chen, C.-A. Huang, C.-T. Chen
FULL PAPER
41.8 (s, CH2), 58.0 [s, C(CH3)2], 119.3, 121.4, 123.3, 124.4, 128.58,
128.62, 128.69, 130.69, 130.75, 131.8 (CH-C6H5), 132.8, 133.4,
137.1, 146.7, 157.9, 158.7 (tert-C) ppm. 31P{1H} NMR (162 MHz):
δ = 31.9 ppm. C31H30N3OP (491.57): calcd. C 75.74, H 6.15, N
8.55; found C 74.96, H 5.83, N 8.22.
tions under relatively mild conditions. In the case of the
four-membered diimine palladacyclic system, the phos-
phane-containing palladacycles exhibit a higher activity for
both the Suzuki and Heck coupling reactions than those
reported in our previous work. In some cases, the CN-type
palladacycle 4 demonstrates a higher catalytic activity than [PhN=CA(CBMe2)(NB-η1-C6H4)CC=N(CH2)2PPh2(CA–NB)(CB–
CC)]Pd(OAc) (3): To a flask containing Pd(OAc)2 (0.45 g,
those with dative groups. Preliminary studies on the fine-
tuning of the ligands and further application of metal com-
plexes to the catalytic reactions are currently underway.
2.0 mmol) and 1 (0.95 g, 2.0 mmol) was added thf (30 mL) at room
temperature. After 18 h of stirring, the volatiles were removed un-
der reduced pressure. The residue was washed with toluene (10 mL)
followed by hexane (10 mL) to afford an orange solid. Yield: 1.05 g,
1
82.0%. H NMR (600 MHz): δ = 1.46 [s, 6 H, C(CH3)2], 1.98 [s, 3
Experimental Section
H, OC(=O)CH3], 2.285 (t, J = 6.6 Hz, 1 H, CH2), 2.296 (t, J =
6.6 Hz, 1 H, CH2), 3.50 (t, J = 7.2 Hz, 1 H, CH2), 3.54 (t, J =
6.0 Hz, 1 H, CH2), 6.95 (d, J = 5.4 Hz, 2 H, CH-Ph), 7.10–7.16
(m, 2 H, CH-Ph), 7.21 (t, J = 7.8 Hz, 1 H, p-Ph), 7.32 (t, J =
8.4 Hz, 2 H, p-Ph), 7.44–7.47 (m, 6 H, CH-Ph), 7.85 (t, J = 8.4 Hz,
General Procedure: All manipulations were carried out under an
atmosphere of nitrogen by using standard Schlenk-line or dry-box
techniques. Solvents were refluxed over the appropriate drying
agent and distilled prior to use. Methanol and dma were used as
1 H, p-Ph), 7.92 (m, 4 H, CH-Ph), 8.20 (d, J = 6.0 Hz, 1 H, o-Ph)
supplied. Deuterated solvents were dried with molecular sieves. 1H
ppm. 13C{1H} NMR (150 MHz): δ = 21.0 [s, C(CH3)2], 24.0 [s,
and 13C{1H} NMR spectra were recorded either on a Varian Mer-
OC(=O)CH3], 30.5 (d, JCP = 21.9 Hz, CH2), 50.9 (d, JCP = 13.4 Hz,
CH2), 57.0 [s, C(CH3)3], 116.6 (d, JCP = 6.0 Hz), 120.9, 124.0, 124.9
(d, JCP = 7.8 Hz), 125.7, 128.80, 128.86, 128.94, 130.8, 133.51,
cury-400 (400 MHz) or on a Varian Inova-600 (600 MHz) spec-
trometer in [D]chloroform at ambient temperature unless stated
otherwise and referenced internally to the residual solvent peak and
133.59, 134.8 (CH-C6H5), 130.25, 130.48, 131.15, 138.1, 139.0,
reported as parts per million relative to tetramethylsilane. 31P{1H}
145.8, 153.5, 159.0, 176.4 (tert-C) ppm. 31P{1H} NMR (162 MHz):
NMR spectra are referenced externally using 85% H3PO4 at δ =
0 ppm. Elemental analyses were performed with an Elementar Va-
rio ELIV instrument. KPPh2 (0.5  in thf, Aldrich), H2O2 (Showa,
δ = 29.5 ppm. C33H32N3O2PPd (640.02): calcd. C 61.93, H 5.04, N
6.57; found C 61.68, H 4.72, N 6.68.
30% in H2O), Pd(OAc)2 (Acros), styrene (Acros), K3PO4 (Lancas-
ter), KF (Acros), Cs2CO3 (Aldrich), TBAB (TCI) and LiCl (Lanc-
{[PhN=CA(CBMe2)(NB-η1-C6H4)CC=N(CH2)2P(O)Ph2(CA–NB)-
(CB–CC)]Pd(OAc)}2 (4): To a flask containing Pd(OAc)2 (0.33 g,
aster) were used as supplied. PhN=C(CMe2)(NPh)C=N(CH2)2Cl
1.47 mmol) and 2 (0.72 g, 1.47 mmol) was added thf (30 mL) at
room temperature. This mixture was heated at reflux for 3 h. The
was prepared by the literature method.[3b]
PhN=CA(CBMe2)(NBPh)CC=N(CH2)2PPh2(CA–NB)(CB–CC) (1):
resulting mixture was filtered, and the filtrate was pumped to dry-
ness. The crude product was washed with toluene (15 mL) at 0 °C
to afford a grey solid. A second portion of product was isolated by
filtering the suspension produced from the addition of hexane to
the resulting toluene solution. Yield: 0.73 g, 76.0 %. 1H NMR
(600 MHz): δ = 1.02 [s, 6 H, C(CH3)2], 1.24 [s, 6 H, C(CH3)2], 2.00
[s, 6 H, OC(=O)CH3], 2.07 (m, 2 H, CH2), 2.84 (m, 2 H, CH2),
3.00 (m, 2 H, CH2), 3.48 (m, 2 H, CH2), 6.60 (m, 2 H, CH-Ph),
6.87 (m, 4 H, CH-Ph), 6.96 (m, 2 H, CH-Ph), 7.05 (m, 2 H, CH-
Ph), 7.11 (m, 2 H, CH-Ph), 7.29 (m, 4 H, CH-Ph), 7.40 (m, 4 H,
CH-Ph), 7.47 (m, 2 H, CH-Ph), 7.49 (m, 4 H, CH-Ph), 7.57 (m, 2
H, CH-Ph), 7.63–7.58 (m, 8 H, CH-Ph), 7.99 (m, 2 H, CH-Ph)
ppm. 13C{1H} NMR (150 MHz): δ = 20.69 [s, C(CH3)2], 20.84 [s,
C(CH3)2], 24.8 [s, OC(=O)CH3], 32.9 (d, JCP = 66.8 Hz, CH2),
116.2, 120.9, 124.15 (d, JCP = 11.6 Hz), 124.8, 128.6 (m), 128.94,
130.52 (d, JCP = 9.15 Hz), 130.88 (d, JCP = 9.75 Hz), 131.9, 134.5
(CH-C6H5), 120.0, 132.59, 132.66, 133.33, 145.4, 154.2, 158.7,
181.4 (tert-C) ppm. 31P{1H} NMR (162 MHz): δ = 29.8 ppm.
C66H64N6O6P2Pd2 (1314.05): calcd. C 60.42, H 4.92, N 6.41; found
C 60.15, H 4.54, N 6.12.
To a flask containing PhN=C(CMe2)(NPh)C=N(CH2)2Cl (0.583 g,
1.79 mmol) in thf (25 mL) was added KPPh2 (3.6 mL, 0.5  in thf,
1.79 mmol) at room temperature. After 3 h of stirring, the volatiles
were removed under reduced pressure. The residue was triturated
with hexane (10 mL), followed by extraction with toluene (10 mL)
and washing with hexane (10 mL) to afford a pale-yellow solid.
Yield: 0.73 g, 86.0%. 1H NMR (600 MHz): δ = 1.24 [s, 6 H,
C(CH3)2], 2.41 (m, 2 H, CH2), 3.50 (m, 2 H, CH2), 6.89 (d, J =
7.2 Hz, 2 H, o-Ph), 7.05 (t, J = 7.2 Hz, 1 H, p-Ph), 7.12 (t, J =
7.2 Hz, 1 H, p-Ph), 7.26 (t, J = 7.8 Hz, 2 H, m-Ph), 7.31 (m, 6 H,
CH-Ph), 7.35 (t, J = 7.8 Hz, 2 H, m-Ph), 7.45 (m, 4 H, CH-Ph),
8.21 (d, J = 7.8 Hz, 2 H, o-Ph) ppm. 13C{1H} NMR (150 MHz): δ
= 21.4 [s, C(CH3)2], 30.9 (d, JCP = 12.2 Hz, CH2), 45.9 (d, JCP
=
23.8 Hz, CH2), 57.9 [s, C(CH3)2], 119.4, 121.5, 123.2, 124.3, 128.4
(d, JCP = 6.6 Hz), 128.63, 128.65, 132.68, 132.81 (CH-C6H5), 137.2,
138.28, 138.36, 146.8, 157.9 (tert-C) ppm. 31P{1H} NMR
(162 MHz): δ = –18.7 ppm. C31H30N3P (475.57): calcd. C 78.29, H
6.36, N 8.84; found C 78.28, H 6.32, N 8.89.
PhN=CA(CBMe2)(NBPh)CC=N(CH2)2P(O)Ph2(CA–NB)(CB–CC) (2):
To a flask containing 1 (1.035 g, 2.18 mmol) in thf (20 mL) was
added H2O2 (0.28 mL, 30% in water, 2.4 mmol) at room tempera-
ture. After 2 h of stirring, the reaction mixture was dried with
MgSO4 for 1 h. The suspension was filtered, and the filtrate was
[PhN=CA(CBMe2)(NB-η1-C6H4)CC=N(CH2)2PPh2(CA–NB)(CB–
CC)]PdCl (5): To a flask containing 3 (0.64 g, 1.0 mmol) and LiCl
(0.25 g, 6.0 mmol) was added methanol (20 mL) at room tempera-
ture. The reaction mixture was heated at reflux for 3 h. The re-
sulting mixture was filtered, and the filtrate was pumped to dryness.
pumped to dryness to afford an off-white solid. Yield: 0.90 g,
1
84.0%. H NMR (600 MHz): δ = 1.32 [s, 6 H, C(CH3)2], 2.69 (m, The residue was washed with methanol (10 mL), followed by tritu-
2 H, CH2), 3.75 (m, 2 H, CH2), 6.89 (d, J = 7.2 Hz, 2 H, o-Ph),
7.06 (t, J = 7.2 Hz, 1 H, p-Ph), 7.12 (t, J = 7.2 Hz, 1 H, p-Ph), 7.27
(t, J = 7.8 Hz, 2 H, m-Ph), 7.32 (t, J = 7.8 Hz, 2 H, m-Ph), 7.44–
rating with hexane (10 mL) to afford a dark green solid. Yield:
0.56 g, 90.0%. 1H NMR (600 MHz): δ = 1.50 [s, 6 H, C(CH3)2],
2.345 (t, J = 7.8 Hz, 1 H, CH2), 2.354 (t, J = 7.8 Hz, 1 H, CH2),
7.46 (m, 4 H, overlap), 7.50 (m, 2 H, overlap), 7.78 (m, 4 H, over- 3.67 (t, J = 7.2 Hz, 1 H, CH2), 3.71 (t, J = 7.2 Hz, 1 H, CH2), 6.95
lap), 8.10 (d, J = 7.8 Hz, 2 H, o-Ph) ppm. 13C{1H} NMR (d, J = 7.2 Hz, 2 H, o-Ph), 7.13 (t, J = 7.8 Hz, 1 H, p-Ph), 7.17 (m,
(150 MHz): δ = 21.3 [s, C(CH3)2], 32.4 (d, JCP = 69.9 Hz, CH2),
2468
1 H, CH-Ph), 7.21 (m, 1 H, CH-Ph), 7.33 (t, J = 7.2 Hz, 2 H, p-
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2463–2470

Palladacycles Containing Phosphane or Phosphane Oxide Functionalities
Ph), 7.42–7.47 (m, 6 H, CH-Ph), 7.93–7.96 (m, 4 H, CH-Ph), 8.25 These data can be obtained free of charge from The Cambridge
(d, J = 4.8 Hz, 1 H, o-Ph), 8.66 (m, 1 H, CH-Ph) ppm. 13C{1H}
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_requ-
NMR (150 MHz): δ = 21.1 [s, C(CH3)2], 29.7 (d, JCP = 22.5 Hz, est/cif.
CH2), 52.0 (d, JCP = 13.95 Hz, CH2), 57.0 [s, C(CH3)3], 116.8 (d,
JCP = 6.6 Hz), 120.9, 124.0, 125.1 (d, JCP = 7.2 Hz), 125.7, 128.91,
Acknowledgments
128.97, 131.0, 133.39, 133.47, 137.8 (CH-C6H5), 129.67, 129.91,
131.45, 139.2, 140.1, 145.7, 153.5, 159.1 (tert-C) ppm. 31P{1H}
NMR (162 MHz): δ = 31.1 ppm. C31H29ClN3PPd (616.34): calcd.
C 60.40, H 4.74, N 6.82; found C 59.99, H 4.25, N 6.98.
Financial support from the National Science Council (grant
number NSC 95–2113-M-005–010-MY3) and Ministry of Educa-
tion (under the ATU plan), Taiwan, ROC, is appreciated.
General Procedure for the Suzuki-Type Coupling Reaction: A pre-
scribed amount of catalyst, base (2 equiv.), phenylboronic acid
(1.5 equiv.), and aryl halides (1 equiv., solids) were placed in a
Schlenk tube under nitrogen. The solvent (2 mL) and aryl halides
(1 equiv., liquids) were added by syringe, and the reaction mixture
was heated to the prescribed temperature for the prescribed time.
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General Procedure for the Heck Reaction: A prescribed amount of
catalyst, base (1.5 equiv.) and aryl halides (1 equiv., solids) were
placed in a Schlenk tube under nitrogen. The solvent (2 mL), sty-
rene (1.3 equiv.) and aryl halides (1 equiv., liquids) were added by
syringe, and the reaction mixture was heated to the prescribed tem-
perature for the prescribed time.
Crystal Structure Data: Crystals were grown from a thf/hexane
solution (3 or 4) or a CH2Cl2/hexane solution (5) and isolated by
filtration. Suitable crystals of 3, 4 or 5 were sealed in thin-walled
glass capillaries under nitrogen and mounted on a Bruker AXS
SMART 1000 diffractometer. The absorption correction was based
on the symmetry equivalent reflections by using the SADABS pro-
gram. The space group determination was based on a check of the
Laue symmetry and systematic absences and was confirmed by
using the structure solution. The structure was solved by direct
methods with a SHELXTL package. All non-H atoms were located
from successive Fourier maps, and hydrogen atoms were refined by
using a riding model. Anisotropic thermal parameters were used
for all non-H atoms, and fixed isotropic parameters were used for
H atoms. Some details of the data collection and refinement are
given in Table 3. CCDC-661014, -661015, -661016 for compounds
3–5 contain the supplementary crystallographic data for this paper.
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Table 3. Summary of crystal data for compounds 3–5.
3
4
5
Formula
Fw
T [K]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
PdC33H33N3O2P Pd4C132H128N12O12P4 PdC31H29ClN3P
640.99
293(2)
Monoclinic
P21/n
2623.94
293(2)
Monoclinic
P21
616.39
293(2)
Monoclinic
P21/c
14.7944(11)
10.4423(8)
19.4410(15)
90
19.3975(12)
13.6855(9)
24.7493(16)
90
15.7977(11)
12.1228(8)
14.9392(10)
90
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β [°]
γ [°]
V [Å3]
94.4190(10)
90
2994.5(4)
4
1.422
0.707
110.2110(10)
90
6165.5(7)
2
1.413
0.691
34883
1477
0.0295
0.0594
0.999
105.6600(10)
90
2754.8(3)
4
1.486
0.854
14978
324
0.0283
0.1047
0.999
Z
ρcalcd. [Mg/m3]
µ(Mo-Kα) [mm–1]
Reflections collected 16331
No. of parameters
379
[a]
R1
0.0276
0.0863
1.010
[a]
wR2
GoF[b]
[a] R1 = [Σ|Fo| – |Fc|]/Σ|Fo|; wR2 = [Σw(Fo – Fc ) /Σw(Fo2)2]1/2; w =
2
2 2
0.10. [b] GoF = [Σw(Fo – Fc ) /(Nrflns – Nparams)]1/2
.
2
2 2
Eur. J. Inorg. Chem. 2008, 2463–2470
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2469

K.-F. Peng, M.-T. Chen, C.-A. Huang, C.-T. Chen
FULL PAPER
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Published Online: April 11, 2008
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