Nonchelate and chelate complexes of palladium(II) with N-heterocyclic carbene ligands of amido functionality

Article abstract of DOI:10.1021/om0610041

The imidazolium ligand precursors [L¹H¹H ²]Cl and [L²H¹₂H²]C1 (H¹ = NHC=O, H² = NCHN) for the potentially bidentate and pincer-type amido-NHC ligands were synthesized in 66-78% yields. Selective deprotonation of H² in these salts with pyridine in the presence of palladium chloride resulted in the monodentate palladium(II) complexes Pd(L ¹H¹)(py)Cl₂ and Pd(L²H ¹₂)(py)Cl₂. The use of K₂CO ₃ in pyridine or DMF led to the double and triple deprotonations of the ligand precursors, giving the bis-bidentate and pincer-type palladium(II) complexes PdL¹₂ and PdL²(py), respectively. Intriguingly, in certain cases, both the cis and the trans isomers of PdL ¹₂ were formed and isolated in pure forms. A theoretical study indicates that the trans-PdL¹₂ is thermodynamically more stable than the cis isomer (ca. 5.8 kcal mol^-1). All the new complexes are characterized by NMR (ID and 2D) and single-crystal X-ray diffraction studies. A systematic study of the new complexes in Suzuki coupling reactions revealed the following order of activities: Pd(L¹H ¹)(py)Cl₂ > PdL²(py) > PdL ¹₂.

Full text of DOI:10.1021/om0610041

1
692
Organometallics 2007, 26, 1692-1702
Nonchelate and Chelate Complexes of Palladium(II) with
N-Heterocyclic Carbene Ligands of Amido Functionality
Chuang-Yi Liao, Kai-Ting Chan, Jing-Yao Zeng, Ching-Han Hu, Cheng-Yi Tu, and
Hon Man Lee*
Department of Chemistry, National Changhua UniVersity of Education, Changhua 50058,
Taiwan, Republic of China
ReceiVed NoVember 1, 2006
1
1
2
2
1
2
1
2
The imidazolium ligand precursors [L H H ]Cl and [L H H ]Cl (H ) NHCdO, H ) NCHN) for
2
the potentially bidentate and pincer-type amido-NHC ligands were synthesized in 66-78% yields. Selective
deprotonation of H in these salts with pyridine in the presence of palladium chloride resulted in the
monodentate palladium(II) complexes Pd(L H )(py)Cl
2
1
1
2
1
2 2 2 2 3
and Pd(L H )(py)Cl . The use of K CO in pyridine
or DMF led to the double and triple deprotonations of the ligand precursors, giving the bis-bidentate and
1
2
pincer-type palladium(II) complexes PdL
2
and PdL (py), respectively. Intriguingly, in certain cases, both
1
the cis and the trans isomers of PdL
2
were formed and isolated in pure forms. A theoretical study indicates
is thermodynamically more stable than the cis isomer (ca. 5.8 kcal mol ). All the
that the trans-PdL1
-1
2
new complexes are characterized by NMR (1D and 2D) and single-crystal X-ray diffraction studies. A
systematic study of the new complexes in Suzuki coupling reactions revealed the following order of
1
1
2
1
activities: Pd(L H )(py)Cl
2
2
> PdL (py) > PdL .
anionic functionalized NHC ligands are rare.10 In fact, these
anionic ligands are more common with electropositive metals1
because the anionic donor can act as an anchor to inhibit the
dissociation of the NHC moiety from the metal center.12 In this
work, our controlled deprotonation of the imidazolium precur-
Introduction
1,12
Palladium complexes of N-heterocyclic carbene (NHC)
ligands are attracting a considerable amount of interest because
of their easy accessibility, high thermal stability, and remarkable
1
catalytic activities in various C-C coupling reactions. Much
1
1
2
2
1
2
1
2
sors, [L H H ]Cl and [L H 2H ]Cl (H ) NHCdO, H )
NCHN), afforded various monodentate and mulitdentate NHC
effort has also been devoted to the synthesis of palladium
complexes with functionalized NHC ligands. For example, the
combination of a nitrogen donor, such as pyridine, and an NHC
moiety is of intense interest, and some palladium complexes
with multidentate ligands display intriguing coordination chem-
istry and effective catalytic activities.2 It is generally accepted
that the chelate effect imparted on their metal complexes offers
extra stability for the generation of robust metal complexes,
which are highly desirable for catalytic applications, especially
those requiring harsh reaction conditions. On the other hand,
chelate ring opening is believed to be important during the
catalytic cycle for incoming substrates. Hence, many transition
metal complexes with functionalized NHC ligands for catalytic
(
5) (a) Wang, X.; Liu, S.; Jin, G.-X. Organometallics 2004, 23, 6002.
b) Wang, X.; Liu, S.; Weng, L.-H.; Jin, G.-X. Organometallics 2006, 25,
565. (c) Field, L. D.; Messerle, B. A.; Vuong, K. Q.; Turner, P.
(
3
-4
Organometallics 2005, 24, 4241. (d) Becht, J.-M.; Bappert, E.; Helmchen,
G. AdV. Synth. Catal. 2005, 347, 1495.
(6) (a) Tsoureas, N.; Danopoulos, A. A.; Tulloch, A. A. D.; Light, M.
E. Organometallics 2003, 22, 4750. (b) Wang, A.-E.; Xie, J.-H.; Wang,
L.-X.; Zhou, Q.-L. Tetrahedron 2005, 61, 259. (c) Wang, A.-E.; Zhong, J.;
Xie, J.-H.; Li, K.; Zhou, Q.-L. AdV. Synth. Catal. 2004, 346, 595. (d) Zhong,
J.; Xie, J.-H.; Wang, A.-E.; Zhang, W.; Zhou, Q.-L. Synlett 2006, 8, 1193.
(
e) Gischig, S.; Togni, A. Eur. J. Inorg. Chem. 2005, 4745.
(7) (a) Wang, R.; Twamley, B.; Shreeve, J. M. J. Org. Chem. 2006, 71,
426. (b) Poyatos, M.; Maisse-Fran c¸ ois, A.; Bellemin-Laponnaz, S.; Gade,
L. H. Organometallics 2006, 25, 2634. (c) C e´ sar, V.; Bellemin-Laponnaz,
S.; Gade, L. H. Organometallics 2002, 21, 5204.
purposes reported by others3 and us were based on neutral
-8
9
donors (i.e., hemilabile functionalized NHC ligands).
(8) (a) Dastgir, S.; Coleman, K. S.; Cowley, A. R.; Green, M. L. H.
Herein, we report on palladium(II) complexes with potential
Organometallics 2006, 25, 300. (b) Frøseth, M.; Netland, K. A.; T o¨ rnroos,
K, W.; Dhindsa, A.; Tilset, M. Dalton Trans. 2005, 1664. (c) Steiner, G.;
Krajete, A.; Kopacka, H.; Ongania, K.-H.; Wurst, K.; Preishuber-Pfl u¨ gl,
P.; Bildstein, B. Eur. J. Inorg. Chem. 2004, 2827.
1
2
chelating ligands, L and L , shown in Scheme 1. Our interest
1
2
in L and L stems from the fact that palladium complexes with
(
9) (a) Lee, C.-C.; Ke, W.-C.; Chan, K.-T.; Lai, C.-L.; Hu, C.-H.; Lee,
*
Corresponding author. Tel: +886 4 7232105, ext. 3523. Fax: +886
7211190. E-mail: leehm@cc.ncue.edu.tw.
1) (a) Hermann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290. (b)
H. M. Chem.-Eur. J. 2007, 17, 582. (b) Chiu, P. L.; Lai, C.-L.; Chang,
C.-F.; Hu, C.-H.; Lee, H. M. Organometallics 2005, 24, 6169. (c) Chiu, P.
L.; Lee, H. M. Organometallics 2005, 24, 1692. (d) Lee, H. M.; Zeng, J.
Y.; Hu, C.-H.; Lee, M.-T. Inorg. Chem. 2004, 43, 6822. (e) Lee. H. M.;
Chiu, P. L.; Zeng, J. Y. Inorg. Chim. Acta 2004, 357, 4313. (f) Zeng, J. Y.;
Hsieh, M.-H.; Lee, H. M. J. Organomet. Chem. 2005, 690, 5662.
(10) (a) Douthwaite, R. E.; Houghton, J.; Kariuki, B. M. Chem. Commun.
2004, 698. (b) Perry, M. C.; Cui, X.; Burgess, K. Tetrahedron: Asymmetry
2002, 13, 1969. (c) Chen, T.; Gao, J.; Shi, M. Tetrahedron 2006, 62, 6289.
(11) (a) Spencer, L. P.; Beddie, C.; Hall, M. B.; Fryzuk, M. D. J. Am.
Chem. Soc. 2006, 128, 12531. (b) Mungur, S.; Liddle, S. T.; Wilson, C.;
Sarsfield, M. J.; Arnold, P. L. Chem. Commun. 2004, 2738. (c) Spencer, L.
P.; Winston, S.; Fryzuk, M. D. Organometallics 2004, 23, 3372. (d) Spencer,
L. P.; Fryzuk, M. D. J. Organomet. Chem. 2005, 690, 5788.
4
(
Christmann, U.; Vilar, R. Angew. Chem., Int. Ed. 2005, 44, 366. (c) Hillier,
A. C.; Grasa, G. A.; Viciu, M. S.; Lee, H. M.; Yang, C.; Nolan, S. P. J.
Organomet. Chem. 2002, 653, 69.
(2) (a) Gr u¨ ndemann, S.; Albrecht, M.; Kovacevic, A.; Faller, J. W.;
Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2002, 2163. (b) Tulloch, A.
A. D.; Danopoulos, A. A.; Eastham, G.; Hursthouse, M. B. Dalton Trans.
003, 699.
2
(
3) Peris, E.; Crabtree, R. H. Coord. Chem. ReV. 2004, 248, 2239.
(4) (a) Zeng, F.; Yu, Z. J. Org. Chem. 2006, 71, 5274. (b) Tulloch, A.
A. D.; Danopoulos, A. A.; Tooze, R. P.; Cafferkey, S. M.; Kleinhenz, S.;
Hursthouse, M. B. Chem. Commun. 2000, 1247. (c) McGuinness, D. S.;
Cavell, K. J. Organometallics 2000, 19, 741. (d) Chen, J. C. C.; Lin, I. J.
B. Organometallics 2000, 19, 5113.
(12) Arnold, P. L.; Mungur, S. A.; Blake, A. J.; Wilson, C. Angew. Chem.,
Int. Ed. 2003, 42, 5981.
1
0.1021/om0610041 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 03/03/2007

Nonchelate and Chelate Complexes of Palladium(II)
Organometallics, Vol. 26, No. 7, 2007 1693
Scheme 1
Scheme 2
complexes of palladium, which are characterized by NMR (1D
and 2D) and solid-state structural studies. A systematic study
on these monodentate and mulitdentate complexes provides
evidence that the stable chelate ring of palladium NHC
complexes has a detrimental effect on catalytic activity.
mide. Simple quaternization reactions with imidazole derivatives
afforded 1 in good yields. Precursor 3 was prepared via the
1
imidazole derivative 2. The H NMR spectra of both 1 and 3
exhibit two sharp, downfield signals at 9.5 and 11.0 ppm,
attributed to either the NH or the NCHN protons. Addition of
D2O, for example, to a solution of 1a in DMSO-d6 shows the
collapse of the downfield signal at 11.25 ppm, revealing its NH
proton identity. The more upfield signal is, therefore, assignable
to the NCHN proton. The NMR data of 1 and 3 are comparable
to those reported for several relevant imidazolium precursors.13
Results and Discussion
Preparation of Imidazolium Derivatives. The preparation
1
1
2
1
2
of the ligand precursors [L H H ]Cl (1) (H ) NHCdO, H )
2
1
2
NCHN) and [L H 2H ]Cl (3) is presented in Scheme 2. The
common intermediate for 1 and 3 is 2-chloro-N-phenylaceta-
(13) Rivera, G.; Crabtree, R. H. J. Mol. Catal. A: Chem. 2004, 222, 59.

1
694 Organometallics, Vol. 26, No. 7, 2007
Liao et al.
Scheme 3
Preparation of Monodentate Complexes of Palladium(II).
signal assignment, we carried out a 2D NMR study and HMBC
correlations were found from the two methylene protons (5.49
and 5.85 ppm) to the signal at 151.1 ppm, indicating that this
CH carbon signal (established by DEPT) is accidentally
equivalent to the carbene resonance (Figure 1). The HMBC
experiment also establishes that the more upfield signal at 5.49
ppm is due to the methylene protons between the amido group
and NHC moiety. In contrast, the carbene singlet of 4d is slightly
more upfield at 150.9 ppm, without overlapping with the CH
signal at 151.2 ppm. Notably, these carbene chemical shifts at
ca. 151 ppm are very upfield compared with those in other NHC
A reaction of the ligand precursor 1a or 1d with PdCl2 in
pyridine produced a mixture of palladium(II) complex 4 and
trans-dichlorobis(pyridine)palladium(II) (5) in ca. 1:1 ratio
(
Scheme 3). The synthetic method is similar to that for the
structurally related NHC-PdCl2-3-chloropyridine complexes
reported in a very recent article.1 The difference is that in our
case an extra potassium carbonate was not added in order to
4a
1
avoid further deprotonation of H in 1 leading to the formation
of a chelate complex (vide infra). Our initial attempt to purify
the crude products resulted in crystals of trans-dichlorobis-
pyridine)palladium(II) only.15 Complexes 4a and 4d in pure
complexes of palladium(II) reported in the literature.
16
(
forms (32 and 28% yields, respectively) can be obtained
eventually by subjecting the respective crude mixtures to a
column of silica gel and eluting with 1:1 ethyl acetate-hexane.
These complexes are highly stable toward air and moisture, with
Complex 7 was similarly prepared by reacting the ligand
2
1
2
precursor, [L H H ]Cl, in neat pyridine (Scheme 4). However,
2
attempted purification of the crude product consisting of 7 and
5 by column chromatography was unsuccessful. Crystals of 7
and 5, however, can be obtained from the mixture by vapor
diffusion of ether into its DMF solution. The structure of 7,
1
good solubility in common organic solvents. Their H NMR
spectra in the downfield region show the absence of sharp
signals due to NCHN protons at ca. 9.4 ppm, indicating the
successful formation of carbene complexes. However, the broad
NH signals at 9.04 ppm and signals due to pyridine are observed.
All these NMR data indicate that 4a and 4d are monodentate
2
1
Pd(L H )(py)Cl , was confirmed by subsequent structural study
2
2
on a crystal picked manually.
Preparation of Bidentate and Pincer-Type Complexes of
Palladium(II). Since complexation reactions in pyridine lead
to the preferential deprotonation of the NCHN but not the NH
protons, we sought to add an additional base, K2CO3, in the
1
1
NHC complexes, Pd(L H )(py)Cl2, which were subsequently
confirmed by solid-state structural studies (vide infra). The
assignment of the carbene signal in the 13C{ H} NMR spectrum
of 4a is tricky. According to the DEPT experiment, only three,
instead of the required four, quaternary carbon signals are
observed at 134.6, 137.6, and 164.5 ppm. The downfield signal
can be due to either CdO or the carbene carbon. To clarify the
1
1
1
2
hope of mediating double deprotonation of [L H H ]Cl and triple
2
1
2
deprotonation of [L H 2H ]Cl for the formation of bidentate and
1
2
pincer-type palladium(II) complexes of L and L , respectively.
1
2
The effort indeed produced the neutral PdL 2 (6) and PdL (py)
(
(
8), which were subsequently confirmed by structural studies
vide infra). Markedly, either the cis or trans isomers of 6 can
be successfully isolated by conducting the reactions in different
solvents. For example, using pyridine as solvent leads to pure
cis-6a, whereas switching to DMF yielded a mixture of cis and
trans isomers (see the cis/trans ratio in Scheme 2; the ratio is
(
14) (a) O’Brien, C. J.; Kantchev, E. A. B.; Valente, C.; Hadei, N.; Chass,
G. A.; Lough, A.; Hopkinson, A. C.; Organ, M. G. Chem.-Eur. J. 2006,
2, 4743. (b) Organ, M. G.; Avola, S.; Dubovyk, I.; Hadei, N.; Kantchev,
E. A. B.; O’Brien, C. J. Valente, C. Chem.-Eur. J. 2006, 12, 4749.
15) Under our conditions, 5 crystallizes in a different polymorphic
1
(
structure; see: (a) Liao, C.-Y.; Lee, H. M. Acta Crystallogr. 2006, E62,
m680. (b) Viossat, B.; Dung, N.-H.; Robert, F. Acta Crystallogr. 1993,
C49, 84.
(16) For representative examples: see refs 2b, 4b,c, 6a.

Nonchelate and Chelate Complexes of Palladium(II)
Organometallics, Vol. 26, No. 7, 2007 1695
Figure 1. HMBC NMR spectrum and selected HMBC (HfC) of 4a.
Scheme 4
1
calculated on the basis of the integration values from the H
carbons becomes diastereotopic and therefore displays geminal
splitting. Generally, except in cis-6a, the two diastereotopic
signals due to the methylene spacer of the chelate rings show
a larger difference in chemical shift than those of the dangling
moiety (cis-6a: 0.43 vs 0.85 ppm; trans-6a: 0.86 vs 0.06 ppm;
trans-6b: 0.62 vs 0.30 ppm; trans-6c: 0.66 vs 0.36 ppm; cis-
6d: 0.43 vs 0.17 ppm). In the C{ H} NMR spectra of cis-6,
there are two downfield quaternary carbon signals resonating
closely at 165 and 166 ppm for the cis isomer and at 169 and
170 ppm for the trans isomer, making the assignments of the
carbene and the carbonyl signals uncertain. For unambiguous
signal assignments, we again carry out HMBC experiments,
NMR spectra of the reaction mixture). The pure trans product
of 6 can be obtained in general by simple washing of the mixture
with methanol. Like 4, both cis and trans isomers of 6 are highly
stable and can be stored in air indefinitely. Generally, the cis
isomer displays a much better solubility than the trans product.
For example, while cis-6a dissolves readily in halogenated
1
3
1
1
solvents, trans-6a is only sparingly soluble. The H NMR data
fully support the formation of bis-bidentate complex 6. Both
cis and trans complexes are symmetry-related and display the
diagnostic absence of the broad NH and the NCHN signals. In
each complex, each proton on the two groups of methylene

1696 Organometallics, Vol. 26, No. 7, 2007
Liao et al.
which enable the assignments of the more upfield signals at
163.7 and 165.5 ppm for the carbene carbons in cis-6a and cis-
6d, respectively (Figure 1S in the Supporting Information shows
the HMBC spectrum of cis-6a). In contrast, the carbene signals
are more downfield at 170.5, 170.4, and 170.3 ppm in trans-
6
a, trans-6b, and trans-6c, respectively. Hence, the general
observation is that monodentate NHC complex 4 has the most
upfield carbene resonance (∼151 ppm), followed by the cis
isomer of the bis-bidentate NHC complex 6 (∼164 ppm) and
then its trans isomer (∼170 ppm). It is worthy to note that 6
1
contains two ligands of L per Pd, indicating that the bidentate
ligand has a smaller steric bulk than many other bidentate NHC
ligands that form 1:1 PdL complexes (L ) bidentate NHC
ligand) reported by us17 and others.
18
Pincer-type complexes with, for example, a traditional [PCP]
donor set displayed rich coordination chemistry and catalytic
activities.1 The pincer-type palladium(II) complex of L featur-
9
2
Figure 2. Thermal ellipsoid plot of 4a at the 35% probability level.
Hydrogen atoms are omitted for clarity. Selected bond distances
(Å): Pd1-C6, 1.975(3); Pd1-Cl1, 2.3080(9); Pd1-Cl2, 2.3028-
2
ing a NHC-based [NCN] donor set, PdL (py) (8), was success-
fully prepared by employing similar condition for 6, giving a
pale yellow solid in 77% yield. Again, the absence of NCHN
and NH proton signals indicates the successful coordination of
L on the palladium(II) ion. The H NMR spectrum displays a
singlet for the four methylene protons, in contrast to those in 6.
The carbene signal was observed at 152.7 ppm, which is
significantly upfield than that in 6 but very similar to those in
(
9); Pd1-N1, 2.073(2). Selected bond angles (deg): C6-Pd1-
Cl1, 92.28(9); C6-Pd1-Cl2, 90.91(9); N1-Pd1-Cl1, 88.14(7);
2
1
N1-Pd1-Cl2, 88.82(7); C6-Pd1-N1, 177.28(15); Cl1-Pd1-Cl2,
175.65(4); N4-C6-Pd1, 127.8(2); N3-C6-Pd1, 127.2(2).
4
. An upfield carbene resonance at ca. 150 ppm seems to be
characteristic for a palladium(II) complex with a trans disposi-
tion of pyridine and carbene ligands.2
a,14
Structural Characterizations. Crystals suitable for X-ray
diffraction studies can be grown typically by either vapor
diffusion or slow evaporation from a solution of the new
compounds in highly polar solvents, such as methanol, DMF,
chloroform, and DMSO. Most of the resultant structures (except
4
a and 4d) show incorporation of these polar guest molecules,
which are involved in hydrogen-bonding interactions with the
amido moieties of the ligands. Figures 2-10 show the molecular
structures with selected bond lengths and bond angles listed in
the captions.
Complexes 4a, 4d, and 7 crystallize with their full molecules
in their respective asymmetric units. A comparison of the three
structures shows that the NHC ligand in 4d exerts the largest
trans influence on the pyridine, resulting in the shortest Pd-C
bond of 1.958(3) Å (compared with 1.967(2) Å in 7 and 1.975-
Figure 3. Thermal ellipsoid plot of 4d at the 35% probability level.
Hydrogen atoms are omitted for clarity (the phenyl group and the
pyridine ligand are disordered; only one of the orientation with
0.40 site occupancy is shown for the phenyl group; the major
orientation of the pyridine ligand with 0.60 site occupancy is
shown). Selected bond distances (Å): Pd1-C9, 1.958(3); Pd1-
Cl1, 2.2966(7); Pd1-Cl2, 2.3105(7); Pd1-N4, 2.133(4). Selected
bond angles (deg): C9-Pd1-Cl1, 86.63(8); C9-Pd1-Cl2, 87.53-
(8); N4-Pd1-Cl1, 94.22(13); N4-Pd1-Cl2, 91.98(12); C9-Pd1-
N4, 173.00(16); Cl1-Pd1-Cl2, 173.31(3); N2-C9-Pd1, 128.2(2);
N3-C9-Pd1, 126.1(2).
(
(
3) Å in 4a) and the longest Pd-N bond of 2.133(4) Å
compared with 2.1167(19) Å in 7 and 2.073(2) Å in 4a). An
obvious difference between 4a and 4d is the almost coplanarity
of the pyridine and the heterocyclic ring in 4a (interplanar angle
)
5.3(1)°), whereas the two rings in 4d are closer to orthogonal,
making an angle of 70.3(1)°. Notably, the new polymorph of 5
15
methanol. The structure containing DMF (cis-6d) also crystal-
lizes in space group C2/c, but with a full molecule appearing
in general positions. On the other hand, the structure with
methanol incorporation (cis-6d′) crystallizes in the hexagonal
space group R 3h . The geometric parameters of cis-6d and cis-
also arised from the different orientation of the pyridine rings.
In each of the structures, the NHC moiety is symmetrically
coordinated to the palladium center with the two Pd-C-N
angles almost equal (for example in 4a, the two angles are 127.8-
(
2)° and 127.2(2)°), contrasting those in the chelate complexes
of 6.
Complex cis-6a crystallizes in the monoclinic space group
6d′ are similar (Figure 2S of the Supporting Information depicts
the molecular structure of cis-6d′), but rather unexpectedly,
the latter displays intriguing supramolecular feature (vide infra).
A comparison of the structural data of chelate complexes
with those of nonchelate complexes shows that in the bidentate
mode the NHC moiety coordinates to the metal quite asym-
metrically. As a typical example, the N-C-Pd bond angles in
cis-6a are uneven, with ∠ N2-C1-Pd1 ) 119.69(12)° and
C2/c with one-half of the molecule in the asymmetric unit, and
the palladium center is positioned at the special position of 2-fold
symmetry. Complex cis-6d can be crystallized from DMF and
(
17) Lee, H. M.; Lu, C. Y.; Chen, C. Y.; Chen, W. L.; Lin, H. C.; Chiu,
P. L.; Cheng, P. Y. Tetrahedron 2004, 60, 5807.
18) For examples: see (a) Herrmann, W. A.; Schwarz, J. Organome-
(
∠
N1-C1-Pd1 ) 135.37(12)°, a difference of ca. 16°. The
tallics 1999, 18, 4082. (b) Hermann, W. A.; Reisinger, C.-P.; Spiegler, M.
J. Organomet. Chem. 1998, 557, 93.
Pd-C bonds in cis-6a (1.9662(15) Å) are similar to those in
4a (1.975(3) Å).
(19) van der Boom, M. E.; Milstein, D. Chem. ReV. 2003, 103, 1759.

Nonchelate and Chelate Complexes of Palladium(II)
Organometallics, Vol. 26, No. 7, 2007 1697
Figure 6. Thermal ellipsoid plot of trans-6b‚2MeOH at the 35%
probability level. Hydrogen atoms (except those on the guest
methanol molecules) are omitted for clarity. Selected bond distances
(
Å): Pd1-C1, 2.016(3); Pd1-N3, 2.057(3). Selected bond angles
(deg): C1-Pd1-N3, 85.16(12); C1-Pd1-N3A, 94.84(12); C1-
Pd1-C1A, 180.0; N3-Pd1-N3A, 180.0; N1-C1-Pd1, 135.2(3);
N2-C1-Pd1, 119.1(2).
Figure 4. Thermal ellipsoid plot of trans-6a‚4DMSO at the 35%
probability level. Hydrogen atoms (except those on the guest DMSO
molecules) are omitted for clarity. Selected bond distances (Å):
Pd1-C1, 2.020(4); Pd1-N3, 2.051(4). Selected bond angles
(
deg): C1-Pd1-N3, 86.24(16); C1-Pd1-N3A, 93.76(16); C1-
Pd1-C1A, 179.999(1); N3-Pd1-N3A, 180.0; N1-C1-Pd1,
36.9(3); N2-C1-Pd1, 118.3(3).
1
3
Figure 7. Thermal ellipsoid plot of trans-6c‚2CHCl at the 35%
probability level. Hydrogen atoms (except those on the guest
chloroform molecules) are omitted for clarity. Selected bond
distances (Å): Pd1-C1, 2.013(3); Pd1-N3, 2.059(2). Selected
bond angles (deg): C1-Pd1-N3, 86.10(10); C1-Pd1-N3A,
9
3.90(10); C1-Pd1-C1A, 180.0; N3-Pd1-N3A, 180.0; N1-C1-
Pd1, 135.4(2); N2-C1-Pd1, 119.24(19).
(
13) Å in cis-6a. From the molecular structures of 6, it can be
Figure 5. Thermal ellipsoid plot of cis-6a‚2MeOH at the 35%
probability level. Hydrogen atoms (except those on the guest
methanol molecules) are omitted for clarity (the two phenyl groups
are disordered; only the major orientations with 0.60 site occupancy
are shown). Selected bond distances (Å): Pd1-C1, 1.9662(15);
Pd1-N3, 2.0870(13). Selected bond angles (deg): C1-Pd1-N3,
seen that the methylene spacers between the N-heterocyclic ring
and the phenyl(naphthyl) ring are essential for the successful
formation of these 1:2 Pd:L complexes. Complex 8 was solved
in the space group P21/c with a full molecule in its asymmetric
unit. The pyridine makes an angle of 36.5(8)° with the
heterocyclic ring. The Pd-C distance of 1.924(3) Å is the
shortest among all the palladium complexes.
1
8
5.77(6); C1-Pd1-C1A, 95.42(9); N3-Pd1-N3A, 93.07(8); C1-
Pd1-N3A, 178.10(6); N1-C1-Pd1, 135.37(12); N2-C1-Pd1,
119.69(12).
Open-Channel Network. The supramolecular feature for the
cis isomer of 6 is worthy of mentioning. While the packing of
the trans isomer shows no special feature, the cis disposition of
the amide carbonyl groups and the presence of guest methanol
molecules allow the assembly of an open-channel coordina-
tion network via intermolecular hydrogen bonds of the type
C-H‚‚‚O. As depicted in Figure 11, the structure of cis-6a‚
2MeOH consists of open channels along the [001] direction.
Unfortunately, the channels are self-penetrated by phenyl groups
of the amido moieties. No such channel structure was observed
Both trans-6a and trans-6c crystallize in space group P 1h ,
whereas trans-6b crystallizes in P21/c. In each case, the
palladium center is situated in a special position of i symmetry
and the two trans NHC moieties are coplanar. The Pd-carbene
bond distance in the trans isomer is generally longer than those
in the cis isomer and in 4. For example, the distance is 2.020-
(
(
4) Å in trans-6a, longer than those of 1.9662(15) and 1.975-
3) Å in cis-6a and 4a, respectively. The Pd-N bond of 2.051(4)
Å in trans-6a is, however, slightly shorter than that of 2.0870-

1698 Organometallics, Vol. 26, No. 7, 2007
Liao et al.
Figure 10. Thermal ellipsoid plot of 8‚2H
2
O at the 35% probability
Figure 8. Thermal ellipsoid plot of cis-6d‚0.5DMF at the 35%
probability level (only the major orientation of the disordered
naphthyl ring, C27-C36, is shown). Hydrogen atoms and the
disordered DMF solvent are omitted for clarity. Selected bond
distances (Å): Pd1-C1, 1.972(2); Pd1-C23, 1.972(2); Pd1-N3,
level. Hydrogen atoms (except those on the guest water molecules)
are omitted for clarity. Selected bond distances (Å): Selected bond
distances: Pd1-C1, 1.924(3); Pd1-N3, 2.051(3); Pd1-N4, 2.053-
(
(
3); Pd1-N5, 2.106(3). Selected bond angles: C1-Pd1-N3, 88.06-
12); C1-Pd1-N4, 87.89(12); N3-Pd1-N5, 93.16(11); N4-Pd1-
2
.0851(19); Pd1-N6, 2.0818(17). Selected bond angles (deg): C1-
N5, 90.91(10); C1-Pd1-N5, 178.44(12); N3-Pd1-N4, 175.90(11);
N1-C1-Pd1, 126.9(2); N2-C1-Pd1, 126.5(2).
Pd1-N3, 86.45(8); C1-Pd1-C23, 95.50(9); C23-Pd1-N6, 84.50-
(
8); C1-Pd1-N6, 177.70(8); C23-Pd1-N3, 177.01(9); N3-Pd1-
N6, 93.46(7); N1-C1-Pd1, 133.51(16); N2-C1-Pd1, 120.89(16).
stability of the cis and trans isomers of 6a. The optimized
geometrical parameters for cis-6a and trans-6a are in fine
agreement with those from the structural data. For example,
the computed Pd-carbene distances in cis-6a and trans-6a are
2.019 and 2.043 Å, respectively, which are comparable to those
of 1.9662(15) and 2.020(4) Å from their structures. With the
CPCM model, the energy of reaction for converting cis-6a to
trans-6a is -5.8 kcal/mol, indicating that the latter isomer is
thermodynamically more stable. A variable-temperature NMR
study for cis-6a in DMF-d7 was performed to see if cis-6a can
be converted to the thermodynamic product. However, no
reaction occurred even when the solution was heated to 95 °C,
reflecting the kinetic stability of cis-6a below this temperature.
Catalytic Studies. The palladium(II) complexes were tested
in Suzuki coupling reactions of aryl bromides with phenylbo-
ronic acid (Table 3). The data clearly show that the monodentate
NHC complex 4 is most reactive (entries 1-6). The tridentate
complex 8 gave intermediate activities (entries 11-13), whereas
Figure 9. Thermal ellipsoid plot of 7‚2DMF at the 35% probability
level. Hydrogen atoms (except those on the nitrogen atoms) are
omitted for clarity. Selected bond distances (Å): Pd1-C1, 1.967-
(
2); Pd1-Cl1, 2.2973(6); Pd1-Cl2, 2.2953(6); Pd1-N6, 2.1167-
19). Selected bond angles (deg): C1-Pd1-Cl1, 88.85(7); C1-
6
is the least efficient (entries 7-10). In general, the activities
(
of 4, 6, and 8 are inferior to other palladium(II) catalysts based
Pd1-Cl2, 88.37(7); N6-Pd1-Cl1, 92.15(5); N6-Pd1-Cl2,
on functionalized NHC ligands with neutral donors, such as
9
0.64(6); C1-Pd1-N6, 178.96(9); Cl1-Pd1-Cl2, 176.98(3); N1-
6
4
phosphine-NHC ligands and pyridine-NHC ligands. In these
catalysts with neutral NHC ligands, generation of vacant coor-
dination sites via decoordination from the neutral donor atoms
is believed to be important (i.e., the ligands are hemilabile).
However, the anionic donor in an anionic functionalized NHC
C1-Pd1, 127.85(19); N2-C1-Pd1, 126.55(19).
in the structure of cis-6d‚DMF, bearing similar N-naphthyl-
methyl groups. The presence of a guest methanol seems to be
crucial, and we were hoping that crystals of cis-6d obtained
from methanol would display similar channel structure. Indeed,
the structure of cis-6d‚MeOH (cis-6d′) contains, in contrast to
that in cis-6a‚2MeOH, a honeycomb motif with hydrophobic
channels parallel to the c-axis (see also Figure 11). The channels
consist of phenyl and naphthyl rings of the ligands with the
channel diameter of about 6.3 Å. The honeycomb motif derived
1
2
ligand, such as L and L , provides an anchor effect on the
metal ion, such that availability of vacant sites becomes
impossible and the stable chelate rings of the complex are most
probably leading to the poor catalytic activities observed,
especially in the bis-bidentate complex 6. Interestingly, for an
electropositive metal ion with an anionic functionalized NHC
ligand, dissociation of the NHC moiety becomes favorable (i.e.,
hard-soft mismatch), which has been observed, for example,
20
from compounds containing amide functionality is known; for
example, an intriguing infinite rosette structure was derived from
2
1
trimesic amide in methanol.2
0a
in a uranium(IV) alkoxy-NHC complex. However, it is
unlikely that such NHC dissociation can occur in palladium(II)
complexes 6 and 8. Recently, structurally relevant complexes
of the type NHC-PdCl2-3-chloropyridine have been shown
Relative Stability of Cis and Trans Isomers of 6. A DFT
calculation was carried out to gain insight into the relative
(20) (a) Palmans, A. R. A.; Vekemans, J. A. J. M. Kooijman, H.; Spek,
A. L.; Meijer, E. W. Chem. Commun. 1997, 2247. (b) Muthu, S.; Yip, J.
H. K.; Vittal, J. J. J. Chem. Soc., Dalton Trans. 2002, 4561.
(21) Arnold, P. L.; Blake, A. J.; Wilson, C. Chem.-Eur. J. 2005, 11,
6095.

Nonchelate and Chelate Complexes of Palladium(II)
Organometallics, Vol. 26, No. 7, 2007 1699
Figure 11. Left: open channels in cis-6a‚2MeOH. Right: hydrophobic channels in cis-6d‚MeOH.
Table 1. Crystallographic Data of 4-6
4a
4d
trans-6a‚4(C2H6OS)
cis-6a‚2(CH3OH)
trans-6b‚2(CH3OH)
empirical formula
C23H22Cl2N4OPd
C27H24Cl2N4OPd
C36H32N6O2Pd
C36H32N6O2Pd
‚2(CH3OH)
751.16
monoclinic
C2/c
16.6080(4)
15.6949(4)
14.2159(4)
90
100.240(2)
90
C36H30F2N6O2Pd
‚2(CH3OH)
787.14
monoclinic
P21/c
10.9128(3)
17.8089(5)
9.3293(3)
90
110.505(2)
90
‚
4(C2H6OS)
fw
547.77
orthorhombic
P212121
5.1199(8)
13.818(2)
32.194(5)
90
90
90
2277.5(6)
1.597
597.80
monoclinic
P21/c
16.5525(11)
16.4142(11)
9.2128(6)
90
97.8550(10)
90
2479.6(3)
1.601
999.59
triclinic
P1h
cryst syst
space group
a, Å
b, Å
c, Å
9.4419(19)
11.375(3)
12.702(3)
65.688(4)
87.358(5)
69.092(5)
1153.2(5)
1.439
R, deg
â, deg
γ, deg
3
V, Å
3646.51(16)
1.368
1698.23(9)
1.539
-
3
Dc, mg m
T, K
Z
150(2)
4
150(2)
4
150(2)
1
150(2)
4
150(2)
2
no. of unique data
5854
6397
5255
4676
4367
no. of params refined
284
0.0355
0.0606
364
0.0354
0.0939
281
0.0680
0.1788
248
0.0264
0.0729
234
0.0444
0.1340
a
R1 [I > 2σI]
b
wR2 (all data)
a
R1 ) ∑(||Fo| - |Fc||)/∑|Fo|. wR2 ) [∑(|Fo| - |Fc| ) /∑(Fo )]1/2.
b
2
2 2
2
Table 2. Crystallographic Data of 6-8
trans-6c‚2(CHCl3)
cis-6d‚0.5(C3H7NO)
cis-6d‚CH3OH (cis-6d′)
7‚2(C3H7NO)
8‚2(H2O)
empirical formula
C38H36N6O4Pd
C44H36N6O2Pd
‚0.5(C3H7NO)
823.77
monoclinic
C2/c
28.8517(14)
17.3518(8)
19.8506(17)
90
130.4840(10)
90
C44H36N6O2Pd
‚CH3OH
819.23
hexagonal
R3h
31.688(9)
31.688(9)
22.273(7)
90
90
120
19369(10)
1.264
C24H23Cl2N5O2Pd
‚2(C3H7NO)
736.97
monoclinic
P21/n
9.0303(2)
23.7591(7)
15.2864(4)
90
94.880(2)
90
C24H21N5O2Pd
‚2(H2O)
553.89
monoclinic
P21/c
8.3775(9)
29.923(3)
9.4386(10)
90
94.538(2)
90
2358.6(4)
1.560
‚2(CHCl3)
fw
985.86
triclinic
P1h
cryst syst
space group
a, Å
b, Å
c, Å
9.4368(3)
10.2941(3)
13.0276(4)
70.192(2)
75.905(2)
63.1950(10)
1056.51(6)
1.550
R, deg
â, deg
γ, deg
3
V, Å
7558.5(8)
1.442
3267.84(15)
1.498
-
3
Dc, mg m
T, K
Z
150(2)
1
150(2)
8
150(2)
18
150(2)
4
150(2)
4
no. of unique data
4702
9732
8460
8047
5274
no. of params refined
260
0.0412
0.0957
557
0.0327
0.0986
541
0.0705
0.2141
401
0.0351
0.0845
323
0.0387
0.0843
a
R1 [I > 2σI]
b
wR2 (all data)
a
R1 ) ∑(||Fo| - |Fc||)/∑|Fo|. wR2 ) [∑(|Fo| - |Fc| ) /∑(Fo )]1/2.
b
2
2 2
2
to be highly effective in Suzuki and Negishi cross-coupling
NCHN) and successfully prepared the monodentate complexes
1
4
1
1
2
1
reactions. The inferior catalytic activities of 4 compared with
those of NHC-PdCl2-3-chloropyridine can also be attributed
to the formation of chelate complexes of the type 6, under the
basic catalytic condition.
Pd(L H )(py)Cl2 (4) and Pd(L H 2)(py)Cl2 (7), the bis-bidentate
1
2
complex PdL (6), and the pincer-type complex PdL (py) (8)
2
with appropriate ligand precursors under different basic condi-
tions. Both the cis and trans isomers of 6 were formed in certain
1
cases, and a DFT study indicates that the trans-PdL 2 (6a) is
Conclusions
thermodynamically more stable than the cis isomer (ca. 5.8 kcal
-
1
In summary, we synthesized the imidazolium precursors
mol ). A systematic study of the new complexes in Suzuki
coupling reactions afforded the following order of catalytic
1
1
2
2
1
2
1
2
[
L H H ]Cl (1) and [L H 2H ]Cl (3) (H ) NHCdO, H )

1
700 Organometallics, Vol. 26, No. 7, 2007
Liao et al.
Table 3. Suzuki Coupling with Aryl Bromidesa
Anal. Calcd for C18
H
17
N
3
FClO: C, 62.52; H, 4.96; N, 12.15.
1
Found: C, 62.30; H, 5.24; N, 12.15. H NMR (DMSO-d
6
): δ 5.30
), 7.08 (t, JHH ) 7.2 Hz,
H, p-Ph-H), 7.26-7.35 (m, 4H, Ar-H and m-Ph-H), 7.54 (t, JHH
HF ) 6.9 Hz, 2H, Ar-H), 7.64 (d, JHH ) 7.2 Hz, 2H, o-Ph-H),
.82 (s, 1H, imi-H), 7.86 (s, 1H, imi-H), 9.38 (s, 1H, NCHN), 11.09
(
1
J
7
2 2
s, 2H, CH CdO), 5.51 (s, 2H, PhCH
)
entry
X
R
yield (%)
1
2
3
4
5
6
7
8
9
4a
4d
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
COMe
Me
OMe
COMe
Me
OMe
COMe
COMe
COMe
COMe
COMe
Me
100
73
79
97
68
56
5
13
1
(s, 1H, NH). C{ H} NMR (DMSO-d
6 2 2
): δ 51.5 (CH ), 51.9 (CH ),
116.3 (d, JCF ) 21.6 Hz, CH), 119.6 (CH), 122.2 (CH), 124.1 (CH),
2
124.8 (CH), 129.2 (CH), 131.2 (CH), 131.6 (CH C), 138.0 (CH),
138.9 (OdCNC), 159.2 (d, JCF ) 102.3 Hz, C-F), 164.1 (CdO).
Synthesis of 1c. The compound was synthesized following a
cis-6a
trans-6a
cis-6d
trans-6b
8
4
9
3
procedure similar to that for 1a. A mixture of 1-(4-methoxybenzyl)-
1H-imidazole (3.00 g, 15.90 mmol) and 2-chloroacetanilide (2.70
g, 15.90 mmol) was used. Yield: 3.75 g, 66%. Mp: 200-202 °C.
10
11
12
13
38
20
17
Anal. Calcd for C19
20 3 2
H N ClO : C, 63.77; H, 5.63; N, 11.74.
1
Found: C, 63.93; H, 5.48; N, 11.72. H NMR (DMSO-d
6
): δ 3.75
CdO), 5.45 (s, 2H, PhCH ), 6.98
d, JHH ) 8.1 Hz, 2H, Ar-H), 7.07 (t, 1H, JHH ) 7.5 Hz, p-Ph-H),
.31 (t, JHH ) 7.5 Hz, 2H, m-Ph-H), 7.45 (d, JHH ) 7.5 Hz, 2H,
o-Ph-H), 7.67 (d, JHH ) 8.1 Hz, 2H, Ar-H), 7.83 (s, 1H, imi-H),
OMe
3
(s, 3H, OCH ), 5.35 (s, 2H, CH
2
2
a
Reaction conditions: 1 mmol of aryl bromides, 1.5 mmol of PhB(OH)2,
.0 mmol of Cs2CO3 as base, 1 mol % of catalyst, 3 mL of 1,4-dioxane, 80
C, GC yield.
(
7
2
°
7
.87 (s, 1H, imi-H), 9.45 (s, 1H, NCHN), 11.32 (s, 1H, NH).
activities: 4 > 8 > 6. Our study reinforces the idea of
incorporation of neutral donors, rather than anionic donors, in
hemilabile functionalized NHC ligands for effective activities
in palladium-catalyzed CC coupling reactions.
1
3
1
C{ H} NMR (DMSO-d
19.6 (CH), 122.1 (CH), 124.7 (CH), 127.2 (CH
30.6 (CH), 137.8 (CH), 139.0 (OdCNC), 156.0 (C-O), 164.2
6
): δ 51.8 (CH
2 2
), 55.6 (CH ), 114.8 (CH),
1
1
2
C), 129.2 (CH),
(CdO).
Synthesis of 1d. The compound was synthesized following a
procedure similar to that for 1a. A mixture of 1-naphthalen-1-
ylmethyl-1H-imidazole (4.60 g, 22.0 mmol) and 2-chloroacetanilide
Experimental Section
General Procedures. All reactions were performed under a dry
nitrogen atmosphere using standard Schlenk techniques. All solvents
used were purified according to standard procedures.22 Com-
mercially available chemicals were purchased from Aldrich or
(
3.70 g, 22.0 mmol) was used. Yield: 6.51 g, 78%. Mp: 218-220
°C. Anal. Calcd for C H N ClO: C, 69.93; H, 5.33; N, 11.12.
22 20
3
1
6
Found: C, 69.29; H, 5.63; N, 10.94. H NMR (DMSO-d ): δ 5.31
1
13
1
(s, 2H, CH CdO), 6.05 (s, 2H, PhCH ), 7.07 (t, J ) 7.5 Hz,
Acros. H and C{ H} NMR spectra were recorded at 300.13 and
5.48 MHz, respectively, on a Bruker AV-300 spectrometer.
2
2
HH
7
1H, p-Ph-H), 7.32 (t, JHH ) 7.5 Hz, 2H, m-Ph-H), 7.53-7.66 (m,
1
13
6H, Np-H), 7.85 (s, 1H, imi-H), 7.88 (s, 1H, imi-H), 8.03 (d, JHH
Chemical shifts for H and C spectra were recorded in ppm relative
1
13
) 7.5 Hz, 2H, o-Ph-H), 8.19 (d, JHH ) 7.8 Hz, 1H, Np-H), 9.40
3
to the residual proton of CDCl ( H: 7.24 ppm; C: 77.0 ppm)
1
13
(s, 1H, NCHN), 11.17 (s, 1H, NH). 13C{
1
H} NMR (DMSO-d ): δ
and DMSO-d
6
( H: 2.50 ppm; C: 39.5 ppm). Elemental analyses
6
and ES-MS mass spectra were performed on a Heraeus CHN-OS
rapid elemental analyzer and a Finnigan/Thermo Quest MAT 95XL,
respectively, at the Instruments Center of National Chung Hsing
University, Taiwan. The syntheses of 1-benzyl-1H-imidazole, 1-(4-
fluorobenzyl)-1H-imidazole, 1-(4-methoxybenzyl)-1H-imidazole,
and 1-naphthalen-1-ylmethyl-1H-imidazole were according to the
literature procedures.17 2-Chloroacetanilide and 2-imidazol-1-yl-
N-phenylacetamide were prepared by following related literature
procedures23 (see Supporting Information for additional details).
Synthesis of 1a. A mixture of 1-benzyl-1H-imidazole (1.06 g,
2 2
50.3 (CH ), 52.0 (CH ), 119.6 (CH), 122.7 (CH), 123.5 (CH), 124.1
(CH), 124.7 (CH), 126.1 (CH), 126.8 (CH), 127.6 (CH), 127.9 (CH),
129.2 (CH), 130.0 (CH), 130.7 (quaternary C), 130.9 (quaternary
2
C), 133.8 (CH C), 138.3 (CH), 139.0 (OdCNC), 164.2 (CdO).
Synthesis of 3. The compound was synthesized following a
procedure similar to that for 1a. A mixture of 2-imidazol-1-yl-N-
phenylacetamide (0.57 g, 2.90 mmol) and 2-chloroacetanilide (0.49
g, 2.90 mmol) was used. Yield: 0.770 g, 73%. Mp: 188-190 °C.
Anal. Calcd for C H N O Cl: C, 61.54; H, 5.16; N, 15.11.
1
9
19
4
2
1
Found: C, 61.19; H, 5.24; N, 15.08. H NMR (DMSO-d ): δ 5.35
6
6
(
.70 mmol) and 2-chloroacetanilide (1.13 g, 6.70 mmol) in THF
30 mL) was heated at 70 °C for 2 days. After cooling, the white
solid formed was filtered, washed with THF, and dried under
(s, 4H, CH CdO), 7.09 (t, J ) 7.5 Hz, 2H, p-Ph-H), 7.34 (t,
2
HH
JHH ) 7.5 Hz, 4H, m-Ph-H), 7.64 (d, JHH ) 7.5 Hz, 4H, o-Ph-H),
7.82 (s, 2H, imi-H), 9.25 (s, 1H, NCHN), 10.94 (s, 1H, NH).
13
1
vacuum. Yield: 1.70 g, 77%. Mp: 206-208 °C. Anal. Calcd for
6 2
C{ H} NMR (DMSO-d ): δ 51.8 (CH ), 119.7 (CH), 123.8 (CH),
C
5
5
J
18
H
18
N
3
OCl: C, 65.95; H, 5.53; N, 12.82. Found: C, 66.11; H,
124.2 (CH), 129.3 (CH), 138.9 (NCHN), 139.1 (OdCNC), 164.1
(CdO).
1
.49; N, 12.55. H NMR (DMSO-d
6 2
): δ 5.34 (s, 2H, CH CdO),
.54 (s, 2H, PhCH ), 7.07 (t, JHH ) 7.4 Hz, 1H, p-Ph-H), 7.32 (t,
2
Synthesis of 4a. A mixture of 1a (0.110 g, 0.350 mmol) and
HH ) 7.4 Hz, 2H, m-Ph-H), 7.40-7.44 (m, 5H, Ph-H), 7.66 (d, JHH
PdCl
2
(0.061 g, 0.350 mmol) in pyridine (15 mL) was heated at
)
7.8 Hz, 2H, o-Ph-H), 7.84 (s, 1H, imi-H), 7.88 (s, 1H, imi-H),
1
00 °C overnight. After cooling, the solvent was removed com-
.46 (s, 1H, NCHN), 11.25 (s, 1H, NH). 13C{ H} NMR (DMSO-
): δ 51.9 (CH ), 52.3 (CH ), 119.6 (CH), 122.3 (CH), 124.1 (CH),
24.8 (CH), 128.7 (CH), 129.1 (CH), 129.2 (CH), 129.4 (CH), 135.3
C), 138.0 (CH), 138.9 (OdCNC), 164.1 (CdO).
Synthesis of 1b. The compound was synthesized following a
procedure similar to that for 1a. A mixture of 1-(4-fluorobenzyl)-
H-imidazole (6.02 g, 34.2 mmol) and 2-chloroacetanilide (5.79
g, 34.2 mmol) was used. Yield: 9.02 g, 76%. Mp: 185-190 °C.
1
9
d
1
pletely under vacuum. The residue was extracted with dichlo-
romethane (25 mL), and the solution was filtered through a plug
of Celite. The solvent was completely removed under vacuum to
give a crude product, which was then purified by subjecting it to
a silica gel column and eluting with 1:1 ethyl acetate-hexane. The
first band afforded pure 4a as a pale yellow solid. Yield: 0.062 g,
6
2
2
(CH
2
1
3
2%. Mp: 210 °C. Anal. Calcd for C23
H, 4.05; N, 10.23. Found: C, 50.04; H, 3.79; N, 10.54. H NMR
CDCl ): δ 5.49 (s, 2H, CH CdO), 5.85 (s, 2H, PhCH ), 6.81 (d,
HH ) 2.1 Hz, 1H, imi-H), 7.05-7.10 (m, 2H, imi-H and Ph-H),
22 4 2
H N OPdCl : C, 50.43;
1
(
J
7
3
2
2
(
22) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory
Chemicals, 5th ed.; Elsevier Science: Burlington, 2003.
23) Tomapatanaget, B.; Tuntulani, T.; Wisner, J. A.; Beer, P. D.
Tetrahedron Lett. 2004, 45, 663.
.24 (t, JHH ) 8.1 Hz, 2H, Py-H), 7.32-7.41 (m, 5H, Ph-H), 7.48-
7.50 (m, 2H, Ph-H), 7.65 (d, JHH ) 8.6 Hz, 2H, Ph-H), 7.78 (t, JHH
(

Nonchelate and Chelate Complexes of Palladium(II)
7.7 Hz, 1H, Py-H), 8.95 (m, 2H, o-Py-H), 9.04 (br s, 1H, NH).
Organometallics, Vol. 26, No. 7, 2007 1701
)
J
HH ) 1.8 Hz, 2H, imi-H), 7.35-7.45 (m, 10H, Ph-H), 7.51 (d, JHH
1
3
1
13
1
C{ H} NMR (CDCl
22.4 (CH), 122.9 (CH), 124.5 (CH), 124.6 (CH), 128.7 (CH), 128.9
CH), 129.0 (CH), 134.6 (CH C), 137.6 (OdCNC), 138.3 (CH),
51.1 (overlapping CH and NCN), 164.5 (CdO). Crystals for
3
): δ 54.8 (CH
2
), 55.6 (CH
2
), 119.9 (CH),
) 7.8 Hz, 4H, Ph-H). C{ H} NMR (DMSO-d
58.0 (CH
127.0 (CH), 127.8 (CH), 128.2 (CH), 129.2 (CH), 138.6 (CH
2
6
): δ 52.1 (ArCH
CdO), 121.4 (CH), 121.7 (CH), 122.2 (CH), 125.4 (CH),
C),
2
),
1
(
1
2
2
150.9 (OdCNC), 169.3 (CdO), 170.5 (NCN). Crystals for struc-
tural determination were obtained by slow evaporation from a
DMSO solution containing the compound.
structural determination were obtained by slow evaporation from
a chloroform solution containing the compound.
Synthesis of 4d. The compound was prepared following a
procedure similar to that for 4a. A mixture of 1d (0.140 g, 0.370
Synthesis of trans-6b. The compound was prepared following
a similar procedure of trans-6a. A mixture of 1b (0.200 g, 0.580
mmol) and PdCl
2
(0.065 g, 0.370 mmol) was used. The eluent used
2 2 3
mmol), PdCl (0.0540 g, 0.300 mmol), and K CO (0.170 g, 1.21
was ethyl acetate-hexane (4:6). Pure 4d was obtained as a pale
yellow solid. Yield: 0.061 g, 28%. Mp: 224 °C. Anal. Calcd for
mmol) was used. A minor modification is that the reaction had to
be conducted at a lower temperature of 55 °C. Heating the mixture
at 65 °C as stated for trans-6a resulted in decomposition products
as evidenced by the formation Pd black. Following the same workup
procedure for trans-6a, the crude product obtained was a mixture
of cis and trans isomers in a ratio of 43:57. Pure trans-6b as a
white solid can be obtained by washing the crude solid with
methanol. Yield: 0.032 g, 15%. Mp: 283-285 °C. Anal. Calcd
C
27
H
24
N
4
OPdCl
H, 4.49; N, 9.29. H NMR (CDCl
.28 (s, 2H, PhCH ), 6.57 (d, JHH ) 2.1 Hz, 1H, imi-H), 6.99 (d,
HH ) 2.1 Hz, 1H, imi-H), 7.07 (t, JHH ) 7.5 Hz, 1H, Ph-H or
2
: C, 54.24; H, 4.05; N, 9.37. Found: C, 54.65;
1
3 2
): δ 5.51 (s, 2H, CH CdO),
6
J
2
Np-H), 7.28 (t, JHH ) 7.5 Hz, 2H, Py-H), 7.36-7.41 (m, 2H, Ph-H
or Np-H), 7.46-7.68 (m, 6H, Ph-H or Np-H), 7.80 (tt, JHH ) 7.5,
1.5 Hz, 1H, Py-H), 7.87-7.93 (m, 2H, Ph-H or Np-H), 8.21-8.24
for C36
H
30
N
6
O
2
F
2
3
Pd‚2CH OH: C, 57.98; H, 4.87; N, 10.68.
1
(
m, 1H, Ph-H or Np-H), 9.00 (m, 2H, o-Py-H), 9.04 (br s, 1H,
Found: C, 57.36; H, 4.21; N, 10.45. H NMR (DMSO-d
6
): δ 4.38
CdO), 4.90 (d, JHH ) 14.6 Hz,
CdO), 5.20
Ph), 6.74 (t, JHH ) 7.2 Hz, 2H,
13
1
2
2
NH). C{ H} NMR (CDCl
19.9 (CH), 121.9 (CH), 122.7 (CH), 123.9 (CH), 124.6 (CH), 124.7
CH), 125.3 (CH), 126.4 (CH), 127.4 (CH), 128.8 (CH), 129.1 (CH),
29.5 (quaternary C), 130.1 (CH), 131.5 (quaternary C), 133.9
CH C), 137.7 (OdCNC), 138.4 (CH), 150.9 (NCN), 151.2 (CH),
64.6 (CdO). Crystals for structural determination were obtained
3
): δ 53.2 (PhCH
2
2
), 55.9 (CH CdO),
(d, JHH ) 14.6 Hz, 2H, NCH
a
H
b
2
1
(
1
(
2H, NCH
c
H
d
Ph), 5.00 (d, JHH ) 14.6 Hz, 2H, NCH
H
a b
2
(d, JHH ) 14.6 Hz, 2H, NCH
c
H
d
Ph-H), 6.95 (t, JHH ) 7.2 Hz, 4H, Ph-H), 7.10 (s, 2H, imi-H), 7.24-
2
7.29 (m, 4H, Ph-H), 7.32 (s, 2H, imi-H), 7.37-7.42 (m, 4H, Ph-H),
7.50 (d, JHH ) 8.1 Hz, 4H, Ph-H). 13C{ H} NMR (DMSO-d
1
1
6
): δ
by vapor diffusion of diethyl ether into a chloroform solution
containing the compound.
51.3 (ArCH
121.6 (CH), 122.2 (CH), 125.4 (CH), 127.0 (CH), 130.0 (CH), 130.1
CH), 134.8 (CH C), 150.8 (OdCNC), 163.8 (d, JCF ) 244.1 Hz,
2 2
), 58.0 (CH CdO), 116.0 (d, JCF ) 21.6 Hz, CH),
(
2
Synthesis of cis-6a. A mixture of 1a (0.110 g, 0.330 mmol),
C-F), 169.3 (CdO), 170.4 (NCN). Crystals for structural determi-
nation were obtained by vapor diffusion of pentane into a methanol
solution containing the compound.
2 2 3
PdCl (0.030 g, 0.170 mmol), and K CO (0.090 g, 0.670 mmol)
in pyridine (5 mL) was heated at 80 °C overnight. After cooling,
the solvent was removed completely under vacuum. The residue
was redissolved in dichloromethane (15 mL), and the organic layer
Synthesis of trans-6c. The compound was prepared following
a procedure similar to that for trans-6a. A mixture of 1c (0.170 g,
4
was washed twice with water and dried with anhydrous MgSO .
The volume of the solvent was reduced to ca. 3 mL under vacuum.
Addition of diethyl ether gave a white solid, which was filtered,
washed with diethyl ether, and dried under vacuum. Yield: 0.060
2 2 3
0.470 mmol), PdCl (0.0420 g, 0.230 mmol), and K CO (0.130 g,
0.940 mmol) was used. A minor modification is the reaction
temperature of 60 °C. Heating the mixture at 65 °C as stated for
trans-6a resulted in decomposition products as evidenced by the
formation Pd black. Following the same workup procedure for
trans-6a, the crude product obtained was a mixture of cis and trans
isomers in a ratio of 37:63. Pure trans-6c as a white solid can be
obtained by washing the crude solid with methanol. Yield: 0.026
g, 53%. Mp: 280-282 °C. Anal. Calcd for C36
32 6 2
H N O Pd: C,
1
6
2.93; H, 4.69; N, 12.23. Found: C, 62.14; H, 4.44; N, 12.08. H
2
NMR (DMSO-d
6
): δ 4.24 (d, JHH ) 15.0 Hz, 2H, NCH
a
2
H
b
Cd
Ph), 4.67 (d, JHH
CdO), 5.22 (d, JHH ) 15.0 Hz, 2H, NCH
Ph), 6.53 (d, JHH ) 7.5 Hz, 4H, Ph-H), 6.63-6.76 (m, 6H, Ph-H),
.08-7.10 (m, 4H, Ph-H), 7.42-7.44 (m, 6H, Ph-H), 7.59 (s, 2H,
2
O), 4.37 (d, JHH ) 15.0 Hz, 2H, NCH
c
H
d
)
H -
c d
2
15.0 Hz, 2H, NCH
H
a b
g, 16%. Mp: 320-323 °C. Anal. Calcd for C38
36 6 4
H N O Pd: C,
1
7
61.09; H, 4.86; N, 11.25. Found: C, 61.15; H, 4.90; N, 11.29. H
13
1
2
imi-H), 7.68 (s, 2H, imi-H). C{ H} NMR (DMSO-d
6
): δ 53.4
CdO), 121.1 (CH), 122.8 (CH), 123.0 (CH),
26.0 (CH), 126.2 (CH), 127.6 (CH), 128.3 (CH), 129.3 (CH), 137.6
C), 147.9 (OdCNC), 163.7 (NCN), 166.6 (CdO). Crystals
NMR (DMSO-d
6
): δ 3.79 (s, 6H, CH
3
), 4.38 (d, JHH ) 14.4 Hz,
Ph), 5.04
CdO), 5.16 (d, JHH ) 14.4 Hz,
Ph), 6.73 (t, JHH ) 7.2 Hz, 2H, Ph-H), 6.92-6.99 (m,
10H, Ph-H), 7.06 (d, JHH ) 1.7 Hz, 2H, imi-H), 7.29 (d, JHH ) 1.7
Hz, 2H, imi-H), 7.33 (d, JHH ) 8.4 Hz, 4H, Ph-H), 7.52 (d, JHH
2
(
PhCH
2
), 58.3 (CH
2
2H, NCH CdO), 4.80 (d, JHH ) 14.4 Hz, 2H, NCH H
a
H
b
c d
2
2
1
(d, JHH ) 14.4 Hz, 2H, NCH
2H, NCH
a b
H
(
CH
2
c d
H
were obtained by vapor diffusion of diethyl ether into a methanol
solution containing the compound.
)
.8 Hz, 4H, Ph-H). 13C{ H} NMR (DMSO-d
5.6 (CH ), 58.1 (CH CdO), 114.5 (CH), 121.3 (CH), 121.4 (CH),
22.2 (CH), 125.5 (CH), 126.9 (CH), 129.4 (CH), 130.6 (CH C),
50.9 (OdCNC), 159.4 (COMe), 169.3 (CdO), 170.3 (NCN).
1
7
5
1
1
6 2
): δ 51.6 (ArCH ),
Synthesis of trans-6a. A mixture of 1a (0.110 g, 0.330 mmol),
PdCl (0.0300 g, 0.170 mmol), and K CO (0.090 g, 0.670 mmol)
2 2 3
in DMF (10 mL) was heated at 65 °C overnight. After cooling, the
solvent was removed completely under vacuum. The residue was
redissolved in dichloromethane (15 mL), and the organic layer was
3
2
2
Crystals for structural determination were obtained by vapor
diffusion of diethyl ether into a chloroform solution containing the
compound.
4
washed twice with water and dried with anhydrous MgSO . After
removal of the solvent under vacuum, the white solid remaining
was a mixture of cis-6a and trans-6a (ratio ) 62:38) according to
Synthesis of cis-6d. The compound was prepared with a
procedure similar to that for cis-6a. A mixture of 1a (0.11 g, 0.290
1
H NMR spectroscopy. Pure trans-6a can be obtained by washing
the off-white solid with methanol. A white solid was obtained.
Yield: 0.029 g, 25%. Mp: 301-304 °C. Anal. Calcd for
mmol), PdCl
mmol) was used. A white solid was obtained. Yield: 0.054 g, 47%.
Mp: 278-280 °C. Anal. Calcd for C44 Pd‚0.5H O: C,
66.37; H, 4.68; N, 10.55. Found: C, 66.21; H, 4.60; N, 10.35. H
2 2 3
(0.0260 g, 0.140 mmol), and K CO (0.0800 g, 0.580
C
36
H
32
N
6
O
2
Pd: C, 62.96; H, 4.70; N, 12.24. Found: C, 62.69; H,
H
36
N O
6 2
2
1
2
1
4
.59; N, 11.95. H NMR (DMSO-d
6
): δ 4.35 (d, JHH ) 14.7 Hz,
CdO), 4.87 (d, JHH ) 4.5 Hz, 2H, NCH Ph), 4.93
Ph), 5.21 (d, JHH ) 14.7 Hz, 2H,
CdO), 6.73 (t, JHH ) 7.1 Hz, 2H, Ph-H), 6.95 (t, JHH
.1 Hz, 4H, Ph-H), 7.01 (d, JHH ) 1.8 Hz, 2H, imi-H), 7.30 (d,
2
2
2H, NCH
a
H
b
c
H
d
NMR (CDCl
3
): δ 3.95 (d, JHH ) 14.4 Hz, 2H, NCH
4.38 (d, JHH ) 14.4 Hz, 2H, NCH CdO), 5.15 and 5.32 (AB
Ph), 6.73-6.89 (m, 14H,
Ph-H, Np-H, imi-H), 7.08 (d, JHH ) 6.9 Hz, 2H, Np-H), 7.43-7.70
a b
H CdO),
2
2
2
(
d, JHH ) 4.5 Hz, 2H, NCH
c
H
d
a b
H
2
NCH
a
H
b
)
c d
doublets, JHH ) 15.3 Hz, 4H, NCH H
7

1
702 Organometallics, Vol. 26, No. 7, 2007
Liao et al.
(
m, 6H, Ph-H or Np-H), 7.68 (d, JHH ) 8.4 Hz, 2H, Np-H), 7.93
were refined with anisotropic displacement parameters. In general,
hydrogen atoms were fixed at calculated positions, and their
positions were refined by a riding model (see Supporting Informa-
tion for specific hydrogen atoms located from the difference maps).
The structures for 4d, cis-6a, cis-6d, and cis-6d′ are disordered.
The details for their disorder models were given in the Supporting
Information. Structural discussion in the text is, generally, referred
to the major orientation. Crystallographic data (excluding structure
factors) for the structures in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supplementary
publication numbers CCDC 625296 (4a), 625297 (4d), 625298 (7),
625299 (8), 625300 (cis-6a), 625301 (cis-6d′), 625302 (cis-6d),
625303 (trans-6a), 625304 (trans-6b), and 625305 (trans-6c).
Copies of the data can be obtained, free of charge, on application
to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK [fax: +44-
(0)-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk].
t, JHH ) 6.6 Hz, 4H, Ph-H or Np-H). 13C{ H} NMR (CDCl
1.5 (PhCH ), 58.5 (CH CdO), 121.0 (CH), 121.6 (CH), 122.1
CH), 122.4 (CH), 125.4 (CH), 125.6 (CH), 125.8 (CH), 125.9 (CH),
26.6 (CH), 127.4 (CH), 129.3 (CH), 129.4 (CH), 130.1 (quaternary
C), 130.7 (quaternary C), 133.7 (CH C), 146.6 (OdCNC), 165.5
NCN), 166.5 (CdO). Crystals for structural determination were
1
): δ
(
5
(
1
3
2
2
2
(
obtained by vapor diffusion of diethyl ether into a DMF or methanol
solution containing the compound.
Synthesis of 7. The compound was prepared according to a
procedure similar to that for 4a. A mixture of 3 (0.32 g, 0.87mmol)
and PdCl
showed a mixture of 7 and 5, which was not separable following
the procedure for 4a. Crystals of 7 for structural determination were
obtained by vapor diffusion of diethyl ether into a DMF solution
of the mixture.
1
2
(0.150 g, 0.870 mmol) was used. The H NMR spectra
Computational Details. We used the three-parameter hybrid of
Synthesis of 8. A mixture of 3 (0.110 g, 0.310 mmol), PdCl
0.055 g, 0.310 mmol), and K CO (0.210 g, 1.50 mmol) in pyridine
5 mL) was heated at 80 °C overnight. After cooling, the solution
2
26
exact exchange and Becke’s exchange energy functional, plus Lee,
(
(
2
3
27
Yang, and Parr’s gradient-corrected correlation energy functional
B3LYP). We used the 6-31G basis sets for H, C, N, and O. For
Pd we used the LANL2DZ effective core potential plus basis
(
was filtered through a plug of Celite. The solvent was removed
completely under vacuum. The residue was redissolved in dichlo-
romethane (ca. 3 mL). Upon addition of diethyl ether, pure 8 as a
pale yellow solid was formed. Yield: 0.13 g, 77%. Mp: 344-346
28
functions. The Gaussian03 suite of programs were used in our
study.29
Suzuki Coupling Reactions. In a typical reaction, a mixture of
aryl bromides (1.0 mmol), phenylboronic acid (1.5 mmol),
Cs CO (2.0 mmol), and palladium(II) precatalyst (1 mol %) in 3
2 3
mL of 1,4-dioxane was stirred at 80 °C for 2 h under nitrogen.
The solution was allowed to cool to ambient temperature for GC
analysis. GC yields were calculated using benzophenone (with
°
C. Anal. Calcd for C24
21 5 2
H N O Pd: C, 55.66; H, 4.09; N, 13.52.
1
Found: C, 55.69; H, 4.08; N, 13.42. H NMR (CDCl
4
7
H). C{ H} NMR (CDCl
1
1
3
): δ 4.89 (s,
), 6.60-6.83 (m, 12H, Ph-H, py-H), 7.00 (s, 2H, imi-H),
.22 (t, JHH ) 7.8 Hz, 1H, py-H), 7.77 (d, JHH ) 4.8 Hz, 2H, py-
H, CH
2
13
1
3
): δ 55.5 (CH
27.0 (CH), 127.9 (CH), 136.4 (CH), 148.7 (OdCNC), 149.8 (CH),
52.7 (NCN), 167.2 (CdO). Crystals for structural determination
2
), 120.8 (CH), 123.6 (CH),
4
4
-acetylbiphenyl and 4-phenyltoluene as products) or biphenyl (with
-phenylanisole as product) as internal standards.
were obtained by vapor diffusion of pentane into a pyridine solution
containing the compound.
Acknowledgment. We are grateful to the National Science
X-ray Data Collection. Typically, the crystals were removed
from the vial with a small amount of mother liquor and immediately
coated with silicon grease on a weighing paper. A suitable crystal
was mounted on a glass fiber with silicone grease and placed in
the cold stream of a Bruker APEX II with graphite-monochromated
Mo KR radiation (λ ) 0.71073 Å) at 150(2) K. Crystallographic
data are listed in Tables 1 and 2.
Solution and Structure Refinements. All structures were solved
by direct methods using SHELXS-97 and refined by full-matrix
least-squares methods against F with SHELXL-97. Tables of
neutral atom scattering factors, f′ and f′′, and absorption coefficients
are from a standard source.25 All atoms except hydrogen atoms
Council of Taiwan for financial support of this work. We thank
the National Center for High-Performance Computing for
computer time and facilities.
Supporting Information Available: Full crystallographic data
for all the structures are provided as a CIF file. Additional
experimental details. A HMBC spectrum of cis-6a. A thermal
ellipsoid plot of cis-6d′. This material is available free of charge
via the Internet at http://pubs.acs.org.
2
24
OM0610041
(26) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(
27) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(
24) Sheldrick, G. M. SHELXTL, Version 5.1; Bruker AXS Inc.:
Madison, WI, 1998.
25) Sutton, L. E. Tables of Interatomic Distances and Configurations
in Molecules and Ions; Chemical Society Publications: UK, 1965.
(28) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270.
(29) Frisch, M. J.; et. al. Gaussian03; Revision B.05; Gaussian, Inc.:
Pittsburgh PA, 2003 (the full author list is provided in the Supporting
Information).
(