Air- and moisture-stable cyclopalladated complexes as efficient catalysts for Suzuki-Miyaura coupling reaction

Article abstract of DOI:10.1021/om049125t

A series of cylcopalladated complexes containing a six-membered chelating ring with the general formula [Pd(Cl)(k²N,C-CH₂C ₆H₂(Me)₂CH=NAr)]₂ [where Ar = 2,6-(Me)₂C₆H₃- (3a); 2,6-(ⁱPr) ₂C₆H₃- (3b)] and the related phosphine-substituted species (PdCl(k²N,C-CH₂C ₆H₂(Me)₂-CH=NAr)(PR₃)] [Ar = 2,6-(Me)₂C₆H₃-, R = Cy (5a); Ar = 2,6-( ⁱPr)₂C₆H₃, R = Cy (5b); Ar = 2,6-(Me)₂C₆H₃-, R = Ph (5c); Ar = 2,6( ⁱPr)₂C₆H₃-, R = Ph (5d)] have been synthesized. In addition, an ortho-metalated complex [PdCl(k²N,C- C₆H₄CH=N(2,6-ⁱPr₂C₆H ₃))(PCy₃)] (7) was prepared by a similar manner. Crystal structures of 3a, 5b,c, and 7 have been determined. The use of these palladium complexes as catalysts for Suzuki-Miyaura coupling reaction of aryl halides with arylboronic acids in ethanol solution was examined. It is found that this series of palladacycles are considerably active under aerobic conditions. Typically, the best activity (TON ≈10⁶) is seen with 3a,b in the coupling reaction of aryl bromide with phenylboronic acid. However, a TEM study showed that the palladium nanoparticles were formed under the reaction conditions, which might be the active species for the catalysis.

Full text of DOI:10.1021/om049125t

Organometallics 2005, 24, 1075-1081
1075
Air- and Moisture-Stable Cyclopalladated Complexes as
Efficient Catalysts for Suzuki-Miyaura Coupling
Reaction
Chuan-Lin Chen, Yi-Hung Liu, Shie-Ming Peng, and Shiuh-Tzung Liu*
Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China
Received November 11, 2004
A series of cylcopalladated complexes containing a six-membered chelating ring with the
general formula [Pd(Cl)(k2N,C-CH2C6H2(Me)2CHdNAr)]2 [where Ar ) 2,6-(Me)2C6H3- (3a);
2,6-(iPr)2C6H3- (3b)] and the related phosphine-substituted species [PdCl(k2N,C-CH2C6H2(Me)2-
CHdNAr)(PR3)] [Ar ) 2,6-(Me)2C6H3-, R ) Cy (5a); Ar ) 2,6-(iPr)2C6H3, R ) Cy (5b); Ar )
2,6-(Me)2C6H3-, R ) Ph (5c); Ar ) 2,6-(iPr)2C6H3-, R ) Ph (5d)] have been synthesized. In
addition, an ortho-metalated complex [PdCl(k2N,C-C6H4CHdN(2,6-iPr2C6H3))(PCy3)] (7) was
prepared by a similar manner. Crystal structures of 3a, 5b,c, and 7 have been determined.
The use of these palladium complexes as catalysts for Suzuki-Miyaura coupling reaction of
aryl halides with arylboronic acids in ethanol solution was examined. It is found that this
series of palladacycles are considerably active under aerobic conditions. Typically, the best
activity (TON ≈ 106) is seen with 3a,b in the coupling reaction of aryl bromide with
phenylboronic acid. However, a TEM study showed that the palladium nanoparticles were
formed under the reaction conditions, which might be the active species for the catalysis.
Introduction
well as their catalytic activities toward Suzuki-Miyaura
coupling reaction in ethanol under an aerobic atmo-
sphere.
Suzuki-Miyaura coupling reaction provides a power-
ful method for preparation of unsymmetrical biaryls,1
and the palladium complexes are known to be the most
efficient catalyst among various metal systems. How-
ever, a high loading of catalyst and an inert atmosphere
in most reactions are generally required for a better
conversion, which does not meet the requirements in
both an economical and an environmental sense.1-6
Thus searching for new palladium complexes as cata-
lysts has received much attention particularly for the
use of aryl chloride as substrates,2-8 under aerobic
conditions4 or even in aqueous solution.5 Accordingly,
palladacycles were found to the most promising cata-
lysts in this regard.1d,6-8 Recently, Bedford7 and Na´jera8
have demonstrated that Suzuki coupling reaction of aryl
chlorides with arylboronic acid in high conversion can
be achieved by using the cyclopalladated imino com-
plexes 1 and 2, respectively. In a previous communica-
tion, we have found that palladium complex 3b could
act as a catalyst for the coupling of aryl chloride with
arylboronic acid in aqueous medium.9 Here, we would
like to report the detailed studies of the preparation and
characterization of a series of benzylic palladacyles as
(2) (a) Na, Y.; Park, S.; Han, S. B.; Han, H.; Ko, S.; Chang, S. J.
Am. Chem. Soc. 2004, 126, 250. (b) Brase, S.; Kirchhoff, J. H.;
Kobberling, J. Tetrahedron 2003, 59, 885. (c) Kranich, R.; Eis, K.; Geis,
O.; Muhle, S.; Bats, J. W.; Schmalz, H. G. Chem. Eur. J. 2000, 6, 2874.
(d) Tao, B.; Boykin, D. W. Tetrahedron Lett. 2002, 43, 4955. (e)
Kolodziuk, R.; Penciu, A.; Tollabi, M.; Framery, E.; Goux-Henry, C.;
Iourtchenko, A.; Sinou, D. J. Organomet. Chem. 2003, 687, 384. (f)
Feuerstein, M.; Doucet, H.; Santelli, M. J. Organomet. Chem. 2003,
687, 327. (g) McLachlan, F.; Mathews, C. J.; Smith, P. J.; Welton, T.
Organometallics 2003, 22, 5350. (h) Loch, J. A.; Albrecht, M.; Peris,
E.; Mata, J.; Faller, J. W.; Crabtree, R. H. Organometallics 2002,
21, 700. (i) Gstottmayr, C. W. K.; Bohm, V. P. W.; Herdtweck, E.;
Grosche, M.; Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1363.
(j) Sava, X.; Ricard, L.; Mathey, F.; Le Floch, P. Organometallics 2000,
19, 4899. (k) Zhang, C. M.; Trudell, M. L. Tetrahedron Lett. 2000, 41,
595.
(3) Aryl chlorides as substrates for Suzuki couplings; see: (a) Li,
G. Y. J. Org. Chem. 2002, 67, 3643. (b) Liu, S.-Y.; Choi, M. J.; Fu, G.
C. Chem. Commun. 2001, 2408. (c) Netherton, M. R.; Fu, G. C. Org.
Lett. 2001, 3, 4295. (d) Zapf, A.; Ehrentraut, A.; Beller, M. Angew.
Chem., Int. Ed. 2000, 39, 4153. (e) Old, D. W.; Wolfe, J. P.; Buchwald,
S. L. J. Am. Chem. Soc. 1998, 120, 9722. (f) Bei, X.; Turner, H. W.;
Weinberg, W. H.; Guram, A. S. J. Org. Chem. 1999, 64, 6797. (g) Zhang,
C.; Huang, J.; Trudell, M. L.; Nolan, S. P J. Org. Chem. 1999, 64, 3804.
(h) Navarro, O.; Kelly, R. A.; Nolan, S. P. J. Am. Chem. Soc. 2003,
125, 16194. (i) Navarro, O.; Oonishi, Y.; Kelly, R. A.; Stevens, E. D.;
Briel, O.; Nolan, S. P. J. Organomet. Chem. 2004, 689, 3722, and
references therein.
* To whom correspondence should be addressed. E-mail:
stliu@ntu.edu.tw.
(1) Recent reviews: (a) Suzuki, A. J. Organomet. Chem. 1999, 576,
147. (B) Stanforth, S. P. Tetrahedron 1998, 54, 263. (c) Hassan, J.;
Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M. Chem. Rev. 2002, 102,
1359. (d) Bedford, R. B. Chem. Commun. 2003, 1787. (e) Tucker, C.
E.; De Vries, J. G. Top. Catal. 2002, 19, 111. (f) Singleton, J. T.
Tetrahedron 2003, 59, 1837. (g) Kotha, S.; Lahiri, K.; Kashinath, D.
Tetrahedron 2002, 58, 9633-9695. (h) Marshall, J. A. Chemtracts 2000,
13, 219. (i) Kocovsky, P.; Malkov, A. V.; Vyskocil, S.; Lloyd-Jones, G.
C. Pure Appl. Chem. 1999, 71, 1425-1433. (j) Herrmann, W. A. Applied
Homogeneous Catalysis with Organometallic Compounds, 2nd ed.;
2002; Vol. 1, 591 pp.
10.1021/om049125t CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/09/2005

1076 Organometallics, Vol. 24, No. 6, 2005
Chen et al.
Scheme 1. Preparation of Palladacycles
Results and Discussion
Preparation of Ligands and Complexes. Substi-
tuted trimethylbenzylideneamines were prepared by
the condensation of 2,4,6-trimethylbenzaldehyde with
a substituted aniline (Scheme 1). Both infrared ab-
sorptions near 1626 cm-1 and 13C NMR shifts around
162-163 ppm of imines 4a,b are characteristic of the
functionality of CdN. Cyclopalladation reactions were
carried out in a mixture of (CH3CN)2PdCl2, sodium
acetate, and the corresponding ligand in tetrahydrofu-
ran at ambient temperature for 38 h. The desired
palladium products 3a,b were isolated as air-stable
solids upon crystallization. In both instances, the cy-
clopalladation readily occurs at the benzylic position to
form an endo six-membered chelating ring, and the
product is in a chloro-bridged dipalladium structure,
which is consistent with most of the related species.10
The C-H activation at the benzylic position is estab-
lished by their 1H NMR and X-ray single-crystal deter-
mination. The appearance of a signal at 3.19 ppm for
3a and 3.24 for 3b with the integration of 2H in the 1H
NMR spectra was assigned to the methylene protons of
Pd-CH2- resulting from the C-H activation with the
palladium complex.
Figure 1. ORTEP drawing of 3a (drawn with 30%
probability ellipsoids; labeling of phenyl groups is omitted
for clarity).
Table 1. Selected Bond Distances (Å) and Bond
Angles (deg) of 3a and 3b
3a
3ba
Pd(1)-N(1)
2.024(3)
2.002(3)
2.3283(7)
2.5051(8)
1.298(4)
86.0(1)
126.5(2)
115.8(2)
176.95(8)
96.96(7)
91.11(9)
174.7(1)
85.81(3)
2.043(3)
2.003(4)
2.498(1)
2.325(1)
1.280(5)
86.2(1)
126.6(3)
116.0(3)
97.28(8)
176.42(9)
90.3(1)
Pd(1)-C(1)
Pd(1)-Cl(1)
Pd(1)-Cl(1A)
N(1)-C(7)
N(1)-Pd(1)-C(1)
Pd(1)-N(1)-C(7)
Pd(1)-C(1)-C(2)
N(1)-Pd(1)-Cl(1)
N(1)-Pd(1)-Cl(1A)
C(1)-Pd(1)-Cl(1)
C(1)-Pd(1)-Cl(1A)
Cl(1)-Pd(1)-Cl(1A)
171.2(1)
86.29(3)
Torsion Angles (deg) along the Chelate Ring of 3a
Pd(1)-N(1)-C(7)-C(8) -2.0 C(8)-C(2)-C(1)-Pd(1) - 47.2
N(1)-C(7)-C(8)-C(2)
C(7)-C(8)-C(2)-C(1)
22.8 C(2)-C(1)-Pd(1)-N(1)
49.6
4.6 C(1)-Pd(1)-N(1)-C(7) - 29.5
a Reference 9.
The detailed structure of palladacyle 3a was proved
by an X-ray diffraction study on single crystals grown
from a hexane/dichloromethane solution, whereas the
structural characterization of 3b has been published
previously.9 Figure 1 displays the ORTEP plot of 3a,
and Table 1 summarizes the selected bond distances,
bond angles, and torsion angles. In both instances, the
palladium metal displays a slightly distorted square-
planar geometry with nitrogen and carbon donors in cis-
fashion. All bond distances and bond angles lie within
normal ranges, which are essentially similar to those
for 3b except Pd(1)-N(1). The distance of Pd(1)-N(1)
[2.024(3) Å] for 3a is slightly shorter than that for 3b
[2.043(3) Å], which is attributed to steric differences
between methyl and isopropyl groups. The length of
C(7)-N(1) [1.298(4) Å] is characteristic for a CdN
double bond. The small bite angle N(1)-Pd(1)-C(1)
[86.0(1)°] is similar to those benzylic-type palladacycles
reported by Sales and co-workers.10e It is noticed that
the angle Pd(1)-C(1)-C(2) [115.8(2)°] deviating from
the angle for a tetrahedral geometry, similar to that for
3b, is presumably due to the strain forced by the
chelating rings. The dihedral angles along the chelating
ring of Pd(1)-N(1)-C(8)-C(7)-C(2)-C(1) in 3a (Table
1) indicate that this ring is adopted into a twist half-
chair conformation, apparently resulting from the oc-
currence of two double bonds in the chelate ring.
(4) (a) Najera, C.; Gil-Molto, J.; Karlstroem, S.; Falvello, L. R. Org.
Lett. 2003, 5, 1451. (b) Badone, D.; Baroni, M.; Cardamone, R.; Ielmini,
A.; Guzzi, U. J. Org. Chem. 1997, 62, 7170. (c) Oehme, G.; Grassert,
I.; Paetzold, E.; Meisel, R.; Drexler, K.; Fuhrmann, H. Coord. Chem.
Rev. 1999, 185-186, 585.
(5) (a) Venkatraman, S.; Li, C.-J. Org. Lett. 1999, 1, 1133. (b) Jensen,
J. F.; Johannsen, M. Org. Lett. 2003, 5, 3025.
(6) (a) Dupont, J.; Pfeffer, M.; Spencer, J. Eur. J. Inorg. Chem. 2001,
1917. (b) Herrmann, W. A.; Bo¨hm, V. P. W.; Reisinger, C.-P. J.
Organomet. Chem. 1999, 576, 23. (c) Dyker, G. Chem. Ber./Recl. 1997,
130, 1567. (d) Ryabov, A. D. Synthesis 1985, 233.
(7) (a) Bedford, R. B.; Cazin, C. S. J.; Coles, S. J.; Gelbrich, T.;
Horton, P. N.; Hursthouse, M. B.; Light, M. E. Organometallics
2003, 22, 987. (b) Bedford, R. B.; Blake, M. E.; Butts, C. P.; Holder, D.
Chem. Commun. 2003, 466. (c) Bedford, R. B.; Cazin, C. S. J.; Coles,
S. J.; Gelbrich, T.; Hursthouse, M. B.; Scordia, V. J. M. Dalton Trans.
2003, 3350. (d) Bedford, R. B.; Cazin, C. S. J. Chem. Commun. 2001,
1540. (e) Bedford, R. B.; Cazin, C. S. J.; Hursthouse, M. B.; Light, M.
E.; Pike, K. J.; Wimperis, S. J. Organomet. Chem. 2001, 633, 171.
(8) (a) Alonso, D. A.; Na´jera, C.; Pacheco, M. C. J. Org. Chem. 2002,
67, 5588. (b) Botella, L.; Na´jera, C. Angew. Chem., Int. Ed. 2002, 41,
179.
(9) Chen, C.-L.; Liu, Y.-H.; Peng, S.-M.; Liu, S.-T. Tetrahedron Lett.,
in press.
Phosphine-Substituted Complexes. Both palla-
dacycles 3a and 3b readily underwent ligand substitu-
tion reaction with phosphines (eq 1) to give the corre-
sponding complex. Both complexes were in air-stable
crystalline forms. The appearance of only one signal
around 40 ppm in the 31P NMR spectra for both
(10) (a) Albert, J.; Ceder, R. M.; Gomez, M.; Granell, J.; Sales, J.
Organometallics 1992, 11, 1536. (b) Bosque, R.; Granell, J.; Sales, J.;
Font-Bardia, M.; Solans, X. J. Organomet. Chem. 1993, 453, 147. (c)
Lopez, C.; Perez, S.; Solans, X.; Font-Bardia, M. J. Organomet. Chem.
2002, 650, 258. (d) De Munno, G.; Ghedini, M.; Neve, F. Inorg. Chim.
Acta 1995, 239, 155. (e) Albert, J.; Granell, J.; Sales, J.; Solans, X.;
Font-Altaba, M. Organometallics 1986, 5, 2567.

Air- and Moisture-Stable Cyclopalladated Complexes
Organometallics, Vol. 24, No. 6, 2005 1077
Figure 2. Molecular structure of 5b (30% probability
ellipsoids).
Figure 3. ORTEP plot of 5d (30% probability ellipsoids).
Table 2. Selected Bond Distances (Å), Bond Angles
(deg), and Torsional Angles (deg) of 5b, 5d, and 7
5b
5d
7
Pd(1)-N(1)
2.148(2)
2.037(3)
2.4136(9)
2.2683(7)
1.275(4)
174.30(7)
82.7(1)
94.62(9)
171.62(9)
93.1(1)
118.9(2)
-8.94
2.144(2)
2.049(3)
2.3682(8)
2.2388(7)
1.282(3)
172.67(6)
84.2(1)
95.25(3)
170.19(6)
88.57(9)
120.5(2)
2.72
-30.28
-6.86
60.11
-62.74
39.23
2.109(2)
2.016(2)
2.3904(7)
2.3049(7)
1.279(3)
171.69(6)
80.22(9)
89.87(2)
168.73(7)
101.38(7)
112.1(2)
Pd(1)-C(1)
Pd(1)-Cl(1)
Pd(1)-P(1)
N(1)-C(8)
P(1)-Pd(1)-N(1)
C(1)-Pd(1)-N(1)
P(1)-Pd(1)-Cl(1)
C(1)-Pd(1)-Cl(1)
P (1)-Pd(1)-C(1)
Pd(1)-N(1)-C(8)
Pd(1)-N(1)-C(8)-C(7)
N(1)-C(8)-C(7)-C(2)
C(8)-C(7)-C(2)-C(1)
C(7)-C(2)-C(1)-Pd(1)
C(2)-C(1)-Pd(1)-N(1)
C(1)-Pd(1)-N(1)-C(8)
-29.07
6.41
Figure 4. Molecular structure of 7 (30% probability
ellipsoids).
47.88
-61.32
47.31
donor trans to each other, presumably due to the trans
influence of these donors. All bond distances and bond
angles lie in the normal range of closely related com-
plexes such as [Pd(TFA)(κ2N,C-C6H4CH2NMe2)(PCy3)]
reported by Bedford and co-workers.7a When two struc-
tures are compared, it is found that all bond distances
and bond angles around the metal center are very close
except the bond angle of P(1)-Pd(1)-C(1) and the bond
length of Pd-P. The P(1)-Pd(1)-C(1) in 5b [93.1(1)°]
is considerably larger than that of the analogous angle
in 5d [88.57(9)°], reflecting a result of steric relief
between the carbon donor and tricyclohexylphosphine.
The Pd-P bond distance of 5b [2.2683(7) Å] is slightly
longer than that of 5d [2.2388(7) Å], which is due to
the contribution of palladium back-donation to the
π-acidic nature of triphenylphosphine. The conformation
of chelating rings associated with the metal center in
5b and 5d remains a twist half-chair form, as illustrated
by the torsional angles along the ring consisting of
Pd(1)-N(1)-C(8)-C(7)-C(2)-C(1) (Table 2).
complexes 5a and 5b suggests the formation of a single
trialkylphosphine-substituted isomer out of the two
possibilities. The benzylic methylene unit cis to the
1
phosphorus in 5a and 5b was established from the H
NMR spectra, where the methylene group bound to the
palladium appears as a doublet with a coupling constant
JP-H ≈ 2-5 Hz. This value is in the typical range
reported for the cis-arrangement of the methylene group
and phosphine in related species.10a,e Even though both
complexes could be easily characterized by means of
spectral and elemental analysis, the crystal structure
of 5b was determined to confirm the details. Figure 2
displays the ORTEP drawing of 5b, and selected bond
distances and bond angles are collected in Table 2. A
method similar to that for the preparation of 5a,b was
employed to produce the triphenylphosphine adduct
5c,d. Both spectroscopic and crystallographic analyses
of 5d verify the structure of 5c,d (Figure 3).
Another phosphine-substituted palladacycle, 7, with
a five-membered chelating ring was prepared via the
substitution of 6 with tricyclohexylphosphine (eq 2).
The 31P NMR chemical shift of 7 appeared at 43.1
ppm, which is in the typical range of trialkylphos-
phine palladium complexes.7a,c The crystal structure of
7 was determined (Figure 4). As expected, the molecular
structure of 7 shows a square planar geometry around
the metal center. Out of four coordination sites, two are
occupied by an N-C ligand in cis-fashion and the other
two by phosphine and chloride with nitrogen and
phosphorus donors in trans arrangement. The bond
lengths between the Pd and C, N, P, and chloride donor
atoms for 7 (Table 2) are within the range and compa-
Both 5b and 5d show the square planar arrangement
around the metal center with the phosphine and imine

1078 Organometallics, Vol. 24, No. 6, 2005
Table 3. Results of Coupling Reactions Catalyzed by Palladacyclesa
Chen et al.
entry
cat. (Pd mmol)
ArBr
[ArBr]/[Pd]
atm
t (h)
convb (%)
1
3a (1 × 10-4
3a (2 × 10-5
3a (2 × 10-6
3a (2 × 10-3
)
)
)
)
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeOC6H4Br
p-MeCOC6H4Br
p-MeCOC6H4Br
p-MeCOC6H4Br
p-MeCOC6H4Br
p-MeCOC6H4Br
p-MeCOC6H4Br
p-MeCOC6H4Br
2,4,6-tri-MeC6H2Br
2,4,6-tri-MeC6H2Br
p-MeOC6H4Cl
p-MeCOC6H4Cl
p-MeCOC6H4Cl
20 000
100 000
1 000 000
1000
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
3
10
18
20c
3
100
91
2
3
62
4
100
100
75
28
100
64
86
57
100
85
95
5
3b (1 × 10-4
3b (1 × 10-4
3b (1 × 10-4
3b (1 × 10-4
3b (1 × 10-4
3b (2 × 10-5
3b (2 × 10-6
3b (2 × 10-3
)
)
)
)
)
)
)
)
20 000
6d
7e
20 000
3
e
f
20 000
3
8f
20 000
3
9
20 000
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26f
27
28
29
30f
31
100 000
1 000 000
1000
10
20
14c
3
5c (1 × 10-4
5d (1 × 10-4
)
20 000
)
20 000
3
5a (1 × 10-4
)
20 000
3
100
92
5b (1 × 10-4
)
20 000
3
6 (1 × 10-4
6 (2 × 10-6
7 (1 × 10-4
)
)
)
20 000
3
86
1 000 000
20 000
16
3
26
83
3b (2 × 10-5
3b (2 × 10-6
3b (2 × 10-6
)
)
)
100 000
1 000 000
1 000 000
1 000 000
1 000 000
1 000 000
20 000
5
3
20
20
20
20
3
3
3
17
1
3
77
40
100
89
3a (2 × 10-6
5a (2 × 10-6
)
)
100
100
100
76
5b (2 × 10-6
)
3b (1 × 10-4
)
3a (1 × 10-3
)
2000
3b (1 × 10-3
)
2000
69
5b (1 × 10-3
3a (2 × 10-4
)
2000
72
)
10 000
96
5b (2 × 10-5
)
10 000
80
a Reaction conditions: ArX (2 mmol), PhB(OH)2 (3 mmol), catalysts, K2CO3 (4 mmol), EtOH (5 mL), reflux. b Determined by 1H
NMR spetroscopy based on ArX. c At 30 °C. d In DMF. e In CH3OH. f In water and 0.5 equiv of TBAB (tetrabutylammonium bromide)
was added.
rable with complex 5b. However, it is noticed that all
bond angles around the metal center in 7 are much more
derivated from square planar than in 5b, due to the five-
membered chelate ring.
in the coupling of aryl chloride with phenylboronic
acid.3h It is noticed that the reactions can be carried out
under an atmosphere of air. Therefore, the activities of
various palladium complexes were screened using etha-
nol as the solvent under aerobic conditions. Results are
summarized in Table 3.
As the molar ratio of [substrate]/[Pd] remains ∼20 000,
all palladacyclic catalysts show good catalytic activities
in Suzuki coupling. Among them, complexes 3a and 3b
ought to be the best ones, even better than the phos-
phine-substituted complexes 5a-d. For 3a and 3b it
appears that the steric hindrance of the ligand has less
influence on the catalysis. However, the yield drops
dramatically within a reasonable period of reaction time
(∼20 h) when the molar ratio of [substrate]/[Pd] in-
creases up to 106 (entries 11, 18), indicating a concen-
tration limitation of these catalysts. Among these
studies, we found that the palladacycle with a six-
membered chelate ring, 5a-d, were slightly better than
those with five-membered rings, 6. This observation also
applies for the phosphine-substituted palladacycles;
That is, the catalytic activities of 5a-d are better than
that of 7 (entries 13-16 versus 19). The catalytic
activities of 3a,b are generally as good as those for
5a-d, indicating that phosphine ligands are not neces-
sary in this reaction. It is worthy to mention that the
coupling reaction can be carried out at room tempera-
ture (entry 4). A quantitative conversion was observed
for the coupling of p-bromoanisole with phenylboronic
acid catalyzed by 3b in water with the presence of
tetraalkylammonium salt (entries 8, 26).
Suzuki-Miyaura Coupling Reaction. All palla-
dacyclic complexes prepared in this work were subjected
to an evaluation of their catalytic activities on the
coupling reaction of phenylboronic acid with aryl ha-
lides. In a typical experiment for the reaction, aryl
bromide, phenylboric acid, and K2CO3 in a ratio of
1:1.5:2 were placed in a flask, followed by the addition
of the solvent and the catalyst. In all instances the
solvent was used as obtained commercially without
further purification, while deionized water was used for
aqueous systems. The organic product was isolated by
extraction and then analyzed by 1H NMR spectroscopy.
The initial screen on solvents was performed using
3b as the catalyst precursor (Table 3, entries 5-8). It
appeared that the protic solvents including water gave
much better results than any other organic solvents.9
This coupling reaction running in DMF only provided
a moderate yield as compared with alcoholic solvents.
This result is quite similar to that reported by Nolan
and co-workers using a palladacycle carbene complex
As for the activated substrate (p-acetylphenyl bro-
mide), the turnover number can reach 106 for 3b, 5a,

Air- and Moisture-Stable Cyclopalladated Complexes
Organometallics, Vol. 24, No. 6, 2005 1079
use of excess arylboronic acid in the Suzuki-Miyaura
reactions is generally required for better conversions.
It should be mentioned that the reduction of aryl halides
or arylboronic acid proceeded superiorly than that of the
homo-coupling reaction.
The decomposition rate of palladcycles in basic etha-
nol solution follows the order 6 > 3b > 5b > 5d (Table
5). Complex 6 appeared to be slower than 3b, but
aggregated into larger nanoparticles (100-200 nm),
which explained the activity difference between 6 and
3b due to the size effect.11 As for the phosphine-
substituted complexes 5b and 5d, the decomposition
was much slower than that of 3b presumably due to
the stabilization of the coordinating phosphine. Another
finding is that the surfactant-stabilized palladium
nanoparticles appear to be less active than those gener-
ated in situ. In the presence of tetrabutylammonium
bromide, palladium nanoparticles was obtained from the
decomposition of complex 3b in ethanol. The resulting
palladium nanoparticles were used as the catalyst for
the coupling reaction of PhB(OH)2 and MeOC6H4Br to
give the desired product but in a slower conversion rate
by ca. 20%.
It has been demonstrated that palladium nanopar-
ticles can catalyze the C-C bond coupling reaction,12
particularly under Jeffery condition for Heck reaction.13
Unlike the palladium clusters stabilized by tetraalky-
lammonium salt, the nanoparticles generated from the
reduction of palladacycles are presumably surrounded
by the imine ligands, which tend to aggregate with the
precipitation of palladium black. This reveals the weak
stabilizing effect of these ligands toward nanoparticles.
On the other hand, the loose protection makes these
palladium particles highly active toward the sub-
strates.12
Figure 5. TEM micrograph of palladium nanoparticles
generated from the coupling reaction catalyzed by 3b.
and 5b (entries 22-25). In addition, complexes 3a and
3b catalyzed the coupling of the sterically bulky sub-
strate such as 2,4,6-(Me)3C6H2Br with phenylboronic
acid in good conversions (entries 27, 28).
Under similar reaction conditions, the catalytic activi-
ties of these palladacycles toward aryl chloride appear
to be lower than the bromo substrates (entry 29).
However, the conversion can be improved by carrying
out the reaction in water medium and in the presence
of tetrabutylammonium salt (entries 30, 31).9 Overall,
the palladium complexes prepared in this work behave
with high catalytic acitivity in the Suzuki-Miyaura
coupling reaction.
Mechanistic Pathway of Catalysis. To probe the
reaction pathway, the course of the coupling reaction
was monitored by taking samples and analyzing them
by 1H NMR and TEM. First, an aliquot from the
reaction of 3b with phenylboronic acid (2 equiv) in the
presence of K2CO3 and ethanol was examined by
transmission electron microscopy, showing the forma-
tion of palladium particles with a diameter in the range
50-60 nm (Figure 5). Upon addition of p-bromoanisole
to the above solution, the coupling reaction proceeded
smoothly to yield p-methoxybiphenyl quantitatively,
suggesting that the palladium nanoparticles might be
the active catalyst for the reaction.
In further studies, we found that complex 3b readily
reacted with ethanol under basic conditions to generate
acetaldehyde and the free ligand 4b accompanied with
palladium nanoparticles, but aggregate to produce pal-
ladium black without the presence of other substrates.
The formation of acetaldehyde is presumably due to the
substitution of chloride ligands by ethoxide under basic
conditions followed by â-elimination.3h Addition of phe-
nylboronic acid to the above solution yielded benzene
and biphenyl immediately (Table 4). On the other hand,
p-acetophenyl bromide was converted into acetophenone
and 4,4′-bisacetobiphenyl, as evidenced by 1H NMR
spectroscopy. However, the reaction of p-acetophenyl
chloride was much slower than that of bromide (Table
4, entry 2). The production of biphenyl derivatives and
the reduced compounds is presumably via the addition
of phenylboronic acid or p-acetophenyl bromide to the
palladium nanoparticles followed by reductive elimina-
tion (Scheme 2). We also found that the decomposition
rate of aryl bromide is much slower than that of
arylboronic acid, revealing that the oxidative addition
of aryl halide to the metal is the rate-limiting step in
the cross-coupling reaction. This also explains that the
Furthermore, the low concentrations of palladium
complexes may also prevent the rapid formation of
palladium black and the formation of larger nanopar-
ticles, suggesting the extreme activity of metal clusters.
However, the conversion decreases when the ratio
[substrate]/[Pd] is higher than 106 (Table 3 entries 3,
11), showing a limitation of these nanoparticles in
catalysis.
Summary
We have synthesized and characterized a new series
of air-stable palladacycles. These palladium complexes
were successfully applied in the Suzuki-Miyaura cou-
pling reaction and had good catalytic activities, for
example, the turnover frequency of up to 107 mol/mol-
(Pd)‚h for 3b in the coupling of p-bromoanisole or
p-bromoacetophenone with phenylboronic acid. Notable
were the reaction conditions employed, i.e., the moisture
and air insensitivity. Several observations confirm that
the Suzuki-Miyaura coupling catalyzed by palladcyclic
complexes is via the palladium nanoparticles. Reactions
of p-bromoacetophenone or arylboronic acid individually
on the nanoparticles leading to homo-coupled and
reduced products were investigated, but the cross-
(11) Narayanan, R.; El-Sayed, M. A. J. Phys. Chem. B 2004, 108,
8572.
(12) For a recent review see: Reetz, M. T.; de Vries, J. G. Chem.
Commun. 2004, 1959.
(13) Jeffery, T. J. Chem. Soc., Chem. Commun. 1984, 1287.

1080 Organometallics, Vol. 24, No. 6, 2005
Chen et al.
Table 4. Decomposition of Aryl Halides or Arylboronic Acids on Palladium Nanopartices Generated in
Situ from Palladacyclic Complexesa
entry
substrate
complex
conditions
time
conversion
reduced product:coupling product (ratio)b
1
2
3
4
5
6
7
8
p-MeCOC6H4Br
p-MeCOC6H4Cl
p-MeCOC6H4Br
p-MeCOC6H4Br
PhB(OH)2
3b
3b
6
5b
3b
3b
3b
3b
reflux
reflux
reflux
reflux
reflux
40 °C
40 °C
40 °C
2 h
10 h
2 h
2 h
1h
8 h
8 h
8 h
100%
46%
MeCOC6H5 (63):(p-MeCOC6H4)2 (37)
MeCOC6H5 (67):(p-MeCOC6H4)2 (33)
MeCOC6H5 (80):(p-MeCOC6H4)2 (20)
MeCOC6H5 (100):(p-MeCOC6H4)2 (0)
C6H6 (98):C6H5-C6H5 (2)
77%
100%
100%
100%
100%
100%
PhB(OH)2
C6H6 (91):C6H5-C6H5 (9)
p-MeOC6H4B(OH)2
p-MeC6H4B(OH)2
MeOC6H5 (98):(p-MeOC6H4)2 (2)
MeC6H5 (98):(p-MeC6H4)2 (2)
a Conditions: Aryl halides (1 mmol) [or ArB(OH)2 (0.5 mmol)], K2CO3 (2 mmol), and Pd complex (mmol) in EtOH (2 mL). b Ratio is
determined by 1H NMR integration and is given in parentheses.
(2,6-Dimethylphenyl)(2,4,6-trimethylbenezylidene)-
amine, 4a: yellow liquid (90%); IR (KBr) 1625 cm-1 (νCdN);
1H NMR (CDCl3, 400 MHz) δ 8.68 (s, 1H, -HCdN), 7.15 (s
2H, Ar H), 7.04-6.95 (m, 3H, Ar H), 2.66 (s, 6H, -Me), 2.40
(s, 3H, -Me), 2.28 (s, 6H, -Me); 13C NMR δ 163.0, 152.6, 139.9,
138.8, 130.0, 129.9, 128.1, 126.7, 123.4, 21.3, 21.1, 18.8; FAB
m/z 251.1 (M+). Anal. Calcd for C18H21N: C, 86.01; H, 8.42; N,
5.57. Found: C, 86.11; H, 8.65; N, 5.55.
Scheme 2
(2,6-Diisopropylphenyl)(2,4,6-trimethylbenzylidene)-
amine, 4b: white solids (91%); mp 99-101 °C; IR (KBr)
1
1627 cm-1 (νCdN); H NMR (CDCl3, 400 MHz) δ 8.64 (s, 1H,
Table 5. Relative Decomposition Rate of
Palladcycle in Basic Etahanol Solutiona
-HCdN), 7.24-7.22 (m, 2H, Ar H), 7.17-7.15 (m, 1H, Ar H),
7.01 (s, 1H, Ar H); 3.12 (sept., J ) 6.8 Hz, 2H, -CH), 2.65 (s,
6H, -Me), 2.39 (s, 3H, -Me), 1.25 (d, J ) 6.8 Hz, 12H, -Me);
13C NMR δ 162.3, 150.5, 140.1, 139.2, 137.4, 130.2, 129.7,
123.8, 122.9, 27.8, 23.7, 21.5, 21.1; FAB m/z 307.2 (M+). Anal.
Calcd for C22H29N: C, 85.94; H, 9.51; N, 4.56. Found: C, 86.24;
H, 9.64; N, 4.57.
3a
3b
5b
5d
% of decompositionb
40%
70%
14%
trace
a A solution of complex (2 × 10-2 mmol) and K2CO3 (2 × 10-1
mmol) in ethanol (2 mL) was stirred at 40 °C for 30 min. bPercent
of decomposition was determined by 1H NMR spectroscopy.
General Procedure for Preparation of Palladacycle
Complexes 3a,b. To a round-bottomed flask with a stir bar
was placed palladium dichloride (118 mg, 0.67 mmol) under
nitrogen. Predried acetonitrile (10 mL) was added, and the
resulting mixture was stirred at room temperature. The
mixture turned yellow immediately. After stirring for 2 days,
the solvent was removed to dryness. Then ligand (0.71 mmol),
excess sodium acetate (110 mg, 10.4 mmol), and tetrahydro-
furan (15 mL) were added. The reaction mixture was stirred
at room temperature for another 38 h. After removal of
solvents, dichloromethane (20 mL) was added and the solution
was filtered through Celite. The filtrate was concentrated, and
the residue was washed with hexane (10 mL × 3) to give the
desired product.
coupled ones were obtained when the aryl halide and
arylboronic acid were present. However, the pathway
for the cross-coupling and reduction processes on these
particles remains unclear. More work is necessary in
order to work out the nature of these nanoparticles.
Experimental Section
General Information. All reactions, manipulations, and
purifications steps were performed under a dry nitrogen
atmosphere. Tetrahydrofuran was distilled under nitrogen
from sodium benzophenone ketyl. Dichloromethane and ac-
etonitrile were dried with CaH2 and distilled under nitrogen.
Other chemicals and solvents were of analytical grade and
were used as received unless otherwise stated.
Nuclear magnetic resonance spectra were recorded in CDCl3
on either a Bruker AM-300 or AVANCE-400 spectrometer.
Chemical shifts are given in parts per million relative to Me4S
for 1H and relative to 85% H3PO4 for 31P NMR. Infrared spectra
were measured on a Perkin-Elmer 983G spectrometer (Series-
II) as KBr pellets, unless otherwise noted. Preparation of 6
followed the procedures published previously.14
General Procedure for Preparation of Schiff Base
Ligands 4a,b. A methanol (15 mL) solution of the sub-
stituted benzylaldehyde (10 mmol) and the substituted ani-
line (10 mmol) was added into a single-necked round-bot-
tomed flask equipped with a condenser. The reaction mix-
ture was stirred at reflux temperature for 24 h. After the
completion of the reaction, the yellow crystal product was
precipitated upon cooling. The solid product was filtered,
washed with the precooled hexane, and dried, whereas the
liquid compound 1b was purified by distilling off the starting
aldehyde and chromatographed on silica gel with elution of
hexane.
Complex 3a: brown solids (80%); mp 252 °C (dec); IR (KBr)
1
1600 cm-1 (νCdN); H NMR (CDCl3, 400 MHz) δ 7.77 (s, 1H,
-HCdN), 7.07-7.01 (m, 4H, Ar H), 6.80 (s, 1H, Ar H), 3.19
(s, 2H, -H2C-Pd), 2.41 (s, 6H, -Me), 2.28 (s, 3H, -Me), 2.27
(s, 3H, -Me); 13C NMR δ 163.1, 150.2, 145.8, 143.8, 139.5,
130.9, 130.0, 128.2, 127.6, 126.2, 125.3, 23.3, 21.4, 19.5, 18.9;
FAB m/z 749.0 (M+ - Cl-). Anal. Calcd for C36H40Cl2N2Pd2:
C, 55.12; H, 5.14; N, 3.57. Found: C, 55.34; H, 5.04; N, 3.44.
Complex 3b: orange solids (90%); mp 270 °C (dec); IR (KBr)
1
1599 cm-1 (νCdN); H NMR (CDCl3, 400 MHz) δ 7.81 (s, 1H,
-HCdN), 7.23 (t, J ) 7.3 Hz, 1H, Ar H), 7.14 (d, J ) 7.3 Hz,
2H, Ar H), 6.98 (s, 1H, Ar H), 6.82 (s, 1H, Ar H), 3.48-3.39
(m, 2H, -CH), 3.24 (s, 2H, -H2C-Pd), 2.30 (s, 3H, -Me), 2.29
(s, 3H, -Me), 1.47 (d, J ) 6.7 Hz, 6H, -Me), 1.11 (d, J ) 6.8
Hz, 6H, -Me); 13C NMR δ 162.7, 148.0, 146.5, 143.7, 140.7,
139.8, 130.6, 127.6, 126.8, 125.4, 123.3, 28.2, 24.8, 23.2,
22.5, 21.4, 19.1; FAB m/z 861.1 (M+ - Cl-). Anal. Calcd for
C44H56Cl2N2Pd2: C, 58.94; H, 6.29; N, 3.12. Found: C, 58.89;
H, 6.35; N, 3.08.
General Procedure for Preparation of Phosphine-
Substituted Palladacycle Complexes. To a degassed flask
loaded with the palladacycle dimer complex (1 mmol) and
dichloromethane (5 mL) was added phosphine (2 mmol). Upon
stirring at room temperature for 2 h, the solvent of the reaction
(14) Chen, C.-L.; Liu, Y.-H.; Peng, S.-M.; Liu, S.-T. J. Organomet.
Chem. 2004, 689, 1806.

Air- and Moisture-Stable Cyclopalladated Complexes
Organometallics, Vol. 24, No. 6, 2005 1081
Table 6. Crystallographic Data of 3a, 5b, 5d, and 7
3a
5b
5d
7
formula
fw
cryst syst
space group
a, Å
C
36H40Cl2N2Pd2
C40H61ClNPPd
728.72
orthorhombic
Pbca
19.3320(2)
17.372092)
22.6590(2)
90
90
90
7609.7(1)
8
C40H43ClNPPd
710.57
monoclinic
P21/c
17.0000(3)
11.6040(2)
18.4260(3)
90
104.528(1)
90
3518.6(1)
4
1.341
1472
C37H55ClNPPd
686.64
monoclinic
P21/n
11.7670(1)
17.0560(1)
18.4730(2)
90
105.267(1)
90
3576.65(5)
4
1.275
1448
784.40
monoclinic
P21/c
12.7010(1)
8.794(1)
15.7000(2)
90
103.978(1)
90
1701.65(3)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
Dcalcd, Mg/m3
F(000)
1.531
792
1.272
3088
cryst size, mm
θ range
no. of reflns collected
no. of indep reflns
R [I > 2σ(I)]
0.25 × 0.20 × 0.15
1.65-25.00
9728
3006 (Rint ) 0.0286)
R1 ) 0.0302
wR2 ) 0.0803
1.187
0.30 × 0.25 × 0.15
1.80-27.48
50 044
8719 (Rint ) 0.0467)
R1 ) 0.0474
wR2 ) 0.1219
1.111
0.25 × 0.20 × 0.15
2.09-27.47
25 239
8026 (Rint ) 0.0367)
R1 ) 0.0404
wR2 ) 0.0973
1.173
0.30 × 0.20 × 0.15
1.65-27.47
26 619
8175 (Rint ) 0.0336)
R1 ) 0.0402
wR2 ) 01069
1.122
goodness-of-fit on F2
mixture was evaporated. The residue was crystallized in
dichloromethane/ether to give the desired complex in crystal-
line solids.
Complex 7: yellow solids 99%; IR (KBr) 1617 cm-1 (νCdN);
1H NMR (CDCl3, 400 MHz) δ 7.98 (d, JH-P ) 6.8 Hz, 1H,
-HCdN), 7.42 (dd, J ) 7.5 Hz, J ) 2.3 Hz, 1H, Ar H), 7.37
(dd, J ) 7.1 Hz, J ) 1.9 Hz 1H, Ar H), 7.19-7.10 (m, 5H, Ar
H), 3.34 (hept, J ) 6.8 Hz 2H, -CH), 1.30 (d, J ) 6.8 Hz, 6H,
-Me), 1.12 (d, J ) 6.8 Hz, 6H, -Me); 13C NMR (CDCl3, 100
MHz) δ 176.1 (d, JC-P ) 3.4 Hz), 159.0, 148.2, 145.6, 141.0,
137.4 (d, JC-P ) 5.1 Hz), 130.7 (d, JC-P ) 3.4 Hz), 129.1, 126.3,
124.1, 122.6, 34.1 (d, JC-P ) 21.7 Hz), 30.4, 28.4, 27.7 (d, JC-P
)10.9 Hz), 26.4, 24.6, 22.9; 31P NMR (CDCl3, 161.9 MHz) 43.1.
Anal. Calcd for C37H55ClNPPd: C, 64.72; H, 8.07; N, 2.04.
Found: C, 64.85; H, 8.04; N, 1.91.
Complex 5a: yellow solids (99%); IR (KBr) 1607 cm-1
(νCdN); 1H NMR (CDCl3, 300 MHz) δ 8.06 (d, J ) 11.0 Hz, 1H,
-HCdN), 7.07-7.00 (m, 3H, Ar H), 6.89 (s, 1H, Ar H), 6.76
(s, 1H, Ar H), 2.90(s, 2H, -H2C-Pd), 2.53 (s, 6H, -Me), 2.34
(s, 3H, -Me), 2.36-2.26 (m, 3H, PCy3), 1.94-1.42 (m, 21H,
PCy3), 1.28-1.22 (m, 9H, PCy3); 13C NMR (CDCl3, 100 MHz)
δ 163.3, 151.3, 146.7, 142.5, 139.5, 130.9 139.9, 127.9, 127.4,
126.2, 125.6, 33.4 (d, JC-P ) 22 Hz), 29.8, 27.7 (d, JC-P ) 10.9
Hz), 26.6, 22.4, 21.3, 20.4, 18.9; 31P NMR (CDCl3, 161.9 MHz)
39.8. Anal. Calcd for C36H35ClNPPd: C, 64.28; H, 7.94; N, 2.08.
Found: C, 63.97; H, 7.65; N, 1.80.
Catalysis. To a 10 mL round-bottom flask equipped with
-3
condenser were placed palladium complex (5 × 10
mmol),
Complex 5b: yellow solids (99%); IR (KBr) 1603 cm-1
aryl halide (2 mmol), K2CO3 (3 mmol), phenylboronic acid (3
mmol), and solvent (5 mL). The mixture was heated under
reflux for a certain period of time. Upon cooling, the reaction
mixture was poured into diluted hydrochloric acid (10%) and
extracted with dichloromethane. The extract was dried, con-
1
(νCdN); H NMR (CDCl3, 400 MHz) δ 8.03(d, JH-P ) 10.9 Hz,
-HCdN), 7.20 (bs, 3H, Ar H), 6.92 (s, 1H, Ar H), 6.80 (s, 1H,
Ar H), 3.85-3.78 (m, 2H, -CH), 2.92(d, J ) 2.4 Hz, 2H,
-H2C-Pd), 2.37 (s, 3H, -Me), 2.37-2.30 (m, 3H, PCy3), 2.30
(s, 3H, -Me), 1.96-1.94 (m, 6H, PCy3) 1.71-1.50 (m, 15H,
PCy3) 1.46 (d, J ) 6.5 Hz, 6H, -Me), 1.30-1.26 (m, 9H, PCy3),
1.21 (d, J ) 6.6 Hz, 6H, -Me); 13C NMR (CDCl3, 100 MHz) δ
163.1, 148.7, 146.8, 142.5, 140.8, 139.6, 131.1, 127.4, 126.5,
126.2, 123.1, 33.6 (d, JC-P ) 22.4 Hz), 29.8, 28.5, 27.6 (d, JC-P
) 10.9 Hz), 26.4, 25.2, 23.6, 21.6, 21.3, 19.4; 31P NMR (CDCl3,
161.9 MHz) 40.3. Anal. Calcd for C40H61ClNPPd: C, 65.92; H,
8.44; N, 1.92. Found: C, 65.86; H, 8.59; N, 1.83
1
centrated, and analyzed by H NMR spectroscopy. Results of
the coupling reactions are listed in Table 3.
Decomposition of Palladacycles in the Presence of
Aryl Halides or Arylboronic Acids. To a 10 mL round-
bottom flask equipped with condenser was placed palladium
complex (1.0 × 10-2 mmol), K2CO3 (2.0 mmol), and aryl halides
or arylboronic acid in ethanol (2 mL). The resulting mixture
was stirred with heating. An aliquot from the reaction mixture
was analyzed by 1H NMR. The results are summarized in
Table 4.
Crystallography. Crystals suitable for X-ray determina-
tion were obtained for 3a, 5b,d, and 7 by slow diffusion of
hexane into a dichloromethane solution at room temperature.
Cell parameters were determined by a Siemens SMART CCD
diffractometer. Crystal data of these complexes are listed in
Table 5. Other crystallographic data are deposited as Sup-
porting Information.
Complex 5c: yellow solids (99%); IR (KBr) 1602 cm-1
(νCdN); 1H NMR (CDCl3, 300 MHz) δ 8.09 (d, J ) 12.3 Hz, 1H,
-HCdN), 7.62-7.56 (m, 6H, Ar H), 7.42-7.32 (m, 9H, Ar H),
7.11-7.04 (m, 3H, Ar H), 6.71 (s, 1H, Ar H), 5.72 (s, 1H, Ar
H), 2.81 (d, J ) 5.1 Hz, 2H, -H2C-Pd), 2.57 (s, 6H, -Me),
2.33 (s, 3H, -Me), 2.10 (s, 3H, -Me); 31P NMR (CDCl3, 161.9
MHz) δ 36.4. Anal. Calcd for C36H35ClNPPd: C, 66.06; H, 5.39;
N, 2.14. Found: C, 66.29; H, 5.39; N, 1.68.
Complex 5d: yellow solids (99%); IR (KBr) 1600 cm-1
1
(νCdN); H NMR (CDCl3, 400 MHz) δ 8.08 (d, JH-P ) 12 Hz,
-HCdN), 7.67-7.60 (m, 6H, Ar H), 7.45-7.37 (m, 9H, Ar H),
7.24 (bs, 3H, Ar H), 6.75 (s, 1H, Ar H), 5.73 (s, 1H, Ar H),
3.85-3.78 (m, 2H, -CH), 2.83 (d, J ) 5.1 Hz, 2H, -H2C-Pd),
2.36 (s, 6H, -Me), 2.14 (s, 3H, -Me), 2.10 (s, 3H, -Me), 1.5
(d, J ) 6.7 Hz, 6H, -Me), 1.28 (d, J ) 6.8 Hz, 6H, -Me); 13C
NMR (CDCl3, 100 MHz) δ 163.6, 148.0, 144.7 (d, JC-P ) 2.3
Hz), 142.4, 140.8, 139.3, 134.6 (d, JC-P ) 11.4 Hz), 131.5, 131.0
Acknowledgment. We thank the National Science
Council for financial support (NSC92-2113-M-002-037).
Supporting Information Available: Complete descrip-
tion of the X-ray crystallographic structure determination of
3a, 5b,d, and 7 including tables of crystal data, atomic
coordinates, isotropic and anisotropic thermal parameters, and
bond distances and angles. This material is available free of
charge via the Internet at http://pubs.acs.org.
(d, JC-P ) 48.6 Hz), 130.1 (d, JC-P ) 2.3 Hz), 128.0 (d, JC-P
)
10.5 Hz), 127.5, 126.5, 126.4, 123.3, 28.6, 27.9, 25.2, 23.7, 21.2,
19.3; 31P NMR (CDCl3, 161.9 MHz) δ 37.7. Anal. Calcd for
C40H43ClNPPd: C, 67.61; H, 6.10; N, 1.97. Found: C, 67.79;
H, 5.97; N, 1.53.
OM049125T