Insight into the steric and electronic effects of ancillary ligands: Synthesis and structure-reactivity relationship of well-defined, air- and moisture-stable (NHC)Pd(sal)Cl complexes (sal = salicylaldimine)

Article abstract of DOI:10.1021/om100906n

Synthesis of a series of (NHC)Pd(sal)Cl complexes, 1-5, bearing a salicylaldimine (sal) unit was described. The structure-reactivity relationship, especially the steric and electronic effects of the salicylaldimine ligands on their catalytic activities, was investigated intensively in the Buchwald-Hartwig coupling reaction. Our study demonstrated that the sterically encumbered N-aryl groups in the salicylaldimine unit give rise to an obviously negative effect in the aryl amination reaction. Additionally, incorporating a steric substituent into the ortho-position of the phenoxide oxygen atom does not appear to be beneficial to their catalytic activity. Notably, the electronic nature of N-substituted aryl groups in the salicylaldimine ligands plays a significant role in their catalytic activities. An electron-rich N-aryl group causes an obviously decreasing yield, while an electron-deficient one, such as complex 5b, leads to enhanced reactivity. The aryl amination reaction with complex 5b was also found to be remarkably tolerant to both air and moisture. Under optimized reaction conditions, a range of aryl chlorides and amines could be coupled smoothly under aerobic conditions.

Full text of DOI:10.1021/om100906n

6578 Organometallics 2010, 29, 6578–6586
DOI: 10.1021/om100906n
Insight into the Steric and Electronic Effects of Ancillary Ligands:
Synthesis and Structure-Reactivity Relationship of Well-Defined,
Air- and Moisture-Stable (NHC)Pd(sal)Cl Complexes (sal=Salicylaldimine)
Zhong Jin,*,† Ling-Ling Qiu,† Yan-Qing Li,† Hai-Bin Song,† and Jian-Xin Fang*,†,‡
†Institute of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People’s Republic of China,
and ‡State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071,
People’s Republic of China
Received September 21, 2010
Synthesis of a series of (NHC)Pd(sal)Cl complexes, 1-5, bearing a salicylaldimine (sal) unit was
described. The structure-reactivity relationship, especially the steric and electronic effects of the
salicylaldimine ligands on their catalytic activities, was investigated intensively in the Buchwald-
Hartwig coupling reaction. Our study demonstrated that the sterically encumbered N-aryl groups in
the salicylaldimine unit give rise to an obviously negative effect in the aryl amination reaction.
Additionally, incorporating a steric substituent into the ortho-position of the phenoxide oxygen atom
does not appear to be beneficial to their catalytic activity. Notably, the electronic nature of
N-substituted aryl groups in the salicylaldimine ligands plays a significant role in their catalytic activities.
An electron-rich N-aryl group causes an obviously decreasing yield, while an electron-deficient one, such
as complex 5b, leads to enhanced reactivity. The aryl amination reaction with complex 5b was also found
to be remarkably tolerant to both air and moisture. Under optimized reaction conditions, a range of aryl
chlorides and amines could be coupled smoothly under aerobic conditions.
Introduction
consist of an accurate ratio (optimally 1:1) of the Pd/ligand that
avoids the use of excess costly ligand but generally also exhibit
enhanced reactivity associated with easy access to a highly
active low-coordinate [LPd0] species. In addition to an essential
NHC ligand, well-defined NHC-containing Pd(II) precatalysts
comprise usually two anionic ligands (e.g., Cl, OAc) and a
fourth, droppable neutral ligand (e.g., H2O,4 pyridine5). These
precatalysts were presumed to be activated through different
pathways, liberating in all cases an active [(NHC)Pd0] species
into the catalytic cycle. Besides the dominant NHC ligand,
other ancillary ligands surrounding the Pd metal center also
play a very crucial role in their catalytic performance. For
example, significant reactivity differences can be seen when the
allyl group in (NHC)Pd(allyl)Cl6 was replaced by a cinnamyl
group.7 It was supposed that as a ancillary ligand, the sterically
demanding cinnamyl group induced a more facile activation
step from PdII to Pd0 than the corresponding allyl group, which
In recent years, prominent advances in transition metal-
mediated homogeneous catalysis have been achieved using
N-heterocyclic carbenes (NHCs) as ligands.1,2 The shielding
steric substitutents in the heterocyclic backbone, high ther-
mal stability, and strong σ-donor character result in very
high stability of the metal-NHC bond. Moreover, these
characteristics render them particularly suitable as the sole
supporting ligand for the formation of the active low-coordi-
nate metal-NHC species in catalytic cycles.3 Particularly in the
field of Pd-catalyzed cross-coupling reactions, well-defined
NHC-containing Pd(II) complexes1b,g have proven to be a
superior alternative for catalytic systems of tertiary phosphines.
These prevailing NHC-containing Pd(II) complexes not only
*Corresponding authors. Tel: þ86 22 2350 5330. E-mail: zjin@
nankai.edu.cn (Z.J.); fjx@nankai.edu.cn (J.-X.F.).
(1) For recent reviews on NHCs in homogeneous catalysis, see: (a)
Bantreil, X.; Broggiw, J.; Nolan, S. P. Annu. Rep. Prog. Chem. Sect B:
Org. Chem. 2009, 105, 232–263. (b) Marion, N.; Nolan, S. P. Acc. Chem.
Res. 2008, 41, 1440–1449. (c) Boeda, F.; Nolan, S. P. Annu. Rep. Prog.
Chem. Sect B: Org. Chem. 2008, 104, 184–210. (d) Hahn, F. E.; Jahnke,
M. C. Angew. Chem., Int. Ed. 2008, 47, 3122–3172. (e) Diez-Gonzalez, S.;
Nolan, S. P. Coord. Chem. Rev. 2007, 251, 874–883. (f) Clavier, H.; Nolan,
S. P. Annu. Rep. Prog. Chem. Sect B: Org. Chem. 2007, 103, 193–222. (g)
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2007, 46, 2768–2813.
(2) (a) Glorius, F. N-Heterocyclic Carbenes in Transition Metal
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N-Heterocyclic Carbenes in Synthesis; Wiley-VCH: Weinheim, Germany,
2006.
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Chem., Int. Ed. 2003, 42, 3810–3813.
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r
pubs.acs.org/Organometallics
Published on Web 11/02/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 23, 2010 6579
Results and Discussion
Synthesis of (NHC)Pd(sal)Cl Complexes. The air- and
moisture-stable NHC-PdCl2 dimers11 have shown robust
reactivity in aryl amination12 and oxidative kinetic resolu-
tion13 processes; in addition, they can be cleaved readily by
two equivalents of third-party anionic ligands, such as a Cp
ring,14 giving rise to a new type of well-defined NHC-Pd
complexes. The requisite NHC-PdCl2 dimers could be
readily available either from (PhCN)2PdCl2 through the
direct displacement of nitrile ligands with two equivalents
of the free carbenes12,15 or from a [Pd(η3-allyl)Cl]2 dimer via
a two-step sequence with high overall yields.13 After a
detailed investigation, we found that the desired (NHC)Pd
(sal)Cl complexes 1-5 could be obtained efficiently through
straightforward cleavage of the intermediate NHC-PdCl2
dimers by two equivalents of salicylaldimine ligands, pre-
pared by condensation of the corresponding salicylaldehydes
with amines,9b,f in the presence of excess base (Scheme 1).
1,4-Dioxane and Cs2CO3 were ascertained to be the best
solvent and base during the course of reaction. An appro-
priate reaction temperature (90-100 °C) is particularly
important to this transformation, and high temperature
(more than 120 °C) led to the rapid formation of palladium
black. Notably, the procedure can be carried out in air
without obvious adverse influence on the yields.16 In addi-
tion, this new class of well-defined NHC-Pd complexes was
also found to show considerable air- and moisture-stability.
Structural Study of (NHC)Pd(sal)Cl Complexes. The
structures of this new class of well-defined (NHC)Pd(sal)Cl
complexes were fully characterized by spectroscopy data.
The change in the 1H NMR chemical shift of the Himine atom
in the salicylaldimine ligands is an absolute proof of [N,O]
chelating coordination. As seen in complexes 1a-c and 2a-c
Figure 1. New [N,O] chelate (NHC)Pd(sal)Cl complexes.
leads to an increased concentration of active [(NHC)Pd0]
catalytic species.
Seeking to further explore new types of well-defined
NHC-Pd complexes, we are interested in the synthesis of a
class of NHC-Pd complexes incorporating a salicylaldimine
(sal) unit,8 a frequently used chelate ligand in organometallic
and inorganic chemistry.9 The sal ligands bind to the Pd
center through the phenoxide oxygen and imine nitrogen to
provide [N,O] chelate complexes (Figure 1). As mentioned
above, the steric and electronic nature of the ancillary ligands is
of great important to the catalytic ability of their metal com-
plexes. As a result, different substitution patterns in the sal
ligands will bring about a significant distinction in their cata-
lytic performance. In order to examine whether such differ-
ences are present in these chelate metal complexes, we herein
report the synthesis and full characterization of a new class
of well-defined (NHC)Pd(sal)Cl complexes. The structure-
catalytic activity relationship of these novel well-defined
NHC-Pd(II) complexes, especially the steric and electro-
nic effects in the sal ligands on their catalytic performances,
were thereby investigated intensively in the Buchwald-
Hartwig amination.10
1
(Scheme 2), compared with the H NMR signals (δ 8.59,
8.31, and 8.31 ppm, respectively) of the Himine atom in the
free salicylaldimine ligands, they are shifted to higher field
upon coordination to the palladium center by approximately
1 ppm. In addition, the corresponding change has also been
observed in the 13C NMR chemical shift of the Cimine atom in
the salicylaldimine ligand.
(8) [C,O,N] tridentate chelating ligands containing an N-heterocyclic
carbene attached by a salicylaldimine unit have been described; see: (a)
Ulusoy, M.; Sahin, O.; Buyukgungor, O.; Cetinkaya, B. J. Organomet.
Chem. 2008, 693, 1895–1902. (b) Li, W.; Sun, H.; Chen, M.; Wang, Z.; Hu,
D.; Shen, Q.; Zhang, Y. Organometallics 2005, 24, 5925–5928.
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3376. (b) Occhipinti, G.; Jensen, V. R.; Bjørsvik, H. J. Org. Chem. 2007, 72,
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Eur. J. Inorg. Chem. 2006, 3088–3098. (d) Connor, E. F.; Younkin, T. R.;
Henderson, J. I.; Waltman, A. W.; Grubbs, R. H. Chem. Commun. 2003,
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N.; Takagi, Y.; Tsuru, K.; Nitabaru, M.; Nakano, T.; Tanaka, H.; Kashiwa, N.;
Fujita, T. J. Am. Chem. Soc. 2001, 123, 6847–6856. (h) Tian, J.; Hustad,
P. D.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 5134–5135. (i) Younkin,
T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs, R. H.;
Bansleben, D. A. Science 2000, 287, 460–462. (j) Gibson, V. C.; Mastroianni,
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Dalton 2000, 1969–1971.
(10) (a) Hartwig, J. F. Synlett 2006, 1283–1294. (b) Jiang, L.; Buch-
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de Meijere, A., Diederich, F., Eds.; Wiley-VCH: Weinheim, Germany,
2004. (c) Schlummer, B.; Scholz, U. Adv. Synth. Catal. 2004, 346, 1599–
1626. (d) Muci, A. R.; Buchwald, S. L. Top. Curr. Chem. 2002, 219, 131–
209. (e) Hartwig, J. F. In Modern Amination Methods; Ricci, A., Ed.; Wiley-
VCH: Weinheim, 2000. (f) Wolfe, J. P.; Wagaw, S.; Marcoux, J. F.; Buchwald,
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1998, 31, 852–860.
Similar to the previous observations,7,13,17 the 13C NMR
chemical shifts of Ccarbene on the unsaturated imidazol-2-
ylidenes appear at higher field relative to their 4,5-dihydro
counterparts. The 13C NMR spectra of complexes 1a-c
exhibited characteristic high-field resonances for the carbe-
nic carbon at around 165 ppm, while the carbenic carbon re-
sonance for the unsaturated complexes 2a-c was found at a
lower field (190-192 ppm). In spite of the same steric nature,
(12) Viciu, M. S.; Kissling, R. M.; Stevens, E. D.; Nolan, S. P. Org.
Lett. 2002, 4, 2229–2231.
(13) Jensen, D. R.; Sigman, M. S. Org. Lett. 2003, 5, 63–65.
(14) Jin, Z.; Guo, S. X.; Gu, X. P.; Qiu, L. L.; Song, H. B.; Fang, J. X.
Adv. Synth. Catal. 2009, 351, 1575–1585.
(15) Diebolt, O.; Braunstein, P.; Nolan, S. P.; Cazi, C. S. J. Chem.
Commun. 2008, 3190–3192.
(16) We also note that well-defined PEPPSI catalysts can be prepared
smoothly in air. See: (a) Organ, M. G.; Avola, S.; Dubovyk, I.; Hadei,
N.; Kantchev, E. A. B.; O’Brien, C. J.; Valente, C. Chem.;Eur. J. 2006,
12, 4749–4755. (b) 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, 12, 4743–4748.
(17) (a) Broggi, J.; Clavier, H.; Nolan, S. P. Organometallics 2008, 27,
5525–5531. (b) Viciu, M. S.; Kelly, R. A., III; Stevens, E. D.; Naud, F.;
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1123–1127.

6580 Organometallics, Vol. 29, No. 23, 2010
Scheme 1. General Procedures for Preparation of (NHC)Pd(sal)Cl Complexes
Jin et al.
σ-donor properties.20 We observed that, among complexes
1 and 2, complex 2a has the longest distances of Pd-Ccarbene
Scheme 2. Structures of Complexes 1a-c and 2a-c
˚
˚
˚
(1.991(3) A), Pd-N (2.075(2) A), and Pd-Cl (2.2896(8) A)
bonds, as well as the CdN double bond (1.292(4) A). Other
˚
bond distances (e.g., the Pd-O bond) are found comparable
to each other. Following the same trend as the Pd-Ccarbene
bond distances, the bond angles (104.6° for 1a, 105.3° for 1b,
and 104.7° for 1c, respectively) of N-Ccarbene-N in the
unsaturated NHC ligands of complexes 1 are significantly
smaller than those (109.6° for 2a, 108.6° for 2b, and 108.5°
for 2c, respectively) in the saturated analogues in complexes 2.
Among the six complexes the four adjacent bite angles around
the palladium atom center are very close to 90°, especially the
O-Pd-Nimine and O-Pd-Ccarbene angles. We observe also
that complex 2a has the largest bond angles of N-Ccarbene-N
(109.6°) and O-Pd-Ccarbene (92.9°) and the smallest bond
angles of Cl-Pd-Ccarbene (83.3°) relative to other complexes.
Structure-Catalytic Activity Relationship in Aryl Amina-
tion Reaction. Since its introduction, Pd-mediated aryl ami-
nation reaction,10 namely, Buchwald-Hartwig reaction, has
become a powerful tool for the construction of C-N bonds.
The bulky tertiary phosphines21 and NHCs5,7,22 have proven
to be superior supporting ligands for this transformation. In
recent years application of well-defined NHC-Pd com-
plexes as catalysts in aryl amination reactions, especially in
the use of inexpensive aryl chlorides as the substrates, has
been found to be quite promising. Therefore, the catalytic
potential of this new class of well-defined (NHC)Pd(sal)Cl
complexes in the amination reaction of aryl chlorides was
examined.
significantly different reactivity of saturated and unsatu-
rated NHCs are often observed in homogeneous catalysis,18
which should be attributed to their different σ-donor pro-
perties.6a,19
To unambiguously establish the structures of this new
class of complexes, single-crystal X-ray analyses of 1a-c and
2a-c were performed (Table 1). Suitable crystals for single-
crystal XRD studies were obtained by slow diffusion of
n-hexane in saturated Et2O solutions of 1 and 2 in air. In
all cases, a slightly distorted square-planar geometry around
the palladium center was observed and the heterocyclic plane
of the NHCs was found to be almost vertical to this central
plane. In order to satisfy the square-planar geometry of the
central plane around the palladium atom, the salicylaldimine
unit is slightly twisted. Just reverse to intramolecular [C,N,O]
tridentate chelating to the palladium center,8a the phenoxide
oxygen anion is located cis to the NHC ligand, in a direction
opposite the chloride anion, while the neutral imine nitrogen
is located trans to the NHC ligand. Probably due to their [N,
O] chelate coordination, the salicylaldimine unit is almost
coplanar with the central plane of the palladium atom. On
the contrary, the N-substituted aryl ring is situated in a
perpendicular orientation to this plane, especially the largely
sterically demanding mesityl (Mes) and 2,6-diisopropanyl-
phenyl (Dipp) groups (Table 1).
First, using 4-chlorotoluene and morpholine as coupling
partners, the catalytic activities of complexes 1a-c and 2a-c
versus the NHC-PdCl2 dimers in the Buchwald-Hartwig
reaction were evaluated (Table 3). In early experiments we
established that coupling reactions were performed in 1,2-
dimethoxyethane (DME) at 80 °C in the presence of 1 mol %
NHC-Pd complex with NaOBut as a base. We observed that
the sterically encumbered substituents on the nitrogen atom of
the salicylaldimine unit have a negative effect on the coupling.
In addition, the saturated NHC ligands are commonly more
Selected bond distances and angles are listed in Table 2.
The Pd-Ccarbene bond distances in unsaturated NHC com-
plexes 1 (1.975(4) A for 1a, 1.976(3) A for 1b, and 1.9879(17)
˚
˚
˚
A for 1c, respectively) are obviously smaller than analogous
distances in the corresponding saturated NHC complexes 2
˚
˚
˚
(1.991(3) A for 2a, 1.988(2) A for 2b, and 1.989(3) A for 2c,
respectively), which is consistent with previous observations
in other well-defined NHC-Pd complexes.17 Generally, the
Pd-Ccarbene distances in 1 and 2 indicate an exclusive single-
bond character, which is in good accordance with their
(20) (a) McGuinness, D. S.; Cavell, K. J.; Skelton, B. W.; White,
A. H. Organometallics 1999, 18, 1596–1605. (b) Herrmann, W. A.; Elison,
M.; Fischer, J.; Kocher, C.; Artus, G. R. J. Angew. Chem., Int. Ed. Engl.
1995, 34, 2371–2374.
(21) For recent examples on the aryl amination reaction using the
tertiary phosphines as ligand, see: (a) Biscoe, M. R.; Fors, B. P.;
Buchwald, S. L. J. Am. Chem. Soc. 2008, 130, 6686–6687. (b) Altman,
R. A.; Hyde, A. M.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2008,
130, 9613–9620. (c) Ogata, T.; Hartwig, J. F. J. Am. Chem. Soc. 2008, 130,
13848–13849. (d) Fors, B. P.; Waston, D. A.; Biscoe, M. R.; Buchwald, S. L.
J. Am. Chem. Soc. 2008, 130, 13552–13554.
(18) (a) Clavier, H.; Nolan, S. P. Chem.;Eur. J. 2007, 13, 8029–8036.
(b) Ritter, T.; Hejl, A.; Wenzel, A. G.; Funk, T. W.; Grubss, R. H. Organo-
metallics 2006, 25, 5740–5745.
(19) (a) Hillier, A. C.; Sommer, W. J.; Yong, B. S.; Petersen, J. L.;
Cavallo, L.; Nolan, S. P. Organometallics 2003, 22, 4322–4326. (b)
Stauffer, S. R.; Lee, S.; Stambuli, J. P.; Hauck, S. I.; Hartwig, J. F. Org.
Lett. 2000, 2, 1423–1426.
(22) For recent examples on the aryl amination reaction involving
other transition metal-NHC complexes as catalysts, see: (a) Kim, M.;
Chang, S. Org. Lett. 2010, 12, 1640–1643. (b) Ntaganda, R.; Dhudshia, B.;
Macdonald, C. L. B.; Thadani, A. N. Chem. Commun. 2008, 6200–6202.

Article
Organometallics, Vol. 29, No. 23, 2010 6581
Table 1. Molecular Structures of Complexes 1a-c and 2a-ca
a Most hydrogen atoms were omitted for clarity.
effective than the corresponding unsaturated analogues.
Among the six (NHC)Pd(sal)Cl complexes, only 1a and 2a
show comparable reactivity to the NHC-PdCl2 dimers, and
complex 2a is the most effective, affording a 100% conversion
within 2 h (Table 3, entry 5), whereas complexes 1b and 2c
failed to give the desired products (Table 3, entries 3 and 7).
Associated with the unique structure factors of complex 2a, it
can been concluded essentially that the sterically hindered
substituents on the nitrogen atom of the salicylaldimine unit
shield the Pd center from nucleophilic attack by the alkoxide
base, which is not beneficial to the activation step of precata-
lysts for liberating the active Pd0 species into the catalytic
cycle. Nevertheless, the electronic effect of the N-aryl group on
the salicylaldimine unit is not excluded yet.
On the basis of above-mentioned results, the catalytic
performance of (NHC)Pd(sal)Cl complexes, with less steric
demand on the nitrogen atom of the salicylaldimine unit, was
assessed subsequently. The (NHC)Pd(sal)Cl complexes 3a

6582 Organometallics, Vol. 29, No. 23, 2010
Table 2. Selected Bonds and Angles for Complexes 1a-c, 2a-c, and 5b
Jin et al.
1a
2a
1b
2b
1c
2c
5b
˚
Pd-Ccarbene (A)
1.975(4)
2.055(4)
2.017(3)
2.2878(12)
1.273(6)
104.6(4)
91.60(13)
91.16(15)
84.69(13)
92.74(11)
1.991(3)
2.075(2)
2.016(2)
2.2896(8)
1.292(4)
109.6(3)
91.61(9)
92.92(10)
92.34(8)
83.27(9)
1.976(3)
2.046(2)
2.0091(17)
2.2788(10)
1.289(3)
105.3(2)
91.64(7)
91.85(8)
92.84(5)
83.67(6)
1.988(2)
1.9879(17)
2.0685(15)
2.0282(13)
2.2861(5)
1.287(2)
104.75(15)
91.10(5)
91.37(6)
1.989(3)
2.071(2)
2.018(2)
2.2850(8)
1.288(4)
108.5(2)
91.01(9)
92.71(10)
82.55(7)
83.76(8)
1.982(6)
2.079(5)
2.014(5)
2.2798(16)
1.297(7)
109.5(4)
91.65(17)
84.31(19)
93.14(13)
90.81(16)
˚
Pd-N (A)
2.0659(17)
2.0190(15)
2.2872(5)
1.286(3)
108.62(17)
91.77(7)
89.56(7)
˚
Pd-O (A)
˚
Pd-Cl (A)
CdNimine (A)
˚
N-Ccarbene-N (deg)
O-Pd-Nimine (deg)
O-Pd-Ccarbene (deg)
Cl-Pd-Nimine (deg)
Cl-Pd-Ccarbene (deg)
91.56(3)
87.03(6)
92.57(4)
84.97(5)
Table 3. Evaluation of Catalytic Activity for (NHC)Pd(sal)Cl
Complexesa
Scheme 3. Structures of Complexes 3-5
conversion
GCb (%)
isolated
yieldc (%)
entry
NHC-Pd cat.
1d
2
3
4
5
6
7
8
((SIPr)-PdCl2)2
100
91
12
33
100
22
11
10
55
71
85
100
72
87
73
-
1a
1b
1c
2a
2b
2c
3a
3b
4
e
Scheme 4. Synthesis of Complex 6
19
86
14
e
-
-
e
9
48
65
37
92
64
10
11
12
13
5a
5b
6
bulkier substituents on the ketimine nitrogen and the phenolic
ring in the sal ligands might block the axial faces of the metal
center, which retards the rate of associative displacement of the
catalysts.23 Additionally, Fujita and co-workers have also
reported that the electronic nature of the ortho-substituent of
the phenoxide oxygen in the sal unit effected the separation of
the cation-anion pair, which increased the degree of unsatura-
tion associated with the cationic active species, and thus
enhanced the reactivity of polymeriaztion.9g On the contrary,
in the present catalytic system, the introduction of a bulky
methyl substitutent might encumber the nucleophilic attack to
the Pd center by the alkoxide base, which decreases the rate of
catalyst activation. Moreover, the electron-donating methyl
group actually enhanced the coordinating ability of the phe-
noide oxygen, retarding the activation rate of the catalyst from
PdII to Pd0 further. Due to this disadvantage, the attempt to
incorporate a larger alkyl group, such as a tert-butyl group, has
been aborted.
Subsequently, the electronic effect of N-substituted aryl
groups in the salicylaldimine ligands on their catalytic per-
formance was investigated. In this case, a dramatically
different reactivity was found between electron-rich complex
5a and electron-deficient complex 5b (Table 3, entries 11
and 12). For complex 5a, only 37% coupling products
was isolated and considerable dehalogenation product
formed, while an isolated yield of 92% was achieved
by replacement of 5a with complex 5b. Compared with
complex 2a and the corresponding SIPr-PdCl2 dimer,
complex 5b, bearing two electron-withdrawing trifluoro-
methyl groups on the N-aryl ring of the salicylaldimine
ligands, displayed a remarkably increasing activity under
the reaction conditions.
a Reaction conditions: 4-chlorotoluene (1 mmol), morpholine (1.1
mmol), (NHC)Pd(sal)Cl (1 mol %), NaOBut (1.2 mmol), DME (2 mL),
reaction temperature 80 °C (oil bath), reaction time 2 h. b Conversions
were calculated by GC/MS using undecane as an internal standard.
c Isolated yields are based on the average of two runs. d 0.5 mol %
((SIPr)-PdCl2)2 was used. e No products were isolated.
and 3b thus were prepared according to the general proce-
dure (Scheme 3). However, screening results exhibit that
complex 3a is completely ineffective for this catalytic process,
while complex 3b has only moderate efficacy (Table 3, entries
8 and 9). It is noteworthy that unsubstituted salicylaldehyde-
containing NHC-Pd complex 6, prepared directly from the
corresponding NHC-PdCl2 dimers and salicylaldehyde in a
similar manner (Scheme 4), shows considerable reactivity in
this process (Table 3, entry 13).
Previous studies9e,g,23 have demonstrated that the steric
dimensions of the substituent at the ortho-position of the
phenoxide oxygen atom in the salicylaldimine unit have a
significant effect on their catalytic activities. As a result, com-
plex 4, bearing a methyl group at the ortho-position of the
phenoxide oxygen atom in the salicylaldimine unit (Scheme 3),
has been synthesized from 2-methylphenol according to the
literature method.24 However, compared with complex 2a, only
a moderate conversion was achieved with it (Table 3, entry 10).
Grubbs and co-workers have shown that the introduction of
(23) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs,
R. H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149–
3151.
(24) (a) Hansen, T. V.; Skattebol, L. Tetrahedron Lett. 2005, 46,
3829–3830. (b) Hofslokken, N. U.; Skattebol, L. Acta Chem. Scand. 1999,
53, 258–262.

Article
Organometallics, Vol. 29, No. 23, 2010 6583
Figure 2. Molecular structure of complex 5b. Most hydrogen
atoms are omitted for clarity.
Figure 3. Coupling reactions between 4-chlorotoluene and
morpholine with the SIPr-PdCl2 dimer and complexes 2a and
5b at 0.1 mol % catalyst loadings (for the SIPr-PdCl2 dimer,
0.05 mol % catalyst was used). Conversion ratios were determined
by GC/MS using undecane as a calibrated internal standard.
In order to ascertain the structure-reactivity of this new
class of well-defined NHC-Pd complexes, a single-crystal
XRD study for complex 5b has been performed (Figure 2).
As outlined in Table 2, due to the presence of two electron-
withdrawing trifluoromethyl groups, the Pd-N bond (2.079
˚
˚
A) andCdNimine double bond (1.297 A) distances in 5b become
larger than those present in complex 2a, while the correspond-
˚
˚
ing Pd-O bond (2.014 A) and Pd-Cl bond (2.2798 A)
distances in 5b are apparently smaller than those in complex
2a. It thus can be concluded that incorporating electron-with-
drawing 3,5-(bis)trifluoromethyl groups into the N-aryl
ring in the salicylaldimine ligands weakens the strength of
the Pd-N bond. It is the decreased strength of the Pd-N
bond that makes complex 5b prone to be activated into
NHC-Pd0 species.
Notably, complex 5b shows a superior reactivity even at
lower catalyst loading. Given the questions about the cost,
product purity, toxicity, and environmental concerns, redu-
cing the amount of palladium in the catalytic process, parti-
cularly on an industrial scale, is quite important.25 Figures 3
and 4 illustrate the catalytic efficacy of complex 5b relative to
complex 2a and the corresponding SIPr-PdCl2 dimer at low
catalyst loadings. When the coupling reactions were performed
at a 0.1 mol % catalyst loadings, only moderate conversions
were attained after 12 h with complex 2a and the SIPr-PdCl2
dimer as catalyst. Meanwhile, complex 5b achieved an almost
quantitative conversion after a period of 12 h (Figure 3). Even
when catalyst loadings were decreased to as little as 0.01 mol
%, over two-thirds conversion was still achieved with complex
5b after 24 h (Figure 4).
Catalytic Studies of Complex 5b in the Buchwald-Hartwig
Amination Reaction. Extensive bases and solvents were
screened for optimized reaction conditions. The role of the
base appears to be very crucial in the aryl amination process
with complex 5b as catalyst. The coupling reactions pro-
ceeded well with the sterically hindered strong bases includ-
ing KOBut, NaOBut, and KOAmt, whereas inorganic bases,
such as K2CO3, Cs2CO3, LiOH, and K3PO4, are completely
ineffective. Among them, NaOBut gives a slightly better
result. A mechanism proposed originally by Hartwig26 is
Figure 4. Coupling reactions between 4-chlorotoluene and
morpholine with the SIPr-PdCl2 dimer and complexes 2a and
5b at 0.01 mol % catalyst loadings (for the SIPr-PdCl2 dimer,
0.005 mol % catalyst was used). Conversion ratios were deter-
mined by GC/MS using undecane as a calibrated internal
standard.
probably involved, in which the alkoxide base acts as an
initiator in the catalytic cycle and leads to the formation of an
alkoxidepalladium species. With regard to reaction solvent,
1,4-dioxane is found to be a superior solvent to DME for this
N-arylation process. In toluene, an incomplete conversion
was observed. In addition, better catalytic performances were
achieved with decreasing reaction mixture concentration.
A remarkable feature of aryl amination utilizing this new
class of well-defined (NHC)Pd(sal)Cl complexes is the tol-
erance of these reactions to both air and moisture. Only a few
examples of Pd-mediated cross-coupling reaction under
similar conditions have been reported to date.12,27 Therefore,
(25) Garret, C. E.; Prasad, K. Adv. Synth. Catal. 2004, 346, 889–900.
(26) Alcazar-Roman, L. M.; Hartwig, J. F. J. Am. Chem. Soc. 2001,
123, 12905–12906.
(27) (a) Kwong, F. Y.; Klapars, A.; Buchwald, S. L. Org. Lett. 2002,
4, 581–584. (b) Li, G. Y.; Zheng, G.; Noonan, A. F. J. Org. Chem. 2001, 66,
8677–8681.

6584 Organometallics, Vol. 29, No. 23, 2010
Jin et al.
Table 4. Aryl Amination Catalyzed by Complex 5b under Aerobic
Conditionsa
performance of their metal complexes have been investigated
inthe aryl amination reaction. Asexpected, changingthe steric
and electronic properties of ancillary ligands, especially in the
salicylaldimine moiety, has led to a significantly different
reactivity in their corresponding metal complexes. The steri-
cally encumbered N-aryl groups in the salicylaldimine unit
have a negative effect on the coupling reaction. In addition,
incorporating a steric substituent into the ortho-position of the
phenoxide oxygen atom in the salicylaldimine unit also ap-
pears not to be beneficial to their catalytic performance.
Particularly, the electronic nature of N-aryl groups in the
salicylaldimine ligands plays a prominent role in their catalytic
performance. Electron-rich N-aryl groups in the salicylaldi-
mine ligands cause an obviously decreased yield, while an
electron-deficient one, such as complex 5b, induced an ob-
viously increasing reactivity. Additionally, the aryl amination
reaction with complex 5b as catalyst was found to be remark-
ably tolerant to both air and moisture. Under optimized
reaction conditions, a range of aryl chlorides and amines
could be coupled smoothly under aerobic conditions. Studies
aimed at exploring the activity of this family of NHC-Pd
precatalysts in other cross-coupling reactions are currently
ongoing in our laboratories.
Experimental Section
General Comments. Toluene, THF, DME (1,2-dimethoxy-
ethane), and 1,4-dioxane were dried and distilled over Ph2CO/
Na prior to use. All aryl chlorides and amines were used as
received from commercial availability. 1H and 13C nuclear mag-
netic resonance (NMR) spectra were recorded on a Bruker AV400
spectrometer at ambient temperature in CDCl3 (Cambridge Iso-
tope Laboratories, Inc.). ESI mass spectra were recorded on
Thermo Finnigan LCQ Advantage spectrometers. Elemental ana-
lyses were performed on a Perkin-Elmer 240C analyzer. Melting
points of compounds were recorded with uncorrected thermo-
meters. Flash column chromatography was performed on silica gel
60 (230-400 mesh). The requisite salicylaldimine ligands were
prepared according to the literature procedures.9 The intermediate
NHC-PdCl2 dimers were prepared either from the commercially
available (PhCN)2PdCl212,15 or from (Pd(η3-allyl)Cl)2 dimer.13
General Procedures for Synthesis of (NHC)Pd(sal)Cl Com-
plexes 1-5. In air, the starting NHC-PdCl2 dimers (0.5 mmol),
the salicylaldimine ligands (1.1 mmol), Cs2CO3 (326 mg, 1 mmol),
and 1,4-dioxane (10 mL) were charged into a 100 mL round-
bottom flask in turn. The reaction mixture was stirred under
aerobic conditions in a 100 °C oil bath for 2 to 4 h and then cooled
to room temperature. Methylene chloride (50 mL) was added,
and the mixture was filtrated via a short pad of silica gel followed
by exhaustive washing with methylene chloride. The combined
eluent was evaporated under vacuum, and the residue was tritu-
rated in n-pentane. After filtration, (NHC)Pd(sal)Cl complexes
were obtained in pure form with moderate to excellent yields.
Compound 1a. Orange powder, yield 93%, mp 252-254 °C.
1H NMR (400 MHz, CDCl3): δ 7.53 (s, 1H, C-Himine), 7.49 (t,
2H, J = 7.7 Hz, Ar-H), 7.33 (d, 4H, J = 7.7 Hz, Ar-H), 7.16
(t, 3H, J = 7.6 Hz, Ar-H), 7.11 (s, 2H, Ar-H), 7.08 (t, 1H, J =
7.5 Hz, Ar-H), 7.00 (d, 1H, J = 7.5 Hz, Ar-H), 6.93 (d, 2H,
J = 7.8 Hz, (CHCH)NHC), 6.68 (d, 1H, J = 8.6 Hz, Ar-H),
6.44 (t, 1H, J = 7.5 Hz, Ar-H), 3.10 (br, 4H, CH(Me)2 ꢀ 4),
a Reaction conditions: aryl chloride (1 mmol), amine (1.1 mmol), 5b
(1 mol %), NaOBut (1.2 mmol), anhydrous 1,4-dioxane (5 mL), T = 80 °C,
reaction time as indicated. b Isolated yields are the average of two runs.
using optimized reaction conditions, the coupling reactions
between a variety of aryl chlorides and amines were carried
out with complex 5b as catalyst under aerobic conditions,
and the results are presented in Table 4. Compared with the
corresponding air-free system (Table 3, entry 12), using
complex 5b as catalyst, the coupling reaction gives a similar
yield under aerobic conditions. A range of amines was tested
as partners for the coupling reaction. In all cases, products
were isolated in excellent yields. Various inactive aryl chlor-
ides react smoothly with morpholine in high yields (Table 4,
entries 1-4). Both primary and secondary anilines are cap-
able coupling substrates with aryl chlorides, giving rise to the
coupling products in excellent yields (Table 4, entries 5-8).
The less reactive benzylamine and sterically hindered dibu-
tylamine also appeared to be compatible with the present
catalytic system (Table 4, entries 9, 11, and 12). The sterically
encumbered substrates commonly required longer reaction
times to provide a complete conversion (Table 4, entry 6).
1.23 (s, 12H, CH3 ꢀ 4), 1.09 (d, 12H, J = 6.3 Hz, CH3 ꢀ 4). 13
C
NMR (100 MHz, CDCl3): δ 165.5, 162.6, 160.9, 152.0, 135.4,
134.9, 133.9, 130.0, 127.6, 125.7, 124.6, 124.3, 123.9, 122.0,
120.1, 114.1, 28.4, 26.1, 23.1. Anal. Calcd for C40H46ClN3OPd:
C, 66.11; H, 6.38; N, 5.78. Found: C, 66.23; H, 6.38; N, 5.74. MS
(ESI): m/z 726 (Mþ þ H).
Conclusion
In summary, we have synthesized a new class of air- and
moisture-stable NHC-Pd complexes containing an [N,O]
chelating coordinated salicylaldimine ligand. The steric
and electronic effects of ancillary ligands on the catalytic
Compound 1b. Yellow powder, yield 94%, mp 277-279 °C.
1H NMR (400 MHz, CDCl3): δ 7.45 (t, 2H, J = 7.7 Hz, Ar-H),

Article
Organometallics, Vol. 29, No. 23, 2010 6585
7.33 (s, 1H, C-Himine), 7.30 (d, 4H, J = 7.7 Hz, Ar-H), 7.18 (t,
1H, J = 7.6 Hz, Ar-H), 7.11 (s, 2H, Ar-H), 6.93 (d, 1H, J =
7.6 Hz, Ar-H), 6.72 (d, 1H, J = 8.6 Hz, Ar-H), 6.66 (s, 2H,
(CHCH)NHC), 6.42 (t, 1H, J = 7.3 Hz, Ar-H), 3.10 (br, 4H, CH
(Me)2 ꢀ 4), 2.16 (s, 3H, CH3), 1.80 (s, 6H, CH3 ꢀ 2), 1.21 (d,
12H, J = 6.5 Hz, CH3 ꢀ 4), 1.08 (d, 12H, J = 6.1 Hz, CH3 ꢀ 4).
13C NMR (100 MHz, CDCl3): δ 165.1, 163.0, 162.8, 147.9,
135.3, 134.8, 134.2, 133.8, 130.5, 129.8, 127.8, 124.4, 123.8,
123.7, 122.0, 119.5, 113.6, 28.4, 26.2, 23.2, 21.0, 18.3. Anal.
Calcd for C43H52ClN3OPd: C, 67.18; H, 6.82; N, 5.47. Found:
C, 67.25; H, 6.83; N, 5.47; MS (ESI): m/z 768 (Mþ þ H).
Compound 1c. Yellow powder, yield 91%, mp 256-257 °C. 1H
NMR (400 MHz, CDCl3): δ 7.46 (t, 2H, J = 7.7 Hz, Ar-H),
7.43 (s, 1H, C-Himine), 7.30 (br, 4H, Ar-H), 7.22 (t, 1H, J =
7.8 Hz, Ar-H), 7.13 (s, 2H, Ar-H), 7.05 (t, 1H, Ar-H), 6.98
(m, 1H, Ar-H), 6.93 (d, 2H, J = 7.7 Hz, (CHCH)NHC), 6.74
(d, 1H, J = 8.6 Hz, Ar-H), 6.45 (t, 1H, J = 7.3 Hz, Ar-H), 3.50
(br, 2H, CH(Me)2 ꢀ 2), 2.87 (m, 2H, CH(Me)2 ꢀ 2), 2.73 (br,
2H, CH(Me)2 ꢀ 2), 1.17 (s, 12H, CH3 ꢀ 4), 1.03 (s, 12H, CH3 ꢀ
4), 0.86 (t, 12H, J=6.5 Hz, CH3 ꢀ 4). 13C NMR (100 MHz,
CDCl3): δ 165.2, 163.1, 162.5, 147.6, 141.0, 135.3, 135.1, 133.9,
129.8, 126.1, 124.5, 122.3, 122.2, 118.5, 113.7, 28.1, 26.3, 24.1,
22.6. Anal. Calcd for C46H58ClN3OPd: C, 68.14; H, 7.21; N, 5.18.
Found: C, 68.09; H, 7.23; N, 5.13. MS (ESI): m/z 810 (Mþ þ H).
Compound 2a. Orange powder, yield 80%, mp 249-251 °C.
1H NMR (400 MHz, CDCl3): δ 7.51 (s, 1H, C-Himine), 7.40 (t,
2H, J = 7.7 Hz, Ar-H), 7.28 (br, 4H, Ar-H), 7.20 (t, 1H, J=
7.5 Hz, Ar-H), 7.13 (t, 2H, J = 7.7 Hz, Ar-H), 7.05(t, 1H,
J =7.5 Hz, Ar-H), 6.99 (d, 1H, J=7.5 Hz, Ar-H), 6.85 (d, 2H,
J =7.7 Hz, Ar-H), 6.78 (d, 1H, J = 7.7 Hz, Ar-H), 6.45 (t, 1H,
J =7.4 Hz, Ar-H), 4.07 (s, 4H, (CH2CH2)NHC), 3.74 (br, 2H,
CH(Me)2 ꢀ 2), 3.39 (br, 2H, CH(Me)2 ꢀ 2), 1.40 (s, 12H, CH3 ꢀ
2), 1.24 (s, 12H, CH3 ꢀ 4), 1.16 (s, 12H, CH3 ꢀ 2). 13C NMR
(100 MHz, CDCl3): δ 190.7, 165.7, 162.6, 152.0, 135.6, 134.9,
133.9, 129.2, 127.6, 125.7, 124.5, 124.4, 124.3, 122.2, 120.1,
114.1, 53.7, 28.7, 28.5, 28.4, 28.3, 26.7, 26.6, 24.1, 24.0. Anal.
Calcd for C40H48ClN3OPd: C, 65.93; H, 6.64; N, 5.77. Found:
C, 66.01; H, 6.71; N, 5.74. MS (ESI): m/z 728 (Mþ þ H).
Compound 2b. Yellow powder, yield 65%, mp 268-269 °C.
1H NMR (400 MHz, CDCl3): δ 7.37 (t, 2H, J = 7.6 Hz, Ar-H),
7.30 (s, 1H, C-Himine), 7.28 (m, 5H, Ar-H), 6.92 (d, 1H, J =
7.6 Hz, Ar-H), 6.81 (d, 1H, J=8.6 Hz, Ar-H), 6.64 (s, 2H,
Ar-H), 6.43 (t, 1H, J = 7.3 Hz, Ar-H), 4.09 (s, 4H, (CH2-
CH2)NHC), 3.75 (br, 2H, CH(Me)2 ꢀ 2), 3.38 (br, 2H, CH-
(Me)2 ꢀ 2), 2.15 (s, 3H, CH3), 1.74 (s, 6H, CH3 ꢀ 2), 1.33 (s, 6H,
CH3 ꢀ 2), 1.24 (s, 6H, CH3 ꢀ 2), 1.21 (s, 12H, CH3 ꢀ 4). 13C
NMR (100 MHz, CDCl3): δ 192.4, 165.3, 163.1, 147.8, 135.6,
134.8, 134.2, 133.8, 130.5, 129.0, 127.8, 124.5, 124.4, 122.1,
119.6, 113.6, 53.6, 28.7, 28.5, 28.4, 26.6, 24.2, 24.1, 24.0, 21.0,
18.3. Anal. Calcd for C43H54ClN3OPd: C, 67.00; H, 7.06; N, 5.45.
Found: C, 67.12; H, 7.10; N, 5.49. MS (ESI): m/z 770 (Mþ þ H).
Compound 2c. Yellow powder, yield 76%, mp 247-249 °C. 1H
NMR (400 MHz, CDCl3): δ 7.40 (s, 1H, C-Himine), 7.37 (t, 2H,
J=7.7 Hz, Ar-H), 7.25 (m, 5H, Ar-H), 7.02 (t, 1H, Ar-H),
6.95 (d, 1H, J=7.7 Hz, Ar-H), 6.90 (d, 2H, J = 7.7 Hz, Ar-H),
6.85 (d, 1H, J = 8.6 Hz, Ar-H), 6.46 (t, 1H, J = 7.3 Hz,
Ar-H), 4.10 (s, 4H, (CH2CH2)NHC), 3.85 (m, 2H, CH(Me)2 ꢀ
2), 3.32 (m, 2H, CH(Me)2 ꢀ 2), 2.79 (m, 2H, CH(Me)2 ꢀ 2), 1.32
(d, 6H, J = 6.3 Hz, CH3 ꢀ 2), 1.25 (d, 6H, J = 6.6 Hz, CH3 ꢀ 2),
1.19 (d, 6H, J = 6.3 Hz, CH3 ꢀ 2), 1.09 (d, 6H, J = 6.3 Hz,
CH3 ꢀ 2), 0.83 (d, 6H, J = 6.9 Hz, CH3 ꢀ 2), 0.79 (d, 6H, J =
6.8 Hz, CH3 ꢀ 2). 13C NMR (100 MHz, CDCl3): δ 192.5, 165.4,
163.1, 147.9, 147.5, 141.0, 135.5, 135.1, 134.0, 129.0, 126.0,
124.4, 123.9, 122.3, 118.7, 113.6, 53.6, 28.7, 28.2, 28.1, 26.8,
26.7, 24.2, 24.0, 23.9, 22.4. Anal. Calcd for C46H60ClN3OPd: C,
67.97; H, 7.44; N, 5.17. Found: C, 68.01; H, 7.43; N, 5.15. MS
(ESI): m/z 812 (Mþ þ H).
Hz, Ar-H), 6.92 (d, 1H, J = 7.7 Hz, Ar-H), 6.74 (d, 1H, J =
7.7 Hz, Ar-H), 6.42 (t, 1H, J=7.3 Hz, Ar-H), 4.04 (s, 4H,
(CH2CH2)NHC), 3.70 (m, 2H, CH(Me)2 ꢀ 2), 3.47 (m, 2H, CH
(Me)2 ꢀ 2), 3.23 (s, 3H, OCH3), 1.50 (s, 6H, CH3 ꢀ 2), 1.25 (s,
12H, CH3 ꢀ 2), 1.09 (s, 6H, CH3 ꢀ 2). 13C NMR (100 MHz,
CDCl3): δ 191.5, 164.6, 162.1, 147.6, 135.5, 134.1, 133.0, 129.2,
124.5, 124.3, 121.6, 119.8, 113.6, 53.8, 50.0, 28.7, 28.3, 26.5, 24.3.
Anal. Calcd for C35H46ClN3OPd: C, 63.06; H, 6.96; N, 6.30.
Found: C, 63.02; H, 7.03; N, 6.33; MS (ESI): m/z 666 (Mþ þ H).
Compound 3b. Yellow powder, yield 64%, mp 198-199 °C.
1H NMR (400 MHz, CDCl3): δ 7.36 (t, 2H, J=7.6 Hz, Ar-H),
7.30 (s, 1H, C-Himine), 7.25 (m, 4H, Ar-H), 6.98 (t, 1H, J = 7.6
Hz, Ar-H), 6.90 (d, 1H, J = 7.7 Hz, Ar-H), 6.42 (t, 2H, J=
7.3 Hz, Ar-H), 4.03 (s, 4H, (CH2CH2)NHC), 3.55 (m, 4H,
CH(Me)2 ꢀ 4), 1.48 (d, 6H, J=5.7 Hz, CH3 ꢀ 2), 1.24 (s, 9H,
CH3 ꢀ 3), 1.22 (s, 12H, CH3 ꢀ 4), 1.18 (d, 6H, J = 5.8 Hz,
CH3 ꢀ 2). 13C NMR (100 MHz, CDCl3): δ 189.0, 165.7, 158.6,
147.5, 147.2, 135.8, 133.5, 133.0, 128.9, 125.1, 124.4, 124.3,
120.9, 114.1, 62.5, 53.6, 31.4, 28.7, 26.6, 26.3, 23.8, 23.6. Anal.
Calcd for C38H52ClN3OPd: C, 64.40; H, 7.40; N, 5.93. Found:
C, 64.38; H, 7.43; N, 5.93. MS (ESI): m/z 708 (Mþ þ H).
Compound 4. Yellow powder, yield 70%, mp 219-220 °C. 1H
NMR (400 MHz, CDCl3): δ 7.56 (s, 1H, C-Himine), 7.42 (t, 2H,
J=7.6 Hz, Ar-H), 7.28 (d, 4H, J=7.6 Hz, Ar-H), 7.18 (d,
1H, J = 7.6 Hz, Ar-H), 7.11 (t, 2H, J=7.6 Hz, Ar-H), 7.03 (t,
1H, J=7.6 Hz, Ar-H), 6.89 (d, 1H, J=7.6 Hz, Ar-H), 6.80 (d,
2H, J=7.7 Hz, Ar-H), 6.41 (t, 1H, J = 7.3 Hz, Ar-H), 4.10 (m,
4H, (CH2CH2)NHC), 3.91 (m, 2H, CH(Me)2 ꢀ 2), 3.30 (m, 2H,
CH(Me)2 ꢀ 2), 2.35 (s, 3H, ArCH3), 1.38 (d, 6H, J = 6.4 Hz,
CH3 ꢀ 2), 1.23 (d, 12H, J = 6.5 Hz, CH3 ꢀ 4), 0.99 (d, 6H, J =
6.4 Hz, CH3 ꢀ 2). 13C NMR (100 MHz, CDCl3): δ 192.6, 164.1,
163.2, 152.0, 147.7, 135.7, 134.9, 133.5, 129.3, 128.9, 127.6,
125.6, 124.6, 124.5, 124.4, 118.9, 113.7, 53.7, 28.9, 28.3, 26.5,
26.0, 24.1, 23.8, 16.6. Anal. Calcd for C41H50ClN3OPd: C,
66.30; H, 6.79; N, 5.66. Found: C, 66.29; H, 6.81; N, 5.68. MS
(ESI): m/z 742 (Mþ þ H).
Compound 5a. Yellow powder, yield 92%, mp 271-272 °C.
1H NMR (400 MHz, CDCl3): δ 7.49 (s, 1H, C-Himine), 7.40 (t,
2H, J=7.6 Hz, Ar-H), 7.28 (m, 4H, Ar-H), 7.18 (t, 1H, J =7.6
Hz, Ar-H), 6.98 (t, 1H, J = 7.6 Hz, Ar-H), 6.78 (m, 3H,
Ar-H), 6.64 (d, 2H, J = 7.6 Hz, Ar-H), 6.45 (t, 1H, J = 7.3
Hz, Ar-H), 4.07 (s, 4H, (CH2CH2)NHC), 3.72 (br, 2H, CH-
(Me)2 ꢀ 2), 3.70 (s, 3H, OCH3), 3.40 (br, 2H, CH(Me)2 ꢀ 2),
1.42 (s, 6H, CH3 ꢀ 2), 1.24 (s, 12H, CH3 ꢀ 4), 1.15 (s, 6H,
CH3 ꢀ 2). 13C NMR (100 MHz, CDCl3): δ 190.8, 165.6, 162.4,
157.2, 147.5, 145.3, 135.6, 134.8, 133.8, 129.2, 125.1, 124.5, 124.4,
124.3, 122.1, 120.3, 114.4, 112.7, 55.2, 53.7, 28.7, 28.4, 26.5, 24.1.
Anal. Calcd for C41H50ClN3O2Pd: C, 64.90; H, 6.64; N, 5.54.
Found: C, 64.92; H, 6.71; N, 5.58. MS (ESI): m/z 758 (Mþ þ H).
Compound 5b. Orange powder, yield 83%, mp 142-143 °C.
1H NMR (400 MHz, CDCl3): δ 7.55 (m, 2H, Ar-H), 7.44 (m,
2H, Ar-H), 7.31 (m, 7H, C-Himine and Ar-H), 7.02 (m, 1H,
Ar-H), 6.83 (m, 1H, Ar-H), 6.49 (m, 1H, Ar-H), 4.12 (d, 4H,
(CH2CH2)NHC), 3.72 (br, 2H, CH(Me)2 ꢀ 2), 3.38 (br, 2H, CH
(Me)2 ꢀ 2), 1.39 (s, 6H, CH3 ꢀ 2), 1.26 (s, 18H, CH3 ꢀ 6). 13
C
NMR (100 MHz, CDCl3): δ 189.4, 166.3, 163.8, 152.9, 147.9,
147.8, 147.6, 147.5, 135.4, 135.3, 135.0, 131.0, 130.6, 129.4,
125.1, 124.7, 124.5, 124.4, 124.3, 124.2, 122.1, 119.4, 119.3,
114.6, 53.7, 28.8, 28.7, 28.6, 28.5, 24.3, 24.2, 24.1, 24.0, 23.9.
Anal. Calcd for C42H46ClF6N3OPd: C, 58.34; H, 5.36; N, 4.86.
Found: C, 58.32; H, 5.41; N, 4.88. MS (ESI): m/z 864 (Mþ þ H).
Synthesis of Complex 6. In air, the starting SIPr-PdCl2
dimers (568 mg, 0.5 mmol), the salicylaldehyde (135 mg, 1.1
mmol), Cs2CO3 (326 mg, 1 mmol), and 1,4-dioxane (10 mL)
were charged into a 100 mL round-bottom flask in turn. The
reaction mixture was stirred under aerobic conditions in a
100 °C oil bath for 4 h and then cooled back to room tempera-
ture. Methylene chloride (50 mL) was added and the mixture
was filtrated via a short pad of silica gel followed by exhaustive
washing with methylene chloride. The combined eluent was
Compound 3a. Yellow powder, yield 84%, mp 234-235 °C.
1H NMR (400 MHz, CDCl3): δ 7.43 (s, 1H, C-Himine), 7.38 (t,
2H, J=7.6 Hz, Ar-H), 7.30 (m, 4H, Ar-H), 7.14 (t, 1H, J = 7.6

6586 Organometallics, Vol. 29, No. 23, 2010
Jin et al.
evaporated under vacuum, and the residue was triturated in
n-pentane. After filtration, complex 6 was obtained as an orange
powder with a yield of 91%. Mp: 244-246 °C. H NMR (400
for the indicated time. After no further conversion was mon-
itored by TLC, and the mixture was cooled back to room
temperature. An aqueous solution of saturated NH4Cl (5 mL)
was added, and the organic layer was extracted with CH2Cl2 and
dried over Na2SO4. After filtration, the solvent was evaporated
in vacuo and the residue was purified by silica gel column
chromatography with a hexane-ethyl acetate system as eluent.
All the coupling products were isolated in more than 95% purity
by 1H NMR.
1
MHz, CDCl3): δ 8.58 (s, 1H, C-Himine), 7.39 (m, 2H, Ar-H),
7.26 (m, 5H, Ar-H), 7.13 (m, 1H, Ar-H), 6.71 (m, 1H, Ar-H),
6.45 (m, 1H, Ar-H), 4.11 (s, 4H, (CH2CH2)NHC), 3.51 (m, 4H,
CH(Me)2 ꢀ 4), 1.40 (br, 6H, CH3 ꢀ 2), 1.25 (d, 18H, J = 6.0 Hz,
CH3 ꢀ 6). 13C NMR (100 MHz, CDCl3): δ 188.6, 184.8, 168.7,
137.3, 136.5, 135.0, 129.6, 124.6, 124.5, 123.4, 121.3, 114.7, 53.7,
28.6, 26.6, 24.2. Anal. Calcd for C34H43ClN2O2Pd: C, 62.48; H,
6.63; N, 4.29. Found: C, 62.49; H, 6.60; N, 4.25. MS (ESI): m/z
653 (Mþ þ H).
Acknowledgment. We thank the National Natural
Science Foundation of China (NNSFC) for financial
support.
General Procedure for Aryl Amination with Complex 5b under
Aerobic Conditions. In air, a 20 mL vial was charged with
complex 5b (8.6 mg, 1 mol %), NaOBut (115 mg, 1.2 mmol),
1,4-dioxane (5 mL), aryl chloride (1 mmol), and amine (1.1
mmol) in turn. The vial was capped to prevent evaporation and
suspended in an 80 °C oil bath. The reaction mixture was stirred
Supporting Information Available: Crystallographic data,
1
CIF files for complexes 1a-c, 2a-c, and 5b, and H and 13C
NMR spectra for complexes 1-6. This material is available free
of charge via the Internet at http://pubs.acs.org.