New PCN and PCP pincer palladium(II) complexes: convenient synthesis via facile one-pot phosphorylation/palladation reaction and structural characterization

Article abstract of DOI:10.1021/om7008364

A series of new PCN pincer palladium(II) complexes with phosphinito group 2a - d and 3 were conveniently prepared via facile one-pot phosphorylation/ palladation reaction of pyrazolyl or aminocontaining m-phenol derivatives with chlorophosphines and PdCl₂. Two PCP pincer complexes 4a,b were also readily obtained from resorcinol in an analogous yet simplified manner. AU of the new complexes have been fully characterized by ¹H NMR, ¹³C{¹H} NMR, ³¹P{¹H} NMR, IR, ESI-MS, and elemental analysis. Additionally, the molecular structures of 2a - d have been determined by X-ray single-crystal diffraction.

Full text of DOI:10.1021/om7008364

Organometallics 2007, 26, 6487-6492
6487
New PCN and PCP Pincer Palladium(II) Complexes: Convenient
Synthesis via Facile One-Pot Phosphorylation/Palladation Reaction
and Structural Characterization
Jun-Fang Gong, Yan-Hui Zhang, Mao-Ping Song,* and Chen Xu
Department of Chemistry, Henan Key Laboratory of Chemical Biology and Organic Chemistry, Zhengzhou
UniVersity, Zhengzhou 450052, People’s Republic of China
ReceiVed August 16, 2007
A series of new PCN pincer palladium(II) complexes with phosphinito group 2a-d and 3 were
conveniently prepared via facile one-pot phosphorylation/palladation reaction of pyrazolyl or amino-
containing m-phenol derivatives with chlorophosphines and PdCl2. Two PCP pincer complexes 4a,b
were also readily obtained from resorcinol in an analogous yet simplified manner. All of the new complexes
1
have been fully characterized by H NMR, 13C{1H} NMR, 31P{1H} NMR, IR, ESI-MS, and elemental
analysis. Additionally, the molecular structures of 2a-d have been determined by X-ray single-crystal
diffraction.
Scheme 1. Synthetic Strategy for Pincer Palladium
Complexes
Introduction
Pincer palladium complexes containing anionic six-electron
donor ligands of the type YCY have received a considerable
amount of interest, primarily due to their feasible structural
modifications with multiple choices of donor atoms and
substituents thereon (Y ) NR2, SR, PR2, OPR2, etc.), high
stability, and remarkable catalytic activities in various C-C
coupling reactions.1 The most common pincer palladacycles are
NCN,2 PCP,3 or SCS4 types, which are symmetrical with two
identical donor groups and two equivalent five-membered
palladacycles. It is generally accepted that the nature of the
donor group greatly influences the reactivity, stability, and
catalytic performances of these compounds. For instance, the
hardness of the chelating N donor versus the softness of P donor
results in the more labile N-Pd coordination and very different
behavior of the corresponding NCN- and PCP-based complexes.
Therefore, it can be anticipated that mixed, nonsymmetrical
YCY′ pincer palladium complexes, especially those containing
potentially hemilabile hybrid PCN ligands, could benefit from
advantages of varied donors and provide unique reactivity. By
contrast, there are very few reports on the synthesis and
applications of PCN pincer palladium complexes. This is partly
because their preparation is a considerable challenge, which is
laborious and requires a series of steps to introduce different
donors. The synthesis of pincer palladium complexes is usually
performed by direct palladation of the aryl ring via C-H
(3) Selected examples: (a) Morales-Morales, D.; Grause, C.; Kasaoka,
K.; Redo´n, R.; Cramer, R. E.; Jensen, C. M. Inorg. Chim. Acta 2000, 300-
302, 958. (b) Bedford, R. B.; Draper, S. M.; Scully, P. N.; Welch, S. L.
New J. Chem. 2000, 24, 745. (c) Morales-Morales, D.; Redo´n, R.; Yung,
C.; Jensen, C. M. Chem. Commun. 2000, 1619. (d) Eberhard, M. R.; Wang,
Z. H.; Jensen, C. M. Chem. Commun. 2002, 818. (e) Wallner, O. A.; Szabo´,
K. J. Org. Lett. 2004, 6, 1829. (f) Olsson, D.; Nilsson, P.; El Masnaouy,
M.; Wendt, O. F. Dalton Trans. 2005, 11, 1924. (g) Chase, P. A.; Gagliardo,
M.; Lutz, M.; Spek, A. L.; van Klink, G. P. M.; van Koten, G.
Organometallics 2005, 24, 2016. (h) Benito-Garagorri, D.; Bocokic´, V.;
Mereiter, K.; Kirchner, K. Organometallics 2006, 25, 3817. (i) Baber, R.
A.; Bedford, R. B.; Betham, M. B.; Blake, M. E.; Coles, S. J.; Haddow, M.
F.; Hursthouse, M. B.; Orpen, A. G.; Pilarski, L. T.; Pringle, P. G.; Wingad,
R. L. Chem. Commun. 2006, 3880. (j) Kimura, T.; Uozumi, Y. Organo-
metallics 2006, 25, 4883. (k) Churruca, F.; SanMartin, R.; Tellitu, I.;
Dom´ınguez, E. Tetrahedron Lett. 2006, 47, 3233. (l) Naghipour, A.;
Sabounchei, S. J.; Morales-Morales, D.; Canseco-Gonza´lez, D.; Jensen, C.
M. Polyhedron 2007, 26, 1445 and references cited therein.
(4) Selected examples: (a) Kanbara, T.; Yamamoto, T. J. Organomet.
Chem. 2003, 688, 15. (b) Meijer, M. D.; Mulder, B.; van Klink, G. P. M.;
van Koten, G. D. Inorg. Chim. Acta 2003, 352, 247. (c) Yu, K.; Sommer,
W.; Weck, M.; Jones, C. W. S. J. Catal. 2004, 226, 101. (d) Akaiwa, M.;
Kanbara, T.; Fukumoto, H.; Yamamoto, T. J. Organomet. Chem. 2005,
690, 4192. (e) Bergbreiter, D. E.; Osburn, P. L.; Frels, J. D. AdV. Synth.
Catal. 2005, 347, 172. (f) Cervantes, R.; Castillejos, S.; Loeb, S. J.; Ortiz-
Frade, L.; Tiburcio, J.; Torrens, H. Eur. J. Inorg. Chem. 2006, 5, 1076.
* To whom correspondence should be addressed. Tel.: +86 371
67763207. Fax: +86 371 67766667. E-mail: mpsong9350@zzu.edu.cn.
(1) For reviews, see: (a) Albrecht, M.; van Koten, G. Angew. Chem.,
Int. Ed. 2001, 40, 3750. (b) Singleton, J. T. Tetrahedron 2003, 59, 1837.
(c) van der Boom, M. E.; Milstein, D. Chem. ReV. 2003, 103, 1759. (d)
Peris, E.; Crabtree, R. H. Coord. Chem. ReV. 2004, 248, 2239. (e) Dupont,
J.; Consorti, C. S.; Spencer, J. Chem. ReV. 2005, 105, 2527. (f) Pugh, D.;
Danopoulos, A. A. Coord. Chem. ReV. 2007, 251, 610.
(2) Selected examples: (a) Jung, I. G.; Son, S. U.; Park, K. H.; Chung,
K.; Lee, J. W.; Chung, Y. K. Organometallics 2003, 22, 4715. (b) Slagt,
M. Q.; Rodr`ıguez, G.; Grutters, M. M. P.; Gebbink, R. J. M. K.; Klopper,
W.; Jenneskens, L. W.; Lutz, M.; Spek, A. L.; van Koten, G. Chem.-Eur.
J. 2004, 10, 1331. (c) Kjellgren, J.; Sunde´n, H.; Szabo´, K. J. J. Am. Chem.
Soc. 2004, 126, 474. (d) Takenaka, K.; Uozumi, Y. Org. Lett. 2004, 6,
1833. (e) Takenaka, K.; Uozumi, Y. AdV. Synth. Catal. 2004, 346, 1693.
(f) Takenaka, K.; Minakawa, M.; Uozumi, Y. J. Am. Chem. Soc. 2005,
127, 12273. (g) Soro, B.; Stoccoro, S.; Minghetti, G.; Zucca, A.; Cinellu,
M. A.; Gladiali, S.; Manassero, M.; Sansoni, M. Organometallics 2005,
24, 53. (h) Soro, B.; Stoccoro, S.; Minghetti, G.; Zucca, A.; Cinellu, M.
A.; Manassero, M.; Gladiali, S. Inorg. Chim. Acta 2006, 359, 1879. (i)
Yoon, M. S.; Ramesh, R.; Kim, J.; Ryu, D.; Ahn, K. H. J. Organomet.
Chem. 2006, 691, 5927.
10.1021/om7008364 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 11/07/2007

6488 Organometallics, Vol. 26, No. 25, 2007
Scheme 2. Synthesis of PCN Pincer Palladium Complexes 2a-d and 3
Gong et al.
Scheme 3. Synthesis of PCP Pincer Palladium Complexes 4
produced in a similar yet simplified way (Scheme 3). All of
the complexes obtained were applied to the Suzuki reactions
of aryl halides and phenylboronic acid.
Results and Discussion
Synthesis of PCN and PCP Pincer Palladium Complexes.
The synthetic routes of PCN complexes 2 and 3 and PCP
complexes 4 are demonstrated in Schemes 2 and 3, respectively.
Nucleophilic substitution of 3-hydroxybenzylbromide with
pyrazole, 3,5-dimethylpyrazole, or diethylamine readily afforded
pyrazolyl or amino-containing m-phenol derivatives, which
reacted with diphenylchlorophosphine or dicyclohexylchloro-
phosphine in the presence of triethylamine in refluxing toluene
for 6 h, followed by the addition of palladium chloride and reflux
for another 18 h. The new PCN pincer palladium complexes 2
and 3 were successfully obtained in 54-72% isolated yields as
white solids after chromatography on silica gel. Encouraged by
the successful preparation of these complexes, we were inter-
ested to see whether those PCP complexes having two phos-
phinito groups could be synthesized by using this facile one-
pot phosphorylation/palladation reaction. To simplify the
procedure, resorcinol, the appropriate chlorophosphine, pal-
ladium chloride, as well as triethylamine were added simulta-
neously to toluene and refluxed for 24 h. We were pleased to
find that the corresponding PCP pincer complexes 4 could be
obtained in 46% isolated yields upon workup. It should be
pointed out that the yields of PCN complexes 2 and 3 decreased
obviously if PdCl2 was added with chlorophosphine and other
reactants at the same time. In the previously reported synthetic
activation, transmetalation reactions from aryllithium, arylm-
ercury, or arylstannyl derivatives, or by oxidative addition of
aryl halide onto Pd(0) precursors (Scheme 1). These methods
were ascribed to metal introduction routes by Uozumi et al.
because all of them must involve a palladation reaction of the
corresponding pincer ligands creating a new Pd-C σ bond in
the final step. Among these methods, the direct palladation
protocol is particularly attractive because it does not require
prefunctionalization of the pincer ligands to achieve regiose-
lective metalation. Recently, Uozumi et al. developed a new
synthetic strategy, which they called ligand introduction route
in comparison to the former methods. In this ligand introduction
method, the metal was introduced to the aromatic ring prior to
the construction of the ligand unit. Novel NCN and PCP pincer
palladium complexes with bulky, sterically demanding groups2d,e
or moisture-sensitive imino2f and phosphinito groups,3j which
were difficult to synthesize via conventional metal introduction
routes, were successfully synthesized.
Among the few examples of PCN pincer palladium com-
plexes, Dupont et al. reported some PCN palladacycles where
C donors were vinyl instead of aryl carbon anions by chloro-
palladation of heterosubstituted alkynes and used them in the
Heck and Suzuki reactions.5 One of such compounds that
contained a phosphinito and amino group was demonstrated to
be highly efficient for the coupling of arylboronic acids and
aryl chlorides. Additionally, Motoyama et al. prepared the first
non-symmetrical PCN chiral pincer palladium complexes with
(oxazolinyl)phenyl phosphinite ligands via oxidative addition
of an appropriate bromo-substituted derivative.6 Herein, we wish
to report a series of new PCN pincer palladium complexes that
feature a phenyl backbone, a phosphinito group, and a pyrazolyl
or amino group. These complexes were conveniently synthesized
via a facile one-pot phosphorylation/palladation reaction of
pyrazolyl or amino-containing m-phenol derivatives (Scheme
2). Two PCP complexes having two phosphinito groups were
(5) (a) Ebeling, G.; Meneghetti, M. R.; Rominger, F.; Dupont, J.
Organometallics 2002, 21, 3221. (b) Rosa, G. R.; Ebeling, G.; Dupont, J.;
Monteiro, A. L. Synthesis 2003, 18, 2894. (c) Consorti, C. S.; Ebeling, G.;
Flores, F. R.; Rominger, F.; Dupont, J. AdV. Synth. Catal. 2004, 346, 617.
(d) Rosa, G. R.; Rosa, C. H.; Rominger, F.; Dupont, J.; Monteiro, A. L.
Inorg. Chim. Acta 2006, 359, 1947.
Figure 1. Molecular structure of 2a. Hydrogen atoms are omitted
for clarity.
(6) Motoyama, Y.; Shimozono, K.; Nishiyama, K. Inorg. Chim. Acta
2006, 359, 1725.

New PCN and PCP Pincer Palladium(II) Complexes
Organometallics, Vol. 26, No. 25, 2007 6489
Figure 2. 2D layer structure of complex 2a formed by hydrogen bonds. Non-hydrogen-bonding H atoms are omitted for clarity.
Figure 3. One-dimensional chain structure of complex 2b formed by C-H‚‚‚Cl hydrogen bonds. Non-hydrogen-bonding H atoms are
omitted for clarity.
methods for the preparation of pincer palladium complexes with
mono- or diphosphinite ligands, the air- and moisture-sensitive
ligands needed to be constructed and isolated before the
metalation reaction, except for the ligand introduction method
described by Uozumi et al. Therefore, the current one-pot
phosphorylation/palladation strategy has the evident advantages
of avoiding this troublesome isolation step and thus simplifying
the synthetic procedure. At the same time, the direct C2
palladation via C-H activation of the related ligands was
successfully accomplished during the reaction by using cheap
and commercially available palladium chloride (about 10$/g).
As for the preparation of PCP-bis(phosphinite) pincer com-
plexes, we noticed that only one account had been reported
concerning one-pot phosphorylation/palladation reaction, and
PdCl2(COD), which could be synthesized from PdCl2,7 was
added after the phosphorylation reaction.3k Uozumi’s synthetic
Figure 4. Molecular structure of 2c. Hydrogen atoms are omitted
route3j required one to prepare 2-iodoresorcinol (72% yield) from
for clarity.
resorcinol.8
All of the pincer complexes are air- and moisture-stable both
in the solid state and in solution. They were fully characterized
by elemental analysis, 1H NMR, 13C{1H} NMR, 31P{1H} NMR,
DEPT, HSQC, IR, and ESI-MS.
Molecular Structures of Complexes 2a-d. The molecular
structures of PCN pincer palladium complexes 2a-d were
determined by X-ray single crystal analysis. The molecules are
shown in Figures 1-6 (displacement ellipsoids are drawn at
the 30% probability level). Selected bond lengths and bond
angles are listed in Table 1. The palladium atom in each complex
adopts a typical distorted-square-planar configuration defined
by the phosphinito P atom, the carbon atom of central aryl ring,
the pyrazolyl N atom, and the chlorine atom. In the two formed
palladacycles, one is five-membered and the other is a six-
membered metallacycle. It is found that the former shows an
envelope conformation and the latter reveals a boat conforma-
tion. All of the bond lengths and angles around Pd(II) in 2a-d
are similar except a smaller N-Pd-P angle (161.2°) in 2b. The
Pd-C bond lengths are around 2.01 Å, which are comparable
to those found in the PCP-bis(phosphinite) pincer palladium
complexes (1.97-2.02 Å).3a,b,j The Pd-P bond lengths (2.18-
2.20 Å) are slightly shorter than those of bis(phosphinite)
complexes (2.26-2.29 Å).3a,b,j The C-Pd-Cl angles are in the
range 168.6-174.7°, and the N-Pd-P angles of 2a, 2c, and
(7) Drew, D.; Doyle, J. R. Inorg. Synth. 1990, 13, 348.
(8) Hamura, T.; Hosoya, T.; Yamaguchi, H.; Kuriyama, Y.; Tanabe, M.;
Miyamoto, M.; Yasui, Y.; Matsumoto, T.; Suzuki, K. HelV. Chim. Acta
2002, 85, 3589.

6490 Organometallics, Vol. 26, No. 25, 2007
Gong et al.
Figure 5. 2D layer structure of complex 2c formed by hydrogen bonds. Non-hydrogen-bonding H atoms are omitted for clarity.
Figure 6. One-dimensional zigzag chain structure of complex 2d formed by C-H‚‚‚Pd hydrogen bonds. Non-hydrogen-bonding H atoms
are omitted for clarity.
Table 1. Selected Bond Lengths [Å] and Angles [deg] for
In complex 2a, chlorine atom forms a CH‚‚‚Cl hydrogen bond
with the adjacent -CH2- group (Cl1J‚‚‚H19X ) 2.890 Å).9 In
addition, Pd atom not only forms a hydrogen bond with the
adjacent C-H group of the benzene ring (Pd1L‚‚‚H10K ) 2.805
Å), but also forms a hydrogen bond with the adjacent -CH3
group (Pd1L‚‚‚H23Z ) 2.981 Å),10 which are attributed to
construct the 2D layer structure of 2a (Figure 2). Complex 2c
also has a 2D layer structure formed by two types of C-H‚‚‚X
hydrogen bonds and a type of CH‚‚‚M hydrogen bond, which
stabilize the conformation with 2.881 Å for Cl1X‚‚‚H9AE, 2.886
Å for Cl1Z‚‚‚H11E, and 3.124 Å for Pd1Z‚‚‚H10E (Figure 5).
In the crystal of 2b, there exist CH‚‚‚Cl hydrogen bonds between
chlorine atom and the adjacent C-H group of benzene ring
(Cl1‚‚‚H17Z ) Cl1Z‚‚‚H17W ) 2.884 Å), giving the one-
dimensional chain structure of complex 2b (Figure 3). Complex
2d like 2b also has a one-dimensional chain structure (Figure
6). However, the chlorine atom does not participate in hydrogen
PCN Complexes 2a-d
compound
2a
2b
2c
2d
Pd(1)-C(13)
Pd(1)-N(1)
Pd(1)-N(2)
Pd(1)-P(1)
Pd(1)-Cl(1)
2.009(4)
2.005(3)
2.139(3)
2.009(3)
2.098(3)
2.012(3)
2.111(2)
2.159(4)
2.1937(12)
2.3931(12)
2.1860(12)
2.3996(10)
2.1823(8)
2.3829(9)
2.1966(8)
2.3959(10)
C(13)-Pd(1)-N(1)
90.86(13)
91.82(12)
92.36(11)
C(13)-Pd(1)-N(2) 90.54(17)
C(13)-Pd(1)-P(1) 79.59(14)
N(1)-Pd(1)-P(1)
80.55(10)
161.20(8)
80.24(9)
171.56(8)
81.70(9)
169.82(7)
N(2)-Pd(1)-P(1) 166.62(10)
C(13)-Pd(1)-Cl(1) 169.71(12)
N(1)-Pd(1)-Cl(1)
168.63(9)
97.74(9)
174.33(9)
93.85(8)
174.69(9)
91.88(8)
N(2)-Pd(1)-Cl(1)
P(1)-Pd(1)-Cl(1)
97.58(11)
93.30(5)
93.25(4)
94.09(4)
93.63(3)
2d are 166.6-171.6°. In comparison with the P-Pd-P angles
(around 160°) in the PCP-bis(phosphinite) complexes, which
have two equivalent five-membered palladacycles,3a,b,j the bigger
N-Pd-P angles in the present PCN complexes suggest that
introduction of a larger metallacycle decreases the steric strain
of the resultant complexes.
(9) (a) Aakero¨y, C. B.; Evans, T. A.; Seddon, K. R.; Pa´linko´, I. New J.
Chem. 1999, 23, 145. (b) Brammer, L.; Bruton, E. A.; Sherwood, P. Cryst.
Growth Des. 2001, 1, 277.
(10) (a) Braga, D.; Grepioni, F.; Tedesco, E.; Biradha, K.; Desiraju, G.
R. Organometallics 1997, 16, 1846. (b) Stambuli, J. P.; Incarvito, C. D.;
Bu¨hl, M.; Hartwig, J. F. J. Am. Chem. Soc. 2004, 126, 1184.

New PCN and PCP Pincer Palladium(II) Complexes
Organometallics, Vol. 26, No. 25, 2007 6491
1.9, 8.0 Hz, 1H, Ar-H), 6.61 (d, J ) 7.5 Hz, 1H, Ar-H), 6.27 (s,
1H, Ar-H), 5.85 (s, 1H, dCH), 5.13 (s, 2H, CH2), 2.09 (s, 3H,
CH3), 2.02 (s, 3H, CH3). IR (KBr, cm-1): 1602, 1554, 1459, 1382,
1267, 1155, 1128, 1038, 866, 781, 742, 711. Anal. Calcd for
C12H14N2O: C, 71.26; H, 6.98; N, 13.85. Found: C, 71.31; H, 7.16;
N, 13.72.
bonding and the Pd atom forms a CH‚‚‚M hydrogen bond
(Pd1‚‚‚H17W ) Pd1W‚‚‚H17L ) 3.200 Å) instead.
The catalytic activities of all of the obtained PCN and PCP
complexes toward Suzuki reactions of aryl halides with phe-
nylboronic acid were tested and compared (see Supporting
Information).
1-(Pyrazol-1-ylmethyl)-3-hydroxybenzene (1b). 256 mg, 74%
yield, pale yellow solids. mp 50-70 °C. 1H NMR (400 MHz,
CDCl3): δ 7.48 (d, J ) 1.7 Hz, 1H, dCH), 7.39 (d, J ) 2.2 Hz,
1H, dCH), 7.09 (t, J ) 7.9 Hz, 1H, Ar-H), 6.69 (dd, J ) 2.0, 8.1
Hz, 1H, Ar-H), 6.63 (d, J ) 7.6 Hz, 1H, Ar-H), 6.45 (s, 1H,
Ar-H), 6.28 (t, J ) 2.0 Hz, 1H, dCH), 5.20 (s, 2H, CH2). IR
(KBr, cm-1): 1618, 1588, 1490, 1381, 1291, 1249, 1219, 1149,
1088, 1055, 977, 934, 881, 765, 689. Anal. Calcd for C10H10N2O:
C, 68.95; H, 5.79; N, 16.08. Found: C, 68.98; H, 5.84; N, 15.84.
Conclusions
We have developed a facile, direct method based on the one-
pot phosphorylation/palladation reaction for the preparation of
PCN and PCP pincer palladium complexes containing phos-
phinito group(s). A wide variety of such complexes can be
readily constructed from various chlorophosphines and/or N-
donors. We are currently extending this one-pot synthetic
strategy to include chiral PCN pincer palladium complexes and
also further investigating the applications of the obtained
complexes in Pd-catalyzed reactions. The results will be reported
in due course.
General Procedure for the Synthesis of PCN Pincer Pal-
ladium Complexes. To a stirred solution of 1a, 1b, or 1-(diethy-
laminomethyl)-3-hydroxybenzene (1 mmol) and triethylamine (168
uL, 1.2 mmol) in toluene (20 mL) was added diphenylchlorophos-
phine or dicylohexylchlorophosphine (1.2 mmol) under N2 atmo-
sphere at rt. The resultant mixture was refluxed for 6 h. PdCl2 (177
mg, 1 mmol) was then added, and the reaction mixture was refluxed
for another 18 h. After cooling, filtration, and evaporation, the
residue was purified by preparative TLC on silica gel plates eluting
with CH2Cl2/petroleum ether (3:1) to afford the corresponding PCN
pincer complexes.
Experimental Section
General Procedures. All reactions were carried out under
nitrogen atmosphere. Solvents were dried with standard methods
and freshly distilled prior to use except that in the Suzuki reactions
the solvents were analytical grade and used without further
purification. 3-Hydroxybenzylbromide11 and 3,5-dimethylpyrazole12
were prepared according to the published procedures. All other
chemicals were used as purchased. Melting points were measured
on a WC-1 microscopic apparatus and were uncorrected. Elemental
analyses were determined with a Thermo Flash EA 1112 elemental
analyzer. IR spectra were collected on a Bruker VECTOR22
spectrophotometer in KBr pellets. 1H, 13C{1H} NMR, and 31P{1H}
NMR spectra were recorded on a Bruker DPX-400 spectrometer
in CDCl3 with TMS as an internal standard for 1H, 13C{1H} NMR
and 85% H3PO4 as the external standard for 31P{1H} NMR. Mass
spectra were performed on the Agilent LC/MSD Trap XCT
instrument.
2-(3,5-Dimethylpyrazol-1-ylmethyl)-6-(diphenylphosphinoxy)-
phenylchloropalladium(II) (2a). 329 mg, 62% yield, white solids.
1
mp 256-258 °C. H NMR (400 MHz, CDCl3): δ 8.06-8.01 (m,
4H, Ph-H), 7.55-7.46 (m, 6H, Ph-H), 7.03 (dt, J ) 1.6, 7.9 Hz,
1H, Ar-H), 6.92 (d, J ) 7.9 Hz, 1H, Ar-H), 6.79 (d, J ) 7.3 Hz,
1H, Ar-H), 5.89 (s, 1H, dCH), 5.04 (s, 2H, CH2), 2.66 (s, 3H,
CH3), 2.36 (s, 3H, CH3). 13C{1H} NMR (100 MHz, CDCl3): δ
163.7, 152.1, 139.9, 138.7, 138.3, 132.9, 132.4, 132.3, 132.1, 128.7,
128.6, 127.0, 120.9, 112.0, 107.2, 53.2, 15.3, 11.8. 31P{1H} NMR
(162 MHz, CDCl3): δ 154.4. IR (KBr, cm-1): υ 1551, 1469, 1428,
1382, 1356, 1286, 1222, 1107, 1031, 991, 836, 781, 742, 710. Anal.
Calcd for C24H22ClN2OPPd: C, 54.67; H, 4.21; N, 5.31. Found:
C, 54.37; H, 4.22; N, 5.05. MS-ESI+: m/z 491.1 ([M - Cl]+).
Synthesis of Pyrazolyl or Amino-Containing m-Phenol De-
rivatives. Under nitrogen atmosphere, a mixture of 3-hydroxyben-
zylbromide (374 mg, 2 mmol), 3,5-dimethylpyrazole or pyrazole
(2 mmol), and NaH (144 mg, 6 mmol) in 30 mL of dioxane was
refluxed with stirring for 3 days. After being cooled, the reaction
was quenched with water, and the pH value of the solution was
adjusted to about 6. The aqueous layer was then extracted with
dichloromethane, and the organic layers were dried over MgSO4,
filtered, and evaporated. The crude was purified by recrystallization
from acetone for 1a or by preparative TLC on silica gel plates
eluting with CH2Cl2/acetone (2:1) for 1b. 1-(Diethylaminomethyl)-
3-hydroxybenzene was prepared by a similar procedure. K2CO3
instead of NaH was used, and the reaction mixture was refluxed
for 5 h. After being cooled, the reaction was quenched with water,
and the pH value of the solution was adjusted to about 6. Saturated
NaHCO3 solution was then added, and the aqueous layer was
extracted with ethyl acetate. The organic layers were dried over
MgSO4, filtered, and evaporated. The residue was purified by
2-(3,5-Dimethylpyrazol-1-ylmethyl)-6-(dicyclohexylphosphi-
noxy)phenylchloropalladium(II) (2b). 364 mg, 68% yield, white
solids. mp > 260 °C. 1H NMR (400 MHz,CDCl3): δ 6.96 (dt, J )
1.3, 7.7 Hz, 1H, Ar-H), 6.74 (d, J ) 7.9 Hz, 1H, Ar-H), 6.73 (d,
J ) 7.2 Hz, 1H, Ar-H), 5.85 (s, 1H, dCH), 5.00 (s, 2H, CH2),
2.65 (s, 3H, CH3), 2.34 (s, 3H, CH3), 2.36-2.33 (m, 2H, Cy), 2.24-
2.22 (m, 2H, Cy), 1.86-1.61 (m, 12H, Cy), 1.40-1.24 (m, 6H,
Cy). 13C{1H} NMR (100 MHz, CDCl3): δ 165.3, 151.7, 139.6,
138.7, 137.4, 126.4, 120.3, 110.8, 107.0, 53.3, 38.1, 37.8, 27.2,
26.9, 26.5, 26.4, 26.3, 25.8, 15.1, 11.7. 31P{1H} NMR (162 MHz,
CDCl3): δ 195.7. IR (KBr, cm-1): υ 2929, 2851, 1548, 1445, 1421,
1293, 1223, 1036, 888, 835, 784, 760. Anal. Calcd for C24H34-
ClN2OPPd: C, 53.44; H, 6.35; N, 5.19. Found: C, 53.74; H, 6.48;
N, 4.86. MS-ESI+: m/z 503.3 ([M - Cl]+).
2-(Pyrazol-1-ylmethyl)-6-(diphenylphosphinoxy)phenylchlo-
ropalladium(II) (2c). 356 mg, 72% yield, white solids. mp
1
> 260 °C. H NMR (400 MHz, CDCl3): δ 8.43 (d, J ) 2.0 Hz,
1
1H, dCH), 8.03-7.98 (m, 4H, Ph-H), 7.64 (d, J ) 2.0 Hz, 1H,
dCH), 7.53-7.44 (m, 6H, Ph-H), 7.07 (dt, J ) 1.7, 7.9 Hz, 1H,
Ar-H), 6.98 (d, J ) 7.5 Hz, 1H, Ar-H), 6.80 (d, J ) 7.1 Hz, 1H,
Ar-H), 6.36 (s, 1H, dCH), 5.22 (s, 2H, CH2). 13C{1H} NMR (100
MHz, CDCl3): δ 164.4, 142.9, 137.2, 136.6, 132.8, 132.2, 132.1,
132.0, 128.8, 128.6, 127.1, 121.1, 112.2, 106.1, 57.3. 31P{1H} NMR
(162 MHz, CDCl3): δ 156.8. IR (KBr, cm-1): υ 2927, 1426, 1371,
1276, 1211, 1163, 1109, 1067, 1028, 984, 940, 848, 778, 747, 704.
Anal. Calcd for C22H18ClN2OPPd: C, 52.93; H, 3.63; N, 5.61.
Found: C, 53.14; H, 3.66; N, 5.43. MS-ESI+: m/z 463.6 ([M -
Cl]+), 523.3 ([M + Na]+), 963.2 ([2M - Cl]+).
preparative TLC on silica gel plates eluting with ethyl acetate. H
NMR (400 MHz, CDCl3): δ 7.10-7.08 (m, 1H, Ar-H), 6.81 (s,
1H, Ar-H), 6.78 (d, J ) 7.5 Hz, 1H, Ar-H), 6.70 (d, J ) 7.9 Hz,
1H, Ar-H), 3.55 (s, 2H, CH2), 2.57 (q, J ) 7.1 Hz, 4H, CH2CH3),
1.05 (t, J ) 7.1 Hz, 6H, CH2CH3).
1-(3,5-Dimethylpyrazol-1-ylmethyl)-3-hydroxybenzene (1a).
316 mg, 78% yield, white solids. mp 150-152 °C. 1H NMR (400
MHz, CDCl3): δ 7.09 (t, J ) 7.8 Hz, 1H, Ar-H), 6.66 (dd, J )
(11) Przybilla, K. J.; Voegtle, F. Chem. Ber. 1989, 122, 347.
(12) U.S. patent 4282361, 04 Aug 1981.

6492 Organometallics, Vol. 26, No. 25, 2007
Table 2. Summary of Crystal Structure Determination for PCN Complexes 2a-d
Gong et al.
2a
2b
2c
2d
formula
Mr
C24H22ClN2OPPd
527.26
C24H34ClN2OPPd
539.35
C22H18ClN2OPPd
499.20
C22H30ClN2OPPd
511.30
cryst size [mm]
a [Å]
b [Å]
0.20 × 0.18 × 0.16
17.515(4)
14.425(3)
18.312(4)
90
103.20(3)
90
4504.4(16)
8
0.20 × 0.18 × 0.17
18.559(4)
8.2434(16)
17.756(4)
90
114.69(3)
90
2468.2(8)
4
0.20 × 0.18 × 0.16
9.798(2)
17.997(4)
11.691(2)
90
100.46(3)
90
2027.3(7)
4
0.20 × 0.16 × 0.16
9.7206(19)
23.522(5)
10.375(2)
90
109.16(3)
90
2240.9(8)
4
c [Å]
R [deg]
â [deg]
γ [deg]
V [Å3]
Z
space group
P2(1)/c
1.555
1.032
1.19-25.50
13990
8056
6909
0.0621
P2(1)/c
1.451
0.943
1.21-25.49
7744
4360
3725
0.0451
P2(1)/n
1.636
1.141
2.10-25.50
6556
3673
3366
0.0365
P2(1)/n
1.516
1.034
1.73-25.50
7353
3978
3655
0.0369
D
calcd [g cm-3
]
µ [mm-1
θ range [deg]
]
no. of data collected
no. of unique data
obsd data [I g 2σ(I)]
R (all data)
Rw (all data)
0.1307
0.0851
0.0735
0.0868
F(000)
2128
0.951/-0.933
1112
0.329/-0.483
1000
0.347/-0.492
1048
0.348/-0.678
peak/hole [e Å-3
]
2-(Pyrazol-1-ylmethyl)-6-(dicyclohexylphosphinoxy)phenyl-
2,6-Bis(dicyclohexylphosphinoxy)phenylchloropalladium-
(II) (4b). 149 mg, 46% yield, white solids. mp 199-202 °C. H
1
chloropalladium (II) (2d). 300 mg, 59% yield, white solids. mp
1
> 260 °C. H NMR (400 MHz, CDCl3): δ 8.43 (s, 1H, dCH),
NMR (400 MHz, CDCl3): δ 6.95 (t, J ) 8.0 Hz, 1H, Ar-H), 6.51
(d, J ) 8.0 Hz, 2H, Ar-H), 2.29-2.23 (m, 4H, Cy), 2.04-2.00
(m, 4H, Cy), 1.93-1.82 (m, 12H, Cy), 1.71-1.53 (m, 12H, Cy),
1.39-1.22 (m, 12H, Cy). 13C{1H} NMR (100 MHz, CDCl3): δ
166.3, 129.6, 127.9, 105.8, 37.9, 37.8, 37.7, 27.0, 26.7, 26.5, 26.4,
26.3, 25.8. 31P{1H} NMR (162 MHz, CDCl3): δ 181.7. IR (KBr,
cm-1): 2928, 2850, 1567, 1442, 1243, 1221, 1179, 1112, 1001,
888, 849, 761. Anal. Calcd for C30H47ClO2P2Pd: C, 55.99; H, 7.36.
Found: C, 55.98; H, 7.18. MS-ESI+: m/z 608.0 ([M - Cl]+),
1251.5 ([2M - Cl]+).
X-ray Diffraction Studies. Crystals of PCN pincer complexes
2a-d were obtained by recrystallization from dichloromethane and
petroleum ether at ambient temperature. All diffraction data were
collected with a Rigaku-IV imaging plate area detector using
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). The
diffraction data were corrected for Lorentz and polarization factors.
The structures were solved by direct methods13 and expanded using
Fourier techniques and refined by full-matrix least-squares methods.
The non-hydrogen atoms were refined anisotropically, and the
hydrogen atoms were included but not refined. Their raw data were
corrected, and the structures were solved using the SHELXL-97
program.14 Details of crystal structure determination of complexes
2a-d are summarized in Table 2.
7.66 (s, 1H, dCH), 7.06 (t, J ) 7.6 Hz, 1H, Ar-H), 6.84 (d, J )
7.9 Hz, 1H, Ar-H), 6.80 (d, J ) 7.3 Hz, 1H, Ar-H), 6.40 (s, 1H,
dCH), 5.25 (s, 2H, CH2), 2.38-2.32 (m, 2H, Cy), 2.25-2.22 (m,
2H, Cy), 1.87-1.62 (m, 12H, Cy), 1.41-1.24 (m, 6H, Cy). 13C-
{1H} NMR (100 MHz, CDCl3): δ 165.7, 142.1, 137.0, 135.6, 131.7,
126.4, 120.4, 110.9, 105.7, 57.3, 37.5, 37.3, 26.8, 26.6, 26.2, 26.1,
26.0, 25.5. 31P{1H} NMR (162 MHz, CDCl3): δ 196.7. IR (KBr,
cm-1): υ 2930, 2852, 1633, 1555, 1445, 1420, 1380, 1281, 1228,
1173, 1116, 1071, 995, 944, 845, 766. Anal. Calcd for C22H30-
ClN2OPPd: C, 51.68; H, 5.91; N, 5.48. Found: C, 51.92; H, 5.99;
N, 5.10. MS-ESI+: m/z 475.7 ([M - Cl]+), 535.4 ([M + Na]+),
987.4 ([2M - Cl]+).
2-(Diethylaminomethyl)-6-(diphenylphosphinoxy)phenylchlo-
ropalladium(II) (3). 272 mg, 54% yield, white solids. mp 216-
1
217 °C. H NMR (400 MHz, CDCl3): δ 8.03-7.97 (m, 4H, Ph-
H), 7.48-7.46 (m, 6H, Ph-H), 7.00 (t, J ) 7.8 Hz, 1H, Ar-H),
6.76 (d, J ) 7.9 Hz, 1H, Ar-H), 6.71 (d, J ) 7.5 Hz, 1H, Ar-H),
4.18 (s, 2H, CH2), 3.46-3.41 (m, 2H, CH2CH3), 2.89-2.82 (m,
2H, CH2CH3), 1.48 (t, J ) 7.1 Hz, 6H, CH2CH3). 13C{1H} NMR
(100 MHz, CDCl3): δ 162.7, 152.0, 145.6, 134.7, 134.1, 132.6,
132.4, 132.3, 129.6, 129.5, 127.4, 116.8, 110.2, 66.4, 56.3, 14.3.
31P{1H} NMR (162 MHz, CDCl3): δ 152.4. IR (KBr, cm-1): υ
3050, 2966, 2925, 2859, 1460, 1430, 1226, 1107, 995, 830, 772,
749, 703. Anal. Calcd for C23H25ClNOPPd: C, 54.78; H, 5.00; N,
2.78. Found: C, 54.92; H, 5.14; N, 2.56. MS-ESI+: m/z 468.3 ([M
- Cl]+), 528.2 ([M + Na]+), 973.1 ([2M - Cl]+).
Acknowledgment. We are grateful to the National Science
Foundation of China (20572102), the Innovation Fund for
Outstanding Scholar of Henan Province (074200510005), and
the Natural Science Foundation of Henan Province (0611012100)
for financial support of this work.
General Procedure for the Synthesis of PCP Pincer Palladium
Complexes. To a stirred solution of resorcinol (55 mg, 0.5 mmol),
PdCl2 (90 mg, 0.5 mmol), and triethylamine (280 uL, 2.0 mmol)
in toluene (20 mL) was added diphenylchlorophosphine or dicy-
clohexylchlorophosphine (1.2 mmol) under N2 atmosphere at rt.
The resultant mixture was refluxed for 24 h. After cooling, filtration,
and evaporation, the residue was purified by preparative TLC on
silica gel plates eluting with CH2Cl2 to afford the corresponding
PCP pincer complexes.
2,6-Bis(diphenylphosphinoxy)phenylchloropalladium(II) (4a).3e
141 mg, 46% yield, white solids. 1H NMR (400 MHz, CDCl3): δ
8.00-7.95 (m, 8H, Ph-H), 7.52-7.47 (m, 12H, Ph-H), 7.09 (t, J
) 8.0 Hz, 1H, Ar-H), 6.75 (d, J ) 8.0 Hz, 2H, Ar-H).
Supporting Information Available: Applications of complexes
1
2-4 to the Suzuki reactions and their H NMR, 13C{1H} NMR,
31P{1H} NMR, as well as ESI-MS spectra. Full crystallographic
data for compounds 2a-d are available as CIF files. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM7008364
(13) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(14) Sheldrick, G. M. SHELXL-97, Program for Refinement of Crystal
Structure; University of Go¨ttingen: Germany, 1997.