Palladium/P,O-Ligand-Catalyzed Suzuki Cross-Coupling Reactions of Arylboronic Acids and Aryl Chlorides. Isolation and Structural Characterization of (P,O)-Pd(dba) Complex

Article abstract of DOI:10.1021/jo990805t

The phenyl backbone-derived P,O-ligands 1 and 2 were investigated for their utility as ligands in palladium/ligand-catalyzed Suzuki reactions. The 2-(2′-dicyclohexylphosphinophenyl)-2-methyl-1,3-dioxolane (ligand 1) in combination with Pd(dba)₂ affords an efficient catalyst for general Suzuki reactions of a wide variety of arylboronic acids and aryl chlorides, bromides, and iodides to afford the desired biaryl products in high isolated yields. Arylboronic acids and aryl chlorides containing electron-poor, electron-rich, and ortho substituents participate effectively. In contrast, the structurally related ligand 2-(2′-dicyclohexylphosphinophenyl)-1,3-dioxolane (ligand 2) was found to be less efficient under similar conditions. The reaction of ligand 1 with Pd(dba)₂ affords the complex LPd-(dba) (14, L = 1). The NMR spectroscopic and X-ray crystallographic data of complex 14 establish that ligand 1 functions as a P,O-chelating ligand in complex 14. The reaction of ligand 2 (2 equiv) with Pd(dba)₂ and excess 4-^tBu-C₆H₄Br or the ligand displacement reaction of {Pd[P(o-tolyl)₃](4-tBu-C₆H₄)(μ-Br)} ₂ with ligand 2 affords the bis-phosphine complex L₂Pd(4-^tBu-C₆H₄)(Br) (13, L = 2). The NMR spectroscopic data of complex 13 establish that ligand 2 in complex 13 functions as a nonchelating ligand. Thus, the higher efficiency of ligand 1 over ligand 2 in Pd/L-catalyzed Suzuki arylation of aryl chlorides can be ascribed to the ability of ligand 1 to generate and stabilize monophosphine P,O-chelating Pd/L intermediates, which appear to be most suitable for Suzuki arylation reactions involving certain substrates and conditions.

Full text of DOI:10.1021/jo990805t

J . Org. Chem. 1999, 64, 6797-6803
6797
P a lla d iu m /P ,O-Liga n d -Ca ta lyzed Su zu k i Cr oss-Cou p lin g Rea ction s
of Ar ylbor on ic Acid s a n d Ar yl Ch lor id es. Isola tion a n d Str u ctu r a l
Ch a r a cter iza tion of (P ,O)-P d (d ba ) Com p lex
Xiaohong Bei,* Howard W. Turner, W. Henry Weinberg, and Anil S. Guram*
Symyx Technologies, 3100 Central Expressway, Santa Clara, California 95051
J effrey L. Petersen
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506
Received May 17, 1999
The phenyl backbone-derived P,O-ligands 1 and 2 were investigated for their utility as ligands in
palladium/ligand-catalyzed Suzuki reactions. The 2-(2′-dicyclohexylphosphinophenyl)-2-methyl-1,3-
dioxolane (ligand 1) in combination with Pd(dba)2 affords an efficient catalyst for general Suzuki
reactions of a wide variety of arylboronic acids and aryl chlorides, bromides, and iodides to afford
the desired biaryl products in high isolated yields. Arylboronic acids and aryl chlorides containing
electron-poor, electron-rich, and ortho substituents participate effectively. In contrast, the structur-
ally related ligand 2-(2′-dicyclohexylphosphinophenyl)-1,3-dioxolane (ligand 2) was found to be less
efficient under similar conditions. The reaction of ligand 1 with Pd(dba)2 affords the complex LPd-
(dba) (14, L ) 1). The NMR spectroscopic and X-ray crystallographic data of complex 14 establish
that ligand 1 functions as a P,O-chelating ligand in complex 14. The reaction of ligand 2 (2 equiv)
with Pd(dba)2 and excess 4-tBu-C6H4Br or the ligand displacement reaction of {Pd[P(o-tolyl)3](4-
tBu-C6H4)(µ-Br)}2 with ligand 2 affords the bis-phosphine complex L2Pd(4-tBu-C6H4)(Br) (13, L )
2). The NMR spectroscopic data of complex 13 establish that ligand 2 in complex 13 functions as
a nonchelating ligand. Thus, the higher efficiency of ligand 1 over ligand 2 in Pd/L-catalyzed Suzuki
arylation of aryl chlorides can be ascribed to the ability of ligand 1 to generate and stabilize mono-
phosphine P,O-chelating Pd/L intermediates, which appear to be most suitable for Suzuki arylation
reactions involving certain substrates and conditions.
In tr od u ction
the industrially significant aryl chlorides as the aryl
electrophiles has remained generally limited to electron-
deficient aryl chlorides or nickel-catalyzed reactions.6,7
Recently, efficient palladium/ligand catalysts for general
reactions of arylboronic acids and aryl chlorides were
The Suzuki cross-coupling reactions of arylboronic
acids and aryl electrophiles provide an effective and
attractive synthetic route to biaryls,1 which are an
important class of organic compounds useful as precur-
sors to pharmaceuticals, polymers, materials, liquid
crystals, and ligands. Among the aryl electrophiles
investigated, aryl iodides, bromides, and triflates have
been found to be the most reactive and are therefore
commonly employed.2,3 The general usefulness of aryl
mesylates4 and diazonium salts5 as suitable aryl electro-
philes has been recently demonstrated, but the utility of
(3) Leading references for Suzuki reactions involving aryl triflates:
(a) Oh-e, T.; Miyaura, N.; Suzuki, A. Synlett 1990, 221-223. (b) Huth,
A.; Beetz, I.; Schumann, I. Tetrahedron 1989, 45, 6679-6682. (c) Fu,
J .-m.; Snieckus, V. Tetrahedron Lett. 1990, 31, 1665-1668. (d) Oh-e,
T.; Miyaura, N.; Suzuki, A. J . Org. Chem. 1993, 58, 2201-2208.
(4) (a) Percec, V.; Bae, J .-Y.; Hill, D. H. J . Org. Chem. 1995, 60,
1060-1065. (b) Percec, V.; Bae, J .-Y.; Zhao, M.; Hill, D. H. J . Org.
Chem. 1995, 60, 176-185. (c) Percec, V.; Bae, J .-Y.; Zhao, M.; Hill, D.
H. J . Org. Chem. 1995, 60, 1066-1069. (d) Percec, V.; Bae, J .-Y.; Hill,
D. H. J . Org. Chem. 1995, 60, 6895-6903. (e) Percec, V.; Zhao, M.;
Bae, J .-Y.; Hill, D. H. Macromolecules 1996, 29, 3727-3735. (f) Percec,
V.; Bae, J .-Y.; Zhao, M.; Hill, D. H. Macromolecules 1995, 28, 6726-
6734.
(1) (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457-2483.
(b) Suzuki, A. Pure Appl. Chem. 1991, 63, 419-422. (c) Stanforth, S.
P. Tetrahedron 1998, 54, 263-303. (d) Martin, A. R.; Yang, Y. Acta
Chem. Sand. 1993, 47, 221-230. (e) Beletskaya, I. P. Bull Acad. Sci.
USSR, Div. Chem. Sci. (Engl. Transl.) 1990, 39, 2013-2028. (f)
Beletskaya, I. P. J . Organomet. Chem. 1983, 250, 551-564.
(2) Leading references for Suzuki reactions involving aryl iodides
and bromides: (a) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun.
1981, 11, 513-519. (b) Thompson, W. J .; Gaudino, J . J . Org. Chem.
1984, 49, 5237-5243. (c) Miller, R. B.; Dungar, S. Organometallics
1984, 3, 1261-1263. (d) Sato, M.; Miyaura, N.; Suzuki, A. Chem. Lett.
1989, 1405-1408. (e) Wallow, T. I.; Novak, B. M. J . Org. Chem. 1994,
59, 5034-5037. (f) Watanabe, T.; Miyaura, N.; Suzuki, A. Synlett 1992,
207-210. (g) Marck, G.; Villiger, A.; Buchecker, R. Tetrahedron Lett.
1994, 35, 3277-3280. (h) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth.
Commun. 1981, 11, 513-519. (i) Fu, J .-m.; Sharp, M. J .; Snieckus, V.
Tetrahedron Lett. 1988, 29, 5459-5462. (j) Bumagin, N. A.; Bykov, V.
V.; Beletskaya, I. P. Bull. Acad. Sci., USSR, Div. Chem. Sci. (Engl.
Transl.) 1989, 38, 2206. (k) Hegedus, L. S. J . Organomet. Chem. 1993,
457, 167-272. (l) Casalnuvo, A. L.; Calabrese, J . C. J . Am. Chem. Soc.
1990, 112, 4324-4330. (m) Genet, J . P.; Blart, E.; Savignac, M. Synlett
1992, 715-717.
(5) (a) Sengupta, S.; Bhattacharyya, S. J . Org. Chem. 1997, 62,
3405-3406. (b) Darses, S.; J effery, T.; Genet, J .-P.; Brayer, J .-L.;
Demoute, J .-P. Tetrahedron Lett. 1996, 37, 3857-3860.
(6) Earlier examples of Pd-catalyzed Suzuki biaryl cross-couplings
involving aryl chlorides: (a) Beller, M.; Fischer, H.; Herrmann, W. A.;
Ofele, K.; Brossmer, C. Angew. Chem., Int. Ed. Engl. 1995, 34, 1848-
1849. (b) Bumagin, N. A.; Bykov, V. V. Tetrahedron 1997, 53, 14437-
14450. (c) Shen, W. Tetrahedron Lett. 1997, 38, 5575-5578. (d) Cornils,
B. Org. Process Res. Dev. 1998, 2, 121-127. (e) Mitchell, M. B.;
Wallbank, P. J . Tetrahedron Lett. 1991, 32, 2273-2276. (f) Firooznia,
F.; Gude, C.; Chan, K.; Satoh, Y. Tetrahedron Lett. 1998, 39, 3985-
3988. (g) Zhang, H.; Chan, K. S. Tetrahedron Lett. 1996, 37, 1043-
1044. (h) Gronowitz, S.; Hornfeldt, A. B.; Kristjansson, V.; Musil, T.
Chem. Scr. 1986, 26, 305-309. (i) Thompson, W. J .; J ones, J . H.; Lyle,
P. A.; Thies, J . E. J . Org. Chem. 1998, 53, 2052-2055. (j) Uemura,
M.; Nishimura, H.; Kamikawa, K.; Nakayama, K.; Hayashi, Y.
Tetrahedron Lett. 1994, 35, 1909-1912. (k) Herrmann, W. A.; Reis-
inger, C. P.; Spiegler, M. J . Organomet. Chem. 1998, 557, 93-96. (l)
Grushin, V. V.; Alper, H. Chem. Rev. 1994, 94, 1047-1062. (m) Haber,
S.; Kleiner, H.-J . US Patent 5,756,804, 1998.
10.1021/jo990805t CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/13/1999

6798 J . Org. Chem., Vol. 64, No. 18, 1999
Bei et al.
Ta ble 1. Ba se Effects in th e Su zu k i Rea ction of
independently reported by the research groups at MIT
and Symyx Technologies.8-10
5-Ch lor o-m -xylen e a n d P h en ylbor on ic Acid a
As part of our overall program to identify, develop, and
utilize high-throughput methods for the discovery of
useful materials,11 a class of phenyl backbone-derived
P,O-ligands were identified to be efficient for the general
palladium/ligand-catalyzed aminations of aryl bromides,
iodides, and chlorides.12 The key P,O-ligand was subse-
quently identified to be also suitable for the general
palladium/ligand-catalyzed Suzuki reactions of aryl
haldies.10 Details of this Suzuki catalyst discovery study
at Symyx Technologies are described herein. The study
illustrates that phenyl backbone-derived P,O-ligand 1
provides an efficient palladium/ligand 1 catalyst for
general Suzuki cross-coupling reactions of aryl halides
including aryl chlorides. The study also illustrates that
slight difference in the P,O-ligand structure influences
the catalytic efficiency of the palladium/P,O-ligand-
catalyzed Suzuki biaryl cross-coupling reactions.
a
Unless indicated otherwise, all reactions were conducted in
toluene (4 mL) at 105 °C using 1.0 equiv of 5-chloro-m-xylene, 1.5
equiv of phenylboronic acid, 3.0 equiv of base, 1 mol % of Pd(dba)2,
b
and 3 mol % of ligand. Calibrated conversions of starting aryl
chloride to the desired biaryl at 3 h, based on GC-MS. c Similar
d
result was obtained using toluene/H2O (3/1) as solvent. Numbers
in parentheses correspond to GC-MS conversions at 5 h at
reaction temperature of 110 °C.
Resu lts
neacetone) reaction of 5-chloro-m-xylene and phenylbo-
ronic acid was chosen as a model reaction for investigat-
ing the efficiencies of ligands and bases (Table 1). While
ligand 1 was found to be efficient, affording the desired
biaryl product in high GC yield, the structurally related
ligand 2 was found to be surprisingly less efficient and
exhibited lower conversions under otherwise similar
reaction conditions.14 Among the bases investigated, CsF
and K3PO4 were found to be the most efficient. Toluene
and 1,4-dioxane were found to be generally suitable
solvents.
I. Syn th esis of Liga n d s 1 a n d 2. Ligands 1 and 2
were prepared in two high-yield steps from the com-
mercially available starting materials, 2′-bromoacetophe-
none and 2-bromobenzaldehyde, respectively, as illus-
trated in eq 1.13 The ligands 1 and 2 were purified by
recrystallization from deoxygenated methanol solvent
and were obtained as white solids and unambiguously
characterized by 1H, 13C, and 31P NMR spectroscopy and
elemental analysis.
The utility of the Pd(dba)2/ligand 1 catalyst for general
Suzuki biaryl cross-coupling reactions of aryl chlorides
was further investigated to determine its scope and
limitations.15 In general and as shown in Table 2, the
Pd(dba)2/ligand 1 catalyst was found to exhibit a broad
scope. The Pd(dba)2/ligand 1 catalyst was found to be
generally efficient in catalyzing the cross-coupling reac-
tions of a wide variety of arylboronic acids and aryl
chlorides to afford the desired biaryl products in high
isolated yields (Table 2). Arylboronic acids and aryl
chlorides containing both electron-poor and electron-rich
substituents participated effectively. Aryl chlorides con-
taining ortho substituents also reacted effectively (entries
C and J , Table 2). More remarkably, o-chlorotoluene
reacted efficiently with o-tolylboronic acid to afford the
desired sterically demanding biaryl product, 2,2′-di-
methyl-1,1′-biphenyl, in 91% isolated yield (entry K,
Table 2). Aryl bromides and iodides were also found to
be suitable substrates (entries G and H, Table 2).
III. Na tu r e of th e P d /L Ca ta lysts. The difference in
efficiency of ligands 1 and 2 in Pd/L-catalyzed Suzuki
biaryl cross-coupling reaction suggests that the potential
catalytic intermediates involved in the catalytic cycle
II. P d /L (L ) 1, 2)-Ca t a lyzed Su zu k i Cr oss-
Cou p lin g Rea ction s of Ar ylbor on ic Acid s a n d Ar yl
Ch lor id es. The Pd(dba)2/L-catalyzed (dba ) dibenzylide-
(7) Ni-catalyzed Suzuki reactions involving aryl chlorides; see ref
6f. See also: (a) Saito, S.; Oh-tani, S.; Miyaura, N. J . Org. Chem. 1997,
62, 8024-8030. (b) Saito, S.; Sakai, M.; Miyaura, N. Tetrahedron Lett.
1996, 37, 2993-2996. (c) Indolese, A. F. Tetrahedron Lett. 1997, 38,
3513-3516.
(8) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. Engl. 1998, 37,
3387-3388.
(9) Old, D. W.; Wolfe, J . P.; Buchwald, S. L. J . Am. Chem. Soc. 1998,
120, 9722-9723.
(10) Bei, X.; Crevier, T.; Guram, A. S.; J andeleit, B.; Powers, T. S.;
Turner, H. W.; Uno, T.; Weinberg, W. H. Tetrahedron Lett. 1999, 40,
3855-3858.
(14) The Pd(dba)2/ligand 2 catalyst is suitable for amination of aryl
chlorides with both cyclic and acyclic secondary amines (Bei, X.;
Guram, A. S. Unpublished results), although the reactions are slower
compared to the analogous reactions catalyzed by Pd(dba)2/ligand 1
(ref 12a). For example, Pd(dba)2/ligand 2-catalyzed reaction of 5-chloro-
m-xylene with N-heptylmethylamine under our standard aryl amina-
tion conditions proceeded to completion overnight to afford the desired
arylamine product.
(15) Although all our studies employed Pd(dba)2 as the metal
precursor, other suitable Pd(0) or Pd(II) metal complexes could also
be used. A variety of different metal complexes have been employed
as catalyst precursors or catalysts for Suzuki reactions; see ref 1. Also,
while most of our studies utilized a Pd/L ratio of 1/3, Pd/L ratios of
1/1-1.5 are also generally suitable under rigorously air-free conditions.
(11) (a) Danielson, E.; Golden, J . H.; McFarland, E. W.; Reaves, C.
M.; Weinberg, W. H.; Wu, X. D. Nature 1997, 389, 944-948. (b)
Boussie, T. R.; Coutard, C.; Turner, H. W.; Murphy, V.; Powers, T. S.
Angew. Chem., Int. Ed. Engl. 1998, 37, 3272-3274. (c) LaPointe, A.
M. J . Combinatorial Chem. 1999, 1, 101-104.
(12) (a) Bei, X.; Uno, T.; Norris, J .; Turner, H. W.; Weinberg, W. H.;
Guram, A. S.; Petersen, J . L. Organometallics 1999, 18, 1840-1853.
(b) Bei, X.; Guram, A. S.; Turner, H. W.; Weinberg, W. H. Tetrahedron
Lett. 1999, 40, 1237-1241.
(13) The synthesis and characterization of ligand 1 was described
previously; see ref 12a. For general utility of ligand 1 in palladium/
ligand-catalyzed amination of aryl chlorides, see ref 12a,b.

Palladium/P,O-Ligand-Catalyzed Suzuki Reactions
J . Org. Chem., Vol. 64, No. 18, 1999 6799
Ta ble 2. P d /Liga n d 1-Ca ta lyzed Su zu k i Cr oss-Cou p lin g of Ar ylbor on ic Acid s a n d Ar yl Ch lor id esa
a
General reaction conditions: 1.0 equiv of aryl halide, 1.5 equiv of boronic acid, 3.0 equiv of CsF, 0.5-1 mol % Pd(dba)2, 1.5-3 mol %
ligand 1, 1,4-dioxane or toluene (4 mL), 100-110 °C. Yields correspond to isolated material of >95% purity by GC and NMR. Reaction
time ) 5-20 h unoptimized, complete conversion of aryl chloride. 80 °C. c o-Xylene as solvent, 130 °C, 2 mol % Pd(dba)2. 2 mol %
b
d
Pd(dba)2.
Ch a r t 1
isolated from the ligand displacement reaction of the
complex [Pd[P(o-tolyl)3](4-tBu-C6H4)(µ-Br)]216 with ligand
2. The solution structure of complex 13 was unambigu-
ously established by solution NMR spectroscopic studies.
The 31P NMR spectrum in CDCl3 exhibits a single
resonance at δ 17.8. This resonance is significantly
downfield shifted compared to the corresponding reso-
nance in the 31P NMR spectrum of the free ligand 2 (δ
-16.8) and establishes that the P atom is coordinated to
1
the Pd center in complex 13. The H NMR spectrum of
complex 13 exhibits two broad partially overlapping
resonances at δ 4.19 and 4.18 (eight protons) for two
-OCH2CH2O- groups. These resonances are nearly
identical to those observed for the free ligand 2 (δ 4.14
and 4.02 in CDCl3) and are most consistent with the lack
of coordination of any O atom(s) to the Pd center and the
presence of two P-coordinating ligands 2 in complex 13.
The presence of only a single resonance in the 31P NMR
spectrum of complex 13 further indicates that the two
P-coordinated ligands adopt a trans configuration, which
makes them equivalent. Attempts to isolate X-ray quality
crystals of complex 13 were unsuccessful. The diphe-
nylphosphino analogue of complex 13 has been structur-
originating from Pd(dba)2/ligand 1 catalyst composition
are different from those originating from Pd(dba)2/ligand
2 catalyst composition. We previously established that
the chelating monophosphine complex (P,O)Pd(4-tBu-
C6H4)Br (12) is generated on contacting Pd(dba)2 and
excess ligand 1 in the presence of excess 4-tBu-C6H4Br
(Chart 1).12a The solution- and solid-state structural
identity of this complex was unambiguously established
by solution NMR spectroscopy and single-crystal X-ray
diffraction studies.12a Additional related studies were
undertaken to gain further insights.
a . Isola t ion a n d Ch a r a ct er iza t ion of L2P d (4-
tBu -C6H4)Br (13, L ) 2). The reaction of ligand 2 (2
equiv) with Pd(dba)2 and excess 4-tBu-C6H4Br in benzene-
d6 at 80 °C afforded complex 13 (Chart 1). The same
complex 13 was also formed and more conveniently
(16) (a) Widenhoefer, R. A.; Zhong, H. A.; Buchwald, S. L. Organo-
metallics 1996, 15, 2745-2754. (b) Paul, F.; Patt, J .; Hartwig, J . F.
Organometallics 1995, 14, 3030-3039.

6800 J . Org. Chem., Vol. 64, No. 18, 1999
Bei et al.
Ta ble 3. Cr ysta l Da ta a n d Str u ctu r e Refin em en ts for
Com p lex 14a
empirical formula
MW
C46H55O3PPd
793.27
T (K)
295(2)
wavelength (Å)
crystal system
space group
unit cell dimensions
0.717073
triclinic
P1h
a ) 11.583(1) Å, R ) 81.675(8)°
b ) 12.424(1) Å, â ) 86.698(7)°
c ) 14.690(1) Å, γ ) 75.112(9)°
volume (Å3)
2021.1(3)
Z
2
density (calcd) (g/cm3)
abs coeff (cm-1)
F(000)
1.304
5.37
832
crystal size (mm)
θ range for data collection
(deg)
0.36 × 0.46 × 0.60
2.06-27.50
index ranges
-1 e h e 15, -15 e k e 15,
-19 e l e 19
F igu r e 1. Molecular structure and atom-numbering scheme
of complex 14.
no. of reflns collected
no. of ind reflns
refinement method
no. of data/restraints/params
goodness-of-fit on F2
R indices (I > 2.0σ(I))
R indices (all data)
10 712
9236 (Rint ) 0.0163)
full-matrix least-squares on F2
8612/9/468
ally characterized previously.12a
1.039
b. Isola tion a n d X-r a y Str u ctu r e of LP d (d ba ) (14,
L ) 1). The complex 14 was formed from the reaction of
Pd(dba)2 with excess ligand 1 in toluene at 95 °C and
was unambiguously characterized by solution NMR
spectroscopic and single-crystal X-ray diffraction studies
(eq 2). The 31P NMR spectrum of complex 14 in C6D6
R1 ) 0.0397, wR2 ) 0.0881
R1 ) 0.0631, wR2 ) 0.0987
0.463 and -0.339
largest diff peak and hole
(e Å-3
)
R1 ) ∑||Fo| - |Fc||/∑ |Fo|, wR2 ) [∑ (wi(F2 - Fc2)2)/∑(wi(
a
o
F2o)2)]1/2, GOF ) [∑(wi(F2o - Fc2)2)/(n - p)]1/2
.
Ta ble 4. Selected Bon d Len gth s a n d Bon d An gles of
Com p lex 14
bond lengths (Å)
bond angles (deg)
Pd-O(1)
Pd-P
Pd-C(32)
Pd-C(33)
C(32)-C(33)
2.249(2)
2.2924(7)
2.138(2)
2.065(2)
1.423(3)
O(1)-Pd-P
87.38(5)
115.68(6)
117.45(8)
39.52(8)
155.15(6)
156.45(7)
C(33)-Pd-P
C(32)-Pd-O(1)
C(32)-Pd-C(33)
P-Pd-C(32)
O(1)-Pd)-C(33)
to the Pd center.18 The P-Pd-O bite angle of 87.38(5)°
in complex 14 is slightly larger than that observed in the
previously characterized (P,O)-Pd(4-tBuC6H4)Br (12, P,O
) ligand 1, 84.95(9)°) complex. The C(32)-C(33) bond
distance and the C(32)-Pd-C(33) bond angle of the
dibenzylideneacetone ligand are usual and are similar
to those observed previously in the (P,P)-Pd(dba) complex
(P,P ) bis(diphenylphosphino)ethane).19,20
exhibits a single resonance at δ 27.9. This resonance is
downfield shifted compared to the corresponding reso-
nance in the 31P NMR spectrum of ligand 1 (δ -8.3 in
C6D6)12a,17 and establishes the coordination of the P atom
to the Pd center. The H NMR spectrum of complex 14
exhibits a set of characteristic resonances for the presence
1
of one ligand 1 and one dibenzylideneacetone ligand (see
1
the Experimental Section). The H NMR resonances of
Discu ssion
the -OCH2CH2O- group are broad and slightly shifted
compared to those of the free ligand, suggesting the
presence of a dynamic interaction between the O atoms
and the Pd center.
The phenyl backbone-derived P,O-ligand 1 affords an
efficient Pd/ligand 1 catalyst for the general and efficient
Suzuki cross-coupling reactions of arylboronic acid and
The X-ray quality crystals of complex 14 were obtained
from a cold concentrated toluene solution. The molecular
structure of complex 14 is shown in Figure 1, and the
crystallographic details and key bond lengths are listed
in Tables 3 and 4. The complex 14 adopts a square-planar
structure in which ligand 1 is bound to the Pd center
through both P and O atoms (Figure 1 and Table 4). The
short Pd-O bond distance of 2.249 Å in complex 14
conclusively establishes the coordination of the O atom
(18) The Pd-O bond distance in complex 14 compares favorably with
the Pd-O covalent bond distances reported for square planar com-
plexes (2.0-2.16 Å) and is similar to the Pd-O bond distance of the
previously characterized complex 12 (2.16 Å); see ref 12a. See also:
(a) Kiers, N. H.; Feringa, B. L.; Kooijman, H.; Spek, A. L.; Van
Leeuwen, P. W. N. M. J . Chem. Soc., Chem. Commun. 1992, 1169-
1170. (b) Kaptejin, G. M.; Grove, D. M.; Kooijman, H.; Smeets, W. J .;
Spek, A. L.; van Koten, G. Inorg. Chem. 1996, 35, 526-533. (c)
Bryndza, H. E.; Tam, W. Chem. Rev. 1988, 88, 1163-1188 and
references therein.
(19) Herrmann, W. A.; Thiel, W. R.; Brossmer, C.; Ofele, K.;
Priermeier, T.; Scherer W. J . Organomet. Chem. 1993, 461, 51-60.
(20) Analogous studies of the reaction of ligand 2 (2 equiv) with Pd-
(dba)2 under otherwise similar reaction conditions did not afford any
unambiguously characterizable complex(es). Both the 1H and 31P NMR
spectra of the reaction mixture exhibited significantly broad reso-
nances.
(17) Ligand 1. 1H NMR (C6D6): δ 7.88 (m, 1H, ArH), 7.53 (m, 1H,
ArH), 7.24-7.06 (overlapping signals, 2H, ArH), 3.60 (m, 2H, OCH-
CHO), 3.40 (m, 2H, OCHCHO), 2.19 (s, 3H, CH3), 2.12-1.0 (22H, CyH).
31P NMR (C6D6): δ - 8.3.

Palladium/P,O-Ligand-Catalyzed Suzuki Reactions
J . Org. Chem., Vol. 64, No. 18, 1999 6801
aryl chlorides. The Pd/ligand 1 catalyst effectively couples
a variety of arylboronic acids and aryl chlorides contain-
ing electron-poor and electron-rich substituents to afford
the desired biaryls in high isolated yields. The catalyst
also appears to be suitable for the coupling of sterically
demanding ortho-substituted arylboronic acids and aryl
chlorides.
cross-coupling catalysis involving certain substrates and
conditions,22 while the PCy2 unit makes the Pd center
sufficiently electron-rich to promote oxidative addition
of the usually unreactive aryl chlorides.
Overall, the catalytic performance of Pd/ligand 1
catalyst for Suzuki biaryl cross-coupling of aryl chlorides
is similar to that of the recently described Pd/tBu3P8 and
Pd/P,N9 (P,N ) 1-(N,N-dimethylamino)-1′-(dicyclohexy-
lphosphino)biphenyl) catalysts, all three of which con-
stitute the current state of the art catalysts for the Suzuki
arylation of aryl chlorides. However, unlike the Pd/tBu3P8
and Pd/P,N9 catalysts, the Pd/ligand 1 catalyst was
observed to be most efficient at slightly higher temper-
atures under the conditions investigated. It also appears
that the Pd/ligand 1 and Pd/P,N catalysts, both of which
involve potentially chelating hemilabile ligands, offer
higher catalyst turnovers than the Pd/tBu3P catalysts
(typically ca. 100-200 for Pd/ligand 1 and Pd/P,N cata-
lysts vs ca. 33 for Pd/tBu3P catalyst).8,9 This suggest that
the ketal group in ligand 1 (similar to the amino group
in the P,N ligand) additionally contributes to the en-
hanced stability of the catalyst.
The difference in efficiency between the Pd(dba)2/ligand
1 catalyst and the Pd(dba)2/ligand 2 catalyst is surprising
given the nearly identical structures of ligands 1 and 2.
This difference in reactivity presumably results from the
generation and involvement of structurally different
catalytic intermediates. The Pd(dba)2/ligand 1 catalyst
system appears to involve “(P,O)-Pd” monophosphine
intermediates in which the P,O-ligand coordinates to the
Pd center via both the P and O atoms, while the Pd(dba)2/
ligand 2 catalyst system appears to involve “(P,O)2-Pd”
bisphosphine intermediates in which each of the P,O-
ligands coordinates to the Pd center only via the P atom.
This is consistent with the isolation and characterization
of the structurally different complexes 12 and 13 from
the reaction of Pd(dba)2/4-tBuC6H4Br with ligands 1 and
2, respectively, and complex 14 from the reaction of Pd-
(dba)2 with ligand 1. In complexes 12 and 14, one
molecule of ligand 1 coordinates to the Pd center via both
the P and O atoms, while in complex 13, two molecules
of ligand 2 coordinate to the Pd center only via the P atom
and in a trans fashion. Both complexes 14 and 12
represent potential catalytic intermediates of subsequent
steps of the catalytic cycle, which suggests that ligand 1
generally favors the generation and stability of mono-
phosphine P,O-chelating (P,O)-Pd intermediates. How-
ever, the isolation and characterization of such complexes
does not preclude the rapid dissociation and association
of the O atom of ligand 1 from the Pd center under
catalytic conditions. In fact, such a dynamic behavior,
which would classify ligand 1 as a hemilabile ligand,21a
would be particularly favorable for cross-coupling cataly-
sis. The chelate structures would favor the oxidative
addition step, while a sterically crowded nonchelate
structure would favor the reductive elimination step of
the catalytic cycle.21b-d This is also consistent with the
fact that the strongly chelating bidentate ligand, bis-1,2-
(dicyclohexylphosphino)ethane, is inefficient for analo-
gous Suzuki biaryl cross-coupling reactions of aryl chlo-
rides.8
Con clu sion s
We have demonstrated that the phenyl backbone-
derived P,O-ligand 1 provides an effective, convenient,
and general Pd/ligand 1 catalyst for efficient Suzuki
cross-coupling reactions of arylboronic acids and aryl
chlorides. The effectiveness of Pd/ligand 1 catalyst results
from the presence of both the PCy2 and ketal units that
favor the generation and stability of electron-rich chelat-
ing monophosphine (P,O)-Pd intermediates. Such (P,O)-
Pd intermediates appear to be ideally suitable for Suzuki
aryl chloride arylations involving this class of ligands.
The Pd/ligand 1 catalyst along with the previously
reported Pd/tBu3P and Pd/P,N catalysts represent the
current state of the art catalysts for the general Pd/L-
catalyzed Suzuki arylation of aryl chlorides.
Exp er im en ta l Section
Gen er a l Com m en ts. All reactions were performed under
argon atmosphere in oven-dried glass Schlenk tubes using
standard Schlenk techniques. All aryl halides, arylboronic
acids, bases (CsF, NaOtBu, K3PO4, NBu3, Cs2CO3, and Na2-
CO3), bis(dibenzylideneacetone)palladium, diethyl ether, me-
thylene chloride, benzene, toluene, o-xylene, and 1,4-dioxane
were purchased from commercial sources and used as such.
All solvents were of the anhydrous, sure-seal grade. Ligand 1
and {Pd[P(o-tolyl)3](4-tBu-C6H4)(µ-Br)}2 were prepared accord-
ing to literature procedures.12a,16 The detailed procedure
described for the synthesis and isolation of compound 3 was
generally followed for all Pd/Ligand 1-catalyzed Suzuki reac-
tions of arylboronic acids with aryl halides. All Pd/Ligand
1-catalyzed Suzuki reactions were performed until complete
consumption of the starting aryl halide, but the reaction times
and conditions have not been thoroughly optimized. Column
chromatography was performed using commercially available
silica gel 60 (particle size: 0.063-0.100 mm), hexanes, and
ethyl acetate. 1H, 13C, and 31P NMR spectra were obtained
Thus, the efficiency of ligand 1 for Pd(dba)2/ligand
1-catalyzed Suzuki cross-coupling reactions of arylboronic
acid and aryl chlorides can be ascribed to both the overall
structure of ligand 1 and the presence of the PCy2 unit.
As described above, the rigid phenyl backbone-derived
structure of ligand 1 favors the generation and stability
of the chelating monophosphine “(P,O)-Pd” intermediates,
which appear to be most suitable for Suzuki and related
(21) For a recent review on hemilabile ligands and their transition-
metal coordination chemistry, see: (a) Slone, S. C.; Weinberger, D. A.;
Mirkin, C. A. Progress in Inorganic Chemistry; Karlin, K. D., Ed.; J ohn
Wiley & Sons: New York, 1999; Vol. 48, pp 233-350. The Pd/L-
catalyzed Suzuki biaryl cross-coupling reactions proceed via the
oxidative addition of an aryl halide to an “LnPd0” intermediate,
formation of “LnPdII(Ar)(Ar′)” intermediate, followed by reductive
elimination of biaryl and regeneration of “LnPd0”; see ref 1. For
mechanistic studies and discussion of the influence of ligand-chelating
structures on the rate of oxidative addition and reductive elimination,
see: (b) Hegedus, L. S. Transition Metals in the Synthesis of Complex
Organic Molecules; University Science Books: Mill Valley, CA, 1994;
p 27 and references therein. (c) Portnoy, M.; Milstein, D. Organome-
tallics 1993, 12, 1655-1664. (d) Portnoy, M.; Milstein, D. Organome-
tallics 1993, 12, 1665-1673.
(22) However, the efficient utility of the recently described mono-
dentate phosphine, tBu3P, in Pd/L-catalyzed general Suzuki biaryl
cross-coupling reactions of aryl chlorides suggest that chelation may
not be required if other ligand structural properties are favorable. The
t
steric properties of the Bu3P ligand presumably are sufficient for the
generation and involvement of the most desired mono-phosphine “LPd”
intermediates. Alternatively, the desired monophosphine “LPd” inter-
mediates could also be accessible because of steric and electronic
properties of certain aryl halide substrates and reaction conditions.

6802 J . Org. Chem., Vol. 64, No. 18, 1999
Bei et al.
using a 300 MHz FT-NMR spectrometer. Chemical shifts in
1H and 13C NMR spectra were calibrated with reference to the
chemical shift of residual protiated solvent. Chemical shifts
in 31P NMR spectra were calibrated with reference to 85% H3-
PO4; a negative value of chemical shift denotes resonance
upfield from H3PO4. J values are reported in Hz. Elemental
analyses were performed by E & R Microanalytical Laboratory
Inc., Parsippany, NJ .
2-Acetyl-4′-m eth yl-1,1′-bip h en yl (5).24 Compound 5 was
obtained as a yellowish oil (176 mg, 83%) from the reaction of
4-methylphenylboronic acid (204 mg, 1.5 mmol), CsF (456 mg,
3.0 mmol), Pd(dba)2 (6 mg, 10 µmol), ligand 1 (11 mg, 31 µmol),
and 2′-chloroacetophenone (0.13 mL, 1.0 mmol) in 1,4-dioxane
1
(4 mL) at 100 °C for 17.5 h. H NMR (CDCl3): δ 7.52 (d, J )
8.4, 1H, ArH), 7.47 (d, J ) 7.2, 1H, ArH), 7.38 (t, J ) 7.2, 2H,
ArH), 7.22 (s, 4H, ArH), 2.39 (s, 3H, C(O)CH3), 2.00 (s, 3H,
ArCH3). 13C{1H} NMR (CDCl3): δ 205.1, 140.9, 140.5, 137.8,
137.7, 130.6, 130.2, 129.4, 128.7, 127.8, 127.2, 30.4, 21.2.
5-(2′-Na p h th a len e)-1,3-ben zod ioxole (6). Compound 6
was obtained as an off-white solid (275 mg, 96%) from the
reaction of 2-naphthaleneboronic acid (297 mg, 1.73 mmol),
CsF (524 mg, 3.45 mmol), Pd(dba)2 (6.6 mg, 11 µmol), ligand
1 (12 mg, 33 µmol), and 5-chloro-1,3-benzodioxole (0.12 mL,
2-(2′-Dicycloh e xylp h osp h in op h e n yl)-1,3-d ioxola n e
(Liga n d 2). A solution of 2-(2′-bromophenyl)-1,3-dioxolane (2.0
g, 8.7 mmol) in anhydrous diethyl ether (50 mL) was cooled
to - 78 °C. A solution of tert-butyllithium (10.3 mL, 1.7 M
solution in hexane, 17.5 mmol) was added dropwise with
stirring. The reaction was allowed to stir for 1 h at -78 °C.
Chlorodicyclohexylphosphine (2.43 g, 10.5 mmol) was added
dropwise via a syringe at -78 °C with stirring. The reaction
was allowed to warm to room temperature and stirred for an
additional 12 h. Deoxygenated H2O (40 mL) was added slowly.
The organic layer was separated. The aqueous layer was
washed with diethyl ether (25 mL), and the combined organic
phase was concentrated under vacuum to afford a yellow oil.
The oil was triturated with air-free methanol (5 mL) at room
temperature to afford ligand 2 (2.4 g, 80% yield) as a crystal-
line white solid. 31P NMR (CDCl3): δ -16.8. 1H NMR
(CDCl3): δ 7.65 (br m, 1H, ArH), 7.47 (d, J ) 7.2, 1H, ArH),
7.34 (m, 2H, ArH), 6.63 (d, J ) 6.9, 1H, CH), 4.14 (m, 2H,
OCHCHO), 4.02 (m, 2H, OCHCHO), 2.0-0.8 (overlapping
signals, 22H, CyH). 13C{1H} NMR (CDCl3): δ 144.0, 143.7,
132.4, 128.9, 128.3, 126.4, 101.3 (J PC ) 31, OCO), 65.5 (OCH2),
34.0 (J PC ) 12), 30.5 (J PC ) 17), 29.2 (J PC ) 8), 27.1 (2C), 26.3.
Anal. Calcd for C21H31O2P: C, 72.80; H, 9.02, P, 8.94. Found:
C, 72.79; H, 9.01; P, 8.77.
1
1.15 mmol) in 1,4-dioxane (4 mL) at 100 °C for 7 h. H NMR
(CDCl3): δ 7.95 (s, 1H, ArH), 7.90-7.80 (m, 3H, ArH), 7.66
(d/d, J ) 8.4/1.8, 1H, ArH), 7.52-7.40 (m, 2H, ArH), 7.21-
7.15 (m, 2H, ArH), 6.92 (d, J ) 8, 1H, ArH), 6.01 (s, 2H,
OCH2O). 13C{1H} NMR (CDCl3): δ 148.2, 147.1, 138.2, 135.5,
133.6, 132.4, 128.3, 128.0, 127.6, 126.3, 125.7, 125.4, 125.3,
120.9, 108.6, 107.9, 101.2. Anal. Calcd for C17H12O2: C, 82.24;
H, 4.87. Found: C, 82.33; H, 4.88.
3-Meth oxyl-4′-tr iflu or om eth yl-1,1′-bip h en yl (7). Com-
pound 7 was obtained as a colorless oil (223 mg, 90%) from
the reaction of 4-trifluoromethylphenylboronic acid (279 mg,
1.47 mmol), CsF (447 mg, 2.94 mmol), Pd(dba)2 (5.6 mg, 10
µmol), ligand 1 (11 mg, 31 µmol), and 3-chloroanisole (0.12 mL,
0.98 mmol) in 1,4-dioxane at 100 °C for 12 h. 1H NMR
(CDCl3): δ 7.68 (4H, ArH), 7.38 (t, J ) 8.1, 1H, ArH), 7.17 (d,
J ) 7.2, 1H, ArH), 7.12 (t, J ) 2.1, 1H, ArH), 6.95 (d/d, J )
8.4/2.1, 1H, ArH), 3.87 (s, 3H, OCH3). 13C{1H} NMR (CDCl3):
δ 160.1, 144.6, 141.2, 130.0, 127.5, 125.6 (q, J ) 4), 119.7,
113.4, 113.1, 55.3. Anal. Calcd. for C14H11F3O: C, 66.66; H,
4.40. Found: C, 66.75; H, 4.35.
Gen er a l P r oced u r e for th e Stu d y of Ba se Effects in
th e Su zu k i Rea ction of 5-Ch lor o-m -xylen e a n d P h en yl-
bor on ic Acid (Ta ble 1). A solid mixture of phenylboronic acid
(1.5 mmol), base (3.0 mmol), Pd(dba)2 (10 µmol), and ligand
(30 µmol) was thoroughly evacuated and purged with argon.
5-Chloro-m-xylene (1.0 mmol) and toluene (4 mL) were added,
and the reaction was heated at 100-105 °C. The reaction was
monitored by GC-MS for conversion of the starting aryl
chloride to desired biaryl product. Only trace amounts, if any,
of the homocoupled byproduct, biphenyl, were detected in all
cases. Calibrated conversions are reported in Table 1.
3,5-Dim eth ylbip h en yl (8).9 Compound 8 was obtained as
a colorless oil (178 mg, 94%; 166 mg, 88%; 170 mg, 96%) from
the reaction of phenylboronic acid (190 mg, 1.56 mmol), CsF
(473 mg, 3.12 mmol), Pd(dba)2 (6 mg, 10 µmol), ligand 1 (11
mg, 31 µmol), and 5-halo-m-xylene (0.14 mL, 1.0 mmol; halo
) chloride, bromide, iodide, respectively) in toluene at 100-
1
110 °C for 5-20 h. H NMR (CDCl3): δ 7.64 (d, J ) 8.1, 2H,
ArH), 7.47 (t, J ) 7.7, 2H, ArH), 7.35 (t, J ) 7.5, 1H, ArH),
7.27 (s, 2H, ArH), 7.05 (s, 1H, ArH), 2.44 (s, 6H, ArCH3’s). 13
C
NMR (CDCl3): δ 141.5, 141.3, 138.2, 128.9, 128.6, 127.2, 127.0,
4-Tr iflu or om eth ylbip h en yl (3). A solid mixture of phen-
ylboronic acid (177 mg, 1.5 mmol), CsF (442 mg, 2.9 mmol),
Pd(dba)2 (3 mg, 5 µmol), and ligand 1 (6 mg, 17 µmol) was
weighed in air and loaded into a Schlenk reaction tube. The
reaction tube was thoroughly evacuated and purged with
argon. 4-Chlorobenzotrifluoride (0.13 mL, 0.97 mmol) and 1,4-
dioxane (4 mL) were added, and the reaction was heated at
80 °C for 16 h. The reaction was taken up in ether (100 mL)
and washed with H2O (30 mL) and brine (30 mL). The organic
phase was dried over MgSO4, filtered, and concentrated under
vacuum. The crude product was purified by column chroma-
tography on silica gel using hexanes/ethyl acetate (4/1) as
eluant to afford compound 3 as a white solid (198 mg, 92%)
after drying under vacuum.1H NMR (CDCl3): δ 7.69 (s, 4H),
7.59 (d, J ) 7.8, 2H), 7.47 (t, J ) 6.9, 2H), 7.41 (d, J ) 6.9,
1H). 13C{1H} NMR (CDCl3): δ 144.7, 139.8, 129.0, 128.2, 127.4,
127.3, 125.7 (q, J ) 4). Anal. Calcd for C13H9F3: C, 70.27; H,
4.08. Found: C, 70.31; H, 3.91.
125.1, 21.4.
4-P h en ylbip h en yl Eth er (9).25 Compound 9 was obtained
as an off-white solid (230 mg, 94%) from the reaction of
phenylboronic acid (181 mg, 1.5 mmol), CsF (451 mg, 3.0
mmol), Pd(dba)2 (11 mg, 19 µmol), ligand 1 (22 mg, 61 µmol),
and 4-chlorobiphenyl ether (0.17 mL, 0.99 mmol) in o-xylene
1
(4 mL) at 130 °C for 20 h. H NMR (CDCl3): δ 7.60-7.50 (m,
4H), 7.47-7.27 (m, 5H), 7.16-7.00 (m, 5H).
2-Meth ylbip h en yl (10).8 Compound 10 was obtained as a
colorless oil (164 mg, 94.8%) from the reaction of phenylboronic
acid (188 mg, 1.54 mmol), CsF (469 mg, 3.09 mmol), Pd(dba)2
(11.8 mg, 21 µmol), ligand 1 (22 mg, 61 µmol), and 2-chloro-
toluene (0.12 mL, 1.03 mmol) in toluene (4 mL) at 100 °C for
13.5 h. 1H NMR (CDCl3): δ 7.44-7.38 (m, 2H, ArH), 7.38-
7.30 (m, 3H, ArH), 7.30-7.20 (m, 4H, ArH), 2.28 (s, 3H, CH3).
13C{1H} NMR (CDCl3): δ 141.9, 135.3, 130.3, 129.8, 129.2,
128.0, 127.2, 126.7, 125.7, 20.4.
2,2′-Dim eth yl-1,1′-bip h en yl (11).8 Compound 11 was ob-
tained as a yellowish oil (171 mg, 91%) from the reaction of
2-methylphenylboronic acid (210 mg, 1.54 mmol), CsF (469 mg,
3.09 mmol), Pd(dba)2 (11.8 mg, 21 µmol), ligand 1 (22 mg, 61
µmol), and 2-chlorotoluene (0.12 mL, 1.03 mmol) in toluene (4
mL) at 105 °C for 13 h. 1H NMR (CDCl3): δ 7.32-7.18 (m,
6H, ArH), 7.13 (d, J ) 6.2, 2H, ArH), 2.08 (s, 6H, CH3’s). 13C-
{1H} NMR (CDCl3): δ 141.6, 135.8, 129.8, 129.3, 127.1, 125.5,
19.8.
4,4′-Bis(tr iflu or om eth yl)-1,1′-bip h en yl (4).23 Compound
4 was obtained as a white solid (273 mg, 97%) from the
reaction of 4-(trifluoromethyl)phenylboronic acid (277 mg, 1.5
mmol), CsF (442 mg, 2.9 mmol), Pd(dba)2 (6 mg, 10 µmol),
ligand 1 (11 mg, 31 µmol), and 1,4-chlorobenzotrifluoride (0.13
mL, 0.97 mmol) in 1,4-dioxane at 95 °C for 12 h. 1H NMR
(CDCl3): δ 7.80 (d, J ) 8.7, 4H), 7.76 (d, J ) 8.7, 4H). 13C{1H}
NMR (CDCl3): δ 127.6, 125.9 (q, J ) 4), ipso carbons were
not observed.
(24) Nello, R. Lab. Chim. Org. Struct., Fac. Sci. Paris, Paris, Fr.
Ann. Chim. 1970, 5, 119-127.
(25) Commercially available.
(23) Marcial, M.-M.; Montserrat, P.; Roser, P. J . Org. Chem. 1996,
61, 2346-2351.

Palladium/P,O-Ligand-Catalyzed Suzuki Reactions
J . Org. Chem., Vol. 64, No. 18, 1999 6803
L2P d (4-tBu -C6H4)Br (L ) 2, Com p lex 13). Methylene
chloride (4 mL) was added to a mixture of [Pd[P(o-tolyl)3](4-
tBu-C6H4)(µ-Br)]2 (256 mg, 0.20 mmol) and ligand 2 (284 mg,
0.8 mmol) at room temperature under argon. The mixture was
stirred for 4 h at room temperature, and the solvent was
removed under vacuum. The crude product was further
purified by recrystallization from methylene chloride and
heptane (1/20) at -30 °C, yielding complex 13 as yellow
showed no indication of crystal decomposition or sample
movement. The raw data were collected for Lorentz-polariza-
tion effects. Initial coordinates for the non-hydrogen atoms
were determined by a combination of heavy atom methods and
difference Fourier calculations performed with the algorithms
provided in SHELXTL-IRIS operating on a Silicon Graphic Iris
Indigo workstation. The hydrogen atom positions were ideal-
ized with isotropic temperature factors at 1.2 times that of
the adjacent carbon. The positions of methyl hydrogens were
optimized by a rigid rotating group refinement with idealized
tetrahedral angles. The atomic coordinates for the hydrogen
atoms attached to C(32) and C(33) were refined. The crystal-
1
crystalline solid. 31P NMR (CDCl3): δ 17.8. H NMR (CDCl3):
δ 7.76 (d/d, J ) 7.8/1.2, 2H, ArH), 7.35 (t, J ) 7.7, 2H, ArH),
7.28 (br, 2H, ArH), 7.05 (t, J ) 7.5, 2H, ArH), 6.60 (br, 2H,
ArH), 6.40 (d, J ) 7.5, 2H, CH), 6.26 (br, 2H, ArH), 4.19 (br,
4H, OCHCHO), 4.18 (br, 4H, OCHCHO), 1.11 (9H, C(CH3)3,
overlap with CyH signals), 2.5-1.0 (overlapping signals, 44H,
CyH). 13C NMR (CDCl3): δ 144.8 (J PC ) 4), 144.6, 139.6, 136.0,
131.4 (J PC ) 31), 130.3, 129.0, 128.1, 127.6, 123.1, 100.9 (J PC
) 7), 65.4, 31.4, 31.2, 30.5, 28.1, 27.8, 26.5. Anal. Calcd for
C52H75BrO4P2Pd: C, 61.69; H, 7.47; P, 6.12. Found: C, 61.39;
H, 7.50; P, 5.96.
lographic asymmetric unit also contained
a molecule of
toluene, which was located in a general position within the
unit cell. The six C-C bond distances within the phenyl ring
and the C-C(Me) distances were restrained at 1.40 ( 0.02 Å
and 1.54 ( 0.02 Å, respectively. Crystal data and refinement
parameters are summarized in Table 3. Further details of the
crystallographic information are provided in the Supporting
Information.
Note Ad d ed in P r oof. The Pd/Imidazol-2-ylidene-catalyzed
efficient Suzuki cross-coupling reactions of aryl chlorides with
arylboronic acids were described recently.27
LP d (d ba ) (L ) 1, Com p lex 14). Toluene-d8 (0.5 mL) was
added to an NMR tube containing Pd(dba)2 (20 mg, 35 µmol)
and ligand 1 (12.5 mg, 35 µmol) under argon. The mixture was
heated at 95 °C for 1 h, yielding complex 14 as the only NMR-
detectable phosphorus-containing product. Cryatals suitable
for X-ray diffraction analysis were grown from the toluene
Su p p or t in g In for m a t ion Ava ila b le: Tables of final
positional parameters, isotropic and anisotropic displacement
for all atoms, and bond lengths and angles for complex 14.
This material is available free of charge via the Internet at
http://pubs.acs.org.
1
solution. 31P NMR (C6D6): δ 27.9. H NMR (C6D6): δ 7.51 (d,
J ) 7.2, 2H), 7.4-6.7 (overlapping signals, 16H), 3.65 (br, 2H,
OCHCHO), 3.27 (br, 2H, OCHCHO), 1.99 (s, 3H, CH3, overlap
with CyH signals), 2.5-0.7 (overlapping signals, 22H, CyH).
X-r a y Cr ysta llogr a p h y. A crystal of compound 14‚C7H8
was sealed in a glass capillary and then optically aligned on
the goniostat of a Siemens P4 X-ray diffractometer. The
reflections that were used for the unit cell determination were
located and indexed by the automatic peak search routine
provided with XSCANS.26 The intensities of three standard
reflections, which were measured after every 100 reflections,
J O990805T
(26) XSCANS (version 2.0) is
a diffractometer control system
developed by Siemens Analytical X-ray Instruments, Madison, WI.
(27) Zhang, C.; Huang, J .; Trudell, M. L.; Nolan, S. P. J . Org. Chem.
1999, 64, 3804-3805.