M-terphenyl anchored palladium diphosphinite PCP-pincer complexes that promote the Suzuki-miyaura reaction under mild conditions

Article abstract of DOI:10.1021/om800626b

Diphosphinite PCP-pincer pro-ligands anchored by a meta-terphenyl backbone were synthesized. These pro-ligands, [2,6-(2-Ph₂POC₆H ₄)₂C₆H₃X] (3a X = I, 3b X = Br) and [2,6-(2-'Pr₂P

Full text of DOI:10.1021/om800626b

188
Organometallics 2009, 28, 188–196
m-Terphenyl Anchored Palladium Diphosphinite PCP-Pincer
Complexes That Promote the Suzuki-Miyaura Reaction Under
Mild Conditions
Mark C. Lipke, Robert A. Woloszynek, Liqing Ma, and John D. Protasiewicz*
Department of Chemistry, Case Western ReserVe UniVersity, CleVeland, Ohio 44106
ReceiVed July 3, 2008
Diphosphinite PCP-pincer pro-ligands anchored by a meta-terphenyl backbone were synthesized. These
pro-ligands, [2,6-(2-Ph2POC6H4)2C6H3X] (3a X ) I, 3b X ) Br) and [2,6-(2-iPr2POC6H4)2C6H3X] (4a X
) I, 4b X ) Br) upon reaction with Pd2(dba)3 yield PCP palladium pincer complexes [2,6-(2-
Ph2POC6H4)2C6H3PdX] (5a X ) I, 5b X ) Br) and [2,6-(2-iPr2POC6H4)2C6H3PdX] (6a X ) I, 6b X )
Br). The structures of 5a-b and 6a-b were determined by single crystal X-ray diffraction analyses.
Complexes 5b and 6b were evaluated for their efficacy in promoting catalytic Suzuki-Miyaura CC
coupling reactions. A variety of aryl bromides efficiently underwent CC coupling reactions with
p-tolylboronic acid with high yields in the presence of either 5b or 6b. Compound 6b also proved to be
a very active pro-catalyst for the coupling of aryl chlorides with p-tolylboronic acid. Excellent to good
yields (in some cases greater than 90%) were achieved even with electron rich or sterically hindered aryl
chlorides.
Pincer ligand complexes have been recognized for their
thermal and chemical stability since they were first reported in
the 1970s.18 More recently, enormous attention has been paid
to these terdentate complexes for the development of new
palladium catalysts.19,20 Numerous palladium pincer complex
variations have been tested for catalytic activity in a variety of
CC coupling reactions. For example, palladium pincer com-
plexes of 1,3-bis(2-pyridyloxy)benzene have been reported to
have extremely high turnover numbers (TON ) 8.4 × 108) in
Heck coupling reactions.21 Other researchers have used chiral
substituents to create a chiral pocket around palladium for
asymmetric catalysis.22-48 For example, enantiomeric excesses
Introduction
Since its introduction in 1979,1 the Suzuki-Miyaura reaction
has become very important to modern synthetic chemists.2-7
This catalytic CC coupling reaction between aryl halides and
aryl boronic acids to form biaryls can occur under mild
conditions and tolerates a wide variety of functional groups. In
addition, boronic acids are of low toxicity and their reaction
byproducts are easily separated from the desired product. As a
result of its utility, much attention has been paid to improving
methods and finding new applications for the Suzuki-Miyaura
reaction.8,9 The development of better catalysts has received
particularly significant attention.10,11 Complexes have ultimately
been reported which show impressive catalytic activity in the
Suzuki-Miyaura reaction at room temperature,12,13 when using
hindered substrates,14 when using aryl chlorides,15 or with very
low catalyst loadings.16,17
(14) Altenhoff, G.; Goddard, R.; Lehmann, C. W.; Glorius, F. J. Am.
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* To whom correspondence should be addressed. E-mail: protasiewicz@
case.edu.
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2009 American Chemical Society
Publication on Web 12/05/2008

Palladium Diphosphinite PCP-Pincer Complexes
Organometallics, Vol. 28, No. 1, 2009 189
Chart 1
as high as 83% have been reported for asymmetric Michael
reactions catalyzed by bispyrroloimidazolone NCN palladium
pincer complexes.34 In regard to the Suzuki-Miyaura reaction,
palladium pincer complexes have recently been reported which
act as effective catalysts for the coupling of aryl chlorides with
aryl boronic acids.49 Inspired by such developments, we set out
to examine the catalytic properties of pincer complexes recently
developed in our laboratories.
These particular pincer complexes are constructed upon a
triaryl ring backbone (m-terphenyl). A m-terphenyl backbone
was designed as it should yield more rigid pincer and nonplanar
(globally) complexes, as compared to those anchored by m-xylyl
and related frameworks (Chart 1, left).50 Control of ligand
dynamics is key to achieving well defined steric profiles and
for projecting possible chirality. For nonplanar pincer ligands,
a C2-symmetric environment can be produced, but for many
pincer complexes interconversion between two possible atro-
pisomers can be facile (Chart 1, right). We have shown that
m-terphenyl based pincer complexes maintain a nonplanar
conformation.51 Herein we examine pincer complexes containing
phosphinite groups and have evaluated their catalytic activity
for the Suzuki-Miyaura reaction using a variety of aryl
bromides and chlorides. The catalytic activity of these complexes
at different reaction temperatures was also examined.
Scheme 1
Results and Discussion
Synthesis of Diphosphinite Pro-Ligands. Compounds 1a
and 1b were synthesized following standard procedures for
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61% yield by use of bromine in place of iodine used in
procedure for 1a. The 1H NMR spectra of 1a and 1b are
consistentwithcharacterizationof1areportedintheliterature.54-56
Two isomers of 1a and 1b are indicated by two individual peaks
near 3.8 ppm whose combined integrals indicate six protons
relative to the signals for the eleven protons in the aromatic
region. It is reasonable to ascribe these species as syn- and anti-
isomers, resulting from different conformations of the flanking
phenyl rings about the aryl-aryl bonds.
The dimethoxy-m-terphenyls, 1a-b were converted to dihy-
droxy compounds 2a and 2b by demethylation promoted by
BBr3 (Scheme 1).57 While it was reported that demethylation
of the nonhalogenated analog, 2,2”-dimethoxy-m-terphenyl (1c,
X ) H, Scheme 1) required only one equivalent of BBr3, full
conversion of 1a-b necessitated use of two equivalents of BBr3.
Workup with HCl followed by purification via precipitation from
CH2Cl2 with hexanes gave 2a and 2b in 88 and 90% yields,
respectively.
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from 2a-b following procedures analogous to those reported
for the syntheses of R2POPh and 1,3-(R2PO)2Ph. Compounds
2a and 2b thus provided 3a and 3b, respectively, after a 3 h
reflux in toluene with chlorodiphenylphosphine in the presence
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2721–2726.

190 Organometallics, Vol. 28, No. 1, 2009
Lipke et al.
Scheme 2. Synthesis of Palladium Pincer Complexes
palladium complexes. The structures of 5a-b are shown in
Figure 1 and 6a-b in Figure 2. As expected, these diphosphinite
complexes are structurally similar to [2,6-(2-Ph2PCH2-
C6H4)2C6H3PdBr] (7), a diphosphine m-terphenyl pincer complex
that was reported previously.50 Key bond lengths and angles
about the palladium centers in 5a-b, 6a-b, and 7 are
summarized in Table 1. The iodide analogs 5a and 6a differ
slightly from their respective bromide counterparts 5b and 6b
with regard to the Pd-X bond which is longer when X ) I than
when X ) Br. Complexes 5a-b are very similar to 7.
Complexes 5a-b and 7 exhibit pseudo square planar
geometries around their Pd(II) centers and crystallographically
imposed C2 axes of symmetry passing through the C(1)-Pd-X
bond. A twist angle, Φ, may be defined for the angle between
the plane of the phenyl ring containing C1 and the plane
containing palladium and the four atoms directly attached to it.
Complex 7, with Φ ) 76.7°, has the highest twist angle of any
reported pincer complex. Complex 5a (Φ ) 73.9°) and 5b (Φ
) 73.8°) are only slightly less twisted than 7.
The structures of complex 6a-b have a few notable differ-
ences compared to complexes 5a-b and 7. These differences
arise from the steric effects of the relatively bulky isopropyl
groups in 6a-b that cause the geometry around the palladium
atom in 6a-b to deviate somewhat from planarity. Steric
interactions between the isopropyl groups and the halogen atom
force the halogen atom out of the plane containing C(1), P(1),
P(2), and Pd. As a result, in 6a-b, the C(1)-Pd-X bond angles
are somewhat smaller than the 180 °C(1)-Pd-X bond angles
found in 5a-b. Another slight difference between 6a-b and
5a-b is a 10% decrease in twist angle for complexes 6a-b
relative to 5a-b. Even with these differences, the structures of
6a-b are still quite similar to 5a-b and 7.
of excess triethylamine. Compounds 4a- b were synthesized in
an analogous manner using chlorodiisopropylphosphine. Moni-
toring of the reaction progress by 31P and 1H NMR spectroscopic
analyses of reaction aliquots showed formation of both 4a and
4b required longer (20 h) reaction times compared to 3a-3b.
Pro-ligands 3a-b were isolated as sticky tan solids and 4a-b
were isolated as pale yellow oils. The 31P{1H} NMR resonances
of the diphosphinite ligands are in agreement with the reported
values for similar phosphinite and diphosphinite ligands.58,59
Spectra of 3a and 3b both showed 31P{1H} NMR resonances at
δ 111.8, while 4a and 4b displayed peaks at δ 146.7 and 146.9,
respectively. The susceptibility of these compounds to oxidation
made complete purification difficult. Reports for related diphos-
phinite ligands indicated that further purification may not be
required for the formation and isolation of complexes with
palladium.59 Diphosphinite pro-ligands 3a-b and 4a-b were
thus used without further purification.
Synthesis of Diphosphinite Pincer Complexes. The pincer
complexes 5a-b and 6a-b were readily synthesized from
ligand precursors by reaction with 0.5 equivalents of Pd2dba3
(dba ) dibenzylideneacetone) in benzene at room temperature
(Scheme 2).44 Reaction progress was monitored using 31P{1H}
NMR spectroscopy to observe the consumption of 3a-b or
4a-b. For the synthesis of 5a-b, complete consumption of
3a-b was observed after reacting for 1 h. The synthesis of 6a
and 6b, however, required a 20 h reaction time for full reaction.
The air stable palladium pincer complexes were readily purified
by column chromatography. Complexes 5a-b were easily
purified by first eluting dibenzylideneacetone with 10% ethyl
acetate in hexanes followed by elution of the desired complex
with CHCl3. Complexes 6a-b required slightly more care to
purify as these metal complexes eluted before dibenzylidene-
acetone with 10% ethyl acetate in hexanes.
All four metal complexes were characterized by 1H, 13C{1H},
and 31P{1H} NMR spectroscopy and elemental analysis. As with
similar diphosphinite complexes, a small downfield shift was
observed for the phosphorus resonance of the metal complex
relative to the free ligand.35 This shift was 8-9 ppm for the
bis(diphenylphosphinite) complexes 5a-b. The bis(diisopro-
pylphosphinite) complexes 6a-b had a downfield shift of
approximately 6 ppm relative to the starting ligands 4a-b. The
complexes were found to have high stability to air as they
remained unchanged in solution after several days of exposure
to air.
Suzuki-Miyaura CC Cross Coupling Reactions Using
Complexes 5b and 6b. Preliminary screening of 5a-b and
6a-b as catalysts for the coupling of phenylboronic acid with
several aryl bromides revealed that the iodide compounds, 5a
and 6a, had nearly the same catalytic activity as their respective
bromide counterparts, 5b and 6b. Examination of 5b and 6b
for catalytic activity in Suzuki-Miyaura cross coupling reactions
of p-tolylboronic acids with a variety of aryl bromides and
chlorides was thus undertaken (Scheme 3). Experiments were
conducted in refluxing 1,4-dioxane in the presence of excess
Cs2CO3, and the products were isolated by filtering reaction
mixtures through a thin pad of silica gel followed by evaporation
of solvent under reduced pressure. This method proved suc-
cessful in most cases to give the product in >95% purity as
1
estimated by H NMR spectroscopy.
Complex 5b proved to be an excellent catalyst precursor for
the coupling reaction between p-tolylboronic acid and a variety
of aryl bromides (Table 2). These tests were carried out in
refluxing 1,4-dioxane in the presence of Cs2CO3 with 1 mol%
of the complex.. After 1 h, desired coupling products were
isolated in >88% yields for all aryl bromides which were
screened. An isolated yield of 99% was obtained when electron-
rich 2-bromoanisole was utilized as the reactant. Even sterically
hindered 2-bromomesitylene underwent coupling to give the
desired biphenyl product in 88% yield. The use of several
different solvents and bases were explored with complex 5b in
an effort to enhance its performance under the reaction condi-
tions. However, complex 5b was unsuccessful in Suzuki-Miyaura
CC coupling reactions utilizing aryl chlorides under a variety
of conditions.
X-Ray Crystallographic Analyses. Single crystal X-ray
diffraction analysis was used to determine the structures of the
(58) Bedford, R. B.; Hazelwood, S. L.; Horton, P. N.; Hursthouse, M. B.
Dalton Trans. 2003, 4164–4174.
(59) Bedford, R. B.; Draper, S. M.; Noelle Scully, P.; Welch, S. L. New
J. Chem. 2000, 24, 745–747.
These studies showed that while complex 5b was effective
for coupling p-tolylboronic acid with aryl bromides, complex

Palladium Diphosphinite PCP-Pincer Complexes
Organometallics, Vol. 28, No. 1, 2009 191
Figure 1. Ortep representations (50% probability ellipsoids) of the molecular structure of 5a (left) and 5b (right).
Figure 2. Ortep representations (50% probability ellipsoids) of the molecular structure of 6a (left) and 6b (right).
Table 1. Selected Bond Lengths and Angles
750
5a
5b50
6a
6b
Pd-C(1) (Å)
Pd-P(1) (Å)
2.067(4)
2.3071(7)
2.3071(7)
2.5024(5)
180.0°
2.058(2)
2.2808(4)
2.2808(4)
2.6408(3)
180.0°
2.063(3)
2.2824(5)
2.2824(5)
2.4918(4)
180.0°
2.053(2)
2.0442(14)
2.3023(4)
2.3271(4)
2.51449(18)
168.20(4)°
172.772(14)°
66.4°
2.3365(5)
2.3026(5)
2.6689(2)
165.90(6)°
172.393(19)°
66.8°
Pd-P(2) (Å)
Pd-X(Å)
C(1)-Pd-X
P(1)-Pd-P(2)
Twist Angle Angle (Φ)
169.48(4)°
76.7°
167.53°
73.9°
167.41(3)°
73.8°
Scheme 3. Suzuki-Miyaura CC Coupling Reactions
6b was shown to promote the CC coupling reaction of
p-tolylboronic acid to either aryl bromides or aryl chlorides.
Complex 6b was chosen for a more thorough evaluation of
its catalytic properties because of its superior performance.
Several aryl bromides and aryl chlorides were used as
substrates for coupling with p-tolylboronic acid (Table 3).
Unless otherwise noted, 1 mol% of complex 6b was used.
Reactions were carried out at three different reaction tem-
peratures in order to determine catalytic activity under a
variety of conditions. In refluxing 1,4-dioxane, the coupling
reaction proceeded in excellent yield for all substrates
evaluated. The most noteworthy results are the coupling of
the boronic acid with chloromesitylene in 86% yield and with
2-chloroanisole in 99% yield. Relatively few palladium
complexes are capable of catalyzing the Suzuki-Miyaura
reaction with sterically hindered or electron rich aryl
chlorides.15,17,60 Furthermore, these yields are, to our knowl-
edge, among the highest attained using PCP pincer complexes
in the Suzuki-Miyaura reaction with such sterically hindered
or electron rich aryl chlorides.49,60,61

192 Organometallics, Vol. 28, No. 1, 2009
Lipke et al.
temperaturehavebeenachievedwithotherpalladiumcomplexes.14,15,62
An additional test was run at 75 °C was done with 2-chloro-
anisole using only 0.5 mol% of 6b which gave a yield of 52%
and thus a turnover number of 104.
Table 2. Suzuki-Miyaura CC Coupling Reactions between
Substituted Arylbromides and p-Tolylboronic Acid Promoted by 5b
Complex 6b was tested for catalytic activity at a reaction
temperature of 50 °C while maintaining all other conditions.
At this temperature, desired coupling was not observed for any
of the aryl chlorides used. Optimization of the reaction condi-
tions was attempted by utilizing alternative bases and even aryl
trihydroxyborates63 as reactants, but all efforts were unsuccessful
in attaining coupling at 50 °C with aryl chlorides as substrates.
While yields were depressed, aryl bromides, with the exception
of bromomesitylene, were successfully coupled at 50 °C.
Two different reaction mechanisms are conceivable for the
coupling of aryl halides and aryl boronic acids by palladium
pincer complexes and other related palladacycles. In one
mechanism, the complex releases colloidal Pd(0) which might
serve as the active catalyst by a Pd(0)/Pd(II) catalytic cycle. In
the other mechanism, the complex remains intact and catalysis
occurs via a Pd(II)/Pd(IV) catalytic cycle. For the majority of
palladacycles, evidence suggests that the Pd(0)/Pd(II) catalytic
cycle is followed.64-68 There have been, however, a small
number of pincer complexes reported for which mechanistic
tests suggest a Pd(II)/Pd(IV) catalytic cycle.49
a Isolated yield from 0.6 mmol aryl halide, 0.9 mmol p-tolylboronic
acid, 1.8 mmol of Cs2CO3, 2 mL dioxane
Table 3. Suzuki-Miyaura CC Coupling Reactions between
Substituted Arylhalides and p-Tolylboronic Acid Promoted by 6b
Observations on these catalysis reactions are consistent with
a classical Pd(0)/Pd(II) catalytic cycle. Reaction mixtures begin
turning yellow fairly soon after being heated in an oil bath. At
100 °C, color changes became evident within about 1 min. After
reacting for 20 h, black precipitates were also clearly evident.
At 75 °C, similar colorations developed more slowly and were
apparent within 5 min. Similar black precipitates were also
evident after 20 h. Reaction mixtures involving aryl chlorides
at 50 °C slowly turned yellow, but no black precipitate was
evident. When using aryl bromides at 50 °C, the reactions slowly
turned yellow and some black precipitate was evident after 20 h.
As the more successful CC coupling reactions were also
accompanied by the visual indicators often attributed to the
formation of elemental palladium, it seems reasonable to ascribe
the efficacy of compound 6b to its ability to release Pd(0) in a
beneficial way. A more definitive analysis involves using
elemental mercury to amalgamate released palladium to remove
participation of Pd(0) in the catalytic cycle.66-71 Catalytic CC
coupling reactions between 2-chloroanisole or chlorobenzene
with p-tolylboronic acid at 75 °C were thus attempted in the
presence of a drop (ca. 120 mg) of mercury (99.999% purity).
Analysis of such reaction mixtures showed no CC coupling
product, indicating that the catalytic activity of complex 6b is
a Isolated yield from 0.6 mmol aryl halide, 0.9 mmol p-tolylboronic
acid, 1.8 mmol of Cs2CO3, 2 mL dioxane. b Analysis of reaction
products by protocol described in text complicated by presence of other
1
impurities, and thus H NMR spectroscopy was used to correct yields.
The same reactions were run at 75 °C while all other
conditions remained the same. Of the aryl bromides, only
bromomesitylene gave a significant decrease in coupling yield
at this temperature. The aryl chlorides, on the other hand, all
had significantly reduced yields at 75 °C. Peculiarly, electron
rich 2-chloroanisole and 4-chloroanisole gave respectable yields
for biaryl formation. Increasing the catalyst loading to 2 mol%,
however, gave a notable increase in yield only for chlorobenzene
and 2-chlorotoluene. Even with these substrates, the increase
in yield was only slightly more than 10%. It is quite notable
that the coupling reaction occurred when using aryl chlorides
at 75 °C since pincer complexes usually do not catalyze such
reactions using unactivated chloroarenes at temperatures below
100 °C (vide infra), though reaction temperatures as low as room
(62) Navarro, O.; Kelly, R. A., III; Nolan, S. P. J. Am. Chem. Soc. 2003,
125, 16194–16195.
(63) Cammidge, A. N.; Goddard, V. H. M.; Gopee, H.; Harrison, N. L.;
Hughes, D. L.; Schubert, C. J.; Sutton, B. M.; Watts, G. L.; Whitehead,
A. J. Org. Lett. 2006, 8, 4071–4074.
(64) Beletskaya, I. P.; Cheprakov, A. V. J. Organomet. Chem. 2004,
689, 4055–4082.
(65) Dupont, J.; Consorti, C. S.; Spencer, J. Chem. ReV. 2005, 105, 2527–
2571.
(66) Yu, K.; Sommer, W.; Richardson, J. M.; Weck, M.; Jones, C. W.
AdV. Synth. Catal. 2005, 347, 161–171.
(67) Bergbreiter, D. E.; Osburn, P. L.; Frels, J. D. AdV. Synth. Catal.
2005, 347, 172–184.
(68) Eberhard, M. R. Org. Lett. 2004, 6, 2125–2128.
(69) Widegren, J. A.; Finke, R. G. J. Mol. Catal. A: Chem. 2003, 198,
317–341.
(70) Phan, N. T. S.; Van Der Sluys, M.; Jones, C. W. AdV. Synth. Catal.
(60) Walker, S. D.; Barder, T. E.; Martinelli, J. R.; Buchwald, S. L.
Angew. Chem., Int. Ed. 2004, 43, 1871–1876.
(61) Rosa, G. R.; Ebeling, G.; Dupont, J.; Monteiro, A. L. Synthesis
2003, 2894–2897.
2006, 348, 609–679.
(71) Sommer, W. J.; Yu, K.; Sears, J. S.; Ji, Y.; Zheng, X.; Davis, R. J.;
Sherrill, C. D.; Jones, C. W.; Weck, M. Organometallics 2005, 24, 4351–
4361.

Palladium Diphosphinite PCP-Pincer Complexes
Organometallics, Vol. 28, No. 1, 2009 193
Chart 2
Chart 3
coupled somehow to the formation of colloidal Pd(0).68 Heating
(75 °C) solutions of 6b alone or in the presence of mercury in
dioxane for extended periods of time (16 h) provided no
evidence of decomposition, attesting to the inherit thermal
robustness of the compound. Solutions of 6b heated in the
presence of Cs2CO3, or a mixture of Cs2CO3 and Hg, however,
became yellow colored and gave new species as indicated by
the presence of new 31P NMR signals (62.2 and 52.6 ppm,
respectively). These new resonances might suggest the presence
72
i
to analyze the structures of these complexes. Complexes 5b and
6bwereevaluatedfortheircatalyticactivityintheSuzuki-Miyaura
coupling reaction between 4-tolylboronic acid and a variety of
aryl halides. Complex 5b proved to be excellent for promoting
the CC coupling of 4-tolylboronic acid with aryl bromides,
including bromomesitylene. Complex 6b had even higher
catalytic activity as it successfully promoted the CC coupling
of the boronic acid with aryl chlorides in high yield and even
at reduced temperatures. Mechanistic investigations using
elemental mercury suggest that these pincer complexes may
ultimately serve as precursors for the release of highly active
colloidal Pd(0) as the actual catalytic species.
of Pr2P()O)OAr functionalities and oxidation of the ligand
system in 6b. One of several possible transformations of
palladium phosphinite ligands involves hydrolysis.73 At this time
a fuller picture of the process leading to collodial Pd(0) is not
available, due to the obvious complexity of the reagents and
additives all playing possible roles in transforming the precata-
lyst 6b into its active form.
Regardless of mechanism, complex 6b displays noteworthy
activity as a precatalyst. Comparisons to some recent work on
PCP diphosphinite pincer complexes (Chart 2) can be made.
Complex A has shown good activity for promoting the coupling
of bromobenzenes with phenyl boronic acid, but is only able to
achieve effective conversions with the activated chloroarene,
4-chloronitrobenzene.59 The closely related derivative B was
also reported to utilize 4-chloronitrobenzene in coupling with
phenylboronic acid at only 40 °C, albeit it at very low
conversions (9-12%).74 Compounds C and C′ (NR2 ) pip-
eridinyl) display impressive activities, and can couple even
unactivated chloroarenes with phenylboronic acid with both high
efficiency and rates at 100 °C.49 This system is very interesting
because no evidence for the participation of colloidal palladium
was found, for example, by the lack of impact on catalysis by
the addition of mercury.
Experimental Section
General Procedures. All reactions, unless otherwise stated, were
carried out utilizing Schlenk techniques or in an MBRAUN
Labmaster 130 drybox under an atmosphere of dry N2. Tetrahy-
drofuran (THF), diethyl ether, hexanes and n-pentane were purified
prior to use by distillation from sodium/benzophenone ketyl under
an atmosphere of dry N2. Benzene (anhydrous) and toluene
(Anhydrous, 99.9%) were purchased from Acros and used as
received. Methylene chloride was passed through alumina and
degassed prior to use. 1,4-Dioxane was dried over 4 Å molecular
sieves and degassed immediately prior to use. Diphenylchloro-
phosphine (95% tech.) and diisopropylchlorophosphine (97%) were
purchased from Acros and used without further purification. para-
Tolylboronic acid was synthesized according to a literature proce-
dure77 and was purified by recrystallization from H2O or by repeated
rinsing with hexanes.
The activity of complex 6b might be attributed to the
differently sized chelate rings, having 7 atoms versus 5 (see
examples in Chart 2). It has been recently reported that in the
Heck reaction involving the olefination of haloarenes, PCP
pincer complex E outperforms complex D (Chart 3) and has a
greater range of accessible substrates.75,76
NMR data were recorded on a Varian Inova spectrometer
operating at 400, 100, and 161.8 MHz for the H, 13C{1H}, and
1
Conclusion
31P{1H} spectra, respectively, unless otherwise stated. 31P{1H} NMR
data are referenced to an external 85% H3PO4 standard, while the
1H and 13C{1H} NMR data are referenced using residual solvent
signals.
We have synthesized four diphosphinite palladium pincer
complexes based on a m-terphenyl framework. The synthesis
of the pincer ligands and complexes was accomplished using
standard methods for the synthesis of diphosphinite pincer
complexes. Single crystal X-ray diffraction methods were used
2,6-(2-CH3OC6H4)2C6H3I (1a). A round-bottom flask was
equipped with a reflux condenser and charged with a stirbar before
the addition of 200 mL of THF. 1,3-Dichlorobenzene (5.00 g, 34.0
mmol) was added via syringe and the contents were cooled to -78
°C. With rapid stirring, n-BuLi (16.3 mL, 40.8 mmol) was added
dropwise via syringe over 30 min during which the clear solution
turned milky white in color. The contents were stirred at -78 °C
for 2 h. To this was added a solution of 2-methoxyphenylmagnesium
bromide (freshly prepared from 2-bromoanisole (22.3 g, 119 mmol)
(72) Keglevich, G.; Tamas, A.; Parlagh, G.; Toke, L. Heteroat. Chem.
2001, 12, 38–41.
(73) Pryjomska, I.; Bartosz-Bechowski, H.; Ciunik, Z.; Trzeciak, A. M.;
Ziolkowski, J. J. Dalton Trans. 2005, 213–220.
(74) Gong, J.-F.; Zhang, Y.-H.; Song, M.-P.; Xu, C. Organometallics
2007, 26, 6487–6492.
(75) Morales-Morales, D.; Redon, R.; Yung, C.; Jensen, C. M. Chem.
Commun. 2000, 1619–1620.
(76) Naghipour, A.; Sabounchei, S. J.; Morales-Morales, D.; Canseco-
Gonzalez, D.; Jensen, C. M. Polyhedron 2007, 26, 1445–1448.
(77) Norrild, J. C.; Eggert, H. J. Am. Chem. Soc. 1995, 117, 1479–
1484.

194 Organometallics, Vol. 28, No. 1, 2009
Lipke et al.
Table 4. Selected Data Collection and Structure Solution Information
compound
5a
C42H31IO2P2Pd
862.91
100
0.71073
5b
6a
6b
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
C42H31BrO2P2Pd
815.92
C30H39IO2P2Pd
726.85
C30H39BrO2P2Pd
679.86
100
0.71073
100
0.71073
100a
0.71073
Orthorhombic
Pbcn
Orthorhombic
Pbcn
Monoclinic
P2(1)/n
Monoclinic
P2(1)/n
Space group
Unit cell dimensions
a ) 15.1802(5)
b ) 11.6483(3)
c ) 19.6981(6)
R ) 90
a ) 14.9444(2)
b ) 11.6289(2)
c ) 19.7745(3)
R ) 90
a ) 9.1944(3)
b ) 16.2698(5)
c ) 19.5100(6)
R ) 90
ꢀ ) 94.999(1)
γ ) 90
2907.4(2)
4
1.661
a ) 9.2586(1)
b ) 16.0146(2)
c ) 19.3448(3)
R ) 90
ꢀ ) 95.296(1)
γ ) 90
2856.06(6)
4
1.581
ꢀ ) 90
ꢀ ) 90
γ ) 90
3483.1(2)
4
1.646
1.548
1712
γ ) 90
3436.55(9)
4
1.577
1.833
Volume (Å3)
Z
Density (calcd. g/cm3)
Absorption coeff. (mm-1
F(000)
)
1.836
1456
2.187
1384
1640
Crystal size (mm)
Crystal color and shape
θ range data collection
Limiting indices
0.58 × 0.40 × 0.10
Lt. brown plate
2.71∼33.17
-23< h < 23
-17< k < 16
-30< l < 30
78927
0.26 × 0.20 × 0.12
Lt. brown block
3.03∼33.14
-22< h < 10
-8< k < 17
-30< l < 23
11657
0.40 × 0.20 × 0.10
Lt. yellow block
1.63∼28.32
-12< h < 12
-21< k < 21
-25< l < 25
48996
0.35 × 0.35 × 0.20
Lt. yellow block
1.65∼27.5
-12< h < 12
-20< k < 16
-25< l < 20
29738
Reflections collected
Independent reflections
Refinement method
6639
6006
7198
6546
Full-matrix least-squares on F2
78927/0/236
1.150
Data/restraints/parameters
11657/0/235
1.018
R1 ) 0.0362
wR2 ) 0.0774
R1 ) 0.0677
wR2 ) 0.0885
48996/0/333
1.102
R1 ) 0.0228
wR2 ) 0.0542
R1 ) 0.0239
wR2 ) 0.0550
29738/0/333
1.068
R1 ) 0.0173
wR2 ) 0.0430
R1 ) 0.0190
wR2 ) 0.0454
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]a b
R1 ) 0.0288
wR2 ) 0.0594
R1 ) 0.0465
wR2 ) 0.0720
,
R indices (all data)
b
a R(F) )Σ||Fo| - |Fc||/Σ|Fo|. RW(F2) ) [Σ{w(Fo - Fc2)2}/Σ{w(Fo )2}]0.5; w-1 ) σ2(Fo ) + (aP)2 + bP, where P ) [Fo + 2 Fc2]/3 and a and b are
2
2
2
2
constants adjusted by the program.
and Mg (4.96 g, 20.4 mmol) in 150 mL THF). The resulting solution
was then warmed to room temperature before heating under reflux
overnight. The contents were cooled to 0 °C before the addition of
excess iodine (15.6 g, 61.5 mmol) which was added in portions
under positive pressure of N2. The mixture with iodine was stirred
for 1 h. The contents were then poured into an aqueous Na2SO3
solution (5% by weight). The organics were extracted with diethyl
ether, washed with 5% Na2SO3 (1 × 100 mL), brine (3 × 100
mL), collected and dried over MgSO4. Rotary evaporation yielded
an off-white solid which was recrystallized from ethanol to give
8.94 g (63%) of white solid. (Chemical shifts of two isomers are
reported without further assigning to syn- or anti-) 1H NMR (CDCl3,
300 MHz): δ 3.81-3.83 (s, 6H), 6.97-7.00 (d, 2H, J ) 8 Hz),
7.03-7.08 (t, 2H, J ) 8 Hz), 7.17-7.27 (m, 4H), 7.38-7.46 (m,
3H).
2,6-(2-HOC6H4)2C6H3I (2a). A round-bottom flask was charged
with a stirbar, 1a (2.00 g, 4.81 mmol), and CH2Cl2 (100 mL). The
flask was equipped with a reflux condenser. A 1.0 M solution of
BBr3 (9.61 mL, 9.61 mmol) was added dropwise via syringe. The
contents were then heated under reflux for 2 h. The solution turned
slightly pink in color during this time. The solution was then cooled
to room temperature and 3 mL concentrated HCl was slowly added
via syringe with rapid stirring. The volatiles were removed via rotary
evaporation to yield a pale yellow residue. This was taken up in
100 mL of ethyl acetate and filtered through a pad of silica gel.
The filtrate was concentrated via rotary evaporation to yield a light
orange solid. The crude solid was taken up in 5 mL CH2Cl2 and
precipitated into hexanes. The precipitate was isolated by filtration,
rinsed with hexanes and dried in Vacuo to yield 2a as a pale tan
solid (1.64 g, 88%). mp 120-122 °C. (Chemical shifts of two
isomers are reported without further assigning to syn- or anti-) 1H
NMR (CDCl3): δ 4.75 (broad s, 2H), 6.90 (d, 1H, J ) 8 Hz),
6.97-7.02 (m, 3H), 7.09-7.15 (m, 2H), 7.24-7.53 (m, 5H).
13C{1H} NMR (CDCl3): δ 107.6, 115.98, 116.00, 120.63, 120.67,
128.64, 129.00, 129.68, 129.95, 130.15, 130.21, 130.53, 131.81,
132.18, 143.65, 144.04, 151.98, 152.19.
2,6-(2-HOC6H4)2C6H3Br (2b). Compound 2b was synthesized
and purified by a method analogous to that outlined for compound
2a. The following quantities of starting materials were used: 4.00 g
(10.8 mmol) 1b, 21.7 mL (21.7 mmol) 1.0 M BBr3 in CH2Cl2, and
75 mL CH2Cl2. Compound 2b was isolated as a light tan solid (3.32
g, 90%). mp 134-136 °C. (Chemical shifts of two isomers are
reported without further assigning to syn- or anti-) 1H NMR
(CDCl3): δ 4.94 (broad s, 2H), 6.94 (d, 1H, J ) 8 Hz), 6.99-7.05
(m, 3H), 7.17-7.22 (m, 2H), 7.28-7.51 (m, 5H). 13C{1H} NMR
(CDCl3): 115.93, 120.66, 126.71, 127.74, 128.10, 128.22, 128.60,
129.66, 129.89, 130.35, 130.66, 131.50, 131.86, 139.42, 139.57,
152.29, 152.45.
2,6-(2-CH3OC6H4)2C6H3Br (1b). Compound 1b was synthesized
in a manner analogous to that outlined for 1a. The 2,6-dichlo-
rophenyllithium solution was prepared from 6.47 g of 1,3-
dichlorobenzene (44.0 mmol) and 21.1 mL of n-BuLi (52.8 mmol)
in 200 mL of THF. To this was added a freshly prepared solution
of the Grignard reagent (prepared from 2-bromoanisole (28.8 g,
154 mmol) and Mg (6.42 g, 264 mmol) in 200 mL THF). After
heating under reflux overnight, bromine (3.10 mL, 60.5 mmol) was
added slowly via syringe. The crude product was obtained as for
compound 1a. Purification was accomplished by rinsing with
n-pentane to yield 9.89 g (61%) of 1b as a white powder. (Chemical
shifts of two isomers are reported without further assigning to syn-
1
or anti-) H NMR (CDCl3): δ 3.80-3.82 (s, 6H), 6.98-7.00 (d,
2H, J ) 8 Hz), 7.04-7.05 (t, 2H, J ) 8 Hz), 7.26 (t, 2H, J ) 8
Hz), 7.27 (d, 2H, J ) 8 Hz), 7.37-7.41 (m, 3H); 13C{1H} NMR
(CDCl3): δ 55.61, 55.66, 110.91, 111.05, 120.21, 120.27, 126.45,
126.57, 129.12, 130.13, 130.22, 130.75, 131.02, 131.12, 131.27,
140.292, 156.57, 156.71. Elemental analysis calculated for
C20H17O2Br: C, 65.05; H, 4.65. Found: C, 64.81; H, 4.70.

Palladium Diphosphinite PCP-Pincer Complexes
Organometallics, Vol. 28, No. 1, 2009 195
2,6-(2-Ph2POC6H4)2C6H3I (3a). A three-neck round-bottom flask
was charged with a stirbar and 2a (0.325 g, 0.837 mmol) before
being equipped with a reflux condenser. To this was added
anhydrous toluene (40 mL) followed by chlorodiphenylphosphine
(0.30 mL, 1.63 mmol). A pale yellow color was evident upon adding
the chlorodiphenylphosphine. Excess triethylamine (0.36 mL, 2.51
mmol) was added and the solution became cloudy and pale pink
in color. The contents were heated to reflux and the solution became
homogeneous. After 3 h, a white precipitate had formed. A small
aliquot was collected via syringe and concentrated in Vacuo for
31P{1H} and 1H NMR analysis, which demonstrated complete
consumption of the starting material by disappearance of the
assigning to syn- or anti-) 1H NMR (CDCl3): δ 0.87-1.05 (m, 18H),
1.16-1.31 (m,6H), 1.66-1.72 (m, 2H), 1.76-1.82 (m, 2H), 7.02
(t, 2H, J ) 8 Hz), 7.11-7.14 (m, 2H), 7.20 (d, 2H, J ) 8 Hz),
7.30-7.38 (m, 4H), 7.47-7.51 (t, 1H, J ) 8 Hz). 31P{1H} NMR
(CDCl3): δ 146.9.
2,6-(2-Ph2POC6H4)2C6H3PdI (5a). A flame dried, 20 mL screw
cap vial was charged with a stir bar, 3a (0.085 g, 0.11 mmol), and
0.051 g (0.056 mmol) Pd2dba3. Anhydrous benzene (5 mL) was
added and the vial was sealed. The contents were stirred at room
temperature and the reaction was monitored by 31P NMR analysis.
After 1 h, complete consumption of the free ligand was shown by
the disappearance of its 31P NMR resonance. The dark- purple
solution was filtered through Celite. The resulting orange solution
was concentrated via rotary evaporation to yield a pale orange solid.
The crude product was purified by flash chromatography over silica
gel. Dibenzylideneacetone was eluted first with 10% EtOAc/hexanes
followed by 5a which was eluted with chloroform. Rotary evapora-
tion of the chloroform gave a pale orange solid which was rinsed
with 5 mL diethyl ether, filtered and dried in Vacuo to yield
analytically pure 5a as a pale-orange solid (0.077 g, 79%). X-ray
quality crystals were grown from vapor diffusion of hexanes into
a concentrated chloroform solution at -5 °C. 1H NMR (CDCl3): δ
6.21 (d, 2H, J ) 8 Hz), 6.76 (d, 2H, J ) 8 Hz), 6.81 (d, 2H, J )
8 Hz), 7.01 (t, 2H, J ) 8 Hz), 7.04 (t, 1H, J ) 8 Hz), 7.17-7.20
(m, 6H), 7.26-7.29 (m, 4H), 7.35-7.44 (m, 8H), 7.68-7.73 (m,
4H). 13C{1H} NMR (CDCl3): δ 121.6, 124.9, 125.2, 127.7 (virtual
triplet, J ) 5 Hz), 128.1 (virtual triplet, J ) 5 Hz), 128.8, 128.9
(virtual triplet, J ) 7 Hz), 130.1, 130.8, 131.4, 133.0 (virtual triplet,
J ) 7 Hz), 134.4 (virtual triplet, J ) 22 Hz), 135.7, 143.2, 146.0,
151.6. 31P{1H} NMR (CDCl3): δ 118.2. Elemental analysis calcd
for C42H31O2P2PdI: C, 58.46; H, 3.62. Found: C, 58.19; H, 3.65.
2,6-(2-Ph2POC6H4)2C6H3PdBr (5b). Complex 5b was synthe-
sized and purified by a method analogous to that outlined for
complex 5a. The following quantities of starting materials were
used: 0.145 g (0.204 mmol) of 3b, 0.093 g (0.102 mmol) Pd2dba3,
and 10 mL of anhydrous benzene. Analytically pure 5b was isolated
as an off-white solid (0.1177 g, 70%). X-ray quality crystals were
grown from vapor diffusion of hexanes into a concentrated
chloroform solution at -5 °C. 1H NMR (CDCl3): δ 6.18 (d, 2H, J
) 8 Hz), 6.75 (d, 2H, J ) 8 Hz), 6.80 (d, 2H, J ) 8 Hz), 6.99 (t,
2H, J ) 8 Hz), 7.22 (t, 1H, J ) 8 Hz), 7.14-7.16 (m, 6H),
7.26-7.29 (m, 4H), 7.35-7.46 (m, 8H), 7.72-7.77 (m, 4H).
13C{1H} NMR (CDCl3): δ 121.6, 124.8, 125.1, 127.7 (virtual triplet,
J ) 5 Hz), 128.0 (virtual triplet, J ) 5 Hz), 128.8 (virtual triplet,
J ) 7 Hz), 130.1, 131.3, 132.9 (virtual triplet, J ) 7 Hz), 133.3,
133.6, 134.2 (virtual triplet, J ) 22 Hz), 135.6, 143.1, 145.9, 151.5.
31P{1H} NMR (CDCl3): δ 118.2. Elemental analysis calculated for
C42H31O2P2PdBr: C, 61.82; H, 3.83. Found: C, 61.07; H, 3.78.
2,6-(2-iPr2POC6H4)2C6H3PdI (6a). A flame dried, 20 mL screw
cap vial was charged with stir bar, 4a (0.160 g, 0.258 mmol), and
0.5 equivalents of Pd2dba3 (0.118 g, 0.129 mmol). Anhydrous
benzene (15 mL) was then added and the vial was sealed. The
contents were stirred at room temperature and the reaction was
monitored by 31P{1H} NMR analysis. After 20 h, 31P{1H} NMR
analysis showed the disappearance of the resonance of the free
ligand. The solution was filtered and solvent was removed from
the filtrate via rotary evaporation to yield a pale yellow solid. The
crude product was purified by flash chromatography over silica gel
(EtOAc:hexanes, 1:10). The product after evaporation of volatiles
was rinsed with 5 mL diethyl ether, filtered and dried in Vacuo to
yield analytically pure 6a as a light-orange solid (0.120 g, 64%).
X-ray quality crystals were grown from vapor diffusion of hexanes
into a concentrated chloroform solution at -5 °C. 1H NMR (CDCl3):
δ 0.64-0.70 (m, 6H), 1.00-1.06 (m, 6H), 1.24-1.29 (m, 6H),
1.40-1.45 (m, 6H), 2.18-2.24 (m, 2H), 3.28-3.32 (m, 2H), 6.99
(d, 2H, J ) 8 Hz), 7.07 (d, 2H, J) 8 Hz), 7.16 (t, 1H, J ) 8 Hz),
7.21 (t, 2H, J ) 8 Hz), 7.26-7.33 (m, 4H). 31P{1H} NMR (CDCl3):
1
resonance assigned to the hydroxyl groups of 2a in the H NMR.
The contents were cooled to room temperature. The solution was
filtered through a thin pad of Celite in a dry box. The Celite was
rinsed with additional toluene (2 × 10 mL). The combined organics
were concentrated in Vacuo, yielding a sticky yellow solid. The
solid was dissolved in 10 mL of diethyl ether, filtered through Celite,
and dried in Vacuo to yield the desired diphosphinite ligand, 3a, as
a pale-yellow solid, which was not purified further (0.522 g, 82%).
(Chemical shifts of two isomers are reported without further
assigning to syn- or anti-) 1H NMR (CDCl3): δ 6.98 (d, 2H, J ) 8
Hz), 7.07 (t, 1H, J ) 4 Hz), 7.11 (d, 2H, J ) 8 Hz), 7.23 (d, 2H,
J ) 8 Hz), 7.26-7.34 (broad m, 20H), 7.38 (t, 4H, J ) 4 Hz).
31P{1H} NMR (CDCl3): δ 111.8.
2,6-(2-Ph2POC6H4)2C6H3Br (3b). Compound 3b was synthe-
sized and purified by a method analogous to that outlined for
compound 3a. The following quantities of starting materials were
used: 0.500 mg (1.47 mmol) 2b, 0.53 mL (2.87 mmol) chlorodiphe-
nylphosphine, 0.36 mL (2.51 mmol) triethylamine, and 40 mL of
anhydrous toluene. Compound 3b was isolated as a pale-tan, sticky
solid, which was not purified further (0.800 g, 77%). (Chemical
shifts of two isomers are reported without further assigning to syn-
or anti-) 1H NMR (CDCl3): δ 7.01 (d, 2H, J ) 8 Hz), 7.08 (t, 1H,
J ) 4 Hz), 7.11 (d, 2H, J ) 8 Hz), 7.24-7.34 (broad m, 22H),
7.38 (t, 4H, J ) 4 Hz). 31P{1H} NMR (CDCl3): δ 111.8.
2,6-(2-iPr2POC6H4)2C6H3I (4a). A three-neck round-bottom
flask was charged with a stirbar and 2a (0.300 g, 0.773 mmol)
before being equipped with a reflux condenser. To this was added
anhydrous toluene (30 mL) followed by chlorodiisopropylphosphine
(0.24 mL, 1.5 mmol) which resulted in a light pink solution.
Triethylamine (0.33 mL, 2.3 mmol) was then added, resulting in
cloudiness that dissipated within 5 min. The contents were heated
to reflux and the solution became homogeneous and clear after 30
min. After heating under reflux for 20 h, the contents were cooled
to room temperature. A small aliquot was collected via syringe and
1
concentrated in Vacuo for 31P{1H} and H NMR analysis, which
demonstrated complete consumption of the starting material by
disappearance of the resonance assigned to the hydroxyl groups of
2a in the 1H NMR. Degassed petroleum ether (10 mL) was added
and a white precipitate was evident after a few minutes of stirring.
The contents were taken into the dry box and filtered through Celite.
The filtrate was concentrated in Vacuo, yielding a pale-brown oil,
which was not purified further (0.308 g, 64%). (Chemical shifts of
two isomers are reported without further assigning to syn- or anti-)
1H NMR (CDCl3, 300 MHz): δ 0.86-1.02 (m, 18H), 0.99-1.26
(m,6H), 1.61-1.84 (m, 4H), 7.02 (t, 2H, J ) 8 Hz), 7.12-7.15
(m, 2H), 7.20 (d, 2H, J ) 8 Hz), 7.30-7.38 (m, 4H), 7.49 (t, 1H,
J ) 8 Hz). 31P{1H} NMR (CDCl3): δ 146.7.
2,6-(2-iPr2POC6H4)2C6H3Br (4b). Compound 4b was synthe-
sized and purified by a method analogous to that outlined for
compound 4a. The following quantities of starting materials were
used: 0.200 g (0.586 mmol) 2b, 0.18 mL (1.14 mmol) of
chlorodiisopropylphosphine, 0.25 mL (1.76 mmol) triethylamine,
and 30 mL of anhydrous toluene. Compound 4b was isolated as a
pale-yellow oil, which was not purified further (0.289 g, 86%).
(Chemical shifts of two isomers are reported without further

196 Organometallics, Vol. 28, No. 1, 2009
Lipke et al.
δ 153.3. Elemental analysis calcd for C30H39O2P2PdI: C, 49.57; H,
5.41. Found: C, 49.63; H, 5.53.
pressure to yield the desired coupling product, typically of >95%
1
purity as judged by H NMR spectroscopy.
2,6-[2-OP(iPr)2C6H4]2C6H3PdBr (6b). Complex 6b was syn-
thesized and purified by a method analogous to that outlined for
complex 6a. The following quantities of starting materials were
used: 0.285 g (0.497 mmol) 4b, 0.228 g (0.249 mmol) Pd2dba3,
and 10 mL of anhydrous benzene. Analytically pure 6b was isolated
as a white solid (0.192 g, 57%). X-ray quality crystals were grown
from vapor diffusion of hexanes into a concentrated chloroform
solution at -5 °C. 1H NMR (CDCl3): δ 0.65-0.71 (m, 6H),
0.98-1.04 (m, 6H), 1.26-1.32 (m, 6H), 1.40-1.45 (m, 6H),
2.13-2.19 (m, 2H), 3.04-3.11 (m, 2H), 6.98 (d, 2H, J ) 8 Hz),
7.08 (d, 2H, J) 8 Hz), 7.14 (t, 1H, J ) 8 Hz), 7.21 (t, 2H, J ) 8
Hz), 7.26-7.33 (m, 4H). 13C{1H} NMR (CDCl3): δ 16.4, 16.6,
17.3 (virtual triplet, J ) 5 Hz), 18.5, 27.4 (virtual triplet, J ) 14
Hz), 29.9 (virtual triplet, J ) 10 Hz), 122.1, 124.5, 124.9, 128.0,
129.3, 132.1, 136.6, 142.9, 144.2, 152.2. 31P{1H} NMR (CDCl3):
δ 152.6. Elemental analysis calcd for C30H39O2P2PdBr: C, 52.98;
H, 5.78. Found: C, 52.58; H, 5.76.
X-Ray Crystallographic Studies. The X-ray intensity data were
measured at 100 K on a Bruker SMART Apex II CCD-based X-ray
diffractometers system equipped with a Mo-target X-ray tubes (λ
) 0.71073 Å) located at either Bruker AXS in Madison WI,
(compounds 5a and 5b) or at Case Western Reserve University
(compounds 6a and 6b). Data collection and solution parameters
are summarized in Table 4. Further information is provided within
the cif files supplied as Supporting Information. Crystals were
mounted on a MiTeGen micromount using paratone-N which were
then frozen. The frames were integrated with the Bruker SAINT
build in APEX II software package using a narrow-frame integration
algorithm, which also corrects for the Lorentz and polarization
effects. Absorption corrections were applied using AXScale. The
structures were solved and refined using the Bruker SHELXTL
(Version 6.14) software. The positions of all non-hydrogen atoms
were derived from the Direct Methods (TREF) solution. With all
non-hydrogen atoms being anisotropic and all hydrogen atoms being
isotropic the structure was refined to convergence by least-squares
method on F2, XSHELL (Version 6.3.1), incorporated in SHELXTL
(Version 6.14).
Typical Procedure for Suzuki-Miyaura CC Coupling
Reactions. A 5 mL conical vial was charged with Cs2CO3 (0.586
g, 1.8 mmol), p-tolylboronic acid (0.122 g, 0.9 mmol), 0.6 mmol
of aryl halide, and 1 mol% of either complex 5b or 6b. The vial
was equipped with a magnetic spinvane and a reflux condenser
before being filled with nitrogen. 1,4-Dioxane (2 mL) was added
and the vial placed in an oil bath maintained at the desired reaction
temperature. After 20 h the reaction was cooled to room temper-
ature, diluted with diethyl ether, and filtered through a thin pad of
silica gel. The silica gel was rinsed with 25 mL of additional diethyl
ether. The combined organics were concentrated under reduced
Acknowledgment. We acknowledge support from the
ACS-PRF (PRF 44644-AC3) and Dr. Charles Campana
(Bruker AXS) for crystallographic assistance.
Supporting Information Available: CIF files having full X-ray
crystallographic data. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM800626B