New trans-chelating ligands and their complexes and catalytic properties in the Mizoroki - Heck arylation of cyclohexene

Article abstract of DOI:10.1021/om800448b

New air-stable chelating diphosphine ligands, 1,8-bis(4-(diphenylphosphino) phenyl)anthracene (2) and 1,8-bis(4-(diphenylphosphino)-3,5-dimethylphenyl) anthracene (3), were synthesized from readily available starting materials. The examination of their coordination modes in Pd(II) and Rh(I) complexes by means of ¹H, ¹³C, and ³¹P NMR spectroscopy and X-ray analysis revealed that 2 is mainly a trans-coordinating ligand but can also adapt smaller coordination angles, while 3 is purely trans-spanning and no formation of identifiable cis-chelated complexes was detected. The catalytic activity of the new compounds was tested in palladium-catalyzed Mizoroki-Heck reactions of aryl bromides with cyclohexene.

Full text of DOI:10.1021/om800448b

Organometallics 2008, 27, 5139–5145
5139
New Trans-Chelating Ligands and Their Complexes and Catalytic
Properties in the Mizoroki-Heck Arylation of Cyclohexene
Luba Kaganovsky,† Kyung-Bin Cho,‡ and Dmitri Gelman*,†
Department of Organic Chemistry and The Lise Meitner-MinerVa Center for Computational Quantum
Chemistry, Institute of Chemistry, The Hebrew UniVersity of Jerusalem, Jerusalem, 91904 Israel
ReceiVed May 16, 2008
New air-stable chelating diphosphine ligands, 1,8-bis(4-(diphenylphosphino)phenyl)anthracene (2) and
1,8-bis(4-(diphenylphosphino)-3,5-dimethylphenyl)anthracene (3), were synthesized from readily available
starting materials. The examination of their coordination modes in Pd(II) and Rh(I) complexes by means
of 1H, 13C, and 31P NMR spectroscopy and X-ray analysis revealed that 2 is mainly a trans-coordinating
ligand but can also adapt smaller coordination angles, while 3 is “purely” trans-spanning and no formation
of identifiable cis-chelated complexes was detected. The catalytic activity of the new compounds was
tested in palladium-catalyzed Mizoroki-Heck reactions of aryl bromides with cyclohexene.
Introduction
During the past few decades, enormous efforts have been
devoted to the synthesis of transition-metal complexes as
promoters for a variety of homogeneously catalyzed transforma-
tions. Most of the catalysis-relevant ligands developed in recent
years are bidentate ligands that can be literally classified into
three groups: (i) cis -chelating ligands, having chelation angles
Figure 1. 1,8-Bis(p-(diphenylphosphino)phenyl)anthracenes.
under 100° (represent a vast majority of known ligands),1 (ii)
wide-bite-angle ligands, with chelation angles ranging between
very unusual and fascinating properties.6 However, their real
synthetic potential is still unexplored.
100 and 160°,2 and (iii) trans-chelating ligands, having chelation
angles over 160°.3 While the reactivities of the transition-metal
complexes bearing cis and wide-bite-angle ligands, as well as
striking differences in their reactivity, are now well-docu-
mented,4 extensive exploration of trans-chelated transition-metal
compounds in catalysis started only in recent years.5 Several
new, very interesting ligands belonging to this family were
prepared and studied in the context of their coordination
chemistry and potential catalytic applications, demonstrating
As a part of our research program aiming the investigation
of such compounds, we became interested in studying the
coordination chemistry and catalytic properties of the potentially
trans-chelating ligands based on 1,8-bis(p-(diphenylphosphi-
no)phenyl)anthracene (Figure 1).
It should be noted that the design and synthesis of effective
trans-spanning ligands requires the installation of donor groups
at large distance and, therefore, is traditionally associated with
certain problems, such as excessive flexibility of the frame
(leading to conformational instability),7 multiple coordination
modes (leading to dimerization or oligomerization),8 etc.5 The
suggested design, however, avoids these structural complica-
tions. As we assumed, the planar anthracene-based scaffold
enables the preferred trans chelation due to the adequately
* To whom correspondence should be addressed. E-mail: dgelman@
chem.ch.huji.ac.il. Fax: +972-2-6585345.
† Department of Organic Chemistry.
‡ The Lise Meitner-Minerva Center for Computational Quantum Chemistry.
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10.1021/om800448b CCC: $40.75
2008 American Chemical Society
Publication on Web 09/11/2008

5140 Organometallics, Vol. 27, No. 19, 2008
KaganoVsky et al.
Scheme 1. Preparation of 2 and 3a
a
Reaction conditions: (a) Pd(OAc)2/2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl, K3PO4, toluene (isolated yield: R ) H, 81%; R )
Me, 73%); (b) BBr3, DCM (isolated yield: R ) H, 95%; R ) Me, 90%); (c) Tf2O, i-Pr2NEt, DCM, DMAP (isolated yield: R ) H, 72%; R ) Me,
82%); (d) Pd(OAc)2/dppp, H(O)PPh2, i-Pr2NEt, DMSO (isolated yield: R ) H, 46%; R ) Me, 74%); (e) HSiCl3, TEA, xylene (isolated yield: R
) H, 65%; R ) Me, 75%).
Scheme 2. Preparation of Transition-Metal Complexes
remote phosphine groups.9 On the other hand, along with the
ligand being mainly trans chelating, some flexibility in coordina-
tion will be allowed due to a limited rotation of the phosphine
donors and phenyl rings around C-P and C-C bonds (Figure
1). This ability of a ligand to adapt different coordination angles
within a certain range is an important factor in catalysis, because
it assists in the stabilization of different intermediates that may
form over the course of a catalytic cycle. In this particular case,
this range may be controlled by installing bulky substituents at
the 3,5- and 3′,5′-positions of the phenyl rings. At the same
time, the all-aromatic scaffold ensures the conformational
stability of the resulting complexes.
Finally, the ligand scaffold is modular and can be easily
prepared using reliable cross-coupling methodology.
Herein we wish to report on the synthesis, characterization,
and catalytic properties of transition-metal complexes bearing
the new trans-spanning anthracene-based ligands 1,8-bis-(4-
(diphenylphosphino)phenyl)anthracene (2) and 1,8-bis(4-(diphe-
nylphosphino)-3,5-dimethylphenyl)anthracene (3). As we found,
in addition to interesting structures, the new ligand 2 demon-
strates high reactivity and unusually high regioselectivity in
palladium-catalyzed Mizoroki-Heck reactions of aryl bromides
with cyclohexene.
spectra at lower temperatures (-30 °C) indicated no presence
of possible rotameric species (face to face or face to tail).
In order to study the coordination preferences of the new
ligands, they were allowed to react with different transition-
metal precursors, as shown in Scheme 2. The products were
studied in solution using NMR, and representative examples
were isolated and characterized by X-ray analysis.
Initially, ligand 3 was reacted with PdCl2(CH3CN)2 and
Rh2(CO)2Cl2 in deuterated chloroform at room temperature.
NMR measurements indicated that the formation of the
complexes 4 and 5 was complete within 2-3 h. The 31P{1H}
NMR spectra of 4 and 5 displayed a sharp singlet with a
resonance frequency of 19.4 ppm for 4 and a doublet centered
at 31.9 ppm with the coupling constant JRh-P ) 96 Hz for 5.
Complexes 4 and 5 form cleanly, and only minor impurities
were detected by NMR.
Suitable single crystals of 4 and 5, grown by the slow
diffusion of pentane into their saturated solutions in chloroform
at room temperature, were subjected to X-ray diffraction
analysis.
Results and Discussion
Ligands and Complexes. Scheme 1 summarizes the synthetic
pathway to 2 and 3 from 1,8-dichloroanthracene, which can be
prepared from the commercially available 1,8-dichloroan-
thraquinone. As was mentioned, the whole synthesis relies on
cross-coupling chemistry and starts from the double Suzuki
reaction leading to 1 (R ) H) or 1′ (R ) Me) in good to
excellent yield.10 The products were converted into the corre-
sponding triflates after deprotection of the p-methoxy groups
and coupled with diphenylphosphine oxide using well-estab-
lished palladium-catalyzed protocols. Phosphine oxide reduction
at the final step yields the desired compounds in 17-25% overall
yield (five steps). Notably, 2 and 3 are perfectly soluble in all
common organic solvents and air-stable, so that they can be
kept for months on a shelf without notable oxidation.
As expected, complexes 4 and 5 exist in almost perfect trans-
spanned form (the ORTEP illustrations are given in Figure 2).
We found that the palladium center in 4 is only slightly
distorted from the square-planar geometry. For example, the
observed P(1)-Pd-P(2) and Cl(1)-Pd-Cl(2) angles and
P(1)-P(2) intramolecular distance between the two phosphorus
groups for 4 are 168.53°, 179.18(2)° and 4.67 Å, respectively.
The corresponding parameters for 5 are 167.68°, 179.02°,and
4.657 Å. The P-metal, Cl-metal and CO-metal bond lengths
lie within the normal range of trans-diphosphine complexes.5,11
Surprisingly, we found that the bridging 3,5-dimethylphenyl
rings are not coplanar, despite the bulkiness of the methyl
substituents. Thus, the ring planes converge with a sharp angle
of 42.30° in 4 and a similar angle in 5.
31P{1H} NMR spectra of 2 and 3 in CDCl3 display single
resonance frequencies at δ -6.1 and -15.6 ppm, respectively,
which are ascribed to the identical phosphine groups. Recording
Reactions of the ligand 2 with the same transition-metal
precursors also led to complete complexation. For example,
the31P{1H} NMR spectra of complexes 7 and 8, taken from
the reaction mixtures, indicated the formation of a predominant
(9) The binding properties of 1,8-bis(p-(diphenylphosphino)phenyl)an-
thracenes may tentatively be compared to those of 1,8-bis(diphenylphos-
phino)anthracene. The latter, however, is prone to carbometalation reactions.
See for example: Haenel, M. W.; Jakubik, D.; Krueger, C.; Betz, P. Chem.
Ber. 1991, 124, 333.
(10) (a) Old, D. W.; Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc.
1998, 120, 9722. (b) Barder, T. E.; Walker, S. D.; Martinelli, J. R. J. Am.
Chem. Soc. 2005, 127, 4685.
(11) (a) Ovchinnikov, M. V.; Brown, A. M.; Liu, X.; Mirkin, C. A.;
Zakharov, L. N.; Rheingold, A. L. Inorg. Chem. 2004, 43, 8233. (b) Burger,
S.; Therrien, B.; Suess-Fink, G. HelV. Chim. Acta 2005, 88, 478. (c) Morgan,
B. P.; Smith, R. C. J. Organomet. Chem. 2008, 693, 11.

Mizoroki-Heck Arylation of Cyclohexene
Organometallics, Vol. 27, No. 19, 2008 5141
Figure 2. ORTEP drawings (50% probability ellipsoids) of the structures of 4 and 5. Hydrogen atoms and solvent molecules are omitted
for clarity. Selected bond lengths (Å) and angles (deg) for 4: Pd1-Cl1 ) 2.3010(17), Pd1-Cl2 ) 2.3029(17), Pd1-P1 ) 2.3636(18),
Pd1-P2 ) 2.3679(18), P1-P2 ) 4.708; Cl1-Pd1-Cl2 ) 179.18(7), P1-Pd1-P2 ) 168.53(6). Selected bond lengths (Å) and angles
(deg) for 5: Rh1-Cl1 ) 2.3719(7), Rh1-C55 ) 1.819(3), C55-O1 ) 1.114(3), Rh1-P1 ) 2.3391(6), Rh1-P2 ) 2.3450(7), P1-P2 )
4.657; Cl1-Rh1-C55 ) 179.03(8), P1-Rh1-P2 ) 167.68(2).
species accompanied by only insignificant impurities. Complex
7 exhibited a single resonance frequency at 23.1 ppm that is
assigned to the identical phosphine donors. Complex 8 appeared
as a doublet at 32.5 ppm with a coupling constant of JRh-P
93.
)
Compounds 7 and 8 displayed chemical shifts and coupling
patterns very similar to those of the fully characterized 4 and
5; therefore, there is no reason to suspect that they have a
different (cis) coordination behavior.
In order to confirm experimentally the assumed ability of the
anthracene-based scaffolds to adapt smaller coordination angles,
we attempted the synthesis of cationic Rh(I) complexes from
the new ligands and strongly cis-directing [Rh(COD)2]BF4.
Unlike previous experiments, we observed a different coordina-
tion behavior of 2 and 3 toward this precursor.
Figure 3. ORTEP drawing (50% probability ellipsoids) of the
structure of 9. Hydrogen atoms, counterion, and solvent molecules
are omitted for clarity. Selected bond lengths (Å) and angles (deg)
for 9: Rh1-C52 () 2.245(5), Rh1-C51 ) 2.221(5), Rh1-C55 )
2.226(5), Rh1-C56 ) 2.230(5), Rh1-P1 ) 2.3576(13), Rh1-P2
) 2.3530(13), P1-P2 ) 3.473; P1-Rh1-P2 ) 95.00(5),
C55-Rh1-C56)78.8(2),C51-Rh1-P1)89.62(15),C55-Rh1-P2
) 92.32(14).
According to 31P NMR analysis, the reaction of 2 with
[Rh(COD)2]BF4 in deuterated chloroform led almost im-
mediately to the formation of one major, apparently cis-chelated
product, 9 (Scheme 1); a doublet centered at 25.9 ppm with a
coupling constant of 108 Hz may be indicative of cationic cis-
diphosphine rhodium complexes.12 To confirm the structural
arrangement at the metal center of 9, a single crystal grown
from a chloroform/hexane mixture was subjected to an X-ray
analysis.
Molecular modeling performed using Gaussian 03 at the
semiempirical PM3 level14 starting from the X-ray coordinates
and applying constraints revealed that coordination angles of
ca. 120° can be conformed by 3 (total energy lies within the 3
kcal/mol flexibility range). However, further constraining of the
ligand geometry to the ideal cis arrangement displays a very
high barrier of 9.1 kcal/mol which, obviously, can not be easily
accessed (Figure 4).
Indeed, we found that 9 is cis chelated with P(1)-Rh(1)-P(2)
) 95.0°; an ORTEP illustration is given in Figure 3. It is
remarkable that the rigid all-aromatic scaffold of 3 experiences
a significant bond deformation in order to achieve such a small
coordination angle. For example, the deviation of the P(1)-C(1)
and C(4)-C(7) bonds from the bridging ring plane averages
0.296 Å. Other bond lengths and angles are within the normal
range.13
The reaction of 3 with the cationic [Rh(COD)2]BF4, in
contrast, resulted in the formation of multiple unidentifiable
compounds according to 31P{1H} NMR analysis at various
temperatures (-30 °C to +30 °C). Apparently, the steric bulk
of the substituents at the 3,5-positions of the ligand limits the
rotation of the phosphine donors and conflicts with the strong
cis-directing effect of the COD spectator.
Catalytic Studies. To check the catalytic activity of the new
ligands, we chose palladium-catalyzed Mizoroki-Heck olefi-
nation as a model reaction.
The reaction has become, arguably, one of the most powerful
methods in synthetic organic chemistry for the construction of
carbon-carbon bonds.15 Over the years, many major problems
of Heck-type chemistry have been solved: new catalysts and
protocols are now available to activate less reactive substrates
and to perform transformations in a chemo- and stereoselective
fashion. In contrast, the problem of regioselectivity has only
(12) (a) Dubrovina, N. V.; Tararov, V. I.; Monsees, A.; Spannenberg,
A.; Kostas, I. D.; Boerner, A. Tetrahedron: Asymmetry 2005, 16, 3640. (b)
Tsuchikama, K.; Kuwata, Y.; Tahara, Y.-K.; Yoshinami, Y.; Shibata, T.
Org. Lett. 2007, 9, 3097.
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17, 668. (b) Liu, C.; Widenhoefer, R. A. Organometallics 2002, 21, 5666.
(14) (a) Frisch, M. J. Gaussian 03, Revision D.01; Gaussian, Inc.,
Wallingford, CT, 2004. (b) Stewart, J. J. P. J. Comput. Chem. 1991, 12,
320. (c) Stewart, J. J. P. J. Mol. Mod. 2004, 10, 155.

5142 Organometallics, Vol. 27, No. 19, 2008
KaganoVsky et al.
completion in the presence of 1 mol % of Pd(OAc)2/2 in DMF
and sodium carbonate as a base at 90 °C.
Under these conditions, a series of differently substituted aryl
bromides were allowed to react with cyclohexene as well as some
other olefins. The yields and selectivities are given in Table 1.
The results of these experiments are very encouraging (entries
2-6, Table 1): (i) full conversion was achieved with electron-
deficient, electron neutral and electron-rich aryl bromides; (ii)
yields vary from good to excellent (the missing percentage
indicates the formation of homocoupled species); (iii) the
regioselectivity toward 4-phenylcyclohex-1-ene (the thermody-
namic product in this case)17b is practical (81% or higher,
depending on the electronic parameters of the substrates).
Figure 4. Potential energy diagram for 9.
been solved partially. For example, predominant formation of
one double-bond regioisomer is still only possible in intramo-
lecular transformations or intermolecular reactions with electron-
rich/-deficient olefins.16 Intermolecular arylation of simple
electron-neutral alkenes, however, normally yields complex
mixtures of all possible regioisomeric products.15a,17
In principle, the distribution of regioisomeric products in this
transformation originates from the reversibility of the product-
forming step (Scheme 3). The kinetic product B is accumulated
if reductive elimination of HX is fast, while the accumulation
of thermodynamic products A and C (depending on the ring
size) occurs if reductive elimination is slow. The majority of
known catalytic systems lead, however, to the formation of
impractical mixtures.15a
There is a very limited number of protocols discussing
regioselectivity issues in such reactions. For example, Beller
suggested a base dependence of the regioselectivity in such cases
and demonstrated that good regioselectivity (toward the ther-
modynamic product) may be achieved when sodium acetate in
DMSO/DMA was employed as a base.17b In this context, it
would be interesting to test whether the same effect may be
achieved under ligand-assisted conditions.
The idea behind this hypothesis is as follows: unlike wide-
bite-angle ligands which are known to enhance the rate of
reductive elimination reactions,4b,e purely trans-spanning ligands
should simply shut it down.18 However, taking into account that
rigid trans-spanning ligands unable to adapt smaller coordination
angles are very rare (if they exist at all),19 one could expect
just a deceleration of the reductive elimination reaction with
complexes bearing such ligands. If so, predominant formation
of the thermodynamic product may be expected.
When 2 was replaced with TPP and Xantphos under the same
reaction conditions, both the yields and selectivity became
unsatisfactory (entries 9 and 10, Table 1). These blank experi-
ments clearly show that the reaction outcome in this case is
ligand-controlled.
Thus, from our point of view, the results support the
hypothesis that trans-chelating ligands can induce isomerization
of a Heck product toward a thermodynamic product due to a
slow reductive elimination step. Also remarkably, the rigid 3
was found inactive in the Heck reaction, apparently due to
insufficient flexibility and its inability to form cis-chelated
species.
Another interesting point that should be noted is the relatively
mild reaction conditions required to drive the reaction to
completion. Usually, only ”privileged” olefins (styrene or alkyl
acrylates) may be arylated under temperatures under 80 °C.
Using Pd(OAc)2/2 as a catalyst, ”difficult” substrates (cycloalk-
enes) react at 90 °C, while the reaction temperature for the
”privileged” alkenes does not exceed 50 °C (entries 7 and 8,
Table 1). We suspect that the higher reactivity of our catalyst
might be attributed to the tendency of trans-chelated complexes
to form more electrophilic cationic species due to a strong trans
effect exerted by the aryl ligand.20 Such cationic species are
known by their affinity toward olefinic ligands and should
facilitate the reaction (Scheme 4).21
To conclude, we prepared two new representatives of the
trans-chelating ligands and studied their coordination to different
palladium and rhodium precursors. We found that in both the
sterically constrained 1,8-bis(4-(diphenylphosphino)-3,5-dim-
ethylphenyl)anthracene (3) and less sterically demanding 1,8-
bis(4-(diphenylphosphino)phenyl)anthracene (2) the trans che-
lation is preferred. However, only 2 has a sufficient flexibility
range to adapt smaller chelation angles. As a consequence, only
2 was found active in reactions where the formation of cis-
chelated species over the course of the catalytic cycle is
obligatory.
Our initial experiments have clearly demonstrated that the
catalyst derived from Pd(OAc)2/2 is indeed an efficient and
regioselectiVe promoter for the Heck reaction between aryl
bromides and cyclohexene.
A short optimization study revealed that the reaction between
bromobenzene (1 equiv) and cyclohexene (1.3 equiv) goes to
(15) (a) Beletskaya, I. P.; Cheprakov, A. V. Chem. ReV. 2000, 100, 3009.
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Synthesis; Beller, M., Bolm, C., Eds.; VCH: Weinheim, Germany, 1998; p
208. (c) Tsuji, J. Palladium Reagents and Catalysts; Wiley: Chichester,
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833.
Our preliminary catalytic studies disclosed very interesting
reactivity of the trans-spanning ligands and, therefore, will be
extended to include kinetic studies.
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(20) The formation of highly active colloidal species upon dissociation
of the ligand may also be suspected (see for example, Phan, N. T. S.; Van
Der Sluys, M.; Jones, C. W AdV. Synth. Catal. 2006, 348, 609). However,
we believe that this is not our case. We did not observe the precipitation of
palladium metal over the course of the reactionsusually, the reaction
mixture remains brown. In addition, the high selectivity of our catalyst
strongly implies ligand assistance.
(21) (a) House, H. O.; Ghali, N. I.; Haack, J. L.; VanDerveer, D. J.
Org. Chem. 1980, 45, 1807. (b) Jutand, A. Eur. J. Inorg. Chem. 2003, 2017.
(c) Svennebring, A.; Sjoeberg, P. J. R.; Larhed, M.; Nilsson, P. Tetrahedron
2008, 64, 1808.

Mizoroki-Heck Arylation of Cyclohexene
Organometallics, Vol. 27, No. 19, 2008 5143
Scheme 3. Plausible Mechanism for the Mizoroki-Heck Reaction
Table 1. Representative Results of Heck Arylation of Alkenesa
entry no.
yield (%)c
conversn (%)b
cat.
olefin
R
selectivity (A:B:C)d
1
2
3
4
5
6
H
H
cyclohexene Pd(OAc)2/3
cyclohexene
cyclohexene
cyclohexene
cyclohexene
Pd(OAc)2/2
Pd(OAc)2/2
Pd(OAc)2/2
Pd(OAc)2/2
Pd(OAc)2/2
>99
82
10:5:85
16:3:81
5:2:93
4-CH3
4-COCH3
4-OCH3
4-COCH3
>99
88
95
71
>99
>99
7:18:78
1-phenyl-1-cyclohexene
no reacn
7e
8e
4-COCH3
4-COCH3
styrene
tert-butyl acrylate
Pd(OAc)2/2
Pd(OAc)2/2
<99
<99
80
91
99% (E)-4-acetylstilbene
99% (E)-tert-butyl 3-(4-acetylphenyl)acrylate
9
10
4-COCH3
4-COCH3
cyclohexene
cyclohexene
Pd(OAc)2/PPh3
Pd(OAc)2/Xantphos
32
54
N/A
N/A
16:31:53
11:52:37
a Conditions: aryl bromide (1 mmol), cyclohexene (1.3 mmol), Pd(OAc)2 (0.02 mmol), 2 (0.03 mmol), K2CO3 (2 mmol), DMF (3 mL), 90 °C for
12 h. b Determined by GC (dodecane as an internal standard). c Isolated yield of mixtures of all regioisomers (average of two runs). d Determined by
GC. e The reactions were conducted at 50 °C for 12 h.
Scheme 4. Formation of Cationic Pd(II) Species
software package.24 Further information may be found in the
Supporting Information.
1,8-Bis(4-methoxyphenyl)anthracene. A mixture of 1,8-dibro-
moanthracene (3 g, 8.9 mmol), (4-methoxyphenyl)boronic acid (3.4
g, 22 mmol), K3PO4 (7.6 g, 36 mmol), Pd(OAc)2 (20 mg, 0.089
mmol), and 2-(dicyclohexylphosphino)-2′,4′,6′-triisopropylbiphenyl
(64 mg, 0.133 mmol) in dry toluene (30 mL) under a nitrogen
atmosphere was heated with stirring at 80 °C for 12 h. After the
mixture was cooled to room temperature, the solvent was removed
in vacuo and the residue was crystallized from toluene to give the
product (2.8 g, 81% yield). 1H NMR (CDCl3): δ 8.67 (s, 1H), 8.54
(s, 1H), 8.03 (d, J ) 8.8 Hz, 2H), 7.54 (dd, J ) 6.8 Hz, J ) 1.6
Hz, 2H), 7.51 (d, J ) 18.8 Hz, 4H), 7.41 (d, J ) 6 Hz, 2H), 7.00
(d, J ) 8.8 Hz, 4H), 3.89 (s, 6H). 13C NMR: δ 158.96, 140.2,
132.9, 131.9, 131.0, 130.2, 127.2, 126.6, 125.85, 125.30, 124.14,
113.67, 55.34. Anal. Calcd for C28H22O2: C, 86.13; H, 5.68. Found:
C, 86.20; H, 5.61.
1,8-Bis(4-hydroxyphenyl)anthracene. To a solution of 1,8-
bis(4-methoxyphenyl)anthracene (2.8 g, 7.2 mmol) in dry CH2Cl2
(120 mL) was slowly added a solution of BBr3 (2.1 mL, 21.5 mmol)
at -78 °C under nitrogen. The reaction mixture was stirred at room
temperature for 3 h and quenched carefully with 10% HCl at 0 °C.
It was then extracted with ethyl acetate, and the organic layer was
dried over anhydrous MgSO4. After evaporation under reduced
pressure the residue was precipitated with methanol to give the
Experimental Section
All manipulations were performed using standard Schlenk
techniques under an atmosphere of dry N2. All chemicals were
purchased elsewhere and used without further purification. 1,8-
Dichloroanthracene was prepared from commercially available
starting materials following the published procedure.6e NMR spectra
were recorded on a Bruker instrument operating at 400 MHz for
protons, 100 MHz for carbons, and 121 MHz for phosphorus.
Diffraction data were collected with a Bruker APEX CCD instru-
ment (Mo KR radiation (λ ) 0.710 73 Å). Crystals were mounted
onto glass fibers using epoxy. Single-crystal reflection data were
collected on a Bruker APEX CCD X-ray diffraction system
controlled by a Pentium-based PC running the SMART software
package.22 The integration of data frames and refinement of cell
structure were done by the SAINT+ program package.23 Refine-
ment of the structure on F2 was carried out by the SHELXTL
(22) SMART-NT, V. 5.6; Bruker AXS GMBH, Karlsruhe, Germany,
2002.
(23) SAINT-NT, V. 5.0; Bruker AXS GMBH, Karlsruhe, Germany,
2002.
(24) SHELXTL-NT, V. 6.1; Bruker AXS GMBH, Karlsruhe, Germany,
2002.

5144 Organometallics, Vol. 27, No. 19, 2008
KaganoVsky et al.
pure product (2.5 g, 95% yield). 1H NMR (DMSO): δ 8.73 (s, 1H),
8.68 (s, 1H), 8.08 (d, J ) 8.4 Hz, 2H), 7.57 (dd, J ) 8.4 Hz, J )
1.6 Hz, 2 H), 7.41 (d, J ) 2 Hz, 4H), 7.37 (d, J ) 2 Hz, 2 H), 6.90
(d, J ) 8.4 Hz, 2 H). 13C NMR: δ 157.3, 140.2, 132.0, 131.4,
130.9, 129.8, 127.4, 127.2, 126.4, 126.0, 115.7. Anal. Calcd for
C26H18O2: C, 86.16; H, 5.01. Found: C, 85.93; H, 5.14.
1,8-Bis(4-(((trifluoromethyl)sulfonyl)oxy)phenyl)anthracene. To
a mixture of 1,8-bis(4-hydroxyphenyl)anthracene (2.4 g, 6.6 mmol),
diisopropylethylamine (2.8 mL), and a few crystals of DMAP in
dry CH2Cl2 (100 mL) was slowly added 2.2 mL of (Tf)2O (13.2
mmol) at 0 °C under nitrogen. The reaction mixture was stirred at
room temperature for 15 min, extracted with CH2Cl2, and washed
with water three times. The organic layer was dried over MgSO4.
After evaporation under reduced pressure, silica gel column
chromatography (hexane/ethyl acetate 90/10) gave the product (3.0
g, 72% yield). 1H NMR (CDCl3): δ 8.60 (s, 1H), 8.32 (s, 1H),
8.11 (d, J ) 8.8 Hz, 2H), 7.57 (t, J ) 6.8 Hz, 2H), 7.55 (d, J )
15.6 Hz, 4H), 7.43 (d, J ) 6.8 Hz, 2H), 7.33 (d, J ) 8.4 Hz, 4H).
13C NMR: δ 148.8, 140.7, 132.0, 138.3, 131.5, 129.9, 128.4, 127.3,
126.6, 125.3, 122.6, 121.2.
1,8-Bis(4-(((trifluoromethyl)sulfonyl)oxy)-3,5-dimethylphenyl)an-
thracene. The procedure was as described for 1,8-bis(4-(((trifluo-
romethyl)sulfonyl)oxy)phenyl)anthracene (82% yield). 1H NMR
(CDCl3): δ 8.56 (δs, 1H), 8.33 (s, 1H), 8.08 (d, J ) 8.8 Hz, 2H),
7.56 (dd, J ) 6.8 Hz, J ) 1.6 Hz, 2H), 7.38 (d, J ) 7.6 Hz, 2H),
7.17 (s, 4H), 2.38 (s, 12H). 13C NMR: δ 145.9, 140.3, 138.8, 131.6,
131.2, 130.1, 128.1, 127.0, 126.2, 125.2, 17.1.
1,8-Bis(4-(diphenylphosphinyl)-3,5-dimethylphenyl)an-
thracene. The procedure was as described for 1,8-bis(4-(diphe-
nylphosphinyl)phenyl)anthracene (74% yield). 1H NMR (CDCl3):
δ 8.90 (δs, 1H), 8.60 (s, 1H), 8.08 (d, J ) 8 Hz, 2H), 7.74 (m,
9H), 7.57 (m, 15H), 7.40 (d, J ) 7.2 Hz, 2H), 2.19 (s, 12H). 31P
NMR: δ 30.09 (s). 13C NMR: δ 144.0, 144.0, 139.1, 136.0, 135.0,
131.8, 131.6, 129.7, 128.9 128.6, 128.4, 127.7, 127.6, 125.2, 122.6,
24.4.
1,8-Bis(4-(diphenylphosphino)-3,5-dimethylphenyl)anthracene
(3). The procedure was as described for 1,8-bis(4-(diphenylphos-
1
phino)phenyl)anthracene (75% yield). H NMR (CDCl3): δ 9.03
(s, 1H), 8.59 (s, 1H), 8.07 (d, J ) 8.4 Hz, 2H), 7.57 (t, J ) 7.2 Hz,
2H), 7.45 (d, J ) 6.4 Hz, 2H), 7.37 (m, 24H). 31P NMR: δ -15.64
(s). 13C NMR: δ 145.3, 142.3, 139.9, 136.4, 131.9, 130.8, 130.4,
129.8, 128.5, 127.9, 127.6, 127.4, 127.1, 125.1, 123.2, 24.0. Anal.
Calcd for C54H44P2: C, 85.92; H, 5.88. Found: C, 86.11; H, 5.73.
Complex 4. 3 (22 mg, 0.03 mmol) and PdCl2(CH3CN)2 (7.8 mg,
0.03 mmol) were dissolved in chloroform (4 mL). The yellow
solution was stirred for 10 min at room temperature. All volatiles
were evaporated under reduced pressure. The residue was rinsed
with diethyl ether and dried in vacuo, affording the product as a
1,8-Bis((4-diphenylphosphinyl)phenyl)anthracene. To a mix-
ture of 1,8-bis(4-(((trifluoromethyl)sulfonyl)oxy)phenyl)anthracene
(2.3 g, 3.7 mmol), diphenylphosphine oxide (3.9 g, 2.2 mmol),
Pd(OAc)2 (83 mg, 0.37 mmol), and 1,3-bis(diphenylphosphino-
)propane (150 mg, 0.37 mmol) were added dry DMSO (30 mL)
and diisopropylethylamine (4.9 mL, 38.4 mmol), and the mixture
was heated with stirring at 100 °C for 12 h. After the mixture was
cooled to room temperature, the solvent was removed by distillation
and the residue was precipitated with methanol to give the pure
1
yellow powder. H NMR (CDCl3): δ 8.51 (s, 1H), 8.04 (m, 4H),
1
product (1.6 g, 59% yield). H NMR (CDCl3): δ 8.80 (δs, 1H),
7.53 (t, J ) 7.2 Hz, 2H), 7.43 (m, 14H), 7.03 (s, 4H), 2.33 (s,
12H). 31P NMR: δ 19.4. Anal. Calcd for C54H44P2Cl2Pd: C, 69.57;
H, 4.76. Found: C, 69.11; H, 4.82.
8.61 (s, 1H), 8.10 (d, J ) 8.8 Hz, 2H), 7.76 (m, 16H), 7.60 (m.
14H), 7.40 (d, J ) 5.6 Hz, 2H), 7.76 (m, 16H), 7.68 (m, 14H),
7.60 (d, J ) 1.6 Hz, 2H). 31P NMR: δ 28.45 (s). 13C NMR: δ
144.4, 139.1, 133.0, 132.4, 132.1, 131.8, 131.4, 130.0, 129.6, 128.7,
128.5, 127.8, 127.7, 125.3, 122.4.
Complex 7. 2 (21 mg, 0.03 mmol) and PdCl2(CH3CN)2 (7.8 mg,
0.03 mmol) were dissolved in chloroform (4 mL). The yellow
solution was stirred for 10 min at room temperature. All volatiles
were evaporated under reduced pressure. The residue was rinsed
with diethyl ether and dried in vacuo, affording the product as a
1,8-Bis((4-diphenylphosphino)phenyl)anthracene (2). To a
mixure of 1,8-bis((4-diphenylphosphinyl)phenyl)anthracene (1.6 g,
2.2 mmol) and diisopropylethylamine (3 mL, 15.5 mmol) in xylene
(30 mL) was added dropwise trichlorosilane (3 mL, 22 mmol) at 0
°C. After the addition was complete, the mixture was heated with
stirring at 120 °C for 12 h. After the reaction mixture was cooled
to room temperature, 30% aqueous NaOH (7 mL) was added. The
organic layer was separated and dried over MgSO4, and the solvent
was removed in vacuo. The residue was precipitated with methanol
1
yellow powder. H NMR (CDCl3): δ 8.57 (s, 1H), 8.22 (s, 1H),
8.10 (d, J ) 8.4 Hz, 2H), 7.86 (m, 8H), 7.71 (m, 16H), 31P NMR:
δ 23.14. Anal. Calcd for C50H36Cl2P2Pd: C, 68.55; H, 4.14. Found:
C, 68.93; H, 3.89.
Complex 5. 3 (22 mg, 0.03 mmol) and Rh2Cl2(CO)4 (5.8 mg,
0.015 mmol) were dissolved in dichloromethane (4 mL). The yellow
solution was stirred for 10 min at room temperature. All volatiles
were evaporated under reduced pressure. The residue was rinsed
with diethyl ether and dried in vacuo, affording the product as a
yellow powder. 1H NMR (CDCl3): δ 8.51 (s, 1H), 8.04 (d, J ) 8.8
Hz, 7H), 7.53 (t, J ) 7.2 Hz, 2H), 7.43 (m, 14H), 7.03 (s, 4H),
2.33 (s, 12H). 31P NMR: δ 31.95 (d, J ) 96 Hz). Anal. Calcd for
C55H44P2ClORh: C, 71.71; H, 4.81. Found: C, 71.93; H, 5.03.
Complex 8. 2 (21 mg, 0.03 mmol) and Rh2Cl2(CO)4 (5.8 mg,
0.015 mmol) were dissolved in dichloromethane (4 mL). The yellow
solution was stirred for 10 min at room temperature. All volatiles
were evaporated under reduced pressure. The residue was rinsed
with diethyl ether and dried in vacuo, affording the product as a
1
to give the pure product (1.0 g, 65% yield). H NMR (CDCl3): δ
8.80 (s, 1H), 8.57 (s, 1H), 8.06 (d, J ) 8.4 Hz, 2H), 7.56 (m, 6H),
7.44 (m, 26H). 31P NMR: δ -6.1 (s). 13C NMR: δ 140.7, 139.9,
137.3, 136.5, 134.0, 133.3, 133.2, 131.9, 130.0, 128.7, 128.6, 127.9,
127.1, 125.3, 123.4. Anal. Calcd for C50H36P2: C, 85.94; H, 5.19.
Found: C, 85.93; H, 5.29.
1,8-Bis(4-methoxy-3,5-dimethylphenyl)anthracene. The pro-
cedure was as described for 1,8-bis(4-methoxyphenyl)anthracene
(73% yield). 1H NMR (CDCl3): δ 8.67 (s, 1H), 8.53 (s, 1H), 8.03
(d, J ) 8.8 Hz, 2H), 7.53 (dd, J ) 6.8 Hz, J ) 1.6 Hz, 2H), 7.38
(d, J ) 6.4 Hz, 2H), 7.12 (s, 4H), 3.80 (s, 6H) 2.31 (s, 12H). 13C
NMR: δ 156.2, 140.4, 136.1, 131.8, 130.3, 130.3, 130.3, 127.3,
126.7, 125.8, 125.1, 124.1, 59.7, 16.1. Anal. Calcd for C32H30O2:
C, 86.06; H, 6.77. Found: C, 85.89; H, 6.68.
1,8-Bis(4-hydroxy-3,5-dimethylphenyl)anthracene. The pro-
cedure was as described for 1,8-bis(4-hydroxyphenyl)anthracene
(90% yield). 1H NMR (CDCl3): δ 8.72 (s, 1H), 8.51 (s, 1H), 8.01
(d, J ) 8.8 Hz, 2H), 7.52 (dd, J ) 6.8 Hz, J ) 2 Hz, 2H), 7.37 (d,
J ) 8 Hz, 2H), 7.09 (s, 4H), 2.27 (s, 12H). 13C NMR: δ 151.4,
140.5, 132.6, 131.8, 130.4, 130.1, 127.1, 126.5, 125.7, 125.2, 124.2,
122.5, 15.9. Anal. Calcd for C30H26O2: C, 86.09; H, 6.26. Found:
C, 86.31; H, 6.39.
1
yellow powder. H NMR (CDCl3): δ 8.55 (s, 1H), 8.25 (s, 1H),
8.08 (d, J ) 8.4 Hz, 2H), 7.92 (m, 7H), 7.86 (m, 4H), 7.70 (t, J )
5.6 Hz, 3H), 7.58 (m, 19H), 31P NMR: δ 32.55 (d, J ) 96 Hz).
Anal. Calcd for C55H44P2ClORh: C, 71.71; H, 4.81. Found: C,
71.93; H, 5.03.
Complex 9. 2 (21 mg, 0.03 mmol) and Rh(COD)2BF4 (12.6 mg,
0.03 mmol) were dissolved in dichloromethane (4 mL). The yellow
solution was stirred for 10 min at room temperature. All volatiles
were evaporated under reduced pressure. The residue was rinsed
with diethyl ether and dried in vacuo, affording the product as a
1
yellow powder. H NMR (CDCl3): δ 8.57 (s, 1H), 8.14 (m, 3H),

Mizoroki-Heck Arylation of Cyclohexene
Organometallics, Vol. 27, No. 19, 2008 5145
7.69 (m, 8H), 7.30 (m, 12H), 31P NMR: δ 25.93 (d, J ) 108 Hz).
Anal. Calcd for C58H48P2BF4Rh: C, 69.90; H, 4.85. Found: C, 70.21;
H, 4.99.
products was isolated by means of silica gel column chromatog-
raphy (hexane) and analyzed by GC.
Catalytic Experiments. An screw-capped reaction tube was
charged with Pd(OAc)2 (0.02 mmol), ligand 2 (0.03 mmol), and
K2CO3 (2 mmol). The reaction vessel was evacuated and back-
filled with N2 (two times). Through a rubber septum, aryl bromide
(1 mmol) and cyclohexene (1.3 mmol) in DMF (3 mL) were added
to the reaction tube. The resulting mixture was heated at the
indicated temperature for 12 h. After it was cooled to ambient
temperature, the reaction mixture was extracted with CH2Cl2 and
washed with water (three times). The organic layer was dried over
MgSO4. After evaporation under reduced pressure, the mixture of
Acknowledgment. We thank the Israel Science Founda-
tion (Grant No. 866/06) for financial support and Dr. Shmuel
Cohen for solving X-ray structures.
Supporting Information Available: CIF files giving crystal data
and figures giving 1H, 13C, and 31P NMR spectra for all compounds
mentioned in the text. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM800448B