Palladium complexes with carbene and phosphine ligands: Synthesis, structural characterization, and direct arylation reactions between aryl halides and alkynes

Article abstract of DOI:10.1021/om9009203

The new palladium complexes with NHC and phosphine ligands, cis-PdCl ₂(L²)(PPh₃) (2), cisPdBr₂(L ²)(PPh₃) (3), and cis-PdCl₂(L ³)(PPh₃) (4) were prepared following a general protocol of a one pot reaction between PdCl₂(COD), PPh₃, and the ligand precursors LH · Y (Y = Cl, Br, BF₄) (L² = l,3-dibenzylimidazolin-2-ylidene; L³ = l,3-dibenzylimidazol-2- ylidene). The cis-PdCl₂(L³)(PCy₃) complex (5) was prepared by the ligand substitution reaction between 4 and PCy₃. The palladium complexes with NHC and pyridine complexes, trans-PdCl ₂(L)(py) (6: L = L²; 7: L = L³) were obtained by heating a mixture Of PdCl₂(COD) and LH · BF₄ in pyridine. A similar reaction condition using CH₃CN as solvent with KO'Bu as base afforded cis-PdCl₂(L³)₂ (8). Complexes 2-8 were successfully characterized by X-ray crystallographic studies, among which, intriguingly, two polymorphs of 8 were obtained. Thermogravimetric analysis showed that the Cis-PdX₂(NHC)(PR₃) complexes are more thermally stable than the trans-PdCl₂(NHC)(py) complexes. Together with the known Cis-PdCl₂(L¹(PCy₃) (1) (L¹ = l-benzyl-3-(N-phenylacetamido)imidazol-2-ylidene), they were screened for the direct arylation reaction between aryl halides and alkynes. The result indicate that the carbene/phosphine complexes 1-5 are superior precatalysts than 6-8 with higher activities than the commonly-used system of Pd(OAc)₂/2PPh₃.

Full text of DOI:10.1021/om9009203

Organometallics 2010, 29, 463–472 463
DOI: 10.1021/om9009203
Palladium Complexes with Carbene and Phosphine Ligands: Synthesis,
Structural Characterization, and Direct Arylation Reactions between
Aryl Halides and Alkynes
Kai-Ting Chan, Yi-Hua Tsai, Wu-Shien Lin, Jia-Rong Wu, Shih-Jung Chen, Fu-Xing Liao,
Ching-Han Hu, and Hon Man Lee*
Department of Chemistry, National Changhua University of Education, Changhua 50058,
Taiwan, Republic of China
Received October 20, 2009
The new palladium complexes with NHC and phosphine ligands, cis-PdCl2(L2)(PPh3) (2), cis-
PdBr2(L2)(PPh3) (3), and cis-PdCl2(L3)(PPh3) (4) were prepared following a general protocol of a
one pot reaction between PdCl2(COD), PPh3, and the ligand precursors LH Y (Y=Cl, Br, BF4) (L2=
3
1,3-dibenzylimidazolin-2-ylidene; L3=1,3-dibenzylimidazol-2-ylidene). Thecis-PdCl2(L3)(PCy3) com-
plex(5) was preparedby theligand substitutionreaction between 4 and PCy3. The palladium complexes
with NHC and pyridine complexes, trans-PdCl2(L)(py)(6: L = L2; 7:L = L3) wereobtainedby heating
a mixture of PdCl2(COD) and LH BF4 in pyridine. A similar reaction condition using CH3CN as
3
solvent with KOtBu as base afforded cis-PdCl2(L3)2 (8). Complexes 2-8 were successfully character-
ized by X-ray crystallographic studies, among which, intriguingly, two polymorphs of 8 were obtained.
Thermogravimetric analysis showed that the cis-PdX2(NHC)(PR3) complexes are more thermally
stable than the trans-PdCl2(NHC)(py) complexes. Together with the known cis-PdCl2(L1)(PCy3) (1)
(L1=1-benzyl-3-(N-phenylacetamido)imidazol-2-ylidene), they were screened for the direct arylation
reaction between aryl halides and alkynes. The result indicate that the carbene/phosphine complexes
1-5 are superior precatalysts than 6-8 with higher activities than the commonly-used system of
Pd(OAc)2/2PPh3.
Introduction
waste and fewer reaction steps.14-18 This direct arylation
reaction involves a kinetically significant aryl C-H bond
activation step, and reactive aryl halides, most commonly
aryl iodides, were required as substrates.15 Pd(OAc)2/2PPh3
represents a widely used catalytic system for direct aryla-
tions.15,19,20 Lately, there has been growing interest in using
palladium NHC complexes in catalyzing direct arylations.21-23
In this regard, Sames et al. reported that palladium NHC
complexes of the type PdI2(NHC)(PPh3) efficiently catalyze
the C-H arylation of SEM-protected azoles.22 These types
of mixed carbene/phosphine complexes offer the distinct
features of a strong donating effect from a robust NHC
ligand as well as a stabilization effect from a labile phosphine
ligand. These types of palladium complexes have already
been applied commonly in cross-coupling reactions.3,24-26
Palladium complexes with N-heterocyclic carbene ligands
(NHCs) have been proven remarkably successful in catalyz-
ing Suzuki-type cross-coupling reactions for the construc-
tion of biaryl motifs.1-9 These reactions, however, required
the use of organometallic reagents as substrates.10-13 The
construction of the biaryl motif without the need of a
preliminary organometallic reagent is more challenging
and has attracted much attention because of the reduced
*To whom correspondence should be addressed. Tel: þ886 4 7232105,
ext. 3523. Fax: þ886 4 7211190. E-mail: leehm@cc.ncue.edu.tw.
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2009 American Chemical Society
Published on Web 12/29/2009
pubs.acs.org/Organometallics

464 Organometallics, Vol. 29, No. 2, 2010
Chan et al.
Chart 1. NHC Ligands and Their Pd(II) Precatalysts for the
Direct Arylation Reactions of Alkynes with Aryl Halides
easily available substrates but is typically catalyzed by a high
loading of Pd(OAc)2 (5 mol %) and PPh3 (10 mol %) at high
temperature over a long duration using aryl iodides as
substrates.20 Considering these harsh catalytic conditions
required, robust palladium carbene complexes may exhibit
better activities. In this regard, we showed that palladium
complexes with rigid bidentate phosphine and NHC groups
are effective catalytic precursors for the direct arylation
reactions between phenyl halides and diphenylacetylene.23
However, extended hours were still needed for utilizing un-
reactive phenyl bromide as substrate. We anticipated that the
new catalyst systems PdX2(NHC)(PR3) andPdCl2(NHC)(py)
will perform better due to the easy availability of vacant
coordination sites and their still-good thermal stability. The
catalytic performance of PdCl2(NHC)2 will also be studied
and compared with those of PdX2(NHC)(PR3) and PdCl2-
(NHC)(py). Instead of one robust and one labile ligands, two
robust NHC ligands are present in PdCl2(NHC)2. The L1
ligand in 1 is an unsymmetrical ligand bearing benzyl and
amido groups. Herein, we investigate the saturated mono-
dentate NHC ligand of 1,3-dibenzylimidazolin-2-ylidene (L2)
and the unsaturated 1,3-dibenzylimidazol-2-ylidene (L3). Our
interest in these ligands is based on the fact that these
symmetrical ligands are easily accessible at low cost. Also, in
contrast to the ubiquitously used IMes and IPr ligands, these
ligands contain N-benzyl groups which are more conforma-
tionallyflexible, giving rise toplausible betteraccommodation
of steric bulk on the palladium coordination sphere. The
results illustrate that, among the three types of precatalysts
screened, PdCl2(NHC)(PR3) complexes represent a promis-
ing class of precatalysts for the direct arylations, capable of
utilizing the unreactive yet cheap aryl bromides as substrates
in producing fluorene derivatives.
Results and Discussion
Palladium carbene complexes of the type trans-PdCl2-
(NHC)(py0) (py0 =3-chloropyridine), known as PEPPSI com-
plexes, share a similar concept and have been highly success-
ful in catalyzing various cross-coupling reactions.9,27
Preparation of Ligand Precursors. The organic salts L2H
3
Y (Y = Cl,32 BF433) and L3H Y (Y = Cl,34 BF4) were the
3
ligand precursors for the NHC ligands L2 and L3, respec-
tively. The salts L2H Cl and L3H Cl were prepared by
reacting benzyl chloride with 1-benzylimidazole and 1-ben-
In a previous report, we had shown that cis-PdCl2(L1)-
(PCy3) (1) is a highly robust precatalyst for Suzuki cross-
coupling reactions.26 This spurred us to check the catalytic
performance of complexes of the type PdX2(NHC)(PR3) as
well as PdCl2(NHC)(py) in the direct arylation reactions of
alkynes with aryl halides for the formation of fluorene
compounds (Chart 1). Molecular and polymeric materials
containing fluorene skeletons have been attracting interest
because they have rich optical properties which can be
applied in optoelectronic applications.28-30 Most recently,
Gevorgyan et al. described an alternative approach of palla-
dium-catalyzed hydroarylation of o-alkynyl biaryls to prepare
relevant fluorene derivatives with high regioselectivity.31 The
cascade reaction in Chart 1 affords fluorene derivatives from
3
3
zyl-4,5-dihydro-1H-imidazole, respectively. The L2H BF4
3
and L3H BF4 salts were similarly prepared, but NaBF4
3
was also added for anion exchange. Either the chloride or
the tetrafluoroborate salts can be used for the preparation of
Pd(NHC) complexes; the tetrafluoroborate salts were pre-
ferred by us because of their nonhygroscopic nature. The
difference in electronic properties between [L2H]þ and
[L3H]þ ions is reflected by the more upfield chemical shift
1
of the H NMR signals of the saturated species compared
with the unsaturated compound. For example, the signals for
the methylene proton and the proton on the C-2 carbon in
L2H BF4 are observed at 4.63 and 8.50 ppm, respectively,
3
whereas those in L3H BF4 are observed at 5.27 and 9.05
3
ppm, respectively. Some iridium complexes with L2 and L3
have been reported recently.35
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Lee, H. M. Chem. Eur. J. 2009, 15, 405.
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G. A.; Lough, A.; Hopkinson, A. C.; Organ, M. G. Chem. Eur. J. 2006,
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Article
Organometallics, Vol. 29, No. 2, 2010 465
Scheme 1. Synthesis of Cis Palladium Complexes Bearing NHC and Phosphine Ligands
Scheme 2. Synthesis of Phosphine-Free Palladium NHC Complexes
Preparation of cis-PdCl2(NHC)(PR3) Complexes. The new
moisture stability and dissolve readily in halogenated solvents.
The cis coordination in complex 1 had been established.26
Complexes 2-5 are similar cis complexes, as revealed by sub-
sequent structural studies (vide infra). Those NHC/phosphine
complexes bearing large aryl groups typically adopt a trans
configuration.25,36-38 Complexes 2-5 are cis compounds,
reflecting the smaller steric bulk of the benzyl groups.
Preparation of Phosphine-Free Pd(NHC) Complexes. New
palladium complexes with NHC and pyridine ligands 6 and 7
were prepared according to Scheme 2. The general procedure
involves the heating of mixture of the appropriate tetrafluo-
roborate salt and PdCl2(COD) in pyridine at 130 °C over-
night.39 The protocol is similar to those unsaturated carbene
compounds published by Ghosh et al.,40 except that our
palladium complexes with NHC and phosphine ligands 2-5
were prepared according to our previously reported proce-
dure for 1 (Scheme 1).26 Pure complexes were obtained,
albeit in low yields. As an example, a one-plot reaction
between L2H Cl, PdCl2(COD), and PPh3 in the presence
3
of KHMDS afforded the pure cis-PdCl2(L2)(PPh3) (2). The
complex cis-PdCl2(L3)(PCy3) (5) was prepared by a ligand
displacement reaction between cis-PdCl2(L3)(PPh3) (4) and
PCy3.
The successful formation of 2-4 is indicated by the
disappearance of signal due to the proton upon the C-2
carbon of the ligand precursor and the downfield coordina-
tion shift of the 31P{1H} NMR signal (for example, from ca.
-6 ppm in free PPh3 to ca. 27 ppm in 2). The 31P NMR
resonance for PCy3 in 5 is even more downfield than that of
PPh3 in 4 (ca. 49 vs 27 ppm). As noted by us earlier in relevant
systems,26 the saturated carbenic carbons resonate as much
as 30 ppm more downfield than the unsaturated carbenic
carbons (ca. 193 ppm in 2 and 3 vs 160 ppm in 4 and 5). This
drastic difference in chemical shift reflects the variation of
electronic properties between the saturated and unsaturated
carbene ligands. Complexes 1-5 have the desirable air and
€
(36) Turkmen, H.; C-etinkaya, B. J. Organomet. Chem. 2006, 691,
3749.
€
€
(37) Sevinc-ek, R.; Turkmen, H.; Aygun, M.; C-etinkaya, B.; Garcıa-
´
Granda, S. Acta Crystallogr. 2007, C63, m277.
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2009, 368, 22.
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H. M. Organometallics 2007, 26, 1692.
(40) Ray, L.; Shaikh, M. M.; Ghosh, P. Dalton Trans. 2007, 4546.

466 Organometallics, Vol. 29, No. 2, 2010
Chan et al.
Figure 4. Molecular structures of 8: (left) C2/c unit cell, with
50% probability ellipsoids for non-H atoms (symmetry code A:
1 - x, y, 0.5 - z); (right) P21/c unit cell, with 50% probability
ellipsoids for non-H atoms. Hydrogen atoms, except those on
the heterocyclic ring, have been omitted for clarity.
Figure 1. Molecular structures of 2 (left) and 3 (right) with 50%
probability ellipsoids for non-H atoms. Hydrogen atoms, except
those on the heterocyclic ring, have been omitted for clarity.
Figure 2. Molecular structures of 4 (left) and 5 (right), with
50% probability ellipsoids for non-H atoms. Hydrogen atoms,
except those on the heterocyclic ring, have been omitted for
clarity. Only one of the independent molecules in the asym-
metric unit of 5 is shown.
Figure 5. Molecular structure of 9 with 30% probability ellip-
soids for non-H atoms. Only one orientation of the disordered
phenyl ring is shown.
intermediate chemical shift of ca. 161 ppm. The structure of 8
was established to be a cis palladium bis(NHC) complex by
an X-ray structural study (vide infra), in contrast to the more
commonly observed trans complexes.41-44 The cis-PdI2(L4)2
complex (L4 = 1,3-dimethylimidazol-2-ylidene) is a closely
related compound reported in the literature.45 Complexes
6-8 are also air and moisture stable and dissolve readily in
halogenated solvents.
Crystallographic Studies. All the new Pd(NHC) complexes
described in this paper have been successfully structurally
characterized. Figures 1-4 display their thermal ellipsoid
plots. The molecular structure of the organic product 9-ben-
zylidene-9H-fluorene (9) was also determined (Figure 5).
Selected bond distances and angles for the cis-PdCl2(NHC)-
(PR3) complexes are given in Table 1, whereas those for the
phosphine-free Pd(NHC) complexes and the organic com-
pound 9 are shown in Table 2. Complexes 2-5 are revealed
as cis complexes. Due to the cis disposition of two bulky
organic ligands, they display distorted square coordination
geometry with C-Pd-P angles greater than the ideal 90°.
For example, complex 5 bearing L3 and the bulky PCy3
ligands has a large C-Pd-P angle of 95.77(14)°, whereas the
corresponding angle in 4, due to the smaller bulk of PPh3, is
92.85(5)°. A perusal of Table 1 reveals that there is no
significant difference in the geometrical parameters between
Figure 3. Molecular structure of 6 (left) and 7 (right), with 50%
probability ellipsoids for non-H atoms. Hydrogen atoms, except
those on the heterocyclic ring, have been omitted for clarity.
Only one of the independent molecules in the asymmetric unit of
6 is shown.
procedure did not involve the addition of K2CO3. Purifica-
tion with column chromatography gave pure complexes 6
and 7 in low yields. They are trans complexes, as revealed by
subsequent X-ray structural studies (vide infra). The cis
palladium bis(NHC) complex 8 was prepared by stirring a
mixture of L3H Cl and PdCl2(COD) in the presence of
3
potassium tert-butoxide. A low 17% yield was obtained for
the pure complex 8 after column chromatography. Notably,
the chloride salt of L3 Cl was necessary for the preparation
3
of 8. The use of the tetrafluoroborate salt instead did not
afford the desirable product.
(41) Peng, H. M.; Song, G.; Li, Y.; Li, X. Inorg. Chem. 2008, 47, 8031.
(42) Fliedel, C.; Schnee, G.; Braunstein, P. Dalton Trans. 2009, 2474.
(43) Yang, W.-H.; Lee, C.-S.; Pal, S.; Chen, Y.-N.; Hwang, W.-S.;
Lin, I. J. B.; Wang, J.-C. J. Organomet. Chem. 2008, 693, 3729.
(44) Huynh, H. V.; Wu, J. J. Organomet. Chem. 2009, 694, 323.
The most important spectroscopic feature in the trans-
PdCl2(NHC)(py) complexes is again the 30 ppm downfield
shift of the carbene resonance in the saturated carbene
complex 6 compared to that in the unsaturated analogue 7
(ca. 181 vs 150 ppm). The carbene signal in 8 resonates at an
€
(45) Herrmann, W. A.; Elison, M.; Fischer, J.; Koher, C.; Artus,
G. R. J. Angew. Chem., Int. Ed. 1995, 34, 2371.

Article
Organometallics, Vol. 29, No. 2, 2010 467
˚
Table 1. Selected Bond Distances (A) and Angles (deg) of 2-5
3 C3H7NO
2
4
5
3
Pd1-C1
Pd1-P1
Pd1-Cl1
Pd1-Cl2
1.981(6)
Pd1-C1
Pd1-P1
Pd1-Br1
Pd1-Br2
1.9903(18)
Pd1-C1
Pd1-P1
Pd1-Cl1
Pd1-Cl2
1.9784(17)
2.2599(4)
2.3570(4)
2.3482(4)
Pd1-C1
Pd1-P1
Pd1-Cl1
Pd1-Cl2
1.997(5)
2.2583(18)
2.3590(17)
2.3487(18)
2.2640(4)
2.4750(2)
2.4784(2)
2.2785(14)
2.3468(12)
2.3684(14)
C1-Pd1-P1
C1-Pd1-Cl2
Cl1-Pd1-P1
Cl1-Pd1;Cl2
C1-Pd1-Cl1
P1-Pd1-Cl2
91.59(18)
85.64(18)
91.09(6)
91.66(7)
176.3(2)
177.20(7)
C1-Pd1-P1
C1-Pd1-Br2
Br1-Pd1-P1
Br1-Pd1-Br2
C1-Pd1-Br1
P1-Pd1-Br2
92.03(5)
83.39(5)
89.979(13)
92.472(8)
176.20(5)
176.683(13)
C1-Pd1-P1
C1-Pd1-Cl1
Cl2-Pd1-P1
Cl1-Pd1-Cl2
C1-Pd1-Cl2
P1-Pd1-Cl1
92.85(5)
84.89(5)
90.929(16)
91.472(16)
174.51(5)
176.886(16)
C1-Pd1-P1
C1-Pd1-Cl2
Cl1-Pd1-P1
Cl1-Pd1-Cl2
C1-Pd1-Cl1
P1-Pd1-Cl2
95.77(14)
85.72(15)
87.78(5)
90.69(5)
176.06(15)
177.88(5)
˚
Table 2. Selected Bond Distances (A) and Angles (deg) of 6-9
6
7
8 (form I)
8 (form II)
9
Pd1-C1
Pd1-N3
Pd1-Cl1
Pd1-Cl2
1.953(3)
2.099(3)
2.3046(13) Pd1-Cl1
2.3021(13) Pd1-Cl2
Pd1-C1
Pd1-N3
1.9682(18) Pd1-C1
2.0932(16) Pd1-Cl1
2.3086(5)
1.982(4)
2.3539(11) Pd1-C18
Pd1-Cl1
Pd1-C1
1.986(7)
1.985(6)
2.3591(15) C1-C13
2.3675(15) C7-C8
C1-C14
C1-C2
1.315(2)
1.475(2)
1.470(2)
1.455(2)
2.3075(5)
Pd1-Cl2
C1-Pd1-Cl1 89.45(11)
C1-Pd1-Cl2 88.17(11)
Cl1-Pd1-N3 92.37(10)
Cl2-Pd1-N3 89.90(10)
C1-Pd1-N3 176.75(13) C1-Pd1-N3 178.55(7)
Cl1-Pd1-Cl2 176.57(4) Cl1-Pd1-Cl2 178.08(2)
C1-Pd1-Cl1 91.37(6)
C1-Pd1-Cl2 88.32(6)
Cl1-Pd1-N3 89.55(5)
Cl2-Pd1-N3 90.80(5)
C1-Pd1-C1A
95.3(2)
C1-Pd1-C18 92.8(2)
C1-Pd1-Cl2 88.87(17)
Cl1-Pd1-Cl2 92.42(6)
C1-C14-Cl5 127.90(16)
C2-C1-Cl4 126.22(14)
Cl3-C1-C14 128.22(15)
Cl-C2-C7 108.67(13)
C1-C13-C8 108.39(14)
C1-Pd1-Cl1A 85.42(10)
Cl1-Pd1-Cl1A 94.19(6)
C1-Pd1-Cl1
175.89(11) Cl1-Pd1-C18 86.11(17)
C1-Pd1-Cl1 175.0(2)
C18-Pd1-Cl2 177.48(18)
the saturated carbene complex 2 and its unsaturated counter-
part 4. Generally, for complexes 2-5, the difference in trans
influence of the carbene and the phosphine ligands is not
obvious. For example, the Pd-Cl distance trans to PCy3 in
one of the independent molecules of 5 is 2.3684(14) A, longer
than that of 2.3468(12) A trans to the carbene. The reverse
trend is observed in the other independent molecule (see the
Supporting Information). The Pd-carbene distances in
these complexes are within the normal range of similar
compounds published in the literature.42,43,46,47
The structural determinations established that the PdCl2-
(NHC)(py) complexes 6 and 7 adopt trans coordination
(Figure 3). For the structure of 6, there are two independent
molecules in an asymmetric unit; their geometrical para-
meters are similar, and only one of the molecules is used for
structural discussion (see also the Supporting Information).
The Pd-C bond in 6 (1.953(3) A) is slightly shorter than that
in 7 (1.9682(18) A), seemingly indicating that coordination
of the saturated carbene L2 is stronger than that of the
unsaturated carbene L3. The Pd-C distance is also strongly
influenced by the N-substituents, as relevant PdCl2(NHC)-
(py) compounds bearing unsaturated carbene can also have
short Pd-C distances as in 6.40,48 The Pd-C distances in the
two trans-PdCl2(NHC)(py) complexes are slightly shorter
than those in the cis-PdX2(NHC)(PR3) complexes (ca. 1.96 A
vs 1.99 A). The Pd-Cl distances of ca. 2.31 A in the trans-
PdCl2(NHC)(py) complexes are also shorter than those of
ca. 2.36 A in 2, 4, and 5. Interestingly, while the Pd-C bonds
in 6 and 7 are similar to those in the related Pd-PEPPSI-IPr
complex,27 their Pd-N bonds are markedly shorter (2.099(3)
and 2.0932(16) A vs 2.1372 A), reflecting the stronger co-
ordination of the pyridine as compared to that of 3-chloro-
pyridine.
The structure of complex 8 was also established by X-ray
crystallography. Intriguingly, two polymorphic single crys-
tals were obtained (Figure 4). One of them crystallizes in the
monoclinic space group C2/c (form I), whereas the other
crystallizes in the monoclinic space group P21/c (form II).
The presence of two polymorphic structures confirms un-
ambiguously the flexible conformation of the N-benzyl
groups on the carbene ligands. In form I, the two benzyl
groups for each ligand are in an anti orientation with respect
to each other, whereas in form II one of the ligands contains
two benzyl groups which are in a syn orientation. The Pd-C
distances in these two structures are comparable to those in
the related cis-PdI2(L4)2 complex.45 However, their C-
Pd-C angles are somewhat larger than that of the known
compound (95.3(2) and 92.8(2)° vs 90.2(1)°),45 attributable
to the larger steric bulkiness of benzyl compared to that of
methyl groups.
The organic product 9-benzylidene-9H-fluorene (9), ob-
tained from a direct arylation reaction between phenyl halide
and diphenylacetylene (vide infra), was also successfully
studied by X-ray crystallography (Figure 5). It crystallizes
in the monoclinic space group C2/c with a full molecule in an
asymmetric unit. The molecule is disordered over two over-
lapping orientations related by a 2-fold rotation opera-
tion along the C1-C14 bond with 50:50 site occupan-
cies. The phenyl ring and the fluorene fragment are nearly
normal to each other with a dihedral angle of 86.57(9)°,
which is in sharp contrast to that of 51.22(5)° in the close-
ly related structure of 9-pentafluorophenylmethylene-9H-
fluorene.49
€
(46) Furstner, A.; Seidel, G.; Kremzow, D.; Lehmann, C. W. Orga-
nometallics 2003, 22, 907.
(47) Chamizo, J. A.; Morgado, J.; Castro, M.; Bernes, S. Organome-
tallics 2002, 21, 5428.
(48) Ray, S.; Mohan, R.; Singh, J. K.; Samantaray, M. K.; Shaikh,
M. M.; Panda, D.; Ghosh, P. J. Am. Chem. Soc. 2007, 129, 15042.
(49) Plater, M. J.; Howie, R. A.; Schmidt, D. M. Acta Crystallogr.
2003, E59, o89.

468 Organometallics, Vol. 29, No. 2, 2010
Chan et al.
tures of 4 are illustrated in the Supporting Information,
and the selected bond distances and bond angles of the cis
isomer were comparable to those obtained by the X-ray
structural study (vide infra). The computational studies
are fully consistent with our previous results obtained for
complex 1.26
Thermogravimetric Analysis (TGA). To understand the
robustness of the new complexes, TGA was conducted on
the PdX2(NHC)(PR3) complexes 2-5 and PdCl2(NHC)(py)
complexes 6 and 7 (Figure 6). The analyses clearly indicate
the high robustness of all these complexes. In general, the
PdX2(NHC)(PR3) complexes are thermally more stable than
the PdCl2(NHC)(py) complexes. Complexes 2-5 are ther-
mally stable up to ca. 250 °C, with complex 3 being the most
thermally stable compound. In contrast, complexes 6 and 7
start thermal decomposition above ca. 200 °C.
Figure 6. Thermogravimetric analyses of 2-7.
Table 3. Direct Arylation Reactions between Phenyl Halides and
Diphenylacetylenea
Catalytic Transformations. Complexes 1-8 were screened
as precatalysts for the direct arylation reactions between
aryl halides and alkynes. We employed the conditions
initially utilized by Larock et al.,20 involving 5 mol % of
precatalyst, 0.25 mmol of phenyl halide, 0.25 mmol of
diphenylacetylene, 0.50 mmol of NaOAc, and 0.25 mmol
of n-Bu4NCl in 5 mL of DMF at 120 °C for a duration of
12 or 24 h. We began our investigation using phenyl
iodide and diphenylacetylene as the benchmark reaction
(Table 3). Entries 1-8 illustrate that good to excellent
yields of 9-benzylidene-9H-fluorene can be achieved using
all the new palladium carbene precatalysts. The effectiveness
among these complexes is more obvious when less reac-
tive phenyl bromide was used as substrate. Entries 11-15
vs 16-18 clearly reveal the higher efficiency of cis-Pd-
X2(NHC)(PR3) complexes over the trans-PdCl2(NHC)-
(py) and cis-PdCl2(NHC)2 complexes. Indeed, comp-
lexes 1-5 afford quantitative production of the product
after prolonging the reaction time to 24 h (entries
11-15). The results indicated that complexes 1-5 are
superior precatalysts to the reported Pd(OAc)2/2PPh3 sys-
tem,20,50 which gives inferior activities under the same
conditions (entries 11-15 vs 20). Intriguingly, while Pd-
(OAc)2 has been generally employed as the precatalyst for
direct arylation,20,50 the simple PdCl2 complex has never
been tested. We showed that the simple PdCl2 complex in
the presence of PPh3 also represents a viable catalytic
system, delivering activities comparable to those of the
Pd(OAc)2/2PPh3 system (entries 9 and 19 vs 10 and 20).20,50
Unfortunately, none of the precatalysts were able to utilize
the unreactive but economic attractive phenyl chloride as
substrate.
entry
cat.
X
time (h) yield (%) time (h) yield (%)a
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
I
I
I
I
I
I
I
I
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
89
87
97
72
84
82
58
88
61
67
97
97
93
82
93
23
40
30
42
39
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
9
PdCl2/2PPh3
Pd(OAc)2/2PPh3
1
2
3
4
5
6
7
I
I
10
11
12
13
14
15
16
17
18
19
20
Br
Br
Br
Br
Br
Br
Br
Br
Br
>99
>99
>99
>99
>99
60
49
35
54
59
8
PdCl2/2PPh3
Pd(OAc)2/2PPh3 Br
a Reaction conditions: 5 mol % of catalyst, 0.25 mmol of phenyl halide,
0.25 mmol of diphenylacetylene, 0.50 mmol of NaOAc, 0.25 mmol of
n-Bu4NCl, 5 mL of DMF, 120 °C, isolated yield (an average of several
runs).
Computational Studies. To understand the relative stabi-
lity between the cis and the trans forms of PdX2(NHC)(PR3),
we conducted density functional theory computations using
the B3LYP functional. The studies indicated that in the gas
phase the trans form of complex 4 is, in contrast with our
structural study, more stable than the cis compound by ca.
7.0 kcal/mol in Gibbs free energy. Since a polar solvent was
employed in the preparation of complexes 2-5, the solvent
effect may play a key role in the relative stability between the
two isomers. When the solvent correction was included using
the polarizable continuum model (PCM, nitromethane as
solvent), the experimentally found cis structure indeed be-
comes lower in energy than the trans isomer by 2.7 kcal/mol.
The stability of the cis form in polar solvent over the
trans form is attributed to the difference of the dipole
moments of the two isomers. The DFT optimized struc-
The substrate scope of the cis-PdCl2(NHC)(PR3) com-
plexes was briefly investigated, using complexes 1, 4, and 5 as
representative examples (Table 4). In general, they are cap-
able of utilizing aryl iodides effectively to form fluorene
products 10-12 and the use of aryl bromides affords lower
yields. By far, complex 1 is the most efficient among the three
complexes tested. Entry 1 illustrated that a 60% yield of a
mixture of 10a and 10b (Z/E ratio 42:58) was obtained with
complex 1 as precatalyst using 4-iodotoluene and dipheny-
lacetylene as substrates (entry 1). A comparable yield (58%)
of the fluorene product can also be obtained with the less
reactive 4-bromotoluene (entry 2). Contrastingly, inferior
yields of 46 and 47% were obtained using 4 and 5 as
precatalysts (entries 8 and 14). The similar activities between
(50) Larock, R. C.; Tian, Q. J. Org. Chem. 2001, 66, 7372.

Article
Organometallics, Vol. 29, No. 2, 2010 469
Table 4. Direct Arylation Reactions between Aryl Halides and Alkynesa
a Reaction conditions: 5 mol % of catalyst, 0.25 mmol of aryl halide, 0.25 mmol of alkyne, 0.50 mmol of NaOAc, 0.25 mmol of n-Bu4NCl, 5 mL of
DMF, 120 °C, isolated yield (an average of several runs). The Z/E ratio was determined by 1H NMR spectroscopy.
4 and 5 suggested that the labile phosphines do not take part
in the rate-determining step of the catalytic cycle (entries
7-12 vs 13-18). Using complex 1 as precatalyst, a decent
yield of 11 (60%) can be obtained from the reaction between
phenyl bromide and 2-methyl-4-phenylbut-3-yn-2-ol in 24 h
(entry 4); also, the reaction between 2-bromobenzonitrile
and diphenylacetylene gave the single stereoisomer of 12 in
pure form with a yield of 76% (entry 6).

470 Organometallics, Vol. 29, No. 2, 2010
Chan et al.
Conclusions. On the basis of the conformationally flexi-
ble 1,3-dibenzylimidazolin-2-ylidene (L2) and 1,3-dibenzy-
limidazol-2-ylidene (L3), we prepared and structurally
characterized cis-PdX2(NHC)(PR3), trans-PdCl2(NHC)-
(py), and cis-PdCl2(NHC)2. An interesting aspect of the
structural studies is the observation of two genuine poly-
morphic forms of 8 due to the flexibility of N-benzyl
conformations. Together with the previously reported
complex 1, these three types of complexes were tested for
the direct arylation reactions of alkynes with aryl halides.
The screening sheds light on the modular design of effective
palladium precatalysts for the catalytic process. Palladium
complexes bearing one robust NHC ligand and one labile
phosphine ligand, cis-PdX2(NHC)(PR3), are confirmed to
deliver good activities, capable of utilizing less reactive aryl
bromides as substrates. The activities from PCy3 and PPh3
ligands are essentially the same. The catalytic performance
from these types of complexes is superior to that of the
commonly used system of Pd(OAc)2/2PPh3. The ineffici-
ency of the cis-PdCl2(NHC)2 precatalyst further confirmed
that one labile ligand is essential. In contrast, replacement
of the phosphine ligand with a pyridine ligand results in
inferior activities from the trans-PdCl2(NHC)(py) com-
plexes. Their poorer thermal stability compared to that
of cis-PdX2(NHC)(PR3) may contribute to their lower
efficiency. The use of aryl chlorides as substrates and better
control of regioselectivity are, however, challenges for fur-
ther studies.
7.12 (s, 2H, imi H), 7.30-7.36 (m, 10H, Ph H), 9.05 (s, 1H,
NCHN). 13C{1H} NMR (CDCl3): δ 53.4 (PhCH2), 122.1 (imi
C), 128.9 (Ph C), 129.4 (Ph C), 129.5 (Ph C), 132.7 (Ph C), 135.7
(NCHN).
Synthesis of cis-PdCl2(L2)(PPh3) (2). A mixture of L2H Cl
3
(0.447 g, 1.32 mmol), KHMDS (0.263 g, 1.32 mmol), PdCl2-
(COD) (0.378 g, 1.32 mmol), and PPh3 (0.347 g, 1.32 mmol) in
DMF (10 mL) was stirred at room temperature for 1 day. After
the mixture was cooled, the solvent was removed completely
under vacuum. The residue was extracted with dichloro-
methane. The organic layer was washed twice with water. After
drying with anhydrous MgSO4, the solvent was removed com-
pletely under vacuum. The residue was washed with THF. The
off-white solid was filtered on a frit and dried under vacuum.
Yield: 0.123 g, 14%. Mp: 264-266 °C dec. Anal. Calcd for
C35H33Cl2N2PPd: C, 60.93; H, 4.82; N, 4.06. Found: C, 60.61;
H, 5.08; N, 3.76. 1H NMR (CDCl3): δ 2.66-2.72 (m, 2H,
NCHAHBC), 3.03-3.09 (m, 2H, NCHAHBC), 4.05 (d, 2JHH
=
2
14.0 Hz, 2H, PhCHAHBN), 5.51 (d, JHH = 14.0 Hz, 2H,
PhCHAHBN), 7.19-7.29 (m, 10H, Ph H), 7.38-7.52 (m, 9H,
Ph H), 7.71-7.77 (m, 6H, Ph H). 13C{1H} NMR (CDCl3): δ 47.4
(NCH2), 54.8 (PhCH2), 128.3 (Ph C), 128.5 (d, 3JPC =11.1 Hz,
Ph C), 129.0 (d, 2JPC =40.4 Hz, Ph C), 129.8 (Ph C), 130.5 (Ph
C), 131.4 (d, 4JPC=2.5 Hz, Ph C), 134.0 (Ph C), 134.5 (d, 1JPC
=
11.1 Hz, Ph C), 192.2 (NCN). 31P{1H} NMR (CDCl3): δ 27.2.
Crystals suitable for X-ray crystallography were obtained by
vapor diffusion of diethyl ether into a DMF solution of the solid
mixture.
Synthesis of cis-PdBr2(L2)(PPh3) (3). A mixture of L2H BF4
3
(0.217 g, 0.643 mmol), KHMDS (0.128 g, 0.643 mmol), PdCl2-
(COD) (0.114 g, 0.643 mmol), PPh3 (0.169 g, 0.643 mmol), and
KBr (0.192 g, 1.61 mmol) in CH3CN (15 mL) was heated at
room temperature for 1 day. The workup procedure is same as
that for 2. An off-white solid was obtained. Yield: 0.0747 g,
15%. Mp: 285 °C dec. Anal. Calcd for C35H33Br2N2PPd: C,
Experimental Section
General Procedure. All reactions were performed under a dry
nitrogen atmosphere using standard Schlenk techniques. All
solvents used were purified according to standard procedures.51
Commercially available chemicals were purchased from Aldrich
or Acros. 1H, 13C{1H}, and 31P{1H} NMR spectra were recor-
ded at 300.13, 75.48, and 121.49 MHz, respectively, on a Bruker
AV-300 spectrometer. The chemical shifts for 1H and 13C
spectra were referenced by the residual solvent signals relative
to tetramethylsilane at 0 ppm. The chemical shifts for 31P spectra
were referenced to an external reference of 85% phosphoric acid
at 0 ppm. Elemental analyses were performed on a Heraeus
CHN-OS Rapid elemental analyzer at the National Chung
Hsing University, Taiwan, or a Thermo Flash 2000 CHN-O
elemental analyzer at NCUE. ESMS spectra were collected on a
Finnigan/Thermo Quest MAT 95XL mass spectrometer at
NCHU. Thermogravimetric analysis (TGA) was performed
on a Perkin-Elmer Pyris 6 thermogravimetric analyzer under
flowing N2 gas (40 mL/min), and the heating rate was 20 °C/min.
9-Benzylidene-9H-fluorene20 and 10-1219 were previously re-
ported.
1
53.97; H, 4.27; N, 3.60. Found: C, 53.90; H, 4.73; N, 3.40. H
NMR (CDCl3): δ 2.66-2.72 (m, 2H, NCHAHBC), 3.03-3.09
(m, 2H, NCHAHBC), 4.05 (d, JHH = 13.8 Hz, 2H,
2
2
PhCHAHBN), 5.45 (d, JHH = 13.8 Hz, 2H, PhCHAHBN),
7.16-7.25 (m, 10H, Ph H), 7.37-7.51 (m, 9H, Ph H),
7.69-7.75 (m, 6H, Ph H). 13C{1H} NMR (CDCl3): δ 47.4
(NCH2), 54.8 (PhCH2), 128.2 (Ph C), 128.4 (d, JPC = 11.0 Hz,
3
2
Ph C), 128.9 (d, JPC = 45.2 Hz, Ph C), 130.2 (Ph C), 130.9
(Ph C), 131.3 (d, 4JPC =2.4 Hz, Ph C), 133.9 (Ph C), 134.5 (d,
1JPC=11.0 Hz, Ph C), 193.1 (d, 2JPC=3.2 Hz, NCN). 31P{1H}
NMR (CDCl3): δ 26.4. Crystals suitable for X-ray crystal-
lography were obtained by vapor diffusion of diethyl ether
into a DMF solution of the solid mixture.
Synthesis of cis-PdCl2(L3)(PPh3) (4). A mixture of L3H Cl
3
(1.09 g, 3.82 mmol), KHMDS (0.76 g, 3.82 mmol), Pd(COD)Cl2
(1.09 g, 3.82 mmol), and PPh3 (1.00 g, 3.82 mmol) in DMF
(10 mL) was stirred at room temperature for 1 day. The workup
procedure was same as that for 2. Yield: 0.892 g, 34%. Mp:
264-268 °C dec. Anal. Calcd for C35H31Cl2N2PPd: C, 61.11; H,
4.54; N, 4.54. Found: C, 61.12; H, 3.97; N, 4.53. 1H NMR
(CDCl3): δ 4.50 (d, 2JHH =14.1 Hz, 2H, PhCHAHBN), 5.68 (d,
2JHH = 14.1 Hz, 2H, PhCHAHBN), 6.37 (s, 2H, imi H),
7.14-7.31 (m, 16H, Ph H), 7.39-7.51 (m, 9H, Ph H). 13C{1H}
NMR (CDCl3): δ 54.4 (CH2), 121.4 (imi C), 128.4 (d, 3JPC=10.9
Hz, Ph C), 128.5 (Ph C), 128.9 (d, 2JPC =35.8 Hz, Ph C), 129.2
(Ph C), 129.9 (Ph C), 131.5 (d, 4JPC =2.3 Hz, Ph C), 133.9 (Ph
Synthesis of L3H BF4. A mixture of 1-benzylimidazole (1.50 g,
3
9.49 mmol), benzyl bromide (1.13 mL, 9.49 mmol), and NaBF4
(5.21 g, 47.4 mmol) in DMF (5 mL) was stirred at room
temperature for 4 h. Upon addition of diethyl ether into the
solution, a white precipitate was formed. The supernatant
liquid was removed, and the residual solid was redissolved in
dichloromethane. The organic layer was washed twice with
water. After drying with anhydrous MgSO4, the solvent was
removed completely under vacuum. The residue was washed
with diethyl ether. The white solid was filtered on a frit and
dried under vacuum. Yield: 2.31 g, 72%. Mp: 87-90 °C. Anal.
Calcd for C17H17BF4N2: C, 60.74; H, 5.10; N, 8.33. Found: C,
60.54; H, 5.02; N, 7.97. 1H NMR (CDCl3): δ 5.27 (s, 4H, CH2),
1
C), 134.0 (d, JPC = 11.1 Hz, Ph C), 160.5 (NCN). 31P{1H}
NMR (CDCl3): δ 27.4. 31P{1H} NMR (CDCl3): δ 27.4. Crystals
suitable for X-ray crystallography were obtained by slow eva-
poration of a CHCl3 solution of the solid mixture.
Synthesis of cis-PdCl2(L3)(PCy3) (5). A solution of 4 (0.572 g,
0.831 mmol) and PCy3 (0.349 g, 1.25 mmol) in dichloromethane
(15 mL) was stirred for 1 day at room temperature. The solvent
was then removed completely under vacuum. The residue was
washed with diethyl ether. The white powder that remained was
(51) Armarego, W. L. F.; Chai, C. L. L., Purification of Laboratory
Chemicals, 5th ed.; Elsevier Science: Burlington, 2003.

Article
Organometallics, Vol. 29, No. 2, 2010 471
Table 5. Crystallographic Data for 2-5
2
3 C3H7NO
3
4
5 C4H8O
3
empirical formula
formula wt
cryst syst
space group
a, A
b, A
c, A
R, deg
β, deg
C
35H33Cl2N2PPd
C35H33Br2N2PPd C3H7NO
C35H31Cl2N2PPd
687.89
monoclinic
P21/c
15.6908(2)
11.1879(2)
17.9775(3)
90
96.9448(14)
90
3132.74(9)
100(2)
4
6779
370
0.0228
0.0568
C35H49Cl2N2PPd C4H8O
3
3
689.90
orthorhombic
Pbca
15.7000(4)
18.927(5)
21.459(5)
90
90
90
6377(3)
150(2)
8
851.92
monoclinic
P21/n
11.5499(4)
16.3133(6)
19.1900(7)
90
96.7120(10)
90
3590.9(2)
150(2)
4
742.09
monoclinic
P21/c
16.8134(4)
16.3899(4)
27.0373(7)
90
103.143(2)
90
7255.5(3)
100(2)
8
γ, deg
V, A3
T, K
Z
no. of unique data
no. of params refined
R1a (I > 2σ(I))
wR2b (all data)
P
8354
371
0.0622
0.1767
9214
417
14 688
811
0.0591
0.1566
0.0224
0.0594
P
P
P
a R1 = (||Fo| - |Fc||)/ |Fo|. b wR2 = [ (|Fo|2 - |Fc|2)2/ (Fo2)]1/2
.
Table 6. Crystallographic Data for 6-9
6
7
8 (form I)
8b (form II)
9
empirical formula
formula wt
cryst syst
space group
a, A
b, A
c, A
R, deg
β, deg
C
22H23Cl2N3Pd
C22H21Cl2N3Pd
504.72
monoclinic
P21/n
9.0547(7)
25.3595(18)
9.7807(7)
90
111.7780(10)
90
2085.6(3)
150(2)
C34H32Cl2N4Pd
673.94
monoclinic
C2/c
15.823(5)
14.132(5)
15.342(5)
90
114.275(17)
90
3127.2(17)
150(2)
4
3413
186
0.0373
0.1145
C34H32Cl2N4Pd
673.94
monoclinic
P21/c
7.5602(9)
33.767(4)
12.2325(15)
90
95.880(3)
90
3106.3(6)
150(2)
4
5314
370
0.0627
0.1876
C20H14
254.31
monoclinic
C2/c
23.555(15)
7.215(5)
19.145(13)
90
119.881(11)
90
2821(3)
150(2)
8
506.73
monoclinic
P21/c
19.941(12)
10.116(6)
22.057(13)
90
93.222(11)
90
4442(4)
150(2)
8
γ, deg
V, A3
T, K
Z
4
4338
253
no. of unique data
no. of params refined
R1a (I > 2σ(I))
wR2b (all data)
P
11 720
505
0.0454
0.1348
3754
224
0.0506
0.1766
0.0219
0.0572
P
P
P
a R1 = (||Fo| - |Fc||)/ |Fo|. b wR2 = [ (|Fo|2 - |Fc|2)2/ (Fo2)]1/2
.
then collected on a frit and dried under vacuum. Yield: 0.306 g,
124.3 (py C), 128.0 (Ph C), 128.7 (2 overlapping signals, Ph C),
135.1 (Ph C), 138.0 (py C), 181.4 (NCN), 151.1 (py C). Crystals
suitable for X-ray crystallography were obtained by vapor diffu-
sion of diethyl ether into a pyridine solution of the solid mixture.
Synthesis of trans-PdCl2(L3)(py) (7). The procedure was same
52%. Mp: 241-243 °C dec. Anal. Calcd for C35H49Cl2N2PPd:
C, 59.54; H, 6.99; N, 3.97. Found: C, 53.25; H, 6.83; N, 3.65. 1H
2
NMR (CDCl3): δ 1.07-2.49 (m, 33H, Cy H), 5.03 (d, JHH
=
2
13.9 Hz, 2H, PhCHAHBN), 6.14 (d, JHH = 13.9 Hz, 2H,
PhCHAHBN), 7.22 (s, 2H, imi H), 7.24-7.35 (m, 6H, Ph H),
7.46-7.54 (m, 4H, Ph H). 13C{1H} NMR (DMSO-d6): δ 25.6
as that for 6. A solution of L3H BF4 (1.50 g, 4.46 mmol) and
3
PdCl2(COD) (1.30 g, 4.46 mmol) in pyridine (20 mL) was used. A
yellow solid was obtained. Yield: 0.529 g, 24%. Mp: 197-199 °C.
Anal. Calcd for C22H21Cl2N3Pd: C, 52.35; H, 4.19; N, 8.32. Found:
C, 52.39; H, 4.10; N, 8.43. 1H NMR (CDCl3): δ 5.89 (CH2), 6.71
(imi H), 7.34-7.44 (m, 8H, Ph H, py H), 7.52-7.55 (m, 4H, Ph H),
7.77 (t, 1H, 3JHH =9.0 Hz, py H), 9.01 (d, 3JHH =6.0 Hz, 2H, py
H). 13C{1H} NMR (CDCl3): δ 54.7 (CH2), 121.7 (imi C), 124.4 (py
C), 128.4 (Ph C), 128.9 (2 overlapping signals, Ph C), 135.3 (Ph C),
138.0 (py C), 149.9 (NCN), 151.2 (py C). Crystals suitable for
X-ray crystallography were obtained by vapor diffusion of diethyl
ether into a DMF solution of the solid mixture.
3
(Cy C), 26.8 (d, JPC = 11.0 Hz, Cy C), 29.5 (Cy C), 36.2 (d,
1JPC =23.8 Hz, Cy C), 54.3 (CH2), 122.5 (imi C), 128.4 (Ph C),
129.1 (Ph C), 135.4 (Ph C), 159.6 (NCN). 31P{1H} NMR (CDCl3):
δ 48.6. Crystals suitable for X-ray crystallography were obtained
by slow evaporation of a THF solution of the solid mixture.
Synthesis of trans-PdCl2(L2)(py) (6). A solution of L2H BF4
3
(0.152 g, 0.449 mmol) and PdCl2(COD) (0.192 g, 0.674 mmol) in
pyridine (20 mL) was heated at 130 °C for 12 h. After the mixture
was cooled, the solvent was removed completely under vacuum.
The residue was extracted with dichloromethane. The organic
layer was washed twice with water. After drying with anhydrous
MgSO4, the solvent was removed completely under vacuum.
The residue was washed with THF. After removal of the solvent
under vacuum, the crude solid was purified by column chroma-
tography with hexane-ethyl acetate (1:1) as eluent to give a
yellow solid. Yield: 0.106 g, 47%. Mp: 204-206 °C. Anal. Calcd
for C22H23Cl2N3Pd: C, 52.14; H, 4.57; N, 8.29. Found: C, 52.02;
H, 4.51; N, 8.20. 1H NMR (CDCl3): δ 3.42 (s, 4H, NCH2), 5.42
Synthesis of cis-PdCl2(L3)2 (8). A solution of L3H Cl (2.38 g,
3
8.34 mmol), KOtBu (0.94 g, 8.34 mmol), and PdCl2(COD)
(1.20 g, 4.17 mmol) in CH3CN (10 mL) was stirred at room tem-
perature for 12 h. The workup procedure was same as that for 2.
The crude product was then purified by column chromatogra-
phy using 1:1 acetone-hexane as eluent. A white solid was
obtained. Yield: 0.478 g, 17%. Mp: 237-242 °C dec. Anal.
Calcd for C34H32Cl2N4Pd: C, 60.59; H, 4.79; N, 8.31. Found: C,
60.28; H, 4.77; N, 8.09. 1H NMR (CDCl3): δ 5.25 (d, 2JHH=14.5
(PhCH2), 7.27-7.39 (m, 8H, Ph H, py H), 7.56 (d, 4H, 3JHH
=
6.9 Hz, Ph H), 7.73 (t, 1H, 3JHH=5.7 Hz, py H), 8.96 (m, 2H, py
H). 13C{1H} NMR (CDCl3): δ 47.6 (NCH2), 54.5 (PhCH2),
2
Hz, 2H, PhCHAHBN), 5.96 (d, JHH = 14.5 Hz, 2H, Ph-
CHAHBN), 6.54 (s, 2H, imi H), 7.11-7.14 (m, 8H, Ph H),

472 Organometallics, Vol. 29, No. 2, 2010
Chan et al.
7.24-7.27 (m, 12H, Ph H). 13C{1H} NMR (CDCl3): δ 54.6
(CH2), 121.6 (imi C), 128.3 (Ph C), 128.5 (Ph C), 129.0 (Ph C),
134.7 (Ph C), 161.3 (NCN). Crystals of forms I and II suitable
for X-ray crystallography were obtained by vapor diffusion of
diethyl ether into a methanol solution of the solid mixture.
Forms I and II are visually indistinguishable.
Catalytic Direct Arylation. In a typical reaction, a mixture of
aryl halides (0.25 mmol), diphenylacetylene (0.25 mmol),
NaOAc (0.50 mmol), n-Bu4NCl (0.25 mmol), and palladium-
(II) precatalyst (5 mol %) in 5 mL of DMF was stirred at 120 °C
for the periods of time indicated in Tables 3 and 4. In the
standard workup, the reaction mixture was cooled to ambient
temperature, diluted with diethyl ether, washed with brine, and
dried with anhydrous MgSO4. The solution was then filtered.
The solvent and any volatiles were removed completely under
high vacuum to give a crude product which was purified by
column chromatography. Crystals of 9-benzylidene-9H-fluor-
ene (9) suitable for X-ray diffraction study were obtained
by slow evaporation of a hexane solution containing the
compound.
were fixed at calculated positions and refined with the use of a
riding model. Crystallographic data are given in Tables 5 and 6.
The file numbers CCDC-747061 (2), CCDC-747062 (3 C3H7NO),
3
CCDC-747063 (4), CCDC-747064 (5 C4H8O), CCDC-747065
3
(6), CCDC-747066 (7), CCDC-747067 (8a), CCDC-747068 (8b),
and CCDC-747069 (9) contain the supplementary crystallographic
data for this paper. These data can obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
Computational Details. We used the three-parameter hybrid
of exact exchange and Becke’s exchange energy functional,54
plus Lee, Yang, and Parr’s gradient-corrected correlation en-
ergy functional (B3LYP).55 The 6-31G(d) basis sets for H, C, N,
P, and Cl were used. For Pd we used the LANL2DZ effective
core potential plus basis functions.56 The solvation free ener-
gies were computed using the polarizable continuum model
(PCM).57 Within the PCM model, we incorporated nitro-
methane as our solvent. The Gaussian03 suite of programs
was used in our study.58
X-ray Data Collection. Typically, the crystals were removed
from the vial with a small amount of mother liquor and
immediately coated with Paratone-N oil on a glass slide. A sui-
table crystal was mounted on a glass fiber with silicone grease
and placed in the cold stream of a Bruker APEX II equipped
with a CCD area detector and a graphite monochromator
utilizing Mo KR radiation (λ = 0.710 73 A) at 150(2) K. The
data were corrected for Lorentz and polarization effects using
the Bruker SAINT software, and an absorption correction was
performed using the SADABS program.52
Acknowledgment. We are grateful to the National
Science Council of Taiwan for financial support of this
work. We also thank the National Center for High-
performance Computing of Taiwan for computing time
and financial support of the Conquest software.
Supporting Information Available: CIF files giving full crys-
tallographic data for all the structures and figures giving mole-
cular structures of 5 and 6 (the other independent molecules)
and optimized structures of cis and trans isomers of 4. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Solution and Structure Refinements. All the structures were
solved by direct methods and refined by full-matrix least-
squares methods against F2 with the SHELXTL software pack-
age.53 All non-H atoms were refined anisotropically; H atoms
(54) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(55) Lee, C. Y., W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(56) Hay, P. J. W.; , W. R. J. Chem. Phys. 1985, 82, 270.
(57) Mennucci, B. T.; , J. J. Chem. Phys. 1997, 106, 5151.
(58) Gaussian 03; Gaussian, Inc., Pittsburgh, PA, 2003.
€
€
(52) Sheldrick, G. M. SADABS; University of Gottingen, Gottingen,
Germany, 2001.
(53) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.