Synthesis and characterization of new potentially hydrosoluble pincer ligands and their application in Suzuki-Miyaura cross-coupling reactions in water Dedicated Prof. Dr. Juventino Garcia with great admiration and respect to the teacher and friend on the

Article abstract of DOI:10.1016/j.tetlet.2013.04.007

Three water soluble pincer ligands, 2,6-bis[(diethanolamine)methyl]pyridine hydrobromide (1:2) (1), 3,11,17,18-Tetraazatricyclo[11.3.1.1 ^5,9]octadeca-1(17),5,7,9(18),13,15-hexaene,3,11- bis(dihydroxymethylmethyl) hydrobromide (1:2) (2), and 1,3

Full text of DOI:10.1016/j.tetlet.2013.04.007

Tetrahedron Letters 54 (2013) 3116–3119
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis and characterization of new potentially hydrosoluble pincer
ligands and their application in Suzuki–Miyaura cross-coupling reactions
in water
⇑
Carmela Crisóstomo-Lucas, Rubén A. Toscano, David Morales-Morales
Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior s/n, Ciudad Universitaria, C.P. 04510, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
Three water soluble pincer ligands, 2,6-bis[(diethanolamine)methyl]pyridine hydrobromide (1:2) (1),
3,11,17,18-Tetraazatricyclo[11.3.1.15,9]octadeca-1(17),5,7,9(18),13,15-hexaene,3,11-bis(dihydroxymeth-
ylmethyl) hydrobromide (1:2) (2), and 1,3-bis[(diethanolamine)methyl]benzene (3) were synthesized
and unequivocally characterized by a number of analytical techniques including single crystal X-ray dif-
fraction analyses. Mixtures of these ligands with PdCl2 proved to be efficient in catalyzing the Suzuki–
Miyaura cross couplings in water. Being the most efficient system that including ligand (1). Further
experiments using this catalytic system were performed to assess the effects of varying temperature,
reaction times, and nature of the base, finding the optimal operational conditions of this system.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 2 March 2013
Revised 1 April 2013
Accepted 2 April 2013
Available online 9 April 2013
Dedicated Prof. Dr. Juventino Garcia with
great admiration and respect to the teacher
and friend on the occasion of his 51st
birthday.
Keywords:
In situ catalysis
Cross coupling reactions
Suzuki–Miyaura coupling
Pincer ligands
Catalysis in water
Introduction
be amines2b, imines,2c or oxazolines.2d The same applies for their
analogous NNN pincer ligand counterparts2e–g and CNC pincer
Catalytic reactions play a fundamental role for the production of
a variety of added value intermediates of industrial relevance. Such
that these reactions have been cataloged as a fundamental pillar of
green chemistry.1 The better comprehension of coordination and
organometallic chemistry and the consistency on the preparation
of these complexes have allowed the in situ generation of the cat-
alysts. This procedure represents an easy method to screen differ-
ent ligands by in situ generating the catalyst for a given reaction
from a mixture of a suitable metal salt for example PdCl2 and the
free ligand. Thus, accelerating the discovery of efficient catalytic
systems. On the other hand, pincer compounds have represented
a fundamental motif in the toolbox for both organometallic and
synthetic organic chemists. This being due to their well known
thermal stability and unusual reactivities and to the easiness in
which both steric and electronic properties can be finely tuned in
the basic pincer backbone.2a For the case of tridentate NCN ligands
this versatility is reflected in the number of different substituents
that can be included in the pincer structure where N donors can
compounds where N-heterocyclic carbenes act as C donors.2h
A
natural consequence of this versatility has been the widespread
applications that transition metal pincer complexes have found
in organic synthesis, materials science, and organometallic
catalysis.2i
Moreover, palladium-catalyzed cross coupling reactions have
become a power tool in organic synthesis.3 The Suzuki–Miyaura
reaction for the attaining of biphenyls, is one of the most important
cross coupling processes that involves the coupling of aryl halides
or triflates with organoboronic acids.4 This reaction allows the use
of a broad variety of functional groups and most importantly the
reaction can be performed in neat water5 minimizing the genera-
tion of hazardous wastes and thus greening the process.6,7 This fact
can be advantageously used, however this also requires the cata-
lyst to be soluble in water favoring at the same time the easy sep-
aration and removal of the organic products. Among the strategies
to water solubilize the catalysts8, the most common involves the
inclusion of hydrophilic groups such as carboxylates9, sulfonates,10
or ammonium groups11 in the structure of the ligands used.
In the last decade, we have been involved in the design and cat-
alytic applications of pincer ligands and their complexes12 in
⇑
Corresponding author. Tel.: +52 55 56224514; fax: +52 55 56162217.
E-mail address: damor@unam.mx (D. Morales-Morales).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.04.007

C. Crisóstomo-Lucas et al. / Tetrahedron Letters 54 (2013) 3116–3119
3117
Scheme 1. Synthesis of the pincer ligands.
Figure 1. Thermal ellipsoids (50% probability) drawings for ligands 1 and 2.
potentially relevant organic transformations. Thus, with this
opportunity we would like to report our findings on the synthesis
and application of three novel pincer ligands including aminoalco-
hol moieties as a motif to favor water solubility on the in situ Pd(II)
catalyzed Suzuki–Miyaura C–C cross couplings in water.
Scheme 2. Suzuki–Miyaura couplings.
Results and discussion
alyze the formation of biphenyl in good yields (96% yield of biphe-
nyl determined by GC–MS) attaining the best conversions with
1% mol catalyst loading using ligands 1 and 2. These results are
coherent with the easiness in the formation of the Pd–NNN pincer
compounds over the organometallic derivative Pd–NCN that re-
quires a C–H activation for its formation. In addition, employing
of lower loadings of Pd(II)/ligand ratio to 0.1% did not lower the
yields of the product except in one case (54%, ligand 3/PdCl2). In
light of these results we chose to use ligand 1/PdCl2 in 0.1% loading
in further experiments aimed to optimize the reaction conditions.
Thus, we investigated the effect of a number of parameters such as
The ligands were synthesized by reacting either 2,6-bis(bromo-
methyl)pyridine or 1,3-bis(bromomethyl)benzene with diethanol-
amine (ligands 113 and 314) or 2-amine-1,3-propanediol (ligand
2
15) using Na2CO3 as base in methanol (Scheme 1). Compounds 1
and 2 were prepared under the same conditions (attempts to pre-
pare ligand 1 using MW were also performed producing poor
yields). Both ligands were characterized by 1H and 13C{1H} NMR
spectroscopy (DMSO-d6). The 1H NMR spectra showed the ex-
pected signals for 1 and 2, including those due to the presence of
the OH groups in d 4.72 ppm and 3.98 ppm (broad), respectively.
In addition, the 13C{1H} NMR spectra exhibit the six carbon signals
expected for each compound. Analysis by FAB+-MS, showed the
molecular ion ([M++Na], m/z 336) for 1. On the other hand, ligand
3 was prepared both in THF and methanol, producing better yields
when the reaction was made in methanol for 24 h. This compound
was obtained as a yellow viscous oil16 and was also characterized
by 1H NMR and 13C NMR, both spectrums exhibiting signals consis-
tent with the proposed formulation, including the broad singlet
due to the OH group in d 4.47 ppm. Analysis by FAB+-MS showed
the molecular ion at m/z 335 corresponding to [M++Na].
The identity of both ligands was unequivocally determined by
single crystal X-ray diffraction analysis.17 Both compounds being
crystallized as their ammonium salts (Fig. 1).
With the ligands on hand we decided to use them in the palla-
dium catalyzed Suzuki–Miyaura cross coupling reactions
(Scheme 2) of bromobenzene and phenyl boronic acid in water
(95 °C, 4 h, Na2CO3).18
95
100
90
80
70
60
50
40
30
20
10
0
88
% biphenyl
49
82
76
66
27
OCH3
CH3
H
Cl
CHO
COCH3
CN
We first evaluated the ligand and catalyst loading using PdCl2 as
palladium source. Preliminary results showed all the ligands to cat-
Figure 2. % Suzuki–Miyaura couplings of p-substituted bromobenzenes using
ligand 1/Pd(II).

3118
C. Crisóstomo-Lucas et al. / Tetrahedron Letters 54 (2013) 3116–3119
Soc. 2005, 127, 12273–12281; (d) Motoyama, Y.; Mikami, Y.; Kawakami, H.;
Aoki, K.; Nishiyama, H. Organometallics 1999, 18, 3584–3588; (e) Small, B. L.;
Brookhart, M. J. Am. Chem. Soc. 1998, 120, 7143–7144; (f) Wanniarachchi, S.;
Liddle, B. J.; Toussaint, J.; Lindeman, S. V.; Bennett, B.; Gardinier, J. R. Dalton
Trans. 2011, 40, 8776–8787; (g) Hollas, A. M.; Gu, W.; Bhuvanesh, N.; Ozerov, O.
V. Inorg. Chem. 2011, 50, 3673–3679; (h) Peris, E.; Loch, J. A.; Mata, J.; Crabtree,
R. H. Chem. Commun. 2001, 201–202; (i) Albrecht, M.; van Koten, G. Angew.
Chem., Int. Ed. Rev. 2001, 40, 3750–3781.
temperature, reaction time, and different bases. By varying the
temperature a notable change in yields is observed from 25% at
50 °C all the way through 96% when the reaction was performed
at 95 °C for 4 h. These results are consistent with the catalytic sys-
tem to be stable. Once the temperature was set to 95 °C, we pro-
ceed to investigate the effect of reaction time. Thus, experiments
were carried out at reduced reaction times from 0.5 h (46% yield)
to 4 h (96% yield) with increases of 0.5 h. The results clearly show
a direct dependence of the yield as a function of time, which in ab-
sence of any additive is consistent with the catalytic system to be
homogeneous. As the Suzuki–Miyaura couplings are strongly
dependant on the base used, several bases that is Li2CO3 (49%
yield), Na2CO3 (95% yield), K2CO3 (65% yield), CaCO3 (0.0% yield),
DIPEA (15% yield), and Et3N (50% yield), were tested under these
optimized conditions. The results obtained reveal that the inor-
ganic bases are more efficient having Na2CO3 with a 95% yield to
biphenyl. Organic bases were also tested showing lowered yields
compared to the inorganic salts. This fact can be due to compe-
tence between the ligand and the amine which upon coordination
with the metallic center may just coordinatively saturate the Pd(II)
avoiding any further catalysis. Although, we assumed the system
to be homogeneous, participation of nano-catalyst cannot be ruled
out in spite of the relatively low reaction temperatures employed.
Thus, in order to confirm the homogeneity of the catalytic system
we performed a catalytic experiment under the optimized condi-
tions but this time adding a couple of drops of elemental mercury19
noticing no appreciable difference in the performance of the cata-
lyst with or without the presence of elemental mercury. Thus, rul-
ing out the participation of palladium nanoparticles.
With the optimized reaction conditions, we completed the
examination of the activity for this catalytic system in the Suzu-
ki–Miyaura cross coupling reactions of some p-substituted bromo-
benzenes. The results are shown in Figure 2. A quick look to this
graphic clearly shows that bromobenzenes including electron
withdrawing substituents led to higher conversions as expected
according to the values of Hammett parameter.20
In summary, we have successfully synthesized a potentially
important set of water soluble pincer ligands and employed them
in Suzuki–Miyaura couplings attaining excellent yields to biphe-
nyls under relatively mild conditions. Noteworthy the fact is that
the reactions are performed in neat water and thus the purification
of the products consists in a mere decantation process. The present
system is interesting given the easiness on the synthesis of the li-
gands form cheap commercially available starting materials. Thus,
turning this system attractive for its potential application in organ-
ic synthesis or other cross coupling reactions. Efforts aimed to
achieve these goals are currently under development in our
laboratories.
3. Metal-Catalyzed Cross-Coupling Reactions; de Meijere, A., Diederich, F., Eds.;
WILEY-VCH: Germany, 2004.
4. (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2427–2483; (b) Suzuki, A. J.
Organomet. Chem. 1999, 576, 147–168; (c) Suzuki, A. J. Organomet. Chem. 2002,
653, 83–90; (d) Bedford, R. B.; Cazin, C. S. J.; Holder, D. Coord. Chem. Rev. 2004,
2419–2440; (e) Frisch, A. C.; Beller, M. Angew. Chem. Int. Ed. 2005, 44, 674–688.
5. (a) Weng, Z.; Koh, L. L.; Hor, T. S. A. J. Organomet. Chem. 2004, 689, 18–24; (b)
Wu, W. Y.; Chen, S. N.; Tsai, F. Y. Tetrahedron Lett. 2006, 47, 9267–9270; (c)
Kostas, I. D.; Coutsolelos, A. G.; Charalambidis, G.; Skondra, A. Tetrahedron Lett.
2007, 48, 6688–6691; (d) Polshettiwar, V.; Decottignies, A.; Len, C.; Fihri, A.
ChemSusChem 2010, 3, 502–522; (e) Conelly-Espinoza, P.; Morales-Morales, D.
Inorg. Chim. Acta 2010, 363, 1311–1315; (f) Lasri, J.; Mac Leod, T. C. O.;
Pombeiro, A. J. L.; Suzuki, A. Appl. Catal. A 2011, 397, 94–102; (g) Zhou, C.;
Wang, J.; Li, L.; Wang, R.; Hong, M. Green Chem. 2011, 13, 2100–2106; (h) Li, L.;
Wang, J.; Zhou, C.; Wang, R.; Hong, M. Green Chem. 2011, 13, 2071–2077.
6. (a)Green Chemistry Theory and Practice; Anastas, P. T., Warner, J. C., Eds.; Oxford
University Press: New York, 1998; (b) Giinter, K.; Iuser, S.; Richter, S.; Greiner,
P.; Penning, J.; Angricker, M. Environ. Sci. Pollut. Res. 2004, 11, 284–290; (c)
Sheldon, R. A. Green Chem. 2005, 7, 267–278; (d) Sheldon, R. A. Green Chem.
2007, 9, 1273–1283; (e) Tang, S. Y.; Bourne, R. A.; Smith, R. L.; Poliakoff, M.
Green Chem. 2008, 10, 268–269; (f) Anastas, P.; Eghbali, N. Chem. Soc. Rev. 2010,
39, 301–312; (g) Bourne, R. A.; Poliakoff, M. Mendeleev Commun. 2011, 21, 235–
238.
7. (a) Sinou, D.; Rabeyrin, C.; Nguefack, C. Adv. Synth. Catal. 2003, 345, 357–363;
(b) Rabeyrin, C.; Sinou, D. Tetrahedron: Asymmetry 2003, 14, 3891–3897; (c)
Dallinger, D.; Kappe, C. O. Chem. Rev. 2007, 107, 2563–2591; (d) Liu, S.; Xiao, J. J.
Mol. Catal. A: Chem. 2007, 270, 1–43; (e) Qu, G. R.; Zhao, L.; Wang, D. C.; Wu, J.;
Guo, H. M. Green Chem. 2008, 10, 287–289; (f) Fujita, K.; Kujime, M.; Muraki, T.
Bull. Chem. Soc. Jpn. 2009, 82, 261–266; (g) Diallo, A. K.; Boisselier, E.; Liang, L.;
Ruiz, J.; Astruc, D. Chem. Eur. J. 2010, 16, 11832–11835; (h) Hamasaka, G.; Muto,
T.; Uozumi, Y. Angew. Chem. Int. Ed. 2011, 50, 4876–4878.
8. (a) Shaughnessy, K. H. Chem. Rev. 2009, 109, 643–710; (b)Metal-catalyzed
Reaction in Water; Dixneuf, P. H., Cadierno, V., Eds., 1st ed.; WILEY-VCH:
Germany, 2013.
9. (a) Amengual, R.; Genin, E.; Michelet, V.; Savignac, M.; Genet, J. P. Adv. Synth.
Catal. 2002, 344, 393–398; (b) Otomaru, Y.; Senda, T.; Hayashi, T. Org. Lett.
2004, 6, 3357–3359; (c) Hattori, H.; Fujita, K.; Muraki, T.; Sakaba, A. Tetrahedron
Lett. 2007, 48, 6817–6820; (d) Baskakov, D.; Herrmann, W. A. J. Mol. Catal. A:
Chem. 2008, 283, 166–170.
10. (a) Papadogianakis, G.; Maat, L.; Sheldon, R. A. J. Mol. Catal. A: Chem. 1997, 116,
179–190; (b) Riisager, A.; Eriksen, K. M.; Hjortkjar, J.; Fehrmann, R. J. Mol. Catal.
A: Chem. 2003, 193, 259–272; (c) Huang, R.; Shaughnessy, K. H. Organometallics
2006, 25, 4105–4112; (d) Korthals, B.; Gottker-Schnetmann, I.; Mecking, S.
Organometallics 2007, 26, 1311–1316; (e) Fleckenstein, C.; Plenio, H. Green
Chem. 2008, 10, 563–570.
11. (a) Huang, R.; Shaughnessy, K. H. Chem. Commun. 2005, 4484–4486; (b)
Snelders, D. J. M.; Kreiter, R.; Firet, J.; van Koten, G.; Gebbink, R. J. M. K. Adv.
Synth. Catal. 2008, 350, 262–266; (c) Chen, S. N.; Wu, W. Y.; Tsai, F. Y. Green
Chem. 2009, 11, 269–274.
12. (a) Naghipour, A.; Sabounchei, S. J.; Morales-Morales, D.; Hernández-Ortega, S.;
Jensen, C. M. J. Organomet. Chem. 2004, 689, 2494–2502; (b) Hahn, F. E.; Jahnke,
M. C.; Gomez-Benitez, V.; Morales-Morales, D.; Pape, T. Organometallics 2005,
24, 6458–6463; (c) Baldovino-Pantaleón, O.; Hernández-Ortega, S.; Morales-
Morales Inorg, D. Chem. Commun. 2005, 955–959; (d) Baldovino-Pantaleón, O.;
Hernández-Ortega, S.; Morales-Morales, D. Adv. Synth. Catal. 2006, 348, 236–
242; (e) Gómez-Benítez, V.; Baldovino-Pantaleón, O.; Herrera-Alvarez, C.;
Toscano, R. A.; Morales-Morales, D. Tetrahedron Lett. 2006, 47, 5059–5062; (f)
Naghipour, A.; Sabounchei, S. J.; Morales-Morales, D.; Canseco-González, D.;
Jensen, C. M. Polyhedron 2007, 26, 1445–1448; (g) Gómez-Benıítez, V.;
Hernández-Ortega, S.; Toscano, R. A.; Morales-Morales, D. Inorg. Chim. Acta
2007, 360, 2128–2138; (h) Naghipour, A.; Ghasemi, Z. H.; Morales-Morales, D.;
Serrano-Becerra, J. M.; Jensen, C. M. Polyhedron 2008, 27, 1947–1952; (i)
Solano-Prado, M. A.; Estudiante-Negrete, F.; Morales-Morales, D. Polyhedron
2010, 29, 592–600; (j) Avila-Sorrosa, A.; Estudiante-Negrete, F.; Hernández-
Ortega, S.; Toscano, R. A.; Morales-Morales, D. Inorg. Chim. Acta 2010, 363,
1262–1268.
Acknowledgment
The financial support of this research by CONACYT (F58692)
and DGAPA–UNAM (IN227008) is gratefully acknowledged.
Supplementary data
Supplementary data associated with this article can be found, in
13. 2,6-Bis[(diethanolamine)methyl]pyridine hydrobromide (1:2) (1). The product
is a microcrystalline white solid with mp = 158–160 °C. MS-FAB+. m/z = 336
[M++Na]. Anal. Calcd (%) for C15H29N3O4Br2Á2H2O: C 35.2, H 6.5, N 8.2. Found: C
the
online
version,
at
http://dx.doi.org/10.1016/
j.tetlet.2013.04.007.
3
35.1, H 6.3, N 8.0. 1H NMR (DMSO-d6): d 7.71 (t, JH–H = 6 Hz, H, CH), 7.27 (d,
3JH–H = 9 Hz, 2H, CH), 4.72–471 (s, a, 4H, OH), 3.72 (s, 4H, CH2), 3.45–3.42 (m,
8H, CH2), 2.55–2.50 (m, 8H, CH2); 13C{1H} (DMSO-d6): d 158.9 (s, CH), 137.03 (s,
C), 120.9 (s, CH), 60.08 (s, CH2), 58.5 (s, CH2), 56.3 (s, CH2). IR (KBr disc, cmÀ1):
3427–3315 (OH, NH2), 2958–2811 (C–H).
References and notes
1. Anastas, P. T.; Kirchhoff, M. M.; Williamson, T. C. Appl. Catal. A 2001, 221, 3–13.
2. (a)The Chemistry of Pincer Compounds; Morales-Morales, D., Jensen, M. C., Eds.,
1st ed.; Elsevier: Amsterdam, 2007; (b) Slagt, M. Q.; van Zwieten, D. A. P.;
Moerkerk, A. J. C. M.; Klein Gebbink, R. J. M.; van Koten, G. Coord. Chem. Rev.
2004, 248, 2275–2282; (c) Takenaka, Z.; Minakawa, M.; Uozumi, Y. J. Am. Chem.
14. 3,11,17,18-Tetraazatricyclo[11.3.1.15,9]octadeca-1(17),5,7,9(18),13,15-
hexaene,3,11-bis(dihydroxymethylmethyl) hydrobromide (1:2) (2). The
product is a microcrystalline white solid with mp >220 °C decompose. Yield
25% (0.25 g, 4.72 Â 10À4 mol) of (2). MS–ESI+. m/z = 411 [M++Na], m/z = 389

C. Crisóstomo-Lucas et al. / Tetrahedron Letters 54 (2013) 3116–3119
3119
[M+]. Anal. Calcd (%) for C20H30N4O4Br2ÁCH3COCH3: C 45.4, H 5.9, N 9.2. Found:
C 45.2, H 5.8, N 9.1. 1H NMR (DMSO-d6): d 7.21 (t, 3JH–H = 6 Hz, H, CH), 6.64 (d,
3JH–H = 6 Hz, 2H, CH), 5.07–5.05 (m, 4H, CH2), 3.98 (m, b, 6H, NH2 and OH),
3.69–3.63 (m, 8H, CH2), 3.34 (s, 4H, CH2), 3.26–3.21 (m, 2H, CH); 13C{1H}
(DMSO-d6): d 158.2 (s, C), 136.2 (s, CH), 121.0 (s, CH), 69.0 (s, CH2), 58.7 (s, CH2),
58.4 (s, CH). IR (KBr disc, cmÀ1): 3337–3292 (OH, NH2), 2943–2840 (C–H).
15. Synthesis of 1,3-bis[(diethanolamine)methyl]benzene (3). The product was
obtained as a yellow oil (0.30 g, 9.78 Â 10À3 mol, 52%). MS-FAB+. m/z = 335
(molecular ion with sodium). Anal. Calcd (%) for C16H28N2O4Á5H2O: C 47.7, H
9.5, N 6.9. Found: C 47.6, H 9.3, N 6.8. 1H (DMSO-d6): 1H, d 7.26–7.20 (m, 4H,
18. Suzuki–Miyaura couplings. In all cases the results presented are the average of
two runs performed in Schlenk tubes: bromobenzene (1.77 mL, 0.0169 mol),
phenyl boronic acid (2.67 g, 0.0219 mol), Na2CO3 (4.47 g, 0.04225 mol),
0.1 mol % of PdCl2 (3 mg, 1.69 Â 10À5 mol) and of the corresponding ligand
(1.69 Â 10À5 mol) in 6 mL of distilled water. The mixtures were stirred and
heated at 95 °C in a silicon oil bath during 4 h. Subsequently, the reaction
mixture was cooled to room temperature and the mixture was extracted with
CH2Cl2 (3 Â 3 mL), the organic phase was treated with anhydrous Na2SO4 after
filter over silica gel and analyzed by Gas Chromatography (GC–MS). Other
experiments of catalysis were carried out under the same reactions conditions
varying the reaction times and temperatures of different bases Na2CO3, Li2CO3,
K2CO3, CaCO3, Et3N, DIPEA and the series of para-substituted bromobenzenes.
19. (a) Anton, D. R.; Crabtree, R. H. Organometallics 1983, 2, 855; (b) Foley, P.;
DiCosimo, R.; Whitesides, G. M. J. Am. Chem. Soc. 1980, 102, 6713. Following the
above described procedures; additionally adding two drops of elemental HgO
to the reaction mixture. After the prescribed reaction times, a sample of the
solution was analyzed by GC–MS: no significant difference in conversion
between these experiments and those in the absence of mercury was observed,
indicating that heterogeneous Pd(0) is not involved. These experiments were
performed under the same condition for the experiments with bromobenzene..
20. Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165–195.
3
CH), 4.47 (s, a, 4H, OH), 3.62 (s, 4H, CH2), 3.45 (t, JH–H = 6 Hz, 8H, CH2), 2.55–
2.51 (m, 8H, CH2); 13C{1H} (DMSO-d6): d 139.4 (s, CH), 128.9 (s, C), 127.7 (s, CH),
127.0 (s, CH) 59.1 (s, CH2), 58.9 (s, CH2), 56.1 (s, CH2). IR (KBr disc, cmÀ1): 3402–
3232 (OH, NH2), 2950–2829 (C–H).
16. Bashiardes, G.; Carry, J. C.; Evers, M.; Filoche, B.; Mignani, S. Pyrazine
derivatives preparation and medicines containing them. PAT. WO 99/03844,
France, 1999.
17. Supplementary data for complexes
1 and 2 have been deposited at the
Cambridge Crystallographic Data Centre. Copies of this information are
available free of charge on request from The Director, CCDC, 12 Union Road,
Cambridge,
CB2
1EZ,
UK
(fax:
+44
1223
336033;
e-mail
deposit@ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk) quoting the
deposition numbers CCDC 926160 (1) and 926161 (2). Relevant H-bond
distances can be consulted in the Supplementary data.