Unexpected structure of palladacycles containing carboxylated schiff bases. Synthesis of some water-soluble metallacycles

Article abstract of DOI:10.1021/om8006807

The action of palladium acetate on carboxylated Schiff bases is herein described. These reactions lead to new metallacycles, some of which are hydrosoluble. Additionally we present the first report of cyclopalladated derivatives having the metalated molec

Full text of DOI:10.1021/om8006807

5108
Organometallics 2008, 27, 5108–5117
Unexpected Structure of Palladacycles Containing Carboxylated
Schiff Bases. Synthesis of Some Water-Soluble Metallacycles
Joan Albert,† Luc´ıa D’Andrea,† Jesu´s Bautista,‡ Asensio Gonza´lez,‡ Jaume Granell,*,†
Merce` Font-Bardia,§ and Teresa Calvet§
Departament de Qu´ımica Inorga`nica i Institut de Biomedicina (IBUB), UniVersitat de Barcelona, Mart´ı i
Franque`s, 1-11, 08028 Barcelona, Spain, Laboratori de Qu´ımica Orga`nica, Facultat de Farma`cia,
UniVersitat de Barcelona, Pl. Pius XII, s/n, 08028 Barcelona, Spain, and Departament de Cristal · lografia,
Mineralogia i Dipo`sits Minerals, UniVersitat de Barcelona, Mart´ı i Franque`s, s/n, 08028 Barcelona, Spain
ReceiVed July 18, 2008
The action of palladium acetate on carboxylated Schiff bases is herein described. These reactions lead
to new metallacycles, some of which are hydrosoluble. Additionally we present the first report of
cyclopalladated derivatives having the metalated molecule as a dianionic (C,N,O) bridging ligand between
two palladium atoms.
cific synthesis of ortho-substituted carboxylated imines, which
can be precursors of pharmaceutical products.5
Introduction
Cyclometalation reactions were one of the first known
examples of C-H bond activation, and cyclometalated com-
plexes of a wide variety of ligands, containing N, P, As, O, or
S as the heteroatom, have been described.1 The cyclometalation
of N-donor ligands has been extensively studied and has
acquired great interest because of the application of the
metallacycles in many areas including organic synthesis,
homogeneous catalysis, the design of new metallomesogens and
antitumoral drugs, asymmetric synthesis, resolution of racemic
ligands, intermolecular aromatic C-H bond activation, or
synthesis and reactivity of organometallic complexes with
biologically important ligands.2
As it is known, water has attracted attention as a potential
replacement for organic solvents due to its low cost, nonflam-
mability, and low toxicity and the fact that it is a renewable
resource.3 Moreover, the use of water in combination with
hydrophilic homogeneous metal catalysts offers the potential
to easily separate and recycle the metal catalyst from organic
product streams. There are a limited number of reports on the
use of cyclopalladated compounds in Heck,3h-k Suzuki,3h,l-n
Stille,3h,o and Sonogashira3p couplings in water solution.
Recently water-soluble palladacycles have been prepared from
sulfonated imines and, in combination with (2-di-tert-butylphos-
phinoethyl)trimethylammonium chloride, have been shown to
be active catalysts for the Suzuki coupling. In contrast, the
attempts described by these authors to obtain cyclopalladated
compounds containing carboxylated imines were unsuccessful.4
The interest of the metalation of these imines is underlined by
the fact that the corresponding metallacycles may be useful
catalysts and, in addition, this process can lead to the regiospe-
With this precedent in mind,4 and following our studies on
cyclometalation reactions,2p,u-w we focused our attention on the
action of palladium acetate on carboxylated Schiff bases. These
reactions lead to new metallacycles, some of them hydrosoluble.
Besides this, cyclopalladated derivatives containing the meta-
lated molecule as a dianionic (C,N,O) bridging ligand between
two palladium atoms have been synthesized for the first time.
(2) For some interesting reactions and applications of cyclopalladated
compounds see: (a) Slagt, M. Q.; Rodr´ıguez, G.; Grutters, M. M. P.; Klein
Gebbink, R. J. M.; Klopper, W.; Jenneskens, L. W.; Lutz, M.; Spek, A. L.;
van Koten, G. Chem.-Eur. J. 2004, 10, 1331. (b) Rodr´ıguez, G.; Lutz, M.;
Spek, A. L.; van Koten, G. Chem.-Eur. J. 2002, 8, 45. (c) Ghedini, M.;
Aiello, I.; Crispini, A.; La Deda, M. Dalton Trans. 2004, 1386. (d) Aiello,
I.; Datillo, D.; Ghedini, M.; Golemme, A. J. Am. Chem. Soc. 2001, 123,
5598. (e) Kleij, A. W.; Klein Gebbink, R. J. M.; van den Nieuwenhuijzen,
P. A. J.; Kooijman, H.; Lutz, M.; Spek, A. L.; van Koten, G. Organome-
tallics 2001, 20, 634. (f) Vicente, J.; Saura-Llamas, I.; Cuadrado, J.; Ram´ırez
de Arellano, M. C. Organometallics 2003, 22, 5513. (g) Mart´ınez, J.; Pereira,
M. T.; Buceta, I.; Alberdi, G.; Amoedo, A.; Ferna´ndez, J. J.; Lo´pez-Torres,
M.; Vila, J. M. Organometallics 2003, 22, 5581. (h) Lo´pez-Torres, M.;
Ferna´ndez, A.; Ferna´ndez, J. J.; Sua´rez, A.; Castro-Juiz, S.; Vila, J. M.;
Pereira, M. T. Organometallics 2001, 20, 1350. (i) Vicente, J.; Saura-Llamas,
I.; Palin, M. G.; Jones, P. G.; Ram´ırez de Arellano, M. C. Organometallics
1997, 16, 826. (j) Ryabov, A. D. Synthesis 1985, 233. (k) Pfeffer, M. Recl.
TraV. Chim. Pays-Bas 1990, 109, 567. (l) Espinet, P.; Esteruelas, M. A.;
Oro, L. A.; Serrano, J. L.; Sola, E. Coord. Chem. ReV. 1992, 117, 215. (m)
Navarro-Ranninger, C.; Lo´pez-Solera, I.; Pe´rez, J. M.; Masaguer, J. R.;
Alonso, C. Appl. Organomet. Chem. 1993, 7, 57. (n) Camargo, M.; Dani,
P.; Dupont, J.; de Souza, R. F.; Pfeffer, M.; Tkatchenko, I. J. Mol. Catal.
1996, 109, 127. (o) Navarro, R.; Urriolabeitia, E.; Cativiela, C.; D´ıaz de
Villegas, M. D.; Lo´pez, M. P.; Alonso, E. J. Mol. Catal. 1996, 105, 111.
(p) Albert, J.; Cadena, J. M.; Gonza´lez, A.; Granell, J.; Solans, X.; Font-
Bardia, M. Chem. Commun. 2003, 528. (q) Moyano, A.; Rosol, M.; Moreno,
R. M.; Lo´pez, C.; Maestro, M. A. Angew. Chem., Int. Ed. 2005, 44, 1865.
(r) Dupont, J.; Pfeffer, M.; Daran, J. C.; Jeannin, Y. Organometallics 1987,
6, 899. (s) Lo´pez, C.; Caubet, A.; Pe´rez, S.; Solans, X.; Font-Bardia, M. J.
Organomet. Chem. 2003, 681, 82. (t) Leung, P. H.; Liu, A.; Mok, K. F.
Tetrahedron: Asymmetry 1999, 10, 1309. (u) Capape´, A.; Crespo, M.;
Granell, J.; Vizcarro, A.; Zafrilla, J.; Font-Bardia, M.; Solans, X. Chem.
Commun. 2006, 4128. (v) Albert, J.; Cadena, M.; Gonza´lez, A.; Granell,
J.; Solans, X.; Font-Bardia, M. Chem.-Eur. J. 2006, 12, 887. (w) Albert,
J.; Bosque, R.; Cadena, M.; Delgado, S.; Granell, J.; Muller, G.; Ordinas,
J. I.; Font-Bardia, M.; Solans, X. Chem.-Eur. J. 2002, 8, 2279. (x)
Bezsoudnova, E. Y.; Ryabov, A. D. J. Organomet. Chem. 2001, 622, 38.
(y) Mawo, R.; Mustakim, S.; Young, V. G.; Hoffmann, M. R.; Smoliakova,
I. Organometallics 2007, 26, 1801. (z) Keuseman, K.; Smoliakova, I.;
Dunina, V. V. Organometallics 2005, 24, 4159.
* Corresponding author. E-mail: jaume.granell@qi.ub.es.
† Departament de Qu´ımica Inorga`nica i Institut de Biomedicina.
‡ Laboratori de Qu´ımica Orga`nica, Facultat de Farma`cia.
§ Departament de Cristal · lografia, Mineralogia i Dipo`sits Minerals.
(1) (a) Trofimenko, S. Inorg. Chem. 1973, 12, 1215. (b) Bruce, M. I.
Angew. Chem., Int. Ed. Engl. 1977, 16, 73. (c) Newkome, G. R.; Puckett,
W. E.; Gupta, V. K.; Kiefer, G. E. Chem. ReV. 1986, 86, 451. (d) Omae, I.
Chem. ReV. 1979, 79, 137. (e) Dunina, V. V.; Zalevskaya, O. A.; Potapov,
V. M. Russ. Chem. ReV. 1988, 57, 250. (f) Ryabov, A. D. Chem. ReV. 1990,
90, 403. (g) Dupont, J.; Consorti, C. S.; Spencer, J. Chem. ReV. 2005, 105,
2527. (h) Vicente, J.; Saura-Llamas, I. Comments Inorg. Chem. 2007, 28,
39.
10.1021/om8006807 CCC: $40.75
2008 American Chemical Society
Publication on Web 09/11/2008

Water-Soluble Metallacycles
Organometallics, Vol. 27, No. 19, 2008 5109
the corresponding acetato cyclopalladated dimers 2a-2e were
isolated. Despite varying the reaction conditions, we were unable
to metalate ligand 1f. Nevertheless, this is not an unexpected
result and may be due to the fact that the electron-withdrawing
nitro group deactivates the aromatic ring to the electrophilic
attack of Pd(II).1,10
Cyclopalladated derivatives 2a-2e were essentially insoluble
in water at pH ) 7, but were soluble in pH ) 10 buffered media,
and no decomposition of these solutions occurred after several
hours.
The metalation of imine 1c could afford two different five-
membered endo-metallacycles. However, only the activation of
the less hindered C-H bond was observed, in agreement with
previous results.8a,b,11
A noticeable feature of all compounds containing a chlorine
substituent in an ortho position on the aromatic ring (derivatives
of imine 1b) is the downfield shift of the HCdN proton as
compared to the nonsubstituted derivatives, hence indicating a
nonconventional hydrogen bond Cl · · · H-Cl, as found for
related palladium and platinum metallacycles.12
Slow crystallization of an acetic acid solution of 2c affords
suitable crystals for X-ray structure determination (Figure 1).
2c is a dinuclear cyclometalated compound with two acetato-
bridging ligands. The palladium atom is in a square-planar
environment, coordinated to carbon, nitrogen, and two oxygen
atoms. The distances between palladium and the coordinated
atoms are in accordance with other cyclopalladated compounds
(Table 1).13 As a consequence of the different trans influence,14
the Pd-O bonds having nitrogen atoms in trans position
[Pd-O(3): 2.0385(16) Å] are significantly shorter than those
having a trans relationship with respect to the aromatic carbon
[Pd-O(4): 2.1492(16) Å]. The five-membered metallacycle is
approximately planar, as suggested by the sum of internal angles,
which is close to 540°.15 The palladium-palladium distance
of 2.8883(16) Å is in the range observed for other related
dimeric palladium complexes.13
It should be noted that compound 2c crystallized with four
acetic acid molecules in the crystal lattice, two of which were
disordered solvent molecules. Both ordered acetic acid mol-
ecules presented hydrogen-bonding interactions with the car-
boxylic groups of compound 2c. The distances O(1)-H(1) · · · O(5)
and O(6)-H(6) · · · O(2) were 2.676(3) and 2.596(3) Å, respec-
tively, which are within the normal range for hydrogen bonds.
On the other hand, inter- and intramolecular π-π stacking
interactions add to the stability of the molecular structure. As
Results and Discussion
Imines can exist as E or Z isomers, but in general N-aldimines
adopt the more stable E form.6 Carboxylated Schiff bases may
exist in two forms, the ionized (zwitterionic) and the free un-
ionized form. Recent studies on these ligands demonstrate that
the predominant isomer is by far the un-ionized form.7
Cyclometalation of N-benzylidenebenzylamines could in
principle produce two different five-membered metallacycles,
one in which the cycle contains the imine functionality (endo)
and one in which it does not (exo).8 The tendency to give endo-
cycles (endo effect) is so strong that it allows activation of an
aliphatic C-H bond with formation of a six-membered palla-
dacycle in preference to the activation of an aromatic C-H bond
with formation of a five-membered exo-palladacycle.9
The N-benzylidenephenylamine ligands 1a-1f were prepared
by a condensation reaction of 4-aminobenzoic acid with the
corresponding aldehyde.7 Proton NMR spectra reveal the
formation of a single isomer, where the methinic proton signal
appears at δ values between 8.3 and 8.8 ppm. Furthermore, 2D
NOESY spectra confirm the E stereochemistry around the CdN
bond, and in addition, no NH signal was detected. Infrared
spectra consistently agree with the un-ionized E form proposed
on the basis of NMR data.
All imines here prepared can afford five-membered endo-
metallacycles, and this fact prompted us to study the cyclopal-
ladation of the carboxylated imines, under different reaction
conditions than those previously reported.4 When the Schiff
bases 1a-1f were treated with palladium acetate in acetic acid,
(3) (a) Cornils, B.; Herrmann, W. A. Aqueous-Phase Organometallic
Catalysis: Concepts and Applications; Wiley/VCH: Weinheim, 2004. (b)
Joo´, F. Aqueous Organometallic Catalysis: Catalysis by Metal Complexes,
Vol. 23; Kluwer Academic Publishers: Dordrecht, 2001. (c) Anastas, P. T.;
Kirchhoff, M. M. Acc. Chem. Res. 2002, 35, 686. (d) Tzschucke, C. C.;
Markert, C.; Bannwarth, W.; Roller, S.; Hebel, A.; Haag, R. Angew. Chem.,
Int. Ed. 2002, 41, 3964. (e) Li, C.-J. and ; Chan, T. K. Organic Reactions
in Aqueous Media; Wiley: New York, 1997. (f) Grieco, P. A. Organic
Synthesis in Water; Blakey Academic and Professional: London, 1998. (g)
Lubineau, A.; Auge´, J. Top. Curr. Chem., Vol. 206; Springer Verleg: Berlin,
1999. (h) Ogo, S.; Takebe, Y.; Uehara, K.; Yamazaki, T.; Nakai, H.;
Watanabe, Y.; Fukuzumi, S. Organometallics 2006, 25, 331. (i) Bergbreiter,
D. E.; Furyck, S. Green Chem. 2004, 6, 280. (j) Botella, L.; Na´jera, C.
Tetrahedron Lett. 2004, 45, 1833. (k) Botella, L.; Na´jera, C. J. Org. Chem.
2005, 70, 4360. (l) Botella, L.; Na´jera, C. Angew. Chem., Int. Ed. 2002,
41, 179. (m) Ma, J.; Cui, X.; Gao, L.; Wu, Y. Inorg. Chem. Commun. 2007,
10, 762. (n) Rosa, G. R.; Rosa, C. H.; Rominger, F.; Dupont, J.; Monteiro,
A. L. Inorg. Chim. Acta 2006, 359, 1947. (o) Wolf, C.; Lerebours, R. J.
Org. Chem. 2003, 68, 7551. (p) Wolf, C.; Lerebours, R. Org. Biomol. Chem.
2004, 2, 2181. (q) Vicente, J.; Arcas, A. Coord. Chem. ReV. 2005, 249,
1135.
(4) Huang, R.; Shaughnessy, K. H. Organometallics 2006, 25, 4105.
(5) (a) Toth, G.; Kramer, T. H.; Knapp, R.; Lui, G.; Davis, P.; Burks,
T. F.; Yamamura, H. I.; Hruby, V. J. J. Med. Chem. 1990, 33, 249. (b)
Saito, N. G.; Chang, H.; Patterson, Y. J. Immunol. 1999, 162, 5998. (c)
Espun˜a, G.; Arsequell, G.; Valencia, G.; Barluenga, J.; Alvarez-Gutie´rrez,
J. M.; Ballesteros, A.; Gonza´lez, J. Angew. Chem., Int. Ed. 2004, 43, 325.
(d) Shetty, M. M.; Sadanandam, Y. S.; Pralhad, P. B. ArchiV. Pharm. 1979,
312, 721.
(6) (a) Tennant, G. ComprehensiVe Organic Chemistry, Vol. 2; Perga-
mon: Oxford, 1979; Chapter 8. (b) Patai, S. The Chemistry of the Carbon-
Nitrogen Double Bond; John Wiley and Sons: Chichester, 1970.
(7) Titinchi, S. J. J.; Abbo, H. S.; Saeed, A. A. H. J. Mol. Struct. 2004,
705, 121.
(8) (a) Albert, J.; Granell, J.; Moragas, R.; Font-Bardia, M.; Solans, X.
J. Organomet. Chem. 1996, 522, 59. (b) Albert, J.; Granell, J.; Moragas,
R.; Sales, J.; Font-Bardia, M.; Solans, X. J. Organomet. Chem. 1995, 494,
95. (c) De Munno, G.; Ghedini, M.; Neve, F. Inorg. Chim. Acta 1995, 239,
155. (d) Bosque, R.; Lo´pez, C.; Sales, J. J. Organomet. Chem. 1995, 498,
147. (e) Albert, J.; Ceder, R.; Go´mez, M.; Granell, J.; Sales, J. Organo-
metallics 1992, 11, 1536. (f) Aguilar, D.; Aragu¨e´s, M. A.; Bielsa, R.;
Serrano, E.; Navarro, R.; Urriolabeitia, E. Organometallics 2007, 26, 3541.
(9) Albert, J.; Granell, J.; Sales, J.; Font-Altaba, M.; Solans, X.
Organometallics 1986, 5, 2567.
(10) Granell, J.; Sales, J.; Vilarrasa, J.; Declerq, J. P.; Germain, G.;
Miravitlles, C.; Solans, X. J. Chem. Soc., Dalton Trans. 1983, 2441.
(11) (a) Valk, J. M.; Maassarani, F.; van der Sluis, P.; Spek, A. L.;
Boersma, J.; van Koten, G. Organometallics 1994, 13, 2320. (b) Vila, J. M.;
Sua´rez, A.; Pereira, M. T.; Gayoso, E.; Gayoso, M. Polyhedron 1987, 6,
1003. (c) Dyke, S. F.; Quessy, S. N. Transition Met. Chem. 1982, 7, 233.
(d) Vila, J. M.; Pereira, M. T.; Gayoso, E.; Gayoso, M. Transition Met.
Chem. 1986, 11, 342.
(12) (a) Albert, J.; Granell, J.; M´ınguez, J.; Muller, G.; Sainz, D.;
Valerga, P. Organometallics 1997, 16, 3561. (b) Bernstein, J. J. Chem.
Soc., Perkin Trans. 1972, 946. (c) Inabe, T.; Gautier-Luneau, I.; Hoshino,
N.; Okaniwa, K.; Okamoto, H.; Mitani, T.; Nagashima, U.; Maruyama, Y.
Bull. Chem. Soc. Jpn. 1991, 64, 801. (d) Crespo, M.; Mart´ınez, M.; Sales,
J.; Solans, X.; Font-Bardia, M. Organometallics 1992, 11, 1288.
(13) (a) Navarro-Ranninger, C.; Zamora, F.; Mart´ınez-Cruz, L. A.; Isea,
R.; Masaguer, J. R. J. Organomet. Chem. 1996, 518, 29. (b) Ghedini, M.;
De Munno, G.; Viterbo, D.; Neve, F.; Armentano, S. Chem. Mater. 1991,
3, 65. (c) Thu, H.-Y.; Yu, W.; Che, C. J. Am. Chem. Soc. 2006, 128, 9048.
(d) Navarro-Ranninger, C.; Zamora, F.; Lo´pez-Solera, I.; Monge, A.;
Masaguer, J. R. J. Organomet. Chem. 1996, 506, 149.
(14) Caygill, G. B.; Steel, P. J. J. Organomet. Chem. 1987, 327, 115.
(15) Klein, H. F.; Camadanli, S.; Beck, R.; Leukel, D.; Flo¨rke, U. Angew.
Chem., Int. Ed. 2005, 44, 975.

5110 Organometallics, Vol. 27, No. 19, 2008
Albert et al.
Figure 1. Molecular structure of compound 2c.
Table 1. Selected Bond Lengths [Å] and Angles [deg] for 2c and 4a
solution, proton NMR spectra showed that these compounds
remain unaltered for several days.
Compound 2c
Dinuclear cyclopalladated derivatives 4 can be synthesized
by treatment of the acetato-bridged compounds 2 with
pyridine (6:1) at room temperature in methanol (4a and 4d)
or CHCl3 solutions (4b and 4c) or in refluxing CHCl3 (4e).
Proton NMR spectra of CDCl3 solutions of 4, in the absence
of free pyridine, exhibit a complex pattern arising from the
different exchange processes in solution involving the labile
pyridine ligands and the solvent or water molecules. Com-
pounds 4 are insoluble in water at pH ) 7 or 10, but can
easily dissolve in water if an excess of pyridine is added to
afford 3. Crystals suitable for X-ray structure determination
can be obtained by slow crystallization of chloroform
solutions of 4a and 4d (Figures 2 and 3).
Surprisingly, the crystal structure determination of 4a and
4d revealed dinuclear cyclopalladated complexes where the
metalated imine acts as a dianionic bridging ligand between
two palladium atoms. The palladium atom is in a square-planar
environment, coordinated to carbon, oxygen, and two nitrogen
atoms. The distances between palladium and the coordinated
atoms are in agreement with those reported for other cyclopal-
ladated compounds (Tables 1 and 2).16 The angles between
adjacent atoms lie in the range 81.00(11)° [C(7)Pd(N14)] and
93.76(11)° [C(7)Pd(N1)] for 4a and 81.54(9)° [C(7)Pd(N1)] and
96.35(9)° [C(7)Pd(N2)] for 4d. The five-membered metalla-
cycles are nearly planar, as suggested by the sum of internal
angles, which is close to 540° in both metallacycles.15
In contrast with the high number of dinuclear cyclometalated
compounds described so far with an acetato-bridging ligand in
the CSD,17 the structures here described for compounds 4a, 4d,
Pd(1)-C(10)
1.956(2)
Pd(1)-O(3)
2.0385(16)
2.0543(18)
2.1492(16)
2.8883(12)
1.306(3)
91.35(8)
81.34(8)
87.09(7)
100.11(7)
Pd(1)-N(1)
Pd(1)-O(4)#1
Pd(1)-Pd(1)#1
N(1)-C(8)
C(10)-Pd(1)-O(3)
C(10)-Pd(1)-N(1)
O(3)-Pd(1)-O(4)#1
N(1)-Pd(1)-O(4)#1
Compound 4a
Pd(1)-C(7)
1.990(3)
2.036(3)
2.037(3)
2.129(2)
93.76(11)
81.00(11)
92.79(9)
92.49(9)
Pd(1)-N(1)
Pd(1)-N(14)
Pd(1)-O(23)#1
C(7)-Pd(1)-N(1)
C(7)-Pd(1)-N(14)
N(1)-Pd(1)-O(23)#1
N(14)-Pd(1)-O(23)#1
expected from a folded open-book acetato-bridged compound,
both palladacycle rings [plane 1: Pd1, N1, C8, C9, and C10;
plane 2: Pd1a, N1a, C8a, C9a, and C10a] are disposed close to
each other [centroid-to-centroid distance ) 3.817(2) Å, and
interplane angle ) 30.25°]. Furthermore, compound 2c exhibits
π-π interactions caused by intermolecular overlapping of the
π-conjugated systems of two neighboring ortho-metalated rings
(C9, C10, C11, C12, C13, and C14) [centroid-to-centroid
distance ) 3.911(2) Å, and interplane angle ) 0.00°].
While compounds 2 were insoluble in water at pH ) 7, when
an aqueous suspension of these dimers was treated with a large
excess of deuterated pyridine (25:1), compounds 3 were obtained
in water solution. Proton NMR and mass spectra permit us to
propose the zwitterionic form depicted in Scheme 1 for these
complexes. The crystal structure of a cyclopalladated cation
containing two pyridine molecules by the metal atom has been
described.16a Regarding the stability of complexes 3 in water
(16) (a) Chakladar, S.; Paul, P.; Venkatsubramanian, K.; Nag, K.
J. Chem. Soc., Dalton Trans. 1991, 2669. (b) Albert, J.; Granell, J.; Zafrilla,
J.; Font-Bardia, M.; Solans, X. J. Organomet. Chem. 2005, 690, 422. (c)
´
Navarro-Ranninger, C.; Lo´pez-Solera, I.; Alvarez-Valde´s, A.; Rodr´ıguez-
Ramos, J. H.; Masaguer, J. R.; Garc´ıa-Ruano, J. L.; Solans, X. Organo-
metallics 1993, 12, 4104. (d) Bosque, R.; Granell, J.; Sales, J.; Font-Bardia,
M.; Solans, X. J. Organomet. Chem. 1993, 453, 147.

Water-Soluble Metallacycles
Organometallics, Vol. 27, No. 19, 2008 5111
Scheme 1a
a
(i) Pd(OAc)2, acetic acid; (ii) pyridine (25:1), D2O; (iii) pyridine (6:1), methanol (4a, 4d), chloroform (4b, 4c, 4e).
Figure 2. Molecular structure of compound 4a.
and 5b (see below) are, to the best of our knowledge, the first
cases in which the metalated molecule acts as a dianionic
bridging (C,N,O) ligand between two palladium atoms. In the
literature only few examples of dinuclear compounds in which
the metalated ligand acts as a dianionic bridging ligand are
described.18 In this context it should be noted that cyclopalla-
dated and cycloplatinated compounds containing terdentate
(C,N,O), (C,N,S), and (C,N,N) ligands adopt tetranuclear or
trinuclear structures, generated by self-assembly of the metalated
units.19 The new structures here described, containing two
square-planar palladium atoms, strongly bonded to a dianionic
(18) (a) Uso´n, R.; Fornie´s, J.; Espinet, P.; Garc´ıa, A.; Toma´s, M. J.
Organomet. Chem. 1985, 282, C35 (C,N,P ligand). (b) Dupont, J.; Pfeffer,
M.; Daran, J. C.; Jeannin, Y. Organometallics 1987, 6, 899 (C,N,S ligand).
(c) Espinet, P.; Garc´ıa, G.; Herrero, F. J.; Jeannin, Y.; Philoche-Levisalles,
M. Inorg. Chem. 1989, 28, 4207 (C,N,N ligand). (d) Lo´pez, C.; Caubet,
A.; Bosque, R.; Solans, X.; Font-Bardia, M. J. Organomet. Chem. 2002,
645, 146 (C,N,S ligand).
(17) Allen, F. H. Acta Crystallogr. Sect. B 2002, B58, 380.

5112 Organometallics, Vol. 27, No. 19, 2008
Albert et al.
Figure 3. Molecular structure of compound 4d.
by 220-240 cm-1, consistent with unidentate acetato coordina-
tion.20 In the proton NMR of compounds 5, the aromatic protons
of the palladated ring were high-field shifted, which is ascribed
to the cis disposition between the phosphine and the metalated
carbon,21 and the HCdN proton was high-field shifted as an
indication of the imine E form.22
Table 2. Selected Bond Lengths [Å] and Angles [deg] for 4d and 5b
Compound 4d
Pd(1)-C(7)
1.974(2)
2.028(2)
2.044(2)
2.1257(17)
1.274(3)
1.254(3)
81.54(9)
96.35(9)
91.63(7)
90.47(7)
119.8(2)
Pd(1)-N(1)
Pd(1)-N(2)
Pd(1)-O(1)
O(1)-C(14)#1
O(2)-C(14)
C(7)-Pd(1)-N(1)
C(7)-Pd(1)-N(2)
N(1)-Pd(1)-O(1)
N(2)-Pd(1)-O(1)
C(1)-N(1)-C(8)
Slow crystallization of a CDCl3 solution of 5b affords crystals
suitable for X-ray structure determination. X-ray crystallographic
studies of 5b (Figure 4) confirmed the structure suggested by
NMR data, the E form adopted by the imine and the cis
arrangement of the PPh3 in relation to the palladated carbon.
5b is a dinuclear cyclopalladated complex containing the
metalated imine as a dianionic bridging ligand between two
palladium atoms. The palladium atom is in a square-planar
environment, coordinated to carbon, nitrogen, oxygen, and
phosphorus atoms. The distances between palladium and the
coordinated atoms are similar to those reported for other
cyclopalladated compounds (Table 2).16 The angles between
adjacent atoms lie in the range 81.47(10)° [C(1)PdN] and
95.76(9)° [C(1)PdP]. The five-membered metallacycle is ap-
proximately planar, as suggested by the sum of internal angles,
539.4°, which is close to 540°.15
The distance between the methinic proton and the chlorine
atom in ortho position on the aromatic ring of 2.757 Å confirms
the intramolecular interaction between these atoms, suggested
by proton NMR spectra (see before).
Crystal structures of compounds 4a, 4d, and 5b reveal
intermolecular π-π stacking interactions among the aromatic
moieties derived from 4-aminobenzoic acid [4a: centroid-to-
centroid distance ) 3.984(3) Å, and interplane angle ) 0.00°;
Compound 5b
Pd(1)-C(1)
2.012(2)
2.101(2)
2.1062(18)
2.2539(11)
1.286(3)
1.268(3)
81.47(10)
89.70(8)
95.76(8)
92.98(6)
120.4(2)
Pd(1)-N(1)
Pd(1)-O(1)#1
Pd(1)-P(1)
O(1)-C(14)
N(1)-C(7)
C(1)-Pd(1)-N(1)
N(1)-Pd(1)-O(1)#1
C(1)-Pd(1)-P(1)
O(1)#1-Pd(1)-P(1)
C(7)-N(1)-C(8)
imine molecule, and two labile pyridine ligands can be
potentially useful new building blocks in supramolecular
chemistry. Note that the coordination of the carboxylate group
to the palladium atom in compounds 4 and 5 also explains the
insolubility of these complexes in water, even at pH ) 10.
On the other hand, reaction of dimer 2 with PPh3 in methanol
afforded the dinuclear complex [Pd(C-N-O)(PPh3)]2, 5. IR
spectra of 4 and 5 showed ν(CO2)asymm and ν(CO2)symm separated
(20) (a) Deacon, G. B.; Phillips, R. J. Coord. Chem. ReV. 1980, 33,
227. (b) Deacon, G. B.; Huber, F.; Phillips, R. J. Inorg. Chim. Acta 1985,
104, 41.
(21) (a) Vicente, J.; Abad, J. A.; Mart´ınez-Viviente, E.; Jones, P. G.
Organometallics 2002, 21, 4454. (b) Vicente, J.; Arcas, A.; Bautista, D.;
Jones, P. G. Organometallics 1997, 16, 2127. (c) Vicente, J.; Abad, J. A.;
Frankland, A. D.; Ram´ırez de Arellano, M. C. Chem.-Eur. J. 1999, 5,
3066.
(22) (a) Albert, J.; Go´mez, M.; Granell, J.; Sales, J.; Solans, X.
Organometallics 1990, 9, 1405. (b) Albert, J.; Granell, J.; Sales, J.; Font-
Bardia, M.; Solans, X. Organometallics 1995, 14, 1393. (c) Crespo, M.;
Granell, J.; Solans, X.; Font-Bardia, M. J. Organomet. Chem. 2003, 681,
143.
(19) (a) Willison, S. A.; Krause, J. A.; Connick, W. B. Inorg. Chem.
2008, 47, 1258. (b) Amoedo, A.; Adrio, L. A.; Antelo, J. M.; Mart´ınez, J.;
Pereira, M. T.; Ferna´ndez, A.; Vila, J. M. Eur. J. Inorg. Chem. 2006, 3016.
(c) Mart´ınez, J.; Adrio, L. A.; Antelo, J. M.; Ortigueira, J. M.; Pereira,
M. T.; J. Ferna´ndez, J.; Ferna´ndez, A.; Vila, J. M. J. Organomet. Chem.
2006, 691, 2721. (d) Zhao, S.; Wang, R.; Wang, S. J. Am. Chem. Soc.
2007, 129, 3092. (e) Lo´pez, C.; Caubet, A.; Pe´rez, S.; Solans, X.; Font-
Bardia, M. J. Organomet. Chem. 2003, 681, 82. (f) Chen, C.; Liu, Y.; Peng,
S.; Liu, S. J. Organomet. Chem. 2004, 689, 1806. (g) Ferna´ndez; J.J.;
Ferna´ndez, A.; Va´zquez-Garc´ıa, D.; Lo´pez-Torres, M.; Su´; arez, A.; Go´mez-
Blanco, N.; Vila, J. M. Eur. J. Inorg. Chem. 2007, 5408.

Water-Soluble Metallacycles
Organometallics, Vol. 27, No. 19, 2008 5113
Figure 4. Molecular structure of compound 5b.
for 1H and to 85% H3PO4 for 31P. Microanalyses were performed
by the Servei de Recursos Cient´ıfics i Te`cnics de la Universidad
Rovira i Virgili (Tarragona). Infrared spectra were recorded as KBr
disks on a FTIR Nicolet 5700 spectrometer. MALDI TOF(+)
spectra were recorded on a VOYAGER-DE-RP spectrometer (with
a dithranol or a 2,5-dihydroxybenzoic acid matrix). CI spectra were
recorded on a ThermoFinnigan TRACE DSQ spectrometer, using
NH3 as reactive gas, and electrospray spectra on an Agilent LC/
MSD-TOF spectrometer, equipped with a dual sprayer source using
purine (m/z ) 121.050873) and HP-0921 (m/z ) 922.009798) as
internal reference masses.
4d: centroid-to-centroid distance ) 3.802(2) Å, and interplane
angle ) 0.00°; and 5b: centroid-to-centroid distance ) 3.790(2)
Å, and interplane angle ) 0.00°].
It is noteworthy that complexes 2 can also be crystallized
from acetic acid solutions of compounds 5 after several days.
This is a remarkable result because the acetato ligand coordinates
to Pd(II) by replacing the soft PPh3 ligand, and thus the Pd-P
is more labile than Pd-C and Pd-N bonds in acid media,
establishing thereby the great stability of the metallacycles here
described.
Preparation of Compounds. Imine 1a. A mixture of 4-ami-
nobenzoic acid (2739 mg, 19.84 mmol), benzaldehyde (2127 mg,
20.04 mmol), glacial acetic acid (two drops), and toluene (150 mL)
was refluxed for 4 h. After the reaction mixture was cooled to room
temperature, the white solid obtained was filtered, washed with
toluene, and recrystallized from methanol to obtain 1a, 3624 mg
Concluding Remarks
In this contribution we described the action of palladium
acetate on carboxylated Schiff bases. These reactions lead to
new metallacycles, some of them hydrosoluble. Furthermore,
cyclopalladated derivatives containing the metalated molecule
as a dianionic bridging ligand between two palladium atoms
have been obtained. In contrast with the high number of
dinuclear cyclometalated compounds described with an acetato-
bridging ligand in the CSD, to the best of our knowledge, the
structures here described for compounds 4a, 4d, and 5b are the
first cases in which the metalated molecule acts as a dianionic
(C,N,O) bridging ligand between two palladium atoms.
1
(80% yield). H NMR (400 MHz, CDCl3, 298 K) δ (ppm): 8.45
(s, 1H, H3), 8.15 (d, AA′XX′, 2H, H1, JHH ) 8.6 Hz), 7.93 (d, 2H,
H4, JHH ) 8.9 Hz), 7.54-7.48 (m, 3H, H5 + H6), 7.24 (d, AA′XX′,
2H, H2, JHH ) 8.6 Hz). IR (KBr), ν (cm-1): 1684 (COOH), 1623
(CdN). MS-CI (NH3), m/z: [M + H]+ ) 226.6. Anal. Calcd for
C14H11NO2: C 74.65, H 4.92, N 6.22. Found: C 74.2, H 4.9, N 6.4.
Imine 1b. A mixture of 4-aminobenzoic acid (778 mg, 5.67
mmol), 2-chlorobenzaldehyde (904 mg, 6.43 mmol), glacial acetic
acid (one drop), and toluene (40 mL) was refluxed for 9 h in a
flask connected to a Dean-Stark apparatus. After the reaction
mixture was allowed to cool to room temperature, the white solid
obtained was filtered, washed with diethyl ether, and dried under
Experimental Section
All solvents were dried and degassed by standard methods. All
chemicals were of commercial grade and used as received.
1H NMR spectra were registered on a Varian Unity 300 and a
Varian Mercury 400 instruments. 31P{1H}NMR spectra were
recorded on a Bruker DRX 250 spectrometer, operating at 101.26
MHz. Chemical shifts (in ppm) were measured relative to SiMe4
1
vacuum to obtain 1b, 1302 mg (88% yield). H NMR (400 MHz,
DMSO-d6, 298 K), δ (ppm): 8.87 (s, 1H, H3), 8.17 (d, 1H, H7, JHH
) 7.4 Hz), 8.00 (d, AA′XX′, 2H, H1, JHH ) 8.3 Hz), 7.63-7.56
(m, 2H, H4 + H5), 7.55-7.47 (m, 1H, H6), 7.35 (d, AA′XX′, 2H,

5114 Organometallics, Vol. 27, No. 19, 2008
Albert et al.
H2, JHH ) 8.3 Hz). IR (KBr), ν (cm-1): 1680 (COOH), 1620
(CdN). MS-ESI (+) {H2O/CH3OH (1:1)}, m/z: [M + H]+ ) 260.3.
Anal. Calcd for C14H10ClNO2: C 64.75, H 3.88, N 5.39. Found: C
65.6, H 3.4, N 5.4.
Synthesis of 3a in D2O Solution. The addition of pyridine-d5
to a suspension of 2a in D2O in 25:1 ratio affords the corresponding
mononuclear compound 3a. H NMR (400 MHz, D2O, 298 K), δ
1
(ppm): 8.21 (s, 1H, H3), 7.58-7.55 (m, 1H, H7), 7.56 (d, AA′XX′,
2H, H1, JHH ) 8.5 Hz), 7.25 (t, 1H, H6, JHH ) 7.5 Hz), 7.11 (td,
1H, H5, JHH ) 7.6 Hz, JHH ) 1.2 Hz), 6.93 (d, 2H, AA′XX′, H2,
JHH ) 8.4 Hz), 6.24 (d, 1H, H4, JHH ) 7.7 Hz). MS-ESI (+) {H2O/
CH3OH (1:1)}, of a chloroform solution with nondeuterated pyridine
derivative, m/z: [M + H]+ ) 488.1, [M + H - py]+ ) 409.0.
Metalation of 1b. A mixture of imine 1b (347 mg, 1.34 mmol)
and palladium acetate (300 mg, 1.34 mmol) in 50 mL of glacial
acetic acid was stirred at 60 °C for 24 h, and the resulting solution
was concentrated at reduced pressure. The orange solid obtained
after addition of hexane was filtered and dried under vacuum to
obtain 2b, 536 mg (95% yield). IR (KBr), ν (cm-1): 1700 (COOH),
1574 (COO), 1394 (COO). MS-ESI (+) {H2O/CH3OH (1:1)}, m/z:
[M/2 - OAc + CH3CN]+ ) 407.4, [M/2 - OAc + 2 CH3CN]+
) 448.4. Anal. Calcd for C32H24Cl2N2O8Pd2: C 45.31, H 2.85, N
3.30. Found: C 45.7, H 2.6, N 3.1.
Imine 1c. A mixture of 4-aminobenzoic acid (788 mg, 5.75
mmol), 3-chlorobenzaldehyde (911 mg, 6.48 mmol), glacial acetic
acid (one drop), and toluene (30 mL) was heated under reflux for
8 h in a flask provided with a Dean-Stark apparatus. After the
reaction mixture was cooled to room temperature, the white solid
obtained was filtered off, washed with diethyl ether, and dried under
1
vacuum to isolate 1c, 1329 mg (89% yield). H NMR (400 MHz,
DMSO-d6, 298 K), δ (ppm): 8.66 (s, 1H, H3), 8.03-7.96 (m, 3H,
H1 + H8), 7.92 (d, 1H, H6, JHH ) 7.5 Hz), 7.67-7.54 (m, 2H, H4
+ H5), 7.34 (d, AA′XX′, 2H, H2, JHH ) 8.5 Hz). IR (KBr), ν
(cm-1): 1689 (COOH), 1635 (CdN). MS-ESI (+) {H2O/CH3OH
(1:1)}, m/z: [M + H]+ ) 260.4. Anal. Calcd for C14H10ClNO2: C
64.75, H 3.88, N 5.39. Found: C 64.5, H 3.9, N 5.4.
Imine 1d. A mixture of 4-aminobenzoic acid (791 mg, 5.77
mmol), 4-chlorobenzaldehyde (814 mg, 5.79 mmol), glacial acetic
acid (one drop) and toluene (40 mL) was refluxed for 24 h in a
flask equipped with a Dean-Stark apparatus. After the reaction
mixture was cooled to room temperature, the white solid obtained
was filtered off, washed with diethyl ether and dried under vacuum
Synthesis of 3b in D2O Solution. The addition of pyridine-d5
to a suspension of 2b in D2O in 25:1 ratio affords the corresponding
1
mononuclear compound 3b. H NMR (400 MHz, D2O, 298 K), δ
(ppm): 8.40 (s, 1H, H3), 7.58 (d, AA′XX′, 2H, H1, JHH ) 8.2 Hz),
7.18 (d, 1H, H6, JHH ) 7.7 Hz), 7.06 (t, 1H, H5, JHH ) 7.7 Hz),
1
to obtain 1d, 1333 mg (89% yield). H NMR (400 MHz, DMSO-
d6, 298 K), δ (ppm): 8.66 (s, 1H, H3), 7.99 (d, AA′XX′, 2H, H1,
JHH ) 8.7 Hz), 7.98 (d, 2H, H5, JHH ) 8.4 Hz), 7.62 (d, 2H, H4,
JHH ) 8.4 Hz), 7.33 (d, AA′XX′, 2H, H2, JHH ) 8.7 Hz). IR (KBr),
ν (cm-1): 1681 (COOH), 1624 (CdN). MS-ESI (+) {H2O/CH3OH
(1:1)}, m/z: [M + H]+ ) 260.3. Anal. Calcd for C14H10ClNO2: C
64.75, H 3.88, N 5.39. Found: C 64.5, H 3.8, N 5.4.
6.89 (d, AA′XX′, 2H, H2, JHH ) 8.2 Hz), 6.06 (d, 1H, H4, JHH
)
7.7 Hz). MS-ESI (+) {H2O/CH3OH (1:1)}, of a chloroform solution
with nondeuterated pyridine derivative, m/z: [M + H]+ ) 522.0,
[M + H - py]+ ) 443.0.
Metalation of 1c. A mixture of imine 1c (174 mg, 0.67 mmol)
and palladium acetate (150 mg, 0.67 mmol) in 25 mL of glacial
acetic acid was stirred at 60 °C for 6 h under nitrogen, and the
resulting solution was concentrated under vacuum. The orange solid
obtained after addition of hexane was filtered off, washed with
glacial acetic acid, and dried under vacuum to obtain 2c, 250 mg
(88% yield). IR (KBr), ν (cm-1): 1711 (COOH), 1582 (COO), 1416
(COO). MS-ESI (+) {H2O/CH3CN (1:1)}, m/z: [M/2 - OAc +
CH3CN]+ ) 405.3, [M/2 - OAc + 2 CH3CN]+ ) 448.3. Anal.
Calcd for C32H24Cl2N2O8Pd2: C 45.31, H 2.85, N 3.30. Found: C
45.6, H 2.6, N 3.4.
Imine 1e. A mixture of 4-aminobenzoic acid (1371 mg, 10.00
mmol) and 4-dimethylamino-benzaldehyde (1491 mg, 9.99 mmol)
in ethanol (75 mL) was refluxed for 3 h. After the reaction mixture
was cooled to room temperature, the yellow solid obtained was
filtered and dried under vacuum to obtain 1e, 2108 mg (79% yield).
1H NMR (400 MHz, CDCl3, 298 K), δ (ppm): 8.31 (s, 1H, H3),
8.09 (d, AA′XX′, 2H, H1, JHH ) 8.3 Hz), 7.78 (d, 2H, H4, JHH
)
8.9 Hz), 7.21 (d, AA′XX′, 2H, H2, JHH ) 8.3 Hz), 6.74 (d, 2H, H5,
JHH ) 9.0 Hz), 3.08 (s, 6H, N(CH3)2). IR (KBr), ν (cm-1): 1681
(COOH), 1625 (CdN). MS-CI (NH3), m/z: [M + H]+ ) 269.6,
[M + H - N(CH3)2]+ ) 225.6. Anal. Calcd for C16H16N2O2: C
71.62, H 6.01, N 10.44. Found: C 71.8, H 6.1, N 10.4.
Synthesis of 3c in D2O Solution. The addition of pyridine-d5
to a suspension of 2c in D2O in 25:1 ratio affords the corresponding
1
mononuclear compound 3c. H NMR (400 MHz, D2O, 298 K), δ
Imine 1f. A mixture of 4-aminobenzoic acid (1377 mg, 10.04
mmol) and 4-nitrobenzaldehyde (1511 mg, 10.00 mmol), glacial
acetic acid (one drop), and toluene (75 mL) was refluxed for 3
days in a flask connected to a Dean-Stark apparatus. After the
reaction mixture was cooled to room temperature, the yellow solid
was recovered by filtration, washed with diethyl ether, and dried
(ppm): 8.08 (s, 1H, H3), 7.57 (d, AA′XX′, 2H, H1, JHH ) 8.4 Hz),
7.44 (d, 1H, H7, JHH ) 2.1 Hz), 7.02 (dd, 1H, H5, JHH ) 8.2 Hz,
JHH ) 2.1 Hz), 6.86 (d, AA′XX′, 2H, H2, JHH ) 8.4 Hz), 6.03 (d,
1H, H4, JHH ) 8.2 Hz). MS-ESI (+) {H2O/CH3OH (1:1)}, of a
chloroform solution with nondeuterated pyridine derivative, m/z:
[M + H]+ ) 522.0, [M + H - py]+ ) 443.0.
1
under vacuum to obtain 1f, 2426 mg (89% yield). H NMR (400
Metalation of 1d. A mixture of imine 1d (349 mg, 1.34 mmol)
and palladium acetate (304 mg, 1.35 mmol) in 50 mL of glacial
acetic acid was stirred at 60 °C for 6 h under nitrogen, and the
resulting solution was concentrated in vacuo. The red solid obtained
after addition of hexane was filtered, washed with glacial acetic
acid and hexane, and dried under vacuum to obtain 2d, 486 mg
(85% yield). IR (KBr), ν (cm-1): 1718 (COOH), 1585 (COO), 1416
(COO). MS-ESI (+) {H2O/CH3CN (1:1)}, m/z: [M/2 - OAc +
CH3CN]+ ) 407.4, [M/2 - OAc + 2 CH3CN]+ ) 448.4. Anal.
Calcd for C32H24Cl2N2O8Pd2: C 45.31, H 2.85, N 3.30. Found: C
45.2, H 2.8, N 3.4.
MHz, acetone-d6, 298 K), δ (ppm): 8.83 (s, 1H, H3), 8.41 (d, 2H,
H5, JHH ) 8.8 Hz), 8.28 (d, 2H, H4, JHH ) 8.8 Hz), 8.11 (d,
AA′XX′, 2H, H1, JHH ) 8.6 Hz), 7.41 (d, AA′XX′, 2H, H2, JHH
)
8.6 Hz). IR (KBr), ν (cm-1): 1681 (COOH), 1630 (CdN). MS-
ESI (+) {H2O/CH3OH (1:1)}, m/z: [M + H]+ ) 270.2. Anal. Calcd
for C14H10N2O4: C 62.22, H 3.73, N 10.37. Found: C 62.3, H 3.8,
N 10.4.
Cyclometalation Reactions. Metalation of 1a. A mixture of
imine 1a (360 mg, 1.60 mmol) and palladium acetate (349 mg,
1.55 mmol) in 35 mL of glacial acetic acid was stirred at 60 °C for
6 h under nitrogen atmosphere. The orange solid obtained was
filtered, washed with ethanol and acetone, and dried under vacuum
to obtain 2a, 505 mg (83% yield). IR (KBr), ν (cm-1): 1700
(COOH), 1570 (COO), 1416 (COO). MS-MALDI TOF (+) (DTH),
m/z: [M/2 - OAc + DTH]+ ) 555.9, [M/2 - OAc]+ ) 329.9.
Anal. Calcd for C32H26 N2O8Pd2: C 49.31, H 3.36, N 3.59. Found:
C 49.5, H 3.6, N 3.5.
Synthesis of 3d in D2O Solution. Mononuclear compound 3d
was synthesized by adding pyridine-d5 to a suspension of 2d in
1
D2O in 25:1 ratio. H NMR (400 MHz, D2O, 298 K), δ (ppm):
8.16 (s, 1H, H3), 7.56 (d, AA′XX′, 2H, H1, JHH ) 8.5 Hz), 7.46
(d, 1H, H7, JHH ) 8.1 Hz), 7.23 (dd, 1H, H6, JHH ) 8.0 Hz, JHH
)
1.8 Hz), 6.90 (d, AA′XX′, 2H, H2, JHH ) 8.5 Hz), 6.07 (d, 1H, H4,
JHH ) 1.8 Hz). MS-ESI (+) {H2O/CH3OH (1:1)}, of a chloroform

Water-Soluble Metallacycles
Organometallics, Vol. 27, No. 19, 2008 5115
solution with nondeuterated pyridine derivative, m/z: [M + H]+
522.0, [M + H - py]+ ) 443.0.
)
period, the undissolved materials were removed by filtration and
discarded. The deep yellow filtrate was concentrated to dryness on
a rotatory evaporator to give an orange solid after adding diethyl
ether. The product was filtered off, dried under vacuum, and finally
redissolved in chloroform. Slow evaporation of the chloroform
solution produced an orange powdery solid, 4e, which was milled
in a mortar and thoroughly dried in vacuo (23 mg, 37% yield). IR
(KBr), ν (cm-1): 1567 (CdO), 1348 (C-O). Anal. Calcd for
C42H38N6O4Pd2: C 55.82, H 4.24, N 9.30. Found: C 55.5, H 4.4, N
9.2.
Compounds Containing PPh3. Compound 5a. A mixture of
2a (155 mg, 0.20 mmol) and triphenylphosphine (104 mg, 0.40
mmol) in 30 mL of methanol was stirred at room temperature for
2 h. The pale pink solid obtained was filtered, washed with
methanol, and dried under vacuum to obtain 5a, 180 mg (76%
yield). 1H NMR (300 MHz, CDCl3, 298 K), δ (ppm): 8.12 (d, 1H,
H3, JHP ) 7.0 Hz), 7.83 (ddd, 6H, ortho-PPh3, JHP ) 11.8 Hz, JHH
) 8.0 Hz, JHH ) 1.5 Hz), 7.42-7.30 (m, 10H, meta-PPh3 + para-
PPh3 + H7), 7.19 (d, AA′XX′, 2H, H1, JHH ) 8.5 Hz), 6.93 (td,
1H, H6, JHH ) 7.3 Hz, JHH ) 0.9 Hz), 6.91 (d, AA′XX′, 2H, H2,
JHH ) 8.4 Hz), 6.62 (td, 1H, H5, JHH ) 7.3 Hz, JHH ) 1.2 Hz),
6.52 (dd, 1H, H4, JHH ) 7.3 Hz, JHP ) 5.6 Hz). 31P{1H} NMR
(101 MHz, CH2Cl2, 298 K), δ (ppm): 39.22 (s). IR (KBr), ν (cm-1):
1618 (CdN), 1599 (COO), 1361 (COO), 1096 (coordinated PPh3,
X-sensitive mode). MS-MALDI TOF (+) (DHB), m/z: [M + H -
PPh3]+ ) 921.2, [M/2 + H]+ ) 592.2. Anal. Calcd for
C64H48N2O4P2Pd2: C 64.93, H 4.09, N 2.37. Found: C 64.8, H 3.9,
N 2.4.
Metalation of 1e. A mixture of imine 1e (182 mg, 0.68 mmol)
and palladium acetate (152 mg, 0.68 mmol) in 25 mL of glacial
acetic acid was stirred at 60 °C for 4 h under nitrogen, and the
resulting solution was concentrated in vacuo. The yellow solid
obtained after addition of hexane was filtered, washed with hexane,
and dried under vacuum to obtain 2e, 253 mg (86% yield). IR
(KBr), ν (cm-1): 1684 (COOH), 1612 (CdN), 1571 (COO), 1419
(COO). MS-MALDI TOF (DTH), m/z: [M/2 - OAc + DTH]+
)
598.7, [M/2 - OAc]+ ) 372.8. Anal. Calcd for C36H36 N4O8Pd2:
C 49.96, H 4.19, N 6.47. Found: C 49.5, H 4.0, N 6.3.
Synthesis of 3e in D2O Solution. The addition of pyridine-d5
to a suspension of 2e in D2O in 25:1 ratio affords the corresponding
1
mononuclear compound 3e. H NMR (400 MHz, D2O, 298 K), δ
(ppm): 8.00 (s, 1H, H3), 7.54 (d, AA′XX′, 2H, H1, JHH ) 8.4 Hz),
7.44 (d, 1H, H7, JHH ) 8.2 Hz), 6.90 (d, AA′XX′, 2H, H2, JHH
8.2 Hz), 6.53 (d, 1H, H6, JHH ) 8.2 Hz), 5.34 (d, 1H, H4, JHH
)
)
1.6 Hz), 2.78 (s, 6H, N(CH3)2). MS-ESI (+) {H2O/CH3OH (1:1)},
of a chloroform solution with nondeuterated pyridine derivative,
m/z: [M + H]+ ) 531.1, [M + H - py]+ ) 452.1.
Dinuclear Pyridine Derivatives, 4. Compound 4a. A suspen-
sion of 2a (69 mg, 0.09 mmol) in 25 mL of methanol was treated
with an excess of pyridine (44 mg, 0.56 mmol). After stirring the
mixture at room temperature for 2 h, the resulting precipitate was
filtered and washed with further portions of methanol. It gave a
beige solid, which upon recrystallization in chloroform led to the
desired product 4a, which was gently powdered in a mortar and
thoroughly dried in vacuo (30 mg, 41% yield). IR (KBr), ν (cm-1):
1609 (CdN), 1597 (CdO), 1369 (C-O). Anal. Calcd for
C38H28N4O4Pd2: C 55.83, H 3.45, N 6.85. Found: C 55.56, H 3.7,
N 7.0.
Compound 5b. A mixture of 2b (100 mg, 0.12 mmol) and
triphenylphosphine (64 mg, 0.24 mmol) in 40 mL of methanol was
stirred at room temperature for 24 h. The white solid obtained was
filtered, washed with methanol, and dried under vacuum to obtain
1
Compound 4b. A mixture containing 2b (69 mg, 0.08 mmol),
an excess of pyridine (45 mg, 0.57 mmol), and 25 mL of chloroform
was stirred at ambient temperature for 3 days. The solvent was
then removed under reduced pressure, and after addition of diethyl
ether, an orange solid was obtained. The product was recovered
by filtration and purified by recrystallization in chloroform, leading
to yellow crystalline solid 4b, which was gently ground in an agate
mortar and thoroughly dried in vacuo (45 mg, 62% yield). IR (KBr),
5b, 116 mg (79% yield). H NMR (400 MHz, CDCl3, 298 K), δ
(ppm): 8.62 (d, 1H, H3, JHP ) 7.0 Hz), 7.84-7.79 (m, 6H, ortho-
PPh3), 7.42-7.32 (m, 9H, meta-PPh3 + para-PPh3), 7.18 (d,
AA′XX′, 2H, H1, JHH ) 8.4 Hz), 6.92 (d, AA′XX′, 2H, H2, JHH
)
8.4 Hz), 6.86 (dd, 1H, H6, JHH ) 7.6 Hz, JHH ) 0.6 Hz), 6.54 (t,
1H, H5, JHH ) 7.6 Hz), 6.40 (dd, 1H, H4, JHH ) 7.6 Hz, JHP ) 5.6
Hz). 31P{1H} NMR (101 MHz, CHCl3, 298 K), δ (ppm): 39.21
(s). IR (KBr), ν (cm-1): 1602 (COO), 1366 (COO), 1096
(coordinated PPh3, X-sensitive mode). MS-MALDI TOF (+)
(DTH), m/z: [M - PPh3 + H]+ ) 990.7, [M/2 + H]+ ) 627.8.
Anal. Calcd for C64H46Cl2N2O4P2Pd2: C 61.36, H 3.70, N 2.24.
Found: C 61.5, H 3.7, N 2.1.
ν
(cm-1): 1604 (CdO), 1384 (C-O). Anal. Calcd for
C38H26Cl2N4O4Pd2: C 51.49, H 2.96, N 6.32. Found: C 51.2, H
2.7, N 6.1.
Compound 4c. To an orange suspension of 2c (93 mg, 0.11
mmol) in chloroform (30 mL) was added an excess of pyridine
(52 mg, 0.66 mmol). The reaction was completed after 2 h of
stirring. The precipitated solid was filtered, dried under vacuum,
and finally redissolved in chloroform. Slow evaporation of the
chloroform solution afforded yellow crystals of 4c, which were
pulverized in a mortar and thoroughly dried in vacuo (70 mg, 72%
yield). IR (KBr), ν (cm-1): 1597 (CdO), 1370 (C-O). Anal. Calcd
for C38H26Cl2N4O4Pd2: C 51.49, H 2.96, N 6.32. Found: C 51.7, H
2.8, N 6.1.
Compound 4d. Compound 4d was synthesized by adding an
excess of pyridine (36 mg, 0.46 mmol) to a suspension of 2d (65
mg, 0.08 mmol) in 25 mL of methanol. After 1 h of stirring, the
beige suspension obtained was filtered off, washed with further
portions of methanol, and dried under vacuum. The required product
recrystallized from chloroform, affording 4d as a yellow crystalline
solid, which was reduced to powder in an agate mortar and
thoroughly dried in vacuo (41 mg, 60% yield). IR (KBr), ν (cm-1):
1607 (CdN), 1598 (CdO), 1366 (C-O). Anal. Calcd for
C38H26Cl2N4O4Pd2: C 51.49, H 2.96, N 6.32. Found: C 51.6, H
3.0, N 6.6.
Compound 5c. A mixture of 2c (100 mg, 0.12 mmol) and
triphenylphosphine (65 mg, 0.25 mmol) in 40 mL of methanol was
stirred at room temperature for 2 h. The white solid obtained was
filtered, washed with methanol, and dried under vacuum to obtain
1
5c, 122 mg (83% yield). H NMR (400 MHz, CDCl3, 298 K), δ
(ppm): 8.10 (d, 1H, H3, JHP ) 7.0 Hz), 7.80 (dd, 6H, ortho-PPh3,
JHP ) 11.4 Hz, JHH ) 7.3 Hz), 7.44-7.30 (m, 10H, meta-PPh3 +
para-PPh3 + H7), 7.19 (d, AA′XX′, 2H, H1, JHH ) 8.3 Hz), 6.90
(d, AA′XX′, 2H, H2, JHH ) 8.3 Hz), 6.61 (dd, 1H, H5, JHH ) 8.3
Hz, JHH ) 2.2 Hz), 6.43 (dd, 1H, H4, JHH ) 8.3 Hz, JHP ) 5.1
Hz). 31P{1H} NMR (101 MHz, CDCl3, 298 K), δ (ppm): 41.24
(s). IR (KBr), ν (cm-1): 1607 (COO), 1358 (COO), 1096
(coordinated PPh3, X-sensitive mode). MS-MALDI TOF (+)
(DTH), m/z: [M/2 + H]+ ) 629.9, [M - PPh3 + H]+ ) 992.9.
Anal. Calcd for C64H46Cl2N2O4P2Pd2: C 61.36, H 3.70, N 2.24.
Found: C 61.1, H 3.7, N 2.1.
Compound 5d. A mixture of 2d (100 mg, 0.12 mmol) and
triphenylphosphine (65 mg, 0.24 mmol) in 40 mL of methanol was
stirred at room temperature for 1 h. The white solid obtained was
filtered, washed with methanol, and dried under vacuum to obtain
1
Compound 4e. A brown suspension of 2e (60 mg, 0.07 mmol)
in 25 mL of chloroform was heated under reflux conditions for 1
day with an excess of pyridine (41 mg, 0.52 mmol). After this
5d, 103 mg (70% yield). H NMR (400 MHz, CDCl3, 298 K), δ
(ppm): 8.10 (d, 1H, H3, JHP ) 6.9 Hz), 7.80 (dd, 6H, ortho-PPh3,
JHP ) 11.7 Hz, JHH ) 7.2 Hz), 7.44-7.34 (m, 9H, meta-PPh3 +

5116 Organometallics, Vol. 27, No. 19, 2008
Albert et al.
Table 3. Crystal Data and Structure Refinement for 2c and 4a
Table 4. Crystal Data and Structure Refinement for 4d and 5b
2c
4a
4d
5b
empirical formula
C
40H40Cl2N2O16Pd2 ·
C
38H18D10N4O4Pd2 ·
empirical formula
C
38H16D10Cl2N4O4Pd2 ·
4(CDCl3) · 3(H2O)
C
68H50Cl14N2O4P2Pd2 ·
4(CH3COOH)
2(CDCl3)
4(CDCl3)
temperature [K]
wavelength [Å]
cryst syst
space group
a [Å]
203(2)
100(2)
temperature [K]
wavelength [Å]
cryst syst
space group
a [Å]
203(2)
203(2)
0.71073
monoclinic
C2/c
26.150(12)
10.014(3)
17.261(7)
90
90.54(2)
90
4520(3)
4
0.71069
monoclinic
0.71073
monoclinic
C2/c
30.086(10)
10.265(2)
18.179(4)
90
97.66(2)
90
4
0.71073
triclinic
j
j
P1
P1
12.4786(6)
8.7293(5)
19.0202(11)
90
102.347(3)
90
2023.94(19)
2
1.733
10.808(5)
12.773(3)
13.722(5)
96.55(3)
94.76(3)
106.22(2)
1
1793.9(11)
1.602
1.116
b [Å]
c [Å]
b [Å]
c [Å]
R [deg]
R [deg]
ꢀ [deg]
ꢀ [deg]
γ [deg]
γ [deg]
volume [Å3]
Z
Z
volume [Å3]
5564(2)
1.693
1.368
calc density [Mg/m3]
1.600
0.984
2192
calc dens [Mg/m3]
abs coeff [mm-1
F(000)
]
1.332
1048
abs coeff [mm-1
F(000)
]
2808
864
cryst size [mm]
0.2 × 0.09 × 0.09
0.16 × 0.10 × 0.07
cryst size [mm]
0.18 × 0.16 × 0.14
0.09 × 0.08 × 0.05
no. reflns collected
23 566
29 624
no. reflns collected
goodness-of-fit on F2
final R indices
[I < 2σ(I)]
R indices (all data)
7448
18 764
goodness-of-fit on F2
final R indices [I > 2σ(I)]
1.148
1.052
1.164
1.083
R1 ) 0.0356
wR2 ) 0.0848
R1 ) 0.0459
wR2 ) 0.0895
R1 ) 0.0302
wR2 ) 0.0674
R1 ) 0.0443
wR2 ) 0.0746
R1 ) 0.0403
wR2 ) 0.1168
R1 ) 0.0418
wR2 ) 0.1180
R1 ) 0.0448
wR2 ) 0.1231
R1 ) 0.0534
wR2 ) 0.1277
R indices (all data)
para-PPh3), 7.23 (d, 1H, H7, JHH ) 8.2 Hz), 7.20 (d, AA′XX′, 2H,
H1, JHH ) 8.3 Hz), 6.97-6.94 (m, 3H, H2 + H6), 6.42 (dd, 1H,
H4, JHP ) 5.5 Hz, JHH ) 1.5 Hz). 31P{1H} NMR (101 MHz, CHCl3,
298 K), δ (ppm): 38.73 (s). IR (KBr), ν (cm-1): 1598 (COO), 1362
(COO), 1097 (coordinated PPh3, X-sensitive mode). MS-MALDI
The structures were solved by direct methods, using the SHELXS
computer program, and refined by full-matrix least-squares method
with the SHELX97 computer program.23 For 2c the function
minimized was ∑w||Fo|2 - |Fc|2|2, where w ) [σ2(I) + (0.0411P)2
+ 1.2034P]-1, and P ) (|Fo|2 + 2|Fc|2)/3,; f, f′, and f′′ were taken
from International Tables of X-Ray Crystallography.24 3H atoms
were located from a difference synthesis and refined with an overall
isotropic temperature factor, and 16H atoms were computed and
refined, using a riding model, with an isotropic temperature factor
equal to 1.2 times the equivalent temperature factor of the atoms
that are linked. The final R (on F) factor was 0.035, wR (on |F|2)
) 0.089 and goodness of fit ) 1.148 for all observed reflections.
Number of refined parameters was 343. Max. shift/esd ) 0.00, mean
shift/esd ) 0.00. Max. and min. peaks in final difference synthesis
were 0.576 and -0.395 e Å-3, respectively. For 4d the function
minimized was ∑w||Fo|2 - |Fc|2|2, where w ) [σ2(I) + (0.0616P)2
+ 6.6461P]-1, and P ) (|Fo|2 + 2|Fc|2)/3, f, f′, and f′′ were taken
from International Tables of X-Ray Crystallography.24 15H atoms
were computed and refined, using a riding model, with an isotropic
temperature factor equal to 1.2 times the equivalent temperature
factor of the atoms that are linked. The final R (on F) factor was
0.040, wR (on |F|2) ) 0.118 and goodness of fit ) 1.164 for all
observed reflections. Number of refined parameters was 313. Max.
shift/esd ) 0.00, mean shift/esd ) 0.00. Max. and min. peaks in
final difference synthesis were 0.397 and -0.432 e Å-3, respec-
tively. For 5b the function minimized was ∑w||Fo|2 - |Fc|2|2, where
w ) [σ2(I) + (0.0674P)2+0.5074P]-1, and P ) (|Fo|2 + 2|Fc|2)/3;
f, f′, and f′′ were taken from International Tables of X-Ray
Crystallography.24 All H atoms were computed and refined, using
a riding model, with an isotropic temperature factor equal to 1.2
times the equivalent temperature factor of the atom that is linked.
The final R (on F) factor was 0.045, wR (on |F|2) ) 0.123 and
goodness of fit ) 1.083 for all observed reflections. Number of
refined parameters was 425. Max. shift/esd ) 0.00, mean shift/esd
) 0.00. Max. and min. peaks in final difference synthesis were
0.730 and -0.546 e Å-3, respectively.
TOF (+) (DTH), m/z: [M - PPh3 + H]+ ) 993.6, [M/2 + H]+
)
628.6. Anal. Calcd for C64H46Cl2N2O4P2Pd2: C 61.36, H 3.70, N
2.24. Found: C 61.2, H 3.6, N 2.0.
Compound 5e. A mixture of 2e (75 mg, 0.09 mmol) and
triphenylphosphine (45 mg, 0.17 mmol) in 40 mL of methanol was
stirred at room temperature for 3 h. The yellow solid obtained was
filtered, washed with methanol, and dried under vacuum to obtain
1
5e, 101 mg (92% yield). H NMR (400 MHz, CDCl3, 298 K), δ
(ppm): 7.82 (d, 1H, H3, JHP ) 7.4 Hz), 7.76 (dd, 6H, ortho-PPh3,
JHP ) 11.6 Hz, JHH ) 8.0 Hz), 7.31-7.21 (m, 9H, meta-PPh3 +
para-PPh3), 7.08 (m, 3H, H1 + H7), 6.80 (d, AA′XX′, 2H, H2, JHH
) 8.0 Hz), 6.94 (dd, 1H, H6, JHH ) 8.6 Hz, JHH ) 2.3 Hz), 5.77
(dd, 1H, H4, JHP ) 6.2 Hz, JHH ) 2.5 Hz), 2.39 (s, 6H, N(CH3)2).
31P{1H} NMR (101 MHz, CHCl3, 298 K), δ (ppm): 39.65 (s). IR
(KBr), ν (cm-1): 1569 (COO), 1350 (COO), 1098 (coordinated
PPh3, X-sensitive mode). MS-MALDI TOF (+) (DTH), m/z: [M
- PPh3 + H]+ ) 1009.8, [M/2 + H]+ ) 635.6. Anal. Calcd for
C68H58N4O4P2Pd2: C 64.31, H 4.60, N 4.41. Found: C 64.0, H 4.8,
N 4.2.
X-ray Crystallography. The crystal data, data collection, and
refinement parameters for the X-ray structures are listed in Tables
3 and 4.
Data were collected for 2c, 4d, and 5b on a MAR345 diffrac-
tometer with an image plate detector. Unit-cell parameters were
determined from 3506, 830, and 3195 reflections (3° < θ < 31°)
for 2c, 4d, and 5b respectively, and refined by least-squares
methods. Intensities were collected with graphite-monochromatized
Mo KR radiation. For 2c 23 566 reflections were measured in the
range 2.82 e θ e 32.43, 6394 of which were nonequivalent by
symmetry (Rint (on I) ) 0.049); 5475 reflections were assumed as
observed applying the condition I > 2σ(I). Lorentz-polarization
but no absortion corrections were made. For 4d 7448 reflections
were measured in the range 2.73 e θ e 31.60; 7035 reflections
were assumed as observed applying the condition I > 2σ(I). For
5b 18 764 reflections were measured in the range 2.62 e θ e 32.31,
9654 of which were nonequivalent by symmetry (Rint (on I) )
0.035); 8055 reflections were assumed as observed applying the
condition I > 2σ(I). Lorentz-polarization and absorption correc-
tions were made.
Data were collected for 4a on a BrukerAXS ApexII-CCD area
detector diffractometer. Unit-cell parameters were determined from
1874 reflections (2.5° < θ < 25.9°) and refined by least-squares
methods. Intensities were collected with graphite-monochromatized
(23) Sheldrick, G. M. SHELX97, A computer program for determination
of crystal structure; University of Go¨ttingen: Germany, 1997.
(24) International Tables of X-Ray Crystallography; Kynoch Press,
Birmingham, 1974; Vol. IV, pp 99-100 and 149.

Water-Soluble Metallacycles
Organometallics, Vol. 27, No. 19, 2008 5117
Scheme 2a
a
(i) Pd(OAc)2, acetic acid; (ii) PPh3, MeOH.
Mo KR radiation, using the ω/2θ scan technique; 3988 reflections
in the range 1.67 e θ e 26.01 were measured, and 3252 reflections
were assumed as observed applying the condition I > 2σ(I).
Lorentz-polarization and absorption corrections were made.
The structure was solved by direct methods, using the SIR97
computer program,25 and refined by full-matrix least-squares
method with the SHELX97 computer program,23 using 3988
reflections (very negative intensities were not assumed). The
function minimized was ∑w||Fo|2 - |Fc|2|2, where w ) [σ2(I) +
(0.0357P)2 + 2.3916P]-1, and P ) (|Fo|2 + 2|Fc|2)/3; f, f′, and f′′
were taken from International Tables of X-Ray Crystallography.24
All H atoms were computed and refined, using a riding model, with
an isotropic temperature factor equal to 1.2 times the equivalent
temperature factor of the atom that is linked. The final R (on F)
factor was 0.030, wR (on |F|2) ) 0.075, and goodness of fit ) 1.052
for all observed reflections. Number of refined parameters was 284.
Max. shift/esd ) 0.002, mean shift/esd ) 0.00. Max. and min. peaks
in final difference synthesis were 0.962 and -0.897 e Å-3
,
respectively.
CCDC-689175 (2c), CCDC-689176 (4a), CCDC-689177 (4d),
and CCDC-689178 (5b) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax (+44)1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgment. We thank the Ministerio de Educacio´n
y Ciencia for financial suport (project: CTQ2006-02007) and
the University of Barcelona for a BRD grant.
(25) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
OM8006807