Versatile behavior of the schiff base ligand 2,5-Me2C 6H3C(H)=N(2,4,6-Me3C6H2) toward cyclometalation reactions: C(sp2,phenyl)-H vs C(sp 3,methyl)-H activation

Article abstract of DOI:10.1021/om100238w

Treatment of the Schiff base ligand a with palladium(II) acetate in toluene gave 1a, with metalation of an aromatic phenyl carbon atom. Reaction at room temperature gave the trinuclear complex 4a. Treatment of a with palladium(II) acetate in refluxing acetic acid gave 1a′. The reaction of complexes 1a and 1a′ with sodium chloride or lithium bromide gave the halogen-bridged complexes 2a, 3a, 2a′, and 3a′.

Full text of DOI:10.1021/om100238w

Organometallics 2010, 29, 3303–3307 3303
DOI: 10.1021/om100238w
Versatile Behavior of the Schiff Base Ligand
2,5-Me2C6H3C(H)dN(2,4,6-Me3C6H2) toward Cyclometalation
Reactions: C(sp2,phenyl)-H vs C(sp3,methyl)-H Activation
†
Digna Vazquez-Garcıa, Alberto Fernandez, Margarita Lopez-Torres,
†
†
ꢀ
Antonio Rodrıguez, Nina Gomez-Blanco, Carlos Viader, Jose M. Vila,* and
ꢀ
ꢀ
†
†
†
,‡
ꢀ
ꢀ
,†
ꢀ
ꢀ
Jesus J. Fernandez*
†
´
~
~
Departamento de Quımica Fundamental, Universidade da Coruna, E-15071 La Coruna, Spain, and
´
‡
ꢀ
Departamento de Quımica Inorganica, Universidad de Santiago de Compostela, E-15782 Santiago de
Compostela, Spain
Received March 27, 2010
Treatment of the Schiff base ligand a with palladium(II) acetate in toluene gave 1a, with metalation of
an aromatic phenyl carbon atom. Reaction at room temperature gave the trinuclear complex 4a.
Treatment of a with palladium(II) acetate in refluxing acetic acid gave 1a0. The reaction of complexes 1a
and 1a0 with sodium chloride or lithium bromide gave the halogen-bridged complexes 2a, 3a, 2a0, and 3a0.
Introduction
to a dimer with bridging acetate ligands in an “open book”
arrangement. However, in a few cases this reaction gives
cyclometalated complexes with an unusual trinuclear struc-
ture15,16 which exhibits interesting catalytic applications.17-20
We have found that this is the case with ligand a when the
reaction is carried out at room temperature. Thus, ligand a can
be metalated at an aliphatic or at a sterically hindered aromatic
carbon and, in the latter case, it may give di- or trinuclear
species, showing an unprecedented and versatile behavior.
In the preceding decades the chemistry of cyclometalated
transition-metal complexes has attracted much attention.
They exhibit a good number of applications1-5 as well as
promote unusual coordination environments,6 and they are
usually classified according to the metal, the donor atom, or
the chelate ring size; by far the most well-studied examples
are five-membered palladacycles containing nitrogen-Pd
and C(phenyl)-Pd bonds.7-10 Analogous compounds con-
taining alkyl C(sp3)-Pd bonds are also known; activation of
the aliphatic carbon can only be achieved when the aromatic
position is unavailable or sterically hindered.11 Examples in
which C(sp3) carbon activation is exclusive are even more
exceptional.12-14
Experimental Section
General Comments. Solvents were purified by standard
methods.21 Chemicals were reagent grade. Microanalyses were
carried out using a Carlo Erba Elemental Analyzer, Model 1108.
IR spectra were recorded as Nujol mulls or polyethylene or KBr
discs on a Satellite FTIR instrument. NMR spectra were obtained
as CDCl3 solutions and referenced to SiMe4 (1H, 13C{1H}) and
were recorded on a Bruker AV-300F spectrometer. All chemical
shifts were reported downfield from standards. The FAB mass
spectra were recorded using a FISONS Quatro mass spectrometer
with a Cs ion gun; 3-nitrobenzyl alcohol was used as the matrix.
Synthesis of [Pd{1-CH2-2-[HCdN(2,4,6-Me3C6H2)]-4-MeC6H3-
C,N}(μ-O2CMe)]2 (1a0). A mixture of 2,5-Me2C6H3C(H)dN-
(2,4,6-Me3C6H2) (0.274 g, 1.09 mmol) and palladium(II) acetate
(0.246 g, 1.10 mmol) in glacial acetic acid (40 cm3) was refluxed
under dry argon for 3 h. After the mixture was cooled to room
temperature, the acetic acid was removed under vacuum. The
Palladium(II) acetate is one of the reagents most fre-
quently used to prepare cyclometalated complexes, leading
(1) Pfeffer, M.; Sutter, J. P.; Rottevel, M. A.; de Cian, A.; Fischer, J.
Tetrahedron 1992, 48, 2427.
(2) Ryabov, A. D.; van Eldik, R.; Le Borgne, G.; Pfeffer, M.
Organometallics 1993, 12, 1386.
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(4) Omae, I. J. Organomet. Chem. 2007, 692, 2608.
(5) Ghedini, M.; Aiello, I.; Crispini, A.; Golemme, A.; La Deda, M.;
Pucci, D. Coord. Chem. Rev. 2006, 250, 1373.
(6) Vila, J. M.; Pereira, M. T.; Ortigueira, J. M.; Fernandez, J. J.;
Fernandez, A.; Lopez-Torres, M.; Adams, H. Organometallics 1999, 18,
5484.
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(8) Dupont, J.; Consorti, C. S.; Spencer, J. Chem. Rev. 2005, 105, 2527.
(9) Omae, I. Coord. Chem. Rev. 2004, 248, 995.
(10) Dupont, J., Pfeffer, M., Eds. Palladacycles; Wiley-VCH: Wein-
heim, Germany, 2008.
(15) Alonso, M. T.; Juanes, O.; de Mendoza, J.; Rodriguez-Ubis,
J. C. J. Organomet. Chem. 1992, 430, 349.
(16) Balavoine, G.; Clinet, J. C. J. Organomet. Chem. 1990, 390, C84.
(17) Giri, R.; Liang, J.; Lei, J.; Li, J.; Wang, D.; Chen, X.; Clement
Naggar, I.; Guo, C.; Foxman, B. M.; Yu, J. Angew. Chem., Int. Ed. 2005,
44, 7420.
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Chem. 2002, 650, 258.
(12) Albert, J.; Cadena, J. M.; Gonzalez, A.; Granell, J.; Solans, X.;
(18) Moyano, A.; Rosol, M.; Moreno, R. M.; Lopez, C.; Maestro,
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M. A. Angew. Chem., Int. Ed. 2005, 44, 1865.
(19) Friedlein, F. K.; Kromm, K.; Hampel, F.; Gladysz, J. A. Chem.
Eur. J. 2006, 12, 5267.
Font-Bardıa, M. Chem. Commun. 2003, 528.
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(13) Albert, J.; Ceder, R. M.; Gomez, M.; Granell, J.; Sales, J.
Organometallics 1992, 11, 1536.
(20) Chitanda, J. M.; Prokopchuk, D. E.; Quail, J. W.; Foley, S. R.
Organometallics 2008, 27, 2337.
(21) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
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Chem. 2007, 5408.
Chemicals, 4th ed.; Butterworth-Heinemann, 1996.
r
2010 American Chemical Society
Published on Web 07/13/2010
pubs.acs.org/Organometallics

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Vazquez-Garcıa et al.
3304 Organometallics, Vol. 29, No. 15, 2010
Scheme 1.a
a Legend: (i) Pd(OAc)2, toluene, 60 °C; (ii) NaCl (2a), LiBr (3a), ethanol-water; (iii) Pd(OAc)2, toluene, room temperature; (iv) toluene, 80 °C;
(v) Pd(OAc)2, acetic acid, reflux; (vi) NaCl (2a0), LiBr (3a0), ethanol-/water.
residue was treated with water and extracted with dichloro-
methane. The combined extracts were dried over anhydrous
sodium sulfate, filtered, and concentrated in vacuo to give a
brown oil which was chromatographed on a column packed
with silica gel. Elution with dichloromethane-ethanol (1%)
afforded the final product as a yellow solid after solvent
removal, which was recrystallized in dichloromethane/hexane.
Yield: 77%. Anal. Found: C, 57.8; H, 5.7; N, 3.5. Calcd for
C40H46N2O4Pd2: C, 50.3; H, 5.0; N, 4.3. νmax/cm-1: 1610 s (CN),
1580 s (νas(COO)), 1420 s (νs(COO)). δH (300 MHz; CDCl3;
Me4Si): 7.49 (1H, s, HCN), 7.13, 6.86 (2H, m, H3, H4), 6.90 (2H,
s, H9, H11), 6.76 (1H, br, H6), 3.29 (2H, br, CH2), 2.79, 1.33 (6H,
br, Mec, Med), 2.26, 2.17 (6H, s, Meb, Mee), 1.33 (3H, s, AcO).
Synthesis of [{Pd[2,5-MeC6H2C(H)dN(2,4,6-Me3C6H2)-
C6,N](μ-O2CMe)}2{Pd(μ-O2CMe)2}] (4a). A pressure tube con-
taining 2,5-Me2C6H3C(H)dN(2,4,6-Me3C6H2) (a; 0.275 g, 1.09
mmol), palladium(II) acetate (0.245 g, 1.10 mmol), and 20 cm3
of dry toluene was sealed under argon. The resulting mixture
was stirred for 76 h at room temperature and the solvent remo-
ved under vacuum to give a green solid which was recrystallized
from dichloromethane-hexane. Yield: 71%. Anal. Found: C,
49.8; H, 4.7; N, 2.5. Calcd for C44H52N2O8Pd3: C, 50.0; H, 4.9;
N, 2.6. νmax/cm-1 1610 sh (CN), 1550s (νas(COO)), 1400 s
(νs(COO)). δH (300 MHz; CDCl3; Me4Si): 8.14, 8.13 (2H, s,
Pd3(OAc)4 core, and second, the behavior of the ligand under
different reaction conditions sheds new light regarding the
choice of metalation at Csp2 or Csp3 carbon atoms, as well as
on the formation of endo or exo metallacycles.
Thus, the reaction of a with palladium acetate in toluene at
room temperature gave the novel trinuclear cyclometalated
complex 4a. This is in agreement with similar trinuclear
cyclometalated complexes previously reported,15-20 when
the reaction is carried out in weakly coordinating solvents.
Treatment of a solution of 4a in toluene at 80 °C for 24 h gave
1a (see below) plus black palladium and a small amount of
other decomposition products, indicating the temperature
dependence of both compounds. It therefore seems that
compounds of type 4a are a reaction intermediate after
C-H activation, which may or may not be isolable, as has
been the case in the present reaction. Change of solvent for
acetic acid (see below) gave altogether different results, and
1
compounds similar to 4a were not detected. The H NMR
spectrum for 4a showed two sets of signals for the syn and
anti isomers (in approximately equimolar ratio) in the
solution.15-20 The HCdN resonances were assigned at 8.14
and 8.13 ppm, shifted to lower frequency, in agreement with
the N-coordination of the ligand. Four signals at ca. 1.8 and
1.0 ppm, two for each isomer, were assigned to the four
acetate methyl groups.
0
0
0
H0CN/HCN), 6.81 (8H, m, H4 /H4, H5 /H5, H9 /H9, H110/H11),
2.67, 2.65 (6H, s, Me), 2.43 (9H, s, Me), 2.36, 2.27, 2.25, 2.24,
2.22 (15H, s, Me), 1.89, 1.83, 1.06, 1.01 (12H, s, AcO). m/z
(FAB): 774 [(L-H)2Pd2(OAc)]þ.
Furthermore, treatment of a with Pd(OAc)2 in toluene at
60 °C for 24 h gave, after column chromatography purifica-
tion, a yellow solid identified as 1a. In the IR spectrum of the
complex the ν(CdN) stretching band, 1587 s cm-1, appeared
at lower frequency than the corresponding one in the free
imine, 1633 m cm-1, in accordance with nitrogen coordina-
tion to the metal center.22 This was supported by the upfield
shift (0.67 ppm, as compared to the free ligand) of the HCdN
Results and Discussion
For the convenience of the reader the compounds and
reactions are shown in Scheme 1.
The reaction of ligand a with palladium acetate has been
studied. The results show that the ligand incorporates two
main features with which we will deal separately. First,
it allows for the making of a species containing a rare
(22) Onoue, H.; Moritani, I. J. Organomet. Chem. 1972, 43, 431.

Article
Organometallics, Vol. 29, No. 15, 2010 3305
Figure 2. Molecular structure of 4a, depicting the S-shape of
the Pd3(OAc)4 core. Hydrogen atoms have been omitted for
clarity.
Figure 1. Molecular structure of 4a, with labeling scheme.
Hydrogen atoms have been omitted for clarity. Selected bond
˚
lengths (A) and angles (deg): Pd(1)-C(6), 1.993(4); Pd(1)-N(1),
the chelated organic ligands are forced to lie above one
another in the dimeric molecule. This leads to interligand
repulsions on the “open” side of the molecule and results in
the coordination planes of the palladium atoms being tilted
at an angle of 51.0°. The tripalladium complex 4a shows a
Pd3(OAc)4 core with the two terminal palladium atoms,
Pd(1) and Pd(3), bonded to a Schiff base ligand and to the
central palladium atom Pd(2) through four bridging acetate
ligands, resulting in an S-shaped complex (Figure 2), in
which the three palladium atoms are in a linear disposition
(Pd-Pd-Pd angle 180°). Such structural arrangements are
rather rare, and to our knowledge it is the sixth example in a
still short list of structurally characterized Pd3(OAc)4
species;17-20 however, it is the first example containing a
monodentate imine. The dihedral angle between the palla-
dium coordination planes of Pd(1) and Pd(2) is 39.0°; how-
ever, the coordination planes of the symmetry-related
terminal palladium atoms are in an exactly parallel arrange-
ment. Each palladium atom is in a slightly distorted square-
planar coordination environment consisting of a CdN nitro-
gen atom, the phenyl ring ortho carbon, and two oxygen
atoms from the bridging acetate; the most noticeable distor-
tion of the ideal coordination sphere corresponds to a C-
Pd-N bite angle of 81.3(1)°. The coordination geometry at
Pd(2) is defined by four oxygen atoms from the bridging
acetate groups, and the coordination angles at palladium
atom are close to the ideal value of 90°. All bond distances
are within the expected values, with allowance for lengthen-
ing of the Pd-O bond trans to carbon, due to the differing
trans influence of the carbon and nitrogen atoms. The
2.001(3); Pd(1)-O(1), 2.144(3); Pd(1)-O(3), 2.057(3); Pd(2)-
O(2), 1.995(3); Pd(2)-O(4), 2.010(3); Pd(1)-Pd(2), 3.031(1).
C(6)-Pd(1)-O(3), 99.9(1); C(6)-Pd(1)-N(1), 81.3(1); N(1)-
Pd(1)-O(1), 90.8(1); O(1)-Pd(1)-O(3), 88.0(1); C(6)-Pd(1)-
O(1), 172.0(1); N(1)-Pd(1)-O(3), 167.1(1).
resonance in the H NMR spectrum.23 The νas(COO) and
1
νs(COO) values were consistent with bridging acetate groups,24
and a singlet resonance at ca. 1.6 ppm in the 1H NMR
spectrum, assigned to the equivalent methyl acetate protons,
was consistent with a trans geometry of the cyclometalated
moieties.25 The FAB mass spectrum showed a cluster of
peaks assigned to [(L-H)2Pd2(OAc)]þ, thereby confirming
the dinuclear nature of the complex.26
Crystal Structures of 1a and 4a. Suitable crystals of 1a and
4a were grown by recrystallization from dichloromethane-
n-hexane solutions. The structure of 4a is given in Figures 1
and 2; the structure of 1a and crystallographic data are given
in the Supporting Information. Selected interatomic dis-
tances and angles for 4a are given in the caption to Figure 1.
The crystals consist of discrete molecules separated by
normal van der Waals distances. The asymmetric unit com-
prises one molecule for 1a and a half-molecule for 4a; the
latter exhibits a crystallographic inversion center located at
the central palladium atom Pd(2).
The molecular configuration of complex 1a is a dimeric
form with the cyclopalladated moieties in an “open book”
arrangement linked by two acetate bridging ligands, as
observed in the related dimers.25,27 As a result of two mutu-
ally cis μ-acetato ligands bridging the Pd(1) and Pd(2) atoms,
˚
palladium-palladium distance of 3.031(1) A is close to the
upper value of the range found in related structures, 3.0457(5)-
(23) Ustinyuk, Y. A.; Chertov, V. A.; Barinov, I. V. J. Organomet.
Chem. 1971, 29, C53.
(24) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 5th ed.; Wiley: New York, 1997.
ꢀ
(25) Teijido, B.; Fernandez, A.; Lopez-Torres, M.; Castro-Juiz, S.;
Suarez, A.; Ortigueira, J. M.; Vila, J. M.; Fernandez., J. J. J. Organomet.
Chem. 2000, 598, 71.
(26) Tusek-Bozic, L.; Curic, M.; Traldi, P. Inorg. Chim. Acta 1997,
254, 49. Tusek-Bozic, L.; Komac, M.; Curic, M.; Lycka, A.; Dalpaos, M.;
Scarcia, V.; Furlani, A. Polyhedron 2000, 19, 937.
2.864(1) A,19 and may be regarded as nonbonding.
˚
The second interesting feature stemming from the reacti-
vity of a is the choice of the metalation site on the phenyl ring.
Metalation may be prompted through C-H activation at an
aromatic or at aliphatic carbon atoms. Even though activa-
tion of the sp2 carbon is usually preferred, the reaction
conditions play an essential role in the regioselectivity of
the cyclometalation reaction.12-14 Nevertheless, the ligand
portrays quite distinct metalation possibilities, as opposed to
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(27) Navarro-Ranninger, C.; Zamora, F.; Lopez-Solera, I.; Monge,
A.; Masaguer, J. R. J. Organomet. Chem. 1996, 506, 149.

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Vazquez-Garcıa et al.
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3306 Organometallics, Vol. 29, No. 15, 2010
those of previously considered imines where endo/exo five- or
six-membered metallacycles were feasible.13 To begin with, a
may be metalated at the C6 carbon to give an endo five-
membered ring, via a Caromatic-Pd bond, or at the C(2)Me
carbon to give an endo six-membered ring, via a Caliphatic-Pd
bond, both cases pertaining to the benzylidene ring. Alterna-
tively, a could undergo metalation at the C(8)Me or C(12)Me
carbons to give an exo five-membered ring bearing a Caliphatic
-
Pd bond, with exo Caromatic-Pd bonds being obviously pre-
cluded. Nevertheless, all attempts to produce the exo five-
membered palladacycle through either of the aniline methyl
groups failed, putting forward the preference in formation of
the endo six-membered species. Therefore, in spite of the fact
that it has been suggested that there is a strong tendency to form
five-membered metallacycles,28 the six-membered ring is the
final choice with the present ligand.
Henceforth, reaction between a and palladium(II) acetate
in refluxing acetic acid gave, even after column chromatog-
raphy and recrystallization, a mixture of compounds. The 1H
NMR spectrum showed the presence of an unidentified
compound, a small amount of 1a, and the major complex,
which was formulated as 1a0, derived from C-H activation
at the C2-methyl group. Although the IR and the 1H NMR
spectra (see the Experimental Section and Scheme 1) were in
agreement for 1a0, unambiguous proof for this species was
obtained after preparation of the corresponding pure chlor-
ide-bridged derivative 2a0 from the aforementioned mixture.
Complexes 1a and 1a0 reacted smoothly with sodium
chloride or bromide in ethanol-water to give the halide-
bridged species 2a,3a,2a0,and3a0. The MS-FAB spectra showed
peaks assigned to [(L-H)2Pd2X2)]þ or [(L-H)2Pd2X)]þ (X =
Cl, Br). The resonance for the metalated -CH2- group was
at 3.38 and 3.37 ppm for 2a0 and 3a0, respectively.
Crystal Structures of 2a and 2a0. Suitable crystals were
grown by recrystallization from dichloromethane-n-hexane
solutions of 2a and 2a0. The structure of 2a0 is given in Figure 3;
the structure of 2a and crystallographic data are given in
the Supporting Information. Selected interatomic distances
and angles for 2a0 are given in the caption for Figure 3. The
crystals consist of discrete molecules separated by normal
van der Waals distances. The asymmetric unit comprises half
of the molecule with a crystallographic inversion center
located at the center of the Pd2(μ-Cl)2 moiety (2a). The
molecules are dimeric, and the coordination sphere around
each palladium atom consists of two halogen atoms, a CdN
nitrogen atom, and the C(6) carbon atom (2a) or the
methylene C(2) carbon atom (2a0).
Figure 3. Molecular structure of 2a0, with labeling scheme.
Hydrogen atoms have been omitted for clarity. Selected bond
lengths (A) and angles (deg): Pd(1)-C(15), 2.008(5); Pd(1)-
N(1), 2.043(3); Pd(1)-Cl(1), 2.327(1); Pd(1)-Cl(1a), 2.501(1);
C(15)-Pd(1)-N(1), 86.7(2); N(1)-Pd(1)-Cl(1a), 93.8(1);
Cl(1a)-Pd(1)-Cl(1), 87.9(1); Cl(1)-Pd(1)-C(15), 91.5(1);
C(15)-Pd(1)-Cl(1a), 177.0(1); N(1)-Pd(1)-Cl(1), 178.2(1);
Cl(1)-Pd(1)-Cl(1a), 92.1(4).
˚
coordination plane and the Pd2Cl2 ring of 3.6°. This situation
is the most common configuration observed in related
species.29 In complex 2a0 the six-membered palladacycle
adopts a half-skew chair conformation, with the palladium
atom out of the plane (1.052 A) defined by the remaining
atoms, and the C(2)-C(15)-Pd(1) bond angle of 109.3(3)° is
in agreement with the sp3 hybridization of the C(15) carbon.
All bond distances are within the expected values, with
allowance for lengthening of the Pd-X bond trans to
carbon, due to the differing trans influence of the carbon
and nitrogen atoms, resulting in an asymmetric Pd(μ-X)2Pd
moiety,
In conclusion, the ligand presents a versatile behavior
dependent on the reaction conditions. In noncoordinating
solvents such as toluene, activation of the Caromatic-H bond
proceeds smoothly at room temperature to give the five-
membered trinuclear metallacyclic species 4a. Higher tem-
peratures are needed to produce the dinuclear compound
either from the trinuclear species or by direct metalation of the
ligand itself. This would be in agreement with Caromatic-H
bond cleavage requiring a low activation energy and should
be the kinetically controlled process: a possible intermediate
step in the formation of the dimer complex.30 Under more
intense conditions, refluxing acetic acid, va ery stable endo
six-membered metallacycle containing Caliphatic-H bonds
seems to be the thermodynamically favorable product under
these conditions.
The coordination environment at the metal center is
slightly distorted square planar, with the most noticeable
deviation corresponding to the C-Pd-N bite angle of
81.29(13)° in 2a. For complex 2a0 the C-Pd-N angle,
86.7(2)°, is closer to the ideal value of 90°, due to the smaller
ring strain of the six-membered cyclometalated ring as
opposed to the five-membered ring.
The [(C-N)Pd(μ-Cl)2Pd(C-N)] fragment adopts a planar
configuration in 2a, with an angle between the palladium
(28) (a) Bruce, M. I. Angew. Chem., Int. Ed. Engl. 1977, 16, 73.
(b) Omae, I. Coord. Chem. Rev. 1988, 83, 137. (c) Dunina, V. V.; Zalevskaya,
O. A.; Potatov, V. M. Russ. Chem. Rev. 1988, 57, 250.
(30) For kinetic-mechanistic studies on cyclometalated compounds:
(a) Ryabov, A. D. Inorg. Chem. 1987, 26, 1252. (b) Ryabov, A. D.
Synthetic and mechanistic aspects of exchange of cyclometallated ligands
in palladium(II) and platinum(II) complexes In Perspectives in Coordination
Chemistry; Williams, A. F., Floriani, C., Merbach, A. E., Eds.; Verlag
Helvetica Chimica Acta: Basel, Switzerland, and VCH Weinheim: New
York, Basel, Cambridge, 1992; p 271.
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J. J.; Thronton-Pett, M. J. Organomet. Chem. 1991, 401, 385. Navarro-
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Masaguer, J. R.; García-Ruano, J. L. J. Organomet. Chem. 1994, 476, 19.
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Article
Organometallics, Vol. 29, No. 15, 2010 3307
tails for 1a, 4a, 2a and 2a0 and text giving details of the syntheses
of new compounds and characterization data. This material is
available free of charge via the Internet at http://pubs.acs.org.
Crystallographic data (excluding structure factors) for the
structures reported in this paper have also been deposited with
the Cambridge Crystallographic Data Centre as Supplementary
Publication Nos. 718085 (1a), 718086 (2a), 718087 (2a0), and
718089 (4a).
ꢀ
Acknowledgment. We thank the Ministerio de Educacion
y Ciencia (Projects CTQ2006-15621-C02-02/BQU, UDC, and
CTQ2006-15621-C02-01/BQU, USC) and the Xunta de Ga-
licia (ref. PGIDIT04PXI10301IF, INCITE07PXI103083ES,
and INCITE08ENA209044ES) for financial support.
Supporting Information Available: Figures, tables, and CIF
files giving crystal structure data and structure refinement de-