Nucleophilic attack on coordinated imines: The synthesis of C-bonded acetylacetonates of palladium(II) and mechanistic insights

Article abstract of DOI:10.1002/ejic.201101434

The reactivity of complexes [PdCl₂(κ²-NN')] [NN' = 2-C₅H₄N-CH=N-Ar; Ar = 2-MeC₆H ₄, a; 4-MeC₆H₄, b; 2-MeOC₆H ₄, c; 4-MeOC₆H₄, d; 4-CF₃C ₆H₄, e; 2,6-Me₂C₆H₃, f; 2-iPrC₆H₄, g] and [Pd(κ²-acac) (κ²-NN')][BF₄] toward the nucleophilic reagent acetylacetonate (acac) has been explored. This reaction starts with nucleophilic attack on the cabonylic atom of the coordinated imine generating a new C-C bond and an amido complex. The next step in the reaction is proton migration leading to the protonation of the amido nitrogen, and finally replacement of this coordinated nitrogen atom with an anionic carbon atom. The final consequence of the nucleophilic attack on the coordinated imines is the formation of new complexes and the generation of new C-C and C-Pd bonds. Pyridine-imine complexes of palladium(II) undergo nucleophilic attack by acetylacetonate to generate an amido complex that evolves to give a γ-acac complex of palladium. Copyright

Full text of DOI:10.1002/ejic.201101434

FULL PAPER
DOI: 10.1002/ejic.201101434
Nucleophilic Attack on Coordinated Imines: The Synthesis of C-Bonded
Acetylacetonates of Palladium(II) and Mechanistic Insights
Thomas Birkle,[a] Arancha Carbayo,[a] José V. Cuevas,*[a] Gabriel García-Herbosa,[a] and
Asunción Muñoz[a]
Keywords: Palladium / N ligands / Schiff bases / Nucleophilic addition
The reactivity of complexes [PdCl2(κ2-_NNЈ)] [_NNЈ = 2-
C5H4N-CH=N-Ar; Ar = 2-MeC6H4, a; 4-MeC6H4, b; 2-Me-
OC6H4, c; 4-MeOC6H4, d; 4-CF3C6H4, e; 2,6-Me2C6H3, f; 2-
iPrC6H4, g] and [Pd(κ2-acac)(κ2-_NNЈ)][BF4] toward the nu-
cleophilic reagent acetylacetonate (acac) has been explored.
This reaction starts with nucleophilic attack on the cabonylic
atom of the coordinated imine generating a new C–C bond
and an amido complex. The next step in the reaction is pro-
ton migration leading to the protonation of the amido nitro-
gen, and finally replacement of this coordinated nitrogen
atom with an anionic carbon atom. The final consequence
of the nucleophilic attack on the coordinated imines is the
formation of new complexes and the generation of new C–C
and C–Pd bonds.
on imines bound to CoIII [3a,3k]
but to the best of our
,
Introduction
knowledge, this is the first reported study of nucleophilic
attack on an imine coordinated to Pd leading to the forma-
tion of a C-bonded acetylacacetonato (carbon-bonded γ-
acac) complex. Carbon-bonded acetylacetonato complexes
(γ-acac) of PdII[6] and PtII[7] have been known for a half
century. The synthetic procedure for preparing these com-
plexes almost exclusively relies on the reaction between
[M(O,O-acac)2] (M = Pd or Pt) and ligands (L) that are
nitrogen based (py and Et2NH), tertiary phosphanes (PPh3,
PCy3 and PEt3) or arsanes, leading to the formation of
complexes with the general formula [M(O,O-acac)(γ-acac)-
L].[8] More recently, the same procedure has been used to
prepare [M(O,O-acac)(γ-acac)L] where M = Pd,[9] L =
N,NЈ-bis(2,6-diisopropylphenyl)imidazol-2-ylidene and M
= Pt,[10] L = dimethyl sulfoxide. At least in one reported
case the donor atom of the ligand (pyridine) and the γ-
carbon of the γ-acac are connected, forming a five-mem-
bered palladacycle [Pd(O,O-acac)(γ-acac-S-py)].[11] A re-
vival of research into this kind of complex containing acac
displaying both coordination modes (O,O-acac and γ-acac)
has recently been observed, and is a consequence of their
reported cytotoxic activity on several cancer lines.[12]
Among metal-based catalysts, complexes with Schiff base
ligands belong indisputably to a very important group be-
cause of their multifunctionality and versatility.[1] One of
the fields in which palladium(II) complexes containing
imine ligands have displayed interesting activity is the allylic
alkylation with soft carbon nucleophiles to form C–C
bonds.[2] In these reactions, the metal activates a substrate
to enhance its reactivity towards carbanionic nucleophilic
reagents. At the same time, the coordinated imine can be
attacked by nucleophilic reagents yielding amido complexes
that can evolve to give different products.[3] Understanding
this reactivity can be very helpful in avoiding the degrada-
tion of the ligands within complexes and extending the life-
span of the catalyst.
Our group has reported the nucleophilic attack of carb-
anionic nitronate on a coordinated imine.[3b] The nitronate
formed by deprotonation of the nitromethane attacks the
carbonylic carbon of the coordinated imine. In this context,
we have been studying the reactivity, in basic media, of
imine complexes with 2,4-pentanedione. This diketone is a
weak acid[4] and its nucleophilic reactivity has been studied
recently.[5] Herein, we report the reactivity of imine com-
plexes of palladium(II) towards acetylacetonate. After the
nucleophilic attack on the imine carbon, a new carbon–car-
bon bond was formed, and then the complex evolves to
give a palladium carbon bonded diketonate. Previous works
have focused on the nucleophilic attack by acetylacetonate
Results and Discussion
The pyridine-imine ligands a–g, which are shown in
Scheme 1, were prepared in a similar way to a previously
reported method by the simple condensation of the
relevant piridine-2-carboxaldehyde with the corresponding
aniline.[13] Reactions of equimolar amounts of the ligands
a–g with [PdCl2(1,5-COD)] afforded the complexes
[PdCl2(_NNЈ)], 1a–g, in high yields.[14]
[a] Departamento de Química, Universidad de Burgos,
Plaza Misael Bañuelos S/N, 09001 Burgos, Spain
Fax: +34-947-258-831
E-mail: jvcv@ubu.es
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201101434.
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J. V. Cuevas et al.
FULL PAPER
proximity between the two methyl groups of the metallated
diketone groups, but the analysis of the exchange spec-
troscopy (EXSY) phase showed no exchange between the
methyl groups, which is consistent with the absence of dy-
namic behaviour.
The ligands present in complexes 2 can be considered as
C-deprotonated 2-C5H4N–CH(NHAr)-CH(COCH3)2 spe-
cies. Attempts to synthesize the molecule 2-C5H4N–
CH(NHPh)-CH(COCH3)2 following published procedures
were unsuccessful.[15] For this reason it was not possible to
synthesize complexes 2 following a direct procedure.
Interestingly, complexes 1f and 1g that bear bulky aryl
substituents did not show this reactivity. In order to shed
light on this reaction, the chlorido ligands in complexes 1
were substituted with O,O-acetylacetonato ligands leading
to the ionic compounds 3 (prepared with ligands a, c, f,
g). The compounds selected for these syntheses displayed
different degrees of steric hindrance, and the substituents
on the aryl groups had different electronic properties. As
shown in Scheme 2, the reaction of complexes 1 with equi-
molar amounts of thallium acetylacetonate and thallium
tetrafluoroborate afforded compounds 3 in good yields.
These compounds were characterized by NMR and IR
spectroscopy, and complex 3a was also subjected to X-ray
Scheme 1. General structure of the ligands a–g.
When complexes 1a–e reacted with a fivefold excess of a
mixture of 2,4-pentanedione and potassium tert-butoxide a
new family of compounds was obtained, 2a–e (see
Scheme 2). These compounds were characterized by NMR
1
and IR spectroscopy. The H NMR spectra of these com-
pounds displayed four singlets that when integrated were
shown to correspond to three protons each.
1
diffraction analysis (see below). The H NMR spectra of
the compounds displayed three singlet signals correspond-
ing to the O,O-β-diketonato ligands and were assigned to
the two methyl groups and the C–H hydrogen atoms of the
central carbon atoms of the acetylacetonato ligands. The
nonequivalent character of the methyl groups of the β-acet-
ylacetonato compounds was consistent with the nature of
the ancillary chelating pyridine-imine ligand, and also indi-
cated the nondynamic behaviour of these compounds in
solution. The signals from the pyridine-imine ligands were
in the same range observed for the related compounds 1.
The reactions of compounds 3 (including 3f and 3g) with a
fivefold excess of a mixture of 2,4-pentanedione and potas-
sium tert-butoxide yielded the corresponding complexes 2.
These results can give us some information about the ini-
Scheme 2. Reactions for the preparation of complexes 2 and 3
.
Two of these singlets (appearing at about 2.5 ppm) were tial stages of the mechanism of the observed process. In the
assigned to the inequivalent methyl groups of the O,O-coor- first place, substitution of the two chlorido ligands of 1 with
dinated β-diketonate, and the other two singlets (appearing chelating O,O-acetylacetonato ligands leading to the cat-
at about 2.1 and 2.0 ppm) were assigned to the methyl ionic complex 3 seems to be necessary.[16] For complexes 1f
groups of the C-metallated diketone (note that the adjacent and 1g that bear bulky aryl substituents on their ligands
asymmetric carbon makes the acetyl groups diastereotopic). there is no reaction, but for compounds 3f and 3g the reac-
The H–C(sp2) iminic hydrogen atoms of compounds 1 dis- tion occurs readily. This fact can be understood by con-
1
played singlets in the H NMR spectra at about 8.5 ppm. sidering the electrostatic attraction between the cations of
In compounds 2 this hydrogen atom is now bonded to sp3 compounds 3 and the anionic nucleophile acetylacetonate.
aminic carbon atoms and thus appears as doublets in the In addition, the cationic charge increases the back-donation
spectra of 2, by coupling with the NH hydrogen atoms, and from the imines to the palladium atoms, thus favouring nu-
its chemical shift is upfield from the corresponding signals cleophilic attack. Once the substitution of the chlorido li-
observed in the spectra of 1. These two hydrogen atoms gands with chelating acetylacetonato has occurred, attack
displayed an AB spin system with coupling constants in the of the carbanionic acetylacetonate anions on the carbonylic
10.2–9.9 Hz range. As expected, the H–C(sp2) of the O,O- carbon atoms of the coordinated imines affords nonisolated
coordinated β-diketonato groups displayed a singlet at amido complexes (see Scheme 3). In spite of the sometimes
about 5.4 ppm in the spectra of 2. NOESY experiments claimed mismatch between soft PdII and hard N(amido),
with 2 demonstrated the expected proximity between the palladium complexes containing terminal Pd–N amido
two methyl groups of the β-diketonato groups, and the bonds have been well characterized in more than few
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Nucleophilic Attack at Coordinated Imines
cases.[17] The formation of this type of amido complex in-
The 1,3-CǞN prototropic shift in Ia-R (Scheme 4) in-
volved transformation of the sp2 iminic carbon atom into volves a hydrogen atom that belongs to a central carbon of
an sp3 carbon atom leading to chirality (R enantiomer the 1,3-diketone, and leads to the formation of a zwitter-
shown in Scheme 3) and the generation of three possible ionic structure II-NR,CR (Scheme 4) where the negative
rotamers (Ia, Ib and Ic). The difference in energy between charge resides on the oxygen or on the central carbon atom
the rotamers is small (around 3 kcal/mol according to DFT of the β-diketonate. Zwitterionic species of platinum group
calculations, see Supporting Information) and the main metal complexes have been described.[18] At this point, note
structural difference between them is the torsional angle that chiral diastereomers NR,CR and NS,CR can be depicted
(H–C–C–N) between the hydrogen atoms of the diketone for II (the enantiomer NR,CR is shown in Scheme 4).
fragments and the amido nitrogen atoms (46.6° in structure
Finally, the conversion of II to IV involves substitution
Ia, 171.3° in structure Ib and –39.0° in structure Ic, see of a coordinated amine by a C-bonded β-diketonate. Two
Supporting Information). As the spatial arrangements of putative pathways can be considered. Pathway 1 involves
the Namido–C–C–H atoms are similar in Ia and Ic, only the oxygen as the donor atom, whereas pathway 2 has the car-
two most stable rotamers, which are those with the greatest bon as the donor atom. Pathway 1 leads to the final product
difference in torsion angles, namely Ia and Ib, have been IV through the intermediate O-bonded 7-membered chelat-
considered.
ing ring III. Pathway 2 involves the direct displacement of
the coordinated nitrogen atom by the carbanionic atom.
Nevertheless, careful analysis of the structure of II (DFT-
optimized, see Supporting Information) shows that in the
process of rotation around the carbon–carbon bond, as
indicated in Scheme 4, the oxygen atom initially binds to
the palladium atom, indicating the formation of III. For
structure III it is possible to propose two enantiomers (con-
sidering that inversion at the uncoordinated nitrogen atom
is very fast, there is only one chiral centre).
Note that by following the Cahn–Ingold–Prelog rules,
IV-S has an S configuration but the chiral carbon atom has
its subsituents in the same order as those in Ia-R, II-CR and
III-R (i.e. no inversion of the configuration takes place in
Scheme 3. Rotamers arising from rotation around the C–C bond
in the nonisolated amido complexes. The values of the angles dis- this mechanism).
played in the Newman projections were determined by DFT calcu-
lations (see Supporting Information).
The 1,3-migration described above is not possible in Ib
because of the transoidal orientation of the hydrogen and
nitrogen atoms (as can be seen in Scheme 3). However, both
structures Ia and Ib can undergo double 1,2-CǞN and 1,2-
CǞC proton migration. This second option can be ruled
out because it involves the participation of a hydrogen atom
that is less acidic in the first 1,2-proton shift (see Scheme 5)
when compared with the hydrogen atom in the 1,3-CǞN
prototropic shift. DFT calculations showed higher barriers
for the steps in the 1,2-CǞN and 1,2-CǞC proton mi-
grations than the barrier calculated for the 1,3-CǞN proto-
tropic shift (see Supporting Information).
Following the formation of Pd–N(amido) bonds, mi-
gration of a proton to the nitrogen atoms takes place. Al-
though intermolecular mechanisms cannot be ruled out, the
spatial arrangement of the atoms in Ia-R suggests a 1,3-
CǞN prototropic shift of the proton bonded to the central
carbon atoms of the diketones, as depicted in Scheme 4.
Scheme 4. Proposed mechanism for the conversion of the noniso-
lated amido complex Ia to the final product IV-S.
Scheme 5. Proposed mechanisms for the double 1,2-CǞN and 1,2-
CǞC proton migrations in the model structures Ia and Ib.
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Structural Characterization of the Complexes
cal environments. All the comments made above concerning
the solid state structure of complex 2d also apply to com-
plexes 2a and 2f. However, the coordination environments
around the palladium atoms in these two complexes are
planar.
Single crystals suitable for X-ray diffraction studies were
obtained by layering hexane or ether over dichloromethane
solutions of the compounds.
The structures of complexes 2a, 2d, and 2f are shown in
Figures 1, 2 and 3, respectively. For complex 2d, the crystal
structure contains only the S isomer S/R enantiomeric pair,
while for complexes 2a and 2f a racemic mixture of S/R
enantiomers is found in the crystals (enantiomer S of 2a is
shown in Figure 1 and enantiomer R of 2f is shown in Fig-
ure 3). Selected bond lengths, bond angles, and torsion
angles for complexes 2a, 2d and 2f are given in Table 1. For
complex 2d, the chelating ligand binds to the metal through
a pyridyl donor atom, N1, and a quaternary carbon atom,
C14. The N1–Pd1–C14 bond angle is 81.84(14)°. The palla-
dium atom has a nearly square planar coordination geome-
try, nevertheless, the atom C14 is slightly out of the plane
as the torsion angle O5–O4–N1–C14 is 3.01°. The Pd–O
bond distances are in good agreement with the values found
for other palladium O,O-coordinated β-diketonates. Also,
the Pd1–C14 bond distance is in good agreement with other
C-bonded β-diketonates. The nonequivalence of the four
methyl groups in the β-diketonates, O,O-coordinated and
C-coordinated complexes in solution (see comments regard-
Figure 2. Molecular structure of complex of 2d. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30%
probability level.
1
ing the H NMR analysis that are given above) is in good
agreement with the structure found in the solid state in
which the four methyl groups are found in different chemi-
Figure 3. Molecular structure of complex of 2f. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30%
probability level.
X-ray diffraction quality crystals were also grown for 3a.
The molecular structure of this complex is shown in Fig-
ure 4, and selected bond lengths, bond angles, and torsion
angles are given in Table 2. In this complex, the bond angles
subtended by the chelating ligand bound to the metal are
94.0(1)° for the angle O1–Pd1–O2, and 80.8(1)° for the an-
gle N1–Pd1–N2. The o-tolyl group bonded to the iminic
nitrogen atom is twisted out of the coordination plane of
Figure 1. Molecular structure of complex of 2a. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30%
probability level.
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Nucleophilic Attack at Coordinated Imines
Table 1. Selected bond lengths [Å], bond angles [°] and torsion angles [°] for complexex 2a, 2d and 2f.
2a
2d
2f
Pd1–C14
Pd1–O4
Pd1–N1
Pd1–O3
N1–C5
C5–C6
C14–C6
O4–Pd1–O3
C14–Pd1–N1
N1–C5–C6–C14
2.070(2)
2.045(2)
2.002(3)
1.989(2)
1.337(3)
1.517(4)
1.542(4)
93.33(9)
82.1(1)
Pd1–C14
Pd1–O4
Pd1–N1
Pd1–O5
N1–C5
C6–C5
C14–C6
O5–Pd1–O4
N1–Pd1–C14
C14–C6–C5–N1
2.077(4)
2.053(3)
2.002(3)
2.002(3)
1.351(5)
1.515(5)
1.545(5)
93.3(1)
Pd1–C15
Pd1–O2
Pd1–N1
Pd1–O1
N1–C1
C6–C1
C6–C15
O2–Pd1–O1
C15–Pd1–N1
C15–C6–C1–N1
2.078(8)
2.072(6)
2.001(6)
1.996(6)
1.35(1)
1.50(1)
1.55(1)
92.6(2)
82.6(3)
–32.2(9)
81.8(1)
33.0(4)
34.5(3)
the metal. The angle between the plane of the o-tolyl group complex, occurring more easily for cationic complexes than
ring and the coordination plane of the palladium atom is for neutral complexes. This reaction should be taken into
66.14°.
account when attempting to understand the degradation of
catalysts in processes in which nucleophiles are involved. In
this reaction a new C–C bond is formed and complexes
with acac displaying both O,O-acac and γ-acac coordina-
tion modes are synthesized. The mechanism for the forma-
tion of these complexes starts with the substitution of the
chlorido ligands with a chelating acetylacetonato ligand,
then a second acetylacetonate anion attacks the coordi-
nated imine to generate a nonisolated amido complex. This
amido complex undergoes a 1,3-CǞN proton migration
process in which protonation of the amido nitrogen occurs
(although other mechanisms can be proposed, these involve
less acidic protons and proceed via pathways of higher en-
ergy). Finally, the displacement of this nitrogen atom by a
carbanionic atom yields the final product.
Experimental Section
General Procedures: All manipulations were carried out in an ambi-
ent atmosphere. All solvents were purified by standard procedures
and distilled. Infrared spectra were obtained on a Nicolet Impact
410 over a frequency range of 4000 cm–1 to 400 cm–1, data collec-
tions were controlled with the Software OMNIC version 3.1. The
spectra were collected with samples prepared as KBr pellets. Deu-
Figure 4. Molecular structure of compound 3a. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30%
probability level.
1
terated solvents for NMR experiments were stored in a fridge. H,
Table 2. Selected bond lengths [Å], bond angles [°] and torsion
13C NMR spectra were recorded on a Varian INOVA 400 MHz
spectrometer and VARIAN MERCURY 300 MHz spectrometer
owned by the technological support team of the University of
Burgos. NMR experiments were carried out with the samples in
deuterated trichloromethane (CDCl3) and deuterated dimethyl sulf-
oxide ([D6]DMSO) with tetramethylsilane (TMS) as an internal
standard. X-ray data were obtained with a Monocrystal BRUKER
instrument equipped with the following parts: SMART APEX
CCD area detector, D8 goniometer, graphite monochromator and
a Kristalloflex K760–80 X-ray generator; this X-ray instrumen-
tation is owned by the technological support team of the University
of Burgos. Elemental analyses (C, H, N) were performed with a
Thermo EuroGlas TN/TS 3000. All reagents were purchased from
Sigma–Aldrich and were used without further purification. The li-
gands and compounds 1 were prepared according to published pro-
cedures.[14]
angles [°] for complex 3a.
Pd1–O2
Pd1–N1
Pd1–O1
Pd1–N2
N1–C5
C5–C6
N2–C6
O2–Pd1–O1
N1–Pd1–N2
N1–C5–C6–N2
1.971(3)
1.996(4)
1.980(4)
2.022(4)
1.365(7)
1.457(7)
1.273(7)
94.0(1)
80.8(2)
2.5(7)
Conclusions
In complexes of palladium with pyridine-imine ligands
nucleophilic attack by acetylacetonate on the carbonylic
atom of the imine is observed. This attack depends on the
Representative Procedure for Synthesis of Complexes 2: With a refer-
ence the amount of complex 1, a fivefold excess of potassium tert-
butoxide was stirred for 1 h with a fivefold excess of acetylacetone
steric nature of the ligand and on the ionic charge of the in dichloromethane. The complex 1 in dichloromethane was added
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J. V. Cuevas et al.
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to the solution. The mixture was stirred for 24 h and then filtered
through kieselgur. The resultant solution was concentrated by evap-
oration, and the product was precipitated from solution by the ad-
dition of a mixture of ether/hexane (1:1). The thus obtained prod-
uct was washed with diethyl ether and dried under high vacuum
(18 mbar). The atom numbering schemes for the complexes is as
shown below.
[Pd(acac){C5H4NCH(NHPh-2-OCH3)C(COCH3)2}] (2c): Starting
materials:
(30 mg, 0.060 mmol), acetylacetone (29.7 mg, 0.297 mmol), potas-
sium tert-butoxide (36.4 mg, 0.297 mmol); yield 19.1 mg
(0.037 mmol, 62%). 1H NMR (400 MHz, CDCl3): δ = 8.41 (d,
[Pd(acac){C5H4N(2-CH=N-Ph-2-OCH3)}]+[BF4 ]
–
3
3
3JHH = 5.5 Hz, 1 H, 6-H), 7.70 (dd, JHH = 7.7, JHH = 7.7 Hz, 1
3
3
H, 4-H), 7.29 (d, JHH = 7.9 Hz, 1 H, 3-H), 7.18 (dd, JHH = 7.7,
3JHH = 5.5 Hz, 1 H, 5-H), 6.85–6.78 (m, 2 H, Har), 6.73–6.67 (m,
2 H, Har), 5.74 (d, JHH = 9.9 Hz, 1 H, 18-H), 5.55 (d, JHH
=
3
3
10.0 Hz, 1 H, 7-H), 5.41 (s, 1 H, 10-H), 3.82 [s, 3 H, R (ortho-
OCH3)], 2.49 (s, 3 H, 13-H), 2.48 (s, 3 H, 17-H), 2.06 (s, 3 H, 8-
H), 2.00 (s, 3 H, 12-H) ppm. 13C NMR (100 MHz, CDCl3): δ =
206.44 (s, 1 C, C-16), 205.49 (s, 1 C, C-14), 187.51 (s, 1 C, C-9),
186.76 (s, 1 C, C-11), 169.82 (s, 1 C, C-2), 146.79 (s, 1 C, C-6 or
Cipso), 146.63 (s, 1 C, C-6 or Cispo), 139.13 (s, 1 C, C-4), 137.22 (s,
1 C, Car)), 122.92 (s, 1 C, C-3 or C-5), 122.50 (s, 1 C, C-3 or C-5),
121.43 (s, 1 C, Cortho), 117.29 (s, 1 C, Car), 110.31 (s, 1 C, Har),
109.15 (s, 1 C, Car), 100.83 (s, 1 C, C-10), 73.06 (s, 1 C, C-15), 62.13
(s, 1 C, C-18), 55.64 [s, 1 C, R (ortho-OCH3)], 31.81 (s, 1 C, C-17),
30.83 (s, 1 C, C-13), 27.76 (s, 1 C, C-8), 27.56 (s, 1 C, C-12) ppm.
Selected IR bands: 738, 1025, 1095, 1234, 1455, 1515, 1573, 1666,
2830, 2921, 3064, 3423 cm–1. C23H29N2O5Pd (519.89): calcd. C
53.13, H 5.62, N 5.39; found C 52.61, H 5.19, N 5.43.
[Pd(acac){C5H4NCH(NHPh-2-CH3)C(COCH3)2}] (2a): Starting
materials:
{Pd(Cl)2[C5H4N(2-CH=N-Ph-4-CH3)]}
(100.0 mg,
0.268 mmol), acetylacetone (134.0 mg, 1.340 mmol), potassium
tert-butoxide (163.8 mg, 1.340 mmol); yield 131.7 mg (0.261 mmol,
1
3
97%). H NMR (400 MHz, CDCl3): δ = 8.43 (d, JHH = 4.8 Hz, 1
[Pd(acac)(C5H4NCH{NHPh-4-OCH3}C(COCH3)2)] (2d): Starting
3
3
H, 6-H), 7.74 (dd, JHH = 7.8, JHH = 7.6 Hz, 1 H, 4-H), 7.30 (d,
materials:
[Pd(Cl)2{C5H4N(2-CH=N-Ph-4-OCH3)}]
(150 mg,
3JHH = 7.9 Hz, 1 H, 3-H), 7.20 (dd, JHH = 7.7, JHH = 4.8 Hz, 1
3
3
0.385 mmol), acetylacetone (193 mg, 1.925 mmol), potassium tert-
H, 5-H), 7.06 (m, 2 H, Har), 6.73–6.66 (m, 2 H, Har), 5.58 (d, JHH
3
butoxide (215 mg, 1.925 mmol); yield 76.6 mg (0.147 mmol, 38%).
= 10.0 Hz, 1 H, 18-H), 5.41 (s, 1 H, 10-H), 5.26 (d, 3JHH = 10.1 Hz,
1 H, 7-H), 2.48 (s, 3 H, 13-H), 2.47 (s, 3 H, 17-H), 2.13 [s, 3 H, R
(ortho-CH3)], 2.07 (s, 3 H, 8-H), 2.00 (s, 3 H, 12-H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 206.84 (s, 1 C, C-16), 206.62 (s, 1 C, C-
14), 187.57 (s, 1 C, C-11), 186.75 (s, 1 C, C-9), 169.62 (s, 1 C, C-
2), 146.73 (s, 1 C, C-6), 145.27 (s, 1 C, Cipso), 139.25 (s, 1 C, C-4),
130.93 (s, 1 C, Car), 127.52 (s, 1 C, Car), 122.97 (s, 1 C, C-3), 122.61
(s, 1 C, C-5), 122.15 (s, 1 C, Cortho), 117.90 (s, 1 C, Car), 109.58 (s,
1 C, Car), 100.88 (s, 1 C, C-10), 73.26 (s, 1 C, C-15), 62.57 (s, 1 C,
C-18), 31.81 (s, 1 C, C-13), 30.71 (s, 1 C, C-17), 27.73 (s, 1 C, C-
8), 27.56 (s, 1 C, C-12), 17.83 [s, 1 C, R (ortho-CH3)] ppm. Selected
IR bands: 667, 750, 808, 1025, 1076, 1145, 1238, 1444, 1519, 1567,
1668, 2923, 2971, 3068, 3320 cm–1. C23H29N2O4Pd (503.89): calcd.
C 54.82, H 5.80, N 5.56; found C 54.82, H 5.63, N 5.75.
3
1H NMR (400 MHz, CDCl3; TMS): δ = 8.41 (d, JHH = 5.0 Hz, 1
3
3
H, 6-H), 7.74 (dd, JHH = 7.9, JHH = 7.7 Hz, 1 H, 4-H), 7.42 (d,
3JHH = 8.0 Hz, 1 H, 3-H), 7.19 (dd, 3JHH = 7.7, 3JHH = 5.0 Hz, 1 H,
5-H), 6.77 (d, 3JHH = 8.9 Hz, 2 H, Hmeta), 6.65 (d, 3JHH = 9.0 Hz, 2
3
H, Hortho), 5.41 (d, JHH = 10.5 Hz, 1 H, 18-H), 5.40 (s, 1 H, 10-
H), 5.01 (d, 3JHH = 10.2 Hz, 1 H, 7-H), 3.75 [s, 3 H, R (para-CH3)],
2.46 (s, 3 H, 13-H), 2.45 (s, 3 H, 17 H), 2.06 (s, 3 H, 8-H), 2.00 (s,
3 H, 12-H) ppm. 13C NMR (100 MHz, CDCl3): δ = 206.02 (s, 2 C,
C-14, C-16), 186 (s, 2 C, C-9, C-11), 163.16 (s, 1 C, C-2), 152.63 (s,
1 C, Cipso), 146.68 (s, 1 C, C-6), 141.41 (s, 1 C, Cpara), 139.11 (s, 1
C, C-4), 123.07 (s, 1 C, C-3), 122.60 (s, 1 C, C-5), 115.37 (s, 2 C,
Cmeta), 114.28 (s, 2 C; Cortho), 100.83 (s, 1 C, C-10), 73.26 (s, 1 C,
C-15), 63.84 (s, 1 C, C-18), 55.96 [s, 1 C, R (para-CH3)], 31.78 (s,
1 C, C-17), 30.79 (s, 1 C, C-13), 27.41 (s, 1 C, C-8), 24.39 (s, 1 C.
C-12) ppm. Selected IR bands: 684, 781, 827, 1035, 1180, 1249,
1380, 1513, 1567, 1662, 2832, 3075, 3353 cm–1. C23H29N2O5Pd
(519.89): calcd. C 53.13, H 5.62, N 5.39; found C 52.73, H 5.52, N
5.72.
[Pd(acac){C5H4NCH(NHPh-4-CH3)C(COCH3)2}] (2b): Starting
materials:
[Pd(Cl)2{C5H4N(2-CH=N-Ph-4-CH3)}]
(73.8 mg,
0.197 mmol), acetylacetone (98.9 mg, 0.987 mmol), potassium tert-
butoxide (120.7 mg, 0.987 mmol); yield 92.4 mg (0.184 mmol,
1
3
93%). H NMR (400 MHz, CDCl3): δ = 8.41 (d, JHH = 5.5 Hz, 1
[Pd(acac){C5H4NCH(NHPh-4-CF3)C(COCH3)2}] (2e): Starting
3
3
H, 6-H), 7.73 (dd, JHH = 7.7, JHH = 7.7 Hz, 1 H, 4-H), 7.37 (d,
materials:
[Pd(Cl)2{C5H4N(2-CH=N-Ph-4-CF3)}]
(188 mg,
3JHH = 7.9 Hz, 1 H, 3-H), 7.19 (dd, 3JHH = 7.7, 3JHH = 5.5 Hz, 1 H,
0.485 mmol), acetylacetone (242.8 mg, 2.425 mmol), potassium
tert-butoxide (272.1 mg, 2.425 mmol); yield 207.6 mg (0.372 mmol,
5-H), 7.00 (d, 3JHH = 7.5 Hz, 2 H, Hmeta), 6.60 (d, 3JHH = 7.2 Hz, 2
3
1
3
H, Hortho), 5.48 (d, JHH = 9.9 Hz, 1 H, 18-H), 5.41 (s, 1 H, 10-H), 77%). H NMR (400 MHz, CDCl3): δ = 8.45 (d, JHH = 5.6 Hz, 1
3
3
3
5.14 (d, JHH = 10.0 Hz, 1 H, 7-H), 2.48 (s, 3 H, 13-H), 2.46 (s, 3
H, 6-H), 7.76 (dd, JHH = 7.8, JHH = 7.7 Hz, 1 H, 4-H), 7.42 (d,
H, 17-H), 2.24 [s, 3 H, R (para-CH3)], 2.06 (s, 3 H, 8-H), 2.00 (s,
3JHH = 8.4 Hz, 2 H, Hmeta), 7.29 (d, 3JHH = 7.9 Hz, 1 H, 3-H), 7.22
3 H, 12-H) ppm. 13C NMR (100 MHz, CDCl3): δ = 206.73 (s, 1 C,
(dd, 3JHH = 7.7, 3JHH = 5.5 Hz, 1 H, 5-H), 6.70 (d, JHH = 8.4 Hz,
3
13-C), 206.06 (s, 1 C, C-16), 187.55 (s, 1 C, C-11), 186.74 (s, 1 C, 2 H, Hortho), 5.61 (s, 1 H, 18-H), 5.61 (s, 1 H, 7-H), 5.42 (s, 1 H,
C-9), 169.81 (s, 1 C, C-2), 146.70 (s, 1 C, C-6), 144.92 (s, 1 C, Cipso),
139.12 (s, 1 C, C-4), 130.32 (s, 2 C, Cmeta), 127.34 (s, 1 C, Cpara),
10-H), 2.49 (s, 6 H, 13-H, 17-H), 2.07 (s, 3 H, 8-H), 2.01 (s, 3 H,
12-H) ppm. 13C NMR (100 MHz, CDCl3): δ = 206.30 (s, 1 C, C-
123.01 (s, 1 C, C-3), 122.60 (s, 1 C, C-5), 112.70 (s, 2 C, Cortho), 16), 206.10 (s, 1 C, C-14), 187.64 (s, 1 C, C-9), 186.68 (s, 1 C, C-
100.84 (s, 1 C, C-10), 73.10 (s, 1 C, C-15), 62.79 (s, 1 C, C-18), 11), 168.73 (s, 1 C, C-2), 149.67 (s, 1 C, Cipso), 144.99 (s, 1 C, C-6),
31.80 (s, 1 C, C-17), 30.78 (s, 1 C, C-13), 27.74 (s, 1 C, C-8), 27.56
(s, 1 C, C-12), 20.59 [s, 1 C, R (para-CH3)] ppm. Selected IR bands:
779, 1020, 1085, 1159, 1199, 1228, 1444, 1479, 1519, 1575, 1668,
2863, 2917, 3077, 3390 cm–1. C23H29N2O4Pd (503.89): calcd. C
54.82, H 5.80, N 5.56; found C 54.50, H 6.12, N 5.89.
139.38 (s, 1 C, C-4), 127.32 (s, 2 C, Cmeta), 126.34 (s, 1 C, Cpara),
122.90 (s, 1 C, C-5), 122.68 (s, 1 C, C-3), 119.90 [s, 1 C, R (para-
CF3)], 111.64 (s, 2 C, Cortho), 100.94 (s, 1 C, C-10), 72.96 (s, 1 C,
C-15), 61.87 (s, 1 C, C-18), 31.81 (s, 1 C, C-13), 30.90 (s, 1 C, C-
17), 27.68 (s, 1 C, C-12), 27.52 (s, 1 C, C-8) ppm. Selected IR bands:
2264
www.eurjic.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 2259–2266

Nucleophilic Attack at Coordinated Imines
688, 713, 771, 829, 1025, 1062, 1101, 1164, 1191, 1249, 1386, 1479,
1519, 1581, 1668, 2925, 2975, 3073, 3411 cm–1. C23H26F3N2O4Pd
(557.86): calcd. C 49.52, H 4.70, N 5.02; found C 48.92, H 4.57, N
5.25.
bands: 669, 717, 782, 1033, 1058, 1236, 1427, 1488, 1519, 1556,
2923, 3037, 3075 cm–1. C18H19BF4N2O2Pd (488.58): calcd. C 44.25,
H 3.92, N 5.73; found C 43.05, H 4.13, N 6.21.
–
[Pd(acac){C5H4N(2-CH=N-Ph-2-OCH3)}]+[BF4 ] (3c): Starting
[Pd(acac){C5H4NCH(NHPh-2,6-CH3)C(COCH3)2}] (2f): Starting
materials: 1c (100 mg, 0.256 mmol), Tl(acac) (74.6 mg,
0.256 mmol), TlBF4 (75.0 mg, 0.256 mmol); yield 76.2 mg
(0.151 mmol, 59%). 1H NMR (300 MHz, CDCl3): δ = 8.71 (s, 1 H,
–
materials:
[Pd(acac){C5H4N(2-CH=N-Ph-2,6-CH3)}]+[BF4 ]
(98.2 mg, 0.262 mmol), acetylacetone (131.6 mg, 1.314 mmol), po-
tassium tert-butoxide (147.45 mg, 1.314 mmol); yield 95.2 mg
(0.183 mmol, 70%). 1H NMR (400 MHz, CDCl3): δ = 8.43 (d,
3
3
13-H), 8.58 [d, J(H,H) = 5.5 Hz, 1 H, 6-H], 8.52 [dd, J(H,H) =
3
3
7.7, J(H,H) = 7.7 Hz, 1 H, 3-H], 8.28 [d, J(H,H) = 7.7 Hz, 1 H,
3
3
3JHH = 5.8 Hz, 1 H, 6-H), 7.74 (dd, JHH = 7.9, JHH = 7.7 Hz, 1
3
3
4-H], 7.83 [dd, J(H,H) = 7.7, J(H,H) = 5.5 Hz, 1 H, 5-H], 7.41–
7.34 (m, 2 H, Har), 7.10–6.95 (m, 2 H, Har), 5.51 (s, 1 H, 10-H),
3.88 [s, 3 H, R (ortho-OCH3)], 2.19 (s, 3 H, 8-H), 1.87 (s, 3 H, 12-
3
3
H, 4-H), 7.32 (d, JHH = 7.7 Hz, 1 H, 3-H), 7.19 (dd, JHH = 7.7,
3JHH = 5.8 Hz, 1 H, 5-H), 6.86–6.69 (m, 3 H, Hmeta, Hpara), 5.77
3
3
1
(d, JHH = 10.2 Hz, 1 H, 18-H), 5.58 (d, JHH = 10.3 Hz, 1 H, 7-
H), 5.42 (s, 1 H, 10-H), 2.51 (s, 6 H, 12-H, 17-H), 2.31 [s, 6 H, R
(di-ortho-CH3)], 2.08 (s, 3 H, 8-H), 2.02 (s, 3 H, 12-H) ppm. Se-
lected IR bands: 3396, 3025, 2919, 2852, 1671, 1573, 1519, 1228,
1415, 1120, 1199, 1025 cm–1. C24H28N2O4Pd·0.5CH2Cl2 (557.38):
calcd. C 52.79, H 5.24, N 5.03; found C 52.07, H 5.25, N 4.80.
H) ppm. H NMR (300 MHz, [D6]DMSO): δ = 8.86 (s, 1 H, 13-
H), 8.62 (s, 1 H, 6-H), 8.49 (s, 1 H, 4-H), 8.29 (s, 1 H, 3-H), 8.03
(s, 1 H, 5-H), 7.46 (m, 2 H, Har), 7.17 (m, 2 H, Har), 5.73 (s, 1 H,
10-H), 3.85 [s, 1 H, R (ortho-OCH3)], 2.21 (s, 1 H, 8-H), 1.86 (s, 1
H, 12-H) ppm. Selected IR bands: 771, 1060, 1257, 1434, 1519,
1556, 2921, 3008, 3029, 3073 cm–1. C18H19BF4N2O3Pd (504.58):
calcd. C 42.85, H 3.80, N 5.55; found C 44.92, H 4.43, N 5.36.
[Pd(acac){C5H4NCH(NHPh-2-iPr)C(COCH3)2}] (2g): Starting ma-
terials: [Pd(acac){C5H4N(2-CH=N-Ph-2-iPr)}]+[BF4 ] (200 mg,
–
–
[Pd(acac){C5H4N(2-CH=N-Ph-2,6-CH3)}]+[BF4 ] (3f): Starting
0.387 mmol), acetylacetone (193.0 mg, 1.935 mmol), potassium
tert-butoxide (236.0 mg, 1.935 mmol); yield 170.1 mg (0.319 mmol,
materials: 1f (100 mg, 0.258 mmol), Tl(acac) (75.2 mg,
0.258 mmol), TlBF4 (75.3 mg, 0.258 mmol); yield 104.8 mg
(0.209 mmol, 81%). 1H NMR (300 MHz, [D6]DMSO): δ = 8.82 (s,
1 H, 13-H), 8.66 [d, 3J(H,H) = 5.5 Hz, 1 H, 6-H], 8.51 [dd, 3J(H,H)
1
3
83%). H NMR (400 MHz, CDCl3): δ = 8.44 (d, JHH = 4.9 Hz, 1
3
3
H, 6-H), 7.72 (dd, JHH = 7.7, JHH = 7.7 Hz, 1 H, 4-H), 7.32 (d,
3JHH = 7.9 Hz, 1 H, 3-H), 7.19 (dd, JHH = 7.7, JHH = 4.9 Hz, 1
3
3
3
= 7.8, J(H,H) = 7.7 Hz, 1 H, 4-H], 8.25 [d, 3J(H,H) = 7.7 Hz, 1
H, 5-H), 7.17 (m, 1 H, Har), 7.05 (m, 1 H, Har), 6.72 (m, 2 H, Har),
H, 3-H], 8.07 [dd, 3J(H,H) = 7.7, 3J(H,H) = 5.5 Hz, 1 H, 5-H],
7.24–7.16 (m, 3 H, Har), 5.72 (s, 1 H, 10-H), 2.32 [s, 3 H, R (di-
ortho-CH3)], 2.21 (s, 3 H, 8-H), 1.73 (s, 3 H, 12-H) ppm. Selected
IR bands: 777, 1062, 1186, 1230, 1434, 1475, 1519, 1556, 2921,
2969, 3039 cm–1. C19H21BF4N2O2Pd (502.61): calcd. C 45.40, H
4.21, N 5.57; found C 42.69, H 3.69, N 5.59.
3
3
5.60 (d, JHH = 10.0 Hz, 1 H, 18-H), 5.51 (d, JHH = 10.0 Hz, 1 H,
7-H), 5.42 (s, 1 H, 10-H), 2.85 [sept, JHH = 6.7 Hz, 1 H, R (ortho-
3
iPr-H)], 2.49 (s, 3 H, 13-H), 2.46 (s, 3 H, 17-H), 2.06 (s, 3 H, 8-H),
2.00 (s, 3 H, 12-H), 1.19 [d, 3JHH = 6.8 Hz, 6 H, R (ortho-iPr-CH3)]
ppm. 13C NMR (100 MHz, CDCl3): δ = 206.81 (s, 1 C, C-14),
206.57 (s, 1 C, C-16), 187.57 (s, 1 C, C-9), 186.77 (s, 1 C, C-11),
169.67 (s, 1 C, C-2), 149.9 (s, 1 C, Cipso), 146.77 (s, 1 C, C-6), 139.18
(s, 1 C, C-4), 132.71 (s, 1 C, Cortho), 127. (s, 1 C, Car), 125.71 (s, 1
C, C-5), 122.91 (s, 1 C, Car), 122.71 (s, 1 C, C-3), 118.0 (s, 1 C,
Car), 109.96 (s, 1 C, Car), 100.84 (s, 1 C, C-10), 73.08 (s, 1 C, C-
15), 62.79 (s, 1 C, C-18), 31.88 (s, 1 C, C-13), 30.72 (s, 1 C, C-17),
29.58 [s, 1 C, R (ortho-iPr-CH3)], 27.58 (s, 1 C, C-12), 27.48 [s, 1
C, R (iPr-C)], 25.67 (s, 1 C, C-8), 22.23 [s, 1 C, R (ortho-iPr-CH3)]
ppm. Selected IR bands: 622, 748, 800, 842, 1024, 1097, 1263, 1446,
1515, 1575, 1673, 2854, 2923, 2960, 3073, 3434 cm–1.
C25H30N2O4Pd (528.92): calcd. C 56.77, H 5.72, N 5.30; found C
56.61, H 5.59, N 5.43.
[Pd(acac){C5H4N(2-CH=N-Ph-2-iPr)}]+[BF4 ] (3g): Starting mate-
–
rials: 1g (100 mg, 0.249 mmol), Tl(acac) (72.3 mg, 0.249 mmol),
TlBF4 (72.7 mg, 0.249 mmol); yield 79.5 mg (0.153 mmol, 62%).
1H NMR (300 MHz, CDCl3): δ = 8.65 (s, 1 H, 13-H), 8.61 [d,
3J(H,H) = 5.4 Hz, 1 H, 6-H], 8.58 [d, 3J(H,H) = 7.8 Hz, 1 H, 3-
H], 8.32 [dd, 3J(H,H) = 7.9, 3J(H,H) = 7.9 Hz, 1 H, 4-H], 7.88 [dd,
3
3
3J(H,H) = 7.8, J(H,H) = 5.5 Hz, 1 H, 5-H], 7.42 [ddd, J(H,H) =
8.1, 3J(H,H) = 7.4, J(H,H) = 1.5 Hz, 1 H, Har], 7.36 [dd, 3J(H,H)
3
= 7.8, 3J(H,H) = 1.2 Hz, 1 H, Har], 7.24 [ddd, 3J(H,H) = 7.8,
3
3J(H,H) = 7.8, J(H,H) = 1.2 Hz, 2 H, Har], 5.50 (s, 1 H, 10-H),
3.60 [s, 3 H, R (iPr-H)], 2.19 (s, 3 H, 8-H), 1.79 (s, 3 H, 12-H), 1.30
[s, 3 H, R (iPr-CH3)], 1.12 [s, 3 H, R (iPr-CH3)] ppm. Selected IR
bands: 779, 1060, 1236, 1278, 1434, 1446, 1519, 1556, 2964,
3033 cm–1. C20H23BF4N2O2Pd (516.63): calcd. C 46.50, H 4.49, N
5.42; found C 45.78, H 4.39, N 5.74.
Representative Procedure for the Synthesis of Complexes 3: To a
solution of complex 1 in acetone was added the equivalent amount
of Tl(acac) and TlBF4, both in acetone. The mixture was stirred for
24 h. Then the precipitated TlCl was removed by filtration through
kieselgur, and the filtrate was evaporated. The substance obtained
after evaporation was dissolved in dichloromethane. This solution
was again filtered through kieselgur, and the solvent partially evap-
orated in vacuo. The final product was precipitated from solution
by the addition of hexane. The thus obtained product was dried
under high vacuum (18 mbar).
X-ray Structure Determination: Crystallographic data for com-
pounds 2a, 2d, 2f and 3a were collected at 173 K on a Bruker
SMART CCD diffractometer, equipped with an area detector, and
with Mo-Kα radiation (λ = 0.71073 Å).[19] Integrated intensities[20]
were obtained from several series of exposures, each exposure
covering 0.3° in ω, and the total datasets comprised complete
[Pd(acac){C5H4N(2-CH=N-Ph-2-CH3)}]+[BF4 ] (3a): Starting ma- spheres of reciprocal space. Absorption corrections were applied
–
terials: 1a (100.0 mg, 0. 268 mmol), Tl(acac) (78.0 mg,
based on multiple and symmetry equivalent measurements.[21] The
0.268 mmol), TlBF4 (78.5 mg, 0.268 mmol); yield 66.6 mg structures were solved by direct methods and refined by least-
(0.136 mmol, 51%). 1H NMR (400 MHz, [D6]DMSO): δ = 8.81 (s, squares methods on weighted F2 values for all reflections.[22] All
1 H, 13-H), 8.63 [d, 3J(H,H) = 5.5 Hz, 1 H, 6-H], 8.50 [dd, 3J(H,H)
non-hydrogen atoms were assigned anisotropic displacement pa-
rameters and refined without positional constraints. All hydrogen
atoms were constrained to ideal geometries and refined with fixed
3
= 7.8, J(H,H) = 7.7 Hz, 1 H, 4-H], 8.28 [d, 3J(H,H) = 7.7 Hz, 1
H, 3-H], 8.04 [dd, 3J(H,H) = 7.7, 3J(H,H) = 5.5 Hz, 1 H, 5-H],
7.40–7.33 (m, 4 H, Har), 5.74 (s, 1 H, 10-H), 2.42 [s, 3 H, R (para- isotropic displacement parameters. Refinements proceeded
CH3)], 2.21 (s, 3 H, 8-H), 1.81 (s, 3 H, 12-H) ppm. Selected IR
smoothly to give the residual values shown in Table S1 (See Sup-
Eur. J. Inorg. Chem. 2012, 2259–2266
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2265

J. V. Cuevas et al.
FULL PAPER
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CCDC-859570 (for 2a), -859571 (for 2d), -859572 (for 2f) and
-859573 (for 3a) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
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Supporting Information (see footnote on the first page of this arti-
cle): Table summarizing the X-ray crystallography data collection
and structure refinement data for compounds 2a, 2d, 2f and 3a
(Table S1). DFT optimization information for model structures of
Ia, Ib and Ic, and DFT estimations of the energetic barriers for
proton migrations.
Acknowledgments
The authors gratefully acknowledge the Junta de Castilla y León
(BU008A09) and Consejería de Educación de la Junta de Castilla
y León (GR78) for financial support. We also acknowledge the
Parque Científico Tecnológico (PCT) of the Universidad de Burgos
for technical support.
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Received: December 23, 2011
Published Online: March 13, 2012
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