Metal-assisted ring-closing/opening process of a chiral tetrahydroquinazoline

Article abstract of DOI:10.1021/ic2017038

The ring-chain tautomerism of a 2-aryl-1,2,3,4-tetrahydroquinazoline has been exploited to induce reversible changes in the aminal-imine equilibrium, as desired, by coordination of a suitable metal ion. This process was studied by NMR and UV-vis spectrosc

Full text of DOI:10.1021/ic2017038

Article
pubs.acs.org/IC
Metal-Assisted Ring-Closing/Opening Process of a Chiral
Tetrahydroquinazoline
Ana M. García-Deibe,† Jesus Sanmartín-Matalobos,*,† Concepcion Gonzalez-Bello,‡ Emilio Lence,‡
́
́
́
Cristina Portela-García,† Luis Martínez-Rodríguez,† and Matilde Fondo†
†Departamento de Química Inorgan
15782 Santiago de Compostela, Spain
‡Centro Singular de Investigacion
́
en Química Biologica y Materiales Moleculares (CIQUS), Universidad de Santiago de Compostela,
́
ica, Facultad de Química, Universidad de Santiago de Compostela,
́
15782 Santiago de Compostela, Spain
S
* Supporting Information
ABSTRACT: The ring−chain tautomerism of a 2-aryl-1,2,3,4-tetrahydroquinazo-
line has been exploited to induce reversible changes in the aminal−imine
equilibrium, as desired, by coordination of a suitable metal ion. This process was
studied by NMR and UV−vis spectroscopies, X-ray crystallography, and molecular
modeling approach. The results obtained show that the imine H2Li undergoes a
selective ring-closing reaction upon complexation with Ni2+. As a result, complexes
of the type Ni(HLa)2 are obtained, whose chirality arises from the chiral ligand H2La
and the helicity of the structure. Hence, helical enantiomers form the following
racemates: [Δ-C(R,R)N(S,S),Λ-C(S,S)N(R,R)]-Ni(HLa)2·2HOAc and [Δ,Λ-C-
(S,R)N(R,S)]-Ni(HLa)2·4MeOH. In contrast to the situation observed for Ni2+,
the cyclic tautomer of the ligand, H2La, undergoes a selective ring-opening reaction
upon complex formation with Pd2+, ultimately yielding Pd(HLi)2·MeOH, in which
the open-chain imine ligand is bidentate through the N,O donor set of the quinoline
residue. Density functional theory calculations were conducted to provide insight into the different behavior of both coordinated
metals (Ni2+ and Pd2+) and to propose a mechanism for the metal-assisted opening/closing reaction of the tetrahydroquinazoline
ring.
ring-closing) and going apart (imidazolidine ring-opening).
Which direction the system will go depends on the relative
importance of the acidity of Cδ+ and Mn+ centers. Weak Lewis
acids (such as Fe2+, Co2+, and Cu2+) are incapable (or only
partly capable) of opening the imidazolidine ring, whereas
stronger Lewis acids (e.g., Fe3+ and Zn2+) can readily do it. In
contrast, Tuchagues et al.6 conclude that the metal size plays a
prominent role in shifting the ligand equilibrium toward the
tautomeric form most appropriate to each specific cation. LS
Fe2+ has a small enough size (75 pm) to stabilize the imine
isomer in its complex, while the size of Ni2+ (83 pm) is probably
too large for allowing coordination of the imine tautomer, and
thus it stabilizes the imidazolidine tautomer.
INTRODUCTION
■
Imines and related compounds that contain a carbon−nitrogen
double bond are very attractive systems because they can easily
undergo reversible reactions under certain conditions. For
instance, imines can undergo E−Z isomerization reactions,
nucleophilic additions, hydrolysis, transamination reactions,
tautomerism, aza Diels−Alder reactions, etc. Among those, we
became interested in a particular tautomerism that involves
ring-closing/opening reactions by reversible cyclization of
imines.1−8
In the absence of metal ions, the formation of imidazoli-
dine,1,6 benzimidazoline,5 and hexahydropyrimidine6 rings from
adequate imines occurs, as a result of an intramolecular
nucleophilic addition of the amino Nδ‑ atom to the electrophilic
Cδ+ center of the imine. As a result, the sp2-hybridized imine
carbon site becomes an sp3-hybridized benzimidazoline,
imidazolidine, and hexahydropyrimidine center, and no extra
gain in the conjugation energy exists. Owing to the absence of
the conjugation effect, the ring-opening is facilitated and readily
observed upon complex formation with Fe3+, Fe2+, Ni2+, Cu2+,
and Zn2+ ions depending on the aminal ring.
Our interest in novel chiral ligands7,9 led us to explore the
reaction between 8-hydroxyquinoline-2-carboxaldehyde and
N-(2-aminobenzyl)-4-methylbenzenesulfonamide in a 1:1 molar
ratio, which could result in a chiral tetrahydroquinazoline H2La
or in an achiral imine H2Li (Scheme 1). We are also interested
in investigating the factors influencing the ring-closing/opening
process leading to H2La or H2Li, and particularly whether metal
coordination could be used to direct not only a ring-opening
reaction, but also a ring-closing one. These processes involving
Boca
̌
et al.1 have postulated that, in the presence of metal
ions, the acidity of the attacking metal ion competes with the
acidity of the −CN− site, so that there is a balance between
a Nδ‑ atom and Cδ+ center coming together (imidazolidine
Received: May 24, 2011
Published: January 23, 2012
© 2012 American Chemical Society
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a
Scheme 1. Open-Chain Tautomer H2Li en Route to the
Final Thermodynamically Favored Aminal Ring Tautomer
H2La
Scheme 2. Proposed Mechanism for the Formation of the
Imine H2Li and 1,2,3,4-Tetrahydroquinazoline H2La
a
The numbering scheme included was used for the assignment of the
NMR signals, which is the same scheme used in the determination of
the crystal structure for ease of understanding.
Ni2+ and Pd2+ ions have been studied by UV−vis and NMR
spectroscopies as well as X-ray crystallography. Spectroscopic
monitoring of the reactions here studied in conjunction with
DFT calculations lead us to propose a mechanism for the
closing/opening of the tetrahydroquinazoline ring.
RESULTS AND DISCUSSION
■
group, but that the four potential donor atoms of H2Li are exo
orientated in two separate binding sites, N,O and N,N, as
shown in Scheme 1. In this exo conformation, H2Li could be
stabilized by an intramolecular N−H···N bond, the existence of
which was deduced from the ν(N−H) and ν(CNimine) bands
observed in the infrared spectrum. On the other hand, and in
contrast to H2Li, cross-peaks between Hax-14···H-3 and
OH···NH show that the three potential donor atoms of H2La
can offer an N,N,O binding site.
In order to understand the thermodynamic preference of the
cyclic compound H2La relative to the open-chain one, H2Li,
geometry optimizations and energy calculations in vacuum
were performed using the Gaussian 09W17 program package at
density functional theory (DFT) level by means of the hybrid
M06 functional18,19 using the standard 6-31G(d) basis set. A
polarizable continuum20 solvation model (methanol as solvent)
was also used for energy calculations to take into account the
solvent effect, but similar trends were found both in vacuum
and methanol (see Supporting Information). According to
these calculations in methanol, the 1,2,3,4-tetrahydroquinazo-
line H2La is 7.93 kcal mol−1 more stable than the most stable
conformation of imine H2Li. This energy difference could
be substantial enough to explain the total predominance of the
cyclic compound over the open-chain imine form when the
reaction time exceeds 4 h and 30 min. Moreover, the calculated
ΔG value in methanol for the cyclization reaction of H2Li to
give H2La (see Supporting Information) is also energetically
favorable (−5.66 kcal mol−1).
The design of imine H2Li for this study was based on the fine
coordinating ability of the 8-hydroxyquinoline residue, which
we have previously investigated,10 as well as on the varied
coordination alternatives offered by its aminal derivative H2La
(Scheme 1). The open-chain tautomer H2Li could provide up
to four donor atoms (usually O,N bidentate and O,N,N,N
tetradentate), whereas the cyclic tetrahydroquinazoline deriv-
ative can simultaneously coordinate a metal center with an
O,N,N donor set at most. We selected for this study a
borderline Lewis acid,11 Ni2+ (η = 8.5 eV), and a soft Lewis
acid, Pd2+ (η = 6.8 eV), that have been widely used to obtain
octahedral12 and square planar complexes,13 respectively. It
must be noted that the metal size of Ni2+ in an octahedral field
(83 pm) is slightly larger than the Pd2+ one in a square planar
field (78 pm).14
Free Ligand Ring-Opening/Closing. Condensation of
the selectively functionalized N-(2-aminobenzyl)-4-methylben-
zenesulfonamide15 with 8-hydroxyquinoline-2-carboxaldehyde
was spectroscopically monitored in order to understand the 6-
endo-trig cyclization process (Scheme 2).16 Tetrahydroquinazo-
line H2La could result from the intramolecular nucleophilic
addition of the sulfonamide N atom to the imine.1,5,6
It can be seen from Figure 1 that the imine H2Li is rapidly
formed first, but already the presence of the chiral aminal H2La
is evident. The maximum imine/aminal ratio appears to be
achieved after a period of about 1 h (ca. 4.5:1 ratio). After this
time, the imine readily evolves to the tetrahydroquinazoline
derivative, and only half an hour later an equimolar ratio is
obtained. After a few hours the imine has virtually disappeared.
A combination of bidimensional spectroscopic correlations
(HMQC, HMBC, COSY, and NOESY) and NOE experiments
enabled good identification of H2Li and H2La in solution (see
Supporting Information). These experiments were used to
elucidate the possible conformations of H2Li and H2La in
solution, and sketches of the conformations are depicted in
Scheme 1. Thus, on one hand, the observation of the inversion
of imine H-9, enhancing exclusively H-10 (4.7%) and not H-3,
indicates not only the typical E configuration of the imine
Metal-Assisted Ring-Opening/Closing Reaction. First,
the behavior of Pd2+ in the tetrahydroquinazoline/imine ring-
opening/closing reaction was studied. Treatment of tetrahy-
droquinazoline H2La or imine H2Li with Pd(OAc)2 in methanol
afforded a palladium complex that was identified as Pd(HLi)2
by a combination of bidimensional spectroscopic correlations
(HMQC, HMBC, COSY, and NOESY). These studies led us
to conclude that the coordinative environment of the Pd2+ ion
is square planar and the imine behaves as monoanionic. The
observation of the sulfonamide NH signal coupled to the
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Figure 1. Sections of the 1H NMR spectra in DMSO-d6 corresponding to the successive samples of crude material extracted from the condensation
reaction between N-(2-aminobenzyl)-4-methylbenzenesulfonamide and 8-hydroxyquinoline-2-carboxaldehyde. The signals at ca. 10 and 9.4 ppm
correspond to phenolic protons of H2Li and H2La, respectively. In all the spectra, integration values refer to the phenol signal of H2Li, which is
considered as 1.00 for ease of comparison.
methylene protons demonstrates the monoanionic behavior of
the ligand (see Supporting Information). As occurs in the free
imine H2Li, the observed cross-peaks between protons H-10
and H-9 indicate that the four donor atoms are in two separate
binding sites (N,O and N,N). NOESY cross-peaks due to
alternative conformations were not detected. Moreover, the
observed cross peaks between H-10 and H-7 indicate the close
proximity of a benzylidene ring to a quinoline one.
The spectroscopic monitoring of the reaction between
tetrahydroquinazoline H2La and Pd(OAc)2 in a 2:1 molar
ratio (Figure 2) showed that Pd(Li) is rapidly formed first. In
Pd(Li), which crystallized as Pd(Li)·CH2Cl2, the imine H2Li
acts as an O,N,N,N-donor. During the first half hour of the
reaction, there is no evidence for the formation of Pd(HLi)2.
After this period, Pd(Li) gradually evolves into Pd(HLi)2 until it
finally disappears. During the reaction, a substantial amount of
cyclic ligand H2La (without any evidence for H2Li) remains in solu-
tion, a situation that is due to the acidic media (pH about 5.5)
caused by the acetic acid that arises from the formation of the
metal complexes. After 2 h under reflux, Pd(HLi)2 could be
isolated and subsequently characterized. It should be noted that
a solution of Pd(HLi)2 under reflux readily yielded Pd(Li) and
the tetrahydroquinazoline ligand H2La, without any evidence
for the formation of H2Li, thus showing the reversibility of the
Pd(Li) + H2La ↔ Pd(HLi)2 equilibrium. In contrast, no evidence
for reversibility was detected after 2 h under reflux at pH 5.5 for
the process H2La + Pd2+ → Pd(Li).
In contrast to the results obtained for Pd2+, the open-chain
ligand H2Li, undergoes a selective ring-closing reaction upon
complexation with Ni2+ in the crystallized octahedral complexes
Ni(HLa)2·4MeOH and Ni(HLa)2·2HOAc, in which the two
units of the chiral cyclic ligand act as O,N,N tridentate donors.
It should be noted that the formation of Ni(HLa)2 complexes
did not depend on the ligand added, i.e., H2Li or H2La. In fact,
Ni(HLa)2 is quickly formed even on using imine H2Li as the
starting free ligand.
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Figure 2. Sections of the 1H NMR spectra in DMSO-d6 corresponding to the successive samples of crude material extracted from the reaction under
reflux of tetrahydroquinazoline H2La and Pd(OAc)2 in a 2:1 molar ratio. The azomethine signals around 9.33(s) and 8.66(s) ppm correspond to
Pd(HLi)2 and Pd(Li), respectively. The integration value for the phenol signal of H2La at 9.38(s) ppm was considered as 1.00 in all the spectra for
ease of comparison.
The UV−vis absorption monitoring of the reaction at room
temperature between H2Li and Ni(OAc)2·4H2O in a 1:1 molar
ratio (Figure 3, top) shows that the reaction goes through the
formation of Ni(Li)·MeOH en route to Ni(HLa)2·4MeOH.
Further evidence of the formation of Ni(Li)·MeOH was found
in the infrared spectrum of the isolated compound that shows
the characteristic ν(CNimine) band and the absence of the
ν(N−H) band (see Supporting Information). Figure 3, top,
clearly shows that the absorbance of the characteristic band of
Ni(Li)·MeOH (at about 304 nm) is decreasing gradually from
start to finish. During 30 min of reaction the spectra show a
decrease of the absorbance for the band at 248 nm that is
accompanied by a considerable increase of absorbance for the
band at 272 nm, which are signs that Ni(HLa)2 is forming
and H2Li is consuming. Besides the mentioned bands that may
be assigned to intraligand transitions, the electronic spectra
exhibit two weak bands characteristic for the d−d transitions
at about 380 nm (ν3) and 510 nm (ν2), as expected for six-
coordinated octahedral nickel(II) complexes.21 The monitoring
of the reaction at room temperature between H2La and
Ni(OAc)2·4H2O in a 2:1 molar ratio (Figure 3, bottom) also
shows the gradual formation of Ni(HLa)2, but in this case
without any evidence for Ni(Li)·MeOH.
Computational Studies: Proposed Mechanism. In
order to gain some insight into the ring-opening/closing
processes that the tautomers H2La/H2Li undergo by complex-
ation to Pd2+ and Ni2+ by forming Pd(HLi)2 and Ni(HLa)2,
respectively, DFT calculations were performed, as described
below.
The relative Gibbs free energy differences for the obtained
Pd(HLi)2 versus other square planar Pd2+ complexes, i.e.
Pd(HLa)(HLi) and Pd(HLa)2, considering both possible
enantiomers of H2La (R or S) were first studied (Figure 4
and Supporting Information). Only a trans disposition of the
coordinated ligands was considered, since a cis disposition
appeared strongly disfavored in any case. Unexpectedly, these
calculations predicted that Pd(HLa)2 complexes are the more
stable ones, with little difference found between (R,R)- and
(R,S)-stereoisomers (Figure 4). The difference in Gibbs free
energy (ΔG) between the experimentally obtained complex
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The minimum energies for the most stable conformers of
Ni2+ complexes with octahedral and square planar geometries
have been calculated, before the calculation of the relative
Gibbs free energy difference. The results indicate a clear
preference for an octahedral geometry over a square planar one,
with energy differences of over 19 kcal mol−1 (see Supporting
Information). The relative Gibbs free energy difference for the
most stable stereoisomers of octahedral Ni(HLa)2 complexes
was calculated combining R and S enantiomers of the
monodeprotonated cyclic ligand (HLa)−, as well as Ni(HLi)2
and Ni(HLa)(HLi) (Figure 5). Among the possible octahedral
Figure 5. Relative Gibbs free energy for the most stable conformers
calculated for octahedral nickel(II) complexes in methanol (from left
to right): Λ-C(S,R)N(R,S)-Ni(HLa)2, Δ-C(S,S)N(R,R)-Ni(HLa)2,
Δ-C(R,R)N(S,S)-Ni(HLa)2, Ni(HLa)(HLi), and Ni(HLi)2 (see also
Supporting Information for more details). In the figure only the
chirality of the N donor atom has been indicated to simplify and
reduce the size of the labels.
Figure 3. UV−vis spectroscopic monitoring of the reaction between
H2Li/H2La and Ni(OAc)2·4H2O (a) in 1:1 and (b) 2:1 molar ratios.
Electronic spectra of H2Li/H2La (pink line), Ni(Li)·MeOH (green
line), and Ni(HLa)2·4MeOH (black line) are included for comparison.
complexes, coordination to the N,N,O donor set provided by
cyclic H2La is clearly favored in comparison to that provided by
H2Li (over 17 kcal mol−1). The most stable species are both of
the crystallized octahedral nickel(II) complexes, under the form
of Ni(HLa)2·4MeOH and Ni(HLa)2·2HOAc.
Spectroscopic monitoring of the reactions between H2La/
H2Li and Pd2+/Ni2+ in 1:1 and 2:1 molar ratios gave important
information that in conjunction with theoretical calculations
have been considered to propose a mechanism for the closing/
opening of the tetrahydroquinazoline ring. First, the final
products are the same either using the open-chain ligand H2Li
or the closed one H2La. The remaining free ligand in solution is
always the closed-chain ligand H2La, with any evidence for H2Li.
The use of a 1:1 molar ratio allows us to obtain complexes of
the type M(Li) with both metal ions. Finally, the differences in
the behaviors of both metals emerge when a 2:1 molar ratio is
used, affording Pd(HLi)2 in one case and Ni(HLa)2 in the
other. Moreover, during the reactions in 2:1 molar ratio, Pd(Li)
was also observed en route to Pd(HLi)2, but any evidence for
Ni(Li) en route to Ni(HLa)2 was found.
Figure 4. Relative Gibbs free energy for the most stable calculated
conformers of (R,S)-Pd(HLa)2, (R,R)-Pd(HLa)2, Pd(HLi)(HLa), and
Pd(HLi)2 in methanol (left to right).
Given all the above, for a 1:1 molar ratio, the reaction would
start with the formation of M(Li) that then evolves to Pd(HLi)2
or Ni(HLa)2. For a 2:1 molar ratio, when the metal is Pd2+, the
reaction pathway would be the same as for a 1:1 molar ratio,
while for Ni2+ the formation of Ni(HLa)2 would follow an
Pd(HLi)2 and the R,S-stereoisomer of Pd(HLa)2 (the most stable
one) is 7.2 kcal mol−1. Moreover, Pd(HLi)2 is 1.5 kcal mol−1 more
stable than Pd(HLa)(HLi).
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alternative path that will be discussed below. A plausible
reaction mechanism is shown in Scheme 3. The key step of the
M(HOAc)(La) (10.85 kcal mol−1 for Pd2+ and 15.55 kcal mol−1
for Ni2+) leads us to propose an associative mechanism.
Attempts to calculate the activation energy involved in the
subsequent ring-opening reaction and displacement of acetic
acid failed because the intermediates rapidly evolve to the final
M(Li) complexes, which is coherent with very low activation
energies.
Scheme 3. General Proposed Mechanism for the Formation
of Complexes of the Types M(HLi)2 and M(HLa)2
Once M(Li) complexes are formed, their coordination with
the free closed-chain ligand in solution, H2La, would afford the
key intermediate complexes M(HLi)(HLa). Examining the
structure of the most stable conformer of both complexes, the
octahedral Ni(HLi)(HLa) (Figure 7c) and the square planar
Pd(HLi)(HLa) (Figure 7d) suggests that the different
coordination of Ni2+ and Pd2+ in their complexes might be
the key to the further evolution of these intermediate
complexes. Figure 7c shows that in Ni(HLi)(HLa) the imine
moiety is coordinated to Ni2+ and the imine carbon atom is
located at 3.0 Å from the sulfonamide N atom. So, this nitrogen
is in the appropriate conformation to perform an intramolecular
nucleophilic addition to the imine carbon atom, which is
activated by the nickel ion. This agrees with the predicted
energetically favorable conversion of Ni(HLi)(HLa) into
Ni(HLa)2, with a calculated ΔG of −12.48 kcal mol−1. In
contrast, such activation is not present in the square planar
Pd(HLi)(HLa) that displays an uncoordinated imine N atom
(Figure 7d). In addition, the free lone pair of the sulfonamide N
atom is rotated 180° against the imine carbon atom because the
mentioned N atom establishes hydrogen bonding with the
imine N atom in Pd(HLi)(HLa). With this in mind, even
though the conversion of Pd(HLi)(HLa) into Pd(HLa)2 is
energetically favorable, the activation energy for this process
might be high. All attempts to locate a transition state with the
free lone pair of the sulfonamide N atom close to Pd2+ failed,
presumably due to steric crowding.
process would involve the intermediate complexes M(HLa)(HLi)
that could undergo an intramolecular ring-closing reaction to
afford Ni(HLa)2 or an intramolecular ring-opening one to give
Pd(HLi)2. The complete Gibbs free energy profile of the pro-
posed pathway for both metals was analyzed, and the results are
summarized in Figure 6.
Considering that the reaction between H2La and Pd2+ always
goes via Pd(Li) regardless the molar ratio used, but any
evidence for Ni(Li) en route to Ni(HLa)2 was found when a 2:1
molar ratio was used, an alternative pathway for the conversion
of Ni(OAc)(HLa) into Ni(HLa)2 must be considered. This
alternative process would involve the displacement of the
acetate ligand in Ni(OAc)(HLa) by the closed-chain ligand
H2La (Scheme 4), which could be initiated by the abstraction of
the phenol hydrogen atom in free H2La by the acetate ligand in
Ni(OAc)(HLa).
The first step would involve the displacement of one of the
acetate ligands in M(OAc)2 by the open-chain ligand H2Li or
the closed one H2La to afford the square planar complexes
M(OAc)(HLi) and M(OAc)(HLa), respectively. The displace-
ment of the remaining acetate in M(OAc)(HLi) by the
uncoordinated sulfonamide N atom of (HLi)− leads to M(Li)
complex. This process might be very fast considering the low
Gibbs free energy involved (Figure 6). The conversion of
M(OAc)(HLa) into M(Li) would involve a ring-opening
reaction that will be initiated with the abstraction of the
hydrogen atom of the aminal group by the acetate (Scheme 4).
In M(OAc)(HLa) complexes, the coordination of the acetate
ligand to the metal through one of the oxygen atoms locates the
carbonyl group in an appropriate orientation for the intra-
molecular proton abstraction to give intermediate species of the
type M(HOAc)(La). Figure 7a,b shows the calculated transition
states for the proton abstraction step. The calculated activation
energy for the conversion of M(OAc)(HLa) into M(HOAc)(La)
is 5.28 kcal mol−1 when M = Pd2+ and 5.55 kcal mol−1 when
M = Ni2+. Therefore, the energy cost of the conversion of
M(OAc)(HLa) into M(Li) basically corresponds to this
hydrogen abstraction (Scheme 4). The next step would involve
the ring-opening reaction with removal of acetic acid. The high
energy required for the dissociation of acetic acid in
Crystal Structure of Tetrahydroquinazoline H2La.
Single crystal X-ray diffraction techniques confirmed that pale
yellow prismatic crystals obtained after slow evaporation of a
methanol solution of the condensed ligand consist of
crystallographically independent molecules that comprise a
1,2,3,4-tetrahydroquinazoline ring. Table 1 shows the main
bond distances and angles for H2La that fall within the expected
ranges.22−24 In order to facilitate comparison, the equivalent
parameters of Ni2+ and Pd2+ complexes (vide infra) were also
included. The very good agreement between the found
geometric parameters and those estimated by using DFT
calculations is clear in Figure 8, which shows both the found
molecular structure and the calculated model.
As these crystals belong to the centrosymmetric P21/n space
group, the compound crystallizes as a racemate. Apart from an
intramolecular H bond (Table 1), corresponding to the major
component of a bifurcated H bond,25 another factor that clearly
influences the molecular conformation is the π−π stacking.
This is evidenced by the interaction that exists between the two
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Figure 6. Complete Gibbs free energy profiles for the reactions between the closed-chain tetrahydroquinazoline H2La and open-chain imine H2Li
with (a) Pd(OAc)2·4H2O and (b) Ni(OAc)2·4H2O.
aromatic rings of the tosyl and diamine residues, with a distance
of ca. 3.7 Å between their respective centroids.
The Ni(HLa)2·4MeOH crystal is formed by crystallo-
graphically independent molecules of the neutral nickel(II)
complex along with some solvated methanol molecules with
partial occupation sites, which interact through H bonding
(Table 2). The O atoms of one of the tosyl groups are
disordered on two sites with an occupation ratio of 0.93:0.07.
An ellipsoid diagram of the neutral complex is shown in Figure 10,
for which the labeling scheme is equivalent to that of the free
ligand, but either preceded by 1 or 2, or using “a” or “b”, for
each of the coordinated ligands.
Crystal Structures of Ni(HLa)2·2HOAc and Ni-
(HLa)2·4MeOH. The asymmetric unit of Ni(HLa)2·2HOAc
only includes half a molecule of the neutral complex, and this is
accompanied by an acetic acid molecule, which is doubly
interacting through N−H··O and O−H···O contacts with the
complex molecule (Table 2). The complete molecule (Figure 9)
1
is generated by means of the symmetry operation −x + /2,
The crystal structures of both Ni(HLa)2·2HOAc and
Ni(HLa)2·4MeOH are very similar as they consist of a
y, −z + 1, related with a C2 rotation axis parallel to b, which
goes through the nickel(II) ion.
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The Ni2+ coordination polyhedrons can be described as
distorted octahedrons, with the axial positions occupied by the
Nquinoline atoms. Since the Ni−Nquinoline bonds are the shortest
for this coordination environment (Table 2), these polyhedrons
are more compressed than elongated, and each N,N,O-donor
set occupies a pseudomeridian. This spatial disposition leads to
a typical double-blade propeller arrangement around the nickel
ion, which involves chirality and will be further discussed in the
corresponding section.
Scheme 4. General Proposed Mechanism for the Conversion
a
of M(OAc)(HLa) to M(Li) and M(HLa)2
Both Ni(HLa)2·2HOAc and Ni(HLa)2·4MeOH show π−π
stacking interactions between tetrahydroquinazoline and tosyl
rings, as occurred in the free ligand, while interactions between
neighboring tetrahydroquinazoline rings are patently different
and related to C−H···π contacts. Thus, for Ni(HLa)2·2HOAc
there are two mutual interactions through one of the methylene
H atoms of each ligand unit, whereas in Ni(HLa)2·4MeOH
there is only one CH−π interaction between them, by means of
a methine H atom.
a
Gibbs free energy difference (kcal mol−1) of the studied steps is
To see if the theoretical methods reproduce the experimental
geometries of the Ni(II) complexes their structures were
optimized using DFT calculations with M06 functional.18,19
The experimental and calculated structures are compared in
Supporting Information through their geometrical data. The
agreement is very good, suggesting that the level of calculation
is relevant to study these complexes.
indicated.
nickel(II) ion coordinated to two monoanionic units of
tetrahydroquinazoline ligand with a practically planar extended
π-conjugated system. (HLa)− units act as tridentate donors
through the N,O set of the quinoline, where the hydroxyl group
of which is deprotonated, in conjunction with the protonated
amine N atom of the tetrahydroquinazoline moiety.
Crystal Structure of Pd(Li)·CH2Cl2. The asymmetric unit
of this crystal structure contains one molecule of the neutral
Figure 7. Transition states for the intramolecular proton abstraction step involving the conversion of M(OAc)(HLa) into M(HOAc)(La) (a for M =
Ni and b for M = Pd) and structures of the most stable conformers of intermediate complexes Ni(HLi)(HLa) and Pd(HLi)(HLa) (c and d). Relevant
distances are indicated.
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Table 1. Main Bond Distances [Å] and Angles [deg] for H2La Collected in the First Column with Equivalent Parameters for
Ni(HLa)2·2HOAc, Ni(HLa)2·4MeOH, and Pd(Li)·CH2Cl2 Included for Ease of Comparison with Configurations of Stereogenic
Centers of the Ligand Molecules Also Indicated
b
H2La
Ra
Ni(HLa)2·2HOAc
Ni(HLa)2·4MeOH
a
a
a
C(R)N(S)
C(R)N(S)
C(S)N(R)
Pd(Li)·CH2Cl2
c
Distance
N1−C2
N1−C8A
C8−O1
C9−N2
N2−C9A
C9−N3
C13A−C14
C14−N3
N3−S1
1.316(3)
1.374(3)
1.355(3)
1.443(3)
1.382(4)
1.470(3)
1.512(4)
1.476(3)
1.645(2)
1.765(3)
1.328(6)
1.363(5)
1.337(5)
1.499(5)
1.435(6)
1.451(5)
1.514(6)
1.476(6)
1.654(4)
1.746(5)
1.316(3)
1.358(3)
1.311(3)
1.494(3)
1.443(3)
1.457(3)
1.501(4)
1.474(3)
1.650(2)
1.760(3)
1.316(3)
1.336(8)
1.343(8)
1.339(8)
1.305(8)
1.428(9)
1.362(3)
1.315(3)
1.486(3)
1.424(3)
1.458(3)
1.507(4)
1.470(3)
1.645(2)
1.759(3)
1.507(9)
1.483(8)
1.600(3)
1.770(7)
S1−C15
d
Angle
C2−N1−C8A
N1−C2−C3
C9−N2−C9A
C9−N3−C14
C9−N3−S1
117.5(2)
119.4(4)
121.8(4)
117.4(4)
112.0(4)
118.2(3)
119.3(3)
109.4(4)
108.6(2)
121.0(2)
121.1(2)
120.6(2)
124.7(6)
118.0(6)
121.3(6)
123.5(2)
121.4(2)
118.6(2)
117.08(19)
111.8(2)
117.9(2)
112.4(2)
113.50(19)
121.13(17)
118.96(17)
109.4(2)
118.62(17)
116.54(17)
111.0(2)
118.67(18)
119.43(17)
110.1(2)
C14−N3−S1
C13A−C14−N3
N3−S1−C15
114.1(4)
113.9(6)
108.8(3)
107.72(12)
107.98(12)
108.58(11)
d
Torsion
O1−C8−C8A−N1
N1−C2−C9−N2
N2−C9A−C13A−C14
N1−C2−C9−N3
C2−C9−N2−C9A
C9−N2−C9A−C13A
C14−N3−S1−C15
S1−N3−C9−N2
C9A−N2−C9−N3
N2−C9−N3−S1
N2−C9−N3−C14
C13A−C14−N3−S1
C9A−C13A−C14−N3
C14−N3−S1−C15
D−H···A
−1.9(4)
−20.8(3)
2.7(4)
0.2(6)
2.6(3)
0.6(3)
−0.1(8)
1.9(9)
21.4(6)
9.7(6)
16.1(3)
−5.4(3)
−9.1(3)
−131.6(2)
−119.7(2)
23.9(3)
7.8(4)
0.9(10)
−142.6(2)
−77.0(3)
−15.6(4)
55.1(2)
147.9(4)
121.0(4)
−25.8(6)
−72.1(4)
−99.2(4)
−2.6(6)
−99.2(4)
45.4(5)
84.3(4)
32.4(6)
−72.1(4)
141.7(2)
108.0(2)
−15.7(3)
−64.9(2)
−93.8(2)
−14.3(3)
−93.8(2)
51.4(3)
178.5(6)
−158.9(6)
−69.5(5)
55.1(2)
79.9(2)
106.7(2)
3.5(3)
43.8(3)
79.9(2)
106.7(2)
−44.9(3)
−94.1(2)
−30.9(3)
55.1(2)
−60.9(3)
−93.3(2)
−19.2(3)
55.1(2)
86.9(2)
−147.7(5)
−46.7(3)
−69.5(5)
28.7(3)
−64.9(2)
<(DHA)
c
c
d
d(D−H)
d(D···A)
D−H···A
e
H Bond Scheme for H2L
O1−H1···N1
0.80(5)
0.80(5)
0.82(3)
0.82(3)
2.714(3)
2.917(3)
3.013(3)
3.465(3)
123(4)
131(4)
119(3)
151(3)
O1−H1···N1
O1−H1···O2#1
O1−H1···O2#1
N2−H2A···N3#2
N2−H2A···N3#2
N2−H2A···O2#1
N2−H2A···O2#1
b
a
Chirality of the stereogenic centers for the enantiomers found in the respective asymmetric units. Despite the different labeling schemes,
c
d
e
#1
#2
the parameters compared are totally equivalent. In Å. In deg. Symmetry transformations used to generate equivalent atoms: x, y, z − 1, x,
1
1
−y + /2, z − /2.
palladium(II) complex along with a solvated dichloromethane
molecule. An ORTEP diagram of Pd(Li) is shown in Figure 11,
and the main bond distances and angles for the coordination
environment are collected in Table 2.
open imine H2Li after bideprotonation. This disposition enables
a practically planar and pseudosquare environment, where the
metal ion protrudes very little (0.017 Å) from the calculated
least-squares plane formed by the four donor atoms.
Since these crystals were obtained from a reaction in which
H2La was the starting material, the molecular structure of
Pd(Li)·CH2Cl2 not only demonstrates tetrahydroquinazoline
ring-opening due to coordination to palladium(II), but also the
180° turn around the C2−C9 bond. As a result, the two
bidentate N,N and N,O domains are endo positioned instead of
exo, as occurred for H2Li. Hence, the metal ion is
tetracoordinated to the O,N,N,N donor set that provides the
Chirality. In solid state, H2La has one chiral atom (C9) and
two prochiral ones (N2 and N3) with same configuration
(R,R,R) or (S,S,S) as shown in Figure 12, top, but in solution,
the energetic barriers should be too low to avoid this structure
flipping inside out. It must be noted that as a result of the metal
coordination the configurations of C9 reverse due to changes in
the Cahn−Ingold−Prelog conventions, as Figure 12 shows.
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the isomers [Δ-C(S,S)N(R,R)]-Ni(HLa)2 and [Λ-C(S,R)N-
(R,S)]-Ni(HLa)2 are virtually isoenergetic (Figure 5). The not
experimentally found isomer [Δ-C(R,R)N(S,S)]-Ni(HLa)2 is
4.9 kcal mol−1 less stable than those stereoisomers found for
crystallized Ni(HLa)2·2HOAc and Ni(HLa)2·4MeOH.
Finally, it is worthy of mention that the helical chirality of
Pd(Li)·CH2Cl2 is merely conformational, as it could disappear
in solution since it is only based on the conformation of the
methylene group and the orientation of the tosyl group. This
situation is illustrated in Figure 14, in which the Δ and the
Λ isomers are represented.
CONCLUSIONS AND FINAL REMARKS
■
The final product of the condensation reaction of 8-
hydroxyquinoline-2-carboxaldehyde with N-(2-aminobenzyl)-
4-methylbenzenesulfonamide strongly depends on the reaction
time. Indeed, reaction times of about 1 h gave the open-chain
imine (E)-N-{2-[(8-hydroxy-quinolin-2-yl)-methyleneamino]-
benzyl}-4-methyl-benzenesulfonamide (H2Li) as the main
product. However, when the reaction time exceeded 4.5 h,
the chiral cyclic aminal rac-2-(3-tosyl-1,2,3,4-tetrahydroquina-
zolin-2-yl)quinolin-8-ol (H2La) was exclusively obtained. The
tetrahydroquinazoline compound H2La is the most stable form
of the two tautomers, and the intramolecular ring-closing
reaction of H2Li to give H2La is energetically favored, as
evidenced by DFT calculations.
The aforementioned ring−chain tautomerism has been
exploited to induce reversible changes in the aminal−imine
equilibrium, as desired, by coordination of a suitable metal ion.
The cyclic tautomeric form of the equilibrium studied is
retained upon fast complexation of tetrahydroquinazoline H2La
to nickel(II) to yield complexes of the type Ni(HLa)2, where
the aminal ligand behaves as a tridentate N,N,O-donor. The
same complex was obtained on using imine H2Li as ligand, what
means that Ni2+ causes imine H2Li to undergo a ring-closing
cyclization process on coordination. In contrast, tetrahydro-
quinazoline H2La undergoes a ring-opening reaction on
complex formation with Pd2+ to yield Pd(HLi)2·MeOH, in
which the linear imine only acts as a bidentate ligand through
the N,O donor set of the 8-hydroxyquinoline residue. The
selective ring-opening is related to the rapidly formed
Pd(Li)·CH2Cl2, in which the linear ligand acts as a
tetracoordinate N,N,N,O-donor. This subsequently yields
Pd(HLi)2·MeOH, in which the ligand has a helical arrange-
ment.
Figure 8. Molecular structure of 2-(1,2,3,4-tetrahydro-3-tosylquinazo-
lin-2-yl)quinolin-8-ol. The figure (top) shows the R enantiomer of
(rac)-H2La with ellipsoids at the 50% probability level. Comparison
(bottom) of the calculated structure (DFT/M06 level in methanol) of
H2La (green) and the experimental X-ray structure of H2La (violet).
Both Ni(HLa)2·2HOAc and Ni(HLa)2·4MeOH are chiral not
only because they combine the R and S enantiomers of the
aminal ligand, but also because they are helical. Thus, (Δ,Λ)-
racemates can be considered for these complexes in the unit
cell, as the crystal structures correspond to nonchiral space
groups. For the nomenclature of these helicates, the helicity
(Δ,Λ) will be first indicated and second, the configurations
(R,S) of the two ligand units arranged in accordance with the
numbering scheme (100 and 200 series) for chiral atoms C9
and N2, respectively. Figure 12, middle, shows a representation
of Ni(HLa)2·4MeOH that combines the R and S enantiomers of
the aminal ligand. In this complex, each helical enantiomer
(Δ,Λ) comprises both R and S enantiomers of (HLa)−, so its
racemate can be described as [Δ,Λ-C(R,S)N(S,R)]-Ni-
(HLa)2·4MeOH. In contrast, each Δ and Λ enantiomer
found for Ni(HLa)2·2HOAc involves two enantiomers of
(HLa)− of identical chirality. Thus, two R enantiomers of
(HLa)− are coordinated in the Λ isomer, while two S
enantiomers of (HLa)− form the Δ isomer, as shown at the
bottom of Figure 12. Consequently, its racemate could be
described as [Δ-C(R,R)N(S,S),Λ-C(S,S)N(R,R)]-Ni-
(HLa)2·2HOAc.
The aminal tautomer H2La is predisposed to a planar N,N,O
tricoordinate behavior, without apparent changes after
complexation. In pseudo-octahedral coordination environ-
ments, as preferred by Ni2+ ions, each ligand occupies a
pseudomeridian, which gives rise to a typical double-blade
propeller disposition and therefore to Λ and Δ enantiomers.
These enantiomers can combine two ligand units with identical
or different chirality. Thus, we determined the crystal structures
of two racemates: [Δ-C(R,R)N(S,S),Λ-C(S,S)N(R,R)]-Ni-
(HLa)2·2HOAc and [Δ,Λ-C(R,S)N(S,R)]-Ni(HLa)2·4MeOH.
DFT studies carried out for the possible diastereoisomers
indicate that [Λ-C(S,S)N(R,R)]-Ni(HLa)2 and [Λ-C(R,S)N-
(S,R)]-Ni(HLa)2 are 4.3 and 4.9 kcal mol−1, respectively, more
stable than [Λ-C(R,R)N(S,S)]-Ni(HLa)2, and which was not
experimentally found. Combined structural and theoretical
calculations show that models obtained from DFT calculations
reproduce the geometry of the crystallized compounds.
To understand the origin of the formation of two isomers
among the three possible ones, [Δ,Λ-C(R,S)N(S,R)]-Ni(HLa)2
(Figure 13, bottom), [Δ-C(R,R)N(S,S),Λ-C(S,S)N(R,R)]-Ni-
(HLa)2 (Figure 13, top), and hypothetical [Δ-C(S,S)N(R,R),Λ-
C(R,R)N(S,S)]-Ni(HLa)2, their relative stabilities were inves-
tigated. Molecular modeling studies at the DFT level by means
of the hybrid M06 functional18,19 (vide supra) predicted that
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Table 2. Main Bond Distances [Å] and Angles [deg] for the Coordination Environments of Ni(HLa)2·2HOAc,
Ni(HLa)2·4MeOH, and Pd(Li)·CH2Cl2
Ni(HLa)2·2HOAc
Ni(HLa)2·4MeOH
Pd(Li)·CH2Cl2
a
a
a
distance
distance
distance
Pd1−N1
Ni1−N1
1.973(3)
1.973(3)
2.054(3)
2.054(3)
2.394(4)
2.394(4)
Ni1−N101
Ni1−N201
Ni1−O101
Ni1−O201
Ni1−N102
Ni1−N202
1.9672(19)
1.9581(19)
2.0388(17)
2.0484(16)
2.382(2)
1.929(5)
c
Ni1−N1#1,
Ni1−O1
Pd1−O1
2.082(4)
Ni1−O1#1
Ni1−N2
Pd1−N2
Pd1−N3
2.027(5)
2.007(5)
Ni1−N2#1
2.292(2)
b
b
b
angle
angle
angle
N1−Ni1−N1#1
N1−Ni1−O1#1
N1#1−Ni1−O1#1
N1−Ni1−O1
N1#1−Ni1−O1
O1#1−Ni1−O1
N1−Ni1−N2#1
N1#1−Ni1−N2#1
O1#1−Ni1−N2#1
O1−Ni1−N2#1
N1−Ni1−N2
N1#1−Ni1−N2
O1#1−Ni1−N2
O1−Ni1−N2
N2#1−Ni1−N2
D−H···A
167.2(2)
N101−Ni1−N201
N101−Ni1−O201
N201−Ni1−O201
N101−Ni1−O101
N201−Ni1−O101
O101−Ni1−O201
N101−Ni1−N202
N201−Ni1−N202
O201−Ni1−N202
O101−Ni1−N202
N101−Ni1−N102
N201−Ni1−N102
O201−Ni1−N102
O101−Ni1−N102
N202−Ni1−N102
179.00(9)
97.94(7)
81.78(7)
82.86(8)
98.11(7)
93.95(7)
103.07(8)
77.19(8)
158.95(7)
89.89(8)
75.49(8)
103.54(8)
89.26(7)
158.35(7)
94.77(8)
N1−Pd1−N3
N1−Pd1−N2
N3−Pd1−N2
N1−Pd1−O1
N3−Pd1−O1
N2−Pd1−O1
N1−Ni1−N2#1
N1#1−Ni1−N2#1
O1#1−Ni1−N2#1
O1−Ni1−N2#1
N1−Ni1−N2
N1#1−Ni1−N2
O1#1−Ni1−N2
O1−Ni1−N2
N2#1−Ni1−N2
172.9(2)
80.0(2)
107.92(13)
80.92(14)
80.93(14)
107.92(13)
95.56(18)
96.80(14)
75.37(14)
154.99(12)
84.38(14)
75.37(14)
96.80(14)
84.37(14)
154.99(12)
106.1(2)
93.0(2)
80.8(2)
106.2(2)
160.79(19
a
a
b
d(D−H)
d(D···A)
<(DHA)
H-Bond Scheme for Ni(HLa)2·2HOAc
N2−H2A···O31#1
N2−H2A···O31#1
N2−H2A···O1#1
O30−H30···O1
0.94(5)
0.94(5)
0.94(5)
1.11
3.009(5)
3.009(5)
2.997(5)
2.519(4)
140(4)
140(4)
110(4)
176
H-Bond Scheme for Ni(HLa)2·4MeOH
N202−H22···O1S
O1S−H1S···O4S
O1S−H1S···O4S′
O2S−H2S···O3S
O3S−H3S···O201
O4S−H4S···O2S#2
0.80(3)
0.99
2.888(3)
2.731(4)
2.336(19)
2.689(3)
2.613(2)
2.710(3)
164
148
134
170
168
170
0.99
0.84
0.84
0.84
a
b
c
#1
1
#2
In Å. In deg. Symmetry transformations used to generate equivalent atoms: −x + 2, y, −z + /2. x, y + 1, z.
Experimental data and theoretical studies suggest that the
processes are directed by the coordinative preferences of the
metal in its complexes: While Ni2+ in octahedral environment
stabilizes the tridentate closed-chain tautomer, the preference
of Pd2+ for a square planar environment leads to a tetra- or
bidentate behavior of the open-chain tautomer.
formation of these complexes involves initially the metal
promoted ring-opening reaction of the tetrahydroquinazoline
H2La to give M(Li) than then evolves to Pd(HLi)2 or Ni(HLa)2
via the intermediate complexes M(HLi)(HLa). The coordina-
tion of the imine present in Ni(HLi)(HLa) allows a subsequent
intramolecular ring-closing reaction of the open-chain ligand to
afford Ni(HLa)2. The opposite conversion, i.e., the intra-
molecular ring-opening reaction of the aminal in Ni(HLi)(HLa)
to give Ni(HLi)2, is energetically unfavorable. In contrast, the
square planar coordination of Pd2+ in Pd(HLi)(HLa) does not
promote a similar metal assisted ring-closing reaction of open-
chain ligand, but an intramolecular ring-opening reaction to
give Pd(HLi)2. While for Pd2+, the reaction always goes via
Pd(Li), for Ni2+, when a 1:2 molar ratio is used, the
experimentally obtained complex Ni(HLa)2 is probably formed
by direct displacement of the acetate ligand in Ni(OAc)(HLa)
by another molecule of H2La.
EXPERIMENTAL SECTION
■
General Procedures. All starting materials and reagents were
commercially available without further purification. Elemental analyses
were performed on a Carlo Erba EA 1108 analyzer. Positive
electrospray ionization mass spectra were recorded on an LC/MSD
Hewlett-Packard 1100 spectrometer, using methanol as solvent (2%
formic acid). The mass spectrometry samples were previously
dissolved in the minimum amount of dimethylsulfoxide. NMR spectra
were recorded on Bruker spectrometers using DMSO-d6 as solvent.
NMR assignments were made by a combination of DEPT-135,
HMQC, HMBC, COSY, NOESY, and NOE experiments. Infrared
spectra were recorded as KBr pellets on a Bio-Rad FTS 135
spectrophotometer in the range 4000−600 cm−1. UV−vis spectra
were performed on 10−4−10−5 M methanol solutions with a CECIL
CE 2021 spectrophotometer.
The studies described here allow us to conclude that Ni2+
and Pd2+ coordination can be used to induce closing and
opening reactions of a tetrahydroquinazoline ring. These
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Figure 9. Ellipsoid representation at the 50% probability level of the molecular structure of Ni(HLa)2·2AcOH. The double H bonding interaction
between Ni(HLa)2 and two acetic acid molecules trapped as solvates is also indicated. The labeling scheme is similar to that used for the free ligand
H2La. The figure shows the Δ-C(R,R)N(S,S) enantiomer.
Figure 10. ORTEP representation of the molecular structure of the Ni(HLa)2 complex found in Ni(HLa)2·4MeOH. Solvates have been omitted for
clarity. Ellipsoids are represented at the 50% probability level. The figure shows the Λ-C(R,S)N(S,R) enantiomer.
Crystal Structure Analysis Data. Diffraction data for H2La,
Ni(HLa)2·2HOAc, Ni(HLa)2·4MeOH, and Pd(Li)·CH2Cl2 were
collected at 100(2) K, using graphite-monochromated Mo Kα
radiation (λ = 0.710 73 Å) from a fine focus sealed tube. Some
significant crystal parameters and refinement data are summarized in
Table 3. Data were processed and corrected for Lorentz and
polarization effects. Multiscan absorption corrections were performed
using the SADABS routine.26 Structures were solved by standard direct
methods27 and then refined by full matrix least-squares on F2.28 All
non-hydrogen atoms were anisotropically refined, except those that
were disordered and had lower occupation sites for Ni(HLa)2·4MeOH.
Hydrogen atoms were mostly included in the structure factor
calculation in geometrically idealized positions, with thermal
parameters depending on the parent atom, by using a riding model.
In most cases, the H atoms that were potentially involved in the H
bonding schemes were located in Fourier maps and isotropically
treated.
However, there is a significant exception to the latter comment
related to Ni(HLa)2·2HOAc. In this case, ΔF maps showed electron
densities at chemically reasonable positions near to one of the O atoms
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Figure 11. Ellipsoid representation at the 50% probability level of the
molecular structure solved for Pd(Li). H atoms and solvates have been
omitted for clarity.
Figure 13. Spacefill representations of the helical Λ (left) and Δ
(right) enantiomers of the two Ni(HLa)2 complexes studied here.
Chiral centers are marked with * (red for N, black for C) for ease of
understanding.
Figure 14. Spacefill representation of the Λ (left) and Δ (right) helical
enantiomers found for Pd(Li) in the crystal structure of
Pd(Li)·CH2Cl2.
equivalent of the parent O atom corresponding to the acetic acid. The
notable length of this bond, with the H atom at 1.11 Å from the O
atom (Table 2), and the short O···O distance indicate the strength
of this interaction and could also indicate an intermediate situation
between the coordinated ligand and the acetic acid molecules. All
the above facts could point to a mixture of complexes with cationic
and neutral natures. However, as possible disorder could not be
adequately modeled, and according to the distance values mentioned,
a formula of the type Ni(HLa)2·2HOAc was assumed instead of
[Ni(H2La)2](OAc)2.
Figure 12. Ball and stick representations of (top) the two enantiomers
of H2La as free ligand, (middle) both monodeprotonated and
coordinated ligand units in Ni(HLa)2·4MeOH and in (bottom)
Ni(HLa)2·2HOAc.
CCDC 814044−814047 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/data_request/cif.
of the acetate fragment. When this was freely refined, this H atom
appeared nearer to the O1 atom of the coordinated ligand. Therefore,
some related bond distances were thoroughly investigated by means of
a search in the Cambridge Structural Database.29 Thus, in nickel(II)
complexes, distances for coordinated Ph−O and Ph−OH average
1.310 and 1.358 Å, respectively. In this case study, d(C8−O1) =
1.337(5) Å shows an intermediate value between relatively common
values reported for Ni−O−Ph interactions [1.237−1.366 Å] and that
is practically at the lowest extreme of the range reported for Ni−OH−Ph
bonds [1.337−1.378 Å].30 In addition, the clear dissimilarity of the
two C−O bonds of the acetate fragment, 1.320(5) and 1.212(5) Å,
seems more indicative of a neutral rather than an anionic nature.
Hence, the coordinates of this hydrogen atom were freely refined, but
its isotropic thermal parameter was set at 1.2 times the isotropic
Theoretical Studies. All calculations were performed by using the
Gaussian 09W17 program package at density functional theory (DFT)
level by means of the hybrid M0618,19 functional. The standard 6-
31G(d) basis set was used for C, H, O, S, and N, and the LANL2DZ
relativistic pseudopotential was used for Pd and Ni. The starting point
of these calculations was the crystallographic structures described in
this Article, the tetrahydroquinozinoline H2La and its PdII and NiII
metal complexes. First, the crystallographic structures obtained were
minimized at a DFT level. The resulting energy value was taken as a
reference for all subsequent calculations. On the optimized geometries
a DFT minimization in methanol solution by means of the polarizable
continuum solvation model20 was performed. Harmonic frequencies
were calculated at the same level of theory to characterize the
stationary points and to determine the zero-point energies (ZPEs). All
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Article
Table 3. Diffraction Data for H2La, Ni(HLa)2·2HOAc, Ni(HLa)2·4MeOH, and Pd(Li)·CH2Cl2
H2La
Ni(HLa)2·2HOAc
Ni(HLa)2·4MeOH
Pd(Li)·CH2Cl2
formula
Mr
C24H21N3O3S
431.50
C52H48N6NiO10S2
1039.79
C52H56N6NiO10S2
1047.86
C25H21Cl2N3O3PdS5
620.81
cryst syst
space group
unit cell
monoclinic
P21/n
monoclinic
C2/c
triclinic
orthorhombic
Pbca
P1
̅
a = 17.6928(9)
b = 14.2748(9)
c = 8.0082(5)
α = 90
a = 27.248(3)
b = 10.2025(11)
c = 17.7389(19)
α = 90
a = 11.3622(5)
b = 14.0882(5)
c = 17.6835(7)
α = 68.245(2)
β = 88.857(2)
γ = 70.718(2)
2464.57(17)
2
a = 9.6380(4)
b = 19.9218(7)
c = 25.9126(9)
α = 90
β = 101.893(3)
α = 90
β = 108.503(4)
γ = 90
β = 90
γ = 90
V (Å3)
Z
1979.1(2)
4
4676.4(8)
4
4975.5
8
Dc (g/cm3)
1.448
1.477
1.412
1.658
−1
μ (mm )
0.198
0.573
0.544
1.078
F(000)
904
2168
1100
2496
θ range (deg)
1.85−26.02
72 839/5158
0.0525
2.15−23.25
27 131/3360
0.0605
1.65−26.02
36 654/9690
0.0475
1.57−25.35
109 274/4556
0.0815
refns collected/refns indep
Rint
data/restraints/params
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
residuals (e Å−3)
3879/0/289
0.0472, 0.1173
0.0662, 0.1245
0.314, −0.422
3360/0/327
0.0467, 0.0857
0.1218, 0.1113
0.403, −0.688
9690/0/677
0.0424, 0.0954
0.0638, 0.1053
0.878, −0.673
4556/0/317
0.0549, 0.0952
0.1306, 0.1241
0.708, −0.960
the calculations were first performed in vacuum, and then in methanol
to compare the solvent effect.
112.5 (C-7), 42.4 (C-14), 21.3 (C-18). UV−vis (MeOH, λ in nm, ε in
parentheses) 206 (24 782), 248 (19 565), 272 (14 565). FTIR (KBr,
To explore the conformational preference of the tetrahydroquino-
zinoline ligand H2La, the dihedral angle C3−C2−C9−N3 was
progressively incremented from 0° to 360°, and the resultant
geometries were minimized using PM6, followed by a DFT single
point energy calculation. The most stable conformers were further
minimized by DFT. A similar protocol was carried out for imine H2Li
in which case several rotations were made, mainly involving C2−C9,
N2−C9a, and C14−C13a bonds.
For palladium(II) and nickel(II) metal complexes, it was considered
that the conformation around the metal might not change significantly.
Therefore, changes were not made around the metal coordination
environment from a defined geometry. A square planar coordination
was used for both metal complexes, and an octahedral geometry was
also studied for NiII complexes. A similar protocol was carried out as
for ligands H2Li and H2La. As a result, four possible conformers were
obtained for PdII complexes and four and seven conformers for square
planar and octahedral nickel(II) complexes, respectively (see
Supporting Information).
cm−1): ν(O−H) 3409(br,m), ν(N−H) 3246(m), ν(CNimi
)
1620(m), ν(CNquin) 1611(sh, m), νas(SO2) 1336(s), νs(SO2)
1162(vs). MS (FAB+, MNBA) m/z (%): 432.2 (100) [M + H]+.
Anal. Calcd for C24H21N3O3S: C, 66.8; H, 4.9; N, 9.7; S, 7.3. Found:
C, 66.70, H, 4.6, N, 9.7, S, 7.0.
(rac)-2-(3-Tosyl-1,2,3,4-tetrahydroquinazolin-2-yl)quinolin-
8-ol (H2La). The experimental procedure was the same as for
compound H2Li, with heating under reflux for 4.5 h. After cooling to
room temperature, the reaction mixture was concentrated under
reduced pressure to yield an oily product, which was dissolved in
ethanol (20 mL) and stirred for 10 min. This resulted in a beige
powder, which was dried under vacuum. Yield = 0.27 g (88%). Mp
126 °C. 1H NMR (500 MHz, DMSO-d6): δ 9.38 (s, 1H, OH), 8.35 (d,
J = 8.6 Hz, 1H, H-4), 7.79 (d, J = 8.3 Hz, 2H, H-16 + H-20), 7.62 (d,
J = 8.6 Hz, 1H, H-3), 7.44 (t, J = 8.0 Hz, 1H, H-6), 7.38 (dd, J = 8.2
and 1.1 Hz, 1H, H-5), 7.25 (d, J = 8.1 Hz, 2H, H-17 + H-19), 7.11
(dd, J = 7.4 and 1.2 Hz, 1H, H-7), 7.07 (d, J = 3.3 Hz, 1H, NH), 6.88
(dt, J = 7.2 and 1.0 Hz, 1H, H-11), 6.77 (d, J = 7.4 Hz, 1H, H-13),
6.63 (d, J = 8.0 Hz, 1H, H-10), 6.48 (dt, J = 7.4 and 0.9 Hz, 1H, H-
12), 6.40 (d, J = 2.8 Hz, 1H, H-9), 4.51 (d, J = 17.1 Hz, 1H, Heq-14),
4.16 (d, J = 17.2 Hz, 1H, Hax-14), 2.30 (s, 3H, H-18). 13C NMR (125
MHz, DMSO-d6): δ 156.8 (C-2), 152.5 (C-8), 143.2 (C-18a), 141.6
(C-9a), 137.7 (C-4), 137.3 (C-8a), 136.1 (C-15), 129.3 (C-17 + C-19),
128.0 (C-4a), 127.7 (C-6), 127.4 (C-16 + C-20), 127.2 (C-11), 126.4
(C-13), 119.1 (C-3), 117.4 (C-12), 117.1 (C-5), 116.2 (C-13a), 115.6
(C-10), 111.1 (C-7), 67.4 (C-9) 42.4 (C-14), 20.9 (C-18). UV−vis
(MeOH, λ in nm, ε in parentheses) 206 (22 173), 248 (23 913), 270
(5434), 298 (2173). FTIR (KBr, cm−1): ν(O−H) 3417(s), ν(N−H)
3398(s), ν(CNquin) 1611(s), νas(SO2) 1322(s), νs(SO2) 1157(vs).
MS (ESI+, 100 V) m/z (%): 432.2 (100) [M + H]+. Anal. Calcd for
C24H21N3O3S: C, 66.8; H, 4.9; N, 9.7; S, 7.3. Found: C, 66.4; H, 5.0;
N, 9.4; S, 7.4.
(E)-N-{2-[(8-Hydroxyquinolin-2-yl)methyleneamino]benzyl}-
4-methylbenzene-sulfonamide (H2Li). A solution of 8-hydrox-
yquinoline-2-carboxaldehyde (127 mg, 0.72 mmol) and 2-tosylamino-
methylaniline (200 mg, 0.72 mmol) in chloroform (40 mL) was
heated under reflux for 1 h. After cooling to room temperature, the
resulting pale yellow solution was concentrated in vacuum to give an
oily product, which was dissolved in ethanol (20 mL) and stirred for
10 min. This resulted in a pale yellow powder, which was dried in
1
vacuum. Yield = 0.13 g (42%). Mp 126 °C. H NMR (500 MHz,
DMSO-d6): δ 10.03 (s, 1H, OH), 8.61 (s, 1H, H-9), 8.42 (d, J = 8.6
Hz, 1H, H-4), 8.11 (d, J = 8.6 Hz, 1H, H-3), 7.93 (t, J = 6.0 Hz, 1H,
NH), 7.66 (d, J = 8.2 Hz, 2H, H-16 + H-20), 7.54 (t, J = 7.8 Hz, 1H,
H-6), 7.48 (dd, J = 8.1 and 0.9 Hz, 1H, H-5), 7.41 (d, J = 7.5 Hz, 1H,
H-13), 7.37 (dt, J = 7.6 and 1.1 Hz, 1H, H-11), 7.29 (d, J = 8.0 Hz,
2H, H-17 + H-19), 7.27 (t, J = 7.5 Hz, 1H, H-12), 7.19 (d, J = 7.7 Hz,
1H, H-10), 7.18 (dd, J = 7.5 and 1.2 Hz, 1H, H-7), 4.18 (d, J = 5.4 Hz,
2H, H-14), 2.32 (s, 3H; H-18). 13C NMR (125 MHz, DMSO-d6): δ
161.2 (C-9), 154.2 (C-8), 152.5 (C-2), 148.8 (C-9a), 142.9 (C-18a),
138.5 (C-8a), 138.0 (C-15), 137.1 (C-3), 131.9 (C-13a), 129.8 (C-17 +
C-19), 129.8 (C-4a), 129.4 (C-13), 129.4 (C-6), 129.1 (C-11), 127.0
(C-12), 126.8 (C-16 + C-20), 118.8 (C-4), 118.1 (C-5), 117.9 (C-10),
Pd(Li)·3H2O. This compound was prepared by heating under reflux
a methanol solution (40 mL) containing H2La and Pd(OAc)2·4H2O in
a 1:1 or 2:1 molar ratio. Alternatively, this reaction could be performed
by stirring at room temperature for 16 h or even after only 4 h under
reflux if Pd(OAc)2 and the aldehyde were first mixed and then the
tosylamine was added to the resulting solution. Filtration of the
resulting green suspension yielded a green powder, which was washed
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Inorganic Chemistry
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1
with diethyl ether and dried under vacuum. Yield = 78%. H NMR
(500 MHz, DMSO-d6): δ 8.70 (s, 1H, H-9), 8.45 (d, J = 8.7 Hz, 1H,
H-4), 7.80 (d, J = 8.8 Hz, 1H, H-3), 7.78 (d, J = 8.3 Hz, 2H, H-16 +
H-20), 7.63 (d, J = 8.0 Hz, 1H, H-10), 7.46 (t, J = 8.0 Hz, 1H, H-6),
7.42 (dt, J = 7.8 and 1.5 Hz, 1H, H-11), 7.34 (t, J = 7.4 Hz, 1H, H-12),
7.30 (dd, J = 7.4 and 1.2 Hz, 1H, H-13), 7.13 (d, J = 8.0 Hz, 2H, H-17
+ H-19), 6.93 (d, J = 8.1 Hz, 1H, H-5), 6.59 (d, J = 8.0 Hz, 1H, H-7),
4.24 (s, 2H, H-14), 2.36 (s, 3H, H-18). 13C NMR (125 MHz, DMSO-
d6): δ 174.1 (C-8), 168.2 (C-9), 148.2 (C-2), 144.2 (C-8a), 142.6 (C-
15), 140.4 (C-18a + C-9a), 138.2 (C-4), 137.3 (C-13a), 136.8 (C-6),
132.0 (C-4a), 131.3 (C-13), 130.7 (C-12), 129.3 (C-11), 129.0 (C-17 +
C-19), 126.9 (C-16 + C-20), 122.6 (C-3), 119.9 (C-10), 114.9 (C-7),
111.7 (C-5), 49.8 (C-14), 21.3 (C-18). FTIR (KBr, cm−1): ν(O−H)
3442(b,m), ν(CNimi) 1586(s), ν(CNquin) 1563(m), νas(SO2)
1336(s), νs(SO2) 1142(vs). MS (FAB+) m/z (%): 536.0 (100) [M+ −
3H2O]. Anal. Calcd for C24H19N3O3PdS·3H2O: C, 48.8; H, 4.2; N, 7.1;
S, 5.4. Found: C, 48.2; H, 3.9; N, 7.0; S, 5.2.
ASSOCIATED CONTENT
* Supporting Information
■
S
CIF data. Energy details of the most stable conformers of
compounds H2Li and H2La, square planar PdII and NiII
complexes, as well as octahedral NiII complexes. Representative
NMR bidimensional spectra of compounds H2Li, H2La and
1
Pd(HLi)2 as well as H NMR spectrum of Pd(HLa)2. IR and
UV−vis spectra of Pd(HLi)2·MeOH, Ni(HLa)2·4MeOH,
Pd(Li)·3H2O, and Ni(Li)·MeOH. Energy details of the reaction
intermediates and transition states. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jesus.sanmartin@usc.es. Fax: +34 981 528073.
■
Pd(HLi)2·MeOH. This compound was obtained from a methanol
solution (40 mL) containing H2La and Pd(OAc)2·4H2O in a 1:2 molar
ratio under reflux for 2 h. During the reaction the color of the solution
changed from the initial green, which is due to the formation of
Pd(Li), to the final maroon. Filtration of the resulting suspension
yielded a maroon powder, which was washed with diethyl ether and
ACKNOWLEDGMENTS
Financial support from the Ministerio de Ciencia e Innovacion
(CTQ2010-19191 to J.S.-M. and SAF2010-15076 to C.G.-B.)
and the Xunta de Galicia (10PXIB2200122PR and GRC2010/
12 to C.G.-B.) is gratefully acknowledged. We are also grateful
■
́
1
dried under vacuum. Yield: 57%. H NMR (500 MHz, DMSO-d6): δ
to the Centro de Supercomputacion de Galicia (CESGA) for
the use of the Finis Terrae computer.
́
9.33 (s, 1H, H-9), 8.16 (d, J = 8.6 Hz, 1H, H-4), 7.90 (t, J = 6.1 Hz,
1H, NH), 7.74 (d, J = 8.5 Hz, 1H, H-3), 7.70 (d, J = 8.1 Hz, 2H, H-16 +
H-20), 7.42 (d, J = 7.4 Hz, 1H, H-13), 7.37 (d, J = 8.1 Hz, 2H, H-17 +
H-19), 7.27 (d, J = 7.3 Hz, 1H, H-10), 7.25 (t, J = 7.4 Hz, 1H, H-12),
7.20 (t, J = 7.4 Hz, 1H, H-11), 7.14 (t, J = 7.6 Hz, 1H, H-6), 6.84 (d, J =
7.8 Hz, 1H, H-5), 6.49 (d, J = 7.8 Hz, 1H, H-7), 4.16 (d, J = 6.0 Hz, 2H,
H-14), 2.37 (s, 3H, H-18). 13C NMR (125 MHz, DMSO-d6): δ 158.6
(C-9), 139.5 (C-4), 130.7 (C-6), 129.8 (C-17 + C-19), 129.3 (C-13),
127.8 (C-11), 127.8 (C-12), 126.8 (C-16 + C-20), 120.0 (C-3), 118.5
(C-10), 114.1 (C-7), 112.7 (C-5), 42.4 (C-14), 21.4 (C-18). FTIR
REFERENCES
■
(1) Boca, M.; Baran, P.; Boca, R.; Fuess, H.; Kickelbick, G.; Linert,
W.; Renz, F.; Svoboda, I. Inorg. Chem. 2000, 39, 3205−3212.
(2) Zeyrek, C. T.; Elmali, A.; Elerman, Y. Z. Naturforsch. 2005, 60b,
520−526.
(3) (a) Bera, M.; Mukhopadhyay, U.; Ray, D. Inorg. Chim. Acta 2005,
358, 437−443. (b) Nanda, P. K.; Mandal, D.; Ray, D. Polyhedron 2006,
25, 702−710.
(4) Emam, S. A.; McArdle, P.; McManus, J.; Mahon, M. Polyhedron
2008, 27, 2379−2385.
(5) (a) Bermejo, M. R.; Sousa, A.; Fondo, M.; Helliwell, M. New J.
Chem. 2000, 24, 33−38. (b) Sousa, A.; Bermejo, M. R.; Fondo, M.;
García-Deibe, A.; Sousa-Pedrares, A.; Piro, O. New J. Chem. 2001, 25,
647−654.
(KBr, cm−1): ν(O−H) 3430(b,m), ν(N−H) 3289(m), ν(CNquin
)
1598(m), ν(CNimi) 1557(s), νas(SO2) 1328(s), νs(SO2) 1161(vs). MS
(MALDI+-TOF) m/z (%): 1005.1 (9) [M − MeOH + K]+. Anal. Calcd
for C48H40N6O6PdS2·MeOH: C, 58.9; H, 4.4; N, 8.4; S, 6.4. Found: C,
58.9; H, 4.0; N, 8.5; S, 6.4.
Ni(Li)·MeOH. This complex was obtained by stirring a methanol
solution (40 mL) containing 0.1 g (0.231 mmol) of H2Li (or H2La)
and 0.057 g of Ni(OAc)2·4H2O (0.231 mmol) at room temperature
for around 5 min. Concentration under reduced pressure of the
resulting brown solution yielded an oily product, which was stirred
with diethyl ether (20 mL) for 10 min. This gave a brown powder,
which was filtered off and dried in vacuum. Yield: 0.053 g (44%). UV−
vis (MeOH, nm) λ 196, 277. MS (FAB, positive) m/z (%): 488.1
(100) [M − MeOH + H]+. FTIR (KBr, cm−1): ν(O−H) 3420 (b,m),
ν(CNimi) 1595 (vs), νas(SO2) 1344(s), νs(SO2) 1162(vs). Anal.
Calcd for C24H19N3NiO3S·MeOH: C, 57.7; H, 4.5; N, 8.1; S, 6.2.
Found: C, 57.9; H, 5.0; N, 8.4; S, 6.1.
(6) Bref
́
uel, N.; Lepetit, C.; Shova, S.; Dahan, F.; Tuchagues, J.-P.
Inorg. Chem. 2005, 44, 8916−8928.
̇
̧olak, A. T.; Tas,̧ M.; Irez, G.; Yesi̧ lel, O. Z.; Buyukgungor, O. Z.
̈ ̈ ̈
̈
(7) C
Anorg. Allg. Chem. 2007, 633, 504−508.
̇
(8) Mutlu, H.; Irez, G.; Turk, J. Chemistry 2008, 32, 731−741.
(9) (a) Vazquez, M.; Bermejo, M. R.; Sanmartín, J.; García-Deibe,
́
A. M.; Lodeiro, C.; Mahia, J. J. Chem. Soc., Dalton Trans. 2002, 870−
877. (b) Fondo, M.; Ocampo, N.; García-Deibe, A. M.; Sanmartín, J.
Inorg. Chem. 2009, 48, 4971−4979.
(10) (a) García-Santos, I.; Sanmartín, J.; García-Deibe, A. M.; Fondo,
́
M.; Gomez, E. Inorg. Chim. Acta 2010, 363, 193−198. (b) García-
Ni(HLa)2·4MeOH. This complex was obtained by stirring a
methanol solution (40 mL) containing H2La (or H2Li) and
Ni(OAc)2·4H2O in 1:2, 2:1, 3:2, or 1:1 molar ratios at room
temperature over a 14 h period or under reflux for around 1 h.
Concentration under reduced pressure of the brown solution yielded
an oily product, which was dissolved in diethyl ether (20 mL) and
stirred for 10 min. This gave an orange crystalline powder, which was
filtered off and dried in vacuum. Single crystals of Ni(HLa)2·4MeOH
and Ni(HLa)2·2HOAc were obtained from the mother liquor. Yield:
78%. UV−vis (MeOH, nm, ε in parentheses) λ 210 (51 142), 270 (42
Santos, I.; Sanmartín, J.; García-Deibe, A. M.; Fondo, M.; Gomez, E.
́
Polyhedron 2009, 28, 3055−3059.
(11) Parr, R. G.; Pearson, R. G. J. Am. Chem. Soc. 1983, 105, 7512−
7516.
(12) For example, see: Karayannis, N. M.; Pytlewsky, L. L.;
Mikulsky, C. M. Coord. Chem. Rev. 1973, 11, 93−159.
(13) For example, see: Cooke, M. W.; Chartrand, D.; Hanan, G. S.
Coord. Chem. Rev. 2008, 252, 903−921.
(14) Shannon, R. D. Acta Crystallogr. 1976, A32, 751−767.
(15) Sanmartín, J.; Novio, F.; García-Deibe, A. M.; Fondo, M.;
Bermejo, M. R. New J. Chem. 2007, 31, 1605−1612.
(16) Baldwin, J. E. J. Chem. Soc., Chem. Commun. 1976, 734−736.
(17) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian,
H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
3
3
285), 380 (3428) [ν2 T1 g(F) ← 3A2 g(F)], 510 (400) [ν3 T1 g(P) ←
3A2 g(F)]. MS (FAB, positive) m/z (%): 919.0 (80) [M+ − 4MeOH].
FTIR (KBr, cm−1): ν(O−H) 3415(b,m), ν(N−H) 3303(m), ν(C
Nquin) 1598(m), νas(SO2) 1347(s), νs(SO2) 1163(vs). Anal. Calcd for
C48H40N6NiO6S2·4MeOH: C, 59.6; H, 5.4; N, 8.0; S, 6.1; S, 7.3.
Found: C, 59.9; H, 5.1; N, 8.4; S, 6.1.
1292
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Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar,
S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.; Knox,
J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels,
̈
A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.
Gaussian 09, Revision A.2; Gaussian, Inc.: Wallingford CT, 2009.
(18) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215−241.
(19) Zhao, Y.; Truhlar, D. G. Acc. Chem. Res. 2008, 41, 157−167.
(20) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105,
2999−3094.
(21) (a) Ochs, C.; Hahn, F. E.; Lugger, T. Eur. J. Inorg. Chem. 2001,
1279−1285. (b) Ochs, C.; Hahn, F. E.; Frohlich, R. Chem.Eur. J.
2000, 6, 2193−2199.
(22) (a) Otter, C. A.; Couchman, S. M.; Jeffery, J. C.; Mann, K. L. V.;
Psillakis, E.; Ward, M. D. Inorg. Chim. Acta 1998, 278, 178−184.
́ ́ ́
(b) Cabaleiro, S.; Castro, J.; Vazquez-Perez, E.; García-Vazquez, J. A.;
Romero, J.; Sousa, A. Polyhedron 1999, 18, 1669−1674. (c) Mahía, J.;
Maestro, M.; Vazquez, M.; Bermejo, M. R.; Sanmartín, J.; Maneiro, M.
Acta Crystallogr. 1999, C55, 1545−1547. (d) Vazquez, M.; Bermejo,
́
́
M. R.; Sanmartín, J.; García-Deibe, A. M.; Lodeiro, C.; Mahía, J.
J. Chem. Soc., Dalton Trans. 2002, 870−877. (e) Bermejo, M. R.;
Sanmartín, J.; García-Deibe, A. M.; Fondo, M.; Novio, F.; Navarro, D.
Inorg. Chim. Acta 2003, 347, 53−60. (f) Garnovskii, A.; Guedes da Silva,
M. F. C.; Koplovich, M. N.; Garnovskii, A. D.; Frausto da Silva, J. J. R.;
Pombeiro, A. J. L. Polyhedron 2003, 22, 1335−1340. (g) Sanmartín, J.;
García-Deibe, A. M.; Fondo, M.; Novio, F.; Ocampo, N.; Bermejo, M. R.
Inorg. Chim. Acta 2006, 359, 3156−3166.
(23) (a) Roychowdhury, P.; Das, B. N.; Basak, B. S. Acta Crystallogr.
1978, B34, 1047−1048. (b) Banerjee, T.; Saha, N. N. Acta Crystallogr.
1986, C42, 1408−1411. (c) Ali, M. A.; Mirza, A. H.; Haniti, M.;
Hamid, S. A.; Bernhardt, P. V. Polyhedron 2005, 24, 383−390.
(24) (a) Lennon, D.; Freer, A. A.; Winfield, J. M.; Landon, P.; Reid,
N. Green Chem. 2002, 4, 181−187. (b) Wang, Z.-G.; Wang, R.; Zhang,
Y.; Zhi, F.; Yang, Y.-L. Acta Crystallogr. 2009, E65, o550.
(25) (a) Jeffrey, G. A. An Introduction to Hydrogen Bonding; Oxford
University Press: Oxford, U.K., 1997. (b) Steiner, T. Angew. Chem., Int.
Ed. 2002, 41, 48−76.
(26) (a) SADABS−Bruker AXS Area Detector Scaling and Absorption
Correction, Version 2008/1; University of Gottingen: Gottingen,
̈
̈
Germany, 2008. (b) Blesing, R. H. Acta Crystallogr. 1995, A51, 33−38.
(27) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.;
Cascarano, G. L.; De Caro, L.; Giacovazzo, C.; Polidori, G.; Spagna, R.
J. Appl. Crystallogr. 2005, 38, 381−388.
(28) Sheldrick, G. M. SHELX97. Acta Crystallogr. 2008, A64, 112−
122.
(29) (a) Allen, F. H. Acta Crystallogr. 2002, B58, 380−388.
(b) Bruno, I. J.; Cole, J. C.; Edginton, P. R.; Kessler, M. C.; Macrae,
F.; McCabe, P.; Pearson, J.; Taylor, R. Acta Crystallogr. 2002, B58,
389−397.
(30) For examples, see: (a) Zimmer, M.; Schulte, G.; Luo, X.-L.;
Crabtree, R. H. Angew. Chem., Int. Ed. 1991, 30, 193−194. (b) Ohta,
H.; Harada, K.; Irie, K.; Kashino, S.; Kambe, T.; Sakane, G.; Shibahara,
T.; Takamizawa, S.; Mori, W.; Nonoyama, M.; Hirotsu, M.; Kojima,
M. Chem. Lett. 2001, 842−843. (c) Okabe, N.; Muranishi, Y. Acta
Crystallogr. 2002, C58, m475−m477. (d) Cui, X.; Calhorda, M. J.;
Costa, P. J.; Delgado, R.; Drewand, M. G. B.; Felix, V. Helv. Chim. Acta
2004, 87, 2613−2628. (e) You, Z.-L.; Zhu, H.-L.; Liu, W.-S. Acta
Crystallogr. 2004, E60, m805−m807. (f) Fondo, M.; García-Deibe,
A. M.; Ocampo, N.; Sanmartín, J.; Bermejo, M. R.; Llamas-Saiz, A. L.
Dalton Trans. 2006, 45, 4260−4270.
1293
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