Synthesis, characterization and study of the catalytic properties of Zn(II) camphor derived complexes Dedicated to Prof. Maria José Calhorda on the occasion of her 65th birthday.

Article abstract of DOI:10.1016/j.jorganchem.2013.10.040

Zinc(II) complexes of general formula [ZnX₂(YNC ₁₀H₁₄O)], [ZnX₂(YNC₁₀H ₁₃NSO₂)], [ZnX₂(H₂NNC ₁₀H₁₄O)₂], [{ZnX₂}

Full text of DOI:10.1016/j.jorganchem.2013.10.040

Journal of Organometallic Chemistry 760 (2014) 186e196
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization and study of the catalytic properties of
Zn(II) camphor derived complexes
Tiago A. Fernandes a, Ana M. Ferraria b, Adelino M. Galvão a, Ana M. Botelho do Rego b,
,
Ana C.M. Suárez a, M.Fernanda N.N. Carvalho a
*
a Centro de Química Estrutural, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
b Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, Technical University of Lisbon, Av.
Rovisco Pais, 1049-001 Lisboa, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Zinc(II) complexes of general formula [ZnX2(YNC10H14O)], [ZnX2(YNC10H13NSO2)], [ZnX2(H2NNC10
H14O)2], [{ZnX2}2(YNC10H14O)] and [{ZnX2}2(YNC10H13NSO2)] were obtained from zinc halides (chloride
or bromide) by reaction with the suitable camphor ligands.
Received 16 September 2013
Received in revised form
21 October 2013
In most of the complexes, the camphor ligands remain unchanged upon coordination, except in
Accepted 23 October 2013
[{Zn(MeNNC10H14O)}2(m-Cl)2] where proton loss from MeHNNC10H14O occurs. The new complexes and
camphor derivatives were characterized by IR, NMR (1H, 13C{H}, DEPT, 2D) and elemental analysis. In
some cases the surface composition was studied by X-ray photoelectron spectroscopy (XPS) and imaged
Dedicated to Prof. Maria José Calhorda on
the occasion of her 65th birthday.
by
Scanning
Electron
Microscopy
(SEM).
Images
of
[ZnCl2(Me2NNC10H14O)]
and
[ZnCl2(Me2NNC10H13NSO2)] obtained by SEM show the solid particles have tubular structures capped in
one or both extremities. The coordination of THF in [ZnCl2(YNC10H14O)THF] was confirmed by X-ray
diffraction analysis. The camphor derivatives YNC10H14NSO2 (Y ¼ NMe2; NHMe) and p-C6H4(NC10H14O)2
were structurally characterized by X-ray diffraction analysis.
The ability of selected Zn(II) camphor complexes to catalyse the cyclization of 4-pentyn-1-ol was
evaluated showing that the binuclear complex [{ZnX2}2(YNC10H14O)] performs better than the mono-
nuclear Zn(II) complexes.
Keywords:
Zinc complexes
Camphor derivatives
Alkynol
Catalysis
XPS
SEM
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
to promote the cyclization of alkynols [12], the one-pot activation of a
second alkynol molecule is characteristic of camphor derived Pd and
Synthesis of several fine organic chemicals, rely, nowadays, on
processes catalysed by transition metals or complexes. Thus, design
of new and more efficient catalysts is an attractive topic for research
on synthesis and catalysis. Under such perspective the design of
catalysts able to activate CC triple bonds in processes with high
regio selectivity and atom economy, difficult to promote in the
absence of a catalyst [1e3]. Within our studies it was verified that
camphor derived Pd and Pt complexes are efficient catalysts for
alkynes cyclization or alkynols cycloisomerization [4e7] extending
the role of the camphor ligands to processes other than the chirality
control of reaction products [8e11].
Pt complexes. In order to verify whether this characteristic is also
present in other camphor complexes, several zinc camphor derived
complexes were synthesized and their reaction with 4-pentyn-1-ol
was studied. Zinc looked a good choice because it is much cheaper
than Pt or Pd, it is more environmental friendly, stabilizes coordina-
tion numbers four and five [13] and was recently considered
outstanding for homogeneous catalysis [14]. Furthermore, there are
reports on zinc complexes reacting under solvent free conditions
[15,16] which is a type of process potentially interesting.
2. Results and discussion
The cyclization of alkynols promoted by palladium or platinum
camphor complexes involves the activation of two molecules of
alkynol forming O-heterocycles with a pending alkyne group (see
Scheme1 inthecatalytic studies). Althoughothercatalysts are known
2.1. Synthesis and structural characterization
Several Zn(II) complexes were obtained by reaction of zinc
halides with camphor derivatives that were labelled with a number
followed by a letter for clarity. Numbers refer to the metal to ligand
ratio and the halide co-ligand; letters relate to the type of camphor
* Corresponding author.
E-mail address: fcarvalho@ist.utl.pt (M.F.N.N. Carvalho).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.10.040

T.A. Fernandes et al. / Journal of Organometallic Chemistry 760 (2014) 186e196
187
Table 1
Selected bond lengths and angles for [ZnCl2(Me2NNC10H14O)(THF)] (1a0).
Angles (ꢀ)
ꢀ
Bond lengths (A)
Zn(1)eO(1)
Zn(1)eO(2)
Zn(1)eCl(2)
Zn(1)eCl(1)
O(1)eC(11)
C(11)eC(12)
C(12)eN(1)
N(1)eN(2)
N(2)eC(21)
N(2)eC(22)
2.044(1)
2.134(1)
2.218(1)
2.220(1)
1.244(2)
1.452(2)
1.307(2)
1.305(2)
1.454(2)
1.455(2)
O(1)eZn(1)eO(2)
O(1)eZn(1)eCl(2)
O(2)eZn(1)eCl(2)
O(1)eZn(1)eCl(1)
O(2)eZn(1)eCl(1)
Cl(2)eZn(1)eCl(1)
C(11)eO(1)eZn(1)
N(2)eN(1)eC(12)
C(21)eN(2)eC(22)
N(1)eN(2)eC(21)
N(1)eN(2)eC(22)
84.06(5)
117.42(4)
98.64(3)
113.54(4)
97.57(3)
127.66(2)
117.0(1)
125.5(1)
117.9(1)
117.8(1)
124.3(1)
Scheme 1. Cyclization of 4-pentyn-1-ol catalysed by Zn(II) complexes.
ligand: [ZnX2(YNC10H14O)] (X ¼ Cl: Y ¼ NMe2 1a, Y ¼ C6H4NH2 1d,
Y ¼ NC6H4N 1e; X ¼ Br: Y ¼ NMe2 2a, Y ¼ C6H4NH2 2d, Y ¼ NC6H4N
2e, Y ¼ m-C6H4NC10H14O 2j); [ZnX2(YNC10H13NSO2)] (X ¼ Cl:
Y ¼ NMe2 1f; X ¼ Br: Y ¼ NMe2 2f); [ZnX2(H2NNC10H14O)2] (X ¼ Cl
3b, X ¼ Br 4b); [{ZnX2}2(YNC10H14O)] (X ¼ Cl: Y ¼ p-C6H4NC10H14
O
6i, Y ¼ m-C6H4NC10H14O 6j; X ¼ Br: Y ¼ p-C6H4NC10H14O 7i) and
[{ZnX2}2(YNC10H13NSO2)] (X ¼ Cl: Y ¼ NH2 6g; X ¼ Br: Y ¼ NHMe
7h).
Most of the complexes crystallize with solvent molecules in the
lattice (see experimental). In the case of [ZnCl2(Me2NNC10H14O)(THF)]
(1a0) analysis by single crystal X-ray diffraction (XRD) showed that one
molecule of THF coordinates the metal. Complex 1a0 crystallizes in the
monoclinic P21 space group (Fig. 1) with a trigonal bipyramidal ge-
ometry. The camphor hydrazone (Me2NNC10H14O, a) coordinates the
metal through the oxygen and the nitrogen atoms, although the dis-
(138.8 ppm) compared to complexes Pd(II) (175.0 ppm) or Pt(II)
(176.0 ppm) [21,22] or the free ligand (a, 143.8 ppm).
The elemental composition obtained by microanalysis (C, N, H,
S) allows formulation of the new complexes, the spectroscopic IR
and NMR data allow an insight into the coordination of the
camphor ligands and the optical rotation shows that a selection of
complexes keep the right-handed rotation of the ligands (see
experimental). XPS provides information on the surface composi-
tion of the powders and SEM shows the respective image.
Camphor derived compounds used as ligands are shown in
Fig. 3. The analytical and spectroscopic characterization of the new
bi-camphor compounds (i and j) is displayed in the experimental
section (5.1).
ꢀ
tance between the nitrogen atom and zinc (2.54 A) is among the longer
ZneN bond lengths reported [17e19]. The calculated Mulliken atomic
overlap population (0.054) and bond order (0.096) are consistent with
a weak ZneN bonding.
The camphor ligand shares the equatorial position of the com-
plex with the two chloride ligands. THF occupies one of the axial
positions and the imine nitrogen atom the other one (Fig. 1).
Selected bond lengths and angles for 1a0 are in the expected
ranges as displayed in Table 1.
Complexes [ZnX2L] (X ¼ Cl, L: d (1d); e (1e); f, (1f); X ¼ Br, L: a
(2a), d (2d), e (2e); f, (2f); j (2j)) and [ZnCl2(Me2NNC10H14O)THF]
(1a0) obtained by reaction of ZnX2 (X ¼ Cl, Br) with camphor ligands
YNC10H14O (Y ¼ NMe2 (a), p-C6H4NH2 (d)), camphor sulphonyli-
mine (Me2NNC10H13NSO2 (f)), camphorquinoxaline (e), or the bi-
camphor (j) have elemental compositions consistent with metal
to ligand ratios 1:1. The FTIR and NMR spectra show that complexes
2a (X ¼ Br) and 1a0 (X ¼ Cl), which essentially differ in the halide co-
ligand, are spectroscopically similar, i.e. the values of the IR bands
In the structure of 1a0 it is worth to highlight that the amine
nitrogenꢀatom (N2) shows no pyramidalization (the three angles
ꢀ
sum 360 ). The bond length N1eN2 (1.305(2) A) is shorter than the
ꢀ
average for a single NeN bond length (1.425 A) [20], pointing to an
extended
p-delocalization through the N2eN1eC12eC11eO sys-
tem. DFT calculations show that the CO and CN (ca. 1.8) bond orders
are lower and the CC and NN (ca. 1.1) bond orders higher, respec-
tively, than the typical values for double and single bonds, in
agreement with electron delocalization (Fig. 2). This also explains
the shifts to lower values observed in the FTIR stretching frequency
(
nCO,
nCN, see Supplementary tables) and 13C{H} NMR chemical
shifts (C]N) decrease upon coordination pointing to an oxygen
bound ligand in 2a such as observed by X-ray diffraction analysis in
1a0. In contrast, complexes 1d and 2d display IR bands (nCO
, nCN) at
(
nCO) of the coordinated camphor hydrazone (Me2NNC10H14O, a)
higher values than those observed for the free ligands pointing to
coordination through the oxygen and imine nitrogen atoms, the
ligand behaving as chelating.
and the lower 13C{H} NMR chemical shift of the imine carbon atom
In complexes [ZnX2{(NC6H4)NC10H14O)}] (X ¼ Cl 1e and X ¼ Br
2e) just one IR band (1516, and 1517 cmꢁ1, respectively) is observed
in the range assigned to the C]N bond pointing to equivalent
stretching of the CN bonds in camphorquinoxaline (e). The values
do not differ much from those for the free ligand (1514 cmꢁ1). In the
Fig. 1. ORTEP drawing for [ZnCl2(Me2NNC10H14O)(THF)] (1a0) showing atom labelling
scheme. Hydrogen atoms were omitted for clarity. Ellipsoids are drawn at 50%
probability.
Fig. 2. Bond orders calculated by DFT B3LYP with Grimme’s dispersion.

188
T.A. Fernandes et al. / Journal of Organometallic Chemistry 760 (2014) 186e196
Fig. 3. Camphor derivatives used as ligands.
13C{H} NMR spectrum, two signals attributed to the imine carbon
atoms (1e, 167.4, 165.1; 2e, 167.8, 165.4 ppm) at values slightly
higher (ca. 2 ppm) than those in the free ligand [23] point to some
deshielding upon coordination.
No complexes of general formula [ZnX2L] were obtained by reac-
tion of H2NNC10H14O or MeHNNC10H14O with zinc halides. In those
cases there is formation of the complexes [ZnX2(H2NNC10H14O)2]
that exhibits one camphor ligand in the E and the other in the Z
configuration [6]. One band in the IR spectrum would be expected
for two equivalent ligands [24].
The above results show that the characteristics of the camphor
substituent (Y) play a relevant role in the type of Zn complex
formed. In order to evaluate the effect of the replacement of a ke-
tone by an imine group in position 2 (see Fig. 3) and introduce more
steric hindrance, reactions of zinc halides with camphor sulpho-
nylimines (YNC10H13NSO2) were performed. Camphor sulphonyli-
mines were chosen because they have coordinative bites that do
not differ much from camphorimines (YNC10H14O).
The structural analysis of camphor sulphonylimines
Me2NNC10H13NSO2 (f) and MeHNC10H13NSO2 (h) show they crys-
tallize in the orthorhombic (P212121) space group in configurations
(Z) (f) and (E) (h), respectively (Fig. 4, for bond lengths and angles,
see Supplementary data).
The bite angles of (f) and (h) are very sensitive to the isomer
type (E or Z) and less sensitive to their bicyclic or tricyclic character,
as verified by comparing data herein with that reported for
Me2NNC10H14O (a) [25] (Fig. 5).
Complexes [ZnX2(Me2NNC10H13NSO2)] (X ¼ Cl 1f; X ¼ Br 2f)
obtained from camphor sulphonylimine ligands (YNC10H13NSO2)
display two IR bands in the region assigned to the C]N stretching
frequencies (1f, 1657, 1547 cmꢁ1; 2f, 1617, 1539 cmꢁ1) that are
shifted to values higher than those of the free ligand
(Me2NNC10H13NSO2, 1584, 1521 cmꢁ1) similarly to Zn(II) complexes
(X ¼ Cl 3b, X ¼ Br 4b) and [{Zn(MeNNC10H14O)}2(
m-Cl)2] (5c1),
respectively.
Hydrogen bonding involving the halide co-ligand, conceivably,
inhibits ligand chelation thus enabling a second camphor ligand to
coordinate in 3b and 4b and promoting HCl release to yield 5c1 (Eq.
(1)). In loco formation of the anionic ligand (MeNNC10H14Oꢁ, c1)
from MeHNNC10H14O was found in [Pd(MeNNC10H14O)2] [5].
2ZnCl2 þ 2MeHNNC10H14O / [{Zn(MeNNC10H14O)}2(
m-
Cl)2] þ 2HCl
(1)
Complexes [ZnX2(H2NNC10H14O)2] display two bands (3b 1636,
1584; 4b 1634, 1581 cmꢁ1) in the region attributed to the C]N
stretching in the IR spectra that point to non-equivalent ligands.
That is also the case in [{Zn(MeNNC10H14O)}2(m-Cl)2], with a
dinuclear formulation, that displays distinct C]O and C]N
stretching frequencies for the two ligands (1709, 1689 (nCO), 1616,
1569 (nCN) cmꢁ1). E/Z isomerization could also account for non-
equivalent ligands such as reported for cis-[PtCl2(PhNC10H14O)2]
Fig. 4. ORTEP drawing for Me2NNC10H13NSO2 (f, left) and MeHNNC10H13NSO2 (h, right). Hydrogen atoms were omitted for clarity. Ellipsoids are drawn at 50% probability. See
Supplementary data for details.

T.A. Fernandes et al. / Journal of Organometallic Chemistry 760 (2014) 186e196
189
Fig. 5. Schematic structures of species a (E-isomer), h (E-isomer) and f (Z-isomer), showing bite angles.
derived from the camphor hydrazones (b, d). The band at higher
value is attributed to the sulphonylimine group. IR data, together
with the need for coordinative saturation, suggest the camphor
derived ligands have a chelating character.
orthorhombic P212121 space group. The two nitrogen atoms depict
sp2 geometry forming angles of 118.6(2)ꢀ (N2) and 121.7(2)ꢀ (N3)
with the neighbour carbon atoms. The bridging phenyl group oc-
cupies a nearly orthogonal position to the two camphorimine
moieties (angles between the nitrogen and phenyl planes are 82.5ꢀ
(N2) and 78.3ꢀ (N3)) inhibiting extended electron delocalization
Camphor sulphonylimines (YNC10H13NSO2) with substituents
such as Y ¼ NHMe, h or Y ¼ NH2, g, (Fig. 3) do not form complexes
of type [ZnX2L]. Instead, complexes [{ZnCl2}2(H2NNC10H13NSO2)]
(6g) and [{ZnBr2}2(MeHNNC10H13NSO2)] (7h) were obtained. At-
tempts to grow single crystals were unsuccessful and, conse-
quently, structural information on ligand bonding in complexes 6g
and 7h could not be obtained. Nevertheless, the shift of the IR
bands (nC¼N and nC¼NSO2) to higher values relative to the free ligands
is consistent with coordination through the two nitrogen atoms.
Aiming to obtain complexes with structural motifs that include
more than one metal atom per ligand, ZnX2 was reacted with the bi-
camphor species (NC10H14O)2C6H4 (i and j, Fig. 3). From reaction of
the bi-camphor ligand with the two camphor moieties in para posi-
tion, the complexes [(ZnCl2)2{(p-NC10H14O)2C6H4}] (6i) and
[(ZnBr2)2{(p-NC10H14O)2C6H4}] (7i) were obtained. [(ZnCl2)2{(m-
NC10H14O)2C6H4}] (7j) was obtained from the ligand in which the
camphor moieties are in meta position. However, no such type of
complexwasobtainedfromreactionofZnBr2 withm-NC10H14O)2C6H4
(j), conceivably due to the steric hindrance by the bromide co-ligand.
The IR bands (nC¼N and nC¼O) observed for complex 7i (1685,
1756 cmꢁ1) do not differ from those of the free ligand (1685,
1756 cmꢁ1) whereas those observed for 6i (1689, 1748 cmꢁ1) and 6j
(1668, 1734 cmꢁ1) differ slightly. The same tendency was observed
by NMR suggesting a weaker coordination of the bi-camphor ligand
in 7i than in 6i or 6j which is attributed to the higher steric re-
quirements of bromide.
between the camphor units through the p-system.
2.2. X-ray photoelectron spectroscopy studies (XPS)
The surface properties of selected compounds were studied by
XPS (X-ray photoelectron spectroscopy) in the regions corre-
sponding to the halogen (Cl 2p or Br 2p), to zinc (Zn 2p3/2), to
carbon (C 1s), to oxygen (O 1s) and, for some of them, sulphur (S
2p). Table 2 summarizes the data obtained for binding energies (BE)
and respective assignments. A few XPS atomic ratios were included.
The Zn 2p3/2 region was fit with a single peak centred at
1022.5 ꢂ 0.2 eV assigned to Zn(II) except for 1e, where the amount
of carbon exceeds the stoichiometric one by a factor of ca. 2. Since
the binding energy of C 1s in CeC and CeH bonds was taken as
reference for correcting binding energy charge shifts, the fact that
in 1e a lot of carbon coming from a different origin exists may be
the reason for larger values found for Zn 2p3/2, Cl 2p and N 1s
binding energy in this sample.
The XPS Cl 2p region was fit with a single doublet having a spin-
orbit split of 1.6 ꢂ 0.1 eV; its main component, Cl 2p3/2 is centred at
198.8 ꢂ 0.2 eV a value very close to the one found in CuCl complexes
[26]. However, when sample 1a0 was irradiated with 5 sweeps, a
second small Cl 2p doublet, with the main component (Cl 2p3/2
)
centred at BE ¼ 200.4 ꢂ 0.2 eV, absent in the single sweep spec-
trum, was needed for a good fit. This BE value is typical of chlorine
bound to carbon [27] suggesting that this bond is promoted by
irradiation. This effect was not observed for 1a that was washed
No crystals of the complexes could be obtained. However,
structural characterization by X-ray diffraction analysis of ligand i
(para) was achieved (Fig. 6). (NC10H14O)2C6H4 crystallizes in the
Fig. 6. ORTEP drawing for ligand (i). Hydrogen atoms were omitted for clarity. Ellipsoids are drawn at 50% probability. (see Supplementary for details).

190
T.A. Fernandes et al. / Journal of Organometallic Chemistry 760 (2014) 186e196
Table 2
XPS binding energy (ꢂ0.2 eV) and ratios (ꢂ10%).
XPS region
(1a0)
(1a)
(1e)a
(1f)
(2a)
(2f)
(7i)
Assignments
Zn 2p3/2
N 1s 1
1022.5
(399.3)
1022.5
(399.4)
1023.1
400.1
1022.7
399.6
1022.7
(399.2)
1022.5
399.5
1022.6
Zn2þ
eNC6H4Ne
eNSO2e
eMe2NNC10e
Cld
N 1s 2
401.0
198.7
200.3
200.4
202.1
401.0
198.7
200.3
400.7
198.7
200.4
199.7
201.4
401.1
400.8
400.5
Cl 2p3/2
Cl 2p1/2
Cl 2p3/2
Cl 2p1/2
Br 2p3/2
Br 2p1/2
S 2p3/2
S 2p1/2
O 1s
C 1s 1
C 1s 2
C 1s 3
Halogen/Zn
N/halogen
C/N
1
1
2
2
199.0
200.6
200.1
201.7
CeCl
Brd
182.7
189.4
182.4
189.1
168.4
169.6
532.2
285.0
286.1
182.7
189.4
168.3
169.5
532.3
285.0
286.1
288.6
2.3
1.1
7.9
1.8
eSO2e
532.2
285.0
286.7
288.6
2.5
0.9
8.5
1.9
532.3
285.0
285.9
288.1
2.0
0.9
7.7
0.7
532.4
285.0
286.1
289.4
2.5
0.7
15.1
2.8
532.3
285.0
286.9
532.4
285.0
285.9
288.1
CeO
CeC, CeH
CeN þ CeO
C]O
2.2
0.9
10.6
2.4
2.1
1.5
7.0
1.6
O/N
a
See text for a comment on the charge shift correction for this sample.
with dichloromethane. In sample 1f, the same effect is noticed.
However, chlorine is more labile than in sample 1a0 since it occurs
even for the single sweep spectrum. The relative importance of the
second doublet increases with the irradiation time. In compound
1e, that was prepared in CH2Cl2, two doublets with similar in-
tensities were needed to reach a good fit. These observations
combined to the enormous difference between the measured C/N
ratio and the stoichiometric one, suggest that occluded solvent
stays in the sample.
Cl 2p3/2 at higher binding energy comes mainly from the sol-
vent. However the hypothesis that a part of it corresponds also to
chlorine from the complex that bonds to carbon atoms, cannot be
discarded since the relative importance of this second doublet in-
creases with radiation time. Another explanation for this compo-
nent increase is the diffusion of the occluded solvent towards the
surface due to the sample heating induced by irradiation.
Analysis of the XPS Br 2p region in the samples with the Br co-
ligand (2a, 2f, 7i) showed that, independently of the number of run
sweeps, a single doublet with the main component Br 2p3/2 centred
at BE ¼ 182.5 ꢂ 0.2 eV fitted the data in agreement with results
reported for Cu(I) camphor derived complexes [21].
SEM pictures obtained from 1f clearly show that the morphology of
the powder consists of tubes with one or both capped extremities.
Solvent retention is, therefore possible (Fig. 8) even in the XPS
ultra-high vacuum conditions.
The experimental halogen/zinc atomic ratios are trendily higher
than the stoichiometric ones which, combined with the fact that C/
N ratio is also much higher than the stoichiometric one, means that,
at least partly, the extra carbon is due to a solvent layer retained
near the surface of the sample. This layer leads to the attenuation of
photoelectrons coming from the complex. Zn 2p having a much
lower kinetic energy (¼1486.6 eV-BE) are more attenuated than the
For samples 1a0 and 2a the N 1s region displays one single
component with BE around 401.0 eV denoting electron depletion in
nitrogen, relatively to imine or amine nitrogen atoms [22]. A single
component was fit also for sample 1e at BE ¼ 400 eV (or lower)
denoting a higher electron density around the nitrogen atom. For
samples 1f and 2f two components were fit at 399.5 and
400.7 ꢂ 0.2 eV the second one having an intensity which is twice
the first one. The first component is attributed to the hydrazide
group (NNMe2) and the second to the sulphonylimine (eNSO2)
group (Fig. 7) showing that around the hydrazide nitrogen atom the
electron density is higher than around the nitrogen atoms of the
sulphonylimine group.
The N 1s components within brackets in Table 2, systematically
at lower BE, are small components that appear with irradiation,
meaning that the irradiation increases the electron density around
some of the nitrogen atoms.
The few XPS atomic ratios included in Table 2 summarize the
main quantitative observations. The nitrogen/halogen ratios are
close to the expected ones, except for samples 1e and 1f where the
ratios are lower than expected (beyond the experimental error).
Since both samples were washed with dichloromethane, some
solvent was probably retained accounting for the results obtained.
Fig. 7. XPS N 1s region for (from bottom to top) samples 1a0, 1a, 1e, 1f, 2a, 2f and 7i.

T.A. Fernandes et al. / Journal of Organometallic Chemistry 760 (2014) 186e196
191
Fig. 8. Images of complexes [ZnCl2(Me2NNC10H13NSO2)] (1f, top) and [ZnCl2(Me2NNC10H14O)] (1a, bottom) obtained by SEM.
N 1s, C 1s or Cl 2p (or Br 2p) ones, decreasing the relative intensity
2.4. Catalysis
of its photoelectrons. The amount of sample 7i analysed by XPS was
very small and, therefore, all the signals coming specifically from
this sample had very low intensity; consequently, the relative er-
rors in peak areas are large.
The reaction of 1a and 1f with 4-pentyn-1-ol (S) was carried out
in the absence of solvent and the composition of the mixture
1
verified by H NMR in CDCl3. After 3 days at 40 ꢀC no products of
Regions C 1s and O 1s contain information coming also from the
sample holder and, therefore will not be further discussed, mainly
for sample 7i where the relative contribution from the sample to
the total signal is small.
cyclization were observed, discouraging further studies.
In solution (CDCl3), 4-pentyn-1-ol (S) reacts with complexes 1a,
2a, 3b and 6i at RT with formation of a compound which was
identified by NMR (1H, 13C{H}) as 2-methyl-2-(pent-4-yn-1-yloxy)
tetrahydrofuran (P, Scheme 1) [5] and by HPLC as an unresolved
mixture of R and S enantiomers (two signals with similar areas (52/
48, RT ¼ 6.35 and 6.70 min). The lack of chirality transfer was ex-
pected due to the weak chelating character of the ligand.
To confirm the complexes were the effective catalysts, the re-
action of S with ZnZl2 was undertaken. No cyclization or other
products were obtained.
Integration of the signal assigned to the methyl group of P
(1.23 ppm in 1H NMR) (normalized by the integration of the methyl
signals of camphor) in spectra obtained from reactions of S with Zn
complexes (1a, 2a, 3b and 6i) shows that all the complexes enable
cyclization of 4-pentyn-1-ol with addition of a second molecule of
alkynol to the heterocycle, within a process similar to that pro-
moted by Pd(II) or Pt(II) camphor derived complexes, that involves
protonation and release of the camphor ligand to generate the
active catalyst [5,7].
2.3. Scanning Electron Microscopy studies (SEM)
The data from XPS strongly suggest that some solvent molecules
exist at the surface of zinc camphor complexes. Data from micro-
analysis also shows that, in the bulk, the complexes tend to keep
solvent molecules. Thus, we decided to have a closer look into the
surface characteristics of some complexes using SEM. Pictures ob-
tained from complexes 1f and 1a are displayed in Fig. 7.
Particles 1f and 1a have tubular forms. Tubes are identified since
a few of them are not capped in, at least, one of the extremities.
Fig. 8 (top) shows the detail of one of the tubes that looks like one
brick with a cavity (ca. 10 ꢃ 10
mm). In such cavities, solvent mol-
ecules can accommodate. Raise of temperature accompanying XPS
irradiation can in principle promote release of solvent captured
molecules, which under the ultra-high vacuum conditions used by
XPS analysis would evaporate. However, if they are occluded in a
closed cavity, they cannot escape. Instead, they migrate towards the
surface this providing an explanation for the high content in car-
bon, oxygen and halogen measured by XPS.
The catalytic activities of the mononuclear complexes (1a, 2a,
3b) are considerably lower at RT (100 mol P per (mol cat ꢃ mol
S ꢃ hr)) than at 40 ꢀC (ca. 400 mol P per (mol cat ꢃ mol S ꢃ hr).
From the catalysts under study, the binuclear complex 6i displays
the highest catalytic activity (Fig. 9).
The cavities observed in the particles of the Zn(II) complexes
and the XPS results became a challenge to check whether there was
a relation between the structure and the reactivity. To test that,
reactions were undertaken in the absence of solvent.
Relevant aspects concerning the catalytic activity of Zn
complexes are: i) the halide co-ligand nature (chloride considerably
enhances
the
catalytic
activity),
as
verified
for

192
T.A. Fernandes et al. / Journal of Organometallic Chemistry 760 (2014) 186e196
80
60
40
20
0
the Y group direct which type of complex forms, in particular when
cat [6i] T=40 ºC
cat [3b] T=40 ºC
cat [2a] T=40 ºC
cat [1a] T=40 ºC
cat [1a] RT
hydrogen atoms are involved (Y ¼ NHMe, NH2). Metal to ligand
ratio 1:2 was found just in the case of Y ¼ NH2 (3b, 4b); ligand
modification (Y ¼ NHMe) induces formation of the dimer species
[{Zn(MeNNC10H14O)}2(m-Cl)2] (5c1).
Analysis by XPS of a selection of Zn camphor complexes showed
that they have high tendency to keep solvent molecules in the
structure. This behaviour was further investigated by Scanning
Electron Microscopy. The images obtained by SEM (1a, 1f) reveal
tubular structures with cavities where solvent can accommodate
and remain, even in ultra-high vacuum conditions. By temperature
increase (e.g. irradiation) the solvent molecules migrate towards
the surface of the powder, entering the range of depths probed by
XPS. This may explain the high content of carbon and oxygen or
halogen found by XPS depending on the solvent characteristics. The
structural characterization of [ZnCl2(Me2NNC10H14O)(THF)] made
by single crystal X-ray diffraction analysis shows that one molecule
of solvent (THF) coordinates the metal.
0
10
20
30
40
50
60
70
80
Time (hr)
Fig. 9. Data obtained by integration of the methyl signal of P (Scheme 1) in the 1H
NMR spectra. For eye guiding, a line connecting symbols is included.
Evaluation of the ability of the complexes to activate CC triple
bonds showed they catalyse the cyclization of 4-pentyn-1-ol with
concomitant addition of a second molecule of alkynol forming 2-
methyl-2-(pent-4-yn-1-yloxy)tetrahydrofuran with activities that
increase considerably by raising the temperature from ca. 20 to
40 ꢀCC. The bi-camphor complexes (6, 7) display higher catalytic
activities than the camphor derived complexes (1, 2, 3, 4).
[ZnCl2(Me2NNC10H14O)] (1a) and [ZnBr2(Me2NNC10H14O)] (2a) and
ii) the number of ligands, as verified for [ZnCl2(H2NNC10H14O)2]
(3b) that displays lower catalytic activity than [ZnCl2(Me2NN-
C
10H14O)] (1a). The weak chelate character of the ligand in 1a
(Fig. 2) favours coordination of 4-pentyn-1-ol enabling the catalytic
process. The binuclear character of complex 6i (two metal sites per
molecule) accounts for the higher catalytic activity (ca. 1000 mol P
per (mol cat ꢃ mol S ꢃ hr)) compared to the mononuclear com-
plexes. Hydration of the triple bond of P by traces of water, leads to
formation of 5-(2-methyltetrahydrofuran-2-yl)oxy)pentan-2-one
in a competitive process responsible for no complete conversion
of S into P, although the alkynol is fully consumed. The highest
conversion of S into P (conversion ca. 60%) is attained after 70 h
reaction at 40 ꢀC using 6i as catalyst.
Comparing the efficiency of the Zn(II) with that of Pd(II) or Pt(II)
camphor derived complexes [5,7] for 4-pentyn-1-ol (S) cyclization
it comes out that the Zn(II) complexes need longer reaction times to
convert S into P (Scheme 1), thus they are less efficient. The higher
basicity of the nitrogen atom of the coordinated ligands at Pd(II) or
Pt(II) complexes is a key parameter, since deprotonation of S is
necessary to enable interaction of the CC triple bond with the metal
and promote cyclization.
Although the catalytic activity of [(ZnCl2)2{(p-NC10H14O)2C6H4}]
(6i) is lower than that of Pd(II) camphor derived complexes it can be
considered as a good alternative for cyclization of 4-pentyn-1-ol (S)
to form 2-methyl-2-(pent-4-yn-1-yloxy)tetrahydrofuran (P) due to
the lower price and less environmental harmful properties of zinc
compared to palladium.
The ability of [ZnCl2(Me2NNC10H14O)(THF)] (1a) to promote re-
action of phenyl acetylene with aniline was also probed. No products
of hydroamination were obtained due to complex decomposition.
Replacement of the camphor ligand by aniline in the coordination
sphere of zinc yields [ZnCl2(NH2C6H5)2] (8) (Eq. (2)) which was
characterized by elemental analysis, IR and NMR (see experimental).
4. Experimental section
The synthesis of the zinc complexes were performed in the
glove box. Other manipulations were undertaken under nitrogen
atmosphere using vacuum and Schlenk techniques. The solvents
were purchased from Lab-Scan purified by conventional techniques
and distilled before use. Zinc bromide was purchased from BDH and
zinc chloride from Aldrich. ZnCl2 was recrystallized from THF
before use.
The camphor derived compounds YNC10H14O (Y ¼ NMe2 (a),
NH2 (b), NHMe (c)) and camphorquinoxaline (e) were prepared by
published methods [7,17,28e30]. The IR spectra were obtained from
KBr pellets using a JASCO FT/IR 4100 spectrometer. NMR spectra
(1H, 13C{H}, DEPT, 2D) were obtained from CDCl3 or MeOH-d4 so-
lutions using Bruker Avance IIþ Spectrometers (300 or 400 MHz)
and referred to tetramethylsilane (
d
¼ 0 ppm). The optical prop-
erties (rotation angle and enantiomers ratio) were measured using
respectively an automatic Atago polarimeter and an HPLC equip-
ment UHPLCþ focused Dionex equipped with a column Lux 5
Cellulose-1 Phenpomenex (isopropanol/n-hexane (1/9); flow rate
0.5 mL/min) and a UV/Vis detector (working at 254 nm).
4.1. Synthesis of bi-camphor compounds
4.1.1. 3,30-(1,4-Phenylenebis(azanylylidene)bis(1,7,7-
trimethylbicyclo[2.2.1]heptan-2-one-(p-NC10H14O)2C6H4 (i)
This synthetic procedure improves that in Ref. [31]. Acetic acid
(0.5 mL) and camphorquinone (0.51 g, 3.0 mmol) were stirred in
EtOH (5 mL) for 1hr. Then p-phenylenediamine (0.16 g, 1.51 mmol)
was added and the mixture further stirred for 18 h at 50 ꢀC
affording a yellow suspension that was filtered off solution, washed
with n-pentane (3 ꢃ 5 mL) and dried. Yield 79%. Elemental analysis
for C26H32N2O2$3/4 EtOH (%): Found C, 75.2; N, 6.9; H, 7.9. Calc. C,
[ZnCl2(Me2NNC10H14O)(THF)] þ 2C6H5NH2 / [ZnCl2(NH2C6H5)2]
þ 2Me2NNC10H14O þ THF
(2)
3. Conclusions
Zn(II) displays high ability to coordinate camphor imines
(YNC10H14O) and camphor sulphonylimines (YNC10H13NSO2)
forming complexes with metal to ligand ratios that range from 1:1
([ZnX2(YNC10H14O)], [ZnX2(YNC10H13NSO2)]) to 1:2 ([ZnX2(H2
NNC10H14O)2]) or 2:1 ([{ZnX2}2(YNC10H14O)]). The characteristics of
75.2; N, 6.4; H, 8.3. ½a D25
ꢄ
þ18.5ꢀ, c 0.065, CH2Cl2. IR (cmꢁ1): 1756
(
yCO), 1685 (yCN). 1H NMR (CDCl3,
d ppm): 6.95 (s, 4H), 2.99 (d,
J ¼ 4.8, 1H), 2.11e1.63 (m, 4H), 1.08 (s, 3H), 0.98 (s, 3H), 0.89 (s, 3H).
13C{H} NMR (CDCl3,
ppm): 206.5, 171.8, 146.9, 121.9, 58.3, 50.4,
44.8, 30.3, 24.5, 21.1, 17.7, 9.2.
d

T.A. Fernandes et al. / Journal of Organometallic Chemistry 760 (2014) 186e196
193
4.1.2. 3,30-(1,3-Phenylenebis(azanylylidene)bis(1,7,7-
4.2.4. [ZnCl2(Me2NNC10H13NSO2)] (1f)
trimethylbicyclo[2.2.1]heptan-2-one - (m-NC10H14O)2C6H4 (j)
Camphorquinone (0.31 g, 1.9 mmol) was stirred in EtOH (5 mL)
acidified with acetic acid (0.5 mL) for 1 h. Then m-phenylenedi-
amine (0.10 g, 0.93 mmol) was added and the mixture fluxed with
nitrogen and stirred overnight at 50 ꢀC. Extraction with CHCl3
(3 ꢃ 5 mL) and drying the organic layer over anhydrous MgSO4 the
solution taken to dryness. The yellow solid was washed with n-
pentane (2 ꢃ 3 mL) to afford the title yellow compound. Yield 91%.
Elemental analysis for C26H32N2O2 (%): Found C, 76.5, N 6.8, H 8.0.
ZnCl2 (0.030 g, 0.22 mmol) and 7-(2,2-dimethylhydrazono)-8,8-
dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methanobenzo[c]isothiazole
2,2-dioxide (f, 0.055 g, 0.20 mmol) yielded 53% of 1f as a light
yellow precipitate. Elemental analysis for ZnCl2C12H19N3SO2$3/4
THF (%): Found C 39.3; N, 8.7; H, 5.6; S, 6.6. Calc. C, 39.2; N, 9.1; H,
5.4; S, 7.0. ½a 2D5
ꢄ
þ3.2ꢀ, c 0.046, CH2Cl2. IR (cmꢁ1): 1657, 1547 (yCN),
1315 (ySO2assym); 1158, 1136 (ySO2sym); 1H NMR (MeOH-d4,
d ppm):
3.36, (s, 6H), 3.17 (d, J ¼ 4.1, 1H), 3.27, 3.24 (2d, J ¼ 13.2, 2H), 2.10e
1.70 (m, 4H), 1.03 (s, 3H), 0.95 (s, 3H). 13C{H} NMR (MeOH0-d4,
Calc. C, 77.2; N, 6.9; H, 8.0. ½a D25
ꢄ
þ5.7ꢀ, c 0.070, CH2Cl2. IR (cmꢁ1):
d ppm): 188.6, 132.6, 63.6, 53.3, 50.5, 46.2, 29.4, 27.1, 26.5, 20.0, 19.1.
1748 (yCO), 1659 (yCN), 1578 (yCCarom). 1H NMR (CDCl3,
d ppm): 7.33
(t, J ¼ 7.9 Hz, 1H), 6.70 (dd, J1 ¼ 7.8, J2 ¼ 1.9, 2H), 6.38 (t, J ¼ 1.9, 1H),
2.81 (d, J ¼ 4.0, 1H), 2.05e1.55 (m, 4H), 1.09 (s, 3H), 0.96 (s, 3H), 0.89
4.2.5. [ZnBr2(Me2NNC10H14O)] (2a)
A procedure similar to that of 1a was used. Camphor imine a
(0.10 g, 0.50 mmol) and ZnBr2 (0.11 g, 0.50 mmol) yielded 78% of 2a.
Elemental analysis for ZnBr2C12H20N2O$½THF (%): Found C 35.9, N
5.7, H 5.0. Calc. C, 35.8, N 6.0, H 5.1. IR (cmꢁ1): 1657 (yCO), 1547 (yCN).
(s, 3H). 13C{H} NMR (CDCl3,
d ppm): 206.7, 172.7, 150.7, 129.8, 117.1,
111.4, 58.4, 50.3, 44.7, 30.3, 24.6, 21.1, 17.6, 9.2.
1H NMR (CDCl3,
d
ppm): 3.42 (s, 6H), 3.24 (d, J ¼ 4.4, 1H), 2.14e1.59
(m, 4H), 1.08 (s, 3H), 1.00 (s, 3H), 0.93 (s, 3H). 13C{H} NMR (CDCl3,
ppm): 210.1, 140.3, 57.0, 51.0, 48.6, 46.6, 30.1, 26.1, 21.3, 18.2, 8.8.
4.2. Synthesis of complexes
d
All complexes, except 1a, 2a and 1d were synthesized using the
typical procedure described for 1e. Slight changes in purification
procedure are mentioned.
4.2.6. [ZnBr2{(H2NC6H4)NC10H14O}] (2d)
ZnBr2 (0.044 g, 0.19 mmol) and camphorimine d (0.050 g,
0.19 mmol) yielded 97% of 2d. Elemental analysis (%) for
ZnBr2C16H20N2O 3/4 H2O: Found: C, 38.7; N, 5.5; H, 4.1. Calc. C, 38.8;
N, 5.7; H, 4.3. IR (cmꢁ1): 3356, 3217 (yNH), 1739 (yCO), 1602 (yCN),
4.2.1. [ZnCl2(Me2NNC10H14O)(THF)] (1a)
ZnCl2 (0.25 g, 1.8 mmol) and (E)-3-(2,2-dimethylhydrazono)-
1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (a, 0.38 g, 1.8 mmol)
were stirred in THF (6 mL) for 2 h. The solvent was partially
evaporated and n-pentane (2 mL) added. The white crystalline
precipitate was filtered off and dried under vacuum. A further crop
of compound was obtained by evaporation of the residual solvent
and washing with CH2Cl2 (1a). Total yield 63%. Elemental analysis
for ZnCl2C16H28N2O2 (%): Found C, 46.1; N, 6.7; H, 7.0%. Calc: C, 46.1;
1507 (NHscissor). 1H NMR (MeOH-d4,
d
ppm): 6.94 (d, J ¼ 8.0, 2H),
6.75 (d, J ¼ 8.0, 2H), 3.04 (d, J ¼ 4.0,1H), 2.25e1.60 (m, 4.0 H),1.07 (s,
3H), 1.05 (s, 3H), 0.83 (s, 3H). 13C{H} NMR (MeOH-d4,
ppm): 208.2,
d
169.8, 148.9, 148.9, 139.1, 125.4, 116.3, 58.7, 52.2, 46.2, 31.6, 24.9,
21.0, 17.8, 9.3.
4.2.7. [ZnBr2{(NC6H4)NC10H14}] (2e)
N, 6.7; H, 6.8. ½a D25
ꢄ
þ3.3ꢀ, c 0.076, CH2Cl2. IR (cmꢁ1): 1653 (nCO),1535
ZnBr2 (0.096 mg, 0.43 mmol) and camphorquinoxaline (e, 0.10 g,
0.43 mmol) yielded 97% of 2e. Elemental analysis (%) for
ZnBr2C16H18N2$THF: Found: C, 45.1; N, 4.8; H, 5.2. Calc. C, 44.8; N,
(
nCN). 1H NMR (CDCl3,
d ppm): 3.75 (m, 4H), 3.49 (s, 6H), 3.25 (d,
J ¼ 4.0, 1H), 2.15e1.60 (m, 4H), 1.83 (m, 4H), 1.10 (s, 3H), 1.01 (s, 3H),
0.93 (s, 3H). 13C{H} NMR (CDCl3,
d
ppm): 211.6, 138.8, 68.2, 57.0,
5.2; H, 4.9. IR (cmꢁ1): 1624 ( CCarom) 1517 (yCN). 1H NMR (CDCl3,
y
50.8, 49.1, 29.8, 25.9, 25.7, 25.6, 21.3, 17.8, 8.5.
d
ppm): 8.69 (d, J ¼ 8.0, 1H), 8.10 (d, J ¼ 8.0, 1H), 7.71 (m, 2H), 2.61
(d, J ¼ 4.0, 1H), 2.32e1.48 (m, 4.0 H), 1,42 (s, 3H), 1.10 (s, 3H), 0.63 (s,
3H). 13C{H} NMR (CDCl3,
ppm): 167.8, 165.4, 142.4, 136,8, 129,9,
4.2.2. [ZnCl2{(H2NC6H4)NC10H14O}] (1d)
d
ZnCl2 (0.060 g, 0.43 mmol) and 3-((4-aminophenyl)imino)-
1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (d, 0.10 g, 0.39 mmol)
were stirred in CH2Cl2 (3 mL) for 18 h. The unreacted ZnCl2 was
filtered and the solvent was fully evaporated. The orange solid
obtained was washed with n-pentane, filtered and dried under
58.1, 55.0, 54.2, 31.4, 24.7, 20.6, 18.4, 10.2.
4.2.8. [ZnBr2(Me2NNC10H13NSO2)] (2f)
ZnBr2 (0.059 g, 0.26 mmol) and 7-(2,2-dimethylhydrazono)-8,8-
dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methanobenzo[c] isothiazole
2,2-dioxide (f, 0.055 mg, 0.20 mmol) yielded 42% of the whitish
precipitate. Elemental analysis (%) for ZnBr2C12H19N3SO2$THF:
Found: C, 33.9; N, 7.4; H, 5.0; S, 5.5. Calc: C, 33.9; N, 7.4; H, 4.8; S, 5.6.
3
vacuum. Yield 61%. Elemental analysis for ZnCl2C16H18N2O /4 H2O
(%): Found C, 47.7; N, 7.0; H, 4.8. Calc. C, 47.5; N, 6.9; H, 4.8. IR
(cmꢁ1): 3444, 3364 (nNH), 1736 (nCO), 1624 (nCN), 1600 (nCCarom), 1507
(
nNH). 1H NMR (MeOH-d4,
d
ppm): 6.95 (d, J ¼ 8.0, 2H), 6.77 (d,
J ¼ 8.0, 2H), 3.03 (d, J ¼ 4.0, 1H), 2.26e1.61 (m, 4H), 1.07 (s, 3H), 1.05
(s, 3H), 0.83 (s, 3H). 13C{H} NMR (MeOH-d4,
ppm): 208.4, 169.9,
½
a 2D5
(
ꢄ
þ4.0ꢀ, c 0.050, CH2Cl2. IR (cmꢁ1): 1617, 1539 (yCN); 1316
ySO2assym); 1159, 1136 (ySO2sym); 1H NMR (CDCl3,
d ppm): 3.50, (s,
d
6H),1H), 3.36 (d, J ¼ 13.6,1H), 3.25e3.19 (m, 2H), 2.16e1.77 (m, 4H),
148.6, 125.5, 116.6, 58.8, 52.1, 46.3, 31.6, 24.9, 21.1, 17.7, 9.2.
1.03 (s, 3H), 0.86 (s, 3H). 13C{H} NMR (MeOH-d4 (due to low solu-
bility in CDCl3)
26.2, 20.3, 19.4.
d ppm): 188.1, 131.4, 60.2, 52.2, 51.5, 50.8, 47.0, 28.1,
4.2.3. [ZnCl2{(NC6H4)NC10H14}] (1e)
A mixture of ZnCl2 (0.057 g, 0.42 mmol) and camphorquinoxa-
line (e, 0.10 g, 0.53 mmol) were stirred in THF (3 mL) for 18 h. The
solvent was evaporated and the orange precipitate was washed
with CH2Cl2 filtered off and dried under vacuum. Yield 78%.
Elemental analysis for ZnCl2C16H18N2 1/8 CH2Cl2 (%): Found C, 50.1;
4.2.9. [ZnBr2{(m-NC10H14O)2C6H4}] (2j)
ZnBr2 (0.067 g, 0.030 mmol) and 3,30-(1,3-phenylen
ebis(azanylylidene)bis(1,7,7-trimethylbicyclo[2.2.1]heptan-2-one
(j, 0.10 g, 0.25 mmol) yielded 62% of 2j. Elemental analysis (%) for
ZnBr2C26H32N2O2 ¼THF: Found: C, 50.0; N, 4.0; H, 5.5. Calc. C, 50.0;
N, 4.3; H, 5.3. IR (cmꢁ1): 1752 (yCO),1677 (yCN),1593 (yCCarom).1H NMR
N, 7.4; H, 5.0. Calc. C, 50.3; N, 7.3; H, 4.7. ½a D25
ꢄ
þ7.8ꢀ, c 0.064, CH2Cl2.
IR (cmꢁ1): 1625 (yCCarom), 1516 (yCN). 1H NMR (CDCl3,
d ppm): 8.57
(d, J ¼ 7.6, 1H), 8.10 (d, J ¼ 6.4, 1H), 7.72 (m, 2H), 3.75 (d, J ¼ 3.2, 1H),
(MeOH-d3,
2.86 (d, J ¼ 4.8, 2H), 2.20e1.65 (m, 8.0 H),1.09 (s, 6H),1.04 (s, 6H), 0.91
(s, 6H). 13C{H} NMR (MeOH-d3,
ppm): 207.4, 174.8, 151.2, 131.3,
118.8, 113.3, 59.2, 51.7, 45.6, 31.2, 25.2, 21.3, 17.6, 9.2.
d
ppm):7.47 (t, J¼ 7.6,1H), 6.84e6.82(m, 2H), 6.51 (s,1H),
2.06e1.42 (m, 4.0 H), 1.42 (s, 3H), 1.10 (s, 3H), 0.62 (s, 3H). 13C{H}
NMR (CDCl3,
d
ppm): 167.4, 165.1, 142.4, 129.9, 129.7, 126.8, 55.0,
d
54.3, 53.8, 31.6, 24.7, 20.6, 18.4, 10.2.

194
T.A. Fernandes et al. / Journal of Organometallic Chemistry 760 (2014) 186e196
4.2.10. [ZnCl2(H2NNC10H14O)2] (3b)
13C{H} NMR (MeOH-d4,
d ppm): 206.0, 173.3, 149.8, 129.9, 117.4,
ZnCl2 (0.090 g, 0.66 mmol) and b (0.12 g, 0.68 mmol) yielded
19% of the white solid 3b. Elemental analysis for
ZnCl2C20H32N2O$½CH2Cl2 (%): Found C, 45.5; N, 10.1; H, 5.9. Calc. C,
45.6; N, 10.4; H, 6.1. IR (cmꢁ1): 3406, 3283 (yNH), 1728 (yCO), 1636,
111.9, 57.8, 50.3, 44.2, 29.8, 23.8, 20.0, 16.3, 7.1.
4.2.16. [(ZnBr2)2(MeHNNC10H13NSO2)] (7h)
Procedure such as used for 1a. Reaction of ZnBr2 (0.27 g,
1.22 mmol) with 8,8-dimethyl-7-(2-methylhydrazono)-4,5,6,7-
1584 (yCN). 1H NMR (MeOH-d4,
d
ppm): 3.14 (d, J ¼ 4.4, 1H), 2.05e
1.43 (m, 4H), 1.02 (s, 3H), 0.98 (s, 3H), 0.84 (s, 3H). 13C{H} NMR
tetrahydro-3H-3a,6-methanobenzo
[c]isothiazole
2,2-dioxide
(MeOH-d4,
18.2, 9.3.
d
ppm): 207.7, 148.7, 59.1, 46.9, 46.6, 32.6, 24.5, 20.6,
(0.15 g, 0.60 mmol) afforded 36% of the title compound.
Elemental analysis for Zn2Br4C11H17N3$7/4THF: Found C, 25.7; N,
4.5; H, 4.0, S, 3.9. Calc. C, 26.0; N, 5.0; H, 3.7, S, 3.9. IR (cmꢁ1): 3310
4.2.11. [ZnBr2(H2NNC10H14O)2] (4b)
( d ppm):
yNH), 1617, 1551 (yCN), 1320, 1157 (ySO2). 1H NMR (MeOH-d4,
ZnBr2 (0.059 g, 0.26 mmol) and camphorimine b (0.51 g,
0.28 mmol) reacted to yield 52%. Elemental analysis for
ZnBr2C20H32N4O2 (%): Found: C 41.2, N 9.4, H 5.7. Calc. C 41.0, N 9.6,
H 5.5. IR (cmꢁ1): 3397, 3274 (yNH), 1725 (yCO), 1634, 1581 (yCN). 1H
3.75 (m, 14 H), 3.20 (s, 3H), 3.31e3.13 (m, 2H), 2.98 (d, J ¼ 4.4, 1H)
2.21e1.51 (m, 4H), 1.87 (m, 14 H), 1.09 (s, 3H), 0.88 (s, 3H). 13C{H}
NMR (MeOH-d4,
d ppm): 186.3, 136.9, 64.9, 50.1, 38.0, 31.1, 29.5,
26.6, 24.7, 19.6, 18.9.
NMR (MeOH-d4,
1.00 (s, 3H), 0.97 (s, 3H), 0.83 (s, 3H). 13C{H} NMR (MeOH-d4,
ppm): 207.5, 148.6, 58.9, 46.8, 46.4, 32.4, 24.3, 20.6, 18.2, 9.2.
d
ppm): 2.97 (d, J ¼ 4.4, 1H), 2.04e1.44 (m, 4H),
4.2.17. [(ZnBr2)2{(p-NC10H14O)2C6H4}] (7i)
d
ZnBr2 (0.054 g, 0.24 mmol) and i (0.050 g, 0.124 mmol) yielded
96% of 7i. Elemental analysis for Zn2Br4C26H32N2O2 2CH2Cl2 (%):
4.2.12. [{Zn(MeNNC10H14O)}2(
m
-Cl)2] (5c1)
Found C, 38.8; N, 3.1; H, 4.3. Calc. C, 38.9; N, 3.2; H, 4.2. ½a D25
ꢄ
þ8.6ꢀ, c
ZnCl2 (0.070 g, 0.51 mmol) and 1,7,7-trimethyl-3-(methylhy-
drazinylidene) byciclo [2.2.1] heptan-2-one (c, 0.10 g, 0.51 mmol)
reacted to form an oily solid that was washed with n-pentane
(6 cm3) to yield a yellow precipitate that was filtered and
dried under vacuum. Yield 49%. Elemental analysis for
Zn2Cl2C22H34N4O2,½THF (%): Found: C, 46.2; N, 9.0; H 6.5. Calc. C,
46.2; N, 9.0; H, 6.1. IR (cmꢁ1): 1709, 1689 (nCO), 1616, 1569 (nCN). 1H
0.064, CH2Cl2. IR (cmꢁ1): 1756 (yCO), 1685 (yCN). 1H NMR (CDCl3,
d
ppm): 6.99 (s, 4H), 2.91 (d, J ¼ 4.7 2H), 2.15e1.65 (m, 8.0 H), 1.00 (s,
6H), 0.90 (s, 6H), 0.896 (s, 6H). 13C{H} NMR (CDCl3,
d
ppm): 206.7,
171.8, 146.8, 122.1, 58.2, 50.4, 45.0, 30.3, 24.6, 21.2, 17.7, 9.2.
4.2.18. [ZnCl2(NH2C6H5)2] (8)
Upon addition of aniline (138
mL, 1.5 mmol) to a mixture of 1a
NMR (CDCl3,
d
ppm): 3.30 (s, 3H), 3.26 (d, J ¼ 4.0, 1H), 3.10 (s, 3H),
(0.012 g, 0.030 mmol) and phenyl acetylene (120 m
L, 1.1 mmol) in
2.44 (d, J ¼ 4.0, 1H), 2.15e1.35 (m, 8H), 0.10 (s, 3H), 0.98 (s, 3H), 0.92
CH2Cl2 (2 mL) a white suspension immediately formed. The
mixture was stirred for 2 h, the white precipitate filtered off and
washed with Et2O to afford the compound. Yield 42%. Elemental
analysis for ZnCl2C12H14N2 (%): Found C, 44.2; N, 8.5; H, 4.4. Calc. C,
44.7; N, 8.7; H, 4.3. IR (cmꢁ1): 3262, 3222 (yNH), 1605 (yNH), 1577
(s, 3H), 0.89 (s, 3H), 0.87 (s, 3H) 0.82 (s, 3H). 13C{H} NMR (CDCl3,
d
ppm): 209.2, 203.5, 141.1, 140.9, 59.3, 57.3, 50.8, 48.6, 48.1, 38.1,
37.2, 30.9, 30.4, 26.3, 25.1, 21.0, 20.5, 18.7, 17.9, 8.9, 8.6.
4.2.13. [(ZnCl2)2(H2NNC10H13NSO2)] (6g)
( d ppm): 7.01 (m, 4H), 6.74 (m, 4H),
yCCarom). 1H NMR (MeOH-d4,
Reaction of ZnCl2 (0.058 g, 0.422 mmol) and g (0.102 g,
0.422 mmol) was performed using a procedure similar to 1d
affording a yellow precipitate. Yield 49%. Elemental analysis for
Zn2Cl4C10H15N3SO2 THFˑH2O (%): Found: C, 28.0; N, 7.2; H, 4.8; S,
5.9. Cal. C, 27.8; N, 7.0; H, 4.1; S, 5.3; IR (cmꢁ1): 3566, 3447 (yNH),
6.68 (m, 2H). 13C{H} NMR (MeOH-d4,
116.8.
d ppm): 148.3, 130.0, 119.5,
4.3. Catalytic experiments
1623, 1559 (yCN). 1H NMR (MeOD-d4,
d
ppm): 7.70 (s, 2H), 3.31e3.13
The catalytic experiments were performed in sure seal NMR
tubes using degassed CDCl3 (CIL) as solvent. Typically CDCl3 (ca.
0.3 mL) was added to the catalyst precursor.
(d, J ¼ 13.6, 2H), 2.68 (d, J ¼ 3.6, 1H), 2.20e1.61 (m, 4H), 1.08 (s, 3H),
0.84 (s, 3H). 13C{H} NMR (MeOD-d4,
50.1, 29.4, 26.1, 24.3, 19.5, 19.3.
d ppm): 177.7, 138.2, 65.7, 53.2,
(0.0050 g) and the 1H NMR spectrum obtained. Then, 50
mL of 4-
pentyn-1-ol (S) were introduced into the tube through the septa
and the reaction followed by 1H NMR. The conversion was calcu-
lated by integration of the methyl signal of the product (P) using as
internal standard the integration of the signals of the methyl
groups of camphor.
4.2.14. [(ZnCl2)2{(p-NC10H14O)2C6H4}] (6i)
ZnCl2 (0.067 g, 0.49 mmol)
and
3,30-(1,4-
phenylenebis(azanylylidene)bis(1,7,7-trimethylbicyclo[2.2.1]hep-
tan-2-one (i, 0.099 g, 0.245 mmol) yielded 53% of 6i. Elemental
analysis for Zn2Cl4C26H32N2O2 1.5THF (%): Found C, 49.0; N, 3.8; H,
From time to time 13C{H} NMR was obtained to corroborate the
presence of the products.
5.3. Calc. 48.9; N, 3.6; H, 5.6. ½a D25
ꢄ
þ3.9ꢀ, c 0.051, CH2Cl2. IR (cmꢁ1):
1748 (yCO), 1689 (yCN), 1589 (CCarom). 1H NMR (MeOH-d4,
d ppm):
7.07 (s, 4H), 2.92 (d, J ¼ 4.8 Hz, 2H), 2.22e1.68 (m, 8.0 H),1.09 (s, 6H)
4.4. XPS and SEM experiments
1.05 (s, 6H), 0.90 (s, 6H). 13C{H} NMR (MeOH-d4,
d
ppm): 207.6,
174.3, 147.9, 123.1, 59.1, 51.8, 45.7 31.3, 25.1, 21.2, 17.6, 9.2.
X-ray photoelectron spectra (XPS) were recorded using non-
monochromatic Al K
a
radiation (h
n
¼ 1486.6 eV) and a power of
4.2.15. [(ZnCl2)2{(m-NC10H14O)2C6H4}] (6j)
120 W (12 kV ꢃ 10 mA) from an XSAM800 (KRATOS) XPS dual
anode spectrometer. Samples were fixed to the sample holder by a
double-side tape. Data acquisition was performed in UHV
(w10ꢁ7 Pa) at room temperature, take-off-angle (TOA) of 45ꢀ, in
FAT operation mode, with high magnification and pass energy of
20 eV. Spectra were recorded using a Sun SPARC Station 4 with
Vision software (KRATOS) by steps of 0.1 eV. In order to detect
possible degradation effects, all the samples were analysed using,
firstly, a single sweep per XPS region and, then, five sweeps per
region. Source satellites and a Shirley background were subtracted
ZnCl2 (0.072 g, 0.53 mmol) and 3,30-(1,3-phenyle
nebis(azanylylidene)bis(1,7,7-trimethylbicyclo[2.2.1]heptan-2-one
(j, 0.11 g, 0.27 mmol) yielded 57% of 6j upon wash of the oily solid
with n-pentane (6 cm3) to afford a precipitate that was filtered and
dried under vacuum. Elemental analysis for Zn2Cl4C26H32N2O2 n-
pentane (%): Found C, 49.5; N, 3.9; H, 5.6. Calc. C, 49.6; N, 3.7; H, 5.9.
IR (cmꢁ1): 1734 (yCO), 1668 (yCN), 1591 (CCarom). 1H NMR (MeOH-d4,
d
ppm): 7.46 (t, J ¼ 7.2, 1H), 6.81 (d, J ¼ 7.2, 2H), 6.51 (s, 1H), 2.85
(sbrl, 2H), 2.17e1.63 (m, 8H), 1.09 (s, 6H), 1.04 (s, 6H), 0.91 (s, 6H).

T.A. Fernandes et al. / Journal of Organometallic Chemistry 760 (2014) 186e196
195
Table 3
Crystallographic data for [ZnCl2(Me2NNC10H14O)THF] (1a0), Me2NNC10H13NSO2 (f), MeHNNC10H13NSO2 (h) and (NC10H14O)2C6H4 (i).
1a0
f
h
i
Empirical formula
Formula weight
Crystal system
C16H28N2O2Cl2Zn
431.73
Monoclinic (vide text)
B21 (vide text)
C12H19N3O2S
269.36
Orthorhombic
P212121
C11H18N3O2S
256.34
Orthorhombic
P212121
C26H32N2O2
404.55
Orthorhombic
P212121
Space group
Unit cell dimensions
ꢀ
a/A
7.4657(6)
13.795(1)
18.779(2)
90
90
90
1934.0(3)
8, 1.431
1.556
7.8568(3)
10.6301(3)
16.1284(6)
90
90
90
1197.3(2)
4, 1.328
0.239
8.4107(5)
11.5410(7)
12.5578(9)
90
90
90
1219.0(1)
4, 1.391
0.260
7.3718(4)
17.256(1)
17.841(1)
90
90
90
2269.6(2)
4, 1.184
0.075
ꢀ
b/A
ꢀ
c/A
a
a
g
/deg
/deg
/deg
ꢀꢁ3
Volume (A
)
Z, Dcal (g/cm3)
Absorption coefficient
(mmꢁ1
)
F(000)
872
576
544
872
Crystal size (mm3)
0.3 ꢃ 0.2 ꢃ 0.3
0.3 ꢃ 0.2 ꢃ 0.25
0.3 ꢃ 0.2 ꢃ 0.2
0.3 ꢃ 0.2 ꢃ 0.3
q
range for data
2.62 to 40.74
2.53 to 30.61
2.40 to 24.96
1.64 to 33.18
collection (deg)
Index ranges
ꢁ12 ꢅ h ꢅ 13, ꢁ24 ꢅ k ꢅ 25,
ꢁ34 ꢅ l ꢅ 33
ꢁ8 ꢅ h ꢅ 11, ꢁ15 ꢅ k ꢅ 15,
ꢁ22 ꢅ l ꢅ 16
ꢁ8 ꢅ h ꢅ 11, ꢁ15 ꢅ k ꢅ 15,
ꢁ22 ꢅ l ꢅ 16
6 ꢅ h ꢅ 11, 26 ꢅ k ꢅ 24,
ꢁ24 ꢅ l ꢅ 27
Reflections collected/
unique
18263/11442
8856/4069
4343/2125
20016/8551
Data/restraints/
parameters
Final R (observed)
[R(int) ¼ 0.0216] 11442/0/213
R1 ¼ 0.0369,wR2 ¼ 0.0621
[R(int) ¼ 0.0342] 4069/0/167
R1 ¼ 0.0643,wR2 ¼ 0.1129
[R(int) ¼ 0.0313] 2125/0/154
R1 ¼ 0.0389, wR2 ¼ 0.0970
[R(int) ¼ 0.0624] 8551/0/277
R1 ¼ 0.0677, wR2 ¼ 0.1588
to all spectra. GaussianeLorentzian products were used to fit
experimental curves with XPSPEAK Version 4.1 (freeware). No
external charge compensation was used: the charge shift was cor-
rected using as reference the binding energy of sp3 C 1s bound to
carbon and hydrogen. The sensitivity factors used in quantification
analysis were: 0.25 for C 1s; 0.66 for O 1s; 0.42 for N 1s, 0.48 for Zn
2p3/2, 0.73 for Cl 2p, 1.39 for Br 2p and 0.54 for S 2p.
supplemented with a Grimme’s C6 dispersion correction term
[36,37].
Acknowledgements
The authors thank Isabel Dias Nogueira for acquisition and
refinement of SEM images. The FCT-Fundação para a Ciência e
Tecnologia, for financial support (Projecto Estratégico e PEst-OE/
QUI/UI0100/2013) and the NMR and MS (IST-Node) Networks for
facilities.
SEM was acquired using a JEOL equipment, model JSM e 7001
with the accelerating voltage equal to 5.0 kV.
4.5. X-ray diffraction analysis
Appendix A. Supplementary material
The X-ray crystallographic data for complex [ZnCl2(Me2NN-
CCDC 937765, 937766, 937767, 937768 contain the supple-
mentary 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.
C
10H14O)THF] (1a0) and the camphor derived species
Me2NNC10H14NSO2 (f) and (NC10H14O)2C6H4 (i) was collected at
150(2) K using a Bruker AXS-KAPPA APEX II area detector apparatus
ꢀ
equipped with a graphite-monochromated Mo K
a
(
l
¼ 0.71073 A)
and were corrected for Lorentz polarization and, empirically, for
absorption effects. The structures were solved by direct methods
using SHELX97 [32] and refined by full matrix least squares against
F2 using SHELX97 all included in the suite of programs WinGX
v1.70.01 for Windows [33]. In the case of complex 1a that crystal-
lizes in the monoclinic P21 space group it was used the following
sequence: c(new) ¼ a(old) þ2 c(old) emulating a orthorhombic B
centred space group. The structure was solved considering that the
crystal depicts a twinning with components related by a binary axis
(matrix 1 0 0; 0 ꢁ1 0; 0 0 ꢁ1). The crystal was refined using the
twinning model (monoclinic B21) with weights respectively 47.2
and 52.8%. The non-hydrogen atoms were refined anisotropically
and the H atoms were inserted in idealized positions and allowed to
refine riding on the parent carbon atom. Crystal data and refine-
ment parameters are summarized in Table 3. Illustrations of the
molecular structures were made with ORTEP3 [34].
Appendix B. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.10.040.
References
[1] J. Hedin-Dahlström, J.P. Rosengren-Holmberg, S. Legrand, S. Wikman,
I.A. Nicholls, J. Org. Chem. 71 (2006) 4845e4853.
[2] M.F.N.N. Carvalho, A.M. Galvão, J. Kredatusová, J. Merna, P.F. Pinheiro,
M.M. Salema, Inorg. Chim. Acta 383 (2012) 244e249.
[3] S. Gou, Z. Ye, Z. Huanga, X. Ma, Appl. Organomet. Chem. 24 (2010) 374e379.
[4] M.F.N.N. Carvalho, F.M.T. Almeida, J. Organomet. Chem. 679 (2003) 143e147.
[5] M.F.N.N. Carvalho, A.S.D. Ferreira, A.M. Galvão, Inorg. Chim. Acta 363 (2010)
1767e1772.
[6] A.S.D. Ferreira, M.F.N.N. Carvalho, A.M. Galvão, L.F. Veiros, Inorg. Chim. Acta
395 (2013) 169e175.
[7] M.F.N.N. Carvalho, A.M. Galvão, A.S.D. Ferreira, J. Organomet. Chem. 694
(2009) 2061e2068.
[8] M.J. Spallek, D. Riedel, F. Rominger, A.Stephen K. Hashmi, O. Trapp, Organo-
metallics 31 (2012) 1127e1132.
[9] N.A. Bokach, I.A. Balova, M. Haukka, V.Y. Kukushkin, Organometallics 30
(2011) 595e602.
[10] H. Paramahamsan, A.J. Pearson, A.A. Pinkerton, E.A. Zhurova, Organometallics
27 (2008) 900e907.
4.6. Computational calculations
Computational calculations were made by DFT with GAMESS-US
[35] version R3 and a B3LYP functional using an SBKJC basis set

196
T.A. Fernandes et al. / Journal of Organometallic Chemistry 760 (2014) 186e196
[11] X.-M. Deng, P. Cai, S. Ye, X.-L. Sun, W.-W. Liao, K. Li, Y. Tang, Y.-D. Wu, L.-
X. Dai, J. Am. Chem. Soc. 128 (2006) 9730e9740.
[12] B.A. Messerle, K.Q. Vuong, Organometallics 26 (2007) 3031e3040.
[13] D.J.D. Wilson, C.M. Beavers, A.F. Richards, Eur. J. Inorg. Chem. (2012) 1130e
1138.
[24] T.E. Kokina, N.B. Gorshkov, L.A. Glinskaya, N.V. Kurat’eva, L.A. Sheludyakova,
A.V. Tkachev, S.V. Larionov, Russ. J. Coord. Chem. 39 (2013) 442e449.
[25] T.A. Fernandes, M.F.N.N. Carvalho, A.M. Galvão, N.A.G. Bandeira, M.J. Calhorda,
A.M. Botelho do Rego, J. Polym. Sci. (A): Polym. Chem. 50 (2012) 1102e1110.
[26] M.F.N.N. Carvalho, M.T. Duarte, T.A. Fernandes, A.M. Galvão, A.M. Botelho do
Rego, Inorg. Chem. 49 (2010) 10330e10337.
[14] S. Enthaler, ACS Catal. 3 (2013) 150e158.
[15] J. Börner, U. Flörke, A. Döring, D. Kuckling, M.D. Jones, M. Steiner, M. Breuning,
S. Herres-Pawlis, Inorg. Chem. Commun. 13 (2010) 369e371.
[16] A. Johansson, E. Wingstrand, M. Håkansson, J. Organomet. Chem. 690 (2005)
3846e3853.
[17] K.L. Klinkel, L.A. Kiemele, D.L. Gin, J.R. Hagadorn, Chem. Commun. (2006)
2919e2921.
[27] M. Raposo, J.M.C. Lourenço, A.M. Botelho do Rego, A.M. Ferraria, P.A. Ribeiro,
Colloids Surf. A 412 (2012) 1e10.
[28] M.O. Forster, A. Zimmerli, J. Chem. Soc. 98 (1910) 2156e2177.
[29] M.O. Forster, T. Thornley, J. Chem. Soc. 95 (1909) 942e956.
[30] H.E. Armstrong, W. Robertson, J. Chem. Soc. Dalton Trans. 87 (1905) 1272e1297.
[31] B.K. Singh, J.K. Mazumder, J. Chem. Soc. 115 (1919) 573.
[18] S.I.G. Dias, F. Heirtzler, T. Bark, G. Labat, A. Neels, Polyhedron 23 (2004) 1011e
1017.
[19] T.-F. Liu, H.-K. Lin, S.-R. Zhu, Z.-M. Wang, H.-g. Wang, H.-W. Sun, X.-B. Leng, Y.-
T. Chen, J. Mol. Struct. 605 (2002) 117e122.
[32] G.M. Sheldrick, SHELX-97- Programs for Crystal Structure Analysis (Release
97-2), Institüt für Anorganische Chemie der Universität, Tammanstrasse 4, D-
3400 Göttingen, Germany, 1998.
[33] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837. WINGX.
[20] F.H. Allen, D.G. Watson, L. Brammer, A.G. Orpen, R. Taylor, Int.
Tables Crystallogr. C (2006) 790e811 (Chapter 9.5).
[21] M.F.N.N. Carvalho, L.M.G. Costa, A.J.L. Pombeiro, A. Schier, W. Scherer,
S.K. Harbi, U. Verfürth, R. Herrmann, Inorg. Chem. 33 (1994) 6270e6277.
[22] M.F.N.N. Carvalho, A.S.D. Ferreira, J.L. Ferreira da Silva, L.F. Veiros, Collect.
Czech. Chem. Commun. 72 (5/6) (2007) 649e665.
[34] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[35] M.W. Schmidt, K.K. Baldridge, J.A. Boatz, S.T. Elbert, M.S. Gordon, J.H. Jensen,
S. Koseki, N. Matsunaga, K.A. Nguyen, S. Su, T.L. Windus, M. Dupuis,
J.A. Montgomery, J. Comput. Chem. 14 (1993) 1347e1363.
[36] S. Grimme, J. Antony, S. Ehrlich, H. Krieg, J. Chem. Phys. 132 (2010) 154104.
[37] R. Peverati, K.K. Baldridge, J. Chem. Theory Comput. 4 (2008) 2030e2048.
[23] E.N. Adamenko, L.L. Frolova, M.V. Panteleeva, A.V. Kuchin, Chem. Nat. Compd.
43 (1) (2007) 59e62.