Structural Preferences in Phosphanylthiolato Platinum(II) Complexes

Article abstract of DOI:10.1002/open.201500136

The transition-metal complexes of heterotopic phosphanylthiolato ligands are useful in various reactions which depend on the stereochemistry of the complexes. Bis-chelate complex [Pt(SCH₂CH₂PPh₂-κ²P,S)₂

Full text of DOI:10.1002/open.201500136

DOI: 10.1002/open.201500136
Structural Preferences in Phosphanylthiolato Platinum(II)
Complexes
Josep Duran,[a] Alfonso Polo,*[a] Julio Real,[b] Jordi Benet-Buchholz,[c] Miquel Solà,[a, d] and
Albert Poater*[a, d]
The transition-metal complexes of heterotopic phosphanylthio-
lato ligands are useful in various reactions which depend on
the stereochemistry of the complexes. Bis-chelate complex
[Pt(SCH2CH2PPh2-k2P,S)2] (1) was obtained in good yields by
direct base-free substitution reaction of the corresponding
phosphanylthiol (HSCH2CH2PPh2) with K2PtCl4 or by oxidative
addition of the same phosphanylthiol to Pt(PPh3)4. In agree-
ment with the antisymbiosis rule, complex 1 shows a cis-P,P ar-
rangement in solid state crystallizing in the monoclinic system
(C2/c). Density functional theory (DFT) calculations on 1 reveal
the right characteristics for the preferred cis-P,P arrangement,
rationalizing its formation. Direct base-free reaction of
[PtCl2(1,5-cyclooctadiene)] with one equivalent of the same
phosphanylthiol produce the trinuclear complex [PtCl(m-
SCH2CH2PPh2-k2P,S)]3 (2) instead of the binuclear structure
common in palladium and nickel derivatives. Crystals of 2 are
¯
triclinic (P1) showing a sulfur-bridging edge-sharing cyclic tri-
nuclear complex with square-planar coordination geometry
around the platinum atoms and a Pt3S3 cycle in skew-boat con-
formation. This preference for the trinuclear structure was ra-
tionalized mechanistically and through conceptual DFT.
Introduction
The transition-metal complexes of heterotopic phosphanylthio-
lato ligands have been widely studied because of their applica-
bility in some interesting reactions,[1] such as S-alkylation/S-
dealkylations,[2,3] carbothiolations,[3] reductions,[4] copolymeriza-
tions,[5] or carbonylations.[6] These complexes also have rele-
vance in desulfurization technologies[7] and in understanding
the biological pathways of certain sulfur-containing metallo-
proteins.[8] For all these applications, the stereochemistry of
these complexes has particular importance, as different stereo-
isomers could present different behavior in a given process.[9]
Among all phosphanylthiolato ligands, we are particularly in-
terested in 2-phosphanylalkylthiolato ligands because they can
support a resolved chiral carbon in the chelate chain.[10,11] For
group 10 metals (M=Ni, Pd, and Pt), the more abundant
2-phosphanylalkylthiolato complexes are the bis-chelates,
[M(ligand-k2P,S)2], and the chlorocomplexes, [MCl(mS-ligand-
k2P,S)]2 or [MCl(ligand-k2P,S)(PR3)].
Taking as a model the 2-(diphenylphosphanyl)ethanethiol
(Hdppet) derivatives, [Ni(dppet)2] shows a trans-P,P arrange-
ment, both in solution and in the solid state.[12] The same pre-
ferred stereochemistry was proposed for other nickel bis-chela-
tes.[10c,12,13] For [Pd(dppet)2], a trans-P,P geometry in solution
was proposed by comparison with the bis[2-(dimethylphospha-
nyl)ethanethiolato] complex which shows characteristic virtual
couplings for the methyl groups in the 1H and 13C{1H} NMR
spectra.[14] The solid-state structure of [Pd(dppet)2] is unknown,
but a trans-P,P arrangement is supported by the stereochemis-
try observed in other bis-chelates with chain-substituted li-
gands.[10a–b,11a] Contrasting with [Pd(dppet)2], some of these
complexes show an equilibrium between the two geometric
isomers (cis/trans) in solution.[10a,11a,13] Also the crystal structure
of [Pt(dppet)2] (1) is unknown, and both cis[11a] and trans[10b] ge-
ometries in solid state were observed for other platinum bi-
s[phosphanylalkylthiolato] complexes. In solution, a cis-P,P ste-
reochemistry was suggested for 1 because of the absence of
NMR virtual couplings in some platinum bis[(2-methylphospha-
nyl)ethanethiolato] analogues,[13,14] and by the large value of
[a] Dr. J. Duran, Dr. A. Polo, Prof. Dr. M. Solà, Dr. A. Poater
Departament de Química, Universitat de Girona
Campus de Montilivi s/n, 17071 Girona (Spain)
E-mail: alfons.polo@udg.edu
[b] Dr. J. Real
Departament de Quıímica, Universitat Autònoma de Barcelona
08193 Bellaterra (Spain)
[c] Dr. J. Benet-Buchholz
Institute of Chemical Research of Catalonia (ICIQ)
Av. Pa¨ısos Catalans 16, 43007 Tarragona (Spain)
[d] Prof. Dr. M. Solà, Dr. A. Poater
Institut de Quıímica Computational i Catàlisi, Universitat de Girona
Campus de Montilivi s/n, 17071 Girona (Spain)
E-mail: albert.poater@udg.edu
Supporting information and ORCID(s) from the author(s) for this article
are available on the WWW under http://dx.doi.org/10.1002/
open.201500136. Data include Cartesian xyz coordinates and energies of
all optimized reactants, products, intermediates, and transition states.
CCDC 1401716 and 1401717 contain the supplementary crystallographic
data for this paper. These data are provided free of charge by The Cam-
bridge Crystallographic Data Centre.
ꢀ 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
This is an open access article under the terms of the Creative Commons
Attribution-NonCommercial License, which permits use, distribution and
reproduction in any medium, provided the original work is properly
cited and is not used for commercial purposes.
1
the JPÀPt coupling constant.[14] However, as we showed previ-
1
ously, the JPÀPt criterion is not always infallible.[10b] In keeping
ChemistryOpen 2016, 5, 51 – 59
51
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

with the chlorocomplexes, nickel has preference for the binu-
clear complex [NiCl(m-SCH2CH2PPh2-k2P,S)]2,[15] also observed for
other phosphanylalkylthiolato ligands, both in solution and in
solid state.[10c,11a] Mononuclear [PdCl(dppet-k2P,S)(PPh3)] proved
to be stable in solution. No loss of PPh3 takes place, and no di-
meric palladium complexes were ever detected.[6] This complex
shows in solution an equilibrium between the two geometric
isomers strongly displaced to the trans-P,P arrangement, but
crystallization yields only the major stereoisomer. When an
alkyl substituent is introduced in the chelate chain, as in the
case of 1-(diphenylphosphanyl)butyl-2-thiolato derivative, dis-
sociation of PPh3 and formation of the dimeric chlorocomplex,
[PdCl(mS-ligand-k2P,S)]2, was described.[11a] For platinum, only
the mononuclear cis-[PtCl(dppet-k2P,S)(PPh3)] was reported.[16]
As part of a project on the analysis of the ligand-based ste-
reoelectronic effects that are determinant in the coordination
conformations of phosphanylthiolato ligands around the
metal,[6,10–12] we now report new preparation methods, and the
solid state structure, for bis-chelate 1 and for the unusual tri-
nuclear complex [PtCl(m-SCH2CH2PPh2-k2P,S)]3 (2). The structures
obtained are also rationalized mechanistically and through
conceptual DFT calculations.
Table 1. Crystal data for 1 and 2
Compound
1
2
Formula
Solvents
Formula weight
Crystal size (mm3)
Crystal color
Temp (K)
Crystal system
Space group
A (Š)
C28H28P2Pt1S2
–
685.65
0.30”0.20”0.10
yellow
153
monoclinic
C2/c
14.6509(3)
10.7332(2)
17.0890(3)
90
C42H42Cl3P3Pt3S3
–
1427.47
0.003”0.003”0.002
yellow
153
triclinic
P1
12.2393(5)
13.4900(6)
15.4706(7)
113.7590(10)
105.505(2)
95.164(2)
2195.42(17)
2
2.159
10.000
31.53
30667
8180 [Rint =0.0821]
SADABS
0.506/1.000
647/834
0.0458/0.0908
0.0910/0.1008
0.857
2.056/À3.358
¯
B (Š)
C (Š)
a (deg)
b (deg)
g (deg)
V (Š3)
109.3020(10)
90
2536.21(8)
4
1.796
5.839
Z
1 (gcmÀ3)
m (mmÀ1
qmax (8)
)
31.52
Reflec. measured
Unique reflections
Absorpt. correct.
Trans. min/max
Parameters/restraints
R1/wR2 [I>2s(I)]
R1/wR2 [all data]
Goodness-of-fit (F2)
Peak/hole (e/Š3)
19126
3948 [Rint =0.0593]
SADABS
0.587/1.000
206
0.0295/0.0709
0.0304/0.0716
1.052
Results and Discussion
1.993/À5.137
Complex 1 was first prepared in moderate yield (52%) from
the reaction of K2PtCl4 and Hdppet in the presence of NEt3 as
a base.[14] The potential problems related to the use of the
base,[10a] together with the low yield of 1 with this method,
prompted us to explore the direct, base-free, procedure. Thus,
reaction of K2PtCl4 with 2 equivalents of Hdppet in a mixture
of methanol/water cleanly afforded bis-chelate 1, which was
isolated in 92% yield (Scheme 1). Alternatively, 1 can be also
veals a mononuclear square-planar complex with C2 symmetry
and the platinum atom placed on the rotation axis (Figure 1).
The PtÀS bond length is similar to those detected in other
cis-[16] and trans-bis(phosphanylthiolato)[15] complexes of plati-
num(II), but the PtÀP is shorter than those observed in the
trans geometries. The large PÀPtÀP angle, nearly 1058, results
from the cis orientation of the bulky PPh2 groups that com-
press the SÀPtÀS angle to about 828. The chelate angle, is in
the order of those observed for mononuclear platinum(II) com-
Scheme 1. Synthesis of bis-chelate 1. Reagents and conditions: a) Hdppet/
MeOH, K2PtCl4/H2O, 30 min, rt, 92%; b) Hdppet (neat), Pt(PPh3)4/CH2Cl2,
30 min, rt, 70%.
obtained by oxidative addition of the phosphanylthiol to
Pt(PPh3)4 and subsequent reductive elimination of hydrogen. In
this case, bis-chelate 1 was isolated in 70% yield (Scheme 1).
According to the 31P{1H} NMR spectrum, bis-chelate 1 exists as
1
a single geometric isomer in solution, with a JPÀPt coupling
constant of 2810.9 Hz which suggest a cis-P,P arrangement.[14]
The cis geometry of bis-chelate 1 in solid state was confirmed
by the X-ray diffraction (XRD) crystal structure.
Figure 1. ORTEP (Oak Ridge Thermal Ellipsoid Plot) figure (50%) of com-
plex 1, H atoms are omitted for the sake of clarity; selected distances (Š)
and angles (8): PtÀP 2.2705(6), PtÀS 2.3233(6), PÀPtÀS 86.45(2), PÀPtÀPi
104.98(3), SÀPtÀSi 82.14(3), PÀPtÀSi 168.56(2). Symmetry transformation
The XRD study was carried out on a crystal of 1 obtained
from dichloromethane–hexane. Crystal data for the structure
are given in Table 1. Selected bond lengths and bond angles
are listed in the caption of Figure 1. The crystal structure re-
used to generate equivalent atoms: -x, y, 1= -z.
2
ChemistryOpen 2016, 5, 51 – 59
www.chemistryopen.org
52
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

plexes with the PPh2 group of a chelated dppet ligand cis to
a PPh3.[16]
phine coordinated to Pt is 20.0 kcalmolÀ1 more stable than the
same complex coordinated through the thiol group. Once
complex V is formed, the next dissociation of a phosphine
ligand is not feasible without the oxidative addition of the SÀH
bond of the Hdppet ligand into the Pt center to form complex
IX. Actually without removing the phosphine ligand, from
complex V, this insertion takes places through a barrier of
11.5 kcalmolÀ1. From IX, bearing the excess of Hdppet, the ex-
change of PPh3 by Hdppet is favored by 1.6 kcalmolÀ1, to form
complex X. The final step that leads to complex 1cis from spe-
cies X takes places through a concerted transition state that in-
volves a second oxidative addition and the reductive release of
a hydrogen molecule in a process that requires 25.9 kcalmolÀ1.
This rather high energy barrier is probably somewhat overesti-
mated. The rate determining step (rds) for the formation of
1cis corresponds to this last X to 1cis transformation.
The observed structural cis preference can be interpreted, in
simple terms, on the basis of the antisymbiosis rule stating
that two soft ligands in mutual trans positions have a destabi-
lizing effect on each other when attached to a soft metal
ion.[17] To shed light into this preference for the cis conforma-
tion and get more detailed information, we envisaged density
functional theory (DFT) calculations. For our study, we used
the M06 exchange-correlation functional that includes disper-
sion corrections. M06/TZVP//M06/SVP calculations on com-
plex 1 reveal a favorable energy difference of only 1.3 kcal
molÀ1 for the cis isomer. This small difference can be the result
of a low antisymbiotic effect (thiolates and phosphines are
both soft bases; for example, hardness of CH3SÀ and PPh2CH3
are 61.8 and 65.9 kcalmolÀ1, respectively) and the steric inter-
actions that favor the trans isomer. When the thermal and en-
tropic effects are not introduced, the energetic preference for
the cis arrangement increases to 3.7 kcalmolÀ1, which brings
the computational results into much better agree-
ment with experimental observations, and reveals
a possible overestimation by our calculations of the
entropic stabilization of the trans isomer as com-
pared to the cis one. The large dipole moment of the
cis isomer provides larger solvation energy in com-
parison with the nonpolar trans isomer.[18] The chemi-
cal potential for the cis isomer of complex 1 is
À70.5 kcalmolÀ1 whereas it is À66.2 kcalmolÀ1 for
the trans conformation.[19] In agreement with the
maximum hardness principle,[20] the chemical hard-
ness of the cis conformation (41.5 kcalmolÀ1) is some-
what higher than that of the trans conformation
(41.3 kcalmolÀ1).[21]
The trans conformation of complex 1 can be formed
through different reaction pathways. First, it might be generat-
ed directly from the cis conformation, that is, complex 1cis,
Given the low energy difference between both iso-
mers, we investigated the reaction pathway to get
complex 1 from Pt(PPh3)4 (see Figure 2) in the cis and
trans conformations to discern whether kinetic effects
are responsible for the formation of exclusively the
cis isomer. Formation of the cis isomer requires the
generation of complex V in Figure 2. These com-
plexes are generated by successive substitutions of
phosphine by Hdppet ligands. The sequential dissoci-
ation of phosphine groups is not energy demanding,
provided that at least two based phosphorous li-
gands remain bonded to platinum, either in the form
of triphenylphosphines or phosphanylthiol ligands.
Indeed the bis-phosphine structure is isoenergetic
with the bis-Hdppet structure (compare complexes III
and VII). This result concurs with the experimental
fact that in the presence of a high concentration of
Hdppet with respect to the Pt(PPh3)4 precursor, the
PPh3 groups are easily substituted. In any case the
coordination of the phosphanylthiolato does not
occur through the thiolate moiety, but through the
phosphine group. Take for instance the coordination
of the second molecule of Hdppet to species VIII,
Figure 2. Reaction pathways of the conversion of Pt(PPh3)4 to complex 1 (red: the values
from which formation of complex X with the phos- of the transition states, relative Gibbs energies in kcalmolÀ1).
ChemistryOpen 2016, 5, 51 – 59
www.chemistryopen.org
53
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

however the barrier to isomerize to the trans conformation is
37.1 kcalmolÀ1. Second, complex V can also evolve to VII
through successive exchange of phosphines by Hdppet li-
gands. Two consecutive SÀH oxidative additions followed by
the reductive release of a hydrogen molecule in complex VII
produce complex 1trans in a process that has to surmount
a Gibbs energy barrier of 26.8 kcalmolÀ1. The XII to 1trans pro-
cess is the rds for the formation of complex 1trans. This
means that kinetically, the cis conformation is favored over the
trans species by 0.9 kcalmolÀ1. A final pathway to form com-
plex 1trans could be the isomerization of complex VIII to its
trans conformation XI, that is, the rotation of the hydride by
908. This transformation requires surpassing a barrier of
33.0 kcalmolÀ1 with respect to I, being the trans isomer 6.4 kcal
molÀ1 higher in energy. Therefore, this latter pathway can be
ruled out. As a whole, our results show that formation of com-
plex 1cis is both thermodynamically and kinetically favored as
compared to complex 1trans formation. In both cases, the rds
corresponds to the last step of the process that involves coor-
dination of the phosphanylthiolato ligand and release of a H2
molecule.
To further evaluate the preference for the cis isomer for
complex 1, its phenyl groups were substituted by either
methyl or tert-butyl (t-Bu) groups, and then the trans isomer
was found to be lower in Gibbs energy by 0.8 and 15.2 kcal
molÀ1, respectively. These energy values reveal that highly ster-
ically demanding groups like t-Bu impedes the formation of
the cis conformation, and the comparison between methyl and
phenyl substituents indicates a major preference of the cis for
the latter substituent because of the p–p stacking between its
aryl groups. The structural deformation due to the substituents
on the phosphorous is translated into the increase of the PÀ
PtÀP angle, by 0.4 and 12.08 with methyl and t-butyl groups,
respectively (see Figure 3).
Figure 3. Optimized cis conformation of a) [Pt(dppet)2] (1), b) [Pt(dmpet)2],
and c) [Pt(dtbpet)2] (selected distances (Š) and angles (8)).
To explore the possibility to obtain the dinuclear complex
[PtCl(m-SCH2CH2PPh2-k2P,S)]2, similar to those observed for
nickel[15] and palladium,[10a] the base-free reaction of
[PtCl2(COD)] (COD=1,5-cyclooctadiene) with 1 equivalent of
Hdppet in dichloromethane was performed, affording a quite
insoluble material. According to the 31P{1H} NMR spectrum, this
solid is formed mainly by two products in a 2/1 ratio. The
minor component shows a singlet with a chemical displace-
1
ment and a JPÀPt coupling constant similar to those observed
for the bis-chelate complex 1. The major constituent of the
mixture also shows a singlet, but at higher fields and with
1
Figure 4. ORTEP figure (50%) of complex 2, H atoms are omitted for the
sake of clarity; selected distances (Š) and angles (8): Pt1ÀP3 2.246(2), Pt1ÀS3
2.283(2), Pt1ÀCl1 2.340(2), Pt1ÀS1 2.3651(19), Pt2ÀP1 2.225(2), Pt2ÀS1
2.2648(19), Pt2ÀCl2 2.3345(19), Pt2ÀS2 2.358(2), Pt3ÀP2 2.248(2), Pt3ÀS2
2.266(2), Pt3ÀCl3 2.328(2), Pt3ÀS3 2.401(2), P3ÀPt1ÀS3 87.67(8), S1ÀPt1ÀS3
95.33(7), Pt1ÀS1ÀPt2 109.66(8), P1ÀPt2ÀS1 88.09(7), S1ÀPt2ÀS2 83.73(7),
Pt2ÀS2ÀPt3 105.20(9), P2ÀPt3ÀS2 86.98(8), S2ÀPt3ÀS3 89.54(7), Pt1ÀS3ÀPt3
111.25(8).
larger JPÀPt coupling constant. Slow evaporation of the NMR
solutions of this mixture produces a microcrystal (3”3”2 mm3)
which was studied by XRD. Crystal data for the structure ob-
tained, complex 2, are given in Table 1. Selected bond lengths
and bond angles are listed in the caption of Figure 4.
The crystal structure reveals a sulfur-bridging edge-sharing
cyclic trinuclear complex with square-planar coordination ge-
ometry around the platinum atoms (Figure 4). Related struc-
tures were found for aminoalkylthiolato, [PtBr(m-SCH2CH2NMe2-
to our knowledge, the first example with phosphanylalkylthio-
lato ligand.
k2N,S)]3,[22] phosphanylarylthiolato, [PtI(m-SC6H4-2-PPh2-k2P,S)]3
[23]
and [PtI{m-SC6H4-2-P(1,1’-biphenyl)-k2P,S}]3, and arsanylarylth-
The cis-Cl,P arrangement is in disagreement with the anti-
symbiosis rule,[17] but the cis-S,S geometry is necessary to build
[24]
iolato ligands, [PtI(m-SC6H4-2-PAs2-k2As,S)]3,[25] but complex 2 is,
ChemistryOpen 2016, 5, 51 – 59
www.chemistryopen.org
54
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

one equivalent of the phosphanylarylthioarsine Ph2AsSC6H4-2-
PPh2 with [PtI2(COD)] shows initially the existence of a mixture
of the bis-chelate and a second complex with chemical dis-
1
placement at lower frequencies and larger JPÀPt coupling con-
stant. The second compound resulted to be the trinuclear
[PtI(m-SC6H4-2-PPh2-k2P,S)]3.[23] This parallelism, and the crystal
structure obtained, allow us to assign the major component of
our reaction mixture to complex 2. Regarding the reaction
pathway, formation of the bis-chelate complex 1 has been
postulated as the kinetically favored process, elapsing through
a mononuclear intermediate (Scheme 2).[23] The subsequent re-
action of 1 with the mononuclear intermediate and unconvert-
ed starting product (path A) can generate a trinuclear inter-
mediate that should isomerize to the final thermodynamic
product 2.
Figure 5. ORTEP figure (50%) of the Pt3S3 cycle with the platinum square-
planar coordination sphere of complex 2. Selected distances and angles are
given in Figure 4.
This pathway is similar to that proposed for the formation of
[PtI(m-SC6H4-2-PPh2-k2P,S)]3, in which the trinuclear intermediate
was identified, and the kinetic product, the bis-chelate, is total-
ly transformed into the ultimate trinuclear complex.[23] In pres-
ent work, the trinuclear intermediate has not been detected,
and no interconversion between complexes 1 and 2 was ob-
served, pointing to a quick association of the mononuclear in-
termediate to give trinuclear complex 2 (pathway B in
Scheme 2).
the six-membered Pt3S3 cycle. This cycle adopts a skew-boat
conformation (Figure 5) with each bridging sulfur atom show-
ing one shorter and one longer PtÀS bond (Figure 4). Similar
unsymmetrical bridging sulfurs were observed in related com-
pounds.[23,24] The SÀPtÀS angles are smaller than PtÀSÀPt ones
because of the restriction imposed by the metal square-planar
coordination. Two of the three five-membered chelate cycles
adopt a d conformation with both phenyl radicals of the PPh2
group in a pseudo equatorial position. The third chelate cycle
shows a l conformation which locates one of the phenyl
groups in axial position (Figure 6). On the face of the Pt3S3
To understand the trinuclear structural preference for com-
plex 2, DFT calculations were carried for this complex and for
the hypothetical binuclear intermediate [PtCl(m-SCH2CH2PPh2-
k2P,S)]2, as well as for any moiety able to link complexes 1 and
2. First, the structural results on
complex 2 showed good agree-
ment between the experimental
and theoretical data. The stan-
dard deviation for the bond dis-
tances is 0.053 Š and that for
the angles is 1.38,[27,28] thus pro-
viding confidence in the reliabili-
ty of the chosen method to re-
produce geometries of the stud-
ied complexes. Furthermore, al-
though there is the experimental
insight that both mononuclear
and trinuclear species are dia-
Figure 6. ORTEP figure (50%) of the Pt3S3 cycle with the platinum square-planar coordination sphere of com-
plex 2. Selected distances and angles are given in Figure 4.
magnetic, we performed calcula-
tions for neutral closed-shell sin-
glet ground-state structures, but
cycle where this phenyl is placed, there is no other group that
generates steric repulsions, resulting in the most favorable sit-
uation. Accordingly, the PtÀP and PtÀS distances are the short-
est. The square-planar geometry around platinum is somewhat
distorted with a chelate angle slightly reduced from the ideal-
ized value of 908. Quite similar distortions from the idealized
geometry are also observed in other platinum(II) complexes
with chelated dppet ligands.[16,26] The intramolecular PtÀPt dis-
tances are greater than 3.65 Š suggesting no metal–metal co-
valent interactions.
we also checked how far was the lowest-lying excited triplet
state. In all cases, the triplet state presented a higher energy
(the difference between these two states for 1 is 31.9 kcal
molÀ1), indicating that the singlet states are the most favored.
This is in agreement with the sharp peaks in the NMR spectra.
Figures 7 and
8 map the paths B and A that drive
[PtCl2(COD)] to 2 and 1, respectively. The first step (a to b in
Figure 7) involves the dissociation of the neutral COD ligand
together with the coordination of a Hdppet ligand. This pro-
cess releases 17.0 kcalmolÀ1. This new square-planar interme-
diate b might be in competition with the cationic moiety
where the leaving group was a chloride instead of the COD.
Concerning the mechanism of the reaction, as we have ob-
served in this work, the 31P{1H} NMR of the reaction mixture of
ChemistryOpen 2016, 5, 51 – 59
www.chemistryopen.org
55
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Scheme 2. Possible reaction pathways in the formation of complex 2.
Figure 8. Reaction pathway of the conversion of intermediate d to com-
plex 1 (red lines display the transition states, in blue is the corresponding
profile with Hdmpet ligand, Gibbs energies relative to 3
[PtCl2(COD)]+3 Hdmpet ligands (in kcalmolÀ1).
Anyway chloride substitution is endergonic by 6.4 kcalmolÀ1
,
and, therefore, COD release is much more favorable. The next
proton transfer from the thiol group to the chloride and re-
lease of HCl molecule requires 23.5 kcalmolÀ1 and drives to
a somewhat unstable intermediate d that trimerizes easily to
complex 2. The formation of this trinuclear complex from com-
plex d is found to be barrierless and quite exergonic (39.4 kcal
molÀ1). Thus this result shows that pathway B involves relative-
ly low-energy-demanding steps, and it is thermodynamically
favored.
Alternatively, instead of the trinuclear interaction, intermedi-
ate d can interact with a new Hddpet substrate molecule to
yield complex e (Figure 8). This complex can easily be trans-
formed into f after overcoming a barrier of 8.5 kcalmolÀ1. Final
release of an HCl molecule yields 1cis complex in a process
that is 21.4 kcalmolÀ1 endergonic. On the other hand, from spe-
cies d, the trans conformation of 1 might be also feasible, over-
coming a barrier 17.0 kcalmolÀ1. Our results show that once
complex d is generated, formation of 2 is kinetically and ther-
modynamically more favorable than obtaining any of the mon-
onuclear species 1. This result is in agreement with the princi-
ple of maximum hardness since the chemical hardness for com-
plex 2 is 7.8 kcalmolÀ1 higher than that of complex 1cis.
The dimerization was also faced, instead of the trimerization.
Although the process to get the dimeric structures, including
Figure 7. Reaction pathway of the conversion of [PtCl2(COD)] to complex 2
(red lines display the transition states, in blue is the corresponding profile
with Hdmpet ligand, Gibbs energies relative to 3 [PtCl2(COD)]+3 Hdmpet li-
gands (in kcalmolÀ1).
ChemistryOpen 2016, 5, 51 – 59
www.chemistryopen.org
56
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

positions are relative to tetramethylsilane (TMS) as internal refer-
ence. 31P{1H} NMR spectra were recorded on the same instrument
operating at 81.0 MHz. Chemical shifts are relative to external 85%
H3PO4, and downfield values are reported as positive.
either two chloride or sulfur bridges is barrierless, thermody-
namically it is 30.2 kcalmolÀ1 less favorable than the formation
of the trinuclear structure. On the other hand, the other trinu-
clear structure proposed as an intermediate in path A
(Scheme 2) was also investigated, but located to be 6.6 kcal
molÀ1 higher in energy than 2. Despite its rather high stability,
its formation requires the formation of complex 1 first, which
is ruled out according to the mechanism proposed in Figure 8.
The substitution of the phenyl groups by methyl or tert-
butyl groups on the phosphorous atoms did not change any
qualitative trend, and quantitatively all barriers were nearly
identical. Thermodinamically, the energy released with respect
to the precursor [PtCl2(COD)] in the formation of 2 is higher
when the phenyl groups in the phosphines are substituted by
methyl (13.2 kcalmolÀ1) or tert-butyl (8.7 kcalmolÀ1) groups.
This confirms that the nature of phosphine substituents is not
determining the feasibility of the formation of trinuclear spe-
cies.
[Pt{SCH2CH2PPh2-k2P,S}2] (1). Method 1: Hdppet (30 mg, 0.12 mmol)
in MeOH (2 mL) was added to a solution of K2PtCl4 (24.7 mg,
0.06 mmol) in deionized H2O (3 mL). The mixture was allowed to
react for 30 min at rt, the solvent is evaporated in vacuo down to
0.5 mL, and Et2O (1 mL) is slowly added to precipitate an intense
yellow microcrystalline solid. The product is separated by filtration,
washed with Et2O, and dried under a current of N2 yielding com-
plex 1 (24 mg, 92%). Method 2: neat Hdppet (112 mg, 0.44 mmol)
was added to a solution of Pt(PPh3)4 (285 mg, 0.22 mmol) in CH2Cl2
(8 mL). The mixture is allowed to react for 30 min at rt, and hexane
(1 mL) is slowly added to precipitate 1 (105 mg, 70%). Completely
dry complex 1 is stable in air, slightly soluble in CH2Cl2 and insolu-
ble in CHCl3, EtOH, MeOH, toluene, Et2O, and hexane. 1H NMR
(200 MHz, CD2Cl2, TMS): d=2.52 (m, 4H, aliphatics), 7–8 ppm (m,
10H, aromatics). 31P{1H} NMR (81 MHz, CD2Cl2, H3PO4): d=
1
61.70 ppm (s, JPÀPt =2810.9 Hz). The low solubility of 1 precluded
the observation of a good-quality 13C NMR spectrum. Anal. calcd
for C28H28P2PtS2 (685,7): C 49.05, H 4.12, S 9.35; found C 49.29, H
4.30, S 9.65.
Conclusions
[PtCl(m-SCH2CH2PPh2-k2P,S)]3 (2): neat Hdppet (123 mg, 0.50 mmol)
was added to a solution of [PtCl2(COD)] (236.5 mg, 0.50 mmol) in
CH2Cl2 (8 mL). The mixture was allowed to react for 1 h at rt, the
solvent was evaporated in vacuo down to 3 mL, and Et2O (5 mL)
was slowly added to give a yellow precipitate. The product was
separated by filtration, washed with Et2O, and dried under a current
of N2, yielding a solid (189.7 mg) practically insoluble in CH2Cl2, and
insoluble in CHCl3, Et2O, and hexane. The low solubility of this solid
precluded the observation of good-quality NMR spectra.
31P{1H} NMR (81 MHz, CD2Cl2, H3PO4): major product d=45.27 ppm
The transition metal complexes of heterotopic phosphanyl-
thiolato ligands are important for their use in many
interesting reactions. In this work, bis-chelate complex
[Pt(SCH2CH2PPh2,k2P,S)2] (1) has been obtained in good yields
by direct base-free substitution reaction of the corresponding
thiol with K2PtCl4 or by oxidative addition of the thiol to
Pt(PPh3)4. The XRD studies of this complex 1 shows a cis-P,P ar-
rangement in agreement with the antisymbiosis rule. Density
functional theory (DFT) calculations on 1 indicate that the cis
geometry is preferred over the trans one for both thermody-
namic and kinetic reasons. The rate determining step for the
formation of complex 1 is the final step, which involves an oxi-
dative addition of the SÀH bond of a phosphanylthiol ligand
into the Pt center and the reductive release of a hydrogen
molecule. Direct base-free reaction of [PtCl2(COD)] with one
equivalent of the thiol produces the trinuclear complex
[PtCl(m-SCH2CH2PPh2-k2P,S)]3 (2) with square-planar coordina-
tion geometry around the platinum atoms and a Pt3S3 cycle in
skew-boat conformation. Our DFT calculations show that for-
mation of the trinuclear structure occurs through ClPt(dppet)
complex d. Once this rather unstable intermediate is formed,
the formation of the trinuclear structure is a barrierless and
quite exergonic process. On the contrary, formation of the
mononuclear and dinuclear species involves non-negligible
energy barriers and leads to thermodynamically less stable
products.
1
1
(s, JPÀPt =ca. 3343 Hz), minor product d=62.18 ppm (s, JPÀPt =ca.
2771 Hz).
X-ray crystal structure determination
Yellow crystals of 1 were obtained by slow evaporation of CH2Cl2/
hexane solutions at rt. Yellow crystals of 2 were obtained by slow
evaporation of a CH2Cl2 solution. Measured crystals were prepared
under inert conditions immersed in perfluoropolyether as protect-
ing oil for manipulation. Crystal data are presented in Table 1, and
selected distances and angles in the captions of Figure 1 and 4.
Data collection: Crystal structure determinations for 1 and 2 were
carried out using a Siemens P4 diffractometer (Munich, Germany)
equipped with an SMART 1000 CCD area detector, a MAC Science
Co. rotating anode with MoKa radiation, a graphite monochroma-
tor, and a Siemens low-temperature device (T=À1208C). Full-
sphere data collection was used with w and f scans. Programs
used: Data collection SMART,[29] data reduction SAINT,[30] and ab-
sorption correction SADABS.[31]
Structure Solution and Refinement: Crystal structure solution was
achieved using direct methods as implemented in SHELXTL[32] and
visualized using the program XP. Missing atoms were subsequently
located from difference Fourier synthesis and added to the atom
list. Least-squares refinement on F2 using all measured intensities
was carried out using the program SHELX-93. All nonhydrogen
atoms were refined including anisotropic displacement parameters.
Experimental Section
Synthesis
General remarks: The complexes were synthesized using standard
Schlenk techniques under N2 atmosphere. The solvents were dried
by standard methods and distilled and deoxygenated before use.
The C, H, and S analyses were carried out using a Carlo–Erba mi-
croanalyser (Lakewood, USA). 1H NMR spectra were recorded at
200 MHz on a Bruker DPX-200 spectrometer (Billerica, USA). Peak
Comments on the structures: Compound 1 crystallizes with a half
molecule in the asymmetric unit showing C2 symmetry. Com-
ChemistryOpen 2016, 5, 51 – 59
www.chemistryopen.org
57
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

pound 2 crystallizes with one molecule in the asymmetric unit.
Four of the benzenes rest linked to the phosphorous atoms are
disordered in two orientations with an approximate ratio of 60:40.
Although the triclinic crystal used for the structure determination
of 2 was of extremely small dimensions (3”3”2 mm3), an excellent
dataset could be collected.
for a Career Integration Grant (CIG09-GA-2011-293900). M. S.
thanks the European Union for a Fonds EuropØen de DØveloppe-
ment RØgional (FEDER) fund (UNGI10-4E-801), the Generalitat de
Catalunya for project 2014SGR931 and the Institució Catalana de
Recerca i Estudis AvanÅats (ICREA) Academia 2014 prize, and
MINECO through project CTQ2014-54306-P.
Computational methods
Keywords: bis-chelate complexes
·
density functional
All the DFT calculations were performed at the generalized gradi-
ent approximation (GGA) level with the Gaussian09 set of pro-
grams,[33] using the M06 functional of Truhlar.[34] The electronic
configuration of the molecular systems was described with the
standard split-valence basis set with a polarization function of Ahl-
richs and co-workers for H, C, N, P, S, and Cl (SVP keyword in Gaus-
sian).[35] For Pt we used the quasi-relativistic Stuttgart/Dresden ef-
fective core potential, with an associated valence basis set (stan-
dard SDD keywords in Gaussian09).[36] The geometry optimizations
were carried out without symmetry constraints, and the characteri-
zation of the stationary points was performed by analytical fre-
quency calculations. These frequencies were used to calculated un-
scaled zero-point energies (ZPEs) as well as thermal corrections
and entropy effects at 298 K and 1 atm by using the standard stat-
istical-mechanics relationships for an ideal gas. Energies were ob-
tained via single point calculations on the M06-optimized geome-
tries with triple zeta valence plus polarization (TZVP keyword in
Gaussian) using the M06 functional as well.[30] In these single-point
energy calculations, H, C, N, P, S, and Cl were described using the
TZVP basis set, while for Pt, the SDD basis set was employed. On
top of the M06/TZVP/M06/SVP energies, we added the ZPEs, ther-
mal corrections obtained at the M06/SVP level. In addition, to cal-
culate the reported Gibbs energies, we included solvent effects of
a CH2Cl2 solution estimated with the polarizable continuous solva-
tion model PCM implemented in Gaussian09.[37] The chemical po-
tential is a measure of the tendency of the electrons to escape
from the system. It is calculated from the partial derivative of the
electronic energy with respect to the total number of electrons.
The hardness, h, is a measure of the resistance of a chemical spe-
cies to change its electronic configuration, and it is defined as the
second-order partial derivative of the total electronic energy with
respect to the total number of electrons. Using a finite difference
approximation and the Koopmans’ theorem, one obtains the ex-
pressions we have used for the calculation of the chemical poten-
tial and the hardness:
calculations · P,S ligands · platinum · trinuclear complexes
[1] For reviews on the use of heterotopic phosphorus-sulfur donor ligands
in catalytic processes, see: a) D. K. Dutta, B. Deb, Coord. Chem. Rev.
2011, 255, 1686–1712; b) J. R. Dilworth, N. Wheatley, Coord. Chem. Rev.
2000, 199, 89–158.
[2] J. S. Kim, J. H. Reibenspies, M. Y. Darensbourg, J. Am. Chem. Soc. 1996,
118, 4115–4423.
[3] H. Kuniyasu, F. Yamashita, T. Hirai, J.-H. Ye, S.-I. Fujiwara, N. Kambe, Or-
ganometallics 2006, 25, 566–570.
[4] a) M. Yuki, Y. Miyake, Y. Nishibayashi, Organometallics 2010, 29, 5994–
6001; b) W.-C. Chu, C.-C. Wu, H.-F. Hsu, Inorg. Chem. 2006, 45, 3164–
3166.
[5] L.-P. He, M. Hong, B.-X. Li, J.-Y. Liu, Y.-S. Li, Polymer 2010, 51, 4336–
4339.
[6] N. Brugat, A. Polo, A. lvarez-Larena, J. F. Piniella, J. Real, Inorg. Chem.
1999, 38, 4829–4837.
[7] a) R. J. Angelici, Organometallics 2001, 20, 1259–1275; b) D. A. Vicic,
W. D. Jones, J. Am. Chem. Soc. 1999, 121, 7606–7617.
[8] a) S. Ye, F. Neese, A. Ozarowski, D. Smirnov, J. Krzystek, J. Telser, J.-H.
Liao, C.-H. Hung, W.-C. Chu, Y.-F. Tsai, R.-C. Wang, K.-Y. Chen, H.-F. Hsu,
Inorg. Chem. 2010, 49, 977–988; b) T.-W. Chiou, W.-F. Liaw, Inorg. Chem.
2008, 47, 7908–7913; c) C.-M. Lee, Y.-L. Chuang, C.-Y. Chiang, G.-H. Lee,
W.-F. Liaw, Inorg. Chem. 2006, 45, 10895–10904; d) T. Ohkubo, H. Saka-
shita, T. Sakuma, M. Kainosho, M. Sekiguchi, K. Morikawa, J. Am. Chem.
Soc. 1994, 116, 6035–6036; e) L. C. Myers, M. P. Terranova, A. E. Ferentz,
G. Wagner, G. L. Verdine, Science 1993, 261, 1164–1167.
[9] P. W. N. M. Van Leeuwen, P. C. J. Kamer, J. N. H. Reek, P. Dierkes, Chem.
Rev. 2000, 100, 2741–2769.
[10] a) N. Brugat, J. Duran, A. Polo, J. Real, A. lvarez-Larena, J. F. Piniella, Tet-
rahedron: Asymmetry 2002, 13, 569–577; b) J. Duran, N. Brugat, A. Polo,
J. Real, X. Fontrodona, J. Benet-Buchholz, Organometallics 2003, 22,
3432–3438; c) J. Duran, A. Polo, J. Real, J. Benet-Buchholz, A. Poater, M.
Solà, Eur. J. Inorg. Chem. 2003, 4147–4151.
[11] a) A. Dervisi, R. L. Jenkins, K. M. A. Malik, M. B. Hursthouse, S. Coles,
Dalton Trans. 2003, 1133–1142; b) A. Dervisi, D. Koursarou, L.-L. Ooi,
P. N. Horton, M. B. Hursthouse, Dalton Trans. 2006, 5717–5724.
[12] Y.-M. Hsiao, S. S. Chojnacki, P. Hinton, J. H. Reibenspies, M. Y. Dare-
nsbourg, Organometallics 1993, 12, 870–875.
[13] P. H. Leung, J. W. L. Martin, S. B. Wild, Inorg. Chem. 1986, 25, 3396–
3400.
[14] M. Kita, T. Yamamoto, K. Kashiwabara, J. Fujita, Bull. Chem. Soc. Jpn.
1992, 65, 2272–2274.
[15] T. Gerdau, W. Klein, R. Kramolowsky, Cryst. Struct. Commun. 1982, 11,
1663–1669.
eLUMO þ eHOMO
ð1Þ
ð2Þ
m ¼
h ¼
;
;
2
eLUMO À eHOMO
2
where eLUMO and eHOMO are the energies of the low unoccupied mo-
lecular orbital (LUMO) and the high occupied molecular orbital
(HOMO), respectively.
[16] P. V. Rao, S. Bhaduri, J. Jiang, D. Hong, R. H. Holm, J. Am. Chem. Soc.
2005, 127, 1933–1945.
[17] R. G. Pearson, Inorg. Chem. 1973, 12, 712–713.
[18] J. N. Harvey, K. M. Heslop, A. G. Orpen, P. G. Pringle, Chem. Commun.
2003, 278–279.
[19] a) R. G. Parr, L. von Szentpaly, S. Liu, J. Am. Chem. Soc. 1999, 121, 1922–
1924; b) P. Geerlings, F. De Proft, W. Langenaeker, Chem. Rev. 2003, 103,
1793–1873; c) R. G. Parr, W. Yang, Density Functional Theory of Atoms
and Molecules, Oxford University Press, New York, 1989; d) R. G. Parr,
R. A. Donnelly, M. Levy, W. E. Palke, J. Chem. Phys. 1978, 68, 3801–3807;
e) R. G. Parr, R. G. Pearson, J. Am. Chem. Soc. 1983, 105, 7512–7516; f) T.
Koopmans, Physica 1934, 1, 104–113.
[20] a) R. G. Pearson, J. Chem. Educ. 1987, 64, 561–562; b) R. G. Pearson,
Chemical Hardness, Applications from Molecules to Solids, Wiley-VCH,
Oxford, 1997.
Acknowledgements
A. Polo thanks the Spanish Dirección General de EnseÇanza Supe-
rior e Investigación Científica (DGESIC) for financial support (proj-
ect BQU2002-04070-C02-01). A. Poater thanks the Spanish Minis-
terio de Economía y Competitividad (MINECO) for a Ramón y
Cajal contract (RYC-2009-05226) and the European Commission
ChemistryOpen 2016, 5, 51 – 59
www.chemistryopen.org
58
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

[21] a) A. J. Bridgeman, N. Harris, N. A. Young, Chem. Commun. 2000, 1241–
1242; b) A. J. Bridgeman, J. Chem. Soc. Dalton Trans. 1996, 2601–2607;
c) A. Poater, J. Phys. Chem. A 2009, 113, 9030–9040; d) A. Poater, A. G.
Saliner, R. Carbó-Dorca, J. Poater, M. Solà, L. Cavallo, A. P. Worth, J.
Comput. Chem. 2009, 30, 275–284; e) A. Poater, A. G. Saliner, M. Solà, L.
Cavallo, A. P. Worth, Expert Opin. Drug Delivery 2010, 7, 295–305.
[22] M. Capdevila, W. Clegg, P. Gonzalez-Duarte, I. Mira, J. Chem. Soc. Dalton
Trans. 1992, 173–181.
[23] I. Sµrosi, A. Hildebrand, P. Lçnnecke, L. Silaghi-Dumitrescu, E. Hey-Haw-
kins, Dalton Trans. 2012, 41, 5326–5333.
[24] A. Hildebrand, I. Sµrosi, P. Lçnnecke, L. Silaghi-Dumitrescu, M. B. Sµrosi,
I. Silaghi-Dumitrescu, E. Hey-Hawkins, Dalton Trans. 2012, 41, 7729–
7736.
[31] a) SADABS: V2001 Bruker, Bruker AXS Inc., Madison, WI, 2001; b) R. H.
Blessing, Acta Crystallogr. Sect. A 1995, 51, 33–38.
[32] SHELXTL version V6.14, G. M. Sheldrick, Acta Crystallogr. Sect. A 2008,
64, 112–122.
[33] Gaussian 09, Revision D.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Men-
nucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian,
A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara,
K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro,
M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Ko-
bayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyen-
gar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg,
S. Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cio-
slowski, D. J. Fox, Gaussian, Inc., Wallingford CT, 2009.
[25] A. Hildebrand, I. Sµrosi, P. Lçnnecke, L. Silaghi-Dumitrescu, M. B. Sµrosi,
I. Silaghi-Dumitrescu, E. Hey-Hawkins, Inorg. Chem. 2012, 51, 7125–
7133.
[26] J. Duran, R. Juanola, A. Polo, J. Real, J. Benet-Buchholz, M. Solà, A.
Poater, Unpublished data..
[27] The chosen bond distances and angles used for the comparison of the
theoretical and experimental data are collected in Table S2 in the Sup-
porting Information.
[28] a) A. Poater, S. Moradell, E. Pinilla, J. Poater, M. Solà, M. A. Martínez, A.
Llobet, Dalton Trans. 2006, 1188–1196; b) M. Costas, X. Ribas, A. Poater,
J. M. López-Valbuena, R. Xifra, A. Company, M. Duran, M. Solà, A. Llobet,
M. Corbella, M. A. Usón, J. Mahía, X. Solans, X. Shan, J. Benet-Buchholz,
Inorg. Chem. 2006, 45, 3569–3581; c) J. Mola, M. Rodríguez, I. Romero,
A. Llobet, T. Parella, A. Poater, M. Duran, M. Solà, J. Benet-Buchholz,
Inorg. Chem. 2006, 45, 10520–10529.
[34] Y. Zhao, D. G. Truhlar, Theor. Chem. Acc. 2008, 120, 215–241.
[35] A. Schäfer, H. Horn, R. Ahlrichs, J. Chem. Phys. 1992, 97, 2571–2577.
[36] a) U. Häussermann, M. Dolg, H. Stoll, H. Preuss, P. Schwerdtfeger, R. M.
Pitzer, Mol. Phys. 1993, 78, 1211–1224; b) W. Küchle, M. Dolg, H. Stoll,
H. Preuss, J. Chem. Phys. 1994, 100, 7535–7542; c) T. Leininger, A. Nick-
lass, H. Stoll, M. Dolg, P. Schwerdtfeger, J. Chem. Phys. 1996, 105, 1052–
1059.
[37] a) V. Barone, M. Cossi, J. Phys. Chem. A 1998, 102, 1995–2001; b) J.
Tomasi, M. Persico, Chem. Rev. 1994, 94, 2027–2094.
[29] Data collection with SMART version 5.060 Bruker-AXS, Bruker AXS Inc.,
Madison, WI, 1999.
Received: May 19, 2015
[30] Data reduction with Bruker SAINT V6.02 Bruker AXS, Bruker AXS Inc.,
Madison, WI, 1999.
Published online on July 30, 2015
ChemistryOpen 2016, 5, 51 – 59
www.chemistryopen.org
59
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim