Complexes of M3S44+ (M = Mo, W) with chiral alpha-hydroxy and aminoacids: Synthesis, structure and solution studies

Article abstract of DOI:10.1016/j.ica.2012.08.023

New complexes of triangular clusters M₃S₄ ⁴⁺ (M = Mo, W) with incomplete cuboidal metal-chalcogenide framework bearing chiral α-hydroxy and amino acids have been prepared. L-lactic acid (H₂lac), L-mandelic acid

Full text of DOI:10.1016/j.ica.2012.08.023

Inorganica Chimica Acta 395 (2013) 11–18
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
4+
Complexes of M3S4 (M = Mo, W) with chiral alpha-hydroxy and aminoacids:
Synthesis, structure and solution studies
Maxim N. Sokolov a,b, , Sergey A. Adonin a,b, Alexander V. Virovets a, Pavel A. Abramov a,b, Cristian Vicent c,
⇑
Rosa Llusar d, Vladimir P. Fedin a,b
a Nikolaev Institute of Inorganic Chemistry, Prospekt Lavrentyeva 3, 630090 Novosibirsk, Russia
b Novosibirsk State University, Faculty of Natural Sciences, Ul. Pirogova 2, 630090 Novosibirsk, Russia
c Serveis Centrals d’Instrumentació Científica, Universitat Jaume I, Avda. Sos Baynat s/n, E-12071 Castello´, Spain
d
´
´
´
Departament de Quimica Fisica i Analitica, Universitat Jaume I, Av. Sos Baynat s/n, E-12071 Castello´, Spain
a r t i c l e i n f o
a b s t r a c t
New complexes of triangular clusters M3S44+ (M = Mo, W) with incomplete cuboidal metal–chalcogenide
Article history:
Received 6 May 2012
Received in revised form 23 August 2012
Accepted 24 August 2012
Available online 25 September 2012
framework bearing chiral
a-hydroxy and amino acids have been prepared. L-lactic acid (H2lac), L-man-
delic acid (H2man), and -alanine (Hala) react with [W3S4Br4(PPh3)3] in 1:1 ratio to yield, respectively,
L
monosubstituted complexes [W3S4(PPh3)3Br3(Hlac)(CH3CN)] (1), [W3S4(PPh3)3Br3(Hman)(CH3CN)] (2),
and [W3S4(PPh3)3Br3(Hala)(CH3CN)]Br (3). In the presence of base [Mo3S4Cl4(PPh3)3] gives trisubstituted
complexes [Mo3S4(PPh3)3(Hlac)2(lac)] (4) and [Mo3S4(PPh3)3(Hman)3]Cl (5). Circular dichroism studies of
4 indicate chirality transfer from the ligand to the Mo3S44+ cluster core. These complexes incorporate Cu+
with the formation of corresponding {M3CuS4}5+ cuboidal derivatives. NMR and ESI-MS studies of solu-
tion behavior are presented.
Keywords:
Sulfide clusters
Chiral complexes
Lactic acid
Mandelic acid
Alanine
Ó 2012 Published by Elsevier B.V.
Crystal structures
1. Introduction
stereoselectivity in the intermolecular cyclopropanation of the al-
kenes have been obtained [10]. It is obvious that the choice of po-
Transition metal chalcogen-bridged clusters with cuboidal
M4Q4 framework are known for most of the transition metals,
and are of interest as models for metalloenzymes and industrial
catalysts [1–5]. Of particular interest are heterometal clusters
M3M0Q4 (M = Mo, W; M0 is a late transition metal, Q = S, Se). When
M0 is Cu, Ni, Pd or Ru, they display catalytic activity in various reac-
tions such as nucleophilic addition to the alkynes [6–9], cycloprop-
anation [10,11], N–N bond cleavage in hydrazines [12]. These
clusters are available in various coordination environments which
can be selected in order to modify the electronic structure or steric
requirements of the cluster. The use of enantiomerically pure li-
tential chiral ligands should by no means be restricted to the
phosphines.
In this respect, naturally occurring chiral
a-hydroxyacids or
amino acids (such as mandelic acid, lactic acid or
a
-alanine) consti-
tute easily accessible and versatile ligand class [13–15]. Complexes
of M2+ (M = Cu, Ni, Zn [16] and Co [17]), Ti(IV) [18] and V(V) [19]
with a-hydroxyacids are well documented. As far as coordination
chemistry of group 6 complexes is concerned, interaction of glyco-
late and lactate with molybdate and tungstate have been reported
[20–24], and polynuclear [Mo2(Hglyc)4] [25], [NH4]3[GdMo6(lact)6-
O15] [26], {Na2[MoO2(S-lact)2]}3, K6[(MoO2)8(glyc)6(Hglyc)2] [27]
4+
gands offers a route for preparation of chiral M3Q4 clusters. For
are known. Tetrakis(D-mandelato)dimolybdenum(II), a complex
4+
example, by coordinating bidentate chiral phosphines, (R,R)-Me-
BPE or (S,S)-Me-BPE, stereoselective formation of [Mo3S4{(R,R)-
Me-BPE}3Cl3]+ (P-enantiomer) and [Mo3S4{(S,S)-Me-BPE}3Cl3]+
(M-enantiomer) was achieved (Me-BPE is 2,5-(dimethylphospho-
with four carboxylates bridging a quadruply bonded Mo2 unit
[28] and two cis-formamidinate Mo24+ entities linked via the
trate [29], have been described by Cotton’s group.
L-tar-
Our interest was motivated primarily by the capability of
a-
lan-1-yl)ethane). By incorporating Cu+ into these clusters, enatio-
hydroxyacids to form optically chiral complexes having metal–me-
5+
merically pure cuboidal Mo3CuS4
clusters with moderate
tal bonded units. However, the coordination of these ligands to the
4+
M3Q4 and M4Q44+clusters has been scarcely explored, the only
example being the preparation of the [Mo3(Nipy)S4(EtO-dtp)3(L-
⇑
lactic)(py)] cluster (EtO-dtp = diethyldithiophosphate) [30]. Herein
we report our exploration of coordination chemistry of Mo3S4
Corresponding author at: Nikolaev Institute of Inorganic Chemistry, Prospekt
Lavrentyeva 3, 630090 Novosibirsk, Russia. Fax: +7 383 3309489.
E-mail address: caesar@che.nsk.su (M.N. Sokolov).
4+
0020-1693/$ - see front matter Ó 2012 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.ica.2012.08.023

12
M.N. Sokolov et al. / Inorganica Chimica Acta 395 (2013) 11–18
and W3S44+ with
L-lactic,
L
-mandelic acids, and
L
-alanine, structural
s, 1356 s, 1280 w, 1188 m, 1088 s, 1027 m, 997 w, 943 w, 846 w,
742 s, 692 s, 618 w, 520 s, 447 m, 419 w.
characterization of the solid products, as well as electrospray ion-
ization (ESI) mass spectrometric studies and spectroscopic NMR,
and circular dichroism spectra in solutions.
2.5. Synthesis of [W3S4(PPh3)3Br3(Hala)(CH3CN)]Br (3)
Similarly the preparation of 1, blue single crystals of 3 were ob-
tained from 50 mg (0.028 mmol) of [W3S4(PPh3)3Br4] and 2.5 mg
(0.035 mmol) of alanine. Yield: 85%. Anal. Calc. for C59H55N2O2P3-
W3S4Br4: C, 37.0; H, 2.9; N, 1.5. Found: C, 37.2; H, 3.0, N, 2.5%.
2. Experimental
2.1. General
Starting complex [Mo3S4Cl4(PPh3)3] was prepared from (Et4N)2
[Mo3S7Cl6] and PPh3 [31]. For the preparation of [W3S4Br4(PPh3)3]
a modified version of the synthesis of [W3S4Cl4(PPh3)3(H2O)2]ꢀ2THF
was adopted [32], based on refluxing the polymeric W3S7Br4 with
6 eq. of PPh3 in CH3CN for 48 h, followed by evaporation of the blue
solution and washing the solid copiously with a 1:1 toluene–hex-
2.6. Synthesis of [Mo3S4(PPh3)3(Hlac)2lac] (4)
Sixty mcl (0.67 mmol) of 85% aqueous solution of L-lactic acid
(H2lac), 70 mcl (0.67 mmol) of Et2NH and 10 ml of acetonitrile
were mixed together. Then 300 mg (0.223 mmol) of [Mo3S4(PPh3)3-
Cl4] was added, the mixture was stirred and refluxed for 1 h. After
cooling down and filtration, the resulting green solution was evap-
orated. Resulting dark green solid was redissolved in dichloro-
methane and kept at ꢁ30 °C overnight. Element analysis data of
recrystallized product correspond to [Mo3S4(PPh3)3(Hlac)3]Cl for-
mula (Anal. Calc. for C63H60ClMo3O9P3S4: C, 50.3; H, 4.0; Cl, 2.35.
Found: C, 50.5; H, 4.2; Cl, 2.38%). When dissolving this product in
CH2Cl2 and adding equal volume of ethanol, the slow evaporation
yields in single crystals of 4. Yield: 75–80%. Anal. Calc. for C63H59-
Mo3O9P3S4: C, 51.50; H, 4.06. Found: C, 50.9; H, 4.2%. IR: 3509 m,
3466 m, 3056 m, 2981 m, 2935 w, 2879 w, 1737 s, 1686 s, 1571
w, 1536 m, 1481 s, 1456 s, 1434 s, 1374 m, 1304 w, 1267 w,
1188 s, 1161 m, 1127 s, 1090 s, 1036 s, 998 s, 923 m, 855 s, 744
s, 693 s, 618 w, 552 w, 519 s, 484 s, 445 s, 418 w.
ane mixture to remove unreacted PPh3 and PPh3S, yield 70%.
L-lactic
(Hlac), -mandelic (Hman) acids and -alanine (HAla) were pur-
L
L
chased from Sigma–Aldrich. PPh3 was recrystallized from hot etha-
nol. Solvents were purified by the standard procedures. All
manipulations were carried out in air unless otherwise stated.
31P{1H} NMR spectra were recorded on Varian Mercury 300 MHz
spectrometer and 1H, 13C{1H} gCOSY and gHSQC spectra were ac-
quired with a Varian System 500 MHz using CDCl3/dimethylform-
amide mixtures as solvents. Circular dichroism measurements
were recorded on a JASCO J-810 spectropolarimeter in dimethyl-
formamide solutions. The IR spectra (4000–400 cmꢁ1) were ob-
tained on a Vertex 80 Fourier spectrometer in KBr.
2.2. Electrospray ionization (ESI) mass-spectrometry
2.7. Synthesis of [Mo3S4(PPh3)3(Hman)3]Cl (5)
A hybrid QTOF I (quadrupole-hexapole-TOF) mass spectrometer
with an orthogonal Z-spray-electrospray interface (Waters, Man-
chester, UK) was used. The drying gas as well as nebulizing gas
was dinitrogen at flow rates of 800 and 20 L/h, respectively. The
temperature of the source block was set to 100 °C and the desolv-
ation temperature was 120 °C. Capillary voltage of 3.5 kV was used
in the positive scan mode, and the cone voltage was varied from 5
to 55 V to explore the characteristic fragmentation reactions of the
identified ions. Sample solutions were infused via syringe pump di-
All manipulations were carried out analogically to 4, taking
10 mg (0.670 mmol)of R-mandelic acid instead. Yield: 80%. Anal.
Calc. for C84H66ClMo3O9P3S4: C, 55.37; H, 3.93; Cl, 2.09. Found: C,
54.95; H, 4.23; Cl, 1.97%.
2.8. X-ray diffractometry
Crystallographic data and structure refinement details for 2–4
are summarized in Table 1. Selected bond distances are given in
Table 2. Further details may be obtained from the Cambridge Crys-
tallographic Data Centre on quoting the depository numbers CCDC
864192–864194. Copies of this information may be obtained free
of charge from The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44 1223 336033; e-mail: deposit@ccdc.cam.a-
c.uk or http://www.ccdc.cam.ac.uk).
rectly connected to the ESI source at a flow rate of 10 lL/min. Mass
calibration was performed using a solution of sodium iodide in 2-
propanol/water (50:50) mixture for m/z range from 50 to 1700.
2.3. Synthesis of [W3S4(PPh3)3Br3(Hlac)(CH3CN)] (1)
Fifty milligrams (0.028 mmol) of [W3S4(PPh3)3Br4] were dis-
solved in 1 ml of acetonitrile and 4 ml (0.04 mmol) of 85% aqueous
solution of L-lactic acid (H2lac) in water was added. The reaction
3. Results and discussion
mixture was put into a thick-glass screw-capped vial, heated to
70 °C within 20 min and maintained for 10 h at this conditions,
then slowly cooled down to room temperature. The product sepa-
rated from the solution as large dark blue crystals. Yield: 91%. Anal.
Calc. for C59H53NO3P3W3S4Br3: C, 38.59; H, 2.91; N, 0.76. Found: C,
38.40; H, 2.85; N, 2.2%. IR: 3465 w, 3053 m, 2316 w, 1653 w, 1518
s, 1480 s, 1432 s, 1350 m, 1190 m, 1122 m, 1088 s, 1029 w, 997 w,
854 w, 743 s, 693 s, 619 w, 518 s, 448 w, 419 w.
4+
3.1. Mono-substituted M3S4 clusters of general formula
[W3S4(PPh3)3Br3(RCO2)(MeCN)]
Reaction of compound [W3S4(PPh3)3Br4] with one equivalent of
L
-lactic or
2 in high yields (up to 90%) according to the Scheme 1. Reaction of
[W3S4(PPh3)3Br4] with -alanine leads to analogous product, but
contrary to the -hydroxyacids, the aminoacid is not deprotonated
L-mandelic acids gives mono-substituted products 1 and
a
a
2.4. Synthesis of [W3S4(PPh3)3Br3(Hman)(CH3CN)] (2)
and coordinates in the zwitterionic form to give [W3S4(PPh3)3Br3
(Hala)(MeCN)]Br (3).
Similarly the preparation of 1, blue single crystals of 2 were ob-
tained from 50 mg (0.028 mmol) of [W3S4(PPh3)3Br4] and 5 mg
(0.032 mmol) of mandelic acid. Yield: 89%. Anal. Calc. for C64H55-
NO3P3W3S4Br3: C, 40.5; H, 2.9; N, 0.7. Found: C, 40.7; H, 2.8; N,
1.6%. IR: 3526 w, 3053 w, 1810 w, 1673 w, 1537 s, 1480 s, 1432
Attempts to use the molybdenum homologue, namely [Mo3S4
(PPh3)3Br4] under identical reaction conditions did not lead to
identifiable products.
Compounds 1–3 are sparingly soluble in common solvents
(H2O, CH3OH, CH3CN, CH2Cl2, DMF), thus precluding further

M.N. Sokolov et al. / Inorganica Chimica Acta 395 (2013) 11–18
13
Table 1
Crystal data and structure refinement details for 1–4.
Crystal data
2
3
4
Chemical formula
Mr
Crystal system, space group
T (K)
a (Å)
b (Å)
c (Å)
a (°)
b (°)
C
70H64Br3N4O3.50P3S4W3
C69.80H71.20Br4N7.40O2P3S4W3
2138.08
triclinic, P1
C63.50H64.50Mo3O11.25P3S4
1516.62
orthorhombic, P212121
293
15.6999 (13)
18.5547 (15)
24.3054 (19)
90
2029.68
monoclinic, P21/c
100
14.5594 (4)
18.7654 (6)
26.2254 (8)
90
90.447 (1)
90
7164.9 (4)
4
ꢀ
100
13.3719 (3)
14.3382 (4)
23.0576 (6)
71.921 (1)
74.761 (1)
73.491 (1)
3954.63 (18)
2
90
90
c
(°)
V (Å3)
7080.3 (10)
4
Z
Radiation type
Mo K
6.71
a
Mo K
6.59
a
Mo K
0.76
a
m (mmꢁ1
)
Crystal size (mm)
Diffractometer
Absorption correction
Tmin, Tmax
0.26 ꢂ 0.14 ꢂ 0.04
0.17 ꢂ 0.16 ꢂ 0.13
0.16 ꢂ 0.16 ꢂ 0.08
Bruker Nonius X8Apex CCD
empirical based on intensities (SADABS
0.721, 1
Bruker Nonius X8Apex CCD
empirical based on intensities (SADABS
0.816, 1
Bruker Nonius X8Apex CCD
empirical based on intensities (SADABS
0.888, 0.942
)
)
)
No. of measured, independent and
observed [I > 2s(I)] reflections
Rint
56458, 21210, 13696
46699, 21344, 15139
45942, 15572, 12160
0.057
0.051, 0.098, 1.04
21210
780
0.048
0.046, 0.088, 1.08
21344
883
0.041
0.042, 0.124, 1.00
15572
782
R[F2 > 2s(F2)], wR(F2), S
No. of reflections
No. of parameters
No. of restraints
0
0
2
H-atom treatment
H-atom parameters constrained
H-atom parameters constrained
H-atom parameters constrained
1.58, ꢁ1.00
D
q
max, Dqmin (e Åꢁ3
)
4.05, ꢁ1.52
1.97, ꢁ1.17
Flack parameter
–
–
ꢁ0.02(3)
w = 1/[s2 (Fo2) + (0.0425P)2 + 26.8562P]
where P = (Fo2 + 2Fc2)/3
w = 1/[s2(Fo2) + (0.022P)2 + 33.4553P]
where P = (Fo2 + 2Fc2)/3
w = 1/[s2(Fo2) + (0.0073P)2 + 16.1946P]
where P = (Fo2 + 2Fc2)/3
Computer programs used for structure solution and refinement: APEX2 (Bruker-AXS, 2004), SAINT (Bruker-AXS, 2004), SHELXS97 (Sheldrick, 1998), SHELXL97 (Sheldrick, 1998), SHELXTL
(Bruker-AXS, 2004), CIFTAB-97 (Sheldrick, 1998).
Table 2
Main bond distances and angles in 2–4.
2
3
4
W1 W2 2.7161(4)
W1 W3 2.7616(4)
W2 W3 2.7459(4)
W1 S1 2.3572(17)
W1 S2 2.3074(17)
W1 S3 2.3158(16)
W2 S1 2.3496(16)
W2 S2 2.3172(17)
W2 S4 2.3072(16)
W3 S1 2.3507(15)
W3 S3 2.3219(17)
W3 S4 2.3075(16)
W-P(av) 2.592(1)
W-Br(av) 2.585(1)
W1 O1 2.205(4)
W1 W2 2.7224(4)
W1 W3 2.7571(4)
W2 W3 2.7429(4)
W1 S1 2.3600(16)
W1 S2 2.3145(15)
W1 S3 2.3023(16)
W2 S1 2.3559(15)
W2 S2 2.3175(15)
W2 S4 2.3020(16)
W3 S1 2.3641(17)
W3 S3 2.3109(15)
W3 S4 2.3054(15)
W-P(av) 2.586(1)
W-Br(av) 2.588(1)
W1 O1 2.198(4)
Mo1 Mo2 2.7578(6)
Mo1 Mo3 2.7749(6)
Mo2 Mo3 2.7501(6)
Mo1 S1 2.3636(14)
Mo1 S3 2.3111(13)
Mo1 S4 2.2976(14)
Mo2 S1 2.3601(15)
Mo2 S2 2.2968(12)
Mo2 S4 2.2950(13)
Mo3 S1 2.3639(13)
Mo3 S2 2.2808(14)
Mo3 S3 2.2944(14)
Mo-P(av) 2.644(1)
Mo1 O11 2.092(3)
Mo1 O12 2.155(4)
Mo2 O22 2.080(4)
Mo2 O21 2.179(4)
Mo3 O32 2.083(4)
Mo3 O31 2.228(4)
W2 O2 2.198(4)
W3 N1L 2.214(6)
W2 O2 2.210(4)
W3 N1L 2.185(5)
Fig. 1. Cluster complex 2 (a.d.p. at 50% probability level). Second position of
mandelate ligand and hydrogen atoms of PPh3 and CH3CN ligands are omitted for
clarity.
characterization in solution. Attempts to improve solubility by
heating produce cloudy solutions due to decomposition.
Our attempts to refine the crystal structure of 1 failed because
of systematic poor quality of crystals, though obtained model
was not inconsistent with the proposed formulation. Single crys-
tals of 2 suitable for X-ray analysis can be prepared directly from
reaction solution after slow cooling. Synthesis of 3 as single crys-
tals is very sensitive to the temperature regime, tending to form
Scheme 1. (i) 1 eq. RCO2H/CH3CN; (ii) 3 eq. RCO2H/CH3CN/HR2N.

14
M.N. Sokolov et al. / Inorganica Chimica Acta 395 (2013) 11–18
Fig. 2. Cluster complex 3 (a.d.p. at 50% probability level). Only one orientation of
MeNH3CHCOOꢁ ligand is shown. The hydrogen atoms of PPh3 and MeCN ligands are
omitted for clarity.
powders if temperature changes too rapidly. Complex 2 contains
only one anionic rest of monodeprotonated
coordinated to the cluster as 2-bridge between two tungsten
atoms. The PPh3 ligands occupy trans-positions to 3-S (Fig. 1).
The absence of counter-ions in 2 indicates that mandelate -hy-
droxy groups remain protonated. Coordination around one of the
tungsten atoms is completed by terminal CH3CN ligand.
The coordination mode of alanine in 3 is similar (Fig. 2). The
crystal contains also Brꢁ anion disordered over three close posi-
tions with relative weights of 0.47/0.42/0.11. The charge balance
of the structure can be achieved if alanine is in neutral zwitter-io-
nic form (CH3)(NH3+)CHCOOꢁ.
a-oxyacid (mandelate),
l
l
a
Fig. 3. The 0.5/0.5 positional disorder of PhC(O)(H)COOꢁ ligand in 2. Carbon and
hydrogen atoms of PPh3 ligands are omitted for clarity.
One of the solvent MeCN molecules follows this disorder. In the
second orientation the configuration of optical center at C(2) is
opposite relative to the first one. The real space group of 2 that de-
scribes the whole (super)structure without any disorder must be
chiral. But super-structural reflections corresponding to it are ex-
pected to be weak because diffraction is almost completely deter-
mined by heavy pseudo-centrosymmetric fragments. Our attempts
to detect them by careful analysis of diffraction pattern (CCD
frames from diffractometer) were unsuccessful and we decided
to leave our centrosymmetric sub-structural description of 2 as is.
In the crystal structure of 3 the explanation of centrosymmetric
space group is the same but here the chirality is additionally ‘hid-
den’ by diffraction similarity of NH3 and CH3 groups (Fig. 2). During
the refinement of structure we had to assume C/N 0.5/0.5 disorder
in these positions.
The
first detected in complexes containing dithiophosphate and car-
boxylate ligands of the general formula [M3S4(dtp)3( -CH3-
l2-bridge type of coordination of carboxylate ligands was
l
COO)(L)] (M = Mo, W) [33,34]. This type of coordination causes a
distortion of the M3 triangle: the M–M bond between the pair of
atoms linked by the carboxylate becomes shorter than two other
M–M bonds. In compounds 2 and 3 this shortening lies between
0.021 and 0.046 Å. In the crystal structures of [W3S4{S2P(OEt)2}3
(py)(l-CH3COO)]
[44]
and
[W3S4{S2P(OEt)2}3(py)(l-CH3
COO)]ꢀ0.5dmf [45] even larger shortening, 0.060–0.077 Å, was
reported. Analysis of 22 crystal structures of this type with
{Mo3S4} core with Cambridge Structural Database (CSD) software
reveals similar tendency, the shortening being from 0.044 to
0.086 Å.
Analysis of data from CSD helped us to find another example
when similar phenomenon was observed. Slawin et al. found cen-
trosymmetric space group P21/c in the crystal structure of cis-
An unusual feature of compounds 2 and 3 is that they crystallize
ꢀ
in centrosymmetric space groups (P21/c and P1), while being
[PdCl2(bdppalO-P,O)]ꢀCHCl3
(bdppalO = (S)-N-(diphenylphos-
intrinsically chiral. In our opinion the reason is that the chiral frag-
ments are relatively small in comparison with whole structure,
while the rest of the structure is not in contradiction with the pres-
ence of inversion symmetry. Indeed, in 2, the whole cluster core
{W3S4} together coordinated PPh3 and Brꢁ is almost ‘racemic’ be-
cause of a pseudo-mirror plane that bisects the W3 triangle in
the mid-point of W(1)–W(2) edge and passes through W(3) atom
(Fig. 1). The same ‘mirror plane’ passes through C(1) and C(2)
atoms of the chiral mandelate ligand. However H, OH and Ph sub-
stituents at C(2) break this pseudo-reflection. Therefore, the cen-
trosymmetric space group corresponds to a substructure that is
disordered due to the presence of chiral fragment. This is the situ-
ation that we clearly observe in 2: the C(OH)(H)Ph fragment is dis-
ordered over two positions with equal weight (Fig. 3).
phino)-N-(diphenylphosphinoyl)alanine) that contains chiral ala-
nine-substituted ligand [46]. The authors mention that ‘there was
some disorder in complex 14. C(4) was refined anisotropically in two
50% occupancy sites’ [46] but give no explanation for this fact and
does not correlate it with the contradiction between chirality of
the molecule and presence of inversion centers in the crystal.
4+
3.2. Trisubstituted M3S4 clusters of general formula
[M3S4(PPh3)3(RCO2)2(RCO2–H)]
Motivated by the successful incorporation of
a-hydroxyacids
and alanine into the coordination sphere of the M3S4 clusters, we
decided to increase the number of chiral ligands coordinated at

M.N. Sokolov et al. / Inorganica Chimica Acta 395 (2013) 11–18
15
[W3S4(Hlac)(lac)(DMF)2]+
1002.9
100
[W3S4(Hlac)(lac)(DMF)3]+
1076.0
1021.9
947.9
0
m/z
800
850
900
950
1000
1050
1100
1150
1200
Fig. 4. Positive ESI(+) mass spectrum of CHCl3/dimethylfomamide solutions of the solid obtained from the reaction mixture of [W3S4(PPh3)3Br4], lactic acid and i-Pr2NH
recorded at a cone voltage Uc = 15 V.
the cluster core. When we reacted [M3S4(PPh3)3Br4] with an excess
of
a-hydroxyacid under prolonged heating (typically 70–80 °C,
acetonitrile, 10–12 h), only the mono-substituted forms 1–3 and
unidentifiable products were obtained for tungsten and molybde-
num, respectively. It is not surprising that once sparingly soluble
compounds 1–3 are formed, they crystallize out from the reaction
mixture providing a rather simple and efficient synthetic protocol
for their preparation. We also attempted to achieve a higher degree
of coordination in the presence of alkylamines that would act as a
base and deprotonate the
a-hydroxyacid (Scheme 1). For M = W
we observed that solutions of [W3S4(PPh3)3Br4] in acetonitrile
changed the color from blue to different shades of violet if lactic
acid or mandelic acid, together with i-Pr2NH, were added. The cor-
responding violet (lactic) or red-violet (mandelic) solid products
were separated and thoroughly washed with CH3OH and diethyl-
ether, redissolved in CDCl3/dimethylformamide mixtures and the
identity of the formed species was investigated by 31P{1H} NMR
and ESI mass spectrometry. The 31P{1H} NMR spectroscopy re-
vealed the presence of free PPh3, thus highlighting that replace-
ment of PPh3 ligands by dimethylformamide occurs in solution.
ESI(+) MS of the solid obtained from the reaction mixture of [W3-
S4(PPh3)3Br4], lactic acid and i-Pr2NH is shown in Fig. 4 and sup-
ports this hypothesis.
Fig. 5. Cluster complex 4 (a.d.p. at 50% probability level). The phenyl groups of PPh3
ligands are omitted for clarity.
The presence of species featuring both coordinated solvent and
4+
lactate ligands and lacking the PPh3 ligands in the W3S4 coordi-
nation sphere is evident from the ESI(+) mass spectrum. On the
basis of the m/z values as well as characteristic isotopic pattern,
the dominant observed peaks were attributed to [W3S4
(Hlac)(lac)(DMF)3]+ (m/z = 1076.0) and [W3S4(Hlac)(lac)(DMF)2]+
(m/z = 1002.9). Negative ESI mass spectra revealed the presence
of [W3S4(DMF)x(Hlac)lac2]ꢁ species (x = 0–2) in which DMF for
PPh3 exchange was also evident. Identical species were identified
for M = Mo, where [Mo3S4(PPh3)3(Hlac)2lac] (4) was isolated in
analytically pure form. We may assume that the bulk of the solids
obtained from [W3S4(PPh3)3Br4], lactic acid (or mandelic acid) and
i-Pr2NH correspond primarily to [W3S4(PPh3)3(Hlac)2lac] and [W3-
S4(PPh3)3(Hman)2man], respectively. However our efforts to isolate
salts of anionic [W3S4(PPh3)3(Hlac)lac2]ꢁ and [W3S4(PPh3)3lac3]2ꢁ
complexes by further deprotonation of hydroxyacids with an ex-
cess of different amines failed to give identifiable products.
(Hlac)2(lac)] (4) as result of further deprotonation of one of the
lactates. Single crystals are obtained by diethyl ether vapor diffu-
sion into solutions of [Mo3S4(PPh3)3(Hlac)3]Cl in CH3OH or CH3CN.
Compound 4 crystallizes in orthorhombic chiral space group
P21212. The lactate ligands are coordinated by both carboxylic
and hydroxy functional groups to form stable five-membered che-
late ring (Fig. 5).
As is the case when acetylacetonate [35–37] and oxalate is coor-
4+
dinated to M3S4 [38] (in [M3S4(acac)3(Py)3]PF6 and [M3Q4(C2-
O4)3(H2O)3]2ꢁ), and contrary to what is routinely observed in the
diphosphine [39,40] and dithiophosphate complexes [30,34], the
coordination type of the lactate is cis–cis regarding the capping
l3-S atom. The trans-positions to the capping
l3-S atom are occu-
pied by PPh3 ligands.
A number of isomers differing in mutual arrangement of the
lactate ligands are potentially feasible (Scheme 2) with carboxylic
In the case of M = Mo, [Mo3S4(PPh3)3Br4] with a-hydroxyacid in
the presence of alkylamines give the tris complexes (see Scheme 1).
In both acetonitrile and chloroform the same product is obtained,
while running the reaction in alcohols leads to separation of
unidentified oils. The yield of [Mo3S4(PPh3)3(Hlac)3]Cl does not de-
pend whether Et2NH or Bu3N were used as base. Coordination of
amine itself does not occur even in 10-fold molar excess of amine.
[Mo3S4(PPh3)3(Hlac)3]Cl is analytically pure, green crystalline solid,
well soluble in polar organic solvents. Evaporation of a solution in a
CH2Cl2/CH3OH (or ethanol) mixture leads to [Mo3S4(PPh3)3
groups pointing in the same direction (considering the capping l3
-
S atom above the Mo3 plane, anticlockwise and clockwise isomers
I and IV, respectively) or when two of them point at each other
(isomers II and III). The observed stereochemistry of 4 (isomer II)
breaks the higher symmetry which could arise if all the lactic li-
gands were oriented clockwise or anticlockwise by their carboxylic
groups (isomers I and IV). The absence of counter-ions presupposes
protonation of only two
a-hydroxy groups of the lactate ligands.

16
M.N. Sokolov et al. / Inorganica Chimica Acta 395 (2013) 11–18
O
O
O
PPh3
O
PPh3
O
PPh3
O
O
O
PPh3
O
O
M
O
M
O
S
S
M
S
S
M
S
S
S
S
S
O
PPh3
S
S
S
O
PPh3
O
Ph3P
O
M
O
M
O
Ph3P
S
S
O
PPh3
M
O
M
S
S
O
PPh3
O
O
Ph3P
M
M
O
Ph3P
M
M
O
O
O
O
O
O
O
O
O
O
O
O
IV
III
II
I
Scheme 2. Possible isomers due to mutual arrangement of the lactate ligands in 4.
From close inspections of the three Mo–Ohydroxyl distances of
2233(3), 2183(4), and 2092(4) Å, these two hydrogen atoms can
be assigned to the first two oxygen atoms with longer Mo–O
distances (coordination of Hlacꢁ), while the shorter Mo–O distance
should correspond to the coordination of the deprotonated
hydroxogroup (lac2ꢁ). It is worth stressing that all the
crystallization techniques mentioned above (either by slow evapo-
ration or by ether vapor diffusion) invariably produced the same
isomer of 4.
An important issue is whether the coordination modes of the
lactate ligands and the overall symmetry might be preserved in
solution. Like in the case of the solids obtained in the reaction of
[W3S4(PPh3)3Br4], lactic acid and i-Pr2NH, dimethylformamide
was found to be the best solvent to dissolve 4. We believe that
DMF for PPh3 substitution is at the origin of the enhanced solubil-
ity of 4 in DMF:
2.5
2.0
1.5
1.0
0.5
0.0
8
6
4
2
0
-2
-4
-6
-8
400
500
600
700
800
λ (nm)
Fig. 7. Uv–Vis (---) and CD (—) spectrum of compound 4 in CHCl3/dimethylform-
amide mixtures.
½Mo3S4ðPPh3Þ3ðHlacÞ2lacꢃ þ DMF
! ½Mo3S4ðDMFÞ3ðHlacÞ2lacꢃ þ PPh3
ð1Þ
31P {1H} NMR of CDCl3/dimethylformamide solutions of 4
showed the presence of free PPh3, thus evidencing the replacement
of PPh3. The 1H NMR spectrum contains signals characteristic of
the CH3 and CH groups of the lactate ligands as a doublet at
icant dichroism is observed for all electronic absorptions. This par-
ticularly holds for the range between 500 and 650 nm which is
associated with the molybdenum centers of the Mo3S44+ core. This
clearly shows that the ligand imposed chirality is transferred to the
Mo3S4 core and that significant diastereoisomeric enrichment
has occurred.
1.25 ppm and
a quadruplet at 4.09 ppm, respectively, with
4+
3JHH = 6.5 Hz. (Fig. 6).
Two minor doublets at 1.30 and 1.36 ppm with intensity ratio
1:6 with respect to the major doublet, together with a broad mul-
tiplet at 4.17 ppm are also observed. This experimental evidence
suggest the presence of a dominant form together with two minor
diastereoisomers in DMF solution for the [Mo3S4(DMF)3(Hlac)2lac]
species, as evidenced by the distinctive CH3 and CH groups in the
coordinated lactic acid molecules. Unfortunately, we could only
detect 13C signals associated to the major isomer (see 13C {1H},
gCOSY and gHSQC in the supplementary material).
UV–Vis and CD spectra were recorded at room temperature for
chloroform/DMF solutions of 4 (Fig. 7). The electronic absorption
studies show charge transfer (S to Mo) transition bands at
378 nm and characteristic d–d transition at around 650 nm. Signif-
ESI(+) mass spectra of DMF solutions of 4 recorded at different
cone voltages are shown in Fig. 8.
Complete replacement of PPh3 is evident in the ESI mass spec-
trum recorded at Uc = 5 V where the main peak corresponds to
[Mo3S4(Hlac)(lac)(DMF)3]+ (m/z = 814.9). Upon increase in the cone
voltage consecutive liberation of DMF molecules occurs to yield
[Mo3S4(Hlac)(lac)(DMF)2]+ (m/z = 741.9), together with minor peak
of [Mo3S4(Hlac)(lac)(DMF)]+ (m/z = 668.8) (see Fig. 8, middle).
Complete loss of DMF takes place at higher sampling cone voltage
(Fig. 8, top), giving rise to dominant peak centered at [Mo3S4
(Hlac)(lac)]+ (m/z = 595.7). Similar stepwise full loss of neutral
ligand was reported for the acetylacetonate-pyridine [37,41] or
4.250
4.200
4.150
4.100
4.050
4.000
1.400
1.350
1.300
1.250
1.200
Fig. 6. 1H regions of the CH and CH3 groups of the lactate ligands in the [Mo3S4(DMF)3(Hlac)2lac] species recorded in CDCl3/dimethylformamide (80:20).

M.N. Sokolov et al. / Inorganica Chimica Acta 395 (2013) 11–18
17
595.7
668.8
741.9
100
-DMF
-DMF
814.9
561.7
0
m/z
m/z
m/z
550 575 600 625 650 675 700 725 750 775 800 825 850 875 900 925 950 975
741.9
100
815.0
-DMF
667.8
707.9
634.8
931.0
0
550 575 600 625 650 675 700 725 750 775 800 825 850 875 900 925 950 975
814.9
100
[Mo3S4(Hlac)(lac)(DMF)3]+
741.9
705.9
782.9
890.1
0
550 575 600 625 650 675 700 725 750 775 800 825 850 875 900 925 950 975
Fig. 8. ESI mass spectra of CHCl3/DMF solutions of compound 4 after 30 min recorded at increasing Uc cone voltages (5 V, bottom, 15 V middle and 25 V top).
diphosphane [42,43] complexes of Mo3S44+. In the negative scan
The formation of the cuboidal cluster was confirmed by the
observation of the signal from [Mo3CuS4(PPh3)I(Hlac)lac2]ꢁ (m/
z = 1006) in the ESI(ꢁ)-MS, and of the daughter peaks resulting
from the loss of PPh3 (m/z = 744), following by the loss of Iꢁ coor-
dinated to copper atom (m/z = 618). Similar behavior was observed
mode peaks corresponding to the complexes with deprotonated
lactates, [Mo3S4(PPh3)3(Hlac)lac2]ꢁ and [Mo3S4(PPh3)2(Hlac)lac2]ꢁ,
are observed.
In order to monitor gradual replacement PPh3 by DMF, stock
solutions of 4 in CHCl3/DMF (80:20) were prepared. At different
time intervals they were diluted with CHCl3/DMF (80:20) to final
concentration of ca. 1 ꢂ 10ꢁ5 M and then directly introduced in
the ESI mass spectrometer. The neutral complex 4 is positively ion-
ized via loss of one lactate ligand, a common ionization mechanism
for closely related neutral carboxylate M3S4 clusters [30]. Fig. 9
illustrates ESI (+) mass spectrum of compound 4.
As can be seen, the forms initially present in DMF solution
consecutively give rise to the following peaks [Mo3S4 (Hlac)(lac)
(PPh3)2]+ (m/z = 1122.0), [Mo3S4(Hlac)(lac)(DMF)(PPh3)]+ (m/z =
930.9), [Mo3S4(Hlac)(lac)(PPh3)]+ (m/z = 857.9), [Mo3S4(Hlac)(lac)
(DMF)3)]+ (m/z = 814.9), [Mo3S4 (Hlac)(lac)(DMF)2]+ (m/z = 741.9),
[Mo3S4(Hlac)(lac)(DMF)]+ (m/z = 668.9).
4+
for corresponding W3S4 species.
4. Conclusions
Coordination of one or three chiral alfa-oxy or alfa-aminoacids
to M3S44+ (M = Mo, W) cluster core was achieved. Chirality transfer
to the cluster core was detected by circular dichroism. Identified
species by ESI-MS and NMR provide complementary information;
while the molecular composition can be determined on the basis
of ESI mass spectrometry, the presence of a number of isomers
can be ascertained as judged by 1H NMR. These chiral triangular
clusters can be used for preparation of chiral cuboidal heterometal
clusters.
3.3. Formation of cubane-type Mo3S4Cu5+ clusters featuring lactic acid
4+
Motivated by the interest in preparation of chiral M3M0S4
Acknowledgements
(M = Mo, W) clusters, we found that complex 4 rapidly adds CuI
(color changes from green to red-brown in dichloromethane),
according to Eq. (2):
S.A.A. thanks the Haldor Topsoe company for a research fellow-
ship. The authors are also grateful to the Serveis Centrals d’Instru-
mentacio Cientifica (SCIC) of the Universitat Jaume I for providing
us with mass spectrometric facilities. The work was supported by
½Mo3S4ðPPh3Þ3ðH2lacÞ2lacꢃ þ CuI
Government
Contracts
GC
No.
02.740.11.0628,
No.
16.740.11.0273 in the framework of Federal Frame Program ‘‘Sci-
entific and Research-Educational Staff for Innovative Russia
! ½Mo3ðCuIÞ4ðPPh3Þ3ðHlacÞ2lacꢃ
ð2Þ
[Mo3S4(Hlac)(lac)(DMF)]+
[Mo3S4(Hlac)(lac)(DMF)2]+
741.9
100
668.8
[Mo3S4(Hlac)(lac)(DMF)3]+
[Mo3S4(Hlac)(lac)(DMF)(PPh3)]+
[Mo3S4(Hlac)(lac)(DMF)(PPh3)]+
930.9
[Mo3S4(Hlac)(lac)(PPh3)2]+
1122.0
857.9
814.9
0
m/z
600
700
800
900 1000 1100 1200 1300 1400 1500 1600 1700 1800
Fig. 9. ESI mass spectrum of CHCl3/dimethylformamide solutions of compound 4, recorded at a cone voltage Uc = 15 V.

18
M.N. Sokolov et al. / Inorganica Chimica Acta 395 (2013) 11–18
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