One-Pot Intermolecular C–S Self-Coupling of Dimethyl Sulfoxide Promoted by Molybdenum Pentachloride

Article abstract of DOI:10.1002/ejic.201600611

The reactions between MoCl₅and 1–2 equiv. of a selection of sulfoxides at room temperature in dichloromethane as solvent were studied. The 1:1 molar reaction between MoCl₅and dimethyl sulfoxide (DMSO) afforded the C–S coupling product [Me₂SCH₂SMe][MoOCl₄] (1), which was isolated in 46 % yield and characterized by analytical and spectroscopic methods and by X-ray diffraction. MoOCl₃, SMe₂and HCl were identified as side products. The reactions between MoCl₅and tetrahydrothiophene 1-oxide, nBu₂SO, MePhSO or (PhCH₂)₂SO yielded the corresponding sulfides and, in the cases of (PhCH₂)₂SO and MePhSO, also C–S activation compounds. According to DFT calculations, the unusual formation of 1 is the consequence of thermodynamically feasible Cl/O interchange between MoCl₅and DMSO, this being a prerequisite for successive C–H bond activation.

Full text of DOI:10.1002/ejic.201600611

DOI: 10.1002/ejic.201600611
Full Paper
Mo Pentachloride in Catalysis
One-Pot Intermolecular C–S Self-Coupling of Dimethyl Sulfoxide
Promoted by Molybdenum Pentachloride
Marco Bortoluzzi,[a] Eleonora Ferretti,[b] Mohammad Hayatifar,[b] Fabio Marchetti,[b]
Guido Pampaloni,*[b] and Stefano Zacchini[c]
Abstract: The reactions between MoCl5 and 1–2 equiv. of a drothiophene 1-oxide, nBu2SO, MePhSO or (PhCH2)2SO yielded
selection of sulfoxides at room temperature in dichloromethane the corresponding sulfides and, in the cases of (PhCH2)2SO and
as solvent were studied. The 1:1 molar reaction between MoCl5 MePhSO, also C–S activation compounds. According to DFT cal-
and dimethyl sulfoxide (DMSO) afforded the C–S coupling prod- culations, the unusual formation of 1 is the consequence of
uct [Me2SCH2SMe][MoOCl4] (1), which was isolated in 46 % thermodynamically feasible Cl/O interchange between MoCl5
yield and characterized by analytical and spectroscopic meth- and DMSO, this being a prerequisite for successive C–H bond
ods and by X-ray diffraction. MoOCl3, SMe2 and HCl were identi- activation.
fied as side products. The reactions between MoCl5 and tetrahy-
Introduction
We have recently described the reactions between MoCl5
and sulfones RR′SO2,[8] showing that both MoV and MoIV coordi-
Molybdenum pentachloride[1] is a cheap and environmentally nation complexes may be obtained, depending on the R/R′ sub-
acceptable chemical[2] that has been employed as a catalytic stituents. In contrast, different structural motifs can arise from
precursor for a large variety of organic reactions.[3] In particular, the reactions between MoCl5 and molecules containing the
MoCl5 is a powerful reagent for oxidative transformations, espe- –SO3 functionality, through oxygen abstraction by the metal
cially the dehydrogenative coupling of arenes.[3a,3b,3d] The inter- centre.[9]
esting reactivity exhibited by MoCl5 in catalytic situations has
triggered the exploration of the related coordination chemistry,
with consequent advances in knowledge.[4] A variety of reaction
pathways may be viable when MoCl5 is allowed to come into
contact with potential ligands, thus often resulting in low se-
lectivity. In particular, the two main pathways observed in the
reactions between MoCl5 and oxygen donors are: (a) Cl/O inter-
change between the metal centre and the organic substrate,
affording oxidomolybdenum complexes,[4c–g,5,6] and (b) MoV to
MoIV reduction with formation of MoCl4 adducts.[4c–4e,5a,5b] As a
consequence, simple derivatives with formula MoCl5L are
rare,[4b,7] and the only cases of crystallographic characterization
relate to the complexes with phosphorus oxychloride[7] and 2,5-
dihydrothiophene 1,1-dioxide.[8]
With regard to completing this picture, it can be observed
that the data available in the literature relating to the chemistry
of MoCl5 with sulfoxides RR′SO are still rather sparse.
MoOCl3(O=SPh2)2 was isolated from MoCl5 and an excess of
diphenyl sulfoxide, but no information on the destiny of the
organic material possibly involved in the formation of the oxide
ligand was supplied.[10] Similarly, MoOCl3(DMSO)2 was believed
to form from MoCl5 and an excess of DMSO, on the basis of
insufficient characterization data.[11]
The scarce knowledge on MoCl5–RR′SO interactions con-
trasts with the fact that sulfoxides are an intensively investi-
gated class of organic compounds;[12] in particular, their deoxy-
genation to sulfides,[13] as well as the reverse transforma-
tion,[14,15] are strategic reactions because of industrial and bio-
chemical concerns. In the class of sulfoxides, dimethyl sulfoxide
(DMSO), playing various roles as an ancillary ligand, is almost
ubiquitous in coordination chemistry.[16] A large number of
complexes of DMSO with transition metals have aroused inter-
est in diverse fields, including catalysis[17] and medicinal chem-
istry.[18]
[a] Ca' Foscari Università di Venezia, Dipartimento di Scienze Molecolari
e Nanosistemi,
Via Torino 155, 30170 Mestre (VE), Italy
[b] Università di Pisa,
Dipartimento di Chimica e Chimica Industriale,
Via Moruzzi 13, 56124 Pisa, Italy
In addition, some well-defined coordination complexes of
sulfoxides with homoleptic halides of high-valent metals have
been reported;[19] however, it seems that the metal oxophilicity
is a condition favouring the deoxygenation of the sulfoxide
moiety. Thus, even though coordination adducts of sulfoxides
with TiCl4 can be isolated,[19b,19c] the same TiCl4 has been em-
ployed as a component of catalytic systems promoting the de-
E-mail: guido.pampaloni@unipi.it.
fabio.marchetti1974@unipi.it
http://www.dcci.unipi.it/guido-pampaloni.html
[c] Università di Bologna, Dipartimento di Chimica Industriale
“Toso Montanari”,
Viale Risorgimento 4, 40136 Bologna, Italy
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejic.201600611.
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oxygenation of sulfoxides to sulfides.[20] In addition, the reac-
tions between niobium or tantalum pentahalides and DMSO or
diphenyl sulfoxide are known to proceed with Cl/O interchange
to produce the corresponding halo-substituted sulfides.[21] This
outcome parallels the reactivity shown by sulfoxides when al-
lowed to interact with oxophilic main group chlorides, such as
SOCl2,[22] BCl3 and SiCl4.[23]
Here we report our study on the reactions between MoCl5
and limited amounts of a selection of sulfoxides; the reaction
between MoCl5 and DMSO, leading to the one-pot conversion
of DMSO into a mercaptomethylsulfonium salt, has been stud-
ied in detail, by means of X-ray crystallography, DFT calculations
and spectroscopic and analytical techniques.
Figure 1. ORTEP drawing of [Me2SCH2SMe][MoOCl4] (1). Displacement ellip-
soids are at the 50 % probability level.
Table 1. Selected interatomic distances [Å] and angles (deg) in 1.
Results and Discussion
Molecule 1
Molecule 2
Molybdenum pentachloride slowly dissolved in dichloro-
methane in the presence of one equivalent of DMSO at room
temperature, under strictly anhydrous conditions. After workup,
the crystalline compound [Me2SCH2SMe][MoOCl4] (1) was iso-
lated in 46 % yield and identified by elemental and magnetic
analysis, IR spectroscopy, and X-ray diffraction (Scheme 1). The
analogous reaction between MoCl5 and DMSO carried out at a
1:2 molar ratio afforded 1 in lower yield.
Mo(1)–O(1)
Mo(1)–Cl(1)
Mo(1)–Cl(2)
Mo(1)–Cl(3)
Mo(1)–Cl(4)
C(5)–S(3)
S(3)–C(6)
C(6)–S(4)
S(4)–C(8)
S(4)–C(7)
1.657(2)
1.660(2)
2.3655(9)
2.3645(8)
2.3598(9)
2.3674(8)
1.806(3)
1.796(3)
1.813(3)
1.789(3)
1.789(3)
2.3750(8)
2.3575(9)
2.3654(8)
2.3560(10)
1.804(4)
1.799(3)
1.812(3)
1.784(3)
1.778(4)
Cl(1)–Mo(1)–Cl(3)
Cl(2)–Mo(1)–Cl(4)
C(5)–S(3)–C(6)
S(3)–C(6)–S(4)
C(6)–S(4)–C(7)
C(6)–S(4)–C(8)
C(7)–S(4)–C(8)
157.51(3)
159.97(3)
99.08(16)
110.59(17)
101.08(16)
99.50(15)
103.21(16)
158.28(3)
159.17(3)
99.85(17)
110.39(17)
101.16(18)
99.88(15)
100.60(19)
Scheme 1. One-pot synthesis of a mercaptomethylsulfonium salt from MoCl5
and DMSO.
The magnetic susceptivity value found for 1 is consistent
with previous findings for [MoOCl4]– salts.[5f,24] The IR spectrum
(solid state) displays a strong band at 985 cm–1, diagnostic of
the presence of the [Mo=O] moiety.[4d,4e,5a,25] X-ray-quality crys-
tals could be collected from a dichloromethane/hexane mix-
ture; the crystal structure of 1 is shown in Figure 1, and a selec-
tion of interatomic distances and angles is listed in Table 1. The
structure is based on ionic packing of [Me2SCH2SMe]+ cations
and [MoOCl4]– anions; two independent cations and anions are
present within the asymmetric unit of the unit cell. The struc-
ture of the [Me2SCH2SMe]+ cation is reported here for the first
time. The [MoOCl4]– anion displays a distorted square-pyrami-
dal structure, as also previously found for other [MoOCl4]–
salts.[5e,24c,26] The Mo(1)–O(1) bond [1.657(2) Å] reveals a strong
π character, as expected for a MoV=O unit.[5e,5f] [MoOCl4]–
anions are usually found in the solid state in different forms:
(A) isolated anions, (B) weak intermolecular adducts with a do-
nor atom of the cation or the co-crystallized solvent molecule,
(C) dimeric {[MoOCl4]–}2 units, or (D) infinite {[MoOCl4]–}∞
chains.[26a,26b] In the case of 1, the [MoOCl4]– anions form weak
interactions with the mercapto groups of the cations, with
The formation of 1 appears to be the result of multiple acti-
vation of DMSO, consisting of oxygen transfer to the metal cen-
tre, C–H cleavage and intermolecular C–S bond formation.
Molybdenum pentachloride behaves in a previously unob-
served way, directing the overall sequence in a one-pot process.
The cation [Me2SCH2SMe]+ had previously been obtained by
the combination of the preliminarily generated MeSCH2Cl with
Me2S, variously as chloride,[28] [SbCl6]– or [BF4]– salts.[29] Alterna-
tive routes to mercapto-substituted sulfonium cations analo-
gous to 1 involve reactions between (1) sulfoxides and trifluoro-
acetic anhydride, followed by treatment with sulfides,[30] or
(2) alkyl chlorosulfinates and DMSO in the presence of SbCl5.[31]
All of these syntheses are believed to proceed through the for-
mation of ionic intermediates [R2SC(H)(R)]+ or neutral interme-
diates R2SC(H)(R)Cl, depending on the procedure.
We carried out a DFT study in order to determine a possible
pathway for the synthesis of 1. The hypothesized metal inter-
mediates are summarized in Scheme 2 (black path), with rela-
tive Gibbs energy values.
The reaction between Mo2Cl10 and DMSO should initially af-
Mo(1)···S(3) contacts of 2.97 and 2.98 Å for the two independ- ford the complex MoCl5(DMSO) [Figure 2, Equation (1)]. A possi-
ent molecules. It should be noted that the sums of the covalent ble following step may involve Cl/O interchange between
and van der Waals radii of Mo and S are 2.56 and 3.80 Å, respec- molybdenum and sulfur (Scheme 2, black path), resulting in the
tively.[27]
formation of the sulfonium salt [S(Cl)Me2][MoOCl4] [Figure S1 in
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Scheme 2. Possible intermediates involved in the reaction between Mo2Cl10 and DMSO, together with relative Gibbs energy values (kcal mol–1, Mo2Cl10 and
DMSO taken as zero).
the Supporting Information, Equation (2)]. Hence, HCl release
from [S(Cl)Me2][MoOCl4] might afford an ylide species [Fig-
ure S2 in the Supporting Information, Equation (3)]. Indeed, HCl
[see Equation (3)] is one of the experimentally detected byprod-
ucts in the synthesis of 1 (see the Experimental Section). All
attempts to optimize the ylide CH2=S(Cl)Me in non-metal-coor-
dinated form afforded MeSCH2Cl as a stationary point.
Mo2Cl10 + DMSO → 2 MoCl5(DMSO)
ΔG = –47.9 kcal mol–1
(1)
(2)
(3)
MoCl5(DMSO) → [S(Cl)Me2][MoOCl4]
ΔG = –22.3 kcal mol–1
Figure 2. DFT-optimized geometry of MoCl5(DMSO). wB97X DFT functional,
C-PCM solvation model for dichloromethane. Selected computed bond
lengths [Å]: Mo–Cl (trans O) 2.308; Mo–Cl (cis O) 2.318, 2.318, 2.335, 2.356;
Mo–O 2.027; O–S 1.584; S–C 1.787, 1.787. Selected computed interatomic
angles [°]: O–Mo–Cl 86.9, 86.9, 86.7, 90.2, 178.1; Mo–O–S 130.9; O–S–C 101.1,
101.1.
[S(Cl)Me2][MoOCl4] → MoOCl3{CH2=S(Cl)Me} + HCl
ΔG = +11.1 kcal mol–1
Despite the fact that the hypothetical formation of
MoOCl3{CH2=S(Cl)Me} is an endoergonic step, this might be fol-
lowed by the favourable nucleophilic attack of the coordinated
ylide onto another sulfonium cation, resulting in C–S bond for-
mation [Equation (4)].[32] According to the computational re-
sults, transfer of one chloride from the sulfonium to the MoOCl3
moiety should take place at this stage. The optimized structure
of [Me2SCH2S(Cl)Me][MoOCl4]2 is reported in Figure S3 in the
Supporting Information. The subsequent rearrangement of this
salt would lead to 1 and MoOCl3 through Cl2 release [Equa-
tion (5)].
MoOCl3{CH2=S(Cl)Me} +
[SClMe2][MoOCl4] → [Me2SCH2S(Cl)Me][MoOCl4]2 (4)
ΔG = –11.0 kcal mol–1
[Me2SCH2S(Cl)Me][MoOCl4]2 → [Me2SCH2SMe][MoOCl4] +
MoOCl3 + Cl–Cl
ΔG = –4.0 kcal mol–1
(5)
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Importantly, MoOCl3 was detected by IR spectroscopy on
analysis of the solid residue obtained from the reaction mixture
(band at ν = 983 cm–1).[33] On the other hand, our attempts to
detect elemental chlorine were unsuccessful, this compound
possibly being consumed in the medium during the reaction
time (18 h).
Because the formation of dimethyl sulfide from MoCl5/DMSO
1
was detected (GC–MS and H NMR; see Experimental), it seems
plausible that reaction pathways alternative to that described
above (Equation 1–5) are also working. In principle, dimethyl
sulfide might be produced by decomposition of the presuma-
ble initial adduct MoCl5(DMSO) [Equation (6) and Scheme 2,
path printed in red].
Scheme 3. Organic compounds identified in the MoCl5/sulfoxide mixtures
after treatment with water.
MoCl5(DMSO) → MoOCl3 + Cl2 + SMe2
ΔG = –4.0 kcal mol–1
(6)
hyde and benzyl-thiol were found, besides traces of dibenzyl
sulfide.[22,35a,36]
MeSPh and traces of MeCl were formed from MoCl5/MePhSO
(Scheme 3). The sulfide nBu2S (major) and the disulfide nBu2S2
(minor) are the two organic compounds that could be detected
from MoCl5/nBu2SO.
We investigated the reactions between MoCl5 and THTO and
between MoCl5 and MePhSO by DFT calculations, in order to
provide an explanation for the different outcomes observed
with respect to MoCl5/DMSO. According to the calculations, the
preliminary O-coordination of the sulfoxide to MoV chloride is a
largely favourable process [Equation (10), to be compared with
Equation (1)]. The calculated structure of MoCl5(THTO) is shown
in Figure 3, whereas that of MoCl5(MePhSO) is included in Fig-
ure S6 in the Supporting Information.
Subsequent coordination of SMe2 to still unreacted MoCl5
(Figure S4 in the Supporting Information) could represent the
preliminary step of another route affording 1 [see Equations (7),
(8), (9)]. Molybdenum pentachloride would behave as a catalyst
along this route (Scheme 2, catalytic Mo2Cl10 is highlighted in
blue).
Mo2Cl10 + 2 SMe2 → 2 MoCl5(SMe2)
ΔG = –18.7 kcal mol–1
(7)
MoCl5(SMe2) → MoCl4(CH2SMe) + HCl
ΔG = 2.4 kcal mol–1
(8)
MoCl4(CH2SMe) + [SClMe2][MoOCl4] →
[Me2SCH2SMe][MoOCl4] + 1/2 Mo2Cl10
(9)
ΔG = –15.3 kcal mol–1
Mo2Cl10 + L=O → 2 MoCl5(L=O)
(10)
We extended our investigation to reactions between MoCl5
and a selection of commercial sulfoxides. We could not cleanly
isolate and characterize any metal compound from these reac-
tions; however, most of the organic products were identified by
means of GC–MS and NMR spectroscopy after hydrolysis of the
reaction mixtures.[34]
L=O: THTO, ΔG = –75.9 kcal mol–1
L=O: MePhSO, ΔG = –48.4 kcal mol–1
The reaction between cyclic tetrahydrothiophene 1-oxide
(THTO) and MoCl5 was selective, and the former component
was almost quantitatively converted into tetrahydrothiophene
when combined with MoCl5 in 2:1 molar ratio (Scheme 3). The
observed process is presumably accompanied by oxygen trans-
fer from the organic reactant to the metal centre (IR spectrum
of the reaction solid residue: Mo=O band at 983 cm–1, disap-
pearance of S=O band around 1010 cm–1).
On the other hand, the reactions between MoCl5 and
(PhCH2)2SO, MePhSO or nBu2SO, performed with use of a 1:2
molar ratio, proved to be nonselective (Scheme 3). The IR spec-
tra of the reaction mixtures in every case suggested the occur-
rence of oxygen abstraction by the Mo centre, whereas DEPT
NMR experiments on the same mixtures treated with water
ruled out the presence of C–H activation products, in contrast
with what had been shown by the MoCl5/DMSO system.
Figure 3. DFT-optimized geometry of MoCl5(THTO). wB97X DFT functional, C-
PCM solvation model for dichloromethane. Selected computed bond lengths
[Å]: Mo–Cl (trans O) 2.280; Mo–Cl (cis O) 2.339, 2.344, 2.376, 2.390; Mo–O
1.916; O–S 1.580; S–C 1.814, 1.832. Selected computed interatomic angles [°]:
O–Mo–Cl 87.4, 87.9, 89.5, 91.3; Mo–O–S 166.4; O–S–C 102.6, 103.2.
In agreement with the experimental observations, the con-
version of MoCl5(L=O) [Equation (10)] into the corresponding
sulfonium salts through Cl/O interchange are nonspontaneous
reactions [Equations (11) and (12), to be compared with Equa-
The prevalent compound originating from MoCl5/(PhCH2)2SO tion (2)]. In other words, the uncommon behaviour exhibited
was benzyl chloride,[35] thus indicating that preferential α- by DMSO in the reaction with MoCl5 should be related to the
chlorination of the sulfoxide moiety took place, accompanied specific nature of the former, making the Cl/O interchange with
by C–S cleavage. In addition, significant amounts of benzalde- the metal complex thermodynamically acceptable.
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MoCl5(THTO) → [S(Cl)C4H8][MoOCl4]
ΔG = +4.2 kcal mol–1
(11) equipped with a BBFO broadband probe at 298 K. GC/MS analysis
was performed with a HP6890 instrument interfaced with MSD-
HP5973 detector and equipped with a Phenonex Zebron column.
Carbon and hydrogen analyses were performed with a Carlo Erba
MoCl5(MePhSO) → [S(Cl)(Me)(Ph)][MoOCl4]
ΔG = +12.0 kcal mol–1
(12)
mod. 1106 instrument. The chloride content was determined by the
Mohr method[41] on solutions prepared by dissolution of the solid in
aqueous KOH at boiling temperature, followed by cooling to room
temperature and addition of HNO3 to neutralization. The molybd-
enum content was determined by the spectrophotometric method
proposed by Crouthamel and Johnson,[42] after dissolution of a
In order to allow the formation of the corresponding sulfides
from THTO and MePhSO, the oxygen transfer to the metal cen-
tre should not be accompanied by Cl transfer to the organic
moiety [Equations (11) and (12)]. DFT analyses suggest the pos-
sibility of Cl2 release [Equation (13)]. This process is slightly
endoergonic in the case of THTO; nevertheless, it could be
driven by the subsequent reactions of the products, including
the possible coordination of THT to the metal species.[37]
weighed amount of sample (30–60 mg) in HCl (4
M, 100 mL). A
calibration curve was obtained with (NH4)6Mo7O24·4 H2O as stan-
dard (R2 = 0.999), whereas MoO2(acac)2 was used as a reference
compound (anal. found: Mo 30.2 %; C10H14MoO4 requires Mo
29.8 %).
MoCl5(L=O) → MoOCl3 + Cl2 + L
(13)
Reaction between MoCl5 and Dimethyl sulfoxide (DMSO)
L: THT, ΔG = 5.0 kcal mol–1
(1) Synthesis and Isolation of [Me2SCH2SMe][MoOCl4] (1): A sus-
pension of MoCl5 (326 mg, 1.19 mmol) in CH2Cl2 (30 mL) was
treated with DMSO (0.086 mL, 1.20 mmol). The mixture was stirred
for 18 h at room temperature. The resulting green solution was
filtered in order to remove a minor amount of a dark green solid,
concentrated to ca. 10 mL, layered with hexane and set aside at
–30 °C. Light green crystals of 1 were collected after one week,
L: MePhS, ΔG = –3.6 kcal mol–1
Interestingly, evolution of HCl from the reaction mixtures
(Scheme 2) was detected in every case (see the Experimental
Section for details). In the absence of C–H activation processes
(see above), this may constitute indirect confirmation of the
formation of elemental chlorine.[38,39]
yield 208 mg, 46 %. IR (solid state): ν = 3003 (m), 2917 (m), 1693
˜
(w), 1594 (m), 1407 (m), 1319 (m), 1201 (w), 1095 (w), 1033 (m),
985 (s, Mo=O) , 927 (vs), 892 (vs), 807 (m), 746 (w), 721 (w), 685
(w) cm–1. Magnetic measurement: ꢀM
= 9.58 × 10–4 cgsu, μeff
=
corr
Conclusions
1.52 BM cm–1. C4H11Cl4MoOS2 (377.00): calcd. C 12.74, H 2.94, Cl
37.61, Mo 25.45; found C 12.65, H 3.00, Cl 37.48, Mo 25.58.
Despite the interest that sulfoxides have attracted in organic
synthesis, and their wide use in coordination chemistry, the re-
activity of this class of compounds with molybdenum penta-
chloride has previously been scarcely elucidated. In general,
chlorination of alkyl sulfoxides by oxophilic metal chlorides is
well known; nevertheless, it typically stops at the formation of
halogen-substituted sulfides. Here we have described the 1:1
reaction between MoCl5 and DMSO, providing an example of
one-pot sulfoxide conversion into a mercapto-substituted
sulfonium compound. This unusual result seems to be directed
by specific electronic and steric properties of the sulfur substit-
uents; different outcomes have thus been found in the reac-
tions between MoCl5 and other sulfoxides.
(2) Detection of HCl and SMe2: MoCl5 (0.300 mmol) and DMSO
(0.300 mmol) were allowed to react in CH2Cl2 (8 mL) in a Schlenk
tube closed with a silicon stopper. After 72 h, an aliquot of gas was
withdrawn from the Schlenk and analyzed by GC–MS. The analysis
revealed the presence of SMe2. Another aliquot of gas was trans-
ferred into an aqueous solution of AgNO3, resulting in the precipita-
tion of a white solid (AgCl).
In a different experiment, MoCl5 (0.300 mmol), CD2Cl2 (0.5 mL),
CHCl3 (0.300 mmol) and DMSO (0.300 mmol) were transferred into
a NMR tube. The tube was sealed, shaken in order to homogenize
the content, and maintained at room temperature. NMR analysis
after 72 h indicated the presence of 1, SMe2 and other unidentified
products (SMe2/CHCl3 ratio = 45 %).
Experimental Section
Reactions between MoCl5 and Tetrahydrothiophene 1-Oxide,
General Considerations: Warning. The metal products reported in
this paper are highly moisture-sensitive, so rigorously anhydrous
conditions were required for the reaction and crystallization proce-
dures. The reaction vessels were oven-dried at 140 °C prior to use,
evacuated (10–2 mmHg) and then filled with argon. MoCl5 was pur-
chased from Strem (99.6 % purity) and stored under argon as re-
ceived. The organic reactants were purchased from Alfa Aesar. Once
isolated, the metal products were conserved in sealed glass tubes
under argon. Solvents (Sigma–Aldrich) were distilled over CaH2 un-
der argon before use. IR spectra were recorded at 298 K with a
Perkin–Elmer FTIR spectrometer equipped with a UATR sampling
accessory. Magnetic susceptibility (reported per Mo atom) was
measured on a solid sample at 298 K with a Magway MSB Mk1
magnetic susceptibility balance (Sherwood Scientific Ltd). Dia-
magnetic corrections were introduced according to König.[40] NMR
spectra were recorded with a Bruker Avance II DRX400 instrument
nBu2SO, MePhSO or (PhCH2)2SO
(1) Identification of Organic Products. General Procedure: The
appropriate sulfoxide (1.60 mmol) was added to a suspension of
MoCl5 (0.800 mmol) in CH2Cl2 (10 mL). The mixture was stirred for
18 h at room temperature, and the volatile materials were then
removed in vacuo. The residue was analyzed by IR and NMR spec-
troscopy. Afterwards, a portion of the residue was treated with
CDCl3 (ca. 2 mL), followed by an excess of H2O (ca. 0.2 mL). The
resulting solution was analyzed by GC–MS and NMR spectroscopy.
(A) From MoCl5/tetrahydrothiophene 1-oxide, green solid. IR (solid
state): ν = 2495 (m), 1598 (m), 1441 (m), 1412 (m), 1307 (w), 1204
˜
(vw), 1175 (vw), 1134 (vw), 1101 (w), 983 (vs), (Mo=O), 875 (w), 800
(m), 731 (m) cm–1 1H NMR: tetrahydrothiophene.[43] NMR/GC–MS
.
(after hydrolysis): tetrahydrothiophene.
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(B) From MoCl5/nBu2SO, green solid. IR (solid state): ν = 2960 (s),
the split-valence polarized basis set of Ahlrichs and Weigend, with
relativistic ECP on the metal centre.[45] The “unrestricted” formalism
was applied for compounds with unpaired electrons, and the lack
of spin contamination was verified by comparing the computed
<S2> values with the theoretical ones. The stationary points were
characterized by IR simulations (harmonic approximation), from
which zero-point vibrational energies and thermal corrections (T =
298.15 K) were obtained. The C-PCM implicit solvation model (ε =
9.08) was added to ωB97XD calculations.[46] Gaussian 09 was used
as software,[47] running on x86–64 workstations.
˜
2932 (m), 2873 (m), 1599 (m), 1463 (m), 1409 (m), 1381 (w), 1276
(w), 1228 (w), 1191 (vw), 1099 (w), 990 (vs., Mo=O) , 938 (s), 781
(w), 732 (m) cm–1. 1H NMR: nBu2S.[43] NMR/GC–MS (after hydrolysis):
nBu2S and nBu2S2 (ratio ca. 3:1).
(C) From MoCl5/MePhSO, green-blue solid. IR (solid state): ν = 3007
˜
(w), 2921 (w), 1601 (m), 1475 (m), 1445 (m), 1409 (m), 1305 (w-m),
1259 (w), 1142 (m), 1082 (m), 978 (vs., Mo=O) , 955 (vs), 811 (s), 747
1
(vs), 716 (m), 684 (vs) cm–1. H NMR: MeSPh.[43] NMR/GC–MS (after
hydrolysis): MeSPh and MeCl (ratio ca. 10:1).
Supporting Information: Selected DFT-optimized structures are re-
ported in the Supporting Information, Figures S1–S10, with relevant
bonding parameters. Cartesian coordinates of the computed geom-
etries are collected in a separated xyz file.
(D) From MoCl5/(PhCH2)2SO, purple solid. IR (solid state): ν = 3062
˜
(w), 3031 (w), 2968 (w), 2910 (w), 1681 (w–m), 1644 (m), 1595 (m),
1579 (m), 1495 (m), 1454 (a), 1399 (w), 1315 (w), 1293 (w), 1218 (w),
1169 (w), 1074 (w), 1028 (w), 990 (s, Mo=O) , 947 (s), 908 (s), 839
1
(w), 814 (w), 764 (s), 695 (vs) cm–1. H NMR: PhCH2Cl. NMR/GC-MS
CCDC 1474430 (for 1) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre.
(after hydrolysis): PhCH2Cl, PhCHO and PhCH2SH (ratio 7:4:1).[43]
(2) Detection of HCl: MoCl5 (0.300 mmol) and the sulfoxide
(0.300 mmol) were allowed to react in CH2Cl2 (8 mL) in a Schlenk
tube closed with a silicon stopper. After 72 h, an aliquot of gas was
withdrawn from the Schlenk and into an aqueous solution of Ag-
NO3. Precipitation of a white solid (AgCl) was observed in every
case.
Acknowledgments
The authors wish to thank the University of Pisa, Italy for finan-
cial support.
X-ray Crystallographic Study: Crystal data and collection details
for 1 are listed in Table 2. The diffraction experiment was carried
out with a Bruker APEX II diffractometer equipped with a CCD de-
tector and with use of Mo-Kα radiation (λ = 0.71073 Å). Data were
corrected for Lorentz polarization and absorption effects (empirical
absorption correction SADABS). The structure was solved by direct
methods and refined by full-matrix, least-squares based on all data
with use of F2. All non-hydrogen atoms were refined with aniso-
tropic displacement parameters. All hydrogen atoms were fixed at
calculated positions and refined by use of a riding model.
Keywords: Molybdenum · Molybdenum pentachloride · S–
O activation · Sulfoxides · Density functional calculations
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Table 2. Crystal data and experimental details for 1.
Formula
Formula weight
T [K]
C4H11Cl4MoOS2
376.99
100(2)
λ [Å]
0.71073
Crystal system
Space group
a [Å]
b [Å]
c [Å]
monoclinic
P21/c
11.4970(8)
20.0019(14)
11.3443(8)
100.9540(10)
2561.2(3)
8
1.955
2.143
1480
ꢀ [°]
Cell volume [Å3]
Z
Dc [g cm–3
]
μ [mm–1
F(000)
]
Crystal size [mm]
θ range [°]
0.16 × 0.12 × 0.11
1.80–28.00
23554
6069 [Rint = 0.0436]
6069/0/217
1.040
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness on fit on F2
R1 [I > 2σ(I)]
0.0350
wR2 (all data)
0.0637
0.605/–0.6904
Largest diff. peak/hole [e Å–3
]
Eur. J. Inorg. Chem. 2016, 3838–3845
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Received: May 23, 2016
Published Online: July 20, 2016
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© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim