Isolation and characterization of thiolato complexes of [CpCr(SBz)]2S, isomeric trans [CpMo(CO)(SBz)]2 and [CpMo(SBz)2]2 (Cp = (η5-C5H5), Bz = PhCH2–) from the reactivity of bibenzyl disulfide towards [CpM(CO)3]2 (M = Cr, Mo)

Article abstract of DOI:10.1016/j.ica.2017.08.029

The reactions of [CpM(CO)₃]₂ (M = Cr (1), Mo (3)) with Bz₂S₂ have been investigated. 1 underwent a facile reaction at ambient temperature which led to the isolation of [CpCr(CO)₂]S (5), [CpCr(CO)₂(SBz)]₂ (6) and [CpCr(SBz)]₂S (7) in 28.8, 42.6 and 11.8% yield, respectively. A similar reaction at 110 °C with its congener, [CpCr(CO)₂]₂ (Cr[tbnd]Cr) (2) yielded only thermolytic products of 5 (40.3%) and Cp₄Cr₄S₄ (8) (10.6%). With the Mo analogue 3, only the decarbonylated [CpMo(CO)₂]₂ (Mo[tbnd]Mo) (4) reacts at 70 °C to give an isomeric pair of trans syn and anti [CpMo(CO)(SBz)]₂ (9a & 9b), [CpMo(SBz)(S)]₂ (10) and [CpMo(CO)(SBz)]₂S (11) in 43.3, 34.1, 5.5 and 3.1% yield, respectively. A totally decarbonylated new complex of [CpMo(SBz)₂]₂ (12) was obtained in 33.2% yield from the co-thermolysis of Bz₂S₂ with 9a at 110 °C. All products were fully characterized with NMR and IR spectroscopy and C, H analysis. The molecular structures of 7, 9b and 12 have been elucidated by single crystal X-ray diffraction. Plausible mechanistic pathways leading to the formation of 7, 9 and 12 were discussed.

Full text of DOI:10.1016/j.ica.2017.08.029

Accepted Manuscript
Research paper
Isolation and characterization of thiolato complexes of [CpCr(SBz)]2S, isomeric
trans [CpMo(CO)(SBz)]2 and [CpMo(SBz)2]2 (Cp = (η5-C5H5), Bz = PhCH2-)
from the reactivity of bibenzyl disulfide towards [CpM(CO)3]2 (M = Cr, Mo)
Mei Lee Ooi, Chu Er Lim, Richard C.S. Wong, Seik Weng Ng
PII:
S0020-1693(17)30572-8
http://dx.doi.org/10.1016/j.ica.2017.08.029
ICA 17823
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
17 April 2017
20 July 2017
14 August 2017
Please cite this article as: M.L. Ooi, C.E. Lim, R.C.S. Wong, S.W. Ng, Isolation and characterization of thiolato
complexes of [CpCr(SBz)]2S, isomeric trans [CpMo(CO)(SBz)]2 and [CpMo(SBz)2]2 (Cp = (η5-C5H5), Bz =
PhCH2-) from the reactivity of bibenzyl disulfide towards [CpM(CO)3]2 (M = Cr, Mo), Inorganica Chimica Acta
(2017), doi: http://dx.doi.org/10.1016/j.ica.2017.08.029
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Isolation and characterization of thiolato complexes of [CpCr(SBz)]2S, isomeric trans
[CpMo(CO)(SBz)]2 and [CpMo(SBz)2]2 (Cp = (η5-C5H5), Bz = PhCH2-) from the
reactivity of bibenzyl disulfide towards [CpM(CO)3]2 (M = Cr, Mo)
Mei Lee Ooia,b*, Chu Er Lima , Richard C. S. Wongb and Seik Weng Ngc
aDepartment of Chemical Science, Universiti of Tunku Abdul Rahman, Kampar, Perak, Malaysia
bDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
cSchool of Pharmacy, University of Nottingham, Malaysia
*Corresponding author. Tel.: +605 4688888 Ext: 4670. E-mail address: ooiml@utar.edu.my (Mei Lee Ooi).
Abstract
The reactions of [CpM(CO)3]2 (M = Cr (1), Mo (3)) with Bz2S2 have been investigated. 1
underwent a facile reaction at ambient temperature which led to the isolation of
[CpCr(CO)2]S (5), [CpCr(CO)2(SBz)]2 (6) and [CpCr(SBz)]2S (7) in 28.8, 42.6 and 11.8%
yield, respectively. A similar reaction at 110 oC with its congener, [CpCr(CO)2]2 (Cr≡Cr) (2)
yielded only thermolytic products of 5 (40.3%) and Cp4Cr4S4 (8) (10.6%). With the Mo
o
analogue 3, only the decarbonylated [CpMo(CO)2]2 (Mo≡Mo) (4) reacts at 70 C to give an
isomeric pair of trans syn and anti [CpMo(CO)(SBz)]2 (9a & 9b), [CpMo(SBz)(S)]2 (10) and
[CpMo(CO)(SBz)]2S (11) in 43.3, 34.1, 5.5 and 3.1% yield, respectively. A totally
decarbonylated new complex of [CpMo(SBz)2]2 (12) was obtained in 33.2% yield from the
o
co-thermolysis of Bz2S2 with 9a at 110 C. All products were fully characterized with NMR
and IR spectroscopy and C, H analysis. The molecular structures of 7, 9b and 12 have been
elucidated by single crystal X-ray diffraction. Plausible mechanistic pathways leading to the
formation of 7, 9 and 12 were discussed.
Keywords: Bibenzyl disulfide; trans syn and anti isomers; Thermolytic studies;
Desulfurization; Monoclinic.
1. Introduction
Dinuclear transition-metal [CpM(CO)3]2 complexes comprising of bridging thiolate
ligands are a well-established class of compounds. The chemistry of these transition-metal

carbonyl complexes which include synthesis, reactivity, novel structures and electrochemistry
remains an area of continuous interest [1a-g]. Potential applications offered by transition-
metal thiolates are diverse such as desulfurization of petroleum feedstock, active catalysts in
various C-C and C-heteroatom bond-forming reactions, to biological models for the sulfur-
rich metal centre of the metalloenzymes involved in the nitrogen cycle [1b-c, 1f].
Previously our group had reported the reaction of [CpM(CO)3]2 [M=Cr, Mo] with Bz-S-S-S-
Bz reaction [2a-b]. However, we noticed that the common [CpM(CO)(SR)]2 and
[CpM(SR)2]2 type products were not isolated in the above mentioned reactions.
Comparatively, it is worthwhile to continue the investigation for the reactivity of these Cr and
Mo dimers toward the analogous Bz-S-S-Bz ligand in order to fully comprehend the
reactivity nature of these benzyl thiolate ligands.
2. Experimental Section
2.1
General procedures
All synthetic manipulations were carried out using standard Schlenk techniques under
1
13
an inert atmosphere of argon or in a Vacuum Atmosphere Dribox. H and C NMR spectra
were measured on a JEOL Lambda 400 MHz and JEOL ECA 400 MHz spectrometer, and
their chemical shifts referenced to residual C6H6 in C6D6. IR spectra in Nujol mulls were
measured in the range of 4000–400 cm-1 by means of a Perkin-Elmer 2000 FTIR instrument.
C, H analyses were performed by the in-house microanalytical laboratory using a Perkin–
Elmer 2400 Series II CHNS System, except for Cr which was determined as CrO42- [3].
Solvents were distilled from sodium/ benzophenone prior to use. Silica gel (Merck Kieselgel
o
60, 230-400 mesh) and Celite (Fluka AG) was activated at 140 C overnight before
chromatographic use. Bibenzyl disulfide was purchased from Sigma. [CpM(CO)3]2 [M =
Cr(1) or Mo(3)] was synthesized as described by Manning [4] from chromium hexacarbonyl
(99% purity from Merck) for 1 and molybdenum hexacarbonyl for 3 (Fluka AG).
[CpM(CO)2]2 [M = Cr (2) or Mo (4)] were synthesized from their respective hexacarbonyl
dimer 1 and 2 by thermolysis at 110 °C and 120 °C, respectively for overnight in toluene.
2.2
(a)
Reactivity studies of [CpCr(CO)3]2 (1) with an equimolar of Bz2S2
At room temperature
A deep green suspension of 1 (200 mg, 0.498 mmol) and Bz2S2 (122 mg, 0.498 mmol)
in toluene (~20mL) was allowed to stir at room temperature for 13.5 h until color had
changed to dirty brown. The resultant reaction mixture was filtered through a disc of Celite

(1 x 1.5 cm), absorbed onto silica gel (3-4 g) before loading onto a silica gel column (1.5 x 10
cm) prepared in n-hexane. Two products were isolated in the following fractions:
(i)
A yellowish brown eluate in n-hexane/toluene (2:1, 35 mL) which when concentrated
to dryness yielded fine deep green crystalline solids of [CpCr(CO)2]2S (5) (54 mg, 0.143
mmol, 28.8% yield), identified by its 1H NMR δ(Cp) 4.36 in benzene-d6 [5] and TLC against
⅓
an authentic sample [Rf = 0.60 with n-hexane:toluene:ether (2:1: ) as eluent].
(ii) A dark brown eluate in toluene (15 mL) which when concentrated to dryness yielded
fine dark brown crystalline solids of [CpCr(CO)2(SBz)]2 (6) (104 mg, 0.212 mmol, 42.6%
yield), identified by its 1H NMR δ(Cp) 4.16 in benzene-d6 [2a] and TLC against an authentic
sample [Rf = 0.72 with n-hexane:toluene:ether (2:1:1) as eluent].
(iii)
A purple eluate in ether (10 mL) which when concentrated to dryness yielded purple
crystalline solids of [CpCr(SBz)]2S (7) (30 mg, 0.058 mmol, 11.8% yield). 1H NMR
(benzene-d6): δ 13.89 (br, Cp, υ½ = 57 Hz), δ 7.42-6.88 (m, C6H5), δ 3.35 (s, CH2). 13C
NMR (benzene-d6): δ 66.25 (CH2), δ 101.04 (Cp), δ 129.20, 128.88, 128.63, 128.39, 128.28,
128.14 (S-CH2-C6H5). IR: υ at 1063 vw, 1015 vw, 840 w, 732 w cm-1 (nujol). Anal. Calcd.
for C24H24Cr2S3: C, 56.25; H, 4.68; Cr, 20.31; S, 18.75. Found: C, 56.57; H, 4.15; Cr, 19.59;
S, 18.31. A greenish blue band remained uneluted on top of the column.
(b)
At 110 ˚C
A similar reaction was repeated at 110 °C for 1 h. Two products were isolated using
a silica gel column (1.5 x 12 cm) prepared in n-hexane.
(i) A yellowish brown fraction in n-hexane-toluene (6:1) (50 mL) which when
concentrated to dryness yielded deep green crystalline solids of 5 (101 mg, 0.267 mmol,
53.7% yield).
(ii)
A dark brown fraction in toluene (15 mL) which when concentrated to dryness
yielded fine dark brown solids of Cp4Cr4S4 (8) (46 mg, 0.076 mmol, 15.4% yield), identified
by its 1H NMR δ(Cp) 4.90 in benzene-d6 [5] and TLC against an authentic sample (Rf= 0.52
with n-hexane:toluene:ether (3:2:2) as eluent).
(iii)
A dark brown fraction in ether-THF (1:1) (30 mL) which when concentrated to
dryness yielded a dark brown residue (119 mg) consisting of an inseparable mixture of two

complexes in the proportion of 2:3 (estimated from TLC analysis). Despite repeated attempts,
1
this mixture was not separated. H NMR analysis of the mixture showed δ 4.94 (s, Cp) and δ
5.13 (s, Cp) in benzene-d6, respectively.
2.3
Reactivity studies of [CpCr(CO)2]2 (2) with equimolar Bz2S2 at 110 ˚C
To a deep green suspension of 2 (150 mg, 0.433 mmol) in toluene (~10 mL) was
added an equimolar amount of Bz2S2 (107 mg, 0.433 mmol). The reaction mixture was
allowed to stir at 110 ˚C for 1 h. Filtration on Celite removed a small amount of dark
insoluble solids. The ensuing chromatographic work up as in reaction above, gave the
following fractions:
(i)
A yellowish brown fraction in n-hexane-toluene (1:2.5) (18 mL) which when
concentrated to dryness gave deep green crystalline solids of [CpCr(CO)2]2S (5) (66 mg,
0.175 mmol, 40.3% yield).
(ii)
A dark brown fraction in toluene (15 mL) which when concentrated to dryness gave
dark brown crystalline solids of Cp4Cr4S4 (8) (27.5 mg, 0.046 mmol, 10.6% yield).
(iii)
A dark brown fraction in ether-THF (1:1) (30 mL) which when concentrated to
dryness gave dark brown solids (62 mg) consisting of an inseparable mixture of two
1
complexes in the proportion of 2:3 (estimated from TLC analysis). H NMR analysis of the
mixture showed δ 4.94 (s, Cp) and δ 5.13 (s, Cp) in benzene-d6, respectively.
2.4
(a)
Reaction of [CpMo(CO)2]2 (4) with Bz2S2
At 70 °C
To a reddish brown solution of [CpMo(CO)2]2 (4) (200 mg, 0.460 mmol) in toluene
(~20 mL) was added an equimolar of Bz2S2 (114 mg, 0.460 mmol) was stirred at 70 °C for
7.5 h. The resultant dark brown reaction mixture was treated with similar procedure as in 2.2
(a) using a silica gel column (9 x 1.5 cm) prepared in n-hexane. Four fractions were eluted:
(i)
A yellowish brown fraction in a 4:1 n-hexane/toluene mixture (20 mL) which upon
concentrated to dryness gave fine dark brown crystalline solids of trans-syn
1
[CpMo(CO)(SBz)]2 (9a) (124 mg, 0.199 mmol, 43.3% yield). H NMR (benzene-d6): δ 7.50-
7.08 (m, C6H5); δ 4.69, 5.05 (s, Cp), δ 3.61, 3.64 (d, CH2), 3.93, 3.96 (d, CH2). 13C NMR
(benzene-d6): δ 52.36 (CH2); δ 91.18, 91.58 (Cp), δ 127.31, 129.00, 129.79, 141.86 (S-CH2-

C6H5); δ 246.50, 250.85 (CO). I.R.: v(CO) at 1835vs, 1796s cm-1; other bands, 800m, 763m,
721vw, 698s, 530w, 489sh, 474m cm-1 (nujol). Anal. Calcd. for C26H24Mo2O2S2: C, 49.7 ; H,
3.8. Found : C, 49.3; H, 3.5%.
(ii)
A yellowish green fraction in a 1:1 n-hexane/toluene mixture (40 mL) which upon
concentration to dryness gave fine green crystalline solids of trans-anti [CpMo(CO)(SBz)]2
(9b) (98 mg, 0.158 mmol, 34.1% yield). 1H NMR (benzene-d6): δ 7.72-7.01 (m, C6H5); δ
4.87 (s, Cp); δ 3.31, 3.34 (d, CH2), 3.93, 3.90 (d, CH2). 13C NMR (benzene-d6): δ 55.04
(CH2); δ 91.18 (Cp), δ 127.26, 128.95, 129.71, 130.56 (S-CH2-C6H5); δ 249.41 (CO). I.R.:
v(CO) at 1837vs, 1828sh, 1796.2sh cm-1; other bands, 799m, 763m, 724vw, 698m, 535w,
490m, 474m cm-1 (nujol). Anal. Calcd. for C26H24Mo2O2S2 : C, 49.7; H, 3.8. Found : C,
49.6; H, 3.7%.
(iii) A brownish pink fraction in toluene (40mL) which upon concentration to dryness
gave fine pink crystalline solids of [CpMo(SBz)S]2 (10) (16 mg, 0.025 mmol, 5.5% yield)
1
identified by its H NMR δ 5.84 (Cp) in benzene-d6 [2b] and TLC against an authentic
sample [Rf = 0.20 with n-hexane:toluene:ether (2:1:⅓) as eluent].
(iv) A reddish brown fraction in ether (8mL) which upon concentration to dryness gave
reddish brown solids of [CpMo(CO)(SBz)]2S (11) (9 mg, 0.014 mmol, 3.1% yield) identified
1
by its H NMR δ(Cp) 4.83 in benzene-d6 [2b] and TLC against an authentic sample [Rf =
0.13 with n-hexane:toluene:ether (2:1:⅓) as eluent].
(b)
At 110 °C
A similar reaction as in 2.3 (a) but repeated at 110 °C for 2 h. The resultant dark
yellowish brown reaction mixture was treated in a similar manner using a silica gel column
(1.5 x 7 cm) prepared in n-hexane. The following fractions were eluted:
(i)
A dark yellowish brown fraction in 4:1 n-hexane/toluene mixture (20 mL) which upon
concentration to dryness gave dark brown crystalline of trans-syn [CpMo(CO)(SBz)]2 (9a)
(125 mg, 0.200 mmol, 43.6%).
(ii)
A yellowish green fraction in 1:1 n-hexane/toluene mixture (40 mL) which upon
concentration to dryness give green crystalline solids of trans-anti[CpMo(CO)(SBz)]2 (9b)
(119 mg, 0.191 mmol, 41.4%).
(iii)
A brownish pink fraction was eluted with toluene (40 mL) which upon concentration
to dryness gave pink solids of [CpMo(SBz)S]2 (10) (15 mg, 0.024 mmol, 5.2%).

(iv)
A reddish brown fraction in ether (8mL) which upon concentration to dryness gave
reddish brown solids of [CpMo(CO)(SBz)]2S (11) (16 mg, 0.024 mmol, 5.3%).
2.5
Co-thermolysis reaction of trans-syn[CpMo(CO)(SBz)]2 (9a) with an equimolar of
Bz2S2 at 110 °C for 2 h
To a yellowish brown suspension of trans-syn [CpMo(CO)(SBz)]2 (9a) (69 mg, 0.111
mmol) in toluene (~10 mL) was added in an equimolar of Bz2S2 (27 mg, 0.111 mmol). The
reaction mixture was refluxed under stirring for 2 h. The resultant dark yellowish brown
reaction mixture was filtered, concentrated (ca. 2 mL) and chromatographed on a silica gel
column (1.5 x 8 cm) in n-hexane. Four fractions were isolated:
(i)
A yellowish brown fraction eluted with 3:1 n-hexane/toluene mixture (8 mL) which
upon concentrated to dryness gave an oily orange solids of [CpMo(SBz)2]2 (12) (30 mg,
1
0.037 mmol, 33.2% yield). H NMR (benzene-d6): δ 4.92 (s, C5H5), δ 3.42 (s, CH2), δ 7.09-
7.15, 7.18-7.24 (m, C6H5). 13C NMR (benzene-d6): δ 90.24 (C5H5), δ 52.36 (CH2), δ 127.45,
127.88, 129.00, 129.71, 130.09, 130.33, 138.27 and 139.07 (S-CH2-C6H5). I.R.: v at 1261w,
1225m, 1199m, 1101sh, 1070s, 1029s, 913vw, 865m, 803w, 766s, 758s, 695vs, 661s, 570m,
564m, 467m, 391 w and 384w cm-1 (nujol). Anal. Calcd. for C38H38Mo2S4 : C, 55.7; H, 4.6.
Found : C, 55.4; H, 4.7 %.
(ii)
A yellowish brown fraction eluted with 1:1.5 n-hexane/toluene mixture (18 mL)
which upon concentrated to dryness gave a yellowish brown residue (32 mg). Analysis by 1H
NMR confirmed a mixture of trans-syn and trans-anti isomers of [CpMo(CO)(SBz)]2 (9a and
9b) in approximately 33 and 15% recovery, respectively.
(iii)
A brownish pink fraction eluted with toluene (17 mL) which when concentrated to
dryness gave a brownish pink precipitate of [CpMo(SBz)S]2 (10) (15 mg, 0.024 mmol, 21.6%
yield).
2.6
NMR Tube Reactions. The following reactions were studied in septum-capped 5 mm
tubes under argon via 1H NMR spectral analysis. Product yields were obtained by integration
of Cp resonances in 1H NMR spectrum of product mixture.

2.6.1 Reaction of [CpCr(CO)2]2 (2) with equimolar Bz2S2 at 60 ºC
A deep green solution of [CpCr(CO)2]2 (2) (20.0 mg, 0.058 mmol) with Bz2S2 (14 mg,
0.058 mmol) in benzene-d6 (~0.5 mL) using 5 mm NMR tube was cothermolyzed at 60 °C
1
and its H NMR spectrum recorded at intervals. The final spectrum showed the presence
and approximate yields of [CpCr(CO)2]2S (5), [CpCr(SBz)]2S (7), Cp4Cr4S4 (8) in 28, 4 and
19%, respectively, together with unreacted 2 (9.7% recovery) after 6 h.
2.6.2 Reaction of [CpCr(CO)2]2S (5) with equimolar Bz2S2 at 60 ºC
A dirty brown solution of [CpCr(CO)2]2S (5) (20 mg, 0.053 mmol) with Bz2S2 (13 mg,
0.053 mmol) in benzene-d6 (~0.5 mL) was cothermolyzed at 110 °C. The reaction was
monitored by recording its 1H NMR spectrum at hourly intervals. The final spectrum showed
only the presence of Cp4Cr4S4 (8) (7% yield) together with unreacted [CpCr(CO)2]2S (5)
(67% recovery) after 5 h.
2.6.3 Thermolysis of trans-anti [CpMo(CO)(SBz)]2 (9b)
A yellowish green solution of trans-anti [CpMo(CO)(SBz)]2 (9b) (20.0 mg, 0.030
mmol) in benzene-d6 (~0.5mL), was thermolyzed at 110 °C and was monitored by 1H NMR
hourly. After 8 h, trans-syn [CpMo(CO)(SBz)]2 (9a) (37%), trans-anti [CpMo(CO)(SBz)]2
(9b) (54%), [CpMo(SBz)S]2 (10) (1%) and [CpMo(SBz)2]2 (12) (1%) were recorded in the
1H NMR spectrum. The final spectrum recorded after 14 h shows the presence of 9a (4%),
9b (55% recovery), 10 (4%), [CpMo(CO)(SBz)]2S (11) (1%) and [CpMo(SBz)2]2 (12) (1%).
2.7
Crystals structure determination
Diffraction quality single crystals of [CpCr(SBz)]2S (7) was obtained as dark purple
plate grown in THF layered with ether after one week at ambient temperature; trans anti
[CpMo(CO)(SBz)]2 (9b) was obtained as green polyhedral from a solution of toluene/n-
hexane after three days at ambient temperature; [CpMo(SBz)2]2 (12) were obtained as bright
yellowish orange solids with irregular shape from a solution of toluene/n-hexane after one
week at ambient temperature. X-ray data for 7 was collected on a Bruker SMART
diffractometer while 9b and 12 were collected on a Bruker APEX-II diffractometer,
respectively. Both diffractometer equipped with a CCD area detector, using Mo Kα radiation
(λ = 0.71073Å). The data were corrected for Lorentz and polarization effects with SMART
suite of programs [6] and for absorption effects with the SHELXTL suite of programs [7].

Details of crystal parameters, data collection, and structures refinement are given in Table 1.
Bonding parameters are given in Table 3-5 and table of observed and calculated structure
factors, hydrogen and non hydrogen atomic coordinates and thermal parameters and
anisotropic thermal parameters are available from the authors.

Table 1. Crystal data and structure refinement for 7, 9b and 12.
Complexes
Empirical formula
Formula weight
Temperature(K)
Wavelength(Å)
Crystal system
Space group
Unit cell dimensions
a(Å)
7
C24 H24 Cr2 S3
512.61
223(2)
0.71073
Monoclinic
C 2/c
9b
C26 H24 Mo2 O2 S2
624.45
12
C38 H38 Mo2 S4
814.80
100(2)
0.71073
Monoclinic
P21/c
123(2)
0.71073
Triclinic
P-1
10.0033(10)
12.2554 (12)
18.9255(18)
90
100.605(2)
90
2280.5(4)
10.7994(3)
13.8427 (5)
8.3960(3)
90
110.621(2)
90
8.67740(10)
9.59540 (10)
12.1821(2)
106.6410(10)
97.7990(10)
116.2150(10)
830.323(19)
b(Å)
c(Å)
α(°)
β(°)
δ(°)
Volume(Å3
)
1174.73(7)
Z
4
2
1
Density (Mg/m3)
1.493
1.765
1.630
-1)
1.236
1.267
1.034
Absorption coefficient(mm
F(000)
Crystal size(mm)
Theta range for data collection
1056
0.38 x 0.18 x 0.04
2.19 to 27.50°.
-12<=h<=12
-8<=k<=15
624
0.08 x 0.07 x 0.06
2.50 to 27.50°
-14<=h<=14
414
0.35 x 0.25 x 0.03
1.83 to 27.49°
-11<=h<=11
-12<=k<=11
-10<=l<=15
Index ranges
-17<=k<=17
-10<=l<=10
-24<=l<=24
Reflections collected
7600
14047
3769
Independent reflections
2613 [R(int) = 0.0512]
2691 [R(int) = 0.0904]
3769 [R(int) = 0.0000]
Max. and min. transmission
Data / restraints / parameters
0.9522 and 0.6509
2613 / 146 / 213
1.092
0.9278 and 0.9054
2691 / 0 / 146
1.015
0.9696 and 0.7135
3769 / 128 / 219
1.295
2
Goodness-of-fit on F
Final R indices [I>2sigma(I)]
R indices (all data)
Largest diff. peak and hole
R1 = 0.0697, wR2 = 0.1717
R1 = 0.1014, wR2 = 0.1890
R1 = 0.0467, wR2 = 0.1074
R1 = 0.0744, wR2 = 0.1238
1.001 and -1.202 e.A-3
R1 = 0.0294, wR2 = 0.0876
R1 = 0.0304, wR2 = 0.0881
3.167 and -3.493 e.A-3
-3
0.879 and -0.845 e.Å

3. Results and discussion
3.1 Isolation of [CpCr(SBz)]2S (7)
[CpCr(CO)3]2 (1) reacted with equimolar Bz2S2 under rigorous stirring at ambient
temperature for 13.5 h to give [CpCr(CO)2]2S (5), [CpCr(CO)2(SBz)]2 (6) and [CpCr(SBz)]2S
(7) in 28.8, 42.6 and 11.8 % yield, respectively. A similar reaction at 110 °C for 1 h, gave
[CpCr(CO)2]2S (5) and the final thermolytic product Cp4Cr4S4 (8) in 53.7 and 15.4% yield,
respectively. With its triply-bonded cogener, [CpCr(CO)2]2 (2) reacted under similar
condition gave [CpCr(CO)2]2S (5) and Cp4Cr4S4 (8) in 40.3 and 10.6 % yield, respectively,
together with an uncharacterizable dark brown residue.
3.2
Mechanistic pathways: Formation of [CpCr(SBz)]2S (7)
The products isolated from the reaction of [CpCr(CO)n]2 (n = 2 or 3) with one
equivalent of Bz2S2 are comparatively similar to our previous reactivity studies with Bz2S3
[2a]. It is noteworthy that the only significant difference is the variation in products amount.
Conversely, both Bz2S2 and Bz2S3 ligands exhibited different reactivity towards the
chromium dimer. Reaction of 1 with Bz2S3 was completed after 2 h at ambient temperature
whereas the disulfide ligand requires 13.5 h under similar condition. Apparently, this
observation agrees with the higher dissociation energy of the disulfide ligand (+69 kcal/mole)
as compared to the trisulfide ligand (+46 kcal/mole) reported by Tobolsky et al [8] using Me-
Sn-Me (n = 2, 3 or 4) as reference models (Table 2) and it explains why the bond scission
between the -S-S- linkage is less facile than that of the -S-S-S- linkage [9a-b]. Similar
hypothesis was also raised by Gee [10] where it was suggested that fragments containing
more than one sulfur atom may be stabilized by resonance interaction of the free electron
with the sulfur chain. Using this concept, the preferable fragmentation patterns could be as
following Eq (1-4):-
Me-S-S-Me
Me-S-S-S-Me
Me-S-S-S-S-Me
Me-S-S⋅
2 Me-S⋅
Me-S⋅ + Me-S-S⋅
2 Me-S-S⋅
. . . . Eqn. (1)
. . . . Eqn. (2)
. . . . Eqn. (3)
. . . . Eqn. (4)
Me
S
S
If the Me
S
S fragments are indeed more stable than the Me-S⋅ fragments, then the
predicted ease of cleavage of the polysulfide linkage is in the order of disulfide < trisulfide <
tetrasulfide ~ S8 ~ polymeric sulfur.

Table 2. Dissociation Energies of polysulfide [8]
Compound
Dissociation energy
(kcal/mole)
Me-S-S-Me
69
46
37
33
33
Me-S-S-S-Me
Me-S-S-S-S-Me
S8 (ring)
⋅S-S6-S⋅
⋅S⋅x + ⋅S⋅y
⋅S⋅x+y
The facile nature of this reaction supports the hypothesis that the reaction pathway
proceeds via the 17-electrons CpCr(CO)3· monomeric species generated from 1. The
propensity of 1 to dissociate into these free radicals species in solution is well-documented
[11]. Apparently, S-S bond cleavage by CpCr(CO)3⋅ radicals resulted in the formation of a
pair of Bz-S⋅ fragments. Comparison with a similar reaction with Bz2S3 from previous study
[2a], a substantially lower yield of 5 (29%) with Bz2S2 as compared to 57% with Bz2S3 is
consistent to a lesser availability of free sulfur atoms. It is significant that 7 was not detected
in the NMR reaction of 5 with Bz2S2, which validates that its formation follows an
independent pathway via both decarbonylation and sulfurization processes as shown in
Scheme 1. Further thermal degradation of 6 afforded [CpCr(CO)2]2S (5), [CpCr(SBz)]2S (7)
and ultimately the cubane Cp4Cr4S4 (8) as the final thermolytic product.

CO
OC
Bz2S2
R.T.
CH2
S
CO
CO
Cr
OC
CO
CO
Cr
Cr
.
R.T., 13.5h
Cr
Cr
Toluene
OC
OC
OC
S
CO
CO
CO
CH2
1
6
CO
CO
CH2
S
Bz2S2
i. 60 °C, 6h
ii. 110 °C, 1h
CO
Cr
CO
Cr
Cr
CO
S
Cr
OC
+
Cr
Cr
CO
OC
S
S
5
2
CH2
7
Cr
S
S
Cr
S
Cr
Cr
S
8
Scheme 1. Proposed synthetic pathways for the reaction of [CpCr(CO)3]2 (1) with Bz2S2 at
R.T and [CpCr(CO)2]2 (2) with Bz2S2 at (i) 60 oC and (ii) 110 oC, respectively.
3.3
Isolation of isomeric [CpMo(CO)(SBz)]2 (9a,b) and [CpMo(SBz)2]2 (12).
A reddish brown solution of [CpMo(CO)2]2 (4) in toluene reacts with an equimolar of
Bz2S2 at 70 °C for 7.5 h to give a dark yellowish brown product from which was isolated
trans-syn [CpMo(CO)(SBz)]2 (9a), trans-anti [CpMo(CO)(SBz)]2 (9b), [CpMo(SBz)S]2 (10)
and [CpMo(CO)(SBz)]2S (11) in 43.3, 34.1, 5.5, and 3.1% yield, respectively. Similar
reaction performed at 110 °C for 2 h, gave 9a, trans-anti [CpMo(CO)(SBz)]2 (9b),

[CpMo(SBz)S]2 (10) and [CpMo(CO)(SBz)]2S (11) in 43.6, 41.4, 5.2 and 5.3% yield,
respectively.
3.4
Mechanistic pathways: Formation of isomeric [CpMo(CO)(SBz)]2 (9a & 9b) and
[CpMo(SBz)2]2 (12)
The E-E linkage in the REER (E = S, Se, Te; R = Me, Et, Ph) [12a-e] are easily
cleaved by nucleophilic, electrophilic or radical processes (Eqn. (5)).
R-E-E-R 2 R-E⋅
. . . . Eqn. (5)
In the reaction of [CpMo(CO)2]2 (4) with Bz2S2, it is postulated that the BzS· moiety
generated as in Eqn (5) underwent an electrophilic attack towards the M≡M bonds to form
the thiolato-bridged isomers trans-syn/trans-anti [CpMo(CO)(SBz)]2 (9a & 9b). The trans-
syn isomer converts to the more stable trans-anti isomer when it was slowly cooled to -28 °C
for a couple of days. Both isomers showed markedly different physical properties. The
trans-syn isomer is yellowish brown whereas the trans-anti isomer is yellowish green in color.
This phenomenon was commonly shared by other similar trans-syn/trans-anti complexes of
[(RC5H4)M(CO)(µ-ER’)]2 [M = Mo or W; E = S, Se or Te; R = H, MeCO, MeO2C, EtO2C;
R’ = Me, Ph, Pri and But] [12f-g].
Thermolytic NMR tube reaction of 9b in the presence of Bz2S2 has shown that the
yields of [CpMo(SBz)S]2 (10) and [CpMo(CO)(SBz)]2S (11) were higher as compared to the
thermolysis of 9b alone. This observation indicates the extra free sulfur moiety S· resulted
from the desulfurization process of the Bz2S2 undergoes an electrophilic attack towards the
Mo=Mo bond in 9b to afford 11. Consequently, decarbonylation and sulfurization of 11 in a
concerted manner give 10.
In a similar manner, formation of [CpMo(SBz)2]2 (12) from the co-thermolysis of 9a
or 9b in the presence of Bz2S2 at 110 °C was initiated by decarbonylation coupled with
oxidative insertion of a pair of benzylthiolate moieties across the doubly bonded Mo=Mo
dimer.
The synthetic pathways for products 9a, 9b, 10, 11 and 12 are shown in Scheme 2.

OC
o
120 C
CO
CO
CO
CO
Mo
Mo
Mo
Mo
OC
OC
OC
OC
CO
4
3
o
70 C
Bz S
2
2
CH2
S
H2C
S
H2C
S
CO
CO
OC
CO
S
+
Mo
Mo
9a
+
Mo
Mo
Mo
Mo
S
S
OC
OC
S
CH2
CH2
CH2
(43.3%)
9b (34.1%)
11 (5.5%)
o
110 C
Bz S
2
2
CH2
S
H2C
CH2
S
S
S
11
+
Mo
+
Mo
Mo
Mo
S
S
S
S
CH2
H2C
CH2
10
(3.1%)
(33.2%)
12
Scheme 2. Synthetic pathways of trans-syn/trans-anti [CpMo(CO)(SBz)]2 (9a & b)
[CpMo(SBz)S]2 (10), [CpMo(CO)(SBz)]2S (11) and [CpMo(SBz)2]2 (12)
3.5
Structural studies of 7, 9b and 12
7 crystallized in monoclinic, space group C2/c. A perspective view of 7 is shown in
Figure 1 and the bonding parameters are given in Table 3. The structure is very similar to the
analogous [CpCr(SPh)]2S [13] and Cp2Cr2(S)(SCMe3)2 complexes [14] where the Cr atoms
are in +3 oxidation state. The bond distance between Cr(1)-Cr(2) [2.692 (1) Å] is close to
those in [CpCr(SPh)]2S [2.676 (1) Å] and Cp2Cr2(S)(SCMe3)2 [2.689 (8) Å] complexes but is
much shorter than the singly bonded [CpCr(CO)3]2 [3.281 (1) Å] [15]. This indicates that the
Cr-Cr bond in 7 is doubly-bonded with a 17 e- configuration, which agrees with the proton

paramagnetic chemical shift at δ 13.89 (br, Cp, v = 57 Hz). Comparable to [CpCr(SPh)]2S,
½
each Cr atom in 7 is in an elongated tetrahedral coordination environment, with the Cp ligand
occupying the apical position. The Cr-S (thiolato) bond distance of Cr1-S1 [2.346(2) Å] and
Cr1-S1’ [2.327(2) Å] in 7 is longer than the Cr-S (sulfido) [2.240(3) Å] which is possibly
due to the partial π-back donation at S(1) is enhanced by the aromatic ring of the benzyl
moiety. The two Cp rings are approximately in an eclipsed configuration about the Cr(1)-
Cr(2) bond.
Figure 1. Molecular structure of 7
Table 3. Selected bond lengths [Å] and angles [°] for 7
______________________________________________________________________
Bond length
Cr(1)-Cr(1’)
Cr(1)-S(2)
Cr(1)-S(1)
Cr(1)-S(1’)
2.692(1)
2.240(3)
2.346(2)
2.327(2)
Cr(1’)-S(1)
Cr(1’)-S(1’)
Cr(1’)-S(2)
S(1)-C(6)
2.327(2)
2.346(2)
2.257(2)
1.880(3)
Bond angles
Cr(1’)-Cr(1)-S(1)
Cr(1’)-Cr(1)-S(2)
Cr(1’)-Cr(1)-S(1’)
S(1)-Cr(1)-S(2)
S(1)-Cr(1)-S(1’)
S(2)-Cr(1)-S(1’)
54.50(2)
53.45(2)
55.21(1)
107.66(1)
89.84(3)
84.64(3)
Cr(1)-Cr(1’)-S(1)
Cr(1)-Cr(1’)-S(2)
Cr(1)-Cr(1’)-S(1’)
S(1)-Cr(1’)-S(2)
S(1)-Cr(1’)-S(1’)
S(2)-Cr(1’)-S(1’)
55.17(2)
53.17(1)
55.70(2)
93.89(2)
90.66(2)
84.79(3)
_____________________________________________________________________
Symmetry transformations used to generate equivalent atoms: 1’: -x+1,y,-z+1/2

9b crystallized in monoclinic, space group P21/c. The molecular structure of 9b is
shown in Figure 2 and its bond lengths and bond angles are tabulated in Table 4. 9b consists
of a trans-anti configuration whereby the two carbonyl moieties are in the trans positions
while the two benzylthiolate moieties are in the trans-anti positions. Both the benzyl thiolate
moieties bridge across the two CpMo(CO)- fragments and form a butterfly core complex.
Consequently, 9b comprises
a
similar framework with trans-anti [(η5-
C5H4R)Mo(CO)(SPh)]2 (R = H or MeCO) [16]. The Mo-Mo bond distance 2.5917(8) Å
indicates a double bond and is comparable to those in other dicarbonyl molybdenum
complexes
of
trans-anti
[(η5-MeCOC5H4)Mo(CO)(SPh)]2
(2.609(1)
Å),
cis[CpMo(CO)(SBut)]2 (2.616(2) Å) [12e] and trans-syn [CpMo(CO)(p-PhCH3)]2 (2.6052(8)
Å) and 2.5751(8) Å) [16]. The planar Mo2S2 ring of 9b is also observed in other known
analogues as mentioned above.
Figure 2. Molecular structure of 9b
Table 4. Selected bond lengths [Å] and angles [°] for 9b
________________________________________________________________________
Bond lengths
Mo(1)-C(6)
Mo(1)-C(4)
Mo(1)-C(5)
Mo(1)-C(1)
1.945(5)
2.304(5)
2.321(5)
2.336(5)
Mo(1)-S(1’)
Mo(1)-S(1)
Mo(1)-Mo(1’)
S(1)-C(7)
2.4106(12)
2.4226(13)
2.5917(8)
1.841(5)

Mo(1)-C(3)
Mo(1)-C(2)
2.344(5)
2.365(5)
S(1)-Mo(1’)
O(1)-C(6)
2.4106(12)
1.153(6)
Bond angles
C(6)-Mo(1)-S(1’)
C(6)-Mo(1)-S(1)
S(1’)-Mo(1)-S(1)
C(6)-Mo(1)-Mo(1)#1
S(1’)-Mo(1)-Mo(1’)
S(1)-Mo(1)-Mo(1’)
80.99(15)
87.51(15)
115.14(3)
79.26(16)
57.79(3)
C(7)-S(1)-Mo(1’)
C(7)-S(1)-Mo(1)
Mo(1’)-S(1)-Mo(1)
O(1)-C(6)-Mo(1)
C(8)-C(7)-S(1)
112.34(17)
111.33(17)
64.85(3)
175.0(5)
110.9(3)
57.35(3)
________________________________________________________________________
Symmetry transformations used to generate equivalent atoms: 1’: -x+1,-y+1,-z+1
12 crystallized in triclinic, space group P-1. The molecular structure is illustrated in
Figure 3 and its bond lengths and bond angles are tabulated in Table 5. 12 consists of four
benzylthiolate moieties and two CpMo fragments. Each Mo atom is in a tetragonal-
pyramidal coordination environment with both the cyclopentadienyl groups occupying the
axial positions. The two Mo atoms are bridged by four benzylthiolate groups. The
benzylthiolate moieties of ‘A’ and ‘C’ are in trans-anti arrangement to each other while the
benzylthiolate moieties of ‘B’ and ‘D’ form another pair of trans-anti arrangement ligand in
order to decrease the steric tension and stabilize the molecule. The Mo-Mo bond distance of
2.616 Å is comparable to other known Mo=Mo double bonded complexes [12e, 17].
Figure 3. Molecular structure of 12

Table 5. Selected bond lengths [Å] and angles [°] for 12
_________________________________________________________________________
Bond lengths
Mo(1)-S(1’)
Mo(1)-S(2’)
Mo(1)-S(1)
Mo(1)-S(2)
Mo(1)-Mo(1’)
S(1)-C(6)
2.446(8)
2.441(8)
2.4514(13)
2.4577(13)
2.616(13)
1.841(5)
Mo(1’)-S(1’)
Mo(1’)-S(2’)
Mo(1’)-S(1)
Mo(1’)-S(2)
S(1’)-C(6’)
S(2')-C(13’)
2.480(8)
2.501(8)
2.451(11)
2.458(11)
1.819(9)
1.803(9)
S(2)-C(13)
1.850(5)
Bond angles
S(2')-Mo(1)-S(1’)
Mo(1)-S(1)-Mo(1’)
Mo(1)-S(2)-Mo(1’)
Mo(1)-S(1’)-Mo(1’)
Mo(1)-S(2’)-Mo(1’)
C(6)-(S1)-Mo(1’)
C(6)-S(1)-Mo(1)
74.4(3)
C(6)-S(1’)-Mo(1)
C(6)-S(1’)-Mo(1’)
C(13)-S(2)-Mo(1’)
C(13)-S(2)-Mo(1)
C(13)-S(2’)-Mo(1)
C(13)-S(2’)-Mo(1’)
117.6(4)
117.5(4)
117.69(16)
115.62(16)
119.2(4)
64.40(4)
64.08(4)
64.16(19)
63.9(2)
117.89(15)
116.11(16)
117.6(4)
________________________________________________________________________
Symmetry transformations used to generate equivalent atoms: 1’ -x+1,-y+1,-z+1
4.0
Conclusions
Benzyl disulfide had shown less facile reactivity towards group 6 metal complexes as
compared to its trisulfide congener. Indeed, the study shows the importance of the C-S bond
strength in the formation of different framework of these metal thiolate complexes.
Acknowledgements
The authors acknowledge supports from UTAR (UTARRF 6200/O10) and University of
Malaya (RG024/09AFR and RG235-12AFR) grants for financial support is gratefully
acknowledged.
Appendix A. Supplementary material
CCDC 867164, 867166 and 867167 contain the supplementary crystallographic data for 7, 9b
and 12, respectively. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223–336-033; or e-mail:
deposit@ccdc.cam.ac.uk.

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Highlights
•
•
•
Bibenzyl disulfide showed different reactivity towards CpM(CO)3 [M = Cr (1) or Mo (3)] as
compare to bibenzyl trisulfide.
Reaction of bibenzyl disulfide with Cp2Cr2(CO)6 give a total decarbonylated metal
sulfide complex.
Reaction of bibenzyl disulfide with Cp2Mo2(CO)4 give a pair of isomer complexes
together with a tetra-µ2-SBz Mo complex.
•
All three molecular structures are structurally characterized.
.

Graphical Abstract - graphical
Isolation and characterization of thiolato complexes of [CpCr(SBz)]2S, isomeric trans
[CpMo(CO)(SBz)]2 and [CpMo(SBz)2]2 (Cp = (η5-C5H5), Bz = PhCH2-) from the
reactivity of bibenzyl disulfide towards [CpM(CO)3]2 (M = Cr, Mo)
Mei Lee Ooia,b*, Chu Er Lima, Richard C. S. Wongb and Seik Weng Ngc
aDepartment of Chemical Science, Universiti of Tunku Abdul Rahman, Kampar, Perak, Malaysia
bDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
cSchool of Pharmacy, University of Nottingham, Malaysia
Reaction of [CpM(CO)n]2 [M=Cr (1), or Mo (3)] with an equivalent molar of Bz2S2
led to the isolation of two new isomers of trans syn and anti [CpMo(CO)(SBz)]2 (9a & 9b)
together with six others known products. Cothermolysis of trans syn [CpMo(CO)(SBz)]2 (9a)
with an equivalent molar of Bz2S2 affords another new complex of [CpMo(SBz)2]2 (12).

CO
CO
OC
B z 2 S 2
R .T .
CH
S
2
2
CO
Cr
OC
CO
CO
Cr
Cr
.
R .T ., 1 3 .5 h
Cr
Cr
T o lu e n e
OC
OC
S
CH
OC
CO
CO
CO
1
6
CO
CH
S
2
2
B z 2 S 2
i . 6 0 ° C , 6 h
i i. 1 1 0 ° C , 1 h
CO
CO
Cr
CO
Cr
Cr
S
Cr
OC
+
Cr
Cr
CO
OC
S
S
CO
5
2
CH
7
Cr
S
S
Cr
S
Cr
Cr
S
8
OC
CO
1 2 0 o
C
CO
CO
4
CO
Mo
Mo
Mo
Mo
OC
OC
OC
OC
CO
3
7 0 o
C
B z2S 2
CH
S
2
H 2
C
H 2
C
S
OC
CO
CO
CO
S
S
Mo
Mo
2
B z2 S 2
Mo
Mo
9 a
Mo
Mo
o r
1 1 0 o
C
S
S
S
OC
OC
CH
CH
CH
2
2
1 1 (5 .5 % )
(4 3.15 % )
9 b (3 4.1 % )
B z2S 2
1 1 0 o
C
1 1 0 o
C
CH
2
H 2
C
S
CH
S
2
S
S
Mo
Mo
Mo
+
Mo
S
S
S
S
H 2
C
CH
2
CH
2
1 0
(3 .1 % )
(33 .2 % )
1 2

Graphical Abstract - synopsis
Isolation and characterization of thiolato complexes of [CpCr(SBz)]2S, isomeric trans
[CpMo(CO)(SBz)]2 and[CpMo(SBz)2]2 (Cp = (η5-C5H5), Bz = PhCH2-) from the
reactivity of bibenzyl disulfide towards [CpM(CO)3]2 (M = Cr, Mo)
Mei Lee Ooia,b, Chu Er Lima, Richard C. S. Wongb* and Seik Weng Ngc
aDepartment of Chemical Science, Universiti of Tunku Abdul Rahman, Kampar, Perak, Malaysia
bDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
cDepartment of Chemistry, University of Nottingham, Malaysia
Reaction of [CpM(CO)n]2 [M=Cr (1) or Mo (3)] with an equivalent molar of Bz2S2 led
to the isolation of two new isomers of trans syn and anti [CpMo(CO)(SBz)]2 (9a & 9b)
together with six others known products. Cothermolysis of trans syn [CpMo(CO)(SBz)]2 (9a)
with an equivalent molar of Bz2S2 affords another new complex of [CpMo(SBz)2] (12).
2
7
9b
12