Reactivity of [Mo(CO)3(NCMe)3] towards pyrimidine-2-thiol (pymSH) and thiophenol (PhSH) in the presence of phosphine auxiliaries: Synthesis of mono- and dinuclear complexes bearing κ2 and μ,κ2-pymS coordination

Article abstract of DOI:10.1016/j.poly.2019.02.023

The reaction of [Mo(CO)₃(NCMe)₃] with added thiol in the presence of a phosphine auxiliary has been investigated. Treatment of [Mo(CO)₃(NCMe)₃] with pyrimidine-2-thiol (pymSH) and PPh₃ at 60 °C in MeC

Full text of DOI:10.1016/j.poly.2019.02.023

Accepted Manuscript
Reactivity of [Mo(CO)3(NCMe)3] towards pyrimidine-2-thiol (pymSH) and thi-
ophenol (PhSH) in the presence of phosphine auxiliaries: Synthesis of mono-
and dinuclear complexes bearing κ 2 and µ,κ 2-pymS coordination motifs
Roknuzzaman, S.M. Tareque Abedin, Mohd. Rezaul Haque, Shishir Ghosh,
Derek A. Tocher, Michael G. Richmond, Shariff E. Kabir
PII:
S0277-5387(19)30124-X
https://doi.org/10.1016/j.poly.2019.02.023
POLY 13767
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
8 January 2019
4 February 2019
5 February 2019
Please cite this article as: Roknuzzaman, S.M.T. Abedin, d.R. Haque, S. Ghosh, D.A. Tocher, M.G. Richmond, S.E.
Kabir, Reactivity of [Mo(CO)3(NCMe)3] towards pyrimidine-2-thiol (pymSH) and thiophenol (PhSH) in the
2
2
presence of phosphine auxiliaries: Synthesis of mono- and dinuclear complexes bearing κ and µ,κ -pymS
coordination motifs, Polyhedron (2019), doi: https://doi.org/10.1016/j.poly.2019.02.023
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Reactivity of [Mo(CO)3(NCMe)3] towards pyrimidine-2-thiol (pymSH) and
thiophenol (PhSH) in the presence of phosphine auxiliaries: Synthesis of
mono- and dinuclear complexes bearing 2 and µ,2-pymS coordination motifs
a
a
a
a,
Roknuzzaman , S.M. Tareque Abedin , Mohd. Rezaul Haque , Shishir Ghosh *, Derek
A. Tocher b, Michael G. Richmond c, Shariff E. Kabir a,*
a Department of Chemistry, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh
b Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ,
UK
c Department of Chemistry, University of North Texas, 1155 Union Circle, Box 305070, Denton,
TX 76203, USA
*Corresponding authors.
E-mail addresses: sghosh_006@yahoo.com (S. Ghosh); skabir_ju@yahoo.com (S.E. Kabir)
Abstract
The reaction of [Mo(CO)3(NCMe)3] with added thiol in the presence of a phosphine
auxiliary has been investigated. Treatment of [Mo(CO)3(NCMe)3] with pyrimidine-2-thiol
(pymSH) and PPh3 at 60 C in MeCN afforded the known mononuclear compounds cis-
[Mo(CO)4(PPh3)2] (1) and [Mo(к2-pymS)4] (2), and the new binuclear compound
[Mo2(CO)4(μ,к2-pymS)2(PPh3)2] (3), which possesses an idealized C2 symmetry. A different
product distribution was found when dppm was employed as the phosphine ligand. Of the five
reaction products isolated, three consisted of mononuclear compounds, [Mo(CO)4(к2-dppm)] (4),
[Mo(CO)3(2-dppm)(1-dppm)] (5) and [Mo(CO)(к2-pymS)2(к2-dppm)] (6), with the remaining
two products corresponding to dinuclear compounds, [Mo2(CO)6(μ,к1-pymS)2(μ,к2-dppm)] (7)
and [Mo2(CO)4(μ,к2-pymS)2(к2-dppm)] (8). Products 6-8 are new and have been fully
characterized in solution by IR and NMR spectroscopy, and by X-ray crystallography in the case
of 6 and 7. The reaction of [Mo(CO)3(NCMe)3] with PhSH and dppm at 60 C in MeCN was
1

also examined to assess the effect of thiol on the product distribution. The two principal products
isolated were identified as the mononuclear compound [Mo(CO)2(κ1-PhS)2(κ2-dppm)] (9) and
the dinuclear compound [Mo2(CO)6(μ,κ1-PhS)2(μ,κ2-dppm)] (10). The bonding in compounds 3,
6 and 7 was also examined by DFT, and highlights between the computational and experimental
structures are discussed.
Keywords: Mono- and di-molybdenum complexes; Thiol activation; Phosphine mediators; X-ray
structures; DFT.
1. Introduction
Reactions of heterocyclic thiols with transition metal complexes have been widely
investigated over the past four decades since the resultant complexes often show exotic structural
motifs due to the ability of these ligands to display a diverse range of coordination modes at
mono- and polynuclear metal centers [1-6]. Consequently, our group and others have also been
studying the reactivity of these heterocyclic thiols with low-valent metal carbonyls over the years
which reveal that the output of these reactions depends on both the structure of these thiols and
the intrinsic reactivity of the metal carbonyls [4-14]. However, in comparison to the number of
Group 7 and 8 metal carbonyl complexes bearing these ligands [5-12], only a few examples of
Group 6 metal carbonyl complexes containing these ligands have been reported [13-18]. In 1990,
Deeming et al. reported the synthesis of the seven-coordinate complexes [M(CO)3(2-pyS)2] (M
= Mo, W) from the direct reactions of [M(CO)3(NCMe)3] with pySH, along with the phosphine
derivative Mo(CO)2(PMe2Ph)(2-pyS)2 [15]. More recently, Shi and co-workers reported that the
reaction of [Mo(CO)3(NCMe)3] with pySH and PPh3 that gave predominantly the dimolybdenum
complexes [Mo2(CO)5(μ,к2-pymS)2(PPh3)] and [Mo2(CO)4(μ,к2-pymS)2(PPh3)2], in addition to a
trace amount of the mixed-valence trimolybdenum complex [Mo3(CO)6(μ,к2-pymS)2(μ3,к2-
pymS)2] [19]. On the contrary, the reaction of [Mo(CO)3(NCMe)3] with pySH and dppm
afforded predominantly the binuclear compound [Mo2(CO)4(μ-κ2-pyS)2(κ2-dppm)] and two
mononuclear complexes [Mo(CO)(κ2-PhS)2(κ2-dppm)] and [Mo(CO)4(κ2-dppm)] (Scheme 1).
2

Scheme 1. Reactions of [Mo(CO)3(NCMe)3] with pySH in the presence of the phosphine
auxiliaries PPh3 and dppm.
In the above scheme, the pyS ligand displays a µ,2 coordination mode in each of the
polynuclear pyS-substituted derivatives. The observed products are also influenced by the nature
of the phosphine ligand, and we suspect that the phosphine auxiliary ligand plays a crucial role in
helping to determine the ratio of dinuclear to mononuclear products. The monodentate PPh3
ligand permits higher order coordination of the pySH ligand relative to dppm, which in turn
favors the formation of di- or even trinuclear complexes. This structural diversity has inspired us
to investigate further the reactivity of [Mo(CO)3(NCMe)3] with the thiols pymSH and PhSH in
the presence of phosphine auxiliary ligands, the results of which are discussed in this
contribution.
2. Experimental section
2.1. General procedures
3

All reactions were performed under a nitrogen atmosphere using standard Schlenk
techniques, unless otherwise stated. Reagent grade solvents were freshly distilled using an
appropriate drying agent prior to use. Infrared spectra were recorded on a Shimadzu IR Prestige-
21 spectrophotometer, while the NMR spectra were recorded on a Bruker DPX 400
spectrometer. All chemical shifts are reported in δ units and are referenced to the residual
protons of the deuterated solvent (1H) and external 85% H3PO4 (31P), as appropriate. Elemental
analyses were performed by the Microanalytical Laboratories of Wazed Miah Science Research
Center at Jahangirnagar University. The reactions products were separated in the air by TLC
plates coated with 0.25 mm of silica gel (HF254-type 60, E. Merck, Germany). Me3NO2H2O
was purchased from Lancaster Chemical. The waters of hydration were removed using a Dean-
Stark apparatus by azeotropic distillation from benzene. The anhydrous Me3NO was stored under
N2. The chemicals dppm, PPh3, pyrimidine-2-thiol and thiophenol were purchased from Sigma-
Aldrich Chemical Co. and used as received. [Mo(CO)3(NCMe)3] was prepared from [Mo(CO)6]
according to a literature method [20]. The calculated yields of the isolated products are based on
[Mo(CO)3(NCMe)3].
2.2. Reaction of [Mo(CO)3(NCMe)3] with pymSH and PPh3
PPh3 (210 mg, 0.801 mmol) and pymSH (90 mg, 0.802 mmol) were added to an MeCN
solution (15 mL) of [Mo(CO)3(NCMe)3] (120 mg, 0.396 mmol) at 60 C and the reaction was
then stirred for 2 h, during which time the color of the solution changed from yellow to red. The
solvent was removed under reduced pressure, the residue was dissolved in a minimum volume of
CH2Cl2 and separated by TLC on silica gel. Elution with hexane/acetone (7:3, v/v) developed
several bands, of which the first three bands were identified as [Mo(CO)6], pymSH and PPh3, in
order of elution. The fourth and fifth bands yielded the known compounds cis-[Mo(CO)4(PPh3)2]
(1) (94 mg, 32%) and [Mo(к2-pymS)4] (2) (64 mg, 30%), whilst the sixth band afforded the new
compound [Mo2(CO)4(μ,к2-pymS)2(PPh3)2] (3) (54 mg, 26%) as black crystals after
crystallization from hexane/CH2Cl2 at 4 C.
4

Analytical and spectral data for 3: Anal. Calc. for C48H36Mo2N4O4P2S2: C, 54.86; H,
3.45; N, 5.33. Found: C, 55.22; H, 3.49; N, 5.39%. IR (ν(CO), CH2Cl2, cm-1): 1920vs, 1845s. 1H
31
NMR (CDCl3, δ, ppm): 7.65 (m, 12H), 7.34 (m, 20H), 6.42 (m, 2H), 5.67 (m, 2H). P{1H}
NMR (CDCl3, δ, ppm): 54.8 (s).
2.3. Reaction of [Mo(CO)3(NCMe)3] with pymSH and dppm
The reactants pymSH (180 mg, 1.605 mmol) and dppm (294 mg, 0.765 mmol) were
added to an acetonitrile solution (15 mL) of [Mo(CO)3(NCMe)3] (230 mg, 0.759 mmol) at 60 C,
and the solution was stirred for an additional 2 h. Upon cooling, the solvent was removed under
reduced pressure, the resulting residue was dissolved in a minimum volume of CH2Cl2 and
purified by chromatography over silica gel. Elution with hexane/acetone (7:3, v/v) developed
several bands which afforded, in order of elution, the known compounds [Mo(CO)4(κ2-dppm)]
(4) (41 mg, 9%) and [Mo(CO)3(к2-dppm)(к1-dppm)] (5) (26 mg, 4%), and the new compounds
[Mo(CO)(к2-pymS)2(к2-dppm) (6)] (52 mg, 9%) as red crystals, [Mo2(CO)6(μ,к1-pymS)2(μ,к2-
dppm)] (7) (80 mg, 22%) as dark red crystals and [Mo2(CO)4(μ,к2-pymS)2(к2-dppm)] (8) (20 mg,
6%) as orange crystals after recrystallization from hexane/CH2Cl2.
Analytical and spectral data for 6: Anal. Calc. for C34H28MoN4OP2S2: C, 55.89; H, 3.86;
1
N, 7.67. Found: C, 56.05; H, 3.92; N, 7.72%. IR (υ(CO), CH2Cl2, cm-1): 1805vs. H NMR
(CDCl3, δ, ppm): 8.93 (m, 1H), 8.31 (m. 1H), 8.19 (m, 2H), 7.80 (m, 8H), 7.55 (m, 7H), 7.20 (m,
31
1H), 6.98 (m, 4H), 6.80 (m, 1H), 6.50 (m, 1H), 4.24 (m, 2H). P{1H} NMR (CDCl3, δ, ppm):
28.6 (s).
Analytical and spectral data for 7: Anal. Calc. for C39H28Mo2N4O6P2S2: C, 48.46; H,
2.92; N, 5.80. Found: C, 48.79; H, 2.95; N, 5.86%. IR (υ(CO), CH2Cl2, cm-1): 2022m, 1980vs,
1
1943m, 1921m, 1869w. H NMR (CD2Cl2, δ, ppm): 8.55 (m, 5H), 7.35 (m, 7H), 7.20 (m, 9H),
7.00 (m, 3H), 5.33 (m, 2H), 2.38 (m, 2H). 31P{1H} NMR (CD2Cl2, δ, ppm): 19.6 (s).
Analytical and spectral data for 8: Anal. Calc. for C37H28Mo2N4O4P2S2: C, 48.80; H,
3.10; N, 6.15. Found: C, 49.06; H, 3.16; N, 6.22%. IR (υ(CO), CH2Cl2, cm-1): 1958vs, 1886w,
1
1850s. H NMR (CDCl3, δ, ppm): 8.82 (d, J 4.8 Hz, 1H), 8.46 (d, J 4.8 Hz, 1H), 8.04 (m, 4H),
7.78 (m, 3H), 7.67 (m, 2H), 7.54 (m, 4H), 7.40 (m, 2H), 7.37 (m, 3H), 6.92 (m, 4H), 5.51 (m,
5

2H), 5.20 (m, 1H), 4.59 (m, 1H). 31P{1H} NMR (CDCl3, δ, ppm): 18.7 (d, J 20 Hz 1P), δ 16.8 (d,
J 20 Hz 1P).
2.4. Reaction of Mo(CO)3(NCMe)3 with PhSH and dppm
To an acetonitrile solution (15 mL) of [Mo(CO)3(NCMe)3] (230 mg, 0.759 mmol) at 60 C
was added sequentially thiophenol (178 mg, 1.62 mmol) and dppm (294 mg, 0.765 mmol). The
reaction was stirred for 2 h, after which time the solution was allowed to cool to room
temperature before the solvent was removed under reduced pressure. Compounds 9 and 10 were
subsequently isolated by TLC using hexane/acetone (7:3, v/v) as the eluent. [Mo(CO)2(κ1-
PhS)2(κ2-dppm)] (9) (72 mg, 13%) was isolated as yellow crystals and [Mo2(CO)6(μ,κ1-
PhS)2(μ,κ2-dppm)] (10) (40 mg, 11%) was isolated as red crystals.
Analytical and spectral data for 9: Anal. Calc. for C39H32MoO2P2S2: C, 62.07; H, 4.27.
Found: C, 62.42; H, 4.34%. IR (υ(CO), CH2Cl2, cm-1): 1896vs. 1H NMR (CD2Cl2, δ, ppm): 7.50
31
(m, 6H) 7.40 (m, 16H), 7.28 (m, 1H), 7.15 (m, 7H), 3.96 (m, 1H), 3.81 (m, 1H). P{1H} NMR
(CD2Cl2, δ, ppm): 12.2 (s).
Analytical and spectral data for 10: Anal. Calc. for C43H32Mo2O6P2S2: C, 53.65; H, 3.35.
1
Found: C, 53.89; H, 3.41%. IR (υ(CO), CH2Cl2 , cm-1): 2021s, 1973vs, 1913s cm-1. H NMR
(CD2Cl2, δ, ppm): 7.84 (d, J 7.6 Hz, 4H), 7.30 (m, 10H), 7.20 (m, 16H), 2.42 (t, J 9.4 Hz, 2H).
31P{1H} NMR (CDCl3, δ, ppm): 17.7 (s).
2.5. X-ray crystallography
Single crystals of 3, 6, 7 and 9 suitable for X-ray diffraction analysis were grown by slow
diffusion of hexane into a CH2Cl2 solution. Suitable crystals were mounted on an Agilent Super
Nova dual diffractometer (Agilent Technologies Inc., Santa Clara, CA) using a Nylon loop with
an inert oil and the diffraction data were collected at 150(1) K using Mo-Kα radiation (λ =
0.71073 Å). Unit cell determination, data reduction and absorption corrections were carried out
using CrysAlisPro [21]. The structures were solved with the ShelXS [22] structure solution
program by direct methods and refined by full-matrix least-squares on the basis of F2 using
6

ShelXL [22,23] within the OLEX2 [24] graphical user interface. Non-hydrogen atoms were
refined anisotropically and hydrogen atoms were included using a riding model. Pertinent
crystallographic parameters are given in Table 1.
2.5. Computational methodology
All calculations were performed with the hybrid meta exchange-correlation functional
M06 [25], as implemented by the Gaussian 09 program package [26]. The molybdenum atoms
were described by Stuttgart–Dresden effective core potentials (ecp) and an SDD basis set [27],
while the 6-31G(d′) basis set was employed for the remaining atoms. The reported geometries
were fully optimized and the analytical second derivatives were evaluated and found to possess
only positive eigenvalues. A scaling factor of 0.94 was employed in the vibrational analysis of
the (CO) band in B. The natural charges and Wiberg indices were computed using Weinhold’s
natural bond orbital (NBO) program (version 3.1) [28,29]. The geometry-optimized structures
have been drawn with the JIMP2 molecular visualization and manipulation program [30].
3. Results and discussion
3.1. Synthesis of dinuclear [Mo2(CO)4(μ,к2-pymS)2(PPh3)2] (3)
The one pot reaction between [Mo(CO)3(NCMe)3], pyrimidine-2-thiol (pymSH) and PPh3
in acetonitrile at 60 C furnished a ternary mixture of compounds with the known mononuclear
compounds cis-[Mo(CO)4(PPh3)2] (1) and [Mo(к2-pymS)4] (2), isolated in 32 and 30% yield,
respectively [31,32]. The dinuclear complex [Mo2(CO)4(μ,к2pymS)2(PPh3)2] (3) is new and was
isolated as a black crystalline solid in 26% yield. This reaction is illustrated in Scheme 2.
7

Scheme 2. Reaction of [Mo(CO)3(MeCN)3] with pymSH and PPh3
An ORTEP plot depicting the molecular structure of 3 is shown in Fig. 1, together with
selected bond distances and bond angles. The asymmetric unit also contains a half dimer, which
is completed through space group symmetry. The molecule consists of two [Mo(CO)2(PPh3)]
fragments linked by a Mo-Mo bond and by two doubly-bridging pymS ligands. The
Mo(1)‒Mo(2) bond distance of 2.9552(4) Å in 3 is consistent with its single bond designation
and is comparable to the Mo-Mo distance in the related dinuclear compounds [Mo2(CO)4(μ,к2-
pyS)2(PPh3)2] [2.974(1) Å] [19] and [Mo2(CO)4(μ,к2-pyS)2(к2-dppm)] [2.9775(5) Å] [14]. There
is a crystallographically imposed two-fold rotational axis through the middle of the Mo-Mo bond
and perpendicular to the Mo2S2 ring, which is non-planar with a dihedral angle of 17.73º between
the Mo(1)Mo(2)S(1) and Mo(1)Mo(2)S(2) planes. Each pymS ligand functions as a chelating
ligand with sulfur and nitrogen coordination to one metal center in addition to bridging the
adjacent molybdenum center via the sulfur group. The metric parameters for the bridging of both
metals by the sulfur moieties are similar to those distances and angles reported for the related
derivative [Mo2(CO)4(μ,к2-pyS)2(PPh3)2] [19]. The two pyrimidine rings are on the same side of
the Mo2S2 skeleton, and each molybdenum center is six-coordinate and exhibits a slightly
distorted octahedral geometry due to the constraints imposed on the metals by the two pymS
ligands. The Mo(1)‒S(1) bond distance [2.5587(10) Å] is 0.0638 Å longer than the Mo(1)‒S(2)
[2.4949(10) Å] bond distance. The average Mo‒N [2.258(3) Å] and Mo‒S [2.4817(8) Å] bond
8

distances in 3 are comparable to the corresponding Mo‒N and Mo‒S bond distances in
[Mo2(CO)4(μ,к2-pyS)2(PPh3)2] [2.261(5) and 2.479(2) Å] [19].
Place Figure 1 Here
The bonding in 3 was examined by electronic structure calculations and the DFT-
optimized structure A is depicted alongside the experimental structure in Fig. 1. Good agreement
between the two structures is noted and the computed Mo‒Mo bond distance of 2.9960 Å closely
matches the experimental Mo‒Mo bond distance [2.9552(4) Å]. The computed Wiberg bond
index (WBI) for the Mo-Mo bond is 0.57, a value consistent with the existence of a metal-metal
single bond in A. The WBI for the Mo-Mo bond in A is similar in magnitude to the WBIs
computed by us for the dinuclear molybdenum compounds trans-[Cp2Mo2(O)(CO)(PPh3)2] and
[Mo2(O)(CO)2(,2-edt)2(2-dppm)] (cis and trans isomers) that exhibit a Mo‒Mo bond order of
one [33]. The Mo‒S bonds display a mean WBI of 0.71, confirming the symmetrical bonding of
each bridging thiolate group to the dimolybdenum core. The molybdenum and nitrogen atoms in
A are electron rich based on Q values of -1.43 (Mo), -0.45 (coordinated N) and -0.48 (free N),
while the bridging thiolate and phosphine atoms are electron poor based on Q values of 0.42 and
1.32, respectively. The computed charges for the latter groups are similar to the values reported
for the isomeric [Mo2(O)(CO)2(,2-edt)2(2-dppm)] [33].
The spectroscopic data recorded for 3 are fully consistent with the solid-state structure.
The IR spectrum shows two strong CO absorptions at 1920 and 1845 cm-1 that closely align with
the computed values of 1900 and 1848 cm-1 found for species A which correspond to the
1
vibrationally coupled symmetric and antisymmetric (CO) bands. The H NMR spectrum
exhibits multiplets at δ 7.65, 7.34, 6.42, and 5.67 ppm, corresponding to the aryl hydrogen atoms
31
of the pyrimidine and phosphine moieties. The P{1H} NMR spectrum exhibits a singlet at δ
54.8 ppm, confirming the presence of equivalent PPh3 groups.
3.2. Synthesis of the mononuclear complex [Mo(CO)(к2-pymS)2(к2-dppm)] (6) and the dinuclear
complexes [Mo2(CO)6(μ,к1-pymS)2(μ,к2-dppm)] (7), and [Mo2(CO)4(μ,к2-pymS)2(к2-dppm)] (8)
9

Use of the diphosphine dppm in place of PPh3 in the reaction of [Mo(CO)3(MeCN)3] with
pymSH led to a different series of products. Heating the three reactants in acetonitrile at 60 C
furnished the known compounds [Mo(CO)4(κ2-dppm)] (4) [34] and [Mo(CO)3(к2-dppm)(к1-
dppm)] (5) [35] in 9 and 4% yields, respectively, along with the new compounds [Mo(CO)(к2-
pymS)2(к2-dppm)] (6), [Mo2(CO)6(μ,к1-pymS)2(μ,к2-dppm)] (7) and [Mo2(CO)4(μ,к2-pymS)2(к2-
dppm)] (8) in 9, 22 and 6% yields, respectively (Scheme 3). Since the formation of 8 could arise
from the loss of CO ligands and rearrangement of the dppm ligand in 7, we performed a control
experiment using isolated 7. Heating 7 at 60 °C in MeCN revealed no evidence for the formation
of 8, monitoring the reaction by TLC and IR spectroscopy; these data support independent
pathways for the formation of these two products.
Scheme 3. Synthesis of [Mo(CO)(к2-pymS)2(к2-dppm)] (6), [Mo2(CO)6(μ,к1-pymS)2(μ,к2-
dppm)] (7), and [Mo2(CO)4(μ,к2-pymS)2(к2-dppm)] (8).
The ORTEP diagram of the molecular structure of [Mo(CO)(к2-pymS)2(к2-dppm)] (6),
shown in Fig. 2, confirms the mononuclear nature of the product and the seven-coordinate
geometry at the molybdenum center. Selected bond distances and bond angles for 6 are given in
the figure caption. The molecule is coordinatively saturated based on a count of 18-valence
10

electrons where the CO and the chelating dppm and pymS ligands contribute a total of 12e to the
overall electron count. The structure of 6 is best viewed as a pentagonal bipyramid whose ligand
arrangement about the metal center is not unlike that found in [Mo(CO)(κ2-pyS)2(κ2-dppm)] [14]
and [Mo(CO)(κ2-pyS)2(κ2-dppe)] [14]. The Mo‒S, Mo‒N and Mo‒P bond distances in 6 are
consistent with the values reported for [Mo(CO)(κ2-pyS)2(κ2-dppm)] [14] and [Mo(CO)(κ2-
pyS)2(κ2-dppe)] [14]. The CO ligand is roughly trans to one of the coordinating nitrogen atoms
of the 2-pymS ligand [C(1)–Mo(1)–N(3) 166.67(15)°], and the remaining five donor atoms
form a nearly planar pentagon arrangement of atoms. The deviation from planarity of the
pentagonal base can be best described in terms of the location of the S(2) atom, which lies 1.094
Å below the mean plane constituted by the remaining four atoms S(1), N(1), P(1) and P(2). The
Mo(1)‒N(1) bond distance [2.223(3) Å] that is “trans” to the phosphorus atom P(2) atom is
0.044 Å shorter than the corresponding Mo(1)‒N(3) bond distance. The mean bite angle
[N(1)‒Mo(1)‒S(1) and N(2)‒Mo(1)‒S(2)] for the chelating pymS ligand of 64.40° is
unremarkable relative to related compounds containing a 2-pymS ligand [14,15,19].
Place Figure 2 Here
Compound 6 was also examined by DFT, and the M06-optimized structure B is depicted
in Fig. 2 (right). The distribution of the ligands about B is similar to that found in the
experimental structure and this confirms the pentagonal bipyramid as a stable ground-state
minimum. The computed (CO) stretch for the lone CO group of 1814 cm-1 is in good agreement
with the experimental value of 1805 cm-1, whose low frequency underscores the high degree of
electron donation of the other ligands to the molybdenum center. The molybdenum and nitrogen
atoms are electron rich with an atomic charge of -1.32 for the metal and a mean Q value of -0.48
for the four nitrogen atoms. The sulfur and phosphine ligands display a positive charge with an
average charge of 0.10 and 1.38 for the sulfur and phosphorus centers, respectively.
An ORTEP plot depicting the molecular structure of 7 is shown in Fig. 3, whose caption
contains selected bond distances and bond angles. The molecule consists of a dinuclear core of
two molybdenum atoms that are bridged by the dppm and a pair of pymS ligands. The
heterocyclic thiolates coordinate the two molybdenum centers via the thiolate moieties. The
11

dppm ligand lies orthogonal to the plane defined by the bridging thiolate ligands and the two
metal centers. There is a crystallographically imposed two-fold axis of rotation through the
middle of the Mo-Mo bond, perpendicular to the Mo2S2 ring. The Mo2S2 square is essentially
planar, based on a dihedral angle of 5.79º that is formed between the Mo1Mo2S1 and Mo1Mo2S2
planes. The pymS ligands function as 3e donors that promote the union of both metals via a
common edge in the edge-bridged bioctahedron. Here each metal is best viewed as a Mo(I)
center, and the observed diamagnetism supports the presence of a Mo-Mo single bond, which is
slightly longer [2.9959(2) Å] than that in 3 [2.9552(4) Å]. The Mo‒P bond distances in 7
[Mo(1)‒P(1) 2.5543(5) and Mo(2)‒P(2) 2.5659(5) Å] are somewhat longer than that observed in
the dinuclear complex 3 [av. 2.4859(8) Å], while the Mo‒S bond distances in 7 [av. 2.4670(5) Å]
are quite similar to those found in 3 [2.4817(8) Å].
Place Figure 3 Here
The DFT-optimized structure C (Fig. 3) reproduces the important structural features
found in the experimental structure. The atomic charges for the Mo, S, N and P atoms parallel
the data in A, with the electron-rich Mo and N centers revealing mean Q values of -1.85 and -
0.51, respectively. The S and P centers are electron poor and exhibit an average charge of 0.43
and 1.30, respectively. The WBI of 0.46 is comparable to the value reported for compound A and
is in concert with a Mo-Mo single bond in C.
The spectroscopic data recorded for 7 are consistent with the solid-state structure, and the
1
IR spectrum verifies the presence of only terminal CO ligands. The H NMR spectrum reveals
several multiplets centered at δ 8.55, 7.35, 7.20, 7.00 and 5.33 ppm, corresponding to the aryl
1
hydrogen atoms of the pyrimidine and dppm aromatic groups. The high-field H multiplet at 
2.38 ppm is ascribed to the diastereotopic methylene hydrogen atoms of the dppm ligand. The
31P{1H} NMR spectrum exhibits a singlet at δ 19.6 ppm that supports the symmetrical
coordination of the Mo2 frame by the diphosphine ligand.
Attempts to grow single crystals of complex 8 were unsuccessful and the identity of this
product was established by spectroscopic and analytical methods. The spectroscopic data are
12

consistent with the formulated structure for complex 8 (Scheme 3) that is isostructural with the
dinuclear compound [Mo2(CO)4(μ,к2-pyS)2(к2-dppm)], where one of the molybdenum centers
supports a chelating dppm ligand [14]. The combustion data agree with [Mo2(CO)4(μ,к2-
pymS)2(к2-dppm)] composition for 8 and the IR spectrum (1958, 1886 and 1850 cm-1) reveals
nearly identical stretching frequencies for the (CO) bands compared to the IR spectrum reported
for [Mo2(CO)4(μ,к2-pyS)2(к2-dppm)] (1954, 1882 and 1846 cm-1) [14]. The 31P{1H} NMR
spectrum exhibits two closely spaced doublets at δ 18.7 and 16.8 ppm that display a geminal
coupling (2JPP) of 20 Hz, supporting the existence of inequivalent phosphorus centers. The
31
recorded P chemical shifts and the magnitude of the P-P coupling are virtually identical to the
31P NMR data reported for the dppm-chelated relative [Mo2(CO)4(µ,2-pyS)2(2-dppm)] [14].
Complex 8 contains 34 valence electrons and one of the metal centers comprising the [Mo2(µ,2-
pymS)2] frame is ligated by a chelating dppm ligand analogous to that found in [Mo2(CO)4(μ,к2-
pyS)2(к2-dppm)].
3.3. Synthesis of [Mo(CO)2(κ1-PhS)2(κ2-dppm)] (10) and [Mo2(CO)6(μ,κ1-PhS)2 (μ,κ2-dppm)] (9)
The role played, if any, by the pymSH reactant in controlling the product distribution was
examined by repeating the reaction using PhSH in place of PymSH. Treatment of
[Mo(CO)3(MeCN)3] with PhSH and dppm at 60 C furnished the thiolate-substituted compounds
[Mo(CO)2(κ1-PhS)2(κ2-dppm)] (9) and [Mo2(CO)6(μ,κ1-PhS)2(μ,κ2-dppm)] (10) in 13 and 11%
yields, respectively (Scheme 4) as the major isolable products of the reaction. The identity of
both products was assigned through a combination of spectroscopic, combustion and
crystallographic methods. We note that the TLC plate exhibited much streaking and there was an
extensive amount of a red-brown colored material that remained at the origin and whose nature
was not established.
13

Scheme 4. Synthesis of [Mo(CO)2(κ1-PhS)2(κ2-dppm)] (9) and [Mo2(CO)6(μ,κ1-PhS)2(μ,κ2-
dppm)] (10).
The unequivocal identity of 9 was established by X-ray crystallography. The ORTEP plot
depicting the molecular structure of 9 is shown in Fig. 4, together with selected bond distances
and bond angles. Complex 9 contains a single, six-coordinate molybdenum center whose
geometry is best viewed as an octahedron, as opposed to a trigonal prismatic geometry exhibited
by numerous Group 6 M(CO)2P2S2 (where P and S = monodentate phosphine and thiolate
ligands) and M(CO)2(PP)(SS) derivatives (where PP and SS = chelating diphosphine and
dithiolate ligands) [14,15,18,36]. The geometry displayed by this genre of d4 complexes is
sensitive to the steric properties and coordination mode adopted by the ancillary phosphine and
thiolate ligands. Hoffmann and co-workers have investigated the theoretical underpinnings for
the octahedral ⇌ trigonal prism transformation where the energetic preference for d4 isomers is
small and the thermodynamically favored species is controlled by secondary ligand effects [37].
Relative the chelating dppm ligand, the two PhS moieties adopt sites in the equatorial plane trans
to the diphosphine ligand. Each CO group occupies an axial site within the octahedron and they
are consequently oriented trans to each other. Both sulfur atoms lie trans to one phosphorus
atom [S(1)‒Mo(1)‒P(1) 155.20(4)°; S(2)‒Mo(1)‒P(2) 156.16(4)°] and cis to the pnictogen donor
[S(1)‒Mo(1)‒P(2) 89.31(4); S(2)‒Mo(1)‒P(1) 90.14(4)°]. The angular arrangement of the S and
14

P ligands in the equatorial plane, along with the C(1)‒Mo(1)‒C(2) bond angle of 178.68(18)°,
strongly support an octahedral environment at the molybdenum center in 9. The mean Mo‒P
[2.5244(10) Å] and Mo‒S [2.3668(12) Å] bond distances in 9 are very similar to those reported
for related molybdenum complexes of the general formula [Mo(CO)2(PR3)2(к2-SR′S)2] [38].
Place Figure 4 Here
The recorded IR and NMR spectroscopic data for 9 are consistent with the solid-state
structure. The IR spectrum exhibits a single carbonyl stretching band at 1896 cm-1, and the aryl
hydrogen atoms of the dppm and PhS ligands appear in the 1H NMR spectrum as four multiplets
at δ 7.50, 7.40, 7.28 and 7.15 ppm, with a relative intensity of 6:16:1:7. The two multiplets
centered at δ 3.96 and 3.81 ppm, each integrating for one hydrogen atom, are assigned to the
diastereotopic methylene protons of the dppm ligand. The observation of two distinct multiplets
for the methylene moiety indicates that any potential ring flipping with the dppm chelate is slow
and that the “puckered” four-membered ring defined by the C(27)‒P(1)‒Mo(1)‒P(2) atoms
maintains its orientation in solution. Finally, the phosphorus atoms of the dppm ligand are
equivalent based on the appearance of a single 31P resonance at δ 12.2 ppm in the 31P{1H} NMR
spectrum.
Despite repeated attempts to grow single crystals of 10 for analysis by X-ray
crystallography, we could not grow publication-acceptable crystals. However, we were able to
establish the gross structural composition of 10 using a set of poor quality crystals [39]. The
crude diffraction data revealed a Mo2 core with bridging thiolate and dppm groups, in a fashion
similar to that exhibited by compound 7. The pattern and frequencies of the (CO) bands in the
IR spectrum of 10 match the spectral data for 7 and support the formulated structure of 10 that is
1
depicted in Scheme 3. The recorded H and 31P NMR data, which are summarized in the
experimental section, are in concert with the asserted composition of 10.
4. Conclusions
15

We have synthesized new mono- and dinuclear thiolate-substituted compounds through a
series of one-pot syntheses. The new compounds have the potential to serve as novel substrates
in redox and photophysical studies involving non-innocent thiolates utilized in light harvesting
and proton-reduction chemistry. The new compound [Mo2(CO)4(μ,к2-pymS)2(к1-PPh3)2] (3),
bearing C2 symmetry, was obtained as one of the three products from the reaction of
[Mo(CO)3(NCMe)3] with pymSH and PPh3 at 60 C. On the other hand, the analogous reaction
involving [Mo(CO)3(NCMe)3] and pyrimidine-2-thiol in the presence of the the diphosphine
dppm gave a total of six products, from which the new compounds [Mo(CO)(к2-pymS)2(к2-
dppm)] (6), [Mo2(CO)6(μ,к1-pymS)2(μ,к2-dppm)] (7) and [Mo2(CO)4(μ,к2-pymS)2(к2-dppm)] (8)
have been isolated. The striking difference between 7 and 8 is the different coordination mode
adopted by the dppm ligand. The dppm ligand functions as a bridging ligand in 7 and as a
chelating ligand in 8. Repeating the last reaction with PhSH in place of pymSH affords a binary
product mixture consisting of [Mo(CO)2(κ1-PhS)2(κ2-dppm)] (9) and [Mo2(CO)6(μ,κ1-PhS)2(μ-
κ2-dppm)] (10). Future studies using different thiols and phosphines are planned in the hope of
determining the precise role played by the ancillary ligands in controlling the product
distribution in these reactions.
Acknowledgments
This research has been sponsored by the Ministry of Science and Technology,
Government of the People’s Republic of Bangladesh. MGR thanks the Robert A. Welch
Foundation (grant B-1093) for financial support and acknowledges UNT computational
resources provided through CASCaM, which is an NSF-supported facility (CHE-1531468). We
also thank the Wazed Miah Science Research Center, Jahangirnagar University, Bangladesh for
providing us with some technical facilities required for this work.
Appendix A. Supplementary material
CCDC 1888840, 1888841, 1888842 and 1888844 contain the supplementary crystallographic
data for 3, 6, 7 and 9, respectively. These data may be obtained free of charge from the
16

Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif, or from the
Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk, while the atomic coordinates of all the
optimized structures are available from MGR upon request.
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21

Table 1. Crystal data and structure refinement details for compounds 3, 6, 7 and 9.
Compound
3
6
7
9
CCDC
1888840
C73.5H56Cl3Mo3N6O6P3S3
1702.50
150(1)
0.71073
1888841
C34H28MoN4OP2S2
730.60
1888842
C40H30Cl2Mo2N4O6P2S2
1051.52
150(1)
1.54184
1888844
C40H34Cl2MoO2P2S2
839.57
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
150(1)
150(1)
1.54184
Monoclinic
P 21/n
1.54184
Monoclinic
P 21/c
Monoclinic
C2/c
Monoclinic
P 21/c
Space group
Unit cell dimensions:
a (Å)
b (Å)
c (Å)
α (°)
14.6215(3)
26.1466(5)
38.0544(7)
90
10.83720(10)
28.02280(18)
11.68248(12)
90
11.23513(6)
17.15723(9)
21.83475(16)
90
10.85737(11)
18.69783(15)
18.89739(15)
90
93.5139(17)
90
14520.9(5)
8
1.558
0.829
117.3289(12)
90
3151.85(6)
4
1.540
5.885
91.0216(6)
90
4208.28(4)
4
1.660
8.128
96.8660(8)
90
3808.83(6)
4
1.464
6.197
 (°)
γ (°)
Volume (Å3)
Z
Density (calculated) (Mg/m3)
Absorption coefficient (mm-1)
F(000)
6856.0
1488.0
2104.0
1712.0
Crystal size (mm3)
2 Range for data collection (°)
Reflections collected
Independent reflections [Rint]
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I2(I)]
R indices (all data)
Largest diff. peak and hole (e Å-3)
0.2 × 0.18 × 0.1
5.444 to 56.932
111247
16672 [Rint = 0.0386]
16672/0/892
1.137
0.3 × 0.28 × 0.04
6.308 to 152.748
64899
6561 [Rint = 0.0571]
6561/0/397
1.222
0.2 × 0.2 × 0.04
6.552 to 152.926
87251
8780 [Rint = 0.0383]
8780/0/542
1.046
0.24 × 0.16 × 0.12
6.674 to 147.398
63863
7619 [Rint = 0.0315]
7619/0/442
1.061
R1 = 0.0493, wR2 = 0.0821 R1 = 0.0470, wR2 = 0.1097 R1 = 0.0246, wR2 = 0.0621 R1 = 0.0566, wR2 = 0.1464
R1 = 0.0638, wR2 = 0.0877 R1 = 0.0475, wR2 = 0.1099 R1 = 0.0269, wR2 = 0.0639 R1 = 0.0590, wR2 = 0.1483
1.16/-1.19
1.34/-1.01
0.52/-0.55
1.75/-2.05
22

Fig. 1. ORTEP drawing of the molecular structure of [Mo2(CO)4(μ,к2pymS)2(к1-PPh3)2] (3) (left) and the DFT-optimized structure A
(right). The thermal ellipsoids in the solid-state structure are at the 50% probability level and the hydrogen atoms are omitted for
clarity. Selected crystallographic bond lengths (Å) and angles (o): Mo(1)‒Mo(2) 2.9552(4), Mo(1)‒S(1) 2.5031(8), Mo(1)‒S(2)
2.4557(8), Mo(2)‒S(1) 2.4646(8), Mo(2)‒S(2) 2.5032(8), Mo(1)‒P(1) 2.4863(8), Mo(2)‒P(2) 2.4855(8), Mo(1)‒N(1) 2.262(3),
Mo(2)‒N(3) 2.254(3), S(1)‒Mo(1)‒Mo(2) 52.897(19), S(2)‒Mo(1)‒Mo(2) 54.16(2), S(2)‒Mo(1)‒S(1) 105.23(3), S(2)‒Mo(1)‒P(1)
170.36(3), P(1)‒Mo(1)‒Mo(2) 134.27(2), P(1)‒Mo(1)‒S(1) 84.19(3), N(1)‒Mo(1)‒Mo(2) 85.63(7), N(1)‒Mo(1)‒S(1) 65.24(7),
N(1)‒Mo(1)‒S(2) 95.67(7), N(1)‒Mo(1)‒P(1) 90.12(7).
23

Fig. 2. ORTEP drawing of the molecular structure of [Mo(CO)(к2-pymS)2(к2-dppm)] (6), and the DFT-optimized structure B (right).
The thermal ellipsoids in the solid-state structure are at the 50% probability level and the hydrogen atoms are omitted for clarity.
Selected crystallographic bond lengths (Å) and angles (o): Mo(1)‒S(1) 2.5587(10), Mo(1)‒S(2) 2.4949(10), Mo(1)‒P(1) 2.4739(10),
Mo(1)‒P(2) 2.4500(10), Mo(1)‒N(1) 2.223(3), Mo(1)‒N(3) 2.267(3), S(2)‒Mo(1)‒S1138.52(3), P(1)‒Mo(1)‒S(1) 77.99(3),
P(1)‒Mo(1)‒S2 134.78(4), P(2)‒Mo(1)‒S(1) 143.26(3), P(2)‒Mo(1)‒S(2) 75.26(3), P(2)‒Mo(1)‒P(1) 65.31(3), N(1)‒Mo(1)‒S(1)
63.94(9), N(1)‒Mo(1)‒S(2) 81.65(9), N(1)‒Mo(1)‒P(1) 141.63(9), N(1)‒Mo(1)‒P(2) 152.15(9), N(1)‒Mo(1)‒N(3) 82.88(12),
N(3)‒Mo(1)‒S(1) 87.46(9), N(3)‒Mo(1)‒S(2) 64.85(9), N(3)‒Mo(1)‒P(1) 100.88(9), N(3)‒Mo(1)‒P(2) 100.78(9), Mo(1)‒P(1)‒P(2)
56.91(3), Mo(1)‒P(2)‒P(1) 57.78(3).
24

Fig. 3. ORTEP drawing of the molecular structure of [Mo2(CO)6(μ,к1-pymS)2(μ,к2-dppm)] (7) (left) and the DFT-optimized structure
C (right). The thermal ellipsoids in the solid-state structure are at the 50% probability level and the hydrogen atoms are omitted for
clarity. Selected crystallographic bond lengths (Å) and angles (o): Mo(1)‒Mo(2) 2.9959(2), Mo(1)‒S(1) 2.4859(5), Mo(1)‒S(2)
2.4604(4), Mo(1)‒P(1) 2.5543(5), Mo(2)‒S(1) 2.4672(5), Mo(2)‒S(2) 2.4546(5), Mo(2)‒P(2) 2.5659(5), S(1)‒Mo(1)‒Mo(2)
52.498(11), S(1)‒Mo(1)‒P(1) 87.636(15), S(2)‒Mo(1)‒Mo(2) 52.357(11), S(2)‒Mo(1)‒S(1) 104.665(15), S(2)‒Mo(1)‒P(1)
88.030(15), P(1)‒Mo(1)‒Mo(2) 90.210(11), S(1)‒Mo(2)‒Mo(1) 53.067(11), S(1)‒Mo(2)‒P(2) 85.742(15), S(2)‒Mo(2)‒Mo(1)
52.532(11), S(2)‒Mo(2)‒S(1) 105.406(15), S(2)‒Mo(2)‒P(2) 90.510(15), P(2)‒Mo(2)‒Mo(1) 90.726(11), Mo(2)‒S(1)‒Mo(1)
74.435(13), Mo(2)‒S(2)‒Mo(1) 75.111(13).
25

Fig. 4. ORTEP drawing of the molecular structure of [Mo(CO)2(κ1-PhS)2(κ2-dppm)] (9),
showing 50% probability thermal ellipsoids and hydrogen atoms omitted for clarity. Selected
bond lengths (Å) and angles (o): Mo(1)‒S(1) 2.3696(12), Mo(1)‒S(2) 2.3639(11), Mo(1)‒P(1)
2.5272(10), Mo(1)‒P(2) 2.5216(10), Mo(1)‒C(1) 2.041(4), Mo(1)‒C(2) 2.020(4),
S(1)‒Mo(1)‒P(1) 155.20(4), S(1)‒Mo(1)‒P(2) 89.31(4), S(2)‒Mo(1)‒S(1) 114.53(4),
S(2)‒Mo(1)‒P(1) 90.14(4), S(2)‒Mo(1)‒P(2) 156.16(4), P(2)‒Mo(1)‒P(1) 66.07(3),
C(1)‒Mo(1)‒S(1) 86.30(14), C(1)‒Mo(1)‒S(2) 94.31(14), C(1)‒Mo(1)‒P(1) 94.68(13),
C(1)‒Mo(1)‒P(2) 86.55(13), C(2)‒Mo(1)‒S(1) 94.04(13), C(2)‒Mo(1)‒S(2) 86.71(12),
C(2)‒Mo(1)‒P(1) 84.49(13), C(2)‒Mo(1)‒P(2) 92.18(12), C(2)‒Mo(1)‒C(1) 178.68(18).
26

Graphical Abstract
Reactivity of [Mo(CO)3(NCMe)3] towards pyrimidine-2-thiol (pymSH) and
thiophenol (PhSH) in the presence of phosphine auxiliaries: Synthesis of
mono- and dinuclear complexes bearing 2 and µ,2-pymS coordination motifs
Roknuzzaman, S.M. Tareque Abedin, Mohd. Rezaul Haque, Shishir Ghosh, Derek A.
Tocher, Michael G. Richmond, Shariff E. Kabir
A number of new mono- and di-molybdenum complexes have been isolated and characterized
from the reactions of [Mo(CO)3(NCMe)3] with pmySH or PhSH in the presence of a phosphine.
27