Dithiolene transfer from nickel to a dimolybdenum centre: The first dithiolene alkyne complex

Article abstract of DOI:10.1016/j.jorganchem.2003.10.041

Transfer of dithiolene ligands from [Ni(S₂C₂ Ph₂)₂] to the dimolybdenum complex [Mo₂(μ-C₂R₂)(CO)₄ Cp₂] (R=CO₂Me, Cp=η-C₅ H₅) affords the first example of a dithiolene alkyne complex, [Mo₂(μ-C₂R₂) (μ-S₂C₂Ph₂)₂ Cp₂], together with [Mo₂(μ-SCR=CR) (μ-SCPh=CPh)Cp₂] in which sulfur transfer from dithiolene to alkyne has occurred.

Full text of DOI:10.1016/j.jorganchem.2003.10.041

Journal of Organometallic Chemistry 689 (2004) 522–527
www.elsevier.com/locate/jorganchem
Dithiolene transfer from nickel to a dimolybdenum centre:
the first dithiolene alkyne complex
*
Harry Adams, Michael J. Morris , Sarah A. Morris, Jeffrey C. Motley
Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
Received 15 September 2003; accepted 21 October 2003
Abstract
Transfer of dithiolene ligands from [Ni(S2C2Ph2)2] to the dimolybdenum complex [Mo2(l-C2R2)(CO)4Cp2] (R ¼ CO2Me,
Cp ¼ g-C5H5) affords the first example of a dithiolene alkyne complex, [Mo2(l-C2R2)(l-S2C2Ph2)2Cp2], together with [Mo2(l-
SCR@CR)(l-SCPh@CPh)Cp2] in which sulfur transfer from dithiolene to alkyne has occurred.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Molybdenum; Dithiolene; Alkyne; Nickel; Sulfur transfer
1. Introduction
Recently we have shown that treatment of [Mo2(l-
C2R2)(CO)4Cp2] (R ¼ H, alkyl, aryl, CO2Me, etc.) with
elemental sulfur results in oxidative decarbonylation to
the Mo(V) species [Mo2S(l-S)2(SCR@CRS)Cp2], in
which the dithiolene ligand arises through insertion of
sulfur into the Mo–alkyne bonds [6]. In attempting to
introduce dithiolene ligands into the dimolybdenum
centre in the absence of additional sulfur, we were in-
spired to adapt the method of Schrauzer (recently im-
proved by Holm) for the synthesis of [Mo(CO)2
(S2C2Ph2)2], involving dithiolene transfer from [Ni(S2C2
Ph2)2] to [Mo(CO)6] or [Mo(CO)3(NCMe)3] [7,8]. Here
we report that this approach is also successful in the
dimolybdenum system and leads to the isolation of the
first dithiolene-alkyne complex.
The chemistry of metal dithiolene complexes is cur-
rently undergoing something of a renaissance, with their
electrochemical properties leading to widespread appli-
cations in materials chemistry and, more recently, a re-
newed interest in the selective separation of olefins from
mixed gas streams [1]. Extensive investigations in the
1960s resulted in the synthesis of dithiolene complexes of
virtually all the transition metals, many of which were
homoleptic species [2]. Heteroleptic complexes contain-
ing co-ligands such as carbonyls, nitrosyls and phos-
phines are relatively widespread, and cyclopentadienyl
dithiolene complexes are also prevalent in the literature
[3]. In contrast however, the organometallic chemistry of
dithiolene complexes with other organic ligands has very
rarely been explored [4]. Remarkably, for example, gi-
ven the fact that dithiolene complexes have often been
prepared either by the reaction of alkynes with metal
sulfido complexes [5] or conversely by the combination
of coordinated alkynes with sulfur [6], it appears that
there is no reported example of a compound which
contains both dithiolene and alkyne ligands.
2. Results and discussion
Heating a toluene solution of [Mo2(l-C2R2)(CO)4-
Cp2] (1; R ¼ CO2Me) with two equivalents of [Ni(S2C2
Ph2)2] for 5 h produced a new olive-green molybdenum-
containing product, [Mo2(l-C2R2)(l-S2C2Ph2)2Cp2] 2,
in 47% yield, accompanied by a brown compound which
appears identical to SchrauzerÕs [Ni(S2C2Ph2)]n [7,9].
Complex 2 shows no remaining m(CO) absorptions in its
IR spectrum, but the presence of an ester peak at 1698
cmꢀ1 confirms the retention of the alkyne ligand. The
* Corresponding author. Tel.: +44-114-2229363; fax: +44-114-
2738673.
E-mail address: m.morris@sheffield.ac.uk (M.J. Morris).
0022-328X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.10.041

H. Adams et al. / Journal of Organometallic Chemistry 689 (2004) 522–527
523
1H NMR spectrum contains peaks for phenyl, Cp and
methyl protons in a ratio of 20:10:6, suggesting the in-
corporation of two dithiolene moieties. Mass spec-
trometry and analytical data were in agreement with this
assessment. The 13C NMR spectrum provided the ad-
ditional information that two peaks are observed for the
dithiolene carbons at d 163.3 and 116.0.
The structure of 2 determined by X-ray diffraction is
shown in Fig. 1, with important bond lengths given in
ꢀ
Table 1. The Mo–Mo bond [2.7233(8) A] is bridged by
the alkyne in a transverse manner, with a C(11)–C(12)
coordination mode is well known in Mo chemistry [11].
Each CpMo unit therefore achieves a four-legged piano-
stool environment consisting of three dithiolene sulfurs
and the alkyne. The bridging sulfurs are asymmetrically
bonded: S(3) is closer to Mo(1) and conversely S(4) is
nearer to Mo(2).
When the reaction between 1 and [Ni(S2C2Ph2)2] was
carried out with a 1:1 ratio of reagents, the yield of 2
dropped to 23% and a second new compound could be
isolated in 17% yield (Scheme 1). This orange complex
was identified as [Mo2(l-SCR@CR)(l-SCPh@CPh)Cp2]
3 by a combination of spectroscopy and crystallogra-
phy. Again its IR spectrum revealed complete decarb-
onylation, but in this case the 1H NMR spectrum
contained peaks for inequivalent Cp ligands and
methyl groups, implying a less symmetrical structure.
The ratio of Ph:Cp:Me protons was 10:10:6, indicating
ꢀ
distance of 1.341(7) A, not significantly changed from
ꢀ
the 1.33 A typically found in the [Mo2(l-alkyne)-
(CO)4Cp2] complexes [10]. In accord with their 13C
NMR shifts, the two dithiolene ligands are each bonded
such that one sulfur atom bridges the two molybdenums
whereas the other is bonded only to one metal; this
Fig. 1. Molecular structure of complex 2 in the crystal showing the atomic numbering scheme.
Table 1
Selected bond lengths [A] and angles [°] for complex 2
ꢀ
Mo(1)–C(11)
Mo(1)–S(3)
Mo(1)–S(4)
Mo(2)–C(12)
Mo(2)–S(4)
Mo(2)–S(3)
C(13)–C(14)
2.143(5)
Mo(1)–C(12)
Mo(1)–S(6)
Mo(1)–Mo(2)
Mo(2)–C(11)
Mo(2)–S(5)
C(11)–C(12)
C(15)–C(16)
2.192(6)
2.4276(14)
2.5265(16)
2.149(6)
2.4751(16)
2.7233(8)
2.181(6)
2.4467(17)
2.5104(16)
1.337(7)
2.4824(16)
1.341(7)
1.354(7)
S(3)–Mo(1)–S(6)
S(6)–Mo(1)–S(4)
S(4)–Mo(2)–S(3)
Mo(1)–S(3)–Mo(2)
C(12)–C(11)–C(41)
C(11)–C(12)–C(42)
79.61(5)
82.71(5)
106.97(5)
66.92(4)
130.7(6)
138.7(6)
S(3)–Mo(1)–S(4)
S(4)–Mo(2)–S(5)
S(5)–Mo(2)–S(3)
107.05(6)
78.97(5)
84.22(5)
66.38(4)
78.1(2)
Mo(2)–S(4)–Mo(1)
Mo(1)–C(11)–Mo(2)
Mo(2)–C(12)–Mo(1)
77.70(19)

524
H. Adams et al. / Journal of Organometallic Chemistry 689 (2004) 522–527
R
R
C
R
R
R
R
C
CO
C
C
C
C
S
CO
Ni(S2C2Ph2)2
+
Mo
Mo
Mo
Mo
Mo
Mo
S
OC
S
C
O
S
S
S
C
C
Ph
R = CO2 Me
Ph
Ph
Ph
Ph
Ph
2
1
3
Scheme 1. Synthesis of complexes 2 and 3.
the incorporation of only one dithiolene unit, again
confirmed by the mass spectrum and analysis. Because
this information was not sufficient to establish the
structure of the compound, an X-ray diffraction study
was carried out, the result of which is shown in Fig. 2.
The structure of 3 contains a dimolybdenum core in
the familiar orthogonal paddle-wheel arrangement ob-
served in [Mo2(l-S)2(l-SMe)2Cp2] [12] and other related
compounds [13]. The metallacyclic unit present in 3 has
been observed previously in di-iron complexes [14]; in-
deed one such complex was prepared by Schrauzer
through the reaction of the methylated nickel dithiolene
complex [Ni(MeSCPh@CPhSMe)(SCPh@CPhS)] with
iron pentacarbonyl [15]. More recently the reaction
of the cluster [Mo2Rh(l3-S)(l-S)3(l-Cl)(S2CNEt2)2-
(PPh3)2] with phenylacetylene was shown to produce
three such units coordinated to the trinuclear centre [16].
The mechanism of the reaction may proceed either by
substitution of CO ligands of 1 by free dithiobenzil
liberated from the nickel precursor or through the in-
termediacy of a Ni–S–Mo bridged species. The mon-
odithiolene intermediate so formed could then undergo
further substitution to give 2 or sulfur transfer to give 3.
In a separate reaction, we verified that 3 is not formed
by the conproportionation of 1 and 2: after heating a
ꢀ
which the Mo–Mo bond length of 2.6048(4) A is con-
siderably shorter than that in 2 (Table 2). It is clear that
transfer of a sulfur atom from a dithiolene ligand to the
original alkyne must have occurred during the reaction,
as this bond is bridged by two different b-thiovinyl li-
gands: one SCPh@CPh and one SCR@CR. A direct
comparison of these two molybdenathiacyclobutene
metallacycles reveals, as expected, that the Mo–C bond
lengths in the latter are shorter than those in the former.
The sulfur atoms are again asymmetrically disposed,
with S(1) closer to Mo(2) and S(2) to Mo(1), but of the
bridging carbon atoms, C(14) is almost symmetrically
bridging. The atoms S(1), S(2), C(12) and C(14) adopt
Fig. 2. Molecular structure of complex 3 in the crystal showing the atomic numbering scheme.

H. Adams et al. / Journal of Organometallic Chemistry 689 (2004) 522–527
525
Table 2
Selected bond lengths [A] and angles [°] for complex 3
ꢀ
Mo(1)–C(12)
Mo(1)–C(13)
Mo(1)–S(1)
Mo(2)–C(14)
Mo(2)–C(11)
Mo(2)–S(2)
C(13)–C(14)
2.169(3)
2.238(3)
2.4556(8)
2.154(3)
2.306(3)
2.4577(8)
1.413(4)
Mo(1)–C(14)
Mo(1)–S(2)
Mo(1)–Mo(2)
Mo(2)–C(12)
Mo(2)–S(1)
C(11)–C(12)
2.185(3)
2.4162(8)
2.6048(4)
2.253(3)
2.3958(8)
1.403(4)
C(12)–Mo(1)–S(2)
C(12)–Mo(1)–S(1)
S(2)–Mo(1)–S(1)
C(12)–Mo(2)–S(1)
C(12)–Mo(2)–S(2)
Mo(2)–S(1)–Mo(1)
C(12)–C(11)–S(1)
C(14)–C(13)–S(2)
75.90(8)
66.61(8)
114.85(3)
66.47(7)
73.61(7)
64.93(2)
105.7(2)
106.7(2)
C(14)–Mo(1)–S(2)
C(14)–Mo(1)–S(1)
C(14)–Mo(2)–S(1)
C(14)–Mo(2)–S(2)
S(1)–Mo(2)–S(2)
67.60(8)
75.84(8)
77.69(8)
67.28(8)
115.52(3)
64.60(2)
72.14(10)
73.78(10)
Mo(1)–S(2)–Mo(2)
Mo(1)–C(12)–Mo(2)
Mo(2)–C(14)–Mo(1)
toluene solution of equimolar amounts of 1 and 2 for 24
h, both compounds were recovered essentially un-
changed, with only minute traces of other products
observable. Heating 1 with SchrauzerÕs P4S10/benzoin
reagent causes mainly decomposition, and no trace of 2
(or 3) is formed. It is notable that reaction of 1 with the
analogous dithiolene complex [Ni(S2C2Me2)2] results in
complete consumption of both starting materials but
does not give any tractable products, perhaps indicating
that the less stable free ligand does not survive the re-
action conditions. The reaction of [Ni(S2C2Ph2)2] with
[Mo2(l-C2H2)(CO)4Cp2], which contains a less strongly
bound alkyne ligand, also produced only decomposi-
tion. The formation of 2 constitutes only the second
known reaction in which all four carbonyl ligands of 1
are lost while the transverse coordination of the alkyne
is retained, the first being the oxidation of 1 with
Me3NO to give the Mo(IV) species [Mo2O2(l-O)(l-
C2R2)Cp2] [17].
Preliminary studies indicate that the reactivity of the
alkyne ligand in 2 is much reduced compared to that in
1. Thus, refluxing a toluene solution of 2 with an excess
of sulfur caused a very slow reaction, the major product
of which was the mono-dithiolene complex [Mo2S(l-
S)2(SCPh@SCPh)Cp2]; and in contrast to the well-
known sequence of alkyne oligomerisation reactions
which take place from 1 [18], heating 2 with an excess of
MeO2CCBCCO2Me produced mainly decomposition.
We attribute this to the lack of readily labile ligands in 2,
coupled with the large steric bulk of the dithiolene
ligands.
are relatively air stable and work-up procedures can be
carried out without special precautions. Toluene and
light petroleum were dried by distillation from sodium.
Light petroleum refers to the fraction boiling between 60
and 80 °C. Dichloromethane and other solvents were
used as received unless otherwise stated. Chromato-
graphic separations were performed under a slight po-
sitive pressure of nitrogen on silica columns (Merck
Kieselgel 60, 230–400 mesh) of varying length. Thin-
layer chromatography (TLC) was carried out on com-
mercial Merck plates coated with a 0.20 mm layer of
silica.
Infra-red spectra were recorded in CH2Cl2 solution
on a Perkin-Elmer 1600 FT-IR machine using 0.5 mm
1
NaCl cells. H and 13C NMR spectra were obtained in
CDCl3 solution on a Bruker AC250 machine with au-
tomated sample-changer or an AMX400 spectrometer.
Chemical shifts are given on the d scale relative to
SiMe4 ¼ 0.0 ppm. The 13C{1H} NMR spectra were re-
corded using an attached proton test technique (JMOD
pulse sequence). Mass spectra were recorded on a Fi-
sons/BG Prospec 3000 instrument operating in fast atom
bombardment mode with 3-nitrobenzyl alcohol as ma-
trix. Elemental analyses were carried out by the Mi-
croanalytical Service of the Department of Chemistry.
Complex 1 was prepared by a slight adaptation of the
literature procedure [10,19].
CAUTION! Although we have no evidence for the
formation of toxic [Ni(CO)4] during these reactions, this
possibility should be borne in mind during work-up.
3.2. Preparation of [Mo2(l-C2R2)(l-S2C2Ph2)2Cp2]
(2)
3. Experimental
A solution of complex 1 (499 mg, 0.87 mmol) and
[Ni(S2C2Ph2)2] (940 mg, 1.74 mmol) in toluene (175 ml)
was heated to reflux for 5 h with TLC monitoring. After
cooling, silica (5 g) was added and the solvent was re-
moved under vacuum. The solid residue was then loaded
3.1. General
All reactions were carried out under nitrogen using
standard Schlenk techniques. The products described

526
H. Adams et al. / Journal of Organometallic Chemistry 689 (2004) 522–527
onto a silica chromatography column made up in light
petroleum. Elution with CH2Cl2-light petroleum (4:1)
separated a green band which was finally eluted with a
2:3 mixture of the same solvents; it proved to be unre-
acted Ni complex (248.8 mg, 26% recovery). Elution
with a 1:1 mixture gave a brown band of [Ni(S2C2Ph2)]n
(231.6 mg), and a minor unidentified green band (19.5
mg) was eluted with a 7:3 mixture. Finally elution with
CH2Cl2-acetone (99:1) produced a large olive-green
zone due to complex 2 (387.3 mg, 47%).
2: M.p. 263 °C (dec.). IR(CH2Cl2): 1698 (CO2Me)
cmꢀ1. 1H NMR d 7.09–6.69 (m, 20 H, Ph), 5.92 (s, 10 H,
Cp), 3.84 (s, 6 H, Me). 13C NMR d 172.6 (CO2Me),
163.3 (CPh), 141.2 (Cipso of Ph), 140.5 (Cipso of Ph),
129.5–125.5 (m, Ph), 116.0 (CPh), 102.1 (Cp), 74.1
(CCO2Me), 52.9 (Me). Anal. Found: C, 55.33; H, 3.92;
S, 13.23. Calc. for C44H36Mo2O4S4: C, 55.70; H, 3.80; S,
13.50%. Mass spectrum m=z 951 (Mþ).
CH2Cl2–acetone (49:1). Continued elution with the
same solvent mixture provided a faint orange band of 1
followed by a further orange band containing 3 (54 mg,
17%).
3: M.p. 221–223 °C. IR(CH2Cl2): 1704, 1698 sh cmꢀ1
.
1H NMR d 7.22–6.68 (m, 10 H, Ph), 5.24 (s, 5 H, Cp),
5.02 (s, 5 H, Cp), 3.70 (s, 3 H, Me), 3.61 (s, 3 H, Me).
13C NMR d 178.1, 166.9 (CO2Me), 149.6 (l-CCO2Me),
139.7 (l-CPh), 129.4–124.8 (m, Ph), 126.7 (Cipso), 116.4
(Cipso), 112.4 (CCO2Me), 96.8 (CPh), 95.9, 95.5 (Cp),
52.4, 51.8 (Me). Anal. Found: C, 49.54; H, 3.64; S, 8.68.
Calc. for C30H26Mo2O4S2: C, 50.10; H, 3.68; S, 9.07%.
Mass spectrum m=z 707 (Mþ).
3.4. X-ray crystal structure determinations
The crystal data for 2 and 3 are given in Table 3.
General procedures were as described in a previous
publication [20]; a Bruker Smart CCD area detector
with Oxford Cryosystems low temperature system was
used for data collection. Complex scattering factors
were taken from the program package SHELXTL [21] as
implemented on the Viglen Pentium computer.
Crystallographic data for the structure determina-
tions have been deposited with the Cambridge Crystal-
lographic Data Centre, CCDC reference numbers
207387 and 207388 for 2 and 3 respectively. Copies of
this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
3.3. Preparation of [Mo2(l-SCR@CR)(l-SCPh@CPh)
Cp2] (3)
A solution of complex 1 (256 mg, 0.444 mmol) and
[Ni(S2C2Ph2)2] (237 mg, 0.444 mmol) in toluene was
heated to reflux for 18 h. The solvent was removed and
the residue chromatographed as above. After elution of
a small amount of starting Ni complex and brown
[Ni(S2C2Ph2)]n (87 mg) as above, and a faint blue band,
complex 2 (98 mg, 23%) was collected with an eluent of
Table 3
Summary of crystallographic data for complexes 2 and 3
2
3
Empirical formula
Formula weight
T/K
Crystal system
Space group
C44H36Mo2O4S4
C30H26Mo2O4S2
706.51
150(2)
948.85
150(2)
Orthorhombic
Pca2ð1Þ
36.803(3)
9.4742(8)
10.8485(9)
90
Monoclinic
P21=c
10.4749(11)
19.994(2)
12.8890(14)
90
ꢀ
a/A
ꢀ
b/A
ꢀ
c/A
a=°
b=°
c=°
90
90
94.147(2)
90
3
ꢀ
V /A
3782.6(5)
4
1.666
2692.4(5)
4
1.743
Z
Density (calcd)/Mg mꢀ3
l/mmꢀ1
0.929
1920
1.122
1416
F (0 0 0)
Crystal size/mm3
h range for data collection/°
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F 2
Final R1, wR2 ½I > 2rðIÞꢂ
(all data)
0.34 ꢁ 0.23 ꢁ 0.09
1.11–23.30
27678
0.43 ꢁ 0.32 ꢁ 0.18
1.88–28.31
16633
5442 [Rint ¼ 0:0853]
5442/1/487
0.952
6445 [Rint ¼ 0:0407]
6445/0/343
0.938
R1 ¼ 0:0335, wR2 ¼ 0:0517
R1 ¼ 0:0497, wR2 ¼ 0:0556
0.465 and )0.421
R1 ¼ 0:0343, wR2 ¼ 0:0747
R1 ¼ 0:0494, wR2 ¼ 0:0799
1.237 and )1.056
ꢀ3
ꢀ
Largest diffraction peak and hole/e A

H. Adams et al. / Journal of Organometallic Chemistry 689 (2004) 522–527
527
[9] This compound has been variously described in the literature as
[Ni(S2C2Ph2)]n and [Ni(S2C2Ph2)]4. Despite persistent attempts we
have so far failed to obtain suitable crystals to establish its true
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
identity. For
a
recently characterised related species,
[Pd{S2C2(CO2Me)2}]6, see C.L. Beswick, R. Terroba, M.A.
Greaney, E.I. Stiefel, J. Am. Chem. Soc. 124 (2002) 9664.
[10] (a) W.I. Bailey Jr., M.H. Chisholm, F.A. Cotton, L.A. Rankel, J.
Am. Chem. Soc. 100 (1978) 5764;
Acknowledgements
This work was supported by the EPSRC and the
University of Sheffield.
(b) J. Zhang, X.-N. Chen, Y.-Q. Yi, X.-Y. Huang, J. Organomet.
Chem. 579 (1999) 304;
(c) L.-C. Song, J.-Y. Shen, Q.-M. Hu, X.-Y. Huang, Inorg. Chim.
Acta 249 (1996) 175.
[11] (a) T. Sugiyama, T. Yamanaka, M. Shibuya, R. Nakase, M.
Kajitani, T. Akiyama, A. Sugimori, Chem. Lett. (1998) 501;
(b) T. Shibahara, M. Tsuboi, S. Nakaoka, Y. Ide, Inorg. Chem.
42 (2003) 935;
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