Acetylenedithiolate as directional bridging ligand in cobalt(I) alkyne platinum dithiolato bimetallic complexes

Article abstract of DOI:10.1039/b913859e

The η²-C,C′-acetylenedithiolate (acdt^2-) complex K[(triphos)Co(acdt)], K-5, {triphos = 1,1,1- tris(diphenylphosphinomethyl)ethane} was obtained by consecutive removal of S-protection groups in [(triphos)Co(1)]PF₆, 3-PF

Full text of DOI:10.1039/b913859e

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Acetylenedithiolate as directional bridging ligand in cobalt(I) alkyne platinum
dithiolato bimetallic complexes†
Wolfram W. Seidel,*a,b Matthias J. Meel,b Florian Hupkab and Jan J. Weigandb
Received 15th July 2009, Accepted 18th November 2009
First published as an Advance Article on the web 26th November 2009
DOI: 10.1039/b913859e
2
The h -C,C¢-acetylenedithiolate (acdt2-) complex K[(triphos)Co(acdt)], K-5, {triphos =
1,1,1-tris(diphenylphosphinomethyl)ethane} was obtained by consecutive removal of S-protection
groups in [(triphos)Co(1)]PF6, 3-PF6 (1 = 1-Trimethylsilyl-7-phenyl-3,6-dithiahept-4-ine). Reaction of
K-5 with selected Pt(II) salts resulted in the formation of the new heterobimetallic complexes
[(phen)Pt(5)]BPh4, 6-BPh4, (phen = 1,10-phenanthroline) and [(dppe)Pt(5)]BPh4, 7-BPh4, {dppe =
1,2-bis(diphenylphosphino)ethane}, which were fully characterized. X-ray diffraction studies showed
2
2
that Co and Pt are linked by acdt2- in the h -C,C¢-k -S,S¢-bridging mode. The electronic structure of
6-BPh4 and 7-BPh4 was investigated by electronic absorption spectroscopy, cyclic voltammetry and
X-band EPR spectroscopy of neutral 7. In addition, NMR spectroscopy, X-ray diffraction and
reactivity studies with the alkyne complexes [(PMe3)3Co(1)]-PF6, 2-PF6, with 3-PF6 and the
2
intermediate product [(triphos)Co{h -(S)C2(SCH2Ph)}], 4, uncovered the flexibility of the
CoC2S2-moiety within the persisting complex scaffold throughout the synthetic scheme.
In our ongoing studies we have demonstrated that the bend-back
Introduction
2
angle in h -C,C¢-alkyne complexes of acdt2- is flexible enough
2
Heteropolymetallic complexes with strong electronic ligand me-
diated cooperation of the metal centers receive continuing at-
tention due to their often attractive photophysical or magnetic
behavior. Functional materials with useful magnetic properties are
frequently constructed by the assembly of mononuclear complexes
by small bridging ligands like cyanide.1-4 In addition, fundamental
catalytic processes caused by light driven charge separation are
generally based on ligand mediated metal–metal interaction and
bimetallic reaction patterns.5-7
to allow for the k -S,S¢-chelate coordination to a second metal
2
ion.16-18 Bi- and trimetallic complexes with acdt2- in this h -
2
C,C¢-k -S,S¢-bridging mode display redox-variability and visible
transitions with high absorptivity. Particularly, investigations on
[{Tp¢W(CO)2(acdt)}2M] {M = Ni, Pd, Pt; Tp¢ = Hydrotris(3,5-
dimethylpyrazolyl)borate; Fig. 1} indicated strong electronic
coupling of metals over acdt2--bridges. However, preparative
access to complexes of this type is hampered by the fact that
the free acetylenedithiol is intrinsically unstable.19-21 Therefore,
the synthetic strategy comprises formation of alkyne complexes
with appropriate acetylenedisulfides and subsequent generation of
alkyne complexes of acdt2- in the complex. This procedure requires
well adapted sulfur-protection groups and respective deprotection
conditions in order to retain the alkyne complex moiety. Anionic
complexes of the type [Tp¢M(CO)(L)(acdt)]- (M = Mo, W; L =
CO, RNC) were obtained by reductive removal of benzyl groups in
the corresponding cationic bis(benzylthio)acetylene complexes.22
Attempts to expand the type of metal bound to carbon from
Mo/W(II) to Co(I) revealed the need for a milder procedure
implying nucleophilic removal of trimethylsilylethyl S-protection
groups.
In this respect we are devoted to the coordination chemistry of
2-
2-
≡
acetylenedithiolate (acdt ), (S–C C–S) , which is furnished with
donor ability at each atom of the ligand. The coordination chem-
istry of related alkyne-1-thiolates and recently emerged8 highly
attractive diynedithiolates (S–C C–C C–S) is dominated by
the thiolato group9-13 and examples exhibiting both h -alkyne- and
2-
≡
≡
2
thiolato-coordination are rare.14,15 Nonetheless, the combination
of both alternatives, side on alkyne binding and dithiolato chelate
coordination, confer to the doubly charged acdt2- directionality.
Provided that two different donor atoms are present, this type
of bridging metals is the shortest possible and is related to the
ubiquitary cyanide ion. However, in addition to the short path
between the metals acdt2- exerts a chelate effect of the dithiolene
type.
aInstitut fu¨r Chemie, Universita¨t Rostock, Albert-Einstein-Straße 3a, 18059,
Rostock, Germany. E-mail: wolfram.seidel@uni-rostock.de; Fax: +49
(0)381 4986382; Tel: +49 (0)381 4986380
Fig. 1 Mesomeric forms of trinuclear complexes linked by acdt2-.
bInstitut fu¨r Anorganische und Analytische Chemie, Westfa¨lische Wilhelms-
Universita¨t Mu¨nster, Corrensstraße 30, 48149, Mu¨nster, Germany
Alkyne complexes of Co(I) are prone to C–C-coupling re-
actions of coordinated alkynes.23,24 This applies particularly to
† Electronic supplementary information (ESI) available: Additional spec-
troscopic data, EPR measurement and simulation details. CCDC reference
numbers 740232–740236. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/b913859e
5
the [(h -C5H5)Co] moiety,25 but it has also been observed at
[(PMe3)3Co].26,27 In order to suppress this reactivity we have chosen
624 | Dalton Trans., 2010, 39, 624–631
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©

◦
+
+
˚
1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) as ancillary
ligand. The ability of the [(triphos)Co(I)] unit to form stable alkyne
complexes has already been shown.28
Table 1 Selected distances (A) and angles ( ) for 2 , 3 and 4
2+
3+
4Aa
4Ba
2
In this contribution we describe the generation of a novel h -
Co–C1
Co–C2
C1–C2
C1–S1
C2–S2
Co–P1
Co–P2
Co–P3
C1–C2–S2
C2–C1–S1
1.836(2)
1.862(2)
1.320(2)
1.703(2)
1.702(2)
2.169(1)
2.220(1)
2.147(1)
148.1(2)
148.9(2)
1.844(5)
1.848(5)
1.342(7)
1.695(5)
1.706(5)
2.221(2)
2.155(2)
2.220(2)
129.8(4)
141.4(4)
1.876(3)
1.821(3)
1.346(5)
1.665(3)
1.691(3)
2.186(1)
2.154(1)
2.193(1)
140.1(3)
142.7(3)
1.865(4)
1.821(3)
1.343(5)
1.669(4)
1.691(3)
2.182(1)
2.151(1)
2.196(1)
140.0(3)
143.1(3)
C,C¢-alkyne complex of acdt2- with the [(triphos)Co(I)] moiety
and the subsequent formation of heterobimetallic complexes with
the building blocks [Pt(phen)]2+ and [Pt(dppe)]2+ {phen = 1,10-
phenanthroline, dppe = 1,2-bis(diphenylphosphino)ethane}. The
molecular structures, the spectroscopic properties and finally the
electronic structures of the bimetallic complexes are discussed.
a A and B represent the two individual molecules in the asymmetric unit.
Results and discussion
Mononuclear alkyne complexes
diffraction. The molecular structures are shown in Fig. 2 and
selected interatomic distances and angles are listed in Table 1.
Alkyne complexes of acetylenedisulfides with [(PMe3)3Co(I)] are
easily accessible by the method of Dartiguenave26 by reaction of
[(PMe3)3Co(Br)] with the appropriate alkyne in acetonitrile and
subsequent addition of an alkali metal salt. This procedure can
also be used for [(triphos)Co(I)] with the tripodal triphosphine. A
competing coordination of the sulfide group was not observed.
Using the unsymmetrically substituted alkyne 1 (Scheme 1),
which was synthesized from Me3SiCCH in a stepwise manner,
the spectroscopically pure complexes [(PMe3)3Co(1)](PF6), 2-PF6,
and [(triphos)Co(1)](PF6), 3-PF6, were obtained after addition of
KPF6 and chromatographic purification of the crude products.
Both complexes are air-stable and crystallization of 2-PF6 from
CH2Cl2–n-hexane solution or slow evaporation of the solvent from
a solution of 3-PF6 in methanol yielded crystals suitable for X-ray
Fig. 2 Molecular structures of cations 2+ (a) and 3+ (b) showing 50%
probability ellipsoids and atom labelling scheme. Hydrogen atoms and
counter ions are omitted for clarity.
The molecular structure of both complex cations shows a
distorted tetrahedral geometry considering the alkyne as occu-
pying a single coordination site. The variations in the CoC2 unit
between 2+ and 3+ are marginal. Considering the more tied
position of the phosphorus atoms at the Co center and the
weaker donor strength of the diarylphosphine group in 3+ this
Scheme 1 Complex synthesis: (i) KPF6, CH3CN; (ii) Bu4NF, thf; (iii)
C8K, thf; (iv) [PtCl2(phen)], NaBPh4, thf; (v) [PtCl2(dppe)], NaBPh4, thf.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 624–631 | 625
©

observation is surprising. Thus, the P–Co–P angles in 2+ fall
around an average of 100.0◦, whereas in 3+ with the chelating
triphos ligand the mean P–Co–P angle amounts to 90.3◦. A
significant difference between complexes of sulfur-substituted and
carbon based alkynes is the Csp–Csp distance being smaller in
˚
the latter case. The C1–C2 bond lengths amount to 1.320(3) A
in 2+ and 1.342(7) A in 3 , while the corresponding values
+
˚
+
˚
˚
≡
are 1.265(7) A in [(PMe3)3Co(PhC CPh)] and 1.264(8) A
+
26,27
≡
in [(PMe3)3Co(PhC CC5H11)] .
The only other structurally
characterized alkyne complex with the [(triphos)Co]+ unit,
[(triphos)Co( BuC C–C C Bu)] , displays a Csp–Csp bond of
1.313(8) A. This medium value is an indication that the longest
Csp–Csp bond in 3+ is due to both sulfur substitution and the triphos
ancillary ligand.
t
t
+
≡
≡
28
˚
A striking difference between 2+ and 3+ applies to the bend-back
angles of the sulfur◦substituents. In 2+ the Csp–Csp–S angles are
both larger than 148 , while one o◦f the corresponding angles in 3+,
C1–C2–S2, is as small as 129.8(4) . Opposing torsion angles in 3+
about the bonds C1–S1 and C2–S2 and related steric interactions
account for this feature. In contrast, the substituents at sulfur in
2+ are both directed away from the [(PMe3)3Co] unit. Likely, the
larger P–Co–P angles discussed above force such a close proximity
of the alkyl substituents at sulfur leading in turn to large Csp–Csp–S
angles. In addition, the position of the CoC2 plane with respect to
the CoP3 unit is different in 2+ and 3+. In 2+ the CoC1C2 plane is
nearly aligned with the Co–P2 vector rendering this bond longer
than Co–P1 and Co–P3. In contrast, the CoC1C2 plane in 3+
is rather staggered rendering the Co–P2 bond perpendicular to
the C1–C2 axis shorter than the other two. However, the alkyne
rotates readily in solution as indicated by the observation of only
one resonance in the 31P NMR spectra. The 13C NMR resonances
of the metal bound carbon atoms at 181.8 and 182.8 ppm are in
accord with a four-electron donor alkyne complex.
Fig. 3 Molecular structure of one specimen of 4 showing 50% probability
ellipsoids and the atom labelling scheme. Hydrogen atoms are omitted for
clarity.
Addition of stoichiometric amounts of Bu4NF to a solution of
3-PF6 in thf at -78 ◦C resulted in an immediate colour change from
green to purple concomitant with ethylene evolution indicating the
formation of [(triphos)Co{h -(S)C2(SCH2Ph)}], 4 (Scheme 1). The
cobalt indicating a contribution of resonance form 4B (Fig. 3).
However, the difference between C1–S1 and C2–S2 is rather
insignificant. Therefore, the longer Co–C1 bond can alternatively
be rationalized by charge repulsion in accord with resonance form
4A. In addition, the position of the benzyl substituent pointing
away from the cobalt alkyne moiety (torsion angle C1A–C2A–
S2A–C44A 18.03◦) is noticeable. Consequently, the bend-back
angles Csp–Csp–S are larger compared with those in 3+ showing
values over 140◦.
Interestingly, the 1H NMR resonance of the SCH2 protons
is found considerably low field shifted from 4.16 ppm in 3+ to
5.56 ppm in 4. Likely, the predominant position of this CH2
group in the anisotropy cone of the cobalt coordinated C–C
bond as observed in the solid state structure of 4 accounts for
this spectroscopic feature. The removal of an alkyl group in 3+
led only to a minor shift of the 31P NMR resonance (36.4 ppm
for 3+, 32.6 ppm for 4), while the 13C NMR resonances of both
cobalt bound carbon atoms are detected low field shifted at 229.9
and 207.7 ppm. A correlation spectrum (qHMBC) revealed the
resonance at 207.7 ppm to belong to the CSBn atom. Therefore,
the change from a sulfide group in 3+ to a terminal sulfur atom in 4
caused a 13C NMR low field shift for the directly attached carbon
atom of Dd = 48.1 ppm. Obviously, absence of a positive charge
in 4 compared to 3+, is effective predominantly at the coordinated
alkyne unit but much less at the metal center itself as indicated by
the negligible 31P NMR shift.
2
rate of this reaction is remarkable with respect to the observation
that the corresponding PMe3 complex 2-PF6 did not react at all
with any fluoride source. The air-sensitive thioalkyne complex
4 was isolated from toluene solution and crystallized from thf/
n-hexane. The result of a X-ray diffraction analysis is depicted
in Fig. 3, selected interatomic distances and angles are listed in
Table 1. Complex 4 crystallizes in the triclinic system with two
individual molecules in the asymmetric unit. Both specimens differ
only marginally.
Going from 3+ to 4, the connectivity of the alkyne complex
and the overall tetrahedral geometry at the cobalt center is
remarkably retained. As observed in 3+, the CoC1C2 plane is
again not aligned with one of the Co–P bonds. The Co–P2 bond,
which lies approx. perpendicular to the C1–C2 vector, is of equal
length in 3+ and 4, while the other two Co–P1 and Co–P3 bonds
are slightly shorter in 4. In addition, the C1–C2 bond lengths
and the mean Co–Csp distances are virtually equal in 3+ and
˚
˚
˚
˚
4 {1.342(7) A vs. 1.346(5) A and 1.846(5) A vs. 1.846(3) A,
respectively}. However, the thioalkyne in 4 is coordinated in a
nonsymmetric fashion leading to a significantly longer Co–C1
bond compared with Co–C2. Thus, the carbon atom with the
terminal sulfur atom attached is somewhat displaced from the
626 | Dalton Trans., 2010, 39, 624–631
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©

◦
+
+
˚
Table 2 Selected interatomic distances (A) and angles ( ) for 6 and 7
6+
7+
6+
7+
Co–C1
C1–S1
Pt–S1
C1–C2
Co–P1
Co–P2
Co–P3
1.821(7)
1.714(7)
2.287(2)
1.346(10)
2.161(2)
2.161(2)
2.178(2)
1.860(5)
1.709(6)
2.358(2)
1.319(8)
2.181(2)
2.146(2)
2.147(2)
Co–C2
C2–S2
Pt–S2
1.832(7)
1.693(7)
2.268(2)
1.815(5)
1.702(5)
2.337(2)
Pt–N1
Pt–N2
Pt–P4
Pt–P5
2.071(6)
2.062(6)
2.256(2)
2.251(1)
C1–C2–S2
C2–C1–S1
S1–Pt–S2
123.3(6)
122.8(6)
89.40(6)
126.5(4)
124.4(4)
89.16(5)
The half wave potential E1/2 of 4 in thf solution was shown
to be -1.44 V vs. Ferrocene/Ferrocenium by cyclic voltammetry.
Stoichiometric reduction of 4 with C8K in thf led to a deep
green solution, which showed a single new resonance at -23 ppm
in the 31P NMR spectrum. A MALDI mass spectrum of the
solid sample displayed an intense peak at m/z = 773 for the
doubly protonated species [(triphos)Co(C2S2H2)]+. Therefore, we
2
concludedthatK[(triphos)Co(h -C2S2)], K-5, ispresentinsolution
(Scheme 1). The complex anion 5- turned out to be highly
reactive rendering the isolation of an analytically pure sample
difficult. However, we used solutions of K-5 successfully for further
coordination attempts.
2
The only known, structurally characterized h -alkyne complex
of acdt2- displays bend-back angles of 138.3◦ and 143.8◦ leading to
a long intermolecular S–S¢ distance of 3.9 A.18 Therefore, consider-
˚
ingthe presumably large S,S¢-bite angle in 5- we felt platinum being
an appropriate candidate for the formation of heterobimetallic
S,S¢-chelate complexes. Indeed, addition of [PtCl2(phen)] or
[PtCl2(dppe)] to solutions of K-5 in thf and the subsequent addi-
tion of NaBPh4 ledtoa colour change to purple or red, respectively.
The 31P NMR spectra of the products revealed the consumption of
K-5 and a remarkable coordination shift of more than 60 ppm. The
dinuclear complexes [(triphos)Co(C2S2)Pt(phen)](BPh4), 6-BPh4,
and [(triphos)Co(C2S2)Pt(dppe)](BPh4), 7-BPh4, were purified
by column chromatography and crystallized in moderate yields
from solutions in CH2Cl2–n-hexane (6-BPh4) or thf (7-BPh4).
The molecular structures of 6+ and 7+ determined by X-ray
diffraction of 6-BPh4 and 7-BPh4 are depicted in Fig. 4 and selected
interatomic distances and angles are listed in Table 2.
In both complex cations acdt2- adopts the h -C,C¢-k -S,S¢-
bridging mode with a largely planar five-membered chelate ring.
The Pt centers are coordinated in a square planar fashion, while
the Co alkyne complex unit is highly similar to that in 3+ and
4. As already observed in 3+ and 4, the position of the C2S2
plane with respect to the P3 unit at Co is rather staggered than
aligned with one of the Co–P bonds. To allow for the S,S¢-
chelate coordination, the bend-back angles in the Co alkyne
complex moiety are noticeably decreased compared with those
in 4 (Table 2). However, the comparatively long intramolecular
Fig. 4 Molecular structures of 6+ (top) and 7+ (below) showing 50%
probability ellipsoids and atom labelling scheme. Hydrogen atoms and
BPh4 anions are omitted for clarity.
2
2
rings in 6+ show virtually local Cs symmetry, which does not
apply to the same extent to 7+. Therefore, the stronger electron-
withdrawing effect of the [Pt(phen)] moiety leads to a higher partial
charge at the alkyne complex unit, which is reflected by resonance
structure A, while 7+ is better represented by resonance structure
B (Fig. 4). The effect is still visible but small at the phosphorus
atoms of the triphos ligand as indicated by the 31P NMR shift.
Generally, the Pt–S bond lengths in 7+ meet those ob-
served in thioether and dithiocarbamate complexes, and they
are longer than usually observed in neutral Pt(II) dithio-
+
+
˚
˚
S1 ◊ ◊ ◊ S2 distances of 3.203(2) A in 6 and of 3.296(2) A in 7
reflect the still large S,S¢- bite angle of 5-. A detailed comparison
of 6+ and 7+ shed light on the effect of sulfur coordination on the
Co alkyne complex unit. The Pt–S bonds in the phen complex
6+ are significantly shorter than in the dppe congener 7+, which is
consistent with an antisymbiotic effect.29 As a result, the CoC2S2Pt
lene complexes with the dppe ancillary ligand (mean value
30-32
˚
2.303 A).
However, taking in to account the 31P-195Pt cou-
pling in NMR experiments, the trans-effect of 5- is even
somewhat stronger compared with maleonitriledithiolate or
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 624–631 | 627
©

Table 3 Electronic property data of 6-BPh4 and 7-BPh4
a sulfur to platinum charge transfer, the intensity of which being
comparatively low.
l/nm (e/103 L
E1/2 (vs. Fc/Fc+)/V
(DEp/V)
Cyclic voltammetry studies revealed that both complexes can
be reduced at fairly low potential (Table 3). The redox wave of 7-
BPh4 shows quasi-reversible behavior with DE = 180 mV (Fig. 6).
Stoichiometric reduction experiments with 7-BPh4 proved the
chemical reversibility of the reduction by subsequent reoxidation
as indicated by electronic absorption spectroscopy. Differing
from 7-BPh4, the voltammogram of 6-BPh4 displays two redox
processes in the potential range of interest. Very likely, the
second process is due to the reduction of the phenanthroline
ligand, which is expected at such a potential.34 Interestingly,
stoichiometric one-electron reduction of 6-BPh4 does not lead to
a paramagnetic complex, while formation of paramagnetic 7 was
proven (vide infra).
mol-1 cm-1)
K-5
6-BPh4
7-BPh4
456a
379 (6.5)
428 (5.9)
593a
554 (8.8)
562 (5.2)
—
—
-1.64 (0.12)
-1.71 (0.18)
-1.96 (0.18)
a Absorptivity uncorrected.
bis(methoxycarbonyl)ethenedithiolate. The corresponding 1J(31P-
195Pt) values are 2794 Hz for [Pt(dppe){S2C2(CN)2}],30 2769 Hz for
[Pt(dppe){S2C2(CO2Me)2}]31 and 2581 Hz for 7+. An exceptional
structural feature of both, 6+ and 7+, is the folding of the
CoC2S2 unit about the Csp ◊ ◊ ◊ Csp axis. The angles between best
calculated planes◦including the atoms CoC1C2 and C1C2S1S2Pt
amount to 7.8(3) in 6+ and 11.4(2)◦ in 7+.
Interestingly, we have not been able to isolate the related
homoleptic complex [Pt(5)2] by reaction of K-5 with various Pt
precursors like [PtCl2(NCPh)2]. In contrast, the related W(II)
complex anion [Tp¢W(CO)2(acdt)]- forms trimetallic neutral
complexes with all divalent group 10 metal ions (see Fig. 1).
Examination of reaction mixtures with Pt2+ and 5- indicated by
mass and 31P NMR spectroscopy the formation of the cation
[(triphos)Co(C2S2)Pt(triphos)]+. Obviously, the triphos ligand is
rather labile in K-5. This observation can be rationalized by the
high field shifted 31P NMR resonance of K-5 (dP = -23.0 ppm),
which is literally equal to the resonance of free triphosphine.
The electronic absorption spectra of heterobimetallic 6-BPh4
and 7-BPh4 display high similarity with the spectrum of
monometallic K-5 (Fig. 5). We conclude that the two high
extinction absorption bands in the visible part of the spectrum
are due to the cobalt alkyne moiety. This assignment is supported
by the observation that both bands are blue shifted as a result
of Pt coordination at the sulfur centers. Combined s-donor and
p-donor effects of sulfur to platinum stabilize the HOMOs of
5- leading to a transition of slightly higher energy. Consistently,
this hypsochromic coordination shift is more pronounced in the
phen complex 6-BPh4 with the shorter Pt–S bonds (Table 3). By
comparison with related tdt2- complexes of Pt(II)33 the shoulders
at 700 and 680 nm for 6+ and 7+, respectively, can be assigned to
Fig. 6 Cyclic voltammograms of 6-BPh4 (dotted line) and 7-BPh4 (line)
in CH2Cl2, scan rate 100 mV s-1, 6-BPh4 measured at -78 ◦C.
In order to gain information on the spin density distribution
and the related physical oxidation states of the metals in 7 we
performed X-band EPR measurements in frozen thf solution. A
sample of neutral 7 was prepared in situ by reduction of 7+ with Na-
naphthalide in thf. The spectrum displays a rhombic g-tensor with
intricate hyperfine splitting (Fig. 7). Due to the high number of
potential hyperfine coupling partners the spectrum is very difficult
to elucidate coherently. However, the signal is clearly based on
a triplet structure originating from coupling to the 31P atoms of
Fig. 5 Electronic absorption spectra of K-5 (broken line), 6-BPh4 (dotted
line) and 7-BPh4 (line) in thf solution, absorptivity of K-5 is uncorrected.
Fig. 7 X-band EPR spectrum of 7 in frozen thf solution (30 K, bottom),
simulation (above).
628 | Dalton Trans., 2010, 39, 624–631
This journal is
The Royal Society of Chemistry 2010
©

dppe together with 195Pt satellites. Because for 59Co with I = 7/2
and 100% abundance a completely different pattern is anticipated,
a noticeable contribution of the spin density at the Co center
can be excluded. Therefore, the neutral complex 7 is preferably
regarded as Pt(I) complex. The result of simulation studies revealed
principle g-tensor component values of g1 = 2.22, g2 = 2.03 and
g3 = 1.93 and hyperfine coupling constants of A(195Pt) = 12–
30 mT and A(31P) = 4–10 mT (see ESI† for details). The g-tensor
anisotropy is larger compared with those in [(dppe)PtS2C2Ph2],35
but it is in agreement with literature data for related bis(dithiolene)
complexes.36-38 However, the hyperfine coupling to Pt is stronger
compared with (Bu4N)[Pt(3,5-bis-tBuC6H2S2)] displaying A(195Pt)-
values about 10 mT. This can be considered as an indication of
less delocalisation of the spin density in the acdt2- ligand and
a higher Pt contribution in the SOMO of 7. Nevertheless, an
interpretation as genuine Pt(I)-5d9 ground state is not appropriate,
because g1 ꢀ g2,3 > gel and A1 ꢀ A2,3 are expected for a square
planar coordination environment.39
Analyzer. MALDI mass spectra were recorded on a Bruker
Reflex IV spectrometer. X-band EPR spectra were recorded
on a Bruker ELEXSYS E500 spectrometer equipped with a
helium flow cryostat (Oxford Instruments ESR 910) and Hewlett-
Packard frequency counter HP5253B. EPR simulations were
performed with the W95epr program written by F. Neese (Uni-
versity of Bonn and MPI for Bioinorganic Chemistry, Mu¨lheim).
Me3SiC2H4SCCSiMe3,40 [(PMe3)3Co(Br)],41 [(triphos)Co(Br)],42
[PtCl2(phen)]43 and [PtCl2(dppe)] were prepared according to
literature methods.
X-Ray crystallographic investigations and crystal data
Single crystals suitable for X-ray diffraction were coated in
paratone oil and mounted on a glass fiber. The intensity data
of the complexes was collected on a Bruker AXS Apex system
equipped with a rotating anode. The data was measured using
either graphite monochromated Mo-Ka radiation (2-PF6, 3-PF6,
4, 7-BPh4) or goebel-mirror monochromated Cu-Ka radiation
(6-BPh4). Data collection, cell refinement, data reduction and
integration as well as absorption correction were performed
with the Bruker AXS program packages SMART, SAINT and
SADABS. Crystal and space group symmetries were determined
using the XPREP program. All crystal structures were solved with
SHELXS44 by direct methods and were refined by full-matrix
Conclusion
Our investigations with the d9 metal ion Co(I) show that alkyne
complexes of the [(triphos)Co] moiety are suitable for the stabi-
2
lization of acetylenedithiolate as h -C,C¢-complexes with two for-
mally negatively charged terminal sulfur atoms. The preparation
of [(triphos)Co(acdt)]-, 5-, was achieved by subsequent removal
of two different S-protection groups in the corresponding cationic
acetylenedisulfide complex 3+ by nucleophilic cleavage in the first
step and a reductive procedure in the second. Several attempts with
different phosphines uncovered that the procedure is very sensitive
to the type of phosphine. Thus, the PMe3 complex 2-PF6 does not
react with fluoride-ions, while a corresponding Co(I) complex with
1 and PPh2Me could not be isolated at all.
least-square techniques against Fo with SHELXL.45 All non-
2
hydrogen atoms were refined anisotropically. The hydrogen atoms
were included at calculated positions. The details of the structure
analyses are listed in Table 4.
Preparations
1-Trimethylsilyl-7-phenyl-3,6-dithiahept-4-ine (1). A solution
of Me3SiC2H4SCCSiMe3 (8.53 g, 37.00 mmol) in thf (100 mL)
was cooled to -78 ◦C. Methyllithium·lithium bromide (2.2 M
solution in Et2O, 16.8 mL, 37.00 mmol) was added and the
resulting yellow solution was stirred for half an hour at this
temperature. Subsequently, the mixture was slowly warmed to
Heterobimetallic complexes with Co(I) and Pt(II) bridged by
2
2
acdt2- in the m-h -C,C¢-k -S,S¢-mode could be isolated with
phen and dppe ancillary ligands at platinum leading to cationic
complexes [(phen)Pt(5)]+, 6+, and [(dppe)Pt(5)]+, 7+. However,
several attempts to isolate the homoleptic complex [Pt(5)2] failed.
Probably, the overall positive charge in 6+ and 7+ releases the high
electron density of the metalla-acetylendithiolate ligand 5-, which
is less effective in neutral complex species. In addition, a mutual
destabilization of 5- in hypothetic [Pt(5)2] can be considered as an
antisymbiotic effect.
0
◦C and stirred for ◦two hours at this temperature. After again
being cooled to -78 C, sulfur (1.18 g, 37.00 mmol) was added.
The mixture was stirred for 20 min at -78 C and then warmed
◦
to room temperature. To the resulting clear solution was added
benzyl bromide (4.4 mL, 37.00 mmol) at 0 ◦C. After stirring
overnight at ambient temperature, the solvents were evaporated
and the residue purified by column chromatography on SiO2 (n–
hexane–toluene 5 : 1). 1 was obtained as a yellow oil (9.97 g,
96%). Found: C, 60.64; H, 7.14; S, 22.67. C14H20S2Si·0.05 C7H8
requires C, 60.45; H, 7.21; S 22.49%; dH(400 MHz; CDCl3) 7.36–
7.30 (5 H, m, Ph-H), 3.92 (2 H, s, CH2Ph), 2.70 (2 H, m,
CH2CH2SiMe3), 0.93 (2 H, m, CH2CH2SiMe3), 0.05 (9 H, s,
Si(CH3)3); dC(101 MHz; CDCl3) 136.6, 129.1, 128.4, 127.6 (Ph-
According to cyclic voltammetry, electronic absorption and
EPR spectroscopy, the visible spectra of 6+ and 7+ are dominated
by the cobalt alkyne complex moiety, while the observable redox
chemistry is rather platinum based. Extension of the investigations
on palladium and nickel on the one hand, and on a broader
variety of ancillary ligands on the other will further strengthen
this perception.
≡
≡
C), 88.5 (Me3SiC2H4SC C), 86.4 (C CSBn), 41.5 (CH2Ph), 33.0
(CH2CH2SiMe3), 17.1 (CH2CH2SiMe3), -1.8 (Si(CH3)3).
Experimental
All manipulations were carried out under a dry argon atmosphere
using standard Schlenk techniques. Solvents were dried by stan-
dard methods and freshly distilled prior to use. NMR spectra
were recorded on Bruker Avance I 400 (400 MHz), Avance II 200
(200 MHz) and Avance III 400 (400 MHz) spectrometers. Elemen-
tal analyses were carried out on a Vario EL III CHNS-Elemental
[(PMe3)3Co(1)](PF6) (2-PF6). A solution of [(PMe3)3Co(Br)]
(300 mg, 0.82 mmol) in CH3CN (20 mL) was treated with 1
(460 mg, 1.64 mmol). The color of the solution turned green
immediately. After 30 min, KPF6 (165 mg, 0.90 mmol) was added
and the solution stirred overnight. The solvent was removed
in vacuo and the residue dissolved in CH2Cl2 (20 mL). After
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 624–631 | 629
©

Table 4 Crystal data, data collection and structure refinement for complexes 2-PF6, 3-PF6, 4, 6-BPh4 and 7-BPh4
Compound
2-PF6
3-PF6
4
6-BPh4
7-BPh4
Formula
C23H47CoF6P4S2Si C55H59CoF6P4S2Si·2CH3OH C100H92Co2P6S4·1.5thf
C79H67BCoN2P3PtS2 C93H83BCoP5PtS2·0.5thf
Formula weight
Crystal system
Space group
712.63
1109.09
Triclinic
1725.76
Triclinic
1466.21
Triclinic
1684.48
Monoclinic
P21/n
Monoclinic
P21/c
¯
P1
¯
P1
¯
P1
˚
a/A
11.7241(7)
23.9821(14)
12.5138(8)
90
101.5140(10)
90
14.5606(14)
15.0042(15)
15.4084(15)
65.400(2)
78.203(2)
67.958(2)
2832.4(5)
2
14.067(2)
15.000(2)
25.050(2)
79.982(3)
78.203(2)
77.636(3)
4615.6(10)
2
11.1143(6)
17.6581(12)
18.2065(11)
64.204(4)
89.668(4)
89.378(5)
3216.9(3)
2
12.3583(3)
19.5334(5)
34.3595(10)
90
94.1190(10)
90
8272.9(4)
4
153
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
3447.7
4
Z
T/K
153
55.76
153
47.00
153
55.76
153
2Hmax (◦)
145.18
7.704
49.70
2.086
m/mm-1
0.885
18610
0.572
20087
0.604
46827
Refls collected
Refls unique (Rint
Parameters/restraints 346/0
19176
10952 (0.1120)
803/0
65527
14303 (0.0467)
949/9
)
8208 (0.0305)
8393 (0.0560)
666/0
21988 (0.0414)
1045/0
R1 [I > 2s(I)]
0.0370
0.0953
0.582/-0.563
0.0700
0.1686
1.584/-0.858
0.0606
0.1689
1.493/-0.694
0.0688
0.1737
3.316/-2.008
0.0467
0.1251
2.359/-1.338
wR2 (all data)
-3
˚
Resid. density/e A
filtration, pure 2-PF6 was obtained as a green solid by crystal-
lization from CH2Cl2–n-hexane (460 mg, 79%). dH(400 MHz;
CDCl3) 7.33 (5 H, m, Ph-H), 4.29 (2 H, s, CH2Ph), 3.12
(2 H, m, CH2CH2SiMe3), 1.49 (27 H, s, P(CH3)3), 0.99 (2
H, m, CH2CH2SiMe3), 0.04 (9 H, s, Si(CH3)3); dC(101 MHz;
(CH2Ph), 38.0 (triphos-Cquart.), 37.2 (triphos-CH3), 32.8 (triphos-
CH2); dP(162 MHz; CDCl3) 32.6 (triphos-P); MS (MALDI) m/z
862 (M+).
K[(triphos)Co(g2-C2S2)] (K-5). At -78 ◦C C8K (56 mg,
0.42 mmol) was added to a solution of 4 (200 mg, 0.23 mmol) in thf
(15 mL) leading to an intensely green solution. The mixture was
stirred for 2 h at room temperature. This solution was used in the
following experiments without further purification. dP(162 MHz;
d8-thf) -23.0 (triphos-P); MS (MALDI) m/z 773 (M- + 2H+).
≡
CD2Cl2) 172.6, 170.6 (C C), 135.3, 129.0, 128.9, 128.0 (Ph-
C), 44.1 (CH2Ph), 36.0 (CH2CH2SiMe3), 19.7 (P(CH3)3), 17.3
(CH2CH2SiMe3), -2.0 (Si(CH3)3); dP(162 MHz; CDCl3) 9.3
(PMe3), -144.2 (PF6).
[(triphos)Co(l-g2-C,C¢-j2-S,S¢-C2S2)Pt(phen)](BPh4) (6-BPh4).
[PtCl2(phen)] (45 mg, 0.10 mmol) was added to a solution of K-5
(75 mg, 0.09 mmol) in thf (20 mL). After subsequent addition
of NaBPh4 (120 mg, 0.35 mmol), the solution was stirred for
18 h. The solvent was removed and the crude product purified by
column chromatography on SiO2 using CH2Cl2–n-hexane (10 : 1)
as eluent. After crystallization (CH2Cl2–n-hexane) the compound
was isolated as a purple solid (48 mg, 32%). Found: C, 64.31; H,
4.58; N, 1.88; S, 4.10. C79H67BCoN2P3PtS2 requires C, 64.71; H,
4.61; N 1.91; S 4.37%; dH(400 MHz; CD2Cl2) 9.52, 8.57, 7.93,
7.82 (8 H, m, phen-H), 7.34 (20 H, m, BPh4), 7.13, 7.03, 6.88
(30 H, m, triphos-Ph), 2.35 (6 H, s, triphos-CH2), 1.66 (3 H, s,
[(triphos)Co(1)](PF6) (3-PF6). The compound was prepared as
described for 2-PF6 using [(triphos)Co(Br)] (800 mg, 1.05 mmol)
and 1 (590 mg, 2.11 mmol). 3-PF6 was obtained as a green
solid after column chromatography on SiO2 using CH2Cl2–MeOH
(10 : 1) as eluent (1.01 g, 87%). dH(200 MHz; CDCl3) 7.35–6.97 (35
H, m, Ph-H), 4.16 (2 H, s, CH2Ph), 3.10 (2 H, m, CH2CH2SiMe3),
2.44 (6 H, s, triphos-CH2), 1.72 (3 H, s, triphos-CH3), 0.97 (2
H, m, CH2CH2SiMe3), -0.12 (9 H, s, Si(CH3)3); dC(101 MHz;
≡
CDCl3) 182.8, 181.8 (C C), 135.5, 134.3, 131.5, 130.0, 128.8,
128.7, 128.5, 127.8 (Ph-C), 43.2 (CH2Ph), 38.0 (triphos-Cquart.),
36.5 (triphos-CH3), 35.3 (CH2CH2SiMe3), 33.5 (triphos-CH2),
17.9 (CH2CH2SiMe3), -1.8 (Si(CH3)3); dP(81 MHz; CDCl3) 36.4
(triphos-P), -143.9 (PF6); MS (MALDI) m/z 963 (M+).
≡
triphos-CH3); dC(101 MHz; CD2Cl2) 230.9 (C C), 164.4 (B-Ci),
151.7, 146.8, 139.0, 136.4, 135.5, 131.9, 131.7, 130.0, 129.3, 129.1,
128.7, 128.3, 126.0 (Ph-C), 38.3 (triphos-Cquart.), 37.3 (triphos-
CH3), 33.4 (triphos-CH2); dP(162 MHz; CD2Cl2) 43.4 (triphos-P);
MS (MALDI) m/z 1146 (M+).
[(triphos)Co{g2-(S)C2(SCH2Ph)}] (4). At -78 ◦C Bu4NF
(110 mg, 0.39 mmol) was added to a solution of 3-PF6 (400 mg,
0.36 mmol) in thf (30 mL) leading to an intensely purple solution.
The mixture was stirred for 12 h at room temperature. The
solvent was evaporated and the residue redissolved in toluene.
The mixture was filtered to remove Bu4NPF6. Crystallization
from thf/n-hexane yielded dark purple crystals (230 mg, 74%).
Found: C, 69.48; H, 5.59; S, 7.04. C50H46CoP3S2·thf requires C,
69.37; H, 5.82; S 6.86%; dH(400 MHz; C6D6) 7.58, 7.10, 6.99
(5 H, m, CH2Ph), 7.39, 6.81, 6.80 (30 H, m, triphos-Ph), 5.56
[(triphos)Co(l-g2-C,C¢-j2-S,S¢-C2S2)Pt(dppe)](BPh4) (7-BPh4).
The compound was prepared as described for 6-BPh4 using K-
5 (74 mg, 0.09 mmol), [PtCl2(dppe)] (63 mg, 0.09 mmol) and
NaBPh4 (117 mg, 0.34 mmol). 7-BPh4 was obtained as a red solid
after column chromatography on SiO2 using CH2Cl2/n–hexane
(5 : 1) as eluent (91 mg, 63%). Found: C, 63.79; H, 4.96; S, 3.45.
C93H83BCoP5PtS2·CH2Cl2 requires C, 63.81; H, 4.84; S 3.62%;
dH(400 MHz; CD2Cl2) 7.89–6.83 (70 H, m, Ph-H), 2.38 (4 H,
m, dppe), 2.28 (6 H, s, triphos-CH2), 1.59 (3 H, s, triphos-CH3);
(2 H, s, CH2Ph), 2.04 (6 H, s, triphos-CH2), 1.13 (3 H, s, triphos-
8
≡
≡
CH3); dC(101 MHz; d -thf) 229.9 (SC CSBn), 207.7 (SC CSBn),
142.2, 139.5, 133.0, 130.7, 129.0, 128.8, 128.5, 128.2 (Ph-C), 35.2
630 | Dalton Trans., 2010, 39, 624–631
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The Royal Society of Chemistry 2010
©

≡
dC(101 MHz; CDCl3) 242.1 (C C), 164.2 (B–Ci), 141.2, 136.3,
134.9, 133.5, 131.8, 131.4, 129.0, 128.7, 127.9, 127.1, 125.4 (Ph-
16 W. W. Seidel, M. Schaffrath and T. Pape, Angew. Chem., 2005, 117,
7976–7979; W. W. Seidel, M. Schaffrath and T. Pape, Angew. Chem.,
Int. Ed., 2005, 44, 7798–7800.
17 W. W. Seidel, M. Schaffrath and T. Pape, Chem. Commun., 2006, 3999–
4000.
C), 37.8 (triphos-Cquart.), 37.2 (triphos-CH3), 33.3 (triphos-CH2),
1
2
27.5 (dd, JCP = 38.7 Hz, JCP = 11.9 Hz, dppe); dP(162 MHz;
CD2Cl2) 45.3 (1JPPt = 2581 Hz, dppe-P), 42.3 (triphos–P); MS
(MALDI) m/z 1365 (M+).
18 W. W. Seidel, M. J. Meel, U. Radius, M. Schaffrath and T. Pape, Inorg.
Chem., 2007, 46, 9616–9629.
19 F. Diehl, H. Meyer, A. Schweig, B. A. Hess Jr. and J. Fabian, J. Am.
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Acknowledgements
We are grateful to the Deutsche Forschungsgemeinschaft and the
Fonds of Chemical Industry (VCI) for an award for M.J.M. We
thank Dr. E. Bill (MPI Mu¨lheim) for the EPR measurement.
W.W.S. thanks Prof. F. E. Hahn for generous support.
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This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 624–631 | 631
©