Rational Synthesis of the Carbonyl(perthiolato)diiron [Fe2(S3CPh2)(CO)6] and Related Complexes

Article abstract of DOI:10.1002/ejic.201600366

The photochemical reaction of Fe₂(S₂)(CO)₆and Ph₂CS affords the perthiolate Fe₂(S₃CPh₂)(CO)₆(1) in good yield. As confirmed crystallographically, 1 contains a previously elusive perthiolate ligand. The related reaction of Fe₂(S₂)(CO)₅(PPh₃) and Ph₂CS gave Fe₂(S₃CPh₂)(CO)₅(PPh₃). Although Fe₃S₂(CO)₉and Ph₂CS failed to efficiently give Fe₂(S₂CPh₂)(CO)₆, this compound could be prepared by desulfurization of 1 using PPh₃.

Full text of DOI:10.1002/ejic.201600366

DOI: 10.1002/ejic.201600366
Communication
Iron Sulfur Clusters
Rational Synthesis of the Carbonyl(perthiolato)diiron
[Fe2(S3CPh2)(CO)6] and Related Complexes
Peihua Zhao,[a,b] Danielle L. Gray,[b] and Thomas B. Rauchfuss*[b]
Abstract: The photochemical reaction of Fe2(S2)(CO)6 and (PPh3) and Ph2CS gave Fe2(S3CPh2)(CO)5(PPh3). Although
Ph2CS affords the perthiolate Fe2(S3CPh2)(CO)6 (1) in good yield. Fe3S2(CO)9 and Ph2CS failed to efficiently give Fe2(S2CPh2)(CO)6,
As confirmed crystallographically, 1 contains a previously elu- this compound could be prepared by desulfurization of 1 using
sive perthiolate ligand. The related reaction of Fe2(S2)(CO)5- PPh3.
Introduction
prepared efficiently, by the reaction of Fe3(CO)12 and methane-
dithiol.[6]
The chemistry of carbonyl(dithiolato)diiron compounds is rich,
consisting of both routine and esoteric complexes. Hundreds
of compounds are known with the formula Fe2(SR)2(CO)6, and
thousands of CO-substituted derivatives of such compounds
have been reported. Foundational compounds include
Fe2(SR)2(CO)6 with R = Me, Et, Ph, as well as the more recently
popularized pdt and adt derivatives.[1] These complexes have
attracted intense attention because of their similarity to the
active site of the [FeFe]-hydrogenases, with the hope that syn-
thetic analogues of the enzyme might underpin technologies
for producing hydrogen.[2]
Scheme 1. Simple but elusive compounds of the type Fe2(SR)2(CO)6.
In this paper, we report a new approach to obtaining some
of the aforementioned elusive targets. The guiding hypothesis
was that stable thioketones (unlike thioformaldehyde), might
add to Fe2(S2)(CO)6. The photoinduced additions of ethylene
and CO to Fe2(S2)(CO)6 afford Fe2(S2C2H4)(CO)6 and
Fe2(S2CO)(CO)6, respectively.[7] The reaction has been extended
to other alkenes.[8] These photoadditions probably proceed via
the diferrous sulfide Fe2(S)2(CO)6, an excited state of
Fe2(S2)(CO)6.[9]
Although the complexes Fe2(SR)2(CO)6 can be produced in
excellent yields for many R groups, a handful of related com-
plexes have only been obtained in trace amounts. Some of
these “esoteric” compounds are quite simple in composition
and could in fact be useful building blocks if they were more
readily prepared. Examples of such esoteric but fundamental
complexes are shown in Scheme 1; they include CS4Fe4(CO)12,
C2S4Fe4(CO)12, CH2S2Fe2(CO)6, and CH2S3Fe2(CO)6. The first two
are obtained in low (1–2 %) or unspecified yields upon reaction
of Fe3(CO)12 with CS2.[3] The third complex in Scheme 1,
Fe2(S3CH2)(CO)6, is
a
derivative of the thiol-perthiol
Results and Discussion
H2C(SH)(S2H), which is unknown and is expected to be labile.
The complex was obtained in low yield from the reaction of
Fe3(CO)12, S8, and styrene.[4] It is difficult to envision how this
combination of reagents produces the observed perthiolate.
This complex is formally an adduct of thioformaldehyde and
Fe2(S2)(CO)6. Since free CH2S is only stable as a dilute gas, it is
not a reasonable reagent.[5] Only the methanedithiolate can be
We confirmed that Fe2(S2)(CO)6 does not readily react with
Ph2CS thermally. This nonreactivity was easily checked, because
the thione is deep blue. More promising results were obtained
upon UV irradiation of a toluene solution of Fe2(S2)(CO)6
(90 mg) and an equimolar amount of Ph2CS (50 mg). The reac-
tion was conducted using an LED emitting at 365 nm to give
the targeted adduct [Equation (1)].
After ca. 1 h, the red product was obtained in 44 % yield
after purification by column chromatography. The new com-
pound 1 exhibited an FT-IR spectrum [2080 (s), 2046 (vs), 2007
(vs) cm–1] that closely ( 5 cm–1) resembled the spectrum for
[a] School of Materials Science and Engineering, North University of China
Taiyuan 030051, PRC
[b] School of Chemical Sciences, University of Illinois at Urbana-Champaign
Urbana, IL 61801, USA
E-mail: rauchfuz@gmail.com
http://www.scs.illinois.edu/rauchfus/
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejic.201600366.
1
Fe2(S2)(CO)6. The H and 13C NMR spectra were consistent but
not informative, but the EI-MS data showed a progression of
peaks for Fe2(S3CPh2)(CO)6–n at m/z = 513.8 – n(28), which are
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Communication
precursor to Fe2(S2CPh2)(CO)6. A reaction between Fe3S2(CO)9
and excess Ph2CS could only be induced in refluxing toluene,
but the desired 3 was only obtained in ca. 10 % yield [Equa-
tion (2)].
(1)
(2)
assigned to [M – n CO]+ for n = 1–6. Once isolated, 1 is robust
in air and ambient light.
This result suggests that 3 is not produced via the Fe3S2
cluster. Indeed, the intermediacy of the dithiirane Ph2CS2 has
been proposed for related reactions.[11b,11c,12]
A more rational route to 3 involves the desulfurization of the
perthiolate 1. Indeed, treatment of a CH2Cl2 solution of 1 with
1 equiv. of PPh3 at room temperature gave 3 in 85 % isolated
yield [Equation (3)].
To test the generality of the new reaction, we also investi-
gated the photoaddition of Fe2(S2)(CO)5(PPh3)[8c] to thiobenzo-
phenone. This reaction proceeded as above to give the adduct
Fe2(S3CPh2)(CO)5(PPh3) (2) in 45 % isolated yield. The 31P NMR
spectrum of the adduct confirmed the presence of a single spe-
cies with a signal at δ(31P) = 70.6 ppm, distinct from that of the
parent Fe2(S2)(CO)5(PPh3) [δ(31P) = 60.81 ppm]. The reaction did
not produce SPPh3, in contrast to a related reaction below.
The structure of 1 was confirmed crystallographically (Fig-
ure 1). The molecule has idealized Cs symmetry but no crystallo-
graphically imposed symmetry. The compound adopts the now
familiar butterfly structure with six terminal CO ligands. The CS3
bridge is planar.
(3)
The coproduct was SPPh3. The product was identical to that
obtained in low yield from Fe3S2(CO)9.
Conclusions
The synthetic chemistry of Fe-S-CO compounds is very old,[13]
and the biological chemistry of related materials is possibly an-
cient.[14] Given this rich context, new routes to fundamental
derivatives of the Fe-S-CO series are always welcome. The addi-
[15]
tion of thioketones to Hieber's classic Fe2S2(CO)6
should en-
courage the development of photoadditions or other hetero-
alkenes, hopefully opening new opportunities for this fascinat-
ing area.
Experimental Section
General Methods: Spectroscopic instrumentation and methodol-
ogy have been described.[16] 1H NMR (500 MHz) and 13C NMR
(162 MHz) spectra were referenced to residual solvent relative to
TMS. 31P{1H} NMR (202 MHz) spectra were referenced to external
85 % H3PO4. Crystallographic data were collected using a Siemens
SMART diffractometer equipped with an Mo-Kα source (λ =
0.71073 Å). The preparation of starting reagents are mentioned
above, and Ph2CS was obtained using Lawesson's reagent.[17] CCDC
1476511 (for 1), and 1440460 (for 3) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre.
Figure 1. Structure of Fe2(S3CPh2)(CO)6 (1) with thermal ellipsoids drawn at
the 50 % probability level. Selected distances [Å] and angles [°]: Fe(1)–Fe(2)
2.5068(6), Fe(1)–S(1) 2.2256(10), Fe(1)–S(3) 2.2427(9), S(1)–S(2) 2.0630(13),
S(2)–C(4) 1.847(3), C(4)–S3 1.856(3); S(1)–Fe(1)–S(3) 81.40(3), S(1)–S(2)–C(4)
102.24(11), S(2)–C(4)–S(3) 109.41(16).
Fe2(S3CPh2)(CO)6 (1): A mixture of Fe2S2(CO)6 (90 mg, 0.25 mmol)
and Ph2CS (50 mg, 0.25 mmol) was dissolved in dry toluene (70 mL)
in a Pyrex Schlenk tube. The reaction mixture was photolyzed at
365 nm for ca. 1 h. After filtration, the resulting deep-green filtrate
was concentrated under vacuum to afford a viscous residue. The
residue was chromatographed on silica gel eluting with hexane/
CH2Cl2 (10:1). The main red band (the second band) was concen-
The reaction of thiobenzophenone with Fe2(S2)(CO)6
prompted investigation of its reaction with Fe3S2(CO)9, the
other main Fe-S-CO cluster.[10] The diphenylmethanedithiolate
has been obtained in 5–25 % yield by the reaction of thio-
benzophenone with Fe2(CO)9 and Fe3(CO)12.[11] These reactions
also produce several other products, including Fe3S2(CO)9. From
1
trated to give the product, a red solid. Yield 60 mg (44 %). H NMR
the perspective of stoichiometry, this triiron cluster is a logical (500 MHz, CD2Cl2): δ = 7.64 (d, J = 6.5 Hz, 4 H, ArH), 7.28 (d, J =
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Communication
6.5 Hz, 6 H, ArH) ppm. 13C NMR (162 MHz, CD2Cl2): δ = 207.5 (FeCO),
143.3 (ArC), 128.57, 128.55, 128.4 (ArCH), 89.8 (S2CPh2) ppm. FT-IR
Keywords: Iron sulfides · Thiones · Photochemistry ·
Perthiolates · Desulfurization
(CH2Cl2): νCO = 2080 (vs), 2046 (vs), 2007 (vs) cm–1. EI-MS: m/z =
˜
513.8 [M – CO]+, 485.8 [M – 2 CO]+, 457.8 [M – 3 CO]+, 401.9 [M –
5 CO]+, 373.9 [M – 6 CO]+. C19H10Fe2O6S3 (541.8): calcd. C 42.09, H
1.86; found C 41.77, H 1.57. The single crystal for X-ray analysis was
grown by slow concentration of a concentrated pentane solution.
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Fe2(S3CPh2)(CO)5(PPh3) (2): A mixture of Fe2S2(CO)5(PPh3) (90 mg,
0.15 mmol) and Ph2CS (30 mg, 0.15 mmol) was dissolved in dry
toluene (60 mL) in a Pyrex Schlenk tube. The mixture was irradiated
at 365 nm for ca. 1 h. After the solvent had been removed under
vacuum, the residue was purified by chromatography on silica gel
eluting with hexane/CH2Cl2 (4:1). The intense red band (the third)
was concentrated to give the product as a red solid. Yield 50 mg
1
(43 %). H NMR (500 MHz, CD2Cl2): δ = 7.58–7.44 (br. d, 16 H, ArH),
7.26–7.13 (m, 9 H, ArH) ppm. 31P NMR (202 MHz, CD2Cl2): δ = 70.6
(s) ppm. FT-IR (CH2Cl2): νCO = 2045 (vs), 1991 (vs), 1975 (s). 1934 (m)
˜
cm–1
.
Fe2(S2CPh2)(CO)6 (3). Method 1: A mixture of Fe2(S3CPh2)(CO)6
(50 mg, 0.09 mmol) and PPh3 (27 mg, 0.10 mmol) was dissolved
in dry CH2Cl2 (10 mL). The reaction solution was stirred at room
temperature until the reaction was completed (3 h) as indicated
by FT-IR spectroscopy. After the solvent had been removed under
vacuum, the residue was purified by chromatography on silica gel
eluting with hexane/CH2Cl2 (10:1). The intense red band (the first
band) was collected and concentrated to yield the product, an or-
ange-yellow solid. Yield 40 mg (87 %). 1H NMR (500 MHz, CD2Cl2):
δ = 7.33 (br. s, 8 H, ArH), 7.23 (br. s, 2 H, ArH) ppm. 13C NMR
(162 MHz, CD2Cl2): δ = 208.7 (FeCO), 150.2 (ArC), 129.0, 128.1, 123.7
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(ArCH), 95.1 (S2CPh2) ppm. FT-IR (CH2Cl2): νCO = 2076 (vs), 2039 (vs),
˜
2000 (vs) cm–1. EI-MS: m/z = 510.1 [M]+, 482.1 [M – CO]+, 454.1 [M
– 2 CO]+, 426.1 [M – 3 CO]+, 398.1 [M – 4 CO]+, 370.1 [M – 5 CO]+,
342.0 [M – 6 CO]+. Method 2: A mixture of Fe3S2(CO)9 (97 mg,
0.20 mmol) and Ph2CS (40 mg, 0.20 mmol) was dissolved in dry
toluene (100 mL). The reaction mixture was heated at 90 °C for 2 h
and then at reflux for 1.5 h. After the solvent had been removed
under vacuum, the residue was purified by chromatography on sil-
ica gel, eluting with hexane/CH2Cl2 (10:1). The intensely red band
(the first band) was collected and concentrated to yield the product
as an orange-yellow solid. Yield 10 mg (10 %).
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Acknowledgments
This research was supported by the US National Institutes of
Health and the National Natural Science Foundation of China
(No. 21301160).
Received: March 30, 2016
Published Online: May 19, 2016
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