Carbon monoxide release properties and molecular structures of phenylthiolatomanganese(i) carbonyl complexes of the type [(OC)4Mn(μ-S-aryl)]2

Article abstract of DOI:10.1039/c4dt03567d

Several phenylthiolatomanganese carbonyl complexes of the type [(OC)₄Mn(μ-SR)]₂ (R = Ph (1a), C₆H₄-4-CH₃ (1b), C₆H₄-4-CF₃ (1c), C₆H₄-4-F (1d), C₆H₄-4-Cl (1e), C₆H₄-4-OMe (1f), C₆F₅ (1g), and CH₂C₆H₄-4-Cl (1h)) have been prepared via the reaction of Mn₂(CO)₁₀ with diaryldisulfane or via the reaction of [(OC)₅MnBr] with arylthiols. These complexes lose two carbon monoxide molecules quite easily yielding tetranuclear [(OC)₃Mn(μ₃-SR)]₄ (2). Derivatives with fluoro-substituted aryl groups commonly form mixtures of dinuclear 1 and tetranuclear 2 which can quantitatively be converted to 2 by heating of the corresponding reaction mixtures. A unique trinuclear structure is found for the mesityl derivative [(OC)₄Mn(μ-SMes)]₃ (3) which is maintained in solution as verified by IR and NMR spectroscopy. Traces of an already known dinuclear by-product of the type [(OC)₃Mn(μ-SC₆H₃(-4-Me)-2-SC₆H₄-4-Me)]₂ (4) have been structurally characterized. The suitability of [(OC)₄Mn(μ-SPh)]₂ (1a) as a CO releasing molecule (CORM) for the administration of carbon monoxide has been studied. Two CO molecules are released upon dissolving in strongly Lewis basic solvents L, yielding [(OC)₃Mn(L)(μ-SPh)]₂, which liberates all the remaining CO molecules upon irradiation (photoCORM behavior). This journal is

Full text of DOI:10.1039/c4dt03567d

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Carbon Monoxide Release Properties and Molecular Structures of
Phenylthiolatomanganese(I) Carbonyl Complexes of the Type [(OC)4Mn(µꢀSꢀAryl)]2
Ralf Mede,a,# Vaneza Paola LorettꢀVelásquez,a,b,# Moritz Klein,c,d,# Helmar Görls,a Michael Schmitt,c,d
Guido Gessner,e Stefan H. Heinemann,e Jürgen Popp,c,d Matthias Westerhausen*,a
a) Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University Jena,
Humboldtstraße 8, Dꢀ07743 Jena, Germany
eꢀmail: m.we@uniꢀjena.de, fax: +49 3641 948132; homepage: http://www.lsac1.uniꢀjena.de/
b) Current address: Department of Chemistry, Universidad Antonio Nariño
Sede Circunvalar, Carrera 3 Este, Bogotá D. C., Colombia
c) Institute of Physical Chemistry, Friedrich Schiller University Jena,
Helmholtzweg 4, Dꢀ07743 Jena, Germany
d) Institute of Photonic Technology (IPHT),
AlbertꢀEinsteinꢀStraße 9, Dꢀ07745 Jena, Germany
e) Center for Molecular Biomedicine (CMB),
Department of Biophysics, Friedrich Schiller University Jena and Jena University Hospital,
HansꢀKnöllꢀStraße 2, Dꢀ07745 Jena, Germany
#) These authors contributed equally.
Abstract
Several phenylthiolatomanganese carbonyl complexes of the type [(OC)4Mn(µꢀSR)]2 (R = Ph (1a),
C6H4ꢀ4ꢀCH3 (1b), C6H4ꢀ4ꢀCF3 (1c), C6H4ꢀ4ꢀF (1d), C6H4ꢀ4ꢀCl (1e), C6H4ꢀ4ꢀOMe (1f), C6F5 (1g), and
CH2C6H4ꢀ4ꢀCl (1h)) have been prepared via the reaction of Mn2(CO)10 with diaryldisulfane or via the
reaction of [(OC)5MnBr] with arylthiols. These complexes lose two carbon monoxide molecules quite
easily yielding tetranuclear [(OC)3Mn(µ3ꢀSR)]4 (2). Derivatives with fluoroꢀsubstituted aryl groups
commonly form mixtures of dinuclear 1 and tetranuclear 2 which can quantitatively be converted to 2
by heating of the corresponding reaction mixtures. A unique trinuclear structure is found for the
mesityl derivative [(OC)4Mn(µꢀSMes)]3 (3) which is maintained in solution as verified by IR and
NMR spectroscopy. Traces of an already known dinuclear byꢀproduct of the type [(OC)3Mn(µꢀ
SC6H3(ꢀ4ꢀMe)ꢀ2ꢀSC6H4ꢀ4ꢀMe)]2 (4) have been structurally characterized. The suitability of
[(OC)4Mn(µꢀSPh)]2 (1a) as a CO releasing molecule (CORM) for administration of carbon monoxide
has been studied. Two CO molecules are released upon dissolving in strongly Lewis basic solvents L
yielding [(OC)3Mn(L)(µꢀSPh)]2 which liberates all remaining CO molecules upon irradiation
(photoCORM behavior).
Keywords: CORMs, Manganese, Carbonyl Complexes, Phenylthiolates, Metal Carbonyls, CO
Detection
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Introduction
Metal carbonyl complexes have been available for many decades1 and recently they have been
reinvestigated as CO releasing molecules (CORMs) to administer the signaling molecule CO in
biological tissues even though also transition metalꢀfree CORMs are known.2 On the one hand, the
advantageous variations of transition metal carbonyls include the content of CO molecules, diverse
CO release triggers, nature of the metals itself (size, oxidation state, Pearson hardness, Lewis acidity),
and nature of coligands (tunable physical and chemical properties such as solubility, Lewis basicity,
charge backdonation, and complex stability).2,3 On the other hand, very few pharmaceutical drugs are
of organometallic nature4 due to supposed toxicity of many transition metals. CORMs have to fulfill
certain requirements such as solubility in aqueous solutions, thermal stability, triggered CO release,
nonꢀtoxicity of the metal complexes as well as of their inactive products (iCORMs). Metal carbonyls
of chromium, manganese, iron, and cobalt as well as of some of their homologous congeners represent
the most intensively studied complexes5 because these 3d metals represent essential elements and
carbonyl complexes are readily available. However, also nonꢀessential elements have been exploited
for medicinal applications.4 Nevertheless, beneficial and toxic effects strongly depend on the
concentration of CORMs and their inactive degradation products.6
Mangenese carbonyl complexes already showed promising properties with respect to CO release, with
CORMꢀ1 [Mn2(CO)10] being the most prominent representative.2 Suitable complexes under
investigation today contain the Mn(CO)3 fragment with cisꢀarranged carbonyl ligands as e.g. in
combination with tridentate ligands.7 Furthermore, manganese(I) carbonyls with bidentate ligands and
a monodentate Lewis base such as bromide or acetonitrile also represent suitable photoCORMs.8 In
waterꢀsoluble manganese(I) tetracarbonyl derivatives one carbon monoxide is easily liberated
reversibly and this release is fast if the CO molecule is removed.9 Generally and in agreement with
quantum chemical calculations, in complexes with Mn(CO)4 units one carbonyl ligand is released
quite easily depending on the nature of the other two coligands whereas the complex with the
Mn(CO)3 moiety shows significantly poorer CO release properties.10 Novel strategies include
immobilization of such CORMs retaining (or withholding) the metalꢀbased degradation products after
liberation of carbon monoxide.11 This strategy reduces the importance of water solubility of such
complexes.
Despite the fact that diverse manganese carbonyl complexes attract the attention of several research
groups, a wellꢀknown class of manganese carbonyls remained unvalued. Carbonyl
phenylthiolatomanganese(I) complexes of the types [(OC)4Mn(µꢀSR)]2 and [(OC)3Mn(µ3ꢀSR)]4 are
easily accessible and known for many decades, however, their CO release properties and kinetics
remained nearly unnoticed. The attractiveness of these complexes relies on the possibility to easily
alter chemical and physical properties by variation of the substitution patterns of the aryl groups.
Numerous procedures have been reported for the preparation of these phenylthiolatomanganese(I)
carbonyl complexes:
ꢀ
The first synthesis of [(OC)4Mn(µꢀSR)]2 12 and homologous [(OC)4Re(µꢀSR)]2 13 was
achieved via the reaction of the pentacarbonylmanganese halides with phenylmercaptan. It
was reported that more vigorous reaction conditions yielded trinuclear [(OC)4Mn(µꢀSR)]3.14
Reaction of HMn(CO)5 with phenylmercaptan and pentafluorophenylmercaptan in benzene or
without solvent led to the formation of [(OC)4Mn(µꢀSR)]2 and [(OC)3Mn(µ3ꢀSR)]4.14
Reaction of BrMn(CO)5 with (phenylthio)ꢀtrimethylsilane in 1,2ꢀdimethoxyethane at above
70 °C yielded [(OC)3Mn(SR)].15
ꢀ
ꢀ
ꢀ
Reaction of [(OC)4Mn(µꢀSC6F5)]2 with CO gas at high pressure allowed the isolation of
mononuclear (OC)5MnꢀSC6F5.16
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ꢀ
ꢀ
Depending on the reaction conditions, the reaction of the [Mn(CO)5]ꢀ with diphenyldisulfane
gave [{(OC)3Mn}2(µꢀSR)3]ꢀ or [(OC)4Mn(µꢀSR)]2.17
The photochemical addition of diphenyldisulfane to Mn2(CO)10 gave [(OC)4Mn(µꢀSPh)]2 with
a yield of 80 %.18 A similar procedure also allowed the isolation of homologous [(OC)4Mn(µꢀ
SePh)]2.19
The reaction of [(η5ꢀthiophene)Mn(CO)3]+ with the paraꢀtolylthiolate anion led to the
formation of [(OC)4Mn(µꢀSTol)]2.20
The complexes [(OC)4Mn(µꢀSPh)]2 and [(OC)3Mn(µ3ꢀSPh)]4 were obtained with rather poor
yields from the reaction of (η4ꢀ1ꢀphenylꢀ3,4ꢀdimethylthiophene)Mn(CO)3 with hydrogen gas
at 30 atm in THF besides other products such as diphenyldisulfane and the major product 2,3ꢀ
dimethylꢀ1,3ꢀbutadiene.21
ꢀ
ꢀ
ꢀ
The transfer of phenylthiolato ligands from the molybdenum complex Cp2Mo(SPh)2 to
Mn2(CO)10 yielded ionic [Cp2Mo(CO)H] [{(OC)3Mn}3(µ3ꢀSPh)(µꢀSPh)3].22
There are only very few reports on trinuclear derivatives of the type [(OC)3Mn(µꢀSR)]3 (R = Ph,
C6F5),14 however, in the light of later studies these molecules had to be formulated as a tetranuclear
cage compound of the type [(OC)3Mn(µꢀSR)]4 with a central Mn4S4 heterocubane moiety. Osborne
and Stone also reported the trinuclear complex [(OC)3Mn(µꢀSMe)]3 that was prepared via the reaction
of manganese pentacarbonyl halides with bis(methylthio)dimethylstannane, however, no spectroscopic
data have been provided to verify this interpretation.23
The photochemical addition of diaryl disulfide to Mn2(CO)10 might yield side products because these
disulfanes also undergo photochemically induced reactions finally giving bis(2ꢀphenylsulfanylꢀphenyl)
disulfide of the type [2ꢀ(PhS)ꢀC6H4ꢀS]2; this disulfane oxidatively added to the manganese carbonyl
complex and gave [(OC)3Mn(µꢀSC6H4ꢀ2ꢀSPh)]2.24 Phenylthiolatomanganese(I) carbonyl complexes of
the types [(OC)4Mn(µꢀSR)]2 and [(OC)3Mn(µ3ꢀSR)]4 can easily be detected by their characteristic
carbonyl stretching vibrations. The dinuclear complex (R = Ph) shows four bands at 1970, 2006, 2022,
and 2079 cmꢀ1 in carbon tetrachloride25 whereas the tetranuclear complex with a central Mn4S4
heterocubane cage exhibits three characteristic bands at 1954, 2020 and 2028 cmꢀ1 in cyclohexane.15
Here we investigated the kinetics of CO release of these dinuclear phenylthiolatomanganese
tetracarbonyls. We were interested not only in the CO release properties but also in the opportunity to
elucidate the influence of the substitution pattern of the aryl substituents on the molecular structures.
Therefore, we investigated the physical and structural properties as well as the liberation of carbon
monoxide after dissolution and irradiation.
Results and Discussion
Synthesis
Two preferred procedures were applied for the synthesis of substituted dimeric
phenylthiolatomanganese tetracarbonyls. Either the diaryl disulfide was oxidatively added to
Mn2(CO)10 or in a metathetical approach, substituted potassium phenylthiolate was added to a solution
of pentacarbonylmanganese halide (Scheme 1). Both protocols offer access to these complexes with
high yields. Often mixtures of [(OC)4Mn(µꢀSR)]2 (1) and [(OC)3Mn(µ3ꢀSR)]4 (2) were obtained,
however, fractional crystallization allowed separation of these compounds. The purity was controlled
by NMR and IR spectroscopy.
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Scheme 1: Synthesis of dinuclear [(OC)4Mn(µꢀSR)]2 (1) and tetranuclear [(OC)3Mn(µ3ꢀSR)]4 (2) (R = Ph (a),
C6H4ꢀ4ꢀCH3 (b), C6H4ꢀ4ꢀCF3 (c), C6H4ꢀ4ꢀF (d), C6H4ꢀ4ꢀCl (e), C6H4ꢀ4ꢀOMe (f), C6F5 (g), and CH2C6H4ꢀ4ꢀCl
(h)).
The metathesis reaction of pentacarbonylmanganese bromide with potassium 2,4,6ꢀ
trimethylphenylthiolate according to Scheme 2 yielded a product that showed two sets of NMR
resonances for the 2,4,6ꢀtrimethylphenyl (mesityl) groups in the 1H NMR spectrum with an intensity
ratio of 2:1. A cis,trans,transꢀarrangement of the 2,4,6ꢀtrimethylphenylthiolato ligands of a trinuclear
complex with a sixꢀmembered Mn3S3 ring would easily explain this spectrum. In addition, the CO
region of the IR spectrum exhibited more than four bands as would be expected for dinuclear
[(OC)4Mn(µꢀSR)]2 (1). Both spectroscopic methods suggest a trinuclear 2,4,6ꢀ
trimethylphenylthiolatomanganese tetracarbonyl 3 with a central sixꢀmembered Mn3S3 ring as
represented in Scheme 2.
The synthesis of dinuclear complexes with paraꢀfluoro substituted phenylthiolato ligands turned out to
be challenging. Thus we were unable to isolate pure [(OC)4Mn(µꢀSꢀC6H4ꢀ4ꢀF)]2 (1d) and
[(OC)4Mn(µꢀSꢀC6F5]2 (1g). The reaction of pentacarbonylmanganese bromide with paraꢀ
fluorophenylmercaptan yielded a mixture of dinuclear [(OC)4Mn(µꢀSꢀC6H4ꢀ4ꢀF)]2 (1d) and
tetranuclear [(OC)3Mn(µꢀSꢀC6H4ꢀ4ꢀF)]4 (2d) regardless of the reaction time. Extended reaction periods
and elevated temperatures enhance the formation of the tetranuclear cage compound 2d. The 1H NMR
(Fig. 1) and the 13C{1H} NMR spectra (Fig. 2) verify the existence of two complexes after a short
reaction time whereas the resonances of the dinuclear complex vanish during extended reaction time
or higher temperatures in agreement to earlier reports.16,26 Tetranuclear cage compounds can be
converted to the dinuclear compound and even to mononuclear (OC)5MnꢀSR if very electronꢀpoor
phenylthiolates are used whereas not even the dinuclear complex is accessible in the case of very
electronꢀrich phenylthiolates (with e.g. trimethylstannyl substituents).16 In order to preparepure
dinuclear 1d, we treated the reaction solution of the tetranuclear derivative 2d in CCl4 with 18 bar of
carbon monoxide. After ten days at room temperature, the formation of 1d has been observed,
however, also degradation products have been observed (Fig. 3). After twenty days, unknown
degradation products of 2d formed the major products. Repetition of this reaction in THF also gave no
pure dinuclear 1d.
Insert Figures 1, 2 and 3
4

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Scheme 2: Synthesis of trinuclear [(OC)4Mn(µꢀSꢀC6H2ꢀ2,4,6ꢀMe3)]3 (3), Mes = 2,4,6ꢀtrimethylphenyl.
During the synthesis of dimeric 4ꢀmethylphenylthiolatomanganese tetracarbonyl, also trace amounts
of crystalline [(OC)3Mn(µꢀSC6H3(ꢀ4ꢀMe)ꢀ2ꢀSC6H4ꢀ4ꢀMe)]2 (4) were isolated (Scheme 3). Knox and
coworkers24 explained the formation of such compounds via an oxidative addition of the
corresponding precursor disulfane that forms during lightꢀinduced radical reaction from diphenyl
disulfane with the first reaction step being the homolytic cleavage of the SꢀS bond.27
Scheme 3: Representation of [(OC)3Mn(µꢀSC6H3(ꢀ4ꢀMe)ꢀ2ꢀSC6H4ꢀ4ꢀMe)]2 (4)
Molecular Structures
Representative molecular structures of dinuclear [(OC)4Mn(µꢀSR)]2 (1) and tetranuclear [(OC)3Mn(µ3ꢀ
SR)]4 (2) are depicted in Fig. 4 and 5, respectively. In Table 1 selected structural data are summarized
and compared with already known values of [(OC)4Mn(µꢀSPh)]2.20,21,28 The dinuclear complexes
contain a central Mn2S2 ring with a transꢀannular trans arrangement of the sulfurꢀbound aryl groups.
Furthermore, two kinds of carbonyl ligands are present in these complexes, namely in trans and in cis
positions to the thiolate anions marked as CtransꢀS and CcisꢀS, respectively. The carbonyl groups in cis
position to the thiolate moieties have another carbonyl ligand in trans position. Therefore, these
carbonyl ligands bind to the same dꢀorbital of the manganese center and, hence, compete for the same
electron density (known as trans influence of metalꢀbound carbonyl molecules) weakening the backꢀ
bonding from the metal to the π*(CO) orbitals. This fact leads to a significant elongation of the Mnꢀ
CcisꢀS bonds by approximately 5 pm and to slightly smaller CcisꢀSꢀO bond lengths. In agreement with
earlier studies, the planar Mn2S2 ring exhibits the acute angle at Mn (approx. 82°) and the obtuse angle
at the sulfur atom.
Insert Figures 4 and 5, Table 1
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A unique molecular structure was observed for the 2,4,6ꢀtrimethylphenylthiolatomanganese
tetracarbonyl 3 which precipitates as a trinuclear complex with a central sixꢀmembered Mn3S3 ring
with a boat conformation (Fig. 6). Due to the fact that the sulfur atoms show pyramidal environments,
two chemically different mesityl groups are observed, namely one aryl group at S3 on the opposite
side of the sixꢀmembered ring than the two other mesityl moieties at S1 and S2. The manganese
centers exhibit distorted octahedral coordination spheres comparable to the dinuclear complexes 1.
The formation of this trinuclear carbonyl complex leads to drastically enhanced MnꢀSꢀMn bond angles
of 133.7° whereas the average SꢀMnꢀS angle shows only a slight widening (Table 1). These distortions
show no influence on the MnꢀCCO bond lengths.
Insert Figure 6
The molecular structure of the already known24 side product [(OC)3Mn(µꢀSC6H3(ꢀ4ꢀMe)ꢀ2ꢀSC6H4ꢀ4ꢀ
Me)]2 (4) is depicted in Fig. 7 and shows a facial arrangement of the carbonyl ligands. Consequently,
short MnꢀC bonds (av. 181.4 pm) are observed that are characteristic for carbonyl ligands of a
pyramidal [(OC)3Mn]+ moiety in trans positions to sulfur bases. The Mn1ꢀS2 bond to the thioether
fragment is significantly shorter [232.6(2) pm] than the distances between manganese and the thiolate
anions [Mn1ꢀS1 236.2(2) and Mn1ꢀS1A 243.2(2) pm] despite the enhanced electrostatic attraction.
This elongation of the endocyclic MnꢀS bonds can be explained by ring strain within the fourꢀ
membered Mn2S2 ring.
Insert Figure 7
Spectroscopic Studies. Selected NMR and IR spectroscopic parameters are listed in Table 2. The
number of resonances in the NMR spectra and CO stretching vibrations is characteristic for the
structure types. The dinuclear complexes 1 show two 13C{1H} NMR resonances and four carbonyl
bands in the IR spectra whereas the tetranuclear cages 2 show only one NMR resonance and three
stretching vibrations for the carbonyl ligands.
Insert Table 2
An unambiguous distinction between diꢀ (1) and tetranuclear compounds (2) is possible by the
chemical 13C NMR shifts of the carbonyl ligands. Dinuclear [(OC)4Mn(µꢀSR)]2 (1) exhibits two δ
values of approximately 213 and 214 ppm whereas for the cage compounds [(OC)3Mn(µꢀSR)]4 (2)
chemical shifts of 221 ppm are observed, regardless of the substitution pattern of the aryl group.
However, these resonances are broad (see e.g. the 13C{1H} NMR spectrum of 1d and 2d, Fig. 2) and
for trinuclear [(OC)4Mn(µꢀSMes)]3 (3) no resonances have been observed in the characteristic region
above 200 ppm.
CO Delivery
The myoglobin assay is the common procedure to quantitatively determine carbon monoxide release
from metal carbonyls. This assay is based on a color change due to formation of a carbon monoxide
adduct of myoglobin and requires dissolution of CORMs in a buffered solution in the presence of
sodium dithionite.7b,30 Recently it has been demonstrated that sulfite and dithionite anions are not only
innocent species but are also responsible for a rapid CO release.31 We could show that this effect is
negligible for photoCORMs with irradiationꢀtriggered liberation of carbon monoxide.32 Due to the
uncertainty with respect to CO detection related to other release mechanisms (such as e.g. ligand
exchangeꢀtriggered CO liberation) we also employed an alternative reliable procedure based on CO
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detection in the gas phase above the CORM solution.33 This assay allows the use of diverse solvents
and release triggers without impact on the detection of the amount of CO, provided that the solubility
of CO in the solvent is very poor. In water, solubility of CO is very low with a value of only 23 ml in 1
L of water at 20 °C leading to concentrations of about 1 mM of CO.34 In addition, degradation of
CORMs can be traced by IR spectroscopic observation of the carbonyl bands of the metal complexes.
Here the general release properties of manganese(I)ꢀbased [(OC)4Mn(µꢀSR)]2 (1a) – denominated as
CORMꢀMnꢀS1 – was studied in vitro and much more sophisticated CO detection in living cells by a
selective fluorescent probe35 or by Raman microspectroscopy36 have not been applied. Due to the fact
that the substitution pattern of the aryl groups show a very minor influence on structural and NMR
data, we limited our studies on [(OC)4Mn(µꢀSPh)]2 (1a). Nevertheless, very similar results have also
been obtained for [(OC)4Mn(µꢀSC6H4ꢀ4ꢀMe)]2 (1b) and [(OC)4Mn(µꢀSC6H4ꢀ4ꢀCl)]2 (1e) with the
myoglobin assay whereas the durability of fluoroꢀsubstituted derivatives in donor solvents is too low
for such investigations.
Myoglobinꢀbased detection of CO release from CORMꢀMnꢀS1: To investigate CO release from
CORMꢀMnꢀS1 in physiological solutions we utilized a myoglobin assay.32,37 Under reducing
conditions, i.e., in the presence of 0.1% dithionite, the soret peak of myoglobin (10 µM in PBS) is
hypsochromicꢀshifted in a concentrationꢀdependent manner upon binding of CO either added directly
to the myoglobin solution to obtain a calibration curve (Fig. 7A,B) or released from CORMs. To
obtain a homogenous stock solution (10 mM), CORMꢀMnꢀS1 was dissolved in DMSO under constant
mixing for 20 min and stored at 4 °C in the dark for up to 8 h. When added to a reduced myoglobin
solution to yield a final concentration of 100 µM, the absorbance at 422 nm (A422) instantaneously
increased (Fig. 7C) due to absorbance of the CORM and previously released CO that was still present
in the stock solution. Afterwards, in the dark, A422 further increased corresponding to a release of 0.1
molecule CO per molecule CORM within 10 min. Illumination of the samples strongly enhanced CO
release as shown in Fig. 7D. After addition of 2 µM CORMꢀMnꢀS1 (which due to dilution slightly
reduced A422 without further significant changes within the following 100 s), A422 started to increase
exponentially upon start of illuminating the sample (470 nm), corresponding to a release of around 3
molecules CO per molecule CORM with a time constant of 420 s. As depicted in Fig. 7E, CO release
gets faster with shorter illumination wavelength whereas the overall amount of CO release is not
affected. To test whether CO release is affected by the reducing agent dithionite, 5 µM CORMꢀMnꢀS1
was preincubated in PBS with/without 0.1% sodium dithionite with or without illumination in a sealed
cuvette. Reduced myoglobin and, if necessary, sodium dithionite were added to the samples after
5 min. The amount of CO released, corresponding to the absorbance at 422 nm, was not significantly
(P = 0.2) reduced in the absence of dithionite for the illuminated samples but slightly reduced (P =
0.02) for the samples incubated in the dark (Fig. 7F). Thus, dithionite is not required for lightꢀtriggered
CO liberation from CORMꢀMnꢀS1 but slightly increases the release rate.
Insert Figure 7
IR gas phase spectroscopy: A solution of CORMꢀMnꢀS1 in DMSO with a concentration of 2 mM and
a volume of about 2 ml was investigated via IR gas phase spectroscopy. The CORMꢀMnꢀS1 powder
was placed in the probe cup (diameter: 26 mm) of an inꢀhouse built cuvette,33 which was filled with air
at atmospheric pressure. The gas phase above this CORM was monitored for longer than 30 min. Then
the cuvette was opened to add the solvent DMSO, sealed again, and IR spectra of the gas phase were
recorded for about three hours. Subsequently, while monitoring the gas phase, the solution was
irradiated by blue light using LEDs (PURꢀLED GmbH) with a wavelength of 470 ± 5 nm and a power
of 12.2 mW/cm2.
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The IR measurement of the gas phase above the CORMꢀMnꢀS1 solution clearly showed that the
CORM powder is stabile in the dark. However, when DMSO was added, CO was released even in the
absence of light but not all carbonyl groups of CORMꢀMnꢀS1 are replaced by DMSO (Fig. 8). About
one hour after mixing CORMꢀMnꢀS1 with DMSO, the amount of CO in the gas phase was nearly
constant, which indicates that no further CO escaped from the CORM solution. An exponential curve
representing a reaction of first order was fitted to CO ratio during the reaction of CORMꢀMnꢀS1 and
DMSO. The reaction had a halfꢀlife of (459 ± 80) s and gave a release of 2.37 ± 0.06 CO per CORMꢀ
MnꢀS1 molecule.
Insert Figure 8
This CO release behavior and the stability of the intermediately formed complex encouraged us to
study this species also by NMR spectroscopy in the dark. After dissolution of CORMꢀMnꢀS1 in
deuterated DMSO the NMR parameters verify the formation of a single product [1H NMR: δ 7.13
(3H) and 7.80 (2H); 13C{1H} NMR: δ 218.8 (CO), 141.5 (iꢀC), 132.2, 127.1, and 124.8 (pꢀC)]. In
addition, the IR bands (1812, 1903, and 1982 cmꢀ1) also prove the formation of a new, yet unknown
complex which we assign to [(OC)3Mn(dmso)(µꢀSPh)]2 as shown in Scheme 4.
dmso
+ 2 DMSO
- 2 CO
S
S
S
S
(OC)3Mn
dmso
Mn(CO)3
(OC)4Mn
Mn(CO)4
1a
CORM-Mn-S1 (
)
Scheme 4: The initial ligand exchange process of CORMꢀMnꢀS1 in DMSO via ligand substitution of carbonyl by
the strong Lewis base DMSO.
When this DMSO solution was irradiated with blue light nearly all carbonyls of CORMꢀMnꢀS1were
liberated; after three hours of irradiation, a CO ratio of 7.41 ± 0.31 was measured in the gas phase
above the CORM solution. A fit of an exponential curve was not suitable for the photoꢀrelease of
carbon monoxide, thus the halfꢀlife of (750 ± 340) s was obtained graphically.
Conclusion
Dinuclear manganeseꢀbased carbonyl complexes of the type [(OC)4Mn(µꢀSR)]2 (1) are valuable COꢀ
releasing molecules (CORMs). These derivatives are easily available via several routes starting either
from Mn2(CO)10 and diaryl disulfide or from [(OC)5MnBr] and arylmercaptan. The substitution pattern
of the aryl substituents strongly influences the durability of these complexes with fluoro groups
destabilizing these complexes and easing the formation of tetranuclear cage compounds of the type
[(OC)3Mn(µꢀSR)]4 (2). Therefore, these complexes cannot be obtained as pure substances. Generally,
thermal stress leads to an accelerated formation of tetranuclear 2. The substitution pattern of the aryl
groups has a very insignificant influence on the structural parameters and chemical 13C NMR shifts of
the carbonyl ligands.
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Dissolution of [(OC)4Mn(µꢀSPh)]2 (1a) in donor solvents (Lewis basic solvents L) initiates the
liberation of two carbon monoxide molecules via a ligand exchange reaction. These intermediately
formed complexes of the type [(OC)3Mn(L)(µꢀSR)]2 are stable in the dark but release all remaining
carbonyl ligands upon irradiation and, hence, represent valuable photoCORMs. The traditional
myoglobin assay only allows to follow the photoCORM activity because these complexes are
dissolved in Lewis bases (such as DMSO), diluted with aqueous media (containing buffer, sodium
dithionate and myoglobin) and then the color change of the myoglobinꢀCO adduct is determined.
During this handling, the ligand exchange reaction occurs and is quite fast in presence of strong Lewis
bases such as DMSO. Alternatively, the determination of gaseous carbon monoxide above the CORM
solution by IR spectroscopy allows to quantitatively measuring the amount of liberated CO regardless
of the release mechanism. Due to the low solubility of CO in aqueous media very reliable results are
obtained.
Experimental Part
All manipulations were carried out in an inert atmosphere (argon or nitrogen) using standard Schlenk
techniques. The solvents were purified and dried by standard techniques prior to use. The yields given
1
are not optimized. H and 13C{1H} NMR spectra were recorded on Bruker AC 200 MHz, AC 400
MHz, and AC 600 MHz spectrometers. Chemical shifts are reported in parts per million. [D8]THF was
dried over sodium, [D7]DMF and [D6]DMSO were dried with molecular sieves. The ligands 1ꢀ bis(pꢀ
chlorophenyl) disulfide as well as the potassium phenylthiolates were synthesized following published
procedures. All other chemicals and solvents are commercially available and were used as received
without further purification, unless stated otherwise. Photoreactions were performed with light using a
LED NSCU033AT Nichia unit. Dinuclear complexes [(OC)4Mn(µꢀSꢀR)]2 with R = Ph (1a), C6H4ꢀ4ꢀ
Me (1b) and C6F5 (1g) were prepared according to literature procedures (see text). The standard
myoglobin assay was performed as described earlier7b,30,40 in order to prove the suitability of the
manganeseꢀbased carbonyl complexes as carbon monoxide releasing molecules (CORMs).
[Mn(CO)4(µꢀSC6H5)]2 (1a)
A suspension of [Mn2(CO)10] (584 mg, 1.5 mmol) and diphenyl disulfide (1005 mg, 4,6 mmol) in 40
mL of heptane (mixture of isomers) was stirred until a clear solution formed. Then the solution was
irradiated for 1 h. An orange solid precipitated. The crude product of the reaction was filtered. The
filtrate was collected, concentrated in vacuum and stored at ꢀ18 °C yielding 490 mg (0.887 mmol,
59.2%) of orange crystals. Dec. above 87.5 °C (without melting). 1H NMR (400 MHz, [D8]THF): δ =
7.23 [m, (broad), 2H, pꢀCH], 7.31 [m, (broad) 4H, mꢀCH], 7.63 [d, J =7.38 Hz, 4H, oꢀCH]. 13C (400
MHz/[D8]THF): 127.4, 129.6, 133.2, 133.5, 137.0, 213.4, 214.8. MS (EI), m/z (%): 552 (10) [M]+, 468
(10) [M ꢀ3CO]+, 440 (30) [M ꢀ4CO]+, 412 (25) [M ꢀ5CO], 356 (5) [M ꢀ7CO], 328 (100) [M ꢀ8CO]. IR
(pure): v(CO): 2072 (m), 1995 (m), 1980 (s), 1935 (s) cmꢀ1. Elemental analysis (C20H10S2O8Mn2, 552 g
molꢀ1): calcd.: C 43.47, H 1.8, S 11.58; found: C 44.12, H 1.87, S 12.05.
[Mn(CO)4(µꢀSC6H4ꢀ4ꢀMe)]2 (1b)
The synthesis of 2 is analogous to the one of complex 1 via the reaction of [Mn2(CO)10] (370 mg,
0.948 mmol), with diꢀpꢀtolyl disulfide (1168.8 mg, 4.7 mmol) in of 50 mL heptanes (mixture of
isomers). Then the solution was irradiated for 3 h and a yellow solid precipitated. After the suspension
was filtered (Caution: the solid is very unstable), the filtrate was collected and stored at ꢀ18 °C giving
a mixture of crystalline products. Furthermore, pure complex 2 was obtained by reduction of the
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mother liquor to dryness and subsequent washing of the residue with nꢀhexane. An orange powder
(150 mg, 0.26 mmol, 27.2%) of [Mn(CO)4(SC6H4ꢀpꢀMe)]2 (2) was isolated. 1H NMR:
(400MHz/[D8]THF): δ = 2.30 [s, 6H, CH3 tolyl], 7.13 [AA′ part of an AA′BB′ spin system, 4H, mꢀ
CH], 7.52 [BB′ part, 4H, oꢀCH]. 13C NMR (400 MHz/[D8]THF): 20.9, 130.5, 133.2, 133.3, 137.6,
213.6, 215. MS (EI), m/z (%): 580 (5) [M ꢀ2H]+, 523 (10) [Mꢀ2H ꢀ2CO]+, 496 (5) [Mꢀ2H ꢀ3CO]+, 468
(20) [Mꢀ2H ꢀ4CO]+, 440 (10) [Mꢀ2H ꢀ5CO]+, 356 (100) [Mꢀ2H ꢀ8CO]+. IR (pure), v(CO): 2080 (w),
2026 (m), 1992 (m), 1944 (m) cmꢀ1. Elemental analysis (C22H16S2O8Mn2, 582 g molꢀ1): calcd.: C 45.53,
H 2.42, S 11.05; found: C 45.82, H 2.65, S 10.08. As secondary products [Mn(CO)3(SC6H3Meꢀoꢀ
SC6H4Me)]2 (4) and [Mn(CO)3(SC6H4ꢀ4ꢀMe)]4 (2b) have been identified. The compound
[Mn(CO)3(SC6H3MeꢀoꢀSC6H4Me)]2 crystallized directly in the filtrate of the reaction at ꢀ18 °C; Xꢀray
diffraction studies have revealed the molecular structure of this compound. 1H NMR: (400
MHz/[D8]THF): δ 2.32, 2.36, 7.29, 7.43 and 7,49.
(SC6H4ꢀ4ꢀCl)2
The ligand bis(pꢀchlorophenyl) disulfide was prepared starting from 418 mg (2.89 mmol) of pꢀ
Chlorophenylmercaptan in 2.5 mL of DMF and 293 mg of Et3N (2.89 mmol). The reaction mixture
was stirred at 40 °C for 5 min in an ultrasonic bath Sonorex Super DigitalꢀDK 102, ultrasonic
frequency 35 KHz. The product was extracted with Et2O/H2O (1:3); the solvent was removed under
vacuum till a dry residue remained. Yield: 381 mg (1.32 mmol, 92 %). Decomposition above 90 °C
1
(without melting). H NMR: (400 MHz/CDCl3): 7.25 [AA′ part of an AA′BB′ spin system, 4H, mꢀ
CH,], 7.38 [BB′ part, 4H, oꢀCH]. 13C NMR (400 MHz/[D8]CDCl3): 129.3, 129.35, 133.6, 135.15. MS
(EI), m/z (%): 286 (50) [M]+, 143 (100) [M – C6H4ClS]+. Elemental analysis (C12H8S2Cl2 286 g molꢀ1):
calcd.: C 50.18, H 2.80, S 22.32; found: C 50.14, H 3.02, S 22.32.
[Mn(CO)4(µꢀSC6H4ꢀ4ꢀCl)]2 (1e)
To a solution of the ligand bis(pꢀchlorophenyl) disulfide (617 mg, 2.15 mmol) in 15 mL heptane was
added a stirred solution of [Mn2(CO)10] (210 mg, 0.53 mmol) in 15 mL heptanes, resulting a yellow
solution which was irradiated for 2 h leading to a yellow solid precipitate. The suspension was filtered
and an orange filtrate collected. Afterwards the filtrate was stored at ꢀ18 °C. After one week afforded
orange crystals suitable for Xꢀray crystallography. Yield: 163 mg (0.26 mmol, 49%). Decomposition
1
above 90 °C (without melting). H NMR: (400 MHz/[D8]THF): 7.36 [AA′ part of an AA′BB′ spin
system, 4H, mꢀCH], 7.6 [BB′ part, 4H, oꢀCH]. 13C NMR (400 MHz/[D8]THF): 129.7, 133.5, 134.5,
135.8, 212.9, 214.4. MS (EI), m/z (%): 536 (5) [M ꢀ3CO]+, 508 (20) [M ꢀ4CO]+, 480 (15) [M ꢀ5CO]+,
395 (100) [M ꢀ8CO]. IR (heptane) v(CO): 2083 (s), (s), 1991 (s), 1979 (m), 1955 (s). Elemental
analysis: (C20H8Cl2O8S2Mn2, 621 g molꢀ1): calcd.: C 38.67, H 1.29, S 10.32; found: C 39.24, H 1.37, S
10.45
[Mn(CO)4(µꢀSC6H4ꢀ4ꢀOMe)]2 (1f)
The reaction was carried starting from 500 mg (1.28 mmol) of [Mn2(CO)10], and 1080 mg (3.8 mmol)
of diꢀpꢀmethoxyphenyl disulfide in 30 mL heptane. The mixture was stirred for 5 min. which leads to
a dissolution of the starting materials resulting in a yellow solution. Subsequently, the solution was
then irradiated for 1h and a yellow solid was precipitate which was removed by filtration (Caution: the
solid is very unstable and, therefore, no reliable elemental analysis was obtained). The filtrate was
collected and stored at 6 °C, yielding 240 mg (0.39 mmol, 30.6%) of red crystals. Decomposition
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above 93 °C (without melting). 1H NMR (400 MHz/[D8]THF): δ 3.76 [s, 6H, OCH3], 6.89 [d, J= 5.16
Hz AA′ part of an AA′BB′ spin system, 4H, mꢀCH], 7.55 [BB′ part, 4H, oꢀCH]. 13C NMR (400
MHz/[D8]THF): 55.32, 115.26, 126.33, 134.26, 159.98, 213.3, 215.08. MS (EI), m/z (%): 500 (10) [M
ꢀ4CO], 472 (5) [ꢀ5CO], 390 (50) [M ꢀ8CO]. IR (nujol), v(CO): 2072 (m), 1995 (m), 1986 (m) 1942
(m) Elemental analysis (C22H14O10S2Mn2 612 g molꢀ1): calcd.: C 43.15 H 2.30 S 10.47; found: C
43.41, H 3.32, S 8.72.
[Mn(CO)4(µꢀSC6F5)]2 (1g)
Mn(CO)5Br (804 mg, 2.92 mmol) was dissolved in 15 mL of methanol. In another flask 590 mg of
pentafluorophenylmercaptan (2.95 mmol) were dissolved in 10 mL of methanol and transferred at
once to the Mn(CO)5Br solution. The reaction mixture was stirred for 9 h at 50 °C. Thereafter, the
solvent was removed in vacuo and the residue dried. The remaining solid was suspended in 10 mL of
nꢀhexane. The filtrate was collected and the residual solid washed twice with 2.5 mL of nꢀhexane. The
volume of the combined red solutions was reduced to 12 mL whereby the product precipitated.
Subsequent purification procedures via recrystallization failed due to decomposition reactions.
[Mn(CO)4(µꢀSCH2C6H4ꢀ4ꢀCl)]2 (1h)
The two solutions of 880 mg of Mn(CO)5Br (3.20 mmol) in 15 mL of methanol and of 510 mg 4ꢀ
chlorobenzylmercaptan (3.21 mmol) in 15 mL of methanol were combined at once and then stirred for
9 h at 50 °C. During this time, a yellow solid precipitated, was collected and dried in vacuo. Yield:
909 mg (1.40 mmol), 88 %. M.p. 121 °C (dec.). 1HꢀNMR (600.129 MHz, [D8]THF): δ 7.35 – 7.30 (m,
part of an AA'XX' spin system, 4H, H3), 7.29 – 7.26 (m, part of an AA'XX' spin system, 4H, H4), 3.71
(s, 4H, H1). 13C{1H}ꢀNMR (150.902 MHz, [D8]THF): δ = 216.1 (s, CCarbonyl), 212.2 (s, CCarbonyl), 139.1
(s, C2), 134.5 (s, C5), 131.6 (s, C3), 129.7 (s, C4), 40.0 (s, C1). MS (DEI): m/z (%) = 648 [M+] (16), 536
[M+ ꢀ 4 CO] (33), 424 [M+ ꢀ 8 CO] (46), 125 (100). IR (neat solid): 2967 (w), 2065 (m), 1990 (m),
1956 (s), 1935 (m), 1596 (w), 1490 (m), 1432 (w), 1406 (w), 1233 (w), 1181 (w), 1092 (m), 1016 (w),
879 (w), 833 (m), 807 (w), 728 (w), 655 (w), 545 (m), 503 (s), 476 (w), 463 (m), 425 (m), 418 (m).
Elemental analysis (C22H12Cl2Mn2O8S2, 649.24): calc.: C 40.70, H 1.86, S 9.88; found: C 40.83, H
1.80; S 9.74.
[Mn(CO)3(SC6H4ꢀ4ꢀF)]4 (2d)
The two solutions of 633 mg of Mn(CO)5Br (2.30 mmol) in 10 mL of methanol and of 295 mg of 4ꢀ
fluorophenolmercaptan (2.30 mmol) in 10 mL of methanol were combined at once. The reaction
mixture was stirred at 50 °C whereby a yellow precipitate formed. This solid was collected, washed
1
with a few milliliters of methanol and dried in vacuo. Yield: 200 mg (0.19 mmol), 33 %. HꢀNMR
(400.075 MHz, [D8]THF): δ 8.15 (m, part of an AA'XX' spin system, 8H, H2), 7.40 (m, part of an
AA'XX' spin system, 8H, H3). 13C{1H}ꢀNMR (100.599 MHz, [D8]THF): δ 221.03 (s, CCarbonyl), 164.2
1
3
4
2
(d, JC,F = 250.1 Hz, C4), 134.2 (d, JC,F = 8.6 Hz, C2), 128.5 (d, JC,F = 3.1 Hz, C1), 118.1 (d, JC,F
=
22.8 Hz, C3). 19F{1H}ꢀNMR (188.310 MHz, THFꢀd8): δ = ꢀ121.11 (s). MS (DEI): m/z (%) = 1064
[M+] (5), 980 [M+ ꢀ 3 CO] (81), 896 [M+ ꢀ 6 CO] (10), 868 [M+ ꢀ 7 CO] (18), 840 [M+ ꢀ 8 CO] (46),
812 [M+ ꢀ 9 CO] (64), 784 [M+ ꢀ 10 CO] (23), 728 [M+ ꢀ12 CO] (40), 633 [M+ ꢀ 12 CO ꢀ PhꢀF] (5),
578 [M+ ꢀ 12 CO ꢀ PhꢀFꢀ Mn] (15), 538 [M+ ꢀ 12 CO ꢀ 2 PhꢀF] (14), 443 [M+ ꢀ 12 CO ꢀ 3 PhꢀF] (100),
364 (53), 348 [M+ ꢀ 12 CO ꢀ 4 PhꢀF] (50), 335 (32), 269 (40), 248 (23), 161 (22). IR (neat solid): 2018
(s), 1940 (s), 1925 (s), 1589 (w), 1486 (s), 1394 (m), 1290 (w), 1233 (m), 1154 (m), 1095 (w), 1077
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(w), 1010 (w), 931 (w), 822 (s), 662 (s), 630 (w), 511 (s), 463 (m), 427 (m). Elemental analysis
(C36H16F4Mn4O12S4, 1064.51): calc.: C 40.62, H 1.51, S 12.05; found: C 41.01, H 1.49, S 9.87.
[(CO)4Mn(µꢀSC6H2ꢀ2,4,6ꢀMe3)]3 (3)
298 mg (1.50 mmol) of potassium bis(trimethylsilyl)amide and 300 mg (1.97 mmol) of 2,4,6ꢀ
trimethylphenylmercaptan in 20 mL of toluene were stirred at room temperature for 2 h to give a white
1
precipitate. Decomposition above 225 °C (without melting). H NMR (400MHz/[D8]THF): δ = 2.09
[s, 3H]; 2.36 [s, 6H]; 6.64 [s, 2H]. 13C NMR (400 MHz/[D8]THF): δ = 18.9, 20.8, 126, 127.4, 130.3
138.8 150. Subsequently 80 mg (0.42 mmol) of product and 130 mg (0.47 mmol) of [BrMn(CO)5]
were suspended in 20 mL of THF and stirred at room temperature for 24 h. An orange solution
formed, containing a white solid (KBr) which was removed by filtration. The filtrate was distilled
under reduced pressure to dryness and the orange residue was recrystallized from 5 mL of nꢀhexane at
1
5 °C yielding 45 mg (0.047 mmol, 30%) of red crystals. Decomposition above 105 °C. H NMR:
([D8]THF, r.t.): δ 2.17 (12 H, oꢀMe), 2.21 (6 H, oꢀMe), 2.53 (3 H, pꢀMe), 2.59 (pꢀMe), 6.75 (2 H,
CHaryl), 6.84 (4 H, CHaryl). 13C{1H} NMR (150.9 MHz, [D8]THF, r.t.); δ 21.1 (pꢀMe), 21.3 (pꢀMe),
21.8 (oꢀMe), 23.4 (oꢀMe), 129.5 (mꢀC), 129.9 (mꢀC), 132.5 (iꢀC), 135.6 (iꢀC), 137.3 (pꢀC), 140.4 (pꢀ
C), 144.1 (oꢀC), 145.2 (oꢀC), carbonyl resonances have not been observed. IR (Nujol): v(CO): 2080 m,
2001 s, 1970 m, 1952 m, 1922 w; other bands: 1652 w, 1601 w, 1460 vs, 1377 s, 1261 w, 1092 m,
1017 m, 847 w, 802 m, 652 m, 618 m, 549 w. Weight on scale was not constant and, hence, no reliable
C,H,N analytical data have been obtained.
Crystal structure determinations
The intensity data for the compounds were collected on a Nonius KappaCCD diffractometer using
graphiteꢀmonochromated MoꢀKα radiation. Data were corrected for Lorentz and polarization effects;
absorption was taken into account on a semiꢀempirical basis using multipleꢀscans.41ꢀ43
The structures were solved by Direct Methods (SHELXS)44 and refined by fullꢀmatrix least squares
techniques against Fo2 (SHELXLꢀ97).44 The hydrogen atoms of compounds 1c, 1e, 1f, 1g, 1h, 2c, and 2d
were located by difference Fourier synthesis and refined isotropically. All other hydrogen atoms were
included at calculated positions with fixed thermal parameters. All nonꢀdisordered, nonꢀhydrogen atoms
were refined anisotropically.44 The crystal of 1d was a nonꢀmerohedral twin. The twin law was
determined by PLATON44 to (ꢀ1.0, 0.0, 0.0) (0.0, ꢀ1.0, 0.0) (0.353, 0.242, 1.0). The contribution of the
main component was refined to 0.680(5). The crystal of 4 contains large voids filled with disordered
solvent molecules. The size of the voids is 388 Å3/unit cell. Their contribution to the structure factors
was secured by backꢀFourier transformation using the SQUEEZE routine of the program PLATON45
resulting in 39 electrons/unit cell.
Crystallographic data as well as structure solution and refinement details are summarized in Table 3.
XP (SIEMENS Analytical Xꢀray Instruments, Inc.) was used for structure representations.46
IR gas phase spectroscopy
A power meter (Thorlabs PM100 with sensor S130A) was applied to control the light intensity. The IR
spectra were recorded by a Varian (now Agilent) 670ꢀIR FTIR spectrometer equipped with a DTGS
detector. The spectra have a resolution of 1 cmꢀ1 in the spectral range between 700 cmꢀ1 and 4000 cmꢀ1
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and were measured in average every 18 s. All IR spectra were analyzed by inꢀhouse written Rꢀ
scripts.38,39 The measured IR spectra of the gas phase were processed by a linear baseline correction,
by integrating over the CO roꢀvibrational band and by calculating the CO amount via a calibration
parameter.33 The measurement was repeated four times and the measured CO ratios (CO molecules per
CORM molecule) were averaged. Before this the values were interpolated to an even grid of 18 s,
where at 30 min DMSO was added and at 3 h 35 min the irradiation started.
Supplementary Material: Crystallographic data (excluding structure factors) has been deposited with
the Cambridge Crystallographic Data Centre as supplementary publication CCDCꢀ1026726 for 1b,
CCDCꢀ1026727 for 1b_2b, CCDCꢀ1026728 for 1c, CCDCꢀ1026729 for 1d, CCDCꢀ1026730 for 1e,
CCDCꢀ1026731 for 1f, CCDCꢀ1026732 for 1g, CCDCꢀ1026733 for 1h, CCDCꢀ1026734 for 2b,
CCDCꢀ1026735 for 2c, CCDCꢀ1026736 for 2d, CCDCꢀ1026737 for 2d_CCl4, CCDCꢀ1026738 for 3,
and CCDCꢀ1026739 for 4. Copies of the data can be obtained free of charge on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK [Eꢀ mail: deposit@ccdc.cam.ac.uk].
Acknowledgement: We are grateful to Dr. A. Malassa and Dr. J. Langer for valuable discussions. We
thank the German Research Foundation (DFG, Bonn/Germany) for generously funding this project in
the frame of the collaborative research group FOR 1738. Infrastructure of the Institute of Inorganic
and Analytical Chemistry of the Friedrich Schiller University Jena was partially provided by the EU
(European Regional Development Fund, EFRE). V. P. LorettꢀVelásquez is grateful to the German
Academic Exchange Service (DAAD, Bonn/Germany) for a generous PhD stipend.
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Dalton Trans., 2011, 40, 4230ꢀ4235.
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10 S. V. C. Vummaletti, D. Branduardi, M. Masetti, M. de Vivo, R. Motterlini, and A. Cavalli,
Chem. Eur. J., 2012, 18, 9267ꢀ9275.
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4367.
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13 W. Hieber and L. Schuster, Z. Anorg. Allg. Chem., 1956, 285, 205ꢀ211.
14 A. G. Osborne and F. G. A. Stone, J. Chem. Soc. A, 1966, 1143ꢀ1146.
15 C. R. Jenkins, J. Organomet. Chem., 1968, 15, 441ꢀ445.
16 V. Küllmer and H. Vahrenkamp, Chem. Ber. 1976, 109, 1569ꢀ1571.
17 P. M. Treichel and P. C. Nakagaki, Organometallics, 1986, 5, 711ꢀ716.
18 K.ꢀW. Lee and T. L. Brown, Inorg. Chem., 1987, 26, 1852ꢀ1856.
19 P. Jaitner, J. Organomet. Chem., 1981, 210, 353ꢀ355.
20 J. Chen, V. G. Young, and R. J. Angelici, Organometallics, 1996, 15, 325ꢀ331.
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276ꢀ281.
23 E. W. Abel, B. C. Crosse, and D. B. Brady, J. Am. Chem. Soc., 1965, 87, 4397ꢀ4398.
24 S. D. Killops, S. A. R. Knox, G. H. Riding, and A. J. Welch, J. Chem. Soc., Chem. Commun.,
1978, 486ꢀ488.
25 E. W. Abel, J. Dalton, I. Paul, J. G. Smith, and F. G. A. Stone, J. Chem. Soc. A, 1968, 1203ꢀ1208.
26 H. Vahrenkamp, Angew. Chem. Int. Ed. Engl., 1975, 14, 322ꢀ329.
27 (a) Y. Schaafsma, A. F. Bickel, and E. C. Kooyman, Tetrahedron, 1960, 10, 76ꢀ80; (b) T.
Fujisawa and T. Kojima, Bull. Chem. Soc. Jpn., 1977, 50, 3061ꢀ3062.
28 S. Onaka and Y. Katukawa, J. Coord. Chem., 1996, 39, 135ꢀ146.
29 P. S. Braterman, J. Chem. Soc. A, 1968, 2907ꢀ2909.
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Westerhausen, M. Schmitt, and J. Popp, J. Phys. Chem. A, 2014, 118, 5381ꢀ5390.
34 R. C. Weast, M. J. Astle, and W. H. Beyer: CRC Handbook of Physics and Chemistry, 66th ed.,
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35 J. Wang, J. Karpus, B. S. Zhao, Z. Luo, P. R. Chen, and C. He, Angew. Chem. Int. Ed., 2012, 51,
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and M. Westerhausen, Eur. J. Inorg. Chem., 2012, 1072ꢀ1078.
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Dalton Transactions
View Article Online
DOI: 10.1039/C4DT03567D
38 R Development Core Team, R: A language and environment for statistical computing. R
Foundation for Statistical Computing, Vienna, Austria, 2012. ISBN 3ꢀ900051ꢀ07ꢀ0, URL;
http://www.Rꢀproject.org.
39 C. Beleites and V. Sergo: hyperSpec: a package to handle hyperspectral data sets in R, in
preparation, R package version 0.98ꢀ20120713; http://hyperspec.rꢀforge.rꢀproject.org.
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Sweet, Macromolecular Crystallography, Part A, Academic Press: New York, 1997, pp.
307–326.
43 SADABS 2.10, BrukerꢀAXS inc., 2002, Madison, WI, U.S.A
44 G. M. Sheldrick, Acta Cryst. 2008, A64, 112ꢀ122.
45 A. L. Spek, A. L. Acta Cryst. 2009, D65, 148ꢀ155.
46 XP, Siemens Analytical Xꢀray Instruments Inc., Karlsruhe, Germany, 1990; Siemens
Analytical Xꢀray Instruments Inc., Madison, Wisconsin/USA, 1994.
15

Dalton Transactions
Page 16 of 32
Table 1: Selected structural parameters (average values) of manganeseꢀbased CORMs of the types [(OC)4Mn(µꢀSR)]2 and [(OC)3Mn(µ3ꢀSR)]4 as well as of
trinuclear [(OC)4Mn(µꢀSMes)]3 (Me methyl, Mes 2,4,6ꢀtrimethylphenyl, Ph phenyl). The subscripts at the carbon atoms CtransꢀS and CcisꢀS characterize carbonyl
ligands in trans and cis positions to the thiolate anions, respectively.
R
Comp. MnꢀCtransꢀS
CtransꢀSꢀO
MnꢀCcisꢀS
CcisꢀSꢀO
MnꢀS
SꢀMnꢀS
MnꢀSꢀMn
Ref.
[(OC)4Mn(µꢀSR)]2
Ph
Ph
181.5
181.4
181.4
182.2
181.2
182.1
181.4
181.7
182.2
182.4
182.7
114.0
114.0
113.7
114.0
114.1
114.3
113.8
114.4
114.0
114.0
114.1
186.1
186.9
186.8
187.2
187.0
187.3
186.8
187.3
187.1
188.5
186.1
112.8
112.0
112.0
113.3
113.3
113.2
113.9
113.1
113.2
113.0
113.6
240.0
239.2
239.7
239.3
238.7
240.2
239.9
240.1
239.4
240.2
238.8
81.7
82.1
82.4
81.0
81.5
82.6
81.6
82.2
81.9
78.4
82.2
97.9
97.9
97.6
98.4
98.4
97.4
98.4
97.8
98.1
101.6
97.8
28
21
20
1a
1a
1b
1b
1b a
1c
1d
1e
1f
C6H4ꢀ4ꢀCH3
C6H4ꢀ4ꢀCH3
C6H4ꢀ4ꢀCH3
a
C6H4ꢀ4ꢀCF3
C6H4ꢀ4ꢀF
C6H4ꢀ4ꢀCl
C6H4ꢀ4ꢀOMe
C6F5
CH2C6H4ꢀ4ꢀCl
[(OC)3Mn(µ3ꢀSR)]4
Ph
1g
1h
179.8
180.6
181.4
181.4
181.4
181.4
181.6
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
239.2
238.4
238.8
239.3
239.8
238.8
238.6
78.7
78.7
78.5
78.7
78.7
78.5
78.4
100.2
100.2
100.4
100.3
100.3
100.4
100.5
28
21
2a
2a
2b
2b
2c
2d
2d
Ph
113.6
114.3
114.4
114.3
114.2
114.4
C6H4ꢀ4ꢀCH3
C6H4ꢀ4ꢀCH3
a
C6H4ꢀ4ꢀCF3
C6H4ꢀ4ꢀF b
C6H4ꢀ4ꢀF c
[(OC)4Mn(µꢀSMes)]3
Mes
181.6
114.5
187.5
113.2
242.6
87.7
133.7
3
a) Crystal structure of [(OC)4Mn(µꢀSR)]2ꢁ[(OC)3Mn(µ3ꢀSR)]4; b) crystals from diethyl ether solution; c) crystals from CCl4 solution, crystal structure of
[(OC)3Mn(µ3ꢀSR)]4ꢁCCl4.
16

Page 17 of 32
Dalton Transactions
Table 2: Selected spectroscopic parameters of manganeseꢀbased CORMs of the types [(OC)4Mn(µꢀSR)]2 and [(OC)3Mn(µ3ꢀSR)]4 as well as of trinuclear
[(OC)4Mn(µꢀSMes)]3 (Me methyl, Mes 2,4,6ꢀtrimethylphenyl, Ph phenyl). The subscripts at the carbon atoms CtransꢀS and CcisꢀS characterize carbonyl ligands in
trans and cis positions to the thiolate anions, respectively. The NMR parameters were obtained from [D8]THF solutions of these complexes.
R
Comp.
δ(13CO)
ν(CO)
[(OC)4Mn(µꢀSR)]2
Ph
C6H4ꢀ4ꢀCH3
C6H4ꢀ4ꢀCF3
C6H4ꢀ4ꢀF
C6H4ꢀ4ꢀCl
C6H4ꢀ4ꢀOMe
C6F5
CH2C6H4ꢀ4ꢀCl
[(OC)3Mn(µ3ꢀSR)]4
Ph
C6H4ꢀ4ꢀCH3
C6H4ꢀ4ꢀCF3
C6H4ꢀ4ꢀF
C6H4ꢀ4ꢀCl
[(OC)4Mn(µꢀSMes)]3
Mes
213.4, 214.8
213.6, 215.0
212.9, 214.0
213.2, 214.7
212.9, 214.4
213.3, 215.1
ꢀ
2072, 1995, 1980, 1935
2080, 2026, 1992, 1944
2083, 2023, 1994, 1936
No pure product, see text
2083, 1991, 1979, 1955
1a
1b
1c
1d
1e
1f
2072, 1995, 1986, 1942
No pure product, see text, no data given16
2065, 1990, 1956, 1935
1g
1h
216.1
220.9
221.0
220.0
221.0
220.7
2028, 2020, 1954 15
2023, 2013, 1949 29
ꢀ
2018, 1940, 1925
2017, 1966, 1926
2a
2b
2c
2d
2e
ꢀ
2080, 2001, 1970, 1952, 1921
3
17

Dalton Transactions
Page 18 of 32
Table 3: Crystal data and refinement details for the Xꢀray structure determinations of the compounds 1b ꢀ 1d.
Compound
formula
1b
1b_2b
C40H28Mn4O12S4,
C22H14Mn2O8S2
1628.96
ꢀ140(2)
1c
1d
C22H14Mn2O8S2
C22H8F6Mn2O8S2
C20H8F2Mn2O8S2
fw (gꢁmolꢀ1)
T/°C
crystal system
space group
a/ Å
b/ Å
c/ Å
α/°
β/°
γ/°
V/Å3
Z
ρ (gꢁcmꢀ3)
µ (cmꢀ1)
580.33
ꢀ140(2)
triclinic
688.28
ꢀ140(2)
monoclinic
P 21/c
11.5033(3)
6.3460(2)
17.4457(3)
90
101.244(1)
90
1249.09(6)
2
588.26
ꢀ140(2)
triclinic
monoclinic
P 21/c
12.2008(3)
31.5255(7)
18.3025(4)
90
106.572(1)
90
6747.4(3)
4
P ī
P ī
9.6294(5)
11.8965(6)
12.0584(5)
116.375(2)
90.353(3)
108.027(2)
1159.97(10)
2
8.5295(2)
9.2910(9)
15.0154(6)
91.833(2)
93.910(2)
115.316(2)
1070.68(11)
2
1.662
13.15
1.604
13.46
1.830
12.7
1.825
14.39
measured data
data with I > 2σ(I)
unique data (Rint)
wR2 (all data, on F2)a)
R1 (I > 2σ(I)) a)
S b)
7115
4329
5000/0.0247
0.1016
0.0449
1.145
0.412/ꢀ0.458
multiꢀscan
0.8963/0.9962
1026726
38279
11059
15345/0.0963
0.1620
0.0902
1.180
1.016/ꢀ0.574
multiꢀscan
0.6622/0.7456
1026727
7171
2674
2840/0.0220
0.0683
0.0291
1.037
0.933/ꢀ0.593
multiꢀscan
0.6486/0.7456
1026728
4710
4496
4710/0.0250
0.2665
0.0988
1.187
2.165/ꢀ1.989
multiꢀscan
0.7080/0.7456
1026729
Res. dens./eꢁÅꢀ3
absorpt method
absorpt corr Tmin max
/
CCDC No.
18

Page 19 of 32
Dalton Transactions
Table 3: Crystal data and refinement details for the Xꢀray structure determinations of the compounds 1e ꢀ 1h.
Compound
Formula
1e
C20H8Cl2Mn2O8S2
621.16
1f
C22H14Mn2O10S2
612.33
1g
C20F10Mn2O8S2
732.20
ꢀ140(2)
monoclinic
P 21/c
9.2997(2)
16.5384(4)
8.6285(1)
90
116.849(1)
90
1h
C22H12Cl2Mn2O8S2
649.22
fw (gꢁmolꢀ1)
T/°C
ꢀ140(2)
triclinic
ꢀ140(2)
monoclinic
P 21/c
10.5593(3)
9.4284(3)
12.5227(3)
90
102.598(2)
90
ꢀ140(2)
triclinic
P ī
crystal system
space group
a/ Å
b/ Å
c/ Å
P ī
8.2467(3)
8.8721(3)
9.5582(3)
66.959(2)
66.175(2)
65.853(1)
561.93(3)
1
7.0206(2)
9.2680(2)
10.1924(3)
99.676(2)
107.547(1)
93.424(2)
619.02(3)
1
α/°
β/°
γ/°
V/Å3
1216.71(6)
2
1184.02(4)
2
Z
ρ (gꢁcmꢀ3)
µ (cmꢀ1)
1.836
15.94
1.671
12.64
2.054
13.7
1.742
14.51
measured data
data with I > 2σ(I)
unique data (Rint)
wR2 (all data, on F2)a)
R1 (I > 2σ(I)) a)
S b)
3755
2451
2554/0.0150
0.0594
0.0246
1.086
0.317/ꢀ0.291
multiꢀscan
0.6699/0.7456
1026730
7160
2546
2791/0.0291
0.0654
0.0279
1.096
0.331/ꢀ0.356
multiꢀscan
0.7070/0.7456
1026731
7216
2530
2702/0.0212
0.0564
0.0233
1.083
0.328/ꢀ0.272
multiꢀscan
0.6302/0.7456
1026732
4079
2677
2795/0.0145
0.0560
0.0239
1.078
0.341/ꢀ0.249
multiꢀscan
0.6877/0.7456
1026733
Res. dens./eꢁÅꢀ3
absorpt method
absorpt corr Tmin max
/
CCDC No.
19

Dalton Transactions
Page 20 of 32
Table 3: Crystal data and refinement details for the Xꢀray structure determinations of the compounds 2b ꢀ 2d_CCl4.
Compound
Formula
2b
C40H28Mn4O12S4
1048.62
ꢀ140(2)
orthorhombic
P n a 21
19.3656(2)
15.9446(1)
14.0502(1)
90
2c
C40H14F12Mn4O12S4
1262.51
ꢀ140(2)
2d
C36H16F4Mn4O12S4
1064.49
ꢀ140(2)
orthorhombic
P b c a
2d_CCl4
C36H16F4Mn4O12S4ꢁCCl4
1218.30
fw (gꢁmolꢀ1)
T/°C
ꢀ140(2)
monoclinic
C c
16.0318(4)
16.1365(5)
17.5547(6)
90
crystal system
space group
a/ Å
b/ Å
c/ Å
monoclinic
C 2/c
10.0188(3)
20.0950(5)
22.9661(6)
90
19.6504(2)
19.5146(3)
20.7347(3)
90
α/°
β/°
90
90
97.568(1)
90
4583.4(2)
4
1.830
13.69
90
90
103.771(2)
90
4410.8(2)
4
γ/°
V/Å3
4338.37(6)
4
7951.13(19)
8
Z
ρ (gꢁcmꢀ3)
µ (cmꢀ1)
1.605
13.9
1.778
15.32
1.835
16.28
measured data
data with I > 2σ(I)
unique data (Rint)
wR2 (all data, on F2)a)
R1 (I > 2σ(I)) a)
S b)
24515
9582
9708/0.0165
0.0619
13457
4578
5151/0.0399
0.0970
44429
7296
9076/0.0555
0.0826
12283
8345
8583/0.0208
0.0652
0.0239
1.039
0.0367
1.110
0.0395
1.128
0.0292
1.085
Res. dens./eꢁÅꢀ3
Flackparameter
absorpt method
1.436/ꢀ0.435
0.009(8)
multiꢀscan
0.7234/0.9991
1026734
0.671/ꢀ0.494
ꢀ
multiꢀscan
0.6782/0.9971
1026735
0.398/ꢀ0.370
ꢀ
multiꢀscan
0.8548/0.9949
1026736
0.397/ꢀ0.331
0.025(11)
multiꢀscan
0.6549/0.9823
1026737
absorpt corr Tmin max
/
CCDC No.
20

Page 21 of 32
Dalton Transactions
Table 3: Crystal data and refinement details for the Xꢀray structure determinations of the compounds 3 ꢀ 4.
Compound
Formula
3
C39H33Mn3O12S3
954.65
4
C34H26Mn2O6S4[*]
768.67[*]
ꢀ140(2)
fw (gꢁmolꢀ1)
T/°C
ꢀ140(2)
crystal system
space group
a/ Å
b/ Å
c/ Å
triclinic
monoclinic
C 2/c
23.9640(15)
12.8427(8)
13.5112(9)
90
110.910(4)
90
3884.4(4)
4
P ī
8.7224(2)
14.5346(6)
16.5814(6)
103.291(1)
91.005(2)
98.173(2)
2022.29(12)
2
α/°
β/°
γ/°
V/Å3
Z
ρ (gꢁcmꢀ3)
µ (cmꢀ1)
1.568
11.39
1.314[*]
9.03[*]
measured data
data with I > 2σ(I)
unique data (Rint)
wR2 (all data, on F2)a)
R1 (I > 2σ(I)) a)
S b)
12266
7537
9033/0.0255
0.1416
0.0572
1.146
0.886/ꢀ0.586
multiꢀscan
0.6095/0.7457
1026738
11081
3296
4369/0.0542
0.1477
0.0618
1.127
0.472/ꢀ0.345
multiꢀscan
0.7854/0.8245
1026739
Res. dens./eꢁÅꢀ3
absorpt method
absorpt corr Tmin max
/
CCDC No.
[*] derived parameters do not contain the contribution of the disordered solvent.
a) Definition of the R indices: R1 = (ΣFoꢀFc)/ΣFo;
21

Dalton Transactions
Page 22 of 32
2
2 2
2
2
wR2 = {Σ[w(Fo ꢀFc2)2]/Σ[w(Fo ) ]}1/2 with wꢀ1 = 2(Fo ) + (aP)2+bP; P = [2Fc2 + Max(FO ]/3;
b) s = {Σ[w(Fo ꢀFc2)2]/(NoꢀNp)}1/2.
2
22

Page 23 of 32
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT03567D
Fig. 1: 1H NMR spectra of the reaction of [(OC)5MnBr] with HSꢀC6H4ꢀ4ꢀF in methanol after 6 h (top)
and 9 h (bottom). The assignment to dinuclear 1d and tetranuclear 2d is given in the upper spectrum.
In the upper spectrum, integration of the resonances yields a ratio of 1d:2d of 1:1.9 is
23

Dalton Transactions
Page 24 of 32
View Article Online
DOI: 10.1039/C4DT03567D
Fig. 2: 13C{1H} NMR spectra of the reaction of [(OC)5MnBr] with HSꢀC6H4ꢀ4ꢀF in methanol after 6 h
(top) and 9 h (bottom). The assignment to dinuclear 1d and tetranuclear 2d is given in the upper
spectrum. The conversion to the tetranuclear cage compound occurs quantitatively and no sideꢀ
products were detected.
24

Page 25 of 32
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT03567D
Fig. 3: 1H NMR spectra of the reaction of [(OC)3Mn SꢀC6H4ꢀ4ꢀF]4 with carbon monoxide (18 bar, r.t.)
in CCl4 at the begin (top), after 10 d (middle), and after 20 d (bottom). The assignment to dinuclear 1d
and tetranuclear 2d is given in the middle spectrum. Initially, a mixture of dinuclear 1d and
tetranuclear 2d is observed before unknown side products were detected.
25

Dalton Transactions
Page 26 of 32
View Article Online
DOI: 10.1039/C4DT03567D
Fig. 4: Molecular structures and numbering schemes of dinuclear [(OC)4Mn(µꢀSR)]2 with R = C6H4ꢀ4ꢀ
Cl (1e, top) and C6F5 (1g, bottom). The ellipsoids represent a probability of 40 %. Atoms generated by
inversion symmetry are marked with the letter "A". The hydrogen atoms are omitted for the sake of
clarity.
26

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DOI: 10.1039/C4DT03567D
Fig. 5: Molecular structure and numbering scheme of tetranuclear [(OC)3Mn(µ3ꢀSR)]4 with R = C6H4ꢀ
4ꢀF (2d). The ellipsoids represent a probability of 40%, H atoms are neglected for the sake of clarity.
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DOI: 10.1039/C4DT03567D
Fig. 6: Molecular structure and numbering scheme of trinuclear [(OC)4Mn(µꢀSMes)]3 (3). The
ellipsoids represent a probability of 40 %, H atoms are omitted for clarity reasons.
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DOI: 10.1039/C4DT03567D
Fig. 7: Lightꢀtriggered CO release by CORMꢀMnꢀS1 in physiological solution. A: Detection of CO
based upon spectral differences of myoglobin (10 µM) in PBS + 0.1% sodium dithionite (SD). CO
was added from a saturated (1 mM) solution at the final concentrations ([CO]) indicated. Absorbance
at 422 nm was determined and averaged from 4 measurements to compile a calibration line, shown in
B. C: Time course of CO release from (1a) without illumination detected upon changes in absorbance
at 422 nm (A422nm) of 10 µM desoxymoyoglobin ion PBS + 0.1% SD. D: Time course of CO release
from 2 µM (1a) with illumination at 470 nm based upon A422nm for 10 µM desoxymyoglobin as in C.
A monoexponential fit to the data is superimposed. E: Averaged (n=4) time constants (top panel) and
the amount of CO released per CORM molecule (bottom panel) from fits as shown in (D) for
illumination of 2 µM (1a) with different wavelengths. F: Absorbance spectra of 10 µM
desoxymyoglobin in PBS + 0.1% SD added to 5 µM (1a) preincubated for 5 min with/without SD and
with/without illumination as indicated. Spectra are averages from 4 independent measurements.
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