Stoichiometric H2 production from H2O upon Mn 2(CO)10 photolysis

Article abstract of DOI:10.1016/j.jorganchem.2012.10.034

Photolysis of Mn₂(CO)₁₀ in an alkane/water biphasic system has resulted in the generation of 1.80 ± 0.16 mol of hydrogen per mol of Mn₂(CO)₁₀. Various studies including deuteration have indeed shown water to be the H₂ source while kinetic studies have indicated a strong correlation between the concentration of the key intermediate MnH(CO)₅ with the production rate of H₂. Some of the oxygen atoms of water have been incorporated into a white solid assigned to MnCO₃. A mechanism accounting for MnH(CO)₅ formation from Mn₂(CO)₁₀ photolysis and subsequently H₂ production from MnH(CO)₅ has been proposed.

Full text of DOI:10.1016/j.jorganchem.2012.10.034

Journal of Organometallic Chemistry 724 (2013) 1e6
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Stoichiometric H2 production from H2O upon Mn2(CO)10 photolysis
*
Jun Wei Kee, Che Chang Chong, Chun Keong Toh, Yuan Yi Chong, Wai Yip Fan
Department of Chemistry, National University of Singapore, 3 Science Drive, Singapore 117543, Singapore
a r t i c l e i n f o
a b s t r a c t
Article history:
Photolysis of Mn2(CO)10 in an alkane/water biphasic system has resulted in the generation of
1.80 ꢀ 0.16 mol of hydrogen per mol of Mn2(CO)10. Various studies including deuteration have indeed
shown water to be the H2 source while kinetic studies have indicated a strong correlation between the
concentration of the key intermediate MnH(CO)5 with the production rate of H2. Some of the oxygen
atoms of water have been incorporated into a white solid assigned to MnCO3. A mechanism accounting
for MnH(CO)5 formation from Mn2(CO)10 photolysis and subsequently H2 production from MnH(CO)5 has
been proposed.
Received 18 July 2012
Received in revised form
10 October 2012
Accepted 19 October 2012
Keywords:
Manganese
Photochemistry
Water activation
Hydride
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
HCl [14], our study demonstrates that the system still works with
water. The key intermediate has been identified as MnH(CO)5 and
Hydrogen production from water upon photolysis of transition
metal complexes has generated considerable interest as a cleaner
source of energy to replace fossil fuels. In recent years, several
examples of metal complexes containing platinum [1,2], cobalt in
cobaloximes [3,4], iron in hydrogenase mimics [5e9], ruthenium
[10], molybdenum [11] and [12] manganese have been reported to
catalytically activate water. Oxidative addition of water to a metal
centre which forms an essential part of the reaction pathway has
been discussed in a recent review [13]. Apart from catalysis,
understanding OeH bond activation of water is also of much
importance. In a previous study by Byers et al. [14], photolysis of
a mechanism has been proposed to account for the general features
of the experimental data.
2. Results and discussion
Broadband irradiation (300e800 nm) of Mn2(CO)10 in a cyclo-
hexane/water biphasic system resulted in the disappearance of its
nCO bands (2045, 2013, 2002 and 1983 cmꢁ1) and the concomitant
appearance of two new peaks at 2015 cmꢁ1 and 2007 cmꢁ1 (Fig.1a).
Thecorresponding 1H NMR spectrum of the sample recorded in C6D6
solvent showed a signal at ꢁ7.9 ppm. These spectroscopic assign-
ments could be matched closely to previously reported data for
MnH(CO)5 [16]. At the same time, the gas phase IR spectrum (Fig.1b)
of the headspace above the solution showed the production of CO,
CO2 and MnH(CO)5 vapour [17]. The presence of MnH(CO)5 was
further confirmed upon formation of MnH(CO)4PPh3 [18] in the
presence of triphenylphosphine (PPh3) under mild heating.
Mn2(CO)8L2 (L
¼
CO, P(OEt)3 and PBu3) and HCl afforded
MnH(CO)4L and MnCl(CO)4L along with traces of H2. Recently, our
group has demonstrated stoichiometric photoactivation of water by
cyclopentadienyl manganese tricarbonyl CpMn(CO)3 to produce
hydrogen and hydrogen peroxide [15]. However, more examples
and extensive studies are still required to understand the various
photopathways, both stoichiometric and catalytic, leading to H2
generation from water especially under ambient conditions.
In this paper, we report the stoichiometric hydrogen production
upon photolysis of commercially-available dimanganese deca-
carbonyl Mn2(CO)10 in a biphasic mixture of alkane and water.
Although Mn2(CO)10 is known to produce H2 upon reaction with
A series ofcontrol experiments has been carried out to understand
how MnH(CO)5 is generated. Photolysis of Mn2(CO)10 in anhydrous
cyclohexane or its thermal heating (up to 100 ꢂC) in wet cyclohexane
resulted in much slower decomposition of Mn2(CO)10 and negligible
signals of MnH(CO)5. In a series of deuteration experiments,
Mn2(CO)10 photolysis in d12-cyclohexane/H2O yielded MnH(CO)5
while the corresponding photolysis in cyclohexane/D2O mixture
afforded carbonyl signals which could be matched to the literature
values for MnD(CO)5 [16] (nCO ¼ 2015 cmꢁ1 and 2006 cmꢁ1) (Fig. 2).
* Corresponding author. Fax: þ65 67791691.
þ
E-mail address: chmfanwy@nus.edu.sg (W.Y. Fan).
The involvement of a cationic MnðCOÞ5 or MnðCOÞ6þ intermediate
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.10.034

2
J.W. Kee et al. / Journal of Organometallic Chemistry 724 (2013) 1e6
Fig. 1. FTIR spectra recorded after a 2-h broadband irradiation of Mn2(CO)10 in biphasic cyclohexane/water. (a) The production of MnH(CO)5 (2015 and 2007 cmꢁ1) taken in the
cyclohexane layer (b) the production of CO (no ¼ 2143 cmꢁ1), CO2
(
no ¼ 2340 cmꢁ1) and MnH(CO)5
(
nCO ¼ 2033, 2028 and 2020 cmꢁ1) in the headspace above the reaction mixture.
(c) XRD analysis of the white precipitate MnCO3.
has been ruled out as the photolysis of Mn2(CO)10 with tetra-n-
butylammonium bromide did not give MnBr(CO)5. In the presence of
tetrafluoroboric acid HBF4 in the aqueous layer, both rates of
Mn2(CO)10 decomposition and MnH(CO)5 formation were not
affected significantly as the pH is decreased from 6 to 2, suggesting
that Hþ ions do not have a significant role in the formation of
MnH(CO)5. From these data, it is evident that only light and water but
no additives are required for MnH(CO)5 formation.
Upon prolonged photolysis (>6 h) of the reaction mixture,
a white solid has been obtained in 5e10% yield. The solid shows
alkaline behaviour as it requires two equivalents of Hþ (from HCl
aqueous solution) for neutralization. An XRD (X-ray powder
diffraction) analysis of the solid in Fig. 1c confirms its identity to be
manganese carbonate MnCO3 (JCPDS Card No.: 83-1763) [19e21].
Along with the MnH(CO)5 formation, H2 evolution has been
observed throughout the photolysis until all the Mn2(CO)10 and
MnH(CO)5 have decomposed. The headspace mass spectrum indi-
cated the production of H2 at 1.80 ꢀ 0.16 mol per mol of Mn2(CO)10
used. D2 was also detected at 1.40 ꢀ 0.10 mol per mol of Mn2(CO)10
for D2O. The time profile of the H2 evolution has been shown
together with those of the respective IR signals of MnH(CO)5 and
Mn2(CO)10 in Fig. 3. The quantification of H2 production is carried
out relative to the amount of Mn2(CO)10 used since the latter could
be weighed accurately, rather than based on the IR absorbance of
2014.7
2005.2
Mn2(CO)10 + D2O
2006.6
Mn2(CO)10 + H2O
2030
2025
2020
2015
2010
2005
2000
1995
1990
Wavenumbers (cm-1)
Fig. 2. FTIR spectrum of MnH(CO)5 (2014.7 cmꢁ1 and 2006.6 cmꢁ1) or MnD(CO)5
(2014.7 cmꢁ1 and 2005.2 cmꢁ1) recorded at 0.5 cmꢁ1 resolution after a 2-h broadband
irradiation of Mn2(CO)10 in
respectively.
a biphasic cyclohexane/H2O or cyclohexane/D2O

J.W. Kee et al. / Journal of Organometallic Chemistry 724 (2013) 1e6
3
To investigate further, MnH(CO)5 has been prepared in a pure
form and photolysed further in the presence of water. Indeed,
significant H2 signal has been detected in the mass spectrum. In
contrast, the absence of photolysis or water (removed using
molecule sieves 4A) did not produce H2. Thermal decomposition of
MnH(CO)5 also failed to yield H2, highlighting the need for light in
this step of the process. Interestingly, photolysis of MnD(CO)5 in
cyclohexane/H2O produced not only the expected HD but also
significant H2 and D2 in a ratio of HD:H2:D2 ¼ 3:7:1. The result is
explained by a fast HeD exchange process between the acidic
MnD(CO)5 (pKa w7) [22] and H2O upon mixing. Indeed, the
appearance of IR signals due to MnH(CO)5 when a mixture of
MnD(CO)5 and H2O was left standing in the dark for 1e3 h gave
strong evidence of the exchange.
The generation of H2 upon Mn2(CO)10 photolysis has been
carried out in polar solvents such as thf and acetonitrile and
resulted in similar yields. H2 can also be generated from acetic acid
with similar efficiency upon Mn2(CO)10 photolysis. The reaction
pathways mirror those in the water system as the production of
MnH(CO)5 was observed. This study demonstrates the further
utility of Mn2(CO)10 in activating OeH bonds in carboxylic acids.
The Mn2(CO)10/H2O photolytic system has also been tested for
its use in the wateregas shift process since a small quantity of CO2
has been detected. However, increasing the CO pressure from
0.1 bar to 1.5 bar not only slowed the reaction but also did not cause
any increase in H2 even after long periods of irradiation.
Preceding this work, numerous studies have been conducted for
the initial photofragmentation of Mn2(CO)10 in various solvents
[23e26]. Limiting the discussion to the photolysis of Mn2(CO)10 in
non-polar solvents, it has been noted that MneMn fission [24] is
much more dominant than MneCO cleavage [25] at wavelengths
longer than 300 nm. The proposed mechanism will be based on the
initial production of Mn(CO)5 radicals from the MneMn fission.
The experimental data suggest that the production of H2 can be
divided into two photoprocesses; first the generation of the key
intermediate MnH(CO)5 from Mn(CO)5 radical and second, the
reaction of MnH(CO)5 with H2O. In the previous study on the
photoreaction of HCl with Mn2(CO)10, Byers et al. [14] has also
suggested that Mn(CO)5 radicals produced upon MneMn dissoci-
ation undergo oxidative addition of HCl to give MnH(CO)5 and
MnCl(CO)5 as the main products. Compare to HCl, the production
of MnH(CO)5 using water has been measured to be only three
times slower. Thus it is reasonable to adopt this mechanism, at
least to account for MnH(CO)5 formation, by substituting HCl for
H2O as illustrated in Fig. 4. Along with MnH(CO)5, a reactive
manganese hydroxyl species, Mn(OH)(CO)5 is expected to have
been generated.
Fig. 3. Time profile showing (a) the absorbance of
D
Mn2(CO)10 (at 2045 cmꢁ1) and ,
MnH(CO)5 (at 2007 cmꢁ1) and (b) the percentage yield of H2 per Mn2(CO)10 used at
different time intervals throughout the photolysis period. The inset in (b) represents
the typical mass spectrum for the m/e ¼ 1 to 10 obtained for the headspace of the
photolytic mixture. (c) Time-dependent mass spectra taken of the headspace content
upon a 5-h photolysis of Mn2(CO)10 in a hexane/H2O mixture, representing the signal
at m/e ¼ 2. The signals obtained for a 50 Torr H2 standard and the headspace content of
a similar mixture prior to photolysis are included for comparison.
The second step of the photolysis is of vital importance as it has
been shown that MnH(CO)5 concentration correlates strongly to
the H2 production rate. Similar to the facile formation of
Mn(CO)4PR3H complexes [18], MnH(CO)5 undergoes thermal CO
dissociation followed by H2O substitution to give MnH(CO)4(H2O).
A simple abstraction of the proton from the adjacent H2O ligand
may liberate H2 through some as yet unknown pathway leaving
a manganese hydroxyl intermediate behind.
MnH(CO)5 which may have a larger error due to the uncertainty in
its extinction coefficient.
As mentioned earlier,
a
manganese hydroxyl species
From Fig. 3, the total yield of H2 increased with the photolytic
duration of 5 h while Mn2(CO)10 decomposed within the first 3 h. A
comparison of the time profiles showed that the rate of H2 evolution
(given by the gradient of Fig. 3b) correlated more closely to the
concentration of MnH(CO)5 rather than to Mn2(CO)10. In fact the total
H2 yield obtained over 5 h (when all the MnH(CO)5 and Mn2(CO)10
have decomposed) doubled that of the 3-h yield (when all Mn2(CO)10
have decomposed) and suggested that the average rate is indepen-
dent of Mn2(CO)10 but proportional to MnH(CO)5 instead.
Mn(OH)(CO)5 is generated alongside MnH(CO)5 in the first step.
This species is expected to be reactive since the OH ligand has been
known to react with the electrophilic CO ligand to give metal-
locarboxylic acids. These complexes tend to decompose to give CO2
and the corresponding metal hydride [27]. In our experiments,
small amounts of CO2 and MnCO3 were indeed detected; the latter
is a resultant of carbonic acid formed in the presence of water. The
resultant 16-electron metal hydride MnH(CO)4 coordinates to H2O
and generates H2 upon photolysis again. Thus by invoking this

4
J.W. Kee et al. / Journal of Organometallic Chemistry 724 (2013) 1e6
a
CO
Mn
CO
CO
CO
CO
OC
OC
CO
CO
CO
CO
OC
OC
H
Mn
CO
+
Mn CO
OC Mn
OC
HO
CO
CO
CO
H O
2
CO
CO
Mn
CO
CO
hv
CO
OH
OC
H
CO
CO
OC Mn
CO + Mn(CO)
5
CO
CO
Mn
CO
CO
H O
2
CO
b
CO
OC
CO
OC
H
CO
CO
OC
Mn CO
+
H2
Mn
CO
HO
OH2
hv
H
CO
c
H O
2
CO
CO
CO2
CO
OC
CO
CO
OC
OC
H
Mn CO
+
H2
Mn
CO
Mn
CO
hv
HO
hv
CO
OH2
HO
CO
Fig. 4. (a) Mechanism showing MneMn bond homolytic fission, leading to an eventual production of MnH(CO)5 and Mn(OH)(CO)5 (adopted from Ref. [14]). (b) Mechanism showing
the H2 production from MnH(CO)5 and H2O. (c) Mechanism showing the H2 production from Mn(OH)(CO)5 and H2O.
pathway, it is possible to explain the generation of almost two
equivalents of H2 from Mn2(CO)10 photolysis in water.
4.2. Mass spectrometric determination of H2 and CO2
H2 gas was detected using a modified residual gas analyser
(Pfeiffer Vacuum PrismaPlus QMG 200 with a high-sensitivity ion
source) where the signals at m/e 1e50 were monitored over time.
Prior to each analysis, a sample of pure H2 gas of known pressure
(5e60 Torr) and air were injected for calibration and baseline
correction respectively.
3. Conclusions
Mn2(CO)10 photolysis in an alkane/water biphasic system has
afforded 1.80 ꢀ 0.16 mol of hydrogen per mol of Mn2(CO)10. A
manganese hydride MnH(CO)5 has been detected as an interme-
diate in the mixture. The H2 source has indeed been found to be
water. The kinetic studies monitored using the IR signatures of
Mn2(CO)10 and MnH(CO)5, indicate a correlation between the latter
complex with the production of H2. Some of the oxygen atoms of
water have been incorporated into a white solid assigned to MnCO3.
A mechanism accounting for the formation of H2 via MnH(CO)5 has
been proposed. We hope that this study is still potentially relevant
to the development of catalytic schemes for H2 generation.
For each analysis, 3.0 cm3 of the gas was injected directly using
a syringe into a pre-evacuated (<1 ꢃ 10ꢁ6 Torr) 20 cm3 stainless
steel chamber connected to the residual gas analyser. Thereafter,
repeated 1 cm3 portions of gas samples were then introduced by
means of two Swagelok ball valves to ensure that repeated
sampling of the gas would not have significant depreciation of the
initial pressure of gas. Subsequently, the amount of H2 present in
the photolytic mixture was calculated while taking into account
volume correction factors.
Similarly, the amount of CO2 produced was determined by
monitoring the signal at m/e 44. Pure CO2 from a cylinder was used
to prepare standards of known pressure (20e60 Torr) and air were
injected for calibration and baseline correction respectively.
4. Experimental details
4.1. Materials and measurements
All chemicals were purchased from SigmaeAldrich and used
without further purification, unless otherwise noted. Chemicals
used in the quantification were calibrated against their respective
primary standards. 1H NMR spectra were recorded in C6D6 on
a Bruker ACF300 and AMX500 NMR spectrometer with chemical
shifts referenced to residual C6D6 peaks. Solution IR spectra were
obtained on a Nexus 870 FT-IR spectrometer using a cell of 0.1 mm
path length equipped with CaF2 windows. All photolysis experi-
ments were conducted using a UV broadband lamp (wavelength
range: 300e800 nm typical power measured at 10 cm distance:
0.80e0.90 W/cm2) at 10 cm distance away from the reaction
mixture in borosilicate glass apparatus. Powder X-ray diffraction
(XRD) measurement of solids was carried out using Siemens
Powder XRD D5005 diffractometer.
4.3. Photolysis of Mn2(CO)10 in cyclohexane/water mixture
A mixture of Mn2(CO)10 (0.0045 g, 1.1 ꢃ 10ꢁ5 mol) in cyclo-
hexane (1.0 cm3) and H2O (0.10 cm3) was photolysed in an evacu-
ated glass apparatus (25 cm3 volume) for 2 h before the reaction
mixture was sampled for IR and 1H NMR. The main metal complex
intermediate was identified as MnH(CO)5
(
n
(CO) in cyclohexane:
2015s and 2007w; 1H NMR (C6D6)
d
ꢁ7.9 ppm). Upon complete
photolysis, headspace mass-spectrometric studies indicated H2
production to be 1.80 ꢀ 0.16 mol of hydrogen per mol of Mn2(CO)10
and IR spectroscopic studies of the headspace indicated CO2
production to be 0.08 ꢀ 0.03 mol per mol of Mn2(CO)10 used
respectively.

J.W. Kee et al. / Journal of Organometallic Chemistry 724 (2013) 1e6
5
4.4. Photolysis of Mn2(CO)10 under a variety of conditions
4.7. Photolysis of MnH(CO)5 in cyclohexane/water
Typically, a 5-h photolysis (unless otherwise stated) was carried
out for Mn2(CO)10 (0.0045 g, 1.1 ꢃ 10ꢁ5 mol) under various condi-
tions. If anhydrous conditions were required, dried cyclohexane
(1.0 cm3) which has been distilled three times from molecular
sieves was used as the solvent.
MnH(CO)5 was generated from the photolysis of Mn2(CO)10
(0.0045 g, 1.1 ꢃ 10ꢁ5 mol) in cyclohexane (1.0 cm3) and water
(0.10 cm3) and then distilled into an evacuated glass apparatus
(25 cm3 volume) containing cyclohexane (1.0 cm3) and water
(0.10 cm3). A 2-h photolysis was carried out for the distillate and the
reaction mixture was then sampled for IR spectroscopic and
headspace mass-spectrometric studies.
For the detection of MnH(CO)4(PPh3), mild heating (40e50 ꢂC)
for 2 h was carried out in the presence triphenylphosphine PPh3
(10ꢁ4 mol) after MnH(CO)5 has been detected in an initial mixture
containing Mn2(CO)10 (0.0045 g, 1.1 ꢃ 10ꢁ5 mol) in cyclohexane
(1.0 cm3) and H2O (0.10 cm3). The main metal complex was iden-
4.8. Photolysis of MnH(CO)5 in dried cyclohexane
tified as MnH(CO)4(PPh3). (n(CO) in cyclohexane: 2062w, 1984m,
1969vs and 1958s; 1H NMR (C6D6)
33 Hz.)
d
ꢁ6.88 ppm doublet, 2J(PeH):
MnH(CO)5 was generated from a 2-h photolysis of Mn2(CO)10
(0.0045 g, 1.1 ꢃ 10ꢁ5 mol) and was distilled into an evacuated glass
apparatus (25 cm3 volume) containing cyclohexane (1.0 cm3) and
molecular sieves (1 g). A 6-h photolysis was carried out for the
distillate and the reaction mixture was then sampled for IR spec-
troscopic and headspace mass-spectrometric studies.
For the bromide ion test, the photolysis was carried out for
a mixture of Mn2(CO)10 (0.0045 g, 1.1 ꢃ 10ꢁ5 mol) in cyclohexane
(1.0 cm3) and a 1 M aqueous tetra-n-butylammonium bromide
solution (0.10 cm3). For the test on the influence of acid, the
photolysis was carried out for a mixture of Mn2(CO)10 (0.0045 g,
1.1 ꢃ 10ꢁ5 mol) in cyclohexane (1.0 cm3) and aqueous tetra-
fluoroboric acid HBF4 (1.0 cm3) whose pH can be monitored and
adjusted from 1 to 6 by varying the acid concentration.
4.9. HeD exchange studies of MnD(CO)5
MnD(CO)5 was distilled from a 2-h photolysis of Mn2(CO)10
(0.0045 g, 1.1 ꢃ 10ꢁ5 mol) in cyclohexane/D2O into an evacuated
glass apparatus (25 cm3 volume) containing cyclohexane (1.0 cm3)
and H2O (0.10 cm3). The resulting mixture was left to stand in the
dark for up to 3 h before an IR spectrum was obtained. Subse-
quently, MnD(CO)5 was distilled into a mixture of cyclohexane
(1.0 cm3) and D2O (0.10 cm3). MnD(CO)5 was photolysed with
cyclohexane/H2O before the head-space was sampled for head-
space mass-spectrometric studies.
For examining the influence of different polar solvents, the
photolysis of Mn2(CO)10 (0.0045 g, 1.1 ꢃ 10ꢁ5 mol) in a solution of
THF (1.0 cm3) and H2O (0.1 cm3) was conducted in an evacuated
glass apparatus (25 cm3 volume) using a UV broadband lamp
before the reaction mixture was sampled for headspace mass-
spectrometric studies. The same procedures were repeated
using acetonitrile. The H2 yield for THF and acetonitrile were at
1.90
respectively.
For CO pressurization studies,
ꢀ
0.20 and 1.87
ꢀ
0.20 mol per mol of Mn2(CO)10
a
mixture of Mn2(CO)10
(0.0045 g, 1.1 ꢃ 10ꢁ5 mol) in cyclohexane (1.0 cm3) and H2O
(0.10 cm3) was photolysed in a glass apparatus (25 cm3 volume,
evacuated and filled with CO pressure of 0.1 bare1.5 bar) for 5 h
before the reaction mixture was sampled for IR and 1H NMR
spectroscopic studies.
4.10. Attempted thermal activation of H2O using Mn2(CO)10 or
MnH(CO)5
Mn2(CO)10 (0.0045 g, 1.1 ꢃ 10ꢁ5 mol) was heated at 100 ꢂC in
a mixture of dodecane (1.0 cm3) and H2O (0.10 cm3) mixture for 3
days before the dodecane layer was sampled for IR spectroscopic
and mass-spectrometric studies. Similarly, MnH(CO)5, synthesized
from a 2-h photolysis of Mn2(CO)10 (0.0045 g, 1.1 ꢃ 10ꢁ5 mol), was
heated in a dodecane/water mixture at 100 ꢂC for 3 days. The
reaction mixture was then sampled for IR spectroscopic and
headspace mass-spectrometric studies.
4.5. Deuteration studies
A 3-h photolysis was carried out for a mixture of Mn2(CO)10
(0.0045 g, 1.1 ꢃ 10ꢁ5 mol) in dried cyclohexane (1.0 cm3) and D2O
(0.10 cm3). The reaction mixture was sampled for IR and the
product was identified as MnD(CO)5. (n(CO) in cyclohexane: 2015s
and 2006w) Upon complete photolysis, D2 was detected at
1.40 ꢀ 0.10 mol per mol of Mn2(CO)10. Similarly, the photolysis was
repeated in a mixture of 1 cm3 of d12-cyclohexane and 1 cm3 of H2O
and the product was identified as MnH(CO)5.
4.11. Chemical analysis of solid residue
A 5-h photolysis was carried out for a mixture of Mn2(CO)10
(0.0045 g, 1.1 ꢃ 10ꢁ5 mol) in cyclohexane (1.0 cm3) and H2O
(0.10 cm3) and a white precipitate was observed. Once Mn2(CO)10
has reacted completely, the solvent and any residual MnH(CO)5
were removed under vacuum, before the residue was washed
further with cyclohexane under reduced air conditions. The solid is
dissolved in water and titrated with 0.1 M HCl solution with methyl
orange as the indicator. Powder X-ray diffraction (XRD) measure-
ment of the solid was carried out using Siemens Powder XRD
D5005 diffractometer.
4.6. Time profile monitoring
The photolysis of Mn2(CO)10 (0.0045 g, 1.1 ꢃ 10ꢁ5 mol) in
cyclohexane (1.0 cm3) and H2O (0.10 cm3) was conducted in an
evacuated glass apparatus (25 cm3 volume) using a UV broadband
lamp for a series of different time intervals before the reaction
mixture was sampled for IR, 1H NMR and headspace mass-
spectroscopic measurements. The relative amount of Mn2(CO)10
was determined by one of its infrared absorption bands at
2045 cmꢁ1. The relative amount of MnH(CO)5 was determined by
following the difference between the observed absorbance at
2007 cmꢁ1 and the corresponding absorbance contributed by
Mn2(CO)10. The H2 signal at m/e 2 was sampled by the residual gas
analyser at different time intervals.
4.12. Photolysis of Mn2(CO)10 in acetic acid
A mixture of Mn2(CO)10 (0.0045 g, 1.1 ꢃ 10ꢁ5 mol) in acetic acid
(1.0 cm3) was photolysed in an evacuated glass apparatus (25 cm3
volume) for 5 h before the reaction mixture was sampled for IR.

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J.W. Kee et al. / Journal of Organometallic Chemistry 724 (2013) 1e6
[16] P.S. Braterman, R.W. Harrill, H.D. Kaesz, J. Am. Chem. Soc. 89 (1967)
Acknowledgements
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The project was supported by a research grant provided by NUS
143-000-430-112. J.W.K., C.K.T. and Y.Y.C. acknowledge the support
of NUS scholarships.
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