Manganese Complexes of Pyrrole- and Indolecarboxamide Ligands: Synthesis, Structure, Electrochemistry, and Applications in Oxidative and Lewis-Acid-Assisted Catalysis

Article abstract of DOI:10.1002/ejic.201500773

This work shows the synthesis and structural, spectroscopic, and electrochemical properties of Mn^III complexes supported with pyrrole- and indolecarboxamide ligands. In all cases, the respective ligand constitutes a N₄ coordination sphere about the Mn^III ion. The Mn^III complexes of pyrrolecarboxamide ligands are square pyramidal with a fifth Cl atom, whereas analogous complexes of indolecarboxamide ligands are essentially square planar. Electrochemical studies reveal highly negative Mn^III/II and moderately positive Mn^IV/III redox potentials. In situ generated Mn⁴⁺ species of the pyrrolecarboxamide ligands were characterized by absorption and electron paramagnetic resonance spectroscopy. All complexes functioned as catalysts in olefin epoxidation reactions by using PhIO as the oxo-transfer agent. All complexes also acted as Lewis acid catalysts for ring-opening reactions of assorted epoxides with various nucleophiles. We also show a one-pot, two-step epoxidation reaction followed by ring opening, which illustrates the catalytic significance of the present complexes. Importantly, Mn^III complexes carrying electron-donating substituents on the ligand were found to be better catalysts.

Full text of DOI:10.1002/ejic.201500773

FULL PAPER
DOI:10.1002/ejic.201500773
Manganese Complexes of Pyrrole- and Indolecarboxamide
Ligands: Synthesis, Structure, Electrochemistry, and
Applications in Oxidative and Lewis-Acid-Assisted
Catalysis
Sunil Yadav,[a] Sushil Kumar,[a] and Rajeev Gupta*[a]
Keywords: Heterogeneous catalysis / Electrochemistry / Manganese / N ligands / Lewis acids
This work shows the synthesis and structural, spectroscopic,
and electrochemical properties of MnIII complexes supported
with pyrrole- and indolecarboxamide ligands. In all cases,
the respective ligand constitutes a N4 coordination sphere
electron paramagnetic resonance spectroscopy. All com-
plexes functioned as catalysts in olefin epoxidation reactions
by using PhIO as the oxo-transfer agent. All complexes also
acted as Lewis acid catalysts for ring-opening reactions of
about the MnIII ion. The MnIII complexes of pyrrolecarbox- assorted epoxides with various nucleophiles. We also show a
amide ligands are square pyramidal with a fifth Cl atom,
whereas analogous complexes of indolecarboxamide ligands
are essentially square planar. Electrochemical studies reveal
one-pot, two-step epoxidation reaction followed by ring
opening, which illustrates the catalytic significance of the
present complexes. Importantly, MnIII complexes carrying
highly negative MnIII/II and moderately positive MnIV/III re- electron-donating substituents on the ligand were found to
dox potentials. In situ generated Mn4+ species of the pyrrole-
carboxamide ligands were characterized by absorption and
be better catalysts.
the past, we have investigated the coordination chemistry
of nickel and copper with several pyrrolecarboxamide and
indolecarboxamide ligands having electronic substituents
on the ligand framework.[100,101] We have delineated a few
ligand architectural parameters, subtly altered by inserting
electronic substituents, to affect the structure–redox rela-
tionship of the metal ion. Herein, we have used a set of
pyrrolecarboxamide and indolecarboxamide ligands
containing electron-donating and electron-withdrawing
substituents for the synthesis of a few MnIII complexes.
These well-characterized MnIII complexes were used as cat-
alysts in PhIO-mediated olefin epoxidation reactions and in
ring-opening reactions of assorted epoxides by using vari-
ous nucleophiles.
Introduction
Metalloenzymes are paramount in utilizing ligand archi-
tecture to modulate the structural, electronic, and redox
properties of the metal cofactor and, therefore, reactiv-
ity.[1–7] Understanding the ligand architectural parameters
that control the structure and redox regulation of a metal
ion is therefore crucial.[8,9] In this context, coordination
complexes with systematically designed ligands are impor-
tant to evaluate the structure–redox–reactivity relation-
ship.[9] The coordination chemistry of amide-based ligands
[10–17]
incorporating additional donors such as Namine
,
[18–29]
[47–52]
[30]
[31]
[32–46]
Npyridine
,
Nimidazole
and Sthiol
,
Npyrrollidine
,
Ophenoxide
,
[53–75]
Oalkoxide
,
has always been interesting
owing to its importance in bioinorganic, synthetic model-
ing, and oxidation chemistry. This interest is further inten-
sified owing to the identification of such functional groups
in several metalloenzymes.[76–86] As a consequence, several
such functional groups have been incorporated with an
amide group(s) to afford assorted hybrid ligands.[10–75] In-
triguingly, pyrrole and indole moieties, despite having im-
portance in anion recognition,[87–91] have been scarcely used
as far as their coordination chemistry is concerned.[92–99] In
Results and Discussion
Synthesis and Characterization
This manuscript discusses the manganese chemistry of a
set of pyrrolecarboxamide (H4L1–3) and indolecarboxamide
ligands (H4L4–6). These ligands are designed to create an
identical N4 basal plane through two Namide atoms and two
Npyrrole/indole atoms. The two sets of ligands further differ
by having electron-donating (–CH3), –H, and electron-with-
drawing (–Cl) substituents on the o-phenylene ring. Treat-
ment of the deprotonated forms of the ligands with (Et4N)2-
[MnCl4] in air affords MnIII complexes 1–6 (Scheme 1).
[a] Department of Chemistry, University of Delhi,
Delhi 110007, India
E-mail: rgupta@chemistry.du.ac.in
http://people.du.ac.in/~rgupta/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201500773.
Eur. J. Inorg. Chem. 2015, 5534–5544
5534
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Typical workup and recrystallization results in the isolation color), which leads to an interesting sandwich-type packing
of highly crystalline materials in good yields. The solution arrangement.
molar conductivity data for complexes 1–3 and complexes
4–6 reveal their 1:2 and 1:1 electrolytic nature, respec-
tively.[102] The absence of νN–H stretches and bathochrom-
ically shifted amidic νC=O stretches (by 45–85 cm–1 com-
pared to the free ligands) in the IR spectra corroborate the
deprotonated nature of the ligands in all of the MnIII com-
plexes.[103] All complexes were also characterized by high-
resolution mass spectrometry, which exhibited the corre-
sponding molecular ion peaks for the complex anions.
Complexes 1–3 display broad absorptions centered between
λ = 610 and 640 nm, whereas complexes 4–6 exhibit even
broader featureless absorptions between λ = 600 and
800 nm (Figures S1 and S2, Supporting Information). Such
broad spectral features are typically observed for MnIII
Figure 1. Molecular structures of the anionic part of complexes 3
(left) and 5 (right); thermal ellipsoids are drawn at the 50% prob-
complexes.[104] In addition, electronic transitions observed
ability level, whereas cation(s) and hydrogen atoms are omitted for
clarity. Selected bond lengths [Å] for 3: Mn–N1 1.966(4), Mn–N2
1.953(3), Mn–N3 1.939(4), Mn–N4 1.980(3), Mn–Cl 2.3988(16); se-
lected bond lengths [Å] for 5: Mn–N1 1.963(7), Mn–N2 1.947(7),
Mn–N3 1.944(7), Mn–N4 1.958(7), Mn···O2# 2.530(7). Selected
bond angles [°] for 3: N1–Mn–N2 81.66(15), N1–Mn–N3
154.45(17), N1–Mn–N4 106.06(15), N2–Mn–N3 80.08(15), N2–
Mn–N4 149.83(16), N3–Mn–N4 81.97(14); selected bond angles [°]
for 5: N1–Mn–N2 82.2(3), N1–Mn–N3 160.9(3), N1–Mn–N4
115.4(3), N2–Mn–N3 81.1(3), N2–Mn–N4 160.9(3), N3–Mn–N4
82.5(3).
below λ = 400 nm are tentatively attributed to intraligand
transitions.
The unit cell of complex 5 consists of two complex
anions and two tetraethylammonium cations. The MnIII ion
is four coordinate and is marginally displaced by 0.002 Å
from the N4 basal plane. A very small value of the tetrahe-
dral distortion parameter (τ4 = 0.002) justifies a nearly per-
fect square-planar geometry around the metal ion.[106] The
average Mn–Namide and Mn–Nindole distances are 1.945 and
1.960 Å, respectively. Interestingly, two indole rings are not
coplanar but make an angle of 30.62° with each other. We
believe that such an arrangement hinders approach of the
fifth ligand. However, the complex anions are packed in a
slipped antiparallel manner that leads the neighboring mol-
ecules to interact weakly through Mn···Oamide bonds with
distances ranging between ca. 2.5 to about 2.6 Å (Figure S4,
Supporting Information). Such a packing results in essen-
tially pseudo-octahedral geometry around the metal ion.
In both crystal structures, the M–Namide bond lengths
are shorter than the M–Npyrrole and M–Nindole bond lengths
owing to the strong anionic σ-donation character of the
former. Further, the observed Mn–Namide bond lengths for
complexes 3 and 5 are in good agreement with our earlier
NiII and CuII complexes supported with similar li-
gands.[100,101] Furthermore, the M–Npyrrole and M–Nindole
distances are also comparable as noted before.[100,101]
Scheme 1. Chemical structures of MnIII complexes 1–6.
Crystal Structures
The crystal structures of manganese complexes 3 and 5
were determined (Figure 1). For complex 3, the unit cell
comprises one complex anion and two tetraethylammonium
cations. The MnIII ion displays a five-coordinate geometry,
in which the ligand constitutes a N4 basal plane, whereas
the Cl atom occupies the fifth coordination site. The
average Mn–Namide and Mn–Npyrrole distances are 1.947
and 1.973 Å, respectively. The MnIII ion is displaced by
0.413 Å from the N4 plane towards the fifth Cl ligand. The
τ5 distortion parameter was found to be 0.076, which sug-
gests a predominantly square-pyramidal geometry.[105] The
ideal value of τ5 is 0 and 1 for a perfect square-pyramidal
and trigonal-bipyramidal geometry, respectively.[105] Com-
plex 3 displays an interesting solid-state packing, in which
every complex anion interacts with the neighboring one
through C–H···Cl hydrogen bonding (Figure S3 and
Table S1, Supporting Information). Further, complex
anions in one layer are connected to the complex anions in
Electrochemistry
All complexes were subjected to electrochemical investi-
the alternate layer by Et4N+ cations (shown in purple color) gation to understand their redox behavior and the extent of
through C–H···Cl and C–H···O interactions. Such layers are stabilization of the manganese ion in the +2, +3, and +4
further stitched together by Et4N+ cations (shown in blue oxidation states. For complexes 1–3, quasireversible redox
Eur. J. Inorg. Chem. 2015, 5534–5544
5535
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
responses are observed in the positive potential region with ents). Along the same direction, complexes 2 and 5 (with
E1/2 values of 0.45 (ΔE = 108 mV), 0.34 (ΔE = 105 mV), –CH3 substituents) exhibit much lower redox potentials.
and 0.56 V (ΔE = 100 mV), respectively. Such responses are Such observations adequately illustrate that ligands with
assigned to the MnIV/MnIII redox couple (Figure 2). On the electron-donating –CH3 substituents are better suited to
further positive side, additional oxidative processes are stabilize the manganese ion in the +4 oxidation state than
noted between 1.6 and 1.7 V versus the saturated calomel ligands with –H or electron-withdrawing –Cl substituents.
electrode (SCE) that are tentatively assigned to ligand-cen- In fact, our attempt to generate a one-electron oxidized spe-
tered oxidation located at the o-benzenediamidate fragment cies clearly supports the electrochemical observations (dis-
(figures not shown). This assignment was made on the basis cussed below).
of our earlier nickel and copper complexes with the iden-
tical ligands. On the negative side, irreversible redox re- Electrochemical and Chemical Generation of MnIV Species
sponses (Epa) are noted at –0.77 (for complex 1), –0.81 (for
On the basis of electrochemical studies, complexes 1–3
2), and –0.59 V (for 3) versus SCE. These redox responses
were subjected to one-electron oxidation to generate Mn4+
are assigned to the MnIII/MnII redox couple.
species. On electrochemical or chemical oxidation with
ferrocenium hexafluorophosphate (FcPF6), brown-colored
complexes 1 and 2 are easily oxidized to deep-green-colored
unstable species 1ox and 2ox. Both 1ox and 2ox display
unique absorption spectra with prominent features at ca. λ
= 470, 530–550, ca. 650, 775–800, and 1000–1050 nm. Fur-
ther, a close similarity in the spectral features for 1ox and
2ox is clearly noticeable. Such a fact suggests very similar
electronic structures for both oxidized species.[107] On the
other hand, complex 3 immediately decomposes upon
either electrochemical oxidation or chemical oxidation with
FcPF6. It is believed that a higher positive potential re-
sulting from the presence of electron-withdrawing –Cl sub-
stituents on the ligand framework results in poor electron
density at the metal center, which makes oxidation difficult.
In fact, a similarly fast decomposition is observed for com-
plexes 4–6 owing to the involvement of poorly electron-do-
nating indole moieties. Importantly, the electrochemical re-
sults for complexes 4–6 do display much higher positive po-
tentials, which therefore justifies our assumption that metal-
based oxidation is difficult.
Chemical oxidation provided an option to calculate the
stoichiometry; therefore, both complexes 1 and 2 were ti-
trated with FcPF6 in CH3CN (Figure 4; see also Fig-
ures S5–S7 in the Supporting Information). Such spectral
titrations confirmed that only 1 equivalent of FcPF6 was
required for complete oxidation. In fact, Coulomb electron
Figure 2. Cyclic voltammograms of complexes 1 (gray), 2 (purple),
and 3 (brown) recorded in DMF.
Complexes 4 and 6 exhibit irreversible oxidative redox
waves at 0.63 and 0.81 V (Epa vs. SCE), respectively (Fig-
ure 3). Notably, complex 5 displays a reversible redox re-
sponse at 0.54 V versus SCE (ΔE = 78 mV). All such re-
sponses are assigned to the MnIV/MnIII redox couple. In
the negative potential region, for complexes 4–6 irreversible
electrochemical behavior similar to that noted for com-
plexes 1–3 is observed. Complexes 4–6 display Epa at –0.49,
–0.48, and –0.23 V versus SCE, respectively. It is to be
noted that the ligand-centered reduction processes are
found to merge with the aforementioned redox responses,
as is evident from comparison of the current height and
Coulomb electron count from the coulometric experiment.
For reference, free ligands display reductive responses at ca.
–1.15 V versus SCE under otherwise identical electrochemi-
cal conditions.
Figure 3. Cyclic voltammograms of complexes 4 (red), 5 (blue), and
6 (green) recorded in DMF.
Interestingly, the MnIV/MnIII redox couple for complexes
3 and 6 (with –Cl substituents) is observed at a higher posi-
tive potential than for complexes 1 and 4 (with –H substitu- CH3CN.
Figure 4. Absorption spectral titration of complex 1 with FcPF6 in
Eur. J. Inorg. Chem. 2015, 5534–5544
5536
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
count(s) from the controlled potential electrolysis experi- cies 1ox and 2ox, the rate of decay was found to be pseudo-
ments further asserted the one-electron nature of the elec- first order in nature with rate constants (k) of 2.104 and
trochemical oxidation both for complexes 1 and 2. To fur- 1.241 min–1, respectively (Figures S9 and S10, Supporting
ther evaluate the nature of the oxidized species, the electron Information). Species 1ox decomposes nearly two times
paramagnetic resonance (EPR) spectra of the oxidized spe- faster than species 2ox. We believe that electron density is
cies, 1ox and 2ox, were recorded after their in situ generation pushed towards the manganese center by the peripheral
in DMF. In each case, the EPR spectrum displays a signal methyl substituents in 2ox and that this leads to better stabi-
at g ≈ 2.0 with a prominent 55Mn hyperfine coupling. The lization of the MnIV species. Collectively, the electrochemi-
EPR spectral simulation provided g and Aʈ values of 2.001 cal and kinetics data suggest that the methyl-substituted
and 37 G, respectively, for 1ox and 2.001 and 27 G, respec- pyrrolecarboxamide ligand stabilizes the MnIV state to a
tively, for 2ox (Figure 5; see also Figure S8 in the Supporting much greater extent.
Information).[108]
Olefin Epoxidation Reactions
The electrochemical studies depict that the present MnIII
complexes have the potential to support multiple oxidation
states. All complexes exhibit highly negative MnIII/II poten-
tials and also show accessible MnIV/III redox potentials. It
is therefore clear that both the pyrrole- and indolecarbox-
amide ligands can efficiently stabilize the manganese ion in
the +3 and +4 oxidation states. Such features suggest their
potential application in oxidation chemistry. Taking this
fact into consideration, we selected external oxidant medi-
Figure 5. X-band EPR spectrum of in situ generated 1ox in DMF
ated epoxidation of olefins anticipating the generation of a
(black color). Microwave power: 0.998 mW, microwave frequency:
high-valent intermediate during the catalysis.[109–113] Ini-
9.12 GHz, modulation frequency: 100 kHz, sweep time: 1 min, tem-
perature: 77 K. The simulated spectrum is shown in red. The fea-
tially, a series of control experiments were performed by
using styrene as a model substrate and complex 1 as the
representative catalyst to identify the optimized reaction
conditions; the results are summarized in Table 1. As evi-
dent, no oxidation was noticed if O2, NaOCl, 2,2,6,6-tet-
ture at ca. 2600 G is due to the presence of a slight excess amount
of FcPF6.
These experiments establish that a potential MnIV species
is generated during electrochemical or chemical oxidation.
However, our attempts to isolate such a MnIV species were
unsuccessful owing to fast decomposition after its genera-
tion. This prompted us to measure the rate of decomposi-
tion of oxidized species 1ox and 2ox. Time-dependent mea-
surements were performed by measuring the spectral
changes at λmax = 655 nm with respect to time after the
generation of the oxidized species (Figure 6). For both spe-
ramethylpiperidin-1-oxyl
(TEMPO),
meta-chloroper-
oxybenzoic acid (mCPBA), H2O2, or isobutyraldehyde + O2
was employed as the oxidant (Table 1, entries 1–7).
tBuOOH provided the oxidation product in 78% yield,
whereas PhIO[114] provided a maximum oxidation of 92%
in CH3CN (Table 1, entries 8 and 9). Notably, a small
amount of benzaldehyde (2–4%) was obtained with the use
of either tBuOOH or PhIO; however, its amount was mea-
gre if PhIO was used, and this led to the use of PhIO in
subsequent reactions.[114] The use of solvent was essential;
this suggests that its presence allows better mixing of the
Table 1. Control experiments for the epoxidation of styrene in
CH3CN solvent.[a]
Entry
Oxidant
Catalyst[b]
Yield [%][c]
1
2
3
4
5
6
7
8
9
10
O2
O2
NaOCl
TEMPO
mCPBA
H2O2
–
0
0
0
0
0
0
0
78
92
2
1
1
1
1
1
isobutyraldehyde[d]
tBuOOH
PhIO
1
1
1
Figure 6. Kinetics of decomposition of in situ generated MnIV spe-
cies with time after the addition of FcPF6 during the chemical oxid-
ation experiment for complexes 1 (black squares) and 2 (blue
PhIO
(Et4N)2[MnCl4]
[a] Reactions conditions: Substrate (1 equiv.), oxidant (2 equiv.),
squares). The absorbance was recorded at 1 min intervals. See text CH3CN, 25 °C, 4 h. [b] Catalyst (1 mol-%). [c] Products were quan-
for details.
tified by GC. [d] Reaction was performed under an O2 atmosphere.
Eur. J. Inorg. Chem. 2015, 5534–5544
5537
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
reagents, which thus accelerates the reaction (data not Ring-Opening Reactions
shown). Finally, negligible oxidation (ca. 2%) was noted
with the use of (Et4N)2[MnCl4] as the catalyst under iden-
Olefinic epoxidation reactions demonstrated the poten-
tical reaction conditions (Table 1, entry 10). Such a fact tial of the present manganese complexes in oxidative reac-
suggests the necessity of a ligand framework for efficient tions. However, MnIII ions are also good Lewis acids and
olefin epoxidation and points toward the stabilization of a have been used for several such reactions.[118–120] The ring
high-valent intermediate before the oxo-transfer reaction. opening of epoxides is an important and well-known reac-
We also attempted to delineate the fate of the oxidized spe- tion that is known to be catalyzed by Lewis acidic metal
cies generated during the reaction of complexes 1–3 with ions.[118–120] In such a reaction, activation of the epoxide
PhIO. Notably, PhIO generated species identical to those ring is a prerequisite, and this can be achieved by using an
generated either electrochemically or chemically with appropriate Lewis acid followed by ring opening by using
FcPF6, that is, 1ox and 2ox. Such an experiment substanti- an appropriate nucleophile.
ates the generation of a MnIV species during the epoxid-
ation reaction.
We utilized the present manganese complexes as hetero-
geneous catalysts for aminolysis under solvent-free condi-
With these optimized reaction conditions, several sub- tions. Thus, if equimolar amounts of styrene oxide and anil-
strates were tested to explore the scope of the catalysis with ine were stirred at room temperature in the presence of only
all six MnIII complexes (Table 2). In general, the yield of 1 mol-% of the catalyst, a smooth reaction took place that
the epoxidation reaction was higher with aromatic olefins led to the formation of the β-amino alcohol in high yield.
having electron-donating substituents in the para position To ascertain the importance of the present MnIII complexes,
than with aromatic olefins having electron-withdrawing the use of the manganese salts MnCl2 and (Et4N)2[MnCl4]
substituents in this position. Furthermore, the epoxidation as the catalysts led to negligible product formation (Ͻ5%)
results were much better with aromatic olefins than with under otherwise identical reaction conditions.
aliphatic substrates. On comparison, complexes 2 and 5
To explore the versatility and scope of the present cata-
served as the most suitable catalysts for the epoxidation lysts, several substrates as well as nucleophiles were utilized
with higher conversion numbers. We suggest that the elec- (Table 3). Thus, if electron-withdrawing and electron-donat-
tron-donating –Me substituents on the ligand framework in ing groups were placed in the para position of the aromatic
these two complexes potentially increase the electron den- amines, as expected, the yields were higher with the latter.
sity at the metal center, which therefore facilitates the gener- This is due to the better nucleophilicity of anilines having
ation of a high-valent manganese intermediate.[115–117] This an electron-donating group in the para position. Notably,
fact is well supported by the electrochemical results of the excellent regioselectivity was observed. Of the two possible
manganese complexes. According to the cyclic voltammetry products resulting from nucleophilic attack at either the
data, a shift towards less positive potentials follows the benzylic carbon atom or the less hindered carbon atom of
trend: 3/6Ͻ1/4Ͻ2/5. This trend suggests the higher sta- the epoxide ring, the nucleophilic predominantly attacked
bility of the manganese ion in the +4 oxidation state in the the benzylic carbon atom of the epoxide. Furthermore,
cases of complexes 2 and 5, which is in perfect sync with the ring-opening reactions of glycidic ethers such as ethyloxir-
catalysis results. Furthermore, subsequent generation and ane-2-carboxylate and 2-(tert-butoxy)oxirane with aniline
characterization of the Mn4+ species for complexes 1 and 2 provided single products, which thus affirms excellent con-
additionally supports the catalysis results.
trol of the regioselectivity (Table 4, entries 1–3). The ring-
Table 2. Epoxidation of assorted olefins by using MnIII complexes.[a]
Entry
Substrate
Yield [%][b]
1
2
3
4
5
6
1
2
3
4
5
6
7
8
styrene
84 (4)
88 (4)
90 (2)
72 (4)
80 (1)
58 (2)
81 (0)
72 (2)
79 (3)
79 (0)
84
96 (2)
98 (0)
99 (0)
89 (1)
95 (0)
70 (0)
98 (0)
88 (2)
89 (2)
88 (3)
97
75 (4)
70 (4)
82 (4)
54 (5)
64 (3)
33 (4)
74 (0)
65 (4)
64 (2)
61 (1)
79
81 (4)
82 (3)
85 (3)
68 (3)
60 (0)
51 (0)
81 (0)
71 (1)
65 (3)
69 (0)
72
92 (4)
98 (0)
98 (0)
86 (1)
75 (0)
69 (2)
99 (0)
89 (2)
90 (2)
87 (4)
88
70 (4)
76 (4)
79 (4)
51 (4)
46 (4)
40 (3)
80 (0)
61 (3)
55 (1)
51 (2)
56
4-tert-butylstyrene
4-methoxystyrene
4-chlorostyrene
1-vinylnaphthalene
9-vinylanthracene
1,2-dihydronaphthalene
cyclopentene
cyclohexene
cyclooctene
cis-stilbene
trans-stilbene
9
10
11
12
13
14
15
82
98
72
71
89
55
1-hexene
1-decene
1-methylcyclohex-1-ene
52 (2)
68 (3)
45 (1)
72 (2)
88 (1)
76 (4)
49 (1)
62 (2)
34 (1)
48 (2)
51 (3)
59 (2)
70 (1)
79 (4)
76 (3)
36 (1)
42 (2)
44 (1)
[a] Reactions conditions: Substrate (1 equiv.), PhIO (2 equiv.), catalyst (1 mol-%), CH3CN, 25 °C, 4 h. [b] Products were quantified by
GC. The values in parentheses correspond to the yields of the respective aldehydes obtained as byproducts.
Eur. J. Inorg. Chem. 2015, 5534–5544
5538
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
opening reaction of 2-(phenoxymethyl)oxirane resulted in dered side, possibly as a result of steric reasons. Epichlo-
two regioisomers, although the minor isomer was obtained rohydrin, possessing an epoxide ring as well as a good Cl
in less than 2% yield.
leaving group, was employed to test the chemoselectivity
of the reaction (Table 4, entry 6). Notably, the reaction of
epichlorohydrin with aniline resulted in a single product,
whereas no product was noted from nucleophilic displace-
ment of the Cl atom with any of the catalysts. This reaction
provides a good example of chemoselectivity.
Table 3. Solvent-free ring-opening reactions of styrene oxide with
substituted anilines in the presence of manganese complexes 1–6.[a]
After performing successful ring-opening reactions with
aromatic amines, we attempted to use aliphatic amines as
nucleophiles (Table 5). Importantly, the use of piperidine
and pyrrolidine as nucleophiles with styrene oxide resulted
in high conversions with yields of the major regioisomers
ranging between 64 and 99%, whereas the minor regioiso-
mers were obtained in less than 3% yield (Table 5, entries 1
and 2). However, cyclohexylamine produced a much larger
amount of the minor regioisomer (5–7%; Table 5, entry 3).
Such an observation is attributed to the nonplanar nature
of cyclohexylamine, which allows it to attack the epoxide
ring from two possible orientations. Figures S16 and S17
Entry
R
H
Yield [%][b]
1
2
3
4
5
6
1
2
3
4
5
92 (0) 99 (0) 72 (2) 74 (4) 78 (0) 52 (2)
C2H5 90 (1) 99 (0) 70 (3) 78 (2) 80 (2) 56 (6)
OCH3 94 (0) 99 (0) 72 (2) 85 (1) 86 (1) 57 (5)
Cl
F
82 (4) 89 (2) 67 (2) 70 (2) 74 (1) 49 (3)
80 (3) 82 (1) 66 (4) 64 (2) 66 (5) 42 (2)
1
[a] Reactions conditions: Catalyst (1 mol-%), 25 °C, 4 h. [b] Prod-
ucts were quantified by GC. The values in parentheses correspond
to the yields of the minor regioisomers [substituted 1-phenyl-2-
(phenylamino)ethanol].
(Supporting Information) provide the H NMR spectra of
two representative cases displaying the presence of both the
major and minor regioisomers in the reaction product. The
ring-opening reaction was further extended to cyclohexene
oxide and to cyclopentene oxide with assorted anilines un-
der identical reaction conditions (Table 6, see also Table S2,
Table 4. Solvent-free ring-opening reaction of a few unsymmetrical
epoxides with aniline in the presence of manganese complexes
1–6.
Table 5. Solvent-free ring-opening reaction of styrene oxide with
aliphatic amines in the presence of manganese complexes 1–6.[a]
Entry Amine
Yield [%][b]
1
2
3
4
5
6
1
2
3
piperidine
pyrrolidine
94 (1) 99 (0) 80 (2) 78 (1) 85 (1) 70 (2)
91 (2) 96 (2) 79 (3) 74 (2) 80 (2) 64 (3)
cyclohexylamine 84 (7) 91 (6) 75 (7) 70 (5) 86 (7) 60 (5)
[a] Reactions conditions: Catalyst (1 mol-%), 25 °C, 4 h. [b] Prod-
ucts were quantified by GC. The values in parentheses correspond
to the yields of the respective minor regioisomers.
Table 6. Solvent-free ring-opening reaction of cyclohexene oxide
with substituted anilines in the presence of manganese complexes
1–6.[a]
[a] Reactions conditions: Catalyst (1 mol-%), 25 °C, 4 h. [b] Prod-
ucts were quantified by GC. The values in parentheses correspond
to the yields of the respective minor regioisomers.
To further evaluate the effect of steric crowding on the
selectivity, the ring-opening reactions of several hindered
epoxides were performed. Exclusive formation of N-phen-
ylamino-3-pentenol and 2-methyl-3-phenylamino-butane-2-
ol from 2,3-epoxypentane and 2,3-epoxy-2-methylbutane,
respectively, demonstrates the high regioselectivity associ-
ated with the present manganese complexes (Table 4, en-
tries 4 and 5). Collectively, these results suggest that the ep-
Entry
R
Yield [%][b]
1
2
3
4
5
6
1
2
3
4
5
H
C2H5
OCH3 95
Cl
F
87
90
96
99
99
81
65
64
69
75
57
48
64
70
78
60
57
74
79
85
74
66
54
58
62
43
40
76
72
[a] Reactions conditions: Catalyst (1 mol-%), 25 °C, 4 h. [b] Prod-
oxide ring interacts with the MnIII ion through its less hin- ucts were quantified by GC.
5539
Eur. J. Inorg. Chem. 2015, 5534–5544
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Supporting Information). As noted with styrene oxide, and aniline in a reaction flask containing a fixed amount
yields were higher with electron-rich anilines than with elec- of complex 2 led to nearly quantitative conversion in each
tron-poor ones. However, owing to the nonplanar nature of case. Such an experiment is shown in Figure 7 (right panel),
the epoxide, the yields are a bit lower in most cases relative for which a = b = c = d ≈ 99% represent nearly quantitative
to those obtained with styrene oxide under otherwise iden- formation of the product in each case (shown by different
tical reaction conditions.
colored bars).
One-Pot, Two-Step Reactions
At this stage, we became interested in exploring a one-
pot, two-step reaction in which first a MnIII complex oxi-
dizes an olefin to an epoxide and then the same catalyst
activates the epoxide ring as a result of its Lewis acidic
character in the second step. Such reactions were performed
by using complex 2, as the best epoxidation and ring-open-
ing results were obtained with this catalyst. Satisfyingly,
complex 2 was efficiently able to perform the one-pot, two-
step reaction in which olefinic substrates (e.g., styrene, 4-
chlorostyrene, and 4-methoxystyrene) were directly con-
verted into the respective β-amino alcohols in yields varying
from 60 to 80% (Table S3, Supporting Information).
Figure 7. (Left) Filtration test performed by using complex 2 in the
ring-opening reaction of styrene oxide with aniline. (Right) One-
pot reaction after adding fresh batches of styrene oxide and aniline
to a fixed amount of complex 2. See text for details.
Conclusions
Recyclability Experiments and Mechanistic Insight
This work showed the synthesis and characterization of
MnIII complexes with pyrrole- and indolecarboxamide li-
gands. The ligands constitute an N4 coordination sphere
around the MnIII ion. Complexes 1–3 exhibit a square-py-
ramidal geometry, whereas complexes 4–6 display essen-
tially square-planar geometry. Electrochemical studies re-
vealed that these MnIII complexes have the ability to sup-
port multiple oxidation states. All complexes exhibited
highly negative MnIII/II redox potentials while also showing
accessible MnIV/III redox potentials. A shift in the redox
potentials on moving from complex 3/6Ͻ1/4Ͻ2/5 towards
negative potentials demonstrated the effect of electronic
substituents on the ligand periphery. Electrochemical and
chemical oxidation resulted in the generation of Mn4+ spe-
cies in the cases of complexes 1 and 2, which were charac-
terized by absorption and EPR spectroscopy. All complexes
were utilized for olefin epoxidation reactions by using PhIO
as the oxo-transfer agent. Amongst all complexes, 2 and 5
were the most effective as a result of the presence of elec-
tron-donating substituents on the ligand. All complexes
also functioned as Lewis acid catalysts for the ring-opening
reactions of assorted epoxides by using various nitrogen-
based nucleophiles. Finally, a challenging one-pot, two-step
epoxidation followed by ring-opening reaction demon-
strated the catalytic importance of the present MnIII com-
plexes.
The heterogeneous nature of the ring-opening reactions
provided an opportunity to ascertain the reusability of the
present MnIII complexes. Importantly, all complexes can be
easily recovered from the reaction mixture by simple fil-
tration and reused several cycles. However, complexes 2 and
5 were used as representative examples to demonstrate the
recyclability in experiments involving styrene oxide and an-
iline. Both of the recovered complexes were characterized
by FTIR spectroscopy (Figures S11 and S12, Supporting
Information) as well as by X-ray powder diffraction (Fig-
ures S13 and S14, Supporting Information). Both the FTIR
spectra and the powder diffraction patterns of the recovered
complexes match those of the pristine samples, which there-
fore suggests that the structural integrity of the complexes
is retained during catalysis.
In addition, recovered complex 2 was tested over five
consecutive cycles and produced the corresponding ring-
opening reaction product in high yield throughout all five
cycles (Figure S15, Supporting Information). To further es-
tablish that the catalysis is indeed heterogeneous and that
the catalytically active species are not leached from this
complex, a filtration test was performed (Figure 7, left
panel). Such an experiment was performed by using com-
plex 2 as the catalyst in a reaction between styrene oxide
and aniline. Notably, if complex 2 was removed from the
reaction mixture by filtration during the course of the reac-
tion (green squares at 150 min; left panel in Figure 7), the
ring-opening reaction stopped immediately. Importantly, if
filtered complex 2 was readded (green squares at 270 min;
left panel in Figure 7), the ring-opening reaction started
again. This simple filtration test undoubtedly confirms the
heterogeneous nature of the ring-opening reactions.
Experimental Section
General Methods: All reagents were obtained from commercial
sources and were used as received. Solvents were dried and/or puri-
fied by using standard literature methods.[121] (Et4N)2[MnCl4] salt
was synthesized according to a literature procedure.[122,123] The li-
Furthermore, the addition of fresh batches of styrene oxide gands were synthesized according to our earlier report.[100,124]
Eur. J. Inorg. Chem. 2015, 5534–5544
5540
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
(Et4N)2[Mn(L1)Cl] (1): Ligand H4L1 (0.10 g, 0.33 mmol) was dis-
solved in DMF (3 mL) and treated with solid NaH (0.032 g,
1.35 mmol) under a nitrogen atmosphere. The mixture was stirred
until H2 evolution had ceased (ca. 10 min). (Et4N)2[MnCl4]
(0.155 g, 0.33 mmol) was added as a solid under the inert atmo-
sphere. The resulting mixture was stirred for another 1 h at room
temperature in open air, which resulted in a brown solution. This
solution was filtered through a pad of Celite in a medium-porosity
frit. The filtrate was directly subjected to vapor diffusion of diethyl
ether, which resulted in a brown crystalline product that was iso-
lated by filtration and dried in vacuo, yield 0.135 g (62%). FTIR
(Et4N)[Mn(L6)] (6): A procedure similar to that adopted for com-
plex 1 was followed with H4L6 (0.10 g, 0.21 mmol), NaH (0.020 g,
0.86 mmol), and (Et4N)2[MnCl4] (0.098 g, 0.21 mmol), yield 0.09 g
(64%). FTIR (Zn-Se ATR): ν = 1601, 1535, 1510, 1485, 1465, 761,
˜
744 cm–1. UV/Vis (CH3CN): λmax (ε, m–1 cm–1) = 340 (4524),
298 nm (7434). MS (ESI–): calcd. for [C24H12N4O2Cl2Mn]–
512.9718; found 512.9714. C32H32Cl2MnN5O2 (644.47): calcd. C
59.64, H 5.00, N 10.87; found C 59.59, H 4.83, N 10.85. Conductiv-
ity (DMF, ca. 1 mm solution, 298 K): ΛM = 85 Ω–1 cm2 mol–1.
Olefin Epoxidation: To a solution of substrate (1 mmol) in CH3CN
(3 mL) was added PhIO (2 mmol) and the MnIII complex as the
catalyst (0.01 mmol). The mixture was stirred at room temperature
for 4 h. The progress of the reaction was monitored by TLC. The
solvent was removed under reduced pressure, and the organic prod-
ucts were separated and purified by column chromatography (silica
gel, EtOAc/hexanes 1:1). The products were identified by GC and
(Zn-Se ATR): ν = 3409, 2981, 2960, 1583, 1473, 769, 740, 548 cm–1.
˜
UV/Vis (CH3CN): λmax (ε, m–1 cm–1) = 618 (80), 327 (11970),
270 nm (32490). MS (ESI–): calcd. for [C16H10ClN4O2Mn]–
379.9873; found 379.9869. C32H50ClMnN6O2 (641.17): calcd. C
59.94, H 7.86, N 13.11; found C 59.80, H 7.88, N 13.07. Conductiv-
ity (DMF, ca. 1 mm solution, 298 K): ΛM = 148 Ω–1 cm2 mol–1 (the
range for 1:2 electrolyte in DMF is 130–170).
1
GC–MS and were also characterized by H NMR spectroscopy in
a few cases.
(Et4N)2[Mn(L2)Cl] (2): A procedure similar to that adopted for
complex 1 was followed with H4L2 (0.10 g, 0.31 mmol), NaH
(0.029 g, 1.24 mmol), and (Et4N)2[MnCl4] (0.141 g, 0.31 mmol).
Crystallization was achieved by vapor diffusion of diethyl ether into
a CH3CN solution of the crude compound, yield 0.12 g (58%).
Ring-Opening Reactions: In a typical aminolysis reaction, the sub-
strate (1 mmol) was treated with the nucleophile (1.2 mmol) in the
presence of the MnIII complex (0.01 mmol) as the catalyst at room
temperature (ca. 25 °C). The progress of the reaction was moni-
tored by TLC and/or GC. After 6 h, EtOAc (5 mL) was added, and
the mixture was filtered. The crude product was purified by flash
column chromatography (60–120 mesh silica gel, EtOAc/hexane,
FTIR (Zn-Se ATR): ν = 3398, 3098, 2980, 1599, 1540, 1481, 1392,
˜
1331, 1181, 1026, 734 cm–1. UV/Vis (CH3CN): λmax (ε, m–1 cm–1) =
634 (75), 320 (9805), 270 nm (24460). MS (ESI–): calcd. for
[C18H15N4O2MnCl]– 409.0264; found 409.0544. C34H54ClMnN6O2
(669.22): calcd. C 61.02, H 8.13, N 12.56; found C 60.80, H 8.10,
1
1:1). The products were analyzed by GC, GC–MS, and H NMR
spectroscopy.
Physical Measurements: The conductivity measurements were done
in DMF by using the digital conductivity bridge from the Popular
Traders, India (model number: PT-825). Elemental analysis data
were obtained from the Elementar Analysen System GmbH Vario
EL-III instrument. The NMR measurements were done by using a
JEOL (400 MHz) instrument. Infrared spectra (Zn-Se ATR) were
recorded by using a Perkin–Elmer FTIR spectrum two spectrome-
ter. The absorption spectra were recorded by using a Perkin–Elmer
Lambda-25 spectrophotometer. Cyclic voltammetry experiments
were performed by using a CH Instruments electrochemical ana-
lyzer (Model 1120 A) with a glassy carbon working electrode, a
platinum wire as the auxiliary electrode, and Ag/Ag+ as the refer-
ence electrode.[125] For constant potential electrolysis experiments,
a Pt mesh was used as the working electrode. The solutions were
ca. 1 mm in complex and ca. 0.1 m in supporting electrolyte, tetra-
butylammonium perchlorate. Under our experimental conditions,
the E1/2 value (in volts) for the Fc+/Fc couple was observed at 0.47
in DMF versus SCE.[126] The potentials were converted into the
SCE throughout the manuscript.[126] The X-band EPR spectra were
recorded with a JES-FA200 spectrometer at 77 K in DMF. The
EPR spectral simulations were performed by using the EasySpin
free software.[108]
N 12.42. Conductivity (DMF, ca. 1 mm solution, 298 K): ΛM
=
135 Ω–1 cm2 mol–1.
(Et4N)2[Mn(L3)Cl] (3): A procedure similar to that adopted for
complex 1 was followed with H4L3 (0.10 g, 0.27 mmol), NaH
(0.026 g, 1.10 mmol), and (Et4N)2[MnCl4] (0.125 g, 0.27 mmol),
yield 0.13 g (67%). FTIR (Zn-Se ATR): ν = 3394, 2988, 1615, 1591,
˜
1562, 1461, 1359, 1319, 1022, 742 cm–1. UV/Vis (CH3CN): λmax (ε,
m
–1 cm–1) = 612 (110), 335 (14620), 275 nm (34380). MS (ESI–):
calcd. for [C18H8N4O2Cl3Mn]– 447.9093; found 447.9089.
C32H48Cl3MnN6O2 (710.06): calcd. C 54.13, H 6.81, N 11.84;
found C 54.15, H 6.42, N 11.83. Conductivity (DMF, ca. 1 mm
solution, 298 K): ΛM = 150 Ω–1 cm2 mol–1.
(Et4N)[Mn(L4)] (4): A procedure similar to that adopted for com-
plex 1 was followed with H4L4 (0.10 g, 0.25 mmol), NaH (0.024 g,
1.01 mmol), and (Et4N)2[MnCl4] (0.115 g, 0.25 mmol). Crystalli-
zation was achieved by vapor diffusion of diethyl ether into a
CH3CN solution of the crude compound, yield 0.095 g (65%).
FTIR (Zn-Se ATR): ν = 2985, 2948, 1598, 1566, 1524, 1474, 1450,
˜
749 cm–1. UV/Vis (CH3CN): λmax (ε, m–1 cm–1) = 356 (9890),
298 nm (21360). MS (ESI–): calcd. for [C24H14N4O2Mn]– 445.0497;
found 445.0496. C32H34MnN5O2 (575.58): calcd. C 66.77, H 5.95,
N 12.17; found C 66.72, H 5.90, N 12.12. Conductivity (DMF, ca.
1 mm solution, 298 K): ΛM = 90 Ω–1 cm2 mol–1.
Crystallography: Single crystals suitable for X-ray diffraction stud-
ies were grown by vapor diffusion of diethyl ether into a MeCN
solution of the complexes. Intensity data were collected with an
Oxford CCD diffractometer having Xcalibur sapphire diffraction
measurement device at 150(2) K by using graphite-monochromated
Mo-Kα radiation (λ = 0.71073 Å).[127] The multiscan absorption
correction was applied.[127] The structures were solved by direct
methods by using SIR-92[128] and were refined by full-matrix least-
(Et4N)[Mn(L5)] (5): A procedure similar to that adopted for com-
plex 1 was followed with H4L5 (0.10 g, 0.23 mmol), NaH (0.022 g,
0.094 mmol), and (Et4N)2[MnCl4] (0.108 g, 0.23 mmol), yield
0.098 g (69%). FTIR (Zn-Se ATR): ν = 2980, 2950, 1516, 1487,
˜
744 cm–1. UV/Vis (CH3CN): λmax (ε, m–1 cm–1) = 340 (6920), squares refinement techniques on F2 by using SHELXL97.[129] The
300 nm (10110). MS (ESI–): calcd. for [C26H18N4O2Mn]– 473.0810; crystal structure of complex 5 shows some unassigned electron den-
found 473.0805. C34H38MnN5O2 (603.64): calcd. C 67.65, H 6.35,
N 11.60; found C 67.51, H 6.32, N 11.42. Conductivity (DMF, ca.
1 mm solution, 298 K): ΛM = 80 Ω–1 cm2 mol–1.
sity near both the Namide atoms as a result of crystallographic arti-
facts related to symmetry. As a consequence, final refinement val-
ues of R and wR are higher and the checkcif shows a few B-level
Eur. J. Inorg. Chem. 2015, 5534–5544
5541
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
[27]
[28]
F. S. Stephens, R. S. Vagg, Inorg. Chim. Acta 1988, 142, 43–50.
R. R. Fenton, F. S. Stephens, R. S. Vagg, P. A. Williams, J. Co-
ord. Chem. 1991, 23, 291–311.
M. A. Anderson, E. F. Birse, M. J. E. Hewlins, J. P. G. Rich-
ards, F. S. Stephens, R. S. Vagg, P. A. Williams, Inorg. Chem.
1991, 30, 3774–3778.
alerts. All calculations were done by using WinGX crystallographic
package.[130] The crystallographic data collection and structure
solution parameters are presented in Table S4 (Supporting Infor-
mation).
[29]
[30]
CCDC-1411467 (for 3) and -1411466 (for 5) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
B. L. Kaiser, R. Guillot, J. Sainton, M. F. Charlot, A. Aukau-
loo, Chem. Eur. J. 2008, 14, 4307–4317.
[31] C. L. Weeks, P. Turner, R. R. Fenton, P. A. Lay, J. Chem. Soc.,
Dalton Trans. 2002, 931–940.
[32]
[33]
[34]
T. J. Collins, B. D. Santarsiero, G. H. Spies, J. Chem. Soc.,
Chem. Commun. 1983, 681–682.
J. A. Christie, T. J. Collins, T. E. Kraft, B. D. Santarsiero, G. H.
Spies, J. Chem. Soc., Chem. Commun. 1984, 198–199.
F. C. Anson, J. A. Christie, T. J. Collins, R. J. Coots, T. T. Furu-
tani, S. L. Gipson, J. T. Keech, T. E. Kraft, B. D. Santarsiero,
G. H. Spies, J. Am. Chem. Soc. 1984, 106, 4460–4472.
F. C. Anson, T. J. Collins, S. L. Gipson, T. E. Kraft, Inorg.
Chem. 1987, 26, 731–736.
F. C. Anson, T. J. Collins, S. L. Gipson, J. T. Keech, T. E.
Kraft, G. T. Peake, J. Am. Chem. Soc. 1986, 108, 6593–6605.
T. J. Collins, J. T. Keech, J. Am. Chem. Soc. 1988, 110, 1162–
1167.
T. J. Collins, R. J. Coots, T. T. Furutani, J. T. Keech, G. T.
Peake, B. D. Santarsiero, J. Am. Chem. Soc. 1986, 108, 5333–
5339.
T. J. Collins, T. Lai, G. T. Peake, Inorg. Chem. 1987, 26, 1674–
1677.
F. C. Anson, T. J. Collins, R. J. Coots, S. L. Gipson, T. G. Rich-
mond, J. Am. Chem. Soc. 1984, 106, 5037–5038.
N. L. Fry, M. J. Rose, D. L. Rogow, C. Nyitray, M. Kaur, P. K.
Mascharak, Inorg. Chem. 2010, 49, 1487–1495.
S. Mukherjee, A. Stassinopoulos, J. P. Caradonna, J. Am.
Chem. Soc. 1997, 119, 8097–8098.
T. L. Foster, J. P. Caradonna, J. Am. Chem. Soc. 2003, 125,
3678–3679.
G. T. Rowe, E. V. Rybak-Akimova, J. P. Caradonna, Inorg.
Chem. 2007, 46, 10594–10606.
G. T. Rowe, E. V. Rybak-Akimova, J. P. Caradonna, Chem. Eur.
Acknowledgments
R. G. acknowledges financial support from the Council of Scien-
tific and Industrial Research (CSIR), New Delhi, and the Univer-
sity of Delhi. The authors acknowledge CIF-USIC of this univer-
sity for instrumental facilities. S. K. thanks the CSIR, New Delhi,
for an RA fellowship.
[35]
[36]
[37]
[38]
[1] R. R. Crichton, Biological Inorganic Chemistry, Elsevier Ltd.,
Oxford, UK, 2008.
[2] S. J. Lippard, J. M. Berg, Principles of Bioinorganic Chemistry,
Panima Corporation, Delhi, India, 2005.
[3] R. M. Roat-Malone, Bioinorganic Chemistry, 2nd ed., Wiley,
Hoboken, NJ, 2007.
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[4] T. Tsukihara, H. Aoyama, E. Yamashita, T. Tomizaki, H. Yam-
aguchi, K. Shinzawa-Itoh, R. Nakashima, R. Yaono, S. Yoshi-
kawa, Science 1995, 269, 1069–1074.
[5] S. Iwata, C. Ostermeier, B. Ludwig, H. Michel, Nature 1995,
376, 660–669.
[6] S. T. Prigge, B. A. Eipper, R. E. Mains, L. M. Amzel, Science
2004, 304, 864–867.
[7] C. Harford, B. Sarkar, Acc. Chem. Res. 1997, 30, 123–130.
[8] I. Zilbermann, E. Maimon, H. Cohen, D. Meyerstein, Chem.
Rev. 2005, 105, 2609–2626.
[9] A. L. Gavrilova, B. Bosnich, Chem. Rev. 2004, 104, 349–384.
[10] S. P. Gavrish, Y. D. Lampeka, J. Coord. Chem. 1996, 38, 295–
303.
[11] S. P. Gavrish, Y. D. Lampeka, P. Lightfoot, Inorg. Chim. Acta
2004, 357, 1023–1030.
[12] S. P. Gavrish, Y. D. Lampeka, P. Lightfoot, H. Pritzkow, Dalton
Trans. 2007, 4708–4714.
[13] S. K. Sharma, S. Upreti, R. Gupta, Eur. J. Inorg. Chem. 2007,
3247–3259.
J. 2008, 14, 8303–8311.
P. J. Cappllino, P. C. Tarves, G. T. Rowe, A. J. Lewis, M. Har-
vey, C. Rogge, A. Stassionopoulos, W. Lo, W. H. Armstrong,
J. P. Caradonna, Inorg. Chim. Acta 2009, 362, 2136–2150.
T. J. Collins, T. G. Richmond, B. D. Santarsiero, B. G. R. T.
Treco, J. Am. Chem. Soc. 1986, 108, 2088–2090.
J. C. Brewer, T. J. Collins, M. R. Smith, B. D. Santarsiero, J.
Am. Chem. Soc. 1988, 110, 423–428.
F. C. Anson, T. J. Collins, T. G. Richmond, B. D. Santarsiero,
J. E. Toth, B. G. R. T. Treco, J. Am. Chem. Soc. 1987, 109,
2974–2979.
T. J. Collins, S. W. Gordon-Wylie, J. Am. Chem. Soc. 1989, 111,
4511–4513.
F. M. McDonnell, N. L. P. Fackler, C. Stern, T. V. O’Halloran,
J. Am. Chem. Soc. 1994, 116, 7431–7432.
[47]
[48]
[49]
[14] J. Singh, G. Hundal, R. Gupta, Eur. J. Inorg. Chem. 2008,
2052–2063.
[15] S. K. Sharma, G. Hundal, R. Gupta, Eur. J. Inorg. Chem. 2010,
621–636.
[16] S. K. Sharma, R. Gupta, Inorg. Chim. Acta 2011, 376, 95–104.
[17] S. Kumar, R. Gupta, Indian J. Chem., Sect. A 2011, 50, 1369–
1379.
[50]
[51]
[52]
[53]
[54]
[55]
[56]
N. L. P. Fackler, S. Zhang, T. V. O’Halloran, J. Am. Chem. Soc.
1996, 118, 481–482.
[18] R. L. Chapman, R. S. Vagg, Inorg. Chim. Acta 1979, 33, 227–
234.
H.-J. Kruger, G. Peng, R. H. Holm, Inorg. Chem. 1991, 30,
734–742.
J. Hanss, H.-J. Kruger, Angew. Chem. Int. Ed. Engl. 1996, 35,
2827–2830; Angew. Chem. 1996, 108, 2989–2991.
J. Hanss, H.-J. Kruger, Angew. Chem. Int. Ed. 1998, 37, 360–
363; Angew. Chem. 1998, 110, 366–369.
S. Chatel, A.-S. Chauvin, J.-P. Tuchagues, P. Leduc, E. Bill,
J. C. Chottard, D. Mansuy, I. Artaud, Inorg. Chim. Acta 2002,
336, 19–28.
R. C. Linck, C. W. Spahn, T. B. Rauchfuss, S. R. Wilson, J.
Am. Chem. Soc. 2003, 125, 8700–8701.
[19] D. J. Barnes, R. L. Chapman, F. S. Stephens, R. S. Vagg, Inorg.
Chim. Acta 1981, 51, 155–162.
[20] R. L. Chapman, F. S. Stephens, R. S. Vagg, Inorg. Chim. Acta
1981, 52, 161–168.
[21] R. L. Chapman, F. S. Stephens, R. S. Vagg, Inorg. Chim. Acta
1981, 52, 169–176.
[22] M. Mulqi, F. S. Stephens, R. S. Vagg, Inorg. Chim. Acta 1981,
52, 177–182.
[23] F. S. Stephens, R. S. Vagg, Inorg. Chim. Acta 1982, 57, 9–13.
[24] F. S. Stephens, R. S. Vagg, Inorg. Chim. Acta 1984, 88, 7–14.
[25] F. S. Stephens, R. S. Vagg, Inorg. Chim. Acta 1984, 90, 17–24.
[26] F. S. Stephens, R. S. Vagg, Inorg. Chim. Acta 1986, 120, 165–
171.
[57]
[58]
O. Hatlevik, M. C. Blanksma, V. Mathrubootham, A. M. Arif,
E. L. Hegg, J. Biol. Inorg. Chem. 2004, 9, 238–246.
Eur. J. Inorg. Chem. 2015, 5534–5544
5542
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
[59] R. Krishnan, J. K. Voo, C. G. Riordan, L. Zahkarov, A. L.
Rheingold, J. Am. Chem. Soc. 2003, 125, 4422–4223.
[60] R. Krishnan, C. G. Riordan, J. Am. Chem. Soc. 2004, 126,
4484–4485.
[61] V. Mathrubootham, J. Thomas, R. Staples, J. McCraken, J.
Shearer, E. L. Hegg, Inorg. Chem. 2010, 49, 5393–5406.
[62] K. N. Green, S. M. Brothers, R. M. Jenkins, C. E. Carson,
C. A. Grapperhaus, M. Y. Darensbourg, Inorg. Chem. 2007, 46,
7536–7544.
[93]
[94]
[95]
[96]
[97]
Y. Li, A. Turnas, J. T. Ciszewski, A. L. Odom, Inorg. Chem.
2002, 41, 6298–6306.
Y. Zhang, A. Thompson, S. J. Rettig, D. Dolphin, J. Am. Chem.
Soc. 1998, 120, 13537–13538.
W. H. Harman, C. J. Chang, J. Am. Chem. Soc. 2007, 129,
15128–15129.
K. M. Wampler, R. R. Schrock, Inorg. Chem. 2007, 46, 8463–
8465.
G. Givaja, M. Volpe, M. A. Edwards, A. J. Blake, C. Wilson,
M. Schroder, J. B. Love, Angew. Chem. Int. Ed. 2007, 46, 584–
586; Angew. Chem. 2007, 119, 590–592.
[63] D. K. Mills, J. H. Reibenspies, M. Y. Darensbourg, Inorg.
Chem. 1990, 29, 4364–4366.
[64] L. Heinrich, Y. Li, J. Vaissermann, G. Chottard, J.-C. Chot-
tard, Angew. Chem. Int. Ed. 1999, 38, 3526–3528; Angew.
Chem. 1999, 111, 3736–3738.
[98]
[99]
S. A. Carabineiro, L. C. Silva, P. T. Gomes, L. C. J. Pereira,
L. F. Veiros, S. I. Pascu, M. T. Duarte, S. Namorado, R. T.
Henriques, Inorg. Chem. 2007, 46, 6880–6890.
V. S. Thoi, J. R. Stork, E. T. Niles, E. C. Depperman, D. L. Ti-
erney, S. M. Cohen, Inorg. Chem. 2008, 47, 10533–10541.
[65] E. M. Gale, A. K. Patra, T. C. Harrop, Inorg. Chem. 2009, 48,
5620–5622.
[66] E. M. Gale, B. S. Narendrapurapu, A. C. Simmonett, H. F.
Schaefer III, T. C. Harrop, Inorg. Chem. 2010, 49, 7080–7096.
[67] E. M. Gale, D. M. Cowart, R. A. Scott, T. C. Harrop, Inorg.
Chem. 2011, 50, 10460–10471.
[68] E. M. Gale, A. C. Simmonett, J. Telser, H. F. Schaefer III, T. C.
Harrop, Inorg. Chem. 2011, 50, 9216–9218.
[69] E. Kimura, Y. Kurogi, T. Tojo, M. Shionoya, M. Shiro, J. Am.
Chem. Soc. 1991, 113, 4857–4864.
[70] E. Kimura, Y. Kurogi, S. Wada, M. Shionoya, J. Chem. Soc.,
Chem. Commun. 1989, 781–783.
[71] T. C. Harrop, M. M. Olmstead, P. K. Mascharak, Chem. Com-
mun. 2003, 410–411.
[72] T. C. Harrop, M. M. Olmstead, P. K. Mascharak, Inorg. Chem.
2006, 45, 3424–3436.
[73] T. C. Harrop, M. M. Olmstead, P. K. Mascharak, J. Am. Chem.
Soc. 2004, 126, 14714–14715.
[74] T. C. Harrop, M. M. Olmstead, P. K. Mascharak, Chem. Com-
mun. 2004, 1744–1745.
[100]
[101]
S. Kumar, M. Munjal, J. Singh, R. Gupta, Eur. J. Inorg.
Chem. 2014, 4957–4965.
M. Munjal, R. Gupta, Inorg. Chim. Acta 2010, 363, 2734–
2742.
W. J. Geary, Coord. Chem. Rev. 1971, 7, 81–122.
K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, Wiley, New York, 1986.
K. D. Magers, C. G. Smith, D. T. Sawyer, Inorg. Chem. 1978,
17, 515–523.
A. W. Addison, T. N. Rao, J. Reedijk, J. Van Rijn, G. C. Ver-
schoor, J. Chem. Soc., Dalton Trans. 1984, 1349–1356.
L. Yang, D. R. Powell, R. P. Houser, Dalton Trans. 2007, 955–
964.
[102]
[103]
[104]
[105]
[106]
[107]
T. Kurahashi, H. Fujii, J. Am. Chem. Soc. 2011, 133, 8307–
8316.
[108]
[109]
S. Stoll, A. Schweiger, J. Magn. Reson. 2006, 178, 42–55.
G. Kumar, G. Kumar, R. Gupta, Inorg. Chem. 2015, 54, 2603–
2615.
W. Zhang, J. L. Loebach, S. R. Wilson, E. N. Jacobsen, J. Am.
Chem. Soc. 1990, 112, 2801–2803.
[75] P. V. Rao, S. Bhaduri, J. Jiang, R. H. Holm, Inorg. Chem. 2004,
[110]
[111]
[112]
[113]
[114]
[115]
[116]
[117]
[118]
43, 5833–5849.
[76] P. M. H. Kroneck, V. Vortisch, P. Hemmerich, Eur. J. Biochem.
1980, 109, 603–612.
M. Sankaralingam, M. Palaniandavar, Dalton Trans. 2014,
43, 538–550.
[77] G. M. Polzin, J. N. Burstyn, Met. Ions Biol. Syst. 2001, 38,
D. Bansal, G. Hundal, R. Gupta, Eur. J. Inorg. Chem. 2015,
1022–1032.
B. M. Choudary, U. Pal, M. L. Kantam, K. V. S. Ranganath,
B. Sreedhar, Adv. Synth. Catal. 2006, 348, 1038–1042.
R. D. Arasasingham, G.-X. He, T. C. Bruice, J. Am. Chem.
Soc. 1993, 115, 7985–7991.
J. P. Collman, L. Zeng, J. I. Brauman, Inorg. Chem. 2004, 43,
2672–2679.
J. T. Groves, M. K. Stern, J. Am. Chem. Soc. 1988, 110, 8628–
8638.
E. M. McGarrigle, D. G. Gilheany, Chem. Rev. 2005, 105,
1563–1602.
W. Holderich, U. Barsnick, Fine Chemicals through Hetero-
geneous Catalysis (Eds.: R. A. Sheldon, H. van Bekkum),
Wiley-VCH, Weinheim, Germany, 2001.
C. J. Morten, J. A. Byers, A. R. Van Dyke, I. Vilotijevic, T. F.
Jamison, Chem. Soc. Rev. 2009, 38, 3175–3192.
K. B. Sharpless, T. R. Verhoeven, Aldrichim. Acta 1979, 12,
63–74.
D. D. Perrin, W. L. F. Armarego, D. R. Perrin, Purification of
Laboratory Chemicals, Pergamon Press, Oxford, UK, 1980.
N. S. Gill, E. B. Taylor, Inorg. Synth. 1967, 9, 136–138.
E. Styczen´, W. K. Józ´wiak, M. Gazda, D. Wyrzykowski, Z.
Warnke, J. Therm. Anal. Calorim. 2008, 91, 979–984.
J. Singh, G. Hundal, R. Gupta, Eur. J. Inorg. Chem. 2009,
3259–3265.
103–143.
[78] C. L. Drennan, T. I. Doukov, S. W. Ragsdale, J. Biol. Inorg.
Chem. 2004, 9, 511–515.
[79] W. Huang, J. Jia, J. Cummings, M. Nelson, G. Schneider, Y.
Lindqvist, Structure 1997, 5, 691–699.
[80] S. Nagashima, M. Nakasako, N. Dohmae, M. Tsujimura, K.
Takio, M. Odaka, M. Yohda, N. Kamiya, I. Endo, Nat. Struct.
Biol. 1998, 5, 347–351.
[81] S. B. Choudhury, J. W. Lee, G. Davidson, Y. I. Yim, K. Bose,
M. L. Sharma, S. O. Kang, D. E. Cabelli, M. J. Maroney, Bio-
chemistry 1999, 38, 3744–3752.
[82] J. W. Peters, M. H. Stowell, S. M. Soltis, M. G. Finnegan,
M. K. Johnson, D. C. Rees, Biochemistry 1997, 36, 1181–1187.
[83] H. Sigel, R. B. Martin, Chem. Rev. 1982, 82, 385–426.
[84] I. Sovago, K. Osz, Dalton Trans. 2006, 3841–3854.
[85] O. Clement, B. M. Rapko, B. P. Hay, Coord. Chem. Rev. 1998,
170, 203–243.
[119]
[120]
[121]
[86]
[87]
[88]
[89]
[90]
[91]
[92]
O. Yamauchi, A. Odani, M. Takani, J. Chem. Soc., Dalton
Trans. 2002, 3411–3421.
Z. Yin, Z. Li, A. Yu, J. He, J.-P. Cheng, Tetrahedron Lett. 2004,
45, 6803–6806.
S. J. Brooks, P. A. Gale, M. E. Light, Chem. Commun. 2005,
4696–4698.
S. J. Brooks, P. R. Edwards, P. A. Gale, M. E. Light, New J.
Chem. 2006, 30, 65–70.
S. O. Kang, R. A. Begum, K. B. James, Angew. Chem. Int. Ed.
2006, 45, 7882–7894; Angew. Chem. 2006, 118, 8048–8061.
G. Cafeo, G. Gattuso, F. H. Kohnke, G. Papanikolaou, A. Pro-
fumo, C. Rosano, Chem. Eur. J. 2014, 20, 1658–1668.
S. A. Harris, J. T. Ciszewski, A. L. Odom, Inorg. Chem. 2001,
40, 1987–1988.
[122]
[123]
[124]
[125]
D. T. Sawyer, J. L. Roberts, Experimental Electrochemistry for
Chemists, Wiley, New York, 1974.
N. G. Connelly, W. E. Geiger, Chem. Rev. 1996, 96, 877–910.
CrysAlisPro, v. 1.171.33.49b, Oxford Diffraction, Ltd., Ab-
ingdon, 2006.
[126]
[127]
Eur. J. Inorg. Chem. 2015, 5534–5544
5543
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
[128] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J.
Appl. Crystallogr. 1993, 26, 343–350.
Single Crystal X-ray Diffraction Data, Department of Chem-
istry, University of Glasgow, 2009.
[129] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
[130] L. J. Farrugia, WinGX, v. 1.80, An Integrated System of Win-
dows Programs for the Solution, Refinement and Analysis of
Received: July 14, 2015
Published Online: 4 November, 2015
Eur. J. Inorg. Chem. 2015, 5534–5544
5544
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim