Synthesis, Structure and Redox Properties of Asymmetric (Cyclopentadienyl)(ene-1,2-dithiolate)cobalt(III) Complexes Containing Phenyl, Pyridyl and Pyrazinyl Units

Article abstract of DOI:10.1002/ejic.201500138

The compounds [(η⁵-C₅H₅)Co{SC(H)CRS}] [R = phenyl (1), pyridin-3-yl (2) or pyrazin-2-yl (3)] have been synthesized and characterized by elemental analysis, ¹H NMR, mass spectrometry and X-ray crystallography. Th

Full text of DOI:10.1002/ejic.201500138

FULL PAPER
DOI:10.1002/ejic.201500138
Synthesis, Structure and Redox Properties of Asymmetric
(
Cyclopentadienyl)(ene-1,2-dithiolate)cobalt(III) Complexes
CLUSTER
ISSUE
Containing Phenyl, Pyridyl and Pyrazinyl Units
[
a]
[b]
[a]
James P. Dicks, Muhammad Zubair, E. Stephen Davies,
[a]
[c]
[d]
C. David Garner,* Carola Schulzke,* Claire Wilson, and
Jonathan McMaster*[
a]
Keywords: Metalloenzymes / Cofactors / Redox chemistry / Cobalt / Molybdenum / Molybdopterins / Oxygen atom
transfer
5
y
y
The compounds [(η -C
5
H
5
)Co{SC(H)CRS}] [R = phenyl (1),
interpreted with the aid of DFT calculations for [1] , [2] and
y
z
pyridin-3-yl (2) or pyrazin-2-yl (3)] have been synthesized
and characterized by elemental analysis, H NMR, mass
[3] (y = 0 or –1) and the monoprotonated forms [2H] and
[3H] (z = +1 or 0), and this has provided insight into the
1
z
spectrometry and X-ray crystallography. The variation in the
UV/Vis and redox properties of these compounds alone and
upon acidification has been investigated. In CH Cl solution
2 2
each compound undergoes a reversible one-electron re-
duction, and the EPR spectrum of each monoanion has been
recorded. In the presence of a 5:1 excess of trifluoroacetic
acid the one-electron reduction of both 2 and 3 occurs at a
less negative potential. The information obtained has been
nature of the redox-active orbitals in these complexes. The
HOMOs and LUMOs of these species are delocalized and
each involves contributions from cobalt, ene-1,2-dithiolate
and R orbitals. The information from the experimental and
theoretical investigations is used to suggest that, for the
pyran ring-opened form of the molybdenum cofactor of
oxygen-atom-transfer enzymes, the pterin may participate in
the redox reactions involved in the catalytic cycle.
[
3]
Introduction
Biochemical investigations and X-ray crystallographic
[
4]
studies have established that, in the active sites of these
enzymes, the metal is coordinated by one or two molybdo-
pterin (MPT) ligands (Scheme 1).
Molybdenum and tungsten are the only 4d and 5d transi-
tion metals with known roles in biology. With the excep-
tions of the nitrogenases[1] and acetylene hydratase, vir-
tually all of the Mo- and W-containing enzymes may be
viewed as catalyzing a two-electron redox reaction that in-
volves the transfer of an oxygen atom to or from a substrate
X or XO, see Equation (1).
[2]
Scheme 1. Ring-closed and ring-opened forms of molybdopterin
(
1)
(
MPT).
[
a] School of Chemistry, University of Nottingham,
University Park, Nottingham, NG7 2RD, U.K
E-mail: dave.garner@nottingham.ac.uk
MPT, which is uniquely found in these enzymes, has a
tricyclic structure consisting of a bicyclic pterin ring fused
2–
j.mcmaster@nottingham.ac.uk
to a pyran ring that incorporates a CH
2
OPO
3
or CH O-
2
http://www.nottingham.ac.uk/chemistry/people/dave.garner
http://www.nottingham.ac.uk/chemistry/people/j.mcmaster
b] School of Chemistry, Trinity College Dublin,
College Green, Dublin 2, Ireland
–
PO (OR) group (R = nucleotide) and an ene-1,2-dithiolate
2
[
3a,5]
(dithiolene) unit, which coordinates the metal.
[
[
The Mo-containing enzymes have been classified into
c] Ernst-Moritz-Arndt-Universität, Institut für Biochemie,
Arbeitskreis Bioanorganische Chemie,
three families on the basis of the nature of the Mo coordi-
VI
nation sphere at the active site in the oxidized (Mo ) form
Felix-Hausdorff-Strasse 4, 17487 Greifswald, Germany
E-mail: schulzkec@uni-greifswald.de
[
6]
of the enzyme. Members of the xanthine oxidase family
http://www.mnf.uni-greifswald.de/institute/institut-fuer-
biochemie/bioanorganische-chemie.html
each possess one MPT ligand coordinated to a fac-
VI
[
d] School of Chemistry, Joseph Black Building, The University of Mo OX(H
O) (X = O or S) centre, members of the sulfite
2
Glasgow,
oxidase family each possess MPT coordinated to a cis-
University Avenue, Glasgow, G12 8QQ, UK
VI
Mo O centre, which is also bound to a cysteinyl residue
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201500138.
2
and H O, and members of the DMSO reductase family
2
Eur. J. Inorg. Chem. 2015, 3550–3561
3550
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
5
2+
each possess a Mo centre coordinated by two MPTs, a Mo cluding unwanted dimerization reactions. [(η -C H )Co]
5
5
=
X (X = O or S) group plus the donor atom of an amino has the added advantage that it is a redox-active metal cen-
[6]
[18]
acid residue. Spectroscopic studies have shown that the tre and undergoes a reversible one-electron reduction.
two-electron oxygen-atom-transfer (OAT) reaction [Equa- Thus, the properties of [(η -C H )Co(dithiolene)] com-
5
5
5
tion (1)] catalyzed by these enzymes involves the cycling of plexes facilitate investigations of how variations in the na-
IV
VI
the metal centre between the Mo and Mo oxidation ture of the dithiolene ligand modulate the inherent redox
V
states. In addition, the Mo state can be readily generated characteristics of the metal centre and, thereby, determine
in many Mo-containing enzymes; studies of, for example, the redox properties of the complex, information of rele-
[
7]
[8]
xanthine oxidase and sulfite oxidase have probed the vance to the potential role of MPT in the catalytic function
relevance of this state in the catalytic cycles of these of Mo- and W-containing enzymes.
enzymes. The interpretation of the structural and spectro-
In this paper we describe the synthesis, structural charac-
scopic studies of the catalytic centres in Mo- and W-con- terization, electrochemical and spectroscopic investigations
5
taining enzymes has been greatly assisted by complemen- of [(η -C H )Co{SC(H)CRS}] [R = phenyl (1), pyridin-3-
5
5
tary investigations on a wide range of synthetic Mo and W yl (2) or pyrazin-2-yl (3)] compounds and present DFT cal-
ene-1,2-dithiolate complexes, and studies of the properties culations to provide a qualitative interpretation of the infor-
and reactions of chemical analogues of the catalytic centres mation obtained. Particular attention is paid to the varia-
of these enzymes have provided significant insights into the tion in the redox and UV/Vis and EPR spectroscopic prop-
role of the metal centre in the catalysis of OAT by Mo- and erties of 1, 2 and 3 in solution and of 2 and 3 in the presence
W-containing enzymes.[
9]
of an excess of trifluoroacetic acid (TFA). The changes in
Although the roles of the Mo or W centres of Mo- and the spectroscopic and redox properties of these compounds,
W-containing enzymes in the catalysis of OAT are well which each possess a simplified asymmetric ene-1,2-dithio-
understood, the role of MPT remains to be defined. In the late ligand that replicates aspects of a ring-opened MPT
majority of the crystallographic characterizations of these ene-1,2-dithiolate ligand system, are assessed as the R sub-
enzymes, MPT exhibits extensive hydrogen bonding within stituent is varied and upon acidification, with the aim of
the protein matrix, which might influence the geometry of providing insights into the nature of the redox-active orbit-
the coordination sphere of the metal centre at the active als in these complexes.
site. Pterins are redox-active and may be obtained in the
fully oxidized, dihydro or tetrahydro forms. The form of
MPT that is found most frequently in the active sites of
Mo- and W-containing enzymes characterized by X-ray
Experimental Results
crystallography involves a closed pyran ring, and the con-
formation resembles that of a tetrahydropterin. However, a
Syntheses
5
form of MPT in which the pyran ring is open (Scheme 1)
Each of the [(η -C H )Co{SC(H)CRS}] compounds [R
5
5
has been identified in the crystal structures of the nitrate = phenyl (1), pyridin-3-yl (2) and pyrazin-2-yl (3)] was
[
10]
5
reductase A from Escherichia coli
hydrogenase from Aromatoleum aromaticum.[
pyran ring-opened form of MPT the pyrazine ring of the corresponding thione-protected 1,3-dithiolate (Scheme 2).
and ethylbenzene de- prepared by treating [(η -C H )Co(CO)I ] with the appro-
5 5 2
11]
In the priate ene-1,2-dithiolate generated by base hydrolysis of the
[
12]
pterin is conjugated to the ene-1,2-dithiolate unit;
this, Compound 3 was prepared from 4-pyrazin-2-yl-[1,3]di-
together with the redox non-innocence of the ene-1,2-di- thiolene-2-one, which was itself synthesized from acetylpyr-
[
13]
thiolate group,
could imply that electron transfer to or azine in three steps: (a) bromination of acetylpyrazine with
from the substrate might involve the metal centre, the ene- 2-pyrrolidinone hydrotribromide in THF, (b) treatment of
[
14]
1,2-thiolate unit and components of the pterin ring.
In 2-pyrrolidinone hydrotribromide with potassium O-iso-
support of this view, an examination of the conformations propyl carbonodithioate to yield O-isopropyl-S-[2-oxo-2-
of the pyranopterin units in 102 MPT-containing X-ray (pyrazin-2-yl)ethyl] carbonodithioate, and (c) cyclization of
crystal structures has suggested that the redox chemistry O-isopropyl-S-[2-oxo-2-(pyrazin-2-yl)ethyl] carbonodithio-
associated with this unit could support the catalytic func- ate in perchloric acid.
tion of the active sites of the Mo- and W-containing en-
The structural, spectroscopic and electrochemical data
[
15]
zymes.
However, the instability of MPT outside of the for 1, 2 and 3 reported here are consistent with the formula-
5
protein matrix has, so far, prevented any direct study of the tion of each compound as [(η -C H )Co{SC(H)C(R)S}]. In
5
5
properties and redox chemistry of this moiety.[ Further- the H NMR spectra the relative chemical shifts of the H
16]
1
8
more, the synthesis of MPT represents a major chemical resonance – 9.01 ppm for 1, 9.00 ppm for 2 and 9.55 ppm
challenge and, although significant advances have been re- for 3 – are consistent with the nature of the ligands in re-
[
14e,17]
ported,
further work is still required. In their synthetic spect of: (i) inductive effects, and (ii) the relative ability of
[
17a–17f]
5
2+
studies,
Joule, Garner et al. used [(η -C H )Co] as the aromatic substituent to stabilize a resonance form in
5
5
the metal centre, with the organic framework being bound which a positive charge is localized at the C atom carrying
to this through its ene-1,2-thiolate group.[
14e,17g,17h]
This the dithiolene proton. A similar order in the chemical shift
8
strategy avoided complications associated with the chemis- of the H resonances has been recognized previously for
IV 2+
V
3+
VI
2+
2–
[19]
try of [Mo O] , [Mo O] and [Mo O ] centres, in- [MO(ene-1,2-dithiolate)2] (M = Mo, W) complexes.
2
Eur. J. Inorg. Chem. 2015, 3550–3561
3551
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
5
Scheme 2. Route used for the syntheses of [(η -C
CRS}] [SC(H)C(R)S, R = phenyl (1), pyridin-3-yl (2), pyrazin-2-yl
3)]. The numbering schemes for the various ligand substituents
5 5
H )Co{SC(H)-
(
1
13
have been used in the assignment of the H and C NMR spectra
of these compounds.
Structural Characterization
The structures of 1, 2 and 3 have been determined by X-
ray crystallography (see Table 1); in each case, the results
obtained (Figure 1) are consistent with the corresponding
molecular details shown in Scheme 2.
5
The {(η -C H )Co(SCCS)} centres of 1, 2 and 3 are sim-
5
5
ilar in nature and exhibit Co–S, C–S and dithiolene C–C
interatomic distances in the ranges of 2.1025(12)–
2.1224(11), 1.709(4)–1.729(4) and 1.363(3)–1.367(7) Å,
respectively. Each {Co(SCCS)} unit is essentially planar,
with the maximum displacement from the mean plane being
Յ0.013(1) Å and the fold angle between the planes defined
by Co(1)S(1)S(2) and S(1)C(1)C(2)S(2) being Յ1.79(14)°
Figure 1. The molecular structures of (a) 1, (b) 2, and (c) 3, with
the H atoms omitted for clarity. Thermal ellipsoids are plotted at
the 50% probability level.
(Table 1). These metrical parameters, together with the
interbond angles (Table 1), correspond to those of other
5
compounds
unit.
containing
the
{(η -C H )Co(SCCS)}
An important aspect to the nature of a dithiolene com-
5
5
[
18c,20]
The essential equivalence in the lengths of the plex is the “non-innocence” of this ligand, the two extreme
Co–S and C–S bonds in 1, 2 and 3 suggests that the forms being the ene-1,2-dithiolate ( S–C=C–S ) and the di-
asymmetric nature of the ene-1,2-dithiolate ligand does not thioketone (S=C–C=S).
–
–
[
21]
Thus, the lengths of the C–C
significantly affect the nature of the metal–ligand interac- and C–S bonds can be used to comment on the nature of a
2
tions. The pendant phenyl and pyridin-3-yl rings in 1 and 2 dithiolene ligand in a complex. For sp -hybridized carbon
are each twisted out of the plane defined by the C(1), C(2), atoms, typical bond lengths are: C–C 1.43–1.48, C=C 1.30–
[
22]
S(1) and S(2) atoms [φ = 41.3(2) and 34.00(9)° for 1 and 2, 1.36, C–S 1.71–1.75, and C=S 1.67–1.68 Å.
respectively], whereas in 3 the pyrazin-2-yl ring is essentially lengths of the C–C [1.363(3)–1.367(6) Å] and the C–S
coplanar with the SCCS unit [φ = 1.9(2)°]. [1.705(2)–1.729(4) Å] bonds of the ligands in 1, 2 and 3 are
Thus, the
Table 1. Selected bond lengths and interbond, metalladithiolene fold (θ) and ene-1,2-dithiolate/aromatic ring plane (φ) angles for 1, 2 and
3.
1
Exp.
2
Exp.
3
Exp.
Bond lengths [Å]
Calcd.
Calcd.
Calcd.
Co(1)–S(1)
Co(1)–S(2)
S(1)–C(1)
S(2)–C(2)
C(1)–C(2)
2.1174(12)
2.1224(11)
1.711(4)
1.729(4)
1.367(6)
2.129
2.137
1.715
1.742
1.368
2.1110(6)
2.1195(6)
1.705(2)
1.7280(19)
1.363(3)
2.131
2.136
1.716
1.743
1.367
2.1025(12)
2.1092(12)
1.709(4)
1.724(4)
1.366(6)
2.132
2.219
1.707
1.738
1.365
Bond angles [°]
S(1)–Co(1)–S(2)
Co(1)–S(1)–C(1)
Co(1)–S(2)–C(2)
S(1)–C(1)–C(2)
S(2)–C(2)–C(1)
91.09(4)
91.0
91.53(2)
91.0
91.26(4)
91.1
105.16(15)
106.04(14)
120.6(3)
105.1
105.9
121.1
116.9
105.02(7)
105.30(7)
120.47(15)
117.68(15)
105.1
105.9
121.0
117.0
105.83(14)
105.64(14)
119.2(3)
104.9
105.8
121.1
117.2
117.1(3)
118.1(3)
θ [°]
φ [°]
0.82(13)
41.3(2)
0.15
0.69(6)
0.06
1.79(14)
1.9(2)
0.21
4.93
34.95
34.00(9)
33.71
Eur. J. Inorg. Chem. 2015, 3550–3561
3552
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
–1
–1
consistent with the ene-1,2-dithiolate form of the dithiolene 30000 m cm ) with other absorptions between 24300 and
in these complexes. Therefore, to a first approximation, 1, 29400 cm–1 (ε = 1500–7800 m cm ) appearing as shoul-
–1
–1
5
III
2
and 3 may be formulated as [(η -C H )Co (ene-1,2-di- ders on the higher-energy band.
5 5
thiolate)] complexes.
The changes in the UV/Vis spectra of 2 and 3 in CH Cl2
2
in the presence of a 5:1 excess of TFA are also shown in
–
1
Figure 2. Upon protonation the absorptions at 17100 cm
–1
–1
–1
UV/Vis Spectroscopic Properties of 1, 2 and 3 in CH Cl2
(ε = 8800–9100 m cm ) and 34000–34400 cm
(ε =
2
–1
–1
and of 2 and 3 in the Presence of an Excess of
Trifluoroacetic Acid
30000–26400 m cm ) in both 2 and 3 show modest shifts:
in 2 to 17400 (ε = 1000 m cm ) and 34000 cm (ε =
2000 m cm ), and in 3 to 17400 (ε = 1000 m cm ) and
4000 cm (ε = 32000 m cm ). In addition, both spectra
–1
–1
–1
–
1
–1
–1
–1
3
3
The UV/Vis spectra of 1, 2 and 3 in CH Cl solution
2
2
–1
–1
–1
are shown in Figure 2. Each spectrum is dominated by two
develop
a
broad absorption between 26700 (ε =
–
1
absorptions at ca. 17000–17100 cm
(ε
(ε
=
6600–
–1
–1
–1
–1
–1
7800 m cm ) and 22300 cm (ε = 7600 m cm ).
–
1
–1
–1
9
100 m cm ) and 34000–34400 cm
=
23000–
Electrochemical and UV/Vis Spectroelectrochemical
Properties of 1, 2 and 3 and of 2 and 3 in the Presence of
an Excess of TFA
The cyclic voltammograms of 1, 2 and 3 in CH Cl solu-
2
2
tion containing [NnBu ][BF ] (0.4 m) as the background
4
4
electrolyte and of 2 and 3 in this medium plus a 5:1 excess
of TFA were each recorded at 298 K. As in the cases of
5
[20h,23]
other [(η -C H )Co(ene-1,2-dithiolate)] complexes,
5
5
each compound exhibited a reversible, one-electron redox
+
couple in the range from –1.09 to –1.20 V versus Fc /Fc
(Figure 3, Table 2).
Figure 3. Cyclic voltammograms of (a) 1, (b) 2, and (c) 3 (1 mm,
solid lines) in CH Cl containing [NnBu ][BF ] (0.4 m) as the back-
2
2
4
4
ground electrolyte and of (b) 2, and (c) 3 (1 mm) in this medium
with a 5:1 excess of TFA (dotted lines). The information was re-
corded at 298 K with use of a glassy carbon working electrode,
a Pt wire secondary electrode and a saturated calomel reference
+
electrode; potentials are expressed versus the [Fc] /[Fc] couple.
The generation of the monoanions of 1, 2 and 3 was
investigated by UV/Vis spectroelectrochemistry. In each
case the one-electron reduction was accompanied by the
observation of isosbestic points, consistent with reduction
proceeding with no long-lived intermediates or transition
Figure 2. Observed (bottom panels) and calculated (DFT, upper
panels) UV/Vis spectra of (a) 1, (b) 2, and (c) 3 in CH Cl , together
with the corresponding information for (b) 2, and (c) 3 in CH Cl
in the presence of a 5:1 excess of TFA. All spectra were recorded
at 298 K.
–
–
–
states, to generate the monoanions [1] , [2] and [3] . At
73 K this reduction was chemically reversible (Figure 4,
2
2
2
2
2
Table 3). The most significant spectroscopic changes in-
volved a decrease in the intensity of the absorptions at ca.
Eur. J. Inorg. Chem. 2015, 3550–3561
3553
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Table 2. Potentials (vs. [Fc] /[Fc]) observed for the reduction of 1, Epa = –0.56 V. Similar shifts in potentials have been ob-
+
2
and 3 (1 mm) in CH
2
Cl containing [NnBu ][BF ] (0.4 m) as back-
ground electrolyte and of 2 and 3 (1 mm) in this medium with a 5:1
2
4
4
5
served for [(η -C H ) Mo{S C(H)C(R)}] (R = pyridin-2-yl,
5
5 2
2
pyridin-3-yl or pyridin-4-yl) in the presence of HBF
etherate and for [(η -C H )Co{S C H(quinoxalin-2-yl)}]
in the presence of TFA.
redox processes clearly developed, at –0.33 and –0.56 V vs.
SCE, each being attributed to the one-electron redox couple
of an isomer of the parent molecule formed by protonation
of an N atom of the quinoxalin-2-yl ring. By analogy, the
processes observed for 3 in the presence of an excess of TFA
are assigned to a one-electron redox couple of one of the
4
excess of trifluoroacetic acid (TFA) at room temperature.
[
24]
5
5
[25]
5
2 2
c
a
ΔE (Fc+/
E
1/2 (ΔE)
E
p
E
p
For the latter compound, two
Fc)
1
2
3
2
TFA
3
TFA
–1.20 (0.08)
–1.15 (0.09)
–1.09 (0.08)
0.08
0.09
0.08
0.09
+ excess
–1.04
–0.94
+ excess
–0.63, –0.85 –0.56
0.08
+
two isomers of [3H] that involve protonation of a pyrazin-
2-yl ring N atom.
7000–17400 and 34000–34400 cm–1 and an increase in the
intensity of absorptions at 22900–25900 and 31100–
Investigations of the redox properties of 1 in the presence
of an excess of TFA were not undertaken because 1 un-
1
–
1
dergoes coupling reactions under acidic conditions to gen-
31300 cm .
[
18a]
erate dinuclear Co-containing products.
EPR Spectroscopic Studies of the Monoanions of 1, 2 and
3
X-band EPR spectra were recorded at 77 K for electro-
–
–
–
chemically generated [1] , [2] and [3] in DMF solution
containing [NnBu ][BF ] (0.2 m). The nature of the EPR
4
4
spectra of these anions was essentially invariant (Figure 5)
and each possesses features that are characteristic of those
5
–
reported for other [(η -C H )Co(ene-1,2-dithiolate)]
species.
5
5
[
23a,23b,26]
–
The EPR spectrum of [1] was simulated
with rhombic spin Hamiltonian parameters (Figure 5)
based on the assumptions of the unpaired electron coupling
with the 59Co (I = 7/2, 100%) nucleus and a coincidence of
the principal g- and A-tensor axes. The latter assumption is
an approximation, given the low symmetry of the Co centre,
and a full interpretation of these EPR spectra, particularly
the high-field features, must await single-crystal and/or
[
26a]
multifrequency EPR experiments.
Nevertheless, the
interpretation of the experimentally measured spectrum re-
59
Figure 4. UV/Vis spectroscopic changes that accompany the elec- quires a value for the A33 hyperfine coupling to the Co
trochemical one-electron reduction of (a) 1, (b) 2, and (c) 3 in
CH Cl containing [NnBu ][BF ] (0.4 m), recorded at an optically
transparent electrode at 273 K.
5
nucleus that is similar to those of other [(η -C H )Co(ene-
5
5
2
2
4
4
1,2-dithiolate)] anions, including that derived from a di-
thiolene-pendant to a 18-membered S N macrocyclic ring
4
2
The redox behaviour of 2 and 3 is significantly different (g11 = 1.993, g22 = 2.043 and g = 2.246; A11 = 30, A
=
=
=
=
33
22
[
23b]
–
in the presence of a 5:1 excess of TFA (Figure 3). Thus, the 15.5 and A33 = 89 G),
[Co(NO){S C (CN) } ] (g
2 2 2 2 iso
–
one-electron reduction of both 2 and 3 occurs at a more 2.063, Aiso = 31.9 G), [Co(NO){S C (CF ) } ] (giso
2
2
3 2 2
c
–
positive potential: 2 exhibits a reduction process at Ep
=
2.059, Aiso = 32.9 G) and [Co(NO)(S C Ph ) ] (giso
2 2 2 2
a
+
[27]
–
1.04 V coupled to a reoxidation at Ep = –0.94 V (vs. Fc / 2.050, Aiso = 29.4 G).
These values of hyperfine cou-
c
Fc), and 3 exhibits successive reduction processes at Ep
=
plings are consistent with a SOMO that involves a relatively
+
–
0.63 and –0.85 V vs. Fc /Fc coupled to a reoxidation at small contribution from Co-based orbitals (vide ultra).
Table 3. UV/Vis spectroscopic changes that accompany the electrochemical reduction of 1, 2 and 3 in CH
(0.4 m), recorded at an optically transparent electrode at 273 K.
2
Cl
2
containing [NnBu
4
][BF
4
]
3
–1
3
–1
3
–1
Neutral [ϫ10 cm ]
Reduced [ϫ10 cm ]
Isosbestic points [ϫ10 cm ]
1
2
3
17.0, 29.4, 34.4
17.1, 24.9, 29.2, 34.4
17.4, 26.7, 34.0
25.9, 31.3, 34.8, 39.0
25.1, 31.1, 34.6, 40.0
22.9, 25.8, 31.1, 37.9
32.3, 36.7
32.1, 36.7
19.3, 26.3, 28.6, 32.1, 36.5
Eur. J. Inorg. Chem. 2015, 3550–3561
3554
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
the gas-phase theoretical and in the crystallographically de-
termined solid-state structures. The principal difference be-
tween the calculated and the experimentally determined
structures involves the dihedral angle (φ) between the
metalladithiolene and phenyl, pyridin-3-yl or pyrazin-2-yl
ring planes, the difference being ca. 6.4, 0.3 and 3.0° for 1,
2
and 3, respectively (Table 1).
The calculated geometrical parameters for the metalla-
+
+
dithiolene ring for [2H] and [3H] (Table S1 in the Sup-
porting Information) are similar to those of 2 and 3, respec-
tively (Table 1), thus suggesting that protonation does not
significantly change the geometry of the metalladithiolene
unit. As indicated by a comparison of the data presented
in Table 1 and in Table S1 in the Supporting Information,
reduction of 1, 2 and 3 to the corresponding monoanion is
accompanied by a minor lengthening of the Co–S and C–S
bonds within the metalladithiolene ring, by ca. 0.05 and
0.03 Å, respectively. Also, the C–C bond increases in length
by ca. 0.10 Å for the one-electron reduction of 1 and 2 but
remains essentially unchanged for the reduction of 3. Re-
+
+
duction of [2H] to [2H] and of [3H] to [3H] (Table S1 in
the Supporting Information) leads to small increases in the
lengths of both the Co–S and the C–S bonds.
The compositions and energies of the frontier orbitals of
+
+
1
, 2, 3, [2H] and [3H] calculated for the gas-phase geome-
try-optimized structures in CH Cl solution are summa-
2
2
–
–
–
Figure 5. X-band EPR spectra of (a) [1] , (b) [2] , and (c) [3] elec-
trochemically generated from 1, 2 and 3, respectively, in DMF solu-
rized in Table 4 and illustrated in Figure S2 in the Support-
ing Information. Corresponding details for the frontier or-
4 4
tion containing [NnBu ][BF ] (0.2 m) at 77 K. The simulation of
–
–
–
–
the EPR spectrum of [1] was achieved with the spin Hamiltonian bitals of [1] , [2] , [3] , [2H] and [3H] are provided in
parameters g11 = 1993, g –2 2 = 2.039 and g33 = 2.230, |A11| = 27, |A22
|
=
Table S2 in the Supporting Information.
–1
=
3 and |A33| = 97ϫ10 4 cm , with linewidths W11 = 39, W22
8 and W33 = 30 MHz. Fluid solution spectra are shown in Fig-
ure S1 in the Supporting Information and were simulated with giso
Each dithiolene ligand possesses four π-symmetry molec-
ular orbitals (π –π ) that resemble the butadienoid orbitals
2
1
4
2– [28]
–1
proposed for ethene-1,2-dithiolate (S C H )
and filled
=
2.092 and |Aiso| = 37ϫ10–4 cm .
2
2
2
in-plane symmetric and antisymmetric sulfur orbital combi-
nations (σ and σ ) that may participate in σ-bonding to
1
2
29]
DFT Calculations and Discussion
[
the metal centre.
The Co–dithiolene interactions within
y
y
y
y
y
We have undertaken DFT calculations for [1] , [2] and the frontier orbital manifolds of [1] , [2] and [3] (y = 0 or
y
z
z
z
[
[
3] (y = 0 or –1) and the monoprotonated forms [2H] and –1) and [2H] and [3H] (z = +1 or 0) involve principally
z
3H] (z = +1 or 0) to provide a qualitative description of the π –π and σ combinations (Table 4 and Table S2 in the
2
4
2
the structure and bonding within these complexes and to Supporting Information, Figure S2 in the Supporting Infor-
provide a framework for interpretation of the spectroscopic mation) and mirror those of the electronic structures calcu-
5
and electrochemical properties of 1, 2 and 3 in the absence lated previously for other [(η -C H )Co(ene-1,2-dithiolate)]
5
5
z
[28b,30]
and in the presence of TFA (vide ultra). For [3H] we exam- compounds.
Thus, the HOMO in each of 1, 2 and 3
ined one protonated form, which involves protonation at is delocalized across the metalladithiolene unit and involves
y
y
the N(1) position (see Figure 1). Models of [1] , [2] and essentially Co d , dithiolene π and R group π combina-
[
yz
3
y
z
z
3] (y = 0 or –1) and of [2H] and [3H] (z = +1 or 0) were tions that combine in a HOMO with dithiolene (54.3–
constructed from the experimentally determined crystallo- 57.1%), R group (16.7–20.1%) and Co (17.4–18.0%) char-
+
+
graphic co-ordinates for 1, 2 and 3 before being geometry- acter. The HOMO in each of [2H] and [3H] has a similar
optimized in the gas phase. Selected bond lengths and in- composition to that of the parent compound, with di-
terbond angles obtained from the DFT calculations for 1, thiolene (60.9–61.5%), R group (13.4–14.8%) and Co
y
y
2
[
and 3 are shown in Table 1, and those for [1] , [2] and (16.1–16.7%) character. Each of these HOMOs involves a
y
z
z
3] (y = 0 or –1) and for [2H] and [3H] (z = +1 or 0) are small amount (8.2–8.6%) of Cp character. The LUMOs of
listed in Table S1 in the Supporting Information. 1, 2 and 3 are essentially identical and are derived princi-
The DFT calculations reproduce the magnitude of the pally from Co d , dithiolene π and Cp orbital combina-
yz
3
crystallographically determined bond lengths, the interbond tions. The LUMOs involve contributions from Co (44.5–
angles within the {MSCCS} metallacycle and the metallad- 45.3%) and dithiolene orbitals (27.7–29.8%), a significant
ithiolene fold angles (θ) in the structures of 1, 2 and 3. Thus, contribution from Cp orbitals (23.5–23.8%) plus a minor
the CoS and S C planes are essentially coplanar both in (1.7–3.2%) contribution from the R group orbitals. The
2
2 2
Eur. J. Inorg. Chem. 2015, 3550–3561
3555
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Table 4. The nature, energy and composition of the frontier orbitals obtained from the DFT calculations for 1, 2, 3, [2H]+ and [3H]+ in
CH
2
Cl
2
solution.
Orbital
designation
78a
Energy
[eV]
% Contribution
Nature
Co
S
2
C
2
H
R
Cp
1
L+3
L+2
L+1
LUMO
HOMO
H-1
Ph
Ph + S
Co dxz + S
Co dyz + S
Co dyz + S
–0.43
–0.97
–1.73
–2.89
–5.74
–6.25
1.3
1.3
45.9
45.0
17.5
45.1
1.5
97.2
59.3
2.3
1.7
20.1
2.3
0.1
0.9
22.8
23.5
8.2
77a
76a
75a
74a
73a
2
C
2
π
4
38.6
29.0
29.8
54.3
49.5
2
C
2
σ
2
+ Cp
+ Cp
2
C
C
2
π
π
3
2
2
3
Co dxy + S
2
C
2
π
2
3.2
2
3
78a
L+3
L+2
L+1
LUMO
HOMO
H-1
Py
Py + S
Co dxz + S
Co dyz + S
Co dyz + S
–0.87
–1.22
–1.79
–2.93
–5.84
–6.30
1.1
2.5
44.4
45.3
18.0
45.7
8.3
90.3
67.3
5.3
1.8
16.7
2.1
0.3
1.4
22.2
23.8
8.6
77a
76a
75a
74a
73a
2
C
2
π
4
28.8
28.1
29.1
57.1
49.1
2
C
2
σ
2
+ Cp
+ Cp
2
2
C
C
2
π
π
3
3
2
Co dxy + S
2
C
2
π
2
3.0
78a
L+3
L+2
L+1
LUMO
HOMO
H-1
Pz
–1.10
–1.82
–1.87
–3.01
–5.91
–6.37
0.7
17.8
26.7
22.8
27.7
56.8
48.9
81.1
25.6
53.9
3.2
17.6
2.3
0.4
15.8
7.7
23.7
8.2
3.2
77a
76a
75a
74a
73a
Co dxz + S
Co dxz + Pz + S C π
2 2 4
Co dyz + S
Co dyz + S
Co dxy + S
2
C
2
σ
2
+ Pz
31.8
15.6
44.5
17.4
45.6
2
C
C
2
π
π
3
+ Cp
2
2
3
2
C
2
2
π
2
2
[
[
2H]+
78a
L+3
L+2
L+1
LUMO
HOMO
H-1
Py + S
Co dxz + S
Py
Co dyz + S
Co dyz + S
Co dxy + S
2
C
2
π
4
–2.00
–2.17
–2.77
–3.35
–6.33
–6.74
2.1
44.9
1.2
45.7
16.7
46.8
24.2
28.9
6.9
24.7
61.5
48.7
72.6
3.0
91.3
4.6
13.4
1.4
1.1
23.3
0.5
24.9
8.4
3.1
77a
76a
75a
74a
73a
2
C
σ
+ Cp
+ Cp
2
2
C
C
2
2
π
π
3
3
2
C
2
π
2
2
3H]+
78a
L+3
L+2
L+1
LUMO
HOMO
H-1
Pz + S
Co dxz + S
Pz
Co dyz + S
Co dyz + S
Co dxy + S
C
π
–2.20
–2.25
–3.31
–3.46
–6.41
–6.83
1.8
46.4
8.0
38.0
16.1
47.4
26.4
28.2
12.4
18.6
60.9
47.4
70.7
0.85
75.2
22.8
14.8
1.9
1.2
24.6
4.4
20.6
8.2
3.3
2
2
4
77a
76a
75a
74a
73a
2
C
2
σ
+ Cp
+ Cp
2
2
C
C
2
2
π
π
3
3
2
C
2
π
2
+
LUMO in [2H] possesses a similar composition to that of thiolene (28.8–38.6%) orbitals. However, in 3 the LUMO+2
and primarily involves the Co (45.7%), dithiolene (24.7%) orbital is delocalized and involves significant contributions
2
and Cp (24.9%) orbitals with a small (4.6%) contribution from the Co (31.8%) and the dithiolene (26.7%) orbitals
from the pyridin-3-yl orbitals. However, the LUMO in plus contributions from orbitals on the R (25.6%) and Cp
+
+
+
[
3H] possesses a greater pyrazin-2-yl character (22.8%) (15.8%) groups. The LUMO+2 orbital in [2H] and [3H]
than that in the parent compound (17.6%), in addition to involves contributions from the Co (44.9 and 46.4%), di-
contributions from Co (38.0%), dithiolene (24.7%) and Cp thiolene (28.9 and 28.2%) and Cp (23.3 and 24.6%) orbit-
+
+
(20.6%) orbitals.
als. The LUMO+3 in 1, 2, 3, [2H] and [3H] possesses
The composition of the LUMO+1 orbital varies within significant contributions from the phenyl, pyridin-3-yl or
the parent compounds. Thus, in 1 and 2 the LUMO+1 pyrazin-2-yl rings (70.7–97.2%) and also shows a similar
possesses Co (44.4–45.9%), dithiolene (29.0–28.1%) and Cp variation in energy (ca. 1.10 eV) relative to the HOMO as
(
22.2–22.8%) character; however, for 3 this orbital has con- observed for the energies of the LUMO+1.
siderable (53.9%) pyrazin-2-yl character with modest con- The relative energies of the LUMOs of these complexes
tributions from Co (15.6%), dithiolene (22.8%) and Cp (Table 4) vary with the substituents in a manner that corre-
+
+
(
3.2%) orbitals. The LUMO+1 orbital in [2H] and [3H]
is essentially localized on the R group and has pyridin-3-yl reduction (Tables 2 and 4): that is, the variation with the
91.3%) and pyrazin-2-yl (75.2%) character with only nature of the substituent is 1 Ͻ 2 Ͻ 3 and, also, protonation
sponds to the variation of the potential of the one-electron
(
minor contributions from Co (1.2 and 8.0%, respectively) of 2 and 3 leads to an increase in the reduction potential of
and dithiolene (6.9 and 12.4, respectively) orbitals. The each compound (i.e., a shift to more positive potential).
LUMO+2 orbital in 1 and 2 is ligand-based with major
A comparison of the experimentally measured (Figure 2)
contributions from the R group (59.3–67.3%) and the di- and calculated theoretical UV/Vis absorption spectra of 1,
Eur. J. Inorg. Chem. 2015, 3550–3561
3556
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
–
–
–
Table 5. Spin Hamiltonian parameters calculated by DFT for [1] , [2] and [3] and those obtained by simulation of the X-band EPR
–
4 4
spectrum of [1] recorded in DMF solution containing [NnBu ][BF ] (0.2 m) at 77 K.
Complex
g
11
g
22
g
33
|A11
|
|A22
[ϫ10 cm ]
|
|A33|
[ϫ10 cm ]
–
4
–1
–4
–1
–4
–1
[ϫ10 cm ]
–
1
2
3
1
(DFT calculated)
2.004
2.005
2.007
1.993
2.026
2.025
2.027
2.039
2.137
2.137
2.138
2.230
32
32
32
27
15
15
15
3
77
77
76
97
–
–
–
(DFT calculated)
(DFT calculated)
(experimental)
+
+
2
, 3, [2H] and [3H] in CH Cl (Table S3 in the Supporting porting Information). The similarity in the composition of
2
2
–
–
–
Information) provides support for the proposed view of the the SOMO in [1] , [2] and [3] is reflected in their very
electronic structure of these complexes. The UV/Vis spectra similar EPR spectra (Figure 5) and the almost identical spin
5
of 1, 2 and 3 are similar to those of other [(η -C H )Co- Hamiltonian parameters calculated for these complexes (see
5
5
(
ene-1,2-dithiolate)] compounds for which the low-energy Table 5). The values of these parameters closely correspond
–
1
–
band at ca. 17000 cm has been assigned to a HOMO to to those of [1] determined by simulation of the X-band
LUMO transition that involves orbitals with both ligand EPR spectrum of this anion recorded in DMF solution
59
and metal character on the basis that the band exhibits little containing [NnBu ][BF ] (0.2 m) at 77 K. The small Co (I
4
4
solvatochromism, in contrast to a transition with significant = 7/2, 100%) hyperfine couplings reflect the relatively mod-
charge transfer character.[ The LUMO – HOMO energy est Co contribution to the SOMOs of these anions (14.5–
difference shows a relatively small variation (ca. 0.1 eV) ac- 15.7% Table S2 in the Supporting Information).
22]
+
+
ross the series 1, 2, 3, [2H] and [3H] , and the low-energy
–
1
+
band between 17000 and 17400 cm in 1, 2, 3, [2H] and
3H] , which does not vary greatly in energy or intensity, is
+
[
assigned to the HOMOǞLUMO transition in each com-
plex.
The calculated theoretical UV/Vis absorption spectra of
1
, 2 and 3 possess a number of transitions above ca.
–
1
27400 cm (Figure 2 and Table S3 in the Supporting Infor-
mation). Using these calculated transitions as a guide sug-
–1
gests that the transitions between 33900–34400 cm , and
–1
for 1, 2 and 3 the shoulders between 24300 to 29400 cm ,
in the experimentally measured spectra (Figure 2) may be
broadly assigned to intraligand charge transfer (ILCT) pro-
cesses involving transitions from ene-1,2-dithiolate-based
orbitals to orbitals with phenyl, pyridin-3-yl or pyrazin-2-
yl π character. The absorptions around 26700 (ε =
–
1
–1
–1
–1
–1
7
800 m cm ) and 22300 cm (ε = 7600 m cm ) in 2 and
3, respectively, in the presence of excess TFA are attributed
to transitions between the HOMO and LUMO+1, the
HOMO-1 and LUMO+1 and the HOMO and LUMO+3
+
of [2H] and the HOMO-1 and LUMO+1 and the HOMO
–
–
–
Figure 6. α-Spin Kohn–Sham frontier orbitals of [1] , [2] , [3] , [2H]
+
and LUMO+3 of [3H] . The lower energy of these transi-
tions reflects the lower energy of the LUMO+1 and characters.
–3
and [3H] at the 0.05 eÅ isosurface level and their percentage
LUMO+3 orbitals when 2 and 3 are protonated.
The calculated theoretical UV/Vis absorption spectra of
–
–
–
[
1] , [2] and [3] in CH Cl solution show correspondences
2 2
Conclusions
with the experimentally measured spectra recorded spectro-
+
+
electrochemically for [2H] and [3H] in CH Cl containing
The information obtained from the structural characteri-
2
2
5
[
NnBu ][BF ] (0.4 m) at 273 K, including the depletion of zation of [(η -C H )Co{SC(H)CRS}] [SC(H)CRS, R =
4
4
5
5
–1
the relatively intense low-energy band at 17000–17100 cm
(
phenyl (1), pyridin-3-yl (2) or pyrazin-2-yl (3)], their electro-
ε = 6600–9100 m cm ) for 1, 2 and 3 (Figure S3 and chemical properties alone and in the presence of a 5:1 excess
–
1
–1
y
Table S4 in the Supporting Information).
of TFA, the UV/Vis spectroscopic characteristics of [1] ,
–
–
–
y
y
+
+
Unrestricted DFT calculations of [1] , [2] , [3] , [2H] and [2] and [3] (y = 0 or –1) and of [2H] and [3H] , plus the
–
–
–
[
3H] indicate that the SOMOs of all these complexes are EPR spectra of [1] , [2] and [3] , have been successfully
very similar and have Co dyz + dithiolene π + Cp character interpreted with the aid of information provided by DFT
3
with small (6–11%) contributions from the phenyl, pyridin- calculations. These calculations were concerned with the
y
y
y
3
-yl or pyrazin-2-yl orbitals (Figure 6, Table S2 in the Sup- electronic structure of [1] , [2] and [3] (y = 0 or –1) and of
Eur. J. Inorg. Chem. 2015, 3550–3561
3557
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
z
z
the monoprotonated forms [2H] and [3H] (z = +1 or 0) The UV/Vis spectroelectrochemical experiments were performed
with an optically transparent electrochemical (OTE) cell (in a
and indicated that, in all of the species investigated, the
modified quartz cuvette, optical path length: 0.5 mm). A three-elec-
trode configuration was employed; this consisted of a Pt/Rh gauze
working electrode, a Pt wire secondary electrode (in a fritted PTFE
sleeve), and a saturated calomel electrode (SCE) that was chemi-
cally isolated from the test solution by a bridge tube containing
electrolyte solution and terminated in a porous frit. The potential
at the working electrode was controlled by a Sycopel Scientific
HOMO is delocalized and involves contributions from the
Co and π orbitals of the ene-1,2-dithiolate and the R sub-
stituent. The significant shift to a more positive potential
for the one-electron reduction of 2 and 3 in the presence of
5
equiv. of TFA indicates that π conjugation involving an
ene-1,2-thiolate unit and the R substituent (i.e., a pendant
N-containing heterocyclic ring) can influence the redox DD10M potentiostat. UV/Vis spectra were recorded on a Perkin–
properties of the metal centre without a significant change Elmer Lamda 16 spectrophotometer; the cavity was purged with
in electronic structure and bonding of the moiety.
dinitrogen, and the temperature of the sample (273 K) was con-
trolled by flowing cooled dinitrogen across the cell surface. Sample
solutions were prepared under argon by use of Schlenk line
These studies suggest that, should a form of MPT in
which the pyran ring is open (Scheme 1) be integral to the
catalytic cycle of the Mo- and W-enzymes, this could facili-
tate the participation of the pterin in the redox activity of
the catalytic centres of these enzymes. In addition, given the
effect of protonation on the redox behaviour of 2 and 3, the
protonation of a pyran ring-opened form of MPT could
4 4 2 2
techniques; each contained [NnBu ][BF ] (0.2 m in CH Cl ) as the
–
3
supporting electrolyte and the compound (ca. 10 m) under investi-
gation. The test compound was electrolysed at a constant potential,
c
typically Ͼ100 mV more negative than E
p
for a reduction experi-
ment. The redox process was considered complete when consecu-
tive spectra were identical. The chemical reversibility of the process
provide a mechanism for linking the proton and electron was investigated by applying a potential at the working electrode
transfer that is essential for the catalytic action of the Mo- sufficient to re-oxidize the electrogenerated product. These poten-
a
and W-oxotransferase enzymes, see Equation (1).
tials were typically Ͼ100 mV more positive than E
p
, to reverse a
reduction process. The process was considered to be reversible if,
under the conditions of the experiment, the UV/Vis profile of the
starting material was reproduced at the end of the redox cycle.
Experimental Section
Bulk electrolysis experiments, at a controlled potential, were carried
out with a two-compartment cell. A Pt/Rh gauze basket working
electrode was separated from a wound Pt/Rh gauze secondary elec-
trode by a glass frit. A SCE was bridged to the test solution
through a Vycor frit that was orientated at the centre of the work-
ing electrode. The working electrode compartment was fitted with a
magnetic stirrer bar and the test solution was stirred rapidly during
electrolysis. An ice-water bath was used to maintain a temperature
General: All reagents were obtained from commercial sources
(Aldrich Chemical Company Ltd, Lancaster Synthesis Ltd., and
Fischer Scientific) and were used without further purification, un-
less otherwise stated. All reactions were carried out at room tem-
perature, unless otherwise stated. All reactions that involved a
metal derivative were accomplished by use of standard Schlenk line
techniques under argon and with anhydrous solvents. 4-Phenyl-1,3-
dithiol-2-one and 4-(pyridin-3-yl)-1,3-dithiol-2-one were prepared
4 4
of 0 °C. Each solution contained [NnBu ][BF ] (0.2 or 0.4 m) as
[
31]
by literature methods.
the supporting electrolyte and the compound under investigation
–
3
(
10 m) and was prepared by use of Schlenk line techniques.
Elemental analyses were performed in the Microanalytical
Laboratories of either the University of Nottingham or Ernst-
Moritz-Arndt-Universität (Greifswald, Germany). IR spectra were
recorded with a Nicolet Avatar 360 FTIR spectrometer. H and
NMR spectra were recorded with a JEOL EX270, Bruker
DPX 300, Bruker DPX 400 or Bruker AV 400 spectrometer, with
Details of the unit cell dimensions and of data collection and re-
finement for the crystal structure determinations of 1, 2 and 3 are
given in Table 6. Data for the structures of 1, 2 and 3 were collected
with a Bruker SMART APEX detector diffractometer, a Bruker
SMART 1000 CCD area detector diffractometer and a Rigaku Sa-
turn-724 diffractometer, respectively. Both Bruker systems were
1
13
C
the chemical shifts (δ) reported in ppm. Mass spectrometry was
performed with a Micromass 70E Spectrometer (EI ). HRMS equipped with an Oxford Cryosystems open flow cryostat. The
+
structures were solved by direct methods (SHELXS-97)[ and re-
33]
analyses were carried out with a Water-Micromass Q-ToF (quadru-
pole – Time of Flight) hybrid mass spectrometer equipped with an
orthogonal electrospray source (z-spray) or by use of a MALDI-
Q-ToF Premier system. All ToF measurements were performed at
high resolution settings (5000 FWHM at mass 1500). EPR spectra
were recorded with a Bruker EMX spectrometer, and spectra were
simulated by use of the MATLAB toolbox EasySpin.[
2
fined against all data by full-matrix least-squares methods on F
(SHELXL-97).[ All non-hydrogen atoms were refined with aniso-
tropic displacement parameters. The hydrogen atoms were refined
isotropically on calculated positions by use of a riding model with
their Uiso values constrained to 1.2 Ueq of their pivotal atoms.
33]
32]
Restricted and unrestricted DFT calculations were performed by
use of the Amsterdam Density Functional (ADF) suite version
2014.01.[ The DFT calculations employed a Slater-type orbital
(STO) all-electron triple-ζ-plus-one polarization function basis set
from the ZORA/TZP database of the ADF suite for all atoms.
Electrochemical measurements were performed with an Autolab
PGSTAT20 potentiostat with a three-electrode configuration con-
sisting of a saturated calomel electrode (SCE) reference electrode,
a Pt wire secondary electrode and a glassy carbon working elec-
34]
trode. All voltammograms were recorded at ambient temperatures The scalar relativistic (SR) approach was used within the ZORA
in CH
2
Cl
2
solutions (1 mm) containing 0.4 m [NnBu
4
][BF
4
] as the
Hamiltonian for the inclusion of relativistic effects, and the B3LYP
hybrid functional[ was used for the gas-phase geometry optimiza-
tions. The TDDFT calculations employed the B3LYP functional,
35]
supporting electrolyte and maintained under argon. All electro-
chemical potentials were measured relative to SCE and were cor-
5
+
[36]
rected for liquid-junction potentials by use of the [(η -C
5
H
5
)
2
Fe] /
and the conductor-like screening model (COSMO) was used to
5
+
[
(η -C
5
H
5
)
2
Fe] (Fc /Fc) couple as an internal redox standard. estimate the effect of CH
2
Cl
2
as a solvent on the electronic struc-
Compensation for internal resistance was not applied.
ture of the complexes in their gas-phase optimized geometries. Cal-
Eur. J. Inorg. Chem. 2015, 3550–3561
3558
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Table 6. Unit cell dimensions and data collection and refinement
(CDCl
3
, 400 MHz, 298 K): δ
H
= 8.91 (s, 1 H), 8.78 (d, J = 7.8 Hz,
for the crystal structures of 1, 2 and 3.
1 H), 8.52 (d, J = 7.1 Hz, 1 H), 5.71 (sept, J = 6.3 Hz, 1 H), 4.79
1
3
1
(
3
s, 2 H), 1.38 (d, J = 6.0 Hz, 6 H) ppm. C{ H} NMR (CDCl ,
1
2
3
7
4
5 MHz, 298 K): δ
0.1, 23.8 ppm. IR (KBr): ν˜ max = 1543 (C=N), 1735 (C=O) cm .
[M + H]+ 257.0418; found
C
= 215.3, 188.1, 154.8, 144.1, 143.2, 141.3, 66.3,
Empirical formula
C
13
H
11CoS
2
C
12
H
10CoNS
2
C
292.25
monoclinic
1
P 2 /n
11.912(2)
6.150(12)
15.995(3)
90
104.84(3)
90
1132.8(4)
4
1.852
11
H
9
CoN S
2 2
–1
M
290.27
monoclinic
C2/c
26.372(4)
5.7902(8)
16.324(2)
90
291.26
monoclinic
P2
7.3456(8)
18.783(2)
8.6882(9)
90
12 2 2 2
HRMS (EI): calcd. for C10H N O S
Crystal system
Space group
a [Å]
b [Å]
c [Å]
257.0335.
1
/c
4-Pyrazin-2-yl-[1,3]dithiolene-2-one (pzdt): A solution of O-iso-
propyl-S-[2-oxo-2-(pyrazin-2-yl)ethyl] carbonodithioate (6.98 g,
7.3 mmol) in a mixture of diethyl ether and dichloromethane (1:1,
2
α [°]
3
3
v/v, 30 cm ) was added slowly to a perchloric acid (70 cm ) solution
in an ice bath. The solution turned black and was allowed to warm
to room temperature. After 24 h stirring, the product was precipi-
tated by pouring into ice-cold water. The brown solid was collected
β [°]
γ [°]
V [Å]
Z
107.455(2)
90
2377.9(6)
8
106.245(2)
90
1150.9(2)
4
3
–1
3
μ [mm ]
1.760
1.820
by filtration and washed with distilled water (3ϫ 20 cm ). The ob-
Reflections collected
Independent reflec-
tions
6897
2734
13030
tained brown solid was recrystallized from chloroform and dried
in air for 2 h and then in an oven at 70 °C overnight, yield 47%,
2
958
0.030
.0455, 0.1290
2644
3382
–1
2
1
.53 g. Molecular formula: C
7
H
4
N
2
OS
2
(196.24 gmol ), m.p. 140–
R
int
0.042
0.0303,
0.0726
0. 0364
0.0592,
0.1925
1
41 °C. H NMR (CDCl
3
, 400 MHz, 298 K): δ = 8.85 (s, 1 H),
H
Final R
wR
1
[IϾ2σ(I)],
0
8.57 (d, J = 7.3 Hz, 1 H), 8.54 (d, J = 7.0 Hz, 1 H), 7.54 (s, 1
2
1
3
1
H) ppm. C{ H} NMR (CDCl
3 C
, 75 MHz, 298 K): δ = 191.1,
1
45.9, 143.6, 143.2, 140.1, 132.4, 117.2 ppm. IR (KBr): ν˜ max = 1759
–
1
–
–
–
(C=O), 1544 (C=N) cm . HRMS (ESI): calcd. for C
7 4 2 2
H N OS
culations of the spin Hamiltonian parameters of [1] , [2] and [3]
[
M + H]+ 196.9843; found 196.9860.
used the gas-phase geometry-optimized structures and the local
density approximation (LDA) with the correlation potential by Vo-
η5-Cyclopentadienyl(1-phenyl-l,2-dithiolato)cobalt(III) (1): Com-
[
37]
[38]
[39]
sko et al.
and gradient corrections by Becke
and Perdew
pound 1 was synthesized by a modification of the procedure de-
y
y
y
(
(
(
BP86). Coordinates for the initial models of [1] , [2] and [3]
y = 0 or –1) and the monoprotonated forms [2H] and [3H]
z = +1 or 0) used in the gas-phase geometry optimizations were
[17e]
scribed by Bradshaw et al.
2
CsOH·H O (0.40 g, 2.4 mmol) was
z
z
dissolved in MeOH (25 cm3), and 4-phenyl-1,3-dithiol-2-one
0.21 g, 1.1 mmol) was added. [(η -C
5
(
5
H
5
)Co(CO)I
2
]
(0.44 g,
derived from the X-ray crystal structures of 1, 2 and 3. Within the
co-ordinate frame employed in the calculations, the z-axis bisects
1.1 mmol) was added to the solution and a deep blue-coloured
solution was obtained and was stirred for 2 h at room temperature.
The solvent was then removed under vacuum, giving a black solid.
2
the S–M–S angle and the x-axis lies in the CoS plane. Pictorial
[40]
representations of the MOs were generated with molEKEL, and
3
This solid was extracted into ethyl acetate (4ϫ 50 cm ) and the
the orbital compositions were calculated with AOMIX.[
41]
fractions were combined, after which the blue solution was filtered.
The solvent was then removed from the filtrate under vacuum. The
2
-Bromo-1-(pyrazin-2-yl)ethanone: A solution of 2-pyrrolidinone
3
3
resultant black solid was dissolved in CH Cl (30 cm ), and n-hex-
hydrotribromide (21.8 g, 44.0 mmol) in tetrahydrofuran (80 cm )
was added dropwise to a solution of acetylpyrazine (4.88 g,
4
The reaction mixture was stirred for 48 h at room temperature,
which resulted in a discolouration of the solution. Then the reac-
tion mixture was cooled in an ice-bath, and cold water (30 cm )
was added until the formed precipitates had redissolved. The aque-
ous layer was extracted with toluene (3ϫ 20 cm ). The combined
organic extracts were washed with brine (50 cm ), dried with
4
MgSO , filtered, and the solvents were evaporated. The obtained
compound 1 was very unstable once isolated and consequently was
used immediately in situ for the next step (with toluene as a solvent)
without any further characterization.
2
2
3
ane (20 cm ) was added. The solution was concentrated to ca.
2 cm under vacuum, resulting in the precipitation of a dark solid.
3
3
0.0 mmol) in tetrahydrofuran (20 cm ) over a period of 10 min.
The mother liquor was removed with a pipette, to leave a dark-
coloured solid that was dried under vacuum, yield 109 mg, (34%).
1
3
H NMR (CDCl , 300 MHz, 298 K): δ = 9.01 (s, 1 H, 8-H), 7.78
3
(
d, J = 7.7 Hz, 2 H, 2-H, 6-H), 7.35 (m, 3 H, 3-H, 4-H, 5-H),
Cp 13
3
5.39 ppm (s, 5 H, H ). C NMR (CDCl , 75 MHz, 298 K): δ =
3
3
172.4 (C-7), 155.2 (C-8), 140.1 (C-1), 128.6 (C-3, C-5), 127.5 (C-4),
Cp
1
26.5 (C-2, C-6), 79.3 (C ) ppm. MS (EI): m/z = 290 [M], 188
[C
5
H
5
S
2
Co], 124 [C
5 5 10 2
H Co]. C13H S Co (289.28): calcd. C 53.8, H
3.8; found C 53.3, H 3.7.
η5-Cyclopentadienyl(1-pyridin-3-yl-1,2-dithiolato)cobalt(III)
(2):
O-Isopropyl-S-[2-oxo-2-(pyrazin-2-yl)ethyl] Carbonodithioate: Po- This compound was synthesized by a modification of procedure
17e]
tassium O-isopropyl carbonodithioate (7.40 g, 43.0 mmol) was
described by Bradshaw et al.[
2
CsOH·H O (0.82 g, 4.9 mmol) was
3
added in small portions to a solution of 2-bromo-1-(pyrazin-2-yl)-
dissolved in dry MeOH (20 cm ), 4-(pyridin-3-yl)-1,3-dithiol-2-one
3
ethanone (7.00 g, 35.0 mmol) in toluene (60 cm ) over a period of
(0.29 g, 1.5 mmol) was added, and the mixture was stirred for
5
30 min. The mixture was heated under reflux for 3 h and the pre-
5 min. [(η -C
5
H
5
)Co(CO)I
2
] (0.60 g, 1.5 mmol) was added, and the
cipitated KBr was removed by filtration. The remaining solvent
was evaporated from the reaction mixture, and then the solid resi-
due was treated with hydrochloric acid (2.5 m, 10 cm ) and stirred
deep blue coloured solution produced was stirred for 1.5 h. After
this time, the solvent was removed under vacuum and the resultant
black solid was subjected to flash column chromatography (sil-
3
for 30 min. The aqueous layer was extracted with diethyl ether (3ϫ
ica 60, CH
as a single band, and the solvent was removed from this under
vacuum, to leave a black solid. This solid was dissolved in CH Cl
2
2 2
Cl /MeOH 95:5, v/v). A dark blue fraction was collected
3
2
0 cm ). The combined organic extracts were washed with brine
3
(50 cm ), dried with MgSO
4
, filtered, and the solvent was evapo-
2
3
3
3
rated. The residue was washed with diethyl ether (2ϫ 10 cm ) and
(50 cm ), and n-pentane was (50 cm ) added. The solution was con-
3
dried to yield a yellowish brown solid, yield 79%, 7.10 g. Molecular
centrated to a volume of ca. 2 cm under vacuum, resulting in the
-
1
1
formula: C10
H
12
N
2
O
2
S
2
(256.34 gmol ), m.p. 98–99 °C. H NMR precipitation of a dark solid. The solid was separated by removing
Eur. J. Inorg. Chem. 2015, 3550–3561
3559
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
the mother liquor with a pipette, and dried under vacuum, yield
Ribbe, Y. Hu, K. O. Hodgson, B. Hedman, Chem. Rev. 2014,
114, 4063–4080.
2] G. Seiffert, G. Ullmann, A. Messerschmidt, B. Schink, P. Kro-
1
200 mg, (45%). H NMR (CDCl
3
, 300 MHz, 298 K): δ = 9.13 (br.
[
[
[
s, 1 H, 2-H), 9.00 (s, 1 H, 8-H), 8.69 (br. s, 1 H, 6-H), 8.08 (d, J =
Cp 13
neck, O. Einsle, Proc. Natl. Acad. Sci. USA 2004, 104, 3073–
7
.9 Hz, 1 H, 4-H), 7.28 (m, 1 H, 5-H), 5.41 ppm (s, 5 H, H ).
NMR (CDCl , 75 MHz, 298 K): δ = 167.9 (C-7), 155.6 (C-8), 148.5
C-6, C-3), 147.3 (C-2), 133.4 (C-4), 124.3 (C-5), 79.5 (C ) ppm.
MS (EI): m/z = 291 [M], 188 [C Co], 124 [C Co].
Co (291.28): calcd. C 49.5, H 3.4, N, 4.8; found C 49.3,
C
3
077.
3] a) R. R. Mendel, S. Leimkuhler, J. Biol. Inorg. Chem. 2015, 20,
37–347; b) S. Leimkuhler, M. M. Wuebbens, K. V. Rajagopa-
3
Cp
(
3
5
H
5
S
2
5 5
H
lan, Coord. Chem. Rev. 2011, 255, 1129–1144.
12 2
C H10NS
4] a) F. Schneider, J. Lowe, R. Huber, H. Schindelin, C. Kisker,
J. Knablein, J. Mol. Biol. 1996, 263, 53–69; b) C. Kisker, H.
Schindelin, D. C. Rees, Annu. Rev. Biochem. 1997, 66, 233–267;
c) D. C. Rees, Y. L. Hu, C. Kisker, H. Schindelin, J. Chem. Soc.,
Dalton Trans. 1997, 3909–3914; d) C. Kisker, H. Schindelin, D.
Baas, J. Retey, R. U. Meckenstock, P. M. H. Kroneck, FEMS
Microbiol. Rev. 1998, 22, 503–521; e) M. J. Romao, Dalton
Trans. 2009, 4053–4068; f) H. Dobbek, Coord. Chem. Rev.
2011, 255, 1104–1116.
H 3.7, N 4.3.
η5-Cyclopentadienyl(1-pyrazin-2-yl-1,2-dithiolato)cobalt(III)
(3):
This compound was synthesized by a modification of the procedure
[
17e]
described by Bradshaw et al.
NaOH (0.21 g, 2.5 mmol) was dis-
3
solved in dry EtOH (10 cm ), and 4-(pyrazin-2-yl)-1,3-dithiol-2-one
0.18 g, 0.90 mmol) was added. [(η -C
.00 mmol) in dry EtOH (5 cm ) was added, and the deep blue
5
(
1
5
H
5
)Co(CO)I
2
] (0.40 g,
3
[
[
[
[
5] R. Hille, J. Hall, P. Basu, Chem. Rev. 2014, 114, 3963–4038.
6] R. Hille, Chem. Rev. 1996, 96, 2757–2816.
coloured solution produced was stirred overnight. After this time,
the solvent was removed under vacuum, and the resultant black
solid was subjected to flash column chromatography (silica 60,
CH Cl /MeOH 99:1, v/v). A dark blue fraction was collected as a
2 2
single band, and the solvent was removed from this under vacuum,
7] G. N. George, R. C. Bray, Biochemistry 1988, 27, 3603–3609.
8] E. L. Klein, A. A. Belaidi, A. M. Raitsimring, A. C. Davis, T.
Krämer, A. V. Astashkin, G. Neese, G. Schwarz, J. H. Ene-
mark, Inorg. Chem. 2014, 53, 961–971.
9] a) J. McMaster, J. M. Tunney, C. D. Garner, in: Progress in
Inorganic Chemistry: Synthesis Properties, and Applications,
vol. 52 (Ed.: E. I. Stiefel), 2004, p. 539–583; b) R. H. Holm,
E. I. Solomon, A. Majumdar, A. Tenderholt, Coord. Chem.
Rev. 2011, 255, 993–1015.
to leave a dark blue solid. The solid was washed with methanol
[
3
(
2ϫ 10 cm ) and dried. The product was crystallized from dichlo-
romethane/hexane (5:2) to give blue shiny crystals that were suit-
1
able for X-ray diffraction, yield 88 mg (33%). H NMR (CDCl
3
,
4
00 MHz, 298 K): δ = 9.54 (s, 1 H, 8-H), 9.34 (s, 1 H, 3-H), 8.52
1
3
(br. s, 1 H, 5-H), 8.49 (br. s, 1 H, 6-H) 5.46 (s, 5 H, Cp) ppm.
C
[10] M. G. Bertero, R. A. Rothery, M. Palak, C. Hou, D. Lim, F.
NMR (CDCl
3
, 75 MHz, 298 K): δ = 165.45 (C-2), 160.18 (C-8),
Blasco, J. H. Weiner, N. C. J. Strynadka, Nat. Struct. Biol.
2003, 10, 681–687.
1
51.71 (C-7), 143.96 (C-3), 142.28 (C-5), 141.33 (C-6), 79.73
Cp
[11] D. P. Kloer, C. Hagel, J. Heider, G. E. Schulz, Structure 2006,
(C
) ppm. HRMS (MALDI-ToF): calcd. for C11
H
10CoN
2 2
S [M
H]+ 292.9617; found 292.9624. C11
14, 1377–1388.
+
H N S Co (292.26): calcd. C
9 2 2
[
[
12] a) J. H. Enemark, C. D. Garner, J. Biol. Inorg. Chem. 1997,
, 817–822; b) J. P. McNamara, J. A. Joule, I. H. Hillier, C. D.
45.20, H 3.10, N, 9.58; found C 44.89, H 3.87, N 9.37.
2
Garner, Chem. Commun. 2005, 177–179.
Supporting Information (see footnote on the first page of this arti-
13] R. Eisenberg, H. B. Gray, Inorg. Chem. 2011, 50, 9741–9751.
[14] a) C. Dong, J. Yang, S. Leimkühler, M. L. Kirk, Inorg. Chem.
cle): Experimentally measured and TDDFT-calculated UV/Vis ab-
+
+
sorption bands for 1, 2, [2H] , 3 and [3H] , geometry-optimized
2
014, 53, 7077–7079; b) B. Stein, M. Kirk, J. Biol. Inorg. Chem.
bond lengths, interbond, metalladithiolene fold and dithiolene –
2
015, 20, 183–194; c) R. Rothery, J. Weiner, J. Biol. Inorg.
–
–
–
z
z
aromatic ring plane angles for [1] , [2] , [3] , [2H] and [3H] (z =
+
Chem. 2015, 20, 349–372; d) M. Gómez, N. Neuman, S. Dalo-
sto, P. González, J. Moura, A. Rizzi, C. Brondino, J. Biol. In-
org. Chem. 2015, 20, 233–242; e) P. Basu, S. Burgmayer, J. Biol.
Inorg. Chem. 2015, 20, 373–383.
–
–
–
1, 0), fluid X-band EPR spectra of [1] , [2] and [3] , energy level
diagram and pictorial representations of the Kohn–Sham frontier
+
+
orbitals of 1, 2, [2H] , 3 and [3H] , the nature, energy and composi-
–
–
–
tion of the α-spin frontier orbitals of [1] , [2] , [3] , [2H] and [3H],
[15] R. A. Rothery, B. Stein, M. Solomonson, M. L. Kirk, J. H.
Weiner, Proc. Natl. Acad. Sci. USA 2012, 109, 14773–14778.
[16] J. L. Johnson, B. E. Hainline, K. V. Rajagopalan, J. Biol. Chem.
1980, 255, 1783–1786.
experimentally measured and DFT-calculated UV/Vis spectra of
[
1] , [2] and [3]y (y = 0 or –1), experimentally measured and
y
y
–
–
TDDFT-calculated UV/Vis absorption bands for [1] , [2] and
–
y
y
[17] a) E. M. Armstrong, M. S. Austerberry, J. H. Birks, R. L. Bed-
does, M. Helliwell, J. A. Joule, C. D. Garner, Heterocycles 1993,
[
3] , and gas-phase geometry-optimized coordinates for [1] , [2]
y
z
z
and [3] (y = 0 or –1) and [2H] and [3H] (z = +1 or 0).
35, 563–568; b) A. Dinsmore, J. H. Birks, C. D. Garner, J. A.
CCDC-1047105 (for 1), -1047106 (for 2) and -1047107 (for 3) con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Joule, J. Chem. Soc. Perkin Trans. 1 1997, 801–807; c) B. Brad-
shaw, A. Dinsmore, C. D. Garner, J. A. Joule, Chem. Commun.
1998, 417–418; d) B. Bradshaw, D. Collison, C. D. Garner, J. A.
Joule, Chem. Commun. 2001, 123–124; e) B. Bradshaw, A. Din-
smore, D. Collison, C. D. Garner, J. A. Joule, J. Chem. Soc.
Perkin Trans. 1 2001, 3232–3238; f) F.-A. Alphonse, R. Karim,
C. Cano-Soumillac, M. Hebray, D. Collison, C. D. Garner,
J. A. Joule, Tetrahedron 2005, 61, 11010–11019; g) B. R. Wil-
liams, Y. Fu, G. P. A. Yap, S. J. N. Burgmayer, J. Am. Chem.
Soc. 2012, 134, 19584–19587; h) I. V. Primov, A. A. Peterson,
D. N. Vaccarello, P. Basu, RSC Adv. 2014, 4, 19072–19076.
Acknowledgments
The authors thank the European Research Council (ERC) (project
MocoModels), the Engineering and Physical Sciences Research
Council (EPSRC), the University of Nottingham, UK, Trinity [18] a) A. Sugimori, T. Akiyama, M. Kajitani, T. Sugiyama, Bull.
College Dublin, Ireland, Ernst-Moritz-Arndt-Universität, Greifs-
wald, Germany and the European Union, COST Action CM1003
for generously supporting this work.
Chem. Soc. Jpn. 1999, 72, 879–908; b) K. Wang, in: Progress
in Inorganic Chemistry: Synthesis Properties, and Applications,
vol. 52 (Ed.: E. I. Stiefel), 2003, p. 267–314; c) N. Nomura, Dal-
ton Trans. 2011, 40, 2112–2140.
[
19] a) E. S. Davies, R. L. Beddoes, D. Collison, A. Dinsmore, A.
Docrat, J. A. Joule, C. R. Wilson, C. D. Garner, J. Chem. Soc.,
Dalton Trans. 1997, 3985–3996; b) E. S. Davies, G. M. Aston,
[
1] a) B. M. Hoffman, D. Lukoyanov, Z.-Y. Yang, D. R. Dean,
L. C. Seefeldt, Chem. Rev. 2014, 114, 4041–4062; b) M. W.
Eur. J. Inorg. Chem. 2015, 3550–3561
3560
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
R. L. Beddoes, D. Collison, A. Dinsmore, A. Docrat, J. A.
Joule, C. R. Wilson, C. D. Garner, J. Chem. Soc., Dalton Trans.
[28] a) S. Alvarez, R. Vicente, R. Hoffmann, J. Am. Chem. Soc.
1985, 107, 6253–6277; b) G. Periyasamy, N. A. Burton, I. H.
Hillier, M. A. Vincent, H. Disley, J. McMaster, C. D. Garner,
Faraday Discuss. 2007, 135, 469–488.
1998, 3647–3656.
[
20] a) E. M. Armstrong, M. S. Austerberry, R. L. Beddoes, M.
Helliwell, J. A. Joule, C. D. Garner, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun. 1993, 49, 1764–1766; b) H. W. Baird,
B. M. White, J. Am. Chem. Soc. 1966, 88, 4744–4745; c) R. L.
Beddoes, A. Dinsmore, M. Helliwell, C. D. Garner, J. A. Joule,
Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1997, 53,
[
29] F. E. Inscore, R. McNaughton, B. L. Westcott, M. E. Helton,
R. Jones, I. K. Dhawan, J. H. Enemark, M. L. Kirk, Inorg.
Chem. 1999, 38, 1401; F. E. Inscore, R. McNaughton, B. L.
Westcott, M. E. Helton, R. Jones, I. K. Dhawan, J. H. Ene-
mark, M. L. Kirk, Inorg. Chem. 1999, 38, 1401–1410.
30] Y.-H. Cui, W. Q. Tian, J.-K. Feng, Z.-Z. Liu, W.-Q. Li, THEO-
CHEM J. Mol. Struct. 2007, 810, 65–72.
2
13–215; d) M. R. Churchill, J. P. Fennesse, Inorg. Chem. 1968,
[
[
7, 1123–1129; e) M. Fourmigue, V. Perrocheau, Acta Crys-
tallogr., Sect. C: Cryst. Struct. Commun. 1997, 53, 1213–1215;
f) E. J. Miller, T. B. Brill, A. L. Rheingold, W. C. Fultz, J. Am.
Chem. Soc. 1983, 105, 7580–7584; g) C. Takayama, M. Kajit-
31] J. M. Tunney, A. J. Blake, E. S. Davies, J. McMaster, C. Wilson,
J. McMaster, Polyhedron 2006, 25, 591–598.
ani, T. Sugiyama, A. Sugimori, J. Organomet. Chem. 1998, 563, [32] S. Stoll, A. Schweiger, J. Magn. Reson. 2006, 178, 42–55.
161–171; h) C. Takayama, E. Suzuki, M. Kajitani, T. Sugi-
[33]
[
G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
34] a) G. te Velde, F. M. Bickelhaupt, S. J. A. van Gisbergen, C.
yama, A. Sugimori, Organometallics 1998, 17, 4341–4343.
21] J. A. McCleverty, Prog. Inorg. Chem. 1968, 10, 49–221.
22] F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G.
Orpen, R. Taylor, J. Chem. Soc. Perkin Trans. 2 1987, S1.
23] a) G. Goretzki, E. S. Davies, S. P. Argent, J. E. Warren, A. J.
Blake, N. R. Champness, Inorg. Chem. 2009, 48, 10264–10274;
b) H. J. Hartigan, G. Seeber, A. R. Mount, L. J. Yellowlees, N.
Robertson, New J. Chem. 2004, 28, 98–103; c) M. Kajitani, T.
Akiyama, A. Sugimori, K. Hirakata, Y. Hoshino, Y. Satsu,
G. P. Sato, K. Shimizu, M. Kaise, C. Nishihara, J. Electroanal.
Chem. 1988, 251, 421–428.
24] J. K. Hsu, C. J. Bonangelino, S. P. Kaiwar, C. M. Boggs, J. C.
Fettinger, R. S. Pilato, Inorg. Chem. 1996, 35, 4743–4751.
25] C. D. Garner, E. M. Armstrong, M. J. Ashcroft, M. S. Aus-
terberry, J. H. Birks, D. Collison, A. J. Goodwin, L. Larsen,
D. J. Rowe, J. R. Russell, in: Molybdenum Enzymes, Cofactors,
and Model Systems (Eds.: E. I. Stiefel, D. Coucouvanis, W. E.
Newton), American Chemical Society, 1993, p. 98–113.
26] a) F. E. Mabbs, D. Collison, Electron Paramagnetic Resonance
of d Transition Metal Compounds, Elsevier, Amsterdam, 1992;
b) C. Takayama, M. Kajitani, T. Sugiyama, T. Akiyama, K.
Shimizu, A. Sugimori, Organometallics 1997, 16, 3498–3503.
27] J. McCleverty, N. Atherton, J. Locke, E. J. Wharton, C. J. Win-
scom, J. Am. Chem. Soc. 1967, 89, 6082–6092.
[
[
Fonseca Guerra, E. J. Baerends, J. G. Snijders, T. Ziegler, J.
Comput. Chem. 2001, 22, 931–967; b) C. Fonseca Guerra, J. G.
Snijders, G. te Velde, E. J. Baerends, Theor. Chem. Acc. 1998,
[
99, 391–403; c) ADF2014, Theoretical Chemistry, Vrije Uni-
versiteit, Amsterdam, The Netherlands, http://www.scm.com.
35] P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J.
Phys. Chem. 1994, 98, 11623–11627.
[
[
36] a) A. Klamt, G. Schüürmann, J. Chem. Soc. Perkin Trans. 2
1
2
9
993, 799–805; b) A. Klamt, J. Phys. Chem. 1995, 99, 2224–
235; c) A. Klamt, V. Jones, J. Chem. Phys. 1996, 105, 9972–
981.
[
[
37] S. H. Vosko, L. Wilk, M. Nusair, Can. J. Phys. 1980, 58, 1200–
[
1
211.
[
[
[
[
38] A. D. Becke, Phys. Rev. A 1988, 38, 3098–3100.
39] J. P. Perdew, Phys. Rev. B 1986, 33, 8822–8824.
40] S. Portmann, H. P. Lüthi, Chimia 2000, 54, 766–770.
41] a) S. I. Gorelsky, AOMix: Program for Molecular Orbital
Analysis, http://www.sg-chem.net/, version 6.82, 2013; b) S. I.
Gorelsky, A. B. P. Lever, J. Organomet. Chem. 2001, 635, 187–
[
[
196.
Received: February 9, 2015
Published Online: April 22, 2015
Eur. J. Inorg. Chem. 2015, 3550–3561
3561
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim