Titanium and manganese complexes supported by a xanthene-bridged bis(tripodal N2O2) ligand: Isomerization, intramolecular hydrogen bonding and metal-binding ability

Article abstract of DOI:10.1039/c3dt51389k

A new bis(N₂O₂) ligand, L^4-, in which two tripodal diamine-bis(phenolate) moieties are bridged by a xanthene backbone, was prepared. The reaction of H₄L with 2 equiv. of [Ti(O ⁱPr)₄] produced C₂ and C_s symmetrical isomers of the dititanium(iv,iv) complex [Ti₂(L)(O ⁱPr)₄]. The isolated C₂ isomer was slowly converted to the C_s isomer via Ti-N bond cleavage to form a 3:2 mixture in equilibrium. A similar dimanganese(iii,iii) complex [Mn ₂(L)(OMe)₂(MeOH)₂] was synthesized from a 1:2 mixture of H₄L and manganese(ii) perchlorate in the presence of triethylamine. An X-ray analysis of [Mn₂(L)(OMe)₂(MeOH) ₂] revealed that two Mn-N₂O₄ octahedrons are connected by intramolecular hydrogen bonds as well as a xanthene bridge to form a C₂ symmetrical structure. The dimanganese(iii,iii) complex further reacted with manganese(ii) acetate to form the mixed-valence trimanganese(iii,ii,iii) complex [Mn₃(L)(μ-OMe) ₂(μ-OAc)₂]. Electrochemical data of the trimanganese(iii,ii,iii) complex indicated that the xanthene-bridged dimanganese(iii,iii) unit effectively binds a Mn^II ion in solution.

Full text of DOI:10.1039/c3dt51389k

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Titanium and manganese complexes supported by a
xanthene-bridged bis(tripodal N2O2) ligand:
isomerization, intramolecular hydrogen bonding and
metal-binding ability†
Cite this: DOI: 10.1039/c3dt51389k
Masakazu Hirotsu,*a Keisuke Kawamoto,a Rika Tanaka,b Yuji Nagai,c Keiji Ueno,c
Yoshio Tekia and Isamu Kinoshitaa
A new bis(N2O2) ligand, L4−, in which two tripodal diamine-bis(phenolate) moieties are bridged by a
xanthene backbone, was prepared. The reaction of H4L with 2 equiv. of [Ti(OiPr)4] produced C2 and Cs
symmetrical isomers of the dititanium(IV,IV) complex [Ti2(L)(OiPr)4]. The isolated C2 isomer was slowly con-
verted to the Cs isomer via Ti–N bond cleavage to form a 3 : 2 mixture in equilibrium. A similar dimanga-
nese(III,III) complex [Mn2(L)(OMe)2(MeOH)2] was synthesized from a 1 : 2 mixture of H4L and manganese(II)
perchlorate in the presence of triethylamine. An X-ray analysis of [Mn2(L)(OMe)2(MeOH)2] revealed that
two Mn–N2O4 octahedrons are connected by intramolecular hydrogen bonds as well as a xanthene
bridge to form a C2 symmetrical structure. The dimanganese(III,III) complex further reacted with
manganese(II) acetate to form the mixed-valence trimanganese(III,II,III) complex [Mn3(L)(μ-OMe)2(μ-OAc)2].
Electrochemical data of the trimanganese(III,II,III) complex indicated that the xanthene-bridged
dimanganese(III,III) unit effectively binds a MnII ion in solution.
Received 29th May 2013,
Accepted 21st June 2013
DOI: 10.1039/c3dt51389k
www.rsc.org/dalton
ions,15,16,20,21 and catalytic activity with cooperative
Introduction
effects.17–19,25–34
Bimetallic systems are constructed in a wide range of metallo-
We recently developed xanthene-bridged Schiff base com-
enzymes by using side chains of amino acid residues or heme plexes, which are derived from 5,5′-(9,9-dimethylxanthene-
groups.1–5 Various types of binucleating ligands have been 4,5-diyl)bis(salicylaldehyde) (H2xansal, Scheme 1).33–35 The
developed to investigate and modulate the enzymatic
function.2–7 Cofacial bisporphyrins with flexible linkers were
studied on catalytic reduction of dioxygen.6–10 Rigid spacer
molecules such as anthracene, xanthene and dibenzofuran
were used as a single pillar of bisporphyrins to provide a wide
range of pocket sizes, which can be tuned by the choice of the
spacers.6,7,9–19 The rigid spacers were also used for anchoring
other multidentate ligands.20–35 The pillared complexes show
an efficient binding ability for small molecules or metal
aDepartment of Chemistry, Graduate School of Science, Osaka City University,
Sumiyoshi-ku, Osaka 558-8585, Japan. E-mail: mhiro@sci.osaka-cu.ac.jp;
Fax: +816 6690 2753; Tel: +816 6605 2519
bX-ray Crystal Structure Analysis Laboratory, Graduate School of Engineering, Osaka
City University, Sumiyoshi-ku, Osaka 558-8585, Japan
cDepartment of Chemistry and Chemical Biology, Graduate School of Engineering,
Gunma University, Kiryu 376-8515, Japan
†Electronic supplementary information (ESI) available: NMR and absorption
spectral data and the results of DFT calculations. CCDC 941072 and 941073.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3dt51389k
Scheme 1 Synthesis of H4L.
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xansal-based ligand system provided cofacial dimanganese
complexes of tetradentate Schiff base ligands with cyclic or
U-shaped structures, which exhibit cooperative effects on the
enantioselectivity for the asymmetric oxidation of sulfides.34
Furthermore, a bis(ONO) Schiff base ligand derived from
H2xansal and 3-amino-1-propanol afforded tetranuclear
manganese complexes by anion-controlled assembly.35 On
the other hand, Ma et al. reported binuclear heteroligated
titanium(IV) complexes of phenoxyimine ligands with a xanthene
linker, which were used as a catalyst for olefin (co)polymeriz-
ation.29 The xansal-based platform shows a wide range of
M⋯M separations (3.4–7.9 Å); therefore the complexes could
provide a cavity for binding small molecules and metal ions.
In this study we designed a new xansal-based bis(N2O2)
ligand, L4−, in which two tripodal diamine-bis(phenolate) moi-
eties are bridged by a xanthene backbone (Scheme 1). Com-
plexes of oxophilic transition metals, such as Ti and Mn, and
the bis(N2O2) ligands would provide two octahedral complex
units with an N2O4 donor set in the presence of O-donor
ligands or solvents. The cavity surrounded by the coordinated
O atoms acts as a potential binding site for metal ions. In this
context, we synthesized dititanium(IV,IV), dimanganese(III,III)
and mixed-valence trimanganese(III,II,III) complexes of the L4−
ligand. Solution behaviour of the Ti2 complex and the metal-
binding ability of the Mn2 complex are reported.
Results and discussion
Ligand synthesis
Scheme 2 Structures of dititanium complexes: (a) C2 symmetrical isomer 1a,
(b) 1b (meso form) formed by isomerization of 1a, (c) a rotamer of 1b with Cs
symmetry, (d) a rotamer of 1b, (e) 1a’ formed by isomerization of 1b is an
enantiomer of 1a. Rotamers of 1a and 1a’ are also possible.
A xanthene-bridged diamine-bis(phenol), H4L, was synthesized
according to Scheme 1. Schiff base condensation of H2xansal
with 2 equiv. of N,N-dimethylethylenediamine was performed
and followed by reduction with NaBH4 to yield a bis(diamine-
phenol) intermediate. Reductive amination of salicylaldehyde
with the crude product produced H4L in 55% yield.
spectrum after the isomerization (δ 31.4, 31.7, toluene-d8,
Fig. S7, ESI†). Thus we assigned 1a and 1b to C2 and Cs
isomers, respectively. The isomerization of 1a to 1b in C6D6
Synthesis and characterization of titanium complexes
The protonated bis(N2O2) ligand H4L was treated with 2 equiv. was monitored by 1H NMR measurements at 40 °C (Fig. S5
of [Ti(OiPr)4] in diethyl ether to afford a yellow solution con- and S6, ESI†). The ratio of 1a and 1b in equilibrium was 3 : 2,
taining [Ti2(L)(OiPr)4]. The 1H NMR spectrum of the reaction which was observed at 10 h.
mixture showed the presence of two species, 1a and 1b, the
The isomerization process requires inversion of the
ratio of which was 6 : 5. The predominant product 1a was iso- absolute configuration around one of the two Ti centers
lated as a yellow crystalline powder from a toluene–THF–n- accompanied by inversion of the central N atom of the tripodal
hexane mixed solution at −30 °C in 50% yield. Isolation of the diamine-bis(phenolate) ligand unit. Variable temperature
other product (1b) from the filtrate was not successful.
NMR experiments of a mixture of 1a and 1b in toluene-d8 were
1
When the H NMR spectrum of 1a in C6D6 was measured carried out up to 90 °C in the equilibrium state (Fig. S8, ESI†),
after one day at room temperature, signals due to 1b appeared. and the thermodynamic parameters were determined: ΔH =
This suggests that 1a is isomerized to 1b. Structures of 1a and 2.5 kJ mol−1 and ΔS = 4.4 J mol−1 K−1 (Fig. S9, ESI†). Line
1b were estimated from mononuclear Ti complexes with broadening of the 1H NMR signals for the N(CH3)2 groups
diamine-bis(phenol) ligands.36 As shown in Scheme 2, C2 sym- (δ 2.23, 2.40 for 1a; 2.11, 2.34 for 1b at 20 °C) was observed
metrical (racemic) and Cs symmetrical (meso) structures are above 60 °C, suggesting the dynamic behaviour of the N,N-
1
possible for [Ti2(L)(OiPr)4]. The H and 13C NMR spectra of 1a dimethylaminoethyl arm in the isomerization. As illustrated
showed only one signal for two methyl groups of the xanthene in Scheme 2, a possible mechanism includes cleavage of the
backbone (δ 30.8, toluene-d8, Fig. S7, ESI†), while 1b showed Ti–N(terminal) bond, inversion of the central N atom, and
the two corresponding methyl signals in the 13C NMR recombination of the terminal N(CH3)2 group. The octahedral
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Ti–N2O4 units can rotate around the anchored C–C bonds to
avoid steric repulsion between them: the rotamers were not
detected in the NMR spectra at 0 °C. Density functional
theory (DFT) calculations of 1a and 1b showed that the opti-
mized structures have a small energy difference (E1b − E1a
=
0.816 kJ mol−1), which is consistent with the observed molar
ratio in the equilibrium state.
Synthesis and characterization of manganese complexes
The protonated ligand H4L reacted with 2 equiv. of Mn-
(ClO4)2·6H2O in the presence of triethylamine to give a
dark brown solution from which dark brown crystals of
[Mn2(L)(OMe)2(MeOH)2] (2) were obtained in 68% yield
(Scheme 3). A single crystal X-ray structure analysis of 2
revealed a dinuclear structure similar to the C2 symmetrical
structure of 1a (Fig. 1, Table 1). Complex 2 contains two octa-
hedral manganese(III) complex units, each of which has a
methanol, a methoxide, and an N2O2 tetradentate ligand. The
axial Mn–O(methanol) and Mn–N(terminal) bonds are signifi-
Fig. 1 (a) ORTEP drawing of 2 with thermal ellipsoids at the 50% probability
level. (b) Side view of 2. Hydrogen atoms are omitted for clarity except for those
of hydroxy groups of the coordinated methanol molecules.
Table 1 Selected bond distances (Å), angles (°) and dihedral angles (°) of 2
cantly longer than the equatorial bonds with chelating ONO Mn(1)–O(1)
1.931(2)
1.891(2)
1.868(3)
2.305(3)
2.119(3)
2.348(3)
2.704(3)
5.2542(11)
Mn(2)–O(5)
Mn(2)–O(6)
Mn(2)–O(7)
Mn(2)–O(8)
Mn(2)–N(3)
Mn(2)–N(4)
O(8)⋯O(1)
1.924(2)
1.880(2)
1.873(2)
2.309(3)
2.119(3)
2.375(3)
2.697(4)
Mn(1)–O(2)
and methoxide O donor atoms, which is consistent with a
Mn(1)–O(3)
Mn(1)–O(4)
Jahn–Teller distortion of high-spin d4 complexes. The Mn–N2O4
complex units are connected by hydrogen bonds between the Mn(1)–N(1)
Mn(1)–N(2)
O(4)⋯O(5)
Mn(1)⋯Mn(2)
OH group of the coordinated methanol and the phenolate
O atom: O4⋯O5, 2.704(3); O8⋯O1, 2.697(4) Å. The intramole-
cular hydrogen bonds stabilize the C2 symmetrical structure of 2.
Treatment of 3 equiv. of Mn(OAc)2·4H2O with H4L in the
presence of triethylamine afforded dark green crystals of the
O(1)–Mn(1)–O(3)
O(1)–Mn(1)–N(1)
O(2)–Mn(1)–N(1)
86.78(10)
90.09(10)
91.85(10)
96.98(11)
80.97(11)
O(5)–Mn(2)–O(7)
O(5)–Mn(2)–N(3)
O(6)–Mn(2)–N(3)
O(7)–Mn(2)–O(8)
N(3)–Mn(2)–N(4)
88.03(10)
92.46(10)
90.40(10)
94.85(11)
80.31(10)
trinuclear manganese complex [Mn3(L)(μ-OMe)2(μ-OAc)2] (3) O(3)–Mn(1)–O(4)
N(1)–Mn(1)–N(2)
(Scheme 3), which was structurally characterized using X-ray
Planes 1 and 3a
51.40(12)
Planes 2 and 4a
60.67(12)
crystallography (Fig. 2, Table 2). Three Mn ions are linearly
arranged, and the terminal Mn ions are bound to the diamine-
bis(phenolate) moieties. The central and terminal Mn ions are
bridged by two methoxide and two acetate ligands in addition
a Planes 1, 2, 3 and 4 are represented in Fig. 1.
Fig. 2 ORTEP drawing of 3 with thermal ellipsoids at the 30% probability level.
Hydrogen atoms are omitted for clarity.
to the two phenolate O atoms of L4−. Bond lengths around the
terminal Mn ions are similar to those of 2, suggesting the
d4 high-spin states of MnIII ions. In 3, the Mn(central)–
O(phenolate) and Mn(central)–O(methoxide) bonds are sig-
nificantly longer than the Mn(terminal)–O(phenolate) and
Scheme 3 Synthesis and structures of manganese complexes 2 and 3.
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complex 2 exhibits an absorption band at 480 nm (sh, ε =
2400 dm3 mol−1 cm−1), which is assignable to charge transfer
(CT) transitions involving the MnIII ion and the phenolate moi-
eties. A similar CT band was observed for the trinuclear
MnIIIMnIIMnIII complex 3 at 442 nm (ε = 2320 dm3 mol−1
cm−1). Although analogous MnIIIMnIIMnIII complexes with no
xanthene bridge show similar absorption spectra in dichloro-
methane,37 their electrochemical behaviour is different from
that of 3, as described below.
Table 2 Selected bond distances (Å), angles (°) and dihedral angles (°) of 3
Mn(1)–O(1)
Mn(1)–O(2)
Mn(1)–O(3)
Mn(1)–O(4)
Mn(1)–N(1)
Mn(1)–N(2)
Mn(3)–O(1)
Mn(3)–O(3)
Mn(3)–O(5)
Mn(1)⋯Mn(3)
Mn(1)⋯Mn(2)
1.913(3)
1.887(3)
1.892(3)
2.218(4)
2.092(4)
2.385(4)
2.230(3)
2.148(3)
2.141(3)
3.1415(14)
6.276(2)
Mn(2)–O(6)
Mn(2)–O(7)
Mn(2)–O(8)
Mn(2)–O(9)
Mn(2)–N(3)
Mn(2)–N(4)
Mn(3)–O(6)
Mn(3)–O(8)
Mn(3)–O(10)
Mn(2)⋯Mn(3)
1.932(3)
1.865(3)
1.870(4)
2.217(3)
2.099(4)
2.350(4)
2.245(3)
2.148(3)
2.150(3)
3.1363(14)
Magnetic properties of manganese complexes
O(1)–Mn(1)–O(3)
O(1)–Mn(1)–N(1)
O(2)–Mn(1)–N(1)
O(3)–Mn(1)–O(4)
N(1)–Mn(1)–N(2)
O(1)–Mn(3)–O(3)
O(5)–Mn(3)–O(10)
Mn(1)–O(1)–Mn(3)
Mn(1)–O(3)–Mn(3)
82.92(13)
91.18(13)
93.39(14)
93.83(15)
79.74(13)
70.22(11)
171.37(13)
98.34(12)
101.88(13)
O(6)–Mn(2)–O(8)
O(6)–Mn(2)–N(3)
O(7)–Mn(2)–N(3)
O(8)–Mn(2)–O(9)
N(3)–Mn(2)–N(4)
O(6)–Mn(3)–O(8)
Mn(1)–Mn(3)–Mn(2)
Mn(2)–O(6)–Mn(3)
Mn(2)–O(8)–Mn(3)
83.62(13)
91.58(14)
92.61(16)
94.41(14)
81.57(18)
70.44(12)
177.57(3)
97.06(12)
102.38(15)
Magnetic susceptibility data of 2 and 3 were measured in the
temperature range of 4.3–300 K and are shown in Fig. 3 in the
form of χmolT vs. T. The χmolT values of 2 and 3 at 300 K are
5.80 and 9.89 cm3 K mol−1, respectively, which are close to the
spin only values expected for high-spin MnIIIMnIII (6.0 cm3 K
mol−1) and MnIIIMnIIMnIII (10.4 cm3 K mol−1) systems with g =
2.0. Decrease of the χmolT values at lower temperatures indi-
cates antiferromagnetic interactions between Mn ions.
Planes 1 and 3a
54.81(17)
Planes 2 and 4a
51.19(18)
a Planes 1, 2, 3 and 4 are represented in Fig. 2.
The susceptibility data for the dinuclear complex 2 (S1 = 2,
S2 = 2) were analyzed based on the spin Hamiltonian H =
–2JS1·S2, where J is the exchange interaction between the two
MnIII ions. The magnetic parameters are J = −0.41 cm−1 and g
= 1.97, which were obtained from a least-squares fitting pro-
cedure for a theoretical expression derived using the Van Vleck
equation.41 The results reveal weak antiferromagnetic
exchange interactions between two MnIII ions, which are con-
nected through hydrogen bonds.
Mn(terminal)–O(methoxide) bonds, respectively. Therefore the
central Mn ion was assigned to the divalent state with a high-
spin d5 configuration. The xanthene-bridged bis(N2O2) ligand
L4− encapsulates three Mn ions to form a mixed-valence
MnIIIMnIIMnIII complex.
We have reported that the linear type MnIIIMnIIMnIII com-
2−
plexes [Mn3(LN O )2(μ-OMe)2(μ-carboxylate)2], where LN O
2
2
2
2
The spin Hamiltonian for the mixed-valence MnIIIMnIIMnIII
complex 3 is given by H = −2(J12S1·S2 + J13S1·S3 + J23S2·S3),
where S1 = S2 = 2 for the terminal MnIII ions and S3 = 5/2 for
denotes diamine-bis(phenolate)-type tripodal tetradentate
ligands, are obtained by the reaction of H2LN O , carboxylic
2
2
acids and manganese(II) salts in methanol in the presence of
bases.37–39 The trinuclear structure of 3 is similar to those of
[Mn3(LN O )2(μ-OMe)2(μ-carboxylate)2] except for the orientation
the central MnII ion. An exchange coupling constant, J = J13
=
J23, was used for evaluating the major interactions between
MnIII and MnII, and the exchange interaction between the
terminal MnIII ions was excluded ( J12 = 0) because of the large
MnIII⋯MnIII distance. An expression for the molar magnetic
2
2
2−
of the methoxide ligands: the trinuclear complexes of LN O
2
22−
have Ci symmetry, while 3 has C2 symmetry. In the LN O
2
2
system, the M(LN O ) unit (M = MnIII, FeIII) acts as a ligand
2
2
toward MnII ions.37–40 The dimanganese complex unit Mn2(L)
in 3 can be regarded as a chelate ligand encapsulating MnII
ions. To confirm the metal binding character of the Mn2(L)
unit, the reaction of 2 with 1.1 equiv. of Mn(OAc)2·4H2O was
carried out to give 3 in 82% yield.
Complexes 2 and 3 show different MnIII⋯MnIII separations:
5.2542(11) Å for 2 and 6.276(2) Å for 3. The flexible structure is
related to the rotation of the octahedral Mn–N2O4 units
around the anchoring C–C bonds. The dihedral angles
between the two connected benzene rings for 2 (51.40(12)
and 60.67(12)°) are similar to those for 3 (54.81(17) and
51.19(18)°); however, the folding structures of 2 and 3 are
different from each other. Complex 2 is highly folded because
of the intramolecular hydrogen bonds. The MnIII⋯MnIII dis-
tance in 2 is similar to those in xanthene-bridged Schiff base
dimanganese(III,III) complexes, which also have intramolecular
hydrogen bonds.33,34
Fig. 3 Temperature dependence of χT for 2 (open circle) and 3 (blue open
square). Solid lines represent the least-squares fits of the data to the model
described in the text.
Electronic absorption spectra of 2 and 3 showed intense
bands in the visible region (Fig. S10, ESI†). Dimanganese(III,III)
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susceptibility is derived using the Van Vleck equation.42 The retained after the oxidation, while the xanthene-bridged ligand
least-squares fitting of the experimental data with this model stabilizes the trinuclear structure of 3, which is retained even
gives J = −1.65 cm−1 and g = 2.00. Analogous mixed-valence after the oxidation.
MnIIIMnIIMnIII complexes with no xanthene bridge show weak
antiferromagnetic or ferromagnetic interactions in the range
of J = −0.25 to 1.43 cm−1, which are dependent on the bridging
carboxylates.37–39
Conclusions
A xanthene-bridged dimer of N,N-dimethyl-N’,N’-bis(2-hydroxy-
benzyl)ethylenediamine, H4L, provided dititanium(IV,IV) and
dimanganese(III,III) complexes with additional alkoxide or
alcohol ligands. Both complexes have two N2O4 octahedral
complex units bearing the tripodal diamine-bis(phenolate)
ligand. The octahedral Ti complex unit undergoes inversion of
the central amine moiety, which results in isomerization of
the Ti2 complex. The isomerization process is related to the
dynamic behaviour of the N,N-dimethylaminoethyl arm in
the diamine-bis(phenolate) moieties. On the other hand, the
complex units in the Mn2 complex are connected by intramole-
cular hydrogen bonds in the solid state, but the solution struc-
ture is not clear.
The dimanganese(III,III) complex acts as a chelate ligand
toward a MnII ion to form a mixed-valence trimanganese-
(III,II,III) complex. This trinuclear structure is retained in
dichloromethane, which enables the observation of a quasi-
reversible MnIII/MnII couple for the central Mn ion in the
cyclic voltammogram. The xanthene-bridged bis(N2O2) ligand
is a useful platform to investigate the function of multimetallic
systems both in the solid state and in solution. Studies on
other multimetallic complexes supported by the bis(N2O2)
ligand are currently under way.
Electrochemical properties of manganese complexes
Electrochemical characterization of 2 and 3 was carried out
using cyclic voltammetry (Fig. 4). The cyclic voltammogram of
2 exhibits several oxidation and reduction waves, suggesting
substitution of methanol and methoxide ligands or isomeriza-
tion as observed for 1. In 3, two redox couples were observed
in the oxidation region. The first oxidation potential is more
positive than that of 2: E1/2 = 0.10 V vs. E°′(Fc+/Fc) (ΔEp
=
116 mV). The first wave is due to the oxidation of the central
MnII ion to give the MnIII complex 3+. This is followed by the
3
second oxidation at Epa = ∼0.55 V, forming 32+, which is likely
because of the oxidation of the terminal MnIII ion to MnIV. A
further positive scan resulted in a large oxidation current and
loss of the cathodic waves in the reverse scan, which is due to
the adsorption of the decomposed complex on the electrode.
In the reduction process, only one reduction wave was
observed at a more positive potential compared with the
reduction of 2. This is attributable to the presence of
the central MnII ion, which makes the +3 oxidation state of the
terminal manganese ions unstable.
The cyclic voltammogram of the mixed-valence MnIIIMnIIMnIII
complexes with no xanthene bridge [Mn3(L′)2(μ-OMe)2(μ-O2CPh)2]
(4, H2L′ = N,N-dimethyl-N′,N′-bis(2-hydroxybenzyl)ethylenedi-
amine) was compared with that of 3 (Fig. 4). A similar oxi-
dation wave was observed at Epa = 0.16 V. The corresponding
cathodic wave, however, was not observed in the reverse scan,
which is in contrast to the two redox couples observed for 3
described above. Therefore the trinuclear structure of 4 is not
Experimental
General procedures
Manipulations of titanium compounds were performed using
a glove box under an atmosphere of oxygen-free dry nitrogen
or standard Schlenk techniques under a nitrogen atmosphere.
Ligands and diethyl ether, hexane, tetrahydrofuran (THF) and
toluene were dried by refluxing over sodium benzophenone
ketyl followed by distillation under a nitrogen atmosphere.
Other chemicals were purchased from commercial sources and
used as received. Syntheses of ligands and manganese com-
plexes were carried out under ambient conditions. N,N-
dimethylethylenediamine, salicylaldehyde, was purchased
from Tokyo Chemical Industry Co., Ltd. 5,5′-(9,9-Dimethyl-
xanthene-4,5-diyl)bis(salicylaldehyde)33,34
(H2xansal)
and
[Mn3(L′)2(μ-OMe)2(μ-O2CPh)2]37 (4) were prepared according to
literature procedures. NMR spectra were recorded on a Bruker
AVANCE 300 FT-NMR spectrometer at room temperature.
IR spectra were recorded on a JASCO FT/IR-6200 spectrometer
with an attenuated total reflection (ATR) accessory. Elemental
analyses were performed by the Analytical Research Service
Center at Osaka City University on J-SCIENCE LAB JM10 or
FISONS Instrument EA1108 elemental analyzers.
Fig. 4 Cyclic voltammograms of 2 (5 × 10−4 M, - - -), 3 (5 × 10−4 M, —) and 4
(5 × 10−4 M, ⋯) in CH2Cl2 containing 0.10 M Bu4NPF6: scan rate, 100 mV s−1
;
working electrode, glassy carbon; auxiliary electrode, platinum wire; reference
electrode, Ag/Ag+. Potentials are versus ferrocenium/ferrocene (Fc+/Fc).
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Preparation of ligands
suspension was stirred at room temperature for 2 h to afford a
clear yellow solution. The solution was concentrated to
dryness under reduced pressure. The residue was dissolved in
tetrahydrofuran (1 mL) and toluene (1 mL) and then n-hexane
(6 mL). The solution was cooled at −30 °C to afford a yellow
precipitate of 1a (0.19 g, 50%). 1H NMR (300 MHz, C6D6):
δ 1.12 (d, J = 6.0 Hz, 6H, OCH(CH3)2), 1.21 (d, J = 6.0 Hz, 6H,
OCH(CH3)2), 1.56 (d, J = 6.0 Hz, 6H, OCH(CH3)2), 1.58 (d, J =
6.0 Hz, 6H, OCH(CH3)2), 1.55–1.60 (6H, xan-C(CH3)2),
1.65–1.80 (m, 2H, NCH2CH2N), 2.00–2.18 (m, 6H, NCH2CH2N),
2.22 (s, 6H, N(CH3)2), 2.41 (s, 6H, N(CH3)2), 2.83 (d, J = 12.9 Hz,
2H, ArCH2N), 2.85 (d, J = 13.2 Hz, 2H, ArCH2N), 4.42 (d, J =
13.2 Hz, 2H, ArCH2N), 4.43 (d, J = 12.6 Hz, 2H, ArCH2N), 4.87
(sept, J = 6.0 Hz, 2H, OCH(CH3)2), 5.28 (sept, J = 6.0 Hz, 2H,
OCH(CH3)2), 6.61–7.67 (m, 20H, Ar + xan). 13C{1H} NMR
(75.5 MHz, C6D6): δ 26.24 (OCH(CH3)2), 26.42 (OCH(CH3)2),
26.48 (OCH(CH3)2), 26.70 (OCH(CH3)2), 31.09 (xan-C(CH3)2),
35.10 (xan-C(CH3)2), 48.92 (N(CH3)2), 49.32 (N(CH3)2), 51.14
(NCH2CH2N), 58.51 (NCH2CH2N), 64.64 (ArCH2), 64.70
(ArCH2), 77.46 (OCH(CH3)2), 77.83 (OCH(CH3)2), 116.68 (Ar +
xan), 117.39, 117.76, 123.53, 123.84, 125.19, 125.22, 127.93,
129.83, 130.15, 130.84, 131.46, 131.77, 132.37, 149.31 (xan-
COC), 163.05 (Ti–O(phenolate)-C), 163.76 (Ti–O(phenolate)-C).
Anal. Calc. for C63H82N4O9Ti2·0.5C4H8O·0.5C6H14: C, 67.26; H,
7.72; N, 4.61. Found: C, 67.50; H, 7.70; N, 4.56%.
H4L. To a suspension of H2xansal (0.63 g, 1.4 mmol) in
methanol (20 mL) was added a solution of N,N-dimethylethylene-
diamine (0.28 g, 3.2 mmol) in methanol (10 mL). The resulting
yellow suspension was refluxed for 1 h and then cooled to
room temperature. Sodium borohydride (0.11 g, 2.8 mmol)
was added, followed by stirring at room temperature for 3 h.
After removal of solvent, chloroform (30 mL) and an aqueous
sodium carbonate solution (2 g per 50 mL) were added, and
the solution was stirred. The aqueous layer was separated
and extracted with chloroform (30 mL). The organic layer and
extract were combined, washed with water (100 mL × 2), dried
over Na2SO4 and concentrated to dryness to give a yellow oily
residue (0.8 g). 1H NMR (300 MHz, CDCl3): δ 1.71 (s, 6H,
C(CH3)2), 2.25 (s, 12H, N(CH3)2), 2.46 (t, J = 6 Hz, 4H,
NCH2CH2N) 2.67 (t, J = 6 Hz, 4H, NCH2CH2N), 3.54 (s, 4H,
ArCH2N), 6.73 (d, J = 8.3 Hz, 2H), 6.92 (d, J = 1.7 Hz, 2H),
7.05–7.22 (m, 6H), 7.37 (dd, J = 7.3, 1.8 Hz, 2H). The residue
was dissolved in methanol (50 mL), and salicylaldehyde
(0.39 g, 3.2 mmol) in methanol (10 mL) was added. The solu-
tion was slightly acidified by a HCl methanol solution. Sodium
cyanoborohydride (0.40 g, 6.4 mmol) was added, and the reac-
tion mixture was stirred at room temperature for 9 h to give a
pale yellow solution. After removal of solvent, chloroform
(30 mL) and an aqueous sodium carbonate solution (2 g per
50 mL) were added, and the solution was stirred. The aqueous
solution was separated and extracted with chloroform (30 mL).
The organic layer and the extract were combined and washed
with water (100 mL). The resulting pale yellow solution was
dried over Na2SO4 and concentrated to dryness. The pale
orange residue was recrystallized twice from dichloromethane–
methanol to afford a white powder of H4L (0.62 g, 55%). 1H
NMR (300 MHz, C6D6): δ 1.56 (s, 6H, C(CH3)2), 2.04 (s, 12H,
N(CH3)2), 2.06–2.20 (m, 8H, NCH2CH2N), 3.18 (s, 4H, ArCH2N),
3.25 (s, 4H, ArCH2N), 6.75 (td, J = 7.2, 1.4 Hz, 2H) 6.88 (dd, J =
7.4, 1.4 Hz, 2H), 6.96–7.11 (m, 8H), 6.96–7.11 (m, 8H),
[Mn2(L)(OMe)2(MeOH)2] (2). Solid H4L (50 mg, 0.062 mmol)
was added to
a solution of Mn(ClO4)2·6H2O (45 mg,
0.12 mmol) in methanol (10 mL). The reaction mixture was
stirred for 1 h to give a red-brown solution. Triethylamine
(52 μL, 0.37 mmol) was added, and the resulting dark brown
solution was stirred for 3 h. Dark brown solid was precipitated,
collected by filtration and washed with methanol. The product
was recrystallized from dichloromethane–methanol to give 2
as dark brown crystals. Yield: 49 mg, 68%. Anal. Calc. for
C55H68Mn2N4O9·2H2O·CH2Cl2: C, 57.98; H, 6.43; N, 4.83.
Found: C, 57.55; H, 6.24; N, 5.32%. IR (ATR, cm−1): 1595, 1498,
1480, 1455, 1432, 1415, 1276, 1242, 958, 883, 794, 758, 752,
636, 619, 607, 579, 563. UV-Vis, λmax(CH2Cl2)/nm (ε/dm3 mol−1
cm−1): 680 sh (760), 480 sh (2450), 350 sh (8200), 305 sh
(34 600), 275 (42 200).
[Mn3(L)(μ-OMe)2(μ-OAc)2] (3). A mixture of H4L (50 mg,
0.062 mmol), Mn(OAc)2·4H2O (46 mg, 0.19 mmol), and metha-
nol (10 mL) was stirred at room temperature for 1 h. To the
resulting dark brown suspension was added triethylamine
(35 μL, 0.25 mmol). The mixture was stirred at room temp-
erature for 1 h to give a dark green suspension. A dark green
precipitate was collected by filtration and washed with metha-
nol. The product was recrystallized from dichloromethane–
methanol to give 3 as dark green needles. Yield: 50 mg, 67%.
Anal. Calc. for C57H66Mn3N4O11·0.5CH3OH·0.5CH2Cl2: C,
57.74; H, 5.76; N, 4.64. Found: C, 57.37; H, 5.71; N, 4.93%. IR
(ATR, cm−1): 1568 [νa (COO)], 1503, 1480, 1456, 1434, 1412
[νs (COO)], 1275, 1238, 1055, 1030, 958, 884, 794, 746, 651, 634,
1
7.16–7.29 (m, 8H), 10.03 (s, br, 4H, OH). H NMR (300 MHz,
CDCl3): δ 1.69 (s, 6H, C(CH3)2), 2.29 (s, 12H, N(CH3)2),
2.44–2.56 (m, 8H, NCH2CH2N), 3.25 (s, 4H, ArCH2N), 3.52
(s, 4H, ArCH2N), 6.70 (d, J = 8.3 Hz, 2H), 6.72 (td, J = 7.3,
1.1 Hz, 2H), 6.79 (dd, J = 8.1, 1.0 Hz, 2H), 6.95 (dd, J = 7.4,
1.5 Hz, 2H), 7.01 (d, J = 2.2 Hz, 2H), 7.06–7.20 (m, 8H), 7.37
(dd, J = 7.6, 1.8 Hz, 2H), 10.00 (s, 4H, OH). 13C{1H} NMR
(75.5 MHz, CDCl3): δ 31.9 (C(CH3)2), 34.6 (C(CH3)2), 44.9
(N(CH3)2), 49.1 (NCH2CH2N), 54.9, 56.05, 56.18 (NCH2CH2N,
ArCH2N, ArCH2N), 116.4, 116.6, 119.1, 121.9, 122.5, 122.9,
124.2, 128.3, 128.8, 129.1, 129.7, 129.9, 130.4, 130.8, 132.4,
147.7 (COC), 156.0 (COH), 157.0 (COH). Anal. Calc. for
C51H58N4O5: C, 75.90; H, 7.24; N, 6.94. Found: C, 75.62; H,
7.21; N, 6.76%.
Preparation of complexes
[Ti2(L)(OiPr)4] (1a). To a solution of [Ti(OiPr)4] (0.19 mL, 583. UV-Vis, λmax(CH2Cl2)/nm (ε/dm3 mol−1 cm−1): 612 (780),
0.63 mmol) in diethyl ether (4 mL) was added solid H4L 574 (750), 470 sh (1970), 442 (2320), 340 sh (9010), 305 sh
(0.25 g, 0.31 mmol) with stirring. The resulting yellow (30 400), 268 (40 100).
Dalton Trans.
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Conversion of 2 to 3. Complex 2 (20.0 mg, 0.017 mmol) was Magnetic susceptibility measurements
dissolved in dichloromethane (2 mL), and a methanol solution
The magnetic susceptibility measurements were carried out
for 2 and 3 by using a superconducting quantum interference
device (SQUID) magnetometer (Quantum Design MPMS2) in
the temperature range 4.3–300 K. The applied magnetic field
was 0.1 T. The diamagnetic components were estimated from
Pascal’s constants.
(2 mL) of Mn(OAc)2·4H2O (4.6 mg, 0.019 mmol) was added to
it. After stirring at room temperature for 3 h, the resulting
dark green-brown solution was filtered through Celite. The fil-
trate was allowed to stand overnight at room temperature to
afford dark green crystals of 3, which were collected by fil-
tration. Yield: 17.1 mg, 82%.
Electrochemistry
X-ray crystallography
Cyclic voltammetric measurements were performed at room
temperature using an ALS/CHI600A voltammetric analyzer
(Bioanalytical Systems Inc.). The working, reference, and
counter electrodes were a glassy carbon disk electrode with a
diameter of 3 mm (Bioanalytical Systems Inc.), a Ag/Ag+ (0.01 M
AgNO3, 1 M = 1 mol dm−3) reference electrode, and a platinum
wire, respectively. Sample solutions in dichloromethane were
prepared at the concentration of 5 × 10−4 M and the supporting
electrolyte was Bu4NPF6 (0.1 M). The observed potentials were
corrected using the redox potential of ferrocenium/ferrocene
(Fc+/Fc) obtained under the same conditions. The sample solu-
tions were degassed using N2 prior to each measurement.
Diffraction data of 2 and 3 were collected on a Rigaku AFC7/
Mercury CCD diffractometer and a Rigaku AFC11/Saturn 724+
CCD diffractometer, respectively, with monochromated Mo-Kα
radiation (λ = 0.7107 Å). The data were processed and corrected
for Lorentz and polarization effects using the CrystalClear soft-
ware package.43 Absorption corrections were applied using the
Multi Scan method. The structures were solved using direct
methods (SIR9744 for 2 and SHELXS9745 for 3) and refined by
full-matrix least-squares on F2 using SHELXL97.45 All non-
hydrogen atoms were refined anisotropically except for dis-
ordered methanol molecules in 3. Hydrogen atoms on co-
ordinated methanol O atoms and a water O atom in 2, and on
O atoms of methanol molecules in 3 were located in a differ-
ence Fourier map. Other hydrogen atoms were located on
calculated positions with C–H(aromatic) = 0.95 Å, C–H(methyl) =
0.98 Å, C–H(methylene) = 0.99 Å and O–H = 0.84 Å. Hydrogen
atoms were refined using a riding model with Uiso(H) =
1.5Ueq(C) for methyl groups and 1.2Ueq(C) for other H atoms,
except that the hydroxy H atoms of coordinated methanol
molecules in 2 were refined isotropically. There are solvent-
accessible voids in the structure of 3. The total void volume
calculated by PLATON is 2417 Å3 per unit cell (23.7%).46 The
largest void is centered at the origin (2332 Å3), which is filled
with heavily disordered solvent molecules. The data were cor-
rected with the SQUEEZE procedure implemented in PLATON
to remove the contribution of the disordered solvent molecules
to the structure factors. The SQUEEZE program suggested that
the void space contains three dichloromethane and three
methanol molecules per unit cell, which were removed from
the model, but included in the formula.
Crystal data for 2. C58H80ClMn2N4O12, M = 1170.59, mono-
clinic, a = 36.540(7), b = 12.330(3), c = 25.680(6) Å, β = 92.290(3)°,
V = 11 561(4) Å3, T = 150 K, space group C2/c (no. 15), Z = 8,
Dcalcd = 1.345 Mg m−3, μ = 0.547 mm−1, F(000) = 4952.00,
44 290 reflections measured, 12 938 independent reflections
(Rint = 0.0655) which were used in all calculations. The final
R indices were R1 [I > 2σ(I)] = 0.0835 and wR2 (all data) =
0.1579. GOF = 1.230. CCDC 941072.
Crystal data for 3. C59H73ClMn3N4O12.5, M = 1238.48, tri-
gonal, a = 28.354(12), c = 14.616(6) Å, V = 10 177(7) Å3, T = 133 K,
space group P3121 (no. 152), Z = 6, Dcalcd = 1.213 Mg m−3, μ =
0.645 mm−1, F(000) = 3882.00, 102 462 reflections measured,
15 561 independent reflections (Rint = 0.0686) which were used
in all calculations. Flack parameter = 0.000(17). The final
R indices were R1 [I > 2σ(I)] = 0.0725 and wR2 (all data) =
0.1992. GOF = 1.208. CCDC 941073.
Computational details
Structures of complexes 1a and 1b were optimized by DFT
calculations using the Gaussian 03 program package.47 Two
models, A1 and A2, were used for the calculations of 1a, and B
for 1b (Fig. S11, ESI†). The B3LYP density functional method
and the LANL2DZ basis set were used for the calculations. The
optimized structures of A1, A2 and B are shown in Fig. S12
(ESI†), and their molecular coordinates are listed in Tables S2–
S4, respectively (ESI†). Harmonic vibrational frequencies were
calculated for the optimized geometries using the same level
of theory. The zero-point energy and thermal contributions at
298.15 K and 1.0 atm to the gas-phase free energy were
obtained from the harmonic vibrational frequencies without
scaling factors. The calculated data and the energy differences
are summarized in Table S5 (ESI†).
Acknowledgements
This work was supported by the Grant-in-Aid for Scientific
Research (B) (no. 21350081 and 24350076) from JSPS, Japan.
Notes and references
1 G. C. Dismukes, Chem. Rev., 1996, 96, 2909–2926.
2 A. L. Gavrilova and B. Bosnich, Chem. Rev., 2004, 104, 349–
383.
3 J. P. Collman, R. Boulatov, C. J. Sunderland and L. Fu,
Chem. Rev., 2004, 104, 561–588.
4 E. Kim, E. E. Chufán, K. Kamaraj and K. D. Karlin, Chem.
Rev., 2004, 104, 1077–1133.
5 C. Tard and C. J. Pickett, Chem. Rev., 2009, 109, 2245–2274.
6 J. P. Collman, Inorg. Chem., 1997, 36, 5145–5155.
This journal is © The Royal Society of Chemistry 2013
Dalton Trans.

View Article Online
Paper
Dalton Transactions
7 J. P. Collman, P. S. Wagenknecht and J. E. Hutchison, 32 M. F. Pilz, C. Limberg and B. Ziemer, J. Org. Chem., 2006,
Angew. Chem., Int. Ed. Engl., 1994, 33, 1537–1554. 71, 4559–4564.
8 R. R. Durand Jr., C. S. Bencosme, J. P. Collman and 33 M. Hirotsu, N. Ohno, T. Nakajima and K. Ueno, Chem.
F. C. Anson, J. Am. Chem. Soc., 1983, 105, 2710–2718. Lett., 2005, 848–849.
9 C. K. Chang, H. Y. Liu and I. Abdalmuhdi, J. Am. Chem. 34 M. Hirotsu, N. Ohno, T. Nakajima, C. Kushibe, K. Ueno
Soc., 1984, 106, 2725–2726. and I. Kinoshita, Dalton Trans., 2010, 39, 139–148.
10 J. P. Collman, J. E. Hutchison, M. A. Lopez, A. Tabard, 35 M. Hirotsu, Y. Shimizu, N. Kuwamura, R. Tanaka,
R. Guilard, W. K. Seok, J. A. Ibers and M. L’Her, J. Am.
Chem. Soc., 1992, 114, 9869–9877.
I. Kinoshita, R. Takada, Y. Teki and H. Hashimoto, Inorg.
Chem., 2012, 51, 766–768.
11 R. Guilard, M. A. Lopez, A. Tabard, P. Richard, C. Lecomte, 36 D. Peri, C. M. Manna, M. Shavit and E. Y. Tshuva,
S. Brandes, J. E. Hutchison and J. P. Collman, J. Am. Chem.
Soc., 1992, 114, 9877–9889.
12 Y. Le Mest, C. Inisan, A. Laouénan, M. L’Her, J. Talarmin,
Eur. J. Inorg. Chem., 2011, 4896–4900.
37 M. Hirotsu, M. Kojima and Y. Yoshikawa, Bull. Chem. Soc.
Jpn., 1997, 70, 649–657.
M. E. Khalifa and J.-Y. Saillard, J. Am. Chem. Soc., 1997, 38 M. Hirotsu, M. Kojima, W. Mori and Y. Yoshikawa, Bull.
119, 6095–6106. Chem. Soc. Jpn., 1998, 71, 2873–2884.
13 C. J. Chang, E. A. Baker, B. J. Pistorio, Y. Deng, Z.-H. Loh, 39 M. Hirotsu, M. Aoyagi, M. Kojima, W. Mori and
S. E. Miller, S. D. Carpenter and D. G. Nocera, Inorg. Chem.,
2002, 41, 3102–3109.
14 C. J. Chang, Z.-H. Loh, C. Shi, F. C. Anson and
D. G. Nocera, J. Am. Chem. Soc., 2004, 126, 10013–10020.
15 J. P. Collman, J. E. Hutchison, M. A. Lopez and R. Guilard,
J. Am. Chem. Soc., 1992, 114, 8066–8073.
Y. Yoshikawa, Bull. Chem. Soc. Jpn., 2002, 75, 259–265.
40 M. Hirotsu, M. Kojima, W. Mori and Y. Yoshikawa, Chem.
Lett., 1999, 229–230.
41 H. Okawa, A. Honda, M. Nakamura and S. Kida, J. Chem.
Soc., Dalton Trans., 1985, 59–64.
42 J. B. Vincent, H.-R. Chang, K. Folting, J. C. Huffman,
G. Christou and D. N. Hendrickson, J. Am. Chem. Soc.,
1987, 109, 5703–5711.
16 J. P. Collman, J. E. Hutchison, M. S. Ennis, M. A. Lopez and
R. Guilard, J. Am. Chem. Soc., 1992, 114, 8074–8080.
17 Y. Naruta, M. Sasayama and T. Sasaki, Angew. Chem., Int. 43 CrystalClear, Rigaku Corporation, 2007.
Ed. Engl., 1994, 33, 1839–1841.
44 A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano,
18 Y. Shimazaki, T. Nagano, H. Takesue, B.-H. Ye, F. Tani and
Y. Naruta, Angew. Chem., Int. Ed., 2004, 43, 98–100.
19 J. Rosenthal, T. D. Luckett, J. M. Hodgkiss and
D. G. Nocera, J. Am. Chem. Soc., 2006, 128, 6546–6547.
20 I. Siewert, C. Limberg, S. Demeshko and E. Hoppe, Chem.–
Eur. J., 2008, 14, 9377–9388.
C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni,
G. Polidori and R. Spagna, J. Appl. Crystallogr., 1999, 32,
115–119.
45 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystal-
logr., 2008, 64, 112–122.
46 A. L. Spek, Acta Crystallogr., Sect. D: Biol. Crystallogr., 2009,
65, 148–155.
21 Z. Guo, W.-L. Tong and M. C. W. Chan, Chem. Commun.,
2009, 6189–6191.
47 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr.,
T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam,
S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi,
G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross,
C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth,
P. Salvador, J. J. Dannenberg, V. G. Zakrzewski,
S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas,
D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford,
J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith,
M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian 03, Revi-
sion B.05, Gaussian, Inc., Pittsburgh PA, 2003.
22 R. Okamura, T. Wada, K. Aikawa, T. Nagata and K. Tanaka,
Inorg. Chem., 2004, 43, 7210–7217.
23 J. R. Hagadorn, M. J. McNevin, G. Wiedenfeld and
R. Shoemaker, Organometallics, 2003, 22, 4818–4824.
24 M. J. McNevin and J. R. Hagadorn, Inorg. Chem., 2004, 43,
8547–8554.
25 T. Wada, K. Tsuge and K. Tanaka, Angew. Chem., Int. Ed.,
2000, 39, 1479–1482.
26 T. Wada, K. Tsuge and K. Tanaka, Inorg. Chem., 2001, 40,
329–337.
27 M. F. Pilz, C. Limberg, B. B. Lazarov, K. C. Hultzsch and
B. Ziemer, Organometallics, 2007, 26, 3668–3676.
28 J. T. Muckerman, D. E. Polyansky, T. Wada, K. Tanaka and
E. Fujita, Inorg. Chem., 2008, 47, 1787–1802.
29 S. Han, E. Yao, W. Qin, S. Zhang and Y. Ma, Macro-
molecules, 2012, 45, 4054–4059.
30 R. P. Bonar-Law, J. F. Bickley, C. Femoni and A. Steiner,
J. Chem. Soc., Dalton Trans., 2000, 4244–4246.
31 K. Aikawa and T. Nagata, Inorg. Chim. Acta, 2000, 306, 223–
226.
Dalton Trans.
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