Change in coordination of NCN pincer iron complexes containing bis(oxazolinyl)phenyl ligands

Article abstract of DOI:10.1021/om300901k

The coordination of bis(oxazolinyl)phenyl (phebox) ligands to an Fe center was investigated in the reaction of (phebox-R)Fe(CO)₂Br (1a: R = Me₂; 1b: R = i-Pr) with phosphine and isocyanide compounds. Reaction of 1 with an excess amount of PMe₃ in toluene proceeded at 50 C to give the corresponding cationic complexes [(phebox-R)Fe(CO)(PMe ₃)₂]Br [2a: R = Me₂ (79%); 2b: R = i-Pr (83%)]. The molecular structures of 2a and 2b were confirmed by X-ray diffraction analysis that revealed the pseudo-octahedral geometry with NCN meridional coordination of the phebox ligand. In contrast, reaction of 1 with PMe ₂Ph gave the neutral phosphine complexes (η²-phebox-R) Fe(CO)(PMe₂Ph)₂Br [3a: R = Me₂ (87%); 3b: R = i-Pr (79%)], in which the phebox ligand was coordinated to Fe as an NC bidentate ligand with the oxazoline and phenyl groups. Subsequent reaction of the neutral phosphine complex 3a resulted in the formation of the corresponding cationic complexes [(phebox-Me₂)Fe(CO)(PMe₂Ph)₂]Br (4) via change in coordination to the tridentate mode. The reaction of 1 with tert-butylisocyanide CN(t-Bu) gave a mixture of neutral isocyanide complexes (phebox-Me₂)Fe(CO)[CN(t-Bu)]Br (5, 6) in 57 and 10% yields, respectively, via exchange of one of the CO ligands. Subsequent reaction of 5 with CN(t-Bu) resulted in formation of the cationic complex {(phebox-Me ₂)Fe[CN(t-Bu)]₃}Br (7a). Similarly, treatment of 1 with an excess amount of CN(t-Bu) afforded {(phebox-R)Fe[CN(t-Bu)]₃}Br [7a: R = Me₂ (83%); 7b: R = i-Pr (69%)].

Full text of DOI:10.1021/om300901k

Article
pubs.acs.org/Organometallics
Change in Coordination of NCN Pincer Iron Complexes Containing
Bis(oxazolinyl)phenyl Ligands
Satomi Hosokawa, Jun-ichi Ito,* and Hisao Nishiyama*
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan
S
* Supporting Information
ABSTRACT: The coordination of bis(oxazolinyl)phenyl
(phebox) ligands to an Fe center was investigated in the
reaction of (phebox-R)Fe(CO)2Br (1a: R = Me2; 1b: R = i-Pr)
with phosphine and isocyanide compounds. Reaction of 1 with
an excess amount of PMe3 in toluene proceeded at 50 °C to
give the corresponding cationic complexes [(phebox-R)Fe-
(CO)(PMe3)2]Br [2a: R = Me2 (79%); 2b: R = i-Pr (83%)].
The molecular structures of 2a and 2b were confirmed by X-
ray diffraction analysis that revealed the pseudo-octahedral
geometry with NCN meridional coordination of the phebox ligand. In contrast, reaction of 1 with PMe2Ph gave the neutral
phosphine complexes (η2-phebox-R)Fe(CO)(PMe2Ph)2Br [3a: R = Me2 (87%); 3b: R = i-Pr (79%)], in which the phebox ligand
was coordinated to Fe as an NC bidentate ligand with the oxazoline and phenyl groups. Subsequent reaction of the neutral
phosphine complex 3a resulted in the formation of the corresponding cationic complexes [(phebox-Me2)Fe(CO)(PMe2Ph)2]Br
(4) via change in coordination to the tridentate mode. The reaction of 1 with tert-butylisocyanide CN(t-Bu) gave a mixture of
neutral isocyanide complexes (phebox-Me2)Fe(CO)[CN(t-Bu)]Br (5, 6) in 57 and 10% yields, respectively, via exchange of one
of the CO ligands. Subsequent reaction of 5 with CN(t-Bu) resulted in formation of the cationic complex {(phebox-
Me2)Fe[CN(t-Bu)]3}Br (7a). Similarly, treatment of 1 with an excess amount of CN(t-Bu) afforded {(phebox-R)Fe[CN(t-
Bu)]3}Br [7a: R = Me2 (83%); 7b: R = i-Pr (69%)].
Rh(II) center contained NN bidentate coordination without an
M−C bond.7 Recently, Milstein reported that a PCN pincer
complex with a hemilabile NMe2 group underwent a
coordination change between PCN and PC chelates.8 In
particular, detachment and attachment of the amine group in a
PNN framework was proposed as a mechanism for formation
of the reaction site on a metal center in a catalytic cycle.9,10
The bis(oxazolinyl)phenyl (phebox) ligand serves as an
NCN meridional ligand with a rigid structure induced by two
oxazolines and the benzene backbone.11 Usually, phebox
complexes containing late transition metals adopt square-planar
and pseudo-octahedral geometries.12 For Au and Sn complexes,
η1-C-coordination of the phebox ligand without the M−N
bonds was observed.12i,j However, intermediate structures
containing NC bidentate chelation have not been directly
observed.
A recent study described the chiral and achiral phebox−Fe
complexes (phebox-R)Fe(CO)2Br (1a: R = Me2; 1b: R = i-Pr),
in which the phebox ligand was meridionally coordinated to the
Fe center with the Fe−C σ-bond.13 Such cyclometalated Fe
complexes are of interest for cyclometalation and trans-
metalation reactions14,15 as well as application to catalytic
reactions.16 The present report describes investigation of the
ligand-exchange reactions of the CO and Br ligands in phebox−
INTRODUCTION
■
Phosphine-based pincer ligands tightly bound to a transition
metal produce a robust structure induced by a metal−carbon σ-
bond and two metallacycles.1 In contrast, introduction of a
hemilabile amino functionality with flexible methylene linkers
allows a change in coordination number by dissociation of the
amino group. Such a change in the coordination mode is
considered to be significant to generate a vacant site on a metal
center. Previously, van Koten described the fluxional behavior
of the amino-based NCN pincer ligand, C6H3(CH2NMe2)2.
For example, the NCN−Ru complex (NCN)RuCl(PPh3)
underwent the rearrangement from tridentate NCN bonding
to bidentate NC bonding in the reaction with Na(C5H5), giving
the NC−Ru complex (NC)Ru(PPh3)(C5H5).2 Similarly, an
NCN−Ta complex was found to afford the corresponding
NC−Ta complex by the reaction with alkoxide or ZnCl(CH2t-
Bu).3 Such an NC bonding coordination of the bis(amino)-
phenyl ligand was also observed in Ti and W complexes.4 In the
case of group 9 metals, coordination geometry depended on the
valence number of the metals. The Rh(III) complex has a
pseudo-octahedral geometry with an NCN coordination,5 while
the Rh(I) and Ir(I) complexes had a square-planar geometry
with a bidentate NC coordination.6 Bergman and Tilley
reported that a bisoxazoline NCN ligand, namely, a benbox
ligand, exhibited different coordination modes depending on
the property of the metal centers. In this system, the Rh(III)
center adopted NCN meridional coordination, whereas the
Received: September 20, 2012
Published: November 12, 2012
© 2012 American Chemical Society
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Fe complexes with two-electron donor ligands, namely,
phosphine and isocyanide ligands. In this system, the fluxional
behavior of the phebox ligand between the NCN meridional
coordination and the NC bidentate coordination proceeded
during the reaction with phosphine.
RESULTS AND DISCUSSION
■
Reaction of 1 with PMe3. Reaction of (phebox-Me2)Fe-
(CO)2Br (1a) with PMe3 in toluene proceeded at room
temperature to give a cationic phosphine complex [(phebox-
Me2)Fe(CO)(PMe3)2]Br (2a) (eq 1). After purification by
Figure 1. ORTEP diagram of 2a-BPh4. Selected bond lengths (Å) and
angles (deg): Fe(1)−C(1) 1.904(2), Fe(1)−C(17) 1.782(2), Fe(1)−
N(1) 2.0113(17), Fe(1)−N(2) 2.0075(18), Fe(1)−P(1) 2.2786(6),
Fe(1)−P(2) 2.2727(7), C(17)−O(3) 1.142(3); N(2)−Fe(1)−N(1)
158.83(8).
column chromatography on silica gel, the complex 2a was
isolated as red crystals in 79% yield. Similarly, the chiral
complex [(phebox-i-Pr)Fe(CO)(PMe3)2]Br (2b) was obtained
in 83% yield by reaction of 1b with PMe3. When the reaction of
1a with PMe3 was also carried out in MeOH at 50 °C for 12 h,
the cationic phosphine complex 2a was also obtained in 94%
yield. The anion-exchange reaction of 2a and 2b with NaBPh4
in methanol gave the corresponding BPh4 salts 2a-BPh4 and
2b-BPh4, respectively.
1
In the H NMR spectrum of 2a-BPh4, the singlet signal for
the methyl groups on the oxazoline rings was observed at δ 1.17
ppm (12H), and a doublet of doublets signal for the PMe3
ligand appeared at δ 0.81 ppm (9H). The integral ratio of the
BPh4 anion indicated formation of the cationic complex. In the
31P NMR spectrum, a signal for PMe3 was observed at δ 19.5
ppm. These spectral features indicated the C2-symmeric
structure with trans arrangement of two PMe3 ligands in
solution. The IR spectrum revealed an absorption for the
carbonyl group at ν = 1922 (2a) and 1953 (2a-BPh4) cm−1,
Figure 2. ORTEP diagram of 2b-BPh4. Selected bond lengths (Å) and
angles (deg): C(1)−Fe(1) 1.917(4), Fe(1)−C(19) 1.796(4), Fe(1)−
N(1) 2.075(3), Fe(1)−N(2) 2.021(3), Fe(1)−P(1) 2.2814(13),
Fe(1)−P(2) 2.2765(13), C(19)−O(3) 1.147(5); N(2)−Fe(1)−
N(1) 157.50(12).
which shifted to lower energy compared to that of 1a (νCO
=
2026, 1965 cm−1), probably due to the increase in the π-back-
donation by coordination of the electron-rich PMe3 ligands.
The molecular structures of 2a-BPh4 and 2b-BPh4 were
confirmed by X-ray diffraction analysis (Figures 1 and 2). The
ORTEP diagrams showed that 2a-BPh4 and 2b-BPh4 had
pseudo-octahedral geometry with N−Fe−N bond angles of
158.83(8)° and 157.50(12)°, respectively. Two PMe3 ligands
occupied the position perpendicular to the phebox plane. In
contrast, the two PMe3 ligands of the (PCP)Fe(H)(PMe3)2
complex took the cis arrangement.14r The Fe−P bond lengths
(2a-BPh4: 2.2786(6) and 2.2727(7) Å; 2b-BPh4: 2.2814(13)
and 2.2765(13) Å) were slightly longer than those of
(CNC)Fe(PMe3)3 (Fe−P = 2.2247(4)−2.2393(4) Å),14n
(PC)FeMe(PMe3)3 (Fe−P = 2.229(4)−2.261(10) Å),14o and
(NC)FeH(PMe3)3 (Fe−P = 2.1739(5)−2.1874(5) Å).14q The
CO ligand was located in the trans position of the phenyl group
of the phebox ligand. The Fe−CO bond length of 1.796(4) Å
was slightly shorter than that of 1a (Fe−CO = 1.839(2) Å).13
As expected, the phebox ligand was bound to the Fe center with
the NCN tridentate coordination. The Fe−C(sp2) bond
lengths (2a-BPh4: 1.904(2); 2b-BPh4: 1.917(4) Å) were
comparable to those of 1a (1.930(2) Å)13 and (PCP)FeCl2
(1.937(2) Å)15d and were longer than those of the (phebox)Ni
complexes (1.8491(19)−1.859(4) Å).12a,b
Substitution reactions of carbonyl ligands with phosphines
have been studied in the CpFe(CO)2 (Fp) and Cp*Fe(CO)2
(Fp*) systems.17 For example, the reaction of CpFe(CO)2X (X
= Cl, I) with PPh3 afforded the cationic substituted products,
[CpFe(CO)2(PPh)3]+, via substitution with a halogen, whereas
CpFe(CO)2Br gave a neutral complex CpFe(CO)(PPh3)Br via
substitution with a carbonyl ligand. The Cp*Fe(CO)2Br also
reacted with PPh3 under UV irradiation to give the neutral
complex Cp*Fe(CO)(PPh3)Br.18 In the reaction of CpFe-
(CO)2X with PMe3, distribution of the products, CpFe-
(CO)2−n(PMe3)nX and [CpFe(CO)3−n(PMe3)n]+, strongly
depended on the reaction conditions and the halogen.19
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Reactivity of the phebox−Fe complex toward PMe3 resembles
that of the Fp system.
Reaction of 1 with PMe2Ph. The reaction of 1a with
PMe2Ph in toluene at 50 °C resulted in formation of neutral
phosphine complex 3a instead of a cationic complex, as
observed in the reaction with PMe3 (Scheme 1). Purification by
Scheme 1. Reaction of 1 with PMe2Ph in Toluene, MeOH,
a b
,
or DMSO
Figure 3. ORTEP diagram of 3a. Selected bond lengths (Å) and
angles (deg): Fe(1)−C(1) 1.977(3), Fe(1)−C(33) 1.728(3), Fe(1)−
Br(1) 2.5105(5), Fe(1)−N(1) 2.073(2), Fe(1)−P(2) 2.2808(8),
Fe(1)−P(1) 2.3076(8); C(1)−Fe(1)−N(1) 82.36(10), P(1)−
Fe(1)−P(2) 174.19(3), C(33)−Fe(1)−N(1) 177.40(12), C(1)−
Fe(1)−Br(1) 176.67(9).
To obtain the insight into the solvent effect, we carried out
the reaction of 1a with PMe2Ph in polar solvents, MeOH or
DMSO, at 50 °C for 12 h (Scheme 1). The heating reaction of
1a in MeOH resulted in the formation of the neutral phosphine
complex 3a in 81% yield. On the other hand, the reaction in
DMSO afforded a cationic phosphine complex [(phebox-
Me2)Fe(CO)(PMe3)2]Br (4). After purification by column
chromatography, complex 4 was isolated in 80% yield.
Complex 3a is considered to be a precursor for the formation
of the cationic phosphine complex 4. Reaction of the phosphine
complex 3a in methanol at 50 °C for 12 h resulted in the
formation of the corresponding cationic complex 4 in 84% yield
(eq 2). When complex 3a was heated in DMSO at 50 °C for 12
h, the yield of 4 was 84%. This reaction was found to be
promoted by a nonprotic polar solvent.
a
b
In toluene. In MeOH.
column chromatography on silica gel afforded 3a in 87% yield.
Similarly, the chiral complex 1b reacted with PMe2Ph to give
the neutral phosphine complex 3b in 79% yield. Complexes 3a
and 3b were identified on the basis of NMR and IR spectra.
1
The H NMR spectrum of 3a exhibited signals for the methyl
groups on the oxazoline at δ 1.58 and 1.89 ppm and two singlet
signals for methylene protons at the 5-position of the oxazoline
ring at δ 3.46 and 3.90 ppm. In addition, the 13C NMR
spectrum exhibited two sets of signals for the oxazoline groups.
These spectral features indicated that the two oxazoline groups
were in different environments. The two methyl groups of
PMe2Ph produced signals at δH 1.10 and 1.35 ppm and δC 16.1
and 17.4 ppm in the 1H and 13C NMR spectra, respectively. In
the 31P NMR spectrum of 3a, the signal for PMe2Ph appeared
at δ 14.7 ppm. The IR spectrum of 3a showed an absorption
signal for CO at 1916 cm−1.
The molecular structure of 3a was determined by X-ray
diffraction analysis (Figure 3). Of particular significance was the
bidentate coordination of the phebox ligand, in which one of
the oxazoline groups did not attach to the Fe center. This
structural feature is quite different from that of other phebox
metal complexes, which usually have NCN coordination
geometry. The Fe−C(1) bond length of 1.977(3) Å was
slightly longer than those of the PMe3 complexes 2, probably
due to the less-hindered bidentate structure of 3a. The two
phosphine ligands occupied the trans position to reduce steric
repulsion. The Fe−P bond lengths were 2.3076(8) and
2.2808(8) Å, which are comparable to those of 2a-BPh4
(2.2786(6), 2.2727(7) Å). The Br and CO ligands were
bound to the trans position to the phenyl and oxazoline groups,
respectively.
The 1H NMR spectrum of 4 exhibited the signal for the four
methyl groups of the oxazoline rings at δ 1.00 ppm. The signal
for the methyl groups of the phosphine ligands appeared at δ
1.19 ppm. In the 31P NMR spectrum, the signal for the two
phosphine ligands was shifted to the lower field and observed at
δ 61.5 ppm. In the HRMS of 4, the peak at m/z = 631.1958
also supported the structure of 4. These spectral data indicated
the formation of the cationic phosphine complex 4.
In this reaction, dissociation of the Br ligand and association
of the oxazoline group proceeded to form the NCN
coordination. Thus, the phebox−Fe complexes underwent a
change in coordination number between bidentate and
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tridentate in both directions. In addition, complex 3a acted as
an intermediate for formation of 4 by reaction of 1 with
phosphines. We assumed that the fluxional behavior of the
phebox ligand might promote the initial substitution reaction
with a phosphine ligand on the Fe center.
than that of the phebox−Ru isocyanide complex (Ru−C =
2.058(3) Å).20 The structural features of 5 suggest that ligand
exchange of 1 occurred readily at the equatorial site.
Complex 6 was identified as a geometrical isomer of 5 on the
1
1
basis of the H and 13C NMR and IR spectra. In the H NMR
spectrum of 6, the signal of the t-Bu group of the isocyanide
ligand was observed at δ 0.49 (9H). Singlet signals for the
methyl groups of the oxazolines appeared at δ 0.91 (6H) and
1.46 (6H). The IR spectrum showed absorption of the CO and
CN(t-Bu) ligands at 1963 and 2149 cm−1, respectively. These
spectral features are consistent with the structure described in
Scheme 2.
Reaction of 1 with CN(t-Bu). In the reaction of 1 with
phosphine, the formation of bisphosphine complexes 2 and 3
proceeded prior to the formation of a monophosphine
complex, even in the presence of an equivalent amount of
phosphine. In this case, the strong σ-donating ability of the
alkylphosphine ligand might promote dissociation of the Br
ligand or the oxazoline of the phebox ligand to accept a second
phosphine ligand. Thus, the ligand-exchange reaction with
isocyanide as a strong π-accepting ligand was also examined.
Reaction of 1 with 1.2 equiv of CN(t-Bu) at 50 °C gave a
mixture of neutral isocyanide complexes (phebox-Me2)FeBr-
(CO)[CN(t-Bu)] (5 and 6). Purification by column
chromatography on silica gel afforded complexes 5 and 6 in
57 and 10% yields, respectively.
Scheme 2. Reaction of 1 with CN(t-Bu)
The major product 5 was identified as the monosubstituted
isocyanide complex on the basis of NMR and IR spectra. In the
1H NMR spectrum of 5, two singlet signals for the methyl
groups of the oxazolines were observed at δ 0.99 (6H) and 1.32
(6H), and the singlet signal for the t-Bu group of the isocyanide
ligands was observed at δ 1.23 (9H). The IR spectrum of 5
showed absorptions for the CO and CN(t-Bu) ligand at 1937
and 2143, respectively.
The molecular structure of 5 was determined by X-ray
diffraction analysis. The ORTEP diagram indicated that the
phebox ligand was meridionally coordinated to the Fe center
(Figure 4). The CN(t-Bu) ligand was trans to the phenyl group
of the phebox ligand. The Br and CO ligands were attached
perpendicular to the phebox plane. This coordination geometry
of the phebox−Fe complex is similar to that of the related
phebox−Ru isocyanide complex.20 The Fe(1)−C(18) bond
length of 1.910(7) Å is comparable to that of
FeCl2[CNC6H3(t-Bu)2]4 (Fe−C: 1.895(6) Å),21 and shorter
To evaluate the kinetic or thermodynamic products in the
reaction of 1 with CN(t-Bu), reaction of 5 in benzene-d6 at 50
1
°C was monitored by H NMR spectroscopy. Although the
decomposition of 5 was observed, the formation of 6 was not
detected after heating for 12 h. Similarly, the heating reaction of
6 in benzene-d6 at 50 °C exhibited decomposition of 6 and no
formation of 5. The lack of conversion between 5 and 6 implied
that 5 and 6 were the kinetic products. In this case, dissociation
of the CO ligand trans to the phenyl fragment of the phebox
ligand occurred easily due to the high trans effect of the phenyl
fragment.
Further reaction of 5 with an excess amount of CN(t-Bu)
gave the cationic complex (phebox-Me2)Fe[CN(t-Bu)3]Br (7a)
quantitatively via ligand exchange of CO and Br. Similarly,
complex 7a was obtained in 80% yield by the reaction of 6 with
CN(t-Bu). Reaction of 1a with CN(t-Bu) also gave the cationic
complex 7a in 83% yield (Scheme 2). Similarly, a chiral
complex 7b was obtained in 69% yield by the reaction of 1b
with CN(t-Bu). Complexes 7a and 7b were purified by column
chromatography on silica gel to yield an air- and moisture-
stable yellow solid. The IR spectrum of 7a showed CN
Figure 4. ORTEP diagram of 5. Selected bond lengths (Å) and angles
(deg): Fe(1)−C(1) 1.923(7), Fe(1)−C(17) 1.804(9), Fe(1)−C(18)
1.910(7), Fe(1)−Br(1) 2.5210(13), Fe(1)−N(1) 2.001(5), Fe(1)−
N(2) 2.026(6), C(17)−O(3) 1.067(9), C(18)−N(3) 1.161(8);
N(1)−Fe(1)−N(2) 158.1(2), C(17)−Fe(1)−Br(1) 179.2(2), C(1)−
Fe(1)−C(18) 174.2(3), N(3)−C(18)−Fe(1) 178.3(7), C(18)−
N(3)−C(19) 172.1(8).
1
stretching absorptions at 2170 and 2118 cm−1. The H NMR
spectrum of 7a showed the singlet signals of the t-Bu groups in
the isocyanide ligands at δ 1.17 and 1.19 in the ratio of
9H:18H, indicating coordination of three isocyanide ligands at
equatorial and axial positions. The molecular structure of 7a,
confirmed by X-ray diffraction analysis, showed pseudo-
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500 spectrometer. 1H NMR chemical shifts were reported in δ units, in
parts per million relative to the singlet at 7.26 ppm for CDCl3 and 7.16
ppm for C6D6. 13C NMR spectra were reported in terms of chemical
shift (δ, ppm) relative to the triplet at δ = 77.1 ppm for CDCl3 and
128.0 ppm for C6D6. 31P NMR spectra were reported in terms of
chemical shift (δ, ppm) relative to the signal at δ = 0 ppm for H3PO4.
Infrared spectra were recorded on a JASCO FT/IR-230 spectrometer.
Complexes 1a and 1b were prepared by the reported method.10
Reaction of 1 with PMe3. To a toluene solution (20 mL) of 1a
(463 mg, 1.0 mmol) was added a 1 M toluene solution of PMe3 (5.0
mL, 5.0 mmol) under an argon atmosphere. The resulting mixture was
stirred at 50 °C for 12 h. After removal of the solvent under reduced
pressure, the residue was crystallized by slow concentration of a mixed
solution of methanol, diethylether, and toluene at room temperature
to give red crystals of 2a (464 mg, 0.79 mmol, 79%). The similar
procedure using 1b (491 mg, 1.0 mmol) gave red crystals of 2b (510
mg, 0.83 mmol, 83%).
octahedral geometry with N−Fe−N bond angles of 157.1(3)°
(Figure 5). The phebox ligand was meridionally coordinated to
the Fe center. The Fe−C and Fe−N bond lengths were similar
to those of the PMe3 complexes 2a-BPh4 and 2b-BPh4.
A methanol solution of 2a (176 mg, 0.30 mmol) and NaBPh4 (123
mg, 0.36 mmol) was stirred for 1 h at room temperature.
Recystallization of the crude product afforded red crystals of 2a-
BPh4 (246.1 mg, 0.30 mmol, 99%). The similar procedure using 1b
(306 mg, 0.50 mmol) gave 2b-BPh4 (412 mg, 0.48 mmol, 96%).
2a: 1H NMR (300 MHz, C6D6, rt): δ 0.81(dd, JPH = 3.9, 3.9 Hz, 18
H, PCH3), 1.27 (s, 12H, C(CH3)2), 4.53 (s, 4H, CH2), 7.55 (t, J = 7.6
Hz, 1H), 7.87 (d, J = 7.6, 2H). 13C NMR (75 MHz, C6D6, rt): δ 14.1
(dd, J = 13.4, 13.4 Hz), 28.2, 65.6, 82.5, 124.6, 126.1 (t, J = 2.2 Hz),
134.2, 170.3, 215.6 (t, J = 15.7 Hz), 216.0 (t, J = 23.9 Hz). 31P NMR
(121 MHz, C6D6, rt): δ 13.7. IR (KBr, cm−1): 2979, 1922, 1601, 1541,
1470, 1397, 1340, 1288, 1204, 949. Anal. Calcd for
C23H37BrFeN2O3P2: C, 47.04; H, 6.35; N, 4.77. Found: C, 46.57;
H, 6.44; N, 3.83. HRMS (FAB, m/z) calcd 507.1629 [M+], found
507.1616.
Figure 5. ORTEP diagram of 7a. Selected bond lengths (Å) and
angles (deg): Fe(1)−C(1) 1.909(9), Fe(1)−C(9) 1.881(7), Fe(1)−
C(13) 1.886(10), Fe(1)−N(1) 2.010(5), C(9)−N(2) 1.160(10),
C(13)−N(3) 1.168(12); N(1)−Fe(1)−N(1) 157.1(3).
This reactivity of the phebox−Fe complex 1 toward
isocyanide was similar to that of CpFe(CO)2X, in which
stepwise substitution of the CO ligand with isocyanide gave
neutral complexes CpFe(CO)(CNR)X and CpFe(CNR)2X
and a cationic complex [CpFe(CNR)3]X.22
1
2b: H NMR (300 MHz, CDCl3, rt): δ 0.76 (d, J = 6.6 Hz, 6H,
CH(CH3)2), 0.87 (dd, JPH = 3.3 Hz, 18H, PCH3), 1.15 (d, J = 6.6 Hz,
6H, CH(CH3)2), 1.94 (br, 2H), 3.23 (br, 2H), 4.50 (m, 2H), 4.81 (m,
2H), 7.53 (t, J = 7.7 Hz, 1H), 7.86 (t, J = 7.7 Hz, 1H). 13C NMR (75
MHz, CDCl3, rt): δ 14.5 (dd, J = 13.1, 13.1 Hz), 17.6, 22.3, 29.8, 71.1,
72.6, 124.2, 126.7, 132.8, 172.4, 214.4 (t, JPC = 35.9 Hz), 218.2 (t, JPC
= 43.9 Hz). 31P NMR (121 MHz, CDCl3, rt): δ 14.3. IR (KBr, cm−1):
2962, 2903, 1937, 1603, 1576, 1543, 1487, 1389, 1284, 1201, 1145,
948. Anal. Calcd for C25H41BrFeN2O3P2: C, 47.80; H, 6.72; N, 4.55.
Found: C, 48.28; H, 6.77; N, 4.09. HRMS (FAB, m/z) calcd 535.1942
[M+], found 535.1948.
CONCLUSIONS
■
The fundamental reactivity of NCN pincer Fe complexes
toward two-electron donor ligands phosphine and isocyanide
was elucidated. Reaction of the carbonyl complex (phebox-
R)Fe(CO)2Br (1) with PMe3 underwent ligand exchange with
both CO and Br ligands to give the cationic phosphine complex
[(phebox-R)Fe(PMe2)2(CO)]Br (2). In contrast, reaction with
PMe2Ph resulted in a change in coordination number of the
phebox ligand to give the NC chelated neutral phosphine
complex 3. Subsequent reaction of 3 in a polar solvent led to
the formation of the NCN pincer complex 4 via a coordination
number change of the phebox ligand. This fluxional behavior of
the Fe complex contrasts with the second-row transition-metal
complexes, which contain a rigid NCN coordination of the
phebox ligand. In the reaction of 1 with a π-accepting ligand
CN(t-Bu), the ligand-exchange reaction with one of the CO
ligands proceeded to give neutral isocyanide complexes
(phebox-Me2)Fe(CO)[CN(t-Bu)]Br (5, 6). The resulting
isocyanide complexes 5 and 6 reacted with excess CN(t-Bu)
to afford the cationic complex {(phebox-Me2)Fe[CN(t-Bu)]3}
Br (7a). These phebox Fe complex coordination processes can
provide fundamental insights into NCN pincer Fe complexes as
a catalyst.
2a-BPh4: 1H NMR (300 MHz, DMSO-d6, rt): δ 0.74 (dd, JPH = 4.2,
4.2 Hz, 18 H, PCH3), 1.17 (s, 12H, C(CH3)2), 4.57 (s, 4H, CH2), 6.78
(t, J = 7.1 Hz, 4H), 6.91 (t, J = 7.2 Hz, 8H), 7.17 (br, 8H), 7.59 (t, J =
7.6 Hz, 1H), 7.92 (d, J = 7.5, 2H). 13C NMR (75 MHz, DMSO-d6, rt):
δ 13.1 (dd, J = 13.1, 13.7 Hz), 27.5, 65.3, 81.8, 121.2, 124.5, 125.0 (t, J
= 2.6 Hz), 125.3, 133.9, 135.2, 162.9 (q, J = 18.8 Hz), 169.4, 215.7,
216.4. 31P NMR (121 MHz, DMSO-d6, rt): δ 19.5. IR (KBr, cm−1):
3054, 2994, 2908, 1953, 1599, 1578, 1542, 1481, 1380, 1335, 1286,
1202, 1147, 945. Anal. Calcd for C47H57BFeN2O3P2: C, 68.29; H, 6.95;
N, 3.39. Found: C, 68.31; H, 7.06; N, 3.02.
2b-BPh4: 1H NMR (300 MHz, DMSO-d6, rt): δ 0.69 (d, J = 6.6 Hz,
6H, CH(CH3)2), 0.76 (dd, JPH = 3.6 Hz, 18H, PCH3), 1.05 (d, J = 6.9
Hz, 6H, CH(CH3)2), 1.85 (br, 2H), 3.28 (br, 2H), 4.59 (m, 2H), 4.71
(m, 2H), 6.78 (t, J = 6.9 Hz, 4H, BPh4), 6.91 (t, J = 7.2 Hz, 8H, BPh4),
7.17 (br, 8H), 7.56 (t, J = 7.5 Hz, 1H), 7.91 (t, J = 7.5 Hz, 1H). 13C
NMR (75 MHz, DMSO-d6, rt): δ 13.2 (dd, J = 13.1, 13.1 Hz), 17.0,
21.4, 29.3, 70.0, 72.2, 121.2 (BPh4), 124.0, 125.0 (d, J = 2.9 Hz, BPh4),
125.9, 132.4, 135.2 (BPh4), 162.9 (q, JBC = 48.9 Hz, BPh4), 171.2,
214.7 (t, JPC = 18.2 Hz), 218.2 (t, JPC = 22.2 Hz). 31P NMR (121
MHz, DMSO-d6, rt): δ 20.0. IR (KBr, cm−1): 3054, 2982, 2914, 1943,
1605, 1577, 1541, 1485, 1389, 1337, 1146, 944. Anal. Calcd for
C49H61BFeN2O3P2: C, 68.86; H, 7.19; N, 3.28. Found: C, 68.89; H,
7.34; N, 3.26.
EXPERIMENTAL SECTION
General Information. All air- and moisture-sensitive compounds
■
Reaction of 1 with PPhMe2. To a toluene solution (20 mL) of 1a
(463 mg, 1.0 mmol) was added a 1 M toluene solution of PMe2Ph (5.0
mL, 5 mmol) under an argon atmosphere. The reaction mixture was
heated at 50 °C for 12 h. After removal of the solvent under reduced
were manipulated using standard Schlenk and vacuum line techniques
1
under an argon atmosphere. H and 13C NMR spectra were obtained
at 25 °C on a Varian Mercury 300 spectrometer and a Varian Inova
8287
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Article
pressure, the crude product was purified by column chromatography
on silica gel with ethyl acetate/hexane (1:3) to give 3a (619 mg, 0.87
mmol, 87%). The similar procedure using 1b (491 mg, 1.0 mmol) gave
red crystals of 3b (584 mg, 0.79 mmol, 79%).
1204, 976, 742. Anal. Calcd for C22H28BrFeN3O3(H2O)0.5: C, 50.12;
H, 5.54; N, 7.97. Found: C, 50.20; H, 5.49; N, 7.68.
To a toluene solution (20 mL) of 1a (463 mg, 1.0 mmol) was
added a 1 M toluene solution of CN(t-Bu) (10 mL, 10 mmol). The
mixture was stirred at 50 °C for 12 h. After removal of the solvent
under reduced pressure, the residue was purified by column
chromatography on silica gel with ethyl acetate/methanol (5:1) to
give 7a (545 mg, 0.83 mmol, 83%). The similar procedure using 1b
(491 mg, 1.0 mmol) gave 7b (472 mg, 0.69 mmol, 69%).
3a: 1H NMR (300 MHz, C6D6, rt): δ 1.10 (m, 6H, PCH3), 1.35 (m,
6H, PCH3), 1.58 (s, 6H), 1.89 (t, J = 3.8 Hz, 6H), 3.46 (s, 2H), 3.90
(s, 2H), 6.70−7.10 (m, 11), 7.23 (d, J = 7.2 Hz, 1H), 7.34 (d, J = 6.6
Hz, 1H). 13C NMR (75 MHz, CDCl3, rt): δ 16.1 (t, JPC = 12.5 Hz,
PCH3), 17.4 (t, JPC = 13.7 Hz, PCH3), 28.6, 67.3, 69.3, 78.3, 82.2,
120.6, 127.1, 127.2 (t, JPC = 4.0 Hz), 128.3, 130.6 (t, JPC = 3.7 Hz),
133.1, 136.3, 137.5 (t, JPC = 14.8 Hz), 144.3, 166.7, 168.8, 187.1 (t, JPC
= 25.4 Hz), 221.4(t, JPC = 32.5 Hz). 31P NMR (121 MHz, C6D6, rt):
14.7. IR (KBr, cm−1): 3047, 2979, 2960, 2914, 1916, 1660, 1621, 1415,
1296, 1134, 910. Anal. Calcd for C33H41BrFeN2O3P2: C, 55.72; H,
5.81; N, 3.94. Found: C, 55.40; H, 5.76; N, 3.39.
1
7a: H NMR (300 MHz, C6D6, rt): δ 1.17 (s, 9H), 1.19 (s, 18H),
4.41 (s, 4H), 7.32 (t, J = 7.2 Hz, 1H), 7.67 (d, J = 7.2 Hz, 2H). 13C
NMR (75 MHz, CDCl3, rt): δ 27.5, 30.6, 31.2, 57.0, 57.6, 64.7, 82.4,
122.0, 124.8, 133.0, 159.8 (CN), 165.0 (CN), 169.1, 217.1. IR (KBr,
cm−1): 2977, 2930, 2870, 2170, 2118, 1609, 1484, 1398, 1203, 974,
747. Anal. Calcd for C31H46BrFeN5O2·H2O2: C, 55.20; H, 7.17; N,
10.38. Found: C, 55.20; H, 7.20; N, 10.15. HRMS (FAB, m/z)
576.2988, calcd 576.3001 [M+].
3b: 1H NMR (300 MHz, C6D6, rt): δ 0.53 (d, J = 6.9 Hz, 3H), 0.62
(d, J = 7.2 Hz, 3H), 0.88 (d, J = 6.9 Hz, 3H), 0.99 (d, J = 6.9 Hz, 3H),
1.09 (d, J = 8.4 Hz, 3H), 1.11 (d, J = 8.1 Hz, 3H), 1.64 (dd, J = 0.9, 9
Hz, 3H), 1.70 (m, 2H), 2.01 (d, J = 9.0 Hz, 3H), 2.44−2.68 (m, 1H),
2.86 (dd, J = 8.4, 9.6 Hz, 1H), 3.58−3.70 (m, 2H), 3.89−4.02 (m,
2H), 6.83 (t, J = 7.4 Hz, 1H), 6.88−6.94 (m, 2H), 7.07−7.19 (m, 4H,
obscured by C6D6), 7.33 (dt, J = 1.8, 8.1 Hz, 2H), 7.41 (dd, J = 1.7, 7.4
Hz, 1H), 7.53 (dd, J = 1.4, 7.4 Hz, 1H), 7.86 (dt, J = 0.9, 8.1 Hz, 2H).
13C NMR (75 MHz, CDCl3, rt): δ 12.5 (d, J = 23.4 Hz), 15.6, 15.9 (d,
J = 30.2 Hz), 16.3 (d, J = 30.2 Hz), 17.8, 18.2 (d, J = 20.9 Hz), 19.3,
20.3, 28.8, 32.2, 68.2, 68.8, 70.4, 71.4, 120.8, 126.5, 127.4 (d, J = 8.5
Hz), 127.6 (d, J = 8.0 Hz), 128.3, 128.8, 130.6 (d, J = 7.4 Hz), 130.7
(d, J = 6.9 Hz), 131.7, 134.6, 137.5 (d, J = 22.2 Hz), 139.5, 140.0,
144.1, 167.4, 170.8, 188.8, 220.3 (dd, J = 31.4, 35.3). 31P NMR (121
MHz, C6D6, rt): δ 13.3 (d, J = 155.4 Hz), 21.6 (d, J = 155.4 Hz). IR
(KBr, cm−1): 2960, 2912, 2871, 1921, 1630, 1415, 1245, 1143, 903,
734. Anal. Calcd for C35H45BrFeN2O3P2: C, 56.85; H, 6.13; N, 3.79.
Found: C, 56.78; H, 6.22; N, 3.27.
7b: 1H NMR (300 MHz, C6D6, rt): δ 0.63 (d, J = 6.6 Hz, 6H), 0.94
(d, J = 7.2 Hz, 6H), 1.18 (s, 18H), 1.77 (s, 9H), 1.92−2.00 (m, 2H),
3.24−3.36 (m, 2H), 4.51−4.58 (m, 4H), 7.33 (t, J = 7.5 Hz, 1H), 7.68
(d, J = 7.5 Hz, 2H). 13C NMR (75 MHz, CDCl3, rt): δ 14.2, 18.8, 21.2,
29.0, 30.4, 31.0, 57.0, 57.2, 68.0, 71.4, 121.1, 124.8, 132.2, 159.7, 163.8,
170.7, 217.4. IR (KBr, cm−1): 2979, 2171, 2132, 1608, 1487, 1388,
1202, 958, 736. Anal. Calcd for C33H50BrFeN5O2·2H2O: C, 55.01; H,
7.55; N, 9.72. Found: C, 55.07; H, 7.45; N, 9.32. HRMS (FAB, m/z)
604.3315, calcd 604.3314 [M+].
Reaction of 5 or 6 with CN(t-Bu). To a toluene solution (1 mL)
of 5 (27 mg, 0.052 mmol) was added a 1 M toluene solution of CN(t-
Bu) (125 μL, 0.125 mmol). The mixture was stirred at 50 °C for 12 h.
After removal of the solvent under reduced pressure, the residue was
purified by column chromatography on silica gel with ethyl acetate/
methanol (5:1) to give 7a (33 mg, 0.050 mmol, 99%). The similar
procedure using 6 (13 mg, 0.025 mmol) gave 7a (13 mg, 0.020 mmol,
80%).
X-ray Diffraction. The diffraction data for 2a-BPh4, 2b-BPh4, 3a,
5, and 7a were collected on a Bruker SMART APEX CCD
diffractometer with graphite monochromated Mo Kα radiation (λ =
0.71073 Å). An empirical absorption correction was applied by using
SADABS. The structure was solved by direct method and refined by
full-matrix least-squares on F2 using SHELXTL. All non-hydrogen
atoms were refined with anisotropic displacement parameters. All
hydrogen atoms were located on calculated positions and refined as
rigid groups.
2a-BPh4: empirical formula, C47H57BFeN2O3P2; formula weight,
826.55; T = 153(2) K; crystal system, monoclinic; space group, P21/n;
a = 15.0715(17) Å, b = 18.818(2) Å, c = 15.2704(17) Å, β =
99.854(2)°; V = 4267.0(8) Å3; Z = 4; dcalcd = 1.287 mg/m3; μ = 0.471
mm−1; F(000) = 1752; θmax = 28.33°; index ranges, −20 ≤ h ≤ 20,
−12 ≤ k ≤ 25, −20 ≤ l ≤ 20; rflns collected, 31408; indep rflns, 10570
[R(int) = 0.0425]; max and min transmission, 1.000000 and 0.799873;
restraints/parameters = 0/515; GOF = 1.119; final R indices [I >
2σ(I)], R1 = 0.0569, wR2 = 0.1262; R indices (all data), R1 = 0.0688,
wR2 = 0.1317; largest diff. peak and hole, 0.719 and −0.318 e·Å−3. 2b-
BPh4: empirical formula, C49H61BFeN2O3P2; formula weight, 854.60;
T = 153(2) K; crystal system, triclinic; space group, P1; a = 9.374(4)
Å, b = 10.985(5) Å, c = 12.126(5) Å, α = 89.317(11)°, β =
73.436(10)°, γ = 82.832(10)°; V = 1187.1(9) Å3; Z = 1; dcalcd = 1.195
mg/m3; μ = 0.426 mm−1; F(000) = 454; θmax = 28.40°; index ranges,
−12 ≤ h ≤ 11, −14 ≤ k ≤ 14, −16 ≤ l ≤ 7; rflns collected, 8992;
indep rflns, 7163 [R(int) = 0.0311]; max and min transmission,
1.000000 and 0.583871; restraints/parameters = 3/533; GOF = 0.951;
final R indices [I > 2σ(I)], R1 = 0.0475, wR2 = 0.0996; R indices (all
data), R1 = 0.0616, wR2 = 0.1041; largest diff. peak and hole, 0.654
and −0.343 e·Å−3. 3a: empirical formula, C33H41BrFeN2O3P2; formula
weight, 711.38; T = 153(2) K; crystal system, monoclinic; space group,
P21/c; a = 11.1090(16) Å, b = 9.2697(14) Å, c = 32.130(5) Å, β =
95.778(3)°; V = 3291.8(8) Å3; Z = 4; dcalcd = 1.435 mg/m3; μ = 1.805
mm−1; F(000) = 1472; θmax = 28.33°; index ranges, −14 ≤ h ≤ 14,
−12 ≤ k ≤ 10, −33 ≤ l ≤ 42; rflns collected, 23974; indep rflns, 8182
[R(int) = 0.0419]; max. and min transmission, 0.749408 and
Heating Reaction of 3a. A methanol solution (2 mL) of 3a (71
mg, 0.10 mmol) was heated at 50 °C for 24 h. After removal of the
solvent under reduced pressure, the crude product was purified by
column chromatography on silica gel with ethyl acetate/methanol
(10:3) to give 4 (60 mg, 0.084 mmol, 84%). Similarly, heating reaction
of 3a (71 mg, 0.10 mmol) in DMSO gave 4 (60 mg, 0.084 mmol,
84%).
4: 1H NMR (300 MHz, C6D6, rt): δ 1.00 (s, 12H), 1.19 (t, JPH = 3.8
Hz, 12H, PCH3), 3.76 (s, 4H), 6.54 (br, 4H), 7.20 (t, J = 7.4 Hz, 4H),
7.32 (t, J = 7.4 Hz, 2H), 7.85 (t, J = 7.4 Hz, 1H), 7.99 (d, J = 7.4 Hz,
2H). 13C NMR (75 MHz, CDCl3, rt): δ 14.6 (t, JCP = 12.5 Hz), 28.1,
65.4, 82.4, 125.4, 126.6, 128.0, 130.0, 130.6, 133.1 (t, JCP = 18.5 H),
136.3, 170.8, 215.2 (t, JCP = 23.4 Hz), 215.7 (t, JCP = 16.0 Hz). 31P
NMR (121 MHz, CDCl3, rt): δ 61.5. IR (KBr, cm−1): 2979, 2905,
1930, 1573, 1537, 1481, 1395, 1334, 1202, 1146, 971, 903. Anal. Calcd
for C33H41BrFeN2O3P2: C, 55.72; H, 5.81; N, 3.94. Found: C, 55.30;
H, 6.15; N, 2.71. HRMS (FAB, m/z) calcd 631.1942 [M+], found
631.1958.
Reaction of 1 with CN(t-Bu). To a toluene solution (20 mL) of
1a (232 mg, 0.5 mmol) was added a 1 M toluene solution of CN(t-
Bu) (600 μL, 0.6 mmol) under an argon atmosphere. The reaction
mixture was stirred at 50 °C for 12 h. After removal of the solvent
under reduced pressure, the residue was purified by column
chromatography on silica gel with ethyl acetate/hexane (1:1) to give
5 (148 mg, 0.29 mmol, 57%) and 6 (26 mg, 0.050 mmol, 10%).
5: 1H NMR (300 MHz, C6D6, rt): δ 0.99 (s, 6H), 1.23 (s, 9H), 1.32
(s, 6H), 3.70 (d, J = 8.1 Hz, 2H), 3.80 (d, J = 8.1 Hz, 2H), 7.09 (t, J =
7.1 Hz, 1H), 7.75 (d, J = 7.1 Hz, 2H). 13C NMR (75 MHz, C6D6, rt):
δ 28.0, 28.2, 30.9, 65.4, 82.6, 122.7, 125.7, 134.8, 165.0, 171.4, 217.3,
218.3. IR (KBr, cm−1): 2978, 2930, 2143, 1937, 1613, 1484, 1379,
1204, 978, 742. Anal. Calcd for C22H28BrFeN3O3: C, 50.99; H, 5.45;
N, 8.11. Found: C, 51.05; H, 5.56; N, 7.68.
6: 1H NMR (300 MHz, C6D6, rt): δ 0.49 (s, 9H), 0.91 (s, 6H), 1.46
(s, 6H), 3.73 (d, J = 8.7 Hz, 2H), 3.77 (d, J = 8.7 Hz, 2H), 7.16 (t, J =
7.6 Hz, 1H), 7.82 (d, J = 7.6 Hz, 2H). 13C NMR (75 MHz, C6D6, rt):
δ 27.8, 28.3, 30.6, 65.7, 82.4, 123.0, 125.3, 134.4, 165.3, 170.4, 215.6,
225.4. IR (KBr, cm−1): 2981, 2928, 2149, 1963, 1611, 1483, 1379,
8288
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1.000000; restraints/parameters = 0/387; GOF = 1.147; final R
indices [I > 2σ(I)], R1 = 0.0495, wR2 = 0.1005; R indices (all data),
R1 = 0.0623, wR2 = 0.1072; largest diff. peak and hole, 0.777 and
−0.546 e.Å−3. 5: empirical formula, C22H28BrFeN3O3; formula weight,
518.23; T = 153(2) K; crystal system, monoclinic; space group, P21/c;
a = 16.697(3) Å, b = 16.925(3) Å, c = 16.737(3) Å, β = 94.476(6) °; V
= 4715.2(15) Å3; Z = 8; dcalcd = 1.460 mg/m3; μ = 2.361 mm−1;
F(000) = 2128; θmax = 28.33°; index ranges, −18 ≤ h ≤ 2, −22 ≤ k ≤
20, −22 ≤ l ≤ 17; rflns collected, 34527; indep rflns, 11679 [R(int) =
0.1229]; max. and min transmission, 1.00000 and 0.542524; data/
restraints/parameters = 11679/0/550; GOF = 1.034; final R indices [I
> 2σ(I)], R1 = 0.0864, wR2 = 0.1707; R indices (all data), R1 =
0.1612, wR2 = 0.2181; largest diff. peak and hole, 1.327 and −0.894
e·Å−3. 7a: empirical formula, C35H54BrFeN5O3; formula weight,
728.59; T = 153(2) K; crystal system, orthorhombic; space group,
cmcm; a = 17.304(4) Å, b = 17.373(4) Å, c = 14.898(4) Å; V =
4478.7(17) Å3; Z = 4; dcalcd = 1.081 mg/m3; μ = 1.261 mm−1; F(000)
= 1536; θmax = 28.43°; index ranges, −23 ≤ h ≤ 23, −14 ≤ k ≤ 23,
−18 ≤ l ≤ 19; rflns collected, 16776; indep rflns, 3018 [R(int) =
0.0707]; max. and min transmission, 1.000000 and 0.734197;
restraints/parameters = 4/139; GOF = 1.106; final R indices [I >
2σ(I)], R1 = 0.0781, wR2 = 0.2311; R indices (all data), R1 = 0.1088,
wR2 = 0.2513; largest diff. peak and hole, 1.676 and −0.628 e·Å−3.
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ASSOCIATED CONTENT
* Supporting Information
■
S
CIF files giving experimental and crystallographic data for 2a-
BPh4, 2b-BPh4, 3a, 5, and 7a. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: jito@apchem.nagoya-u.ac.jp (J.-i.I.), hnishi@apchem.
nagoya-u.ac.jp (H.N.).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(13) Hosokawa, S.; Ito, J.; Nishiyama, H. Organometallics 2010, 29,
5773−5775.
This research was supported by a Grant-in-Aid for Scientific
Research from the Japan Society for the Promotion of Science
(Nos. 22245014, 24750084).
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