Facile entry to iron complexes supported by quinoline-Based PNN pincer ligand

Article abstract of DOI:10.1246/bcsj.20180124

New quinoline-based PNN pincer ligands were prepared via Friedl?nder synthesis and phosphination reaction. The ligation reaction of PNN ligands with FeX₂ (X = Cl, OTf ) preferentially led to the formation of mono-chelated (PNN)FeX₂ a

Full text of DOI:10.1246/bcsj.20180124

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Facile Entry to Iron Complexes Supported by Quinoline-Based PNN Pincer Ligand
Masahiro Kamitani,* Haruki Kusaka, Takumi Toriyabe, and Hidetaka Yuge
Advance Publication on the web July 7, 2018
doi:10.1246/bcsj.20180124
© 2018 The Chemical Society of Japan
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Facile Entry to Iron Complexes Supported by Quinoline-Based PNN Pincer Ligand
Masahiro Kamitani,*1 Haruki Kusaka,1 Takumi Toriyabe,1 and Hidetaka Yuge1
1Department of Chemistry, School of Science, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara 252-0373
E-mail: <kamitani@kitasato-u.ac.jp>
Masahiro Kamitani
Masahiro Kamitani received his B.Sc. (2008), M.Sc. (2010), and Ph.D. (2013) degrees from Osaka City University
under the supervision of Professor Hiroshi Nakazawa. From 2012 to 2014, he worked as a research fellow at the Japan
Society for the Promotion of Science (JSPS). He worked as a postdoctoral researcher with Prof. Daniel J. Mindiola at
Indiana University (2013) and Pennsylvania University (2014). Since 2015, he has been an assistant professor at
Kitasato University.
Abstract
New quinoline-based PNN pincer ligands were prepared
via Friedländer synthesis and phosphination reaction. The
ligation reaction of PNN ligands with FeX2 (X = Cl, OTf)
preferentially led to the formation of mono-chelated
(PNN)FeX2 and bis-chelated [(PNN)2Fe]2+ complexes
depending on phosphorus substituents and
X ligands.
Molecular structures and electron configurations of the
mono-chelated and bis-chelated complexes were determined by
X-ray diffraction analysis and NMR measurements.
1. Introduction
A PNN pincer ligand is composed of three Lewis bases:
two nitrogen donors and a phosphorus donor. According to hard
and soft acids and bases (HSAB) theory,1 nitrogen donors
(amines, pyridines, quinolines, etc.) and phosphorus donors
(phosphines) are defined as hard and soft Lewis bases,
respectively. Hence, the hybrid ligands containing both hard
and soft bases are expected to effectively stabilize the
respective high- and low-valent transition metal centers,
formed in a catalytic reaction. In the past decade, the iron
complexes of PNN ligands were extensively developed,
especially for catalytic applications in several reactions,
including olefin polymerization,2 hydroborylation,3 and
hydrosilylation.4 To the best of our knowledge, all reported
Scheme 1. PNN pincer ligands and related reactions on the
PNN backbone.
For example, phosphinomethyl groups in pincer
complexes were deprotonated by the addition of base
(Scheme 1, A).5 The imino groups in PNN ligands cause
hydrolysis in the presence of water under acidic conditions
(Scheme 1, B).3b The reactivity of the pincer ligand offers
an unusual catalytic reaction6 and causes unexpected side
reactions, including, in some cases, its decomposition.4c On
the other hand, quinolines are thermally and chemically
robust heterocyclic aromatic compounds.7 These can be
produced from anilines in one step via a variety of named
condensation reactions.8-10 These reactions allow easy
access to diversely functionalized quinolines. Here, we
report the facile entry to the quinoline-based PNN pincer
ligand and the ligation reactions of these ligands with
iron(II) salts.
PNN-iron complexes contain
a phosphinomethyl group
(-CH2PR2, i, iv) and/or imino group (i, ii, iii, v) in the ligand
backbone (Figure 1). No iron complex of anionic PNN pincer
ligand has been reported to date. However, these functional
groups act as reactive sites under both acidic and basic
conditions.
2. Results and Discussion
The
quinoline
backbone,
2-(2-pyridyl)-5-fluoro-8-bromoquinoline (2), was synthesized
by modification of a previously reported Friedländer quinoline
synthesis
(Scheme
2).10,11
The
reaction
of
o-aminobenzaldehyde (1) with 2-acetylpyridine and KOH in
ethanol resulted in the formation of 2.
Figure 1. Iron complexes supported by PNN pincer ligand.
Scheme 2. Synthesis of PNN pincer ligand.

Lithiation of 2, followed by the addition of secondary
the diamagnetic ranges (0–10 ppm), which indicated a low-spin
d6 configuration in octahedral coordination geometry. However,
the NMR signals of 5b appeared broad. These spectroscopic
features stem from the diamagnetic (S = 0) Fe(PNN)2 dication
core and the paramagnetic (S = 2) FeCl4 dianion core.14,15 The
high-resolution mass spectrum of bis-chelated complexes
showed the characteristic dicationic (z = 2) isotope patterns by
every 0.5 m/z.16
chlorophosphines, R2PCl (R
=
iPr, Ph), produced the
corresponding PNN ligands (R = iPr: 3a (76%), Ph: 3b (59%)).
The ligation reactions of PNN ligands with iron dichloride in
THF proceeded readily to give the mono-chelated iron
i
complexes (R = Pr: 4a (83%), Ph: 4b (74%)). However, the
reaction of 3a with iron(II) triflate produced the bis-chelated
dication complex 5a with two triflate anions (Scheme 3). The
dicationic complex 5a was predominantly obtained even in the
reaction of 3a and the iron salt in a 1:1 ratio (77% isolated yield
based on Fe). A dichloromethane solution of 4b slowly
afforded the product 5b as a blue precipitate; in contrast, 4a
remains stable in solution. The dicationic complexes 5a and 5b
were insoluble in non-polar solvents but were soluble in polar
solvents such as methanol or water.
.
Scheme 3. Formation of mono-chelated and bis-chelated iron
complexes.
All isolated compounds 2-5 were characterized by NMR
measurements and high-resolution ESI-MS method. These
compounds are stable in solid state under ambient conditions
and their NMR spectra showed no detectable changes even
after a month. Molecular structures of 3a, 3b, 4a, and 5a were
confirmed by X-ray analysis; the ORTEP drawings of 4a and
5a are depicted in Figure 2. Complex 4a exhibits a distorted
square pyramidal geometry (5 = 0.31).12 The torsion angles
containing two nitrogen and phosphorus atoms are 4.52° for
NCCN and 2.40° for NCCP bonds. In comparison to related
bipyridine-based PNN pincer ligands,5a 4a has high planarity,
which indicates the rigidity of the pyridylquinoline backbone.
The molecular structure of 5a shows a distorted octahedral
geometry. The bond lengths of FeN (1.930(3), 1.932(3),
1.987(3), 1.992(3)) and FeP (2.2740(11), 2.2749(11)) in 5a
are significantly shortened compared to those of 4a (FeN:
2.154(3), 2.239(3); FeP: 2.4969(9)). These differences in bond
lengths presumably arise from the differences in the electron
configuration of these complexes: a high-spin state in 4a and a
low-spin state in 5a (Table 1).5a The FeN bonds of pyridine
are slightly longer than those of quinoline due to the trans
influence of phosphine. Other bond lengths and angles were
akin to those reported for PNN pincer complexes.2-4,5a In the 1H
NMR spectra of 4a and 4b, chemical shifts appeared in the
ranges of paramagnetic species (170 to −20 ppm for 4a, 130 to
−20 ppm for 4b). The effective magnetic moment in solution of
mono-chelated iron complexes was determined by the Evans
method.13 The results obtained for 4a (eff = 5.2 B) and 4b
(eff = 5.1 B) were consistent with S = 2, a high-spin state. In
contrast, all signals of bis-chelated complexes were observed in
Figure 2. ORTEP drawings of 4a (top) and 5a (bottom,
cation core) with 50% thermal ellipsoid plots: Hydrogen
atoms and methyl groups on isopropyl moieties were
omitted for clarity.
Table 1. Selected bond distances (Å) and angles (°) of 4a and
5a.
4a
5a
2.154(3),
2.239(3)
1.930(3), 1.932(3),
1.987(3), 1.992(3)
2.2740(11),
FeN
FeP
2.4969(9)
2.2749(11)
2.3219(6),
2.3311(7)
131.45(5)
119.52(5)
108.25(2)
150.06(5)
77.40(5)
FeCl
N2-Fe-Cl1
N2-Fe-Cl2
Cl1-Fe-Cl2
N1-Fe-P1
N2-Fe-P1
N1-Fe-N2
N1-Fe-N3
164.1(1)
84.6(1)
80.6(1)
73.21(6)
178.45(1)

ellipsoid plot: The solvent molecules, hydrogen atoms, and
methyl groups on isopropyl and tert-butyl moieties were
omitted for clarity.
The formation of two structurally different iron
complexes, namely, the mono-chelated complex and
bis-chelated complex, seems to depend on the iron salt used
and the substituent of phosphorus atoms. The preferential
formation of bipyridine-based PNN complexes similar to 4 and
5 was studied by Milstein and co-workers in the cases where
chloride and bromide salts were used.5a The reaction of 3a and
3b with chloride salts afforded mono-chelated species 4a and
4b. In this study, the mono-chelated complex bearing a
diphenylphosphino substituent 4b was converted to the
corresponding bis-chelated complex 5b in solution. However,
no conversion of PNN complex with diisopropyl substituted
phosphine 4a to the bis-chelated complex was observed in
solution.17 The difference in the stability of diphenyl phosphino
complex and diisopropyl complex was similar to that observed
in bipyridine-based PNN complexes; this arises from the steric
repulsion of the phosphorus substituents. In the work of
Milstein,5a the thermodynamic stability of mono-chelated
PNN iron complexes (dichloride and dibromide) was explained
considering the equilibrium between their mono-chelated and
bis-chelated species. Although the thermodynamic aspects of
the two triflate complexes were unexplored, the triflate anion is
known as a good leaving group, which could accelerate the
formation of cationic species.
3. Conclusion
Quinoline-based PNN-type pincer ligands were
synthesized and characterized. The pyridylquinoline scaffold 2
was prepared by
o-aminobenzaldehyde with 2-acetyl pyridine via Friedländer
quinoline synthesis. Simple phosphination reaction of
a
facile one-pot reaction from
2
provides the corresponding PNN ligand 3. X-ray diffraction
study and NMR measurements revealed the formations of two
structurally different complexes 4 and 5 in the reactions of 3
with an iron salt. The chemical tolerance of the PNN backbone
was confirmed by the reaction of 4a with bases.
4. Experimental
General Experimental Procedures
All manipulations for air sensitive materials were carried
out using Schlenk techniques under a dry argon or nitrogen
atmosphere. Tetrahydrofuran (THF), benzene, and n-hexane
used for air sensitive materials were distilled from sodium and
benzophenone prior to use and stored under a nitrogen
atmosphere. Compound 1 was prepared according to the
reported procedure,10d and the other chemicals used were
commercially available. NMR spectra (1H, 13C{1H} and
31P{1H}) were recorded on a Bruker AVANCE-II-400 or on a
In the reactions catalyzed by iron pincer complexes,
strong bases were used as promoters.2-4 For verification of the
reactivity of quinoline-based PNN complexes toward bases, the
reaction of 4a with KOtBu and KOPv (KOPv = KOOCtBu) was
carried out. In the case of KOtBu, a dissociation of PNN ligand
1
Bruker AVANCE-III-600 spectrometer. H and 13C{1H} NMR
data were assigned using the solvent residual peak as an
internal standard (CDCl3:  = 7.26 ppm, C6D6:  = 7.16 ppm,
CD3OD:  = 3.31 ppm), whereas those of the 19F{1H} and
31P{1H} NMR spectra were referenced to C6F6 (-162.90 ppm)
1
was observed by H NMR measurement (Scheme 4). Similar
phenomena in the reaction of NaOtBu with NNN-type iron
pincer complexes have been reported.4b, 18 However, thermally
stable 6a bearing two carboxylate ligands was obtained in the
reaction of 4a with an excess amount of KOPv. No
deprotonation of PNN backbone was observed in both cases.
Molecular structure of 6a was confirmed by X-ray analysis and
depicted in Figure 3. The distances of FeP and FeN bonds
were similar to those of high-spin species. The broaden 1H
NMR signals of 6a appeared in a wide range (174 ppm to −12
ppm), which supports high-spin state of 6a.16
and 85% H3PO4 (
= 0 ppm) as external references,
respectively. High-resolution mass spectra were recorded on a
Thermo Scientific, Exactive Plus Orbitrap Mass Spectrometer
for electrospray ionization (ESI).
2-pyridyl-5-fluoro-8-bromoquinoline, 2
To an ethanol solution (72 mL) of 3-bromo-6-fluoro-
2-nitrobenzaldehyde10d,19 (6.00 g, 24.4 mmol) was added iron
powder (6.00 g, 1.07 mmol, ~4.5 eq.), water (12 mL) and conc.
HCl (15 drops with a standard Pasteur pipette) in this order.
The resulting mixture was refluxed for 1.5 h. After cooling to
room temperature, EtOAc (420 mL) and MgSO4 were added to
the solution. The mixture was stirred for 30 min for dryness.
The insoluble materials were removed by filtration and the pale
yellow filtrate was evaporated. Crude material obtained after
the evaporation (1) was used for the synthesis of 2 without
further purification (~100% conversion to 110d was confirmed
by 1H NMR measurement). To a pale yellow-green solid 1 was
added absolute ethanol (180 mL, dried over 3A molecular
sieves prior to use), 2-acetylpyridine (2.74 mL, 24.4 mmol) and
KOH (672 mg, 11.6 mmol). After the mixture was refluxed for
1 h, the solution was gradually cooled to 0 ºC. The white
precipitates were filtered and washed with cold ethanol (15 mL,
twice) and hexane (30 mL, twice). The solid was dissolved into
CH2Cl2 (50 mL) and the resulting solution was filtered. The
filtrate was evaporated to give an analytically pure white
powder 2 (6.15 g, 20.3 mmol, 84%). 1H NMR (400 MHz,
Chloroform-d) δ 8.89 (dt, JHH = 8.0, 1.1 Hz, 1H, aromatic),
8.80 – 8.76 (m, 1H, aromatic), 8.77 (d, JHH = 8.8 Hz, 1H,
Scheme 4. Reaction of 4a with bases.
aromatic), 8.59 (d, JHH = 8.8 Hz, 1H, aromatic), 8.03 (dd, JHH
8.4, JHF = 5.5 Hz, 1H, aromatic), 7.95 (ddd, J = 8.0, 7.5 1.8 Hz,
1H, aromatic), 7.44 (ddd, J = 7.5, 4.8, 1.2 Hz, 1H, aromatic),
=
Figure 3. ORTEP drawing of 6a (one of the two
independent molecule in the unit cell) with 50% thermal

7.16 (dd, JHF = 9.1, JHH = 8.3 Hz, 1H, aromatic). 13C{1H} NMR
(101 MHz, Chloroform-d) δ 157.45 (d, JCF = 256.1 Hz,
aromatic), 157.38 (s, aromatic), 155.26 (s, aromatic), 149.09 (s,
aromatic), 144.99 (d, JCF = 3.3 Hz, aromatic), 137.03 (s,
stirred for 30 min. The yellow colored solution was separated
by filtration and evaporated. The yellow solid was washed with
cold hexane (10 mL, twice). The resulting residue was dried
under a high vacuum condition to give a pure 3b (1.35 g, 3.89
mmol, 59%) as a yellow solid. Yellow crystals for X-ray
analysis were grown from CH2Cl2 solution at room temperature.
1H NMR (400 MHz, Chloroform-d) δ 8.71 – 8.63 (m, 2H,
aromatic), 8.62 (d, J = 8.9 Hz, 1H, aromatic), 8.53 (d, J = 8.8
Hz, 1H, aromatic), 8.06 (dt, J = 8.0, 1.1 Hz, 1H, aromatic), 7.66
(td, J = 7.8, 1.8 Hz, 1H, aromatic), 7.46 – 7.38 (m, 4H,
aromatic), 7.37 – 7.30 (m, 6H, aromatic), 7.29 – 7.27 (m, 1H,
aromatic), 7.16 – 7.07 (m, 1H, aromatic), 7.06 – 6.99 (m, 1H,
aromatic). 13C{1H} NMR (101 MHz, Chloroform-d) δ 158.84
(d, JCF = 257.0 Hz, aromatic), 155.59 (d, J = 1.8 Hz, aromatic),
155.49, 149.15 (dd, J = 17.1, 3.3 Hz, aromatic), 148.73, 137.26
(d, J = 10.2 Hz, aromatic), 137.02 (s, aromatic), 134.65 (dd, J =
11.5, 4.8 Hz, aromatic), 134.26 (d, J = 20.8 Hz, aromatic),
133.72 (dd, J = 8.5, 1.5 Hz, aromatic), 130.40 (dd, J = 4.4, 1.1
Hz, aromatic), 128.74 (s, aromatic), 128.49 (d, J = 7.4 Hz,
aromatic), 128.35 (s, aromatic), 124.32 (s, aromatic), 122.40 (s,
aromatic), 119.06 (dd, J = 2.4, 0.8 Hz, aromatic), 118.67 (dd, J
= 16.3, 2.0 Hz, aromatic), 110.59 (d, J = 18.8 Hz, aromatic).
19F{1H} NMR (376 MHz, Chloroform-d) δ 122.25. 31P{1H}
NMR (162 MHz, Chloroform-d) δ 13.51. HRMS (ESI) Calcd.
for C26H19N2FP [M+H]+: 409.1264, Found 409.1262. Multiple
attempts to obtain satisfactory elemental analysis data failed.
aromatic), 132.04 (d, JCF = 8.5 Hz, aromatic), 130.55 (d, JCF
=
4.1 Hz, aromatic), 124.63 (s, aromatic), 122.43 (s, aromatic),
120.01 (d, JCF = 17.1 Hz, aromatic), 119.83 (d, JCF = 4.5 Hz,
aromatic), 119.56 (d, JCF = 2.9 Hz, aromatic), 110.97 (d, JCF
=
20.8 Hz, aromatic). 19F{1H} NMR (376 MHz, Chloroform-d) δ
122.75. HRMS (ESI) Calcd. for C14H9N2FBr [M+H]+:
302.9928, Found 302.9926. Elemental analysis, Found: C,
55.07; H, 2.35; N, 9.19%, Calcd for C14H8N2FBr: C, 55.47; H,
2.66; N, 9.24%.
2-pyridyl-5-fluoro-8-diisopropylphosphinoquinoline, 3a
Compound 2 (2.0 g, 6.60 mmol) was dissolved in dry THF (40
n
mL). To the colorless solution was slowly added 2.5 M BuLi
solution in hexane (2.78 mL, 6.93 mmol) at 78 ºC and stirred
i
for 1 h. To the deep purple solution was added Pr2PCl (1.16
mL, 7.26 mmol) at 78 ºC, allowed to gradually warm to room
temperature, and stirred overnight (~16 h). Volatile materials
were removed from the yellow brown solution. Hexane (40
mL) and degassed H2O (20 mL) were added to the residue. The
mixture was vigorously stirred for 30 min. Organic layer (upper
phase, typically yellow colored) was separated and dried over
anhydrous MgSO4. Insoluble materials were filtered off. The
volume of the hexane solution was reduced by evaporation to ~
1 mL. The solution was stored in a freezer (20 ºC) overnight.
Precipitated yellow solid was filtered and quickly washed with
cold hexane (1 mL, twice). The resulting solid was dried under
a high vacuum condition to give a pure 3a (1.71 g, 5.02 mmol,
76%) as a crystalline yellow solid. Crystals suitable for X-ray
analysis were grown from concentrated hexane solution at
Dichloro(2-pyridyl-5-fluoro-8-diisopropylphosphinoquinoli
ne)iron(II), 4a
Under an air free condition, a THF solution (10 mL) containing
3a (690.0 mg, 2.03 mmol) was added to a suspension of
FeCl2/THF (252 mg, 1.99 mmol, in 10 mL). The solution was
stirred overnight at room temperature. The precipitated green
solid was filtered, washed with dry THF (5 mL, twice), and
dried under a high vacuum condition to give the title complex
(770.7 mg, 1.65 mmol, 83%) as a pale green powder. Single
crystals suitable for X-ray diffraction were obtained from
1
20 °C. H NMR (400 MHz, Benzene-d6) δ 9.07 (dt, J = 8.0,
1.1 Hz, 1H, aromatic), 8.86 (d, J = 8.8 Hz, 1H, aromatic), 8.54
(ddd, J = 4.7, 1.8, 0.9 Hz, 1H, aromatic), 8.20 (d, J = 8.8 Hz,
1H, aromatic), 7.51 (ddd, J = 8.0, 6.5, 4.7 Hz, 1H, aromatic),
7.28 (td, J = 7.7, 1.8 Hz, 1H, aromatic), 6.82 (dd, J = 9.6, 7.9
Hz, 1H, aromatic), 6.70 (ddd, J = 7.5, 4.8, 1.2 Hz, 1H,
aromatic), 2.55~2.39 (m, 2H, PCH(CH3)2), 1.24 (dd, JHP = 14.1,
JHH = 7.0 Hz, 6H, PCH(CH3)2), 0.99 (dd, JHP = 11.9, JHH = 6.9
Hz, 6H, PCH(CH3)2). 13C{1H} NMR (101 MHz, Benzene-d6) δ
158.66 (d, JCF = 256.5 Hz, aromatic), 156.02 (s, aromatic),
155.86 (s, aromatic), 151.17 (dd, JCP = 12.5, JCF = 2.9 Hz),
148.99 (s, aromatic), 136.37 (s, aromatic), 135.23 – 134.50 (m,
aromatic), 133.34 (dd, JCF = 25.3, JCP = 4.9 Hz), 130.01 (d, JCF
= 4.5 Hz, aromatic), 123.94 (s, aromatic), 121.94 (s, aromatic),
1
concentrated CH2Cl2 solution layered with hexane. H NMR
(400 MHz, Chloroform-d) δ 168.72, 146.40, 77.10, 75.38,
51.90, 22.76, 12.93, 10.32, 9.36, 3.75, 2.09, 1.86, 19.76.
Magnetic susceptibility (Evans): eff = 5.2 B. HRMS (ESI)
Calcd. for C20H22N2FPClFe [M-Cl]+: 431.0537, Found
431.0538. Elemental analysis, Found: C, 51.21; H, 4.59; N,
6.03%, Calcd for C20H22N2FPCl2Fe: C, 51.42; H, 4.75; N,
6.00%.
Dichloro(2-pyridyl-5-fluoro-8-diphenylphosphinoquinoline)
iron(II), 4b
119.01 (dd, JCP = 15.4, JCF = 1.8 Hz, aromatic), 118.79 (d, JCF
2.9 Hz, aromatic), 109.58 (dd, JCP = 18.4, JCF = 4.3 Hz,
aromatic), 23.42 (d, JCP = 15.1 Hz, PCH(CH3)2), 20.42 (d, JCP
=
Under an air free condition, a THF solution (10 mL) containing
3b (435.4 mg, 1.07 mmol) was added to a suspension of
FeCl2/THF (133.8 mg, 1.06 mmol, in 10 mL). The solution was
stirred overnight (~16 h) at room temperature. The formed pale
blue solid was filtered, washed with dry THF (5 mL, twice),
and dried under a high vacuum condition to give the title
complex (423.3 mg, 0.789 mmol, 74%) as a pale blue powder.
1H NMR (400 MHz, Chloroform-d) δ 130.52, 81.26, 71.67,
55.64, 16.93, 16.83, 3.76, 1.87, -3.78, -19.16. Magnetic
susceptibility (Evans): eff = 5.1 B. HRMS (ESI) Calcd. for
C26H18N2FPClFe [M-Cl]+: 499.0224, Found 499.0230.
Elemental analysis, Found: C, 57.88; H, 3.45; N, 5.35%, Calcd
for C26H18N2FPCl2Fe: C, 58.35; H, 3.39; N, 5.23.
=
19.1 Hz, PCH(CH3)2), 19.81 (d, JCP = 12.2 Hz, PCH(CH3)2).
19F{1H} NMR (376 MHz, Benzene-d6) δ 122.24. 31P{1H}
NMR (162 MHz, Benzene-d6): δ 3.39. HRMS (ESI) Calcd. for
C20H23N2FP [M+H]+: 341.1577, Found 341.1582. Elemental
analysis, Found: C, 70.53; H, 6.53; N, 8.21%, Calcd for
C20H22N2FP: C, 70.57; H, 6.52; N, 8.23%.
2-pyridyl-5-fluoro-8-diphenylphosphinoquinoline, 3b
Compound 2 (2.0 g, 6.60 mmol) was dissolved in dry THF (40
n
mL). To the colorless solution was slowly added 2.5 M BuLi
solution in hexane (2.78 mL, 6.93 mmol) at 78 ºC and stirred
for 1 h. To the deep purple solution was added Ph2PCl (1.34
mL, 7.26 mmol) at 78 ºC, allowed to gradually warm to room
temperature, and stirred overnight (~16 h). Volatile materials
were removed from the yellow brown solution. Toluene (50
mL) was added to the residue. The mixture was vigorously
Bis(2-pyridyl-5-fluoro-8-diisopropylphosphinoquinoline)iro
n(II) triflate, 5a
Under an air free condition, a THF solution (10 mL) containing
3a (174.8 mg, 0.514 mmol, 1.0 equiv.) and Fe(OTf)2 (90.0 mg,

0.254 mmol, 0.5 equiv.) was stirred overnight (~16 h) at room
temperature. The precipitated blue-purple solid was filtered,
washed with THF (5 mL, twice), and dried under a high
vacuum condition to give the title complex (182.7 mg, 0.177
mmol, 69%) as a blue solid. Single crystals suitable for X-ray
diffraction were obtained from concentrated THF solution
C30H40FFeN2O4P [M]+: 598.2054, Found 598.2055. Elemental
analysis, Found: C, 61,67; H, 6.76; N, 4.03%, Calcd. For
C32.7H42.7FFeN2O4P [M + 0.45 C6H6]: C, 61.99; H, 6.79; N,
4.42%.
X-ray diffraction structure analysis
1
layered with hexane. H NMR (400 MHz, Methanol-d4) δ 9.02
Single crystals of 3a, 3b, 4a, 5a, and 6a suitable for X-ray
diffraction analysis were mounted on tip of a MiTeGen loop
coated in NVH oil. All data were collected at 173K (3a, 3b, 5a,
6a) or 120K (4a) on a Bruker Apex-Ⅱ CCD diffractometer
with monochromated MoKα radiation. Final cell constants
were calculated from the xyz centroids of a particular number
of strong reflections for each crystal from the actual data
collection after integration using SAINT20. The intensity data
were corrected for absorption using SADABS21. The structure
was solved with the ShelXT22 structure solution program using
Intrinsic Phasing and refined with the olex2.refine23,24
refinement package using Gauss-Newton minimisation. A
full-matrix least-squares refinement was performed for the
non-hydrogen atoms with anisotropic thermal parameters.
Hydrogen atoms were located by assuming the ideal geometry,
and were included in the structure calculation without further
refinement of the parameters. Crystal Data for 3a: C20H22FN2P,
M = 340.38, triclinic, space group P-1, a = 9.9696(17) Å, b =
10.0771(17) Å, c = 19.595(3) Å, α = 81.756(2)°, β = 81.726(2)°,
γ = 74.268(2)°, V = 1863.8(6) Å3, Z = 4, T = 173 K, μ(Mo
Kα) = 0.160 mm-1, Dcalc = 1.2129 g/cm3, 18620 reflections
measured (2.1° ≤ 2θ ≤ 50.88°), 6836 unique (Rint = 0.0348,
Rsigma = 0.0422) which were used in all calculations. The final
R1 was 0.0513 (I>=2σ(I)) and wR2 was 0.1567 (all data).
Crystal Data for 3b: C26H18FN2P, M = 408.42, monoclinic,
space group P21/c (no. 14), a = 9.3731(7) Å, b = 9.4270(7) Å,
c = 23.4590(18) Å, β = 98.398(1)°, V = 2050.6(3) Å3, Z = 4,
T = 173 K, μ(Mo Kα) = 0.158 mm-1, Dcalc = 1.3228 g/cm3,
20068 reflections measured (4.4° ≤ 2θ ≤ 51.04°), 3811 unique
(Rint = 0.0241, Rsigma = 0.0163) which were used in all
calculations. The final R1 was 0.0309 (I>=2σ(I)) and wR2 was
0.0835 (all data). Crystal Data for 4a: C20H22Cl2FFeN2P, M =
467.13, triclinic, space group P-1, a = 8.0216(14) Å, b =
9.4162(16) Å, c = 14.281(2) Å, α = 76.513(2)°, β = 77.774(2)°,
γ = 81.060(3)°, V = 1018.7(3) Å3, Z = 2, T = 120 K, μ(Mo
Kα) = 1.098 mm-1, Dcalc = 1.5228 g/cm3, 11741 reflections
measured (2.98° ≤ 2θ ≤ 54.90°), 4580 unique (Rint = 0.0455,
Rsigma = 0.0622) which were used in all calculations. The final
R1 was 0.0455 (I>=2σ(I)) and wR2 was 0.1187 (all data).
Crystal Data for 5a: C40H44F2FeN4P2 2(CF3O3S) C4H8O, M =
1106.86, monoclinic, space group P21/n, a = 11.7640(17) Å,
b = 27.854(4) Å, c = 14.649(2) Å, β = 97.271(2)°, V =
4761.4(12) Å3, Z = 4, T = 173 K, μ(Mo Kα) = 0.559 mm-1,
Dcalc = 1.5439 g/cm3, 47109 reflections measured (3.16° ≤ 2θ
≤ 50.78°), 8719 unique (Rint = 0.0463, Rsigma = 0.0354) which
were used in all calculations. The final R1 was 0.0632
(I>=2σ(I)) and wR2 was 0.1814 (all data). Crystal Data for 6a:
C30H40FFeN2O4P, 1.5(C6H6), M = 715.65, monoclinic, space
group Pbca, a = 22.435(4) Å, b = 26.513(4) Å, c = 26.513(4) Å,
V = 15684(4) Å3, Z = 16, T = 173 K, μ(Mo Kα) = 0.559 mm-1,
Dcalc = 1.2122 g/cm3, 147876 reflections measured (2.84° ≤
2θ ≤ 50.74°), 14363 unique (Rint = 0.0484, Rsigma = 0.0286)
which were used in all calculations. The final R1 was 0.0599
(I>=2σ(I)) and wR2 was 0.1935 (all data). Crystallographic data
reported in this manuscript have been deposited with
Cambridge Crystallographic Data Centre as supplementary
(d, J = 8.9 Hz, 2H, aromatic), 8.95 (d, J = 9.0 Hz, 2H,
aromatic), 8.90 (d, J = 8.1 Hz, 2H, aromatic), 8.60 – 8.42 (m,
2H, aromatic), 8.17 (td, J = 7.8, 1.4 Hz, 2H, aromatic), 7.88 (t,
J = 8.6 Hz, 2H, aromatic), 7.79 (d, J = 5.6 Hz, 2H, aromatic),
7.42 – 7.30 (m, 2H, aromatic), 2.40 – 2.20 (m, 2H, PCH(CH3)2),
2.06 – 1.94 (m, 2H, PCH(CH3)2), 1.36 (dd, JHP = 11.4 Hz, JHH
= 7.3 Hz, 6H, PCH(CH3)2), 0.36 (d, JHP = 14.0 Hz, JHH = 7.2
Hz, 6H, PCH(CH3)2), 0.23 (d, JHP = 14.5 Hz, JHH = 7.2 Hz, 6H,
PCH(CH3)2), 0.07 (d, JHP = 15.7 Hz, JHH = 7.0 Hz, 6H,
PCH(CH3)2). 13C{1H} NMR (151 MHz, Methanol-d4) δ 161.94
(s, aromatic), 160.24 (d, JCF = 263.1 Hz, aromatic), 157.87 (s,
aromatic), 157.13 (td, J = 9.9, 4.3 Hz, aromatic), 151.33 (s,
aromatic), 138.67 (s, aromatic), 138.42 (d, J = 9.6 Hz,
aromatic), 130.29 (d, J = 4.4 Hz, aromatic), 128.66 – 127.65 (m,
aromatic), 127.54 (s, , aromatic), 125.95 (s, aromatic), 121.09
(s, aromatic), 119.44 (dt, J = 19.1, 3.9 Hz, aromatic), 114.02 (d,
J = 19.8 Hz, aromatic), 28.65 (t, J = 8.3 Hz, PCH(CH3)2), 26.75
(t, J = 10.3 Hz, PCH(CH3)2), 18.92 (s, PCH(CH3)2), 18.80 (t, J
= 3.6 Hz, PCH(CH3)2), 18.16 (s, PCH(CH3)2), 17.41 (s,
PCH(CH3)2). 19F{1H} NMR (376 MHz, Methanol-d4) δ 80.08
(s, CF3), 115.58 (s, ligand). 31P{1H} NMR (162 MHz,
Methanol-d4)
δ
56.58 (s). HRMS (ESI) Calcd. for
C40H44N4F2P2Fe [M-2OTf]2+: 368.1174, Found 368.1176.
Multiple attempts to obtain satisfactory elemental analysis data
failed.
Bis(2-pyridyl-5-fluoro-8-diisopropylphosphinoquinoline)iro
n(II) tetrachloroferrate(II), 5b
Under an air free condition, a CH2Cl2 solution (10 mL)
containing 4b (50.0 mg, 93.4 mol) was stirred overnight (~16
h) at room temperature. The precipitated blue-purple solid was
filtered, washed with CH2Cl2 (10 mL, twice), and dried under a
high vacuum condition to give the title complex (46.6 mg, 43.5
mol, 83%) as a deep blue solid. 1H NMR (400 MHz,
Methanol-d4) δ 9.26 (br, 2H, aromatic), 8.91 (br, 2H, aromatic),
8.45 (br, 2H, aromatic), 8.11 (br, 2H, aromatic), 7.78 (br, 2H,
aromatic), 7.30 (s, 2H, aromatic), 7.14 (br-d, J = 30.0 Hz, 6H,
aromatic), 6.84 (br-d, J = 28.4 Hz, 8H, aromatic), 6.39 (br, 4H,
aromatic), 6.20 (br, 4H, aromatic). 19F{1H} NMR (376 MHz,
Methanol-d4)
δ
-112.77. 31P{1H} NMR (162 MHz,
Methanol-d4) δ 56.32 (s). Magnetic susceptibility (Evans): eff
= 4.7 B. HRMS (ESI) Calcd. for C52H36N4F2P2Fe [M-FeCl4]2+:
436.0861, Found 436.0859. Multiple attempts to obtain
satisfactory elemental analysis data failed.
Bis(pivaloate)(2-pyridyl-5-fluoro-8-diisopropylphosphinoqu
inoline)iron(II), 6a
Under an air free condition, a benzene solution (5 mL)
containing 4a (100.0 mg, 0.214 mmol) and KOPv (300.2 mg,
2.14 mmol, 10 equiv.) was stirred for 1 h at room temperature.
The insoluble materials were filtered off. To the filtrate was
added hexane (10 mL). The precipitated green solid was
filtered, washed with hexane (5 mL, twice), and dried under a
high vacuum condition to give the title complex (85.8 mg,
0.143 mmol, 67%) as a green solid. Single crystals suitable for
X-ray diffraction were obtained from concentrated benzene
publication
no.
CCDC-1589155,
CCDC-1815918,
solution layered with hexane.
1H NMR (600 MHz,
CCDC-1815917, CCDC-1834048, and CCDC-1839338.
Copies of the data can be obtained free of charge via CCDC
Website.
benzene-d6) δ 174.38, 136.08, 67.35, 61.97, 47.22, 27.48, 20.44,
9.92, 4.46, 2.88, 12.26. HRMS (ESI) Calcd. for

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19. Fluoro group in o-nitrobenzaldehyde prevents the
formation of undesired nitro compounds in the nitration
of 3-bromobenzaldehyde.
20. SAINT v8.34a, 2013, Bruker AXS Inc., Madison, WI.
21. SADABS-2014/4, 2014, Bruker AXS Inc., Madison, WI.
22. G. M. Sheldrick, Acta Cryst. 2015, A71, 3-8.
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Acknowledgement
This work was supported by a Grant-in-Aid for Young
Scientists (B) (JSPS KAKENHI Grant Number 16K17880), the
Kitasato University Research Grant for Young Researchers.
Supporting Information: NMR spectrum of isolated compounds.
This is available on http://dx.doi.org/10.1246/bcsj.***.
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17. No conversion from 4a to dicationic species was
observed in the 1H NMR and high-resolution MS
measurements after 1 day.