Synthesis, Structures, and Reactivities of Iron Complexes Bearing an Isoindoline-Based, Polyprotic Pincer-Type Pyrazole Ligand

Article abstract of DOI:10.1002/zaac.202100103

The synthesis and properties of polyprotic NNN pincer-type bis(pyrazole) iron complexes derived from a 1,3-bis(pyrazol-3-ylimino)isoindoline 1 were investigated. When 1 was treated with iron(II) chloride, the paramagnetic, square-pyramidal complex [FeCl₂(LH₃)] (2; LH₃=3-(5-tert-butylpyrazol-3-ylamino)-1-(5-tert-butylpyrazol-3-ylimino)-1H-isoindole) was obtained. Reaction of 2 with two equiv. of silver triflate followed by addition of two equiv. of trimethylphosphine yielded the diamagnetic, octahedral complex [Fe(OTf)(PMe₃)₂(LH₃)]OTf (3), which was converted to the carbonyl complex [Fe(CO)(PMe₃)₂(LH₃)](OTf)₂ (4). Treatment of 4 with triethylamine led to deprotonation of the chelate backbone to give the isoindolin-2-yl complex [Fe(CO)(PMe₃)₂(LH₂)]OTf (5). The structures of the LH₃ and LH₂ ligands were compared in details. The NH groups in the pincer ligand in 2–5 are accompanied by hydrogen bonds, showing their Br?nsted acidic nature. In addition, 3 catalyzed disproportionation of hydrazine, although the catalytic activity was lower than that of a related pyridine-based pincer complex 6 a.

Full text of DOI:10.1002/zaac.202100103

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.202100103
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Synthesis, Structures, and Reactivities of Iron Complexes
Bearing an Isoindoline-Based, Polyprotic Pincer-Type
Pyrazole Ligand
Tatsuro Toda[a] and Shigeki Kuwata*[a]
The synthesis and properties of polyprotic NNN pincer-type bis
(pyrazole) iron complexes derived from a 1,3-bis(pyrazol-3-
ylimino)isoindoline 1 were investigated. When 1 was treated
with iron(II) chloride, the paramagnetic, square-pyramidal
complex [FeCl2(LH3)] (2; LH3 =3-(5-tert-butylpyrazol-3-ylamino)-
1-(5-tert-butylpyrazol-3-ylimino)-1H-isoindole) was obtained. Re-
action of 2 with two equiv. of silver triflate followed by addition
of two equiv. of trimethylphosphine yielded the diamagnetic,
octahedral complex [Fe(OTf)(PMe3)2(LH3)]OTf (3), which was
converted to the carbonyl complex [Fe(CO)(PMe3)2(LH3)](OTf)2
(4). Treatment of 4 with triethylamine led to deprotonation of
the chelate backbone to give the isoindolin-2-yl complex
[Fe(CO)(PMe3)2(LH2)]OTf (5). The structures of the LH3 and LH2
ligands were compared in details. The NH groups in the pincer
ligand in 2–5 are accompanied by hydrogen bonds, showing
their Brønsted acidic nature. In addition, 3 catalyzed dispropor-
tionation of hydrazine, although the catalytic activity was lower
than that of a related pyridine-based pincer complex 6a.
Introduction
The meridional pincer ligands have been prominent scaffolds
for
bond
activation,
homogeneous
catalysis,
and
supramolecular chemistry.[1,2] Typical examples include 2,2’:6’,2“-
terpyridines[3] and 2,6-bis(oxazolinyl)pyridines[4] as tri(nitrogen)-
donors. Unlike these electronically neutral NNN tridentate
ligands, 1,3-bis(2-pyridylimino)isoindolines (BPI), readily acces-
sible from phthalonitrile, bind to the metal in both neutral 1H-
isoindole and monoanionic isoindolin-2-yl forms owing to facile
deprotonation of the central pyrrole NH group and tautomeri-
zation (Scheme 1).[5,6] With the proton-responsive nature of the
highly π-conjugated chelate backbone as well as the structural
relevance to phthalocyanine, BPI and related isoindoline-
centered compounds are attractive templates of multiproton-
responsive pincer-type complexes, which would exhibit metal-
ligand cooperative catalysis[2,7] through multiple hydrogen bond
formation and proton transfer between the ligand and sub-
strate molecule(s).[8] However, such isoindoline-based ligand
design is still in its infancy.[9,10] Szymczak and co-workers
demonstrated that a ruthenium complex bearing a bis(hydroxy)
derivative of BPI behaves as a polyprotic acid and catalyzes
hydroboration of nitriles[9] as well as CO2 hydrogenation and
HCOOH dehydrogenation.[11]
Scheme 1. (a) Coordination of 1,3-bis(2-pyridylimino)isoindoline
(BPI) associated with ligand tautomerization. (b) Deprotonation of
1-imino-3-amino-1H-isoindole complex.
mainly containing pyrazole units.[12,13] We report here the
synthesis of iron complexes bearing a 1H-isoindole flanked by
two multiproton-responsive pyrazolylimino arms. Deprotona-
tion of the resulting pincer-type complex with three ionizable
NH groups as well as the catalytic activity was also explored.
The structures and reactivities are compared with those of 2,6-
bis(pyrazol-3-yl)pyridine (PzH2Py) complexes having a related
meridional bis(pyrazole) framework.[14]
During the past years, we have been working on the
development of proton-responsive chelate ligands for catalysis
Results and Discussion
Synthesis of 1,3-Bis(pyrazol-3-ylimino)isoindoline Ligand
and Its Complexation
[a] Dr. T. Toda, Prof. Dr. S. Kuwata
Department of Chemical Science and Engineering
School of Materials and Chemical Technology
Tokyo Institute of Technology
2-12-1 E4-1 O-okayama, Meguro-ku, Tokyo 152-8552 (Japan)
E-mail: skuwata@cap.mac.titech.ac.jp
The target 1,3-bis(pyrazol-3-ylimino)isoindoline ligand 1 as a
pyrazole analogue of BPI was obtained by condensation of
phthalonitrile and a 3-aminopyrazole (Scheme 2).[5] The syn-
thesis and crystal structures of 5-methyl- and 5-phenylpyrazole
congeners of 1 have been reported recently[15] but their
coordination chemistry was unexplored.
Supporting information for this article is available on the WWW
under https://doi.org/10.1002/zaac.202100103
Z. Anorg. Allg. Chem. 2021, 647, 1–8
1
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
tilted from the isoindole plane with the interplane angles of
°
20.25(9) and 14.52(9) . Consequently the six-membered chelates
are slightly folded. The Fe1 atom is displaced from the isoindole
plane by 0.539(3) Å. In the crystal, 2 forms a centrosymmetric
dimer structure with a short N6···Cl1* contact of 3.157(2) Å,
substantiating the hydrogen bonding between the NH group
and the apical chlorido ligand (Figure S1). The bond alternation
in the N6À C4À N5À C11À N7 linkage also supports the 3-amino-1-
imino-1H-isoindole formulation of the pincer ligand. Meanwhile,
the pyrazole NH groups are engaged in intramolecular hydro-
gen bonds with the basal chlorido ligand (N···Cl: 3.152(2) and
3.113(2); NH···Cl: 2.60 and 2.53 Å). These non-covalent inter-
actions indicate the Brønsted acidity of the three NH groups in
the neutral, L3-type LH3 ligand.
Derivatization to Diamagnetic Complexes
Figure 1. Crystal structure of 2·DMF. The CH hydrogen atoms as
well as the co-crystallized DMF molecule are omitted for clarity.
Ellipsoids are drawn at the 30% probability level.
Because the paramagnetic nature of 2 hampered deeper
investigations of the properties of the NH groups in the pincer
ligand, we installed soft phosphine ligands to stabilize the low-
spin state. Chloride abstraction of 2 followed by addition of two
equiv. of trimethylphosphine afforded the diamagnetic triflate
complex [Fe(OTf)(PMe3)2(LH3)]OTf (3) as the corresponding
reaction of
a
PzH2Py complex (Scheme 3).[20] The crystal
structure of the iron(II) complex 3 is shown in Figure 2. In
contrast to the chlorido complex 2, the coordination geometry
of the iron center is distorted octahedral, and the pincer ligand
is almost planar. The FeÀ N distances in the low-spin complex 3
(1.919(2)–1.936(2) Å) are significantly shortened[21] from the
high-spin complex 2 and a related 1H-isoindole iron complex
derived from BPI[22] (2.057(2)–2.219(2) Å). The two pyrazole
groups and the amino hydrogen in the chelate backbone make
hydrogen bonds with the O atoms in the triflate ligand and
countercation, respectively, as evidenced by the short NH···O
contacts (1.83–2.46 Å). The 1H NMR spectrum of 3 exhibits three
sharp, 1H-intensity singlets ascribed to the NH groups in
agreement with the 1H-isoindole structure featuring clear bond
alternation. The signals of the two tert-butyl groups as well as
the four isoindole CH protons appear inequivalent. These
observations indicate that prototropic tautomerization of the
pincer ligand, which would make the two pincer arms
equivalent, is slow in contrast to related 1H-isoindole complexes
of cadmium and zinc derived from BPI.[23] The 19F NMR spectrum
Scheme 2. Synthesis of 1,3-bis(pyrazol-3-ylimino)isoindoline 1.
The reaction of 1 with anhydrous iron(II) chloride in a ratio
of 1:1 led to the formation of the iron(II) complex [FeCl2(LH3)]
(2; LH3 =3-(5-tert-butylpyrazol-3-ylamino)-1-(5-tert-butylpyrazol-
3-ylimino)-1H-isoindole) as illustrated in Scheme 3. Compound
2 is NMR silent, suggesting the paramagnetic nature. The
structure of 2 has been established by X-ray analysis (Figure 1).
Selected bond distances and angles are summarized in Table 1.
The iron center adopts a distorted square pyramidal geometry
with the τ5 value of 0.27,[16] where the Cl1 atom lies at the apical
position. The structure contrasts with the trigonal bipyramid
found in the NNN pincer-type terpy[17] or PzH2Py[18,19] dichlor-
idoiron(II) complexes. The two protic pyrazole rings in 2 are
Scheme 3. Synthesis and transformations of iron(II) complexes 2–4 bearing a 3-(pyrazol-3-ylamino)-1-(pyrazol-3-ylimino)-1H-isoindole ligand
LH3.
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
2
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
°
Table 1. Selected bond lengths /Å and angles / for 2–5
2
3
4
5[a]
Fe1À N2
2.072(2)
2.057(2)
2.150(2)
2.3177(7)
2.4325(7)
1.359(3)
1.351(3)
1.336(3)
1.344(3)
1.331(3)
1.415(3)
1.397(3)
1.394(3)
1.327(3)
1.281(3)
112.7(2)
112.7(2)
104.0(2)
105.2(2)
107.1(2)
126.8(2)
121.9(2)
1.936(2)
1.919(2)
1.935(2)
2.3278(8)
2.3181(8)
1.363(3)
1.355(3)
1.335(3)
1.351(3)
1.336(3)
1.412(3)
1.390(3)
1.377(3)
1.342(3)
1.287(3)
112.0(2)
112.5(2)
104.4(2)
104.8(2)
107.7(2)
126.8(2)
123.1(2)
1.964(4)
1.968(4)
2.005(3)
2.2912(14)
2.3078(14)
1.373(4)
1.346(5)
1.339(5)
1.371(5)
1.314(5)
1.437(5)
1.399(5)
1.376(5)
1.344(5)
1.255(5)
111.9(4)
114.5(3)
103.0(4)
103.7(4)
107.2(4)
125.1(4)
124.3(4)
1.959(3)/1.961(3)
1.978(3)/1.959(3)
1.996(3)/2.005(3)
2.2928(12)/2.2853(12)
2.2857(12)/2.2943(12)
1.373(4)/1.373(4)
1.376(4)/1.369(4)
1.352(5)/1.356(5)
1.355(5)/1.354(5)
1.377(5)/1.374(5)
1.382(5)/1.378(5)
1.378(5)/1.364(5)
1.367(5)/1.374(5)
1.301(5)/1.313(5)
1.287(5)/1.308(5)
111.7(3)/112.1(3)
111.6(3)/112.0(3)
104.9(3)/105.0(3)
105.6(3)/104.7(3)
108.4(3)/108.1(3)
121.9(3)/121.7(3)
121.8(3)/121.2(3)
Fe1À N4
Fe1À N5
Fe1À X1[b]
Fe1À X2[b]
N1À N2
N3À N4
N2À C3
N4À C12
N5À C4
N5À C11
N6À C3
N7À C12
N6À C4
N7À C11
N2-N1-C1
N4-N3-C14
N1-N2-C3
N3-N4-C12
C4-N5-C11
C3-N6-C4
C11-N7-C12
[a] Values for two crystallographically independent molecules. [b] X=Cl (for 2), P (for 3–5).
gen atom[24] accompanied by hydrogen bonding with the
triflate counteranion (NH···O: 2.06 and 2.43 Å). The CÀ NÀ C angle
also appears diagnostic of the presence of the NH hydrogen in
the chelate backbone in 2–4. The angles around the protic
°
amine (N6) fall in the range of 125.1(4)–126.8(2) whereas those
°
around the imine (N7) are slightly smaller (121.9(2)–124.3(4) ).
Deprotonation of Isoindole Complex
When the dicationic carbonyl complex 4 was treated with an
equimolar amount of triethylamine, the monocationic complex
[Fe(CO)(PMe3)2(LH2)]OTf (5) was obtained as shown in Scheme 4.
The CO stretching frequency shifted to a lower wavenumber
upon deprotonation (1963 vs 1979 cmÀ 1) in line with the
increased π back donation from the iron center with a reduced
Figure 2. Crystal structure of 3. The CH hydrogen atoms as well as
the minor component of the disordered triflate counteranion are
omitted for clarity. Ellipsoids are drawn at the 30% probability
level.
1
positive charge. The reaction also rendered the H NMR signals
of 3 shows only one resonance, suggesting a rapid exchange
between the coordinated and uncoordinated triflates.
of the two pyrazole rings equivalent, indicating that the
deprotonation occurred at the chelate backbone to give a
monoanionic 1,3-bis(pyrazol-3-ylimino)isoindolin-2-yl ligand
As expected, the triflate ligand in 3 was easily replaced by
carbon monoxide to afford the carbonyl complex [Fe-
(CO)(PMe3)2(LH3)](OTf)2 (4; Scheme 3). The IR spectrum of 4
shows a CO stretching band at 1979 cmÀ 1. The wavenumber is
lower than that of the PzH2Py analogue (2005 cmÀ 1),[19] indicat-
ing that the central isoindole is a stronger donor than pyridine.
Figure 3 depicts the crystal structure of 4. The carbonyl ligand
lies in the equatorial plane. The metric parameters in the
Fe(LH3) unit are comparable with those in the triflate complex 3
(Table 1). As in 2 and 3, the NÀ NÀ C angles around the
uncoordinated nitrogen atom in the pyrazole rings in 4
Scheme 4. Deprotonation of amino-1H-isoindole complex 4 to give
iminoisoindolin-2-yl complex 5.
°
(111.9(4) and 114.5(3) ) suggest the presence of an NH hydro-
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
3
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
supra). The two pyrazole NH groups make a hydrogen bond
network involving the triflate counteranion and co-crystallized
water molecule.
Catalytic Disproportionation of Hydrazine with Isoindole
Complex
We have previously demonstrated that the diprotic, pincer-type
PzH2Py complexes of iron catalyze disproportionation of
hydrazine into ammonia and dinitrogen through 2H+/2eÀ
shuttling between the iron-pincer unit and hydrazine.[12,20,25] The
three proton-responsive sites in the LH3 complexes may be
effective to promote such bidirectional proton transfer. We thus
examined the disproportionation reaction catalyzed by the
isoindole complex 3 bearing a labile triflate ligand. Treatment
of 3 with 20 equiv. of hydrazine in dichloromethane[26] led to
catalytic disproportionation of hydrazine, although the catalytic
activity was lower than that of a PzH2Py complex 6a (Table 2).
The 1H NMR spectrum of a stoichiometric mixture of 3 and
hydrazine revealed signals that may be attributed to a C2v-
symmetric, deprotonated LH2 complex (δ 1.40, s, 18H for tBu;
6.31, d, J=2.4 Hz, 2H for pyrazole CH; 9.55, br s, 2H for NH in
CD3CN) and a hydrazinophosphonium salt (Me3PNHNH2)OTf.[13]
Formation of the latter salt and a low catalytic activity have also
been observed in the amide-decorated PzH2Py complex 6b and
ascribed to slow re-protonation of the pincer ligand in the high-
valent iron intermediate due to the electron-withdrawing amide
substituent.[13] The triprotic nature of 3 would also retard the
proton transfer of this direction and consequently the catalysis.
Figure 3. Crystal structure of 4·CH2Cl2. The CH hydrogen atoms as
well as the co-crystallized dichloromethane molecule are omitted
for clarity. The asterisk denotes atoms generated by a symmetry
operation (1–x, 1–y, 1–z). Ellipsoids are drawn at the 30%
probability level.
LH2. In fact, X-ray analysis revealed the symmetrical structure of
the pincer ligand in 5, which sharply contrasts with the neutral
1H-isoindole ligand in 2–4 (Figure 4 and Table 1). The N5À C(4/
11) bonds in the isoindoline ring (1.374(5)–1.382(5) Å) are much
longer than the exo-C(4/11)À N(6/7) bonds (1.287(5)–1.313(5) Å).
The CÀ NÀ C angles around both of the N6 and N7 atoms,
°
121.2(3)–121.9(3) , are also consistent with the imine form (vide
Conclusions
We have newly synthesized the protic pincer-type iron(II)
complexes 2–4 bearing an isoindoline-based bis(pyrazole)
ligand LH3. These complexes contain proton-responsive sites at
positions β (pyrazole) and γ (amine) to the metal. The residing
proton at these remote positions is characterized by the 1H
Table 2. Catalytic disproportionation of hydrazine with protic
pincer complexes of iron.
Cat
conv. of N2H4, %[a]
Yields[b]
NH3
Ref
[a]
[c]
N2
3
36
87
57
7.2
21.3
12.8
1.1
4.2
2.4
This work
[13]
[13]
Figure 4. Crystal structure of 5·H2O·0.5(CH2Cl2). Only one of the
two crystallographically independent molecules is shown. The CH
hydrogen atoms as well as the co-crystallized dichloromethane
molecule are omitted for clarity. Ellipsoids are drawn at the 30%
probability level.
6a[d]
6b[d]
[a] Determined by colorimetry. [b] In moles per Fe complex. [c]
Determined by GC. [d] In dichloromethane-methanol.
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
4
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
room temperature for additional 1 h. After removal of the solvent in
vacuo, subsequent recrystallization from dichloromethane-diethyl
ether (5 mL/60 mL) afforded as green crystals (614.2 mg,
0.6858 mmol, 79%). H NMR (CD2Cl2): δ 0.81 (br s, 18H, PMe3), 1.43
(br s, 18H, tBu), 6.76, 6.92, 8.03, 8.31 (br s, 1H each, aryl), 7.59 (br m,
2H, aryl), 10.70, 10.82, 12.16 (br s, 1H each, NH). 19F NMR (CD2Cl2): δ
À 78.7 (s). 31P{1H} NMR (CD2Cl2): δ 13.0 (s). C30H45F6FeN7O6P2S2: calcd.
C, 40.23; H, 5.06; N, 10.95%; found: C, 39.95; H, 4.93; N, 11.03%.
NMR and hydrogen bonding contacts found in the crystal along
with the NÀ NÀ C and CÀ NÀ C angles around the nitrogen atoms.
The CO stretching frequency of the carbonyl complex 4 clearly
indicated that the central 1H-isoindole unit in the pincer ligand
is more electron-donating than pyridine. Deprotonation of the
dicationic complex 4 afforded the monocationic complex 5
bearing an amphoteric bis(pyrazol-3-ylimino)isoindolin-2-yl li-
gand LH2. Isolation of 5 substantiated that the amino group in
the chelate backbone in 4 is more Brønsted acidic than the
pyrazole in the arms. Further investigation on deprotonation at
the pyrazole sites and catalytic applications of the 1H-isoindole/
isoindolin-2-yl pincer-type complexes 2–5 along with the
coordination of 1 to other metals is now in progress.
3
1
Synthesis of [Fe(CO)(PMe3)2(LH3)](OTf)2 ·0.5CH2Cl2 (4·0.5CH2Cl2):
Carbon monoxide (1 atm) was introduced to a solution of 3
(47.0 mg, 0.0525 mmol) in dichloromethane (3 mL) by freeze-pump-
thaw cycle (three times), and the mixture was stirred for 14 h at
room temperature. After removal of the solvent in vacuo, subse-
quent recrystallization from dichloromethane-hexane (2 mL/15 mL)
afforded dark red crystals of 4·CH2Cl2. The thoroughly dried sample
led to partial loss of co-crystallized dichloromethane to give
4·0.5CH2Cl2 on the basis of combustion analysis (39.4 mg,
1
0.0408 mmol, 78%). H NMR (CD2Cl2): δ 0.97 (vt, JPH =4.0 Hz, 18H,
Experimental Section
PMe3), 1.38 (s, 18H, tBu), 6.51, 6.80, 8.22, 8.64 (br s, 1H each, aryl),
7.88 (br s, 2H, aryl), 10.64 (br s, 2H, NH), 12.86 (br s, 1H, NH). 31P{1H}
General: All manipulations were performed under an atmosphere
of argon using standard Schlenk techniques unless otherwise
specified. Solvents were dried by refluxing over sodium benzophe-
none ketyl (diethyl ether and hexane), P2O5 (dichloroethane and
NMR (CD2Cl2):
δ
21.4 (s). IR (KBr): ν=1979 cmÀ 1 (C�O).
C
31.5H46ClF6FeN7O7P2S2: calcd. C, 39.16; H, 4.80; N, 10.15%; found: C,
39.15; H, 4.44; N, 10.20%.
1
acetonitrile), and Mg(OMe)2 (methanol), and distilled before use. H
(399.8 MHz), 13C{1H} (100.5 MHz), 19F (376.2 MHz), and 31P{1H}
(161.8 MHz) NMR spectra were obtained on a JEOL JNM-ECX-400
Synthesis of [Fe(CO)(PMe3)2(LH2)]OTf·H2O (5·H2O): To a solution of
4·0.5CH2Cl2 (49.4 mg, 0.0511 mmol) in dichloromethane (5 mL) was
added triethylamine (8.0 μL, 0.0574 mmol). The mixture was stirred
at room temperature for 14 h. The resultant mixture was washed
with degassed water (3 mL×3) and evaporated to dryness.
Recrystallization from dichloromethane-hexane (1 mL/20 mL) af-
forded 5·H2O as red crystals (0.0273 g, 0.0353 mmol, 67%). 1H NMR
(CD2Cl2): δ 0.88 (vt, JHP =4.0 Hz, 18H, PMe3, 1.36 (s, 18H, tBu), 6.18 (d,
4JHH =2.4 Hz, 2H, pyrazole CH), 7.64–8.01 (m, 4H, aryl), 9.89 (br s, 2H,
NH). 19F NMR (CD2Cl2): δ À 77.4 (s). 31P{1H} NMR (CD2Cl2): δ 23.6 (s).
IR (KBr): ν=1963 cmÀ 1 (C�O). C30H46F3FeN7O5P2S: calcd. C, 45.52; H,
5.86; N, 12.39%; found: C, 45.63; H, 5.85; N, 12.50%.
1
spectrometer. H NMR shifts are relative to the residual CHDCl2 (δ
5.32) and DMSO-d5 (δ 2.50). The 13C, 19F, and 31P shifts are
referenced to DMSO-d6 (δ 39.52), trifluoroacetic acid (δ 76.5), and
phosphoric acid (δ 0.0), respectively. Infrared spectra were recorded
on a JASCO FT/IR-6100 spectrometer, while UV-Vis spectra were
obtained on a JASCO V-630 spectrometer. Nitrogen gas evolved in
disproportionation of hydrazine was determined by GLC analysis
using Shimadzu GC-2010 Plus gas chromatograph equipped with a
Molecular Sieve 5 A column. Elemental analyses were performed on
a Perkin-Elmer 2400II CHN analyzer.
Catalytic disproportionation of hydrazine: To a solution of 3
(18.26 mg, 0.0204 mmol) in dichloromethane (4 mL) in a Schlenk
tube (inside volume: ca. 78 mL) was added anhydrous hydrazine
(13.58 mg, 0.424 mmol), and the mixture was stirred at room
temperature for 18 h. An aliquot (2 mL) of the gas phase was
subjected to GC analysis. In a separate run, all volatile material
inside was distilled into an aqueous 1 N H2SO4 solution after the
reaction, and the residue was further extracted with an additional
amount of water. The amount of ammonia and unreacted
hydrazine were quantified by indophenol[27] and p-(dimethylamino)
benzaldehyde[28] method, respectively.
Synthesis of 1,3-bis(5-tert-butylpyrazol-3-ylimino)isoindoline (1):
A mixture of phthalonitrile (4.02 g, 31.4 mmol) and 3-amino-5-tert-
butylpyrazole (10.6 g, 75.9 mmol) was heated under reduced
°
pressure at 200 C for 22 h. After cooling to room temperature, the
brown sticky solid was washed with diethyl ether (80 mL), and dried
in vacuo, giving 1 as analytically pure, pale yellow powder (10.0 g,
1
25.7 mmol, 82%). H NMR (DMSO-d6): δ 1.30 (s, 18H, tBu), 6.06 (s,
2H, pyrazole CH), 7.65–7.92 (m, 4H, aryl), 11.94 (br s, 1H, NH), 12.51
(br s, 2H, NH). 13C{1H} NMR (DMSO-d6): δ 29.9 (C(CH3)3), 30.7
(C(CH3)3), 99.0, 121.8, 131.3, 135.1, 148.7, 153.5, 155.2. C22H27N7:
calcd. C, 67.84; H, 6.99; N, 25.17%; found: C, 67.78; H, 7.13; N,
25.14%.
Crystallography: Single crystals suitable for X-ray analyses were
mounted on a fiber loop. Diffraction experiments were performed
on a Rigaku Saturn CCD area detector with graphite monochro-
Synthesis of [FeCl2(LH3)] (2): A mixture of anhydrous iron(II)
chloride (0.1611 g, 1.27 mmol) and 1 (0.4978 g, 1.28 mmol) in
methanol (20 mL) was stirred at room temperature for 1 h. The
yellowish-green microcrystals that formed was collected by filtra-
tion, washed with methanol (5 mL), diethyl ether (5 mL), and
pentane (5 mL), and dried in vacuo (0.4683 g, 0.8898 mmol, 70%).
Single crystals of 2 for X-ray analysis were obtained from a dilute
solution in N,N-dimethylformamide-diethyl ether. C22H27Cl2FeN7:
calcd. C, 51.18; H, 5.27; N, 18.99%; found: C, 50.18; H, 5.68; N,
18.73%.
°
mated MoÀ Kα radiation (λ=0.710 73 Å). Intensity data (6 <2θ<
°
55 ) were corrected for Lorentz-polarization effects and for
absorption. Details of crystal and data collection parameters are
summarized in Table 3. Structure solution and refinements were
carried out by using the CrystalStructure program package.[29] The
heavy-atom positions were determined by
a direct methods
program (SIR92[30]) and the remaining non-hydrogen atoms were
found by subsequent Fourier syntheses and refined by full-matrix
least-squares techniques against F2 using the SHELXL-2014/7
program.[31] The CH and NH hydrogen atoms were included in the
refinements with a riding model. The triflate counteranion in 3 was
refined at two disordered positions with restraint geometries. In
5·H2O·0.5CH2Cl2, the co-crystalized dichloromethane and one of
the two water molecules were severely disordered and unmodeled.
The SQUEEZE procedure[32] has been used to treat these molecules
Synthesis of [Fe(OTf)(PMe3)2(LH3)]OTf (3):
A mixture of 2
(446.5 mg, 0.865 mmol) and silver trifluoromethanesulfonate
(451.8 mg, 1.76 mmol) in acetonitrile (10 mL) was stirred for 10 min
at room temperature. Silver chloride that formed was filtered off,
and a solution of trimethylphosphine in toluene (1.0 M, 1.90 mL,
1.90 mmol) was added to the filtrate and the mixture was stirred at
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
5
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Table 3. X-ray crystallographic data for 2–5.
2·DMF
3
4·CH2Cl2
5·H2O·0.5(CH2Cl2)
Chemical formula
Formula weight
Crystal size /mm3
Crystal system
Space group
a/Å
C25H34Cl2FeN8O
589.35
0.33×0.15×0.12
monoclinic
P21/c
8.6749(9)
28.753(3)
11.5746(12)
90
101.2504(19)
90
C30H45F6FeN7O6P2S2
895.63
0.20×0.16×0.14
monoclinic
C2/c
36.870(4)
12.0820(14)
18.843(2)
90
97.4559(15)
90
C32H47Cl2F6FeN7O7P2S2
1008.58
0.17×0.14×0.10
triclinic
C30.5H47ClF3FeN7O5P2S
834.05
0.20×0.11×0.10
monoclinic
P21/c
16.032(3)
17.274(3)
29.508(5)
90
101.427(3)
90
P1À
12.5365(18)
13.0827(19)
14.8863(19)
75.720(6)
71.394(6)
82.655(6)
2239.2(5)
2
b/Å
c/Å
°
α/
°
β/
°
γ/
V/Å3
2831.6(5)
4
8322.9(17)
8
8010(2)
8
Z
T/K
93
1.382
1232
0.754
93
1.429
3712
0.614
93
1.496
1040
0.696
93
1.383
3480
0.634
1calcd./gcmÀ 3
F(000)
μ/mmÀ 1
Transmission factors
No. reflns measured
Independent reflns (Rint)
Parameters
R1 [I>2σ(I)]
wR2 (all data)
Goodness of fit
Max. diff. peak and hole/e ÅÀ 3
0.649–0.913
22782
6384 (0.0623)
336
0.0505
0.1286
0.952
1.70/À 0.58
0.884–0.918
33005
9511 (0.0751)
560
0.0577
0.1573
0.979
1.41/À 0.52
0.892–0.933
18548
9868 (0.0669)
532
0.0615
0.1344
1.004
1.12/À 0.67
0.641–0.939
65328
18295 (0.1175)
881
0.0787
0.2312
1.034
3.29/À 0.72
(209 total electrons present in 816 Å3 of voids, corresponding to
four dichloromethane and four water molecules per unit cell). The
OH hydrogen atoms in the rest water molecule were found in the
difference Fourier map and included in the refinement with
restraint geometries.
3825–3842; f) L. S. Merz, J. Ballmann, L. H. Gade, Eur. J. Inorg.
Chem. 2020, 2023–2042.
[2] A. Singh, D. Gelman, ACS Catal. 2020, 10, 1246–1255.
[3] a) A. Winter, U. S. Schubert, ChemCatChem 2020, 12, 2890–
2941; b) S. M. Elahi, M. Raizada, P. K. Sahu, S. Konar, Chem. Eur.
J. 2021, 27, 5858–5870.
Crystallographic data for the structures in this paper have been
deposited with the Cambridge Crystallographic Data Centre, CCDC,
12 Union Road, Cambridge CB21EZ, UK. Copies of the data can be
obtained free of charge on quoting the depository numbers CCDC-
2069922 to CCDC-2069925 (Fax: +44-1223-336-033; E-mail: depos-
it@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
[4] K. R. Rohit, S. M. Ujwaldev, S. Saranya, G. Anilkumar, Asian J.
Org. Chem. 2018, 7, 2338–2356.
[5] a) R. Csonka, G. Speier, J. Kaizer, RSC Adv. 2015, 5, 18401–
18419; b) D. C. Sauer, R. L. Melen, M. Kruck, L. H. Gade, Eur. J.
Inorg. Chem. 2014, 4715–4725.
[6] Q.-H. Deng, R. L. Melen, L. H. Gade, Acc. Chem. Res. 2014, 47,
3162–3173.
[7] a) T. Shimbayashi, K.-I. Fujita, Catalysts 2020, 10, 635; b) T.
Higashi, S. Kusumoto, K. Nozaki, Chem. Rev. 2019, 119, 10393–
10402; c) L. V. A. Hale, N. K. Szymczak, ACS Catal. 2018, 8,
6446–6461; d) A. Matsunami, Y. Kayaki, Tetrahedron Lett. 2018,
59, 504–513; e) R. H. Morris, Dalton Trans. 2018, 47, 10809–
10826; f) J. R. Khusnutdinova, D. Milstein, Angew. Chem. 2015,
127, 12406–12445; Angew. Chem. Int. Ed. 2015, 54, 12236–
12273.
[8] S. Kuwata, in Molecular Technology: Energy Innovation (Eds.: H.
Yamamoto, T. Kato), Weinheim, 2018, pp. 81–103.
[9] J. B. Geri, N. K. Szymczak, J. Am. Chem. Soc. 2015, 137, 12808–
12814.
Supporting Information (see footnote of the first page of this
article): NMR spectra of compounds 1, 3, 4, and 5.
Acknowledgements
This work was supported by JSPS KAKENHI Grant Number
JP18 K19070 and JP19H02732. T.T. acknowledges
Research Fellowship for Young Scientists.
a JSPS
Keywords: Hydrogen bonds · Iron · N ligands · Pincer ligands ·
[10] a) J. S. Pap, B. Kripli, V. Banyai, M. Giorgi, L. Korecz, T. Gajda, D.
Arus, J. Kaizer, G. Speier, Inorg. Chim. Acta 2011, 376, 158–169;
b) J. Kaizer, B. Kripli, G. Speier, L. Párkányi, Polyhedron 2009, 28,
933–936.
Pyrazole
[11] J. B. Geri, J. L. Ciatti, N. K. Szymczak, Chem. Commun. 2018, 54,
7790–7793.
[12] a) S. Kuwata, T. Ikariya, Chem. Commun. 2014, 50, 14290–
14300; b) T. Toda, A. Yoshinari, T. Ikariya, S. Kuwata, Chem. Eur.
J. 2016, 22, 16675–16683; c) T. Toda, K. Saitoh, A. Yoshinari, T.
Ikariya, S. Kuwata, Organometallics 2017, 36, 1188–1195; d) H.
[1] a) Y. Wang, B. Zhang, S. Guo, Eur. J. Inorg. Chem. 2021, 188–
204; b) L. Piccirilli, D. L. J. Pinheiro, M. Nielsen, Catalysts 2020,
10, 773–115; c) R. Taakili, Y. Canac, Molecules 2020, 25, 2231;
d) M. Vogt, R. Langer, Eur. J. Inorg. Chem. 2020, 3885–3898;
e) S. Budweg, K. Junge, M. Beller, Catal. Sci. Technol. 2020, 10,
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
6
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Yamagishi, H. Konuma, S. Kuwata, Polyhedron 2017, 125, 173–
[21] a) B. Cordero, V. Gómez, A. E. Platero-Prats, M. Revés, J.
178; e) Y. Nakahara, T. Toda, A. Matsunami, Y. Kayaki, S.
Kuwata, Chem. Asian J. 2018, 13, 73–80; f) T. Toda, S. Suzuki, S.
Kuwata, Chem. Commun. 2019, 55, 1028–1031; g) N. Tashima,
T. Sawazaki, Y. Kayaki, S. Kuwata, Chem. Lett. 2019, 48, 787–
790; h) N. Tashima, S. Ohta, S. Kuwata, Faraday Discuss. 2019,
220, 364–375; i) T. Toda, S. Kuwata, J. Organomet. Chem. 2020,
917, 121270; j) T. Takamura, T. Harada, T. Furuta, T. Ikariya, S.
Kuwata, Chem. Asian J. 2020, 15, 72–78; k) Y. Kashiwame, T.
Ikariya, S. Kuwata, Polyhedron 2021, 197, 115036.
Echeverría, E. Cremades, F. Barragán, S. Alvarez, Dalton Trans.
2008, 2832–2838; b) J. Olguín, S. Brooker, Coord. Chem. Rev.
2011, 255, 203–240.
[22] J. S. Pap, M. A. Cranswick, É. Balogh-Hergovich, G. Baráth, M.
Giorgi, G. T. Rohde, J. Kaizer, G. Speier, L. Que Jr., Eur. J. Inorg.
Chem. 2013, 3858–3866.
[23] a) O. P. Anderson, A. La Cour, A. Berg, A. D. Garrett, M.
Wicholas, Inorg. Chem. 2003, 42, 4513–4515; b) M. Wicholas,
A. D. Garrett, M. Gleaves, A. M. Morris, M. Rehm, O. P.
Anderson, A. La Cour, Inorg. Chem. 2006, 45, 5804–5811.
[24] a) S. Kuwata, T. Ikariya, Chem. Eur. J. 2011, 17, 3542–3556; b) Y.
Kashiwame, M. Watanabe, K. Araki, S. Kuwata, T. Ikariya, Bull.
Chem. Soc. Jpn. 2011, 84, 251–258.
[25] H. Tanaka, S. Hitaoka, K. Umehara, K. Yoshizawa, S. Kuwata, Eur.
J. Inorg. Chem. 2020, 1472–1482.
[26] Because partial decomposition of 3 was observed in methanol,
the catalytic reaction with 3 was conducted in dichloro-
methane.
[27] M. W. Weatherburn, Anal. Chem. 1967, 39, 971–974.
[28] G. W. Watt, J. D. Chrisp, Anal. Chem. 1952, 24, 2006–2008.
[29] CrystalStructure 4.3: Crystal Structure Analysis Package, Rigaku
Corporation, Tokyo 196–8666, Japan, 2000–2018.
[30] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. C.
Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 1994, 27, 435.
[31] G. M. Sheldrick, Acta Crystallogr. Sect. C 2015, 71, 3–8.
[32] A. L. Spek, Acta Crystallogr. Sect. C 2015, 71, 9–18.
[13] Y. Nakahara, T. Toda, S. Kuwata, Polyhedron 2018, 143, 105–
110.
[14] a) A. Yoshinari, A. Tazawa, S. Kuwata, T. Ikariya, Chem. Asian J.
2012, 7, 1417–1425; b) T. Jozak, D. Zabel, A. Schubert, W. R.
Thiel, Eur. J. Inorg. Chem. 2010, 5135–5145; c) N. S. Labrum,
A. C. Cabelof, K. G. Caulton, Chem. Eur. J. 2020, 26, 13915–
13926; d) J. L. Kuo, K. I. Goldberg, J. Am. Chem. Soc. 2020, 142,
21439–21449.
[15] M. Nozari, A. W. Addison, G. T. Reeves, M. Zeller, J. P. Jasinski,
M. Kaur, J. G. Gilbert, C. R. Hamilton, J. M. Popovitch, L. M. Wolf,
L. E. Crist, N. Bastida, J. Heterocycl. Chem. 2018, 55, 1291–1307.
[16] a) A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn, G. C.
Verschoor, J. Chem. Soc. Dalton Trans. 1984, 1349–1356;
b) A. G. Blackman, E. B. Schenk, R. E. Jelley, E. H. Krenske, L. R.
Gahan, Dalton Trans. 2020, 49, 14798–14806.
[17] D. J. Robinson, C. H. L. Kennard, Aust. J. Chem. 1966, 19, 1285–
1286.
[18] B. J. Cook, C.-H. Chen, M. Pink, R. L. Lord, K. G. Caulton, Inorg.
Chim. Acta 2016, 451, 82–91.
[19] K. Umehara, S. Kuwata, T. Ikariya, Inorg. Chim. Acta 2014, 413,
136–142.
[20] K. Umehara, S. Kuwata, T. Ikariya, J. Am. Chem. Soc. 2013, 135,
Manuscript received: March 22, 2021
Revised manuscript received: April 26, 2021
6754–6757.
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
7
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

ARTICLE
Dr. T. Toda, Prof. Dr. S. Kuwata*
1 – 8
Synthesis, Structures, and Reactiv-
ities of Iron Complexes Bearing an
Isoindoline-Based, Polyprotic
Pincer-Type Pyrazole Ligand