Effectiveness and Mechanism of the Ene(amido) Group in Activating Iron for the Catalytic Asymmetric Transfer Hydrogenation of Ketones

Article abstract of DOI:10.1021/acs.organomet.0c00636

I-interacting ligands of the diphosphino amido-ene(amido) type are effective in activating iron to resemble the properties of precious metals in the catalytic asymmetric transfer hydrogenation of ketones. To further verify the effectiveness of the ene(amido) group, we synthesized four amine(imine) diphosphine iron precatalyst complexes with substituents at α and β positions relative to imino groups (1-3) or with enlarged chelate ring sizes (5,5,6-membered rings) (4). In comparison with the parent trans-(R,R)-[Fe(CO)(Cl)(PPh2CH2CHaNCHPhCHPhNHCH2CH2PPh2)]BF4 (I), the introduction of a methyl group in 1 and 2 reduced the catalytic activity but led to undiminished enantioselectivity as reaction proceeded. In comparison to the iron complexes 1-3 with a 5,5,5-coordination geometry, the complex 4 derived from the new (R,R)-P-NH-NH2 tridentate ligand showed high reactivity comparable to that of I but was unfortunately not enantioselective. The catalytic reactivity of 1, 2, and 4 illustrates the effectiveness of the ene(amido) group. An electronic structure study on the important catalytic intermediate amido-ene(amido) complex 1b proved that iron was activated by an additional I-back-donation-interaction ligand to participate in the traditional metal-ligand bifunctional pathway in the asymmetric transfer hydrogenation reactions.

Full text of DOI:10.1021/acs.organomet.0c00636

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Effectiveness and Mechanism of the Ene(amido) Group in Activating
Iron for the Catalytic Asymmetric Transfer Hydrogenation of
Ketones
Qingquan Xue,† Rongliang Wu,† Di Wang, Meifang Zhu,* and Weiwei Zuo*
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ABSTRACT: π-interacting ligands of the diphosphino amido-
ene(amido) type are effective in activating iron to resemble the
properties of precious metals in the catalytic asymmetric transfer
hydrogenation of ketones. To further verify the effectiveness of the
ene(amido) group, we synthesized four amine(imine) diphosphine
iron precatalyst complexes with substituents at α and β positions
relative to imino groups (1−3) or with enlarged chelate ring sizes
(5,5,6-membered rings) (4). In comparison with the parent trans-
(R,R)-[Fe(CO)(Cl)(PPh2CH2CHNCHPhCHPhNHCH2CH2PPh2)]BF4 (I), the introduction of a methyl group in 1 and 2
reduced the catalytic activity but led to undiminished enantioselectivity as reaction proceeded. In comparison to the iron complexes
1−3 with a 5,5,5-coordination geometry, the complex 4 derived from the new (R,R)-P-NH-NH2 tridentate ligand showed high
reactivity comparable to that of I but was unfortunately not enantioselective. The catalytic reactivity of 1, 2, and 4 illustrates the
effectiveness of the ene(amido) group. An electronic structure study on the important catalytic intermediate amido-ene(amido)
complex 1b proved that iron was activated by an additional π-back-donation-interaction ligand to participate in the traditional
metal−ligand bifunctional pathway in the asymmetric transfer hydrogenation reactions.
good turnover frequency (9430 h−1) in the ATH of
INTRODUCTION
■
ketones.39−44
Asymmetric hydrogenation (AH) or transfer hydrogenation
(ATH) plays a pivotal role in the pharmaceutical, fragrance,
Although iron catalysts have been successfully applied in
asymmetric (transfer) hydrogenation, the mechanism of iron
and agriculture industries.1−3 Previously, most catalysts used in
catalysis remains to be further explored. Several typical
AH or ATH were based on noble metals such as ruthenium,
rhodium, iridium, etc. Recent years have witnessed significant
mechanistic studies on iron catalysts have been reported.45,46
Morris47 envisioned an outer-sphere hydride transfer mecha-
progress in the application of iron catalysts in AH or ATH.4,5
nism for AH or ATH with iron catalysts. Mezzetti48 reported
Gao et al.6 reported the ATH of ketones by carbonyl iron
complexes with chiral P,N ligands. Guan7 and others8−11
the role of the base in ATH of ketones catalyzed by dicationic
N2P2 macrocyclic iron complexes by combined experimental
̈
reported a series of Knolker-type iron complexes which
and theoretic studies. Yang49 discovered a direct reduction
mechanism for the hydrogenation of ketones catalyzed by PNP
pincer complexes on the basis of quantum chemical
computations.
showed good enantioselectivity for the reduction of CO
and CN bonds under mild conditions. Kirchner and co-
workers also developed well-defined PNP iron(II) complexes,
which also exhibited rather excellent activities for the
hydrogenation of ketones and aldehydes at room temper-
ature.12−16 Beller’s group reported chiral iron catalysts from
Fe3(CO)12 with nitrogen-containing ligands, and these iron
catalysts showed good conversion and enantioselectivities for
the AH or ATH of ketones.17−24 Pyridine-based pincer
iron(II) complexes were synthesized by Milstein et al. for
the hydrogenation of unsaturated CO bonds with a good
conversion.25−31 Morris32−38 et al. developed P2N2 ligand iron
catalysts for the ATH of imines and ketones with excellent
catalytic activities (up to 242 s−1). Mezzetti et al. reported iron
catalysts bearing macrocyclic P-chirogenic N2P2 ligands which
exhibited splendid enantioselectivities (up to 99% ee) and
We have demonstrated the crucial role of π-interacting
ene(amido) group in activating the iron center50 (Scheme 1, II
and III) or cobalt center51 in the amido-ene(amido) metal
catalysts for catalyzing the ATH of ketones. The flexible charge
transfer facilitated by a π-back-donation interaction between
Received: September 22, 2020
Published: December 31, 2020
https://dx.doi.org/10.1021/acs.organomet.0c00636
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Scheme 1. Parent Unsubstituted Amine(imine) Diphosphine iron complex (I), the Catalytic Intermediate Amido-Ene(amido)
a
Iron Complex (II), and the Iron Hydride Complex (III) and Their Representative Qualitative Molecular Orbital Diagrams
a
The doubly occupied HOMO-1 orbital of II has a 7.5% ene(amido) π* and a 20.5% Fe d character. The HOMO-3 orbital of III exhibits an iron d
π-back-donation interaction to the ene(amido) and carbonyl ligands, with 23.3%, 9.6%, and 6.2% components of iron d, ene(amido), and carbonyl
moieties, respectively.50
the metal center and the ene(amido) moiety was found to
stabilize the catalytic intermediates against deactivation.50,51
To further study the effect of the ene(amido) group in
activating the iron center for catalysis, we describe the
synthesis of new amine(imine) diphosphine iron complexes
with various substituent groups or with varied chelate ring
sizes. The catalytic reactivity of all these iron complexes for the
asymmetric transfer hydrogenation of acetophenone was
studied. Furthermore, the electronic structure of the important
catalytic intermediate amido-ene(amido) complex 1b was
explored to further elucidate the real function of the
ene(amido) group.
69.23, 58.27, JPP = 38.9 Hz; δ 68.27, 56.32, JPP = 37.2 Hz), due
to the absolute configurations at the methyl-substituted carbon
and ligand disposition at the metal center. A stretching
vibration of the CO ligand at 1964 cm−1 was observed in FT-
IR spectrum of complex 2.
Complex 3. Complex 3 was obtained via the reaction of 2-
(diphenylphosphino)-2-fluoroacetaldehyde with the tridentate
ligand (R,R)-P-NH-NH2 under the coordination of iron(II)
tetrafluoroborate, sodium chloride, and carbon monoxide
(Scheme 2, eq 6). Fluorine substitution and carbonylation of
methyldiphenylphosphine produced 2-(diphenylphosphino)-2-
fluoroacetaldehyde. The introduction of a fluorine atom was
accessed by electrophilic C−F bond formation between the
carbanion and the fluorinating reagent N-fluorobenzenesulfo-
nimide (NFSI). A carbonyl group was introduced via
deprotonation of the fluoromethyl group followed by
quenching the carbanion with ethyl formate and H2O (Scheme
2, eq 5). Protection with borane was also necessary during the
synthesis, and deboronation was accessed with methanol to
give 2-(diphenylphosphino)-2-fluoroacetaldehyde. Complex 3
has two diastereomers and exhibits two sets of phosphorus
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Related Iron
Complexes. Complex 1. As shown in Scheme 2, eq 2,
complex 1 was synthesized by a similar template reaction
between the tridentate ligand (R,R)-P-NH-NH2 and 1-
(diphenylphosphino)propanone in the presence of an iron(II)
cation, followed by reacting with NaCl and CO according to
the reported procedure.38 The key step for the synthesis of
complex 1 was the synthesis of 1-(diphenylphosphino)-
propanone shown in Scheme 2, eq 1. The introduction of a
carbonyl group was accessed by deprotonation of the CH3
group of the methyldiphenylphosphine in THF followed by
sequential quenching of the carbanion with ethyl acetate and
deionized water (eq 1). The protection with borane is
necessary during the synthesis, and the compound can be
easily deprotected by reacting it with diethylamine at room
temperature. The carbonyl group of 1-(diphenylphosphino)-
propanone exhibits a doublet CO signal at δ 203.5 ppm with
a JCP coupling of 8.9 Hz in its 13C{1H} NMR spectrum. The
31P{1H} NMR spectrum of 1-(diphenylphosphino)propanone
shows a phosphorus resonance at −18.57 ppm. The 31P{1H}
NMR spectrum of complex 1 shows two doublets at δ 54.22
and 58.01 ppm with a JPP coupling of 42.57 Hz. The FT-IR
spectrum of complex 1 displays a stretching vibration of the
CO ligand at 1953 cm−1.
signals (δ 54.97 (JPP = 42.10 Hz), 84.73 (JPP = 42.10 Hz, JPF
=
25.23 Hz); δ 56.77 (JPP = 42.10 Hz), 75.46 (JPP = 42.10 Hz, JPF
= 25.23 Hz)) in the 31P{1H} NMR spectrum, due to the
absolute configuration at the fluoro-substituted carbon and the
ligand disposition at the metal center. Consistently, the crystal
of complex 3 (Figure 2) contains two diastereomers. In the
FT-IR spectrum of complex 3, a stretching vibration of the CO
ligand was found at 1974 cm−1.
Complex 4. Complex 4 was synthesized by reacting the new
tridentate P-NH-NH2 ligand (N1-[[2-(diphenylphosphino)-
phenyl]methyl]-1,2-diphenyl-(1R,2R)-1,2-ethanediamine)
with 2-(diphenylphosphino)acetaldehyde in the presence of
Fe(H2O)6(BF4)2, NaCl, and CO (Scheme 2, eq 8). N1-[[2-
(Diphenylphosphino)phenyl]methyl]-1,2-diphenyl-(1R,2R)-
1,2-ethanediamine was synthesized by the template reaction
between (1R,2R)-1,2-diphenylethane-1,2-diamine ((R,R)-
Dpen) and 2-(diphenylphosphino)benzaldehyde in the pres-
ence of FeCl2 followed by reduction with LiAlH4 according to
the literature (Figure S1).38 The 31P{1H} NMR spectrum of
complex 4 exhibits two sets of phosphorus resonances (δ
40.18, 51.70, JPP = 42.34 Hz; δ 43.83, 51.87, JPP = 42.34 Hz).
The CO ligand showed a stretching vibration at 1961 cm−1 in
the FT-IR spectrum of complex 4.
Complex 2. A template procedure similar to that reported in
previous literature was adopted for the synthesis of complex 2
using a new phosphonium dimer (Scheme 2, eq 4).38 The new
phosphonium dimer was synthesized according to the reported
literature by starting from diphenylphosphine and 2-bromo-
1,1-dimethoxypropane52 (Scheme 2, eq 3). Four isomers were
observed in the 31P{1H} NMR spectrum of complex 2 (δ
80.47, 56.03, JPP = 38.6 Hz; δ 74.06, 57.21, JPP = 39.5 Hz; δ
Single crystals of complex 1 and 3 suitable for X-ray
diffraction were obtained by crystallization in hot methanol or
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Scheme 2. Synthesis of New Chiral Ligands and Iron Complexes 1−4
slow diffusion of diethyl ether into a dichloromethane solution
of the complex. The molecular structures of 1 and 3 are shown
in Figures 1 and 2, respectively. Complexes 1 and 3 have an
octahedral geometry around the iron center. Interestingly, the
introduction of a methyl group in the α position relative to the
imino group in 1 led to a syn location of the proton in the
amine N−H bond and the chloride in the Fe−Cl bond. This is
opposite to the case for I.38 This is consistent with the different
reaction behaviors between them (vide infra).
Catalytic Studies of the Iron Precatalysts. The catalytic
reactivity of all these iron complexes (1−4) in the asymmetric
transfer hydrogenation of acetophenone using isopropyl
alcohol as the solvent and hydrogen source in the presence
of 8 equiv of KOtBu was studied. It was found that precatalysts
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comparable to that of I but was unfortunately not
enantioselective.
Substrate Scope. The asymmetric transfer hydrogenation of
various ketone substrates was conducted with the iron
i
precatalyst 1 in PrOH with 8 equiv of base. The catalytic
results are shown in Table 2. The introduction of electron-
withdrawing groups including bromo and chloro substituents
in the ortho, meta, or para position of the benzene ring of
acetophenone enhanced the catalytic activity, probably by
increasing the electrophilicity of the acetyl carbon (shown in
Table 2). In contrast, the introduction of electron-donating
groups in these positions of the benzene ring decreased the
catalytic activity due to a decrease in the electrophilicity of the
acetyl carbon. In a word, most of the substrates showed good
conversion and good enantioselectivity.
Stoichiometric Reactions of Iron Complexes 1−4
with Base and Isopropyl Alcohol. To study the relationship
between catalyst structure and catalytic performance, stoichio-
metric reactions of iron complexes with strong base and
isopropyl alcohol were explored.
Figure 1. ORTEP (thermal ellipsoids at 50% probability) plot of the
molecular structure of 1. The BF4 anion and hydrogen atoms are
omitted for clarity.
Stoichiometric Reaction of Complex 1 with 1 equiv of
Strong Base. The reaction of complex 1 with 1 equiv of KOtBu
to produce 1a was conducted at room temperature in THF
(Scheme 3). The structure of 1a was fully characterized by a
series of NMR spectra including 1H−13C HSQC (Figure S47),
1H−1H COSY (Figure S48), etc. The proton chemical shift of
N−H in 1a at δ 5.50 ppm is similar to that (5.32 ppm) in the
analogous complex derived from I.53 In addition, the 31P{1H}
NMR spectrum of 1a showed only one set of a doublet at 48.9
and 55.6 ppm with a JPP coupling of 35.2 Hz. This indicated
that 1a has only one isomer in comparison with the previously
reported53 unsubstituted II, which has two isomers.
3.2. Stoichiometric Reaction of Complex 1 with 2 equiv of
Strong Base. Complex 1 was reacted with 2 equiv of strong
base to produce the doubly deprotonated amido-ene(amido)
1b (Scheme 4). Different from the case of I in which two
diastereomers were produced, 1b has only one isomer in its
1, 2, and 4 were all active but 3 did not show any catalytic
activity (Table 1). The introduction of substituents in 1 and 2
led to significantly reduced catalytic activities in comparison to
I. Interestingly, the introduction of a methyl group at the α
position relative to the imino group in 1 avoided the
enantioselectivity erosion that is frequently encountered in
transfer hydrogenation reactions. The (S)-1-phenylethanol
produced by catalyst 1 exhibited the same enantioselectivity
as that of the nonsubstituted I. The introduction of methyl
group at the β position in 2 also led to a nonracemization
process but with lower enantioselectivity. In the reactions
catalyzed by 1 and 2, the enantiomeric excess (ee) of (S)-1-
phenylethanol was maintained for more than 7 h, while that in
the reaction of I decreased rapidly within 3 min. The
substitution of a fluorine atom at the β position in 3 totally
deactivates the catalyst. Precatalyst 4 showed high reactivity
Figure 2. ORTEP (thermal ellipsoids at 50% probability) plots of the molecular structures of the two diastereomers of 3. The BF4 anions and
hydrogen atoms are omitted for clarity.
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a
Table 1. Asymmetric Transfer Hydrogenation of Ketones Catalyzed by Complexes 1−4
catalyst precursor TOF at 10 s (s−1
)
ee at 10 s (%) ee at equilibrium (%) time to equilibrium (h) TON at equilibrium yield at equilibrium (%)
1
2
3
4
7.9
6.5
87
76
86 (S)
73 (S)
7
3
4181
5464
68
89
85
0
0
1
5498
90
a
General conditions for ketones: [cat.] = 6.48 × 10−7 M, [KOtBu] = 5.24 × 10−6 M, [ketone] = 3.97 × 10−3 M, 28 °C. The absolute configuration
was determined by GC by a comparison with known standards.
a
Table 2. Asymmetric Transfer Hydrogenation of Various Ketones Catalyzed by Precatalyst 1
a
Reactions were performed under argon at 28 °C. [cat.]:[base]:[ketones] = 1:8:612. Volume of iPrOH 10.0 mL. [ketone] = 0.397 M. [1] = 6.48 ×
10−4 .; [KOtBu] = 5.24 × 10−3 M. The (S)-alcohol was the major product in all substrates. Conversions and ee values were determined by a gas
chromatograph containing a chiral column.
hydride NMR pattern is very similar to that of III.50 Catalytic
reaction experiments demonstrated that, under the same
conditions, the catalytic ATH of acetophenone using the
reaction mixture of 1c in the presence of an additional 4 equiv
of KOtBu exhibited exactly the same reaction kinetics as that
using 1 as precatalyst with 8 equiv of base.38 This indicates that
the hydride complex 1c is an on-cycle active species.
31P{1H} NMR spectrum (Figure 3) with chemical shifts at δ
85.73, 69.67 ppm and a JPP coupling constant of 31.4 Hz.
3.3. Stoichiometric Reaction of 1b with Isopropyl Alcohol.
The reaction of 1b and isopropyl alcohol in the presence of
KOtBu produced amino iron hydride 1c. The 31P{1H} NMR
spectrum of the reaction mixture (Figure 4) indicated that 20%
of 1b was converted to 1c. A hydride resonance at −1.5 ppm
1
was observed in the H NMR spectrum (Figure 5) with JHP
3.4. Stoichiometric Reactions of Iron Complexes 2−4 with
Base and Isopropyl Alcohol. Complexes 2−4 were also
coupling constants of 64.7 and 75.8 Hz, respectively. This
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and 3a both exhibit isomeric mixtures arising from the variable
disposition of the CO ligands over the PNNP coordination
planes (eq 11). Unfortunately, the fluoro-substituted analogues
3a/3a′ were not very stable and decomposed easily during
their synthesis. Therefore, their further reactions with
isopropyl alcohol to prepare the putative amino iron hydride
complexes were not pursued, and this may account for the lack
of reactivity of complex 3 in the catalytic reactions.
Scheme 3. Stoichiometric Reaction of Complex 1 with 1
equiv of Strong Base
Electronic Study of 1b. To explore the real mechanism of
the function of the ene(amido) group, we further studied the
electronic structure of 1b by a combination of spectroscopic
and computational studies. The FT-IR spectrum of 1b
exhibited a CO stretching frequency at 1900 cm−1, which
Scheme 4. Stoichiometric Reaction of Complex 1 with 2
equiv of Strong Base
was close to that of II, indicating an electron-rich iron center in
57
̈
1b. The Fe Mossbauer spectrum of 1b (Figure 6a) afforded
an isomer shift of 0.13 mm/s and a quadrupole splitting of 2.5
mm/s. This indicated the existence of a metal−ligand bonding
covalence54,55 in 1b, similar to the case for II.50 Furthermore,
XPS analysis (Figure 6b) on 1b revealed a 2p3/2 binding energy
of 708.4 eV, consistent with a Fe(II) center and thus ruling out
the possibility of a redox-active ligand.56 A quantum chemical
computation at the B3LYP/LANL2DZ level of theory50 was
conducted to explore the electronic structure of 1b. As shown
in Figure 7, the HOMO-1 of 1b consists of 26.4% metal d and
16.8% amido N atom character, respectively. In addition, the
same orbital also contains 4.3% ene(amido) π* character,
implying the presence of a π-back-donation interaction in 1b.
This is similar to the electronic structure of II. We have
previously demonstrated the capability of this π-back-donation
interaction in II to transfer the electron density on iron to an
ene(amido) group to avoid the high electron density on iron,
which has a high propensity to deactivate the mother iron
complex.50
reacted with excess base to produce the doubly deprotonated
products 2a−4a and further reacted with isopropyl alcohol to
give the putative amino iron hydrides 2b′−4b′ (Scheme 5, eqs
11−13). All of the products were characterized by multiple
NMR spectra (Table 3). The amido-ene(amido) complexes 2a
Figure 3. 31P{1H} NMR (243 Hz, C6D6) spectrum of 1b.
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Figure 4. 31P{1H} NMR (243 Hz, C6D6) spectrum of the reaction mixture of 1b with isopropyl alcohol. The NMR sample was prepared by
removing the reaction solvent (isopropyl alcohol) and extracting the residue with C6D6. The 31P{1H} NMR spectrum of the reaction mixture
showed two sets of doublets: the major doublets are ascribed to 1b, and the minor doublets at 86.47 and 65.42 ppm belong to 1c.
1
Figure 5. H NMR (600 Hz, C6D6) spectrum of the reaction mixture of 1b with isopropyl alcohol. The NMR sample was prepared by removing
the reaction solvent (isopropyl alcohol) and extracting the residue with C6D6.
ring sizes. Except for the catalyst that contains a β-fluorine
substituent and decomposes readily, all of the other catalysts
were found to be active. This reveals the effectiveness of the
ene(amido) group in facilitating rapid asymmetric transfer
hydrogenation reactions. A combined study of the electronic
structure of the amido-ene(amido) diphosphine complex 1b
has further uncovered the real mechanism of the ene(amido)
CONCLUSION
■
The effectiveness of the ene(amido) group in activating iron
for catalyzing rapid asymmetric transfer hydrogenation
reactions was explored by synthesizing a series of amine-
(imine) diphosphine iron precatalyst complexes that possess
either substituted phosphino-imine moieties or varied chelate
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Scheme 5. Stoichiometric Reactions of Iron Complexes 2−4 with Base and Isopropyl Alcohol
Table 3. NMR properties of the Amido-Ene(amido) and
a
Hydride Complexes
complex
δ(31P) (ppm)
2JPP (Hz)
δ(1H) (ppm)
2JPH (Hz)
2a′
3a
4a
85.75, 79.80
85.84, 66.29
100.41, 68.81
87.85, 55.54
85.24, 73.07
29.5
27.4
21.3
2b′
−8.78
−9.54
79.4, 58.1
69.6, 76.6
4b′
37.4
a
2
3a: JPF = 16.5 Hz.
group in activating the iron center for ATH reaction: a π-back-
donation interaction that transfers the electron density of the
iron center to the π-coordinating ligands so as to stabilize the
catalytic intermediates.
EXPERIMENTAL SECTION
■
General Comments. Manipulations and procedures involving air-
sensitive compounds were performed under an inert atmosphere with
argon or nitrogen using Schlenk techniques or in an inert-gas-
protected glovebox. Solvents were dried and degassed using standard
procedures before manipulations and reactions. Ketone substrates
were distilled under an inert atmosphere and stored in a glovebox
prior to catalytic reactions. Deuterated solvents were purchased from
Figure 7. Qualitative HOMO-1 molecular orbital diagram of 1b.
Cambridge Isotope Laboratories, and some of them were distilled and
dried over activated molecular sieves if necessary. All of the other
Figure 6. (a) 57Fe Mossbauer spectrum of 1b (recorded at 80 K in zero field). (b) XPS spectrum of 1b (recorded under the protection of argon).
̈
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chemicals were purchased from commercial sources and used without
further purification. NMR spectra were recorded at ambient
temperature and pressure using BRUKER AVANCE III, HD 600
MHz spectrometers (1H (600 MHz), 13C{1H} NMR (151 MHz), and
31P{1H} NMR (243 MHz)). The 31P{1H} NMR spectra were
referenced to 85% H3PO4 (0 ppm). Fourier transform infrared spectra
were obtained using a Thermo Fisher Escalab 250Xi spectrometer at
Donghua University. An X-ray photoelectron spectrum was obtained
using a Thermo Fisher Nicolet 6700 spectrometer at Donghua
flask with a stirring bar. Then a solution of (1R,2R)-N1-(2-
(diphenylphosphanyl)ethyl)-1,2-diphenylethane-1,2-diamine ((R,R)-
P-NH-NH2; 2.18 g, 5.13 mmol) in MeOH (10.0 mL) and a solution
of [Fe(H2O)6][BF4]2 (1.73 g, 5.13 mmol) in MeCN (10.0 mL) were
placed in the flask. The pure reaction mixture was stirred for 36 h at
room temperature. The flask was taken out from the glovebox, and
the solvent was removed under vacuum to give a deep purple solid.
The purple solid was mixed with sodium chloride (0.60 g, 10.26
mmol) and redissolved in acetone (25.0 mL). Then the mixture was
placed under an atmosphere of carbon monoxide (1.1 atm) and
stirred for 1 h at room temperature to give an orange solution with a
white precipitate. Acetone was removed under vacuum, and an
additional portion of acetone (25.0 mL) was added to the obtained
yellow solid. The solution was stirred under an atmosphere of carbon
monoxide (1.1 atm) for another 1 h. Acetone was removed by rotary
evaporation. The residue was extracted with dichloromethane (5.0
mL), and the solution was filtered with a syringe filter PTFE
membrane, followed by filtration through a pad of Celite. The
dichloromethane solvent was removed using rotary evaporation to
give a yellow oil. The oil was dissolved in a minimum volume of
DCM, and diethyl ether (50.0 mL) was added dropwise to afford a
yellow solid. The solution was filtered using a filter paper, and the
solid was dried overnight. The precatalyst was dissolved in a small
amount of MeOH and stirred vigorously until a brown precipitate
formed. The brown precipitate was washed with MeOH (1.0 mL) and
dried under vacuum. Crystals of complex 1 suitable for X-ray single
crystal diffraction were obtained from hot methanol solution. Yield:
University. The 57Fe Mossbauer spectra were recorded at 80 K in zero
̈
field at the Dalian Institute of Chemical Physics, Chinese Academy of
Sciences. The electrospray ionization mass spectrometry (ESI-MS)
data were collected on an Xevo G2 XS QTOFMS mass spectrometer
with an ESI source at the Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, and a Waters Xevo G2-XS QT mass
spectrometer with an ESI source at the Instrumental Analysis Center
of Shanghai Jiao Tong University. Single-crystal X-ray diffraction data
were collected using a Nonius Kappa-CCD diffractometer with Mo
Kα radiation (λ = 0.71073 Å) at the Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences. The structures were solved
and refined using SHELXTL V6.1. Crystallographic data for 1
(1885122) and 3 (1885130) were deposited with the Cambridge
Crystallographic Data Centre and are available free of charge from
https://www.ccdc.cam.ac.uk/.
Synthesis of 1. 1-(Diphenylphosphino)propanone was initially
synthesized as the starting material for the synthesis of complex 1.
The scheme of synthesis of 1-(diphenylphosphino)propanone is
shown in Scheme 2, eq 1.
1
2.00 g, 45.6%. H NMR (600 MHz, CDCl3): δ 7.60−6.86 (m, 30H,
ArH), 5.15−4.84 (m, 1H, CH(Ph)), 4.70−4.65 (m, 1H, NHCH2),
4.42−4.38 (m, 2H, PCH2), 4.26−4.21 (m, 1H, CH(Ph)), 3.31−3.24,
2.85−2.81 (m, 2H, PCH2), 3.38−3.33, 2.60−2.55 (m, 2H, NHCH2),
2.10 (s, 3H, CH3). 13C{1H} NMR (151 MHz; CDCl3): δ 188.1 (d,
In a nitrogen glovebox, chlorodiphenylphosphine (5.00 g, 22.7
mmol) was dissolved in THF (100.0 mL) in a Schlenk flask (200
mL). Methyllithium (14.2 mL, 1.6 M, 22.7 mmol) was placed in the
flask dropwise at −78 °C. The mixture was stirred for 30 min at −78
°C. Then a BH3·THF (27.7 mL, 1.1 equiv, ca. 0.9 M) solution was
added to the mixture at room temperature. 31P{1H} NMR was used to
monitor whether the reaction was complete. After the reaction, the
flask was taken out from the glovebox and 10.0 mL of distilled water
was added slowly. The solvent was removed using a rotary evaporator,
and the mixture was extracted with DCM (150.0 mL × 3). The
organic phase was dried with sodium sulfate and concentrated to
obtain a colorless liquid. The residue was purified by running column
chromatography (the eluent was petroleum ether/ethyl acetate 20/1)
to obtain a colorless liquid (borane adduct of methyldiphenylphos-
phine) (3.50 g, 72.2%).
J
CP = 4.0 Hz, CO), 138.2 (s, ArC), 134.4 (s, ArC), 134.2 (d, JCP = 10.2
Hz, ArC), 133.9 (d, JCP = 8.6 Hz, ArC), 132.4 (d, JCP = 9.4 Hz, ArC),
131.6 (m, ArC), 130.9 (d, JCP = 2.2 Hz, ArC), 130.7 (d, JCP = 9.1 Hz,
ArC), 130.1 (m, ArC), 129.9 (s, ArC), 129.6 (s, ArC), 129.3 (m,
ArC), 128.8 (s, ArC), 128.7 (m, ArC), 126.8 (m, ArC), 79.6 (s,
CH(Ph)), 76.6 (s, CH(Ph)), 53.8 (d, JCP = 26.3 Hz, PCH2), 50.2 (s,
NHCH2), 31.7 (d, JCP = 24.8 Hz, PCH2), 24.2 (s, CH3). 31P{1H}
NMR (243 MHz; CDCl3): δ 54.22, 58.01, JPP = 42.57 Hz. HRMS
(ESI-TOF, CH3CN): m/z calculated for (C44H42ClFeN2OP2)
767.1810, found 767.1812, Anal. Calcd for C44H42BClF4FeN2OP2:
C, 61.82; H, 4.95; N, 3.28. Found: C, 61.62; H, 5.05; N, 3.10. FT-IR
(cm−1): 648w, 694s, 743s, 826w, 846w, 883w, 921w, 967s, 999s,
1056s, 1161w, 1193w, 1243w, 1310w, 1333w, 1373w, 1411w, 1435s,
1455m, 1485m, 1573w, 1587w, 1604w, 1625m, 1704w, 1824w, 1953s,
2936w, 3031w, 3061m, 3200w, 3545w, 3626w.
In a nitrogen glovebox, the borane adduct of methyldiphenylphos-
phine (2.00 g, 9.34 mmol) was dissolved in THF (75.0 mL) in a
Schlenk flask (200 mL). The flask was sealed with a rubber plug, and a
balloon was connected to the neck of the Schlenk flask (see Figure S2
for details). Then the flask was taken out from the glovebox. sec-
Butyllithium (1.3 M, 36.1 mL, 46.7 mmol) was injected into the flask
at −78 °C with stirring for 3 h. Ethyl acetate (10.0 mL) was added to
the solution, followed by the addition of 10.0 mL of distilled water at
−78 °C. The solvent was removed, and the residue was extracted with
DCM (100.0 mL × 3). The organic phase was dried with sodium
sulfate and concentrated to give a colorless liquid. The crude product
was purified by running column chromatography (the eluent was
petroleum ether/ethyl acetate 9/1) to obtain a colorless liquid (1.08
g, 45.0%). In an argon glovebox, the product above was dissolved in
diethylamine and stirred for 12 h. The solvent was removed to obtain
Synthesis of 2. Diphenylphosphinopropionaldehyde hydrochlor-
ide dimer was synthesized according to the reported literature52 for
the synthesis of complex 2. The scheme of synthesis of
diphenylphosphinopropionaldehyde hydrochloride dimer is shown
in Scheme 2, eq 3.
In a nitrogen glovebox, a suspension of KH (1.13 g, 28.2 mmol) in
THF (100.0 mL) was added to diphenylphosphine (4.37 g, 23.5
mmol) dropwise at room temperature in a Schlenk flask (250 mL).
The solution turned red. The solution was stirred for 1 h. 2-Bromo-
1,1-diethoxypropane (4.30 g, 23.5 mmol) was added to the mixture
dropwise at −78 °C and the flask was taken out from the glovebox.
The diluted HCl solution (13.0 mL) was injected into the flask with
stirring overnight at room temperature. A white precipitate was
produced gradually in the flask. The precipitate was filtered in air and
washed twice with distilled water. Then the mixture was filtered using
a filter paper to give a white solid. The white solid was dried under
vacuum overnight. Yield: 3.41 g, 52.1%. 1H NMR (600 MHz,
MeOD): δ 8.16−8.09 (m, 2H, ArH), 8.01−7.95 (m, 1H, ArH), 7.87−
7.82 (m, 3H, ArH), 7.80−7.75 (m, 2H, ArH), 7.74−7.69 (m, 2H,
ArH), 5.95 (d, JHP = 24.8 Hz, 1H, CHOH), 4.60−4.55 (m, 1H,
CHCH3), 1.92−1.86 (m, 3H, CH3). 13C{1H} NMR (151 MHz,
MeOD): δ 135.2 (d, JCP = 30.3 Hz, ArC), 134.3 (m, ArC), 134.2 (m,
ArC), 130.0 (m, ArC), 129.9 (m, ArC), 116.9 (m, ArC), 116.3 (m,
1
a colorless liquid. H NMR (600 MHz, C6D6): δ 7.36−7.30 (m, 4H,
ArH), 7.20−6.90 (m, 6H, ArH), 2.93 (s, 2H, CH2), 1.80 (s, 3H,
CH3). 13C{1H} NMR (151 MHz; C6D6): δ 203.5 (d, JCP = 8.9 Hz,
CO), 137.9 (d, JCP = 15.3 Hz, ArC), 132.6 (d, JCP = 19.9 Hz, ArC),
128.8 (s, ArC), 128.5 (d, JCP = 6.7 Hz, ArC), 45.1 (d, JCP = 23.2 Hz,
CH2), 30.1 (s, CH3). 31P {1H} NMR (243 MHz; C6D6): δ −18.57.
FT-IR (cm−1): 697s, 742s, 768w, 849w, 964w, 999w, 1028m, 1045m,
1069m, 1096m, 1170s, 1225s, 1273w, 1307w, 1332w, 1356m, 1378m,
1434s, 1463m, 1480m, 1586w,1706s, 2130w, 2279m, 2327m, 2383s,
2927s, 2976m, 3000m, 3054w, 3504w.
In an argon glovebox, 1-(diphenylphosphanyl)propanone (1.31 g,
5.13 mmol) was dissolved in 45.0 mL of MeOH in a 200 mL Schlenk
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ArC), 66.9 (dd, JCP = 62.8 Hz, JCP = 9.2 Hz, PCHOH), 29.5 (d, JCP
=
19F{1H} NMR (564.2 MHz, CDCl3): δ −237.03 (d, JFP = 36.62 Hz).
ATR-FTIR (cm−1): 611m, 627m, 692s, 705s, 736s, 867m, 1000m,
1020s, 1060s, 1110s, 1133m, 1189w, 1310w, 1437s, 1485m, 2252w,
2344s, 2389s, 3059m.
51.1 Hz, CHCH3), 12.4 (d, JCP = 2.92 Hz, CH3). 31P{1H} NMR (243
MHz, MeOD): δ 20.37. ATR-FTIR (cm−1): 635m, 692s, 722s, 746s,
847w, 968w, 997s, 1035s, 1066s, 1109s, 1162m, 1193m, 1270w,
1339w, 1382w, 1437m, 1586m, 1632m, 2889s, 3054s, 3314s.
In a nitrogen glovebox, a solution of the diphenylphosphinopro-
pionaldehyde hydrochloride dimer (1.00 g, 1.78 mmol) in MeOH
(10.0 mL) was added to a suspension of NaOMe (0.212 g, 3.92
mmol) in MeOH (5.0 mL) in a 200 mL Schlenk flask charged with a
stirring bar. The solution mixture was stirred at room temperature for
2 min. Then a solution of (1R,2R)-N1-(2-(diphenylphosphanyl)-
ethyl)-1,2-diphenylethane-1,2-diamine ((R,R)-P-NH-NH2; 1.53 g,
3.60 mmol) in MeOH (5.0 mL) and a solution of [Fe(H2O)6][BF4]2
(1.50 g, 4.44 mmol) in MeCN (5.0 mL) were placed in the flask in
sequence. The purple mixture was stirred overnight at room
temperature. The flask was taken out from the glovebox, and the
solvent was removed under vacuum to give a deep purple solid. This
purple solid was mixed with sodium chloride (0.416 g, 7.12 mmol)
and redissolved in acetone (25.0 mL). Then the mixture was placed
under an atmosphere of carbon monoxide (1.1 atm) and stirred for 1
h at room temperature to give an orange solution with a white
precipitate. Acetone was removed under vacuum, and an additional
portion of acetone (25.0 mL) was added to the obtained yellow solid.
The solution was stirred under an atmosphere of carbon monoxide
(1.1 atm) for 1 h. Acetone was removed by using rotary evaporation.
The product was extracted with dichloromethane (5.0 mL), and the
solution was filtered with a syringe filter PTFE membrane, followed
by filtration through a pad of Celite. The dichloromethane solvent
was removed by using rotary evaporation to give a yellow oil. The oil
was dissolved into a minimum volume of DCM, and diethyl ether
(30.0 mL) was added dropwise to afford a yellow solid. The solution
was filtered using a filter paper and the solid was dried overnight. The
solid (0.50 g, 5.85 mmol) was dissolved in 5.0 mL of MeOH and
added to a solution of NaBPh4 (0.22 g, 6.64 mmol) in MeOH (∼2.0
mL) to form a yellow solid as a precipitate. The mixture was filtered,
and the solid was washed with diethyl ether during filtration. The
solid was dried overnight. Yield: 97.0 mg, 16.0%. Various isomers of 2
were detected by a 31P{1H} NMR spectrum. 31P{1H} NMR (243
MHz; CDCl3): δ 80.47, 56.03, JPP = 38.6 Hz; 74.06, 57.21, JPP = 39.5
Hz; 69.23, 58.27, JPP = 38.9 Hz; 68.27, 56.32, JPP = 37.2 Hz. HRMS
(ESI-TOF, CH3CN): m/z calculated for (C44H42ClFeN2OP2)
767.1810, found 767.1812, Anal. Calcd for C68H62BClFeN2OP2: C,
75.12; H, 5.75; N, 2.58. Found: C, 74.88; H, 5.55; N, 2.62. ATR-
FTIR (cm−1): 613m, 639w, 703s, 734s, 844w, 961m, 1000m, 1031m,
1072m, 1098s, 1185m, 1268w, 1435s, 1455m, 1481m, 1580m, 1964s,
2983m, 2999m, 3055s.
In a nitrogen glovebox, the compound Ph2PCH2F·BH3 (0.60 g,
2.59 mmol) was dissolved in THF (10.0 mL) in a Schlenk flask (100
mL). sec-Butyllithium (1.3 M, 2.0 mL, 2.59 mmol) was placed in the
flask dropwise at −78 °C with stirring for 30 min. Excess ethyl
formate was placed in the flask at −78 °C. The flask was taken out
from the glovebox, and distilled water (5.0 mL) was added. The
solvent was removed by using rotary evaporation, and the mixture was
extracted with DCM (50.0 mL × 3). The organic phase was dried
with sodium sulfate and concentrated to obtain a colorless liquid. The
colorless liquid decomposed readily; therefore it was used rapidly
without further purification. 1H NMR (600 MHz, CDCl3): δ 9.85 (d,
1H, JHP = 11.41 Hz, CHO), 7.82−7.78 (m, 4H, ArH), 7.63−7.59 (m,
2H, ArH), 7.55−7.51 (m, 4H, ArH), 5.92 (dd, 1H, JHF = 47.69 Hz,
JHP = 5.76 Hz, CHF), 1.18−1.12 (m, 3H, BH3). 31P{1H} NMR (243
MHz, CDCl3): δ 22.16. 19F{1H} NMR (564.2 MHz, CDCl3): δ
−209.06 (d, JFP = 36.10 Hz, CHF). The product above was taken into
the glovebox and dissolved in methanol (15.0 mL) with stirring for 24
h at room temperature. The 31P{1H} NMR spectrum indicated that
the purity was about 30.0%. The compound decomposed readily, and
it was be used rapidly without further purification. 31P{1H} NMR
(243 MHz, CDCl3): δ −9.11.
Using the same procedure as for 1, 3 was synthesized in a 40.5%
yield. Crystals of complex 3 suitable for X-ray singl-crystal diffraction
were obtained from slow diffusion of diethyl ether into a solution of
1
complex 3 in DCM. H NMR (600 MHz, CDCl3): δ 8.48−6.70,
6.64−6.56 (m, 30H, ArH), 6.70−6.65 (m, 1H, CHF), 4.99−4.95 (m,
1H, CH(Ph)), 4.67−4.63 (m, 1H, NH), 4.49−4.44 (m, 1H,
CH(Ph)), 3.56−3.50 (m, 1H, CH2NH), 3.19−3.15 (m, 1H,
CH2P), 3.17−3.13 (m, 1H, CH2NH), 2.90−2.86 (m, 1H, CH2P).
13C{1H} NMR (150 MHz, CDCl3): δ 102.0 (m, CHF), 71.2 (s,
CH(Ph)), 76.3 (s, CH(Ph)), 45.9 (m, CH2NH), 34.5 (m, CH2P).
31P{1H} NMR (243 MHz, CDCl3): δ 54.97 (d, JPP = 42.10 Hz,
CH2P), 84.73 (dd, JPP = 42.10 Hz, JPF = 25.23 Hz), 56.77 (d, JPP
=
42.10 Hz), 75.46 (dd, JPP = 42.10 Hz, JPF = 25.23 Hz). 19F{1H} NMR
(564.2 MHz, CDCl3): δ −237.03 (d, JFP = 36.62 Hz) −197.61,
−201.81. HRMS (ESI-TOF, CH3CN): m/z calculated for
(C43H39ClFFeN2OP2) 771.1552, found 771.1561, Anal. Calcd for
C43H39BClF5FeN2OP2: C, 60.14; H, 4.58; N, 3.26. Found: C, 61.41;
H, 4.65; N, 3.18. ATR-FTIR (cm−1): 695s, 723s, 747s, 998s, 1062s,
1163m, 1283w, 1313w, 1437s, 1456w, 1485w, 1589w, 1974s, 3060m.
Synthesis of 4. N1-[[2-(Diphenylphosphino)phenyl]methyl]-1,2-
diphenyl-(1R,2R)-1,2-ethanediamine was synthesized as the starting
material for the synthesis of complex 4. The scheme of synthesis of 1-
N1-[[2-(diphenylphosphino)phenyl]methyl]-1,2-diphenyl-(1R,2R)-
1,2-ethanediamine is shown in Figure S1 in the Supporting
Information.
Synthesis of 3. 2-(Diphenylphosphino)-2-fluoroacetaldehyde was
synthesized as the starting material for the synthesis of complex 3.
The scheme of synthesis of 2-(diphenylphosphino)-2-fluoroacetalde-
hyde is shown in Scheme 2, eq 5.
In a nitrogen glovebox, the borane adduct of methyldiphenylphos-
phine (1.00 g, 4.67 mmol) was dissolved in THF (10.0 mL) in a
Schlenk flask (100 mL). sec-Butyllithium (1.3 M, 3.6 mL, 4.67 mmol)
was placed in the flask dropwise at −78 °C followed by stirring for 1
h. N-Fluorobenzenesulfonimide (fluorinating reagent) (1.47 g, 4.67
mmol) was dissolved in THF (3.0 mL) and placed in the flask at −78
°C with stirring for 5 min. The flask was taken out from the glovebox
followed by the addition of distilled water (5.0 mL). The solvent was
removed by rotary evaporation, and the mixture was extracted with
DCM (70.0 mL × 3). The organic phase was dried with sodium
sulfate and concentrated to give a colorless liquid. The residue was
purified by running column chromatography (the eluent was
petroleum ether/ethyl acetate 60/1, 40/1, and then 20/1) to obtain
a colorless liquid. Yield: 0.60 g, 55.4%. 1H NMR (600 MHz, CDCl3):
δ 7.82−7.77 (m, 4H, ArH), 7.62−7.56 (m, 2H, ArH), 7.54−7.50 (m,
In a nitrogen glovebox, 2-(diphenylphosphino)benzaldehyde (1.00
g, 3.44 mmol) was dissolved in THF (5.0 mL) and MeOH (50.0 mL)
in a 200 mL round-bottomed flask. Then a solution of (1R,2R)-1,2-
diphenylethane-1,2-diamine ((R,R)-dpen; 0.88 g, 4.13 mmol) in
MeOH (5.0 mL) and a solution of FeCl2 (0.52 g, 4.13 mmol) in
MeCN (5.0 mL) were placed in the flask in sequence. The solution
was stirred for 15 min at room temperature and then taken out from
the glovebox. The solvent was evaporated using a rotary evaporator at
30 °C. The product was dried under vacuum for 2 h and taken into
the glovebox. A solution of LiAlH4 (0.16 g, 4.13 mmol) in THF (20.0
mL) was placed in the flask. The mixture was stirred vigorously for 5
min and taken out from the glovebox. Distilled water (5.0 mL) was
injected by syringe at −78 °C, and the solvent was removed to give a
dark brown solid. Then the solid was dissolved in DCM (100.0 mL)
and the mixture was filtered through a pad of Celite. The filtrate was
extracted with DCM (100.0 mL × 2). Then the organic phase was
dried with sodium sulfate and concentrated to give a colorless liquid.
The residue was purified by running column chromatography (the
eluent was petroleum ether/ethyl acetate 1/1) to obtain a yellow
solid. Yield: 0.55 g, 32.2%. 1H NMR (600 MHz, CDCl3): δ 7.36−7.32
4H, ArH), 5.30 (d, 2H, JHF = 46.46 Hz, CH2F), 0.94 (d, 3H, JHP
=
=
88.43 Hz, BH3). 13C{1H} NMR (150 MHz, CDCl3): δ 132.9 (d, JCP
8.70 Hz, ArC), 131.4 (d, JCP = 2.02 Hz, ArC), 129.5 (d, JCP = 10.42
Hz, ArC), 125.8 (d, JCP = 52.15 Hz, ArC), 81.3 (dd, JCP = 36.37 Hz,
J
CF = 197.40 Hz, CH2F). 31P{1H} NMR (243 MHz, CDCl3): δ 17.58.
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(m, 6H, ArH), 7.30−7.26 (m, 3H, ArH), 7.25−7.21 (m, 5H, ArH),
7.20−7.15 (m, 5H, ArH), 7.13−7.08 (m, 2H, ArH), 7.06−7.02 (m,
2H, ArH), 6.94−6.89 (m, 1H, ArH), 4.17−4.12 (m, 1H, NH), 3.84
(d, 1H, CH(Ph)), 3.82 (d, 1H, CH2), 3.75 (d, 1H, CH2), 3.73 (d, 1H,
CH(Ph)), 1.85−1.95 (m, 2H, NH2). 13C{1H} NMR (150 MHz,
CDCl3): δ 144.9 (d, JCP = 22.35 Hz, ArC), 143.4 (s, ArC), 141.0 (s,
ArC), 137.2 (d, JCP = 4.37 Hz, ArC), 137.0 (d, JCP = 6.72 Hz, ArC),
135.8 (d, JCP = 14.29 Hz, ArC),, 134.2 (d, JCP = 8.67 Hz, ArC), 133.9
(d, JCP = 6.41 Hz, ArC), 133.7 (d, JCP = 6.53 Hz, ArC), 133.4 (s,
1062s, 1492s, 1176m, 1234w, 1259w, 1306w, 1324w, 1417s, 1434s,
1492s, 1571w, 1586w, 1660w, 1900s, 1979w, 2860m, 2920m, 2961m,
3022w, 2054m, 3501w, 3777w. Anal. Calcd for C44H40FeN2OP2: C,
72.33; H, 5.52; N, 3.83. Found: C, 71.75; H, 5.39; N, 3.67.
Synthesis of 2a/2a′. Similar to the synthesis of 1b, 2a/2a′ were
synthesized. 1H NMR (600 MHz, C6D6): δ 8.04−8.00 (m, 2H, ArH),
7.64−7.54, 7.48−6.68 (m, 28H, ArH), 7.54−7.49 (m, 1H, CHN),
4.83−4.78 (m, 1H, CH(Ph)), 4.33−4.27 (m, 1H, CH(Ph)), 2.63−
2.59 (m, 1H, CH2N), 2.53−2.48 (m, 1H, CH2N), 2.31−2.27 (m, 1H,
CH2P), 2.14−2.08 (m, 1H, CH2P), 1.88−1.83 (m, 3H, CH3).
ArC), 129.6 (d, JCP = 5.77 Hz, ArC), 129.3 (s, ArC), 128.9 (d, JCP
4.12 Hz, ArC), 128.7 (d, JCP = 7.01 Hz, ArC), 128.6 (s, ArC), 128.5
(d, JCP = 7.01 Hz, ArC), 128.3 (d, JCP = 7.83 Hz, ArC), 128.0 (d, JCP
=
13C{1H} NMR (151 MHz, C6D6): δ 225.6 (dd, JCP = 22.08 Hz, JCP
=
=
30.91 Hz, CO), 167.0 (d, JCP = 25.80 Hz, NCHC), 148.4 (s, ArC),
145.0 (s, ArC), 136.2 (d, JCP = 33.01 Hz, ArC), 135.4 (d, JCP = 48.24
Hz, ArC), 134.9 (d, JCP = 24.12 Hz, ArC), 134.5 (d, JCP = 40.62 Hz,
ArC), 133.2 (d, JCP = 5.93 Hz, ArC), 133.1 (d, JCP = 4.81 Hz, ArC),
132.5 (d, JCP = 11.38 Hz, ArC), 131.6 (d, JCP = 9.88 Hz, ArC), 129.7
(s, ArC), 128.9 (s, ArC), 128.6 (s, ArC), 128.2 (s, ArC), 127.0 (d, JCP
= 16.16 Hz, ArC), 126.5 (s, ArC), 90.1 (s, CH(Ph)), 79.8 (s,
CH(Ph)), 77.2 (d, JCP = 4.93 Hz, CHCP), 56.7 (d, JCP = 9.52 Hz,
NCH2), 36.2 (d, JCP = 35.15 Hz, CH2P), 12.1 (s, CH3). 31P{1H}
NMR (243 MHz, C6D6): δ 85.75, 79.80, JPP = 29.5 Hz. ATR-FTIR
(cm−1): 625w, 696s, 720s, 742m, 925w, 1035s, 1067s, 1095s, 1164m,
1252m, 1285w, 1308w, 1363w, 1434s, 1453w, 1481w, 1549s, 1574m,
1601w, 1626w, 1915s, 1980w, 2874m, 2930m, 3057m, 4463m. Anal.
Calcd for C44H40FeN2OP2: C, 72.33; H, 5.52; N, 3.83. Found: C,
72.06; H, 5.36; N, 3.75.
18.54 Hz, ArC), 127.3 (s, ArC), 127.1 (s, ArC), 126.9 (s, ArC), 126.8
(s, ArC), 69.4 (s, CH(Ph)), 61.8 (s, CH(Ph)), 50.64 (d, JCP = 19.65
Hz, CH2). 31P{1H} NMR (243 MHz, CDCl3): δ −16.19. HRMS
(ESI-TOF, CH3CN): m/z calculated for [(C33H31N2P) + H]+
487.2299, found 487.2298. ATR-FTIR (cm−1): 697s, 722s, 748s,
851s, 1027m, 1070m, 1118s, 1186s, 1308w, 1435s, 1453s, 1478m,
1492m, 1587m, 1980w, 2162w, 2850m, 2917m, 3021s, 3056s, 3304w.
Using the same procedure as for 2, 4 was synthesized in a 19.3%
1
yield. H NMR (600 MHz, CDCl3): δ 7.93−6.91, 6.86−6.29 (m,
54H, ArH), 6.90−6.87 (m, 1H, CHN), 4.79−4.74 (m, 1H,
CH(Ph)), 4.47−4.43 (m, 1H, NH), 4.17−4.13 (m, 1H, CH(Ph)),
3.76−3.72 (m, 2H, NHCH2), 3.11−3.08 (m, 1H, CH2P), 2.89−2.85
(m, 1H, CH2P). 13C{1H} NMR (151 MHz, CDCl3): δ 176.8 (s,
CHN), 136.3 (s, BPh4C), 125.8 (s, BPh4C), 121.8 (s, BPh4C), 75.8
(s. CH(Ph)), 75.2 (s, CH(Ph)), 54.7 (d, JCP = 6.97 Hz, NHCH2),
45.1 (d, JCP = 26.99 Hz, CH2P). 31P{1H} NMR (243 MHz, CDCl3): δ
40.18, 51.70, JPP = 42.34 Hz; 43.83, 51.87, JPP = 42.34 Hz. HRMS
(ESI-TOF, CH3CN) m/z calculated for (C48H42ClFeN2OP2)
815.1813, found 815.1812, Anal. Calcd for C72H62BClFeN2OP2: C,
76.17; H, 5.50; N, 2.47. Found: C, 75.54; H, 5.28; N, 2.31. ATR-
FTIR (cm−1): 613m, 701s, 734s, 999m, 1030m, 1071s, 1092s, 1121s,
1436s, 1455m, 1480s, 1580m, 1961s, 2984m, 3055s.
Synthesis of 3a/3a′. Similar to the synthesis of 1b, 3a/3a′ were
synthesized. 1H NMR (600 MHz, C6D6): δ 8.20−8.15 (m, 1H,
CHN), 7.98−5.85 (m, 30H, ArH), 4.62−4.56 (m, 1H, CH(Ph)),
4.28−4.22 (m, 1H, CH(Ph)), 2.41−2.36 (m, 2H, CH2N), 2.30−2.24
(m, 1H, CH2P), 2.13−2.08 (m, 1H, CH2P). 13C{1H} NMR (151
MHz, C6D6): δ 224.3 (m, CO), 157.2 (dd, JCP = 24.98 Hz, JCF
=
36.91 Hz, CHN), 147.6 (s), 144.0 (s), 133.0 (s), 132.9 (s), 132.8 (s),
132.5 (s), 132.4 (s), 132.2 (s), 132.1 (s), 131.9 (s), 131.8 (s), 130.9
(s), 129.9 (s), 129.3 (s), 129.2 (s), 128.9 (s), 127.1 (s), 126.9 (s),
126.6 (s), 90.3 (s, CH(Ph)), 79.6 (s, CH(Ph)), 57.2 (d, JCP = 8.41
Hz, NCH2), 36.5 (d, JPP = 24.47 Hz, CH2P). 31P{1H} NMR (243
MHz, C6D6): δ 85.84 (d, JPP = 27.4 Hz), 66.29 (dd, JPP = 27.4 Hz, JPF
Synthesis of 1a. In an argon glovebox, 1 (20.0 mg, 0.023 mmol)
and KOtBu (2.6 mg, 0.023 mmol) were place in a vial charged with a
stirring bar. Then THF (15.0 mL) was placed in the vial. The reaction
mixture was stirred vigorously at room temperature for 5 min to yield
a dark blue solution. The solvent was removed under vacuum, and the
= 16.5 Hz), 84.10 (d, JPP = 29.4 Hz), 67.99 (dd, JPP = 29.4 Hz, JPF
=
1
17.8 Hz). ATR-FTIR (cm−1): 627w, 697s, 742s, 801s, 915w, 1026s,
1098s, 1120s, 1181m, 1223m, 1259s, 1435s, 1454m, 1480m, 1527m,
1557m, 1575m, 1652w, 1930s, 2050w, 2162w, 2926s, 2961s, 3056s,
3343m. Anal. Calcd for C43H37FeN2OP2: C, 70.31; H, 5.08; N, 3.81.
Found: C, 69.96; H, 5.16; N, 3.60.
residue was extracted with C6D6 for NMR analysis. H NMR (600
MHz, C6D6): δ 7.95−6.16 (ArH, 30H), 5.52−5.48 (m, 1H), 5.17 (d, J
= 10.1 Hz, 1H), 4.26−4.22 (m, 1H), 3.85 (dd, J = 12.3, 10.1 Hz, 1H),
2.57−2.52 (m, 1H), 2.30−2.26 (m, 1H), 2.16−2.11 (m, 1H), 2.10−
2.08 (m, 1H), 1.89 (s, 3H). 31P{1H} NMR (243 MHz, C6D6): δ 48.9,
55.6, JPP = 35.2 Hz. Anal. Calcd for C44H41ClFeN2OP2: C, 68.90; H,
5.39; N, 3.65. Found: C, 68.65; H, 5.18; N, 3.37.
Synthesis of 4a/4a′. Similar to the synthesis of 1b, 4a/4a′ were
synthesized. 1H NMR (600 MHz, C6D6): δ 8.05−7.34, 7.27−5.53 (m,
34H), 7.33−7.28 (m, 1H, CHN), 4.46−4.40 (m, 2H, CHP), 4.30−
4.24 (m, 1H, CH(Ph)), 4.20−4.16 (m, 1H, CH(Ph)), 3.27−3.21 (m,
2H, CH2N). 13C{1H} NMR (151 MHz, C6D6): δ 221.6 (m, CO),
164.6 (d, JCP = 25.6 Hz, CHN), 149.0 (d, JCP = 26.64 Hz, ArC), 142.8
(d, JCP = 69.9 Hz, ArC), 136.9 (d, JCP = 35.52 Hz, ArC), 136.8 (d, JCP
= 42.18 Hz, ArC), 136.3 (d, JCP = 48.84 Hz, ArC), 134.6 (s, ArC),
134.0 (s, ArC), 133.8 (d, JCP = 9.1 Hz, ArC), 132.9 (s, ArC), 132.4 (d,
Synthesis of 1b. In an argon glovebox, 1 (20.0 mg, 0.023 mmol)
and KOtBu (5.2 mg, 0.046 mmol) were placed in a vial charged with a
stirring bar. Then THF (15.0 mL) was placed in the vial. The reaction
mixture was stirred vigorously at room temperature for 5 min to yield
a dark blue solution. The solvent was removed under vacuum, and the
1
residue was extracted with C6D6 for NMR analysis. H NMR (600
MHz, C6D6): δ 8.12−8.08 (m, 2H, ArH), 7.69−7.65 (m, 2H, ArH),
7.56−7.35 (m, 8H, ArH), 7.15−6.92 (m, 16H, ArH), 6.82−6.77 (m,
2H, ArH), 5.09−5.05 (m, 1H, CH(Ph)), 4.33−4.29 (m, 1H,
CH(Ph)), 3.99−3.94 (m, 1H, CHP), 2.60−2.55 (m, 1H, CH2N),
2.45−2.40 (m, 1H, CH2N), 2.32−2.28 (m, 1H, CH2P), 2.12−2.09
(m, 1H, CH2P), 2.08−2.06 (m, 3H, CH3). 13C{1H} NMR (150 MHz,
C6D6): δ 225.0 (dd, JCP = 22.88 Hz, JCP = 36.76 Hz, CO), 175.3 (d,
J
CP = 9.6 Hz, ArC), 131.9 (d, JCP = 11.4 Hz, ArC), 131.5 (d, JCP = 9.4
Hz, ArC), 131.2 (s, ArC), 130.9 (d, JCP = 9.0 Hz, ArC), 130.8 (d, JCP
= 12.7 Hz, ArC), 129.5 (s, ArC), 129.1 (s, ArC), 128.9 (s, ArC), 128.8
(s, ArC), 126.9 (s, ArC), 126.7 (s, ArC), 126.6 (s, ArC), 126.4 (s,
ArC), 126.2 (d, JCP = 6.94 Hz, ArC), 124.8 (d, JCP = 53.54 Hz, ArC),
85.7 (s, CH(Ph)), 80.5 (s, CH(Ph)), 76.3 (d, JCP = 45.9 Hz, CHP),
65.5 (d, JCP = 16.2 Hz, CH2N). 31P{1H} NMR (243 MHz, C6D6): δ
100.41, 68.81, JPP = 21.3 Hz. ATR-FTIR (cm−1): 607w, 624w, 696s,
722s, 743s, 846w, 999m, 1027m, 1070m, 1096s, 1119s, 1182s, 1254m,
1308m, 1378m, 1435s, 1454s, 1479s, 1528s, 1602m, 1902s, 1979w,
2050w, 2113w, 2139w, 2162w, 2188w, 2286w, 2323w, 2926m, 3056s,
3365m. Anal. Calcd for C48H40FeN2OP2: C, 74.04; H, 5.18; N, 3.60.
Found: C, 73.93; H, 5.02; N, 3.75.
J
CP = 20.7 Hz), 147.7 (s, ArC), 145.1 (s, ArC), 140.5 (d, JCP = 23.85
Hz, ArC), 138.6 (d, JCP = 53.67 Hz, ArC), 135.2 (d, JCP = 22.23 Hz,
ArC), 135.0 (d, JCP = 17.63 Hz, ArC), 133.1 (d, JCP = 10.39 Hz, ArC),
132.7 (d, JCP = 9.45 Hz, ArC), 132.5 (d, JCP = 11.02 Hz, ArC), 132.1
(d, JCP = 9.76 Hz, ArC), 129.7 (s, ArC), 129.1 (s, ArC), 128.5 (s,
ArC), 128.3 (s, ArC), 128.2 (s, ArC), 128.0 (s, ArC), 127.0 (d, JCP
=
9.59 Hz, ArC), 126.4 (s, ArC), 91.3 (s, CH(Ph)), 74.8 (s, CH(Ph)),
73.0 (d, JCP = 55.45 Hz, CHP), 56.2 (d, JCP = 9.17 Hz, NCH2), 36.3
(d, JCP = 26.96 Hz, CH2P), 18.8 (d, JCP = 17.04 Hz, CH3). 31P{1H}
NMR (243 MHz, C6D6): δ 85.73, 69.67, JPP = 31.4 Hz. ATR-FTIR
(cm−1): 625w, 696s, 741m, 765w, 842m, 914w, 943w, 965w, 1029s,
Synthesis of 1c. In an argon glovebox, 1 (20.0 mg, 0.023 mmol)
and KOtBu (5.2 mg, 0.046 mmol) were placed in a 100 mL round-
bottom flask with a stirring bar. Then THF (15.0 mL) was placed in
the flask and stirring was continued for 5 min. The solvent was
144
https://dx.doi.org/10.1021/acs.organomet.0c00636
Organometallics 2021, 40, 134−147

Organometallics
pubs.acs.org/Organometallics
Article
removed under vacuum. Another portion of KOtBu (5.2 mg, 0.046
mmol) and PrOH were placed in the flask, and the solution was
and Engineering, Donghua University, Shanghai 201620,
People’s Republic of China
i
stirred for 5 min. The solvent was removed under vacuum. The
residue was dissolved in C6D6 and filtered through a syringe filter
PTFE membrane (pore size 0.45 μm). 1H NMR (600 MHz, C6D6): δ
−1.56 (dd, JHP = 64.7 Hz, JHP = 75.8 Hz, 1H). 31P{1H} NMR (243
MHz, C6D6): δ 86.47, 65.42, JPP = 29.8 Hz.
Synthesis of 2b/2b′. Similar to the synthesis of 1c, 2b/2b′ were
synthesized. 1H NMR (600 MHz, C6D6): δ −8.78 (dd, JHP = 79.4, JHP
= 58.1 Hz, 1H). 31P{1H} NMR analysis revealed the product 1b
combined at least two different structures in which the chemical shifts
of phosphorus were 87.85 and 55.54 ppm.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00636
Author Contributions
†Q.X. and R.W. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Synthesis of 3b/3b′. Similar to the synthesis of 1c, 3b/3b′ were
synthesized. 31P{1H} NMR analysis revealed 3b/3b′ would be
decomposed easily in presence of excessive base (more than 4 equiv).
Synthesis of 4b′. Similar to the synthesis of 1c, 4b′ was
synthesized. 1H NMR (600 MHz, C6D6): δ −9.54 (dd, JHP = 69.6 Hz,
■
This work was sponsored by the Natural Science Foundation
of China (21772021), “Shanghai Rising-Star Program”
(16QA1400100), The Program for Professor of Special
Appointment (Eastern Scholar) at Shanghai Institutions of
Higher Learning (TP2014035), the National Key Research
Program of China (No. 2016YFA0201702 of
2016YFA0201700), and the International Joint Laboratory
for Advanced Fiber and Low-dimension Materials
(18520750400).
J
HP = 76.6 Hz, 1H). 31P{1H} NMR (243 MHz, C6D6): δ 89.03, 73.40,
JPP = 27.3 Hz; 85.24, 73.07, JPP = 37.4 Hz. The ratio of two different
4b′ is almost 1/1.1.
Computational Details. The Gaussian09 program package at the
B3LYP/LANL2DZ level of theory under a vacuum state was used for
geometry optimizations and frequency calculations. Calculation
parameters were referenced to our previous report.50
REFERENCES
■
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00636.
■
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Meifang Zhu − State Key Laboratory for Modification of
Chemical Fibers and Polymer Materials, College of Materials
Science and Engineering, Donghua University, Shanghai
201620, People’s Republic of China; Email: zhumf@
dhu.edu.cn
Weiwei Zuo − State Key Laboratory for Modification of
Chemical Fibers and Polymer Materials, College of Materials
Science and Engineering, Donghua University, Shanghai
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Science and Engineering, Donghua University, Shanghai
201620, People’s Republic of China; orcid.org/0000-
0002-7217-5016
Rongliang Wu − State Key Laboratory for Modification of
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