Reactions of Low-Coordinate Cobalt(0)-N-Heterocyclic Carbene Complexes with Primary Aryl Phosphines

Article abstract of DOI:10.1021/acs.inorgchem.8b02937

Aiming to get knowledge on the reactivity of low-coordinate cobalt(0) species toward primary phosphines, the reactions of [(IPr)Co(vtms)₂] and [(ICy)₂Co(vtms)] (IPr = 1,3-bis(2′,6′-diisopropylphenyl)imidazol-2-ylidene, ICy = 1,3-dicyclohexylimidazol-2-ylidene, and vtms = vinyltrimethylsilane) with several primary aryl phosphines have been examined. The reactions of [(IPr)Co(vtms)₂] and [(ICy)₂Co(vtms)] with H₂PDmp (Dmp = 2,6-dimesitylphenyl) at 80 °C furnish the diamagnetic cobalt(I) phosphido complexes [(NHC)Co(PHDmp)] (NHC = IPr, 1; ICy, 2) that feature the Co-(η⁶-mesityl) interaction. Complex 1 can coordinate CO to generate the terminal phosphido complex [(IPr)Co(CO)₃(PHDmp)] (3) and can be oxidized by [Cp₂Fe][BAr^F₄] to yield the cobalt(II) phosphido complex [(IPr)Co(PHDmp)][BAr^F₄] (4, BAr^F₄ = tetrakis(3,5-di(trifluoromethyl)phenyl)borate). For the reactions with sterically less-hindered primary phosphines, [(IPr)Co(vtms)₂] is inert toward H₂PC₆H₂-2,4,6-Me₃ (H₂PMes) at room temperature, whereas [(ICy)₂Co(vtms)] can react with H₂PMes at room temperature to produce the cobalt(II) phosphido alkyl complex trans-[(ICy)₂Co(CH₂CH₂SiMe₃)(PHMes)] (5). At 80 °C, the cobalt(0) alkene complexes [(IPr)Co(vtms)₂] and [(ICy)₂Co(vtms)] and also the cobalt phosphido complexes, 1, 2, and 5 can serve as precatalysts for the dehydrocoupling reaction of H₂PMes to afford MesHPPHMes. NHC-Co(I)-phosphido species are proposed as the in-cycle intermediates for these cobalt-catalyzed dehydrocoupling reactions.

Full text of DOI:10.1021/acs.inorgchem.8b02937

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Reactions of Low-Coordinate Cobalt(0)−N-Heterocyclic Carbene
Complexes with Primary Aryl Phosphines
Dongyang Wang, Qi Chen, Xuebing Leng, and Liang Deng*
State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic
Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, P. R.
China
S
* Supporting Information
ABSTRACT: Aiming to get knowledge on the reactivity of low-coordinate
cobalt(0) species toward primary phosphines, the reactions of [(IPr)Co-
(vtms)2] and [(ICy)2Co(vtms)] (IPr = 1,3-bis(2′,6′-diisopropylphenyl)-
imidazol-2-ylidene, ICy = 1,3-dicyclohexylimidazol-2-ylidene, and vtms =
vinyltrimethylsilane) with several primary aryl phosphines have been examined.
The reactions of [(IPr)Co(vtms)2] and [(ICy)2Co(vtms)] with H2PDmp
(Dmp = 2,6-dimesitylphenyl) at 80 °C furnish the diamagnetic cobalt(I)
phosphido complexes [(NHC)Co(PHDmp)] (NHC = IPr, 1; ICy, 2) that
feature the Co−(η6-mesityl) interaction. Complex 1 can coordinate CO to
generate the terminal phosphido complex [(IPr)Co(CO)3(PHDmp)] (3) and
can be oxidized by [Cp2Fe][BArF ] to yield the cobalt(II) phosphido complex
4
[(IPr)Co(PHDmp)][BArF ] (4, BArF = tetrakis(3,5-di(trifluoromethyl)-
4
4
phenyl)borate). For the reactions with sterically less-hindered primary
phosphines, [(IPr)Co(vtms)2] is inert toward H2PC6H2-2,4,6-Me3 (H2PMes)
at room temperature, whereas [(ICy)2Co(vtms)] can react with H2PMes at room temperature to produce the cobalt(II)
phosphido alkyl complex trans-[(ICy)2Co(CH2CH2SiMe3)(PHMes)] (5). At 80 °C, the cobalt(0) alkene complexes
[(IPr)Co(vtms)2] and [(ICy)2Co(vtms)] and also the cobalt phosphido complexes, 1, 2, and 5 can serve as precatalysts for the
dehydrocoupling reaction of H2PMes to afford MesHPPHMes. NHC−Co(I)-phosphido species are proposed as the in-cycle
intermediates for these cobalt-catalyzed dehydrocoupling reactions.
exploration on other transition-metal complexes is
scarce.9,20,22,25,28,29,41,42 This status quo urges further explora-
tion on reactions of primary phosphines with metal complexes.
Recently, we synthesized a series of three-coordinate NHC−
cobalt(0)-alkene complexes in the forms of (NHC)Co-
(dvtms), (NHC)Co(vtms)2, and (NHC)2Co(vtms).43−46
These cobalt(0) complexes can perform oxidative addition
reactions with organic azides to form cobalt imido com-
plexes.43,44,46 They can also react with hydrosilanes to produce
cobalt silyl complexes.45 The observed reactivity prompted our
further exploration on their reactions toward hydrophosphines.
Herein, we wish to report the reactions of two representative
NHC−cobalt(0)-alkene complexes [(IPr)Co(vtms)2]44 and
[(ICy)2Co(vtms)]45 with primary phosphines, bearing differ-
ent aryl groups. The study revealed the capability of the low-
coordinate cobalt(0) species of performing oxidative addition
with P−H bonds, leading to the preparation of NHC-bound
cobalt(I) and cobalt(II) phosphido complexes. Moreover, the
low-coordinate NHC−cobalt(0)-alkene complexes as well as
the resultant cobalt phosphido complexes proved to be
effective catalysts for the dehydrocoupling reaction of primary
INTRODUCTION
■
Primary phosphines H2PR are useful precursors in the
synthesis of phosphorous compounds, and there is great
interest in metal-mediated reactions of primary phosphines.1,2
Similar to secondary and tertiary phosphines, primary
phosphines can coordinate to metal to form phosphine
complexes. However, primary phosphines are sterically less
demanding as compared to their secondary and tertiary
congeners and thus can more readily form metal complexes
with coordination saturation.3−5 The P−H bonds of primary
phosphines can be activated by metal species to form
phosphido and phosphinidene metal complexes that com-
monly exist in bi- and multinuclear forms with the
phosphorous ligands behaving as bridging ligands.6−15 The
bridging nature renders further transformation of the
phosphorous ligands difficult. Probably related to these factors,
while a series of metal-catalyzed transformations of primary
phosphines have been developed,16−18 for example hydro-
phosphination of alkenes and alkynes12,19−32 and phosphine
dehydrocoupling;25,26,33−35 these known catalytic systems
generally suffer from low catalytic efficiency. In terms of
catalysts, the majority of them are the complexes of rare earth
metals,19 the group 4 metals Ti and Zr,21,24,31,35−39 the group 9
metal Rh,33,34 and the group 10 metals Ni, Pd, and Pt.36,40 The
Received: October 16, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b02937
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Article
phosphines to form diphosphines, adding a rare example of an
effective cobalt catalyst for the dehydrocoupling of hydro-
phosphine.
The solid-state structure of 1 established by X-ray
crystallography revealed its structure as an NHC−cobalt(I)-
phosphido complex, featuring the Co−(η6-arene) interaction
between the metal center and a flanking mesityl group (Figure
1). The displacement of the cobalt center toward the centroid
RESULTS AND DISCUSSION
■
Reactions of NHC−Cobalt(0)-Alkene Complexes with
2,6-Dimesitylphenylphosphine. Only a handful of reports
on the reaction of cobalt(0) complexes with hydrosphosphines
are known in the literature. Geoffroy et al. showed that
Co2(CO)8 can react with the secondary phosphine HPPh2 to
form di- and trinuclear cobalt complexes, bearing bridging
diphenylphosphido ligand [μ-PPh2]1−.47 Huttner et al. found
that the cobalt(0) species generated in situ by the interaction
of (CH3C(CH2PPh2)3)CoCl2 with KC8 (2 equiv) reacts with
the primary phosphine H2PPh to produce the diphosphene
complex [(CH3C(CH2PPh2)3)Co(η2-PhPPPh)].48 Noting the
rarity, we started our exploration on the reactions of NHC−
Co(0)-alkene complexes with the sterically hindered primary
phosphine H2PDmp49 (Dmp = 2,6-dimesitylphenyl) with the
aim to access terminal phosphido cobalt complexes.
H2PDmp is found inert toward the cobalt(0) complexes
[(IPr)Co(vtms)2] and [(ICy)2Co(vtms)] at room temper-
ature. Heating the 1:1 mixture of H2PDmp with the cobalt(0)
complexes at 80 °C, however, leads to the occurrence of
reaction as evidenced by color change from green to brown.
After workup, the cobalt(I) phosphido complexes [(NHC)-
Co(PHDmp)] (NHC = IPr, 1; ICy, 2) were isolated in 46 and
62% yields, respectively, as red crystalline solids from the
resultant mixtures (Scheme 1). Complexes 1 and 2 have been
Figure 1. Molecular structure of 1 showing 30% probability ellipsoids.
Except the hydrogen atom on phosphorous, all other hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and angles (°):
Co1−C1 1.892(3), Co1−P1 2.2254(9), P1−H1 1.16(4), C1−Co1−
P1 90.16(9), and Co1−P1−H1 103.2(19).
Scheme 1. Reactions of NHC−Co(0)-Alkene Complexes
with H2PDmp
of the flanking aryl ring is 1.586 Å, which is slightly shorter
than the corresponding distance in the cobalt(II) thiolate
complex [Co(SC6H3-2,6-(C6H3-2,6-Pri2)2)2] (1.621 Å),50
indicating a strong Co−(η6-arene) interaction in the cobalt(I)
complex. The high quality of the crystal structure data of 1
allows the location of hydrogen atoms on the Fourier
diffraction map. The sum of the angles around the
phosphorous atom is 300°. The phosphido ligand has a Co−
P distance of 2.2254(9) Å that is comparable to those of the
low-spin cobalt(I) phosphido complexes [Co(κ3-P-
(CH2CH2PMe2)2)(κ2-P(CH2CH2PMe2)3)] (2.297(1) Å)51
and Thomas’ [(PPP)Co(CO)2] (2.2386(6) Å)52 and is
apparently longer than those in the cobalt(III) phosphido
complex [K(THF)4][Co(1,2-(PBut)2C2B10H12)2] (2.1437(5)
Å),53 the cobalt terminal phosphinidene complex [(Cp)Co-
(PPh3)(PMes*)] (2.1102(8) Å),54 and the bridging phosphi-
nidene complex [(IMe4)2Co(PMes)]2 (2.163(1) Å).55 These
metric data indicate the single bond nature of the Co−P
interaction in 1. The IPr ligand has the short Co−C bond of
1.892(3) Å that is comparable to its counterparts in the
reported low-spin cobalt(I)−NHC complexes having two-
legged piano stool geometry, for example CpCo(IPr)(CO)
(1.888(3) Å),56 CpCo(IPr2H2)(PPh3) (1.880(2) Å),57 and
Cp*Co(IPr)(CO) (1.902(5) Å).58
characterized by 1H, 13C, and 31P NMR spectroscopies,
infrared (IR) spectroscopy, absorption spectroscopy, and
combustion analysis (C, H, and N). The molecular structure
of 1 has been established by a single-crystal X-ray diffraction
study.
Complexes 1 and 2 are air- and moisture-sensitive. They are
diamagnetic. Their 1H NMR spectra show characteristic
doublets at 2.06 and 2.70 ppm, respectively, with the same
H−P coupling constant of JP−H = 152 Hz (Figures S7 and
S11), assignable to the phosphorous-bound hydrogen atoms.
Accordingly, the 31P NMR spectra of 1 and 2 exhibit doublets
at −28.3 and −35.0 ppm, respectively, with the coupling
constants JP−H identical to those obtained from their 1H NMR
spectra. The 31P NMR chemical shifts are low-field shifted as
compared to the free phosphine ligand H2PDmp (−147 ppm).
Being supportive to the presence of hydrogen atoms on their
phosphorous atoms, the IR spectra of 1 and 2 measured on
KBr pellets feature P−H stretchings at 2196 and 2164 cm−1,
respectively (Figures S43 and S44).
The attainment of the phosphido complexes 1 and 2
indicates the capability of the low-coordinate NHC−cobalt(0)-
alkene complexes in mediating P−H bond activation. The
reactions might proceed via the sequential steps of oxidative
addition of the cobalt(0) species with the primary phosphine
to form cobalt(II) phosphido hydride species (NHC)Co-
(PHDmp)(H) that undergo further Co−H bond homolytic
cleavage to produce the cobalt(I) phosphido complexes.
B
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However, the high reaction temperature prevents the isolation
of the cobalt hydride intermediate, we noted that the oxidative
addition of cobalt(0) species with hydrophosphine was
observed on Co2(CO)8,47 and homolytic cleavage of the
Co−H bond is also a well-recognized reaction of cobalt(II)
hydrides species.59 Notably, NMR analysis indicated that, in
addition to the cobalt(I) phosphido complexes, the prepara-
tion of 1 and 2 also gave vinyltrimethylsilane in high yields and
without the alkene hydrogenation product ethyltrimethylsilane
o r t h e a l k e n e h y d r o p h o s p h i n a t i o n p r o d u c t
Me3SiCH2CH2PHDmp. This observation implies that the
steric encumbrance of the Dmp group might render the
proposed cobalt(II) phosphido hydride intermediate (NHC)-
Co(PHDmp)(H) devoid of the coordination of vinyl-
trimethylsilane.
Reactivity of the Cobalt(I) Phosphido Complex
[(IPr)Co(PHDmp)]. Complexes 1 and 2 are among the rare
examples of transition-metal complexes, featuring terminal
primary phosphido ligands.12,34,36,38,41 With them in hand, we
further investigated their reactivity. Complex 1 is found inert
toward vinyltrimethylsilane and styrene at room temperature.
Heating the reaction mixtures of 1 with the alkenes (8 equiv)
in C6D6 at 80 °C for 2 days led to the formation of trace
amounts of new species that shows the 31P NMR signal at ca.
−60 ppm with molecular mass equaling the alkene hydro-
phosphination products (Figure S42). However, the low yields
of these new species render the attempts to isolate them
unsuccessful. With the aim of converting the phosphido
complex into a phosphinidene complex, the reactions of 1 with
2,4,6-tri(tert-butyl)phenoxyl radical, KH, and NaN(SiMe3)2
were examined. To our disappointment, the former reaction
gave H2PDmp and an intractable paramagnetic mixture,
whereas no reaction occurred for the latter two trials. In
contrast to these unsuccessful attempts, the reactions of 1 with
Figure 2. Molecular structure of 3 showing 30% probability ellipsoids.
Except the hydrogen atom on phosphorous, all other hydrogen atoms
were omitted for clarity. Selected bond lengths (Å) and angles (°):
Co1−C1 1.970(2), Co1−P1 2.3701(7), P1−H1 1.25(4), C1−Co1−
P1 170.66(6), and Co1−P1−H1 117.7(19).
presence of a hydrogen atom on the phosphorous atom. A P−
H stretching resonance at 2329 cm−1 is also observed in the IR
spectrum of 3 (Figure S45).
Complex 4 is a low-spin cobalt(II) phosphido complex. It
has a solution magnetic moment of 2.3(1) μB that is slightly
larger than the spin-only value of 1.73 μB for 3d metal ions
with an S = 1/2 spin state. Owing to its paramagnetism, no 31
P
NMR signal was observed in the range of −400 to +300 ppm
in the spectrum of 4. The X-band electron paramagnetic
resonance (EPR) spectrum of the solid sample of 4 measured
at 5 K displays noticeable 59Co (I = 7/2) nuclear hyperfine
splitting (Figure 3) and can be simulated as an S = 1/2 system
CO (1 atm) or with [Cp2Fe][BArF ] (ArF = 3,5-di-
4
(trifluoromethyl)phenyl, 1 equiv) proceed cleanly, from
which the new phosphido complexes [(IPr)Co-
(CO)3(PHDmp)] (3) and [(IPr)Co(PHDmp)][BArF ] (4)
4
were isolated in 71 and 88% yields, respectively (Scheme 2).
Scheme 2. Reactions of 1 with CO and [Cp2Fe][BArF ]
4
Figure 3. EPR spectra (black) of 4 recorded in the solid at 5 K.
Instrumental parameters: ν = 9.38 GHz, modulation frequency = 100
kHz, modulation amplitude = 5 G, microwave power = 0.03991 mW,
conversion time = 58.59 ms, time constant = 0 ms, and sweep time =
60 s. Simulation (red) provides g1 = 2.37, g2 = 2.04, and g3 = 2.02;
A_Co1 = 155 MHz, A_Co2 = 73 MHz, and A_Co3 = −39 MHz.; line
width = 4.43 G.
Complex 3 is a cobalt(I) phosphido complex devoid of the
π-interaction between its cobalt center and the flanking arene
rings of the ligands (Figure 2). Its IPr and phosphido ligand
[PHDmp]1− on the axial positions have the Co−P and Co−
C(carbene) distances of 2.3701(7) and 1.970(2) Å,
respectively, which are longer than the corresponding ones
in 1 by 0.15 and 0.08 Å. The elongation should be related to
the strong trans-influence of NHC and phosphido anions.36,60
The 31P NMR spectrum of 3 exhibits a doublet at −89.07 ppm
with a JP−H value of 187 Hz (Figure S18), supporting the
with g1 = 2.37, g2 = 2.04, and g3 = 2.02; A_Co1 = 155 MHz,
A_Co2 = 73 MHz, and A_Co3 = −39 MHz. The crystal
structure of 4 consists of well-separated cations [(IPr)Co-
(PHDmp)]1+ and anions [BArF ]1−. The cation [(IPr)Co-
4
(PHDmp)]1+ displays a two-legged piano stool geometry that
is similar to 1 (Figure 4) and its Co−P distance is also
C
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Reactions of NHC−Cobalt(0)-Alkene Complexes with
Sterically Less-Hindered Primary Aryl Phosphines. The
successful preparation of the aforementioned terminal
phosphido complexes prompted further study on the reactions
of the NHC−Co(0)-alkene complexes with sterically less-
demanding primary aryl phosphines, which then revealed the
ability of the cobalt(0) complexes in catalyzing the
dehydrocoupling of primary aryl phosphines to afford
diphosphines.
Heating the C6D6 solution of H2PC6H2-2,4,6-Me3
(H2PMes) with [(IPr)Co(vtms)2] (10 mol %) at 80 °C led
to the slow formation of the diphosphine MesHPPHMes as a
mixture of its meso- and racemic isomers as indicated by 31P
NMR analysis. The reaction in 10 h can give the diphosphine
in 61% yield along with partial retaining of the primary
phosphine (36%) (entry 1, Table 2). Further extending the
Table 2. Cobalt−NHC Complex-Catalyzed
a
Dehydrocoupling of Hydrophosphines
Figure 4. Structure of the cation in 4 showing 30% probability
ellipsoids. Except the hydrogen atom on phosphorous, all other
hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and
angles (°): Co1−C1 1.962(4), Co1−P1 2.2363(13), P1−H1 1.239,
C1−Co1−P1 92.76(10), and Co1−P1−H1 105.56.
ratio of
b
c
entry
1
2
Catalyst
H2PAr
yield
meso/rac
[(IPr)Co(vtms)2]
[(IPr)Co(vtms)2]
[(ICy)2Co(vtms)]
CoCl2
[(PPh3)3CoCl]
[(IPr)CoCl2]2
IPr
H2PC6H2-2,4,6-Me3
H2PC6H2-2,4,6-Me3
H2PC6H2-2,4,6-Me3
H2PC6H2-2,4,6-Me3
H2PC6H2-2,4,6-Me3
H2PC6H2-2,4,6-Me3
H2PC6H2-2,4,6-Me3
H2PC6H2-2,4,6-Me3
H2PC6H2-2,4,6-Pri3
H2PPh
61%
53%
55%
trace
trace
14%
17%
6%
1.6:1
1.7:1
1.5:1
d
3
4
5
6
7
comparable to that in [(IPr)Co(PHDmp)] (1) (2.2254(9)
and 2.2363(1) Å, respectively). These Co−P bonds are located
on the long end of the Co−P bonds of cobalt phosphido
complexes.51−53 Orbital composition analysis on the frontier
orbitals of [(IPr)Co(PHDmp)] and [(IPr)Co(PHDmp)]1+
indicated that the Co−P interaction is essentially a σ-bond
in nature (Figures S47 and S48). On the other hand, the Co−
C(carbene) and Co−C(arene) distances in the cation
[(IPr)Co(PHDmp)]1+ of 4 is longer than the corresponding
ones in 1 (Table 1). The long Co−C distances in 4 hint
weakened metal−ligand interactions between the cobalt center
and IPr and the η6-mesityl moiety, which might be because of
decreased metal-to-ligand backdonation in cobalt(II) species
over the cobalt(I) complex. The structure resemblance
between the cation [(IPr)Co(PHDmp)]1+ and 1 suggests the
reversibility of the one-electron redox event [(IPr)Co-
(PHDmp)]1+/0. Indeed, a redox wave with the half-wave
potential E1/2 = −0.70 V [vs saturated calomel electrode
(SCE)] has been observed in the cyclic voltammogram of 1
(Figure S1).
1.7:1
1.7:1
1.4:1
1.2:1
1.1:1
d
8
[Co2(CO)8]
9
[(IPr)Co(vtms)2]
[(IPr)Co(vtms)2]
[(IPr)Co(vtms)2]
[(IPr)Co(vtms)2]
73%
47%
7%
10
11
12
13
HPPh2
H2PBut
H2PC6H2-2,4,6-Me3
8%
0.6:1
1.7:1
[(IPr)Co(PHDmp)]
67%
(1)
14
15
[(ICy)Co(PHDmp)]
H2PC6H2-2,4,6-Me3
H2PC6H2-2,4,6-Me3
63%
47%
1.7:1
1.7:1
(2)
[(ICy)2Co(PHMes)
(CH2CH2SiMe3)]
(5)
a
Conditions: hydrophosphine (0.05 mmol) and cobalt complex (10
b
mol %) in C6D6 (0.35 mL) at 80 °C for 10 h. NMR yields
c
determined by 31P NMR using P(OPh)3 as an internal standard. The
assignment of the 31P NMR signals to the rac- or mesoisomer has not
d
been made. 5 mol % metal complex was used.
Table 1. Selected Bond Distance (Å) and Angles (deg) of [(IPr)Co(PHDmp)] (1), [(IPr)Co(CO)3(PHDmp)] (3), and
[(IPr)Co(PHDmp)][BArF ] (4)
4
1
3
4
Co−C(carbene)
Co−C(arene)
1.892(3)
1.970(2)
1.962(4)
a
2.044(3)−2.184(3)
2.123(3)
1.586
1.413(4)
2.2254(9)
1.16(4)
2.069(4)−2.263(3)
2.172(4)
1.661
1.403(6)
2.2363(1)
1.23(9)
Co−C(arene) in average
b
Co−X
c
C(arene)−C(arene)
Co−P
P−H
2.3701(7)
1.25(4)
354.34
d
ΣP
299.92
311.11
C(carbene)−Co−P
90.16(9)
170.66(6)
92.76(10)
a
b
Distances between the cobalt center and the carbon atoms on the flanking arene ring. Distances between the cobalt center and the centroid of the
c
d
flanking arene ring. C(arene)−C(arene) distances of the flanking arene ring. The sum of angles around the phosphorous atom.
D
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reaction time to 24 h or adding one more equivalent of
H2PMes to the mixture for further reaction did not lead to
further production of the dehydrocoupling product. The
reaction employing a 5 mol % catalyst can still afford the
diphosphine in 53% yield (entry 2). Similar to [(IPr)Co-
(vtms)2], the bis(NHC)cobalt(0) complex [(ICy)2Co(vtms)]
can also catalyze the dehydrocoupling reaction and exhibits
comparable catalytic activity as that of [(IPr)Co(vtms)2]
(entry 3). In contrast, the reactions using [(IPr)CoCl2]2, IPr,
and Co2(CO)8 gave MesHPPHMes in poor yields (14, 17, and
6% yields, respectively), and CoCl2 and (PPh3)3CoCl are
found ineffective in promoting the dehydrocoupling reaction
(entries 4−8). In addition to the dehydrocoupling reaction of
H2PMes, the cobalt(0) complex [(IPr)Co(vtms)2] can also
catalyze the conversion of H2PC6H2-2,4,6-Pri3 and H2PPh to
the corresponding diphosphines in 73 and 47% yields,
respectively,(entries 9 and 10). The catalytic system is sensitive
to the steric nature, and the cobalt(0) complex-catalyzed
dehydrocoupling reaction of HPPh2 and H2PBut only afford
the diphosphines in 7 and 8% yield, respectively,(entries 11
and 12).
possibly, the sequential steps of α-H elimination and migratory
insertion. The further reaction of B with H2PMes might give
the cobalt(II) phosphido hydrido species (IPr)Co(H)-
(PHMes) (C) and Me3SiCH2CH2PHMes via either oxidative
addition and reductive elimination or σ-bond metathesis
mechanism. Species C could then undergo Co−H bond
cleavage to convert into the cobalt(I) phosphido intermediate
(IPr)Co(PHMes) (D) that could be the in-cycle species for
the cobalt-catalyzed dehydrocoupling reaction. Scheme 3
illustrates an oxidative addition-reductive elimination path-
way33 for the catalytic dehydrocoupling reaction of H2PMes.
However, other mechanisms with σ-bond metathesis19 or the
nucleophilic attack of hydrophosphine toward cobalt phosphi-
nidene species as the step of P−P bond formation37 cannot be
excluded.
Being supportive to the proposed mechanism (Scheme 3), a
cobalt(II) phosphido alkyl complex trans-[(ICy)2Co-
(CH2CH2SiMe3)(PHMes)] (5), as an analog of intermediate
B, has been isolated in 67% yield from the equimolar reaction
of [(ICy)2Co(vtms)] with H2PMes at room temperature
(Scheme 4). Complex 5 has been characterized by solution
As aforementioned, effective late transition-metal catalysts
for the dehydrocoupling of hydrophosphine are rare. Hence,
the NHC−cobalt complexes showed above add new examples
to the category after the rhodium(I) complexes [Cp*Rh-
(CH2CHSiMe3)2]33 and [(Pri2PCH2CH2PPri2)Rh(CH2Ph)]34
and the iron(II) complexes [(DippNCMeCHCMeNDipp)Fe-
(CH2SiMe3)] and [((xyl)NCMeCHCMeN(xyl))Fe-
(CH2SiMe3) (THF)].25 Considering the different steric nature
of H2PMes versus H2PDmp, it can be proposed that the
interaction of [(IPr)Co(vtms)2] with H2PMes might allow the
formation of the cobalt(0)-alkene-phosphine intermediate
(IPr)Co(PH2Mes) (CH2CHSiMe3) (A in Scheme 3).
Intermediate A could convert to the cobalt(II) phosphido
alkyl species (IPr)Co(CH2CH2SiMe3)(PHMes) (B) via,
Scheme 4. Reaction of [(ICy)2Co(vtms)] with H2PMes
magnetic susceptibility measurement (2.6(1) μB), single-
crystal X-ray diffraction study (Figure 5), and elemental
Scheme 3. Possible Mechanism for the Reaction of
[(IPr)Co(vtms)2] with H2PMes
Figure 5. Structure of 5 showing 30% probability ellipsoids. Except
the hydrogen atom on phosphorous, all other hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles (°): Co1−
C1 1.912(5), Co1−C2 1.907(5), Co1−C3 2.046(5), Co1−P1
2.2766(16), C1−Co1−P1 85.26(16), C1−Co1−C2 178.0(2), and
C3−Co1−P1 174.24(14).
analysis. In addition, the cobalt(I) phosphido complexes
[(NHC)Co(PHDmp)] (NHC = IPr, 1; ICy, 2) obtained
from the reactions of the NHC−Co(0)-alkene complexes with
H2PDmp also give credence to the formation of cobalt(I)
phosphido species D in the proposed mechanism. Moreover, a
secondary phosphine species that shows the 31P NMR doublet
at −74 ppm and has the mass of 252 as indicated by GC−MS
analysis, presumably Me3SiCH2CH2PHMes, has been ob-
served as a byproduct in the catalytic dehydrocoupling
reactions of H2PMes using [(IPr)Co(vtms)2] as catalysts
(Figure S21). Intriguingly, all the cobalt phosphido complexes
1, 2, and 5 proved to be competent catalysts for the
dehydrocoupling reaction of H2PMes (entries 13−15 in
Table 2). It should be mentioned that a close examination
E
DOI: 10.1021/acs.inorgchem.8b02937
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
on the 31P NMR spectra of the reaction mixtures revealed the
formation of H2PDmp, rather than DmpHPPHMes, in the
catalytic reactions using 1 and 2 as catalysts (Figures S39 and
S40), suggesting that the interaction of H2PMes with 1 and 2
might proceed in an σ-bond metathesis pathway to form
(NHC)Co(PHMes) (D) and H2PDmp. This reaction mode is
different from the P−P bond formation reaction of (NHC)-
Co(PHMes) with H2PMes (Scheme 3) and might be caused
by the existence of the Co−(η6-arene) interaction in the
terphenyl-substituted phosphido complexes.
performed by the Analytical Laboratory of Shanghai Institute of
Organic Chemistry (CAS). Solution magnetic moments were
measured at room temperature by the method originally described
by Evans with stock and experimental solutions containing a known
amount of a (CH3)3SiOSi(CH3)3 standard.65,66 Absorption spectra
were recorded with a Shimadzu UV-3600 UV−vis−NIR spectropho-
tometer. IR spectra were recorded with a Nicolet Avatar 330 FT-IR
spectrophotometer or Bruker TENSOR 27 ATR−FTIR spectropho-
tometer. The X-band EPR experiments were performed in sealed
quartz tubes on a Bruker EMX plus spectrometer (microwave
frequency ca. 9.38 GHz) equipped with a He temperature control
cryostat system. Electrochemical measurements were carried out in a
glovebox under an argon atmosphere with a CHI 600D
potentiostation. A glassy carbon was used as the working electrode,
a platinum wire was used as the auxillary electrode, and a SCE was
CONCLUSIONS
■
In this study, we examined the reactions of low-coordinate
NHC−Co(0)-alkene complexes with primary aryl phosphines
and found that the reactions can lead to either the formation of
cobalt phosphido complexes or catalytic dehydrocoupling
reactions of primary aryl phosphines to form diphosphines.
The study showed that the reactions of [(IPr)Co(vtms)2] and
[(ICy)2Co(vtms)] with H2PDmp at 80 °C furnish low-spin
cobalt(I) phosphido complexes [(IPr)Co(PHDmp)] (1) and
[(ICy)Co(PHDmp)] (2), whereas catalytic dehydrocoupling
of the primary phosphines to afford diphosphines in the form
of ArHPPHAr takes place when the NHC−Co(0)-alkene
complexes were treated with the sterically less-demanding
hydrophosphines, H2PMes, H2PC6H2-2,4,6-Pri3, and H2PPh, at
80 °C. In contrast to these reactions, a cobalt(II) phosphido
alkyl complex trans-[(ICy)2Co(CH2CH2SiMe3)(PHMes)] (5)
has been isolated from the reaction of [(ICy)2Co(vtms)] with
H2PMes at room temperature. The distinct reaction outcomes
should originate from the different steric nature of the aryl
phosphines and also the NHCs. In addition to the reactions of
cobalt(0) complexes, a preliminary reactivity study on the
cobalt phosphido complexes has been performed, which led to
the preparation of the cobalt(I) phosphido complex [(IPr)-
Co(PHDmp)(CO)3] (3) devoid of the Co−(η6-arene)
interaction from the reaction of 1 with CO and the cobalt(II)
used as the reference electrode. 0.1 M [Bun N][PF6] in tetrahy-
4
drofuran (THF) was used as the supporting electrolyte and was
prepared in the glovebox. Under these conditions, E1/2 = 0.55 V for
the [Cp2Fe]0,+ couple.
X-ray Structure Determination. Crystals were coated with
Paratone-N oil and mounted on a Bruker APEX CCD-based
diffractometer equipped with an Oxford low-temperature apparatus.
Cell parameters were retrieved with SMART software and refined
using SAINT software on all reflections. Data integration was
performed with SAINT, which corrects for Lorentz-polarization and
decay. Absorption corrections were applied using SADABS.67 Space
groups were assigned unambiguously by analysis of the symmetry and
systematic absences determined by XPREP.68 All structures were
solved and refined using SHELXTL. The metal and first coordination
sphere atoms were located from direct-method E maps. Nonhydrogen
atoms were found in alternating difference Fourier synthesis and least-
squares refinement cycles and during the final cycles were refined
anisotropically. Hydrogen atoms on the coordination sphere of
phosphorous were located from the difference maps and refined.
Other hydrogen atoms were placed in calculated positions employing
a riding model. CCDC 1871977−1871980 contains the supplemen-
tary crystallographic data for complexes 1, 3, 4, and 5. These data can
be obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Computational Details. To have a better understanding of the
electronic structure of [(IPr)Co(PHDmp)] (1) and the cation
[(IPr)Co(PHDmp)]+ in 4, density functional theory69,70 study has
been performed with the ORCA 3.03 program71 using the B3LYP72,73
method. Coordinates of the calculated structures are based on the
crystal structure data without geometry optimization. The SVP basis
set74,75 was used for the C, N, and H atoms, and the TZVP basis set76
was used for the Co and P atoms. The RIJCOSX approximation77
with matching auxiliary basis sets74,75 was employed to accelerate the
calculations. The Mulliken spin population and Mayer bond orders of
selected bonds of 1 and the cation [(IPr)Co(PHDmp)]+ in 4 are
shown in the Supporting Information (Figures S47−S50).
phosphido complex [(IPr)Co(PHDmp)][BArF ] (4) from the
4
one electron-oxidation of 1 by the ferrocenium cation. The
cobalt phosphido complexes 1, 2, and 5 proved to be effective
catalysts in promoting the dehydrocoupling reaction of
H2PMes. The accessibility of these cobalt phosphido
complexes and their fine performance in catalyzing the
dehydrocoupling reactions should benefit from the use of
these strongly σ-donating and sterically demanding NHCs as
ancillary ligands.
Preparation of [(IPr)Co(PHDmp)] (1). To the solution of
[(IPr)Co(vtms)2] (130 mg, 0.20 mmol) in toluene (15 mL) was
added H2PDmp (70 mg, 0.20 mmol). After stirring for 10 h at 80 °C,
the color of the solution changed from green to brown red. After
removal of the solvent under vacuum, the brown red solid was washed
by n-hexane (3 mL) quickly, extracted by diethyl ether (5 mL), and
filtered to give a brown red solution. Removal of the solvent by
vacuum afforded 1 as a brown red solid (73 mg, 46%). Red crystals of
1 were obtained by standing its diethyl ether solution at room
EXPERIMENTAL SECTION
■
General Considerations. All manipulations on air- and moisture-
sensitive materials were performed under an atmosphere of dry
dinitrogen with the rigid exclusion of air and moisture using standard
Schlenk or cannula techniques or in a glovebox. Solvents were dried
with a solvent purification system (Innovative Technology) and
degassed prior to use. [(IPr)Co(vtms)2],44 [(ICy)2Co(vtms)],45
H2PDmp,49 H2PC6H2-2,4,6-Pri3,61 H2PMes,62 [Cp2Fe][BArF ],63
4
and 2,4,6-tris-tert-butylphenoxyl radical64 were synthesized according
1
temperature after evaporation of the solvent. H NMR (400 MHz,
to literature procedures. All other chemicals were purchased from
chemical vendors and used as received unless otherwise noted. H,
C6D6, 293 K): δ (ppm) 7.29 (t, 2H), 7.19 (d, 4H), 7.10−7.02 (m,
2H), 6.51 (s, 2H), 6.96 (s, 2H), 6.84 (d, 1H), 5.60 (s, 2H), 3.43 (br,
2H), 3.08 (br, 2H), 2.36 (s, 3H), 2.15 (s, 6H), 2.06 (d, J = 152 Hz,
1H), 1.74 (s, 6H), 1.64 (s, 3H), 1.44 (br, 6H), 1.15 (br, 6H), 0.95
(br, 12H). 13C NMR (101 MHz, C6D6, 292 K): δ (ppm) 195.26 (d, J
= 5 Hz), 155.8 (d, J = 35 Hz), 148.36 (d, J = 8 Hz), 146.18 (d, J = 9
Hz), 145.08 (d, J = 13 Hz), 140.11, 138.96, 136.00, 135.36, 129.32,
128.35, 128.24, 126.28, 125.14, 124.83, 124.30, 96.61, 94.85, 94.07,
90.57, 28.84, 26.68, 26.20, 23.27, 21.35, 21.18, 20.41, 19.51. 31P{1H}
1
13C, and 31P spectra were recorded with a Varian 400 MHz, Agilent
400 MHz, or Bruker 400 MHz spectrometer at 400, 100, and 162
MHz, respectively. Chemical shifts were reported in units of ppm with
references to the residual protons of the deuterated solvents for
proton chemical shifts, the 13C of deuterated solvents for carbon
chemical shifts, and the 31P of 85% phosphorous acid (external
standard) for phosphine chemical shifts. Elemental analysis was
F
DOI: 10.1021/acs.inorgchem.8b02937
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
NMR (162 MHz, C6D6, 292 K): δ (ppm) −28.30. 31P NMR (162
MHz, C6D6, 292 K): δ (ppm) −28.28 (d, J = 152 Hz). Anal. Calcd for
C51H62CoN2P: C, 77.25; N, 3.53; H, 7.88. Found: C, 76.89; N, 3.47;
H, 7.96. Absorption spectrum (THF, 295 K): λmax, nm (ε, M−1
cm−1): 283 (11 000), 334 (9190), 443 (4600), 583 (1690) nm. IR
spectrum (KBr, cm−1): νP−H 2196.
(THF, 295 K): λmax, nm (ε, M−1 cm−1): 438 (2030), 578 (1370),
1216 (210) nm.
Preparation of [(ICy)2Co(CH2CH2SiMe3)(PHMes)] (5). To the
solution of [(ICy)2Co(vtms)] (125 mg, 0.20 mmol) in n-hexane (15
mL) was added H2PMes (31 mg, 0.20 mmol). After stirring for 10 h
at room temperature, the color of the solution changed to green. After
removal of the solvent under vacuum, the green solid was washed by
n-hexane (5 mL) quickly, extracted by diethyl ether (8 mL), and
filtered to give a green solution. Removal of the solvent by vacuum
afforded 5 as a green solid (104 mg, 67%). Green crystals of 5 were
obtained by standing its diethyl ether solution at room temperature
after evaporation of the solvent. 1H NMR (400 MHz, C6D6, 293 K): δ
Preparation of [(ICy)Co(PHDmp)] (2). To the solution of
[(ICy)2Co(vtms)] (125 mg, 0.20 mmol) in toluene (15 mL) was
added H2PDmp (70 mg, 0.20 mmol). After stirring for 10 h at 80 °C,
the color of the solution changed to brown red. After removal of the
solvent under vacuum, the brown red solid was washed by n-hexane
(3 mL), extracted by diethyl ether (5 mL), and filtered to give a
brown red solution. Removal of the solvent by vacuum afforded 2 as a
brown red solid (79 mg, 62%). Brown red crystals of 2 were obtained
by standing its diethyl ether solution at room temperature after
(ppm) 42.75 (ν1/2 = 161 Hz), 20.37 (ν1/2 = 116 Hz), 17.53 (ν1/2
=
113 Hz), 4.84 (ν1/2 = 24 Hz), 0.26 (ν1/2 = 6 Hz), 0.07 (ν1/2 = 35 Hz),
−0.76 (ν1/2 = 10 Hz), −4.11 (ν1/2 = 31 Hz), −5.70 (ν1/2 = 25 Hz),
−7.52 (ν1/2 = 34 Hz), −10.36 (ν1/2 = 184 Hz), −10.99 (ν1/2 = 31
Hz), −19.68 (ν1/2 = 77 Hz), −24.03 (ν1/2 = 87 Hz). Anal. Calcd for
C44H73CoN4PSi: C, 68.10; N, 7.22; H, 9.48. Found: C, 68.12; N,
7.23; H, 9.88. Magnetic susceptibility (C6D6, 293 K): μeff 2.6(1) μB.
Absorption spectrum (THF, 295 K): λmax, nm (ε, M−1 cm−1): 324
(14 010), 351 (11 860), 408 (3910), 598 (910) nm. IR spectrum
(KBr, cm−1): νP−H 2315.
1
evaporation of the solvent. H NMR (400 MHz, C6D6, 293 K): δ
(ppm) 7.37 (d, 1H), 7.22 (t, 1H), 6.93 (d, 1H), 6.88 (s, 2H), 6.28 (s,
2H), 5.92 (br, 4H), 2.70 (d, J = 152 Hz, 1H), 2.31 (s, 6H), 2.26 (s,
6H), 2.18 (s, 3H), 2.07 (br, 2H), 1.76 (br, 4H), 1.58−1.34 (br, 8H),
1.17 (br, 5H), 0.97 (br, 4H). 13C NMR (101 MHz, C6D6, 292 K): δ
(ppm) 187.46 (d, J = 19 Hz), 156.18 (d, J = 35 Hz), 145.80 (d, J = 11
Hz), 145.30 (d, J = 9 Hz), 139.99, 135.48, 135.16, 128.03, 125.69,
125.29, 124.96, 116.57, 94.50, 92.76, 84.31, 59.70, 34.21, 33.76, 33.73,
26.22, 25.82, 25.55, 21.00, 20.48, 20.43, 19.61. 31P{1H} NMR (162
MHz, C6D6, 298 K): δ (ppm) −34.99. 31P NMR (162 MHz, C6D6,
298 K): δ (ppm) −34.99 (J = 152 Hz). Anal. Calcd for
C39H50CoN2P: C, 73.57; N, 4.40; H, 7.92. Found: C, 72.78; N,
4.38; H, 7.72. Absorption spectrum (THF, 295 K): λmax, nm (ε, M−1
cm−1): 275 (11 000), 321 (6590), 384 (3000), 463 (1540), 561
(690) nm. IR spectrum (KBr, cm−1): νP−H 2164.
General Procedure for the Cobalt-Catalyzed Dehydrocou-
pling Reactions of Hydrophosphines. A J-Young NMR tube was
charged with a hydrophosphine (0.05 mmol), a cobalt catalyst (10 or
5 mol %), and C6D6 (0.35 mL). The mixture was heated at 80 °C and
followed by 31P NMR, which indicated the slow formation of
diphosphine. After 10 h, the yield of diphosphine did not show
apparent increase. Then, the mixture was cooled to room temper-
ature, and OPPh3 (5.5 mg, 0.02 mol) was added to the mixture as an
internal standard to quantify the yield of diphosphine by 31P NMR.
The diphosphines, MesHPPHMes,78 2,4,6-Pri3H2C6-HPPHC6H2-
Preparation of [(IPr)Co(CO)3(PHDmp)] (3). The toluene (5
mL) solution of [(IPr)Co(PHDmp)] (1, 160 mg, 0.20 mmol) in a 25
mL flask was quickly frozen with liquid N2 and subjected to vacuum
to remove the N2 atmosphere in the flask. Then, CO was introduced
to the mixture via a CO balloon (1 atm). The reaction mixture was
allowed to warm to room temperature. The color of the solution
changed from brown red to yellow immediately. After 10 min, the
volatiles were removed under vacuum to yield yellow solid that was
then extracted with diethyl ether and filtered. Yellow crystals of 3
(125 mg, 71%) were obtained by standing its diethyl ether solution at
81
2,4,6-Pri3,79 PhHPPHPh,80 Ph2PPPh2,29 ButHPPHBut show identi-
cal 31P NMR chemical shifts as those reported in the literature. The
performance of different cobalt catalysts is compiled in Table 2.
Figures S21−S42 depict the 31P NMR spectra of the resultant
mixtures.
ASSOCIATED CONTENT
■
1
room temperature after evaporation of the solvent. H NMR (400
S
* Supporting Information
MHz, C6D6, 294 K): δ (ppm) 7.22 (t, 2H), 7.12 (d, 2H), 7.07 (t,
1H), 6.99 (d, 2H), 6.93 (d, 4H), 6.87 (s, 2H), 6.44 (s, 2H), 3.80 (d, J
= 187 Hz, 1H), 2.55 (m, 4H), 2.28 (br, 18H), 1.37 (d, J = 7 Hz, 6H),
1.24 (d, J = 7 Hz, 6H), 0.99 (d, J = 7 Hz, 6H), 0.91 (d, J = 7 Hz, 6H).
13C NMR (101 MHz, C6D6, 294 K): δ (ppm) 200.82, 187.38 (d, J = 3
Hz), 147.64, 147.52, 146.44, (d, J = 7 Hz), 145.52, 144.94, 140.62,
136.74, 135.90, 130.70, 129.20, 128.76, 128.37, 126.98, 125.46,
124.59, 124.44, 28.88, 28.83, 25.83, 23.18, 22.74, 21.61, 21.53, 21.49,
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b02937.
Crystallographic data, table for crystal data, absorption
spectra, IR spectra, NMR spectra, cyclic voltammogram,
MO diagrams, Mulliken spin populations, and bond
orders of the calculated structure (PDF)
21.26. 31P{1H} NMR (162 MHz, C6D6, 292 K): δ (ppm) −89.07. 31
P
NMR (162 MHz, C6D6, 292 K): δ (ppm) −89.84 (J = 187 Hz). Anal.
Calcd for C54H62CoN2O3P: C, 73.96; N, 3.19; H, 7.13. Found: C,
73.96; N, 3.22; H, 7.21. Absorption spectrum (THF, 295 K): λmax, nm
(ε, M−1 cm−1): 287 (1330), 326 (840), 419 (570) nm. IR spectrum
(KBr, cm−1): νP−H 2329, νCO 2028, 1962, 1943.
Accession Codes
CCDC 1871977−1871980 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Preparation of [(IPr)Co(PHDmp)][BArF ] (4). To a diethyl ether
4
(10 mL) solution of [(IPr)Co(PHDmp)] (1, 160 mg, 0.20 mmol)
was added [Cp2Fe][BArF ] (210 mg, 0.20 mmol) slowly. The color of
4
the solution changed to dark green immediately. The reaction mixture
was stirred for 10 min at room temperature and then subjected to
vacuum to remove all the volatiles. The resulting dark green solid was
washed with n-hexane (3 mL × 3) first, then extracted with diethyl
ether (5 mL) and filtered. The dark green crystalline solid of 4 (290
mg, 88%) was obtained by slow evaporation of its diethyl ether
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: deng@sioc.ac.cn.
1
solution at room temperature. H NMR (400 MHz, C6D6 and THF-
ORCID
d8, 293 K): δ (ppm) 8.25 (ν1/2 = 20 Hz), 7.60 (ν1/2 = 22 Hz), 6.80
(ν1/2 = 42 Hz), 5.88 (ν1/2 = 104 Hz), 4.03 (ν1/2 = 179 Hz), 2.04, 1.28,
−0.96 (ν1/2 = 246 Hz). Anal. Calcd for C83H74BCoF24N2P: C, 60.19;
N, 1.69; H, 4.50. Found: C, 59.88; N, 1.47; H, 4.51. Magnetic
Susceptibility (C6D6, 293 K): μeff 2.3(1) μB. Absorption spectrum
Liang Deng: 0000-0002-0964-9426
Notes
The authors declare no competing financial interest.
G
DOI: 10.1021/acs.inorgchem.8b02937
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
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ACKNOWLEDGMENTS
■
The work was supported by the National Key Research and
Development Program (2016YFA0202900), the National
Natural Science Foundation of China (nos. 21725104,
21690062, 21432001, and 21821002), and the Strategic
Priority Research Program of the Chinese Academy of
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