Stable monovalent aluminum(i) in a reduced phosphomolybdate cluster as an active acid catalyst

Article abstract of DOI:10.1039/d0sc05277a

Low-valent aluminum Al(i) chemistry has attracted extensive research interest due to its unique chemical and catalytic properties but is limited by its low stability. Herein, a hourglass phosphomolybdate cluster with a metal-center sandwiched by two benzene-like planar subunits and large steric-hindrance is used as a scaffold to stabilize low-valent Al(i) species. Two hybrid structures, (H₃O)₂(H₂bpe)₁₁[Al^III(H₂O)₂]₃{[Al^I(P₄MoV6O₃₁H₆)₂]₃·7H₂O (abbr. Al₆{P₄Mo₆}₆) and (H₃O)₃(H₂bpe)₃[Al^I(P₄MoV6O₃₁H₇)₂]·3.5H₂O (abbr. Al{P₄Mo₆}₂) (bpe =trans-1,2-di-(4-pyridyl)-ethylene) were successfully synthesized with Al(i)-sandwiched polyoxoanionic clusters as the first inorganic-ferrocene analogues of a monovalent group 13 element with dual Lewis and Br?nsted acid sites. As dual-acid catalysts, these hourglass structures efficiently catalyze a solvent-free four-component domino reaction to synthesize 1,5-benzodiazepines. This work provides a new strategy to stabilize low-valent Al(i) species using a polyoxometalate scaffold.

Full text of DOI:10.1039/d0sc05277a

Chemical
Science
View Article Online
View Journal
EDGE ARTICLE
Stable monovalent aluminum(I) in a reduced
phosphomolybdate cluster as an active acid
Cite this: DOI: 10.1039/d0sc05277a
catalyst†
Ya-Qi Zhang,‡a Lai-Yun Zhou,‡a Yuan-Yuan Ma,
All publication charges for this article
have been paid for by the Royal Society
of Chemistry
a
b
*
Kamran Dastafkan,
b
a
a
*
*
Chuan Zhao,
Lan-Zhi Wang
and Zhan-Gang Han
Low-valent aluminum Al(I) chemistry has attracted extensive research interest due to its unique chemical
and catalytic properties but is limited by its low stability. Herein, a hourglass phosphomolybdate cluster
with
a
metal-center sandwiched by two benzene-like planar subunits and large steric-hindrance is
as scaffold to stabilize low-valent Al(I) species. Two hybrid structures,
used
a
(H3O)2(H2bpe)11[AlIII(H2O)2]3{[AlI(P4MoV6O31H6)2]3$7H2O (abbr. Al6{P4Mo6}6) and (H3O)3(H2bpe)3[AlI(P4Mo6VO31H7)2]$
3.5H2O (abbr. Al{P4Mo6}2) (bpe ¼ trans-1,2-di-(4-pyridyl)-ethylene) were successfully synthesized with Al(I)-
sandwiched polyoxoanionic clusters as the first inorganic-ferrocene analogues of a monovalent group 13
element with dual Lewis and Brønsted acid sites. As dual-acid catalysts, these hourglass structures efficiently
catalyze a solvent-free four-component domino reaction to synthesize 1,5-benzodiazepines. This work
provides a new strategy to stabilize low-valent Al(I) species using a polyoxometalate scaffold.
Received 24th September 2020
Accepted 6th December 2020
DOI: 10.1039/d0sc05277a
rsc.li/chemical-science
Low- or sub-valence aluminum compounds are increasingly or heating conditions. In contrast to organometallic Al(I)
growing into a signicant frontier subject in coordination and compounds, inorganic Al(I) structures, i.e. monomeric mono-
modern organic synthetic chemistry owing to their unique halides, only exist in gaseous form at high temperature8 and to
singlet carbene character, Lewis acid/base properties and cata- the best of our knowledge, no stable inorganic Al(I) compound
lytic reactivity.1 However, low-valence aluminum(I) compounds is known at room temperature due to thermodynamic insta-
have inherent electron deciency and exhibit thermodynamic bility. Therefore, exploring efficient strategies to synthesize
instability, making them prone to self-polymerization with stable inorganic Al(I) compounds remains highly desired but
metal–metal bonds2 or disproportionation3 to metallic Al and a great challenge.
Al(III) species. Inspired by the special stabilizing effect of met-
Polyoxometalates (POMs), a diverse family of inorganic
allocene compounds, a ligand stabilization strategy has recently molecular clusters based on early-transition metals (W, Mo, V,
been undertaken to stabilize the low-valence aluminum Nb, and Ta), have extensively attracted attention in research in
center.4,5 In this regard, the utilized ligand should satisfy two various elds of materials science, coordination chemistry,
key criteria: (i) sufficient steric hindrance is required to inhibit medicinal chemistry and catalysis science.9–11 Owing to their
monomer polymerization; and (ii) a suitable electronic effect is adjustable constituent elements and well-dened structures,
needed to stabilize the aluminum(I) center. A few organome- POMs have been considered as promising inorganic ligands to
tallic Al(I) compounds protected by bulky organic groups have stabilize high- and low-valent metal ions. For instance, Rompel
been prepared such as [(Cp*Al)4] (Cp* ¼ C5Me5),6 and et al.12 reported one Keggin-type [a-CrW12O40]5ꢀ anion in which
[(CMe3)3SiAl4].7 However, despite having the ligand effect, most a labile {CrIIIO4} tetrahedral unit was assembled at the center of
of these Al(I) compounds still decompose in aqueous solutions the cluster. Li and co-workers employed a monolacunary Keggin-
type inorganic ligand to stabilize a high-valent Cu3+ ion.13 As
a unique member of the POM family, the hourglass-type phos-
phomolybdate cluster {M[P4MoV6O31]2}nꢀ (abbr. M{P4Mo6}2),
aHebei Key Laboratory of Organic Functional Molecules, National Demonstration
Center for Experimental Chemistry Education, College of Chemistry and Material
Science, Hebei Normal University, Shijiazhuang, Hebei 050024, People's Republic of consisting of two [P4MoV6O31]12ꢀ (abbr. {P4Mo6}2) subunits
China. E-mail: mayy334@hebtu.edu.cn; wanglanzhi@126.com; hanzg116@126.
bridged by one metal (M) center, represents a fully reduced
com; hanzg116@hebtu.edu.cn
metal-oxo cluster. With all Mo atoms in the oxidation state of
bSchool of Chemistry, The University of New South Wales, Sydney, NSW 2052,
(+5), a more negative charge is endowed to the cluster surface.14,15
Australia. E-mail: chuan.zhao@unsw.edu.au
Such high electron density of {M[P4MoV6O31]2}nꢀ polyoxoanions
† Electronic supplementary information (ESI) available. CCDC 1970140 for Al
provides an electron-rich local environment for the possible
stabilization of unusual-valence metals. It is worth noting that
{P4Mo6}2 and 1970141 for Al6{P4Mo6}6. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/d0sc05277a
‡ Y. Q. Zhang and L. Y. Zhou contributed equally to this work.
This journal is © The Royal Society of Chemistry 2020
Chem. Sci.

View Article Online
Chemical Science
Edge Article
Fig. 1 Ball-and-stick diagram showing the assembly of the hourglass-
type cluster {Al(P4Mo6)2}.
Scheme 1 Similar ferrocene-like sandwich structure features of an
inorganic hourglass-type [AlI(P4MoV6O31)2]23ꢀ polyanion to an organ-
ometallic [(h5-Cp*)2AlI]+ cation.
Single crystal X-ray diffraction revealed the hourglass-type
{Al(P4Mo6)2} cluster in Al6{P4Mo6}6 and Al{P4Mo6}2 (Table
S1†), in which the [P4Mo6O31]12ꢀ subunits have a C3 symmetry
and display a near-planar structure formed by six edge-sharing
{MoO6} octahedra with alternating short Mo–Mo single bonds
and long non-bonding Mo/Mo contacts. The side sizes of the
the [P4MoV6O31]12ꢀ subunit presents near-planar triangular
˚
structures with the side sizes ranging from 7.50–7.92 A (Fig. S1†).
The structural feature can supply sufficient steric hindrance to
restrain the polymerization of low-valence metal species. More-
over, the six Mo atoms in each [P4MoV6O31]12ꢀ subunit arrange in
a planar hexagonal-ring structure like a benzene ring, implying
that such {M[P4MoV6O31]2}nꢀ clusters may have a similar delo-
calized electron structure to conjugated benzene or cyclo-
pentadiene. These features make [P4MoV6O31]12ꢀ a promising
candidate with respect to organic protecting groups to construct
an inorganic ‘ferrocene’ analogue of Al(I) (Scheme 1). Therefore,
we hypothesize that hourglass-type polyoxoanion clusters are
promising to stabilize the labile Al(I) center and isolate inorganic
Al(I) species.
˚
{P4Mo6} subunit range from 7.50–7.92 A, which supplies suffi-
cient steric hindrance to restrain the polymerization or
disproportionation of low-valence Al(I) species. All Mo atoms are
in a reduced oxidation state of +5 and the central Al atoms are in
the +1 oxidation state, as conrmed by bond valence calcula-
tions (Table S2†). Thus, the synthesized Al{P4Mo6}2 represents
a fully reduced metal–oxygen cluster. Moreover, the six Mo
atoms in each {P4Mo6} subunit present a benzene-like planar
hexagonal-ring structure with a similar p-type delocalization
electron interaction with Al(I) instead of organic bulky groups.
Such p-type delocalization electron interaction constructs an
inorganic ‘ferrocene’ analogue of Al(I) and produces sufficient
delocalization energy to stabilize Al(I) species. Considering the
formation mechanism of traditional metallocenes, {P4Mo6}
subunits with a similar strong electron-donating ability and
suitable steric-hindrance effect on Cp rings, augment the
stability of Al(I) species. Al6{P4Mo6}6 and Al{P4Mo6}2
compounds also present the rst isolation of aluminum-
sandwiched hourglass-type clusters in POM chemistry. Impor-
tantly, regarding the inherent and strong hydrolysis of
aluminum species in water, these low-valent Al(I)-containing
clusters represent the rst example of stable solid-state inor-
ganic sub-valent Al(I) compounds at room temperature.
The asymmetric structure of Al6{P4Mo6}6 consists of two
crystallographically independent {Al(P4Mo6)2} clusters sand-
wiched by central Al(1) and Al(4) atoms, two bridging
[Al(H2O)2]3+ (Al(2) and Al(3)) cations and six protonated bpe
cations (Fig. S2†). Aluminum centers involve two kinds of
oxidation states: the central Al(1) and Al(4) are in the +1 state,
while the bridging Al(2) and Al(3) are in the +3 state. Both Al(1)
and Al(4) display the six-coordinated octahedral conguration
and bridge two {P4Mo6} subunits to form two {AlI(P4Mo6)2}
Herein, we show a [P4MoV6O31]12ꢀ cluster as an inorganic
scaffold to stabilize the Al(I) center in two hybrid compounds,
(H3O)2(H2bpe)11[AlIII(H2O)2]3{[AlI(P4Mo6VO31H6)2]3$7H2O (abbr.
Al6{P4Mo6}6)
3.5H2O (abbr. Al{P4Mo6}2) (bpe
and
(H3O)3(H2bpe)3[AlI(P4Mo6VO31H7)2]$
trans-1,2-di-(4-pyridyl)-
¼
ethylene), in which the labile Al(I) center is sandwiched by two
[P4MoV6O31]12ꢀ sides, forming an inorganic moiety of a ‘ferro-
cene’ analogue. Both Al6{P4Mo6}6 and Al{P4Mo6}2 are experi-
mentally determined at room temperature for the rst time, and
prepared by hydrothermal reactions of Na2MoO4$2H2O, H3PO4,
AlCl3$6H2O, ethanol and N-containing bpe at 160 ꢁC with
slightly different pH values. Notably, the combination of
ethanol, N-containing bpe and high hydrothermal temperature
is a prerequisite to the isolation of Al(I) species. First, both
ethanol and N-containing bpe were used to provide a reducing
environment under hydrothermal conditions. By combining
high temperature and pressure, sufficient energy is supplied to
reduce Mo6+ and Al3+ ions to Mo5+ and Al+ species, respectively.
Then, Mo5+ species and phosphoric acid molecules are assem-
bled to form [P4Mo6O31]12ꢀ subunits, which are subsequently
combined with Al+ ions to form hourglass-type [Al(P4Mo6-
O31)2]23ꢀ, hence effectively stabilizing Al(I) species (Fig. 1). From
the perspective of stereochemistry, two highly negative
[P4Mo6O31]12ꢀ fragments, resembling the methyl cyclo-
pentadiene organic group, sandwich one low-valent metal Al(I)
center. Hence, the construction of a strong reducing hourglass-
like skeleton makes it possible to stabilize the existing Al+
species.
˚
clusters. The average lengths of Al–O bonds are 2.318–2.324 A
for Al(1) and Al(4) (Table S3†), which are slightly longer than
˚
those of classic Al–O bonds (1.90 A) for Al(2) and Al(3), but close
to that of the Al–O bond in silica-supported alkylaluminum(I)
composites.16–20 The long Al–O lengths for Al(1) and Al(4) centers
may be ascribed to the lower electron cloud density located at
Chem. Sci.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Edge Article
Chemical Science
Fig. 3 (a and b) 27Al NMR spectra of solid Al6{P4Mo6}6 and Al{P4Mo6}2;
(c and d) XPS spectra of Al in Al6{P4Mo6}6 and Al{P4Mo6}2.
Fig. 2 (a) One-dimensional (1D) inorganic structure in Al6{P4Mo6}6
with a length of repeating units of 81.69 A˚, consisting of twelve Al-
containing fragments ({–Al2–Al1–Al3–Al4–Al3–Al1–Al2–Al1–Al3–
Al4–Al3–Al1–}). (b) Four kinds of coordination environments of {AlO6}
octahedra, respectively (i ¼ 1 ꢀ x, y, 0.5 ꢀ z; ii ¼ 0.5 ꢀ x, 1.5 ꢀ y, 1 ꢀ z).
octahedrally coordinated AlIII and AlI sites, respectively (Fig. 3a),
indicating two types of Al local environments in Al6{P4Mo6}6. In
contrast, Al{P4Mo6}2 displays only one sharp signal at d ¼
7.20 ppm due to the octahedrally coordinated AlI sites (Fig. 3b).
The observed narrow peak-width corresponds to the highly
symmetric charge distribution at the aluminum nucleus,
similar to the ferrocene analogue [(h5-Cp*)2AlI]+.5 Noticeably, AlI
resonance in Al6{P4Mo6}6 appears at a lower magnetic eld
compared to Al{P4Mo6}2, due to the different peripheral envi-
ronment around the hourglass {Al(P4Mo6)2} cluster. XPS spectra
of Al6{P4Mo6}6 and Al{P4Mo6}2 further affirm the valence states
of Al and Mo elements (Fig. S7 and Table S5†). The Al 2p XPS
prole of Al6{P4Mo6}6 reveals two peaks at 74.39 and 73.75 eV
ascribed to AlIII and AlI, respectively (Fig. 3c). The area ratio of
the two peaks is close to 1 : 1, in consistence with the chemical
structure of Al6{P4Mo6}6. The high-resolution Al 2p XPS spec-
trum of Al{P4Mo6}2 displays a weaker broad peak attributed to
the low amount of Al+ (Fig. 3d). Moreover, the structural
stabilities of Al6{P4Mo6}6 and Al{P4Mo6}2 were investigated by
soaking them in water for 24 hours. Fig. S9–S11† show the
comparison of XRD, IR and XPS spectra of Al6{P4Mo6}6 and Al
{P4Mo6}2 before and aer soaking in water. It can be found that
the characteristic diffraction peaks in XRD aer soaking for 24
hours still show good agreement with the simulated data
(Fig. S9†). The characterized absorption bands in IR spectra also
exhibit good match with the original Al6{P4Mo6}6 and Al
{P4Mo6}2 (Fig. S10†). The XPS spectra of Al6{P4Mo6}6 aer
soaking in water were also obtained. There is basically no
change in the high-resolution spectra of Al 2p with the AlI/AlIII
atomic ratios of ca. 1 : 1 (Fig. S11†). The spectroscopic and
theoretical observations verify that the low valence Al(I) species
can stably exist in the reduced phosphomolybdates in the solid
state (Fig. S12 and Table S6†). Moreover, the acidities of
Al6{P4Mo6}6 and Al{P4Mo6}2 were measured to be 0.27 and
the surface of the Al(I) cation, resulting in slightly longer bonds
with the surrounding oxygen donors.5,21 Moreover, the small
distorted extents (sum((dij ꢀ dave)/dave)2/coordination number)
of {Al(1)O6} (3.86 ꢂ 10ꢀ4) and {Al(4)O6} (1.89 ꢂ 10ꢀ3) indicate
that they are in regular octahedral geometry. Moreover, another
structural feature of Al6{P4Mo6}6 is that {AlI(P4Mo6)2} clusters
are connected by bridging [Al(H2O)2]3+ cationic fragments (Al(2)
and Al(3)), forming an unusual chain-like arrangement (Fig. 2a).
It is worth noting that the 1-D chain contains a large repeating
˚
monomer with the maximum spacing of 81.69 A, consisting of
twelve Al-containing fragments ({–Al2–Al1–Al3–Al4–Al3–Al1–
Al2–Al1–Al3–Al4–Al3–Al1–}). Such a long repeating monomer is
rare. Each repeating monomer has two types of symmetric
systems: Al(2) in the middle of the monomer plays a center of
mirror symmetry and divides the whole repeating monomer
into two equidistant half-units of {–Al1–Al3–Al4–Al3–Al1–}; Al(4)
in each half-unit further acts as the reverse symmetric center of
two {–Al3–Al1–Al2–} subunits. The two types of symmetrical
systems form the innitely extending chain-like structure in
Al6{P4Mo6}6. Since bpe is a rigid and conjugated molecular
structure, an effective p/p stacking interaction emerges and
results in a honeycomb-like supramolecular organic moiety,
which accommodates these 1-D inorganic chains and stabilizes
the whole Al6{P4Mo6}6 framework (Fig. S3 and S4†).
Al{P4Mo6}2 has a similar structure to Al6{P4Mo6}6 (Table S4†),
wherein the most obvious difference is that {AlI[P4Mo6]2} clus-
ters exist in isolated form and interact with the surrounding
protonated bpe cations via hydrogen bonding to form into a 3-D
supramolecular framework (Fig. S5 and S6†). The different
peripheral environment around the {AlI[P4Mo6]2} cluster can
affect its acidity and catalytic activity.
The solid-state 27Al NMR spectrum of Al6{P4Mo6}6 depicts
two distinct resonances at d ¼ ꢀ22.34 and 27.33 ppm due to the
This journal is © The Royal Society of Chemistry 2020
Chem. Sci.

View Article Online
Chemical Science
Edge Article
Table 1 Comparison tests of one-pot synthesis of 1,5-benzodiazepine 8aaa via a four-component domino reactiona
f
f
f
Entry
Catalystb
t1 (h)
Yieldc (%) 3a
t2 (h)
Yieldd (%) 5aa
T3 (ꢁC)
t3 (min)
Yielde (%) 8aaa
1
2
3
4
5
6
Al6{P4Mo6}6
Al{P4Mo6}2
No catalyst
p-TsOH
AlCl3
{Na[P4Mo6]2}
3.0
3.2
7.0
4.0
4.5
3.5
98
97
98
92
94
95
1.8
2.0
5.5
3.0
3.0
2.5
92
89
62
73
82
86
25
25
25
25
25
25
20
20
120
26
58
30
83
75
Trace
43
29
72
a
One-pot reaction conditions: acetophenone 1a (1.00 mmol), N,N-dimethylformamide dimethyl acetal 2 (1.00 mmol), 1,2-phenylenediamine 4a
b
c
(1.00 mmol), ethyl pyruvate 6a (1.00 mmol) and catalyst (10.00 mg) for the four-component domino reaction. Catalyst (10.00 mg). Isolated
yield in the rst step. d Total isolated yield for the rst two steps. e Overall isolated yield for the 3 steps. f The time taken for the reaction to complete.
0.442 mmol gꢀ1, respectively, demonstrating the promising (Fig. S14†). The acquired XRD pattern, and IR and XPS spectra
potential of Al6{P4Mo6}6 and Al{P4Mo6}2 as dual-acid catalysts.
aer 5 runs further revealed the good structural integrity and
The catalytic performance of Al6{P4Mo6}6 and Al{P4Mo6}2 was high solid-state stability of Al6{P4Mo6}6 (Fig. S15–S17†).
evaluated via a solvent-free four-component domino reaction Accordingly, the Al6{P4Mo6}6 cluster coupled with dual-acid
for the synthesis of pharmaceutical intermediate 1,5-benzodi- sites presents great potential application towards the four-
azepine (Table 1). With Al6{P4Mo6}6 and Al{P4Mo6}2 as catalysts, component domino reaction.
the yields of the nal product 8aaa reach 83% and 75%,
In summary, two cases of low valence Al-centered hourglass-
respectively (Table 1, entries 1 and 2). Almost no 8aaa is type phosphomolybdates have been reported for the rst time.
observed without the acid catalysts, even when the reaction is {P4Mo6} subunits with highly negative charge and a benzene-like
set for a long time (Table 1, entry 3). This claries the excellent planar hexagonal-ring structure, display a similar p-type electron
catalytic performance of Al6{P4Mo6}6 and Al{P4Mo6}2. Typical interaction with Al(I) to construct inorganic ‘ferrocene’ analogues
Brønsted acid p-TsOH and Lewis acid AlCl3 as control samples of Al(I), thus effectively stabilizing Al(I) species. Al(I)-POM structures
yield only 43% and 29% 8aaa, respectively (Table 1, entries 4 are conrmed and characterized using 27Al NMR and XPS spectra.
and 5), much lower than those attained by Al6{P4Mo6}6 and Al When used as acid catalysts, both Al6{P4Mo6}6 and Al{P4Mo6}2
{P4Mo6}2 catalysts. Moreover, (H2en)12[{Na0.8K0.2(H2O)}2{Na efficiently catalyze a solvent-free domino reaction to synthesize 1,5-
[Mo6O12(OH)3(HPO4)2(PO4)2]2}2]$7H2O22,23 (abbr. {Na[P4Mo6]2}) benzodiazepines with high yield and selectivity. The Al(I)-stabilized
in contrast achieved 72% yield of 8aaa in 30 min, slower than reduced POM structures also exhibit excellent substrate compati-
that of Al6{P4Mo6}6 and Al{P4Mo6}2. This indicates the advan- bility and cycle stability. The design, synthesis and successful
tage of the unique dual-acid features of Al(I)-stabilized reduced stabilization of the subvalent metallic aluminum compounds in
phosphomolybdate clusters with multiple Lewis and Brønsted the solid state unravel the signicance of this study. This work is
acid active centers, in which the synergistic effect between the also important to develop highly active and multifunctional cata-
Al species and reduced phosphomolybdate cluster contributes lysts for organic reactions.
to the catalytic activity.
Furthermore, the Al6{P4Mo6}6 catalyst displays a wide
substrate scope of auto-tandem catalytic reactions. A series of
Author contributions
functional groups including carboxyl, ester and acyl groups on
Y. Y. Ma, L. Z. Wang, C. Zhao and Z. G. Han proposed and
the 2-position of the seven-membered rings can be smoothly
supervised the project. Y. Y. Ma, L. Z. Wang and Z. G. Han
converted into the desired 1,5-benzodiazepine products with
conceived and designed the experiments. Y. Q. Zhang carried
high and even excellent yields (Table S7†). 1,2-Phenylenedi-
out the synthesis and structural characterization of the
samples. L. Y. Zhou performed the catalytic experiments. K.
amines 4 which contain both electron-decient (p-Cl and p-Br)
and electron-rich (p-Me and 3,4-di(Me)) 1,2-phenylenediamines
Dastaan, Y. Q. Zhang and L. Y. Zhou co-wrote the original
also undergo the reaction smoothly, providing the corre-
dra. All the authors discussed the results and commented on
sponding products in high yields within the given reaction
the manuscript.
times (Table S7†).
Additionally, the Al6{P4Mo6}6 catalyst can be easily recovered
by simple ltration. No signicant decay in the catalytic activity
or selectivity was observed even aer 5 recycles of Al6{P4Mo6}6
There are no conicts to declare.
Conflicts of interest
Chem. Sci.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Edge Article
Chemical Science
C. Wang, C. Wang, S. Gao and Y. Chen, Inorg. Chim. Acta,
2012, 384, 8–17.
Acknowledgements
10 (a) S. Kim, J. Yeo and W. Choi, Appl. Catal., B, 2008, 84, 148–
155; (b) Z. Han, X. Xin, R. Zheng and H. Yu, Dalton Trans.,
2018, 47, 3356–3365; (c) H. Yang, D. Yang and X. Wang,
Angew. Chem., Int. Ed., 2020, 59, 15527–15531.
11 (a) Q. Liu, P. He, H. Yu, L. Gu, B. Ni, D. Wang and X. Wang,
Sci. Adv., 2019, 5, eaax1081; (b) Y. Benseghir, A. Lemarchand,
M. Duguet, P. Mialane, M. Gomez-Mingot, C. Roch-Marchal,
T. Pino, M.-H. Ha-Thi, M. Haouas, M. Fontecave, A. Dolbecq,
C. Sassoye and C. Mellot-Draznieks, J. Am. Chem. Soc., 2020,
142, 9428–9438.
This work was supported by the National Natural Science
Foundation of China (Grants 21871076, 21776060, and
21901060), Natural Science Foundation of Hebei Province
(Grants B2016205051, B2020205008 and B2019205074), Natural
Science Foundation of Hebei Education Department (Grant
BJ2020037) and Graduate Student Innovation Funding Project
of Hebei Normal University (CXZZSS2020041). C. Z. is grateful
for the award of Future Fellowship from Australian Research
Council (FT170100224, DP210103892).
12 N. I. Gumerova, A. Roller, G. Giester, J. Krzystek, J. Cano and
A. Rompel, J. Am. Chem. Soc., 2020, 142, 3336–3339.
13 X. Li, Y. Ren, Z. Weng, B. Yue and H. He, Chem. Commun.,
2020, 56, 2324–2327.
14 (a) L. Xu, Y. Sun, E. Wang, E. Shen, Z. Liu, C. Hu, Y. Xing,
Y. Lin and H. Jia, Inorg. Chem. Commun., 1998, 1, 382–385;
(b) H. Fu, W. Chen, E. Wang, J. Liu and S. Chang, Inorg.
Chim. Acta, 2009, 362, 1412–1420.
References
1 (a) S. G. Gallardo, T. Bollermann and R. A. Fischer, Chem.
Rev., 2012, 112, 3136–3170; (b) Y. Liu, J. Li, X. Ma, Z. Yang
and H. W. Roesky, Coord. Chem. Rev., 2018, 374, 387–415;
(c) A. Dmitrienko, M. Pilkington, J. F. Britten,
B. M. Gabidullin, A. Est and G. I. Nikonov, Angew. Chem.,
Int. Ed., 2020, 59, 16147–16153; (d) S. Grams, J. Eyselein,
J. Langer, C. Farber and S. Harder, Angew. Chem., Int. Ed.,
2020, 59, 15982–15986.
15 X. Xin, N. Hu, Y. Ma, Y. Wang, L. Hou, H. Zhang and Z. Han,
Dalton Trans., 2020, 49, 4570–4577.
2 C. Dohmeier, D. Loos and H. Schnoeckel, Angew. Chem., Int.
Ed. Engl., 1996, 35, 129–149.
3 U. Werner, Rev. Inorg. Chem., 1998, 18, 239–282.
4 S. Harder and M. H. Prosenc, Angew. Chem., Int. Ed. Engl.,
1994, 33, 1744–1746.
5 C. Dohmeier, H. Schnoeckel, C. Robl, U. Schneider and
R. Ahlri-chs, Angew. Chem., Int. Ed. Engl., 1993, 32, 1655–
1657.
6 C. Dohmeier, C. Robl, M. Tacke and H. Schnoeckel, Angew.
Chem., 1991, 103, 594–595.
7 (a) C. Schnitter, H. W. Roesky, C. Ropken, R. Herbst-Irmer,
H.-G. Schmidt and M. Moltemeyer, Angew. Chem., Int. Ed.,
1998, 37, 1952–1955; (b) A. Purath and H. Schnockel, J.
Organomet. Chem., 1999, 579, 373–375; (c) C. Cui,
H. W. Roesky, M. Noltemeyer, H. G. Schmidt,
M. Noltemeyer, H. Hao and F. Cimpoesu, Angew. Chem.,
2000, 39, 4444–4446; (d) P. Henke and H. Schnoeckel,
Chem.–Eur. J., 2009, 15, 13391–13398.
16 Y. Kikukawa, S. Yamaguchi, Y. Nakagawa, K. Uehara, S. Uch-
ida, K. bYamaguchi and N. Mizuno, J. Am. Chem. Soc., 2008,
130, 15872–15878.
17 C. N. Kato, Y. Makino, M. Yamasaki, Y. Kataoka, Y. Kitagawa
and M. Okumura, Adv. Cryst. Processes, 2012, 23, 593–611.
18 Z.-G. Han, X.-Q. Chang, J.-S. Yan, K.-N. Gong, C. Zhao and
X.-L. Zhai, Inorg. Chem., 2014, 53, 670–672.
19 C. Coperet, I. Moroz, P. Florian, J. Viger Gravel, C. P. Gordon
and A. Lesage, Angew. Chem., Int. Ed., 2020, 59, 16167–16172.
20 G. Nikonov, A. Dmitrienko, M. Pilkington, J. F. Britten,
B. M. Gabidullin and A. van der Est, Angew. Chem., Int. Ed.,
2020, 59, 16147–16153.
21 D. C. Hutchison, R. D. Stern, L. N. Zakharov, K. A. Persson
and M. Nyman, Inorg. Chem., 2020, 59, 2900–2909.
22 J. Du, Y.-Y. Ma, X. Xin, H. Na, Y.-N. Zhao, H.-Q. Tan,
Z.-G. Han, Y.-G. Li and Z.-H. Kang, Chem. Eng. J., 2020,
398, 125518–125526.
23 X.-R. Tian, L. Hou, J.-J. Wang, X. Xin, H. Zhang, Y.-Y. Ma,
Y.-L. Wang, L.-N. Zhang and Z.-G. Han, Dalton Trans.,
2018, 47, 15121–15130.
8 M. Tacke and H. Schnoeckel, Inorg. Chem., 1989, 28, 2895–
2896.
9 (a) S. Omwoma, C. T. Gore, Y. Ji, C. Hu and Y.-F. Song, Coord.
Chem. Rev., 2015, 286, 17–29; (b) K. Yu, B. Zhou, Y. Yu, Z. Su,
This journal is © The Royal Society of Chemistry 2020
Chem. Sci.