A micro-environment tuning approach for enhancing the catalytic capabilities of lanthanide containing polyoxometalate in the cyanosilylation of ketones

Article abstract of DOI:10.1039/d0cc01216e

The as-synthesized (TBA)₈H₅[Nd(SiW₁₁O₃₉)₂] manifested high catalytic activity for cyanosilylation of ketones, and its catalytic activity could be improved further through rational design of the reacti

Full text of DOI:10.1039/d0cc01216e

View Article Online
View Journal
ChemComm
Chemical Communications
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Y. Nie, S. Li, M. Lin
and J. Yan, Chem. Commun., 2020, DOI: 10.1039/D0CC01216E.
Volume 54
Number
January 2018
Pages 1-112
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
1
4
ChemComm
Chemical Communications
rsc.li/chemcomm
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1359-7345
COMMUNICATION
S. J. Connon, M. O. Senge et al.
Conformational control of nonplanar free base porphyrins:
towards bifunctional catalysts of tunable basicity
rsc.li/chemcomm

Page 1 of 6
Please d oC hn eo mt Ca do mj u ms t margins
View Article Online
DOI: 10.1039/D0CC01216E
COMMUNICATION
A Micro-environment Tuning Approach for Enhancing the
Catalytic Capabilities of lanthanide containing Polyoxometalate
on cyanosilylation of ketones
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
ab
DOI: 10.1039/x0xx00000x
Yan-Mei Nie, Sang-Hao Li, Lin-Ming Yuan and Jun Yan *
8 5 39 2
As synthesized (TBA) H [Nd(SiW11O ) ] manifested high catalytic homogeneous POM particles are three ways to implement
1
4-16
activity for cynosilylation of ketones, its catalytic activity could be these strategies.
Also, the most facile and effective
improved further through rational designing of the reaction micro- method is counter ion exchange with different functional
environment beyond molecular level, and the corresponding cations which remaining POMs structure integrity and their
1
7, 18
mechanism has been systematically studied.
intrinsic catalytic properties.
Micro-environment tailoring
beyond molecular level could lead to the forming of
supramolecular aggregations, nano particles, or micelles units
instead of monomolecular species, and these different packing
modes of components do further affect the macro nature of
Polyoxometalates (POMs) usually composed of early
transition-metal anions (M = V, Nb, Ta, Mo, W) in their highest
1
oxidation state
.
With tuneable sizes and structures, POMs
manifested unparalleled properties from medicine,
19-21
the compounds.
For example, in a classic Lewis Acid−Base
2
-7
magnetism, catalysis, bionics to material science.
POM
catalysis reaction, POM molecules always contain multiple
terminal oxygen atoms as Lewis base active sites and merely
cluster containing lanthanide ions (Ln-POM) is an important
subclass of polyoxoanions because Ln ions bear abundant
fluorescing advantages, intriguing magnetic and catalytic
properties as a result of their unique 4f electron configuration,
and the synthesis and application of Ln-POM are receiving
20, 22
one or two Lewis Acid active sites.
Tuning the micro-
environment of the POM clusters and matching the Lewis
Acid−Base active site numbers could definitely improve the
performance of the polyoxoanions, which are also crucial for
making better use of POM based molecular materials, but
8
, 9
increasingly attentions. As noticed, many reports have focus
on new structures discovery and catalytic performance
improvements that caused by new functional fragments
formation, while the uncertain reliability of the resulted
compound remains the key issue for their further catalytic
application. 1
0, 11
Also, as typical inorganic compounds, Ln-POM
also has their own drawbacks such as high crystalline energies,
low solubility and low recyclability, which seriously limit their
applications.1
2,
13
Enhancing the catalytic capabilities of the
POM clusters by developing approaches other than
coordination structure altering is essential.
Generally, increasing the surface area of the Ln-POM and
tuning the micro-environment around the polyoxoanions are
two useful strategies to improve the catalytic properties, and
incorporating POM with porous crystalline framework,
constructing POM based micelles or forming mono-dispersed
a. College of Chemistry and Chemical Engineering, Central South University,
Changsha 410083, P.R. China
b.
Hunan Provincial Key Laboratory of Chemical Power Sources, Central South
University, Changsha, 410083, P.R. China
Corresponding author
Electronic Supplementary Information (ESI) available: [details of any
Fig. 1 Lewis Acid−Base Catalysis mechanism for rare earth
contained POMs for cyanosilylation Dark teal: W, pink: O,
*
Ds uOp I p: l1e 0m. 1e 0n 3t 9a /r yx 0x xi 0n 0f o0 r0m0 ax tion available should be included here]. See orange: Si, teal: Ln ion
Please do not adjust margins

Please d oC hn eo mt Ca do mj u ms t margins
Page 2 of 6
COMMUNICATION
Journal Name
there are seldom reports on these owing to the complex
micro-environment regulation mechanism and the inherent
mismatching Lewis acid and Lewis base sites originated from
available catalysts.2
View Article Online
DOI: 10.1039/D0CC01216E
0, 23
Targeting better understanding the micro-environmental
effect in the homogeneous catalysis process, the Lewis
Acid−Base catalytic system based on Ln containing mono-
lacunary POMs clusters beyond molecular level is excavated in
III
detail. The Nd ion with big ion radii was chosen as Lewis Acid
centre and the Nd-containing sandwiched type cluster
1
3-
[
39 2
Nd(SiW11O ) ]
was used as model POM. The Lewis acid-
base catalysis reaction of cyanosilylation was selected as the Fig. 2 Conversion rate for the cyanosilylation of cyclohexanone
model system owing to the significant role of its products- with different type and amount of impressed electrolytes.
2
4-26
cyanohydrins (important industrial precursors).
compounds {(DMA) (2-Melm) [Nd(SiW11
(1) (DMA=CH NH HCl and 2-Melm=2- Solvent free. Reaction temperature: 30 °C,)
methylimidazole) and (TBA) [Nd(SiW11 (2) were
synthesized and characterized. (details see SI) By tuning the tuning the solubility of the cluster. Although no single crystal
Two new (Reaction conditions: compound 2 (6mg, 0.064 mol%), ketone
5
8
O
39
)
2
]•(2-Melm)
2
(0.5 mmol), (TMS)CN (1.5 equiv with respect to ketone),
(H
2
O)10
}
)
3 2
·
H
8 5
39 2
O ) ]
1
3-
micro-environment around the [Nd(SiW11
O
39
)
2
]
cluster, with enough quality for X-RAY single crystal diffraction was
nanosized supramolecular of aggregated POMs with different isolated yet, its structure was confirmed by comprehensive
size and morphology were obtained, as well as the highest characterization of ESI-MS (Fig. S2), TGA-DSC (Fig. S3.1-2), IR
1
conversion efficiency (the turnover number (1562) and (Fig. S4.1-2), UV-Vis (Fig. S5.1-2), HNMR (Fig. S6.1-2) and ICP-
-1
turnover frequency (26777 h ) for the cyanosilylation of 2- OES (Tab. S3.3).
Acetylpyridine was achieved so far. Further, the intrinsic By using 2 as catalyst, a typical procedure for cyanosilylation of
synergistic effect on this catalytic process has also been carbonyl compounds was conducted and the controlled
probed for the first time.
8 11 39
experiments employed 1, or precursor K [α-SiW O ] as
As shown in Fig. 1, the POM based catalytic process at catalysts were performed in similar condition. As expected, 2
molecular level is relatively clear for the cyanosilylation showed supreme catalytic activities over 1, and this
reaction, the cyanosilylation of carbonyl compounds with improvement of catalytic properties is benefit from the change
(TMS)CN are activated synergistically by both the rare earth of solubility and the forming of “pseudo liquid phase”, and the
ions and the surface oxygen atoms of POMs, of which rare initial diffusion reflection spectrum (DRS) studies in CH CN also
3
earth metal ions and oxygen atoms on a same POM molecule confirmed that 2 dispersed better in reactant than 1. The
acted as electrophilically Lewis acid center and nucleophilically average size distribution for 1 and 2 were around 1 μm and
2
2, 23
Lewis base centers respectively.
To simplified the catalytic 27.62 nm respectively. Unexpectedly,
2 even showed
system and match the Lewis Acid−Base active site numbers, enhanced catalytic activities over reported Nd-POMs with
2
2,
the reliable cluster without solvent on the POM surface, better matching of the Lewis Acid−Base active site numbers.
1
3-
23
[
39 2
Nd(SiW11O ) ]
(1a), was used instead of other cluster with
To understanding the detail micro-environment effect
multiple Ln metal ion centers. The cluster was synthesized by a between the components and enhancing the catalytic
8
-
reaction of [α-SiW11
Nd(NO , CH NH·HCl and 2-Melm, and high quality block performed by merging different types of electrolytes into the
single crystal was isolated as compound 1. As shown in Fig. 1, system. Different amount of quaternary ammonium salts,
the main framework of compound is an anionic including
tetramethylammonium bromide (TMABr),
Nd(SiW11 } building unit consisted of two monolacunary tetraethylammonium bromide (TEABr), tetrapropylammonium
kegging type polyoxotungstates sandwiched by an bromide (TPABr) and tetrabutylammonium (TBABr), were in
encapsulated {NdO } group with average Nd-O bond length impressed into this catalysed system separately. As illustrated
.445(1)Å, {NdO } group formed a distorted square antiprism in Fig. 2 (detailed information in Tab. S4.1), without additional
geometry through the linkage of Ln ions with eight octahedral electrolytes, the conversion rate for cyanosilylation of
WO }. Five molecules of pronated DMA and eight 2-Melm cyclohexanone catalysed by 2 in 20 min is 83%, after
O
39
]
precursor polyoxotungstate with capabilities, further micro-environmental tuning was
)
3 3
3 2
)
1
{
39 2
O )
8
2
8
{
6
cations surrounded the main structure as counter ions. impressed different amount of electrolytes (0 ≤ molar
Although the polyoxoanion was surrounded by organic cations, ratioelectrolyte/2 ≤ 24), the best conversion rate are 94%, 67%,
the interaction between 2-Melm and POM are weak, and only 83%, 96% for TMABr, TEABr, TPABr and TBABr respectively.
the DMA cations can form H-bonds with terminal O on POM The minimum conversion efficiency is 89%, 31%, 63% and 90%
surface. Also, two co-crystallized 2-Melm and a few solvent respectively. The addition of TMA and TBA are beneficial to
waters were well located around the cluster (see Fig. S1.a). this catalysed system on the whole while TEA and TPA
Compound 2 was generated by using a cation exchange supressed. TEA deactivated the cyanosilylation reaction of
procedure under acidic solution to remove the solvent and
ketone dramatically when compared with TPA. Interestingly,
the catalytic activity all ascend first and descend at last along
2
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 6
Please d oC hn eo mt Ca do mj u ms t margins
Journal Name
COMMUNICATION
View Article Online
DOI: 10.1039/D0CC01216E
Scheme 1. Schematic demonstration of blackberry emulsion
droplets
Fig. 3 TEM images of compound 2 added with different
elyctrolytes,(a)-(b) without additives,(c)-(d) TMA ,(e)-(f) TEA, (g)-
condensed catalysed system added TMA and TBA, we expect
that the increasing of Lewis sites should have a stronger
impact than the size growing of catalyst, while TEA and TPA
conversely. Taking the severe negative effects of TEA to this
catalysed system into consideration, though the size of
aggregates caused by TEA is smaller than that of TPA,
blackberry structure is more favoured for the cyanosilylation
of ketones when compared with condensed hexagon
morphology. For incompact blackberry induced by the addition
of TBA, size growing in a mono dispersed formation
accompanied by increasing accessible Lewis Acid catalytic sites
contributed to the improvement of catalytic performance
jointly. The TEM image proved that the amphiphilic catalyst
does not assemble in continuous phase or gather in the
interior of the emulsion droplet but form assemblies on the
interface of emulsion droplets.
(h)
TPA,(i)-(l)
TBA
with addition of impressed cations. Therefore, simulated
catalysed system with extra added cations of extremum value
(best catalytic activity) and without exogenous cations, were
evaluated by TEM. By adding extra quaternary ammonium
cations as encapsulating components to wrap compound 2
with high catalytic properties, the surfactant encapsulated
clusters (SECs) were created. It was found that this amphiphilic
SECs could assemble into spherical nanosized aggregates in
reaction system (see Fig. 3). Hydrophilic 1 dispersed in H O
2
showed an average size of 1.9 nm, which was just the same
size of anion cluster. (Fig. S1b) Water insoluble compound 2
dispersed in CH CN displayed an average particle size of 12 nm.
3
When TMA added, condensed blackberries (20 nm) formed,
nano-particles of anion cluster distributed evenly in the
surface of blackberries. For the system added with TEA, regular
hexagonal quasi-single crystals with diameter around 112 nm
appear, nano-particles of cluster anion were closely attached
to the edges of hexagonal crystal. When TPA joined the system,
bigger dense black berry with diameter around 160 nm begin
As shown in Scheme 1, the amphiphilic catalysts demonstrated
in 1a not only serve as catalysts but also emulsifiers to stabilize
the emulsion droplets. The emulsion droplets dispersed evenly
to behave like homogenous catalysts with high activity. In
addition, catalysts with special morphology of blackberry could
be easily separated and recycled by demulsifying and
sedimentation. NaCl and NaBr were also added in the system
as control reagent. The catalytic activity is almost unchanged
with the addition of NaCl and NaBr (Tab.S4.2), which exclude
the halogen ion effect for this catalysed system. Further,
different amount of solid NaOH were added to preliminarily
explore to the effects of protons. It can be seen from Tab.S4.3
7-29 that the decreasing of protons on the POM cluster slowed
down the catalytic process, but the detail mechanism is still
unclear yet due to the uncertain of molecular composition
after the deprotonation treatment. Furthermore, as noticed,
the synergistic effect could play an important role during the
catalysis process. The completion time of the cyanosilylation
3
to take shape. For 2 dispersed in CH CN with bonus TBA,
incompact “vesicle” like blackberries with different sizes
appeared, of which anionic clusters concentrated in grooved
channel of the vesicles to form a mono-dispersed system.
Though previous study conducted by Liu et al elaborately
studied the relationship between inherent cations size, the
2
polarity and pH of solvent to the formation of blackberry,
it was the first time the type and amount of electrolytes found
to be related to the formation of blackberry. Due to different
detection mode, though not the same, DRS result shows
apparent regularity with TEM data , the average size of 2
dispersed in CH
addition of TMA, TEA TPA and TBA average size aggregated to
4.32 nm, 78.90 nm 133.1 nm and 50.63 nm respectively.
3
CN detected by DRS is 27.62 nm, with the
reaction shortened and conversion rate in a limited time
increased with increasing dosage of catalyst while
accompanied with the decreasing of TON and TOF. As
demonstrated in Tab.S4.6, the catalyst dosage employed in
this reaction is much smaller than other studies (Tab.S4.6).
6
Further, though the introduction of cations increases Lewis
acid sites, it also grows the size of catalyst. Catalysed
experiments showed that the addition of TMA and TBA
facilitate the catalytic process while TEA and TPA suppress. For
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please d oC hn eo mt Ca do mj u ms t margins
Page 4 of 6
COMMUNICATION
Journal Name
Finally, a series of carbonyl compounds including aliphatic, 2.
aromatic cyclic and heterocyclic ketones are chosen as
reaction substrates to probe the catalysis reaction. The
P. Yang, W. Zhao, A. Shkurenko, Y. Belmabkhout, M.
View Article Online
Eddaoudi, X. Dong, H. N. AlshareefDaOnId: 1N0..1M03.9K/Dha0sChCa0b1,2J1.6E
Am. Chem. Soc., 2019, 141, 1847-1851.
D. L. Long, R. Tsunashima and L. Cronin, Angew. Chem.
Int. Ed., 2010, 49, 1736-1758.
Z. Peng, Angew. Chem. Int. Ed., 2004, 43, 930-935.
S. S. Wang and G. Y. Yang, Chem. Rev., 2015, 115, 4893-
3
.
introductions of different type of substituent at the same
position also have effect on the catalytic activity, the reaction
rates slowed with the prolonging chain of aliphatic ketones,
4
5
.
.
3
the introduction of electron-donating group like –CH to
4
962.
Y. F. Song and R. Tsunashima, Chem. Soc. Rev., 2012, 41,
384-7402.
acetophenone decreases the reaction rate while the
introduction of electron-withdrawing group –Cl to
6
.
7
acetophenone increases. For 2-Acetylpyridine, 2-Acetylfuran 7.
and 2-Acetylthiophene, a series of organic compounds which
can be regarded as acetaldehyde substituted by different
heteroaromatic compounds, their reaction rates are in
8
.
accordance with electron-withdrawing ability either.
Nucleophilic addition reactions are easy to take place in
electron-withdrawing group substituted compounds, all the
results proved the nucleophilic addition mechanism among the
cyanosilylation of carbonyl compounds with TMSCN when
employed TBA-Ln-POMs as catalyst. It is obviously that
environmentally friendly and energy saving reactions
performed with solvent free method, mild temperature, small
9
1
1
.
0.
1.
catalyst amount but high conversion rate and reproducibility 12.
Fig. S7.1, Fig. S8.1-2) are attractive for all researchers.
Bassem S. Bassil and U. Kortz, Z. Anorg. Allg. Chem., 2010,
636, 2222-2231.
H. An, Y. Zhang, Y. Hou, T. Hu, W. Yang, S. Chang and J.
Zhang, Dalton Trans., 2018, 47, 9079-9089.
X. L. Ni, X. Xiao, H. Cong, Q. J. Zhu, S. F. Xue and Z. Tao,
Acc. Chem. Res., 2014, 47, 1386-1395.
(
1
1
1
1
1
3.
4.
5.
6.
7.
In summary, a new strategy of enhancing the catalytic
capabilities of lanthanide containing Polyoxometalate on
cyanosilylation of ketones was developed and the micro-
environment tuning mechanism of electrolytes addition was
explored. Beside the highest conversion efficiency (the
turnover number (1562) and turnover frequency (26777 h )
for the cyanosilylation of 2-Acetylpyridine was achieved so far,
the conversion rate for the cyanosilylation of carbonyl
compounds could be enhanced further through rational
B. Zhang, P. Yin, F. Haso, L. Hu and T. Liu, J. Clust. Sci.,
2
013, 25, 695-710.
W. Li, W. Bu, H. Li, L. Wu and M. Li, Chem. Commun.,
005, 3785-3787.
-1
2
A. Proust, R. Thouvenot and P. Gouzerh, Chem. Commun.,
2008, 1837-1852.
tailoring of the type and amount of electrolytes beyond 18.
T. J. Wilke and M. A. Barteau, J. Catal., 2019, 371, 357-
3
67.
P. P. Mishra, P. Joe and L. Tianbo, J. Am. Chem. Soc., 2008,
30, 1548-1549.
molecular level. By tuning the micro-environment around the
1
2
2
2
9.
0.
1.
2.
Ln-POM cluster, nanosized supramolecular of aggregated
POMs with different size and morphology were obtained, and
it was the first time the formation of blackberry found to be
related to the amount and type of cations synergistically, as
well as two new POM compounds were synthesized and
characterized. This study not only probes the formation of
blackberry through a unique perspective but also provides new
strategies for the designing and refining of the next
1
J. Gao, Y. Zhang, G. Jia, Z. Jiang, S. Wang, H. Lu, B. Song
and C. Li, Chem. Commun., 2008, 332-334.
J. M. Pigga, M. L. Kistler, C. Y. Shew, M. R. Antonio and T.
Liu, Angew. Chem. Int. Ed. Engl., 2009, 48, 6538-6542.
Y. Kikukawa, K. Suzuki, M. Sugawa, T. Hirano, K. Kamata,
K. Yamaguchi and N. Mizuno, Angew. Chem. Int. Ed. Engl,
2012, 51, 3686-3690.
generations of POMs based catalyst system beyond molecular 23.
level.
K. Suzuki, M. Sugawa, Y. Kikukawa, K. Kamata, K.
Yamaguchi and N. Mizuno, Inorg. Chem., 2012, 51, 6953-
6
961.
2
2
4.
5.
A. M. Nauth, T. Konrad, Z. Papadopulu, N. Vierengel, B.
Lipp and T. Opatz, Green Chem., 2018, 20, 4217-4223.
Z. Zhang, H. Y. Bae, J. Guin, C. Rabalakos, M. van
Gemmeren, M. Leutzsch, M. Klussmann and B. List, Nat.
Commun., 2016, 7, 12478.
Conflicts of interest
“There are no conflicts to declare”.
2
2
2
2
6.
7.
8.
9.
X. P. Zeng and J. Zhou, J. Am. Chem. Soc, 2016, 138, 8730-
Acknowledgements
This work was supported by the innovation project for postgraduate
students of Central South University (2019zzts221) and the
Recruitment Program of Global Youth Experts.
8
733.
L. Guang, C. Yuguang and L. Tianbo, J. Am. Chem. Soc.,
004, 126, 16690-16691.
G. Liu, M. L. Kistler, T. Li, A. Bhatt and T. Liu, J. Clust. Sci.,
006, 17, 427-443.
2
2
M. L. Kistler, B. Anish, L. Guang, C. Diego and L. Tianbo, J.
Am. Chem. Soc., 2007, 129, 6453-6460.
1
.
N. I. Gumerova and A. Rompel, Nat. Rev. Chem., 2018, 2,
112.
0
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 6
Please d oC hn eo mt Ca do mj u ms t margins
Journal Name
COMMUNICATION
View Article Online
DOI: 10.1039/D0CC01216E
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

ChemComm
Page 6 of 6
View Article Online
DOI: 10.1039/D0CC01216E
Polyoxometalate molecular based catalyst manifested the highest catalytic activities and the
catalytic activities improved greatly through micro-environment tuning.