Synthesis, molecular structure, and stability of a zirconocene derivative with α-Keggin mono-aluminum-substituted polyoxotungstate

Article abstract of DOI:10.1039/c2dt32107f

The synthesis and crystal structure of a zirconocene derivative with α-Keggin mono-aluminum-substituted polyoxotungstate, [α-PW ₁₁Al(OH)O₃₉ZrCp₂]₂^6- (Cp = C₅H₅^-) (1), which was obtained by the reaction of α-Keggin mono-aluminum-substituted polyoxotungstate with a biscyclopentadienylzirconium(iv) complex, is described herein. Analytically pure, homogeneous, yellow crystals of the tetra-n-butylammonium salt of polyoxoanion 1, [(n-C₄H₉)₄N] ₆[α-PW₁₁Al(OH)O₃₉ZrCp₂] ₂ (TBA-1), were obtained from the ca. 1:1 reaction of [(n-C ₄H₉)₄N]₄[α-PW ₁₁{Al(OH₂)}O₃₉] with Cp₂Zr(OTf) ₂·THF (OTf = O₃SCF₃^-) in acetonitrile solution under an argon atmosphere, followed by precipitation from water and crystallization from acetonitrile. TBA-1 was characterized based on X-ray structure analysis, elemental analysis, thermogravimetric/differential thermal analysis (TG/DTA), Fourier transform infrared (FTIR), and solution (³¹P, ²⁷Al, ¹⁹F, ¹H, and ¹³C) nuclear magnetic resonance (NMR) spectroscopy. Single-crystal X-ray structure analysis revealed that the two {PW₁₁AlO₄₀} units are bridged by two bent sandwich Cp₂Zr ²⁺ fragments with C₂ symmetry. Each zirconium center was bound to a terminal oxygen atom of the aluminum and tungsten sites and an edge-sharing oxygen atom at the Al-O-W linkage. Further, the stability towards water was investigated by NMR (³¹P, ¹H, and ¹³C) and FTIR spectroscopy. The η⁵- cyclopentadienylzirconium fragments were not eliminated from the surface of [α-PW₁₁{Al(OH₂)}O₃₉]^4- even after 24 h exposure to 50 equiv. of water. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c2dt32107f

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Synthesis, molecular structure, and stability of a
zirconocene derivative with α-Keggin mono-aluminum-
substituted polyoxotungstate†
Cite this: Dalton Trans., 2013, 42, 1129
Chika Nozaki Kato,*a Yuki Makino,a Wataru Unnoa and Hidemitsu Unob
The synthesis and crystal structure of a zirconocene derivative with α-Keggin mono-aluminum-substituted
6−
polyoxotungstate, [α-PW11Al(OH)O39ZrCp2]2 (Cp = C5H5−) (1), which was obtained by the reaction of
α-Keggin mono-aluminum-substituted polyoxotungstate with
a
biscyclopentadienylzirconium(IV)
complex, is described herein. Analytically pure, homogeneous, yellow crystals of the tetra-n-butylammo-
nium salt of polyoxoanion 1, [(n-C4H9)4N]6[α-PW11Al(OH)O39ZrCp2]2 (TBA-1), were obtained from the ca.
1 : 1 reaction of [(n-C4H9)4N]4[α-PW11{Al(OH2)}O39] with Cp2Zr(OTf)2·THF (OTf = O3SCF3−) in acetonitrile
solution under an argon atmosphere, followed by precipitation from water and crystallization from
acetonitrile. TBA-1 was characterized based on X-ray structure analysis, elemental analysis, thermogravi-
metric/differential thermal analysis (TG/DTA), Fourier transform infrared (FTIR), and solution (31P, 27Al,
19F, 1H, and 13C) nuclear magnetic resonance (NMR) spectroscopy. Single-crystal X-ray structure analysis
revealed that the two {PW11AlO40} units are bridged by two “bent sandwich” Cp2Zr2+ fragments with C2
symmetry. Each zirconium center was bound to a terminal oxygen atom of the aluminum and tungsten
sites and an edge-sharing oxygen atom at the Al–O–W linkage. Further, the stability towards water was
Received 12th September 2012,
Accepted 24th October 2012
investigated by NMR (31P, 1H, and 13C) and FTIR spectroscopy. The η5-cyclopentadienylzirconium frag-
DOI: 10.1039/c2dt32107f
4−
ments were not eliminated from the surface of [α-PW11{Al(OH2)}O39
]
even after 24 h exposure to 50
www.rsc.org/dalton
equiv. of water.
been synthesized by using complete and intact polyoxometa-
Introduction
8− 3
lates2 containing d0 transition metals, e.g., Nb6O19
,
Polyoxometalates1 are soluble metal oxide clusters that
resemble discrete fragments of the solid metal oxides widely
used as supports for transition metal heterogeneous catalysts.
Given the difficulties in determining the structures and there-
fore the operative mechanisms of oxide-supported catalysts,
rational improvement of such catalysts is problematic, and the
attractiveness of using polyoxoanion-supported, atomically dis-
persed transition metals as analogs becomes apparent. To
date, numerous polyoxoanion-supported compounds have
4− 4
7−
Nb2W4O19
,
A-β-SiW9M3O40
(M
=
NbV, VV),5 B-
3− 8
α-P2W15M3O629− (M = NbV, VV),6 α-PW11NbO404−,7 ClTiW5O18
,
and MW5O19 (M = NbV, TaV),9 and some of which have
been applied as oxidation catalysts,6b,10 precursors in the prep-
aration of nanoclusters,11 and transfer reagents;7a however, the
available sites for grafting organic and organometallic frag-
ments that have been constructed in mixed-metal polyoxo-
metalates remain limited. Meanwhile, the organic–inorganic
hybrids area has undergone significant expansion during the
last 10 years.12 The organic–inorganic hybrid materials that
were obtained via non-covalent interactions or strong covalent
bonds between organic/organometallic fragments and polyoxo-
metalates have attracted considerable interest with respect to
their catalytic and sorption properties and potential appli-
cations to optical, photochemical, and electrochemical
materials. Thus, the development of the available sites in
mixed-metal polyoxometalates for grafting reactions of organic
and organometallic fragments still has great potential to
further expand polyoxometalate chemistry.
3−
aDepartment of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya,
Suruga-ku, Shizuoka 422-8529, Japan. E-mail: sckatou@ipc.shizuoka.ac.jp
bDepartment of Chemistry and Biology, Graduate School of Science and Engineering,
Ehime University, Matsuyama, 790-8577, Japan
†Electronic supplementary information (ESI) available: Bond lengths and bond
angles for TBA-1 (Table S1); bond valence sum calculations for TBA-1 (Table S2);
19F NMR spectrum of the product which was obtained by the reaction of
[(n-C4H9)4N]4[α-PW11{Al(OH2)}O39] with Cp2Zr(OTf)2·THF in acetonitrile (Fig. S1);
solid-state packing of TBA-1 (Fig. S2); TG/DTA data of TBA-1 (Fig. S3); 1H, 13C,
and 31P NMR spectra of the product after a 24 h exposure to water (Fig. S4); FTIR
spectrum of the product after a 24 h exposure to water (Fig. S5); 1H and 13C NMR
spectra of Cp2Zr(OTf)2·THF (Fig. S6). CCDC 885643. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c2dt32107f
Here, we focused on the mono-aluminum-substituted site
in α-Keggin structure as a support, and single crystals of a
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 1129–1135 | 1129

View Article Online
Paper
Dalton Transactions
biscyclopentadienylzirconium(IV) compound with α-Keggin
mono-aluminum-substituted phosphotungstate, [(n-C4H9)4N]6-
[α-PW11Al(OH)O39ZrCp2]2 (Cp = C5H5−) (TBA-1), suitable for
X-ray structure analysis, were successfully obtained. In this
study, we report the complete details of the synthesis, mole-
cular structure, and water stability of complex 1.
Results and discussion
The
α-Keggin mono-aluminum-substituted phosphotungstate
with C2 symmetry was obtained in 29% yield, based on the
tetra-n-butylammonium salt [(n-C4H9)4N]6[α-PW11Al(OH)-
biscyclopentadienylzirconium(IV)
compound
with
1
O39ZrCp2]2 (TBA-1). Compound TBA-1 was prepared by the ca.
1 : 1 reaction of [(n-C4H9)4N]4[α-PW11{Al(OH2)}O39] with Cp2Zr-
(OTf)2·THF in acetonitrile, under an argon atmosphere, fol-
lowed by precipitation from water in ambient atmosphere.
Finally, yellow crystalline products were obtained by crystalliza-
tion from acetonitrile at 25 °C. The formation of polyoxoanion
1 can be shown by an ionic balance (eqn (1)). The 19F NMR
spectrum in CDCl3 of the product which was obtained by the
reaction of [(n-C4H9)4N]4[α-PW11{Al(OH2)}O39] with Cp2Zr-
(OTf)2·THF in acetonitrile, followed by evaporation to dryness,
showed elimination of TfO− (δ −78.3) from Cp2Zr(OTf)2·THF;
however, the formation of trifluoromethanesulfonic acid
(TfOH) was not observed, as shown in Fig. S1.† Cp2Zr2+ frag-
ments were affixed to the surface of the polyoxoanion support,
after which treatment with water in air was used to purify the
target compound by a precipitation step.
2½ðn-C4H9Þ4Nꢀ4½α-PW11fAlðOH2ÞgO39ꢀ þ 2Cp2ZrðOTfÞ2 !
½ðn-C4H9Þ Nꢀ ½α-PW11AlðOHÞO39ZrCp2ꢀ þ 2½ðn-C4H9Þ Nꢀþ
6
2
4
þ 2Hþ þ44TfOꢁ
ð1Þ
Single crystals of TBA-1 that were suitable for X-ray crystallo-
graphy could be obtained by crystallization from acetonitrile
via slow-evaporation. X-ray structural analysis of crystalline [(n-
C4H9)4N]6[α-PW11Al(OH)O39ZrCp2]2 revealed the presence of
discrete [(n-C4H9)4N]+ cations and [α-PW11Al(OH)O39ZrCp2]2
6−
anions, shown in Fig. 1, in which two {PW11AlO40} units are
bridged by two “bent sandwich” Cp2Zr2+ fragments with C2
symmetry. The solid-state packing of TBA-1 is illustrated in
Fig. S2.† Selected bond lengths and angles around the zirco-
nium center in 1 are summarized in Table 1, while other bond
lengths (Å) and angles (°) (Table S1†) and the bond valence
sum (BVS) calculations of the W, P, Al, and O atoms (Table S2)
are given in ESI.† Each zirconium center was bound to the
terminal oxygen atoms of the Al and W sites and to the edge-
sharing oxygen atom of the Al–O–W linkage with 5-coordi-
nation geometry. The bond lengths of the two W–O linkages
bound to the zirconium centers, W(1)–O(24) and W(3)–O(22),
were 1.754(14) and 1.730(14) Å, respectively. In addition, the
bond lengths of the Al–O linkages bound to the zirconium
centers (Al(1)–O(26) and Al(2)–O(23)) were 1.858(14) and
6−
Fig. 1 (a) Molecular structure of the polyoxoanion [α-PW11Al(OH)O39ZrCp2]2
(1), (b) the partial structure around the zirconium and aluminum sites, and (c)
the partial structures of Keggin units with atom numberings.
1130 | Dalton Trans., 2013, 42, 1129–1135
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Paper
Table 1 Selected bond distances and angles around zirconium and aluminum
sites in 1
Distances (Å)
Al(1)–O(25)
Al(1)–O(26)
Al(1)–O(27)
Al(1)–O(31)
Al(1)–O(32)
Al(1)–O(48)
Al(2)–O(9)
Al(2)–O(11)
Al(2)–O(13)
Al(2)–O(14)
Al(2)–O(23)
Al(2)–O(58)
Zr(1)–O(14)
Zr(1)–O(23)
Zr(1)–O(24)
Zr(2)–O(22)
Zr(2)–O(26)
Zr(2)–O(27)
P(1)–O(9)
P(2)–O(32)
Zr(1)⋯Zr(2)
Al(1)⋯Al(2)
Zr(1)–centroid Cp(1–5)
Zr(1)–centroid Cp(6–10)
Zr(2)–centroid Cp(11–15)
Zr(1)–centroid Cp(16–20)
Angles (°)
1.911(15) W(1)–O(24)
1.858(14) W(1)–O(25)
1.923(16) W(1)–O(33)
1.848(16) W(1)–O(42)
2.117(14) W(1)–O(43)
1.864(15) W(1)–O(44)
2.119(14) W(3)–O(1)
1.899(15) W(3)–O(2)
1.889(14) W(3)–O(11)
1.955(15) W(3)–O(22)
1.848(14) W(3)–O(60)
1.865(14) W(3)–O(63)
2.275(14) W(8)–O(9)
2.263(14) W(8)–O(14)
2.220(14) W(8)–O(15)
2.251(13) W(8)–O(16)
2.194(13) W(8)–O(17)
2.211(13) W(8)–O(55)
1.527(14) W(13)–O(27)
1.512(15) W(13)–O(28)
1.754(14)
1.826(14)
2.000(14)
1.958(15)
1.890(14)
2.356(14)
1.934(15)
2.010(14)
1.798(14)
1.730(14)
1.871(13)
2.371(13)
2.462(14)
1.895(14)
1.910(14)
1.963(14)
1.929(13)
1.686(15)
1.927(13)
1.689(15)
1.907(15)
2.451(14)
1.925(16)
1.873(16)
Fig. 2 FTIR spectrum in the polyoxoanion region (1800–400 cm−1), as acquired
from KBr disks of TBA-1.
129.67(9)°, which were similar to that of [(PW11O39NbO)2
ZrCp2]6− (131°).
The values of the bond valence sums (BVSs) for TBA-1,15
which were calculated based on the observed bond lengths,
were in the range of 5.664–6.485 (average 5.997) for the 22 W
atoms, 4.816–5.125 (4.971) for the two P atoms, 2.673–2.740
(2.707) for two Al atoms, and 1.488–2.075 (1.897) for the 78 O
atoms, excluding O(23) and O(26); these values were within
reasonable agreement with the formal valences of W6+, P5+,
Al3+, and O2−, respectively (Table S2†). The calculated BVS
values of O(23) and O(26) at the two Al–O–Zr linkages were
0.9444 and 1.013, respectively, suggesting that a proton was
bound to each of the two bridging oxygen atoms between the
aluminum and zirconium atoms.
Elemental analysis of TBA-1 dried overnight at room temp-
erature under 10−3–10−4 Torr of vacuum prior to analysis was
consistent with the composition [(n-C4H9)4N]6[α-PW11Al(OH)
O39ZrCp2]2. The elemental analysis result also supported the
presence of two protons in TBA-1. The weight loss observed
during the course of drying prior to analysis was 0.30%,
7.917(2)
W(13)–O(29)
5.3178(8) W(13)–O(32)
2.222(11) W(13)–O(46)
2.264(11) W(13)–O(47)
2.259(9)
2.236(10)
Al(1)–O(26)–Zr(2)
Al(2)–O(23)–Zr(1)
Average
O(14)–Zr(1)–O(23)
O(26)–Zr(2)–O(27)
Average
O(26)–Al(1)–O(27)
O(14)–Al(2)–O(23)
Average
105.4(6)
105.0(7)
105.3
68.9(5)
69.2(5)
69.1
82.9(6)
84.9(7)
84.0
W(1)–O(24)–Zr(1) 158.9(8)
W(3)–O(22)–Zr(2) 160.4(8)
Average
159.7
W(1)–O(25)–Al(1)
W(3)–O(11)–Al(2)
Average
143.3(8)
145.5(8)
144.5
O(24)–W(1)–O(25) 101.4(6)
O(11)–W(3)–O(22) 100.8(6)
Average
101.2
Cp(1–5)–Zr(1)–Cp(6–10)
Cp(11–15)–Zr(2)–Cp(16–20) 129.67(9)
Average 127.7
125.75(9)
1.848(14) Å, respectively. These lengths were markedly longer suggesting the absence of solvent molecules. This was also
than those of the tungsten and terminal oxygen linkages supported by the 1H NMR spectrum, as shown in the Exper-
(average 1.7 Å); thus, the Al–O and W–O bonds were stretched imental section. A weight loss of 23.0% with an exothermic
to facilitate coordination to the zirconium centers. The bond point at 364 °C was observed within the temperature range
lengths of the six Zr–O linkages were in the range of 2.194(13) from 24.3 to 500 °C in the TG/DTA performed under atmos-
to 2.275(14) Å (average 2.2 Å), which were similar to those of pheric conditions (Fig. S3†); calculations were consistent with
[Zr(α2-P2W17O61)2]16− (average 2.2 Å) and [Zr(α-PW11O39)2]10− the loss of six [(n-C4H9)4N]+ (calcd 19.8%) and four cyclopenta-
(average 2.2 Å).13 The Zr–centroid Cp distances were in the dienyl groups (calcd 3.6%) (total: 23.4%).
range of 2.222(11) to 2.264(11) Å (average 2.25 Å), which were
The FTIR spectrum acquired in the polyoxometalate region
similar to those of [LAlMe(μ-O)ZrMeCp2] (2.254(2) Å) and of TBA-1 from a KBr disk of the compound is presented in
[LAlMe(μ-O)ZrClCp2] (L = HC[(CMe)(2,6-iPr2C6H3N)]2) (2.246(3) Å).14 Fig. 2. The IR spectrum of TBA-1 (1080, 1065, 1026, 971, 890,
The two Al–O–Zr bonds were significantly bent; the bond 812, 788, 752, 703, and 631 cm−1) was different from that of
angles of Al(1)–O(26)–Zr(2) and Al(2)–O(23)–Zr(1) were 105.4 [(n-C4H9)4N]4[α-PW11{Al(OH2)}O39] (1078, 964, 887, 818, 749,
(6)° and 105.0(7)°, respectively. The angles of the W–O–Zr and 702 cm−1). In particular, coordination of the Cp2Zr2+ frag-
linkages in polyoxoanion 1 were also bent; the bond angles of ment is evidenced by a split in the P–O band of [α-PW11{Al-
W(1)–O(24)–Zr(1) and W(3)–O(22)–Zr(2) were 158.9(8)° and (OH2)}O39]4− at 1078 cm−1 into two peaks at 1080 and
160.4(8)°, respectively. For [(PW11O39NbO)2 ZrCp2]6− 7a
angles of two Nb–O–Zr linkages between the two {PW11NbO40
units were 159(1)° and 148(1)°, which were larger than those of Zr–O linkages. A Zr–O linkage was observed at 590 cm−1 in the
Al–O–Zr linkages of polyoxoanion 1. The angles between the FTIR spectrum of the alumina–zirconia composite powder.16
centroid Cp rings and zirconium centers were 125.75(9)° and band assigned to the Cp ligands was clearly observed at
,
the 1065 cm−1. In addition, a new band appeared at 631 cm−1 in
}
the TBA-1 spectrum, which might be due to the formation of
A
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 1129–1135 | 1131

View Article Online
Paper
Dalton Transactions
Fig. 4 27Al NMR spectrum of TBA-1 in CD3CN.
Fig. 3 31P NMR spectra of (a) as-prepared TBA-1, (b) the sample after 12 h
exposure to 10 equiv. of water in air, and (c) the sample after 24 h exposure to
50 equiv. of water in air; acquired in CD3CN.
3120 cm−1. These results suggested that the cyclopentadienyl-
zirconium fragments were coordinated to the [α-PW11{Al(OH2)}-
O39]4− surface.
Two signals were observed at −12.25 ppm and −12.33 ppm
in the 31P NMR spectrum of TBA-1 acquired in CD3CN at 25 °C
(Fig. 3(a)). The main signal at −12.25 ppm was assigned to the
internal phosphorus atom in polyoxoanion 1, which was
shifted from that of [(n-C4H9)4N]4[α-PW11{Al(OH2)}O39] (δ
−12.48), whereas the minor signal might be due to a proto-
nated isomer given that the intensity of the signal increased
with the addition of 1 equiv. of water, as reported for
[(CH3)2NH2]10[Hf(PW11O39)2]·8H2O.17 The 27Al NMR spectrum
of TBA-1 in CD3CN acquired at 25 °C was characterized by a
broad signal at 17.5 ppm, as shown in Fig. 4. The signal was
shifted relative to that of [(n-C4H9)4N]4[α-PW11{Al(OH2)}O39] (δ
16.1), suggesting that the cyclopentadienylzirconium frag-
ments were coordinated to the mono-aluminum-substituted
sites in 1. The 1H NMR spectrum (Fig. 5(a)) of TBA-1 in CD3CN
Fig. 5 (a) 1H NMR and (b) 13C NMR spectra of TBA-1 in CD3CN.
at ∼25 °C showed two signals at 6.67 ppm and 6.56 ppm with
an intensity ratio of 1 : 1; these peaks were shifted relative to
that of Cp2Zr(OTf)2·THF (δ 6.52). Two signals were also
observed in the 13C NMR spectrum (Fig. 5(b)) at 117.5 ppm
and 116.7 ppm with an intensity ratio of 1 : 1; these peaks were
shifted from that of Cp2Zr(OTf)2·THF (δ 117.0). These two
signals are attributed to the two pairs of η5-cyclopentadienyl
ligands at each zirconium center, shown in the X-ray crystal
structure of 1.
The stability of TBA-1 towards water was also evaluated
using 31P and 1H NMR spectroscopy. Two signals were
observed at −12.25 ppm and −12.34 ppm in the 31P NMR
1132 | Dalton Trans., 2013, 42, 1129–1135
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Paper
spectrum of TBA-1 acquired in CD3CN at ∼25 °C after 12 h
exposure to 10 equiv. of water in air (Fig. 3(b)). No signals due
Experimental section
Materials
3−
7−
to the [α-PW12O40
]
(δ −14.6) and [α-PW11O39
]
(δ −12.0)
were observed.18 The H NMR spectrum acquired in CD3CN at [(n-C4H9)4N]4[α-PW11{Al(OH2)}O39] was synthesized by a pre-
1
−
∼25 °C also exhibited two signals at 6.66 and 6.56 ppm, and viously published method.18 Cp2Zr(OTf)2·THF (OTf = CF3SO3
)
no signal due to the elimination of Cp2Zr2+ fragments from was prepared by a modified literature method as follows.19
A
the polyoxoanion surface was observed. Even after a month, solution of AgOTf (1.290 g; 5.02 mmol) dissolved in 10 mL of
the molecular structure of polyoxoanion 1 was completely THF was slowly added to a solution of Cp2ZrCl2 (0.737 g;
retained in acetonitrile solution containing 10 equiv. of water. 2.52 mmol) dissolved in 15 mL of THF in a dry box filled with
No decomposition of polyoxoanion 1 was observed after 24 h argon (>99.9995 vol% purity), and the mixture was stirred for
exposure to 50 equiv. of water based on the 31P NMR spectrum 4 h in the dark. A white precipitate was filtered off through a
acquired in CD3CN at ∼25 °C (Fig. 3(c)). When the polyoxo- folded filter paper (Whatman #5), and the filtrate was added to
anion 1 (0.081 g; 0.011 mmol) after 24 h exposure to 50 equiv. 30 mL of n-hexane. At this stage, a white precipitate, AgCl, was
of water in acetonitrile (4 mL) was precipitated by the addition obtained in 98% yield based on the formula 2[moles of AgCl]/
of water (50 mL), a white-yellow precipitate was obtained in [moles of Cp2ZrCl2] × 100. The reaction mixture was allowed to
0.030 g yield. The NMR {31P, 1H, and 13C} spectra in CD3CN stand overnight in the dark, after which the supernatant solu-
and the FTIR spectrum of the obtained product were the same tion was removed via decantation, and the white crystalline
as those of as-prepared TBA-1 under the present conditions, as precipitate was washed with a small amount of n-hexane. The
shown in Fig. S4 and S5.† Beer and co-workers reported that product was obtained in 30% yield (0.445 g) based on the
[(PW11O39NbO)2 ZrCp2]6− was hydrolyzed in the presence of formula [moles of Cp2Zr(OTf)2·THF]/[moles of Cp2ZrCl2] × 100.
excess water in acetonitrile to form [PW11NbO40]4− and the 1H NMR (CD3CN, 23.7 °C, Fig. S6(a)†): δ 6.52 (Cp), 3.65 and
acid condensation product [(PW11NbO39)2O]6− 7a Klemperer 1.80 (THF). 13C NMR (CD3CN, 25.1 °C, Fig. S6(b)†): δ 117.0
.
and co-workers previously reported that the polyoxoanion {[(η5- (Cp), 26.3 and 68.4 (THF). n-Hexane (containing ≤0.001%
C5H5)2U]2(μ-κ2O-TiW5O19)2}4− was quite stable and was not water) and acetonitrile (containing ≤0.001% water) were used
readily attacked by electrophilic and weakly nucleophilic as received from commercial sources.
reagents such as H2O, CH3CH2OH, (CH3)2CHNO2, and
CH3CN; however, <10% decomposition was observed after 2 h
1
Instrumentation/analytical procedures
exposure to 10 equiv. of water based on H NMR data.8a These
results show that the η5-cyclopentadienylzirconium fragments Elemental analysis was carried out by using a Mikroanaly-
of polyoxoanion 1 are significantly stable towards water under tisches Labor Pascher (Remagen, Germany) instrument. The
the given conditions.
samples were dried overnight at room temperature under
10−3–10−4 Torr vacuum before analysis. Infrared spectra were
recorded on a Perkin Elmer Spectrum100 FT-IR spectrometer,
in KBr disks, at room temperature. Thermogravimetric (TG)
and differential thermal analysis (DTA) data were obtained
using a Rigaku Thermo Plus 2 series TG/DTA TG 8120. TG/DTA
Conclusion
An α-Keggin mono-aluminum-substituted polyoxotungstate zir- measurements were performed in air with a temperature
conocene derivative [α-PW11Al(OH)O39ZrCp2]2 was success- increase of 4 °C min−1 between 20 and 500 °C. Solution 1H
6−
fully obtained as single crystals of the acetonitrile-soluble (600.17 MHz), 13C (150.92 MHz), 31P-{1H} (242.95 MHz), and
tetra-n-butylammonium
salt
[(n-C4H9)4N]6[α-PW11Al(OH)- 19F (564.72 MHz) nuclear magnetic resonance (NMR) spectra
O39ZrCp2]2 (TBA-1) by reacting Cp2Zr(OTf)2·THF with the were recorded in 5 mm outer diameter tubes on a JEOL
1
mono-aluminum-substituted polyoxoanion. TBA-1 was charac- ECA-600 NMR spectrometer (Shizuoka University). H and 13C
terized by X-ray structure analysis, elemental analysis, TG/DTA, NMR spectra were measured in CD3CN with reference to tetra-
FTIR, and solution (31P, 27Al, 19F, 1H, and 13C) NMR spec- methylsilane (TMS). Chemical shifts are reported as positive
troscopy. The crystal structure shows that the two {PW11AlO40} for resonances downfield of TMS (δ 0). The 31P NMR spectra
units are bridged by two “bent sandwich” Cp2Zr2+ fragments were measured in CD3CN with reference to an external stan-
with C2 symmetry. Each zirconium center is bound to the dard of 85% H3PO4 in a sealed capillary. Chemical shifts were
terminal oxygen atoms of aluminum and tungsten sites, and reported as negative on the δ scale for resonances upfield of
an edge-sharing oxygen atom of the Al–O–W linkage. Further- H3PO4 (δ 0). The 19F NMR spectra were measured in CDCl3
more, the polyoxoanion
1
(dissolved in acetonitrile) with reference to an external standard of [(n-C4H9)4N]OTf (δ =
exhibited high stability towards water. To the best of our −78.27 from CFCl3).20 Chemical shifts were reported as posi-
knowledge, the polyoxoanion 1 is the first example of the poly- tive on the δ scale for resonances downfield of AlCl3 (δ 0). The
oxoanion-supported organometallic compound prepared by 27Al NMR (156.36 MHz) spectrum in CD3CN was recorded on a
using a mono-aluminum-substituted site constructed in a JEOL ECA-600 NMR spectrometer (Kyushu University) using
complete and intact polyoxometalate as an atomic-level tubes of 5 mm outer diameter. The 27Al NMR spectrum was
support.
referenced to an external standard of the saturated AlCl3–D2O
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 1129–1135 | 1133

View Article Online
Paper
Dalton Transactions
solution (substitution method). Chemical shifts were X-ray crystallography
reported as positive on the δ scale for resonances downfield
A yellow prism-shaped crystal of TBA-1 (0.20 × 0.10
×
0.05 mm3) was mounted on a glass fiber. Data were collected
on a Rigaku VariMax instrument with Saturn connected to a
multi-layer mirror using monochromated Mo Kα radiation (λ =
0.71075 Å) at 121 1 K. Data were collected and processed
using the software CrystalClear for Windows. The structural
analysis was performed using the CrystalStructure for
Windows software. All structures were solved using SHELXS-97
(direct methods) and refined using SHELXL-97.21 For polyoxo-
anion 1, 22 tungsten atoms, 2 zirconium atoms, 2 phosphorus
atoms, 2 aluminum atoms, and 80 oxygen atoms were clearly
identified. Thus, the main features of the molecular structure
of the polyoxometalate were clarified. The six tetra-n-butyl-
ammonium ions were also identified; however, acetonitrile
solvent molecules could not be modeled due to disorder of the
atoms.22 Accordingly, the residual electron density was
removed using the SQUEEZE routine in PLATON.23
of AlCl3 (δ 0).
Preparation
[(n-C4H9)4N]6[α-PW11Al(OH)O39ZrCp2]2 (TBA-1). The follow-
ing manipulations were performed in a drybox filled with
argon (>99.9995 vol% purity). A solution of Cp2Zr(OTf)2·THF
(0.5 g; 0.85 mmol) dissolved in 10 mL of acetonitrile was
slowly added to a solution of [(n-C4H9)4N]4[α-PW11{Al(OH2)}-
O39] (3.0 g; 0.81 mmol) dissolved in 10 mL of acetonitrile until
the solution became cloudy. After stirring for 4 h at 25 °C, the
mixed solution was filtered through a folded filter paper
(Whatman #5). At this stage, the filtrate was removed from the
drybox, and was combined with water (400 mL) in ambient
1
atmosphere. [Note: H NMR spectra in CD3CN of the reaction
mixture of [(n-C4H9)4N]4[α-PW11{Al(OH2)}O39] and Cp2Zr-
(OTf)2·THF in acetonitrile showed three signals at 6.70, 6.65,
and 6.57 ppm; however the species observed at 6.70 ppm was
completely removed by precipitation from water.] The yellow-
white precipitate was collected using a membrane filter (JG
0.2 μm), and washed with a small amount of ethanol. The
yield of the crude product was 2.621 g. The obtained product
was returned to the drybox and dissolved in 10 mL of aceto-
nitrile; yellow crystals were formed after one week. [Note:
TBA-1 can be crystallized from acetonitrile in air; however, the
quality of the crystals degrades gradually upon exposure to
moisture.] The yield of the product was 1.74 g (the percentage
Crystal data for TBA-1. C116H238Al2N6O80P2W22Zr2; M =
7340.20, orthorhombic, space group P212121 (#19),
a =
14.8501(10), b = 28.331(2), c = 47.428(3) Å, V = 19953(3) Å3,
Z = 4, Dc = 2.443 g cm−3, μ(Mo Kα) 128.370 cm−1. R1 = 0.0835
(I > 2σ(I)), wR2 = 0.1613 (for all data). GOF = 1.143 (201 629
total reflections, 44 976 unique reflections where I > 2σ(I)).
CCDC reference number 885643 contains the supplementary
crystallographic data for this paper.
yield of 29% was calculated on the basis of the following: Acknowledgements
[moles of TBA-1]/[moles of [(n-C4H9)4N]4[α-PW11{Al(OH2)}O39]]
× 100). Elemental analysis results showed C, 19.02, H, 3.24;
Al, 0.73; N, 1.23; P, 0.86; W, 55.2; Zr, 2.46%. Calculations
This work was supported by a Grant-in-Aid for Scientific
Research on Innovative Areas (No. 21200055) of the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
This research was partially carried out using equipment at the
Center for Instrumental Analysis, Shizuoka University.
for [(n-C4H9)4N]6[α-PW11Al(OH)O39ZrCp2]2
=
C116H238Al2-
N6O80P2W22Zr2: C, 18.98; H, 3.27; Al, 0.74; N, 1.14; P, 0.84; W,
55.1; Zr, 2.49%. A weight loss of 0.30% was observed during
drying overnight at room temperature, under a vacuum of
10−3–10−4 Torr prior to analysis, suggesting the removal of
weakly solvated or adsorbed acetonitrile molecules; this was
also supported by the absence of any signal due to acetonitrile
Notes and references
1
molecules in the H NMR spectrum of the sample after drying
1 (a) M. T. Pope, Heteropoly and Isopoly Oxometalates,
Springer-Verlag, Berlin, 1983; (b) M. T. Pope and A. Müller,
Angew. Chem., Int. Ed. Engl., 1991, 30, 34;
(c) Polyoxometalates: From Platonic Solids to Anti-Retroviral
Activity, ed. M. T. Pope and A. Müller, Kluwer Academic
Publishers, Dordrecht, The Netherland, 1994; (d) Chem.
Rev., 1998, 98, 1 (special issue on polyoxometalates; Hill,
C. L., guest editor); (e) V. W. Day and W. G. Klemperer,
Science, 1985, 228, 533; (f) P. Gouzerh and A. Proust, Chem.
Rev., 1998, 98, 77.
overnight acquired in DMSO-d6. TG/DTA performed under
atmospheric conditions showed a weight loss of 23.0% with an
exothermic point at 364.4 °C (observed below 500 °C); the cal-
culated weight loss of 23.4% was consistent with the loss of
four Cp ligands and six tetra-n-butylammonium ions. IR (KBr
disks) in the 1300–400 cm−1 region (polyoxometalate region):
1080(s), 1065(m), 1026(w), 971(s), 890(s), 812(s), 788(s), 752(s),
703(m), and 631(m) cm−1
.
NMR results gave 1H NMR
(CD3CN, 24.5 °C): δ 6.67 (singlet) and 6.56 (singlet) (Cp),
3.14 (triplet), 1.64 (multiplet), 1.39 (multiplet), and
0.98 (triplet) ([(n-C4H9)4N]+); 13C NMR (CD3CN, 24.2 °C):
δ 117.49 and 116.65 (Cp), 59.42, 24.48, 20.47, and 14.02
2 The definition of complete (plenary)1b polyoxometalates
excludes syntheses that involve oxygen-ligand-substitution
reactions or the addition of metal fragments into vacancies
created by removing {MO}n+ units.
3 (a) C. M. Flynn, Jr. and G. D. Stucky, Inorg. Chem., 1969, 8,
178; (b) C. M. Flynn, Jr. and G. D. Stucky, Inorg. Chem.,
([(n-C4H9)4N]+); 31P NMR (CD3CN, 22.8 °C):
δ −12.25
(main signal), −12.33 (minor signal); 27Al NMR (CD3CN,
27.1 °C): δ 17.5.
1134 | Dalton Trans., 2013, 42, 1129–1135
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Paper
1969, 8, 332; (c) C. M. Flynn, Jr. and G. D. Stucky, Inorg.
Chem., 1969, 8, 335.
9 V. W. Day, W. G. Klemperer and D. J. Maltbie, Organometal-
lics, 1985, 4, 104.
4 (a) C. J. Besecker and W. G. Klemperer, J. Am. Chem. Soc., 10 (a) N. Mizuno, H. Weiner and R. G. Finke, J. Mol. Catal.
1980, 102, 7598; (b) C. J. Besecker, W. G. Klemperer and
V. W. Day, J. Am. Chem. Soc., 1982, 104, 6158;
A: Chem., 1996, 114, 15; (b) H. Weiner, A. Trovarelli and
R. G. Finke, J. Mol. Catal. A: Chem., 2003, 191, 253.
(c) C. J. Besecker, V. W. Day, W. G. Klemperer and 11 (a) Y. Lin and R. G. Finke, Inorg. Chem., 1994, 33, 4891;
M. R. Thompson, J. Am. Chem. Soc., 1984, 106, 4125;
(d) C. J. Besecker, V. W. Day, W. G. Klemperer and
M. R. Thompson, Inorg. Chem., 1985, 24, 44; (e) V. W. Day,
T. A. Eberspacher, W. G. Klemperer, R. P. Planalp,
P. W. Schiller, A. Yagasaki and B. Zhong, Inorg. Chem.,
1993, 32, 1629; (f) V. W. Day, W. G. Klemperer and
(b) Y. Lin and R. G. Finke, J. Am. Chem. Soc., 1994, 116,
8335; (c) S. Özkar and R. G. Finke, J. Am. Chem. Soc., 2002,
124, 5796; (d) M. A. Watzky, E. E. Finney and R. G. Finke,
J. Am. Chem. Soc., 2008, 130, 11959; (e) B. J. Hornstein and
R. G. Finke, Chem. Mater., 2004, 16, 139; (f) L. S. Ott and
R. G. Finke, J. Nanosci. Nanotechnol., 2008, 8, 1551 and
references therein.
D.
J.
Main,
Inorg.
Chem.,
1990,
29,
2345;
(g) W. G. Klemperer and D. J. Main, Inorg. Chem., 1990, 29, 12 (a) A. Dolbecq, E. Dumas, C. R. Mayer and P. Mialane,
2355 and references therein.
Chem. Rev., 2010, 110, 6009; (b) A. Dolbecq, P. Mialane,
F. Sècheresse, B. Keita and L. Nadjo, Chem. Commun., 2012,
48, 8299; (c) A. Proust, R. Thouvenot and P. Gouzerh, Chem.
Commun., 2008, 1837.
5 (a) R. G. Finke, B. Rapko and P. J. Domaille, Organometal-
lics, 1986, 5, 175; (b) R. G. Finke, C. A. Green and B. Rapko,
Inorg. Synth., 1990, 27, 128; (c) R. G. Finke, K. Nomiya,
C. A. Green and M. W. Droege, Inorg. Synth., 1992, 29, 239; 13 C. N. Kato, A. Shinohara, K. Hayashi and K. Nomiya, Inorg.
(d) R. G. Finke, B. Rapko, R. J. Saxton and P. J. Domaille, Chem., 2006, 45, 8108.
J. Am. Chem. Soc., 1986, 108, 2947; (e) Y. Lin, K. Nomiya 14 G. Bai, S. Singh, H. W. Roesky, M. Noltemeyer and
and R. G. Finke, Inorg. Chem., 1993, 32, 6040; H. Schmidt, J. Am. Chem. Soc., 2005, 127, 3449.
(f) B. M. Rapko, M. Pohl and R. G. Finke, Inorg. 15 (a) I. D. Brown and D. Altermatt, Acta Crystallogr., Sect. B:
Chem., 1994, 33, 3625; (g) R. G. Finke and
M. W. Droege, J. Am. Chem. Soc., 1984, 106, 7274 and
references therein.
6 (a) D. K. Lyon and R. G. Finke, Inorg. Chem., 1990, 29, 1787;
(b) D. J. Edlund, R. J. Saxton, D. K. Lyon and R. G. Finke,
Struct. Sci., 1985, 41, 244; (b) I. D. Brown and
R. D. Shannon, Acta Crystallogr., Sect. A: Cryst. Phys., Diffr.,
Theor. Gen. Crystallogr., 1973, 29, 266; (c) I. D. Brown, Acta
Crystallogr., Sect. B: Struct. Sci., 1992, 48, 553;
(d) I. D. Brown, J. Appl. Crystallogr., 1996, 29, 479.
Organometallics, 1988, 7, 1692; (c) K. Nomiya, N. Mizuno, 16 J. Chandradass and K. H. Kim, Met. Mater. Int., 2009, 15,
D. K. Lyon, M. Pohl and R. G. Finke, Inorg. Synth., 1997, 31, 1039.
186; (d) R. G. Finke, D. K. Lyon, K. Nomiya, S. Sur and 17 Y. Hou, X. Fang and C. L. Hill, Chem.–Eur. J., 2007, 13,
N. Mizuno, Inorg. Chem., 1990, 29, 1784; (e) A. Trovarelli 9442.
and R. G. Finke, Inorg. Chem., 1993, 32, 6034; (f) M. Pohl 18 C. N. Kato, Y. Makino, M. Yamasaki, Y. Kataoka,
and R. G. Finke, Organometallics, 1993, 12, 1453;
(g) M. Pohl, Y. Lin, T. J. R. Weakley, K. Nomiya, M. Kaneko,
Y. Kitagawa and M. Okumura, Advances in Crystallization
Processes, InTech, Croatia, 2012.
H. Weiner and R. G. Finke, Inorg. Chem., 1995, 34, 767; 19 S. J. Angus-Dunne, L. E. P. Lee Chin, R. C. Burns and
(h) M. Pohl, D. K. Lyon, N. Mizuno, K. Nomiya and G. A. Lawrence, Transition Met. Chem., 2006, 31, 268.
R. G. Finke, Inorg. Chem., 1995, 34, 1413; (i) K. Nomiya, 20 R. A. T. M. Abbenhuis, I. del Río, M. M. Bergshoef,
C. Nozaki, M. Kaneko, R. G. Finke and M. Pohl, J. Organo-
met. Chem., 1995, 505, 23; ( j) K. Nomiya, H. Torii,
J. Boersma, N. Veldman, A. L. Spek and G. van Koten,
Inorg. Chem., 1998, 37, 1749.
C. N. Kato and Y. Sado, Chem. Lett., 2003, 32, 664 and refer- 21 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystal-
ences therein. logr., 2008, 46, 112.
7 (a) E. V. Radkov, V. G. Young, Jr. and R. H. Beer, J. Am. 22 Some acetonitrile molecules were observed in a single
Chem. Soc., 1999, 121, 8953; (b) E. V. Radkov and
R. H. Beer, Inorg. Chim. Acta, 2000, 297, 191.
8 (a) V. W. Day, C. W. Earley, W. G. Klemperer and
D. J. Maltbie, J. Am. Chem. Soc., 1985, 107, 8261;
crystal of TBA-1; however, no acetonitrile solvent molecules
were observed by elemental analysis and 1H NMR spec-
troscopy. Thus, the solvent molecules evaporate gradually
when crystals are removed from acetonitrile solution.
(b) W. G. Klemperer and B. Zhong, Inorg. Chem., 1993, 32, 23 A. L. Spek, Acta Crystallogr., Sect. D: Biol. Crystallogr., 2009,
5821.
65, 148.
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 1129–1135 | 1135