Construction of larger molecular aluminophosphate cages from the cyclic four-ring building unit

Article abstract of DOI:10.1021/ic500083a

New molecular aluminophosphates of different nuclearity are synthesized by a stepwise process and structurally characterized. The alkane elimination reaction of bis(trimethylsiloxy)phosphoric acid, OP(OH)(OSiMe₃) ₂, with trialkylalanes, AlR₃ (R = Me, Et, ⁱBu), provides the cyclic dimeric aluminophosphates, [(AlR₂{μ ₂-O₂P(OSiMe₃)₂})₂] (R = Me (1), Et (2), ⁱBu (3)). Unsymmetrically substituted cyclic aluminophosphonate [(AlMe₂{μ₂-O₂P(OSiMe ₃)(^cHex)})₂] (cis/trans-4) is prepared by dealkylsilylation reaction of ^cHexP(O)(OSiMe₃)₂ with AlMe₃. Molecules 1-4 containing the [Al₂(μ ₂-O₂P)₂] inorganic core are structural and spectroscopic models for the single four-ring (S4R) secondary building units (SBU) of zeolite frameworks. Compound 1 serves as a starting point in construction of larger molecular units by reactions with OP(OH)(OSiMe ₃)₂ as a cage-extending reagent and with diketones, such as Hhfacac (1,1,1,5,5,5-hexafluoropentan-2,4-dione) and Hacac (pentan-2,4-dione), as capping reagents. Reaction of 1 with 4 equiv of Hhfacac leads to new cyclic aluminophosphate [(Al(hfacac)₂{μ₂- O₂P(OSiMe₃)₂})₂] (5), existing in two isomeric (D₂ and C_2h) forms. Reaction of 1 with 2 equiv of OP(OH)(OSiMe₃)₂ and 1 equiv of Hhfacac provides a molecular aluminophosphate [AlMe{Al(hfacac)}₂{μ₃- O₃P(OSiMe₃)}₂{μ₂-O ₂P(OSiMe₃)₂}₂{OP(OSiMe ₃)₃}] (6), while by adding first the Hhfacac and using 3 equiv of OP(OH)(OSiMe₃)₂ we isolate [Al{Al(hfacac)} ₂{μ₃-O₃P(OSiMe₃)} ₂{μ₂-O₂P(OSiMe₃) ₂}₂H{OP(O)(OSiMe₃)₂}₂] (7). These molecules contain units in their cores that imitate 4=1 SBU of zeolite frameworks. Reaction with the order of component mixing 1, Hhfacac, OP(OH)(OSiMe₃)₂ at a 1:2:2 molar ratio lead to formation of a larger cluster [(Al(AlMe){Al(hfacac)}{μ₃-O ₃P(OSiMe₃)}₂{μ₂-O ₂P(OSiMe₃)₂}₃)₂] (8) containing both S4R and 4=1 structural units. Similarly, Hacac (pentan-2,4-dione) provides an isostructural [(Al(AlMe){Al(acac)} {μ₃-O₃P(OSiMe₃)}₂{μ ₂-O₂P(OSiMe₃)₂}₃) ₂] (9). Both molecules display Al centers in three different coordination environments.

Full text of DOI:10.1021/ic500083a

Article
pubs.acs.org/IC
Construction of Larger Molecular Aluminophosphate Cages from the
Cyclic Four-Ring Building Unit
Jan Chyba,†,‡ Zdenek Moravec,†,‡ Marek Necas,†,‡ Sanjay Mathur,§ and Jiri Pinkas*,†,‡
†Department of Chemistry, Faculty of Science, Masaryk University, Kotlarska 2, CZ-61137 Brno, Czech Republic
‡Central European Institute of Technology (CEITEC), Masaryk University, CZ-62500 Brno, Czech Republic
§Institute of Inorganic Chemistry, University of Cologne, Greinstrasse 6, D-50939, Cologne, Germany
S
* Supporting Information
ABSTRACT: New molecular aluminophosphates of different nuclearity
are synthesized by a stepwise process and structurally characterized. The
alkane elimination reaction of bis(trimethylsiloxy)phosphoric acid, OP-
(OH)(OSiMe3)2, with trialkylalanes, AlR3 (R = Me, Et, iBu), provides the
cyclic dimeric aluminophosphates, [(AlR2{μ2-O2P(OSiMe3)2})2] (R = Me
i
(1), Et (2), Bu (3)). Unsymmetrically substituted cyclic aluminophosph-
onate [(AlMe2{μ2-O2P(OSiMe3)(cHex)})2] (cis/trans-4) is prepared by
c
dealkylsilylation reaction of HexP(O)(OSiMe3)2 with AlMe3. Molecules 1−4 containing the [Al2(μ2-O2P)2] inorganic core are
structural and spectroscopic models for the single four-ring (S4R) secondary building units (SBU) of zeolite frameworks.
Compound 1 serves as a starting point in construction of larger molecular units by reactions with OP(OH)(OSiMe3)2 as a cage-
extending reagent and with diketones, such as Hhfacac (1,1,1,5,5,5-hexafluoropentan-2,4-dione) and Hacac (pentan-2,4-dione),
as capping reagents. Reaction of 1 with 4 equiv of Hhfacac leads to new cyclic aluminophosphate [(Al(hfacac)2{μ2-
O2P(OSiMe3)2})2] (5), existing in two isomeric (D2 and C2h) forms. Reaction of 1 with 2 equiv of OP(OH)(OSiMe3)2 and 1
equiv of Hhfacac provides a molecular aluminophosphate [AlMe{Al(hfacac)}2{μ3-O3P(OSiMe3)}2{μ2-O2P(OSiMe3)2}2{OP-
(OSiMe3)3}] (6), while by adding first the Hhfacac and using 3 equiv of OP(OH)(OSiMe3)2 we isolate [Al{Al(hfacac)}2{μ3-
O3P(OSiMe3)}2{μ2-O2P(OSiMe3)2}2H{OP(O)(OSiMe3)2}2] (7). These molecules contain units in their cores that imitate 4=1
SBU of zeolite frameworks. Reaction with the order of component mixing 1, Hhfacac, OP(OH)(OSiMe3)2 at a 1:2:2 molar ratio
lead to formation of a larger cluster [(Al(AlMe){Al(hfacac)}{μ3-O3P(OSiMe3)}2{μ2-O2P(OSiMe3)2}3)2] (8) containing both
S4R and 4=1 structural units. Similarly, Hacac (pentan-2,4-dione) provides an isostructural [(Al(AlMe){Al(acac)}{μ3-
O3P(OSiMe3)}2{μ2-O2P(OSiMe3)2}3)2] (9). Both molecules display Al centers in three different coordination environments.
other linear structures, layers, and finally to open frameworks
was proposed.17 The chains are built of corner- or edge-sharing
[Al2(μ2-O2PO2)2] single four rings (S4R), and their hydrolysis/
condensation leads to cross-linking to the porous layers and
subsequently to three-dimensional framework structures. In
related work on open-framework zinc phosphates, a similar
conclusion on the mechanism was formulated as it was shown
that low-dimensional structures, such as small clusters, serve as
the starting species that condense to chains or ladders and
subsequently transform to layers to finally form 3D frame-
works.18,19 This increasing tendency to rationalize the synthesis
turned the focus of research on finding new bottom-up
approaches to aluminophosphates. In an effort to contribute to
elucidation of the crystallization mechanism, the synthesis and
transformations of molecular aluminophosphate and -phospho-
nate compounds soluble in organic solvents were studied as
potential precursors and spectroscopic models for secondary
building units (SBU, Chart 1S, Supporting Information).20,21
The simplest of them are S4R,22−28 and they also proved to be
convenient single-source precursors for nonaqueous synthesis
INTRODUCTION
■
Aluminophosphates constitute an important and extensive class
of inorganic open-framework materials.1 They form porous
zeolite-like structures based on networks of alternating corner-
sharing AlOx (x = 4, 5, 6) polyhedra and PO4 tetrahedra. The
self-assembly process is influenced by the templating effect2 in
hydrothermal,3 solvothermal,4 or ionothermal5 synthetic
reactions. Because of the presence of channels and pores of
molecular dimensions, aluminophosphates have been used as
adsorbents and catalysts.6 Isomorphous substitution of
transition metals for Al and/or P in the framework7 led to
catalysts possessing, besides the shape selectivity, Brønsted and
Lewis acidity and redox functionality.8,9 The synthetic process
is still mostly empirical, although some advances in the
direction of rational design have been made.10 While the
traditional four-connected AlPO4 phases are usually prepared
under hydrothermal conditions, low-dimensional, chain, and
layer aluminophosphates with an Al/P ratio lower than 1 were
synthesized in mostly nonaqueous solvents.11−13 Besides the
classical view of assembly of molecular building units as the
underlying mechanism of crystallization of porous solids,14−16
a
new complementary model for formation of aluminophos-
phates based on stepwise transformations of a parent chain to
Received: January 13, 2014
Published: March 11, 2014
© 2014 American Chemical Society
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dx.doi.org/10.1021/ic500083a | Inorg. Chem. 2014, 53, 3753−3762

Inorganic Chemistry
Article
of aluminophosphate materials.23,27 Other molecular structural
units include complexes of various nuclearity and geometries of
central inorganic cores, such as cubic D4R,20,22,28−32 hexagonal
drum D6R,28,32,33 single six-ring S6R,34 tricyclic 6≡1,35 bicyclic
4=1,36,37 or large octameric,38 decameric,28,32,38,39 and dodeca-
meric40,41 clusters.
Molecular aluminophosphates and -phosphonates have been
predominantly synthesized by reactions of phosphonic acids or
alkoxy and aryloxy esters of phosphoric acid with aluminum
alkyls, alkoxides, or halides (for selected examples see Scheme 1
aluminum centers by forming chelates. Here we report our
results on the synthesis of nine new molecular aluminophos-
phates and -phosphonates as well as their structural analyses
and spectroscopic characterization.
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were performed under a
dry nitrogen atmosphere by Schlenk techniques or in a MBraun Unilab
drybox maintained under 1 ppm of O2 and H2O. Solvents were dried
over and distilled from Na/benzophenone under nitrogen. C6D6 and
toluene-d8 were dried over and distilled from Na/K alloy, while P4O10
was used for CDCl3 and CD2Cl2. Solvents were degassed prior to use.
AlMe3, AlEt3 (Sigma-Aldrich, 2 M in toluene), and AliBu3 (Sigma-
Aldrich, 1 M in hexane) were used as received. OP(OH)(OSiMe3)2
was prepared by a modified procedure from KH2PO4 and Me3SiCl.44
NMR spectra (1H, 13C, 27Al, 29Si, and 31P) were acquired on Bruker
AVANCE DRX 500 and 300 MHz spectrometers. Chemical shifts
were referenced to the residual protic impurities or solvent resonances
(1H and 13C) or externally to Al(acac)3, SiMe4, and H3PO4 (27Al, 29Si,
and 31P). Solid-state NMR spectra (13C, 27Al, 29Si, and 31P) were
collected on a wide-bore Varian INOVA 400 NMR spectrometer
(University of Tennessee) with a broad-band Chemagnetic 5 mm
MAS probe. Inside a drybox, samples were loaded into 5 mm pencil
rotors, stoppered with Teflon plugs, and sealed with silicon grease and
paraffin wax. Magic angle spinning rates were 5 kHz for 29Si and 13C
CPMAS and 10 kHz for 27Al and 31P MAS spectra. Chemical shifts
were referenced externally to 31P δ [H3PO4 (85%)] 0.0 ppm, 29Si δ
[(Me3SiO)8Si8O20] 11.72 ppm, 27Al δ [Al(H2O)63+] 0.0 ppm, 13C δ
[adamantane] 38.68 ppm. IR spectra (4000−400 cm−1) were collected
on Bruker EQUINOX 55/S/NIR and TENSOR 27 FTIR
spectrometers. Samples were prepared as KBr pellets. CHN elemental
Scheme 1. Elimination Reactions Leading to S4R
Aluminophosphates and Aluminophosphonates
Table 1. Cyclic Aluminophosphates and
Aluminophosphonates (S4R) Synthesized by Different
Elimination Reactions According to Scheme 1
X
Y
Z
R
G
X−G
product
SiMe3
SiMe3
SiMe3
SiMe3
SiMe3
SiMe3
H
OSiMe3
OSiMe3
OSiMe3
OSiMe3
OSiMe3
OSiMe3
OtBu
OSiMe3
OSiMe3
OSiMe3
OSiMe3
OSiMe3
cHex
Me
Et
tBu
Me
Et
Cl
Me3SiCl 124
Me3SiCl 224
Me3SiCl 1022
́
Cl
analyses were carried out by Instituto de Quimica, UNAM. Melting
points were measured in sealed capillaries and are uncorrected.
Thermal analysis (TG/DSC) was measured on a Netzsch STA 449C
Jupiter apparatus from 25 to 1100 °C under flowing air (70 mL min−1)
with a heating rate of 5 K min−1. APCI-MS measurement was
performed on an Agilent 6224 TOF LC-MS system. Solid samples
were dissolved in toluene. Samples were injected via syringe pump
KDS model 100 Series (KD Scientific, Inc., USA) into the electrospray
ion source at a flow rate of 30 μL min−1 for 2 min long analyses.
Spectra were recorded both in positive and in negative mode for m/z
30−3200 Da at 4 GHz tuning for high-resolution instrument mode. A
drying gas temperature of 200 °C and drying gas flow of 7 l/min with
30 psig for the nebulizer pressure were used for ionization of analytes
in ion source/ESI. The fragmentor was set to 10 V, and the capillary
voltage was −2000/4000 V ( APCI). Single-crystal diffraction data
were collected on a KUMA KM-4 κ-axis diffractometer with graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å) and a CCD camera
at 120 K. Intensity data were corrected for Lorentz and polarization
effects. Details of data collection and refinement are summarized in
Table 2. The structure was solved by direct methods and refined by
full-matrix least-squares methods using the SHELXTL program
package.45 H atoms were positioned geometrically and refined as
riding.
Cl
Me
Et
Me4Si
Me3SiEt 224
124
Me
Me
Me
Me
Et
iBu
Me
Et
tBu
OiPr
tBu
Me
Me
Me
Me
Et
iBu
Me
Et
tBu
OiPr
tBu
Me4Si
MeH
MeH
MeH
EtH
iBuH
MeH
EtH
tBuH
iPrOH
tBuH
4, this work
OtBu
tBu
1123
H
OSiMe3
OSiMe3
OSiMe3
OSiMe3
OPh
1225
H
OSiMe3
OSiMe3
OSiMe3
OPh
1, this work
2, this work
3, this work
26
H
H
H
H
OPh
OPh
26
1326
H
OPh
OPh
OtBu
23
H
OtBu
(14)2
a
H
OH
Me
28
a
OH was subsequently silylated by Me3SiNMe2 to OSiMe3.
and Table 1). These reactions are based on elimination of
trimethylsilylchloride, alkanes, alkylsilanes, or alcohols. We are
interested in developing reaction protocols leading to
polyhedral aluminophosphates and -phosphonates and specif-
ically in our novel synthetic route based on dealkylsilylation of
trimethysilylesters of phosphoric and phosphonic acids in the
reaction with organoaluminum compounds.24,42,43 As the
number of well-characterized molecular aluminophosphates
and -phosphonates, which could serve as precursors and models
of aluminophosphate structural units, is relatively limited, we
decided to study the synthesis of new S4R molecules by alkane
and alkylsilane elimination. Furthermore, we explored their
subsequent transformations to larger entities with the Al/P
ratio lower than 1 by employing OP(OH)(OSiMe3)2 as cage-
extending reagent. We also applied reactions with Hhfacac and
Hacac as capping agents that would modify the reactivity of
Synthesis of [(AlR2{μ2-O2P(OSiMe3)2})2], R = Me (1), Et (2). A
solution of OP(OH)(OSiMe3)2 (2.00 mmol, 484 mg) in toluene (2.0
mL) and a 2.0 M solution of AlR3 (2.0 mmol, 1.0 mL) were
simultaneously added to 5.0 mL of toluene at 0 °C. After mixing of
components, an ice bath was removed and the reaction mixture stirred
at room temperature until gas evolution ceased. All volatile
components were removed under vacuum. Crystals were grown by
slow cooling of a saturated hexane solution. Yields of 1 and 2 (80%)
were comparable to previously published results, and crystal and
spectroscopic data agree with the literature.24
Synthesis of [(AliBu2{μ2-O2P(OSiMe3)2})2] (3). A solution of
OP(OH)(OSiMe3)2 (2.00 mmol, 484 mg) in hexane (2.0 mL) and
a solution of AliBu3 (1.0 M, in hexane, 2.0 mmol, 2.0 mL) were
simultaneously added dropwise to hexane (5.0 mL) at 0 °C. The
resulting mixture was stirred at room temperature for 2 days. All
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Inorganic Chemistry
Article
Table 2. Crystallographic Data and Structure Refinement Parameters for Compounds 4 and 6−9
4
6
7
8
9
empirical formula
C22H52Al2O6P2Si2
C38H86Al3F12O24P5Si9 C40H93Al3F12O28P6Si10· 1/8
C60H152Al6F12O44P10Si16·
2THF
C60H164Al6O44P10Si16
C6H14
fw
584.72
1643.67
monoclinic
P21/c
1808.58
triclinic
2871.04
triclinic
2510.93
triclinic
cryst syst
triclinic
space group
P1
̅
P1
̅
P1
̅
P1
̅
temp., K
120(2)
120(2)
120(2)
120(2)
120(2)
λ, Å
0.71073
0.71073
17.207(2)
21.720(3)
21.770(3)
90
0.71073
0.71073
0.71073
a, Å
8.5098(10)
10.6686(10)
10.8765(17)
98.789(14)
112.477(12)
107.401(9)
829.76(23)
1
14.6903(2)
16.3775(2)
23.1011(4)
92.7310(10)
107.4470(10)
114.682(2)
4721.04(12)
2
13.9324(3)
16.0191(4)
16.7797(5)
81.927(2)
77.855(2)
77.631(2)
3558.29(16)
1
13.9640(4)
17.0083(8)
17.4120(7)
61.565(3)
83.837(3)
79.157(4)
3570.8(2)
1
b, Å
c, Å
α, deg
β, deg
91.442(13)
90
γ, deg
V, Å3
8134(2)
4
Z
μ, mm−1
0.287
0.365
0.352
0.378
0.354
no. of reflns collected
6386
86 474
56 277
42 811
41 330
no. of indep reflns (Rint) 2860 (0.0382)
14 302 (0.0185)
14 302/108/908
16 544 (0.0281)
16 544/928/1292
12 482 (0.0386)
12 482/6/747
11 822 (0.0706)
11 822/427/805
no. of data/restraints/
params
2860/0/154
GoF on F2
0.979
1.075
1.088
1.058
1.040
a
b
R1, wR2 (I > 2σ(I))
0.0457, 0.1132
0.0803, 0.1227
0.357/−0.282
0.0448, 0.1228
0.0654, 0.1331
1.106/−0.779
0.0686, 0.2194
0.0990, 0.2317
1.426/−0.622
0.0539, 0.1439
0.0976, 0.1739
0.709/−0.410
0.0702, 0.2290
0.1050, 0.2409
1.886/−0.723
a
b
R1, wR2 (all data)
largest diff. peak/hole,
e·Å−3
a
b
2
2
R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = [∑w (Fo − Fc2)2/∑(Fo )2]1/2
.
volatile components were removed under vacuum. Crystals grown at
Synthesis of [(Al(hfacac)2{μ2-O2P(OSiMe3)2})2] (5). To a stirred
solution of 1 (0.680 mmol, 407 mg) in toluene (10 mL), excess
Hhfacac (0.4 mL, 20 mmol) was added dropwise at 0 °C. The reaction
was accompanied by exothermic evolution of gaseous byproducts. The
resulting clear colorless solution was then stirred at room temperature
for 30 min, and then all volatile components were evaporated under
vacuum. Slow cooling of a saturated solution of 5 in hexane to −25 °C
provided colorless crystals that were used for X-ray diffraction analysis.
Yield: 0.88 g (95%). Mp: subl. 216 °C. 1H NMR (300.1 MHz, toluene-
d8): δ 0.09 (s, C2h, 9H, POSi(CH3)3), 0.23 (s, D2, 36H, POSi(CH3)3),
0.34 (s, C2h, 9H, POSi(CH3)3), 6.26 (s, 6H, both isomers,
(CF3CO)2CH). 19F{1H} NMR (282.4 MHz, toluene-d8): δ −76.4
(s, 2F, D2), −76.5 (s, 1F, C2h), −77.6 (s, 2F, D2), −77.7 (s, 1F, C2h).
27Al NMR (78.1 MHz, toluene-d8): δ −6.0 (s). 29Si{1H} NMR (99.3
−25 °C from saturated hexane solution were unsuitable for X-ray
1
diffraction analysis. Yield: 0.50 g (65%). Mp: 96−98 °C. H NMR
3
(300.1 MHz, CDCl3): δ −0.18 (d, JHH = 7.0 Hz, 8H, AlCH2CH-
3
(CH3)2), 0.26 (s, 36H, POSi(CH3)3), 0.89 (d, JHH = 6.6 Hz, 24H,
3
AlCH2CH(CH3)2), 1.81 (app-non, JHH
= 6.6 Hz, 4H,
AlCH2CH(CH3)2). 13C APT NMR (75.5 MHz, CDCl3): δ 0.84 (d,
3JPC = 2.1 Hz, POSi(CH3)3), 22.55 (br s, AlCH2CH(CH3)2), 26.16 (s,
AlCH2CH(CH3)2), 28.49 (s, AlCH2CH(CH3)2). 29Si{1H} NMR (59.6
MHz, CDCl3): δ 22.9 (d, 2JPSi = 5.1 Hz). 31P{1H} NMR (121.5 MHz,
CDCl3): δ −29.6 (s). IR (KBr pellet, cm−1): ν 2948 m, 2862 m, 2784
vw, 1465 w, 1421 w, 1377 w, 1361 w, 1319 w, 1259 s (δCH3), 1223 s,
1180 m, 1129 s (νPO), 1062 vs (νSiO), 855 vs (ρCH3), 762 m
(ρCH3), 680 m, 613 w. MS (EI 30 eV), m/z (rel int %): 702 (42) [M
− iBu]+, 648 (100) [M − SiMe3 − (CH3)2CH]+, 73 (90) [Si(CH3)3]+.
Anal. Calcd for C28H72Al2O8P2Si4: C, 43.95; H, 9.49. Found: C, 42.94;
H, 9.27.
MHz, toluene-d8) 22.6 (s, C2h), 23.8 (s, D2), 24.2 (s, C2h). 31P{1H}
NMR (121.5 MHz, toluene-d8): δ −31.0 (br s, POSi(CH3)3). IR (KBr
pellet, cm−1): ν 2970 w, 2908 w, 1670 m, 1654 s (νCO), 1569 m,
(νCO) 1540 m, 1497 m (νCO + νCC), 1468 m, 1258 vs (νCF3), 1218
s (νCF3), 1162 s, 1146 s (δCH), 1123 m, 1054 m (νSiO), 854 s
(ρCH3), 805 m, 764 w (ρCH3), 747 w, 671 m, 614 w, 604 w, 593 w,
534 w, 419 w. MS (m/z, rel int): APCI(−) 1364.0098 (100) [M]−
(theor 1364.0116), 1290.9625 (51) [M − SiMe3]− (theor 1290.9643).
Anal. Calcd for C32H40Al2F24O16P2Si4: C, 28.16; H, 2.95. Found: C,
28.00; H, 2.84. TG/DSC: sublimes at 240−270 °C at atmospheric
pressure.
Synthesis of [(AlMe2{μ2-O2P(OSiMe3)(cHex)})2] (4). To a stirred
c
solution of HexP(O)(OSiMe3)2 (2.06 mmol, 634 mg) in toluene (5
mL), a solution of AlMe3 in toluene (2.0 M, 1.0 mL, 2.0 mmol) was
added. The reaction mixture was heated under reflux at 120 °C for 3
days and then concentrated to 1 mL. Subsequent slow cooling to −25
°C provided colorless crystals suitable for X-ray diffraction analysis.
Yield: 0.261 g (45%). Mp: 96−100 °C. 1H NMR (300.1 MHz,
CDCl3): δ −1.18 (s, cis-Al(CH3)2), −1.16 (s, trans-Al(CH3)2), −1.15
(s, cis-Al(CH3)2), all three signals 12H, 0.06 (s, 18H, POSi(CH3)3),
1.00−1.71 (m, 22H, PC6H11). 13C APT NMR (75.5 MHz, CDCl3): δ
Synthesis of [AlMe{Al(hfacac)}2{μ3-O3P(OSiMe3)}2{μ2-O2P-
(OSiMe3)2}2{OP(OSiMe3)3}] (6). A solution of OP(OH)(OSiMe3)2
(1.00 mmol, 242 mg) in toluene (5.0 mL) was added at room
temperature to a solution of 1 (0.494 mmol, 295 mg) in toluene (5.0
mL). After evolution of gas ceased, the solution of Hhfacac (0.500
mmol, 104 mg) in toluene (2.0 mL) was added to the reaction
mixture. Further evolution of gas was observed. After reaction, all
volatile components were removed under vacuum and crystals were
grown by slow cooling of the saturated solution of 6 in hexane to −25
°C. Identical product was obtained when the reaction was carried out
3
−9.57 (br s, AlCH3), 1.07 (d, JPC = 1.1 Hz, POSi(CH3)3), 1.12 (d,
3JPC = 1.4 Hz, POSi(CH3)3), 26.03−26.42 (m, PCH(CH2)5), 36.63 (d,
1
1JPC = 156.0 Hz, PCH(CH2)5), 36.67 (d, JPC = 156.6 Hz,
PCH(CH2)5). 29Si{1H} NMR (59.6 MHz, CDCl3): δ 22.4 (s), 22.6
(s). 31P{1H} NMR (121.5 MHz, CDCl3): δ 12.7 (s, cis), 13.0 (s,
trans). IR (KBr pellet, cm−1): ν 2933 s, 2857 m, 1452 m, 1283 m, 1258
s (δCH3), 1219 s, 1204 vs, 1177 m, 1130 s, 1105 vs (νPO), 1062 vs
(νSiO), 899 w, 892 w, 851 vs (ρCH3), 830 m, 771 m, 763 m (ρCH3),
683 vs, 619 w, 604 w, 566 w, 545 w. MS (EI 30 eV), m/z (rel int %):
569 (100) [M − CH3]+.
1
in THF. Yield: 0.235 g (43% based on Al). Mp: 179−182 °C. H
NMR (300.1 MHz, benzene-d6): δ −0.38 (s, 3H, AlCH3), 0.28 (s,
27H, POSi(CH3)3), 0.29 (s, 18H, POSi(CH3)3), 0.32 (s, 18H,
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POSi(CH3)3), 0.52 (s, 18H, POSi(CH3)3), 6.23 (s, 1H,
(CF3CO)2CH), 6.24 (s, 1H, (CF3CO)2CH). H NMR (500.1 MHz,
−24.6(s), −29.0 (br s). IR (KBr pellet, cm−1): ν 2965 w, 2905 vw,
1670 w (νCO), 1560 w, 1529 w, 1508 w, 1503 w, 1421 vw, 1258 s
(νCF3), 1205 s (νCF3), 1148 s (δCH), 1119 m, 1053 s (νSiO), 851 vs
(ρCH3), 795 w, 764 w (ρCH3), 694 w, 671 w, 609 w, 509 w. MS (m/z,
rel int) APCI(+): 2903.1256 (7) [M − 2Me + hfacac]+, 2711.1597
(10) [M − Me]+, 2695.1107 (8), 2677.1032 (7), 2639.1199 (5),
2623.0919 (11), 2605.0632 (12), 2485.1384 (40) [M − O2P-
(OSiMe3)2]+, 2413.0953 (17) [M − O2P(OSiMe3)2 − SiMe3]+,
2397.0676 (78) [M − O2P(OSiMe3)2 − SiMe3 − Me]+, 2362.0099
(25) [M − 2O2P(OSiMe3)2 − SiMe3 − Me + hfacac]+, 2324.0298
(17) [M − O2P(OSiMe3)2 − SiMe3 − OSiMe3]+, 1661.1630 (47) [M/
2 + OP(OSiMe3)3 − Me]+, 1627.1046 (23) [M/2 + SiMe3 + hfacac −
Me]+, 1589.1239 (38) [M/2 + OP(OSiMe3)2(OH) − Me]+,
1435.1400 (100) [M/2 + SiMe3]+, 1363.1007 (40) [M/2 + H]+.
Synthesis of [(Al(AlMe){Al(acac)}{μ3-O3P(OSiMe3)}2{μ2-O2P-
(OSiMe3)2}3)2] (9). A solution of Hacac (1.00 mmol, 101 mg) in
toluene (2 mL) was added dropwise to a solution of 1 (298 mg, 0.500
mmol) in toluene (5 mL) at room temperature. After the evolution of
gas ceased, the solution of OP(OH)(OSiMe3)2 (1.00 mmol, 242 mg)
in toluene (2.0 mL) was transferred dropwise to the reaction mixture
and the resulting system stirred at room temperature for 3 h. Volatile
components were removed under vacuum, and the solid residue was
combined with hexane (4 mL). Formation of crystalline phase was
achieved by slow cooling of the saturated solution to −25 °C. Yield:
0.095 g, (23% based on Al). Mp: 138−142 °C. 1H NMR (300.1 MHz,
benzene-d6): δ −0.34 (s, 6H, AlCH3), 0.26, 0.27, 0.30, 0.41, 0.48
(144H, POSi(CH3)3,), 1.87 (12H, (CH3CO)2CH), 5.28 (2H,
(CH3CO)2CH). 31P{1H} NMR (121.5 MHz, benzene-d6): δ −21.8
(s, 2P), −23.2 (s, 1P), −28.1 (s, 2P). 13C CP MAS NMR (100.55
MHz): δ 1.71 (POSi(CH3)3), 27.2 (CH3CO)2CH), 188.6
(CH3CO)2CH). 27Al MAS NMR (182.6 MHz): δ −15.7 (AlVI), 5.4
(AlV), 45.1 (AlIV). 29Si CP MAS NMR (79.4 MHz): δ 15.1, 16. 9, 17.6,
18.2, 19.7, 20.0, 20.4, 21.1. 31P MAS NMR (161.9 MHz): δ −26.9
(2P), −31.4 (2P), −37.9 (1P). IR (KBr pellet, cm−1): ν 2962 w, 2902
vw, 1618 w(νCO), 1535 w, 1460 w, 1414 w, 1255 s (δCH3), 1207 m,
1144 m, 1115 m, 1045 s (νSiO), 930 vw, 850 vs (ρCH3), 762 w
(ρCH3), 692 w, 660 vw, 609 w, 579 vw. MS (m/z, rel int) ESI(+):
2511.3375 (7) [M + H]+ (theor 2511.3360), 2269.2810 (25) [M −
O2P(OSiMe3)2]+, 2197.2400 (15) [M − O2P(OSiMe3)2 − SiMe3 +
H]+, 1954.1831 (13) [M − 2 O2P(OSiMe3)2 − SiMe3]+, 1327.2113
(17) [M/2 + SiMe3]+, 1255.1724 (26) [M/2 + H]+, 1013.1155 (100)
[M/2 − O2P(OSiMe3)2]+.
1
dichloromethane-d2): δ −0.99 (s, 3H, AlCH3), 0.12 (br s, 18H,
POSi(CH3)3), 0.22 (s, 18H, POSi(CH3)3), 0.26 (br s, 18H,
POSi(CH3)3), 0.30 (s, 27H, POSi(CH3)3), 6.01 (s, 1H,
(CF3CO)2CH), 6.07 (s, 1H, (CF3CO)2CH). 19F{1H} NMR (282.4
MHz, benzene-d6): δ −75.7 (s, 6F, (CF3CO)2CH), −77.0 (s, 6F,
(CF3CO)2CH). 31P{1H} NMR (121.5 MHz, benzene-d6): δ −23.1 (br
s, 2P, μ3-O3P(OSiMe3)), −27.6 (s, 1P, μ2-O2P(OSiMe3)2), −28.9 (br
s, 1P, μ2-O2P(OSiMe3)2), −32.3 (br s, 1P, OP(OSiMe3)3). 31P{1H}
NMR (202.4 MHz, dichloromethane-d2): δ −24.7 (br s, 2P, μ3-
O3P(OSiMe3)), −29.3 (s, 1P, μ2-O2P(OSiMe3)2), −30.6 (br s, 1P, μ2-
O2P(OSiMe3)2), −33.9 (br s, 1P, OP(OSiMe3)3). 13C CP MAS NMR
(125.8 MHz):δ −0.86 (AlCH3), 0.24 (POSi(CH3)3), 90.4
(CF3CO)2CH), 117.4 (CF3CO)2CH), 178.3 (CF3CO)2C H). 27Al
MAS NMR (130.3 MHz): δ −11.5 (AlVI), −8.7(AlVI), 46.8 (AlIV). 29Si
CP MAS NMR (99.4 MHz): δ 15.8, 16.9, 17.6, 18.6, 20.5, 21.1, 22.3,
25.3 IR (KBr pellet, cm−1): ν 2965 w, 2906 w, 1670 m (νCO), 1559 w
(νCO), 1529 m, 1513 m, 1424 w, 1258 vs (νCF3), 1247 s, 1241 s,
1201 s (νCF3), 1145 s (δCH), 1117 s (νPO), 1069 s (νSiO), 1046 s,
850 vs (ρCH3), 795 w, 764 m (ρCH3), 696 w, 671 w, 613 w, 592 w,
532 w, 489 w. MS (m/z, rel int) APCI(+): 1627.1072 (27) [M −
Me]+ (theor 1627.1140); 1435.1430(63) [M − hfacac]+ (theor
1435.1494); 1121.0494 (100) [M − hfacac − OP(OSiMe3)3]+ (theor
1121.0534). APCI(−): 1535.0356 (58) [M + hfacac − OP-
(OSiMe3)3]− (theor 1535.0301); 1328.0469 (100) [M − OP-
(OSiMe3 )3 ]− (theor 1328. 0420). Anal. Calcd for
C38H86Al3F12O24P5Si9: C, 27.77; H, 5.27. Found: C, 27.38; H, 5.13.
Synthesis of [Al{Al(hfacac)}2{μ3-O3P(OSiMe3)}2{μ2-O2P-
(OSiMe3)2}2H{OP(O)(OSiMe3)2}2] (7). To a stirred cooled solution (0
°C) of 1 (0.500 mmol, 298 mg) in toluene (5 mL), Hhfacac (0.500
mmol, 104 mg) diluted in toluene (5.0 mL) was added dropwise. The
reaction mixture was then warmed to room temperature. After gas
evolution ceased, the reaction was cooled down in ice bath and a
solution of OP(OH)(OSiMe3)2 (1.500 mmol, 373 mg) in toluene (5
mL) was added. The reaction mixture was stirred at 70 °C for 3 h, and
then all volatile components were removed under vacuum. Dissolution
of an oily residue in a minimum amount of hexane (0.5 mL) with
subsequent cooling in a freezer (−25 °C) provided colorless crystals
within 2 weeks. Yield: 0.145 g (24% based on Al). Mp: 134−138 °C.
1H NMR (300.1 MHz, benzene-d6): δ 0.26 (s, 36H, POSi(CH3)3),
0.31 (s, 18H, POSi(CH3)3), 0.32 (s, 18H, POSi(CH3)3), 0.54 (s, 18H,
POSi(CH3)3), 6.25 (s, 2H, (CF3CO)2CH), 14.72 (br s, 1H, POH).
19F{1H} NMR (282.4 MHz, benzene-d6): δ −75.9 (s, (CF3CO)2CH).
27Al NMR (182.6 MHz, toluene-d8): δ −9.9 (AlVI), 50.3 (AlIV).
31P{1H} NMR (202.4 MHz, toluene-d8): δ −22.7 (s, 1P), −24.8 (s,
RESULTS AND DISCUSSION
■
Reactions of equimolar amounts of OP(OH)(OSiMe3)2 with
i
AlR3 (R = Me, Et, Bu) led to elimination of particular alkanes
2P), −27.7 (br s, 2P), −30.2 (s, 1P). 27Al MAS NMR (182.6 MHz): δ
−17.2 (AlVI), −11.9 (AlVI), 47.7 (AlIV). IR (KBr pellet, cm−1): ν 2966
w, 2906 vw, 1672 m (νCO), 1618 vw (νCC), 1560 w (νCO), 1529 w,
1514 w, 1419 vw, 1257 s (νCF3), 1205 s (νCF3), 1153 s (δCH), 1147
s (δCH), 1119 m, 1059 s, 850 vs (ρCH3), 793 w, 762 m (ρCH3), 696
vw, 671 w, 611 w, 592w, 532w, 501 w. MS (m/z, rel int) APCI(−):
1795.1145 (100) (theor 1795.1148) [M − H]−, 1761.0554 (78),
1723.0750 (52) [M − SiMe3]−, 1588.1099 (34) [M − hfacac]−,
1554.0666 (82) [M − O2P(OSiMe3)2]−, 1515.0778 (43) [M − hfacac
− SiMe3]−, 1481.0193 (15) [M − O2P(OSiMe3)2 − SiMe3]−.
(Scheme 1, Table 1) and provided molecular aluminophos-
phates 1−3 in good yields. These molecules possess cyclic
[Al2(μ2-O2PO2)2] cores as shown by the single-crystal X-ray
diffraction analyses, mass spectrometry, and NMR spectroscopy
measurements. Their synthesis represents a useful extension of
known routes for compounds 1 and 2 that were previously
prepared by both trimethylsilylchloride and trimethylalkylsilane
elimination.24 In contrast to previously published deal-
kylsilylation condensation of OP(OSiMe3)3 with trialkylalumi-
num compounds, this new approach requires only mild
reaction conditions. Moreover, it employs homoleptic alumi-
num alkyls AlR3 which unlike AlR2Cl do not undergo R/Cl
ligand scrambling reactions that may complicate product
mixtures. Most reactions were accompanied by formation of
gaseous byproducts which provided a visible tool for observing
the course of the reaction. This synthetic method proved to be
Synthesis of [(Al(AlMe){Al(hfacac)}{μ3-O3P(OSiMe3)}2{μ2-O2P-
(OSiMe3)2}3)2] (8). To a stirred solution of 1 (0.500 mmol, 298 mg)
in toluene (5.0 mL) a solution of Hhfacac (1.00 mmol, 208 mg) in
toluene (2.0 mL) was added dropwise followed by slow addition of a
solution of OP(OH)(OSiMe3)2 (1.00 mmol, 242 mg) in toluene (2.0
mL). Both steps were accompanied by evolution of gas. Volatile
components were removed under vacuum, and a white solid residue
was redissolved in tetrahydrofuran. Cooling below 0 °C provided
crystalline product within several days. Yield: 0.120 g (26% based on
i
particularly useful in producing the new Bu derivative 3
1
Al). Mp: 154.5−155.5 °C. H NMR (300.1 MHz, dichloromethane-
because bulkier organic groups on the Al atoms hinder
dealkylsilylation of OP(OSiMe3)3 with AliBu3 and the adduct
AliBu3·OP(OSiMe3)3 showed only a low conversion to cyclic
aluminophosphate 3. An extension of our dealkylsilylation
d2): δ −0.89 (s, 6H, AlCH3), 0.23, 0.24, 0.26, 0.27, 0.30 (s, 144H,
POSi(CH3)3), 6.10 (s, 1H, (CF3CO)2CH). 19F{1H} NMR (282.4
MHz, dichloromethane-d2): δ −76.8 (s, (CF3CO)2CH). 31P{1H}
NMR (121.5 MHz, dichloromethane-d2): δ −22.8 (br s), −23.8 (s),
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c
principle to the reaction of HexP(O)(OSiMe3)2 with AlMe3
showed it applicability to the synthesis of aluminophospho-
nates. Unsymmetrically substituted cyclic [(AlMe2{μ2-O2P-
(OSiMe3)(cHex)})2] (cis/trans-4, Chart 2S, Supporting In-
formation) was prepared by Me4Si elimination, and its trans
isomer was structurally characterized. The molecular structure
of trans-4 is presented in Figure 1, and the bonding metrics are
Figure 1. Molecular structure of trans-4. All CH3 groups at Si and H
c
atoms of Hex and Al−CH3 substituents were omitted for clarity.
Thermal ellipsoids are drawn at the 30% probability level.
gathered in Table 3. Bond distances and angles compare well
with the corresponding parameters in the related molecule 1225
and other cyclic [Al2(μ2-O2PO2)2] cores.
1H NMR spectra of 4 revealed the presence of both isomers.
Molecular symmetry of the cis isomer (C2v) resulted in two
resonances of the Al(CH3)2 moieties at −1.18 and −1.15 ppm,
while the trans isomer (C2h) revealed only one at −1.16 ppm.
The resonances of POSi(CH3)3 were not resolved in two
separate lines. Even though the 13C{1H} NMR spectra
displayed only one broad resonance for Al(CH3)2 at −9.57
ppm, the presence of two isomers was revealed in two doublets
of POSi(CH3)3 groups at 1.07 and 1.12 ppm and two doublets
c
for the tertiary carbons of the Hex substituents at 36.63 and
36.67 ppm. Similarly, 31P{1H} NMR spectra show two expected
singlet resonances at 12.7 (cis) and 13.0 (trans) ppm of integral
intensities of 0.8:1; presumed higher thermodynamic stability
of the trans configuration prompted us to assign to it the latter
signal.25 The 29Si{1H} NMR spectrum also revealed two
different resonances at 22.4 and 22.6 ppm for cis and trans,
respectively. The stability of the cyclic [Al2(μ2-O2PO2)2] core
in the gas phase was exhibited in the EI mass spectrum by the
base peak at m/z 569 for the [M − CH3]+ fragment.
For our further studies of reactivity of the aluminophosphate
S4R molecules, we selected compound 1 as a starting point.
This simplest building unit can be used for structural
description and computer modeling of many types of zeolitic
frameworks.46 Interestingly, molecular four rings were identi-
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Chart 1. Two Isomeric Forms of Cyclic Aluminophosphate 5
Scheme 2. Reactions Leading to Molecular Aluminophosphates 6, 7, and 8
fied by NMR spectroscopic methods in hydrothermal reaction
solutions during the course of aluminophosphate crystalliza-
tion.47,48 The precursor 1 possesses reactive functionalities both
on Al and on P atoms and could be used for building larger
units. We selected two reagents; OP(OH)(OSiMe3)2 was
expected to react preferentially with the Al−CH3 groups, by
either CH4 or Me4Si elimination, extend the molecule, and
change the Al/P ratio. The second reagent was chelating
pentanedione as a capping agent that would saturate the
coordination sphere of Al and prevent uncontrolled oligo/
polymerization of these polyfunctional reagents and formation
of untractable mixtures. Hhfacac was chosen over Hacac, which
reacts with 1 to completely dismember its cyclic molecule to
Al(acac)3. Interestingly, Hacac was shown to promote cage
rearrangement of a cubic aluminophosphonate [{tBuAl(μ3-
O3PMe)}4] to decameric [{tBuAl(μ3-O3PMe)}10] without
being incorporated in the product.28
The combination 1 with excess Hhfacac led to gas evolution,
which suggested replacement of methyl groups originally
bonded to the Al atoms by hfacac ligands accompanied by
CH4 release. The reaction proceeded quantitatively according
to NMR measurements, no byproducts were observed, and a
crystalline product was obtained. X-ray diffraction analysis
revealed molecular structures of 5 belonging to the D2 point
group (Chart 1).49 The inorganic [Al2(μ2-O2PO2)2] core of the
starting aluminophosphate is retained; however, both Al atoms
in 5 are chelated by two hfacac ligands and display octahedral
coordination environments. Multinuclear NMR study of the
reaction mixture reveals two sets of signals representing two
isomeric forms of 5. The isomerism arises from two different
orientations of the hfacac substituents (Chart 1). The integral
intensity of representative signals in the NMR spectra suggests
a 1:2 ratio of C2h and D2 forms. Compound 5 was surprisingly
stable against hydrolysis. No changes were observed after 24 h
treatment with H2O at room temperature. The 31P NMR
spectrum of 5 at room temperature contained only one broad
resonance at −31.0 ppm, but after cooling to −20 °C the signal
shifted downfield and split to two resonances (−30.1 and −30.4
ppm, approximately 2:1) representing the two isomers of 5.
The 1H NMR spectrum contained three signals of Me3Si
groups; their integral intensities were in the 1:4:1 ratio and thus
agreed with the 1:2 molar ratio of isomers (C2h:D2). Methine
hydrogens showed only one resonance at room temperature,
which was split in two signals at −20 °C. The dynamic nature
of the C2h/D2 isomer equilibrium was revealed in the 19F NMR
spectra. Four singlets of the CF3 groups were observed at room
temperature, while at 90 °C, the two low-field singlets
coalesced and the two high-field ones started to overlap.
Reaction of cyclic 1 with 2 equiv of OP(OH)(OSiMe3)2
followed by addition of 1 equiv of Hhfacac (Scheme 2)
provided a new aluminophosphate cluster 6. Single-crystal X-
ray diffraction analysis revealed the molecule to contain three
Al and five P atoms (Figure 2). One aluminum atom is four
coordinate with one unreacted CH3 group, while the other two
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and the longest Al−O(P) distance in complex 6 is the
coordination bond to OP(OSiMe3)3 (Al2−O7 1.891(2) Å).
Interestingly, the P3−O7 bond in this moiety is at the shortest
end of the P−O(Al) range (1.469(2)−1.532(2) Å). The P−
O(Al) bonds involving tetrahedral Al atoms and tridentate [μ3-
O3P(OSiMe3)]2− are longer (1.53 Å) in comparison with
octahedral (1.50 Å). Al−O−P bond angles are from 130.1(2)°
to 146.5(1)°.
1H, 19F{1H}, and 31P{1H} NMR spectra correspond with the
Cs molecular symmetry of 6 in solution. The methyl group on
aluminum presents a high-field singlet in the 1H NMR at −0.38
ppm. The resonances at 0.28, 0.29, 0.32, and 0.52 ppm in a
3:2:2:2 intensity ratio represent the inequivalent trimethylsilyl
groups. The pair of singlet resonances at 6.23 and 6.24 belongs
to methine hydrogens of two distinct hfacac ligands. Their CF3
resonances in the 19F{1H} spectrum at −75.69 and −76.98
ppm are in the expected 1:1 ratio. The 31P{1H} NMR spectrum
displays four broadened resonances at −23.1, −27.6, −28.9,
and −32.3 in a 2:1:1:1 ratio that may be assigned to [μ3-
O3P(OSiMe3)]2−, [μ2-O2P(OSiMe3)2]−, [μ2-O2P(OSiMe3)2]−,
and OP(OSiMe3)3 moieties, respectively. The most shielded
signal represents tris(timethylsilyl)ester coordinated to one Al
atom. Broadening of signals points to a dynamic chemical
exchange process. Low-temperature 1H and 31P{1H} NMR
spectra were acquired in the range from +30 to −80 °C. The
width of signals decreased on cooling; however, the number of
signals remained unchanged. Solid-state 13C CP MAS NMR
spectra revealed only one set of resonances for the hfacac
ligands (178.3, 117.4, and 90.4 ppm) and two signals (0.24 and
−0.86 ppm) for unresolved trimethysilyl groups. The 27Al MAS
NMR spectrum featured four-coordinate Al at 46.8 ppm and
octahedral Al atoms at −8.7 and −11.5 ppm. Eight resolved
resonances in the 29Si CP MAS NMR spectrum is in accord
with 9 trimethylsilyl groups in 6 considering a general position
of the molecule in the unit cell. The mass spectra APCI( )
demonstrate the stability of the Al3(PO4)4 inorganic core.
Changing the order of reagent addition and using one extra
equivalent of OP(OH)(OSiMe3)2 (Scheme 2) we isolated 7
that is closely related to 6 in having the same inorganic core.
However, 7 differs from 6 in substitution of the CH3 group at
tetrahedral Al by the −OP(O)(OSiMe3)2 moiety and one
molecule of OP(OH)(OSiMe3)2 instead of OP(OSiMe3)3
being coordinated to the octahedral Al atom. The molecular
structure of 7 is shown in Figure 3 and features a Cs molecular
symmetry. The Al−O(P) bonds at the tetrahedral Al atom are
in the range Al(3A) 1.729(4)−1.757(3) Å, while at the
octahedral Al atoms are longer 1.823(3)−1.888(3) Å. Similarly
to 6, one can distinguish longer P−O(Al) bonds directed
toward tetrahedral Al atoms in comparison to the bonds with
Figure 2. Molecular structure of 6. All SiMe3 and H atoms at CH3 and
hfacac groups were omitted for clarity. Thermal ellipsoids are drawn at
the 30% probability level.
Al are six coordinate with capping hfacac ligands. The Al
centers are connected by two tridentate [μ3-O3P(OSiMe3)]2−
and two bidentate [μ2-O2P(OSiMe3)2]− bridging phosphates.
One of the octahedral Al atoms is coordinated by the
phosphoryl oxygen of OP(OSiMe3)3. This points to a silylation
of the starting diester OP(OH)(OSiMe3)2 during the reaction.
One can identify the 4=1 zeolitic SBU (Chart 2) in the
framework of 6. This unit, however, is extended by two [μ2-
O2P(OSiMe3)2]− bridges and a terminal OP(OSiMe3)3 group.
A related aluminophosphonate cage 15 was structurally
characterized, possesses all Al atoms in octahedral coordination
environment, and also contains two extra AlCl3 molecules
coordinated at the periphery (Chart 2).50
The bonding distances reveal elongation of the Al−O(P)
bonds with increasing coordination number of Al. Tetrahedral
Al3−O(P) bonds fall into a narrow range 1.770(2)−1.777(2) Å
(average 1.774 Å), which corresponds well with the values
found in corner CH3−AlO3 groups (average 1.76 Å) of
tetrameric cubic aluminophosphonate [{MeAl(μ3-O3PPh)}4].51
Octahedral Al−O(P) bonds are longer (1.818(2)−1.891(2) Å),
Chart 2. Molecules Containing the Structural Motif of a 4=1 Secondary Building Unit
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−9.9 ppm and one at 50.3 ppm representing the unique Al
center. Four broad signals in the 31P{1H} NMR spectrum at
−22.7, −24.8, −27.7, and −30.2 ppm in a 1:2:2:1 intensity ratio
also suggest an intramolecular dynamic process. The solid-state
27Al MAS NMR spectrum represents the static structure of 7
with three inequivalent Al atoms, two octahedral at −17.2 and
−11.9 ppm and one four-coordinate at 47.7 ppm. Mass spectra
display as the base peak the molecular fragment [M − H]− at
m/z 1795 attesting to a good stability of the cluster framework.
Using a relatively large proportion of the capping Hhfacac
reagent in comparison to OP(OH)(OSiMe3)2 (Scheme 2), we
isolated the hexanuclear cluster 8. Single-crystal X-ray
diffraction analysis revealed the molecular structure depicted
in Figure 4. This aluminophosphate contains Al and P atoms in
Figure 3. Molecular structure of 7. All SiMe3 groups and H atoms of
hfacac and OP(OH)(OSiMe3)2 ligands were omitted for clarity.
Thermal ellipsoids are drawn at the 30% probability level.
Figure 4. Molecular structures of 8. All SiMe3 groups and H atoms of
Al−CH3 and hfacac ligands were omitted for clarity. Thermal
ellipsoids are drawn at the 30% probability level.
six-coordinate Al atoms. The Al−O−P bond angles in the
molecule 7 are found in a broader range (115.6(4)−162.3(2)°)
than in 6.
Disorder in the crystal structure of 7 at O2P(OSiMe3)2
groups connected to a four-coordinate Al atom together with
the results of the NMR spectroscopy showing a higher
molecular symmetry C2v than expected from X-ray structural
analysis suggest a dynamic tautomeric exchange in solution
(Scheme 3). Although the P−OH proton was not located in
the electron density map, a low-field resonance at 14.72 ppm
a 3:5 ratio. The centrosymmetric molecule (point group Ci) is
constructed from one four ring of the starting molecule 1 and
two 4=1 units analogous to 6 and 7 (Charts 2 and 3). The Al
atoms of the central four ring are shared with the peripheral
units making them five coordinate. That contributes to the
presence of Al centers in three different coordination
environments: 4, 5, and 6. There are two types of phosphate
bridging units: four tridentate [μ3-O3P(OSiMe3)]2− and six
bidentate [μ2-O2P(OSiMe3)2]−.
Al−O(P) bond distances correspond to a particular
coordination number of the Al atoms and fall in the following
ranges: Al(CN 4) 1.754(3)−1.772(3) Å, Al(CN 5) 1.789(3)−
1.864(3) Å, and Al(CN 6) 1.829(3)−1.877(3) Å. The P−
1
may be assigned to it in the H NMR spectrum. It contains
only 4 resonances of the trimethylsilyl groups (0.26, 0.31, 0.32,
and 0.54 ppm) in a 2:1:1:1 ratio, and also the methines of the
hfacac groups display only one singlet at 6.25 ppm. Similarly,
only one resonance in the 19F{1H} NMR spectrum suggests
chemical equivalence of the hfacac groups. The 27Al NMR
spectrum reveals only one signal of the octahedral Al atoms at
Scheme 3. Possible Dynamic Exchange Process in 7
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Reaction of 1 with excess Hhfacac results in replacement of
all four methyl groups by chelating hfacac ligands, and the
obtained molecular compound 5 contains two octahedrally
coordinated Al atoms. The molecules of 5 display geometric
isomerism caused by two possible mutual positions of hfacac
substituents. The presence of both C2h and D2 forms in the
reaction mixture was evidenced by NMR spectroscopy. Further
linking of cyclic molecule 1 to higher aluminophosphates by
excess OP(OH)(OSiMe3)2 leads to cage molecules 6 and 7.
They contain in their inorganic core the [Al3{μ3-O3P-
(OSiMe3)}2{μ2-O2P(OSiMe3)2}2] units that can be thought
of as the 4=1 building units of zeolites with two extra phosphate
bridges. Finally, tuning the reagent ratio lead to formation of
large cluster [(Al(AlMe){Al(hfacac)}{μ3-O3P(OSiMe3)}2{μ2-
O2P(OSiMe3)2}3)2] 8 containing the central S4R ring with two
peripheral 4=1 structural units attached. Isostructural com-
pound 9 is isolated when Hacac is used instead of Hhfacac.
Both molecules display the Al centers in four-, five-, and six-
coordinate environments. The isolated series of aluminophos-
phate molecules demonstrates the ability to build larger
structural units by a controlled step-by-step process employing
a simple molecular four-ring (S4R) precursor 1, OP(OH)-
(OSiMe3)2 as a phosphate source, and Hhfacac as a capping
reagent. The single four ring is first extended to a bridged four
ring (4=1) and then to a complex structure containing a larger
assembly of the building blocks.
Chart 3. Schematic Representation of Molecule of 8
Emphasizing the 4=1 and S4R Structural Motifs
O(Al) bonds are in the 1.460(3)−1.5439(3) Å range. The
coordination geometry around Al centers is thus described as
deformed tetrahedral (CN 4), trigonal bipyramidal (CN 5, β =
174.89°, α = 123.29°, τ = 86%),52 and deformed octahedral
(CN 6). Al−O−P bond angles are 134.7(2)−160.8(2)°.
1
The H NMR spectrum displays a singlet at −0.89 ppm for
the methyl group on a four-coordinate Al atom. Five singlet
resonances at 0.23−0.30 ppm represent trimethylsilyl groups,
and one at 6.13 ppm belongs to hfacac methines. The 19F{1H}
spectrum displays only one singlet at −76.8 ppm for the CF3
groups. This suggests a conformational fluxional process at the
five-coordinate Al centers as there is no plane of symmetry in
the molecule in the solid state (point group Ci) (Figure 4). The
31P{1H} NMR spectrum features only four signals at −22.8,
−23.8, −24.6 (sharp), −29.0 ppm that represent symmetry
inequivalent P atoms of the phosphate groups, pointing again
to a fluxional process introducing mirror symmetry.
ASSOCIATED CONTENT
* Supporting Information
Complete X-ray data for compounds 4−9. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
Replacing Hhfacac by Hacac as the capping agent, we
prepared and structurally characterized 9 that is isostructural
with 8. The molecular structure of 9 is shown in Figure 1S,
Supporting Information. Al−O(P) bond distances are Al(CN
4) 1.752(4)−1.81(3) Å, Al(CN 5) 1.780(3)−1.870(4) Å, and
Al(CN 6) 1.826(4)−1.904(8) Å. P−O(Al) bonds fall in the
range 1.465(8)−1.528(4) Å. The environment of the Al atom
in the trigonal bipyramidal site is slightly deformed (β =
175.41°, α = 123.46°, τ = 87%52). Al−O−P bond angles are
133.9(3)−159.4(2)°.
AUTHOR INFORMATION
Corresponding Author
■
*Phone: +420549496493. Fax: +420549492443. E-mail:
jpinkas@chemi.muni.cz.
Notes
The authors declare no competing financial interest.
CONCLUSIONS
Reactions of equimolar OP(OH)(OSiMe3)2 and trialkylalanes
provide molecular cyclic compounds [(AlR2{μ2-O2P-
(OSiMe3)2})2], R = Me (1), Et (2), Bu (3), by alkane
ACKNOWLEDGMENTS
■
■
This work was supported by CEITEC (Central European
Institute of Technology (CZ.1.05/1.1.00/02.0068)), by the
project Employment of Best Young Scientists for International
Cooperation Empowerment (CZ.1.07/2.3.00/30.0037), and by
MOBILITY 7AMB13DE006. The authors thank Dr. Z. Zdrahal
and B. Vrbkova (MU) for MS measurements, Dr. C. E. Barnes
and Dr. J. Abbott for solid-state NMR (University of
Tennesse), and Dr. V. Jancik (UNAM) for CHN analyses.
i
elimination, while unsymmetrically substituted [(AlMe2{μ2-
O2P(OSiMe3)(cHex)})2] (cis/trans-4) is prepared by deal-
kylsilylation reaction of cHexP(O)(OSiMe3)2 with AlMe3.
These molecules present cyclic [Al2(μ2-O2PO2)2] alumino-
phosphate cores that mimic the single four-ring building unit
(S4R) of zeolitic, layered, and chain aluminophosphates. The
findings represent a useful extension of known methods leading
to molecular aluminophosphates as it allows preparation of
cyclic aluminophosphates bearing bulkier organic groups on Al
atoms. The presence of reactive methyl groups bonded to Al
atoms motivated us to further study the reactivity of a selected
representative of this family of building units. Compound 1 was
used in reactions with Hhfacac, used as a capping agent to
control growth of aluminophosphate molecules by saturating Al
coordination sites, and with OP(OH)(OSiMe3)2, employed as
a bridging reagent, with the aim to extend this simplest four
ring to larger cage aluminophosphates. We successfully
prepared and structurally characterized a series of five new
molecular aluminophosphates 5−9 of different nuclearity.
DEDICATION
■
Dedicated to Professor J. G. Verkade on the occasion of his
79th birthday.
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