Adamantane-like aluminum amide-phosphate from alumazene

Article abstract of DOI:10.1021/ic0257625

A dealkylsilylation reaction between alumazene [2,6-(i-Pr)₂C₆H₃NAlMe]₃ (1) and tris(trimethylsilyl) ester of phosphoric acid (2) in a 1:3 molar ratio provides the heteroadamantane molecule (MeAl)[2,6-(i-Pr)₂C₆H₃ N]₃{Al[OP(OSiMe₃)₃]}₂- (O₃POSiMe₃) (3). Compound 3 was characterized by analytical and spectroscopic methods, and its molecular structure was established by a single-crystal X-ray diffraction experiment. Moreover, trialkyl and triaryl phosphates and dialkyl phosphonates react with 1 at elevated temperature to afford an intractable mixture of products. The reaction of phosphonic acids with 1 proceeds under decomposition to yield 2,6-diisopropylaniline and aluminophosphonates.

Full text of DOI:10.1021/ic0257625

Inorg. Chem. 2002, 41, 6914−6918
Adamantane-like Aluminum Amide-Phosphate from Alumazene
,†
Jiri Pinkas,* Jiri Lo1bl,† Dalibor Dastych,† Marek Necas,† and Herbert W. Roesky‡
Department of Inorganic Chemistry, Masaryk UniVersity, CZ-61137 Brno, Czech Republic, and
Institut fu¨r Anorganische Chemie, UniVersita¨t Go¨ttingen, D-37077 Go¨ttingen, Germany
Received June 2, 2002
A dealkylsilylation reaction between alumazene [2,6-(i-Pr)2C H NAlMe]3 (1) and tris(trimethylsilyl) ester of phosphoric
6
3
acid (2) in a 1:3 molar ratio provides the heteroadamantane molecule (MeAl)[2,6-(i-Pr)2C H N]3{Al[OP(OSiMe3)3]}2-
6
3
(O POSiMe3) (3). Compound 3 was characterized by analytical and spectroscopic methods, and its molecular
3
structure was established by a single-crystal X-ray diffraction experiment. Moreover, trialkyl and triaryl phosphates
and dialkyl phosphonates react with 1 at elevated temperature to afford an intractable mixture of products. The
reaction of phosphonic acids with 1 proceeds under decomposition to yield 2,6-diisopropylaniline and alumino-
phosphonates.
Introduction
ols, triaminosilanes, and piano-stool metal trifluorides pro-
vided products with related adamantane-like cores. Silane-
triols and triaminosilanes react with 1 by a formal 3-fold
addition of their O-H and N-H groups on the Al-N bonds,
respectively.6 A different reactivity mode was observed in
the case of metal trifluorides. The fluorine atoms coordinate
to the aluminum centers, and a subsequent fluorine-nitrogen
exchange leads to new bimetallic amidofluorides.7 Finally,
an incremental fluorination of 1, with a stepwise substitution
of the three methyl groups by fluorides, was accomplished
by Me3SnF.8
We are also interested in developing new routes to
aluminophosphate microporous materials by nonaqueous and
building-block synthetic methods. To this end, we developed
reactions of phosphoric acid triesters with aluminum amides9
and alkyls.10 In these reaction mixtures we have evidenced
Alumazene [2,6-(i-Pr)2C6H3NAlMe]3 (1) still remains, after
more than a dozen years from its first synthesis,1 the sole
example of a trimeric iminoalane ring isoelectronic with
benzene, borazine, and the B-P, Al-P, Ga-P, and Al-
As2 analogues. This exclusivity can be ascribed to the
extreme reactivity of 1, which stems from a high polarity of
the Al-N bonds and from a small delocalization of the π
electrons in the ring. The fortunate choice of substituents
stabilizes a very reactive electronically and coordinately
unsaturated system. Other combinations of organic groups
on Al and N led to the formation of higher iminoalane
oligomers or to the activation of ligand C-H bonds.3
Alumazene is also important as the first example of imino-
alanes with coordination numbers of three at both aluminum
and nitrogen. More recent examples of such compounds
include monomeric4 and dimeric5 iminoalanes. In contrast
to the extensive and well-understood chemistry of borazine,
the reactions of its heavier counterparts are much less
developed. The chemical reactivity of 1 was examined on
several occasions. Interestingly, the reactions with silanetri-
(5) (a) Schulz, S.; Ha¨ming, L.; Herbst-Irmer, R.; Roesky, H. W.; Sheldrick,
G. M. Angew. Chem. 1994, 106, 1052; Angew. Chem., Int. Ed. Engl.
1994, 33, 969. (b) Fisher, J. D.; Shapiro, P. J.; Yap, G. P. A.;
Rheingold, A. L. Inorg. Chem. 1996, 35, 271. (c) Wehmschulte, R.
J.; Power, P. P. J. Am. Chem. Soc. 1996, 118, 791. (d) Schulz, S.;
Voigt, A.; Roesky, H. W.; Ha¨ming, L.; Herbst-Irmer, R. Organome-
tallics 1996, 15, 5252. (e) Wehmschulte, R. J.; Power, P. P. Inorg.
Chem. 1998, 37, 6906.
* Author to whom correspondence should be addressed. Phone:
+420541129335; fax: +420541211214; e-mail: jpinkas@chemi.muni.cz.
† Masaryk University.
(6) Wessel, H.; Rennekamp, C.; Waezsada, S.-D.; Roesky, H. W.;
Montero, M. L.; Uson, I. Organometallics 1997, 16, 3243.
(7) (a) Wessel, H.; Rennekamp, C.; Roesky, H. W.; Montero, M. L.;
Mu¨ller, P.; Uso´n, I. Organometallics 1998, 17, 1919. (b) Wessel, H.;
Montero, M. L.; Rennekamp, C.; Roesky, H. W.; Yu, P.; Uso´n, I.
Angew. Chem. 1998, 110, 862; Angew. Chem., Int. Ed. 1998, 37, 843.
(8) Wessel, H. Ph.D. Dissertation, Go¨ttingen University, Go¨ttingen,
Germany, 1999.
(9) Pinkas, J.; Wessel, H.; Yang, Y.; Montero, M. L.; Noltemeyer, M.;
Fro¨ba, M.; Roesky, H. W. Inorg. Chem. 1998, 37, 2450.
(10) Pinkas, J.; Chakraborty, D.; Yang, Y.; Murugavel, R.; Noltemeyer,
M.; Roesky, H. W. Organometallics 1999, 18, 523.
‡ Universita¨t Go¨ttingen.
(1) (a) Wagonner, K. M.; Hope, H.; Power, P. P. Angew. Chem. 1988,
100, 1765; Angew. Chem., Int. Ed. 1988, 27, 1699. (b) Wagonner, K.
M.; Power, P. P. J. Am. Chem. Soc. 1991, 113, 3385.
(2) Wehmschulte, R. J.; Power, P. P. J. Am. Chem. Soc. 1996, 118, 791.
(3) Power, P. P. J. Organomet. Chem. 1990, 400, 49.
(4) Hardman, N. J.; Cui, C.; Roesky, H. W.; Fink, W. H.; Power, P. P.
Angew. Chem. 2001, 113, 2230; Angew. Chem., Int. Ed. 2001, 40,
2172.
6914 Inorganic Chemistry, Vol. 41, No. 25, 2002
10.1021/ic0257625 CCC: $22.00 © 2002 American Chemical Society
Published on Web 11/12/2002

Aluminum Amide-Phosphate from Alumazene
a
Table 1. Crystal Data and Structure Refinement Details for 3‚C7H8
or surmised the presence of cyclic and polyhedral species
that are analogous to the secondary building units of
zeolites.11 In a parallel effort, we also prepared and structur-
ally characterized a series of molecular organic-soluble
aluminophosphonates that can serve as models mimicking
some of the structural motifs of microporous aluminophos-
phates, such as a single four-ring (4R),12 a single six-ring
(6R),13 a double four-ring (D4R),14 a double six-ring (D6R),15
and an incomplete cubic unit 6 ≡ 1.16 In our previous
attempts to employ 1 as a source of aluminum, the reaction
of OP(OMe)3 with 1 yielded a bis-adduct 1(OP(OMe)3)2.9
Here we report further investigation on the reactivity of
alumazene 1. The tris(trimethylsilyl) ester of phosphoric acid
(2) reacts with 1 with a dealkylsilylation and provides an
aluminum amide-phosphate cage compound with the central
heteroadamantane core, (MeAl)[2,6-(i-Pr)2C6H3N]3{Al[OP-
(OSiMe3)3]}2(O3POSiMe3) (3). This compound could serve
as a precursor for developing other structural units as it still
contains reactive groups.
empirical formula
C65H125Al3N3O12P3Si7
fw
T, K
1511.16
120(2)
cryst syst
space group
a, Å
b, Å
c, Å
triclinic
P1h (No. 2)
14.377(3)
21.051(4)
28.948(6)
96.93(3)
96.52(3)
90.28(3)
8639(3)
4
R, deg
â, deg
γ, deg
V, Å3
Z
calcd density, g cm-3
µ, mm-1
1.162
0.248
cryst size, mm
θ range, deg
no. of reflns colld
no. of unique reflns
no. of params
GOF on F2
R1 [I > 2σ(I)]
wR2 (all data)
largest diff. peak and hole, e A-3
0.20 × 0.10 × 0.10
3.07-25.00
56012
29447
1639
1.100
0.1219
0.1371
0.377, -0.378
2
2
2 2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑w(|Fo | - |Fc |)2/∑w|Fo | ]1/2
.
Experimental Section
General Procedures. All manipulations were performed under
a dry nitrogen atmosphere by Schlenk techniques or in a M. Braun
Unilab drybox. Solvents were dried over and distilled from Na/
benzophenone under nitrogen. Deuterated solvents were dried over
and distilled from Na/K alloy and degassed prior to use. Compound
1 was prepared according to the previously published procedure.1
NMR spectra (1H, 13C, 29Si, and 31P) were acquired on Avance
DRX 500 and 300 MHz spectrometers in C6D6 or toluene-d8.
Chemical shifts were referenced to the residual resonances of
solvents (7.15 and 128.5 ppm for 1H and 13C in C6D6, respectively)
or externally to SiMe4 and H3PO4 (29Si and 31P). Diffraction data
were collected on a KUMA KM-4 κ-axis diffractometer with
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) and a
CCD camera at 120 K. The intensity data were corrected for Lorentz
and polarization effects. Details of the data collection and refinement
are summarized in Table 1. The structure was solved by direct
methods and refined by full-matrix least-squares methods using the
SHELXTL program package.17 The H atoms were positioned
geometrically and refined as riding. Mass spectra were measured
on Finnigan MAT 8230 and MAT 95 (Fisons Instruments) systems.
IR spectra (4000-400 cm-1) were collected on an EQUINOX 55/
S/NIR FTIR spectrometer. Samples were prepared as KBr pellets.
The FT Raman spectral measurements with FT-RA module FRA
106/S were performed with a resolution of 1.5 cm-1. An air-cooled
Nd:YAG laser (1064 µm, max output 500 mW) was used for spectra
excitation. Elemental analyses were carried out by the Analytisches
Labor des Anorganischen Instituts, Go¨ttingen. Melting points were
measured in sealed capillaries and are uncorrected.
Synthesis of (MeAl)[2,6-(i-Pr)2C6H3N]3{Al[OP(OSiMe3)3]}2-
(O3POSiMe3) (3). Neat OP(OSiMe3)3 (0.740 g, 2.35 mmol) was
added dropwise by a syringe to alumazene 1 (0.502 g, 0.770 mmol)
in dry deoxygenated toluene (20 mL). The reaction mixture was
refluxed for 24 h under a flow of dry nitrogen. After being cooled
to room temperature, colorless crystals of 1 (0.39 g, 36%)
1
precipitated from the solution. mp: 268 °C dec. H NMR (500
1
MHz, toluene-d8): δ -0.904 (s, 13C satellites, JCH ) 113 Hz,
AlCH3, 3 H), 0.114 (s,29Si satellites, 2JSiH ) 6.7 Hz, 13C satellites,
1JCH ) 120 Hz, SiMe3 coordinated, 54 H), 0.632 (s,13C satellites,
1JCH ) 119 Hz, 29Si satellites, 2JSiH ) 7.1 Hz, SiMe3 apical, 9 H),
3
1.462, 1.470, 1.557, 1.615, 1.664, 1.674 (all d, JHH ) 6.8 Hz,
(CH3)2CH, 3 H, for the assignment see Supporting Information),
3
3
4.863 (sept, JHH ) 6.8 Hz, (CH3)2CH-on, 2 H), 4.962 (sept, JHH
) 6.8 Hz, (CH3)2CH-off, 4 H), 6.94 (t, p-C6H3, 3 H), 7.25 (m,
m-C6H3, 6 H). 13C{1H} NMR (125.76 MHz, benzene-d6): δ -13
(broad s, AlCH3), 1.40 (d, JPC ) 1.5 Hz, 29Si satellites, JSiC
)
3
1
60.3 Hz, SiMe3 coordinated), 2.19 (d, 3JPC ) 1.5 Hz, SiMe3 apical),
26.02, 27.15, 27.52, 28.07 (CH3)2CH-off, 27.78 (CH3)2CH-off,
27.21, 27.44 (CH3)2CH-on, 28.11 (CH3)2CH-on, 117.96, 118.00,
123.29, 123.51, 123.81, 123.90, 144.95, 145.57, 146.47, 147.42,
154.94, 155.83 (C6H3, for the assignment see Supporting Informa-
tion). 31P{1H} NMR (202.40 MHz, benzene-d6): δ -8.7 (s, apical,
1 P), -38.5 (s, coordinated, 2 P). 29Si{1H} NMR (99.36 MHz,
(11) Meier, W. M.; Olson, D. H. Atlas of Zeolite Structure Types;
Butterworth-Heinemann: London, 1992.
(12) Chakraborty, D.; Horchler, S.; Kra¨tzner, R.; Varkey, S. P.; Pinkas, J.;
Roesky, H. W.; Uso´n, I.; Noltemeyer, M.; Schmidt, H.-G. Inorg. Chem.
2001, 40, 2620.
(13) Yang, Y.; Pinkas, J.; Noltemeyer, M.; Roesky, H. W. Inorg. Chem.
1998, 37, 6404.
(14) Yang, Y.; Schmidt, H.-G.; Noltemeyer, M.; Pinkas, J.; Roesky, H.
W. J. Chem. Soc., Dalton Trans. 1996, 3609.
(15) Yang, Y.; Walawalkar, M. G.; Pinkas, J.; Roesky, H. W.; Schmidt,
H.-G. Angew. Chem. 1998, 110, 101; Angew. Chem., Int. Ed. 1998,
37, 96.
(16) Yang, Y.; Pinkas, J.; Schaefer, M.; Roesky, H. W. Angew. Chem. 1998,
110, 2795; Angew. Chem., Int. Ed. 1998, 37, 2650.
(17) SHELXTL, version 5.1; Bruker AXS: GmbH, Karlsruhe, Germany,
1998.
2
2
benzene-d6): δ 17.05 (d, JPOSi ) 2.7 Hz, apical), 26.47 (d, JPOSi
) 6.9 Hz, coordinated). IR (KBr pellet, cm-1): 3043 vw, 2960 s,
2905 w, 2866 w, 1582 vw, 1461 w, 1420 m, 1377 vw, 1357 vw,
1317 w, 1260 s, 1238 s, 1204 s, 1085 vs, 1062 vs, 899 m, 850 vs,
766 s, 724 w, 702 w, 618 w, 550 w, 492 w, 454 w. RA (cm-1):
3056 m, 3037 m, 2961 s, 2904 vs, 2866 s, 1585 s, 1462 m, 1442
m, 1417 m, 1260 s, 1237 w, 1207 w, 1155 w, 1104 w, 1042 m,
1003 m, 898 w, 784 w, 709 w, 642 m, 626 m, 283 m, 174 w, 148
w. Anal. Calcd for C58H117Al3N3O12P3Si7: C, 49.10; H, 8.32; Al,
5.71; N, 2.96; P, 6.55; Si, 13.82. Found: C, 50.78; H, 8.16; Al,
5.48; N, 2.79; P, 6.19; Si, 13.63.
Inorganic Chemistry, Vol. 41, No. 25, 2002 6915

Pinkas et al.
Results and Discussion
Synthesis and Spectroscopy. The reaction of alumazene
[2,6-(i-Pr)2C6H3NAlMe]3 (1) with tris(trimethylsilyl) phos-
phate (2) in a 1:3 molar ratio in boiling toluene resulted in
the formation of (MeAl)[2,6-(i-Pr)2C6H3N]3{Al[OP(OSi-
Me3)3]}2(O3POSiMe3) (3). Compound 3 was isolated in a
moderate yield and characterized by analytical and spectro-
scopic methods. Its molecular structure was established by
a single-crystal X-ray diffraction experiment, which revealed
an Al3N3O3P heteroadamantane core (vide infra).
The solution NMR spectra of 3 were consistent with the
Cs symmetry of the molecule. The high-field resonances in
both 1H (-0.904 ppm) and 13C{1H} NMR (-13 ppm) spectra
pointed to the presence of a remaining Al-CH3 group in the
molecule. Two proton singlets with a 1:6 intensity ratio
possessing 29Si satellites were assigned to the OSiMe3
Figure 1. Molecular structure of (MeAl)[2,6-(i-Pr)2C6H3N]3{Al[OP-
(OSiMe3)3]}2(O3POSiMe3) (3).
1
moieties. A set of six doublets in the H NMR spectrum
attested to the diastereotopicity of some i-Pr groups. The
corresponding methine septets display a 2:1 intensity ratio.
This implies that one 2,6-diisopropylphenyl group lies on
the molecular mirror plane. Its two i-Pr groups are chemically
inequivalent when the phenyl group rotates around the N-C
bond slowly on the NMR time scale. The other two aromatic
substituents are equivalent and situated away from the mirror.
Therefore, their methyl groups are diastereotopic and furnish
four separate signals. The assignment of the i-Pr signals to
on- and off-the-mirror-plane groups was accomplished by
the combination of H-1H COSY45 and H-13C HMQC
NMR experiments. We also recorded the 13C APT NMR
spectrum at room temperature, and it also revealed six
resonances for the isopropyl CH3 groups and thus confirmed
our insight gleaned from the proton spectrum. Moreover, 12
aromatic carbon signals that could be grouped in two sets
of six lines with an approximate 2:1 intensity ratio attest to
the slow rotation of the bulky 2,6-diisopropylphenyl groups
1
1
Figure 2. View of the molecular core of 3. All carbon and hydrogen atoms
were omitted for clarity.
Al-O-P angle can be estimated from the structural data
for related cubic alumino- and gallophosphonates21 to be as
large as 150°.
1
on the NMR time scale. The H-13C correlation table is
given in the Supporting Information.
Two singlets with a 2:1 intensity ratio in the 31P{1H} NMR
spectrum and two doublets in the 29Si{1H} NMR spectrum
displaying P-O-Si couplings evidenced the presence of two
types of the POSiMe3 moieties. The extremely deshielded
31P NMR signal at -8.7 ppm belongs to the apical phosphate
group (atom P(3) in Figures 1 and 2). In comparison with
other (SiO)nP(OAl)4-n moieties,10 this considerable downfield
shift may be ascribed to geometrical constraints to the bond
angles exerted by the adamantane framework. The decreasing
mean Al-O-P angle around a phosphorus center (i.e.,
closing) in aluminophosphates is known to correlate with
deshielding of its 31P NMR signal.18,19 The average of the
Al-O-P angles around the apical phosphorus in 3 is 117.4-
(7)°. In contrast, the 31P chemical shift of the (AlO)3POSiMe3
vertex in the cubic aluminophosphate [t-BuAl(µ-O)3P-
(OSiMe3)]4 (4) is -28.4 ppm,20 and the corresponding mean
1
The stepwise reaction course was followed by H, 29Si,
and 31P{1H} NMR spectroscopy in toluene-d8. We observed
the presence of intermediates and a small amount of the final
product 3 in the reaction mixture shortly after mixing. The
intensity of phosphorus resonances with the chemical shifts
of -18.3, -22.5, and -38.4 ppm and 29Si chemical shifts
of 27.7 and 20.6 ppm evolved with time, and the complete
disappearance of the starting ester 2 and the intermediates
1
was observed only after 48 h at room temperature. H and
29Si NMR spectra gave evidence to the formation of SiMe4
(18) Mu¨ller, D.; Jahn, E.; Ladwig, G.; Haubenreisser, U. Chem. Phys. Lett.
1984, 109, 332.
(19) Ramdas, S.; Klinowski, J. Nature 1984, 308, 521.
(20) Mason, M. R.; Matthews, R. M.; Mashuta, M. S.; Richardson, J. F.
Inorg. Chem. 1996, 35, 5756.
(21) (a) Mason, M. R.; Mashuta, M. S.; Richardson, J. F. Angew. Chem.
1997, 109, 249; Angew. Chem., Int. Ed. Engl. 1997, 36, 239. (b)
Mason, M. R.; Perkins, A. M.; Ponomarova, V. V.; Vij, A. Organo-
metallics 2001, 20, 4833.
6916 Inorganic Chemistry, Vol. 41, No. 25, 2002

Aluminum Amide-Phosphate from Alumazene
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 3
as the byproduct in a dealkylsilylation reaction. This kind
of reactivity is relatively rare, and we recently observed this
type of reaction between tris(trimethylsilyl) phosphate and
aluminum trialkyls.10
P(3)-O(7)
P(3)-O(8)
P(3)-O(9)
P(3)-O(10)
Al(1)-N(1)
Al(1)-N(3)
Al(2)-N(1)
Al(2)-N(2)
Al(3)-N(2)
Al(3)-N(3)
1.544(5)
1.523(5)
1.519(5)
1.527(4)
1.801(6)
1.812(6)
1.853(6)
1.844(6)
1.809(6)
1.819(6)
Si(7)-O(7)
1.645(5)
1.846(5)
1.885(5)
1.817(5)
Al(1)-O(9)
Al(2)-O(10)
Al(3)-O(8)
Although the detailed mechanism of this reaction is still
under investigation, from the changes in the NMR spectra
we can draw some preliminary conclusions. The primary
reaction step most probably involves an adduct formation
of 1 with OP(OSiMe3)3, similar to the one observed crys-
tallographically in the bis-adduct 1(OP(OMe)3)2.9 Coordina-
tion of the phosphate oxygen manifests a high acidity of the
three-coordinate aluminum centers in 1, which is caused by
a low degree of delocalization within the alumazene ring.22
This picture is further supported by the chemical shift values
of a reaction intermediate (31P -38.4 and 29Si 27.7 ppm)
that are very close to the resonances of a metal-coordinated
OP(OSiMe3)3 moiety in the final product 3 (31P -38.5 and
29Si 26.5 ppm) and also in R3Al(µ-O)P(OSiMe3)3 (R ) Me,
Et, 31P -31.7 and 29Si 26.7 ppm, both derivatives) and [Cl3-
Ti(µ-O2P(OSiMe3)2)(µ-Cl)2TiCl2OP(OSiMe3)3] (5, 31P -35.2
ppm).23
As the subsequent reaction event we envision the forma-
tion of a bridging O2P(OSiMe3)2 group in the bicyclic
intermediate B through dealkylsilylation of A. The NMR
signals of the intermediate B (31P -22.5 and 29Si 20.6 ppm)
are comparable to the values for the bis(trimethylsilyl)
phosphate bridge in 5 (31P -29.8 ppm)23 and the cyclic
molecule [Me2Al(µ-O)2P(OSiMe3)2]2 (31P -29.3 and 29Si
23.4 ppm).10 The formation of 3 is finally completed by a
second dealkylsilylation in B.
N(1)-Al(1)-N(3)
N(1)-Al(2)-N(2)
N(2)-Al(3)-N(3)
Al(1)-N(1)-Al(2)
Al(3)-N(2)-Al(2)
Al(1)-N(3)-Al(3)
114.7(3)
110.4(3)
114.8(3)
111.7(3)
111.6(3)
108.3(3)
products arise necessarily through the amide transfer from
the aluminum centers in 1 to phosphorus. This is similar to
our findings in the study of the Al(NMe2)3 reaction with OP-
(OPh)3.9 Such a ligand exchange prevents the desired
formation of Al-O-P bonds in the product, and aryl esters
of phosphoric acid are therefore not suitable starting com-
pounds for the preparation of aluminophosphates.
Phosphonic acids, RP(O)(OH)2 (R ) t-Bu, Ph), caused a
complete breakdown of the alumazene cycle, and we found
2,6-(i-Pr)2C6H3NH2 and poorly crystalline solid alumino-
phosphonate as the decomposition product.
Crystal Structure. To establish molecular geometry of
3, we performed an X-ray diffraction experiment on single
crystals grown by slow cooling of the toluene solution.
Compound 3 crystallizes with one toluene molecule of
solvation. The molecular structure of 3 is shown in Figure
1, and the pertinent crystallographic data are listed in Table
1. Selected bond distances and angles are gathered in Table
2.
There are two independent molecules in the unit cell. The
molecule contains a central Al3N3O3P adamantane unit with
pseudo-Cs symmetry (Figure 2). The connectivity in the six-
membered alumazene cycle is preserved, but the ring lost
its planarity. All aluminum atoms increased their coordination
number to four by forming bonds to the apical phosphate
moiety. Two of the aluminum atoms eliminated their methyl
groups in the dealkylsilylation reaction, and their coordination
sphere is supplemented by oxygens from the coordinated
phosphate esters. The nitrogen centers remained three-
coordinate, in contrast to the adamantane-like products of
reactions of 1 with silantriols and triaminosilanes.6 Further
comparison with 1 (Al-N ) 1.782(4) Å) reveals that the
Al-N bond distances in 3 are not equal and span a range of
1.80-1.85 Å. The two involving Al(2)-CH3 are slightly
elongated. Average intra-ring angles in the Al3N3 moiety are
wider on aluminum (110-114°) than on nitrogen (108-
112°). This situation is opposite to the one in compound 1
(Al-N-Al ) 124.7°, N-Al-N ) 115.3°) and may be
explained by the increased coordination number of aluminum
and the retained planar environment of nitrogen (average sum
of angles around N is 357°). The apical P(OSi)1(OAl)3 moiety
represents an addition to the list of molecular models of
various T-units in silicoaluminophosphates (SAPO).24 Phos-
Reactions of 1 with trialkyl and triaryl phosphates and
dialkyl phosphonates in toluene at ambient and elevated
temperatures gave only intractable mixtures of products. The
31P{1H} NMR spectra contained a number of resonances of
disparate intensities and attested to a more complex reaction
course. Interestingly, the spectrum of the triphenyl phosphate
reaction mixture contains signals that can be attributed to
compounds with P-N bonds. One can conclude that these
phate bond lengths are unremarkable. The average Papical
O-Si bond angle is 143.5(4)°.
-
(22) (a) Power, P. P.; Moezzi, A.; Pestana, D. C.; Petrie, M. A.; Shoner,
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Conclusions
We have shown a new reactivity mode for alumazene 1,
namely, the dealkylsilylation reaction with tris(trimethylsilyl)
Inorganic Chemistry, Vol. 41, No. 25, 2002 6917

Pinkas et al.
phosphate. A new cage compound 3 possessing the het-
eroadamantane core was isolated and characterized by
spectroscopic methods, and its structure was established by
the single-crystal X-ray diffraction experiment. This com-
pound may serve as a model for the structural moiety
P(OSi)1(OAl)3 in SAPO and also as a suitable starting
material for developing other structural units as it still
contains reactive groups.
GACR 203/01/1533 is gratefully acknowledged. J.P. thanks
the Humboldt Foundation for a generous donation of the
drybox and the M. Braun company for providing the moisture
analyzer.
Supporting Information Available: Complete X-ray data for
3 in CIF format, listing of the NMR spectra of 3, and the signal
assignment table. This material is available free of charge via the
Internet at http://pubs.acs.org.
Acknowledgment. Financial support for this work by the
VW Stiftung I-76833/2001, FRVS G4/597/2001 and the
IC0257625
6918 Inorganic Chemistry, Vol. 41, No. 25, 2002