Synthesis and characterization of the coordination polymer [(THF)K(μ-OPri)2Al(μ-OPri)2]n

Article abstract of DOI:10.1515/mgmc-2018-0004

Reaction of [Al(OPrⁱ)₃] with K(OPrⁱ), in 1:1 molar ratio in refluxing anhydrous tetrahydrofuran yields a polymeric complex [(THF)K(μ-OPrⁱ)₂Al(μ-OPrⁱ)₂]_n. The complex is characterized by spectroscopic studies and single crystal X-raydiffraction analysis.

Full text of DOI:10.1515/mgmc-2018-0004

Main Group Met. Chem. 2018; 41(1–2): 43–46
Short Communication
Ram Gopal, Nikita Sharma, Meena Nagar, Archana Chaudhary, Shaikh M. Mobin
and Rakesh Bohra*
Synthesis and characterization of the coordination
i
i
polymer [(THF)K(μ-OPr ) Al(μ-OPr ) ]
2
2 n
https://doi.org/10.1515/mgmc-2018-0004
(Meese-Marktscheffel et al., 1993). More recently, highly
pure α-Al O nano-rods have been synthesized by sol–gel
method from a new class of precursor of salicylaldehyde
modified aluminum (III) isopropoxide (Sanwaria et al.,
Received January 29, 2018; accepted March 20, 2018; previously
published online April 17, 2018
2
3
i
i
Abstract: Reaction of [Al(OPr ) ] with K(OPr ), in 1:1 molar
3
2
014).
Here we report the corresponding polymeric complex
ratio in refluxing anhydrous tetrahydrofuran yields a pol-
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ymeric complex [(THF)K(μ-OPr ) Al(μ-OPr ) ] . The com-
2
2
n
i
i
i
−
[
(THF)K(μ-OPr ) Al(μ-OPr ) ] (1) in which the [Al(OPr ) ]
2
2
n
4
plex is characterized by spectroscopic studies and single
crystal X-raydiffraction analysis.
anion and the potassium cation show an interesting coor-
dination mode with tetrahydrofuran (THF) (Figure 1). The
i
Keywords:
aminopyramidiene;
catalytic
activity; reaction of [Al(OPr ) ] (3.1785 g in ~30 mL of anhydrous
K{Al(OPr ) }]; [(THF)K(μ-OPr ) Al(μ-OPr ) ] ; X-ray structure. THF) with KOPr (1.5267 g) in 1:1 molar ratio in anhydrous
3
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i
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i
[
4
2
2 n
THF yields (1)
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anhydrous THF
Al(OPr ) +KOPr →
3
∆/3 h
There appears to be a growing interest in the chemistry
of heterometal alkoxides as synthons for the prepara-
tion of ultra homogeneous ceramic materials by sol–gel
technique (Caulton and Hubert-Pfalzgraf, 1990; Bradley
i
i
1
/n [(THF)K(µ-ΟPr ) Al(µ-ΟPr ) ]
2 2 n
1
This reaction was found to be quite simple and quan-
et al., 2001; Turova et al., 2002; Sakka et al., 2005; Kessler titative, yielding (4.66 g, 94%) compound 1 as a white
et al., 2006; Seisenbaeva et al., 2008; Dhayal et al., 2012; hygroscopic solid material. It is insoluble in non-coordi-
Potdevin et al., 2016; Schubert, 2016). The potassium nating solvents but can be recrystallized from THF to give
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alkoxido aluminate [K{Al(OPr ) }] in benzene, propen-2-ol a transparent crystal of [(THF)K(μ-OPr ) Al(μ-OPr ) ] . The
4
2
2 n
solution is an excellent and extensively used synthetic characteristic peaks observed in a mass spectrum of this
material (Caulton and Hubert-Pfalzgraf, 1990; Bradley compound are summarized in the Experimental section.
i
+
et al., 2001; Turova et al., 2002), which may catalyze a The most intense peak is [KAl(OPr ) CH CHO ], and major
2
3
variety of unusual reactions, particularly in coordinat- fragments occur which contain as many as two potassium
ing solvents. Sometime ago Meese-Marktscheffel and col- and two aluminum atoms.
1
leagues reported the crystal and molecular structure of
The nuclear magnetic resonance (NMR) ( H and
C{ H}) spectra of [(THF)K(μ-OPr ) Al(μ-OPr ) ] were
OPr ) Al(μ-OPr ) ] in which chains of alternating K and recorded in DMSO-d . It is difficult to assign bridging and
Al atoms are joined together by double OPr bridges terminal ligand. Since the polymer will break apart upon
dissolution, the spectra could very well be interpreted in
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1
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a polymeric potassium aluminum alkoxide [(Pr OH) K(μ-
2
2 2 n
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2
2
n
6
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terms of free and coordinated OPr groups only. There may
even be an equilibrium between both sets of signals. The
characteristic NMR signals of complex (1) are summarized
in the Experimental section. The important signals of the
NMR spectral studies are observed at the expected posi-
tions, supporting the crystal structure. The other chemi-
cal shift values appeared in the range of 4.10 and 1.91 ppm
*
Corresponding author: Rakesh Bohra, Department of Chemistry,
University of Rajasthan, Jaipur 302004, Rajasthan, India,
e-mail: rkbohrachem@gmail.com
Ram Gopal and Meena Nagar: Department of Chemistry, University
of Rajasthan, Jaipur 302004, Rajasthan, India
Nikita Sharma: Department of Chemistry, Government Girls College,
Chomu, Jaipur, Rajasthan, India
Archana Chaudhary and Shaikh M. Mobin: Discipline of Chemistry,
School of Basic Sciences, Indian Institute of Technology Indore,
Khandwa Road, Indore 452017, India
1
3
in proton and 66.97 and 28.38 ppm in C for O-CH and
CH , respectively, indicating coordination of THF with
2
-
2
potassium.
Unauthenticated
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4ꢀꢀꢀꢀꢁꢀR. Gopal et al.: [(THF)K(μ-OPr ) Al(μ-OPr ) ] synthesis and characterization
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4
2
2 n
Figure 1:ꢀORTEP plot of a cutout of the polymeric chain of
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[
(THF)K(μ-OPr ) Al(μ-OPr ) ] .
2 2 n
Selected interatomic distances (Å): K(2)-O(1) 2.722(3), K(2)-O(9)
.660(2), K(2)-O(8) 2.720(3), K(2)-O(10) 2.721(4), K(1)-O(5)2.667(4),
K(1)-O(3) 2.669(3), Al(2)-O(7) 1.748(3), Al(2)-O(9) 1.747(2), Al(2)-O(8)
2
1
.742(3), Al(1)-O(2) 1.742(3), Al(1)-O(4)1.745(3). Selected interatomic
angles (°): O(10)-K(2)-O(1)#2 91.81(13), O(9)-K(2)-O(8) 59.33(7), O(9)-
K(2)-O(10) 99.93(14), O(8)-K(2)-O(10) 92.97(13), O(2)#2-K(2)-O(8)
Figure 2:ꢀORTEP plot of [C HN (CH ) NH ].
1
11.50(8), O(9)-K(2)-O(1)#2 130.47(10), O(9)-K(2)-O(2)#2 118.86(9),
4
2
3
2
2
Selected interatomic distances (Å): N(2)-C(3) 1.342(3), N(3)-
C(1)1.338(3), N(1)-C(1) 1.326(3), N(3)-C(5) 1.327(2), N(1) H(2)N
O(9)-Al(2)-O(7) 114.84(13), O(6)-Al(2)-O(9) 113.38(13), O(8)-Al(2)-O(7)
1
14.52(13), Al(2)-O(8)-K(2) 99.52(11), Al(2)-O(7)-K(1) 99.38(10), Al(2)-
0
.85(3), N(1)-H(1)N 0.85(3), C(2)-C(1) 1.391(3), C(6)-H(6)A 0.9600,
C(6)-H(6)B 0.9600, C(6)-H(6)C 0.9600. Selected interatomic angles
°): C(5)-N(3)-C(1) 116.94(17), N(2)-C(3)-C(4) 115.59(18), N(2)-C(3)-C(2)
21.65(17), N(2)-C(5)-N(3) 126.67(18).
O(6)-K(1) 101.06(11), Al(2)-O(9)-K(2) 101.62(11).
(
1
Single crystals of 1 suitable for X-ray diffraction analy-
sis were obtained from its solution in THF. Surprisingly, the
Cambridge structural database indicates that only a few
structurally characterized potassium aluminum alkoxides
have been reported (Allen et al., 1979). To our knowledge,
no polymeric potassium aluminum alkoxide in which THF
is attached to the potassium cation in penta-coordination
mode has been structurally characterized. Compound 1 is
believed to be the first example for such a structure. An
attempt to prepare the corresponding acetonitrile deriva-
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(
Figure 1) in which four [(THF)K(μ-OPr ) Al(μ-OPr ) ] units
2 2
containing penta-coordinated potassium cations and
tetra- coordinated aluminate anions are linked by double
i
OPr bridges. The geometry around aluminum is distorted
tetrahedral, and potassium is distorted square pyramidal.
In compound 1, each potassium atom is coordinated by
i
four oxygen of OPr and one oxygen of THF molecule.
The K-O distance of 2.721 Å for the THF ligand in 1 is
quite comparable with that reported in potassium THF
coordinated complexes (Brooker et al., 1991; Janiak and
Hemling, 1994; Ruhlandt-Senge and English, 1996). The
observed K-O distances of potassium alkoxide range from
i
tive by the reaction of K[Al(OPr ) ] (0.74g) with anhydrous
4
CH CN (~10 mL) resulted in the formation of an unex-
3
pected aminopyramidiene (2) (0.81 g, 10%) after crystal-
lization in acetonitrile (Figure 2), which is characterized
only by single crystal X-ray analysis. It appears that the
2
.669(4) to 2.799(4) Å (average 2.700 Å). These values are in
i
reaction is catalyzed by K[Al(OPr ) ]. The action of the
4
good agreement with the range found in other potassium
alkoxide derivatives (2.7–2.9 Å) (Veith and Rosler, 1986;
Vaartstra et al., 1990; Brooker et al., 1991; Coan et al., 1991;
McGeary et al., 1991, 1992; Meese-Marktscheffel et al., 1993).
Most of the interatomic distances and angles of 1
are very similar to those reported earlierin the poly-
alkoxide catalyst in the trimerization of acetonitrile could
be the effect of a base/nucleophile. The structure of 2 has
already been reported by Zhaoxiang and Wenfeng (2004).
i
anhydrous CH CN
3
K[Al(Opr ) ] → C HN (CH ) NH
2
4
∆/3 h
4
2
3
2
2
The important signals of the spectroscopic studies meric structure (Meese-Marktscheffel et al., 1993). The
[
Electrospray ionization (ESI)] of the (1) are observed at observed average Al-O bond distance in 1 is 1.743 Å,
the expected positions, supporting the crystal structure. which may be comparable with that of an average
i
The mass spectrometric studies (ESI) and X-ray crystallo- Al-O distance in [{Al(OPr ) } ] (Turova et al., 1979;
3
4
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1
graphic details suggest formation of a polymeric structure Folting et al., 1991), [(Pr OH) K(μ-OPr ) Al(μ-OPr ) ] and
2
2
2
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R. Gopal et al.: [(THF)K(μ-OPr ) Al(μ-OPr ) ] synthesis and characterizationꢂꢁꢀꢀꢀꢂ45
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2
2 n
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[
C H O{CH=N(C H )}] Al(μ-OPr ) Al(OPr ) (Sharma et al., with a low-temperature attachment. Data were collected at 150(2)
6
4
6
5
2
2
2
K using graphite-monochromated Mo-Kα radiation (λ ꢀ=ꢀ0.71073 Å).
2
002). The crystal structure of 2 observed by us (Figure 2)
isvery similar to that reported earlier by Zhaoxiang and
α
The strategy for the data collection was evaluated by using the
CrysAlisPro CCD software. The data were collected by the standard
ϕ-ω scan techniques and were scaled and reduced using CrysAlis
Pro RED software. The structure was solved by direct methods using
Wenfeng (2004).
i
The above studies suggest that [K{Al(OPr ) }] is not
4
only an excellent synthon in common organic solvents but SHELXS-97 and refined by full matrix least squares with SHELXL-97,
2
refining on F , giving R and Rw values of 0.0744 and 0.2092, respec-
may also behave differently in coordinating solvents. It
tively. The positions of all the atoms were obtained by direct methods.
can easily catalyze the trimerization of anhydrous CH CN
3
All non-hydrogen atoms were refined anisotropically. The remaining
to aminopyramidiene.
hydrogen atoms were placed in geometrically constrained positions
and refined with isotropic temperature factors, generally 1.2ꢀ×ꢀ9 Ueq
of their parent atoms. All the H-bonding interactions, mean plane
analyses, and molecular drawings were obtained using the program
Experimental details
Ortep. Atomic coordinates, bond lengths and angles, and thermal
parameters have been deposited at the Cambridge crystallographic
All the experimental manipulations were carried out under strictly data center (CCDC No. 1547839, 1548137). Symmetry transformations
anhydrous conditions. Solvents and reagents (RANKEM, India) were used to generate equivalent atoms were #1 x, −yꢀ+ꢀ1, zꢀ−ꢀ1/2, #2 x,
dried and purified by conventional methods and distilled/sublimed −yꢀ+ꢀ1, zꢀ+ꢀ1/2.
prior to use (Vogel, 1989). Due precautions were taken to handle
hazardous chemicals like benzene. Aluminum(III) isopropoxide was
The crystal data and refinement are summarized below:
ψ
Crystal data (1): C H Al K O , Mꢀ=ꢀ1498.11, crystal sizeꢀ=ꢀ0.33ꢀ×ꢀ
6
4
144
4
4
20
synthesized and purified as reported in the literature (Bradley et al., 0.26ꢀ×ꢀ0.21 mm
, monoclinic, space groupꢀ=ꢀC 2/c, Uꢀ=ꢀ9217.6(8),
3
1
13
2
001). The H and C NMR data were collected on a Bruker 300 FT aꢀ=ꢀ44.603(3) Å, bꢀ=ꢀ9.7009(3) Å, cꢀ=ꢀ25.9657(14) Å, αꢀ=ꢀ90°, βꢀ=ꢀ124.872°,
NMR spectrometer at 300.1 and 75.45 MHz, respectively, in a solution γꢀ=ꢀ90°, Zꢀ=ꢀ4, tetramer, Dcꢀ=ꢀ1.080 Mg m−3, μ(Mo-Kα)ꢀ=ꢀ0.71073; 30 783
of DMSO-d using TMS as internal standard. ESI mass spectra were reflections collected with 3.12ꢀ<ꢀ2θꢀ<ꢀ25.00° at 150(2) K, of these
6
performed on an Agilent 1100 LC/MSD SL quadrupole mass spectro- 30 783 were unique and 8114 which had Fꢀ>ꢀ1.0325 were used in struc-
meter (Agilent LC/MSD API-Electrospray SL G2708DA).
tural analysis.
ψψ
Crystal data (2): C H N , Mꢀ=ꢀ246.32, crystal sizeꢀ=ꢀ0.90ꢀ×ꢀ
1
2
18
6
3
3
0
.80ꢀ×ꢀ0.60 mm , monoclinic, space groupꢀ=ꢀP2 /n, Uꢀ=ꢀ665.16(8) Å ,
aꢀ=ꢀ7.4018(4) Å, bꢀ=ꢀ7.7991(6) Å, cꢀ=ꢀ11.6748(8), αꢀ=ꢀ90°, βꢀ=ꢀ99.267(6)°,
γꢀ=ꢀ90°, Zꢀ=ꢀ2, Dcꢀ=ꢀ1.230 Mg m , μ(Mo-Kα)ꢀ=ꢀ0.71073; 4533 reflections
collected with 3.8440ꢀ<ꢀ2θꢀ<ꢀ31.20 at 150(2) K, of these 4533 were
unique and 1170 which had Fꢀ>ꢀ1.195 were used in structural analysis.
1
i
Preparation of [K{Al(OPr ) }THF]
4
n
−3
i
Potassium metal (0.6088 g) was dissolved in dry Pr OH (~50 mL).
When hydrogen evolution had stopped, a solution of Al(OPr )
i
3
(
3.1785 g in ~30 mL of anhydrous THF) was added. The mixture was
Acknowledgments: We are highly thankful to CSIR and
heated to reflux. After being heated at reflux for 4 h, the mixture was
allowed to cool at room temperature and filtered to remove a small DST-New Delhi for financial support. Ram Gopal thanks
amount of insoluble material. The clear filtrate was distilled to remove UGC for providing a fellowship.
excess amount of azeotrop to about one fourth of its original volume.
The resulting solution was concentrated in vacuo to give a white solid
material (4.66 g, 94%). Re-crystallization of the latter from THF solu-
i
i
tion gave [(THF)K(μ-OPr ) Al(μ-OPr ) ] as colorless crystals.
2
2 n
References
1
H NMR (300.13 MHz, DMSO d , at 25°C, δ ppm): 3.91 (m, O-CH<,
6
i
i
OPr ); 1.16 (d, CH , OPr ), 4.10 (m, O-CH , THF); 1.91 (m, -CH , THF).
3
2
2
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i
13
i
13
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3
2
i
+
2
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2
3
8
2
2
2
i
+
i
+
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8
2
2
2
7
2
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6
+
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i
+
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(
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2
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4
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4
i
+
i
+
i
33.11 [KAl(OPr ) O(THF)] , 317.11 [KAl(OPr ) (THF)] , 302.11 [KAl(OPr ) C
3 3 2
+ + +
i
i
H CHO(THF)] , 287.11 [KAl(OPr ) CHO(THF)] , 231.11 [KAl(OPr )(THF)] ,
3
2
i
+
i
+
i
2
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+
+
i
+
i
+
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THF)] , 129.11 [KO(THF)] , 303 [KAl(OPr ) ] , 288 [KAl(OPr ) CH CHO] ,
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3
i
+
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i
2
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+
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−
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Unauthenticated
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