Aluminum phosphinate and phosphates of salen ligands

Article abstract of DOI:10.1021/ic052090k

A new dealkylation reaction between organophosphate esters and Salen aluminum bromide compounds has been used to prepare three new aluminum salen compounds salen(^tBu)AlOP(O)Ph₂ (1) (salen = N,N′-ethylenebis(3,5-di-tert-butylsalicylideneimine)), [(MeOH)Alsalen(^tBu){OMePO₂(O)}Alsalen(^tBu) {OMePO₂(O)}Alsalen(^tBu)]Br (2). and [salpen( ^tBu)AlO]₂[(BuO)₂PO]₂ (3) (salpen = N,N′-propylenebis(3,5-di-tert-butylsalicylideneimine)). Compounds 1-MeOH, 2, and 3 were characterized by single-crystal X-ray diffraction. Compound 1 is the first example of a monomeric aluminum Schiff base phosphinate. Compound 2 is a cationic Salen aluminum phosphate, and compound 3 contains an aluminophosphate ring. This work is the first example of the intentional use of an aluminum-based dealkylation reaction to form new compounds.

Full text of DOI:10.1021/ic052090k

Inorg. Chem. 2006, 45, 3970−3975
Aluminum Phosphinate and Phosphates of Salen Ligands
Amitabha Mitra, Sean Parkin, and David A. Atwood*
Department of Chemistry, UniVersity of Kentucky, Lexington, Kentucky 40506-0055
Received December 6, 2005
A new dealkylation reaction between organophosphate esters and Salen aluminum bromide compounds has been
used to prepare three new aluminum salen compounds salen(tBu)AlOP(O)Ph2 (1) (salen
N,N -ethylenebis(3,5-
di-tert-butylsalicylideneimine)), [(MeOH)Alsalen(tBu) Alsalen(tBu) Alsalen(tBu)]Br (2), and
OMePO2(O) OMePO2(O)
[salpen(tBu)AlO]2[(BuO)2PO]2 (3) (salpen
N,N -propylenebis(3,5-di-tert-butylsalicylideneimine)). Compounds 1
)
′
{
}
{
}
)
′
‚
MeOH, 2, and 3 were characterized by single-crystal X-ray diffraction. Compound 1 is the first example of a
monomeric aluminum Schiff base phosphinate. Compound 2 is a cationic Salen aluminum phosphate, and compound
3 contains an aluminophosphate ring. This work is the first example of the intentional use of an aluminum-based
dealkylation reaction to form new compounds.
Introduction
reported.7 Also, aluminum trialkyls undergo adduct formation
and subsequent dealkylsilylation to produce molecular alu-
minophosphates.8 Most of the aluminophosphate molecules
and materials contain four-coordinate aluminum.11 There are
relatively few higher-coordinate aluminum compounds bound
to either a phosphate, phosphonate, or phosphinate. One such
example is [Al(OiPr)2O2P(OtBu)2]4 where the aluminum atom
is five-coordinate.12 Group 13 molecular phosphates and
phosphinates are predominantly dimeric, and almost all of
them have four-coordinate aluminum.
Group 13 phosphates and phosphonates are of potential
utility in areas such as catalysis, molecular sieves, ion-
exchange resins, and adsorption media.1-3 Aluminophosphate
molecular sieves4 have traditionally been prepared by hy-
drothermal synthetic methods at temperatures between 100
and 200 °C where a source of aluminum, e.g., Al(OiPr)3, is
combined with aqueous H3PO4.5,6 The nonaqueous prepara-
tion of aluminum phosphate molecules and materials has
recently been discovered.7-10
Previously, we reported that six-coordinate aluminum
phosphinates may be readily obtained in combinations with
the tetradentate Salen class of ligand.13,14 In these chelated
phosphinates, [Salen(tBu)AlO2P(H)Ph]n, the degree of ag-
gregation may be manipulated by changing the length of the
ligand “backbone”. Some of the compounds revealed unique
coupling of the Salen ligand with THF. Recently, our group
has been studying the cleavage of organophosphate esters
with group 13 Schiff base chelates,15-18 and one of our goals
has been to elucidate the structures of the dealkylated
The syntheses of molecular aluminophosphates by a
dealkylation reaction between aluminum amides and phos-
phoric acid triesters, and also by a dealkylsilylation reaction
between aluminum chloride and OP(OSiMe3)3 have been
* To whom correspondence should be addressed. E-mail:
datwood@uky.edu.
(1) Thomas, J. M.; Raja, R.; Sankar, G.; Bell, R. G. Acc. Chem. Res.
2001, 34, 191-200.
(2) Hartmann, M.; Kevan, L. Chem. ReV. 1999, 99, 635-663.
(3) Kongshaug, K. O.; Fjellvag, H.; Lillerud, K. P. Microporous Meso-
porous Mater. 1999, 32, 17-28.
(4) Wilson, S. T.; Lok, B. M.; Messina, C. A.; Cannan, T. R.; Flanigen,
E. M. J. Am. Chem. Soc. 1982, 104, 1146-1147.
(11) Chen, P.; Li, J. Y.; Yu, J. H.; Wang, Y.; Pan, Q. H.; Xu, R. R. J.
Solid State Chem. 2005, 178, 1929-1934.
(12) Lugmair, C. G.; Tilley, T. D.; Rheingold, A. L. Chem. Mater. 1999,
11, 1615-1620.
(5) Wilson, S. T. Zeolite Science and Practice. In Studies in Surface
Science and Catalysis; van Bekkum, H., Flanigen, E. M., Jansen, J.
C., Eds.; Elsevier: Amsterdam, 1991; Vol. 58, p 137.
(6) Song, Y.; Li, J. Y.; Yu, J. H.; Wang, K. X.; Xu, R. R. Top. Catalysis
2005, 35, 3-8.
(13) Wang, Y.; Parkin, S.; Atwood, D. Chem. Commun. 2000, 1799-1800.
(14) Wang, Y.; Parkin, S.; Atwood, D. Inorg. Chem. 2002, 41, 558-565.
(15) Keizer, T. S.; De Pue, L. J.; Parkin, S.; Atwood, D. A. J. Organomet.
Chem. 2003, 666, 103-109.
(7) Pinkas, J.; Wessel, H.; Yang, Y.; Montero, M. L.; Noltemeyer, M.;
Froeba, M.; Roesky, H. W. Inorg. Chem. 1998, 37, 2450-2457.
(8) Pinkas, J.; Chakraborty, D.; Yang, Y.; Murugavel, R.; Noltemeyer,
M.; Roesky, H. W. Organometallics 1999, 18, 523-528.
(9) Medina, M. E.; Iglesias, M.; Gutierrez-Puebla, E.; Monge, M. A. J.
Mater. Chem. 2004, 14, 845-850.
(16) Keizer, T. S.; De Pue, L. J.; Parkin, S.; Atwood, D. A. Can. J. Chem.
2002, 80, 1463-1468.
(17) Keizer, T. S.; De Pue, L. J.; Parkin, S.; Atwood, D. A. J. Am. Chem.
Soc. 2002, 124, 1864-1865.
(10) Wang, M.; Li, J. Y.; Pan, Q. H.; Song, X. W.; Xu, R. R. Inorg. Chem.
2005, 44, 4604-4607.
(18) Mitra, A.; DePue, L. J.; Parkin, S.; Atwood, D. A. J. Am. Chem. Soc.
2006, 128, 1147-1153.
3970 Inorganic Chemistry, Vol. 45, No. 10, 2006
10.1021/ic052090k CCC: $33.50
© 2006 American Chemical Society
Published on Web 04/21/2006

Aluminum Phosphinate and Phosphates of Salen Ligands
t
(M+ - Bu, 100%), 517 (M+ - Ph2P(O)O, 8%). Anal. Calcd for
products resulting from the dealkylation reaction. This paper
reveals for the first time the use of Salen aluminum
compounds for the dealkylation of phosphinates and phos-
phates at room temperature in an organic solvent to prepare
soluble monomeric aluminum phosphates and phosphinates
with five- and six-coordinate aluminum.
C44H56O4N2Al: C 71.91, H 7.68, N 3.81. Found: C 71.40, H 8.18,
N 3.57.
Synthesis of [(MeOH)Alsalen(tBu){OMePO2(O)}Alsalen(tBu)-
{OMePO2(O)}Alsalen(tBu)]Br (2). To a rapidly stirred solution
of salen(tBu)AlBr (0.62 g, 1.05 mmol) in toluene (MeO)3PO (0.062
g, 0.44 mmol) was added. The reaction mixture was stirred for 7
d. After concentration to about one-third of its volume and cooling
for several days at -30 °C, yellow crystals precipitated which were
filtered, washed with hexane, and dried under vacuum. Yield: 0.34
Experimental Section
All air-sensitive manipulations were conducted using standard
benchtop Schlenk line techniques in conjunction with an inert-
atmosphere glovebox. All solvents were rigorously dried prior to
use. All glassware was cleaned and dried in an oven at 130 °C for
at least 12 h prior to use. The compounds salen(tBu)AlBr and
salpen(tBu)AlBr were prepared according to the literature method.18
All other chemicals were purchased from Sigma-Aldrich. NMR data
were obtained on Varian Gemini-200 and Varian VXR-400
1
g (54.3%). mp: 284 °C. H NMR (CDCl3): δ 1.30 (s, C(CH3)3),
1.43 (s, C(CH3)3), 2.1 (d, 3JPH ) 12.2 Hz, OCH3), 2.91 (d, 3JPH
)
11.6 Hz, OCH3), 3.76 (m, NCH2), 7.11-7.18 (m, Ph-H), 7.48 (s,
br, Ph-H) 8.35 (s, br, NdCH); 13C NMR (CDCl3): δ 29.6
(C(CH3)3), 30.0 (C(CH3)3), 31.3 (C(CH3)3), 31.4 (C(CH3)3), 34.0
2
(CCH3)3), 35.5 (CCH3)3), 53.1 (OCH3, JPOC ) 27.4 Hz), 53.9
(OCH3), 54.4 (NCH2), 118.3 (Ph), 127.5 (Ph), 127.8 (Ph), 130.4
(Ph), 130.6 (Ph), 130.9 (Ph), 131.1 (Ph), 138.9 (Ph), 139.9 (Ph)
140.5 (Ph), 162.6 (Ph), 171.5 (N ) CH); 27Al NMR (CDCl3): δ
-1 (W1/2 ) 8701 Hz). 31P{1H} NMR(CDCl3): δ -13 (s), -21
(s). IR (cm-1): 3053w, 2956s, 2909m, 2869w, 1642s, 1625vs,
1547w, 1537w, 1478w, 1469w, 1444m, 1391m, 1360s, 1257m,
1236w, 1178m, 1139w, 1058w, 1025, 861w, 843m, 788w,756m,
726m, 607m, 587vw. MS (MALDI-TOF): 1644 (M+ - Br - tBu,
17%), 1608 (M+ - Br - 2tBu, 10%), 1160 (M+ - salen(tBu)Al -
3CH2, 100%). Anal. Calcd for C101H153O16N6Al3P2Br: C 62.85, H
7.99, N 4.35. Found: C 64.12, H 6.36, N 4. 50.
Synthesis of [salpen(tBu)AlO]2[(BuO)2PO]2 (3). To a rapidly
stirred solution of salpen(tBu)AlBr (0.83 g, 1.35 mmol) in toluene
(BuO)3PO (0.13 g, 0.47 mmol) was added. The yellow reaction
mixture was stirred for 48 h. After filtration and concentration to
about one-third of its volume and cooling for several days at -30
°C, yellow crystals precipitated which were filtered, washed with
ether (twice) and hexane, and dried under vacuum. Yield: 0.35 g
(100%). mp: softens at 196 °C and melts at 236-238 °C. 1H NMR
(CDCl3): δ 0.65 (m, phosphate CH2CH2CH2CH3), 0.89 (m,
phosphate CH2CH2CH2CH3), 1.30 (s, C(CH3)3), δ 1.32 (s, br,
phosphate CH2CH2CH2CH3 and C(CH3)3), 1.41 (s, C(CH3)3), 1.46
(s, br, phosphate CH2CH2CH2CH3 and C(CH3)3), 2.1 (m, CH2CH2-
CH2), 3.4 (m, phosphate CH2CH2CH2CH3), 3.72 (m, NCH2), 7.20-
7.54 (m, Ph-H), 8.41 (s, br, NdCH), 8.50 (s, br, NdCH); 13C
NMR (CDCl3, 200 MHz): δ 13.6 (phosphate CH2CH2CH2CH3),
18.3 (phosphate CH2CH2CH2CH3), 27.2 (CH2), 29.6 (C(CH3)3),
(29.8 (C(CH3)3), 31.5 (C(CH3)3), 31.6(C(CH3)3), 31.9 (phosphate
CH2CH2CH2CH3), 34.2 (CCH3)3), 34.3 (CCH3)3), 35.5 (CCH3)3),
55.1 (NCH2), 67.8 (CH2CH2CH2CH3), 118.4 (Ph), 125.6 (Ph), 126
(Ph), 128.1 (Ph), 128.5 (Ph), 129.3 (Ph), 131.4 (Ph),139.4 (Ph),
140.6 (Ph), 166.9 (Ph), 172.0 (N ) CH);27Al NMR (CDCl3): δ
-5 (W1/2 ) 997 Hz), 40 (W1/2 ) 3704 Hz). 31P{1H} NMR-
(CDCl3): δ -18 (s). IR ν/cm-1: IR ν/cm-1: 2957s, 2906s, 2870m,
1620s, 1547m, 1479s, 1467s, 1442s, 1418s, 1391m, 1361m, 1342w,
1326w, 1312w, 1271s, 1259s, 1236m, 1201m, 1174s, 1091w,
1068w, 1028w, 860w, 847m, 786w, 751w, 599w, 568w. MS
1
instruments. Chemical shifts are reported relative to SiMe4 for H
and 13C, 85% H3PO4 for 31P, and AlCl3 in D2O for 27Al and are
reported in ppm. Infrared transmission spectra were recorded at
room temperature in a potassium bromide pellet on a Fourier
transform Magna-IR ESP 560 spectrometer. Thermogravimetric
analyses were performed on a TA Instruments Hi-Res TGA 2950
Analyzer. Elemental analyses were performed on a LECO CHN-
2000 Analyzer.
X-ray data were collected on either a Bruker-Nonius X8 Proteum
diffractometer (1; Cu KR radiation) or a Nonius Kappa-CCD (2
and 3; Mo KR radiation). All calculations were performed using
the software package SHELXTL-Plus.19,20 The structures were
solved by direct methods and successive interpretation of difference
Fourier maps, followed by least-squares refinement. All non-
hydrogen atoms were refined with anisotropic thermal parameters.
The hydrogen atoms were included using a riding model with
isotropic parameters tied to the parent atom. Crystallographic data
for 1, 2, and 3 were deposited with the Cambridge Crystallographic
Data Center (CCDC reference numbers: 267092, 269612, and
290877, respectively) and copies of the data can be obtained free
of charge on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (Fax: +44-1223-336033, e-mail: deposit@
ccdc.cam.ac.uk).
Synthesis of salen(tBu)AlOP(O)Ph2 (1). To a rapidly stirred
solution of salen(tBu)AlBr (0.50 g, 1.77 mmol) in toluene Ph2P-
(O)OMe (0.197 g, 0.85 mmol) was added. The reaction mixture
was stirred for 24 h and then refluxed for 17 h. It was then cannula
filtered, and the resulting pale yellow residue was dried under
1
vacuum. Yield: 0.400 g (65.0%). mp: 302-304 °C. H NMR
(CDCl3): δ 1.29 (s,18H, C(CH3)3), 1.59 (s,18H, C(CH3)3), 3.64
(m, 2H, NCH2), 4.40 (m, 2H, NCH2), 6.90 (d, 2H, Ph-H), 6.99
(m, 5H, Ph-H)7.26 (d, 2H, Ph-H), 7.52 (m, 5H, Ph-H) 8.17 (s,
2H, NdCH); 13C NMR (CDCl3): δ 29.7 (C(CH3)3), 31.3 (C(CH3)3),
33.9 (CCH3)3), 35.6 (CCH3)3), 54.7 (NCH2), 118.3 (Ph), 127.2 (Ph),
127.4 (Ph), 127.5 (Ph), 129.9 (Ph), 130.8 (Ph), 130.9 (Ph), 131.1
(Ph), 138.4 (Ph), 140.5 (Ph), 162.8 (Ph), 170.3 (N ) CH); 27Al
NMR (CDCl3): δ 30 (W1/2 ) 1951 Hz). 31P{1H} NMR(CDCl3):
δ 35. IR (cm-1): 3053 (w), 2955s, 2905m, 2858w, 1643s, 1625s,
1547w, 1536w, 1478m, 1468m, 1441m, 1390m, 1359m, 1259m,
1176s, 1131m, 1071w, 1025, 857w, 847m, 786w, 753m, 726m,
700m, 605m, 555m. MS (EI, positive): 734(M+, 17%), 677
(MALDI-TOF): 1272 (M+ - (BuO)2PO2, 1.9%), 531 (M+
2(BuO)2PO2, 100%). Anal. Calcd for C82H132O12N4Al2P2: C 66.46,
H 8.98, N 3.78. Found:C 65.85, H 9.66, N 4.15.
-
Results and Discussion
Compound 1 was prepared by dealkylation by salen(tBu)-
AlBr of methyl diphenyl phosphinate by stirring in toluene
at room temperature (Figure 1). Compound 1 was soluble
in the organic solvents toluene and chloroform. It was fully
(19) Sheldrick, G. M. SHELXS97 and SHELXL97; University of Go¨ttin-
gen: Go¨ttingen, Germany, 1997.
(20) Sheldrick, G. M. SHELXTL, version 5.0; Bruker AXS, Inc.: Madison,
WI, 1998.
Inorganic Chemistry, Vol. 45, No. 10, 2006 3971

Mitra et al.
Figure 1. Synthesis of Salen aluminum phosphinate (1).
Figure 3. Synthesis of compound 2.
example of a structurally characterized monomeric aluminum
phosphinate compound bound by a Salen ligand. The
aluminum atom has a six-coordinate distorted octahedral
environment with MeOH and the phosphinate group at the
axial positions. The O3-Al-O4 angle is nearly linear
(∼175°). The Al-O-P linkage is bent with a bond angle
of 151°, which is considerably narrower than the Al-O-P
angle (∼159°) in [Salen(tBu)Al{O2P(H)Ph}]∞. 14 The Al-O
(ligand) bond distances (∼1.80-1.81 Å) are marginally
shorter than the Al-O(P) bond distance (∼1.87 Å).
Figure 2. Crystal structure of 1‚MeOH (hydrogen atoms are omitted for
The reaction of salen(tBu)AlBr and trimethyl phosphate
after stirring in toluene for 7 days at room temperature gave
2 (Figure 3), which could be isolated as yellow crystals after
concentration and filtration of the reaction mixture followed
by cooling. Compound 2 is a trimetallic cation with three
salenAl units connected by phosphate linkages. It is soluble
in the organic solvents toluene and chloroform. It was
clarity).
characterized using 1H, 13C, 27Al, and 31P NMR, IR, and MS
1
(EI, positive). The H NMR spectrum of 1 was very close
to the corresponding chloride analogues reported in the
literature21 and also the bromide starting materials.18 There
t
are two singlets for the Bu-Ph groups at δ 1.29 and 1.58.
Two methylene peaks corresponding to the ethylene back-
bone protons from the ligand appear at δ 3.64 and 4.40.
There is only one imine singlet at δ 8.17. The 27Al NMR
showed a broad peak centered at δ 30 for five-coordinate
aluminum, which is similar to the shift observed in many
other five-coordinate aluminum Salen compounds (e.g.,
Salen(tBu)AlOSiMe3 (δ 30.5) and Salen(tBu)AlN3 (δ 31.9)).22
However, this is upfield from the related chloride analogue
(δ 57).21 The 31P{H} NMR of 1 contained a single peak at
δ 35. Interestingly, this is considerably downfield compared
to dimeric or polymeric Salen aluminum phosphinates (δ
7.08-9.16).14
Compound 1 was recrystallized by slow evaporation of a
methanol solution at room temperature under atmospheric
conditions to produce 1‚MeOH. The compound was stable
in the atmosphere, and no nucleophilic displacement of the
phosphinate group by methanol or atmospheric moisture was
observed. The molecular structure is shown in Figure 2.
There are two molecules in the asymmetric unit; only one is
shown in the figure. Previously, the only structurally
characterized examples of Salen aluminum phosphinate
compounds were polymeric [Salen(tBu)Al{O2P(H)Ph}]n (n
) ∞) for salen, salophen, and salomphen and dimeric (n )
2) for salpen and salben.13,14 In these compounds, two
phosphinate groups bridge between the Salen(tBu)Al units.
They were synthesized by alkane elimination between Salen-
(tBu)Me and phenyl phosphinic acid, Ph(H)P(O)OH, and
some of the compounds revealed unique coupling of the
Salen ligand with THF. Typically, the Salen ligands are not
so readily derivatized. Compound 1‚MeOH is the first
1
characterized by IR, H NMR, 27Al NMR, 31P NMR, mp,
and MS. The 1H and 13C NMR contain peaks corresponding
to salen(tBu) units and phosphate methoxy groups. Interest-
ingly, there are two 31P peaks at δ -13 and -21. These
shifts are close to that of other bridging phosphate com-
pounds. For example, the 31P shift in Mg2(XDK)DPP(CH3-
OH)3(H2O)(NO3) (H2XDK ) m-xylenediaminebis (Kemp’s
triacid imide), HDPP ) diphenyl phosphate) is δ -15.4623
and in Me2AlO2P(OtBu)2]2 is δ -22.57.12 The two 31P peaks
imply different shielding environments for the two phos-
phorus atoms. There is only one very broad 27Al NMR peak
at δ -1, which confirms the presence of a six-coordinate
aluminum atom. Surprisingly, another aluminum peak for
the five-coordinate aluminum was not observed in the 27Al
NMR. It is possible that it was overshadowed by the broad
six-coordinate aluminum peak. Interestingly, one methanol
molecule was coordinated to one of the aluminum atoms.
The formation of methanol in the reaction system could occur
by adventitious hydrolysis of the reaction byproduct methyl
bromide.
The X-ray crystal structure of 2 (Figure 4) reveals three
aluminum salen units connected by two phosphate groups.
The compound is monocationic with two six-coordinate and
one five-coordinate aluminum atom. The phosphate groups
are monodealkylated with two methoxy groups attached to
each phosphorus atom. It is interesting to note that out of
the four P-O bonds around P1P, P1P-O1P (1.476(3) Å)
and P1P-O2P (1.480(3) Å), have bond lengths close to a
phosphorus-oxygen double bond; the other two P-O bonds,
P1P-O3P and P1P-O4P, are longer and their bond lengths
(21) Rutherford, D.; Atwood, D. A. Organometallics 1996, 15, 4417-4422.
(22) Munoz-Hernandez, M.-A.; Keizer, T. S.; Wei, P.; Parkin, S.; Atwood,
D. A. Inorg. Chem. 2001, 40, 6782-6787.
(23) Yun, J. W.; Tanase, T.; Pence, L. E.; Lippard, S. J. J. Am. Chem.
Soc. 1995, 117, 4407-4408.
3972 Inorganic Chemistry, Vol. 45, No. 10, 2006

Aluminum Phosphinate and Phosphates of Salen Ligands
t
Figure 4. Molecular structure of 2. The Bu groups on the phenyl rings, the disordered atoms, and the hydrogen atoms are omitted for clarity.
Table 1. Crystallographic Data and Refinement Details for Compounds 1-3
compound 1
C45H60AlN2O5P2
766.90
yellow
0.22 × 0.10 × 0.10
orthorhombic
P212121
11.6850(2)
26.1840(5)
28.1148(5)
90.00
compound 2
compound 3
empirical formula
C
115H169Al3BrN6O15P2
C96H148Al2N4O12P2
1666.08
pale yellow
0.20 × 0.20 × 0.08
monoclinic
P21/c
10.6546(2)
17.6944(3)
24.9473(5)
90.00
95.9921(7)
90.00
M/g mol-1
color
2098.35
pale yellow
0.35 × 0.10 × 0.10
triclinic
cryst size/mm3
cryst syst
space group
a/Å
b/Å
c/Å
P1h
15.02320(10)
18.8031(2)
21.9993(3)
89.9924(4))
71.8021(4)
82.2916(4)
5844.49(11)
1.191
R/°
â/°
90.00
90.00
8602.0(3)
1.184
γ/°
V/Å3
4677.54(15)
1.183
F
calc/g cm-3
Z
8
2
2
F(000)
radiation used
µ/mm-1
T/K
3296
Cu KR
1.121
90.0(2)
2244
Mo KR
0.463
90.0(2)
1808
Mo KR
0.126
90.0(2)
hkl range
-14 e h e 13,
-11 e k e 31,
-33 el e 32
2.31-68.22
48 842
-17 e h e 17,
-21 ek e 21,
-25 el e 25
1.46-24.00
36 627
-12 e h e12,
-21 e k e 21,
-29 e l e 29
1.41-25.00
91 792
Θ range/°
reflns measured
unique reflns (Rint
)
15 283 (0.0524)
14 037
18337 (0.0604)
11 102
8238 (0.1476)
4803
obsd reflns, n [I g 2σ(I)]
refinement method
refined params/restraints
R1 [I > 2σ]
full-matrix least-squares on F2
1018/120
full-matrix least-squares on F2
1315/235
full-matrix least-squares on F2
538/0
R1 ) 0.0408, wR2 ) 0.0996
R1 ) 0.0457, wR2 ) 0.1030
1.050
R1 ) 0.0720, wR2 ) 0.1783
R1 ) 0.1426, wR2 ) 0.2108
1.032
R1 ) 0.0566, wR2 ) 0.1079
R1 ) 0.1236, wR2 ) 0.1307
0.998
R1 (all data)
GOF on F2
largest diff. peak and hole/e‚Å-3
0.415 and -0.277
0.713 and -0.600
0.314 and -0.559
(1.568(3) and 1.559(3) Å) fall in the range of P-O single
bonds (Table 2).
of 109.5° is shown for P1P by O1P-P1P-O2P (116.48-
(19)° and for P2P by O5P-P2P-O6P (120.1(2)°). Al1A and
Al1B have distorted octahedral geometries, whereas Al1C
has a distorted geometry between trigonal bipyramidal and
square pyramidal. The compound is cationic with bromide
(not shown in the crystal structure) present as the counter-
anion.
A quantitative measure has been proposed to describe the
distortion from perfectly sqare pyramidal or trigonal bipy-
ramidal geometry in five-coordinate compounds. The amount
of this distortion is expressed by a value “τ”. (For a
description of the calculation of the “τ value” see Supporting
For the phosphorus atom P2P, the P2P-O5P bond length
1.469(4) Å indicates double-bond character but the other
three P-O bonds (P2P-O6P ) 1.531(4), P2P-O7P )
1.575(5), and P2P-O8P ) 1.554(4) Å) show normal P-O
single bond lengths. The variation of the P-O bond lengths
around the two phosphorus atoms P1P and P2P could partly
explain the presence of two different 31P chemical shifts.
Each phosphorus atom has a distorted tetrahedral geometry
and is connected to the aluminum atoms through the oxygen
atoms. The largest deviation from the ideal tetrahedral angle
Inorganic Chemistry, Vol. 45, No. 10, 2006 3973

Mitra et al.
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Compounds 1-3
1
Al1A-N1A
Al1A-N2A
Al1A-O1A
2.0023(19) Al1A-O2A
1.9977(19) Al1A-O3A
1.8033(16) Al1A-O4A
O4A-P1A
1.8133(16)
2.0255(17)
1.8729(17)
1.5052(17)
88.76(7)
Figure 5. Synthesis of compound 3.
O1A-Al1-O2A
O1A-Al1-O3A
O1A-Al1A-N1A
O2A-Al1A-N2A
O2A-A1lA-O3A
95.97(7)
87.18(7)
91.34(7)
91.22(7)
89.79(7)
O3A-Al1A-N1A
O3A-Al1A-N2A
82.36(7)
O3A-Al1A-O4A 175.39(7)
N1A-Al1A-N2A 81.27(8)
Al1A-O4A-P1A 151.12(11)
2
Al1A-N1A
Al1A-N2A
AlA-O1A
1.988(4)
2.008(4)
1.808(3)
1.795(3)
2.038(3)
1.847(3)
1.997(4)
2.005(4)
1.801(3)
1.814(3)
1.883(3)
1.921(4)
1.977(4)
96.55(14)
87.37(14)
91.38(15)
Al1C-N2C
AlC-O1C
AlC-O2C
Al1C-O6P
P1P-O1P
P1P-O2P
P1P-O3P
P1P-O4P
P2P-O5P
P2P-O6P
P2P-O7P
P2P-O8P
1.996(4)
1.758(3)
1.797(3)
1.798(4)
1.476(3)
1.480(3)
1.568(3)
1.559(3)
1.469(4)
1.531(4)
1.575(5)
1.554(4)
AlA-O2A
Al1A-O3A
Al1A-O1P
Al1B-N1B
Al1B-N2B
AlB-O1B
AlB-O2B
Al1B-O2P
Al1B-O5P
Al1C-N1C
O1A-Al1A-O2A
O1A-Al1A-O3A
O1A-Al1A-N1A
Figure 6. Molecular structure of 3. Hydrogen atoms are not shown for
clarity.
O1B-Al1B-O2B
O1B-Al1B-O2P
O1B-Al1B-N1B
97.70(15)
93.39(15)
91.87(15)
O1A-Al1A-N2A 169.73(16)
O1B-Al1B-N2B 172.19(16)
found to be 0.31. Thus, it cannot be reasonably defined as
either of the geometries but is closer to square pyramidal.
The Al-O-P linkages in 2 are bent. However, the angle
Al1A-O1P-P1P (163.5(2)°) is considerably less bent than
the other Al-O-P angles (151.1(3)-153.4(2)°) in the
molecule.
O2A-Al1A-N2A
O2A-A1lA-O3A
O3A-Al1A-N1A
O3A-Al1A-N2A
91.32(15)
89.67(13)
84.38(14)
86.09(14)
O2B-Al1B-N2B
O2B-A1lB-O2P
O2P-Al1B-N1B
O2P-Al1B-N2B
O2P-Al1B-O5P
N1B-Al1B-N2B
Al1B-O5P-P2P
O5P-P2P-O6P
O5P-P2P-O7P
O5P-P2P-O8P
O6P-P2P-O7P
O6P-P2P-O8P
O7P-P2P-O8P
P2P-O5P-Al1B
O2C-Al1C-N2C
89.97(16)
93.30(17)
87.58(15)
84.64(17)
169.04(17)
80.50(16)
151.2(3)
120.1(2)
111.1(3)
108.8(2)
100.7(2)
108.3(3)
106.9(2)
151.2(3)
88.55(15)
O3A-Al1A-O1P 173.56(15)
N1A-Al1A-N2A
Al1A-O1P-P1P
O1P-P1P-O2P
O1P-P1P-O3P
O1P-P1P-O4P
O2P-P1P-O3P
O2P-P1P-O4P
P1P-O2P-Al1B
O3P-P1P-O4P
N1C-Al1C-N2C
N1C-Al1C-O1C
O1C-Al1C-O2C
N1C-Al1C-O6P
O2P-Al1B-O5P
P2P-O6P-Al1C
80.12(16)
163.6(2)
116.48(19)
105.60(18)
110.28(19)
111.2(2)
Compound 3 was prepared by the reaction of salpen(tBu)-
AlBr with tributyl phosphate in toluene at room temperature
(Figure 5). Only one of the three methoxy groups on each
phosphate molecule undergoes dealkylation. The compound
is soluble in toluene and chloroform. It was characterized
by IR, 1H NMR, 27Al NMR, 31P NMR, mp, and MS. The 1H
NMR has peaks corresponding to the ligand and the alkoxy
groups of the mono-dealkylated phosphate. The 27Al NMR
shows two peaks. The peak at δ -5 corresponds to
six-coordinate aluminum. However, the peak at δ 40 falls
in the region of five-coordinate aluminum. This does not
correspond to the solid-state structure of the compound which
shows the presence of six-coordinate aluminum only. It could
be possible that in solution one phosphate linkage from one
of the aluminum atoms dissociates, thus making it five-
coordinate. The 31P NMR has a single peak at δ -18. The
TGA curve (Supporting Information Figure S3) of 3 shows
a weight loss of about 10% around 100-120 °C, which is
probably due to the entrapped solvent. There is a second
weight loss of about 90% in the temperature range 300-
600 °C that is probably due to the thermal oxidation of the
organic species leaving behind some inorganic aluminophos-
phate material.
106.98(18)
153.4(2)
105.86(19)
79.14(15)
90.02(15)
92.14(15)
93.67(17)
169.04(17)
151.6(3)
N2C-Al1C-O1C 143.45(17)
N1C-Al1C-O2C 161.90(17)
O1C-Al1C-O6P 111.64(16)
3
Al1-N1
2.026(2)
2.001(2
1.8274(19) P1-O5
1.8597(19) P1-O6
1.8816(19)
P1-O3
P1-O4
1.4827(18)
1.4778(18)
1.5750(19)
1.5836(18)
Al1-N2
Al1-O1
Al-O2
Al1-O3
Al1-O4
1.8611(19)
O1-Al1-N1
O1-Al1-N2
O1-Al1-O2
O1-Al1-O3
O1-Al1-O4
O2-Al1-N1
O2-Al1-N2
O2-A1l-O3
O3-P1-O5
O5-P1-O6
88.32(9)
176.15(10)
93.01(9)
93.64(8)
93.45(8)
90.45(9)
85.94(9)
172.64(9)
111.59(10)
105.78(10)
O2-Al1-O4
91.34(8)
86.60(9)
87.23(9)
91.40(8)
87.98(9)
150.46(12)
165.22(12)
118.52(11)
110.32(10)
O3-Al1-N1
O3-Al1-N2
O3-Al1-O4
N1-Al1-N2
Al1-O3-P1
Al1-O4-P1
O3-P1-O4
O4-P1-O6
The molecular structure of 3 (Figure 6) contains an
aluminum-phosphate ring formed by two Salen aluminum
units and two mono-dealkylated phosphate units. Two
aluminum and two phosphorus atoms are part of an eight-
membered Al-O-P ring. The ring P-O bond distances P1-
O3 and P1-O4 (1.4827(18) and 1.4778(18) Å, respectively)
Information Figure S2).24 A perfectly sqp geometry has a τ
value equal to zero, whereas a perfectly trigonal bipyramidal
geometry has a τ value equal to 1. This value may be
important in determining the accessibility of a sixth coor-
dination site. 25 For compound 2, the calculated τ value was
3974 Inorganic Chemistry, Vol. 45, No. 10, 2006

Aluminum Phosphinate and Phosphates of Salen Ligands
are essentially equal and have double-bond character (Table
2). The other P-O distances, P1-O5 and P1-O6, are longer
(1.5750(19) and 1.5836(18) Å, respectively) and in the range
of P-O single bonds.
used to synthesize the first structurally characterized mon-
omeric Salen aluminum phosphinate. Furthermore, the
dealkylation reaction with alkyl phosphates has been used
to prepare a cationic aluminum phosphate and an alumino-
phosphate ring. These compounds are the first examples of
aluminum phosphates with Salen ligands. They contain five-
and six-coordinate aluminum, which is rare for molecular
aluminophosphate compounds. The reaction conditions for
the preparation of all of the compounds are very mild.
This method could be developed to prepare alumino-
phosphate cage and chain structures for potential application
as molecular sieves and catalysts. This is the first example
of the intentional use of an aluminum-based dealkylation
reaction to form new compounds. The utility of this reaction
in forming other unique products is currently being
explored.
Each phosphorus atom is in a distorted tetrahedral
geometry. The biggest distortion is found in the O-P-O
bond angle (118.52(11) °) inside the aluminophosphate ring.
Each aluminum atom is six-coordinate with a distorted
octahedral geometry. The phosphate oxygen atoms occupy
two of the equatorial positions. The other two equatorial
positions are occupied by one nitrogen atom and one oxygen
atom from the ligand. Another pair of nitrogen and oxygen
from the ligand occupy the axial positions. The axial Al-O
distance (1.8274(19)Å) is slightly shorter than the equatorial
Al-O distances (1.8597(19), 1.8816(19) and 1.8611(19) Å).
However, the axial Al-N2 distance (2.001(2) Å) is almost
the same as the equatorial Al-N1 distance (2.026(2) Å). The
longer Al-N distances compared to Al-O distances are a
reflection of the larger atomic radius of nitrogen. The Al-
O-P angles are not equal. Al1-O4-P1 (165.22(12) Å) is
larger than Al1-O3-P1 (150.46(12) Å).
The crystal packing diagram of 3 (Supporting Information
Figure S4) shows that the aluminophosphate rings stack on
top of each other with alkyl chains on phosphorus and ligand
groups on aluminum extending away from the ring. The
distance between two aluminum atoms is 5.108 Å, which is
comparable to the pore diameter (6.6 Å) of layered alu-
minphosphate templated by 2-methylpiperazine.26
Acknowledgment. This work was supported by Kentucky
Science and Engineering Foundation (KSEF Grant No. 148-
502-04-100). Instruments used in this research were obtained
from the CRIF (NMR, CHE 997841) and MRI (X-ray, CHE
0319176) programs of the National Science Foundation and
from the Research Challenge Trust Fund of the University
of Kentucky. Partial support from the University of Kentucky
Tracy Farmer Center for the Environment is acknowledged.
Thanks are also expressed to the University of Kentucky
Mass Spectrometry Facility and the Center for Applied
Energy Research.
Conclusion
The dealkylation reaction between a Salen aluminum
Schiff base halide and methyl diphenylphosphinate has been
Supporting Information Available: The crystal packing
diagrams of 2‚MeOH and 3; figure showing the calculation of τ
value; TGA curve for 3; figure of 3 showing the Al-O-P ring;
and CIF files for compounds 1-3. This material is available free
of charge via the Internet at http://pubs.acs.org.
(24) Addison, A. W.; Rao, T. N.; Reedijk, J.; Vanrijn, J.; Verschoor, G.
C. J. Chem. Soc.-Dalton Trans. 1984, 1349-1356.
(25) El-Bahraoui, J.; Wiest, O.; Feichtinger, D.; Plattner, D. A. Angew.
Chem., Int. Ed. 2001, 40, 2073-2076.
(26) Tuel, A.; Gramlich, V.; Baerlocher, C. Microporous Mesoporous
Mater. 2002, 56, 119-130.
IC052090K
Inorganic Chemistry, Vol. 45, No. 10, 2006 3975