Tetrahydrofurfuryloxide derivatives of alkyl aluminum species

Article abstract of DOI:10.1021/om0493199

Tetrahydrofurfuryl alcohol (H-OTHF) was successfully reacted with a series of aluminum alkyls (AlR₃) to yield compounds of the general formula [R₂Al(μ-OTHF)]₂ where R = CH₃ (1), CH ₂CH₃ (2), and CH₂CH(CH₃)₂ (3). Further, reactivity studies showed that the alkyls for 1 were easily exchanged, forming compounds of the general formula [Me(OR)Al(μ-OTHF)] ₂ where OR = OC₆H₃(Me)₂-2,6 (4), OC₆H₃(CMe₃)₂-2,6 (5a), and OSi(C₆H₅)₃ (6). For 5a, reflux temperatures were required to get the full exchange; otherwise the asymmetric derivative [Me(OR)Al(μ-OTHF)₂AlMe₂] (5b) was isolated. The bulk powders of 1-6 were found to be in agreement with the crystal structures on the basis of elemental analyses and multinuclear solid state NMR studies. Multinuclear solution state NMR studies indicate that the alkyl OTHF derivatives have cis/trans isomers due to the chiral proton on the OTHF ligand.

Full text of DOI:10.1021/om0493199

Organometallics 2005, 24, 731-737
731
Tetrahydrofurfuryloxide Derivatives of Alkyl Aluminum
Species
Timothy J. Boyle,* Todd M. Alam, Scott D. Bunge, Judith M. Segall,
Gabriel R. Avilucea, Ralph G. Tissot, and Mark A. Rodriguez
Sandia National Laboratories Advanced Materials Laboratory, 1001 University Boulevard,
SE, Albuquerque, New Mexico 87106
Received September 1, 2004
Tetrahydrofurfuryl alcohol (H-OTHF) was successfully reacted with a series of aluminum
alkyls (AlR3) to yield compounds of the general formula [R2Al(µ-OTHF)]2 where R ) CH3
(1), CH2CH3 (2), and CH2CH(CH3)2 (3). Further, reactivity studies showed that the alkyls
for 1 were easily exchanged, forming compounds of the general formula [Me(OR)Al(µ-OTHF)]2
where OR ) OC6H3(Me)2-2,6 (4), OC6H3(CMe3)2-2,6 (5a), and OSi(C6H5)3 (6). For 5a, reflux
temperatures were required to get the full exchange; otherwise the asymmetric derivative
[Me(OR)Al(µ-OTHF)2AlMe2] (5b) was isolated. The bulk powders of 1-6 were found to be in
agreement with the crystal structures on the basis of elemental analyses and multinuclear
solid state NMR studies. Multinuclear solution state NMR studies indicate that the alkyl
OTHF derivatives have cis/trans isomers due to the chiral proton on the OTHF ligand.
Introduction
One method often employed to garner control during
synthesis is to selectively introduce steric bulk around
the metal center. For early transition metals, this has
led to the dominant use of cyclopentadienyl ligands;
however, introduction of the cyclopentadienyl ligand15,16
has not been as successful in controlling structure prop-
erties for Al3+ compounds. Alternatively, alkoxide ligands
have also proven to be a useful ligand set, since their
steric bulk can be easily manipulated. Numerous alkoxy
aluminum alkyl systems have been reported in the
literature.17
Of these, one report revealed the use of 8-thio-
phenemethanol (H-OCH2-2-C4H3S, H-OTPM)-modified
AlMe3, which led to the isolation of [(Me2Al)3(µ-OCH2-
2-C4H3S)6Al.18 This compound contained both four- and
six-coordinated Al metal centers and was of interest
since the alkyl ligands were still accessible while the
remainder of the molecule was sterically hindered. An
identical structure for 2-furanmethanol (tetrahydrofur-
furyl alcohol, H-OCH2-2-C4H8O, H-OTHF) was pro-
posed.18 This species is of interest to us, since again the
core of the structure would be isolated from the external
reactive species and thus could be used as a template
to build large, more complex species. In addition, the
OTHF ligand is of more interest than the OTPM ligand
since there are no potential S contaminants after
processing.
The family of trialkyl aluminum (AlR3) reagents has
found extensive use in catalyst, organic synthesis,
materials production, and many other complex systems.
We are interested in exploring the utility of these
precursors for the production of H-storage materials. To
exploit the properties of the starting precursors for any
of these systems, it is necessary to understand the role
of AlR3. Therefore, numerous structurally characterized
compounds that possess an AlR3 moiety as a co-ligand
have been reported in the literature.1 Two predominant
binding modes for this compound have been observed:
(i) coordination through a bridging five-coordinate car-
bon center and (ii) reactively binding through loss of a
proton to bind a methylene group.2-14 Control over the
final structures of these precursors is limited due to the
high reactivity of AlR3.
* To whom correspondence should be sent. Tel: (505) 272-7625.
Fax: (505) 272-7336. E-mail: tjboyle@Sandia.gov.
(1) More than 60 compounds with AlR3 were observed using the
Cambridge Crystallographic Data Centre; 12 Union Road, Cambridge
CB2 1EZ, U.K., www.ccdc.cam.ac.uk; searched using ConQuest v 5.25
(April 2004).
(2) Busch, M. A.; Harlow, R.; Watson, P. L. Inorg. Chim. Acta 1987,
140, 15.
(3) Kruger, C.; Mynott, R.; Siedenbiedel, C.; Stehling, L.; Wilke, G.
Angew. Chem., Int. Ed. Engl. 1991, 30, 1668.
(4) Fischbach, A.; Herdtweck, E.; Anwander, R.; Eickerling, G.;
Scherer, W. Organometallics 2003, 22, 499.
(5) Scollary, G. R. Aust. J. Chem. 1978, 31, 41.
(6) Giesbrecht, G. R.; Gordon, J. C.; Brady, J. T.; Clark, D. L.; Keogh,
D. W.; Michalczyk, R.; Scott, B. L.; Watkin, J. G. Eur. J. Inorg. Chem.
2002, 723.
(7) Klabunde, U.; Tebbe, F. N.; Parshall, G. W.; Harlow, R. L. J.
Mol. Catal. 1980, 8, 37.
(8) Niemeyer, M.; Power, P. P. Chem. Commun. 1996, 1573.
(9) Evans, W. J.; Boyle, T. J.; Ziller, J. W. J. Am. Chem. Soc. 1993,
115, 5084.
(13) Klimpel, M. G.; Eppinger, J.; Sirsch, P.; Sherer, W.; Anwander,
R. Organometallics 2002, 21, 4021.
(14) Hartner, F. M.; Clift, S. M.; Schwartz, J.; Tulip, T. H. Orga-
nometallics 1987, 6, 1346.
(15) Fisher, J. D.; Shapiro, P. J.; Budzelaar, P. M. H.; Staples, R. J.
Inorg. Chem. 1998, 37, 1295.
(16) Fisher, J. D.; Shapiro, P. J.; Yap, G. P. A.; Rheingold, A. L.
Inorg. Chem. 1996, 35, 271.
(10) Evans, W. J.; Boyle, T. J.; Ziller, J. W. J. Organomet. Chem.
1993, 462, 141.
(11) Erker, G.; Albrecht, M.; Kruger, C.; Werner, S.; Binger, P.;
Lanhauser, F. Organometallics 1992, 11, 3517.
(12) Evans, W. J.; Anwander, R.; Ziller, J. W. Organometallics 1995,
14, 1107.
(17) More than 300 compounds with AlR2(OC) were observed using
the Cambridge Crystallographic Data Centre; searched using Con-
Quest v. 5.25 (April 2004).
(18) Kumar, R.; de Mel, V. S. J.; Sierra, M. L.; Hendershot, D. G.;
Oliver, J. P. Organometallics 1994, 13, 2079.
10.1021/om0493199 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 01/15/2005

732 Organometallics, Vol. 24, No. 4, 2005
Boyle et al.
Figure 1. Plot of 1. Thermal ellipsoids are drawn for
heavy atoms at the 30% level, and carbon atoms are drawn
as ball and sticks for clarity.
Figure 3. Plot of 3. Thermal ellipsoids are drawn for
heavy atoms at the 30% level, and carbon atoms are drawn
as ball and sticks for clarity.
Figure 2. Plot of 2. Thermal ellipsoids are drawn for
heavy atoms at the 30% level, and carbon atoms are drawn
as ball and sticks for clarity.
Figure 4. Plot of 4. Thermal ellipsoids are drawn for
heavy atoms at the 30% level, and carbon atoms are drawn
as ball and sticks for clarity.
The product isolated from our attempts of the litera-
ture preparation18 had been heated and stirred for a
longer time than the original reaction and had several
analytical results that were not consistent with the
proposed structure. Therefore, we isolated crystals from
the reaction and found the resultant material was [Me2-
Al(µ-OTHF)]2 (1, Figure 1). The elevated temperatures
and longer stir times allow for greater ligand redistribu-
tion and may explain the variations between the ob-
served products and the literature product.18
glovebox techniques. All solvents were stored under argon and
used as received (Aldrich) in Sure Seal bottles. The following
chemicals were used as received from (Aldrich) under argon
atmosphere: AlMe3, AlEt3, 1 M AlBui3 (toluene), H-OTHF,
H-DMP, H-DBP, and H-TPS. Note! Extreme care must be taken
in the handling and storage of aluminum alkyl compounds and
the subsequent waste due to the inherent pyrophoricity of these
precursors.
FT-IR data were obtained on a Bruker Vector 22 instrument
using KBr pellets under an atmosphere of flowing nitrogen.
Elemental analysis was performed on a Perkin-Elmer 2400
CHN-S/O elemental analyzer. Melting points were determined
on samples sealed in a glass tube under an atmosphere of
argon using an Electrothermal melting point apparatus.
Thermal gravimetric analysis/differential thermal analysis
(TGA/DTA) data were acquired on a Universal V3.0G TA
instrument by heating from room temperature to 650 °C at a
ramp rate of 5 °/min under an argon atmosphere.
All NMR samples were prepared from dried crystalline
materials that were handled and stored under an argon
atmosphere and redissolved in the appropriate deuterated
solvent (toluene-d8) at saturated solution concentrations. All
solution spectra were obtained on a Bruker DRX400 spectrom-
eter at 399.8, 100.1, and 104.2 MHz for 1H, 13C, and 27Al
experiments, respectively. A 5 mm broadband probe was used
for all experiments. The 1H NMR spectra were obtained using
a direct single pulse excitation, with a 10 s recycle delay and
eight signal averages. The 13C{1H} NMR spectra were obtained
using a WALTZ-16 composite pulse 1H decoupling, a 5 s recycle
delay, and a π/4 pulse excitation. The 27Al NMR spectra were
AlR3 + H-OTHF f [R2Al(µ-OTHF)]2
R ) Me, Et, Bui
(1)
Once isolated, the general reactivity of 1 was inves-
tigated. Due to the presence of the OTHF ligand, the
remainder of the molecule could be selectively reacted
in an effort to build controlled complex precursors. This
report details the synthesis and characterization of a
novel family of aluminum alkyl compounds using the
OTHF template, including [R2Al(µ-OTHF)]2 (R ) CH3
(1, Me); CH2CH3 (2, Et); CH2CH(Me)2 (3; Bui)) and
(OR)xMe4-xAl2(µ-OTHF)2 [x ) 2: OR ) OC6H3(Me)2-2,6
(4, DMP), OC6H3(CMe3)-2,6 (5a, DBP), OSi(C6H5)3 (6,
TPS); x ) 1, OR ) DBP (5b)] shown in Figures 2-6.
Experimental Section
All compounds described below were handled with rigorous
exclusion of air and water using standard Schlenk line and

OTHF Derivatives of Alkyl Aluminum Species
Organometallics, Vol. 24, No. 4, 2005 733
spinning frequency of 4 kHz. Typical 13C acquisition conditions
utilized a direct single pulse Bloch decay with a 4.5 µs π/2
pulse, with two-phase modulation (TPPM) 1H decoupling,20
128-432 scan averages, and a 240 s recycle delay. Acquisition
conditions for the 13C cross-polarization (CP) MAS NMR
spectra included a 1 ms CP contact pulse, TPPM 1H decou-
pling, 1024 scan averages, and a 10 s recycle delay. The 13C
NMR data were referenced to the carbonyl of the secondary
standard glycine (δ ) 176 ppm with respect to TMS δ ) 0
ppm).
General Reaction. The appropriate AlR3 was added to
toluene (or hexanes) and stirred under an argon atmosphere.
H-OTHF was added dropwise to this mixture (note the reaction
is very exothermic and large volumes of gas are generated),
followed by stirring for 12 h. If after this time, a precipitate
was present, the reaction mixture was heated until the solution
was clear and then allowed to sit at glovebox temperatures or
cooled to -35 °C until X-ray quality crystals formed.
[Al(Me)2(OTHF)]2 (1). AlMe3 (15.0 g, 20.8 mmol), H-OTHF
(21.3 g, 20.8 mmol), and 20 mL of toluene were used. Yield:
29.0 g (88.1%). FT-IR (KBR, cm-1): 2980(s), 2926(s), 2889(s),
2872(s), 2824(s), 1466(w), 1450(w), 1361(w), 1333(w), 1260-
(w), 1185(s), 1133(w, sh), 1108(m, sh), 1075(s, br), 1063(s,br),
1014(m), 993(m), 959(w). 1H NMR (399.8 MHz, tol-d8): δ 3.67-
(1H, m, OTHF), 3.63(1H, m, OTHF), 3.46(1H, m, OTHF), 3.54-
(1H, m, OTHF), 3.12(1H, m, OTHF) 1.39 to 1.19(3.0H, m,
OTHF), 0.89(1H,m, OTHF), -054(6H, m, CH3). 13C{1H} NMR
(100.1 MHz, tol-d8): δ 79.3, 67.3, 63.1, 26.9, 26.1 (OTHF), -9.3
(CH3). 27Al (104.2 MHz, tol-d8): δ 120.3, 63.1, 0.8. Anal. Calcd
for C7H15AlO2: 53.15 C, 9.55 H. Found: 53.33 C, 9.41 H.
[Al(Et)2(OTHF)]2 (2). AlEt3 (10.0 g, 87.6 mmol), H-OTHF
(8.95 g, 87.5 mmol), and 20 mL of toluene were used. Yield:
10.9 g (67.2%). FT-IR (KBR, cm-1): 2981(s, sh), 2926(s), 2886-
(s), 2853(s), 2791(s), 2715(m), 1466(m), 1460(m), 1412(m),
1358(w), 1331(w), 1261(m), 1230(w), 1187(m), 1077(s), 1063-
(s), 1017(m), 991(m), 946(m), 918(m), 640(s, br). 1H NMR (399.8
MHz, tol-d8): δ 3.78(1H, m, OTHF), 3.64(1H, dq, OTHF), 3.53-
(1H, m, OTHF), 3.38(1H, q, OTHF), 3.15(1H, q, OTHF), 1.36
to 1.28(9H, m, OTHF and CH2CH3), 0.90(1H, m, OTHF), 0.09-
(4.5H, m, CH2CH3). 13C{1H} NMR (100.1 MHz, tol-d8): δ 79.5,
Figure 5. Plots of (a) 5a and (b) 5b. Thermal ellipsoids
are drawn for heavy atoms at the 30% level, and carbon
atoms are drawn as ball and sticks for clarity.
68.1, 64.5, 26.9, 21.1(OTHF), 10.9(CH2CH3), 1.32(CH2CH3). 27
-
Al (104.2 MHz, tol-d8): δ 131.2, 63.9, 5.1. Anal. Calcd for C9H19-
AlO2: 58.05 C, 10.28 H. Found: 58.13 C, 9.97 H.
[Al(Bui)2(OTHF)]2 (3). AlBui3 (1.0 M, 32.5 mL, 32.5 mmol),
H-OTHF (3.33 g, 32.5 mmol), and 20 mL of toluene were used.
Yield: 6.83 g/7.84 (87.1%). FT-IR (KBR, cm-1): 2940(s), 2888-
(s), 2858(s), 2782(s), 1460(m), 1405(w), 1372(w), 1356(m), 1331-
(w), 1313(w), 1259(w), 1179(m), 1064(s), 1014(s), 991(m),
939(m), 921(w), 828(m), 817(m), 672(s), 642(s), 594(w), 562-
(w), 513(w), 469(w), 444(m), 420(w). 1H NMR (399.8 MHz, tol-
d8): δ 3.81(1H, m, OTHF), 3.69-3.56(3H, m, OTHF), 3.37(1H,
m, OTHF), 3.19(1H, q, OTHF), 1.19(29.0H, m, OTHF and
(CH2)3CH3), 0.90(1H, m, (CH2)3CH3), 0.081(6H, m, (CH2)3CH3).
13C{1H} NMR (100.1 MHz, tol-d8): δ 79.3, 68.1, 64.7, 30.9, 29.9
(OTHF) 27.3, 27.0, 26.5, 24.1, 23.7, 23.2 (CH2)3CH3). 27Al (104.2
MHz, tol-d8): δ 121.9, 65.1. Anal. Calcd for C13H27AlO2: 64.43
C, 11.23 H. Found: 64.60 C, 10.95 H.
General Alkoxylation Reaction. Under an atmosphere
of argon, compound 1 was dissolved in toluene, and the
appropriate H-OR dissolved in toluene was slowly added by
pipet. The reaction is exothermic, but the rate of methane gas
evolution is highly dependent on the alcohol used. After
stirring for 12 h, the mixture was heated to ensure complete
exchange and/or to redissolve any precipitates that may have
formed. After this, the mixture was allowed to cool slowly and
then set aside to slowly evaporate until X-ray quality crystals
formed.
Figure 6. Plot of 6. Thermal ellipsoids are drawn for
heavy atoms at the 30% level, and carbon atoms are drawn
as ball and sticks for clarity.
obtained using a WALTZ-16 composite pulse 1H decoupling, a
500 ms recycle delay, a π/2 pulse excitation, and 128 signal
averages.
(19) Dumazy, Y.; Amoureux, J.-P.; Fernandez, C. Mol. Phys. 1997,
90, 959.
(20) Bennett, A. E.; Rienstra, C. M.; Auger, M.; Lakshmi, K. V.;
Griffin, R. G. J. Chem. Phys. 1995, 103, 6951.
The solid state 13C NMR MAS and cross-polarization (CP)
MAS NMR experiments were collected on a Bruker Avance400
NMR spectrometer with a 4 mm broadband probe at a

734 Organometallics, Vol. 24, No. 4, 2005
Boyle et al.
Table 1. Data Collection Parameters for 1-3
[Al(Me)(DMP)(OTHF)]2 (4). Compound 1 (0.500 g, 1.58
mmol), H-DMP (0.386 g, 3.16 mmol), and 20 mL of toluene
were used. Yield: 0.65 g (77.7%). FT-IR (KBR, cm-1): 3070-
(w, sh), 3005 (w, sh), 2980(m, sh), 2927(s, br), 2892(m), 2877-
(m), 2825(w, sh), 1618(m), 1470(s, br), 1432(s), 1288(s), 1240-
(m), 1190(s), 1074(s), 1015(m), 994(m), 917(w), 888(m), 934(m,
1
2
3
chemical
formula
fw
temp (K)
space group
C
14H28Al2O4
C
18H38Al2O4
C
26H54Al2O4
314.32
273(2)
monoclinic
C2/c
16.242(4)
9.887(2)
13.764(3)
372.44
484.65
293(2)
triclinic P1h
203(2) K
monoclinic
P2(1)/n
br), 769(m), 752(m), 754(m), 6801(s, br), 587(w), 561(w), 509-
1
(w). H (399.8 MHz, tol-d8): δ 7.07(2H, d, OCMe-2,6, JH-H
)
3.6 Hz), 6.72(1H, t, OCMe-2,6, JH-H ) 7.6 Hz), 3.77-3.42(4H,
m, OTHF), 3.29-2.95(3.0H, m, OTHF), 2.83(0.2H, t, OTHF,
JH-H ) 10 Hz), 2.41(8.4H, m, OC6H3(CH3)2), 1.33-0.51(8.2H,
m, OTHF), -0.42, -0.44, -0.46,-0.53, -0.61(3.5H, s, CH3).
13C{1H} (100.1 MHz, tol-d8): δ 131.2, 128.8, 127.4, 127.3, 118.0,
117.9(OC6H3(CH3)2), 80.3, 80.2, 80.1, 80.0, 79.5, 79.4, 68.7,
68.6, 68.3, 68.1, 68.0, 63.7, 63.6, 63.5, 63.4, 63.3, 32.4, 26.9,
26.1, 26.0, 25.8, 23.5(OTHF, OC6H3(CH3)2), 18.7, 18.6, 18.5-
(CH3). 27Al (104.2 MHz, tol-d8): δ 69.6. Anal. Calcd for C28H42-
Al2O6: 63.62 C, 8.00 H. Found: 63.15 C, 7.81 H.
[Al(Me)(DBP)(OTHF)]2 (5a). This reaction mixture was
heated at reflux temperatures for 12 h prior to attempting to
grow crystals. Compound 1 (1.00 g, 3.16 mmol), H-DBP (1.31
g, 6.37 mmol), and 20 mL of toluene were used. Yield: 1.85 g
(83.4%). FT-IR (KBR, cm-1): 2957(s), 2926(s), 2889(s), 2874-
(s), 1363(w), 1261(w), 1184(m), 1100(m, sh), 1076(s, br), 1063-
a (Å)
15.3187(16)
7.9024(8)
18.3558(19)
9.298(2)
9.535(2)
10.182(3)
91.508(4)
109.772(4)
115.180(4)
753.3(3)
1
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
123.231(4)
96.019(2)
1848.7(7)
4
1.129
2209.8(4)
4
1.119
Dcalcd
1.068
(Mg/m3)
µ(Mo KR)
0.166
0.148
0.122
(mm-1
)
R1a (%)
(all data)
wR2b (%)
(all data)
8.74 (11.68)
24.72 (27.60)
7.63 (9.45)
19.11 (20.64)
6.98 (7.71)
18.08 (18.82)
2
a R1
)
∑||Fo|
-
|Fc||/∑|Fo|
×
100. b wR2
)
[∑w(Fo
-
2
2
Fc )2/∑(w|Fo| )2]1/2 × 100.
1
(s, br), 1016(s), 806(m), 747(m), 680(s, br), 465(w). H (399.8
MHz, tol-d8): δ 7.38-7.30(1.2H, m, OC6H3(C(CH3)3)2), 7.11-
(0.7H, d, OC6H3(C(CH3)3)2, JH-H ) 4 Hz), 6.81(0.6H, t, OC6H3-
(C(CH3)3)2, JH-H ) 5.2 Hz), 3.97-2.99(4.5H, M, OTHF), 1.66,
1.648, 1.62(11.3H, s, OC6H3(C(CH3)3)2), 1.33(7.6H, s, OC6H3-
(C(CH3)3)2), -0.20, -0.30, -0.31, -0.32, -0.48, -0.50, -0.53,
-0.54, -0.55(2H, s, CH3). 13C{1H} (100.1 MHz, tol-d8): δ 139.6,
125.9, 125.6, 120.7, 117.6 (OC6H3(C(CH3)3)2)), 87.9, 81.9, 79.3,
79.1, 69.9, 64.1, 63.2, 62.8, 36.1, 35.8, 34.7, 32.4, 32.1, 30.7,
31.6, 23.5 (OTHF, OC6H3(C(CH3)3)2), 14.5 (CH3). Anal. Calcd
for C20H33AlO5: 68.94 C, 9.55 H. Found: 68.83 C, 9.38 H.
Al2(Me)3(OTHF)2(DBP) (5b). Compound 1 (1.00 g, 3.16
mmol), H-DBP (0.653 g, 3.16 mmol), and 10 mL of toluene were
used. Reflux temperatures are not necessary to isolate 5b.
Yield: 1.40 g (86.9%). FT-IR (KBr, cm-1): 3034(w), 2956(s),
2927(s), 2873(m), 1720(w), 1655(w), 1561(w), 1466(m), 1460-
(m), 1420(s), 1288(s), 1280(s), 1188(m), 1071(s), 1018(m, sh),
902(m), 883(m), 819(m), 752(m), 701(s), 670(s), 623(m), 473-
Table 2. Data Collection Parameters for 4
chemical formula
fw
temp (K)
space group
a (Å)
b (Å)
c (Å)
C28H42Al2O6
528.58
203(2)
triclinic P1h
7.9767(8)
13.2255(13)
14.4924(15)
85.607(2)
81.167(2)
76.769(2)
1469.3(3)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
Dcalcd (Mg/m3)
1.195
0.136
7.83 (9.16)
17.85 (18.85)
µ(Mo KR) (mm-1
)
R1a (%) (all data)
wR2b (%) (all data)
2
1
a R1
)
∑||Fo|
-
|Fc||/∑|Fo|
×
100. b wR2
)
[∑w(Fo
-
(m). H (399.8 MHz, tol-d8): δ 7.38, 7.36(d, OC6H3(C(CH3)3)2,
2
2
Fc )2/∑(w|Fo| )2]1/2 × 100.
JH-H ) 4.0 Hz), 6.81, 6.08(t, OC6H3(C(CH3)3)2, JH-H ) 8.0 Hz),
3.90-2.98(5.4H, m, OTHF), 1.66, 1.63, 1.61(10.4H, s, OC6H3-
(C(CH3)3)2), -0.21, -0.30, -0.32, -0.39, -0.49, -0.53, -0.54,
-0.56(4.3H, s, CH3). 13C{1H} (100.1 MHz, tol-d8): δ 139.1,
125.9, 125.5, 117.5, 117.4 (OC6H3(C(CH3)3)2), 79.6, 19.2, 78.9,
68.9, 68.7, 67.7, 64.2, 63.1, 62.8, 35.8, 32.4, 32.1, 31.9, 31.6,
31.6, 30.7, 27.1, 25.8, 25.6, 23.5 (OTHF, OC6H3(C(CH3)3)2),
14.7(CH3). 27Al (104.2 MHz, tol-d8): δ 63.8. Anal. Calcd for
C27H48Al2O5: 64.01 C, 9.55 H. Found: 64.01 C, 9.34 H.
[Al(Me)(TPS)(OTHF)]2 (6). Compound 1 (0.500 g, 1.58
mmol), H-TPS (0.874 g, 3.16 mmol), and 20 mL of toluene were
used. Yield: 1.25 (85.1%). FT-IR (KBR, cm-1): 3134(s), 3066-
(s), 3047(s), 3021(s), 2997(s), 2926(s, br), 2877(s), 1428(s), 1261-
(w), 1192(w), 1113(s), 1076(s, br), 1064(s, br), 1026(m), 998(m),
825(m), 744(s), 705(s), 663(m, br), 560(w), 516(s), 468(m), 424-
(w). 1H (399.8 MHz, tol-d8): δ 7.85, 7.19(2.5H, br m, C6H5),
3.6-2.8, 2.50, 1.25-0.87(1.0H, m, OTHF), -0.34, -0.37, -0.40,
-0.42, and -0.57(0.5H, m, CH3). 13C{1H} (100.1 MHz, tol-d8):
δ 140.9, 140.3, 140.1, 137.2, 136.2, 136.1, 136.0, 136.0, 129.6,
129.4, 128.8, 128.1, 126.0(OSi(C6H5)3) 81.9, 79.5, 79.3, 79.1,
68.0, 67.7, 66.2, 64.3, 64.2, 63.3, 32.5, 26.8, 25.8, 25.7, 23.4
(OTHF), 14.6 (CH3). 27Al (104.2 MHz, tol-d8): δ 70.5. Anal.
Calcd for C55H62Al2O6Si2: 71.09 C, 6.73 H. Found: 71.12 C,
6.77 H.
graphite-monochromatized Mo Ka radiation (λ ) 0.7107 Å).
The lattice parameters were optimized from a least-squares
calculation on carefully centered reflections. Lattice determi-
nation and data collection were carried out using SMART
Version 5.054 software. Data reduction was performed using
SAINT Version 6.01 software. The structure refinement was
performed using XSHELL 3.0 software. The data were cor-
rected for absorption using the SADABS program within the
SAINT software package. Data collection parameters are given
in Tables 1-4 for 1-3, 4, 5a,b, and 6, respectively.
Each structure was solved using direct methods. This
procedure yielded the heavy atoms, along with a number of
C, N, and O atoms. Subsequent Fourier synthesis yielded the
remaining atom positions. In cases in which the C, N, and O
atoms were not significantly disordered, the hydrogen atoms
were fixed in positions of ideal geometry and refined within
the XSHELL software. These idealized hydrogen atoms had
their isotropic temperature factors fixed at 1.2 or 1.5 times
the equivalent isotropic U of the C atoms to which they were
bonded. Therefore, idealized hydrogen bond distances were
excluded from the finalized structural tables. In cases in which
the atoms were not significantly disordered, the final refine-
ment of each compound included anisotropic thermal param-
eters on all non-hydrogen atoms. Additional information
concerning the data collection and final structural solutions
of 1-6 can be found in the Supporting Information. Any
General X-ray Crystal Structure Information. Each
crystal was mounted onto a thin glass fiber from a pool of
Fluorolube and immediately placed under a liquid N2 stream,
on a Bruker AXS diffractometer. The radiation used was

OTHF Derivatives of Alkyl Aluminum Species
Organometallics, Vol. 24, No. 4, 2005 735
Table 3. Data Collection Parameters for 5a and 5b
addition was complete, the reaction was stirred for 0.5
h and then was warmed until the reaction boiled to
ensure complete exchange. For the DBP derivative
where n ) 2, the reaction required longer reflux times.
After this, the reaction was allowed to cool to room
temperature and set aside until crystals formed. No
change in color was noted throughout the reaction. FTIR
data indicated that the alcohol had been de-protonated
and was coordinated to the Al metal center. To charac-
terize these species, X-ray crystallographic studies were
undertaken. The products from each of these reactions
were isolated as 1-6, and the plots are shown in Figures
1-6, respectively.
Solid State Structure. The solid state structures of
compounds 1-6 are all dinuclear with each Al adopting
a five-coordinated distorted square base pyramidal
(SBP) geometry. The bond distances and angles are
consistent within this family and with what was re-
ported in the literature for similar Al/OTHF systems.21-23
The OTHF ligand acts as a chelating bridging moiety
where the alcohol oxygen acts as the bridge and the THF
oxygen coordinates to the metal. The remaining two
sites are filled by either the starting alkyl or modifying
alkoxides. The degree of substitution is controlled by
the steric bulk of the ligand. For instance, the H-DMP
and H-TPS reagents easily add 2 equiv to the Al metal
centers, forming 4 and 6 at room temperature; however,
we were not able to isolate the monosubstituted species
for this ligand set under these conditions. However,
reflux temperatures were required to obtain the disub-
stituted species 5a, whereas room-temperature condi-
tions with DBP-H led to the monosubstituted species
5b. Additional substitution becomes difficult for any of
the ligands investigated, and we have not been able to
isolate a fully substituted aryloxide species. The IR
spectra show the expected loss of OH stretch and the
various substituents for the different substitutions.
5a
5b
chemical formula
fw
C
40H66Al2O6
C
27H48Al2O5
696.89
506.61
temp (K)
203(2)
monoclinic
P2(1)/n
9.6840(16)
12.117(2)
17.288(3)
92.609(3)
2026.4(6)
2
1.142
0.114
6.30 (7.82)
15.85 (14.14)
203(2)
monoclinic
P2(1)/n
12.793(2)
14.875(3)
16.615(3)
110.777(3)
2956.2(9)
4
1.138
0.130
7.46 (10.79)
15.60 (14.22)
space group
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
Dcalcd (Mg/m3)
µ(Mo KR) (mm-1
)
R1a (%) (all data)
wR2b (%) (all data)
2
a R1
)
∑||Fo|
-
|Fc||/∑|Fo|
×
100. b wR2
)
[∑w(Fo
-
2
2
Fc )2/∑(w|Fo| )2]1/2 × 100.
Table 4. Data Collection Parameters for 6
chemical formula
fw
C55H62Al2O6Si2
929.19
temp (K)
space group
a (Å)
203(2)
monoclinic C2/c
11.542(3)
19.145(5)
23.515(6)
98.444(4)
5140(2)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
4
Dcalcd (Mg/m3)
1.201
µ(Mo KR) (mm-1
)
0.151
R1a (%) (all data)
wR2b (%) (all data)
8.18 (21.49)
11.89(23.71)
2
a R1
)
∑||Fo|
-
|Fc||/∑|Fo|
×
100. b wR2
)
[∑w(Fo
-
2
2
Fc )2/∑(w|Fo| )2]1/2 × 100.
variations from standard structural solution associated with
the representative compounds are discussed below.
Results and Discussion
While the previous literature report indicated the
structure of the H-OTHF substituted-AlMe3 was
[(Me2Al)3(µ-OTHF)6]Al,18 under the conditions reported
here, which differed by higher synthesis temperatures
and longer reaction times, the product isolated was
determined to be 1. A literature search of other H-OTHF
Al adducts indicates that there are only a few struc-
turally characterized species that use both this metal
and ligand;21,22 however, these structures involve
either other metals or halide ligands that may be un-
desired for materials synthesis. Another Al complex
with similar ligand constructs involves the quinaldinato
ligand, yielding the dinculear complexes [(Bui)2Al(µ-O-
8-C10H9N)]2 and [(Bui)Al(µ-O-8-C10H9N)2]2,23 which ex-
hibited strong fluorescent emissions. Our initial inves-
tigations explored the effect that the steric bulk of the
alkyl group would have on the structure and investi-
gated the ability to exchange OR on the central core of
1. The following shows the results of these studies.
Synthesis. H-OTHF dissolved in toluene was slowly
added via pipet to a solution of AlR3 in the same solvent
(eq 1, note: this reaction is very exothermic!). After
Thermal Properties. The high reactivity of the
alkyls does not appear to affect their stability at high
temperatures, since the elemental analyses of these
species are, surprisingly, in full agreement with the
crystal structure. The melting point was determined for
each of the alkyl derivatives: 1 at 145 °C, 2 at 65 °C, 3
at 85 °C.
TGA/DTA data obtained on these compounds shows
almost complete volatilization of 1-3 before 300 °C in
a single step in the TGA. The observed TGA weight loss
for conversion to the expected Al2O3 is substantially
beyond the theoretical amount. The DTA reveals an
endotherm at ∼150, 73, and 88 °C for 1-3, respectively,
which correlates with the observed melting points, vide
infra. This is followed by another endotherm for 1
around 200 °C but two exotherms for 2 and 3 at 260/
300 and 287/328 °C associated with the weight loss. The
TGA weight loss revealed only a very small amount of
material was left in the sample holder upon completion
of the thermal treatment. These traits (high volatility,
low melting point, and low decomposition temperature)
make 1-3 suitable candidates for metal organic chemi-
cal vapor deposition (MOCVD) precursors or for nano-
particle generation. Additional work to verify this is
underway.
(21) Sobota, P.; Utko, J.; Brusilovets, A. I.; Jerzykiewicz, L. B. J.
Organomet. Chem. 1998, 553, 1998.
(22) Sobata, P.; Utko, J.; Ejfler, J.; Jerzykiewics, L. B. Organome-
tallics 2000, 19, 4929.
Thermal analysis of 4-7 showed multistep weight
loss in the TGA coupled with an exothermic event in
(23) Toulokhonova, I. S.; Guzei, I.; Kavana, M.; West, R. Main Group
Met. Chem. 2002, 25, 489.

736 Organometallics, Vol. 24, No. 4, 2005
Boyle et al.
the DTA profile for each sample. The DBP derivative
shows two exothermic peaks in the DTA. The weight
loss of the species is less than calculated for complete
conversion to Al2O3. The additional weight observed is
most likely a result of the presence of amorphous carbon
due to incomplete combustion, which is consistent with
the final black-colored powder isolated. The alkoxide
derivatives all exhibit a small endotherm associated
with melting of the precursor. Decomposition of the
precursor is initiated after 250 °C, and complete weight
loss is achieved prior to 500 °C with no further thermal
events.
Solution State NMR. Crystalline material of 1-6
was dried and then redissolved in the appropriate
solvent to investigate the solution behavior of these
compounds. Several characteristics of the OTHF ligand
were known to complicate the solution behavior of these
compounds. Once bound to the Al metal center through
the alcohol atom, the OTHF ligand has nine protons
that are no longer equivalent. In addition, the â-hydro-
gen can be oriented above or below the plane defined
by the Al2O2 central core, leading to the formation of
cis/trans isomers. Furthermore, an equilibrium between
the solid state dinuclear and mononuclear species of
1-6 may also occur.
For the iso-structural compounds 1-3, the observed
1H NMR spectra were, as expected, very similar, reveal-
ing eight multiplets for the OTHF. Additional peaks
representing the different pendant hydrocarbon alkyl
groups (methyl, ethyl, or iso-butyl) were also observed.
For 1, three types of methyl groups were observed in
the negative 1H chemical shift region. For 2 and 3, the
alkyl shifts are further upfield than a normal shift but
not as significant as observed for the directly bound
methyls of 1. The 13C{1H} for each shows the expected
five resonances associated with the OTHF, but the
majority of these peaks are present as multiplets or as
broad singlets. The 13C{1H} methyl chemical shifts of 1
are again negative and very broad. For 2 and 3 similar
duplicate resonances are noted and broad alkyl peaks
observed.
that a rapid equilibrium between the different species
is not present, the cis/trans isomers must be present
in an almost 1:1 ratio.
VT analysis of 2 shows a simplification of the CH2-
CH3 region upon warming to 95 °C. The initial 12-14
proton resonances partially coalesce into six somewhat
overlapping resonances. This spectral simplification
reflects some dynamic equilibrium within the system
(perhaps monomer/dimer interconversion), but the re-
tention of multiple resonances at elevated temperatures
suggests that the cis/trans isomers do not interconvert.
The spectral variations observed therefore are more
likely related to an equilibration of the ethyl group
configuration on 2. The major peaks have been tenta-
tively assigned as the overlapping inequivalent meth-
ylene resonances of the inequivalent cis/trans isomers.
Due to the increased complexity of the NMR spectrum
of 3 over 2, VT NMR measurements were not obtained.
To further elucidate the solution behavior, 27Al NMR
data were collected. For 1-3, two broad peaks were
noted at around δ 118 and 63 ppm. The relative amount
of the upfield (δ 118 ppm) resonance becomes larger
with increasing temperature. If the cis/trans species are
present, they would have the same coordination and two
very similar peaks should be present. Since 27Al NMR
chemical shifts are very dependent upon coordination,
assignments based on the chemical shift can be made.
Four-coordinated Al metal centers are in agreement
with the resonance at δ 118 ppm, while the 65 ppm
resonance is the result of an increase in Al coordination.
The NMR experiments reflect that there is a change in
coordination due to the coordination and subsequent
loss of the oxygen of the THF ring of the OTHF ligand.
An additional minor, very sharp peak around δ +5 ppm
was noted for some samples, which is most likely a
decomposition product due to the high reactivity of these
compounds and may correspond to an AlO6 species. This
indicates that the THF ring coordinates more as the
temperature is lowered prior to crystallization. Interest-
ingly this variation in the coordination does not allow
for the interconversion between cis/trans, which is
1
confirmed by the H NMR studies.
Combined, these data indicate that in solution either
there are different isomers present or an equilibrium
exists. Due to the chiral proton on the THF ring, isomers
with the methoxy substituent either cis (both up or
down) and/or trans (one up and one down) may be
The 1H and 13C{1H} NMR spectra of 4-6 reveal
resonances associated with OTHF, but there is signifi-
cantly more fine structure than was noted for the simple
dialkyl derivatives. In addition, there are numerous Me
resonances in the negative chemical shift region. The
presence of multiple resonances observed in the 1H
NMR is also carried over into the data observed for the
13C NMR spectra. The large number of resonances
observed for these species implies that cis/trans isomers
are present. Due to the asymmetry of the alkoxy
molecules, a number of arrangements are possible and
potentially reflected in the NMR spectrum.
1
present. Variable-temperature H NMR spectra were
obtained to differentiate between these two explana-
tions. Upon warming compound 1 to 70 °C in tol-d8,
minor changes in the different spectra were observed,
with the relative chemical shift differences between the
different 1H resonances narrowing slightly. No broaden-
ing or coalescence due to dynamic ligand exchange
behavior was observed. This demonstrates that the two
isomeric species present in solution do not interconvert
on the NMR time scale, arguing against the dynamic
equilibrium description.
Initial solid state NMR data for 124 suggest that the
Al is indeed in an asymmetric bonding environment
with a 27Al quadrupolar coupling constant (CQ) of ∼22
MHz and an asymmetry parameter (ηQ) of ∼1. These
experimental results are consistent with the predicted
CQ based on the crystal structure of 1. The size of CQ is
consistent with other reported alkylaluminoxane bound
Al environments.25 Previous studies of methylalumi-
noxane (MAO) gels and related compounds determined
The 1H NMR spectrum of the methyl region of 1
reveals three resonances at room temperature in the
approximate 1.0:2.2:1.0 ratio, but is not a multiplet due
to J coupling. The observed fine structure in the methyl
1
region of the H NMR is the result of three distinct,
overlapping proton species produced from the presence
of cis/trans isomers. Since the VT experiments show
(24) Schurko, R. W.; Alam, T. M.; Boyle, T. J. Unpublished results.

OTHF Derivatives of Alkyl Aluminum Species
Organometallics, Vol. 24, No. 4, 2005 737
CQ ranging from 12 to 37 MHz for the methylaluminum
oxane subunits and aminato- and propanolato-alumi-
num clusters. Additional wide-line analyses of the
spectra of these compounds are currently being inves-
tigated.24
alkoxide ligand. The bulk powders were investigated by
multinuclear NMR and elemental analyses and found
to be consistent with the single-crystal X-ray structures.
This system offers a scaffold to build more complex
metal alkoxides with the ubiquitous Al cation in a
controlled manner due to an accessible reactive site on
the Al metal center.
Summary and Conclusions
Acknowledgment. For support of this research, the
authors would like to thank the Office of Basic Energy
Sciences of the Department of Energy and the United
States Department of Energy. Sandia is a multiprogram
laboratory operated by Sandia Corporation, a Lockheed
Martin Company, for the United States Department of
Energy under contract DE-AC04-94AL85000.
We have developed a family of alkyl-OTHF aluminum
species with characteristics that are promising for
materials synthesis (i.e., MOCVD and nanoparticle
production). These derivatives form the identical di-
nuclear species [R2Al(µ-OTHF)]2. The systematic sub-
stitution of the alkyls was demonstrated for the first
two equivalents forming [R(OR)Al(µ-OTHF)2AlR2] or
[R(OR)Al(µ-OTHF)]2 depending on the steric bulk of the
Supporting Information Available: X-ray crystallo-
graphic files in CIF format for the structures 1-6 are available
free of charge via the Internet at http://pubs.acs.org.
(25) Bryant, P. L.; Harwell, C. R.; Mrse, A. A.; Emery, E. F.; Gan,
Z. H.; Caldwell, T.; Reyes, A. P.; Kuhns, P.; Hoyt, D. W.; Simeral, L.
S.; Hall, R. W.; Butler, L. G. J. Am. Chem. Soc. 2001, 123, 12009.
OM0493199