Preparation, characterization, and reactions of [(EDBP)Al(μ-OiPr)]2, a novel catalyst for MPV hydrogen transfer reactions

Article abstract of DOI:10.1021/om9909690

The reaction of [(μ-EDBP)AlMe]₂ (EDBP-H₂ = 2,2′-ethylidenebis(4,6-di-tert-butylphenol) with 2 mol equiv of 2-propanol at ambient temperature yields [(EDBP)Al(μ-OⁱPr)]₂ (1), which has shown excellent catalytic activities toward hydrogen transfer reactions between aldehydes and 2-propanol (Meerwein-Ponndorf-Verley (MPV) reactions). The addition of 4 mol equiv of benzaldehyde, 4-methoxybenzaldehyde, or 4-chlorobenzaldehyde to [(EDBP)Al(μ-OⁱPr)]₂ yields [(EDBP)Al(μ-OBz-p-X)(O=CHC₆H₄-p-X)]₂ (2, X = H; 3, X = OMe; 4, X = Cl). However, in the reaction of 1 with excess 4-nitrobenzaldehyde, only the four-coordinated complex [(EDBP)Al(μ-OBz-P-NO₂)]₂ (5) was obtained. Complex 1 further reacts with 2 mol equiv of OPPh₃ or hexamethylphosphoramide (HMPA), yielding the four-coordinated monomeric complex [(EDBP)Al(OⁱPr)(S)] (6, S = OPPh₃; 7, S = HMPA). Compounds 1, 3, 6, and 7 have been characterized by X-ray crystal structure determinations, enabling us to describe the intermediate of the MPV reactions.

Full text of DOI:10.1021/om9909690

1864
Organometallics 2000, 19, 1864-1869
P r ep a r a tion , Ch a r a cter iza tion , a n d Rea ction s of
[(EDBP )Al(µ-OiP r )]2, a Novel Ca ta lyst for MP V Hyd r ogen
Tr a n sfer Rea ction s
Bao-Tsan Ko, Chen-Chang Wu, and Chu-Chieh Lin*
Department of Chemistry, National Chung-Hsing University, Taichung 402,
Taiwan, Republic of China
Received December 7, 1999
The reaction of [(µ-EDBP)AlMe]2 (EDBP-H2 ) 2,2′-ethylidenebis(4,6-di-tert-butylphenol)
with 2 mol equiv of 2-propanol at ambient temperature yields [(EDBP)Al(µ-OiPr)]2 (1), which
has shown excellent catalytic activities toward hydrogen transfer reactions between aldehydes
and 2-propanol (Meerwein-Ponndorf-Verley (MPV) reactions). The addition of 4 mol equiv
of benzaldehyde, 4-methoxybenzaldehyde, or 4-chlorobenzaldehyde to [(EDBP)Al(µ-OiPr)]2
yields [(EDBP)Al(µ-OBz-p-X)(OdCHC6H4-p-X)]2 (2, X ) H; 3, X ) OMe; 4, X ) Cl). However,
in the reaction of 1 with excess 4-nitrobenzaldehyde, only the four-coordinated complex
[(EDBP)Al(µ-OBz-p-NO2)]2 (5) was obtained. Complex 1 further reacts with 2 mol equiv of
OPPh3 or hexamethylphosphoramide (HMPA), yielding the four-coordinated monomeric
complex [(EDBP)Al(OiPr)(S)] (6, S ) OPPh3; 7, S ) HMPA). Compounds 1, 3, 6, and 7 have
been characterized by X-ray crystal structure determinations, enabling us to describe the
intermediate of the MPV reactions.
Sch em e 1
In tr od u ction
Although aldehydes and ketones can be reduced to
alcohols by a variety of reagents,1 Meerwein-Ponndorf-
Verley (MPV) reductions of aldehydes and ketones are
still interesting, as they are highly selective and can be
performed under mild conditions. In general, the re-
ductants in MPV reactions are simple organic molecules,
such as 2-propanol, and these reductions employ an
aluminum alkoxide2 or a transition-metal complex as a
catalyst.3 Since the discovery of MPV reactions, many
aluminum alkoxides have been used,2 and their reaction
mechanisms have been studied. The generally accepted
mechanism for MPV reactions proceeds via a complex
in which both the carbonyl compound and the reducing
alcohol are bound to the metal ion as shown in Scheme
1. The carbonyl is then activated upon coordination to
Al(III), followed by a hydride transfer from the alcohol-
ate to the carbonyl group via a six-membered transition
state.4 But interestingly, none of the intermediates for
MPV reactions have ever been isolated and thoroughly
characterized. Therefore, the crystal structure deter-
mination of an MPV reaction intermediate as well as
the catalyst will be of immense help in understanding
the MPV reactions and thereby modifying the catalytic
activity. Our recent interest has been the preparation
and use of some novel aluminum derivatives as Lewis
acids for the catalysis of various reactions such as
Diels-Alder reactions,5 ring-opening polymerizations
(ROP) of lactones,6 and MPV reactions. We report herein
the synthesis, characterization, and catalytic studies of
a novel aluminum alkoxide. Preliminary results show
that this complex efficiently catalyzes the reduction of
different aldehydes in the presence of 2-propanol.
(1) (a) Brown, W. G. Organic Reactions; Roger, A., Ed.; Wiley: New
York, 1951; Vol. 6, p 469. (b) Hajos, A. Complex Hydrides & Related
Reducing Agents in Organic Synthesis; Elsevier: New York, 1979. (c)
Subha Rao, Y. V.; Choudary, B. M. Synth. Commun. 1992, 22, 2711.
(d) Hudlicky, M. Reductions in Organic Synthesis; Ellis Horwood:
Chichester, U.K., 1984. (e) Hutchins, R. O.; Kandasamy, D. J . Am.
Chem. Soc. 1973, 95, 6131.
(2) (a) Ooi, T.; Takahashi, M.; Maruoka, K. J . Am. Chem. Soc. 1996,
118, 11307. (b) Akamanchi, K. G.; Noorani, V. R. Tetrahedron Lett.
1995, 36, 5085. (c) Konishi, K.; Makita, K.; Aida, T.; Inoue, S. J . Chem.
Soc., Chem. Commun. 1988, 643. (d) Namy, J . L.; Scouppe, J .; Collin,
J .; Kagon, H. B. J . Org. Chem. 1984, 49, 2045.
(3) (a) Evans, D. A.; Nelson, S. G.; Gagn˜e, M. R.; Muci, A. R. J . Am.
Chem. Soc. 1993, 115, 9800. (b) Noyori, R.; Hashiguchi, S. Acc. Chem.
Res. 1997, 30, 97. (c) Chowdhury, R. L.; Backvall, J .-E. J . Chem. Soc.,
Chem Commun. 1991, 1063. (d) Krasik, P.; Alper, H. Tetrahedron 1994,
50, 4347.
Resu lts a n d Discu ssion
Syn th esis. The reaction of [(µ-EDBP)AlMe]27 (EDBP-
H2 ) 2,2′-ethylidenebis(4,6-di-tert-butylphenol)) with 2
(5) (a) Lin, C. H.; Yan, L. F.; Wang, F. C.; Sun, Y. L.; Lin, C. C. J .
Organomet. Chem. 1999, 587, 151. (b) Ko, B. T.; Lee, M. D.; Lin, C. C.
J . Chin. Chem. Soc. 1997, 44, 163.
(4) (a) Moulton, W. N.; van Atta, R. E.; Ruch, R. R. J . Org. Chem.
1960, 26, 290. (b) Ashby, E. C. Acc. Chem. Res. 1988, 21, 414.
(6) Ko, B. T.; Lin, C. C. Macromolecules 1999, 32, 8296.
(7) Ko, B. T.; Chao, Y. C.; Lin, C. C. Inorg. Chem., in press.
10.1021/om9909690 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 04/21/2000

Novel Catalyst for MPV Hydrogen Transfer Reactions
Organometallics, Vol. 19, No. 10, 2000 1865
Sch em e 2
Sch em e 3
mol equiv of 2-propanol at ambient temperature, fol-
lowed by crystallization from toluene, affords the cata-
lyst [(EDBP)Al(µ-OiPr)]2 (1) in high yield. The reaction
of 4 mol equiv of benzaldehyde, 4-methoxybenzaldehyde,
or 4-chlorobenzaldehyde with [(EDBP)Al(µ-OiPr)]2 yields
the pentacoordinated complex [(EDBP)Al(µ-OBz-p-X)-
(OdCHC6H4-p-X)]2 (2, X ) H; 3, X ) OMe; 4, X ) Cl),
as shown in Scheme 2. The compound 2 can also be
prepared in high yield from the reaction of [(µ-EDBP)-
AlMe]2 with 2 mol equiv of benzyl alcohol in the
presence of 2 mol equiv of benzaldehyde or from the
reaction of [(EDBP)Al(µ-OBz)]2 with 2 mol equiv of
benzaldehyde.6 However, unlike other benzaldehydes,
in the reaction of 2 with 4 equiv of 4-nitrobenzaldehyde,
only the four-coordinated complex [(EDBP)Al(µ-OBz-p-
NO2)]2 (5) was isolated. The isolation of the four-
coordinated complex 5 instead of a pentacoordinated
complex indicates that the strongly electron withdraw-
ing -NO2 group decreases its basicity of 4-nitrobenzal-
dehyde, thereby retarding further coordination.
In contrast to complexes 2-5, the reaction of 1 with
2 mol equiv of triphenylphosphine oxide or HMPA yields
the four-coordinated monomeric compound [Al(EDBP)-
(OiPr)(OPPh3)] (6) or [Al(EDBP)(OiPr)(HMPA)] (7)
(Scheme 3). The Al-O (bridging alkoxide) bond of the
Al2O2 core is broken by the presence of OPPh3 or HMPA.
1H NMR spectra and microanalyses of complexes 1-7
are consistent with our expectations. The observation
of two singlet peaks for both tert-butyl groups in the
NMR spectra of these complexes suggests that these two
F igu r e 1. Molecular structure of 1 as 20% ellipsoids. All
hydrogen atoms are omitted for clarity.
aryl moieties are chemically equivalent, which requires
a σ plane of symmetry passing through the methine
carbon bridging of two phenyl rings and the aluminum
atom. Similar results have been found in [(MMBP)Al-
(R)(S)] and [(MDBP)Al(R)(S)] systems.5,6 This is further
verified by the crystal structure studies of 1, 3, 6, and
7.
Molecu la r Str u ctu r e Stu d ies of 1, 3, 6, a n d 7. The
molecular structures of 1 and 3 are shown in Figure 1
and Figure 2, respectively. Selected bond lengths and
bond angles of 1-3 and a are given in Table 1. The
structure of 1 shows a dimeric feature containing an
Al2O2 core bridging through the oxygen atom of the

1866 Organometallics, Vol. 19, No. 10, 2000
Ko et al.
F igu r e 3. Molecular structure of 6 as 20% ellipsoids. All
hydrogen atoms are omitted for clarity.
F igu r e 2. Molecular structure of 3 as 30% ellipsoids. All
hydrogen atoms and carbon atoms of the tert-butyl groups
are omitted for clarity.
Ta ble 1. Com p a r ison of Selected Bon d Dista n ces
a n d Bon d An gles for [(EDBP )Al(µ-OiP r )2] (1),
[(EDBP )Al(µ-OBz)2] (a ),6
[(EDBP )Al(µ-OBz)(OCHP h )]2 (2),6 a n d
[(EDBP )Al(µ-OBz)(OdCHC6H4-p-OMe)]2 (3)
1
a
2
3
Al-O(1)
1.693(3)
1.694(3)
1.813(3)
1.689(2) 1.753(4) 1.765(2)
1.683(2) 1.745(6) 1.742(2)
1.812(2) 1.809(3) 1.816(2)
Al-O(2)
Al-O(3)
Al-O(3a)
Al-O(4)
1.816 (3) 1.816(2) 1.900(3) 1.906(2)
2.030(3) 2.017(2)
O(1)-C(1)
O(2)-C(13)
O(3)-C(31)
O(4)-C(39)
1.378(5)
1.380(4)
1.462(5)
1.379(4) 1.352(5) 1.367(3)
1.368(3) 1.358(8) 1.358(3)
1.452(4) 1.442(5) 1.444(3)
1.241(8) 1.239(3)
F igu r e 4. Molecular structure of 7 as 20% ellipsoids. All
hydrogen atoms are omitted for clarity.
Ta ble 2. Selected Bon d Dista n ces a n d Bon d
An gles for [(EDBP )Al(OiP r )(OP P h 3)] (6) a n d
[(EDBP )Al(OiP r )(HMP A)] (7)
O(4)-C(39)-C(40)
125.0(5) 125.3(3)
6
7
isopropoxide group, and the geometry around Al is
distorted from tetrahedral. The bridging oxygen atom
bond distances are roughly equivalent to the two Al
centers with an Al-O(3) distance of 1.813(3) Å and Al-
O(3a) distance of 1.816(3) Å. The terminal Al-O bond
distances from the aryloxide ligand are Al-O(1) )
1.693(3) Å and Al-O(2) ) 1.694(3) Å, well within the
normal range previously reported for a four-coordinated
aluminum compound, [(EDBP)AlX(S)].7 The X-ray struc-
ture analysis of 3 reveals a dimeric form, and the
geometry around Al is a distorted trigonal bipyramid,
with the carbonyl oxygen O(4) and one bridging benzyl-
oxy oxygen O(3) on axial positions and the two phenoxy
oxygens O(1) and O(2) and the bridging benzyloxy
oxygen O(3a) on the equatorial positions. As may be
seen from the comparison in Table 1, the Al-O dis-
tances are shorter for the four-coordinated compounds
1 and a than for the pentacoordinated compounds 2 and
3, as expected. However, there is little effect in the Al-O
distance of the methoxy group on the phenyl ring. The
electronegativity of the oxygen of the methoxy substitu-
ent on the para position to the carbonyl group in the
phenyl ring has no effect on the aluminum-oxygen
Al-O(1)
1.709(2)
1.739(2)
1.701(2)
1.794(2)
1.512(2)
1.354(3)
1.359(3)
1.388(5)
1.726(2)
1.733(2)
1.684(2)
1.790(2)
1.502(2)
1.342(3)
1.343(3)
1.305(5)
Al-O(2)
Al-O(3)
Al-O(4)
P-O(4)
O(1)-C(1)
O(2)-C(13)
O(3)-C(31)
Al-O(4)-P
Al-O(3)-C(31)
150.6(1)
136.4(3)
155.2(1)
146.4(3)
bond, as indicated by the almost identical bond lengths
in the isostructural complexes 2 and 3.
The molecular structures of 6 and 7 are shown in
Figure 3 and Figure 4, respectively. Selected bond
lengths and bond angles of 6 and 7 are given in Table
2. Compound 6 crystallizes in the space group P21/n,
and the geometry around Al is a distorted tetrahedron
with the bond distances of Al-O(1) (phenoxy) at 1.709(2)
Å, Al-O(2) (phenoxy) at 1.739(2) Å, Al-O(3) (isopro-
poxy) at 1.701(2) Å, and Al-O(4) (OPPh3) at 1.794(2)
Å, which are all compatible with the bond lengths
observed for four-coordinated aluminum derivatives of
steric bulky phenoxides. Compound 7, which differs

Novel Catalyst for MPV Hydrogen Transfer Reactions
Organometallics, Vol. 19, No. 10, 2000 1867
Ta ble 3. Ca ta lytic MP V Red u ction of Ald eh yd es
w ith 2-P r op a n ol in th e P r esen ce of 1 (10 m ol %)
forming the alkoxy-bridged intermediate C, which then
loses acetone to give the four-coordinated intermediate
D, as observed in 5. In the presence of excess aldehyde,
D readily reacts with aldehyde, yielding the pentaco-
ordinated complexes 2-4. D can also exchange slowly
with 2-propanol to regenerate the catalyst 1, thereby
restarting the reaction cycle. We believe that during the
catalysis the bridging alkoxide skeleton remains un-
changed, because the Al-O (bridging alkoxide) bond of
the Al2O2 core can only be broken by a very strong Lewis
base such as HMPA or triphenylphosphine oxide.
hydride source
(amt, equiv)
conversn
time (h) yield (%)
entry
substrate
PhCHO
1
2
3
4
5
6
7
8
9
iPrOH (2)
iPrOH (2)
iPrOH (2)
iPrOH (1)
iPrOH (2)
iPrOH (2)
iPrOH (2)
iPrOH (2)
iPrOH (2)
1
9
64
85
93
85
25
53
60
99
99
PhCHO
PhCHO
PhCHO
24
24
1
9
24
1
4-MeO-C6H4CHO
4-MeO-C6H4CHO
4-MeO-C6H4CHO
4-Cl-C6H4CHO
4-NO2-C6H4CHO
0.5
In conclusion, a new catalyst, [(EDBP)Al(µ-OiPr)]2, for
the reduction of aldehydes has been synthesized and
this catalyst has demonstrated excellent activities to-
ward the reduction of aldehydes. Its catalytic activity
is better than those of other aluminum alkoxides and
can be used in catalytic amounts. The crystal structure
studies of [(EDBP)Al(µ-OBz-p-X)(OdCHC6H4-p-X)]2 (X
) H, OMe) have enabled us to describe the intermediate
of the MPV reactions. The isolation of [(EDBP)Al(µ-OBz-
p-NO2)]2 also offers useful information toward an un-
derstanding of these reactions. Further studies of this
catalyst in the reduction of ketones are currently
underway.
from compound 6 by replacing the OPPh3 with HMPA,
crystallizes in the space group P212121. The geometry
around Al is nearly identical with that for 6, with the
bond distances of Al-O(1) (phenoxy) at 1.726(2) Å, Al-
O(2) (phenoxy) at 1.733(2) Å, Al-O(3) (isopropoxy) at
1.684(2) Å, and Al-O(4) (HMPA) at 1.790(2) Å, similar
to the values for compound 6.
Ca ta lytic MP V Rea ction s. The catalytic activities
of 1 toward MPV hydrogen transfer reactions have been
studied. In general, reduction of aldehydes in the
presence of 2-propanol was carried out at 25 °C in CDCl3
(1.2 mL) using 10 mol % of 1 (0.05 mmol) as the
initiator. Reduction of different aldehydes has been
systematically conducted as shown in Table 3. Prelimi-
nary results reveal that [(EDBP)Al(µ-OiPr)]2 shows
great catalytic activities toward 4-nitrobenzaldehyde
and 4-chlorobenzaldehyde. These two aldehydes were
reduced to give their corresponding alcohols in quanti-
tative yield at room temperature within 1 h by employ-
ing 1 as catalyst (entries 8 and 9). Compound 1 can also
catalyze the reduction of benzaldehyde (entries 1-4)
and 4-methoxybenzaldehyde (entries 5-7), with reduced
reaction rates compared to those of 4-nitrobenzaldehyde
and 4-chlorobenzaldehyde. The enhanced reaction rate
is probably due to the increasing positive charge of the
carbonyl carbon atom caused by the electron-withdraw-
ing group on the para position.8 The catalytic activity
of 2 is compatible with the trifluoroacetic acid/aluminum
isopropoxide system reported by Akamanchi9 but is
better than other aluminum alkoxide systems. In ad-
dition, the drawback of aldol condensation, which is
usually found in MPV reactions, is not observed in our
system.10
The structural determination of the pentacoordinated
compound 3 suggests that, during the catalytic MPV
reductions of aldehydes, an aldehyde molecule coordi-
nates to the aluminum center to form the pentacoordi-
nated intermediate A, followed by a hydride transfer
from the alcoholate to the carbonyl group via a six-
membered transition state to give the bridging ketone
B, as depicted in Scheme 4. Double coordination of
carbonyl groups with two metals has been observed on
several occasions.11 Because acetone is a much weaker
base than a bridging alkoxide, B isomerizes rapidly,
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All experiments were carried out
under a dry nitrogen atmosphere. Solvents were dried by
refluxing at least for 24 h over sodium/benzophenone (toluene,
hexane), phosphorus pentaoxide (CH2Cl2), or magnesium (2-
propanol) and freshly distilled prior to use. Deuterated solvents
were dried over molecular sieves. 2,2′-Ethylidenebis(4,6-di-tert-
butylphenol), 4-nitrobenzaldehyde, 4-chlorobenzaldehyde,
4-methoxybenzaldehyde, and benzaldehyde were dried prior
to use. AlMe3 (2.0 M in toluene) was purchased and used
without further treatment. Melting points were determined
1
with a Buchi 535 digital melting point apparatus. H and 13C
NMR spectra were recorded on a Varian VXR-300 (300 MHz)
or a Mercury-400 (400 MHz) spectrometer with chemical shifts
given in ppm and TMS as internal standard. Microanalyses
were performed using a Heraeus CHN-O-RAPID instrument.
Infrared spectra were obtained from a Bruker Equinox 55
spectrometer.
[Al(EDBP )(µ-OiP r )]2 (1). To a rapidly stirred solution of
[Al(µ-EDBP)Me]2 (0.96 g, 1.0 mmol) in toluene (30 mL) was
added 2-propanol (0.15 mL, 2.0 mmol) at 25 °C. Stirring was
continued for 16 h, during which time a white precipitate was
formed. The volatile materials were removed under vacuum,
and the residue was redissolved in hot toluene (30 mL) and
this solution cooled to room temperature, affording a colorless
crystalline solid after 12 h. Yield: 0.98 g (86%). Anal. Calcd
for C66H102Al2O6: C, 75.82; H, 9.83. Found: C, 75.20; H, 9.75.
1H NMR (CDCl3, ppm): δ 7.40 (d, 2H, Ph, J ) 2.4 Hz); 7.16
(d, 2H, Ph, J ) 2.4 Hz); 4.63 (m, 1H, OCH(CH3)2, J ) 6.4 Hz);
4.26 (q, 1H, CH(CH3), J ) 6.8 Hz); 1.82 (d, 3H, CH(CH3), J )
6.8 Hz); 1.59 (d, 6H, OCH(CH3)2, J ) 6.4 Hz); 1.40 (s, 18H,
C(CH3)3); 1.32 (s, 18H, C(CH3)3). 13C NMR (CDCl3, ppm): δ
150.58, 140.79, 136.98, 132.39, 121.72, 120.92 (Ph); 71.64
(OCH(CH3)2); 35.45, 34.47, 31.78, 30.40 (t-Bu); 33.21 (CH-
(CH3)); 24.99 (OCH(CH3)2), 22.61 (CH(CH3)). IR (KBr, cm-1):
2959 (s), 2908 (s), 1476 (s), 1445 (s), 1270 (s), 1239 (m), 938
(s), 878(s). Mp: 196-198 °C dec.
(8) Pickkart, D. E.; Hancock, C. K. J . Am. Chem. Soc. 1955, 77, 4642.
(9) Akamanchi, K. G.; Varalakshmy, N. R.; Chaudhari, B. A. Synlett
1997, 371.
(10) de Graauw, C. F.; Peters, J . A.; van Bekkum, H.; Huskens, J .
Synthesis 1994, 1007.
(11) (a) Adams, H.; Bailey, N. A.; Gauntlett, J . T.; Winter, M. J . J .
Chem. Soc., Chem. Commun. 1984, 1360. (b) Rao, C. P.; Rao, A. M.;
Rao, C. N. R. Inorg. Chem. 1984, 23, 2080. (c) Bachand, B. Wuest, J .
D. Organometallics 1991, 10, 2015. (d) Palm, J . H.; Macgillavry, C. H.
Acta Crystallogr. 1963, 16, 963.
[Al(EDBP )(µ-OBz)(OdCHP h )]2 (2). To a rapidly stirred
solution of [Al(EDBP)(µ-OiPr)]2 (0.52 g, 0.50 mmol) in CH2Cl2
(30 mL) was added benzaldehyde (0.20 mL, 2.0 mmol) at room
temperature; the mixture was stirred for a further 4 h, and

1868 Organometallics, Vol. 19, No. 10, 2000
Ko et al.
Sch em e 4
the volatile materials were removed in vacuo, giving an orange
solid. The residue was washed with hexane twice and dried
[Al(EDBP )(µ-OCH2C6H4-p-NO2)]2 (5). 4-Nitrobenzalde-
hyde (0.15 g, 1.0 mmol) in CH2Cl2 (10 mL) was added to a
rapidly stirred solution of [Al(EDBP)(µ-OiPr)]2 (0.52 g, 0.5
mmol) in CH2Cl2 (30 mL). The reaction mixture was stirred
at room temperature for 12 h. The volatile materials were
removed under vacuum. The residue was washed twice with
hexane (10 mL), followed by crystallization induced by a slow
diffusion of hexane into a CH2Cl2 solution, resulting in yellow
solids. Yield: 0.48 g (77%). Anal. Calcd for C37H50AlNO5: C,
under vacuum. Yield: 0.54 g (79%). Anal. Calcd for C88H114
-
1
Al2O8: C, 78.07; H, 8.49. Found: C, 77.81; H, 8.55. H NMR
(CDCl3, ppm): δ 8.74 (s, 1H, PhCHO); 6.99-7.59 (m, 14H, Ph);
5.60 (s, 2H, OCH2); 4.21 (q, 1H, CH(CH3), J ) 6.8 Hz); 1.36 (s,
18H, C(CH3)3); 1.24 (s, 18H, C(CH3)3); 1.04 (d, 3H, CH(CH3),
J ) 6.8 Hz). 13C NMR (CDCl3, ppm): δ 195.1(CdO); 151.9,
140.2, 137.8, 137.1, 135.9, 134.6, 134.1, 130.8, 128.8, 120.3,
127.1, 125.9, 121.0, 120.9 (Ph); 67.4 (OCH2); 35.4, 34.3, 31.8,
30.8 (t-Bu); 31.1 (CH(CH3)); 22.0 (CH(CH3)). IR (KBr, cm-1):
2954 (s), 2904 (s), 1639 (s), 1476 (s), 1456 (m), 1441 (s), 1268
(m), 1238 (m), 855 m). Mp: 224-226 °C dec.
1
72.17; H, 8.18; N, 2.27. Found: C, 71.59; H, 7.62; N, 2.88. H
NMR (CDCl3, ppm): δ 7.07-8.13 (m, 8H, Ph); 5.68 (s, 2H,
OCH2); 4.00 (q, 1H, CH(CH3), J ) 6.8 Hz); 0.89 (d, 3H, CH-
(CH3), J ) 6.8 Hz); 1.39, 1.23 (s, 36H, C(CH3)3). 13C NMR
(CDCl3, ppm): δ 151.2, 147.1, 145.1, 140.9, 136.8, 133.3, 126.1,
123.7, 121.3, 121.1 (Ph); 66.3 (OCH2); 35.5, 34.4, 31.7, 30.7 (t-
Bu); 30.5 (CH(CH3)); 21.9 (CH(CH3)). IR (KBr, cm-1): 2957
(s), 2906 (s), 2869 (s), 1689 (m), 1526 (s), 1475 (s), 1445 (s),
1416 (m), 1347 (s), 1301 (s), 1268 (s), 1240 (s), 1046 (m), 878
(s), 674 (m). Mp: 172-174 °C dec.
[Al(E DBP )(µ-OC6H4-p -OMe)(OdCHC6H4-p -OMe)]2 (3).
This compound was prepared according to the method de-
scribed for 2 using 4-methoxybenzaldehyde (0.24 mL, 2.0
mmol). Yield: 0.59 g (80%). Anal. Calcd for C92H122Al2O12: C,
74.97; H, 8.34. Found: C, 74.46; H, 8.10. 1H NMR (CDCl3,
ppm): δ 8.46 (s, 1H, PhCHO), 6.73-7.47 (m, 14H, Ph); 5.52
(s, 2H, OCH2); 4.32 (q, 1H, CH(CH3), J ) 6.8 Hz); 3.84 (s, 3H,
OCH3); 3.73 (s, 3H, OCH3); 1.36 (s, 18H, C(CH3)3); 1.25 (s, 18H,
C(CH3)3); 1.11 (d, 3H, CH(CH3), J ) 6.8 Hz). 13C NMR (CDCl3,
ppm): δ 192.87 (CdO); 165.9, 158.6, 152.3, 139.8, 137.0, 134.3,
133.5, 130.6, 127.9, 127.4, 120.9, 114.3, 113.7 (Ph); 66.9
(OCH2); 55.7, 55.3 (OCH3); 35.4, 34.3, 31.9, 30.8 (t-Bu); 30.5
(CH(CH3)); 22.3 (CH(CH3)). IR (KBr, cm-1): 2958 (s), 2905 (s),
1640 (s), 1600 (s), 1568 (s), 1514 (s), 1474 (s), 1442 (s), 1303
(s), 1270 (s), 1246 (m), 1163 (s), 1026 (m), 880 (m). Mp: 124-
126 °C dec.
[Al(EDBP )(OiP r )(OP P h 3)] (6). To a rapidly stirred solu-
tion of [Al(EDBP)(µ-OiPr)]2 (1.04 g, 1.0 mmol) in toluene (30
mL) was added triphenylphosphine oxide (0.56 mL, 2.0 mmol).
The reaction mixture was stirred at room temperature for 2
h, and the volatile materials were removed under vacuum. The
residue was extracted with hot toluene (15 mL), and the
extractor was then cooled to room temperature, affording
colorless crystals after standing overnight. Yield: 1.28 g (80%).
Anal. Calcd for C51H66AlO4P: C, 76.47; H, 8.30. Found: C,
1
76.87; H, 8.67. H NMR (CDCl3, ppm): δ 6.99-7.87 (m, 19H,
Ph); 4.68 (q, 1H, CH(CH3), J ) 7.0 Hz); 4.04 (m, 1H, OCH-
(CH3)2, J ) 6.0 Hz); 1.66 (d, 3H, CH(CH3), J ) 7.0 Hz); 1.28,
1.20 (s, 36H, C(CH3)3); 0.87 (d, 6H, OCH(CH3)2, J ) 6.0 Hz).
Mp: >260 °C.
[Al(E DBP )(µ-OC6H 4-p -Cl)(OdCH C6H 4-p -Cl)]2 (4). This
compound was prepared according to the method described for
2 using 4-chlorobenzaldehyde (0.28 g, 2.0 mmol). Yield: 0.61
g (81%). Anal. Calcd for C88H110Al2Cl2O8: C, 70.86; H, 7.43.
Found: C, 70.88; H, 7.38. 1H NMR (CDCl3, ppm): δ 8.73 (s,
1H, PhCHO); 7.01-7.51 (m, 14H, Ph); 5.55 (s, 2H, OCH2); 4.11
(q, 1H, CH(CH3), J ) 7.2 Hz); 1.35 (s, 18H, C(CH3)3); 1.25 (s,
18H, C(CH3)3); 1.06 (d, 3H, CH(CH3), J ) 7.2 Hz). 13C NMR
(CDCl3, ppm): δ 194.6 (CdO); 151.7, 143.5, 140.5, 137.0, 136.6,
134.1, 132.9, 132.3, 132.1, 129.4, 128.4, 127.2, 121.1, 121.0
(Ph); 66.7 (OCH2); 35.4, 34.4, 31.9, 30.8 (t-Bu); 30.1 (CH(CH3));
22.1 (CH(CH3)). IR (KBr, cm-1): 2959 (s), 2905 (s), 1643 (s),
1593 (s), 1473 (s), 1443 (s), 1299 (s), 1269 (s), 1236 (s), 1092
(m), 1033 (m), 875 (s), 851 (s). Mp: 154-156 °C dec.
[Al(EDBP )(OiP r )(HMP A)] (7). The procedure is the same
as for [Al(EDBP)(OiPr)(OPPh3)], except hexamethylphosphor-
amide (0.35 mL, 2.0 mmol) was used. Yield: 1.19 g (85%).
Anal. Calcd for C39H69AlN3O5P: C, 66.73; H, 9.91; N, 5.99.
1
Found: C, 66.75; H, 9.41; N, 5.79. H NMR (CDCl3, ppm): δ
7.35, 7.03 (d, 4H, Ph, J ) 2.8 Hz); 4.65 (q, 1H, CH(CH3), J )
6.8 Hz); 4.28 (m, 1H, OCH(CH3)2, J ) 6.0 Hz); 2.74 (d, 18H,
OdP[N(CH3)2], J H-P ) 9.6 Hz); 1.68 (d, 3H, CH(CH3), J ) 6.8
Hz); 1.39, 1.29 (s, 36H, C(CH3)3); 1.12 (d, 6H, OCH(CH3)2, J )
6.0 Hz). 13C NMR (CDCl3, ppm): δ 153.35, 137.84, 135.51,

Novel Catalyst for MPV Hydrogen Transfer Reactions
Organometallics, Vol. 19, No. 10, 2000 1869
Ta ble 4. Cr ysta llogr a p h ic Da ta for 1, 3, 6, a n d 7
1‚C7H8
3
6
7
formula
fw
C
614.9
40H59AlO3
C46H61AlO6
763.9
C51H66AlO4P
801.0
C39H69AlN3O4P
701.9
space group
a (Å)
b (Å)
P21/c
P1h
P21/n
P212121
19.121(2)
10.935(1)
19.650(2)
11.9923(7)
12.1666(7)
15.3901(9)
77.511(1)
87.329(1)
73.994(1)
2107.2(2)
2
14.044(3)
21.008(4)
17.004(3)
12.955(1)
14.170(1)
23.612(2)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
109.41(1)
97.19(4)
3875.1(7)
4
1.054
0.7107
0.085
4.0-45.0
5002 (F > 4σ(F))
397
4977.2(2)
4
1.069
0.7107
0.112
3.50-52.24
9736 (F > 4σ(F))
514
4334.7(6)
4
1.076
0.7107
0.122
3.44-52.00
8462 (F > 4σ(F))
433
Z
Dcalcd (Mg m-3
λ(Mo KR) (Å)
)
1.161
0.7107
0.094
3.54-50.04
7319 (F > 4σ(F))
478
0.0640
0.1997
abs coeff (mm-1
2θ range, deg
)
no. of obsd rflns
no. of refined params
R1a
0.0737
0.1094
1.45
0.0567
0.1625
1.12
0.0449
0.1323
1.05
wR2b
GOFc
1.55
R1 ) |∑(|Fo - Fc|)/|∑|Fo||. wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2; w ) 0.10. c GOF ) [∑w(|Fo - Fc|)2/(Nrflns - Nparams)]1/2
.
a
b
2
134.07, 120.82, 120.47 (Ph); 63.26 (OCH(CH3)2); 36.86 (d,
determined by a least-squares fit of 5316 reflections for 3, 7740
OdP[N(CH3)2], J C-P ) 21.2 Hz), 35.30, 34.31, 31.94, 30.04 (t-
Bu); 30.69 (CH(CH3)); 28.08 (OCH(CH3)2); 21.99 (CH(CH3)).
Mp: 200-202 °C dec.
reflections for 6, and 5507 reflections for 7. The absorption
correction was based on symmetry-equivalent reflections using
the SADABS program. The space group determination was
based on a check of the Laue symmetry and systematic
absences and was confirmed using the structure solution. The
structure was solved by direct methods using a Siemens
SHELXTL PLUS package. All non-H atoms were located from
successive Fourier maps, and hydrogen atoms were refined
using a riding model. Anisotropic thermal parameters were
used for all non-H atoms, and fixed isotropic parameters were
used for H atoms. Crystallographic data for 1, 3, 6, and 7 are
listed in Table 4.
Typ ica l Exp er im en ta l P r oced u r e for MP V Red u ction
of Ald eh yd es. To a solution of 1 (26 mg, 0.05 mmol) in CDCl3
(1.2 mL) was added benzaldehyde (50 µL, 0.5 mmol), followed
by the addition of 2-propanol (77 µL, 1.0 mmol). The reaction
mixture was stirred for 1 h at 25 °C. The conversion yield was
1
determined by H NMR spectroscopic studies, on the basis of
the integration in the methylene and the CHO region of the
benzyl group.
X-r a y Cr ysta llogr a p h ic Stu d ies. Suitable crystals of 1
were sealed in thin-walled glass capillaries under a nitrogen
atmosphere and mounted on a a Siemens P4 diffractometer.
The crystallographic data were collected using a ω-2θ scan
mode with Mo KR radiation. Cell constants were obtained by
least-squares analysis on positions of 35 randomly selected
reflections. Suitable crystals of 3, 6, and 7 were sealed in thin-
walled glass capillaries under a nitrogen atmosphere and
mounted on a Bruker AXS SMART 1000 diffractometer.
Intensity data were collected in 1350 frames with increasing
ω (width of 0.3° per frame). Unit cell dimensions were
Ack n ow led gm en t. Financial support from the Na-
tional Science Council of the Republic of China is
gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables giving fur-
ther data from the crystal structure determinations of 1, 3, 6,
and 7. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM9909690