Bidentate N, O-aluminum complexes: Synthesis, characterization and catalytic study for MPV reduction reactions

Article abstract of DOI:10.1016/j.jorganchem.2015.06.011

Treatment of AlMe₃ with bidentate N, O-ligands, HOC(Me)(Ph)C₆H₄-NMe₂-2 (L¹H) or HOC(CH₂)₅C₆H₄-NMe₂-2 (L²H) in different molar ratios, four novel aluminum complexes [Me₂AlOC(Me)(C₆H₅) C₆H₄-NMe₂-2] (1), [Me₂AlOC(Me)(CH₂) C₆H₄-NMe₂-2] (2), [Me₂Al{OC(Me)(C₆H₅) C₆H₄-NMe₂-2}₂] (3) and[Me₂Al{OC(Me)(CH₂)₅ C₆H₄-NMe₂-2}₂] (4) were obtained in good yield. Complexes 1-4 were characterized by ¹H and ¹³C NMR spectroscopy, elemental analyses and single crystal X-ray diffraction techniques. Each of the complexes 1, 2, 3 and 4 was tested for the capable of catalyzed Meerwein-Ponndorf-Verley (MPV) reduction of ketones or aldehydes with low catalyst loadings under mild conditions and showed good to excellent catalytic activities.

Full text of DOI:10.1016/j.jorganchem.2015.06.011

Journal of Organometallic Chemistry 794 (2015) 59e64
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Bidentate N, O-aluminum complexes: Synthesis, characterization
and catalytic study for MPV reduction reactions
,
,
, *
Yupeng Hua a b, Zhiqiang Guo c *, Hongyi Suo a, Xuehong Wei a
a School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, PR China
b College of Ordos, Inner Mongolia University, Ordos 017000, Inner Mongolia, PR China
c Institute of Applied Chemistry, Shanxi University, Taiyuan 030006, PR China
a r t i c l e i n f o
a b s t r a c t
Treatment of AlMe3 with bidentate N, O-ligands, HOC(Me)(Ph)C6H4eNMe2-2 (L1H) or HOC(CH2)5C6H4
Article history:
eNMe2-2
(L2H)
in
different
molar
ratios,
four
novel
aluminum
complexes
Received 11 April 2015
Received in revised form
2 June 2015
(1),
(2),
(3)
and
(4) were obtained in good yield. Complexes 1e4 were characterized by
Accepted 6 June 2015
Available online 30 June 2015
1H and 13C NMR spectroscopy, elemental analyses and single crystal X-ray diffraction techniques. Each of
the complexes 1, 2, 3 and 4 was tested for the capable of catalyzed MeerweinePonndorfeVerley (MPV)
reduction of ketones or aldehydes with low catalyst loadings under mild conditions and showed good to
excellent catalytic activities.
Keywords:
N, O-Ligand
Aluminum complex
Crystal structure
Catalyst
© 2015 Elsevier B.V. All rights reserved.
MPV reduction
1. Introduction
high loading of catalyst, high temperature, long reaction time or
removal of produced acetone. Attempts to design and development
Selective synthesis of primary and secondary alcohols is an
important process for the pharmaceutical, fragrance and food
aroma industries [1]. They can be produced by alkylation of alde-
hydes [2] or by oxidation of olefins [3], but a general route is the
of new catalysts to improve the MPV reaction in a milder and less
expensive environment has been attracted much more attentions.
Very recently, McNerney and co-workers reported that siloxide-
supported aluminum isopropoxide was used to promote the MPV
reaction in good yield under mild conditions and with low catalyst
loadings [6j]. We now report the synthesis of heteroleptic bidentate
N, O-aluminum complexes 1e4 (Scheme 1) and their use as pre-
catalysts for the reduction of carbonyl moieties to produce their
analogous alcohols.
selective
reduction
of
carbonyls
to
alcohols.
Meer-
weinePonndorfeVerley (MPV) reduction appears to be one of the
potential answers because of its characteristic features, i.e., high
chemoselectivity, mild reaction conditions, simple and safe oper-
ations, and the low cost and toxicity of reagents [4].
The MPV reaction was first reported in the mid 1920s [5], it is
performed with aluminum isopropoxide as a catalyst and 2-
propanol as a hydride source. Subsequently, a number of catalyst
systems of metal alkoxide/hydride source combinations have been
investigated. For example, aluminum alkoxides [6], alkali metal
alkoxides [7], rare earth metal alkoxides [8], metal oxides [9],
transition metal complexes of zirconium, hafnium, iridium, ruthe-
nium [10], MCM-41-grafted metal isopropoxides [11] and various
other catalysts [12] have been reported. But, the reaction is usually
conducted under the influence of excessive amounts of 2-propanol,
2. Results and discussions
2.1. Synthesis and characterization
Treatment of 2-Me2NeC6H4Li with acetophenone or cyclohex-
anone afforded the corresponding ligand HOC(Me)(Ph)
C6H4eNMe2-2 (L1H) or HOC(CH2)5C6H4eNMe2-2 (L2H) as pale
yellow oil in 73% yield and colorless oil in 78% yield, respectively.
Deprotonation of L1H and L2H by equivalent of AlMe3 in hexane
with the releasing of methane gave the four-coordinated alumi-
numedialkyl
complexes
(1)
and
* Corresponding authors.
E-mail addresses: gzq@sxu.edu.cn (Z. Guo), xhwei@sxu.edu.cn (X. Wei).
(2) in almost quantitative yields,
http://dx.doi.org/10.1016/j.jorganchem.2015.06.011
0022-328X/© 2015 Elsevier B.V. All rights reserved.

60
Y. Hua et al. / Journal of Organometallic Chemistry 794 (2015) 59e64
Scheme 1. Preparation of complexes 1e4.
respectively. Accordingly, treatment of L1H or L2H with 0.5 equiv-
alent of AlMe3 in hexane generated the five-coordinated alumi-
geometry in the title complex 1 (Fig. 1). The four-coordination
around the Al atom involves the N atom and the O atom from the
ligand and two methyl-C atoms. The six-membered chelate ring,
O1Al1N1C1C2C9, has a boat conformation with the C9 and N1
atoms occupying the apex positions. In comparison with the
idealized tetrahedral angle, the intra-ring angle O(1)eAleN(1)
(93.42 (6) ꢀ) is remarkably narrow. The Al(1)eO(1) (1.7277 (14) Å) is
slightly longer than the classic normal AleO bonds (1.69 Å) [13],
while the Al(1)eN(1) (2.0156 (15) Å) is slightly shorter than the
average bond length of AleN (2.08 Å) [13,14]. The molecular
structure of complex 2 is very similar to that of 1, and its selected
bond lengths and angles are given in Fig. 2.
The Al atom in 3 adopts five-coordination mode (Fig. 3), where
two mono-anionic ligands coordinated to the central aluminum
atom by their O atom and N atom, forming two distorted six-
membered rings. The structural features of the both of the six-
member ring are similar to that of 1. The bond length of Al(1)e
O(1) (1.7212 (15) Å) is very closely to that of 1, while the bond
numemonoalkyl complexes
(3) and
(4) in good yields, respectively (Scheme
1). Further more, 1 and 2 were transferred readily to 3 and 4 via
treatment of 1 or 2 with equivalent amount of L1H or L2H in diethyl
ether at 0 ꢀC, respectively.
The structures of complexes 1e4 were characterized by 1H NMR,
13C NMR spectroscopy and elemental analyses, as shown in
Experimental Section. Fortunately, the colorless crystals of 1e4
suitable for X-ray diffraction analysis were also isolated. The ORTEP
drawing of the molecular structure and selected bond lengths and
angles of complexes 1e4 are given in Figs. 1e4, respectively.
2.2. X-ray single crystal structures of 1e4
The Al atom is four-coordinated in a distorted tetrahedral

Y. Hua et al. / Journal of Organometallic Chemistry 794 (2015) 59e64
61
Fig. 3. Molecular structure of the complex 3. Hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (ꢀ): Al(1)eO(1) 1.7212(15), Al(1)eO(1)0
1.7212(15), Al(1)eC (17) 1.970(4), Al(1)eN(1) 2.2056(19), Al(1)eN(1)0 2.2056(19);
O(1)0eAl(1)eO(1) 122.48(12), O(1)0eAl(1)eC(17) 118.76(6), O(1)eAl(1)eC(17)
118.76(6), O(1)0eAl(1)eN(1) 87.88(7), O(1)eAl(1)eN(1) 87.03(7), C(17)eAl(1)eN(1)
95.29(6), O(1)0eAl(1)eN(1)0 87.03(7), O(1)eAl(1)eN(1)0 87.88(7), C(17)eAl(1)eN(1)0
95.29(6), N(1)eAl(1)eN(1)0 169.41(12).
Fig. 1. Molecular structure of the complex 1. Hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (ꢀ): Al(1)eO(1) 1.7277(14), Al(1)eN(1)
2.0156(15), Al(1)eC(17) 1.952(2), Al(1)eC(18) 1.951(2); O(1)eAleN(1) 93.42(6), O(1)e
AleC(17) 114.79(9), O(1)eAleC(18) 113.25(9).
Fig. 2. Molecular structure of the complex 2. Hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (ꢀ): Al(1)eO(1) 1.7317(14), Al(1)eN(1)
2.0089(18), Al(1)eC(15) 1.959(2), Al(1)eC(16) 1.966(2); O(1)eAleN(1) 93.25(7), O(1)e
AleC(15) 117.66(9), O(1)eAleC(16) 112.22(9).
Fig. 4. Molecular structure of the complex 4. Hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (ꢀ): Al(1)eO(1) 1.7385(18), Al(1)eO(2)
1.7332(17), Al(1)eC(29) 1.983(3), Al(1)eN(1) 2.213(2), Al(1)eN(2) 2.190(2); O(2)e
Al(1)eO(1) 123.38(9), O(2)eAl(1)eC(29) 117.74(11), O(1)eAl(1)eC(29) 118.79(10),
O(2)eAl(1)eN(1) 89.67(8), O(1)eAl(1)eN(1) 85.60(9), C(29)eAl(1)eN(1) 91.80(11),
O(2)eAl(1)eN(2) 87.17(8), O(1)eAl(1)eN(2) 92.64(8), C(29)eAl(1)eN(2) 93.38(11),
N(1)eAl(1)eN(2) 174.74(9).
length of Al(1)eN(1) (2.2056 (19) Å) is longer than that of 1. The
molecular structure of complex 4 is similar to that of complex 3,
and the corresponding bond lengths and angles of 4 are given in
Fig. 4. The dihedral angle (56.60ꢀ) between the N(1)O(1)Al(1) and
N(2)O(2)Al(1) planes is slightly narrower than that in complex 3
(58.14ꢀ).
employed as the catalyst within 15 min (Table 1, entry 2). As we
hoped, the similar yield was obtained by increasing the reaction
time to 60 min, 135 min or 90 min when 1, 3 or 4 was used as
catalyst, respectively (Table 1, entries 1e7). The further tests
showed that the reduction of benzaldehyde by 2 under solvent-free
condition also gave the quantitative yield (Table 1, entry 9) while 1,
3 and 4 gave a 95%, 91%, or 94% yield of benzyl alcohol, respectively
(Table 1, entries 8, 10 and 11). With the decrease of 2-propanol and
catalyst, the yield was decreased (Table 1, entries 12e27). Hope-
fully, complex 2 at 5 mol % loading and 1.2 equivalents of 2-
propanol under solvent-free in 15 min promoted the almost
2.3. The MPV reduction reaction catalyzed by 1e4
The MPV reduction reactions were systematically studied with
complexes 1e4 as precatalysts. Firstly, benzaldehyde was selected
as a model substrate and dry 2-propanol was employed as the
reducing agent. As shown in Table 1, the reduction reaction of
benzaldehyde was carried out in toluene with 10% mole of 1e4
under reflux condition. All of complexes 1e4 showed good catalytic
activity (ꢁ90%, Table 1, entries 1e4) and the corresponding benzyl
alcohol was obtained in almost quantitative yield when 2 was

62
Y. Hua et al. / Journal of Organometallic Chemistry 794 (2015) 59e64
Table 1
Table 2
Complex 1e4 catalyzed MPV reduction of benzaldehyde.a
Complex 2 catalyzed MPV reduction of selected carbonyl compounds.a
Entry Catalyst
Catalyst [mol%] 2-propanol [Equiv] Solvent Yield (%)b
1
2
3
4
5
6
7
8
1
2
3
4
1
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
5
5
5
5
5
5
5
5
5
2
2
2
2
2
2
2
2
Toluene
Toluene >99
93
Entry
1
Carbonyl compound
Product
Yield(%)b
99
Toluene
Toluene
90
92
Toluene >99c
Toluene
Toluene
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
99d
99e
95
2
98
9
2
2
2
>99
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
91
94
94
>99
88
92
90
99
85
88
74
83
71
73
89
99
83
87
92
3
4
99
78
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1
1
1
1
1.2
1.2
1.2
1.2
1.2
5
93
6
7
79
73
2
3
4
5
5
5
5
8
9
87c
67c
Al(OiPr)3
a
Conditions: reflux, 15 min.
b
c
Determined by 1H NMR spectroscopy.
60 min.
135 min.
90 min.
d
e
a
Conditions: reflux, 5% mol catalyst, 1.2 equiv 2-propanol, solvent-free, 15 min.
Determined by 1H NMR spectroscopy.
b
c
Determined by GCeMS.
quantitative reduction of benzaldehyde to benzyl alcohol (Table 1,
entry 25). For comparison, the traditional Al(OiPr)3 as catalyst for
MPV reduction reaction also been carried out with 92% yield
(Table 1, entries 28). In any case, the catalytic activity was in the
sequence of 2 > Al(OiPr)3 > 1 > 4 > 3 under the tested conditions. It
would attribute to the benzyloxy for 1 and the steric hindrance for 3
and 4, which reduced the Lewis acidity and the electrophilicity of
aluminum center, decreased the attack probability to benzalde-
hyde. The results are consistent with the literature reports [6].
With the above results in hand, a variety of aldehyde and ketone
substrates were examined for the MPV reaction, using 2 as catalyst
(Table 2). As expected, the aromatic aldehydes with an electron-
withdrawing group on the phenyl ring gave higher yields than
the aldehyde with an electron-donating group (Table 2, entries
2e4). Citronellal, a raw material for the spice, could achieve 93%
yield under the optimized conditions (Table 2, entry 5), and some
3. Conclusions
In conclusion, four novel bidentate N, O-aluminum complexes
1e4 have been synthesized, characterized and used for catalytic
study of MPV reduction reactions. Reductions were conducted with
low catalyst loadings (5% mol) and low equivalents of 2-propanol
(1.2 equiv) under mild conditions. The complex 2 showed the
best catalytic activities toward the MPV reaction and a range of
aldehydes and ketones are rapidly, selectively transferred to the
corresponding primary or secondary alcohols in good or excellent
yields.
challenging a, b-unsaturated aldehydes selectively reduced to al-
4. Experimental section
cohols were also achieved in good yields with lower 2-propanol
loadings, such as cinnamaldehyde and citral (Table 2, entries 6,
7). It should be noted that the side reaction of Tishchenko or aldol,
which is usually found in MPV reactions, is not observed in our
system. Generally, low active cyclohexanone and acetophenone
were also reduced to corresponding alcohols under our catalytic
system in 67% and 87% yields (GCeMS yield), respectively (Table 2,
entries 8, 9).
4.1. General remarks
All experiments were carried out under purified dry nitrogen
atmosphere by using standard Schlenk techniques. Solvents were
dried and freshly distilled under nitrogen. Elemental analyses were
performed on a Vario ELIII instrument. Melting points were
determined on a STUART SMP10 melting point apparatus and un-
corrected. The NMR spectra were recorded in CDCl3 and C6D6 with
an AVANCE DRX 300 spectrometer (Bruker), using TMS as an in-
ternal standard.

Y. Hua et al. / Journal of Organometallic Chemistry 794 (2015) 59e64
63
4.2. Preparation
N, 5.09. Found: C, 69.37; H, 9.97; N, 5.42.
4.2.1. HOC(Me)(Ph)C6H4eNMe2-2 (L1H)
(3)
A dry 250 mL two-necked flask was filled with N, N-dimethy-
laniline (9.65 g, 0.0797 mol), 100 mL of anhydrous diethyl ether and
11.87 mL of TMEDA and the solution was stirred under nitrogen
atmosphere. 33 mL of a 2.87 M of n-butyllithium in hexane was
added at ꢂ78 ꢀC. The solution was allowed to warm to room
temperature and stirred for 2 h. Acetophenone (11.2 mL, 0.096 mol)
was added dropwise to the reaction mixture at 0 ꢀC and stirred for
2 h. The solution was hydrolyzed by 50 mL of distilled water, and
then washed with aqueous 5% hydrochloric acid (5 ꢃ 50 mL). The
aqueous phase was combined and made alkaline with 10% sodium
hydroxide aqueous solution. The aqueous phase was then extracted
with diethyl ether (3 ꢃ 20 mL) and the organic phase was dried
over anhydrous magnesium sulfate. The crude product by vacuum
distillation at 134 ꢀC to give the product as pale yellow oil in 73%
1.2 mL AlMe3 (hexane, 2 M solution) was added dropwise
at ꢂ78 ꢀC to a solution of L1H (1.13 g, 4.8 mmol) in hexane (10 mL).
The reaction mixture was then warmed to room temperature and
stirred for 2 h. The reaction mixture was cooled to ꢂ20 ꢀC, and a
colorless solid was obtained that was recrystallized from diethyl
ether to give the product as colorless crystals. Yield: 1.13 g (92%).
Mp 231e235 ꢀC. 1H NMR (CDCl3,
d/ppm): ꢂ1.62 (s, 2H,
AlCH3), ꢂ0.70 (s, H, AlCH3), 0.71 (s, 2H, CH3), 1.85 (s, 5H, CH3),
2.11e3.15 (br, 12H, 2(NC2H6)), 7.03 (m, 4H, C6H4), 7.40e7.42 (m, 9H,
C6H5 and C6H4), 7.37e7.39 (m, 2H, C6H5), 7.56e7.59 (m, 2H, C6H4),
7.65(m, H, C6H5). 13C NMR (CDCl3,
d
/ppm): ꢂ12.10 (AlCH3), 31.47
(CCH3), 37.26 (CCH3), 39.12(CCH3), 47.5(CCH3), 42.87e51.97(br, 2N
(C2H6)), 119.42, 123.17, 125.84, 126.83, 127.99, 129.64, 129.89, 146.87,
148.68(C6H5 and C6H4), 151.38 (C6H5). Anal. Calcd for C33H39AlN2O2:
C, 75.83; H, 7.52; N, 5.36. Found: C, 75.48; H, 7.83; N, 5.75.
yield. 1H NMR (CDCl3,
d
/ppm): 1.84 (s, 3H, CCH3), 2.93 (s, 6H,
NC2H6), 7.11e7.51 (m, 4H, C6H4). 13C NMR (C6D6,
d/ppm): 32.12
(CCH3), 45.15e46.36(br, NC2H6), 77.30 (CCH3), 123.81 (C6H4), 125.61
(C6H5), 126.15 (C6H4), 126.49 (C6H5), 127.73 (C6H5), 128.22 (C6H4),
128.65 (C6H4), 143.44 (C6H4), 150.94 (C6H5), 151.98 (C6H4).
(4)
1.1 mL AlMe3 (hexane, 2 M solution) was added dropwise
at ꢂ78 ꢀC to a solution of L2H (0.96 g, 4.4 mmol) in diethyl ether
(10 mL). The reaction mixture was then warmed to room temper-
ature and stirred for 2 h. Colorless crystals were obtained from
diethyl ether at ꢂ20 ꢀC. Yield: 1.98 g (94%). Mp 142e145 ꢀC. 1H NMR
4.2.2. HOC(CH2)5C6H4eNMe2-2 (L2H)
The reaction was carried out by a similar procedure as described
for L1H, except that 16.0 g (0.08 mol) of cyclohexanone was used
instead of acetophenone, and the product as colorless oil was ob-
tained by vacuum distillation at 118 ꢀC in 78% yield. 1H NMR (CDCl3,
(CDCl3,
d
/ppm): ꢂ1.03 (s, 3H, AlCH3), 7.15e7.33 (m, 20H, C6H4), 3.04
(s, 12H, 2(NC2H6)), 7.23 (m, 4H, C6H4), 7.40e7.42 (d, 2H, C6H4),
7.53e7.55 (d, 2H, C6H4). 13C NMR (CDCl3,
d
/ppm): ꢂ9.39 (AlCH3),
d
/ppm): 0.99e2.56 (br., 10H, C5H10), 2.60 (s, 6H, NC2H6), 7.30e8.01
23.75(C6H10), 24.05(C6H10), 27.45 (C6H10), 42.51 (C6H10), 43.54
(C6H10), 76.40 (C5H10COe), 121.13 (C6H4), 126.16 (C6H4), 127.63
(C6H4), 129.88 (C6H4), 146.87 (C6H4), 150.82 (C6H4). Anal. Calcd for
(m, 4H, C6H4). 13C NMR (C6D6,
d/ppm): 22.41(C6H10), 26.27 (C6H10),
40.38 (NC2H6), 47.03 (C6H10), 75.24 (C5H10COe), 123.90 (C6H4),
126.67 (C6H5), 127.03 (C6H4), 127.91 (C6H4), 144.72 (C6H4), 151.82
(C6H4).
C
29H43AlN2O2: C, 72.77; H, 9.06; N, 5.85. Found: C, 72.36; H, 10.27;
N, 6.34.
(1)
4.3. Typical procedure employed for MPV reactions
0.93 mL AlMe3 (hexane, 2 M solution) was added dropwise
at ꢂ78 ꢀC to a solution of L1H (0.45 g, 1.85 mmol) in diethyl ether
(10 mL). The reaction mixture was then warmed to room temper-
ature and stirred for 2 h. The reaction mixture was cooled to ꢂ30 ꢀC,
and a colorless solid was obtained that was recrystallized from
hexane to give the product as colorless crystals. Yield: 0.53 g (96%).
A 25 mL Schlenk flask was charged with aluminum complex
(0.2 mmol) and the carbonyl compound (4.0 mmol) was added,
followed by the addition of 2-propanol (0.37 mL, 4.8 mmol). The
reaction mixture was then refluxed for 15 min, and the yield was
determined by 1H NMR spectroscopic studies based on the inte-
gration in the methylene and the CHO region of the benzyl group.
Mp 206e210 ꢀC. 1H NMR (CDCl3,
d/ppm): ꢂ1.25 (s, 3H,
AlCH3), ꢂ0.94 (s, 3H, AlCH3), 1.69 (s, 3H, CCH3), 2.34 (br. s, 3H,
NCH3), 2.67 (br. s, 3H, NCH3), 6.92e6.94(m, H, C6H4), 7.00e7.02 (m,
2H, C6H4), 7.11 (m, 2H, C6H5), 7.27e7.30 (m, 2H, C6H5), 7.34 (s, H,
4.4. X-ray crystallography
C6H4). 13C NMR (CDCl3,
d
/ppm): ꢂ11.19 (AlCH3), ꢂ10.03 (AlCH3),
All crystals were coated in oil and then directly mounted on the
diffractometer under a stream of cold nitrogen gas. Single X-ray
diffraction data of the compounds were collected on a Bruker Smart
37.80 (CCH3), 45.78 (NCH3), 49.58 (NCH3), 78.26 (CCH3), 120.28
(C6H4), 126.43 (C6H5),126.82 (C6H4), 127.40 (C6H5), 128.58 (C6H5),
131.94 (C6H4), 143.64 (C6H4), 146.07 (C6H4), 152.35 (C6H5). Anal.
Calcd for C18H24AlNO: C, 72.70; H, 8.13; N, 4.71. Found: C, 72.43; H,
8.27; N, 5.02.
Apex CCD diffractometer using monochromated Mo K
a
radiation,
scan
l
¼ 0.71073 Å. A total of N reflections were collected by using
u
mode. Corrections were applied for Lorentz and polarization effects
as well as absorption using multi-scans (SADABS) [15]. Each
structure was solved by direct method and refined on F2 by full
matrix least squares (SHELX97) using all unique data [16]. Then the
remaining non-hydrogen atoms were obtained from the successive
difference fourier map. All non-hydrogen atoms were refined with
anisotropic displacement parameters, whereas the hydrogen atoms
were constrained to parent sites, using a riding mode (SHELXTL)
[17]. Details of the modeling of disorder in the crystals can be found
in their CIF files.
(2)
The reaction was carried out as described for complex 1 except
that 0.54 g (2.44 mmol) of L2H was used instead of L1H. Colorless
crystals were obtained from hexane at ꢂ20 ꢀC. Yield: 0.63 g (93%).
Mp 112e114 ꢀC. 1H NMR (C6D6,
d
/ppm): ꢂ0.46 (s, AlC2H6), 1.35e1.39
(m, H, C6H10), 1.69e2.02 (m, 7H, C6H10), 2.33 (s, 6H, NC2H6),
2.37e2.45 (m, 2H, C6H10), 6.72e6.75 (d, 2H, JHeH ¼ 9 Hz, C6H4),
6.92e6.97 (t, 2H, C6H4), 7.02e7.04 (s, 2H, C6H4), 7.24e7.27 (d, 2H,
JHeH ¼ 9 Hz, C6H4). 13C NMR (C6D6,
d/ppm): ꢂ11.05 (AlC2H6),
22.08(C6H10), 26.27 (C6H10), 42.50 (C6H10), 46.95 (NC2H6), 75.13
(C5H10COe), 119.08 (C6H4), 126.74 (C6H5), 129.84 (C6H4), 145.75
(C6H4), 146.21 (C6H4). Anal. Calcd for C16H26AlNO: C, 69.79; H, 9.52;
Acknowledgments
Financial support from the National Natural Science Foundation

64
Y. Hua et al. / Journal of Organometallic Chemistry 794 (2015) 59e64
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of China (No. 20572065), Special Fund for Agro-scientific Research
in the Public Interest (No. 201303106), Natural Science Foundation
of Shanxi Province (No. 2011021011-1, 2014011049-26) and the
Inner Mongolia Natural Science Foundation (No. 2013MS0214) are
gratefully acknowledged.
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CCDC 1047506e1047509 contains the supplementary crystal-
lographic data for 1, 2, 3 and 4, respectively. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif,
or from the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; fax: (þ44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found in the online version or by direct contacting the
authors.
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