Addition Reactions of Me3SiCN with Aldehydes Catalyzed by Aluminum Complexes Containing in their Coordination Sphere O, S, and N Ligands

Article abstract of DOI:10.1002/chem.201505162

The reaction of one equivalent of LAlH₂ (1; L=HC(CMeNAr)₂, Ar=2,6-iPr₂C₆H₃, β-diketiminate ligand) with two equivalents of 2-mercapto-4,6-dimethylpyrimidine hydrate resulted in LAl[(μ-S)(m-C₄

Full text of DOI:10.1002/chem.201505162

DOI: 10.1002/chem.201505162
Full Paper
&
Lewis Acid Catalysis
Addition Reactions of Me3SiCN with Aldehydes Catalyzed by
Aluminum Complexes Containing in their Coordination Sphere
O, S, and N Ligands
Zhi Yang,*[a, b] Yafei Yi+,[a] Mingdong Zhong+,[a] Sriman De,[c] Totan Mondal,[c] Debasis Koley,*[c]
Xiaoli Ma,[a] Dongxiang Zhang,[a] and Herbert W. Roesky*[d]
Abstract: The reaction of one equivalent of LAlH2 (1; L=
HC(CMeNAr)2, Ar=2,6-iPr2C6H3, b-diketiminate ligand) with
two equivalents of 2-mercapto-4,6-dimethylpyrimidine hy-
drate resulted in LAl[(m-S)(m-C4N2H)(CH2)2]2 (2) in good yield.
Similarly, when N-2-pyridylsalicylideneamine, N-(2,6-diisopro-
pylphenyl)salicylaldimine, and ethyl 3-amino-4,5,6,7-tetrahy-
drobenzo[b]thiophene-2-carboxylate were used as starting
materials, the corresponding products LAl[(m-O)(o-C6H4)-
CN(C5NH4)]2 (3), LAlH[(m-O)(o-C4H4)CN(2,6-iPr2C6H3)] (4), and
LAl[(m-NH)(o-C8SH8)(COOC2H5)]2 (5) were isolated. Com-
1
pounds 2–5 were characterized by H and 13C NMR spectros-
copy as well as by single-crystal X-ray structural analysis. Sur-
prisingly, compounds 2–5 exhibit good catalytic activity in
addition reactions of aldehydes with trimethylsilyl cyanide
(TMSCN).
prising the terminal AlÀSH unit was reported,[8] more and more
soluble organic AlÀS bond containing compounds have been
synthesized.[9] The use of organic aluminum compounds for
the mediation of various organic transformations has a long-
standing tradition,[4,5,10] and aluminum-mediated organic reac-
tions have been extensively reviewed.[4,5,7,11] The b-diketiminate
substituent has found widespread applications as a supporting
ligand owing to its strong electron-donating ability and steric
constraints that can stabilize main-group metal compounds.[12]
However, aluminum compounds with chelating ligands incor-
porating soft donors that can be as moderate and stable Lewis
acid catalysts are less known.[13]
Introduction
The Lewis acid properties of organic aluminum compounds
are well established in organic chemistry. They are responsible
for a plethora of organic reactions,[1] polymerizations,[2] and
catalytic cycles.[3–6] Among those compounds, Lewis acidic de-
rivatives prepared from AlCl3 are primarily used, although poor
selectivity and control of reactivity are often the major issues
in using these compounds.[4,7] Increasing the selectivity of
these compounds and controlling their reactivity can be ach-
ieved by increasing the steric bulk and by varying the electron
density at the central aluminum atom. For thermodynamic sta-
bility reasons, aluminum compounds containing O, S, and N li-
gands have been less-well studied compared with aluminox-
anes. Since the first unique monomeric aluminum moiety com-
Monomeric aluminum hydrides with an electron-withdraw-
ing and bulky group, which increases the positive charge at
the aluminum center, are relatively rare and few of these com-
pounds have been structurally characterized.[14,12a] Recently, we
reported an aluminum hydride, LAlH(OTf), (Tf=SO2CF3), which
effectively acts as a bifunctional catalyst and initiates the addi-
tion reaction of trimethylsilyl cyanide (TMSCN) to aldehydes
and ketones.[3b] Thus, to investigate the catalytic properties of
aluminum compounds containing O, S, and N organic ligands
is an important task.[15,16] Herein, we report the synthesis and
structural characterization of four aluminum compounds with
soft donor properties. Their catalytic activity was studied in the
addition reaction of TMSCN to aldehydes.
[a] Prof. Z. Yang, Y. Yi,+ Dr. M. Zhong,+ Dr. X. Ma, Dr. D. Zhang
School of Chemical Engineering and Environment
Beijing Institute of Technology, 100081 Beijing (P. R. China)
E-mail: zhiyang@bit.edu.cn
[b] Prof. Z. Yang
State Key Laboratory of Elemento-organic Chemistry
Nankai University (P. R. China)
[c] S. De, T. Mondal, Dr. D. Koley
Department of Chemical Sciences
Indian Institute of Science Education and Research Kolkata
Mohanpur 741246 (India)
E-mail: koley@iiserkol.ac.in
[d] Prof. H. W. Roesky
Results and Discussion
Institut für Anorganische Chemie, Universität Gçttingen
Tammannstrasse 4, 37077 Gçttingen (Germany)
E-mail: hroesky@gwdg.de
The reaction of 1 with 2-mercapto-4,6-dimethylpyrimidine hy-
drate, N-2-pyridylsalicylideneamine, N-(2,6-diisopropylphenyl)-
salicylaldimine, and ethyl 3-amino-4,5,6,7-tetrahydrobenzo[b]-
thiophene-2-carboxylate, respectively, in a molar ratio of 1:2 or
[+] These authors contributed equally to this work.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201505162.
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1:1 resulted in products (LAl[(m-S)(m-pyrimidine)(CH2)2]2 (2),
LAl[(m-O)(o-C6H4)CN(C5NH4)]2 (3), LAlH[(m-O)(o-C4H4)CN(2,6-
rangement of compound 4. The resonances (d=3.54 and
4.27 ppm for 5) were assigned to the -NH and the -OCH2CH3
groups, respectively.
iPr2C6H3)] (4), and LAl[(m-NH)(o-C8SH8)(COOC2H5)]2 (5;
Scheme 1). During the course of the reactions, hydrogen gas
evolution was observed. Compounds 2, 3, and 5 were isolated
after growing colorless crystals from the concentrated toluene
solution, whereas 4 was crystallized from n-hexane. The crys-
tals are soluble in common organic solvents such as toluene,
dichloromethane, and tetrahydrofuran. They are stable for
a few days even in the open air.
Compounds 2–5 were characterized by single-crystal X-ray
diffraction. The molecular structures are shown in Figures S1–
S4 (in the Supporting Information). Selected bond lengths and
angles are listed in the legends of Figures S1–S4. In the struc-
tures of 2, 3, and 5, the aluminum center is four-coordinate,
and surrounded by a b-diketiminate ligand and two bridging
sulfur, oxygen, or nitrogen atoms, respectively. The two AlÀS
bond lengths in 2 are a little different (2.2844 Š and 2.3137 Š),
which could be attributed to the interaction between Al(1) and
N(5) (distance 2.1208 Š; Figure S1 in the Supporting Informa-
tion). In compound 4, the aluminum atom is also four-coordi-
nate and the AlÀO bond length (1.7176 Š) is shorter than that
in 3 (av. 1.7229 Š), and they are both longer than those in
LAl(OH)2 (1.705 Š).[17] The difference in the bond lengths of 3
and 4 compared with those in LAl(OH)2 could be attributed to
the conjugative effect of the O atoms with the adjacent aro-
matic ring as well as with the repulsive force between the
bulky groups on the O atoms with those of the iPr2C6H3
groups on the ligand.
1
All complexes were characterized by H and 13C NMR spec-
troscopic investigations in CDCl3 or C6D6 solution. Compound
2 exhibits a resonance for the g-H proton on the pyrimidine
rings at d=6.06 ppm, which is populated approximately in
a 2:1 ratio compared with that of the g-H proton of the free
ligand at d=5.39 ppm. A broad resonance at d=1.25 ppm, as-
signed to the methyl on the pyrimidine rings, shows a down-
field shift relative to the methyl (d=1.10 ppm) on the phenyl
1
group in 2. The H NMR spectra of 2, 3, and 5 exhibit one char-
acteristic septet (d=3.06–3.37 ppm) attributed to the symme-
try-related methyne, indicating symmetric molecules. The
1H NMR spectra of 3 and 5 each exhibit one set of resonances
for the aryl groups. Compound 3 shows the CH=NÀAr reso-
To investigate the catalytic properties of compounds 2–5,
addition reactions were performed by adding TMSCN to alde-
hydes. As shown in Table 1, the reaction of benzaldehyde
(PhCHO) with TMSCN in CDCl3 in the presence of 2, 3, 4, or 5
as catalysts (Table 1, entries 2b, 3a, 4a, and 5a) at ambient
temperature afforded the desired product PhCH(CN)OTMS in
1
nance at d=9.48 ppm. Similarly, the H NMR spectrum of com-
pound 4 exhibits a CH=NÀAr resonance at d=8.29 ppm. Three
septet resonances (d=3.40–3.05 ppm) were assigned to the
1
methyne in the H NMR spectrum of 4, and two of the three
peaks are partly overlapping, which indicate an asymmetric ar-
Scheme 1. Synthesis of aluminum monohydride complexes 2, 3, 4, and 5 and their corresponding gas-phase free energy change (DGL) and gas-phase enthal-
py change (DHL) values in kcalmolÀ1 calculated at the M06/def2-TZVP//BP86/def2-SVP level of theory.
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to be effective in the presence of 2 (Table 1, entries 2 f, 2g).
However, compounds 3, 4, and 5 show low catalytic activity
compared with 2 (Table 1, entries 3e, 3 f, 4e, 4 f, 5e, 5 f). Ali-
phatic aldehydes (Table 1, entries 2h, 3g, 4g, 5g) were select-
ed for the addition with TMSCN at room temperature using
catalyst loadings of 2 mol% and the reaction time of 3 h. The
products were formed in essentially quantitative yield (99%).
In general, we observed that better catalytic performance oc-
curred with aldehydes of small molecular weight. Based on the
results of Table 1, compound 2 shows high catalytic activity for
all the selected aldehydes, whereas compounds 3, 4, and 5 ex-
hibit high selectivity for some specific aldehydes, which might
be due to the more bulky groups around the Al center of com-
pounds 3, 4, and 5 than those of 2 and some other known cat-
alysts.[3b,18] The X-ray structures of compounds 2, 3, 4, and 5
are illustrated in the Supporting Information, which shows that
the steric effect of the bulky groups on the Al center decreases
the catalytic activity.
Table 1. Addition reaction of TMSCN to aldehydes catalyzed by 2, 3, 4,
and 5. R=alkyl or aryl group.[a]
Entry
Substrate
Initiator
Cat. [mol%]
t [h]
Yield [%][b]
2a
2b
2c
2d
2e
2 f
2g
2h
3a
3b
3c
3d
3e
3 f
3g
4a
4b
4c
4d
4e
4 f
4g
5a
5b
5c
5d
5e
5 f
C6H5CHO
C6H5CHO
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
4
4
4
4
4
4
4
5
5
5
5
5
5
5
0
2
1.5
2
2
1
1
2
2
1.5
2
2
1
1
2
2
1.5
2
2
1
1
2
2
2
2
1.5
2
2
4
4
4
6
4
4
4
3
4
4
6
4
4
4
3
4
4
6
4
4
4
3
4
4
6
3
4
4
3
trace
99
99
76
79
98
99
99
96
40
10
92
30
0
99
95
45
30
95
90
20
99
65
10
10
99
50
15
99
p-MeC6H4CHO
C6H5CH=CHCHO
o-FC6H4CHO
2-C4H3OCHO
2-C4H3SCHO
(CH3)3CHO
C6H5CHO
p-MeC6H4CHO
C6H5CH=CHCHO
o-FC6H4CHO
2-C4H3OCHO
2-C4H3SCHO
(CH3)3CHO
We next performed DFT calculations with an aim to investi-
gate the mechanistic pathways in the addition reaction of
TMSCN to PhCHO in the presence of AlIII catalysts (Scheme 1).
Four catalysts 2, 3, 4, and 5 were formed by ligand exchange
from 1 by liberating H2 gas through a highly exergonic step
(Scheme 1). The respective energy changes during the forma-
tion of species 2–5 from initial precursor 1 are À40.2, À68.4,
À33.5, and À45.9 kcalmolÀ1 (DGL at the M06/def2-TZVP//BP86/
def2-SVP level), indicating facile conversions. In this current
contribution, only the catalytic cycle utilizing catalyst 4 is thor-
oughly discussed (Figure 1 and Scheme 2), however, the ener-
gies of the key intermediates for the other catalytic systems (2,
3, and 5) are collected in the Supporting Information (Figur-
es S5–S7). As the ligands coordinated to the Al center exhibit
considerable steric congestion that might hinder the progress
of the substrate, we decided to dissociate one such ligand to
generate a more active cationic species. Unfortunately, the
ligand dissociation step from 4 is highly endoergic (DGLS =
63.8 kcalmolÀ1, Scheme S1 in the Supporting Information),
which is probably due to the electron deficiency at the AlIII
center, proving its unlikeliness as a step in the reaction mecha-
nism. Therefore, the reaction proceeds through initial substrate
coordination to the Al center of 4. The approach of TMSCN
from the N-end to the tetrahedral Al center along the opposite
side of one AlÀN bond leads to the formation of an encounter
adduct of the type 4A. The weakly bound intermediate, 4A is
less stable than the starting material comprising of 4 and
TMSCN (DGLS =4.2 kcalmolÀ1). The calculated activation barrier
for the transition state 4A-TS is quite small (D°GLS =3.7 kcal
molÀ1). The activated complex 4A-TS is characterized by
a single imaginary mode concerning the approach of the in-
coming TMSCN towards the Al atom. The Mulliken group
charge of TMSCN in the transition state is 0.094 e, indicating
an electron transfer from the TMSCN to the electrophilic Al
center. The effect of such electron transfer is manifested with
the elongation of the C1ÀSi bond in 4A-TS by 0.010 Š with re-
spect to the free TMSCN. In the resulting intermediate 4B, the
Al center adopts a five-coordinate distorted trigonal-bipyrami-
dal-like geometry (Figure 2), where the incoming N1 (TMSCN) is
C6H5CHO
p-MeC6H4CHO
C6H5CH=CHCHO
o-FC6H4CHO
2-C4H3OCHO
2-C4H3SCHO
(CH3)3CHO
C6H5CHO
p-MeC6H4CHO
C6H5CH=CHCHO
o-FC6H4CHO
2-C4H3OCHO
2-C4H3SCHO
(CH3)3CHO
5g
2
[a] Conditions: aldehyde, 1 mmol; TMSCN, 1.2 mmol; at ambient tempera-
ture. [b] Yield was obtained according to 1H and 13C NMR spectral analy-
sis.
1
good yield (as determined by H NMR analyses of the reaction
mixture). No reaction was observed under the same conditions
in the absence of the catalyst (Table 1, entry 2a). p-Tolylalde-
hyde was investigated for the addition reaction with TMSCN at
room temperature by using catalyst 2 with a loading of
1.5 mol% to afford the product in essentially quantitative yield
(99%, Table 1, entry 2c). Relatively lower yields of the product
were observed in the presence of 2 mol% of catalyst 5, and
1.5 mol% of catalysts 3 and 4 (Table 1, entries 3b, 4b, 5b).
Phenylacrolein and o-fluorobenzaldehyde, with different elec-
tron-donating and electron-withdrawing abilities, were investi-
gated to study the electronic effect on the activation using
a variety of compounds. Catalyst 2 shows good catalytic activi-
ty when each of the two aldehydes were employed (Table 1,
entries 2d, 2e), whereas 3, 4, and 5 only gave excellent yields
for o-fluorobenzaldehyde (Table 1, entries 3d, 4d, 5d). This can
be explained by the steric as well as the electronic properties
of the substituents at the carbonyl functionality of the alde-
hydes. In addition, the interaction between the metal center
and the carbonyl oxygen, sulfur, or nitrogen atoms has
a strong influence on the catalytic activity. The analogous reac-
tions with substrates including heterocycles were also found
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Figure 1. Energy profile for the addition reaction of TMSCN to PhCHO in the presence of catalyst 4. The energy terms, DGLS/(DHLS) are in kcalmolÀ1 and were
calculated at the M06/def2-TZVP/SMD//BP86/def2-SVP level of theory.
Scheme 2. Reaction mechanism for the addition reaction of TMSCN to PhCHO in the presence of the catalyst 4. For energy conventions, refer to Figure 1.
in an axial position. During this nucleophilic addition of
TMSCN (4!4B), the Mulliken charge of the Al center is reduced
by 0.119 e (Table 2, Table S2 in the Supporting Information).
An alternative route of initial nucleophilic attack by PhCHO to
the Al center was not considered because of the formation of
an unrealistic geometry as reported in a previous contribu-
tion.[3b]
Interestingly, the C1ÀSi bond of TMSCN is elongated by
0.025 Š in 4B, because the electron density of the -C1N1 group
in TMSCN is delocalized to the Al center and the charge sepa-
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rate should be faster for more electronic charge on C1 in the XB
intermediate (X=2 to 5) and less on C2 of the aldehyde and
vice versa. The C2 center of p-MeC6H4CHO is relatively more
electron rich than that of PhCHO and o-FC6H4CHO (Table 2), re-
sulting in the slower reaction rate compared with the other
two. For catalysts 3, 4, and 5, the reaction of p-MeC6H4CHO re-
sults in product formation with very poor yields (that is, 40, 45,
and 10%, respectively). However, this observation does not
hold for catalyst 2, where excellent product yield (99%) is re-
ported under experimental conditions. This is due to the very
high electron density at the C1 center of 2B [qC1(2B)=À0.041 e],
which provides sufficient driving force for the nucleophilic
attack at the C2 center of the aldehyde.
Figure 2. Optimized geometry of 4B and 4C-TS at the BP86/def2-SVP level of
theory.
We have reported similar investigations of TMSCN addition
to PhCHO in the presence of the other three catalysts 2, 3, and
5. The three energy profiles including the optimized intermedi-
ates are drawn in Figures S5–S7 (in the Supporting Informa-
tion). All the corresponding intermediates connecting to the
catalytic pathways for catalysts 2, 3, and 5 are higher in energy
than that of catalyst 4 owing to the greater steric influence of
the bulky ligands at the Al center (Figure S8 in the Supporting
Information). Generally, the relative energies of the intermedi-
ates for all the computed catalytic systems (2–5) follow the
trend: 4<3<5<2, except that of the intermediate 5B, which
is slightly more stabilized than 3B.
Table 2. The Mulliken charges (e) of selected atoms in selected inter-
mediates and reactants.
Al
N1
C1
Si
C2
O1
PhCHO
o-FC6H4CHO
p-MeC6H4CHO
TMSCN
4B
0.398 À0.435
0.400 À0.434
0.384 À0.441
À0.233 À0.088 0.440
À0.126 À0.144 0.053
À0.132 À0.169 0.102
0.400
0.363 0.388 À0.458
4C
4D
À0.228 À0.110
À0.055 0.433 0.397 À0.402
ration of the Si and -C1N1 group is increased by 0.190 e from
free TMSCN (Table 2). Therefore, the weaker C1ÀSi bond is now
able to undergo activation by the carbonyl compound. The ad-
dition of PhCHO to the intermediate 4B results in another
weakly bound complex, 4C, which may not be sustained in the
condensed phase. The formation of 4C is endergonic (DGLS =
9.4 kcalmolÀ1) owing to the entropic energy during the associ-
ation. Species 4C then undergoes cycloaddition of C1ÀSi with
the C2=O1 bond of the incoming PhCHO through a four-mem-
bered cyclic transition state, 4C-TS (Figure 1). The cyanohydrin
is already formed and remains coordinated to the Al center in
the resulting intermediate 4D. This step corresponds to an acti-
vation barrier of 30.0 kcalmolÀ1. The transition state vector de-
picts a single imaginary mode of the C1ÀSi bond cleavage and
concomitant formation of the C1ÀC2 and O1ÀSi bonds. The in-
creased C1ÀSi and C1ÀO1 bond lengths in 4C-TS amount to
2.781 and 1.269 Š, respectively (Figure 2). The overall insertion
step is exergonic [DGLS(4B!4D)=À5.0 kcalmolÀ1] and also
highly exothermic [DHLS =À18.5 kcalmolÀ1], suggesting an ad-
equate thermodynamic driving force for 4D formation. Finally,
there is a very shallow PES (potential energy surface) found in
the product decoordination step. The calculated transition
state 4D-TS is lower than the intermediate 4D by 2.3 kcalmolÀ1,
signifying a barrierless, facile ligand dissociation step to furnish
the desired product and to regenerate the catalyst 4 (Figure 1).
In the reaction pathway described in Figure 1, the highest
activation barrier (D°GLS =30.0 kcalmolÀ1) is required for the
insertion step, which is referred to as the rate-determining
step. Therefore, the rate-determining step is governed by nu-
cleophilic charge transfer from C1 to C2 and thus the reaction
Conclusion
Four Lewis acidic aluminum compounds 2, 3, 4, and 5 have
been synthesized and fully characterized by single-crystal X-ray
structural analysis. Compounds 2–5 each contain in their coor-
dination sphere a b-diketiminate ligand and two bridging
sulfur, oxygen, or nitrogen atoms, respectively, at the alumi-
num center. They efficiently catalyze the addition reactions of
trimethylsilyl cyanide (TMSCN) to aldehydes. DFT studies reveal
that the reaction proceeds through a stepwise mechanism via
an intermediate, 4B, where the C1ÀSi bond in the coordinated
TMSCN is lengthened as a result of adequate charge separa-
tion between the C1 and Si atoms. The polarized C1ÀSi bond is
then activated by addition to the C=O group of the aldehyde.
Further exploration of the detailed mechanistic studies for all
catalysts (2–5) are currently in progress in our laboratory.
Experimental Section
General information
Unless otherwise noted, all manipulations were performed by
using a vacuum line and standard Schlenk techniques with an at-
mosphere of nitrogen or by using glovebox techniques. All sol-
vents, including CDCl3 and C6D6, were heated at reflux over the ap-
propriate drying agent and distilled prior to use. H and 13C NMR
spectra were recorded with a Varian Mercury Plus 400 MHz. Com-
mercially available chemicals were purchased from Alfa and used
as received. LH[19] and LAlH2 were prepared as described in the
1
[20]
literature.
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Synthesis of 2
Synthesis of 5
A solution of 1 (0.446 g, 1.0 mmol) in toluene (10 mL) was added
drop by drop to a solution of 2-mercapto-4,6-dimethylpyrimidine
hydrate (0.283 g, 2 mmol) in toluene (15 mL) at 08C. After the addi-
tion was complete, the reaction mixture was allowed to warm to
room temperature and stirring was continued for 12 h to give
a white suspension, which was filtered. The crude product was
crystallized from toluene to afford colorless crystals of 2. An addi-
tional crop of 2 was obtained from the mother liquor. Total yield:
0.621 g (86%); m.p.: 240.3–241.28C; 1H NMR (400 MHz, CDCl3,
258C, TMS): d=7.25–7.09 (m, 8H, Ar-H), 6.06 (br, 2H, g-H), 5.39 (s,
1H, g-H), 3.37 (br, 4H, CHMe2), 1.82 (br, 12H, Pyr-Me), 1.25 (br, 6H,
Me), 1.10 ppm (br, 24H, CHMe2); 13C NMR (101 MHz, CDCl3, 258C,
TMS): d=170.3 (Pyr-NCN), 166.1 (Pyr-C=N), 161.9 (C=N), 144.9 (o-
Ar), 142.5 (o-Ar), 140.7 (i-Ar), 129.0, 128.2, 126.7, 126.5, 125.1, 124.0,
123.0 (C of Ar), 114.3 (g-Pyr), 93.2 (g-C), 28.6, 28.2 (CHMe2), 25.4,
25.2, 24.9, 24.2, 23.2, 22.7, 20.7 ppm (Me); elemental analysis calcd
(%) for C41H55AlN6S2 (Mr =723.01): C 68.11, H 7.67, N 11.62; found: C
68.44, H 7.60, N 11.72.
Compound 5 was prepared in a similar manner to 2 from
1 (0.446 g, 1.0 mmol) and ethyl 3-amino-4,5,6,7-tetrahydrobenzo[b]-
thiophene-2-carboxylate (0.451 g, 2 mmol). The crude product was
crystallized from toluene to afford colorless crystals of 5, and the
extract was stored at room temperature for 1 d to afford 5 as col-
orless crystals. An additional crop of 5 was obtained from the
1
mother liquor. Total yield: 0.732 g (82%); m.p.: 205–2088C; H NMR
(400 MHz, CDCl3, 258C, TMS): d=7.32–6.99 (m, 6H, Ar-H), 5.29 (s,
1H, g-H), 4.27 (m, 4H, OCH2CH3), 3.54 (s, 2H, NH), 3.14 (sept, 4H,
CHMe2), 2.66 (t, J=7.2 Hz, 6H, OCH2CH3), 1.78 (s, 24H, CHMe2), 1.67
(s, 6H, Me), 1.35 (m, 4H, CH2), 1.24 (m, 4H, CH2), 1.13 (m, 4H, CH2),
0.88 ppm (m, 4H, CH2); 13C NMR (101 MHz, CDCl3, 258C, TMS): d=
169.19 (C=N), 161.20 (COOCH2CH3), 161.01, 144.97, 142.29, 132.45,
125.09, 124.19, 123.02, 117.64 (C of Ar and thiophene), 98.05 (g-C),
59.35 (OCH2CH3), 28.47, 28.19 (CHMe2), 26.9, 25.36 (CH3), 24.55,
21.22 (CHMe2), 14.49 ppm (OCH2CH3); elemental analysis calcd (%)
for C51H69AlN4O4S2 (Mr =893.20): C 68.58, H 7.79, N 6.27; found: C
68.83, H 7.89, N 6.21.
General catalytic procedure for the addition reactions of tri-
methylsilyl cyanide (TMSCN) to aldehydes
Synthesis of 3
Compound 3 was prepared in a similar manner to 2 from
1 (0.446 g, 1.0 mmol) and N-2-pyridylsalicylideneamine (0.396 g,
2 mmol). The crude product was crystallized from toluene to afford
colorless crystals of 3, and the extract was stored at room tempera-
ture for 2 d to afford 3 as colorless crystals. An additional crop of 3
was obtained from the mother liquor. Total yield: 0.586 g (70%);
1H NMR (400 MHz, CDCl3, 258C, TMS): d=9.48 (s, 2H, CH=N),
8.40--6.66 (m, 22H, Ar-H) 5.37 (s, 1H, g-H), 3.06 (sept, 4H, CHMe2),
1.94 (s, 6H, Me), 1.23 (d, J=6.8 Hz, 12H, CHMe2), 1.13 ppm (d, J=
6.8 Hz, 12H, CHMe2); 13C NMR (101 MHz, CDCl3, 258C, TMS): d=
164.79 (CH=N), 161.92, 161.20, 157.61 (C=N), 148.99, 142.46,
140.73, 138.49, 133.86, 133.50, 129.05, 128.24, 125.08, 123.02,
120.49, 119.23, 117.29 (C of Ar and Pyr), 93.24 (g-C), 28.19 (CHMe2),
24.24, 23.22 (CHMe2), 20.75 ppm (b-Me); elemental analysis calcd
(%) for C53H59AlN6O2 (Mr =839.06): C 75.87, H 7.09, N 10.02; found:
C 76.33, H 7.21, N 9.78.
The catalyst (0.02 mmol), the aldehyde (1 mmol), TMSCN
(1.2 mmol), and CDCl3 (2 mL) were placed in a dried J. Young’s
Tube. The solution was stirred at ambient temperature for an ap-
propriate time. The reaction was quenched by exposure to air. The
1
products were identified and quantified by H and 13C NMR spec-
troscopy.
CCDC 1406398 (2), 1416414 (3), 1416416 (4), and 1416415 (5) con-
tain the supplementary crystallographic data for this paper. These
data are provided free of charge by The Cambridge Crystallograph-
ic Data Centre.
Acknowledgments
This work was supported by the International Science & Tech-
nology Cooperation Program of China (2014DFR61080) and
the Deutsche Forschungsgemeinschaft (RO224/64-1). T.M. is
thankful to the CSIR for the SRF fellowship. D.K. and S.D. ac-
knowledge IISER-Kolkata and the CSIR project fund (01(2770/
13/EMR-II) for financial support. S.D. and T.M. are grateful to
Bholanath Maity for scientific discussions.
Synthesis of 4
Compound 4 was prepared in a similar manner to 2 from
1 (0.446 g, 1.0 mmol) and N-(2,6-diisopropylphenyl)salicylaldimine
(0.282 g, 1.0 mmol). The crude product was crystallized from n-
hexane to afford colorless crystals of 4. The solvent was removed
in vacuo. The solid was extracted with n-hexane (15 mL), and the
extract was stored at room temperature for 1 d to afford 4 as col-
orless crystals. An additional crop of 4 was obtained from the
mother liquor. Total yield: 0.429 g (58%); m.p.: 212–2158C; IR (KBr):
Keywords: addition reactions · aluminum complexes · DFT
studies · Lewis acid catalyst
[1] H. Yamamoto, Lewis Acids in Organic Synthesis, Wiley-VCH, Weinheim,
2000.
1
n=1740 cmÀ1(d, Al-H); H NMR (400 MHz, C6D6, 258C): d=8.29 (s,
1H, CH=N), 7.17--6.81 (m, 13H, Ar-H), 4.97 (s, 1H, g-H), 3.35 (sept,
2H, CHMe2), 3.19–3.07 (m, 4H, CHMe2), 2.01 (s, 3H, Me), 1.65 (s, 3H,
Me), 1.33–1.31 (m, 18H, CHMe2), 1.28–1.21 (m, 12H, CHMe2), 1.11–
1.09 (m, 3H, CHMe2), 1.03–1.01 ppm (m, 3H, CHMe2); 13C NMR
(101 MHz, C6D6, 258C): d=171.02 (CH=N), 159.61 (C=N), 159.41
(C=N), 144.15, 142.13, 140.89, 138.92, 137.31, 131.75, 128.82,
127.58, 127.01, 126.57, 125.52, 125.31, 124.28, 124.21, 124.02,
123.44, 123.35, 122.68 (C of Ar), 97.06 (g-C), 28.20, 27.91, 27.90
(CHMe2), 24.70, 24.35, 24.14, 23.97, 23.12, 23.06, 22.90 ppm (CH3);
elemental analysis calcd (%) for C48H64AlN3O (Mr =726.00): C 79.41,
H 8.89, N 5.79; found: C 79.59, H 8.95, N 5.68.
[2] a) M. Bochmann, D. M. Dawson, Angew. Chem. Int. Ed. Engl. 1996, 35,
2226–2228; Angew. Chem. 1996, 108, 2371–2373; b) D. A. Atwood, J. A.
Jegier, D. Rutherford, J. Am. Chem. Soc. 1995, 117, 6779–6780; c) M. P.
Coles, R. F. Jordan, J. Am. Chem. Soc. 1997, 119, 8125–8126.
[3] a) C. A. Koellner, N. A. Piro, W. S. Kassel, C. R. Goldsmith, C. R. Graves,
Inorg. Chem. 2015, 54, 7139–7141; b) Z. Yang, M. Zhong, X. Ma, S. De,
C. Anusha, P. Parameswaran, H. W. Roesky, Angew. Chem. Int. Ed. 2015,
54, 10225–10229; Angew. Chem. 2015, 127, 10363–10367.
[4] S. Saito, Main Group Metals in Organic Synthesis (Eds.: H. Yamamoto, K.
Oshima), Wiley-VCH, Weinheim, 2004, pp. 189–306.
[5] T. Ooi, K. Maruoka in Lewis Acids in Organic Synthesis (Ed.: H. Yamamo-
to), Wiley-VCH, Weinheim, 2000, pp. 191–282.
Chem. Eur. J. 2016, 22, 6932 – 6938
www.chemeurj.org
6937
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[6] W. Wulff in Lewis Acids in Organic Synthesis (Ed.: H.Yamamoto), Wiley-
VCH, Weinheim, 2000, pp. 282–354.
[7] W. Li, W. Wu, Y. Wang, Y. Yao, Y. Zhang, Q. Shen, Dalton Trans. 2011, 40,
11378–11381.
[8] V. Jancik, Y. Peng, H. W. Roesky, J. Li, D. Neculai, A. M. Neculai, R. Herbst-
Irmer, J. Am. Chem. Soc. 2003, 125, 1452–1453.
Mazzeo, S. Milione, V. Bertolasi, D. Pappalardo, Organometallics 2012,
31, 5551–5560; c) L. Postigo, M. C. Maestre, M. E. G. Mosquera, T.
Cuenca, G. JimØnez, Organometallics 2013, 32, 2618–2624; d) C. H.
Huang, F. C. Wang, B. T. Ko, T. L. Yu, C. C. Lin, Macromolecules 2001, 34,
356–361; e) Q. Ni, L. P. Yu, J. Am. Chem. Soc. 1998, 120, 1645–1646; f) B.
Lian, H. Ma, T. P. Spaniol, J. Okuda, Dalton Trans. 2009, 41, 9033–9042.
[14] a) W. Wang, Z. Yang, X. Ma, H. W. Roesky, Y. Ju, P. Hao, Z. Anorg. Allg.
Chem. 2015, 641, 684–687; b) Z. Yang, P. Hao, X. Ma, H. W. Roesky, Y.
Yang, J. Li, Z. Anorg. Allg. Chem. 2014, 640, 1081–1085.
[15] a) J. Casas, C. Nµjera, J. M. Sansano, J. M. Saµ, Tetrahedron 2004, 60,
10487–10496; b) J. Casas, C. Nµjera, J. M. Sansano, J. M. Saµ, Org. Lett.
2002, 4, 2589–2592; c) E. J. Campbell, H. Zhou, S. T. Nguyen, Org. Lett.
2001, 3, 2391–2393; d) T. Ooi, T. Miura, K. Maruoka, Angew. Chem. Int.
Ed. 1998, 37, 2347–2349; Angew. Chem. 1998, 110, 2524–2526; e) I.
Simpura, V. Nevalainen, Angew. Chem. Int. Ed. 2000, 39, 3422–3425;
Angew. Chem. 2000, 112, 3564–3567; f) T. Yamaguchi, K. Matsumoto, B.
Saito, T. Katsuki, Angew. Chem. Int. Ed. 2007, 46, 4729–4731; Angew.
Chem. 2007, 119, 4813–4815.
[9] a) V. Jancik, H. W. Roesky, D. Neculai, A. M. Neculai, R. Herbst-Irmer,
Angew. Chem. Int. Ed. 2004, 43, 6192–6196; Angew. Chem. 2004, 116,
6318–6322; b) V. Jancik, H. W. Roesky, Angew. Chem. Int. Ed. 2005, 44,
6016–6018; Angew. Chem. 2005, 117, 6170–6172; c) S. P. Sarish, B. Ne-
koueishahraki, A. Jana, H. W. Roesky, T. Schulz, D. Stalke, Chem. Eur. J.
2011, 17, 890–894; d) V. Jancik, L. W. Pineda, J. Pinkas, H. W. Roesky, D.
Neculai, A. M. Neculai, R. Herbst-Irmer, Angew. Chem. Int. Ed. 2004, 43,
2142–2145; Angew. Chem. 2004, 116, 2194–2197; e) P. C. Kuo, I. C.
Chen, J. C. Chang, M. T. Lee, C. H. Hung, H. M. Lee, J.-H. Hung, C. H. Hu,
Eur. J. Inorg. Chem. 2004, 24, 4898–4906; f) V. Jancik, A. P. Gómora-Fig-
ueroa, M. M. Moya-Cabrera, R. A. Toscano, R. Cea-Olivares, Synth. React.
Inorg. Met.-Org. Nano-Met. Chem. 2007, 37, 741–744; g) V. Jancik, F.
Rascón-Cruz, R. Cea-Olivares, R. A. Toscano, Chem. Commun. 2007, 43,
4528–4530; h) F. Rascón-Cruz, R. Huerta-Lavorie, V. Jancik, R. A. Toscano,
R. Cea-Olivares, Dalton Trans. 2009, 7, 1195–1200; i) S. P. Sarish, H. W.
Roesky, M. John, A. Ringe, J. Magull, Chem. Commun. 2009, 17, 2390–
2392; j) V. Jancik, H. W. Roesky, Inorg. Chem. 2005, 44, 5556–5558;
k) A. P. Gómora-Figueroa, V. Jancik, R. Cea-Olivares, R. A. Toscano, Inorg.
Chem. 2007, 46, 10749–10753.
[16] Y. Hamashima, D. Sawada, M. Kanai, M. Shibasaki, J. Am. Chem. Soc.
1999, 121, 2641–2642.
[17] G. Bai, Y. Peng, H. W. Roesky, J. Li, H.-G. Schmidt, M. Noltemeyer, Angew.
Chem. Int. Ed. 2003, 42, 1132–1135; Angew. Chem. 2003, 115, 1164–
1167.
[18] Y. Li, J. Wang, Y. Wu, H. Zhu, P. P. Samuel, H. W. Roesky, Dalton Trans.
2013, 42, 13715–13722.
[10] J. A. Miller, Chemistry of Aluminum, Gallium, Indium and Thallium (Ed.:
A. J. Downs), Chapman and Hall, London, 1993, pp. 372–429.
[11] T. W. Myers, L. A. Berben, J. Am. Chem. Soc. 2013, 135, 9988–9990.
[12] a) M. Cheng, E. B. Lobkovsky, G. W. Coates, J. Am. Chem. Soc. 1998, 120,
11018–11019; b) P. L. Holland, W. B. Tolman, J. Am. Chem. Soc. 1999,
121, 7270–7271; c) C. Cui, H. W. Roesky, H. G. Schmidt, M. Noltemeyer,
H. Hao, F. Cimpoesu, Angew. Chem. Int. Ed. 2000, 39, 4274–4276;
Angew. Chem. 2000, 112, 4444–4446.
[19] B. Qian, D. L. Ward, M. R. Smith III, Organometallics 1998, 17, 3070–
3076.
[20] C. Cui, H. W. Roesky, H. J. Hao, H.-G. Schmidt, M. Noltemeyer, Angew.
Chem. Int. Ed. 2000, 39, 4531–4533; Angew. Chem. 2000, 112, 4705–
4707.
Received: December 25, 2015
[13] a) J. C. Chang, Y. C. Chen, A. Datta, C. H. Lin, C. S. Hsiao, J. H. Huang, J.
Organomet. Chem. 2011, 696, 3673–3680; b) M. Lamberti, I. D. Auria, M.
Published online on April 8, 2016
Chem. Eur. J. 2016, 22, 6932 – 6938
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