Aluminum alkyl complexes supported by bidentate N,N ligands: Synthesis, structure, and catalytic activity for guanylation of amines

Article abstract of DOI:10.1021/acs.organomet.5b00101

The reactions of AlMe₃ or AlEt₃ with 2-pyridyl- or indolyl-substituted imines were studied, leading to the formation of different organoaluminum complexes. While the reactions of the iminopyridine Cy[N=CMe-2-(C₅H₄N)]₂ (L¹) derived from 1-(pyridin-2-yl)ethanone and trans-1,2-cyclohexanediamine with AlEt₃ gave the aluminum complex Cy[NC(Me)(Et)-2-(C₅H₄N)AlEt₂]₂ (1), in which the two ketimine groups of the ligand were transformed into the amido functionality through the addition of two ethyl groups, the reaction of L¹ with AlMe₃ afforded the aluminum complex Cy[NC(=CH₂)-2-(C₅H₄N)AlMe₂]₂ (2) via a sp³ C-H activation with elimination of two methane molecules. The reactions of indolyl-2-aldimines (2-(RN=CH)C₈H₅NH (R = ^tBu (L²H), C₆H₅ (L³H), 2,6-Me₂C₆H₃ (L⁴H)) with AlMe₃ or AlEt₃ afforded only the deprotonated indolyl aluminum complexes [2-(RN=CH)C₈H₅N]AlMe₂ (R = ^tBu (3), C₆H₅ (4), 2,6-Me₂C₆H₃ (5)) and [2-(2,6-Me₂C₆H₃N=CH)C₈H₅N]AlEt₂ (6), respectively. The structures of complexes 2-6 were characterized by spectral methods and X-ray crystallographic analyses. These aluminum complexes showed a high catalytic activity in the addition of amines to carbodiimides to form guanidines. The mechanism of the catalytic process was studied by control experiments and ¹H NMR monitoring. Together with the isolation of the complex [2-(2,6-Me₂C₆H₃N=CH)C₈H₅N][CyN=C(4-MeC₆H₃N)(NHCy)]AlMe (7), a probable mechanism for the guanylation reaction was proposed.

Full text of DOI:10.1021/acs.organomet.5b00101

Article
pubs.acs.org/Organometallics
Aluminum Alkyl Complexes Supported by Bidentate N,N Ligands:
Synthesis, Structure, and Catalytic Activity for Guanylation of Amines
Yun Wei,† Shaowu Wang,*,†,‡ Shuangliu Zhou,*,† Zhijun Feng,† Liping Guo,† Xiancui Zhu,†
Xiaolong Mu,† and Fangshi Yao†
†Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials, College of
Chemistry and Materials Science, Anhui Normal University, Wuhu, Anhui 241000, People’s Republic of China
‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, People’s Republic of China
S
* Supporting Information
ABSTRACT: The reactions of AlMe3 or AlEt3 with 2-pyridyl-
or indolyl-substituted imines were studied, leading to the
formation of different organoaluminum complexes. While the
reactions of the iminopyridine Cy[NCMe-2-(C5H4N)]2
(L1) derived from 1-(pyridin-2-yl)ethanone and trans-1,2-
cyclohexanediamine with AlEt3 gave the aluminum complex
Cy[NC(Me)(Et)-2-(C5H4N)AlEt2]2 (1), in which the two
ketimine groups of the ligand were transformed into the amido
functionality through the addition of two ethyl groups, the
reaction of L1 with AlMe3 afforded the aluminum complex Cy[NC(CH2)-2-(C5H4N)AlMe2]2 (2) via a sp3 C−H activation
with elimination of two methane molecules. The reactions of indolyl-2-aldimines (2-(RNCH)C8H5NH (R = tBu (L2H), C6H5
(L3H), 2,6-Me2C6H3 (L4H)) with AlMe3 or AlEt3 afforded only the deprotonated indolyl aluminum complexes [2-(RN
t
CH)C8H5N]AlMe2 (R = Bu (3), C6H5 (4), 2,6-Me2C6H3 (5)) and [2-(2,6-Me2C6H3NCH)C8H5N]AlEt2 (6), respectively.
The structures of complexes 2−6 were characterized by spectral methods and X-ray crystallographic analyses. These aluminum
complexes showed a high catalytic activity in the addition of amines to carbodiimides to form guanidines. The mechanism of the
1
catalytic process was studied by control experiments and H NMR monitoring. Together with the isolation of the complex [2-
(2,6-Me2C6H3NCH)C8H5N][CyNC(4-MeC6H3N)(NHCy)]AlMe (7), a probable mechanism for the guanylation reaction
was proposed.
straightforward and atom-economical route to guanidines.11
Since the pioneering work reported in 2003 by Richeson and
INTRODUCTION
■
Organometallic aluminum complexes have attracted increasing
co-workers on the catalytic guanylation reaction of primary
aromatic amines with carbodiimides by using titanium imido
complexes,12 complexes of transition metals,13 rare-earth
metals,14 and other main-group metals15 have all been used
for the catalytic guanylation of various amines with
carbodiimides. Recently, aluminum alkyl reagents such as
AlEt3, AlEt2Cl, and AlMe3 have been used as efficient
precatalysts for this reaction.15a We report herein the
preparation of novel neutral organoaluminum complexes from
the reactions of AlMe3 or AlEt3 with 1,2-trans-diaminocyclo-
hexane-derived iminopyridine or indolyl-2-aldimines and their
catalytic activity toward the guanylation reation of arylamines.
The coordinating ligand’s effect on the catalytic activity of these
aluminum complexes for the guanylation and the catalytic
mechanism have also been probed.
attention due to their widespread applications in organic
synthesis1 and polymerization,2 as well as their ready availability
at relatively low cost. As the catalytic properties of the
aluminum complexes are greatly influenced by modifying the
structures of the coordinating ligands, various organic ligands
have been synthesized and investigated in this field. Bidentate
or multidentate ligands bearing N- or O-donor atoms, such as
iminopyridine,3 β-diketiminato,4 guanidinato,5 biphenol,6 phe-
noxy-imine,7 and related Schiff base derivatives,8 are used
extensively in synthesizing organoaluminum complexes. In
particular, in the reactions of imine ligands with aluminum
alkyls, alkylation of the ligand may occur depending on the
nature of the alkyl group or ligand.9 Moreover, reaction of an
iminopyridine ligand with alkyllithium was serendipitously
found to proceed via an initial alkylation of the pyridine N atom
followed by elimination of methane.10 However, the reaction of
iminopyridine ligands with aluminum alkyls still remains to be
revealed.
Over the past decades, metal complex catalyzed C−N bond
formation for the construction of N-substituted guanidines has
attracted much attention, as it was one of the most
Received: February 5, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.5b00101
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Scheme 1. Preparation of Complexes 1 and 2
surrounded by two alkyl groups and two nitrogen atoms. In the
structure of 1 (Figure 1), the imino groups have been
transformed into the amido functionality, forming the cyclo-
hexyl-bearing dinuclear aluminum metallacycle, and the N1−
C3 bond length of 1.473(4) Å is consistent with a typical C−N
single bond. The C3−C4 bond length of 1.348(2) Å in 2 is an
indicative of a CC double bond, which is supported by the
1H NMR spectrum, showing the resonance of the protons of
CCH2 at δ 4.87 and 4.48 ppm. The N1−C3 bond length of
1.378(2) Å is shorter than that of a typical C−N single bond,
suggesting electron delocalization between the CC double
bond and N1 lone pair electrons. The Al−N2(pyridine) bond
of 1.973(1) Å is longer than that of Al−N1 at 1.861(1) Å,
mainly due to the difference of the donor bond character of
Al−N2 and the σ-bond character of Al−N1. The two high-field
singlet resonances in 1H NMR spectrum of 2 (−0.13 and −0.56
ppm) are attributed to the two methyl groups at the Al site with
a rational integral ratio. The observed different reactivities of
AlEt3 and AlMe3 toward L1 may be attributed to steric factors;
the sterically bulkier AlEt3 may prevent the Et of AlEt3 from
interaction with the protons of the methyl group connected to
the imino carbon. Thus, the observed result of AlEt3 shows a
preference for nucleophilic addition.9b However, the activity of
aluminum trialkyls cannot be ruled out. Elemental analysis
results of complexes 1 and 2 are also in agreement with those of
NMR and X-ray studies.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Aluminum Alkyl
Complexes. The reactions of the iminopyridine Cy[NCMe-
2-(C5H4N)]2 (L1, Cy = cyclohexyl) with aluminum alkyls AlR3
(R = Et, Me) are shown in Scheme 1. The treatment of L1 with
2 equiv of AlEt3 in toluene afforded the aluminum complex
Cy[NC(Me)(Et)-2-(C5H4N)AlEt2]2 (1) via nucleophilic addi-
tion of one of the ethyl groups of AlEt3 to the imine, which has
also been previously observed in the reactions of related neutral
imine ligands with alkyaluminum reagents.16 However, the
same reaction of L1 with AlMe3 instead of AlEt3 proceeded via
elimination of two methane molecules to provide the dinuclear
four-coordinate dimethylaluminum complex 2 in good yield.
The structures of complexes 1 and 2 have been confirmed by
single-crystal X-ray diffraction and are shown in Figures 1 and
The above results prompted us to examine the reactivities of
other imino-functionalized hetroaromatic compounds with
aluminum alkyls. Three different 2-imino-functionalized indoles
Figure 1. ORTEP representation of the X-ray structure of complex 1.
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
drawn at the 30% probability level.
t
2-(RNCH)C8H5NH (R = Bu (L2H), C6H5 (L3H), 2,6-
Me2C6H3 (L4H)) were subjected to reaction with 1 equiv of
AlR3 (R = Me, Et), producing the corresponding dialkylalumi-
num complexes formulated as [2-(RNCH)C8H5N]AlMe2 (R
2, and a selection of bond distances and angles is collected in
Table 1. The coordination geometry around the Al center is
described as a four-coordinate distorted tetrahedron, being
=
tBu (3), C6H5 (4), 2,6-Me2C6H3 (5)) and [2-(2,6-
Me2C6H3NCH)C8H5N]AlEt2 (6) in good yields (Scheme
2). Different from the formation of complexes 1 and 2, neither
sp3 C−H activation nor alkyl addition to the imino CN bond
was observed; only the acid−base process was observed in the
preparation of 3−6. This observation could be attributed to
different pKa values of corresponding protons of the methyl
group connected to the imine group (the pKa value of protons
of the methyl group connected to imine should be between
those of propylene (pKa = 43) and acetonitrile (pKa = 25), and
the pKa value of indole is 16.2). X-ray analyses reveal that the
N1−Al1−N2 angles ((84.9(1)° for 3, 84.6(1)° for 4, 84.3(1)°
for 5, and 84.1(1)° for (6)) largely deviated from ideal
tetrahedral angles, leading to a distorted-tetrahedral geometry
around the aluminum (the structure of complexs 3−6 are
shown in Figures 3−6). The N1−Al1−N2 angles of 84.9(1)°
for 3, 84.6(1)° for 4, 84.3(1)° for 5, and 84.1(1)° for 6 are
smaller than that the 86.6(1)° observed in [2-
(2,6-iPr2C6H3NCH)-5-tBuC4H2N]AlMe(Cl).1c The Al−N-
(imino) bond lengths of compounds 3−6 (1.993(2) Å for 3,
Figure 2. ORTEP representation of the X-ray structure of complex 2.
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
drawn at the 30% probability level.
B
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Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) of Complexes 1−6
1
2
3
4
5
6
Al(1)−N(1)
Al(1)−N(2)
Al(1)−C(1)
Al(1)−C(2)
C(3)−N(1)
C(4)−C(3)
N(1)−Al(1)−C(1)
N(1)−Al(1)−C(2)
C(1)−Al(1)−C(2)
N(1)−Al(1)−N(2)
C(1)−Al(1)−N(2)
C(2)−Al(1)−N(2)
1.832(3)
1.974(4)
1.964(5)
2.010(5)
1.473(4)
1.611(2)
124.6(2)
119.9(2)
109.8(2)
85.2(2)
1.861(1)
1.973(1)
1.959(2)
1.959(2)
1.378(2)
1.348(2)
115.7(1)
122.2(1)
114.7(1)
83.9(1)
1.882(2)
1.993(2)
1.943(3)
1.942(3)
1.901(2)
2.011(3)
1.944(4)
1.960(4)
1.902(2)
1.989(2)
1.952(2)
1.952(2)
1.910(2)
1.997(2)
1.959(2)
1.959(2)
113.7(1)
111.0(1)
119.3(1)
84.9(1)
112.8(2)
114.6(1)
119.8(2)
84.6(1)
114.3(1)
111.4(1)
118.8(1)
84.3(1)
111.2(1)
114.1(1)
119.9(1)
84.1(1)
104.3(2)
105.6(2)
109.2(1)
104.4(1)
112.3(1)
110.5(1)
111.6(2)
107.7(1)
110.0(1)
113.0(1)
114.6(1)
107.5(1)
Scheme 2. Preparation of Complexes 3−6
Figure 5. ORTEP representation of the X-ray structure of complex 5.
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
drawn at the 30% probability level.
Figure 6. ORTEP representation of the X-ray structure of complex 6.
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
drawn at the 30% probability level.
Figure 3. ORTEP representation of the X-ray structure of complex 3.
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
drawn at the 30% probability level.
and the monopyrrolylaldiminato aluminum complex [2-
(2,6-iPr2C6H3NCH)-5-tBuC4H2N]AlMe(Cl) (1.944 Å),1c
which is similar to the average Al−N(imino) bond length of
1.993 Å found in the complex [2-(2,6-iPr2C6H3NCH)-
C4H3N]2AlCl.8b The Al−N(indole) bond lengths of complexes
3−6 (1.882(2) Å for 3, 1.901(2) Å for 4, 1.902(2) Å for 5,
1.910(2) Å for 6) are slightly shorter than the Al−N(pyrrole)
bond length (1.96 Å) found in the complex [2-
(2,6-iPr2C6H3NCH)C4H3N]2AlCl and are similar to the
Al−N(pyrrole) bond length in the complex [2-
(2,6-iPr2C6H3NCH)-5-tBuC4H2N]AlMe(Cl) (1.905 Å), in-
dicating different electronic and steric effects of the
corresponding ligands. The 1H NMR spectra of these
indolylaldiminato Al complexes show the proton resonances
of the two methyl groups at δ −0.21 ppm for 3, −0.48 ppm for
4, and −0.18 ppm for 5, respectively. The proton resonances of
the imino group appear at δ 7.23 ppm for 3, 7.11 ppm for 4,
and 7.05 ppm for 5, which are consistent with the X-ray data.
Figure 4. ORTEP representation of the X-ray structure of complex 4.
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
drawn at the 30% probability level.
2.011(3) Å for 4, 1.989(2) Å for 5, 1.997(2) Å for 6) are
similar, which are slightly longer than those found in
salicylaldiminato aluminum complexes (range 1.94−1.98 Å)17
C
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The 13C NMR spectra show the methyl carbon resonance at
−9.5 ppm for 3, −9.9 ppm for 4, and −9.3 ppm for 5. The
proton resonances of the methlene groups of L4Al(CH2CH3)2
in complex 6 appear at 0.40−0.28 ppm, and the corresponding
methyl protons appear at 1.30−1.33 ppm.
Therefore, complex 2 was selected as the precatalyst for
subsequent reaction scope studies.
Next, the guanylation of a variety of aromatic amines by
carbodiimides was examined with complex 2 in toluene, and the
results are summarized in Table 3. Generally, a wide range of
Catalytic Activities of the Complexes on Guanylation
of Aromatic Amines. With the above dinuclear and
mononuclear aluminum complexes in hand, their catalytic
activities for the guanylation reaction were studied.
Table 3. Results of Reactions of Different Anilines with
Carbodiimides Catalyzed by Complex 2
a
Complex 2 was employed as the precatalyst for screening the
optimal conditions for the model reaction between aniline and
N,N′-dicyclohexylcarbodiimide, and the results are given in
Table 2. It was found that the catalytic guanylation reaction of
cat. loading
(mol %)
temp
time
(h)
yield
b
Entry
1
R
Ar
(°C)
(%)
Table 2. Reaction of Aniline with N,N′-
0.5
Cy C6H5
room
temp
1
1
1
1
1
1
1
1
1
1
1
1
1
1
97
96
97
96
99
98
98
97
97
96
98
97
99
96
Dicyclohexylcarbodiimide Catalyzed by Different Aluminum
a
2
1
iPr
room
temp
Complexes under Various Conditions
b
loading
time
(h)
yield
(%)
3
0.5
1
Cy 4-MeC6H4
room
temp
entry
1
cat.
(mol %)
solvent
toluene
temp (°C)
4
iPr
room
temp
2
2
room
temp
0.5
0.5
1
98
97
97
78
98
96
96
0
5
0.5
1
Cy 4-tBuC6H4
iPr
room
temp
2
2
1
toluene
toluene
toluene
THF
room
temp
3
2
0.5
0.1
0.5
0.5
0.5
room
temp
6
room
temp
4
2
room
temp
6
7
0.5
1
Cy 4-
room
temp
OMeC6H4
8
iPr
room
temp
5
2
room
temp
1
6
2
solvent-
free
room
temp
1
9
0.5
1
Cy 4-ClC6H4
room
temp
10
11
12
13
14
iPr
room
temp
7
2
hexane
room
temp
1
8
none
solvent-
free
110
24
1
0.5
1
Cy 4-BrC6H4
room
temp
iPr
room
temp
9
1
3
0.5
0.5
toluene
room
temp
95
71
10
toluene
room
temp
1
0.5
1
Cy 1-naphthyl
iPr
room
temp
11
12
13
14
3
4
5
6
1
1
1
1
toluene
toluene
toluene
toluene
60
60
60
60
3
3
3
3
91
90
92
91
room
temp
15
16
17
1
1
2
Cy 2-MeC6H4
iPr
60
3
3
95
94
79
60
a
Cy 2,6-
Me2C6H3
iPr
100
12
The reaction was performed by treating 1 equiv of aniline with 1
b
equiv of N,N′-dicyclohexylcarbodiimide in 3.0 mL of solvent. Isolated
yield.
18
19
20
21
22
23
24
2
1
1
1
1
1
1
100
60
12
3
75
90
87
92
91
90
88
Cy 2-C5H4N
iPr
60
3
Cy 4-NO2C6H4 60
iPr
60
Cy 2-NO2C6H4 60
iPr
60
3
aniline could be completed in toluene at room temperature
within 1 h, producing the product in 97% yield in the presence
of 0.5 mol % of catalyst (entry 3). Increasing the catalyst
loading did not improve the yield of the reaction, while
decreasing the catalyst loading to 0.1 mol % led to a
significantly decreased yield of 78% (entry 4). Performing the
reaction in other solvents such as THF and hexane gave
comparable results, and up to 96% yield could still be obtained
when the reaction was carried out under solvent-free conditions
(entries 5−7). It should be noted that no product formation
was observed in the absence of the catalyst even when the
reaction mixture was heated at 110 °C for 24 h. Then the
catalytic activities of complexes 1 and 3−6 were examined. In
general, the catalytic activities of dinuclear aluminum complexes
1 and 2 were higher than those of mononuclear complexes 3−6
(entries 9−14) under the same reaction conditions, probably
due to dinuclear aluminum complexes with two active sites.
3
3
3
a
The reaction was performed by treating 1 equiv of anilines with 1
equiv of N,N′-dialkylcarbodiimide. Isolated yield.
b
substituted aromatic amines are suitable for the catalytic
reaction. In the case of iPrNCNiPr, probably due to steric
reasons, the catalytic reactions required 1 mol % of the
precatalyst to give satisfactory yields of the desired products.
Anilines with strongly electron donating substituents such as
t
CH3O−, CH3−, and Bu− are favored for the reaction to
provide excellent yields (>96%) within 1 h at room
temperature (Table 3, entries 3−8), while those with strongly
electron withdrawing substituents required longer reaction
times at elevated reaction temperatures (Table 3, entries 21−
D
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24). As observed in previous relevant studies,15a anilines with
substituents at the ortho positions required a higher reaction
temperature and longer reaction time to give high yields, which
might be ascribed to steric reasons (Table 3, entries 15−18).
Catalytic Mechanism. In recent reports, mixed Al alkyl/
halide and guanidinate-supported Al complexes were successful
precatalysts for the guanylation of anilines with carbodiimi-
des.The catalytic cycle has been proposed to proceed via amine
exchange with the supporting ligand to form a catalytically
active three-coordinate Al species, which could subsequently
add to carbodiimides to form Al guanidinate species.5a,15a
To provide evidence for the catalytic reaction mechanism of
the above aluminum complexes, the 1:1:1 reaction of complex
5, 4-MeC6H4NH2, and CyNCNCy was carried out in
toluene at 80 °C to give the aluminum guanidinate complex 7
(Figure 7). This result could be explained by the interaction of
MeC6H4NH2 in C6D6 at 80 °C was probed by H NMR
techniques, it showed no change in Al−CH3 signals after 12 h,
indicating inactivity of the methyl group of the complex to the
aniline. For the addition of CyNCNCy to the mixture at
room temperature, the resonances of the guanidine product 4-
MeC6H4NC(NHCy)2 and the free ligand L4H were
1
1
observed after 1 h in the H NMR spectra, and more strong
resonances of the free ligand L4H were observed after 16 h at
room temperature. Surprisingly, the resonances of the
corresponding free ligand L4H gradually disappeared in the
1H NMR spectra when the reaction was prolonged to 22 h, and
the resonances of complex 7 were observed as the
disappearance of the free ligand L4H. This observation
suggested that the methyl moieties on the metal center are
not involved in the initiation step of the catalytic reaction; the
interaction of aniline with complex 5 produced the amido
intermediate B with release of the free ligand L4H probably due
to the small Al ion, and insertion of the carbodiimide into the
Al−N (amido intermediate B) bond gave the guanidinate
intermediate C. The released free ligand then interacted with
one of methyl groups, resulting in the final complex 7. In the
catalytic cycle, interaction of the intermediate C with aniline
produced the guanidine products (Scheme 3, path b; 1H NMR
probing spectra are provided in the Supporting Information).
CONCLUSIONS
■
In summary, reactions of different heteroaromatic imines with
trialkylalanes showed different reactivities, with the isolation of
different types of aluminum alkyl complexes. A study of the
catalytic activities of aluminum complexes toward the
guanylation of aryl amines showed that the dinuclear aluminum
complexes 1 and 2 exhibited catalytic activities higher than
those of mononuclear aluminum complexes 3−6. The 1H
NMR probing experiments gave evidence that the methyl
groups of the complexes are inactive toward the aniline, and the
results supported the dissociation of the supporting ligand in
the initiation step, which is different from the catalytic
mechanism of aluminum trialkyl catalyzed guanylation
reactions. The results suggested that different aluminum
complex catalyzed guanylation reactions would involve different
catalytic mechanisms. Further works in this field are now in
progress.
Figure 7. ORTEP representation of the X-ray structure of complex 7.
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
drawn at the 30% probability level. Selected bond lengths (Å) and
angles (deg): Al(1)−N(1), 1.968(2); Al(1)−N(2), 2.037(2); Al(1)−
N(3), 2.027(2); Al(1)−N(4), 1.921(2); Al(1)−C(38), 1.969(3);
N(1)−Al(1)−N(2), 80.4(1); N(4)−Al(1)−N(3), 67.4(1).
aniline with the methyl ligand of the complex to produce
intermediate A, which then interacted with carbodiimide via an
insertion reaction to give the final product (Scheme 3, path a).
However, when the 1:1 reaction of complex 5 with 4-
Scheme 3. Proposed Mechanism and the Formation of the Aluminum Guanidinate Complex 7
E
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Article
1577 (w), 1427 (w), 1346 (m), 1296 (m), 1207 (w), 1128 (m), 1045
(w), 931 (w), 796 (m), 756 (w), 678 (m). Anal. Calcd for
C15H21N2Al: C, 70.29; H, 8.26; N, 10.93. Found: C, 70.07; H, 8.21;
N, 11.04.
Preparation of [2-(C6H5-NCH)C8H5N]AlMe2 (4). This com-
plex was prepared following a procedure similar to that described for 1
from L3H (0.220g, 1.0 mmol) and AlMe3 (0.5 mL, 2.0 M, 1.0 mmol).
Yellow crystals were obtained after recrystallization from hexane at 0
°C for several days (0.243 g, 88% yield). Mp: 185−188 °C under Ar.
1H NMR (300 MHz, C6D6): δ 7.41 (d, J = 8.1 Hz, 1H), 7.20 (s, 1H),
7.12 (d, J = 8.4 Hz, 1H), 6.90−6.85 (m, 1H), 6.78−6.70 (m, 1H), 6.60
(s, 1H), 6.63−6.56 (m, 5H), −0.48 (s, 6H). 13C NMR (75 MHz,
CDCl3): δ 157.0, 146.7, 143.5, 140.0, 132.2, 129.7, 127.5, 127.2, 123.2,
120.8, 120.6, 115.7, 114.2, −9.9. IR (KBr pellet, cm−1): ν 2945 (w),
1604 (m), 1570 (s), 1531 (w), 1489 (w), 1344 (m), 1301 (m), 1120
(m), 1029 (m), 943 (m), 792 (w), 759 (m), 690 (m), 648 (m). Anal.
Calcd for C17H17N2Al: C, 73.93; H, 6.20; N, 10.14. Found: C, 73.68;
H, 6.17; N, 10.02.
Preparation of [2-(2,6-Me2C6H3-NCH)C8H5N]AlMe2 (5). This
complex was prepared following a procedure similar to that described
for 1 from L4H (0.248g, 1.0 mmol) and AlMe3 (0.5 mL, 2.0 M, 1.0
mmol). Yellow crystals were obtained after recrystallization from
hexane at 0 °C for several days (0.277 g, 91% yield). Mp: 160−162 °C
under Ar. 1H NMR (300 MHz, C6D6): δ 7.85 (d, J = 8.1 Hz, 1H), 7.58
(d, J = 8.1 Hz, 1H), 7.33 (t, J = 7.5 Hz, 1H), 7.19 (t, J = 7.5 Hz, 1H),
7.05 (s, 1H), 7.0−6.94 (m, 3H), 6.92 (s, 1H), 2.05 (s, 6H), −0.18 (s,
6H). 13C NMR (75 MHz, C6D6): δ 165.3, 146.5, 143.4, 139.4, 132.0,
131.4, 128.7, 127.0, 127.0, 123.3, 120.5, 115.8, 113.7, 18.1, −9.3. IR
(KBr pellet, cm−1): ν 2922 (w), 1627 (s), 1414 (s), 1589 (m), 1566
(m), 1465 (m), 1425 (w), 1344 (m), 1290 (m), 1193 (m), 1118 (m),
1089 (m), 796 (m), 761 (m), 684 (m), 657 (m). Anal. Calcd for
C19H21N2Al: C, 74.98; H, 6.95; N, 9.20. Found: C, 74.87; H, 7.00; N,
9.18.
Preparation of [2-(2,6-Me2C6H3-NCH)C8H5N]AlEt2 (6). A
solution of AlEt3 (1.0 mL, 1.0 M in toluene, 1.0 mmol) was added
slowly to a solution of L4H (0.248 g, 1.0 mmol) in 20 mL of toluene.
The resulting solution was then heated to 100 °C for 12 h. The solvent
was removed under vacuum, and the residue was diluted with hexane
and filtered. Yellow crystals that were suitable for X-ray diffraction
were obtained from the solution after several days at −35 °C (0.259 g,
78% yield). Mp: 168−170 °C under Ar. 1H NMR (500 MHz, C6D6): δ
7.75 (d, J = 8.0 Hz, 1H), 7.61 (d, J = 8.0 Hz, 1H), 7.27 (t, J = 7.7 Hz,
1H), 7.10 (t, J = 7.4 Hz, 1H), 6.95 (s, 1H), 6.92−6.87 (m, 1H), 6.83
(t, J = 6.4 Hz, 3H), 1.96 (s, 6H), 1.31 (t, J = 8.2 Hz, 6H), 0.40−0.28
(m, 4H). 13C NMR (125 MHz, C6D6): δ 165.4, 147.1, 143.9, 139.8,
128.9, 128.4, 127.4, 127.3, 120.8, 116.3, 114.1, 18.3, 9.2, 0.4. IR (KBr
pellet, cm−1): ν 2941 (w), 1627 (s), 1614 (s), 1589 (m), 1465 (m),
1425 (m), 1338 (m), 1294 (m), 1193 (m), 1126 (m), 1089 (m), 800
(m), 750 (m), 736 (m). Anal. Calcd for C21H25N2Al: C, 75.88; H,
7.58; N, 8.43. Found: C, 75.67; H, 7.59; N, 8.45.
Preparation of [2-(2,6-Me2C6H3-NCH)C8H5N][CyNC(4-
MeC6H3N)(NHCy)]AlMe (7). A Schlenk flask was charged with
complex 5 (0.304 g, 1.0 mmol), p-toluidine (0.107 g, 1.0 mmol), N,N′-
dicyclohexylcarbodiimide (0.206 g, 1.0 mmol), and toluene (30 mL).
The reaction mixture was stirred overnight at 80 °C. The solvent was
evaporated to yield the crude product, which was recrystallized from
toluene and hexane to give yellow crystals at 0 °C after several days
(0.493 g, 82%). Mp: 171 °C under Ar. 1H NMR (500 MHz, C6D6): δ
7.95 (d, J = 8.5 Hz, 1H), 7.84 (d, J = 8.0 Hz, 1H), 7.36 (t, 1H), 7.15−
7.07 (m, 2H), 7.03−6.89 (m, 4H), 6.85 (d, J = 7.5 Hz, 2H), 6.35 (s,
2H), 3.93 (d, J = 8.5 Hz, 1H), 2.89 (m, 2H), 2.19 (s, 3H), 2.04 (s,
6H), 1.76−1.59 (m, 4H), 1.54−1.26 (m, 6H), 1.17−1.02 (m, 4H),
0.79−0.66 (m, 6H), −0.01 (s, 3H). 13C NMR (125 MHz, C6D6): δ
166.0, 162.3, 147.8, 144.9, 139.3, 132.7, 130.8, 129.2, 128.4, 126.4,
125.6, 124.7, 123.3, 119.8, 117.7, 111.6, 54.4, 51.2, 35.3, 34.4, 34.0,
33.6, 33.2, 26.5, 25.8, 25.6, 24.9, 24.7, 20.9, 18.9, −6.8. IR (KBr pellet,
cm−1): ν 2927 (w), 2852 (m), 1629 (s), 1616 (s), 1504 (m), 1448
(w), 1344 (m), 1193 (m), 1126 (m), 1089 (m), 804 (m), 752 (m),
736 (m). Anal. Calcd for C38H48Al N5: C, 75.84; H, 8.04; N, 11.64.
Found: C, 76.06; H, 7.98; N, 11.81.
EXPERIMENTAL SECTION
■
General Methods. All syntheses and manipulations of air- and
moisture-sensitive materials were performed under dry argon and
under an oxygen-free atmosphere using standard Schlenk techniques
or in a glovebox. All solvents were refluxed and distilled over sodium
benzophenone ketyl under argon prior to use unless otherwise noted.
Iminopyridine18 and indolyl-2-aldimine19 ligands were prepared
according to literature procedures. All amines were predried, sublimed,
recrystallized, or distilled before use, and N,N-dicyclohexylcarbodii-
mide and N,N-diisopropylcarbodiimide were purified before use.
AlMe3 and AlEt3 were purchased from Acros and used as received.
Elemental analyses were performed on a PerkinElmer 2400 CHN
analyzer. Melting points were determined in sealed capillaries without
correction. 1H NMR and 13C NMR spectra for analyses of compounds
were recorded on a Bruker AV-300 NMR or AV-500 NMR
spectrometer (300 or 500 MHz in C6D6 for aluminum complexes).
Organometallic samples for NMR spectroscopic measurements were
prepared in a glovebox by use of J. Young valve NMR tubes. Chemical
shifts (δ) were reported in ppm. J values were reported in Hz. IR
spectra were recorded on a Shimadzu FTIR-8400S spectrometer (KBr
pellet). Data for X-ray crystal structure determinations were obtained
with a Bruker diffractometer equipped with a Smart CCD area
detector.
Preparation of Cy[NC(Me)(Et)-2-(C5H4N)AlEt2]2 (1). A solution
of AlEt3 (1.0 mL, 2.0 M in toluene, 2.0 mmol) was added slowly to a
solution of L1 (0.320g, 1.0 mmol) in 20 mL of toluene. The resulting
solution was stirred at room temperature for 12 h. The solvent was
removed under vacuum, and the residue was diluted with toluene and
filtered. The toluene solution was cooled to −35 °C. Pale yellow
crystals that were suitable for X-ray diffraction were obtained from the
solution after several days. (0.466 g, 85%). Mp: 178−180 °C under Ar.
1H NMR (500 MHz, C6D6): δ 7.89 (t, J = 5.0 Hz, J = 5.5 Hz, 2H),
6.83 (t, J = 5.0 Hz, J = 7.0 Hz, 2H), 6.70 (d, J = 3.5 Hz, 2H), 6.33 (d, J
= 5.0 Hz, 2H), 3.37 (d, J = 9.0 Hz, 2H), 2.58−2.29 (m, 4H), 2.18−
1.97 (m, 4H), 1.95−1.93 (m, 2H), 1.59 (s, 6H), 1.52 (s, 6H), 1.51−
1.42 (m, 6H), 1.35−1.31 (m, 2H), 0.69 (t, J = 7.0 Hz, J = 7.5 Hz, 6H),
0.62−0.57 (m, 8H). 13C NMR (75 MHz, C6D6): δ 171.3, 171.2, 171.0,
143.0, 142.9, 139.1, 122.2, 122.1, 122.0, 121.7, 67.5, 67.4, 57.0, 56.7,
56.6, 56.3, 33.2, 32.8, 32.6, 32.0, 31.9, 31.7, 31.6, 31.0, 22.4, 21.9, 21.7,
21.4, 11.4, 11.2, 11.0, 10.6, 9.6, 9.5, 9.0, 4.8, 1.4. IR (KBr pellet, cm−1):
ν 3049 (s), 2966 (m), 2929 (w), 2854 (m), 1587 (s), 1570 (s), 1460
(m), 1429 (m), 1375 (s), 1300 (s), 1153 (s), 777 (m), 748 (m), 684
(m). Anal. Calcd for C32H54Al2N4: C, 70.04; H, 9.92; N, 10.21. Found:
C, 69.92; H, 9.72; N, 10.53.
Preparation of Cy[NC(CH2)-2-(C5H4N)AlMe2]2 (2). Complex
2 was prepared following a procedure similar to that described for 1
from L1 (0.320 g, 1.0 mmol) and AlMe3 (2.0 mL, 1.0 M in toluene, 2.0
mmol). The reaction yielded yellow crystals of 2 (0.385 g, 89%). Mp:
181−182 °C under Ar. 1H NMR (500 MHz, C6D6): δ 7.49 (d, J = 5.0
Hz, 2H), 7.35 (d, J = 8.5 Hz, 2H), 6.68 (t, J = 7.5 Hz, J = 8.0 Hz, 2H),
6.17 (t, J = 6.0 Hz, J = 6.0 Hz, 2H), 4.87 (s, 2H), 4.48 (s, 2H), 3.93
(m, 2H), 3.03 (m, 2H), 1.77 (m, 2H), 1.46 (m, 4H), −0.13 (s, 6H),
−0.56 (s, 6H). 13C NMR (125 MHz, C6D6): δ 158.1, 148.9, 142.7,
138.7, 128.4, 122.4, 120.4, 81.5, 60.9, 30.9, 26.3, −7.3, −7.8. IR (KBr
pellet, cm−1): ν 2922 (m), 1627 (s), 1614 (s), 1589 (m), 1560 (m),
1465 (m), 1425 (w), 1344 (m), 1290 (m), 1190 (m), 1118 (m), 1089
(m), 1033 (m), 948 (m), 796 (m), 738 (m), 684 (m). Anal. Calcd for
C24H34Al2N4: C, 66.65; H, 7.92; N, 12.95. Found: C, 66.90; H, 7.88;
N, 12.59.
Preparation of [2-(tBu-NCH)C8H5N]AlMe2 (3). This complex
was prepared following a procedure similar to that described for 1
from L2H (0.200 g, 1.0 mmol) and AlMe3 (0.5 mL, 2.0 M, 1.0 mmol).
Light yellow crystals were obtained after recrystallization from hexane
at 0 °C for several days (0.231 g, 90% yield). Mp: 158−160 °C under
1
Ar. H NMR (500 MHz, C6D6): δ 7.82 (d, J = 7.5 Hz, 1H), 7.63 (s,
1H), 7.54 (d, J = 8.4 Hz, 1H), 7.26 (t, 1H), 7.14 (t, 1H), 6.94 (s, 1H),
0.90 (s, 12H), −0.21 (s, 6H). 13C NMR (75 MHz, C6D6): δ 157.7,
144.8, 138.5, 131.0, 125.1, 121.9, 119.2, 114.6, 110.2, 56.2, 28.7, −9.5.
IR (KBr pellet, cm−1): ν 2970 (m), 1664 (w), 1635 (s), 1616 (m),
F
DOI: 10.1021/acs.organomet.5b00101
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
X-ray Crystallographic Analyses of Aluminum Complexes.
Suitable crystals of complexes 1−7 were each mounted in a sealed
capillary. Diffraction was performed on a Bruker SMART APEXII
CCD area detector diffractometer using graphite-monochromated Mo
Kα radiation (λ = 0.71073 Å) at 293(2) K, with φ and ω scan
techniques. An empirical absorption correction was applied using the
SADABS program.20 All structures were solved by direct methods,
completed by subsequent difference Fourier syntheses, and refined
anisotropically for all non-hydrogen atoms by full-matrix least-squares
calculations based on F2 using the SHELXTL program package.21 The
hydrogen atom coordinates were calculated with SHELXTL by using
an appropriate riding model with varied thermal parameters. The
residual electron densities were of no chemical significance. Selected
bond lengths and angles are compiled in Table 1, and crystal data and
details of the data collection and structure refinements are given in the
Supporting Information.
2014, 33, 5730−5739. (e) Tsai, C.-F.; Chen, H.-J.; Chang, J.-C.; Hung,
C.-H.; Lai, C.-C.; Hu, C.-H.; Huang, J.-H. Inorg. Chem. 2004, 43,
2183−2188. (f) Roesky, H. W.; Kumar, S. S. Chem. Commun. 2005,
4027−4038.
(2) (a) Wu, J.; Yu, T.-L.; Chen, C.-T.; Lin, C.-C. Coord. Chem. Rev.
2006, 250, 602−626. (b) Lamberti, M.; D’Auria, I.; Mazzeo, M.;
Milione, S.; Bertolasi, V.; Pappalardo, D. Organometallics 2012, 31,
5551−5560. (c) Wang, Y.; Ma, H. Chem. Commun. 2012, 48, 6729−
6731. (d) Liu, J.; Ma, H. Dalton Trans. 2014, 43, 9098−9110.
(e) Nomura, N.; Ishii, R.; Akakura, M.; Aoi, K. J. Am. Chem. Soc. 2002,
124, 5938−5939. (f) Hormnirun, P.; Marshall, E. L.; Gibson, V. C.;
White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 2004, 126, 2688−
2689. (g) Yu, R.-C.; Hung, C.-H.; Huang, J.-H.; Lee, H.-Y.; Chen, J.-T.
Inorg. Chem. 2002, 41, 6450−6455.
(3) (a) Myers, T. W.; Kazem, N.; Stoll, S.; Britt, R. D.; Shanmugam,
M.; Berben, L. A. J. Am. Chem. Soc. 2011, 133, 8662−8672. (b) Jurca,
T.; Dawson, K.; Mallov, I.; Burchell, T.; Yap, G. P. A.; Risheson, D. S.
Dalton. Trans. 2010, 39, 1266−1272. (c) Scott, J.; Gambarotto, S.;
Korobkov, I.; Knijnenburg, Q.; Bruin, B.; Budzelaar, P. H. M. J. Am.
Chem. Soc. 2005, 127, 17204−17206. (d) Tay, B.-Y.; Wang, C.; Chia,
S.-C.; Stubbs, L. P.; Wong, P.-K.; Meurs, M. V. Organometallics 2011,
General Procedure for the Direct Synthesis of Guanidines
from the Reaction of Aromatic Amines with Carbodiimides
Catalyzed by Complex 2. A 25.0 mL Schlenk tube was charged with
the dinuclear dimethylaluminum complex 2 (0.005 or 0.01 equiv),
aromatic amine (1.0 equiv), and toluene (3.0 mL) under dried argon.
To the mixture was added carbodiimide (1.0 equiv). The resulting
mixture was stirred at room temperature or was heated to 60 or 100
°C, as shown in Table 3. After the reaction was completed, the
reaction mixture was hydrolyzed by water (3.0 mL), extracted with
dichloromethane (3 × 10.0 mL), dried over anhydrous Na2SO4, and
filtered. After the solvent was removed under reduced pressure, the
final products were further purified by washing with diethyl ether or
hexane.
30, 6028−6033. (e) Zimmermann, M.; Tornroos, K. W.; Anwander, R.
̈
Angew. Chem., Int. Ed. 2007, 46, 3126−3130.
(4) (a) Yang, Y.; Li, H.-P.; Wang, C.; Roesky, H. W. Inorg. Chem.
2012, 51, 2204−2211. (b) Gong, S.; Ma, H. Dalton Trans. 2008,
3345−3357. (c) Yang, Y.; Gurubasavaraj, P. M.; Ye, H.; Zhang, Z.;
Roesky, H. W.; Jones, P. G. J. Organomet. Chem. 2008, 693, 1455−
1461. (d) Cui, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer, M.;
Hao, H.; Cimpoesu, F. Angew. Chem., Int. Ed. 2000, 39, 4274−4276.
(5) (a) Bergman, R. G.; Koller, J. Organometallics 2010, 29, 5946−
5952. (b) Koller, J.; Bergman, R. G. Organometallics 2010, 29, 3350−
3356.
1H NMR Monitoring of the Catalytic Reaction. In a glovebox, a
J. Young valve NMR tube was charged with complex 5 (9.1 mg, 0.03
mmol), C6D6 (0.5 mL), and aniline (3.2 mg, 0.03 mmol), and the
reaction was run at 80 °C for 12 h in an oil bath, at which time no
1
change in Al−CH3 signals was monitored by H NMR spectroscopy.
(6) (a) Li, L.; Liu, B.; Liu, D.; Wu, C.; Li, S.; Liu, B.; Cui, D.
Organometallics 2014, 33, 6474−6480. (b) Li, W.; Wu, W.; Wang, Y.;
Yao, Y.; Zhang, Y.; Shen, Q. Dalton Trans. 2011, 40, 11378−11381.
(c) Ko, B.-T.; Lin, C.-C. Macromolecules 1999, 32, 8296−8300.
(d) Chen, C.-T.; Huang, C.-A.; Huang, B.-H. Macromolecules 2004, 37,
7968−7973. (e) Chen, H.-L.; Ko, B.-T.; Huang, B.-H.; Lin, C.-C.
Organometallics 2001, 20, 5076−5083. (f) Liu, Y.-C.; Ko, B.-T.;
Huang, B.-H.; Lin, C.-C. Organometallics 2002, 21, 2066−2069.
(7) (a) Chen, H.-L.; Dutta, S.; Huang, P.-Y.; Lin, C.-C. Organo-
metallics 2012, 31, 2016−2025. (b) Zhong, Z.; Dijkstra, P. J.; Feijen, J.
Angew. Chem., Int. Ed. 2002, 41, 4510−4513. (c) Iwasa, N.; Katao, S.;
Liu, J.; Fujiki, M.; Furukawa, Y.; Nomura, K. Organometallics 2009, 28,
2179−2187. (d) Nomura, N.; Akita, A.; Ishii, R.; Mizuno, M. J. Am.
Chem. Soc. 2010, 132, 1750−1751.
Then the reaction mixture was cooled to room temperature, followed
by the addition of N,N′-dicyclohexylcarbodiimide (6.2 mg, 0.03
1
mmol). The reaction process was monitored by H NMR spectros-
copy.
ASSOCIATED CONTENT
* Supporting Information
■
S
Figures, tables, and CIF files giving characterization data and
spectral data and X-ray crystallographic data and structure
refinement details for complexes 1−7. The Supporting
Information is available free of charge on the ACS Publications
website at DOI: 10.1021/acs.organomet.5b00101.
(8) (a) Pracha, S.; Praban, S.; Niewpung, A.; Kotpisan, G.;
Kongsaeree, P.; Saithong, S.; Khamnaen, T.; Phiriyawirut, P.;
Charoenchaidetc, S.; Phomphrai, K. Dalton Trans. 2013, 42, 15191−
15198. (b) Hao, H.; Bhandari, S.; Ding, Y.; Roesky, H. W.; Magull, J.;
Schmidt, H.-G.; Noltemeyer, M.; Cui, C. Eur. J. Inorg. Chem. 2002,
1060−1065. (c) Liu, X.; Gao, W.; Mu, Y.; Li, G.; Ye, L.; Xia, H.; Ren,
Y.; Feng, S. Organometallics 2005, 24, 1614−1619.
AUTHOR INFORMATION
Corresponding Authors
*E-mail for S. Wang: swwang@mail.ahnu.edu.cn.
*E-mail for S. Zhou: slzhou@mail.ahnu.edu.cn.
■
Notes
The authors declare no competing financial interest.
(9) (a) Bruce, M.; Gibson, V. C.; Redshaw, C.; Solan, G. A.; White,
A. J. P.; Williams, D. J. Chem. Commun. 1998, 2523−2524. (b) Li, J.;
Zhang, K.; Huang, H.; Yu, A.; Hu, H.; Cui, H.; Cui, C. Organometallics
2013, 32, 1630−1635. (c) Wei, P.; Atwood, D. Chem. Commun. 1997,
1427−1428. (d) Gibson, V. C.; Redshaw, C.; Solan, G. A.; White, A. J.
P.; Williams, D. J. Organometallics 2007, 26, 5119−5123.
ACKNOWLEDGMENTS
■
The authors thank the National Natural Science Foundation of
China (21432001, 21372010, 21372009), the National Basic
Research Program of China (No. 2012CB821600), and a grant
from Anhui Normal University for financial support for this
work.
(10) (a) Sugiyama, H.; Gambarotta, S.; Yap, G. P. A.; Wilson, D. R.;
Thiele, S. K.-H. Organometallics 2004, 23, 5054−5061. (b) Khorobkov,
I.; Gambarotta, S.; Yap, G. P. A. Organometallics 2002, 21, 3088−3090.
REFERENCES
(11) (a) Alonso-Moreno, C.; Antinolo, A.; Carrillo-Hermosilla, F.;
̃
■
Otero, A. Chem. Soc. Rev. 2014, 43, 3406−3425. (b) Zhang, W.-X.;
Hou, Z. Org. Biomol. Chem. 2008, 6, 1720−1730. (c) Zhang, W.-X.;
Xu, L.; Xi, Z. Chem. Commun. 2015, 51, 254−265.
(1) (a) Timoshkin, A. Y. Coord. Chem. Rev. 2005, 249, 2094−2031.
(b) Normand, M.; Kirillov, E.; Roisnel, T.; Carpentier, J.-F.
Organometallics 2012, 31, 5511−5519. (c) Yang, Y.; Zhao, N.; Zhu,
H.; Roesky, H. W. Organometallics 2012, 31, 1958−1964. (d) Romain,
C.; Fliedel, C.; Bellemin-Laponnaz, S.; Dagorne, S. Organometallics
(12) Ong, T.-G.; Yap, G. P. A.; Richeson, D. S. J. Am. Chem. Soc.
2003, 125, 8100−8101.
G
DOI: 10.1021/acs.organomet.5b00101
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(13) (a) Montilla, F.; Pastor, A.; Galindo, A. J. Organomet. Chem.
2004, 689, 993−996. (b) Shen, H.; Wang, Y.; Xie, Z. Org. Lett. 2011,
13, 4562−4565. (c) Shen, H.; Chan, H.-S.; Xie, Z. Organometallics
2006, 25, 5515−5517. (d) Li, D.; Guang, J.; Zhang, W.-X.; Wang, Y.;
Xi, Z. Org. Biomol. Chem. 2010, 8, 1816−1820. (e) Shen, H.; Xie, Z. J.
Organomet. Chem. 2009, 694, 1652−1657.
(14) (a) Zhu, X.; Du, Z.; Xu, F.; Shen, Q. J. Org. Chem. 2009, 74,
6347−6349. (b) Du, Z.; Li, W.; Zhu, X.; Xu, F.; Shen, Q. J. Org. Chem.
2008, 73, 8966−8972. (c) Li, Q.; Wang, S.; Zhou, S.; Yang, G.; Zhu,
X.; Liu, Y. J. Org. Chem. 2007, 72, 6763−6767. (d) Wu, Y.; Wang, S.;
Zhang, L.; Yang, G.; Zhu, X.; Liu, C.; Yin, C.; Rong, J. Inorg. Chim.
Acta 2009, 362, 2814−2819. (e) Zhou, S.; Wang, S.; Yang, G.; Li, Q.;
Zhang, L.; Yao, Z.; Zhou, Z.; Song, H.-B. Organometallics 2007, 26,
3755−3761. (f) Zhang, W.-X.; Nishiura, M.; Hou, Z. Chem.Eur. J.
2007, 13, 4037−4151. (g) Wei, P.-H.; Xu, L.; Song, L.-C.; Zhang, W.-
X.; Xi, Z. Organometallics 2014, 33, 2784−2789. (h) Zhang, W.-X.;
Nishiura, M.; Hou, Z. Synlett 2006, 1213−1216.
(15) (a) Zhang, W.-X.; Li, D.; Wang, Z.; Xi, Z. Organometallics 2009,
28, 882−887. (b) Li, D.; Guang, J.; Zhang, W.-X.; Wang, Y.; Xi, Z. Org.
Biomol. Chem. 2012, 10, 6266−6270. (c) Crimmin, M. R.; Barrett, A.
G. M.; Hill, M. S.; Hitchcock, P. B.; Procopiou, P. A. Organometallics
2008, 27, 497−499. (d) Rowley, C. N.; Ong, T.-G.; Priem, J.; Woo, T.
K.; Richeson, D. S. Inorg. Chem. 2008, 47, 9660−9668. (e) Xu, L.;
Wang, Y.-C.; Ma, W.; Zhang, W.-X.; Xi, Z. J. Org. Chem. 2014, 79,
12004−12009.
(16) (a) Klerks, J. M.; Stufkens, D. J.; Koten, G.; Vrieze, K. J.
Organomet. Chem. 1979, 181, 271−283. (b) Gibson, V. C.; Redshaw,
C.; White, A. J. P.; Williams, D. J. J. Organomet. Chem. 1998, 550,
453−456. (c) Milione, S.; Cavallo, C.; Tedeso, C.; Grass, A. J. Chem.
Soc., Dalton Trans. 2002, 8, 1839−1846. (d) Knijnenburg, Q.; Smits, J.
M. M.; Budzelaar, P. H. M. Organometallics 2006, 25, 1036−1046.
(17) (a) Hill, M. S.; Hutchison, A. R.; Keizer, T. S.; Parkin, S.;
VanAelstyn, M. A.; Atwood, D. A. J. Organomet. Chem. 2001, 628, 71−
75. (b) Cameron, P. A.; Gibson, V. C.; Redshaw, C.; Segal, J. A.; Solan,
G. A.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 2001,
1472−1476.
(18) Zhang, Y.; Xiang, L.; Wang, Q.; Duan, X.-F.; Zi, G. Inorg. Chim.
Acta 2008, 361, 1246−1254.
(19) Li, J.; Gao, T.; Zhang, W.; Sun, W. Inorg. Chem. Commun. 2003,
6, 1372−1374.
(20) Sheldrick, G. M. SADABS: Program for Empirical Absorption
Correction of Area Detector Data; University of Gottingen, Gottingen,
̈
̈
Germany, 1996.
(21) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray Systems,
Inc., Madison, WI, 1997.
H
DOI: 10.1021/acs.organomet.5b00101
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