Aluminum compounds containing pyrrole-imine ligand systems - Synthesis, characterization, structure elucidation, ring-opening polymerization, and catalytic meerwein-ponndorf-verley reaction

Article abstract of DOI:10.1002/ejic.201400082

The reactions of AlMe₃ with the tridentate pyrrole ligand precursor C₄H₃NH(2-CH=NCH₂Py) and subsequent treatment of the derivatives with small organic molecules such as 2,6-diisopropylphenol or dibenzoylmethane were conveniently performed, and the products were characterized. The reaction between 1 equiv. of AlMe₃ and 1 equiv. of a pyrrole-imine-pyridine ligand in toluene affords [Al{C ₄H₃N(CHNCH₂Py)Me₂}] (1) in high yield. In addition, the use of 2 equiv. of AlMe₃ with the same tridentate precursor results in the formation of a dialuminum compound [AlMe₃{C₄H₃N(CHNCH₂-Py)AlMe ₂}] (2) in moderate yield. Furthermore, the combination of 1 with either 1 or 2 equiv. of 2,6-diisopropylphenol or 2 equiv. of dibenzoylmethane in toluene yields aluminum monophenoxide or diphenoxide compounds [Al{C ₄H₃N(CHNCH₂-Py)Me(O-2,6-iPr₂C ₆H₃)}] (3) and [Al{C₄H₃N(CHNCH ₂-Py)}(O-2,6-iPr₂C₆H₃)₂] (4), respectively, as well as an aluminum bis-diketonate compound, [Al{C ₄H₃N(CHNCH₂-Py)}(PhCOCHCOPh)₂] (5). All of the aforementioned derivatives were characterized by ¹H and ¹³C NMR spectroscopy, and their solid-state molecular structures were determined by single-crystal X-ray diffraction. The geometries of 1-5 show that the pyrrole ligand exists in the pyrrolyl-imine and azafulvene-amido resonance forms. Compounds 1, 3, 4 and 5 were used in the ring-opening polymerization of caprolactone in the presence of BnOH and in the catalytic Meerwein-Ponndorf- Verley (MPV) reaction of 1-naphthalenemethanol and 2-naphthalenecarbaldehyde. Copyright

Full text of DOI:10.1002/ejic.201400082

FULL PAPER
DOI:10.1002/ejic.201400082
Aluminum Compounds Containing Pyrrole–Imine Ligand
Systems – Synthesis, Characterization, Structure
Elucidation, Ring-Opening Polymerization, and Catalytic
Meerwein–Ponndorf–Verley Reaction
Shu-Ya Hsu,[a] Ching-Han Hu,[a] Cheng-Yi Tu,[a] Chia-Her Lin,[b]
Ren-Yung Chen,[a] Amitabha Datta,[a] and Jui-Hsien Huang*[a]
Keywords: Polymerization / Aluminum / N ligands
The reactions of AlMe3 with the tridentate pyrrole ligand
[Al{C4H3N(CHNCH2-Py)Me(O-2,6-iPr2C6H3)}]
(3)
and
precursor C4H3NH(2-CH=NCH2Py) and subsequent treat- [Al{C4H3N(CHNCH2-Py)}(O-2,6-iPr2C6H3)2] (4), respectively,
ment of the derivatives with small organic molecules such as
2,6-diisopropylphenol or dibenzoylmethane were conve-
niently performed, and the products were characterized. The
reaction between 1 equiv. of AlMe3 and 1 equiv. of a pyrrole–
imine–pyridine ligand in toluene affords [Al{C4H3N-
(CHNCH2Py)Me2}] (1) in high yield. In addition, the use of
2 equiv. of AlMe3 with the same tridentate precursor results
as well as an aluminum bis-diketonate compound,
[Al{C4H3N(CHNCH2-Py)}(PhCOCHCOPh)2] (5). All of the
aforementioned derivatives were characterized by 1H and
13C NMR spectroscopy, and their solid-state molecular struc-
tures were determined by single-crystal X-ray diffraction.
The geometries of 1–5 show that the pyrrole ligand exists in
the pyrrolyl–imine and azafulvene–amido resonance forms.
Compounds 1, 3, 4 and 5 were used in the ring-opening poly-
merization of ε-caprolactone in the presence of BnOH and in
the catalytic Meerwein–Ponndorf–Verley (MPV) reaction of
1-naphthalenemethanol and 2-naphthalenecarbaldehyde.
in the formation of
a dialuminum compound [AlMe3-
{C4H3N(CHNCH2-Py)AlMe2}] (2) in moderate yield. Further-
more, the combination of 1 with either 1 or 2 equiv. of 2,6-
diisopropylphenol or 2 equiv. of dibenzoylmethane in toluene
yields aluminum monophenoxide or diphenoxide compounds
supporting ligands used to generate the designated com-
pounds. Various supporting ligands, including chiral[4] and
achiral[5] ligands, have been bound to aluminum atoms and
used in organic reactions.[6]
Introduction
To improve the reaction selectivity of organoaluminum
compounds with organic molecules, a detailed knowledge
of the mechanisms and factors that control product distri-
bution is required. The first step toward this aim is to
understand how steric and electronic effects control the co-
ordination and subsequent reactivity of organic molecules
with organoaluminum compounds.[1] The aryloxide com-
pounds of aluminum have also been used with success in
regio- and stereospecific organic syntheses and catalytic sys-
tems.[2] The reactions of organoaluminum compounds
(specifically, alkylaluminum compounds) with sterically
hindered ketones are less common but can also be selec-
tive.[3] With sterically demanding reagents, the reaction can
be forced to occur in a specific manner. A key point related
to the catalytic reactivity of aluminum compounds is the
Aromatic pyrrolyl-based tridentate anionic ligands,
which incorporate N-donor atoms in different metal–or-
ganic combinations, are widely used. With respect to the
aforementioned pyrrolyl linkage, different tridentate an-
ionic precursors and their corresponding metal derivatives
have been previously reported.[7] The major consideration
of these ligand systems is that the deprotonated pyrrole NH
fragment acts as a nucleophile and attacks the metal atom
to form a metal–pyrrole bond, and the imine nitrogen atom
is also linked to the metal center (Scheme 1). To continue
our exploration of organometallic systems by introducing a
N-donor aromatic-based tridentate pyrrole–imine–pyridine
system, we herein report the preparation of several alumi-
[a] Department of Chemistry, National Changhua University of
Education,
Changhua 50058, Taiwan
E-mail: juihuang@cc.ncue.edu.tw
http://chem.ncue.edu.tw/people/bio.php?PID=12
[b] Department of Chemistry, Chung-Yuan Christian University,
Chun-Li 320, Taiwan
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201400082.
Scheme 1.
Eur. J. Inorg. Chem. 2014, 1965–1973
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num derivatives with organic molecules and systematically
When 2 equiv. of AlMe3 reacted with the pyrrole–imine
dialuminum compound [AlMe3{C4H3N-
demonstrate the resonance of the bonding modes between ligand,
a
its pyrrolyl–imine and azafulvene–amido forms.[7g,8]
(CHNCH2-Py)AlMe2}] (2) was obtained in moderate yield.
Compound 2 can also be obtained from the reaction of 1
1
with one additional equiv. of AlMe3 according to the H
NMR spectra. Compound 2 dissolves in toluene and
dichloromethane; however, when 2 is dissolved in THF and
stirred for 1 h, compound 1 and AlMe3·THF are generated,
as indicated by the 1H NMR spectra (Scheme 3). This result
can also be achieved by the reaction of the substituted pyr-
role–imine ligand C4H3NH(2-CH=NCH2Py) with 2 equiv.
Results and Discussion
Synthesis and Characterization of 1–5
The synthesis of 1–5 is shown in Scheme 2. The triden-
tate pyrrole ligand C4H3NH(2-CH=NCH2Py) was synthe-
sized according to a method reported in the literature.[7d]
The reaction between 1 equiv. of AlMe3 and the pyrrole–
imine ligand in toluene generates [Al{C4H3N(CHNCH2-
Py)Me2}] (1) in high yield. We found that 1 is insoluble in
diethyl ether; however, it is soluble in toluene, dichloro-
methane, and tetrahydrofuran (THF). The 1H and 13C
NMR spectra of 1 show the characteristic AlMe resonances
at δ = –0.84 and –6.0 ppm, respectively. These resonance
peaks remain unchanged when 1 is heated at 100 °C in [D8]-
toluene for 12 h. However, compound 1 is highly air-sensi-
tive and quickly decomposes in air.
1
of AlMe3 in THF. The H NMR spectrum of 2 show two
characteristic methyl resonances of the AlMe3 and AlMe2
fragments at δ = –0.70 and –0.86 ppm, and the 13C NMR
spectrum shows the corresponding resonances at δ = –10.30
and –6.54 ppm, respectively.
The reaction of 1 with 1 or 2 equiv. of 2,6-diisoprop-
ylphenol results in aluminum monophenoxide or diphenox-
ide compounds, namely, [Al{C4H3N(CHNCH2-Py)Me(O-
2,6-iPr2C6H3)}] (3) and [Al{C4H3N(CHNCH2-Py)}(O-2,6-
iPr2C6H3)2] (4), respectively. The addition of exactly
1 equiv. of 2,6-diisopropylphenol to 1 is important to suc-
cessfully synthesize 3, because an excess of 2,6-diisoprop-
ylphenol results in a mixture of 3 and 4. The 1H NMR
spectrum of 3 shows the AlMe signal at δ = –0.77 ppm;
however, no corresponding resonance is observed in the 13
C
NMR spectrum, presumably owing to the spin–quadruple
interaction of Al (I = 5/2).[9] In addition, a doublet and a
septet at δ = 0.96 and 3.18 ppm are assigned to the iso-
3
propyl fragment of 3 with JH,H = 6.9 Hz, and the methyl-
ene fragment of CHNCH2 appears at δ = 4.96 ppm as a
doublet of doublets. This phenomenon is attributed to the
diastereotopic nature of these hydrogen atoms. The NMR
spectra of 4 are similar to those of 3, except that no AlMe
resonance is observed in the high-field region. The
CHNCH2 methylene protons of 4 show a singlet at δ =
4.89 ppm. A careful study of the corresponding resonances
of 3 and 4 reveals that when 3 is dissolved in C6D6 in a
Young NMR tube at low concentration (ca. Ͻ0.005 m) and
heated at 70 °C for 24 h, it is completely converted into 4
and 1, presumably through ligand redistribution. However,
when the concentration of 3 is increased (ca. Ͼ0.01 m), only
1
30% of 3 is converted into 4 and 1, according to the H
NMR spectra. Presumably, the more stable aluminum bis-
aryloxide can also react with the aluminum dimethyl com-
pound at high concentrations.[10]
Scheme 2. Synthesis of 1–5.
Scheme 3. The formation of 1 from 2 in THF or from AlMe3 and C4H3NH(2-CH=NCH2Py).
1966
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Compound 1 reacts with 2 equiv. of dibenzoylmethane in Npyridine bond length [Al(1)–N(3) = 2.196(3) Å], which is
toluene to generate an aluminum bis-diketonate compound consistent with the results previously reported.[12]
1
[Al{C4H3N(CHNCH2-Py)}(PhCOCHCOPh)2] (5). The H
NMR spectrum of 5 shows one singlet at δ = 8.19 ppm for
the imino proton and two doublets at δ = 5.10 and
4.90 ppm for the methylene protons of the CHNCH2 frag-
ment. The two methine groups of the diketonate fragments
Crystals of 2 were obtained from a saturated dichloro-
methane solution at –20 °C. Compound 2 contains two
nonidentical aluminum centers in the solid state. The Al(1)
atom adopts a four-coordinate geometry best described as
a distorted tetrahedron; this geometry is formed by the par-
ticipation of the Npyridine and Nimido atoms as well as two
methyl groups to generate a N(2)–Al(1)–N(3) bond angle
of 83.4(1)°, which presumably suffers ring-strain owing to
the formation of the five-membered chelate ring. The Al(2)
atom is surrounded by the Npyrrole atom and three methyl
carbon atoms to form a distorted tetrahedral geometry. The
tridentate pyrrole ligand C4H3N(2-CHNCH2Py) bridges
two aluminum atoms and acts as a monoanion with the
negative electron density at the amido nitrogen atom N(2)
(vide infra).
1
generate two singlets at δ = 6.65 and 6.81 ppm in the H
NMR spectrum and two resonances at δ = 94.1 and
94.2 ppm in the 13C NMR spectrum. This information is
1
also confirmed by a 2D H–13C heteronuclear correlation
(HETCOR) NMR spectrum (see Supporting Information).
Molecular Geometries of 1–5
The molecular geometries of 1–5 were determined by sin-
gle-crystal X-ray diffraction; their crystallographic param-
eters and selected bond lengths and angles are summarized
Pale brown crystals of 3 and 4 were obtained from satu-
in Tables 1 and 2, respectively. Figures 1–5 show perspective rated dichloromethane solutions at –20 °C. The unit cell of
drawings of 1–5 together with selected atomic labels. Crys- 4 contains one dichloromethane molecule. The molecular
tals of 1 were obtained from a saturated dichloromethane geometries of 3 and 4 are very similar to the trigonal-bipy-
solution at –20 °C. The central Al atom is five-coordinate ramidal geometry of 1 with τ values of 0.57 for 3 and 0.62
with a tridentate orientation of the pyrrole–imine ligand for 4. The three nitrogen atoms of C4H3N(CHNCH2-Py) in
and two methyl groups; thus, it possesses a distorted trigo- 3 and 4 retain their planar geometry; the nitrogen atoms
nal-bipyramidal geometry as indicated by its τ value of 0.62 occupy two axial positions and one equatorial position to
[τ = degree of trigonality = (β – α)/60; β = the largest angle, create N(1)–Al(1)–N(3) axial bond angles of 156.0(1) and
α = the second largest angle; ideal square-pyramidal geome- 158.55(7)° for 3 and 4, respectively. The corresponding alu-
try, τ = 0; ideal trigonal-bipyramidal geometry, τ = 1].[11] minum phenoxide bond lengths and angles are notable ow-
The two nitrogen atoms of the pyrrole and pyridine rings ing to the π bonding between the oxygen and aluminum
occupy the axial positions with a bond angle of 154.9(1)° atoms.[13] In five-coordinate aluminum phenoxide com-
and form two five-membered chelate rings that introduce pounds, the Al–Ophenoxide bond lengths and the Al–O–
an overall strain into the molecule. The Al–Npyrrole bond Cphenyl bond angles typically range from 1.696 to 1.744 Å
length [Al(1)–N(2) = 2.029(3) Å] is shorter than the Al– and from 172.54 to 152.67°, respectively.[14] The Al–
Table 1. Summary of crystallographic data for 1–5.
1
2
3
4·CH2Cl2
5·CH2Cl2
Formula
FW
T [K]
Crystal system
C13H16AlN3
241.27
200(2)
monoclinic
Pn
C16H25Al2N3
313.35
200(2)
monoclinic
P21/c
C24H30AlN3O
403.49
200(2)
orthorhombic
Pbca
C36H46AlCl2N3O2 C42H34AlCl2N3O4
650.64
200(2)
monoclinic
P21/n
742.60
200(2)
triclinic
¯
Space group
P1
a [Å]
b [Å]
c [Å]
α [°]
7.1544(8)
7.0653(7)
13.0795(15)
90
90.846(7)
90
661.07(12)
2
1.212
11.2649(16)
10.5673(14)
16.374(2)
90
103.737(10)
90
1893.4(4)
4
1.099
12.1257(11)
17.1886(12)
21.814(2)
90
90
90
4546.6(7)
8
1.179
14.5378(4)
11.1044(3)
22.0621(7)
90
97.479(2)
90
3531.26(18)
4
1.224
10.3001(5)
12.1693(5)
16.1203(9)
69.984(4)
82.407(4)
80.544(3)
1866.46(16)
2
β [°]
γ [°]
V [Å3]
Z
ρcalcd. [Mgm–3]
1.321
0.244
μ [mm-1]
0.135
0.151
0.108
0.244
F(000)
Reflections collected
Independent reflections
256
4626
2679
672
20051
4909
1728
45693
5884
1384
51090
9153
772
31485
9725
(Rint = 0.0366)
2679/2/156
1.082
(Rint = 0.0950)
4909/0/195
0.965
0.0566, 0.1232
0.1592, 0.1613
0.172, –0.180
(Rint = 0.2257)
5884/0/268
0.934
0.0623, 0.1403
0.2142, 0.2044
0.201, –0.192
(Rint = 0.0663)
9153/0/405
1.025
0.0524, 0.1227
0.0933, 0.1428
0.596, –0.589
(Rint = 0.1030)
9725/0/470
0.942
0.0660, 0.1501
0.1670, 0.1901
0.732, –0.459
Data/restraints/parameters
Goodness-of-fit on F2
R1, wR2 [IϾ2σ(I)]
0.0429, 0.0959
0.0643, 0.1181
R1, wR2 (all data)
Largest diff. peak, hole [eÅ–3] 0.295, –0.364
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Table 2. Selected bond lengths [Å] and angles [°] for 1–5.
1
Al(1)–C(12)
Al(1)–N(1)
1.973(3)
1.985(2)
Al(1)–C(13)
Al(1)–N(2)
1.975(3)
2.030(3)
Al(1)–N(3)
2.196(3)
N(2)–Al(1)–N(3)
C(13)–Al(1)–N(1)
N(1)–Al(1)–N(2)
154.93(11)
117.28(12)
79.95(12)
C(12)–Al(1)–N(1)
C(13)–Al(1)–C(12) 124.16(13)
N(1)–Al(1)–N(3)
117.47(12)
74.99(11)
2
Al(1)–N(2)
1.915(2)
Al(1)–C(15)
1.932(3)
Al(1)–C(16)
1.939(3)
Al(1)–N(3)
1.963(2)
Al(2)–N(1)
1.965(2)
Al(2)–C(14)
1.985(3)
Al(2)–C(13)
1.987(3)
Al(2)–C(12)
1.990(3)
N(2)–Al(1)–C(15)
C(15)–Al(1)–C(16)
C(15)–Al(1)–N(3)
N(1)–Al(2)–C(14)
C(14)–Al(2)–C(13)
C(14)–Al(2)–C(12)
113.27(12)
120.55(15)
112.56(13)
105.46(12)
113.70(14)
111.90(14)
N(2)–Al(1)–C(16)
N(2)–Al(1)–N(3)
C(16)–Al(1)–N(3)
N(1)–Al(2)–C(13)
N(1)–Al(2)–C(12)
111.16(12)
83.38(10)
109.90(14)
105.29(13)
105.06(12)
Figure 1. Molecular structure of 1. Thermal ellipsoids drawn at
30% probability. All hydrogen atoms omitted for clarity.
C(13)–Al(2)–C(12) 114.37(16)
3
Al(1)–O(1)
Al(1)–N(2)
Al(1)–N(3)
1.752(2)
1.971(3)
2.120(3)
Al(1)–C(24)
Al(1)–N(1)
C(12)–O(1)
1.960(4)
1.991(3)
1.341(3)
O(1)–Al(1)–C(24) 116.69(15)
C(24)–Al(1)–N(2) 121.88(15)
C(24)–Al(1)–N(1) 98.96(15)
O(1)–Al(1)–N(2) 120.48(12)
O(1)–Al(1)–N(1) 101.06(12)
N(2)–Al(1)–N(1) 80.08(12)
C(24)–Al(1)–N(3) 95.96(15)
N(1)–Al(1)–N(3) 155.95(12)
O(1)–Al(1)–N(3)
N(2)–Al(1)–N(3)
88.81(11)
76.03(11)
C(12)–O(1)–Al(1) 141.6(2)
4
Figure 2. Molecular structure of 2. Thermal ellipsoids drawn at
30% probability. All hydrogen atoms omitted for clarity.
Al(1)–O(1)
Al(1)–N(2)
C(24)–O(1)
1.7382(14)
1.9645(16)
1.355(2)
Al(1)–O(2)
Al(1)–N(1)
Al(1)–N(3)
1.7442(13)
1.9684(16)
2.0690(17)
C(12)–O(2)
1.352(2)
O(1)–Al(1)–O(2)
O(2)–Al(1)–N(2)
N(2)–Al(1)–N(1)
118.18(7)
121.27(7)
80.95(7)
O(1)–Al(1)–N(2) 119.93(7)
N(2)–Al(1)–N(3) 77.61(7)
N(1)–Al(1)–N(3) 158.55(7)
C(24)–O(1)–Al(1) 142.65(12)
C(12)–O(2)–Al(1) 139.95(12)
5
Al(1)–O(2)
Al(1)–O(1)
Al(1)–N(1)
O(2)–Al(1)–O(1)
O(3)–Al(1)–O(4)
O(3)–Al(1)–N(2)
1.8680(19)
1.877(2)
1.963(3)
89.38(9)
90.43(9)
169.14(9)
Al(1)–O(3)
Al(1)–O(4)
Al(1)–N(2)
O(2)–Al(1)–O(4)
O(1)–Al(1)–N(1) 173.02(11)
N(1)–Al(1)–N(2) 80.11(10)
1.873(2)
1.883(2)
2.046(3)
174.24(10)
Ophenoxide bond length and Al–O–Cphenyl bond angle in 3
are 1.752(2) Å and 141.6(2)°, respectively. The two Al–
Ophenoxide bond lengths and two Al–O–Cphenyl bond angles
in 4 are 1.738(1) and 1.744(1) Å and 142.7(1) and 140.0(1)°,
respectively. This result is consistent with the data reported
Figure 3. Molecular structure of 3. Thermal ellipsoids drawn at
30% probability. All hydrogen atoms omitted for clarity.
in the literature. Presumably, the lone pair of electrons of pyridine ring of the tridentate C4H3N(CHNCH2-Py) ligand
the oxygen atoms lightly donate to the vacant aluminum p dangles outside of the aluminum coordination sphere. The
orbitals, which results in slightly shortened Al–O bond three axes of the octahedron are close to linearity: N(2)–
lengths and enlarged Al–O–C bond angles.
Al(1)–O(3) 169.1(1)°; O(2)–Al(1)–O(4) 174.2(1)°; N(1)–
Yellowish crystals of 5 were obtained from a saturated Al(1)–O(1) 173.0(1)°. The two chelated β-diketonate ligands
dichloromethane solution at –20 °C. Compound 5 has tri- bind to an aluminum atom to form two six-membered rings
clinic symmetry and one dichloromethane molecule per unit with O(1)–Al(1)–O(2) and O(3)–Al(1)–O(4) bond angles of
cell. The geometry of 5 can be best described as a distorted 89.38(9) and 90.4(1)°, respectively; these bond angles are
octahedron surrounded by four β-diketonate oxygen atoms similar to those of six-coordinate aluminum β-diketonate
and two nitrogen atoms of a pyrrole–imine fragment. The compounds reported previously.[15]
Eur. J. Inorg. Chem. 2014, 1965–1973
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FULL PAPER
role and amido N atom. Therefore, we used 1 as an exemp-
lary sample and performed theoretical calculations to locate
the electron density of the tridentate ligand.
Scheme 4. The resonant pyrrolyl–imine and azafulvene–amido
forms. R1–R6 represent the bond lengths of specific bonds.
Figure 4. Molecular structure of 4. Thermal ellipsoids drawn at
30% probability. All hydrogen atoms omitted for clarity.
Table 3. A comparison of bond lengths [Å] for compounds 1–5, A,
B, C and D.
Figure 5. Molecular structure of 5. Thermal ellipsoids drawn at
30% probability. All hydrogen atoms omitted for clarity.
1
2
3
4
5
A[20] B[20] C[21] D[22]
R1
R2
R3
R4
R5
R6
R7
1.342 1.330 1.352 1.344 1.349 1.328 1.331 1.293 1.378
1.402 1.393 1.381 1.398 1.391 1.403 1.419 1.460 1.369
1.393 1.370 1.370 1.384 1.378 1.369 1.378 1.349 1.414
1.392 1.413 1.407 1.397 1.378 1.428 1.424 1.450 1.370
1.384 1.401 1.381 1.382 1.373 1.401 1.403 1.417 1.382
1.416 1.402 1.399 1.407 1.424 1.390 1.393 1.343 1.500
Resonance of Pyrrolyl–Imine and Azafulvene–Amido Forms
The most intriguing observation regarding structures 1–
5 relates to the resonances of the pyrrolyl–imine and aza-
fulvene––amido skeleton (Scheme 4).[7g,8] Notably, the con-
jugated π electrons of the anionic pyrrolyl ring relocate to
form an azafulvene fragment (vide infra). Therefore, the
geometries of 1–5 are all considered to be in either the pyr-
rolyl–imine format or the azafulvene–amido format de-
pending upon the bond lengths of the tridentate pyrrole
ligand. A comparison of the bond lengths of 1–5 and those
1.305 1.304 1.297 1.300 1.293 2.005 1.998 –
1.498
DFT Calculation of the Electron Density of 1
To better understand the electron distribution of the pyr-
of the previously reported A–D is provided in Table 3. role–imine ligands of 1–5, we applied density functional
Either the pyrrolyl–imine or azafulvene–amido framework theory (DFT) to investigate the electronic structure of 1.
dominates the mode of the structures, and the dominant The M06 functional developed by the Truhlar group[16] and
framework can be determined by two criteria: (1) the bond the 6-31G(d) basis set were chosen for our DFT computa-
lengths of R2 vs. R3 and R1 vs. R5 (Scheme 4) and (2) tions. The DFT-optimized bond lengths are in good agree-
the bond length of R6. For the azafulvene–amido dominant ment with those from the X-ray data. The optimized struc-
structure, as shown in Scheme 4, the R2 bond length is ture and Mulliken charges for atoms of 1 and its electro-
longer than that of R3, and the R5 bond length is longer static potential map are shown in Figure 6. The results are
than that of R1. Considering the results from Table 3, we consistent with the structure determined by X-ray diffrac-
find that 1–5 all assume geometries between the pyrrolyl– tion. The electron density of the original anionic pyrrolyl–
imine and azafulvene–amido forms and that the anionic imine form is in resonance with the azafulvene form; the
character of this tridentate ligand is delocalized on the pyr- resulting electron densities on the nitrogen atoms of the
Eur. J. Inorg. Chem. 2014, 1965–1973
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FULL PAPER
pyrrole ring and the imine C=N are –0.534 and –0.522, polymer products had polydispersity (PDI) values in the
respectively. Therefore, we concluded that the pyrrole–imine range 1.19–1.51 and 1.02–1.29, respectively, with or without
ligand systems are best described as the resonance forms the presence of BnOH. Notably, for 4, the conversation rate
shown in Scheme 2.
during polymerization slightly decreases with an increase in
concentration of BnOH, whereas 5 remains inactive even in
the presence of BnOH. This phenomenon presumably oc-
curs because steric hindrance prevents coordination with
the aluminum center in 5. In general, the molecular weight
of polycaprolactone (PCL) is proportional to the [Al]/
[BnOH] ratio in the cases of 1, 3, and 4.
Meerwein–Ponndorf–Verley Catalytic Reactions
The Meerwein–Ponndorf–Verley (MPV) reduction reac-
tion reduces the carbonyl groups of aldehydes or ketones to
primary or secondary alcohols through the use of catalysts
in the presence of a sacrificial alcohol.[18] The merits of
MPV reductions include the mild reaction conditions re-
quired and their good chemoselectivity. Therefore, we tested
the synthesized compounds as catalysts for the MPV re-
duction. The proton-transfer reactions were performed by
using 1-naphthalenemethanol and 2-naphthalenecarbal-
Figure 6. (a) Mulliken charges for the atoms of 1. (b) The electro-
static potential of 1. The red and blue colors represent the most
negative and positive potentials on the electron isodensity surface,
respectively.
Ring-Opening Polymerization of ε-Caprolactone by 1, 3, 4,
and 5
The ring-opening reaction of ε-caprolactone with a dehyde in the presence of 1, 3, 4, and 5 (Scheme 5) in
number of Lewis acids including aluminum compounds has CDCl3; the results were monitored by 1H NMR spectrome-
been intensively investigated.[17] The results of the ring- try. Approximately 20 equiv. of the corresponding alcohol
opening polymerization of ε-caprolactone with 1, 3, 4, and and aldehyde and 1 equiv. of catalyst were used. The char-
5 as catalysts are summarized in Table 4. The monomeric acteristic resonance of the methylene protons of 1-naphth-
compounds 1 and 3 with the tridentate pyrrole–imine–pyr- alenemethanol (δ = 5.12 ppm) and the formyl proton of 2-
idine ligand exhibited noticeable catalytic activity toward naphthalenecarbaldehyde (δ = 10.31 ppm) were used to
the ring-opening polymerization of ε-caprolactone, and the monitor progress of the catalytic reaction. Similarly, the for-
Table 4. The ring-opening polymerization of ε-caprolactone (CL) initiated by 1, 3, 4, and 5.[a]
[c]
[c]
Entry
Catalyst CL/Al/BnOH
T [h]
Mn (calcd.)[b]
Mn
Mw
Conversion [%]
PDI
1[d]
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
3
4
5
1
3
4
5
1
3
4
5
1
3
4
5
200:1:0
200:1:0
200:1:0
200:1:0
200:1:1
200:1:1
200:1:1
200:1:1
200:1:2
200:1:2
200:1:2
200:1:2
200:1:5
200:1:5
200:1:5
200:1:5
16[d]
48
48
48
21
48
48
48
4
48
48
48
4
14907
13811
1484
–
21909
21293
10175
–
11180
6169
4959
–
4555
2108
3688
–
10343
16293
–
14530
20933
–
65.3
60.5
6.5
1.51
1.29
–
–
–
0
–
12440
9738
5768
–
9022
2409
3643
–
5357
1765
2218
–
19197
9900
7002
–
12398
2613
4135
–
6373
1811
2424
–
95.5
92.8
44.1
0
97.0
53.1
42.5
0
97.4
43.8
78.4
0
1.54
1.02
1.21
–
1.37
1.09
1.13
–
1.19
1.02
1.09
–
48
16
48
[a] Reaction conditions: [Al]0 0.1 mmol, toluene 20 mL, reaction temperature, 40 °C. [b] Molecular weight of ε-caprolactone times conver-
sion of monomer times the [CL]0/[BnOH]0 ratio + molecular weight of BnOH. [c] Obtained from GPC analysis and calibrated with
polystyrene standard; multiplied by 0.56. [d] Reaction temperature: 60 °C. [e] Reaction solidified.
Scheme 5. The MPV reduction with 1, 3, 4, and 5 as catalysts (20 equiv. of the corresponding alcohol and aldehyde and 1 equiv. of
catalyst were used).
Eur. J. Inorg. Chem. 2014, 1965–1973
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FULL PAPER
mation of 1-naphthalenecarbaldehyde and 2-naphthal-
Experimental Sections
enemethanol also indicated the progress of the reaction.
The conversions of 1-naphthalenemethanol to 1- and of 2-
naphthalenecarbaldehyde to 2-naphthalenemethanol were
calculated by using the integrated peak areas of the signals
of the formyl protons of the corresponding aldehydes in the
1H NMR spectra. The results are shown in Figure 7. The
reaction reached equilibrium after 12 h when 1 and 4 were
used as catalysts. However, it reached equilibrium after 24 h
when 3 was used, and no reaction occurred when 5 was
used. Presumably, the steric hindrance of 5 prevents the co-
ordination of reactants to the aluminum atom.
General Procedure: All reactions were performed under a nitrogen
atmosphere by using standard Schlenk techniques or in a glovebox.
Toluene and diethyl ether were dried at reflux over sodium benzo-
phenone ketyl. Methylene chloride (CH2Cl2) was dried with P2O5.
All solvents were distilled and stored in nitrogen-purged solvent
1
reservoirs that contained 4 Å molecular sieves. H and 13C NMR
spectra were recorded by using a Bruker Avance 300 spectrometer.
1
Chemical shifts (in ppm) for H and 13C spectra are relative to the
residual protons of CDCl3 (δ = 7.24, 77.0 ppm) and C6D6 (δ =
7.15, 128.0 ppm). Elemental analyses were performed with a
Heraeus CHN-OS Rapid elemental analyzer at the Instrument
Center of the NCHU. The C4H3NH(2-CH=NCH2Py) ligand was
prepared by a procedure similar to that reported in the literature.[7d]
[Al{C4H3N(2-CHNCH2Py)Me2}] (1): A flask was charged with
AlMe3 (2.0 m in toluene, 13.5 mL, 27.0 mmol) and toluene (20 mL)
and cooled to 0 °C. A solution of C4H3NH(2-CH=NCH2Py)]
(5.0 g, 27.0 mmol) in toluene (20 mL) was added to the first solu-
tion dropwise, and the mixture was stirred for 1 h after the addition
was complete. The resulting solution was vacuum-dried, and the
solid was recrystallized from a dichloromethane solution at –20 °C
1
to generate 1 (7.19 g, 95.0% yield). H NMR (CDCl3): δ = –0.84
(s, 6 H, AlMe2), 4.92 (s, 2 H, CH=NCH2), 6.36 (m, 1 H, CH pyr-
role), 6.80 (m, 1 H, CH pyrrole), 7.32–7.24 (m, 2 H, CH pyridine
and pyrrole), 7.40 (m, 1 H, CH pyridine), 7.82 (m, 1 H, CH pyr-
idine), 8.18 (s, 1 H, CHNCH2), 8.59 (m, 1 H, CH pyridine) ppm.
13C NMR (CDCl3): δ = –6.0 (q, JC,H = 112 Hz, AlMe2), 52.5 (t,
JC,H = 138 Hz, CHNCH2), 114.1, 117.7, 121.6, 123.5, 135.3, 136.3,
138.5, 146.3, 154.3, 158.9 (d, JC,H = 165 Hz, CH=N) ppm.
C13H16AlN3 (241.27): calcd. C 64.72, H 6.68, N 17.42; found C
64.57, H 7.05, N 17.07.
Figure 7. Plot of conversion of 1-naphthalenemethanol and 2-
naphthalenecarbaldehyde to 1-naphthalenecarbaldehyde and 2-
naphthalenemethanol vs. time. H NMR spectroscopy was used to
[AlMe3{C4H3N(2-CHNCH2Py)AlMe2}] (2): A flask was charged
with AlMe3 (2.0 m in toluene, 1.08 mL, 2.16 mmol) and toluene
1
monitor the reaction.
(10 mL) and cooled to 0 °C.
A solution of C4H3NH(2-
CH=NCH2Py) (0.20 g, 1.08 mmol) in toluene (10 mL) was added
to first the solution dropwise, and the mixture was stirred for 1 h
after the addition was complete. The resulting solution was vac-
uum-dried, and the solid was recrystallized from a dichloromethane
solution at –20 °C to generate colorless crystals of 2 (0.18 g, 51.0%
yield). 1H NMR (CDCl3): δ = –0.86 (s, 6 H, AlMe2), –0.70 (s, 9 H,
AlMe3), 5.19 (s, 2 H, NCH2Py), 6.43 (m, 1 H, CH pyrrole), 6.96
(m, 1 H, CH pyrrole), 7.26–7.49 (m, 3 H, CH pyridine and pyrrole),
7.98 (m, 1 H, CH pyridine), 8.06 [s, 1 H, CHNCH2Py], 8.83 (m, 1
H, CH pyridine) ppm. 13C NMR (CDCl3): δ = –10.3 (AlMe2), –6.5
(AlMe3), 55.8 (NCH2Py), 115.7 (CH pyrrole), 120.8 (CH pyrrole),
124.4, 125.0, 137.0 (aromatic C), 135.2 (Cipso), 141.1 (CH pyridine),
148.7 (CH pyridine), 162.2 (CHNCH2Py) ppm. C16H25Al2N3
(313.35): calcd. C 61.33, H 8.04, N 13.41; found C 61.25, H 7.64,
N 13.72.
Conclusions
Herein, we have described the synthesis of 1–5 by using
a pyrrole–imine–pyridine ligand with AlMe3 and the subse-
quent addition of a substituted phenol or diketone. The
structures of the products were determined. The neutral
pyrrole–imine–pyridine ligand can assume a monoanionic
pyrrolic–imine or an azafulvene–amido format after coordi-
nation to a metal atom. By comparing the bond lengths
with those in similar architectures, we observed that the
structures of 1–5 all exhibit the characteristic mode of the
[Al{C4H3N(2-CHNCH2Py)Me(O-2,6-iPr2C6H3)}] (3): A flask was
azafulvene–amido format, that is, the electron density of the charged with 1 (0.20 g, 0.83 mmol) and toluene (10 mL) and cooled
to 0 °C. A solution of 2,6-diisopropylphenol (0.15 g, 0.83 mmol) in
toluene (10 mL) was added to the first solution dropwise, and the
mixture was stirred for 2 h at room temperature after the addition
was complete. The resulting solution was vacuum-dried, and the
solid was recrystallized from a dichloromethane solution at –20 °C
to generate pale brown crystals of 3 (0.28 g, 85.0% yield). 1H NMR
(CDCl3): δ = –0.77 (s, 3 H, AlMe), 0.96 (m, 12 H, CHMe2), 3.18
(m, 2 H, CHMe2), 4.96 (m, 2 H, CHNCH2), 6.12 (m, 1 H, CH
pyrrole), 6.74–6.62 (m, 3 H, CH pyrrole and phenyl), 6.88, 7.39,
7.88 (m, 5 H, CH pyridine and phenyl), 8.16 (s, 1 H, CHNCH2),
8.76 (m, 1 H, CH pyridine) ppm. 13C NMR (CDCl3): δ = 23.2 (q,
monoanionic ligand is located on the amido nitrogen atom;
this is consistent with the results of DFT calculations. Com-
pounds 1, 3, and 4 show moderate activities toward the
ring-opening polymerization of ε-caprolactone in the pres-
ence of BnOH. In addition, these compounds also exhibit
MPV catalytic activity toward 1-naphthalenemethanol and
2-naphthalenecarbaldehyde. In our future work, we will ex-
plore the design and synthesis of new substituted pyrrolyl
ligands and study their reactivity toward alkaline-earth
metals and different organic molecules.
Eur. J. Inorg. Chem. 2014, 1965–1973
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FULL PAPER
JC,H = 125 Hz, CHMe2), 23.3 (q, JC,H = 125 Hz, CHMe2), 27.0 (d,
JC,H = 127 Hz, CHMe2), 51.6 (d, JC,H = 138 Hz, CH=NCH2),
114.6, 116.8, 118.9, 138.5, 121.7, 122.6, 123.8, 135.5, 137.3, 139.3,
147.7, 154.3, 154.7, 158.0 (d, JC,H = 165 Hz, CHNCH2) ppm.
C24H30AlN3O (403.50): calcd. C 71.44, H 7.49, N 10.41; found C
70.22, H 7.03, N 9.82. The CHN microanalysis for 3 is outside of
the normal +/– 0.4% range presumably owing to the presence of a
small amount of mixtures of 4 and 1 formed by ligand redistri-
bution.
Supporting Information (see footnote on the first page of this arti-
cle): Copies of NMR spectra.
Acknowledgments
This work was financially supported by the National Science Coun-
cil of Taiwan. The authors also thank the National Changhua Uni-
versity of Education for providing support for an X-ray dif-
fractometer and an NMR spectrometer.
[Al{C4H3N(2-CH=NCH2Py)}(O-2,6-iPr2C6H3)2] (4): The pro-
cedure for the synthesis of 4 is similar to that for the synthesis
of 3. Compound 1 (0.20 g, 0.83 mmol) and 2,6-diisopropylphenol
(0.30 g, 1.66 mmol) were used, and pale brown crystals of 5 were
[1] a) S. Pasynkiewicz, E. Sliwa, J. Organomet. Chem. 1965, 3, 121–
128; b) S. Pasynkiewicz, Pure Appl. Chem. 1972, 30, 509–522;
c) J. A. Francis, C. N. McMahon, S. G. Bott, A. R. Barron,
Organometallics 1999, 18, 4399–4416, and references cited
therein.
[2] a) M. D. Healy, M. R. Mason, P. W. Gravelle, S. G. Bott, A. R.
Barron, J. Chem. Soc., Dalton Trans. 1993, 441–454; b) M.
Akakura, H. Yamamoto, S. G. Bott, A. R. Barron, Polyhedron
1997, 16, 4389–4392; c) K. Maruoka, H. Imoto, S. Saito, H.
Yamamoto, J. Am. Chem. Soc. 1994, 116, 4131–4132; d) S.
Saito, H. Yamamoto, Chem. Commun. 1997, 1585–1592; e) C.-
H. Lin, L.-F. Yan, F.-C. Wang, Y.-L. Sun, C.-C. Lin, J. Or-
ganomet. Chem. 1999, 587, 151–159.
[3] a) Y. Ooi, T. Miura, K. Maruoka, Angew. Chem. 1998, 110,
2524; Angew. Chem. Int. Ed. 1998, 37, 2347–2349; b) H. Yama-
moto, Lewis Acids in Organic Synthesis vol. 1, Wiley-VCH,
Weinheim, Germany, 2000; c) P. Li, H. Yamamoto, Top. Or-
ganomet. Chem. 2011, 37, 161–183; d) M.-A. Munoz-Hernan-
dez, V. Montiel-Palma, Inorg. Chim. Acta 2009, 362, 4328–
4339; e) S. Nagendran, H. W. Roesky, Organometallics 2008,
27, 457–492; f) A. Y. Timoshkin, Coord. Chem. Rev. 2005, 249,
2094–2131.
[4] a) P. Hormnirum, E. L. Marshall, V. C. Gibson, A. J. P. White,
D. J. Williams, J. Am. Chem. Soc. 2004, 126, 2688–2689; b) N.
Nomura, R. Ishii, Y. Yamamoto, T. Kondo, Chem. Eur. J. 2007,
13, 4433–4451; c) H. Du, A. H. Velders, P. J. Dijkstra, Z.
Zhong, X. Chen, J. Feijen, Macromolecules 2009, 42, 1058–
1066; d) N. Emig, H. Nguyen, H. Krautscheid, R. Réau, J.-B.
Cazaux, G. Bertrand, Organometallics 1998, 17, 3599–3608.
[5] a) H. Du, A. H. Velders, P. J. Dijkstra, J. Sun, Z. Zhong, X.
Chen, J. Feijen, Chem. Eur. J. 2009, 15, 9836–9845; b) M.
North, D. L. Usanov, C. Young, Chem. Rev. 2008, 108, 5146–
5226; c) K. Nishioka, H. Goto, H. Sugimoto, Macromolecules
2012, 45, 8172–8192; d) M. North, E. L. Stewart, C. Young,
Tetrahedron: Asymmetry 2012, 23, 1218–1225.
1
obtained (0.38 g, 85.0% yield). H NMR (CDCl3): δ = 0.92 (m, 24
H, CHMe2), 3.23 (m, 4 H, CHMe2), 4.89 (s, 2 H, CHNCH2), 6.07
(m, 1 H, CH pyrrole), 6.65–6.73 (m, 4 H, CH pyrrole and phenyl),
6.87, 7.39, 7.89 (m, 7 H, CH pyridine and phenyl), 8.13 (s, 1 H,
CHNCH2), 8.95 (m, 1 H, CH pyridine) ppm. 13C NMR: δ = 22.9
(q, JC,H = 125 Hz, CHMe2), 23.4 (q, JC,H = 125 Hz, CHMe2), 26.7
(d, JC,H = 125 Hz, CHMe2), 51.0 (t, JC,H = 140 Hz, CHNCH2),
115.3, 117.3, 120.2, 121.9, 122.6, 123.8, 135.7, 137.3, 140.1, 148.5,
153.9, 154.8, 157.5 (d, JC,H
= 167 Hz, CHNCH2) ppm.
C35H44AlN3O2 (565.72): calcd. C 74.31, H 7.84, N 7.431; found C
74.52, H 8.06, N 7.47.
[Al{C4H3N(2-CHNCH2Py)}(PhCOCHCOPh)2] (5): A flask was
charged with 1 (0.20 g, 0.83 mmol) and toluene (10 mL) and cooled
to 0 °C. A solution of dibenzoylmethane (0.37 g, 1.66 mmol) in tol-
uene (10 mL) was added to the first solution dropwise, and the
mixture was stirred for 3 h at room temperature after the addition
was complete. The resulting solution was vacuum-dried, and the
solid was recrystallized from a dichloromethane solution at –20 °C
to generate pale yellowish crystals of 3 (0.39 g, 71.0% yield). 1H
NMR (CDCl3): δ = 4.90 (dd, 2 H, CH=NCH2), 6.65 (s,1 H
PhCOCHCOPh), 6.81 (s, 1 H, PhCOCHCOPh), 6.25–8.25 (m, 27
H, aromatic CH), 8.19 (s, 1 H, CH=NCH2) ppm. 13C NMR
(CDCl3): δ = 60.3 (t, JC,H = 141 Hz, CHNCH2), 94.1 (d, JC,H
=
160 Hz, PhCOCHCOPh), 94.2 (d, JC,H = 160 Hz, CH, PhCOCH-
COPh), 159.4 (d, JC,H = 165 Hz, CH=NCH2), 111.8, 149.0, 133.5,
133.9, 138.2, 138.4, 158.7, 184.0, 184.4, 185.0, 185.6, 186.2 ppm.
C41H32AlN3O4 (657.69): calcd. C 74.42, H 5.48, N 6.35; found C
74.15, H 5.55, N 5.90.
[6] a) S.-I. Hashimoto, N. Komeshima, K. Koga, J. Chem. Soc.,
Chem. Commun. 1979, 437–438; b) M. Shimizu, M. Kawam-
oto, Y. Yamamoto, T. Fujisawa, Synlett 1997, 501–502; c) K.
Maruoka, S. Saito, H. Yamamoto, J. Am. Chem. Soc. 1995,
117, 1165–1166; d) K. Maruoka, T. Itoh, M. Sakurai, K. Non-
oshita, H. Yamamoto, J. Am. Chem. Soc. 1988, 110, 3588–
3597; e) T. Hashimoto, Y. Naganawa, K. Maruoka, J. Am.
Chem. Soc. 2011, 133, 8834–8837; f) M. Roberson, A. S.
Jepsen, K. A. Jørgensen, Tetrahedron 2001, 57, 907–913.
[7] a) M. Lin, W. Liu, Z. Chen, L. Yang, H. Pei, J. Wu, X. Wan,
T. Lei, Y. Li, RSC Adv. 2012, 2, 3451–3457; b) Z. Chen, J. Wu,
Y. Chen, L. Li, Y. Xia, Y. Li, W. Liu, T. Lei, L. Yang, D. Gao,
W. L i , Organometallics 2012, 31, 6005–6013; c) C. Stern, F.
Franceschi, E. Solari, C. Floriani, N. Re, R. Scopelliti, J. Or-
ganomet. Chem. 2000, 593–594, 86–95; d) R. Li, B. Moubaraki,
K. S. Murray, S. Brooker, Eur. J. Inorg. Chem. 2009, 2851–2859;
e) B.-C. Xu, T. Hu, J.-Q. Wu, N.-H. Hu, Y.-S. Li, Dalton Trans.
2009, 8854–8863; f) R. Li, B. Moubaraki, K. S. Murray, S.
Brooker, Dalton Trans. 2008, 6014–6022; g) S. D. Reid, C. Wil-
son, A. J. Blake, J. B. Love, Dalton Trans. 2010, 39, 418–425;
h) Y. Liao, J. J. Novo, A. Arif, J. S. Miller, Chem. Commun.
2002, 3008–3009; i) B. de Bruin, R. J. N. A. M. Kicken,
N. F. A. Suos, M. P. J. Donners, C. J. den Reijer, A. J. Sandee,
Crystallographic Structural Determination of 1–5: A summary of
the crystal data collection and selected bond lengths and angles are
listed in Tables 1 and 2, respectively. The crystals were mounted in
capillaries and transferred to a goniostat. The data were collected
at 150 K with a Bruker SMART CCD diffractometer with graph-
ite-monochromated Mo-Kα radiation. The intensity data were col-
lected using a combination of ω and f scans. All data were corrected
for Lorentz and polarization effects, and the program
SADABS in the APEX2 software suite[19] was used for the absorp-
tion correction. The structures were solved by direct and difference
Fourier methods. Crystallographic computing was performed by
using SHELXTL[19] program package. All refinements were per-
formed by full-matrix least-squares methods with anisotropic dis-
placement parameters for all non-hydrogen atoms. All hydrogen
atoms were included in calculated positions in the refinements.
CCDC-961035 (for 1), -961036 (for 2), -961037 (for 3), -961038 (for
4), and -961039 (for 5) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
Eur. J. Inorg. Chem. 2014, 1965–1973
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FULL PAPER
R. de Gelder, J. M. M. Smits, A. W. Gal, A. L. Spek, Eur. J.
Inorg. Chem. 1999, 1581–1592.
[8] D. Gerlach, E. Brendler, T. Heine, J. Wagler, Organometallics
2007, 26, 234–240.
Chem. Commun. 2002, 5, 946–948; c) A. Gairola, G. V. Kunte,
D. Chopra, T. N. G. Row, A. M. Umarji, S. A. Shivashankar,
Polyhedron 2010, 29, 2680–2688; d) V. G. Kessler, S. Gohil, S.
Parola, Dalton Trans. 2003, 544–550; e) Y.-L. Lien, Y.-C.
Chang, N.-T. Chuang, A. Datta, S.-J. Chen, C.-H. Hu, W.-Y.
Huang, C.-H. Lin, J.-H. Huang, Inorg. Chem. 2010, 49, 136–
143; f) V. A. Montes, G. V. Zyryanov, E. Danilov, N. Agarwal,
M. A. Palacios, P. Anzenbacher Jr., J. Am. Chem. Soc. 2009,
131, 1787–1795.
[9] a) W.-Y. Huang, S.-J. Chuang, N.-T. Chuang, C.-S. Hsiao, A.
Datta, S.-J. Chen, C.-H. Hu, J.-H. Huang, T.-Y. Lee, C.-H. Lin,
Dalton Trans. 2011, 40, 7423–7433; b) J. Turunen, T. T. Pak-
kanen, B. Löfgren, J. Mol. Catal. A 1997, 123, 35–42; c) R.
Anwander, C. Palm, O. Groeger, G. Engelhardt, Organometal-
lics 1998, 17, 2027–2036.
[10] a) H. M. El-Kaderi, M. J. Heeg, C. H. Winter, Eur. J. Inorg.
Chem. 2005, 2081–2088; b) A. A. Karpov, A. V. Cherkasov,
G. K. Fukin, A. S. Shavyrin, L. Luconi, G. Giambastiani,
A. A. Trifonov, Organometallics 2013, 32, 2379–2388; c) F.
Drouin, P. O. Oguadinma, T. J. J. Whitehorne, R. E.
Prud’homme, F. Schaper, Organometallics 2010, 29, 2139–2147;
d) S. Latreche, F. Schaper, Organometallics 2010, 29, 2180–
2185.
[16] Y. Zhao, D. Truhlar, Theo. Chem. Acc. 2008, 120, 215–241.
[17] a) M. H. Chisholm, N. W. Eilerts, J. C. Huffman, S. S. Iyer, M.
Pacold, K. Phomphari, J. Am. Chem. Soc. 2000, 122, 11845–
11854; b) M. H. Chisholm, S. T. Haubrich, J. C. Huffman,
W. E. Streib, J. Am. Chem. Soc. 1997, 119, 1634–1647; c) D.
Chakraborty, E. Y.-X. Chen, Organometallics 2003, 22, 769–
774; d) D. Chakraborty, E. Y.-X. Chen, Macromolecules 2002,
35, 13–15; e) D. Chakraborty, A. Rodriguez, E. Y.-X. Chen,
Macromolecules 2003, 36, 5470–5481.
[11] A. W. Addison, T. N. Rao, J. Reedijk, J. Van Rijin, G. C. Ver-
schoor, J. Chem. Soc., Dalton Trans. 1984, 1349–1356.
[12] a) J. Vestfrid, M. Botoshansky, J. H. Palmer, A. C. Durrell,
H. B. Gray, Z. Gross, J. Am. Chem. Soc. 2011, 133, 12899–
12901; b) Y. Yang, H. Li, C. Wang, H. W. Roesky, Inorg. Chem.
2012, 51, 2204–2211; c) G. J. E. Davidson, L. H. Tong, P. R.
Raithbyy, J. K. M. Sanders, Chem. Commun. 2006, 3087–3089.
[13] W. A. Nugent, U. M. Mayer, Metal-Ligand Multiple Bonds,
Wiley-lnterscience, New York, 1988.
[14] a) T. J. Boyle, T. M. Alam, S. D. Bunge, J. M. Segall, G. R. Avil-
ucea, R. G. Tissot, M. A. Rodriguez, Organometallics 2005, 24,
731–737; b) J. Francis, S. G. Bott, A. R. Barron, J. Organomet.
Chem. 2000, 597, 29–37; c) I.-C. Chen, S.-M. Ho, Y.-C. Chen,
C.-Y. Lin, C.-H. Hu, C.-Y. Tu, A. Datta, J.-H. Huang, C.-H.
Lin, Dalton Trans. 2009, 8632–8643.
[18] a) Y.-C. Liu, B.-T. Ko, B.-H. Huang, C.-C. Lin, Organometal-
lics 2002, 21, 2066–2069; b) M. Normand, E. Kirillov, T. Rois-
nel, J.-F. Carpentier, Organometallics 2012, 31, 5511–5519; c)
O. Pàmies, J.-E. Bäckval, Chem. Eur. J. 2001, 7, 5052–5058.
[19] a) APEX2, v. 1.0, SADABS, v. 2.1, SAINT+, v. 6.28a,
SHELXTL, v. 6.14, Bruker AXS Inc., Madison, 2004; b)
APEX2, v. 2010, SADABS, v. 2008/1, SAINT+, v. 7.66a,
SHELXTL, v. 6.14, Bruker AXS Inc., Madison, 2010.
[20] C.-Y. Lin, C.-F. Tsai, H.-J. Chen, C.-H. Hung, R.-C. Yu, P.-C.
Kuo, H. M. Lee, J.-H. Huang, Chem. Eur. J. 2006, 12, 3067–
3073.
[21] C.-Fu Tsai, H.-J. Chen, C. J. Chang, C.-H. Hung, C.-C. Lai,
C.-H. Hu, J.-H. Huang, Inorg. Chem. 2004, 43, 2183–2188.
[22] F. Meyers, C. Adant, J. Brédas, J. Am. Chem. Soc. 1991, 113,
3715.
[15] a) G. Szigethy, A. F. Heyduk, Dalton Trans. 2012, 41, 8144–
8152; b) E. Suslova, G. A. Seisenbaeva, V. G. Kessler, Inorg.
Received: January 23, 2014
Published Online: February 27, 2014
Eur. J. Inorg. Chem. 2014, 1965–1973
1973
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