Reactions of dimeric aluminium hydride compounds containing bidentate dianionic pyrrolyl ligands and their applications in ring-opening polymerization of ε-caprolactone

Article abstract of DOI:10.1002/ejic.201100031

A series of dimeric aluminium compounds containing substituted bidentate dianionic pyrrolyl ligands have been synthesized and their reactivity and application in the ring-opening polymerization of ε-caprolactone have been studied. The reactions of [{C₄H₃N(2-CH₂NtBu)} AlH]₂ (1) with 2 equiv. of 1-indanone and 9-fluorenone in dichloromethane generated [{C₄H₃N(2-CH₂NtBu)} Al(μ-OC₉H₉)]₂ (2) and [{C₄H ₃N(2-CH₂NtBu)}Al{μ-OCH(C₁₂H ₈)}]₂ (3), respectively, by hydroalumination. Similarly, the reactions of 1 with 2 equiv. of 2-cyclohexen-1-one, 1-(2,4,6- trimethylphenyl)-1-ethanone, benzophenone, and 1,1-diphenylacetone in dichloromethane afforded NtBu-bridged dialuminium compounds 4-7, [{C ₄H₃N(2-CH₂NtBu)}Al(OR)]₂ [4, R = C₆H₉; 5, R = CH(Me)(C₆H₂-2,4,6- Me₃); 6, R = CHPh₂; 7, R = CH(Me)(CHPh₂)] by insertion. A similar insertion occurred when 1 was treated with 2 equiv. of 2,4-pentandione and dibenzoylmethane in dichloromethane to yield NtBu-bridged dioxylate aluminium dimeric compounds 8 and 9, respectively. The Al atoms in compounds 2 and 4-7 possess a distorted tetrahedral geometry whereas the Al atoms in 8 and 9 have a square-pyramidal environment. All the compounds have been well characterized by NMR spectroscopy and compounds 2 and 4-9 in the solid state were subjected to X-ray diffraction analysis. A study of the polymerization of ε-caprolactone revealed that the activity of the Al complexes is largely reliant on the steric nature of the substituents of their alkoxide groups.

Full text of DOI:10.1002/ejic.201100031

FULL PAPER
DOI: 10.1002/ejic.201100031
Reactions of Dimeric Aluminium Hydride Compounds Containing Bidentate
Dianionic Pyrrolyl Ligands and Their Applications in Ring-Opening
Polymerization of ε-Caprolactone
Ya-Chi Chen,[a] Che-Yu Lin,[a] Wen-Yen Huang,[a] Amitabha Datta,[a] Jui-Hsien Huang,*[a]
Meng-Shiue Tsai,[b] Ting-Yu Lee,*[b] Cheng-Yi Tu,[a] and Ching-Han Hu[a]
Keywords: Aluminium / Hydrides / N ligands / Ring-opening polymerization
A series of dimeric aluminium compounds containing substi-
tuted bidentate dianionic pyrrolyl ligands have been synthe-
sized and their reactivity and application in the ring-opening
polymerization of ε-caprolactone have been studied. The re-
actions of [{C4H3N(2-CH2NtBu)}AlH]2 (1) with 2 equiv. of 1-
(CHPh2)] by insertion. A similar insertion occurred when 1
was treated with 2 equiv. of 2,4-pentandione and dibenzo-
ylmethane in dichloromethane to yield NtBu-bridged di-
oxylate aluminium dimeric compounds 8 and 9, respectively.
The Al atoms in compounds 2 and 4–7 possess a distorted
indanone and 9-fluorenone in dichloromethane generated tetrahedral geometry whereas the Al atoms in 8 and 9 have
[{C4H3N(2-CH2NtBu)}Al(μ-OC9H9)]2 (2) and [{C4H3N(2-
CH2NtBu)}Al{μ-OCH(C12H8)}]2 (3), respectively, by hydro-
alumination. Similarly, the reactions of 1 with 2 equiv. of 2-
a square-pyramidal environment. All the compounds have
been well characterized by NMR spectroscopy and com-
pounds 2 and 4–9 in the solid state were subjected to X-ray
diffraction analysis. A study of the polymerization of ε-capro-
lactone revealed that the activity of the Al complexes is
largely reliant on the steric nature of the substituents of their
alkoxide groups.
cyclohexen-1-one,
1-(2,4,6-trimethylphenyl)-1-ethanone,
benzophenone, and 1,1-diphenylacetone in dichloromethane
afforded NtBu-bridged dialuminium compounds 4–7,
[{C4H3N(2-CH2NtBu)}Al(OR)]2 [4, R = C6H9; 5, R = CH(Me)-
(C6H2-2,4,6-Me3); 6,
R
=
CHPh2; 7,
R
=
CH(Me)-
ganic ligands at the metal hydride centers to increase their
steric controllability and solubility in organic solvents.
From the point of view of ligand design, nitrogen donor
ligands, for which in principle a great variety of synthetic
strategies are available, may generate catalytically active
complexes. Nitrogen-based polydentate ligands such as
phenoxyimine[3–6] and 2,6-bis(N-aryliminomethyl)pyr-
idine,[7] which serve as supporting ligands for polymeriza-
tion catalysts, have attracted particular interest because of
their advantageous ease of synthesizing and flexibility in
introducing sterically and electronically demanding features
into the ligand.[8,9] Concerning different ligand systems, the
pyrrolyl entity has the ability to bring metal centers into
close proximity and provides an intra- or intermolecular
pathway for bonding interactions. Further changes in the
substituents on the pyrrolyl ring can facilitate favorable
configurations and control the metal polyhedron coordina-
tion. Aluminium hydride complexes with pyrrolyl-based li-
gands react with ketones to generate aluminium alkoxide
complexes by hydroalumination[10] and we have also de-
scribed the reactivity of monomeric aluminium hydride
complexes with pyrrolyl ligands[11] in insertion and C–C
coupling reactions. Thus, we have focused our research on
finding new organoaluminium hydrides with ketiminate or
donor-substituted pyrrole ligands and have discussed their
Introduction
Metal hydrides and their complexes are considered valu-
able synthons in chemistry. It has been demonstrated that
main-group and transition-metal hydrides are important in-
termediates in some industrial processes and also function
as catalysts.[1] Early-transition-metal hydride derivatives are
thought to be responsible for an over abundance of organic
transformations, catalytic cycles, and olefin polymerization
intermediates or deactivation products.[2] The problems as-
sociated with the application of metal hydride complexes
are the selectivity of the reduction and the solubility of the
reducing agents even though some soluble hydride reagents
such as iBu2AlH, DIBALH, LiAl(OtBu)3H, or super-
hydride LiBEt3H are commercially available. To overcome
these problems, researchers have tried to introduce large or-
[a] Department of Chemistry, National Changhua University of
Education,
50058 Changhua, Taiwan
E-mail: juihuang@cc.ncue.edu.tw
[b] Department of Applied Chemistry, National University of
Kaohsiung,
811 Kaohsiung, Taiwan
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100031.
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J.-H. Huang, T.-Y. Lee et al.
FULL PAPER
reactions with PhNCO, CO2, H2O, and tertiary alcohols.[12] troscopy. Again, the reactions of 1 with 2 equiv. of 2-
To extend our research of the above-mentioned aluminium cyclohexen-1-one, 1-(2,4,6-trimethylphenyl)-1-ethanone,
hydride chemistry mediated by pyrrolyl-linked architec- benzophenone, and 1,1-diphenylacetone in dichlorometh-
tures, we report herein a series of novel aluminium com- ane afforded NtBu-bridged dialuminium compounds 4–7,
plexes in different reaction conditions and their applications [{C4H3N(2-CH2NtBu)}Al(OR)]2 [4, R = C6H9; 5, R =
in the ring-opening polymerization of ε-caprolactone. All CH(Me)(C6H2-2,4,6-Me3); 6,
R = CHPh2; 7, R =
the products were investigated in detail by multinuclear CH(Me)(CHPh2)]. The carbonyl group on insertion into
NMR spectroscopy and seven compounds have also been Al–H readily generates terminal aluminium alkoxide di-
characterized by single-crystal X-ray diffraction.
meric compounds. All the chemical shifts of the methylene
protons of CH2NtBu in compounds 4–7 show two doublets
at δ = 3.66–5.03 ppm. The molecular geometries of 4 and 5
were also verified by 1H–13C HSQC 2D NMR spec-
troscopy.
Thus, the alkoxide fragments can participate in bridging
between the aluminium atoms (compounds 2 and 3) or
form terminal groups (compounds 4–7), as discussed in the
literature.[14] However, there is no trend to allow prediction
of the bonding modes of the hydroalumination reaction.
The geometries of these compounds should be determined
entirely by electronic and steric effects.
Results and Discussion
Reactions and Characterizations
The dimeric aluminium hydride compound 1 shows good
reactivity towards unsaturated organofunctional groups
such as C=O or C=NOH forming aluminium alkoxides or
oximates.[13] The reactions of 1 with mono- and diketones
are summarized in Scheme 1 and Scheme 2, respectively.
The reactions of 1 with 2 equiv. of 1-indanone and 9-
fluorenone in dichloromethane resulted in moderate yields
The reaction of 2 equiv. of 2,4-pentandione with 1 in
of [{C4H3N(2-CH2NtBu)}Al(μ-OC9H9)]2 (2) and [{C4H3N- dichloromethane generated yellow NtBu-bridged diket-
(2-CH2NtBu)}Al{μ-OCH(C12H8)}]2 (3), respectively, by iminate aluminium dimeric compound [{C4H3N(2-
hydroalumination. Compounds 2 and 3 form dialkoxy- CH2NtBu)}Al{κO,κO-(OCMeCHCOMe)}]2 (8) in 71%
bridged dialuminium compounds by insertion of 1-in- yield (Scheme 2). The 1H NMR spectrum of 8 at room tem-
danone and 9-fluorenone into the aluminium hydride perature shows one broad signal at δ = 1.14 ppm for the
bonds. The methylene protons of CH2NtBu show charac- methyl protons of the tBu group of the substituted pyrrolyl
1
teristic H NMR resonances with two doublets at δ = 4.19 and the diketiminate fragments, which indicates a fast ex-
1
and 4.96 ppm for 2 and two doublets at δ = 3.94 and change of the geometry of this compound. The H NMR
4.74 ppm for 3. The chemical shift of the methine proton spectrum of 8 in [D8]toluene at 0 °C reveals that the tBu
of the bridged alkoxy fragment appears at δ = 5.55 and groups and the methyl groups of the diketiminate fragments
5.89 ppm, respectively. The molecular geometries of 2 and show several sharp singlets between 1.06–1.69 ppm, which
3 were also verified by 1H–13C HSQC 2D NMR spec- indicates a slow exchange limit of the geometry at low tem-
Scheme 1.
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Eur. J. Inorg. Chem. 2011, 2459–2469

Dimeric Aluminium Hydrides Containing Pyrrolyl Ligands
Scheme 2.
1
perature. In addition, two sharp singlets appear at δ = 4.13 ligand [C4H3N(2-CH2NHtBu)]– in compound 10. The H
and 5.09 ppm in a ratio of 2:1 assigned to the methylene NMR spectrum of 10 shows the methylene protons of
protons of the CH2NtBu fragments and the methine pro- CH2NHtBu as two multiplets at δ = 3.45 and 3.78 ppm.
tons of diketiminate further confirmed the geometry of Although the proton signal (δ = 2.32 ppm) of NHtBu is
compound 8.
decoupled, the resonances for the methylene protons of
Again, the reaction of 1 with 2 equiv. of dibenzoylmeth- CH2NHtBu are present as two simple doublets. In addition,
ane in dichloromethane afforded an orange powder of the reaction of [{C4H3N(2-CH2NtBu)}AlD]2 (1-D), ob-
[{C4H3N(2-CH2NtBu)}Al{κO,κO-(OCPhCHCOPh)}]2 (9) tained from the reaction of AlD3·NMe3 and [C4H3NH(2-
in 69% yield by deprotonation of one of the two methylene CH2NHtBu)],
with
benzil
afforded
[{C4H3N(2-
protons of the diketiminate backbone of the diketone li- CH2NDtBu)}Al{κO,κO-(PhOC=COPh)}]2 (10-D). No res-
1
1
gands. The H and 13C NMR spectra of the methyl groups onance is observed at δ = 2.32 ppm in the H NMR spec-
of the NtBu fragments both show broad bands at δ = 1.27 trum, which indicates that the amino proton of NHtBu has
and 30.1 ppm, respectively. The methylene protons of been replaced by the deuterium atom in 10-D. A possible
CH2NtBu appear as one singlet at δ = 4.28 ppm and an AB reaction mechanism is shown in Scheme 3. Compound 1-D
spin system in which two doublets are observed at δ = 4.24 reacts with benzil by hydroalumination to form an alumin-
and 4.69 ppm. The methine protons of the two diketiminate ium ketone–alkoxide intermediate and then the amido ni-
backbones are observed at δ = 7.03 and 7.18 ppm, which trogen of the CH2NtBu extracts one proton from the
was also confirmed by H–13C HSQC 2D NMR spectra. ketone–alkoxide fragment to form an ene–diolate interme-
1
All the information indicates that the geometry of 9 in solu- diate. The same procedure is repeated again to form the
tion is relatively rigid and shows an asymmetrical confor- final product 10-D. The reduction of benzil to diphenyl-
mation.
ethene–diolate using low-valent metal complexes has been
The reaction of 1 with organic diketone benzil in dichlo- reported in the literature,[15] however, there is no report of
romethane at 0 °C in a 2:1 ratio resulted in diketonate the reduction by metal complexes in high oxidation states.
compound [{C4H3N(2-CH2NHtBu)}Al{κO,κO-(PhOC= Metal hydride induced benzil reduction to diphenylethene–
COPh)}]2 (10) in 47% yield. One triplet signal is observed diolate is even less well explored.[11] Previously dialuminium
1
at δ = 2.32 ppm in the H NMR spectrum and has been compounds were generated with mono- or bidentate orien-
assigned to the amino proton of the NHtBu fragment. This tation of acetone or acetone oxime into [{C4H3N(2-
1
was confirmed by the H–13C HSQC 2D and homonuclear CH2NtBu)}AlH]2,[13] whereas in this work we prepared two
1
decoupled H NMR spectra. Apparently, the original dian- dialkoxy-bridged dialuminium compounds by insertion of
ionic pyrrolyl ligand [C4H3N(2-CH2NtBu)]2– in compound 1-indanone and 9-fluorenone into the aluminium hydride
1 has been reprotonated to form a mono-anionic pyrrolyl bonds.
Eur. J. Inorg. Chem. 2011, 2459–2469
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J.-H. Huang, T.-Y. Lee et al.
FULL PAPER
Scheme 3.
dentate orientation of the pyrrolyl ligand and bridging of
the indanone O atoms. The Al–N(pyrrolyl) bond lengths
are rather similar to those of previously reported alumin-
ium pyrrolyl compounds.[13]
Molecular Structures of 2 and 4–9
Crystals of 2 and 4–9 suitable for X-ray analysis were
obtained by the evaporation of different solvents. The de-
The solid-state structures of compounds 4–7 were deter-
tails of data collection and selected bond lengths and angles mined similarly and their molecular structures are shown in
are shown in Table 1 and Table 2, respectively. Crystals of Figures 2, 3, 4 and 5, respectively. There are two indepen-
2 were generated from a mixture of toluene and pentane at dent molecules of 4 in one unit cell and the disordered cy-
–20 °C and possess a center of symmetry. The molecular clohexenyl fragment shows a carbon–carbon double bond
geometry of 2, shown in Figure 1, may be described as an length of 1.260(7) Å. Compounds 4–7 all possess a dis-
Al2O2 parallelogram into which two O atoms from each torted tetrahedral geometry around the central aluminium
indanone molecule bridge the two aluminium atoms with center as a result of the coordination of the bidentate pyrrol-
Al(1)–O(1)–Al(1A) and O(1)–Al(1)–O(1A) angles of yl ligand and two oxygen atoms from 2-cyclohexen-1-one,
99.35(4) and 80.65(4)°, respectively. The substituted pyr- 1-(2,4,6-trimethylphenyl)-1-ethanone, benzophenone, and
rolyl ligands chelate an aluminium atom with a bite angle 1,1-diphenylacetone, respectively. The two aluminium
of 94.09(5)° and the corresponding Al(1)–N(1) and Al(1)– atoms and two bridging nitrogen atoms of the NtBu frag-
N(2) bond lengths are 1.8273(11) and 1.7791(10) Å, respec- ments form an Al2N2 parallelogram with Al–N–Al bond
tively. The Al–N(tBu) bond length is shorter than that of angles and Al–N bond lengths ranging from 90.89(10)–
Al–N(pyrrolyl), which indicates the stronger σ-donating 91.34(6)° and 1.9395(9)–1.9766(2) Å, respectively. The two
ability of the NtBu fragment to the Al atom. The two alu- pyrrolyl rings shuffle in the trans positions of the Al2N2
minium atoms adopt a distorted tetrahedral geometry con- plane presumably due to steric congestion. The lengths of
sisting of a (NNOO) coordination mode generated by bi- the bonds between the aluminium atoms and the terminal
Table 1. Crystal data for compounds 2 and 4–9.
2
4
5
6
7
8
9
Formula
Mr
C21.5H27AlN2O
356.43
C30H46Al2N4O2 C40H58Al2N4O2
C44H50Al2N4O2
720.84
C62H74Al2N4O2
961.21
C28H42Al2N4O4 C50H54Al2Cl4N4O4
548.67
680.86
552.62
970.73
Crystal system
Space group
a [Å]
b [Å]
c [Å]
triclinic
P1
triclinic
P1
triclinic
P1
triclinic
P1
triclinic
P1
monoclinic
P21/n
14.8664(7)
12.1660(6)
17.7969(8)
monoclinic
C2/c
28.1450(14)
12.2188(6)
17.1129(8)
¯
¯
¯
¯
¯
9.3554(4)
10.2952(4)
11.9025(5)
107.160(2)
98.425(2)
109.793(2)
991.18(7), 2
1.194
9.8142(3)
10.0249(4)
15.3380(5)
90.074(2)
93.162(2)
93.573(2)
1503.81(9), 2
1.212
8.705(3)
8.709(3)
13.712(5)
89.527(6)
72.007(7)
79.420(6)
970.6(6), 1
1.165
9.8094(7)
10.2384(7)
10.7064(8)
72.5830(10)
74.8260(10)
70.5330(10)
951.51(12), 1
1.258
9.5164(2)
10.1659(3)
14.8496(4)
100.790(2)
95.017(2)
104.1840(10)
1354.70(6), 1
1.178
α [°]
β [°]
113.2050(10)
124.482(3)
γ [°]
V [Å3], Z
2958.4(2), 4
1.241
0.137
150(2)
1184
4851.1(4), 4
1.329
0.329
150(2)
2032
Dcalcd. [Mgm–3
]
Absol. coeff. [mm–1
T [K]
]
0.114
150(2)
382
0.130
150(2)
592
0.113
150(2)
368
0.120
150(2)
384
0.100
150(2)
516
F(000)
Reflections collected
Independent refl.
15209
4744
31599
7768
14004
4672
14292
4592
26441
5868
22902
7146
18165
5036
(Rint = 0.0193)
Data/restraints/params 4744/0/254
(Rint = 0.0575) (Rint = 0.0569)
(Rint = 0.0242)
4592/0/238
1.046
R1 = 0.0351
wR2 = 0.963
R1 = 0.0392
wR2 = 0.992
0.304/–0.305
(Rint = 0.0288)
5868/0/321
1.075
R1 = 0.0497
wR2 = 0.1351
R1 = 0.0686
wR2 = 0.1459
0.797/–0.287
(Rint = 0.0523) (Rint = 0.0438)
7768/0/380
0.981
4672/0/224
1.036
7146/0/353
1.042
5036/2/351
1.007
Goodness of fit on F2
Final R indices
[IϾ2σ(I)]
R indices
(all data)
1.070
R1 = 0.0383
wR2 = 0.1076
R1 = 0.0468
wR2 = 0.1128
R1 = 0.0774
wR2 = 0.1950
R1 = 0.1277
wR2 = 0.2241
0.734/–0.571
R1 = 0.0401
wR2 = 0.1183
R1 = 0.0803
wR2 = 0.1372
0.474/–0.584
R1 = 0.0536
wR2 = 0.1243
R1 = 0.1017
wR2 = 0.1427
0.601/–0.325
R1 = 0.0660
wR2 = 0.1839
R1 = 0.1057
wR2 = 0.2230
0.773/–0.653
Largest diff. peak/hole 0.375/–0.225
[eÅ–3
]
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Eur. J. Inorg. Chem. 2011, 2459–2469

Dimeric Aluminium Hydrides Containing Pyrrolyl Ligands
Table 2. Selected bond lengths [Å] and angles [°] for compounds 2
and 4–9.
2
Al(1)–N(2)
Al(1)–O(1A)
O(1)–C(10)
1.7791(10)
1.8229(9)
1.4756(15)
122.59(5)
Al(1)–O(1)
Al(1)–N(1)
1.8175(9)
1.8273(11)
N(2)–Al(1)–O(1)
N(2)–Al(1)–O(1A) 127.21(5)
O(1)–Al(1)–O(1A) 80.65(4)
O(1)–Al(1)–N(1) 120.60(5)
C(10)–O(1)–Al(1A) 129.20(7)
N(2)–Al(1)–N(1)
C(10)–O(1)–Al(1)
Al(1)–O(1)–Al(1A) 99.35(4)
94.09(5)
129.27(7)
4
Al(1)–O(1)
1.674(3)
1.940(3)
1.940(3)
1.260(7)
1.501(8)
116.75(14)
Al(1)–N(1)
Al(1)–N(2)
C(10)–C(11)
C(12)–C(13)
C(14)–C(15)
1.825(3)
1.957(2)
1.526(8)
1.528(7)
1.442(8)
Al(1)–N(2A)
N(2)–Al(1A)
C(11)–C(12)
C(13)–C(14)
O(1)–Al(1)–N(1)
O(1)–Al(1)–N(2A) 112.08(13)
N(1)–Al(1)–N(2A) 118.66(12)
N(1)–Al(1)–N(2) 91.74(12)
Al(1A)–N(2)–Al(1) 90.89(10)
O(1)–Al(1)–N(2)
N(1)–Al(1)–N(2)
C(10)–O(1)–Al(1)
124.91(12)
89.11(10)
121.4(3)
Figure 1. Molecular structure of compound 2. Thermal ellipsoids
are drawn at the 30% probability level. The toluene molecules and
hydrogen atoms have been omitted for clarity.
5
Al(1)–O(1)
Al(1)–N(2)
C(11)–O(1)
C(10)–C(11)
O(1)–Al(1)–N(1)
N(1)–Al(1)–N(2)
1.7049(12)
1.9766(12)
1.4364(17)
1.521(2)
114.70(6)
91.62(6)
Al(1)–N(1)
1.8320(15)
1.9358(13)
1.9358(13)
1.532(2)
Al(1)–N(2A)
N(2)–Al(1A)
C(11)–C(12)
O(1)–Al(1)–N(2)
O(1)–Al(1)–N(2A) 109.86(6)
N(1)–Al(1)–N(2A) 122.14(6)
127.94(6)
Al(1A)–N(2)–Al(1) 91.34(6)
N(2A)–Al(1)–N(2) 88.66(6)
C(11)–O(1)–Al(1)
127.66(11)
6
7
Al(1)–O(1)
Al(1)–N(2)
C(10)–O(1)
O(1)–Al(1)–N(1)
N(1)–Al(1)–N(2)
Al(1)–N(2)–Al(1A) 91.03(4)
N(2)–Al(1)–N(2A) 88.97(4)
1.7129(8)
1.9395(9)
1.4241(12)
115.84(4)
119.03(4)
Al(1)–N(1)
1.8305(9)
1.9656(9)
1.9656(9)
113.10(4)
Al(1)–N(2A)
N(2)–Al(1A)
O(1)–Al(1)–N(2)
O(1)–Al(1)–N(2A) 123.99(4)
N(1)–Al(1)–N(2A) 92.22(4)
C(10)–O(1)–Al(1)
126.48(7)
Figure 2. Molecular structure of compound 4. Thermal ellipsoids
are drawn at the 30% probability level. The hydrogen atoms except
those on the cyclohexyl ring have been omitted for clarity.
Al(1)–O(1)
Al(1)–N(2)
C(11)–O(1)
C(10)–C(11)
O(1)–Al(1)–N(1)
N(1)–Al(1)–N(2)
Al(1A)–N(2)–Al(1) 91.09(6)
N(2A)–Al(1)–N(2) 88.91(6)
1.6712(14)
1.9644(15)
1.407(2)
1.509(3)
117.07(7)
92.01(6)
Al(1)–N(1)
1.8316(15)
1.9471(15)
1.9471(15)
1.536(3)
Al(1)–N(2A)
N(2)–Al(1A)
C(11)–C(12)
O(1)–Al(1)–N(2)
O(1)–Al(1)–N(2A) 111.03(7)
N(1)–Al(1)–N(2A) 118.79(7)
125.69(7)
C(11)–O(1)–Al(1)
149.75(12)
8
Al(1)–O(2)
Al(1)–O(1)
Al(1)–N(4)
Al(2)–N(2)
1.8106(17)
1.8963(16)
2.1055(19)
2.152(2)
Al(1)–N(3)
Al(1)–N(2)
Al(2)–N(4)
1.871(2)
1.9586(19)
1.936(2)
O(2)–Al(1)–N(3)
N(3)–Al(1)–O(1)
N(3)–Al(1)–N(2)
O(2)–Al(1)–N(4)
O(1)–Al(1)–N(4)
O(4)–Al(2)–N(2)
125.57(8)
89.05(8)
125.82(8)
93.29(8)
173.70(8)
177.22(8)
O(2)–Al(1)–O(1)
O(2)–Al(1)–N(2)
O(1)–Al(1)–N(2)
N(3)–Al(1)–N(4)
N(2)–Al(1)–N(4)
Al(1)–N(2)–Al(2)
89.55(7)
108.17(8)
98.42(8)
84.72(8)
86.05(8)
92.33(8)
9
Al(1)–O(1)
Al(1)–O(2)
Al(1)–N(2A)
C(18)–O(1)
O(1)–Al(1)–N(1)
N(1)–Al(1)–O(2)
Al(1)–N(2)–Al(1A) 95.05(10)
N(1)–Al(1)–N(2A) 84.52(10)
O(2)–Al(1)–N(2)
1.816(2)
1.909(2)
2.139(3)
1.312(4)
116.69(112)
87.47(11)
Al(1)–N(1)
Al(1)–N(2)
C(16)–O(2)
C(11)–C(12)
O(1)–Al(1)–O(2)
O(1)–Al(1)–N(2)
N(1)–Al(1)–N(2)
O(2)–Al(1)–N(2A) 169.08(10)
N(2)–Al(1)–N(2A) 84.52(10)
1.871(3)
1.939(3)
1.278(4)
1.361(6)
89.50(10)
121.25(11)
122.05(11)
Figure 3. Molecular structure of compound 5. Thermal ellipsoids
are drawn at the 30% probability level. The hydrogen atoms have
been omitted for clarity.
93.17(10)
Eur. J. Inorg. Chem. 2011, 2459–2469
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J.-H. Huang, T.-Y. Lee et al.
FULL PAPER
alkoxide oxygen atoms of compounds 4–7 are very similar atom from the bridged NtBu fragment occupy the axial po-
and lie in the range 1.674(3)–1.7129(8) Å. However, the Al– sitions with O(1)–Al(1)–N(4) and O(4)–Al(2)–N(2) angles
O–C bond angle in 7 [149.75(12)°] is much larger than those of 173.70(8) and 177.22(8)°, respectively.
in compounds 4–6 [121.4(3)–127.66(11)°], presumably due
to the large steric congestion of the 1,1-diphenyl-2-propyl
fragment.
Figure 4. Molecular structure of compound 6. Thermal ellipsoids
are drawn at the 30% probability level. The hydrogen atoms have
been omitted for clarity.
Figure 6. Molecular structure of compound 8. Thermal ellipsoids
are drawn at the 30% probability level. The hydrogen atoms have
been omitted for clarity.
Figure 5. Molecular structure of compound 7. Thermal ellipsoids
are drawn at the 30% probability level. The toluene molecules and
the hydrogen atoms except the methane proton of the di-
phenylmethoxy group have been omitted for clarity.
Figure 7. Molecular structure of compound 9. Thermal ellipsoids
are drawn at the 30% probability level. The methylene molecules
and hydrogen atoms have been omitted for clarity.
Unlike the geometry of 8, compound 9 exhibits a center
of symmetry in which the Al2N2 forms a perfect plane.
The molecular structures of compounds 8 and 9 are Compound 9 consists of two five-coordinate aluminium
shown in Figure 6 and Figure 7, respectively. For com- centers, which can be described as distorted trigonal bi-
pound 8, the two nitrogen atoms of the NtBu fragments pyramidal. One oxygen atom of the diketiminate ligand and
bridge two aluminum atoms forming an Al2N2 four-mem- one of the bridged NtBu nitrogen atoms are located in axial
bered square with a dihedral angle of 14.2°. Again, the two positions with O(2)–Al(1)–N(2A) angles of 169.08(10)°.
pyrrolyl rings are located trans in the Al2N2 plane. Both the Note that the two pyrrolyl rings of 9 remain on the same
aluminium centers of 8 possess a five-coordinate geometry side of the Al2N2 plane, presumably due to the large steric
best described as distorted trigonal bipyramidal. One oxy- hindrance of the diphenyl–diketiminate ligands. Consider-
gen atom from the diketiminate fragment and one nitrogen ing the Al2N2 parallelograms of the dimeric aluminium
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 2459–2469

Dimeric Aluminium Hydrides Containing Pyrrolyl Ligands
compounds containing bidentate ligands, similar geome- gies and dipole moments of the bridged (B) and terminal
tries, presumably due to steric congestion, have been re- (T) forms of compounds 2–7, determined by the DFT ap-
ported by several groups.[16] The Al–N bond lengths of the proach, are shown in Scheme 4. The calculations show that
four-membered molecular units of compounds 4–7 the bridged forms of compounds 2–7 have lower energies,
[1.9395(9)–2.139(3) Å] are comparable to those previously but these results are only consistent with the experimental
published [1.993(2)–1.982(2) Å].[16] The Al–N–Al and N– findings for compounds 2 and 3. Note, the calculations can
Al–N bond angles of the molecular parallelograms of com- only be used to determine the gas-phase energies of com-
pounds 4–9 lie in the range 90.89(10)–95.05(10) and pounds 2–7, which favor the bridged form. The possible
86.05(8)–88.97(4)°, respectively, which are comparable to reasons for the differences between the calculations and the
those of previously reported dimeric aminoalanes, 89.21(13) results observed are solvent effects and different dipole mo-
and 91.03(10)°,[16a] 88.8(1) and 91.2(1)°,[16b] 91.63(12) and ments of the molecules. Different solvents can affect the
88.37(12)°,[16c] and 92.27(7) and 86.83(8)°.[16d]
molecular geometry and crystal packing during product
formation. In product formation, the solvent system and
molecular dipole moment are crucial for determining the
final geometries. The results shown in Scheme 4 demon-
strate that the crystal packing (formation of the crystal) fa-
vors the terminal form due to larger dipole moments.
Theoretical Calculations
The hydroalumination reactions of 1 with monoketones
generated two different Al–alkoxide bonding modes, that is,
bridged (compounds 2 and 3) and terminal alkoxides (com-
pounds 4–7). The reasons for the bonding of the alkoxide
fragment to aluminium at either terminal or bridging posi-
tions are still unclear. Therefore theoretical computations
Ring-Opening Polymerization of ε-Caprolactone
Compounds 2–10 were used as catalysts in the ring-open-
were performed by using the three-parameter hybrid of ex- ing polymerization of ε-caprolactone.[20] The results are
act exchange and Becke’s exchange energy functional,[17] presented in Table 3. The aluminium alkoxides 2–7 showed
plus Lee, Yang, and Parr’s gradient-corrected correlation good activity (entries 1–7) in the ring-opening polymeriza-
energy functional[18] (B3LYP). The Gaussian 03 suite of tion of ε-caprolactone, giving very high conversions. The
programs[19] was used in our study. The theoretical calcula- activity decreased in the order 7≈3=6≈5Ͼ4≈2. Com-
tions show that the total formation energies of these com- pounds 2 and 4 required a higher temperature and longer
pounds are determined by steric effects. The relative ener- time than other catalysts to reach full conversion, which
Scheme 4. Relative energies [kcal/mol] of the terminal and bridged forms of the aluminium complexes and their dipole moments [Debye].
Eur. J. Inorg. Chem. 2011, 2459–2469
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2465

J.-H. Huang, T.-Y. Lee et al.
FULL PAPER
suggests that alkoxide groups with greater angles between
the α carbon atoms and the neighboring two carbon atoms
possess greater activity. These angles are around 113.0,
112.2, 113.0, 109.6, and 103.3° for 7, 6, 5, 4, and 2, respec-
tively. This phenomenon might be a result of bulky substit-
uents on the α carbon of the alkoxides. However, the poly-
merization activities of the Al complexes might also be af-
fected by the lability of the alkoxides towards dissociation
or transformation of the dimeric aluminium species and the
number of sites of initiation. Compounds 3 and 6 yielded
PCL with higher Mw, which implies that the initiation effi-
ciency strongly depends on the nature of the alkoxide as
well as on the structure of the catalyst. The diketonate com-
pounds 8–10 exhibited very low or no activity (entries 9–
11) in the polymerization due to inertia of the ligands aris-
ing from the chelation of the alkoxides and therefore lack
of initiation group. The range of the polydispersity index
(PDI) of the poly(ε-caprolactone) product (1.26–1.47) is
comparable to or a little broader than that of polymers ob-
tained with other aluminium catalysts.[13,21]
Experimental Section
General Procedure: All reactions were performed under dry nitro-
gen using standard Schlenk or glove-box techniques. Toluene, di-
ethyl ether, and tetrahydrofuran were dried by heating at reflux
over sodium benzophenone ketyl. CH2Cl2 was dried with P2O5. All
solvents were distilled and stored in solvent reservoirs containing
4 Å molecular sieves and were purged with nitrogen. 1H and 13C
NMR spectra were recorded with a Bruker Avance 300 spectrome-
ter. Chemical shifts for 1H and 13C NMR spectra are given in ppm
relative to residual protons and 13C in CDCl3 (δ = 7.24, 77.0 ppm)
and C6D6 (δ = 7.15, 128.0 ppm). Elemental analyses were per-
formed with a Heraeus CHN-OS Rapid Elemental Analyzer at the
Instrument Center, National Chung Hsing University. [{C4H3N(2-
CH2NtBu)}AlH]2 (1) was prepared according to a previously re-
ported procedure.[13] All the chemicals (Aldrich, Acros) were used
as received.
[{C4H3N(2-CH2NtBu)}Al(OC9H9)]2 (2): 1-Indanone (0.38 g,
2.8 mmol) in dichloromethane (20 mL) solution was added through
a cannula to a solution of 1 (0.50 g, 1.4 mmol) in dichloromethane
(20 mL) at –78 °C. The reaction was complete within 30 min at
room temperature and the volatiles were removed under vacuum to
generate a pale-orange solid that was recrystallized from a toluene/
pentane mixed solution at –20 °C to yield 0.37 g of the final prod-
Table 3. Polymerization of ε-caprolactone (CPL) using compounds
1–10 as catalysts.
1
uct (42.5% yield). H NMR (CDCl3): δ = 0.74 (s, 18 H, NCMe3),
2.02, 2.59 (m, 4 H, CH2), 2.81, 3.03 (m, 4 H, CH2), 4.19, 4.96 (dd,
2JHH = 16.5 Hz, 4 H, CH2NCMe3), 5.55 (t, JHH = 6.6 Hz, 2 H,
OCH), 6.07 (s, 2 H, pyrrolyl CH), 6.45 (s, 2 H, pyrrolyl CH), 6.69
(s, 2 H, pyrrolyl CH), 7.27 (s, 8 H, phenyl CH) ppm. 13C{1H}
I[a] Temp. [°C]/ Conv. Activity
Mn,theor Mn,cor PDI
[b]
[c]
time [min]
[%]
[gpol molcat–1 h–1]
1
2
3
4
5
6
7
8
9
2
3
4
4
5
6
7
8
9
40/120
40/30
40/120
25/120
25/30
25/30
25/30
40/1080
40/1440
99
100
100
77
99
100
100
8
6000
24400
6050
4720
24200
24400
24600
80
11300
11414
11414
8789
11300
11414
11414
913
14494 1.47
17555 1.46
14027 1.43
NMR (CDCl3): δ = 28.7 (q, JCH = 128 Hz, NCMe3), 29.6 (t, JCH
=
130 Hz, CH2), 38.6 (t, JCH = 130 Hz, CH2), 44.0 (t, JCH = 138 Hz,
CH2NCMe3), 56.7 (s, NCMe3),76.7 (d, JCH = 137 Hz, OCH), 103.4
(d, JCH = 166 Hz, pyrrolyl CH), 114.1 (d, JCH = 167 Hz, pyrrolyl
7895
7001
1.26
1.26
31972 1.45
12111 1.37
12285 1.42
CH), 120.5 (d, JCH = 181 Hz, pyrrolyl CH), 123.9 (d, JCH
=
157 Hz, phenyl CH), 124.7 (d, JCH = 157 Hz, phenyl CH), 126.3
(d, JCH = 160 Hz, phenyl CH), 127.4 (d, JCH = 159 Hz, phenyl
CH), 137.2 (s, pyrrolyl Cipso), 142.4 (s, phenyl Cipso), 147.2 (s, phenyl
Cipso) ppm.
0
0
0
0
–
–
–
–
–
–
10 10 40/1440
[a] I = initiator. [b] Mn,theor = ([CPL]0/[4]0)ϫ114.14ϫconversion
1.073
for CPL.[20]
[{C4H3N(2-CH2NtBu)}Al{OCH(C12H8)}]2 (3): Similar procedures
as for compound 2 were used to synthesize 3. Reactants 1 (0.50 g,
1.4 mmol) and 9-fluorenone (0.52 g, 2.8 mmol) were used and the
reaction was carried out at room temperature for 1 h. A dark-pur-
ple solid was obtained in 63.2% yield (0.636 g). 1H NMR (CDCl3):
[%] for CPL. [c] Mn,cor = 0.259(Mn,GPC,St
)
2
δ = 0.89 (s, 18 H, NCMe3), 3.94, 4.74 (dd, JHH = 16.8 Hz, 4 H,
Conclusions
CH2NCMe3), 5.28 (s, 2 H, CH2Cl2), 5.89 (br. s, 4 H, OCH, pyrrolyl
CH), 6.30 (t, JHH = 2.7 Hz, 2 H, pyrrolyl CH), 6.33 (s, 2 H, pyrrolyl
CH), 7.23–7.66 (m, 16 H, C12H8) ppm. 13C{1H} NMR (CDCl3): δ
= 28.6 (q, JCH = 126 Hz, NCMe3), 44.0 (t, JCH = 141 Hz,
CH2NCMe3), 56.8 (s, NCMe3), 75.9 (d, JCH = 144 Hz, OCH),
103.3 (d, JCH = 165 Hz, pyrrolyl CH), 113.9 (d, JCH = 172 Hz,
pyrrolyl CH), 119.8 (d, JCH = 154 Hz, phenyl CH), 120.8 (d, JCH
= 182 Hz, pyrrolyl CH), 125.3 (d, JCH = 161 Hz, phenyl CH), 127.5
(d, JCH = 164 Hz, phenyl CH), 128.5 (d, JCH = 159 Hz, phenyl
CH), 136.9 (s, pyrrolyl Cipso), 139.7 (s, phenyl Cipso), 147.2 (s, phenyl
Cipso) ppm.
The reactivities of [{C4H3N(2-CH2NtBu)}AlH]2 (1) with
different ketones have been investigated and different types
of products, formed by either hydroalumination or insertion
reactions, were identified by NMR spectroscopic analyses.
We chose [{C4H3N(2-CH2NtBu)}AlH]2 as a starting mate-
rial because of its strong reactivity towards C=O-containing
functional organic molecules. The aluminium dihydride
shows high reactivity in these reactions. More interestingly,
we prepared two new dialkoxy-bridged dialuminium com-
plexes showing the reactivity of carbonyl towards hydro-
alumination. The activities of the Al complexes in the poly-
merization of ε-caprolactone are strongly dependent on the
nature of the alkoxide groups. Future work will explore the
mechanisms of the reactions of highly reactive symmetric
aluminium dihydride compound 1 in several applications in
organic synthesis.
[{C4H3N(2-CH2NtBu)}Al(OC6H9)]2 (4): Similar procedures as for
compound 2 were used to synthesize 4. Reactants 1 (0.50 g,
1.4 mmol) and 2-cyclohexen-1-one (0.280 mL, 2.8 mmol) were used
and the reaction was carried out at room temperature for 1 h. An
orange solid was obtained that was recrystallized from a dichloro-
methane/pentane mixed solution at –20 °C to yield 0.36 g of the
1
final product (yield 46.8%). H NMR (CDCl3): δ = 0.74 (s, 18 H,
NCMe3), 1.56–2.01 (m, 12 H, cyclohexene CH2), 4.13, 4.87 (dd,
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Dimeric Aluminium Hydrides Containing Pyrrolyl Ligands
2JHH = 17.1 Hz, 4 H, CH2NCMe3), 4.47 (br., 2 H, OCH), 5.69,
toluene CH) ppm. 13C{1H} NMR (CDCl3): δ = 21.4 (q, JCH
=
5.73 (m, 4 H, cyclohexene CH), 5.98 (s, 2 H, pyrrolyl CH), 6.37 (t, 26 Hz, toluene CH3), 25.3 (q, JCH = 126 Hz, CH3CHO), 28.4 (q,
JHH = 2.4 Hz, 2 H, pyrrolyl CH), 6.74 (s, 2 H, pyrrolyl CH) ppm.
JCH = 125 Hz, NCMe3), 43.3 (t, JCH = 141 Hz, CH2NCMe3), 56.2
(s, NCMe3), 62.5 (d, JCH = 126 Hz, CH3CHO), 71.1 (d, JCH
13C{1H} NMR (CDCl3): δ = 19.7 (t, JCH = 129 Hz, cyclohexene
=
CH2), 25.1 (t, JCH = 124 Hz, cyclohexene CH2), 28.6 (q, JCH
124 Hz, NCMe3), 34.5 (t, JCH = 130 Hz, cyclohexene CH2), 43.9
(t, JCH = 140 Hz, CH2NCMe3), 56.7 (s, NCMe3), 66.5 (d, JCH
141 Hz, OCH), 103.0 (d, JCH = 167 Hz, pyrrolyl CH), 113.8 (d,
JCH = 170 Hz, pyrrolyl CH), 120.4 (d, JCH = 181 Hz, pyrrolyl CH),
128.1 (d, JCH = 153 Hz, cyclohexene CH), 132.8 (d, JCH = 157 Hz,
cyclohexene CH), 137.5 (s, pyrrolyl Cipso) ppm.
=
142 Hz, Ph2CH), 103.1 (d, JCH = 167 Hz, pyrrolyl CH), 113.7 (d,
JCH = 170 Hz, pyrrolyl CH), 120.1 (d, JCH = 181 Hz, pyrrolyl CH),
125.3, 126.1, 128.1, 128.2, 128.3, 128.4, 128.8, 129.0, 137.4, 143.5
(m, phenyl CH, Cipso, toluene CH, pyrrolyl Cipso) ppm.
=
[{C4H3N(2-CH2NtBu)}Al{κO,κO-(OCMeCHCOMe)}]2 (8): Sim-
ilar procedures as for compound 2 were used to synthesize 8. Reac-
tants 1 (0.50 g, 1.4 mmol) and 2,4-pentanedione (0.28 g, 2.8 mmol)
were used and the reaction was carried out at room temperature
for 1 h. A yellow powder was obtained that was recrystallized from
a dichloromethane/toluene mixed solution at –20 °C to yield 0.55 g
[{C4H3N(2-CH2NtBu)}Al{OCH(Me)(C6H2-2,4,6-Me3)}]2 (5): Sim-
ilar procedures as for compound 2 were used to synthesize 5. Reac-
tants 1 (0.50 g, 1.4 mmol) and 1-(2,4,6-trimethylphenyl)-1-ethanone
(0.46 g, 2.8 mmol) were used and the reaction was carried out at
room temperature for 1 h. A pale-pink solid was obtained that was
recrystallized from a dichloromethane/heptane mixed solution at
–20 °C to yield 0.584 g of the final product (yield 61.2%). 1H NMR
1
of the final product (yield 70.9%). H NMR ([D8]toluene, 270 K):
δ = 1.06, 1.26, 1.49 (s, 18 H, NCMe3), 1.55 (s, 6 H, OCMe), 1.69
(s, 6 H, OCMe), 4.11 (s, 4 H, CH2NCMe3), 5.09 (s, 2 H,
OCCHCO), 6.18 (s, 2 H, pyrrolyl CH), 6.70 (s, 2 H, pyrrolyl CH),
(CDCl3): δ = 0.87 (s, 18 H, NCMe3), 1.56 (d, JHH = 6.6 Hz, 3 H, 6.98 (s, 2 H, pyrrolyl CH) ppm. 13C{1H} NMR ([D8]toluene,
OCHCH3), 2.13 (br. s, 3 H, phenyl CH3), 2.20 (s, 3 H, phenyl CH3), 270 K): δ = 26.1 (q, JCH = 128 Hz, OCMe), 27.1 (q, JCH = 128 Hz,
2
2.54 (br. s, 3 H, phenyl CH3), 4.10, 4.81 (dd, JHH = 16.5 Hz, 4 H,
CH2NCMe3), 5.60 (q, JHH = 2.8 Hz, OCHCH3), 5.98 (s, 2 H, pyr-
OCMe), 29.7 (q, JCH = 126 Hz, NCMe3), 44.6 (t, JCH = 131 Hz,
CH2NCMe3), 58.4 (s, NCMe3), 102.2 (d, JCH = 157 Hz, pyrrolyl
rolyl CH), 6.39 (t, JHH = 2.4 Hz, 2 H, pyrrolyl CH), 6.73 (s, 4 H, CH), 104.3 (d, JCH = 164 Hz, OCCHCO), 112.8 (d, JCH = 158 Hz,
pyrrolyl CH, phenyl CH) ppm. 13C{1H} NMR (CDCl3): δ = 20.5
(q, JCH = 139 Hz, phenyl CH3), 20.6 (q, JCH = 139 Hz, phenyl
CH3), 20.7 (q, JCH = 129 Hz, phenyl CH3), 24.9 (q, JCH = 126 Hz,
OCHCH3), 28.3 (q, JCH = 127 Hz, NCMe3), 45.6 (t, JCH = 140 Hz,
CH2NCMe3), 56.5 (s, NCMe3), 67.5 (q, JCH = 139 Hz, OCHCH3),
103.4 (d, JCH = 168 Hz, pyrrolyl CH), 114.0 (d, JCH = 164 Hz,
pyrrolyl CH), 120.5 (m, pyrrolyl CH, phenyl CH), 135.5 (s, phenyl
pyrrolyl CH), 124.0 (d, JCH = 178 Hz, pyrrolyl CH), 140.5 (s, pyr-
rolyl Cipso), 191.6 (s, OCCHCO), 197.0 (s, OCCHCO) ppm.
[{C4H3N(2-CH2NtBu)}Al{κO,κO-(OCPhCHCOPh)}]2 (9): Similar
procedures as for compound 2 were used to synthesize 9. Reactants
1 (0.50 g, 1.4 mmol) and dibenzoylmethane (0.63 g, 2.8 mmol) were
used and the reaction was carried out at room temperature for 1 h.
An orange powder was obtained that was recrystallized from a
dichloromethane/pentane mixed solution at –20 °C to yield 0.77 g
Cipso), 137.1 (s, phenyl Cipso), 139.0 (s, pyrrolyl Cipso) ppm.
[{C4H3N(2-CH2NtBu)}Al{OCH(C6H5)2}]2 (6): Similar procedures
as for compound 2 were used to synthesize 6. Reactants 1 (0.50 g,
1.4 mmol) and benzophenone (0.52 g, 2.8 mmol) were used and the
reaction was carried out at room temperature for 1 h. A yellow-
brown solid was obtained that was recrystallized from a dichloro-
methane/diethyl ether mixed solution at –20 °C to yield 0.502 g of
of the final product (yield 68.5%). 1H NMR (CDCl3): δ = 1.27 (br.,
2
18 H, NCMe3), 4.28 (s, 2 H, CH2NCMe3), 4.25, 4.69 (dd, JHH
=
17.1 Hz, 2 H, CH2NCMe3), 5.80 (s, 2 H, pyrrolyl CH), 6.12 (t, JHH
= 2.7 Hz, 1 H, pyrrolyl CH), 6.27 (t, JHH = 2.7 Hz, 1 H, pyrrolyl
CH), 6.35 (s, 1 H, pyrrolyl CH), 6.74 (s, 1 H, pyrrolyl CH), 7.03
(s, 1 H, COCHOC), 7.18 (s, 1 H, COCHOC), 7.40–8.27 (m, 20 H,
1
the final product (yield 49.7%). H NMR (CDCl3): δ = 0.89 (s, 18
phenyl CH) ppm. 13C{1H} NMR (CDCl3): δ = 30.1 (q, JCH
=
2
H, NCMe3), 4.24, 5.03 (dd, JHH = 16.7 Hz, 4 H, CH2NCMe3),
126 Hz, NCMe3), 43.7 (t, JCH = 135 Hz, CH2NCMe3), 44.5 (t, JCH
= 135 Hz, CH2NCMe3), 57.8 (s, NCMe3), 97.5 (d, JCH = 162 Hz,
6.09 (s, 2 H, Ph2CHO), 6.11 (s, 2 H, pyrrolyl CH), 6.25 (t, JHH
=
1.1 Hz, 2 H, pyrrolyl CH), 6.37 (s, 2 H, pyrrolyl CH), 7.15–7.49 COCHOC), 98.0 (d, JCH = 163 Hz, COCHOC), 100.6 (d, JCH
(m, 20 H, phenyl CH) ppm. 13C{1H} NMR (CDCl3): δ = 28.5 (q, 165 Hz, pyrrolyl CH), 100.8 (d, JCH = 165 Hz, pyrrolyl CH), 110.3
JCH = 125 Hz, NCMe3), 43.8 (t, JCH = 140 Hz, CH2NCMe3), 56.8 (d, JCH = 168 Hz, pyrrolyl CH), 111.0 (d, JCH = 156 Hz, pyrrolyl
(s, NCMe3), 77.1 (d, JCH = 141 Hz, Ph2CHO), 103.7 (d, JCH CH), 122.1 (d, JCH = 179 Hz, pyrrolyl CH), 122.5 (d, JCH
167 Hz, pyrrolyl CH), 114.0 (d, JCH = 169 Hz, pyrrolyl CH), 121.0 180 Hz, pyrrolyl CH), 128.1 (d, JCH = 160 Hz, phenyl CH), 128.5
=
=
=
(d, JCH = 182 Hz, pyrrolyl CH), 125.9 (d, JCH = 161 Hz, phenyl
CH), 126.2 (d, JCH = 154 Hz, phenyl CH), 126.7 (d, JCH = 160 Hz,
(d, JCH = 161 Hz, phenyl CH), 129.0 (d, JCH = 166 Hz, phenyl
CH), 132.3 (d, JCH = 161 Hz, phenyl CH), 133.8 (d, JCH = 162 Hz,
phenyl CH), 135.8, 137.5 (s, phenyl Cipso), 140.4, 140.9 (s, pyrrolyl
phenyl CH), 127.1 (d, JCH = 160 Hz, phenyl CH), 128.1 (d, JCH
=
160 Hz, phenyl CH), 128.3 (d, JCH = 160 Hz, phenyl CH), 136.8 (s, Cipso), 184.3, 186.9 (s, COCHOC) ppm.
pyrrolyl Cipso), 146.1 (s, phenyl Cipso), 147.0 (s, phenyl Cipso) ppm.
[{C4H3N(2-CH2NHtBu)}Al{κO,κO-(PhOC=COPh)}]2 (10): Similar
[{C4H3N(2-CH2NtBu)}Al{OCH(Me)(CHPh2)}]2 (7): Similar pro-
cedures as for compound 2 were used to synthesize 7. Reactants 1
(0.50 g, 1.4 mmol) and 1,1-diphenylacetone (0.2 g, 2.8 mmol) were
used and the reaction was carried out at room temperature for 1 h.
A pale-orange solid was obtained that was recrystallized from a
procedures as for compound 2 were used to synthesize 10. Reac-
tants 1 (0.50 g, 1.4 mmol) and benzil (0.59 g, 2.8 mmol) were used
and the reaction was carried out at room temperature for 1 h. A
brown solid was obtained that was recrystallized from a dichloro-
methane/pentane mixed solution at –20 °C to yield 0.73 g of the
1
dichloromethane/pentane mixed solution at –20 °C to yield 0.686 g
final product (yield 67.0%). H NMR (CDCl3): δ = 1.22 (s, 18 H,
1
of the final product (yield 63.0%). H NMR (CDCl3): δ = 0.85 (s, NCMe3), 2.32 (t, JHH = 8.4 Hz, 2 H, CH2NHCMe3), 3.45, 3.78 (m,
18 H, NCMe3), 1.26 (d, JHH = 5.1 Hz, 6 H, CH3CHO), 2.42 (s, 3 4 H, CH2NHCMe3), 5.92 (s, 2 H, pyrrolyl CH), 6.27 (t, JHH
=
2
H, toluene CH3), 3.66, 4.21 (dd, JHH
=
16.8 Hz,
4
H,
2.1 Hz, 2 H, pyrrolyl CH), 6.97 (s, 12 H, phenyl CH), 7.07 (s, 2 H,
CH2NCMe3), 3.85 (d, JHH = 8.1 Hz, 2 H, Ph2CH), 4.90 (m, JHH pyrrolyl CH), 7.36 (s, 8 H, phenyl CH) ppm. 13C{1H} NMR
= 6.3 Hz, 2 H, CH3CHO), 5.92 (s, 2 H, pyrrolyl CH), 6.44 (s, 2 H,
(CDCl3): δ = 27.4 (q, JCH = 128 Hz, NCMe3), 41.9 (t, JCH
=
pyrrolyl CH), 6.71 (s, 2 H, pyrrolyl CH), 7.19–7.51 (m, phenyl CH,
140 Hz, CH2NHtBu), 55.3 (s, NCMe3), 103.2 (d, JCH = 167 Hz,
Eur. J. Inorg. Chem. 2011, 2459–2469
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2467

J.-H. Huang, T.-Y. Lee et al.
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Crystallographic Structural Determination of 2 and 4–9: All the
crystals were mounted in capillaries, transferred to a goniostat, and
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with anisotropic displacement parameters. For all structures, the
positions of the hydrogen atoms were calculated and constrained
in idealized geometries by using a riding model in which the H
atom displacement parameters were calculated from the equivalent
isotropic displacement parameters of the bound atoms. The struc-
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and structure refinement parameters for 2 and 4–9 are summarized
in Table 1.
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CCDC-787609 (for 2), -787613 (for 4), -787611 (for 5), -787610 (for
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supplementary crystallographic data for this paper. These data can
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Acknowledgments
The authors gratefully acknowledge the National Science Council
of Taiwan for financial assistance. J. H. H. would also like to thank
the National Changhua University of Education for providing the
X-ray facility.
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Eur. J. Inorg. Chem. 2011, 2459–2469

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Received: January 11, 2011
Published Online: April 7, 2011
Eur. J. Inorg. Chem. 2011, 2459–2469
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2469