Syntheses and reactions of derivatives of (Pyrrolylaldiminato)germanium(II) and -aluminum(III)

Article abstract of DOI:10.1021/om201252k

(Pyrrolylaldiminato)germanium(II) chloride, LGeCl (1), was prepared by reacting LLi (L = 2-(ArN=CH)-5-tBuC₄H₂N; Ar = 2,6-iPr ₂C₆H₃) with 1 equiv of GeCl₂? (dioxane). Treatment of LGeCl (1) with KOtBu or LiN(H)Ar yielded LGeR (R = OtBu (2), N(H)Ar (3)) by halide metathesis. (Pyrrolylaldiminato)methylaluminum chloride, LAlMe(Cl) (4), was obtained from the reaction of LLi and MeAlCl ₂ or by treating LH with Me₂AlCl in toluene. Treatment of LH with Me₂AlCl or AlCl₃ in Et₂O at -18 °C resulted in the 1:1 adducts LH?AlMe₂Cl (5) and LH?AlCl ₃ (5′), respectively. Further reaction of 4 with 2 equiv of LiNEt₂ led to the insertion of the NEt₂ group into the C=N bond together with the elimination of LiCl, to afford L′(NEt ₂)AlMe(NEt₂)Li(THF) (6). Similarly, treatment of 4 with 2 equiv of LiPPh₂(THF)₂ gave L′(PPh ₂)AlMe(OC₄H₈-PPh₂)Li(THF) ₂ (7) accompanied by ring opening of THF. Single-crystal X-ray structure determinations revealed that 3 and 4 each contained enantiomeric pairs, while 6 and 7 each adopted a single enantiomer.

Full text of DOI:10.1021/om201252k

Article
pubs.acs.org/Organometallics
Syntheses and Reactions of Derivatives of
(Pyrrolylaldiminato)germanium(II) and -Aluminum(III)
Ying Yang,†,‡ Na Zhao,† Hongping Zhu,*,† and Herbert W. Roesky*,§
†State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University,
361005 Xiamen, People's Republic of China
‡School of Chemistry and Chemical Engineering, Central South University, 410083 Changsha, People's Republic of China
§Institut fur Anorganische Chemie, Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: (Pyrrolylaldiminato)germanium(II) chloride,
LGeCl (1), was prepared by reacting LLi (L = 2-(ArN
CH)-5-tBuC4H2N; Ar = 2,6-iPr2C6H3) with 1 equiv of
GeCl2·(dioxane). Treatment of LGeCl (1) with KOtBu or
LiN(H)Ar yielded LGeR (R = OtBu (2), N(H)Ar (3)) by
halide metathesis. (Pyrrolylaldiminato)methylaluminum chlor-
ide, LAlMe(Cl) (4), was obtained from the reaction of LLi and
MeAlCl2 or by treating LH with Me2AlCl in toluene.
Treatment of LH with Me2AlCl or AlCl3 in Et2O at −18 °C
resulted in the 1:1 adducts LH·AlMe2Cl (5) and LH·AlCl3
(5′), respectively. Further reaction of 4 with 2 equiv of LiNEt2
led to the insertion of the NEt2 group into the CN bond together with the elimination of LiCl, to afford
L′(NEt2)AlMe(NEt2)Li(THF) (6). Similarly, treatment of 4 with 2 equiv of LiPPh2(THF)2 gave L′(PPh2)AlMe(OC4H8-
PPh2)Li(THF)2 (7) accompanied by ring opening of THF. Single-crystal X-ray structure determinations revealed that 3 and 4
each contained enantiomeric pairs, while 6 and 7 each adopted a single enantiomer.
ization of LGeCl (1) and LAlMe(Cl) (4) stabilized by a
pyrrolylaldiminato ligand (L = 2-(ArNCH)-5-tBuC4H2N; Ar
= 2,6-iPr2C6H3). Further derivatives were obtained through
metathesis with lithium or potassium reagents.
INTRODUCTION
■
Monoanionic bidentate nitrogen ligands are of particular
interest in stabilizing well-defined complexes with low-valent
or low-coordinate metal centers for the intriguing significance
of structure and reactivity. Representative examples are β-
diketiminato,1 amidinato,2 guanidinato,3 and aminotroponimi-
nato4 derivatives with advantageous feasibility in steric and
electronic modification of their auxiliary substituents to serve as
spectator ligands. In contrast, pyrrolylaldiminato ligands,5
which have a close resemblance to the salicylaldiminato
stereotype,6 have been less explored. Nevertheless, increasing
attention is being paid to the synthesis and application of
pyrrolylaldiminato complexes by virtue of their versatility in
bonding modes.7,8 Moreover, they are used in the polymer-
ization of ethylene,9−11 norbornene,12 and methyl methacry-
late,13 as well as in copolymerization of methyl acrylate and
olefins14 and oligomerization of ethylene.15 In this regard, we
have reported the synthesis of pyrrolylaldiminato complexes of
Zn, Mg, and Al.16 In terms of their structural features it was
noticed that most of the bis(pyrrolylaldiminato) complexes are
chiral. To our surprise, studies of the synthesis and reaction of
heteroleptic mono(pyrrolylaldiminato) complexes containing
mixed substituents are scarce. They might lead to interesting
enantiomers. Some mono(pyrrolylaldiminato) systems of
Ni(II)12,15 and Pt(II)17 exhibit cis/trans arrangement in a
square-planar conformation. In continuation of our research
interest, we describe herein the preparation and character-
RESULTS AND DISCUSSION
■
Reaction of LLi (L = 2-(ArNCH)-5-tBuC4H2N; Ar = 2,6-
iPr2C6H3) with 1 equiv of GeCl2·(dioxane) in Et2O resulted in
the facile elimination of LiCl and formation of the
pyrrolylaldiminato chlorogermylene LGeCl (1; Scheme 1) as
a pale yellow solid in moderate yield. In the 1H NMR spectrum
of 1 in C6D6, characteristic isopropyl patterns of two sets of
septets for methylene groups (3.12, 3.57 ppm) and four sets of
doublets for methyl groups (0.91−1.34 ppm) are observed due
to the asymmetric conformation with restricted rotation. This
result is in sharp contrast to the one septet and one doublet
pattern observed for LNa(THF).18 A high-field singlet (1.38
ppm) is assigned to the tBu group. A recent example of
enantiomeric chlorogermylene was reported using a bis-
(oxazoline) ligand.19 Further treatment of LGeCl (1) with
KOtBu and LiN(H)Ar resulted in the isolation of LGeOtBu
(2) and LGeN(H)Ar (3), respectively, by elimination of alkali-
metal chloride. The 1H NMR spectrum of LGeOtBu (2)
displays a pattern similar to that of LGeCl (1) with respect to
Received: December 17, 2011
Published: February 22, 2012
© 2012 American Chemical Society
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Scheme 1. Formation of Compounds 1−7 (Ar = 2,6-iPr2C6H3)
Figure 1. Molecular structures of the (a) SGe and (b) RGe forms of LGeN(H)Ar (3). Thermal ellipsoids are drawn at the 50% level, and all hydrogen
atoms, except those of the amine group, are omitted for clarity. Selected bond lengths (Å) and angles (deg): SGe, Ge(1)−N(1) = 2.104(4), Ge(1)−
N(2) = 2.006(4), Ge(1)−N(3) = 1.885(4), N(1)−Ge(1)−N(2) = 79.26(16), N(1)−Ge(1)−N(3) = 92.48(18), N(2)−Ge(1)−N(3) = 93.93(17);
RGe, Ge(3)−N(7) = 2.071(4), Ge(3)−N(8) = 2.008(4), Ge(3)−N(9) = 1.890(4), N(7)−Ge(3)−N(8) = 79.58(15), N(7)−Ge(3)−N(9) =
90.91(16), N(8)−Ge(3)−N(9) = 98.11(16).
the isopropyl resonances, but an additional singlet (1.48 ppm)
is assignable to the OtBu group, with the expected integral
ratios relative to those of the ligand backbone. In the 1H NMR
spectrum of LGeN(H)Ar (3) three sets of septets are observed,
which are due to the pyrrolylaldiminato ligand (3.31, 3.42 ppm)
and the arylamido substituent (3.11 ppm). The amido proton
resonance appears at 4.70 ppm, which is consistent with the
presence of a NH stretching absorption in the IR spectrum
(3399 cm−1).
Compounds LGeCl (1) and LGeOtBu (2) are readily soluble
in common organic solvents, and it is difficult to form crystals
of good quality. Crystals of LGeN(H)Ar (3) suitable for single-
crystal X-ray structural analysis were obtained from a
concentrated n-hexane solution. Compound 3 crystallizes in
are four crystallographically independent molecules per unit
cell. Three molecules can be described as having a SGe
configuration (Figure 1a), and the other one can be treated
as their enantiomer (RGe; Figure 1b).20 The Ge centers are all
three-coordinate, and each displays a pyramidal geometry, while
corresponding bond lengths and angles of discrete molecules
are highly comparable to each other. The terminal Ge−N
distances (1.885(4), 1.890(4) Å) are noticeably shorter than
those of the corresponding endocyclic pairs (2.006(4)−
2.104(4) Å). This observation is consistent with the previous
study of the β-diketiminato analogue iPrLGeN(H)Ar (iPrL =
CH[C(Me)N(Ar)]2).21
Treatment of LLi with 1 equiv of MeAlCl2 in Et2O resulted
in the formation of (pyrrolylaldiminato)methylaluminum
1
the triclinic space group P1. The molecular structure of 3 is
chloride, LAlMe(Cl) (4; Scheme 1), in modest yield. The H
̅
depicted in Figure 1, and crystal data and collection parameters
are given in Table S1 (see the Supporting Information). There
NMR spectrum of 4 features the isopropyl resonances as two
septets (3.03, 3.58 ppm) and four doublets (0.88−1.34 ppm).
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This is in marked contrast to the one septet and two doublets
pattern observed for LAlCl2 or LAlMe2.16,18 The high-field
singlet (−0.13 ppm) is due to a methyl group at the Al site with
correct integral ratio, which is shifted slightly downfield in
comparison with that of LAlMe2 (−0.23 ppm).16,18 Compound
4 crystallizes in the orthorhombic space group Pna21 (Table S1,
Supporting Information). The distorted-tetrahedral Al center is
surrounded by one methyl group, one chlorine, and two
nitrogen atoms. RAl-4 (Figure 2) and SAl-4 (Figure S1,
Me2AlCl conducted in toluene under reflux for 2 h afforded
LAlMe(Cl) (4) in high yield, by cleaving one of the Al−C
bonds with elimination of methane. The comparable adduct
LH·AlCl3 (5′) was also available from LH and AlCl3 in Et2O at
−18 °C. In sharp contrast to that of 5, the X-ray analysis of 5′
reveals that the NH functionality and the Ar group adopt a
trans arrangement (Figure S3, Supporting Information).
An equimolar reaction of LAlMe(Cl) (4) with LiNEt2
monitored with NMR spectroscopy indicated a partial (nearly
half) conversion of 4 into a new compound. Accordingly, the
reaction of LAlMe(Cl) (4) with 2 equiv of LiNEt2 was carried
out in THF on a preparative scale. From the concentrated n-
hexane extract a colorless crystalline solid of 6 was obtained. An
1
initial H NMR spectroscopic study of 6 reveals a upfield shift
of the AlMe proton resonance (−0.33 ppm) relative to that of
the precursor 4 (−0.13 ppm). Furthermore, a singlet emerges
at 4.87 ppm, which may imply a change other than a simple
metathesis process is involved in this reaction. The structure of
L′(NEt2)AlMe(NEt2)Li(THF) (6) was established by single-
crystal X-ray crystallography (Figure 3). Compound 6
Figure 2. Molecular structure of LAlMe(Cl) (RAl-4). Thermal
ellipsoids are drawn at the 50% level, and all hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Al(1)−N(1) = 1.9440(11), Al(1)−N(2) = 1.9053(11), Al(1)−C(22)
= 1.819(2), Al(1)−Cl(1) = 2.0911(9); N(1)−Al(1)−N(2) =
86.56(5), N(1)−Al(1)−C(22) = 113.46(11), N(2)−Al(1)−C(22) =
117.52(10), N(1)−Al(1)−Cl(1) = 109.71(4), N(2)−Al(1)−Cl(1) =
116.08(4), C(22)−Al(1)−Cl(1) = 111.09(11).
Supporting Information) share the same ligand skeleton in a
ratio of 2:1. The Al−C (1.819(2), 1.833(6) Å) and Al−Cl
(2.0911(9), 2.0607(14) Å) bond lengths are correspondingly
shorter than those observed in LAlMe2 (1.950(7) Å) and
LAlCl2 (2.111(2) Å).18
To modify the preparation of LAlMe(Cl) (4), an alternative
route was explored by intermolecular elimination of methane
from the ligand (LH) and metal alkyls (Me2AlCl). When this
reaction was first carried out in a small amount of Et2O at −18
°C, no precipitate or gas evolution was observed. After the
solution was stored at −18 °C for 2 days in a freezer, a colorless
crystalline solid was obtained. According to the spectroscopic
study, it turned out to be the 1:1 adduct of LH·AlMe2Cl (5)
instead of the initially targeted LAlMe(Cl) (4). In the IR
spectrum of 5, the NH stretching frequency is found at 3424
cm−1, corresponding to the singlet for the NH proton
resonance (8.49 ppm) in the 1H NMR spectrum. Furthermore,
the 1H NMR spectrum also exhibits a singlet (−0.14 ppm) due
to the AlMe2 group with expected integral ratio. The formation
of 5 was further documented by single-crystal X-ray structural
analysis (Figure S2, Supporting Information). Compound 5
crystallizes in the monoclinic space group P21/c, containing an
open chain like ligand, together with a slightly distorted
tetrahedral geometry around the aluminum center completed
by one nitrogen, one chlorine, and two methyl carbon atoms.
The short N(1)−C(1) bond length (1.290(5) Å) supports the
double-bond character, which is shorter in comparison with
that of the free pyrrolylaldiminato ligand stabilized nickel
complex (1.307(5) Å).8 The NH functionality is arranged cis to
the Ar group relative to the C(1)−C(2) bond. Compound 5 is
stable in the solid state or in Et2O solution at room temperature
but gradually degraded to LAlMe(Cl) (4) in toluene at elevated
temperatures. Consequently, the same reaction of LH with
Figure 3. Molecular structure of L′(NEt2)AlMe(NEt2)Li(THF) (6).
Thermal ellipsoids are drawn at the 50% level, and all hydrogen atoms,
except that of C(1), are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Al(1)−N(1) = 1.9023(19), Al(1)−N(2) = 1.895(2),
Al(1)−N(3) = 1.879(2), Al(1)−C(22) = 1.960(2), Al(1)···Li(1) =
2.781(4), N(1)−Li(1) = 2.352(5), N(3)−Li(1) = 2.101(5), N(4)−
Li(1) = 2.086(5), C(1)···Li(1) = 2.656(5), O(1)−Li(1) = 1.978(5);
N(1)−Al(1)−N(2) = 89.54(9), N(3)−Al(1)−C(22) = 117.03(11),
N(1)−Al(1)−C(22) = 110.95(9), N(2)−Al(1)−C(22) = 122.29(10).
crystallizes in the monoclinic space group P21/c. To our
surprise, 6 contains two NEt2 groups. One is bound to the Al
center, and the other is inserted into the CN bond of the
ligand. It has been previously reported that the CN moiety
can undergo alkylation or reduction to result in an amido-type
ligand. For example, an intramolecular benzylation of the imino
function of a (pyrrolylaldiminato)zirconium complex resulted
in an amidopyrrolyl complex,11 while the reduction of one
imino moiety of a bis(imino)pyrrolyl ligand of a lutetium
−
complex with BH4 generated a complex with both imino and
amido functionalities.22 In the current case, the pyrrolylaldimi-
nato ligand degraded to a dianionic amidopyrrolyl ligand,
denoted as L′(NEt2), so that compound 6 can be regarded as a
1:1 adduct of the neutral L′(NEt2)AlMe and LiNEt2(THF). To
accommodate the latter, the former acts both as a Lewis base
through its N sites and as a Lewis acid through its Al site. This
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could be the driving force to allow the reactions of NEt2
insertion and LiNEt2 inclusion under very mild conditions. This
is in sharp contrast to the metathesis reactions in the case of
LGeCl (1) and its derivatives. It is noticeable that in the core
structure of 6 those atoms that concomitantly form two
distorted four-membered Al(1)−N(3)−Li(1)−N(1) and
N(1)−Li(1)−N(4)−C(1) rings are all of tetrahedral geometry.
The coordination sphere of Al(1) is completed by three
nitrogen atoms and one methyl carbon atom, while Li(1) is
supported by three nitrogen atoms and one THF molecule.
According to the orientation of the Al−C bond relative to the
ligand backbone, it is suggested that the absolute configuration
of the parent RAl-4 is retained in 6. Moreover, the C(1) atom
forms a new chiral center adopting the R configuration. The
Al(1)−C(22) distance (1.960(2) Å) of 6 is relatively longer
than those observed in 4. The nonplanar Al(1)−N(3)−Li(1)−
N(1) core has long Li−N (2.101(5), 2.352(5) Å) and short
Al−N (1.879(2), 1.9023(19) Å) edges, which are consistent
with those observed in Me2Al[(PhCH2)2N]2Li(THF) (2.09 vs
1.912 Å).23
one methyl carbon, two nitrogens, and one oxygen atom. The
Al(1)−C(22) bond length (1.938(7) Å) is slightly shorter
relative to that of 6, while the Al(1)−O(1) distance (1.775(5)
Å) is marginally longer than those in [Me2AlN(2-C5H4N)-
Ph]2(O)Li2(THF)2 (1.746(5), 1.763(5) Å).25 In contrast to 6,
there are no intramolecular short contacts observed between Li
and N/C atoms in 7. In compensation, the LiOC4H8-PPh2
fragment is solvated by two THF molecules, and the Li+ cation
is coordinated by the phosphorus atom at C(1) to complete the
distorted-tetrahedral geometry. This arrangement generates an
AlOLiPCN six-membered heterocycle, sharing the C(1)−Al(1)
and Al(1)−N(1) edges with the contiguous C2N2Al ring. The
chiral C(1) atom adopts the R configuration, while Al(1)
follows the configuration of precursor SAl-4, as indicated by the
projecting direction of the Al−C linkage. Likewise, compound
7 can be viewed as a 1:1 adduct of the neutral L′(PPh2)AlMe
and LiOC4H8-PPh2(THF)2. Since RAl-4 is the major
component in the starting material, the exclusive formation of
7 with inherited SAl configuration may imply a flexible Al−
methyl inversion occurring via the possible intermediate
L′(PPh2)AlMe with a quasi-planar geometry around Al.26
In both 6 and 7 each methyl group on Al is oriented trans
with respect to the inserted R group (R = NEt2, PPh2) at the
chiral C(1) site. It is therefore suggested that the formation of
RAl-6 and SAl-7 is exclusively determined by the absolute
configuration of C(1) (Schemes S1 and S2, Supporting
Information). The preferred formation of the R configuration
at C(1) might be due to stereoselective reasons.
In a similar route, treatment of LAlMe(Cl) (4) with 2 equiv
of LiPPh2(THF)2 in toluene resulted in the formation of 7. In
1
the H NMR spectrum, the AlMe proton resonance (−0.22
ppm) is found shifted moderately upfield in comparison with
that of precursor 4 (−0.13 ppm). The 31P NMR spectrum
shows two resonances (−17.12, −40.74 ppm), indicating
different bonding modes of the phosphorus centers. The
structure of compound 7 (L′(PPh2)AlMe(OC4H8-PPh2)Li-
(THF)2) was studied by single-crystal X-ray structural analysis
(Figure 4). Compound 7 crystallizes in the triclinic space group
CONCLUSION
■
The novel pyrrolylaldiminato chlorogermylene LGeCl (1) and
methylaluminum chloride LAlMe(Cl) (4) have been prepared
and shown to be useful precursors for metathesis reactions. The
pyrrolylaldiminato ligand has several distinct features. First, it
can act as a neutral ligand to stabilize a chemically active species
such as dimethylaluminum chloride to form the 1:1 adduct
LH·AlMe2Cl (5) under mild conditions. Second, its asymmetric
character gives rise to enantiomerism in the derived complexes,
as observed in the single-crystal X-ray structural analysis of
LGeN(H)Ar (3) and LAlMe(Cl) (4), respectively. Third, the R
group from aluminum can be inserted into the CN bond of
the ligand L, which results in interesting complexes such as
L′(NEt2)AlMe(NEt2)Li(THF) (6) and L′(PPh2)AlMe(OC4H8-
PPh2)Li(THF)2 (7). Compound 6 as well as 7 adopts a single
enantiomer due to the preferential formation of the R
configuration at the newly created chiral carbon center.
Figure 4. Molecular structure of L′(PPh2)AlMe(OC4H8-PPh2)Li-
(THF)2 (7). Thermal ellipsoids are drawn at the 50% level, and all
hydrogen atoms, except that of C(1), are omitted for clarity. Selected
bond lengths (Å) and angles (deg): Al(1)−N(1) = 1.861(6), Al(1)−
N(2) = 1.898(5), Al(1)−C(22) = 1.938(7), Al(1)−O(1) = 1.775(5),
Al(1)···Li(1) = 3.163(13), P(2)−Li(1) = 2.722(15); N(1)−Al(1)−
N(2) = 88.6(2), O(1)−Al(1)−C(22) = 114.2(3), N(1)−Al(1)−
C(22) = 114.4(3), N(2)−Al(1)−C(22) = 121.2(3).
EXPERIMENTAL SECTION
■
Materials and Methods. All manipulations were carried out
under nitrogen by using Schlenk techniques or inside a MBraun
glovebox filled with argon, in which the calibrated values of O2 and
H2O were controlled below 1.2 ppm. Organic solvents, including
toluene, n-hexane, THF, and Et2O, were predried with sodium wire
and then heated with sodium/potassium benzophenone under
nitrogen prior to use. C6D6 was degassed, dried with sodium/
potassium alloy, and filtered before use. NMR spectra were recorded
on a Bruker AV 500 spectrometer. Melting points were measured in a
P1. Two PPh groups are involved in this compound; one is (as
̅
2
expected) to be inserted into the CN moiety, while the other
is bound to the metal centers through a ring-opened THF
molecule. An analogous insertion of ring-opened THF into the
M−P bond was previously demonstrated when iPrLYI2(THF)
was treated with [KP(H)Ar*(THF)]2 (Ar* = 2,6-(2,4,6-
iPr3C6H2)2C6H3).24 The Al(1) atom of 7 is surrounded by
sealed glass tube using a Buchi B-540 instrument without correction.
̈
IR spectra were recorded on a Nicolet 380 (Thermo Fisher Scientific)
spectrometer. Elemental analysis was performed with a Thermo Quest
Italia SPA EA 1110 instrument. Chemicals commercially available were
purchased from Aldrich and used as received. LH (L = 2-(ArNCH)-
5-tBuC4H2N; Ar
=
2,6-iPr2C6H3),10 GeCl2·(dioxane),27
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LiPPh2(THF)2,28 LiNEt2, and LiN(H)Ar29 were prepared as described
in the literature or by modified methods.
(w), 767.15 (s), 748.33 (s), 700.2 (w), 649.51 (vw), 566.5 (w), 462.44
(vw). Anal. Calcd for C33H47GeN3 (558.4): C, 70.98; H, 8.48; N, 7.53.
Found: C, 69.85; H, 8.43; N, 7.49.
LGeCl (1). At −18 °C nBuLi (0.42 mL, 2.4 M, 1 mmol) was added
drop by drop to a solution of LH (0.310 g, 1 mmol) in Et2O (30 mL).
The mixture was stirred and warmed to room temperature. Additional
stirring for 12 h ensured complete formation of LLi. To a solution of
GeCl2·(dioxane) (0.232 g, 1 mmol) in Et2O (20 mL) was added the
above solution of LLi at −18 °C. After stirring for another 12 h at
room temperature, the formed precipitate was filtered off and the
solvent was removed in vacuo. The residue was treated upon quick
washing with cold n-hexane (2 × 2 mL) and then dried under vacuum
to afford a pale yellow solid (0.26 g, 62%). Mp: 107 °C. 1H NMR (500
MHz, C6D6): δ 7.35 (s, 1H, CHN), 7.00−7.12 (m, 3H, Ar), 6.76 (d,
J = 3.9 Hz, 1H, pyrrole CH), 6.26 (d, J = 3.9 Hz, 1H, pyrrole CH),
3.57 (septet, 1H, CHMe2), 3.12 (septet, 1H, CHMe2), 1.38 (s, 9H,
CMe3), 1.34 (d, J = 6.7 Hz, 3H, CHMe2), 1.12 (d, J = 6.9 Hz, 3H,
CHMe2), 1.00 (d, J = 6.9 Hz, 3H, CHMe2), 0.91 (d, J = 6.8 Hz, 3H,
CHMe2) ppm. 13C NMR (126 MHz, C6D6): δ 163.80 (Ar), 155.59
(CHN), 144.81, 143.06, 138.64, 135.39, 124.86, 123.45 (Ar),
122.54, 113.39 (pyrrole CH), 33.50 (CMe3), 30.66 (CMe3), 29.32,
28.03 (CHMe2), 25.77, 24.42, 24.18, 23.91 (CHMe2) ppm. IR (Nujol
LAlMe(Cl) (4). Method a. To a solution of in situ formed LLi
(1 mmol) in Et2O (30 mL) was added a solution of MeAlCl2 (1
mL, 1.0 M, 1 mmol) at −18 °C with continuous stirring. The
resulting mixture was slowly warmed to room temperature and
stirred for 12 h. After workup, the LiCl precipitate was filtered
off and the solvent was removed in vacuo to give an off-white
solid. From the concentrated n-hexane extract at −18 °C,
colorless crystals of 4 were obtained (0.22 g, 56%).
Method b. A mixture of LH (1.552 g, 5 mmol) and Me2AlCl (5 mL,
1.0 M, 5 mmol) in toluene was heated under reflux for 2 h. After
workup, the volatile components were removed under vacuum to
afford a crystalline solid. From the concentrated n-hexane extract,
crystals of 4 were afforded (1.76 g, 91%). Mp: 147 °C. 1H NMR (500
MHz, C6D6): δ 7.36 (s, 1H, CHN), 7.00−7.12 (m, 3H, Ar), 6.70 (d,
J = 3.8 Hz, 1H, pyrrole CH), 6.27 (d, J = 3.8 Hz, 1H, pyrrole CH),
3.58 (septet, 1H, CHMe2), 3.03 (septet, 1H, CHMe2), 1.36 (s, 9H,
CMe3), 1.34 (d, J = 6.5 Hz, 3H, CHMe2), 1.13 (d, J = 6.8 Hz, 3H,
CHMe2), 0.94 (d, J = 6.9 Hz, 3H, CHMe2), 0.88 (d, J = 6.8 Hz, 3H,
CHMe2), −0.13 (s, 3H, AlMe) ppm. 13C NMR (125 MHz, C6D6): δ
165.20 (Ar), 159.88 (CHN), 144.41, 143.20, 139.36, 133.96, 124.52
(Ar), 124.41 (pyrrole CH), 123.68 (Ar), 113.63 (pyrrole CH), 33.53
(CMe3), 30.58 (CMe3), 28.20, 28.11 (CHMe2), 25.54, 25.54, 23.35,
22.49 (CHMe2), −6.1 (br, AlMe) ppm. 27Al NMR (130 MHz, C6D6):
mull, cm−1): ν
̃
1627 (m), 1592.72 (m), 1574.94 (vs), 1266.51 (s),
1231.34 (s), 1179.89 (m), 1099.65 (m), 1056.1 (s), 960.49 (m), 933.1
(m), 896.02 (m), 801.85 (m), 769.76 (m), 754.01 (m), 650.69 (w),
570.18 (w). Anal. Calcd for C21H29ClGeN2 (417.6): C, 60.4; H, 7.00;
N, 6.71. Found: C, 61.72; H, 7.02; N, 6.58.
LGeOtBu (2). To a solution of LGeCl (0.418 g, 1 mmol) in Et2O
(30 mL) was added a suspension of KOtBu (0.112 g, 1 mmol) in Et2O
at −18 °C with rigorous stirring. The reaction mixture was slowly
warmed to room temperature and stirred for an additional 12 h. After
filtration, the solvent was removed in vacuo to leave an oily paste. The
residue was extracted with a small portion of n-hexane (5 mL) and
then dried again under vacuum overnight to afford a light yellow solid
(0.31 g, 68%). Mp: 78 °C. 1H NMR (500 MHz, C6D6): δ 7.51 (s, 1H,
CHN), 7.00−7.11 (m, 3H, Ar), 6.82 (d, J = 3.8 Hz, 1H, pyrrole
CH), 6.37 (d, J = 3.8 Hz, 1H, pyrrole CH), 3.53 (septet, 1H, CHMe2),
3.32 (septet, 1H, CHMe2), 1.48 (s, 9H, OCMe3), 1.34 (s, 9H, CMe3),
1.26 (d, J = 6.6 Hz, 3H, CHMe2), 1.19 (d, J = 6.9 Hz, 3H, CHMe2),
0.96 (d, J = 6.9 Hz, 3H, CHMe2), 0.88 (d, J = 6.8 Hz, 3H, CHMe2)
ppm. 13C NMR (126 MHz, C6D6): δ 161.59 (Ar), 154.82 (CHN),
144.02, 142.87, 140.52, 135.16, 123.66, 123.44 (Ar), 120.10, 112.14
(pyrrole CH), 70.74 (OCMe3), 33.53 (CMe3), 33.43 (CMe3), 30.46
(OCMe3), 28.71, 27.57 (CHMe2), 26.45, 24.52, 24.31, 23.56 (CHMe2)
δ 62.21 ppm. IR (Nujol mull, cm−1): ν
̃
1593.28 (m), 1573.69 (s),
1397.21 (w), 1326.38 (w), 1268.18 (m), 1233.47 (m), 1199.87 (w),
1186.91 (w), 1108.2 (vw), 1061.08 (s), 1031.65 (w), 933.8 (vw),
910.29 (w), 804.96 (w), 779.05 (w), 758.81 (w), 694.49 (vw), 664.08
(w), 572.57 (vw), 473.74 (w). Anal. Calcd for C22H32AlClN2 (386.9):
C, 68.29; H, 8.34; N, 7.24. Found: C, 67.94; H, 8.13; N, 7.08.
LH·AlMe2Cl (5). To a solution of LH (0.310 g, 1 mmol) in Et2O (5
mL) was added a solution of Me2AlCl (1 mL, 1.0 M, 1 mmol) at −18
°C with stirring. The resulting mixture was stored at −18 °C in a
freezer for 2 days. Colorless crystals of 5 were formed (0.19 g, 48%).
1
Mp: 146 °C. H NMR (500 MHz, C6D6): δ 8.49 (s, 1H, NH) 6.93−
7.07 (br, 3H, Ar), 6.98 (s, 1H, CHN), 6.19 (d, J = 3.8 Hz, 1H,
pyrrole CH), 5.56 (d, J = 3.8 Hz, 1H, pyrrole CH), 3.37 (septet, 2H,
CHMe2), 1.24 (d, J = 6.8 Hz, 6H, CHMe2), 0.68 (d, J = 6.7 Hz, 6H,
CHMe2), 0.62 (s, 9H, CMe3), −0.14 (s, 6H, AlMe) ppm. 13C NMR
(125 MHz, C6D6): δ 160.46, 156.45, 142.33 (Ar), 128.17 (CHN),
125.02 (Ar), 129.07, 107.58 (pyrrole CH), 31.30 (CMe3), 28.57
(CMe3), 28.24 (CHMe2), 23.61 (CHMe2), −8.07 (br, AlMe) ppm. 27Al
ppm. IR (Nujol mull, cm−1): ν
̃
1623.44 (vs), 1592.43 (vs), 1574.95
(vs), 1509.25 (vs), 1485.82 (vs), 1382.26 (vs), 1328.99 (s), 1298.8
(vs), 1268.21 (vs), 1232.98 (vs), 1181.89 (vs), 1106.02 (s), 1054.15
(vs), 1024.08 (s), 935.39 (vs), 892.73 (s), 858.22 (s), 800.73 (vs),
765.96 (vs), 754.34 (vs), 744.9 (s), 727.89 (s), 710.12 (s), 652.11 (s),
613.53 (vs), 567.46 (s). Anal. Calcd for C25H38GeN2O (455.2): C,
65.96; H, 8.41; N, 6.15. Found: C, 65.5; H, 8.51; N, 5.99.
NMR (130 MHz, C6D6): δ 61.48 ppm. IR (Nujol mull, cm−1): ν
̃
3424.18 (vw, NH), 1605.62 (w), 1584.16 (w), 1528.81 (w), 1258.68
(w), 1237.76 (w), 1186.47 (w), 1055.17 (w), 995.38 (w), 961.66 (w),
934.53 (vw), 895.05 (w), 807.85 (w), 785.41 (w), 675.19 (w), 569.17
(vw), 530.43 (vw), 470.15 (vw), 435.04 (vw). Anal. Calcd for
C23H36AlClN2 (403.0): C, 68.55; H, 9.00; N, 6.95. Found: C, 66.62;
H, 8.84; N, 6.85.
LGeN(H)Ar (3). The preparation of 3 is similar to that of 2 using
LiN(H)Ar (0.183 g, 1 mmol) and LGeCl (0.418 g, 1 mmol) as starting
materials. Compound 3 was obtained as pale yellow crystals from n-
LH·AlCl3 (5′). The preparation of 5′ was carried out as for 5 using
1
LH (0.310 g, 1 mmol) and AlCl3 (0.133 g, 1 mmol) to afford a
hexane extract at −18 °C (0.40 g, 71%). Mp: 91 °C. H NMR (500
1
colorless crystalline solid (0.21 g, 48%). Mp: 208 °C. H NMR (500
MHz, C6D6): δ 7.52 (s, 1H, CHN), 7.00−7.12 (m, 6H, Ar), 6.81 (d,
J = 3.8 Hz, 1H, pyrrole CH), 6.36 (d, J = 3.8 Hz, 1H, pyrrole CH),
4.70 (s, 1H, NH), 3.42 (septet, 1H, CHMe2), 3.31 (septet, 1H,
CHMe2), 3.11 (septet, 2H, CHMe2), 1.37 (s, 9H, CMe3), 1.31 (d, J =
6.8 Hz, 3H, CHMe2), 1.19 (d, J = 6.8 Hz, 6H, CHMe2), 1.09 (d, J = 6.9
Hz, 3H, CHMe2), 1.01 (d, J = 6.7 Hz, 6H, CHMe2), 0.94 (d, J = 6.8
Hz, 3H, CHMe2), 0.92 (d, J = 6.8 Hz, 3H, CHMe2) ppm. 13C NMR
(126 MHz, C6D6): δ 161.62 (Ar), 154.39 (CHN), 144.03, 143.37,
143.07, 140.51, 135.06, 134.84, 124.26, 123.43, 123.37 (Ar), 120.75
(pyrrole CH), 118.08 (Ar), 112.57 (pyrrole CH), 33.30 (CMe3), 30.99
(CMe3), 29.23 (CHMe2), 29.02, 28.54 (CHMe2), 24.50, 23.09
(CHMe2), 26.03, 24.74, 23.41, 23.41 (CHMe2) ppm. IR (Nujol
MHz, C6D6): δ 8.42 (s, 1H, NH), 6.96−7.06 (br, 3H, Ar), 6.98 (s, 1H,
CHN), 6.17 (m, 1H, pyrrole CH), 5.55 (m, 1H, pyrrole CH), 3.41
(septet, 2H, CHMe2), 1.32 (d, J = 6.8 Hz, 6H, CHMe2), 0.67 (d, J =
6.8 Hz, 6H, CHMe2), 0.59 (s, 9H, CMe3) ppm. 13C NMR (125 MHz,
C6D6): δ 157.75, 156.79, 143.60 (Ar), 129.33 (CHN), 125.43 (Ar),
132.59, 109.26 (pyrrole CH), 31.53 (CMe3), 28.57 (CHMe2), 28.33
(CMe3), 23.76, 23.56 (CHMe2) ppm. 27Al NMR (130 MHz, C6D6): δ
61.79 ppm. IR (Nujol mull, cm−1): ν
̃
3361.64 (m, NH), 1600.64 (s),
1584.41 (s), 1417.07 (s), 1405.08 (s), 1262.97 (s), 1206.68 (m),
1098.26 (w), 1067.21 (m), 1028.68 (w), 988.36 (m), 963.98 (m),
915.61 (s), 819.21 (w), 804.64 (m), 796.15 (s), 781.73 (m), 695.25
(w), 653.83 (w), 549.95 (m), 530.04 (m), 495.93 (m), 438.12 (m),
417.52 (m). Anal. Calcd for C21H30AlCl3N2 (443.8): C, 56.83; H, 6.81;
N, 6.31. Found: C, 57.01; H, 6.72; N, 6.45. Crystals of 5′ suitable for
single-crystal X-ray analysis were grown from Et2O solution.
mull, cm−1): ν
̃
3399.42 (vw, −NH), 1593.51 (s), 1575.52 (vs),
1509.74 (m), 1335.28 (s), 1268.37 (s), 1231.75 (s), 1203.47 (m),
1178.45 (m), 1153.71 (m), 1108.15 (m), 1054.2 (vs), 1023.05 (m),
961.47 (w), 932.31 (m), 884.94 (m), 842.97 (m), 801.69 (m), 784.99
1962
dx.doi.org/10.1021/om201252k | Organometallics 2012, 31, 1958−1964

Organometallics
Article
L′(NEt2)AlMe(NEt2)Li(THF) (6). To a THF solution (40 mL) of
LAlMe(Cl) (4; 0.387 g, 1 mmol) at −18 °C was added a solution of
LiNEt2 (0.158 g, 2 mmol) in THF (10 mL). The mixture was stirred
for 12 h at room temperature, and all volatiles were removed in vacuo.
From the concentrated Et2O extract, a crystalline solid was obtained
(0.41 g, 72%). Mp: 124 °C. 1H NMR (500 MHz, C6D6): δ 7.06−7.37
(m, Ar), 6.48 (d, J = 3.4 Hz, 1H, pyrrole CH), 6.26 (d, J = 3.0 Hz, 1H,
pyrrole CH), 4.87 (s, 1H, CHN), 3.38 (m, 4H, O-CH2 THF), 3.25 (q,
J = 6.9 Hz, 2H, −CH2CH3), 3.02 (q, J = 6.9 Hz, 2H, −CH2CH3), 3.01
(septet, 1H, CHMe2), 2.87 (q, J = 6.9 Hz, 4H, −CH2CH3), 2.58
(septet, 1H, CHMe2), 1.63 (s, 9H, CMe3), 1.37 (d, J = 6.9 Hz, 3H,
CHMe2), 1.35 (d, J = 6.9 Hz, 3H, CHMe2), 1.26 (m, 4H, CH2 THF),
1.23 (d, J = 6.9 Hz, 3H, CHMe2), 1.15 (d, J = 6.7 Hz, 3H, CHMe2),
0.93 (t, J = 6.9 Hz, 6H, −CH2CH3), 0.64 (t, J = 7.0 Hz, 6H,
−CH2CH3), −0.32 (s, 3H, AlMe) ppm. 13C NMR (126 MHz, C6D6):
δ 159.47, 151.97, 146.50, 145.90, 141.56, 136.53, 125.88, 122.72,
122.28 (Ar), 107.41, 106.19 (pyrrole CH), 82.52 (CH−N), 68.34 (O−
CH2 THF), 42.89, 41.49 (CHMe2), 40.47 (−CH2CH3), 32.71
(CMe3), 31.79 (CMe3), 28.44, 27.19 (−CH2CH3), 25.63, 25.97,
25.91, 24.61 (CHMe2), 24.90 (CH2 THF), 13.71 (−CH2CH3), −11.7
(br, AlMe) ppm.; 27Al NMR (130 MHz, C6D6): δ 61.45 ppm. IR
ASSOCIATED CONTENT
■
S
* Supporting Information
Molecular structures of LAlMe(Cl) (SAl-4, Figure S1),
LH·AlMe2Cl (5, Figure S2), and LH·AlCl3 (5′, Figure S3),
cell parameters, data collection, and structure solution and
refinement details for compounds 3−7 (Table S1), and CIF file
giving crystallographic data for 3−5, 5′, 6, and 7. This material
is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*H.Z.: fax, (+86) 592-2181912; e-mail, hpzhu@xmu.edu.cn.
H.W.R.: fax, (+49) 551-393-373; e-mail, hroesky@gwdg.de.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the NSFC (Nos. 20902112,
20972129, and 20423002), the China Postdoctoral Science
Foundation (No. 20090460748), and the Deutsche For-
schungsgemeinschaft.
(Nujol mull, cm−1): ν
̃
1572.54 (vw), 1300.34 (m), 1283.99 (m),
1249.33 (w), 1232.67 (w), 1205.14 (w), 1181.2 (w), 1161.73 (w),
1139.81 (w), 1106.68 (w), 1073.83 (w), 1037.81 (w), 1002.74 (w),
941.74 (w), 894.3 (w), 872.7 (w), 799.75 (vw), 761.36 (w), 740.75
(w), 700.63 (vw), 660.58 (w), 618.73 (vw), 586.27 (vw), 511.1 (vw),
412.07 (w). Anal. Calcd for C34H60AlLiN4O (574.8): C, 71.05; H,
10.54; N, 9.75. Found: C, 70.26; H, 10.83; N, 9.68. Crystals of 6
suitable for single-crystal X-ray analysis were grown from n-hexane
solution.
REFERENCES
■
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1963
dx.doi.org/10.1021/om201252k | Organometallics 2012, 31, 1958−1964

Organometallics
Article
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