Versatile Bulky N,N′,N′-Substituted 1,2-Ethanediamine Ligands and Their Lithium, Aluminium, and Gallium Derivatives

Article abstract of DOI:10.1002/ejic.201601355

Sterically demanding N,N′,N′-substituted 1,2-ethanediamine ligands have been prepared from commercially available starting materials by applying a facile one-step procedure. These ligands offer advantages compared to known systems: a suppressed delocalization due to the saturated backbone inhibits a noninnocent behaviour and the low symmetry of the related metal complexes makes them potential candidates for asymmetric catalysis. The ligands are readily transformed into the corresponding lithium derivatives 4, which in turn act as starting materials to access the corresponding aluminium and gallium dichlorides 5 and 6, respectively. In addition, deprotonation by Al(CH₃)₃gives rise to the related dimethylalane 7. All main-group element compounds have been studied by means of single X-ray crystallography and spectroscopic methods.

Full text of DOI:10.1002/ejic.201601355

DOI: 10.1002/ejic.201601355
Full Paper
Main-Group Metal–Amide Compounds
Versatile Bulky N,N′,N′-Substituted 1,2-Ethanediamine Ligands
and Their Lithium, Aluminium, and Gallium Derivatives
Robert Kretschmer,*[a] Maximilian Dehmel,[a] and Michael Bodensteiner[b]
In memoriam Alvin Toffler
Abstract: Sterically demanding N,N′,N′-substituted 1,2-ethane- asymmetric catalysis. The ligands are readily transformed into
diamine ligands have been prepared from commercially avail- the corresponding lithium derivatives 4, which in turn act as
able starting materials by applying a facile one-step procedure. starting materials to access the corresponding aluminium and
These ligands offer advantages compared to known systems: a gallium dichlorides 5 and 6, respectively. In addition, deproto-
suppressed delocalization due to the saturated backbone inhib- nation by Al(CH3)3 gives rise to the related dimethylalane 7. All
its a noninnocent behaviour and the low symmetry of the re- main-group element compounds have been studied by means
lated metal complexes makes them potential candidates for of single X-ray crystallography and spectroscopic methods.
Introduction
Monoanionic N,N′-chelating ligands are valuable tools in main-
group and coordination chemistry with amidines (A),[1] ꢀ-diket-
imines (nacnac, B)[2] and guanidines (C)[1c,1d,3a,3b] being the
most prominent examples (Scheme 1). These systems allow for
the isolation of numerous main-group compounds in unusual
(low) oxidation states yielding species that show a versatile re-
activity.[4] In this context, the steric demands and electronic
properties of the ligand are of crucial importance and new
classes of ligands might provide access to so far unknown spe-
Scheme 1. Known monoanionic N,N′-chelating ligands in the deprotonated
cies. Recently, Stalke and co-workers introduced heterocyclic
substituted methanides (D)[5] as promising alternatives and also
other monoanionic N,N′-chelating ligands such as aminotro-
ponimines,[6] formazans[7] and anilidoimines[8] have been de-
scribed in the literature. Although most of them are conceived
as spectator ligands, recent results indicate a noninnocent be-
haviour and the redox activity becomes more likely in expan-
sively delocalized ligands.[9] In consequence, the intrinsic char-
acteristics of the metal centre within a certain complex are of-
ten masked and cannot be investigated to the full extent.
Inspired by the different chemical reactivity and coordination
chemistry of cyclic (alkyl)(amino)carbenes (CAACs, E)[10] com-
pared to “classical” N-heterocyclic carbenes (NHCs)[11] we be-
came interested in mimicking the steric properties of the
former within a monoanionic nonconjugated N,N′-chelating li-
form (A–D), cyclic (alkyl)(amino)carbenes (E) and the N,N′,N′-substituted 1,2-
ethanediamine ligand F presented in this work.
gand frame. The N,N′,N′-substituted 1,2-ethanediamines F meet
this characteristics and the saturated backbone should prevent
conjugation and therefore delocalization. Compound F differs
also in the donation behaviour compared to A–D; while for the
latter ligands, both nitrogen atoms act as σ and π donors, in F
this only holds true for the sp2-hybridized nitrogen as the terti-
ary amine renders merely σ donation. In addition, the steric
properties of the 1,2-ethanediamines are easily adjusted by
varying the substituents R, R′ and R′′, which makes them inter-
esting ligands also for transferring stereochemical information
in catalysis.
[a] Institut für Anorganische Chemie, Universität Regensburg,
Universitätsstraße 31, 93053 Regensburg, Germany
E-mail: robert.kretschmer@ur.de
http://www.ur.de/chemie-pharmazie/anorganische-chemie-kretschmer/
index.html
[b] Zentrale Analytik, Röntgenstrukturanalyse, Universität Regensburg,
Universitätsstrasse 31, 93053 Regensburg, Germany
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejic.201601355.
Results and Discussion
Synthesis of N,N′,N′-Substituted 1,2-Ethanediamines
The synthesis of the parent uncharged N,N′,N′-substituted 1,2-
ethanediamine ligand is achieved by the two procedures given
in Scheme 2. Route 1, that is the reaction of acetanilides 1 with
an excess of piperidine, gives rise to amino acetamides 2 that
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are subsequently reduced with lithium aluminium hydride.[12] that mirror symmetry of the ligands is maintained in these com-
This sequential procedure gives the corresponding 1,2-ethane- pounds. In addition, nitrogen and piperidine ring inversion
diamines 3b and 3e in an overall yield of 66 % and 79 %, re- within 3b and 3e proceeds smoothly at room temperature and
spectively. A more convenient one-step procedure is based on no separate signals are observed for the conformational iso-
the treatment of 2-chloro-N,N-dialkylethylamine hydrochlorides mers on the NMR time scale.
with an excess of the aniline of interest in the absence of sol-
vent. The N-aryl-N′,N′-dialkyl-1,2-ethanediamines are thus
formed quantitatively and obtained in good yields (71–77 %)
by a simple workup procedure. With 3f a ligand is obtained
that gives rise to a chiral nitrogen centre when bound to a
metal, which potentially allows for the transfer of stereochemi-
cal information. It is worthy to note that although N,N-dialk-
ylated products are usually observed in such nucleophilic sub-
stitution reactions,[13] no dialkylated anilines are detectable in
the reaction mixture. Depending on the substitution pattern,
the 1,2-ethanediamines are either liquids (3a–c,f) or solids (3d–
e) at ambient temperature.
Figure 1. Molecular structure of 3e (50 % probability ellipsoids), hydrogen
atoms (besides H1) have been omitted for clarity. Selected bond lengths [Å]
and angles [°]: C1–N1 1.4271(13), N1–C13 1.4637(13), C13–C14 1.5220(14),
C14–N2 1.4627(15), N2–C15 1.4633(14), N2–C19 1.4619(14), C1–N1–C13
115.71(8), C14–N2–C15 111.90(9), C15–N2–C19 109.73(9).
Synthesis and Characterization of the Lithium Derivatives
4
Deprotonation of the 1,2-ethanediamines 3b and 3e with n-
butyllithium in THF affords the lithium derivatives 4a and 4b,
respectively (Scheme 3). While 4b [R = CH(CH3)2] has only been
prepared in situ and used directly for the preparation of the
group 13 species 5 and 6 (vide infra), 4a (R = CH3) could be
isolated as a crystalline solid in 72 % yield. Overall, 4a possesses
a centrosymmetric, dimeric structure in the solid state (Figure 2)
Scheme 2. Synthetic routes to the parent N,N′,N′-substituted 1,2-ethanedi-
amine ligands 3.
similar to other bidentate lithium amides.[14] The core of the
tricyclic [5.3.0.0] ring system corresponds to a planar, diamond-
As an example, the molecular structure of 3e is depicted in shaped four-membered Li2N2 ring with a N1–Li1–N2 bond an-
Figure 1. Compound 3e crystallizes in the triclinic space group gle of 91.35(14)° that is significantly smaller than that of other
P1¯ with two molecules in the unit cell. Within 3e, the binding dimeric lithium amides, for which values between 103.5 and
pocket is preformed with an N1–C13–C14–N2 dihedral angle of 113.3° are observed.[14] The steric demands originating from
55.65(12)° and the piperidine ring shows the expected chair both the piperidine and the 2,6-dimethylphenyl moiety most
1
conformation. The H NMR spectroscopic data of 3a–e indicate likely account for this behaviour and also for the primary tran-
Scheme 3. Synthesis of the lithium species 4 and of a series of group 13 amidoamine compounds (5–7).
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soid laddering as observed for other lithium compounds with
bulky substituents.[15] As anticipated, N2 behaves as an sp3-ni-
trogen atom with a C10–N2–C11 angle of 109.65(15)°. The C1–
N1–C9 angle [115.908(14)°] is to some extent sharper as sup-
posed for an sp2 nitrogen, which is explained by the additional
bonding to Li1′. The piperidine ring shows the expected chair
conformation with C10 being in equatorial position. The ligand
backbone remains largely unaffected as indicated by C–C and
C–N bond lengths similar to the values we obtained for 3e.
Figure 3. Molecular structure of 5 (50 % probability ellipsoids), hydrogen
atoms have been omitted for clarity. Selected bond lengths and angles are
given in Table 1.
Table 1. Selected bond lengths and angles [Å] and angles [°] for 5 and 6.
5 (M = Al)
6 (M = Ga)
M–N1
M–N2
M–Cl1
M–Cl2
N1–C13
C13–C14
C14–N2
N1–M–N2
Cl1–M–Cl2
N1–M–Cl1
N1–M–Cl2
1.7899(17)
1.9863(17)
2.1248(7)
2.1332(7)
1.456(3)
1.529(3)
1.506(3)
90.16(8)
1.8406(15)
2.0381(17)
2.1777(5)
2.1669(5)
1.455(3)
1.532(3)
1.504(2)
89.10(7)
Figure 2. Molecular structure of 4a (50 % probability ellipsoids), hydrogen
atoms have been omitted for clarity. Selected bond lengths [Å] and angles
[°]: Li1–N1 1.962(3), Li1–N2 2.059(4), L1–N1′ 2.014(3), L1–L1′ 2.440(6), N1–C9
1.461(2), C9–C10 1.526(2), C10–N2 1.483(2), C1–N1–C9 115.90(14), C10–N2–
C11 109.62(15), N1–Li1–N2 91.35(14), N1–Li1–N1′ 104.27(15), N2–Li1–N1′
135.33(1).
107.73(3)
114.28(6)
120.52(6)
107.51(3)
120.41(5)
115.09(6)
Both, the 1H and the 13C NMR spectra in deuterated benzene
show only one singlet for the methyl groups, which suggests
mirror symmetry of the ligand. As anticipated, the coordination
of N2 by lithium inhibits both the nitrogen and ring inversion[16]
as indicated by separate signals for the axial and equatorial
protons; as a result of anisotropic effects, the axial protons show
smaller chemical shift values than their equatorial counterparts.
Ga–N (1.82–1.94 Å) bonds.[18] The brevity of the M–N1 bonds
has already been described before for similar aluminium[19] and
gallium[20] species and was attributed to a double-bond charac-
ter in the former case. However, currently there is general ac-
ceptance that the shortening results from an ionic bonding
component, which is due to an increased positive charge of the
metal, rather than from multiple bonding.[18,21a,21b] This argu-
ment is supported by the different Al–N1 bond lengths in 5 and
7 (vide infra); substitution of the electron-withdrawing chlorine
groups by the electron-donating methyl groups causes a bond
lengthening of about 0.05 Å. The N2–M bond lengths in 5 and
6 exceed the sum of the covalent radii in agreement with their
dative character. The aluminium–chlorine bonds within 5
[2.1248(7)–2.1332(7) Å] behave similar to those previously de-
scribed for the amidoamines AlCl2[N(C2H5)C2H4N(Me)2][19] and
AlCl2{N[C(Me)3]Si(Me)2N[C(Me)3]},[22] that is 2.125(1)–2.139(1)
and 2.109(1)–2.168(1) Å, respectively. They also match with the
bond lengths of 2.1185(4)–2.1344(4) Å observed for the ꢀ-diket-
iminatoaluminium dichloride AlCl2({(2,6-iPr2C6H3N)[C(Me)]}2-
CH).[23] In contrast, the Ga–Cl bonds [2.1669(5)–2.1777(5) Å] are
considerably shorter than for GaCl2{N[C(Me)3]C2H4NH[C(Me)3]}-
[2.172(1)–2.214(1) Å][20] and their nacnac analogue [2.218(1)–
Synthesis and Molecular Structures of the Group 13
Compounds
If the lithium derivative 4b [R = CH(CH3)2, generated in situ
from 3e and n-butyllithium] is treated with AlCl3 and GaCl3,
respectively, the corresponding aluminium and gallium species
5 and 6 can be obtained in good yields (79 % and 83 %, respec-
tively; Scheme 3). Crystals suitable for an X-ray diffraction analy-
sis of both, 5 and 6, are obtained by recrystallization from tolu-
ene. The isomorphous compounds 5 and 6 each crystallize in
the monoclinic space group P212121 with four molecules in the
asymmetric unit. Hence, the molecular structure of just one of
them, namely that of 5, is shown in Figure 3; the molecular
structure of 6 is given in the Supporting Information (Figure S1).
Selected structural parameters for both are listed in Table 1.
As expected, the N1–M distances are significantly shorter 2.228(1) Å].[23] The Cl1–M–Cl2 angles are nearly equal, having
than that of the N2–M bonds, reflecting the different nature of values of 107.73(3) and 107.51(3)° for M = Al and M = Ga, re-
bonding. The former fall quite below the values obtained from spectively. The N1–M–N2 bite angles of 5 and 6 reflect the dif-
the covalent radii approach for single bonds,[17] that is Al–N ferent M–N1 and M–N2 distances resulting in a narrower angle
(1.97 Å) and Ga–N (1.95 Å), but both N1–M distances match for the gallium [89.10(7)°] compared to that of the aluminium
values typically observed for covalent Al–N (1.78–1.85 Å) and derivative [90.16(8)°]. Finally, the impact of the metal atom on
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the ligand backbone is negligible and the differences in the chlorides. The corresponding lithium derivatives 4 and the re-
N1–C13, C13–C14 and C14–N2 bond lengths are within the lated dimethylalane 7 are easily obtained by deprotonation
standard deviations; they are all in accordance with values for with n-butyllithium and trimethylaluminium, respectively. Treat-
C–C and C–N single bonds.
ment of 4b with metal trichlorides MCl3 (M = Al, Ga) gives rise
to the corresponding aluminium and gallium dichlorides 5 and
6, respectively. The group 1 and 13 element compounds were
fully characterized by NMR spectroscopy and crystal structure
analysis. While 4a exists as a dimer in the solid state, 5, 6 and
7 are monomeric. In all main-group element compounds, the
metal atom is normally bonded to the amide nitrogen (N1),
while with the amine nitrogen (N2) a dative bond is formed
and the saturated ligand backbone remains unaffected from
metal chelation. Thus, the ligand system presented in this work
offers an interesting alternative to well established classes of
ligands such as amidines, ꢀ-diketimines and guanidines. The
low symmetry of the metal derivatives makes them potential
candidates for asymmetric catalysis. The reactivity of these new
group 13 species and the ligand behaviour of the 1,2-ethanedi-
amine towards transition metals is under active investigation.
Ligand 3e reacts selectively with trimethyl alane with elimi-
nation of methane and provides the dimethylalane 7 in good
yield (81 %; Scheme 3). In the H NMR spectrum of 7, the ab-
1
sence of any N–H proton and a sharp singlet at –0.80 ppm give
evidence of the desired product. Separate signals for the axial
and equatorial protons of the piperidine moiety indicate the
absence of ring inversion on the NMR time scale and the line
broadening is caused by additional diaxial couplings. X-ray
quality crystals were grown from n-pentane at –20 °C and the
molecular structure is shown in Figure 4. The aluminium atom
in 7 is normally bonded to amide N1 and datively bonded to
amine N2. The N1–Al and N2–Al distances [1.8359(7) and
2.0488(12) Å] in 7 are to some extent longer than those in 5.
This is probably due to the decreased positive charge on the
aluminium centre in 7 and a less ionic character of the N1–Al
bond as a result of the opposed electronic properties of the
methyl substituents compared to the chlorine atoms in 5. Simi-
lar values of 1.876(2) and 2.043(2) Å have been described for a
dibenzofuran-bridged bis(amidoamine)dimethylalane.[24] Along
with the increased Al–N bond lengths, the N1–Al–N2 angle de-
creases in comparison with that in 5 to 87.13(4)°. Finally, the
Experimental Section
General Remarks: All manipulations were performed by using
standard Schlenk and glovebox techniques under an atmosphere
of dry dinitrogen. Traces of oxygen and moisture were removed
C20–Al1–C21 angle of 112.37(7)° is significantly smaller than from the inert gas successively by passing it over a BASF R 3–11
(CuO/MgSiO3) catalyst, through concentrated sulfuric acid, over
coarsely granulated silica gel, and finally P4O10. Toluene and THF
were distilled from Na/benzophenone prior to use. The deuterated
solvents C6D6 and CDCl3 were dried by distillation from potassium
and CaH2, respectively. 1H, 13C and 27Al NMR spectra were recorded
with Bruker Avance 300 or 400 spectrometers and referenced to the
the corresponding angle in the nacnac-based dimethylalane
Al(Me)2{[(2,6-iPr2C6H3N)(CMe)]2CH} [117.40(13)°][25] but more
obtuse compared to the CH3–Al–CH3 angle of 108.48(7)°
in the amidoimine species Al(Me)2[(2,6-iPr2C6H3N)(CMe2)CH-
(2,6-iPr2C6H3N)].[26]
deuterated solvent (1H, 13C) and Al(NO3)3 27Al). High-resolution
(
mass spectra were measured by using a Jeol AccuTOF GCX (EI) and
a Waters LCT Micromass spectrometer, while elemental analyses of
4a, 5, 6 and 7 were performed with a Vario micro cube (Elementar
Analysensysteme GmbH). Compound 7 was too air and moisture
sensitive for reproducible, accurate microanalyses. Nevertheless, the
chemical integrity is established by crystallographic and spectro-
scopic data (HRMS, NMR). All the commercially purchased starting
materials were used as received. 2-[Ethyl-(methyl)amino]ethyl chlor-
ide hydrochloride has been prepared according to a literature pro-
cedure.[27]
Synthesis of N,N′,N′-Substituted 1,2-Ethanediamines
General Procedure: The related 2-chloro-N,N-dialkylethylamine
hydrochloride (97 mmol, 1 equiv.) was treated with either 2,6-di-
methylaniline or 2,6-diisopropylaniline (291 mmol, 3 equiv.). The
mixture was stirred at 130 °C for 3 d before it was transferred to a
beaker containing a sodium hydroxide solution (2 mol/L; 3 equiv.).
The biphasic mixture was extracted with ethyl acetate (2 ×) and the
combined organic layers were concentrated in vacuo. The remain-
ing oil was dissolved in n-pentane and the solution was extracted
with acetic acid (5 %, 1.5 equiv.). The aqueous layer was washed
with n-pentane (2 ×) to remove potential traces of aniline, before
the pH was adjusted to more than 12 by the addition of NaOH
chunks. The product was extracted (2 ×) with diethyl ether and the
combined organic layers were dried with Na2SO4 and concentrated
in vacuum to afford the desired product. All compounds are pure
Figure 4. Molecular structure of 7 (50 % probability ellipsoids), hydrogen
atoms and solvents molecules have been omitted for clarity. Selected bond
lengths [Å] and angles [°]: Al1–N1 1.8359(12), Al1–N2 2.0488(12), Al1–C20
1.9697(16), Al1–C21 1.9700(15), N1–Al1–N2 87.13(5), C20–Al1–C21 112.37(7).
Conclusions
In summary, a variety of N,N′,N′-substituted 1,2-ethanediamine
ligands 3 has been prepared by using a facile one-step proce-
dure. Their steric bulk is readily adjusted by the combination of
1
according to H and 13C NMR spectroscopy and the pale colour of
different anilines and 2-chloro-N,N′-dialkylethylamine hydro- 3a–d most likely arises from trace impurities in the corresponding
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anilines used as starting materials. Due to the lubricious nature of
[d, J = 7.0 Hz, 12 H, CH(CH3)2], 2.29 (s, 3 H, CH3-N), 2.51 [q, J =
3d, it was not possible to derive reproducible, accurate microanaly- 7.2 Hz, 2 H, CH2-CH3], 2.62 [t, J = 6.1 Hz, 2 H, CH2-N(CH3)(C2H5)],
ses.
2.99 [t, J = 6.1 Hz, 2 H, CH2-NH], 3.37 [sept, J = 7.2 Hz, 2 H, CH(CH3)2],
7.04–7.07 (m, 1 H, p-CHarom), 7.11–7.13 (m, 2 H, m-CHarom) ppm. 13
C
N-(2,6-Dimethylphenyl)-N′,N′-dimethylethane-1,2-diamine (3a):
Yield: 13.97 g (75 %), pale brown liquid. H NMR (CDCl3, 300 MHz):
NMR (100 MHz, CDCl3): δ = 12.68 (CH2-CH3), 24.40 [CH(CH3)2], 27.60
[CH(CH3)2], 41.47 (CH3-N), 49.09 (CH2-NH), 51.74 (CH2-CH3), 57.62
[CH2-N(CH3)(C2H5)], 123.24 (p-CHarom), 123.55 (m-CHarom), 142.07 (o-
1
δ = 2.32 (s, 6 H, CH3), 2.35 [s, 6 H, N(CH3)2], 2.52 [t, J = 5.9 Hz, 2 H,
CH2-N(CH3)2],3.11 [t, J = 5.9 Hz, 2 H, CH2-NH], 3.90 [s (broad), 1 H,
NH], 6.84 [t, J = 7.4 Hz, 1 H, p-CHarom], 7.03 [d, J = 7.4 Hz, 2 H, m-
CHarom] ppm. 13C NMR (CDCl3, 75 MHz): δ = 18.67 (CH3), 45.36
[N(CH3)2], 45.85 (CH2-NH), 59.35 [CH2-N(CH3)2], 121.26 (p-CHarom),
128.79 (m-CHarom), 128.84 (o-Carom), 146.73 (ipso-Carom) ppm. HR
ESI-MS: calcd. for C12H20N2 [M + H]+ 193.1705; found 193.1709.
C
arom), 144.05 (ipso-Carom) ppm. HR ESI-MS: calcd. for C17H30N2 [M +
H]+ 263.2487; found 263.2483.
Metallation Reactions
Compound 4a: A solution of 3b (2.32 g, 10 mmol) in THF (20 mL)
was cooled with an ice bath and treated dropwise with n-butyllith-
ium (7.5 mL, 1.6 mol/L in hexanes) yielding a yellow solution. After
stirring overnight at room temp., a green solution was formed. The
volatiles were removed in vacuo; the residue was washed with n-
hexane (2 × 10 mL) and dried in vacuo giving 4a as a colourless
crystalline solid. Yield: 1.76 g (7.2 mmol, 72 %). Crystals suitable for
an X-ray diffraction analysis were grown from a concentrated THF
solution at room temp. 1H NMR (300 MHz, C6D6): δ = 0.78 [t, J =
12.5 Hz, 1 H, CH2(4-pip,axial)], 0.93 [q, J = 12.5 Hz, 2 H, CH2(3,5-
pip,axial)] 1.20–1.38 [m, 5 H, CH2(pip)], 2.23–2.26 [m, 4 H, CH2(pip),
CH2-N(CH2)5], 2.39 (s, 6 H, CH3), 3.31 [t, J = 5.7 Hz, CH2-N], 6.82 [t,
J = 7.4 Hz, 1 H, p-CHarom], 7.16 [d, J = 7.4 Hz, 2 H, m-CHarom] ppm.
13C NMR (75 MHz, C6D6): δ = 21.68 (CH3), 24.41 [CH2(4-pip)], 26.50
[CH2(3,5-pip)], 50.43 (CH2-N), 53.85 [CH2(2,6-pip)], 62.14 [CH2-
N(CH2)5], 117.40 (p-CHarom), 129.69 (m-CHarom), 131.71 (o-Carom),
160.84 (ipso-Carom) ppm. C30H46Li2N4 (476.60): calcd. C 75.60, H 9.73,
N 11.76; found C 75.92, H 10.11, N 11.71.
2,6-Dimethyl-N-[2-(piperidin-1-yl)ethyl]aniline
(3b):
Yield:
17.33 g (77 %), pale yellow liquid. 1H NMR (CDCl3, 400 MHz): δ =
1.48–1.51 [m, 2 H, CH2(4-pip)], 1.63 [quin, J = 5.7 Hz, 4 H, CH2(3,5-
pip)], 2.33 (s, 6 H, CH3), 2.44 [s (broad), 4 H, CH2(2,6-pip)], 2.53 [t,
J = 5.7 Hz, 2 H, CH2-N(CH2)5], 3.09 [t, J = 5.7 Hz, 2 H, CH2-NH], 4.00
[s (broad), 1 H, NH], 6.80 [t, J = 7.5 Hz, 1 H, p-CHarom], 7.00 [d, J =
7.5 Hz, 2 H, m-CHarom] ppm. 13C NMR (CDCl3, 101 MHz): δ = 18.73
(CH3), 24.58 [CH2(4-pip)], 26.20 [CH2(3,5-pip)], 44.99 (CH2-NH), 54.51
[CH2(2,6-pip)], 58.60 [CH2-N(CH2)5], 121.10 (p-CHarom), 128.77 (m-
CHarom), 135.01 (o-Carom), 146.80 (ipso-Carom) ppm. HR ESI-MS: calcd.
for C15H25N2 [M + H]+ 233.2012; found 233.2011.
N-(2,6-Diisopropylphenyl)-N′,N′-dimethylethane-1,2-diamine
(3c): Yield: 17.56 g (73 %), pale red viscous liquid. 1H NMR (300 MHz,
CDCl3): δ = 1.28 [d, J = 6.9 Hz, 12 H, CH(CH3)2], 2.32 [s, 6 H, N(CH3)2],
2.54 [t, J = 5.7 Hz, 2 H, CH2-N(CH3)2], 2.99 [t, J = 5.7 Hz, 2 H, CH2-
NH], 3.34 [sept, J = 6.9 Hz, 2 H, CH(CH3)2], 3.68 [s (broad), 1 H, NH],
7.04–7.14 (m, 3 H, CHarom) ppm. 13C NMR (75 MHz, CDCl3): δ = 24.46
[CH(CH3)2], 27.60 [CH(CH3)2], 45.64 [N(CH3)2], 49.22 (CH2-NH), 59.62
[CH2-N(CH3)2], 123.36 (p-CHarom), 123.58 (m-CHarom), 142.15 (o-
Compound 5: Compound 3e (1.15 g, 4 mmol) was dissolved in
toluene (20 mL), cooled with an ice bath and treated dropwise with
n-butyllithium (2.5 mL, 1.6 mol/L in hexanes). The pale yellow solu-
tion was warmed to room temperature and stirred for 2 h. After
cooling to –78 °C, a solution of aluminium trichloride (525 mg,
4 mmol) in THF (10 mL) was added with a cannula. The ice bath
was removed and the mixture was stirred overnight at room temp.
The volatiles were removed in vacuo and the residue was extracted
with toluene (2 × 10 mL). The combined extracts were concentrated
(to about 3 mL) and crystals of 5, suitable for an X-ray diffraction
study, were grown upon standing at room temp. within 3 d. Yield:
1.20 g (3.1 mmol, 78 %), beige crystals. 1H NMR (300 MHz, C6D6):
δ = 1.22–1.27 [m, 12 H, CH(CH3)2], 1.51–1.58 [m, 1 H, CH2(pip)], 1.85
[d (broad), 3 H, CH2(pip)], 2.08–2.15 [m, 2 H, CH2(pip)], 2.67 [t
(broad), 2 H, CH2-N(CH2)5], 3.15–3.23 [m, 4 H, CH2-N, CH2(pip)], 3.59
[sept, J = 7.0 Hz, 2 H, CH(CH3)2], 3.62–3.68 [m, 2 H, CH2(pip)],7.11–
7.14 (m, 3 H, CHarom) ppm. 13C NMR (75 MHz, C6D6): δ = 22.53
[CH2(pip)], 23.01 [CH2(pip)], 24.97 [CH(CH3)2], 25.85 [CH(CH3)2], 27.63
[CH(CH3)2], 48.25 (CH2), 54.98 (CH2), 58.75 (CH2), 123.80 (m-CHarom),
124.80 (p-CHarom), 142.76 (o-Carom), 148.32 (ipso-Carom) ppm. HR EI-
MS: calcd. for C19H31AlCl2N2 [M]+ 384.1674; found 384.1680.
C19H31AlCl2N2·0.1C7H8: calcd. C 59.97, H 8.12, N 7.10; found C 59.75,
H 8.49, N 7.17.
C
arom), 143.80 (ipso-Carom) ppm. HR ESI-MS: calcd. for C16H28N2 [M
+ H]+ 249.2331; found 249.2359.
N-(2,6-Diisopropylphenyl)-N′,N′-diethylethane-1,2-diamine
(3d): Yield: 19.54 g (73 %), pale olive-green oil that crystallizes upon
standing. 1H NMR (300 MHz, CDCl3): δ = 1.12 [t, J = 7.1 Hz, 6 H,
CH3CH2], 1.30 [d, J = 6.9 Hz, 12 H, CH(CH3)2], 2.63 [q, J = 7.1 Hz, 4
H, CH3CH2], 2.73 [t, J = 5.8 Hz, 2 H, CH2-N(C2H5)2], 2.99 [t, J = 5.8 Hz,
2 H, CH2-NH], 3.41 [sept, J = 6.9 Hz, 2 H, CH(CH3)2], 3.84 [s (broad),
1 H, NH], 7.05–7.16 (m, 3 H, CHarom) ppm. 13C NMR (75 MHz, CDCl3):
δ = 11.88 (CH3CH2), 24.35 [CH(CH3)2], 27.55 [CH(CH3)2], 46.73
(CH3CH2),49.24 (CH2-NH), 53.60 [CH2-N(C2H5)2], 123.16 (p-CHarom),
123.49 (m-CHarom), 142.03 (o-Carom), 144.22 (ipso-Carom) ppm. HR ESI-
MS: calcd. for C18H32N2 [M + H]+ 277.2644; found 277.2653.
2,6-Diisopropyl-N-[2-(piperidin-1-yl)ethyl]aniline (3e): Yield:
19.83 g (71 %), white solid, after recrystallization from ethanol. 1H
NMR (400 MHz, CDCl3): δ = 1.27 [d, J = 6.9 Hz, 12 H, CH(CH3)2],
1.45–1.54 [m, 2 H, CH2(4-pip)], 1.64 [quin, J = 5.5 Hz, 4 H, CH2(3,5-
pip)], 2.48 [s (broad), 4 H, CH2(2,6-pip)], 2.58 [t, J = 5.7 Hz, 2 H, CH2-
N(CH2)5], 2.97 [t, J = 5.7 Hz, 2 H, CH2-NH], 3.37 [sept, J = 6.9 Hz, 2
H, CH(CH3)2], 3.96 (s, 1 H, NH), 7.05 [t, J = 7.5 Hz, 1 H, p-CHarom],
7.11 (d, J = 7.5 Hz, 2 H, m-CHarom) ppm. 13C NMR (101 MHz, CDCl3):
δ = 24.39 [CH(CH3)2], 24.67 [CH2(4-pip)], 26.33 [CH2(3,5-pip)], 27.56
[CH(CH3)2], 48.34 (CH2-NH), 54.84 [CH2(2,6-pip)], 58.67 [CH2-N(CH2)5],
123.27 (p-CHarom), 123.53 (m-CHarom), 142.15 (o-Carom), 144.06 (ipso-
Compound 6: Compound 3e (1.15 g, 4 mmol) was dissolved in
toluene (20 mL), cooled with an ice bath and treated dropwise with
n-butyllithium (2.5 mL, 1.6 mol/L in hexanes). The pale yellow solu-
tion was warmed to room temp. and stirred for 2 h. After cooling
to –78 °C, a solution of gallium trichloride (704 mg, 4 mmol) in
toluene (10 mL) was added with a cannula. The ice bath was re-
moved and the mixture was stirred overnight at room temp. The
solids were filtered off and washed with toluene (5 mL). The com-
C
arom) ppm. HR ESI-MS: calcd. for C19H33N2 [M + H]+ 289.2638; found
289.2640. C19H32N2 (288.48): calcd. C 79.11, H 11.18, N 9.71; found
C 78.99, H 10.90, N 9.49.
N-(2,6-Diisopropylphenyl)-N′-ethyl-N′-methylethane-1,2-di- bined filtrates were concentrated (to about 3 mL) and crystals, suit-
1
amine (3f): Yield: 18.81 g (74 %), pale red-brown viscous liquid. H
NMR (400 MHz, CDCl3): δ = 1.13 [t, J = 7.2 Hz, 3 H, CH2-CH3], 1.28
able for an X-ray diffraction study, were grown upon standing at
room temp. within three days. Yield: 1.42 g (3.3 mmol, 83 %), colour-
Eur. J. Inorg. Chem. 2017, 965–970
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969
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Full Paper
less crystals. 1H NMR (300 MHz, C6D6): δ = 0.68–0.78 [m, 1 H,
CH2(pip)], 1.06–1.16 [m, 3 H, CH2(pip)], 1.35 [d, J = 6.9 Hz, 6 H,
CH(CH3)2], 1.46 [d, J = 6.9 Hz, 6 H, CH(CH3)2], 1.70–1.82 [m, 4 H,
CH2(pip)], 2.30 [t, J = 5.8 Hz, 2 H, CH2-N(CH2)5], 3.04 [t, J = 5.8 Hz, 2
H, CH2-N], 3.13–3.17 [m, 2 H, CH2(pip)], 3.82 [sept, J = 6.9 Hz, 2 H,
CH(CH3)2], 7.18–7.20 (m, 3 H, CHarom) ppm. 13C NMR (75 MHz, C6D6):
δ = 22.57 [CH2(pip)], 22.68 [CH2(pip)], 25.30 [CH(CH3)2], 26.00
[CH(CH3)2], 28.07 [CH(CH3)2], 49.07 (CH2), 54.61 (CH2), 59.60 (CH2),
124.26 (m-CHarom), 126.04 (p-CHarom), 143.64 (o-Carom), 148.90 (ipso-
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1
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–0.80 [s, 6 H, Al(CH3)2], 1.19 [d, J = 7.0 Hz, 6 H, CH(CH3)2], 1.23 [d,
J = 7.0 Hz, 6 H, CH(CH3)2], 1.45–1.51 [m, 1 H, CH2(pip)], 1.81–1.85
[m, 5 H, CH2(pip)], 2.44–2.50 [m, 2 H, CH2(pip)], 3.02 [t, J = 5.8 Hz, 2
H, CH2-N(CH2)5], 3.16 (t, J = 5.8 Hz, 2 H, CH2-N), 3.39–3.45 [m, 2 H,
CH2(pip)], 3.66 [sept, J = 7.0 Hz, 2 H, CH(CH3)2], 7.06–7.12 (m, 3 H,
CHarom) ppm. 13C NMR (75 MHz, C6D6): δ = –7.38 [Al(CH3)2], 22.98
[CH2(pip)], 23.25 [CH2(pip)], 25.33 [CH(CH3)2], 26.30 [CH(CH3)2], 27.68
[CH(CH3)2], 50.24 (CH2), 53.99 (CH2), 59.27 (CH2), 123.93 (m-CHarom),
124.49 (p-CHarom), 146.95 (ipso-Carom), 148.80 (o-Carom) ppm. HR EI-
MS: calcd. for C21H37AlN2 [M]+ 344.2767; found 344.2764.
Supporting Information (see footnote on the first page of this
article): Ligand synthesis and analytical data and crystallographic
data for compounds 3e, 4a, 5, 6 and 7.
CCDC 1499676 (for 5), 1499677 (for 3e), 1499678 (for 6), 1499679
(for 7), and 1499680 (for 4a) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre.
Acknowledgments
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The project was financially supported by the Fonds der Chemis-
chen Industrie and the University of Regensburg. R. K. is grate-
ful to the Stiftung Stipendien-Fonds des Verbands der Chemis-
chen Industrie for a Liebig fellowship. Thanks are due to the
central analytical services of the University of Regensburg for
assistance with the analysis. Additionally, generous support
from Professor Manfred Scheer is gratefully acknowledged.
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Keywords: Aluminium · Gallium · Group 13 elements ·
Lithium · N ligands
Received: November 10, 2016
Eur. J. Inorg. Chem. 2017, 965–970
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970
© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim