Synthesis and Structures of Dinuclear Aluminum Complexes Based on Bis(β-diketiminate) Ligands

Article abstract of DOI:10.1002/zaac.201900193

A series of ten dinuclear aluminum alkyl complexes based on rigid, semirigid, and flexible bis(β-diketiminate) ligands (NacNac) has been obtained from the reaction of trimethylaluminum and the corresponding bis(β-diketimine)s. All compounds were fully characterized using NMR and IR spectroscopy and elemental analysis. The molecular structures of five compounds have been investigated by means of single-crystal X-ray diffraction analysis.

Full text of DOI:10.1002/zaac.201900193

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.201900193
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Synthesis and Structures of Dinuclear Aluminum Complexes Based
on Bis(β-diketiminate) Ligands
Marcella E. Desat[a] and Robert Kretschmer*[a,b]
Dedicated to Manfred Scheer on the Occasion of his 65th Birthday
Abstract. A series of ten dinuclear aluminum alkyl complexes based terized using NMR and IR spectroscopy and elemental analysis. The
on rigid, semirigid, and flexible bis(β-diketiminate) ligands (NacNac)
has been obtained from the reaction of trimethylaluminum and the
corresponding bis(β-diketimine)s. All compounds were fully charac-
molecular structures of five compounds have been investigated by
means of single-crystal X-ray diffraction analysis.
Introduction
ketiminates do not necessarily behave as spectator ligands and
their (hidden) non-innocence is an interesting feature in terms
of reactivity.[3,4] Poly(β-diketiminate)s have been recently
emerged as useful tools in coordination chemistry,[5] and the
respective bis(β-diketiminate)s grant access to both, mono-[6]
and polynuclear complexes,[7] not only depending on the re-
spective element and the experimental protocol, but also on
the ligand framework. In this regard, three types of bis(β-di-
ketimine)s have to be considered: (i) nitrogen-bridged, (ii)
backbone-bridged, and (iii) macrocyclic derivatives (Fig-
Since the first reports on transition-metal complexes of β-
diketiminate ligands, also known as β-diiminate or NacNac
ligands, in 1968,[1] these ligand class has been frequently used
to stabilize a variety of elements from all sections of the
periodic table and in unusual oxidation states.[2] Today,
β-diketiminates belong to the most ubiquitous ligands in coor-
dination chemistry, mostly because their electronic and steric
features can readily be altered through variation of the ligand
backbone and/or the terminal substituents at the nitrogen
atoms, Figure 1a.[3] However, it has been shown that β-di- ure 1b).
Figure 1. (a) β-diketimines and (b) various types of bis(β-diketimine)s.
The steric constraints of the ligand impact both, the element-
element separation and the relative orientation of the two ele-
mental centers. These aspects are very relevant in terms of
cooperative catalysis, i.e. the concept of utilizing two or more
catalytically active centers in one reaction system,[8] which is
one of the most promising concepts in catalysis by main-group
elements as it allows promoting chemical transformations that
hitherto have been believed to be limited to transition metals.
In their seminal work, Normand et al. could prove that a dinu-
clear aluminum complex excels its mononuclear counterpart in
terms of activation free energy giving rise to a 5-to-10 fold
increase in activity in the ring-opening polymerization (ROP)
of racemic lactide.[9] Although in the following years various
dinuclear aluminum(III) complexes have been probed as coop-
erative catalysts, mostly in the ROP of lactide,[10] systematic
* Prof. Dr. R. Kretschmer
E-Mail: robert.kretschmer@uni-jena.de
[a] Institute for Inorganic and Analytical Chemistry
Friedrich Schiller University Jena
Humboldtstraße 8
07743 Jena, Germany
[b] Jena Center for Soft Matter (JCSM)
Friedrich Schiller University Jena
Philosophenweg 7
07743 Jena, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201900193 or from the au-
thor.
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH &
Co. KGaA. · This is an open access article under the terms of the
Creative Commons Attribution-NonCommercial-NoDerivs Li-
cense, which permits use and distribution in any medium, provided
the original work is properly cited, the use is non-commercial and
no modifications or adaptations are made.
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Scheme 1. Syntheses of dinuclear organoaluminum complexes II starting from bis(β-diketimine)s I with different linker (L) groups. Dipp = 2,6-
diisopropylphenyl.
studies that investigate the role of the bridging unit and hence
the metal-metal distance with respect to activity and selectivity
are still missing to the best of our knowledge. Hence, the syn-
thesis and structural characterization of a whole set of dinu-
clear aluminum alkyl complexes is worthy of pursuit as they
are suitable pre-catalyst for example in the ROP of cyclic es-
ters.[11]
Herein we report the synthesis of a library of ten dinuclear
aluminum complexes (II) based on bis(β-diketiminate) ligands
(I), Scheme 1, and their structural characterization. We choose
the β-diketiminate framework as the related mononuclear alu-
minum complexes have been shown to be active catalysts in
polymerization reactions[12] or hydroboration reactions.[13]
Figure 2. Solid state structures (hydrogen atoms are omitted for the
sake of clarity) with selected bond lengths /Å and angles /° of IIa:
Al1–Al2 3.8866(6), Al1–N1 1.917(1), Al1–N2 1.928(1), Al2–N3
1.929(1), Al2–N4 1.921(1), Al1–C18 1.965(1), Al1–C19 1.962(2),
Al2–C25 1.967(2), Al2–C26 1.974(2), N2–N3 1.432(2), N1–Al1–N2
93.64(5), N3–Al2–N4 93.04(5), C18–Al1–C19 117.92(7), C25–Al2–
C26 118.52(7).
Results and Discussion
The protio-ligands Ia–j were synthesized by alkylation
of
2-(2,6-diisopropylphenyl)imido-2-penten-4-one
using
Meerwein’s salt ([O(C2H5)3][BF4]) followed by condensation formational flexibility of both binding sites. A similar pattern
with various primary diamines as described before.[6b,6e,7b,7i,7l] has also been observed for the thallium(I)[7l] and copper(I)[7i]
The protio-ligands were subsequently converted into the re- derivatives of IId.
spective dinuclear dimethylaluminum complexes IIa–j using
For the thallium congener of IIe, however, a pattern compar-
trimethylaluminum, Scheme 1. All compounds were isolated able to that of the respective protio-ligand Ie, with one iso-
in good to quantitative yields using a simple work-up pro- propyl methine septet and two methyl doublets was observed,
cedure and were obtained as (pale) yellow (IIa,b,c,e,g,h,i,j), demonstrating a symmetric or averaged structure in solution.
brown (IIf) or colorless (IId) powders. The species IIa–j were This difference most likely arises from the increased steric de-
found to be thermally stable and melt without decomposition mands of the Al(CH3)2 group in comparison with the “naked“
with values in between 162 °C and 296 °C; noteworthily, melt- TlI center bearing a diffuse s-type lone pair of electrons. This
ing points above 200 °C were only found for bis(β-diketimin- argument might also account for the difference in the 1H NMR
ate)s containing aryl linker.
spectrum of IIi in comparison to the respective thallium deriv-
Except for IId, IIe, and IIi, common features observed in ative. While for the latter, conformational flexibility has been
the respective 1H NMR spectra include one singlet for the alu- evidenced, two distinct peaks corresponding to the Al(CH3)2
minum methyl groups and one septet for the methine groups groups are observed at –0.77 and –1,18 ppm, respectively, and
(Figure 2) consistent with a symmetrical substitution pattern at the signals associated with the Dipp methyl and methine group
aluminum. Notably, for IIf only one doublet (δ = 1.29 ppm) appear as four doublets and two septets, respectively. Variable-
1
corresponding to the methyl protons of the isopropyl groups is temperature H NMR experiments have been conducted in the
observed, indicating a lower barrier of rotation about the C–N temperature range of 223–298 K (IIa–c, f, g, j) and 223–334 K
1
bond. In case of IId and IIe, respectively, the H NMR spec- (IId, e, h) (Figures S1–S11, Supporting Information) in order
trum shows two separated groups of septets and more complex to derive information about the rotational dynamics of the
peaks for the respective isopropyl methine and methyl proton complex. Across the investigated temperature range, only a
resonances of the isopropyl groups, indicating a hindered con- minor dependence of the chemical shifts on temperature were
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observed and the absence of a coalescence point indicates
small rotational barriers in case of IIa–c, f, and j, while the
rotation has a significantly higher activation barrier for the spe-
cies IId, e, and h. In case of IIg, coalescence could be ob-
served between 223 and 233 K but due to the overlap of two
singlets we could not extract the relevant data. In addition,
27Al-NMR resonances are only observed in case of IIb, IIc,
IId, IIh, and IIj as broad signals with values in between 150.5
and 154.3 ppm. The IR spectra show characteristic bands asso-
ciated with C–H stretching in the region between 2800 and
3100 cm–1 as well as C–N stretches of the ligand framework
between 1500 and 1550 cm–1.
Besides the behavior in solution, we became interested in
the solid-state structures of the dinuclear complexes and crys-
tals of IIa, IIb, IIc, IIe, and IIi were grown from toluene
solutions at room temperature; their molecular structures are
depicted in Figure 2, Figure 3, and Figure 4. All structures fea-
ture two distorted tetrahedral aluminum centers that are pro-
jected out of the plane of each NacNac unit; the smallest and
largest deviation from the least-squares N–C–C–C–N plane
amount to 0.235(1) Å and 0.831(1) Å for IIi and IId, respec-
tively. The N–Al–N bite angles with values between
93.04(5)° and 95.23(4)° are in the range regularly observed for
mononuclear alkylaluminum β-diketiminate complexes.[12,13]
The same holds true for the Al–C bond lengths [1.958(1)–
1.975(2) Å] and the C–Al–C bond angles [113.22(5)–
118.52(7)°] of the Al(CH3)2 group, whose values are compar-
able to those observed for the mononuclear counterparts.
Figure 4. Solid state structures (hydrogen atoms are omitted for the
sake of clarity) with selected bond lengths /Å and angles /° of (a) IIe:
Al1–Al1’ 6.4023(8), Al1–N1 1.923(1), Al1–N2 1.927(1), Al1–C18
1.958(1), Al1–C19 1.973(1), N1–Al1–N2 95.14(4), C18–Al1–C19
115.14(6); (b) IIi: Al1–Al1’ 7.396(1), Al1–N1 1.930(1), Al1–N2
1.9193(9), Al1–C18 1.970(1), Al1–C19 1.967(1),N1–Al1–N2
95.23(4), C18–Al1–C19 113.22(5).
It is obvious that the Al–Al separations increase in the order
IIa [3.8866(6) Å] Ͻ IIe [6.4023(8) Å] Ͻ IIb [6.482(1) Å] Ͻ
IIc [7.3823(4) Å] Ͻ IIi [7.396(1) Å] as a result of the length
and the rigidity of the bridging unit. The molecular structures
1
also rationalize the respective H resonance pattern observed
in solution. For IIa, rotation about the N1–N2 is cancelled out
due to the repulsion of the backbone CH3 groups. In contrast,
the alkyl bridges of IIb and IIc warrant conformational flexi-
bility in agreement with chemically and magnetically equiva-
lent binding sites in solution. For IIe and IIi, rotation about
the N2–Cbridge bond becomes more restricted, which readily
explains the diverse pattern of resonance in the 1H NMR spec-
trum.
Figure 3. Solid state structures (hydrogen atoms are omitted for the
sake of clarity) with selected bond lengths /Å and angles /° of (a)
IIb: Al1–Al1’ 6.482(1), Al1–N1 1.918(1), Al1–N2 1.907(1), Al1–C18
1.969(2), Al1–C19 1.975(2), N1–Al1–N2 96.71(6), C18–Al1–C19
113.96(9); (b) IIc: Al1–Al2 7.3823(4), Al1–N1 1.904(1), Al1–N2
1.915(1), Al2–N3 1.912(1), Al2–N4 1.911(1), Al1–C18 1.963(2), Al1–
C19 1.974(2), Al2–C28 1.968(1), Al2–C29 1.967(1), N1–Al1–N2
95.02(5), N3–Al2–N4 94.22(4), C18–Al1–C19 116.53(8), C28–Al2–
C29 117.85(6).
Conclusions
In summary, the synthesis of ten dinuclear methylaluminum
complexes based on bis(β-diketiminate) ligands with various
alkylene and (hetero)arylene bridges is reported. The molecu-
lar structures of five compounds have been elucidated by
X-ray diffraction techniques. In future experiment, we will in-
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General Procedure for the Synthesis Employing Trimethylalumi-
vestigate the impact of the metal-metal separation and the flex-
num: Trimethylaluminum (2.8 mL, 5.5 mmol, 2 M in Toluene) was
added dropwise to a solution of the respective bis(β-diketimine)
(2.5 mmol) in Toluene (20 mL). The reaction solution was stirred for
16 h at 90 °C. The volatile substances were removed in vacuo and the
residue was washed with pentane (3ϫ10 mL). The residue was then
extracted with toluene (20 mL) and the concentration of the filtered
extract yielded the products. IIc has already reported in the litera-
ture.[15]
ibility of the bridging unit on the catalytic performance in vari-
ous reactions such as the ring-opening polymerization of cyclic
esters or the hydroboration of unsaturated compounds.
Experimental Section
General Considerations: All preparations were performed under an
inert atmosphere of dinitrogen by means of Standard Schlenk-line or
glovebox techniques (GS-Systemtechnik and MBraun). Traces of oxy-
gen and moisture were removed from the inert gas by passing it over
a BASF R 3–11 (CuO/MgSiO3) catalyst, through concentrated sulfuric
acid, over coarsely granulated silica gel, and finally P4O10. Dichloro-
methane was freshly collected from a Solvent Purification System by
M. Braun (MB SPS-800). Toluene was used as p.a. grade and distilled
from Na/benzophenone prior to use. CDCl3 was dried by distillation
from calcium hydride. Trimethylaluminum (2 m in Toluene) was pur-
chased from Sigma Aldrich.
Colorless crystals suitable for an X-ray diffraction analysis were ob-
tained from concentrated toluene solutions of IIa, IIb, IIc, IIe, and IIi
at room temperature.
IIa: Pale yellow powder, 0.97 g (62%). 1H NMR: (400 MHz, CDCl3):
3
δ = –0.97 [s, 6 H, AlMe2], –0.73 [s, 6 H, AlMe2], 1.08 [d, 6 H, JHH
= 6.8 Hz, CHMe2], 1.17–1.21 [m, 18 H, CHMe2], 1.75 [s, 6 H, CMe],
3
2.06 [s, 6 H, CMe], 3.05 [sept, 2 H, JHH = 6.8 Hz, CHMe2], 3.19
3
[sept, 2 H, JHH = 6.8 Hz, CHMe2], 4.95 [s, 2 H, CH], 7.13–7.15 [m,
2 H, ArH], 7.18–7.20 [m, 2 H, ArH], 7.22–7.27 ppm [m, 2 H, ArH].
13C{1H} NMR: (101 MHz, CDCl3): δ = –11.2 [AlMe2], –8.6 [AlMe2],
21.3 [CMe], 23.7 [CMe], 24.3 [CHMe2], 24.6 [CHMe2], 24.9 [CHMe2],
25.9 [CHMe2], 27.7 [CHMe2], 28.0 [CHMe2], 94.9 [β-CH], 124.1 [m-
C(Dipp)], 124.3 [m-C(Dipp)], 126.7 [p-C(Dipp)], 140.8 [o-C(Dipp)],
143.6 [o-C(Dipp)], 144.8 [ipso-C(Dipp)], 168.0 [CN], 169.3 ppm
[CN]. IR (ATR): ν˜ = 2964, 2926, 2868, 1524, 1443, 1357, 1318, 1254,
1184, 1104, 1020, 925, 800, 764, 731, 676 cm–1. Elemental analysis
calcd. (found) C38H60Al2N4·0.2C7H8: C 73.33 (73.47), H 9.62 (9.79),
N 8.68 (8.57). M.p. 201 °C.
Characterization: The NMR spectra were recorded with a Bruker
Avance 400 spectrometer (T = 300 K) with δ referenced to external
1
tetramethylsilane (1H, 13C and 27Al). H and 13C NMR spectra were
calibrated by using the solvent residual peak (CHCl3: δ(1H) = 7.26)
and the solvent peak [CDCl3: δ(13C) = 77.16], respectively. 27Al NMR
spectra were calibrated relative to external Al(NO3)3·9H2O. IR spectra
were recorded with a Bruker ALPHA spectrometer equipped with a
diamond ATR unit IIb–j and a Thermo Scientific Nicolet iS5 spec-
trometer with an ATR-coated diamond crystal 1e and IIa. Elemental
analysis was performed with a Vario MICRO cube (Elementar Ana-
lysensysteme GmbH); the presence of residual solvent molecules was
IIb: Yellow powder, 1.64 g (100%). 1H NMR: (400 MHz, CDCl3):
3
δ = –0.94 [s, 12 H, AlMe2], 1.12 [d, 12 H, JHH = 6.8 Hz, CHMe2],
1
3
verified by H NMR spectroscopy. Melting points were determined in
1.18 [d, 12 H, JHH = 6.8 Hz, CHMe2], 1.68 [s, 6 H, CMe], 2.16 [s, 6
H, CMe], 3.01 [sept, 4 H, 3JHH = 6.8 Hz, CHMe2], 3.43 [s, 4 H, CH2],
4.97 [s, 2 H, CH], 7.13–7.15 [m, 4 H, ArH], 7.19–7.23 ppm [m, 2 H,
ArH]. 13C{1H} NMR: (101 MHz, CDCl3): δ = –10.5 [AlMe2], 21.7
[CMe], 23.3 [CMe], 24.6 [CHMe2], 24.9 [CHMe2], 27.9 [CHMe2],
48.1 [CH2], 98.3 [β-CH], 123.9 [m-C(Dipp)], 126.4 [p-C(Dipp)], 140.9
[o-C(Dipp)], 144.2 [ipso-C(Dipp)], 168.3 [CN], 168.9 ppm [CN].
27Al{1H} NMR: (104 MHz, CDCl3): δ = 154.0 ppm [AlMe2]. IR
(ATR): ν˜ = 2963, 2925, 2869, 1552, 1522, 1441, 1380, 1312, 1294,
1261, 1184, 1098, 1014, 871, 798, 760, 668, 576 cm–1. Elemental
analysis calcd. (found) C40H64Al2N4: C 73.36 (73.25), H 9.85 (9.48),
N 8.55 (8.36). M.p. 199 °C.
sealed capillaries with an Apotec melting point apparatus.
Ligand Synthesis: 4-((2,6-Diisopropylphenyl)amino)pent-3-en-2-
one,[6b] triethyloxonium tetrafluoroborate[14] and the bis(β-diket-
imine)s Ia–d, and If–j[[6b,6e,7b,7i,7l] were prepared according to pub-
lished procedures.
Ie: A solution of [Et3O]+[BF4]– (14.26 g, 75.0 mmol) in CH2Cl2
(40 mL) was added to a solution of 4-((2,6-diisopropylphenyl)amino)-
pent-3-en-2-one (19.46 g, 75.0 mmol) in CH2Cl2 (70 mL) at 0 °C. The
orange reaction mixture was stirred for 19 h at room temperature and
then Et3N (7.59 g, 75.0 mmol) was added. After 30 min a solution of
o-phenylenediamine (4.06 g, 37.5 mmol) in Et3N (24 g) was added to
the mixture. After stirring at room temperature for 1 d all volatiles
were removed in vacuo. Toluene (80 mL) was added to extract the
product from the oily precipitate of [Et3NH]+[BF4]–. Toluene was re-
moved from the extract and the crude product was dissolved in ethanol
(3 mL). A yellow solid was obtained. Drying in vacuo gave 10.04 g
IIc: Pale yellow powder, 1.53 g (91%). The analytic data are in agree-
ment with published data.[15] 1H NMR: (400 MHz, CDCl3): δ = –0.98
3
[s, 12 H, AlMe2], 1.12 [d, 12 H, JHH = 6.8 Hz, CHMe2], 1.16[d, 12
3
H, JHH = 6.8 Hz, CHMe2], 1.66 [s, 6 H, CMe], 1.73–1.81 [m, 2 H,
3
CH2], 2.09 [s, 6 H, CMe], 3.01 [sept, 4 H, JHH = 6.8 Hz, CHMe2],
3
3.33 [t, 4 H, JHH = 8.1 Hz, CH2], 4.94 [s, 2 H, CH], 7.11–7.13 [m, 4
1
H, ArH], 7.18–7.21 ppm [m, 2 H, ArH]. 13C{1H} NMR: (101 MHz,
CDCl3): δ = –10.8 [AlMe2], 20.8 [CMe], 23.3 [CMe], 24.5 [CHMe2],
24.9 [CHMe2], 27.9 [CHMe2], 32.7 [CH2], 45.5 [CH2], 98.0 [β-CH],
123.9 [m-C(Dipp)], 126.3 [p-C(Dipp)], 141.1 [o-C(Dipp)], 144.4 [ipso-
C(Dipp)], 167.8 [CN], 168.3 ppm [CN]. 27Al{1H} NMR: (104 MHz,
CDCl3): δ = 152.5 ppm [AlMe2]. IR (ATR): ν˜ = 2961, 2927, 2868,
1559, 1515, 1399, 1355, 1317, 1253, 1186, 1094, 1016, 800, 754, 670,
574 cm–1. Elemental analysis calcd. (found) C41H66Al2N4: C 73.61
(73.42), H 9.94 (9.56), N 8.38 (8.07). M.p. 195 °C.
(45%) of the product. H NMR: (400 MHz, CDCl3): δ = 1.12 [d, 12
3
3
H, JHH = 6.8 Hz, CHMe2], 1.21 [d, 12 H, JHH = 6.8 Hz, CHMe2],
1.67 [s, 6 H, CMe], 1.83 [s, 6 H, CMe], 3.06 [sept, 4 H, 3JHH = 6.8 Hz,
CHMe2], 4.82 [s, 2 H, CH], 6.87–6.90 [m, 2 H, ArH], 7.00–7.03 [m,
2 H, ArH], 7.14 [br, 6 H, ArH], 12.12 ppm [s, 2 H, NH]. 13C{1H}
NMR: (101 MHz, CDCl3): δ = 20.9 [CMe], 23.0 [CMe], 24.5
[CHMe2], 28.4 [CHMe2], 95.3 [β-CH], 123.1 [m-C(Dipp)], 124.3
[C(Aryl)], 125.0 [p-C(Dipp)], 125.2 [C(Aryl)], 139.6 [o-C(Dipp)],
141.0 [ipso-C(Dipp)], 142.6 [C(Aryl)], 160.5 [CN], 160.8 ppm [CN].
IR (ATR): ν˜ = 3066, 2958, 2923, 1622, 1542, 1501, 1439, 1361, 1255,
1175, 1103, 1022, 930, 789, 756, 701 cm–1. Elemental analysis calcd.
1
IId: Colorless powder, 1.47 g (83%). H NMR: (400 MHz, CDCl3):
3
(found) C40H54N4: C 81.31 (81.47), H 9.21 (8.97), N 9.48 (9.34). M.p. δ = –0.85 [s, 6 H, AlMe2], 0.82 [s, 6 H, AlMe2], 1.04 [d, 6 H, JHH
=
3
135 °C.
6.8 Hz, CHMe2], 1.15 [d, 6 H, JHH = 6.8 Hz, CHMe2], 1.17 [d, 6 H,
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3JHH = 6.8 Hz, CHMe2], 1.19 [d, 6 H, JHH = 6.8 Hz, CHMe2], 1.30 CHMe2], 1.89 [s, 6 H, CMe], 2.22 [s, 6 H, CMe], 3.15 [sept, 4 H, 3JHH
3
[br, 2 H, ring-CH2], 1.58 [br, 2 H, ring-CH2], 1.66 [s, 6 H, CMe], 1.72 = 6.8 Hz, CHMe2], 5.33 [s, 2 H, CH], 6.82 [d, 2 H, JHH = 7.8 Hz,
[br, 4 H, ring-CH2], 2.24 [s, 6 H, CMe], 2.84 [sept, 2 H, 3JHH = 6.8 Hz, ArH], 7.24–7.26 [m, 4 H, ArH], 7.30–7.35 [m, 2 H, ArH], 7.69 ppm
3
3
CHMe2], 3.23 [sept, 2 H, JHH = 6.8 Hz, CHMe2], 4.24 [br, 2 H, ring- [t, 1 H, JHH = 7.8 Hz, ArH]. 13C{1H} NMR: (101 MHz, CDCl3): δ =
CH], 5.05 [s, 2 H, CH], 7.09–7.11 [m, 2 H, ArH], 7.15–7.23 ppm [m,
–11.6 [AlMe2], 22.5 [CMe], 22.6 [CMe], 23.5 [CHMe2], 23.7
4 H, ArH]. 13C{1H} NMR: (101 MHz, CDCl3): δ = –9.8 [AlMe2], –6.7 [CHMe2], 27.0 [CHMe2], 99.4 [β-CH], 113.8 [C(Aryl)], 123.0 [m-
[AlMe2], 23.4 [CMe], 24.2 [CMe], 24.3 [CHMe2], 24.7 [CHMe2], 25.4 C(Dipp)], 125.6 [p-C(Dipp)], 137.7 [C(Aryl)], 140.1 [o-C(Dipp)],
[ring-CH2], 25.5 [CHMe2], 27.8 [CHMe2], 27.9 [CHMe2], 35.5 [ring- 142.7 [ipso-C(Dipp)], 156.6 [C(Aryl)], 165.0 [CN], 169.7 ppm [CN].
CH2], 62.0 [ring-CH], 100.1 [β-CH], 123.6 [m-C(Dipp)], 123.7 [m-
C(Dipp)], 126.1 [p-C(Dipp)], 141.7 [o-C(Dipp)], 144.1 [o-C(Dipp)],
145.1 [ipso-C(Dipp)], 166.9 [CN], 168.7 ppm [CN]. 27Al{1H} NMR:
(104 MHz, CDCl3): δ = 153.9 ppm [AlMe2]. IR (ATR): ν˜ = 2965,
2926, 2868, 1546, 1526, 1459, 1382, 1316, 1251, 1189, 1091, 1021,
949, 800, 763, 673, 572 cm–1. Elemental analysis calcd. (found)
C44H70Al2N4: C 74.54 (74.17), H 9.95 (10.16), N 7.90 (7.64). M.p.
217 °C.
27Al{1H} NMR: (104 MHz, CDCl3): δ = 154.3 ppm [AlMe2]. IR
(ATR): ν˜ = 2966, 2927, 2868, 1549, 1530, 1447, 1430, 1370, 1317,
1257, 1179, 1108, 1019, 934, 797, 759, 671, 583, 467 cm–1. Elemental
analysis calcd. (found) C43H63Al2N5: C 73.37 (73.27), H 9.02 (8.99),
N 9.95 (9.66). M.p. 197 °C.
IIi: Pale yellow powder, 1.54 g (77%). 1H NMR: (400 MHz, CDCl3):
3
δ = –1.18 [s, 6 H, AlMe2], –0.77 [s, 6 H, AlMe2], 0.77 [d, 6 H, JHH
3
= 6.8 Hz, CHMe2], 0.89 [d, 6 H, JHH = 6.8 Hz, CHMe2], 1.20 [d, 6
IIe: Pale yellow powder, 1.23 g (70%). 1H NMR: (400 MHz, CDCl3):
δ = –1.17 [s, 6 H, AlMe2], –0.81 [s, 6 H, AlMe2], 1.14–1.23 [m, 24
H, CHMe2], 1.76 [s, 6 H, CMe], 1.88 [s, 6 H, CMe], 2.98 [sept, 2 H,
3JHH = 6.8 Hz, CHMe2], 3.25 [sept, 2 H, 3JHH = 6.8 Hz, CHMe2], 5.21
[s, 2 H, CH], 6.87–6.93 [m, 2 H, ArH], 7.11–7.22 ppm [m, 8 H, ArH].
13C{1H} NMR: (101 MHz, CDCl3): δ = –10.0 [AlMe2], –9.6 [AlMe2],
23.7 [CMe], 24.6 [CMe], 24.6 [CHMe2], 24.7 [CHMe2], 25.4 [CHMe2],
25.5 [CHMe2], 27.9 [CHMe2], 28.1 [CHMe2], 99.2 [β-CH], 124.0 [m-
C(Dipp)], 124.0 [m-C(Dipp)], 126.5 [C(Aryl)], 127.0 [p-C(Dipp)],
128.7 [C(Aryl)], 141.2 [o-C(Dipp)], 143.2 [o-C(Dipp)], 144.0 [ipso-
C(Dipp)], 144.7 [C(Aryl)], 169.2 [CN], 169.8 ppm [CN]. IR (ATR): ν˜
= 2962, 2923, 1542, 1521, 1448, 1364, 1318, 1185, 1109, 1042, 1021,
869, 802, 763, 750, 673, 583, 482, 440 cm–1. Elemental analysis calcd.
(found) C44H64Al2N4: C 75.18 (74.19), H 9.18 (8.73), N 7.97 (7.95)
+ silicon grease, shown in the NMR. M.p. 296 °C.
H, 3JHH = 6.9 Hz, CHMe2], 1.22 [d, 6 H, 3JHH = 6.9 Hz, CHMe2], 1.73
3
[s, 6 H, CMe], 2.00 [s, 6 H, CMe], 2.86 [sept, 2 H, JHH = 6.8 Hz,
3
CHMe2], 3.15 [sept, 2 H, JHH = 6.8 Hz, CHMe2], 5.17 [s, 2 H, CH],
6.81–6.83 [m, 2 H, ArH], 7.05–7.21 ppm [m, 12 H, ArH]. 13C{1H}
NMR: (101 MHz, CDCl3): δ = –11.2 [AlMe2], –8.9 [AlMe2], 23.2
[CMe], 23.5 [CMe], 24.3 [CHMe2], 24.7 [CHMe2], 24.9 [CHMe2], 25.7
[CHMe2], 27.8 [CHMe2], 27.8 [CHMe2], 97.8 [β-CH], 120.0
[C(Aryl)], 123.8 [m-C(Dipp)], 124.1 [m-C(Dipp)], 126.6 [p-C(Dipp)],
126.9 [C(Aryl)], 127.3 [C(Aryl)], 137.0 [C(Aryl)], 140.6 [C(Aryl)],
143.9 [o-C(Dipp)], 144.3 [ipso-C(Dipp)], 151.5 [C(Aryl)], 169.3 [CN],
169.8 ppm [CN]. IR (ATR): ν˜ = 3062, 2965, 2934, 2925, 2866, 1551,
1530, 1486, 1439, 1389, 1317, 1260, 1178, 1108, 1019, 796, 758, 671,
586, 467 cm–1. Elemental analysis calcd. (found) C50H68Al2N4O: C
75.53 (75.43), H 8.62 (8.63), N 7.05 (7.00). M.p. 267 °C.
IIf: Pale brown powder, 1.76 g (100%). 1H NMR: (400 MHz,
1
IIj: Yellow powder, 1.72 g (94%). H NMR: (400 MHz, CDCl3): δ =
3
3
CDCl3): δ = –0.94 [s, 12 H, AlMe2], 1.28 [d, 24 H, JHH = 6.8 Hz,
–1.03 [s, 12 H, AlMe2], 1.14 [d, 24 H, JHH = 6.9 Hz, CHMe2], 1.70
[s, 6 H, CMe], 2.00 [s, 6 H, CMe], 3.09 [sept, 4 H, JHH = 6.8 Hz,
CHMe2], 1.87 [s, 6 H, CMe], 2.00 [s, 6 H, CMe], 3.19 [sept, 4 H, 3JHH
3
3
= 6.8 Hz, CHMe2], 5.26 [s, 2 H, CH], 6.69 [t, 1 H, JHH = 2.0 Hz,
CHMe2], 4.58 [s, 4 H, CH2], 4.99 [s, 2 H, CH], 7.07–7.14 [m, 7 H,
ArH], 7.18–7.21 [m, 2 H, ArH], 7.24–7.28 ppm [m, 1 H, ArH].
13C{1H} NMR: (101 MHz, CDCl3): δ = –10.8 [AlMe2], 22.0 [CMe],
23.4 [CMe], 24.7 [CHMe2], 24.9 [CHMe2], 27.9 [CHMe2], 50.9 [CH2],
98.0 [β-CH], 123.9 [m-C(Dipp)], 125.0 [m-C(Dipp)], 125.5 [C(Aryl)],
126.4 [p-C(Dipp)], 128.9 [C(Aryl)], 140.0 [o-C(Dipp)], 141.0 [ipso-
C(Dipp)], 144.3 [C(Aryl)], 168.6 [CN], 170.0 ppm [CN]. 27Al{1H}
NMR: (104 MHz, CDCl3): δ = 150.5 ppm [AlMe2]. IR (ATR): ν˜ =
2962, 2928, 2868, 1555, 1520, 1466, 1439, 1389, 1319, 1258, 1184,
1099, 1015, 800, 763, 672, 441 cm–1. Elemental analysis calcd. (found)
C46H68Al2N4: C 75.58 (75.72), H 9.38 (9.50), N 7.66 (7.59). M.p.
162 °C.
3
3
ArH], 6.92 [d, 1 H, JHH = 2.0 Hz, ArH], 6.94 [d, 1 H, JHH = 2.0 Hz,
ArH], 7.24–7.25 [m, 4 H, ArH], 7.29–7.35 ppm [m, 2 H, ArH].
13C{1H} NMR: (101 MHz, CDCl3): δ = –10.9 [AlMe2], 23.0 [CMe],
23.5 [CMe], 24.5 [CHMe2], 24.8 [CHMe2], 28.0 [CHMe2], 98.5 [β-
CH], 122.9 [m-C(Dipp)], 123.2 [m-C(Dipp)], 124.0 [C(Aryl)], 126.5
[p-C(Dipp)], 129.8 [C(Aryl)], 141.0 [o-C(Dipp)], 144.1 [ipso-
C(Dipp)], 147.0 [C(Aryl)], 167.1 [CN], 169.6 ppm [CN]. IR (ATR): ν˜
= 2962, 2928, 2868, 1551, 1521, 1441, 1376, 1317, 1252, 1185, 1106,
1018, 899, 798, 757, 674, 578, 443 cm–1. Elemental analysis calcd.
(found) C44H64Al2N4: C 75.18 (75.15), H 9.18 (9.12), N 7.97 (7.78).
M.p. 199 °C.
IIg: Pale yellow powder, 1.76 g (100%). 1H NMR: (400 MHz,
Supporting Information (see footnote on the first page of this article):
Crystallographic details, NMR and IR spectra are found in the SI.
3
CDCl3): δ = –1.06 [s, 12 H, AlMe2], 1.17 [d, 12 H, JHH = 6.8 Hz,
3
CHMe2], 1.18 [d, 12 H, JHH = 6.8 Hz, CHMe2], 1.76 [s, 6 H, CMe],
3
1.91 [s, 6 H, CMe], 3.08 [sept, 4 H, JHH = 6.8 Hz, CHMe2], 5.15 [s,
2 H, CH], 6.94 [s, 4 H, ArH], 7.13–7.15 [m, 4 H, ArH], 7.19–7.23 ppm
[m, 2 H, ArH]. 13C{1H} NMR: (101 MHz, CDCl3): δ = –11.2 [AlMe2],
22.8 [CMe], 23.4 [CMe], 24.4 [CHMe2], 24.7 [CHMe2], 27.9
[CHMe2], 98.3 [β-CH], 123.8 [m-C(Dipp)], 126.2 [C(Aryl)], 126.3 [p-
C(Dipp)], 140.9 [o-C(Dipp)], 143.2 [ipso-C(Dipp)], 144.0 [C(Aryl)],
167.1 [CN], 169.2 ppm [CN]. IR (ATR): ν˜ = 2964, 2927, 2866, 1552,
1526, 1491, 1440, 1380, 1316, 1258, 1180, 1016, 893, 800, 759, 673,
577, 445 cm–1. Elemental analysis calcd. (found) C44H64Al2N4: C
75.18 (75.20), H 9.18 (8.91), N 7.97 (7.74). M.p. 279 °C.
Acknowledgements
The project was financially supported by the Fonds der Chemischen
Industrie, the Deutsche Forschungsgemeinschaft (DFG, KR4782/2–1
and KR4782/3–1), the University of Regensburg and the Friedrich
Schiller University Jena. M.E.D. is grateful to the Stiftung Stipendien-
Fonds des Verbands der Chemischen Industrie for a PhD fellowship.
Additionally, helpful discussions with Dr. Stefanie Gärtner, and assist-
ance with the VT-NMR experiments by Maximilian Dehmel and the
NMR facility of the Friedrich Schiller University Jena is gratefully
acknowledged.
IIh: Pale yellow powder, 1.43 g (81%). 1H NMR: (400 MHz, CDCl3):
δ = –0.87 [s, 12 H, AlMe2], 1.25 [“t“, 24 H, 3JHH = 6.5, 3JHH = 6.6 Hz,
Z. Anorg. Allg. Chem. 2019, 1–7
www.zaac.wiley-vch.de
5
© 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Eur. J. Inorg. Chem. 2009, 2009, 3569; e) J. Spielmann, D. F.-J.
Keywords: Aluminum alkyl compounds; Aluminum;
Bis(β-diketiminate); Dinuclear aluminum complexes;
Group 13; Synergy
Piesik, S. Harder, Chem. Eur. J. 2010, 16, 8307; f) J. P. Falken-
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DOI: 10.1021/acs.inorgchem.9b02868
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Received: August 13, 2019
Published Online: ᭿
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© 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
M. E. Desat, R. Kretschmer* ............................................ 1–7
Synthesis and Structures of Dinuclear Aluminum Complexes
Based on Bis(β-diketiminate) Ligands
Z. Anorg. Allg. Chem. 2019, 1–7
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© 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim