Ditopic bis(: N, N ′, N ′-substituted 1,2-ethanediamine) ligands: Synthesis and coordination chemistry

Article abstract of DOI:10.1039/d0dt03124k

The synthesis of two different types of bis(N,N′,N′-substituted 1,2-ethanediamine)s, bridged either through the secondary (type 1) or tertiary (type 2) amine groups is reported. Selected protio-ligands have been applied in subsequent metallation reactions

Full text of DOI:10.1039/d0dt03124k

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Ditopic bis(N,N’,N’-substituted 1,2-ethanediamine)
ligands: synthesis and coordination chemistry†
Cite this: DOI: 10.1039/d0dt03124k
Andreas Rösch,a Christoph M. Herzog,a Simon H. F. Schreiner,a Helmar Görlsb and
b,c
Robert Kretschmer
*
The synthesis of two different types of bis(N,N’,N’-substituted 1,2-ethanediamine)s, bridged either
through the secondary (type 1) or tertiary (type 2) amine groups is reported. Selected protio-ligands have
been applied in subsequent metallation reactions using aluminium, magnesium, tin, and zinc sources
allowing to isolate five mononuclear and eight dinuclear complexes. All complexes have been fully
characterized and their solid-state structures have been studied by means of single-crystal X-ray diffrac-
tion analysis. Nine of the 13 complexes carry reactive alkyl, amide or hydride groups, which indicates their
potential as catalysts or supports for (transition) metals.
Received 7th September 2020,
Accepted 23rd September 2020
DOI: 10.1039/d0dt03124k
rsc.li/dalton
attention: bis(N-heterocyclic carbene)s4 and N,N-dinucleating
ligands.1h With respect to the latter, bis(amidine)s (A)5 have
Introduction
Ligands possessing two binding sites play a pivotal role in been frequently used and noticeable effort has been directed
modern coordination chemistry as they grant access to mono-, towards bis(guanidine)s (B)6 and bis(β-diketimine)s (C),7
di- and polynuclear species from all sections of the periodic Fig. 1. However, the redox activity and non-innocence is well
table.1 As multidentate chelates, they give rise to stable mono- document for β-diketimines8 and related ligands and ligand-
nuclear metal complexes and allow controlling the steric con- centered side reactions have also been reported for bis
straints with respect to both, shielding of the metal centre and (β-diketiminate) complexes.7r The saturated backbone of N,N′,
adjusting the stereochemical properties of the thus formed N′-substituted 1,2-ethanediamines (D) prevents conjugation
complex. Furthermore, these ditopic ligands also offer the and hence delocalization,9 which makes the related bis(N,N′,
advantage of bringing two and sometimes more metal centres N′-substituted 1,2-ethanediamine)s interesting targets for
in close proximity. With respect to catalysis, dinuclear com- ligand design. Due to the asymmetric nature of N,N′,N′-substi-
plexes allow cooperative or synergistic effects to arise2 and tuted 1,2-ethanediamines, bridging is either achieved through
framing two metals within a single molecule avoids ill-defined the secondary or tertiary amine groups giving rise to protio-
monomer/dimer equilibria. Hence, such complexes regularly ligands of type 1 and 2, respectively, Fig. 1.
excel their mononuclear counterparts in terms of reactivity
In 2003, the group of Hagadorn reported about the first
and selectivity and allow achieving reactions that are not acces- example of a type 1 bis(N,N′,N′-substituted 1,2-ethanediamine)
sible with complexes possessing only one metal centre. In this containing a dibenzofuran-bridge.10 Notably, the authors
regard, selecting appropriate ligands is crucial and even small defined the new ligand class as bis(amidoamine)s and as this
changes with respect to electronic and/or steric implications notation has been adopted in the literature, we will also make
may have a significant impact on the coordination behaviour.
In main-group chemistry, which attracted much interest
within the last decades,3 two ligand classes received particular
aInstitute of Inorganic Chemistry, University of Regensburg, Universitätsstraße 31,
93053 Regensburg, Germany
bInstitute of Inorganic and Analytical Chemistry (IAAC), Friedrich Schiller University
Jena, Humboldtstraße 8, 07743 Jena, Germany
cJena Center for Soft Matter (JCSM), Friedrich Schiller University Jena
Philosophenweg 7, 07743 Jena, Germany. E-mail: robert.kretschmer@uni-jena.de
†Electronic supplementary information (ESI) available: Experimental details
concerning the ligand synthesis, crystallographic data and NMR as well as IR
spectra. CCDC 2026430–2026444. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/d0dt03124k
Fig. 1 Bis(amidine)s (A), bis(guanidine)s (B), bis(β-diketimine)s (C), N,N’,
N’-substituted 1,2-ethanediamines (D), and bis(amidoamine)s of type 1
and 2 reported herein.
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use of it in the following. Although, the related dinuclear
metal complexes showed remarkable reactivity and catalytic
activity,10,11 no further investigations with respect to the
ligand itself have been reported. However, its non-innocence
in terms of hydride abstraction from a methylene group by
forming a CvN double bond was observed when treating
dinuclear zinc enolate complexes with tris(pentafluorophenyl)
borane.11c As such a kind of reactivity was previously observed
for N,N-alkylated anilines,12 this behavior might be due to the
aromatic linker group and could be avoided by using alterna-
tive bridging units. In addition, type 2 bis(amidoamine)s have
no precedence in the literature. Hence, we set out to synthesize
new bis(amidoamine)s of type 1 and 2 and investigated their
reactivity towards aluminium, magnesium, tin, and zinc pre-
cursors. Our findings are reported herein.
Scheme 2 Synthesis of bis(amidoamine)s of type
diamines.
1 from primary
aluminium hydride allowed to isolate the bis(amidoamine)s
1h–o in yields between 51 and 76%.
Results and discussion
Bis(amidoamine)s of type 2, which are bridged through the
tertiary instead of the secondary amine, are also synthesized
via two routes, Scheme 3. The piperazine-bridged compound
2a is obtained in 52% yield by reacting piperazine with an
α-chloroanilide and subsequent reduction using LiAlH4. The
acyclic species 2b–g, however, were alternatively synthesized
from N-methyl-N′-aryl substituted ethylenediamines and a suit-
able dihalide and obtained in yields ranging from 21 to 99%.
The 1H NMR spectra of the protio-ligands in CDCl3 have
the expected pattern characteristic for a symmetric or averaged
structure in solution. In order to elucidate the situation in the
solid state, single-crystals of 2a and 2b, suitable for an X-ray
diffraction analysis could be obtained. Their molecular struc-
tures are shown in Fig. 2. In brief, the piperazine unit within
2a possesses the expected chair conformation and the two
binding pockets occupy the equatorial positions while
directing in opposite directions, a behaviour well known for
other piperazine-bridged ligands.14 In 2b, the two binding
pockets are also directed away from each other. Both species
feature comparable N–C–C–N dihedral angles of 55.79(12) to
59.11(12)° as well as C–N bond lengths in between 1.4629(16)
and 1.4682(16) Å, which are in good agreement with values of
the related N,N′,N′-substituted 1,2-ethane-diamines (55.65(12)°
and 1.4627(15)–1.4637(13) Å).9a
Protio-ligand synthesis
The only yet reported dibenzofuran-bridged type 1 bis(amido-
amine)s have been synthesized by the copper-catalyzed coup-
ling of 4,6-diiodibenzofurane and alkylated ethylene-
diamines.10,11a As this approach is limited to aromatic linker
groups, we established alternative synthetic protocols towards
the bis(amidoamine)s 1 and 2, respectively, which will be dis-
cussed consecutively in the following.13
With respect to type 1 bis(amidoamine)s possessing term-
inal tertiary and lateral secondary amine functions, two
general approaches have been applied, Schemes 1 and 2. The
first one originates from N,N-substituted ethylene diamines
and a dicarbonyl precursor, i.e., diethyl oxalate, dimethyl suc-
cinate and isophthalaldehyde. The thus formed amides and
imines were subsequently reduced using LiAlH4 and NaBH4,
respectively, affording the ethylene, butylene, and 1,3-xylylene
bridged bis(amidoamine)s 1a–g in yields ranging from 41 to
88%. The second approach starts from aromatic diamines that
are converted first to the respective bis(α-haloamide)s by using
chloro acetylchloride. Nucleophilic substitution of the halide
with aliphatic secondary amines and reduction using lithium
Scheme 1 Synthesis of bis(amidoamine)s of type 1 starting from dicar-
Scheme 3 Synthesis of bis(amidoamine)s of type 2. DMP = 2,6-di-
bonyl precursors.
methylphenyl, Dipp = 2,6-diisopropylphenyl, X = Br, Cl.
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Scheme 4 Deprotonation of 1n by magnesium bis[bis(trimethylsilyl)
amide] or diethyl zinc.
X-ray diffraction (XRD) analyses and their molecular structures
in the solid state are shown in Fig. 4; 1nZn crystallizes as two
independent molecules, which differ in their conformation,
Fig. S1.† Within the homoleptic complexes 1nMg and 1nZn,
the metal centre is four-fold-coordinated by the two N,N-che-
lates. As expected, the dative M–N1 and M–N4 bonds (Mg:
2.1679(14) and 2.1731(14) Å; Zn: 2.1685(12) and 2.1690(13) Å)
are longer compared to the normal M–N2 and M–N3 bonds by
about 0.16 (Mg) and 0.23 Å (Zn). Notably, only the normal
bonds are significantly affected by the central atom, with
shorter bond lengths in case of zinc (1.9383(13) and 1.9448(14)
Å) as compared to magnesium (2.0071(15) and 2.0112(14) Å).
The N–M–N bite angles, finally, remain by and large unaffected
by the central metal, i.e., 82.95(5) and 83.5(6)° in case of mag-
nesium and 83.69(5) and 84.59(5)° for zinc. Notably, anagostic
Mg⋯HC interactions (2.3324(5) and 2.3667(5) Å) with the
methylene unit of the backbone are observed, while the con-
tacts are significant longer in case of 1nZn (2.4260(3) and
2.4391(4) Å).
Fig. 2 Solid-state structures (hydrogen atoms except the NH are
omitted for clarity) with selected bond lengths [Å]: (a) 2a: N1–C9 1.4682
(16), C9–C10 1.5221(19), N2–C10 1.4629(16); (b) 2b: N1–C9 1.4675(14),
C9–C10 1.5188(12), N2–C10 1.4657(14).
Synthesis and structural characterization of mono- and
dinuclear complexes
The stereochemistry of the mono- and dinuclear complexes
originating from the protio-ligands of type 1 and 2 is signifi-
cantly affected by the way both binding pockets are connected.
Upon complexation, rapid inversion of the nitrogen atom of
the tertiary amine is effectively cancelled out locking the
overall configuration. In case of the protio-ligands 1a–n this
does not affect the overall stereochemistry of the thereby
formed mono- and dinuclear complexes, Fig. 3. Complexation
of the protio-ligands 2b–g, however, gives rise to two chiral
nitrogen-donor atoms and possibly induces the formation of
several diastereomers.
The behaviour in solution differs for both complexes. In
case of 1nMg, a complex pattern of sharp resonances indicates
a species of low symmetry. Notably, the number of resonances
While repeated attempts to obtain magnesium or zinc com-
plexes starting from the protio-ligand 1m remained unsuccess-
ful, we were able to isolate well-defined compounds using 1n,
Scheme 4. In detail, 1nMg was obtained by using magnesium
bis[bis(trimethylsilyl)amide] while diethyl zinc was used to
synthesize the respective zinc complex 1nZn. Both complexes
could be isolated as colourless crystals, which were suitable for
Fig. 4 Solid-state structures (hydrogen atoms except those of the ana-
gostic bonds are omitted for clarity) with selected bond lengths [Å] and
angles [°]: (a) 1nMg: Mg1–N1 2.1679(14), Mg1–N2 2.0071(15), Mg1–N3
2.0112(14), Mg1–N4 2.1731(14), N1–Mg1–N2 83.55(6), N1–Mg1–N3
115.0866(8), N1–Mg1–N4 111.1091(7), N2–Mg1–N3 148.36256(7), N2–
Mg1–N4 115.3234(9), N3–Mg1–N4 82.95(5); (b) 1nZn: Zn1–N1 2.1685
(12), Zn1–N2 1.9448(14), Zn1–N3 1.9383(13), Zn1–N4 2.1690(13), N1–
Zn1–N2 83.69(5), N1–Zn1–N3 116.3320(4), N1–Zn1–N4 110.8010(8),
N2–Zn1–N3 146.9457(2), N2–Zn1–N4 113.9624(4), N3–Zn1–N4
84.59(5).
Fig. 3 Coordination modes of (a) mono- and (b) dinuclear complexes
originating from the protio-ligands 1 and 2, respectively. The ethylene-
bridge was chosen as an example assuming R’ having the lowest Cahn–
Ingold–Prelog-priority.
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is strongly solvent-dependent and increases in going from
THF-d8 to C6D6. In the former case, one triplet and one
quartet account for the terminal ethyl substituents, while they
are split into two triplets and two quartets in C6D6 solution.
The same holds true for the methylene groups of both, the
ligands’ backbone and the bridge which appear as three and
six multiplets in THF-d8 and in C6D6, respectively. 1nZn was
only soluble in a mixture of THF-d8 and C6D6 and the 1H NMR
spectrum features broadened resonances for the ethyl groups,
indicating slow conformational exchange at room temperature
on the NMR time scale, while well-resolved signals were
observed for the protons of both, the methylene units and the
aromatic ring. The latter finding is consistent with a pseudo
C2-symmetric structure of the ligand framework in solution.
We next became interested if dinuclear aluminium(III) and
tin(II) complexes are accessible starting from the protio-ligands
1. Hence, 1j and 1k were allowed to react with aluminium
hydride trimethylamine, while 1m and 1n were treated with
tin bis[bis(trimethylsilyl)amide], Scheme 5. Please note that
the reactions of 1a and 1d with Sn(HMDS)2 yielded only a
complex reaction mixture. The dinuclear aluminium(III)
hydride complexes 1jAlH2 and 1kAlH2 were obtained in excel-
lent yields of 92% and 99%, respectively. Although we could
also isolate the dinuclear tin(II) complexes 1mSnHMDS and
1nSnHMDS, the yields were significantly lower (14 and 41%,
respectively). As all four compounds were isolated as crystal-
line material, an XRD analysis allowed to derive their mole-
cular solid-state structures, which are shown in Fig. 5 and 6.
1jAlH2 and 1kAlH2 feature two tetra-coordinated aluminium
Fig. 5 Solid-state structures (hydrogen atoms except the AlH and
cocrystallized THF in case of 1kAlH2 are omitted for clarity) with
selected bond lengths [Å] and angles [°]: (a) 1jAlH2: Al1–N1 1.9972(12),
Al1–N2 1.8479(15), Al1–H1 1.54 (2), Al1–H2 1.516(15), N1–Al1–N2 87.40
(5), H1–Al1–H2 119.5(11); (b) 1kAlH2: Al1–N1 2.0042(14), Al1–N2 1.8473
(14), Al1–H1 1.56(2), Al1–H2 1.54(2), N1–Al1–N2 88.80(6), H1–Al1–H2
113.7(12).
Fig. 6 Solid-state structures (hydrogen atoms are omitted for clarity)
with selected bond lengths [Å] and angles [°]: (a) 1mSnHMDS: Sn1–N1
2.453(3), Sn1–N2 2.139(2), Sn1–N3 2.154(3), Sn2–N4 2.165(2), Sn2–N5
2.374(3), Sn2–N6 2.165(3), N1–Sn1–N2 75.58(9), N4–Sn2–N5 76.07(9);
(b) 1nSnHMDS: Sn1–N1 2.3904(18), Sn1–N2 2.1690(18), Sn1–N3 2.1520
(17), Sn2–N4 2.1513(16), Sn2–N5 2.3666(17), Sn2–N6 2.1440(17), N1–
Sn1–N2 79.27(6), N4–Sn2–N5 78.32(6).
1
centres that are facing away from eachother. The Al1–N1 and group was established by H NMR spectroscopy and the AlH2
Al1–N2 bond lengths of both compounds are comparable and resonances appear as broad singlets at 3.90 and 3.97 ppm,
resemble values of aluminium complexes of N,N′,N′-substi- respectively. Further evidence is given by the asymmetric and
tuted 1,2-ethanediamine ligands.9a The Al–H bond lengths symmetric Al–H stretches that occur at 1780 and 1808 cm−1 as
(1.516(15)–1.56(2) Å) and H–Al–H bond angles (109.6(12) and well as 1775 and 1805 cm−1. The mean values, i.e., 1794 and
119.5(11)°) are reminiscent of values reported before for mono- 1790 cm−1, are significantly red-shifted compared to alu-
nuclear aluminium dihydride complexes based on N,N-chelat- minium hydrides based on other N,N-chelating ligands.6i,16
ing ligands (1.379(45)–1.611(19) Å; 109.4(16)–122(2)°).15 The
Within the distannylenes 1mSnHMDS and 1nSnHMDS the
room temperature 1H NMR spectra 1jAlH2 and 1kAlH2 in tin(II) centres are surrounded by an overall pyramidal ligand
CDCl3 are distinctly different: in the first case, a simple set of array and reside in a distorted tetrahedral environment with
resonances, i.e. one triplet and quartet representing the term- one vertex occupied by a stereo-chemically active lone pair of
inal ethyl rests but also the expected singlet : doublet : triplet electrons, Fig. 6. The Sn–N(TMS)2 bond lengths (2.1440(17)–
pattern of the aryl-bridge, account for a symmetric or averaged 2.165(3) Å) are in good agreement with those reported
structure in solution. In case of 1kAlH2, however, a series of of related mono- (2.109(4)–2.150(2) Å)17 and distannylenes
sharp multiplets including the resonances of the 1,3-pheny- (2.124(2)–2.140(5) Å)18 involving N,N-chelating ligands. The room
lene-bridge indicate the presence of at least two conformers temperature 1H NMR spectrum of 1mSnHMDS in toluene-d8
that do not undergo rapid exchange. The presence of an AlH2 consists of a series of broad resonances that eventually col-
lapse upon heating to 353 K to well-defined signals being in
agreement with a symmetric or averaged structure in solution.
This indicates hindered motion of the molecule likely due to
the more rigid oxydiphenylene-bridge. In contrast, the reso-
nance sets of 1nSnHMDS in C6D6 are symmetrical due to con-
formational averaging on the NMR time scale illustrating the
increased flexibility of the bridging group.
After having studied the coordination behaviour of the
protio-ligands 1, we became interested in the complexation
Scheme 5 Synthesis of dinuclear aluminium(III) and tin(II) complexes.
abilities of 2. As discussed above, the coordination of the
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lateral tertiary nitrogen atoms induces chirality and possibly
leads to various diastereomers, Fig. 3. 2a possesses a bridging
piperazine ring and the two lateral nitrogen atoms do not
become chiral upon complexation. However, two isomers, i.e.,
anti and syn, are conceivable when assuming a chair confor-
mation of the central piperazine ring.
Reacting 2a with trimethylaluminium or diethyl zinc
affords the complexes 2aAlMe2 and 2aZnEt in 81% and 21%
yield, respectively, as colourless crystals, Scheme 6. Their mole-
cular structures in the solid state are given in Fig. 7 and as
expected, both complexes exist in the anti-configuration, i.e.,
both binding sites are directed in opposite directions. The
Fig. 8 Solid-state structures (hydrogen atoms are omitted for clarity)
with selected bond lengths [Å] and angles [°]: (a) 2bMg: Mg1–N1
2.0027(9), Mg1–N2 2.1781(10), Mg1–N3 2.1968(10), Mg1–N4 2.0009(8),
structural parameters including the Al–N (1.8361(13) and N1–Mg1–N2 85.42(4), N3–Mg1–N4 85.89(4); (b) 2bZn: Zn1–N1 1.9291
(13), Zn1–N2 2.1882(12), Zn1–N3 2.2091(11), Zn1–N4 1.9281(13), N1–
Zn1–N2 85.81(5), N3–Zn1–N4 86.49(5).
2.0723(13) Å) and Al–C (1.9680(17)–1.9722(16) Å) bond lengths
of 2aAlMe2 are comparable to those of the related mono-
nuclear counterpart.9a While for 2aZnEt no related mono-
nuclear relative has so far been reported, the Zn–C bond
lengths (1.958(2)–1.972(2) Å) are in good agreement with
values reported for comparable mononuclear complexes based
on N,N-chelating ligands (1.964(5)–2.002(2) Å).19
In going from 2a to the more flexible protio-ligand 2b, the
reaction with diethyl zinc does not afford a heteroleptic dinuc-
lear complex but instead the mononuclear homoleptic
complex 2bZn is formed in 82% yield, Scheme 7. As expected,
the same holds true for the reaction of 2b with magnesium bis
[bis(trimethylsilyl)amide], which gives rise to 2bMg (65%
yield). Single crystals of both compounds could be obtained
and their molecular structures have been investigated by an
XRD analysis, Fig. 8.
2bMg and 2bZn crystallize in the centrosymmetric space
groups P21/c and P21/n, respectively, and accommodate hence
equal numbers of the R,R- and S,S-diastereomers. While the
obtained molecular structures do not allow deducing infor-
mation of the bulk sample, 1H NMR spectroscopic data
(measured in THF-d8 and in C6D6/THF-d8, respectively) give no
evidence for the presence of the meso-diastereomer.
Characteristic features are two singlets integrating for 12 and 6
protons, respectively, accounting for the methyl groups at the
2,6-DMP substituent and at the lateral nitrogen atoms. The
latter resonance is significantly affected by the central metal
and appears at 2.59 ppm in case of magnesium while it is
shifted to higher field in case of zinc (2.14 ppm). The methyl-
ene resonances of the formed macrocycle split into several
multiplets indicating separate signals for the axial and equa-
torial protons. Furthermore and due to anisotropic effects, the
axial protons show smaller chemical shift values compared to
their equatorial counterparts. The Mg–N and Zn–N bond
lengths with values of 2.0009(8) to 2.1968(10) Å and 1.9281(13)
to 2.2091(11) Å, respectively, as well as the N–M–N bite angles
(85.42(4) and 85.89(4)° (Mg) and 85.81(5) and 86.49(5)° (Zn))
resemble those of the mononuclear complexes 1nMg and
1nZn discussed before. However, the shorter ethylene-bridge
in case of 2bMg and 2bZn induces wider NMN plane to plane
twist angles (118.73(4) and 118.12(4)°, respectively) as com-
pared to the related complexes of 1n (99.17(6) and 98.75(5)°
for 1nMg and 1nZn, respectively).
Scheme 6 Synthesis of dinuclear aluminium(III) and zinc(II) complexes
starting from 2a.
Fig. 7 Solid-state structures (hydrogen atoms are omitted for clarity)
with selected bond lengths [Å] and angles [°]: (a) 2aAlMe2: Al1–N1
1.8361(13), Al1–N2 2.0723(13), Al1–C13 1.9722(16), Al1–C14 1.9680(17),
N1–Al1–N2 87.35(5), C13–Al1–C14 113.28(7); (b) 2aZnEt: Zn1–N1
1.8920(17), Zn1–N2 2.2060(12), Zn1–C25 1.972(2), Zn2–N3 2.1842(12),
Zn2–N4 1.8966(17), Zn2–C27 1.958(2), N1–Zn1–N2 85.33(6), N3–Zn2–
N4 85.27(6).
Reacting the protio-ligand 2b with aluminium hydride tri-
methylamine yields the mononuclear complex 2bAlH, regard-
less of whether one or two equivalents of AlH3·NMe3 were
used, Scheme 8. Its molecular solid-state structure has been
Scheme 7 Synthesis of homoleptic magnesium and zinc complexes
starting from 2b.
Scheme 8 Synthesis of mono- and dinuclear aluminium complexes.
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Fig. 9 Solid-state structures (hydrogen atoms except the AlH and in case of 2bAlMe2 a second independent molecule are omitted for clarity) with
selected bond lengths [Å] and angles [°]: (a) 2bAlH: Al1–N1 1.8924(13), Al1–N2 2.0771(11), Al1–N3 2.3482(13), Al1–N4 1.8520(11), Al1–H1 1.522(17),
N1–Al1–N2 83.17(5), N3–Al1–N4 79.31(5); (b) 2bAlMe2: Al1–N1 1.8324(16), Al1–N2 2.021(10), Al1–C13 1.984(6), Al1–C14 1.939(8), N1–Al1–N2 87.0
(2), C13–Al1–C14 114.7(3); (c) 2dAlMe2: Al1–N1 1.8352(14), Al1–N2 2.0400(16), Al1–C26 1.975(2), Al1–C27 1.9759(19), N1–Al1–N2 87.21(6), C26–
Al1–C27 114.09(9).
analysed by single-crystal XRD revealing the presence of the trical substitution pattern at aluminium gives rises to two sing-
meso-diastereomer and the two NCH3 groups and the hydride lets accounting for the two Al(CH3) groups and the N(CH3)
ligand are oriented in the same direction, Fig. 9a. The 1H NMR groups appear as one singlet. Notably, the longer propylene-
spectrum recorded in C6D6 shows two singlets for the DMP bridge in case of 2dAlMe2 might causes the equivalence of the
methyl groups indicating hindered rotation about the N–Caryl proton resonances of the meso- and R,R/S,S-diastereomers. In
bond. One singlet accounts for the methyl groups bound to both complexes, free rotation about the N–Caryl bond is evi-
the lateral nitrogen atoms while the resonances of the linkers’ denced by a simples set of resonances of the DMP group, i.e.,
methylene groups appear a several multiplets in agreement one singlet, one doublet, and one triplet integrating for 12, 4
with a locked conformation of the macrocycle. The Al–N bonds and 2 protons, respectively.
(1.8520(11) to 2.3482(13) Å) are in the range of the dinuclear
complexes 1jAlH2 and 1kAlH2 discussed above. The Al–H bond
length (1.522(17) Å) is in good agreement with values reported
before for other aluminium(III) monohydride complexes invol-
Conclusions
ving four Al–N bonds (1.48(4) to 1.607(15) Å).20 The Al–H In summary, we report about the synthesis of two general
stretching frequency of 1735 cm−1 falls well in between pre- types of bis(amidoamine) ligands, in which the tertiary amine
viously reported values of 1693 to 1836 cm−1 20b,d,21
.
functions reside either on the lateral (type 2) or terminal (type
Changing the aluminium source to trimethyl aluminium 1) positions. Five synthetic procedures starting from readily
does not afford the respective mononuclear complex but available precursors have been employed and allowed for the
instead the dinuclear aluminium alkyl complex 2bAlMe2 is gram-scale synthesis of the protio-ligands with yields ranging
formed in 50% yield. The same holds true for the propylene- from 21 to 99%. Starting from the protio-ligands of type 1, we
bridged protio-ligand 2d, which affords the dinuclear complex could successfully isolate and fully characterize six complexes.
2dAlMe2 in 70% yield. Their molecular structures in the solid Due to the flexibility of bridging groups, the reactions incor-
state are shown in Fig. 9. In case of 2bAlMe2, the meso-diaster- porating Mg(HMDS)2 or ZnEt2 afforded the mononuclear
eomer was observed by XRD, while in case of 2dAlMe2 the S,S- homoleptic complexes 1nMg and 1nZn, respectively, in-line
diastereomer was detected, but the centrosymmetric P21/c with a Schlenk equilibrium. In contrast, originating from
space group indicates that 2dAlMe2 is obtained as a mixture of AlH3·NMe3 and Sn(HMDS)2 gave rise to the dinuclear com-
enantiomers. Please note, that increasing the lengths of the plexes 1jAlH2, 1kAlH2, 1mSnHMDS, and 1nSnHMDS. The pres-
linker group changes the priorities according to the Cahn– ence of reactive amide and hydride functions in the dinuclear
Ingold–Prelog priority rules although 2bAlMe2 and 2dAlMe2 complexes indicates possible applications, i.e., as ligands for
are virtually identical.22 Both species possess two tetra-co- (transition) metals or as catalysts in their own rights. Using the
ordinated aluminium centres. The Al–C and Al–N bond piperazine-bridged ligand 2a, dinuclear Janus-type complexes
lengths (1.939(8)–1.984(6)
Å and 1.8302(14)–2.0400(16) Å, of aluminium and zinc could be obtained. The flexible ethyl-
respectively) as well as the C–Al–C and N–Al–N bond angles ene-bridged ligand 2b shows a variety of coordination modes
(113.08(13)–114.7(3)° and 87.0(2)–87.21(6)°, respectively) are in upon complexation and the pro-chirality of the lateral tertiary
good agreement with those of 2aAlMe2 and the related mono- amine groups affects the overall geometry of the obtained pro-
nuclear congeners.9a The 1H NMR spectrum of 2bAlMe2 ducts. Mononuclear complexes of aluminium, magnesium,
recorded in CDCl3 contains two sets of four and two partially and tin were isolated after the reaction with AlH3·NMe3, Mg
overlapping singlets that were assigned to the respective Al (HMDS)2, and ZnEt2, respectively, while dinuclear complexes
(CH3) and N(CH3) groups and indicate a mixture of the meso- were derived from 2b and trimethyl aluminium. The related
and R,R/S,S-diastereomers. In case of 2dAlMe2, the unsymme- species crystallize in centrosymmetric space groups and
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different diastereomers were identified from their molecular toluene (8 mL) and stirred at 100 °C overnight resulting in a
solid-state structures. The R,R or S,S form was observed in case yellow suspension. After cooling to room temperature the
of 2bMg, 2bZn, 2dAlMe2, while the meso form was observed solids were filtered off and the filtrate concentrated to 5 mL.
for 2bAlH and 2bAlMe2. In solution, however, a second set of After standing at room temperature overnight, 1nZn (195 mg,
resonances in the 1H NMR spectrum indicates a mixture of the 0.41 mmol, 72%) was isolated as clear colourless crystals.
meso and the R,R/S,S-diastereomers for 2bAlMe2, while the
1H NMR (400 MHz, C6D6 + THF-d8): δ (ppm) = 7.25 (t, J =
spectra of 2bAlH, 2bMg, 2bZn, and 2dAlMe2 shown only one 7.5 Hz, 2H, C6H4), 7.08 (d, J = 7.1 Hz, 2H, C6H4), 6.64 (d, J = 8.2
set of resonances. The catalytic activity of the heteroleptic com- Hz, 2H, C6H4), 6.55 (t, J = 7.2 Hz, 2H, C6H4), 3.96–3.89 (m, 2H,
plexes and their coordination capabilities towards transition C6H4CH2CH2C6H4), 3.42–3.37 (m, 2H, NCH2CH2NC6H4),
metals will be further investigated in the future.
3.06–2.98 (m, 2H, NCH2CH2NC6H4), 2.56–2.24 (m, 14H,
C6H4CH2CH2C6H4 + NCH2CH2NC6H4 + NCH2CH3), 0.57 (br,
12H, NCH2CH3); 13C{H} NMR (101 MHz, C6D6 + THF-d8): δ
(ppm) = 154.8 (C6H4), 130.5 (C6H4), 128.1 (C6H4), 126.6 (C6H4),
112.8 (C6H4), 111.8 (C6H4), 53.1 (C6H4CH2CH2NC6H4), 47.2
Experimental section
General considerations
(NCH2CH3), 46.0 (NCH2CH2N), 40.9 (NCH2CH3), 33.5
∼
All preparations were performed under an inert atmosphere of (NCH2CH2N), 8.1 (ZnCH2CH3), 6.5 (ZnCH2CH3); IR (ATR): v
dinitrogen by means of standard Schlenk-line techniques, [cm−1] = 3039 (w), 2931 (w), 2867 (w), 2799 (w), 1588 (m), 1473
while the samples for analytics were handled in a glovebox (m), 1439 (m), 1306 (vs), 1085 (m), 924 (m), 745 (vs), 726 (vs);
(MBraun). Yields are nonoptimized and refer to isolated crys- anal. calc. (found) for [C26H40ZnN4]: C 65.88 (65.88), H 8.51
talline material. All solvents (toluene, n-pentane, n-hexane, (8.40), N 11.82 (11.70).
tetrahydrofuran) were distilled from Na/benzophenone prior to
use while C6D6, THF-d8 and toluene-d8 were dried using mole- was cooled to −78 °C before it was added to AlH3·NMe3
cular sieves (4 Å). (1.13 g, 12.6 mmol) followed by stirring at room temperature
1jAlH2: A solution of 1j (1.84 g, 6.00 mmol) in THF (60 mL)
1nMg: Mg(HMDS)2 (485 mg, 1.40 mmol) was added to a for 15 hours. The solvent was removed and the resulting solid
stirred solution of 1n (275 mg, 0.67 mmol) in toluene (8 mL) was dried in vacuum to obtain 1jAlH2 (2.00 g, 0.55 mmol,
and stirred at 110 °C overnight resulting in a pale brown solu- 92%) as a white powder. Crystals suitable for an XRD analysis
tion. After cooling to room temperature the solvent was were obtained from a saturated THF solution upon standing at
removed and the brown solid was washed with n-pentane (1 × room temperature.
10 mL). The solid was dissolved in THF (5 mL), filtered off and
1H NMR (400 MHz, CDCl3): δ (ppm) = 6.92 (t, J = 7.9 Hz,
a few drops of n-pentane were added to the solution. After 1H, C6H4), 5.90 (dd, J = 7.9; 2.1 Hz, 2H, C6H4), 5.77 (s, 1H),
standing at room temperature overnight, 1nMg (171 mg, 3.90 (br, 4H, AlH2), 3.21 (t, J = 5.8 Hz, 4H, NCH2CH2N),
0.40 mmol, 59%) could be isolated as clear colourless crystals.
3.07–2.95 (m, 8H, NCH2CH3), 2.91–2.79 (m, 4H, NCH2CH2N),
1H NMR (400 MHz, C6D6): δ (ppm) = 7.49 (t, J = 7.5 Hz, 2H, 1.17 (t, J = 7.2 Hz, 12H, NCH2CH3); 13C{1H} NMR (101 MHz,
C6H4), 7.28 (d, J = 7.3 Hz, 2H, C6H4), 6.78–6.75 (m, 4H, C6H4), CDCl3): δ (ppm) = 153.9 (C6H4), 129.4 (C6H4), 101.9 (C6H4),
3.55–3.47 (m, 2H, C6H4CH2CH2C6H4), 3.34–3.30 (m, 2H, 98.02 (C6H4), 53.0 (CH2CH2), 43.9 (CH2CH2), 42.1 (CH3CH2),
NCH2CH2NC6H4), 3.04–2.96 (m, 2H, NCH2CH2NC6H4), 8.5 (CH3CH2); IR (ATR): ∼v [cm−1] = 2967 (w), 2924 (w), 2866 (w),
2.86–2.77 (m, 2H, C6H4CH2CH2C6H4), 2.43–2.15 (m, 10H, 2804 (w), 1808 (m), 1780 (m), 1579 (m), 1466 (m), 1353 (m),
NCH2CH2NC6H4
+
NCH2CH3),
2.06–1.97
(m,
2H, 1264 (m), 1014 (m), 778 (s), 658 (vs), 535 (vs); anal. calc.
NCH2CH2NC6H4), 0.51 (t, J = 7.2 Hz, 6H, NCH2CH3), 0.38 (t, J = (found) for [C18H36N4Al2·0.15 THF]: C 60.39 (60.73), H 10.14
7.2 Hz, 6H, NCH2CH3); 1H NMR (400 MHz, THF-d8): δ (ppm) = (10.50), N 13.81 (14.13).
6.87 (dt, J = 8.0 Hz, 2H, C6H4), 6.79 (dd, J = 7.1 Hz, 2H, C6H4),
6.28 (d, J = 8.0 Hz, 2H, C6H4), 6.16 (dt, J = 7.2 Hz, 2H, C6H4), (15 mL) was cooled to −78 °C before it was added to
3.41–3.28 (m, 4H, C6H4CH2CH2C6H4 NCH2CH2NC6H4), AlH3·NMe3 (180 mg, 2.00 mmol) followed by stirring at room
1kAlH2: A solution of 1k (330 mg, 1.00 mmol) in THF
+
3.13–2.97 (m, 6H, NCH2CH2NC6H4), 2.87 (q, 8H, J = 7.1 Hz, temperature for 1 hour. Upon standing at room temperature
NCH2CH3), 2.40–2.30 (m, 2H, C6H4CH2CH2C6H4), 1.03 (t, J = crystals of 1kAlH2 (382 mg, 0.99 mmol, 99%) formed, which
8.3 Hz, 12H, NCH2CH3); 13C{H} NMR (101 MHz, C6D6): δ were collected and dried in vacuum.
(ppm) = 156.6 (C6H4), 130.4 (C6H4), 128.7 (C6H4), 126.8 (C6H4),
1H NMR (400 MHz, CDCl3): δ (ppm) = 6.98–6.91 (m, 1H,
112.5 (C6H4), 110.7 (C6H4), 52.7 (C6H4CH2CH2C6H4), 45.0 C6H4), 6.00–5.90 (m, 2H, C6H4), 5.88–5.80 (m, 1H, C6H4), 3.97
(NCH2CH2N), 45.0 (NCH2CH2N), 39.2 (NCH2CH3), 33.8 (br, 4H, AlH2), 3.36–3.25 (m, 8H, α-pip + C6H4NCH2CH2), 3.01
(NCH2CH3), 8.6 (NCH2CH3), 8.5 (NCH2CH3); IR (ATR): ∼v [cm−1
]
(t, J = 6.0 Hz, 4H, C6H4NCH2CH2), 2.34 (dt, J = 11.9 Hz, J = 2.6
= 3048 (w), 2966 (w), 2925 (w), 2865 (w), 2795 (w), 1590 (m), Hz, 4H, α-pip), 2.02–1.74 (m, 8H, β-pip), 1.47–1.25 (m, 4H,
1486 (m), 1440 (m), 1304 (s), 1155 (m), 1083 (m), 746 (s), 728 γ-pip); 13C{1H} NMR (101 MHz, CDCl3): δ (ppm) = 153.9
(vs); anal. calc. (found) for [C26H40MgN4]: C 72.13 (72.23), H (C6H4), 129.7 (C6H4), 102.1 (C6H4), 98.3 (C6H4), 59.8
9.31 (8.91), N 12.94 (12.75).
(C6H4NCH2CH2), 54.8 (α-pip), 41.7 (C6H4NCH2CH2), 24.2
∼
1nZn: Zn(Et)2 (1.20 mL, 1.20 mmol, 1.0 M in hexanes) was (β-pip), 23.4 (γ-pip); IR (ATR): v [cm−1] = 2942 (w), 2856 (w),
added to a stirred solution of 1n (235 mg, 0.57 mmol) in 1805 (w), 1775 (w), 1590 (m), 1469 (m), 1339 (m), 1229 (m),
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1029 (m), 777 (s), 674 (vs); despite repeated attempts no suit-
able elemental analysis could be obtained.
1H NMR (400 MHz, THF-d8): δ (ppm) = 6.66 (d, J = 7.3 Hz,
4H, m-C6H3), 6.22 (t, J = 7.2 Hz, 2H, p-C6H3), 3.09–2.92 (m, 6H,
1mSnHMDS: Sn(HMDS)2 (706 mg, 0.62 mL, 1.61 mmol) NCH2CH2NC6H3), 2.89–2.82 (m, 2H, NCH2CH2N), 2.59 (s, 6H,
was added to a stirred solution of 1m (320 mg, 0.80 mmol) in NCH3) 2.57–2.53 (m, 2H, NCH2CH2NC6H3), 2.19 (s, 12H,
toluene (8 mL) followed by stirring at 100 °C overnight result- CH3C6H3); 13C{1H} NMR: due to the low solubility of the
ing in a black solution. After cooling to room temperature the complex, even after extended scans no suitable 13C NMR spec-
∼
solvent was removed and n-pentane (5 mL) was added to the trum could be obtained; IR (ATR): v [cm−1] = 3045 (w), 2965
black oil resulting in the instant formation of crystals. After (w), 2804 (w), 2788 (w), 1588 (m), 1470 (m), 1415 (m), 1280 (m),
washing the crystals with n-pentane (3 × 2 mL), 1mSn (110 mg, 1074 (m), 760 (vs), 740 (s); anal. calc. (found) for
0.12 mmol, 14%) could be isolated as slightly brownish [C24H36MgN4]: C 71.20 (71.13), H 8.96 (8.63), N 13.84 (13.72).
crystals.
2aZnEt: Zn(Et)2 (2.43 mL, 2.43 mmol, 1.0 M in hexanes) was
1H NMR (400 MHz, 353 K, toluene-d8): δ (ppm) = 7.22–7.20 added to a stirred solution of 2a (440 mg, 1.16 mmol) in
(m, 1H, C6H4), 7.04–7.00 (m, 3H, C6H4), 6.68–6.64 (m, 2H, toluene (8 mL) and stirred at 100 °C overnight resulting in a
C6H4), 6.52–6.41 (m, 2H, C6H4), 3.37–3.23 (m, 4H, NCH2CH2N), clear solution. Upon slow cooling to room temperature 2aZn
2.74–2.58 (m, 8H, NCH2CH2N + NCH2CH3), 2.51–2.42 (m, 4H, (140 mg, 0.25 mmol, 21%) crystallized as clear colorless
NCH2CH3), 0.89–0.79 (m, 12H, NCH2CH3), 0.26–0.22 (m, 36H, blocks.
SiCH3); 13C{1H} NMR: even after repeated attempts at various
1H NMR (400 MHz, C6D6): δ (ppm) = 7.27 (d, J = 7.4 Hz, 4H,
temperatures no suitable 13C NMR spectrum could be p-C6H3), 7.02 (t, J = 7.5 Hz, 2H, m-C6H3), 3.07 (t, J = 5.4 Hz, 4H,
∼
obtained; IR (ATR): v [cm−1] = 3052 (vw), 2944 (w), 2894 (vw), NCH2CH2NC6H3), 2.48 (s, 12H, CH3C6H3), 3.35 (d, J = 8.8 Hz,
2865 (w), 2831 (w), 1594 (m), 1491 (s), 1305 (s), 1243 (s), 1126 4H, NCH2CH2N), 2.13 (t, J = 5.4 Hz, 4H, NCH2CH2NC6H3), 1.99
(m), 930 (vs), 732 (vs), 662 (s); anal. calc. (found) for (d, J = 8.8 Hz, 4H, NCH2CH2N), 1.32 (t, J = 8.0 Hz, 6H,
[C36H72N6OSi4Sn2]: C 45.29 (45.46), H 7.60 (7.11), N 8.80 (8.69). ZnCH2CH3), 0.38 (q, J = 8.1 Hz, 4H, ZnCH2CH3); 13C{H} NMR
1nSnHMDS: Sn(HMDS)2 (503 mg, 0.44 mL, 1.14 mmol) was (101 MHz, C6D6): δ (ppm) = 154.9 (i-C6H3), 133.3 (o-C6H3),
added to a stirred solution of 1n (235 mg, 0.57 mmol) in 129.3 (m-C6H3), 121.2 (p-C6H3), 62.3 (NCH2CH2NC6H3), 52.0
toluene (8 mL) followed by stirring at 100 °C overnight result- (NCH2CH2N), 48.0 (NCH2CH2NC6H3), 20.4 (CH3C6H3), 12.3
∼
ing in an orange solution and a grey precipitate. After cooling (ZnCH2CH3), 3.6 (ZnCH2CH3); IR (ATR): v [cm−1] = 3052 (w),
to room temperature the solids were filtered off and the filtrate 2939 (w), 2893 (w), 2852 (w), 1585 (m), 1460 (m), 1418 (s),
was concentrated to dryness affording a dark orange solid. 1273 (s), 1087 (s), 955 (s), 755 (vs); anal. calc. (found) for
n-pentane (5 mL) was added causing the instant formation of [C28H44Zn2N4]: C 59.27 (59.59), H 7.82 (7.41), N 9.87 (9.70).
1nSn (225 mg, 0.23 mmol, 41%) as an orange crystalline solid.
2aAlMe2: AlMe3 (2.00 mmol, 1.00 mL, 2.0 M in toluene) was
Crystals suitable for an X-Ray diffraction analysis were added slowly to a stirred solution of 2a (382 mg, 1.00 mmol) in
obtained from recrystallization in a mixture of THF/n-pentane toluene (10 mL) and stirred at reflux overnight. Upon slow
(1 : 1) at room temperature.
1H NMR (400 MHz, C6D6): δ (ppm) = 7.55 (d, J = 6.1 Hz, 2H, 81%) crystallized as clear colorless crystals.
C6H4), 7.36 (t, J = 7.4 Hz, 2H, C6H4), 6.96 (t, J = 6.9 Hz, 2H,
1H NMR (400 MHz, CDCl3): δ (ppm) = 7.06 (d, J = 8.0 Hz, 4H,
C6H4), 6.89 (d, 8.1 Hz, 2H, C6H4), 3.64 (s, 4H, m-C6H3), 6.90 (t, J = 7.5 Hz, 2H, p-C6H3), 3.59 (d, J = 9.3 Hz,
cooling to room temperature 2aAlMe2 (400 mg, 0.81 mmol,
J
=
C6H4CH2CH2C6H4), 3.29–3.26 (m, 4H, NCH2CH2N), 2.48–2.45 4H, NCH2CH2N), 3.25 (t, J = 5.7 Hz, 4H, NCH2CH2NC6H3), 3.13
(m, 12H, NCH2CH2N + NCH2CH3), 0.60 (t, J = 7.3 Hz, 12H, (t, J = 5.7 Hz, 4H, NCH2CH2NC6H3), 2.99 (d, J = 9.1 Hz, 4H,
NCH2CH3), 0.36 (s, 36H, SiCH3); 13C{1H} NMR (101 MHz, NCH2CH2N), 2.31 (s, 12H, C6H3CH3), −0.74 ( s, 12H, Al(CH3)2);
C6D6): δ (ppm) = 154.4 (C6H4), 130.0 (C6H4), 127.5 (C6H4), 13C{1H} NMR (101 MHz, CDCl3): δ (ppm) = 149.1 (i-C6H3),
116.7 (C6H4), 115.6 (C6H4), 54.0 (C6H4CH2CH2C6H4), 49.8 137.8 (o-C6H3), 128.3 (m-C6H3), 123.2 (p-C6H3), 61.4
(NCH2CH2N), 43.9 (NCH2CH2N), 36.1 (NCH2CH3), 8.6 (NCH2CH2NC6H3), 51.7 (NCH2CH2NC6H3), 45.8 (NCH2CH2N),
∼
∼
(NCH2CH3), 6.8 (SiCH3); IR (ATR): v [cm−1] = 3057 (vw), 2945 19.0 (C6H3CH3), −6.9 (Al(CH3)2); IR (ATR): v [cm−1] = 2935 (w),
(w), 2892 (vw), 2826 (w), 1591 (m), 1483 (m), 1438 (m), 1243 (s), 2916 (w), 2838 (w), 2809 (w), 1466 (m), 1229 (m), 1184 (m),
904 (vs), 821 (vs), 744 (s), 664 (s); anal. calc. (found) for 1095 (m), 944 (m), 886 (m), 653 (s); anal. calc. (found)
[C38H76N6Si4Sn2·0.15 C5H12]: C 47.61 (47.83), H 8.02 (7.67), N for [C28H47N4Al2·0.15 C7H8]: C 68.89 (68.96), H 9.39 (9.44),
8.60 (8.51).
2bMg: Mg(HMDS)2 (1.57 g, 4.56 mmol) was added to a
N 11.06 (11.22).
2bZn: Zn(Et)2 (5.10 mL, 5.10 mmol, 1.0 M in hexanes) was
stirred solution of 2b (830 mg, 2.17 mmol) in toluene (8 mL) added to a stirred solution of 2b (930 mg, 2.43 mmol) in
and stirred at 100 °C overnight resulting in the formation of a toluene (8 mL) and stirred at 100 °C overnight resulting in a
white precipitate. After cooling to room temperature, the clear solution. Upon slow cooling to room temperature 2bZn
solids were filtered off and washed with n-pentane (3 × 5 mL) (890 mg, 2.00 mmol, 82%) crystallized as clear colourless
to obtain 2bMg (570 mg, 1.40 mmol, 65%) as a white solid. blocks.
Crystals suitable for an X-Ray diffraction analysis were
obtained by extraction with hot THF (40 mL) followed by slow 7.3 Hz, 4H, m-C6H3), 6.71 (t, J = 7.4 Hz, 2H, p-C6H3), 3.34–3.28
1H NMR (400 MHz, C6D6 + THF-d8): δ (ppm) = 6.99 (d, J =
cooling to room temperature.
(m, 2H, NCH2CH2NC6H3), 2.83–2.77 (m, 2H, NCH2CH2NC6H3),
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2.37–2.35 (m, 2H, NCH2CH2N), 2.28–2.17 (m, 4H,
2dAlMe2: AlMe3 (5.00 mmol, 2.50 mL, 2.0 M in toluene) was
NCH2CH2NC6H3), 2.14–2.12 (m, 18H, NCH3 + CH3C6H3), added slowly to a stirred solution of 2d (970 mg, 2.45 mmol)
1.80–1.77 (m, 2H, NCH2CH2N); 13C{H} NMR (101 MHz, C6D6 + in toluene (20 mL) and stirred under reflux overnight. After
THF-d8): δ (ppm) = 156.9 (i-C6H3), 133.6 (o-C6H3), 128.6 (m- cooling to room temperature, the solution was concentrated to
C6H3), 119.4 (p-C6H3), 61.2 (CH3NCH2CH2NCH3), 51.3 about 6 mL to initiate crystallization. After standing at room
(NCH2CH2N), 50.1 (NCH2CH2N), 44.3 (CH3NCH2CH2NCH3), temperature overnight 2dAlMe2 (710 mg, 1.22 mmol, 50%) was
∼
20.4 (CH3C6H3); IR (ATR): v [cm−1] = 3046 (w), 2966 (w), 2853 isolated as clear colourless crystals.
(w), 2836 (w), 1587 (m), 1469 (m), 1412 (m), 1279 (m), 1084
(m), 764 (vs), 740 (s); anal. calc. (found) for [C24H36ZnN4]: C 4H, m-C6H3), 6.90 (t, J = 7.4 Hz, 2H, p-C6H3), 3.46–3.38 (m,
64.64 (64.59), H 8.14 (7.70), N 12.56 (12.30). 2H, NCH2CH2NC6H3), 3.33–3.25 (m, 2H, NCH2CH2CH2N),
2bAlH: A solution of 2b (300 mg, 0.78 mmol) in Et2O 3.03–2.79 (m, 6H, NCH2CH2NC6H3 NCH2CH2CH2N),
1H NMR (400 MHz, CDCl3): δ (ppm) = 7.06 (d, J = 7.4 Hz,
+
(10 mL) was cooled to −78 °C before it was added to AlH3·NMe3 2.67–2.61 (m, 8H, NCH2CH2NC6H3 + NCH3), 2.32 (s, 12H,
(77 mg, 0.86 mmol) followed by stirring at room temperature C6H3CH3), 2.21–2.11 (m, 2H, CH2CH2CH2) −0.78–0.81 (m,
overnight. The solvent was removed and the resulting crystalline 12H, Al(CH3)2); 13C{1H} NMR (101 MHz, CDCl3): δ (ppm) =
solid was washed with n-pentane (2 × 5 mL) to obtain 2bAlH 149.6 (i-C6H3), 138.1 (o-C6H3), 128.2 (m-C6H3), 123.0 (p-C6H3),
(298 mg, 0.73 mmol, 93%) as a white crystalline solid.
60.4/59.4
(NCH2CH2NC6H3),
56.4/56.1,
(CH2CH2CH2),
1H NMR (400 MHz, C6D6): δ (ppm) = 7.07–7.02 (m, 4H, 46.8/46.7 (NCH2CH2NC6H3), 40.2/40.0 (NCH3), 22.6/20.4
m-C6H3), 6.97–6.93 (m, 2H, p-C6H3), 3.13–3.06 (m, 2H, (CH2CH2CH2) 18.9/18.9 (C6H3CH3), −8.0 /-9.0 (Al(CH3)2); IR
∼
NCH2CH2NC6H3), 2.61–2.50 (m, 4H, NCH2CH2N
+
(ATR): v [cm−1] = 2913 (w), 2812 (w), 1474 (m), 1422 (m), 1338
NCH2CH2NC6H3), 2.46 (s, 6H, NCH3), 2.11–2.04 (m, 2H, (m), 1236 (m), 1103 (m), 936 (m), 654 (vs), 566 (s); anal. calc.
NCH2CH2N), 1.99 (s, 6H, C6H3CH3), 1.96 (s, 6H, C6H3CH3), (found) for [C29H50N4Al2]: C 68.47 (68.50), H 9.91 (9.62),
1.94–1.91 (m, 2H, NCH2CH2NC6H3), 1.77–1.70 (m, 2H, N 11.01 (10.85).
NCH2CH2NC6H3); 1H NMR (400 MHz, CDCl3): δ (ppm) =
X-ray crystallography
6.75–6.66 (m, 6H, C6H3), 3.21–3.15 (m, 2H, NCH2CH2NC6H3),
3.08–2.98 (m, 4H, NCH2CH2N + NCH2CH2NC6H3), 2.83–2.75
(m, 2H, NCH2CH2N), 2.64–2.60 (m, 4H, NCH2CH2NC6H3), 2.55
(s, 6H, NCH3), 2.10 (s, 6H, C6H3CH3), 1.76 (s, 6H, C6H3CH3);
13C{1H} NMR (101 MHz, C6D6): δ (ppm) = 153.0 (i-C6H3), 137.5
(o-C6H3), 128.4 (m-C6H3), 122.6 (p-C6H3), 58.8 (NCH2CH2NC6H3),
54.5 (NCH2CH2N), 47.8 (NCH2CH2NC6H3), 41.0 (NCH3), 20.6
(C6H3CH3), 18.5 (C6H3CH3); IR (ATR): ∼v [cm−1] = 2956 (w), 2910
(w), 2861 (w), 2806 (w), 1753 (w), 1590 (m), 1466 (m), 1339 (s),
1262 (s), 1217 (s), 1092 (s), 920 (m), 758 (vs), 654 (vs); anal.
calc. (found) for [C24H37AlN4]: C 70.55 (69.93), H 9.13 (8.66),
N 13.71 (13.42).
2bAlMe2: AlMe3 (15.7 mmol, 7.85 mL, 2.0 M in toluene) was
added slowly to a stirred solution of 2b (3.00 g, 7.80 mmol) in
toluene (35 mL) and stirred under reflux overnight. After
cooling to room temperature, the white suspension was fil-
tered and the remaining white solid was dried in vacuum to
obtain 2bAlMe2 (2.73 g, 5.50 mmol, 70%). Crystals suitable for
an XRD analysis grew from the filtrate upon standing at room
temperature.
The intensity data were collected on a GV-50 diffractometer
with TitanS2 detector from Rigaku Oxford Diffraction (for-
merly Agilent Technologies) applying Cu-Kβ radiation (λ =
1.39222 Å) for 1mSnHMDS and 1nZn and Cu-Kα radiation (λ =
1.54184 Å) for all other compounds. Analytical absorption cor-
rections were applied to the data.23 The structures were solved
by direct methods (SHELXT)24 and refined by full-matrix least
squares techniques against Fo2 (SHELXL-2018).25 The hydrogen
atoms bonded to the Aluminium-ion of 1jAlH2, 1kAlH2,
2bAlH2 and to the amine groups of compound 2a and 2b were
located by difference Fourier synthesis and refined isotropi-
cally. All other hydrogen atoms were included at calculated
positions with fixed thermal parameters. All non-hydrogen
atoms were refined anisotropically.25 Crystallographic data as
well as structure solution and refinement details are summar-
ized in Table S1 of the ESI.† Olex2 was used for structure
representations.26
Crystallographic data (excluding structure factors) has been
deposited with the Cambridge Crystallographic Data Centre
as supplementary publication CCDC-2026438 for 1jAlH2,
CCDC-2026439 for 1kAlH2, CCDC-2026440 for 1mSnHMDS,
CCDC-2026441 for 1nMg, CCDC-2026442 for 1nSnHMDS,
CCDC-2026443 for 1nZn, CCDC-2026444 for 2a, CCDC-2026430
for 2aAlMe2, CCDC-2026431 for 2aZnEt, CCDC-2026432 for 2b,
CCDC-2026433 for 2bAlH, CCDC-2026434 for 2bAlMe2,
CCDC-2026435 for 2bMg, CCDC-2026436 for 2bZn, and
CCDC-2026437 for 2dAlMe2.†
1H NMR (400 MHz, CDCl3): δ (ppm) = 7.07 (d, J = 7.4 Hz,
4H, m-C6H3), 6.91 (t, J = 7.4 Hz, 2H, p-C6H3), 3.48–3.30 (m, 6H,
NCH2CH2N + NCH2CH2NC6H3), 3.01–2.87 (m, 6H, NCH2CH2N
+ NCH2CH2NC6H3), 2.71–2.69 (m, 6H, NCH3), 2.32 (s, 12H,
C6H3CH3), −0.72–0.74 (m, 6H, Al(CH3)2), −0.79–0.81 (m, 6H, Al
(CH3)2); 13C{1H} NMR (101 MHz, CDCl3): δ (ppm) = 149.3 (i-
C6H3), 138.0 (o-C6H3), 128.3 (m-C6H3), 123.2 (p-C6H3), 61.2
(NCH2CH2NC6H3), 54.2 (NCH2CH2N), 46.5 (NCH2CH2NC6H3),
40.3 (NCH3), 18.9 (C6H3CH3),–7.4 (Al(CH3)2), −9.00 (Al(CH3)2);
∼
IR (ATR): v [cm−1] = 2922 (w), 2796 (w), 1589 (vw), 1471 (m),
1263 (m), 1215 (m), 1107 (m), 953 (m), 886 (s), 769 (s), 648 (vs);
anal. calc. (found) for [C28H48N4Al2·0.11 C7H8]: C 67.98 (68.68),
H 9.78 (9.67), N 11.33 (11.35).
Conflicts of interest
There are no conflicts to declare.
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Dalton Transactions
Chem. Commun., 2002, 958; (i) J.-F. Li, L.-H. Weng,
X.-H. Wei and D.-S. Liu, J. Chem. Soc., Dalton Trans., 2002,
1401; ( j) H. A. Jenkins, D. Abeysekera, D. A. Dickie and
J. A. C. Clyburne, J. Chem. Soc., Dalton Trans., 2002, 3919;
(k) C.-T. Chen, C.-A. Huang, Y.-R. Tzeng and B.-H. Huang,
Dalton Trans., 2003, 2585; (l) J. Grundy, M. P. Coles and
P. B. Hitchcock, J. Organomet. Chem., 2002, 662, 178;
(m) B. Clare, N. Sarker, R. Shoemaker and J. R. Hagadorn,
Inorg. Chem., 2004, 43, 1159; (n) M. S. Hill, P. B. Hitchcock
and S. M. Mansell, Dalton Trans., 2006, 1544; (o) S.-D. Bai,
J.-P. Guo and D.-S. Liu, Dalton Trans., 2006, 2244;
(p) S.-D. Bai, J.-P. Guo, D.-S. Liu and W.-Y. Wong,
Eur. J. Inorg. Chem., 2006, 2006, 4903; (q) M. Ohashi,
A. Yagyu, T. Yamagata and K. Mashima, Chem. Commun.,
2007, 3103; (r) Z. Lu, N. J. Hill, M. Findlater and
A. H. Cowley, Inorg. Chim. Acta, 2007, 360, 1316;
(s) M. V. Yakovenko, A. V. Cherkasov, G. K. Fukin, D. Cui
and A. A. Trifonov, Eur. J. Inorg. Chem., 2010, 2010, 3290;
(t) K. Stippich, R. Kretschmer, R. Beckert and H. Goerls,
Synthesis, 2010, 1311; (u) A. O. Tolpygin, A. S. Shavyrin,
A. V. Cherkasov, G. K. Fukin and A. A. Trifonov,
Organometallics, 2012, 31, 5405; (v) G. G. Skvortsov,
G. K. Fukin, S. Y. Ketkov, A. V. Cherkasov, K. A. Lyssenko
and A. A. Trifonov, Eur. J. Inorg. Chem., 2013, 2013, 4173;
(w) S.-D. Bai, R.-Q. Liu, T. Wang, F. Guan, Y.-B. Wu,
J.-B. Chao, H.-B. Tong and D.-S. Liu, Polyhedron, 2013, 65,
161; (x) A. O. Tolpygin, G. G. Skvortsov, A. V. Cherkasov,
G. K. Fukin, T. A. Glukhova and A. A. Trifonov, Eur. J. Inorg.
Chem., 2013, 2013, 6009; (y) M. Bayram, D. Bläser,
C. Wölper and S. Schulz, Organometallics, 2014, 33, 2080;
(z) A. O. Tolpygin, A. V. Cherkasov, G. K. Fukin and
A. A. Trifonov, Inorg. Chem., 2014, 53, 1537;
(aa) M. V. Yakovenko, N. Y. Udilova, T. A. Glukhova,
A. V. Cherkasov, G. K. Fukin and A. A. Trifonov, New J.
Chem., 2015, 39, 1083; (ab) M. Stollenz, J. E. Raymond,
L. M. Pérez, J. Wiederkehr and N. Bhuvanesh, Chem. – Eur.
J., 2016, 22, 2396; (ac) N. Kazeminejad, D. Munzel,
M. T. Gamer and P. W. Roesky, Chem. Commun., 2017, 53,
1060; (ad) C. O’Dea, O. Ugarte Trejo, J. Arras, A. Ehnbom,
N. Bhuvanesh and M. Stollenz, J. Org. Chem., 2019, 84,
14217; (ae) A. Rösch, S. H. F. Schreiner, P. Schüler, H. Görls
and R. Kretschmer, Dalton Trans., 2020, 49, DOI: 10.1039/
D0DT01923B, accepted for publication.
Acknowledgements
The work is dedicated to Winfried Plass on the occasion of his
60th birthday. The project was financially supported by the
Deutsche Forschungsgemeinschaft (DFG, KR4782/3-1), the
Friedrich Schiller University Jena and the Elite Network of
Bavaria. We thanks the reviewers for valuable comments and
suggestions.
Notes and references
1 (a) R. Robson, Inorg. Nucl. Chem. Lett., 1970, 6, 125;
(b) R. Robson, Aust. J. Chem., 1970, 23, 2217;
(c) N. H. Pilkington and R. Robson, Aust. J. Chem., 1970, 23,
2225; (d) A. E. Allen and D. W. C. Macmillan, Chem. Sci.,
2012, 2012, 633; (e) I. Bratko and M. Gomez, Dalton Trans.,
2013, 42, 10664; (f) J. A. Mata, F. E. Hahn and E. Peris,
Chem. Sci., 2014, 5, 1723; (g) P. Buchwalter, J. Rosé and
P. Braunstein, Chem. Rev., 2015, 115, 28; (h) R. Kretschmer,
Chem. – Eur. J., 2020, 26, 2099–2119.
2 (a) R. E. Mulvey, Organometallics, 2006, 25, 1060;
(b) Cooperative Catalysis: Designing Efficient Catalysts for
Synthesis, ed. R. Peters, Wiley, 2015; (c) P. Kalck, Homo- and
Heterobimetallic
Complexes
in
Catalysis,
Springer
International Publishing, Cham, 2016, vol. 59;
(d) L. Tebben, C. Mück-Lichtenfeld, G. Fernández,
S. Grimme and A. Studer, Chem. – Eur. J., 2017, 23, 5864;
(e) R. E. Mulvey, Acc. Chem. Res., 2009, 42, 743;
(f) S. D. Robertson, M. Uzelac and R. E. Mulvey, Chem. Rev.,
2019, 119, 8332.
3 (a) P. P. Power, Nature, 2010, 463, 171; (b) S. Yadav, S. Saha
and S. S. Sen, ChemCatChem, 2016, 8, 486; (c) R. Rochat,
M. J. Lopez, H. Tsurugi and K. Mashima, ChemCatChem,
2016, 8, 10; (d) M. S. Hill, D. J. Liptrot and C. Weetman,
Chem. Soc. Rev., 2016, 45, 972; (e) S. Dagorne and
R. Wehmschulte, ChemCatChem, 2018, 10, 2509;
(f) C. Weetman and S. Inoue, ChemCatChem, 2018, 10,
4213–4228; (g) L. C. Wilkins and R. L. Melen, Coord. Chem.
Rev., 2016, 324, 123; (h) S. Harder, Early Main Group Metal
Catalysis. Concepts and Reactions, John Wiley & Sons,
Incorporated, Newark, 2020.
4 A. Röther and R. Kretschmer, J. Organomet. Chem., 2020,
918, 121289.
6 (a) S. Herres-Pawlis, A. Neuba, O. Seewald, T. Seshadri,
H. Egold, U. Flörke and G. Henkel, Eur. J. Org. Chem., 2005,
2005, 4879; (b) G. Jin, C. Jones, P. C. Junk, K.-A. Lippert,
R. P. Rose and A. Stasch, New J. Chem., 2009, 33, 64;
(c) X. Zhang, C. Wang, M. Xue, Y. Zhang, Y. Yao and
Q. Shen, J. Organomet. Chem., 2012, 713, 182; (d) X. Zhang,
C. Wang, M. Xue, Y. Zhang, Y. Yao and Q. Shen,
J. Organomet. Chem., 2012, 716, 86; (e) C. Wang, X. Zhang,
M. Xue, Y. Zhang and Q. Shen, Organometallics, 2013, 32,
3618; (f) C. Wang, X. Zhang, M. Xue, Y. Zhang and Q. Shen,
Dalton Trans., 2013, 42, 7009; (g) J. Stanek, T. Rösener,
A. Metz, J. Mannsperger, A. Hoffmann and S. Herres-
Pawlis, in Topics in Heterocyclic Chemistry, Springer Berlin
5 (a) R. T. Boeré, R. T. Oakley and R. W. Reed, J. Organomet.
Chem., 1987, 331, 161; (b) D. Lindauer, R. Beckert,
M. Döring, P. Fehling and H. Görls, J. Prakt. Chem., 1995,
337, 143; (c) J. R. Hagadorn and J. Arnold, Angew. Chem.,
Int. Ed., 1998, 37, 1729; (d) J. R. Babcock, C. Incarvito,
A. L. Rheingold, J. C. Fettinger and L. R. Sita,
Organometallics, 1999, 18, 5729; (e) G. D. Whitener,
J. R. Hagadorn and J. Arnold, J. Chem. Soc., Dalton Trans.,
1999, 1249; (f) S. Bambirra, A. Meetsma, B. Hessen and
J. H. Teuben, Organometallics, 2001, 20, 782; (g) C.-T. Chen,
L. H. Rees, A. R. Cowley and M. L. H. Green, J. Chem. Soc.,
Dalton Trans., 2001, 1761; (h) H. Kawaguchi and T. Matsuo,
Dalton Trans.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Dalton Transactions
Paper
Heidelberg, Berlin, Heidelberg, 2015; (h) V. Vass, 15 (a) H. V. R. Dias, W. Jin and R. E. Ratcliff, Inorg. Chem.,
M. Dehmel, F. Lehni and R. Kretschmer, Eur. J. Org. Chem.,
2017, 2017, 5066; (i) M. Dehmel, V. Vass, L. Prock, H. Görls
and R. Kretschmer, Inorg. Chem., 2020, 59, 2733.
1995, 34, 6100; (b) N. Kuhn, S. Fuchs and M. Steimann, Z.
Anorg. Allg. Chem., 2000, 626, 1387; (c) W. Uhl and B. Jana,
Chem. – Eur. J., 2008, 14, 3067; (d) B. Lyhs, D. Bläser,
C. Wölper and S. Schulz, Chem. – Eur. J., 2011, 17, 4914;
(e) Y. Yang, H. P. Li, C. Wang and H. W. Roesky, Inorg.
Chem., 2012, 51, 2204; (f) Z. Yang, M. Zhong, X. Ma,
K. Nijesh, S. De, P. Parameswaran and H. W. Roesky, J. Am.
Chem. Soc., 2016, 138, 2548; (g) A. R. Leverett,
V. Diachenko, M. L. Cole and A. I. McKay, Dalton Trans.,
2019, 48, 13197; (h) C. G. Gianopoulos, K. Kirschbaum and
M. R. Mason, Organometallics, 2014, 33, 4503.
7 (a) D. V. Vitanova, F. Hampel and K. C. Hultzsch, Dalton
Trans., 2005, 1565; (b) D. V. Vitanova, F. Hampel and
K. C. Hultzsch, J. Organomet. Chem., 2005, 690, 5182;
(c) M. F. Pilz, C. Limberg and B. Ziemer, J. Org. Chem.,
2006, 71, 4559; (d) M. F. Pilz, C. Limberg, S. Demeshko,
F. Meyer and B. Ziemer, Dalton Trans., 2008, 1917; (e) D.
F.-J. Piesik, S. Range and S. Harder, Organometallics, 2008,
27, 6178; (f) S. Gong, H. Ma and J. Huang, Dalton Trans.,
2009, 8237; (g) D. F.-J. Piesik, R. Stadler, S. Range and 16 A. Caise, D. Jones, E. L. Kolychev, J. Hicks,
S. Harder, Eur. J. Inorg. Chem., 2009, 2009, 3569;
(h) J. P. Falkenhagen, P. Haack, C. Limberg and B. Braun,
J. M. Goicoechea and S. Aldridge, Chem. – Eur. J., 2018, 24,
13624.
Z. Anorg. Allg. Chem., 2011, 637, 1741; (i) I. El-Zoghbi, 17 (a) S. R. Foley, G. P. A. Yap and D. S. Richeson,
T. J. J. Whitehorne and F. Schaper, Dalton Trans., 2013, 42,
9376; ( j) S. Sun, Q. Sun, B. Zhao, Y. Zhang, Q. Shen and
Y. Yao, Organometallics, 2013, 32, 1876; (k) L. Li, C. Wu,
D. Liu, S. Li and D. Cui, Organometallics, 2013, 32, 3203;
(l) J. Intemann, M. Lutz and S. Harder, Organometallics,
2014, 33, 5722; (m) M. E. Desat, S. Gärtner and
R. Kretschmer, Chem. Commun., 2017, 53, 1510;
Organometallics, 1999, 18, 4700; (b) P. B. Hitchcock, J. Hu,
M. F. Lappert and J. R. Severn, Dalton Trans., 2004, 4193;
(c) I. A. Guzei, V. I. Timokhin and R. West, Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun., 2006, 62, m90–m92;
(d) Z.-Y. Chai and Z.-X. Wang, Dalton Trans., 2009, 8005;
(e) M. K. Barman, A. Baishya, T. Peddarao and
S. Nembenna, J. Organomet. Chem., 2014, 772–773, 265.
(n) A. Phanopoulos, A. H. M. Leung, S. Yow, D. Palomas, 18 (a) W.-P. Leung, K.-P. Chan, K.-W. Kan and T. C. W. Mak,
A. J. P. White, K. Hellgardt, A. Horton and M. R. Crimmin,
Dalton Trans., 2017, 46, 2081; (o) A. Phanopoulos,
M. Warren, A. J. P. White, A. Horton and M. R. Crimmin,
Dalton Trans., 2017, 46, 2077; (p) M. E. Desat and
R. Kretschmer, Chem. – Eur. J., 2018, 24, 12397–12404;
Organometallics, 2008, 27, 2767; (b) S. Krupski,
J. V. Dickschat, A. Hepp, T. Pape and F. E. Hahn,
Organometallics, 2012, 31, 2078; (c) R. K. Raut, P. Sahoo,
D. Chimnapure and M. Majumdar, Dalton Trans., 2019, 48,
10953.
(q) M. E. Desat and R. Kretschmer, Inorg. Chem., 2019, 58, 19 (a) F. Dannenberg, G. Thiele, S. Dehnen and M. Mehring,
16302–16311; (r) M. E. Desat and R. Kretschmer, Dalton
Trans., 2019, 48, 17718–17722; (s) M. E. Desat and
R. Kretschmer, Z. Anorg. Allg. Chem., 2020, 646, 625–630.
8 C. Camp and J. Arnold, Dalton Trans., 2016, 14462–14498.
Z. Anorg. Allg. Chem., 2017, 643, 360; (b) I. D’auria,
M. C. D’Alterio, C. Tedesco and C. Pellecchia, RSC Adv.,
2019, 9, 32771; (c) G. Ballmann, S. Grams, H. Elsen and
S. Harder, Organometallics, 2019, 38, 2824.
9 (a) R. Kretschmer, M. Dehmel and M. Bodensteiner, 20 (a) W.-P. Leung, C.-W. So, K.-H. Chong, K.-W. Kan,
Eur. J. Inorg. Chem., 2017, 2017, 965; (b) N. A. Phillips,
J. O’Hanlon, T. N. Hooper, A. J. P. White and
M. R. Crimmin, Org. Lett., 2019, 21, 7289.
H.-S. Chan and T. C. W. Mak, Organometallics, 2006, 25,
2851; (b) C.-Y. Lin, C.-F. Tsai, H.-J. Chen, C.-H. Hung,
R.-C. Yu, P.-C. Kuo, H. M. Lee and J.-H. Huang, Chem. –
Eur. J., 2006, 12, 3067; (c) S. G. Alexander, M. L. Cole,
C. M. Forsyth, S. K. Furfari and K. Konstas, Dalton Trans.,
2009, 2326; (d) B. Goswami, R. Yadav, C. Schoo and
P. W. Roesky, Dalton Trans., 2020, 49, 675; (e) M. L. Cole,
A. J. Davies, C. Jones, P. C. Junk, A. I. McKay and A. Stasch,
Z. Anorg. Allg. Chem., 2015, 641, 2233.
10 M. L. Hlavinka and J. R. Hagadorn, Chem. Commun., 2003,
2686.
11 (a) M. L. Hlavinka and J. R. Hagadorn, Organometallics,
2005, 24, 5335; (b) M. L. Hlavinka and J. R. Hagadorn,
Organometallics, 2005, 24, 4116; (c) L. E. Garner, H. Zhu,
M. L. Hlavinka, J. R. Hagadorn and E. Y.-X. Chen, J. Am.
Chem. Soc., 2006, 128, 14822; (d) M. L. Hlavinka and 21 B. Nekoueishahraki, H. W. Roesky, G. Schwab, D. Stern and
J. R. Hagadorn, Organometallics, 2006, 25, 3501; D. Stalke, Inorg. Chem., 2009, 48, 9174.
(e) M. L. Hlavinka, M. J. McNevin, R. Shoemaker and 22 R. S. Cahn, C. Ingold and V. Prelog, Angew. Chem., Int. Ed.
J. R. Hagadorn, Inorg. Chem., 2006, 45, 1815. Engl., 1966, 5, 385.
12 N. Millot, C. C. Santini, B. Fenet and J. M. Basset, 23 CrysAlisPro, version 171.38.42b, Agilent Technologies Inc.,
Eur. J. Inorg. Chem., 2002, 2002, 3328. Oxford, GB, 2015.
13 C. M. Herzog, Master Thesis “Synthese und 24 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Adv., 2015,
Charakterisierung von Bis(amidoamin)liganden sowie 71, 3.
deren Umsetzung zu dinuklearen Gruppe 25 G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem.,
13-Elementverbindungen”, Universität Regensburg, 2016. 2015, 71, 3.
14 M. Ostermeier, C. Limberg, C. Herwig and B. Ziemer, Z. 26 O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard
Anorg. Allg. Chem., 2009, 635, 1823.
and H. Puschmann, J. Appl. Crystallogr., 2009, 42, 339.
This journal is © The Royal Society of Chemistry 2020
Dalton Trans.