Coordination Chemistry of N-(2-Pyridylethyl)-Substituted Bulky Amidinates and Triazenides of Magnesium

Article abstract of DOI:10.1002/ejic.201800890

The amidines Dipp-N=C(R)-NH(C₂H₄R′) [R = tBu, R′ = Ph (1a); R = Ph, R′ = Py (1b)] as well as 1-(2,4,6-triisopropylphenyl)-3-(2-pyridylethyl)triazene (1c) are magnesiated with commercially available dibutylmagnesium yielding the compl

Full text of DOI:10.1002/ejic.201800890

A Journal of
Accepted Article
Title: Coordination Chemistry of N-(2-Pyridylethyl)-Substituted Bulky
Amidinates and Triazenides of Magnesium
Authors: Diana Kalden, Sven Krieck, Helmar Görls, and Matthias
Westerhausen
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201800890
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10.1002/ejic.201800890
European Journal of Inorganic Chemistry
FULL PAPER
Coordination Chemistry of N-(2-Pyridylethyl)-Substituted Bulky
Amidinates and Triazenides of Magnesium
Diana Kalden,[a] Sven Krieck,[a] Helmar Görls,[a] and Matthias Westerhausen*[a]
Dedicated to Professor Alexander C. Filippou on the occasion of his 60th birthday
Abstract: The amidines Dipp-N=C(R)-NH(C2H4R') [R = tBu, R' = Ph
(1a); R = Ph, R' = Py (1b)] as well as 1-(2,4,6-triisopropylphenyl)-3-
(2-pyridylethyl)triazene (1c) are magnesiated with commercially
available dibutylmagnesium yielding the complexes [(thf)Mg{Dipp-
N=C(tBu)-N(C2H4Ph)}2] (3a), [Mg{Dipp-N=C(Ph)-N(C2H4Py)}2] (3b),
and [Mg{Tripp-N=N-N(C2H4Py)}2] (3c). Handling and isolation of
triazene 1c has been performed at room temperature or below to
avoid elimination of dinitrogen and formation of 2-pyridylethyl-(2,4,6-
triisopropylphenyl)amine (2). In the solid state, the compounds 1b
and 1c form dimers via intermolecular hydrogen bridges to the
pyridyl groups of neighboring molecules.
another strong Lewis donor site in the pending sidearm leading
to tridentate Lewis bases. Therefore the coordination behavior of
asymmetric amidinates of the type [Dipp-NC(R)N(C2H4Py)]- have
been studied.[12] Depending on the s-block metal of the
metalation reagent and the steric pressure introduced by R, two
different reaction pathways are observed, namely (i)
deprotonation of the amidine yielding the expected amidinates
and (ii) deprotonation of the ethylene unit leading to elimination
of 2-vinylpyridine and formation of bidentate [Dipp-NC(R)NH]-
ions (Scheme 1). Attack of CH moieties in ß-position to a
nitrogen base has been observed earlier for the reaction of alkali
metalation reagents with 1,2-bis(diethylamino)ethane[13] and
phenylethyl-dimethylamine.[14]
The
use
of
bis(1-
phenylethyl)amine in deprotonation reactions leads to C-N bond
cleavage depending on the alkali metal and the Lewis donor
solvent.[15] Based on these reports and our experiments the
Introduction
Oligodentate ligands with nitrogen donor sites represent a widely
used class of strong Lewis bases in coordination chemistry[1]
including bis- and tris(pyrazolyl)boranates and methanides
(scorpionates)[2] as well as acyclic anionic ligands of the type
[RN(CR’)nNR]- [n = 3: ß-diketiminates,[3] n = 1: amidinates (R’ =
coordination
behavior
of
N-(2-pyridylethyl)-substituted
amidinates and triazenides attracted our attention. Starting N-(2-
pyridylethyl)triazenes are rarely reported[16] and the coordination
chemistry has been totally neglected. In contrast to the missing
knowledge
on
the
coordination
chemistry
of
2-
H, alkyl, aryl) and guanidinates (R’
=
NR2)].[4] In these
pyridylethyltriazenides, there exist very few magnesium
complexes of N-aryl-N’-(2-pyridylethyl)amidinates[12,17] that were
structurally authenticated.
For comparison reasons we included amidinate complexes of
the type [Mg{Dipp-NC(R)N(C2H4R’)}2] (R = tBu, Ph; R’ = Ph, Py)
in our investigations.
amidinates and guanidinates charge delocalization within a π-
system is characteristic leading to negatively charged nitrogen
bases enhancing the stability of metal complexes with such
ligands, allowing to isolate highly reactive species like Mg(I)[5] or
soluble and thermally stable hydridomagnesium complexes.[6]
Furthermore, such a charge distribution is only possible for
deprotonated amidines (amidinates L-) leading to an enhanced
acidity of the neutral forms HL.[7] This property eases metalation
and synthesis of metal complexes via deprotonation of HL with
common reagents. Despite the fact that triazenes show very
similar pKa values[8] the coordination chemistry of their anionic
congeners is strongly underdeveloped.
Symmetrically substituted magnesium 1,3-diaryltriazenides of
the type [(Solv)nMg(RNNNR)2] are accessible by metalation of
the corresponding triazenes with dibutylmagnesium in an
ethereal solvent. Depending on the bulkiness of the aryl groups
coordination numbers of 6 [R = C6H4-4-Me (Tol), C6H2-2,4,6-Me3
(Mes), Solv = thf, n = 2][9,10] and 5 (R = C6H3-2,6-iPr2 (Dipp), Solv
= Et2O, n = 1)[11] are observed.
Further stabilization of the complexes should be possible by
[a]
D. Kalden, Dr. S. Krieck, Dr. H. Görls, Prof. Dr. M. Westerhausen
Institute of Inorganic and Analytical Chemistry
Friedrich Schiller University Jena
Humboldtstraße 8, 07743 Jena, Germany
homepage: http://www.lsac1.uni-jena.de/
E-mail: m.we@uni-jena.de
Scheme 1. Two possible reaction pathways for the metalation of N-aryl-N'-(2-
pyridylethyl)amidines, namely either (i) deprotonation of the amidine unit or (ii)
deprotonation in ß-position to the amidine moiety with subsequent elimination
of 2-vinylpyridine.
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejic.201800890
European Journal of Inorganic Chemistry
FULL PAPER
Results and Discussion
solubility of the magnesium complexes. The isolated magnesium
complexes [(thf)Mg{Dipp-N=C(tBu)-N(C2H4Ph)}2] (3a), [Mg{Dipp-
N=C(Ph)-N(C2H4Py)}2] (3b), and [Mg{Tripp-N=N-N(C2H4Py)}2]
(3c), are depicted in Scheme 4 together with already known
[Mg{Dipp-N=C(tBu)-N(C2H4Py)}2] (3d).[12] Smaller groups R at
the backbone of the amidinate moiety allow larger coordination
numbers at magnesium.
Synthesis. The preparation of the amidines followed a previously
published protocol.[12] Dipp-N=C(R)Cl was added at room
temperature to a toluene solution of phenylethylamine or 2-
pyridylethylamine yielding the amidines
NH(C2H4R') [R = tBu, R' = Ph (1a); R = Ph, R' = Py (1b)]
Dipp-N=C(R)-
according to Scheme 2.
Scheme 2. Syntheses of the amidines Dipp-N=C(R)-NH(C2H4R') [R = tBu, R' =
Ph (1a); R = Ph, R' = Py (1b)] in toluene at room temperature.
The
reaction
of
2-pyridylethyl
bromide
azide
with
2,4,6-
in
triisopropylphenylmagnesium
(Tripp-MgBr)
tetrahydrofuran (THF) and subsequent aqueous work-up yielded
the corresponding 1-(2,4,6-triisopropylphenyl)-3-(2-
pyridylethyl)triazene (1c) as depicted in Scheme 3. This triazene
easily lost dinitrogen already in boiling n-pentane solution
leading
to
the
formation
of
2-pyridylethyl-(2,4,6-
triisopropylphenyl)amine (2). Therefore, during synthesis and
recrystallization of 1c from aliphatic hydrocarbons, temperatures
may not exceed room temperature.
Scheme 4. Drawings of the magnesium complexes with asymmetric amidinate
(3a, 3b and 3d[12]) and triazenide ligands (3c)containing N-bound phenylethyl
(3a) or 2-pyridylethyl groups (3b, 3c, 3d[12]).
NMR studies. Selected NMR parameters are listed in Table 1.
For complex [Mg{Dipp-N=C(Ph)-N(C2H4Py)}2] (3b) and
[Mg{Dipp-N=C(tBu)-N(C2H4Py)}2] (3d)[12] two sets of resonances
are observed in the 13C{1H} NMR spectra. For complex 3d, this
finding is in agreement with the solid state structure. However,
for 3b two different isomers are present in solution leading to
two sets of signals with different intensities.
< Insert Table 1 >
Deprotonation of the amidines leads to a significant low field
shift of the NCN carbon resonance due to formation of a 1,3-
diazaallyl anion. The influence of magnesiation on the chemical
shifts of the ipso-carbon atoms of the N-bound Dipp (amidinates)
and Tripp groups (triazenide) is negligible. However, the
methylene resonances of the N'-bound phenylethyl and 2-
pyridylethyl substituents show a small but significant low field
shift due to the bidentate binding mode.
Scheme 3. Synthesis of Tripp-N=N-NH(C2H4Py) (1c) in tetrahydrofuran at
room temperature and degradation in hot pentane yielding Tripp-NH(C2H4Py)
(2).
Molecular structures. Molecular structure and the atom labeling
scheme of 2-pyridylethyl-(2,4,6-triisopropylphenyl)amine (2) are
depicted in Figure 1. The hydrogen atom at N2 was located in
the difference Fourier map and refined isotropically (N2-H 84(3)
pm). This amine allows to determine undisturbed N-C single
bonds to a bulky aryl group (N2-C8 144.2(3) pm) and the 2-
The amidines 1a and 1b and the triazene 1c were magnesiated
with commercially available dibutylmagnesium in hydrocarbons
with additional small amounts of THF to ensure sufficient
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10.1002/ejic.201800890
European Journal of Inorganic Chemistry
FULL PAPER
pyridylethyl moiety (N2-C7 147.2(3) pm). The N2 atom with an
angle sum of 345° shows a pyramidal environment. A weak
and forms an intermolecular N2-H···N3 hydrogen bridge to the
pyridyl group of the neighboring molecule. The bonding
parameters are rather similar to those of N-(3,5-dimethylphenyl)-
intramolecular N2-H···N1 hydrogen bridge secures
backbonding of the pyridyl fragment to the amine functionality.
a
N'-(2-pyridylethyl)-para(tert-butyl)benzamidine[17]
(pentafluorophenyl)-N'-(2-pyridylethyl)-para-
and
N-
methylbenzamidine[18] confirming comparable intramolecular
steric pressure.
Figure 1. Molecular structure and atom labeling scheme of 2-pyridylethyl-
(2,4,6-triisopropylphenyl)amine (2). The ellipsoids represent a probability of
30 %, hydrogen atoms are drawn with arbitrary radii. Selected bond lengths
(pm): N1-C1 134.6(4), N1-C5 133.4(4), N2-C7 147.2(3), N2-C8 144.2(3), C5-
C6 151.1(4), C6-C7 153.7(4); angles (deg.): C7-N2-C8 113.1(2), C7-N2-H
111(2), C8-N2-H 111(2), N2-C8-C9 121.6(2), N2-C8-C13 118.7(2), C9-C8-
C13 119.7(2).
For the orientation of the amidines and triazenes as well as of
ligated amidinates and the triazenides the convention shown in
Scheme 5 is applied. The orientation at the double bond
NAr=CNCN/NNNN is given as E/Z-isomers whereas syn and anti
orientation designates whether the NAr-aryl and the NCH2-alkyl
groups are located at the same or at contrary sides of the
molecule.
Figure 2. Molecular structure and atom labeling scheme of anti-E-isomeric N-
(2,6-diisopropylphenyl)-N'-(2-pyridylethyl)benzamidine (1b). At the top the
molecule is depicted. The ellipsoids represent a probability of 30 %, only the
hydrogen atom at N2 is shown with an arbitrary radius. At the bottom, the
hydrogen-bridged dimer is shown and here, the atoms are drawn with arbitrary
radii. Selected bond lengths (pm): N1-C1 128.54(15), N2-C1 135.77(15), C1-
C2 150.11(16), N1-C8 141.52(15), N2-C20 144.90(15), N3-C22 134.60(17),
N3-C26 134.18(17); angles (deg.): C1-N1-C8 121.5(1), C1-N2-C20 121.5(1),
C1-N2-H 120(1), C20-N2-H 118(1), N1-C1-N2 119.8(1), N1-C1-C2 127.0(1),
N2-C1-C2 113.8(1).
Scheme 5. Nomenclature to describe the orientation of the amidines and
amidinates (see text); a similar description is used to express the orientation of
the triazene and ligated triazenide ions.
Molecular structure and atom labeling scheme of anti-E-isomeric
N-(2,6-diisopropylphenyl)-N'-(2-pyridylethyl)benzamidine (1b) is
shown in Figure 2. The N1-C1 bond length of 128.5(2) pm is a
characteristic double bond whereas the N2-C1 bond is shorter
than a typical N-C single bond as found in derivative 2. In 1b the
N2 atom is in a planar environment (angle sum at N2 360°). The
hydrogen atom at N2 was refined isotropically (N2-H 90(2) pm)
As also observed for 1b, 1-(2,4,6-triisopropylphenyl)-3-(2-
pyridylethyl)triazene (1c) forms intermolecular hydrogen bridges
to the pyridyl base of the neighboring molecule and crystallizes
as an anti-E-isomeric dimer. Molecular structure and atom
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10.1002/ejic.201800890
European Journal of Inorganic Chemistry
FULL PAPER
labeling scheme are depicted in Figure 3. The N-bound
hydrogen atom was refined isotropically (N3-H 89(2) pm).
Figure 4. Molecular structure and atom labeling scheme of [(thf)Mg{Dipp-
N=C(tBu)-N(C2H4Ph)}2] (3a). Ellipsoids represent a probability of 30 %, H
atoms are omitted for clarity reasons. Selected bond lengths (pm): Mg1-O1
206.20(12), Mg1-N1 209.48(14), Mg1-N2 209.84(13), Mg1-N3 209.62(14),
Mg1-N4 210.64(14), N1-C1 134.4(2), N2-C1 133.1(2), N1-C6 141.1(2), N2-
C18 145.1(2), C1-C2 155.1(2), N3-C26 134.2(2), N3-C26 133.1(2), N3-C31
141.1(2), N4-C43 145.5(2), C26-C27 155.1(2); angles (deg.): N1-C1-N2
110.7(1), N1-C1-C2 125.8(1), N2-C1-C2 123.5(1), N3-C26-N4 110.7(1), N3-
C26-C27 125.4(1), N4-C26-C27 123.9(1), C1-N1-C6 130.5(1), C1-N2-C18
128.4(1), C26-N3-C31 131.0(1), C26-N4-43 128.5(1).
In [Mg{Dipp-N=C(Ph)-N(C2H4Py)}2] (3b) the tridentate ligands
bind meridionally leading to a distorted octahedral coordination
sphere of the metal center. The distortions are enforced by the
small bites of the amidinate fragments (N1-Mg1-N2 61.23(5)°,
N4-Mg1-N5 61.61(5)°). Molecular structure and atom numbering
scheme are shown in Figure 5. The negative charges are
delocalized within the 1,3-diazaallyl fragments and very similar
N-C bond lengths are observed. This finding is a bit surprising in
the light of significantly different Mg-N distances to the amidinate
moieties. This coordination behavior is a consequence of
intramolecular strain induced by the bulky aryl groups at the
nitrogen atoms N1 and N4.
Figure 3. Molecular structure and numbering scheme of 1-(2,4,6-
triisopropylphenyl)-3-(2-pyridylethyl)triazene (1c). At the top the molecule is
depicted with the ellipsoids representing a probability of 30 %. The hydrogen
atoms are shown with arbitrary radii. At the bottom, the hydrogen-bridged
dimer is shown. Here the atoms are drawn with arbitrary radii. Selected bond
lengths (pm): N1-N2 127.0(2), N2-N3 133.2(2), N1-C1 143.3(2), N3-C16
145.0(2), N4-C18 134.4(2), N4-22 134.2(2); angles (deg.): N1-N2-N3
113.59(13), C1-N1-N2 112.42(13), N2-N3-C16 124.03(14), N2-N3-H 114.4(13),
C16-N3-H 121.5(13).
In the magnesium complex 3a the amidinate ligands adopts a
syn-E-conformation and acts as bidentate ligand. A thf ligand
completes the coordination sphere of the magnesium atom.
Molecular structure and atom labeling scheme are shown in
Figure 4. The negative charges are delocalized within the 1,3-
diazaallyl moieties leading to rather similar N-C bond lengths.
Due to the small bite angles of the amidinate ligands, very
narrow N1-Mg1-N2 and N3-Mg1-N4 bond angles of 63.31(5)°
and 63.10(5)° are found.
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10.1002/ejic.201800890
European Journal of Inorganic Chemistry
FULL PAPER
Figure 5. Molecular structure and atom labeling scheme of [Mg{Dipp-
N=C(Ph)-N(C2H4Py)}2] (3b). The ellipsoids represent a probability of 30 %, H
atoms are neglected for the sake of clarity. Selected bond lengths (pm): Mg1-
N1 228.73(15), Mg1-N2 206.71(14), Mg1-N3 226.52(15), Mg1-N4 226.68(14),
Mg1-N5 206.80(15), Mg1-N6 223.46(15), N1-C1 133.4(2), N2-C1 133.1(2),
N1-C15 141.7(2), N2-C2 144.7(2), C1-C9 150.3(2), N4-C27 133.4(2), N5-C27
132.3(2), N4-C 41 141.8(2), N5-C28 144.4(2), C27-C35 149.7(2); angles
(deg.): N1-C1-N2 113.27(15), N1-C1-C9 123.50(15), N2-C1-C9 123.14(15),
N4-C27-N5 113.88(14), N4-C27-C35 123.38(15), N5-C27-C35 122.62(14),
C1-N1-C15 122.89(15), C1-N2-C2 126.41(14), C27-N4-C41 123.10(14), C27-
N5-C28 125.24(14).
number of the magnesium atom. The pyridyl anchor base
enhances significantly the asymmetric coordination mode of the
triazenide and amidinate fragments with the shortest Mg-N
bonds to the middle nitrogen base. The Mg-N distance to the
electroneutral pyridyl base can even be shorter than to the outer
triazenide and amidinate nitrogen donor.
Table 2. Mg-N bond lengths (average values, pm) in homoleptic magnesium
complexes with aryl-substituted triazenide (top part) and amidinate ligands
(bottom part).[a]
Molecular structure and atom labeling scheme of [Mg{Tripp-
N=N-N(C2H4Py)}2] (3c) are depicted in Figure 6. The magnesium
atom is in a distorted octahedral environment due to the small
bites of the triazenide anions (N1-Mg1-N3 56.83(6)°, N5-Mg1-N7
57.74(6)°). Similar to the amidinates, the negative charge is
delocalized within the triazaallyl units leading to very similar N-N
distances. However, the very bulky triisopropylphenyl group
induces steric strain and significantly different Mg-N bond
lengths are observed.
Compound
C.N.[b]
5
Mg-NAryl
211.7(1)
Mg-NR
Mg-NPy
-
Ref.
[11]
[(Et2O)Mg(Dipp-
NNN-Dipp)2]
215.7(1)
[(thf)2Mg(Tol-NNN-
Tol)2]
6
6
6
4
4
4
4
4
5
214.8(3)
217.8(2)
235.8
221.7(2)
218.4(2)
203.8
-
[9]
[(thf)2Mg(Mes-NNN-
Mes)2]
-
[10]
Here
[11]
[19]
[20]
[21]
[21]
Here
[Mg{Tripp-N=N-N-
C2H4-Py}2] (3c)
223.6
[Mg{(Dipp-N)2C-
Me}2]
204.3
204.5
-
-
-
-
-
-
[Mg{(Mes-N)2C-
tBu}2]
204.0
204.2
[Mg{(Dipp-N)2C-
Tol}2]
204.7(2)
205.9
206.9(2)
207.5
[Mg{(Dipp-N)2C-
Cy}2]
[Mg{(Dipp-N)2C-
C6H3-3,5-Me2}2]
204.8
206.3
[(thf)Mg{Dipp-
N=C(tBu)-
209.6
210.2
N(C2H4Ph)}2] (3a)
[Mg{Dipp-N=C(tBu)-
N(C2H4Py)}2] (3d)[c]
5
6
6
221.0(1)
220.5
205.2(1)
210.7
230.7(1)
226.2
[12]
Figure 6. Molecular structure and atom numbering scheme of [Mg{Tripp-N=N-
N(C2H4Py}2] (3c). The ellipsoids represent a probability of 30 %, H atoms are
omitted for clarity reasons. Selected bond lengths (pm): Mg1-N1 239.3(2),
Mg1-N3 202.82(2), Mg1-N4 223.1(2), Mg1-N5 232.3(2), Mg1-N7 204.8(2),
Mg1-N8 224.1(2), N1-N2 131.1(2), N2-N3 131.0(2), N5-N6 131.4(2), N6-N7
130.9(2), N1-C8 142.0(2), N3-C1 144.7(2), N5-C30 142.4(3), N7-C23
144.9(2); angles (deg.): N1-N2-N3 108.55(15), N5-N6-N7 108.20(15), N2-N1-
C8 114.19(15), N2-N3-C1 116.51(16), N6-N5-C30 114.87(16), N6-N7-C23
117.88(16).
[Mg{Ph-N=C(Tol)-
N(C2H4Py)}2]
[17]
[Mg{Dipp-N=C(Ph)-
N(C2H4Py)}2] (3b)
227.7
206.8
225.0
Here
[a] The group
R can be aryl or alkyl; Cy cyclo-hexyl, Dipp 2,6-
diisopropylpohenyl, Mes 2,4,6-trimethylphenyl (mesityl), Ph phenyl, Py 2-
pyridyl, tBu tert.-butyl, Tol para-tolyl, Tripp 2,4,6-triisopropylphenyl. [b]
Coordination number of magnesium atom. [c] Only the values of the tridentate
ligand are listed (see Scheme 3).
in Table 2, the Mg-N bond lengths of magnesium-bound
triazenides and amidinates are listed. Different Mg-N bond
lengths have also been observed for magnesium-bound
symmetric
triazenides
in
[(thf)2Mg(Tol-NNN-Tol)2],[9]
[(Et2O)Mg(Dipp-NNN-
[(thf)2Mg(Mes-NNN-Mes)2],[10]
and
Due to this asymmetric coordination behavior of 2-pyridylethyl-
substituted triazenides and amidinates a disturbed delocalization
of the negative charge within the NNN- and NCN-allylic systems
may be expected. Selected structural parameters of the
amidines and triazenes as well as of the magnesium complexes
Dipp)2][11] with Mg-N distances varying between 211.7 to 221.7
pm for penta- and hexa-coordinate metal atoms. Symmetric
N,N'-diarylamidinate ligands bind less asymmetric to the metal
atom with Mg-N distances depending on the coordination
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10.1002/ejic.201800890
European Journal of Inorganic Chemistry
FULL PAPER
of their deprotonated congeners are listed in Table 3. In the
amidines 1b and 1d as well as in triazene 1c the E=N double
bond character is more pronounced to the aryl-bound nitrogen
base NAryl whereas the E-N distances to the NCH2 bases (which
also carry the hydrogen atoms) are approximately 5 % larger.
Deprotonation leads to delocalization of the negative charge
within the NCN (amidinates) and NNN (triazenides) allylic
systems. The E-NCH2 bonds are even slightly shorter than the E-
azaallyl systems to magnesium with short Mg-NCH2 bonds to the
middle nitrogen donor site and with significantly larger Mg-NAryl
distances to the outer nitrogen base. This asymmetric binding
mode has no disturbing influence on the delocalization of the
negative charge in the allyl anion.
Experimental Section
NAryl bonds. This finding suggests
a mainly electrostatic
interaction between the alkaline earth ion and the amidinate and
triazenide anions with a negligible influence of the Mg-N bond
lengths on binding parameters of the NCN- and NNN-allyl
anions.
General Considerations. All manipulations were carried out in a nitrogen
atmosphere using standard Schlenk techniques. The solvents THF and
toluene were dried over KOH and subsequently distilled over sodium/
benzophenone under a nitrogen atmosphere prior to use. Deuterated
solvents were dried over sodium, degassed, and saturated with nitrogen.
The indicated yields are not optimized and refer to crystalline yields. 1H
and 13C{1H} NMR spectra were recorded on Bruker Avance 400 and
Avance 250 spectrometers. Chemical shifts are reported in parts per
< Insert Table 3 >
The N-E-N bond angles of the NCN- and NNN-allyl systems
significantly decrease upon metalation. This reduction of the
bond angles releases steric repulsion between the bulky aryl
group and the group at the NCN-moieties of the amidinates, also
leading to slightly larger E-NAryl-CAryl bond angles. The bond
lengths between the N-E-N allylic system and the NAryl-bound
triisopropylphenyl (triazene, triazenide) and diisopropylphenyl
groups (amidines, amidinates) on the one hand and NCH2-bound
2-pyridylethyl substituent on the other do not depend on charge
(or rather deprotonation) of the allyl unit. This finding can be
expected because the aryl groups and the allyl units are oriented
perpendicular to each other for steric reasons. Nevertheless,
these NAryl-CAryl and NCH2-CH2 bonds are significantly shorter
than observed for the N2-C7 and N2-C8 bonds in amine 2. The
reason for this observation is the lower s-orbital contribution in
the N-C bonds in 2 with a pyramidal environment of N2,
suggesting a sp3 hybridization.
1
million relative to SiMe4 as external standard. In some cases H,13C{1H}-
HSQC, 1H,13C{1H}-HMBC, and H,H-COSY NMR experiments were
performed for the assignment of the resonances. The residual signals of
[D8]THF, chloroform, and C6D6 were used as internal standards. For
mass spectrometric investigations the spectrometers ThermoFinnigan
MAT95XL and Finnigan SSQ710 were at our disposal. IR spectra were
recorded with a Bruker ALPHA FT-IR spectrometer. All amines were
distilled before use and purchased from TCI GmbH, Fluorochem or abcr
GmbH, Mg(nBu)2 solution was purchased from Sigma-Aldrich.
N-(2,6-diisopropylphenyl)-N’-(2-phenylethyl)pivalamidine, Dipp-N=C(tBu)-
N(H)-C2H4-Ph (1a). Dipp-N=C(tBu)Cl was prepared according to our
previous work.[12] To a toluene (15 mL) solution of NH2C2H4-Ph (1.0 g, 8.2
mmol) was added dropwise Dipp-N=C(tBu)Cl (2.3 g, 8.2 mmol) at room
temperature. The reaction mixture was stirred at 120 °C for 24 h to give a
clear orange solution. Subsequently, all volatiles were removed in in
vacuo. The remaining solid was dissolved in 100 ml of dichloromethane
and washed two times with aqueous Na2CO3 solution (50 mL, 2%).
Removal of the solvent led to formation of 2.8 g of 1a (93%) as a
yellowish oil. 1H NMR (CDCl3, 297.0 K, 400.13 MHz): δ 7.26-7.17 (m, 3H,
Har), 7.01-6.88 (m, 4H, Har), 6.93-6.89 (m, 1H, Har), 4.22 (s, broad, 1H,
NH), 2.97 (sept, 3JHH = 6.8 Hz, 2H, CH(CH3)2), 2.91-2.88 (m, 2H, N–CH2–
Conclusions
The amidines Dipp-N=C(R)-NH(C2H4R') [R = tBu, R' = Ph (1a);
R = Ph, R' = Py (1b)] as well as 1-(2,4,6-triisopropylphenyl)-3-(2-
pyridylethyl)triazene (1c) are easily available by straightforward
procedures. During synthesis, isolation and handling of triazene
1c the temperature may not rise above room temperature to
avoid elimination of N2 and formation of 2-pyridylethyl-(2,4,6-
triisopropylphenyl)amine (2). The compounds 1b and 1c forms
hydrogen-bridged dimers in the crystalline state. The nitrogen
atom of amine 2 is in a pyramidal environment suggesting an sp3
hybridization, whereas the N atoms in the amidines and triazene
are sp2 hybridized and hence, show shorter N-C bonds to the
aryl and alkyl substituents.
Magnesiation of the amidines 1a and 1b and triazene 1c
succeeds with dibutylmagnesium yielding the complexes
[(thf)Mg{Dipp-N=C(tBu)-N(C2H4Ph)}2] (3a), [Mg{Dipp-N=C(Ph)-
N(C2H4Py)}2] (3b), and [Mg{Tripp-N=N-N(C2H4Py)}2] (3c).
Magnesiation in ß-position to the amidine moiety (see Scheme
3
), 2.51 (t, JHH = 6.8 Hz, 2H, Ph–CH2–), 1.20 (s, 9H, C(CH3)3, 1.17-1.14
1
(m, 12H, CH(CH3)2). H NMR (C6D6, 300.0 K, 250.13 MHz): δ 7.19-7.16
(m, 2H, Dipp m-CH), 7.12-6.99 (m, 4H, Ph p-CH, Dipp p-CH, Ph o-CH),
3
6.81-6.78 (m, 2H, Ph m-CH), 4.07 (t, JHH = 4.9 Hz, 1H, NH), 3.21 (sept,
3JHH = 6.9 Hz, 2H, CH(CH3)2), 2.89 (q, 2H, 3JHH = 6.7 Hz, N–CH2–), 2.16
3
3
(t, JHH = 6.7 Hz, 2H, Ph–CH2–), 1.31 (dd, JHH = 7.0 Hz, 6.8 Hz, 12H,
CH(CH3)2), 1.18 (s, 9H, C(CH3)3. 13C{1H} NMR (C6D6, 300.0 K, 62.90
MHz): δ 156.6 (NC(tBu)N), 147.0 (Dipp i-C), 138.9 (Ph i-C), 137.5 (Dipp
o-C), 128.9 (Ph o-C, Ph m-C), 126.8 (Ph p-C), 122.6 (Dipp m-C), 121.7
(Dipp p-C), 44.2 (N–CH2–), 38.8 (C(CH3)3), 36.7 (Ph–CH2–), 29.2
(C(CH3)3), 29.0 (CH(CH3)2), 23.6 (CH(CH3)2), 22.6 (CH(CH3)2). MS (DEI):
m/z (%) 364 (20, [M]+), 321 (40, [M-C3H7]+), 217 (30, [C15H23N]+), 186 (10,
[C13H16N]+), 146 (5, [C11H14]+; [C10H12N]+), 121 (20, [C8H11N]+; [C7H9N2]+),
105 (20, [C8H9]+), 91 (30, [C7H7]+), 77 (10, [C6H5]+), 57 (5, [C4H9]+), 28 (90,
[CH2N]+). IR (pure, /cm-1): 3436 (w), 3060 (w), 3025 (w), 2955 (m), 2865
(m), 1654 (s), 1586 (m), 1508 (s), 1496 (m), 1454 (m), 1429 (s), 1394 (m),
1379 (m), 1359 (m), 1277 (m), 1258 (m), 1217 (m), 1158 (m), 1108 (m),
1083 (m), 1060 (m), 1042 (m), 1029 (m), 933 (m), 881 (m), 799 (m), 787
(m), 744 (s), 699 (s), 621 (vw), 575 (vw), 549 (vw), 495 (w). Elemental
analysis for C25H36N2 (364.29 g/mol): calcd.: C 82.36, H 9.95, N 7.68;
found: C 82.51, H 10.07, N 7.72.
1) is not observed. In complex 3a
a penta-coordinate
magnesium atom is observed whereas in 3b and 3c the ligands
act as tridentate Lewis bases leading to distorted octahedral
coordination spheres of the magnesium centers. The strong
pyridyl Lewis bases enforce an asymmetric binding of the
N-(2,6-diisopropylphenyl)-N’-(2-pyridylethyl)benzamidine, Dipp-N=C(Ph)-
N(H)-C2H4-Py (1b). Dipp-NH2 (9.5 mL, 50.0 mmol) in 40 mL of anhydrous
This article is protected by copyright. All rights reserved.

10.1002/ejic.201800890
European Journal of Inorganic Chemistry
FULL PAPER
pyridine and benzoyl chloride (5.8 mL, 50.0 mmol) gave 12.98 g (46.1
mmol, 92%) of Dipp-N(H)C(O)Ph. The reaction of Dipp-N(H)C(O)Ph
(11.9 g, 42.3 mmol) with SOCl2 (6.0 mL, 82.7 mmol) yielded 12.64 g
(42.2 mmol, 99%) of pure Dipp-N=C(Ph)Cl. The purity of the intermediate
products were controlled by NMR spectroscopy. To a toluene (15 mL)
solution of Dipp-N=C(Ph)Cl (3.3 g, 11.1 mmol) was added dropwise
NH2C2H4-Py (1.4 g, 11.1 mmol) at room temperature. The reaction
mixture was stirred at 120 °C for 24 h to give a pale brown suspension.
Subsequently, all volatiles were removed in in vacuo. The remaining solid
was dissolved in 100 ml of dichloromethane and washed two times with
aqueous Na2CO3 solution (50 mL, 2%). After removal of the solvent the
precipitate was recrystallized from n-pentane/toluene (5:1) yielding 2.9 g
of 1b (68%). Physical data show a coexistence of two rotameric
structures of 1b in solution at 273 K (ratio ca. 1:1), but cooling of the
NMR sample to 273 K only slightly enhanced the line width. M. p. 104 -
3JHH = 7.8 Hz, 1H, Py o-CH), 6.58-6.55 (m, 2H, Py p-CH), 3.99 (m, 2H,
N–CH2–), 3.36-3.33 (m, 2H, o-CH(CH3)2), 2.91-2.84 (m, 3H, Py–CH2–, p-
CH(CH3)2), 1.30-1.27 (m, 18H, CH(CH3)2). 13C{1H} NMR (C6D6, 297.0 K,
100.61 MHz): δ 160.0 (Py i-C), 149.7 (Py N–CH), 146.3 (Tripp i-C), 143.6
(Tripp p-C), 140.6 (Tripp o-C), 136.0 (Py m-C), 123.2 (Py o-C), 121.4
(Tripp m-C), 121.3 (Py p-C), 43.1 (N–CH2–), 34.8 (p-CH(CH3)2), 28.5 (o-
CH(CH3)2), 24.6 (p-CH(CH3)2), 24.0 (o-CH(CH3)2). MS (DEI): m/z (%)
353 (5, [M]+), 324 (5, [M-N2]+), 309 (5, [M-C3H7]+; [C21H29N2]+), 281 (10
[C19H25N2]+), 246 (5, [C17H28N]+), 232 (20, [C16H26N]+), 218 (100,
[C15H23N]+), 204 (25, [C15H24]+), 188 (10, [C12H16N2]+), 175 (25,
[C10H13N3]+; [C12H17N]+), 145 (5, [C9H9N2]+; [C11H13]+), 133 (15, [C9H11N]+;
[C10H12]+), 119 (20, [C9H9N]+; [C9H11]+; [C7H7N2]+), 106 (95, [C7H8N]+), 91
(25, [C7H7]+), 78 (10, [C6H6]+), 43 (25, [C3H7]+). MS (Micro-ESI pos. in
MeOH): m/z (%) 375 (100, [M+Na]+). IR (pure, /cm-1): 3245 (m), 3070
(m), 3007 (m), 2957 (m), 2943 (m), 2863 (m), 1594 (m), 1567 (m), 1476
(m), 1461 (m), 1452 (m), 1437 (s), 1393 (m), 1350 (m), 1313 (m), 1300
(m), 1267 (w), 1249 (m), 1230 (m), 1192 (s), 1165 (m), 1121 (m), 1105
(m), 1068 (w), 1054 (m), 1001 (m), 978 (m), 955 (w), 943 (w), 920 (w),
872 (m), 817 (w), 778 (m), 768 (m), 757 (m), 717 (m), 654 (m), 637 (m),
606 (m), 509 (m), 406 (m). Elemental analysis for C22H32N4 (352.53
g/mol): calcd.: C 74.96, H 9.15, N 15.89; found: C 75.25, H 9.30, N 15.54.
1
105 °C. H NMR (CDCl3, 272.9 K, 400.13 MHz): δ 8.53 (m, 0.5H, Py N–
CH), 8.25 (m, 0.5H, Py N–CH), 7.61-6.86 (m, 11H, Har), 5.37 (broad,
0.5H, NH), 5.22 (broad, 0.5H, NH), 3.95 (m, 1H, N–CH2–), 3.37-3.36 (m,
1H, N–CH2–), 3.24 (m, 1H, Py–CH2–), 3.13-3.07 (m, 2H, CH(CH3)2), 2.74
(m, 1H, Py–CH2–), 1.17-1.16 (m, 10H, CH(CH3)2), 0.89-0.88 (m, 2H,
CH(CH3)2). 13C{1H} NMR (CDCl3, 313.0 K, 100.61 MHz): δ 159.5 (Py i-C),
156.2 (NC(Ph)N), 149.3 (Py N–CH), 144.6 (Dipp i-C), 139.1 (Ph i-C),
136.4 (Py m-C), 136.0 (Dipp o-C), 129.2 (Ph Car), 128.3 (Ph Car), 127.9
(Ph Car), 123.2 (Car), 122.9 (Car), 121.4 (Car), 42.5 (N–CH2–), 38.1 (Py–
CH2–), 28.2 (CH(CH3)2), 23.8 (CH(CH3)2), 22.8 (CH(CH3)2). 1H NMR
([D8]THF, 297.0 K, 400.13 MHz): δ 8.47 (m, 1H, Py N–CH), 7.60 (m, 1H,
Py m-CH), 7.24-6.76 (m, 10H, Har), 6.37 (broad, 1H, NH), 3.87 (m, 2H,
Tripp-N(H)-C2H4-Py (2). Heating a solution of 1c (260 mg, 0.73 mmol) in
n-pentane to the boiling temperature led to formation of 2 under gas
evolution. Crystallization at -20 °C, separating from solvent and drying in
vacuo yielded 70 mg of a light brown solid (30%). M. p. 74 - 75 °C. 1H
NMR (CDCl3, 297.0 K, 400.13 MHz): δ 8.58-8.57 (m, 1H, Py N–CH), 7.63
(td, 3JHH = 8.0 Hz, 4JHH = 2.0 Hz, 1H, Py m-CH) 7.24 (d, 3JHH = 8.0 Hz, 1H,
Py o-CH), 7.17-7.14 (m, 1H, Py p-CH), 6.91 (s, 2H, Tripp, m-CH), 3.24 (t,
3JHH = 6.4 Hz, 2H, N–CH2–), 3.18-3.10 (m, 4H, o-CH(CH3)2, Py–CH2–),
2.84 (sept, 3JHH = 6.8 Hz, 1H, p-CH(CH3)2), 1.23 (d, 3JHH = 6.8 Hz, 6H, p-
3
N–CH2–), 3.27-3.18 (m, 2H, Py–CH2–), 3.10 (sept, JHH = 6.9 Hz, 2H,
3
CH(CH3)2), 1.19 (d, JHH = 6.8 Hz, 6H, CH(CH3)2), 0.93-0.91 (m, 6H,
CH(CH3)2). 13C{1H} NMR ([D8]THF, 297.0 K, 100.62 MHz): δ 161.8 (Py i-
C), 154.9 (NC(Ph)N), 150.1 (Py N–CH), 147.6 (Dipp i-C), 139.0 (Dipp o-
C), 136.8 (Py m-C), 133.6 (Ph i-C), 129.6 (Ph Car), 128.9 (Ph Car), 128.5
(Ph Car), 124.0 (Car), 123.8 (Car), 123.1 (Car), 121.9 (Car), 42.3 (N–CH2–),
38.6 (Py–CH2–), 29.1 (CH(CH3)2), 24.5 (CH(CH3)2), 22.7 (CH(CH3)2). MS
(Micro-ESI pos. in MeOH): m/z (%) 408 (10, [M+Na]+), 386 (100, [M+H]+),
281 (5, [C18H23N3]+), 265 (10, [C19H23N]+; [C17H8N3]+), 264 (20,
[C17H18N3]+; [C19H22N]+). IR (pure, /cm-1): 3238 (m), 3042 (m), 2954 (m),
2862 (m), 1624 (s), 1596 (m), 1567 (m), 1536 (s), 1489 (m), 1475 (m),
1459 (m), 1443 (m), 1419 (m), 1380 (m), 1357 (m), 1340 (m), 1314 (m),
1300 (m), 1280 (m), 1257 (m), 1246 (m), 1212 (m), 1145 (m), 1110 (w),
1055 (w), 1039 (m), 1009 (w), 993 (w), 785 (m), 774 (m), 761 (s), 696 (s),
659 (m), 618 (m), 535 (w), 497 (m), 429 (w). Elemental analysis for
C26H31N3 (385.25 g/mol): calcd.: C 81.00, H 8.10, N, 10.90; found: C
81.02, H 8.28, N 10.36.
3
CH(CH3)2), 1.18 (d, JHH = 6.8 Hz, 12H, o-CH(CH3)2). 13C{1H} NMR
(CDCl3, 297.0 K, 100.61 MHz): δ 160.5 (Py i-C), 149.4 (Py N–CH), 143.8
(Tripp p-C), 142.6 (Tripp o-C), 141.2 (Tripp i-C), 136.4 (Py m-C), 123.6
(Py o-C), 121.4 (Tripp m-C), 120.8 (Py p-C), 51.3 (N–CH2–), 39.1 (Py–
CH2–), 34.0 (p-CH(CH3)2), 27.7 (o-CH(CH3)2), 24.4 (o-CH(CH3)2), 24.3
(p-CH(CH3)2). MS (DEI): m/z (%) 324 (80, [M]+), 309 (5, [M-CH3]+), 281
(10 [M-C3H7]+), 232 (80, [C16H26N]+), 219 (100, [C15H24N]+), 204 (25,
[C15H24]+), 117 (5, [C9H9]+), 106 (15, [C7H8N]+), 93 (35, [C6H7N]+), 78 (5,
[C5H4N]+), 43 (10, [C3H7]+). IR (pure, /cm-1): 3331 (m), 2998 (w), 2959
(m), 2926 (m), 2883 (m), 2864 (m), 2837 (m), 1591 (m), 1564 (w), 1469
(m), 1453 (m), 1433 (m), 1419 (m), 1378 (m), 1361 (m), 1314 (m), 1298
(m), 1262 (w), 1241 (m), 1225 (m), 1204 (m), 1192 (m), 1177 (m), 1445
(w), 1118 (m), 1103 (m), 1066 (w), 1050 (w), 1003 (m), 985 (m), 936 (w),
877 (m), 859 (m), 790 (m), 775 (m), 755 (m), 744 (m), 729 (m), 646 (w),
625 (w), 475 (m). Elemental analysis for C22H32N2 (324.51 g/mol): calcd.:
C 81.43, H 9.94, N 8.63, found: C 81.43, H 9.75, N 8.91.
N-(2,4,6-triisopropylphenyl)-N’-(2-pyridylethyl)triazene, Tripp-N=N-N(H)-
C2H4-Py (1c). Py-C2H4OH (9.7 mL, 73.4 mmol) was reacted with TsCl
(15.2 g, 80.0 mmol) in a mixture of THF (25 mL) and aqueous NaOH
solution (25 mL, 30%) at 0 °C, the mixture was further stirred at room
temperature for 24 h to give 18.5 g (66.7 mmol, 91%) of Py-C2H4Ts. The
reaction of Py-C2H4Ts (18.5 g, 66.7 mmol) with NaN3 (6.7 g, 103.1 mmol)
in DMF (130 mL) and subsequent purification by column chromatography
(EtOAc/n-hexane 2:1  1:0) yielded 6.5 g (43.8 mmol, 60%) of Py-
C2H4N3 as a yellow liquid. The purity of the intermediate products were
controlled by NMR spectroscopy. TrippMgBr(thf)2 (0.9 M in THF, 17 mL,
15.3 mmol) was added dropwise to a solution of Py-C2H4N3 (1.9 g, 12.8
mmol) in THF (40 mL) at 0 °C with stirring. After 24 h the reddish solution
was quenched carefully with water (100 mL), extracted with Et2O (50 mL)
and the organic layer was washed three times with water (100 mL).
Drying over anhydrous Na2SO4 and removal of volatiles in vacuo gave a
light yellow solid, recrystallized from n-pentane (1.9 g, 43%). M. p. 62 -
63 °C, dec. > 70 °C (N2 evolution). 1H NMR (C6D6, 297.0 K, 400.13 MHz):
δ 8.36-8.35 (m, 1H, Py N–CH), 8.29 (broad, 1H, NH), 7.18 (s, 2H, Tripp
[(thf)Mg{Dipp-N=C(tBu)-N-C2H4-Ph}2] (3a). To a solution of amidine 1a
(280 mg, 0.77 mmol) in THF (10 mL) was added 1.1 mL of a 1 M
Mg(nBu)2 solution in n-heptane at room temperature and the reaction
mixture was stirred for 3 h. Thereafter all volatiles were removed in vacuo
and 130 mg of 3a (42%) as colorless crystals were isolated after
recrystallization from toluene. M. p. 154 - 158 °C (dec.). 1H NMR
3
([D8]THF, 297.0 K, 400.13 MHz): δ 7.05 (t, JHH = 7.2 Hz, 4H, Dipp m-
3
CH), 6.99-6.96 (m, 6H, Ph o-CH, Ph p-CH) 6.86 (t, JHH = 7.2 Hz, 2H,
3
Dipp p-CH), 6.70 (d, JHH = 7.6 Hz, 4H, Ph m-CH), 3.61 (m, 2H, thf O–
CH2–), 3.54-3.47 (m, 4H, CH(CH3)2), 3.40-3.35 (m, 4H, N–CH2–), 2.03-
1.99 (m, 4H, Ph–CH2–), 1.76 (m, 2H, thf –CH2–), 1.30-1.24 (m, 24H,
CH(CH3)2), 1.13 (s, 18H, C(CH3)3). 13C{1H} NMR ([D8]THF, 297.0 K,
100.62 MHz): δ 177.2 (NC(tBu)N), 148.5 (Ph i-C), 143.2 (Dipp i-C), 142.1
(Dipp o-C), 129.5 (Ph m-C), 128.6 (Dipp m-C), 126.1 (Ph o-C), 123.7 (Ph
p-C), 122.9 (Dipp p-C), 68.4 (thf, O–CH2–), 52.0 (N–CH2–), 41.3
(C(CH3)3), 40.5 (Ph–CH2–), 30.8 (C(CH3)3), 28.9 (CH(CH3)2), 26.5 (thf, –
3
4
m-CH), 6.98 (td, JHH = 7.6 Hz, JHH = 1.7 Hz, 1H, Py m-CH), 6.66 (d,
This article is protected by copyright. All rights reserved.

10.1002/ejic.201800890
European Journal of Inorganic Chemistry
FULL PAPER
CH2–), 24.0 (CH(CH3)2). MS (DEI): m/z (%) 751 (15, [M-thf]+), 707 (35,
[M-thf-C3H7]+), 387 (25, [MgL]+), 364 (65, [L]+), 321 (100, [L-C3H7]+), 307
(50, [C21H27N2]+), 259 (10, [C17H27N2]+), 244 (20, [C16H24N2]+; [C17H26N]+),
217 (100, [C14H21N2]+), 186 (35, [C13H16N]+; [C12H12N2]+), 146 (20,
[C11H14]+; [C10H12N]+), 105 (50, [C8H9]+), 91 (30, [C7H7]+), 57 (10,
[C3H7N]+). IR (pure, /cm-1): 3059 (vw), 2957 (m), 2864 (m), 1657 (m),
1587 (w), 1479 (m), 1449 (m), 1431 (m), 1380 (m), 1361 (m), 1344 (m),
1329 (m), 1315 (m), 1258 (m), 1209 (m), 1183 (m), 1161 (m), 1089 (s),
1054 (m), 1030 (s), 1016 (s), 934 (w), 918 (w), 880 (m), 797 (m), 767 (m),
745 (m), 730 (m), 698 (m), 636 (m), 612 (m), 574 (m), 487 (m), 463 (m),
452 (m). Elemental analysis for C54H78MgN4O (823.55 g/mol): calcd.: C
78.76, H 9.55, N 6.80, found: C 77.68, H 9.49, N 6.27.
7.14-7.12 (m, 2H, Tol m-CH), 7.10 (s, 4H, Tripp m-CH), 7.05-7.00 (m, 3H,
Tol o-CH, Tol p-CH), 6.91 (td, 3JHH = 7.6 Hz, 4JHH = 1.8 Hz, 2H, Py m-CH),
6.56 (d, 3JHH = 7.6 Hz, 2H, Py o-CH), 6.49 (t, 3JHH = 6.4 Hz, 2H, Py p-CH),
3
3
4.15 (t, JHH = 5.8 Hz, 4H, N–CH2–), 3.22 (sept, JHH = 6.8 Hz, 4H, o-
CH(CH3)2), 2.91-2.81 (m, 6H, p-CH(CH3)2, Py–CH2–), 2.11 (s, 3H, Tol
3
3
CH3), 1.29 (d, 12H, JHH = 7.2 Hz, p-CH(CH3)2), 1.09 (d, JHH = 6.8 Hz,
24H, o-CH(CH3)2). 13C{1H} NMR (C6D6, 297.0 K, 100.61 MHz): δ 162.6
(Py i-C), 150.3 (Py N–CH), 145.2 (Tripp i-C), 143.3 (Tripp p-C), 141.9
(Tripp o-C), 138.2 (Py m-C), 137.9 (Tol i-C), 129.3 (Tol o-C), 128.6 (Tol
m-C), 125.7 (Tol p-C), 125.5 (Py o-C), 122.1 (Py p-C), 121.2 (Tripp m-C),
50.5 (N–CH2–), 38.6 (Py–CH2–), 34.8 (p-CH(CH3)2), 28.5 (o-CH(CH3)2),
24.7 (p-CH(CH3)2), 24.5 (o-CH(CH3)2), 21.4 (Tol CH3). MS (DEI): m/z (%)
324 (30, [L-N2]+), 309 (5, [L-C3H7]+), 281 (15, [C19H25N2]+), 232 (30,
[C16H26N]+), 218 (100, [C15H24N]+), 204 (70, [C15H24]+), 175 (20,
[C12H17N]+), 133 (15, [C9H11N]+), 119 (15, [C9H11]+), 106 (90, [C7H8N]+),
93 (50, [C6H7N]+), 78 (15, [C5H4N]+), 43 (15, [C3H7]+). IR (pure, /cm-1):
2956 (w), 2865 (w), 1593 (w), 1568 (w), 1463 (w), 1436 (m), 1401 (w),
1381 (w), 1358 (w), 1311 (w), 1263 (w), 1234 (w), 1192 (w), 1166 (w),
1121 (w), 1103 (w), 1069 (w), 1052 (w), 1012 (w), 1000 (w), 943 (w), 919
(w), 874 (w), 799 (w), 767 (w), 757 (w), 730 (w), 695 (w), 639 (w), 629
(w), 612 (w), 603 (w), 584 (w), 560 (w), 536 (w), 496 (m), 483 (w).
Elemental analysis for 3c·toluene, C51H70MgN8 (819.48 g/mol): calcd.: C
74.75, H 8.61, N 13.67, found: C 74.82, H 8.76, N 13.78. Elemental
analysis for 3c, C44H62MgN8 (727.34 g/mol): calcd.: C, 72.66; H, 8.59; N,
15.41. Found: C, 72.82; H, 8.77; N, 15.06.
[Mg{Dipp-N=C(Ph)-N-C2H4-Py}2] (3b). [Mg{Dipp-N=C(Ph)-N-C2H4-Py}2]
was prepared in analogy to 3a using 200 mg (0.52 mmol) of 1b and THF
(3 mL) with additive tmeda (1 mL) as solvent. Recrystallization from a
mixture of n-pentane, toluene and THF at -20 °C led to formation of 80
mg of 3b as pale yellow crystals (38%). Physical data show
coexistence of at least three isomeric structures of the ligand in solution
at room temperature in ratio of approximately 2:1:0.5 making
a
a
spectroscopic data very complex (in the 1H NMR spectra the intensity
has been adjusted so that the two major isomers yield one isomer). M. p.
155 - 158 °C (dec.). 1H NMR (C6D6, 297.0 K, 400.13 MHz): δ 7.97-7.74
(m, 2H, Py N−CH), 7.55-7.37 (m, 4H, Ph o-CH), 7.07-6.88 (m, 12H, Ph
m-CH, Ph p-CH, Dipp m-CH, Dipp p-CH), 6.83-6.78 (m, 2H, Py m-CH),
6.54-6.48 (m, 2H, Har), 6.34-6.25 (m, 2H, Har), 4.29-4.22 (m, 1H, N−CH2−
3
minor), 3.72 (m, 3H, CH(CH3)2 major), 3.69-3.66 (t, JHH = 5.6 Hz, 3H,
Crystal structure determinations. The intensity data for the compounds
were collected on a Nonius KappaCCD diffractometer using graphite-
monochromated Mo-K radiation. Data were corrected for Lorentz and
polarization effects; absorption was taken into account on a semi-
empirical basis using multiple-scans.[22-24] The structures were solved by
Direct Methods (SHELXS[25]) and refined by full-matrix least squares
techniques against Fo2 (SHELXL-97[25] and SHELXL-2014[26]). All hydrogen
atoms of the compounds 1b and 1c and the hydrogen atom bonded to N2 of
2 were located by difference Fourier synthesis and refined isotropically. All
other hydrogen atoms were included at calculated positions with fixed
thermal parameters. The crystal of 2 was a non-merohedral twin. The twin
law was determined by PLATON[25] to (-0.505 -0.000 -1.484) (0.0 -1.0 0.0) (-
0.502 0.000 -0.505). The contribution of the main component was refined to
0.553(2). The crystal of 3b contains large voids, filled with disordered
solvent molecules. The size of the voids is 7473 Å3/unit cell. Their
contribution to the structure factors was secured by back-Fourier
transformation using the SQUEEZE routine of the program PLATON[27]
resulting in 1804 electrons/unit cell. All non-disordered, non-hydrogen
atoms were refined anisotropically.[27] Crystallographic data as well as
structure solution and refinement details are summarized in Table S1
(see Supporting Information). XP (SIEMENS Analytical X-ray Instruments,
Inc.)[28] and POV-Ray[29] were used for structure representations.
3
N−CH2− major), 3.43-3.26 (m, 1H, CH(CH3)2 minor), 2.51 (t, JHH = 5.2
Hz, 3H, Py−CH2− major), 2.06 (m, 1H, Py−CH2− minor), 1.36-1.29 (m,
6H, CH(CH3)2 minor), 1.13 (d, 3JHH = 6.8 Hz, 6H, CH(CH3)2 minor), 0.88-
0.70 (m, 12H, CH(CH3)2 major). 13C{1H} NMR (C6D6, 297.0 K, 100.62
MHz): δ 172.1 (NC(Ph)N), 171.6 (NC(Ph)N), 165.2 (Py i-C), 164.0 (Py i-
C), 162.8 (qC), 162.1 (qC), 150.8 (Car), 149.0 (Py N−CH), 148.9 (Py
N−CH), 146.9 (Py N−CH), 146.9 (Dipp i-C), 145.7 (Car), 143.2 (Car),
142.2 (Car), 139.0 (Py m-C), 137.8 (Py m-C), 137.5 (Py m-C), 135.1 (Car),
134.0 (Car), 130.9 (Ph o-C), 129.7 (Ph o-C), 129.3 (Car), 128.6 (Ph o-C),
128.5 (Ph Car), 128.4 (Ph Car), 127.7 (Ph Car), 125.7 (Car), 124.9 (Car),
124.8 (Car), 123.3 (Dipp m-C), 123.3 (Dipp m-C), 122.9 (Car), 121.7 (Car),
121.5 (Car), 121.3 (Car), 120.9 (Car), 120.0 (Car), 49.3 (N−CH2− minor),
47.9 (N−CH2− major), 39.9 (Py−CH2− minor), 39.8 (Py−CH2− major),
28.8 (CH(CH3)2 major), 27.9 (CH(CH3)2 minor), 25.8 (CH(CH3)2), 25.3
(CH(CH3)2), 24.8 (CH(CH3)2). MS (DEI): m/z (%) 408 (5, [MgL]+), 385 (90,
[L]+), 342 (69, [L-C3H7]+), 292 (20, [C20H24N2]+), 279 (25, [C19H23N2]+),
264 (70, [C18H20N2]+), 249 (90, [C17H17N2]+), 235 (100, [C16H15N2]+), 206
(20, [C14H10N2]+), 117 (10, [C7H5N2]+), 106 (40, [C7H8N]+), 93 (10,
[C6H7N]+), 43 (5, [C3H7]+). MS (Micro-ESI pos. in MeOH): m/z (%) 386
(100, [L+H]+), 264 (80, [C18H20N2]+). IR (pure, /cm-1): 3242 (w), 3029 (w),
2954 (m), 2921 (w), 2861 (w), 1624 (m), 1597 (m), 1567 (m), 1536 (m),
1474 (m), 1459 (m), 1446 (m), 1435 (m), 1420 (m), 1379 (w), 1347 (m),
1313 (m), 1301 (m), 1255 (m), 1177 (m), 1145 (m), 1099 (w), 1070 (m),
1054 (w), 1038 (w), 1025 (w), 1011 (w), 993 (w), 913 (vw), 838 (vw), 816
(w), 784 (w), 761 (m), 730 (w), 696 (m), 676 (m), 637 (w), 616 (w), 588
(m), 561 (m), 535 (m), 498 (m), 473 (m), 463 (m), 445 (m). Elemental
analysis for C52H60MgN6 (793.40 g/mol): calcd.: C 78.72, H 7.62, N 10.59,
found: C 78.25, H 8.00, N 9.98.
Acknowledgements
We acknowledge the support by the NMR service platform
(www.nmr.uni-jena.de) and of the mass spectrometry platform
(www.ms.uni-jena.de) of the Faculty of Chemistry and Earth
Sciences of the Friedrich Schiller University Jena.
[Mg{Dipp-N=N-N-C2H4-Py}2] (3c). Triazene 1c (190 mg, 0.54 mmol) and
0.6 mL of a 1 M Mg(nBu)2 solution in n-heptane were reacted in THF (4
mL) at 0 °C and the mixture was stirred for 24 h at room temperature. All
volatiles were removed in vacuo and 115 mg of 3c (59%) as yellowish
crystals were isolated after recrystallization from toluene/THF (7:1) at -
20 °C. Physical data show cocrystalline toluene (1 eq), which is partly
lost by drying in vacuo. M. p. 191 - 195 °C (dec. N2 evolution). 1H NMR
The authors declare no conflict of interest.
Supporting Information
3
(C6D6, 297.0 K, 400.13 MHz): δ 8.60 (d, JHH = 4.8 Hz, 2H, Py N–CH),
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10.1002/ejic.201800890
European Journal of Inorganic Chemistry
FULL PAPER
Sutcliffe, C. A. Lamsfus, G. B. Deacon, L. Maron, C. Jones, Chem.
Commun. 2018, 54, 786-789.
Crystallographic data (excluding structure factors) has been
deposited with the Cambridge Crystallographic Data Centre as
supplementary publication CCDC-1855573 for 1b, CCDC-
1855574 for 1c, CCDC-1855575 for 2, CCDC-1855576 for 3a,
CCDC-1855577 for 3b, and CCDC-1855578 for 3c. Copies of
the data can be obtained free of charge on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK [E- mail:
deposit@ccdc.cam.ac.uk].
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Keywords: amidinates • magnesiation • magnesium complexes
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10.1002/ejic.201800890
European Journal of Inorganic Chemistry
FULL PAPER
Table 1: Selected 13C{1H} NMR data of Dipp/Tripp-N=E-N(H)-C2H4-R' (E = C-tBu, C-Ph, N; R' = Ph, Py) and of the magnesiated anions [Dipp-N=C(tBu)-N(H)-
C2H4-Ph (1a), Dipp-N=C(Ph)-N(H)-C2H4-Py (1b), Tripp-N=N-N(H)-C2H4-Py (1c), Dipp-N=C(tBu)-N(H)-C2H4-Py (1d), [(thf)Mg{Dipp-N=C(tBu)-N-C2H4-Ph}2] (3a),
[Mg{Dipp-N=C(Ph)-N-C2H4-Py}2] (3b), [Mg{Tripp-N=N-N-C2H4-Py}2] (3c), [Mg{Dipp-N=C(tBu)-N-C2H4-Py}2] (3d)].
Comp.
1a
E
R'
Solvent
C6D6
δ(CNCN
156.6
156.2
-
)
δ(iCDipp/Tripp
)
δ(CCMe3
)
δ(CNCH2
44.2
)
δ(CCH2Aryl
36.7
)
δ(iCPy/Ph
138.9
159.5
160.0
160.6
148.5
164.0
162.6
)
Ref.
[12]
[12]
C-tBu
C-Ph
N
Ph
Py
Py
Py
Ph
Py
Py
Py
147.0
38.8
1b
CDCl3
C6D6
144.6
-
42.5
38.1
1c
146.3
-
43.1
39.1
1d
C-tBu
C-tBu
C-Ph
N
C6D6
157.2
177.2
147.7
39.1
41.3
-
43.1
37.1
3a
[D8]THF
C6D6
143.2
52.0
40.5
3b
172.1, 171.6
-
146.9
47.9, 49.3
50.5
39.8, 39.9
38.6
3c
C6D6
145.2
-
3d
C-tBu
C6D6
176.7, 164.5
151.8, 146.9
40.3
49.2, 46.7
40.0, 38.1
166.0, 162.8
Table 3: Selected structural parameters (average values, bond lengths (pm) and angles (deg.)) of Dipp/Tripp-N=E-N(H)-C2H4-R' (1; E = C-tBu, C-Ph, N; R' = Ph,
Py) and of the magnesiated compounds [(L)nMg{Dipp/Tripp-N=E-N-C2H4-R'}2] (3; E = C-tBu, C-Ph, N; R' = Ph, Py; L = thf, n = 0, 1) [Dipp-N=C(Ph)-N(H)-C2H4-Py
(1b), Tripp-N=N-N(H)-C2H4-Py (1c), Dipp-N=C(tBu)-N(H)-C2H4-Py (1d), [(thf)Mg{Dipp-N=C(tBu)-N-C2H4-Ph}2] (3a), [Mg{Dipp-N=C(Ph)-N-C2H4-Py}2] (3b),
[Mg{Tripp-N=N-N-C2H4-Py}2] (3c), [Mg{Dipp-N=C(tBu)-N-C2H4-Py}2] (3d)].
Comp.
E
R'
Isomer
CAryl-NAryl
ENEN-NAryl
ENEN-NCH2
ENEN-CER
NCH2-CCH2
CAryl-NAryl
ENEN
-
NAryl-ENEN
NCH2
-
ENEN-NCH2
CCH2
-
Ref.
1b
1c
C-Ph
N
Py
Py
Py
Ph
Py
Py
Py
Py
Anti-E
Anti-E
Syn-Z
Syn-E
Syn-E
Syn-E
Syn-E
Syn-Z
141.5
143.3
141.1
141.1
141.8
142.2
141.5
139.6
128.5
127.0
127.9
134.3
133.4
131.3
134.0
131.1
135.8
133.2
135.9
133.1
132.7
131.0
132.9
135.1
150.1
-
144.9
145.0
145.3
145.1
144.6
144.8
145.0
147.5
121.5
112.4
126.4
130.8
123.0
114.5
127.4
131.9
119.8
113.6
128.6
110.7
113.6
108.4
110.3
130.3
121.5
124.0
129.4
128.4
125.8
117.2
129.4
112.7
1d
3a
C-tBu
C-tBu
C-Ph
N
154.0
155.1
150.0
-
[12]
3b
3c
3d[a]
C-tBu
C-tBu
155.5
155.8
[12]
[12]
a) Compound contains two different ligand isomers; the syn-E isomeric ligand binds as a tridentate Lewis base whereas the syn-Z isomeric base acts as a
bidentate ligand.
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10.1002/ejic.201800890
European Journal of Inorganic Chemistry
FULL PAPER
Entry for the Table of Contents
FULL PAPER
1-(2,4,6-Triisopropylphenyl)-3-(2-
pyridylethyl)triazene has to be
D. Kalden, S. Krieck, H. Görls, M.
Westerhausen*
handled below room temperature to
suppress elimination of dinitrogen.
Magnesiation of this triazene yields
the corresponding triazenide with a
hexa-coordinate magnesium atom.
Page No. – Page No.
Coordination Chemistry of N-(2-
Pyridylethyl)-Substituted Bulky
Amidinates and Triazenides of
Magnesium
Key Topic: Magnesium Amidinates
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