Magnesium Stung by Nonclassical Scorpionate Ligands: Synthesis and Cone-Angle Calculations

Article abstract of DOI:10.1002/chem.201803067

A series of tris(pyrazolyl)alkane (RCTp) scorpionate ligands of the type RCTp^3-R′ (R=Me, nBu, SiMe₃; R′=H, Me, Ph, iPr, tBu) were synthesized and their ability to coordinate methylmagnesium moieties was examined. The reaction of Mg(AlMe₄)₂ with neutral proligands HCTp^3-Ph or Me₃SiCTp^3-Me, containing a non-innocent backbone methine moiety, led to deprotonation/rearrangement and SiMe₃/AlMe₃ exchange to afford [(Me₃AlCTp^3-Ph)₂Mg] and [(Me₃AlCTp^3-Me)Mg(AlMe₄)], respectively, with monoanionic tripodal ligands. Treatment of sterically less demanding RCTp^3-R′ with Mg(AlMe₄)₂ produced isostructural dicationic “metal-in-a-box” complexes of the type [(RCTp^3-R′)₂Mg][AlMe₄]₂ (R=Me, nBu; R′=H, Me). Utilization of the superbulky ligands MeCTp^3-Ph and MeCTp^3-tBu gave monocationic complexes [(MeCTp^3-Ph)MgMe][AlMe₄] and [(MeCTp^3-tBu)MgMe][Al₂Me₇] as separated ion pairs. The reaction of Mg(AlMe₄)₂ with nBuCTp^3-Ph led to the formation of the dimagnesium complex [{(nBuCTp^3-Ph)Mg(AlMe₄)}₂(μ-CH₃)], which features a bridging methyl moiety and terminal η¹-coordinated tetramethylaluminato ligands. Isopropyl-substituted ligand MeCTp^3-iPr emerged from further fine-tuning of the steric and electronic parameters and, upon reaction with Mg(AlMe₄)₂, gave (MeCTp^3-iPr)Mg(AlMe₄)₂; this represents the first example of a magnesium bis(alkyl) complex with an intact RCTp^3-R′ ligand. The exact ligand cone angles Θ^° of all magnesium complexes were determined according to the mathematical analysis developed by Allen et al. [J. Comput. Chem. 2013, 34, 1189–1197].

Full text of DOI:10.1002/chem.201803067

A Journal of
Accepted Article
Title: Magnesium Stung by Non-Classical Scorpionate Ligands:
Synthesis and Cone Angle Calculations
Authors: Reiner Anwander, Christoph Stuhl, and Cäcilia Maichle-
Mössmer
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Magnesium Stung by Non-Classical Scorpionate Ligands:
Synthesis and Cone Angle Calculations
Christoph Stuhl,[a] Caecilia Maichle-Mössmer,[a] and Reiner Anwander*[a]
Abstract: A series of tris(pyrazolyl)alkane scorpionate ligands of the type RCTp3-R’ (R = Me, nBu, SiMe3; R’ = H, Me, Ph, iPr, tBu) was
synthesized and their ability to coordinate magnesium methyl moieties was examined. The reaction of Mg(AlMe4)2 with neutral
proligands HCTp3-Ph or Me3SiCTp3-Me, containing a non-innocent backbone methine moiety, led to deprotonation/rearrangement and
SiMe3/AlMe3 exchange to afford [(Me3AlCTp3-Ph)2Mg] and [(Me3AlCTp3-Me)Mg(AlMe4)], respectively, with monoanionic tripodal ligands.
Treatment of sterically less demanding RCTp3-R’ with Mg(AlMe4)2 produced isostructural dicationic “metal-in-a-box” complexes of the
type [(RCTp3-R’)2Mg][AlMe4]2 (R = Me, nBu; R’ = H, Me). Utilization of the superbulky ligands MeCTp3-Ph and MeCTp3-tBu gave
monocationic complexes [(MeCTp3-Ph)MgMe][AlMe4] and [(MeCTp3-tBu)MgMe][Al2Me7] as separated ion pairs. The reaction of
Mg(AlMe4)2 with nBuCTp3-Ph led to the formation of the dimagnesium complex [{(nBuCTp3-Ph)Mg(AlMe4)}2(-CH3)], featuring a bridging
methyl moiety and terminal 1-coordinated tetramethylaluminato ligands. Isopropyl-substituted ligand MeCTp3-iPr emerged from further
fine-tuning of the steric and electronic parameters and when reacted with Mg(AlMe4)2 gave (MeCTp3-iPr)Mg(AlMe4)2, representing the
first example of a magnesium bis(alkyl) complex with an intact RCTp3-R’ ligand. The exact ligand cone angles of all magnesium
complexes were determined according to the mathematical analysis developed by Allen et al.
Overall,
the
synthesis
approaches
to
magnesium
Introduction
tris(pyrazolyl)methane or -methanide complexes seem limited to
(1) protonolysis of Grignard reagents or reactive
organomagnesium complexes by the methine C−H moiety
affording mono- or bis-methanide complexes I and II (Chart1),
(2) reprotonation of the methanide moiety by a Brønsted acid
generating III or IV, respectively, and (3) Lewis acid−base
Organomagnesium compounds, and in particular Grignard
reagents [RMgX] (R = alkyl, X = halogenido), belong to the most
popular and most studied organometallic reagents.[1] Ongoing
immense interest is emphasized by a rapidly growing library of
magnesium alkyl complexes bearing multidentate N- and O-
chelating ligands, which routinely displace the halogenido ligand
X.[2] Several types of scorpionate ligands have been employed
in an effort to stabilize monomeric complexes[3] and to counteract
the Schlenk equilibrium.[4] The classical Trofimenko ligand[5] and
polypyrazolyls with different main group elements in the bridging
position (Al,[6] Ga,[7] C[8], Si[9] or P[10]), as well as tridentate ligands
with different heterocycles[11] or hybrid scorpionates[12] can
efficiently encapsulate the magnesium center and protect from
agglomeration.[8,9b,10,13] According to the concepts of modern
coordination chemistry such scorpionates display highly
versatile ligand scaffolds the steric and electronic properties of
which can be efficiently fine-tuned by varying the substituents of
the pyrazole and the central boron or carbon atom linking the
heterocycles.[14]
reactions
of
methanide
sandwich
complexes
with
organoaluminum reagents giving trimetallic MgAl2 complexes V.
Furthermore, alkaline-earth metal methanide complexes can
degrade via C−N bond cleavage to form pyrazolate
complexes.[15] Breher and Mountford have comprehensively
examined reactions of alkaline-earth metal complexes with
tris(pyrazolyl)methanes,[14b,14c] while the proneness of the
methine moiety for C–H bond activation in the presence of a
strong
base
was
particularly
emphasized.[14b]
Tris(pyrazolyl)methane (HCTp) was initially synthesized by
Hückel in 1937, by treating chloroform with potassium pyrazolate
(Kpz).[16] Later on, Elguero applied a phase transfer catalysis to
access the desired tris(3-R-pyrazolyl)methane derivatives
HCTp3-R (R = H, Me, Ph, iPr, tBu), but had to deal with mixtures
of four structural isomers.[17]
We have recently embarked on the feasibility of well-defined
magnesium alkyl species.[18] For example, the reaction of
hydrotris(pyrazolyl)borate KTpMe,Me with dimethylmagnesium or
Mg(AlMe4)2, initially described by Ziegler in 1957,[19] afforded the
[a]
Institut für Anorganische Chemie, Eberhard Karls Universität
Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
E-Mail: reiner.anwander@uni-tuebingen.de
terminal
hydrocarbyls
[(TpMe,Me)MgMe]
and
http://uni-tuebingen.de/syncat-anwander
[(TpMe,Me)Mg(AlMe4)].[4] Interestingly, polymeric [MgMe2]n and
bimetallic Mg(AlMe4)2 can be mutually interconverted by either
Supporting information for this article is given via a link at the end of
the document.
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addition of organoaluminum reagent or diethyl ether, clearly
being reminiscent of the donor-induced tetraalkylaluminate
cleavage of Ln(AlMe4)3 into [LnMe3]n (Ln= Y, Ho, Lu).[20]
Moreover, the tris(pyrazolyl)borato ligand can stabilize reactive
rare-earth metal hydride, alkyl, imide or methylidene
complexes.[21] Spurred by these findings we set out to elaborate
the chemistry of neutral tris(pyrazolyl)alkane ligands RCTp with
organomagnesium compounds. It was evident from the previous
studies that the feasibility of discrete magnesium alkyl
complexes will require more resilient backbone C–R functional
groups. Herein, we systematically extend the limited library of
neutral symmetrical tris(pyrazolyl) scorpionates of the general
type RCTp3-R’ and assess the reactivity toward highly reactive
magnesium methyl complexes.
Tolman cone angles were calculated by adopting the
mathematical model, which was extensively studied for
phosphine ligands coordinating to nickel.[22] Trofimenko applied
this concept to tris(pyrazolyl)borato ligands, but at that time
several restraints have been introduced such as fixed metal
ligand atom distances or by selecting distinct ligand atoms for
the calculations which resulted in significant deviations from the
mathematically exact ligand cone angle.[23] Allen and his group
developed a mathematical analysis in order to determine the
right cone axis from the experimental crystal data with major
implications for structure-reactivity correlations, e.g., in kinetic
studies and catalysis.[24] The present cone angle calculation is
therefore performed according to Allen et al.[24]
For a comprehensive understanding of the structural diversity in
magnesium tris(pyrazolyl)alkane and -methanide complexes the
Chart1. Structurally characterized tris(pyrazolyl)methane and -methanide magnesium complexes (a 2(N,N’) mode)
transfer catalysis protocol, which generates a mixture of complex
isomers.[17] The ratios of the isomeric mixture can be optimized
by refluxing in toluene and via addition of catalytic amounts of
pTsOH, promoting the formation of the symmetric species 2 (see
Scheme 1). As the C–H methine backbone requires substitution
with a more resilient group, the reaction mixture is lithiated with
Results and discussion
Tris-3-alkylpyrazolylalkane RCTp3-R’ Ligand Synthesis and
Library. Crucial criteria for the ligand selection were enhanced
solubility/cone angle variation and ligand backbone modification.
The former two are routinely achieved via derivatization of the
pyrazolyl rings with alkyl and aryl groups. Functionalization of the
apical methine carbon atom provides protection against
nucleophilic attack. Substitution of the pyrazolyl rings in 3-
position is efficient for such tripodal ligands with respect to fine-
tuning of the ligand cone angle. Routinely, the RCTp3-R’ ligands
coordinate to metal centers in a 3(N,N’,N’’) fashion, through
three nitrogen atoms, but other coordination modes such as the
2(N,N’) mode with either an intermolecular bridging pyrazolyl
ring or one non-coordinating/dangling pyrazolyl moiety have
been reported as well.[25] Figure 1 shows the selection of tris(3-
alkylpyrazolyl)alkane ligands used in this study. The tris(3-
alkylpyrazolyl)methane precursors HCTp3-R’(2) were synthesized
from the parent pyrazoles (1)[23,26] by applying Elguero’s phase
nBuLi or Li[N(SiMe3)2], respectively, generating LiCTp3-R’
.
Subsequent in situ addition of alkyl halides R-X affords the
neutral RCTp3-R’ (3) via nucleophilic substitution.[27] Compounds
3 were purified by recrystallization, if not otherwise stated, and
3d-3k have been characterized by single-crystal X-ray diffraction
analyses (see Supporting Information). The synthesis route is
efficient for the preparation of a variety of functionalized ligands
RCTp3-R’ (R = Me, nBu, Me3Si, Bn; R’ = H, Me, Ph, iPr, tBu). In
this study we were able to add five new ligands to the library of
neutral pyrazolyl alkane ligands,[28] nBuCTp (3b), nBuCTp3-Me
(3e), Me3SiCTp3-Me (3f), nBuCTp3-Ph (3h) and MeCTp3-iPr (3j)
(Figure 1).
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Choice of Magnesium Methyl Precursor. Pre-screening
Studies. Since non-coordinating aliphatic or aromatic solvents
were envisioned as the most appropriate for the synthesis of the
targeted discrete organomagnesium tris(pyrazolyl)alkane
complexes
of
the
type
[RCTp3-R’]MgR2,
bis(tetramethyl)aluminate complex Mg(AlMe4)2 was selected as
a well-defined, highly soluble metal precursor.[19,29] A pre-
screening study with [MgMe2]n revealed that not only the methine
moiety of tris(pyrazolyl)methane 2 gets readily deprotonated by
this strong base, which is in agreement with previously reported
respective reactivity of MgnBu2 or MeMgX,[14b,14c] but also the
functionalized alkane ligands RCTp3-R’ (3) suffer from
degradation. Monitoring reaction mixtures of sterically less
demanding ligands 3 with [MgMe2]n (4) in equimolar ratios by 1H
NMR spectroscopy in [D6]benzene or [D8]thf, indicated
decomposition of the RCTp ligands within minutes (3a-c) up to
several weeks (3d-f). This degradation process appeared
interesting since it might indeed hint to transient species
“(RCTp)MgMe2”, which would then undergo decomposition. To
gain further insight into the decomposition process of putative
(RCTp)MgMe2 a series of experiments was performed. On one
occasion, by reacting 4 with 3c in a dme/thf mixture at −40 °C,
colorless cuboid crystals of [(dme)(thf)Mg(pz)3MgMe] (5) formed,
suitable for analysis by X-ray diffraction (Figure 2, monoclinic,
P21/n).
Scheme 1. Synthesis of RCTp3-R’ Ligands 3 via Phase Transfer Catalysis of 3-
Substitued Pyrazoles and Electrophilic Backbone Substitution.
Me
C
Me
C
Me
C
Me
Me
C
C
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
H
Me
Ph
iPr
t
iPr
Bu
H
Me
Ph
iPr
t
Bu
H
Me
Ph
t
B
u
MeCTp3-H (3a)
MeCTp3-Me (3d)
MeCTp3-Ph (3g)
MeCTp3-iPr (3j)
MeCTp3-tBu (3k)
32%
39%
62%
11%
5%
nBu
nBu
nBu
C
C
C
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
H
Me
Ph
H
Me
Ph
H
Me
Ph
nBuCTp3-H (3b)
nBuCTp3-Me (3e)
nBuCTp3-Ph (3h)
66%
17%
35%
Bn
C
SiMe3
C
Bn
C
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
H
Me
Ph
H
Me
Ph
H
Me
Ph
BnCTp3-Ph (3i)
BnCTp3-H (3c)
Me3SiCTp3-Me (3f)
40%
80%
35%
Figure 1. Overview of RCTp ligands with overall yields, starting from 1-H-pyrazole (3a-c), 3-Me-pyrazole (3d-f), acetophenone (3g-i)[26b], 3-methylbutan-2-one
(3j)[23], pinacolone (3k)[26a]. Representative solid-state structure of 3e. X-ray structure analyses were performed on tris(pyrazolyl)alkane ligands 3d-3k (see
Supporting Information).
The metal centers in dimagnesium complex 5 are bridged by
three pyrazolyl ligands in 2-1:1 fashion. Mg2 adopts an
octahedral geometry by accommodating additionally one thf and
one dme molecule, with the [Mg(thf)(dme)] moiety replacing the
former CBn backbone moiety. Atom Mg1 features one terminal
methyl group, suggesting the initial coordination of the intact
ligand to dimethylmagnesium. The Mg–C bond length of
2.131(2) Å is similar to four-coordinate 4a (vide infra) and is
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significantly shorter in comparison to the metrical parameter in
4b (CN 5, vide infra). Moreover, complex 5 shows distinctly
different Mg–N bond distances of av. 2.087 Å (Mg1–N =
diffraction analysis were grown from saturated solutions of
[MgMe2]n (4) in 1,4-dioxane. The perspective view of complex 1a
(orthorhombic, Cmcm) is depicted in Figure 3. For comparison,
the Mg–C bond length of 2.135(1) Å is similar to the metrical
parameters in isostructural dialkylmagnesium 1,4-dioxane
polymers of the general type [MgR2(dioxane)]n (Mg–C [Å]: R =
Et, 2.142(2); R = iPr, 2.157(2); R = Np, 2.133(2); R = Ph,
2.076(2)-2.106(2) Å) and 2.153 Å (Mg2–N
=
2.137(2)-
2.175(2) Å). For comparison, the Mg–N(2-pz) bond lengths of
av. 2.024 Å in four-coordinate Mg2(pz-tBu2-3,5)4 are slightly
shorter.[30] The isolation of 5 indicates that the C–N bonds of the
tris(pyrazolyl)methane ligands are still susceptible to attack by
strong nucleophiles (Scheme 2, transition state): The feasibility
of a reaction intermediate as shown in Scheme 2 is further
corroborated by the existence of magnesates, such as [Mg2Me5]–
or [Mg3Me8]2–.[31]
2.135(2); R = Bn, 2.156(2) / 2.155(2))[33]
.
D
Et2O, do, rt, 1 d
[MeMgX]
[MgMe2(do)]
[MgMe2]n
– [MgX2(do)]
4a (X = Br; do = 1,4-dioxane)
4b (X = Cl; do = diglyme)
4
n-hexane, 2 AlMe3
rt, 16 h
[MgMe2]n
Mg(AlMe4)2
4
6
Scheme 3. Synthesis of Mg(AlMe4)2 (6) from Grignard Reagents.
Figure 2. Solid-state structure of complex [(dme)(thf)Mg(pz)3MgMe] (5).
Hydrogen atoms have been omitted for clarity. Atomic displacement ellipsoids
are set at the 50% probability level.
3c
+
[MgMe2]n (4)
1:1 thf, dme,
–40 °C, 30 s
O
O
Bn
C
O
Mg
N
N
N
N
N
N
N
N
N
N
N
N
Mg
Mg
Me
Me
Me
Me
5
Mg
Me
Figure 3. Solid-state structure of polymeric 4a (top) and monomeric 4b
(bottom). Hydrogen atoms have been omitted for clarity. Atomic displacement
ellipsoids are set at the 50% probability level.
Scheme 2. Proposed Scenario for the Formation of [(dme)(thf)Mg(pz)3MgMe]
(5).
The reaction of [MeMgCl(thf)2] with tridentate donor ligand bis(2-
methoxyethyl)ether (diglyme) afforded magnesium complex
[MgMe2(diglyme)] (4b). Its solid-state structure revealed a 5-
coordinate magnesium center surrounded by three diglyme
oxygen atoms und two methyl carbon atoms. As expected, the
Mg–C(CH3) bond lengths of 2.193(2) and 2.197(2) Å are slightly
elongated in comparison to the ones found in polymeric
For the synthesis of Mg(AlMe4)2,[19] we attempted to optimize the
reaction conditions starting from two different Grignard reagents,
namely [MeMgBr] and [MeMgCl] (Scheme 3). Shifting the
[MeMgBr]-Schlenk equilibrium by the addition of 1,4-dioxane,
polymeric [MgMe2(dioxane)]n (4a) was isolated upon separation
of solid [MgBr2(dioxane)].[32] Single crystals of 4a suitable for
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[MgMe2(1,4-dioxane)]n with 4-coordinate magnesium (vide
supra). The isolation and purification of 4 via thermal treatment
of 4b in vacuum is hampered by the high boiling point of diglyme
(186 °C). Decomposition of 4b started at temperatures >100 °C
and despite several drying cycles, remaining diglyme was
indicated by 1H NMR spectroscopy. The absence of diglyme in 4
is a crucial factor for synthesizing Mg(AlMe4)2 (6) as for
comparison undesired separated ion pair [Mg(thf)6][AlMe4]2 was
shown to form by treating 6 with thf.[18a] Finally, the purest
samples of donor-free [MgMe2]n (4) were obtained by de-
solvating 1,4-dioxane adduct 4a under high vacuum (10-4 mbar)
at 130 °C,[34] and used for the synthesis of Mg(AlMe4)2 (6) by
standard procedures (Scheme 3).[35]
The reactions of
methane ligands 3c and 3i, prone to backbone cleavage, led to
multiple decomposition products.
6
with benzyl-substituted tris(pyrazolyl)
Reactivity of Mg(AlMe4)2 towards RCTp3-R’ (Scheme 4). The
main emphasis of this study was to examine the steric and
electronic implications of the tris(pyrazolyl)alkanes for the
coordination to magnesium and the stabilization of reactive alkyl
magnesium complexes by steric protection. In order to avoid
extensive backbone functionalization and nucleation to highly
aggregated Mg/Al complexes it is essential that the RCTp ligand
stays neutral. As expected, only RCTp ligands with a resilient C–
R backbone are suitable for accommodating 6. For example, the
reaction of methylaluminate 6 with HCTp3-Ph (2-Ph) led to the
Figure 4. Solid-state structure of 7. Hydrogen atoms and the phenyl groups of
the second lower Me3AlCTp3-Ph ligand are omitted for clarity. Atomic
displacement ellipsoids are set at the 50% probability level.
isolation of magnesium bis(methanide) complex
7
via
displacement of the methine hydrogen by AlMe3 under
elimination of methane. In 7, the magnesium metal center is
encapsulated by two anionic Me3AlCTp3-Ph scaffolds to yield
(Me3AlCTp3-Ph)2Mg as a neutral “metal-in-a-box” complex (Figure
4, tetragonal, P42/n). The same structural motif was previously
observed for (Et3AlCTp3-H)2Mg (V, Chart 1). The 1H NMR
spectrum of 7 shows two doublets at 8.90 and 5.86 ppm for the
4- and 5-pyrazolic protons and one singlet at 0.26 ppm for the
AlMe3 groups.
A similar product was isolated from the equimolar reaction of 3
with Me3SiCTp3-Me (3f) under elimination of SiMe4. The initial
suspension cleared up and afforded neutral complex
(Me3AlCTp3-Me)Mg(AlMe4) (8, Figure 5, monoclinic, P21/c). In
accordance with 7 the 1H NMR spectrum of 8 in [D6]benzene
revealed two doublets for the pyrazolic protons at 8.49 and 5.31
ppm, indicating equivalent pyrazolyl anchors. One sharp singlet
at 0.02 ppm for AlMe3, 1-coordinated by the methanide carbon,
and one singlet at –0.19 ppm for the [AlMe4] moiety was
observed. In the solid state, the magnesium center adopts a
distorted octahedral geometry, with the anionic methanide ligand
coordinating in a tripodal 3(N,N’,N’’) fashion (av. Mg−N,
2.125 Å). The Mg…Al distance of 2.595(1) Å and Mg–C bond
lengths (2.501(2)-2.680(2) Å) of the 3-coordinated [AlMe4] unit
are in average shorter than the metrical parameters in
(TpMe,Me)Mg(AlMe4) (Mg–C, 2.434(2)-2.853(2) Å, Mg…Al,
2.676(1) Å, Mg–N, 2.079(2)-2.115(2) Å).[4] The Al2–C01 bond
lengths are 2.203(1) Å for 7 and 2.189(1) Å for 8, comparable to
the Al–C bond distance of 2.178(2) Å in (Et3AlCTp3-H)2Mg.[14c]
Figure 5. Solid-state structure of 8. Hydrogen atoms are omitted for clarity.
Atomic displacement ellipsoids are set at the 50% probability level.
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Scheme 4. Synthesis of Tris(pyrazolyl)alkane and -Methanide Complexes 7-12.
Toluene/n-hexane solutions of ligands 3 (3a-b, 3d-e) and 6 in 2:1
ratios caused instant precipitation of white powders in
quantitative yields. When the powders were dissolved in thf fast
decomposition was observed. However, rapid handling and
immediate removal of thf by evaporation gave clear colorless
single crystals. X-Ray crystallographic analyses indicated the
formation of separated ion pairs [(RCTp)2Mg][AlMe4]2 (9a-d,
Figure 6). The molecular structures of 9a-d revealed six-
coordinate magnesium centers with two tris(pyrazolyl)alkane
ligands in 3(N,N’,N’’) modus, adopting a distorted octahedral
geometry. The Mg–N bond lengths lie in the expected range of
similar magnesium tris(pyrazolyl)alkane compounds (Table
1).[3b,10,14b,14c,15,36]
Complexes 9 are insoluble in non-coordinating solvents, but
dissolve readily in thf. The 3(N,N’,N’’) coordination of the ligands
observed in the solid-state of the separated ion pairs 9 is labile
since two or three sets of signals for backbone and pyrazolyl
1
moieties are indicated by H and 13C{1H} NMR spectroscopy in
thf-d8. The resonances can be assigned to ion pairs 9, free ligand
and
mono
tris(pyrazolyl)alkane
complex
[(RCTp)MgMe(thf)2][AlMe4] (cf., supporting information).
A
coupling constant of 1JAl–C = 70.2 Hz was observed in the 13C{1H}
NMR spectrum of 9b (9d, 72.5 Hz), which is attributed to the
anionic [AlMe4]– fragment, in accord with the spectroscopic data
of similar complexes.[37]
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Figure 6. Solid-state structure of separated ion pair [(nBuCTp3-Me)2Mg][AlMe4]2
(9d). Complexes 9a, 9b, and 9c are isostructural and shown in the Supporting
Information. One [AlMe4]– anion and hydrogen atoms are omitted for clarity.
Atomic displacement ellipsoids are set at the 50% probability level.
Treatment of 6 with superbulky MeCTp3-Ph (3g) or MeCTp3-tBu
(3k, “tetrahedral enforcer”), gave separated ion pairs
[(MeCTp3-Ph)MgMe][AlMe4] (10a, 64%, = 283), and
[(MeCTp3-tBu)MgMe][Al2Me7] (10b, 91%, = 275) with one
ligand coordinating to the [MgMe]+ cation. By providing the
substituents in the 3-position of the pyrazoles with aryl and alkyl
groups the solubility was significantly enhanced. Single crystals
of 10 were grown from either hot toluene solutions by slow
cooling to ambient temperature or toluene/1,2-difluorobenzene
mixtures. X-ray diffraction studies confirmed the cationization of
isostructural complexes 10a (Figure 7, top) and 10b (Figure 7,
bottom), while the anionic units are serendipitously [AlMe4] or
[Al2Me7]. The Mg–C(methyl) bond lengths of 2.091(2) Å (10a)
and 2.115(2) Å (10b) are relatively short and similar to those in
[(TpMe,Me)MgMe] (2.097(4) Å) or [(TptBu,Me)MgMe] (2.119(3)
Å).[36d] For further comparison, the Mg–C(CH3) bond distances in
Figure
7.
Solid-state
structures
of
separated
ion
pairs
[(MeCTp3-Ph)MgMe][AlMe4] (10a, top) and [(MeCTp3-tBu)2Mg][Al2Me7] (10b,
bottom). Hydrogen atoms are omitted for clarity. Atomic displacement
ellipsoids are set at the 50% probability level.
Notably, the reaction of 6 with nBuCTp3-Ph (3h) led to a very rare
2(N’,N’’) coordination of the ligand. Complex 11 was obtained
as colorless crystals from saturated toluene or benzene solutions
at ambient temperature. The structural elucidation by X-ray
diffraction studies revealed the formation of a monocationic
dimagnesium species [{(nBuCTp3-Ph)Mg(AlMe4)}2(-CH3)] with
magnesium centers bridged by one methyl group and [AlMe4] as
̅
a counteranion (triclinic P1). Obviously, the substituent (nBu
versus Me) in the backbone carbon has a major impact on the
structure in the solid state (monomer 10a versus dimagnesium
species 11). Each magnesium center in 11 is 4-coordinate by
two pyrazolyl nitrogen atoms, a -coordinated [(-CH3)Al(CH3)4]
fragment and the bridging methyl group. The Mg–C bond lengths
of 2.250(2) and 2.209(2) Å in dimagnesium moiety Mg(-CH3)Mg
are considerably shorter compared to the bridging methyl groups
of the 1-coordinated unit in neutral Mg(-CH3)Al(CH3)3 (Mg–C,
2.322(2), 2.337(2) Å). For further comparison, the Mg–C bond
lengths of the cationic unit Mg(-CH3)Mg in 11 are considerably
shorter than in cationic [Mg2(-CH3)3(tacn)2]+ (av. Mg–C,
2.355 Å, tacn = N,N’,N’’-trimethyl-1,4,7-triazacyclononane) or
magnesate [Mg3(-CH3)4(CH3)4]2– (av. Mg–C, 2.295 Å)[31b], but
compare well to neutral [Mg(-CH3)(CH3)(thf)]2 (av. Mg–C, 2.263
Å).[18a]
four-coordinate
magnesium
complexes
[(SiMe3ArN)MgMe(thf)2]38 are in the range of 2.129(4) to
2.173(4) Å.
The 1H NMR spectrum of 10a in [D6]benzene/1,2-
difluorobenzene (1,2-DFB) displays doublets at 7.94 and 6.12
ppm for the 4- and 5-pyrazolic protons indicating free rotation of
the phenyl substituents in solution. However, the broad
resonances of the metal-bonded methyl groups at –0.03 ppm
(Al–CH3, 12H) and –1.16 ppm (Mg−CH3, 3H) give evidence for
strong interactions and redistributions in solution (Figure S28).
The 1H NMR spectrum of the tert-butyl derivative 10b in
[D6]benzene-d6/1,2-difluorobenzene at ambient temperature
revealed only one set of signals for the tris(pyrazolyl)methane
ligand, indicating the absence of a rotational barrier in solution,
and sharp singlets for the Mg−CH3 and [Al2Me7] moieties at
−0.35 and −0.22 ppm (Figure S30).
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10.1002/chem.201803067
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between the iPr group counteract the formation of a “metal-in-a-
box” complex.
Figure 9. Solid-state structure of compound [(MeCTp3-iPr)Mg(AlMe4)2] (12).
Hydrogen atoms are omitted for clarity. Atomic displacement ellipsoids are set
at the 50% probability level.
Figure 8. Solid-state structure of dimagnesium species 11. Lattice solvent and
hydrogen atoms are omitted for clarity. Atomic displacement ellipsoids are set
at the 50% probability level.
The 1H NMR spectrum of 11 in [D6]benzene/1,2-DFB at ambient
temperature shows a broad singlet at −0.57 ppm for the methyl
groups and one set of broad signals for the
tris(pyrazpolyl)pentane ligand, indicating highly fluxional
processes in solution. This originates from rapid methyl group
exchange and a 2→3 coordination shift of nBuCTp3-Ph (3h).
Further investigations by VT NMR spectroscopy were hampered
by the limited solubility of 11 at lower temperatures. Compound
11 is stable against thermal treatment at 80 °C under inert
atmospheres. Upon heating to 100 °C resulted generally in the
decomposition of the tris(pyrazolyl)alkane ligands 3.
1
The ambient-temperature H NMR spectrum of 12 shows two
doublets in the aromatic region for the pyrazolyl hydrogen atoms
at 7.77 and 5.78 ppm. A very sharp singlet appeared at –0.14
ppm with an integral ratio matching eight methyl groups,
indicating rapid exchange of bridging and terminal methyl
groups. VT 1H NMR spectroscopic studies of 12 in [D8]toluene
revealed that the singlet at –0.14 ppm splits into two dominant
and four low-intensity signals at –50 °C (Figures S36 and S37).
Moreover, the backbone methyl group appeared as two signals
at –40 °C (2:1 ratio). This manifests a very complicated fluxional
behavior in solution which might involve species similar to
dimagnesium complex 11 and dissociated AlMe3. However, at
elevated temperature only one sharp singlet –0.39 ppm could be
observed for all methyl ligands, with the dynamic behavior of 12
being fully reversible.
Finally, the tris(pyrazolyl)ethane ligand MeCTp3-iPr (3j) seems to
provide an ideal cone angle (248.76) for Mg(AlMe4)2. The
envisaged reaction of 3j and 6 in n-hexane/toluene (1:1) afforded
complex [MeCTp3-iPrMg{(2-Me)AlMe3}{(2-Me)2AlMe2}] (12).
Single crystals were grown from 1,2-difluorobenzene and X-ray
crystallographic studies revealed the formation of the sought-
after neutral “(RCTp3-R’)MgR2” motif. The six-coordinate
magnesium center in 12 adopts an octahedral geometry with two
methyl carbon atoms and two pyrazolyl nitrogen atoms of the
3(N,N’,N’’) coordinated CTp ligand in the equatorial plane and
each one nitrogen and carbon atom in the axial positions. As
expected, the Mg–C(2-CH3) bond lengths of 2.493(3) and
2.520(5) Å are markedly elongated compared to the Mg–C bond
lengths determined by Stucky and coworkers in the donor ligand-
free Mg(AlMe4)2 (2.194(9)-2.222(9) Å).[29] The Mg–C15–Al2
bond angle of 175.6(2)° probably indicates the pending formation
of a separated ion pair with [AlMe4] as the anionic fragment.
Intriguingly, subtle changes of the steric bulk in tripodal
tris(pyrazolyl)ethane ligands 3j and 3k (iPr versus tBu) entail the
formation of ion pair [(MeCTp3-tBu)MgMe][Al2Me7] (10b) or neutral
Cone Angle Calculation and Examination. Spurred by the
distinct coordination behavior of the tris(pyrazolyl)alkane ligands
RCTp3-R’ and the diverse reactivity patterns with Mg(AlMe4)2 we
became interested in evaluating the steric effect of the ligands in
more detail (Table 1). Although predominantly developed for
tertiary phosphines the steric effect of any multipodal ligand can
be mathematically described.[24] In previous work, the cone
angles were determined, inter alia, by the ligand hydrogen
atoms, which are closest to the metal center.[26a,39] In this work,
we calculated the cone angles with respect to the shortest
magnesium ligand side arm hydrogen distances (), taking into
account the van der Waals radii (vdw) or the maximum and
“exact” cone angle determined by the Mathematica package
(°).[40] The exact procedure is given in the supporting
information.[24] Strictly speaking, comparison among the ligands
is only feasible, if (a) the metal centers have the same
coordination number (CN) and (b) in case of the same overall
metal-ligand charge (meaning either dicationic, monocationic or
neutral complexes).
[(MeCTp3-iPr)Mg{(2-Me)AlMe3}{(2-Me)2AlMe2}]
(12),
respectively (see Table 1). The tris(pyrazolyl)ethane ligand
MeCTp3-iPr (3j) is less encapsulating, but repulsive interactions
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Table 1. Overview of Selected Bond Lengths and Cone Angles vdw and  of Magnesium Tris(pyrazolyl)alkane and -Methanide Complexes as well as
Hydrotris(pyrazoyl)borate Derivatives (see Supporting Information for calculations).a
Mg–C01 /
Mg–B1
CN
Mg–N2
Mg–N4
Mg–N6
avg. Mg–N

vdw
°
ref.
[(Me3AlCTp3-Ph)2Mg] (7)
6
5
6
6
6
6
4
2.256(1)
2.116(1)
2.113(1)
2.127(1)
2.164(1)
2.150(1)
2.138(2)
2.190(1)
2.123(1)
2.141(1)
2.151(1)
2.141(1)
2.196(1)
2.142(2)
2.188(1)
2.138(2)
2.138(1)
2.131(1)
2.164(1)
2.160(1)
2.128(2)
2.211
2.126
2.131
2.136
2.156
2.169
2.136
3.188(1)
3.180(1)
3.222(1)
3.231(2)
3.216(1)
3.230(2)
3.167(3)
218.04
208.41
165.42
165.73
207.58
207.45
217.17
263.06
252.50
206.20
206.66
252.40
252.00
265.78
272.87
252.46
206.22
206.70
252.42
252.01
282.84
b
b
b
b
b
b
b
b
[(Me3AlCTp3-Me)Mg(AlMe4)] (8)
[(MeCTp3-H)2Mg][AlMe4]2 (9a)
[(nBuCTp3-H)2Mg][AlMe4]2 (9b)
[(MeCTp3-Me)2Mg][AlMe4]2 (9c)
[(nBuCTp3-Me)2Mg][AlMe4]2 (9d)
[(MeCTp3-Ph)MgMe][AlMe4] (10a)
[(MeCTp3-tBu)MgMe][Al2Me7]
(10b)
4
2.125(1)
2.120(1)
N2 = N6
2.123
3.1244(2)
226.23
276.35
275.00
i
b
[(MeCTp3- Pr)Mg(AlMe4)2] (12)
6
2.211(3)
2.200(4)
N2 = N6
2.207
3.276(5)
204.31
248.78
248.76
b
[(dme)(thf)Mg(pz)3MgMe] (5)
4
2.078(2)
2.106(2)
2.076(2)
2.087
–
191.09
232.82
232.75
2.172(3)
2.173(3)
2.157(3)
2.162(3)
2.185(3)
2.160(3)
3.144
3.162
205.43
205.85
249.71
250.54
249.74
250.56
36a
[(HCTpMe,Me)2Mg][OTf]2
6
2.170
[(CTp)2Mg]
6
6
6
2.145(3)
2.189(1)
2.185(2)
2.195(2)
N2 = N4
N2 = N4
N4 = N6
N2 = N6
N2 = N6
2.178
2.189
2.185
3.249
3.198
3.215
162.31
204.58
205.08
201.78
248.43
249.14
201.89
248.45
249.14
41
36a
15
[(CTpMe,Me)2Mg]
[(CTpMe,Me,Me)2Mg]
2.186(3)
2.197(3)
2.1609(1)
2.177(2)
N4 = N6
N4 = N6
2.169
2.184
3.267
3.196
161.02
205.15
200.69
248.33
200.68
248.32
14b
[(CTp)Mg(CTpMe,Me)]
6
[(CTpAd,Me)MgMe]
[(Et3AlCTp) 2Mg]
4
6
4
4
4
4
5
6
2.130(1)
2.130(2)
2.084(2)
2.130(10)
2.129(1)
2.103(1)
2.079(2)
2.115(2)
N2 = N4
2.150(2)
2.084(4)
2.137(7)
N2 = N4
2.148(1)
2.183(2)
2.112(2)
N2 = N6
2.154(2)
N2 = N6
N4 = N6
N2 = N6
2.134(1)
2.089(2)
2.115(2)
2.130
2.144
2.084
2.195
2.129
2.128
2.117
2.114
3.046
3.264
3.071
3.068
3.037
3.132
3.037
3.073
233.58
164.87
216.79
217.89
225.48
230.79
208.73
208.38
283.51
205.45
264.46
265.26
273.01
279.33
249.96
248.85
301.47
205.46
262.21
274.25
273.47
279.40
252.01
248.82
44
41
4
[(TpMe,Me)MgMe]
[(Tp3-tBu)MgMe]
42
4
[(TptBu,Me)MgMe]
[(PhTp3-tBu)MgMe]
[(TpMe,Me)Mg-AlMe4)]
[(TpMe,Me)Mg-AlMe4)]
43
4
4
a  directly determined from atomic positions; vdw = consideration of Van der Waals radiimathematical exact. b this work.
A
general overview of the determined cone angles is
CN = 6, a series of Tp/CTp-analogues were considered showing
clear alignment/compliance: 9a
(° = 206.22°)/9b
(° = 206.70)/[(CTp)2Mg] (° = 201.89)41/[(Et3AlCTp)2Mg]
as as 9c
(° = 252.42)/9d
summarized in Table 1. Cone angle calculations of [(Me3AlCTp3-
Me)Mg(AlMe4)] (8) (° = 252.46°, CN = 5) compare well with
earlier reported [(TpMe,Me)Mg(AlMe4)] (° = 252.01, CN = 5;
° = 248.82, CN = 6). It is noteworthy that the exact cone angle
in the latter is significantly affected already by variation of the
coordination number 5→6. For metal-in-a-box complexes with
a
(° = 205.46),[41]
well
(° = 252.01)/[(HCTpMe,Me)2Mg][OTf]2
(° = 249.74/250.56)[36a]/[(CTpMe,Me)2Mg]
(° = 248.45)[36a] /[(CTpMe,Me,Me)2Mg] (° = 249.14).[15] For 3-Ph
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Combining Mg(AlMe4)2 with sterically less demanding RCTp3-R
’
substituted ligands it remains challenging to predict a distinct
range due to conformational changes of the phenyl rings towards
the metal center (7 (° = 272.87, CN = 6)/10a (° = 282.84, CN
= 4)). Magnesium complexes with a terminal Mg-Me moiety
embedded in tert-butyl-substituted polypyrazolyl ligands display
an exclusive tetrahedral coordination geometry and hence very
ligands afforded homoleptic dicationic complexes [(RCTp3-R’)2
Mg] with [AlMe4] or [Al2Me7] counterions, the reactivity and
structural elucidation of which being reminiscent of solvent-
separated ion pairs involving [Mg(do)6]2+ cations (e.g., do = thf).
Remarkably, the sterically demanding ligands MeCTp3-Ph and
MeCTp3-tBu stabilize the monocationic fragment [MeMg]+ bearing
relevance to postmetallocene-based olefin polymerization.
Providing the CN3 backbone carbon atom with an nBu
substituent, that is changing the solubility of the ligand, resulted
in the unusual structure of a methyl-bridged dimagnesium
species with a rare 2-coordinated nBuCTp3-Ph ligand. iPropyl-
substituted ligand MeCTp3-iPr seems to comply perfectly with any
similar cone angles 10b (° = 275.00)
(° = 274.25)[42]/[(TptBu,Me)MgMe]
/
[(Tp3-tBu)MgMe]
(° = 273.47)/[(PhTp3-tBu)MgMe] ( = 279.40).[43] The most
sterically demanding ligand known to date HCTpAd,Me adopts an
extreme cone angle ° = 301.47 in [(CTpAd,Me)MgMe].[44] An
important finding is that the ligand cone angle ° = 248.76 for
[(MeCTp3-iPr)Mg{(2-Me)AlMe3}{(2-Me)2AlMe2}] (12, illustrated
in Figure 10) is slightly decreased in comparison to supposedly
sterically less demanding systems in [(RCTp3-Me)2Mg][AlMe4]2
(9c-d). However, the intramolecular repulsion of the iPr groups
would not allow the formation of a bis-CTp metal-in-a-box
complex. Moreover, effects such as coordinating ligands (e.g.,
donor solvents) and coordination mode of the CTp ligand (3/2)
must also be taken into account.
size/sterics
criteria,
giving
access
to
an
intact
bis(tetramethyl)aluminate complex, (MeCTp3-iPr)2Mg(AlMe4)2,
and efficiently counteracting “metal-in-a-box” formation. As
detected previously in rare-earth metal chemistry, the [AlMe4]
moiety extends to the entire range of coordination modes
comprising 1, 2, and 3 as well as 0 in separated ion pairs.
Why Mg(AlMe4)2? Reactions conducted with [MgMe2]n are
particularly difficult to control resulting in complex mixtures and
rapid decomposition of the ligands RCTp3-R’. Hence, the
organoaluminum moieties seem to have a stabilizing effect
facilitating controlled reactions and the isolation of complexes
with intact tris(pyrazolyl)alkane or methanide ligands.
Finally, cone angles have been calculated for the complexes
under study and put into perspective with related ones reported
in literature. The current work features the determination of cone
angles of such potentially tripodal ligands in particular on the
premise that it might have a major impact on our understanding
of the coordination chemistry and kinetics involved as well as
any emerging catalytic properties of the complexes accessed.
Figure 10. Exact ligand cone angle calculation for MeCTp3-iPr in 12. The top of
the cone represents the center of the metal (see ESI).
Experimental
General Considerations. All manipulations were performed
with rigorous exclusion of air and water in an argon-filled
glovebox (MBraun MB150B-G; <1 ppm O2, <1 ppm H2O) or
according to standard Schlenk techniques. Solvents were
purified by using Grubbs columns (MBraun SPS-800, solvent
purification system) and stored in a glovebox. Acetophenone
(>98%), 3-methylbutanone (99%), pinacolone (98%), n-
butyliodide (99%), chlorotrimethylsilane (99%) benzylbromide
Conclusions
Following Elguero’s phase transfer catalysis protocol and
subsequent electrophilic backbone substitution, the library of
tris(pyrazolyl)alkane ligands RCTp3-R’ could be substantially
expanded. Depending on the R/R’ substitution pattern such
potentially tripodal scaffolds exhibit distinct reactivity toward
thermally stable homoleptic magnesium tetramethylaluminate
Mg(AlMe4)2. Importantly, the substitution at the CN3 backbone
carbon atom is a crucial factor as the C−H, C−SiMe3, and C−Bn
moieties are prone to nucleophilic attack. This is in accord with
previous studies on the reactivity of tris(pyrazolyl)alkane ligands
with alkylating agents, resulting in deprotonation and methanide
formation. We found that introducing alkyl substituents at the
CN3 backbone carbon atom leads to an overall markedly
enhanced stabilization of the RCTp3-R’ ligands, facilitating the
synthesis of a variety of magnesium methyl complexes.
(98%),
diethyleneglycolydimethyl
tetra-n-butylammonium
ether
bromide
(diglyme,
(98%),
>99%),
methylmagnesium bromide (3.0 M in Et2O), methylmagnesium
chloride (3.0 M in thf), hydrazine hydrate (50-60%) were
purchased from Sigma Aldrich and used as received. 1-H-
Pyrazole (98%), 3-methyl-1H-pyrazole (99%), iodomethane,
methyl tert-butyl ether (mtbe) (99%) were purchased from Acros
Organics and used as received. Li[N(SiMe3)2] was synthesized
according to standard procedures by treatment of the proligand
with nBuLi. MeCTp, BnCTp,[27] MeCTp3-Me [45] MeCTp3-Ph [27]
,
,
BnCTp3-Ph [27]
,
MeCTp3-tBu [27]
,
[MgMe2]n (4)[35] Mg(AlMe4)2 (6)[29]
10
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3
were synthesized according to literature procedures. Solvent-
free [MgMe2]n (4) was obtained by de-solvating 1,4-dioxane
adduct 4a under high vacuum (10-4 mbar) at 130 °C (4) for 24 h.
1,2 difluorobenzene (1,2-DFB) was purchased from Sigma
Aldrich, dried over CaH2, distilled and degassed prior to use.
[D6]benzene, [D8]toluene and [D8]thf were purchased from
Eurisotop, dried over NaK alloy for two days and filtered prior to
use. 1H NMR and 13C{1H} NMR spectra were recorded on a
Bruker AVII+400 (1H: 400.13 MHz; 13C 125.76 MHz)
spectrometer at 299 K. 1H NMR spectra of 12 were recorded by
using a J. Young valve NMR tube at variable temperatures on a
Bruker AVII+500 instrument (1H: 500.13 MHz; 13C: 125.76 MHz).
Infrared spectra were recorded on a Thermo Fisher Scientific
NICOLET 6700 FTIR spectrometer using a DRIFT chamber with
dry KBr/sample mixtures and KBr windows. DRIFT data were
converted using the Kubelka-Munk refinement. CHN elemental
analyses were performed on an Elementar vario MICRO cube.
EI mass spectra were measured using a Thermo Finnigan TSQ
70.
CH3CH2CH2), 0.90 (t, 3H, JHH = 7.3 Hz, CH3CH2) ppm.
13C{1H} NMR (100.6 MHz, CDCl3, 26 °C): δ = 150.5 (3-C(pz)),
130.7 (5-C(pz)), 106.2 (4-C(pz)), 91.6 (C(pz)3), 40.2
(CH2C(pz)3), 26.1 (CH2CH2C(pz)3), 22.9 (CH3CH2), 14.1
(CH3CH2), 14.0 ((pz)-CH3) ppm. DRIFT: ṽmax = 3138 (vw), 3114
(w), 2987 (w), 2952 (s), 2928 (m), 2868 (m), 2965 (m), 1721 (vw),
1711 (vw), 1621 (vw), 1530 (vs), 1460 (s), 1453 (s), 1391 (s),
1372 (m), 1354 (s), 1341 (m), 1209 (vs), 1198 (vs), 1132 (vw),
1118 (vw), 1062 (s), 963 (w), 934 (m), 907 (m), 844 (vs), 765
(vs), 723 (vw), 680 (m), 650 (w), 618 (vw) cm–1. C17H24N6 (312.4
g·mol–1) calcd. C 65.36, H 7.74, N 26.90; found C 65.43, H 7.96,
N 27.01.
Me3SiCTp3-Me (3f). Following the procedure described above for
3b, HCTp3-Me (5.00 g, 19.5 mmol), nBuLi (8.59 mL, 21.5 mmol,
2.5 M in n-hexane) and Me3SiCl (4.1 mL, 32.2 mmol) yielded a
yellow solid as crude product. Further purification was achieved
by recrystallization from mtbe and gave 3f as colorless crystals
(4.05 g, 12.3 mmol, 63%) suitable for X-ray diffraction analysis.
1H NMR (400.1 MHz, CDCl3, 26 °C): δ = 6.57 (d, 3H, 3JHH = 2.4
nBuCTp (3b). HCTp3-H (3.00 g, 14.9 mmol) was dissolved in 100
mL of thf and cooled to –78 °C. Li[N(SiMe3)2] (3.05 g, 18.2 mmol)
dissolved in 50 mL of thf was added via syringe. The chilled
reaction mixture was stirred for another 30 min at ambient
temperature and cooled again to –78°C. After dropwise addition
of nBuI (4.13 g, 22.4 mmol) the reaction was stirred overnight at
ambient temperature. Brine solution (50 mL) was added and the
aqueous phase was extracted with Et2O (3x50 mL). The
combined organic layers were dried over Na2SO4 and filtered.
Removing the solvent in vacuo gave 3b (2.35 g, 8.68 mmol,
3
Hz, 5-H(pz)), 6.03 (d, 3H, JHH = 2.5 Hz, 4-H(pz)), 2.28 (s, 9H,
(pz)-CH3), 0.28 (s, 9H, Si(CH3)3) ppm. 13C{1H} NMR (100.6 MHz,
CDCl3, 26 °C): δ = 150.1 (3-C(pz)), 129.4 (5-C(pz)), 105.8 (4-
C(pz)), 89.4 (C(pz)3), 14.0 ((pz)-CH3), –0.59 (Si(CH3)3) ppm.
DRIFT: ṽmax = 3134 (m), 3119 (m), 2982 (m), 2955 (m), 2928 (m),
2899 (m), 1608 (w), 1525 (vs), 1449 (s), 1391 (s), 1356 (vs),
1243 (vs), 1203 (vs), 1058 (vs), 997 (m), 936 (w), 921 (w), 837
(vs), 788 (vs), 758 (vs), 700 (m), 675 (m), 660 (m), 632.78 (s),
619 (w) cm–1. C16H24N6Si (328.5 g·mol–1) calcd. C 58.50, H
7.36, N 25.58; found C 58.11, H 6.80, N 25.83.
1
62%) as yellow oil. H NMR (400.1 MHz, [D8]toluene, 26 °C): δ
3
= 7.43 (dd, 3H, JHH = 1.7 Hz, 4JHH = 0.6 Hz, 3H, 3-H(pz)), 6.73
3
4
(dd, 3H, JHH = 2.6 Hz, JHH = 0.7 Hz, 5-H(pz)), 5.90 (dd, 3H,
3JHH= 2.6 Hz, 4JHH = 1.8 Hz, 4-H (pz)), 3.43 (m, 2H, CH2C(pz)3),
nBuCTp3-Ph (3h). Following the procedure described for 3b,
HCTp3-Ph (3.30 g, 7.46 mmol), Li[N(SiMe3)2] (1.62 g, 9.69 mmol)
and n-BuI (1.50 mL, 11.2 mmol) yielded a yellow solid as crude
product. Further purification was achieved by recrystallization
from Et2O yielding 3h as colorless crystals (1.95 g, 3.91 mmol,
52%) suitable for X-ray structure analysis. 1H NMR (400.1 MHz,
CDCl3, 26 °C): δ = 7.86 (m, 6H, o-H(Ph)), 7.38 (m, 9H, m-H(Ph),
3
1.75 (m, 2H, CH2CH2C(pz)3), 1.27 (sext, 2H, JHH = 7.3 Hz,
CH3CH2CH2), 0.80 (t, 3H, JHH = 7.8 Hz, CH3CH2) ppm.
3
13C{1H} NMR (100.6 MHz, [D8]toluene, 26 °C): δ = 141.0 (3-
C(pz)), 129.9 (5-C(pz)), 106.2 (4-C(pz)), 92.8 (C(pz)3), 40.8
(CH2C(pz)3), 26.5 (CH2CH2C(pz)3), 23.1 (CH3CH2), 14.1
(CH3CH2) ppm. IR[Nujol]: ṽmax = 3107 (w), 1765 (vw), 1587 (w),
1516 (m), 1421 (m), 1328 (m), 1257 (m), 1238 (m), 1198 (m),
942 (m), 916 (m), 880 (w), 846 (m), 748 (s), 676 (w), 637 (w),
612 (w) cm–1. MS (EI): 270.1, 214.1, 203.2, 173.1, 160.1, 147.1,
135.1, 119.1, 106.1, 93.1, 81.1, 69.1.
p-H(Ph)), 7.07 (d, 3H, JHH = 2.7 Hz, 5-H(pz)), 6.62 (d, 3H, 3JHH
3
= 2.7 Hz, 4-H(pz)), 3.49 (m, 2H, CH2C(pz)3), 1.83 (m, 2H,
CH2CH2C(pz)3), 1.50 (sext, 2H, 3JHH = 7.6 Hz, CH3CH2CH2), 1.00
(t, 3H, JHH = 7.4 Hz, CH3CH2) ppm. 13C{1H} NMR (100.6 MHz,
3
CDCl3, 26 °C): δ = 153.1 (3-C(pz)), 133.1 (1-C(Ph)), 131.5 (5-
C(pz)), 128.8 (o-C(Ph)), 128.3 (p-C(Ph)), 126.1 (m-C(Ph)), 103.6
(4-C(pz)), 92.9 (C(pz)3), 40.1 (CH2C(pz)3), 26.3 (CH2CH2C(pz)3),
23.0 (CH3CH2), 14.1 (CH3CH2) ppm. DRIFT: ṽmax = 3145 (vw),
3118 (w), 3087 (vw), 3061 (vw), 3035 (vw), 2953 (w), 2978 (w),
2870 (vw), 1974 (vw), 1954 (vw), 1887 (vw), 1808 (vw), 1762
(vw), 1700 (vw), 1604 (vw), 1528 (w), 1498 (m), 1456 (s), 1385
(m), 1358 (m), 1271 (m), 1238 (m), 1213 (s), 1099 (w), 1074 (m),
1047 (m), 842 (m), 751 (s), 694 (s), 662 (w) cm–1. C32H30N6
(498.4 g·mol–1) calcd. C 77.08, H 6.06, N 16.85; found C 77.22,
H 6.15, N 16.04.
nBuCTp3-Me (3e). Following the procedure described for 3b,
HCTp3-Me (5.00 g, 19.5 mmol), nBuLi (8.59 mL, 21.5 mmol, 2.5
M in n-hexane) and nBuI (2.44 mL, 21.5 mmol) yielded a yellow
solid as crude product. Further purification was achieved by
recrystallization from mtbe generating 3e as colorless crystals
(1.44 g, 4.60 mmol, 24%) suitable for X-ray diffraction analysis.
1H NMR (400.1 MHz, CDCl3, 26 °C): δ = 6.80 (dd, 3H, 3JHH = 2.5
4
3
4
Hz, JHH = 0.5 Hz, 5-H(pz)), 6.03 (dd, 3H, JHH = 2.6 Hz, JHH
=
0.4 Hz, 4-H(pz)), 3.18 (m, 2H, CH2C(pz)3), 2.28 (s, 9H, (pz)-
CH3), 1.55 (m, 2H, CH2CH2C(pz)3), 1.38 (sex, 2H, 3JHH = 7.5 Hz,
11
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MeCTp3-iPr (3j). Following the procedure described for 3b,
HCTp3-iPr (8.91 g, 26.2 mmol), Li[N(SiMe3)2] (5.69 g, 34.0 mmol)
and MeI (2.44 mL, 39.3 mmol) yielded a dark brown solid as
crude product. Further purification was achieved by
recrystallization from mtbe generating 3j as colorless crystals
(2.36 g, 6.65 mmol, 25%) suitable for X-ray diffraction analysis.
(Me3AlCTp3-Ph)2Mg (7). To a suspension of HCTp3-Ph (134 mg,
302 mol) in 2 mL of toluene a solution of 6 (60.0 mg, 302 mol)
in 2 mL of n-hexane was added dropwise. The reaction cleared
up and was stirred for 2 h at ambient temperature. After
removing the solvent under reduced pressure, the crude product
was recrystallized in n-hexane at ambient temperature
producing colorless crystals of 7 suitable for X-ray diffraction
analysis. A better elemental analysis could not be obtained due
3
1H NMR (400.1 MHz, CDCl3, 26°C): δ = 6.42 (d, 3H, JHH = 2.6
Hz, 5-H(pz)), 6.07 (d, 3H, 3JHH = 2.7 Hz, 4-H(pz)), 3.00 (sept, 3H,
3JHH = 7.1 Hz, (CH3)2CH(pz)), 2.90 (s, 3H, CH3C(pz)3), 1.24 (d,
3
18H, JHH = 7.0 Hz, (CH3)2CH(pz)) ppm. 13C{1H} NMR (100.6
to residual n-hexane and toluene (141 mg, 134 mol, 89%). 1H
3
MHz, CDCl3, 26 °C): δ = 161.3 (3-C(pz)), 129.6 (5-C(pz)), 103.3
(4-C(pz)), 90.4 (C(pz)3), 28.13 ((CH3)2CH(pz)), 25.8 (CH3C(pz)3),
23.0 ((CH3)2CH(pz)) ppm. DRIFT: ṽmax = 3138 (vw), 3120 (vw),
2963 (vs), 2927 (m), 2869 (m), 1608 (vw), 1524 (s), 1470 (w),
1449 (m), 1386 (m), 1370 (s), 1298 (m), 1258 (vs), 1217 (vs),
1156 (vw), 1113 (w), 1049 (m), 985 (m), 975 (m), 924 (vw), 881
(vw), 792 (vs), 769 (vs), 721 (w), 641 (vw), 577 (vw) cm–1.
C20H30N6 (498.4 g·mol–1) calcd. C 67.76, H 8.53, N 23.71; found
C 67.63, H 7.92, N 23.87.
[MgMe2(dioxane)]n (4a). Solid [MgMe2]n (100 mg, 1.85 mmol)
was dissolved in 2 mL of 1,4-dioxane, sealed in a scintillation vial
and stored inside a glovebox at ambient temperature. After
several months the solution contained colorless crystals of 4a
suitable for single-crystal structure analysis. Since 4a is
insoluble in [D6]benzene the 1H NMR spectrum was recorded in
NMR (400.1 MHz, [D6]benzene, 26 °C): δ = 8.90 (d, 6H, JHH
=
2.8 Hz, 5-H(pz)), 6.70 (m, 18H, o-H(Ph)/p-H(Ph)), 6.54 (m, 12H,
3
m-H(Ph)), 5.68 (d, 6H, JHH = 2.8 Hz, 4-H(pz)), 0.26 (s, 18H,
Al(CH3)3) ppm. 13C{1H} NMR (100.6 MHz, [D6]benzene, 26 °C):
δ = 156.4 (3-C(pz)), 138.6 (5-C(pz)), 131.1 (1-C(Ph)), 128.4 (o-
C(Ph)), 128.0 (p-C(Ph)), 127.3 (m-C(Ph)), 105.93 (4-C(pz)), 87.5
(C(pz)3), –2.2 (Al(CH3)3) ppm. DRIFT: ṽmax = 3157 (vw), 3137
(vw), 3027 (vw), 2923 (w), 2887 (w), 2820 (vw), 1603 (vw), 1531
(w), 1496 (vw), 1470 (w), 1447 (w), 1404 (w), 1404 (w), 1380 (w),
1249 (vw), 1226 (vw), 1182 (m), 1110 (vw), 1071 (m), 1057 (m),
1028 (vw), 1001 (vw), 952 (vw), 918 (vw), 810 (m), 779 (m), 759
(s), 709 (vs), 644 (m), 619 (w), 579 (w) cm–1. C62H62MgAl2N12
(1053.53 g·mol–1) calcd. C 70.68, H 5.93, N 15.95; found C
71.32, H 5.80, N 15.01.
(Me3AlCTp3-Me)Mg(AlMe4) (8). Following the procedure
described for 7, 6 (70.0 mg, 353 mol) and Me3SiCTp3-Me (116
mg, 353 mol) yielded 8 as a white powder in almost quantitative
yield (149 mg, 340 mol, 96%). Colorless crystals of 8 were
grown from saturated 1:1 n-hexane/toluene mixture at –40 °C.
1H NMR (400.1 MHz, [D6]benzene, 26 °C): δ = 8.49 (d, 3H, 3JHH
= 2.6 Hz, 5-H(pz)), 5.31 (d, 3H, 3JHH = 2.5 Hz, 4-H(pz)), 1.82 (s,
9H, (pz)-CH3), 0.03 (s, 9H, Al(CH3)3), –0.19 (s, 12H, [Al(CH3)4])
ppm. 13C{1H} NMR (100.6 MHz, CDCl3, 26 °C): δ = 151.4 (3-
C(pz)), 137.4 (5-C(pz)), 105.6 (4-C(pz)), 84.9 (C(pz)3), 13.7
((pz)-CH3), –3.6 (Al(CH3)3), –5.13 ([Al(CH3)4]) ppm. DRIFT: ṽmax
= 3156 (vw), 2925 (w), 2890 (vw), 1525 (w), 1495 (vw), 1414
(vw), 1389 (vw), 1369 (w), 1227 (vw), 1181 (m), 1063 (s), 1040
(vw), 1002 (vw), 810 (s), 770 (s), 723 (vs), 712 (vs), 677 (m), 655
(w), 638 (w), 608 (vw), 570 (vw), 532 (w) cm–1. C20H36MgAl2N6
(438.82 g·mol–1) calcd. C 54.74, H 8.27, N 19.15; found C 54.38,
H 8.04, N 18.49.
[D8
2-Me)(thf)]2. C16H14MgO2
(142.48 g mol–1) calcd. C 50.58, H 9.90; found C 50.40, H 9.85.
Further analytical data are found in literature.18a
[MgMe2(diglyme)] (4b). To a stirred solution of [MeMgCl(thf)2]
(70.0 mg, 320 mol) in 5 mL of toluene diglyme (21.4 mg, 160
mol) was added. A white precipitate of MgCl2(diglyme) formed
immediately. After 30 min the mixture was centrifuged and the
solid residue was extracted with 3x3 mL toluene. To the filtrate
0.5 mL diglyme was added and excess toluene was removed
under reduced pressure. Colorless crystals of 4b were obtained
from a saturated diglyme solution at –40 °C (25.2 mg, 84%). The
1H NMR
[MgMe2(diglyme)]∙1.5diglyme.
[D6]benzene, 26 °C): δ = 3.17 (s, 4H, H3C–O–CH2CH2), 3.12 (s,
4H, H3C–O–CH2CH2), 3.12 (s, 6H, H3C–O–CH2CH2), –0.91 (s,
2.34H, MgCH3) ppm. Further analytical data are found in the
literature.46
spectrum
revealed
adduct
((400.1
formation
MHz,
1H NMR
[(MeCTp3-H)2Mg][AlMe4]2 (9a). To a solution of 6 (52.3 mg, 263
mol) in 2 mL of n-hexane a solution of MeCTp (120 mg, 526
mol) in 2 mL of toluene was added dropwise. A white precipitate
formed immediately. After stirring overnight at ambient
temperature, the reaction mixture was dried under reduced
pressure. The crude product was washed with n-pentane (3x5
mL) affording 9a as white powder in almost quantitative yield
(168 mg, 257 mol, 97%). Colorless crystals of 9a were grown
by diluting 50 mg product in 1 mL of thf and evaporation of the
solvent in vacuo. The resulting brownish oil crystallized at
[(dme)(thf)Mg(pz)3MgMe] (5). To a suspension of [MgMe2]n (4)
(50.0 mg, 920 mol, evaporated to dryness under high vacuum)
in 1.5 mL of toluene a solution of BnCTp (280 mg, 920 mol)
dissolved in 1.5 mL of toluene was added dropwise. The solution
cleared up and turned immediately yellow. After addition of a 1:1
mixture dme/thf (2 mL) and stirring for 30 s, the reaction mixture
was stored at –40 °C. Some brown single crystals of 5 as
decomposition product suitable for X-ray diffraction analysis
were collected. Due to ongoing rapid decomposition, further
characterization was not successful.
12
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ambient temperature. The NMR sample contained a mixture of
mg, 61.6 mol, 83%). Colorless crystals of 9c were grown by
dissolving 25 mg product 9c in 1 mL of diglyme and subsequent
slow diffusion of n-pentane at ambient temperature. 1H NMR
complex 9a (species a), free ligand and mono-ligand species b
1
in 1:3:1 ratio. H NMR (400.1 MHz, [D8]thf, 26 °C): δ = 8.59 (d,
3H, 3JHH = 2.9 Hz, 5-H(pz), free ligand), 8.51 (s, 1.2 H, 5-H(pz),
3
(400.1 MHz, [D8]thf, 26 °C): δ = 8.53 (d, 6H, JHH = 2.9 Hz, 5-
3
3
species a), 8.01 (s, 1.2H, 3-H(pz), species a), 7.65 (d, 3H, JHH
H(pz)), 6.48 (s, 6H, JHH = 2.6 Hz, 4-H(pz)), 3.51 (s, 6H,
= 2.1 Hz, 3-H(pz), free ligand), 7.56 (s, 1.1H, 5-H(pz), species
b), 6.76 (s, 1.1 H, 3-H(pz), species b), 6.64 (s, 1.2H, 4-H(pz),
species a), 6.60 (t, 3H, 3JHH = 2.4 Hz, 4-H(pz), free ligand), 6.26
(s, 1.1H, 4-H(pz), species b), 3.52 (s, 3H, CH3C(pz)3, free
ligand), 3.44 (s, 3H, CH3C(pz)3, species a), 3.52 (s, 3H,
CH3C(pz)3, species b), –1.34 (m, 24H, [Al(CH3)4]) ppm.
13C{1H} NMR (100.6 MHz, [D8]thf, 26 °C): (100.6 MHz, CDCl3,
CH3C(pz)3, overlapped by diglyme), 1.71 (s, 18H, (pz)-CH3),
−1.30 (m, 24H, [Al(CH3)4]) ppm. 13C{1H} NMR (100.6 MHz,
[D8]thf, 26 °C): δ = 155.3 (3-C(pz)), 134.1 (5-C(pz)), 108.6 (4-
C(pz)), 84.5 (C(pz)3), 24.0 (CH3C(pz)3), 12.5 ((pz)-CH3), –4.6
(sext, 1JC-Al = 73.1 Hz, [Al(CH3)4]) ppm. DRIFT: ṽmax = 3160 (vw),
3130 (vw), 3017 (vw), 2902 (m), 2800 (w), 1534 (m), 1482 (w),
1446 (vw), 1416 (vw), 1392 (m), 1374 (m), 1352 (m), 1300 (vw),
1214 (vs), 1154 (w), 1075 (s), 1036 (w), 990 (vw), 777 (vs), 757
(m), 741 (m), 696 (vs), 688 (vs), 662 (m), 615 (w), 576 (vw), 541
(m) cm–1. C36H60MgAl2N12∙C7H8 (831.37 g·mol–1) calcd. C 62.12,
H 8.24, N 20.22; found C 61.69, H 8.23, N 19.70.
26 °C):
δ = 144.3/141.7 (3-C(pz)), 133.4/129.8 (5-C(pz)),
108.6/108.4 (4-C(pz)), 85.1 (C(pz)3), 23.7/23.4 (CH3C(pz)3),
– 4.5 (sext, 1JC-Al = 74.9 Hz, [Al(CH3)4]) ppm. DRIFT: ṽmax = 3158
(w), 3142 (w), 3111 (vw), 2904 (m), 2800 (w), 1523 (vw), 1416
(m), 1389 (w), 1322 (s), 1233 (s), 1218 (vw), 1207 (vw), 1134
(m), 1123 (m), 1090 (m), 1065 (s), 977 (m), 921 (vw), 862 (vw),
775 (vs), 764 (vs), 734 (w), 694 (s), 603 (m), 590 (w), 546 (m)
cm–1. C30H48MgAl2N12 (655.07 g·mol–1) calcd. C 55.01, H 7.39, N
25.66; found C 55.46, H 7.44, N 23.75.
[(nBuCTp3-Me)2Mg][AlMe4]2 (9d). Following the procedure
described for 9a, 6 (38.1 mg, 192 mol) and nBuCTp3- Me (120
mg, 384 mol) yielded 9d as white powder in quantitative yield
(157 mg, 191 mol, 99%). Colorless crystals of 9d were grown
by heating a solution of 6 (5.00 mg, 25.2 mol) and nBuCTp3-Me
(7.87 mg, 25.2 mol) in 0.7 mL [D6]benzene in a J. Young valve
NMR tube to 90 °C for 1 h. 1H NMR (400.1 MHz, [D8]thf, 26 °C):
δ = 8.43 (s, 6H, 5-H(pz)), 6.56/6.38 (s, 6H, 4-H(pz)), 3.85 (m,
4H, CH2C(pz)3), 2.16/1.58/1.34 (s, 18H, (pz)-CH3), 2.03 (m, 4H,
CH2CH2C(pz)3), 1.89 (sext, 4H, 3JHH = 7.3 Hz, CH3CH2CH2), 1.14
(t, 6H, 3JHH = 7.3 Hz, CH3CH2), –1.30 (m, 24H, [Al(CH3)4]) ppm.
13C{1H} NMR (100.6 MHz, [D8]thf, 26 °C): δ = 155.5 (3-C(pz)),
150.2 (3-C(pz), free ligand), 135.6/132.5 (5-C(pz)), 131.2 (5-
C(pz), free ligand), 109.6/108.9 (4-C(pz)), 106.0 (4-C(pz), free
ligand), 87.3 (C(pz)3, free ligand), 40.6 (CH2C(pz)3), 35.0
(CH2C(pz)3, free ligand), 28.1 (CH2CH2C(pz)3, free ligand), 26.7
(CH2CH2C(pz)3), 23.5 (CH3CH2, free ligand), 14.1 ((pz)-CH3, free
ligand), 13.6 (CH3CH2, free ligand), 13.0 (CH3CH2), 12.6 (((pz)-
[(nBuCTp3-H)2Mg][AlMe4]2 (9b). Following the procedure
described for 9a, 6 (50.0 mg, 252 mol) and nBuCTp (136 mg,
504 mol) yielded 9b as a white powder (168 mg, 227 mol,
90%). Colorless crystals were grown analogously to 9a. For
compound 9b a concentration-dependent decomposition in
solution was observed. In order to counteract degradation the
NMR spectra of 9b were recorded as highly diluted, 25 molar
solutions. When increasing the concentration to record the 13C
NMR spectrum the sample started to decompose and distinct
ligand species were detected. 1H NMR (400.1 MHz, [D8]thf,
26 °C): δ = 7.60 (s, 4H, 5-H(pz)), 7.04 (s, 4H, 3-H(pz)), 6.29 (s,
4H,
4-H(pz)), 3.29 (m, 4H, CH2C(pz)3), 1.59 (m, 4H,
CH2CH2C(pz)3), 1.39 (sext, 4H, 3JHH = 7.2 Hz, CH3CH2CH2), 0.89
3
CH3), –4.6 (sext, 1JC-Al = 72.5 Hz, [Al(CH3)4]) ppm. DRIFT: ṽmax
=
(t, 6H, JHH = 7.4 Hz, CH3CH2), −0.96 (s), −1.30 (s), −1.67 (s)
(24H, Al(CH3)3(thf), [Al(CH3)4], [nBuCTpMg(CH3)(thf)2]) ppm.
13C{1H} NMR (100.6 MHz, [D8]thf, 26 °C): (100.6 MHz, CDCl3,
26 °C): δ = 144.2 (3-C(pz)), 141.4 (3-C(pz), free ligand), 134.3
(5-C(pz)), 130.6 (5-C(pz), free ligand), 109.1 (4-C(pz)), 106.6 (4-
C(pz), free ligand), 92.4 (C(pz)3, free ligand), 87.2 (C(pz)3), 40.3
(CH2C(pz)3), 34.5 (CH2C(pz)3, free ligand), 28.1 (CH2CH2C(pz)3,
free ligand), 27.9 (CH2CH2C(pz)3), 26.8 (CH3CH2), 23.4
(CH3CH2, free ligand), 14.1 (CH3CH2, free ligand), –4.7 (sext,
1JC-Al = 70.2 Hz, [Al(CH3)4]) ppm. DRIFT: ṽmax = 3161 (vw), 3140
(w), 3111 (vw), 2959 (w), 2898 (m), 2800 (w), 1520 (vw), 1414
(m), 1336 (m), 1221 (m), 1198 (w), 1157 (w), 1099 (s), 1069 (s),
956 (m), 923 (vw), 837 (s), 782 (m), 760 (vs), 689 (vs), 639 (m),
539 (m) cm–1. C38H60MgAl2N12 (739.23 g·mol–1) calcd. C 58.49,
H 8.18, N 22.74; found C 58.36, H 7.43, N 21.38.
3159 (vw), 3137 (vw), 2964 (vw), 2899 (m), 2970 (w), 2797 (w),
1532 (m), 1481 (w), 1481 (vw), 1445 (vw), 1408 (vw), 1392 (w),
1381 (w), 1353 (vw), 1288 (vw), 1252 (vw), 1223 (vw), 1190 (m),
1145 (m), 1075 (s), 1035 (w), 978 (vw), 953 (vw), 887 (vw), 836
(w), 820 (w), 776 (s), 693 (vs), 622 (vw), 552 (m) cm–1.
C36H60MgAl2N12∙C7H8 (823.39 g·mol–1) calcd. C 61.27, H 8.81, N
20.41; found C 60.93, H 8.74, N 20.24.
[(MeCTp3-Ph)MgMe][AlMe4] (10a). To a solution of MeCTp3-Ph
(150 mg, 329 mol) in 2 mL of toluene a solution of 6 (65.2 mg,
329 mol) in 2 mL of n-hexane was added dropwise. Instant
formation of a white precipitate was observed. After removing
the solvent under reduced pressure, the crude product was
washed with n-pentane (3x3 mL) yielding 10a as a white powder
(123 mg, 211 mol, 64%). Colorless crystals of 10a suitable for
X-ray diffraction analysis were grown from a hot toluene solution
by cooling to ambient temperature. 1H NMR (400.1 MHz,
[(MeCTp3-Me)2Mg][AlMe4]2∙C7H8 (9c). Following the procedure
described for 9a, 6 (14.8 mg, 74.3 mol) and MeCTp3-Me (40.0
mg, 148 mol) yielded 9c as a white powder in high yields (51.2
13
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[D6]benzene/1,2-DFB, 26 °C): δ = 7.95 (d, 3H, 3JHH = 2.5 Hz, 5-
H(pz)), 7.26 (m, 6H, m-H(Ph)), 7.06 (m, 9H, o-H(Ph)/p-H(Ph)),
6H, 5-H(pz)), 7.53 (m, 6H, m-H(Ph)), 7.21 (m, 24H, o-H(Ph)/p-
H(Ph)), 6.34 (s, 6H, 4-H(pz)), 3.58/2.95 (m, 4H, CH2C(pz)3), 1.39
(m, 4H, CH3CH2CH2), 1.01 (s, 4H, CH2CH2C(pz)3), 0.86 (t, 6H,
3JHH = 7.2 Hz, CH3CH2), –0.57 (s, 39H, 13xCH3: [Al(CH3)4], Mg-
CH3-Mg, 2x Mg-CH3-Al, 2x Al(CH3)3) ppm. 13C{1H} NMR (100.6
MHz, [D6]benzene /1,2-DFB, 26 °C): δ = 158.5 (3-C(pz)), 134.5
(1-C(Ph)), 131.2 (5-C(pz)), 129.8 (o-C(Ph)), 126.0 (m-C(Ph)),
107.26 (4-C(pz)), not observed (C(pz)3), 39.6 (CH2C(pz)3), 26.2
(CH2CH2C(pz)3), 22.6 (CH3CH2), 13.8 (CH3CH2), –6.02
([Al(CH3)4], Mg-CH3–Mg, 2x Mg-CH3-Al, 2x Al(CH3)3) ppm.
DRIFT: ṽmax = 3153 (vw), 2959 (w), 2911 (m), 2875 (w), 2806
(w), 1606 (vw), 1582 (vw), 1531 (w), 1495 (w), 1466 (w), 1390
(w), 1377 (w), 1360 (w), 1305 (vw), 1259 (vw), 1231 (vw), 1190
(m), 1100 (vw), 1076 (m), 1045 (vw), 974 (vw), 839 (m), 761 (vs),
699 (vs), 596 (w) cm–1. C77H99Mg2Al3N12 (1320.73 g·mol–1) calcd.
C 69.94, H 7.55, N 12.71; found C 69.70, H 7.22, N 12.13.
3
6.13 (d, 3H, JHH = 2.7 Hz, 4-H(pz)), 3.24 (s, 3H, CH3C(pz)3), –
0.03 (s, 12H, [Al(CH3)4]), –1.16 (s, 3H, Mg-CH3) ppm.
13C{1H} NMR (100.6 MHz, [D6]benzene/1,2-DFB, 26 °C): δ =
158.3 (3-C(pz)), 133.7 (1-C(Ph)), 130.8 (5-C(pz)), 129.2 (o-
C(Ph)), 128.2 (p-C(Ph)), 127.9 (m-C(Ph)), 107.1 (4-C(pz)), 84.7
(C(pz)3), 25.2 (CH3C(pz)3), –3.1 (Mg-CH3/[Al(CH3)4], very weak)
ppm. DRIFT: ṽmax = 3162 (vw), 3144 (vw), 3060 (vw), 3030 (vw),
2905 (m), 2846 (w), 2846 (vw), 2800 (w), 1604 (vw) 1582 (vw),
1534 (m), 1501 (m), 1465 (m), 1384 (m), 1359 (w), 1304 (vw),
1216 (m), 1148 (w), 1118 (w), 1077 (m), 1065 (m), 1028 (vw),
945 (vw), 917 (vw), 772 (s), 756 (s), 695 (vs), 542 (m) cm–1.
C34H39MgAl2N6 (583.01 g·mol–1) calcd. C 70.05, H 6.74, N 14.42;
found C 70.20, H 6.18, N 13.76.
[(MeCTp3-tBu)MgMe][Al2Me7] (10b). Following the procedure
described for 10a, 6 (100 mg, 504 mol) and MeCTp3-tBu (200
mg, 504 mol) yielded 10b as a white powder in high yields (274
mg, 470 mol, 91%). Colorless crystals of 10b suitable for X-ray
(MeCTp3-iPr)Mg(AlMe4)2 (12). To a solution of MeCTp3-iPr (100
mg, 282 mol) in 2 mL of toluene a solution of 6 (56.0 mg, 282
mol) in 2 mL of toluene was added dropwise. A white precipitate
formed immediately. After removing the solvent under reduced
pressure, the crude product was washed with n-pentane (3x3
mL) yielding 12 as a white powder (142 mg, 257 mol, 91%).
Colorless crystals of 12 suitable for X-ray diffraction analysis
were grown from a 1,2-DFB solution at –40 °C. 1H NMR (400.1
MHz, [D6]benzene/1,2-DFB, 26 °C): δ = 7.77 (dd, 3H, 3JHH = 3.0
Hz, 4JHH = 0.5 Hz, 5-H(pz)), 5.78 (d, 9H, 3JHH = 2.9 Hz, 4-H(pz)),
3.08 (s, 3H, CH3C(pz)3), 2.94 (sept, 3H, CH(CH3)2), 0.91 (d, 18
diffraction analysis were grown from
a
toluene/1,2-
difluorobenzene solution. 1H NMR (400.1 MHz, [D6]benzene/1,2-
3
DFB, 26 °C): δ = 7.45 (d, 3H, JHH = 3.0 Hz, 5-H(pz)), 5.88 (d,
3H, 3JHH = 2.8 Hz, 4-H(pz)), 2.72 (s, 3H, CH3C(pz)3), 1.20 (d, 27
H, C(CH3)3), –0.22 (s, 21H, [Al2(CH3)7]), –0.35 (s, 3H, Mg-CH3)
ppm. 13C{1H} NMR (100.6 MHz, [D6]benzene/1,2-DFB, 26 °C): δ
= 168.9 (3-C(pz)), 131.6 (5-C(pz)), 105.3 (4-C(pz)), 83.4
(C(pz)3), 32.3 (C(CH3)3), 30.2 (C(CH3)3), 25.4 (CH3C(pz)3), –4.1
(MgCH3), –4.4 ([Al2(CH3)7]) ppm. DRIFT: ṽmax =3166 (w), 3149
(w), 2964 (m), 2917 (s), 2876 (w), 2805 (w), 1746 (vw), 1525 (m),
1485 (w), 1462 (w), 1382 (w), 1366 (s), 1304 (vw), 1264 (w),
1221 (s), 1169 (m), 1126 (w), 1079 (s), 1028 (w), 1016 (m), 965
(w), 932 (w), 874 (vw), 771 (vs), 700 (vs), 633 (s), 608 (s), 559
(s), 538 (s), 510 (m) cm–1. C31H60MgAl2N6 (593.13 g·mol–1) calcd.
C 62.56, H 10.16, N 14.12; found C 61.93, H 9.98, N 14.79.
3
H, JHH = 7.0 Hz, CH(CH3)2), –0.14 (s, 24H, Mg-CH3, Al-CH3)
ppm. 13C{1H} NMR (100.6 MHz, [D6]benzene/1,2-DFB, 26 °C): δ
= 165.2 (3-C(pz)), 133.1 (5-C(pz)), 104.7 (4-C(pz)), 83.3
(C(pz)3), 27.8 (CH(CH3)2), 24.9 (CH3C(pz)3), 22.7 (CH(CH3)2), -
4.4 (Mg-CH3, Al-CH3) ppm. DRIFT: ṽmax = 3154 (w), 3141 (vw),
3027 (vw), 2969 (w), 2906 (m), 2803 (w), 1532 (m), 1508 (w),
1482 (w), 1462 (w), 1397 (m), 1359 (m), 1303 (w), 1269 (vw),
1215 (s), 1154 (w), 1086 (m), 1070 (w), 1049 (m), 1020 (m), 971
(vw), 930 (vw), 880 (vw), 771 (vs), 691 (vs), 613 (m), 546 (m)
cm–1. C34H39MgAl2N6 (553.05 g·mol–1) calcd. C 60.81, H 9.84, N
15.20; found C 60.28, H 9.64, N 14.42.
[(BnCTp3-Ph)MgMe][AlMe4]. A solution of BnCTp3-Ph (15.3 mg,
28.8 mol) in 0.3 mL of [D6]benzene was added to a solution of
1
6 (5.72 mg, 28.8 mol) in a J. Young valve NMR tube. The H
NMR spectra indicated the coordination of the ligand to
magnesium, but further attempts to isolate any discrete species
failed.
Crystallography and Crystal Structure Determinations.
Single crystals were grown by standard techniques from
saturated solutions (3d, diethyl ether; 3e-f, methyl tert-butyl
ether (mtbe); 3g-i, benzene; 3j, mtbe; 3k, diethyl ether; 4a, 1,4-
dioxane; 4b, diglyme; 5, 1:1 thf / dme; 7, n-hexane; 8, 1:1 n-
hexane/toluene; 9a-b, thf; 9c, diglyme/n-pentane diffusion; 9d,
benzene; 10a-b, toluene; 11, benzene; 12, 1,2-difluorobenzene).
Single crystals suitable fofdistinctr X-ray structure analyses were
selected in a glovebox and coated with Parabar 10312
(previously known as Paratone N, Hampton Research) and fixed
on a nylon loop / glass fiber.
[{(2-(N,N’)nBuCTp3-Ph)Mg(AlMe4)}2(2-Me)][AlMe4]
(11).
Following the procedure described for 10a, 6 (70.0 mg, 353
mol) and nBuCTp3-Ph (176 mg, 353 mol) yielded 11 as a white
powder in quantitative yield (226 mg, 171mol, 97%). Single
crystals grown from a hot toluene solution showed a highly
disordered lattice toluene and indicated the formation of [Al2Me7]
as a counter ion. Colorless crystals of 11 suitable for an accurate
X-ray diffraction analysis were grown from a [D6]benzene
solution in a J. Young valve NMR tube at ambient temperature.
1H NMR (400.1 MHz, [D6]benzene/1,2-DFB 26 °C): δ = 7.81 (s,
Crystallographic data for compounds 3d-k, 4a-b, 5, 7, 8, 9a-d,
10a-b, 11, and 12 were collected on a Bruker APEX DUO
instrument equipped with an IμS microfocus sealed tube and
14
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10.1002/chem.201803067
Chemistry - A European Journal
FULL PAPER
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We are grateful to the German Science Foundation DFG for
generous support (Grants:AN 238/15-1).
Conflict of interest
The authors declare no conflict of interest.
Keywords: magnesium • cone angle • trispyrazolylmethane •
scorpionate • alkyl
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16
This article is protected by copyright. All rights reserved.

10.1002/chem.201803067
Chemistry - A European Journal
FULL PAPER
Entry for the Table of Contents
FULL PAPER
Christoph Stuhl, Cäcilia Maichle-
Mössmer, and Reiner Anwander *
Page No. – Page No.
Magnesium Stung by Non-Classical
Scorpionate Ligands:
Synthesis and Cone Angle
Calculations
Introducing alkyl substituents at the CN3 backbone carbon atom leads to enhanced
stabilization of neutral RCTp3-R’ ligands, facilitating the synthesis of a variety of
distinct magnesium methyl complexes.
This article is protected by copyright. All rights reserved.