Group 13 metal complexes containing the bis-(4-methylbenzoxazol-2-yl)-methanide ligand

Article abstract of DOI:10.1039/c5dt03913d

To focus on the high importance of low-valent main group metal complexes, which can be applied to catalytic transformations, this article deals with the promising new ligand system (4-MeNCOC₆H₃)₂CH₂ (1). It is patterned on the well known nacnac ligand and further development of the parent bisheterocyclo methanes. In comparison with the results of previous studies based on the bisheterocyclo methanes (NCOC₆H₄)₂CH₂ and (NCOC₆H₄)₂CH₂ derivative 1 was modified by adding a methyl group to the annulated benzene perimeters to enhance the steric protection of a potentially coordinated main group metal cation. On reaction of 1 with group 13 trimethyl reagents and dialkyl aluminium halides the ligand backbone gets deprotonated and the two endocyclic nitrogen donor atoms coordinate with the remaining organometallic fragment to form a six-membered metalla heterocycle. The synthesis of [Me₂Al{(4-MeNCOC₆H₃)₂CH}] (2), [Me₂Ga{(4-MeNCOC₆H₃)₂CH}] (3), [Me₂In{(4-MeNCOC₆H₃)₂CH}] (4), [ClMeAl{(4-MeNCOC₆H₃)₂CH}] (5), [IMeAl{(4-MeNCOC₆H₃)₂CH}] (6) and [IEtAl{(4-MeNCOC₆H₃)₂CH}] (7) could be accomplished. A structural comparison of those metallated species based on single crystal X-ray analyses identifies them as ideal precursors generating new low-valent main group complexes.

Full text of DOI:10.1039/c5dt03913d

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Group 13 metal complexes containing the bis-(4-methyl-
benzoxazol-2-yl)-methanide ligand†‡
David-R. Dauer, Melchior Flügge, Regine Herbst-Irmer, Dietmar Stalke*a
Received 00th January 20xx,
Accepted 00th January 20xx
To focus on the high importance of low-valent main group metal complexes, which can be applied to cataytic
transformations, this article deals with the promising new ligand system (4-Me-NCOC6H3)2CH2 (1). It is patterned on the
well known nacnac ligand and a further development of the parent bisheterocyclo methanes. In comparison to the results
of previous works based on the bisheterocyclo methanes (NCOC6H4)2CH2 and (NCOC6H4)2CH2 derivative 1 was modified by
adding a methyl group to the annulated benzene perimeters to enhance the steric protection of a potentially coordinated
main group metal cation. Upon reaction of 1 with group 13 trimethyl reagents and dialkyl aluminium halides the ligand
backbone gets deprotonated and the two endocyclic nitrogen donor atoms coordinate the remaining organometallic
fragment to form a six-membered metalla heterocycle. The synthesis of [Me2Al{(4-Me-NCOC6H3)2CH}] (2), [Me2Ga{(4-Me-
NCOC6H3)2CH}] (3), [Me2In{(4-Me-NCOC6H3)2CH}] (4), [ClMeAl{(4-Me-NCOC6H3)2CH}] (5), [IMeAl{(4-Me-NCOC6H3)2CH}] (6)
and [IEtAl{(4-Me-NCOC6H3)2CH}] (7) could be accomplished. A structural comparison of those metallated species based on
single crystal X-ray analyses identifies them as ideal precursors generating new low-valent main group complexes.
DOI: 10.1039/x0xx00000x
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and corresponding β-diketiminate Ca(II) complexes,10 which
were successfully applied for epoxide/CO2 copolymerisation11
or hydrogenation reactions of alkenes with H2,12 should be
Introduction
In the context of the ongoing increasing demand in the
activation of small molecules like H2, N2, NH3 or CO2 the
development of new synthetic approaches for generating
catalytic active species is of high interest. Even though this
research area of catalytic activation is mostly focussed on the
field of transition metal complexes the transfer to suitable
main group metal complexes, which should adopt the same
catalytic reactivity compared to the transition metals or even
exceed them, plays a key role in current research.1
highlighted as alkaline earth metal complexes performing in
catalysis. Switching to group 13 elements also a variety of
Al(III) and Ga(III) containing complexes was synthesised and
fully characterized.13 Subsequently also the low-valent Al(I)14
and Ga(I)15 species employing the Dipp-substituted (Dipp = 2,6-
diisopropylphenyl) nacnac ligand were accessible. More
recently the catalytic activity of the related alumoxanes was
studied in detail.16 Other common ligand types, which are used
for stabilisation of dimeric low-valent group 13 species
involving metal-metal multiple bonds, are the substituted
terphenyls, which are also prone for interaction with small
molecules like H2.17
As figurehead for efficient small molecule activation the FLP
chemistry (frustrated Lewis pairs) developed to a promising
research area over the last decade.2 In this course the usage of
mainly phosphorus/boron, nitrogen/boron or carbon/boron
FLP systems offers a simple access to the efficient splitting of
dihydrogen3 or ring opening of THF.4 Also the aluminium based
FLP’s were found to be advantageous for B-H or N-H bond
activation5, polymerisation reactions of methyl methacrylate6
and conversion of CO2.7 Furthermore, the well-known nacnac
ligand and the derived main group metal complexes,
respectively, facilitate the stabilisation of metal ions in low
oxidation states.8 The synthesis of the first Mg(I) compound9
With this in mind in the field of main group transformations
ligand design in particular and the choice of the suitable main
group element has a significant influence on the stability and
the catalytic abilities of the resulting compounds. In this work
we tried to mimick the omnipresent nacnac ligand by two
methylene bridged substituted benzoxazole moieties. The
corresponding group 13 metal complexes were synthesised to
get the best from two words: the stabilisation abilities to get
low-valent metal complexes and the reactivity of group 13
metals. To tie up to earlier studies concerning related
bisheterocyclo methanide18 and amide derivatives19 this work
focuses on bis-(4-methylbenzoxazol-2-yl)-methane
1. The
previous results of the methanide containing metal complexes
have shown that upon deprotonation of the methylene bridge
of the parent ligand systems the coordination of the metal
cation is preferentially accomplished by the endocyclic
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nitrogen donor atoms in a chelating fashion.20 Due to this fact
and to further shield the coordinated metal the bis-
(benzoxazol-2-yl)-methane ligand was additionally methyl
substituted in
same side of the coordinating nitrogen atoms. Neither in the
case of the methanide nor the amide derivatives
1 to increase the kinetic stabilisation at the
a
coordination via the other feasible O- or S-coordinating sites
was observed in the solid state yet.19, 18
The issue of steric shielding of metal centres within the group
13 complexes is an important aspect for the further
applications and reactions, because in the future we plan to
convert these Al(III) containing species to the low-valent Al(I)
compounds like e. g. [Al{Dipp2nacnac}].14e Because of the high
electrophilicity of the Al(I) species steric protection is essential
to maintain the monomeric carbene-like structural motif and
prevent dimerisation or nucleophilic attacks.21 The challenge
to synthesise a low-valent species containing a bisheterocyclo
methanide ligand backbone is still the guiding idea of ongoing
Scheme 1. Synthetic routes to the parent ligand system 1 including the side product 1a.
The first route is along the synthesis of the unsubstituted bis-
(benzoxazol-2-yl)-methane, in which a bisimidate linker was
used for the coupling of the two phenol derivatives. This
pathway, however, leads to a smaller yield of the desired
research and
1 seems to be a promising ligand system for
subsequent reduction steps (vide infra).
product
1 and also promotes the formation of a specific side
Among the nacnac derivatives and the bisheterocyclo
methanides the efficient metal shielding is within some limits
comparable. In the case of the nacnac ligands the residues at
the bulky imine moieties are twisted nearly perpendicular with
respect to the chelating C3N2M-plane, which causes the metal
atoms to be most protected. In the case of the complexes
product 1a. The side product could be identified as 4-
methylbenzoxazol-2-yl-carboxamide, which occurs, if just one
equivalent of the starting material has cyclised and the
remaining imidate unit has been hydrolysed upon further
purification. On the second improved route malonic dinitrile
was added to the phenolic starting material. In that case
polyphosphoric acid (ppa) was added as solvent and
catalytically facilitates the cyclisation reaction to give the
derived from
1 the methyl groups shield as well but due to less
steric congestion the metal centres are slightly more accessible
to allow some specific substitution reactions. The new metal
complexes containing a central six-membered metalla hetero-
cycle are reminiscent to the analogue metal complexes with
the omnipresent nacnac ligand. Following similarities between
the herein discussed bisheterocyclo methanides and the
nacnac ligands can be stated due to the structural comparison
of the corresponding metal complexes: At first the
deprotonation of the bridging moiety leads to the formation of
parent ligand system 1.
a
negative charge in the ligand’s backbone, which is
completely delocalised to give a 6π electrons containing
metalla heterocycle (see Table 1). Secondly, the chelating
coordination of the metal cation is achieved exclusively by the
two nitrogen donor atoms in the ligand periphery.
Figure 1. Molecular structure of (4-Me-NCOC6H3)2CH2 (1). Anisotropic displacement
parameters are depicted at the 50 % probability level. C-H hydrogen atoms are omitted
for clarity except the bridging ones. Structural data are given in Tables 1 – 3.
Results and Discussion
ꢀ
1 crystallises in the triclinic space group P1 and the
Compound
Ligand synthesis:
asymmetric unit contains one molecule. Like the other
symmetrically substituted bisheterocyclo methanes18 the
central carbon atom C1’ is also coordinated in a distorted
tetrahedral fashion and the benzoxazol moieties are twisted
nearly perpendicular (81.53(4) °) relative to each other. Due to
the higher steric demand of the heterocycles the C1-C1’-C8
angle is widened to 110.8(1) °, whereas all other angles around
C1’ are slightly compressed in comparison to an ideal
The synthesis of the parent uncharged ligand system is
achieved as reported earlier for the corresponding unsubsti-
tuted bis-(benzoxazol-2-yl)- and bis-(benzothiazol-2-yl)-
methanes.18,
22
A
cyclocondensation reaction of two
equivalents of 2-amino-3-methylphenol and one equivalent of
a C3-linker unit derived from malonic acid yields the ligand.
Two different synthesis routes were performed and optimised
to give a moderate overall yield of 56 % (see Scheme 1).
tetrahedral angle. Interestingly in the solid state
1 forms a 3D
network of quite remarkable C-HꢀꢀꢀN hydrogen bonds, in which
the two acidic methylene hydrogen atoms of the bridge are
coordinated by imine nitrogen atoms of two adjacent
2 | J. Name., 2012, 00, 1-3
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molecules (see Figure 2). The experimentally determined resulting in different feasible resonance structures: carb-
values show two hydrogen bonds each, which are energetically anionic, amidic or completely delocalised. On the other hand
more favourable (H1’BꢀꢀꢀN2: 2.39 Å; C1’-H1’BꢀꢀꢀN2: 171.1 °), the hybridisation of the central carbon atom changes from sp3
and two which are less pronounced (H1’AꢀꢀꢀN1: 2.62 Å; C1’- in the starting material
1
to sp2 in the metallated species
2
–
4
H1’AꢀꢀꢀN1: 150.9 °).
based on the trigonal planar coordination geometry of C1’.
Structural comparison of 2 – 4:
A closer look at the experimentally determined geometry of
1
shows that the Cipso-Cbridge distance is slightly shorter than it is
to be expected for a typical C(sp2)-C(sp3) single bond (1.51 Å).
This deviation can be explained by the presence of the four
electronegative adjacent heteroatoms, which cause the Cipso
-
Cbridge bonds to shrink due to their electron withdrawing
ability.
In comparison to compounds
2 – 4 the observed Cipso-Cbridge
distances (1.384 Å to 1.390 Å) are half way between a typical
C(sp2)-C(sp2) single bond (1.47 Å) and a C(sp2)=C(sp2) double
bond (1.34 Å), which is a result of the efficient delocalisation of
the double bonds. The same explanation is valid for the Cipso-N
bond lengths, which are in a narrow range from 1.337 Å to
1.351 Å. These values for the Cipso-N bond lengths can also be
seen as the average of a typical C(sp2)-N(sp2) single bond
(1.40 Å) and a C(sp2)=N(sp2) double bond (1.29 Å).23 In the light
of previous results of the methanides [Me2Al{(NCOC6H4)2CH}]
and [Me2Al{(NCSC6H4)2CH}]18 and the analogue amide bridged
species [Me2Al{(NCSC6H4)2N}] and [Me2Al{(4-MeNCSC6H4)2N}]19
the discussed structural values are matching well (Table 1).
Figure 2. Hydrogen bonding properties of the parent ligand system (4-Me-
NCOC6H3)2CH2 (1).
Table 1. Selected averaged bond lengths (Å) and angles (deg) of the ligand backbone
for compounds 1 – 4 and reference structures.
Syntheses of the group 13 metal complexes:
Cipso–C1‘
1.487(2)
1.384(2)
1.388(3)
1.390(13)
1.380(3)
1.390(2)
-
Cipso–N
1.291(2)
1.351(2)
1.341(2)
1.337(12)
1.346(3)
1.352(2)
1.331(3)
1.343(2)
C1–C1‘–C8
110.79(12)
121.13(14)
121.62(18)
123.6(6)
119.5(2)
123.54(14)
-
The reaction of
1 in toluene with pure trimethyl aluminium,
(4-MeNCOC6H4)2CH2 (1)
gallium or indium lead to the formation of the monoanionic
methanides containing the corresponding MMe2 fragment (see
Scheme 2). By addition of these organometallic reagents the
acidic methylene bridge gets deprotonated under evolution of
gaseous methane and in a concerted manner the remaining
dimethyl group 13 metal cation gets chelated by the two ring
nitrogen donor atoms.
[Me2Al{(4-MeNCOC6H4)2CH}] (2)
[Me2Ga{(4-MeNCOC6H4)2CH}] (3)
[Me2In{(4-MeNCOC6H4)2CH}] (4)
[Me2Al{(NCOC6H4)2CH}]18
[Me2Al{(NCSC6H4)2CH}]18
[Me2Al{(NCSC6H4)2N}]19
[Me2Al{(4-MeNCSC6H4)2N}]19
-
-
Compounds
the monoclinic space group P21/c and the asymmetric unit
contains one molecule. crystallises in the monoclinic space
2 and 3 are equi-structural and crystallise each in
4
group Pn and contains two metallated molecules in the
asymmetric unit.
Scheme 2. Metallation reactions of 1.
The structural comparison of the MMe2 derivatives shows that
in each case the metal coordination again is accomplished by
the two nitrogen atoms of the benzoxazole moieties and the
oxygen atoms are pointing away from the metal. In all three
cases this leads to a distorted tetrahedral coordination
geometry at the particular metal ion. As expected the ligand
Upon deprotonation the concerning Cipso-Cbridge distances are
shortened in comparison to
1 and the Cipso-N distances are
slightly elongated (Table 1). This is caused by two facts, which
are important for the structural features. On the one hand the
deprotonation of the central methylene moiety generates a
framework in
2 – 4 exhibits nearly no folding of the
free electron pair. Because of the adjacent conjugated
π-
heterocyclic residues. Additionally the metal ion is located in
the C3N2 plane of the central six-membered metalla
systems of the two benzoxazole units this free electron pair
tends to be delocalised over the whole ligand framework
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heterocycle without any significant deviation (see Table 2).
Only this arrangement facilitates total conjugation of the
whole anionic ligand. Due to the fourfold coordination of the
metal ion the methyl residues at that metal are aligned
perpendicularly with respect to the N1-M-N2 plane. This V-
shaped arrangement of the MMe2 fragments allows the
organometallic fragment to slot in between the methyl groups
of the ligand. The four methyl groups frame the group 13
metal to stay in plane (see Figure 6).
Table 2. Selected folding parameters for compounds 1 – 7.
folding angle [deg]
M-plane distance [Å]
1
2
3
-
-
3.721(20)
3.803(20)
0.0054(22)
0.0068(23)
4.925(122)
6.225(263)
0.0572(287)
0.1545(269)
4*
5
6
7
3.394(20)
3.042(16)
4.425(71)
0.0090(19)
0.0226(37)
0.0483(20)
* two values are given due to the discrepancy of the two
molecules within the unit cell.
In the row of the investigated group 13 metal complexes
2 – 4
of the bis-(4-methylbenzoxazol-2-yl)-methanide ligand some
clear trends from the obtained structural data could be
deduced (see Table 3):
•
The transannular N1ꢀꢀꢀN2 distance, which is indicative for
the size of the chelated metal atom, increases from over
to as expected, because the bigger the coordinated ion
is, the wider the chelating distance has to open.
2
Figure 3. Molecular structure of [Me2Al{(4-Me-NCOC6H3)2CH}] (2). Anisotropic
displacement parameters are depicted at the 50 % probability level. C-H hydrogen
atoms are omitted for clarity except the one at the bridging CH group. Structural data
are given in Tables 1 – 3.
3
4
•
•
Also the observed N-M distances are increasing according
to the increasing ionic radii of the Al3+, Ga3+ or In3+ ion,
respectively.
As a further consequence of this bond elongation and due
to the fact, that the metal stays in the ligand plane the
resulting N1-M-N2 bite angles are decreasing from
to
2 over 3
4
.
Figure 4. Molecular structure of [Me2Ga{(4-Me-NCO C6H3)2CH}] (3). Anisotropic
displacement parameters are depicted at the 50 % probability level. C-H hydrogen
atoms are omitted for clarity except the one at the bridging CH group. Structural data
are given in Tables 1 – 3.
Figure 6. Space filling models from different perspectives (left column: front view, right
column: bottom view) of the compared aluminium complexes 2 (top), [Me2Al{Dipp2-
nacnac}]13i (A) (middle) and [Al{Dipp2nacnac}]14e (B) (bottom).
Figure 5. Molecular structure of one molecule of [Me2In{(4-Me-NCOC6H3)2CH}] (4).
Anisotropic displacement parameters are depicted at the 50 % probability level. C-H
hydrogen atoms are omitted for clarity except the one at the bridging CH group.
Structural data are given in Tables 1 – 3.
4 | J. Name., 2012, 00, 1-3
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In Figure 6 compound 2 is exemplarily compared to the in Figure 6: by chelation of the two nitrogen donor atoms of
literature known nacnac derivatives [Me2Al{Dipp2nacnac}]13i the ligand the AlMe2 fragment is aligned in the C3N2 plane
) and [Al{Dipp2nacnac}]14e
(A (B) containing also the Al(III)Me2 without any significant deviation. This planarity is also
or Al(I) moiety, respectively. From the space filling model the supported by the ligand's methyl groups, which fit nearly
steric demand of each ligand can be visualised and provides a perfectly in between the pocket made up by the V-shaped
fair estimate of the shielding abilities around the metal atoms.
coordinated AlMe2 cation. So in comparison to
kinetic shielding considered from the bottom view is even
more pronounced. As opposed to this the side view of shows
that the planar arrangement of the complex leads to less steric
congestion from this point of view. The shielding abilities in
are not that embracing like in the case of and , so that still
A and B the
Table 3. Selected averaged bond lengths (Å) and angles (deg) for compounds 1 – 7.
2
N1···N2
N1/2–M
-
C15/16···M
-
N1–M–N2
-
2
1
2
3
4
5
6
7
A
B
3.5448(18)
2.8534(19)
2.9010(23)
3.0485(55)
2.8500(20)
2.8775(37)
2.8753(21)
2.870(4)
A
B
1.9400(14)
2.0043(15)
2.217(9)
1.9097(14)
1.909(2)
1.9140(16)
1.929(2)
1.958(2)
3.4478(19)
3.4474(22)
3.4805(167)
3.4736(19)
3.5380(25)
3.5341(22)
3.789(3)
94.68(6)
92.73(6)
86.89(14)
96.52(6)
97.84(12)
97.38(7)
96.18(9)
89.86(8)
beneficial, specific substitution reactions at the metal centre
can take place. This advantageous property is exploited by the
synthesis of 5 described in the following paragraph.
2.764(3)
3.606(3)
Starting with the crystal structure of the Al(I) species
B it is
evident, that the metal atom is located almost ideally within
the chelating C3N2 plane (Figure 6, bottom). The N,N’-
coordinated metal atom fits well into the pocket made up
from the four iPr groups of the Dipp substituents and the
carbon atoms in ortho-position of the associated phenyl rings.
Furthermore, these phenyl rings are nearly perpendicularly
aligned with respect to the C3N2 plane (89 ° and 91 °). The
ortho-carbon atoms provide the closest contact to the
aluminium atom (averaged 3.606 Å) and presumably are
equally important for the shielding of low-valent Al(I) species
(listed in column C15/16∙∙∙M in Table 3), because these
distances are located between the nacnac species and the
Scheme 3: Synthesis route for the mono halide substituted aluminium complexes 5 – 7.
Structural comparison of 5 – 7:
In addition to the dimethyl substituted group 13 metal
complexes
2 – 4 three Al(III) derivatives, in which one of the
methyl groups is replaced by a halide, were successfully
synthesised as well. This substitution is necessary to improve
the reactivity of those species compared to the relative high
stability of the dimethyl aluminium complexes. These reaction
products should facilitate the access to Al(I) or Al(II) species
upon reductive dehalogenation reactions.
complexes derived from 1. The bottom view also shows that
the aluminium atom is not exhaustively coordinated so that
coordination of the Lewis acidic site is facilitated. The side view
highlights the good shielding abilities of the iPr groups,
preventing the molecule from aggregation.
The synthesis of compounds
to the abovementioned dimethyl derivatives. To a solution of
the parent ligand in toluene the pure organometallic reagent
AlMe2Cl or AlEt2I, respectively, was added in a slight excess at
0 °C (Scheme 3, pathway a). Differently was prepared
starting from the metallated species by reaction with an
5 and 7 parallels the procedures
Continuing with the dimethyl aluminium species
structure clearly deviates from the reduced species
central six-membered metalla heterocycle is less planar than in
, because the AlMe2 unit is not located in the chelating C3N2
A
the crystal
1
B. The
6
B
2
plane. Furthermore, one of the two phenyl rings of the Dipp-
substituents is considerably twisted away from orthogonality
with respect to the C3N2 plane (112 °). This deviation is caused
by the additional methyl groups at the aluminium, which
increases the steric demand compared to the naked metal in
excess of trimethyl silyl iododide to prompt a methyl iodide
exchange at the metal atom (Scheme 3, pathway b).
Having a closer look at the geometrical data of those halide
substituted species
The derivatives (Figure 7) and
monoclinic space group P21/c each and the asymmetric unit
consists in both cases of one target molecule. Compound
5
–
7
following conclusions can be made:
5
7
(Figure 9) crystallise in the
B. The formed pocket in B is not appropriate in size to
accommodate the additional methyl groups. Instead of
retaining the perpendicular alignment of the Dipp-substituents
one of them is pushed away.
6
(Figure 8) crystallises in the orthorhombic space group Pbcm
and the asymmetric unit contains half a molecule.
As mentioned earlier the methyl substituents of the chelating
ligand in
2 adopt the shielding role of the Dipp residues of the
comparable nacnac complexes. This efficient shielding abilities
are visualised in the space filling model at the bottom view of
2
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Within the triple estimated standard deviations the values for
both species are the same, indicating that the slightly
enhanced steric demand in
7 due to the ethyl group instead of
a methyl group has no significant effect on those structural
features.
Figure 7. Molecular structure of [ClMeAl{(4-Me-NCOC6H3)2 CH}] (5). Anisotropic
displacement parameters are depicted at the 50 % probability level. C-H hydrogen
atoms are omitted for clarity except the one at the bridging CH group. Structural data
are given in Tables 1 – 3.
In the halogenated complexes the aluminium atom adopts also
the distorted tetrahedral coordination by means of the two
nitrogen donors and the remaining substituents at the metal
Figure 9. Molecular structure of [IEtAl{(4-Me-NCOC6H3)2 CH}] (7). Anisotropic
displacement parameters are depicted at the 50 % probability level. C-H hydrogen
atoms are omitted for clarity except the one at the bridging CH group. Structural data
are given in Tables 1 – 3.
atom. In direct comparison to the AlMe2 derivative
2 the N-Al
distances in 5 – 7 are increased and consequentially the
corresponding N-Al-N bite angle is widened (see Table 3).
Those observed changes are caused by the electron
withdrawing halide ligands Cl or I. These substituents increase
the partial positive charge at the metal atom due to the
negative inductive effect and their reduced electronegativity
compared to carbon. The substituted aluminium atom needs
less electron density from the donating nitrogen ring atoms
and the nitrogen Lewis donors are less attractive.
Conclusions
Within this work the successful syntheses and solid state
structure determinations of six metallated bis-(4-methylbenz-
oxazol-2-yl)-methanides
2 – 7 and the parent uncharged
methane derivative 1 could be presented. As a consequence of
tuning the previously reported bisheterocyclo methanes by
introducing methyl groups to the benzannulated heterocycles
(in this case benzoxazole) a promising ligand system for metal
complexation could be obtained, which exhibits a nearly
perfect planar coordination geometry concerning the ligand
side arms in all discussed solid state structures. This fact is
displayed by the small values in the folding angles between
both heteroaromatic planes and the just slight deviations of
the metal cations from the chelating C3N2 plane in each
complex, which is outstanding in the row of the previously
investigated methanide and amide complexes. The observed
arrangement in the solid state can be explained by the steric
strain induced by the additional methyl groups, which fit inside
the properly shaped pocket made up from the particular V-
shaped MR2 fragments, so that a kind of intramolecular
Figure 8. Molecular structure of [IMeAl{(4-Me-NCOC6H3)2 CH}] (6). Anisotropic
displacement parameters are depicted at the 50 % probability level. C-H hydrogen interlocking is responsible for the overall planar arrangement.
atoms are omitted for clarity except the one at the bridging CH group. Structural data
Due to the relatively pronounced inertness of the dimethyl
are given in Tables 1 – 3.
group 13 metal complexes the switch to the mono halide
substituted compounds
5 – 7 offers the access to low-valent
The influence of the present halide atom on specific binding
properties is displayed in Table 3. compared to shows the
bigger halide iodide to cause the transannular N1∙∙∙N2 distance
to increase by about 0.03 Å (2.8500 Å in vs. 2.8775 Å in ).
group 13 complexes, which hopefully can be obtained by
reductive salt elimination analogue to the synthesis route of
[Al{Dipp2nacnac}] or [Ga{Dipp2nacnac}]. The steric protection
around the metal centre resulting from the planar organic
ligand is quite efficient for kinetic stabilisation, but in the case
5
6
5
6
This widening of the coordination pocket is also displayed in
the bite angle, which also gets enlarged from 96.52 ° to
97.84 °. Predominantly the higher steric demand of the iodide
compared to the chloride accounts for the structural changes
in the ligand. The observed differences among the two iodide
of
2 the reaction with an excess of trimethyl silyl iodide
showed, that specific substitution reactions can still take place,
which is beneficial in contrast to the former nacnac
derivatives. Nevertheless, it is worth to mention, that even an
excess of TMSI does not lead to a dual halide substituted
derivatives
6 and 7 concerning those values are negligible.
6 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C5DT03913D
ARTICLE
derivative. Because of the beneficial planar arrangement of C4), 125.58 (s, 2 C, C5), 108.58 (s, 2 C, C3), 29.69 (s, 1 C, C1’),
the ligand system and the metal cation within the precursors 16.41 (s, 2 C, C15); δ15N{1H} (30 MHz, thf-d8): −135.9 (s); EI-MS,
2, 5 – 7
the generation of new Al(I) species is feasible. The m/z (%): 278 (100) [M]+, 146 (10) [M – NCOC7H6]+.
planar coordination geometry should enable optimal orbital
overlapping between the endocyclic nitrogen donors and the
Metallation reactions:
chelated future low-valent metal atom to obtain a more To a solution of the corresponding ligand
1 (1.00 eq.) in
efficient delocalisation. Further substitution and reduction toluene a slight excess of the pure organometallic reactant
attempts on aluminium containing complexes of this promising AlMe3, GaMe3, InMe3, AlMe2Cl or AlEt2I, respectively,
ligand system are under investigation.
(1.10 eq.) was slowly added at 0 °C. The reaction mixture was
stirred overnight and allowed to warm to rt. Afterwards the
volume of the solution was reduced to a few mL and the
Experimental Section
resulting concentrated solution stored at −32 °C in
a
refrigerator. Overnight crystals suitable for X-ray diffraction
experiments could be obtained. The crystals thus formed were
filtered, washed twice with pre-cooled toluene or hexane
(0 °C) and finally dried in vacuum. The given yields below are
just based on the received crystals unless stated otherwise. No
further improvement of the yields was attempted.
General Procedures:
All manipulations were carried out under an atmosphere of
dried and purified N2 or Ar by using Schlenk techniques.24 All
solvents used within metallation reactions were distilled from
Na or K prior to use. The starting materials were purchased
commercially and used as received. H, 13C, 15N and 27Al NMR
1
[Me2Al{(4-Me-NCOC6H3)2CH}] (2):
1 (4.66 g, 16.7 mmol,
spectroscopic data were recorded on
a Bruker Avance
1.00 eq.) dissolved in toluene (120 mL) and trimethyl
aluminium (1.80 mL, 1.33 g, 18.4 mmol, 1.10 eq.) were treated
like stated in the general procedure above. Yellow crystals
were obtained in a yield of 3.79 g (11.3 mmol, 68 %). Anal.
Calcd. for C19H19AlN2O2 (334.35 g/mol): C, 68.25; H, 5.73; N,
8.38. Found: C, 68.21; H, 6.18; N, 8.30; δ1H (500 MHz, thf-d8):
7.26 – 7.22 (m, 2 H, H3), 7.11 – 7.06 (m, 4 H, H4 + H5), 5.33 (s,
1 H, H1’), 2.66 (s, 6 H, H15), −0.38 (s, 6 H, H1M); δ13C{1H}
(125 MHz, thf-d8): 168.70 (s, 2 C, C1), 149.29 (s, 2 C, C2),
136.98 (s, 2 C, C7), 127.63 (s, 2 C, C5), 124.33 (s, 2 C, C6),
123.81 (s, 2 C, C4), 108.01 (s, 2 C, C3), 59.95 (s, 1 C, C1’), 19.51
(s, 2 C, C15), −3.86 (s, 2 C, C1M); δ15N{1H} (50 MHz, thf-
d8): −230.5 (s); δ27Al{1H} (130 MHz, thf-d8): 153 (s); EI-MS, m/z
(%): 334.1 (10) [M]+, 319.1 (64) [M − Me]+, 303.1 (5)
[M − 2 Me]+, 278.1 (100) [M – AlMe2]+.
500 MHz, Bruker Avance 400 MHz and a Bruker Avance
300 MHz spectrometer and referenced to the deuterated
solvent (thf-d8).25 Elemental analyses (C, H, N and S) were
carried out on a Vario EL3 at the Mikroanalytisches Labor,
Institut für Anorganische Chemie, University of Göttingen. All
EI-MS spectra (70 eV) were recorded on a Finnigan MAT 95.
(4-Me-NCOC6H3)2CH2 (1):
Method 1: 2-Amino-3-methylphenol (2.91 g, 23.6 mmol,
2.00 eq.) and ethylbisimidate dihydrochloride (2.73 g,
11.8 mmol, 1.00 eq.) were dissolved in methanol (55 mL). The
heating time of the reaction mixture was extended for reflux
overnight and after cooling to rt stored at −32 °C in a
refrigerator. The resulting crystalline material was filtered off,
washed with saturated aqueous NaHCO3 solution (3 x 50 mL)
and water (3 x 50 mL) and dried under reduced pressure.
Crystals suitable for X-ray diffraction experiments could be
obtained upon recrystallisation from toluene. Pale brown
crystals were obtained in a yield of 1.43 g (5.15 mmol, 44 %).
[Me2Ga{(4-Me-NCOC6H3)2CH}] (3):
1 (1.39 g, 5.00 mmol,
1.00 eq.) dissolved in toluene (25 mL) and trimethyl gallium
(0.56 mL, 632 mg, 5.50 mmol, 1.10 eq.) were treated like
stated in the general procedure above. Brownish yellow
crystals were obtained in a yield of 308 mg (0.82 mmol, 17 %;
not optimised). Anal. Calcd. for C19H19GaN2O2 (377.10 g/mol):
C, 60.52; H, 5.08; N, 7.43. Found: C, 60.84; H, 5.24; N, 7.45; δ1H
(400 MHz, thf-d8): 7.22 – 7.13 (m, 2 H, H3), 7.07 – 6.99 (m, 4 H,
H4 + H5), 5.18 (s, 1 H, H1’), 2.57 (s, 6 H, H15), 0.06 (s, 6 H,
H1M); δ13C{1H} (75 MHz, thf-d8): 167.84 (s, 2 C, C1), 149.20 (s,
2 C, C2), 137.57 (s, 2 C, C7), 127.27 (s, 2 C, C5), 123.60 (s, 2 C,
C6), 123.15 (s, 2 C, C4), 107.85 (s, 2 C, C3), 58.83 (s, 1 C, C1’),
19.01 (s, 2 C, C15), −0.95 (s, 2 C, C1M); δ15N{1H} (40 MHz, thf-
d8): −229.7 (s); EI-MS, m/z (%): 376.1 (17) [M]+, 361.0 (100)
[M − Me]+, 346.0 (20) [M − 2 Me]+, 277.1 (12) [M – GaMe2]+,
68.9 (41) Ga+.
Method 2:
A mixture of 2-amino-3-methylphenol (9.85 g,
80.0 mmol, 2.00 eq.) and malonic acid (4.16 g, 40.0 mmol,
1.00 eq.) was suspended in polyphosphoric acid (100 mL) with
the use of a sealed precision glass (KPG) stirrer. Under vigorous
stirring the reaction mixture was heated to 150 °C and the
resulting dark blue viscous solution was kept stirring at this
elevated temperature for 5 h. Then the solution was allowed
to cool to about 90 °C and poured over ice. The formed grey
solid was filtered off, washed several times with saturated
aqueous NaHCO3 solution (9 x 50 mL) and distilled water
(10 x 50 mL) to pH neutrality. Remaining solvent was
evaporated in vacuo to obtain
pale grey powder.
1 (6.26 g, 22.5 mmol, 56 %) as
[Me2In{(4-Me-NCOC6H3)2CH}] (4):
1 (278 mg, 1.00 mmol,
Anal. Calcd. for C17H14N2O2 (278.31 g/mol): C, 73.37; H, 5.07; N,
10.07. Found: C, 72.90; H, 5.14; N, 9.90; δ1H (300 MHz, thf-d8):
1.00 eq.) dissolved in toluene (60 mL) and trimethyl indium
(0.30 mL) were treated like stated in the general procedure
above. Because the used InMe3 solution had an unknown
concentration, no further statements regarding the
equivalents or yield can be made. Orange crystals were
obtained in a yield of 78 mg (0.18 mmol). Anal. Calcd. for
3
7.33 (d, JHH = 8.1 Hz, 2 H, H3), 7.20 (t, JHH = 7.8 Hz, 2 H, H4),
3
3
7.11 (d, JHH = 7.5 Hz, 2 H, H5), 4.68 (s, 2 H, H1’), 2.55 (s, 6 H,
H15); δ13C{1H} (75 MHz, thf-d8): 160.62 (s, 2 C, C1), 152.05 (s,
2 C, C2), 141.74 (s, 2 C, C7), 131.32 (s, 2 C, C6), 125.62 (s, 2 C,
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
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ARTICLE
Journal Name
Table 4. Crystal structure data for 1 – 7.
1
2
C19H19AlN2O2
334.35
1429357
0.71073
monoclinic
P21/c
3
C19H19GaN2O2
377.10
1429403
0.56086
monoclinic
P21/c
4
C19H19InN2O2
422.18
1429339
0.56086
monoclinic
Pn
5
C18.1H16.3AlCl0.9N2O2
352.59
6
7
Formula
C17H14N2O2
278.31
C18H16AlIN2O2
446.21
1429342
0.56086
orthorhombic
Pbcm
C19H18AlIN2O2
460.23
1429343
0.71073
monoclinic
P21/c
Mol. w., g mol−1
CCDC no.
Wavelength, Å
Crystal system
Space group
a, Å
1429338
0.71073
triclinic
1429341
0.56086
monoclinic
P21/c
ꢁ
P1
4.741(2)
11.471(3)
13.084(3)
79.15(2)
85.84(2)
78.19(2)
683.6(4)
2
8.029(2)
14.773(3)
14.072(3)
90
7.986(2)
14.852(3)
14.087(3)
90
15.629(3)
7.894(2)
15.631(3)
90
7.982(2)
14.727(3)
13.890(2)
90
8.015(2)
13.868(3)
15.566(3)
90
9.102(3)
7.647(2)
26.711(4)
90
b, Å
c, Å
α, deg
β, deg
90.03(2)
90
90.12(2)
90
117.04(2)
90
91.73(2)
90
90
96.59(2)
90
γ, deg
V, Å3
90
1669.1(6)
4
1670.81(9)
4
1717.7(7)
4
1632.0(6)
4
1730.2(6)
4
1846.9(8)
4
Z
Refl. measured
Refl. unique
R1 [I>2σ(I)]a
wR2 (all refl.)b
Rint
Abs. stru. para.26
Δρfin, e Å−3
23615
57930
45271
49033
20579
25400
38660
2495
3060
3069
8534
2904
1915
4398
0.0364
0.0938
0.0369
-
0.0306
0.0868
0.0384
-
0.0248
0.0672
0.0445
-
0.0248
0.0546
0.0481
0.11(4)
0.334 / −0.463
0.0322
0.0222
0.0542
0.0431
-
0.0210
0.0534
0.0231
-
0.0885
0.0370
-
0.170 / −0.162
0.222 / −0.323
0.386 / −0.372
0.206 / −0.314
0.502 / −0.894
0.730 / −0.406
2
w(Fo2 − Fc2
)
c
1
(
Fo2 + 2Fc2
)
Fo − F
∑
∑
wR2 =
R1=
; w =
; P =
.
w(Fo2
)
2
2
a
b
σ2
(
Fo2
)
+
(
g1P
)
+ g2P
3
Fo
∑
∑
C19H19InN2O2 (422.18 g/mol): C, 54.05; H, 4.54; N, 6.64. Found: reduced pressure. The mono iodide substituted derivative
C, 54.52; H, 4.92; N, 6.70; δ1H (500 MHz, thf-d8): 7.18 – 7.13 could be isolated as a brown powder (111 mg, 0.25 mmol,
(m, 2 H, H3), 7.00 – 6.95 (m, 4 H, H4 + H5), 5.12 (s, 1 H, H1’), 25 %). After recrystallization from toluene also crystals suitable
2.54 (s, 6 H, H15), 0.13 (s, 6 H, H1M); δ13C{1H} (125 MHz, thf- for structure determination were obtained. Calcd. for
d8): 168.36 (s, 2 C, C1), 148.95 (s, 2 C, C2), 139.27 (s, 2 C, C7), C18H16AlIN2O2 (446.22 g/mol): C, 48.45; H, 3.61; N, 6.28. Found:
126.58 (s, 2 C, C5), 122.94 (s, 2 C, C6), 122.66 (s, 2 C, C4), C, 45.53; H, 3.32; N, 6.07 (deviation due to slight
107.81 (s, 2 C, C3), 59.07 (s, 1 C, C1’), 18.59 (s, 2 C, C15), −2.91 contamination with the AlI2 derivative); δ1H (300 MHz, thf-d8):
(s, 2 C, C1M); δ15N{1H} (50 MHz, thf-d8): −226.2 (s).
[ClMeAl{(4-Me-NCOC6H3)2CH}] (5):
(1.39 g, 5.00 mmol, 1 H, H1’), 2.77 (s, 6 H, H15), −0.47 (s, 3 H, H1M); δ13C{1H}
7.29 – 7.25 (m, 2 H, H3), 7.14 – 7.10 (m, 4 H, H4 + H5), 5.47 (s,
1
1.00 eq.) dissolved in toluene (35 mL) and dimethyl aluminium (125 MHz, thf-d8): 168.90 (s, 2 C, C1), 149.13 (s, 2 C, C2),
chloride (0.51 mL, 509 mg, 5.50 mmol, 1.10 eq.) were treated 136.66 (s, 2 C, C7), 127.72 (s, 2 C, C5), 125.12 (s, 2 C, C6),
like stated in the general procedure above. A pale yellow 124.11 (s, 2 C, C4), 108.05 (s, 2 C, C3), 60.58 (s, 1 C, C1’), 18.88
powder was obtained in a yield of 1.37 g (3.9 mmol, 77 %). (s, 2 C, C15), −6.83 (s, 1 C, C1M); δ15N{1H} (50 MHz, thf-
Anal. Calcd. for C18H16AlClN2O2 (354.77 g/mol): C, 60.94; H, d8): −230.8 (s); EI-MS, m/z (%): 278 (100) [M − AlMeI]+, 146
4.55; N, 7.90. Found: C, 60.99; H, 4.57; N, 8.17; δ1H (400 MHz, (37) [M − AlMeI – NCOC7H6]+, 132 (9) [NCOC7H6]+.
thf-d8): 7.33 – 7.27 (m, 2 H, H3), 7.17 – 7.11 (m, 4 H, H4 + H5), [IEtAl{(4-Me-NCOC6H3)2CH}] (7): To a solution of
1 (1.39 g,
5.55 (s, 1 H, H1’), 2.78 (s, 6 H, H15), −0.14 (s, 3 H, H1M); 5.00 mmol, 1.00 eq.) dissolved in toluene (80 mL) and
δ13C{1H} (125 MHz, thf-d8): 168.67 (s, 2 C, C1), 149.14 (s, 2 C, diethylaluminium iodide (0.73 mL, 1.17 g, 5.50 mmol, 1.10 eq.)
C2), 136.07 (s, 2 C, C7), 128.02 (s, 2 C, C5), 125.05 (s, 2 C, C6), were treated like stated in the general procedure above.
124.54 (s, 2 C, C4), 108.24 (s, 2 C, C3), 61.18 (s, 1 C, C1’), 19.93 Orange crystals were obtained in a yield of 1.16 g (2.52 mmol,
(s, 2 C, C15), −3.68 (s, 1 C, C1M); δ15N{1H} (50 MHz, thf- 50 %; not optimised). Calcd. for C19H18AlIN2O2 (460.24 g/mol):
d8): −246.9 (s); δ27Al{1H} (78 MHz, thf-d8): 128 (s); EI-MS, m/z C, 49.58; H, 3.94; N, 6.09. Found: C, 49.35; H, 4.02; N, 6.09; δ1H
(%): 278 (100) [M − AlMeCl]+, 146 (45) [M − AlMeCl – (400 MHz, thf-d8): 7.29 – 7.24 (m, 2 H, H3), 7.14 – 7.11 (m, 4 H,
NCOC7H6]+, 132 (8) [NCOC7H6]+.
H4 + H5), 5.46 (s, 1 H, H1’), 2.79 (s, 6 H, H15), 0.85 (t,
3
[IMeAl{(4-Me-NCOC6H3)2CH}] (6): To a solution of
2
(334 mg, 3JHH = 8.2 Hz, 3 H, H2M), 0.21 (q, JHH = 8.2 Hz, 2 H, H1M);
1.00 mmol, 1.00 eq.) in toluene (20 mL) was added δ13C{1H} (75 MHz, thf-d8): 169.09 (s, 2 C, C1), 149.12 (s, 2 C,
trimethylsilyl iodide (0.31 mL, 440 mg, 2.20 mmol, 2.20 eq.). C2), 136.72 (s, 2 C, C7), 127.73 (s, 2 C, C5), 125.15 (s, 2 C, C6),
The reaction mixture was heated to reflux temperature and 124.10 (s, 2 C, C4), 108.05 (s, 2 C, C3), 60.52 (s, 1 C, C1’), 18.74
stirred for additional 3.5 d at reflux. The formed precipitate (s, 2 C, C15), 8.66 (s, 1 C, C2M), 3.13 (s, 1 C, C1M); δ15N{1H}
was filtered off and residual solvent was removed under (40 MHz, thf-d8): −232.3 (s); EI-MS, m/z (%): 278 (100)
8 | J. Name., 2012, 00, 1-3
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[M − AlEtI]+, 146 (41) [M − AlEtI – NCOC7H6]+, 132 (7)
[NCOC7H6]+.
G. Kehr, K. Bergander, B. Wibbeling, R. Fröhlich and G.
Erker, Dalton Trans., 2009, 1534-1541; c) G. C. Welch, R. R.
S. Juan, J. D. Masuda and D. W. Stephan, Science, 2006,
314, 1124-1126.
X-ray Crystallographic Studies
4. G. C. Welch, J. D. Masuda and D. W. Stephan, Inorg. Chem.,
2006, 45, 478-480.
5. C. Appelt, J. C. Slootweg, K. Lammertsma and W. Uhl,
Angew. Chem., 2013, 52, 4256-4259; Angew. Chem. Int.
Ed., 2013, 52, 4256-4259.
Single crystals were selected from a Schlenk flask under argon
or nitrogen atmosphere and covered with perfluorinated
polyether oil on a microscope slide, which was cooled with a
nitrogen gas flow using the X-TEMP2 device.27 An appropriate
crystal was selected using a polarise microscope, mounted on
the tip of a MiTeGen©MicroMount or glass fibre, fixed to a
goniometer head and shock cooled by the crystal cooling
6. Y. Zhang, G. M. Miyake and E. Y. X. Chen, Angew. Chem.,
2010, 122, 10356-10360; Angew. Chem. Int. Ed., 2010, 49,
10158-10162.
7. a) G. Ménard and D. W. Stephan, Angew. Chem., 2011, 123
,
8546-8549; Angew. Chem. Int. Ed., 2011, 50, 8396-8399; b)
G. Ménard and D. W. Stephan, J. Am. Chem. Soc., 2010,
132, 1796-1797.
device. The data for
crystals at 100(2) K. The data of
an Incoatec Mo Microsource28 and compounds
1
−
7
were collected from shock-cooled
and were collected on
were
1,
2
7
3−6
8. L. Bourget-Merle, M. F. Lappert and J. R. Severn, Chem.
Rev., 2002, 102, 3031-3065.
collected on an Incoatec Ag Microsource,29 each equipped with
mirror optics and APEX II detector with a D8 goniometer. All
diffractometers were equipped with a low-temperature device
and used either MoKα radiation of λ = 0.71073 Å or AgKα
radiation of λ = 0.56086 Å. The data were integrated with
Saint30 and an semi-empirical absorption correction (Sadabs)29
was applied. The structures were solved by direct methods
(Shelxt)31 and refined by full-matrix least-squares methods
against F2 (Shelxl2014).32 All non-hydrogen-atoms were refined
with anisotropic displacement parameters. The hydrogen
atoms were refined isotropically on calculated positions using
a riding model with their Uiso values constrained to equal to 1.5
times the Ueq of their pivot atoms for terminal sp3 carbon
atoms and 1.2 times for all other carbon atoms. Disordered
moieties were refined using bond lengths restraints and
isotropic displacement parameter restraints. The positions of
the amine hydrogen atoms are taken from the difference
Fourier map and refined freely.
9. a) J. Overgaard, C. Jones, A. Stasch and B. B. Iversen, J. Am.
Chem. Soc., 2009, 131, 4208-4209; b) M. Westerhausen,
Angew. Chem., 2008, 120, 2215-2217; Angew. Chem. Int.
Ed., 2008, 47, 2185-2187; c) S. P. Green, C. Jones and A.
Stasch, Science, 2007, 318, 1754-1757.
10. a) C. Ruspic and S. Harder, Inorg. Chem., 2007, 46, 10426-
10433; b) S. Harder, Organometallics, 2002, 21, 3782-3787.
11. D. F. J. Piesik, S. Range and S. Harder, Organometallics,
2008, 27, 6178-6187.
12. J. Spielmann, F. Buch and S. Harder, Angew. Chem., 2008,
120, 9576-9580; Angew. Chem. Int. Ed., 2008, 47, 9434-
9438.
13. a) Y. Cheng, D. J. Doyle, P. B. Hitchcock and M. F. Lappert,
Dalton Trans., 2006, 4449-4460; b) S. Singh, H.-J. Ahn, A.
Stasch, V. Jancik, H. W. Roesky, A. Pal, M. Biadene, R.
Herbst-Irmer, M. Noltemeyer and H.-G. Schmidt, Inorg.
Chem., 2006, 45, 1853-1860; c) Z. Yang, H. Zhu, X. Ma, J.
Chai, H. W. Roesky, C. He, J. Magull, H.-G. Schmidt and M.
Noltemeyer, Inorg. Chem., 2006, 45, 1823-1827; d) N.
Kuhn, S. Fuchs and M. Steimann, Z. Anorg. Allg. Chem.,
2002, 628, 458-462; e) N. Kuhn, S. Fuchs and M. Steimann,
Eur. J. Inorg. Chem., 2001, 2001, 359-361; f) M. Stender, B.
E. Eichler, N. J. Hardman, P. P. Power, J. Prust, M.
Crystallographic data for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Data
Centre. The CCDC numbers, crystal data and experimental
details for the X-ray measurements are listed in the ESI. Copies
of the data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif or from the corresponding author.
Noltemeyer and H. W. Roesky, Inorg. Chem., 2001, 40
2794-2799; g) N. Kuhn, J. Fahl, S. Fuchs, M. Steimann, G.
Henkel and A. H. Maulitz, Z. Anorg. Allg. Chem., 1999, 625
,
,
2108-2114; h) C. E. Radzewich, I. A. Guzei and R. F. Jordan,
J. Am. Chem. Soc., 1999, 121, 8673-8674; i) B. Qian, D. L.
Ward and M. R. Smith, Organometallics, 1998, 17, 3070-
3076.
14. a) S. Nagendran and H. W. Roesky, Organometallics, 2008,
27, 457-492; b) X. Li, X. Cheng, H. Song and C. Cui,
Organometallics, 2007, 26, 1039-1043; c) H. W. Roesky and
S. S. Kumar, Chem. Commun., 2005, 4027-4038; d) M. N.
Sudheendra Rao, H. W. Roesky and G. Anantharaman, J.
Organomet. Chem., 2002, 646, 4-14; e) C. Cui, H. W.
Roesky, H.-G. Schmidt, M. Noltemeyer, H. Hao and F.
Cimpoesu, Angew. Chem., 2000, 112, 4444-4446; Angew.
Chem. Int. Ed., 2000, 39, 4274-4276.
Acknowledgements
Thanks to the Danish National Research Foundation (DNRF93)
funded Center for Materials Crystallography (CMC) for partial
support and the Land Niedersachsen for providing a fellowship
in the GAUSS PhD program.
15. N. J. Hardman, B. E. Eichler and P. P. Power, Chem.
Commun., 2000, 1991-1992.
16. a) P. Hao, Z. Yang, W. Li, X. Ma, H. W. Roesky, Y. Yang and J.
Li, Organometallics, 2015, 34, 105-108; b) B. Li, C. Zhang, Y.
Notes and references
The authors declare no competing financial interest.
Yang, H. Zhu and H. W. Roesky, Inorg. Chem., 2015, 54
6641-6646; c) Z. Yang, M. Zhong, X. Ma, S. De, C. Anusha, P.
Parameswaran and H. W. Roesky, Angew. Chem., 2015,
127, 10363-10367.; Angew. Chem. Int. Ed., 2015, 54
10225-10229; d) Y. Yang, H. Li, C. Wang and H. W. Roesky,
Inorg. Chem., 2012, 51, 2204-2211.
,
1. P. P. Power, Nature, 2010, 463, 171-177.
2. a) D. W. Stephan, Organic & Biomolecular Chemistry, 2008,
6
, 1535-1539; b) W. Tochtermann, Angew. Chem., 1966,
355-375.; Angew. Chem. Int. Ed. Engl., 1966, , 351-371; c)
G. Wittig and E. Benz, Chem. Ber., 1959, 92, 1999-2013.
3. a) D. W. Stephan and G. Erker, Angew. Chem., 2010, 122
7,
,
5
,
50-81; Angew. Chem. Int. Ed., 2010, 49, 46-76; b) P. Spies,
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
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Dalton Transactions
Page 10 of 10
View Article Online
DOI: 10.1039/C5DT03913D
ARTICLE
Journal Name
17. a) Z. Zhu, X. Wang, Y. Peng, H. Lei, J. C. Fettinger, E. Rivard
and P. P. Power, Angew. Chem., 2009, 121, 2065-2068;
Angew. Chem. Int. Ed., 2009, 48, 2031-2034; b) R. J. Wright,
M. Brynda and P. P. Power, Angew. Chem., 2006, 118
,
6099-6102; Angew. Chem. Int. Ed., 2006, 45, 5953-5956; c)
R. J. Wright, A. D. Phillips, S. Hino and P. P. Power, J. Am.
Chem. Soc., 2005, 127, 4794-4799; d) N. J. Hardman, R. J.
Wright, A. D. Phillips and P. P. Power, Angew. Chem., 2002,
114, 2966-2968; Angew. Chem. Int. Ed., 2002, 41, 2842-
2844; e) J. Su, X.-W. Li, R. C. Crittendon and G. H. Robinson,
J. Am. Chem. Soc., 1997, 119, 5471-5472.
18. D.-R. Dauer and D. Stalke, Dalton Trans., 2014, 43, 14432-
14439.
On the basis of the deprotonated bis-(4-methylbenzoxazol-2-yl)-methane ligand 1 a
19. D.-R. Dauer, M. Flügge, R. Herbst-Irmer and D. Stalke, series of group 13 metal complexes was synthesised and fully characterised. The
Dalton Trans., 2015, submitted
.
detailed comparison of the solid state structures demonstrates clearly the similarity of
20. a) F. Baier, Z. Fei, H. Gornitzka, A. Murso, S. Neufeld, M. the methanide and the omnipresent nacnac ligand, suggesting this ligand system as a
Pfeiffer, I. Rüdenauer, A. Steiner, T. Stey and D. Stalke, J. promising candidate to stabilise metals in low oxidation states.
Organomet. Chem., 2002, 661, 111-127; b) H. Gornitzka
and D. Stalke, Angew. Chem., 1994, 106, 695-698; Angew.
Chem. Int. Ed. Engl., 1994, 33, 693-695; c) H. Gornitzka and
D. Stalke, Organometallics, 1994, 13, 4398-4405.
21. W. W. Schoeller, Inorg. Chem., 2011, 50, 2629-2633.
22. H. Ben Ammar, J. Le Nôtre, M. Salem, M. T. Kaddachi and P.
H. Dixneuf, J. Organomet. Chem., 2002, 662, 63-69.
23. a) P. Müller, R. Herbst-Irmer, A. L. Spek, T. R. Schneider and
M. R. Sawaya, Crystal Structure Refinement
A
Crystallographer's Guide to SHELXL, Oxford University
Press, New York, 2006; b) P. Rademacher, Strukturen
organischer Moleküle, VCH, Weinheim, 1987.
24. Georg-August-Universität Göttingen, Virtuelles Labor,
http://www.stalke.chemie.uni-
goettingen.de/virtuelles_labor/advanced/13_de.html
.
25. Georg-August-Universität Göttingen, Virtuelles Labor,
http://www.stalke.chemie.uni-
goettingen.de/virtuelles_labor/nmr/de.html
.
26. S. Parsons, H. D. Flack and T. Wagner, Acta Crystallogr.,
Sect. B, 2013, 69, 249-259.
27. a) D. Stalke, Chem. Soc. Rev., 1998, 27, 171-178; b) T.
Kottke, R. J. Lagow and D. Stalke, J. Appl. Crystallogr., 1996,
29, 465-468; c) T. Kottke and D. Stalke, J. Appl. Crystallogr.,
1993, 26, 615-619; d) Georg-August-Universität Göttingen,
Virtuelles
goettingen.de/virtuelles_labor/special/22_de.html
Labor,
http://www.stalke.chemie.uni-
.
28. T. Schulz, K. Meindl, D. Leusser, D. Stern, J. Graf, C.
Michaelsen, M. Ruf, G. M. Sheldrick and D. Stalke, J. Appl.
Crystallogr., 2009, 42, 885-891.
29. L. Krause, R. Herbst-Irmer, G. M. Sheldrick and D. Stalke, J.
Appl. Crystallogr., 2015, 48, 3-10.
30. Bruker AXS Inc., in Bruker Apex CCD, SAINT v8.30C, ed.
Bruker AXS Inst. Inc., WI, USA, Madison, 2013.
31. G. Sheldrick, Acta Crystallogr., Sect. A, 2015, 71, 3-8.
32. a) G. Sheldrick, Acta Crystallogr., Sect. C, 2015, 71, 3-8; b)
G. M. Sheldrick, Acta Crystallogr., Sect. A, 2014, 70, C1437;
c) G. M. Sheldrick, Acta Crystallogr., Sect. A, 2008, 64, 112-
122.
10 | J. Name., 2012, 00, 1-3
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