Organoelement complexes of a dinucleating double β-diiminato ligand - Precedent cases from groups 1, 2, and 13

Article abstract of DOI:10.1002/zaac.201100352

Main group chemistry of dinucleating ligands based on a xanthene backbone and two parallel diiminato binding sites (Xanthdim) has been investigated. To complement studies concerning the coordination modes adopted by Xanthdim in combination with alkali metal ions a di-rubidium complex with toluene co-ligands has been prepared. Its structural parameters lie in between those previously observed for corresponding K⁺ and Cs⁺ complexes. Furthermore, the complexes [ Me 2C 6H 3Xanthdim](MgMe(thf))₂ (2) and [ Me 2C 6H 3Xanthdim](MgBr(thf))₂ (3) were synthesised by reaction of [ Me 2C 6H 3Xanthdim](K(thf)₂)₂ and [ Me 2C 6H 3Xanthdim]H₂, respectively, with MeMgBr. Both compounds proved stable against ligand exchange according to the Schlenk equilibrium. After reaction of [ Me 2C 6H 3Xanthdim]H₂ and [ F 2C 6H 3Xanthdim]H₂, respectively, with AlMe₃ the complexes [ Me 2C 6H 3Xanthdim](AlMe₂)₂ (4) and [ F 2C 6H 3Xanthdim](AlMe ₂)₂ (5) were isolated and fully characterised. They were found to be dynamic in solution and Al-CH₃...F-aryl interactions were detected in case of 5. The solid-state structures and NMR spectroscopic properties of all compounds were determined and analysed. Copyright

Full text of DOI:10.1002/zaac.201100352

ARTICLE
DOI: 10.1002/zaac.201100352
Organoelement Complexes of a Dinucleating Double β-Diiminato Ligand –
Precedent Cases from Groups 1, 2, and 13
Jan P. Falkenhagen,[a] Peter Haack,[a] Christian Limberg,*[a] and Beatrice Braun[a]
In Memory of Professor Kurt Dehnicke
Keywords: Rubidium; Aluminium; Magnesium; Coordination chemistry; Dinuclear complexes; Main group chemistry
Abstract. Main group chemistry of dinucleating ligands based on a with MeMgBr. Both compounds proved stable against ligand exchange
xanthene backbone and two parallel diiminato binding sites according to the Schlenk equilibrium. After reaction of
Me2C6H3
F2C6H3
(Xanthdim) has been investigated. To complement studies concerning
the coordination modes adopted by Xanthdim in combination with al-
kali metal ions a di-rubidium complex with toluene co-ligands has
[
Xanthdim]H2 and
[
Xanthdim]H2, respectively, with
Xanthdim](AlMe2)2 (4) and
Me2C6H3
AlMe3 the complexes
[
F2C6H3
[
Xanthdim](AlMe2)2 (5) were isolated and fully characterised.
been prepared. Its structural parameters lie in between those previously They were found to be dynamic in solution and Al–CH3···F-aryl inter-
observed for corresponding K+ and Cs+ complexes. Furthermore, the
actions were detected in case of 5. The solid-state structures and NMR
and spectroscopic properties of all compounds were determined and ana-
Xanthdim](MgBr(thf))2 (3) were synthesised by reaction of lysed.
Me2C6H3
complexes
[
Xanthdim](MgMe(thf))2
(2)
Me2C6H3
[
[
Xanthdim](K(thf)2)2 and [Me C H Xanthdim]H2, respectively,
Me2C6H3
2
6 3
Introduction
β-Diketiminates (Scheme 1) have proved versatile ligand sys-
tems, both, in main group and transition metal chemistry. They
stabilise high as well as low oxidation states, and they can also
be employed for the synthesis of coordinatively unsaturated
complexes, which often show interesting reactivities.[1–25]
Scheme 2. The ligand precursors [Me C H Xanthdim]H2 (left) and
2
6 3
F2C6H3
[
Xanthdim]H2 (right).
In their deprotonated forms they have been employed suc-
cessfully as ligands in transition metal chemistry, including di-
nuclear organozinc complexes that were investigated as epox-
ide/CO2 copolymerisation catalysts,[27] diiron(II) complexes
that proved to react with O2 to give FeIII–O–FeIII com-
pounds,[28] and a dicopper(I) complex, which activates O2 in-
volving a highly unusual CuII–O–CuII species.[29] Furthermore,
an unprecedented binding and activation of CS2 was realised
by a dicopper(I) complex.[30] Recently, these studies were ex-
tended to alkali and alkaline-earth metal chemistry for various
reasons:[31] First, alkali metal complexes represent valuable
starting materials in the synthesis of transition metal com-
plexes via salt metathesis, and we were interested, whether any
structural differences occur on going from lithium to the higher
homologues. Moreover, the questions arose, whether hetero-
leptic bimetallic complexes, [Xanthdim](MR)2, are stable
against ligand exchange through the Schlenk equilibrium and
whether they can be employed as polymerisation catalysts. Ini-
tial work included the successful synthesis and characterisation
Scheme 1.
As these reactivities are often based on the cooperation of
two metal centres, we have synthesised two ligand precursors
where two β-diiminato units are oriented parallel to each other:
[RXanthdim]H2 (Scheme 2) with R = 2,3-dimethylphenyl or
2,4-difluorophenyl.[26,27]
* Prof. Dr. C. Limberg
Fax: +49-30-2093-6966
E-Mail: christian.limberg@chemie.hu-berlin.de
[a] Humboldt-Universität zu Berlin
Institut für Chemie
Brook-Taylor-Str. 2
12489 Berlin, Germany
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J. P. Falkenhagen, P. Haack, C. Limberg, B. Braun
ARTICLE
Scheme 3. Synthesis of 1(tol)2 (R = 2,3-dimethylphenyl).
of lithium, potassium, caesium, magnesium and calcium com- β-diiminato units are doubly bridged by the two Rb+ ions,
plexes (whereas the second valences of magnesium and cal- which complete their coordination spheres by interactions with
cium were saturated by amido and diiminato ligands, respec- the central oxygen atom of the xanthene-based backbone and
tively).[31]
by toluene ligands binding in a η6 mode. The Rb···Rb distance
The research described here expands these investigations to of 6.0492(5) Å lies exactly between the distances of the corre-
organometallic chemistry of the elements rubidium and mag- sponding dinuclear potassium (5.662(1) Å) and caesium
nesium. Moreover, for the first time a group 13 element, (6.284(2) Å) complexes.[31] As found for the molecular struc-
namely aluminium, has been included, as the Xanthdim ligand tures of those, also in the structure of 1(tol)2·2(tol) each metal
matrix may also be expected to support the cooperation of two ion binds to the β-diiminato units with one short (Rb1–
aluminium atoms in polymerisation catalysis.
N3: 2.854(2) Å and Rb2–N1: 2.868(2) Å) and one long (Rb1–
N2: 3.01(2) Å and Rb2–N4: 2.924(2) Å) contact. The C–N and
C–C distances within the binding pockets match the ones de-
termined for the potassium and caesium complex, respectively,
quite well, too.
Results and Discussion
Group 1 Organometallics: Coordination of Rubidium Ions
with Toluene Co-Ligands
Addition of RbOtBu·0.81tBuOH to
a
solution of
Me2C6H3
[
Xanthdim]H2 in thf caused a rapid colour change from
yellow to orange indicating a spontaneous deprotonation of the
ligand precursor. Subsequent addition of excessive hexane to
a concentrated solution of the product in toluene led to the
precipitation of [Me C H Xanthdim](Rb(tol))2 (1(tol)2, Scheme
3). It is noteworthy that the toluene molecules coordinated to
the rubidium ions can be removed completely in vacuo, re-
2
6 3
sulting in [Me C H Xanthdim](Rb)2 (1), which could be isolated
in 81% yield. Complex 1 is readily soluble in benzene, tolu-
ene, thf and dichloromethane; stability in dichloromethane is
clearly limited, though, due to the not unexpected reactivity of
1 against halogenated solvents. However, NMR spectroscopic
characterisation of a [D2]dichloromethane solution was off-
2
6 3
Figure 1. Molecular structure of 1(tol)2 co-crystallised with two mole-
cules of toluene. All hydrogen atoms and solvent molecules were omit-
ted for clarity. Selected bond lengths in Å and angles in deg: Rb1···Rb2
6.0492(5), Rb1–N2 3.01(2), Rb1–N3 2.854(2), Rb2–N1 2.868(2),
Rb2–N4 2.924(2), Rb1–O1 3.0503(18), Rb2–O1 3.0530(18),
Rb1···Arcentre 3.1407(3), Rb2···Arcentre 3.1599(3), N1–C9 1.309(4),
C9–C10 1.401(4), C10–C11 1.409(4), N2–C11 1.308(4), N3–C28
1.312(4), C27–C28 1.399(4), C27–C37 1.410(4), N4–C37 1.310(4),
Rb1–O1–Rb2 164.74(7), N3–Rb1–N2 111.03(6), N3–Rb1–O1
68.75(6), N3–Rb1–Arcentre 149.16(5), N1–Rb2–N4 109.15(7), N1–
Rb2–O1 64.53(6), N1–Rb2–Arcentre 138.79(5).
1
handedly possible, and the H NMR spectrum showed charac-
teristics that confirmed the quantitative formation of
Me2C6H3
[
[
Xanthdim]2– and thus a complete conversion of
Me2C6H3
Xanthdim]H2 to 1: a singlet resonance at δ = 7.84 ppm
for the diiminato protons instead of a doublet (as observed in
case of [Me C H Xanthdim]H2), and the absence of the signal at
around 12 ppm corresponding to the acidic NH protons of the
ligand precursor.
2
6 3
A First Organoelement Representative from Group 2:
Methyl Magnesium Chemistry
Crystals of 1(tol)2·2(tol) suitable for single-crystal X-ray dif-
fraction analysis could be obtained by slow evaporation of the
solvent from a concentrated solution of 1 in toluene at room
Having confirmed the stability of a dinuclear amido magne-
temp. The molecular structure is shown in Figure 1. As re- sium Xanthdim complex against ligand exchange through the
cently reported for dinuclear potassium as well as caesium Schlenk equilibrium[32–34] in a previous study[31] we now fo-
complexes of the [Me C H Xanthdim]2– ligand,[31] also in 1(tol)2· cused on the investigation of an analogous species coordinated
2(tol) the β-diiminato binding pockets have a W-conformation. by alkyl functionalities. Corresponding mononuclear com-
This is not surprising since the ion radius of Rb+ (148 pm) lies plexes bearing β-diketiminato ligands were shown to be ac-
between the radii of K+ (133 pm) and Cs+ (167 pm). The two cessible via two different routes: either by direct reaction be-
2
6 3
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Organoelement Complexes of a Dinucleating Double β-Diiminato Ligand
tween the ligand precursor [Me
L
iPr]H (Me2LiPr = CH{(CMe) plex molecules under discussion; the sites affected by substitu-
2
(2,6-iPr2C6H3N)}2) and Me2Mg[35] or by deprotonation with tional disorder are occupied randomly by -Me and -Br ligands
the aid of an external base (nBuLi) followed by treatment of with no disturbance of the crystal lattice. Occurrence of this
Me2
the resulting lithium β-diketiminate,
[
L
iPr]Li, with solid solution can be explained principally by an anion ex-
MeMgCl.[36]
change between 2 and KBr, formed as a by-product, or by a
Following the latter strategy, but with KH instead of nBuLi Schlenk equilibrium between [Me C H Xanthdim](MgMe(thf))2
2
6 3
as the deprotonation agent, we set out, reacting (2) and unreacted MeMgBr. However, a solution of 2 does not
Me2C6H3
Xanthdim]H2 with KH in thf to access readily react to give [Me C H Xanthdim](MgBr(thf))2 (3) either
2
6 3
[
[
Me2C6H3
Xanthdim](K(thf)2)2 as described previously.[31] Sub- on addition of KBr or MeMgBr as evidenced by NMR spec-
sequent treatment of this solution with MeMgBr in thf caused troscopy. We therefore assume that this transformation takes
an immediate colour change from orange to yellow ac- place very slowly during the crystallisation process, where ob-
companied by a clouding of the reaction mixture. After workup viously small amounts of bromide were present. However, we
Me2C6H3
[
Xanthdim](MgMe(thf))2 (2) could be isolated as an did not repeat crystallisation with rigorously purified 2 as the
orange solid in 71% yield (Scheme 4). The 1H NMR spectrum adequate treatment of the data collection revealed the complete
recorded for a [D2]dichloromethane solution showed the com- structural information. The molecular structure of one of the
plete set of signals expected for [Me C H Xanthdim] . The ab- independent molecules in the asymmetric unit of the solid
sence of a signal at around 12 ppm again indicated successful solution is shown in Figure 2.
deprotonation of the precursor. Moreover, a singlet at
2–
2
6 3
–1.54 ppm corresponding to the six protons of the Mg bound
methyl groups ensured selective formation of 2.
Figure 2. Molecular structure of one of the independent molecules in
the asymmetric unit of the solid solution involving 2 co-crystallised
with 0.5 molecules of thf and 0.25 molecules of hexane. All hydrogen
atoms and solvent molecules were omitted for clarity. Selected bond
lengths in Å and angles in deg: Mg1···Mg2 6.028(3), Mg1–C66
2.09(2), Mg2–C71 2.162(17), Mg1–Br1 2.33(4), Mg2–Br2 2.35(3),
Mg1–O2 2.068(4), Mg2–O3 2.050(4), Mg1–N1 2.092(4), Mg1–N2
2.079(5), Mg2–N3 2.097(5), Mg2–N4 2.070(4), N1–C25 1.329(6),
N2–C34 1.320(6), N3–C44 1.327(7), N4–C53 1.329(6), C24–C25
1.392(8), C24–C34 1.397(7), C43–C44 1.391(7), C43–C53 1.401(7),
N1–Mg1–N2 92.72(18), N1–Mg1–C66 123.2(6), N1–Mg1–Br1
126.4(19), N1–Mg1–O2 104.75(18), N3–Mg2–N4 91.61(17), N3–
Scheme 4. Synthesis of 2 and 3.
Mg2–C71 140.9(8), N3–Mg2–O3 92.90 (17).
Slow evaporation of the volatiles from a concentrated solu-
The two Mg–C bond lengths (Mg1–C66: 2.09(2) Å, Mg2–
tion of 2 in a mixture of thf and hexane (1:2) led to crystals C71: 2.162(7) Å) are similar to those found for other nitrogen
suitable for single-crystal X-ray diffraction analysis. However, ligated methyl magnesium complexes.[35–40] The determined
these represented disordered binary crystals, in which the mag- Mg–Br bond lengths of 2.33(4) Å and 2.35(3) Å, respectively,
nesium bound methyl groups were partly substituted by bro- are somewhat shorter than those observed in similar systems
SiMe3
mide anions. The latter applied to 5% of the magnesium bound ([LSiMe Mg(Br)(thf)]: 2.4692(15) Å, L
= SiR{(C(2,6-
3
methyl groups as determined by population refinements of Me2C6H3)((R)N)}2, R = SiMe3,[41] [(thf)2MgBr{(NtBu)2-
these sites. Two independent complex molecules which only SMe}]: 2.4960(13) Å).[42] However, this might be a result of
exhibit minor differences (except for the observed metal-to- the substitutional disorder. The C–C, C–N and Mg–N bonds
metal distance, vide infra) were found in the asymmetric unit. within the diiminato binding pockets pairwise have very sim-
Therefore only one molecule will be discussed below. The de- ilar lengths, that is, the diiminato-Mg units are highly symmet-
gree of MeǞBr substitution in the solid solution is not homo- ric. The distance between the two distorted tetrahedrally coor-
geneous for all four sites inherent to the two independent com- dinated Mg2+ ions within one of the two independent mole-
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J. P. Falkenhagen, P. Haack, C. Limberg, B. Braun
ARTICLE
cules in the asymmetric unit cell amounts to 6.028(3) Å dinuclear diiminato diorgano aluminium compounds. Only few
(6.351(3) Å for the second independent molecule), which is representatives (shown in Scheme 5) are known so far,[45,46]
significantly
[
shorter
than
the
one
found
in though, and corresponding Xanthdim complexes would add to
Me2C6H3
Xanthdim](MgN(SiMe3)2(thf))2 (8.003(3) Å).[31] This the variety with a new structural motif based on a vis-à-vis
underlines again the strong dependence of the metal-to-metal arrangement of two diiminato AlMe2 units. Hence, we have
distances in Xanthdim complexes on the steric bulk of the co- started a corresponding investigation.
ligands[29] and the flexibility of the Xanthdim ligand in this
respect.
Me2C6H3
[
Xanthdim](AlMe2)2 (4)
Selective synthesis of the pure bromido complex
Me2C6H3
Treating a solution of [Me C H Xanthdim]H2 in toluene with
2 6 3
[
Xanthdim](MgBr(thf))2 (3) can be achieved by reac-
tion of MeMgBr directly with an excess of
a sixfold excess of trimethylaluminium in toluene caused a
rapid colour change from intensively yellow to bright orange
Me2C6H3
[
Xanthdim]H2 in thf (Scheme 4). After workup 3 was
indicating deprotonation of [Me C H Xanthdim]H2, which did
not occur, if thf was used as the solvent. After stirring at room
accessible in 58% yield, and its identity as well as purity was
ensured with the aid of NMR spectroscopy. The 1H NMR spec-
trum recorded for a [D2]dichloromethane solution showed
slightly different chemical shifts for the Xanthdim2– signals
as compared to those of 2, especially in the aromatic region.
However, as in case of 2 just one signal is observed for each
of the methyl groups in the 2- and 3-positions at the nitro-
gen bound aryl residues. The main difference between the
spectra of 2 and 3 obviously is the singlet at –1.54 ppm be-
longing to the magnesium bound methyl groups.
2 6 3
temp. overnight and precipitation from hot toluene
Me2C6H3
[
Xanthdim](AlMe2)2·tol (4·tol) was isolated in 51%
yield as a yellow powder (Scheme 6). Complete deprotonation
of the ligand precursor was confirmed by the absence of the
respective triplet resonance around 12 ppm in the 1H NMR
spectrum of a solution of 4 in [D6]benzene. Instead a broad
singlet (ν1/2 = 22 Hz) at –0.13 ppm was observed for the alu-
minium-bound methyl groups. Significant line broadening of
this signal is attributed both to the coupling of the respective
protons to the 27Al nuclei and to a dynamic process that causes
both methyl groups to be chemically equivalent on the NMR
timescale. In a variable temperature NMR investigation per-
formed for a solution of 4 in deuterated toluene decoalescence
Group 13 Chemistry: Complexation of Two
Dimethylaluminium Units in the Binding Pockets of
Xanthdim2–
In recent years poly(ε-caprolactone) and polylactides have of the AlMe2 resonance was observed below 273 K giving rise
emerged as being among the most promising sustainable poly- to two signals at 0.23 (ν1/2 = 14 Hz, 243 K) and –0.36 ppm
mers. Their production from renewable resources, their biode- (ν1/2 = 31 Hz, 243 K), respectively. Even after days solutions
gradability and their versatile biomedical applications have of 4 in dry and degassed toluene, benzene, thf or dichlorometh-
spurred numerous studies in this field of research. A key step ane did not show any sign of decomposition.
to obtain well defined materials with beneficial mechanical
properties is rigid control of the polymer chain microstructure.
Although there are reports on highly active and very selective
dinuclear organoaluminium catalysts for ring opening poly-
merisations (ROP) of cyclic esters, structural studies and
analyses concerning potential cooperative effects remain rela-
tivly scarce.[56–58] On the other hand, in the last twenty years
numerous examples of β-diketiminato aluminium complexes
have been published,[1,43,44,47–54] including a homoleptic tris-
β-diketiminato aluminium complex,[55] an aluminium(I) com-
plex[52] and a complex containing an Al–O–Al moiety, claimed
to be the smallest MAO model conceivable.[54] The favourable
Scheme 6. Synthesis of 4.
properties of dinuclear organoaluminium compounds as poly-
Single crystals suitable for X-ray diffraction analysis were
merisation catalysts and the rich knowledge available on β- obtained by layering a concentrated solution of 4 in thf with
diketiminato aluminium complexes suggest attempts to prepare hexane. The molecular structure is shown in Figure 3. It shows
Scheme 5. Known aluminium complexes of dinucleating β-diketiminato-based ligands.[45,46]
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Organoelement Complexes of a Dinucleating Double β-Diiminato Ligand
that as envisaged both of the diiminato binding sites are occu- ROP catalysts, which we intend to investigate in future work.
pied by AlMe2 groups. The aluminium atoms are coordinated Hence, the synthesis of the fluorinated derivative of 4,
F2C6H3
in a distorted tetrahedral fashion by the nitrogen donor atoms
of the diiminato pockets and the methyl groups. The relatively
[
Xanthdim](AlMe2)2 (5) was pursued, too.
2 6 3
Treating a solution of [F C H Xanthdim]H2 in toluene with a
large metal-to-metal distance of 6.9354(12) Å reflects the in- sixfold excess of trimethylaluminium in toluene caused a rapid
creased steric bulk at the aluminium atoms in comparison to colour change from intensively yellow to bright orange due to
Me2C6H3
[
Xanthdim](MgMe(thf))2, 2, due to the additional co- deprotonation of the ligand precursor. After stirring at room
valently bound methyl groups (obviously, the coordinated thf temp. overnight and subsequent recrystallisation from hot tolu-
ligands in 2 are more flexible). The aluminium–carbon dis- ene the product [F C H Xanthdim](AlMe2)2·tol (5·tol) was iso-
tances (C62–Al1 1.943(4), C63–Al1 1.951(3), C64–Al2 lated in a yield of 79% as a microcrystalline solid (Scheme 7).
1.954(3) and C65–Al2 1.951(3) Å) correspond well with those Compound 5 is indefinitely stable in dry and degassed toluene,
2
6 3
reported previously for [Me pTol](AlMe2) (L = CH{(CMe) benzene, thf, dichloromethane or ethyl ether. As it is the case
L
((pTol)N)}2 1.955(4) and 1.961(3) Å).[47] However, the alu- for 4, also 5 shows a dynamic behaviour in solution, so that
minium–nitrogen bonds within 4 are slightly longer (Al1–N1 only one signal is observed for all aluminium bound methyl
1
1.932(2), Al1–N2 1.932(2), Al2–N(4) 1.917(2) and Al2–N3 groups in the H NMR spectrum. However, while this gives
1.936(2) Å vs. 1.905(3) and 1.907(3) Å). In both of the binding rise to a singlet in the case of 4, a broad pseudo-triplet (JFH
=
units charge delocalisation is very effective as reflected by 2.85 Hz) at –0.39 ppm is found in the spectrum of a solution
highly symmetric β-diiminato pockets exhibiting C–C and C– of 5 in deuterated toluene (Figure 4).
N distances, which pairwise are very similar.
Scheme 7. Synthesis of 5.
Figure 3. Molecular structure of 4. All hydrogen atoms were omitted
for clarity. Selected bond lengths in Å and angles in deg: Al1···Al2
6.9354(12), Al1–C62 1.943(4), Al1–C63 1.951(3), Al1–N1 1.932(2),
Al1–N2 1.932(2), N1–C25 1.329(3), N2–C34 1.310(3), C25–C24
1.405(3), C34–C24 1.395(3), Al2–C64 1.954(3), Al2–C65 1.951(3),
Al2–N3 1.936(2), Al2–N4 1.917(2), N3–C44 1.314(3), N4–C53
1.317(3), C43–C44 1.396(3), C43–C53 1.402(3), C63–Al1–C62
114.55(13), N1–Al1–N2 94.10(8), N1–Al1–C62 106.45(12), N1–Al1–
C63 118.15(12), N3–Al2–N4 92.96(9), C64–Al2–C65 114.03(14),
N3–Al2–C64 114.13(11), N3–Al2–C65 110.37(11).
F2C6H3
[
Xanthdim](AlMe2)2 (5)
In previous work we have investigated the catalytic activity
Figure 4. Decoalescence of the AlMe2 resonance in a variable tem-
perature 1H NMR spectroscopic investigation of a solution of 5 in
[D8]toluene.
displayed by zinc complexes of both, the methylated and the
fluorinated Xanthdim2– ligand (Figure 1) in epoxide/ CO2 co-
polymerisations.[27] Both complexes proved to be active, but
the selectivity of [Me C H Xanthdim](ZnEt)2 was found to be
The splitting of this signal can be attributed to a coupling
2
6 3
distinctly
different
from
the
one
of of the methyl-protons to the ortho-19F nuclei of the two flank-
F2C6H3
[
Xanthdim](ZnEt(thf))2, which mainly led to products of ing aryl-substituents belonging to each diiminato unit as
cyclohexene oxide homopolymerisation. This was ascribed to proved by a H{19F} NMR experiment. According to the mo-
1
the increased Lewis acidity of the zinc ion in lecular structure revealed for the solid state (see below and
F2C6H3
[
Xanthdim](ZnEt(thf))2 due to the electron withdrawing Figure 5), there are contacts between the protons of the exo
effect of the fluorine substituents. This effect should thus also AlMe groups and the aforementioned fluorine substituents
increase the potential of [Xanthdim](AlMe2)2 complexes as (2.593(3), 2.564(2) Å), which are considerably smaller than
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J. P. Falkenhagen, P. Haack, C. Limberg, B. Braun
ARTICLE
the sum of the van-der-Waals radii of the respective atoms (F 1.960(5), C56–Al2 1.961(5), C57–Al2 1.951(5) Å).[47] The ob-
1.47, H 1.20).[59] Therefore it seems reasonable that a “through served aluminium–nitrogen bond lengths are nearly similar to
space” coupling occurs,[60] and the same can be imagined for those in 4 (N1–Al1 1.934(4), N2–Al1 1.941(4), N3–Al2
the endo AlMe groups. As due to the rotational fluxionality 1.954(4), N4–Al2 1.934(4) Å). Moreover, very similar C–C
of the aryl residues each of the methyl groups is exposed to and N–C distances within the diiminato units again indicate
interactions with two fluorine substituents, and as further both effective charge distribution.
methyl groups belonging to one AlMe2 are equal on the NMR
timescale only one pseudo-triplet resonance is observed. Deco-
Conclusions
alescence of this signal is observed below 243 K, giving rise
to two distinctive pseudo triplet signals (–0.08 ppm and
–0.24 ppm at 193 K, Figure 4). Both the lowering of the deco-
alescence temperature by 30 K and the reduction of the differ-
ence in the chemical shifts between the respective signals ob-
served at 243 K indicate a significantly lower exchange barrier
for the AlMe2 groups of 5 as compared to those of 4. Although
it is possible to detect the signal of 5 in an 27Al NMR experi-
ment (188.9 ppm), application of this method is clearly limited
due to the very large linewidth (ν1/2 Ն 2000 Hz) and the very
low intensity of the signal.
A rubidium complex of Xanthdim2– with toluene co-ligands
was synthesised by the reaction of [Me2C6H3Xanthdim]H2 with
RbOtBu in a toluene solution. The Rb+ ions do not utilise the
binding pockets offered by the ligand, but act as bridges be-
tween the two diiminato units, which adopt a W-conformation.
The resulting structure can be viewed as intermediate between
the structures of corresponding Cs+ and K+ compounds.
Furthermore [MgBr]+ and [MgMe]+ complexes of Xanthdim2–
have been prepared. They proved stable against ligand ex-
change in course of a Schlenk equilibrium in solution. Finally,
dinuclear [AlMe2]+ complexes have been synthesised em-
ploying two electronically different variants of Xanthdim2–.
The AlMe2 moieties proved to be fluxional within the binding
pockets and for the fluorinated complex Al–CH3···F-aryl inter-
actions were revealed, both in the solid state and in solution.
In future work the conversion of the aluminium compounds
into complexes bearing two potentially cooperating Lewis
acidic sites and their application in polymerisation catalysis
will be investigated. The magnesium complexes will be tested
in CO2 activation studies.
Experimental Section
General Considerations: All manipulations were carried out in a
glove-box, or else by means of Schlenk-type techniques involving the
use of a dry argon atmosphere. The 1H, 13C and 19F NMR spectra were
recorded on a Bruker DPX 300 (1H 300.1 MHz, 13C 75.5 MHz, 19F
282.4 MHz) or Bruker Avance III NMR spectrometer (1H 400.1 MHz,
13C 100.6 MHz, 27Al 104.3 MHz) with [D2]dichloromethane, [D8]tol-
uene or [D6]benzene as the solvent at 20 °C. The 1H NMR spectra
were calibrated against the residual proton, the 13C NMR spectra
against natural abundance 13C resonances of the deuterated solvents
([D2]dichloromethane δH = 5.32 ppm and δC = 53.5 ppm, [D6]benzene
δH = 7.16 ppm and δC = 128.0 ppm and [D8]toluene δH = 2.08 ppm
and δC = 20.4 ppm, respectively). Calibration against CFCl3 and
Al(H2O)63+ as external standards was performed for 19F and 27Al NMR
spectroscopy. Flame sealed tubes were used for low temperature NMR
experiments. Microanalyses were performed with a Leco CHNS-932
or a HEKA Euro 3000 elemental analyser. Infrared (IR) spectra were
recorded using samples prepared as KBr pellets with a Shimadzu
FTIR-8400S-spectrometer.
Figure 5. Molecular structure of 5·thf. The non-coordinating thf mole-
cule incorporated in the unit cell and all hydrogen atoms except for
those of two of the AlMe groups were omitted for clarity. Selected
bond lengths in Å and angles in deg: Al1···Al2 6.327(2), Al1–C54
1.953(5), Al1–C55 1.960(5), Al1–N1 1.933(3), Al1–N2 1.938(4), N1–
C25 1.340(5), N2–C32 1.317(5), C25–C24 1.383(6), C24–C32
1.406(5), Al2–C56 1.961(5), Al2–C57 1.951(5), Al2–N3 1.954(4),
Al2–N4 1.934(4), N3–C40 1.331(5), N4–C47 1.347(5), C39–C40
1.394(6), C39–C47 1.396(6) Å, C54–Al1–C55 115.3(2), N1–Al1–N2
91.66(15), N1–Al1–C54 117.80(19), N1–Al1–C55 110.57(19), C56–
Al2–C57 115.5(2), N3–Al2–N4 92.06(16), N3–Al2–C56 114.4(2),
N3–Al2–C57 104.40(18)°.
As in the case of 4, single crystals suitable for X-ray diffrac-
tion analysis were obtained by layering a concentrated solution
of 5 in thf with hexane. The molecular structure is shown in
Figure 5. The metal-to-metal distance within 5·thf is somewhat
shorter than in 4, amounting to 6.327(2) Å, which reflects the
decrease of the steric crowding within the ligand binding pock-
ets due to the lower steric demand of the fluorido substituents
compared to the methyl groups. However, the aluminium–car-
bon distances are similar to those in 4 and excellently match
Materials: Solvents were purified, dried, degassed and stored over
Me2C6H3
molecular sieves prior to use.
[
[
Xanthdim]H2 and
F2C6H3
Xanthdim]H2 were prepared by published literature pro-
cedures.[26,27] RbOtBu·0.81tBuOH was prepared by refluxing rubidium
metal and an excess of tBuOH in thf for 20 h. A filtration, subsequent
removal of the solvent and drying in vacuo gave a white solid, the
purity of which was ensured by NMR spectroscopy. The composition
previously reported data (C54–Al1 1.953(5), C55–Al1 of RbOtBu·0.81tBuOH was determined by elemental analysis. Solu-
1746 www.zaac.wiley-vch.de
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 1741–1749

Organoelement Complexes of a Dinucleating Double β-Diiminato Ligand
Table 1. Crystallographic data and structure refinement for 1(tol)2·2(tol), the solid solution 2·0.5(thf)·0.25(hexane), 4 and 5·thf.
1(tol)2·2(tol)
2·0.5(thf)·0.25(hexane)
4
5·thf
Formula
C89H100N4ORb2
1412.67
monoclinic
P21/c
C148.79H191.37Br0.21Mg4N8O7
C65H80Al2N4O
987.29
monoclinic
P21/c
C61H64Al2F8N4O2
1091.12
weight /g·mol–1
2317.97
triclinic
crystal system
space group
triclinic
¯
¯
P1
P1
a /Å
b /Å
c /Å
α /°
25.5865(7)
13.7266(4)
21.5311(8)
90
92.179(2)
90
7556.6(4)
4
1.242
16.0882(5)
18.1457(6)
24.1793(8)
77.827(3)
76.905(2)
89.363(3)
6715.6(4)
4
23.2697(19)
21.0177(16)
11.9568(9)
90
99.8530(15)
90
5761.5(8)
4
1.138
10.0758(3)
13.2037(9)
22.7600(12)
104.753(8)
95.635(7)
98.494(9)
2866.7(3)
2
β /°
γ /°
V /Å3
Z
Density /g·cm–3
μ(Mo-Kα) /mm–1
F(000)
1.146
0.148
2503
1.264
0.122
1144
1.344
2976
0.095
2128
GoF
1.185
0.990
1.056
1.038
R1
0.0490
0.0918
0.0497
0.0846
wR2
0.0991
0.1874
0.0688
0.2004
R1 (all data)
Rind (all data) wR2
Δρmin / Δρmax /e·Å–3
CCDC
0.0649
0.1037
–0.60 / 0.68
837208
0.1748
0.2227
–0.82 / 0.63
837209
0.1148
0.0773
0.22 / –0.24
837210
0.1468
0.2285
0.94 / –0.59
837211
tions of AlMe3 (2 m in toluene) and MeMgBr (1 m in thf) were ob-
tained from Sigma–Aldrich.
precipitate, which was filtered off. Drying of the residue under vacuum
yielded 192 mg (184 μmol, 81%) of 1. Crystal samples of 1(tol)2
·2(tol), which contained two molecules of coordinated as well as two
molecules of co-crystallised toluene could be obtained by slow evapo-
ration of the solvent from a concentrated solution of 1 in toluene at
room temp. Extensive drying in vacuo led to the loss of all toluene
molecules. The content of toluene in the samples submitted to elemen-
tal analysis was determined by 1H NMR spectroscopy. Elemental
analysis (%) calcd. for C75H84N4Rb2O·0.73(C7H8) (1295.69 g·mol–1):
C 74.26, H 6.99, N 4.32; found: C 74.27, H 7.08, N 4.24. IR (KBr):
ν˜ = 2962 (m), 2922 (m), 2860 (m), 1639 (w), 1586 (m), 1564 (m),
1517 (vs), 1458 (s), 1425 (s), 1369 (m), 1353 (m), 1261 (m), 1210 (s),
1159 (w), 1090 (w), 1052 (m), 1028 (w), 986 (w), 943 (w), 915 (w),
853 (w), 787 (m), 730 (m), 696 (m)cm–1. 1H NMR (300.1 MHz,
[D2]dichloromethane): δ = 7.84 (s, 4 H, NCH), 7.54 (d, 4JHH = 2.3 Hz,
2 H, CH), 7.43 (d, 4JHH = 2.3 Hz, 2 H, CH), 7.00 (ps-t, 4 H, CH), 6.73
Crystal
Structure
Determinations:
Crystals
of
Me2C6H3
[
Xanthdim](Rb(tol))2·2(tol) (1(tol)2·2(tol)), suitable for single
crystal analysis were obtained by slow evaporation of the solvent from
a solution of 1 in toluene. Crystals of [Me C H Xanthdim](MgMe(thf))2
·0.5(thf)·0.25(hexane) (2·0.5(thf)·0.25(hexane)), were obtained by slow
evaporation of the solvent from a concentrated solution of 2 in a mix-
ture of thf and hexane (1:2) at room temp. These crystals were twinned
and represented a solid solution, in which the magnesium atoms bound
methyl groups are partly replaced by bromide substituents. The ratio
MgMe:MgBr within the solid solution amounts to 95:5 as determined
by refining the population of the corresponding groups. For the refine-
ment of the -Me vs. -Br disorder, Mg–Me and Mg–Br distances were
freely refined. The components of the anisotropic displacement param-
eters for the related -Me and -Br substituents were constrained to be
2
6 3
3
3
(d, JHH = 7.3 Hz, 4 H, CH), 6.42 (d, JHH = 7.9 Hz, 4 H, CH), 2.18
(s, 12 H, CCH3), 2.03 (s, 12 H, CCH3), 1.78 (s, 6 H, C(CH3)2), 1.40
(s, 18 H, C(CH3)3); 13C{1H} NMR (75.5 MHz, [D2]dichloromethane):
equal. Single crystals both of [Me C H Xanthdim](AlMe2)2 (4) and
2
6 3
F2C6H3
[
Xanthdim](AlMe2)2·thf (5·thf) were obtained by layering con-
centrated solutions of these complexes in thf with hexane. All data
collections were performed at 100 K with a STOE IPDS 2T dif-
fractometer except for 4, for which data collection was performed at
180 K with a STOE IPDS I diffractometer. In all cases Mo-Kα radiation
(λ = 0.71073 Å) was used; radiation source was a sealed tube generator
with graphite monochromator. Multi-scan correction (PLATON)[61]
was applied for complex 1(tol)2·2(tol). The structures were solved by
direct methods (SHELXS-97)[62] and refined by full-matrix least-
squares procedures based on F2 with all measured reflections
(SHELXL-97) (Table 1).[62] All non-hydrogen atoms were refined an-
isotropically. Hydrogen atoms were introduced in their idealised posi-
tions and refined as riding.
δ
= 163.6 (NCH), 154.8 (C), 146.7 (C), 144.3 (C), 137.5 (C),
132.7 (CH), 129.1 (C), 129.1 (C), 128.7 (C), 127.1 (CH), 122.8 (CH),
121.9 (CH), 116.6 (CH), 106.3 (C), 35.1 (C(CH3)2), 34.9(C(CH3)2),
34.9 (C(CH3)3), 31.9 (C(CH3)3), 20.5 (CH3), 13.9 (CH3).
Me2C6H3
Synthesis of
[
Xanthdim](MgMe(thf))2 (2): KH (20 mg,
solution of
Xanthdim]H2 (200 mg, 228 μmol) in thf (3 mL). After stirring
499 μmol, 2.2 equiv.) was suspended in
a
Me2C6H3
[
the reaction mixture for 15 h at room temp. excessive KH was removed
by filtration, and a MeMgBr solution (502 μL, 1 m in thf, 502 μmol,
2.2 equiv.) was added to the orange filtrate. After stirring of the re-
sulting yellow suspension for additional 5 h, all volatiles were re-
moved. The residue was redissolved in benzene (2 mL), and addition
Synthesis of [Me2C6H3Xanthdim](Rb)2 (1): After stirring of an orange of hexane (10 mL) caused the precipitation of a pale yellow solid that
Me2C6H3
solution of
[
Xanthdim]H2 (200 mg, 228 μmol) and was filtered off and washed with hexane (2 mL). Evaporation of the
RbOtBu·0.81tBuOH (110 mg, 503 μmol, 2.2 equiv.) in thf (5 mL) for
15 h at room temp. all volatiles were removed in vacuo. The resulting
orange solid was completely dissolved in toluene (5 mL), and the vol-
ume of the solution was concentrated under reduced pressure to
0.5 mL. Addition of hexane (5 mL) caused the formation of a yellow
solvent from the combined filtrates and drying of the resulting orange
residue yielded 176 mg (161 μmol, 71%) 2, which is pure by NMR
spectroscopy. Crystallisation by slow evaporation of the volatiles from
a concentrated thf/hexane solution yielded in crystals that represented
a solid solution incorporating 5% of MgBr units. Elemental analysis
Z. Anorg. Allg. Chem. 2011, 1741–1749
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1747

J. P. Falkenhagen, P. Haack, C. Limberg, B. Braun
ARTICLE
(%) calcd. for C69H84N4Mg2O3(CH3)1.7Br0.3 (1115.57 g·mol–1): C CCH3), 1.57 (s, 6 H, C(CH3)2), 1.29 (s, 18 H, C(CH3)3), –0.13 (br. s,
76.12, H 8.05, N 5.02, Br 2.1; found: C 76.01, H 8.39, N 4.89, Br 12 H, Al(CH3)2); 1H NMR (400.1 MHz, [D8]toluene): δ = 7.75 (s, 4 H,
4
2.4. IR (KBr) ν˜ = 2924 (m), 2862 (m), 1642 (m), 1588 (m), 1576 (m), CHN), 7.49 (d, JHH = 7.7 Hz, 4 H, CH), 7.37 (d, JHH = 2.4 Hz, 2 H,
4
3
1550 (m), 1481 (s), 1461 (vs), 1458 (vs), 1441 (s), 1384 (w), 1363 (w),
CH), 7.31 (d, JHH = 2.4 Hz, 2 H, CH), 6.89 (t, JHH = 7.7 Hz, 4 H,
3
1321 (vs), 1260 (m), 1241 (w), 1223 (m), 1093 (m), 1061 (m), CH), 6.79 (d, JHH = 7.4 Hz, 4 H, CH), 2.30 (s, 12 H, CCH3), 1.95 (s,
988 (w), 957 (w), 876 (w), 857 (w), 782 (m)cm–1. 1H NMR 12 H, CCH3), 1.59 (s, 6 H, C(CH3)2), 1.29 (s, 18 H, C(CH3)3), –0.22
(300.1 MHz, [D2]dichloromethane): δ = 7.66 (s, 4 H, NCH), 7.24 (d,
(br. s, 12 H, Al(CH3)2); 13C{1H} NMR (100.1 MHz, [D6]benzene): δ
= 164.3 (CHN), 147.6 (Cq), 145.8 (Cq), 145.5 (Cq), 138.9 (Cq), 131.0
4
4JHH = 2.4 Hz, 2 H, CH), 7.14 (d, JHH = 2.4 Hz, 2 H, CH), 6.85–6.98
(m, 8 H, CH), 6.42 (ps-t, JHH = 7.5 Hz, 4 H, CH), 3.79 (m, 8 H, CH2), (Cq), 130.7 (Cq), 128.3 (CH), 128.1 (CH), 127.4 (CH), 126.3 (CH),
2.27 (s, 12 H, CH3), 2.24 (s, 12 H, CH3), 1.80 (m, 8 H, CH2), 1.63 (s, 124.3 (CH), 121.6 (CH), 104.1 (CqCHN), 35.3 (C(CH3)2), 34.3
6 H, C(CH3)2), 1.34 (s, 18 H, C(CH3)3), –1.54 (s, 6 H, CH3); 13C{1H} (C(CH3)3), 33.4 (C(CH3)2), 31.5 (C(CH3)3), 20.6 (CCH3), 15.5
NMR (75.5 MHz, [D2]dichloromethane): δ = 163.8 (NCH), 152.1 (C), (CCH3), –7.54 (Al(CH3)2.
145.1 (C), 144.5 (C), 137.9 (C), 130.4 (C), 129.6 (C), 129.1 (C),
126.9 (CH), 126.0 (CH), 125.6 (CH), 122.0 (CH), 120.4 (CH),
103.1 (C), 69.4 (CH2), 34.9 (C(CH3)3), 34.2 (C(CH3)2), 33.7 (C(CH3)2),
F2C6H3
Synthesis
[
of
[
Xanthdim](AlMe2)2·tol
(5·tol):
F2C6H3
Xanthdim]H2 (400 mg, 441 μmol) was dissolved in toluene
(15 mL) giving a yellow solution. A solution of trimethylaluminium
(1.4 mL, 2 m in toluene, 2.8 mmol, 6 equiv.) was added, which led to
an orange solution. After stirring at room temp. for 24 h, all volatiles
were removed in vacuo (50 °C, overnight) and the yellow residue was
31.4 (C(CH3)3),
–16.4 (MgCH3).
25.3 (CH2),
20.5 (CCH3),
15.2 (CCH3),
Synthesis of [Me C H Xanthdim](MgBr(thf)))2 (3): A solution of
2
6
3
recrystallised from toluene (8 mL) giving 252 mg (227 μmol, 51%) of
MeMgBr (95 μL, 1 m in thf, 285 μmol) was added to
F2C6H3
Me2C6H3
[
Xanthdim](AlMe2)2·tol (5·tol). Cooling of the filtrate to –30 °C
[
Xanthdim]H2 (300 mg, 343 μmol, 1.2 equiv.) dissolved in thf
for several days yielded another 135 mg (122 μmol, 28%) of the de-
sired product. The content of toluene was determined by 1H NMR
(5 mL), and the resulting clear yellow reaction mixture was stirred for
17 h at room temp. Subsequently all volatiles were removed in vacuo
and the residue was dissolved in thf (1 mL). Addition of hexane
(10 mL) and storage of the solution at 4 °C for 14 h led to the forma-
tion of a yellow precipitate, which was filtered off. Drying of the resi-
due in vacuo yielded 101 mg (82 μmol, 58%) 3, which was pure ac-
cording to NMR spectroscopy. IR (KBr): ν˜ = 2923 (m), 2864 (m),
1637 (vs), 1587 (m), 1545 (s), 1471 (s), 1461 (m), 1442 (m), 1386 (w),
1363 (w), 1321 (vs), 1288 (s), 1266 (m), 1242 (m), 1224 (m),
1096 (m), 1051 (m), 1017 (m), 877 (w), 857 (w)cm–1. 1H NMR
(300.1 MHz, [D2]dichloromethane): δ = 7.70 (s, 4 H, NCH), 7.24 (d,
spectroscopy.
Elemental
analysis
(%)
calcd.
for
C57H56Al2F8N4O·C7H8: C 69.18, H 5.81, N 5.04; found: C 68.85, H
5.79, N 4.90. IR (KBr): ν˜ = 2962 (w), 2937 (w), 2927 (w), 2904 (vw),
2869 (vw), 1597 (m), 1506 (s), 1473 (vs), 1445 (s), 1433 (m), 1420
(w), 1387 (w), 1363 (m), 1316 (vs), 1282 (m), 1264 (s), 1230 (m),
1198 (m), 1141 (m), 1099 (m), 1078 (w), 977 (w), 967 (m), 957 (w),
850 (w), 811 (w), 789 (vw), 733 (w), 706 (w), 683 (w), 602 (vw), 556
1
(w), 526 (vw)cm–1. H NMR (400.1 MHz, [D6]benzene): δ = 7.65 (d,
4
JFH = 1.0 Hz, 4 H, CHN), 7.52 (d, JHH = 2.4 Hz, 2 H, CH), 7.30 (d,
4JHH = 2.4 Hz, 2 H, CH), 6.61 (m, 4 H, CH), 6.36 (m, 4 H, CH), 6.30–
6.22 (m, 4 H, CH), 1.72 (s, 6 H, C(CH3)2), 1.25 (s, 18 H, C(CH3)3),
4JHH = 2.4 Hz, 2 H, CH), 7.11 (d, JHH = 2.4 Hz, 2 H, CH), 7.03 (d,
3JHH = 7.5 Hz, 4 H, CH), 6.91 (d, JHH = 7.2 Hz, 4 H, CH), 6.42 (ps-
t, JHH = 7.7 Hz, 4 H, CH), 3.86 (m, 8 H, CH2), 2.28 (s, 12 H, CCH3),
2.27 (s, 12 H, CCH3), 1.85 (m, 8 H, CH2), 1.63 (s, 6 H, C(CH3)2), 1.34
(s, 18 H, C(CH3)3); 13C{1H} NMR (75.5 MHz, [D2]dichloromethane):
4
3
1
–0.30 (ps-t, J(F,H) = 2.9 Hz, 12 H, Al(CH3)2); H NMR (400.1 MHz,
[D8]toluene): δ = 7.71 (d, JFH = 1.0 Hz, 4 H, CHN), 7.51 (d, JHH
=
2.4 Hz, 2 H, CH), 7.29 (d, JHH = 2.4 Hz, 2 H, CH), 6.69 (m, 4 H, CH),
6.39–6.33 (m, 4 H, CH), 6.29–6.22 (m, 4 H, CH), 1.74 (s, 6 H,
C(CH3)2), 1.28 (s, 18 H, C(CH3)3), –0.39 (ps-t, JFH = 2.9 Hz, 12 H,
Al(CH3)2); 19F{1H} NMR (282.4 MHz, [D6]benzene): δ = –112.67 (d,
4JFF = 5.5 Hz), –117.62 (d, 4JFF = 6.0 Hz). 13C{1H} NMR (100.1 MHz,
[D6]benzene): δ = 162.7 (Cq), 160.4 (dd, 1JCF = 248.0, 3JCF = 11.4 Hz,
δ
= 165.4 (NCH), 151.5 (C), 145.1 (C), 144.9 (C), 138.6 (C),
130.1 (C), 129.8 (C), 129.4 (C), 126.8 (CH), 126.4 (CH), 126.4 (CH),
122.7 (CH), 121.1 (CH), 103.2 (C), 70.1 (CH2), 35.1 (C(CH3)3),
34.6 (C(CH3)2),
34.1 (C(CH3)2),
31.7 (C(CH3)3),
25.6 (CH2),
20.9 (CCH3), 15.7 (CCH3).
1
3
CF), 155.9 (dd, JCF = 250.0, JCF = 12.2 Hz, CF), 146.5 (Cq), 145.7
2
4
Me2C6H3
(Cq), 132.5 (dd, JCF = 11.3, JCF = 3.6 Hz, Cq), 130.3 (Cq), 128.3
(CH), 126.8 (CH), 125.5 (dd, JCF = 9.4, JCF = 2.2 Hz, CH), 122.4
(CH), 112.0 (dd, JCF = 22.3, JCF = 3.6 Hz, CH), 108.1 (Cq), 104.9
(ps-t, JCF = 25.4 Hz, CH), 35.1 (Cq), 34.4 (Cq), 33.6 (C(CH3)2), 31.4
(C(CH3)3), –9.4 (br. m, Al(CH3)2); 27Al NMR (104.3 MHz, [D6]ben-
zene): δ = 188.9 (br., m, Al(CH3)2).
Synthesis
of
[
Xanthdim](AlMe2)2·tol
(4·tol):
3
5
Me2C6H3
[
Xanthdim]H2 (400 mg, 457 μmol) was dissolved in toluene
2
4
(15 mL) giving an intensively yellow solution. Trimethylaluminium
(1.4 mL, 2 m in toluene, 2.8 mmol, 6 equiv.) was added afterwards,
which led to an orange solution. After stirring at room temp. for 24 h,
all volatiles were removed in vacuo (50 °C, overnight) and after dissol-
ution of the yellow residue in hot toluene (3 mL) cooling led to the
2
precipitation of 251 mg (233 μmol, 51%) of [Me C H Xanthdim](-
AlMe2)2·tol (4·tol). The content of toluene was determined by 1H NMR
spectroscopy. Elemental analysis (%) calcd. for C65H80Al2N4O·C7H8:
C 80.11, H 8.22, N 5.19; found: C 79.85, H 7.96, N 5.59. IR (KBr):
ν˜ = 2962 (vs), 2928 (s), 2865 (w), 1650 (s), 1639 (vs), 1622 (m), 1612
(w), 1602 (w), 1580 (m), 1575 (m), 1556 (vs), 1544 (vs), 1527 (m),
1511 (w), 1507 (w), 1472 (vs), 1461 (vs), 1442 (vs), 1424 (w), 1382
(w), 1302 (vs), 1263 (vs), 1225 (m), 1187 (vw), 1096 (s), 1076 (s),
1044 (s), 875 (vw), 857 (w), 801 (vs), 771 (w), 703 (w), 683 (w), 672
(w)cm–1. 1H NMR (400.1 MHz, [D6]benzene): δ = 7.79 (s, 4 H, CHN),
2
6 3
Acknowledgement
We are grateful to the Fonds der Chemischen Industrie, the Bundesmi-
nisterium für Bildung und Forschung, as well as to Bayer Services
GmbH & Co. OHG, BASF AG, and Sasol GmbH for the supply of
chemicals. Furthermore we thank the Cluster of excellence “Unifying
concepts in catalysis“ for valuable discussions.
References
4
7.55 (d, JHH = 7.9 Hz, 4 H, CH), 7.37 (d, JHH = 2.3 Hz, 2 H, CH),
4
3
7.33 (d, JHH = 2.3 Hz, 2 H, CH), 6.91 (t, JHH = 7.7 Hz, 4 H, CH),
6.81 (d, 3JHH = 7.4 Hz, 4 H, CH), 2.30 (s, 12 H, CCH3), 1.92 (s, 12 H,
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Published Online: September 27, 2011
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© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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