Stabilization and activation: New alkyl complexes of zinc, magnesium and cationic aluminium featuring chelating bisguanidine ligands

Article abstract of DOI:10.1002/ejic.200900591

In this work we report on the synthesis of new zinc, magnesium and cationic aluminium alkyl as well as Mg aryl complexes featuring chelating bisguanidine ligands [2,8-bis(tetramethylguanidino)naphthalene (btmgn) and 1,2-bis(tetramethylguanidino)benzene (b

Full text of DOI:10.1002/ejic.200900591

FULL PAPER
DOI: 10.1002/ejic.200900591
Stabilization and Activation: New Alkyl Complexes of Zinc, Magnesium and
Cationic Aluminium Featuring Chelating Bisguanidine Ligands
Matthias Reinmuth,[a] Ute Wild,[a] Daniel Rudolf,[a] Elisabeth Kaifer,[a] Markus Enders,[a]
Hubert Wadepohl,[a] and Hans-Jörg Himmel*[a]
Keywords: Zinc / Magnesium / Aluminum / Alkyl complexes / Guanidine
In this work we report on the synthesis of new zinc, magne- studies shed light on the fluxional processes within the com-
sium and cationic aluminium alkyl as well as Mg aryl com- plexes and their activation barriers. The compounds are
plexes featuring chelating bisguanidine ligands [2,8-bis-
(tetramethylguanidino)naphthalene (btmgn) and 1,2-bis-
(tetramethylguanidino)benzene (btmgb)]. The bond proper-
ties in the complexes are analyzed with a combination of ex-
periments and quantum chemical calculations. VT NMR
stable against alkylation of the C=N imine bonds of the gua-
nidino groups and might represent interesting alkyl transfer
reagents and (co-)catalysts.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
additional ligands. Cationic aluminium alkyl complexes in-
corporating amidinate ligands were shown to polymerize
ethylene under mild conditions.[8] Olefin polymerization
with such complexes was analyzed also by means of quan-
tum chemical calculations.[9] In the following years, a
number of complexes featuring other ligands, for example,
Introduction
Alkyl and aryl compounds of the elements zinc, magne-
sium and aluminium are of interest for several applications.
Hence they are widely used as alkylation agents. In ad-
dition, some of these Lewis-acidic compounds, especially
with (coordinatively unsaturated) cationic Al atoms, have
been shown to be alternatives to transition-metal catalysts,
for example, olefin or cyclic ether polymerization.[1,2]
[(C5R5)2Al]+, being isoelectronic to magnesocene deriva-
tives, [(C5R5)2Mg], was first synthesized by Schnöckel et
al.,[3] and later studies showed that [(C5H5)2Al]+-
[MeB(C6F5)3]– is an initiator for the cationic polymerization
of isobutylene and the synthesis of butyl rubber.[4] Some
alkylaluminium species [R2Al]+ (R = Me, tBu) were gener-
ated in toluene solutions, but turned out to be very reactive,
aminotroponiminate,[10]
bidentate
aminophenolate,[11]
imino-amide and imino-phenoxido,[12] were synthesized and
their catalytic activities evaluated. Zinc and magnesium
alkyl complexes were also shown to be active in polymeriza-
tion reactions.[13]
In this work we report on the use of chelating bisguanid-
ines as ligands in zinc, magnesium and cationic aluminium
alkyl (and Mg aryl) complexes. Because of their high basic-
ity,[14] guanidines are interesting complex ligands. Hitherto
a number of chelating bisguanidine complexes have already
been prepared and characterized.[15] Guanidine-stabilized
zinc complexes were shown to be promising catalysts for
the synthesis of polylactide.[16] We reported on the synthesis
of the first B(II) cationic complexes in which two guanidin-
ate units bridge two B atoms.[17] Recently we also synthe-
sized the first metal complexes of the bisguanidine btmgn
[bis(tetramethylguanidino)naphthalene, see Scheme 1],[18]
which had previously been shown to be a kinetically active
proton sponge.[19] The molecular structure of protonated
btmgn features the proton in a bridging position between
the two imine N atoms.[19] Pt2(C2H4)2Cl4 was shown to re-
act with btmgn to give first [(κ1-btmgn)PtCl2(C2H4)] with
κ1-coordination of the btmgn ligand and then, upon heat-
ing, [(κ2-N,NЈ-btmgn)PtCl2] with κ2-N,NЈ coordination.[18]
According to quantum chemical (DFT) calculations, the
C2H4 elimination is associated with a change in energy and
Gibbs free energy (at 298 K, 1013 mbar) of 45.4 and
–3.2 kJmol–1, respectively. The molecular structure of [(κ2-
–
abstracting, for example, C6F5 from the [B(C6F5)4]– anion
to form neutral aluminium and boron compounds.[5] The
isolation of the salt [Et2Al]+[CB11H6X6]– (X = Cl, Br)
showed that these species are indeed accessible by use of
more robust anions, although even in these compounds rel-
atively short Al···X contacts were observed.[6] More re-
cently, it was shown that cationic species of this sort can be
stabilized by sterically shielding, bulky aryl groups. Hence
in [(2,6-Mes2C6H3)2Al]+[B(C6F5)4]– the anion does not in-
teract significantly with the almost linear, quasi-two-coordi-
nate, diorganoaluminium cation.[7] Generally, however, the
aluminium alkyl cation is stabilized by the coordination of
[a] Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität
Heidelberg,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: +49-6221-54-5707
E-mail: hans-jorg.himmel@aci.uni-heidelberg.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900591.
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Scheme 1.
N,NЈ-btmgn)PtCl2] revealed some interesting details:[18] (i) Zn Complexes
the naphthyl group abandons its planar structure, (ii) the
The ethyl complex [Et2Zn(κ2-N,NЈ-btmgb)], 1, was pre-
pared by a reaction between Et2Zn and the btmgb ligand.
The purity was confirmed by elemental analysis (see Exp.
Pt atom is located 133.1 pm above the “best plane” of the
naphthyl aromatic system and (iii) because of different ori-
entations of the guanidino groups relative to the naphthyl
system the molecules are chiral in the crystalline phase.
On the basis of these results, we were interested in de-
veloping further the chemistry of this and related ligands
by synthesizing some alkyl complexes, for example cationic
aluminium complexes of the general formula [R2Al-
(btmgn)]+ (R = alkyl). Because of the expected unusual
bonding situation in these complexes it might be possible
to switch relatively easily from κ2- to κ1-coordination of the
btmgn ligand. This would make the complexes attractive
for catalytic applications. Herein we report on the synthesis
and structural characterization of the neutral alkyl com-
plexes [Et2Zn(κ2-N,NЈ-btmgb)], [Et2Zn(κ2-N,NЈ-btmgn)]
and [(nBu)2Mg(κ2-N,NЈ-btmgn)], the aryl complexes [(Ph)2-
Mg(κ2-N,NЈ-btmgn)] and [(Ph)2Mg(κ2-N,NЈ-btmgb)], as
well as, for comparison, the more stable halides [(κ2-N,NЈ-
btmgn)ZnCl2] and [(κ2-N,NЈ-btmgn)MgBr2], and the cat-
ionic complex [Me2Al(κ2-N,NЈ-btmgn)]+ (which is isoelec-
tronic to [R2Mg(κ2-N,NЈ-btmgn)]). Of course the N=C
double bonds of the guanidine ligands could be alkylated
so that alkyl transfer reactions might occur. However it will
be shown that such an alkyl transfer, although mildly exo-
thermic according to quantum chemical calculations, does
not take place.
1
Sect.). A singlet signal at δ = 2.76 ppm in the H NMR
spectrum recorded at 23 °C can be assigned to the 24 hydro-
gen atoms of the eight guanidino methyl groups. The CH2
and CH3 groups of the ethyl ligands give rise to a quartet
at –0.39 ppm and a triplet at δ = 0.96 ppm. Furthermore,
two signals at δ = 6.75 and 6.42 ppm belong to the aromatic
ring hydrogen atoms. The IR spectrum of 1 (KBr disc)
shows a very strong absorption at 1528 cm–1, which can be
assigned to a mode with high character from the stretch
ν(C=N). The corresponding band in free btmgb is located
at about 1600 cm–1. The large redshift upon coordination
indicates
a relatively strong ligand–metal interaction.
Colourless crystals of 1 were grown at –21 °C by layering
the toluene/THF reaction mixture with n-hexane. The
structure as derived from X-ray diffraction is depicted in
Figure 1 (see Table S1 of the Supporting Information for
selected structural parameters). Interestingly, the Zn atom
is located 85.1 pm above the plane defined by the aromatic
C6 ring of the ligand. While such a coordination seems to
be common for the btmgn ligand (see below), it is unusual
for btmgb.[20] As expected, the ligand N=C bonds [measur-
ing 131.8(2) and 131.6(2) pm] are slightly elongated with
respect to the values in the free btmgb ligand [129.1(3) and
130.1(3) pm]. However, the imine bond lengths are still sig-
nificantly smaller than, for example, in [(κ2-N,NЈ-btmgb)-
PtCl2], where 136.0(8) and 135.2(8) pm were measured.[20]
The Zn–N bond lengths amount to 223.5(1) and
Results and Discussion
In the following, we report on the results obtained with 222.3(1) pm and compare with distances of 222.0(5) pm in
Zn, Mg and Al complexes. As ligands we applied 2,8-bis(te- [Et2Zn(2,2Ј-bipy)][21] and 229.4(5) pm in [Et2Zn(tmeda)].[22]
tramethylguanidino)naphthalene (btmgn, see Scheme 1)[19] The Zn–C distances of 202.5(2) and 201.8(2) pm are also in
and 1,2-bis(tetramethylguanidino)benzene (btmgb, see the region typical for this class of compounds. For example,
Scheme 1).[20]
in [Et2Zn(2,2Ј-bipy)], Zn–C distances of 202.2(7) pm were
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New Alkyl Complexes of Zn, Mg and Cationic Al
found, while in [Et2Zn(κ2-N,NЈ-tmeda)] the Zn–C distances groups point to the same side of the naphthyl ring plane, in
are, at 217(2) pm, slightly larger. The N1–Zn–N4 angle contrast to the situation in [(κ2-N,NЈ-btmgn)PdCl2] or [(κ2-
measures 75.02(5)°, while the C17–Zn–C19 bond angle is N,NЈ-btmgn)PtCl2] with planar coordination at the
remarkably large (136.73°). This first result shows that metal.[18] Also in contrast to these two complexes, the naph-
bisguanidines are suitable ligands for Zn alkyls.
thyl system remains planar. An interesting and important
detail, which will be the subject of more detailed analysis
in the course of the discussion, is the position of the Zn
atom 109.8 pm above the ligands’ aromatic ring plane (see
Figure 2). As shown here and previously (for Pd and Pt
complexes[18]), this displacement is a common feature in the
coordination chemistry of the btmgn ligand. The Zn–C
bond lengths of 202.0(2) and 202.0(2) pm are in good agree-
ment with the distances measured in other complexes. How-
ever, at 218.4(2) and 214.9(2) pm the Zn–N bond lengths in
2 are significantly shorter than those in [Et2Zn(2,2Ј-bipy)]
[222.0(5) pm][21] or [Et2Zn(tmeda)] [229.4(5) pm].[22] They
also are shorter than in 1, arguing for stronger ligand–metal
bonding. Bond lengths of 132.1(3) and 132.3(3) pm were
derived for the N=C imine bonds in the guanidino groups
(N4–C16 and N1–C11). For comparison, in free btmgn val-
ues of 128.1(3) and 128.3(3) pm were measured.[19] In other
complexes this bond was already shown to be elongated
significantly upon complexation (cf. 135.2(7)/132.4(7) pm in
[(κ2-N,NЈ-btmgn)PdCl2] and 135.7(5)/133.5(5) pm in [(κ2-
Figure 1. Molecular structure of 1. Thermal ellipsoids drawn at the
50% probability level.
Reaction between Et2Zn and btmgn afforded the neutral
alkyl complex [Et2Zn(κ2-N,NЈ-btmgn)], 2, which is much
more air- and water-sensitive than free Et2Zn. Coordination
to the btmgn ligand seems to activate Et2Zn significantly.
The different ring size in 2 and 1 (six- vs. five-membered
ring) is probably responsible for the reactivity differences.
1
In the H NMR spectrum of 2 in benzene, the protons of
the ethyl groups attached to Zn give rise to a triplet at δ =
1.49 ppm and a quartet at δ = 0.32 ppm, shifted slightly
with respect to Et2Zn [1.09 (triplet) and 0.10 ppm (quartet)
in toluene]. The guanidino CH3 groups give rise to a strong
singlet at δ = 2.49 ppm. This singlet splits into four signals
at lower temperature (see the VT NMR spectra shown in
the Supporting Information). The fluxional processes be-
hind these temperature effects will be discussed in detail
below for the simpler case of the corresponding dichloro
complex. A strong band at 1541 cm–1 due to the stretching
modes ν(N=C) in the IR spectrum argues for the presence
of intact bisguanidino ligand units. Pale yellow crystals of
2 were grown directly from the reaction mixture. The molec-
ular structure in the crystalline phase as derived from an
X-ray diffraction analysis is depicted in Figure 2. Selected
structural parameters are given in Table S2 (see Supporting
Information). As anticipated, the btmgn ligand is bound by
Figure 2. Molecular structure of 2. Thermal ellipsoids drawn at the
both imine N atoms to the Zn atom. The two guanidino 50% probability level.
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N,NЈ-btmgn)PtCl2]).[18] As anticipated, the other C–N bond sis. The likely structure of this molecule was previously ac-
lengths within the guanidino groups are shorter in 2 than cessed in quantum chemical calculations.[26] Figure 3 (a)
in free btmgn.
displays the structure of 3 as derived from X-ray diffraction
Complexes with dialkylzinc coordinated to 1,4-diaza-1,3- experiments. The orientation of the two guanidino groups
butadienes (DAB) are examples of zinc alkyls featuring che- resembles that in 2. The Zn–N distances are, at 201.0(2) and
lating imine groups synthesized previously.[23] These com- 200.8(2) pm, significantly shorter than in 2. The C=N bond
plexes undergo interesting reactions. Hence a complex reac- lengths within the guanidino groups (N1–C11 and N4–C16)
tion sequence is initiated by thermal- or photo-induced Zn– measure 133.7(3) and 132.7(3) pm (see Table S3), respec-
C bond cleavage and formation of a radical pair, one of the tively, and are thus slightly larger than in 2. Consequently
final products being the N-alkylated species. Complex 2 all other C–N bonds involving the C atoms C11 and C16
also features two C=N double bonds, which can be alkyl- are shorter. This implies that the degree of electron do-
ated. To see if similar reactions are possible for 2, we first nation from the btmgn ligand to the ZnCl2 unit is slightly
carried out some quantum chemical calculations. In these stronger than to Et2Zn, in line with the higher electronega-
calculations we used the model bisguanidine complex tivity of the Cl atoms.
[Me2Zn{C2H2[NC(NMe2)2]2}] in which the aromatic unit is
To obtain more information about the conformational
replaced by a C2H2 bridge (see Scheme 2 and Supporting properties, we carried out variable temperature (VT) 1H
Information). The results of these calculations indeed sug- NMR studies for 3 in CH2Cl2 solutions. Similar studies had
gest the complex is slightly metastable with respect to alkyl already been performed for the free bisguanidine btmgn be-
transfer from Zn to the bisguanidine ligand. Transfer to the fore and after protonation[19] as well as for the complexes
central C atom of one of the guanidino groups leads to an [(κ2-N,NЈ-btmgn)PdCl2] and [(κ2-N,NЈ-btmgn)PtCl2].[27] In
imine-stabilized alkylzinc amide. A gas-phase ∆H (0 K) the case of [(κ2-N,NЈ-btmgn)PdCl2], three different flux-
value of –9 kJmol–1 was calculated for this isomerization in ional processes of the guanidino groups were identified and
the case of our model compound. This species could in a their rate constants determined. Figure 3 (b) shows the
1
second step eliminate dimethylamine (see Scheme 2). To test measured VT H NMR spectra of 3 in CH2Cl2 together
this possibility experimentally, a THF solution of 2 was with spectra from the results of line shape analysis (see also
heated up to 80 °C in an NMR experiment. The appearance the spectra in the Supporting Information for 3 dissolved
of a precipitate in this experiment argues for slow decompo- in CD3CN in the temperature range –30 °C to +60 °C). In
sition. The NMR spectra found, however, no direct evi- contrast to [(κ2-N,NЈ-btmgn)PdCl2], for which the 1H
dence for alkyl transfer, which possibly points to significant NMR spectrum at 178 K showed eight signals (the maxi-
barriers for such reactions. One factor at work might be mum number), the CH3 groups in 3 split into four signals
1
steric shielding of the imino C atoms. Photolysis using at this temperature. The H signals at the aromatic ligand
broad-band irradiation emitted from a Hg high-pressure backbone give only three multiplets. Together with the ob-
lamp resulted in no reaction. Next we tested the reactivity servation of four CH3 signals, this shows that the two tet-
of 2 towards O2. Reaction of [Me2Zn(tBu-DAB)] with O2 ramethylguanidino moieties are equivalent. The four CH3
was recently shown to lead to a methyl peroxide cluster.[24] NMR signals have been assigned to the CH3 groups as de-
Moreover, Et2Zn was shown to initiate radical addition of picted in Scheme 3. The assignment was made on the basis
ethers such as THF to imines in the presence of air O2.[25] of NOE correlations. The fluxional processes in 3 with the
Reaction of O2 with 2 in THF occurred very rapidly. How- metal coordinated in a distorted tetrahedral fashion are
ever, a complex mixture of different products was formed, thus significantly different to those found in the PdII and
from which it proved impossible to isolate or identify a sin- PtII complexes where the metal is coordinated in a distorted
gle compound.
square-planar fashion. The analysis of the spectra gave evi-
We also synthesized, for comparison, the more stable dence for two dynamical processes. At low temperature the
complex [(κ2-N,NЈ-btmgn)ZnCl2], 3, which can be obtained interchange between the methyl groups 1 and 4 as well as
(in contrast to 2) very purely as shown by elemental analy- 2 and 3 (see Scheme 3, with a rate constant k1) becomes
Scheme 2.
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New Alkyl Complexes of Zn, Mg and Cationic Al
Figure 3. (a) Molecular structure of 3. Thermal ellipsoids drawn at the 50% probability level. (b) VT NMR spectra of 3 in CH2Cl2 (left
side), together with the results of line shape analysis simulations (right side). The numbers (1–4) correspond to the CH3 positions shown
in Scheme 3.
observable. This process can also be described as a motion groups. The guanidino methyl groups give rise to a broad
of the Zn atom from one side of the aromatic plane to the signal around 2.40 ppm. This singlet splits again into four
other. Arrhenius and Eyring plots derived from the tem- signals at low temperatures. Pale yellow crystals were ob-
perature dependence of the rate constants yielded estimates tained by layering the solution with n-hexane at –20 °C. The
for the activation enthalpy and entropy. At standard condi- molecular structure as derived from X-ray diffraction is
tions, ∆H# amounts to (+43Ϯ2) kJmol–1 and ∆S#
=
shown in Figure 4. Selected structural parameters can be
(–41Ϯ10) Jmol–1. A second process can be described as ro- found in Table S4 (see Supporting Information). The qual-
tation around the C–N bonds (with a rate constant k2), ity of the structure determination is hampered by the pres-
leading to interchange of the methyl groups 3 and 4 as well ence of highly disordered solvent molecules (alkanes from
as 1 and 2 (see Scheme 3). In this case a standard activation petroleum ether) in the crystal and by additional disorder
enthalpy of (+45Ϯ2) kJmol–1 [∆S# = (–67Ϯ10) Jmol–1] of the n-butyl substituents (see Experimental Section).
was obtained.
Interesting details of the molecular structure include: (i) the
position of the Mg atom being 121.3(2) pm displaced from
the plane of the btmgn ligand and (ii) the short N=C bond
lengths of 132.2(5) and 132.4(4) pm, indicating the weak
donor character of the btmgn ligand and consequently rela-
Scheme 3.
Mg Alkyl and Aryl Complexes
The Mg alkyl complex [(nBu)2Mg(κ2-N,NЈ-btmgn)], 4,
was synthesized by a reaction between (nBu)2Mg (1  in n-
heptane) and btmgn dissolved in toluene. It turned out to
be an extremely unstable compound, so that we were not
able to characterize it adequately. In the 1H NMR spectrum
of 4 in toluene, a number of broad signals in the region
Figure 4. Molecular structure of 4. Thermal ellipsoids drawn at the
from 2.09 to –0.45 ppm can be assigned to the two n-butyl 50% probability level.
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tively weak ligand–metal bonding. Quantum chemical cal- pound such as MeMgBr and the ligand btmgn. The com-
culations again suggest the isomer formed by alkyl transfer plex [(κ2-N,NЈ-btmgn)MgBr2], 5, is formed according to
from the Mg atom to the imine C atom is more stable [∆H Equation (1) (neglecting any Schlenk equilibrium).
(0 K) = –15 kJmol–1]. However, similar to the situation in
the Zn compounds, no direct evidence for alkyl transfer was
observed. Nevertheless, the compound is highly unstable
and decomposes already at room temperature. We also syn-
Crystals of 5 were obtained and the molecular structure
thesized the related alkyl complex [Me2Mg(κ2-N,NЈ- determined by X-ray diffraction. The compound crystallizes
btmgn)], but this complex turned out to be even more sensi- together with equimolar amounts of THF. The resulting
tive.
molecular structure is displayed in Figure 5a. Table S5 (see
As in the case of the Zn alkyl complexes, we synthesized Supporting Information) lists some structural parameters.
for comparison a more stable Mg halide complex, with the The shorter Mg–N bond lengths [204.9(3)/205.2(3) pm in 5
main aim of analyzing the fluxional processes and to com- vs. 214.0(3)/215.2(3) pm in 4] signal stronger ligand–metal
pare the results with the Zn complex. Especially the evalu- bonding in 5 than in 4. The Mg atom is located 116.6 pm
ation of the vibration of the metal atom from one side of above the btmgn aromatic plane. Figure 5 (b) shows the VT
the ligands’ aromatic ring plane to the other should provide 1H NMR spectra experimentally measured and simulated.
useful information about the bond properties. However, it At r.t., only one signal of the CH3 groups is observed (δ =
turned out to be surprisingly difficult to synthesize such a 3 ppm), which splits into four signals at lower temperatures.
compound with the required purity. Probably the best ac- Two additional signals at δ = 1.89 and 4.00 ppm can be
cess turned out to be a reaction between a Grignard com- assigned to THF, which was cocrystallized with the guan-
Figure 5. (a) Molecular structure of 5. Thermal ellipsoids drawn at the 50% probability level. (b) VT NMR spectra of 5 in CH2Cl2 (left
side), together with the results of line shape analysis simulations (right side). The numbers (1–4) correspond to the CH3 positions depicted
in Scheme 3.
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New Alkyl Complexes of Zn, Mg and Cationic Al
1
idine complex. The dynamic behaviour can be modelled pared by reaction between Ph2Mg[28] and btmgn. In the H
with an interchange between methyl groups 2–3 and 1–4 NMR spectrum recorded in benzene, the two phenyl groups
(see Scheme 3), corresponding to a motion of the Mg atom give rise to extra signals at δ = 8.16 ppm (protons in the
from one side of the ligand aromatic ring to the other. The ortho positions) and in the region 7.48–7.18 ppm. This time
activation parameters for this process have been determined two signals due to the guanidino methyl groups (at δ = 2.51
as ∆H# = (53Ϯ2) kJmol–1 and ∆S# = (–4Ϯ8) Jmol–1. The and 1.85 ppm) already appear at 303 K, arguing for differ-
activation entropy value around zero is in accordance with ences in the fluxional processes with respect to the other
a unimolecular process and low steric hindrance in the tran- Mg complexes. The two signals further split to give a quar-
sition state. As the chemical exchanges of the CH3 reso- tet at low temperatures (233 K). Figure 6 displays its molec-
nances are monomolecular processes, activation entropies ular structure (see Table S6 for structural information).
are expected which are around zero for transition states that Again, the two imine N=C bonds of the guanidino groups
are not sterically encumbered or negative when more re- point to the same side, so that the two phenyl groups experi-
strictions are present in the transition states. Thus, the ence different environments. As expected, the Mg–N dis-
smaller Zn (or Al, see below) ions lead to more negative tances in 6 are slightly shorter than in 4 [210.6 and
activation entropies compared to complex 5 with the larger 212.6 pm in 6 vs. 214.0(3) and 215.2(3) pm in 4], but longer
Mg ion.
than in 5. With 87.5(1)°, the N–Mg–N angle in 6 is larger
As an example of a Mg aryl complex we synthesized than in 4.
[Ph2Mg(κ2-N,NЈ-btmgb)], 7. This complex turned out to be
significantly more stable than the alkyl complex 4, and also
complex 6. Therefore it can be isolated more easily in rela-
tively high yield (85%, see Exp. Sect.). Unfortunately only
small crystals which appeared to be twinned were obtained,
so that a satisfying X-ray diffraction analysis was imposs-
ible. Better analytical data can be obtained with the aryl
complex [Ph2Mg(κ2-N,NЈ-btmgn)], 6, which can be pre-
Synthesis of Stable Cationic Al Alkyl Complexes
A major aim of this work was the synthesis and charac-
terization of a stable cationic Al alkyl complex featuring
btmgn or btmgb as the ligand. We used the monoproton-
ated form of btmgn[19] for the synthesis of [Me2Al(κ2-N,NЈ-
btmgn)]+, 8, according to Equation (2). A similar strategy
was used previously for the preparation of other cationic
aluminium alkyl species, for example, recently by Coles et
al. in the case of [H2C{hpp}2AlMe2]+[BPh4]– ([8(B-
(C6H5)4)], see Scheme 4, hpp = 1,3,4,6,7,8-hexahydro-2H-
pyrimido[1,2-a]pyrimidinate).[29] We tried to crystallize the
new cationic Al alkyl complex with [PF6]–, [B(C6H5)4]– and
[B(C6F5)4]– as counterions and finally obtained crystals
suitable for X-ray diffraction for the salt [8(BPh4)] (see Fig-
ure 7). This salt turned out to be stable and was obtained
in good yield and purity according to elemental analysis. In
the mass spectrum the most intense signal shows at m/z =
1
411 ([M]+). In the H NMR spectrum measured at room
temp. a singlet at –0.88 ppm can be assigned to the two
methyl groups attached to Al. The X-ray diffraction mea-
surements gave a molecular structure in which the Al atom
is located 79.0 pm above the plane defined by the naphthyl
group. The Al–C and Al–N bond lengths were measured to
be 197.0(5)/197.3(5) and 191.8(3) pm, respectively (see also
Table S7 in the Supporting Information). These values are
close to those obtained for the related species 9, 10 and 11
(see Scheme 4). Thus the salt [9(BPh4)] features Al–C and
Al–N bond lengths of 197.0(4)/196.4(3) and 190.7(2)/
192.0(2) pm, respectively.[29] Al–C and Al–N bond lengths
of 201.0(2)/201.6(2) and 193.4(2)/193.2(2) pm, respectively,
were measured in [10(B(C6F5)4)] (see Scheme 3).[30] Finally,
in [11(B(C6F5)4)] (see Scheme 4) Al–C and Al–N bond
lengths of 196.4(3)/199.3(3) and 189.4(2)/193.5(2) pm,
respectively, were obtained.[31] With 109.6(2)° the N–Al–N
angle is significantly larger than in all other compounds
discussed in this work.
Figure 6. Molecular structure of 6. Thermal ellipsoids drawn at the
50% probability level. The side view (hydrogen atoms omitted for
sake of clarity) is also provided.
Eur. J. Inorg. Chem. 2009, 4795–4808
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Scheme 4.
Reaction of the salt [(btmgbH)B(C6F5)4], prepared from
equimolar amounts of btmgb and [H(OEt2)2][B(C6F5)4],
with AlMe3 yielded the cationic alkyl-Al complex [Me2-
Al(κ2-N,NЈ-btmgb)][B(C6F5)4]. However, it was not possible
to grow crystals of sufficient quality for an XRD analysis.
Quantum chemical (DFT) calculations were applied to
estimate the strength of the bonding between the btmgn
ligand and the Me2Al+ unit in 8. The energy required for
conversion from κ2- to κ1-coordination of the btmgn ligand
(see Figure 8) amounts to 151 kJmol–1 according to BP86/
SV(P). The geometry of the btmgn ligand and the location
of the metal in [Me2Al(κ1-btmgn)]+ with a three-coordinate
Al atom resembles that of [(κ1-btmgn)PtCl2(C2H4)] (see
Scheme 1).[18] It is possible that the Al atom of this complex
can interact with an ethylene unit if the complex is used for
ethylene polymerization. The complete removal of the
btmgn unit requires a further 362 kJmol–1.
1
Finally, a VT H NMR study of complex 8 was carried
out (see Figure 9, only the region containing the guanidine
and aluminium methyl group signals is shown). A conse-
quence of freezing the motion of the metal from one side
of the ligands’ aromatic system to the other on the NMR
Figure 7. Molecular structure of 8[BPh4]. Thermal ellipsoids drawn
at the 50% probability level. A side view of the molecular structure
of 8 is shown underneath.
Figure 8. VT NMR spectra of 8[PF6] in CH2Cl2 (left side), together with the results of line shape analysis simulations (right side).
4802 Eur. J. Inorg. Chem. 2009, 4795–4808
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New Alkyl Complexes of Zn, Mg and Cationic Al
timescale is the nonequivalence of the two methyl groups in 9 [189.9(2) and 190.6(3) pm] are significantly shorter
attached to the Al atom. The observation of an Al-methyl than those measured in 10 [197.9(5) and 198.2(6) pm]. Con-
signal splitting at low temperatures thus serves as direct sequently, with 216.72(10) and 216.01(9) pm, the Ga–Cl
confirmation of the correct description of the process. bond lengths in 9 are larger than those in 10 [210.5(2) and
Moreover, the spectra simulation showed that the inter- 210.4(2) pm]. The metal atom in 9 is again displaced (by
change between the guanidino and the aluminium methyl 74.0 pm) from the plane defined by the aromatic rings.
groups occurs with the same rate constant. From Eyring Other structural parameters are listed in Table S8. Com-
plots the activation enthalpy and entropy for this pro- pound 10 exhibits a relatively low melting point of 155–
cess can be estimated to be (+41Ϯ2) kJmol–1 and 156 °C. With 242 °C, the melting point of 9 is significantly
(–35Ϯ9) Jmol–1, respectively. The activation parameters of higher.
8 are therefore very similar to the parameters determined
for the btmgn-ZnCl2 complex 3.
Conclusions
In this work we reported on the synthesis and characteri-
zation of the first zinc, magnesium and cationic aluminium
alkyl and aryl complexes of the bisguanidino ligands btmgb
and btmgn (see Scheme 1). For comparison and further
analysis, we also isolated some corresponding halide com-
plexes. Generally, the metal-organic complexes turned out
to be highly reactive and sensitive. As expected, the average
N=C bond length in the guanidino units increases over the
course of complex formation. The following order is ob-
served for the metal complexes of btmgn known so far:
btmgn (128.2 pm)[19]
Ͻ
[(nBu)2Mg(κ2-N,NЈ-btmgn)]
Figure 9. Quantum chemical (DFT) calculations on the change
(132.0 pm)
Ͻ
[Et2Zn(κ2-N,NЈ-btmgn)] (132.2 pm)
Ͻ
from κ2-N,NЈ- to κ1-coordination of the btmgn ligand in 8.
[Ph2Mg(κ2-N,NЈ-btmgn)] (133.0 pm) Ͻ [(κ2-N,NЈ-btmgn)-
ZnCl2] ≈ [(κ2-N,NЈ-btmgn)MgBr2] (δ = 133.2 ppm) Ͻ [(κ2-
N,NЈ-btmgn)PdCl2] (δ =133.8 ppm)[18] Ͻ [(κ2-N,NЈ-btmgn)-
NiCl2][33] (δ = 134.1 ppm) Ͻ [(κ2-N,NЈ-btmgn)PtCl2][18] (δ
=134.6 ppm) ≈ [Me2Al(κ2-N,NЈ-btmgn)]+ (134.5 pm) Ͻ
[(κ2-N,NЈ-btmgn)GaCl2]+ (δ = 136.0 ppm). The electron do-
nation from btmgn to the metal increases in the same order
and the stability of the complexes follows a similar order.
Hence the magnesium and zinc alkyl complexes are highly
unstable and decompose slowly in solution already at room
temperature, while the cationic aluminium complex is re-
markably stable. Another interesting detail is the displace-
ment of the metal atom from the plane defined by the aro-
matic system. This displacement reaches a maximum of
121.3 pm in [(nBu)2Mg(κ2-N,NЈ-btmgn)] and is relatively
small in [Me2Al(κ2-N,NЈ-btmgn)]+ (79.0 pm). Complexes of
the bisguanidine btmgb are generally more stable than the
corresponding ones of btmgn. Alkylation of the C=N
double bonds of the guanidino groups was not observed,
although intramolecular alkyl transfer is mildly exothermic
according to quantum chemical calculations.
Cationic gallium halide complexes are easily accessible.
Hence GaCl3 reacts with btmgn to give the salt [(κ2-N,NЈ-
btmgn)GaCl2]+[GaCl4]–, 9, according to Equation (3). The
first evidence for the formation of such a salt came from
mass spectroscopy. Hence the mass spectra (FAB+) dis-
played a strong signal at m/z = 495.2 because of the
[(btmgn)GaCl2]+ cation. The product was then confirmed
by XRD analysis of single crystals grown from THF solu-
tions. Figure 10 illustrates the molecular structure obtained
from this analysis. Similar reactions were previously re-
ported for diimines. For example, it had been shown that
DAB (1,4-di-tert-butyl-1,4-diazabutadiene) reacts with
GaCl3 to give [(DAB)GaCl2][GaCl4] (10).[32] Because of the
higher basicity of the btmgn ligand, the Ga–N bond lengths
All compounds in this study showed dynamic behaviour
at the CH3 groups of the guanidino units. A detailed VT
NMR analysis of compounds 3, 5 and 8 shows that the
fast exchange between two pairs of CH3 signals is due to a
movement of the metal atoms from one side of the naphthyl
backbone to the other side. This movement also exchanges
the positions of the additional ligands (e.g., the two Al-CH3
groups in 8). The rotations around the C–MCl2 bonds of
Figure 10. Molecular structure of 9. Thermal ellipsoids drawn at
the 50% probability level.
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H.-J. Himmel et al.
FULL PAPER
ppm. 13C NMR (100.56 MHz, [D8]THF, 297.4 K): δ = 150.46,
the guanidino groups occur at slower rates, so that at high
temperatures all four guanidine-CH3 signals collapse into
one singlet.
Ongoing studies in our group focus on i. direct applica-
tions of these alkyl complexes in catalysis,[34] ii. the possibil-
ity to synthesize cationic alkyl complexes stabilized by the
strong electron-donating character of the bisguanidino li-
gands and iii. the possibility to use the complexes as start-
ing reagents for the preparation of di- and oligonuclear
alkyl complexes.
138.59, 126.20, 123.93, 121.55, 116.91 (Carom.), 40.27 (CH3), 14.45
1
(CH3), 3.55 (CH2) ppm. H NMR (200 MHz, [D8]THF, 203 K): δ
= 3.16 (s, 4 H), 2.95 (s, 4 H), 2.79 (m, 8 H), 2.60 (s, 4 H), 2.15 (s,
4 H) ppm. IR (KBr): ν = 3043 (w), 3002 (w), 2929 (s), 2861 (s),
˜
2787 (sh), 1541 (vs), 1462 (vs), 1398 (vs), 1372 (vs), 1279 (m), 1234
(s), 1145 (s), 1061 (s), 988 (s), 925 (m), 837 (s), 761 (s), 686 (m),
584 (m), 472 (m) cm–1.
[(κ2-N,NЈ-btmgn)ZnCl2] (3): btmgn (216.8 mg, 0.61 mmol) was dis-
solved in CH3CN (12 mL) and a ZnCl2 solution (0.6 mL, 1 ) in
Et2O was added dropwise. The reaction mixture was stirred for 24 h
at room temperature. Subsequently the solvent was removed under
vacuum and the residue washed three times with toluene (5 mL) to
clean unreacted btmgn from the product. After removal of all sol-
vent traces under vacuum, [(κ2-N,NЈ-btmgn)ZnCl2] (279.9 mg,
0.57 mmol, 95%) was obtained as a white powder. Recrystallization
from CH3CN at –21 °C afforded colourless crystals suitable for X-
ray diffraction. C20H30Cl2N6Zn (490.77): calcd. C 48.94, H 6.16, N
17.12, Cl 14.45, Zn 13.32; found C 48.95, H 6.21, N 17.19. 1H
NMR (400 MHz, CD2Cl2, 23 °C): δ = 7.46 (d, J = 8.14 Hz, 2 H,
CHarom.), 7.28 (dd, J = 7.55 Hz, 2 H), 6.32 (d, J = 7.36 Hz, 2 H,
CHarom.), 2.92 (m, 24 H, CH3) ppm. 13C NMR (100.55 MHz,
CD2Cl2, 296 K): δ = 165.57 (CN3), 146.29 (Carom.), 138.33 (Carom.),
126.45 (Carom.), 123.62 (Carom.), 121.71 (Carom.), 118.21 (Carom.),
Experimental Section
General: The bisguanidine btmgn was purchased from Fluka
(grade: “purum”). Et2Zn solutions in toluene (1.5 ) were delivered
by Acros. Me3Al (2  in toluene) was purchased from Aldrich.
While all compounds are air- and water-sensitive, there are some
distinctive reactivity differences. Thus compound 2 is the most sen-
sitive among the Zn complexes reported herein. The Mg alkyl com-
plexes show signs of decomposition already at room temp. IR spec-
tra were recorded with a Bruker Vertex 80v spectrometer. VT NMR
measurements were performed on a Bruker DPX200 and a Bruker
AvanceII 400 spectrometer equipped with an N2 gas/liq. N2 heat
exchanger and a BVT 3200 control unit [NMR chemical shifts rela-
tive to TMS (13C and 1H), BF3·OEt2 (11B), H3PO4 (31P) and CFCl3
(19F)]. The temperature was calibrated with a [D4]MeOH NMR
thermometer.[35] “PE 40/60” stands for petroleum ether with a boil-
ing range of 40–60 °C.
41.60, 40.35 (CH ) ppm. IR: ν = 3005 (w), 2952 (m), 2865 (m),
˜
3
2789 (w), 1555 (s), 1527 (vs) 1467 (s), 1403 (vs), 1377 (s), 1332 (s),
1280 (m), 1233 (m), 1157 (s), 1108 (w), 1065 (m), 988 (s), 922 (w),
850 (w), 809 (m), 757 (m), 691 (m), 624 (w), 505 (w), 478 (w) cm–1.
HR-EI+: calcd. m/z = 490.1170 [C20H30N6Cl2Zn], exp. m/z =
490.1139 [M]+. EI+: m/z = 490.3 [M]+, 453.3 [M – Cl]+, 354.4
[btmgn]+.
[Et2Zn(κ2-N,NЈ-btmgb)] (1): btmgb (0.100 g, 0.329 mmol) was dis-
solved in THF (2 mL). After dropwise addition of an Et2Zn solu-
tion (0.3 mL, 1.5 ) in toluene the reaction mixture was stirred for
2 h. Layering of the solution with n-hexane (4 mL) and storage at
–21 °C yielded colourless crystals of [Et2Zn(κ2-N,NЈ-btmgb)] (yield
79%). C20H38N6Zn (427.93): calcd. C 56.13, H 8.95, N 19.64, Zn
15.28; found C 56.27, H 9.03, N 19.52. 1H NMR (400 MHz,
CD2Cl2, 23 °C): δ = 6.75 (m, 2 H, CHarom.), 6.42 (m, 2 H, CHarom.),
2.76 (m, 24 H, Me), 0.96 (t, 6 H, ZnCH2CH3), –0.39 (q, 4 H,
ZnCH2CH3) ppm. 13C{1H} NMR (100.55 MHz, CD2Cl2, 23 °C):
δ = 143.75 (arom. C), 121.60 (arom. CH), 121.04 (arom. CH), 39.77
[(nBu)2Mg(κ2-N,NЈ-btmgn)] (4): btmgn (103 mg, 0.29 mmol) was
dissolved in toluene (5 mL). After addition of a (nBu)2Mg solution
(0.3 mL, 1 ) in heptane by syringe at –20 °C, the clear yellow solu-
tion was stirred for an additional 10 min at –20 °C and a further
10 min at room temp. Pale yellow crystals were obtained by layer-
ing the solution with PE40/60 at –20 °C. 1H NMR (200 MHz, [D8]-
toluene, 298 K): δ = 7.40 (d, J = 7.65 Hz, 2 H, CHarom.), 7.20 (t, J
= 7.75, 1 Hz, 2 H, CHarom.), 6.04 (d, J = 7.29 Hz, 2 H, CHarom.),
2.40 (m, 24 H, CH3), 2.09, 2.03, 1.77, 1.65, 1.56, 1.07, 0.3, 0.16,
1
–0.45 (m, 19 H, butyl) ppm. H NMR (200 MHz, C6D6, 303 K): δ
= 7.43 (d, J = 7.58 Hz, 2 H, CHarom.), 7.20 (t, J = 7.74, 1 Hz, 2 H,
CHarom.), 6.05 (d, J = 7.34 Hz, 2 H, CHarom.), 2.31 (m, CH3), 2.20–
1.11 (butyl), 0.42, –0.3 (m, butyl) ppm. 13C NMR (100.56 MHz,
C6D6, 296.9 K): δ = 165.26 (CN3), 147.66, 138.31, 126.09, 122.93,
118.01 (Carom.), 40.2, 39.3 (CH3), 34.55, 32.66, 31.13, 25.13, 22.74,
15.33, 14.75, 13.93, 13.31 (coupling with 1H signal at δ = 1.42 ),
10.4 (butyl) ppm. At low-temperature 1H NMR (200 MHz, [D8]-
toluene, 213 K) the CH3 group resonances of the btmgn ligand split
into four signals at 3.28 (s, 6 H), 2.39 (s, 6 H), 1.86 (s, 6 H), 1.66
(s, 6 H), and the signals from the butyl groups showed at 2.13, 1.92,
1.78, 1.48, 1.23, 1.19, 0.21, –0.28 (m, 20 H) ppm.
(NCH ), 14.61 (CH ), 3.49 (CH ) ppm. IR (KBr): ν = 3046 (w),
˜
3
3
2
3003 (w), 2924 (m), 2866 (m), 2831 (m), 2694 (w), 1528 (vs) 1468
(s), 1390 (vs), 1338 (m), 1273 (m), 1236 (m), 1211 (m), 1148 (s),
1109 (m), 1061 (m), 1022 (s), 984 (m), 928 (m), 870 (w), 826 (m),
737 (vs), 706 (m), 627 (w), 590 (m), 560 (m) cm–1.
[Et2Zn(κ2-N,NЈ-btmgn)] (2): btmgn (103 mg, 0.29 mmol) was dis-
solved in dry THF (5 mL) and an Et2Zn solution (0.3 mL, 1.5 )
in toluene was added dropwise. The clear yellow reaction mixture
was stirred for a period of 2 h at room temperature. Subsequently
the solution was layered with n-hexane at –20 °C to obtain pale
yellow crystals (73 mg, 0.15 mmol, 52% yield). C24H40N6Zn
(477.98): calcd. C 60.31, H 8.43, N 17.58; found C 58.31, H 8.03,
[(κ2-N,NЈ-btmgn)MgBr2] (5): The btmgn ligand (118 mg,
0.33 mmol) was dissolved in THF (15 mL). Then a solution of
1
N 16.13. H NMR (399.89 MHz, C6D6, 296.2 K): δ = 7.45 (dd, J
= 8.16, 1 Hz, 2 H, CHarom.), 7.26 (t, J = 7.69 Hz, 2 H, CHarom.), MeMgBr (0.22 mL, 0.66 mmol, 2 equiv., 3  in Et2O) was added
6.32 (m, 2 H, CHarom.), 2.49 (m, 24 H, CH3), 1.49 (m, 6 H, dropwise by a syringe. The reaction mixture was stirred for 1.5 h
ZnCH2CH3), 0.32 (m,
4
H, ZnCH2CH3) ppm. 13C NMR
at room temp. Colourless, cloudy crystals suitable for X-ray diffrac-
tion were obtained by layering the reaction mixture with PE 40/60.
(100.56 MHz, C6D6, 297.4 K): δ = 149.90, 138.07, 125.98, 123.48,
121.45, 116.52 (Carom.), 39.65 (CH3), 15.35 (CH3), 3.73 (CH2) ppm. 1H NMR (399.89 MHz, CD2Cl2, 294.6 K): δ = 7.46 (dd, J = 8.05,
1H NMR (399.89 MHz, [D8]THF, 296.2 K): δ = 7.20 (d, J =
7.91 Hz, 2 H), 7.09 (t, J = 7.68 Hz, 2 H), 6.15 (d, J = 7.30 Hz, 2
H), 2.75 (m, 24 H, CH3), 0.92 (m, 6 H, CH3), –0.33 (m, 4 H, CH2)
0.65 Hz, 2 H, CHarom.), 7.29 (t, J = 7.78 Hz, 2 H, CHarom.), 6.31
(dd, J = 7.45, 0.86 Hz, 2 H, CHarom.), 3.1–2.4 (br. s, 24 H, CH3)
ppm. 1H NMR (200 MHz, CD2Cl2, 303 K): δ = 7.47 (d, J =
4804
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New Alkyl Complexes of Zn, Mg and Cationic Al
8.08 Hz, 2 H, CHarom.), 7.29 (t, J = 7.77 Hz, 2 H, CHarom.), 6.31 In addition, colourless and clear crystals of the free btmgb ligand
(d, J = 7.35 Hz, 2 H, CHarom.), 2.92, 2.80 (br. s, 24 H, CH3) ppm. precipitated. C28H38MgN6·THF (627.15): calcd. C 69.24, H 8.35,
1
13C NMR (100.56 MHz, CD2Cl2, 296.0 K): δ = 165.98 (CN3), N 15.14; found C 63.61, H 8.14, N 15.94. H NMR (399.89 MHz,
145.75, 137.84, 126.06, 123.22, 121.87, 118.11 (Carom.), 41.0, 40.00 C6D6, 295 K): δ = 8.27 (m, 4 H, CHarom.), 7.51 (t, J = 7.25 Hz, 4
(br., CH3) ppm. The guanidino CH3 group resonances were split at
lower temperatures in the 1H NMR (399.89 MHz, CD2Cl2, 243 K)
spectra to give four signals at 3.29 (s, 6 H), 2.97 (s, 6 H), 2.80 (s, 6
H) and 2.18 (s, 6 H) ppm. MS (EI): m/z (%) = 538 (90) [M+], 459
H, CHarom.), 7.39 (t, J = 7.24 Hz, 2 H, CHarom.), 6.90 (dd, J = 5.88,
3.47 Hz, 2 H, CHarom.), 6.42 (dd, J = 5.87, 3.49 Hz, 2 H, CHarom.),
2.84 (m, 6 H, CH3), 1.96 (br. s, 18 H, CH3) ppm. 13C NMR
(100.56 MHz, C6D6, 296.5 K): δ = 142.07, 141.33, 129.02, 128.55,
126.28, 124.41, 122.07, 120.29 (Carom.), 39.51 (CH3) ppm. 1H NMR
(78) [M+ – Br–], 354 (96) [L+]. IR (KBr): ν = 2945 (s), 2885 (s),
˜
2789 (m), 1554 (vs), 1466 (s), 1403 (s), 1375 (s), 1336 (s), 1279 (m), (200 MHz, [D8]toluene, 298 K): δ = 8.11 (m, 4 H), 7.5–7.2 (m, 6
1234 (m), 1158 (s), 1109 (m), 1063 (m), 1022 (s), 922 (m), 875 (m),
H), 6.85 (m, 2 H), 6.39 (m, 2 H), 2.98–1.83 (m, 24 H, CH3) ppm.
At lower temperatures (193 K, 200 MHz, [D8]THF, H NMR) the
1
848 (m), 808 (w), 768 (w), 693 (w), 623 (w) cm–1.
signals arising from the btmgb ligand CH3 groups split into four
signals at 2.92 (s, 6 H), 1.97 (s, 6 H), 1.84 (s, 6 H) and 1.78 (s, 6
H) ppm.
[(κ2-N,NЈ-btmgn)MgCl2]: A solution of tmgn (103 mg, 0.29 mmol)
in THFabs. (10 mL) was prepared and CH3CH2MgCl (0.29 mL,
0.58 mmol, 2 equiv., 2  in THF) added with a syringe at room
temp. over a period of 1 h. After removal of the solvent one obtains
the product (200 mg) in the form of a white powder. 1H NMR
(399.89 MHz, CD2Cl2, 295 K): δ = 7.46 (d, J = 8.00 Hz, 2 H,
CHarom.), 7.28 (t, J = 7.77 Hz, 2 H, CHarom.), 6.31 (d, J = 7.38 Hz,
2 H, CHarom.), 3.2–2.4 (br. s, 24 H, CH3) ppm. 1H NMR (200 MHz,
CD2Cl2, 303 K): δ = 7.46 (d, J = 8.10 Hz, 2 H, CHarom.), 7.29 (t,
J = 7.70 Hz, 2 H, CHarom.), 6.32 (d, J = 7.37 Hz, 2 H, CHarom.),
2.92, 2.82 (br. s, 24 H, CH3) ppm. 13C NMR (100.56 MHz, CD2Cl2,
296.5 K): δ = 165.64 (CN3), 145.85, 137.85, 126.03, 123.14, 121.90,
118.06 (Carom.), 41.0, 39.66 (br., CH3) ppm. MS (EI): m/z (%) =
[H{O(C2H5)2}2][B(C6F5)4]: The preparation followed the procedure
described in the literature.[36] However, instead of crystallization of
the product, the solvent was removed under vacuum and the solid
residue dissolved in CH2Cl2 was filtered through silica. Starting
with LiB(C6F5)4·2.5C2H5OC2H5 (305.4 mg), aqueous HCl (1.5 mL,
2 ) in Et2O and Et2O (6 mL), we obtained the product (287 mg,
90%) in the form of a pale yellow oil.
[btmgnH][B(C6F5)4]: A solution of [H(OEt2)2][B(C6F5)4] (149 mg,
0.18 mmol) in CH3CN (3 mL) was added by syringe to a solution
of btmgn (65 mg, 0.18 mmol) in CH3CN (3 mL). The colourless
clear reaction mixture was stirred for 2 h at room temp. After re-
moval of the solvent under vacuum the beige solid residue was
washed three times with PE 40/60 leading to the product (156 mg,
0.15 mmol, 84%) in the form of a beige solid foam. 1H NMR
(399.89 MHz, CD2Cl2, 295.6 K): δ = 15.02 (s, 1 H, H+), 7.46 (d, J
= 8.08 Hz, 2 H, CHarom.), 7.36 (t, J = 7.67 Hz, 2 H, CHarom.), 6.43
(d, J = 7.24 Hz, 2 H, CHarom.), 2.90 (s, 24 H, CH3) ppm. 13C NMR
(100.56 MHz, CD2Cl2, 295.6 K): δ = 159.32 (CN3), 141.64, 135.07,
126.27, 122.72, 113.90 (Carom.), 40.10 (CH3) ppm. 11B NMR
(128.30 MHz, CD2Cl2, 295.6 K): δ = –16.66 (s) ppm. 19F NMR
(376.27 MHz, CD2Cl2, 295.6 K): δ = –133.11 (m), –163.72 (t, J =
20.37 Hz), –167.60 (t, J = 18.52 Hz) ppm. MS (ESI, CH2Cl2): m/z
(%) = 355.26 (100) [M]+.
448 (43) [M+], 354 (98) [L+]. IR (KBr): ν = 2952 (s), 2873 (s), 2794
˜
(sh), 1547 (vs), 1536 (vs), 1466 (s), 1401 (vs), 1335 (s), 1280 (m),
1234 (m), 1137 (s), 1063 (m), 1018 (m), 996 (m), 923 (w), 887 (w),
808 (w), 764 (w), 692 (w), 623 (w) cm–1.
[Ph2Mg(κ2-N,NЈ-btmgn)] (6): A solution of Ph2Mg·3THF (201 mg,
0.51 mmol, 1.5 equiv.) and btmgn (120 mg, 0.34 mmol) in THF
(10 mL) was stirred for 2 h at room temp. After layering the reac-
tion mixture with PE 40/60 and addition of an excess of
Ph2Mg·3THF at –20 °C colourless, slightly cloudy crystals suitable
for X-ray diffraction were obtained. In addition the free btmgn
ligand crystallized in the form of colourless and clear crystals. The
solvent was removed under vacuum and the remaining colourless
solid washed three times with PE 40/60 to obtain the product
(258 mg, 0.49 mmol, (95% yield). 1H NMR (200 MHz, C6D6,
303 K): δ = 8.16 (d, J = 7.31 Hz, 4 H, CHarom.), 7.48–7.18 (m, 10
H, Ph), 6.09 (d, J = 7.31 Hz, 2 H, CHarom.), 2.51 (m, 12 H, CH3),
1.85 (s, 12 H, CH3) ppm. 13C NMR (100.56 MHz, C6D6, 296.3 K):
δ = 165.03 (CN3), 147.59, 141.19, 138.44, 129.02, 128.55, 126.18,
126.13, 124.18, 123.13, 118.05 (Carom.), 38.89, 36.3 (br., CH3) ppm.
1H NMR (200 MHz, [D8]THF, 303 K): δ = 7.61 (m, 4 H, CHarom.),
7.41 (d, J = 7.91 Hz, 2 H, CHarom.), 7.22–7.17 (m, 2 H, CHarom.),
6.8 (m, 6 H, CHarom.), 6.32 (d, J = 7.14 Hz, 2 H, CHarom.), 2.89–
2.26 (m, 24 H, CH3) ppm. The btmgn CH3 group resonances were
split in the 1H NMR (200 MHz, [D8]THF, 233 K) spectrum at
lower temperatures into four signals located at 3.03 (s, 6 H), 2.76
[btmgbH][B(C6F5)4]: A solution of [H(OEt2)2][B(C6F5)4] (197 mg,
0.24 mmol) in Et2O (5 mL) was added by syringe to a solution of
btmgb (73 mg, 0.24 mmol) in Et2O (5 mL). The colourless clear
solution was stirred for 2 h at room temp. After removal of the
solvent under vacuum the white solid obtained was washed three
times with PE 40/60 yielding the product (220 mg, 0.22 mmol) in
the form of a colourless foam (93% yield). C40H29BF20N6 (984.47):
1
calcd. C 48.80, H 2.97, N 8.54; found C 47.71, H 3.49, N 7.73. H
NMR (399.89 MHz, CD2Cl2, 295.6 K): δ = 6.96 (dd, J = 5.92,
3.46 Hz, 2 H, CHarom.), 6.58 (dd, J = 5.92, 3.48 Hz, 2 H, CHarom.),
2.86 (s, 24 H, CH3) ppm. 13C NMR (100.56 MHz, CD2Cl2,
295.6 K): δ = 159.46 (CN3), 134.77, 123.12, 119.10, (Carom.) 39.88
(CH3) ppm. 11B NMR (128.30 MHz, CD2Cl2, 295.6 K): δ = –16.67
(s) ppm. 19F NMR (376.27 MHz, CD2Cl2, 295.6 K): δ = –133.13
(m), –163.74 (t, J = 20.40 Hz), –167.60 (t, J = 18.10 Hz) ppm. IR
1
(s, 6 H), 2.34 (s, 6 H) and 2.10 (s, 6 H) ppm. H NMR (200 MHz,
[D8]toluene, 298 K): δ = 8.03 (m, 4 H, CHarom.), 7.5–7.2 (m, 10 H,
Ph), 6.06 (m, 2 H, CHarom.), 2.85–2.34 (m, 12 H, CH3), 1.91 (br. s,
12 H, CH3) ppm. Again splitting of the signal due to the btmgn
CH3 groups in the 1H NMR (200 MHz, [D8]toluene, 223 K) spectra
was observed leading to four signals at 2.95 (s, 6 H), 1.95 (s, 6 H),
1.80 (s, 6 H) and 1.72 (s, 6 H) ppm.
(KBr): ν = 2938 (m), 2878 (sh), 1643 (m), 1535 (vs), 1464 (vs), 1391
˜
(s), 1273 (m), 1149 (m), 1090 (s), 1026 (m), 980 (vs), 752 (m), 663
(m), 559 (w) cm–1.
[Me2Al(κ2-N,NЈ-btmgn)][B(C6F5)4]: [(btmgnH)B(C6F5)4] (156 mg,
0.15 mmol) was dissolved in toluene (5–10 mL). After dropwise ad-
dition of a Me3Al solution (0.15 mL, 2 ) in toluene, the colourless
clear reaction mixture was stirred for a period of 2 h at room tem-
perature. Subsequently the solvent was removed in vacuo leaving a
colourless solid, which was washed three times with PE 40/60. Yield
[Ph2Mg(κ2-N,NЈ-btmgb)] (7): A solution of Ph2Mg·3THF (119 mg,
0.30 mmol, 1.6 equiv.) and btmgn (58 mg, 0.19 mmol) in THF
(6 mL) was stirred for 2 h at room temp. After removal of the sol-
vent under vacuum the beige residue was washed three times with
PE 40/60 to obtain the product (77 mg, 0.16 mmol, 85% yield).
Eur. J. Inorg. Chem. 2009, 4795–4808
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4805

H.-J. Himmel et al.
150 mg (0.14 mmol, 93%). 1H NMR (399.89 MHz, CD2Cl2, obtained, which was washed three times with PE 40/60 to yield
FULL PAPER
295.7 K): δ = 7.64 (d, J = 8.15 Hz, 2 H, CHarom.), 7.40 (t, J =
7.83 Hz, 2 H, CHarom.), 6.44 (d, J = 7.35 Hz, 2 H, CHarom.), 2.98
(s, 12 H, CH3), 2.77 (m, 12 H, CH3), –0.87 (s, 6 H, Al-CH3) ppm.
the product together with approx. equimolar amounts of toluene
(220 mg, 0.194 mmol, 97% yield). 1H NMR (399.89 MHz, CD2Cl2,
295.9 K): δ = 7.03 (dd, J = 5.94, 1 Hz, 2 H, CHarom.), 6.61 (dd, J
13C NMR (100.56 MHz, CD2Cl2, 297.3 K): δ = 165.65 (CN3), = 5.93, 3.43 Hz, 2 H, CHarom.), 2.98 (s, 12 H, CH3), 2.78 (m, 12 H,
149.44, 147.04, 140.82, 139.53, 137.30, 135.28, 129.04, 128.23,
126.71, 125.07, 120.47, 117.94 (Carom.), 41.30, 40.05 (CH3), –11.45
(Al-CH3) ppm. 11B NMR (128.30 MHz, CD2Cl2, 295.9 K): δ =
CH3), –0.77 (s, 6 H) ppm. 13C NMR (100.56 MHz, CD2Cl2,
297.2 K): δ = 163.31 (CN3), 149.37, 147.04, 137.41, 135.10, 124.20,
119.17 (Carom.), 40.71, 39.85 (CH3), –10.2 (Al-CH3) ppm. 11B NMR
–16.65 (s) ppm. 19F NMR (376.23 MHz, CD2Cl2, 295.9 K): δ = (128.30 MHz, CD2Cl2, 295.9 K): δ = –16.67 (s) ppm. 19F NMR
–133.07 (m), –163.66 (t, J = 20.41 Hz), –167.53 (t, J = 17.24 Hz) (376.23 MHz, CD2Cl2, 295.9 K): δ = –133.12 (m), –163.73 (t, J =
ppm. MS (FAB): m/z (%) = 411 (100) [M+], 355 (28) [btmgnH+].
20.39 Hz), –167.58 (t, J = 17.76 Hz) ppm. MS (FAB): m/z (%) =
305 (100) [btmgbH+]. IR (KBr): ν = 2952 (s), 2883 (sh), 1642 (s),
˜
[Me2Al(κ2-N,NЈ-btmgn)][PF6]: A solution of Me3Al in toluene (2 ,
0.46 mL, 0.92 mmol, 3.3 equiv.) was added dropwise to a solution
of [(btmgnH)PF6] (140 mg, 0.28 mmol) (prepared as described in
the literature, see ref.[19]) in THF (50 mL). The reaction mixture
was stirred for 20 h at room temp. The solvent was removed under
vacuum and the residue was washed several times with toluene to
obtain [Me2Al(κ2-N,NЈ-btmgn)][PF6] in 128 mg (0.23 mmol, 82%)
yield. 1H NMR (399.89 MHz, 295 K, CD2Cl2): δ = 7.61 (d, J =
1562 (s), 1529 (s), 1464 (vs), 1413 (s), 1333 (m), 1273 (m), 1089 (s),
980 (s), 834 (m), 754 (m), 681 (m) cm–1.
[(κ2-N,NЈ-btmgn)GaCl2][GaCl4]·THF (9): A solution of GaCl3
(104 mg, 0.59 mmol) in THF (5 mL) was added dropwise by sy-
ringe to a solution of btmgn (118 mg, 0.33 mmol) in THF (5 mL)
at –78 °C. After stirring the reaction mixture for 30 min it was
warmed to room temperature and the solvent was removed under
7.74 Hz, 2 H, CHarom.), 7.41 (t, J = 7.30 Hz, 2 H, CHarom.), 6.47 vacuum. The residue was washed twice with toluene. After removal
(d, J = 7.02 Hz, 2 H, CHarom.), 3.01 (s, 12 H, CH3), 2.78 (br. s, 12 of all solvent traces under vacuum [(κ2-N,NЈ-btmgn)GaCl2][GaCl4]
H, CH3), –0.88 (s, 6 H) ppm. 13C NMR (100.56 MHz, 296.7 K, (151 mg, 0.19 mmol, 66%) (containing traces of solvent and pro-
CD2Cl2): δ = 165.53, 159.23 (CN3), 142.12, 141.02, 137.17, 126.69,
tonated ligand) was obtained as
a
white powder.
126.21, 124.71, 122.16, 120.45, 117.90, 113.69, (Carom.), 41.31, 40.04
C24H38Cl6Ga2N6O (778.74): calcd. C 37.02, H 4.92, Cl 27.32, Ga
(CH3), –11.43 (br., Al-CH3) ppm. 19F NMR (376.23 MHz, CD2Cl2, 17.9, N 10.79; found C 34.26, H 4.31, N 11.58. Crystallization from
193.4 K): δ = –72.7 (d). 31P NMR (242.92 MHz, 295 K, CD3CN): THF afforded colourless crystals suitable for XRD. 1H NMR
δ = –144.64 [sept, J(31P,19F) = 706.3 Hz] ppm. Low-temperature
1H NMR (399.89 MHz, CD2Cl2, 193.4 K) shows the splitting of
the btmgn CH3 groups [3.11 (s, 6 H), 2.98 (s, 6 H), 2.90 (s, 6 H),
2.25 (s, 6 H)] and of the CH3 groups at the Al [–0.98 (s, 3 H), –1.00
(s, 3 H)].
(399.89 MHz, CD2Cl2, 296 K): δ = 7.77 (d, J = 8 Hz, 2 H,
CHarom.), 7.52 (t, J = 8 Hz, 2 H, CHarom.), 6.49 (d, J = 7.6 Hz, 2
H, CHarom.), 3.13 (s, 12 H, CH3), 2.93 (s, 12 H, CH3) ppm. 13C
NMR (100.56 MHz, CD2Cl2, 296 K): δ = 164.36 (CN3), 139.74
(arom. C), 137.87 (arom. C), 127.31 (arom. C), 126.58 (arom. C),
119.0 (arom. C), 42.12 (CH ), 41.02 (CH ) ppm. IR (CsI): ν = 2940
˜
3
3
[Me2Al(κ2-N,NЈ-btmgn)][B(C6H5)4], 8[B(C6H5)4]: A solution of
Me3Al (2 ) in toluene (0.46 mL, 0.92 mmol, 3.3 equiv.) was added
dropwise to a solution of [(btmgnH)PF6] (140 mg, 0.28 mmol) (pre-
pared as described in the literature, see ref.[19]) in 50 mL THF. The
reaction mixture was stirred for 20 h at room temp. The solvent
was removed under vacuum and the residue washed several times
with toluene to obtain [Me2Al(κ2-N,NЈ-btmgn)][PF6] in 128 mg
(0.23 mmol, 82%) yield. Then a solution of [Me2Al(κ2-N,NЈ-
btmgn)][PF6] in THF (50 mL) was prepared, NaBPh4 (79 mg,
0.23 mmol) was added and the mixture was stirred for 1 h at room
temp. The solution was filtered through silica and the filtrate con-
centrated. Colourless crystals were obtained from the THF solu-
tion layered by n-hexane. C46H56AlBN6 (730.76): calcd. C 75.60, H
7.72, N 11.50; found C 75.60, H 7.70, N 10.93. 1H NMR
(399.89 MHz, CD2Cl2): δ = 7.64 (d, J = 8.3 Hz, 2 H, CHarom.),
(m), 1958 (m), 1410 (s), 1311 (vs), 1157 (s), 1016 (s), 869 (s), 820
(vs), 762 (vs), 629 (m), 507 (m) cm–1. MS (FAB+): m/z (%) = 495.2
(30) [M+ – GaCl4 – THF].
X-ray Crystallographic Study: Suitable crystals were taken directly
out of the mother liquor, immersed in perfluorinated polyether oil
and fixed on top of a glass capillary. Intensity measurements were
made at low temperature on Nonius Kappa CCD (complexes 1–3
and 5–8 at 200 K) and Bruker AXS Smart 1000 diffractometers
(complex 4 at 100 K) (Mo-Kα radiation, graphite monochromator,
λ = 0.71073 Å). The data collected were processed with the stan-
dard Nonius[37] or Bruker[38] software. The structures were solved
by conventional direct methods[37] (complexes 1–3 and 5–8) or by
direct methods with dual-space recycling (“Shake-and-Bake”)[39]
(complex 4). Because of severe disorder and unresolvable composi-
7.47–7.36 (m, 2 H, CHarom.), 7.32 (m, 8 H, CHarom.), 7.02 (t, J = tion, electron density attributed to solvent of crystallization (al-
7.4 Hz, 8 H, CHarom.), 6.87 (t, J = 7.2 Hz, 4 H, CHarom.), 6.41 (d, kanes from petroleum ether) was removed from the structure (and
J = 7.5 Hz, 2 H, CHarom.), 2.91 (s, 12 H, CH3), 2.73 (br. s, 12 H, the corresponding Fobs) of 4 with the BYPASS procedure,[40] as
CH3), –0.88 (s, 6 H) ppm. 13C NMR (100.56 MHz, CD2Cl2): δ =
165.54 (CN3), 164.82, 164.33, 163.84, 163.35 (BPh4) 140.81, 137.26,
135.96, 126.73, 125.70, 125.02, 121.79, 117.90, 113.84 (Carom.),
41.42, 40.14 (CH3), –11.79 (br., Al-CH3) ppm. MS (ESI): m/z (%)
implemented in PLATON (SQUEEZE).[41] Restraints had to be
applied to the bond lengths and the adps of the carbon atoms of
the n-butyl groups in 4. All further calculations were performed
using the SHELXTL-PLUS software package. Graphical handling
= 411 (100) [M]+. IR (CsI): ν = 3041 (w), 2945 (m), 2913 (sh), 2807 of the structural data during solution and refinement was per-
˜
(w), 1583 (vs), 1529 (vs), 1474 (s), 1411 (s), 1381 (s), 1318 (s), 1235
(m), 1169 (s), 1154 (w), 1069 (m), 1023 (m), 1009 (m), 865 (vs), 840
(vs), 771 (s), 706 (m), 675 (s), 558 (s), 512 (m) cm–1.
formed with XPMA.[42] Structural representations were generated
using Winray 32.[43] Atomic coordinates and anisotropic thermal
parameters of non-hydrogen atoms were refined by full-matrix le-
ast-squares calculations. Table 1 contains some information on the
crystals of the btmgn complexes.
[Me2Al(κ2-N,NЈ-btmgb)][B(C6F5)4]: [(btmgbH)B(C6F5)4] (197 mg,
0.20 mmol) was dissolved in toluene (20 mL). A Me3Al solution
(2 ) in toluene (0.2 mL, 0.4 mmol) was added dropwise by syringe.
The colourless clear solution was stirred for 1 h at room temp. Af-
ter removal of the solvent under vacuum a colourless residue was
CCDC-732382 (for 8), -732383 (for 4), -732384 (for 3), -732385 (for
1), -732386 (for 2), -732387 (for 5), -732388 (for 6) and
-734798 (for 9) contain the supplementary crystallographic data for
4806
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4795–4808

New Alkyl Complexes of Zn, Mg and Cationic Al
Table 1. Crystal data and refinement details for complexes 1–9.
1
2
3
4
Formula
Mr [gmol–1]
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C20H38N6Zn
427.93
C24H40N6Zn·0.75C4H8O C20H30Cl2N6Zn
C28H48MgN6
493.03
532.07
490.77
0.50ϫ0.40ϫ0.40
0.40ϫ0.35ϫ0.30
P21/c
monoclinic
14.959(3)
10.988(2)
18.961(4)
0.20ϫ0.15ϫ0.15
P21/c
monoclinic
11.288(2)
11.438(2)
17.965(4)
0.26ϫ0.24ϫ0.05
¯
¯
P1
P1
triclinic
8.4230(17)
9.0370(18)
17.103(3)
92.57(3)
102.49(3)
116.77(3)
1119.5(4)
1.269
triclinic
10.9961(16)
11.4850(17)
14.087(2)
95.632(3)
110.202(3)
101.911(3)
1605.6(4)
1.020
108.37(3)
94.56(3)
γ [°]
V [Å3]
2957.7(10)
0.858
4
2312.2(8)
1.410
4
ρcalcd. [gcm–3]
Z
2
2
F(000)
hkl range
460
1144
1024
540
–12 Յ h Յ 12
–13 Յ k Յ 13
–26 Յ l Յ 26
1.24–33.10
1.113
–21 Յ h Յ 21
–15 Յ k Յ 15
–26 Յ l Յ 26
1.43–30.00
0.858
–15 Յ h Յ 15
–16 Յ k Յ 16
–25 Յ l Յ 25
1.81–30.01
1.312
–13 Յ h Յ 12
–13 Յ k Յ 13
0 Յ l Յ 16
1.84–25.12
0.079
θ range [°]
µ [mm–1]
Measured reflections
Unique reflections (Rint
Observed reflections [I Ͼ 2σ(I)]
Refined parameters/restraints
Goodness-of-fit
15634
8472 (0.0285)
8472
254/0
1.075
54801
8622 (0.0705)
8622
317/0
1.068
64545
6738 (0.0676)
6738
270/0
0.965
26784
5710 (0.0448)
3527
326/16
1.148
)
R1 [I Ͼ 2σ(I)]
0.0365
0.1008
0.0512
0.1544
0.0436
0.1055
0.0753
0.2479
wR2 (all data)
Residual electron density [eÅ–3]
(max./min.)
0.463/–0.472
1.251/–0.407
0.617/–0.473
1.009/–0.488
5
6
8
9
Formula
Mr [gmol–1]
Crystal size [mm]
Crystal system
Space group
a [Å]
C20H30Br2MgN6
538.63
0.40ϫ0.20ϫ0.20
P21/c
monoclinic
11.445(2)
11.678(2)
C32H40MgN6·C4H8O
605.11
0.50ϫ0.40ϫ0.20
P21/c
monoclinic
20.101(4)
10.145(2)
C46H56AlBN6
730.76
0.15ϫ0.15ϫ0.07
Pbcm
orthorhombic
9.0443(9)
16.9810(17)
27.639(3)
C20H30Cl6Ga2N6·C4H8O
778.74
0.25ϫ0.20ϫ0.20
P21/n
monoclinic
17.291(4)
10.310(2)
b [Å]
c [Å]
18.167(4)
17.502(4)
18.968(4)
α [°]
β [°]
93.25(3)
109.47(3)
98.84(3)
γ [°]
V [Å3]
2424.2(8)
1.476
4
3365.1(12)
1.194
4
4244.8(7)
1.143
4
3341.3(12)
1.548
4
ρcalcd. [gcm–3]
Z
F(000)
hkl range
1096
1304
1568
1584
–15 Յ h Յ 16
–16 Յ k Յ 16
–24 Յ l Յ 25
1.78 to 30.22
3.388
–28 Յ h Յ 28
–14 Յ k Յ 14
–24 Յ l Յ 24
2.15–30.01
0.090
0 Յ h Յ 10
0 Յ k Յ 20
0 Յ l Յ 32
2.25–25.01
–23 Յ h Յ 23
–14 Յ k Յ 14
–26 Յ l Յ 26
2.17–29.58
2.121
θ range [°]
µ [mm–1]
Measured reflections
Unique reflections (Rint
Observed reflections [I Ͼ 2σ(I)]
Refined parameters/restraints
Goodness-of-fit
48743
7140 (0.1057)
7140
270/0
1.014
19457
9818 (0.0696)
9818
405/0
1.022
71870
3832 (0.0987)
2591
256/0
1.086
18664
9359 (0.0720)
9359
360/0
1.019
)
R1 [I Ͼ 2σ(I)]
0.0496
0.1338
0.0592
0.1392
0.0643
0.1691
0.0473
0.1095
wR2 (all data)
Residual electron density [eÅ–3]
(max./min.)
0.757/–1.399
0.287/–0.271
0.813/–0.667
0.775/–0.744
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
functional[45] in combination with an SV(P) basis set[46] was ap-
plied.
Supporting Information (see also the footnote on the first page of
this article): Selected structural parameters of 1–8, selected IR spec-
tra, VT-NMR spectra for 3 (–30 to +60 °C) and structures of the
Quantum Chemical Calculations: DFT calculations were carried
out with the help of the TURBOMOLE program.[44] The BP86
Eur. J. Inorg. Chem. 2009, 4795–4808
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4807

H.-J. Himmel et al.
FULL PAPER
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Received: June 26, 2009
Published Online: October 8, 2009
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