Syntheses and structures of bis-amidinate-alane complexes

Article abstract of DOI:10.1021/om5002217

Insertion reactions of α,ω-bis-carbodiimides (RNCN) ₂X (1-5: R = Et, t-Bu, Ph; X = C₃H₆, C ₄H₈) with 2 equiv of AlMe₃ yielded the dinuclear tethered bis-amidinate-alane complexes [RNC(Me)NA

Full text of DOI:10.1021/om5002217

Article
pubs.acs.org/Organometallics
Syntheses and Structures of Bis-Amidinate−Alane Complexes
Melike Bayram, Dieter Blaser, Christoph Wolper, and Stephan Schulz*
̈
̈
Institute of Inorganic Chemistry, University of Duisburg-Essen, 45117 Essen, Germany
S
* Supporting Information
ABSTRACT: Insertion reactions of α,ω-bis-carbodiimides
(RNCN)2X (1−5: R = Et, t-Bu, Ph; X = C3H6, C4H8) with
2 equiv of AlMe3 yielded the dinuclear tethered bis-
amidinate−alane complexes [RNC(Me)NAlMe2]2X (R = Et,
X = C4H8 (6); R = t-Bu, X = C3H6 (7), C4H8 (8)). Analogous
reactions with 4 equiv of AlMe3 resulted in the coordination of
two additional AlMe3 molecules, yielding the tetranuclear bis-
amidinate complexes [EtN(AlMe3)C(Me)NAlMe2]2X (X =
C3H6 (9), C4H8 (10)) and [t-BuNC(Me)N(AlMe3)AlMe2]2X
(X = C3H6 (11), C4H8 (12)). In addition, equimolar reactions
between (RNCN)2X (R = Et, X = C3H6, C4H8; R = Ph, X =
C4H8) and 2 equiv of AlMe3 at elevated temperatures occurred
with intramolecular cyclization and formation of [EtNC(Me)NC3H6N(AlMe3)CNEt]AlMe2 (13) and [RNC(Me)NC4H8N-
(AlMe3)CNR]AlMe2 (R = Et (14), Ph (15)). Hydrolysis of 11 gave the protonated free ligand PhNC(Me)NC4H8N(H)CNPh
(16) in high yield. 6−16 were characterized by elemental analyses, multinuclear NMR (1H, 13C) and IR spectroscopy, and single-
crystal X-ray diffraction (7, 10−14, 16).
Scheme 1. Bis- and Tris-Amidines as well as Spacer-Bridged
Bis-Carbodiimines
INTRODUCTION
■
Bimetallic metal organic complexes, in which two active metal
centers are tethered within a single molecule, have received
increasing attention within the last decades due to their
promising technical application in catalysis.1 They are expected
to provide new reactivity patterns by cooperative electronic
effects between the (different) metal atoms which are in close
proximity to one another, enhancing the catalytic activity as
well as selectivity of multimetallic complexes. As a consequence,
several homobimetallic and heterobimetallic complexes have
been investigated in the past for catalytic reactions such as
asymmetric aldol condensation, olefin polymerization, and
ROP of lactide as well as alternating copolymerization of
epoxides with CO2.2
Ligand design plays a crucial role in the synthesis of tailor-
made complexes containing a bridging unit that allows precise
adjustment of the metal−metal separation. Several multifunc-
tional ligands such as bidentate N,N′-chelating monoanionic
amidinates, guanidinates, β-diketiminates, and N,O-chelating
dianionic phenoxyamido ligands as well as tridentate ligands
such as tris(pyrazolyl)methanes, triazacyclohexanes, tris-
(imidazoles), and β-triketimines have been established in the
past for the synthesis of such multinuclear complexes.3,4 In
addition, bis-amidines of the type 1,4-C6H4[C{NSiMe3}{N-
(SiMe3)2}]2,5 1,4-C6H4[C{NR}{N(H)R}]2,6 1,2-[NC(Ph)N-
(H)R]2C6H10 (I),7 [PhN(NH-t-Bu)C]2 (II),8 and 1-[C(NR)-
N(H)R]-2,4-Ph2-6-[2-[C(NR)N(H)R]C6H4]C6H2 (III)9 have
been used as multifunctional ligand systems and several metal
complexes were reported (Scheme 1). Moreover, CH2-bridged
[H2C{NC(Ph)NR}2]Li2 (IV)10 and SiMe2-bridged bis-amidi-
nates [Me2Si{NC(Ph)NR}2]Li2 (V)11 as well as tris-amidines
of type VI12 have been prepared. Very recently, we synthesized
methanetris-amidines of type VII13 by hydrolysis of the
corresponding tetranuclear zinc amidinate complexes {C[C-
(NR)2ZnMe]4}14 and reported on their capability to form
dinuclear, trinuclear, and tetranuclear homometallic complexes
as well as heterobimetallic tetranuclear complexes in metalation
reactions with ZnMe2, AlMe3, GaMe3, and i-Bu2AlH,
respectively.13,15
CxH2x-bridged α,ω-bis-carbodiimides RNCN−Xn−NCNR
(Xn = C2H4, C3H6, ...) of type VIII are of potential interest
for the formation of tethered bimetallic bis-amidinate
Received: March 4, 2014
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om5002217 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
complexes, since they are more flexible in comparison to the
CH2- and SiMe2-bridged systems, which is expected to be a
prerequisite for cooperative effects between two metal centers.
In principle, ansa-bridged mononuclear bis-amidinates might
also be accessible. Early studies showed that α,ω-bis-amidinate
complexes can be prepared either by reaction of α,ω-bis-
carbodiimides with a transition-metal complex such as
CpTiMe3 or by reaction of a lithium salt with a metal halide
such as YCl3.9,16 Sita et al. reported on the use of bimetallic Zr
complexes based on α,ω-bis-amidinates containing different
CnH2n alkyl spacers in olefin polymerization.17 The results
clearly demonstrated the benefit of a dinuclear catalyst, which
allowed the stereoselective living coordinative chain transfer
polymerization of propene to provide isotactic stereoblock
polypropylene (PP), whereas a mononuclear catalyst gave
atactic PP.
Herein we report on reactions of different α,ω-bis-
carbodiimides with trimethylalane, which proceeded with
formation of dinuclear tethered bis-amidinate complexes via
insertion of the α,ω-bis-carbodiimides into the Al−Me bond of
two AlMe3 molecules. Reactions with 4 equiv of AlMe3 at
ambient temperature gave the tetranuclear complexes, in which
two additional AlMe3 molecules are coordinated by either the
inner or the outer imine center of the amidinate group. Neutral
as well as cationic aluminum amidinate complexes have been
investigated in the past as catalyst in different catalytic
processes18 such as olefin polymerization19,20 as well as in the
ring-opening polymerization (ROP) of cyclic esters such as
lactide and ε-caprolactone.21
Scheme 3. Syntheses of Binuclear Bis-Amidinate Aluminum
Complexes 6−8
NAlMe2]2C3H6, but this compound could not be isolated in
its pure form.
The NMR spectra of 6−8 showed additional resonances due
to the C−Me group of the amidinate unit. In addition, the
AlMe2 groups were observed as a single resonance in the NMR
spectra. The relative intensities of the resonances, which were
determined by integration of the signals, of the AlMe2 groups,
the R groups (Et, t-Bu) of the α,ω-bis-amidinate, and the
bridging unit (C3H6, C4H8) clearly proved the formation of the
binuclear complexes 6−8.
Colorless crystals of 7 suitable for single-crystal X-ray
diffraction were obtained upon slow evaporation of the solvent
of a concentrated toluene solution at ambient temperature for 2
days. 7 crystallizes in the monoclinic space group P21 with one
molecule in the asymmetric unit (Figure 1).
RESULTS AND DISCUSSION
■
Our attempts to synthesize α,ω-bis-carbodiimides (RNCN)2X
(R = Et, X = C3H6 (1), C4H8 (2); R = t-Bu, X = C3H6 (3),
C4H8 (4); R = Ph, X = C4H8 (5)) by reaction of the
corresponding isocyanate with a cyclic bis-amidostannylene as
described by Sita et al. gave only very low yields (<20%).10 We
therefore decided to synthesize the α,ω-bis-carbodiimides 1−5
by an alternate synthetic route.17a In the first step, the
corresponding α,ω-bis-ureas are synthesized (Supporting
Information), which then react to give the α,ω-bis-carbodii-
mides 1−5 (Scheme 2). Unfortunately, any attempts to obtain
5 in its pure form failed.
Figure 1. Solid-state structure of 7. Thermal ellipsoids are shown at
the 50% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg) of 7: Al(1)−N(1)
1.9345(13), Al(1)−N(2) 1.9224(12), Al(2)−N(3) 1.9339(13),
Al(2)−N(4) 1.9283(14); C(4)−N(1)−C(1) 124.33(13), C(4)−
N(1)−Al(1) 90.54(9), C(1)−N(1)−Al(1) 144.94(11), C(4)−
N(2)−C(5) 129.26(13), C(4)−N(2)−Al(1) 91.00(9), C(5)−N(2)−
Al(1) 139.55(11), C(12)−N(3)−C(3) 124.75(14), C(12)−N(3)−
Al(2) 90.56(9), C(3)−N(3)−Al(2) 144.65(12), C(12)−N(4)−C(13)
128.95(13), C(12)−N(4)−Al(2) 90.68(10), C(13)−N(4)−Al(2)
140.21(10); N(3)−C(3)−C(2)−C(1) 55.54(18), C(3)−C(2)−
C(1)−N(1) 59.12(17).
Scheme 2. Synthesis of 1−5
Reactions of 2 equiv of AlMe3 with 1 equiv of the α,ω-bis-
carbodiimides (RNCN)2X (R = Et, t-Bu; X = C3H6, C4H8)
proceeded with insertion of both carbodiimide groups into the
Al−Me bonds of two AlMe3 molecules and formation of the
dinuclear α,ω-bis-acetamidinate−alane complexes [RNC(Me)-
NAlMe2]2X (R = Et, X = C4H8 (6); R = t-Bu, X = C3H6 (7),
C4H8 (8); Scheme 3). The reaction of (EtNCN)2C3H6 1 with 2
equiv of AlMe3 only gave a complex mixture of different
compounds, in which complexes 9 and 14 could clearly be
The bis-amidinate ligand in 7 acts as an N,N′-chelating
ligand to two AlMe2 moieties. The average endocyclic N−C−N
(109.76(13)°) and N−Al−N (68.84(6)°) and exocyclic C−
Al−C (116.03(8)°) bond angles within the amidinate moieties
are comparable to those reported for aluminum amidinate
complexes. A CSD database search gave 38 hits on
mononuclear aluminum amidinate complexes with the
substructure CC(NC)2AlC2 with bond types set to “any”,
showing comparable endocyclic N−C−N (average 109.4(18)°)
and N−Al−N bond angles (average 68.9(6)°) as well as
exocyclic C−Al−C (average 118(2)°) bond angles. In addition,
1
identified by H NMR spectroscopy. Additional resonances
most likely indicate the formation of [EtNC(Me)-
B
dx.doi.org/10.1021/om5002217 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
five binuclear bis-amidinate alane complexes have been
structurally characterized to date, whose average endocyclic
N−C−N (110.27°) and N−Al−N (68.70°) and exocyclic C−
Al−C (117.87°) bond angles are comparable.6,25,26
Carbodiimide insertion reactions with AlMe3 are known to
be a convenient route for the synthesis of aluminum
acetamidinate complexes.22,23 Moreover, reactions with alumi-
num amides yield the corresponding guanidinate complexes.24
While mononuclear aluminum amidinate complexes have been
prepared in very large numbers, binuclear complexes have been
studied to a lesser extent. Hagadorn et al. synthesized dinuclear
bis(amidinate) aluminum complexes based on dibenzofuran
and 9,9-dimethylxanthene backbones,25 whereas Coles et al.
and Luo et al. reported on 1,4-phenyl- and 1,4-cyclohexyl-
bridged binuclear aluminum complexes.6,26 In addition,
structurally related bis-phosphaguanidine aluminum complexes
were structurally characterized.27
Analogous reactions with 4 equiv of AlMe3 resulted in the
coordination of two additional AlMe3 molecules, yielding the
tetranuclear bis-amidinate complexes [EtN(AlMe3)C(Me)-
NAlMe2]2X (X = C3H6 (9), C4H8 (10)) and [t-BuNC(Me)-
N(AlMe3)AlMe2]2X (X = C3H6 (11), C4H8 (12)), respectively
(Scheme 4). Jordan et al. reported on the reaction of the
Figure 2. Temperature-dependent 1H NMR spectra of 11 measured in
toluene-d8 (resonances marked with asterisks are due to grease).
11 crystallizes in the orthorhombic space group Pbca with
the molecules placed on the general positions (Figure 4). 10
(Figure 3) and 12 (Figure 5) crystallize in a monoclinic lattice
(10, P21/n; 12, P21/c) with the molecules placed on centers of
inversion. The overall conformations of the bridging amidinate
ligands are fairly similar; however, because of the odd number
of atoms in the linking alkyl chain in 11 and the sp3
hybridization of the middle atom (i.e., local tetrahedral
symmetry) exact centrosymmetry is not possible. The
molecular structures are depicted in Figures 3−5. The bis-
Scheme 4. Syntheses of Tetranuclear Bis-Amidinate
Aluminum Complexes 9−12
Figure 3. Solid-state structure of 10. Thermal ellipsoids are shown at
the 50% probability level. Hydrogen atoms are omitted for clarity. The
pale colored part of the molecule is generated via 1 − x, 1 − y, 1 − z.
Selected bond lengths (Å) and angles (deg) of 10: Al(1)−N(1)
1.9510(11), Al(1)−N(2) 2.0077(11), Al(2)−N(2) 2.0567(11),
N(1)−C(1) 1.2873(16), N(1)−C(2) 1.4619(17), N(2)−C(1)
1.4151(17); C(1)−N(1)−C(2) 124.37(11), C(1)−N(1)−Al(1)
93.31(8), C(2)−N(1)−Al(1) 42.20(8), C(1)−N(2)−Al(1) 87.18(7),
C(1)−N(2)−Al(2) 109.30(8), Al(1)−N(2)−Al(2) 113.29(5); C(2)−
C(3)−C(3)#2−C(2)#2 180, N(1)−C(2)−C(3)−C(3)#2 −179.79(14).
comparable thioamidinate alane complex {MeC(NAd)S}AlMe2
with AlMe3, which was shown by H NMR spectroscopy to
1
form the corresponding sulfur adduct {MeC(NAd)S(AlMe3)}-
AlMe2.28
The NMR spectra of 9−12 showed broad resonances of the
AlMe moieties in comparison to those obtained for 5−8,
indicating fast exchange reactions on the NMR time scale.
However, the relative intensities clearly prove the formation of
amidinate ion in 9−12 acts as an N,N′-chelating ligand to the
AlMe2 moiety and also as a monodentate σ ligand to a second
AlMe3 molecule, thus coordinating two Al atoms per amidinate
function. The central alkyl chains show a staggered
conformation with torsion angle close to or (because of
symmetry) exactly 180°.
10−12 show comparable endocyclic N−C−N (10,
110.45(11)°; 11, 109.94(14)°; 12, 110.00(11)°) and N−Al−
N (10, 68.24(4)°; 11, 68.65(10)°; 12, 68.40(4)°) bond angles
within the amidinate moieties as well as exocyclic C−Al−C (10,
119.34(7)°; 11, 119.4(6)°; 12, 119.61(8)°) bond angles
(average values where applicable), which are almost identical
with those observed for 7. The endo- and exocyclic Al−N−C
angles differ for the N atoms of the amidinate unit, which can
be attributed to the different steric demands of the nonequal
residual groups. This observation is in accordance with the Al−
N−C bond angles found for asymmetrically substituted
aluminum amidinate complexes in the CSD search and to
1
tetranuclear complexes. Therefore, temperature-dependent H
NMR spectra of 10−12 were measured. As an example, Figure
2 shows the 1H NMR spectra recorded for 11 in the
temperature range from −70 to +25 °C. The broad resonance
as observed for the AlMe groups at ambient temperature
separates into two resonances at 0 °C for the AlMe3 (broad
resonance) and the bridging AlMe2 unit (sharp resonance).
The latter signal separates upon cooling into two resonances of
equal intensity due to the magnetically inequivalent Me groups.
The spectrum at −70 °C finally shows three well-resolved
resonances in the regime typically observed for AlMe units (−1
to 0 ppm) in a relative intensity of 6:6:18. Comparable findings
were observed for 10 and 12, respectively (see the Supporting
Information).
Single crystals of 10−12 were obtained upon storage of
solutions in hexane at −30 °C for 24 h.
C
dx.doi.org/10.1021/om5002217 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
coordination number of the coordinating N atom increases to
4, resulting in a tetrahedral environment and a change of
hybridization from sp2 to sp3. As a consequence, the p orbital is
no longer available for an electron delocalization within the
amidinate group, leading to significantly different C−N bond
lengths (10, N(1)−C(1) 1.2873(16), N(2)−C(1) 1.4151(17)
Å; 11, N(1)−C(4) 1.425(3), N(2)−C(4) 1.290(3) Å; 12,
N(1)−C(3) 1.2839(16), N(2)−C(3) 1.4225(15) Å) within the
amidinate backbone of 10−12. The shorter C−N bond
distances are comparable to those reported for N-hetero-
aromatic compounds (1.336(14) Å)29 but longer than those
reported for carbodiimides (mean value 1.215(4) Å),30 whereas
the longer ones are slightly shorter than those reported for
C(sp2)−N single bonds (1.47 Å).31 In accordance with this
finding, the mean Al−N(sp3) bond lengths (10, 1.98(2) Å; 11,
2.026(17) Å; 12, 2.03(2) Å) are longer than the mean Al−
N(sp2) lengths (10, 1.9510(11) Å; 11, 1.952(2) Å; 12,
1.9501(11) Å). These findings are in remarkable contrast to
those observed in the mononuclear aluminum amidinate
complexes, whose N−C (average 1.340 Å) and N−Al bond
lengths (average 1.929 Å) are very similar, indicating almost
perfect π-delocalization within the amidinate backbone.
We also investigated reactions between (RNCN)2X (R = Et,
X = C3H6, C4H8; R = Ph, X = C4H8) and an equimolar amount
of AlMe3 at elevated temperatures in order to investigate the
possible formation of an ansa-type complex by twofold
insertion of both carbodiimide moieties into two Al−Me
bonds of a single AlMe3 molecule. However, these reactions
proceeded with intramolecular cyclization due to the
nucleophilic attack of the inner amidinate N atom to the
electrophilic carbon atom of the second carbodiimide unit and
subsequent formation of [EtNC(Me)NC3H6N(AlMe3)CNEt]-
AlMe2 (13) and [RNC(Me)NC4H8N(AlMe3)CNR]AlMe2 (R
= Et (14), Ph (15)), respectively, rather than with formation of
the ansa-type complexes (Scheme 5). 13−15 were also
prepared in higher yields by analogous reaction with 2 equiv
of AlMe3 at 90 °C.
Figure 4. Solid-state structure of 11. Thermal ellipsoids are shown at
the 50% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg) of 11: Al(1)−N(1)
1.9889(19), Al(1)−N(2) 1.950(2), Al(2)−N(1) 2.0655(19), Al(3)−
N(4) 1.954(2), Al(3)−N(3) 1.995(2), Al(4)−N(3) 2.053(2), N(1)−
C(4) 1.425(3), N(2)−C(4) 1.290(3), N(3)−C(15) 1.431(3), N(4)−
C(15) 1.284(3); C(4)−N(1)−Al(1) 87.18(13), C(4)−N(1)−Al(2)
109.37(13), Al(1)−N(1)−Al(2) 114.05(9), C(4)−N(2)−Al(1)
92.73(14), C(15)−N(3)−Al(3) 87.70(14), C(15)−N(3)−Al(4)
112.02(14), Al(3)−N(3)−Al(4) 113.41(10), C(15)−N(4)−Al(3)
93.79(15); N(1)−C(1)−C(2)−C(3) 177.65(18), C(1)−C(2)−
C(3)−N(3) −178.56(18).
Figure 5. Solid-state structure of 12. Thermal ellipsoids are shown at
the 50% probability level. Hydrogen atoms are omitted for clarity. The
pale colored part of the molecule is generated via −x, −y, 1 − z.
Selected bond lengths (Å) and angles (deg) of 12.: Al(1)−N(1)
1.9501(11), Al(1)−N(2) 1.9961(10), Al(2)−N(2) 2.0639(11),
N(1)−C(3) 1.2839(16), N(2)−C(3) 1.4225(15), N(2)−C(2)
1.4996(14); C(3)−N(1)−C(4) 130.00(12), C(3)−N(1)−Al(1)
93.36(8), C(4)−N(1)−Al(1) 36.27(9), C(3)−N(2)−C(2)
111.84(9), C(3)−N(2)−Al(1) 87.34(7), C(2)−N(2)−Al(1)
118.67(8), C(3)−N(2)−Al(2) 110.82(7), C(2)−N(2)−Al(2)
112.14(8), Al(1)−N(2)−Al(2) 113.49(5;, C(2)−C(1)−C(1)#1−C-
(2)#1 180, N(2)−C(2)−C(1)−-C(1)#1 174.49(13).
Scheme 5. Syntheses of 13−15
those reported for the binuclear bis-amidinate alane com-
plexes.6,25,26
The most surprising difference among the tetranuclear
complexes is revealed by the coordination of the AlMe3
Lewis acid. The additional AlMe3 molecules in 10 are
coordinated by the outer Namidinate atom, whereas the inner
Namidinate atom binds to the AlMe3 Lewis acid in 11 and 12.
Obviously, the sterically more demanding t-Bu groups in 11
and 12 favor the coordination of the AlMe3 molecules to the
inner Namidinate atom in order to reduce the steric (repulsive)
interactions, whereas the somewhat smaller Et groups in 10
allow the coordination of the AlMe3 molecules by the outer
Namidinate atom. Moreover, the σ-coordination mode strongly
influences the electronic structure of the ligand, since the
The NMR spectra of 13−15 each showed two sets of
resonances for the different Al−Me groups (AlMe2, AlMe3) in a
relative intensity of 2:3. In addition, 13 and 14 also showed two
triplets and two quartets for the Et groups. Unfortunately, all
attempts to obtain 15 in its pure form failed. The H NMR
spectra of different samples always showed additional
resonances, which could not be addressed.
Single crystals of 13 and 14 were obtained upon storage of
solutions in hexane at −30 °C for 24 h. 13 and 14 (Figures 6
and 7, respectively) crystallize in the monoclinic space groups
P21/c (13) and P21/n (14). In both molecules, the AlMe2
1
D
dx.doi.org/10.1021/om5002217 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1.3869(19), N(2)−C(2) 1.4168(19), N(2)−C(3) 1.4818(18),
N(3)−C(2) 1.3320(19), N(4)−C(2) 1.3210(18) Å; 14,
N(1)−C(1) 1.283(3), N(2)−C(1) 1.394(3), N(2)−C(2)
1.427(3), N(2)−C(3) 1.489(3), N(3)−C(2) 1.330(3),
N(4)−C(2) 1.320(3) Å) suggest only limited delocalization
of the π electrons.
Finally, the raw product of 15 was reacted with an excess of
methanol in order to synthesize the free ligand PhNC(Me)-
NC4H8N(H)CNPh (16; Scheme 6). 16 was obtained in the
form of X-ray-quality crystals after workup in reasonable yield.
Scheme 6. Synthesis of 16
Figure 6. Asymmetric unit of 13. Thermal ellipsoids are shown at the
50% probability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) and angles (deg) for one molecule of 13: N(1)−
C(1) 1.2897(19), N(2)−C(1) 1.3869(19), N(2)−C(2) 1.4168(19),
N(2)−C(3) 1.4818(18), N(3)−C(2) 1.3320(19), N(4)−C(2)
1.3210(18); C(1)−N(1)−Al(1) 119.32(10), C(1)−N(2)−C(2)
126.44(12), C(1)−N(2)−C(3) 120.30(12), C(2)−N(2)−C(3)
113.21(11), C(2)−N(4)−Al(1) 120.22(10), N(4)−C(2)−N(2)
118.20(13), N(4)−C(2)−N(3) 126.44(14), N(3)−C(2)−N(2)
115.35(12).
16 crystallizes in the monoclinic space group P21/n (Figure
8). In remarkable contrast to 13 and 14, the sp2-hybridized N
atoms and the central C atoms C1 and C2 in 16 are far from
forming a plane (C1−N1−C2−N3 62.9(2)°). Interestingly, to
achieve the cisoid arrangement of the N atoms as observed for
13 and 14, a rotation around the double bonds (C1N1,
C2N3) is necessary. However, the N2H−C2−N3 unit shows
a strong hydrogen bond (H···A 2.037 Å, D−H···A 170.99°)
Figure 7. Solid-state structure of 14. Thermal ellipsoids are shown at
the 50% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg) of 14: N(1)−C(1)
1.283(3), N(2)−C(1) 1.394(3), N(2)−C(2) 1.427(3), N(2)−C(3)
1.489(3), N(3)−C(2) 1.330(3), N(4)−C(2) 1.320(3); C(1)−N(1)−
Al(1) 119.94(15), C(1)−N(2)−C(2) 125.49(17), C(1)−N(2)−C(3)
117.48(17), C(2)−N(2)−C(3) 116.75(17), C(2)−N(4)−Al(1)
122.24(14), N(1)−C(1)−N(2) 120.58(18), N(4)−C(2)−N(3)
125.39(18), N(4)−C(2)−N(2) 117.06(17), N(3)−C(2)−N(2)
117.55(18).
Figure 8. Solid-state structure of 16. Thermal ellipsoids are shown at
the 50% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg) of 16: N(1)−C(1)
1.384(2), N(1)−C(2) 1.417(2), N(1)−C(6) 1.472(2), N(2)−C(2)
1.337(2), N(2)−C(3) 1.465(2), N(3)−C(2) 1.294(2), N(3)−C(7)
1.408(2), N(4)−C(1) 1.281(2), N(4)−C(13) 1.416(2); C(1)−
N(1)−C(2) 123.96(14), C(1)−N(1)−C(6) 120.19(13), C(2)−
N(1)−C(6) 115.85(13), C(2)−N(2)−C(3) 124.96(14), C(2)−
N(3)−C(7) 123.33(14), C(1)−N(4)−C(13) 22.03(16), N(4)−
C(1)−N(1) 116.84(15), N(4)−C(1)−C(19) 126.79(16), N(1)−
C(1)−C(19) 116.37(15), N(3)−C(2)−N(2) 20.17(15), N(3)−
C(2)−N(1) 126.12(16), N(2)−C(2)−N(1) 113.67(14).
moieties are κ2-coordinated by the N,N′-chelating amidinate
groups while the AlMe3 groups are σ-bonded. The nitrogen
atoms N1−N4 as well as the central C atoms C1 and C2 adopt
an almost planar arrangement in both molecules (rms deviation
from best plane; 13, 0.1379 and 0.1281 Å; 14, 0.4975 Å, C3 and
C6 with approximately 1 Å deviate most) and can be best
described as sp2 hybridized. However, the corresponding C−N
bond lengths (13, N(1)−C(1) 1.2897(19), N(2)−C(1)
E
dx.doi.org/10.1021/om5002217 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
4 H, NCH2). 13C NMR (75 MHz, C6D6, 25 °C): δ 29.2 (CH2), 31.5
(NCMe3), 46.5 (NCH2), 54.7 (NCMe3), 139.9 (NCN). IR: ν 2968,
2930, 2868, 2106, 2061, 1461, 1392, 1365, 1351, 1272, 1237, 1187,
1092, 1015, 975, 922, 778, 671, 618, 541, 446, 386 cm−1.
forming a centrosymmetric R2 (8) motif comparable to that
2
found in carbonic acid dimers, which might influence the π
system. The different conformation fulfills the steric demands
of this interaction and might be a consequence of this
interaction.
(PhNCN)2C4H8 (5). Purification of 5 failed. 5 was obtained as a
mixture with so far unidentified products. However, some resonances
1
1
in the H NMR can be most likely attributed to 5. H NMR (300
MHz, CHDCl2, 25 °C): δ 1.80 (m, 4 H, CH2), 3.49 (m, 4 H, NCH2),
7.08 (m, 4 H, Ar) 7.28 (t, 4 H, Ar). 13C NMR (75 MHz, CD2Cl2, 25
°C): δ 28.6 (CH2), 46.1 (CH2), 124.0 (Ar), 124.9 (Ar), 128.5 (Ar),
129.7 (Ar), 141.3 (NCN).
CONCLUSIONS
■
A series of dinuclear α,ω-bis-amidinate−alane complexes 6−8
have been prepared by the reaction of α,ω-bis-carbodiimides
with a twofold amount of AlMe3 at ambient temperature.
Reactions with a fourfold amount of AlMe3 yielded tetranuclear
bis-amidinate complexes 9−12, in which two additional AlMe3
molecules are coordinated by either the inner or outer imine
centers, depending on the steric demand of the organic
substituent attached to the outer imine moiety. In addition,
cyclization reactions were observed in reactions of α,ω-bis-
carbodiimides with 2 equiv of AlMe3 at higher temperatures,
yielding 13−15. The free heterocyclic ligands, which can be
obtained from hydrolysis reactions of the corresponding alane
complexes as was shown for the bis-amidine 16, might be used
in the future in reactions with metal organic complexes
containing different metal centers.
General Experimental Procedure for the Synthesis of 6−8. A
solution of AlMe3 in toluene (6, 1.84 mL, 3.6 mmol; 7, 8, 1.76 mL, 3.6
mmol) was added at −80 °C to a solution of the corresponding α,ω-
bis-carbodiimide (6, 0.40 g, 1.8 mmol; 7, 8, 0.44 g, 1.8 mmol) in 15
mL of toluene. The solution was warmed to ambient temperature
within 12 h. All volatiles were evaporated under vacuum, yielding 6−8
as colorless solids. Analytically pure 6−8 were obtained upon
recrystallization of solutions in hexane/toluene at −30 °C.
[EtNC(Me)NAlMe2]2C4H8 (6). Yield: 0.50 g (80.3%). Melting point:
81 °C dec. Anal. Found (calcd) for C16H36Al2N4 (338.44 g/mol): H,
1
10.60 (10.72); C, 56.90 (56.78). H NMR (300 MHz, CHDCl2, 25
°C): δ −0.76 (s, 12 H, AlMe2), 1.10 (t, 6 H, CH2CH3), 1.48 (m, 4 H,
CH2), 1.98 (s, 6 H, CMe), 3.13 (m, 4 H, CH2CH3), 3.18 (quart, 4 H,
CH2). 13C NMR (75 MHz, CD2Cl2, 25 °C): δ −8.2 (AlMe2), 12.3
(CH3), 16.4 (CMe), 29.3 (CH2), 40.4 (CH2), 45.7 (CH2), 178.2
(NCN). IR: ν 2974, 2926, 2886, 2817, 1625, 1528, 1466, 1389, 1243,
1184, 1156, 1105, 1054, 992, 932, 908, 827, 678, 621, 585, 524, 474,
417, 385 cm−1.
[t-BuNC(Me)NAlMe2]2C3H6 (7). Yield: 0.57 g (83.2%). Melting
point: 118 °C dec. Anal. Found (calcd) for C19H42Al2N4 (380.52 g/
mol): H, 10.78 (11.12); C, 60.30 (59.97). 1H NMR (300 MHz,
C6D6H, 25 °C): δ −0.25 (s, 12 H, AlMe2), 1.08 (s, 18 H, CMe3), 1.52
(s, 6 H, CMe), 1.57 (t, 2 H, CH2), 2.91 (t, 4 H, NCH2). 13C NMR (75
MHz, C6D6, 25 °C): δ −9.6 (AlMe2), 14.1 (CMe), 31.5 (NCMe3), 33.3
(CH2), 42.0 (NCH2), 50.4 (NCMe3), 173.9 (NCN). IR: ν 2966, 2928,
2885, 1653, 1606, 1492, 1452, 1415, 1362, 1334, 1314, 1265, 1221,
1182, 1095, 1028, 845, 794, 676, 589, 537, 434, 381 cm−1.
[t-BuNC(Me)NAlMe2]2C4H8 (8). Yield: 0.58 g (81.7%). Melting
point: 121.4 °C dec. Anal. Found (calcd) for C20H44Al2N4 (394.55 g/
mol): H, 10.9 (11.24); C, 59.00 (60.88). 1H NMR (300 MHz, C6D6H,
25 °C): δ −0.25 (s, 12 H, AlMe2), 1.09 (s, 18 H, CMe3), 1.44 (m, 4 H,
NCH2), 1.48 (s, 6 H, CMe), 2.79 (m, 4 H, CH2). 13C NMR (75 MHz,
C6D6, 25 °C): δ −9.5 (AlMe2), 14.0 (CMe), 29.8 (CH2), 31.5
(NCMe3), 44.3 (NCH2), 50.3 (NCMe3), 173.6 (NCN). IR: ν 2925,
2860, 1653, 1508, 1483, 1439, 1421, 1359, 1249, 1183, 1069, 1035,
1021, 820, 785, 685, 654, 623, 590, 556, 476, 442, 396 cm−1.
General Experimental Procedure for the Synthesis of 9−12.
A solution of AlMe3 in toluene (9, 10, 3.68 mL, 7.2 mmol; 11, 12, 3.52
mL, 7.2 mmol) was added at room temperature to a solution of the
α,ω-bis-carbodiimide (9, 10, 0.40 g, 1.8 mmol; 11, 12, 0.44 g 1.8
mmol) in 15 mL of hexane and stirred for 15 min. All volatiles were
evaporated under vacuum, yielding 9−12 as colorless solids.
Analytically pure 9−12 were obtained upon recrystallization of
solutions in toluene at −30 °C.
EXPERIMENTAL SECTION
■
General Procedures and Materials. All manipulations were
performed in a glovebox (MBraun) under an Ar atmosphere or with
standard Schlenk techniques. Dry solvents were obtained from a
solvent purification system (MBraun) and degassed prior to use. A 2
M solution of AlMe3 in toluene was obtained from Sigma-Aldrich and
used as received. A Bruker DMX 300 was used for NMR spectroscopy.
1H and 13C{1H} NMR spectra were referenced to internal
deuteriobenzene (C6D5H, 1H δ 7.154; C6D6, 13C δ 128.0) and
deuteriodichloromethane (CHDCl2, 1H δ 5.32; CD2Cl2, 13C δ 53.84).
IR spectra were recorded on a Bruker ALPHA-T FT-IR spectrometer
equipped with a single reflection ATR sampling module. Melting
points were measured in sealed capillaries and were not corrected.
Elemental analyses were performed at the Elementaranalyse Labor of
the University of Duisburg-Essen.
General Experimental Procedure for the Synthesis of 1−5.
α,ω-Bis-carbodiimides were prepared according to a procedure
previously reported by Sita et al. for compound 4.17a The products
crystallized from the raw product upon storage at −30 °C. The yields
(isolated crystalline products) are based on the bis-ureas, which were
prepared in high yields (see the Supporting Information).
(EtNCN)2C3H6 (1). Yield: 2.10 g (43.4%). 1H NMR (300 MHz,
C6D6H, 25 °C): δ 0.95 (t, 6 H, CH2CH3), 1.50 (quint, 2 H, CH2),
2.92 (quart, 4 H, NCH2), 3.09 (t, 4 H, CH2CH3). 13C NMR (75 MHz,
C6D6, 25 °C): δ 16.8 (CH3) 33.0 (CH2), 41.4 (CH2CH3), 43.9
(NCH2), 140.4 (NCN). IR: ν 2972, 2933, 2871, 2115, 1692, 1631,
1574, 1518, 1489, 1451, 1433, 1403, 1375, 1335, 1308, 1281, 1200,
1131, 1087, 937, 887, 845, 785, 744, 697, 610, 500, 422 cm−1.
(EtNCN)2C4H8 (2). Yield: 2.28 g (51.3%). 1H NMR (300 MHz,
C6D6H, 25 °C): δ 0.97 (t, 6 H, CH2CH3), 1.41 (m, 4 H, CH2), 2.94
(m, 8 H, NCH2, CH2CH3). 13C NMR (75 MHz, C6D6, 25 °C): δ 16.9
(CH3) 29.0 (CH2), 41.4 (CH2CH3), 46.2 (NCH2), 140.4 (NCN). IR:
ν 2966, 2930, 2867, 2117, 1728, 1649, 1585, 1448, 1434, 1355, 1259,
1157, 1087, 1015, 912, 871, 798, 743, 696, 645, 610, 541, 500, 396
cm−1.
[EtN(AlMe3)C(Me)NAlMe2]2C3H6 (9). The samples always contained
mixtures of 9 and 13 (35:65). Fractionated crystallization from a
solution in toluene yielded pure 9. Melting point: 82 °C dec. Anal.
Found (calcd) for C21H52Al4N4 (468.58 g/mol): H, 10.90 (11.18); C,
1
53.48 (53.82). H NMR (300 MHz, C6D6H, 25 °C): δ −0.27 (bs, 30
H, AlMe), 0.91 (t, 6 H, CH2CH3), 1.33 (bs, 8 H, CH2, CMe), 2.77 (m,
8 H, CH2CH3, CH2). 13C NMR (75 MHz, C6D6, 25 °C): δ −11.1
(AlMe), −7.0 (AlMe), 13.4 (CH3), 15.9 (CH3), 32.2 (CH2), 41.5
(CH2), 47.2 (CH2), 179.6 (NCN). IR: ν 2962, 2920, 2884, 2820, 1663,
1620, 1524, 1437, 1342, 1260, 1176, 1121, 1083, 1025, 796, 727, 679,
616, 537, 511, 442, 392 cm−1.
1
(t-BuNCN)2C3H6 (3). Yield: 2.70 g (46.2%). H NMR (300 MHz,
C6D6H, 25 °C): δ 1.16 (s, 18 H, CMe3) 1.56 (m, 2 H, CH2), 3.12 (m,
4 H, NCH2, CH2CH3). 13C NMR (75 MHz, C6D6, 25 °C): δ 31.5
(CH2), 33.4 (NCMe3), 44.1 (NCH2), 54.8 (NCMe3), 139.8
(NCN).IR: ν 2952, 2902, 2107, 2061, 1642, 1459, 1392, 1365,
1334, 1309, 1245, 1186, 1083, 1018, 953, 918, 831, 792, 747, 679, 618,
566, 471, 440, 396 cm−1.
[EtN(AlMe3)C(Me)NAlMe2]2C4H8 (10). Yield: 0.77 g (88.6%).
Melting point: 84 °C dec. Anal. Found (calcd) for C22H54Al4N4
1
1
(t-BuNCN)2C4H8 (4). Yield: 2.62 g (47.6%). H NMR (300 MHz,
(482.61 g/mol): H, 10.93 (11.28); C, 54.34 (54.75). H NMR (300
C6D6H, 25 °C): δ 1.17 (s, 18 H, CMe3), 1.44 (m, 4 H, CH2), 2.95 (m,
MHz, CHDCl2, 25 °C): δ −0.67 (s (br), 30 H, AlMe2), 1.14 (t, 6 H,
F
dx.doi.org/10.1021/om5002217 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
CH2CH3), 1.53 (m, 4 H, CH2), 2.05 (s, 6 H, CMe), 3.15 (m, 4 H,
CH2CH3), 3.18 (q, 4 H, CH2). 13C NMR (75 MHz, CD2Cl2, 25 °C): δ
−11.5 (AlMe), −7.6 (AlMe), 16.0 (CMe), 29.1 (CH2), 30.4 (CH3),
41.1 (CH2), 46.3 (CH2), 176.8 (NCN). IR: ν 2963, 2926, 2886, 2819,
1625, 1526, 1437, 1343, 1281, 1260, 1184, 1157, 1082, 1016, 857, 790,
744, 675, 538, 524, 496, 474, 385 cm−1.
vacuum, yielding a white solid, from which analytically pure 16 was
isolated after extraction with CH2Cl2 followed by evaporation of the
solvent.
PhNC(Me)NC4H8N(H)CNPh (16). Yield: 0.14 g (48%). Melting
point: 145.5 °C dec. Anal. Found (calcd) for C19H22N4 (306.41 g/
mol): H, 7.18 (7.24); C, 74.37 (74.48). 1H NMR (300 MHz, CHDCl2,
25 °C): δ 1.62 (m, 2 H, CH2), 1.77 (m, 2 H, CH2), 2.09 (s, 3 H,
CMe), 3.28 (m, 2 H, CH2), 3.95 (m, 2 H, CH2), 4.77 (s, 1 H, NH),
6.75 (d, 2 H, Ar), 6.88 (d, 2 H, Ar), 7.00 (m, 2 H, Ar), 7.21−7.34 (t, 4
H, Ar). 13C NMR (75 MHz, CD2Cl2, 25 °C): δ 17.9 (CMe3), 27.1
(CH2), 29.5 (CH2), 44.1 (CH2), 45.7 (CH2), 121.4 (Ar), 121.8 (Ar),
122.3 (Ar), 123.0 (Ar), 129.0 (Ar), 129.2 (Ar), 130.0 (Ar). IR: ν 3677,
2962, 2909, 2827, 2783, 1650, 1611, 1584, 1506, 1472, 1456, 1412,
1367, 1339, 1281, 1259, 1189, 1088, 1067, 1012, 928, 859, 794, 732,
692, 388 cm−1.
Single-Crystal X-ray Analyses. Crystallographic data of 7, 10−14
and 16, which were collected on a Bruker AXS SMART diffractometer
(Mo Kα radiation, λ = 0.71073 Å) at low temperatures, are
summarized in Table 1 in the Supporting Information. The solid-
state structures of 7, 10−14, and 16 are shown in Figures 1 and 3−8,
respectively. The structures were solved by direct methods (SHELXS-
97) and refined anisotropically by full-matrix least squares on F2
(SHELXL-97).32,33 14 was a pseudomerohedral twin and was refined
accordingly. The major component comprised approximately 90% of
the sample. Absorption corrections were performed semiempirically
from equivalent reflections on the basis of multiscans (Bruker AXS
APEX2). Hydrogen atoms were refined using a riding model or rigid
methyl groups. The crystallographic data of 7, 10−14, and 16
(excluding structure factors) have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication nos.
CCDC-992931 (7), CCDC-976671 (10), CCDC-976669 (11),
CCDC-976670 (12), CCDC-987539 (13), CCDC-976672 (14),
and CCDC-976673 (16). Copies of the data can be obtained free of
charge on application to the CCDC, 12 Union Road, Cambridge CB2
1EZ, U.K. (fax, (+44) 1223/336033; e-mail, deposit@ccdc.cam-ak.uk).
[t-BuN(AlMe3)C(Me)NAlMe2]2C3H6 (11). Yield: 0.84 g (88.9%).
Melting point: 126.0 °C dec. Anal. Found (calcd) for C25H60Al4N4
1
(524.69 g/mol): H, 11.33 (11.5); C, 55.97 (57.2). H NMR (300
MHz, C6D6H, 25 °C): δ −0.35 (s, 18 H, AlMe3), −0.30 (s, 12 H,
AlMe2), 1.02 (s, 18 H, CMe3), 1.59 (s, 6 H, CMe), 1.72 (quint, 2 H,
CH2CH2CH2), 2.87 (m, 4 H, CH2).13C NMR (75 MHz, C6D6, 25
°C): δ −9.3 (AlMe3), −6.6 (AlMe2), 14.8 (CMe), 31.0 (CMe3), 32.5
(CH2), 43.1 (CH2), 51.1 (CMe3), 175.7 (CNC). IR: ν 2968, 2928,
2884, 2819, 1611, 1496, 1475, 1398, 1371, 1266, 1188, 1128, 1099,
1081, 1038, 988, 938, 915, 839, 798, 678, 618, 522, 436, 391 cm−1.
[t-BuN(AlMe3)C(Me)NAlMe2]2C4H8 (12). Yield: 0.87 g (89.8%).
Melting point: 127.0 °C dec. Anal. Found (calcd) for C26H62Al4N4
1
(538.72 g/mol): H, 11.41 (11.60); C, 58.05 (57.97). H NMR (300
MHz, C6D6H, 25 °C): δ −0.35 (s, 18 H, AlMe3), −0.26 (s, 12 H,
AlMe2), 1.04 (s, 18 H, CMe3), 1.52 (m, 10 H, CH2, CCH3), 2.79 (m, 4
H, NCH2). 13C NMR (75 MHz, C6D6, 25 °C): δ −9.1 (AlMe3), −6.6
(AlMe2), 15.1 (CMe), 29.4 (CH2), 30.9 (NCMe3), 45.6 (NCH2), 51.4
(NCMe3), 176.2 (NCN). IR: ν 2957, 2924, 2886, 2871, 2819, 1613,
1474, 1371, 1268, 1219, 1195, 1180, 1092, 1038, 982, 933, 845, 799,
682, 624, 595, 524, 483, 437, 394 cm−1.
General Experimental Procedure for the Synthesis of 13−
15. A solution of AlMe3 in toluene (9, 1.76 mL, 3.6 mmol; 10, 1.84
mL, 3.6 mmol; 11, 1.76 mL, 2.8 mmol) was added to a solution of the
α,ω-bis-carbodiimide (9, 0.40 g, 1.8 mmol; 10, 0.40 g, 1.8 mmol; 11,
0.40 g, 1.4 mmol) in 15 mL of toluene, and the mixture was heated to
90 °C and stirred for 15 min. All volatiles were evaporated under
vacuum after the solution was cooled to ambient temperature, yielding
13−15 as colorless crystalline solids. Analytically pure 13 and 14 were
obtained upon recrystallization of solutions in hexane/toluene at −30
°C.
[EtNC(Me)NC3H6N(AlMe3)CNEt]AlMe2 (13). Yield: 0.52 g (89.0%).
Melting point: 96 °C dec. Anal. Found (calcd) for C15H34Al2N4
ASSOCIATED CONTENT
* Supporting Information
■
S
1
(324.42 g/mol): H, 10.32 (10.56); C, 55.18 (55.53). H NMR (300
Text, figures, a table, and CIF files giving crystallographic data
of 7, 10−14, and 16, 1H and 13C NMR spectra (25 °C) of 1−4,
1H NMR spectra (25 °C) of compounds 6−14 and 16, and
MHz, C6D6H, 25 °C): δ −0.55 (s, 6 H, AlMe2), −0.21 (s, 9 H, AlMe3),
0.61 (t, 3 H, CH2CH3), 0.96 (s, 3 H, CMe), 1.04 (t, 3 H, CH2CH3),
1.62 (quint, 2 H, CH2), 2.64 (q, 2 H, CH2), 2.74 (t, 2 H, CH2), 3.07
(t, 2 H, CH2), 3.67 (q, 2 H, CH2). 13C NMR (75 MHz, C6D6, 25 °C):
δ −11.1 (AlMe2), −6.7 (AlMe2), 14.6 (CH3), 15.7 (CH3), 16.2 (CH3),
41.1 (CH2), 41.5 (CH2), 42.9 (CH2), 44.7 (CH2), 163.8 (NCN), 165.3
(NCN). IR: ν 2977, 2919, 2883, 2816, 1664, 1618, 1563, 1475, 1461,
1438, 1379, 1338, 1312, 1268, 1175, 1115, 1082, 1064, 1027, 983, 936,
921, 903, 876, 838, 800, 746, 670, 613, 577, 523, 398 cm−1.
1
temperature-dependent H NMR spectra (−70 °C) of 10−12.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
■
[EtNC(Me)NC4H8N(AlMe3)CNEt]AlMe2 (14). Yield: 0.53 g (85.2%).
Melting point: 98 °C dec. Anal. Found (calcd) for C16H36Al2N4
*S.S.: tel, +49 0201-1834635; fax, + 49 0201-1833830; e-mail,
stephan.schulz@uni-due.de.
1
(338.44 g/mol): H, 10.54 (10.72); C, 56.35 (56.78). H NMR (300
MHz, CHDCl2, 25 °C): δ −1.00 (s, 9 H, AlMe3), −0.83 (s, 6 H,
AlMe2), 0.92 (t, 3 H, CH2CH3), 1.22 (t, 3 H, CH2CH3), 1.76 (m, 4 H,
CH2), 2.47 (s, 3 H, CMe), 3.47−3.50 (m, 6 H, CH2CH3, CH2). 13C
NMR (125 MHz, CD2Cl2, 25 °C): δ −11.5 (AlMe3), −7.0 (AlMe2),
15.0 (CH3), 16.2 (CH3), 17.6 (CH3), 27.0 (CH2), 27.6 (CH2), 43.0
(CH2), 43.7 (CH2), 49.3 (CH2), 52.0 (CH2), 164.3 (NCN), 168.8
(NCN). IR: ν 2966, 2923, 2884, 2816, 1657, 1616, 1559, 1449, 1376,
1341, 1324, 1265, 1183, 1116, 1064, 1038, 920, 871, 793, 678, 627,
588, 515, 441 cm−1.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
S.S. thanks the University of Duisburg-Essen for financial
support.
■
REFERENCES
[PhNC(Me)NC4H8N(AlMe3)CNPh]AlMe2 (15). Any attempts to
■
1
(1) (a) Gavrilova, A. L.; Bosnich, B. Chem. Rev. 2004, 104, 349−383.
(b) Adams, R. D.; Captain, B. Acc. Chem. Res. 2009, 42, 409−418.
(c) Haak, R. M.; Wezenberg, S. J.; Kleij, A. W. J. Chem. Soc., Chem.
Commun. 2010, 46, 2713−2723. (d) Gambarotta, S.; Scott, J. Angew.
Chem., Int. Ed. 2004, 43, 5298−5308.
purify 15 failed. The H NMR spectrum always showed additional
1
resonances aside from those, which were addressed to 15. H NMR
(300 MHz, CHDCl2, 25 °C): δ −1.38 (s, 6 H, AlMe3), −1.07 (s, 9 H,
AlMe2), 1.85 (m, 4 H, CH2), 2.32 (s, 3 H, CMe), 3.30 (m, 2 H, CH2),
3.73 (m, 2 H, CH2), 6.93 (t, 2 H, Ar), 6.96 (d, 2 H, Ar), 7.08 (t, 2 H,
Ar), 7.24 (t, 2 H, Ar), 7.44 (t, 2 H, Ar).
Synthesis of 16. MeOH (0.20 mL, 5 mmol) was added at ambient
temperature to the raw product of 15 (0.44 g, 1 mmol), and the
mixture was stirred for 30 min. MeOH was then evaporated under
(2) (a) Matsunaga, S.; Yoshida, T.; Morimoto, H.; Kumagai, N.;
Shibasaki, M. J. Am. Chem. Soc. 2004, 126, 8777−8785. (b) Trost, B.
M.; Fettes, A.; Shireman, B. T. J. Am. Chem. Soc. 2004, 126, 2660−
2661. (c) Li, H.; Li, L.; Marks, T. J.; Liable-Sands, L.; Rheingold, A. L.
G
dx.doi.org/10.1021/om5002217 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
J. Am. Chem. Soc. 2003, 125, 10788−10789. (d) Guo, N.; Li, L.; Marks,
T. J. J. Am. Chem. Soc. 2004, 126, 6542−6543. (e) Li, H.; Li, L.; Marks,
T. J. Angew. Chem., Int. Ed. 2004, 43, 4937−4940. (f) Piesik, D. F.-J.;
Range, S.; Harder, S. Organometallics 2008, 27, 6178−6187.
(g) Mandal, S. K.; Roesky, H. W. Acc. Chem. Res. 2010, 43, 248−
259. (h) Mandal, S. K.; Roesky, H. W. Adv. Catal. 2011, 54, 1−61.
(i) Delferro, M.; Marks, T. J. Chem. Rev. 2011, 111, 2450−2485.
(j) Cooper, B. G.; Napoline, J. W.; Thomas, C. M. Catal. Rev. Sci. Eng.
2012, 54, 1−40. (k) Normand, M.; Roisnel, T.; Carpentier, J.-F.;
Kirillov, E. J. Chem. Soc., Chem. Commun. 2013, 49, 11692−11694.
(l) Radlauer, M. R.; Buckley, A. K.; Henling, L. M.; Agapie, T. J. Am.
Chem. Soc. 2013, 135, 3784−3787. (m) Normand, M.; Roisnel, T.;
Carpentier, J.-F.; Kirillov, E. J. Chem. Soc., Chem. Commun. 2013, 49,
11692−11694. (n) Li, L.; Wu, C.; Liu, D.; Li, S.; Cui, D.
Organometallics 2013, 32, 3203−3209.
(3) (a) Lu, M.; Yao, Y.; Zhang, Y.; Shen, Q. J. Chem. Soc., Dalton
Trans. 2010, 39, 9530−9537. (b) Li, L.; Wu, C.; Liu, D.; Li, S.; Cui, D.
Organometallics 2013, 32, 3203−3209. (c) Sun, S.; Sun, Q.; Zhao, B.;
Zhang, Y.; Shen, Q.; Yao, Y. Organometallics 2013, 32, 1876−1881.
For review articles see: (d) Ma, J.-A.; Cahard, D. Angew. Chem., Int. Ed.
2004, 43, 4566−4583. (e) Park, J.; Hong, S. Chem. Soc. Rev. 2012, 41,
6931−6943. (f) Barnes, D.; Brown, G. L.; Brownhill, M.; German, I.;
Herbert, C. J.; Jolleys, A.; Kennedy, A. R.; Liu, B.; McBride, K.; Mair,
F. S.; Pritchard, R. G.; Sanders, A.; Warren, J. E. Eur. J. Inorg. Chem.
2009, 1219−1233.
(17) (a) Zhang, W.; Sita, L. R. Adv. Synth. Catal. 2008, 350, 439−
447. (b) Wei, J.; Hwang, W.; Zhang, W.; Sita, L. R. J. Am. Chem. Soc.
2013, 135, 2132−2135.
(18) Edelmann, F. T. Adv. Organomet. Chem. 2013, 61, 55−374.
(19) (a) Meier, R. J.; Koglin, E. J. Phys. Chem. A 2001, 105, 3867−
3874. (b) Talarico, G.; Budzelaar, P. H. M. Organometallics 2000, 19,
5691−5695. (c) Ghorbani, N.; Ghohe, N. M.; Torabi, S.; Yates, B. F.;
Ariafard, A. Organometallics 2013, 32, 1687−1693.
(20) For recent review articles see: (a) Dagorne, S.; Atwood, D. A.
Chem. Rev. 2008, 108, 4037−4071;. (b) Dagorne, S.; Fliedel, C.;
Woodward, S.; Dagorne, S. Modern Organoaluminium Reagents. Top.
Organomet. Chem. 2013, 41, 125−172.
(21) (a) Qian, F.; Liu, K.; Ma, H. J. Chem. Soc., Dalton Trans. 2010,
39, 8071−8083. (b) Ruan, J. M.; Xiao, A. G.; Wu, H. W.; Yang, H. L.
Des. Monomers Polym. 2014, 17, 345−355.
(22) (a) Coles, M. P.; Swenson, D. C.; Jordan, R. F. Organometallics
1997, 16, 5183−5194. (b) Kincaid, K.; Gerlach, C. P.; Giesbrecht, G.
R.; Hagadorn, J. R.; Whitener, G. D.; Shafir, A.; Arnold, J.
Organometallics 1999, 18, 5360−5366. (c) Zhang, W.-X.; Li, D.;
Wang, Z.; Xi, Z. Organometallics 2009, 28, 882−887.
(23) For a recent review article see: Edelmann, F. T. Adv. Organomet.
Chem. 2008, 57, 183−352.
(24) Rowley, C. N.; DiLabio, G. A.; Barry, S. T. Inorg. Chem. 2005,
44, 1983−1991.
(25) Clare, B.; Sarker, N.; Shoemaker, R.; Hagadorn, J. R. Inorg.
Chem. 2004, 43, 1159−1166.
(26) Lei, Y.; Chen, F.; Luo, Y.; Xu, P.; Wang, Y.; Zhang, Y. Inorg.
Chim. Acta 2011, 368, 179−186.
(4) (a) Pettinari, C.; Pettinari, R. Coord. Chem. Rev. 2005, 249, 525−
543. (b) Nenu, C. N.; Weckhuysen, B. M. J. Chem. Soc., Chem.
Commun. 2005, 1865−1867. (c) Zhou, L.; Powell, D.; Nicholas, K. M.
Inorg. Chem. 2007, 46, 2316−2321. (d) Barnes, D.; Brown, G. L.;
Brownhill, M.; German, I.; Herbert, C. J.; Jolleys, A.; Kennedy, A. R.;
Liu, B.; McBride, K.; Mair, F. S.; Pritchard, R. G.; Sanders, A.; Warren,
J. E. Eur. J. Inorg. Chem. 2009, 1219−1233.
(27) Mansfield, N. E.; Coles, M. P.; Avent, A. G.; Hitchcock, P. B.
Organometallics 2006, 25, 2470−2474.
(28) Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G., Jr.
Organometallics 1998, 17, 4042−4048.
(29) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
G. A.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, , S1−S19.
(30) A CSD database search gave 12 hits for a C−NCN−C
fragment, ranging from 1.174 to 1.251 Å.
́
(5) Boere, R. T.; Oakley, R. T.; Reed, R. W. J. Organomet. Chem.
1987, 331, 161−167.
(6) Grundy, J.; Coles, M. P.; Hitchcock, P. B. J. Organomet. Chem.
2002, 662, 178−187.
(31) Sutton, L. E. In Interatomic Distances and Configuration in
Molecules and Ions; The Chemical Society: London, 1965; Special
Publication No. 18.
(32) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467−473.
(33) Sheldrick, G. M. SHELXL-97, Program for the Refinement of
(7) (a) Hagadorn, J. R.; Arnold, J. Angew. Chem., Int. Ed. 1998, 37,
1729−1731. (b) Kawaguchi, H.; Matsuo, T. J. Chem. Soc., Chem.
Commun. 2002, 958−959. (c) Li, J. F.; Weng, L. H.; Wei, X. H.; Liu,
D. S. J. Chem. Soc., Dalton Trans. 2002, 1401−1405.
(8) Chen, C. T.; Rees, L. H.; Cowley, A. R.; Green, M. L. H. J. Chem.
Soc., Dalton Trans. 2001, 1761−1767.
Crystal Structures; University of Gottingen, Gottingen, Germany, 1997.
̈
̈
See also:. Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, A64, 112−
122.
(9) Jenkins, H. A.; Abeysekera, D.; Dickie, D. A.; Clyburne, J. A. C. J.
Chem. Soc., Dalton Trans. 2002, 3919−3922.
(10) Babcock, J. R.; Incarvito, C.; Rheingold, A. L.; Fettinger, J. C.;
Sita, L. R. Organometallics 1999, 18, 5729−5732.
(11) Bai, S.-D.; Guo, J.-P.; Liu, D.-S.; Wong, W.-Y. Eur. J. Inorg.
Chem. 2006, 4903−4907.
(12) (a) Kraft, A. J. Chem. Soc., Perkin Trans. 1 1999, , 705−714.
(b) Cordes, A. W.; Haddon, R. C.; Hicks, R. G.; Oakley, R. T.; Palstra,
T. T. M.; Schneemeyer, L. F.; Waszczak, J. V. J. Am. Chem. Soc. 1992,
114, 5000−5004.
(13) Gutschank, B.; Schulz, S.; Marcinkowski, M.; Jansen, G.;
Bandmann, H.; Blaser, D.; Wolper, C. Angew. Chem., Int. Ed. 2012, 51,
̈
̈
10893−10897.
(14) (a) Schmidt, S.; Gutschank, B.; Schulz, S.; Blaser, D.; Boese, R.;
Wolper, C. Eur. J. Inorg. Chem. 2011, 4464−4470. (b) Gutschank, B.;
Schulz, S.; Blaser, D.; Boese, R.; Wolper, C. Organometallics 2010, 29,
̈
̈
̈
̈
6133−6136. (c) Gutschank, B.; Schulz, S.; Westphal, U.; Blaser, D.;
̈
Boese, R. Organometallics 2010, 29, 2093−2097. (d) Schmidt, S.;
Gondzik, S.; Schulz, S.; Blaser, D.; Boese, R. Organometallics 2009, 28,
̈
4371−4376. (e) Munch, M.; Florke, U.; Bolte, M.; Schulz, S.; Gudat,
̈
̈
D. Angew. Chem., Int. Ed. 2008, 47, 1512−1514.
(15) Gutschank, B.; Bayram, M.; Schulz, S.; Blaser, D.; Wolper, C.
̈
̈
Eur. J. Inorg. Chem. 2013, 5495−5502.
(16) Bambirra, S.; Meetsma, A.; Hessen, B.; Teuben, J. H.
Organometallics 2001, 20, 782−785.
H
dx.doi.org/10.1021/om5002217 | Organometallics XXXX, XXX, XXX−XXX