Mendeleev Commun., 2013, 23, 265–267
does not occur in C1. The two-fold rotational axis is located on
the coplanar relationship of the corresponding four atoms. The
lengths of Li–Cl bonds vary from 2.31 to 2.43 Å.
the inner line crossing Li(2) and Li(3). C2 differs from C1 on the
substitution of naphthyl for phenyl, which causes another notable
feature in C2. The C–C single bond between naphthyl and C
atom of N–C–N unit can rotate to some extent, while it cannot
act as a C2 axis for the naphthyl group. Additionally, the naphthyl
plane is almost perpendicular to the [NCN] plane; these factors
will lead to different orientation combinations when two naphthyl
groups anchored on the N–C–N–Si–N–C–N skeleton. It is pre-
dictable that the cis- or trans-like isomerization caused by the
same or opposite directions of two naphthyl groups exists in C2.
Figure 2 only displays the trans-like situation for a clear view.
In fact, the naphthyl group attached on C(5) has a disordered
counterpart, which is cis to the naphthyl group attached at C(18).
Though the ligand in C2 molecule has both cis and trans forms,
as found in Group IV metal complexes, it will merely adopt a cis
form in the Ti complex and a trans form in Zr and Hf complexes.
C3 was prepared in the same way as C1, while the only
change was the starting amine used. Cyclohexylamine was used
for synthesizing C3. It caused a significant change in their
molecular structures. C3 (Figure 3)‡ is a pentanuclear lithium
species. Correspondingly, there are two bianionic ansa-bis-
(amidinate) ligands and one chloride ion in it. Overall, the
composition of C3 could be thought of as the similar components
in C1 plus a LiCl moiety and three THF molecules. The terminal
cyclohexyl groups adopt a typical chair-like configuration. Two
N–C–N–Si–N–C–N skeletons tend to be close to each other with
one of their ends. The other two ends are much wider, and the
chloride ion is settled at the middle position between the two N
ends. All the lithium metal centers are embedded in the interior
space enclosed by two ansa-bis(amidinate) ligands. Each lithium
ion is tetracoordinated in a tetrahedral geometry. They are arranged
in a unique sequence of 1, 2 and 2. On the top side of the molecule
of C3, there is a THF molecule attached to the lithium ion, which
is free from the chloride ion. The bottom two lithium ions are
separated by the chloride ion and both are covered with one THF
molecule from opposite sides. Besides the bottom two lithium
ions, the chloride ion is also bound by two lithium ions in the
middle layer. A resulting quadrilateral [Li(3)–Li(4)–Cl(1)–Li(5)]
in the core has four inner angles summed to 360°, which reflects
By comparing the molecular structures of C1, C2 and C3, we
can see that C1 is closely similar to C2 in the arrangement of
lithium ions and ligands, while they are quite different from C3.
Three lithium complexes adopt two different types of aggregation
in a crystalline state. According to ligand changes in substituents
on the same skeleton, the different aggregation is obviously
caused by the terminal group, which is originated from the
primary amine used. Meanwhile, it reflects that the terminal
group has a notable impact on the property of corresponding
ligand and its compatibility to metal ions.
In conclusion, a newly developed synthetic method with direct
and efficient features for alkyl-ended ansa-bis(amidinate) ligands
is reported. It has a wide range of product array as there are three
variable sites, which can also result in numerous combinations
of steric and electronic properties in ligands and complexes. The
chain-like skeleton with the bianionic property of ligands causes the
lithium derivatives to demonstrate the similar multinuclear feature.
This work was supported by the Natural Science Foundation of
China (grant nos. 20702029, 20872084 and 21272142) and the Natura
l
Science Foundation of Shanxi Province (grant no. 2008011024).
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C(40)
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C(50)
C(41)
Li(4)
C(55)
N(6)
Li(5)
Li(2)
C(56)
Li(1)
C(36)
C(39)
C(38)
C(8)
C(12)
C(7)
C(13)
C(35)
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N(1)
C(37)
C(34)
Cl(1)
C(60)
C(61)
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C(1)
O(2)
C(6)
C(57)
C(63)
C(29)
C(5)
C(3)
C(59)
C(62)
C(33)
C(58)
C(2)
C(64)
C(30)
C(4)
C(32)
C(31)
Figure 3 Molecular structure of compound C3. Hydrogen atoms and a
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Received: 13th May 2013; Com. 13/4121
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