Guanidinatoaluminum complexes: Synthesis, crystal structures and reactivities

Article abstract of DOI:10.1039/c6ra18367k

Treatment of diethylaminolithium with carbodiimide (CyNCNCy or CyNCNC₆H₅) and dimethylaluminium chloride (AlMe₂Cl) in a molar ratio of 1:1:1 afforded two kinds of guanidinatoaluminum complexes, [{(Et₂N)C(NR₁)(NR₂)}AlMe₂] (R₁, R₂ = Cy (1); R₁ = Cy, R₂ = C₆H₅ (2)) and [{(Et₂N)C(NCy)(NC₆H₅)}₂AlMe] (3). The reactivities of the mononuclear guanidinatoaluminum complexes (1 and 2) with O₂ or carbodiimide were studied. The complexes of [{(Et₂N)C(NCy)₂}AlMe(μ-OMe)]₂ (4) and [{N(C₆H₅)C(NCy)N(C₆H₅)C(NEt₂)N(Cy)}AlMe₂] (5) were produced by introducing dry oxygen or carbodiimide (CyNCNC₆H₅) slowly into the solution of the mononuclear guanidinatoaluminum complex (1 or 2). Meanwhile, the addition of O₂ or carbodiimide (ArNCNC₆H₅, Ar = 2,6-Me₂C₆H₃) to the reaction solution of diethylaminolithium with ArNCNC₆H₅ and AlMe₂Cl in a molar ratio of 1:1:1 yielded [(Et₂N)C(NC₆H₅)(NAr)AlMe(μ-OMe)]₂ (6) and [{N(C₆H₅)C(NAr)N(C₆H₅)C(NEt₂)N(Ar)}AlMe₂] (7). In addition, a one-pot reaction of diethylaminolithium with CyNCNCy and AlMe₂Cl in a molar ratio of 1:1:1 in the presence of H₂O produced a tetranuclear guanidinatoaluminum complex, (8), which was also prepared by treatment of complex 1 with equivalent AlMe₃ and H₂O in 35% yield. All complexes 1-8 were characterized by ₁H, ₁₃C NMR spectroscopy and single crystal X-ray diffraction analysis.

Full text of DOI:10.1039/c6ra18367k

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Guanidinatoaluminum complexes: synthesis,
crystal structures and reactivities†
Cite this: RSC Adv., 2016, 6, 101437
c
a
a
c
Hong-Fei Han,ab Zhi-Qiang Guo, Shao-Feng Zhang, Jie Li and Xue-Hong Wei
*
Treatment of diethylaminolithium with carbodiimide (CyN]C]NCy or CyN]C]NC6H5) and
dimethylaluminium chloride (AlMe2Cl) in molar ratio of 1 : 1 : 1 afforded two kinds of
a
guanidinatoaluminum complexes, [{(Et2N)C(NR1)(NR2)}AlMe2] (R1, R2 ¼ Cy (1); R1 ¼ Cy, R2 ¼ C6H5 (2)) and
[{(Et2N)C(NCy)(NC6H5)}2AlMe] (3). The reactivities of the mononuclear guanidinatoaluminum complexes
(1 and 2) with O2 or carbodiimide were studied. The complexes of [{(Et2N)C(NCy)2}AlMe(m-OMe)]2 (4) and
[{N(C6H5)C(NCy)N(C6H5)C(NEt2)N(Cy)}AlMe2] (5) were produced by introducing dry oxygen or
carbodiimide (CyN]C]NC6H5) slowly into the solution of the mononuclear guanidinatoaluminum
complex (1 or 2). Meanwhile, the addition of O2 or carbodiimide (ArNC]NC6H5, Ar ¼ 2,6-Me2C6H3) to
the reaction solution of diethylaminolithium with ArN]C]NC6H5 and AlMe2Cl in a molar ratio of 1 : 1 : 1
yielded [(Et2N)C(NC6H5)(NAr)AlMe(m-OMe)]2 (6) and [{N(C6H5)C(NAr)N(C6H5)C(NEt2)N(Ar)}AlMe2] (7). In
addition, a one-pot reaction of diethylaminolithium with CyN]C]NCy and AlMe2Cl in a molar ratio of
Received 19th July 2016
Accepted 19th October 2016
1 : 1 : 1 in the presence of H2O produced
a
tetranuclear guanidinatoaluminum complex,
(8), which was also prepared by treatment of complex 1 with equivalent
AlMe3 and H2O in 35% yield. All complexes 1–8 were characterized by 1H, 13C NMR spectroscopy and
single crystal X-ray diffraction analysis.
DOI: 10.1039/c6ra18367k
www.rsc.org/advances
Group 13 guanidinate complexes, especially highly electro-
philic aluminium species, are widely studied due to their
Introduction
potential applications as gaseous precursors to technologically
important materials8 and excellent candidates for several well-
known catalytic applications.9 These aluminum complexes
with guanidinate ligands were synthesized8a,10 by (i) insertion of
carbodiimides into Al–N bonds, (ii) a salt-metathesis reaction
between an aluminum halide and an alkali metal guanidinate
and (iii) the deprotonation reaction of a neutral guanidine and
aluminum alkyls. Because of the sensitivity of mononuclear
guanidinatoaluminum alkyls, their applications are usually
under the protection of N2.9 We have been trying to synthesize
some more stable guanidinato-aluminum complexes. Due to
guanidinates considered as amidinates by substitution of the
central C–R substituent by an amino group, some special
reactions of amidinates, e.g., amidinatoaluminum complexes
with O2 or carbodiimides reported in the literature have caused
our attention.11 Although the high oxophilicity ability of alu-
minum(III) have been demonstrated by several examples of the
interaction of aluminum complexes with oxygen, and the reac-
tion mechanism about the reaction has been also detailed in
the reported papers,12 the rst oxo amidinatoaluminum
complex, [{HC(NDipp)2}AlMe(m-OMe)]2, was isolated unexpect-
edly until 2010 by Richards' group.11a Recently, our team has
synthesized several amidinatoaluminum complexes containing
the m-OCH3 moiety by the reaction of aluminum amidinate
Amidinates and guanidinates are popular ligands due to their
ease of synthesis and modication by changing various groups,
as well as their robust nature. These amidinato or guanidinato
ligands involving metals from across the periodic table have
been synthesized and applied in many areas, including
synthesis,1 coordination chemistry2 and materials science.3 In
particular, many complexes containing amidinato or guanidi-
nato ligands were specically identied as being excellent
initiators or catalysts for various reactions, and especially used
to initiate electrophilic polymerization reactions,4 e.g., titanium
amidinates were used as the initiators of polymerization of
propylene,5 and guanidinato complexes of neodymium or
ytterbium catalyzed the polymerization of styrene.6 Recently,
our group explored a series of amidinatoaluminum and gua-
nidinato metal (Al and Zn) complexes used as the catalysts
in the Tishchenko reaction and Meerwein–Ponndorf–Verley
reduction.7
aThe School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan
030006, P. R. China
bDepartment of Chemistry, Taiyuan Normal University, Taiyuan 030031, P. R. China
cScientic Instrument Center, Shanxi University, Taiyuan 030006, P. R. China. E-mail:
xhwei@sxu.edu.cn; Fax: +86-351-7011688; Tel: +86-351-7018390
† Electronic supplementary information (ESI) available. CCDC 1447460–1447465,
1493286 and 1493287. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c6ra18367k
alkyls with oxygen. In addition, Tomas Chlupaty11b explored two
´ˇ
´
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unique amidinato-guanidinato
Paper
based
aluminium(III)
complexes, {[iPrNC(iPrNC(Me)NiPr)NiPr]AlMeCl}$Me2AlCl and
{[CyNC(CyNC-(Me)NCy)NCy]AlMeCl}$Me2AlCl, which can be
described as products of nucleophilic attack of an insufficiently
stabilize amidinate anion to another carbodiimide molecule.
One can therefore anticipate that mononuclear guanidinatoa-
luminum complex could react with O2 or carbodiimide.
Scheme 2 The proposed equilibrium between 2 and 3.
We herein report on (i) the synthesis of [{(Et2N)C(NR1)(NR2)}
AlMe2] (R1, R2 ¼ Cy (1); R1 ¼ Cy, R2 ¼ C6H5 (2)) and [{(Et2N)
C(NCy)(NC6H5)}2AlMe] (3), in which process we proposed the
existence of an equilibrium between (bis)guanidinatoalumi-
num complex (3), AlMe3 and (mono)-guanidinatoaluminum
complex (2); (ii) the reactivities of mononuclear guanidinatoa-
luminum complexes by the reactions of 1, 2 or the solution
preparing the (mono)guanidinatoaluminum complexes with O2
or carbodiimide; and (iii) the reaction of the equilibrium
mixtures with H2O, affording a tetranuclear guanidinatoalu-
minum complex (8), which was also prepared by treatment of
the complex 1 with AlMe3 and H2O in a molar ratio of 1 : 1 : 1.
1 : 1 : 1 or 2 : 1 : 2.7b The reason that different products ((bis)
guanidinatoaluminum complex or (mono)guanidinato-
aluminum complex) from the similar reaction solutions is
maybe attributed to group types bound to carbodiimide.
According to the successful experiences,7c,11b we considered
that the mononuclear guanidinatoaluminum complexes (1 and
2) should react with dry oxygen or carbodiimide. As shown
in Scheme 3, two relatively stable guanidinatoaluminum
complexes, [{(Et2N)C-(NCy)2}AlMe(m-OMe)]2 (4) and [{N(C6H5)
C(NCy)N(C6H5)C(NEt2)N(Cy)}AlMe2] (5), were successfully ob-
tained by insertion of oxygen atom or carbodiimide into the Al–
C or Al–N bond of the mononuclear guanidinatoaluminum
complex (1 or 2), respectively. The dimeric complex 4 was iso-
lated in good yield by introducing dry oxygen into tetrahydro-
furan solution of complex 1 at ꢀ78 ꢁC, which was also
synthesized by a one-pot reaction of Et2NH with sequentially
AlMe3 and CyN]C]NCy in the presence of dry oxygen. The
complex 5 was obtained in 79% yield, when another 1 equiv. of
CyN]C]NC6H5 was dropped into the solution of 2. The
complex 5 can also be produced by one-pot reaction of Et2NH
with AlMe3, and CyN]C]NC6H5 in relative molar ratio of
1 : 1 : 2. Attempts to isolate the analogue of 4 with Cy and Ph
substituents were failed. In addition, treatment of 1 with CyN]
C]NCy was studied, in which a complex similar to 5 wasn't
obtained. Although the (mono)guanidinato analogue of 30
wasn't isolated by the treatment of diethylaminolithium with
sequentially PhN]C]NAr (Ar ¼ 2,6-Me2C6H3) and AlMe2Cl in
a molar ratio of 1 : 1 : 1, [(Et2N)C(NC6H5)(NAr)AlMe(m-OMe)]2
(6) and [{N(C6H5)C(NAr)-N(C6H5)C(NEt2)N(Ar)}AlMe2] (7),
similar to the complexes of 4 and 5, respectively, were isolated
Results and discussion
Synthesis and reactivities of guanidinatoaluminum
complexes
As shown in Scheme 1, treatment of Et2NH with n-BuLi and car-
bodiimine (CyN]C]NCy, CyN]C]NC6H5 or ArN]C]NC6H5,
Ar ¼ 2,6-Me2C6H3) afforded guanidinatolithium as described in
the literatures.4a,10 The guanidinatolithium salts were not isolated
but rather reacted in situ with equivalent AlMe2Cl yielded two
kinds of guanidinatoaluminum complexes, [{(Et2N)C(NR1)(NR2)}
AlMe2] (R1, R2 ¼ Cy (1); R1 ¼ Cy, R2 ¼ C6H5 (2)) and [{(Et2N)
C(NR1)(NR2)}2AlMe] (R1 ¼ Cy, R2 ¼ C6H5 (3); R1 ¼ C6H5, R2 ¼ 2,6-
Me2C6H3 (30)7b). The two mononuclear guanidinato-aluminum
complexes of 1 and 2 were synthesized by the salt-metathesis
reaction between guanidinatolithium and equivalent AlMe2Cl,
respectively. Surprisingly, complex 3, a (bis)guanidinatoalumi-
num complex, was also isolated from the reaction solution
yielding 2. In addition, treatment of the complex 3 with AlMe3 was
studied, which also afforded the complex 2. So we proposed the
existence of an equilibrium between 3, AlMe3 and 2 (Scheme 2).
Furthermore, treatment of diethylaminolithium with ArN]C]
NC6H5 (Ar ¼ 2,6-Me2C6H3) and AlMe2Cl in a molar ratio of 1 : 1 : 1
isolated only the (bis)guanidinatoaluminum complex 30, which
was also prepared by the treatment of Et2NH with sequentially
AlMe3 and carbodiimine ArN]C]NC6H5 in a molar ratio of
Scheme 3 Synthetic routes to complexes 4–5.
Scheme 1 Synthetic routes to complexes 1–3.
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Scheme 4 Synthetic routes to complexes 6–7.
˚
via introducing the dry oxygen or carbodiimide into the reaction radiation (l ¼ 0.71073 A) on a Bruker Smart Apex CCD diffrac-
solution of the guanidinatolithium,7b [{(C2H5)2N}C(NC6H5)(- tometer at 223(2) K. Corrections were applied for Lorentz and
NAr)LiOEt2]2, with AlMe2Cl (Scheme 4).
polarization effects as well as absorption using multiscans
We also explored the possibility of incorporating degassing (SADABS).13 Each structure was solved by direct methods and
H2O (the water molecules could be quantitatively introduced by rened on F2 by full matrix least-squares (SHELX97)14 using all
an aqueous solvent) in solution of the mononuclear guanidina- unique data. Then the remaining non-hydrogen atoms were
toaluminum complexes (1 and 2) to prepare several interesting obtained from the successive difference Fourier map. All non-
and relatively stable oxo guanidinatoaluminum complexes or its hydrogen atoms were rened with anisotropic displacement
derivatives. This strategy wasn't successful with the mononuclear parameters, whereas the hydrogen atoms were constrained to
guanidinatoaluminum complexes (1 and 2), and no new guani- parent sites, using a riding mode (SHELXTL).15 Details of the
dinatoaluminum complex was obtained. However, while intro- modeling of disorder in the crystals can be found in their CIF
ducing degassing H2O into the treatment solution of les.
diethylaminolithium with sequentially carbodiimide (CyN]C]
Crystals of 1 were obtained from a saturated hexane solution
NCy, CyN]C]NC6H5 or ArN]C]NC6H5, Ar ¼ 2,6-Me2C6H3) at ꢀ5 ꢁC. As is shown in Fig. 1, the aluminum centre of the
and AlMe2Cl in a molar ratio of 1 : 1 : 1, the only complex that we complex 1 is four coordinate with one chelating guanidinato
have been able to isolate successfully is a tetranuclear complex, unit and two C atoms coming from methyl groups giving it
(8), produced in 19% yield, which a distorted tetrahedral geometry, which is similar to the struc-
can also be synthesized by the reaction of the complex 1 with 1 ture of the molecular of [(iPr2N)C{N(2,6-iPr2C6H3)}2]AlMe2.16
equiv. of AlMe3 in the presence of H2O. 8 may be formed by the Complex 1 possesses a C2 symmetry axis passing through the
reaction of H2O with two methyl groups from the (mono)guani- metal Al, C7 and N2 atoms. The Al1–N1 and Al1–N10 bond
˚
dinatoaluminum complex (1) and AlMe3 (Scheme 5). Each of 1–8 distances (1.9187(15) and 1.9188(15) A, respectively) are obvi-
˚
was easily puried by crystallization from appropriate solvent, ously shorter than those (1.9287(15) and 1.9239(16) A, respec-
1
characterized by satisfactory C, H, and N microanalysis, H and tively) in [(iPr2N)C{N(2,6-iPr2C6H3)}2]AlMe2. The Al–C bond
13C NMR spectra in C6D6 or CDCl3 at ambient temperature, and distances of 1.961(2) and 1.960(2) A for Al1–C10 and Al1–C10 ,
0
˚
single crystal X-ray diffraction analysis.
respectively, reect the symmetrical coordination of the guani-
dinato ligand to the Al metal center. In addition, the bite angle
of 70.00(8)ꢁ for N1–Al1–N10 is closely to that (69.06(6)ꢁ) of
[(iPr2N)C{N(2,6-iPr2C6H3)}2]AlMe2. In the guanidinato moiety
X-ray structure determination for complexes 1–8
The crystals of 1–8 suitable for single crystal X-ray diffraction
analysis were recrystallized from the appropriate solvents.
Crystallographic measurements were performed with Mo Ka
˚
C7N3, C7–N2 bond length is 1.361(3) A, which is shorter than
i
i
˚
that (1.371(2) A) in [( Pr2N)C{N(2,6- Pr2C6H3)}2]AlMe2. Virtually
Scheme 5 Synthetic routes to complex 8.
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Fig. 1 ORTEP diagram of complex 1. Thermal ellipsoids are drawn at
the 30% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (A˚) and bond angles (deg): C7–N1 1.3448(18),
C7–N10 1.3448(19), C7–N2 1.361(3), Al1–N1 1.9187(15), Al1–N10
1.9188(15), C10–Al1 1.961(2), Al1–C10 1.960(2); N1–C7–N2 125.08(10),
N10–C7–N2 125.08(10), N10–C7–N1 109.8(2), C7–N1–Al1 90.09(11),
N1–Al1–N10 70.00(8), N1–Al1–C100 117.15(9), N1–Al1–C10 114.53(8),
C10–Al1–C100 115.74(15). Symmetry elements for 1: 1 ꢀ x, y, 1/2 ꢀ z.
Fig. 3 ORTEP diagram of complex 3. Thermal ellipsoids are drawn at
the 30% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (A˚) and bond angles (deg): N1–C13 1.339(2),
N2–C13 1.337(2), N3–C13 1.370(2), Al1–N1 1.9502(14), Al1–N2
2.0404(14), Al1–C18 1.953(3), N–C13–N2 110.02(15), N1–C13–N3
124.53(15), N2–C13–N3 125.40(15), Al1–N1–C13 93.60(10), Al1–N2–
C13 89.71(10), N1–Al1–N2 66.61(6), N1–Al1–C18 118.96(5), N2–Al1–
C18 103.13(5).
identical C7–N1 and C7–N10 bond distances of 1.3448(18) and
˚
1.3448(19) A, which are also shorter than those (1.356(2) and
˚
structures of complex 3 is also penta-coordinated with a dis-
torted trigonal bipyramidal environment in which four N atoms
correspondingly come from two chelating guanidinato units
and one C atom is from methyl group. The dihedral angle
between the planes of AlNCN in complex 3 is 58.75(4)ꢁ, which is
larger than that (45.37(14)ꢁ) in 30. The Al–N bond lengths
1.354(2) A, respectively) in the reported guanidinatoaluminum
complex, substantiated a high degree of electron delocalization
within the guanidinate backbone.
The molecular structure of complex 2 is depicted in Fig. 2.
Complex 2 crystallize in the monoclinic C2/c space group.
Apart from the exocyclic substituents at the nitrogen atoms N2
(corresponding to N10 in 1), its geometry is closely similar to
that of 1.
The molecular structure of 3 is illustrated in Fig. 3. The X-ray
diffraction studies showed that complex 3 has similar structure
to complex 30.7b The geometry around the Al atom in the
˚
˚
(1.950(1) A and 2.040(1) A) in complex 3 0are different from those
˚
˚
(1.964(4) A and 1.968(3) A) in complex 3 . The C13–N1 and C13–
N2 bond distances within N1C13N2 fragment of complex 3 are
˚
in the range of 1.331(5)–1.349(5) A which are close to known
C–N distances of the guanidinato metal complex.2f In addition,
˚
the Al–C bond length of 2.434(2) A is consistent with the value
previously reported.9d
The molecular structure of complex 4 is depicted in Fig. 4.
Complex 4 crystallize in the monoclinic C2/c space group.
Crystalline 4 is a centrosymmetric dimer with a central, virtually
rhombus Al1O1Al10O10 core, which is close to that of
[{MeC(NCy)2}AlMe(m-OMe)]2.7c The geometry around the Al
atom in the structures of complex 4 is penta-coordinated with
a distorted trigonal bipyramidal environment in which the
nitrogen atom N1 and oxygen atom O1 occupy axial positions.
In molecular structure of 4, the dihedral angle between the
planes of Al1N3C7N1 and Al1O1Al10O10 is 61.179(65)ꢁ, which is
similar to that (61.322(42)ꢁ) in above reported complex.7c The
˚
Al–O bond lengths (1.8308(13)–1.9143(13) A) lie in the reason-
˚
able range for those (1.8270(11)–1.9190(11) A) in [{MeC(NCy)2}
AlMe(m-OMe)]2. The Al1–N1 and Al1–N2 bonds (1.9429(15) and
Fig. 2 ORTEP diagram of complex 2. Thermal ellipsoids are drawn at
the 30% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (A˚) and bond angles (deg): C7–N1 1.342(4), C7–
N2 1.360(4), C7–N3 1.359(4), Al1–N1 1.930(3), Al1–N2 1.922(3), C18–
Al1 1.963(4), Al1–C19 1.955(4); N1–C7–N2 108.7(3), N2–C7–N3
125.1(3), N1–C7–N3 126.2(3), C7–N1–Al1 136.5(2), C7–N2–Al1
90.79(19), N1–Al1–N2 69.48(11), N1–Al1–C19 118.47(16), N1–Al1–C18
113.77(15), N2–Al1–C18 115.10(15), N2–Al1–C19 114.42(16), C18–Al1–
C19 116.94(17).
˚
2.0431(16) A, respectively) of the guanidinate ligand are
˚
different from those (1.9280(14) and 2.0524(14) A, respectively)
in [{MeC(NCy)2}AlMe(m-OMe)]2, suggesting a greater degree of
electronic delocalization within the guanidinate backbone of 4,
an observation that is further substantiated by the similar C7–
˚
N1 and C7–N3 bond distances of 1.334(2) and 1.325(2) A,
respectively. In addition, the Al1–C18 bond distance of
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a distorted tetrahedral geometry. The central metal ring
AlNCNCN displays a twisted geometry. The four atoms Al1, N1,
˚
C7, and N4 are essentially planar with a deviation of 0.0458 A,
and the dihedral angle between the mean planes of Al1N1C7N4
and C7N3C20 is 61.8(3)ꢁ. The bond distances of Al1–N1 and
˚
Al1–N4 are 1.890(3) and 1.944(3) A, respectively, which fall in
˚
the reasonable range for those (1.851(4)–1.9841(9) A) in the re-
ported guanidinatoaluminum complexes.8,16,17 In addition, the
bond angle of N1–Al1–N4 is 94.16(11)ꢁ in 5. For the guanidinato
˚
moiety C7N3, the N2–C7 bond distances of 1.280(4) A is char-
acteristic for a C]N imine double bond, while the bond
˚
distances of C7–N3 is 1.474(4) A, showing single bond char-
˚
acter. N1–C7 bond (1.343(4) A) possesses partial double bond
character, which can be attributed to the lone pair on the amine
N2 atom to delocalize into the N1–C7 imine p*-antibonding
orbital. For the other guanidinato moiety C20N3, the C–N bond
Fig. 4 ORTEP diagram of complex 4. Thermal ellipsoids are drawn at
the 30% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (A˚) and bond angles (deg): N1–C7 1.334(2), N2–
C7 1.394(2), N3–C7 1.325(2), Al1–N1 1.9429(15), Al1–N3 2.0431(16),
Al1–C18 1.9744(19), Al1–O1 1.8308(13), Al1–O10 1.9143(13), O1–C19
1.427(2), Al1–C7 2.4080(19), Al1–Al10 2.9504(11); N1–C7–N2
125.66(16), N1–C7–N3 111.70(16), N3–C7–N2 122.64(17), C7–N1–Al1
92.71(11), C7–N3–Al1 88.62(11), N1–Al1–N3 66.94(6), N1–Al1–C18
119.87(8), C18–Al1–N3 100.68(8), O1–Al1–O10 76.06(6), O1–Al1–C18
121.44(8), O10–Al1–C18 99.30(8), C19–O1–Al1 129.57(11), C19–O1–
Al10 124.21(11), Al1–O1–Al10 103.94(6). Symmetry elements for 4: 1/2 ꢀ
x, 1/2 ꢀ y, 2 ꢀ z.
˚
lengths are in the range of 1.331(4)–1.362(4) A, suggesting
a greater degree of electronic delocalization within the guani-
dinate backbone C20N3 of 5.
The molecular structure of the crystalline complex 6 is
shown as an ORTEP diagram in Fig. 6. Apart from the exocyclic
substituents at the carbon atom C9 (corresponding to C7 in 4)
and nitrogen atom N2 (corresponding to N3 in 4), its geometry
is closely similar to that of 4.
The molecular structure of 7 is illustrated in Fig. 7. Crystal-
lographic studies of 7 conrmed tetrahedral geometries about
Al and a boat conformation of the six membered chelate ring.
The boat conformation of 7 results in an angle of 80.4(2)ꢁ
between the mean planes through AlN2 and C2N atoms of the
˚
˚
1.9744(19) A is a little shorter than that (1.9769(18) A) in
[{MeC(NCy)2}AlMe(m-OMe)]2.
The molecular structure of complex 5 is illustrated in Fig. 5.
The X-ray diffraction studies showed that being surrounded by
two nitrogen atoms of the chelating diguanidinato ligand and
two alkyl groups, the aluminum center in complex 5 possesses
Fig. 6 ORTEP diagram of complex 6. Thermal ellipsoids are drawn at
the 30% probability level. Hydrogen atoms are omitted for clarity.
Fig. 5 ORTEP diagram of complex 5. Thermal ellipsoids are drawn at Selected bond lengths (A˚) and bond angles (deg): N1–C9 1.348(2), N3–
the 30% probability level. Hydrogen atoms are omitted for clarity. C9 1.357(2), N2–C9 1.352(3), Al1–N1 1.9445(16), Al1–N2 2.0315(17),
Selected bond lengths (A˚) and bond angles (deg): N1–C7 1.343(4), N2– Al1–C20 1.967(2), Al1–O1 1.8322(15), Al1–O10 1.8861(15), O1–C21
C7 1.280(4), N3–C7 1.474(4), N3–C20 1.352(4), N4–C20 1.331(4), N5– 1.425(3), Al1–C9 2.440(2), Al1–Al10 2.9313(11); N1–C9–N3 126.33(18),
C20 1.362(4), Al1–N1 1.890(3), Al1–N4 1.944(3), Al1–C31 1.960(4), Al1– N1–C9–N2 108.86(16), N3–C9–N2 124.80(18), C9–N1–Al1 93.90(12),
C32 1.960(4); Al1–N1–C7 119.3(2), N1–C7–N2 125.0(3), N1–C7–N3 C9–N2–Al1 90.00(12), N1–Al1–N2 67.00(7), N1–Al1–C20 113.86(9),
113.8(3), N2–C7–N3 121.1(3), C7–N3–C20 120.8(2), N3–C20–N4 C20–Al1–N2 102.59(9), O1–Al1–O10 75.95(7), O1–Al1–C20 117.80(9),
118.7(3), N3–C20–N5 118.6(2), N4–C20–N5 122.6(3), Al1–N4–C20 O10–Al1–C20 103.32(9), C21–O1–Al1 129.82(14), C21–O1–Al10
117.32(19), N1–Al1–N4 94.16(11), N1–Al1–C31 116.60(14), N1–Al1–C32 124.47(14), Al1–O1–Al10 104.05(7). Symmetry elements for 6: 1 ꢀ x, 1 ꢀ
115.29(18), N4–Al1–C31 109.13(15), N4–Al1–C32 111.89(17).
y, 1 ꢀ z.
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Fig. 7 ORTEP diagram of complex 7. Thermal ellipsoids are drawn at
the 30% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (A˚) and bond angles (deg): N1–C9 1.313(3), N2–
C9 1.351(3), N3–C9 1.396(3), N1–Al1 1.946(2), N5–Al1 1.901(2), N3–
C20 1.459(3), N4–C20 1.280(3), N5–C20 1.359(3), Al1–C35 1.956(3),
Al1–C36 1.950(3); N1–C9–N2 125.1(2), N1–C9–N3 117.8(2), N2–C9–
N3 117.0(2), Al1–N1–C9 117.25(16), C9–N3–C20 123.69(19), N3–
C20–N4 114.3(2), N3–C20–N5 113.86(18), N4–C20–N5 131.9(2), Al1–
N5–C20 117.74(14), N1–Al1–N5 91.44(9), N1–Al1–C35 111.69(11), N1–
Al1–C36 107.42(13), N5–Al1–C35 112.31(11), N5–Al1–C36 113.14(12).
Fig. 8 ORTEP diagram of complex 8. Thermal ellipsoids are drawn at
the 30% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (A˚) and bond angles (deg): N1–C1 1.384(2), N3–
C1 1.347(3), N2–C1 1.346(3), N2–Al1 1.890(2), N3–Al20 1.965(2), O1–
Al1 1.799(2), O1–Al2 1.800(2), O1–Al10 1.812(1), Al1–C18 1.941(2), Al2–
C19 1.970(2), Al2–C20 1.966(3); N1–C1–N3 121.09(19), N1–C1–N2
120.12(18), N2–C1–N3 118.77(17), Al1–N2–C1 116.29(13), Al20–N3–C1
121.02(13), N2–Al1–O10 103.01(7), N2–Al1–C18 112.31(9), O1–Al1–C18
115.48(9), O1–Al1–O10 87.09(7), N30–Al2–C19 113.37(10), N30–Al2–
C20 114.94(10), O1–Al2–C19 113.37(10), O1–Al2–C20 106.62(9),
C19–Al2–C20 112.98(12), Al1–O1–Al10 92.91(7), Al1–O1–Al2
140.34(8), Al2–O1–Al10 114.39(7). Symmetry elements for 8: 2 ꢀ x, 2 ꢀ
y, 2 ꢀ z.
chelate ring. This puckering results in an approach of the Al1
˚
atom and N3 at 2.899(2) A. The four atoms N1, C9, C20, and N5
˚
are essentially planar with a deviation of 0.0375 A, and the
dihedral angle between N1C9C20N5 and C9N3C20 is 39.70(20)ꢁ.
The dihedral angle between N1C9C20N5 and N1AlN5 is
40.756(97)ꢁ. The bond distances of Al1–N1 and Al1–N5 are
the known Al–O bond lengths. For the guanidinato moiety
˚
C1N3, the signicantly similar N–C distances (1.346(3) A for C1–
˚
˚
1.946(2) and 1.901(2) A, respectively, similar to those in 5, and
N2 and 1.347(3) A for C1–N3, respectively) indicate a greater
the bond angle of N1–Al1–N5 is 91.44(9)ꢁ in 7, which is narrower
than that in 5. In the NCNCN moiety, the bond angles of N1–C9–
N3, C9–N3–C20, and N3–C20–N5 are 117.8(2), 123.69(19), and
113.86(18)ꢁ, respectively. For each of the two guanidinato units
C9N3 and C20N3, three N–C bonds are showed single bond,
double bond, and partial double bond characters, respectively,
which feature is similar to that in the guanidinato moiety C7N3
of complex 5.
Complex 8 crystallizes from n-hexane in the monoclinic
space group P21/c (Fig. 8). Crystalline 8 is centrosymmetric
dimer with Al2O2 quadrilateral core structure which is similar to
that of reported organoaluminum complex Al4(O)2(CH3)6(dpa)2
degree of electronic delocalisation over the NCN backbone in
the complex 8. The bond angles of C1–N2–Al1, N2–C1–N3, and
C1–N3–Al20 are 116.29(13), 118.77(17), and 121.02(13)ꢁ,
respectively.
Conclusions
In summary, we have successfully synthesized two kinds of new
guanidinatoaluminum complexes, the (mono)guanidinato-
aluminum complexes (1 and 2) and (bis)guanidinatoalumi-
num complex (3), and found that the reaction of dieth-
ylaminolithium with carbodiimide (CyN]C]NCy or CyN]C]
NC6H5) and dimethylaluminium chloride (AlMe2Cl) in a molar
ratio of 1 : 1 : 1 yielded the (mono)guanidinatoaluminum and
(bis)guanidinatoaluminum complexes, which is attributed to
group types bound to carbodiimide. The reactivities of the
mononuclear guanidinatoaluminum complexes (1 and 2) with
O2 or carbodiimide were studied. The dimeric guanidinatoalu-
minum complex (4) containing m-OCH3 moiety and the mono-
nuclear bisguanidinatoaluminum complex (5) were produced in
reasonable yield by introducing dry oxygen or carbodiimide
into the solution of the mononuclear guanidinatoaluminum
complex (1 or 2). Meanwhile, the analogues of 4 and 5, 6 and 7
were produced under similar procedure. The dimeric
guanidinatoaluminum complex (4 or 6) was obtained by
insertion of oxygen atom into the Al–C bond of mononuclear
(dpa
¼
deprotonated di-2-pyridylamine).18 The central
Al2O1Al20O10 core is anked by two twisted six-membered rings.
The two nitrogen atoms in guanidinato NCN backbone are
bound to two different aluminum centers, respectively, and an
oxygen atom bridges three aluminum centers with an approxi-
mately pyramidal geometry. The Al2 atom exhibits a tetrahe-
drally distorted coordination made up by the one nitrogen atom
of guanidinato ligand, an oxygen atom, and two carbon atoms
from two methyl groups. Different from Al2 atom, there is only
one methyl group connected to the Al1 atom. The coordination
environments around the two aluminum atoms are almost
identical, and the geometry of the Al1 ion is also tetrahedral.
˚
The Al1–N2 bond distance (1.890(2) A) is signicantly shorter
0
˚
than that of Al2–N3 (1.965(2) A) in the complex 8. The Al–O
˚
bond lengths (1.799(2)–1.812(1) A) are in the normal range of
guanidinatoaluminum
complex,
while
mononuclear
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bisguanidinatoaluminum complex (5 or 7) was afforded by
insertion of carbodiimide into the Al–N bond of the mono-
nuclear guanidinatoaluminum complex. In addition, while
introducing degassing H2O into the treatment solution of
diethylaminolithium with sequentially carbodiimide (CyN]
Synthesis of 1, [{(Et2N)C(NCy)2}AlMe2]
To a stirred solution of LiNEt2 (0.159 g, 2.0 mmol) in Et2O (15
mL), N,N0-dicyclohexylcarbodiimide (0.413 g, 2.0 mmol) was
added dropwise. The resulting mixture was stirred at ambient
temperature for 60 min. The pale yellow solution was subse-
C]NCy, CyN]C]NC6H5 or ArN]C]NC6H5, Ar
¼
2,6-
ꢁ
quently cooled to 0 C, and AlMe2Cl (2.00 mL, 2.0 mmol) was
Me2C6H3) and AlMe2Cl in a molar ratio of 1 : 1 : 1, a unique
tetranuclear complex (8) was produced, which can also be
synthesized by the reaction of complex 1 with 1 equiv. of AlMe3
in the presence of H2O.
added dropwise. The resulting mixture was allowed to warm to
room temperature and stirred for another 12 h to afford
a cloudy solution, which was ltered. Hexane (ca. 10 mL) was
subsequently added into the ltrate, and then the ltrate was
concentrated to ca. 10 mL in vacuo and stored at ꢀ5 ꢁC, yielding
colorless crystals of 1 (0.503 g, 75%). Anal. calc. for C19H38AlN3:
C, 68.02; H, 11.42; N, 12.52. Found: C, 67.85; H, 11.34; N,
12.61%. d1H (300 MHz, C6D6, 293 K): 3.04 (t, 3JHH ¼ 9.9 Hz, 2H,
C6H11), 2.91 (q, 3JHH ¼ 6.9 Hz, 4H, NCH2CH3), 2.00–1.96 (m, 4H,
C6H11), 1.78–1.74 (m, 4H, C6H11), 1.63–1.59 (m, 2H, C6H11),
1.46–1.13 (m, 10H, C6H11), 0.90 (t, 3JHH ¼ 7.2 Hz, 6H, NCH2CH3),
ꢀ0.05 (s, 6H, AlCH3). d13C (75 MHz, C6D6, 293 K): 166.75 (NCN),
53.80 (C6H11), 42.51 (NCH2CH3), 35.72 (C6H11), 26.04 (C6H11),
12.98 (NCH2CH3), ꢀ8.06 (AlCH3).
Experimental
General remarks
All manipulations were performed under a nitrogen atmo-
sphere with rigorous exclusion of oxygen and water using
standard Schlenk and cannula techniques. Solvents were dried
with appropriate drying agents, degassed, and stored over
˚
a potassium mirror or activated molecular sieves (4 A) prior to
use. Deuterated solvent C6D6 and CDCl3 were dried over acti-
˚
vated molecular sieves (4 A) and vacuum transferred before use.
n-BuLi (2.0 M solution in hexane; Alfa Aesar), AlMe2Cl (1.0 M
solution in hexane; Alfa Aesar) and AlMe3 (2.0 M solution in
hexane; Alfa Aesar) were obtained commercially and used as
received. CyN]C]NC6H5 and ArN]C]NC6H5 (Ar ¼ 2,6-
Me2C6H3) were prepared according to the literature proce-
dures.19 Diethylamine was dried over MgSO4 and redistilled
before use. Elemental analyses were performed on a Vario EL-III
instrument. 1H NMR (300 MHz) and 13C NMR (75 MHz) spectra
of the complexes (1–8) were recorded on a Bruker DRX 300
instrument and referenced internally to the residual solvent
resonances (chemical shi data in d).
Synthesis of 2, [{(Et2N)C(NCy)(NC6H5)}AlMe2]
To a stirred solution of LiNEt2 (0.159 g, 2.0 mmol) in Et2O (15
mL), N-cyclohexyl-N0-phenyl carbodiimide (0.401 g, 2.0 mmol)
was added dropwise. The resulting mixture was stirred at
ambient temperature for 60 min. The pale yellow solution was
subsequently cooled to 0 ꢁC, and AlMe2Cl (2.00 mL, 1.0 M
solution in hexane, 2.0 mmol) was added dropwise. The
resulting mixture was allowed to warm to room temperature
and stirred for another 12 h to afford a cloudy solution, which
was ltered. Hexane (ca. 10 mL) was subsequently added into
the ltrate, and then the ltrate was concentrated to ca. 10 mL
in vacuo and stored at room temperature, immediately yielding
a light pink solid. The solid was isolated by ltration and
recrystallized from hexane solution at ꢀ10 ꢁC to give the
colorless crystals of complex 2 (0.204 g, 31%). Anal. calc. for
Synthesis of diethylaminolithium, LiNEt2
Diethylaminolithium was prepared by treating diethylamine
with n-BuLi at 0 ꢁC as described in the literature.20 To a stirred
solution of diethylamine (2.00 mL, 20.0 mmol) in hexane (15
mL), n-BuLi (10.30 mL, 20.0 mmol) was added dropwise at 0 ꢁC.
The mixture was allowed to warm to room temperature and
stirred for an additional 1 h. The solution was ltered and all
volatiles were removed under reduced pressure. The resulting
solid was washed with pentane (2 ꢂ 10 mL) and dried in vacuo
to give LiNEt2 as a white solid (1.503 g, 95%).
C
19H32AlN3: C, 69.27; H, 9.79; N, 12.75. Found: C, 69.07; H, 9.71;
N, 12.86%. d1H (300 MHz, CDCl3, 293 K): 7.21 (t, 3JHH ¼ 7.5 Hz,
3
3
2H, C6H5), 6.92 (t, JHH ¼ 7.5 Hz, 1H, C6H5), 6.85 (d, JHH
¼
¼
3
7.8 Hz, 2H, C6H5), 3.17–3.10 (m, 1H, C6H11), 3.13 (q, JHH
6.9 Hz, 4H, NCH2CH3), 1.94–1.90 (m, 2H, C6H11), 1.77 (s, 2H,
C6H11), 1.68–1.43 (m, 2H, C6H11), 1.32–1.20 (m, 4H, C6H11), 1.13
(t, 3JHH ¼ 6.9 Hz, 6H, NCH2CH3), ꢀ0.79 (s, 6H, AlCH3). d13C (75
MHz, CDCl3, 293 K): 164.60 (NCN), 147.66, 130.66, 123.22,
122.81 (C6H5), 55.20 (C6H11), 44.10 (NCH2CH3), 36.25, 27.17,
27.00 (C6H11), 14.31 (NCH2CH3), ꢀ8.81 (AlCH3).
Synthesis of [{(C2H5)2N}C(NC6H5)(NAr)LiOEt2]2
[{(C2H5)2N}C(NC6H5)(NAr)LiOEt2]2 was synthesized referring to
our group previously reported methods.7b To a stirred solution
Synthesis of 3, [{(Et2N)C(NCy)(NC6H5)}2AlMe]
of LiNEt2 (0.159 g, 2.0 mmol) in Et2O (15 mL), N-(2,6-dimethyl) To a stirred solution of LiNEt2 (0.159 g, 2.0 mmol) in Et2O (15
phenyl-N0-phenyl carbodiimide (0.444 g, 2.0 mmol) was added mL), N-cyclohexyl-N0-phenyl carbodiimide (0.401 g, 2.0 mmol)
dropwise at 0 ꢁC. The mixture was allowed to warm to room was added dropwise. The resulting mixture was stirred at
temperature and stirred for an additional 4 h. The volatiles were ambient temperature for 60 min. The pale yellow solution was
removed under reduced pressure. The residue was washed with subsequently cooled to 0 ꢁC, and AlMe2Cl (2.00 mL, 1.0 M
pentane (2 ꢂ 5 mL) and dried in vacuo to give [{(C2H5)2N} solution in hexane, 2.0 mmol) was added dropwise. The
C(NC6H5)(NAr)LiOEt2]2 as a white solid (0.691 g, 92%).
resulting mixture was allowed to warm to room temperature
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and stirred for another 12 h to afford a cloudy solution, which carbodiimide (0.401 g, 2.0 mmol) was slowly dropped into the
was ltered. Hexane (ca. 10 mL) was subsequently added into above solution at ambient temperature. Aer being stirred for
the ltrate, and the ltrate was concentrated to ca. 10 mL in 2 h, the white solid was isolated by ltration, washed with
vacuo, immediately yielding light pink solid. The mixture was hexane (2 ꢂ 10 mL) and dried in vacuo, which was recrystallized
ꢁ
ltered, and the ltrate was stored at ꢀ10 ꢁC to yield the colorless from hexane–tetrahydrofuran (1 : 1) solution at ꢀ10 C to give
crystals of complex 3 (0.288 g, 49.1%). Anal. calc. for C35H55AlN6: the colorless crystals of complex 5 (0.837 g, 79%).
C, 71.63; H, 9.45; N, 14.32. Found: C, 71.45; H, 9.21; N, 14.48%.
Method 2. To a stirred solution of diethylamine (0.20 mL,
2.0 mmol) in hexane (15 mL), trimethylaluminum (1.00 mL,
3
d1H (300 MHz, C6D6, 293 K): 7.32 (s, 1H, C6H5), 7.26 (d, JHH
¼
6.0 Hz, 2H, C6H5), 7.19 (s, 4H, C6H5), 7.07 (d, 3JHH ¼ 6.0 Hz, 1H, 2.0 mmol) was added dropwise. The mixture was heated to
C6H5), 6.98 (t, 3JHH ¼ 6.0 Hz, 2H, C6H5), 3.20 (q, 2H, 3JHH ¼ 6.9 Hz, 60 ꢁC for 6 h and then cooled to room temperature, N-(2,6-
C6H11), 2.78 (s, 8H, NCH2CH3), 1.97–1.94 (m, 4H, C6H11), 1.83– dimethyl)phenyl-N0-phenyl carbodiimide (0.801 g, 4.0 mmol)
1.79 (m, 8H, C6H11), 1.63–1.59 (m, 2H, C6H11), 1.30–1.22 (m, 4H, was added. Aer being stirred for 2 h, the white solid was
3
C6H11), 1.14–1.09 (m, 2H, C6H11), 0.80 (t, JHH ¼ 5.0 Hz, 12H, isolated by ltration, washed with hexane (2 ꢂ 10 mL) and
NCH2CH3), 0.01 (s, 3H, AlCH3). d13C (75 MHz, CDCl3, 293 K): dried in vacuo, which was recrystallized from hexane–tetra-
166.89 (NCN), 148.32, 129.35, 125.20, 122.78, 121.82, 121.27 hydrofuran (1 : 1) solution at ꢀ10 ꢁC to give the colorless
(C6H5), 55.19 (C6H11), 43.28 (NCH2CH3), 34.68, 34.06, 26.78, crystals of complex
5 (0.731 g, 69%). Anal. calc. for
25.87, 25.40 (C6H11), 13.05 (NCH2CH3) (Al–CH3 resonances were
not observed due to the poor solubility of the complex 3).
C32H48AlN5: C, 72.55; H, 9.13; N, 13.22. Found: C, 72.38; H,
9.05; N, 13.31%. d1H (300 MHz, C6D6, 293 K): 7.28–7.22 (m,
2H, C6H5), 7.14–7.11 (m, 2H, C6H5), 7.08–7.01 (m, 4H, C6H5),
6.98–6.89 (m, 2H, C6H5), 2.89–2.75 (m, 3H, NCH2CH3), 2.57–
2.52 (m, 1H, C6H11), 2.48–2.41 (m, 1H, NCH2CH3), 2.34–2.29
(m, 1H, C6H11), 2.14–2.01 (m, 2H, C6H11), 1.89–1.84 (m, 4H,
C6H11), 1.74–1.57 (m, 6H, C6H11), 1.45–1.27 (m, 4H, C6H11),
Synthesis of 4, [{(Et2N)C(NCy)2}AlMe(m-OMe)]2
Method 1. To a stirred solution of complex 1 (0.671 g, 2.0
mmol) in tetrahydrofuran (10 mL), dry oxygen was introduced
slowly via a balloon and the reaction was carried out for 30 min
at ꢀ78 ꢁC. Then the resulting mixture was warmed to room
temperature and stirred overnight. The volatiles were removed
under reduced pressure. The residue was washed with hexane (2
ꢂ 5 mL) and dried in vacuo to give the product as a white solid,
which was recrystallized from hexane–tetrahydrofuran (1 : 2)
solution at ꢀ10 ꢁC to give the colorless crystals of complex 4
(0.598 g, 85%).
3
1.22–0.93 (m, 4H, C6H11), 0.61 (t, JHH ¼ 6.9 Hz, 3H,
NCH2CH3), 0.49 (t, 3JHH ¼ 6.9 Hz, 3H, NCH2CH3), ꢀ0.05 (s, 3H,
AlCH3), ꢀ0.32 (s, 3H, AlCH3). d13C (75 MHz, C6D6, 293 K):
164.27, 160.75 (NCN), 152.51, 148.52, 146.28, 130.35, 129.34,
125.42, 124.50, 123.72, 122.95, 121.40 (C6H5), 61.65, 58.43
(C6H11), 44.41, 43.17 (NCH2CH3), 35.95, 34.75, 32.85, 32.57,
32.36, 27.69, 27.36, 27.07, 26.79, 26.45 (C6H11), 12.06
(NCH2CH3), ꢀ5.19, ꢀ8.72 (AlCH3).
Method 2. To a stirred solution of diethylamine (0.20 mL, 2.0
mmol) in hexane (15 mL), trimethylaluminum (1.00 mL, 2.0
mmol) was added dropwise. The mixture was heated to 60 ꢁC for
12 h and then cooled to room temperature, N,N0-dicyclohex-
ylcarbodiimide (0.413 g, 2.0 mmol) was added. Aer being stirred
for 6 h, dry oxygen was introduced slowly into the solution via
a balloon and the reaction was carried out for 30 min at ꢀ78 ꢁC.
Then the resulting mixture was warmed to room temperature and
stirred overnight. The white precipitate was collected by ltration,
then washed with hexane (2 ꢂ 5 mL) and dried in vacuo to give the
product as a white solid, which was recrystallized from hexane–
tetrahydrofuran (1 : 2) solution at ꢀ10 ꢁC to give the colorless
crystals of complex 4 (0.499 g, 71%). Anal. calc. for C38H76Al2N6O2:
C, 64.92; H, 10.90; N, 11.95. Found: C, 64.74; H, 10.81; N, 12.08%.
d1H (300 MHz, C6D6, 293 K): 3.76 (s, 6H, OCH3), 3.19–3.12 (m, 4H,
C6H11), 3.05–2.98 (q, 3JHH ¼ 7.2 Hz, 8H, NCH2CH3), 2.00–1.91 (m,
16H, C6H11), 1.75–1.72 (m, 12H, C6H11), 1.36–1.34 (m, 12H,
C6H11), 1.05–1.00 (t, 3JHH ¼ 6.9 Hz, 12H, NCH2CH3), ꢀ0.17 (s, 6H,
AlCH3). d13C (75 MHz, C6D6, 293 K): 168.91 (NCN), 54.89 (C6H11),
52.02 (OCH3), 43.28 (NCH2CH3), 35.64, 35.10, 26.95, 26.49
(C6H11), 13.44 (NCH2CH3) (Al–CH3 resonances were not observed
due to the poor solubility of the complex 4).
Synthesis of 6, [(Et2N)C(NC6H5)(NAr)AlMe(m-OMe)]2 (Ar ¼ 2,6-
Me2C6H3)
To a stirred solution of [{(C2H5)2N}C(NC6H5)(NAr)LiOEt2]2
(0.751 g, 1.0 mmol) in Et2O (15 mL), AlMe2Cl (2.00 mL, 2.0
ꢁ
mmol) was added dropwise at 0 C. The resulting mixture was
allowed to warm to room temperature and stirred for another
12 h to afford a cloudy solution, which was ltered. Dry oxygen
was introduced via a balloon into the ltrate for 30 min at
ꢀ78 ꢁC. Then the resulting mixture was warmed to room
temperature and stirred overnight. The volatiles were removed
under reduced pressure. The residue was washed with hexane (2
ꢂ 5 mL) and dried in vacuo to give the product as a white solid,
which was recrystallized from hexane–tetrahydrofuran (1 : 2)
solution at ꢀ10 ꢁC to give the colorless crystals of complex 6
(0.537 g, 73%). Anal. calc. for C42H60Al2N6O2: C, 68.64; H, 8.23;
N, 11.44. Found: C, 68.46; H, 8.12; N, 11.56%. d1H (300 MHz,
CDCl3, 293 K): 7.19–6.88 (m, 16H, C6H5, ArH), 3.10–2.77 (m, 8H,
NCH2CH3), 2.52 (s, 6H, OCH3), 2.40 (s, 3H, PhCH3), 2.27 (s, 6H,
3
PhCH3), 2.16 (s, 3H, PhCH3), 0.71–0.67 (t, JHH ¼ 6.9 Hz, 12H,
NCH2CH3), ꢀ1.02 (s, 6H, AlCH3). d13C (75 MHz, CDCl3, 293 K):
165.70 (NCN), 149.62, 135.07, 134.86, 129.38, 128.98, 125.97,
125.12, 124.65, 124.30, 122.85, 122.16, 119.28 (C6H5), 51.10
Synthesis of 5, [{N(C6H5)C(NCy)N(C6H5)C(NEt2)N(Cy)}AlMe2]
Method 1. To a stirred solution of complex 2 (0.659 g, 2.0 (OCH3), 42.56 (NCH2CH3), 20.08 (PhCH3), 13.41 (NCH2CH3),
mmol) in hexane (10 mL), 1 equiv. of N-cyclohexyl-N0-phenyl ꢀ11.77 (AlCH3).
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6H, AlCH3). d13C (75 MHz, CDCl3, 293 K): 171.21 (NCN), 59.85
(C6H11), 58.18 (C6H11), 43.24 (NCH2CH3), 43.14 (NCH2CH3),
35.50, 34.63, 32.82, 32.49, 27.23, 26.74, 26.34, 25.47, 24.81, 22.66
(C6H11), 14.12 (NCH2CH3), 12.98 (NCH2CH3), ꢀ2.14(AlCH3),
ꢀ6.73(AlCH3), ꢀ9.63(AlCH3).
Synthesis of 7, [{N(C6H5)C(NAr)N(C6H5)C(NEt2)N(Ar)}AlMe2]
(Ar ¼ 2,6-Me2C6H3)
To a stirred solution of [{(C2H5)2N}C(NC6H5)(NAr)LiOEt2]2
(0.751 g, 1.0 mmol) in Et2O (15 mL), AlMe2Cl (2.00 mL, 2.0
ꢁ
mmol) was added dropwise at 0 C. The resulting mixture was
allowed to warm to room temperature and stirred for another
12 h to afford a cloudy solution, which was ltered. Another
2.0 mmol N-(2,6-dimethyl)phenyl-N0-phenyl carbodiimide
(0.444 g) was added slowly at ambient temperature into the
ltrate. Aer being stirred for 2 h, the mixture afforded white
solid. The solid was isolated by ltration, washed with hexane (2
ꢂ 10 mL) and recrystallized from hexane–tetrahydrofuran (1 : 1)
solution at ꢀ10 ꢁC to give the colorless crystals of complex 7
(0.987 g, 86%). Anal. calc. for C36H44AlN5: C, 75.36; H, 7.73; N,
12.21. Found: C, 75.15; H, 7.65; N, 12.33%. d1H (300 MHz,
CDCl3, 293 K): 7.96 (s, 2H, C6H5), 7.01–7.30 (m, 6H, C6H5), 6.63–
6.73 (m, 6H, C6H5), 6.41 (s, 2H, C6H5), 3.45–2.75 (m, 4H,
NCH2CH3), 2.45 (s, 3H, PhCH3), 2.30 (s, 6H, PhCH3), 1.73 (s, 3H,
PhCH3), 0.89 (s, 3H, NCH2CH3), 0.49 (s, 3H, NCH2CH3), ꢀ0.55
(s, 3H, AlCH3), ꢀ1.72 (s, 3H, AlCH3). d13C (75 MHz, CDCl3, 293
K): 161.10 (NCN), 146.48, 144.09, 143.79, 142.59, 133.20, 130.15,
129.58, 128.94, 127.51, 126.45, 126.16, 125.73, 124.65, 123.44,
123.04, 120.86 (C6H5), 43.97, 42.24 (NCH2CH3), 20.56, 19.61
(PhCH3), 13.37, 10.78 (NCH2CH3), ꢀ6.39, ꢀ11.57 (AlCH3).
Acknowledgements
Financial support from the National Natural Science Founda-
tion of China (No. 20572065), Special Fund for Agro-scientic
Research in the Public Interest (No. 201303106), Natural
Science Foundation of Shanxi Province (No. 2011021011-1,
2014011049-26 and 201601D202091), and the Shanxi Coal
Based Key Scientic and Technological Project (No. MH2014-07)
are gratefully acknowledged.
Notes and references
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Synthesis of 8,
Method 1. To a stirred solution of LiNEt2 (0.159 g, 2.0 mmol)
in Et2O (15 mL), N,N0-dicyclohexylcarbodiimide (0.413 g, 2.0
mmol) was added dropwise. The resulting mixture was stirred at
ambient temperature for 60 min. The pale yellow solution was
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was added dropwise. The resulting mixture was allowed to
warm to room temperature and stirred for another 12 h to afford
a cloudy solution, which was ltered. 2.0 mmol of degassing
H2O (1.0 M solution in tetrahydrofuran, 2.00 mL) was intro-
duced slowly into the ltrate at ꢀ78 ꢁC. Then the resulting
mixture was warmed to room temperature and stirred for 4 h to
afford a cloudy solution, which was ltered. The ltrate was
concentrated to ca. 10 mL in vacuo and stored at ambient
temperature for 2 days to give colorless crystals of 8 (0.150 g,
19%).
Method 2. To a stirred solution of complex 1 (0.671 g, 2.0
mmol) in hexane (15 mL), trimethylaluminum (1.00 mL, 2.0
mmol) and 2.0 mmol of degassing H2O (1.0 M solution in
tetrahydrofuran, 2.00 mL) were successively added dropwise at
ꢀ78 ꢁC. Then the resulting mixture was warmed to room
temperature and stirred for 4 h to afford a cloudy solution,
which was ltered. The ltrate was concentrated to ca. 10 mL in
vacuo and stored at ambient temperature for 2 days to give
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8 (0.275 g, 35%). Anal. calc. for
C
40H82Al4N6O2: C, 61.04; H, 10.50; N, 10.68. Found: C, 60.88; H,
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3
C6H11), 3.08 (q, JHH ¼ 7.8 Hz, 8H, NCH2CH3), 1.88–1.72 (m,
16H, C6H11), 1.66–1.58 (m, 12H, C6H11), 1.35–1.29 (m, 4H,
3
C6H11), 1.24–1.16 (m, 8H, C6H11), 1.10 (t, JHH ¼ 6.6 Hz, 12H,
NCH2CH3), ꢀ0.62 (s, 6H, AlCH3), ꢀ0.75 (s, 6H, AlCH3), ꢀ0.96 (s,
This journal is © The Royal Society of Chemistry 2016
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101446 | RSC Adv., 2016, 6, 101437–101446
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