Syntheses and structures of a class of bridged bis(amidinate)s and derivatives

Article abstract of DOI:10.3184/174751918X15260497205682

A series of different types of 'bridge' linked bis(amidinate)s have been prepared. Reactions of a variety of linked diamines with pivaloyl chloride yielded the corresponding diamides in very high yields. Conversion of the diamides to the diimine chloride

Full text of DOI:10.3184/174751918X15260497205682

JOURNAL OF CHEMICAL RESEARCH 2018
VOL. 42 MAY, 239–243
RESEARCH PAPER 239
Syntheses and structures of a class of bridged bis(amidinate)s and
derivatives
Fen-Hua Wang*, Song Wang, Jiang-Sheng Huang, Jun Zhang and Chun-Mei Ding
College of Biological and Chemical Engineering, Anhui Polytechnic University, Wuhu 241000, P.R. China
A series of different types of ‘bridge’ linked bis(amidinate)s have been prepared. Reactions of a variety of linked diamines with pivaloyl
chloride yielded the corresponding diamides in very high yields. Conversion of the diamides to the diimine chloride is achieved with
PCl in CH Cl . Reactions of the diimine chloride with aniline or t-butyl amine yielded the bis(amidinate)s in good yields, while reaction
5
2
2
with pyrrolyl sodium or 2,5-dimethyl pyrrolyl potassium afforded the corresponding derivatives. Their structures were characterised
by NMR and HRMS, and some products were further characterised by X-ray crystal structure analysis. It was found that the locations
of the hydrogen atoms within the two amidine fragments vary. The structures showed that in the phenylene-linked bis(amidinate)s, the
hydrogen atoms were attached to different nitrogen atoms in the amidine groups, and in the cyclohexylene-linked bis(amidinate)s or their
derivatives, the C=N of the amidine groups were conjugated with the aromatic rings.
Keywords: bridged bis(amidinate)s, phenylene linker, cyclohexylene linker
Amidinates are versatile ligands used in the fields of
coordination and organometallic chemistry because their
steric and electronic properties can be easily modulated by
two types: the traditional silylated and robust nonsilylated
amidinates. This study details our efforts to extend the range
of nonsilylated amidinates and derivatives with a variety of
‘bridges’ and N-aryl substituents. Here we report the synthesis
and structures of a class of bridged bis(amidinate)s and their
derivatives containing pyrrole rings.
1
varying the substituents on the C and N atoms. Bridged
bis(amidinate)s as a special branch of amidinates have proven
to be very versatile as they permit changes to the ‘bridge’ and
2
–5
the substituents of the amidine groups. The frameworks
have a rigid coordination sphere and provide a control over the
geometry of the active metal centre. For example, the phenylene
Results and discussion
The linked bis(amidinate)s of 1–6 were synthesised by similar
2
−
i
19
bridged ligands [1,4-C H C(NR) } ] (R = cyclohexyl, Pr,
methods to those described in the literature. Reactions
6
4
2 2
6
7
SiMe ) and the oxalic amidinates have been used to form
of bridged diamines with pivaloyl chloride yielded the
corresponding diamides. Then conversion of the diamides to
the diimine chlorides was achieved by treatment with PCl5.
Reactions of the diimine chlorides with aniline or t-butyl amine
yielded the bis(amidinate)s. All the reactions proceeded easily
with high yields, providing facile variation of the ‘bridge’ and
N-substituents (Scheme 1).
3
8
,9
10,11
bimetallic complexes. o-Phenylene-,
and propane- linked bis(amidinate) complexes have been
chelated to a monometal. Silyl-
naphthalene-,
12
13–15
16–18
and cyclohexyl-
bridged
bis(amidinate)s lead to different configurations by variation
of the terminal substituents on the framework. The reported
examples of bridged bis(amidinate)s are mainly divided into
tBu
O
O
NH2
2
tBu
tBu
2 PCl5
N
Cl
Cl
Cl
NH
toluene
CH Cl2
2
NH2
tBu
N
NH
tBu
tBu
O
tBu
tBu
R
R
R
R
N
N
N
H
NH
N
N
NH
N
Et N
3
or
or
2
RNH2
H
N
H
N
N
NH
R
R
tBu
tBu
tBu
NH2
NH2
NH2
R = Ph (3),
R = Ph (1),
t
t
Bu (4)
Bu (2)
NH2
NH2
NH2
NH2
NH2
NH2
R = Ph (5)
R = Ph (6)
NH2
(R,R)
Scheme 1 Synthesis of compounds 1–6.
*
Correspondent. E-mail: wfh@ahpu.edu.cn

2
40 JOURNAL OF CHEMICAL RESEARCH 2018
Attempted synthesis of compound 7, using a diimine chloride
had to be used instead of the sodium salt. This may be attributed
to the larger steric hindrance of 2,5-dimethyl pyrrole; hence, a
stronger nucleophile was needed (Scheme 3).
The crystal structures of compounds 1, 5 and 7 were
determined. The details of the structure refinement for the
compounds are listed in Table 1. Selected bond lengths and
bond angles are given in Table 2.
and reaction with pyrrole or pyrrolyl lithium, gave no product.
This may be attributed to the large steric hindrance of pyrrole.
Therefore, the stronger nucleophile pyrrolyl sodium was needed
(
Scheme 2). In the synthesis of 8, the pyrrolyl potassium salt
Table 1 Crystal and structure refinement data for compounds 1, 5 and 7
X-ray analysis showed that compound 1 crystallises in the
Crystal data
1
5
7
monoclinic crystal system, P2 /n space group, and the molecular
1
Empirical formula C H N
C H N
C H N
2
8
34
4
28 40
4
24 30 4
structure is shown in Fig. 1. In compound 1, unlike in previously
Formula weight 426.59
432.64
374.52
19
reported linked bis(amidinate) groups, the hydrogen atoms in
the amidine groups were attached to different nitrogen atoms.
This fact was evident from analysis of the intramolecular
N···H hydrogen bonds. The distance of N(3)···H(1) is 2.329
Å, which corresponds to that reported for naphthalene-linked
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Monoclinic
Monoclinic
Monoclinic
P2 /n
P2 /n
P2 /n
1
1
1
10.0943(7)
20.1523(12)
11.9989(7)
90
9.2163(9)
23.394(2)
12.4499(13)
90.00
11.8992(14)
8.1080(10)
23.811(3)
90.00
12
bis(amidine)s.
α (°)
Compound 5 crystallises in the monoclinic crystal system,
91.420(2)
90
2440.1(3)
296.15
1.161
93.755(2)
90.00
2678.5(5)
293(2)
1.174
97.822(2)
90.00
2275.9(5)
293(2)
1.093
P2 /n space group, and the molecular structure is shown in
β (°)
1
Fig. 2. For compound 5, the structure features the cyclohexyl
backbone in its more stabilised chair form with one of the
amidine groups in an equatorial position and the other in
γ (°)
3
V (Å )
T (K)
Dcalc (g cm )
μ (mm )
Z
−
3
−1
0.069
4
0.064
4
0.066
4
Table 2 Selected bond lengths and bond angles for compounds 1, 5
and 7
F(0 0 0)
Reflections
920
944
808
1
5
7
Bond length (Å)
C1–N1
C7–N1
C7–N2
C6–N3
C18–N4
C18–N3
Bond angle (°)
21186/5657
23319/4981
0.0513
22231/4189
0.0393
(
collected/unique)
1.408(2) C1–N1
1.378(2) C7–N1
1.275(2) C7–N2
1.416(2) C6–N3
1.381(2) C18–N4
1.283(2) C18–N3
1.473(4) C10–N2
1.355(4) C5–N2
1.267(5) C5–N1
1.459(4) C14–N3
1284(5) C16–N3
1.364(4) C16–N4
1.419(3)
1.261(3)
1.432(3)
1.422(3)
1.260(3)
1.426(3)
R (int)
Completeness to
θ (%)
0.0493
9
0
9.9
99.8
99.2
λ (Mo Kα
.71073
0.71073
0.71073
radiation) (Å)
θ range (°)
GOF
2.021–27.601
1.015
1.741–25.334
1.039
1.73–25.44
1.002
C1–N1–C7 128.78(14) C1–N1–C7 130.3(3) C10–N2–C5 122.61(19)
N1–C7–N2 117.51(15) N1–C7–N2 128.1(3) N2–C5–N1 121.99(19)
C6–N3–C18 121.52(13) C6–N3–C18 128.8(3) C14–N3–C16 123.4(2)
N3–C18–N4 125.49(15) N3–C18–N4 127.2(3) N3–C16–N4 122.3(2)
R , wR [I > 2σ(I)] 0.0546, 0.1199
0.0741, 0.2033
0.1100, 0.2306
0.430 and
−0.349
0.0562, 0.1585
0.0963, 0.1888
1
2
R , wR (all data) 0.0866, 0.1334
1
2
Largest diff. peak
−
3
0.278 and −0.270
0.501 and −0.307
and hole (e Å )
tBu
C
tBu
C
N
N
N
N
Cl
Cl
Na
N
+
DMF
(
7)
C
N
N
C
tBu
tBu
Scheme 2 Synthesis of compound 7.
tBu
C
tBu
C
N
N
N
N
Cl
Cl
DMF
(8)
+
N
K
N
N
C
C
tBu
tBu
Scheme 3 Synthesis of compound 8.

JOURNAL OF CHEMICAL RESEARCH 2018 241
Fig. 1 Molecular structure of compound 1.
Fig. 2 Molecular structure of compound 5.
Fig. 3 Molecular structure of compound 7.
an axial position. The C=N of the amidine group is in a ZZ
configuration with the large t-butyl group on the opposite side
of the aryl group. The bond lengths of N(1)–C(7) 1.355(4) Å
and N(3)–C(18) 1.364(4) Å, are close to those found in other
related structures. In addition, the C(7)–N(2) and C(18)–N(4)
bond lengths of 1.267(6) Å and 1.284(6) Å, respectively, are in
the range of normal C=N double bonds. The N(1)–C(7)–N(2)
and N(3)–C(18)–N(4) bond angles are 128.1(3)° and 127.2(3)°,
respectively.
For compound 7, the spatial structure is similar to that of
compound 5. The molecular structure is shown in Fig. 3. The
solid-state structure of 7 features both C=N bonds in their
Z-syn forms due to steric repulsion between the large t-butyl
and the neutral pyrrolyl groups. In compound 7, the bond length
of N(3)–C(16) is 1.260(3) Å and that of N(2)–C(5) is 1.261(3)
Å; the N(3)–C(16)–N(4) and N(2)–C(5)–N(1) bond angles are
diaminocyclohexyl-linked bis(amidinate)s may be a useful
ligand in the construction of chiral structures and materials,
and this is being explored in our group.
18
Experimental
Materials and general methods
All commercial reagents were used as received without further
purification. Toluene was distilled from sodium under nitrogen before
use. CH Cl was distilled from CaH under nitrogen before use. A
2
2
2
series of diimine chlorides were prepared under nitrogen in an oxygen-
free atmosphere using standard Schlenk techniques and a glove box.
2
0
Pyrrolyl sodium was prepared by deprotonation of pyrrole by NaH.
,5-Dimethyl pyrrolyl potassium was synthesised from 2,5-dimethyl
2
21
pyrrole and KH. Column chromatography was performed on
silica gel 300–400 mesh. Melting points were measured on an XT-4
micromelting apparatus and are uncorrected. Optical rotations were
recorded using a standard cell with a 10 cm pass on a Shanghai-
122.3(3) and 121.99(3)°, respectively. The bond angle of N–
1
13
Shenguang WZZ-1 polarimeter. H NMR and C NMR spectra for
analyses of compounds were recorded on a Bruker AV-300 NMR
C=N is approximately 5° smaller than in 5 with a more crowded
pyrrolyl ring.
1
13
spectrometer (300 MHz for H; 75 MHz for C) or Bruker AV-500
1
13
NMR spectrometer (500 MHz for H; 125 MHz for C). Chemical
shifts (δ) are reported in ppm. J values are reported in Hz. HRMS
measurements were conducted with an Agilent model G6220 APCI-
TOF mass spectrometer.
Conclusion
A class of new linked bis(amidinate)s have been designed
and synthesised with high yields. Typical products were
characterised by X-ray crystal structure analysis. It is revealed
that with the o-phenylene-linked bis(amidinate)s, the hydrogen
atoms between the amidine groups were attached to different
nitrogen atoms owing to intramolecular hydrogen bonds.
While with the cyclohexylene-linked bis(amidinate)s and the
bis(amidinate) derivatives, the C=N of the amidine groups
were symmetrical and conjugated with the aromatic rings
in ZZ configurations. A chiral compound based on R,R-1,2-
Structure determination for compounds 1, 5 and 7
Colourless single crystals of compounds 1, 5 and 7 were selected
for X-ray diffraction analysis. Diffraction was performed on a
Burker SMART CCD area detector diffractometer using graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å). An empirical
2
2
absorption correction was applied using the SADABS program. All
structures were solved by direct methods, completed by subsequent
difference Fourier syntheses and refined anisotropically for all non-

2
42 JOURNAL OF CHEMICAL RESEARCH 2018
2
24
hydrogen atoms by full-matrix least-squares calculations on F using
give (1R, 2R)-diaminocyclohexane. The rest of the synthesis was in
2
3
the SHELXTL program package. CCDC numbers are 1836316 (1),
569196 (5) and 1568147 (7). These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.
accordance with the general procedure. 1,2-Diaminocyclohexane were
used in place of linked diamines in the general procedure.
1
t
{[(R, R)-C H ]-1,2-[NC( Bu)N(C H )H] } (6): Colourless crystals;
6
12
6
5
2
cam.ac.uk/data_request/cif.
yield 87% (after recrystallisation from ethyl acetate); m.p. 98–99 °C;
2
0
1
[
α] = 27.3° (c = 1 g per 100 mL MeOH); H NMR (300 MHz, CDCl ):
ꢀ
3
Synthesis of linked diamides; general procedure
δ 7.23–7.18 (m, Ph–H), 6.87–6.72 (m, Ph–H), 4.33 (br, N–H), 2.67 (s,
br, N–H), 1.78–159 (m, cyclohexyl), 1.37 (bm, cyclohexyl), 1.23 (s,
Pivaloyl chloride (2 equiv.) was added dropwise to a solution of Et N
3
(
2 equiv.) and linked diamines (1 equiv.) in CH Cl to form a white
t
13
2
2
Bu), 0.63 (m, cyclohexyl); C NMR (125 MHz, CDCl ): δ 161.7, 152.4,
3
precipitate. The mixture was heated under reflux for 3 h, then the
solution was cooled to room temperature and diluted with CH Cl ,
which caused all of the precipitate to dissolve. The organic layer was
added to water, separated, washed with water (3 × 100 mL) and dried
1
29.0, 121.1, 120.8, 55.7, 39.1, 33.4, 29.7, 24.6. HRMS (ESI): calcd for
+
2
2
C H N [M + H ]: 433.3326; found: 433.3330.
28 41 4
t
Synthesis of C H -1,3-[NC( Bu)NH(C H N)] (7)
6
4
4
4
2
over MgSO before removal of the solvent under reduced pressure to
Under N , NaH (1.44 g, 60 %, 60 mmol) was suspended in DMF (20
4
2
yield a colourless crystalline solid.
mL), and a solution of pyrrole (2.01 g, 30 mmol) in DMF (10 mL) was
added dropwise at 0 °C. The reaction mixture was stirred for 1 h at
room temperature, then a diimine chloride (4.69 g, 15 mmol) dissolved
in DMF (20 mL) was slowly added dropwise at room temperature
giving an exothermic reaction (see Scheme 2). The reaction mixture
was stirred for 24 h. After completion, water (50 mL) was added and
the solution was extracted with ethyl acetate (2 × 50 mL), and washed
Conversion of diamides to diimine chlorides; general procedure
Under N , PCl was added in portions to the diamides in toluene giving
2
5
a transparent light yellow solution, which was stirred for 3 d. Most of the
solvent was removed under reduced pressure, and then the remaining
solution was transferred by cannula filtration. Removal of volatiles under
reduced pressure yielded a moisture-sensitive yellow oil.
with water (3 × 20 mL). After drying over MgSO , the ethyl acetate
4
Synthesis of linked bis(amidinate)s (1–6); general procedure
was removed under reduced pressure to yield a yellow solid. The crude
product was purified by column chromatography on silica gel using
To a solution of the yellow oil (1 equiv.) in toluene, the aniline (pyrrolyl
sodium or pyrrolyl potassium, 2 equiv.) was added, forming a white
precipitate. The reaction mixture was heated under reflux for 3 d, after
ethyl acetate/petroleum ether (1/20, V/V) as eluent to give compound
1
7
as: Colourless crystals; yield 63% (3.53 g); m.p. 68–70 °C; H NMR
(
6
300 MHz, CDCl ): δ 6.85–6.82 (m, Ph), 6.39 (d, J = 2.0 Hz, Py–H),
which removal of the solvent yielded a light brown solid. Et O and
3
2
.14–6.12 (m, Ph–H), 6.05–6.02 (m, Ph–H), 6.01 (d, J = 2.0 Hz, Py–
saturated Na CO solution was added. The solid dissolved upon 30 min
2
3
t
13
H), 1.32 (s, Bu); C NMR (125 MHz, CDCl ): δ 162.5, 148.2, 128.6,
1
[
stirring and the organic layer was separated, washed with water and
3
21.1, 114.9, 112.4, 108.3, 40.3, 28.4. HRMS (ESI): calcd for C H N
M + H ]: 375.2543; found: 375.2540.
dried over MgSO . Evaporation of the solvent under reduced pressure
24 31
4
4
+
yielded the bis(amidinate)s or derivatives, which were recrystallised or
purified by column chromatography.
t
Synthesis of C H -1,3-[NC( Bu)NH(2,5-Me -C H N)] (8)
6
4
2
4
2
2
t
C H -1,2-[NC( Bu)N(C H )H] (1): Colourless crystals; yield
6
4
6
5
2
The synthesis of 8 was carried out in the same way as that for the
synthesis of 7, except 2,5-dimethyl pyrrolyl potassium was used.
Compound 8 was obtained as: Colourless crystals; yield 48% (after
recrystallisation from hexane/ethyl acetate (1:1)); m.p. 95–97 °C;
6
5% (after column chromatography using petroleum ether/ethyl
1
acetate (10:1) as eluent); m.p. 101–102 °C; H NMR (300 M, CDCl ):
3
t
13
δ 6.96–6.79 (m, Ph–H), 6.65–6.21 (m, Ph–H), 1.37 (s, Bu); C NMR
125 MHz, CDCl ): δ 160.0, 151.1, 139.3, 128.8, 121.2, 40.9, 39.7, 30.0,
(
3
1
H NMR (300 MHz, CDCl ): δ 6.93–6.88 (m, Ph), 6.25–6.16 (m,
+
3
29.6. HRMS (ESI) calcd for C H N [M + H ]: 427.2856; found:
28 35 4
t
13
Ph–H), 5.67 (s, Py–H), 2.01 (s, PyMe–H), 1.28(s, Bu); C NMR
4
27.2856.
C H -1,2-[NC( Bu)NH Bu] (2): Colourless crystals; yield 72%
(
4
125 MHz, CDCl ): δ 163.0, 146.9, 128.7, 126.2, 116.8, 116.1, 106.9,
t
t
3
6
4
2
+
1.0, 29.5, 13.7. HRMS (ESI) calcd for C H N [M + H ]: 431.3175;
2
8
39
4
(
after column chromatography using petroleum ether/ethyl acetate
found: 431.3171.
1
(
10:1) as eluent); m.p. 84–85 °C; H NMR (300 MHz, CDCl ): δ
3
t t
6
.46–6.44 (m, Ph–H), 4.11 (s, br, N–H), 1.34 (s, Bu), 1.10 (s, Bu);
Acknowledgements
13
C NMR (125 MHz, CDCl ): δ 155.6, 143.4, 119.5, 119.4, 50.4, 39.7,
3
+
The project was sponsored by the National Natural Science
Foundation of China (No. 21502001) and Key Laboratory of
Chemical and Functional Materials and Technology of Anhui
Polytechnic University (KLCFMT1502).
2
9.6, 28.9. HRMS (ESI) calcd for C H N [M + H ]: 387.3482; found:
2
4
43
4
3
87.3486.
C H -1,3-[NC( Bu)N(C H )H] (3): Colourless crystals; yield 78%
t
6
4
6
5
2
1
(after recrystallisation from ethyl acetate); m.p. 98–99 °C; H NMR
(
300 MHz, CDCl ): δ 6.98–6.84 (m, Ph–H), 6.65–6.58 (m, Ph–H),
3
t
t
Electronic Supplementary Information
6
.21–5.93 (m, Ph–H), 3.71 (s, br, N–H), 1.33 (s, Bu), 1.30 (s, Bu);
13
C NMR (125 MHz, CDCl ): δ 162.9, 148.6, 129.0, 121.5, 115.3, 112.7,
The ESI is available through:
http://ingentaconnect.com/content/stl/jcr/2018/00000042/00000005/art00003
3
+
1
08.7, 40.7, 28.8. HRMS (ESI) calcd for C H N [M + H ]: 427.2856;
2
8
35
4
found: 427.2849.
t
t
C H -1,3-[NC( Bu)NH Bu] (4): Colourless crystals; yield 68%
Received 8 April 2018; accepted 29 April 2018
Paper 1805366
https://doi.org/10.3184/174751918X15260497205682
Published online: 30 May 2018
6
4
2
1
(after recrystallisation from ethyl acetate); m.p. 97–99 °C; H NMR
(
4
300 MHz, CDCl ): δ 6.93–6.90 (m, Ph–H), 6.10–6.00 (m, Ph–H),
3
t
t
13
.18 (s, br, N–H), 1.34 (s, C– Bu), 1.13 (s, N– Bu); C NMR (125 MHz,
CDCl ): δ 156.1, 152.2, 128.2, 112.3, 112.0, 51.1, 40.7, 30.5, 29.1.
HRMS (ESI) calcd for C H N [M + H ]: 387.3482; found: 387.3486.
3
+
References
2
4
43
4
t
{
(cis-C H )-1,2-[NC( Bu)N(C H )H] } (5): Colourless crystals; yield
6 12 6 5 2
1
2
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1
9
0% (after recrystallisation from ethyl acetate); m.p. 72–74 °C; H NMR
(
6
300 MHz, CDCl ): δ 7.18–7.13 (m, 2H, Ph–H), 6.88–6.84 (m, Ph–H),
3
3
4
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t
13
cyclohexyl), 1.25 (s, Bu), 0.99 (bm, cyclohexyl); C NMR (125 MHz,
CDCl ): δ 160.0, 151.3, 128.6, 120.8, 120.5, 50.2, 39.0, 29.4, 28.7, 21.8.
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7258.
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2
8
41
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6
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1

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