Organometallics
Article
(s, 2H), 2.56 (q, J = 7.2 Hz, 2H), 1.08 (t, J = 7.2 Hz, 3H). 13C NMR
which suppresses the formation of 3,4-regularity resulting in a
19
(
1
(
100 MHz, CDCl , 298 K): δ 160.65, 148.82, 139.66, 136.34, 128.79,
higher content of cis-1,4-regularity. As for myrcene and β-
farnesene polymerization, the longer tail of the monomer
promoted the steric effects that control the regiochemistry of
insertion.
3
28.20, 126.84, 122.73, 121.75, 59.74, 58.13, 47.71, 12.01. HRMS-ESI
+
m/z): [M + H] calcd for C H N , 227.1548; found, 227.1549.
15 19 2
N,N-Dibenzyl-1-(pyridin-2-yl)methanamine (3c). Product 3c was
produced as a yellow oil (1.21 g, 28% yield) by an approach identical
to that for the preparation of 3a by using 2-(chloromethyl)pyridine
hydrochloride (15.0 mmol, 1 equiv), sodium iodide (2.0 mmol, 1.3
CONCLUSION
■
A library of well-defined aminopyridine iron(II) precatalysts
were synthesized via the introduction of bulky alkyl groups
instead of active hydrogen [N(H)]. The Fe-Me, Fe-Et, and
equiv), potassium carbonate (100.0 mmol, 6.6 equiv), and dibenzyl-
1
amine (50.0 mmol, 3.3 equiv). H NMR (400 MHz, CDCl , 298 K):
3
δ 8.49 (d, J = 4.8 Hz, 1H), 7.70−7.60 (m, 2H), 7.41 (d, J = 7.2 Hz,
i
4H), 7.32 (t, J = 7.4 Hz, 4H), 7.23 (s, 2H), 7.13 (t, J = 6.6 Hz, 1H),
Fe- Pr complexes showed a similar structure, which has
1
3
3
1
1
.74 (s, 2H), 3.62 (s, 4H). C NMR (100 MHz, CDCl , 298 K): δ
3
chloride-bridged centrosymmetric binuclear geometry verified
by single-crystal X-ray diffraction. These precatalysts showed
excellent activities toward isoprene polymerization (≤2.34 ×
60.40, 148.91, 139.45, 136.59, 128.91, 128.41, 127.10, 122.85,
22.02, 59.94, 58.40. HRMS-ESI (m/z): [M + H]+ calcd for
C H N , 289.1705; found, 289.1695.
2
0
21
2
6
−1 −1
1
0 g
mol h ) upon activation by MAO, delivering
polymer
N-Benzyl-N-isopropyl-1-(pyridin-2-yl)methanamine (3d). Prod-
5
polyconjugated dienes with high M values (1.5−4.4 × 10 g/
uct 3d was produced as a yellow oil (1.01 g, 30% yield) by an
approach identical to that for the preparation of 3a using N-
n
mol) and a narrow Đ range (1.8−2.0). More importantly, the
i
1
Fe- Pr catalyst is a highly thermally stable bidentate iron(II)
isopropylbenzylamine as the raw material (22.5 mmol, 1.5 equiv). H
NMR (400 MHz, CDCl , 298 K): δ 8.47 (d, J = 4.8 Hz, 1H), 7.62
complex, which could efficiently promote the polymerization
even at 100 °C. In addition, two renewable biodienes, myrcene
3
(
dd, J = 5.0, 1.6 Hz, 2H), 7.40 (d, J = 7.2 Hz, 2H), 7.29 (t, J = 7.4 Hz,
i
2H), 7.21 (t, J = 7.4 Hz, 1H), 7.11−7.06 (m, 1H), 3.77 (s, 2H), 3.64
and β-farnesene, were also efficiently polymerized by Fe- Pr to
1
3
(s, 2H), 2.96 (hept, J = 6.8 Hz, 1H), 1.10 (d, J = 6.6 Hz, 6H).
C
produce the poly-β-isomer with high-molecular weight “green
rubber”. Further insightful explorations of Fe-catalyzed
polyolefin synthesis are under progress in our laboratory.
NMR (100 MHz, CDCl , 298 K): δ 161.65, 148.58, 140.61, 136.38,
3
1
28.53, 128.18, 126.69, 122.39, 121.62, 55.38, 53.97, 49.28, 17.81.
+
HRMS-ESI (m/z): [M + H] calcd for C H N , 241.1705; found,
1
6
21
2
2
41.1706.
EXPERIMENTAL SECTION
General Procedure. The standard Schlenk technique was used to
deal with all water and oxygen sensitive reagents and complexes. All
solvents and monomers need to be purified according to standards
Synthesis of Ferrous Chloride Complexes. N-Benzyl-N-
■
methyl-1-(pyridin-2-yl)methanamine Ferrous Chloride (Fe-Me).
Under anhydrous and oxygen-free conditions, anhydrous FeCl2
(1.00 mmol, 1.0 equiv) and a dichloromethane (10 mL) solution of
ligand 3a (1.00 mmol, 1.0 equiv) were added in sequence to a 25 mL
Schlenk tube, and the heterogeneous solution was kept stirring for 48
h at room temperature. Finally, the compound was obtained by
filtration, concentration, washing with distilled hexane (2 × 10 mL),
and evaporation under vacuum. Fe-Me was afforded as a pale yellow
used previously. CDCl was selected as a deuterated reagent, and the
3
Bruker Avance III 400 MHz spectrometer was utilized to record NMR
spectra. The Shanghai Institute of Organic Chemistry carried out an
elemental analysis test under anhydrous and oxygen-free conditions
on a Vario EL III elemental analyzer. Shanghai Jiao Tong University
recorded mass spectra under anhydrous and oxygen-free conditions
by maXis II of Bruker Daltonics Corp. and ACQUITYTM UPLC and
Q-TOF MS Premier. The Bruker Smart diffractometer with a Mo Kα
−1
powder (272.2 mg, 81% yield). ATR-IR (cm ): 3098, 3012, 2924,
1
1605, 1508, 1455, 1444, 1213, 1156, 970, 850, 753, 703. H NMR
(400 MHz, CDCl
73.1, 58.5 (Δν1/2 = 480 Hz), 52.0 (Δν1/2 = 450 Hz), 38.3 (Δν1/2
500 Hz), 7.9 (Δν1/2 = 150 Hz), −9.6 (Δν1/2 = 457 Hz). HRMS (ESI,
, 298 K): δ 124.5 (Δν1/2 = 1100 Hz), 105.9, 83.3,
3
X-ray source was used to collect data at 298 K. M and Đ values of
=
n
polymers were collected at PL-GPC 220 of Agilent Technologies.
DMAO was obtained by removing the solvent and residual
trimethylaluminum of MAO. Other chemical materials were
purchased without further purification before use.
+
m/z): [M − FeCl
515.1666. Anal. Calcd for C14
Found: C, 49.09; H, 4.88; N, 8.26.
]
calcd for C28
16Cl FeN
2
H
32ClFeN
: C, 49.60; H, 4.76; N, 8.26.
, 515.1665; found,
4
3
H
2
Synthesis of Ligands. N-Benzyl-N-methyl-1-(pyridin-2-yl)-
N-Benzyl-N-ethyl-1-(pyridin-2-yl)methanamine Ferrous Chloride
(Fe-Et). Fe-Et was afforded by an approach identical to that for the
preparation of Fe-Me by using ligand 3b as a yellow powder (302.3
methanamine (3a). At room temperature, the raw materials 2-
(
chloromethyl)pyridine hydrochloride (20 mmol, 1 equiv), sodium
iodide (2.0 mmol, 0.1 equiv), and potassium carbonate (100 mmol, 5
equiv) were added in sequence in a 50 mL two-neck flask, and 50 mL
−
1
mg, 85% yield). ATR-IR (cm ): 3098, 2971, 2912, 1608, 1470, 1448,
1
1296, 1215, 1104, 1021, 993, 872, 752. H NMR (400 MHz, CDCl ,
3
of CH CN was used as the solvent. After 5 min, the N-
298 K): δ 165.6 (Δν = 450 Hz), 124.2 (Δν1/2 = 457 Hz), 89.7,
3
1/2
methylbenzylamine (50 mmol, 2.5 equiv) was added dropwise, and
the solution was kept stirring for 12 h until thin layer chromatography
showed that the reaction was over. Product 3a was achieved as a
yellow oil (3.63 g, 86% yield) purified by filtration, concentration, and
75.4, 59.5 (Δν = 387 Hz), 49.4 (Δν = 468 Hz), −1.7 (Δν1/2 =
1
/2
1/2
230 Hz), −9.4 (Δν = 295 Hz), −33.4 (Δν = 750 Hz). HRMS
1
/2
1/2
+
(ESI, m/z): [M − FeCl + H] calcd for C H Cl FeN , 579.1745;
found, 579.1746. Anal. Calcd for C H Cl FeN : C, 51.03; H, 5.14;
2
30 37
2
4
1
5
18
2
2
1
silica gel column purification (1:1 PE:EtOAc). H NMR (400 MHz,
N, 7.93. Found: C, 50.99; H, 5.39; N, 7.83.
CDCl , 298 K): δ 8.54 (d, J = 4.8 Hz, 1H), 7.64 (t, J = 7.6 Hz, 1H),
N,N-Dibenzyl-1-(pyridin-2-yl)methanamine Ferrous Chloride
(Fe-Bn). Fe-Bn was afforded by an approach identical to that for
the preparation of Fe-Me by using ligand 3c as a yellow powder
3
7
.51 (d, J = 7.8 Hz, 1H), 7.37 (d, J = 7.6 Hz, 2H), 7.31 (t, J = 7.6 Hz,
H), 7.24 (d, J = 7.2 Hz, 1H), 7.16−7.10 (m, 1H), 3.70 (s, 2H), 3.59
2
1
3
−1
(
s, 2H), 2.24 (s, 3H). C NMR (100 MHz, CDCl , 298 K): δ 159.79,
(176.0 mg, 85% yield). ATR-IR (cm ): 3048, 3024, 2931, 1607,
3
1
1
6
2
49.02, 139.04, 136.42, 128.98, 128.28, 127.04, 122.97, 121.94, 63.50,
1490, 1451, 1301, 1203, 1160, 1053, 965, 749. H NMR (400 MHz,
+
2.15, 42.55. HRMS-ESI (m/z): [M + H] calcd for C H N ,
CDCl , 298 K): δ 61.0 (Δν = 175 Hz), 53.9 (Δν = 153 Hz),
1
4
17
2
3
1/2
1/2
13.1392; found, 213.1392.
N-Benzyl-N-ethyl-1-(pyridin-2-yl)methanamine (3b). Product 3b
10.2 (Δν = 360 Hz), 7.5 (Δν = 67 Hz), −8.73 (Δν = 90 Hz).
1
/2
1/2
1/2
Anal. Calcd for C H Cl FeN : C, 57.86; H, 4.86; N, 6.75. Found: C,
2
0
20
2
2
was achieved as a yellow oil (4.24 g, 94% yield) by an approach
57.70; H, 4.91; N, 6.94.
identical to that for the preparation of 3a using N-ethylbenzylamine as
N-Benzyl-N-isopropyl-1-(pyridin-2-yl)methanamine Ferrous
1
i
i
the raw material (50.0 mmol, 2.5 equiv). H NMR (400 MHz, CDCl ,
Chloride (Fe- Pr). Fe- Pr was afforded by an approach identical to
that for the preparation of Fe-Me by using ligand 3d as a yellow
3
2
(
7
98 K): δ 8.49 (d, J = 4.8, 1H), 7.61 (td, J = 7.6, 1.8 Hz, 1H), 7.55
dt, J = 7.8, 1.2 Hz, 1H), 7.41−7.34 (m, 2H), 7.34−7.25 (m, 2H),
.27−7.16 (m, 1H), 7.09 (dd, J = 6.8, 4.8 Hz, 1H), 3.75 (s, 2H), 3.63
−1
powder (310.0 mg, 84% yield). ATR-IR (cm ): 3102, 2965, 2830,
1
1608, 1571, 1469, 1444, 1397, 1298, 1150, 1023, 845, 784. H NMR
F
Organometallics XXXX, XXX, XXX−XXX