Z. Zulu, et al.
Inorganica Chimica Acta xxx (xxxx) xxxx
3
13
1
amine [20] and (phenoxy)imine [30] ligands in which the catalytic
performances of these complexes were controlled by the ligand archi-
tecture. In our continued pursuit for both active and stable catalysts for
methoxycarbonylation of 1-alkenes, we herein report the syntheses of
palladium(II) complexes of iminopyridine ligands, containing potential
hemi-labile ether or hydroxy pendant donor groups. The structural
elucidation of the complexes, effect of complex structure and olefin
substrate on the activity and regioselectivity of the resultant catalysts
are herein discussed.
1H, 6-py, JHH = 8.0); C { H} NMR (DMSO‑d
(CH -O), 128.55 (3-py-C), 128.98 (5-py-C), 141.84 (4-py-C), 150.56 (6-
py-C), 156.33 (2-py-C), 172.12 (C]N), ESI-MS: m/z (%) 293 [(M - Cl,
6
): 59.19 (CH -N), 62.10
2
2
+
−1
65%)]. FT-IR (cm ):
υ
(C]N)imine = 1650 Anal. Calcd for
C
8
H
10Cl
N
2 2
OPd: C, 29.34; H, 3.08; N, 8.55. Found: C, 29.05; H, 3.14; N,
8.29.
2
.2.3. Synthesis of [PdCl
2
(L3)] (4)
Complex 4 was prepared according to the procedure described for 1
using L3 (0.06 g, 0.35 mmol) and [PdCl
2
(COD)] (0.10 g, 0.35 mmol) in
2
. Experimental section and methods
CH
2
Cl
2
(20 mL). Complex
4
was isolated as
a
yellow solid.
(ppm): 2.06
-O,
1
Yield = 0.087 g (70%). H NMR (400 MHz, DMSO‑d
6
): δ
H
2.1. General instrumentation and material
3
(
q, 2H, CH
2
,
J
HH = 6.6); 3.25 (s, 3H, CH
3
-O); 3.42 (t, 2H, CH
2
3
3
3
3
3
J
J
J
HH = 6.1); 3.80 (t, 2H, CH
2
-N,
J
HH = 6.9); 7.89 (t, 1H, 5-py,
All synthetic manipulations were performed under nitrogen atmo-
HH = 7.4); 8.12 (d, 1H, 3-py,
J
HH = 7.6); 8.37 (t, 1H, 4-py,
sphere using standard Schlenk line techniques. All solvents were pur-
chased from Merck and were dried and distilled prior to use. Diethyl
ether, hexane and toluene were dried over sodium wire and benzo-
phenone, methanol and absolute ethanol over calcium oxide, while
dichloromethane was dried and distilled over phosphorus pentoxide.
Methylheptanoate, methylnonanoate, sodium hydroxide (NaOH) and
3
13
HH = 7.8); 8.59 (s, 1H, CeH); 8.99 (d, 1H, 6-py,
J
HH = 5.6 Hz)
.
3
C
1
{
H} NMR (DMSO‑d
6
): 30.20 (CH
2
), 57.13 (CH
2
-N), 58.30 (CH
-O),
6
9.26 (CH -O), 128.66 (3-py), 129.00 (5-py), 141.78 (4-py), 150.57 (6-
2
+ +
py), 156.34 (2-py), 172.01 (C]N). ESI-MS: m/z (%) 201 [(M + Na
,
−1
1
00%)]. FT-IR (cm ):
υ(C]N)imine = 1648. Anal. Calcd for
C
10
H
14Cl
2
N OPd: C, 33.78; H, 3.97; N, 7.88. Found: C, 33.75; H, 4.01;
2
DMSO‑d were purchased from Merck Chemicals. Ethanolamine, 2-
6
N, 7.84.
methoxyethylamine, 2-pyridinecarboxaldehyde, olefins, hydrochloric
acid, p-TsOH (≥98.5%), PPh (99%) and CDCl were purchased from
Sigma Aldrich and used as received. [PdCl (COD)] [31], [PdCl(Me)
COD)] [32], ligands 2-methoxy-N-((pyridin-2-yl)methylene)ethana-
mine (L1), 2-((pyridin-2-yl)methyleneamino)ethanol (L2), 3-methoxy-
N-((pyridin-2-yl)methylene)propan-1-amine (L3), and complex
PdClMe(L1)] (2) were prepared by following our recently published
3
3
2
.3. X-ray crystallography
2
(
X-ray data collection for complex 1 was recorded on a Bruker Apex
Duo equipped with an Oxford Instruments Cryojet operating at 100(2)
K and an Incoatec microsource operating at 30 W power. Crystal and
structure refinement data are given in Table 1. The data were collected
with Mo Kα (λ = 0.71073 Å) radiation at a crystal-to-detector distance
of 50 mm. The data were collected using omega and phi scans with
exposures taken at 30 W X-ray power and 0.50° frame widths using
APEX2 [33]. The data were reduced with the programme SAINT [33]
using outlier rejection, scan speed scaling, as well as standard Lorentz
and polarisation correction factors. A SADABS semi-empirical multi-
scan absorption correction [33] was applied to the data. Direct
methods, SHELXS-2016 [34] and WinGX [35] were used to solve the
data. All non-hydrogen atoms were located in the difference density
map and refined anisotropically with SHELXL-2016 [34]. All hydrogen
atoms were included as idealized contributors in the least squares
process. Their positions were calculated using a standard riding model
with C–Haromatic distances of 0.93 Å and Uiso = 1.2 Ueq and C–Hmethylene
distances of 0.99 Å and Uiso = 1.2 Ueqand C–Hmethyl distances of 0.98 Å
and Uiso = 1.5 Ueq.
[
1
13
1
procedures [28]. H NMR and C { H} NMR spectra were recorded on
1
13
1
a Bruker Ultrashield 400 ( H NMR 400 MHz, C { H} NMR 100 MHz)
spectrometer in CDCl solution at room temperature and chemical shifts
δ) were determined relative to internal TMS and are given in ppm. The
infrared spectra were recorded on a PerkinElmer Spectrum 100 in the
3
(
−
1
4
000–400 cm
range. Elemental analyses were performed on a
Thermal Scientific Flash 2000 and mass spectra were recorded on an LC
premier micromass spectrometer.
2
.2. Syntheses of palladium(II) complexes
.2.1. Synthesis of [PdCl (L1)] (1)
2
2
To a solution of [PdCl (COD)] (0.10 g, 0.35 mmol) in CH
2
2
2
Cl
2
2
(
(
10 mL) was added a solution of L1 (0.06 g, 0.35 mmol) in CH
Cl
10 mL). The mixture was stirred at room temperature, under nitrogen
for 24 h. The yellow precipitate formed was filtered and washed with
diethyl ether (2 × 20 mL), filtered and dried to afford 1 as a yellow
2
.4. Typical procedure for the methoxycarbonylation reactions
solid. Recrystallization from CH
2
Cl
2
-hexane mixture afforded single
1
crystals suitable for X-ray analysis. Yield = 0.09 g (75%). H NMR
The methoxycarbonylation catalytic reactions were performed in a
(
400 MHz, DMSO‑d
6
): δ
HH = 8.0 Hz); 3.91 (t, 2H, CH -O, JHH = 8.0 Hz); 7.89 (t, 1H, 5-py,
3
H
(ppm): 3.29 (s, 3H, CH
3
); 3.71 (t, 2H, CH -N,
2
3
3
3
1
3
400 mL stainless steel autoclave Parr reactor equipped with a
J
J
2
HH = 8.0 Hz); 8.18 (d, 1H, 3-py,
J
HH = 8.0 Hz); 8.36 (t, 1H, 4-py,
3
Table 1
J
HH = 8.0 Hz); 8.55 (s, 1H, CeH); 8.99 (d, 1H, 6-py,
J
HH = 8.0 Hz).
3
1
Methoxycarbonylation of 1-hexene using complexes 1–4.
C { H} NMR (DMSO‑d
6
): 58.57 (CH
3
-O), 58.76 (CH
2
-N), 69.76 (CH -
2
a
bb/l ratio
TOF h−1
O), 128.89 (3-py-C), 129.27 (5-py-C), 141.93 (4-py-C), 150.75 (6-py-C),
Entry
Catalyst
Time(h)
Conv. (%)
+
1
56.03 (2-py-C), 172.75 (C]N). ESI-MS: m/z (%) 269 [(M - Cl
2
,
−
1
1
2
3
4
5
6
1
2
3
4
1
1
24
24
24
24
12
36
91
39/61
40/60
40/60
35/65
20/80
48/52
7.6
5.2
4.8
3.3
3.9
8.2
1
00%)]. FT-IR (cm ):
υ
(C]N)imine = 1598. Anal. Calcd for
62
58
40
47
98
C
9
H12Cl
2
N
2
OPd·0.1C H14: C, 32.93; H, 3.80; N, 8.00. Found: C, 32.98;
6
H, 3.67; N, 7.99.
2
.2.2. Synthesis of [PdCl
2
(L2)] (3)
Complex 3 was prepared according to the procedure described for 1
Reaction conditions: pre-catalyst (0.081 mmol), Solvent: methanol.
5 mL and toluene 25 mL; Pd:PPh :HCl = 1:2:10:200 ; Pd (0.0806 mmol), PPh
using L2 (0.05 g, 0.35 mmol) and [PdCl (COD)] (0.10 g, 0.35 mmol) in
2
2
3
3
CH
2
Cl
2
(20 mL). Complex
3
was obtained as
a
yellow solid.
(ppm): 3.75 (s,
(
42.26 mg, 0.1612 mmol), HCl (0.0249 mL) and 1-hexene (2 mL, 16.11 mmol),;
1
Yield = 0.08 g (70%). H NMR (400 MHz, DMSO‑d
6
): δ
H
a
p(CO) = 60 bar; temperature: 90 °C; Time: 24 h; % of 1-hexene converted to
3
b
4
H, CH
2
-N + CH
2
-O); 7.87 (t, 1H, 5-py, JHH = 8.0); 8.18 (d, 1H, 3-py,
esters determined from GC assuming 100% mass balance; Molar ratio between
3
3
J
HH = 8.0); 8.34 (t, 1H, 4-py, JHH = 8.0); 8.48 (s, 1H, CeH); 8.98 (d,
branched and linear ester determined from GC.
2