S.O. Akiri and S.O. Ojwach
InorganicaChimicaActa489(2019)236–243
olefins thus calls for a need to explore more immobilized catalysts,
which are amenable to separation and recycling.
6.00 mmol) in dichloromethane (30 mL), a solution of APTES (1.33 g,
6.00 mmol) in dichloromethane (10 mL) was added dropwise followed
by stirring for 12 h. The organic solvent was then evaporated under
vacuum to obtain HL2 as a yellow oil. Yield = 1.54 g (75%). 1H NMR
In attempts to bridge this gap, we herein design palladium(II)
complexes supported on (phenoxy)imine ligands bearing silane alkoxy
groups. We envisage that by incorporating the alkoxy groups on the
ligand backbone, immobilization of the systems on for instance silica
support, would be made possible [28]. In this paper, we therefore
(II) complexes and their applications in the methoxycarbonylation of
higher olefins under homogeneous conditions. The effect of catalyst
structure, solvent, nature of acid promoter, type of phosphine additive,
olefin substrate and reaction conditions on the catalytic activity and
regioselectivity would be discussed.
3
(400 MHz, CDCl3, δ ppm): 0.71 (t, 2H, JHH = 8.0 Hz, Si-CH2), 1.26 (t,
3
9H, JHH = 4.0 Hz, OCH2-CH3), 1.90 (m, 2H, C-CH2-C), 2.31 (s, 3H,
3
3
CH3), 3.61 (t, 2H, JHH = 8.0 Hz, NCH2C), 3.86 (q, 6H, JHH = 8.0 Hz,
3
O-CH2), 6.88 (d, 1H, JHH = 8.0 Hz, Ph), 7.05 (s, 1H, Hd), 7.13 (d, 1H,
3JHH = 8.0 Hz, Ph), 8.31 (s, 1H, Ph-CHN). 13C NMR (100 MHz, CDCl3, δ
ppm): 164.8 (Ph-C), 159.1 (Ph-CH-N), 132.7 (Ph-C), 131.2 (Ph-C),
127.4 (Ph-C), 118.5 (Ph-C), 116.7 (Ph-C), 62.1 (NCH2C), 58.4 (O-CH2),
24.4 (CH3), 20.3 (C-CH2-C), 18.3 (OCH2-CH3), 7.9 (Si-CH2). MS (ESI)
m/z (%) 454 (M+, 100). HRMS-ES; Calc: 339.1901; Found: 340.1806.
IR νmax/ cm−1: ν(OH) = 2974, ν(C]N) = 1634, ν(Si-O) = 1073.
2. Experimental section and methods
2.2.3. Synthesis of [Pd (L1)2] (1)
2.1. General instrumentation and material
To a solution of HL1 (0.34 g, 1.00 mmol) in methanol (20 mL), a
solution of [Pd(OAc)2] (0.11 g, 0.50 mmol) in methanol (15 mL) was
added and refluxed for 8 h. The resultant mixture was then filtered and
washed with methanol. Recrystallization of the crude product from
CH2Cl2-hexane mixture afforded complex 1 as a yellow powder.
Yield = 0.31 g (79%). 1H NMR (400 MHz, CDCl3, δ ppm): 0.79 (t, 4H,
All air sensitive manipulations were performed under inert atmo-
sphere and moisture free conditions using standard Schlenk techniques.
All solvents purchased from Merck were of analytical grade and were
dried before use. Toluene solvent was dried over sodium wire and
benzophenone while methanol was dried and distilled by heating over
magnesium metal activated with iodine. Dichloromethane was distilled
using phosphorus pentoxide and stored in molecular sieves, DMF was
dried over calcium oxide and chlorobenzene was dried over phosphorus
pentoxide [29]. The reagents; (3-aminopropyl) triethoxy silane (99%),
(98%), palladium(II) dichloride (59%), palladium (II) acetate (98%),
olefins, hydrochloric acid, p-TsOH (≥98.5% ), PPh3 (99%), dppe
(98%), P(Cy)3 (98%) were obtained from Sigma-Aldrich. NMR spectra
were recorded on a Bruker Ultrashield 400 (1H NMR 400 MHz, 13C
NMR 100 MHz) spectrometer in CDCl3 solution at room temperature.
The chemical shift values (δ) were referenced to the residual proton and
carbon signals at 7.24 and 77.0 ppm respectively of the CDCl3 NMR
solvent. The infrared spectra were recorded on a Perkin-Elmer Spec-
trum 100 in the 4000–400 cm−1 range. Mass spectral analyses were
carried out using LC premier micromass, Elemental analyses were
performed on a Thermal Scientific Flash 2000 whereas GC and GC–MS
analyses was performed on a Varian CP-3800 and QP2010 respectively.
3
3JHH = 8.0 Hz, Si-CH2), 1.22 (t, 18H, JHH = 8.0 Hz, OCH2-CH3) , 2.02
3
(m, 4H, C-CH2-C) , 2.45 (s, 6H, CH3), 3.80 (q, 16H, JHH = 8.0 Hz,
3
NCH2C, O-CH2), 6.58 (t, 2H, JHH = 8.0 Hz, Ph), 6.87 (d, 2H,
3
3JHH = 8.0 Hz, Ph), 7.11 (t, 4H, JHH = 8.0 Hz, Ph),7.37 (d, 2H,
3JHH = 8.0 Hz, Ph). 13C NMR (100 MHz, CDCl3,
δ ppm): 183.9
(CH3CN), 166.8 (Ph-C), 132.4 (Ph-C), 131.2 (Ph-C), 128.7 (Ph-C), 118.9
(Ph-C), 115.1 (Ph-C), 58.4 (O-CH2), 54.5 (NCH2C), 26.6 (CH3), 23.6
(OCH2-CH3), 18.3 (C-CH2-C) 7.9 (Si-CH2). IR νmax
/
cm−1
: ν
(C]N) = 1655, ν (Si-O) = 1098. Anal. Calcd for C34H56N2O8PdSi2: C,
52.13; H, 7.21; N, 3.58. Found: C, 52.58; H, 6.93; N, 3.36.
2.2.4. Synthesis of [Pd(L2)2] (2)
Complex 2 was synthesised following the procedure employed for
complex 1 using [Pd(OAc)2] (0.14 g, 0.64 mmol) and HL2 (0.43 g,
1.28 mmol). Yield = 0.44 g (87%). 1H NMR (400 MHz, CDCl3, δ ppm):
0.69 (t, 4H, 3JHH = 8.0 Hz, Si-CH2), 1.20 (t, 18H, 3JHH = 8.0 Hz, OCH2-
CH3), 1.90 (m, 4H, C-CH2-C), 2.24 (s, 6H, CH3), 3.71 (t, 4H,
3
3JHH = 8.0 Hz, NCH2C); 3.80 (q, 12H, JHH = 8.0 Hz, O-CH2), 6.78 (d,
3
3
2H, JHH = 8.0 Hz, Ph), 6.95 (s, 2H, Ph), 7.05 (d, 2H, JHH = 8.4 Hz,
Ph),7.60 (s, 2H, Ph-CHN), 13C NMR (100 MHz, CDCl3, δ ppm): 190.4
(PhCN), 162.8 (Ph-C), 161.7 (Ph-C), 135.8 (Ph-C), 133.2 (Ph-C), 123.5
(Ph-C), 120.0 (Ph-C), 60.7 (NCH2C), 58.4 (O-CH2), 25.6 (CH3), 19.9 (C-
2.2. Synthesis of (phenoxy)imine ligands and their palladium(II) complexes
2.2.1. Synthesis of 2-phenyl-2-((3-(triethoxysilyl)propyl)phenoxy)imine
(HL1)
CH2-C)
,
18.3 (OCH2-CH3), 7.6 (Si-CH2). IR νmax
/
cm−1
: ν
A solution of 2-hydroxyacetophenone (1.36 g, 10.00 mmol) in to-
luene (25 mL) was refluxed in Dean-Stark apparatus for 3 h and a so-
lution of (3-aminopropyl) triethoxy silane, APTES, (2.21 g,
10.00 mmol) in toluene (15 mL) was added and the mixture was further
refluxed for 24 h. The organic fraction was then evaporated in vacuo to
give HL1 as an analytically pure yellow oil. Yield = 3.20 g (94%). 1H
NMR (400 MHz, CDCl3): δH (ppm) 0.79 (t, 2H, J = 8.4 Hz, Si-CH2) ,
(C]N) = 1621, ν (Si-O) = 1085. Anal. Calcd. for C34H56N2O8PdSi2: C,
52.13; H, 7.21; N, 3.58. Found: C, 52.46; H, 7.11; N, 3.54.
2.2.5. Synthesis of [Pd(HL1)(Cl2)] (3)
To
a solution of [Pd(NCMe)Cl2] (0.30 g, 1.20 mmol) in di-
chloromethane (20 mL), was added ligand HL1 (0.41 g, 1.20 mmol)
dissolved in dichloromethane (10 mL). The resulting orange solution
was then stirred for 24 h. The solvent was then reduced to about 10 mL
and recrystallization by layering the solution with hexane (5 mL) pro-
duced complex 3 as an analytically pure orange solid. Yield = 0.51 g
(83%). 1H NMR (400 MHz, CDCl3): δH (ppm) 0.72 (t, 2H, J = 8.0 Hz, Si-
1.26 (t, 9H, 3JHH = 7.2 Hz, OCH2-CH3), 1.91 (m, 2H, C-CH2-C), 2.38 (s,
3
3H, CH3)
,
3.60 (t, 2H, JHH = 7.2 Hz, NCH2C)
,
3.86 (q, 6H,
3JHH = 7.2 Hz, O-CH2), 6.76 (d, 1H, JHH = 7.2 Hz, Ph) 7.02 (d, 2H,
3
3JHH = 8.4 Hz, Ph), 7.28 (dt, 1H, JHH = 7.2 Hz, Ph) 7.52 (d, 1H,
3
3JHH = 8.0 Hz, Ph). 13C NMR (100 MHz, CDCl3,
δ
ppm): 171.5
CH2) , 1.19 (t, 9H, JHH = 8.0 Hz, OCH2-CH3), 1.91 (m, 2H, C-CH2-C),
3
(CH3CN), 165.2 (Ph-C), 132.6 (Ph-C), 129.0 (Ph-C), 127.9 (Ph-C), 119.2
(Ph-C), 116.5 (Ph-C), 58.5 (O-CH2), 51.4 (NCH2C), 23.9 (CH3), 18.3
2.23 (s, 3H, CH3) , 3.74 (t, 2H, 3JHH = 8.0 Hz, NCH2C) , 3.85 (m, 6H, O-
3
3
CH2), 7.02 (d, 1H, JHH = 7.2 Hz, Ph) 7.21 (d, 2H, JHH = 8.4 Hz, Ph),
(OCH2-CH3), 14.1 (C-CH2-C) 8.2 (Si-CH2). MS (ESI) m/z (%) 255 (M+
100). HRMS-ESI; Calc: 339.1901; Found: 339.0817. IRνmax/cm−1
ν(OH) = 2973, ν(C]N) = 1615, ν(Si-O) = 1071.
,
:
7.46 (t, 1H, JHH = 7.2 Hz, Ph) 7.55 (d, 1H, JHH = 8.0 Hz, Ph). 13C
NMR (100 MHz, CDCl3, δ ppm): 181.6 (CH3CN), 164.4 (Ph-C), 131.2
(Ph-C), 129.4 (Ph-C), 126.6 (Ph-C), 117.5 (Ph-C), 113.2 (Ph-C), 56.9
(O-CH2), 52.8 (NCH2C), 24.7 (CH3), 21.8 (OCH2-CH3), 18.1 (C-CH2-C)
7.7 (Si-CH2). IR νmax/ cm−1: ν(OH) = 2993,ν (C]N) = 1650, ν
O) = 1080. Anal. Calcd. for C17H29Cl2NO4PdSi: C, 39.51; H, 5.66; (NSi,-
2.71. Found: C, 39.25; H, 5.34; N, 2.65.
3
3
2.2.2. Synthesis of 4-methyl-2-(((3-(triethoxysilyl)propyl)imino)phenoxy)
imine (HL2)
To
a
solution of 2-hydroxy-5-methylbenzaldehyde (0.82 g,
237