N.N. Omosun and G.S. Smith
Journal of Organometallic Chemistry 951 (2021) 122022
131 °C. 1H NMR (300 MHz, DMSO-d6): δ (ppm) = 8.48 (s, 2H, H-
11), 7.72 – 7.67 (overlapping m, 6H, H-10 and H-8), 7.56 (d, 3J = 8.2
Hz, 2H, H-9), 7.09 (d, 3J = 8.5 Hz, 4H, H-4), 6.98 (d, 3J = 8.3 Hz,
4H, H-5), 6.83 (d, 3J = 8.4 Hz, 4H, H-7), 5.57 (br s, 4H, H-6), 4.15
(t, 3J = 6.1 Hz, 4H, H-3), 3.98 (t, 3J = 6.4 Hz, 4H, H-3∗), 2.55
– 2.28 (overlapping m, 8H, H-1 and H-1∗), 2.12 – 1.96 (overlap-
ping m, 8H, H-2 and H-2∗). 13C{1H} NMR (151 MHz, DMSO-d6):
δ (ppm) = 160.30, 158.40, 154.19 (Cimine), 142.51, 137.15, 136.04,
130.95, 129.25, 127.90, 122.65, 122.04, 119.65, 115.21, 109.61, 69.57,
67.36, 48.33, 25.49. FT-IR (ATR, cm−1): ν = 1176 (O=S=O), 1608
(C=N). HR-ESI-MS(+): Calculated for C52H50N4Na4O16 S4 (m/z):
[M+H+Na]2+, 615.0832; found 615.0889.
for C60H62N4Na4O16 S4Rh (m/z): [M+H+2Na]3+, 558.4861; found
558.4189.
4.7. Synthesis of C2
Silver tetrafluoroborate (0.020 g, 0.102 mmol, 1.0 eq.) and
[RhCl(COD)]2 (0.025 g, 0.0507 mmol, 0.5 eq.) were stirred in ace-
tonitrile (10 mL) for one hour at room temperature. The precipi-
tated silver chloride was removed using a syringe filter (PTFE, 0.25
μm). The resulting solution was evaporated to dryness under re-
duced pressure. Ligand L4 (0.05 g, 0.083 mmol) dissolved in DMSO
(3 mL) was added to a stirring solution of the previously syn-
thesised [Rh(COD)(MeCN)2]BF4 (0.031 g, 0.083 mmol) in DMSO (5
mL) and stirred for one hour at room temperature. The reaction
mixture was poured into acetone, the precipitate formed was iso-
lated by filtration and washed with acetone (10 mL). The product
(C2) was purified by precipitation from DMSO and acetone mixture
(1:1) and dried in vacuo. Product: Pale green. Yield: 0.0433 g, 58%.
4.5. Synthesis of L4
Sodium hydride (0.948 g, 3.95 mmol) dispersed in mineral oil
was suspended in anhydrous THF (20 mL) under argon in a two-
necked flask. A solution of L2 (0.500 g, 1.58 mmol) dissolved in
anhydrous THF (2 mL) was added. The mixture was allowed to
stir for one hour at room temperature. 1,3-Propanesultone (0.386
g, 3.16 mmol) in dry THF (2 mL) was added and allowed to stir
for 24 hours at 55 °C. The reaction mixture was cooled to room
temperature and the resulting precipitate was collected by suction
filtration and washed with acetone (20 mL) to remove the unre-
acted sultone. The product (L4) was purified by precipitation from
DMSO/acetone (1:1) and dried in vacuo. Product: White powder.
Yield: 0.822 g, 86%. M.P. 114 – 120 °C. 1H NMR (300 MHz, DMSO-
d6): δ (ppm) = 7.69 – 7.64 (overlapping m,3H, H-4, H-6), 7.44 (d,
3J = 6.4 Hz, 1H, H-3), 7.33 – 7.16 (m, 2H, H-1, H-2), 7.08 (d, 3J = 8.8
Hz, 2H, H-7), 6.94 (d, 3J = 8.7 Hz, 2H, H-8), 6.84 (d, 3J = 8.8 Hz,
2H, H-9), 5.48 (s, 2H, H-5), 4.14 (t, 3J = 6.5 Hz, 2H, H-10∗), 3.99
(t, 3J = 6.3 Hz, 2H, H-10), 2.61 – 2.58 (m, 2H, H-12∗), 2.47 – 2.33
(m, 2H, H-12), 2.08 – 2.01 (m, 2H, H-11∗), 2.01 – 1.92 (m, 2H, H-
11). 13C{1H} NMR (151 MHz, DMSO-d6): δ (ppm) = 160.24, 158.19,
153.39 (Cimine), 143.20, 136.15, 131.18, 129.12, 127.86, 122.47, 119.41,
116.01, 115.16, 111.47, 69.53, 67.32, 60.82, 48.30, 29.16, 25.63. FT-
IR (ATR, cm−1): ν = 1171 (O=S=O), HR-ESI-MS(+): Calculated for
C26H26N2Na2O8S2 (m/z): [M+H]+, 605.0972; found 605.1008.
C2 is soluble in H2O (S25
°
C
≈ 103 mg/mL) and DMSO. M.P. 209
– 212 °C. 1H NMR (300 MHz, DMSO-d6): δ (ppm) = 8.28 – 8.17
(overlapping br s, 3H, H-4, H-6), 7.51 (d, 3J = 8.0 Hz, 1H, H-3), 7.41
(t, 1H, H-1), 7.31 (t, 1H, H-2), 7.26 (d, 3J = 8.8 Hz, 2H, H-7), 6.92
(d, 3J = 8.7 Hz, 2H, H-8), 6.83 (d, 3J = 8.8 Hz, 2H, H-9), 5.47 (s, 2H,
H-5), 4.35 (br s, 4H, H-13), 4.22 (t, 3J = 6.5 Hz, 2H, H-10∗), 3.96
(t, 3J = 6.3 Hz, 2H, H-10), 2.69 – 2.59 (m, 2H, H-11∗), 2.49 – 2.47
(m, 2H, H-11), 2.33 (br s, 4H, H-14), 2.13 – 2.08 (m, 2H, H-12∗),
1.99 – 1.94 (m, 2H, H-12). 1.80 (br s, 4H, H-15). 13C{1H} NMR (151
MHz, DMSO-d6): δ (ppm) = 161.01, 158.53 (Cimine), 152.75, 140.90,
134.77, 132.19, 129.84, 128.10, 123.59, 120.87, 119.67, 115.97, 115.16,
112.22, 86.31 (CCOD), 69.49, 67.55, 67.05, 60.77, 48.29, 30.73 (CCOD),
29.09, 27.98, 25.56. FT-IR (ATR, cm−1): ν = 1171 (O=S=O), 1613
(C=N). HR-ESI-MS(+): Calculated for C34H38N2Na2O8S2Rh (m/z):
[M]+, 815.0972; found 815.0464.
4.8. General procedure for the hydroformylation reactions
The hydroformylation reactions were carried out in a 90 mL
stainless steel pipe reactor equipped with a Teflon-coated magnetic
stirrer bar. The reactor was charged with distilled water (5 mL), the
substrate, 1-octene (7.175 mmol), the internal standard, n-decane
(1.435 mmol) and catalyst precursor (either C1 or C2) (2.87 × 10−3
mmol or 1.44 × 10−3 mmol). The air-tight reactor was de-aerated
by purging with nitrogen three times, followed by purging with
syngas (CO/H2, 1:1), The reactor was pressurised with syngas and
heated to the required temperature. After each set of reaction, the
reactor was depressurised and the reaction transferred to a vial
and cooled to room temperature. The organic layer was decanted
and analysed using gas chromatography. Samples were analysed
using a Perkin-Elmer Clarus 580 GC instrument equipped with a
flame ionisation detector and SGE Analytical capillary column (30
m x 0.25 mm). Authentic iso-octenes and aldehydes were used to
confirm the products.
4.6. Synthesis of C1
Silver tetrafluoroborate (0.020 g, 0.102 mmol, 1.0 eq.) and
[RhCl(COD)]2 (0.025 g, 0.0507 mmol, 0.5 eq.) were stirred in ace-
tonitrile (10 mL) for one hour at room temperature. The precip-
itated silver chloride was removed using a syringe filter (PTFE,
0.25 μm). The resulting solution was evaporated to dryness un-
der reduced pressure. Ligand L3 (0.05 g, 0.414 mmol) dissolved
in DMSO (3 mL) was added to a stirring solution of the previ-
ously synthesised [Rh(COD)(MeCN)2]BF4 (0.015 g, 0.0414 mmol) in
DMSO (5 mL) for one hour at room temperature. The reaction mix-
ture was poured into acetone and the precipitate that formed was
washed with acetone (10 mL). The product (C1) was purified by
precipitation from DMSO and acetone mixture (1:1) and dried in
vacuo. Product: Pale green. Yield: 0.0392 g, 63%. C1 is soluble in
H2O (S25
°
C
≈ 108 mg/mL) and DMSO. M.P. 215 – 220 °C. 1H NMR
Declaration of Competing Interest
(300 MHz, DMSO-d6): δ (ppm) = 8.39 (s, 2H, H-11), 8.07 (br s,
2H, H-10), 7.80 (s, 4H, H-8), 7.68 (d, 3J = 7.5 Hz, 2H, H-9), 7.22
(d, 3J = 7.6 Hz, 4H, H-4), 6.96 (d, 3J = 8.1 Hz, 4H, H-5), 6.83 (d,
3J = 8.5 Hz, 4H, H-7), 5.56 (br s, 4H, H-6), 4.15 (overlapping m,
12H, H-3, H-12), 3.97 (t, 3J = 6.4 Hz, 4H, H-3∗), 2.67 – 2.55 (over-
lapping m, 8H, H-1 and H-1∗), 2.34 (br s, 8H, H-13), 2.12 – 1.96
(overlapping m, 8H, H-2 and H-2∗), 1.78 (br s, 8H, H-14). 13C{1H}
NMR (151 MHz, DMSO-d6): δ (ppm) =160.65, 158.75 (Cimine),
153.91, 136.35, 131.77, 129.09, 128.07, 115.14, 109.76, 102.49, 85.10
(CCOD), 69.52, 67.09, 48.32, 30.77 (CCOD), 27.97, 25.67. FT-IR (ATR,
cm−1): ν = 1176 (O=S=O), 1609 (C=N). HR-ESI-MS(+): Calculated
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
Acknowledgements
We gratefully acknowledge and thank the University of Cape
Town and the NRF-DST Centre of Excellence in Catalysis - c∗change
for financial support.
7