YUAN Maolin et al. / Chinese Journal of Catalysis, 2010, 31: 1093–1097
temperature for 24 h and then poured into 100 ml of ice-water.
(SE-30, 30 m × 0.25 mm × 0.25 μm).
The aqueous phase was extracted with CH2Cl2 (30 ml × 3). The
combined extracts were washed in turn with a saturated
Na2CO3 solution, water, and brine. The organic layer was dried
over anhydrous MgSO4 and the solvent was evaporated in
vacuum. The residue was distilled under reduced pressure to
give 4-bromo-1,2-dimethoxybenzene (3.5 g, 74.3%) as a col-
orless oil. 1H NMR (CDCl3): δ 4.15 (s, 3H, CH3O), 4.26 (s, 3H,
CH3O), 6.73–7.10 (m, 3H, Ar ); MS: m/z 216/218 (M+).
Because hydroformylation is highly dependent on the reac-
tion conditions, the effect of P/Rh molar ratio was evaluated
using 1-dodecene as a substrate. The conversion and the L/B
ratio (molar ratio of linear aldehyde to branched aldehyde) are
given in Table 1. At a lower P/Rh ratio, the catalytic system
already showed a high reaction rate. The conversion of
1-dodecene increased with an increase in the P/Rh molar ratio
and it showed a decline when the P/Rh ratio exceeded 7.5. The
reason may be that TDMOPP contains six electron-donating
methoxy groups, which coordinate to rhodium well and many
catalytically active species are formed at a low P/Rh ratio and
at low temperature resulting in high reactivity. The number of
catalytically active species formed by TDMOPP and rhodium
increased and in turn enhanced the catalytic activity further
when the P/Rh ratio increased. When the P/Rh ratio increased,
the charge and steric hindrance at the rhodium center increased
and this increases the difficulty of 1-dodecene coordination to
rhodium. As a result, the conversion of 1-dodecene decreased.
The effect of the P/Rh ratio on L/B was also obvious and the
L/B increased with an increase in the P/Rh molar ratio [10],
especially over 7.5. Considering the conversion of 1-dodecene
and L/B, the optimized P/Rh molar ratio was found to be 5.0 as
the conversion of 1-dodecene was as high as 97.0%. The
widely used TPP was also studied for comparison. From Table
1 the Rh-TDMOPP catalyst is shown to be superior to the
Rh-TPP catalyst for the hydroformylation of 1-dodecene. The
results show that the conversion of 1-dodecene for TDMOPP
was about two times higher than that obtained for TPP at a low
P/Rh molar ratio and temperature. We attribute the difference
to two factors. One is that the TDMOPP that contains no or-
tho-substituent is capable of avoiding the exclusion of coor-
dination of 1-dodecene to rhodium. The other may be that the
bulky methoxy that is meta-substituted on the phenyl ring
prevents the complete saturation coordination of TDMOPP at
the rhodium center at a high P/Rh ratio. In the rhodium com-
plex with a low coordination number, the shortage of charge at
the rhodium center is satisfied by the electron-rich methoxy at
the para position on the phenyl ring. As a result, the coordina-
tion of TDMOPP to rhodium forms a stable catalytically active
species and promotes the reaction, which results in higher
Subsequently, 5.2 ml of a hexane solution containing
n-C4H9Li (2.89 mol/L, 15.0 mmol) was added dropwise to a
solution of 4-bromo-1,2-dimethoxybenzene (3.2 g, 15.0 mmol)
in THF (20 ml) at –78 °C over 30 min. Then, freshly distilled
phosphorus trichloride (1.4 ml, 5.0 mmol) in 10 ml THF was
added dropwise over 15 min at such a rate that the reaction
temperature did not exceed –50 °C. The reaction mixture was
warmed to room temperature within 1 h and left overnight. The
mixture was then quenched with 20 ml of 10% aqueous NH4Cl.
The resulting light yellow solution was evaporated to dryness
under reduced pressure. The residue was extracted with CH2Cl2
(30 ml × 3). The combined organic solution was washed with
deoxygenated brine and the CH2Cl2 layer was dried over an-
hydrous MgSO4. After filtration, the solvent was removed
under reduced pressure. The crude product was recrystallized
from C2H5OH to give TDMOPP as white needle-shaped crys-
tals in good yield (4.7 g, 71.9%) based on
1
4-bromo-1,2-dimethoxybenzene. H NMR (CDCl3): δ 3.75 (s,
9H, OCH3), 3.87 (s, 9H, OCH3), 6.78–6.88 (m, 9H, Ar); 31P
NMR (CDCl3): δ –4.48; MS: m/z 442 (M+).
The catalytic performance of the ligand TDMOPP was in-
vestigated using a 60 ml stainless steel autoclave equipped with
a magnetic stirrer. After being charged with the ligand, the
catalyst precursor Rh(acac)(CO)2, 1-dodecene, and toluene, the
reaction mixture was degassed three times with syngas. The
autoclave was then pressurized to the desired pressure with
syngas. The catalyst was formed in situ with the ligand
TDMOPP and Rh(acac)(CO)2. After stirring for 1 h at the
desired temperature, the autoclave was quickly cooled in an
ice-water bath to room temperature and carefully depressur-
ized. The hydroformylation products were analyzed using an
HP 1890II GC equipped with an FID and a capillary column
Table 1 Effect of molar ratio of phosphine to rhodium on 1-dodecene hydroformylation
Conversion of
Product distribution (%)
n(L)/n(Rh)
L/B
TOFd (h−1)
Aldehydea
99.0
Isomerizationb
Alkanec
0.6
1-dodecene (%)
0.0
2.5
5.0e
5.6
92.8
32.7
97.0
90.0
75.3
0.4
0.0
0.0
1.2
0.0
0.0
1.8
3.0
2.6
2.8
2.9
3.7
77
1276
450
100.0
100.0
98.4
0.0
0.0
5.0
0.4
1334
1238
1035
7.5
100.0
99.2
0.0
10.0
0.8
Reaction conditions: [Rh] = 1.0 × 10−3 mol/L, toluene 5.0 ml, 1-dodecene 2.0 ml, 70 °C, initial pressure 1.5 MPa (CO/H2 = 1), 1 h.
b
c
aSelectivity for aldehyde product of 1-dodecene. Selectivity for isomerization product of 1-dodecene, mainly 2-dodecene. Selectivity for hydrogenation
product of 1-dodecene. dMole of converted olefin per mole rhodium per hour. eTPP as ligand.