Stibines Modified Rh-Catalyzed Hydroformylation
J. Chin. Chem. Soc., Vol. 54, No. 3, 2007 683
yellow solution was analyzed using GC and GC-MS. In the
case of reactions at different time intervals, several experi-
ments in the same conditions were performed.
Rh/TFS catalytic system. It is to be mentioned here that
these experimental conditions do not give reduction prod-
ucts.
Runs 29 to 31 shows that Rh/TDMBAS, in a ratio 1/1,
2
is an active catalytic system even at 1:3 CO/H pressure ra-
RESULTS AND DISCUSSION
tio and produces an appreciable yield of aldehyde in less
time. This study also confirms that a Rh/TDMBAS cata-
From runs 1 to 9, it was observed that Rh/TDMBAS
in a 1:2 ratio produces a catalytic system which is very ac-
tive and is independent of synthesis gas partial pressures. It
also produces higher selectivity in comparison to the other
two systems. The catalytic system Rh/TMS is more active
and selective in comparison to the Rh/TFS system. The last
system exhibits very good activity depending on CO and
lytic system is independent of CO/H
On comparing the catalytic precursors viz. RhClCO-
, RhClCO(PPh + TMS, RhClCO(PPh + TFS,
RhClCO(PPh + TDMBAS, it was observed that ligand
2
partial pressures.
(PPh
3
)
2
3
)
2
3 2
)
3 2
)
effect on the catalytic activity of the system shows a (2-
N,N-dimethylbenzylamine)stibine > (2,4,6-mesityl)stibine
> (2-furyl)stibine pattern which indicates that not only ba-
sicity of the ligand alone is playing role in the activity but
steric effect is also very important and it is a combination of
these two factors which explain the resulting catalytic ac-
2
H partial pressures. It is to be mentioned that none of the
catalytic systems favors the hydrogenation reaction, and
formation of pentane is less than 2%.
6
,7
Runs 10 to 16 show the variation of aldehydes yield
as a time function at different partial pressures using
Rh/TMS as catalytic system. The highest yield of alde-
tivity. It was concluded that the better acceptor character
of stibines is responsible for its important trans effect and
in the homogeneously catalyzed hydroformylation pro-
6
-8
12,13
hydes was obtained at a partial pressure ratio of CO/H
Run 14 shows that without the stibine ligand, the aldehyde
yield is lower. It was also observed that though H partial
2
1:1.
cess. The trans effect
of these stibine ligands may be
responsible for the enhancement of exchange of ligands.
2
pressure is higher, the system does not favour the formation
of pentane.
Received May 15, 2006.
In runs 17 to 20, on comparing the conversions in run
3
, it was observed that there is a decrease in the product
conversion with the increase of temperature. This indicates
REFERENCES
that reaction favours 120 °C, and at a higher temperature of
1
50 °C probably uncoordination of the stibine ligand favors
1. Sellin, M. F.; Bach, I.; Webster, J. M.; Montilla, F.; Rosa, V.;
Aviles, T.; Poliakoff, M.; Cole-Hamilton, D. J. J. Chem. Soc.
Dalton Trans. 2002, 4569.
producing an inactivated species in the Rh/TMS system.
On comparing run 4 with runs 23 to 25 it was ob-
served that the optimum ligand/catalyst TFS/Rh ratio is 2/1
and gives higher yields with high selectivity for linear alde-
hydes. An increase in ligand/catalyst ratio produces a less
active catalytic species than without the modified catalyst.
Reactions 1 and 7 show that Rh/TMS and Rh/TDMBAS
catalytic systems are less active under these conditions, al-
though these appear more selective toward the linear alde-
hyde.
2
. Yonker, C. R.; Linehan, J. C. J. Organomet. Chem. 2002,
50, 249.
6
3
. Beller, M.; Cornill, B.; Frohning, C. D.; Kohlpainter, C. W.
J. Mol. Catal. (A): Chem. 1995, 17104.
4
5
. Carlock, J. T. Tetrahedron 1984, 40, 185.
. Liu, Y. H.; Liu, X. L.; Lei, X. Y.; Liu, L.; Wang, Y. P.
Yingyong Huaxue 2001, 18(2), 146.
6
7
. Sharma, P.; Cabrera, A.; Lagadec, R.; Manzo, R. L.; Arias, J.
L.; Sharma, M. Main Group Met. Chem. 1995, 22, 95.
. Cabrera, A.; Sharma, P.; Arias, J. L.; Perez, J. F.; Velasco, L.;
Gomez, R. M. J. Mol. Catal. (A): Chem. 2001, 170, 271.
Runs 26 and 27 shows that the reaction does not pro-
ceed practically < 100 °C using the Rh/TFS catalytic sys-
tem. The formation of aldehyde increases notably at 120
8. Cabrera, A.; Sharma, P.; Arias, J. L.; Perez, J. F.; Velasco, L.;
Gomez, R. M. J. Mol. Catal. (A): Chem. 2004, 212, 19.
9. Breunig, H. J.; Ates, M.; Soltani, Nashen A. Organomet.
Synth. 1988, 4, 593.
°
C. Reaction carried out without the ligand exhibits less
conversion with low selectivity toward linear aldehyde in
comparison to run 4. This comparison indicates that cata-
10. Vela, J.; Sharma, P.; Cabrera, A.; Alvarez, C.; Rosas, N.;
3 2
lytic precursor RhClCO(PPh ) is less active than the
Sharma, Pankaj
