Hydroaminomethylation of styrene with morpholine catalysed by a rhodium complex with a phosphino amino alcohol ligand

Article abstract of DOI:10.1039/a904041b

Hydroaminomethylation of styrene with morpholine catalysed by a cationic rhodium complex with a P,N ligand possessing a hydroxy group and the influence of the temperature on the chemo- and regio-selectivity are described.

Full text of DOI:10.1039/a904041b

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630 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 630^631y
Hydroaminomethylation of Styrene with
Morpholine catalysed by a Rhodium Complex
with a Phosphino Amino Alcohol Ligandy
Ioannis D. Kostas*
National Hellenic Research Foundation, Institute of Organic and Pharmaceutical Chemistry, 48
Vas. Constantinou Ave., 116 35 Athens, Greece
Hydroaminomethylation of styrene with morpholine catalysed by a cationic rhodium complex with a P,N ligand
possessing a hydroxy group and the influence of the temperature on the chemo- and regio-selectivity are
described.
Hydroaminomethylation of alkenes, originally discovered
by Reppe and Vetter1 was ¢rst applied to styrenes by Rische
and Eilbracht2 using [Rh(cod)Cl]2 as catalyst and led with
high yields predominantly to the corresponding iso-amines.
The regioselectivity in the primary hydroformylation step
appears to be in£uenced by the amine used for the reaction.
Here a cationic rhodium complex 1 with a P,N ligand
possessing a hydroxy group is applied to hydroamino-
methylation of styrene with morpholine.
CHO
CHO
+
+
+
4
5
CO/H2
N
O
+
HN
O
1
6
2
3
N
O
OH
7
+
Rh
Me
N
–
BF4
PPh2
Scheme 1
1
styrene : catalyst ratio of 100 : 1 was necessary in order to
obtain up to quantitative conversions and yields of n-
and iso-amines.2 Thus, it is important to point out that
the catalytic activity of the rhodium complex 1 in the
hydroaminomethylation reaction is higher than that of
[Rh(cod)Cl]2, and it is reasonable to suppose that this is
due to the presence of the P,N ligand having an additional
alcohol function. The reaction is temperature dependent.
As shown in Table 1, at 60 8C with a styrene : 1 ratio of
509 : 1, the chemoselectivity towards the amines 6 and 7
was poor. A signi¢cant amount of aldehydes 4 and 5,
obtained in the primary hydroformylation step, did not
react further with morpholine. The regioselectivity towards
the total of iso-products 5 and 7 (86.8%) is slightly lower
than that obtained for the iso-aldehyde (89.4%), prepared
by hydroformylation of styrene by complex 1, at 60 8C.4
Thus it appears that the presence of the amine affects the
regioselectivity during the hydroformylation of styrene
catalysed by complex 1. At higher temperatures the
The increased catalytic activity of some complexes by the
use of P,N-bidentate ligands is well known.3 Rhodium
complex 1 for instance, the synthesis and characterization
of which were reported in a previous paper, showed such
activity in hydroformylation of styrene.4 The presence of
the uncoordinated hydroxy group lowers the rate of
hydroformylation with no in£uence on the regioselectivity
of the reaction.4 The hydroaminomethylation of styrene
with morpholine catalysed by complex 1 (Scheme 1, Table
1) proceeds to quantitative conversions of styrene and gives
high yields of the n-amine 6 and iso-amine 7 with a good
regioselectivity towards
7 and with no enamines as
by-products, under a pressure of 100 bar ꢀCO : H2 ˆ 1 : 1†
and with a high styrene:1 ratio of about 1500 : 1. On the
other hand, it has been reported that, when [Rh(cod)Cl]2
was used as catalyst for hydroaminomethylation of
1-alkenes under 110 bar total pressure of CO/H2,
a
Table 1 Hydroaminomethylation of styrene with morpholine catalysed by complex 1a
Aldehydes(%) Amines(%)
Styrene:1
Total iso/n
Entry
ratio
T/8C
t/h
4
5
6
7
Samb(%)
ratioc
1
2
3
509
1484
1500
60
80
100
39
24
24
2.0
3.2
1.1
38.1
ö
ö
11.2
11.3
13.3
48.7
85.5
85.6
59.9
96.8
98.9
6.6 : 1
5.9: 1
5.9: 1
aReaction conditions: solvent, 1,4-dioxane^THF (1: 1, entry 1; 5: 1, entries 2 and 3); initial total pressure of CO/H2 (1: 1) ˆ 100 bar.
b
Conversion of styrene (in all experiments): 100%. Sam ˆ selectivity towards amines. cRepresents the iso (aldehyde ‡ amine† : n
ꢀaldehyde ‡ amine† ratio.
* E-mail: ikostas@eie.gr.
chemoselectivity towards the amines 6 and 7 is high. Best
y This is a Short Paper as de¢ned in the Instructions for Authors,
results were obtained at 100 8C, yielding the corresponding
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is
amines, while only 1.1% of the aldehyde 4 was detected as
therefore no corresponding material in J. Chem. Research (M).

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J. CHEM. RESEARCH (S), 1999 631
by-product. However, the regioselectivity towards the total
iso-products 5 and 7, which is the same for both 80 and
100 8C, is slightly lower than that obtained at 60 8C.
The in£uence of the solvent plays an important role on
the course of the reaction. In 1,4-dioxane^dichloromethane
(1 : 1), polymerization and side reactions are predominant
and signi¢cant amounts of oligomers were detected, which
were not investigated further. An analogous polymerization
has also been reported during hydroaminomethylation of
1-octene in 1,2-dichloroethane as solvent.5;6
The investigation was supported by the National Hellenic
Research Foundation.
Received, 20th May 1999; Accepted, 12th July 1999
Paper E/9/04041B
References
1
2
3
W. Reppe and H. Vetter, Liebigs Ann. Chem., 1953, 582, 133.
T. Rische and P. Eilbracht, Synthesis, 1997, 1331.
P. Molina, A. Arques, A. Garc|a and M. C. Ram|rez de
Arellano, Eur. J. Inorg. Chem., 1998, 1359 and refs. therein.
I. D. Kostas and C. G. Screttas, J. Organomet. Chem., 1999,
585, 1.
T. Baig and P. Kalck, J. Chem. Soc., Chem. Commun., 1992,
1373.
T. Baig, J. Molinier and P. Kalck, J. Organomet. Chem., 1993,
455, 219.
Experimental
Styrene (1.7 ml, 14.84 mmol), morpholine (1.3 ml, 14.92 mmol) and
the rhodium complex 1 (0.01 mmol) in 1,4-dioxane^THF (30 ml, 5 : 1)
were placed under argon in an oven-dried autoclave, which was then
closed, pressurized with syngas (CO : H2 ˆ 1 : 1) to 100 bar and heated
at the required temperature. After the required reaction time the auto-
clave was cooled to room temperature, the pressure carefully released
and the solution passed through Celite and analysed by GC, GCMS
and 1H NMR. Conversions were determined by GC.
4
5
6