N-Pyrrolylphosphines as ligands for highly regioselective rhodium-catalyzed 1-butene hydroformylation: Effect of water on the reaction selectivity

Article abstract of DOI:10.1039/c7cy00200a

The hydroformylation of 1-butene catalyzed by Rh(acac)(CO)₂ with an excess of N-pyrrolylphosphine ligands, L = P(NC₄H₄)₃, PPh₂(NC₄H₄) or PPh(NC₄H₄)₂, was investigated under constant pressure of synthesis gas (4-10 bar, H₂/CO = 1) and 2 bar of 1-butene at temperatures ranging from 50 to 80 °C. N-Pyrrolylphosphine ligands facilitated excellent selectivity towards aldehydes and regioselectivity towards linear aldehydes. The application of a higher temperature, the presence of a small amount of water, and a [L]/[Rh] ratio of ca. 13 resulted in the achievement of the highest n/iso values in a short time. A further increase in selectivity was achieved after the addition of water to the reaction mixture. The catalytic performance of the studied systems showed an increase in selectivity (n/iso) with the increase of the number of pyrrolyl groups in phosphine: (P(NC₄H₄)₃ > PPh(NC₄H₄)₂ > PPh₂(NC₄H₄)) > PPh₃.

Full text of DOI:10.1039/c7cy00200a

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N-pyrrolylphosphines as ligands for highly regioselective rhodium-catalyzed 1-butene
hydroformylation. Effect of water on the reaction selectivity.
W. Alsalahia, R. Grzybekb, A.M. Trzeciaka*
a University of Wrocław, Faculty of Chemistry, 14 F. JoliotꢀCurie St., 50ꢀ383 Wrocław,
Poland
b Grupa Azoty, Zakłady Azotowe KędzierzynꢀKoźle S.A., Mostowa 30A, KędzierzynꢀKoźle,
Poland
Abstract
The hydroformylation of 1ꢀbutene catalyzed by Rh(acac)(CO)2 with an excess of Nꢀ
pyrrolylphosphine ligands, L = P(NC4H4)3, PPh2(NC4H4) or PPh(NC4H4)2, was investigated
under the constant pressure of the synthesis gas (4ꢀ10 bar, H2/CO = 1) and 2 bar of 1ꢀbutene
at temperatures ranging from 50 to 80 °C. Nꢀpyrrolylphosphine ligands facilitated excellent
selectivity towards aldehydes and regioselectivity towards linear aldehyde. The application of
a higher temperature, the presence of a small amount of water, and a [L]/[Rh] ratio of ca. 13
resulted in the achievement of the highest n/iso values in a short time. A further increase in
selectivity was achieved after the addition of water to the reaction mixture. The catalytic
performance of the studied systems showed an increase in selectivity (n/iso) with the increase
of the number of pyrrolyl groups in phosphine (P(NC4H4)3 > PPh(NC4H4)2 > PPh2(NC4H4)) >
PPh3.
1. Introduction
The olefin hydroformylation reaction (also known as the Oxo Synthesis or Roelen’s
Reaction) is the oldest, largest, and most important homogeneously catalyzed industrial
process for the production of aldehydes. This reaction was accidentally discovered by Otto
Roelen in 1938 at Ruhrchemie, Germany, while he was studying the cobaltꢀcatalyzed
Fischer–Tropsch reaction.
Today rhodium is a metal of choice in industrial installations which produce mainly C4
aldehydes by the conversion of propylene. To achieve a high yield and selectivity towards
aldehydes, the rhodium precursor should be modified by applying a ligand (preferably
phosphorus), in high excess with respect to the metal [1–9]. Several factors are used to
characterize the activity of the catalytic system, such as the turnover number (TON), turnover
frequency (TOF), yield, reaction rate, selectivity, and n/iso ratio [10].

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Nꢀvaleraldehyde, manufactured by the hydroformylation of 1ꢀbutene, is used as a
chemical building block in the production of amyl alcohol (nꢀpentanol) and valeric acid. It is
also employed as a flavoring, a fragrance additive, a rubber accelerator, and in resin
chemistry [11–12].
The catalytic system composed of Rh(acac)(CO)2 and an Nꢀpyrrolylphosphine ligand
exhibited high regioselectivity towards linear aldehydes in the hydroformylation of 1ꢀhexene
[9] and vinylsilanes [10]. The results were significantly better than when Rh(acac)(CO)2 was
applied with an excess of PPh3. During the reaction, rhodium hydrido complexes containing
pyrrolylphosphine ligands of the type HRh[PPhx(NC4H4)3−x 4
]
(x=0–2) and
HRh(CO)[PPhx(NC4H4)3−x]3 were identified as catalytically active species. These complexes
also exhibited good catalytic activity in the hydrogenation of olefins and arenes [13].
Jackstell et al. applied the same catalytic system in the hydroformylation of 2ꢀpentene
at a high pressure (50 bar) and 120 °C with an [L]/[Rh] ratio of 100. A good n/iso ratio was
also obtained at a low pressure of the syngas (10 bar) with a P(NC4H4) ligand [14]. Van
Leeuwen et al. demonstrated the high activity (TOF) and excellent selectivity of ethene
hydroformylation in the presence of P(NC4H4)3 [15]. Similarly, Luo et al. reported high
selectivity towards dialdehyde in the hydroformylation of dicyclopentadiene in the presence
of P(NC4H4)3 [16]. The same system used by Zheng et al. exhibited a high activity in the
hydroformylation of αꢀmethylstyrene and enhanced regioselectivity towards the linear
aldehyde (99%) with a high TOF (5786 hꢀ1) under mild conditions (syngas pressure of 6 MPa,
110 °C) [17]. In contrast, Breit used the P(NC4H4)3 phosphine for the hydroformylation of
styrene with low conversion and poor regioselectivity [18]. A good regioselectivity and high
activity has been achieved in rhodium catalyzed hydroformylation of 1ꢀoctene with bidentate
Nꢀpyrrolyl phosphine [19].
In this paper, we present the application of rhodium systems modified by Nꢀ
pyrrolylphosphines in the hydroformylation of 1ꢀbutene in toluene and in a tolueneꢀwater
mixture. These systems showed a high regioselectivity towards nꢀvaleraldehyde, in most
cases higher than with the use of PPh3.
2. Experimental
2.1. Materials
The rhodium complex Rh(acac)(CO)2 was synthesized according to the literature [20]. Nꢀ
pyrrolylphosphine ligands, P(NC4H4)3, PPh(NC4H4)2, and PPh2(NC4H4), were synthesized as
described in the literature [21]. Triphenylphosphine (PPh3) was purchased from Avocado; 1ꢀ

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butene was purchased from Air Liquide; hydrogen (H2, 99.999%) and carbon monoxide (CO,
99.97%) were procured from Air Products.
2.2. Synthesis of HRh(CO){P(NC4H4)3}3 and HRh{P(NC4H4)3}4
The synthesis of HRh(CO){P(NC4H4)3}3 and HRh{P(NC4H4)3}4 were performed in stainless
autoclave (50 ml) under pressure of syngas (H2/CO =1) and hydrogen respectively. In a
typical synthesis Rh(acac)(CO)2, P(NC4H4)3 and toluene were introduced into the autoclave
under nitrogen atmosphere (Table 1), the autoclave was closed and flushed with H2 (5 bar)
three times, and thereafter pressurized with the syngas (H2/CO =1) or hydrogen respectively,
heated to 80 °C and stirred for 1 h. After that time, the solvent was removed under vacuum
and ethanol was added to precipitate the white complex [9] which was filtered and dried. In a
case of HRh{P(NC4H4)3}4 [13], the product was filtered and dried.
Table 1. Synthesis of HRh(CO){P(NC4H4)3}3 and HRh{P(NC4H4)3}4 complexes a
Complex
Rh(acac)(CO)2 P(NC4H4)3
P, bar
Yield
10 bar of syngas
(H2/CO=1)
HRh(CO){P(NC4H4)3}3
HRh{P(NC4H4)3}4
0.078 g
0.054 g
0.24 g
0.25 g
0.18 g
5 bar of H2
0.085 g b
a
b
reaction condition: toluene as a solvent (3 ml), 80 oC,
1 h.
0.05 g of
HRh(CO){P(NC4H4)3}3 was also formed.
2.3. Hydroformylation of 1-butene
Hydroformylation reactions were carried out in 50 and 100 ml stainless steel autoclaves, each
provided with a manometer, a thermostat, a magnetic stirrer, and a gas inlet/outlet system.
The catalyst, Rh(acac)(CO)2 (1.5 × 10ꢀ5 mol), with a 13ꢀfold excess of PPh3, P(NC4H4)3,
PPh2(NC4H4), or PPh(NC4H4)2, was introduced into the autoclave. Next, 0.5 mL of toluene
(solvent) and 0.25 mL of cyclohexane (internal standard) were added under a dinitrogen
atmosphere. In the case of reactions carried out with water, 0.5–2 mL of distilled water was
added. The autoclave was closed, flushed with 1ꢀbutene (2 bar) two or three times, and
thereafter pressurized with 1ꢀbutene (2 bar) and then with the synthesis gas (H2:CO =1:1) to
10 bar and heated to 50–80 °C. After the reaction was finished, the autoclave was cooled to
room temperature and the residual gases were depressurized. The catalyst was separated by
vacuum transfer, and the obtained products were analyzed by means of GC and GCꢀMS
(Hewlett Packard).
3. Results and discussion
The hydroformylation of 1ꢀbutene catalyzed by four catalytic systems containing the catalyst
precursor Rh(acac)(CO)2 with a 13ꢀfold excess of Nꢀpyrrolylphosphine, P(NC4H4)3,

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PPh(NC4H4)2, PPh2(NC4H4), or triphenylphosphine PPh3, was first investigated in toluene.
Aldehydes were formed as the main reaction products, namely 1ꢀpentanal (linear aldehyde)
and 2ꢀmethylꢀbutanal (branched aldehyde) together with small amounts of 2ꢀbutene
(isomerization product) (Scheme 1).
Scheme 1. Hydroformylation of 1ꢀbutene
The results presented in Table 2 and on Fig. S1 illustrate the effect of temperature
increase from 50 °C to 80 °C on the hydroformylation of 1ꢀbutene catalyzed by the catalytic
system Rh(acac)(CO)2 + PPh2(NC4H4) with 2 bar of 1ꢀbutene and 10 bar of the synthesis gas
(H2/CO = 1). An increase in the yield of aldehydes was observed with an increase in
temperature. Thus, when temperature raised from 50 to 80 °C, the n/iso ratio increased from
8.2 to 11.2. The TOF values also increased.
Table 2. Effect of temperature on 1ꢀbutene hydroformylation in toluene
Conv.a %
aldehydes, mol
TOFb,
Entry
T, oC
n/iso
mol x molꢀ1 x
hꢀ1
1
2
3
4
80
70
60
50
95.0
94.6
92.7
45.5
0.010
0.011
0.010
0.003
11.2
10.2
8.3
667
733
667
200
8.2
Reaction condition: [Rh] = 1.5 x 10-5 mol, [L]/[Rh] = 13, L =PPh2(NC4H4), P1-Butene= 2 bar, P(H2:CO =
1:1) = 10 bar, toluene (0.5 mL), cyclohexane (0.25 mL), t = 1 h. a Conversion of 1-butene was
calculated according to GC-FID analyses of post-reaction mixture. b The TOF values were
calculated as moles of the aldehyde/([mol of catalyst] × reaction time).
Much better results, in particular a higher rate and higher selectivity, were obtained in
reactions performed with the addition of water to the reaction mixture. Thus, an increase of

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the water amount from 0.5 to 2 mL caused a remarkable increase in the n/iso ratio with a
maximum value of 16.2. However, the TOF decreased during the same time from 800 to
667 hꢀ1 (Table 3, Fig. S2). This is in agreement with our previous observation that
regioselectivity was higher in the presence of water in the reaction mixture [22–23].
However, in contrast to other olefins [22], the hydroformylation of 1ꢀbutene only in water
was not successful because aldehydes were not formed.
Table 3. Results of 1ꢀbutene hydroformylation in a toluene/water solution
Conv.a %
aldehydes, mol
TOFb,
mol x molꢀ
1 x hꢀ1
800
Entry
Water, mL
n/iso
1
2
3
4
0.5
1
92.7
94.0
93.0
94.7
0.012
0.010
0.012
0.010
12.9
16.2
15.9
15.4
667
1.5
2
800
667
Reaction condition: [Rh] = 1.5 x 10-5 mol, [L]/[Rh] = 13, L = PPh2(NC4H4), P1-Butene= 2 bar, P(H2:CO =
1:1) = 10 bar, toluene (0.5 mL), cyclohexane (0.25 mL), t = 1 h, T = 80 oC. a Conversion of 1-butene
was calculated according to GC-FID analyses of post-reaction mixture. b The TOF values
were calculated as moles of the aldehyde/([mol of catalyst] × reaction time).
The effect of time was also studied in the catalytic system Rh(acac)(CO)2 + PPh2(NC4H4) at
80 °C (Table 4). The results showed an increase in the yield of aldehydes with the
prolongation of the reaction time. However, simultaneously n/iso also increased from 14.5
after a short time (4 min) (Table 3, entry 1) to 19.1 and 19.7 after 6 and 8 min of reaction
time, respectively (Table 3, entries 2 and 3). Then, the n/iso ratio decreased to ca. 14 again.
Figure S3 displays the effect of time on the n/iso, pressure drop, and the yield of n and iso
aldehydes.
Table 4. Results of 1ꢀbutene hydroformylation in toluene
Conv.a%
aldehydes, mol
TOFb,
mol x molꢀ1
x hꢀ1
Entry
t, min
n/iso
1
2
4
6
38.0
53.9
0.003
0.005
14.5
19.1
3000
3333

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3
4
5
6
8
57.9
75.3
82.9
87.2
0.006
0.008
19.7
15.5
14.4
14.2
3000
3200
2800
2565
10
15
17
0.0105
0.0109
Reaction condition: [Rh] = 1.5 x 10-5mol, [L]/[Rh] = 13 L=PPh2(NC4H4), P1-Butene= 2 bar, P(H2:CO = 1:1)
= 10 bar, toluene (0.5 mL), cyclohexane (0.25 mL), T = 80 oC. a Conversion of 1-butene was
calculated according to GC-FID analyses of post-reaction mixture. b The TOF values were
calculated as moles of the aldehyde/([mol of catalyst] × reaction time).
The effect of the [PPh2(NC4H4)]/[Rh] ratio on the reaction course was studied in the range
from 2 to 13 at 80 °C at 10 bar. The results listed in Table 5 and on Fig. S4 show that, as the
[PPh2(NC4H4)]/[Rh] ratio increased from 2 to 13, the n/iso ratio increased from 2.1 to 11.2.
While selectivity increased parallel to the amount of the phosphorus ligand, the highest TOF
value was achieved at [L]/[Rh] = 6. A further increase in the PPh2(NC4H4) amount caused a
decrease of the TOF.
Table 5. Effect of the [L]/[Rh] ratio on 1ꢀbutene hydroformylation
Conv.a %
aldehydes, mol
TOFb,
mol x molꢀ1
x hꢀ1
Entry
[L]/[Rh]
n/iso
1
2
3
4
5
6
2
4
83.2
91.7
96.7
95.2
96.6
95.0
0.008
0.010
0.011
0.010
0.010
0.010
2.1
2.4
4.3
7.2
8.9
11.2
533
667
6
733
8
667
10
13
667
667
Reaction condition: [Rh] = 1.5 x 10-5mol, PPh2(NC4H4) as ligand, P1-Butene= 2 bar, P(H2:CO = 1:1) = 10
bar, toluene (0.5 mL), cyclohexane (0.25 mL), t= 1 h, T = 80 oC a Conversion of 1-butene was
calculated according to GC-FID analyses of post-reaction mixture. b The TOF values were
calculated as moles of the aldehyde/([mol of catalyst] × reaction time).
Applying optimized reaction conditions, we tested three other catalytic systems
composed of Rh(acac)(CO)2 and P(NC4H4)3, PPh(NC4H4)2 or PPh3 (Table 6). It should be
underlined that regioselectivity to nꢀpentanal was very high in both systems containing
P(NC4H4)3, PPh(NC4H4)2 ligands. An excellent conversion and lower regioselectivity were

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obtained by utilizing PPh3. On the other hand, a remarkable increase in the n/iso ratio was
achieved after addition of water to the reaction media. It is also worth noting that the n/iso
ratio increased with the increase of the number of pyrrolyl groups present in phosphine. It
means that the n/iso ratio decreased in the following order: P(NC4H4)3 > PPh(NC4H4)2 >
PPh2(NC4H4) > PPh3 (Scheme 2).
Table 6. Results of 1ꢀbutene hydroformylation using P(NC4H4)3, PPh(NC4H4)2 and PPh3 as
modifying ligands
L
Conv.b%
aldehydes, mol
TOFc, mol
x molꢀ1 x hꢀ1
467
Entry
n/iso
1
2a
3
80.2
85.8
88.0
88.5
96.8
94.5
0.007
0.0082
0.009
18.6
23.1
15.4
18.2
5.8
P(NC4H4)3
PPh(NC4H4)2
PPh3
547
600
4a
0.009
600
5
6a
0.0132
0.0129
880
7.9
860
Reaction condition: [Rh] = 1.5 x 10-5mol, [L]/[Rh] = 13, P1-Butene= 2 bar, P(H2:CO = 1:1) = 10 bar,
toluene (0.5 mL), cyclohexane (0.25 mL), t = 1 h, T = 80 oC. a water (0.5 mL), ), b Conversion of 1-
butene was calculated according to GC-FID analyses of post-reaction mixture. c The TOF
values were calculated as moles of the aldehyde/([mol of catalyst] × reaction time).
Scheme 2. The impact of the P ligand on the activity and the n/iso ratio
Fig. S5 shows an increase of hydroformylation selectivity achieved by addition of
water to the reaction mixture. The effect was noted for all studied phosphines, however it was
most pronounced for the best πꢀacceptor one, P(NC4H4)3.

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It should be noted that the yield of aldehydes increased with an increase in the
autoclave volume. It was demonstrated for the Rh(acac)(CO)2 + PPh3 system (Table 7). The
yields of aldehydes were 0.022 and 0.013 mol in reactions carried out using 100 and 50 mL
autoclaves, respectively, and 2 mL of toluene (Table 7). The n/iso ratio was, however, almost
the same.
Table 7. Hydroformylation of 1ꢀbutene using PPh3 as the ligand
Toluene,
aldehydes,
mol
Entry
Conv.c %
n/iso
TOFc, hꢀ1
mL
2
1a
2
97
95
0.022
3.6
3.8
733
867
2
0.013
Reaction condition: [Rh] = 1.5 x 10-5mol, PPh3 as ligand, [L]/[Rh] = 13, P1-Butene= 2 bar,
P(H2:CO = 1:1) = 10 bar, cyclohexane (0.25 mL), t = 1 h, T = 80 oC. aautoclave 100 mL, t = 2h. b
Conversion of 1-butene was calculated according to GC-FID analyses of post-reaction
mixture. c The TOF values were calculated as moles of the aldehyde/([mol of catalyst] × reaction
time).
Considering the fact that a higher yield of aldehydes could be obtained in a largerꢀ
volume autoclave, the effect of the total pressure of the syngas (H2:CO = 1:1) on the catalytic
activity and regioselectivity towards the linear aldehyde was studied using a 100 mL
autoclave. The results obtained at 4–10 bar and 80 °C for 2 h employing the catalytic systems
[Rh(acac)(CO)2/ P(NC4H4)3, PPh(NC4H4)2, or PPh2(NC4H4)] are shown in Table 8. Thus, the
pressure affected on the catalytic activity of the three systems and the amount of aldehydes
decreased when the pressure of the syngas decreased from 10 to 4 bar. The n/iso ratio
performed differently, greatly increasing with a pressure decrease from 10 to 6 bar and then
starting to decrease at 4 bar. As a result, the highest selectivity (n/iso) was achieved at 6 bar,
whereas for P(NC4H4)3 the maximum was reached at 8 bar. Addition of water caused a
significant increase of regioselectivity, and the n/iso ratio reached 50.9 at 6 bar using
P(NC4H4)3 (Table 8, entry 5). The positive effect of water was also evidenced for other
phosphines (Fig. 1).
Table 8. Effect of CO/H2 pressure on hydroformylation of 1ꢀbutene catalyzed by
Rh(acac)(CO)2 modified with different ligands.

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Conv.b %
aldehydes,
P, bar
TOFc,
mol x
molꢀ1 x hꢀ1
633
Entry
Ligand
n/iso
mol
1
2
3a
10
8
93.0
80.0
84.9
78.2
80.8
45.4
96.0
94.0
90.7
93.2
81.5
68.8
94.2
93.6
86.2
86.8
88.6
47.0
0.019
0.014
0.013
0.009
0.011
0.004
0.021
0.018
0.017
0.017
0.011
0.007
0.018
0.020
0.016
0.017
0.017
0.004
18.0
21.7
46.2
16.5
50.9
17.8
11.2
22.5
26.8
24.2
31.2
20.0
5.2
467
437
P(NC4H4)3
4
300
6
5a
6
367
4
133
7
10
700
8
600
8
6
9a
10
11a
12
13
14
15a
16
17a
18
567
PPh(NC4H4)2
563
367
4
233
10
600
8.2
667
8
PPh2(NC4H4)
14.8
13.3
17.9
7.3
533.3
567
6
4
567
133
Reaction condition: [Rh] = 1.5 x 10-5mol, [L]/[Rh] = 13, P1-Butene= 2 bar, P(H2:CO = 1:1), toluene (0.5
mL), cyclohexane (0.25 mL), t = 2h, T = 80 oC. a water (0.5 mL), b Conversion of 1-butene was
calculated according to GC-FID analyses of post-reaction mixture. c The TOF values were
calculated as moles of the aldehyde/([mol of catalyst] × reaction time).

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60
50
40
30
20
10
0
P(NC4H4)3
50.9
46.2
PPh(NC4H4)2
31.2
26.8
24.2
toluene
waterꢀ toluene
PPh2(NC4H4)
22.5
21.7
17.9
16.5
14.8
13.3
8.2
8
6
8
6
8
6
Pressure, bar
Fig. 1. Effect of water and pressure on 1ꢀbutene hydroformylation catalyzed by
Rh(acac)(CO)2 modified with different ligands at 80oC in 100 mL autoclave.
The 31P NMR spectra measured after the hydroformylation of 1ꢀbutene evidenced
rhodium species formed during the catalytic reaction. Catalytically active hydridoꢀcarbonyl
rhodium species [RhH(CO)L3] were formed in the reactions of Rh(acac)(CO)2 with an excess
of Nꢀpyrrolylphosphine ligands during hydroformylation. As shown in Table 9, the 31PꢀNMR
data of the reaction products are in agreement with those reported earlier [9, 13]
Table 9. 31P NMR (CDCl3) data for [RhH(CO)L3] complexes obtained in situ during 1ꢀbutene
hydroformylation catalyzed by Rh(acac)(CO)2
Complex
1H [J(PꢀH), J(RhꢀH)/Hz]
ꢀ8.9 [12.0, < 1]
31P [J(RhꢀP),Hz]
87.7 [168.8]
108.5 [187]
RhH(CO){PPh2(NC4H4)}3 [9]
RhH(CO){PPh(NC4H4)2}3
RhH(CO){P(NC4H4)3}3 [9]
ꢀ9.0 [9.3, 1.8]
ꢀ9.1 [7.8, 2.7]
108.6 [211.5]
The effect of water on hydrofomylation of 1ꢀbutene was also studied by utilizing
HRh(CO){P(NC4H4)3}3 and HRh{P(NC4H4)3}4 complexes as catalysts. In the absence of
added ligand, HRh(CO){P(NC4H4)3}3 exhibited high catalytic activity in both reaction media,
namely toluene and waterꢀ toluene mixture. Conversion and selectivity were almost the same
in both system, however n/iso ratio was slightly higher in waterꢀ toluene mixture (Table 10,

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DOI: 10.1039/C7CY00200A
entries 1 and 2). Addition of 3ꢀfold excess of P(NC4H4)3 ligand increased the n/ iso ratio to 4
and 4.8 respectively (Table 10, entries 3 and 4). The reaction rate and conversion decreased at
13ꢀfold excess of P(NC4H4)3 with significant increase of regioselectivity towards linear
aldehyde. Thus, n/iso ratio increased from 19.7 to 31.3 (Table 10, entries 5 and 6). The
unmodified HRh{P(NC4H4)3}4 catalyst also displayed higher n/iso ratio after addition of
water to the reaction (Table 10, entries 7 and 8).
Table10. The effect of water on hydroformylation of 1ꢀbutene catalyzed by
HRh(CO){P(NC4H4)3}3 and HRh{P(NC4H4)3}4
TOFb,
Water, aldehydes,
mol x
mol ꢀ1
x hꢀ1
860
Entry
Catalyst
[L]/[Rh] Conv.a%
n/iso
mL
mol
1
2
3
4
5
6
7
8
95.0
ꢀ
0.5
ꢀ
0.0129
0.012
1.7
1.9
4.0
4.8
0
96.5
800
95.5
0.0112
0.012
746.7
800
HRh(CO){P(NC4H4)3}3
HRh{P(NC4H4)3}4
3
96.0
0.5
ꢀ
83.3
0.0097
0.0096
0.0115
0.0123
19.7 646.7
13
84.5
0.5
ꢀ
31.3
2.5
640
766.7
820
94.0
0
90.0
0.5
3.0
Reaction condition: [Rh] = 1.5 x 10-5mol, L= P(NC4H4)3, P1-Butene= 2 bar, P(H2:CO = 1:1) = 10 bar,
toluene (0.5 mL), cyclohexane (0.25 mL), t = 1h, T = 80 oC. ), a Conversion of 1-butene was
calculated according to GC-FID analyses of post-reaction mixture. b The TOF values were
calculated as moles of the aldehyde/([mol of catalyst] × reaction time).
Conclusions
The hydroformylation of 1ꢀbutene catalyzed by Rh(acac)(CO)2 with an excess of Nꢀ
pyrrolylphosphine and PPh3 ligands at 50–80 °C and 4–10 bar of syngas (H2:CO = 1:1) in
toluene and in a toluene/water mixture was investigated. Hydridoꢀcarbonyl rhodium species
were formed in situ during the hydroformylation. Regioselectivity towards the linear
aldehyde increased with the increase of the number of the pyrrolyl groups in phosphine
ligands. At the same time, the reaction rate decreased in the same order. Thus, better πꢀ
acceptor properties of the ligand promote the increase of the n/iso ratio.

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Regioselectivity is highly dependent on the reaction conditions, such as temperature
or the [L]/[Rh] molar ratio. In addition, remarkably high regioselectivity towards the linear
aldehyde was noted in a shorter reaction time or at a lower syngas pressure.
Interestingly, a similar effect, namely a selectivity increase, was also observed after
the introduction of water to the reaction mixture. Moreover, an increase in the n/iso ratio was
in this case dependent on the kind of phosphine used. It can be, therefore, assumed that water
interacted with the hydridoꢀolefin rhodium intermediate facilitating the formation of the
linear alkyl complex in the migratory insertion step. The effect of water on the increase of the
n/iso ratio was most clearly pronounced for the P(NC4H4)3 ligand, suggesting an important
role of N atoms in the formation of hydrogen bondings. Such interaction caused the decrease
of electron density on the rhodium center, which is then reflected in the migratory insertion
step (Scheme 3) leading to antiꢀMarcovnikov (linear) product. In summary, we suppose that
selectivity of hydroformylation increased because
πꢀacceptor properties of Pꢀligands were
further enhanced by interaction with water molecules.
However, interaction of water with hydride ligand or with coordinated olefin could be
also considered. Water can also facilitate formation of rhodium hydride, which is catalytically
active. It is possible that water enhance the hydride transfer step [24].
According to the well accepted scheme of hydroformylation, based on theoretical calculations
published till now, insertion step is determining for hydroformylation regioselectivity [25ꢀ
28]. Thus, stabilization of transition state leading to the linear Rhꢀalkyl intermediate results in
increase of linear aldehyde amount and, consequently, in higher n/iso ratio. This is observed
in the presence of water in our system. It could be therefore proposed that nonbonding
interactions of water molecules with phosphines, olefin and hydride ligand present in
coordination sphere of rhodium, decrease activation energy of the transition state leading to
the linear Rhꢀalkyl intermediate. In this way, the reaction pathway that leads to the linear
aldehyde in favored. This hypothesis, based on experimental results, should be verified by
theoretical calculations which are in progress.

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DOI: 10.1039/C7CY00200A
H
R
O
HC
R
CH2
CH
O
P
CHCH2CH3
CH3
R
Rh
HC CH2CH2CH2CH3
R
P
R
R
CH2CH3
CO
H2/CO
CH3
H2/CO
R
R
R
CHCH2CH3
P
R
R
Rh
P
CH2CH2CH2CH3
CO
R
CO
P
R
Rh
R
R
R
R
P
R
Scheme 3. The tentative illustration of the effect of water on hydroformylation selectivity
Acknowledgements
This work was done within the coꢀoperation between Grupa Azoty Zaklady Azotowe Kedzierzyn S.A.
and Faculty of Chemistry, University of Wroclaw with the financial support from Polish Ministry of
Development under the grant POIR.02.01.00ꢀ00ꢀ0074/15ꢀ01.
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DOI: 10.1039/C7CY00200A
H
R
R
R
O
HC
R
CH2
CH
P
P
CH2CH2R
CO
R
CH2CH2R
R
Rh
Rh
R
R
R
P
R
P
R
R
CO
R
O
HC
CHR
CH3
Addition of water to the hydroformylation of 1-butene resulted in an increase of n/iso up to 50.