Rhodium(I) complexes with 1′-(diphenylphosphino)ferrocenecarboxylic acid as active and recyclable catalysts for 1-hexene hydroformylation

Article abstract of DOI:10.1016/j.jorganchem.2005.02.053

The rhodium complex trans-[Rh(CO)(Hdpf-κP)(dpf-κ²O, P)] (1), (Hdpf = 1′-(diphenylphosphino)ferrocenecarboxylic acid) was used as an efficient and recyclable catalyst for 1-hexene hydroformylation producing ca. 80% of aldehydes at 10 atm CO/H

Full text of DOI:10.1016/j.jorganchem.2005.02.053

Journal of Organometallic Chemistry 690 (2005) 3260–3267
www.elsevier.com/locate/jorganchem
Rhodium(I) complexes with
10-(diphenylphosphino)ferrocenecarboxylic acid as active
and recyclable catalysts for 1-hexene hydroformylation
a,
Anna M. Trzeciak , Petr Stepnicka , Ewa Mieczynska , Jozef J. Ziołkowski
b,
a
a
ˇ
*
*
ˇ
ˇ
´
´
´
a
Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie Street, 50 383 Wroclaw, Poland
Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 40 Prague, Czech Republic
b
Received 2 November 2004; revised 28 February 2005; accepted 28 February 2005
Available online 23 May 2005
Abstract
The rhodium complex trans-[Rh(CO)(Hdpf-jP)(dpf-j2O,P)] (1), (Hdpf = 10-(diphenylphosphino)ferrocenecarboxylic acid) was
used as an efficient and recyclable catalyst for 1-hexene hydroformylation producing ca. 80% of aldehydes at 10 atm CO/H2 and
80 ꢀC. After the reaction, unchanged complex 1 was separated from the reaction mixture and used again three times with the same
catalytic activity. The effect of modifying ligands, phosphines and phosphites, on the reactivity of 1 was investigated. The active
catalytic systems containing 1 or trans-[Rh(CO)(L)(dpf-j2O,P)] (2) were formed in situ from acetylacetonato rhodium(I) precursors
[Rh(CO)2(acac)] (3) or [RhL(CO)(acac)] (4) and Hdpf or Medpf (L = phosphine, Medpf = methyl ester of Hdpf).
ꢁ 2005 Elsevier B.V. All rights reserved.
Keywords: Rhodium; Hydroformylation; Ferrocenyl ligands; Recyclable catalyst
1. Introduction
reoelectronic properties of the substituents at the
ferrocene unit (Y in Scheme 1) or the substituents on
the phenyl ring [2].
Ferrocene-based donors and their catalytic properties
have attracted considerable attention ever since the dis-
covery of ferrocene in the early 1950s. Until now,
numerous ferrocene phosphines have been synthesized
and used in various reactions as catalyst components [1].
As far as hydroformylation reactions are concerned,
rhodium(I) and platinum(II) complexes involving ferro-
cene phosphines (I and II, Scheme 1, Y = P(OPh)2),
including chiral ones, have been tested in hydroformyla-
tion of styrene, 1-octene, 1-hexene, and cyclohexene [2].
It has been found that regioselectivity of the hydro-
formylation reactions can be changed by varying the ste-
Novelty of the ligand used in the present study, 10-
(diphenylphosphino)ferrocenecarboxylic acid (Hdpf,
Scheme 1), results from its bifunctional, ‘‘hybrid’’ nat-
ure, which enables it to coordinate to a transition metal
either via the phosphorus atom (as a neutral ligand) [3]
or via one or more of the oxygen atoms of the carboxylic
group (as a carboxylate ligand) [4]. Combined donor
mode, bidentate chelating coordination of the 10-(diph-
enylphosphino)ferrocenecarboxylate anion (dpfꢀ) was
observed in a rhodium(I) complex featuring two forms
of the Hdpf ligand, acid and carboxylate, trans-
[Rh(CO)(Hdpf-jP)(dpf-j2O,P)] (1), and in the related
compounds trans-[Rh(CO)(L)(dpf-j2O,P)] (2), where L
is a monodentate phosphine (L = PPh3 (a), PCy3 (b),
FcPPh2 (c); Cy = cyclohexyl, Fc = ferrocenyl). These
complexes are readily accessible by acid-base reactions
*
Corresponding authors. Tel.: +48 71 3757 253; fax: +48 71 3757
356 (A.M. Trzeciak).
E-mail addresses: ania@wchuwr.chem.uni.wroc.pl (A.M. Trzeciak),
ˇ
stepnic@natur.cuni.cz (P. Stepnicka).
ˇ
ˇ
0022-328X/$ - see front matter ꢁ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.02.053

A.M. Trzeciak et al. / Journal of Organometallic Chemistry 690 (2005) 3260–3267
3261
System A
PPh
PPh
Y
PPh
2
2
2
ð1Þ or ð2aÞ or ð2bÞ
1-hexene
ðn þ isoÞaldehydes
ðn þ isoÞaldehydes
ƒƒƒƒƒƒƒƒƒƒ!
Fe
I
Fe
II
Fe
System B
ð3Þ or ð4aÞ or ð4cÞ
ƒƒƒƒƒƒƒƒƒƒ!
þHdpf or Medpf
PPh
CO R
2
2
1-hexene
Hdpf (R = H)
Medpf (R = Me)
Scheme 1.
2. Results and discussion
of Hdpf with [Rh(CO)2(acac)] (3) and the respective
[RhL(CO)(acac)] (4) precursors (Hacac = pentane-2,5-
dione, L = phosphine) [5].
2.1. Catalytic activity of the trans-[Rh(CO)(Hdpf-jP)
(dpf-j2O,P)(CO)] (1) precursor in hydroformylation of
1-hexene (system A)
Since these complexes are analogues of the archetypal
hydroformylation catalysts, we decided to test them in
hydroformylation reactions and to study the behavior
of the Hdpf ligand under the hydroformylation condi-
tions. Our interest in the influence of the carboxyphos-
phine was prompted by earlier findings that proton
donor ligands negatively impact on the rate of hydro-
formylation reactions [6,7]. The inhibiting effect of car-
boxylic acids on the catalytic activity of the catalyst
precursor [RhH(CO)(PPh3)3] (5) [8] has been explained
by an interaction between a catalytically active rhodium
hydrido complex and the proton of carboxylic acid (Eq.
(1)), leading to the formation of dihydrogen and deacti-
vation of the catalysts [6].
From the very start, tests showed that rhodium(I)
complexes containing the O,P-chelating anion dpfꢀ,
trans-[Rh(CO)(Hdpf-jP)(dpf-j2O,P)(CO)] (1), trans-
[Rh(CO)(PPh3)(dpf-j2O,P)(CO)] (2a), and trans-[Rh-
(CO)(PCy3)(dpf-j2O,P)(CO)] (2b) (Scheme 3), are good
hydroformylation catalysts producing 84–91% of
(n + iso) aldehydes even without added modifying li-
gands (Table 1). The n/iso ratios are 2.4–2.5 for com-
plexes 1 and 2a, whereas complex 2b exhibits a lower
n/iso ratio, 1.6, like other catalytic systems involving
PCy3 [9]. On the other hand, very low catalytic activities
were observed for complexes with halogen ligands and
P-monodentate Hdpf, trans-[RhCl(CO)(Hdpf-jP)2
(CO)] (6a) and trans-[RhBr(CO)(Hdpf-jP)2(CO)] (6b)
(Scheme 3) [5]. These complexes hardly catalyze hydro-
formylation at all (only ca. 1% aldehydes) and show
insignificant activity in hexene isomerization, producing
4–10% of 2-hexene after 5 h.
½RhHðCOÞðPPh3Þ ꢁ þ RCO2H
3
! ½RhðRCO2ÞðCOÞðPPh3Þ ꢁ þ PPh3 þ H2
ð1Þ
2
A significant retardation of hydroformylation reac-
tion has also been reported for (2-hydroxyphenyl)diphe-
nylphosphine, which coordinates to rhodium(I) as an
O,P-chelating ligand [7]. The catalytic process is ham-
pered by the high stability of the O,P-chelate ring, which
does not permit the formation of an active catalyst from
the precursor complex [Rh(CO)(2-HOC6H4PPh2-jP)(2-
OC6H4PPh2-j2O,P)]. Likewise, the inhibiting effect of
(2-hydroxyphenyl)diphenylphosphine in reactions cata-
lyzed with hydridorhodium precursors [RhH(CO)L3]
(L = PPh3 (5) and P(OPh)3) can be most likely attrib-
uted to the formation of stable phosphinophenolate
complexes (Scheme 2).
In this paper, we report on our studies of the catalytic
properties of rhodium(I) complexes with coordinated
Hdpf-type ligands (system A) in the model hydroformy-
lation reaction of 1-hexene and on the behavior of Hdpf
as a co-catalyst with acetylacetonato rhodium(I) com-
plexes (system B).
Ph
Ph
CO
Ph
P
C
Rh
Fe
P
O
Ph
Fe
HO
O
C
O
1
Ph
Ph
Ph
Ph
P
CO
CO
P
C
Rh
Ph
CO H
Rh
X
P
Fe
Fe
PR
3
Ph
O
Fe
2
L
HO C
O
OC
O
L
2
[RhH(CO)L ] + (2-HOC H )PPh
6 4
Rh
+ H + L
3
2
2
PR
PPh
PCy
3
Medpf
3
3
6a (X = Cl)
6b (X = Br)
PPh
2
2a
2b
2c
L = PPh3 or P(OPh)3
Scheme 2.
Scheme 3.

3262
A.M. Trzeciak et al. / Journal of Organometallic Chemistry 690 (2005) 3260–3267
Table 1
Hydroformylation of 1-hexene catalyzed by Rh(I)-Hdpf complexes trans-[Rh(CO)(Hdpf-jP)(dpf-j2O,P)] (1), trans-[Rh(CO)(PPh3)(dpf-j2O,P)] (2a),
trans-[Rh(CO)(PCy3)(dpf-j2O,P)] (2b), trans-[RhCl(CO)(Hdpf-jP)2] (6a), and trans-[RhBr(CO)(Hdpf-jP)2] (6b) (system A)
Catalyst precursor
Co-catalyst
Aldehydes (n + iso) (%)
2-Hexene (%)
1-Hexene (%)
n/iso
1a,c
1a,b
1
None
None
82
76
84
4
17
23
15
21
2
–
1.8
1.9
2.5
1.3
2.6
2.4
4.6
4
1
None
Hdpf
1
1
75
59
47
–
1
Medpf
PPh3
39
21
81
88
79
68
63
88
77
82
41
89
91
87
1
1
32
20
12
21
6
1
P(OPh)3
P(OC6H4-3-CH3)3
P(OCH2CF3)3
P(C6H4-4-OCH3)3
PPh2(C6H4-2-OCH3)
PCy3
1
–
1
–
3
1
26
23
–
2.6
2.7
2.4
2.8
2.4
2.4
2.4
1.6
1.6
–
1
14
12
23
18
7
1
1
P(NC4H4)3
PPh(C6F5)2
PPh2(C6F5)
None
–
1
–
1
52
–
2a
2b
2ba
6aa,c
6ba,c
11
8
None
None
1
12
11
4
1
None
None
88
96
–
–
General reaction conditions: [Rh] = 7.5 lmol, [1-hexene] = 0.012 mol in toluene (1.5 ml), 80 ꢀC, 2 h, 10 atm CO/H2 (CO:H2 = 1).
a
[Rh] = 15 lmol
Reaction time 3 h.
Reaction time 5 h.
b
c
2.2. Testing of various modifying ligands
two double doublets at dP 14.4 and 110.0 ppm due to
Rh-bonded dpfꢀ and P(OPh)3, respectively. The high
2
value of the JPP coupling constant (564 Hz) points to
In most of the catalytic systems applied in hydro-
formylation, an excess of free phosphorus ligand is used,
due to its beneficial effect on both the reaction rate and
reaction selectivity [10]. Therefore, for further evalua-
tion of the catalytic properties of catalysts based on
complex 1, we selected several phosphines (PR3) and
phosphites (P(OR)3) with different steric and electronic
properties and used them as modifying ligands ([PR3/
P(OR)3]:[Rh] = 1). The results are summarized in Table
1. At first sight, the most attractive ligands for 1 are tri-
phenyl phosphites, which increased the n/iso hydro-
formylation selectivity ratio to 4.6 (P(OPh)3) and 4.0
(P(OC6H4CH3-4)3) at a total yield of aldehydes amount-
ing to 81% and 88%, respectively. A lower increase in
the n/iso ratio, to ca. 3, and similar levels of activity
(77–79% yields of aldehydes) were achieved with
P(NC4H4)3 (NC4H4 = 1-pyrrolyl) and P(OCH2CF3)3.
The obtained results confirmed earlier observations for
many catalytic systems that an increase in hydroformy-
lation reaction selectivity towards a higher n/iso ratio is
caused by p-acceptor phosphorus ligands [10].
the trans arrangement of the P-donors (Scheme 4). This
is surprising because a more basic ligand, Hdpf, was
substituted by a less basic one, P(OPh)3; however, we
had already found a similar substitution in our previous
studies [7]. The observed effect may be explained not
only by electronic but also by steric influence of ligands.
In contrast to phosphites, phosphines, which are
stronger r-donors, inhibited the catalytic activity of
complex 1, decreasing the yield of aldehydes (Table 1).
The strongest inhibiting effect was observed for Hdpf
(phosphine), which, when used together with 1, de-
creased the yield of aldehydes to just 4%. At the same
time, the presence of Hdpf not only did not prevent
the isomerization of 1-hexene to 2-hexene but even
slightly increased its rate compared to 1 alone. The in-
crease in the yield of the isomerization reaction with
the concurrent decrease in the yield of aldehydes was
Ph
Ph
CO
It is generally assumed that modification of the prop-
erties of catalysts with added ligands is usually accom-
plished by means of their coordination to the metal.
This step was confirmed for 1 and P(OPh)3. In reaction
of 1 with P(OPh)3 at 60 ꢀC in C6D6, the complex
[Rh(CO)(P(OPh)3)(dpf-jP)] 2d was identified in the
31P NMR spectra, showing a characteristic pattern of
P
C
Rh
+ Hdpf
1 + P(OPh)
Fe
3
P(OPh)
3
O
O
Scheme 4.

A.M. Trzeciak et al. / Journal of Organometallic Chemistry 690 (2005) 3260–3267
3263
also observed with PPh3. Meanwhile, Medpf showed a
different behavior, decreasing the yields of both
reactions. Of the phosphines tested, only PCy3 did not
decrease the yield of aldehydes. Instead, a slight promot-
ing effect was observed (88% yield of aldehydes), which
is in agreement with the high activity of 2b (Table 1).
complex 3 gives a catalytic system producing 82% of
aldehydes (n/iso = 2.1) and 18% of 2-hexene.
The effect of free Hdpf and Medpf is distinctly posi-
tive when combined with Rh(I) acetylacetonato com-
plexes, [Rh(CO)(PPh3)(acac)] (4a) or [Rh(CO)(Medpf)
(acac)] (4c). Addition of Hdpf results in the replacement
of the acacꢀ ligand (O,O) to give the O,P-chelated com-
plexes 2a and trans-[Rh(CO)(Medpf-jP)(dpf-j2O,P)]
(2c) (Scheme 5). As a result, the catalytic activity of
the 4a/Hdpf system is nearly the same as the activity
of 2a alone.
2.3. Catalytic activity of Rh(I) acetylacetonato
precursors (3, 4a, 4c) and [RhH(CO)(PPh3)3] (5)
modified with Hdpf or Medpf in 1-hexene
hydroformylation (system B)
Addition of Hdpf phosphine also has a positive effect
on reactions catalyzed with [RhH(CO)(PPh3)3] (5), lead-
ing to a higher yield and selectivity towards the n-alde-
hyde. The reaction between 5 and Hdpf performed
separately produced a mixture of rhodium complexes
of which none was identified as a rhodium-hydride.
Instead, using NMR and MS techniques, two com-
plexes, 1 and 2a, were identified in the reaction mixture
(Eq. (2)).
Relatively active catalytic systems were obtained with
[Rh(CO)2(acac)] (3) as the catalyst precursor and Hdpf
or Medpf (Table 2). The effect of Hdpf is observed al-
ready at the ratio [3]:[Hdpf] = 1:1, at which 61% yield
of aldehydes was obtained, while only 20% yield of alde-
hydes was obtained with 3 without the added phosphine
ligand. The high contribution of the isomerization reac-
tions (39% of 2-hexene) can be accounted for by the
presence of unreacted complex 3, which is known to
be a very active isomerization catalyst [11]. This obser-
vation is in accordance with the fact that Hdpf reacts
with 3 to give 1 regardless of the ratio of the educts
[5]. Thus, under the initial reaction conditions, the pre-
catalyst mixture contains equimolar amounts of 1 and
3. An increase in Hdpf concentration relative to 3
caused an increase in the yield of aldehydes. However,
at higher Hdpf concentrations (four equivalents and
more), the reaction rate and conversion decreased.
Addition of the ester Medpf, which, unlike the parent
acid, cannot displace the acac ligand, to the precursor
5 þ Hdpf ! 1 þ 2a þ PPh3 þ ꢂ ꢂ ꢂ
ð2Þ
In view of these results, we can attribute the inhibit-
ing effect of free Hdpf as observed in hydroformylation
reactions with 1 and 3 as precatalysts (see above) to the
decomposition of the rhodium-hydride complex in a
way similar to that shown in Eq. (1).
2.4. Spectroscopic identification of catalytically active
rhodium complexes
IR analysis of post-reaction mixtures after hydro-
formylation catalyzed with complex 1 revealed new
m(CO) bands at 2065, 2047, and 1817 cmꢀ1, which could
be attributed to a new complexes 7 and 8, formed under
the hydroformylation reaction conditions (Table 3,
Scheme 6). The complexity of the IR spectra suggests
coexistence of complexes 1, 7, and 8, and the presence
of isomers of 7 (trigonal bypiramide and square planar
pyramide) cannot be ruled out either. Unfortunately,
the concentration of this new species was too low to re-
cord its NMR spectra. Only a doublet at dP 19.5
(1JRhP = 135 Hz) characteristic for 1 was observed. Mea-
surements taken after 25 and 50 min of the reaction
course showed gradual formation of the new compound.
Table 2
Hydroformylation of 1-hexene catalyzed with catalyst precursors
[Rh(CO)2(acac)] (3), [Rh(CO)(PPh3)(acac)] (4a), [Rh(CO)(Medpf-
jP)(acac)] (4c) and [RhH(CO)(PPh3)3] (5) and Hdpf/Medpf modifying
ligands (system B)
Catalyst
Added
Aldehydes
precursor phosphine (n + iso) (%) (%)
2-Hexene 1-Hexene n/iso
(%)
3
1 Hdpf
2 Hdpf
2 Hdpfa
4 Hdpf
6 Hdpf
1 Medpf
2 Medpf
–
61
78
83
69
61
55
82
67
90
65
89
89
88
93
97
39
20
17
4
–
2.5
2.3
2
3
2
3
–
3
26
36
2
2.6
2.7
2.6
2.1
2.4
2.5
2.3
2.2
2.3
2.3
2.8
3.1
3
3
3
43
18
33
10
9
3
–
4a
4a
4c
4c
4c
5
–
Ph
Ph
CO
1 Hdpf
–
–
P
26
–
Rh
1 Hdpf
1 Medpf
–
11
11
12
7
[RhL(CO)(acac)] + Hdpf
+ Hacac
Fe
L
–
O
4a (L = PPh3)
4c (L = Medpf)
–
C
5
1 Hdpf
2 Hdpf
–
O
5
3
–
2a (L = PPh )
3
Reaction conditions: [Rh] = 7.5 lmol, [1-hexene] = 0.012 mol, toluene
1.5 ml, 80 ꢀC, 2 h, 10 atm CO/H2 (CO:H2 = 1).
2c (L = Medpf)
a
[Rh] = 15 lmol.
Scheme 5.

3264
A.M. Trzeciak et al. / Journal of Organometallic Chemistry 690 (2005) 3260–3267
Table 3
likely because a new compound, probably a rhodium-
hydrido-carbonyl complex such as 7, was formed. The
presence of a m(CO) band at ca. 1800 cmꢀ1 in most of
the measured spectra, indicative of bridging CO ligands,
made it possible to propose an equilibrium between
the rhodium(I) hydrido-carbonyl complex and the
rhodium(0) carbonyl one, 8 (Scheme 6). Complex 8
was present already in the reaction mixture or, more
likely, was formed during evaporation of the solvent
in the process of the preparation of samples for IR
measurements.
IR studies of the post-reaction mixtures involving 1
as the catalyst precursor (Table 3) and different modify-
ing ligands allowed us to observe both the formed
hydrido-carbonyl rhodium complex 7 and unchanged
1. The IR data (Table 3) indicate the presence of a pro-
tonated carboxylic group [5] with vibration at ca.
1700 cmꢀ1 in the spectra of all post-reaction mixtures.
The bands observed in the region 1600–1400 cmꢀ1 are
characteristic of a chelating carboxylic group. The car-
IR data (in KBr) in the region 2200–1500 cmꢀ1 of the post-reaction
mixtures involving pre-catalyst 1 (after 2 h of hydroformylation unless
noted otherwise)
Catalytic system
IR (m/cmꢀ1
)
1a
1979vs, 1706sc, 1562s, 1466s, 1435m
2071w, 2042w, 1979vs, 1709w, 1624m, 1564s
Solid: 1979vs, 1706m
1b
1 after 25 min
Reaction solution: 2065m, 1982m, 1820vw,
1709vs, 1650m, 1630m, 1570m, 1550m
Solid: 2065w, 2042m, 2006m, 1979vs, 1825vw,
1709m, 1564vs
1 after 50 min
Reaction solution: 2065m, 2045m, 2006m,
1989m, 1822s, 1713vs, 1594s, 1570m
2065w, 2047w, 1977s, 1817m, 1711s,
1688m, 1589s, 1574s, 1560s
1
1 + Hdpf
2050m, 1976m, 1825m, 1740vs, 1563m, 1530w
2047w, 1979vs, 1816vw, 1720vs, 1589s, 1561s
2049s, 1988s, 1821s, 1732vs, 1598s
2054vw, 1991vw, 1821m, 1715vs, 1598w,
1560vw, 1530vw
1 + Medpf
1 + PPh3
1 + P(OPh)3
1 + P(O-C6H4CH3)3 2070w, 2047w, 1994w, 1964w, 1721w, 1588w
1 + P(OCH2CF3)3
1 + P(C6H4OCH3)3
2047w, 1979vs, 1706s, 1653m, 1594s, 1556vs
2054m, 1969vs, 1817w, 1720s, 1680m, 1595vs,
1565s, 1503m
bonyl m(CO) frequency for
1 was observed at
1979 cmꢀ1. We may conclude that 1 is transformed
under hydroformylation reaction conditions into the
Rh(I) hydrido-carbonyl complex 7, playing the role of
catalyst, and then converted back into 1 (Table 3). Such
transformation may proceed via Rh-O bond breaking
during activation of the H2 molecule and reproduction
of that bonding after reductive elimination of aldehyde
(Scheme 7). The stability of complex 1 under hydro-
formylation reaction conditions (note that 1 is quite sta-
ble when heated to 80 ꢀC for 2 h under 10 atm of H2/
CO) and its high catalytic activity make it a very
attractive catalyst precursor and prompted us to test
its repeated use.
1 + PCy3
1 + P(NC4H4)3
1 + PPh(C6F5)2
2050m, 2025m, 1969vs, 1825w, 1720vs, 1608s
2047m, 1967m, 1821m, 1721s, 1597vs
2047w, 1973m, 1818vs, 1718w, 1690w, 1640w,
1597s, 1519m
a
Before hydroformylation.
b
After 2 h under 10 atm H2/CO at 80 ꢀC in toluene without added 1-
hexene.
c
Cf. data in Nujol from [5]: 1962s, 1703s, 1551s.
After 25 min of the reaction, the reaction solution was
pale yellow and some amount of 1 remained undissolved
as confirmed by its IR and UV–Vis spectra. The IR
spectrum of the solution showed two new bands at
2065 and 1820 cmꢀ1 from 8. After 50 min, the color of
the solution turned to deep red, and several new IR
2.5. Repetitive hydroformylation of 1-hexene with 1
bands appeared in the region 2100–1800 cmꢀ1
,
suggesting the formation of at least two new
compounds.
The color changes of the reaction solution correlate
well with the reaction course. Within 50 min a signifi-
cant CO + H2 pressure drop in the autoclave occurred,
and the real hydroformylation reaction started – most
Results obtained for repetitive hydroformylation of
1-hexene catalyzed with 1 as the catalyst precursor are
presented in Table 4. After each reaction cycle (2 h),
the reaction mixture was separated using the vacuum-
transfer procedure. The organic products were analyzed
and the solid residue was used as catalyst for the next
= Hdpf
HO
P
H
O
C
CO
OC
P
P
CO/H
2
CO
P
P
- H
HO
HO
2
Rh
Rh
Rh
Rh
+ H
OH
2
P
P
C
O
O
OC
OC
alkene
aldehydes
HO
HO
1
7
8
1979, 1706 cm-1
2047 cm-1
2065, 1820 cm-1
Scheme 6.

A.M. Trzeciak et al. / Journal of Organometallic Chemistry 690 (2005) 3260–3267
3265
3. Conclusions
1
= Hdpf
HO
P
CO/H
2
Complex 1 is an efficient catalyst precursor for hydro-
formylation reaction. It can be applied even without co-
catalysts and/or modifying ligands and used repeatedly
without a loss of activity and selectivity during the first
three cycles. The selectivity of the catalytic system based
on 1 as the precursor can be tuned by adding phospho-
rus modifying ligands, of which aromatic phosphites
showed the highest selectivity (n/iso ratio) without any
loss of catalyst activity.
R
H
H
Rh
P
R
P
HO
CO
P
P
HO
Rh
OC
CO
OC
HO
HO
7
R
CHO
The spectral data of the reaction mixture indicate
that 1 is not the true hydroformylation catalyst, as it re-
quires prior activation. Under the hydroformylation
conditions, it is most likely converted to the hydrido-
carbonyl complex 7, the real catalyst, with P-monoden-
tate Hdpf ligands.
H
+ CO
2
R
R
O
P
CO
P
HO
P
HO
Rh
Rh
P
OC
OC
4. Experimental
HO
HO
4.1. Materials and methods
Scheme 7.
Syntheses of the complexes were performed under an
argon atmosphere. NMR grade C6D6 was used without
purification. Compounds [Rh(acac)(CO)2] [12], 1, 2a, 2b,
6a, 6b [5], 4a [12], 5 [8], and the ligands Hdpf and Medpf
[13] were synthesized by the literature procedures.
NMR spectra were recorded on a Varian UNITY In-
ova 400 spectrometer at 25 ꢀC (1H, 399.95; 31P,
161.90 MHz) and on a Bruker 300 spectrometer (1H,
300.0; 31P, 121.5 MHz). Chemical shifts (d/ppm) are gi-
ven relative to internal tetramethylsilane (1H and 13C)
or to external 85% aqueous H3PO4 (31P). Electrospray
mass spectra (ESI MS) were obtained on a Bruker Es-
quire 3000 spectrometer operating in positive ion mode.
The samples were dissolved in a small amount of chloro-
form and diluted with a large excess of acetonitrile. GC–
MS was performed on a Hewlett–Packard 8452A
instrument.
Table 4
Repeated hydroformylation of 1-hexene catalyzed by trans-
[Rh(CO)(Hdpf-jP)(dpf-j2O,P)] (1)
Catalytic
runa
Aldehydes
(n + iso) (%)
2-Hexene
(%)
1-Hexene
(%)
n/iso
1
2
3
4
5
6
a
84
89
83
69
48
13
16
11
17
29
38
34
–
2.4
2.1
2.3
2.5
2.7
2.4
–
–
2
14
53
[Rh] = 7.1 lmol, [1-hexene] = 0.012 mol (in each catalytic cycle),
toluene 1.5 ml, 80 ꢀC, 10 atm H2/CO (CO:H2 = 1). After each reaction
the mixture was separated by vacuum transfer, 1-hexene (1.5 ml,
0.012 mol) and toluene (1.5 ml) were added to the catalyst residue, and
the mixture was transferred to the autoclave. The reaction time was 2 h
for each catalytic run.
IR spectra were recorded on an FT-IR Nicolet Im-
pact spectrometer. Small samples of the reaction mix-
ture were condensed in vacuo and used for
measurements as films on KBr pellets.
hydroformylation reaction with a new portion of 1-hex-
ene. It is worth noting that the first reaction cycle started
after an induction period (ca. 50 min), which represents
the time necessary for the formation of complex 7. How-
ever, the second cycle started immediately after the
insertion of the reactants into the autoclave. In such a
way the reaction was carried out three times with the
total yield of aldehydes of more than 80% (TON ca.
4500). In the fourth reaction cycle, catalyst activity
decreased (see 1-hexene conversion in Table 4) while
the concentration of aldehyde condensation products
(e.g. 2-pentyl-2-nonenal) increased. Accumulation of
that side-product can cause a decrease in the catalytic
activity of 1 in subsequent reactions.
4.2. Hydroformylation reactions
Hydroformylation reactions have been performed in
a steel autoclave (50 ml) with magnetic stirring at
80 ꢀC and 10 atm H2/CO (1:1). A suitable amount of
pre-catalyst in a small Teflon vessel, toluene (1.5 ml)
and 1-hexene (1.5 ml, 0.012 mol) were introduced into
the autoclave under N2 atmosphere. Then, the autoclave
was closed, filled with H2 (5 atm) and with CO up to
10 atm. After the reaction, the autoclave was cooled
down and the liquid sample was analyzed by GC–MS.

3266
A.M. Trzeciak et al. / Journal of Organometallic Chemistry 690 (2005) 3260–3267
4.3. Micro-scale preparation of trans-[Rh(CO)(Medpf-
jP)(acac)] (4c) and trans-[Rh(CO)(Medpf-j P)-
(dpf-j2O,P)] (2c)
1H NMR spectra reproducibly showed a broad mul-
tiplet due to phenyl groups (dH 7.27–8.82, PPh3 and
ÔHdpfÕ), two sets of signals typical for 1,10-disubstituted
ferrocene unit (ÔHpdfÕ), but no rhodium-hydride signal
(cf. 5 gives a broad singlet at dH ꢀ9.71 in C6D6). The fer-
rocene signals at dH 4.13, 4.35, 4.46 and 4.82 (same inte-
gral intensity) corresponded nicely to the shifts observed
for 2a [5]. The other, more abundant set had dH 3.27 and
3.89 (2 · apparent q), 3.91 and 4.00 (2 · apparent t)
(equal intensities). In 31P NMR spectra, the mixture
showed a broad band at dP ꢀ4.78 attributable to liber-
ated PPh3, a doublet originated from 1 [dP 19.5 (d,
1JRhP = 131 Hz)] and pair of double doublets due to 2a
A solution of Medpf (8.6 mg, 20 lmol) in C6D6
(0.7 ml, containing 0.1% SiMe4) was added to solid com-
plex 3 (5.2 mg, 20 lmol). The solid quickly dissolved
with effervescence (CO evolution) to give a clear orange
solution, which was allowed to stand at room tempera-
ture for 90 min and then analyzed with NMR and MS
spectroscopy. Evaporation of the reaction solution gave
pure 4c as an orange glassy solid, which was used di-
rectly in the next step.
1
2
Complex 4c (11.4 mg, 17 lmol) and Hdpf (7.1 mg,
17 lmol) were dissolved in C6D6 (1.0 ml, containing
0.1% SiMe4). The clear mixture was stirred for 90 min
at room temperature and evaporated under reduced
pressure to give 2c in quantitative yield. The compound
was analyzed as above.
[dP 18.73 (dd, JRhP = 130, JPP ꢃ 350 Hz) and 28.10
1
2
(dd, JRhP = 134, JPP ꢃ 350 Hz)]. Signals due to free
Hdpf or the corresponding phosphine oxide [13] were
not detected.
ESI mass spectra (in CHCl3 + MeOH) clearly showed
the peaks due to {[Rh(dpf)(Hdpf)] + H}+ (m/z 960),
{[Rh(CO)(PPh3)(dpf)] + H}+ (m/z 808), {[Rh(PPh3)
(dpf)] + H}+ (m/z 779) and peaks {Rh(PPh3)2}+ at m/z
627.
In the analogous reaction performed at room temper-
ature (3 h) only 1 was detected by means of 31P {1H}
NMR spectrum together with unreacted 5 [dP 41.0 (d,
1JRhP = 154.3 Hz)].
1
Analytical data for 4c: H NMR (C6D6): d 1.58 and
1.95 (2 · s, 3H, Me of acac); 3.45 (s, 3H, OMe), 4.20
(d of apparent t, 2H), 4.45 (apparent q, 2H), 4.55
(apparent t, 2H), and 4.96 (apparent t, 2H) (4 · CH of
fc); 5.32 (s, 1H, CH of acac), 6.98–7.77 (m, 10H,
1
PPh2). 31P{1H} NMR (C6D6): d 41.6 (d, JRhP
=
178 Hz). ESI MS: m/z 681 ([M + Na]+), 630 ([M ꢀ
CO]+), 559 ([Rh(Medpf)(CO)]+).
1
Analytical data for 2c: H NMR (C6D6): d 3.76 (s,
3H, OMe), 4.12 (apparent t, 2H), 4.30 (apparent q,
Acknowledgements
2H), 4.46 (m, 4H), 4.51 (apparent q, 2H), 4.82 (apparent
t, 2H), and 4.89 (br s, 4H) (8 · CH of fc); 7.35–7.81 (m,
1
10H, PPh2). 31P{1H} NMR (C6D6): d 18.7 (dd, JRhP
=
The financial support by the State Committee for
Scientific Research KBN (Poland) with the Grant
3T09A 115 26 is gratefully acknowledged (AMT, EM,
JJZ).
2
1
132 Hz, JPP = 355 Hz) and 22.9 (dd, JRhP = 133 Hz,
2JPP = 355 Hz). ESI MS: m/z 995 ([M + Na]+), 973
([M + H]+).
4.4. NMR study of the reaction between 1 and P(OPh3)3
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