Synthesis and characterization of new RhI complexes bearing CO, PPh3 and chelating P,O- or Se,Se-ligands: Application to hydroformylation of styrene

Article abstract of DOI:10.1016/j.jorganchem.2007.06.032

The complexes [Rh(CO)(PPh₃){Ph₂PNP(O)Ph₂-P,O}] (3), [Rh(CO)₂{Ph₂P(Se)NP(Se)Ph₂-Se,Se′ }] (5), and [Rh(CO)(PPh₃){Ph₂P(Se)NP(Se)Ph₂-Se,Se ′}] (6), were synthesised by stepwise reactions of CO and PPh₃ with [Rh(cod){Ph₂PNP(O)Ph₂-P,O}] (2) and [Rh(cod){Ph₂P(Se)NP(Se)Ph₂-Se,Se′}] (4), respectively. The complexes 3, 5 and 6 have been studied by IR, as well as ¹H and ³¹P NMR spectroscopy. The ν(CO) bands of complexes 3 and 6 appear at approximately 1960 cm^-1, indicating high electron density at the Rh^I centre. The structure of complexes 3 and 6 has been determined by X-ray crystallography, and the ³¹P NMR chemical shifts have been resolved via low temperature NMR experiments. Both complexes exhibit square planar geometry around the metal centre, with the five-membered ring of complex 3 being almost planar, and the six-membered ring of complex 6 adopting a slightly distorted boat conformation. The C-O bond of the carbonyl ligand is relatively weak in both complexes, due to strong π-back donation from the electron rich Rh^I centre. The catalytic activity of the complexes 2, 3 and 6 in the hydroformylation of styrene has been investigated. Complexes 2 and 3 showed satisfactory catalytic properties, whereas complex 6 had effectively no catalytic activity.

Full text of DOI:10.1016/j.jorganchem.2007.06.032

Journal of Organometallic Chemistry 692 (2007) 4129–4138
www.elsevier.com/locate/jorganchem
Synthesis and characterization of new RhI complexes
bearing CO, PPh3 and chelating P,O- or Se,Se-ligands:
Application to hydroformylation of styrene
a
b
a
Konstantinos A. Chatziapostolou , Kalliopi A. Vallianatou , Alexios Grigoropoulos ,
c
c
b,
*
Catherine P. Raptopoulou , Aris Terzis , Ioannis D. Kostas
,
a,
a
Panayotis Kyritsis *, Georgios Pneumatikakis
a
Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis,
Zografou, 15771 Athens, Greece
National Hellenic Research Foundation, Institute of Organic and Pharmaceutical Chemistry, Vas. Constantinou 48, 11635 Athens, Greece
b
c
Institute of Materials Science, NCSR ‘‘Demokritos’’, 153 10 Aghia Paraskevi Attikis, Greece
Received 3 May 2007; received in revised form 14 June 2007; accepted 19 June 2007
Available online 27 June 2007
Abstract
The complexes [Rh(CO)(PPh3){Ph2PNP(O)Ph2-P,O}] (3), [Rh(CO)2{Ph2P(Se)NP(Se)Ph2-Se,Se0}] (5), and [Rh(CO)(PPh3){Ph2P
(Se)NP(Se)Ph2-Se,Se0}] (6), were synthesised by stepwise reactions of CO and PPh3 with [Rh(cod){Ph2PNP(O)Ph2-P,O}] (2) and
[Rh(cod){Ph2P(Se)NP(Se)Ph2-Se,Se0}] (4), respectively. The complexes 3, 5 and 6 have been studied by IR, as well as 1H and
31P NMR spectroscopy. The m(CO) bands of complexes 3 and 6 appear at approximately 1960 cmꢀ1, indicating high electron density
at the RhI centre. The structure of complexes 3 and 6 has been determined by X–ray crystallography, and the 31P NMR chemical
shifts have been resolved via low temperature NMR experiments. Both complexes exhibit square planar geometry around the metal
centre, with the five-membered ring of complex 3 being almost planar, and the six-membered ring of complex 6 adopting a slightly
distorted boat conformation. The C–O bond of the carbonyl ligand is relatively weak in both complexes, due to strong p-back
donation from the electron rich RhI centre. The catalytic activity of the complexes 2, 3 and 6 in the hydroformylation of styrene
has been investigated. Complexes 2 and 3 showed satisfactory catalytic properties, whereas complex 6 had effectively no catalytic
activity.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: P,O-Ligand; Se,Se-Ligand; Hemilabile ligand; Rhodium complex; Homogeneous catalysis; Hydroformylation
1. Introduction
highly important industrial reactions involving CO inser-
tion to organic substrates, such as hydroformylation of
alkenes and carbonylation of methanol [1–4]. In particular,
complexes bearing the so-called hemilabile ligands that
have at least two different donor-atoms, such as P and
E = N, O, S, Se, exhibit interesting coordination chemistry
and have been successfully applied to homogeneous catal-
ysis [5,6]. Complexes cis-[RhCl(CO){Ph2P(CH2)nP(O)Ph2-
P,O}], n = 1, 2, for instance, were shown to be efficient
catalyst precursors towards carbonylation of methanol
Rhodium-based catalyst precursors with phosphorus-
containing ligands exhibit remarkable catalytic activity in
*
Corresponding authors. Tel.: +30 210 7274268; fax: +30 210 7274782
(P. Kyritsis); tel.: +30 210 7273878; fax: +30 210 7273831 (I.D. Kostas).
E-mail addresses: ikostas@eie.gr (I.D. Kostas), kyritsis@chem.uoa.gr
(P. Kyritsis).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.06.032

4130
K.A. Chatziapostolou et al. / Journal of Organometallic Chemistry 692 (2007) 4129–4138
at low temperature [7]. Also, the complex cis-[RhI-
(CO){Ph2PCH2P(S)Ph2-P,S}] [8] exhibited better catalytic
activity for this reaction compared to the classic Monsanto
catalyst [RhI2(CO)2]ꢀ, under mild conditions. Likewise, in
a series of papers, Dutta et al. have explored the efficiency
of RhI catalyst precursors modified with P,O- [9] and P,Se-
[10,11] diphosphine ligands, including kinetic studies with
respect to oxidative addition reactions on these complexes.
In addition, RhI complexes with bidentate P,O-ligands,
were shown to catalyze the hydrogenation and the isomer-
ization of 1-hexene, as well as the transfer dehydrogenation
of cyclooctane [12]. Trzeciak et al. have investigated RhI
catalysts modified either with (2-hydroxyphenyl)diphenyl-
phosphine [13] or ferrocene-based P,O-ligands for the hyd-
roformylation of 1-hexene [14,15].
The results of the above studies demonstrate the ability
of mixed donor P,E-ligands (E = O, S, Se) to regulate the
electronic properties of the metal centre in such a way, that
an efficient catalyst is produced. The aforementioned com-
plexes show characteristically low m(CO) bands, between
1960 cmꢀ1 and 1990 cmꢀ1 (Table 1). Most probably, the
electron-donating P,E-ligands increase the electron density
of the metal centre, thus enhancing p-back-bonding to the
p*-orbitals of the CO ligands. In this context, the use of a
Se,Se-bidentate ligand is expected to produce also an elec-
tron rich RhI centre.
In recent years, we have engaged in preparing several
functionalized phosphorus ligands containing additional
potent donors such as N, O or S, which were found to
lead to improved systems for the rhodium-catalyzed
hydroformylation [16–22]. In the work described here,
RhI–carbonyl complexes with the P,O-ligand [Ph2PNP-
(O)Ph2]ꢀ [23], or the Se,Se-ligand [Ph2P(Se)NP(Se)Ph2]ꢀ
[24], have been explored. These chelating ligands form
five- and six-membered rings with the metal centre, respec-
tively. The complexes were structurally and spectroscopi-
cally characterized, and shown to contain electron rich
RhI centres. Thereafter, their catalytic behavior towards
hydroformylation of styrene was investigated, in an
attempt to elucidate the structural or electronic factors that
determine their activity.
2. Results and discussion
2.1. Synthesis and spectroscopic characterization of the
rhodium complexes
2.1.1. RhI complexes with the P,O-ligand
The synthetic pathway for these complexes is outlined in
Scheme 1. Reaction of [RhCl(cod)2]2 with two equivalents
of the ligand Ph2PNHP(O)Ph2 yields complex [RhCl(cod)-
{Ph2PNHP(O)Ph2-P}] (1). Deprotonation of the coordi-
nated P,O-ligand in 1 by treatment with potassium
tert-butoxide (tBuOK) yields complex [Rh(cod){Ph2PN-
P(O)Ph2-P,O}] (2), according to already reported
procedures [23]. The stepwise reaction of 2 with CO and
PPh3, yields the yellow solid [Rh(CO)(PPh3){Ph2PN-
P(O)Ph2-P,O}] (3). The reaction of 2 with CO in a CH2Cl2
solution was recorded by IR spectroscopy. The spectrum of
the reaction mixture shows two terminal m(CO) bands at
2084 cmꢀ1 and 1992 cmꢀ1, whereas the (cod) bands are
absent, thus confirming the replacement of (cod) by two
CO ligands. Subsequent treatment of the Rh–dicarbonyl
complex solution with a stoichiometric quantity of PPh3
afforded complex 3. The IR spectrum of 3 exhibits a single
terminal m(CO) band at 1964 cmꢀ1, a value characteristic of
an electron rich rhodium centre [3,25]. The shift to lower
energy of the m(CO) band, compared to the intermediate
dicarbonyl complex, indicates a weaker C–O bond due to
the enhanced p-back-bonding to the only remaining CO
ligand. Other characteristic changes in the IR bands
between complexes 1 and 2 have already been reported
elsewhere [23]. An overall list of the IR bands of 1–3 is pre-
sented in Table 2. One can observe the shift to lower energy
of the m(PO) band going from 1 to 2 due to deprotonation
and chelation of the bidentate ligand, the generation of the
dicarbonyl complex in solution upon reaction with CO
and, finally, the existence of a single m(CO) band in 3 after
the reaction series is complete. Such RhI complexes have
been shown to exhibit high catalytic activity towards hyd-
roformylation of olefins [26], or similar catalytic reactions
like carbonylation of methanol [11,25].
The three P atoms of 3 are chemically and magnetically
non-equivalent (Fig. 1); therefore, the 31P NMR spectrum
of 3 exhibits three ddd-peaks (Figs. 2, S1 and S3). The low-
field peak (dP = 80.6, ddd) is assigned to the P(III) atom
(PA) of the bidentate ligand, which is directly attached to
the RhI centre and thus deshielded. The JRhP coupling
1
Table 1
constant of 119.0 Hz lies within the typical values of similar
systems [12,27,28]. The extremely strong coupling with the
P atom of the phosphine ligand (2JPP = 327.5 Hz) can only
be rationalized in the context of a trans arrangement
between PA and PPh3 [13–15,27–31]. The oxidized P(V)
atom (PX) of the bidentate ligand is not directly coordi-
nated to the metal centre, thus coupling with 103Rh is weak
(3JRhP = 3.7 Hz), as expected [23,32,33]. Coupling with
PA(2JPP = 52.8) and PPh3(3JPP = 41.3 Hz) gives rise to a
ddd-peak (dP = 68.9). The chemical shifts for the two
non-equivalent P-atoms of the bidentate P,O-ligand are
Comparison of the m(CO) in RhI complexes with some P,E-ligands (E = O, S, Se)
Complex
m(CO) (cmꢀ1
)
Reference
[7]
cis-[RhCl(CO){Ph2P(CH2)nP(O)Ph2-P,O}], n = 1,
2
1985, 1995
cis-[RhI(CO){Ph2PCH2P(S)Ph2-P,S}]
[RhCl(CO){4-Ph2PC6H4COOMe-P,O}]
[RhCl(CO){Ph2PCH2P(Se)Ph2-P,Se}]
[RhCl(CO){Ph2PN(CH3)P(Se)Ph2-P,Se}]
trans-[Rh{dpf-P,O}(CO)(PPh3)]
1992
1977
1977
1981
1965
1963
1964
1962
[8]
[9]
[10]
[10]
[14]
[Rh{OC6H4PPh2-P,O}(CO)(PPh3)]
[Rh(CO)(PPh3){Ph2PNP(O)Ph2-P,O}]
[Rh(CO)(PPh3){Ph2P(Se)NP(Se)Ph2-Se,Se0}]
[13]
This work
This work

K.A. Chatziapostolou et al. / Journal of Organometallic Chemistry 692 (2007) 4129–4138
4131
Scheme 1. Synthetic pathway for the preparation of complexes 3 and 6.
assigned on the basis of published NMR data for 2 [23].
2.1.2. RhI complexes with the Se,Se-ligand
Finally, the high-field multiplet (dP = 30.1, ddd) is assigned
The ligand [Ph2P(Se)NP(Se)Ph2]ꢀ has already been
employed to synthesize numerous complexes with several
transition metals [34]. The synthesis of the complex
[Rh(cod){Ph2P(Se)NP(Se)Ph2-Se,Se0}] (4) has been
reported by Bhattacharyya et al. [24]. The (cod) ligand is
1
to PPh3(1JRhP = 123.8 Hz). Regarding the H NMR spec-
trum of complex 3, the phenyl protons of the P,O-ligand
are observed in the aromatic region of the spectrum,
between 7.6 (ortho, para) and 8.2 ppm (meta).
Table 2
Characteristic IR bands of the complexes containing the P,O-ligand
Complex
m(CO)
m(PNP)
m(PO)
m(NH)
m(CH)
RhCl(cod){Ph2PNHP(O)Ph2-P} (1)
Rh(cod){Ph2PNP(O)Ph2-P,O} (2)
Rh(CO)2{Ph2PNP(O)Ph2-P,O}a
–
–
931
1101
1220
1124
3183
–
2981–3064
2824–3059
2084, 1992
1964
Rh(CO)(PPh3){Ph2PNP(O)Ph2-P,O} (3)
1103
1125
–
–
a
Data in a CH2Cl2 solution.

4132
K.A. Chatziapostolou et al. / Journal of Organometallic Chemistry 692 (2007) 4129–4138
atom. Therefore, complex 6 as a whole, including the
NMR active 103Rh atom, can be best described as an
ABMX spin-system (Fig. 4). The P atom of the phosphine
ligand (PX) is directly coordinated to the metal centre, thus
giving rise to a low-field ddd-peak (dP = 39.4). Coupling
with 103Rh (1JRhX = 160.2 Hz) is similar to the values of
other complexes bearing PPh3 directly coordinated to RhI
[12,27,28]. The two high-field peaks are assigned to the
two P atoms of the chelate ligand. In agreement with
the stronger p-acidity of CO compared to PPh3 and the
J(trans) > J(cis) trend described for complex 3, the dd-peak
at 27.4 ppm is assigned to the PB atom, located trans to CO
(3JBX = 8.4 Hz). On the other hand, the PA atom, located
trans to PPh3 and hence cis to CO, is slightly less
deshielded, giving rise to an up-field doublet (dP = 26.1),
but exhibits stronger coupling with PX(3JAX = 29.1 Hz).
Line broadening prevented us from calculating JRhP, for
this nucleus, even when we recorded the spectrum at
ꢀ80 ꢁC. Likewise, coupling between PA and PB was not
resolved, as was also the case in the [Pd{Ph2PNP(Se)-
Ph2-P,Se}{N(SePPh2)2-Se,Se0}] complex, bearing the same
Se,Se-ligand [24]. However, the 77Se-satellites are observed
for both nuclei, exhibiting typical coupling constants
(1JPSe = 550 Hz and 552 Hz for PA and PB, respectively)
[24,34]. Furthermore, they provide strong evidence in
favour of assigning the down-field peaks to the P atoms
of the bidentate and not the phosphine ligand. It has to
be noted that in a recent report on the synthesis of 6, fol-
lowing a different synthetic procedure, the peak assignment
was the opposite of the one presented here [35].
Fig. 1. P atom labeling used for the NMR spectrum of complex 3.
replaced by two CO ligands upon treatment of 4 with an
excess of CO, affording complex [Rh(CO)2{Ph2P(Se)NP-
(Se)Ph2-Se,Se0}] (5) (Scheme 1). Complex 5 shows, as
expected, two terminal m(CO) bands at 1981 cmꢀ1 and
2046 cmꢀ1 and no (cod) bands. Reaction of 5 with an
equimolar quantity of PPh3 yields the orange-yellow
complex [Rh(CO)(PPh3){Ph2P(Se)NP(Se)Ph2-Se,Se0}] (6)
(Scheme 1). The IR spectrum of 6 shows a single terminal
m(CO) band at 1962 cmꢀ1, that is again indicative (vide
supra) of an electron rich RhI centre. The shift of the
m(CO) band of 6 to lower frequencies, compared to 5, sug-
gests a reduction of the C–O bond order due to stronger p-
back-bonding to the single remaining CO group. The
m(PSe) bands for complexes 5 and 6 appear at 541 cmꢀ1
and 544 cmꢀ1, respectively.
The sequence of reactions can be followed via the
changes in the characteristic IR bands of 4, 5 and 6 pre-
sented in Table 3. In particular, the m(CH) bands of the
(cod) ligand in 4 disappear, while two new m(CO) bands
appear in the metal–carbonyl region of the IR spectrum
of 5. Finally, the replacement of one CO ligand by PPh3
results in one single m(CO) band in 6.
2.2. Single-crystal X-ray studies of complexes 3 and 6
The 31P–{1H} NMR spectrum of 6 could only be
resolved at lower temperatures in toluene-d8 (Figs. 3, S4
and S5). More specifically, only at ꢀ60 ꢁC, the multiplets
corresponding to the Se,Se-chelating ligand are clearly
resolved, including the satellites resulting from coupling
to 77Se. The two P atoms of the Se,Se-chelate are no longer
equivalent, due to the different ligands trans to each Se
Suitable crystals of complexes 3 and 6 were grown by
slow diffusion of n-hexane into a dichloromethane solution
of each complex. The crystal structures of both complexes
(Figs. 5, 6) were determined by single-crystal X-ray diffrac-
tion studies, and support the spectroscopic observations
described above. Crystallographic data and refinement
Fig. 2. The 31P–{1H} NMR spectrum of complex 3.

K.A. Chatziapostolou et al. / Journal of Organometallic Chemistry 692 (2007) 4129–4138
4133
Table 3
Characteristic IR bands of the complexes containing the Se,Se-ligand
Complex
m(CO)
m(PNP)
m(PSe)
m(CH)
[Rh(cod){Ph2P(Se)NP(Se)Ph2-Se,Se0}] (4)
[Rh(CO)2{Ph2P(Se)NP(Se)Ph2-Se,Se0}] (5)
[Rh(CO)(PPh3){Ph2P(Se)NP(Se)Ph2-Se,Se0}] (6)
–
1165
1172
1168
543
541
544
2821–3059
–
–
2046, 1981
1962
Fig. 3. The 31P–{1H} NMR spectrum of complex 6 at ꢀ60 ꢁC.
parameters for both complexes are shown in Table 4, while
the most characteristic bond lengths and angles of com-
plexes 3 and 6 are listed in Tables 5 and 6, respectively.
The structure of complex 3 reveals a square-planar RhI
centre coordinated by two P atoms at trans positions, one
O atom and one CO group. The coordination of PPh3 is
trans to the P-atom of the bidentate P,O-ligand, due to
the stronger trans effect of the P-atom, compared to the
one of the O-atom, during the synthesis of 3 starting from
the [Rh(CO)2{Ph2PNP(O)Ph2-P,O}] complex [12]. The
five-membered Rh–P–N–P–O ring is slightly distorted from
planar, in which, among the ring atoms, the N atom shows
the delocalization of p-electron density along the ring, as
has already been postulated by structural data [36,37]
and theoretical calculations [38]. Furthermore, the C–O
˚
bond length of 1.165 A is slightly bigger compared to sim-
I
˚
ilar Rh –carbonyl complexes (1.12–1.15 A) [14,39,40], indi-
˚
the biggest deviation (0.09 A) from the Rh–O–P–N–P
mean plane. The bond lengths in the chelate ring fall
between those of typical single and double bonds, due to
Fig. 5. Partially labeled ORTEP plot of 3 with ellipsoids drawn at the 30%
Fig. 4. P atom labeling used for the NMR spectrum of complex 6.
probability level. Hydrogen atoms have been omitted for clarity.

4134
K.A. Chatziapostolou et al. / Journal of Organometallic Chemistry 692 (2007) 4129–4138
Table 5
Selected bond lengths and angles for complex 3
˚
Bond lengths (A)
Bond angles (ꢁ)
Rh–P(1)
Rh–P(3)
2.271(1)
2.294(1)
2.092(3)
1.801(4)
1.637(3)
1.517(3)
1.576(3)
1.165(5)
C(43)–Rh–O(1)
C(43)–Rh–P(1)
O(1)–Rh–P(1)
C(43)–Rh–P(3)
O(1)–Rh–P(3)
P(1)–Rh–P(3)
N(1)–P(1)–Rh
O(1)–P(2)–N(1)
P(2)–O(1)–Rh
P(2)–N(1)–P(1)
O(2)–C(43)–Rh
177.0(1)
94.7(1)
83.7(1)
96.0(1)
85.6(1)
169.4(1)
107.4(1)
113.6(2)
118.5(1)
116.3(2)
178.1(4)
Rh–O(1)
Rh–C(43)
P(1)–N(1)
P(2)–O(1)
P(2)–N(1)
C(43)–O(2)
Table 6
Selected bond lengths and angles for complex 6
Fig. 6. Partially labeled ORTEP plot of 6 with ellipsoids drawn at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
˚
Bond lengths (A)
Bond angles (ꢁ)
Rh–Se(1)
Rh–Se(2)
Rh–P(3)
Rh–C(43)
Se(1)–P(1)
Se(2)–P(2)
C(43)–O(1)
P(1)–N(1)
P(2)–N(1)
2.516(1)
2.506(1)
2.279(1)
1.816(5)
2.170(1)
2.191(1)
1.146(6)
1.591(4)
1.600(3)
C(43)–Rh–P(3)
C(43)–Rh–Se(2)
P(3)–Rh–Se(2)
C(43)–Rh–Se(1)
P(3)–Rh–Se(1)
Se(2)–Rh–Se(1)
P(1)–Se(1)–Rh
P(2)–Se(2)–Rh
O(1)–C(43)–Rh
N(1)–P(1)–Se(1)
N(1)–P(2)–Se(2)
P(1)–N(1)–P(2)
88.9(1)
179.7(1)
91.4(1)
80.8(1)
169.7(1)
98.9(1)
100.2(1)
107.6(1)
176.1(1)
115.9(1)
119.02(1)
124.2(1)
cating high electron density at the RhI centre and stronger
p-back-bonding. This observation verifies the analysis
based on the IR spectrum of complex 3, in which the low
m(CO) band would imply an electron rich metal centre.
The core of complex 6, RhSeSeP(CO), adopts a square-
planar geometry around the metal centre. The six-mem-
bered Rh–Se–P–N–P–Se ring is not planar, since atoms
P(1) and N(1) are displaced 1.54 A and 1.14 A, respec-
tively, out of the mean plane of the remaining four atoms,
resulting in a slightly distorted boat ring conformation,
with Se(1) and P(2) located at the apices.
˚
˚
In analogy to complex 3, the bond lengths along the
Rh–Se–P–N–P–Se ring fall between those of typical single
and double bonds due to the delocalization of p-electron
density along the chelate ring [36–38]. The bond length
difference between the Rh–Se(1) and Rh–Se(2) bonds
˚
˚
(2.516 A and 2.506 A, respectively), is due to the stronger
trans influence of the PPh3 ligand compared to CO. Similar
observations have been made in analogous systems, such
as [Pd{Ph2PNP(Se)Ph2-P,Se}{N(SePPh2)2-Se,Se0}] [24],
[PtCl2{PPh2N(Ph)P(S)Ph2-P,S}] [33] and [Rh(CO)(PPh3)-
{Ph2P(S)NP(S)Ph2-S,S0}] [41].
Table 4
Crystal data and structure refinement details for complexes 3 and 6
Furthermore, as in the case of complex 3, the C–O bond
Compound
3
6
I
˚
length, at 1.147 A, is larger than in other Rh –carbonyl
Empirical formula
Formula weight
Temperature (K)
Space group
C
793.54
298
43H35NO2P3Rh
C43H35NOP3RhSe2
935.46
298
complexes [14,39,40], indicating high electron density at
the RhI centre which, through strong p-back donation,
weakens the carbonyl C–O bond. This observation is also
in agreement with the IR spectroscopic data of complex 6
presented above.
ꢀ
ꢀ
P1
P1
Unit cell dimensions
˚
a (A)
10.785(5)
18.937(9)
9.525(5)
93.86(2)
95.49(2)
97.48(2)
1913.7(16)
2
9.791(2)
11.971(3)
18.390(4)
107.43(1)
98.14(1)
101.30(1)
1969.9(8)
2
˚
b (A)
The bond length of the Rh–PPh3 bond in complex 3 is
˚
c (A)
˚
larger by 0.015 A compared to complex 6, possibly due
a (ꢁ)
b (ꢁ)
c (ꢁ)
to the stronger trans influence exerted by the Rh-coordi-
nated P atom of the P,O-ligand, compared to the Se atom
of the Se,Se-ligand, respectively. This difference might
explain the smaller 1J(Rh–PPh3) in the case of 3
(123.8 Hz) compared to 6 (160.2 Hz) (vide supra).
3
˚
Volume (A )
Z
qcalc (Mg mꢀ3
)
1.377
1.577
l (mmꢀ1
R1a
)
5.080
2.438
0.0361b
0.0963b
0.0409c
0.1021c
wRa2
2.3. Catalytic activity of complexes 2, 3 and 6 towards
hydroformylation of styrene
a
w = 1/[r2(Fo2) + (aP)2 + bP] and P = max(Fo2,0) + (2Fc2)/3; R1 =
P
P
P
P
2
(jFoj ꢀ jFcj)/ (jFoj) and wR2 = { [w(Fo ꢀ Fc2)2]/ [w(Fo2)2]}1/2
.
b
c
For 4928 reflections with I > 2r(I).
For 5833 reflections with I > 2r(I).
The complexes 2 and 3 were studied as catalysts in the
hydroformylation of styrene (7) under variable conditions

K.A. Chatziapostolou et al. / Journal of Organometallic Chemistry 692 (2007) 4129–4138
4135
Scheme 2. Hydroformylation of styrene.
Table 7
Hydroformylation of styrene catalyzed by complexes 2 and 3a
Entry
Complex
Pb (bar)
T (ꢁC)
Time (h)
Conversion (%)
Rcc (%)
Rdbr (%)
TONe
1
2
3
4
5
6
7
8
9
a
2
3
2
3
2
2
3
3
3
100
100
100
100
50
30
30
30
10
60
60
30
40
60
60
60
40
40
2
2
20
4
78.6
96.1
88.2
31.3
72.3
87.7
99.8
49.3
40.8
97.1
99.5
99.3
99.1
100.0
97.7
99.4
98.7
98.5
89.8
93.6
98.3
96.6
83.3
77.1
85.6
92.4
75.5
1110
1391
1274
451
1052
1247
1443
708
2
20
20
20
72
585
A 4 mM solution in CH2Cl2. Styrene:catalyst = 1455:1.
P = initial total pressure of CO/H2 (1/1).
Rc = chemoselectivity for aldehydes.
Rbr = regioselectivity towards branched aldehyde.
Turnover number (TON) = aldehydes fraction · substrate:[Rh] ratio.
b
c
d
e
of pressure and temperature (Scheme 2, Table 7). The cat-
alytic experiments were performed in an autoclave, by mix-
ing styrene and a stock solution of the rhodium complex
(4 mM in CH2Cl2) with a molar ratio styrene/catalyst of
1455:1, using syngas CO/H2 (1:1). Complexes 2 and 3 dis-
played good activity, high chemoselectivity for aldehydes
(97–100%), and high regioselectivity for the formation of
the branched aldehyde of up to 98%. The variation
observed in this work in the conversions of styrene and
the regioselectivities in the resulting branched aldehyde,
under variable conditions of pressure and temperature,
was as expected for hydroformylation of styrene using rho-
dium systems, that is, an increased temperature speeds up
the catalytic reaction, but at the same time decreases the
regioselectivity, and an increased pressure increases both
the reaction rate and the regioselectivity. The results were
acceptable even at the low pressures of 30 or 10 bar (entries
6–9). Complex 3 bearing one more phosphorus donor com-
pared to complex 2 displayed higher reaction rates and
selectivities than 2 (compare entries 1–2 and 6–7). The good
activity of complexes 2 and 3 could partly be attributed to
free coordination sites that would be easily formed in both
complexes during the course of the catalytic reaction. The
(cod) ligand of complex 2 would be easily removed, while
the strong trans effect of CO could weaken the Rh–O bond
in complex 3, opening the five-membered chelate ring. Sim-
ilar hemilabile behavior of phosphorous chelate ligands has
been considered as beneficial for hydroformylation reac-
tions [42]. The PPh3 group in complex 3 could also be
served for an additional stabililization of the active species
during the course of the metal-mediated reaction.
On the other hand, complex 6 in which rhodium is
bound to a CO, PPh3 and a Se,Se-ligand forming a six-
membered chelate ring, showed none or very low catalytic
activity, for reasons being still unclear. Perhaps, this is due
to the saturated coordinated-rhodium atom, being unable
to obtain free coordination sites and to proceed the cata-
lytic cycle.
3. Conclusions
In summary, complexes containing electron rich RhI
centres and bearing (cod), CO, PPh3 and P,O- or Se,Se-
ligands have been synthesized, structurally and spectro-
scopically characterized, and applied as catalysts for the
hydroformylation of styrene. The IR and NMR spectra
have been thoroughly analyzed, and compared with similar
systems in the literature. In the structures of complexes 3
and 6, different trans influence effects of the ligands are
clearly manifested. The complexes 2 and 3, which contain
the P,O-ligand forming a five-membered ring with Rh,
exhibit the best catalytic activity for the hydroformylation
of styrene.

4136
K.A. Chatziapostolou et al. / Journal of Organometallic Chemistry 692 (2007) 4129–4138
4. Experimental
4.1. General procedures
the colour turned from orange to yellow-green. The volume
of the reaction mixture was reduced to 2–3 mL and addi-
tion of n-hexane (30 mL) afforded an orange solid which
was filtered in vacuo and washed with small portions of
n-hexane. Yield: 0.053 g (81%). Selected IR data (KBr,
cmꢀ1): 2046 [mas(CO)], 1981 [msym(CO)], 1172 [m(PNP)],
541 [m(PSe)].
Unless otherwise stated, all manipulations were carried
out under an inert Ar atmosphere, using pre-dried sol-
vents and standard Schlenk techniques.[RhCl(cod){Ph2-
PNHP(O)Ph2-P}] (1), [Rh(cod){Ph2PNP(O)Ph2-P,O}] (2)
and [Rh(cod){Ph2P(Se)NP(Se)Ph2-Se,Se0}] (4) were pre-
pared from [RhCl(cod)2]2 (Aldrich) and the appropriate
diphosphine ligands, according to reported procedures
[23,24]. All the other chemicals were commercially avail-
able. Hydroformylation using syngas (CO–H2, 1:1) was
performed in a stainless steel autoclave (300 mL) with
magnetic stirring. Elemental analyses (C, H and N) were
performed in a Perkin–Elmer PE 2400II, CHNS/O ana-
lyzer. Infrared spectra were recorded between 4000 and
200 cmꢀ1 on a Perkin–Elmer 833 spectrometer. NMR
spectra were recorded in a Varian Unity Plus spectrome-
ter. TMS (1H NMR) and 85% H3PO4 in D2O (31P NMR)
were used as reference. The products of the catalytic reac-
tions were detected and quantified by Gas Chromatogra-
phy (Varian Star 3400 CX with a 30 m · 0.53 mm DB5
column).
4.4. [Rh(CO)(PPh3){Ph2P(Se)NP(Se)Ph2-Se,Se0}] (6)
[Rh(cod){Ph2P(Se)NP(Se)Ph2-Se,Se0}] (0.050 g, 0.065
mmol) was dissolved in 20 mL of toluene and the solution
was subjected to CO bubbling for 20 min, during which the
colour turned from orange to yellow-green. At this point,
an equivalent amount of PPh3 was added (0.020 g,
0.070 mmol), changing the colour of the solution to pale-
yellow. The reaction mixture was stirred for 1.5 h at room
temperature and, subsequently, it was concentrated under
reduced pressure up to 2–3 mL. Addition of n-hexane
(20 mL) afforded the orange solid compound
[Rh(CO)(PPh3){Ph2P(Se)NP(Se)Ph2-Se,Se0}], which was
collected by filtration, washed with small portions of n-hex-
ane and finally dried in vacuo. Yield: 0.055 g (77%). Anal.
Calc. for C43H35NOP3RhSe2: C, 57.07; H, 4.28; N, 1.86.
Found: C, 51.02; H, 2.61; N, 1.73%. Selected IR data
(KBr, cmꢀ1): 1962 [m(CO)], 1168 [m(PNP)], 544 [m(PSe)].
1H NMR (300 MHz, toluene-d8): dH 8.36 (m, 14H, m-
C6H5), 7.74 (m, 21H, o,p-C6H5). 31P–{1H} NMR
(121.5 MHz, toluene-d8): dP 39.4 [ddd, PX, 1J(RhPX) =
160.2 Hz, 3J(PAPX) = 29.1 Hz, 3J(PBPX) = 8.4 Hz], 27.4
[dd, PB, 3J(PBPX) = 8.4 Hz, 2J(RhPB) = 3.9 Hz, 1J(PBSe) =
552 Hz, satellites], 26.1 [d, PA, 3J(PAPX) = 29.1 Hz,
1J(PASe) = 550 Hz, satellites].
4.2. [Rh(CO)(PPh3){Ph2PNP(O)Ph2-P,O}] (3)
[Rh(cod){Ph2PNHP(O)Ph2-P,O}] (0.128 g, 0.209 mmol)
was dissolved in toluene (25 mL) and the solution was sub-
jected to CO bubbling for 20 min, during which the colour
rapidly turned from yellow to orange, indicating the gener-
ation of the dicarbonyl intermediate. At this point, an
equivalent amount of PPh3 was added (0.058 g,
0.221 mmol), changing the colour of the solution to pale-
yellow. The reaction mixture was stirred for 1.5 h at room
temperature, and, subsequently, it was concentrated under
reduced pressure up to 2–3 mL. Addition of n-hexane
(30 mL) afforded the yellow solid compound, [Rh(CO)-
(PPh3){Ph2PNHP(O)Ph2-P,O}], which was collected by
filtration, washed with 10 mL of n-hexane and finally dried
in vacuo. Yield: 0.202 g (82%). Anal. Calc. for C43H35-
NO2P3Rh: C, 65.09; H, 4.45; N, 1.77. Found: C, 65.88;
H, 4.58; N, 1.84%. Selected IR data (KBr, cmꢀ1): 1964
[m(CO)], 1125 [m(PO)], 1103 [m(PNP)]. 1H NMR
(300 MHz, toluene-d8):dH 8.13 (m, 14H, m-C6H5), 7.67
(m, 21H, o,p-C6H5). 31P–{1H} NMR (121.5 MHz, tolu-
ene-d8): dP 80.6 [ddd, PA, 2J(PAPPh3) = 327.5 Hz,
4.5. Hydroformylation of styrene
In a typical experiment, styrene (2 mL, 17.456 mmol), a
4 mM solution of rhodium complex in dichloromethane
(3 mL, 0.012 mmol) were placed under argon in an oven-
dried autoclave, which was then closed, pressurized with
syngas (CO–H2, 1:1) to the appropriate pressure and
brought to the required temperature. After the required
reaction time, the autoclave was cooled to room tempera-
ture, the pressure was carefully released, the solution was
diluted with dichloromethane, passed through celite and
analyzed by GC. Conversions were determined by GC.
2
1J(RhPA) = 119.0 Hz, J(PAPX) = 52.8 Hz], 68.9 [ddd, PX,
4.6. X-ray crystallography
2J(PAPX) = 52.8 Hz, 3J(PXPPh3) = 41.3 Hz, 2J(RhPX) =
3.7 Hz], 30.1 [ddd, PPh3, 2J(PAPPh3) = 327.5 Hz,
A light yellow prismatic crystal of 3 (0.10 · 0.25 ·
0.35 mm) was mounted in capillary and a yellow prismatic
crystal of 6 (0.20 · 0.30 · 0.75 mm) was mounted in air and
covered with epoxy glue. Diffraction measurements were
made on a P21 Nicolet diffractometer upgraded by Crystal
Logic for 3 using graphite-monochromated Cu radiation,
and on a Crystal Logic Dual Goniometer diffractometer
1J(RhPPh3) = 123.8 Hz, J(PXPPh3) = 41.3 Hz].
3
4.3. [Rh(CO)2{Ph2P(Se)NP(Se)Ph2-Se,Se0}] (5)
[Rh(cod){Ph2P(Se)NP(Se)Ph2-Se,Se0}] (0.070 g, 0.092
mmol) was dissolved in CH2Cl2 (15 mL), and the solution
was subjected to CO bubbling for 20 min, during which
for
6 using graphite-monochromated Mo radiation.

K.A. Chatziapostolou et al. / Journal of Organometallic Chemistry 692 (2007) 4129–4138
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Acknowledgements
The project is co-funded by the European Social Fund
and National Resources – (EPEAEK II) PYTHAGORAS.
The Special Research Account of NKUA, the EPEAEK
program ‘‘Catalysis and its Applications’’, and the General
Secretariat of Research and Technology of Greece are also
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