Asymmetric hydroformylation of olefins with Rh catalysts modified with chiral phosphine-phosphite ligands

Article abstract of DOI:10.1021/om700744b

Rhodium complexes stabilized by modularly designed chiral phosphine-phosphite ligands (P-OP) have been tested in the asymmetric hydroformylation of styrene, vinyl naphthalenes, and allyl cyanide. Based on single-crystal X-ray diffraction analysis and NMR studies, restricted aryl rotation has been found to characterize ligands 1e and If. The outcome of the rhodium-catalyzed hydroformylation reactions is highly dependent on the nature of the two coordinating functions of the phosphine-phosphite and of the ligand backbone as well. Among the ligands studied, those with an oxyphenylene backbone and PAr₂ ends gave the best results, outperforming those with P-stereogenic phosphine groups. The 1-naphthyl-substituted catalyst brought about the hydroformylation of styrene with a 71% ee, while the xylyl catalyst afforded the best results in the hydroformylation of allyl cyanide, yielding an iso/n ratio of 13 and 53% ee in the branched isomer. Several hydrido(carbonyl) species of the formula RhH(CO)₂(P-OP) have been generated by reacting Rh(acac)(CO)₂/P-OP with syngas. In situ high-pressure NMR experiments showed the phosphine group to occupy an apical position of the trigonal bipyramidal coordination geometry, which allows an aryl-aryl interaction between the phosphine substituents and the substrate during the hydroformylation of vinyl arenes. In line with this finding, a remarkable enantioselectivity of 89% ee was obtained with the naphthyl catalyst and 1-vinyl naphthalene as substrate.

Full text of DOI:10.1021/om700744b

6428
Organometallics 2007, 26, 6428-6436
Asymmetric Hydroformylation of Olefins with Rh Catalysts
Modified with Chiral Phosphine-Phosphite Ligands
Miguel Rubio,† Andre´s Sua´rez,† Eleuterio AÄ lvarez,† Claudio Bianchini,‡
Werner Oberhauser,‡ Maurizio Peruzzini,*,‡ and Antonio Pizzano*,†
Instituto de InVestigaciones Qu´ımicas, Consejo Superior de InVestigaciones Cient´ıficas and UniVersidad de
SeVilla, AVda Ame´rico Vespucio n° 49, Isla de la Cartuja, 41092 SeVilla, Spain, and Istituto di Chimica
dei Composti Organometallici (ICCOM-CNR), Area di Ricerca CNR di Firenze, Via Madonna del Piano
10, 50019 Sesto Fiorentino (FI), Italy
ReceiVed July 23, 2007
Rhodium complexes stabilized by modularly designed chiral phosphine-phosphite ligands (P-OP)
have been tested in the asymmetric hydroformylation of styrene, vinyl naphthalenes, and allyl cyanide.
Based on single-crystal X-ray diffraction analysis and NMR studies, restricted aryl rotation has been
found to characterize ligands 1e and 1f. The outcome of the rhodium-catalyzed hydroformylation
reactions is highly dependent on the nature of the two coordinating functions of the phosphine-phosphite
and of the ligand backbone as well. Among the ligands studied, those with an oxyphenylene backbone
and PAr2 ends gave the best results, outperforming those with P-stereogenic phosphine groups. The
1-naphthyl-substituted catalyst brought about the hydroformylation of styrene with a 71% ee, while the
xylyl catalyst afforded the best results in the hydroformylation of allyl cyanide, yielding an iso/n ratio
of 13 and 53% ee in the branched isomer. Several hydrido(carbonyl) species of the formula
RhH(CO)2(P-OP) have been generated by reacting Rh(acac)(CO)2/P-OP with syngas. In situ high-
pressure NMR experiments showed the phosphine group to occupy an apical position of the trigonal
bipyramidal coordination geometry, which allows an aryl-aryl interaction between the phosphine
substituents and the substrate during the hydroformylation of vinyl arenes. In line with this finding, a
remarkable enantioselectivity of 89% ee was obtained with the naphthyl catalyst and 1-vinyl naphthalene
as substrate.
the carbonylation of olefins. From a perusal of the best-
performing P-ligands, one may conclude that these ligands do
not share many common characteristics: they are often structur-
ally diverse with different symmetries (C1 or C2) and contain
various types of phosphorus donor groups like phosphines,
phosphoramidites, or phosphites. For instance, azaphospholanes6
and diphosphites7 have been shown to generate very efficient
rhodium catalysts for the hydroformylation of vinyl arenes, vinyl
acetate, and allyl cyanide. Likewise, a recently reported phenyl-
substituted bisphospholane has also provided excellent results.8
Moreover, Zhang has recently described a binaphthyl-based
phosphine-phosphoramidite ligand capable of inducing an
excellent enantioselectivity in the hydroformylation of several
olefins.9 In terms of catalyst scope, the work developed by
Takaya and Nozaki with the BINAPHOS ligands occupies a
prominent place in this field. By using these phosphine-
phosphites, a wide variety of olefins, encompassing vinyl arenes,
enamides, enol esters, heterocyclic olefins, dienes, or vinyl
Introduction
The enantioselective hydroformylation of prochiral alkenes
is one of the most challenging processes in asymmetric catalysis.
Indeed, a strict control of enantio-, chemo-, and regioselectivity
is required to efficiently produce the desired branched isomer
in high optical purity.1 Motivated by the convenience of this
process to obtain synthetically valuable aldehydes, extensive
studies with several types of catalysts have been developed.2
Among the many catalysts investigated, those based on Rh and
chelating phosphorus ligands have shown superior activity and
selectivity.3-5 A vast range of P-ligands have been tested, but
only very few of them have provided high enantioselectivity in
* Corresponding authors. E-mail: mperuzzini@iccom.cnr.it (M.P.);
pizzano@iiq.csic.es (A.P.).
† Universidad de Sevilla.
‡ ICCOM-CNR.
(1) (a) Homogeneous Catalysis: Understanding the Art; van Leeuwen,
P.W. N. M., Ed.; Kluwer Academic Publishers: Dordrecht, 2004. (b)
Nozaki, K. In ComprehensiVe Asymmetric Catalysis; Jacobsen, E. N.,
Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin, 1999; Vol. 1. (c)
Consiglio, C. In Catalytic Asymmetric Catalysis; Ojima, I., Ed.; VCH: New
York, 1993.
(2) (a) Agbossou, F.; Carpentier, J.-F.; Mortreux, A. Chem. ReV. 1995,
95, 2485. (b) Gladiali, S.; Bayo´n, J. C.; Claver, C. Tetrahedron: Asymmetry
1995, 6, 1453.
(6) (a) Clark, T. P.; Landis, C. R.; Freed, S. L.; Klosin, J.; Abboud, K.
A. J. Am. Chem. Soc. 2005, 127, 5040. (b) Breeden, S.; Cole-Hamilton, D.
J.; Foster, D. F.; Schwarz, G. J.; Wills, M. Angew. Chem., Int. Ed. 2000,
39, 4106.
(7) (a) Babin J. E.; Whiteker, G. T. WO 93/0389, U.S. Patent US911,-
518, 1992. (b) Die´guez, M.; Pa`mies, O.; Ruiz, A.; Castillo´n, S.; Claver C.
Chem. Eur. J. 2001, 7, 3086. (c) Buisman, G. J. H.; van der Veen, L. A.;
Klootwijk, A.; de Lange, W. G. J.; Kamer, P. C. J.; van Leeuwen, P. W.
N. M.; Vogt, D. Organometallics 1997, 16, 2929. (d) Cobley, C. J.; Froese,
R. D. J.; Klosin, J.; Qin, C.; Whiteker, G. T.; Abboud, K. A. Organometallics
2007, 26, 2986.
(3) Other catalysts with either Rh complexes based on different ligands
or Pt/Sn systems have been studied in detail.4,5
(4) (a) Stille, J. K.; Su, H.; Brechot, P.; Parrinello, G.; Hegedus, L. S.
Organometallics 1991, 10, 1183. (b) Casey, C. P.; Martins, S. C.; Fagan,
M. A. J. Am. Chem. Soc. 2004, 126, 5585.
(5) (a) Arena, D. G.; Nicolo´, F.; Drommi, D.; Bruno, G.; Faraone, F. J.
Chem. Soc., Chem. Commun. 1994, 2251. (b) Castellanos-Pa´ez, A.;
Castillo´n, S.; Claver, C. J. Organomet. Chem. 1997, 539, 1.
(8) Axtell, A. T.; Cobley, C. J.; Klosin, J.; Whiteker, G. T.; Zanotti-
Gerosa, A.; Abboud, K. A. Angew. Chem., Int. Ed. 2005, 44, 5834.
(9) Yan, Y.; Zhang, X. J. Am. Chem. Soc. 2006, 108, 7198.
10.1021/om700744b CCC: $37.00 © 2007 American Chemical Society
Publication on Web 11/01/2007

Asymmetric Hydroformylation of Olefins
Organometallics, Vol. 26, No. 25, 2007 6429
â-lactams, were hydroformylated with generally high levels of
regio- and enantioselectivity.10 These outstanding results have
attracted much interest on phosphine-phosphites for the enan-
tioselective hydroformylation of olefins, and several new ligand
families of this type have been prepared and tested.11 Although
some of these ligands share PAr2 and P(OAr)2 groups with
BINAPHOS, lower enantioselectivities are generally obtained,
which reflects the great influence of the ligand backbone in
driving the reaction outcome.
In our laboratories, we are studying the application of
phosphine-phosphites in asymmetric hydrogenation reactions.
To this purpose, a modular synthesis of phosphine-phosphite
ligands, containing phenylene or ethylene bridges, has been
developed.12 The easily tunable structure of these compounds
has been fruitfully exploited in the reduction of several olefins
and imines.13
Herein, we report on the use of rhodium catalysts modified
with chiral phosphine-phosphite ligands in the hydroformyla-
tion of vinyl arenes and allyl cyanide that are capable of inducing
enantioselectivities as high as 89% ee. In situ high-pressure
NMR studies (HP-NMR) have provided valuable information
on the course of the catalytic process.
Results and Discussion
Ligand Features. The phosphine-phosphite ligands used in
this study are shown in Figure 1. Ligands of type 1 contain a
phenylene backbone connecting the phosphine and phosphite
donor atoms. They possess a bulky phosphite group and differ
from each other in the substituents on the phosphine P-atom.
All ligands have been previously described, except for the novel
naphthyl derivative 1f (Scheme 1) synthesized from o-anisyl-
di(1-naphthyl)phosphine.14 The phosphine-phosphite ligands
of type 2 bear a less bulky phosphite group, while a more
flexible ethylene bridge features ligand 3. Finally, ligands 4 and
5 contain P-stereogenic phosphine groups.
Figure 1.
Scheme 1
Broad signals were observed in the 31P{1H} spectrum of
ligand 1f at room temperature. Heating the sample to 40 °C
narrowed the phosphine signal and allowed the observation of
2
the JPP (40 Hz) coupling constant, while the phosphite signal
remained broad. Moreover, the o-tolyl ligand 1e displayed two
broad signals at room temperature that sharpened into doublets
(2JPP ) 36 Hz) upon warming at 40 °C. Interestingly, com-
pounds 1a and 1d, whose aryl rings can rotate easily around
the P-C bonds, showed sharp doublets. In view of these
findings, we interpret the solution behavior of ligands 1e and
1f as due to a slow interconversion between rotational isomers.
This feature seems to be generated by steric effects, as ligands
2e and 2f, which possess a smaller phosphite group, showed
only sharp signals.13d Aware of the impact that the structure of
the PAr2 group may have on the catalytic performance of these
ligands,12b we first tried to gain additional information about
the observed restricted rotation. To this purpose, the solid-state
structures of 1a and 1e in the complexes PdCl2(P-OP) [P-OP
) 1a (7a), 1e (7e)] have been determined by single-crystal X-ray
diffraction analyses and compared to each other. Complexes 7
were straightforwardly prepared by adding a stoichiometric
amount of the appropriate phosphine-phosphite ligand to a
toluene solution of PdCl2(MeCN)2 (see Experimental Section
for details).
(10) (a) Sakai, N.; Mano, S.; Nozaki, K.; Takaya, H. J. Am. Chem. Soc.
1993, 115, 7033. (b) Nozaki, K.; Sakai, N.; Nanno, T.; Higashijima, T.;
Mano, S.; Horiuchi, T.; Takaya, H. J. Am. Chem. Soc. 1997, 119, 4413. (c)
Horiuchi, T.; Ohta, T.; Shirakawa, E.; Nozaki, K.; Takaya, H. J. Org. Chem.
1997, 62, 4285. (d) Nozaki, K.; Li, W.; Horiuchi, T.; Takaya, H. J. Org.
Chem. 1996, 61, 7658. (e) Horiuchi, T.; Ohta, T.; Nozaki, K.; Takaya, H.
Chem. Commun. 1996, 155. (f) Sakai, N.; Nozaki, K.; Takaya, H. J. Chem.
Soc., Chem. Commun. 1994, 4285.
(11) (a) Deerenberg, S.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.
Organometallics 2000, 19, 2065. (b) Pa`mies, O.; Net, G.; Ruiz, A.; Claver,
C. Tetrahedron: Asymmetry 2002, 12, 3441. (c) Kless, A.; Holz, J.; Heller,
D.; Kadyrov, R.; Selke, R.; Fischer, C.; Bo¨rner, A. Tetrahedron: Asymmetry
1996, 7, 33.
(12) (a) Sua´rez, A.; Me´ndez-Rojas, M. A.; Pizzano, A. Organometallics
2002, 21, 4611. (b) Vargas, S.; Rubio, M.; Sua´rez, A.; del R´ıo, D.; AÄ lvarez,
E.; Pizzano, A. Organometallics 2006, 25, 961.
(13) (a) Rubio, M.; Sua´rez, A.; AÄ lvarez, E.; Pizzano, A. Chem. Commun.
2005, 628. (b) Sua´rez, A.; Pizzano, A. Tetrahedron: Asymmetry 2001, 12,
2501. (c) Vargas, S.; Rubio, M.; Sua´rez, A.; Pizzano, A. Tetrahedron Lett.
2005, 46, 2049. (d) Rubio, M.; Vargas, S.; Sua´rez, A.; AÄ lvarez, E.; Pizzano,
A. Chem. Eur. J. 2007, 13, 1821.
Figures 2 and 3 show ORTEP representations of these
complexes along with selected bond distances and angles. The
structure of compound 7a is very similar to that previously
determined for RhCl(CO)(1a), especially in regards to the
(14) Laitinen, R. H.; Haukka, M.; Koskinen, A. M. P.; Koskianen, J. J.
Organomet. Chem. 2000, 598, 235.

6430 Organometallics, Vol. 26, No. 25, 2007
Rubio et al.
Figure 2. ORTEP drawing of complex 7a. Selected bond distances [Å] and angles [deg]: Pd(1)-P(1) ) 2.1948(18), Pd(1)-P(2) )
2.2659(17), Pd(1)-Cl(1) ) 2.3172(16), Pd(1)-Cl(2) ) 2.3341(18); P(1)-Pd(1)-P(2) ) 90.38(6), P(1)-Pd(1)-P(2)-C(37) ) -84.9(2),
P(1)-Pd(1)-P(2)-C(31) ) 151.3(3).
Figure 3. ORTEP drawing of complex 7e. A and B denote the two rotational isomers. Selected bond distances [Å] and angles [deg]:
Pd(1)-P(1) ) 2.1933(8), Pd(1)-P(2) ) 2.2717(8), Pd(1)-Cl(1) ) 2.3407(8), Pd(1)-Cl(2) ) 2.3469(7); P(1)-Pd(1)-P(2) ) 90.44(3),
P(1)-Pd(1)-P(2)-C(38A) ) -85.45(19), P(1)-Pd(1)-P(2)-C(38B) ) -75.09(18), P(1)-Pd(1)-P(2)-C(31) ) 156.69(11).
conformation of 1a, and, for this reason, it does not deserve
any further comment. In contrast, complex 7e coexists in the
solid state as a 1:1 mixture of two rotational isomers, differing
from each other in the orientation of the pseudoaxial o-tolyl
group15 with the methyl substituent pointing either to the Pd
atom or to the backbone. Noteworthy, the rest of the structure
is practically coincident in the two rotamers as well as with the
structure of 7a. Likewise, the 1H and 31P{1H} NMR spectra of
7e showed the existence of two species in solution, identified
by two groups of signals in a 1.5:1 ratio. An analysis of the 1H
NMR spectra acquired at different temperatures showed the
coalescence of homologous methyl signals of the two isomers
(Figure 4) with the exception of one methyl substituent of a
tolyl fragment that did not reach the fast exchange regime even
at the higher temperature investigated. Interestingly, the reso-
nances of this group in either isomer show an important
difference in chemical shift (ca. 1.8 ppm), suggesting a
significantly different environment for this substituent in the
two species. A perusal of the X-ray structure of 7e indicates
that this methyl group may be that located in the pseudoaxial
tolyl ring (C44). Moreover, as C44A points directly to the
phenylene backbone, one would expect a considerable shielding
(15) For other examples of structures with o-tolyl phosphines, see: (a)
Tsuruta, H.; Imamoto, T.; Yamaguchi, K.; Gridnev, I. D. Tetrahedron Lett.
2005, 46, 2879. (b) Casas, J. M.; Fornie´s, J.; Fuertes, S.; Mart´ın, A.; Sicilia,
V. Organometallics 2007, 26, 1674.

Asymmetric Hydroformylation of Olefins
Organometallics, Vol. 26, No. 25, 2007 6431
Figure 4. Methyl region of 1H NMR spectrum of complex 7e (C6D6, 500 MHz), registered at different temperatures. A and B refer to the
two isomers observed in the X-ray structure.
Table 1. Styrene Hydroformylation with Catalysts Based on
vessel containing a rack for six glass tubes to run parallel
catalytic reactions. No significant decrease in the gas pressure
was observed during the whole reaction.
P-OP Ligandsa
entry
P-OP
% conversion (time)
i:n
% ee (conf.)
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
2a
3
4a
4b
5a
5b
93 (24 h)
34 (48 h)
55 (18 h)
97 (24 h)
28 (24 h)
48 (24 h)
7 (24 h)
100 (24 h)
85 (16 h)
47 (18 h)
100 (24 h)
94 (24 h)
98:2
98:2
93:7
98:2
96:4
98:2
n.d.
96:4
97:3
96:4
94:6
93:7
43 (S)
25 (R)
32 (R)
47 (S)
33 (S)
71 (S)
n.d.
25 (R)
39 (S)
28 (R)
25 (R)
19 (S)
An examination of the results obtained indicates that the
catalyst performance is very sensitive to the ligand employed.
Indeed, the conversion obtained with ligands of type 1 ranges
between 28% (1e, entry 5) and 97% (1d, entry 4) for the same
reaction time. The well-known effect due to bulky phosphites
on the catalyst activity17 is highlighted by a comparison of the
reactions catalyzed by Rh complexes modified with 1a and 2a
(entries 1, 7). The effect is opposite on the phosphine side as
ligands 1e and 1f (entries 5, 6) produce lower conversions than
less hindered 1a or 1d (entries 1, 4). On the other hand,
increasing the ligand flexibility does not seem to exert a
detrimental effect on either catalytic activity or regioselectivity
as shown by comparing the performance of the Rh complex
with ligand 3 (entry 8) to those obtained with ligand 1a.
As expected, the enantioselectivity is very dependent on the
phosphine-phosphite ligand used, from 19% ee obtained with
ligand 5b (entry 12) to a remarkable 71% ee afforded by 1f
10
11
12
a Reactions were carried out at 50 °C with an initial gas pressure of 20
bar, in toluene at a S/C ) 1000 in a 750 mL reaction vessel. Conversion
1
was determined by H NMR and enantiomeric excess (ee) by chiral GC.
Configuration was determined by comparison of optical rotation to the
literature value.
for this group.16 On this basis, it is reasonable to assign the
singlet at 1.50 ppm to the rotamer A. Conversely, the singlet at
δ 3.35 can be ascribed to compound B, which is the preferred
isomer in solution.
Catalytic Hydroformylation Reactions. Styrene hydro-
formylation reactions (eq 1) were carried out in toluene at
50 °C with a substrate to catalyst ratio (S/C) of 1000 and at an
initial pressure of 20 bar. The results obtained are summarized
in Table 1. The experiments were carried out in a 750 mL Parr
(17) See, for instance: (a) van Rooy, A.; Kamer, P. C. J.; van Leeuwen,
P. W. N. M.; Goubitz, K.; Fraanje, J.; Veldman, N.; Spek, A. L.
Organometallics 1996, 15, 835. (b) Van Rooy, A.; Orij, E. N.; Kamer, P.
C. J.; van den Aardweg, F.; van Leeuwen, P. W. N. M. J. Chem. Soc.,
Chem. Commun. 1991, 1096.
(16) Gridnev, I. D.; Higashi, N.; Asakura, K.; Imamoto, T. J. Am. Chem.
Soc. 2000, 122, 7183.

6432 Organometallics, Vol. 26, No. 25, 2007
Rubio et al.
Table 2. Allyl Cyanide Hydroformylationa
complexes RhH(CO)2(1) exhibit in solution a single set of
resonances, which is consistent either with the presence of a
single complex in solution or with a fast interchange between
several species. The 31P{1H} NMR spectra of these complexes
show the expected AMX (X ) 103Rh) spin system with
resonances in the region of coordinated phosphines and phos-
phites with 1JRhP of 95 and 235 Hz, respectively, and 2JPP values
of ca. 60 Hz, similar to those already reported for RhCl(CO)-
(1) complexes.12a
entry
P-OP
% conversion
i:n
% ee (conf.)
1
2
3
4
5
6
7
1a
1c
1d
1e
1f
70
65
75
10
30
85
90
94:6
90:10
93:7
23 (S)
6 (R)
53 (S)
22 (S)
31 (S)
11 (S)
40 (R)
95:5
84:16
90:10
91:9
4a
4b
a Reactions were carried out at 50 °C with an initial gas pressure of 20
bar, in toluene at a S/C ) 1000 in a 750 mL reaction vessel. Conversion
1
At room temperature, the H NMR spectrum of RhH(CO)2-
(1b) shows a doublet of doublets at -8.80 ppm with a 1JHRh of
9.4 Hz and a 2JHP of 117.5 Hz. The latter is due to the coupling
of the hydride ligand to the phosphine phosphorus nucleus. Upon
cooling, the chemical shifts and coupling constants did not
change significantly. Interestingly, no coupling of the hydride
to the phosphite P-atom was observed at any temperature, which
is consistent with a cis disposition of the hydride and phosphite
ligands in a trigonal bipyramidal coordination geometry where
the phosphine group occupies an apical coordination site
(structure C).11a
1
was determined by H NMR and enantiomeric excess (ee) by chiral GC.
Configuration was determined by comparison of optical rotation to the
literature value.
(entry 6). However, the configuration of the aldehyde product
seems to be driven by a rather complex correlation between
the type of phosphine, phosphite, and backbone fragments.
Indeed, despite all of the members of the 1 family having a
phosphite group with S configuration, the ligands with a
diarylphosphino group produce the aldehyde with S configu-
ration (entries 1, 4-6), while the R enantiomer is predominant
in the reactions performed with the dialkylphosphino ligands
1b and 1c (entries 2, 3). Interestingly, the aldehyde configuration
changes, with respect to that obtained with 1a, by using the
ethylene bridged ligand 3. On the other hand, reactions
performed with the P-stereogenic ligands 4 and 5 indicate that
the configuration of the phosphite group determines the chirality
of the final product (entries 9-12). Like for ligand 1a, for the
pair of ligands 4 S phosphite favors the formation of the S
product. Otherwise, for ligands 5 the preferred product for the
S phosphite is R, as found for ligand 3. No enantioselectivity
enhancement was observed by using the P-stereogenic ligands
4 and 5 as compared to their nonstereogenic phosphine
congeners 1 and 3. This finding contrasts with the behavior of
aminophosphine-phosphinite ligands for which an important
increase in the enantioselectivity was observed by substituting
the PPh2 group with a stereogenic P(Ph)Me fragment.18
Phosphine-phosphites 1 and 4 have also been examined in
the Rh-catalyzed hydroformylation of allyl cyanide (eq 2).19 The
results are reported in Table 2. Catalytic conversions up to 90%
in 24 h were obtained (entry 7). In all cases, the regioselectivity
was remarkably high, with a branched to linear ratio up to 15.7
with ligand 1a (entry 1), while the enantioselectivity was from
low to moderate, with the highest value (53% ee) for ligand 1d
(entry 3).
The rhodium-hydrido(dicarbonyl) complexes with ligands
1a and 1f showed a somewhat different behavior in the
temperature range between 50 and -90 °C, which is consistent
with scrambling of the two phosphorus atoms with respect to
axial and equatorial positions of the bipyramidal structure. The
1
value of the coupling constant JHRh is around 10 Hz for both
complexes in the temperature range investigated, pointing to
an apical hydride with a trans phosphorus atom. Values of
2JHP(phosphite) of 40 and 32 Hz were observed at 50 °C for the
complexes stabilized by 1a and 1f, respectively. This coupling
constant decreases with temperature and for RhH(CO)2(1a) has
the value of 15.2 Hz at -60 °C. Extensive signal broadening
2
precludes a reliable evaluation of JHP(phosphite) below this
2
temperature. Notably, the magnitude of JHP(phosphine) increases
from 90 Hz at 50 °C to 112 Hz at -90 °C. These observations
are consistent with an equilibrium between species C and D
for the rhodium hydride dicarbonyls derived from 1a and 1f.11b
On the other hand, the spectroscopic data of RhH(CO)2(1b)
2
provide a JHP value of ca. 115 Hz for the trans hydride and
phosphine groups, while previous studies of the BINAPHOS
2
hydrido(dicarbonyl) report a JHP value of 160 Hz.11a Finally,
irrespective of the phosphine or phosphite, 2JHP should be around
0-5 Hz for hydride and phosphorus groups occupying mutually
cis positions of a trigonal bipyramid. Therefore, the observed
2JHP values for the rhodium hydride dicarbonyls of 1a and 1f
indicate a fast exchange between species C and D at 50 °C,
with a prevalence of the former species, which is further on
favored on decreasing the temperature. On the basis of the values
2
of JHP, a C:D ratio of ca. 4:1 at 50 °C can be estimated for
both complexes.20
To obtain mechanistic information, we studied the hydro-
formylation reactions assisted by ligands 1a-1c, 1e, and 1f by
means of in situ HP-NMR spectroscopy, which allowed us to
intercept hydride species of the formula RhH(P-OP)(CO)2. As
previously reported,11a,b these complexes may be generated from
the stoichiometric reaction of Rh(acac)(CO)2 with the corre-
sponding phosphine-phosphite upon heating the resulting
mixture at 50-60 °C for 2-4 h under 20 bar of H2/CO (1:1).
Selected 31P{1H} and 1H chemical shifts and coupling constants
for these rhodium hydrides are collected in Table 3. With the
exception of the derivative of 1e (see below), all of the
The isopropyl derivative RhH(CO)2(1c) exhibits a less clear
2
behavior. The values of the JHP coupling constants do not
significantly change with temperature, as observed for Rh(H)-
2
(CO)2(1b). Analogously, the JHP(phosphine) maintains the char-
acteristic values of a trans relation between the hydride and the
phosphine ligands. However, 2JHP(phosphite) is significantly higher
than the near null value expected for a cis arrangement. These
data may be ascribed to the presence of a mixture of species
(C and D). Alternatively, the high value of the cis constant
may be attributed to a distortion of species C11a from the
ideal trigonal bipyramidal geometry due to steric congestion.
(18) Ewalds, R.; Eggeling, E. B.; Hewat, A. C.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M.; Vogt, D. Chem. Eur. J. 2000, 6, 1496.
(19) (a) Lambers-Verstappen, M. M. H.; de Vries, J. G. AdV. Synth. Catal.
2003, 345, 478. (b) Cobley, C. J.; Gardner, K.; Klosin, J.; Praquin, C.;
Hill, C.; Whiteker, G. T.; Zanotti-Gerosa, A. J. Org. Chem. 2004, 69, 4031.
(20) Casey, C. P.; Paulsen, E. L.; Beuttenmueller, E. W.; Proft, B. R.;
Petrovich, L. M.; Matter, B. A.; Powell, D. R. J. Am. Chem. Soc. 1997,
119, 11817.

Asymmetric Hydroformylation of Olefins
Organometallics, Vol. 26, No. 25, 2007 6433
Table 3. NMR Data for the Hydride Resonance of RhH(P-OP)(CO)2 Complexesa
b
entry
P-OP
T (°C)
δHRh
1JHRh
δPC
2JHPC
δPO
2JHPO
1
2
3
4
5
6
7
8
9
1a
50
25
-90
50
25
-90
50
25
-90
50
-9.10
-9.01
-8.64
-8.88
-8.80
-8.32
-8.96
-8.78
-8.29
-9.37
-9.33
10.1
9.7
br d
br d
9.4
10.0
10.1
10.3
br d
8.9
19.0
20.7
21.9
-19.2
-18.8
-17.2
35.6
34.7
33.6
12.0
18.5
7.6
21.3
3.6
5.1
5.1
5.5
92.5
96.3
111.8
117.7
117.5
113.8
91.1
92.4
97.4
75.6
br
br
120
108
89.6
101.5
112.9
159.2
161.6
165.5
158.3
159.3
162.9
151.4
151.9
151.9
156.0
161.4
154.4
157.2
152.8
155.3
156.2
157.2
40
33
br d
1b
1c
1e
50
47
br d
53
br
10
11c
25
8.8
br
12d
-90
-8.61
-9.33
-9.63
-9.53
-9.6
br
br
10.3
8.4
br d
13
14
15
1f
50
25
-90
32
28
br d
a In toluene-d8. Chemical shifts in ppm, coupling constants in Hz. b br d: broad doublet in the 1H NMR spectrum. c One group of signals in the 1H NMR
1
spectrum and two groups of resonances in the 31P{1H} NMR spectrum. d Two groups of NMR signals in the H and 31P{1H} NMR spectra.
In this respect, it should be noted that, as the coupling
constant JHP(phosphite) changes from ca. 0 to 160 Hz in going
lation results. Previous studies on rhodium complexes with
phosphine-phosphite ligands indicate that the concurrence of
both coordinating functions is necessary to achieve a high
enantiomeric excess, while the equatorial group mostly influ-
ences the enantioselectivity of the reaction.10,11 Indeed, in the
reactions catalyzed by the rhodium complexes with the ligands
4 and 5, containing two stereogenic elements, the phosphite
group determines the configuration of the branched aldehyde.
On the other hand, this trend is not always preserved along the
series investigated, as both the nature of the phosphine group
and the backbone can affect the product configuration as well.
Recently, detailed theoretical calculations on aminophosphine-
phosphinite rhodium complexes (also displaying an apical-
equatorial coordination mode) have identified the formation of
π-π stacking interactions between the apical aminophosphine
and the bonded styrene as an important stereoregulating factor.22
Therefore, it is not strictly correct to compare results obtained
with ligands bearing dialkyl- and diarylphosphino groups.
Concerning the latter, our present data show that a good
enantioselectivity is observed in the hydroformylation of styrene
with the catalyst containing the ligand 1f, which possesses
neither a P-stereogenic phosphine group nor a chiral backbone.
Previous studies have demonstrated that ligands 1a-1f are rather
rigid due to interactions beween the phenylene backbone and
the bulky phosphite.12a As a consequence, ligands with PAr2
groups display a propeller-like chiral arrangement of the aryl
substituents typical of diphosphines with a chiral backbone, also
observed in the structures of complexes 7. On the other hand,
earlier works on the ethane-based phosphine-phosphite ligand
3 demonstrated that this ligand displays a different aryl
arrangement that switches the face and edge oriented phenyl
rings around the plane defined by Rh and P atoms (Figure 5).
From these considerations, it is possible that a similar π-π
stacking effect may operate in the present catalytic systems as
well. Thus, the increased enantioselectivity in the hydroformy-
lation of styrene found for the naphthyl catalyst in view of the
higher interaction calculated between the substrate and model
catalysts with PH2(1-naphthyl) with respect to PH2Ph analogues
is not surprising.22 Noteworthy, the naphthyl catalyst can benefit
2
from cis-hydride-phosphite to trans-hydride-phosphite, a small
distortion of the geometry may produce a significant increase
in the value of 2JHP(phosphite). Additional support to this hypothesis
is provided by stereoelectronic considerations. Indeed, according
to literature data, the more σ-donor group (phosphine) should
occupy the apical position with the equatorial position occupied
by the better π-acceptor (phosphite).21 Following this assump-
tion, the hydride complex with ligand 1b should have an
electronic preference for structure C, in good accord with the
experimental observations. In contrast, for derivatives of the
less basic ligands 1a and 1f, this preference is less pronounced
and structure D becomes, as observed, energetically competitive.
Finally, as ligand 1c contains the most basic phosphine group
of the series,12a it is reasonable to expect a marked preference
for structure C for the related rhodium hydrido(dicarbonyl)
complex.
At variance with the rest of the hydrides investigated, the
o-tolyl derivative RhH(CO)2(1e) displays two groups of signals
1
2
in the 31P{1H} NMR spectrum at -90 °C, with JRhP and JPP
values similar to those for RhH(CO)2(1a) at the same temper-
ature. In addition, the H NMR spectrum acquired at -90 °C
shows two broad doublets with JHP of ca. 120 and 108 Hz.
1
2
These data can be interpreted with the existence of two type-C
species. The occurrence of rotational isomers observed in PdCl2-
(1e) led us to propose that the two isomers observed for RhH-
(CO)2(1e) at low temperature differ in the orientation of the
o-tolyl substituents.
The HP-NMR data therefore indicate a preference for
structure C of (hydride)dicarbonyls derived from 1. This
coordination mode is also preferred by other phosphine-
phosphites described by van Leeuwen11a and Claver,11b while
the structure of type D is the preferred one by ligands of the
BINAPHOS family.10b
(21) (a) Zuidema, E.; Daura-Oller, E.; Carbo´, J. J.; Bo, C.; van Leeuwen,
P. W. N. M. Organometallics 2007, 26, 2234. (b) Casey, C. P.; Paulsen, E.
L.; Beuttenmueller, E. W.; Proft, B. R.; Matter, B. A.; Powell, D. R. J.
Am. Chem. Soc. 1999, 121, 63.
(22) Carbo´, J. J.; Lledo´s, A.; Vogt, D.; Bo, C. Chem. Eur. J. 2006, 12,
1457.
The preferred apical coordination of the phosphine group
deserves a further comment in view of the styrene hydroformy-

6434 Organometallics, Vol. 26, No. 25, 2007
Rubio et al.
Figure 5. Structures of complexes RhH(P-OP)L2 (L ) CO, olefin). P-OP ) 1a (a), 3 (b).
Table 4. Hydroformylation of Vinyl Naphthalenes
phosphite group occupying an equatorial position. With regards
to the influence of the structure of the diarylphosphino groups
on product configuration, the π-π/aryl-aryl interaction between
phosphine and olefin substituents seems to exert an important
role. Consistently, 1-naphthyl substituents provided a significant
enhancement on the selectivity. The highest enantioselectivity
was 89% ee in the carbonylation of 1-vinyl naphthalene with
the rhodium catalyst bearing the naphthyl-substituted ligand 1f.
Ar-CHdCH2 with P-OP-Based Catalysts
% conversion
entry
Ar
P-OP
(time)
i:n
% ee (conf.)
1
2
3
4
2-naphthyl
2-naphthyl
1-naphthyl
1-naphthyl
1a
1f
1a
1f
100
45
100
100
98:2
98:2
95:5
99:1
44 (S)
75 (S)
68 (S)
89 (S)
a Reactions were carried out at 50 °C for 24 h with an initial gas pressure
of 20 bar, in toluene at a S/C ) 1000 in a 750 mL reaction vessel.
1
Experimental Section
Conversion was determined by H NMR and enantiomeric excess (ee) by
chiral GC. Configuration was determined by comparison of optical rotation
General Comments. All reactions and manipulations were
performed under nitrogen or argon, either in a Braun Labmaster
100 glovebox or using standard Schlenk-type techniques. All
solvents were distilled under nitrogen using the following dessi-
cants: sodium-benzophenone-ketyl for benzene, diethylether
(Et2O), and tetrahydrofuran (THF); sodium for petroleum ether and
toluene; CaH2 for dichloromethane (CH2Cl2); and NaOMe for
methanol (MeOH). Enantiomers of 3,3′-di-tert-butyl-5,5′,6,6′-
tetramethyl-2,2′-bisphenoxyphosphorus chloride and ligands 1a-
1e, 2-5 were prepared as described previously.12,13 o-Anisyl-di-
1-naphthylphosphine was prepared according to a literature
procedure.14 1-Vinyl naphthalene was purified by extraction in
n-hexane. All other reagents were purchased from commercial
suppliers and used as received. NMR spectra were obtained on a
Bruker DPX-300, DRX-400, or DRX-500 spectrometer. 31P{1H}
NMR shifts were referenced to external 85% H3PO4, while 13C-
{1H} and 1H shifts were referenced to the residual signals of
deuterated solvents. All data are reported in ppm downfield from
Me4Si. All NMR measurements were carried out at 25 °C, unless
otherwise stated. HP-NMR experiments were carried out on a
Bruker ACP 200 spectrometer, using a 10 mm tube (Saphikon
sapphire tube; titanium high-pressure charging head constructed at
the ICCOM).25 GC analyses were performed by using a Hewlett-
Packard model HP 6890 chromatograph. HPLC analyses were
performed by using a Waters 2690 system. HRMS data were
obtained using a Jeol JMS-SX 102A mass spectrometer. Elemental
analysis was run by the Analytical Service of the Instituto de
Investigaciones Qu´ımicas in a Leco CHNS-932 elemental analyzer.
Optical rotations were measured on a Perkin-Elmer model 341
polarimeter. IR spectra were acquired on a Bruker Vector 22
instrument.
to the literature value.24
from a restricted rotation of the aryl substituents, which would
facilitate a defined interaction between the aromatic rings.23
With the intention to confirm the positive role ascribed to
the substrate to ligand aryl-aryl interaction for achieving higher
enantioselectivities in the carbonylation of aryl-substituted
alkenes, the hydroformylation of 1- and 2-vinyl naphthalenes
has also been examined. The corresponding results are collected
in Table 4. These data indicate that, while 2-vinyl naphthalene
shows a small increase in the enantioselectivity as compared to
styrene (entries 1, 2), 1-vinyl naphthalene gives significantly
higher enantioselectivities than styrene (entries 3, 4). With
catalyst 1a, where the supposedly beneficial interaction between
the 1-naphthyl and Ph substituents is still active, although with
reversed reciprocal position of the aryl groups, a 68% ee was
obtained (versus 43% ee in styrene hydroformylation with the
same catalyst). Finally, the effect is maximized by confronting
two R-naphthyl substituents, and a significant increase up to
89% ee was observed.
Conclusions
Rhodium(I) complexes bearing chiral phosphine-phosphite
ligands have been evaluated in the hydroformylation of vinyl
arenes and allyl cyanide. High regioselectivities, ranging from
93% to 98% in the branched aldehyde, were obtained with all
substrates. The highest ee values observed in the hydroformy-
lation of styrene and allyl cyanide were 71% and 53% ee,
respectively. Structural studies on complexes 7a and 7e have
shown the occurrence in solution of restricted rotation of the
pseudoaxial tolyl group in the latter complex. HP-NMR studies
have allowed us to determine the coordination mode of ligands
of type 1 in the hydrido(dicarbonyl) species RhH(CO)2(1)
formed in situ. This study has shown a clear preference for an
axial-equatorial coordination of the bidentate ligand with the
Synthesis of 2-Hydroxyphenyldi(1-naphthyl)phosphine. To a
solution of o-anisyl-di-1-naphthylphosphine (1.22 g, 3.1 mmol) in
CH2Cl2 (50 mL) cooled at -78 °C was added BBr3 (0.70 mL, 7.6
mmol). The resulting solution was left to warm to room temperature
(24) Menicagli, R.; Piccolo, O.; Lardicci, L.; Wis, M. L. Tetrahedron
1979, 35, 1301.
(23) Kojima, T.; Hayashi, K.; Matsuda, Y. Inorg. Chem. 2004, 43, 6793.
(25) Bianchini, C.; Meli, A.; Traversi, A. Ital Patent FI A000025, 1997.

Asymmetric Hydroformylation of Olefins
Organometallics, Vol. 26, No. 25, 2007 6435
and stirred for 16 h. The solution was evaporated, and a portion of
toluene (25 mL) was added and re-evaporated to ensure complete
elimination of volatiles. The remaining solid was treated with
MeOH (20 mL) at 0 °C and stirred for 2 days at room temperature.
The mixture was evaporated to dryness, resulting in a white solid
that was suspended in Et2O (30 mL). Next, NEt3 (0.70 mL, 4.5
mmol) was added, and the suspension was stirred for 2 h, filtered,
and the solvent was evaporated to dryness, resulting in the
compound as a white foamy solid (0.54 g, 45%). IR (nujol mull,
cm-1): 3492 (s, ν(OH)). 1H NMR (CDCl3, 300 MHz): δ 6.29 (brs,
1H, OH), 6.74-6.91 (m, 2H), 6.97 (t, JHH ) 6.0 Hz, 1H), 7.08 (t,
JHH ) 6.0 Hz, 2H), 7.25-7.38 (m, 3H), 7.39-7.55 (m, 4H), 7.80-
7.92 (m, 4H), 8.34 (dd, JHH ) 8.0, 4.0 Hz, 2H). 31P{1H} NMR
(CDCl3, 121 MHz): δ -47.0. 13C{1H} NMR (CDCl3, 75 MHz):
δ 115.9 (CH), 119.1 (Cq arom), 121.6 (CH), 126.0 (2 CH), 126.2
(s, CH), 126.4 (s, 2 CH), 126.6 (s, CH), 126.8 (s, 2 CH), 129.0 (s,
2 CH), 130.3 (s, 2 CH), 131.2 (d, JCP ) 5.0 Hz, 2 Cq), 132.1 (CH),
133.0 (2 CH), 133.9 (d, JCP ) 5.0 Hz, 2 Cq arom), 135.4 (Cq),
arom), 7.13 (s, 1H, H arom), 7.19 (t, JHH ) 8.0 Hz, 1H, H arom),
7.41 (m, 6H, H arom), 7.53 (m, 3H, H arom), 7.79 (dd, JHH
)
13.0, 7.0 Hz, 2H, H arom). 31P{1H} NMR (C6D6, 162 MHz): δ
11.5 (d, JPP ) 16.0 Hz, PC), 113.2 (d, PO). 13C{1H} NMR (CD2-
Cl2, 126 MHz): δ 16.7 (Ar-Me), 17.0 (Ar-Me), 20.6 (2 Ar-
Me), 31.2 (CMe3), 32.0 (CMe3), 34.7 (CMe3), 34.9 (CMe3), 118.3
(dd, JCP ) 56, 12 Hz, Cq arom), 122.7 (d, JCP ) 3.0 Hz, CH arom),
125.1 (s, Cq arom), 125.5 (Cq arom), 126.2 (Cq arom), 126.5 (d,
JCP ) 7.0 Hz, CH arom), 126.7 (Cq arom), 127.9 (Cq arom), 128.7
(CH arom), 128.8 (CH arom), 128.9 (CH arom), 129.0 (CH arom),
129.2 (CH arom), 129.3 (CH arom), 131.9 (d, JCP ) 2.0 Hz, CH
arom), 132.4 (d, JCP ) 2.0 Hz, CH arom), 133.8 (Cq arom), 134.1
(CH arom), 134.2 (CH arom), 134.3 (CH arom), 134.5 (CH arom),
134.6 (CH arom), 134.7 (CH arom), 134.7 (Cq arom), 136.0 (Cq
arom), 136.7 (d, JCP ) 4.0 Hz, Cq arom), 137.5 (Cq arom), 145.1
(d, JCP ) 8.0 Hz, Cq arom), 145.4 (d, JCP ) 15.0 Hz, Cq arom),
153.2 (d, JCP ) 8.0 Hz, Cq arom). Anal. Calcd for C42H46Cl2O3P2-
Pd: C, 60.2; H, 5.5. Found: C, 60.1; H, 5.6.
Synthesis of the Complex PdCl2(1e) (7e). This compound was
prepared following a synthetic procedure analogous to that described
for 7a, obtaining a yellow solid with 65% yield. Compound 7e
exists in solution as a mixture of rotational isomers (A and B) in
a 0.7:1 ratio.26 1H NMR (C6D6, 400 MHz): δ 1.13 (s, 9H, CMe3
B), 1.19 (s, 9H, CMe3 A), 1.48 (s, 12H, CMe3 A and C6H4Me A),
1.50 (s, 9H, CMe3 B), 1.67 (s, 3H, Me-ArO B), 1.67 (s, 3H, Me-
ArO A), 1.72 (s, 3H, Me-ArO A), 1.76 (s, 3H, Me-ArO B), 1.97
(s, 3H, Me-ArO B), 1.99 (s, 3H, Me-ArO A), 2.09 (s, 3H, Me-
ArO B), 2.09 (s, 3H, Me-ArO A), 2.81 (s, 3H, C6H4Me A), 2.86
(s, 3H, C6H4Me B), 3.35 (s, 3H, C6H4Me B), 6.53 (m, 6H, 3 H
arom A and 3 H arom B), 6.73 (m, 6H, 3 H arom A and 3 H arom
B), 6.96 (m, 7H, 3 H arom A and 4 H arom B), 7.11 (m, 4H, 2 H
arom A and 2 H arom B), 7.21 (s, 1H, H arom B), 7.23 (s, 1H, H
arom A), 7.27 (1H, H arom B), 7.28 (s, 1H, H arom A), 9.57 (brs,
1H, H arom A). 31P{1H} NMR (CDCl3, 162.1 MHz): δ 1.3 (d,
P-C B), 10.2 (brs, PC A), 109.1 (d, JPP ) 15.0 Hz, PO B), 112.2
(brs, PO A). 13C{1H} NMR (CDCl3, 75.5 MHz): δ 16.6 (s, Ar-
Me, B), 16.6 (s, Ar-Me, A), 16.8 (s, Ar-Me, B), 16.9 (s, Ar-Me,
A), 20.4 (s, 2 Ar-Me, B), 20.4 (s, 2 Ar-Me, A), 20.5 (s, 2 Me,
B), 20.5 (s, 2 Me, A), 22.7 (d, JCP ) 3.0 Hz, Ar-Me, A), 24.3 (d,
JCP ) 9.0 Hz, Ar-Me, A), 24.4 (d, JCP ) 9.0 Hz, Ar-Me, B),
26.4 (d, JCP ) 9.0 Hz, Ar-Me, B), 30.7 (s, CMe3, A), 30.9 (s,
CMe3, B), 31.8 (s, CMe3, B), 31.8 (s, CMe3, A), 34.4 (s, CMe3, B),
34.4 (s, CMe3, A), 34.7 (s, CMe3, B), 34.7 (s, CMe3, A), 118.9
(dd, JCP ) 58, 11 Hz, Cq arom), 122.4 (s, Cq arom), 123.2 (m, CH
arom), 123.4 (m, CH arom), 125.0 (dd, JCP ) 55, 4 Hz, Cq arom),
126.1 (s, CH arom), 126.3 (s, CH arom), 126.4 (s, CH arom), 126.5
(s, CH arom), 127.4 (m, CH arom), 127.7 (s, Cq arom), 128.5 (s,
CH arom), 128.8 (s, 2 CH arom), 129.2 (m, Cq arom), 131.7 (s,
CH arom), 131.8 (s, CH arom), 131.9 (s, CH arom), 132.1 (s, CH
arom), 132.2 (s, CH arom), 132.5 (s, CH arom), 132.6 (s, CH arom),
132.9 (s, CH arom), 133.0 (s, CH arom), 133.3 (s, CH arom), 133.4
(s, CH arom), 133.6 (s, Cq arom), 133.7 (s, Cq arom), 133.8 (s, Cq
arom), 134.2 (s, CH arom), 135.7 (s, Cq arom), 135.7 (s, Cq arom),
135.9 (s, Cq arom), 136.4 (m, Cq arom), 137.1 (m, Cq arom), 141.2
(m, Cq arom), 142.1 (s, Cq arom), 143.0 (d, JCP ) 11.0 Hz, Cq
arom), 143.7 (d, JCP ) 11.0 Hz, Cq arom), 145.2-145.9 (m, Cq
arom), 152.6 (dd, JCP ) 8.3 Hz, Cq arom), 153.2 (d, JCP ) 8.0 Hz,
Cq arom). Anal. Calcd for C44H52Cl2O3P2Pd‚CH2Cl2: C, 56.8; H,
5.5. Found: C, 56.4; H, 5.4.
135.5 (Cq arom), 135.8 (d, JCP ) 4.0 Hz, CH), 159.6 (d, JCP
)
19.0 Hz, Cq arom). HRMS (CI): m/z 378.1172, [M]+ (exact mass
calculated for C26H19OP: 378.1174).
Synthesis of the Phosphine-Phosphite Ligand 1f. To a
solution of (S)-3,3′-di-tert-butyl-5,5′,6,6′-tetramethyl-2,2′-bisphe-
noxyphosphorus chloride (0.49 g, 1.27 mmol) and NEt3 (0.3 mL,
1.9 mmol) in toluene (40 mL) was added a solution of 2-hydrox-
yphenyldi(1-naphthyl)phosphine (0.48 g, 1.27 mmol) in toluene (20
mL). The resulting suspension was stirred for 16 h, filtered, volatiles
evaporated, and the remaining residue treated with Et2O (20 mL),
filtered through a pad of neutral alumina, and the solution obtained
was evaporated, yielding 1f as a white foamy solid (0.44 g, 45%).
1
[R]20 ) 262 (c 1.0, THF). H NMR (CDCl3, 500 MHz): δ 1.14
D
(s, 9H, CMe3), 1.40 (s, 9H, CMe3), 1.82 (s, 3H, Me), 1.86 (s, 3H,
Me), 2.23 (s, 3H, Me), 2.29 (s, 3H, Me), 6.72 (m, 1H, H arom),
6.90 (t, JHH ) 7.0 Hz, H arom), 6.96 (m, 3H, H arom), 7.03 (s,
1H, H arom), 7.24 (m, 4H, H arom), 7.33 (t, JHH ) 7.0 Hz, 1H, H
arom), 7.39 (t, JHH ) 7.0 Hz, 1H, H arom), 7.47 (q, JHH ) 8.0 Hz,
2H, H arom), 7.83 (dd, JHH ) 6.2 Hz, 2H, H arom), 7.87 (dd, JHH
) 8.2 Hz, 2H, H arom), 8.40 (m, 2H, H arom). 31P{1H} NMR
(313 K, CDCl3, 202 MHz): δ -35.0 (d, JPP ) 40.0 Hz, PC), 129.2
(brs, PO). 13C{1H} NMR (CDCl3, 126 MHz): δ 16.7 (Ar-Me),
16.8 (Ar-Me), 20.5 (Ar-Me), 20.5 (Ar-Me), 31.1 (CMe3), 31.2
(d, JCP ) 5.0 Hz, CMe3), 34.5 (CMe3), 34.7 (CMe3), 122.0 (brs,
CH arom), 124.6 (CH arom), 125.7 (CH arom), 125.8 (CH arom),
125.8 (CH arom), 125.9 (CH arom), 126.1 (CH arom), 126.8 (d,
JCP ) 27.0 Hz, CH arom), 127.0 (d, JCP ) 26.0 Hz, CH arom),
127.8 (CH arom), 128.2 (d, JCP ) 11.0 Hz, Cq arom), 128.3 (CH
arom), 128.4 (CH arom), 128.5 (CH arom), 129.3 (2 CH arom),
130.3 (CH arom), 130.6 (Cq arom), 131.6 (Cq arom), 132.4 (d, JCP
) 5.0 Hz, Cq arom), 132.7 (CH arom), 132.9 (CH arom), 133.5
(CH arom), 133.7 (Cq arom), 134.2 (Cq arom), 135.2 (Cq arom),
135.4 (Cq arom), 135.6 (Cq arom), 135.7 (Cq arom), 137.6 (Cq
arom), 138.4 (Cq arom), 144.7 (Cq arom), 145.3 (d, JCP ) 4.0 Hz,
Cq arom), 154.6 (d, JCP ) 16.0 Hz, Cq arom). HRMS (FAB): m/z
760.3250, [M]+ (exact mass calculated for C50H50O3P2: 760.3235).
Synthesis of the Complex PdCl2(1a) (7a). To a solution of
PdCl2(MeCN)2 (0.052 g, 0.2 mmol) in toluene (5 mL) was added
a solution of 1a (0.139 g, 0.21 mmol) in toluene (5 mL). The
mixture was stirred for 3 h, and then the solvent was removed under
reduced pressure. The resulting solid was dissolved in CH2Cl2 (10
mL) and filtered through Celite. The obtained solution was
concentrated up to one-fourth of its original volume, and n-hexane
(30 mL) was added to precipitate the product. The resulting solid
was filtered off, washed with n-hexane (3 × 20 mL), and dried
under vacuum. Yellow solid (0.10 g, 60%). 1H NMR (CDCl3, 500
MHz): δ 1.05 (s, 9H, CMe3), 1.34 (s, 9H, CMe3), 1.79 (s, 3H,
Me), 1.80 (s, 3H, Me), 2.21 (s, 3H, Me), 2.26 (s, 3H, Me), 6.67 (t,
JHH ) 7.0 Hz, 1H, H arom), 6.83 (m, 1H, H arom), 7.11 (s, 1H, H
Procedure for Catalytic Hydroformylation Reactions. (a)
Styrene and Allyl Cyanide. A 750 mL Parr reaction vessel that
holds six kilmax 35 mL tubes in a Teflon rack was introduced in
a glovebox. Each tube was charged with styrene (0.78 g, 7.5 mmol)
or allyl cyanide (0.50 g, 7.5 mmol) and Rh(acac)(CO)2 (2 mg, 0.008
(26) Because of the complexity of the 1H NMR spectra, only NMR
signals of aliphatic groups have been assigned. In the 1H NMR spectra, the
intensities are calibrated to normalized unit value per each isomer.

6436 Organometallics, Vol. 26, No. 25, 2007
Rubio et al.
Table 5. Summary of Crystallographic Data and Structure Refinement Results for 7a and 7e
7a
7e
chem formula
C
203H224Cl8O12P8Pd4
C
123H140Cl4O6P4Pd2
[4(C42H46Cl2O3P2Pd), 5(C7H8)]
3812.78
[2(C44H50Cl2O3P2Pd), 5(C7H8)]
2192.83
fw
cryst size, mm
crystal system
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
0.26 × 0.18 × 0.09
monoclinic
P21
21.3901(11)
10.2591(4)
23.6159(12)
90
111.5820(10)
90
4819.0(4)
1
0.22 × 0.20 × 0.12
triclinic
P1
10.4905(6)
14.6466(9)
18.4648(11)
101.028(2)
96.166(2)
92.380(2)
2763.0(3)
1
Z
D
calcd, g cm-3
1.314
0.602
1978
1.318
0.535
1146
µ, mm-1
F(000)
θ range
2.56-26.18°
2.90-30.58°
no. of measd reflns
no. of unique reflns
min, max transm fact
no of data/restraints/param
R1(F) [F2 > 2σ(F2)]a
observed reflections
wR2(F2)b (all data)
Sc [all data]
26 937
74 197
22 869 (Rint ) 0.0317)
0.8592, 0.9478
22 869/347/1093
0.0646
15 866
0.1823
31 966 (Rint ) 0.0454)
0.8915, 0.9386
31 966/1299/1452
0.0447
26 744
0.1115
1.037
0.990
absolute structure
-0.03(3)
parameterd
2
-
2
2
2
-
2
a R1(F) ) ∑(|Fo| - |Fc|)/∑|Fo| for the observed reflections [F2 > 2σ(F2)]. b wR2(F2) ) {∑[w(Fo
Fc )2]/∑w(Fo )2}1/2
.
c S ) {∑[w(Fo
Fc )2]/(n -
p)}1/2; n ) number of reflections, p ) number of parameters. d Flack, H. D. Acta Crystallogr. 1983, A39, 876-881.
mmol) and 4 equiv of the corresponding phosphine-phosphite
dissolved in toluene (7 mL) and a magnetic stirrer. The reactor
was then removed from the glovebox, purged three times with a
1:1 mixture of H2/CO, followed by pressurizing it to 20 bar and
heated to 50 °C. The reaction solutions were stirred for the desired
reaction time. Next, the reactor was slowly depressurized, and
of the conversion into Rh(acac)(P-OP) complexes, the tube was
purged three times with a 1:1 mixture of CO/H2 and then pressurized
to 20 bar with the same gas mixture. The tube was inserted in the
probe and heated to 50 °C for 2-4 h, until Rh(acac)(P-OP)
converted completely into the corresponding RhH(P-OP)(CO)2
complexes. Both 31P{1H} and 1H NMR spectra of these latter
complexes were carried out in the temperature range from 50 to
-90 °C. Selected NMR data for RhH(P-OP)(CO)2 complexes at
50, 25, and -90 °C are reported in Table 3.
X-ray Structure Determinations. Suitable crystals for a single-
crystal X-ray structure analysis were grown by slow diffusion of
n-hexane into a CH2Cl2 solution of 7a and 7e. A single crystal, of
each compound, of suitable size was mounted on a glass fiber using
perfluoropolyether oil (FOMBLIN 140/13, Aldrich) in the cold N2
stream. A summary of crystallographic data is reported in Table 5.
Intensity data for complexes 7a and 7e were collected on a Bruker-
AXS X8Kappa diffractometer equipped with an Apex-II CCD area
detector, using a graphite monochromator Mo KR1 (λ ) 0.71073
Å) and a Bruker Cryo-Flex low-temperature device. A semiem-
pirical absorption correction was applied (SADABS).28 The struc-
tures were solved by direct methods (SIR-2002)29 and refined
against all F2 data by full-matrix least-squares techniques (SHELXTL-
6.14).30,31
1
conversion and iso/n ratio were determined by H NMR from an
aliquot of the resulting solution. The mixture of aldehydes was then
obtained by the evaporation of the solvent to dryness. Styrene
hydroformylation: 2-Phenylpropanal was oxidized to the corre-
sponding carboxylic acid10a and analyzed by GC (Chrompack
â-236M, 170 °C (5 min), then 10 °C/min up to 180 °C (5 min),
28.0 psi He) (S) t1 ) 3.60 min, (R) t2 ) 3.68 min. Allyl cyanide
hydroformylation: The enantiomeric excess was analyzed by GC
(Astec Chiraldex A-TA 30 m, 90 °C (7 min), 5 °C/min up to 150
°C (5 min), 24.5 psi He) (S) t1 ) 13.20 min, (R) t2 ) 13.60 min.
(b) Vinyl Naphthalenes. These olefins were hydroformylated
following the procedure described above using olefin (598 mg, 3.9
mmol), Rh(acac)(CO)2 (1 mg, 0.004 mmol), and 4 equiv of the
corresponding phosphine-phosphite dissolved in toluene (4 mL).
1-Vinyl naphthalene hydroformylation: The product aldehyde was
reduced to the corresponding alcohol27 and analyzed as follows by
HPLC (Chiralcel OK, 30 °C, n-hexane/2-propanol (99:1), flow 1.0
mL/min; tR ) 49.0 min (R), tR ) 53.5 min (S)). 2-Vinyl naphthalene
hydroformylation: The obtained aldehyde was reduced to the
corresponding alcohol as above and analyzed as follows by HPLC
(Chiralcel OK, 30 °C, n-hexane/2-propanol (98:2), flow 1.0 mL/
min; tR ) 33.7 min (R), tR ) 37.4 min (S)).
Acknowledgment. We gratefully acknowledge the Minis-
terio de Educacio´n y Ciencia (CTQ2006-05527) and Fundacio´n
Ramo´n Areces for financial support. M.R. thanks the Ministerio
de Educacio´n y Ciencia for a FPU fellowship. Thanks are also
due to EC through COST D17 Chemistry Action (WGD17/0003/
00) to support the visit of A.S. at ICCOM CNR via the STSM
Program.
Supporting Information Available: CIF files giving crystal-
lographic data. This material is available free of charge via the
Internet at http://pubs.acs.org.
HP-NMR Measurements. Preparation of NMR Samples of
RhH(P-OP)(CO)2. A 10 mm sapphire HP NMR tube was charged
with a solution of Rh(acac)(CO)2 (5.8 mg, 0.022 mmol) and P-OP
(0.023 mmol) in toluene-d8 (2.5 mL) under argon. After 31P{1H}
1
and H NMR spectra were recorded to monitor the completeness
OM700744B
(27) Halimjani, A. Z.; Saidi, M. R. Synth. Commun. 2005, 35, 2271.
(28) Sheldrick, G. SADABS; Bruker AXS, Inc.: Madison, WI, 1999.
(29) Burla, M. C.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.;
Giacovazzo, C.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 2003, 36,
1103.
(30) SHELXTL 6.14; Bruker AXS, Inc.: Madison, WI, 2000-2003.
(31) Sheldrich, G. M. SHELX-97. Programs for crystal structure Analysis
(release 97-2); Institu¨t fu¨r Anorganische Chemie der universita¨t: Go¨ttingen,
Germany, 1998.