Synthesis, coordination to Rh(I), and hydroformylation catalysis of new β-aminophosphines bearing a dangling nitrogen group: An unusual inversion of a Rh-coordinated P center

Article abstract of DOI:10.1021/ic011035i

Variants of the β-aminophosphine L¹ [Ph₂PCH₂CH(Ph)NHPh] containing additional nitrogen donor functions have been prepared. These functions are branched off the C atom adjacent to the P atom, or the P atom itself. Ligand [Ph₂PCH(o-C₆H₄NMe₂)CH(Ph)NHPh] has been obtained as a mixture of two diastereomers L^3A and L^3B by lithiation of L² [Ph₂PCH₂(o-C₆H₄NMe₂)] with n-BuLi followed by PhCH = NPh addition and hydrolysis. The diastereomers have been separated by fractional crystallization from ethanol. Ligand Et₂NCH₂P(Ph)CH₂CH(Ph)NHPh has been obtained as a mixture of two diastereomers L^5A and L^5B starting with P-Ph reductive cleavage of L¹ by lithium and subsequent hydrolysis to give PhP(H)CH₂CH(Ph)NHPh (mixture of two diastereomers L^4A and L^4B). The latter reacts with diethylamine and formaldehyde to afford the L⁵ diastereomeric mixture. Complexes RhCl(CO)(L) (L = L^3A, 1^A; L^3B, 1^B; L^5A/B, 2^A/B) were obtained by reaction of [RhCl(CO)₂]₂ and the appropriate ligand or ligand mixture. Complexes 1^A, 1^B, and 2^A have been isolated in pure form and characterized by classical techniques and by single-crystal x-ray diffraction. All structures exhibit a bidentate κ-P,κ-N(NHPh) mode similar to the complex containing L¹. While complexes 1^A or 1^B are stable in CDCl₃ solution, complex 2^A slowly converts to its diastereomer 2^B. This unexpected epimerization appears to take place by inversion at the Rh-coordinated P center, an apparently unprecedented phenomenon. A mechanism based on a reversible P-C bond oxidative addition is proposed. The influence of the pendant nitrogen function of the diaminophosphines L^3A and L^5A/B on the rhodium catalytic activity in styrene hydroformylation has been examined and compared to that of the aminophosphines L¹ or L². The observed trends are related to the basicity of the dangling amine function and to its proximity to the metal center.

Full text of DOI:10.1021/ic011035i

Inorg. Chem. 2002, 41, 3876−3885
Synthesis, Coordination to Rh(I), and Hydroformylation Catalysis of New
â-Aminophosphines Bearing a Dangling Nitrogen Group: An Unusual
Inversion of a Rh-Coordinated P Center
Jacques Andrieu,* Philippe Richard, Jean-Michel Camus, and Rinaldo Poli
Laboratoire de Synthe`se et d’Electrosynthe`se Organome´talliques, UniVersite´ de Bourgogne,
Faculte´ des Sciences “Gabriel”, 6 BouleVard Gabriel, 21000 Dijon, France
Received October 8, 2001
Variants of the â-aminophosphine L1 [Ph2PCH CH(Ph)NHPh] containing additional nitrogen donor functions have
2
been prepared. These functions are branched off the C atom adjacent to the P atom, or the P atom itself. Ligand
[Ph2PCH(o-C H NMe2)CH(Ph)NHPh] has been obtained as a mixture of two diastereomers L3A and L3B by lithiation
6
4
of L2 [Ph2PCH (o-C H NMe2)] with n-BuLi followed by PhCHdNPh addition and hydrolysis. The diastereomers
2
6 4
have been separated by fractional crystallization from ethanol. Ligand Et2NCH P(Ph)CH CH(Ph)NHPh has been
2
2
obtained as a mixture of two diastereomers L5A and L5B starting with P−Ph reductive cleavage of L1 by lithium and
subsequent hydrolysis to give PhP(H)CH CH(Ph)NHPh (mixture of two diastereomers L4A and L4B). The latter
2
reacts with diethylamine and formaldehyde to afford the L5 diastereomeric mixture. Complexes RhCl(CO)(L) (L )
L3A, 1A; L3B, 1B; L5A/B, 2A/B) were obtained by reaction of [RhCl(CO)2]2 and the appropriate ligand or ligand mixture.
Complexes 1A, 1B, and 2A have been isolated in pure form and characterized by classical techniques and by
single-crystal X-ray diffraction. All structures exhibit a bidentate κ-P,κ-N(NHPh) mode similar to the complex containing
L1. While complexes 1A or 1B are stable in CDCl3 solution, complex 2A slowly converts to its diastereomer 2B. This
unexpected epimerization appears to take place by inversion at the Rh-coordinated P center, an apparently
unprecedented phenomenon. A mechanism based on a reversible P−C bond oxidative addition is proposed. The
influence of the pendant nitrogen function of the diaminophosphines L3A and L5A/B on the rhodium catalytic activity
in styrene hydroformylation has been examined and compared to that of the aminophosphines L1 or L2. The
observed trends are related to the basicity of the dangling amine function and to its proximity to the metal center.
Introduction
preparation of chiral versions of â-P,N ligands requires in
general tedious multistep procedures,12-15 some have been
shown to be efficient in asymmetric enantioselective allylic
alkylations,16 hydroformylation,7 and hydrogenation.12
Aminophosphine ligands are being intensively investigated
because of the catalytic applications of their corresponding
Ru,1,2 Ni,3,4 Rh,5-8 and Pd9-11 complexes. Although the
* Author to whom correspondence should be addressed. E-mail: Jacques.
Andrieu@u-bourgogne.fr.
(8) Kostas, I. D.; Screttas, C. G. J. Organomet. Chem. 1999, 585, 1-6.
(9) Scrivanti, A.; Matteoli, U.; Beghetto, V.; Antonaroli, S.; Scarpelli,
R.; Crociani, B. J. Mol. Catal. A 2001, 170, 51-56.
(10) Drent, E.; Amoldy, P.; Budzelaar, P. H. M. J. Organomet. Chem. 1993,
455, 247-253.
(11) Newkome, G. R. Chem. ReV. 1993, 93, 2067-2089.
(12) Dahlenburg, L.; Go¨tz, R. J. Organomet. Chem. 2001, 619, 88-98.
(13) Habtemariam, A.; Watchman, B.; Potter, B. S.; Palmer, R.; Parsons,
S.; Parkin, A. J. Chem. Soc., Dalton Trans. 2001, 8, 1306-1318.
(14) Albinati, A.; Lianza, F.; Berger, H.; Pregosin, P. S.; Rilegger, H.; Kunz,
R. W. Inorg. Chem. 1993, 32, 478-486.
(1) Yang, H.; Alvarez, M.; Lugan, N.; Mathieu, R. J. Chem. Soc., Chem.
Commun. 1995, 1721-1722.
(2) Yang, H.; Alvarez-Gressier, M.; Lugan, N.; Mathieu, R. Organome-
tallics 1997, 16, 1401-1409.
(3) Hayashi, T.; Konishi, M.; Fukushima, M.; Kanehira, K.; Hioki, T.;
Kumada, M. J. Org. Chem. 1983, 48, 2195-2202.
(4) Nagel, U.; Nedden, H. G. Chem. Ber. 1997, 535-542.
(5) Suomalainen, P.; Reinius, H. K.; Riihimaki, H.; Laitinen, R. H.;
Jiaskelainen, S.; Haukka, M.; Pursiainen, J. T.; Pakkanen, T. A.;
Krause, A. O. I. J. Mol. Catal. A 2001, 169, 67-78.
(6) Payne, N. C.; Stephan, D. W. Inorg. Chem. 1982, 21, 182-188.
(7) Arena, C. G.; Nicolo`, F.; Drommi, D.; Bruno, G.; Faraone, F. J. Chem.
Soc., Chem. Commun. 1994, 2251-2252.
(15) Isslieb, K.; Ku¨mmel, R.; Oehme, H.; Meisser, I. Chem. Ber. 1968,
101, 3612-3618.
(16) Anderson, J. C.; Cubbon, R. J.; Harling, J. D. Tetrahedron: Asymmetry
2001, 12, 923-935.
3876 Inorganic Chemistry, Vol. 41, No. 15, 2002
10.1021/ic011035i CCC: $22.00 © 2002 American Chemical Society
Published on Web 06/26/2002

â-Aminophosphines Bearing a Dangling Nitrogen Group
Scheme 1
Scheme 3
the behavior of complex [CuL2]+ [L ) N,N-CH3(o-C6H4-
CH2PPh2)NCH2CH2OH], showing a double exchange be-
tween [Cu(L-κ-P)(L-κ-P′,κ-N′,κ-O′)]+ and [Cu(L-κ-P,κ-N,κ-
O)(L-κ-P′)]+ forms, see Scheme 2.23
Scheme 2
It has been reported that rhodium catalysts containing
achiral â-aminophosphines have a greater activity when the
ligand bears an ether vs an alcohol function.8 The preparation
of a P,N,N ligand with a chiral â-aminophosphine moiety
has not so far been considered. These ligands, however, could
provide advantages linked to the different basicity of the
residual (dangling) N function and to an increased steric
control via the nitrogen substituents.
In this paper, we describe the synthesis of new types of
â-aminophosphines (P,N,N) bearing a dangling nitrogen
group, the latter being linked either to the carbon atom
adjacent to the phosphorus atom (type I) or directly to the
phosphorus atom (type II), see Scheme 3. The type II ligands
that we have developed have a chiral phosphorus atom. We
shall refer to these ligands as â,ω-diaminophosphines (ω )
R or γ depending on the distance between the second N
function and the P donor).
We also report on (i) the coordination modes of these
ligands in rhodium chloride carbonyl complexes showing an
unusual rhodium-coordinated P-atom epimerization and (ii)
their catalytic properties in styrene hydroformylation in
comparison to related but simpler â- or γ-P,N ligands.
We have recently reported a novel and relatively simple
synthetic procedure for the preparation of chiral â-amino-
phosphines, which consists of the nucleophilic addition of a
phosphinomethyl carbanion onto an imine. This procedure
is exemplified by the formation of ligand Ph2PCH2CH(Ph)-
NHPh (L1), in Scheme 1.17 Ligands of this type have been
shown to coordinate in a chelating fashion (κ2-P,N) and
stereoselectively. However, we noted that only one of the
two possible diastereomers is formed upon bidentate coor-
dination of L1 to PdCl2. Thus, there is 100% transmission
of the chiral information to the nitrogen atom from the
adjacent carbon atom, making ligands of this kind potentially
useful in enantioselective catalysis.
More recently, interest is developing toward the prepara-
tion of aminophosphines, with additional functional groups
(P,N,N′; P,N,O; etc.). One reason for this interest is the
possibility to use the third functionality for anchoring the
ligand to a solid support. Solid-supported aminophosphines
(Merrifield resin type) have in fact shown promise for
catalytic applications in biphasic media.18
In the case of â-P,N ligands of the pyridinylphosphine
type, the κ2-P,N chelating behavior was shown to be reduced
or even suppressed by the introduction of other donor
functions which compete with the pyridine for coordina-
tion.19,20 This competition may result in a double hemilability
behavior (termed “wiper” by Braunstein).21 For instance, the
N,P,O ligand C5H3N(2-CH2P(Ph)(o-anisyl))(6-CH3)19 shows
a reversible P,O and P,N chelate exchange in cationic
complexes of rhodium, see Scheme 2, while a P,P,N,N′
ligand [Ph2PCH(2-Py)CH(2-Py)PPh2] shows a similar P,P′,N
and P,P′,N′ exchange for a Rh(I) complex.22 Also notable is
Experimental Section
All manipulations were carried out under purified argon and in
the dark using standard Schlenk techniques, and all solvents were
dried and deoxygenated prior to use. NMR measurements (1H,
13C{1H}, and 31P{1H}) were carried out with a Bruker AC200
spectrometer in CDCl3 at room temperature. The peak positions
are reported with positive shifts in ppm downfield of TMS as
calculated from the residual solvent peaks (1H) or downfield of
external 85% H3PO4 (31P). 1H-1H and 13C-1H correlation experi-
ments were carried out on a Bruker DRX500 spectrometer. IR
spectra were recorded in CH2Cl2 solution with a Bruker IFS 66V
spectrophotometer with KBr optics. Elemental analyses were carried
out by the analytical service of the LSEO with a Fisons Instruments
EAl108 analyzer. Compounds PhCHdNPh, n-BuLi (1.6 M in
hexanes), CH2O (37% in water), NHEt2 (Aldrich), and [RhCl(CO)2]2
(Strem) were commercial products and were used as received. The
preparation of Ph2PCH2CH(Ph)NHPh (L1) has been previously
described.17 Ligand Ph2PCH2(o-C6H4NMe2) (L2) was prepared
according to the literature procedure.24
Synthesis of Ph2PCH(o-C6H4NMe2)CH(Ph)NHPh, L3. To a
solution of L2 (1.0 g, 3.13 mmol) in Et2O (12 mL) was added
(17) Andrieu, J.; Camus, J.-M.; Dietz, J.; Richard, P.; Poli, R. Inorg. Chem.
2001, 40, 1597-1605.
(18) Mansour, A.; Portnoy, M. J. Chem. Soc., Perkins Trans. 1 2001, 952-
954.
(19) Yang, H.; Lugan, N.; Mathieu, R. Organometallics 1997, 16, 2089-
(22) Bookham, J. L.; Smithies, D. M.; Pett, M. T. Dalton 2000, 975-980.
(23) Andrieu, J.; Steele, B. R.; Screttas, C. G.; Cardin, C. J.; Fornies, J.
Organometallics 1998, 17, 839-845.
(24) Rauchfuss, T. B.; Patino, F. T.; Roundhill, D. M. Inorg. Chem. 1975,
14, 652-656.
2095.
(20) Bookham, J. L.; Smithies, D. M. J. Organomet. Chem. 1999, 577,
305-315.
(21) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680-699.
Inorganic Chemistry, Vol. 41, No. 15, 2002 3877

Andrieu et al.
n-BuLi (2.0 mL, 1.6 M in hexanes). After refluxing for 4 h, the
resulting white suspension was cooled to room temperature, fol-
lowed by slow addition of an Et2O solution (15 mL) of N-ben-
zylideneaniline (0.567 g, 3.13 mmol). An orange solution im-
mediately formed, which then changed to a white suspension after
a few minutes. After stirring for 12 h, the mixture was hydro-
lyzed by addition of a few milliliters of degassed water. The sol-
vents were removed by evaporation under reduced pressure, and
Synthesis of HP(Ph)CH2CH(Ph)NHPh, L4A/B. To a colorless
solution of L1 (0.875 g, 2.30 mmol) in 20 mL of THF was added
lithium (35 mg, 5.0 mmol). After 4 days under stirring, the resulting
solution was yellow-orange. Addition of 0.7 mL of water afforded
a colorless solution. All solvent was evaporated under reduced
pressure, and the white residue was dried in vacuo for 1 h at 50
°C, followed by extraction with 2 × 10 mL of toluene. After
filtration through Celite, solvent evaporation afforded a viscous oil
which was dried in vacuo at 100 °C for 2 h. NMR spectroscopic
analyses of the crude product showed only the presence of the
expected ligand L4 (1:1 mixture of diastereomers) (0.670 g, 95%).
Since the two isomers could not be separated, the NMR analy-
1
the very viscous residue was dried for /2 h at 50 °C, followed
by extraction with 2 × 10 mL of toluene and filtration through
Celite to eliminate the lithium salts. The solution was evap-
orated to dryness under reduced pressure, and the residue was
dried for 1 h at 130 °C. No starting ligand L2 was detected in the
crude product by NMR. After two crystallizations from hot ethanol
(20 mL) the pure L3A ligand was recovered as white crystals (355
1
ses did not allow an intimate structural assignment. H-1H and
13C-1H NMR correlation experiments allowed a complete peak
1
assignment. H NMR: 7.39-6.51 (15H+H′, m, aromatics), 4.53
1
1
mg, 23% based on the starting ligand). H NMR: 8.00-6.16 (24
(1H+H′, m, NCH, 4.36 (1H or 1H′, dt, PH, J(PH) ) 215 Hz,
3
H, m, aromatics), 5.44 (lH, s, br, NH, exchange with D2O), 5.03
(2H, m, NCH + PCH), 2.25 (6H, s, N(CH3)). 31P{1H} NMR: -6.83.
13C{1H} NMR: 153.20-113.01 (30C, m, aromatics), 61.26 (1C,
3J(H, HPCHa) ) J(H, HPCHb) ) 7 Hz), 4.32 (1H or 1H′, d, NH,
3
3J(H,H) ) 6 Hz), 4.19 (1H′ or 1H, PH, J(PH) ) 215 Hz, J(H,
3
3
H
PCHa) ) J(H, HPCHb) ) 7 Hz), 4.18 (1H′ or 1H, d, NH, J(H,H)
2
d, NCH, J(P,C) ) 18 Hz), 45.51 (2C, s, CH3N), 44.45 (1C, d,
) 6 Hz), 2.47 (2H+H′, PCH2, m). 31P{1H} NMR: - 62.00 (s,
1
PCH, J(P,C) ) 14 Hz). IR: 3410 (w, br, νNH). The combined
filtrates were concentrated to half volume. After 10 days at room
temperature, pure white crystals of the second diastereomer L3B
P+P′). 31P NMR: -62.00 (d, J(P,H) ) 211 Hz). 13C{1H} NMR:
147.11-113.57 (15C+C′, m, aromatics), 57.18 (1C+C′, d, NCH,
2J(P,C) ) 9 Hz), 34.04 (1C or 1C′, d, PCH, J(P,C) ) 15.5 Hz),
33.07 (1C′ or 1C, d, PCH, J(P,C) ) 15.5 Hz). An elemental analysis
could not be carried out because of the combined air sensitivity
and high viscosity. The mixture was used for the synthesis below
without further purification.
1
were recovered (315 mg, 20% based on the starting ligand). H
NMR: 7.70-6.31 (24H, m, aromatics), 4.93 (1H, s, br, NH,
exchange with D2O), 4.66 (2H, s, br, NCH + PCH), 2.10 (6H, s,
CH3N). 31P{1H} NMR: -4.05. 13C{1H} NMR: 148.40-113.95
(30C, m, aromatics), 60.68 (1C, d, NCH, 2J(P,C) ) 19 Hz), 45.89
(3C, s, PCH + CH3N). IR: 3409 (w, br, νNH). Anal. Calcd for
C34H33N2P: C 81.57, H 6.64, N 5.60. Found: C 81.96, H 6.78, N
5.61.
Synthesis of Et2NCH2P(Ph)CH2CH(Ph)NHPh, L5. The L4
diastereomeric mixture obtained in the above procedure (0.670 g,
2.20 mmol) was dissolved in 10 mL of degassed ethanol. Diethyl-
amine (260 µL, 2.50 mmol) was added, and the resulting solution
was stirred for 10 min. Formaldehyde in water (195 µL, 2.50 mmol)
was then added. After 10 min a white precipitate appeared. After
2 h of stirring at room temperature, the suspension was cooled to
0 °C for 20 min and then filtered. The resulting white powder was
dried in vacuo for 4 h at room temperature. (0.751 g, 83%). By 1H
and 31P{1H} NMR spectroscopic analyses, the product consists of
a mixture of two diastereomers L5A and L5B in a 3:2 ratio. The
1H-1H and 13C-1H NMR correlation experiments allowed a
complete peak assignment. The attribution of the resonances for
each isomer was possible following the separation of the rhodium
complexes of the ligands (see next section). NMR properties of
Synthesis of [RhCl(CO)(L3A-K-P,K-N)], 1A. To a mixture of
[RhCl(CO)2]2 (36 mg, 0.092 mmol) and L3A (92 mg, 0.184 mmol)
was added 5 mL of THF. The resulting yellow solution was stirred
for 1 h. Addition of pentane afforded a yellow powder, which was
isolated by filtration and dried in vacuo (84 mg, 76%). Yellow
single crystals suitable for an X-ray diffraction analysis were
obtained by slow diffusion from a THF/pentane mixture. 1H
3
NMR: 7.82-6.45 (24H, m, aromatics), 6.05 (1H, d, NH, J(P,H)
) 8 Hz), 5.88 (1H, dd, PCH, 2J(P,H) ) 8 Hz, 3J(H,H) ) 13
3
3
Hz), 4.29 (1H, dd, NCH, J(P,H) ) 23 Hz, J(H,H) ) 13 Hz),
2.00 (6H, s, N(CH3)). 31P{1H} NMR: 74.0 (d, 1J(Rh,P) ) 170 Hz).
13C{1H} NMR: 154.52-121.30 (30C, m, aromatics), 75.10 (1C,
d, NCH, 2J(P,C) ) 13 Hz), 48.63 (1C, d, PCH, 1J(P,C) ) 17 Hz).
45.50 (2C, s, CH3N). IR: 3249 (w, νNH), 1983 (vs, νCO). Anal.
Calcd for C35H33N2OPRhCl: C, 63.03; H, 4.98; N, 4.20. Found:
C, 62.90; H, 5.17; N, 4.38.
compound L5A 1H NMR 7.59-6.31 (15H, aromatics + 1H, NH),
:
4.42 (1H, CHN, m), 2.89 (8H, all CH2, m), 1.12 (3H, CH3, t);
31P{1H} NMR -35.86 (s); 13C{1H} NMR 147.11-113.04 (m,
aromatics), 57.78 (2C, s, CH3CH2N), 57.06 (1C, d, CH2CHN,
1
2J(PC) ) 20 Hz), 48.50 (1C, d, PCH2N, J(P,C) ) 7 Hz), 41.60
(1C, d, PCH2C, 1J(P,C) ) 19 Hz), 11.16 (2C, s, CH3). NMR
Synthesis of [RhCl(CO)(L3B-K-P,K-N)], 1B. To a mixture of
[RhCl(CO)2]2 (27 mg, 0.069 mmol) and L3B (70 mg, 0.140 mmol)
was added 5 mL of THF. The yellow solution was stirred for 1 h.
Addition of pentane afforded a yellow powder, which was isolated
by filtration and dried in vacuo (71 mg, 78%). Yellow single crystals
suitable for an X-ray diffraction analysis were obtained by slow
diffusion from a THF/pentane mixture. 1H NMR: 9.38-7.34 (24H,
m, aromatics), 5.75 (1H, dd, PCH, 2J(P,H) ) 15 Hz, 3J(H,H) ) 5
1
properties of compound L5B: H NMR 7.59-6.31 (15H, aromatics),
3
5.82 (1H, d, NH, J(H,H) ) 5 Hz), 4.73 (1H, CHN, m), 2.89
(8H, all CH2, m), 1.05 (3H, CH3, t); 31P{1H} NMR -43.35 (s);
13C{1H} NMR 147.11-113.04 (m, aromatics), 57.46 (2C, s,
CH3CH2N), 56.03 (1C, d, CH2CHN, 2J(P,C) ) 14 Hz), 48.21 (1C,
1
1
d, PCH2N, J(P,C) ) 8 Hz), 39.73 (1C, d, PCH2C, J(P,C) ) 19
Hz), 11.45 (2C, s, CH3). IR: 3418 (w) and 3242 (w) (both νNH).
Anal. Calcd for C25H31N2P (390.50): C, 76.89; H, 8.00; N, 7.17.
Found: C, 76.72; H, 7.75; N, 7.15.
3
Hz), 5.08 (1H, d, NH, J(P,H) ) 11 Hz), 4.41 (1H, dd, NCH,
3J(P,H) ) 12 Hz, 3J(H,H) ) 5 Hz), 1.80 (6H, s, N(CH3)). 31P{1H}
1
NMR: 69.36 (d, J(Rh,P) ) 172 Hz). 13C{1H} NMR: 144.77-
Synthesis of [RhCl(CO)(L5A-K-P,K-N)], 2A, and [RhCl(CO)-
(L5B-K-P,K-N)], 2B. A compound [RhCl(CO)2]2 (53 mg, 0.136
mmol) and L5 (3:2 diastereomeric mixture) from the above
procedure (107 mg, 0.273 mmol) were dissolved in 5 mL of THF.
The brown-red solution was stirred for 1 h. Addition of pentane
with stirring afforded a yellow-brown powder, which was isolated
122.61 (30C, m, aromatics), 74.45 (1C, d, NCH, 2J(P,C) ) 12 Hz),
47.32 (1C, d, PCH, J(P,C) ) 26 Hz), 45.10 (2C, s, CH3N). IR:
1993 (vs, νCO) and 3271 (w, νNH). Anal. Calcd for C35H33N2-
OPRhCl‚C4H8O: C, 63.38; H, 5.59; N, 3.79. Found: C, 64.12; H,
5.26; N, 3.74.
3878 Inorganic Chemistry, Vol. 41, No. 15, 2002

â-Aminophosphines Bearing a Dangling Nitrogen Group
Table 1. Crystal Data and Structure Refinement for All Compounds
1A
1B
2A
formula
M
T, K
C35H33N2OPClRh‚C4H8O
739.07
110
C35H33N2OPClRh‚1.5 (C4H8O)
C26H31N2OPClRh
556.86
110
775.12
110
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
monoclinic
P21/c
9.5846(1)
18.3642(2)
19.6147(2)
90
93.460(1)
90
3446.16(6)
4
triclinic
P1h
11.8621(4)
12.7054(4)
12.9551(5)
75.371(1)
82.537(1)
78.473(1)
1844.6(1)
2
monoclinic
P21/c
9.8922(1)
21.4323(3)
12.5571(2)
90
106.622(1)
90
2551.01(6)
4
F(000)
D
1528
1.424
804
1.396
1144
1.450
calcd, g/cm3
diffractometer
scan type
Kappa CCD
mixture of φ rotations and ω scans
0.71073
0.618
0.45 × 0.30 × 0.30
λ, Å
µ, mm-1
0.657
0.857
crystal size, mm3
sin(θ)/λmax, Å-1
index ranges
h
0.25 × 0.22 × 0.20
0.50 × 0.38 × 0.25
0.65
0.65
0.65
-12; 12
-23; 23
-25; 25
24975
7871/0.0201
7002
-15; 15
-12; 12
-27; 20
-16; 12
14013
5785/0.0227
4990
k
l
-16; 16
-16; 16
RC ) reflns collected
IRC ) unique RC/R(int)
IRCGT ) IRC and [I > 2σ(I)]
refinement meth
data/restraints/params
R for IRCGT
R for IRC
13427
8258/0.0236
6479
full-matrix least-squares on F2
8258/0/435
7871/0/514
5785/0/383
R1a ) 0.0253, wR2b ) 0.0627
R1a ) 0.0305, wR2b ) 0.0652
1.030
R1a ) 0.0448, wR2b ) 0.1188
R1a ) 0.0582, wR2b ) 0.1248
1.087
R1a ) 0.0252, wR2b ) 0.0552
R1a ) 0.0339, wR2b ) 0.0582
1.010
goodness-of-fitc
∆F, max, min, e Å-3
0.99 and -0.54
1.177 and -1.190
0.457 and -0.546
2
2
2
2
a R1 ) ∑(||Fo| - |Fc||)/|Fo|. b wR2 ) [∑w(Fo2 - Fc )2/∑[w(Fo )2]1/2 where w ) 1/[σ2(Fo ) + (0.032P)2 + 2.32P] for 1 and w ) 1/[σ2(Fo ) + (0.063P)2
2
2
2
2
2
+ 0.80P] for 1′ and w ) 1/[σ2(Fo ) + (0.024P)2 + 1.33P] for 2 where P ) (Max(Fo ,0) + 2Fc )/3. c Goodness of fit ) [∑w(Fo - Fc )2/(No - Nv)]1/2
.
by filtration and dried in vacuo. (97 mg, 64%). A 31P NMR
spectrum of the crude product indicated a mixture of 2B/2A in a
45:55 ratio in the presence of a byproduct 2′. The same ratio of
products was also observed in solution after 10 min when the
reaction was carried out in CDCl3 solution instead of THF.
Diastereomer 2A was isolated by two routes. The first procedure
consisted of a crystallization from CH2Cl2/pentane, affording pure
2A as yellow-red single crystals. The second procedure consisted
of the addition of a few milliliters of toluene to the crude mixture,
followed by cooling of the resulting solution to -30 °C for a few
days. This procedure afforded a 79:21 mixture (by integration of
the 31P resonances) of complexes 2A and 2′ as a yellow-brown
powder in a higher yield (52 mg, 25%). Compound 2A: 1H NMR
8.13-7.00 (15H, m, aromatics), 6.12 (1H, NH, s, br), 4.68 (1H,
CHN, s, br), 3.34-3.09 (8H, all CH2 groups, m), 1.12 (3H, CH3,
methods (SHELXL-97)26 with the aid of the WINGX program.27
Except for some carbon atoms in 1B, non-hydrogen atoms were
anisotropically refined. In 1A, the hydrogen atoms belonging to the
complex were located in the final difference Fourier maps and
refined freely with their temperature factors fixed at 1.2 or 1.5 (for
CH3) times the Ueq of their parent atoms. The hydrogen atoms of
the solvate (one THF molecule) were included in calculated
positions and refined in a riding model. In 1B, the two phenyl groups
attached to the phosphorus atom were found to be disordered over
two positions. The occupancies of the pairs of phenyl groups
converged to m1 ) 0.55 and m2 ) 1 - m1, and one of the
disordered phenyl groups was left isotropic. Two THF solvate
molecules were located in the Fourier map, one in general position
and the other around an inversion center. These molecules were
badly disordered, and any attempt to refine a model failed. Thus a
BYPASS procedure, implemented in the PLATON program,28 was
used to handle this problem. In this procedure the contribution of
the solvent (1.5 THF molecules) electron density was subtracted
from the structure factor. The refinement was carried out with this
solvent-corrected data set. In 2A, the hydrogen atoms were located
in the final difference Fourier maps and refined freely with their
temperature factors fixed at 1.2 or 1.5 (for CH3) times the Ueq of
their parent atoms. Crystallographic data and selected geometrical
1
s, br); 31P{1H} NMR 42.39 (d, J(Rh,P) ) 166 Hz); no 13C{1H}
NMR data could be obtained due to the appearance of a decom-
position product after ca. 5 h in CDCl3; IR 3262 (w, νNH), 1985
(vs, νCO). Compound 2′: 31P{1H} NMR 47.36 (d, 1J(Rh,P) ) 163
Hz). 1H NMR and IR data for 2B were deduced by difference from
the spectra of the crude mixture. Compound 2B: 1H NMR 8.13-
7.00 (15H, m, aromatics), 6.39 (1H, NH, s, br), 3.83 (1H, CHN, s,
br), 3.34-3.09 (8H, all CH2 groups, m), 1.12 (3H, CH3, s, br); IR
3249 (w, νNH), 1983 (vs, νCO); 31P{1H} NMR 57.51 (d, 1J(Rh,P) )
160 Hz). Anal. Calcd for C26H31N2OPRhCl: C, 56.07; H, 5.61; N,
5.03. Found: C, 56.12; H, 5.62; N, 5.12.
(25) Sheldrick, G. M. SHELXS97. Program for Crystal Structure solution;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
Crystal Structure Analyses of Complexes 1A, 1B, and 2A.
Intensity data were collected on a Nonius Kappa CCD at 110 K
for all complexes. The structures were solved by the heavy-atom
method (SHELXS-97)25 and refined by full-matrix least-squares
(26) Sheldrick, G. M. SHELXL97. Program for Crystal Structure refine-
ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(27) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.
(28) van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A.: Found.
Crystallogr. 1990, 46, 194-201.
Inorganic Chemistry, Vol. 41, No. 15, 2002 3879

Andrieu et al.
Scheme 4
Table 2. Selected Bond Lengths (Å), Angles (deg), and Dihedral
Angles (deg) for All Compounds
1A
1B
2A
Rh-P
2.2026(4)
2.1606(13)
2.3809(4)
1.8152(18)
1.146(2)
0.89(2)
3.25
3.22
2.73
3.47
2.2041(8)
2.169(2)
2.3758(7)
1.801(4)
1.142(4)
0.70
2.98
3.23
2.75
3.44
2.2075(5)
2.1860(15)
2.3954(5)
1.796(2)
1.155(2)
0.85(2)
3.35
3.29
2.57
3.39
Rh-N(1)
Rh-Cl
Rh-C(3)
C(3)-O(1)
N(1)-H
H‚‚‚Cl
N(1)‚‚‚Cl
H‚‚‚Cla
N(1)‚‚‚Cla
other bond
N(2)‚‚‚Rh
3.66
C(3)-Rh-N(1)
C(3)-Rh-P
176.63(6)
92.19(6)
84.82(4)
93.01(5)
90.03(4)
174.46(2)
179.37(17)
73(2)
173.23(18)
92.12(11)
84.39(7)
93.24(12)
90.64(7)
173.57(2)
176.6(5)
-52(1)
175.25(7)
91.36(6)
84.01(4)
92.81(6)
91.74(4)
174.44(2)
178.7 (2)
78(2)
N(1)-Rh-P
Scheme 5
C(3)-Rh-C1
N(1)-Rh-C1
P-Rh-Cl
O(1)-C(3)-Rh
H-N(1)-Rh-Cl
other angles
H-C(1)-C(2)-H
H-C(1)-N(1)-H
Rh-P-C(22)
P-C(22)-N(2)
H-C(2)-N(1)-H
Rh-P-C(22)-N(2)
175(2)
167(2)
-47
172
119.18(7)
109.69(13)
-179(2)
44.2(2)
a Atom of the closest symmetrically related molecule.
Table 3. Catalytic Properties of P,N and P,N,N Ligands in Rhodium
Styrene Hydroformylationa
it is known that the aminophosphines Ph2PCH2(o-C6H4NRR′)
(R, R′ ) CH3, CH2CH2OH) can easily undergo benzylic
deprotonation with n-BuLi,23 we have now applied the same
procedure starting from the known o-diphenylphosphino-
N,N-dimethylbenzylamine (L2).24 The deprotonation reaction
leads to the Ph2PCH-(Li+)(o-C6H4N(CH3)2), anion which
reacts with PhCHdNPh to afford a 1:1 mixture (by NMR)
of the L3A (RC1,RC2)/(SC1,SC2) and L3B (SC1,RC2)/(RC1,SC2)
ligands after hydrolysis in 48% yields, see Scheme 4. Both
diastereoisomers could be obtained in a pure form by
fractional crystallization from ethanol. The relative config-
uration is known for both isomers from the X-ray analysis
of the corresponding Rh(I) derivatives 1 (vide infra).
2. Synthesis of â,R-Diaminophosphines. The new ligand
Et2NCH2P(Ph)CH2CH(Ph)NHPh, L5 (as a mixture of two
racemic diastereomers), is available by P-functionalization
of the â-P,N L1 ligand in only two steps as shown in Scheme
5. The first step consists of the reductive cleavage of one
P-C(phenyl) bond by lithium. Alkali metals are known to
perform this reaction selectively and under mild conditions
in ether or liquid NH3.29-31 The presence of the secondary
amine function in L1 does not interfere with the reaction.
After hydrolysis, a 1:1 mixture of the diastereomeric L4A
(RP1,SC)/(SP,RC) and L4B (RP1,RC)/(SP,SC) ligands containing
a new P-H bond was obtained in excellent yields (95%)
conversion,b
%
TOF
c
ligand
TON
(h-1
)
regioselectivityb
L1 (â-P,N)
32
17
24
87
320
200
240
870
16
91/9
92/8
86/14
91/9
L2 (γ-P,N)
8.5
12
50
L3A (â,γ-P,N,N)
L5A/B (â,R-P,N,N)
a [RhCl(COD)]2 (12 mg), styrene/Rh/L )1000/1/1, CHCl3 (40 mL), 55
°C, CO/H2 ) 1, 600 psi. TON ) turnover number. b The regioselectivity
is defined by the branched/linear ratio and measured after 20 h. c TOF
calculated from the conversions at different times.
parameters for all compounds are reported in Table 1 and Table 2,
respectively.
Catalytic Runs. The hydroformylation reactions were carried
out in a 300 mL stainless steel Parr autoclave equipped with a
magnetic drive and an internal glass vessel. The temperature was
controlled by a rigid heating mantle and by a single loop cooling
coil. The autoclave was purged three times under vacuum/argon
before the catalytic solution and the styrene were introduced. The
CO/H2 mixture in a 1:1 ratio was prepared by mixing the pure gases
in a 500 mL stainless steel cylinder before introduction into the
autoclave at the desired pressure. Aliquots of the mixture were
withdrawn periodically and rotary evaporated at room temperature,
and the resulting yellow-orange residue was analyzed by 1H NMR
spectroscopy (see Table 3).
Results and Discussion
1. Synthesis of â,γ-Diaminophosphines. The new ligand
Ph2PCH(o-C6H4NMe2)CH(Ph)NHPh, L3 (as a mixture of two
racemic diastereomers), has been synthesized by an exten-
sion of our previous work which led to the formation of the
(29) Barclay, C. E.; Deeble, G.; Doyle, R. J.; Elix, S. A.; Salem, G.; Jones,
T. L.; Wild, S. B.; Willis, A. C. J. Chem. Soc., Dalton Trans. 1995,
57-65.
(30) Doyle, R. J.; Salem, G.; Willis, A. C. J. Chem. Soc., Dalton Trans.
1997, 2713-2723.
-
â-P,N ligand L1 by nucleophilic addition of Ph2PCH2 to
(31) Carmona, A.; Corma, A.; Iglesias, M.; Sanjose, A.; Sanchez, F. J.
Organomet. Chem. 1995, 492, 11-21.
the CdN double bond of benzaldimine (Scheme 1).17 Since
3880 Inorganic Chemistry, Vol. 41, No. 15, 2002

â-Aminophosphines Bearing a Dangling Nitrogen Group
Scheme 6
Scheme 7
(see Scheme 5). The presence of the P-H bond was
confirmed by 31P{1H} NMR resonances (accidentally over-
1
lapping at -62 ppm for the two isomers) and H spectra.
or the NMe2 function should lead to significant shifts for
the proton (and/or carbon) resonances of the concerned
moiety, as previously shown for rhodium complexes contain-
ing â-P,N or γ-P,N ligands (∆δ ) 2.5 ppm for NH and 0.5
ppm for N(CH3)2 protons).6,12,24 On the other hand, the
chemical shifts of both the NH and NMe2 protons for 1A
and 1B were found to be identical to those of the corre-
sponding free ligand.
The formation of the new asymmetric center on the P atom
leads to the formation of two diastereomers without any
diastereomeric excess. The second step consists of a standard
Mannich-type addition to formaldehyde, similar to the
previously reported synthesis of Ph2PCH2NR2 from Ph2PH,
R2NH, and CH2O,15 and gives rise to L5A and L5B in a ca.
3:2 ratio. This step is also characterized by excellent yields
and chemoselectivity. The two diastereomers could not be
separated from each other. It is worth underlining that this
synthetic procedure is more convenient and efficient relative
to that previously described for simpler, achiral â,R-
diaminophosphines,15 since it avoids the use of tedious PhPH2
or Na/NH3 reagents.
The second step of Scheme 5 was also carried out at -78
°C in an attempt to increase the diastereoselectivity. How-
ever, the same diastereomeric excess was obtained after the
workup, as indicated by the NMR analyses. Moreover, in
contrast to the diastereomeric mixture for L3, different
separation attempts of the L5 isomers by crystallization from
hot ethanol (cooling to either room temperature or -30 °C)
did not alter the diastereomeric ratio. These observations
could be the consequence of a rapid interconversion, which
in fact slowly takes place when the ligand is coordinated to
a Rh(I) center in complexes 2A and 2B (vide infra). However,
the relative intensities and shape of the PCH signals in the
1H NMR spectrum in C6D6 solution do not change in the
20-60 °C range, in disagreement with such a proposal. In
addition, it is well-known that the pyramidal inversion
barriers for tertiary phosphines are rather large.32 Although
the NMR properties of L5A and L5B are rather similar, the
two ligands show markedly different IR absorptions in the
The X-ray analysis of both complexes (Figure 1), however,
confirms that the ligand adopts a bidentate coordination mode
via the P and NH donors in both cases, whereas the NMe2
group remains dangling. In contrast to complexes 2 (see
1
below) the H NMR resonances for the NCH-CHP moiety
give rise to a simple and distinct pattern for each isomer.
3
Their J(H,H) coupling constants are quite different, sug-
gesting a near 180° NCHax-CHaxP dihedral angle (13 Hz)
for 1A and a near 60° NCHax-CHeqP dihedral angle (5 Hz)
for 1B in solution.33 This assignment corresponds to the
geometry observed in the solid state.
Selected geometrical parameters are given in Table 2. Both
structures show a nearly ideal square planar geometry around
the rhodium atom. The largest discrepancy is along the
P-Rh-Cl axis with angles of 174.46(2)° and 173.57(2)° for
1A and 1B, respectively. The related complex [RhCl(CO)-
{Ph2P(o-C6H4NMe2)-κ-P,κ-N}] has a similar P-Rh-N angle
of 174.7(2)°.34 The Rh-C(3) bond lengths, on the other hand,
are significantly shorter and the C(3)-O(1) bond lengths are
significantly longer than those of the above-mentioned
complex [Rh-C, 1.827(5) Å; C-O, 0.989(5) Å],34 suggest-
ing that the -CH(Ph)NHPh function is transmitting more
electron density to the metal center than the -C6H4NMe2
function. This assertion is in agreement with the lower νCO
of 1A (1983 cm-1) and 1B (1993 cm-1) relative to the above-
reported complex (1995 cm-1). Moreover, the strong coor-
dination is also confirmed by a large decrease of νNH (161
cm-1 for 1A and 140 cm-1 for 1B relative to L3A and L3B
free ligands).
ν
N-H region. We attribute this difference to the greater ability
of one of the two diastereomers to establish an intramolecular
N-H‚‚‚N hydrogen bond between the NHPh group as a
proton donor and the NEt2 group as a proton acceptor, see
Scheme 6.
3. Coordination of Ligands L3A/B to Rh(I). The reaction
between the L3 ligands with [RhCl(CO)2]2 led to the
stereospecific formation of complexes 1, see Scheme 7. In
each case, the presence of only one broad carbonyl absorption
band at ca. 1990 cm-1 is consistent with a square planar
monocarbonyl rhodium chloride structure bearing a P,N
chelating ligand. However, the NMR analysis does not
provide a clear indication of the chelating nature of the R,γ-
diaminophosphine ligand. N-Coordination by either the NH
Since we have recently found examples of intra- and
intermolecular N-H‚‚‚Cl-M (M ) RhI, PdII) interac-
tions,17,35 we have investigated the presence of this interaction
in complexes 1 both in the solid state though the X-ray data
(33) Haasnoot, C. A. G.; De Leeuw, F. A. A. M.; Altona, C. Tetrahedron
1980, 36, 2783-2792.
(34) Suomalainen, P.; Ja¨a¨skela¨inen, S.; Haukka, M.; Laitinen, R. H.;
Pursiainen, J. T.; Pakkanen, T. A. Eur. J. Inorg. Chem. 2000, 2607-
2613.
(35) Andrieu, J.; Camus, J. M.; Richard, P.; Poli, R.; Baldoli, C.; Maiorana,
S., submitted.
(32) Beachler, R. D.; Mislow, K. J. Am. Chem. Soc. 1970, 92, 3090-3093.
Inorganic Chemistry, Vol. 41, No. 15, 2002 3881

Andrieu et al.
Figure 1. ORTEP views of diastereomers 1A (a) and 1B (b). Thermal ellipsoids are drawn at the 50% probability level. For clarity, the solvate molecules
are omitted and only relevant hydrogen atoms are shown.
Scheme 8
and in solution through NMR and IR. No intramolecular
N-H‚‚‚Cl-Rh interaction exists in the solid state, since the
H-N(1)-Rh-Cl dihedral angle is very far from zero in both
structures. The H‚‚‚Cl distances (3.24-3.35 Å) are quite
close to the sum of the H and Cl van der Waals radii (3.35
Å). Furthermore, complexes with a genuine N-H‚‚‚Cl-M
intramolecular interaction in four-membered rings show
H‚‚‚Cl average values of 2.63 Å.36 In principle, an intramo-
lecular interaction could still be established in solution via
a dynamic ring configuration exchange, by analogy with a
similar Rh complex of the â-P,N ligand (1R,2R)-Ph2PCH-
(Ph)CH(Me)NHMe,12 leading to expected significant changes
1
of the H-C(1)-C(2)-H dihedral angles. However, the H
NMR spectra of our complexes 1 in CDCl3 solution show
3J(H,H) coupling constants that, as mentioned above, are
perfectly consistent with the corresponding solid-state
H-C(1)-C(2)-H conformations according to the Karplus
pseudoaxial position. A high diastereoselectivity was also
relationship.33
observed by us for the coordination of the simpler â-P,N
Thus, the NMR data indicate that the solid-state struc-
ture is maintained in solution. This still leaves open the
possibility of intermolecular hydrogen bonding interactions.
Indeed, in the solid state, the three structures 1A, 1B, and 2A
(see below) stack in an almost identical fashion. Two
coordination square planes are related by an inversion center
showing a self-assembling interaction of two molecules by
ligand L1 to Pd(II).17
4. Coordination of Ligands L5 to Rh(I). The inseparable
mixture of ligands L5 reacts with [RhCl(CO)2]2 to afford the
corresponding complexes 2 [doublets at 42.4 (1JRhP ) 166
Hz) for 2A and 57.5 ppm (1JRhP ) 166 Hz) for 2B] in a ca.
55:45 ratio, i.e., very close to that of the two isomeric free
ligands, see Scheme 8. As for complexes 1, a chelating
means of N-H‚‚‚Cl intermolecular hydrogen bonds (see
coordination mode is indicated by the presence of only one
Table 2). Infrared studies in CH2Cl2 solution, however,
(broad) carbonyl absorption band at 1985 cm-1 in the infrared
indicate that no hydrogen bonding is present. The νNH bands
1
spectrum. However, in contrast to complexes 1, the H and
at 3249 and 3270 cm-1 for 1A and 1B agree with a simple
31P NMR spectra show broad signals. The 31P spectrum of
NH-Rh coordination mode.36
the reaction mixture also shows the presence of small
It is worth noting that the observed κ2-P,N(H) coordination
amounts of an unidentified complex 2′ (δ 47.36 ppm with
mode generates a new asymmetric center at the N atom.
1J(Rh,P) ) 163 Hz), in addition to the diastereomeric
Therefore, each ligand L3 should yield in principle a mixture
complexes 2. Crystallization from CH2Cl2/pentane afforded
of two diastereomeric complexes. However, one diastereomer
single crystals of the major complex 2A. When these pure
was obtained (1A from L3A and 1B from L3B), indicating that
single crystals were dissolved in CDCl3, the 31P NMR
the coordination reaction is highly (>98%) diastereoselective.
This feature must be the result of a strong preference for
placing the bulkier Ph group in the less congested, pseu-
spectrum recorded after only 2 min shows a mixture of 2A
and 2′ in an approximate 8:2 ratio (see also section 5). It
cannot be established unambiguously, however, whether
doequatorial position and the smaller H group in the
complex 2′ forms rapidly from 2A when this is dissolved or
the solid sample, which looks homogeneous at a visual
(36) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. J. Am. Chem Soc. 1987,
109, 2803-2817.
microscope inspection, contained in fact another cocrystal-
3882 Inorganic Chemistry, Vol. 41, No. 15, 2002

â-Aminophosphines Bearing a Dangling Nitrogen Group
Figure 2. ORTEP view of diastereomer 2A. Thermal ellipsoids are drawn
at the 50% probability level. For clarity, only relevant hydrogen atoms are
shown.
lized specimen. Cooling a toluene solution to -30 °C gave
a microcrystalline powder, which, upon dissolution and NMR
analysis, consisted again of 2A and the byproduct 2′ in the
same 8:2 ratio. However, both crystallization methods gave
samples with no contamination by 2B.
The molecular structure of 2A was elucidated by X-ray
diffraction methods (see Figure 2). This demonstrates a
κ2-P,N(H) chelating mode of the â,R-P,N,N ligand, similar
to that observed for complexes 1, and establishes the
(SN,SC,SP)relative configuration for this diastereomer. Se-
lected geometrical parameters for 2A are given in Table 2.
The geometry around the rhodium atom is similar to those
of 1A and 1B, with similar slight deviations from ideal. All
bond lengths and angles of the coordination sphere as well
as the P,N chelate moiety of 2A are also quite similar to those
found for 1A and 1B. In particular, the Rh-C(3) and C(3)-O
bond lengths show once again the strong electron-donor
character of the -CH(Ph)NHPh function. As discussed for
1A and 1B, the geometry in complex 2A is not compatible
with an intramolecular NH‚‚‚Cl interaction, but as observed
for 1, two adjacent molecules are linked by intermolecular
hydrogen bonds. The main difference with respect to
complexes 1 is the position of the dangling amine function
relative to the Rh atom. The small Rh-P-C(22)-N(2)
dihedral angle [44.2(2)°] places the N(2) atom near the apical
axis of the complex, at a relatively close contact with the
Rh atom (3.66 Å). Even though this distance precludes NEt2
coordination to the metal center, the metal reactivity may
be affected by the presence of this function (see section 6).
Given the established (SN,SC,SP) relative configuration for
complex 2A, a relative (SN,SC,RP) configuration is attributed
to diastereomer 2B. This attribution is based on the similar
2B/2A and L5B/L5A ratios, suggesting the opposite relative
configurations of the P and C chiral centers (as also happens
for complexes 1 above), and on the demonstrated effect of
the carbon configuration on that of the coordinated N atom.
Even though a diastereoselective N coordination has been
observed in this work for complexes 1 and previously on
complex PdCl2(Ph2PCH2CH(Ph)NHPh),17 the literature re-
ports at least one precedent for diastereoisomers differing
by the absolute configuration at the coordinated N atom,
Figure 3. 31P NMR monitoring of the epimerization of diastereomer 2A
in CDCl3 solution. (a) After 2 min. (b) After 15 min. (c) After 5 h. (d)
Crystallization filtrate or crude product.
namely, for complexes [M(COD){Ph2PCH(Ph)CH(Me)-
NHMe}]+ (M ) Rh, Ir).12 Therefore, it cannot be excluded
that a ring conformer with a different absolute configuration
at nitrogen is responsible for the minor product 2′. The
alternative interpretation of 2′ as a dinuclear species contain-
ing P,N bridges seems excluded because the relative intensi-
ties of all complexes do not significantly change upon 4-fold
dilution.
5. Epimerization of Complexes 2A and 2B. As stated
above, the 31P NMR analysis of a CDCl3 solution of single
crystals of 2A showed an 8:2 mixture of 2A and 2′ after 2
min. However, the continued monitoring of this solution
revealed further evolution, with appearance of the diastere-
omer 2B. The relative intensity of 2B slowly increased with
time while that of 2A correspondingly decreased. The
evolution stopped when the composition became identical
with that of the crude product (see Figure 3). The filtrate of
the crystallization process also exhibited the same product
distribution.
This observation may be rationalized by inversion of either
the skeletal sp3 C atom or the P atom. As mentioned above,
the skeletal sp3 C inversion has at least one precedent in
coordination compounds.33 There seems to be no precedent,
however, for the racemization of a metal-coordinated chiral
P atom. Of relevance is a previous report of a P atom
inversion in a rhodium-coordinated tetraphosphine ligand,
although the phosphorus center undergoing the inversion
process does not appear to be formally coordinated to the
metal.37 When the equilibrium mixture of 2A/B and 2′ in
CDCl3 was treated with D2O, the intensity of the PCH proton
Inorganic Chemistry, Vol. 41, No. 15, 2002 3883

Andrieu et al.
P-C bond cleavage.39,40 This mechanism also allows an
additional possible interpretation of the “byproduct” 2′ as
being the Rh(III) intermediate complex.
Scheme 9
We should also consider the alternative possibility of a
reversible P-C6H5 rather than P-CH2NEt2 oxidative addi-
tion. Indeed, a related reversible P-Ph bond activation was
shown to take place with triaryl phosphine rhodium com-
plexes at 120-130 °C under propene hydroformylation
conditions, leading to an aryl group exchange and to the
formation of free Ph2P(C3H7).41,42 However, since the epi-
merization of 2A occurs at room temperature, it seems rea-
sonable to exclude this mechanistic pathway. It is important
to underline that the solutions containing the 2A/2B/2′ mixture
are not indefinitely stable. After several hours, all signal
intensities in the 31P NMR spectrum decreased, accompany-
ing a color change from yellow to dark brown. A similar
behavior was reported during the formation of phosphido
compounds from Rh-PPh3 complexes, giving rise to a
clustering process. This observed instability is also the reason
for the limited yield with which complex 2A was recovered.
1
signals in the H NMR spectrum remained unaltered even
after 12 h (which is much longer than the half-life of the
epimerization reaction). This observation is inconsistent with
a CH inversion. Since this C-H bond is close to the metal
center, it is possible to imagine a reversible oxidative addition
to generate a Rh(III) hydride species. However, this process
would not easily lead to inversion at carbon (this would
require further R-H elimination from the Rh-coordinated
amine function to generate an imine-dihydride intermediate,
migration of the metal onto the opposite imine face, and
reversal of the above processes).
6. Catalytic Properties in Rhodium Hydroformylation.
The newly developed â,γ- and â,R-diaminophosphines were
used for preliminary studies of rhodium-catalyzed styrene
hydroformylation, in comparison with previously developed
â- and γ-aminophosphines, in order to find out whether the
dangling nitrogen function can affect the activity and/or the
selectivity. The relevant results are assembled in Table 3.
All catalytic runs were carried out under identical conditions,
and in all cases the catalyst was prepared in situ by the
reaction of [RhCl(COD)]2 with 2 equiv of the appropriate
P,N or P,N,N ligands under syngas pressure. More detailed
mechanistic investigations of this catalytic process with the
aminophosphine complexes are underway and will be
presented in due course.
The proposal of a P inversion seems more appealing. A
first and obvious possibility consists of a reversible rupture
of the Rh-P bond to afford a κ-N or a κ2-N,N coordination
mode, followed by inversion at the free phosphorus atom
and recoordination since inversion barriers are high for free
tertiary phosphines.32 This possibility, however, does not
seem very likely since Rh(I)-P bonds are stronger than
Rh(I)-N bonds. Another way to accomplish the P-racem-
ization is via a reversible P-C bond oxidative addition as
shown in Scheme 9. The key transformation, formally
analogous to an R-alkyl elimination, is the transfer of the
P-bound CH2NEt2 group onto the metal center, while the
phosphine donor becomes a phosphido donor. The metal
formally becomes Rh(III) along the process, and the elec-
tronic unsaturation would be satisfied by π donation from
the P lone pair. As is well-known, metal-phosphido moieties
with a 4-electron (σ + π) M-P bond adopt a planar-at-P
configuration. Consequently, we need to invoke a ligand
rearrangement in the 5-coordinate Rh(III) intermediate which
places the -CH2NEt2 moiety on the opposite face of the
phosphido plane, and final reversal of the P-C oxidative
addition process. This proposed mechanism has close analo-
gies with the recently reported Rh(I)-catalyzed epimerization
of Ph2P(E)CH(Ph)NHCH(Me)Ph (E ) O, S), which involves
inversion at a chiral C center and seems to take place via a
reversible P-C oxidative addition to Rh(I).38 It is also
relevant to mention here that R-aminophosphines of the
P-C-N(H) type have been shown to undergo reversible
The results show that the product isomer ratio is always
in favor of the branched isomer, as is usual for the Rh-cat-
alyzed hydroformylation of styrene.43 The catalyst containing
the â,γ-diaminophosphine L3A has a comparable activity with
the catalysts based on the â- and γ-aminophosphines L1 and
L2. The slight decrease of regioselectivity for the branched
aldehyde observed for L3A relative to L1 and L2 remains
without a reasonable interpretation. This result would be
rationalized if L3A coordinates more strongly and/or exerts
a greater steric hindrance. However, this does not seem to
be confirmed by the solid state structural data. The NMe2
group does not strongly affect the catalytic activity because
of its remote position from the rhodium coordination sphere,
as suggested by the X-ray investigation of the catalyst
precursor (see Figure 1). On the other hand, the activity of
the catalyst containing L5 is three times greater than that of
(39) Andrieu, J.; Dietz, J.; Poli, R.; Richard, P. New J. Chem. 1999, 23,
581-583.
(40) Andrieu, J.; Baldoli, C.; Maiorana, S.; Poli, R.; Richard, P. Eur. J.
Org. Chem. 1999, 3095-3097.
(41) Abatjoglou, A. G.; Billig, E.; Bryant, D. R. Organometallics 1984, 3,
923-926.
(37) Hunt, C.; Fronczek, F. R.; Billodeaux, D. R.; Stanley, G. G. Inorg.
Chem 2001, 40, 5192-5198.
(38) Andrieu, J.; Camus, J.-M.; Poli, R.; Richard, P. New J. Chem. 2001,
25, 1015-1023.
(42) Abatjoglou, A. G.; Bryant, D. R. Organometallics 1984, 3, 932-934.
(43) van Leeuwen, P. W. N. M., Claver, C., Eds. Rhodium Catalyzed
Hydroformylation; Kluwer: Dordrecht, 2000; Vol. 22.
3884 Inorganic Chemistry, Vol. 41, No. 15, 2002

â-Aminophosphines Bearing a Dangling Nitrogen Group
the catalyst containing L1, while a high regioselectivity was
maintained. As suggested by the molecular structure of the
catalytic precursor 2A (see Figure 2), the placement of the
dangling NEt2 group close to the metal center may play a
beneficial effect on the activity relative to the catalysts
containing L1, L2, or L3A. We believe that the high basicity
and the close proximity of this dangling nitrogen function
to the metal center may facilitate a heterolytic dihydrogen
activation, during the initial conversion of the Rh-Cl
precursor to the Rh-H active species. Our current mecha-
nistic studies are intended to clarify the intimate action of
this dangling amine group and to rationalize its beneficial
effect in the rhodium-catalyzed hydroformylation process.
have observed a relatively slow epimerization which we
propose to involve inversion at the coordinated P atom. A
remote NMe2 function (in ligand L3A) does not significantly
modify the activity in rhodium-catalyzed styrene hydro-
formylation. However, a relatively close but uncoordinated
NEt2 function (in ligands L5) increases the conversion rate
by a factor of 3. Although the latter ligand is more efficient
in rhodium-catalyzed styrene hydroformylation and it pos-
sesses an asymmetric P atom, it is not expected to induce
large e.e.’s if used in the enantiomerically pure form, because
of the established epimerization process. Further fundamental
investigations are currently in progress in order to rationalize
the beneficial effect of a dangling amine function, with the
target of developing new active and enantioselective hydro-
formylation catalysts.
Conclusions
We have described in this paper simple access routes to
new classes of â-aminophosphines bearing a dangling
nitrogen function (â,γ- and â,R-diaminophosphines), includ-
ing the diastereoselective resolution by crystallization in the
first case. All new diaminophosphines L3 and L5 adopt a
chelating κ-P,κ-N mode when binding the RhCl(CO) moiety,
like the L1 â-aminophosphine. The diastereomers obtained
from L3A or L3B, i.e., complexes 1A and 1B, are stable in
solution. However, when a phenyl group on the P atom is
replaced by a CH2NEt2 fragment, i.e., in complexes 2, we
Acknowledgment. We are grateful to the Ministe`re de
la Recherche, the Centre National de la Recherche Scienti-
fique (CNRS), and the Conseil Re´gional de Bourgogne for
financial support. We are also grateful to Ce´dric Balan for
technical assistance.
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC011035I
Inorganic Chemistry, Vol. 41, No. 15, 2002 3885