Rh(I) coordination chemistry of chiral α-aminophosphine(η6-arene)chromium tricarbonyl ligands

Article abstract of DOI:10.1021/ic025588k

The diastereoselective addition of Ph₂PH to the chiral ortho-substituted η⁶-benzaldimine complexes (η⁶-o-X - C₆H₄CH=NAr)Cr(CO)₃ (1, X = MeO, Ar = p-C₆H₄OMe; 2, X = Cl, Ar = Ph) leads to the formation of the corresponding chiral aminophosphines (α-P,N) Ph₂P-CH(Ar¹)-NHAr² (3, Ar¹ = o-C₆H₄(OCH₃)[Cr(CO)₃], Ar² = p-C₆H₄OCH₃; 4, Ar¹ = o-C₆H₄Cl[Cr(CO)₃], Ar² = Ph) in equilibrium with the starting materials. The uncomplexed benzaldimine (o-ClC₆H₄CH=NPh), 2′, analogously produces an equilibrium amount of the corresponding aminophosphine Ph₂PCH(Ar¹)-NHAr² (4′, Ar¹ = o-C₆H₄Cl, Ar² = Ph). Depending on the equilibrium constant, the subsequent addition of 1/2 equiv of [RhCl(COD)]₂ (COD = 1,5-cyclooctadiene) leads to either Ph₂PH oxidative addition in the case of 3 or to the corresponding [RhCl(COD)(α-P,N)] complexes [RhCl(COD)(Ph₂P-CH{o-C₆H₄Cl[Cr(CO)3]}-NHPh)] (5) and [RhCl(COD)(Ph₂P-CH(o-C₆H₄Cl)-NHPh)] (5′) in the cases of the aminophosphines 4 and 4′. The addition of the latter ligands, as racemic mixtures, to 1/4 equiv of [Rh(CO)₂Cl]₂ leads to the [RhCl(CO)(α-P,N)₂] complexes [RhCO(Ph₂P-CH{o-C₆H₄Cl[Cr (CO)₃]}-NHPh)₂Cl] (7) or [RhCO(Ph₂P-CH(o-C₆H₄Cl)-NHPh)₂Cl] (7′) as mixtures of (Rc,Sc)/(Sc,Rc) and (Rc,Rc)/(Sc,Sc) diastereomers. The rhodium complexes 5 and 7′ have been fully characterized by IR and ³¹P NMR spectroscopies and X-ray crystallography. These compounds exhibit intramolecular Rh-Cl... H-N interactions in the solid state and in solution. The stability of the new rhodium complexes has been studied under different CO pressures. Under 1 atm of CO, 5 is converted to an unstable complex [RhCl(CO)₂(α-P,N)], 6, which undergoes ligand redistribution leading to 7 plus an unidentified complex. This reaction is inhibited under higher CO or syngas pressure, as confirmed by the observation of the same catalytic activity in hydroformylation when styrene was added to a catalytic mixture that was either freshly prepared or left standing for 20 h under high CO pressure.

Full text of DOI:10.1021/ic025588k

Inorg. Chem. 2003, 42, 2384−2390
Rh(I) Coordination Chemistry of Chiral
r-Aminophosphine(η6-arene)chromium Tricarbonyl Ligands
,†
Jean-Michel Camus,† Jacques Andrieu,* Rinaldo Poli,† Philippe Richard,† Clara Baldoli,‡ and
Stefano Maiorana‡
Laboratoire de Synthe`se et d’Electrosynthe`se Organome´talliques, UMR 5632, UniVersite´ de
Bourgogne, Faculte´ des Sciences “Gabriel”, 6 bouleVard Gabriel, 21000 Dijon, France, and
Dipartimento di Chimica Organica e Industriale e CNR Centro, Studio Sintesi Stereochimica
Speciali Organici, UniVersita` di Milano, Via C. Golgi 19, I-20133 Milano, Italy
Received March 13, 2002
The diastereoselective addition of Ph2PH to the chiral ortho-substituted η6-benzaldimine complexes (η6-o-XsC H -
6
4
CHdNAr)Cr(CO)3 (1, X) MeO, Ar ) p-C H OMe; 2, X) Cl, Ar ) Ph) leads to the formation of the corresponding
6
4
chiral aminophosphines (R-P,N) Ph2P−CH(Ar1)−NHAr2 (3, Ar1 ) o-C H (OCH )[Cr(CO)3], Ar2 ) p-C H OCH ; 4,
6
4
3
6
4
3
Ar1 ) o-C H Cl[Cr(CO)3], Ar2 ) Ph) in equilibrium with the starting materials. The uncomplexed benzaldimine
6
4
(o-ClC H CHdNPh), 2′, analogously produces an equilibrium amount of the corresponding aminophosphine Ph2P−
6
4
CH(Ar1)−NHAr2 (4′, Ar1 ) o-C H Cl, Ar2 ) Ph). Depending on the equilibrium constant, the subsequent addition
6
4
of 1/2 equiv of [RhCl(COD)]2 (COD ) 1,5-cyclooctadiene) leads to either Ph2PH oxidative addition in the case of
3 or to the corresponding [RhCl(COD)(R-P,N)] complexes [RhCl(COD)(Ph2P−CH{o-C H Cl[Cr(CO)3]}−NHPh)] (5)
6
4
and [RhCl(COD)(Ph2P−CH(o-C H Cl)−NHPh)] (5′) in the cases of the aminophosphines 4 and 4′. The addition of
6
4
the latter ligands, as racemic mixtures, to 1/4 equiv of [Rh(CO)2Cl]2 leads to the [RhCl(CO)(R-P,N)2] complexes
[RhCO(Ph2P−CH{o-C H Cl[Cr(CO)3]}−NHPh)2Cl] (7) or [RhCO(Ph2P−CH(o-C H Cl)−NHPh)2Cl] (7′) as mixtures
6
4
6 4
of (RC,SC)/(SC,RC) and (RC,RC)/(SC,SC) diastereomers. The rhodium complexes 5 and 7′ have been fully characterized
by IR and 31P NMR spectroscopies and X-ray crystallography. These compounds exhibit intramolecular Rh−Cl‚‚‚
H−N interactions in the solid state and in solution. The stability of the new rhodium complexes has been studied
under different CO pressures. Under 1 atm of CO, 5 is converted to an unstable complex [RhCl(CO)2(R-P,N)], 6,
which undergoes ligand redistribution leading to 7 plus an unidentified complex. This reaction is inhibited under
higher CO or syngas pressure, as confirmed by the observation of the same catalytic activity in hydroformylation
when styrene was added to a catalytic mixture that was either freshly prepared or left standing for 20 h under high
CO pressure.
Introduction
proposed that the nitrogen function increases the electron
density on the metal and subsequently promotes the oxidative
addition reactions.8 When both heteroatom donors are
separated by only one carbon atom (hereafter termed R-P,N
ligand), the nitrogen function has been shown to coordinate
to a second metal center9,10 or to remain uncoordinated in a
Since the discovery that bidentate bifunctional P,N ligands
increase considerably the activity and selectivity of Pd, Ni,
Ru, and Ir catalysts relative to PR3, their preparation has
been the subject of extensive investigations.1-7 It has been
* Author to whom correspondence should be addressed. E-mail:
jacques.andrieu@u-bourgogne.fr.
(4) Gao, J.-X.; Ikariya, T.; Noyori, R. Organometallics 1996, 15, 1087-
1089.
† Universite´ de Bourgogne.
‡ Universita` di Milano.
(5) Gravilov, K. N.; Polosukhin, A. I. Russ. Chem. ReV. 2000, 69, 661-
(1) Drent, E.; Arnoldy, P.; Budzelaar, P. H. M. J. Organomet. Chem. 1993,
455, 247-253.
682.
(6) Rauchfuss, T. B.; Clements, J. L.; Agnew, S. F.; Roundhill, D. M.
Inorg. Chem. 1977, 16, 775-778.
(2) Denis, P.; Jean, A.; Crizy, J. F.; Mortreux, A.; Petit, F. J. Am. Chem.
Soc. 1990, 112, 1292-1294.
(7) Roundhill, D. M.; Bechtold, R. A.; Roundhill, S. G. N. Inorg. Chem.
1980, 19, 284-289.
(3) Yang, H.; Alvarez, M.; Lugan, N.; Mathieu, R. J. Chem. Soc., Chem.
Commun. 1995, 1721-1722.
(8) Collman, J. P. Acc. Chem. Res. 1968, 1, 136-143.
2384 Inorganic Chemistry, Vol. 42, No. 7, 2003
10.1021/ic025588k CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/05/2003

Rh(I) Coordination Chemistry
Scheme 1
of the LSEO with a Fisons Instruments EA1108 analyzer. The
commercial compounds [RhCl(COD)]2 and [Rh(CO)2Cl]2 (Strem)
were used as received, and diphenylphosphine (Aldrich) was
distilled prior to use. The R-aminophosphine ligands Ph2P-CH-
(Ar1)-NHAr2 (3, Ar1 ) o-C6H4(OCH3)[Cr(CO)3], Ar2 ) p-C6H4-
OCH3; 4, Ar1 ) o-C6H4Cl[Cr(CO)3], Ar2 ) Ph; 4′, Ar1 ) o-C6H4Cl,
Ar2 ) Ph) were isolated or generated as previously described.12
Synthesis of [RhCl(COD)(Ph2P-CH{o-C6H4Cl[Cr(CO)3]}-
NHPh)], 5. To a solution of 2 (57 mg, 0.162 mmol) in CDCl3 (2
mL) was added Ph2PH (30 µL, 0.162 mmol). After 3 h, the complete
formation of the R-P,N ligand 4 was achieved. The solution was
then transferred into [RhCl(COD)]2 (40 mg, 0.081 mmol) and stirred
for 3 h. The solvent was then removed, and the residue was
dissolved in THF. The addition of pentane afforded the air-sensitive
pale-yellow crystals 5. Yield: 92 mg, 72%. 1H NMR (C6D6): 8.00
(1H, s, br, NH), 7.94-6.86 (15H, m, aromatics), 7.28 (1H, d, C6H4-
Cl, 3J(H,H) ) 6 Hz), 6.00 (1H, dd, PCH, 3J(H,H) ) 10 Hz, 2J(P,H)
) 13 Hz), 5.96 (1H, s, br, H1), 5.95 (1H, s, br, H2), 4.57 (1H, t,
C6H4Cl, 3J(H,H) ) 6 Hz), 4.41 (1H, d, C6H4Cl, 3J(H,H) ) 6 Hz),
a Without Cr(CO)3.
mononuclear complex.11 In the latter case, monodentate
R-P,N ligands display a free amine group which may assist
the proton-transfer steps in catalytic cycles, as was shown
in Ni and Pd catalysis.1,2
We have recently described a synthesis of R-P,N ligands,
where the N donor is a secondary amine function, which is
based on the reversible addition reaction of Ph2PH to a wide
range of benzaldimines. The newly formed P-C bond was
found to be stabilized by electron-withdrawing substituents
on the N or C atom or by P coordination.11 Moreover, the
use of chiral (η6-benzaldimine)tricarbonyl chromium com-
plexes has allowed access to chiral versions of this ligand
architecture via a diastereoselective reaction;12 see Scheme
1.
By analogy with our reported stabilization of Ph2PCH-
(Ph)NHPh by coordination to Cu(I),11 we explored whether
the stabilizing coordination effect could be generalized to a
metal center such as Rh(I) for potential applications to
homogeneous catalysis work. We report in this paper the
preparation of rhodium complexes, including some unusual
features of the solid-state and solution properties and an
initial testing of their catalytic behavior in styrene hydro-
formylation.
3
4.13 (1H, t, C6H4Cl, J(H,H) ) 6 Hz), 3.08 (1H, s, br, H5), 2.87
(1H, s, br, H6), 2.22-1.45 (8 H, m, H3,4,7,8). 13C{1H} NMR
(C6D6): 231.6 (3C, s, Cr(CO)3), 146.7-114.3 (m, C-aromatics),
116.9 (1C, s, C6H4Cl), 109.0 (1C, s, C6H4Cl), 106.5 (2C, m, C1,
C2), 97.0 (1C, s, C6H4Cl), 94.1 (1C, s, C6H4Cl), 86.3 (1C, s, C6H4-
Cl), 85.3 (1C, s, C6H4Cl), 73.1 (1C, d, C5, 1J(Rh,Colefin) ) 12 Hz),
71.9 (1C, d, C6, 1J(Rh,Colefin) ) 13 Hz), 58.2 (1C, d, PCH, 1J(P,C)
) 20 Hz), 33.1 (1C, s, C3), 33.0 (1C, s, C8), 29.4 (1C, s, C4), 28.9
1
(1C, s, C7). 31P{1H} NMR (C6D6): 44.1 (d, J(Rh,P) ) 155 Hz).
IR (CH2Cl2): 3285 (b, νNH), 1982 (vs, νCO), 1911 (vs, vb, νCO
)
cm-1. IR (Nujol): 3288 (w, b, νNH) cm-1. Anal. Calcd for C36H33-
Cl2CrNO3PRh (784.4): C, 55.12; H, 4.24; N, 1.70. Found: C,
55.15; H, 4.25; N, 1.70.
Synthesis of [RhCl(COD)(Ph2P-CH(o-C6H4Cl)-NHPh)], 5′.
By using operating procedures identical with those described above
for compound 5, compound 2′ (35 mg, 0.162 mmol) and Ph2PH
(30 µL, 0.162 mmol) were initially mixed in CDCl3. After 3 h, an
equilibrium with the R-P,N ligand 4′ was achieved. The complex
5′ was obtained as single yellow crystals after addition to [RhCl-
(COD)]2 (40 mg, 0.065 mmol) and workup as described in the
1
previous section. Yield: 63 mg, 60%. H NMR (C6D6): 9.26-
2
6.50 (19H, aromatics + NH), 6.35 (1H, dd, PCH, J(P,H) ) 14.6
3
Hz, J(H,H) ) 9 Hz), 5.83 (2H, s, br, H1 + H2), 3.08 (1H, s, br,
Experimental Section
H5), 2.90 (1H, s, br, H6), 2.20-1.44 (8H, m, br, H3,4,7,8). 13C{1H}
NMR (C6D6): 147.4-113.4 (m, C-aromatics), 105.6 (s, br, C1,2),
71.9 (d, 1C, C5, 1J(Rh,Colefin) ) 14 Hz), 71.0 (d, 1C, C6,
1J(Rh,Colefin) ) 14 Hz), 56.7 (d, 1C, PCH, 1J(Rh,P) ) 28 Hz), 33.35
(s, 1C, C3), 32.4 (s, 1C, C8), 29.3 (s, 1C, C4), 28.4 (s, 1C, C7).
All manipulations were carried out under purified argon and in
the dark using standard Schlenk techniques. All solvents were dried
and deoxygenated prior to use by standard methods. NMR
measurements (1H, 13C{1H}, and 31P{1H}) were carried out with a
Bruker AC200 spectrometer. 1H-1H and 1H-13C correlation spectra
were recorded on a Bruker 500 DRX Advance instrument. The peak
positions are reported with positive shifts in parts per million
downfield of tetramethylsilane, as calculated from the residual
solvent peaks (1H and 13C), or downfield of external 85% H3PO4
(31P). The coordinated 1,5-cyclooctadiene (COD) C and H nuclei
are labeled from 1 to 8, C1 and C2 being trans to P. IR spectra
were recorded with a Bruker IFS 66V spectrophotometer using KBr
optics. Elemental analyses were carried out by the analytical service
1
31P{1H} NMR (C6D6): 34.7 (d, J(Rh,P) ) 154 Hz). Anal. Calcd
for C33H33Cl2CrNPRh (648.4): C, 61.13; H, 5.13; N, 2.16. Found:
C, 61.02; H, 5.18; N, 2.66.
Synthesis of [RhCO(Ph2P-CH{o-C6H4Cl[Cr(CO)3]}-
NHPh)2Cl], 7. A solution of 4 (87 mg, 0.16 mmol) in toluene (5
mL) was added to a solution of [RhCl(COD)]2 (20 mg, 0.04 mmol)
in toluene (5 mL). After stirring for 1 h, a CO stream was bubbled
through the solution for 15 min, causing the formation of a yellow
suspension. After stirring overnight, the mixture was concentrated
to half its original volume and filtered. The yellow powder was
washed two times with pentane (20 mL) and dried under vacuum.
Yield: 80 mg, 80%. 1H NMR (CDCl3): 8.09-6.67 (30H, m,
aromatics + 4H from C6H4Cl), 7.81 (2H, s, br, NH, exchange with
(9) Newkome, G. R. Chem. ReV. 1993, 93, 2067-2089.
(10) Dervisi, A.; Edwards, P. G.; Newman, P. D.; Tooze, R. P.; Coles, S.
J.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1998, 3771-3776.
(11) Andrieu, J.; Dietz, J.; Poli, R.; Richard, P. New J. Chem. 1999, 23,
581-583.
(12) Andrieu, J.; Baldoli, C.; Maiorana, S.; Poli, R.; Richard, P. Eur. J.
Org. Chem. 1999, 3095-3097.
3
D2O), 5.82 (2H, m, PCH), 5.55 and 5.50 (2H, t, C6H4Cl, J(H,H)
) 6 Hz), 5.00 and 4.95 (2H, t, C6H4Cl, 3J(H,H) ) 6 Hz). 1H NMR
Inorganic Chemistry, Vol. 42, No. 7, 2003 2385

Camus et al.
Table 1. Crystal Data and Structure Refinement for 5 and 7′
[(CD3)2CO]: 8.14-6.51 (32H, m, aromatics), 5.92 and 5.88 (2H,
t, C6H4Cl, 3J(H,H) ) 6 Hz), 5.80 and 5.77 (2H, t, PCH, 3J(H,H) )
5
7′
3
2J(P,H) ) 5 Hz), 5.35 and 5.31 (2H, t, C6H4Cl, J(H,H) ) 6 Hz),
chemical formula
C36H33Cl2NO3PCrRh
C51H42N2OP2Cl3Rh‚
1/4C5H12
988.10
110(2)
3
5.28 and 5.22 (2H, d, C6H4Cl, J(H,H) ) 6 Hz), 2.75 (2H, s, br,
NH, exchange with D2O). 13C{1H} NMR [(CD3)2CO]: 232.8 (s,
Cr(CO)3), 206.9 (Rh-CO, masked by acetone), 147.1-114.0 (m,
C-aromatics), 108.1 and 108.0 (2C, s, C6H4Cl), 98.9 and 98.1 (2C,
s, C6H4Cl), 89.3 and 89.1 (2C, s, C6H4Cl), 86.7 and 86.2 (2C, s,
C6H4Cl), 57.8 (t, 2C, PCN, 1J(P,C) ) 2J(Rh,C) ) 14 Hz). 31P{1H}
NMR [(CD3)2CO]: 36.98 and 34.54 (d, 1J(Rh,P) ) 129 Hz) in 1:2
ratio. IR (THF): 3320 (br, νNH), 1994 (s, νCO, Rh-CO), 1980 (vs,
fw
T, K
784.41
110(2)
space group
a, Å
b, Å
Ph1
I41/a
11.9308(3)
12.4015(3)
12.5645(3)
68.8459(15)
89.439(2)
76.449(2)
1679.76(7)
2
42.6851(4)
42.6851(4)
10.2428(1)
90
90
90
18 662.6(3)
16
1.407
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
ν
CO, Cr(CO)3), 1914 (vs, br, νCO, Cr(CO)3) cm-1. Anal. Calcd for
C57H42Cl3Cr2N2O7P2Rh (1242.2): C, 55.12; H, 3.41; N, 2.26.
Found: C, 55.37; H, 3.48; N, 2.44.
D
calc, g/cm3
1.551
λ, Å
0.710 73
1.058
0.047
0.710 73
0.647
0.076
Synthesis of [RhCO(Ph2P-CH(o-C6H4Cl)-NHPh)2Cl], 7′. To
a solution of 2′ (59 mg, 0.27 mmol) in CHCl3 (5 mL) was added
Ph2PH (49 µL, 0.27 mmol). After 3 h, an equilibrium with the R-P,N
ligand 4′ was achieved. The solvent was removed and a solution
of [RhCl(COD)]2 (30 mg, 0.06 mmol) in THF (5 mL) was added.
µ, mm-1
R(Fo)a (all data)
2
Rw(Fo )b (all data)
0.080
0.090
a R(Fo) ) ∑||Fo| - |Fc||/∑|Fc|. b Rw(Fo2) ) {∑w(Fo - Fc )2/
2
2
2
2
∑[w(Fo )2}1/2, where w ) 1/[σ2(Fo + (0.038P)2 + 1.37P] for 5 and w )
1
After stirring for /2 h, CO was bubbled through the solution for
2
2
2
1/[σ2(Fo + (0.033P)2 + 27.39P] for 7′ and P ) [Max(Fo ,0) + 2Fc ]/3.
15 min. The resulting yellow solution was further stirred for 30
min and concentrated to 2 mL. The addition of pentane (10 mL)
afforded the product as a yellow powder, which was isolated by
filtration, washed with pentane (2 × 10 mL), and dried under
vacuum (98 mg, 84%). A slow diffusion of pentane onto a THF
solution of the product afforded suitable yellow crystals for the
X-ray analysis. 1H NMR (C6D6): 9.15-6.55 (38H, m, aromatics),
Table 2. Selected Lengths (Å) and Angles (deg) for Compounds 5 and
7′
5
7′
Rh-Cl(2)
Rh-P
2.3978(6)
2.3134(6)
2.230(3)
2.240(3)
2.110(3)
2.133(3)
2.004(4)
2.128(3)
1.899(2)
1.440(3)
0.82(3)
Rh-Cl(1)
Rh-P(1)
Rh-P(2)
Rh-C(1)
C(1)-O
N(1)-H
N(1)-H‚‚‚Cl(1)
N(1)‚‚‚Cl(1)
N(2)-H
N(2)-H‚‚‚Cl(1)
N(2)‚‚‚Cl(1)
2.3871(7)
2.3358(7)
2.3332(7)
1.818(3)
1.145(3)
0.78(3)
2.40(3)
3.135(3)
0.89(3)
Rh-C(29)
Rh-C(30)
Rh-C(33)
Rh-C(34)
Rh-Ct(1)a
Rh-Ct(2)a
P-C(10)
C(10)-N
N-H
1
8.05 (2H, s, br, NH, exchange with D2O), 6.48 (2H, m, PCH). H
NMR [(CD3)2CO]: 8.81-6.49 (38H, m, aromatics), 6.28 (2H, m,
PCH), 2.88 (2H, s, br, NH, exchange with D2O). 13C{1H} NMR
1
(C6D6): 187.6 (2C, d, CO, J(Rh,C) ) 67 Hz), 147.0-113.3 (m,
C-aromatics), 57.0 and 56.7 (2C, d, PCH, 1J(C,P) ) 14 Hz). 31P-
1
{1H} NMR (C6D6): 31.68 and 29.87 (d, J(Rh,P) ) 128 Hz). IR
2.24(4)
3.116(3)
(THF): 3314 (w, b, νNH), 1990 (ws, νCO) cm-1. IR (Nujol): 3296
(w, b, νNH) cm-1. Anal. Calcd for C51H43Cl3N2OP2Rh (970.1): C,
63.14; H, 4.36; N, 2.89. Found: C, 62.99; H, 4.50; N, 3.40.
Stability of Compound 6 under CO Pressure. A mixture of 4
(36 mg, 0.066 mmol) and [RhCl(COD)]2 (16.5 mg, 0.033 mmol)
was dissolved in 10 mL of CHCl3, resulting in the formation of
complex 5 as described above. The resulting yellow solution was
introduced into the autoclave and pressurized with CO (300 psi) at
55 °C. After stirring for 12 h, the resulting red solution was analyzed
by IR spectroscopy. IR (CHCl3): 2097 and 2015 (s, νCO, Rh-
CO), 1985 and 1916 (s, br, νCO, Cr(CO)3) cm-1. No stretching
vibration corresponding to compound Cr(CO)6 was observed.
Crystal Structure Analysis of Complexes 5 and 7′. Intensity
data were collected on a Nonius Kappa charge-coupled device at
110 K for 5 and 7′. The structure was solved by the heavy atom
method and refined by full-matrix least-squares methods13 with the
aid of the WINGX program.14 Non-hydrogen atoms were aniso-
tropically refined. For 5, the hydrogen atoms were located in the
final difference Fourier maps and refined freely. For 7′, with the
exception of the NH hydrogen atom, which was located in the final
difference Fourier maps and refined freely, all hydrogen atoms were
included in a rigid model. Compound 7′ crystallizes with one
pentane molecule, which is located on a fourfold inversion axis
N-H‚‚‚Cl(2)
N‚‚‚Cl(2)
2.42(3)
3.199(2)
P-Rh-Cl(2)
93.32(2)
P(1)-Rh-Cl(1)
P(1)-Rh-C(1)
P(2)-Rh-Cl(1)
P(2)-Rh-C(1)
N(1)-H‚‚‚Cl(1)
N(2)-H‚‚‚Cl(1)
90.85(2)
89.79(8)
88.82(2)
90.48(8)
157(3)
Ct(1)-Rh-Ct(2)
Ct(2)-Rh-Cl(2)
Ct(1)-Rh-P
86.2(2)
87.3(1)
93.0(2)
158(3)
N-H‚‚‚Cl(2)
167(3)
a Ct(1) is the centroid of C(29) and C(30), and Ct(2) is the centroid of
C(33) and C(34).
resolved. Crystallographic data and selected bond lengths and angles
for the compounds 5 and 7′ are reported respectively in Tables 1
and 2.
Catalytic Runs. The hydroformylation reactions were carried
out in a 300-mL stainless-steel Parr autoclave equipped with a
magnetic drive, an internal glass vessel, and an immersion tube
connected to a valve for solution withdrawals under pressure. The
temperature was controlled by a rigid heating mantle and by a
single-loop coil. The autoclave was purged three times under
vacuum/argon before introducing the catalytic solution. The 1:1
CO/H2 mixture was prepared by mixing the pure gases in a 500-
mL stainless-steel cylinder before introduction into the autoclave
at the desired pressure. Catalytic conditions were as follows:
styrene/Rh ) 1000, 12 mg of [RhCl(COD)]2 in 35 mL of
chloroform, P(syngas) ) 600 psi, T ) 55 °C. The zero time for
the kinetic runs was considered to be the time at which the desired
pressure was reached inside the autoclave. To maintain as constant
as possible temperature and pressure conditions during each kinetic
run, only a few milliliters of the catalytic solution mixture were
1
5
close to the inversion center (0, /4, /8), leading to disorder over
two positions. However, the rather large values of the isotropic
temperature factors may indicate a further disorder that was not
(13) Sheldrick, G. M. SHELX97: Programs for Crystal Structure Analysis,
Release 97-2; University of Go¨ttingen: Go¨ttingen, Germany, 1998
(includes SHELXS97 and SHELXL97).
(14) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.
2386 Inorganic Chemistry, Vol. 42, No. 7, 2003

Rh(I) Coordination Chemistry
Scheme 2
The quantitative formation of 5′, however, shows that
coordination to Rh(I) brings the same stabilizing effect
previously demonstrated for Cu(I) toward the rupture of the
ligand P-C bond. Hence, the presence of the Cr(CO)3
fragment is not necessary to ensure the stability of the Rh(I)
complex. However, its presence allows the introduction of
chirality in complex 5.
Both complexes 5 and 5′ are characterized by a doublet
in the 31P NMR spectra at 44.1 and 34.7 ppm, respectively,
1
with a J(Rh,P) coupling constant of 155 Hz in each case.
An X-ray diffraction analysis of 5 (vide infra) confirms the
monodentate (P) coordination of the ligand. Addition of 1
equiv (additional) of 4 or 4′ to 5 or 5′ does not induce
displacement of the coordinated COD moiety (see Scheme
3, path a). However, when CO gas is introduced into this
reaction mixture, the new complexes 7 or 7′ are formed (see
Scheme 3, path b) via the formation of intermediates 6 or 6′
(see below for their identification). The same complexes can
also be obtained directly by treatment of 4 equiv of the
appropriate R-P,N ligand with [Rh(CO)2Cl]2 (path e).
carefully withdrawn each time from the autoclave. The CHCl3
solvent was then rotary-evaporated at room temperature and the
yellow-orange residue was analyzed by H NMR spectroscopy to
1
quantify the conversion by integration.
Results and Discussion
The solutions of compounds 7 and 7′ are characterized
by two doublets in the 31P NMR spectra with J(Rh,P) of
(a) Synthesis and Characterization. The same synthetic
procedure previously used for the formation of Cu(I)
complexes has now been applied to the formation of Rh(I)
complexes. It consists of the addition of the stoichiometric
amount of [RhCl(COD)]2 to a mixture of Ph2PH and the
imines 1, 2, or 2′, after it has reached thermodynamic
equilibrium with the corresponding R-P,N product. When
the Cr(CO)3-benzaldimine 1 or 2 was used, this reaction
led selectively to a single diastereomer as a racemic mixture.
As shown in our previous study,12 the resulting products 3
and 4 have the configuration (RAr,RC)/(SAr,SC), where the first
descriptor refers to the arene planar chirality and the second
one refers to the chirality of the carbon center (see Scheme
1). The equilibrium constants shown in Scheme 1 had been
determined during our previous study.12 When the benzaldi-
mine 1 was used, the 1H NMR spectrum showed the presence
of three different hydride complexes that are characterized
1
128 Hz and only one carbonyl vibration in the IR spectra
around 1990 cm-1 in a THF solution. These spectroscopic
data are consistent with a trans-[RhCl(CO)L2] square-planar
geometry,15-17 which is confirmed by an X-ray diffraction
study for 7′ (see below). The two 31P NMR resonances are
attributed to the different pairs of diastereomers (RC,RC)/
(SC,SC) and (RC,SC)/(SC,RC), whose formation is due to the
use of the racemic ligand. The resonances are observed at
37.0 and 34.5 ppm (1:2 ratio) for 7 and 31.7 and 29.9 ppm
(1:1 ratio) for 7′. Several resonances in the 1H NMR spectrum
are also distinct for the two diastereomeric pairs, whereas
others overlap (see the Experimental Section). The complete
resonance assignment was made possible by the spectro-
scopic analysis of (RAr,RC)/(RAr,RC)-7, obtained from optically
pure (RAr,RC)-4, showing that the higher field resonance for
7 (major product) is due to the (RAr,RC)/(SAr,SC) diastereomer.
1
by H NMR resonances at -14.00 (hept), -17.20 (dt), and
The νCO in the mononuclear complexes allows an estima-
tion of the σ-donor/π-acceptor character of the phosphine
ligands and an evaluation of the electron density at the
metal.18,19 The comparison of the CO stretching frequencies
of compounds 7 (1994 cm-1) and 7′ (1990 cm-1) with those
of different trans-[RhCl(CO)L2] complexes indicates that the
σ-donor/π-acceptor properties of ligands 4 and 4′ are
comparable to those of diphenylpyrrolylphosphine and P(p-
CF3C6H4).20,21 The shift of only 4 cm-1 to a higher frequency
-18.70 (dt) ppm with coupling constants of 11.6, 35, and
26, and 11.6 and 24 Hz, respectively. However, the 31P NMR
spectrum exhibits only one broad signal at 9.0 ppm for all
complexes. The mixture presumably results from Ph2P-H
oxidative addition to Rh(I), while the imine remained
unreacted. These hydride products were not further charac-
terized. Nevertheless, the phosphorus chemical shift excludes
the formation of bridging phosphido moieties in dinuclear
complexes. The use of 2 or 2′, on the other hand, led to the
desired mononuclear rhodium complexes 5 or 5′ without the
observation of any product resulting from P-H oxidative
addition (see Scheme 2).
This observation suggests that the outcome of the reaction
is controlled by the relative concentration of free Ph2PH and
R-P,N in the reaction mixture. Because both reactions with
the Rh(I) center are irreversible, the P-C bond-formation
equilibrium is displaced completely either way, depending
on which reactivity pathway prevails. Given the quantitative
formation of 4, the clean formation of 5 is not surprising.
(15) Sharp, P. R. In ComprehensiVe Organometallic Chemistry II; Abel,
E. W., Stone, F. G., Wilkinson, G., Eds.; Pergamon: Oxford, U.K.,
1995; Vol. 8.
(16) Slawin, A. M. Z.; Smith, M. B.; Woollins, J. D. J. Chem. Soc., Dalton
Trans. 1996, 1283-1293.
(17) Kuznetsov, V. F.; Facey, G. A.; Yap, G. P. A.; Alper, H. Organo-
metallics 1999, 18, 4706-4711.
(18) Poulton, J. T.; Sigalas, M. P.; Folting, K.; Streib, W. E.; Eisenstein,
O.; Caulton, K. G. Inorg. Chem. 1994, 33, 1476-1485.
(19) Ohgomori, Y.; Yoshida, S.; Watanabe, Y. J. Chem. Soc., Dalton Trans.
1987, 12, 2969-2974.
(20) Moloy, K. G.; Petersen, J. L. J. Am. Chem. Soc. 1995, 117, 7696-
7710.
Inorganic Chemistry, Vol. 42, No. 7, 2003 2387

Camus et al.
Scheme 3
Figure 2. ORTEP view of complex 7′. Thermal ellipsoids are drawn at
the 50% probability level. For clarity, the pentane solvate molecule is
omitted, and only the relevant hydrogen atoms are shown.
features in the complexes is(are) the intramolecular Rh-Cl‚
‚‚H-N interaction(s) between the NH amine function(s) and
the Rh-Cl moiety. The N‚‚‚Cl distances in the 3.12-3.20-Å
range for 5 and 7′ (see Table 2) are significantly smaller
than the sum of the N-H bond length and the van der Waals
radii of H and Cl atoms25 and even smaller than an analogous
interaction (3.33 Å) recently reported for a palladium allyl
complex.26 Other reported intramolecular M-Cl‚‚‚H-N
interactions for neutral aminophosphine complexes involve
four- or seven-membered rings,27-29 but no previous example
is available for six-membered rings.
Figure 1. ORTEP view of complex 5. Thermal ellipsoids are drawn at
the 50% probability level. For clarity, only the relevant hydrogen atoms
are shown.
on going from 7′ to 7 indicates that ligand 4 is only slightly
affected by the electron-withdrawing Cr(CO)3 group.
(b) Unusual Features of 5 and 7′ Complexes in the Solid
State and in Solution. The X-ray diffraction analyses of 5
and 7′ (see Figures 1 and 2) show that the aminophosphine
ligands are only P-coordinated in the square-planar rhodium
complexes. For complex 7′, only one racemic diastereomer
(RC,RC)/(SC,SC) is observed in the unit cell, whereas both
diastereomers were present in the solution before crystal-
lization. The essential geometrical features and metric
parameters are quite typical for the RhCl(CO)2L and RhCl-
(COD)L structures.22-24 The more interesting structural
(23) Boyd, S. E.; Field, L. D.; Hambley, T. W.; Partridge, M. G.
Organometallics 1993, 12, 1720-1724.
(24) Chang, A. S. C.; Chen, C. C.; Cao, R. Organometallics 1997, 16,
3469-3473.
(25) Bondi, A. J. Phys. Chem. 1964, 68, 441-451.
(26) Andrieu, J.; Camus, J.-M.; Dietz, J.; Richard, P.; Poli, R. Inorg. Chem.
2001, 40, 1597-1605.
(27) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. J. Am. Chem. Soc. 1987,
109, 2803-2817.
(21) Clarke, M. L.; Cole-Hamilton, D. J.; Slawin, A. M. Z.; Woollins, J.
D. Chem. Commun. 2000, 2065-2066.
(22) Ceriotti, A.; Ciani, G.; Sironi, A. J. Organomet. Chem. 1983, 247,
345-350.
(28) Fryzuk, M. D.; Le Page, M. D.; Montgomery, C. G.; Rettig, S. J.
Inorg. Chem. Commun. 1999, 2, 378-380.
(29) Petrucci, M. G. L.; Lebuis, A.-M.; Kakkar, A. K. Organometallics
1998, 17, 4966-4975.
2388 Inorganic Chemistry, Vol. 42, No. 7, 2003

Rh(I) Coordination Chemistry
Scheme 4
(c) Identification of the Dicarbonyl Complex cis-Rh-
(CO)2Cl(L). When two equivalents of ligand 4 or 4′ (in
equilibrium with 2′ and Ph2PH) are added at room temper-
ature to a THF solution of [Rh(CO)2Cl]2, an unstable
mononuclear dicarbonyl derivative cis-Rh(CO)2Cl(L) (6 or
6′) is formed (see Scheme 3, path d). The proposed geometry
is demonstrated by the characteristic IR and 31P NMR
1
data.32-37 The presence of only one doublet with J(Rh,P)
) 132 Hz (32.7 ppm for 6, 28.1 ppm for 6′) in the 31P NMR
spectrum and two carbonyl bands (at 2017 and 2095 cm-1
for 6 and 2015 and 2094 cm-1 for 6′) in the IR spectrum
unambiguously excludes the formation of a binuclear inter-
mediate, which could result from the potential assembling
character of the R-P,N ligands.9,38,39
Under a di-nitrogen purge, the unstable complexes 6 and
6′ rapidly undergo quantitative decarbonylation to afford
complexes 7 and 7′, respectively, as shown by the IR and
31P NMR monitoring. The IR spectrum of the crude mixture
also showed two weak carbonyl bands at 2070 and 2080
cm-1, while no additional 31P resonance is observed in the
NMR spectrum. Therefore, the transformation of 6 to 7 must
be accompanied by the formation of a second product that
does not contain phosphine ligands. However, the IR data
are not consistent with the formation of [Rh(CO)2Cl]2. This
product is formulated as “RhCl(CO)n” in Scheme 3. We have
not made any further attempt to fully characterize this
byproduct. A separate experiment shows that complexes 5
and 5′ transform into 6 and 6′ immediately when exposed
to CO at atmospheric pressure (path c), but these are
converted completely to the same final mixture within 30
min. On the other hand, the solutions obtained by decom-
position of 6 (or 6′) regenerate these precursors when
pressurized under CO (see also the following catalytic
studies). It is interesting to note that a similar behavior was
observed by Alper et al. for the analogous complex RhCl-
(CO)2(L-κ1-P) (L ) Ph2POCH(Ph)CH(Me)NHMe),17 whose
transformation into [RhCl(CO)L2] and [RhCl(CO)2]2 was
proposed on the basis of 31P NMR spectra. In another study,
the formation of a µ-CO species was found when using a
pyridinylphosphine ligand.38 Our IR investigation excludes
the formation of such species, although it could play a role
as an intermediate, as found for other ligand-redistribution
processes.30
The H-bonding interactions observed for 5 and 7′ in the
solid state are maintained in CH2Cl2 and even in THF. This
is demonstrated by the following IR spectroscopic results.
The NH absorption band in the free ligand 4 is found at
3327 cm-1 in the solid state and 3409 cm-1 in a THF
solution. This is due to the dimeric structure of 4 exhibiting
P‚‚‚H-N interactions.12 Therefore, the solution band can be
attributed to the stretching vibration of the free N-H moiety.
Compound 5, on the other hand, exhibits the N-H stretching
vibration at 3283 cm-1 in THF and 3285 cm-1 in CH2Cl2
(these are close to the value of 3288 cm-1 observed for the
solid dispersed in Nujol). Furthermore, a 10-fold dilution of
the solution does not alter the form of the spectrum; notably,
no absorption is visible in the free N-H region. The large
red shift of about 125 cm-1 relative to the free N-H group
indicates a rather strong H-bonding interaction. For com-
pound 7′, the N-H vibration is observed at 3312 cm-1 in a
THF solution (a red shift of 97 cm-1 relative to free N-H)
and 3296 cm-1 for the solid dispersed in Nujol. The lower
shift for 7′ relative to 5 indicates a weaker H-bonding
interaction, which can be rationalized on the basis of the
higher NH/Cl ratio. It is important to remark that this
H-bonding interaction does not engage the nitrogen lone pair.
Consequently, the inversion at nitrogen should remain free,
and no new chiral center is generated.
(30) Garrou, P. E.; Hartwell, G. E. J. Chem. Soc., Chem. Commun. 1974,
381-382.
When crystals of the pure diastereomer (RC,RC)/(SC,SC)-
7′ are dissolved in C6D6, the compound immediately
establishes an equilibrium with the (SC,RC)/(RC,SC) diastereo-
isomer (1:1 ratio; see Scheme 4). This is proven by the
immediate recording of 31P and 1H NMR spectra. Therefore,
a rapid intermolecular ligand-exchange process must occur.
A similar phosphine-scrambling process has been previously
reported for compounds RhCl(CO)(L)(L′), with L, L′ )
triphenylphosphine, tricyclohexylphosphine, or dimethyl-
phenylphosphine, and has been rationalized in terms of either
the formation of dinuclear rhodium complexes30 or through
a dissociation-recoordination process.31
(31) Fackler, J. P. Inorg. Chem. 1970, 9, 2625-2626.
(32) Le Gall, I.; Laurent, P.; Toupet, L.; Salau¨n, J.-Y.; des Abbayes, H.
Organometallics 1997, 16, 3579-3581.
(33) Le Gall, I.; Laurent, P.; Soulier, E.; Salau¨n, J. Y.; des Abbayes, H. J.
Organomet. Chem. 1998, 567, 13-20.
(34) Rotondo, E.; Battaglia, G.; Giuseppe, G.; Priolo, C. F. J. Organomet.
Chem. 1993, 450, 245-252.
(35) Wegman, R. W.; Abatjoglou, A. G.; Harrison, A. M. J. Chem. Soc.,
Dalton Trans. 1987, 1891-1892.
(36) Wu, M. L.; Desmond, M. J.; Drago, R. S. Inorg. Chem. 1979, 18,
679-686.
(37) Pribula, A. J.; Drago, R. S. J. Am. Chem. Soc. 1976, 98, 2784-2788.
(38) Farr, J. P.; Olmstead, M. M.; Hunt, C. H.; Balch, A. L. Inorg. Chem.
1981, 20, 1182-1187.
(39) Turpin, R.; Dagnac, P.; Poilblanc, R. J. Organomet. Chem. 1987, 319,
247-255.
Inorganic Chemistry, Vol. 42, No. 7, 2003 2389

Camus et al.
equilibrated overnight under a CO pressure in the absence
of styrene to ensure the quantitative formation of compound
6. The autoclave was then depressurized, and the complete
and slow transformation of 6 to 7 was verified by IR
spectroscopy. At this point, styrene was introduced, and the
subsequent catalytic run (squares in Figure 3) indicates the
same turnover frequency as that for the previous experiment.
These results suggest that the same catalytic species is present
in both systems and confirm that the ligand-redistribution
process can be reversed only under high CO pressure.
Conclusion
We have shown that chiral R-aminophosphine ligands form
stable Rh(I) complexes, provided that the equilibrium
constant of the ligand formation from the benzaldimine and
diphenylphosphine is sufficiently high. Otherwise, the di-
phenylphosphine oxidative addition reaction prevails. The
Rh(I) complexes containing one or two monodentate (P)
R-P,N ligands display Rh-Cl‚‚‚H-N interactions with the
dangling secondary amine function in the solid state and in
solution. The NMR and IR studies have highlighted ligand-
redistribution processes in solution, some of which are
dependent on the CO pressure. The stabilization of dicarbonyl
rhodium compounds by high CO pressure allows the forma-
tion of a hydroformylation catalytic precursor. The influence
of the P,N ligand on the hydroformylation catalytic activity
will be the topic of a separate contribution.40
Figure 3. Rate conversion for the styrene hydroformylation with complex
5 (see the Experimental Section for the catalytic conditions). (2) Styrene
introduced at t ) 0. (9) Styrene introduced after 20 h.
Independent of how complex 6 is generated, it remains
the major species in solution, as shown by IR spectroscopy,
when it is maintained overnight under a high CO pressure
(20 atm). The subsequent release of the CO pressure induces
the evolution of 6 to 7 as previously described. The
stabilizing effect of the high CO pressure suggests that the
initial step of the ligand-redistribution process in Scheme 3
is a CO dissociation. To establish the reversibility of this
ligand-redistribution process, the decomposed mixture ob-
tained as described above (containing no residual complex
6) was pressurized with CO (20 atm) for several hours in an
autoclave. Upon depressurization, an immediate IR analysis
revealed the presence of compound 6 together with 7 and
the subsequent quantitative transformation into 7.
Further evidence that complex 6 is stable under a high
CO pressure was obtained through hydroformylation catalysis
studies. A first run was carried out by charging the autoclave
with [RhCl(COD)]2, ligand 4 (L/Rh ) 1), styrene, the
chloroform solvent, and syngas. A kinetic follow-up (tri-
angles in Figure 3) shows a turnover frequency of 45 h-1. It
is interesting to note the absence of any induction period.
A second experiment was carried out under the same
conditions. However, the precatalyst solution was initially
Acknowledgment. We are grateful to the Ministe`re de
la Recherche, the Centre National de la Recherche Scienti-
fique, and the Conseil Re´gional de Bourgogne for support
of this work. J.-M.C. thanks the Ministe`re de la Recherche
for a Ph.D. fellowship. We are also grateful to Professor
Elena Shubina for a helpful discussion. S.M. and C.B. thank
the Italian National Research Council, the MIUR of Rome,
and the University of Milano (joint national project “Stereo-
selezione in Sintesi Organica. Metodologie e applicazioni”)
for support of this work.
Supporting Information Available: X-ray crystallographic data
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC025588K
(40) Andrieu, J.; Camus, J.-M.; Poli, R. Manuscript in preparation.
2390 Inorganic Chemistry, Vol. 42, No. 7, 2003