Rhodium complexes with chiral aminophosphinite derivatives of ephedrine

Article abstract of DOI:10.1021/om990442n

Aminophosphinites Ph₂POCHPhCHMeNMeR (2a-c: a, R = H; b, R = Me; c, R = Ph₂-CH), prepared from the corresponding N-substituted (1S,2R)-ephedrines, cleanly react with [Rh(CO)₂Cl]₂ in benzene, affording complexes with P,N-chelating (3a, 4b) or monodentate (5b,c and 7c) ligands, depending on the steric bulk of the amino group and metal-to-ligand ratio. Treatment of the chloro-bridged dimer 7c with AgClO₄ in methylene chloride gives the cationic complex 8c, containing not only P,N-chelating aminophosphinite but also a Ph group of a N-diphenylmethyl fragment coordinated to Rh in an unusual η² fashion. Formation of the chiral center at nitrogen occurs stereoselectively, and complexes 3a and 8c exist as single diastereomers in the solid state and in solution. The structures of 3a and 8c were established by single-crystal X-ray diffraction.

Full text of DOI:10.1021/om990442n

4706
Organometallics 1999, 18, 4706-4711
Rh od iu m Com p lexes w ith Ch ir a l Am in op h osp h in ite
Der iva tives of Ep h ed r in e
Vladimir F. Kuznetsov, Glenn A. Facey, Glenn P. A. Yap, and Howard Alper*
Department of Chemistry, University of Ottawa, 10 Marie Curie,
Ottawa, Ontario K1N 6N5, Canada
Received J une 8, 1999
Aminophosphinites Ph2POCHPhCHMeNMeR (2a -c: a , R ) H; b, R ) Me; c, R ) Ph2-
CH), prepared from the corresponding N-substituted (1S,2R)-ephedrines, cleanly react with
[Rh(CO)2Cl]2 in benzene, affording complexes with P,N-chelating (3a , 4b) or monodentate
(5b,c and 7c) ligands, depending on the steric bulk of the amino group and metal-to-ligand
ratio. Treatment of the chloro-bridged dimer 7c with AgClO4 in methylene chloride gives
the cationic complex 8c, containing not only P,N-chelating aminophosphinite but also a Ph
group of a N-diphenylmethyl fragment coordinated to Rh in an unusual η2 fashion. Formation
of the chiral center at nitrogen occurs stereoselectively, and complexes 3a and 8c exist as
single diastereomers in the solid state and in solution. The structures of 3a and 8c were
established by single-crystal X-ray diffraction.
In tr od u ction
therefore allowing for fine-tuning of the coordination
properties of these ligands. The affinity of “soft” transi-
tion metals toward N-donors is generally considered to
be lower than that toward phosphorus; in contrast, the
strength of the M-N bond is affected much more by
steric effects than that of the corresponding M-P bond.8
As a result, depending on the steric bulk of the N-
substituents, aminophosphinites may act as chelating,
monodentate, or bridging ligands. Here we wish to
report the preparation and characterization of Rh
complexes with aminophosphinite derivatives of ephe-
drine, emphasizing the factors which affect the structure
of the complexes and the selectivity for the formation
of chiral centers at nitrogen.
Metallocomplexes containing chiral P,N-chelating
ligands have attracted considerable attention because
they often display interesting structural, chemical, and
catalytic properties.1 The vast majority of these com-
plexes, however, possess chirality associated with car-
bon and sometimes phosphorus atoms, while the nitro-
gen is sp2-hybridized or bears identical substituents and
therefore cannot be chiral. It is well-known that the N
atom in an amino group undergoes very fast inversion
of configuration; however, donation of the lone pair to
a metal retards the inversion and the coordinated
nitrogen becomes stereogenic. The formation of chiral
N centers was proposed or implied in a number of
publications;2 however, structurally characterized com-
plexes featuring stereogenic nitrogen are rare.1a,3,4
Chiral amino alcohols such as ephedrine are very
attractive for application in metalloorganic chemistry.
They are inexpensive, are readily available in enantio-
merically pure form, and can be easily transformed to
the corresponding aminophosphinites.5 The chemistry
of an amino group is well-developed; thus, it is possible
to introduce virtually any substituent at the nitrogen,6,7
Resu lts a n d Discu ssion
P r ep a r a tion of Am in op h osp h in ites 2a -c. The
aminophosphinite ligands were prepared by treatment
of N-substituted ephedrines with Ph2PCl in the presence
of Et3N in benzene (eq 1) in a way similar to that
described for prolinol based aminophosphinites.5 The
(1) See for example: (a) Gao, J .-X.; Ikariya, T.; Noyori, R. Organo-
metallics 1996, 15, 1087. (b) Yamada, T.; Ohkouchi, M.; Yamaguchi,
M.; Yamagishi, T. J . Chem. Soc., Perkin Trans. 1997, 1, 1869. (c)
Schnyder, A.; Togni, A.; Wiesli, U. Organometallics 1997, 16, 255. (d)
Hampton, C. R. S. M.; Butler, I. R.; Cullen, W. R.; J ames, B. R.;
Charland, J .-P.; Simpson, J . Inorg. Chem. 1992, 31, 5509 and refer-
ences therein. (e) Payne, N. C.; Tobin, G. R. Acta Crystallogr. 1992,
C48, 45. (f) Yamamoto, K.; Tomita, A.; Tsui, J . Chem Lett. 1978, 3.
(2) See for example: (a) Takehara, J .; Hashiguchi, S.; Fujii, A.; Shin-
ichi, I.; Ikariya, T.; Noyori, R. Chem. Commun. 1996, 233. (b) Brunner,
H.; Weber, H. Chem. Ber. 1985, 118, 3380. (c) Kobayashi, S.; Uchiro,
H.; Fujishita, Y.; Shiina, I.; Mukaiyama, T. J . Am. Chem. Soc. 1991,
113, 4247. (d) Asami, M.; Inoe, S. Chem. Lett. 1991, 685. (e) Yamada,
S.; Mashiko, T.; Terashima, S. J . Am. Chem. Soc. 1977, 99, 1988.
(3) Togni, A.; Rihs, G.; Pregosin, P. S.; Ammann, C. Helv. Chim.
Acta 1990, 73, 723.
compounds were isolated as colorless oils and character-
1
ized by 31P, H, and 13C NMR. According to 31P NMR
spectra of the reaction mixture, the transformation of
1b to 2b was very clean and took less than 5 min at
room temperature. Under the same conditions N-(diphen-
ylmethyl)ephedrine (1c) reacted more slowly (ca. 6 h at
(4) Oishi, T.; Hirama, M. J . Org. Chem. 1989, 54, 5834.
(5) Agbossou, F.; Carpentier, J .-F.; Hatat, C.; Kokel, N.; Mortreux,
A.; Betz, P.; Goddard, R.; Kruger, C. Organometallics 1995, 14, 2480.
(6) Bowman, R. E. J . Chem. Soc. 1950, 1346.
(7) Neelakantan, L. J . Org. Chem. 1971, 36, 2256.
(8) Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. Engl. 1994,
33, 497.
10.1021/om990442n CCC: $18.00 © 1999 American Chemical Society
Publication on Web 10/24/1999

Rh Complexes with Derivatives of Ephedrine
Organometallics, Vol. 18, No. 23, 1999 4707
pyridyl)-2-(diphenylphosphino)ethane)10 and some Ru
complexes.11 The six-membered chelate rings of the
complex adopt the thermodynamically more stable chair
conformation with the bulky Ph groups at C(13) and
C(35) in equatorial positions, while the sterically less
demanding Me substituents at C(20) and C(42) occupy
axial sites (chirality of the ligands dictates a cis orienta-
tion of the neighboring Ph and Me groups). Both
nitrogen atoms possess the R configuration with the
attached Me substituents in axial positions. It should
be noted that the chiral centers at the N atoms in 3a
arise only upon coordination to the metal; therefore,
another diastereomer with a sterically more favorable
equatorial orientation of the N-Me groups could be
formed. Since this does not happen, it seems reasonable
to assume that the selective formation of the R diaste-
reomer, which occurs despite unfavorable 1,3-diaxial
interaction of the N-Me and P-Ph groups, is explained
by the strong hydrogen bonding between the Cl anion
and the two equatorial protons attached to the nitro-
gens. The N(H)‚‚‚Cl interatomic separations (3.158(5)
and 3.176(5) Å) in 3a are consistent with strong Cl-H
hydrogen bonds, while the hypothetical S diastereomer
would possess two trans-N-H substituents in axial
positions, a situation unsuitable for simultaneous for-
mation of two hydrogen bonds with the Cl anion. The
1H NMR spectrum of 3a displays a broad resonance at
8.3 ppm which is typical for hydrogen-bonded N-H
protons. It should be noted that formation of the chiral
centers occurs stereoselectively and 3a exists as a single
diastereomer, not only in the solid state but also in
solution, as can be seen from the 31P{1H} NMR of the
reaction mixture (sharp doublet at 141 ppm) and 31P-
{1H}, 13C{1H}, and 1H NMR spectra of the isolated
complex.12
F igu r e 1. Perspective diagram of 3a with 30% probability
ellipsoids. The hydrogen atoms (except for N-H) and phenyl
carbon atoms (except for ipso) are omitted for clarity.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 3a
Rh-N(1)
Rh-N(2)
Rh-P(1)
2.182(3)
2.201(3)
2.1855(9)
Rh-P(2)
O(1)-P(1)
2.1887(8)
1.633(3)
N(1)-Rh-P(1)
89.34(8)
C(22)-N(1)-Rh
106.7(2)
N(1)-Rh-N(2) 85.77(10)
C(22)-N(1)-C(20) 111.1(3)
N(2)-Rh-P(2)
P(1)-Rh-P(2)
88.98(7)
98.74(3)
C(20)-N(1)-Rh
123.3(3)
room temperature). No intermediates were observed
during this time. The 31P NMR spectra showed only the
signals of 2c and unreacted Ph2PCl (δ 113 and 82.5,
respectively). Similar reaction of 1a and Ph2PCl at 20
°C led predominantly to the formation of N-(diphen-
ylphosphino)ephedrine (identified by a signal at δ 60.5
in 31P NMR);5,9 however, heating the reaction mixture
to reflux for ca. 30 min led to complete rearrangement
to the desired 2a . The reaction was accompanied by
formation of unidentified side products (ca. 20%), and
therefore column chromatography was employed in
order to purify 2a .
Rea ction of P OEp h w ith Rh 2(CO)4Cl2. X-r a y
Str u ctu r e of [Rh (P OEp h )2]+Cl- (3a ). Treatment of
a benzene solution of Rh2(CO)4Cl2 with 2 equiv of 2a
led to the evolution of CO and clean formation of
complex 3a according to eq 2. According to the31P NMR
Rea ction of P OMep h w ith Rh 2(CO)4Cl2. Ch a r a c-
ter iza tion of Rh (P OMep h )(CO)Cl (4b) a n d Rh -
(P OMep h )2(CO)Cl (5b). In a comparison with 2a ,
aminophosphinite 2b gives two different products de-
pending on the metal-to-ligand ratio employed. The
reactions are very clean and occur easily at room
temperature according to eqs 3 and 4. The complexes
spectra, complex 3a was the only metalloorganic product
even when less than 2 equiv of the aminophosphinite
was used. The signal of unreacted 2a appeared in the
spectrum only when more than 2 equiv of the ligand
was added. The complex was isolated in high yield as
air-stable yellow crystals soluble in benzene, CH2Cl2,
and methanol but insoluble in Et2O and saturated
hydrocarbons. The structure of 3a was established by
single-crystal X-ray diffraction. An ORTEP plot of the
complex is shown in Figure 1; selected bond distances
and angles are presented in Table 1.
The coordination environment of the Rh is noticeably
distorted from a square-planar geometry (the trans-P-
Rh-N angles are 164.9 and 166.4°), with the distortion
presumably due to steric repulsion between the cis-PPh2
fragments. The observed arrangement with two phos-
phorus atoms cis to each other seems to be quite
common for bis-P,N-chelated metallocomplexes and was
reported for closely related [Rh(PN)2]PF6 (PN ) 1-(2-
4b and 5b were isolated in high yield and characterized
by elemental analysis and IR and NMR spectra. The
carbonyl group of the complex 4b appears as a doublet
(9) Mortreux, A.; Petit, F.; Buono, G.; Peiffer, G. Bull. Soc. Chim.
Fr. 1987, 631.
(10) Anderson, M. P.; Casalnuovo, A. L.; J ohnson, B. J .; Mattson,
B. M.; Mueting, A. M.; Pignolet, L. H. Inorg. Chem. 1988, 27, 1649.
(11) Guo, Z.; Habtemariam, A.; Sadler, P. J .; J ames, B. R. Inorg.
Chim. Acta 1998, 273, 1 and references therein.
(12) The spectra recorded in CD2Cl2 at 173-313 K show the presence
of a single diastereomer.

4708 Organometallics, Vol. 18, No. 23, 1999
Kuznetsov et al.
Sch em e 1
of doublets in the 13C{1H} NMR spectrum (J C-P ) 18
Hz; J C-Rh ) 71 Hz), indicating that there is only one
phosphinite ligand in the molecule and that CO is cis
to the phosphorus. The diastereotopic N-Me groups of
the complex give two signals in the spectrum. Coordina-
tion of the nitrogen to the metal was unequivocally
confirmed by the 15N{1H} NMR spectrum, which showed
F igu r e 2. Perspective diagram of the cation of 8c with
30% probability ellipsoids. All hydrogen atoms and non-
ipso-phenyl carbon atoms on P and C(13) are omitted for
clarity.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 8c
a doublet of doublets, due to coupling with Rh (J N-Rh
)
11.5 Hz) and phosphorus (J N-P ) 3.5 Hz). In contrast
to the case for 4b, complex 5b shows a doublet of triplets
in the carbonyl region of the 13C{1H} NMR spectrum
as a result of CO carbon coupling with Rh (J C-Rh ) 74.5
Hz) and with two P ligands (J C-P ) 17 Hz). The two
phosphinites are equivalent (sharp doublet in 31P{1H}
NMR) and hence are trans to each other. The N-Me
groups of the complex appear as a single line in the 13C-
{1H} NMR spectrum, indicating that the two nitrogens
of 5b are equivalent and are not coordinated to the
metal.
Rh-N
2.127(5)
2.2015(16)
1.835(9)
1.146(10)
2.334(6)
2.449(7)
1.546(10)
1.514(10)
C(28)-C(29)
C(24)-C(29)
C(24)-C(25)
C(25)-C(26)
C(26)-C(27)
C(27)-C(28)
P-O(1)
1.434(11)
1.383(11)
1.370(12)
1.404(13)
1.337(12)
1.405(12)
1.605(5)
Rh-P
Rh-C(36)
C(36)-O(2)
Rh-C(29)
Rh-C(28)
C(23)-C(35)
C(23)-C(29)
N-Rh-P
92.34(13)
174.4(3)
92.4(3)
C(20)-N-Rh
C(23)-N-Rh
Rh-C(29)-C(28)
114.9(4)
95.2(3)
77.0(4)
N-Rh-C(36)
C(36)-Rh-P
C(20)-N-C(22) 109.9(5)
Rh-C(29)-C(24) 106.6(5)
C(22)-N-C(23) 111.9(5)
Rh-C(29)-C(23)
88.4(3)
Rea ction of P OP h ep h w ith Rh 2(CO)4Cl2. Ch a r -
a cter iza tion of Rh 2(P OP h ep h )2(CO)2Cl2 (7c). X-r a y
C(22)-N-Rh
113.0(4)
Str u ctu r e of [Rh (P OP h ep h )CO]+ClO4 (8c). The
-
-342 ppm in the 15N{1H} NMR spectrum. The available
spectral data do not contradict the proposed structure
of 7c as a dimer with two phosphinites coordinated in
an anti fashion. We cannot exclude, however, that these
ligands occupy syn positions in the dimer or that the
complex exists as a mixture of both isomers. It seemed
conceivable that substitution of the bridging chlorides
with weakly coordinating anions such as perchlorate
would destroy the dimeric structure of 7c, bringing
about coordination of the pendant amino group to the
metal. Indeed, treatment of 7c with AgClO4 leads to
precipitation of silver chloride and formation of the
cationic complex 8c containing P,N-chelating amino-
phosphinite and, surprisingly, a Ph group of the N-
(diphenylmethyl) fragment coordinated to rhodium in
an unusual η2 fashion. The complex was isolated in high
yield as yellow air-stable crystals soluble in CH2Cl2 and
methanol and insoluble in THF and aromatic hydro-
carbons. The structure of 8c was established by single-
crystal X-ray diffraction. An ORTEP plot and selected
bond distances and angles of the complex cation are
shown in Figure 2 and Table 2, respectively.
The coordination environment of the Rh is formed by
a cis P,N-chelating aminophosphinite, a carbonyl group
which is trans to the nitrogen, and a Ph group coordi-
nated to the metal via the ipso and ortho carbons. The
phenyl ring remains approximately planar (rms devia-
tion 0.02 Å) and assumes a dihedral angle of 104° with
the plane defined by the two coordinated carbons and
the Rh atom. The Rh-ipso-C distance (2.334(6) Å) is
very close to the average value for π-arene Rh complexes
reaction of Rh2(CO)4Cl2 and 2 equiv of 2c occurs
according to eq 4 in the same way as described for 2b.
The resulting 5c was isolated in high yield as an air-
stable orange solid and characterized by elemental
analysis and IR and NMR spectroscopy (see Experi-
mental Section).
Treatment of Rh2(CO)4Cl2 with 1 equiv of 2c in
benzene at room temperature leads to the appearance
of two broad doublets at 125 (J P-Rh ) 192 Hz) and 110
ppm (J P-Rh ) 144 Hz) and a sharp doublet at 116 ppm
(J P-Rh ) 136 Hz) in the 31P{1H} NMR spectrum of the
reaction mixture. The sharp doublet was identified as
the signal of 5c on the basis of its chemical shift and
coupling constant. It seemed reasonable to assume that
the reaction involves the set of equilibria shown in
Scheme 1.
The removal of CO from the solution with a stream
of inert gas resulted in the disappearance of the doublets
of 5c (116 ppm) and 6c (110 ppm) from the NMR
spectrum, while the doublet corresponding to 7c became
sharp. Bubbling CO through the solution restored the
original equilibrium. Complex 7c was isolated from the
degassed reaction mixture in high yield and character-
ized by elemental analysis and IR and NMR spectra.
The carbonyl groups of the complex appear as a doublet
of doublets (δ 183.5, J C-P ) 19 Hz, J C-Rh ) 82 Hz) with
the value of the C-P coupling constant indicative of a
cis relationship between the CO and phosphorus. The
amino groups of 7c are equivalent and are not coordi-
nated to rhodium, as indicated by a sharp singlet at

Rh Complexes with Derivatives of Ephedrine
Organometallics, Vol. 18, No. 23, 1999 4709
(2.33(5) Å),13 while the distance to the coordinated ortho
carbon (2.449(7) Å) is substantially longer. A similar
situation was reported for (η3-CH2C6Me5)Rh[P(OPri)3]2,
which was described as the benzyl analogue of π-allyl
Rh complexes.14 The Rh-C(23) separation (2.746(7) Å)
in 8c, however, is too long for any bonding interaction,
and 8c thus represents a new example of still quite rare
η2-arene metallocomplexes.15-17
The six-membered P-N-Rh chelate is in a chair
conformation. As anticipated, the bulky diphenylmethyl
group at the nitrogen and Ph at C(13) occupy equatorial
positions, rendering the sterically less demanding meth-
yl substituents at C(20) and at the nitrogen in axial
sites. The stereogenic N-center thus adopts the S
absolute configuration. Coordination of Rh to one of the
two Ph groups of the diphenylmethyl fragment brings
about formation of a chiral center at C(23), with the
absolute configuration depending on which phenyl is
coordinated. The two possible diastereomers should
differ from each other by the position of the uncoordi-
nated Ph group relative to Me substituents at N and
C(20). The observed structure of 8c displays an S
configuration at C(23) with the uncoordinated Ph group
cis to the N-Me unit, while the hypothetical R diaste-
reomer would possess the uncoordinated Ph cis to the
Me group at C(20). The cis interaction in 8c is relieved
to some extent by pivoting of the diphenylmethyl group
around the C(23)-N bond (the C(22)-N-C(23)-C(35)
torsion angle is 31.8(5)°), while the cis interaction
between the uncoordinated Ph and Me at C(20) is
probably severe enough to prevent formation of the R
diastereomer. The structure of 8c thus incorporates six
stereogenic centers. Two of them (C(13) and C(20)) were
present in the ligand, while the others (C(23), C(28),
C(29). and N) arise upon coordination of the η2-Ph and
amino groups to the metal. Formation of the new chiral
centers occurs stereoselectively, and 8c exists as a single
diastereomer, not only in the solid state but also in
solution (31P{1H} NMR of the reaction mixture18 and
F igu r e 3. 125 MHz VT 13C{1H} NMR spectra (aromatic
region) of 8c in CD2Cl2.
rotation of the coordinated Ph group around the σ-bond
(C(23)-C(29) on Figure 2). It should be noted that the
other Ph groups of the complex have low rotational
barriers, as indicated by the pairwise equivalence of the
ortho and meta carbons in the VT 13C{1H} NMR spectra.
The ortho protons of the η2-Ph group are nonequiva-
lent and are well-separated from the other aromatic
protons in the 1H NMR spectra of the complex (see
Figure 4). At 260 K they appear as sharp doublets
centered at 8.6 and 7.9 ppm. Increasing the temperature
leads to broadening and finally collapse of the signals
at 305 ( 5 K. The value of the rotational barrier of the
η2-Ph group calculated for 8c (13.7 ( 0.3 kcal/mol)
compares well with the value obtained for “ring whiz-
zing” in (η2-arene)pentammineosmium(II) complexes
(11.8-17.2 kcal/mol)20 and is significantly higher than
the corresponding value14 for (η3-CH2C6Me5)Rh[P(OPri)3]2,
where two sides of the benzyl ligand appear to be
equivalent even at 193 K.
1
31P{1H}, 13C{1H}, and H NMR spectra of the isolated
complex).
F lu xion a l Beh a vior of 8c in Solu tion . The η2-
coordinated Ph group of 8c gives six sharp resonances
in the 125 MHz 13C{1H}NMR spectra19 recorded below
260 K (see Figure 3). At higher temperatures the signals
of the ortho and meta carbons become broad and cannot
be observed at 285 K. The meta carbons show a broad
averaged resonance (δ 134.3) at 310 K, while the ortho
carbons still cannot be seen in the spectrum. The signals
of the ipso and para carbon atoms of the η2-Ph group
remain sharp in the temperature interval 210-310 K.
Taken together, these data suggest that the observed
fluxional behavior of 8c is explained by restricted
Con clu sion s
The present study demonstrates that coordination
properties of aminophosphinites are very sensitive to
the steric bulk of the amino group. Reaction of 2a and
Rh2(CO)4Cl2 occurs with displacement of the Cl anion
and all carbonyls from the coordination sphere of Rh-
(I). The two P,N-chelate cycles of the resulting complex
3a remain intact in the presence of excess ligand,
indicating high affinity of the NHMe fragment for the
metal. The NMe2 terminus of 1b easily cleaves the Cl
(13) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1.
(14) Burch, R. R.; Muetterties, E. L.; Day, V. W. Organometallics
1982, 1, 188.
(15) Muetterties, E. L.; Bleeke, J . R.; Wucherer, E. J . Chem. Rev.
1982, 82, 499.
(16) Belt, S. T.; Duckert, S. B.; Helliwell, M.; Perutz, R. N. J . Chem.
Soc., Chem. Commun. 1989, 928.
(17) Harman, W. D.; Gebhart, M.; Taube, H. Inorg. Chem. 1990,
29, 567.
(18) The spectrum shows a sharp doublet for 8c, and other unidenti-
fied signals were of low intensity (ca. 5% altogether).
(19) The resonances were assigned using a combination of 13C DEPT,
COSY, TOCSY, NOESY, and HMQC techniques.
(20) Harman, W. D.; Sekine, M.; Taube, H. J . Am. Chem. Soc. 1988,
110, 5725.

4710 Organometallics, Vol. 18, No. 23, 1999
Kuznetsov et al.
ephedrine (11.16 mmol) in 30 mL of benzene. The resulting
suspension was heated to reflux for 1 h, cooled, and filtered.
The filtered white solid was washed with benzene (3 × 10 mL),
and the combined filtrates were evaporated and dried under
vacuum at 100 °C. The oily residue was stirred with heptane/
Et2O (4:1, 15 mL), the white precipitate which formed was
filtered off, and the filtrate was passed through a short column
with basic alumina (50 × 25 mm) and the column eluted with
30 mL of heptane/Et2O (1:2 for 2a or 2:1 for 2b,c). Removal of
the solvent in a vacuum afforded the corresponding 2a -c as
a colorless oil.
2a (P OEp h ).21 The compound was purified by column
chromatography on basic alumina (250 × 25 mm, heptane-
2:1 heptane/Et2O). Yield: 63%. 31P{1H} NMR (CDCl3; δ):
113.1. 1H NMR (CDCl3; δ): 1.1 (d, J ) 6.4 Hz, 3H); 2.3 (s, 3H);
2.9 (m, 1H); 5.0 (dd, J H-H ) 4.6 Hz, J H-P ) 9.7 Hz, 1H); 7.2-
7.7 (m, 15H). 13C{1H} NMR (CDCl3; δ): 15.2 (s, Me); 33.8 (s,
Me); 60.6 (d, J C-P ) 5.5 Hz, CH); 83.9 (d, J C-P ) 18.7 Hz, CH);
127.0-131.1 (12 lines, Ph); 140.1 (d, J C-P ) 2.5 Hz, Ph); 142.05
20
(d, J C-P ) 15.4 Hz, Ph); 142.15 (d, J C-P ) 20 Hz, Ph). [R]D
-5.9° (c ) 3.9, toluene).
)
2b (P OMep h ). Yield: 81%. 31P{1H} NMR (CDCl3; δ): 112.8.
1H NMR (CDCl3; δ): 1.2 (d, J ) 6.7 Hz, 3H); 2.3 (s, 6H); 3.0
(m, 1H); 5.1 (dd, J H-H ) 5.5 Hz, J H-P ) 8.9 Hz, 1H); 7.3-7.8
(m, 15H). 13C{1H} NMR (CDCl3; δ): 9.6 (s, Me); 41.4 (s, Me);
65.1 (d, J C-P ) 6.2 Hz, CH); 83.4 (d, J C-P ) 18.6 Hz, CH);
F igu r e 4. 500 MHz VT 1H NMR spectra (fragment of
aromatic region) of 8c in CD2Cl2.
127.0-131.2 (12 lines, Ph); 141.6 (d, J C-P ) 2 Hz, Ph); 142.1
20
(d, J C-P ) 17 Hz, Ph); 142.4 (d, J C-P ) 14 Hz, Ph). [R]D
+21.4° (c ) 22.5, benzene).
)
bridges but is not able to displace carbonyl, and the
chelate ring in the formed 4b can be opened by an excess
of the ligand. The amino group of 2c, which possesses
a rather large N-(diphenylmethyl) substituent, is not
able to cleave the relatively weak Cl bridges. The P,N-
ligand in 7c is connected to Rh only via phosphorus. It
does not mean, however, that the NMeCHPh2 fragment
cannot be coordinated, and treatment of the complex
with AgClO4 leads to the formation of a chelate cycle.
The affinity of the amino group of 2a -c toward Rh(I)
thus can be arranged in the following order: -NHMe
> CO > -OPPh2 > -NMe2 > µ-Clj > -NMeCHPh2 >
ClO4j.
The superior stability of the P,N-chelate in 3a is
probably explained by the formation of strong hydrogen
bonds between the Cl anion and the two N-H protons.
The hydrogen bonds render the N-H protons of the six-
membered chelate rings in equatorial positions and thus
define the configuration of the stereogenic nitrogen
atoms in the complex. The selective formation of the
chiral centers at the nitrogen in 8c is governed by the
well-known tendency of nonrigid six-membered rings to
adopt a chair conformation with the sterically more
demanding substituents in equatorial positions.
2c (P OP h ep h ).21 Yield: 71%. 31P{1H} NMR (CDCl3; δ):
112.2. 1H NMR (CDCl3; δ): 1.1 (d, J ) 6.7 Hz, 3H); 2.1 (s, 3H);
3.2 (m, 1H); 4.4 (s, 1H); 4.8 (apparent t, J H-H ≈ J H-P ≈ 8.5
Hz, 1H); 6.8-7.6 (m, 25H). 13C{1H} NMR (CDCl3; δ): 9.5 (s,
Me); 34.2 (s, Me); 59.3 (d, J C-P ) 7.4 Hz, CH); 74.1 (s, CH);
85.1 (d, J C-P ) 18.6 Hz, CH); 126.6-131.4 (18 lines, Ph);
20
141.8-142.1 (6 lines, Ph); 142.9 (s, Ph); 143.9 (s, Ph). [R]D
+105° (c ) 2.1, benzene).
)
Syn th esis of ClRh (P OEp h )2 (3a ). POEph (1.8 mmol,
0.313 M in C6H6) was added to a stirred solution of Rh2(CO)4-
Cl2 (170 mg, 0.437 mmol) in 6 mL of benzene. The resulting
bright yellow solution was reduced in volume to ca. 5 mL under
vacuum and diluted with 6 mL of heptane to form a volumi-
nous yellow precipitate. Heating the reaction flask in boiling
water led to transformation of the precipitate into a yellow oil
which spontaneously crystallized. The flask was allowed to
stay at room temperature for 1 h; the crystals were separated,
washed with copious amounts of pentane, and dried under
vacuum to give 670 mg (0.800 mmol, 91%) of analytically pure
3a as a light yellow microcrystalline solid. Anal. Calcd for
C
44H48ClN2O2P2Rh: C, 63.1; H, 5.8; N, 3.3. Found: C, 62.8; H,
5.6; N, 3.1. 31P{1H} NMR (C6D6; δ): 141 (d, J P-Rh ) 189.5 Hz).
1H NMR (C6D6; δ): 1.8 (d, J ) 6.3 Hz, 3H); 2.8 (m, 4H); 4.7
(broad s, 1H); 6.7-7.8 (m, 15H); 8.3 (broad s, 1H). 13C{1H}
NMR (C6D6; δ): 14.8 (s, Me); 39.7 (s, Me); 61.2 (s, CH); 73.8
(s, CH); 126-141 (Ph). 15N{1H} NMR (1:10 C6D6/C6H6; δ): -
20
Exp er im en ta l Section
364.3 (second-order m). [R]D ) +28° (c ) 1.0, toluene).
All manipulations were carried out under an inert atmo-
sphere using standard Schlenk techniques. Solvents were dried
and distilled prior to use. (1R,2S)-N-(diphenylmethyl)ephe-
drine (1c) was prepared according to the published procedure.7
Other chemicals were purchased from Aldrich and were used
as received. The following instruments were used: Varian XL-
300 and Bruker AMX 500 (NMR), Bomem MB-100 (FT-IR),
and Perkin-Elmer 2400 Series II (combustion microanalysis).
The natural-abundance 15N{1H} NMR spectra were acquired
using 0.5-0.7 M solutions of the Rh complexes, a 10 mm probe,
CH3NO2 as external standard, D1 ) 12 s, and gated decou-
pling. Acceptable spectra were observed after 12-24 h.
Syn th esis of Am in op h osp h in ites (2a -c). A solution of
Ph2PCl (2.0 mL, 11.14 mmol) and Et3N (4 mL) in 30 mL of
benzene was added to a stirred solution of the corresponding
Syn th esis of ClRh (CO)(P OMep h ) (4b). POMeph (2.6
mmol, 0.618 M in C6H6) was added to a stirred solution of
Rh2(CO)4Cl2 (505 mg, 1.3 mmol) in 12 mL of benzene. The
resulting orange solution was evaporated, and the pale yellow
mass was dissolved in 10 mL of hot MeOH and allowed to stay
at room temperature for 1 h and then in a freezer (-17 °C)
overnight. The precipitated yellow crystals were separated,
rinsed with cold MeOH, and dried under vacuum to give
analytically pure 4b (1174 mg, 2.219 mmol, 85%). Anal. Calcd
for C24H26ClNO2PRh: C, 54.4; H, 5.0; N, 2.6. Found: C, 54.4;
H, 5.0; N, 2.5. 31P{1H} NMR (C6D6; δ): 134 (d, J P-Rh ) 184
1
Hz). H NMR (C6D6; δ): 0.8 (d, J ) 6.4 Hz, 3H); 1.75 (m, 1H);
(21) The compound was g95% pure according to 31P NMR and
contained up to 5% of heptane (1H and 13C NMR).

Rh Complexes with Derivatives of Ephedrine
Organometallics, Vol. 18, No. 23, 1999 4711
2.5 (s, 6H); 5.2 (d, J ) 7.7 Hz, 1H); 6.8-7.9 (m, 15H). 13C{1H}
NMR (C6D6; δ): 12.2 (s, Me); 47.7 (s, Me); 48.1 (s, Me); 70.8
(d, J C-P ) 3.8 Hz, CH); 77 (s, CH); 125.3-138.7 (Ph); 187.9
(dd, J C-Rh ) 71 Hz, J C-P ) 18 Hz, CO). 15N{1H} NMR (1:10
C6D6/C6H6; δ): -355.4 (dd, J N-Rh ) 11.5 Hz, J N-P ) 3.6 Hz).
Ta ble 3. Su m m a r y of Cr ysta llogr a p h ic Da ta for 3a
a n d 8c
3a
8c
formula
fw
C
46H48ClN2O2P2Rh
C36H34ClNO6PRh
746.01
915.31
IR (KBr; νCO): 1985 cm-1. [R]D ) +38.7° (c ) 0.506, C6H6).
20
cryst dimens, mm 0.1 × 0.1 × 0.1
0.4 × 0.1 × 0.1
cryst syst
lattice params
a (Å)
orthorhombic
tetragonal
Syn th esis of ClRh (CO)(P OMep h )2 (5b). POMeph (0.804
mmol, 0.618 M in C6H6) was added to a stirred solution of
Rh2(CO)4Cl2 (77 mg, 0.198 mmol) in 10 mL of benzene. The
reaction mixture was evaporated under vacuum, and the
resulting yellow oil was stirred with 10 mL of methanol to give
a yellow precipitate that was separated, washed with MeOH
(2 × 5 mL), and vacuum-dried to form 312 mg (0.349 mmol,
88%) of 5b as a yellow microcrystalline solid. Anal. Calcd for
C47H52ClN2O3P2Rh: C, 63.2; H, 5.9; N, 3.1. Found: C, 63.5; H,
6.1; N, 3.0. 31P{1H} NMR (C6D6; δ): 114 (d, J P-Rh ) 136.5 Hz).
1H NMR (C6D6; δ): 1.3 (d, J ) 6.6 Hz, 3H); 2.1 (s, 6H); 3.1
(quint, J ) 6.9 Hz, 1H); 6.3 (m, 1H); 6.8-8.1 (m, 15H). 13C-
{1H} NMR (C6D6; δ): 10.6 (s, Me); 42.1 (s, Me); 65.3 (vt, J C-P
) 6.5 Hz, CH); 84.2 (s, CH); 127.8-141.8 (Ph); 186.8 (dt, J C-Rh
10.9890(5)
19.4833(9)
20.1668(9)
P212121
10.6135(4)
10.6135(4)
34.797(2)
P43
b (Å)
c (Å)
space group
Z
4
4
V, Å3
4317.8(4)
1.291
3919.8(3)
1.264
d
calcd, g/cm3
T, K
203(2)
204(2)
radiation (λ)
abs coeff, mm-1
transmissn
(max/min)
R(F),%a
Mo KR (0.710 73 Å)
Mo KR (0.710 73 Å)
0.568
0.585
0.801 520/0.609 815 0.928 077/0.778 905
4.07
9.55
1.058
-0.03(3)
3.96
Rw(F2),%b
GOF
10.75
1.015
0.02(4)
) 74.5 Hz, J C-P ) 17 Hz, CO). IR (KBr; νCO): 1992 cm-1
.
Flack param
Syn th esis of Rh 2(µ-Cl)2(CO)2(P OP h ep h )2 (7c). POPheph
(1.028 mmol, 0.381 M in C6H6) was added to a stirred solution
of Rh2(CO)4Cl2 (200 mg, 0.514 mmol) in 15 mL of benzene, and
nitrogen was passed through the homogeneous reaction mix-
ture for 15 min. The resulting orange solution was diluted with
40 mL of heptane and reduced in volume to ca. 30 mL under
vacuum to give a yellow precipitate and pale yellow solution.
The precipitate was separated by decantation, washed with
pentane (2 × 20 mL), and dried under vacuum to give 575 mg
(0.421 mmol, 82%) of 7c as a yellow microcrystalline solid.
Anal. Calcd for C72H68Cl2N2O4P2Rh2: C, 63.4; H, 5.0; N, 2.0.
Found: C, 63.9; H, 5.2; N, 1.8. 31P{1H} NMR (CDCl3; δ): 123
a
b
R(F) ) ∑∆/∑(Fo), ∆ ) |(Fo - Fc)|. Quantity minimized )
Rw(F2) ) ∑[(w(Fo - Fc2)2]/∑(wFo
) ;
2
2 1/2
4.7; N, 1.6. 31P{1H} NMR (CD2Cl2; δ): 128 (d, J P-Rh ) 209 Hz).
1H NMR (CD2Cl2; δ): 2.1 (d, J ) 6.3 Hz, 3H); 2.8 (s, 3H); 3.05
(m, 1H); 5.3 (m, 1H); 6.3 (s, 1H); 7.1-8.2 (m, 25H). 13C{1H}
NMR (CD2Cl2; δ): 14.3 (s, Me); 46.2 (s, Me); 68.1 (d, J C-P
)
2.3 Hz, CH); 71.8 (s, CH); 77.1 (s, CH); 110.2 (d, J ) 7.5 Hz,
Ph); 126.1 (s, Ph); 129.2-138.1 (Ph); 187.1 (dd, J C-Rh ) 73 Hz,
J C-P ) 21 Hz, CO). 15N{1H} NMR (1:10 CD2Cl2/CH2Cl2; δ):
-356.7 (d, J N-Rh ) 10.5 Hz). IR (KBr; νCO): 2014 cm-1. [R]D
20
) +45.1° (c ) 1.35, CH2Cl2).
1
(d, J P-Rh ) 192 Hz). H NMR (CDCl3; δ): 1.5 (d, J ) 6.5 Hz,
Sin gle-Cr ysta l X-r a y Diffr a ction Stu d y of 3a a n d 8c.
Crystal data and refinement parameters are summarized in
Table 3. The crystals suitable for X-ray analysis were obtained
by slow diffusion of Et2O into a benzene solution of 3a or of
THF into a solution of 8c in CH2Cl2, respectively. The crystals
were mounted on glass fibers with viscous oil and cooled to
the data collection temperature. Data were collected on a
Bruker AX SMART 1k CCD diffractometer using 0.3° ω-scans
at 0, 90, and 180° in φ. Unit cell parameters were determined
from 60 data frames collected at different sections of the Ewald
sphere. Semiempirical absorption corrections based on equiva-
lent reflections were applied.22 Systematic absences in the
diffraction data and unit cell parameters were consistent
uniquely with the reported space group for 8c and with P41,
P43, P4122, and P4322 for 3a . Only the solution in P43 yielded
chemically reasonable and computationally stable results for
the refinement of 3a . The structures were solved by direct
methods, completed with difference Fourier synthesis, and
refined with full-matrix least-squares procedures based on F2.
Refinement of the Flack parameter yielded nil values, indicat-
ing that the true hands of the data sets were determined
correctly. All non-hydrogen atoms were refined with anisotro-
pic refinement parameters. All hydrogen atoms were treated
as idealized contributions. All atomic scattering and anomalous
dispersion factors are contained in the SHEXTL 5.1 program
library.23
3H); 2.5 (s, 3H); 3.8 (m, 1H); 4.5 (s, 1H); 6.6 (dt, J H-H ) 9.5
Hz, J H-P ) 11.7 Hz, 1H); 6.8-8.0 (m, 25H). 13C{1H} NMR
(CDCl3; δ): 10.2 (s, Me); 34.2 (s, Me); 59.1 (d, J C-P ) 8 Hz,
CH); 74.1 (s, CH); 85.9 (s, CH); 126.7-143.9 (Ph); 183.5 (dd,
J C-Rh ) 82 Hz, J C-P ) 19 Hz, CO). 15N{1H} NMR (1:10 C6D6/
C6H6; δ): -341.6 (s). IR (KBr; νCO): 1993 cm-1
.
Syn t h esis of ClR h (CO)(P OP h ep h )2 (5c). Ph2POPheph
(0.721 mmol, 0.381 M in C6H6) was added to a solution of
Rh2(CO)4Cl2 (70 mg, 0.180 mmol) in 10 mL of benzene, and
the reaction mixture was evaporated under vacuum. The
obtained yellow mass was stirred with MeOH; a pale yellow
solid was separated and vacuum-dried to give 387 mg (0.323
mmol, 90%) of 5c as a light yellow powder. Anal. Calcd for
C
71H68ClN2O3P2Rh: C, 71.2; H, 5.7; N, 2.3. Found: C, 71.1; H,
5.9; N, 2.3. 31P{1H} NMR (C6D6; δ): 115 (d, J P-Rh ) 136 Hz).
1H NMR (C6D6; δ): 1.5 (d, J ) 6.2 Hz, 3H); 2.4 (s, 3H); 3.7 (m,
1H); 4.5 (s, 1H); 6.6 (m, 1H); 6.8-8.1 (m, 25H). 13C{1H} NMR
(C6D6; δ): 10.2 (s, Me); 34.6 (s, Me); 59.6 (vt, J C-P ) 8 Hz,
CH); 74.4 (s, CH); 85.1 (s, CH); 126.8-144.4 (Ph); 186.8 (dt,
J C-Rh ) 74.5 Hz, J C-P ) 17 Hz, CO). IR (KBr; νCO): 1986 cm-1
.
Syn t h esis of [R h (CO)(P OP h ep h )]ClO4 (8c). AgClO4
(0.733 mmol, 0.218 M in toluene) was added to a stirred
solution of Rh2(µ-Cl)2(CO)2(POPheph)2 (500 mg, 0.366 mmol)
in 10 mL of CH2Cl2. The bright yellow solution was filtered
from precipitated AgCl diluted with 8 mL of benzene and
reduced in volume to ca. 10 mL to give a brown oil and pale
yellow solution. The oil crystallized upon standing overnight.
The formed crystals were separated, washed with THF (3 ×
10 mL), and dried under vacuum to give 526 mg of crude 8c‚
C6H6 as green-yellow crystals. Recrystallization from CH2Cl2/
C6H6 afforded analytically pure 8c‚C6H6 (482 mg, 0.584 mmol,
80%) as yellow crystals with a green tint. Anal. Calcd for
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council of Canada (NSERC)
for support of this research.
Su p p or tin g In for m a tion Ava ila ble: Listings of crystal-
lographic details, atomic parameters, bond distances and
angles, and isotropic and anisotropic thermal parameters and
ORTEP drawings for 3a and 8c. This material is available free
of charge via the Internet at http://pubs.acs.org.
C
42H40ClNO6PRh: C, 61.2; H, 4.9; N, 1.7. Found: C, 61.2; H,
(22) Blessing, R. Acta Crystallogr. 1995, A51, 33.
(23) Sheldrick, G. M. SHELXTL (5.03); Siemens XRD, Madison, WI,
1994.
OM990442N