P-chirogenic benzo-fused phenoxaphosphane: Synthesis, resolution and study of the stereochemical properties of the corresponding palladium complexes

Article abstract of DOI:10.1002/ejic.200700887

The synthesis and resolution of chiral phenoxaphosphane 3, with the stereogenic center at the phosphorus atom, is described. Compound 3 has been synthesized following a well-known procedure for trapping a phosphorus atom within a six-membered ring. The resolution of the racemic mixture of 3 was achieved through separation of its diastereomeric palladacycle derivatives 7a,b and 9a,b. The absolute configuration of enantiopure phosphanes 3a,b was assigned unequivocally by means of X-ray crystal structure determination for complex 9a and by combination of NOE(¹H-¹H)/COSY-(¹H, ¹H) spectroscopy and DFT calculations for complexes 7a,b, which in both cases led to identical results. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200700887

FULL PAPER
DOI: 10.1002/ejic.200700887
P-Chirogenic Benzo-Fused Phenoxaphosphane: Synthesis, Resolution and Study
of the Stereochemical Properties of the Corresponding Palladium Complexes
Franco Doro,[a] Martin Lutz,[b] Joost N. H. Reek,[a] Anthony L. Spek,[b] and
Piet W. N. M. van Leeuwen*[a]
Keywords: Phosphacycles / P-Chirogenic ligands / Spectroscopic studies
The synthesis and resolution of chiral phenoxaphosphane 3,
with the stereogenic center at the phosphorus atom, is de-
scribed. Compound 3 has been synthesized following a well-
known procedure for trapping a phosphorus atom within a
six-membered ring. The resolution of the racemic mixture of
3 was achieved through separation of its diastereomeric pal-
ladacycle derivatives 7a,b and 9a,b. The absolute configura-
tion of enantiopure phosphanes 3a,b was assigned unequivo-
cally by means of X-ray crystal structure determination for
complex 9a and by combination of NOE(1H–1H)/COSY-
(1H,1H) spectroscopy and DFT calculations for complexes
7a,b, which in both cases led to identical results.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
unexpressed as is demonstrated by the very few articles re-
garding the applications of these compounds.[9,10] Despite
the scarce interest in this class of phosphanes, our group
has extensively worked with phenoxaphosphane-based sys-
tems and in particular with phenoxaphosphanyl-substituted
XantPhos ligands which have been successfully applied in
metal-catalyzed reactions, such as hydroformylation of in-
ternal alkenes, outperforming their diphenylphosphane
counterparts.[10]
In this context, the synthesis of chiral benzo-fused phen-
oxaphosphane compounds represents the next step due to
the high degree of enantio-discrimination chiral phos-
phacycles can induce in asymmetric metal-catalyzed reac-
tions.[1–6] In this work we describe the synthesis and optical
resolution of the first benzo-fused phenoxaphosphane 3 in
which a hydroxyl moiety, amenable to further functionaliza-
tion, is attached to the rigid phenoxaphospanyl skeleton.
Moreover, given the influence exerted by the ligand/metal
stereoelectronic interactions in controlling a catalytic pro-
cess and in view of the employment of chiral phenoxaphos-
phane-based ligands in asymmetric catalysis we carried out
an in-depth investigation of the stereochemical properties
of 3 and derivatives thereof.
Introduction
Chiral phosphacyclic compounds are currently attracting
the interest of the homogeneous catalysis community after
having been neglected for many decades.[1,2] This attention
for these P-heterocycles can be ascribed to the incessant
search for novel structures, suitable as chiral ligands in
asymmetric catalysis, pursued by researchers involved in the
field of ligand development. In this regard, chiral phos-
phacycle-based ligands, which as a consequence of their
ring constraints bear unique steric and electronic properties
often remarkably different from their acyclic counterparts,
are a new intriguing class of enantio-inductors for asym-
metric transformations.[3] The first major breakthrough in
the application of phosphacyclic ligands in asymmetric ca-
talysis is represented indubitably by the five-membered
DuPhos ligands.[4a,4b] An increasing variety of chiral phos-
phacycles of different ring extensions, ranging from four to
seven units, have since then been prepared and applied suc-
cessfully in asymmetric catalysis.[2,3,5,6]
Benzo-fused phenoxaphosphanes, a class of conjugated
phosphorus-based heterocycles, were initially introduced by
Mann and Millar in the late 1950’s and since then have
found applications mostly in the development of new poly-
meric materials.[7,8] The potential of these cyclic analogues
of triphenylphosphane in catalysis has remained hitherto
Results and Discussion
[a] Van ’t Hoff Institute for Molecular Sciences (HIMS), Univer-
sity of Amsterdam,
Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Nether-
lands
Racemic 3 was prepared starting from m-phenoxyphenol,
successively protected as 1-(1-ethoxyethoxy)-3-phenoxyben-
zene (1). Metallation of 1 with n-butyllithium, in the pres-
ence of TMEDA, followed by internal ring closure with
dichlorophenylphosphane gives 2, which after deprotection
affords the racemic mixture 3 (Scheme 1).[11]
E-mail: PWNM@science.uva.nl
[b] Department of Crystal and Structural Chemistry, Utrecht Uni-
versity,
Padualaan 8, 3584 CH Utrecht, The Netherlands
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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P. W. N. M. van Leeuwen et al.
FULL PAPER
complexes, respectively 7b and 7a, using 1,2-bis(diphenyl-
phosphanyl)ethane (dppe) in the presence of excess ammo-
nium chloride as proton source (Scheme 2).[14]
Scheme 1. Synthesis of chiral phosphane 3 (EVE = ethyl vinyl ether
or 1-ethoxyethoxy group). i) 2 equiv. TMEDA, 2 equiv. BuLi,
Et2O/hexane, 0 °C to r.t., overnight; ii) 1.1 equiv. PhPCl2, –70 °C,
3 h; iii) PPTS, ethanol/CH2Cl2, reflux; overall yield 32%.
Resolution of racemic phosphanes based on the transfor-
mation of both enantiomers into a pair of diastereoisomers
is common practice.[12] In our particular case, we envisaged
that derivatization of the hydroxyl group in 3 to a chiral
menthyl carbonate would be exploitable for the separation
of the resultant diastereomeric mixture. Functionalization
of phosphane 3 was successfully accomplished to yield the
mixture of diastereoisomers 4a,b, but all attempts towards
resolution failed.[13]
Scheme 2. Chiral resolution of phosphane 3. i) 0.5 equiv. of (S)-5,
NEt3, CH2Cl2, room temp., 30 min; ii) dppe, NH4Cl, CH2Cl2, room
temp., 1 h.
Isolation of adequate amounts of enantiopure 3a,b,
which might be required at a later stage for purposes such
as ligand screening for homogeneous catalysis, is an essen-
tial prerequisite of any considered chiral resolution tech-
nique. Consequently, the scale up of the aforementioned
chromatography separation was investigated, but led only
to the recovery of diastereomerically enriched mixtures.
Clearly the structures of complexes 7a,b do not differ suffi-
ciently for being optimally separated. In order to enhance
the structural differences between 3a,b derivatives we
turned our attention towards the more conformationally ri-
gid palladacycle (S)-6 and for this purpose the synthesis of
Alternatively, it was considered to employ chiral metal
complexes as resolving agents. Thus ortho-palladated deriv-
atives of (S)-dimethyl(1-phenylethyl)amine (S)-5 and (S)-di-
methyl(1-naphthylethyl)amine (S)-6, which have demon-
strated their effectiveness towards a wide range of racemic
phosphanes, were chosen (Figure 1).[14–16]
compound
8
was undertaken and successfully ac-
complished, following the same procedure reported for 7.
Disappointingly, the chromatographic separation of the dia-
stereomeric mixture of 8, despite the large array of solvents
employed as eluents was fruitless and at best, afforded only
diastereomerically enriched mixtures and decomposed ma-
terial.
Figure 1. Chiral palladacycles.
The diastereomeric mixture of 7a,b was prepared by reac-
tion of the racemate of 3 with palladate complex (S)-5 in
CH2Cl2 in the presence of triethylamine. The 31P-NMR
spectrum of compounds 7a,b showed a set of two well re-
solved singlets of equal intensity at δ = –5.76 and
–4.97 ppm. Compounds (S,Sa)-7a and (R,Sa)-7b were suc-
cessfully separated by careful radial chromatography and
The Pd–C–N ring of palladacycle (S)-6 is known to
1
characterized by IR, mass analysis, H, 31P, and 13C NMR adopt a λ conformation, with the Meα taking up the axial
spectroscopy. Moreover, it was possible to determine the position, which is normally retained in its derivatives in or-
absolute configurations at the phosphorus atom and assign der to avoid the steric congestion that would be present
the λ/δ conformations of the organometallic five-membered otherwise between Hγ and an equatorial Meα in a confor-
Pd–C–N ring in the same complexes, see below. Enantio- mation of type δ.[17] Indeed, the H NMR spectrum of the
1
pure phosphanes 3a and 3b were obtained by decomplex- diastereomeric mixture of complex 8 shows, for Hα, two
ation from their corresponding diastereomeric palladium peaks partially overlapping with chemical shifts in the range
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P-Chirogenic Benzo-Fused Phenoxaphosphane
Scheme 3. Chiral resolution of phosphanes 3 and 4.
δ = 4.3–4.6 ppm, in agreement with a conformation type λ
Yellow crystals of 9a, suitable for X-ray diffraction, were
for both diastereoisomers. Much to our dismay, the strain obtained by slow diffusion of hexane into a solution of 9a
caused by both the Pd–C–N ring and the heterobidentate in dichloromethane. Due to the disorder of the menthyl
phosphane in 8 is not beneficial, in contrast with previous group the geometrical parameters of this group have large
reports, for the resolution of this diastereomeric mixture standard uncertainties. However, this does not affect the
and furthermore is at the origin of the instability of these Flack parameter[29] for the determination of the absolute
highly strained complexes.[17]
configuration, which is established to be S at the phospho-
Thus, the resolution route employing directly P,O-phos- rus atom (Figure 2). Selected bond lengths and bond angles
phane 3 was discarded and another route, employing pro- of structure 9a are given in Table 1.
tected phosphane 4a,b, was considered instead. This resolu-
tion method consists as a first step in reacting dia-
stereomeric mixture 4a,b, which as such could not be re-
solved, to palladacycle (S)-6.[15] The resultant dia-
stereomeric mixture 9a,b was successfully resolved by
chromatography into its two components 9a and 9b with
high yields (Scheme 3). Most importantly, employing this
route we could scale up the separation of these diastereoiso-
mers by at least one order of magnitude compared to the
separation of diastereoisomers 7a,b. Diastereopure phos-
phanes 4a,b were obtained by decomplexation from their
corresponding diastereomeric palladium complexes using
dppe.[15] Hydrolysis of the carbonate group of 4a and 4b
affords enantiopure 3a and 3b, respectively.[13] The enantio-
pure ligands were isolated in good yields and found to be
configurationally stable after refluxing in water/ethanol
overnight. This was confirmed by preparing compound 4
Figure 2. Displacement ellipsoid plot of the structure of 9a in the
and checking the diastereopurity by 1H and 31P NMR spec-
crystal (50% probability level). Hydrogen atoms and disordered
solvent molecules are omitted for clarity. Only the major disordered
component of the menthyl moiety is shown (58.3% occupancy).
troscopy.
Table 1. Selected bond lengths [Å] and angles [°] for 9a.
P1–Pd1
P1–C15
P1–C26
P1–C27
Pd1–Cl1
N1–Pd1
Pd1–C1
2.2405(8)
1.807(3)
1.808(3)
1.826(3)
2.4019(9)
2.123(3)
2.009(3)
C26–P1–C15
P1–C26–C21
C26–C21–O1 124.5(3)
O1–C20–C15 125.7(3)
P1–C15–C20
C15–P1–C27
C26–P1–C27
99.48(15)
123.2(3)
123.0(3)
105.51(15)
102.52(14)
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P. W. N. M. van Leeuwen et al.
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As expected, the tertiary phosphane is coordinated trans turned out to be particularly useful for investigating stereo-
to the NMe2 group of the naphthylamine.[14] The palla- chemical properties of chiral phosphanes.[23]
dium–phosphorus distance of this structure is very similar
The absolute configuration of the phosphorus atom, in
to those observed in related complexes such as (S)-6-(PPh3), compounds 7a,b, has been unambiguously assigned by
containing an unstrained triphenylphosphane. The sum of complementing the study of the NOE(1H–1H) contacts and
the three C–P–C angles of 9a (307.5°) is smaller than that of the NMR chemical shift regularities with DFT calculations
(S)-6-(PPh3) (310.9°) hence confirming that the phosphorus performed using SPARTAN.[23,24] The assignment of all the
1
atom is slightly pyramidalized owing to its incorporation in resonances from H NMR spectra of complexes 7a,b was
a six-membered ring.[18,20] As a consequence, the P-lone accomplished by analyzing the COSY(1H,1H) spectra and
pair of 3 has a greater s-character than its analogue PPh3. NOE(1H–1H) interactions. In the case of complex 7a, the
This is further confirmed by the enhancement of the π-ac- NOE(1H–1H) signals of the contacts between Me17 and H19
ceptor properties of phenoxaphosphane-based ligands com- and between H22 and H3 permitted the full characteriza-
pared to strainless analogues, which was established pre- tion, by COSY(1H,1H), respectively, of the metallated
viously by high pressure FT-IR studies of the stretching fre- phenyl ring and the adjacent benzo-fused phenyl ring of
quencies of CO, in phenoxaphosphane-based ligand/rho- the phosphacycle. The resonance of H11 is determined by
dium carbonyl complexes.[19,20]
analysis of the COSY(1H,1H) spectrum, which shows inter-
Assignment of the Absolute Stereochemistry in 7: Com- actions with both upfield H10 and H12 protons. The signals
pound 7 represents one of the few examples of neutral chiral of the protons Portho, Pmeta and Pipso of the uncondensed
palladacycles containing a hetero-bidentate phosphane and phenyl group of the phosphacycle were assigned by analysis
the only known example with a P,O-hetero-bidentate phos- of the COSY(1H,1H) spectrum (Figure 3). The spatial dis-
phane reported to date. Such a low level of diversity, amid position of the Me groups was established by NOE (1H–
1
this class of complexes, finds its rationalization in that chiral 1H) experiments. The H NMR spectrum of 7a (Figure 4)
organopalladium complexes, such as 5–6, have been mainly is shown below along with the enlargement of the aromatic
used as resolving agents for monophosphanes.[14a,21,22] Con- region of the corresponding COSY(1H,1H) spectrum and
sequently, the uniform, large body of data regarding their the complete list of NOE(1H–1H) contacts. Complex 7b was
structural and spectroscopic features, available in literature, fully characterized in a similar manner.
Figure 3. COSY(1H,1H) spectrum of the aromatic region of 7a.
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P-Chirogenic Benzo-Fused Phenoxaphosphane
scale, pointing out a totally different magnetic field experi-
enced by this proton in the δ–λ conformations of the Pd–
C–N ring.[17]
1
Table 2. Selected 1D H-NMR NOE data for 7a.
MeN1 (3.11) – H17 (4.56) (m)
Me17 (1.46) – H17 (4.56) (m), H19 (6.95) (m)
MeN2 (2.69) – MeN1 (3.11) (w), Me17 (1.46) (w)
H19 (6.96) – H20 (7.07) (s), H17 (4.56) (m), Me17 (1.46) (s)
H17 (4.56) – H19(6.96) (m), MeN1 (3.11) (s), Me17 (1.46) (s)
H22 (7.2) – H3 (7.8) (s), H21 (6.87) (s)
H3 (7.8) – H22 (7.2) (s)
H20 (7.07) – H19 (6.96) (s), H21 (6.87) (s)
H21 (6.87) – H20 (7.07) (s), H22 (7.2) (s)
1
Figure 4. H NMR of 7a. The symbol ∆ refers to H2O.
The 1D 1H-NMR NOE data for structure 7a clearly
show a strong interaction between MeN1 and H17 while they
do not show any interaction between MeN2 and H17
(Table 2). The Newman projection of this structure is in
agreement with a conformation type δ where H17 is axial
and MeN1 and MeN2 correspond to Me(eq) and Me(ax),
respectively. On the contrary, for complex 7b it was possible
Figure 5. Newman projections for the λ and δ conformations of
the palladacycle in 7.
Calculations at the HF-DFT SDF level of theory, using
to see a NOE(1H–1H) signal for the interaction between RB3LYP as method and LACVP* as basis set, have been
H17 with both MeN1,N2, albeit weak, in agreement with a carried out for the four most stable conformers 7, namely
conformation type λ with Me17 axial (Figure 5). Irradiation the structures containing the combination of the two dif-
of Me17 for both complexes 7a,b did not show any appreci- ferent absolute configurations at the phosphorus atom R/S
able NOE(1H–1H) interaction with MeN1,N2. Furthermore, with the two possible conformations δ–λ of the pallada-
the H NMR spectra of both complexes 7a and 7b show cycles, (Figure 6). The distance between H3–H22 in complex
1
for H17 a chemical shift difference of about 1 ppm on the δ (S)-δ-7 (I) is 2.08 Å while in (S)-λ-7 (II) it is 2.58 Å. Clearly,
Figure 6. Structures of the four most stable conformers calculated at the HF-DFT SDF level of theory. (S)-δ-7 (I), (S)-λ-7 (II), (R)-λ-7
(III), (R)-δ-7 (IV).
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1-(1-Ethoxyethoxy)-3-phenoxybenzene (1):[25] To a solution of 3-
phenoxyphenol (15.4 g, 83 mmol) in dichloromethane (250 mL)
was added (pyridinium p-toluenesulfonate) PPTS (2.08 g,
8.3 mmol) at room temperature. The resultant mixture was cooled
to 0 °C and subsequently ethyl vinyl ether (EVE) (132.8 mmol) was
added dropwise. The mixture was allowed to stir overnight at room
temperature. The resultant solution was washed with brine (20 mL)
and the phases were subsequently separated. The organic layer was
washed twice with aqueous 1  NaOH (20 mL) and dried with
MgSO4. The solvent and all volatiles were removed in vacuo. The
the second structure experiences a higher steric relief com-
pared to the former, which results in an energy difference
of 2.92 kcal/mol. This value indicates the presence of only
one of the two possible structures I–II in solution thus sug-
gesting that 7b corresponds to (S)-λ-7 (II). The determi-
nation of the absolute configuration at the phosphorus
atom was applied likewise for (R)-7-(III–IV) complexes. In
this case, the distance between H3–H22 in complex (R)-λ-5
(III) is 2.01 Å while in (R)-δ-7 (IV) it is 2.46 Å hence fav-
ouring the formation of the latter by 2.17 kcal/mol. These crude of reaction is a yellow oil which after filtration through silica
(eluent: CH2Cl2) yielded a colorless oil (20.12 g, 78 mmol, 94%).
results are consistent with 7a corresponding to structure
(R)-δ-7 (IV). The modelled structures reported in Figure 6
show that steric relief is indeed achieved when the Pd–C–N
ring flips in response to the tension caused by the rigid P–O
ligand. Enantiopure phosphanes 3a,b have been freed from
complexes 7a,b and further reacted with (–)-menthyl chlo-
1H NMR (CDCl3): δ = 1.19 (t, 3J = 7.1 Hz, 3 H), 1.48 (d, 3J =
3
5.3 Hz, 3 H), 3.50 (m, 1 H), 3.70 (m, 1 H), 5.35 (q, J = 5.3 Hz, 1
3
3
H), 6.64 (dd, J = 8.10 Hz, 1 H), 6.68 (t, J = 2.3 Hz, 1 H), 6.76
(dd, 3J = 8.2 Hz, 1 H), 7.03 (d, 3J = 7.6 Hz, 2 H), 7.10 (t, 3J =
7.3 Hz, 1 H), 7.20 (t, J = 8.2 Hz, 1 H), 7.34 (t, J = 7.6 Hz, 2 H)
ppm. EI-MS (70 eV): m/z = 258, 213, 186, 73, 45.
3
3
1
roformate to give rise to compounds 4a,b of which the H,
31P-NMR spectra corroborated the correct assignment of
the absolute configuration at the phosphorus atom.
(؎)-1-(1-Ethoxyethoxy)-10-phenyl-10H-phenoxaphosphane (2): To a
solution of O-protected 3-phenoxyphenol (4.4 g, 17.0 mmol) and
TMEDA (35.90 mmol, 3.5 mL) in 300 mL of diethyl ether/hexane
(1:2) was added dropwise a solution of n-butyllithium in hexane
(2.5 , 36 mmol, 14.4 mL) at 0 °C and the reaction mixture was
allowed to stir overnight at room temperature. The resultant orange
solution was cooled to –60 °C and subsequently a solution of
Cl2PPh, (19.30 mmol, 2.7 mL) in 5 mL of hexane, was slowly
added. The reaction mixture was slowly warmed to room tempera-
In summary, we have synthesized the first chiral benzo-
fused phenoxaphosphane 3 and determined the absolute
configuration at the phosphorus atom in its metal com-
plexes. DFT calculations underpin structural features of the
molecules determined spectroscopically and give more in-
sight into structural preferences in solution. Currently com-
pound 3 and other achiral benzo-fused phenoxaphosphane ture and allowed to stir for 5 h. The color of the solution changed
from orange to colorless with the formation of a precipitate (LiCl).
The solution was canulated into another Schlenk tube and the sol-
vent was removed in vacuo. The crude of reaction was dissolved in
CH2Cl2 and washed with deoxygenated 0.1  aqueous HCl. The
crude product is a yellow oil which after filtration through silica
(eluent: CH2Cl2) and removal of the solvent in vacuo is obtained
as colorless oil (2.6 g, 7.14 mmol, 42%). 31P NMR (CDCl3): δ =
are being used as building blocks in the syntheses of mono-
dentate and bidentate phenoxaphosphane-based ligands.
Results regarding the applications of these ligands, as en-
antio-inductors in asymmetric catalysis, will be published in
due course.
3
–63.80, –64.80 ppm. 1H NMR (CDCl3): δ = 0.90 (t, J = 7.2 Hz, 3
3
3
H), 1.12 (t, J = 7.2 Hz, 3 H), 1.27 (d, J = 5.1 Hz, 3 H), 1.32 (d,
3J = 5.1 Hz, 3 H), 2.95 (m, 1 H), 3.20 δ (m, 1 H), 3.50 (m, 1 H),
3.72 (m, 1 H), 5.35 (m, 2 H), 6.60–7.50 (m, 3J = 7.3 Hz, 12 H)
ppm. EI-MS (70 eV): m/z = 364, 335, 320, 282, 215.
Experimental Section
General: All chemical manipulations were carried out under argon
atmosphere using standard Schlenk techniques. Solvents were dried
by standard procedures and freshly distilled under nitrogen atmo-
sphere. NMR spectra were recorded at 295°K on a Varian Gemini
300 spectrometer operating at 300.07 MHz (1H), 121.47 MHz (31P)
and 75.46 MHz (13C) unless otherwise stated; NOESY, COSY and
NOE were recorded at 499.79 MHz (1H) on a Varian Gemini 500
spectrometer. Chemical shifts are quoted with reference to Me4Si
(1H) and 85% H3PO4 (31P). The optical rotations were measured
using a Perkin–Elmer 241-MC polarimeter. Infrared spectra were
recorded as KBr pallets on a Nicolet Nexus 670-FT-IR spectrome-
ter and processed with the OMNIC software. High resolution mass
spectra were measured on a JEOL IMS-SX/SX102A. Elemental
analyses were performed at the H. Kolbe Mikroanalytisches Labor-
atorium in Mülheim (Germany). Chiral compounds 7a–b were ob-
tained in pure form by preparative thin layer radial chromatog-
raphy (Chromatotron®, Harrison Research, model 7924T) em-
ploying silica gel 60 PF254 containing gypsum. The resolving
agents di-µ-chlorobis[(S)-dimethyl(1-phenylethyl)aminato-C2,N]di-
palladium(II) (S)-5 and di-µ-chlorobis[(S)-dimethyl(1-naphthyl-
ethyl)aminato-C2,N]dipalladium(II) (S)-6 were prepared according
to literature procedure.[14,15]
(؎)-10-Phenyl-10H-phenoxaphosphan-1-ol (3): 1-(1-Ethoxyethoxy)-
10-phenyl-10H- phenoxaphosphane (2.6 g, 7.14 mmol) was dis-
solved in a 3:1 mixture of degassed ethanol and dichloromethane
(80 mL). PPTS (0.07 mmol) was added and the solution was heated
to 65 °C and stirred overnight. The mixture was cooled down and
subsequently the solvent and all volatiles were evaporated in vacuo
to leave a white viscous oil. The product is filtered through silica
(eluent: CH2Cl2) after that the solvent was removed in vacuo to
yield a white solid (1.7 g, 5.8 mmol, 81%). 31P NMR (CDCl3): δ =
–72.78 ppm. 13C NMR (75.4 MHz, CDCl3): δ = 105.83, 110.18,
110.56, 116.93, 118.22, 124.03–124.19, 128.80, 128.88–129.04,
131.63–131.76, 131.83–132.02, 135.21, 135.71, 139.09–139.33,
155.59, 156.43, 158.31, 158.53 ppm. 1H NMR (CDCl3): δ = 6.10
3
(s, 1 H, OH), 6.70 (m, 1 H) 6.82 (d, J = 8.2 Hz, 1 H), 7.10–7.35
(m, 8 H), 7.40 (m, 1 H), 7.60 (m, 1 H) ppm. (HRMS, FAB+): m/z
calcd. for C18H13O2P: 292.070; found: 292.065. C18H13O2P
(292.07): calcd. C 73.97, H 4.48; found C 73.82, H 4.41.
(1R)-(–)-Menthyl 10-Phenyl-10H-phenoxaphosphan-1-yl Carbonate
(4a,b): To a solution of 10-phenyl-10H-phenoxaphosphan-1-ol
(100 mg, 0.342 mmol) in dichloromethane (5 mL) was added NEt3
(0.1 mL) and the resultant mixture was allowed to stir for 30 min
at room temperature. Subsequently (–) menthyl chloroformate
All the calculations were performed with the Spartan “041,0,0
(Sept. 17, 2003) suite of programs.[31]
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P-Chirogenic Benzo-Fused Phenoxaphosphane
(1 equiv.) was added and the solution was stirred for an additional
2h at room temp. The solvent and all the volatiles were removed in
vacuo and the product obtained was dissolved again in toluene
(1 mL) and filtered through a short silica column (eluent: toluene).
The evaporation of the volatiles yields the product as a white oil
(138 mg, 0.29 mmol, 86%). 31P NMR (CDCl3): δ = –66.36, –65.54
ppm. (HRMS, FAB+): m/z calcd. for C29H31O4P: 474.319; found:
475.200 [M + H]+.
MeN), 3.70 (m, 1 H, H17), 6.30 (dd, 1 H, H10), 6.53 (dd, 1 H, H12),
6.83 (t, 3J = 7.2 Hz, 1 H, H21), 7.02 (t, 3J = 7.5 Hz, 1 H, H20), 7.10
3
(d, J = 8.4 Hz, 1 H, H19), 7.10–7.30 (m, 3 H), 7.3 (m, 1 H, Phm),
7.35 (m, 1 H, Phi), 7.40 (m, 1 H, H6), 7.52 (t, 3J = 7.5 Hz, 1 H,
H5), 7.66 (m, 2 H, Pho), 7.80 (m, 1 H, H3) ppm. [α]2D5 = –33.9 (c =
0.24, CHCl ). IR (KBr): ν
= 1588 (s), 1535 (m), 1452 (s), 1429
˜
3
max
(m), 1312 (m), 1218 cm–1 (m). (HRMS, FAB+): m/z calcd. for
C28H26NO2PPd: 545.07; found: 545.07.
Compound 8: Experimental procedure as reported for 7; yield 63%.
31P NMR (121.5 MHz, CDCl3): δ = –5.40 ppm. 1H NMR
(300.1 MHz, CDCl3): δ = 1.80 (m, 6 H), 2.8–3.1 (m, 12 H), 4.30–
4.60 (m, 2 H), 6.20–6.50 (m, 2 H), 6.60–6.80 (m, 3 H), 7.00–8.20
(m, 29 H) ppm. (HRMS, FAB+): m/z calcd. for C32H28NO2PPd:
595.09; found 595.09.
Compound 7: To a solution of 3 (25 mg, 0.086 mmol) in dichloro-
methane (5 mL) was added triethylamine (1.1 equiv.) and the solu-
tion was stirred for 30 min. At this point (S)-5 (25 mg, 0.043 mmol)
was added and the solution was stirred for an additional hour. The
solution was filtered through a short pad of silica (eluent: CH2Cl2),
next the solvent was evaporated off to give rise to the dia-
stereomeric mixture of compounds 7a,b as a yellow solid (36 mg,
0.066 mmol, 72%). Subsequently the diastereoisomers were sepa-
rated by radial chromatography (eluent: CH2Cl2/hexane = 20:1).
31P NMR (CDCl3): δ = –5.76, –4.97 ppm. (HRMS, FAB+):
m/z calcd. for C28H26NO2PPd: 545.070; found: 545.070.
C28H26NO2PPd (545.07): calcd. C 61.60, H 4.80; found C 61.55, H
4.76.
Compounds 9a,b: Compound 4a,b (498 mg, 0.975 mmol) and (S)-6
(333 mg, 0.427 mmol) were placed in a Shlenk tube and sub-
sequently solubilized in dichloromethane (20 mL).The resultant
solution was allowed to stir for 30 min. Next, the solvent was evap-
orated to give rise to the diastereomeric mixture of compounds
9a,b as a yellow solid. Subsequently the diastereoisomers were sep-
arated by chromatography (eluent: CH2Cl2). 31P NMR: δ = –8.20,
–12.70 ppm.
Compound (RP)-7a: First diastereoisomer eluted (21 mg, 84%). 31
P
NMR (121.5 MHz, CDCl3):
δ
=
–5.76 ppm. 13C NMR
Compounds (SP)-9a: First diastereoisomer eluted (300 mg, 86%).
31P NMR (121.5 MHz, CDCl3): δ = –12.72 ppm. 13C NMR
(75.4 MHz, CDCl3): δ = 15.89, 21.17, 22.27, 22.90–22.96, 25.71,
31.58, 31.83, 34.14, 41.18, 47.44, 48.50, 51.5, 73.67, 79.83, 107.08,
107.76, 110.20, 110.85, 114.70, 117.40–117.45, 117.75, 123.54,
124.01, 124.64–124.73, 124.73–125.00, 125.65, 128.11, 128.25,
128.83, 130.50, 131.23, 132.34, 133.12, 133.40, 133.60, 134.11,
134.59, 134.75, 137.00, 137.23, 148.78–148.81, 151.53, 151.90,
151.95, 153.53, 154.36 ppm. 1H NMR (300.1 MHz, CDCl3): δ =
0.65 (d, 3J = 6.6 Hz, 3 H), 0.80–2.00 (m, 15 H), 2.16 (d, J = 6.6 Hz,
(125.7 MHz, CDCl3): δ = 10.59, 42.07–42.10, 47.63–47.65, 72.14–
72.16, 101.95–101.98, 106.13, 106.57, 112.98, 113.42, 113.93–
114.00, 119.50, 124.27–124.49, 126.32–126.36, 128.97–129.06,
130.89–130.91, 132.44–132.56, 132.78, 133.42–133.53, 134.21–
134.57, 140.32–140.41, 148.65–148.68, 152.94–152.96, 157.88–
157.89, 158.54–158.56, 175.37–175.47 ppm. 1H NMR (499.8 MHz,
3
3
CDCl3): δ = 1.46 (d, J = 6.6 Hz, 3 H, Me17), 2.70 (d, J = 1.8 Hz,
3
3 H, MeN2), 3.10 (d, J = 1.8 Hz, 3 H, MeN1), 4.50 (q, 1 H, H17),
6.30 (dd, 1 H, H10), 6.55 (dd, 1 H, H12), 6.88 (t, J = 7.5 Hz, 1 H,
3
H21), 6.96 (d, 3J = 7.8 Hz, 1 H, H19), 7.08 (t, 3J = 7.5 Hz, 1 H,
H20), 7.10–7.20 (m, 2 H, H11, H4), 7.20–7.25 (m, 1 H, H22), 7.30
3
3 H), 2.59 (s, 3 H), 3.03 (d, J = 3.6 Hz, 3 H), 4.20–4.50 (m, 2 H),
3
3
6.60 (m, 2 H), 6.90 (d, J = 8.7 Hz, 3 H), 7.10 (d, J = 8.4 Hz, 3
(m, 1 H, Phm), 7.34 (m, 1 H, Phi), 7.40 (m, 1 H, H6), 7.53 (t, J =
3
H), 7.20–7.80 (m, 13 H), 8.6 (m, 1 H) ppm. [α]2D5 = +107 (c = 0.42,
8.7 Hz, 1 H, H5), 7.66 (m, 2 H, Pho), 7.80 (m, 1 H, H3), ppm
CHCl ). IR (KBr): ν
= 1753 (s) (C=O), 1588 (m), 1453 (m),
˜
3
max
(complex 7a see Figure 3). [α]2D5 = +46.6 (c = 0.42, CHCl3). IR
1435 (s), 1218 cm–1 (s). (HRMS, FAB+): m/z calcd. for
C43H47ClNO4PPd: 813.20, found: 813.1967. C43H47ClNO4PPd
(813.20): calcd. C 63.39, H 5.81; found C 63.42, H 5.93.
(KBr): νmax = 1588 (s), 1541 (m), 1447(s), 1429 (m), 1312 (m), 1218
˜
cm–1 (m). (HRMS, FAB+): m/z calcd. for C28H26NO2PPd: 545.070;
found: 545.074.
Compounds (RP)-9b: Second diastereoisomer eluted (250 mg, 72%).
31P NMR (121.5 MHz, CDCl3): δ = –8.20 ppm. 13C NMR
(126.7 MHz, CDCl3): δ = 16.32, 20.72, 22.24, 23.11, 24.29, 25.83,
31.68, 34.32, 40.96, 46.98, 48.88, 51.79–51.81, 73.45–73.48, 80.38,
108.8, 109.24, 110.93, 111.34, 115.18–115.21, 116.73–116.77,
118.23–118.26, 123.60, 124.24, 124.45–124.50, 124.68–124.79,
125.81, 128.30–128.39, 128.85, 129.12, 130.49–130.50, 131.41,
131.91, 132.78–133.13, 133.35, 136.41, 136.57–136.59, 136.69,
149.82, 150.00–150.02, 152.27–152.34, 153.79–153.81, 154.80 ppm.
1H NMR (300.1 MHz, CDCl3): δ = 0.46 (d, 3J = 6.6 Hz, 3 H),
Compound (SP)-7b: Second diastereoisomer eluted (7 mg, 29%). 31
P
NMR (121.5 MHz, CDCl3):
δ
=
–4.97 ppm. 13C NMR
(126.7 MHz, CDCl3): δ = 25.22, 46.19–46.21, 51.41–51.44, 75.40–
75.43, 101.97–102.00, 106.22, 106.65, 113.17, 113.61, 113.97–
114.03, 119.51–119.54, 123.32, 124.47, 124.57, 125.81–125.85,
128.95–129.04, 130.88–130.90, 132.41–132.52, 132.74–132.75,
133.41–133.53, 134.15–134.51, 140.51–140.85, 145.02–145.06,
156.53–156.55, 157.93–157.95, 158.55–158.57, 175.55–175.65 ppm.
1H NMR (499.8 MHz, CDCl3): δ = 1.70 (d, 3J = 6.3 Hz, 3 H,
3
3
Me17), 2.87 (d, J = 3.3 Hz, 3 H, MeN), 2.92 (d, J = 1.8 Hz, 3 H,
3
0.80–2.00 (m, 15 H), 2.14 (d, J = 6.6 Hz, 3 H), 2.74 (s, 3 H), 2.95
3
(d, J = 3.6 Hz, 3 H), 4.20 (m, 1 H), 4.60 (m, 1 H), 6.70 (m, 2 H),
6.90 (d, 1 H), 7.00–7.80 (m, 14 H), 8.20 (m, 1 H) ppm. [α]2D5 = –85
(c = 0.78, CHCl ). IR (KBr): ν
= 1753 (s) (C=O), 1588 (m),
˜
3
max
1453 (m), 1429 (s), 1218 cm–1 (s). (HRMS, FAB+): m/z calcd. for
C43H47ClNO4PPd: 813.20; found: 813.20. C43H47ClNO4PPd
(813.20): calcd. C 63.39, H 5.81; found C 63.78, H 6.01.
(–)-(1R)-Menthyl (RP)-10-Phenyl-10H-phenoxaphosphan-1-yl Car-
bonate (4a): Compound 9a (30.0 mg) and 1,2-bis(diphenylphos-
phanyl)ethane (14.7 mg) were placed in a Shlenk tube and dis-
solved in dichloromethane (3 mL). The resultant light yellow solu-
tion was stirred for 30min at room temperature and subsequently
the volume of solvent was reduced to about half mL. The solution
Eur. J. Inorg. Chem. 2008, 1309–1317
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1315

P. W. N. M. van Leeuwen et al.
FULL PAPER
was filtered through a short pad of silica (eluent: CH2Cl2) and the
organic solvent removed in vacuo to give a colourless oil (17 mg,
yield 97%). 31P NMR (121.4 MHz, CDCl3): δ = –65.60 ppm. 13C
crystal structure contains voids (398 Å3/unit cell) filled with disor-
dered solvent molecules. Their contribution to the structure factors
was secured by back-Fourier transformation using the routine
NMR (75.4 MHz, CDCl3): δ = 16.70, 21.02, 22.23, 23.54, 26.33, SQUEEZE of the program PLATON,[27] resulting in 66 electrons/
31.60, 34.27, 40.69, 47.23, 79.95, 115.89, 117.01, 117.27, 117.95, unit cell. The structure was refined with SHELXL-97[28] against F2
124.05–124.19, 128.69–129.09, 131.05, 131.29, 132.31, 132.59,
of all reflections. Non-hydrogen atoms were refined with aniso-
135.09, 135.60, 139.38, 139.67, 153.03, 153.24–153.45, 154.70, tropic displacement parameters. Hydrogen atoms were introduced
155.61 ppm. 1H NMR (300 MHz, CDCl3): δ = 0.80–1.20 (m, 14 in calculated positions and refined with a riding model. The men-
H), 1.51 (m, 2 H), 1.70 (m, 2 H), 1.96 (m, 1 H), 2.22 (m, 1 H), 4.60
(m, 1 H), 6.90–7.00 (m, 1 H), 7.00–7.50 (m, 11 H) ppm. [α]2D5
thyl moiety was refined with a disorder model. 533 Parameters were
refined with 119 restraints. R1/wR2 [IϾ2σ(I)]: 0.0301/0.0661. R1/
wR2 (for all reflections): 0.0360/0.0682, S = 1.085, Flack x param-
eter: –0.07(3).[29] Residual electron density was between –0.37 and
0.53 e/Å3. Geometry calculations and checking for higher sym-
metry was performed with the PLATON program.[27]
=
–110 (c = 0.21, CHCl ). IR (KBr): νmax = 2953 (s), 2879 (m), 1759
˜
3
(s) (C=O), 1453 (m), 1429 (s), 1259 (s), 1212 cm–1 (s).
(+)-(1R)-Menthyl (SP)-10-Phenyl-10H-phenoxaphosphan-1-yl Car-
bonate (4b): The same procedure described for 4a was followed to
obtain 4b. 31P NMR (121.4 MHz, CDCl3): δ = –66.40 ppm. 13C
NMR (75.4 MHz, CDCl3): δ = 16.40, 21.02, 22.25, 23.42, 26.23,
31.65, 34.27, 40.76, 47.13, 79.97, 115.89, 116.83, 117.36, 117.98,
124.22–124.06, 128.66–128.90, 131.13, 131.41, 131.96, 132.22,
135.22, 135.73, 139.27, 139.56, 153.00, 153.47–153.70, 155.06,
155.91 ppm. 1H NMR (300 MHz, CDCl3): δ = 0.60–1.80 (m, 16
H), 1.98 (m, 1 H), 2.20 (m, 1 H), 4.60 (m, 1 H), 7.02 (m, 1 H),
7.06–7.45 (m, 10 H), 7.53 (t, 1 H) ppm. [α]2D5 = +44 (c = 0.39,
CCDC-657165 (for 9a) contains supplementary crystallographic
data. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Supporting Information (see also the footnote on the first page of
this article): 1H NMR, 31P NMR, 13C-NMR spectra of compounds
1, 2, 3, 4a, 4b, 7a, 7b, 8, 9a, 9b and three-dimensional coordinates
of the calculated structures I–IV (7) are provided. HPLC chromato-
grams of racemic 3 and enantiopure 3a are provided.
CHCl ). IR (KBr): νmax = 2953 (s), 2879 (m), 1759 (s) (C=O), 1588
˜
3
(m), 1453 (m), 1429 (s), 1250 (s), 1212 cm–1 (s).
(–)-(R)-10-Phenyl-10H-phenoxaphosphanyl-1-ol (3a). Method A:
Compound 4a (151.6 mg, 0.32 mmol) was dissolved in a small
amount of THF (1 mL). To this solution was added a degassed
KOH ethanolic solution (600 mg of KOH, 20 mL H2O, 20 mL
EtOH) and subsequently the reaction mixture was set to the tem-
perature of 85 °C and vigorously stirred for 2 h. The reaction mix-
ture was cooled down and ethanol removed in vacuo. The aqueous
solution was extracted several times with dichloromethane, next the
organic solution was dried with magnesium sulfate and the solvent
evaporated off. The residue was filtered through a short pad of
silica using as eluent CH2Cl2 and subsequently the solvent was
evaporated off to yield a white solid (73 mg, 0.25 mmol, 78%).
Acknowledgments
We would like to thank J. Geenevasen for the (1H,1H) NOE and
(1H,1H) COSY experiments of compounds 7a,b and the University
of Amsterdam for financial support. This work was supported in
part (to M. L., A. L. S.) by the Council for the Chemical Sciences
of the Netherlands Organization for Scientific Research (CW-
NWO).
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X-ray Crystal Structure Determination of 9a: C43H47ClNO4PPd
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disordered solvent, Fw
=
814.64,[30] yellow plate,
0.36ϫ0.33ϫ0.03 mm3, monoclinic, C2 (no. 5), a = 22.4031(4), b
= 9.6277(3), c = 19.5494(3) Å, β = 97.813(1)°, V = 4177.49(15) Å3,
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Published Online: January 11, 2008
Eur. J. Inorg. Chem. 2008, 1309–1317
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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