P-chirogenic phosphines. MOP/diPAMP hybrids, their oxide crystal structures, reduction studies and alternative syntheses

Article abstract of DOI:10.1016/j.jorganchem.2004.09.015

The novel P-chirogenic anisylphenylMOP derivatives (R,R) and (R,S)-2-(anisylphenylphosphino)-2′-methoxy-1,1′-binaphthyl (10a and b) have been synthesized and their corresponding oxides characterised by X-ray crystallography. The results of a parallel scre

Full text of DOI:10.1016/j.jorganchem.2004.09.015

Journal of Organometallic Chemistry 690 (2005) 211–219
www.elsevier.com/locate/jorganchem
P-chirogenic phosphines. MOP/diPAMP hybrids, their oxide
crystal structures, reduction studies and alternative syntheses
,1
*
Lee J. Higham , Eoin F. Clarke, Helge Muller-Bunz, Declan G. Gilheany
*
¨
Chemistry Department, Conway Institute of Biomolecular and Biomedical Sciences, The Centre for Synthesis and Chemical Biology,
University College Dublin, Belfield, Dublin 4, Ireland
Received 4 July 2004; accepted 10 September 2004
Available online 14 October 2004
Abstract
The novel P-chirogenic anisylphenylMOP derivatives (R,R) and (R,S)-2-(anisylphenylphosphino)-20-methoxy-1,10-binaphthyl
(10a and b) have been synthesized and their corresponding oxides characterised by X-ray crystallography. The results of a parallel
screening regimen with various reducing agents highlight the sensitivity of the tertiary phosphine oxides to epimerisation and, inter-
estingly, reveal that the P@O, O–CH3 and P–C6H5 bonds can all be cleaved selectively depending on the reducing agents employed.
An alternative synthesis was provided by direct coupling of the secondary phosphine with (R)-methoxytriflate 4, which led to the
isolation of the optically pure P-chirogenic phosphines via their borane adducts. A brief study of the coordination chemistry of
10a with different rhodium precursors, relevant to the catalytic asymmetric addition of boronic acids to aldehydes is also reported.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Monophosphine; Asymmetric; Chirogenic; Synthesis and characterisation
1. Introduction
P-chirogenic phosphorus ligands is superior to those
with chirality located in the ligand backbone. They
surmised that this was because of the potentially more
inefficient secondary transfer of chirality from the ligand
backbone compared to that from P-chirality. P-chiro-
genic ligands are not necessarily better per se at a given
catalytic procedure, but manipulation of the phosphorus
in this manner provides a powerful tool in the search for
improved enantioselection.
Hayashiꢀs MOP ligand, built around the binaphthyl
backbone, has been highly successful in a variety of
asymmetric transformations [1]. In certain cases it is
desirable to improve still further its propensity for chiral
induction [2]. One potential method of achieving this is
to incorporate additional chirality at the phosphorus
centre. In a recent study, Lipkowitz et al. [3] have shown
the potential of such an approach when they demon-
strated that, in most cases in their best catalysts, the re-
gions of maximum stereoinduction by the ligands were
near the site of the chemistry. For the particular case
P
´
of phosphorus ligands, Crepy and Imamoto, in a recent
review [4] provide many examples where the use of
PPh2
OCH3
OCH3
OCH3
P
*
Corresponding authors. Tel.: +35317162316; fax: +35317162308.
E-mail addresses: leehigham@eircom.net (L.J. Higham), declan.
gilheany@ucd.ie (D.G. Gilheany).
1
L.J. Higham presented this paper at the ICPC in Birmingham this
(R,R)-diPAMP
(R)-MOP
year.
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.09.015

212
L.J. Higham et al. / Journal of Organometallic Chemistry 690 (2005) 211–219
Our choice of substituents on the phosphorus was
recently improved this resolution [8]), to give the meth-
oxy alcohol 5, followed by treatment with trifluorometh-
anesulfonic anhydride. We encountered problems in
following this because we often found small quantities
of the dimethoxy compound 6, which was tedious to re-
move. A more convenient procedure was to instead pre-
pare the monotriflate alcohol 7 [9] from resolved binol
and the mild triflating reagent N-phenyl trifluorometh-
anesulfonimide. Treating 7 with methyl iodide and so-
dium hydroxide routinely afforded 4 in good yield.
For the synthesis of the anisylphenylMOP
phosphines, our first approach was to investigate the
reduction of a 50:50 mixture of the diastereomeric phos-
phine oxides 8. Our studies revealed that the reductions
gave products that are highly dependent on the reducing
agent employed Scheme 2. Thus, upon treatment of the
mixture 8 with lithium aluminium hydride in THF we
found that reduction took place accompanied by cleav-
age of the phenyl group. The 31P NMR spectrum was
consistent with the formation of the racemic secondary
phosphines (R,R) and (R,S)-anisylMOP 9a and b, on ac-
count of the chemical shifts and doublet splittings ob-
served for both peaks in the 31P–1H coupled spectrum
guided by our desire to prepare a hybrid MOP/DiP-
AMP monophosphine, in view of the acknowledged
success of the latter P-chirogenic bisphosphine [5].
Hence we report here our successful synthesis of the
chiral-at-phosphorus, diastereomeric monophosphines
(R,R) and (R,S)-2-(anisylphenylphosphino)-20-meth-
oxy-1,10-binaphthyl; the anisylphenylMOPs 10a and b.
2. Results and discussion
The standard route to MOP ligands involves the cou-
pling of a single diphenylphosphine oxide unit to (R) or
(S)-2,20-bis(trifluoromethanesulfonyloxy)-1,10-binaph-
thyl, followed by treatment with sodium hydroxide,
methyl iodide/potassium carbonate and finally trichlo-
rosilane/triethylamine reduction to yield the phosphine
[6]. We prepared the diastereomeric anisylphenylMOP
oxides 8 following this route (Scheme 1) using anisylphe-
nylphosphine oxide via, in turn, phosphinyloxy triflates
2 and alcohols 3. Frustratingly we found that 8a and b
could not be separated. However we were able to sepa-
rate the triflates 2a and b by column chromatography
and take these through, via the alcohols 3a and b, to
the optically pure oxides 8a and b. Recrystallisation of
8a and b gave crystals suitable for an X-ray crystallo-
graphic study and the structures are given for compari-
son in Fig. 1. The pertinent bond lengths and angles are
collected in Table 1, and the crystallographic parameters
are summarised in Table 2.
1
(d ꢀ47.3 ppm, JP–H = 219.5 Hz; d ꢀ47.7 ppm,
1JP–H = 218.6 Hz) and the parent ion in the mass spec-
trum, which indicated the phenyl group was cleaved.
The two distinct resonances indicate that epimerisation
does not occur at room temperature in the absence of
acid. Work-ups involving the addition of aqueous acid
to the reaction solution cause the signals to broaden,
indicative of acid-catalysed epimerisation. The forma-
tion of 9a and b should allow for unusual MOP deriva-
tives to be prepared by hydrophosphination of
unsaturated compounds across the reactive P–H bond.
In contrast, when hexachlorodisilane in acetonitrile
was used to reduce the phosphine oxide functionality,
we observed only cleavage of the ether methyl–oxygen
bond, to produce the phosphine oxide alcohols 3a and
It was also a goal of ours to prepare quantities of the
potentially useful methoxy triflate 4, which is more sui-
ted to our parallel synthesis work in that it would allow
the rapid screening of coupling reactions with a number
of chiral racemic secondary phosphine oxides/phos-
phines. The reported route [7] to compound 4, is via
the mono-methylation of resolved binol (we have
OSO2CF3
OSO2CF3
P(O)PhAn
OSO2CF3
P(O)PhAn
OCH3
PPhAn
OCH3
2a and b
(R)-1
resolved (R,R) and (R,S) 10a and b
8a and b
2: R=AnPhP(O), R1=OSO2CF3
3: R=AnPhP(O), R1=OH
4: R=OSO2CF3, R1=OCH3
5: R=OH, R1=OCH3
R
R1
6: R=OCH3, R1=OCH3
7: R=OSO2CF3, R1=OH
Scheme 1. Planned synthetic route to (R,R) and (R,S) anisylphenylMOP (10a and b).

L.J. Higham et al. / Journal of Organometallic Chemistry 690 (2005) 211–219
213
Fig. 1. The crystal structures of (R,R)-and (R,S)-anisylphenylMOP oxides 8a and b.
Table 1
In the coupling step, we noted an asymmetric induc-
tion effect in favour of one of the phosphines 10a/b
(ꢁ60/40) in the 31P NMR spectra. The reaction proceeds
reasonably cleanly and pure 10a could be easily
obtained by column chromatography (ethyl acetate:pen-
tane, 50:1). The isolation of 10b by this route was more
problematic and therefore we opted instead to convert
diastereomeric mixtures of 10a and b to the correspond-
ing boranes (see Section 4). The separation of the bora-
nes is more facile and was accomplished by column
chromatography (ethyl acetate:cyclohexane, 1:19). The
subsequent deprotection step was sensitive to the reac-
tion conditions; for instance epimerisation occurred at
50 ꢁC overnight with diethylamine as the base. However,
using trifluoromethanesulphonic acid in a procedure
similar to that of McKinstry and Livinghouse [13],
deprotection of both 11a and b occurred without loss
of optical integrity to give 10a and b.
˚
Bond distances (A) and angles (ꢁ) for (R,R) and (R,S) anisylphenyl-
MOP oxides (8a and b)
8a Æ acetone
8b
˚
Bond lengths (A)
P(1)–O(1)
P(1)–C(2)
1.4890(10)
1.8138(13)
1.8050(13)
1.8167(13)
1.3653(17)
1.3613(17)
1.4258(18)
1.4260(18)
1.4842(10)
1.8200(13)
1.8117(14)
1.8088(14)
1.3665(18)
1.3541(18)
1.4317(17)
1.4289(18)
P(1)–C(22)
P(1)–C(29)
C(12)–O(2)
C(23)–O(3)
O(2)–C(21)
O(3)–C(28)
Bond angles (ꢁ)
O(1)–P(1)–C(2)
O(1)–P(1)–C(22)
O(1)–P(1)–C(29)
C(12)–O(2)–C(21)
C(23)–O(3)–C(28)
110.62(6)
109.40(6)
109.58 (6)
118.68(12)
117.70(12)
117.51(6)
113.58(6)
110.59(6)
118.44(11)
118.14(12)
In order to assign the configuration of 10a and b, oxi-
dation of the phosphines with hydrogen peroxide – a
reaction known to proceed with retention [14] – was car-
ried out. We found that 10a was oxidized cleanly (in
d-chloroform at room temperature) by this reagent to
the oxide 8b (R,S) and hence, according to convention,
10a has the corresponding R,R configuration. In other
words 10a is related to 8b by a process of oxidation with
retention of configuration [15].
The rhodium coordination chemistry of the anisyl-
phenylMOPs was briefly investigated by reacting 10a
with [Rh2Cl2(CO)4] in dichloromethane at room temper-
ature, and the product was found to be cis-
[RhCl(CO)(10a-anisylphenylMOP)] 12a by 31P NMR
and mass spectroscopy. In addition, and as a prelude
to our catalytic studies on the rhodium-catalysed addi-
tion of boronic acids to aldehydes [2a] (Scheme 4), we
reacted a diastereomeric mixture (1:1) of 10a and b with
[Rh(acac)(C2H4)2] (1:1, Rh:P) in an attempt to form
[Rh(acac)(10)] complexes. We found two major prod-
ucts in the 31P NMR spectrum in d-chloroform; two
b. Reduction to phosphine could be achieved with the
mild reducing agent phenylsilane, which has been used
successfully in the past to reduce P-chirogenic groups
whilst retaining the optical integrity of the compound
[10]. In a test study, neat phenylsilane slowly reduced
a diastereomeric mixture of the oxides to the phosphines
10a and b, over 3 days at 80 ꢁC. However when the reac-
tion was carried out on an optically pure sample, epime-
risation occurred even when the reduction was still
incomplete. Finally, when 8a was treated overnight with
trichlorosilane (10 mole equivalents) in benzene at room
temperature, full reduction to phosphine occurred but
there was still significant epimerisation (18%).
As a result of the difficulties associated with the
reduction of the phosphine oxides, we sought an alterna-
tive route to the optically pure phosphines 10a and b.
We noted that they were separable (with difficulty) by
chromatography and so we adapted the general Merck
procedure of coupling secondary phosphines to aryl
triflates [11] by reacting (R)-methoxy triflate 4 with race-
mic anisylphenylphosphine [12] Scheme 3.

214
L.J. Higham et al. / Journal of Organometallic Chemistry 690 (2005) 211–219
Table 2
Crystal data for (R,R) and (R,S) anisylphenylMOP oxides (8a and b)
Crystal
[8a] Æ acetone
[8b]
Formula
Colour, habit
C34H27O3P Æ C3H6O
Colourless block
100(2)
C34H27O3P
Colourless block
100(2)
Temperature (K)
k of Mo Ka radiation
Formula weight
Crystal system
Space group
0.71073
572.60
0.71073
514.53
Monoclinic
P21
Orthorhombic
P212121
Unit cell dimensions
˚
a (A)
˚
12.5476(11)
15.7599(14)
8.0294(7)
16.4643(14)
b (A)
˚
c (A)
15.8394(14)
90.00
19.7512(17)
90.00
a (ꢁ)
b (ꢁ)
c (ꢁ)
108.5100(10)
90.00
2970.2(5)
90.00
90.00
2611.1(4)
3
˚
Volume (A )
Z
4
1.281
4
1.309
Density (calculated) (mg/m3)
Absorption coefficient (mmꢀ1
Crystal size (mm3)
Reflections collected
)
0.133
0.70 · 0.70 · 0.50
51368
0.140
0.60 · 0.50 · 0.50
22518
Independent reflections (Rint
Absorption correction
Refinement method
Goodness-of-fit on F2
Final R indices [I>2r(I)]
R indices (all data)
)
14014 (0.0237)
Multiscan
6184 (0.0209)
Multiscan
Full-matrix least-squares on F2
1.034
Full-matrix least-squares on F2
1.061
R1 = 0.0337 wR2 = 0.0838
R1 = 0.0355 wR2 = 0.0851
R1 = 0.0345 wR2 = 0.0875
R1 = 0.0351 wR2 = 0.0881
1
broad overlapping doublets (d 47.3 ppm, JRh–P ꢁ 189
minium hydride was used as the reductant. In an alter-
native approach we reacted anisylphenylphosphine
with the methoxy triflate intermediate 4, which we syn-
thesized by an improved route to that reported. From
the diastereomeric mixture we prepared the correspond-
ing boranes 11a and b, and following separation by col-
umn chromatography and deprotection, we isolated the
optically pure diastereomeric phosphines 10a and b. The
coordination chemistry with rhodium was explored with
a view to utilizing the complexes in the asymmetric addi-
tion of boronic acids to aldehydes.
1
Hz; d 45.7 ppm, JRh–P ꢁ 182 Hz) tentatively assigned
to [Rh(acac)(10a/b)], together with some minor reso-
nances characteristic of Rh complexes of a higher oxida-
tion state. The coordination chemistry of MOP itself has
come under scrutiny recently as it ligates in unusual
modes to a number of palladium centres [16]. It is note-
worthy that there is no reaction of 10a with [Rh-
(acac)(g4-cod)] as the rhodium precursor, implying these
MOP ligands do not bind strongly enough to displace
the bidentate cyclooctadiene ligand from the metal cen-
ter. The nature of the rhodium precursors and the result-
ant phosphine complexes have been shown to be critical
in the asymmetric addition of phenylboronic acid to
2-cyclohexenone [17]. The ramifications of the coordina-
tion chemistry with regard to the catalysis and the
catalytic results themselves will be the subject of a forth-
coming report.
4. Experimental
4.1. General methods
All operations were carried out under a N2 atmos-
phere using standard Schlenk-line techniques. Solvents
were dried according to standard procedures [18]
although DMF and DMSO were purchased in an anhy-
drous state from Aldrich and purged with N2 before use.
Bis(diphenylphosphino)butane (dppb), [1,2-bis(diph-
enylphosphino)ethane]dichloronickel(II), borane–THF
complex (1.0 M in THF), diazabicyclo[2.2.2]octane
(DABCO), N,N-diisopropylethylamine, hexachlorodisi-
lane, lithium aluminium hydride (1.0 M solution in
THF), methyl iodide, palladium(II) acetate, phenylsi-
3. Conclusion
Two diastereomeric anisylphenylMOP oxides (8a and
b) have been prepared and characterized. A variety of
reducing agents were employed on them and the
reactions demonstrate that the chemistry is highly rea-
gent-specific, the highlight being the formation of a
secondary anisylnaphthylphosphine when lithium alu-

L.J. Higham et al. / Journal of Organometallic Chemistry 690 (2005) 211–219
215
Scheme 2. The reduction of the phosphine oxides 8a and b with a variety of reagents.
H3C
H3C
O
O
H3B
OSO2CF3
OCH3
P
P
i
ii
iii
Resolved
10a and 10b
OCH3
OCH3
4
10a and b
11a and b
i). [NiCl2(dppe)]/DMSO/AnPhPH/100 oC ii). BH3.THF iii). Column separation of diastereomers then treat with CF3SO2H/-5 oC
Scheme 3. Actual synthetic route to (R,R) and (R,S) anisylphenylMOP (10a and b).
lane, N-phenyl trifluoromethanesulfonimide, trichloros-
ilane, triethylamine, trifluoromethanesulfonic acid and
trifluoromethanesulfonic anhydride were purchased
from Aldrich. Silica gel 60 (0.040–0.063 mm) was pur-
chased from Merck. Anisylphenylphosphine was pre-
pared according to the literature method [12].
[Rh2Cl2(CO)4] [19], [Rh(acac)(C2H4)2] [20] and [Rh(a-
cac)(g4-cod)] [21] were prepared according to the known
procedures. The d-chloroform was purged with N2 and
stored over molecular sieves. The NMR spectra were re-
corded at 25 ꢁC on a Varian Unity 300 MHz spectrom-
eter with chemical shifts relative to tetramethylsilane for
1H and 13C spectra and 85% H3PO4 for 31P spectra. IR
spectra (KBr) were recorded on a Mattson Instruments
Galaxy Series FTIR3000 spectrophotometer. Elemental
analyses and mass spectra were carried out at UCD.
Melting point measurements were carried out on a Reic-
hert thermovar instrument.

216
L.J. Higham et al. / Journal of Organometallic Chemistry 690 (2005) 211–219
ArH), 3.55 (s, 3H, OCH3); 13C (75 MHz, CDCl3) d
PhB(OH)2 (2equiv.)
160.7–110.9 (multiple signals, ArC and CF3), 54.9
(OCH3); 31P (121 MHz, CDCl3) d 30.78; m/z (% inten-
sity): [MH]+ 633.0 (100); HRMS Calc. for [MH]+
(C34H25O5F3SP): 633.1112, Found: 633.1117%.
[Rh(acac)(C2H4)2] 3 mol% / L*
Ph
CHO
C
L* = (S)-MOP 6 mol%
*
OH
Scheme 4. The catalytic asymmetric addition of phenylboronic acid to
naphthaldehyde.
4.3.2. (R,S)-AnPhMOP(O)OSO2CF3 (2b)
m.p. 285–289 ꢁC; [a]D = 59.0 (c 0.40, CHCl3);
(Found: C, 64.72; H, 4.00. C34H24F3O5PS requires C,
64.55; H, 3.82%.); IR (KBr, cmꢀ1) 3066, 2940, 2839,
4.2. Synthesis of anisylphenylphosphine oxide
1
1589, 1477, 1401, 1214, 1154; H (300 MHz, CDCl3) d
7.97–7.79 (m, 4H, ArH), 7.66–7.52 (m, 4H, ArH),
7.42–7.08 (m, 10H, ArH), 6.95 (m, 1H, ArH), 6.71–
6.65 (m, 2H, ArH), 3.51 (s, 3H, OCH3); 13C (75 MHz,
CDCl3) d 159.9–110.7 (multiple signals, ArC and CF3),
55.0 (OCH3); 31P (121 MHz, CDCl3) d 30.46; m/z (%
intensity): [MH+] 633.1 (100); HRMS Calc. for [MH]+
(C34H25O5F3SP) 633.1112. Found: 633.1101%.
Anisylphenylphosphine oxide was synthesized by
simple air oxidation of the neat phosphine (2 g, 8.6
mmol) over 2 weeks in the fume cupboard. Over this
time the oily solid which formed was broken-up with a
spatula to prevent the formation of a crust, which other-
wise traps secondary phosphine underneath. Using these
conditions we observed no over-oxidation to the P(V)
acid. Yield was quantitative. 31P NMR (121 MHz,
CDCl3): d 18.89 ppm (1JP–H = 500.1 Hz).
4.4. Synthesis of (R,R) and (R,S)-2-(anisylphenylphos-
phinyl)-20-hydroxy-1,10-binaphthyl (3a and b). Both
diastereomers are prepared in the same manner
4.3. Synthesis of (R,R) and (R,S)-2-(anisylphenylphosphi-
nyl)-20-((trifluoromethanesulfonyl)oxy)-1,10-binaphthyl (2a
and b)
To a solution of AnPhMOP(O)OSO2CF3 (300 mg,
0.474 mmol) in a 2:1 mixture of 1,4-dioxane and metha-
nol (15 cm3) was added 3N aqueous sodium hydroxide
(0.51 cm3, 1.54 mmol) at room temperature. The yellow
solution was stirred for 2 days. The mixture was then
acidified by the addition of conc. HCl until the pH
had reached around 1.5. The now clear solution was ex-
tracted with dichloromethane (3 · 10 cm3), dried over
magnesium sulphate, and concentrated under reduced
pressure to yield an off-white solid (220 mg, 93%).
A mixture of (R)-2,20-bis(trifluoromethanesulfonyl-
oxy)-1,10-binaphthyl 1 (2.72 g, 4.94 mmol), anisylphe-
nylphosphine oxide (2.31 g, 9.95 mmol), palladium
diacetate (56.0 mg, 0.249 mmol), 1,4-bis(diph-
enylphosphino)butane (dppb) (106.0 mg, 0.249 mmol),
and anhydrous diisopropylethylamine (2.56 g, 19.8
mmol) in dry degassed dimethylsulfoxide (30 cm3) were
heated at 100–110 ꢁC for 16 h. After this time TLC anal-
ysis (ethyl acetate/hexane 1:1) indicated that the binaph-
thyl triflate reactant had been consumed. The mixture
had changed from its initial deep red colour to a dark
brown. After cooling to room temperature, the mixture
was concentrated under reduced pressure to yield a
brown residue, which was diluted with ethyl acetate
(250 cm3). The resultant pink precipitate was filtered
and recrystallised from ethyl acetate to give 0.906 g of
white crystals (60% based on one diastereomer) of 2b.
The remaining solution of crude product was washed
with water (2 · 150 cm3) and dried over magnesium sul-
phate. The mixture was filtered and concentrated under
reduced pressure, yielding a light brown solid (3.24 g).
This crude mixture was chromatographed on silica gel
(pentane:ethyl acetate, 2:1) to yield 0.88 g (58% based
on one diastereomer) of 2a.
4.4.1. (R,R)-AnPhMOP(O)OH (3a)
m.p. 247–252 ꢁC; [a]D = ꢀ111.7 (c 0.30, CHCl3); IR
(KBr, cmꢀ1) 3058, 2955, 2850, 2360, 1589, 1434, 1275,
1133; 1H (300 MHz, CDCl3) d 8.05–7.98 (m, 1H,
ArH), 7.93–7.88 (m, 2H, ArH), 7.60–7.08 (m, 12H,
ArH), 7.09–6.94 (m, 2H, ArH), 6.80–6.74 (m, 1H,
ArH), 6.64–6.58 (m, 3H, ArH), 3.74 (s, 3H, OCH3);
13C (75 MHz, CDCl3) d 160.3, 153.7, 140.6–111.1 (mul-
tiple signals, ArC), 55.2 (OCH3); 31P (121 MHz, CDCl3)
d 35.90; m.p. 247–252 ꢁC; m/z (% intensity): [MH]+ 501.2
(100); HRMS Calc. for [MH]+ (C33H26O3P) 501.1620.
Found: 501.1626%.
4.4.2. (R,S)-AnPhMOP(O)OH (3b)
m.p. 242–246 ꢁC; [a]D = 55.0 (c 0.30, CHCl3); IR
(KBr, cmꢀ1) 3053, 2932, 2853, 2360, 1590, 1435, 1274,
1
1130, 748, 694; H (300 MHz, CDCl3) d 8.03–7.87 (m,
4.3.1. (R,R)-AnPhMOP(O)OSO2CF3 (2a)
4H, ArH), 7.61–7.04 (m, 14H, ArH), 6.91–6.75 (m,
2H, ArH), 6.41–6.36 (m, 2H, ArH), 6.07–6.02 (m, 1H,
ArH), 3.46 (s, 3H, OCH3); 13C (75 MHz, CDCl3) d
158.5, 153.5, 139.7, 109.2 (multiple signals, ArC), 54.2
(OCH3); 31P (121 MHz,CDCl3) d 35.49; m/z (% inten-
[a]D = 35.0 (c 0.43, CHCl3); IR (KBr, cmꢀ1) 3060,
2937, 2839, 1589, 1478, 1432, 1209, 1140; 1H (300
MHz, CDCl3) d 7.97–7.84 (m, 4H, ArH), 7.70–7.15
(m, 14H, ArH), 7.05 (m, 1H, ArH), 6.97–6.81 (m, 2H,

L.J. Higham et al. / Journal of Organometallic Chemistry 690 (2005) 211–219
217
sity): [MH]+ 501.2 (100); HRMS Calc. for [MH]+
(C33H26O3P) 501.1620. Found: 501.1618%.
4.6.2. (R,S)-AnPhMOP(O)OMe (8b)
m.p. > 230 ꢁC; [a]D = 22.1 (c 0.41, CHCl3); IR (KBr,
1
cmꢀ1) 2797, 2363, 1590, 1477, 1283, 1195, 803, 644; H
(300 MHz, CDCl3) d 7.90 (m, 2H, ArH), 7.78–7.47 (m,
6H, ArH), 7.31–7.10 (m, 9H, ArH), 6.97 (m, 1H,
ArH), 6.73 (m, 1H, ArH), 6.65 (m, 1H, ArH), 6.40 (m,
1H, ArH), 3.67 (s, 3H, OCH3), 3.39 (s, 3H, OCH3);
13C (75 MHz, CDCl3) d 159.7–110.4 (multiple P-coupled
signals, ArC), 56.1 (OCH3), 54.7 (OCH3); 31P (121
MHz, CDCl3) d 26.1; m/z (% intensity): [MH]+ 515.2
(100); HRMS Calc. for [MH]+ (C34H28O3P) 515.1776.
Found: 515.1765%.
4.5. Synthesis of (R)-2-((trifluoromethanesulfonyl)oxy)-
20-methoxy-1,10-binaphthyl (4) from (7)
To
a solution of (R)-2-((trifluoromethanesulfo-
nyl)oxy)-20-hydroxy-1,10-binaphthyl (4.64 g, 11.1 mmol)
in acetone (40 cm3) was added potassium carbonate
(2.30 g, 16.6 mmol) and methyl iodide (1.04 cm3, 16.7
mmol). The mixture was stirred for 24 h by which time
TLC analysis (silica, dichloromethane:pentane, 3:1)
showed the reaction to be complete. After removal of
solvent, 10% HCl was added until the pH of the solution
was approximately 3. The product was extracted with
ethyl acetate (2 · 75 cm3), washed with water and brine,
and dried over magnesium sulphate. Removal of solvent
yielded a brown oil (4.85 g) which was recrystallised
from ethanol/water to yield white needles (3.06 g,
64%). A further crop of crystals was recovered from
the mother liquor after standing for a few days. m.p.
99–101 ꢁC; 1H (300 MHz, CDCl3) d 8.05 (m, 1H,
ArH), 8.02 (m, 1H, ArH), 7.97 (m, 1H, ArH), 7.88 (m,
1H, ArH), 7.57–7.22 (m, 7H, ArH), 7.00 (m, 1H,
ArH), 3.82 (s, 3H, OCH3).
4.7. Synthesis of (R,R) and (R,S)-2-(anisyl-
phenylphosphino)-20-methoxy-1,10-binaphthyl (10a and
b)
To a solution of [NiCl2(dppe)] (0.183 g, 0.347 mmol)
in DMF (6.5 cm3) was added anisylphenylphosphine
(0.48 g, 2.08 mmol) via a syringe. After heating at
100 ꢁC for 0.5 h,
a
solution of (R)-2-((trif-
luoromethanesulfonyl)oxy)-20-methoxy-1,10-binaphthyl
(1.5 g, 3.47 mmol) and DABCO (1.56 g, 13.9 mmol) in
DMF (10 cm3) was added, causing an immediate colour
change from red to green. After 1 h a further 0.48 g (2.08
mmol) of the secondary phosphine was added. The tem-
perature was maintained at 100 ꢁC for 2 days, after
which a colour change to light brown was apparent.
31P NMR of the solution at this point revealed that
the major components (81% conversion by NMR) were
the desired diastereomers 10a and b.
4.6. Synthesis of (R,R) and (R,S)-2-(anisylphenylphos-
phinyl)-20-methoxy-1,10-binaphthyl (8a and b). Both
diastereomers are prepared in the same manner
To AnPhMOP(O)OH (3a) (480 mg, 0.960 mmol)
and potassium carbonate (528 mg, 3.83 mmol) in
anhydrous acetone (15 cm3) was added methyl iodide
(0.240 mL, 3.83 mmol). The mixture was refluxed
overnight, and then cooled to room temperature, at
which point some of the product precipitated out of
solution. Dichloromethane (50 cm3) was added to
redissolve the precipitate and the solution was filtered
through celite. Removal of the solvent in vacuo and
recrystallisation from acetone yielded white crystals
(520 mg, 75%).
The volatiles were removed in vacuo on a warm water
bath and THF added (40 cm3). The mixture was treated
with an excess (20 cm3, 20 mmol) of 1 M borane–THF
complex to give the corresponding borane adducts.
These were separated from the rest of the reaction mix-
ture by employing a silica column with dichloromethane
as eluent, followed by a second column to separate 10a
from 10b. A sample second column (ethyl acetate:cyclo-
hexane, 1:19) loaded with 253 mg of an approximate 1:1
mixture of the boranes yielded 52 mg (21%) of 10a in the
first fraction, a fraction containing a mixture of the bor-
anes and a second fraction containing 63 mg (25%) of
10b. The column procedure can be repeated on the mid-
dle fraction to give further quantities of both boranes.
4.6.1. (R,R)-AnPhMOP(O)OMe (8a)
m.p. 211–216 ꢁC; [a]D = ꢀ41.9 (c 0.25, CHCl3); IR
(KBr, cmꢀ1) 3060, 2938, 2836, 2361, 1589, 1477, 1271,
1
1182, 1080, 732; H (300 MHz, CDCl3) d 7.89 (m, 2H,
4.7.1. (R,R)-AnPhMOP Æ BH3 (11a)
ArH), 7.80–7.74 (m, 1H, ArH), 7.67–7.60 (m, 2H,
ArH), 7.51–7.45 (m, 3H, ArH), 7.34–6.99 (m, 10H,
ArH), 6.86–6.77 (m, 2H, ArH), 6.69–6.65 (m, 1H,
ArH), 3.57 (s, 3H, OCH3), 3.44 (s, 3H, OCH3); 13C
(126 MHz, CDCl3) d 160.7–111.0 (multiple P-coupled
signals, ArC), 56.0 (OCH3), 55.2 (OCH3); 31P (121
MHz, CDCl3) d 26.9; m/z (% intensity): [MH]+ 515.2
(100); HRMS Calc. for [MH]+ (C34H28O3P) 515.1776.
Found: 515.1785%.
1H (300 MHz, CDCl3) d 7.90–6.59 (m, 21H, ArH),
3.40 (s, 3H, OCH3), 3.33 (s, 3H, OCH3); 31P (121
MHz, CDCl3) d 19.3.
4.7.2. (R,S)-AnPhMOP Æ BH3 (11b)
1H (300 MHz, CDCl3) d 7.90–6.62 (m, 21H, ArH),
3.57 (s, 3H, OCH3), 3.46 (s, 3H, OCH3); 31P (121
MHz, CDCl3) d 19.4.

218
L.J. Higham et al. / Journal of Organometallic Chemistry 690 (2005) 211–219
˚
10a from borane deprotection of 11a (10b is produced
using Mo Ka X-radiation, a = 0.71073 A. It should be
noted that there are two independent but identical mol-
ecules of 8a and acetone in the unit cell. Crystal and
refinement data are given in Table 2. Absorption correc-
tions were based on equivalent reflections and structures
refined against all F 2o data. In 8a, the hydrogen atoms of
the solvent acetone were added at calculated positions
and refined using a riding model. All other hydrogens
were located in the difference fourier map and allowed
to refine freely including isotropic temperature factors.
Anisotropic thermal parameters were refined for all
non-hydrogen atoms. Crystallographic data for the
structural analyses have been deposited with the Cam-
bridge Crystallographic Data Centre [22].
in identical fashion from 11b).
To a dichloromethane solution (1 cm3) of 11a (30 mg,
0.0586 mmol) on a sodium chloride/water bath, was
added dropwise 10 equivalents of trifluoromethanesul-
phonic acid (88 mg, 0.586 mmol). Effervescence was ob-
served, after which the cooling bath was removed. 31P
NMR showed that quantitative deprotection had taken
place without epimerisation. The reaction was worked
up by diluting with dichloromethane (2 cm3) and adding
degassed saturated sodium bicarbonate (2 cm3). The sol-
vent layers were separated and the aqueous phase ex-
tracted twice with dichloromethane (2 · 2 cm3). The
organic portions were combined and washed with de-
gassed water, degassed brine and dried over magnesium
sulphate. The solution was filtered and the solvent re-
moved in vacuo to give 10a (29.2 mg, 100% yield).
Acknowledgement
4.7.3. (R,R)-(+)-AnPhMOP (10a)
1
The authors thank Enterprise Ireland for a Scholar-
ship (E.F.C), the European Commission for a Marie
Curie Development Host Fellowship HPMD-CT-2000-
00053 (L.J.H.) and Johnson Matthey for the loan of me-
tal salts.
[a]D = 83.5 (c 0.82, CHCl3); H (300 MHz, CDCl3) d
7.96–7.80 (m, 4H, ArH), 7.46–7.11 (m, 14H, ArH), 6.81–
6.62 (m, 3H, ArH), 3.50 (s, 3H, OCH3), 3.05 (s, 3H,
OCH3); 13C (126 MHz, CDCl3) d 160.9–109.9 (multiple
P-coupled signals, ArC), 55.1 (OCH3), 54.9 (OCH3); 31
P
(121 MHz, CDCl3) d ꢀ24.60; HRMS Calc. for [MH]+
(C34H28O2P) 499.1827. Found: 499.1811%.
References
4.7.4. (R,S)-(+)-AnPhMOP (10b)
[1] T. Hayashi, Acc. Chem. Res. 33 (2000) 354, and references cited
therein.
[a]D = 72.3 (c 0.415, CHCl3); 1H (300 MHz, CDCl3) d
8.00–7.76 (m, 4H, ArH), 7.50–6.96 (m, 12H, ArH), 6.89–
6.76 (m, 4H, ArH), 3.59 (s, 3H, OCH3), 3.46 (s, 3H,
OCH3); 13C (126 MHz, CDCl3) d 161.1–110.0 (multiple
[2] The following examples cite the use of MOPs in catalysis which
resulted in low ee values: (a) M. Sakai, M. Ueda, N. Miyaura,
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(C34H28O2P) 499.1827. Found: 499.1829%.
´
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romethane (10 cm3) was added [Rh2Cl2(CO)4] (0.010 g,
0.026 mmol). The resulting orange solution was stirred
for 0.5 h and then the volatiles were removed in vacuo.
Further dichloromethane was added (10 cm3), the solu-
tion stirred for 0.5 h again and the volatiles were re-
moved once more to give an orange solid. The yield
was quantitative. 31P (121 MHz, CDCl3) d 47.1 ppm
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1
(d, JP–Rh = 159.3 Hz). m/z 630 [MH+ ꢀ Cl]; HRMS
´
[12] A. Togni, C. Breutel, M.C. Soares, N. Zanetti, T. Gerfin, V.
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630.0800%.
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elution by column chromatography, i.e., 8a precedes 8b and 10a
precedes 10b.
4.9. X-ray crystal structures of (R,R) and (R,S)-
anisylphenylMOP oxides (8a and b)
X-ray diffraction experiments on 8a and b were car-
ried out at 100 K on a Bruker SMART diffractometer
[16] P. Dotta, P.G.A. Kumar, P.S. Pregosin, A. Albinati, S. Rizzato,
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[22] Crystallographic data for the structural analysis has been depos-
ited with the Cambridge Crystallographic Data Centre, CCDC
No. 242810 for 8a (R,R) and 242809 for 8b (R,S). Copies of this
information may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
336033 or e-mail: deposit@ccdc.cam.ac.uk or www.ccdc.cam.
ac.uk/conts/retrieving.html.
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