Asymmetric synthesis of bis(tertiary arsines): Highly stereoselective alkylations of diastereomers of a chiral phosphine-stabilized bis(arsenium triflate)

Article abstract of DOI:10.1021/ic900797y

The addition of organolithium reagents to an equilibrating mixture of diastereomers of a phosphine-stabilized 1, 2-ethanediylbis(phenylarsenium triflate) containing chiral arsenic stereocenters and an enantiomerically pure, atropisomeric tertiary phosphep

Full text of DOI:10.1021/ic900797y

7482 Inorg. Chem. 2009, 48, 7482–7490
DOI: 10.1021/ic900797y
Asymmetric Synthesis of Bis(tertiary arsines): Highly Stereoselective Alkylations
of Diastereomers of a Chiral Phosphine-Stabilized Bis(arsenium triflate)
Michelle L. Weir, Ian A. Cade, Nathan L. Kilah, Xiangting Zhou, and S. Bruce Wild*
Research School of Chemistry, Institute of Advanced Studies, Australian National University, Canberra,
ACT 0200, Australia
Received April 23, 2009
The addition of organolithium reagents to an equilibrating mixture of diastereomers of a phosphine-stabilized 1,
2-ethanediylbis(phenylarsenium triflate) containing chiral arsenic stereocenters and an enantiomerically pure, atrop-
isomeric tertiary phosphepine derived from lithiated (aR)-2,20-dimethyl-1,10-binaphthalene generates unequal
mixtures of diastereomers and enantiomers of chelating 1,2-ethanediylbis(tertiary arsines), chiral at arsenic, with
liberation of the (aRP)-phosphepine. Thus, the addition of methyllithium in diethyl ether at -95 °C to a dichloromethane
solution of the complex (R*As,R*As)-(()/(R*As,S*As)-1,2-[(R3P)PhAsCH2CH2AsPh(PR3)](OTf)2, where R3P is (aRP)-
[2-(methoxymethyl)phenyl]phosphepine, generates (R*As,R*As)-(()-1,2-ethanediylbis(methylphenylarsine) in 78%
diastereoselectivity and 95% enantioselectivity in favor of the (RAs,RAs) enantiomer. Under similar conditions, the
addition of n-butyllithium in hexanes to a solution of the bis(phosphepine-stabilized)-diarsenium triflate at -95 °C gives
the corresponding (R*As,R*As)-(()-1,2-ethanediylbis[(n-butyl)phenylarsine) in 77% diastereoselectivity and 93%
enantioselectivity in favor of the (RAs,RAs) enantiomer.
Introduction
merically pure compounds in the natural pool.3 Never-
theless, there are reactions that proceed with greater
efficiency when the phosphorus stereocenter is itself
chiral.4 There are also examples of asymmetric syntheses
where As-chiral tertiary arsines out-perform the phos-
phorus isosteres.5 In view of our long-standing interest
in the synthesis and resolution of arsines chiral at
arsenic,6 we have now embarked on a program con-
cerned with the asymmetric synthesis of chiral tertiary
arsines.7 Tertiary arsines are less air-sensitive than ter-
tiary phosphines and are frequently easier to synthesize
and liberate from metal complexes used for their resolu-
tion, which is the current preferred method for the
synthesis of P- and As-chiral phosphines and arsines of
high enantiomeric purity.6
Chiral tertiary phosphines are of great importance as
auxiliaries in homogeneous, metal-catalyzed asymmetric
syntheses. Although the pioneering work in the field
focused on the use of P-chiral mono- and diphosphines,1,2
the difficulty of synthesizing and resolving tertiary phos-
phines chiral at phosphorus soon led to investigations of
the use of chelating C2-bis(diphenylphosphines) in which
the chirality resided in a spacer group between the two
phosphine groups and was transmitted to the coordinated
substrate by a dissymmetric edge-face array of two
C2-related pairs of phenyl groups on the phosphorus
atoms. Apart from the high enantioselectivities achieved
with many of the C2-bis(diphenylphosphines), the chief
advantage of the bis(diphenylphosphines) was their
ready preparation from C2-diols derived from enantio-
We recently reported the asymmetric synthesis of
(S)-(+)-n-butylmethylphenylarsine by the addition of n-
butyllithium at low temperature to a dichloromethane solu-
tion of a phosphine-stabilized methylphenylarsenium salt in
*To whom correspondence should be addressed. E-mail: sbw@rsc.anu.
edu.au. Fax: +61 2 6125 0750. Phone: +61 2 6125 4236.
(1) (a) Horner, L.; Siegel, H.; Buthe, H. Angew. Chem., Int. Ed. Engl.
::
1968, 7, 942. (b) Knowles, W. S.; Sabacky, M. J. Chem. Commun. (London)
1968, 1445. (c) Knowles, W. S.; Sabacky, M. J.; Vineyard, B. D. J. Chem.
Soc., Chem Commun. 1972, 10–11.
(2) Vineyard, B. D.; Knowles, W. S.; Sabacky, M. J.; Bachman, G. L.;
Weinkauff, D. J. J. Am. Chem. Soc. 1977, 99, 5946–5952.
ꢀ
(4) Crepy, K. V. L.; Imamoto, T. Top. Curr. Chem. 2003, 229, 1–40.
(5) (a) Allen, D. G.; Wild, S. B.; Wood, D. L. Organometallics 1986, 5,
1009–1015. (b) Mokhlesur Rahman, A. F. M.; Wild, S. B. J. Mol. Catal.
1987, 39, 155–160.
(3) (a) Kagan, H. B.; Dang, T-. P. J. Am. Chem. Soc. 1972, 6429–6433. (b)
Fryzuk, M. D.; Bosnich, B. J. Am. Chem. Soc. 1977, 99, 6262–6267. (c)
Burke, M. J.; Feaster, J. E.; Nugent, W. A.; Harlow, R. L. J. Am. Chem. Soc.
1993, 115, 10125–10138. (d) Noyori, R. Asymmetric Catalysis in Organic
Synthesis; Wiley: New York, 1994.
(6) (a) Wild, S. B. In The Chemistry of Organic Arsenic, Antimony and
Bismuth Compounds; Patai, S., Ed.; John Wiley and Sons: Chichester, 1994;
Chapter 3. (b) Wild, S. B. Coord. Chem. Rev. 1997, 166, 291–311.
(7) Coote, M. L.; Krenske, E. H.; Porter, K. A.; Weir, M. L.; Willis, A. C.;
Zhou, X.; Wild, S. B. Organometallics 2008, 27, 5099–5107.
r
pubs.acs.org/IC
Published on Web 06/25/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 15, 2009 7483
MPF6
which the phosphine was an enantiomerically pure phosphe-
pine derived from (aR)-1,10-binaphthol, (aRP)-1. Thus, (SAs)-
(n-butyl)methylphenylarsine was synthesized in high yield
and 85% enantioselectivity (70% enantiomeric excess) by
the addition of n-butyllithium to a dichloromethane solution
of (aRP,RAs)/(aRP,SAs)-[1fAsMePh]PF6 at -95 °C.7 Here
we report our results concerning the asymmetric synthesis of
As-chiral 1,2-ethanediylbis(tertiary arsines) by the addition
of organolithium reagents to phosphine-stabilized 1,2-etha-
nediylbis(phenylarsenium triflates).
½R3PfAsR2ꢀPF6
ð1Þ
ð2Þ
H2O
Me3SiOTf
R3P þ ClAsR2
½R3PfAsR2ꢀOTf
-Me3SiCl
TlPF6
R3P þ ClAsR2
½R3PfAsR2ꢀPF6 ð3Þ
-TlCl
Angular, six-electron, arsenium ions of the type
R1R2As+ are prochiral: addition of a phosphine to
the pro-R or pro-S face of the unsymmetrical arsenium
ion will generate a phosphine-stabilized arsenium cation
of the type (()-[R3PfAsR1R2]+, which has a structure
based on the trigonal pyramid in which the arsenic-
carbon atoms of the R groups of the arsenium ion and
the lone pair of electrons occupy the base and the
phosphine-P atom the apex.8 The absolute configurations
of the enantiomers of the chiral cation can be assigned by
viewing the structure down the axis containing the ligand
of lowest Cahn-Ingold-Prelog (CIP) priority (the lone
pair of electrons, priority 4) and observing the direction of
rotation of the remaining ligands of priorities 1 f 3 at the
corners of the triangular face at the base of the pyramid.17
Furthermore, since the phosphorus-arsenic bond in a
phosphine-stabilized arsenium complex is labile, the en-
antiomers of the chiral complex will be in equilibrium
through dissociation of the phosphine.8 For (aRP,RAs)/
(aRP,SAs)-[1fAsMePh]PF6, the slow exchange limit for
phosphine exchange is reached at -70 °C, as determined
by variable temperature 1H NMR spectroscopy based on
the observation of 31P coupling to the arsenic-methyl
protons.7
The phosphine in a phosphine-stabilized arsenium
complex of the type (()-[R3PfAsR1R2]+ is readily dis-
placed by the n-butyl anion in an SN2-type substitution
reaction that results in the synthesis of a chiral tertiary
arsine (with displacement of the phosphine) having the
configuration at arsenic that corresponds to the config-
uration of the enantiomer of the substrate phosphine-
stabilized arsenium cation.7 In the reaction of (aRP,RAs)/
(aRP,SAs)-[1fAsMePh]PF6 with n-butyllithium, how-
ever, the enantioselectivity of the reaction is less than
the diastereoselectivity of coordination of the phosphine
at the reaction temperature (85% vs 97%, respectively),
apparently because of indiscriminate attack of the nu-
cleophile on the more reactive, dissociated methylphenylar-
senium ion.7
Results and Discussion
General Considerations and Methodology. Phosphine-
stabilized arsenium hexafluorophosphates are usually
air- and moisture-stable solids that can be prepared in a
two-phase system in which a dichloromethane solution
of a tertiary phosphine and a secondary iodoarsine is
exposed to aqueous ammonium or potassium hexafluor-
ophosphate (eq 1).8 When the complexes or reactants
are moisture sensitive, however, phosphine-stabilized
arsenium complexes can be prepared by the addition of
trimethylsilyl triflate (eq 2)9-11 or thallium(I) hexafluor-
ophosphate (eq 3)12 to a solution of a secondary chlor-
oarsine containing the phosphine.9 These methods are
expedient routes to phosphine-stabilized phosphe-
nium,13 stibenium,12,14 and bismuthenium12 salts, as
well as arsine-stabilized arsenium,9,15 stibenium,16 and
bismuthenium16 salts.
R3P þ IAsR2
h
½R3PfAsR2ꢀI
CH2Cl2
(8) Porter, K. A.; Willis, A. C.; Zank, J.; Wild, S. B. Inorg. Chem. 2002, 41,
6380–6386.
(9) Kilah, N. L.; Weir, M. L.; Wild, S. B. Dalton Trans. 2008, 2480–2486.
(10) Burford, N.; Ragogna, P. J.; Sharp, K.; McDonald, R.; Ferguson, M.
J. Inorg. Chem. 2005, 44, 9453–9460.
ꢀ
(11) Payrastre, C.; Madaule, Y.; Wolf, J. G.; Kim, T. C.; Mazieres, M-.
R.; Wolf, R.; Sanchez, M. Heteroatom. Chem. 1992, 3, 157–162.
(12) Kilah, N. L.; Petrie, S.; Stranger, R.; Wielandt, J. W.; Willis, A. C.;
Wild, S. B. Organometallics 2007, 26, 6106–6113.
(13) (a) Burford, N.; Cameron, T. S.; Ragogna, P. J.; Ocando-Mavarez,
E.; Gee, M.; McDonald, R.; Wasylishen, R. E. J. Am. Chem. Soc. 2001, 123,
7947–7948. (b) Burford, N.; Ragogna, P. J.; McDonald, R.; Ferguson, M. J.
Am. Chem. Soc. 2003, 125, 14404–14410. (c) Burford, N.; Herbert, D. E.;
Ragogna, P. J.; McDonald, R.; Ferguson, M. J. Am. Chem. Soc. 2004, 126,
17067–17073. (d) Burford, N. C.; Dyker, C. A.; Decken, A. Angew. Chem.,
Int. Ed. 2005, 44, 2364–2367. (e) Weigand, J. J.; Riegel, S. D.; Burford, N.;
Decken, A. J. Am. Chem. Soc. 2007, 129, 7969–7976. (f) Slattery, J. M.; Fish,
C.; Green, M.; Hooper, T. N.; Jeffery, J. C.; Kilby, R. J.; Lynam, J. M.;
McGrady, J. E.; Pantazis, D. A.; Russell, C. A.; Willans, C. E. Chem. Eur. J.
2007, 13, 6967–6974. (g) Dyker, C. A.; Burford, N. Chem. Asian J. 2008, 3,
28–36. (h) Carpenter, Y. -Y.; Dyker, C. A.; Burford, N.; Lumsden, M. D.;
Decken, A. J. Am. Chem. Soc. 2008, 130, 15732–15741.
A key element in the diastereofacial discrimination of the
prochiral methylphenylarsenium ion by (aRP)-1 is the
2-(methoxymethyl)phenyl substituent, the oxygen atom of
which interacts with both the arsenic and phosphorus atoms
and hinders rotation around the arsenic-phosphorus bond.
This anchimeric interaction weakens the arsenic-phos-
phorus bond by a destabilizing chelate effect, which is
indicated by a lengthening of the appropriate bonds in the
complexes containing 2-(methoxymethyl)phenyl-substi-
tuted phosphines.7,9 Detailed NMR investigations and
density functional theory (DFT) calculations on the diaster-
(14) Wielandt, J. W.; Kilah, N. L.; Willis, A. C.; Wild, S. B. Chem.
Commun. 2006, 3679–3680.
(15) Conrad, E.; Burford, N.; McDonald, R.; Ferguson, M. Inorg. Chem.
2008, 47, 2952–2954.
(16) Conrad, E.; Burford, N.; McDonald, R.; Ferguson, M. J. J. Am.
Chem. Soc. 2009, 131, 5066–5067.
(17) Cahn, R. S.; Ingold, C.; Prelog, V. Angew. Chem., Int. Ed. Engl. 1966,
5, 385–415.

7484 Inorganic Chemistry, Vol. 48, No. 15, 2009
Weir et al.
Scheme 1
eomers (aRP,RAs)/(aRP,SAs)-[1fAsMePh]+ indicated a
very high propensity of (aRP)-1 for coordination to the
pro-S face of the methylphenylarsenium ion.7
Model Complexes. (a). Syntheses. The addition of
trimethylsilyl triflate to a dichloromethane solution
of (R*As,R*As)-(()/(R*As,S*As)-1,2-ethanediylbis(chloro-
phenylarsine), (R*As,R*As)-(()/(R*As,S*As)-2, contain-
ing triphenylphosphine or methyldiphenylphosphine
produced the corresponding bis(phosphine-stabilized)
diarsenium triflates (R*As,R*As)-(()/(R*As,S*As)-3 or -
4 after evaporation of the solvent and trimethylsilyl
chloride byproduct (Scheme 1). The salts crystallized
readily from dichloromethane by the addition of diethyl
ether, but were sensitive to hydrolysis, unlike closely
related monoarsenium salts.8
Figure 1. Variable temperature 31P{H} NMR spectra (121.47 MHz) in
dichloromethane-d2 of (R*As,R*As)-(()/(R*As,S*As)-4.
(b). NMR Spectroscopy. Because of the lability of the
As-P bonds in (R*As,R*As)-(()/(R*As,S*As)-3 and -4,
the complexes exist in solution as equilibrium mixtures of
two diastereomers (Scheme 2). At elevated temperatures,
As-P bond dissociation in the complexes is fast on the
NMR time-scale and the resonances for the individual
diastereomers are not distinguishable, but as the tempera-
ture is lowered the averaged resonances broaden and split
into the resonances of the individual diastereomers at the
slow exchange limit. The 31P{1H} NMR spectra of (R*As,
R*As)-(()/(R*As,S*As)-3 and -4 in dichloromethane-d2
at 25 °C consist of sharp singlet peaks at 17.45 and 12.91
ppm, respectively. Triphenylphosphine is a weak ligand
for arsenium ions18 and at -95 °C only minor splitting of
the 31P{1H} NMR peak for the diastereomers (R*As,
R*As)-(()/(R*As,S*As)-3 is evident. Alkylphosphines
form more stable adducts, however, and the 31P{1H}
NMR resonance for (R*As,R*As)-(()/(R*As,S*As)-4
broadens and coalesces as the temperature is lowered
and separates into two peaks of equal intensity with base-
line separation at -50 °C that correspond to the indi-
vidual diastereomers (Figure 1). By substitution of these
Scheme 2
values into the equation ΔGq =19.14 Tc (10.32+log Tc/Kc),
c
where Tc is the coalescence temperature and Kc =
2.22 Δv s-1 is the rate of site exchange in hertz at the
slow exchange limit,19 the free energy of activation for
phosphine dissociation in (R*As,R*As)-(()/(R*As,S*As)-4
is calculated tobe about 55kJ mol-1. This value for ΔGq is
similar to the value calculated for phosphine dissociation
c
(18) (a) Coates, G. E.; Livingstone, J. G. Chem. Ind. 1958, 1366.
(b) Braddock, J. M. F.; Coates, G. E. J. Chem. Soc. 1961, 3208–3211.
(19) (a) Watson, A. A.; Willis, A. C.; Wild, S. B. J. Organomet. Chem.
1993, 445, 71–78. (b) Eliel, E. L.; Wilen, S. H.; Mander, L. N. Stereochem-
istry of Organic Compounds; John Wiley and Sons, Inc.: New York, 1994.
in (()-[PhMe2PfAsMePh]OTf in the same solvent,
namely, 60 kJ mol-1 9
.
(c). Crystal Structure. The diastereomer (R*As,S*As)-
4 crystallizes from dichloromethane-diethyl ether by an

Article
Inorganic Chemistry, Vol. 48, No. 15, 2009 7485
is replaced by a ligand (the metal) of CIP priority 1.] The
31P{1H} NMR spectrum of the mixture of C2 diastereomers
of the complex will consist of two singlets (along with
the satellites due to the coupling with the 195Pt nuclei of
33.8% abundance23); the C1 diastereomer of the complex
exhibits in its 31P{1H} NMR spectrum a pair of doublets
for the two non-equivalent phosphorus nuclei. The 31P{1H}
NMR spectrum in dichloromethane-d2 of the mixture
of diastereomers (SP,SP)(RAs,RAs)/(SP,SP)(SAs,SAs)/(SP,
SP)(RAs,SAs)-7, which were obtained from the reaction of
(R*As,R*As)-(()/(R*As,S*As)-5 (1/1) with (SP,SP)-6 in
dichloromethane, is shown in Figure 3(a). The stereo-
isomeric composition of (R*As,R*As)-(()/(R*As,S*As)-
1,2-ethanediylbis[(n-butyl)phenylarsine], (R*As,R*As)-(()/
(R*As,S*As)-8, was determined in the same manner;
thus, the reaction of (R*As,R*As)-(()/(R*As,S*As)-8, which
was prepared by a modification of literature procedures,24
with (SP,SP)-6 in dichloromethane resulted in the diastereo-
meric mixture (SP,SP)(RAs,RAs)/(SP,SP)(SAs,SAs)/(SP,SP)-
(RAs,SAs)-9 (Scheme 3, R = n-Bu), as indicated in the
31P{1H} NMR spectrum of the mixture shown in Figure 4(a).
The diastereomers of (R*As,R*As)-(()/(R*As,S*As)-5
were separated by flash column chromatography of the
complexes (R*As,R*As)-(()/(R*As,S*As)-[Pd(5)Cl2], which
were prepared by the reaction of the ligand with palladium
(II) chloride in methanol containing excess lithium chloride.25
The complex (R*As,R*As)-(()-[Pd(5)Cl2] was the first
compound to be eluted from the silica column with dichlor-
omethane-tetrahydrofuran (95/5 v/v). The racemic diaster-
eomer of the diarsine, (R*As,R*As)-(()-5, was liberated from
(R*As,R*As)-(()-[Pd(5)Cl2] by treatment with an aqueous
sodium cyanide solution and was distilled with retention of
configuration at arsenic, bp = 168-170 °C (0.2 mmHg)
[Lit.25 156-158 °C (0.1 mmHg)].
The chiral ligand (R*As,R*As)-(()-5 was resolved by
complexation with the enantiomerically pure platinum com-
plex (SP,SP)-6; the two diastereomers resulting, (SP,SP)(RAs,
RAs)- and (SP,SP)(SAs,SAs)-7, were separated by fractional
crystallization from methanol by the addition of diethyl
ether. After two recrystallizations of the mixture, the less-
soluble diastereomer was obtained as colorless needles that
exhibited in chloroform-d a single resonance at 39.48 ppm in
the 31P{1H} NMR spectrum. The identity and absolute
configuration of the diastereomer was determined by a
single-crystal X-ray structure analysis. The molecular struc-
ture of the cation of the complex is shown in Figure 5. The
absolute configuration of the arsenic stereocenters in the
complex are (RAs,RAs) based on the known absolute con-
figuration of the resolving complex (SP,SP)-6 and refine-
ment of the Flack parameter. Thus, the free diarsine has
the (SAs,SAs) configuration.
Figure 2. Structure of cation of (R*As,S*As)-4 (hydrogen atoms omitted
˚
for clarity) showing 30% probability ellipsoids. Selected bond lengths (A)
and interbond angles (deg): As1-P1 = 2.3239(12), As1-C1 = 1.986(4),
As1-C2 = 1.958(4), P1-C8 = 1.798(5), P1-C9 = 1.794(4), P1-C15 =
1.796(5), C1-C1i = 1.527(8), P1-As1-C1 = 94.29(15), P1-As1-C2 =
97.22(13), C1-As1-C2 = 100.15(18), As1-P1-C8 = 113.81(17), As1-
P1-C9 = 106.45(15), As1-P1-C15 = 109.24(17), C1i-C1-As1 =
109.6(4).
asymmetric transformation of the second kind19b as
colorless prisms in the monoclinic space-group P21/c;
the structure of the cation is shown in Figure 2. The
crystallographic asymmetric unit consists of half of the
bis(phosphine-stabilized) diarsenium dication and one
triflate ion related by a crystallographic inversion center;
the triflate counterion is disordered. The As-P distance
˚
of 2.3239(12) A in the complex is longer than the sum of
the covalent radii for the two main group elements,
20
namely, 2.29 A, and compares closely with the value
˚
˚
of 2.3402(8) A measured for the corresponding bond in
(()-[PhMe2PfAsMePh]OTf.9 The C1-As1-C2 angles
in the cation are 100.15(18)°, and the As-P bonds are
almost orthogonal to the plane of the arsenium ion,
namely, P1-As1-C1 = 94.29(15)° and P1-As1-C2 =
97.22(13)°.
Enantiomeric Purity and Absolute Configuration. (a).
Reference Compounds. The stereoisomeric composition
of (R*As,R*As)-(()/(R*As,S*As)-1,2-ethanediylbis(methyl-
phenylarsine), (R*As,R*As)-(()/(R*As,S*As)-5, was deter-
mined by the reaction of ligand mixture, which was
prepared by a modification of the literature synthesis,21
with enantiomerically pure (SP,SP)-[Pt(diphos)(OTf)2],
(SP,SP)-6;22 the products of this facile displacement reac-
tion are the diastereomeric salts (SP,SP)(RAs,RAs)- and (SP,
SP)(SAs,SAs)-7, which are derived from (R*As,R*As)-(()-5
and have C2 symmetry, and (SP,SP)(RAs,SAs)-7, which is
derived from (R*As,S*As)-5 and has C1 symmetry
(Scheme 3, R=Me). [Note that coordination of an
As-chiral arsine to a metal is stereospecific: the apparent
inversion of configuration that takes place at arsenic when a
chiral arsine coordinates to an element of higher atomic
number than 12 is a consequence of the Cahn-Ingold-
Prelog (CIP) rules.17,19b Upon coordination to the palla-
dium, the lone pair on the free arsine of CIP priority 4
The diastereomers of the bis[(n-butyl)phenylarsine],
(R*As,R*As)-(()/(R*As,S*As)-8, could not be separated by
flash chromatography of the complex (R*As,R*As)-(()/
(R*As,S*As)-[Pd(8)Cl2] under conditions similar to those
used for the separation of the bis(methylphenylarsine).26
(23) Akitt, J. W.; Mann, B. E. NMR and Chemistry, 4th ed.; Stanley
Thornes: Cheltenham, 2000, pp 3-4.
(24) Chatt, J.; Mann, F. G. J. Chem. Soc. 1939, 610–615.
(25) Bosnich, B.; Wild, S. B. J. Am. Chem. Soc. 1970, 92, 459–464.
(26) The diastereomers of (R*As,R*As)-(()/(R*As,S*As)-8 can be recov-
ered following tedious mechanical separation of the complexes (R*As,R*As)-(()/
(R*As,S*As)-[Pd(8)Cl2].21
(20) Blom, R.; Haaland, A. J. Mol. Struct. 1985, 128, 21–27.
(21) Chatt, J.; Mann, F. G. J. Chem. Soc. 1939, 1622–1634.
(22) Appelt, A.; Ariaratnem, V.; Willis, A. C.; Wild, S. B. Tetrahedron:
Asymmetry 1990, 1, 9–12.

7486 Inorganic Chemistry, Vol. 48, No. 15, 2009
Weir et al.
Figure 3. 31P{1H} NMR spectra (121.47 MHz, 25 °C) spectra in dichloromethane-d2 of the diastereomers (SP,SP)(RAs,RAs)/(SP,SP)(SAs,SAs)/(SP,SP)(RAs
,
SAs)-7 arising from the reaction of (R*As,R*As)-(()/(R*As,S*As)-5 with a stoichiometric amount of the reference complex (SP,SP)-6 (a) and the
corresponding spectrum resulting from the asymmetric synthesis (b).
Scheme 3
Thus, the configuration of the major stereoisomer of (R*As,
R*As)-(()/(R*As,S*As)-8 arising from the asymmetric
synthesis was assumed to be the same as that observed in
the synthesis of the bis(methylphenylarsine) and is in agree-
ment with previous results concerning alkylations of a closely
related mono(phosphepine-stabilized) arsenium complex.7
Bis(chiral phosphine-stabilized) Diarsenium Com-
plexes. (a). Synthesis. The bis(phosphine-stabilized) dia-
rsenium salt (aRP)(RAs,RAs)(aRP)/(aRP)(SAs,SAs)(aRP)/
(aRP)(RAs,SAs)(aRP)-10 was isolated in 65% yield from
the reaction between the phosphepine (aRP)-1 (2.1 equiv),
(R*As,R*As)-(()/(R*As,S*As)-2 (1 equiv), and trimethyl-
silyl triflate (2.1 equiv) in dichloromethane (Scheme 4).
The moisture-sensitive salt (aRP)(RAs,RAs)(aRP)/(aRP)
(SAs,SAs)(aRP)/(aRP)(RAs,SAs)(aRP)-10 crystallized from
the equilibrating mixture of diastereomers in 65% yield as
fine, feather-like clumps of needles from dichloro-
methane-diethyl ether having mp = 240-242 °C and
[R]2D5 = +76 (c 1.0, CH2Cl2). A number of attempts at
growing crystals of the complex suitable for X-ray crystal-
lography were unsuccessful.
(b). NMR Spectra. The 31P{1H} NMR spectrum of
(aRP)(RAs,RAs)(aRP)/(aRP)(SAs,SAs)(aRP)/(aRP)(RAs,SAs)-
(aRP)-10 in dichloromethane-d2 at 25 °C contains three
overlapping peaks between 39.6 and 40.2 ppm and a
singlet at 17.8 ppm that correspond to a mixture of the
three diastereomers of the complex (Scheme 5). On cool-
ing the solution, the intensity of the peak in the spectrum
at 17.8 ppm decreased and at -25 °C the overlapping
peaks at 39.6 and 40.0 ppm had coalesced. At -95 °C, an

Article
Inorganic Chemistry, Vol. 48, No. 15, 2009 7487
Figure 4. 31P{1H} NMR spectra (121.47 MHz, 25 °C) spectra in chloroform-d showing the three diastereomers of (SP,SP)(RAs,RAs)/(SP,SP)(SAs,SAs)/
(SP,SP)(RAs,SAs)-9 arising from the reaction of (R*As,R*As)-(()/(R*As,S*As)-8 with a stoichiometric amount of the reference complex (SP,SP)-6 (a) and the
corresponding spectrum resulting from asymmetric synthesis (b).
Scheme 4
diastereomer in large excess (ca. 90%), together with
several smaller peaks corresponding to the two other
two diastereomers (Figure 6). Comprehensive NMR
spectroscopic investigations and DFT calculations on
the complex (aRP,RAs)/(aRP,SAs)-[1fAsMePh]PF6,
which crystallized by an asymmetric transformation of
the second kind as the (aRP,SAs) diastereomer, indicated
that the (aRP)-phosphepine preferentially binds to the
pro-S face of the methylphenylarsenium ion.7 On the
basis of this observation, it was reasonable to assume
that the diastereomer in large excess in the diarsenium
system was (aRP)(SAs,SAs)(aRP)-10.
Figure 5. Structure of the cation (SP,SP)(RAs,RAs)-7 (hydrogen atoms
omitted for clarity). Ellipsoidsshow30% probability levels. Selectedbond
lengths (A) and interbond angles (deg): Pt1-P2 = 2.2704(10), Pt1-P3 =
2.2810(9), Pt1-As4 = 2.4307(4), Pt1-As5 = 2.4139(4), P2-C20 =
1.803(4), P2-C21 = 1.808(4), P2-C27 = 1.820(4), P3-C30 = 1.800(4),
P3-C31 = 1.806(4), P3-C37 = 1.931(4), As4-C40 = 1.921(5), As4-
C41 = 1.912(4), As4-C47 = 1.963(5), As5-C50 = 1.914(4), As5-
C51 = 1.910(4), As5-C57 = 1.963(4), P2-Pt1-P3 = 86.80(4), P2-
Pt1-As4 = 95.06(3), P3-Pt1-As5 = 95.34(3), As4-Pt1-As5 = 83.821
(14), P2-Pt1-As5 = 172.65(3), P3-Pt1-As4 = 171.69(3).
˚
(b). Stereoselective Synthesis of (RAs,RAs)-5. A solu-
tion of methyllithium (2.2 equiv, 1.6 M in diethyl ether)
was added to a solution of (aRP)(RAs,RAs)(aRP)/(aRP)
intense peak was observed in the spectrum at 39.23 ppm,
which was consistent with the presence of a single C2

7488 Inorganic Chemistry, Vol. 48, No. 15, 2009
Weir et al.
Scheme 5
(SAs,SAs)(aRP)/(aRP)(RAs,SAs)(aRP)-10 (1 equiv) in di-
chloromethane at -95 °C. [Dichloromethane does not
appreciably react with alkyllithium reagents at tempera-
tures below -74 °C.27] After about 5 min, water was
added to the reaction mixture, and the cooling bath was
removed. The stereoselectivity of the nucleophilic addi-
tions at the two prochiral arsenium stereocenters in the
complex under these conditions was determined by reac-
tion of the resulting diarsine, (R*As,R*As)-(()/(R*As,
S*As)-5, with the enantiomerically pure platinum
complex (SP,SP)-6 (after treatment of the reaction mix-
ture with borane dimethyl sulfide to deactivate the phos-
phepine coordination to the platinum) (Scheme 5, R = Me).
Integration of the peaks in the 31P{1H} NMR spectrum of
the resulting complex gave the following result for the
synthesis: (SP,SP)(RAs,RAs)-7:(SP,SP)(RAs,SAs)-7:(SP,SP)
(SAs,SAs)-7 = 4:22:74, Figure 3(b). Thus, the stereoselec-
tivity of the synthesis of the diarsine (R*As,R*As)-(()/
(R*As,S*As)-5 is 78% (R*As,R*As) diastereomer and 22%
(R*As,S*As) diastereomer, the former consisting of 95%
of the (RAs,RAs) enantiomer.
(c). Stereoselective Synthesis of (RAs,RAs)-8. By the
procedure described above for the synthesis of the 1,2-
ethanediylbis(methylphenylarsine), the bis[(n-butyl)phe-
nylarsine] (R*As,R*As)-(()/(R*As,S*As)-8 was synthe-
sized by the addition of n-butyllithium (2.2 equiv, 1.5 M
in hexanes) to a dichloromethane solution of (aRP)(RAs,
RAs)(aRP)/(aRP)(SAs,SAs)(aRP)/(aRP)(RAs,SAs)(aRP)-10
at -95 °C (Scheme 5, R = n-Bu). After workup and
complexation with (SP,SP)-6, the 31P{1H} NMR spectrum
shown in Figure 4(b) was obtained; integration of the
resonances gave (SP,SP)(RAs,RAs)-9:(SP,SP)(RAs,SAs)-9:
(SP,SP)(SAs,SAs)-9 = 5:23:72. Thus, the diastereoselectiv-
ity of the n-butyllithium addition to the (aRP)-phosphe-
pine-stabilized bis(arsenium triflate) (10) leading to (R*As,
R*As)-(()/(R*As,S*As)-8 is 77% in favor of the (R*As,
R*As) diastereomer, which, inturn, isenrichedto the extent
of 93% in the (RAs,RAs) enantiomer. [The enantioselec-
tivity of the synthesis of (SAs)-As(n-Bu)MePh was 85% by
a similar route.7 The opposite configuration at arsenic
obtained for the asymmetric synthesis of (SAs)-As(n-Bu)
MePh to the (RAs,RAs)-diarsines is due to a reversal of the
CIP priority of the nucleophile when proceeding from the
Figure 6. Variable temperature 31P{H} NMR spectra (121.47 MHz) in
dichloromethane-d2 of (aRP)(RAs,RAs)(aRP)/(aRP)(SAs,SAs)(aRP)/(aRP)-
(RAs,SAs)(aRP)-10.
::
(27) Kobrich, G.; Merkle, H. R. Chem. Ber. 1966, 99, 1782–1792.

Article
Inorganic Chemistry, Vol. 48, No. 15, 2009 7489
monoarsine to the diarsine, rather than an inversion of
configuration.]
(77%); mp = 136-138 °C. Anal. Calcd for C42H40As2-
F6O6P2S2: C, 48.94; H, 3.91. Found: C, 49.21; H, 3.98. 1H
2
NMR (CDCl3): δ 2.33 (d, JHP = 13.2 Hz, 6H, PCH3), 2.47
(s, br, 4H, AsCH2), 7.15-7.68 (m, 30H, ArH). 31P{1H} NMR
(CDCl3): δ 12.91 (s).
Conclusion
The first bis(phosphine-stabilized) diarsenium salts have
been synthesized by the addition of trimethylsilyl triflate to
anhydrous solutions of the appropriate tertiary phosphine
and (R*As,R*As)-(()/(R*As,S*As)-1,2-ethanediylbis(chloro-
phenylarsine) in dichloromethane. The addition of methyl-
and n-butyllithium reagents to solutions of a bis[(aRP)-
phosphepine-stabilized] 1,2-ethanediylbis(phenylarsenium
triflate) at -95 °C in dichloromethane results in stereoselec-
tive syntheses of the corresponding 1,2-ethanediylbis(tertiary
arsines): the methyllithium addition gave (R*As,R*As)-(()-
1,2-ethanediylbis(methylphenylarsine) with 78% diastereos-
electivity and 95% enantioselectivity in favor of the (RAs,RAs)
enantiomer; the addition of n-butyllithium to the diarsenium
salt under similar conditions gave (R*As,R*As)-(()-1,2-ethane-
diylbis[(n-butyl)phenylarsine] with 77% diastereoselectivity
and 93% enantioselectivity for the same enantiomer.
(aRP)(RAs,RAs)(aRP)/(aRP)(SAs,SAs)(aRP)/(aRP)(RAs,SAs)(aRP)-
1,2-Ethanediylbis{[(4-(2-methoxymethyl)phenyl)-4,5-dihydro-3H-di-
naphtho(2,1-c;10,20-e)phosphepine-P]phenylarsenium triflate},
(aRP)(RAs,RAs)(aRP)/(aRP)(SAs,SAs)(aRP)/(aRP)(RAs,SAs)(aRP)-10.
(R*As,R*As)-(()/(R*As,S*As)-2 (0.2 g, 0.6 mmol), (aRP)-1
(0.6 g, 1.2 mmol), Me3SiOTf (0.3 g, 0.2 mL, 1.2 mmol). Colorless
needles: 0.57 g (65%); mp=240-242 °C, [R]2D5 =+76 (c 1.0,
CH2Cl2). Anal. Calcd for C76H64As2F6O8P2S2: C, 61.05; H,
4.31. Found: C, 60.84; H, 4.47. 1H NMR (CD2Cl2, 300 MHz):
δ 1.53-2.38, 3.36-4.44 (m, 22H, aliphatic H), 6.94-8.54
(m, 42H, ArH). 31P{1H} NMR (CD2Cl2, 500 MHz): δ 17.76
(s), 39.68 (s), 39.8 (s), 40.20 (s). 31P{1H} NMR (CD2Cl2, -95 °C,
500 MHz): 17.97 (s), 37.74 (s), 39.23 (s), 39.74 (s), 40.66 (s), (see
Figure 6).
(R*As,R*As)-(()/(R*As,S*As)-1,2-Ethanediylbis(methylphenyl-
arsine), (R*As,R*As)-(()/(R*As,S*As)-5. This compound was pre-
pared by a modification of the literature method.21 Methyllithium
(63 mL, 1.6 M in diethyl ether) was slowly added to a solution of
(R*As,R*As)-(()/(R*As,S*As)-2 (16.17 g, 40.0 mmol) in dry THF
(300 mL) at 0 °C. The reaction mixture was stirred for 30 min, and
then the unreacted methyllithium was quenched with water (50
mL); the volatiles were removed and replaced with dichloro-
methane (250 mL) and water (200 mL) was added. The organic
phase was separated, the aqueous phase was extracted with
dichloromethane (2 ꢁ 50 mL), and the combined orga-
nic fractions were dried (MgSO4) and filtered. The solvent was
removed from the filtrate to leave a cloudy oil that was purified by
distillation. Yield: 12.81 g (88%); bp = 158-164 °C (0.5 mmHg)
[Lit.21 140-155 °C (0.05 mmHg)]. Anal. Calcd for C16H20As2: C,
53.06; H, 5.57. Found: C, 52.87; H, 5.65. 1H NMR (CDCl3): δ1.19
(s, 6H, AsCH3), 1.69-1.85 (m, 4H, AsCH2), 7.33-7.47 (m, 10H,
ArH).
Experimental Section
General Methods. Manipulations involving air-sensitive com-
pounds were performed under dinitrogen with use of Schlenk
techniques. Solvents were dried over appropriate drying agents
and distilled before use.28 Reaction temperatures of -95 °C were
achieved with an ethanol-liquid nitrogen slush bath. NMR
spectra were recorded at 25 °C, unless otherwise stated, on
Varian Inova 300 and 500 spectrometers: for 1H spectra,
chemical shifts are reported in ppm and referenced to the
residual solvent peaks; for 31P{1H} spectra, chemical shifts are
quoted relative to external 85% aq. H3PO4 with positive shifts
lying downfield of the standard. Optical rotations were mea-
sured on the specified solutions with a Perkin-Elmer Model
241 spectropolarimeter. Specific rotations are within ( 0.05 deg
cm2 g-1. (R*As,R*As)-(()/(R*As,S*As)-2,24 MePh2P,29 (aRP)-
1,7 and (SP,SP)-622 were prepared by the literature methods.
Elemental analyses were performed by staff within the Research
School of Chemistry.
[SP-4-(R*As,R*As)]-(()-Dichloro[1,2-ethanediylbis(methylphenyl-
arsine)]palladium(II), [SP-4-(R*As,R*As)]-(()-[Pd(5)Cl2]. This
compound was prepared by the published procedure.25 Palla-
dium(II) chloride (6.14 g, 34.6 mmol), lithium chloride (8.00 g,
188.7 mmol), (R*As,R*As)-(()/(R*As,S*As)-5 (12.57 g,
1
General Procedure for Preparation of 1,2-Ethanediylbis[(phos-
phine)phenylarsenium Triflates]. The tertiary phosphine (2.0-
34.7 mmol). Yellow solid: 16.36 g (88%). H NMR (CDCl3):
1.76 (dd, 2JHH = 21.6 Hz, 3JHH = 13.8 Hz, 2H, (R*As,R*As)-
CHHCHH), 2.02 (s, 6H, AsCH3), 2.08 (s, 6H, AsCH3), 2.24-
2.1 equiv) was added to a solution of (R*As,R*As)-(()/(R*As
,
S*As)-2 (1.0 equiv) in dichloromethane containing Me3SiOTf
(2.0-2.1 equiv). After about 0.5 h, the solvent and Me3SiCl
were removed in vacuo. The residues were dissolved in
small quantities of dichloromethane, and the crude products
were precipitated by the addition of diethyl ether to separate
them from the excess phosphine. The crude product in each
case was dried and crystallized from dichloromethane-diethyl
ether.
2.34 (m, 2H, (R*As,S*As)-CHHCHH), 2.38-2.48 (m, 2H,
=
2
(R*As,S*As)-CHHCHH), 2.75 (dd, JHH = 21.6 Hz, 3JHH
13.8 Hz, 2H, (R*As,R*As)-CHHCHH), 7.36-7.87 (m, 20H,
ArH). The complex was dissolved in the minimum quantity of
dichloromethane and loaded onto a silica column made up
with dichloromethane; the first band was eluted with dichlor-
omethane/THF (95/5 v/v) and contained the (R*As,R*As)-(()
diastereomer of the complex. Yellow microcrystals: 6.49 g
1
(79%); mp = 285-287 °C (dec). [Lit.25 287-288 °C (dec)]. H
(R*As,R*As)-(()/(R*As,S*As)-1,2-Ethanediylbis[(triphenylphos-
phine-P)phenylarsenium Triflate], (R*As,R*As)-(()/(R*As,S*As)-3.
(R*As,R*As)-(()/(R*As,S*As)-2 (1.0 g, 2.5 mmol), PPh3 (1.4 g,
5.2 mmol), Me3SiOTf (1.2 g, 1.0 mL, 5.2 mmol). Colorless prisms:
2.05 g (71%); mp = 157-159 °C. Anal. Calcd C52H44As2-
F6O6P2S2: C, 54.08; H, 3.84. Found: C, 53.89; H, 3.91. 1H NMR
(CDCl3): δ 2.45 (s, br, 4H, AsCH2), 6.22-7.73 (m, 40H, ArH). 31P-
{1H} NMR (CDCl3): δ 17.45 (s).
(R*As,S*As)-1,2-Ethanediylbis[(methyldiphenylphosphine-P)-
phenylarsenium Triflate], (R*As,S*As)-4. (R*As,R*As)-(()/
(R*As,S*As)-2 (0.79 g, 2.0 mmol), PMePh2 (0.8 g, 4.1 mmol),
Me3SiOTf (0.9 g, 0.8 mL, 4.1 mmol). Colorless prisms: 1.58 g
2
NMR (CDCl3): 1.76 (dd, 2H, JHH = 21.6 Hz, JHH =13.8 Hz,
3
2
CHHCHH), 2.02 (s, 6H, AsCH3), 2.75 (dd, 2H, JHH = 21.6
Hz, 3JHH = 13.8 Hz, CHHCHH), 7.45-7.87 (m, 10 H, ArH).
(R*As,R*As)-(()-1,2-Ethanediylbis(methylphenylarsine), (R*As,
R*As)-(()-5. This compound was prepared by a published
procedure.25 Sodium cyanide (3.50 g, 71 mmol), (R*As
,
R*As)-(()-[PdCl2(5)] (6.46 g, 11.9 mmol). Colorless oil: 3.50
g (80%); bp=168-170 °C (0.2 mmHg) [Lit.25 156-158 °C (0.1
mmHg)]. 1H NMR (CDCl3): 1.16 (s, 6H, AsCH3), 1.72 (dd, 2H,
3
2JHH = 6.9 Hz, JHH = 5.1 Hz, CHHCHH), 1.73 (dd, 2H
3
2JHH = 6.9 Hz, JHH = 5.1 Hz, CHHCHH), 7.26-7.44 (m,
10H, ArH).
[SP-4-(SP,SP)(RAs,RAs)]-[1,2-Ethanediylbis(methylphenyl-
arsine)][1,2-phenylenebis(methylphenylphosphine)]platinum(II)
Triflate, [SP-4-(SP,SP)(RAs,RAs)]-7. A solution of (R*As,R*As)-
(28) Armarego, W. F. L.; Chai, C. L. L. Purification of Laboratory
Chemicals, 5th ed.; Butterworth-Heinemann: Amsterdam, 2003.
(29) Bianco, V. D.; Doronzo, S. Inorg. Synth. 1976, 16, 155–163.

7490 Inorganic Chemistry, Vol. 48, No. 15, 2009
Weir et al.
3
(()-5 (0.48 g, 1.32 mmol) in dichloromethane was added to a
solution of the complex (SP,SP)-6 (1.03 g, 1.26 mmol) in the same
solvent (10 mL). After 1 h, the volume of resulting solution was
reduced by half, and diethyl ether (20 mL) was added. The
mixture was stirred for 0.5 h, and the colorless product was
filtered off and recrystallized from methanol by the addition of
diethyl ether. After two recrystallizations, configurationally
pure (SP,SP)(RAs,RAs)-7 was obtained as colorless needles:
mp = >350 °C; [R]2D5= +199 (c 1.0, CH2Cl2). Anal. Calcd.
for C38H40As2F6O6P2PtS2: C, 38.75; H, 3.42. Found: C,
(CD2Cl2, 121.46 MHz): δ 38.58 (d, JPP = 11.05 Hz, 11%,
(SP,SP)(RAs,SAs)-7), 38.91 (s, 74%, (SP,SP)(SAs,SAs)-7), 40.03
(s, 4%, (SP,SP)(RAs,RAs)-7), 40.32 (d, JPP=11.05 Hz, 11%,
3
(SP,SP)(RAs,SAs)-7), 43.83 (br s, (aRP)-1 BH3).
3
Stereoselective Synthesis of (R*As,R*As)-(()/(R*As,S*As)-8.
n-Butyllithium (1.5 M in hexanes, 20 μL), (aRP)(RAs,RAs)(aRP)/
(aRP)(SAs,SAs)(aRP)/(aRP)(RAs,SAs)(aRP)-10 (0.01915 g, 12.8
μmol), (SP,SP)-6 (0.0087 g, 10.4 μmol). 31P{1H} NMR (CDCl3,
121.46 MHz): δ 37.86 (s, 72%, (SP,SP)(SAs,SAs)-9), 38.16 (d,
=
3JPP= 10.90 Hz, 11.5%, (SP,SP)(RAs,SAs)-9), 38.42 (d, JPP
3
1
38.75; H, 3.64. H NMR (300 MHz, CD2Cl2): δ 1.52 (d, 6H,
10.90 Hz, 11.5%, (SP,SP)(RAs,SAs)-9), 39.58 (s, 5%, (SP,SP)
(RAs,RAs)-9), 42.70 (br s, (aRP)-1 BH3).
3
4JHP(trans) = 1.8 Hz, JHPt = 16.2 Hz, AsCH3), 1.89 (d, 6H,
3
3
2JHP = 11.1 Hz, JHPt = 33.9 Hz, 6 H, PCH3), 2.22-2.35
X-ray Crystallography. X-ray diffraction data were collected
at 200 K on a Nonius Kappa CCD diffractometer. Data were
processed with the Denzo/Scalepack software30 with absorption
corrections31 being applied. The structures were solved by direct
methods with the program SIR92.32 Non-hydrogen atoms with-
in the cation were refined anisotropically and hydrogen atoms
were placed at idealized positions. Full-matrix least-squares
refinement on F was performed with the CRYSTALS pro-
gram.33 The absolute configuration of the complex [SP-4-2-
(SP,SP)(RAs,RAs)]-7 was determined by refinement of a Flack
parameter, final value -0.024(4), and was consistent with the
known configuration of the phosphorus stereocenters in the
platinum complex (SP,SP)-6.
(m, 2H, CHHCHH), 2.46-2.61 (m, 2H, CHHCHH), 7.41-
7.71 (m, 24H, ArH). 31P{1H} NMR (121.47 MHz, CD2Cl2) δ
39.48 (s, 1JPtP=2700 Hz).
(R*As,R*As)-(()/(R*As,S*As)-1,2-Ethanediylbis(n-butylphenyl-
arsine), (R*As,R*As)-(()/(R*As,S*As)-8. This compound
was prepared by a modification of the literature method.24
A
solution of n-butyllithium (47.3 mL, 2.5 M) was added to a
solution of (R*As,R*As)-(()/(R*As,S*As)-2 (18.00 g, 45.0
mmol) in THF (400 mL) at 0 °C. The reaction mixture was
stirred for 30 min and then the excess n-BuLi was quenched with
water (50 mL). The solvent was evaporated from the mixture
and replaced with dichloromethane (250 mL) and water (200
mL). The organic phase was separated, and the aqueous phase
was extracted with dichloromethane (2 ꢁ 50 mL). The combined
organic fraction was dried (MgSO4), filtered, and the solvent
evaporated to leave the crude product that was purified by
distillation. Colorless oil: 17.54 g (87%); bp = 178-181 °C (0.05
mmHg) [Lit.24 184-188 °C (0.06 mmHg)]. Anal. Calcd for
C22H32As2: C, 59.20; H, 7.23. Found: C, 59.26; H, 7.06. 1H
Crystal data for (R*As,S*As)-4, M= 1030.69, monoclinic, space
˚
group P21/c, a = 11.5468(2), b = 11.2427(2) c = 17.0825(3) A,
3
-3
˚
β = 95.6724(12)°, V=2206.74(7) A , Z=2, D=1.438 g cm
,
μ(Mo KR) = 1.752 mm-1, T = 200 K, colorless prism, crystal size
0.35 ꢁ 0.20 ꢁ 0.19 mm, 45490 reflections measured, 5057 unique
reflections (Rint = 0.037), 2863 independent observed reflections
(I>3.00u(I)), 326 parameters, F refinement, R = 0.0373, wR=
0.0427.
3
NMR (CDCl3): δ 0.85 (t, 6H, JHH = 6.9 Hz, As(CH2)3CH3),
1.27-1.44 (m, 8H, AsCH2(CH2)2), 1.61-1.81 (m, 8H, AsCH2),
Crystal data for [SP-4-(SP,SP)(RAs,RAs)]-7, M=1171.71, ortho-
rhombic, space group P212121, a=13.9541(2), b=16.5910(1) c=
7.29-7.43 (m, 10H, ArH).
3
18.8238(2) A, V=4357.94(8) A , Z=4, D=1.795 g cm-3, μ(Mo
KR) = 0.71073 mm-1, T = 200 K, colorless plate, crystal size
0.52 ꢁ 0.36 ꢁ 0.22 mm, 61481 reflections measured, 10011 unique
reflections (Rint=0.065), 8962 independent observed reflections
(I>2.00u(I)), 583 parameters, F2 refinement, R= 0.0241, wR=
0.0524.
˚
˚
Asymmetric Syntheses. General. A solution of the appropriate
alkyllithium reagent was added to a solution of (aRP)(RAs,RAs)-
(aRP)/(aRP)(SAs,SAs)(aRP)/(aRP)(RAs,SAs)(aRP)-10 in CH2Cl2
(2 mL) at -95 °C. After stirring for about 5 min, the reaction
mixture in each case was quenched with water (100 μL), and the
cooling bath removed. When the reaction mixture had reached
room temperature, it was dried (MgSO4), filtered, and an excess
of Me2S BH3 was added to complex the displaced phosphine.
After a further 10 min, the solution was evaporated to dryness
and heated under vacuum to remove the excess Me2S BH3.
Acknowledgment. This work was supported by the Australian
Research Council.
3
3
The residue was dissolved in dichloromethane (2 mL), and a
solution of (SP,SP)-6 in the same solvent (2 mL) was added.
After 10 min, the solvent was removed from the solution, and the
stereoselectivities of the resulting 1,2-ethanediylbis(tertiary ar-
sines) were determined by recording the 31P{1H} NMR spectra
of the appropriate platinum complexes, as described below.
Stereoselective Synthesis of (R*As,R*As)-(()/(R*As,S*As)-5.
Supporting Information Available: Additional crystallogra-
phic data in CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.
(30) Otwinowski, Z.; Minor, W. Methods Enzymol. 1996, 276, 307–326.
(31) Coppens, P. In Crystallographic Computing; Ahmed, F. R., Hall, S.
R., Huber, C. P. Eds.; Munksgaard: Copenhagen, 1970; pp 255-270.
(32) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(33) Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.; Prout, K.;
Watkin, D. J. J. Appl. Crystallogr. 2003, 36, 1487.
Methyllithium (1.6 M in diethyl ether, 20 μL), (aRP)(RAs,RAs
)
(aRP)/(aRP)(SAs,SAs)(aRP)/(aRP)(RAs,SAs)(aRP)-10 (0.0229 g,
15.3 μmol), (SP,SP)-6 (0.0087 g, 10.7 μmol). 31P{1H} NMR