Tertiary arsine-stabilised arsenium salts: Syntheses and comparisons with phosphine analogues

Article abstract of DOI:10.1039/b800965a

The first tertiary arsine-stabilised arsenium salts, [(L)AsMePh]OTf (L = Ph₃As, Me₂PhAs, [2-(MeOCH₂)C₆H ₄]Ph₂As, [2-(MeOCH₂)C₆H ₄]Me₂As), have been prepared by chloride abstraction from chloromethylphenylarsine with trimethylsilyl triflate in the presence of the arsine. The complexes have been characterised by crystallography and ¹H NMR spectroscopy. The chiral cations in the complexes have structures based on the trigonal pyramid in which the arsine is coordinated orthogonally to the prochiral, six-electron MePhAs⁺ ion that forms the base of the pyramid. The NMR data for the complexes in dichloromethane- d₂ are consistent with rapid exchange of the arsine on the arsenium ion, even at 183 K. The corresponding phosphine-stabilised complexes are considerably more stable than their arsine counterparts in dichloromethane- d₂ with the free energy of activation ΔG?c = ca. 60 kJ mol^-1 being calculated for phosphine exchange in [(Me ₂PhP)AsMePh]OTf at 281 K; for [(Me₂{2-(MeOCH ₂)C₆H₄}P)AsMePh]OTf in the same solvent, ΔG?c = ca. 70 kJ mol^-1 at 323 K. The Royal Society of Chemistry.

Full text of DOI:10.1039/b800965a

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www.rsc.org/dalton | Dalton Transactions
Tertiary arsine-stabilised arsenium salts: syntheses and comparisons with
phosphine analogues†
Nathan L. Kilah, Michelle L. Weir and S. Bruce Wild*
Received 18th January 2008, Accepted 26th February 2008
First published as an Advance Article on the web 20th March 2008
DOI: 10.1039/b800965a
The first tertiary arsine-stabilised arsenium salts, [(L)AsMePh]OTf (L = Ph3As, Me2PhAs,
[2-(MeOCH2)C6H4]Ph2As, [2-(MeOCH2)C6H4]Me2As), have been prepared by chloride abstraction
from chloromethylphenylarsine with trimethylsilyl triflate in the presence of the arsine. The complexes
have been characterised by crystallography and 1H NMR spectroscopy. The chiral cations in the
complexes have structures based on the trigonal pyramid in which the arsine is coordinated
orthogonally to the prochiral, six-electron MePhAs+ ion that forms the base of the pyramid. The NMR
data for the complexes in dichloromethane-d2 are consistent with rapid exchange of the arsine on the
arsenium ion, even at 183 K. The corresponding phosphine-stabilised complexes are considerably more
stable than their arsine counterparts in dichloromethane-d2 with the free energy of activation DG‡c = ca.
60 kJ mol−1 being calculated for phosphine exchange in [(Me2PhP)AsMePh]OTf at 281 K; for
[(Me2{2-(MeOCH2)C6H4}P)AsMePh]OTf in the same solvent, DG‡c = ca. 70 kJ mol−1 at 323 K.
Introduction
Arsenium ions (R2As+) are six-electron species containing a lone
pair of electrons and a vacant p-orbital; they are thus Lewis acids,
as well as potential Lewis bases.1 Initial evidence for the presence
of arsenium ions came from the mass spectra of certain arsenic
Phosphine-stabilised arsenium hexafluorophosphates are usu-
heterocycles, where they were frequently observed as the base
ally air- and moisture-stable and can be prepared in a two-phase
peaks in the spectra.2 Direct syntheses of arsenium salts have been
system in which a dichloromethane solution of the phosphine and
achieved by chloride abstraction from secondary chloroarsines
the iodoarsine is exposed to a solution of ammonium or potassium
with aluminium chloride or trimethylsilyl triflate; the electron-
hexafluorophosphate in water (eqn (1)).1 In the structure of
poor arsenium centres in 13 and 24 are considered to be stabilised
[(Ph3P)AsMePh]PF6, the arsenium group has an angular geometry
by lone-pair delocalisation from neighbouring heteroatoms. Arse-
with the stereochemically active lone pair, methyl, and ipso-carbon
nium ions can be stabilised by Lewis base-donation of an electron
atom of the phenyl group being directed to the corners of a triangle.
pair into the vacant p-orbital on the arsenic. Thus, the addition
The phosphine is coordinated orthogonally to one of the faces of
of a tertiary phosphine to a solution of a secondary chloro- or
the prochiral arsenium ion to give a chiral coordination complex
iodoarsine in diethyl ether or cyclohexane furnishes adducts of
having a structure based on the trigonal pyramid. Although
the type [(R3P)AsMePh]X (X = Cl, I). The iodides precipitate
they are thermodynamically stable, phosphine-stabilised arsenium
from the solutions, sublime on heating, and have the characteristic
salts undergo rapid phosphine exchange in solution.1 A number
odour of the parent iodoarsine when heated.5 The adducts were
of phosphine-stabilised arsenium salts have been prepared from
originally described as arsinophosphonium salts, but they react with
mono- and bis-(tertiary phosphines) by reaction with 10-chloro-
sodium alkoxides or n-butyllithium to give arsinous acid esters or
5-hydrophenarsazine and gallium(III) chloride or Me3SiOTf.7
tertiary arsines, respectively, with liberation of a phosphine. This
is consistant with the positive charge on the cation being centred
(1)
on arsenic. Accordingly, the term ligand-stabilised arsenium salt
is now used to describe compounds of this type.1 Arsenium ions
can also be stabilised by nitrogen ligands, such as pyridine and
diethylamine, these compounds being prepared under anhydrous
conditions from a secondary chloroarsine and the ligand in the
presence of trimethylsilyl triflate (Me3SiOTf).6
The stibine-stabilised stibenium complex [(Me3Sb)SbMe2]-
[(MeSbBr3)2] was isolated from the redistribution of
bromodimethylstibine and structurally characterised.8 The
phosphine-stabilised stibenium complex [(Me3P)SbPh2]PF6
self-assembles around halide ions to give complexes of the
type [{(Me3P)SbPh2}4X](PF6)3 (X = Cl, Br) in which attractive
edge-to-face interactions between the two sets of phenyl groups
above and below the square plane containing the halide ion
appear to be a crucial stabilising force in the supramolecular
assembly.9 Coordination of two triphenylphosphine ligands
to a central stibenium ion has been observed in the complex
Research School of Chemistry, Australian National University, Canberra,
Australian Capital Territory, 0200, Australia. E-mail: sbw@rsc.anu.edu.au;
Fax: +61 2 6125 0750; Tel: +61 2 6125 4236
† Electronic supplementary information (ESI) available: Rotatable 3D
crystal structure diagrams in CHIME format. CCDC reference numbers
675869–675874. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b800965a
2480 | Dalton Trans., 2008, 2480–2486
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[(Ph3P)2SbPh2]PF6, which has a structure based on a distorted
trigonal bipyramid.10
There are no reported syntheses of arsine-stabilised arsenium
salts. A series of arsine-stabilised arsenium triflates has therefore
been synthesised and their properties compared with those of the
analogous phosphine complexes by variable temperature 1H NMR
spectroscopy and X-ray crystallography.
Results and discussion
Syntheses
The arsine-stabilised arsenium triflates ( )-3, ( )-5, ( )-6, and
( )-8 were prepared by the reaction of a dichloromethane solu-
tion of chloromethylphenylarsine with the tertiary arsine in the
presence of trimethylsilyl triflate; evaporation of the solvent from
the solutions, which also removes the by-product trimethylsilyl
chloride, furnished the crude arsine-stabilised arsenium triflates,
which were recrystallised from dichloromethane by the addition of
diethyl ether (eqn (2)). The phosphine analogues ( )-4 and ( )-7
were prepared by the same method (Table 1).
(2)
NMR spectra
The resonances for the PhPMe2 groups in the 1H NMR spectrum
of the phosphine-stabilised arsenium complex ( )-4 at 308 K in
dichloromethane-d2 appear as a doublet (JHP = 13.2 Hz) and the
AsMe peak as a singlet because of rapid phosphine exchange
on the NMR timescale. On cooling the solution to 281 K, the
coalescence temperature for the PMe signals is reached; further
cooling of the solution to 253 K results in baseline separation of the
PMe doublets (Fig. 1). The free energy of activation for phosphine
dissociation (DG‡c ) in ( )-4 was calculated from the NMR data to
be 60 kJ mol−1 from the expression DGc‡ = 19.14Tc(10.32 + log
Tc/Kc), where Tc is the coalescence temperature and Kc = 2.22
Dv s−1 is the rate of site exchange in Hz at the slow exchange
limit.11 In the spectrum of the arsine-stabilised arsenium salt ( )-
5, however, no diastereotopic splitting was observed for the AsMe2
groups, even at 183 K, although there was some broadening of the
AsMe resonance for the arsenium group (Fig. 2). The anchimeric
stabilising effect of a 2-(methoxymethyl)phenyl group attached
to the arsine or phosphine was investigated by comparing the
Fig. 1 Variable temperature 1H NMR spectra of ( )-4 (CD2Cl2).
variable temperature NMR spectra of ( )-7 and ( )-8 with those
obtained for the parent complexes. At 298 K, the slow exchange
limit was reached for the phosphine-stabilised arsenium salt ( )-
7, as was evident by the baseline separation of the resonances
for the diastereotopic PMe2 groups. The coalescence temperature
for the PMe2 resonances in the spectrum of ( )-7 was reached
at 323 K. From these data, the free energy of activation for
phosphine exchange was calculated to be 70 kJ mol−1 (Fig. 3).
Despite an expected stabilising effect due to chelation of the 2-
(methoxymethyl)phenyl group for the arsine complex ( )-8, the
Table 1 Ligand-stabilised arsenium salts
NMRa
Compound
mp/◦C
d(AsMe)
d(P)
8.89
9.59
[(Ph3As)AsMePh]OTf (( )-3)b
135–137
93–94
90–92
104–107
107–108
97–98
1.90
1.65
1.79
[(Me2PhP)AsMePh]OTf (( )-4)
[(Me2PhAs)AsMePh]OTf (( )-5)
[({2-(MeOCH2)C6H4}Ph2As)AsMePh]OTf (( )-6)b
[({2-(MeOCH2)C6H4}Me2P)AsMePh]OTf (( )-7)
[({2-(MeOCH2)C6H4}Me2As)AsMePh]OTf (( )-8)
1.93
1.60 (16.8)c
1.75
a NMR samples were prepared to a standard concentration in dichloromethane-d2 and recorded at 298 K unless otherwise stated. b In chloroform-d1.
c JHP (Hz).
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Fig. 4 Variable temperature 1H NMR spectra of ( )-8 (CD2Cl2).
Fig. 2 Variable temperature 1H NMR spectra of ( )-5 (CD2Cl2).
Fig. 5 Molecular ellipsoid diagram for the S enantiomer of the cation of
(
)-3 showing 30% probability ellipsoids. Hydrogen atoms and triflate ion
omitted for clarity.
C21 = 94.95(9)◦. The coplanarity of the phenyl group with the
arsenium ion is evident from the torsion angle C11–As1–C21–C22,
which is −2.6(3)◦. The [2-(methoxymethyl)phenyl]diphenylarsine
¯
complex ( )-6 crystallises in the triclinic space group P1 with
Fig. 3 Variable temperature 1H NMR spectra of ( )-7 in (CD2Cl2).
one molecule of each enantiomer of the cation and associated
anions in the unit cell. The structure of the S enantiomer of the
cation is shown in Fig. 6; critical bond lengths and angles are
1H NMR spectrum showed no splitting for the AsMe2 resonances
down to 183 K in dichloromethane-d2 (Fig. 4).
˚
listed in Table 2. The As1–As2 distance of 2.4881(3) A is longer
than the sum of the covalent radii for the two arsenic atoms
Crystal structures
in the complex.12 The As1 · · · O51 distance of 3.065(2) A in the
˚
The arsine complex ( )-3 crystallises in the monoclinic space
group P21/c with two molecules of each enantiomer of the cation
and associated anions in the unit cell. The structure of the S
enantiomer of the complex is shown in Fig. 5 and important
distances and angles in the cation are given in Table 2. The
cation is longer than the sum of the covalent radii for the two
12
˚
atoms (1.92 A), but is less than the sum of the corresponding
13
˚
van der Waals radii (3.36 A). The chelating interaction of the
2-(methoxymethyl)phenyl group results in a lengthening of the
As–As bond compared to the one in the triphenylarsine adduct,
˚
˚
˚
As1–As2 distance of 2.4518(5) A is longer than the sum of
viz. 2.4881(3) A in ( )-6 and 2.4518(5) A in ( )-3 (Table 2). An
12
˚
covalent radii for the two arsenic atoms, viz. 2.40 A, and the
electrostatic interaction is observed between O61 of the triflate ion
˚
arsine coordination is essentially orthogonal to the plane of the
and As1 of the arsenium ion of ( )-6 at a distance of 2.734(2) A; the
arsenium ion, with As2–As1–C11 = 91.21(12)◦ and As2–As1–
O61–As1–As2 angle in the complex is 172.35◦. The As1 · · · O51
2482 | Dalton Trans., 2008, 2480–2486
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◦
a
˚
Table 2 Selected bond distances (A) and angles ( ) in the complexes
(
)-3
(
)-4
(
)-5
(
)-6
(
)-7
(
)-8
As1–E2
As1–C11
As1–C21
E2–C31
E2–C41
E2–C51
As1 · · · O51
E2 · · · O51
E2–As1–C11
E2–As1–C21
C11–As1–C21
C11–As1–C21–C22
2.4518(5)
1.961(4)
1.956(3)
1.926(3)
1.917(4)
1.916(3)
2.3402(8)
1.965(3)
1.956(3)
1.790(3)
1.792(3)
1.794(3)
2.4448(6)
1.969(5)
1.959(4)
1.914(4)
1.918(4)
1.910(4)
2.4881(3)
1.962(2)
1.954(2)
1.923(2)
1.938(2)
1.941(2)
3.065(2)
2.855(2)
92.06(7)
93.83(6)
2.3482(6)
1.953(3)
1.954(2)
1.801(2)
1.797(2)
1.817(2)
2.947(2)
2.965(2)
97.68(8)
92.23(7)
2.4394(3)
1.960(3)
1.951(2)
1.927(2)
1.917(3)
1.931(2)
3.027(2)
2.942(2)
97.25(9)
91.06(7)
91.21(12)
94.95(9)
102.33(17)
−2.6(3)
95.69(10)
96.54(8)
100.65(14)
5.2(3)
94.94(14)
96.05(12)
99.9(2)
101.45(10)
−24.7(2)
100.81(11)
−7.2(2)
101.15(12)
−4.0(3)
4.0(4)
a Where E = P or As.
Fig. 7 Molecular ellipsoid diagram for the S enantiomer of the cation of
)-5 showing 30% probability ellipsoids. Hydrogen atoms and triflate ion
(
omitted for clarity.
of atoms and the stereochemically active lone pair of electrons
occupy the base and the donor phosphorus or arsenic atom the
apex. The coplanarity of the phenyl group with the AsC2 core of
the arsenium ion in each case is evident from the torsion angles
C11–As1–C21–C22 of 5.2(3)◦ for ( )-4 and 4.0(4)◦ for ( )-5.
The 2-(methoxymethyl)phenyl-substituted phosphine and ar-
sine complexes ( )-7 and ( )-8 are isomorphous and crystallise in
Fig. 6 Molecular ellipsoid diagram for the S enantiomer of the cation
of ( )-6 showing 30% probability ellipsoids. Hydrogen atoms omitted for
clarity.
¯
distance is significantly less than the sum of the van der Waals
the triclinic space group P1 with one molecule of each enantiomer
13
˚
radii for the two atoms (3.36 A). The As1–As2 bond in the
of the complexes in the unit cell. The structure of the R enantiomer
of the cation of ( )-8 is depicted in Fig. 8. As observed for
the parent compounds ( )-4 and ( )-5, the E2–As1 distances in
the 2-(methoxymethyl)phenyl-substituted compounds are longer
than the sums of the covalent radii, viz. 2.3482(6) for P2–As1
cation is orthogonal to the plane containing the methyl (As2–
As1–C11 = 92.06(7)◦) and ipso-phenyl-carbon (As2–As1–C21 =
93.83(6)◦) atoms. Unlike the small torsion angle observed between
the phenyl group and the arsenium ion in ( )-3, the corresponding
torsion angle in ( )-6 is −24.7(2)◦.
˚
˚
and 2.4394(3) for As2–As1 compared to 2.29 A and 2.40 A,
respectively. The orthogonal coordination of the P or As donor
atom to the arsenium is evident from the angles P2–As1–C11
of 97.68(8)◦ and P2–As1–C21 of 92.23(7)◦ in ( )-7 and As2–
As1–C11 of 97.25(9)◦ and As2–As1–C11 of 91.06(7)◦ in ( )-8.
The incorporation of the 2-(methoxymethyl)phenyl group into the
aryldimethyl-phosphine and -arsine ligands influences the length
of the E2–As1 bonds to a lesser extent than it does for the triaryl-
phosphine and -arsine ligands. The As1–P2 bond in ( )-7 is
The complexes ( )-4 and ( )-5 are isomorphous with both
compounds crystallising in the monoclinic space group P21/n with
two molecules of each enantiomer and associated anions in the unit
cell. The structure of the S enantiomer of ( )-5 is shown in Fig. 7
and important distances and angles in the cations of the two salts
are given in Table 2. The E2–As1 distances in the cations are longer
than the sum of the covalent radii for the two elements, 2.3402(8)
˚
˚
˚
A in ( )-4 (sum of the covalent radii: 2.29 A) and 2.4448(6) A
12
˚
˚
in ( )-5 (sum of the covalent radii: 2.40 A). The angles P2–
0.0080 A longer than the corresponding bond in the PMe2Ph
As1–C11 and P2–As1–C21, 95.69(10)◦ and 96.54(8)◦, respectively,
and A2–As1–C11 and As2–As1–C21, 94.94(14)◦ and 96.05(12)◦,
respectively, allow the coordination geometry around the arsenium
centres in each cation to be described as being based on a distorted
trigonal pyramid in which the angular six-electron AsC2 group
adduct ( )-4. Interactions were observed between As1 and O51 at
˚
˚
2.947(2) A and P2 and O51 at 2.965(2) A in ( )-7. These distances
are longer than the corresponding covalent distances but shorter
than the sums of the corresponding van der Waals radii. The
˚
˚
As1–As2 bond in ( )-8 of 2.4394(3) A is 0.0054 A shorter than
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was slowly added to a cold solution (−78 ◦C) of the Grignard
reagent prepared from magnesium turnings (5.57 g, 229 mmol)
and 1-bromo-2-(methoxymethyl)benzene (46.00 g, 229 mmol)
in the same solvent (300 mL). The mixture was stirred at room
temperature for 1 h and then the solvent was removed and
replaced with n-hexane (600 mL). After ca. 15 h, the mixture was
filtered and the filtrate treated with anhydrous HCl for 20 min.
The mother liquor was decanted from the inorganic salts and the
solvent was removed from the filtrate t◦o afford a cloudy oil that
was distilled: 28.45 g (69%); bp 84–87 C (0.15 mmHg). Found:
C, 43.11; H, 4.29. C8H9Cl2OP requires C, 43.08; H, 4.07%. dH
(300 MHz; CDCl3; 298 K) 3.40 (3 H, s, OMe), 4.71 (2 H, s, CH2),
7.26–7.55, 8.20–8.24 (4 H, m, ArH). dP (300 MHz; CDCl3; 298 K)
158.7 (s). Mass spec. (EI) 222 ([M]+), 185 ([M − Cl]+), 153 amu
([M − 2Cl]+).
[2-(Methoxymethyl)phenyl]dimethylphosphine.
Dichloro[2-
(methoxymethyl)phenyl]phosphine (3.06 g, 13.7 mmol) in diethyl
ether (25 mL) was added to a cold solution (0 ◦C) of a Grignard
reagent prepared from magnesium turnings (0.81 g, 33.2 mmol)
and iodomethane (1.90 mL, 30.2 mmol). After the addition, the
reaction mixture was heated under reflux for 30 min. The mixture
was then cooled to 0 ◦C and treated with a saturated aqueous
solution of ammonium chloride (25 mL) with stirring. The mixture
was left to warm to room temperature and then the phases were
separated. The aqueous phase was extracted with diethyl ether
(2 × 50 mL); the combined organic fraction was dried (MgSO4),
filtered, and the solvent removed in vacuo to leave an oil that was
distilled: 1.78 g (70%); bp 78 ◦C (0.7 mmHg). Found: C, 66.03; H,
8.38. C10H15OP requires C, 65.92; H, 8.30%. dH (300 MHz; CDCl3;
298 K) 1.18 (6 H, d, JHP = 3.30 Hz, PMe), 3.32 (3 H, s, OMe), 4.60
(2 H, s, CH2), 7.21–7.40 (4 H, m, ArH). dP (300 MHz; CDCl3; 298
K) −58.04 (s). Mass spec. (EI) 183 amu ([M]+).
Fig. 8 Molecular ellipsoid diagram for the R enantiomer of the cation of
)-8 showing 30% probability ellipsoids. Hydrogen atoms and triflate ion
omitted for clarity.
(
the corresponding distance in the AsMe2Ph adduct. Interactions
˚
of the [2-(MeOCH2)C6H4]-O atom at As1 · · · O51 3.027(2) A and
˚
As2 · · · O51 2.942(2) A in ( )-8 place the oxygen closer to the
arsenic atom of the tertiary arsine than the methylphenylarsenium
ion, which could indicate that crystal packing effects are important
in these complexes.
Conclusions
Tertiary arsine-stabilised arsenium complexes are readily prepared
by chloride abstraction from secondary chloroarsines in the
presence of tertiary arsines. The complexes have structures based
on a trigonal pyramid and undergo ligand exchange in solution at
faster rates than the corresponding phosphine-stabilised arsenium
complexes.
[2-(Methoxymethyl)phenyl]diphenylarsine.
Iododiphenylar-
sine (10.36 g, 29.1 mmol) in THF (30 mL) was added to
a cooled solution of a Grignard reagent (0 ◦C) prepared
from magnesium turnings (0.86 g, 35.2 mmol) and 1-bromo-2-
(methoxymethyl)benzene (6.44 g, 32.0 mmol) in THF (20 mL).
After the addition, the reaction mixture was heated under reflux
for 1 h. The THF was removed in vacuo from the cooled solution
and diethyl ether (50 mL) was added to the residue, followed by
saturated aqueous ammonium chloride (25 mL). The two-phase
mixture was left to warm to room temperature before the phases
were separated. The aqueous phase was extracted with diethyl
ether (2 × 50 mL) and the combined organic fraction was dried
(MgSO4), filtered, and the solvent removed from the filtrate to leave
a pale yellow solid that crystallised from hot ethanol as colourless
needles: 7.52 g (74%); mp 84–86 ◦C. Found: C, 68.22; H, 5.18.
C20H19AsO requires C, 68.58; H, 5.47%. dH (300 MHz; CDCl3;
298 K) 3.23 (3 H, s, OMe), 4.60 (2 H, s, CH2), 7.00–7.46 (14 H, m,
ArH). Mass spec. (EI) 350 ([M]+), 241 amu ([M − MeOPh]+).
Experimental
General methods
Reactions involving air-sensitive compounds were carried out
under a positive pressure of nitrogen using conventional Schlenk
techniques. Dry, degassed solvents were obtained by distillation
over appropriate drying agents.14 Chloromethylphenylarsine,15
dimethylphenylarsine,16 [2-(methoxymethyl)phenyl]dimethylar-
sine,17 dimethylphenylphosphine,18 iododiphenylarsine,19 chloro-
bis(diethylamino)phosphine,20 and 1-bromo-2-(methoxymethyl)-
benzene21 were prepared by literature methods. H and 31P{ H}
NMR spectra were recorded at 298 K on a Varian Inova
300 spectrometer operating at 299.945 and 121.419 MHz,
respectively; resonances were referenced against the solvent or
external aqueous H3PO4 (85%). Melting points were determined
with use of a Reichert hot-stage melting point apparatus. Mass
spectra and elemental analyses were performed by staff within the
Research School of Chemistry.
1
1
General procedure for preparation of phosphine- and
arsine-stabilised arsenium triflates
The tertiary phosphine or arsine (1.1 equiv.) was added to
a solution of chloromethylphenylarsine (1.0 equiv.) containing
Me3SiOTf (1.1 equiv.). After ca. 0.5 h, the solvent and Me3SiCl
were removed in vacuo. The residues were redissolved in small
Syntheses
Dichloro[2-(methoxymethyl)phenyl]phosphine. Chlorobis(die-
thylamino)phosphine (39.00 g, 196 mmol) in THF (50 mL)
2484 | Dalton Trans., 2008, 2480–2486
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quantities of dichloromethane and precipitated by the addition
of diethyl ether to remove the small excesses of arsine or
phosphine. The product in each case was dried and crystallised
from dichloromethane–diethyl ether.
CDCl3; 298 K) 1.93 (3 H, s, As+Me), 3.15 (3 H, s, OMe), 4.53
(2 H, s, CH2), 7.09–7.78 (19 H, m, ArH).
(
)-[(2-{Methoxymethyl}phenyl)dimethylphosphine-P]-methyl-
phenylarsenium triflate ( )-(7). Chloromethylphenylarsine
(1.20 g, 5.93 mmol), [2-(methoxymethyl)phenyl]dimethyl-
phosphine (1.28 g, 7.03 mmol), Me3SiOTf (1.28 mL, 7.03 mmol).
Colourless plates: 2.13 g (72%); mp 107–108 ◦C. Found: C,
43.46; H, 4.70. C18H23AsF3O4PS requires C, 43.38; H, 4.65%. dH
(300 MHz; CD2Cl2; 298 K) 1.60 (3 H, d, JHP = 16.8 Hz, As+Me),
1.97 (3 H, d, JHP = 13.2 Hz, PMe), 2.04 (3 H, d, JHP = 12.9 Hz,
PMe), 3.51 (3 H, s, OMe), 4.57 (1 H, d, JHH = 12.6 Hz, CH2),
4.63 (1 H, d, JHH = 12.6 Hz, CH2), 7.31–7.86 (9 H, m, ArH). dP
(300 MHz; CD2Cl2; 298 K) 9.59 (s).
( )-(Triphenylarsine-As)methylphenylarsenium triflate ( )-(3).
Chloromethylphenylarsine (1.36 g, 6.72 mmol), triphenylarsine
(2.26 g, 7.39 mmol), Me3SiOTf (1.34 mL, 7.39 mmol). Colourless
prisms: 2.26 g (51%); mp 135–137 ◦C. Found: C, 50.18; H,
3.75. C26H23As2F3O3S requires C, 50.18; H, 3.72%. dH (300 MHz;
CDCl3; 298 K) 1.90 (3 H, s, As+Me), 7.27–7.65 (20 H, m, ArH).
( )-(Dimethylphenylphosphine-P)methylphenylarsenium triflate
( )-(4). Chloromethylphenylarsine (1.20 g, 5.93 mmol),
dimethylphenylphosphine (0.95 g, 6.88 mmol), Me3SiOTf
(1.18 mL, 6.52 mmol). Colourless prisms: 2.29 g (85%); mp 93–
94 ◦C. Found: C, 42.42; H, 4.16. C16H19AsF3O3PS requires C,
42.30; H, 4.22%. dH (300 MHz; CD2Cl2; 298 K) 1.68 (3 H, s,
As+Me), 2.13 (6 H, d, JHP = 13.2 Hz, PMe), 7.30–7.74 (10 H, m,
ArH). dP (300 MHz; CDCl3; 298 K) 8.89 (s).
(
)-[(2-{Methoxymethyl}phenyl)dimethylarsine-As]-methyl-
phenylarsenium triflate ( )-(8). Chloromethylphenylarsine
(1.33 g, 6.57 mmol), [2-(methoxymethyl)phenyl]dimethylarsine
(1.72 g, 6.71 mmol), Me3SiOTf (1.31 mL, 7.23 mmol). Colourless
prisms: 2.81 g (79%); mp 97–98 ◦C. Found: C, 39.46; H, 4.49.
C18H23As2F3O4S requires C, 39.87; H, 4.28%. dH (300 MHz;
CD2Cl2; 298 K) 1.75 (3 H, s, As+Me), 1.84 (6 H, s, AsMe), 3.56
(s, 3 H, OMe), 4.67 (2 H, s, CH2), 7.28–7.59 (9 H, m, ArH).
( )-(Dimethylphenylarsine-As)methylphenylarsenium
triflate
( )-(5). Chloromethylphenylarsine (1.10 g, 5.43 mmol),
dimethylphenylarsine (1.12 g, 6.15 mmol), Me3SiOTf (1.08 mL,
5.97 mmol). Colourless needles: 2.22
g (75%); mp 104–
Crystallography
107 ◦C. Found: C, 38.25; H, 4.21. C16H19As2F3O3S requires C,
38.57; H, 3.84%. dH (300 MHz; CD2Cl2; 298 K) 1.79 (3 H, s,
As+Me), 2.04 (6 H, s, AsMe), 7.25–7.55 (10 H, m, ArH).
Crystallographic data was recorded on a Nonius Kappa CCD
diffractometer (Mo-Karadiation) and processed using Denzo and
Scalepack software22 and corrected for absorption by the Gaussian
integration method implemented in maXus.23 The structures
were solved by direct methods (SIR92)24 and refined by full
matrix on F with use of CRYSTALS.25 Non-hydrogen atoms
were refined with anisotropic displacement parameters. Hydrogen
atoms were included at calculated positions and were allowed
to ride on the atoms to which they were attached. Molecular
(
)-[(2-{Methoxymethyl}phenyl)diphenylarsine-As]-methyl-
phenylarsenium triflate ( )-(6). Chloromethylphenylarsine
(1.14 g, 5.63 mmol), [2-(methoxymethyl)phenyl]diphenylarsine
(2.17 g, 6.19 mmol), Me3SiOTf (1.1◦3 mL, 6.19 mmol). Colourless
prisms: 2.48 g (66%); mp 104–107 C. Found: C, 50.40; H, 4.32.
C28H27As2F3O4S requires C, 50.47; H, 4.08%. dH (300 MHz;
Table 3 Crystallographic data and experimental parameters for X-ray structural analyses
)-3 )-4 )-5
(
(
(
(
)-6
(
)-7
( )-8
Empirical formula
Mr
C26H23As2F3O3S
622.37
Monoclinic
C16H19AsF3O3PS
454.28
Monoclinic
C16H19As2F3O3S
498.23
Monoclinic
C28H27As2F3O4S
666.42
Triclinic
¯
P1
11.0285(2)
11.4661(2)
13.0560(2)
93.6545(9)
111.8762(9)
112.4184(9)
1374.93(4)
2
C18H23AsF3O4PS
498.33
Triclinic
¯
P1
8.8425(2)
10.9751(2)
12.9116(3)
110.7028(11)
93.8352(10)
110.9885(11)
1067.16(4)
2
C18H23As2F3O4S
542.28
Triclinic
¯
P1
8.8619(2)
11.0590(2)
13.0115(3)
110.8090(13)
93.8889(14)
111.3757(12)
1081.11(4)
2
Crystal system
Space group
P21/c
P21/n
P21/n
˚
a/A
11.1040(2)
17.8688(3)
13.5567(3)
8.0376(2)
15.2874(3)
15.9712(3)
8.13690(10)
15.2484(4)
15.7429(4)
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
106.5477(12)
101.5155(12)
99.2222(15)
3
˚
V/A
2578.45(8)
4
1.603
1922.94(7)
4
1.569
1928.05(7)
4
1.716
Z
D/ g cm−3
1.610
1.551
1.666
Crystal size/mm
0.26 × 0.21 × 0.16 0.29 × 0.24 × 0.23 0.22 × 0.13 × 0.12 0.20 × 0.19 × 0.16 0.40 × 0.16 × 0.08 0.33 × 0.27 × 0.25
l/mm−1
2.721
1.999
3.614
2.559
1.812
3.233
Reflections collected
Number of unique
64865
5927 (0.056)
40958
4412 (0.038)
42193
4437 (0.040)
42711
6580 (0.033)
36502
5107 (0.038)
33824
5172 (0.032)
reflections (Rint
)
Number of observed
reflections (I > 3r(I))
T/K
2287
2569
2463
4611
3274
3785
200
200
200
200
200
200
Final R1, wR2 (all
data)
0.0819, 0.0397
0.0534, 0.0445
0.0671, 0.0420
0.0401, 0.0344
0.0444, 0.0413
0.0375, 0.0356
Final R1, wR2 (I >
3r(I))
0.0215, 0.0244
0.0294, 0.0346
0.0386, 0.0408
0.0264, 0.0305
0.0265, 0.0307
0.0275, 0.0305
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 2480–2486 | 2485
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graphics were produced with ORTEP-3.26 Crystallographic data
and experimental parameters for X-ray structural analyses are
collated in Table 3.
10 N. L. Kilah, S. Petrie, R. Stranger, J. W. Wielandt, A. C. Willis and S. B.
Wild, Organometallics, 2006, 26, 6106–6113.
11 E. L. Eleil, S. H. Wilen and L. N. Mander, Stereochemistry of Organic
Compounds, Wiley, New York, 1994.
12 R. Blom and A. Haaland, J. Mol. Struct., 1985, 128, 21–27.
13 A. Bondi, J. Phys. Chem., 1964, 68, 441–451.
Acknowledgements
14 W. L. F. Armarego and C. L. L. Chai, Purification of Laboratory
Chemicals, Butterworth-Heinemann, Amsterdam, 5th edn, 2003.
15 E. J. Cragoe, R. J. Andres, R. F. Coles, B. Elpern, J. F. Morgan and
C. S. Hamilton, J. Am. Chem. Soc., 1947, 69, 925–926.
16 G. J. Burrows and E. E. Turner, J. Chem. Soc., Trans., 1920, 117, 1373–
1383.
S. B. W gratefully acknowledges the Australian Research Council
for a grant in support of this work.
References
17 P. G. Kerr, P. H. Leung and S. B. Wild, J. Am. Chem. Soc., 1987, 109,
4321–4328.
1 K. A. Porter, A. C. Willis, J. Zank and S. B. Wild, Inorg. Chem., 2002,
41, 6380–6386.
2 R. H. Anderson and R. H. Cragg, J. Chem. Soc. D, 1971, 1414.
3 N. Burford, B. W. Roylan and P. S. White, J. Am. Chem. Soc., 1989,
111, 3746–3747.
18 F. G. Mann and E. J. Chaplin, J. Chem. Soc., 1937, 527–535.
19 G. I. Kokorev, F. D. Yambushev and L. A. Alꢀmetkina, Zh. Obshch.
Khim., 1988, 58, 330–333.
20 R. B. King and P. M. Sundaram, J. Org. Chem., 1984, 49, 1784–1789.
21 F. G. Holliman and F. G. Mann, J. Chem. Soc., 1947, 1634–1642.
22 Z. Otwinowski and W. Minor, Methods Enzymol., 1997, 276,
307–326.
23 S. Mackay, C. J. Gilmore, C. Edwards, N. Stewart and K. Shankland,
maXus Computer Program for the Solution and Refinement of Crystal
Structures, Nonius, Delft, The Netherlands, MacScience, Japan, and
University of Glasgow, Glasgow, UK, 1999.
4 C. Payrastre, Y. Madaule and J. G. Wolf, Tetrahedron Lett., 1992, 33,
1273–1276.
5 J. M. F. Braddock and G. E. Coates, J. Chem. Soc., 1961, 3208–3211;
G. E. Coates and J. G. Livingstone, Chem. Ind., 1958, 1366.
6 C. Payrastre, Y. Madaule, J. G. Wolf, T. C. Kim, M. R. Mazie`res, R.
Wolf and M. Sanchez, Heteroat. Chem., 1992, 3, 157–162.
7 N. Burford, P. J. Ragogna, K. Sharp, R. McDonald and M. J. Ferguson,
Inorg. Chem., 2005, 44, 9453–9460.
8 H. Althaus, H. J. Breunig and E. Lork, Chem. Commun., 1999, 1971–
1972.
9 J. W. Wielandt, N. L. Kilah, A. C. Willis and S. B. Wild, Chem.
Commun., 2006, 3679–3680.
24 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. C. Burla,
G. Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27, 435.
25 P. W. Betteridge, J. R. Caruthers, R. I. Cooper, K. Prout and D. J.
Watkin, J. Appl. Crystallogr., 2003, 36, 1487.
26 L. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.
2486 | Dalton Trans., 2008, 2480–2486
This journal is
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