The stannylphosphide anion reagent sodium bis(triphenylstannyl) phosphide: Synthesis, structural characterization, and reactions with indium, tin, and gold electrophiles

Article abstract of DOI:10.1021/ic403178j

Treatment of P₄with in situ generated [Na][SnPh₃] leads to the formation of the sodium monophosphide [Na][P(SnPh₃) ₂] and the Zintl salt [Na]₃[P₇]. The former was isolated in 46% yield as the crystalline salt [Na(benzo-15-crown-5)] [P(SnPh₃)₂] and used to prepare the homoleptic phosphine P(SnPh₃)₃, isolated in 67% yield, as well as the indium derivative (XL)₂InP(SnPh₃)₂ (XL = S(CH ₂)₂NMe₂), isolated in 84% yield, and the gold complex (Ph₃P)AuP(SnPh₃)₂. The compounds [Na(benzo-15-crown-5)][P(SnPh₃)₂], P(SnPh ₃)₃, (XL)₂InP(SnPh₃)₂, and (Ph₃P)AuP(SnPh₃)₂ were characterized using multinuclear NMR spectroscopy and X-ray crystallography. The bonding in (Ph ₃P)AuP(SnPh₃)₂ was dissected using natural bond orbital (NBO) methods, in response to the observation from the X-ray crystal structure that the dative P:→Au bond is slightly shorter than the shared electron-pair P-Au bond. The bonding in (XL)₂InP(SnPh ₃)₂ was also interrogated using ³¹P and ¹³C solid-state NMR and computational methods. Co-product [Na] ₃[P₇] was isolated in 57% yield as the stannyl heptaphosphide P₇(SnPh₃)₃, following salt metathesis with ClSnPh₃. Additionally, we report that treatment of P₄ with sodium naphthalenide in dimethoxyethane at 22 °C is a convenient and selective method for the independent synthesis of Zintl ion [Na]₃[P₇]. The latter was isolated as the silylated heptaphosphide P₇(SiMe₃)₃, in 67% yield, or as the stannyl heptaphosphide P₇(SnPh₃)₃ in 65% yield by salt metathesis with ClSiMe₃ or ClSnPh₃, respectively.

Full text of DOI:10.1021/ic403178j

Article
pubs.acs.org/IC
The Stannylphosphide Anion Reagent Sodium Bis(triphenylstannyl)
Phosphide: Synthesis, Structural Characterization, and Reactions
with Indium, Tin, and Gold Electrophiles
Christopher C. Cummins,*,† Chao Huang,†,‡ Tabitha J. Miller,† Markus W. Reintinger,† Julia M. Stauber,†
Isabelle Tannou,† Daniel Tofan,† Abouzar Toubaei,§ Alexandra Velian,*,† and Gang Wu*,§
†Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, United States
‡Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian, China
§Department of Chemistry, Queen’s University, Kingston, Ontario, Canada K7L3N6
S
* Supporting Information
ABSTRACT: Treatment of P4 with in situ generated [Na]-
[SnPh3] leads to the formation of the sodium monophosphide
[Na][P(SnPh3)2] and the Zintl salt [Na]3[P7]. The former was
isolated in 46% yield as the crystalline salt [Na(benzo-15-
crown-5)][P(SnPh3)2] and used to prepare the homoleptic
phosphine P(SnPh3)3, isolated in 67% yield, as well as the
indium derivative (XL)2InP(SnPh3)2 (XL = S(CH2)2NMe2),
isolated in 84% yield, and the gold complex (Ph3P)AuP-
(SnPh3)2. The compounds [Na(benzo-15-crown-5)][P-
(SnPh3)2], P(SnPh3)3, (XL)2InP(SnPh3)2, and (Ph3P)AuP-
(SnPh3)2 were characterized using multinuclear NMR spec-
troscopy and X-ray crystallography. The bonding in (Ph3P)AuP(SnPh3)2 was dissected using natural bond orbital (NBO)
methods, in response to the observation from the X-ray crystal structure that the dative P:→Au bond is slightly shorter than the
shared electron-pair P−Au bond. The bonding in (XL)2InP(SnPh3)2 was also interrogated using 31P and 13C solid-state NMR
and computational methods. Co-product [Na]3[P7] was isolated in 57% yield as the stannyl heptaphosphide P7(SnPh3)3,
following salt metathesis with ClSnPh3. Additionally, we report that treatment of P4 with sodium naphthalenide in
dimethoxyethane at 22 °C is a convenient and selective method for the independent synthesis of Zintl ion [Na]3[P7]. The latter
was isolated as the silylated heptaphosphide P7(SiMe3)3, in 67% yield, or as the stannyl heptaphosphide P7(SnPh3)3 in 65% yield
by salt metathesis with ClSiMe3 or ClSnPh3, respectively.
one operation, directly from white phosphorus and using a
more streamlined protocol. For the present investigation we
settled on sodium naphthalenide as the reducing agent, as this
is conveniently generated in a nitrogen-atmosphere glovebox
upon stirring a mixture of sodium and naphthalene at ambient
temperature in tetrahydrofuran (THF).8 We were pleased to
discover that subsequent addition of ClSnPh3 (to generate
[Na][SnPh3]) followed by P4 delivers the new phosphide anion
[P(SnPh3)2]−, which was isolated in 46% yield as its
[Na(benzo-15-crown-5)]+ salt and fully characterized including
an X-ray diffraction study (see Figure 1). The optimized
reaction conditions also give rise to formation of the well-
known P73− anion, which can be converted in situ to P7R3 (R =
SiMe3, SnPh3) for isolation if desired (see Scheme 1). As
expected, treatment of [P(SnPh3)2]− salts with ClSnPh3
produces P(SnPh3)3, for which an X-ray structural study is
provided (see Figure 2). Further illustrating the potential utility
of the new stannylphosphide reagent, reaction with (XL)2InI
1. INTRODUCTION
Simple phosphide reagents have diverse applications in
inorganic and materials synthesis, and unique among them
are salts of the [P(SiMe3)2]− anion in terms of being able to
generate new P-element bonds by salt elimination as well as by
production of XSiMe3 species.1−6 For example, phosphaalkynes
were prepared by treatment of the monophosphide Li[P-
(SiMe3)2] with acyl chlorides;1 gallium mono and diphosphides
(tBu-DAB)(X)GaP(SiMe3)2, (DAB = [(tBu)NC(H)]2, X = I,
P(SiMe3)2) were prepared by treatment of [(tBu-DAB)GaI]2
with Li[P(SiMe3)2],3 and the disilylphosphido complex Cp*-
(CO)2(NO)MnP(SiMe3)2 was obtained from the reaction of
[Cp*(CO)2(NO)Mn]BF4 with LiP(SiMe3)2.2 Despite this
considerable versatility, there is a synthetic barrier to be
overcome in obtaining alkali metal salts M[P(SiMe3)2]; for
example, Li[P(SiMe3)2] has been obtained by methyllithium
reaction with P(SiMe3)3, which in turn must be either
synthesized (typically by initial treatment of white phosphorus
with hazardous Na/K alloy in a procedure that generates
pyrophoric waste) or purchased at high cost.7 Accordingly, we
wondered if it might be possible to prepare such a reagent in
Received: December 31, 2013
Published: March 12, 2014
© 2014 American Chemical Society
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Figure 2. Solid-state molecular structure of P(SnPh3)3 with ellipsoids
at the 50% probability level and rendered using PLATON.11 Hydrogen
atoms and the solvent molecule are omitted for clarity. Selected
interatomic distances [Å] and angles [deg]: P1−Sn1 2.5068(6), P1−
Sn2 2.5082(6), P1−Sn3 2.5108(6), Sn1−P1−Sn3 104.25(2), Sn1−
P1−Sn2 103.04(2), Sn2−P1−Sn3 102.26(2).
Figure 1. Solid-state molecular structure of [Na(benzo-15-crown-
5)][P(SnPh3)2] with ellipsoids at the 50% probability level and
rendered using PLATON.11 The other [Na(benzo-15-crown-5)][P-
(SnPh3)2] molecule present in the asymmetric unit and hydrogen
atoms are omitted for clarity. Selected interatomic distances [Å] and
angles [deg]: P1−Na1 2.891(2), P1−Sn1 2.439(1), P1−Sn2 2.438(1),
P2−Sn3 2.438(2), P2−Sn4 2.442(2), P2−Na2 2.927(2), Sn1−P1−
Sn2 101.07(5), Sn2−P1−Na1 108.56(6), Sn1−P1−Na1 108.63(6).
according to the literature procedure.10 White phosphorus was
acquired from ThermPhos International BV, Ph3SnCl 95% was
purchased from Alfa Aesar, (Ph3P)AuCl was purchased from Strem
Chemicals, while all other reagents were purchased from Aldrich and
were used without further purification. Deuterated solvents were
purchased from Cambridge Isotope Laboratories. Benzene-d6 was
degassed and stored over molecular sieves (4 Å beads, 8−12 mesh) for
at least 2 d prior to use. Celite 435 (EM Science) was dried by heating
above 200 °C under dynamic vacuum for at least 24 h prior to use. All
glassware was oven-dried for at least 3 h prior to use, at temperatures
greater than 150 °C. NMR spectra were obtained on Bruker Avance
400 instruments equipped with Magnex Scientific superconducting
a
Scheme 1
1
magnets. H and 13C{1H} NMR spectra were referenced to residual
solvent proton resonances in benzene-d6 (1H = 7.16 ppm, 13C =
128.06 ppm, respectively); spectra were referenced externally to 85%
H3PO4 (0 ppm). 119Sn NMR spectra were referenced externally to 5%
SnMe4 in CH2Cl2 (0 ppm). Elemental combustion analyses were
performed by Intertek USA, Inc., by Complete Analysis Laboratories
Inc., or by Robertson Microlit Laboratories. Solid-state 31P and 13C
NMR spectra were acquired under the cross-polarization (CP) magic-
angle spinning (MAS) condition on a Bruker Avance-600 NMR
spectrometer (14.0 T) operating at the 1H, 31P, and 13C Larmor
frequencies of 600.17, 242.95, and 150.93 MHz, respectively. High-
power 1H decoupling was applied during data acquisition. Solid
(XL)2InP(SnPh3)2 was packed into a ZrO2 rotor (4 mm o.d.) inside a
glovebox. A 4 mm Bruker H/X MAS probe was used with a sample
spinning frequency of 14.5 kHz. Typically, relaxation delays of 2−5 s
were employed. All 31P and 13C chemical shifts were referenced to the
signals of 85% H3PO4 (aq) and tetramethylsilane, respectively, using
solid NH4H2PO4 and glycine as secondary referencing samples.
Spectral simulations were performed using WSolids1.12
Crude Triphenylstannylsodium ([Na][SnPh3]). This was
synthesized using a slightly modified literature procedure.13 THF
(10 mL) was added to a mixture of sodium metal (0.138 g, 6.00 mmol,
2.00 equiv) and naphthalene (0.768 g, 5.99 mmol, 2.00 equiv). The
reaction mixture was stirred vigorously for at least 5 h, until all the
sodium metal was consumed. The resulting dark green reaction
mixture was added dropwise to a solution of Ph3SnCl (1.156 g, 3.00
mmol, 1.00 equiv) in THF (20 mL) under vigorous stirring, resulting
in an orange-brown mixture. 119Sn NMR analysis of an aliquot showed
a single broad peak at −105 ppm corresponding to the [Na][SnPh3].
The volatile materials from the reaction mixture were removed under
reduced pressure, and the resulting oily residue was stirred in n-hexane
(10 mL), then again brought to constant mass under reduced pressure.
The orange-brown powder obtained this way was slurried in n-hexane
(20 mL), and the supernatant was decanted away. The precipitated off-
a
A series of tetrel phosphides were obtained by reaction of white
phosphorus with either the stannyl salt [Na][SnPh3] or sodium
naphthalenide, [Na][C10H8]. The corresponding phosphides were
obtained via salt metathesis with RCl, where R = SiMe3, SnPh3 (crown
= benzo-15-crown-5).
(XL = S(CH2)2NMe2)9,10 was found efficiently to furnish a
terminal indium phosphanide species, (XL)2In−P(SnPh3)2,
featuring an unsupported indium-PR2 linkage. Characterization
data provided for the latter stem from both a crystallographic
structure determination and interrogation by solid-state NMR
methods (see Table 1). Additionally, the gold complex
(Ph3P)AuP(SnPh3)2 could be prepared in the salt elimination
reaction of [Na(benzo-15-crown-5)][P(SnPh3)2] with (Ph3P)-
AuCl.
2. EXPERIMENTAL SECTION
General Information. All manipulations were performed in a
Vacuum Atmospheres model MO-40 M glovebox under an inert
atmosphere of purified N2. All solvents were obtained anhydrous and
oxygen-free by bubble degassing (N2) and purification through
columns of alumina and Q5 using a Glass Contours Solvent
Purification System built by SG Water. (XL)2InI was prepared
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white powder containing the [Na][SnPh3] salt was used in the next
steps without any further purification, under the assumption that the
transformation had been quantitative.
(10 mL), during which addition the reaction mixture turned colorless.
The volatile materials were then removed under reduced pressure, and
the resulting white residue was washed with n-hexane (20 mL) and
suspended in Et2O (20 mL). This suspension was subjected to
filtration through a pad of Celite in a fritted filter funnel, and the filter
cake was washed with additional toluene (20 mL). The combined
filtrate was concentrated under reduced pressure and brought to
constant mass to afford colorless solids of spectroscopically pure
P(SnPh3)3 (0.98 g, 0.97 mmol, 65% yield). Analytically pure
P(SnPh3)3 was obtained by collecting the crystals formed upon
cooling a saturated solution of the spectroscopically pure material in
Et2O, at −35 °C. 1H NMR (benzene-d6, 20 C, 400 MHz) δ: 6.98 (m,
18 H), 7.09 (9 H), 7.24 (m, 3J119SnH = 58 Hz, 3J117SnH = 44 Hz, 18 H)
ppm. 13C{1H} NMR (benzene-d6, 20 °C, 100.6 MHz) δ: 128.77,
129.06, 137.62 (2JSnC = 5 Hz), 140.62 (dt, 2JPC = 40 Hz) ppm. 31P{1H}
NMR (benzene-d6, 20 °C, 161.9 MHz) δ: −325.2 (s, 1J119SnP = 886 Hz,
1J117SnP = 855 Hz) ppm. 119Sn NMR (149.2 MHz, benzene-d6) δ:
Reaction of P4 with [Na][SnPh3]. A 100 mL round-bottom flask
was charged with THF (10 mL), Et2O (30 mL), crude [Na][SnPh3]
(ca. 3 mmol, 2 equiv) and a Teflon-coated stir bar. To this mixture, a
solution of P4 (0.186 g, 1.50 mmol, 1.20 equiv) in toluene (15 mL)
was added dropwise under vigorous stirring. The color of the reaction
mixture changed to vivid orange, and an orange-red precipitate
formed. The resulting slurry was filtered through a pad of Celite in a
sintered glass frit. The orange filter cake containing the [Na]3[P7] was
set aside and worked up separately, as described below.
[Na(benzo-15-crown-5)][P(SnPh3)2]. To the orange filtrate
obtained as described in the previous section was added, in one
portion, benzo-15-crown-5 (0.402 g, 1.50 mmol, 1.00 equiv), effecting
the immediate precipitation of red solids. The reaction mixture was
subjected to filtration through a fritted filter funnel, and the resulting
filtrate was stirred for another 30 min before the volatile materials were
removed under reduced pressure. The residue was slurried in toluene
(5 mL), then allowed to settle, and the pale yellow supernatant was
decanted by pipet and discarded. The oily solids so obtained were
placed under vacuum before being slurried in Et2O (8 mL) for 1 h,
effecting the formation of a powder, which was then allowed to settle.
The supernatant was again separated by pipet and discarded, and all
volatile materials were removed from the resulting yellow powder
under reduced pressure. Next, this material was extracted three times
with toluene (3 × 5 mL), to remove traces of P7(SnPh3)3, and then six
times with Et2O (6 × 5 mL) to remove P(SnPh3)3. The residue,
brought to constant mass under reduced pressure, was deemed
spectroscopically pure [Na(benzo-15-crown-5)][P(SnPh3)2] (713 mg,
1
−69.2 (d, J119SnP = 886 Hz) ppm. Elemental analysis (%) found
(calculated) for C54H45PSn3: C 60.14(60.00), H 4.09(4.20), P
2.79(2.87). Melting point: 208−210 °C.
(XL)2InP(SnPh3)2 (XL = S(CH2)2NMe2). Cold toluene (−35 °C, 5
mL) was added to a 100 mL round-bottom flask containing solid
(XL)2InI (90 mg, 0.20 mmol, 1.00 equiv) and [Na(benzo-15-crown-
5)][P(SnPh3)2] (0.204 g, 0.20 mmol, 1.00 equiv). The reaction
mixture was stirred for 20 min before adding more cold toluene (5
mL). After 1.5 h of stirring at 22 °C, the reaction mixture was filtered
through a pad of Celite in a fritted filter funnel. The volatile materials
were removed from the colorless filtrate under reduced pressure,
resulting in spectroscopically pure (XL)21InP(SnPh3)2 as a white
powder (176 mg, 0.167 mmol, 84% yield). H NMR (benzene-d6, 20
°C, 400 MHz) δ: 1.86 (s, 12 H), 1.98 (broad s, 4 H), 2.41 (broad s, 4
H), 7.12 (m, 18 H), 7.70 (m, 12 H) ppm. 13C{1H} NMR (benzene-d6,
20 °C, 100.6 MHz) δ: 24.62 (CH3), 45.36 (CH2), 61.35 (CH2), 128.67
(SnC6H5), 128.88 (SnC6H5), 137.94 (2JSnC = 40 Hz, SnC6H5), 142.6
ppm (SnC6H5). 31P{1H}NMR (benzene-d6, 20 °C, 161.9 MHz) δ:
1
0.69 mmol, 46%). H NMR (benzene-d6, 20 °C, 400 MHz) δ: 3.01
(m, 4 H), 3.08 (m, 4 H), 3.16 (m, 4 H), 3.26 (m, 4 H), 6.41 (m, 2 H),
3
6.78 (m, 2 H), 7.10 (m, 18 H), 7.82 (m, JSnH = 50 Hz, 12 H) ppm.
13C{1H} NMR (benzene-d6, 20 °C, 100.6 MHz) δ: 66.76 (CH2), 67.53
(CH2), 68.82 (CH2), 69.11 (CH2), 112.83, 121.98, 127.37, 127.87,
137.74 (2JSnC = 38 Hz, SnC6H5), 147.13 (SnC6H5), 147.68 (d, 2JPC = 3
Hz, SnC6H5) ppm. 31P{1H} NMR (benzene-d6, 20 °C, 161.9 MHz) δ:
1
1
−309.9 (s, J119SnP = 990 Hz, J117SnP = 950 Hz) ppm. 119Sn NMR
1
(149.2 MHz, benzene-d6) δ: −65.9 (d, J119SnP = 990 Hz) ppm.
Elemental analysis (%) found (calculated) for C44H50InN2S2Sn2P: C
50.08(50.13), H 4.69(4.78), N 2.53(2.66), P 2.79(2.94)
1
1
−367.2 (s, J119SnP = 1395 Hz, J117SnP = 1329 Hz) ppm. 119Sn NMR
1
(149.2 MHz, benzene-d6) δ: −11.0 (s, J119SnP = 1395 Hz) ppm.
Elemental analysis (%) found (calculated) for C50H50NaO5PSn2: C
58.60(58.74), H 4.43(4.93), and P 3.13(3.03). Melting point: 185−
186 °C.
P7(SiMe3)3. To a solution of naphthalene (3.540 g, 27.60 mmol,
3.00 equiv) in dimethoxyethane (DME) (20 mL) were added small
pieces of freshly cut sodium metal (0.635 g, 27.60 mmol, 3.00 equiv).
The reaction mixture was vigorously stirred for 8 h or longer, until all
the sodium metal was consumed. The sodium naphthalenide solution
was then added to a slurry of P4 (2.000 g, 16.14 mmol, 1.75 equiv) in
DME (30 mL), in a round-bottom flask covered in Al foil. The
reaction mixture was stirred for 8 h, at which point ClSiMe3 (3.000 g,
27.60 mmol, 3.00 equiv) was added dropwise. The resulting orange-
red slurry was stirred for 2 h, then brought to constant mass under
reduced pressure. The dark red solids were transferred to the bottom
of a sublimation apparatus, which was then evacuated. The apparatus
was then removed from the glovebox and set up for sublimation in an
oil bath preheated to 60 °C, with the circulating water at 6 °C. After
approximately 7 h when all the naphthalene had been removed by
sublimation, the apparatus was returned to the glovebox, where dark
red solids at the bottom of the sublimation apparatus were slurried in
n-pentane (100 mL) and then subjected to filtration through a Celite
pad contained within a fritted filter funnel. The Celite pad was washed
with additional n-pentane until the filtrate ran colorless. The combined
yellow filtrate was concentrated before being set at −35 °C for
crystallization. Yellow crystals of P7(SiMe3)3 formed overnight and
were collected by filtration in several crops (2.700 g, 6.10 mmol, 67%
P7(SnPh3)3 (Method A). The orange filter cake obtained as
described above and contained on a bed of Celite in a fritted glass filter
funnel was washed with THF (15 mL), and the resulting orange
filtrate containing [Na]3[P7] (31P NMR δ = −120 ppm) was
collected.14 To this mixture, a solution of ClSnPh3 (0.578 g, 1.50
mmol, 3.00 equiv with respect to the theoretical amount of [P7]−3
anion formed in the reaction, based on the equation in Scheme 1) in
THF (8 mL) was added dropwise, effecting a color change from
orange to brown. The reaction mixture was brought to constant mass
under reduced pressure, and the resulting brown residue was
suspended in a mixture of n-hexane (10 mL) and Et2O (20 mL).
The suspension was subjected to filtration through a fritted filter
funnel, and the volatile materials were removed from the resulting
filtrate under reduced pressure. The obtained residue was suspended
in a mixture of Et2O (10 mL) and toluene (10 mL) and subjected
again to filtration through a pad of Celite. The filtrate was brought to
constant mass under reduced pressure, yielding spectroscopically pure
P7(SnPh3)3 as a yellow powder (0.341 g, 0.285 mmol, 57% yield). The
NMR spectra (1H, 31P) were consistent with reported values.15
P(SnPh3)3. A 100 mL round-bottom flask was charged with THF
(10 mL), Et2O (30 mL), crude [Na][SnPh3] (ca. 3 mmol, 2 equiv),
and a Teflon-coated stir bar. A solution of P4 (0.186 g, 1.50 mmol,
1.20 equiv) in toluene (15 mL) was added dropwise under vigorous
stirring as the color of the reaction mixture changed to vivid orange
and an orange-red precipitate formed. The resulting slurry was
subjected to filtration through a pad of Celite in a fritted filter funnel.
To the orange filtrate containing [Na][P(SnPh3)2] salt was added
dropwise a slurry of ClSnPh3 (0.578 g, 1.50 mmol, 1.00 equiv) in THF
1
yield). The observed H and 31P NMR signals were consistent with
reported values.16
P7(SnPh3)3 (Method B). To a solution of naphthalene (0.897 g,
7.00 mmol, 3.00 equiv) in DME (7 mL) were added small pieces of
freshly cut sodium metal (0.161 g, 7.00 mmol, 3.00 equiv). The
reaction mixture was vigorously stirred for 5 h or longer, until all the
sodium metal was consumed. The sodium naphthalenide solution was
then added to a slurry of P4 (0.500 g, 4.04 mmol, 1.73 equiv) in DME
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(5 mL), with the aid of additional DME (5 mL), and the reaction flask
was protected from light by covering in Al foil. The reaction mixture
was stirred for 10 h, at which point solid ClSnPh3 (2.700 g, 7.00 mmol,
1.73 equiv) was added in one portion. The orange-red slurry was
stirred for 4 h and then brought to constant mass under reduced
pressure. The yellow-orange solids were transferred to the bottom of a
sublimation apparatus, which was then evacuated. The apparatus was
then removed from the glovebox and set up for sublimation in an oil
bath preheated to 60 °C, with the circulating water at 6 °C. After
approximately 8 h, when all the naphthalene had been removed by
sublimation, the apparatus was returned to the glovebox, where the
yellow solids at the bottom of the sublimation apparatus were slurried
in n-pentane (100 mL) and then subjected to filtration through a
Celite pad contained within a fritted filter funnel. The Celite pad was
washed with additional n-pentane until the filtrate ran colorless. The
volatile materials were then removed from the combined filtrate under
reduced pressure, resulting in an orange-yellow residue, which was
slurried in n-hexane (5 mL), then brought back to constant mass. The
collected yellow powder was identified as pure P7(SnPh3)3 (1.982 g,
pair P−Au bonds were analyzed with the aid of natural bond order
(NBO)29 and natural resonance theory (NRT) analysis.30
X-ray Diffraction Studies. Diffraction-quality, light yellow crystals
of [Na(benzo-15-crown-5)][P(SnPh3)2] were obtained by vapor
diffusion of n-pentane into a concentrated solution of the salt in
THF. Colorless crystals of P(SnPh3)3 were grown upon cooling a
warm solution in Et2O/n-hexane (1:1) to 22 °C. X-ray quality crystals
of (Ph3P)AuP(SnPh3)2 were grown at room temperature by vapor
diffusion of n-pentane into a concentrated solution of the gold
phosphide in toluene. Low-temperature (100 K) data were collected
on a Siemens Platform three-circle diffractometer coupled to a Bruker-
AXS Smart Apex CCD detector with graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å) and on a Bruker-AXS X8 Kappa Duo
diffractometer coupled to a Smart Apex2 charge-coupled device
(CCD) detector with Mo Kα radiation (φ- and ω-scans). A
semiempirical absorption correction was applied to the diffraction
data using SADABS.31 All structures were solved by direct or Patterson
methods using SHELXS32,33 and refined against F2 on all data by full-
matrix least-squares with SHELXL-97.33,34 All non-hydrogen atoms
were refined anisotropically. All hydrogen atoms were included in the
model at geometrically calculated positions and refined using a riding
model. The isotropic displacement parameters of all hydrogen atoms
were fixed to 1.2 times the Ueq value of the atoms they are linked to
(1.5 times for methyl groups).35 Descriptions of the individual
refinements follow below. Details of the data quality and a summary of
the residual values of the refinements for all structures are provided in
Supporting Information, Table S.1 and in the form of .cif files available
from the CCDC under the deposition numbers 943071, 943072,
974655, and 974656.36
The sodium phosphide [Na(benzo-15-crown-5)][P(SnPh3)2] crys-
tallized in the monoclinic space group P21 with two molecules in the
asymmetric unit. One of the twelve phenyl rings and one of the two
phenylene groups were each disordered over two positions. The
phosphide P(SnPh3)3 crystallized in the orthorhombic space group
P21/n, with an asymmetric unit containing two molecules of
compound and one molecule of diethyl ether, which was disordered
over two positions. The two occupancies of each disordered position
were refined freely, and their sums were restrained to unity. The
indium phosphide (XL)2InP(SnPh3)2 crystallized in the monoclinic
space group P21, with an asymmetric unit containing one molecule of
compound and one molecule of toluene, which was disordered over
the inversion center. Additionally, one of the six phenyl rings was
disordered over two positions, and the two S(CH2)2NMe2 arms on the
indium atom were disordered over a total of five positions.
15
1
1.56 mmol, 65%) using H and 31P NMR spectroscopy.
(Ph3P)AuP(SnPh3)2. A solution of (Ph3P)AuCl (243 mg, 0.49
mmol, 1 equiv) in toluene (20 mL) was added dropwise, at room
temperature, to a slurry of [Na(benzo-15-crown-5)][P(SnPh3)2] (500
mg, 0.49 mmol, 1 equiv) in toluene (20 mL). The reaction mixture
was stirred for 30 min and then was subjected to filtration through a
pad of Celite. All volatile materials were removed under reduced
pressure from the yellow filtrate. The resulting yellow powder was
washed with Et2O (2 × 5 mL and 1 × 10 mL) and was then brought to
constant mass under reduced pressure to afford 322 mg of a beige
powder. 31P NMR spectroscopy confirmed the composition of the
material to be a mixture of free PPh3 (ca. 7%) and (Ph3P)AuP-
(SnPh3)2 (estimated 0.27 mmol, 55%). Further purification efforts,
including recrystallization and Et2O extraction of the PPh3 impurity,
were unsuccessful. Satisfactory combustion elemental analysis was not
obtained for this compound. 1H NMR (benzene-d6, 20 °C, 400 MHz)
δ: 6.92 (m, 8 H), 6.99 (m, 16 H), 7.09 (m, 9 H) ppm. 13C{1H} NMR
(benzene-d6, 20 °C, 100.6 MHz) δ: 128.47, 128.71, 129.19, 129.30,
131.09, 134.46, 134.60, 137.60 ppm. 31P{1H} NMR (benzene-d6, 20
°C, 161.9 MHz) δ: −303.9 (d, 2JPP = 78 Hz, 1J119SnP = 524 Hz), 46.68
2
3
(d, JPP = 78 Hz, J119SnP = 27 Hz) ppm. 119Sn NMR (149.2 MHz,
benzene-d6) δ: −44.10 (dd, 1J119SnP = 1046 Hz, 3J119SnP = 55 Hz) ppm.
Computational Methods. NMR parameters were computed
using the Amsterdam Density Functional (ADF) software package.17
The Vosko−Wilk−Nusair (VWN) exchange-correlation functional18
was used for the local density approximation (LDA), and the Perdew−
Burke−Ernzerhof (PBE) exchange-correlation functional19 was
applied for the generalized gradient approximation (GGA). Standard
Slater-type-orbital (STO) basis sets with triple-ζ quality plus
polarization functions (TZ2P) were used for all the atoms. The
spin−orbital relativistic effect was incorporated via the zero-order
regular approximation (ZORA).20 The crystallographically determined
molecular structure of (XL)2InP(SnPh3)2 was used directly in the
computations. The 31P chemical shift (δ) was converted from the
computed shielding constant (σ) using the absolute 31P shielding
scale:21 δ = 328.35 − σ. All quantum-chemical calculations pertaining
to the analysis of (XL)2InP(SnPh3)2 were performed at the High
Performance Computing Virtual Laboratory (HPCVL) at Queen’s
University.
The gold phosphide (Ph3P)AuP(SnPh3)2 crystallized in the triclinic
space group P1 with four molecules per asymmetric unit. Two phenyl
̅
rings (SnPh3) were disordered over two positions. Refinement of the
structure against a smaller unit cell, which contained only two
molecules per asymmetric unit, led to the generalized disorder of the
phenyl groups and an unsatisfying solution. The occupancies of each
disordered position were refined freely, and their sums were restrained
to unity. Similarity restraints on 1−2 and 1−3 distances and
displacement parameters, as well as rigid bond restraints for
anisotropic displacement parameters, were applied to the disordered
fragments.
3. RESULTS AND DISCUSSION
Synthesis and Structure. Treatment of a 1:3 THF/Et2O
solution of the in situ-generated stannyl anion [SnPh3]− with a
solution of P4 in toluene at 22 °C led to the formation of
monophosphide [Na][P(SnPh3)2] and the Zintl ion coproduct
[Na]3[P7].37 The Zintl ion, which precipitated as an orange-red
solid from the reaction mixture upon mixing the two reagents,
was separated by suction filtration from the supernatant and
identified by its diagnostic single broad resonance at −122.0
ppm in the 31P NMR spectrum38 obtained by analyzing a
solution of the precipitated solid in THF. Multinuclear NMR
analysis of the supernatant revealed the formation of a major
The calculations pertaining to the gold model complex H3P−Au−
PH2, built using Molden,22 were performed at the second-order
Møller−Plesset perturbation theory (MP2) level,23 as well as at the
B3LYP level, and were carried out using the ORCA 3.0.1 quantum
chemistry program package.24 The LDA functional employed was
LYP25 or PW-LDA,26 while the GGA part was handled using the
functionals of Becke and Perdew (BP86 or BLYP).27 The TZVPP
basis set was used for all atoms,28 the spin−orbital relativistic effect
was incorporated via the zero-order approximation (ZORA),20 and
tight self-consistent field convergence criteria (provided by ORCA)
were employed. The nature of the dative P:→Au and shared electron
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Table 1. Summary of P−Sn Bond Distances, Sn−P−Sn Bond Angles, and 31P and 119Sn NMR Data for R*P(SnPh3)2 Derivatives
a
R*
P−Sn [Å]
Sn−P−Sn [deg]
31P NMR (δ, ppm)
119Sn NMR (δ, ppm)
Na(crown)
2.439(1)
2.438(1)
2.4984(8)
2.4933(8)
2.492(1)
2.502(1)
2.5068(6)
2.5082(6)
2.5108(6)
101.07(5)
−367.2
−11
(XL)2In
(Ph3P)Au
SnPh3
103.55(3)
107.66(6)
−309.9
−303.9
−325.2
−65.9
−44.1
−69.2
104.25(2)
103.04(2)
102.26(2)
a
R* = Na(benzo-15-crown-5), SnPh3, (XL)2In (XL = S(CH2)2NMe2), and (Ph3P)Au.
new species with resonances at −11.0 ppm in the 119Sn NMR
spectrum, at −367.2 ppm in the 31P NMR spectrum, and a
coupling constant of 1J119SnP = 1395 Hz, as well as the presence
of small amounts of unreacted P4. To aid the purification and
characterization of the new salt, the sodium cation was partially
sequestered by addition of benzo-15-crown-5 to the super-
natant, as described in the Experimental Section.
indium phosphide (XL)2InP(SnPh3)2 was obtained in 84%
isolated yield as a monomeric species (see Scheme 2). Several
indium diorganophosphides, including [Cp*(Cl)InP-
(SiMe3)2]2, have been investigated previously as single-source
precursors to indium phosphide particles.49,51
a
Scheme 2
The synthesis of the monophosphide [Na(benzo-15-crown-
5)][P(SnPh3)2] salt in a one-pot reaction from white
phosphorus is advantageous and constitutes, to our knowledge,
the first report of direct P4 functionalization by a stannyl anion.
Select aryl and silyl phosphides have been synthesized by direct
activation of P4 with aryllithium and bulky alkali silanides,
respectively.39,40 In the case of aryl phosphides the steric bulk
of the organolithium reagent determined the nuclearity of the
aryl phosphide obtained. Thus, only one of the six P−P bonds
of the P4 cage was cleaved with 2,4,6-tri-tert-butylphenyl-
lithium,41 whereas all six P−P bonds were cleaved with
phenyllithium.42 When bulky silyl nucleophiles [M][SitBu3],
[M][SitBu2Ph], and [M][Si(SiMe3)3] (M = Li, Na, K, Cs) were
used, the extent of fragmentation of the P4 cage increased with
the number of silanide equivalents and solvent polarity.40,43−45
For example, the 1:1 reaction of the hypersilyl salt [K(18-
crown-6)][Si(SiMe3)3] with P4, in toluene, led to formation of
t h e d i s u b s t i t u t e d n o r t r i c y c l i c Z i n t l i o n
[K(18-crown-6)]2[P7(PR)(R)] (R = Si(SiMe3)3) in ca. 30%
yield, ostensibly via dimerization of the putative [RP4]−
anion.44 In contrast, in the 2:1 reaction of supersilyl salt
[Na][SitBu3] with P4 in THF or DME, [Na][P(R′)−PP−
P(R′)][Na] (R′ = SitBu3) formed quantitatively.43 It is
noteworthy that the complete fragmentation of the P4 cage
to synthetically useful silyl monophosphides was negligible.
The monophosphide [P(SnPh3)2]− anion has the potential
to form homo- and heteroleptic tin phosphides by appropriate
selection of a salt metathesis partner. Investigating this
possibility, we first demonstrated that treatment of [Na-
(benzo-15-crown-5)][P(SnPh3)2] with ClSnPh3 leads to the
formation of the homoleptic phosphide P(SnPh3)3, isolated in
65% yield. The latter phosphide has been traditionally prepared
a
The sodium phosphide salt [Na(benzo-15-crown-5)][P(SnPh3)2]
was used to prepare the indium phosphide (XL)2InP(SnPh3)2, isolated
in 84% yield (crown = benzo-15-crown-5).
Additionally, the Zintl ion [Na]3[P7], formed as a coproduct
in the synthesis of the monophosphide [P(SnPh3)2]− anion,
can be prepared selectively via an independent method that
entails the treatment of a slurry of P4 with freshly prepared
sodium naphthalenide in DME at 22 °C. The corresponding
polyphosphides P7R3 (R = SiMe3, SnPh3) obtained by salt
metathesis from this reaction were isolated in better than 65%
yield. The traditional synthesis of the heptaphosphide
[Na]3[P7] entails harsher reaction conditions, either of
refluxing white phosphorus and Na/K alloy in DME16 or of
heating the elements in a sealed and evacuated ampule at 770
K.52,53
Typically, the reaction of P4 with alkali metals gives rise to
numerous products.53,54 For example, in refluxing DME the
reduction with alkali metals gives rise to a mixture of the
polyphosphide ions P37−, P , P , P , P , and even to cyclo-
3−
4−
3−
2−
19
26
21
16
P−5 , when 18-crown-6 is present.55−57 In contrast, the reduction
of P4 with Na/K napthalenide in DME at low temperatures
allows the isolation of [Na/K][HP4] solutions, the [HP4]−
anion being a key intermediate in the formation of higher-
nuclearity polyphosphide anions.40,58
46
47
using either PH3 or PCl3 as the phosphorus source, and
more recently by effective [SnPh3] radical addition to molecular
phosphorus, in analogy with the phosphorus chlorination
process.48
Seeking to prepare heteroleptic tin phosphides to serve as
potential single-source precursors49 to indium phosphide
materials, we turned to the reported indium monoiodide
(XL)2InI,10 which we expected to give rise to a molecule with a
1:1 ratio of In/P. Additionally, its thiolate XL units will
potentially be removable subsequently as Ph3SnXL.50 The
The solid-state structure of [Na(benzo-15-crown-5)][P-
(SnPh3)2] is the first example of a monomeric bis(stannyl)
monophosphide. The only other reported structure of a
bis(stannyl) phosphide is that of {Li(THF)2[P(SnMe3)2]}2,
the latter having a structure that features two lithium bridges
between the two phosphorus atoms of the dimeric unit.4 The
P−Sn interatomic distances in both [Na(benzo-15-crown-
5)][P(SnPh3)2], of 2.439(1) and 2.438(1) Å, and {Li-
(THF)2[P(SnMe3)2]}2, of 2.439(2) and 2.424(2) Å, fall right
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between 2.51 and 2.32 Å, these being the values indicated for a
P−Sn single and double bond, respectively.59 This is suggestive
of a bond order that is >1 between the electron-rich
phosphorus and the tin atoms.
The cage phosphide P4(SnMe2)6, obtained from P(SnMe3)3
in the presence of small amounts of (ZnCl)2Fe-
(CO)4(THF)2,60 provides the closest reported structural
match to P(SnPh3)3. The P−Sn interatomic distances of
2.5068(6), 2.5082(6), and 2.5108(6) Å for P(SnPh3)3, and
averaging 2.505 Å in P4(SnMe2)6, are typical values for single
P−Sn bonds. The pyramidalization at phosphorus in the two
compounds is also similar, as measured by the sum of bond
angles at phosphorus of 309.55(2)° in P(SnPh3)3 and averaging
308° in P4(SnMe2)6. Among the reported homoleptic stannyl
monophosphides P(SnR″3)3 (R″ = CH3,61 n-C4H9,62 tert-
C4H963), the phosphide P(SnPh3)3 appears to be the first one
to be crystallographically characterized.36
Similar to the phosphide [Na(benzo-15-crown-5)][P-
(SnPh3)2], the indium phosphide (XL)2InP(SnPh3)2 is also
monomeric (see Figure 3). Analogous indium phosphides
Figure 4. Solid-state molecular structure of (Ph3P)AuP(SnPh3)2 with
ellipsoids at the 50% probability level and rendered using PLATON.11
The other three molecules of (Ph3P)AuP(SnPh3)2 present in the
asymmetric unit and hydrogen atoms are omitted for clarity. Selected
interatomic distances [Å] and angles [deg]: P21−Au2 2.293(1), Au2−
P22 2.320(1), P22−Sn22 2.492(1), P22−Sn21 2.502(1), Sn22−P22−
Sn21 107.66(6), Au2−P22−Sn22 95.83(6), P21−Au2−P22
175.18(6).
well to those reported together with complete structural data
for gold phosphane and phosphanido complexes.65,66 The
arrangement of the two phosphorus atoms is almost linear
around the Au(I) center, with an angle of P21−Au−P22 of
175.18(6)°. The interatomic distance of 2.320(1) Å between
P22, the X-type phosphorus ligand,9 and the gold center is only
slightly shorter than 2.35 Å, the calculated value for a P−Au
single bond.59 The P21−Au2 interatomic distance of 2.293(1)
Å is typical for a gold−phosphine bond.67
In accordance with general trends observed for 31P NMR
shifts,68 the electronegativity of the R* (R* = Na(benzo-15-
crown-5), SnPh3, In(XL)2, (Ph3P)Au) substituent on R*P-
(SnPh3)2 phosphide correlates inversely with an upfield shift in
the observed 31P NMR resonances (see Table 1).
Figure 3. Solid-state molecular structure of (XL)2InP(SnPh3)2 with
ellipsoids at the 50% probability level and rendered using PLATON.11
Hydrogen atoms and the solvent molecule are omitted for clarity.
Selected interatomic distances [Å] and angles [deg]: P1−Sn1
2.4984(8), P1−Sn2 2.4933(8), P1−In 2.5470(9), In−N1 2.451(6),
In−S1 2.463(4), In−N2 2.465(8), In−S1 2.463(4), Sn1−P1−Sn2
103.55(3), Sn1−P1−In 119.71(3), Sn2−P1−In 105.21(3).
NBO Study of Dative versus Shared Electron-Pair Au−
P Bonding in the Same Molecule. It is interesting to note
that (Ph3P)AuP(SnPh3)2 is an example of a gold(I) compound
that offers an intramolecular comparison of two different bond
types. The covalent single bond between gold and the
phosphanide ligand should have a distance close to the sum
of covalent radii for the two elements (1.24 + 1.11 = 2.35 Å),59
and this is found experimentally to be the case (2.320(1) Å).
On the other hand, since dative or donor−acceptor bonds are
generally weaker than shared electron-pair bonds,69 there is also
the expectation that the interatomic distance Au−P(phosphine)
should be longer than that to the phosphanide ligand, but
experimentally we find that it is marginally shorter: 2.293(1) Å.
That this is not an anomaly is suggested by the corresponding
distances calculated for the simple model system H3P−Au−
PH2 using MP2 theory: 2.30, 2.26 Å; here too, the gold−
phosphine distance is shorter by ca. 0.04 Å than is the gold−
phosphanide distance. A similar circumstance was reported also
for the only other structurally characterized phosphine/
phosphanide system.65 The basis for the closeness in the
interatomic distances displayed for these two very different
bond types (covalent versus dative) is that the hybrid orbital
used by phosphorus for the dative bond very rich in s character
supported by less bulky ligands form oligomers, such as
64
[Me2InP(SnMe3)2]3 or [Cp*(Cl)InP(SiMe3)2]2.51 A lighter
congener, the monomeric aluminum phosphide (2,6-
Me2Pip)2AlP(SnMe3)2,4 (Pip = piperidide) is structurally
similar to the indium phosphide (XL)2InP(SnPh3)2 as seen
from the sum of angles at phosphorus of 328.47(3)° in
(XL)2InP(SnPh3)2 and 326.32(5)° in (2,6-Me2Pip)2AlP-
(SnMe3)2, and the P−Sn interatomic distances of 2.4984(8)
and 2.4933(8) Å in (XL)2InP(SnPh3)2 and of 2.479(1) and
2.478(1) Å in (2,6-Me2Pip)2AlP(SnMe3)2, consistent with a P−
Sn single bond. The P−In bond distance of 2.5470(9) Å is
slightly longer than 2.53 Å, the value expected for a P−In single
bond.59
The monomeric gold phosphide (Ph3P)AuP(SnPh3)2
crystallizes in the triclinic space group P1 with four almost-
̅
identical molecules per asymmetric unit, one of which is
discussed herein (see Figure 4). The structure is not remarkable
with respect to the metrical parameters; indeed, these compare
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(NBO analysis shows the phosphine lone pair to be 52% s, 48%
p), while for the shared electron-pair bond it is much less so
(15% s, 85% p) (Figure 5). Keep in mind that assignment of
Figure 5. (a) The natural bond orbitals (NBOs) corresponding to the
dative bond phosphine−gold interaction, (b) the covalent phospha-
nido−gold bond, and (c) the natural localized molecular orbital
(NLMO) corresponding to the phosphine lone pair donation into the
Au−P(phosphanide) σ* orbital in the model complex H3P−Au−PH2,
built and optimized at the MP2 level of theory22,71 and visualized using
NBOView 2.0.72
Figure 6. Solid-state (a) MAS and (b) static 31P NMR spectra of
(XL)2InP(SnPh3)2 recorded at 14.0 T. Spinning sidebands (ssb) are
marked with *. (inset) The (black) observed and (red) simulated line
shape for the central band.
the triphenylphosphine ligand as a dative ligand is not arbitrary:
its structural parameters in the complex are nearly the same as
in the free ligand.70 Furthermore, natural resonance theory
(NRT) analysis shows that H3P: Au−PH2 is the dominant
resonance structure for the model. This makes sense given that
the d10 gold center has only its 6s orbital available for bonding,
such that any gold−phosphine bonding must come at the
expense of gold−phospanide bonding. Phosphine lone-pair
donation into the Au−P(phosphanide) σ* orbital indeed is
associated with a large second-order perturbation theory
stabilization energy (ΔE(i→2)j*) of ca. 168 kcal/mol. The natural
valence of gold in the model system is 1.0, meaning that the
gold forms a total of one electron-pair bond. The natural
valence for the phosphanide phosphorus is 2.7, reduced from 3
by the same amount that the natural valence for the phosphine
phosphorus (3.3) exceeds it. These computational descriptors
for the model system at the MP2 level, where this model has
previously been considered in a study on aurophilic
interactions,73 are well reproduced at the B3LYP level of
theory.
Solid-State NMR Analysis of (XL)2InP(SnPh3)2. To
further investigate the chemical bonding in (XL)2InP(SnPh3)2,
we recorded solid-state 31P and 13C NMR spectra at 14.0 T. As
seen from Figure 6a, the 31P CP/MAS NMR spectrum of
(XL)2InP(SnPh3)2 exhibits a broad peak centered at −304
ppm. This 31P isotropic chemical shift is in good agreement
with that measured in solution, δ(31P) = −309.9 ppm,
suggesting that the molecular structures of (XL)2InP(SnPh3)2
in the solid and solution states are essentially the same. This
was further confirmed by the excellent agreement between the
13C chemical shifts observed in the two phases (data are
provided in the Supporting Information). Furthermore, the
sharp peaks observed in the solid-state 13C NMR spectrum of
(XL)2InP(SnPh3)2 suggest that the solid sample used in our
study is highly crystalline. It is important to note that the 31P
NMR peak is rather broad, with a full-width at the half-height
(fwhh) of ca. 2800 Hz, and exhibits an asymmetrical line shape.
In general, such features in MAS NMR spectra of spin-1/2
nuclei are caused by the presence of a neighboring quadrupolar
(I > 1/2) nucleus. In the present case, both residual dipolar
coupling and indirect spin−spin (J) coupling between 31P and
115In (I = 9/2, natural abundance 95.72%) nuclei contribute to
the observed line shape. To properly analyze the observed line
shape, it is necessary to know the magnitude of the 115In
quadrupole coupling constant CQ(115In). However, our
attempts to directly observe a solid-state 115In NMR signal
for (XL)2InP(SnPh3)2 at 14.0 T were unsuccessful, suggesting
that the value of CQ(115In) in (XL)2InP(SnPh3)2 must be very
large. Indeed, the ADF calculation predicts that CQ(115In) =
255 MHz in (XL)2InP(SnPh3)2; see Table 2. Recently,
Table 2. Experimental and Computed NMR Parameters for
(XL)2InP(SnPh3)2
exp.
ADF-ZORA
a
a
a
a
δiso(31P)/ppm
δ11(31P)/ppm
δ22(31P)/ppm
δ33(31P)/ppm
Ω/ppm
−304
−255
−322
−335
−311
−286
−312
−333
47
a
80
a
1J(31P, 115In)/Hz
1J(31P, 117/119Sn)/Hz
250
361
b
993
808
d
c
δiso(
115In)/ppm
ND
248
d
CQ(115In)/MHz
ηQ(115In)
ND
255
d
ND
0.08
a
b
Measured by solid-state 31P NMR. Measured by solution 31P NMR.
c
Computed 115In shielding constant was converted to the 115In
chemical shift with reference to 0.1 M In(NO3)3 (aq) using the
following equation: δiso(115In) = 3840 −σiso(115In).74 Not determined.
d
Wasylishen and co-workers74,75 reported solid-state 115In
NMR spectra of several indium(III) compounds. We note
that the largest CQ(115In) value for which they were able to
record a solid-state 115In NMR spectrum at an ultrahigh
magnetic field, 21 T, is about 200 MHz. At 14.0 T, a CQ(115In)
value of 255 MHz produces a static 115In NMR spectrum of 3.4
MHz wide. The very large CQ(115In) value in (XL)2InP-
1
(SnPh3)2 also explains why J(31P, 115In) is completely self-
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decoupled in the solution 31P NMR spectrum. If we assume a
CQ(115In) value of 255 MHz, the observed 31P NMR line shape
can be qualitatively reproduced by simulation from which we
ASSOCIATED CONTENT
■
S
* Supporting Information
Additional synthetic and spectroscopic details, including NMR
spectra and crystallographic tables, may be found in the
Supporting Information document accompanying this manu-
script. This material is available free of charge via the Internet at
http://pubs.acs.org.
1
obtained an estimate for J(31P, 115In), 250 Hz; see Figure 6a.
To obtain the full 31P chemical shift tensor for (XL)2InP-
(SnPh3)2, we recorded a solid-state 31P NMR spectrum under
the static condition, as shown in Figure 6b. The experimental
31P chemical shift tensor parameters are listed in Table 2,
together with the ADF computational results. In general, the
experimental NMR parameters are qualitatively reproduced by
ADF computations.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: gang.wu@chem.queensu.ca (G.W.).
*E-mail: ccummins@mit.edu (C.C.C.).
*E-mail: avelian@mit.edu (A.V.).
The 31P chemical shift observed for (XL)2InP(SnPh3)2 is
among the most negative (most shielded) 31P chemical shifts
reported for phosphorus compounds, for example, PH3(g),
−271.58 ppm;25 AsP3(s), −413 ppm;76 P4(g), −551.5 ppm.77
The 31P chemical shift tensor observed in (XL)2InP(SnPh3)2 is
also strikingly similar to that for PH3(g), δ11 = −228.5 ppm, δ22
= δ33 = −293.0 ppm.78,79 Both (XL)2InP(SnPh3)2 and PH3
exhibit rather small 31P chemical shift anisotropy, which is
generally measured by the span of the chemical shift tensor (Ω
= δ11 − δ33). For (XL)2InP(SnPh3)2, Ω = 80 ppm, which
compares to Ω = 64.5 ppm found for PH3(g). The nearly
axially symmetric 31P chemical shift tensor (δ22 ≈ δ33) observed
for (XL)2InP(SnPh3)2 also suggests that the three chemical
bonds around the P atom are similar. Indeed, the crystal
structure of (XL)2InP(SnPh3)2 shows that the In−P1 and Sn1−
P1 bond lengths are 2.5470(9) and 2.4984(8) Å, respectively.
The trigonal pyramidal core of (XL)2InP(SnPh3)2 is slightly
“flatter” than that in PH3: the In−P−Sn1, In−P−Sn2, and
Sn1−P−Sn2 angles range from 103.55(3) to 119.71(3)°, these
being larger than those in PH3: 93°. It is interesting to note that
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This material is based upon work supported by the National
Science Foundation under CHE-1111357. C.H. thanks the
China Scholarship Council for their financial support. Runyu
Tan is thanked for crystallographic assistance. Thermphos
International is thanked for a gift of white phosphorus. G.W.
thanks NSERC of Canada for financial support.
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the value of J(31P, 115In) in (XL)2InP(SnPh3)2, 250 Hz, is
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1
for which the J(31P, 115In) values are in a range between 550
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̈
and 2500 Hz. This difference can be understood on the basis of
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pair orbital from the phosphorus atom participates in the
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