2,3-Diphosphino-1,4-diphosphonium ions

Article abstract of DOI:10.1021/ja805911a

Salts of the first crystallographically characterized chlorophosphinophosphonium ions have been prepared, and their reaction with Ph₃P results in reductive coupling of the chlorophosphine centers to give the first acyclic 2,3-diphosphino-1,4-diphosphonium ions, representing a key framework in the development of catena-phosphorus chemistry. These new salts of general formula [R₃P-PR′-PR′-PR₃][OTf] ₂ are also obtained in a one-pot diastereoselective reaction of a dichlorophosphine, a tertiary phosphine, and trimethylsilyltrifluoromethanesulfonate. The structural and spectroscopic features of the new dications complement those of the known diphosphonium and 2-phosphino-1,3-diphosphonium dications. Quantitative ligand exchange reactions are observed when derivatives of [Ph₃P-PR′-PR′-PPh ₃][OTf]₂ are combined with Me₃P, demonstrating the coordinative nature of the phosphine-phosphonium P-P bonds and implicating a bonding model involving the diphosphenium dication acceptor. The observed solid state structures have been interpreted in the context of computational studies.

Full text of DOI:10.1021/ja805911a

Published on Web 10/22/2008
2,3-Diphosphino-1,4-diphosphonium Ions
Yuen-ying Carpenter,† C. Adam Dyker,† Neil Burford,*,† Michael D. Lumsden,‡ and
Andreas Decken§
Department of Chemistry, Dalhousie UniVersity, Halifax, NS, B3H 4J3, Canada, Atlantic Region
Magnetic Resonance Center, Dalhousie UniVersity, Halifax, NS, B3H 4J3, Canada, and
Department of Chemistry, UniVersity of New Brunswick, Fredericton, NB, E3A 6E2, Canada
Received July 28, 2008; E-mail: Neil.Burford@dal.ca
Abstract: Salts of the first crystallographically characterized chlorophosphinophosphonium ions have been
prepared, and their reaction with Ph3P results in reductive coupling of the chlorophosphine centers to give
the first acyclic 2,3-diphosphino-1,4-diphosphonium ions, representing a key framework in the development
of catena-phosphorus chemistry. These new salts of general formula [R3P-PR′-PR′-PR3][OTf]2 are also
obtained in a one-pot diastereoselective reaction of a dichlorophosphine, a tertiary phosphine, and
trimethylsilyltrifluoromethanesulfonate. The structural and spectroscopic features of the new dications
complement those of the known diphosphonium and 2-phosphino-1,3-diphosphonium dications. Quantitative
ligand exchange reactions are observed when derivatives of [Ph3P-PR′-PR′-PPh3][OTf]2 are combined with
Me3P, demonstrating the coordinative nature of the phosphine-phosphonium P-P bonds and implicating
a bonding model involving the diphosphenium dication acceptor. The observed solid state structures have
been interpreted in the context of computational studies.
Introduction
catena-phosphorus cations that have been isolated and com-
prehensively characterized, and other P-P bonded cationic
The strong homoatomic bond is a feature of phosphorus
chemistry that has been highlighted in discussion of the diagonal
relationship with carbon but has yet to be fully exploited. In
this context, a diverse and extensive catena-phosphorus chem-
istry is evolving that is made possible by versatile synthetic
methods for new catenated cationic frameworks.1-8 Derivatives
of phosphinophosphonium i,2 diphosphonium ii,9-12 1,3-diphos-
phino-2-phosphonium iii,5,13 and 2-phosphino-1,3-diphospho-
nium iv14 cations represent the prototypical examples of acyclic
frameworks have been reported.15 We now report the application
of a new reductive coupling reaction and a ligand exchange
reaction as high yield synthetic approaches to the first examples
of acyclic 2,3-diphosphino-1,4-diphosphonium ions v.8 In
addition, counterintuitive conformational features that are
observed in the solid state structures are rationalized using
computational models.
† Department of Chemistry, Dalhousie University.
‡ Atlantic Region Magnetic Resonance Center, Dalhousie University.
§ University of New Brunswick.
(1) 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.
Synthetic Procedures and Characterization Data
General. Unless otherwise specified, reactions were carried out
in a glovebox under an inert N2 atmosphere. Solvents were dried
on a MBraun solvent purification system and stored over 4 Å
molecular sieves unless otherwise specified. MeCN was purchased
anhydrous from Aldrich and used as received, Et2O was dried by
refluxing over Na/benzophenone and distilled before use, and CHCl3
was degassed by three freeze-pump-thaw cycles and stored over
molecular sieves for 24 h before use. Deuterated solvents were
purchased from Aldrich or Cambridge Isotope Laboratories and
used as received (CD3CN, CD3NO2 in ampoules) or stored over
molecular sieves for 24 h prior to use (CDCl3). [Ph3P-PPhCl][OTf],
[1a][OTf]; [Ph3P-PPh-PPh-PPh3][OTf]2, [4a][OTf]2; and [Me3P-
PPh-PPh-PMe3][OTf]2, [4′a][OTf]2, were prepared as described in
the preliminary communication.8 CyPCl2 was prepared according
to literature methods.16 Me2PCl and MePCl2 were purchased from
(2) Burford, N.; Ragogna, P. J.; McDonald, R.; Ferguson, M. J. Am. Chem.
Soc. 2003, 125, 14404–14410.
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Commun. 2003, 2066–2067.
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44, 2364–2367.
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Int. Ed. 2005, 44, 6196–6199.
(7) Weigand, J. J.; Burford, N.; Lumsden, M. D.; Decken, A. Angew.
Chem., Int. Ed. 2006, 45, 6733–6737.
(8) Preliminary Communication: (a) Dyker, C. A.; Burford, N.; Lumsden,
M. D.; Decken, A. J. Am. Chem. Soc. 2006, 128, 9632–9633.
(9) Romakhin, A. S.; Palyutin, F. M.; Ignat’ev, Yu., A.; Nikitin, E. V.;
Kargin, Yu., M.; Litvinov, I. A.; Naumov, V. A. IzV. Akad. Nauk.
SSSR, Ser. Khim. 1990, 3, 664–669.
(10) Kilian, P.; Slawin, A. M. Z.; Woollins, J. D. Dalton Trans. 2006, 2175–
2183.
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Chem., Int. Ed. Engl. 1985, 24, 975–976.
(14) Schmidpeter, A.; Lochschmidt, S.; Karaghiosoff, K.; Sheldrick, W. S.
Chem. Commun. 1985, 1447–1448.
(12) Alder, R. W.; Ganter, C.; Harris, C. J.; Orpen, A. G. Chem. Commun.
1992, 1170–1172.
(15) Dyker, C. A.; Burford, N. Chem. Asian J. 2008, 3, 28–36.
(16) Weferling, N. Z. Z. Anorg. Allg. Chem. 1987, 548, 55–62.
(13) Krossing, I. Dalton Trans. 2002, 500–512.
9
15732 J. AM. CHEM. SOC. 2008, 130, 15732–15741
10.1021/ja805911a CCC: $40.75
2008 American Chemical Society

2,3-Diphosphino-1,4-diphosphonium Ions
A R T I C L E S
Strem and used as received. Ph3P, iPrPCl2, tBuPCl2, and Me3P (1.0
M solution in toluene) were purchased from Aldrich and used as
received. Ph2PCl, PhPCl2, EtPCl2, and Me3SiOTf were purchased
from Aldrich and purified by vacuum distillation prior to use. GaCl3
was purchased from Strem and sublimed under static vacuum prior
to use.
SHELX97.24 Non-hydrogen atoms were refined anisotropically.
Refinement details are summarized in Table 1.
Preparation and Isolation. [Ph3P-PPh(Cl)][GaCl4], [1a][GaCl4]:
PhPCl2 (27.1 µL, 0.20 mmol), was added to a stirred solution of
Ph3P (52 mg, 0.20 mmol) and GaCl3 (39 mg, 0.22 mmol) in CH2Cl2
(1 mL). After 15 min, the 31P{1H} NMR spectrum of the reaction
showed near quantitative formation of [1a][GaCl4] (94%) along
with PhPCl2-GaCl3 (156 ppm). Attempted isolation by addition
of Et2O yielded an oil.
[Me3P-PPh(Cl)][OTf], [1′a][OTf]: Me3P (1.0 M in toluene, 2
× 100.0 µL, 0.20 mmol) was added to a stirred solution of PhPCl2
(27.1 µL, 0.20 mmol) and Me3SiOTf (39.8 µL, 0.22 mmol) in
CH2Cl2 (0.80 mL). After 1.5 h, the 31P{1H} NMR spectrum of
this reaction mixture showed quantitative formation of [1′a][OTf].
Solution 1H, 13C, and 31P NMR spectra were collected at room
temperature on Bruker AC-250 (5.9 T) and Bruker Avance 500
(11.7 T) NMR spectrometers. Chemical shifts are reported in ppm
relative to trace protonated solvent (1H), to perdeuterated solvent
(13C), or to an external reference standard (31P, 85% H3PO4). NMR
spectra of reaction mixtures were obtained by transferring an aliquot
of the bulk solution to a 5 mm NMR tube. These tubes were flame
sealed, or capped and sealed with Parafilm. All reported 31P{1H}
NMR parameters for second-order spin systems were derived by
iterative simulation of experimental data obtained at both fields (31P
Larmor frequencies of 101.3 and 202.6 MHz) using gNMR, version
4.0.17 Typically, the higher field experimental spectrum was used
to find the spin system parameters, and the lower field data was
subsequently used to ensure the parameters were valid at both fields.
Difference calculations between simulated and experimental spectra
were produced with Bruker Topspin, version 2.0,18 using data at
202.6 MHz. The signs of the P-P coupling constants reported in
General Procedure for [Ph3P-PR′(Cl)][OTf], [1b-e][OTf]:
R′PCl2 (0.20 mmol) was added to a stirring solution of Ph3P (52
mg, 0.20 mmol) in CH2Cl2 (0.5-1 mL) followed immediately by
the addition of Me3SiOTf (39.8 µL, 0.22 mmol). Attempted isolation
of [1c-e][OTf] by addition or vapor diffusion of Et2O yielded an
oil.
[Ph3P-PMe(Cl)][OTf], [1b][OTf]: After 1 h, the 31P{1H} NMR
spectrum of the reaction showed quantitative formation of
[1b][OTf]. Vapor diffusion of Et2O into this solution overnight at
room temperature afforded colorless needle-like crystals that were
washed with Et2O (2 × 1 mL) and dried in Vacuo. Yield
(crystalline): 63 mg (64%), mp 117-119.5 °C; FT-IR: 3063 (19),
1586 (10), 1443 (5), 1260 (1), 1189 (20), 1144 (13), 1106 (15),
1029 (7), 996 (16), 891 (18), 873 (8), 751 (6), 725 (14), 690 (4),
637 (2), 573 (11), 545 (9), 506 (3), 460 (17), 301 (12).
[Ph3P-PEt(Cl)][OTf], [1c][OTf]: Quantitative formation of
[1c][OTf] was observed after 10 min by 31P{1H} NMR spectroscopy.
[Ph3P-PiPr(Cl)][OTf], [1d][OTf]: [1d][OTf] was observed as
broad resonances (82 ppm and 16 ppm) at 298 K in the 31P{1H}
NMR spectrum of the solution after 1 h, together with iPrPCl2 (ca.
15%). Quantitative formation of [1d][OTf] was observed at 213
K.
1
Table 2 and Table 3 have been established by assigning the JPP
coupling constants as negative.19,20 Product distributions for in situ
reaction mixtures were assessed by integration of assigned signals
in the 31P NMR spectra. 31P NMR integrations are approximate,
but are estimated to be accurate to within (10% for identical
coordination numbers or (20% otherwise.21 Letter designations
for the phosphorus spin systems have been assigned by calculating
the ratio |∆ν/J|, where ∆ν is the difference in 31P chemical shifts
in Hz, and using a value of 10 at the lower field as the threshold
between a first and second order letter designation.
Infrared spectra were collected on samples prepared as nujol
mulls between CsI plates using a Bruker Vector FT-IR spectrometer.
Peaks are reported in wavenumbers (cm-1) with ranked intensities
in parentheses, where a value of one corresponds to the most intense
peak in the spectrum. Melting points were obtained on samples
flame-sealed in glass capillaries under dry nitrogen using an
Electrothermal apparatus. Chemical analyses were performed on
selected compounds by Canadian Microanalytical Services Ltd.,
Delta, British Columbia, Canada.
Unless otherwise stated, crystals for single crystal X-ray dif-
fraction studies were obtained by vapor diffusion at room temper-
ature. Samples were dissolved in a minimal amount (1-2 mL) of
a polar solvent in a 5 mL vial placed within a capped 20 mL vial
containing ∼5 mL of a less polar solvent (solvents are indicated in
the text as polar/nonpolar pairs). After deposition of crystals, the
solvent was carefully removed using a pipet and the crystals were
coated with Paratone oil. Single crystal X-ray diffraction data were
collected using a Bruker AXS P4/SMART 1000 diffractometer. All
measurements were made with graphite monochromated Mo KR
radiation. The data were reduced (SAINT)22 and corrected for
absorption (SADABS)23 and were corrected for Lorentz and
polarization effects. The structures were solved by direct methods
and expanded using Fourier techniques. Full matrix least-squares
refinement was carried out on F2 data using the program
[Ph3P-PCy(Cl)][OTf], [1e][OTf]: [1e][OTf] was observed as
broad resonances (76 ppm and 18 ppm) at 298 K in the 31P NMR
spectrum of the reaction mixture after 1 h, together with CyPCl2
(ca. 23%). Quantitative formation of [1e][OTf] was observed at
202 K.
[Me3P-PCy(Cl)][OTf], [1′e][OTf]: Me3P (1.0 M in toluene, 3
× 73.4 µL, 0.22 mmol) was added to a stirred solution of CyPCl2
(41.4 mg, 0.22 mmol) in CH2Cl2 (1 mL) yielding a white precipitate.
Upon addition of Me3SiOTf (43.8 µL, 0.24 mmol), this solid
redissolved and produced a white precipitate after 5 min of stirring.
The 31P{1H} NMR spectrum of this reaction mixture after 1 h
showed the presence of only [1′e][OTf].
[Ph3P-PtBu(Cl)][OTf], [1f][OTf]: A solution of Ph3P (105 mg,
t
0.40 mmol) in CH2Cl2 was added to a stirred solution of BuPCl2
(64 mg, 0.40 mmol) in CH2Cl2 (total volume ca. 1 mL) followed
immediately by the addition of Me3SiOTf (79.6 µL, 0.44 mmol).
The 31P{1H} NMR spectrum (213 K) of the reaction mixture after
t
2 h was interpreted as a mixture of [1f][OTf] and BuPCl2 (200.0
ppm). The 31P{1H} NMR spectrum (213 K) of the reaction mixture
after 48 h indicated the presence of small amounts of [Ph3PCl][OTf]
and [5f][OTf] ([Ph3P-PtBu-PtBu(Cl)][OTf], AMX spin system, not
simulated, approximate shifts -2 ppm (t), 24 ppm (dd), and 112
ppm (dd)).
(17) Budzelaar, P. H. M. gNMR for Windows, 4.0; Cherwell Scientific
Publishing Limited: Oxford, UK, 1997.
(18) Topspin for Windows, 2.0, patchlevel 5; Bruker Biospin GmbH:
Germany, 2006.
(19) Finer, E. G.; Harris, R. K. Prog. Nucl. Magn. Reson. Spectrosc. 1971,
6, 61–118.
(20) Forgeron, M. A. M.; Gee, M.; Wasylishen, R. E. J. Phys. Chem. 2004,
108, 4895–4908.
(21) Huynh, K.; Rivard, E.; LeBlanc, W.; Blackstone, V.; Lough, A. J.;
Manners, I. Inorg. Chem. 2006, 45, 7922–7928.
(22) SAINT 7.23A; Bruker AXS, Inc: Madison, Wisconsin, 2006.
(23) Sheldrick, G. M. SADABS; Bruker AXS, Inc.: Madison, Wisconsin,
2004.
[Ph3P-PtBuCl][GaCl4], [1f][GaCl4]: A mixture of Ph3P (52
mg, 0.20 mmol), tBuPCl2 (32 mg, 0.20 mmol) and GaCl3 (39 mg,
0.22 mmol) in CH2Cl2 (1 mL) was stirred for 1 h at room
temperature, and the 31P{1H} NMR spectrum at 298 K was
t
interpreted as a mixture of BuPCl2-GaCl3 (184 ppm, 98%,) and
[1f][GaCl4] (2%).
9
J. AM. CHEM. SOC. VOL. 130, NO. 46, 2008 15733

A R T I C L E S
Carpenter et al.
Table 1. Crystallographic Data
(a) Crystallographic Data for Chlorophosphinophosphonium Triflate Salts
[Ph3P-PPh(Cl]][OTf]
[1a][OTf]8
[Ph3P-PMe(Cl)][OTf]
[1b][OTf]
CCDC #
605574
694816
Formula
molecular weight (g/mol)
C25H20ClF3O3P2S
554.86
C20H18ClF3O3P2S
492.79
crystal system
space group
monoclinic
Pn
triclinic
P1
j
color, habit
a /Å
b /Å
c /Å
colorless plate
10.0707(16)
8.8891(15)
14.166(2)
90
104.192(3)
90
1229.5(3)
173(1)
colorless plate
8.3728(10)
11.0797(13)
12.4662(15)
83.4150(10)
72.798(2)
85.040(2)
1095.8(2)
198(1)
R /°
ꢀ /°
γ /°
V /Å3
T /K
Z
2
2
crystal size/mm3
0.40 × 0.125 × 0.025
0.50 × 0.30 × 0.10
µ/mm-1
2θmax /°
reflections collected
independent reflections
Rint
0.420
0.461
54.98
8149
4027
0.0256
54.98
7617
4767
0.0177
parameters
396
0.0256
0.0630
1.031
358
0.0347
0.0972
1.065
a
R1 (I > 2σ(I))
b
wR2 (all data)
GOFc
∆F max and min /e Å-3
0.309, -0.176
0.382, -0.228
(b) Crystallographic Data for Salts of 2,3-Diphosphino-1,4-diphosphonium Triflate Salts
[Ph3P-PPh-PPh-PPh3][OTf]2
[4a][OTf]28
[Ph3P-PMe-PMe-PPh3][OTf]2
[Ph3P-PEt-PEt-PPh3][OTf]2
[Me3P-PPh-PPh-PMe3][OTf]2
[4′a][OTf]28
[Me3P-PMe-PMe-PMe3][OTf]2
[4b][OTf]2
[4c][OTf]2
[4′b][OTf]2
CCDC #
Formula
605575
C10H24F6O6P4S2
694391
C40H36F6O6P4S2
914.69
694390
C42H40F6O6P4S2
942.74
605576
C20H28F6O6P4S2
666.42
694392
C10H24F6O6P4S2
542.29
molecular weight (g/mol) 1038.82
crystal system
Space group
monoclinic
P21/n
monoclinic
P21/c
monoclinic
C2/c
monoclinic
P21/c
monoclinic
P21/c
color, habit
A /Å
B /Å
C /Å
Colorless plate
10.942(4)
20.769(7)
11.462(4)
90
113.120(6)
90
2395.7(15)
173(1)
colorless rod
8.761(5)
27.114(17)
17.578(11)
90
96.807
90
4146(4)
173(1)
colorless rod
15.5968(16)
14.5043(16)
19.895(2)
90
102.483(2)
90
4394.3(8)
173(1)
colorless irregular
8.9520(14)
16.597(3)
10.0504(16)
90
101.328(3)
90
1464.1(4)
173(1)
colorless irregular
12.431(2)
13.520(3)
13.883(3)
90
94.872(3)
90
2324.7(7)
198(1)
R /°
ꢀ /°
γ /°
V /Å3
T /K
Z
2
4
4
2
4
crystal size/mm3
0.45 × 0.275 × 0.075 0.45 × 0.10 × 0.10
0.50 × 0.20 × 0.20
0.60 × 0.40 × 0.20
0.50 × 0.25 × 0.20
µ/mm-1
2θmax /°
reflections collected
independent reflections
Rint
0.318
55.00
0.356
55.00
27998
9274
0.0583
525
0.0460
0.1070
1.007
0.338
0.473
0.574
55.00
15089
4932
0.0263
272
0.0461
0.1282
1.069
55.00
9319
3253
0.0477
228
0.0479
0.1393
1.056
55.00
15518
5164
0.0380
261
0.0659
0.2112
1.177
16121
5349
0.0239
387
0.0499
0.1450
1.087
parameters
a
R1 (I > 2σ(I))
b
wR2 (all data)
GOFc
∆F max and min /e Å-3
1.913, -0.409
0.457, -0.359
0.820, -0.579
1.226, -0.466
0.806, -0.461
2
2 2
a R1 ) Σ | |Fo| - |Fc| |/Σ |Fo|. b wR2 ) (Σ[w(Fo - Fc ) ]/Σ[w(Fo4])1/2
.
c GOF ) [ Σw(|Fo| - |Fc|)2/(n - p)]1/2, where n ) number of reflections and p
) number of parameters.
[Me3P-PtBu(Cl)][OTf], [1′f][OTf]: Me3P (1.0 M in toluene,
2 × 100 µL, 0.20 mmol) was added to a stirred solution of tBuPCl2
(32 mg, 0.20 mmol) in CH2Cl2 (0.5-1 mL) followed immediately
by the addition of Me3SiOTf (39.8 µL, 0.22 mmol) and the 31P{1H}
NMR spectra of this solution showed nearly quantitative formation
of [1′f][OTf].
(32 mg, 0.20 mmol) in CH2Cl2 (0.5 mL) followed immediately by
the addition of GaCl3 (79.6 µL, 0.44 mmol) in CH2Cl2 (0.5 mL).
After 1 h, the 31P{1H} NMR spectrum showed essentially quantita-
tive formation of [1′f][GaCl4].
[Me3P-PtBu(Cl)][GaCl4], [1′f][GaCl4]: Me3P (1.0 M in tolu-
ene, 220 µL, 0.22 mmol) was added to a stirred solution of tBuPCl2
(24) Sheldrick, G. M. SHELXL-97, Program for crystal structure deter-
mination; University of Go¨ttingen: Germany, 1997.
9
15734 J. AM. CHEM. SOC. VOL. 130, NO. 46, 2008

2,3-Diphosphino-1,4-diphosphonium Ions
A R T I C L E S
Table 2. 31P{1H} NMR Parameters for Phosphinophosphonium Triflate Saltsa
31
P
[δ]
(phosphonium)
31PA[δ]
(phosphine)
1JPP
[Hz] (T)
B or X
cation
donor
acceptor
anion
spin system
3a
Ph3P
PPh2
[OTf]2
[GaCl4]2
[OTf]5
[OTf]2
[GaCl4]35
[GaCl4]35
[OTf]8
[GaCl4]
[OTf]
[OTf]
[OTf]
[OTf]
[OTf]
s
15
13
18
25
73
99
22
22
26
24
18
22
23
23
16
17
23
20
-10
-12
-60
-21
0
-33
55
55
46
61
76
72
65
76
90
98
95
n/a
AB
AX
AX
AX
AX
AB
AB
AB
AX
s
AX
AX
AX
AX
AX
AX
AX
-340
3b
3c
2a
2b
1a
1a
1′a
1b
1c
1d
1e
1′e
1f
Me3P
Cy3P
Ph2(Cl)P
Me2(Cl)P
Ph3P
Ph3P
Me3P
Ph3P
Ph3P
Ph3P
Ph3P
Me3P
Ph3P
PMe2
PCy2
PPh2
PMe2
-275
-361
-393
-340
PPh(Cl)
PPh(Cl)
PPh(Cl)
PMe(Cl)
PEt(Cl)
PiPr(Cl)
PCy(Cl)
PCy(Cl)
PtBu(Cl)
PtBu(Cl)
PtBu(Cl)
PtBu(Cl)
-333 (213 K)
-338
-305
-313 (202 K)
n/a (203 K)
-344 (213 K)
-343 (202 K)
-326
[OTf]
[OTf]
[GaCl4]
[OTf]
[GaCl4]
-390 (213 K)
-398
-350
-356
1f
1′f
1′f
Ph3P
Me3P
Me3P
94
a Data are reported for spectra obtained at 298 K unless otherwise indicated.
Table 3. 31P{1H} NMR Parameters at 101.3 MHz for 2,3-Diphosphino-1,4-diphosphonium Triflate Saltsa
1
2
solvent
δA
δB
1JAA′
1JAB) JA′B′
2JA′B) JAB′
3JBB′
4a
[Ph3P-PPh-PPh-PPh3]8
minor diastereomer
CH2Cl2
CH2Cl2
MeCN
MeCN
CH2Cl2
MeCN
MeCN
MeCN
MeCN
CH2Cl2
-33
-42
-52
-56
-71
-67
-73
-53.6
-25.5
-34
24
22
25
23
26
32
26
24.1
22.2
20
-124
not simulated
-105
not simulated
-278
not simulated
-238
-276
-318
not simulated
-343
-305
-282
69
51
4′a
4b
[Me3P-PPh-PPh-PMe3]8
minor diastereomer
66
78
56
62
[Ph3P-PMe-PMe-PPh3]
4′b
4c
4d
4e
[Me3P-PMe-PMe-PMe3]
[Ph3P-PEt-PEt-PPh3]
[Ph3P-PiPr-PiPr-PPh3]
[Ph3P-PCy-PCy-PPh3]
-269
-297
-348
80
82
98
58
59
63
a All spectra are AA′BB′ spin systems, with parameters derived by iterative fitting of experimental data at 298 K. Minor diastereomer shifts could not
be simulated and thus are approximate if given. Chemical shifts (δ) are given in ppm and coupling constants (J) in Hz.
Formation of [Ph3P-PPh2][OTf], [3a][OTf], from
[Ph3P-PPh(Cl)][OTf], [1a][OTf]: Addition of Ph2PCl (26.9 µL,
0.15 mmol) to a stirred solution of [1a][OTf], (83 mg, 0.15 mmol)
in CH2Cl2 afforded partial conversion to [3a][OTf] and PhPCl2 (162
ppm) after 30 min (5:1 ratio of 3a:1a, as observed by 31P{1H}
NMR spectroscopy).
(10), 1262 (1), 1223 (12), 1152 (7), 1103 (10), 1030 (4), 995 (14),
879 (15), 755 (9), 721 (8), 692 (5), 637 (2), 572 (13), 543 (6), 511
(3), 306 (16).
[Me3P-PMe-PMe-PMe3][OTf]2, [4′b][OTf]2: Me3P (0.235 mL,
1.0 M in toluene, 0.235 mmol) was added dropwise to a stirred
mixture of [Ph3P-PMe-PMe-PPh3][OTf]2, ([4b][OTf]2, 0.106 g,
0.116 mmol) in CH2Cl2 (3 mL). After stirring for 30 min, the white
precipitate was collected by filtration, and washed with CH2Cl2 (1
mL). Recrystallization over 1 day, by vapor diffusion with CD3CN/
Et2O at -25 °C gave crystals that were washed with Et2O (2 × 1
mL), and dried in Vacuo, yield: 0.032 g (0.059 mmol, 51%); Mp
221-224 °C; elemental analysis calc’d (found): %C 22.15 (21.18),
%H 4.46 (4.11); 1H NMR (500.1 MHz, CD3NO2, 298 K): δ )
2.21 ppm (m, 18H), 1.93 ppm (m, 6H); 13C NMR (125.8 MHz,
DEPTQ135, CD3NO2, 298 K): δ ) 7.78 ppm (m, +), -0.4 ppm
(m, +); FT-IR: 1426 (14), 1260 (1), 1301 (13), 1225 (10), 1152
(5), 1029 (3), 966 (4), 901 (8), 861 (9), 809 (17), 768 (16), 758
(15), 680 (11), 636 (2), 573 (7), 517 (6).
[Ph3P-PEt-PEt-PPh3][OTf]2, [4c][OTf]2: [1c][OTf] (1.0 mmol)
was prepared in situ in a 50 mL 1-necked bulb containing 5 mL
CHCl3. Me3SiOTf (100.0 µL, 0.55 mmol) and Ph3P (132 mg, 0.50
mmol, in ca. 2 mL CHCl3) were added, and the solution was
degassed by three freeze-pump-thaw cycles and sealed at reduced
pressure. This solution was heated at reflux (∼55 °C) in the closed
system for 48 h. The supernatant was decanted from the resulting
white precipitate, which was then washed with cold CH2Cl2 (-40
°C, 2 × 0.5 mL) and Et2O (2 × 1 mL). Addition of Et2O (∼4 mL)
to the supernatant gave a white precipitate, which was isolated by
decantation and washed with cold CH2Cl2. Colorless needle-like
[Ph3P-PPh-PPh-PPh3][OTf]2, [4a][OTf]2: [4a][OTf]2 was pre-
pared as described in the preliminary communication8 for analysis
by solid state NMR spectroscopy on a Bruker Avance 400 (9.4 T)
spectrometer. 31P CP/MAS NMR (162.0 MHz, 6.5 kHz spin rate,
4 mm rotor, ice cooled carrier gas): Major diastereomer δ ) 24
ppm, -40 ppm; Minor diastereomer δ ) 19 ppm, -31 ppm;
[Ph3P-PMe-PMe-PPh3][OTf]2, [4b][OTf]2: MePCl2 (0.079 mL,
0.885 mmol) and Me3SiOTf (0.266 mL, 1.47 mmol) were added
to a solution of Ph3P (0.35 g, 1.34 mmol) in CHCl3 (9 mL) in a 50
mL 1-necked bulb with a Teflon stopper. The mixture was degassed
by three freeze-pump-thaw cycles and subsequently heated to
reflux within the closed system by use of an oil bath (∼ 60 °C).
After 4 days, the resulting white precipitate was filtered, washed
with CHCl3 (1.5 mL) and dried in Vacuo. Crystals were obtained
by vapor diffusion from CH3CN/Et2O. Yield (powder): 0.224 g
(0.245 mmol, 55%). D.p. 225-237 °C; elemental analysis calc’d
(found): %C 52.52 (52.79), %H 3.97 (3.98); 1H NMR (500.1 MHz,
CD3CN, 298 K): δ ) 7.97 ppm (t, 3JHH ) 7.5 Hz, 6H), 7.90 ppm
(m, 12H), 7.81 ppm (m, 12H), 0.76 ppm (m, 6H); 1H NMR (500.1
MHz, CD3NO2, 298 K): δ ) 8.03 ppm (m, 18H), 7.88 ppm (m,
12H), 0.95 ppm (m, 6H); 13C NMR (125.8 MHz, DEPTQ135,
CD3NO2, 298 K): δ ) 136.0 ppm (s, +), 134.0 ppm (s, +), 131.1
ppm (m, +), 117.1 ppm (m, -), 0.0 ppm (m, +); FT-IR: 1439
9
J. AM. CHEM. SOC. VOL. 130, NO. 46, 2008 15735

A R T I C L E S
Carpenter et al.
Scheme 1. Synthesis of Chlorophosphinophosphonium Cations 1
or 1′ as Triflate or Gallate Salts
crystals were obtained by vapor diffusion from MeCN/Et2O, yield
(powder): 0.249 g (53% based on EtPCl2), mp 201-203 °C; H
1
NMR (500.1 MHz, CD3CN, 298 K): δ ) 7.91 ppm (vt, 6H, Ha),
7.85 ppm (vq, 12H, Hb), 7.74 ppm (vt, 12H, Hc), 1.93 ppm (m,
3H, He), 0.55 ppm (m, 6H, Hf); 13C NMR (125.8 MHz, DEPTQ135,
CD3CN, 298 K): δ ) 136.91 ppm (s, +, Ca/b), 135.07 ppm (s, +,
Ca/b), 132.06 ppm (t, +, Cc), 119.07 ppm (t, -, Cd), 14.26 ppm (t,
-, Ce), 12.42 ppm (m, +, Cf); FT-IR: 1584 (15), 1439 (6), 1270
(1), 1224 (7), 1147 (4), 1101 (5), 1031 (2), 996 (11), 754 (10), 721
(12), 690 (8), 637 (3), 572 (14), 542 (9), 509 (13).
[1e][OTf], [4e][OTf]2, [Ph3PCl][OTf], and [5e][OTf] ([Ph3P-PCy-
PCyCl][OTf], AMX spin system, not simulated, approximate shifts
-44 ppm (t), 22.5 ppm (dd), and 93 ppm (dd)).
Computational Methods. Density functional theory calculations
were performed using the Gaussian 03W software package.25 Initial
geometry optimizations were performed using B3LYP/3-21G*,
then further optimized to find SCF and zero-point energies with a
6-31+G(d) basis set. Initial calculations were performed on both
diastereomers of [H3P-PR′-PR′-PH3]2+ (R′ ) Me, Ph, Pr), where
i
[Ph3P-PiPr-PiPr-PPh3][OTf]2, [4d][OTf]2: iPrPCl2 (36.0 µL,
0.29 mmol) and Me3SiOTf (58.1 µL, 0.32 mmol) were added to a
solution of Ph3P (77 mg, 0.29 mmol) in CH2Cl2 (0.60 mL). After
stirring for 1 h at room temperature, this solution was transferred
to a vial containing 39 mg (0.15 mmol) Ph3P, followed by
subsequent addition of Me3SiOTf with stirring (29.1 uL, 0.16
mmol). This solution was stirred for 5 days at room temperature,
resulting in the precipitation of a white powder. This solid was
isolated by filtration and washed with cold CH2Cl2 (-40 °C, 2 ×
1 mL). Dissolution of this sparingly soluble powder in MeCN and
removal of the solvent in Vacuo provided [4d][OTf]2 (45 mg). The
supernatant was analyzed by 31P{1H} NMR spectroscopy and
showed a mixture of [1d][OTf], [Ph3PCl][OTf] and a new AMX
spin system (δA ) -35.7 ppm, δM ) 23.0 ppm, δX ) 96.5 ppm,
the initial C-P-P-C torsion angles (τR′) were set at 0°, 60°, or
180°. Calculations on the [Me3P-PR′-PR′-PMe3]2+ derivatives (4′)
were performed using the optimized geometry results from the
simplified PH3 structure as starting geometries. Although a recent
study26 of the conformational preferences in neutral diphosphines
favored the use of the B3PW91 functional for reproducing
qualitative trends, experimental observations for 2,3-diphosphino-
1,4-diphosphonium cations are consistent with the results provided
by B3LYP.
Results and Discussion
Reaction mixtures containing a tertiary phosphine, a chloro-
phosphine and a chloride ion abstracting agent provide an
efficient and general synthetic approach to salts of phosphino-
phosphonium cations i.2,15 The process is considered to involve
chloride ion abstraction from a chlorophosphine assisted by P-P
coordination of a phosphine at the phosphorus center of the
chlorophosphine, thereby stabilizing the resulting phosphenium
cation. In this context, two bonding models have been employed
to describe the P-P bond in phosphinophosphonium cations,
one involving a covalent bond between a phosphonium and a
phosphine center and the other a homoatomic coordinate bond
between a phosphine donor and a phosphenium acceptor.2 While
the structural features are consistent with either bonding model,
much of the established chemistry of phosphinophosphonium
cations involves ligand exchange reactions, invoking a coordi-
nate bond between the phosphorus centers.3
1
2
1JAM ) -309 Hz, JAX ) -305 Hz, JMX ) 59 Hz), tentatively
assigned to [Ph3P-PiPr-PiPrCl][OTf], [5d][OTf]. Slow evaporation
of the supernatant and CH2Cl2 washes over 2 days yielded an
additional 18 mg of [4d][OTf]2 as a semicrystalline material. In
contrast, 31P{1H} NMR spectra of reactions performed in more
dilute solutions (<0.50 M) shown no evidence of 4d. Instead, a
mixture resembling the supernatant in more concentrated reactions
1
was observed, with a 1:2 ratio of [Ph3PCl][OTf] to [5d][OTf]. H
NMR spectra of a dilute reaction mixture (0.25 M in iPrPCl2) show
overlapping septets assigned as the methine resonances in 1d (2.42
1
ppm) and 5d (2.50 ppm and 2.56 ppm). The remaining H NMR
signals could not be assigned. Yield ([4d][OTf]2): 63 mg (45%);
mp 170-171.5 °C; 31P{1H} NMR (101.3 MHz, MeCN, 298 K):
1
AA′BB′ spin system, δA ) -25.2 ppm, δB ) 22.2 ppm, JAA′
)
1
1
2
2
3
-318 Hz, JAB ) JA′B′ ) -348 Hz, JAB′ ) JA′B ) 98 Hz, JBB′
) 63 Hz; 1H NMR (500.1 MHz, CD3NO2, 298 K): δ ) 7.87 ppm
(vt, 6H, HA), 7.68 ppm (m, 24H, HB/C), 3.26 ppm (m, 2H, HE),
0.93 ppm (m, 12H, HF); 13C NMR (125.8 MHz, DEPTQ135,
CD3CN, 298 K): δ ) 136.60 ppm (s, +, CA/B), 135.83 ppm (s, +,
C
A/B), 131.68 ppm (t, +, CC), 118.86 ppm (t, -, CD), 28.11 ppm
(t, +, CE), 23.13 ppm (broad s, +, CF); FT-IR (nujol, cm-1, ranked
intensities): 1439 (6), 1266 (1), 1225 (7), 1150 (4), 1098 (5), 1032
(2), 996 (11), 757 (10), 720 (13), 690 (9), 638 (3), 539 (8), 500
(12);
Reaction mixtures containing a tertiary phosphine, a dichlo-
rophosphine and a chloride ion abstracting agent (Scheme 1)
further generalize the quantitative synthetic approach and yield
salts containing the chlorophosphinophosphonium cations 1 and
1′, which represent isomers of the previously described phos-
[Ph3P-PCy-PCy-PPh3][OTf]2, [4e][OTf]2: The synthesis of
[4e][OTf]2 was attempted following the procedure for [4d][OTf]2
but with an additional equivalent of both Ph3P and Me3SiOTf and
stirring for 40 h to maximize the yield of 4e as observed by 31P{1H}
NMR spectroscopy of the reaction mixture, which contains
(25) Frisch, M. J. et al. Gaussian 03, revision B.05; Gaussian, Inc.:
Pittsburgh, PA, 2003.
(26) Katsyuba, S.; Schmutzler, R. Dalton Trans. 2008, 1465–1470.
9
15736 J. AM. CHEM. SOC. VOL. 130, NO. 46, 2008

2,3-Diphosphino-1,4-diphosphonium Ions
A R T I C L E S
Scheme 2. Phosphenium (Acceptor) Exchange Reaction Yielding
[3a][OTf] from [1a][OTf]
Scheme 3. Reductive Coupling Reaction of [1][OTf] to Give
[4][OTf]2
phinochlorophosphonium cations 22 and variants of the organo-
substituted phosphinophosphonium cations 3.2
The solid state structures of [1a][OTf] and [1b][OTf] have
been determined by X-ray crystallography (Table 1a) and show
structural features that are consistent with those in derivatives
of 2 and 3.2 In contrast to known derivatives of [2][GaCl4],
[3a][GaCl4], and [3b-c][OTf], which exhibit two doublets at
room temperature in the 31P{1H} NMR spectra (Table 2), the
P-P coupling is unresolved for [1][OTf]; indeed, the 31P{1H}
NMR spectra of [1a-c][OTf] exhibit two sharp singlets. This
implicates increased lability of the P-P bond, and in this
context, we have observed by 31P{1H} NMR spectroscopy
phosphenium exchange behavior for derivatives of 1. Solutions
containing equimolar amounts of [1a][OTf] and Ph2PCl give
[3a][OTf] and PhPCl2 (Scheme 2) indicating that [PPh2]+
exhibits a greater Lewis acidity toward Ph3P than [PPhCl]+,
presumably due to π-interaction of nonbonding pairs on chlorine
with phosphorus in [PPhCl]+. In this context, diaminophosphe-
nium cations have been shown to form Cl-bridged adducts rather
than the phosphinophosphonium framework.27 Assuming that
cation 1a dissociates in solution, we envisage exchange of
chloride ion between Ph2PCl and [PPhCl]+ via [Ph2P · · ·
Cl· · ·PPhCl]+ to give PhPCl2 and enabling formation of the
pentaphenylphosphinophosphonium cation 3a.
Figure 1. ORTEP representations of the solid state structure of (a) the
centrosymmetric meso-dication in [4a][OTf]2 and the (S,S)-enantiomer of
the dication in (b) [4b][OTf]2 and (c) [4c][OTf]2. Thermal ellipsoids are
shown at the 50% probability level and hydrogen atoms omitted for clarity.
τ
R′ indicates the C-P-P-C torsion angle between the central substituents,
while τPR3 indicates the P-P-P-P torsion angle of the phosphorus
backbone.
show AA′BB′ spin systems (Figure 3, Table 3) assigned to 4
and a singlet corresponding to [Ph3PCl][OTf]28 (δ ) 66 ppm).
The 31P{1H} NMR spectra of solutions containing [1d][OTf]
or [1e][OTf] at room temperature show significant broadening
of the upfield signal as well as the presence of unreacted
dichlorophosphine implicating the establishment of a dissocia-
tion equilibrium. Presumably, the enhanced steric bulk at the
acceptor phosphenium site favors the dissociation of the P-P
The AA′BB′ spin system is not observed for mixtures of
[1a-d][OTf] with Ph3P in the absence of Me3SiOTf, suggesting
that the formation of [Ph3PCl][OTf] is a key thermodynamic
driving force in the P-P coupling process, rather than formation
of Ph3PCl2. Mixtures of Ph3P, GaCl3 and [1a][GaCl4] likewise
show no evidence of reaction. Furthermore, reactions of
[1a][OTf] with comparatively strong reducing agents such as
t
bond. In addition, reaction mixtures of Ph3P and BuPCl2 with
Me3SiOTf or GaCl3 give 31P{1H} NMR spectra at 213 K
showing only 64% formation of 1f. Nevertheless, the stronger
donor Me3P enables the quantitative formation of [1′f][OTf].
Unlike [1a-e][OTf], for which P-P coupling is not resolved
in 31P{1H} NMR spectra at room temperature, the 31P{1H}
NMR spectrum of the reaction mixture containing [1′f][OTf]
showed doublets for both phosphorus centers (1JPP ) -350 Hz),
indicative of a stronger P-P interaction.
29,30
Na or Mg give complex mixtures containing cyclo-Ph5P5
as the only product identifiable by 31P{1H} NMR spectroscopy.
The 31P{1H} NMR spectra of reaction mixtures containing
weaker reducing agents, such as Zn, SnCl2, or cyclohexene,
showed the presence of 4 together with a number of unidentified
phosphorus containing products. Formation of derivatives of 4
contrast the previously reported reaction of PhPCl2, Ph3P and
As illustrated in Scheme 3, addition of Ph3P and Me3SiOTf
to derivatives of [1a-d][OTf] result in the formation of the
corresponding 2,3-diphosphino-1,4-diphosphonium salts [4a-
d][OTf]2. The 31P{1H} NMR spectra of these reaction mixtures
(28) Schmidpeter, A.; Lochschmidt, S. Inorg. Synth. 1990, 27, 253–258.
(29) Hoffman, P. R.; Caulton, K. G. Inorg. Chem. 1975, 14, 1997–1999.
(30) Smith, L. R.; Mills, J. L. J. Chem. Soc., Chem. Commun. 1974, 808–
809.
(27) Burck, S.; Gudat, D. Inorg. Chem. 2008, 47, 315–321.
9
J. AM. CHEM. SOC. VOL. 130, NO. 46, 2008 15737

A R T I C L E S
Carpenter et al.
a
Scheme 4. Proposed Mechanism for the Reductive Coupling of [1][OTf] to [4][OTf]2
i
t
a Intermediate [5d-f][OTf]2 has been observed by 31P{1H} NMR spectroscopy for sterically encumbered derivatives (R′ ) Pr, Cy, Bu).
AlCl3 to give [Ph3P-PPh-PPh3][AlCl4]2 (iv),14 however, the
formation of [4a][AlCl4]2 and its solid state structure has been
described.31
The 31P{1H} NMR spectra of solutions containing Ph3P,
Me3SiOTf and [1e][OTf] (prepared in situ) show partial
formation of [4e][OTf]2 after 2 days, while solutions of Ph3P,
Me3SiOTf and [1f][OTf] show no evidence of [4f][OTf]2. These
observations are indicative of steric restrictions at the phosphe-
nium site. Both of these solutions exhibit an AMX spin system,
which we tentatively assign to [Ph3PM-PAR′-PXR′Cl][OTf],
[5][OTf]. A similar pattern is observed as a component in
solutions of Ph3P and Me3SiOTf with [1d][OTf]. In contrast to
the analogue of 5 proposed by Dillon and co-workers,32 the
terminal PX signal in this new AMX spin system (e.g.,
[5d][OTf]: δA ) -35.7 ppm, δM ) 23.0 ppm, δX ) 96.5
1
1
2
ppm, JAM ) -309 Hz, JAX ) -305 Hz, JMX ) 59 Hz) is
shifted significantly downfield relative to the PM terminus (∆δ
g 70 ppm). Nonetheless, while smaller magnitude 1JPP coupling
constants (<300 Hz) are typically observed between P(III)-P(III)
spin pairs, the introduction of an electronegative substituent such
1
as chlorine is expected to increase the magnitude of JAX
,
1
1
1
justifying the similar JAX and JAM in 5. Finally, H NMR
spectra of reaction mixtures containing both [1d][OTf] and
[5d][OTf] indicate that the isopropyl methine 1H signals in 5d
are 0.08-0.14 ppm downfield of the corresponding resonances
in 1d, a difference that is too small to correspond to an additonal
ꢀ-Cl or positive charge adjacent to the terminal isopropyl
group.33 As shown in Scheme 4, dissociation of [1][OTf] is
proposed to give R′PCl2, which is subsequently reductively
coupled to another molecule of [1][OTf] to give [5][OTf]. In
the case of [5d][OTf], slow evaporation of the solvent over two
days allows for the complete conversion of this mixture to
[4d][OTf]2 and [Ph3PCl][OTf], supporting the proposal that 5
is an intermediate en route to 4.
Figure 2. ORTEP representations of the solid state structure of (a) the
centrosymmetric meso-dication in [4′a][OTf]2 and (b) the (S,S)-enantiomer
of the dication in [4′b][OTf]2. Thermal ellipsoids are shown at the 50%
probability level and hydrogen atoms omitted for clarity. τR′ indicates the
C-P-P-C torsion angle between the central substituents, while τPR3
indicates the P-P-P-P torsion angle of the phosphorus backbone.
P-P-P-P torsion angle of the phosphorus backbone. Crystals
of [4a][OTf]2 contain the R,S meso-isomer of the dication, which
is centrosymmetric with central torsion angles (τPR3 and τR′) of
180°. The solid state 31P CP/MAS NMR spectrum for a bulk
sample of crystalline [4a][OTf]2 reveals four distinct doublet-
like signals (two of lower intensity) that are also present (as
more resolved AA′BB′ spin systems) in 31P NMR solution
spectra for redissolved crystalline samples and reaction mixtures.
We conclude that the crystallographically characterized R,S meso
isomer as well as the (R,R)/(S,S) diastereomeric pair are all
Selected structural parameters from the solid state structures
of the dications in the triflate salts of 4a-c (Figure 1) are
presented in Table 4, where τR′ indicates the C-P-P-C torsion
angle between the central substituents and τPR3 indicates the
(31) Karaghiosoff, K. Ph.D. Thesis, Ludwig-Maximilians-Universita¨t, Mu-
nich, Germany, 1986.
(32) Boyall, A. J.; Dillon, K. B.; Howard, J. A. K.; Monks, P. K.;
Thompson, A. L. Dalton Trans. 2007, 1374–1376.
(33) Beauchamp, P. S.; Marquez, R. J. Chem. Educ. 1997, 74, 1483–1485.
9
15738 J. AM. CHEM. SOC. VOL. 130, NO. 46, 2008

2,3-Diphosphino-1,4-diphosphonium Ions
A R T I C L E S
Table 4. Selected Solid State Structural Parameters of 2,3-Diphosphino-1,4-diphosphonium Triflate Salts
P-P (Å)a
CR′-P-P (°)a
τR′ (°)
τPR3(°)
4a
[Ph3P-PPh-PPh-PPh3]8
[Me3P-PPh-PPh-PMe3]8
[Ph3P-PMe-PMe-PPh3]
2.258(1)
[mid] 2.221(1)
2.2041(9)
[mid] 2.2318(12)
2.2061(13)
[mid] 2.2284(12)
2.2125(13)
101.65(8)
180
180
4′a
4b
101.02(8)
180
180
109.3(1)
107.9(1)
0.95(14)
-159.98(4)
4′b
[Me3P-PMe-PMe-PMe3]
[Ph3P-PEt-PEt-PPh3]
2.192(2)
[mid] 2.243(2)
2.191(2)
2.2048(8)
[mid] 2.2153(11)
101.1(2)
102.8(2)
31.25(11)
3.49(13)
-126.72(3)
-142.35(3)
4c
109.52(9)
a [mid] indicates the central P-P bond, while the indicated CR′-P-P values describe the angle subtended by the central substituent (Me, Et, Ph) and
this bond. τR′ indicates the C-P-P-C torsion angle between the central substituents, while τPR3 indicates the P-P-P-P torsion angle of the
phosphorus backbone.
Scheme 5. Phosphine Exchange Reactions on Phosphinophosphonium and 2,3-Diphosphino-1,4-diphosphonium Cations
present in the bulk solid sample and in solution. The 31P{1H}
NMR spectrum for the major isomer (δ ) 24 and -33 ppm)
has been simulated; however, the downfield signal for the minor
constituent (δ ) 22 and -42 ppm) was not sufficiently resolved
to allow for an accurate determination of coupling constants.
evidence for the presence of the monosubstituted product. In
this context, the transformation of derivatives of [4][OTf]2 into
derivatives of [4′][OTf]2 is conveniently understood in terms
of two ligand exchange processes in which the dicationic
framework of 4 (or 4′) can be described as a bisphosphine
complex of a diphosphenium ion (Scheme 5).
1
Integration of the H NMR spectrum reveals a 62% diastere-
omeric excess. Although the favored diastereomer in solution
could not be definitively identified, the computational results
described below indicate that the R,S meso-isomer is thermo-
dynamically favored in the gas phase.
As observed for solutions of [4a][OTf]2, 31P{1H} NMR
spectra of [4′a][OTf]2 show the presence of R,S and (R,R)/(S,S)
1
diastereomeric pair as an unequal mixture (d.e. ) 72% by H
NMR integration). Again, the favored diasteromer in solution
could not be definitively identified, but the isolated crystalline
sample contained only the centrosymmetric R,S meso-isomer
(Figure 2). In contrast, only one diastereomer of [4′b][OTf]2 is
evident in solution, and the solid state structure (Figure 2, Table
4) contains the racemic (R,R)/(S,S) mixture in a gauche
conformation. The smaller steric presence of the Me3P termini
Crystals of [4b][OTf]2 contain a racemic mixture of the (R,R)/
(S,S) enantiomeric pair. As shown in Figure 1, the cation adopts
an essentially eclipsed conformation of the methyl substituents
with a central C-P-P-C torsion angle (τR′) of 0.95(14)°.
Unlike [4a][OTf], NMR analysis of either the redissolved
crystals or the reaction mixtures showed only one diastereomer,
indicating that the (R,R)/(S,S) racemic mixture of [4b][OTf]2 is
formed exclusively in the reductive coupling of the racemic
[1b][OTf]. Likewise, crystals of [4c][OTf]2 contain an (R,R)/
(S,S) racemic mixture of configurational isomers of the cation
(Figure 1, Table 4), which adopt an eclipsed conformation of
the ethyl substituents [τR′ ) 3.49(13)°] in spite of their slightly
greater steric presence. Correspondingly, both 4b and 4c adopt
larger central CR′-P-P angles [107.9(1)-109.52(9)°] relative
to 4a [101.65(8)°] in order to minimize steric congestion.
Reaction of [4a][OTf]2 or [4b][OTf]2 with excess Me3P
results in quantitative formation of the corresponding derivatives
of 4′[OTf]2 (Scheme 5), as indicated by the new AA′BB′ spin
system in each of the 31P{1H} NMR spectra of the reaction
mixtures. The reactions are best described as exchange of both
terminal Ph3P ligands for the more basic Me3P ligands,
consistent with the established ligand exchange reactivity of
phosphinophosphonium cations (2 and 3).2,3 Addition of only
1 equiv of Me3P to a solution of [4a][OTf]2 affords a 1:1 mixture
of the starting dication in [4a][OTf]2 and [4′a][OTf]2, with no
in 4′b allows for a smaller P-P-P-P torsion angle [τPR3
)
-126.72(3)°] compared to that in 4b [τPR3 ) -159.98(4)°],
thereby permitting a corresponding decrease in the proximity
of the central methyl substituents [τR′ ) 31.35(11)°]. Consistent
with the lower steric strain in 4′b, the central CR′-P-P angles
[max. 102.8(2)] in 4′b are smaller than those in 4b [min.
107.9(1)°].
The second-order AA′BB′ spin systems observed in solution
phase 31P{1H} NMR spectra for all derivatives of 4 are
characteristic and the patterns have been simulated for most
derivatives by iterative fitting with the chemical shift and
coupling constant parameters listed in Table 3. An exemplar
comparison of the simulated and experimental pattern is shown
for [4b][OTf]2 in Figure 3. Chemical shift parameters for the
terminal phosphonium centers (δB) occur in a typical narrow
range (20-32 ppm), while the phosphine centers (δA) exhibit
more varied shifts (∆δ > 40 ppm). This is consistent with the
dependence of the chemical shielding on the geometry of the
phosphorus center,34 as the tetracoordinate phosphonium centers
9
J. AM. CHEM. SOC. VOL. 130, NO. 46, 2008 15739

A R T I C L E S
Carpenter et al.
Figure 3. Comparison of simulated and experimental 31P{1H} NMR spectra of [4b][OTf]2. The signal at 5.6 ppm corresponds to an impurity in the sample.
Additional comparison spectra for derivatives 4′b, 4c, and 4d can be found in the Supporting Information.
Table 5. Calculated Structural Parameters for
2,3-Diphosphino-1,4-diphosphonium Cations
(S,S) diastereomer is favored for 4′b (R′ ) Me, |∆E | ) 15.3
kJ/mol). It is noteworthy that the energy difference between
[Me3P-PPh-PPh-PMe3], 4′a
(R,S) meso-diastereomer favored (∆E ) 6.3 kJ/mol)
anti conformer favored
the two diastereomers of 4′a is small, providing a rationale for
observation of a mixture of diastereomers in the solution state
31P NMR spectra.
The thermodynamically favored staggered conformation for
the R,S meso-diastereomer is explained (Figure 4) in terms of
the minimization of steric interactions between both the Me3P
termini and the central substituents [τR′ ) τPR3 ) 180°] in this
rotamer. Indeed, computational studies that begin with an
eclipsed initial geometry for the R,S meso-diastereomer undergo
geometry optimization to give the staggered conformation. The
thermodynamic preference of the (R,R)/(S,S) diastereomer for
the eclipsed conformation seems counterintuitive, but it suggests
that steric interactions between the terminal phosphonium
substituents play a dominant role in determining the lowest
energy conformer (Figure 4). Even for smaller terminal ligands
(PH3) or larger central alkyl substituents at the internal phos-
phine sites, computational models indicate that the eclipsed
conformation of the (S,S) diastereomer is favored over the
gauche or staggered conformers. In addition, calculations on
P-P (Å)a
CR′-P-P (°)a
τR′ (°)
τPR3 (°)
experimental
calculated
2.2041(9)
[mid] 2.2318(12)
2.259
101.02(8)
180
180
102.2
180.0
180.0
[mid] 2.286
[Me3P-PMe-PMe-PMe3], 4′b
(R,R)/(S,S)-diastereomer favored (∆E ) 15.3 kJ/mol)
eclipsed conformer favored
P-P (Å)a
CR′-P-P (°)a
τ
R′ (°)
τ
PR3 (°)
experimental 2.192(2)
[mid] 2.243(2)
101.1(2)
102.8(2)
31.25(11) -126.72(3)
2.191(2)
2.242
[mid] 2.265
calculated
107.2
-1.9
-152.3
i
the theoretical structure of 4′d (R′ ) Pr) demonstrate that the
a [mid] indicates the central P-P bond, while the indicated CR′-P-P
values describe the angle subtended by the central substituent (Me, Et,
Ph) and this bond. τR′ indicates the C-P-P-C torsion angle between
the central substituents, while τPR3 indicates the P-P-P-P torsion
angle of the phosphorus backbone.
(R,R)/(S,S) racemic mixture is thermodynamically favored over
the meso-diastereomer even for more sterically hindered alkyl
derivatives (|∆E | ) 19.5 kJ/mol), suggesting that the single
diastereomer observed for both 4c and 4d in solution is the
(R,R)/(S,S) racemic mixture.
have less geometric flexibility than tricoordinate phosphine
The calculated structural parameters for 4′a closely parallel
those experimentally determined in the solid state (Table 5). In
contrast, the calculated parameters for 4′b more closely resemble
those of the conformer for 4b that is observed in the solid state,
possessing a nearly idealized eclipsed conformation [τR′ ) 1.9°],
centers. The 1JAB coupling constants for derivatives of 4 (Table
1
3) are consistent with the established range of JPP values for
phosphinophosphonium cations.2 However, the 1JAA′ values are
significantly smaller (ca. 100 Hz) for derivatives with phenyl
substituents at the phosphine centers (4a, 4′a).
and a correspondingly larger P-P-P-P torsion angle [τPR3
)
To assess the factors responsible for defining the conformers
and diastereoselectivity that are observed in the solid state
structures, comparative ground-state energy calculations were
performed using B3LYP/6-31+G(d) for staggered, eclipsed and
gauche conformations of the meso- and (S,S)-diastereomers for
dications 4′a and 4′b in the gas phase. Calculated structural
parameters for the lowest energy structures are presented in
Table 5. In all cases, the results are in agreement with the
experimental solid state structures: the R,S meso-isomer is
favored for 4′a, (R′ ) Ph, |∆E | ) 6.3 kJ/mol) while the (R,R)/
152.3°] and CR′-P-P angle [107.2°]. Crystal packing effects
and lattice energy in the solid state may be a significant
contributor to the deviation from calculated gas-phase param-
eters of 4′b.
Summary
New chlorophosphinophosphonium ions have been prepared
and comprehensively characterized. Reductive coupling of these
cations using Ph3P gives the first acyclic catena-2,3-diphos-
9
15740 J. AM. CHEM. SOC. VOL. 130, NO. 46, 2008

2,3-Diphosphino-1,4-diphosphonium Ions
A R T I C L E S
Figure 4. Representative conformations of the meso- and (S,S)-diastereomers. Idealized torsion angles between the central R-substituents are indicated (τR),
and the preferred conformation in the gas phase is highlighted.
Canada Research Chairs Program, the Canada Foundation for
Innovation, the Nova Scotia Research and Innovation Trust Fund,
the Walter C. Sumner Foundation, and the Eliza Ritchie Scholarship
for funding, Ulli Werner-Zwanziger for obtaining solid state NMR
spectroscopic data, and Sarah Whittleton for invaluable discussions
on computational methodology.
phino-1,4-diphosphonium ions. These new dications are also
formed in a one-pot combination of a dichlorophosphine, a
tertiary phosphine and Me3SiOTf. Quantitative ligand exchange
reactions are observed when derivatives of [Ph3P-PR′-PR′-
PPh3][OTf]2 react with Me3P, demonstrating the coordinative
nature of the terminal phosphine-phosphonium bonds and
implicating the diphosphenium cation acceptor. The diastereo-
selectivity of the reactions and the conformational preferences
observed in the solid state structures have been interpreted in
the context of computational models.
Supporting Information Available: Comparisons of simulated
and experimental 31P{1H} NMR spectra for [4c][OTf]2,
[4d][OTf]2, and [4′b][OTf]2, the solid-state 31P CP/MAS NMR
spectrum of [4a][OTf]2, complete ref 25, and crystallographic
information files. This material is available free of charge via
the Internet at http://pubs.acs.org.
Acknowledgment. We thank the Natural Sciences and Engi-
neering Research Council of Canada, the Killam Foundation, the
(34) Gee, M.; Wasylishen, R. E.; Ragogna, P. J.; Burford, N.; McDonald,
R. Can. J. Chem. 2002, 80, 1488–1500.
(35) Burford, N.; Cameron, T. S.; LeBlanc, D. J.; Losier, P.; Sereda, S.;
Wu, G. Organometallics 1997, 16, 4712–4717.
JA805911A
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