New synthetic procedures to Catena-phosphorus cations: Preparation and dissociation of the first cyclo-phosphino-halophosphonium salts

Article abstract of DOI:10.1021/ja907693f

Chlorination of 1,2,3,4-tetracyclohexyl-cyclo-tetraphosphine (2) by PhICl₂ or PCl₅ in the presence of Me₃SiOTf or GaCl₃ provides a stepwise approach to salts of the first cyclo-phosphino-chlorophosphonium cation

Full text of DOI:10.1021/ja907693f

Published on Web 11/13/2009
New Synthetic Procedures to Catena-Phosphorus Cations:
Preparation and Dissociation of the First
cyclo-Phosphino-halophosphonium Salts
Jan J. Weigand,*,† Neil Burford,*,‡ Reagan J. Davidson,†,‡ T. Stanley Cameron,‡
and Patrick Seelheim†
Department of Inorganic and Analytical Chemistry, Westfa¨lische Wilhelms-UniVersity Mu¨nster,
Corrensstrasse 30, 48149 Mu¨nster, Germany, and Department of Chemistry, Dalhousie
UniVersity, Halifax, NoVa Scotia B3H 4J3, Canada
Received September 10, 2009; E-mail: jweigand@uni-muenster.de; Neil.Burford@dal.ca
Abstract: Chlorination of 1,2,3,4-tetracyclohexyl-cyclo-tetraphosphine (2) by PhICl2 or PCl5 in the presence
of Me3SiOTf or GaCl3 provides a stepwise approach to salts of the first cyclo-phosphino-chlorophosphonium
cations [Cy4P4Cl]+ ([19]+) and [Cy4P4Cl2]2+ ([20]2+). The analogous iodo derivative [Cy4P4I]+ ([17]+) is obtained
as the tetraiodogallate salt from reaction of 2 with I2 in the presence of GaI3. Reactions of the dication
[20]2+ with PMe3 or dmpe effect a dissociation of the cyclic framework resulting in the formation of salts
containing [Me3PPCyPCyPMe3]2+ ([27]2+), [dmpeCyP]2+ ([29]2+), and [dmpeCyPCyP]2+ ([30]2+), respectively.
The new cations represent phosphine complexes of the [PCy]2+ and [P2Cy2]2+ cationic fragments from
[20]2+, demonstrating the coordinate nature of the phosphinophosphonium bonds in cyclo-phosphino-
halophosphonium cations. The compounds have been characterized by NMR spectroscopy, single crystal
X-ray crystallography, and Raman spectroscopy.
Scheme 1. Sequential Alkylation of Diphosphines and
Cyclophosphines
Introduction
Catena-phosphinophosphonium cations represent a potentially
diverse new class of compounds that represent analogues of
the homoatomic frameworks of carbon.1 The presence of a
molecular cationic charge enhances the P-P bond energy and
provides for high yield preparative reactions. A variety of
synthetic approaches have been described. Most obvious are
the single or double alkylation of a polyphosphine.2-6 For
example, diphosphines 1 are precursors to phosphinophospho-
nium cations 33 and diphosphonium cations 5,2 and cyclo-
tetraphosphines 2 are precursors to cyclo-triphosphino-2-
phosphonium cations 44,5 and cyclo-1,3-diphosphino-2,4-
diphosphonium dications 66 (Scheme 1).
Scheme 2. Halogenation of Tertiary Phosphines
Halogenation reactions of polyphosphines offer a potentially
versatile alternative approach to cationic electrophile addition
recognizing that a phosphine 7 reacts with a dihalogen, X2, to
give a P-X-X linear adduct 87,8 or a halophosphonium salt
the basicity of the anion X-,11,12 and the solvent.13 As shown
in Scheme 3, halogenation of diphosphines (1) gives halophos-
phines (10) via adduct 11 and ion pair [12][X], as the presence
of the halide anion X- anion leads to the cleavage of P-P bonds
by an SN2 reaction.14 Correspondingly, halogenation of cyclic-
phosphines 14 by reaction with dihalogens also results in P-P
bond cleavage to give dihalophosphines 16 (Scheme 4), and
9
9,10 (Scheme 2), depending on the basicity of the phosphine,7,8
† Westfa¨lische Wilhelms-University Mu¨nster.
‡ Dalhousie University.
(1) Dyker, C. A.; Burford, N. Chem. Asian J. 2008, 3, 28–36.
(2) Weigand, J. J.; Riegel, S. D.; Burford, N.; Decken, A. J. Am. Chem.
Soc. 2007, 129, 7965–7976.
(3) Burford, N.; Dyker, C. A.; Decken, A. Angew. Chem., Int. Ed. 2005,
44, 2364–2367.
(8) du Mont, W.-W.; Ba¨tcher, M.; Pohl, S.; Saak, W. Angew. Chem., Int.
Ed. Engl. 1987, 26, 912–913.
(4) Burford, N.; Dyker, C. A.; Lumsden, M. D.; Decken, A. Angew. Chem.,
Int. Ed. 2005, 44, 6196–6199.
(9) du Mont, W.-W.; Stenzel, V.; Jeske, J.; Jones, P. G.; Sebald, A.; Pohl,
S.; Saak, W.; Ba¨tcher, M. Inorg. Chem. 1994, 33, 1502–1505.
(10) Stenzel, V.; Jeske, J.; du Mont, W.-W.; Jones, P. G. Inorg. Chem.
1997, 36, 443–448.
(5) Dyker, C. A.; Riegel, S. D.; Burford, N.; Lumsden, M. D.; Decken,
A. J. Am. Chem. Soc. 2007, 129, 7464–7474.
(6) Riegel, S. D.; Burford, N.; Lumsden, M. D.; Decken, A. Chem.
Commun. 2007, 4668–4670.
(11) Pohl, S. Z. Anorg. Allg. Chem. 1983, 498, 15–19.
(12) Pohl, S. Z. Anorg. Allg. Chem. 1983, 498, 20–24.
(13) du Mont, W.-W.; Kroth, H.-J. J. Organomet. Chem. 1976, 113, C35–
C37.
(7) Godfrey, S. M.; Kelly, D. G.; McAuliffe, C. A.; Mackie, A. G.;
Pritchard, R. G.; Watson, S. M. J. Chem. Soc., Chem. Commun. 1991,
1163–1164.
9
10.1021/ja907693f CCC: $40.75  2009 American Chemical Society
J. AM. CHEM. SOC. 2009, 131, 17943–17953 17943

A R T I C L E S
Weigand et al.
Scheme 3. Halogenation Reaction of Diphosphines via a
Phosphinophosphonium Cation
of the homocyclic framework and forming phosphinodiphos-
phonium cations and diphosphinodiphosphonium dications.
Experimental Section
General Considerations. All reactions were carried out in a dry
box under an inert N2 atmosphere. Dichloromethane and pentane
were dried on an MBraun solvent purification system, degassed
with three freeze-pump-thaw cycles, and stored under nitrogen
and over molecular sieves prior to use. Acetonitrile (sure seal),
phosphorus pentachloride, gallium(III) chloride, gallium(III) iodide,
trimethylsilyl trifluoromethansulfonate (Me3SiOTf), and 1,2-bis-
(dimethylphosphino)ethane (dmpe) were purchased from Sigma-
Aldrich. Dichloroiodobenzene (PhICl2) and tetracyclohexyltetra-
phosphinane (2) were prepared according to literature procedures.21,22
All new compounds (unless otherwise stated) were characterized
by 31P{1H}, including measurement of 31P (non-decoupled) and
31P-31P DQF COSY. Measurements were performed at 25 °C.
Bruker AVANCE 500 (31P (202.46 MHz)) and chemical shifts are
referenced to δH3PO4(85%) ) 0.00 and are reported in ppm; J values
are reported in Hz. For compounds that give rise to higher order
spin-systems in their 31P{1H} NMR spectra, the resolution-enhanced
31P{1H} spectra were transferred to the software program gNMR,
version 5.0, by Cherwell Scientific.23 After examining the line
properties and noise, peak picking was performed. The full line-
shape iteration procedure of gNMR was applied to obtain the best
match of the fitted to the experimental spectra along with the
assignment of all the peaks revealed in the resolution-enhanced
Scheme 4. Halogenation Reaction of cyclo-Polyphosphinesa
a (i) (n+2)/2 X2; (ii) (n+2) X2 (n ) 1-4).
Chart 1
1
spectra. The signs for the J(31P,31P) coupling constants were set
negative and all other signs were obtained accordingly.24,25 Melting
points were recorded on an electrochemical melting point apparatus
in sealed capillary tubes under dinitrogen atmosphere and are
uncorrected. Raman spectra were obtained for powdered and
crystalline samples on a Bruker RFS 100 instrument equipped with
a Nd:YAG laser (1064 nm). Chemical analyses were determined
by Canadian Microanalytical Service LTD., Delta, BC, Canada.
Preparation of [17][GaI4]·1/2 CH2Cl2. A solution of I2 (5 mL,
0.05M, in CH2Cl2; 0.25 mmol) was added dropwise to a stirred
solution of (CyP)4 (114 mg, 0.25 mmol) and GaI3 (113 mg, 0.25
mmol) in CH2Cl2 (8 mL). The reaction mixture was stirred at room
temperature for 10 min, and the formation of the monocation was
confirmed by 31P NMR spectroscopy. The solvent was partially
removed in vacuo (∼5 mL), and the solution was filtered and
layered with pentane (5 mL) and stored at -32 °C. Pale-yellow
crystals of [17][GaI4]·1/2 CH2Cl2 were obtained after 4 days. Data
for [17][GaI4]·1/2 CH2Cl2: Yield: 42% (122 mg, 0.11 mmol); m.p.
118-120 °C; Raman (300 mW, 25 °C, cm-1): 2968 (18), 2933
(100), 2889 (39), 2867 (40), 2846 (57), 1439 (24), 1343 (17), 1297
(18), 1266 (16), 1187 (16), 1103 (12), 1076 (12), 1025 (27), 997
(15), 848 (18), 814 (21), 737 (20), 506 (17), 479 (18), 465 (17),
427 (20), 398 (28), 363 (16), 328 (15), 267 (37), 214 (36), 189
(34), 167 (31), 145 (87), 123 (34); 31P{1H} NMR (CD2Cl2, 300 K,
[ppm]): -44.2 (2P, PA), -31.1 (1P, PM), 34.8 (1P, PX, A2MX spin
the intermediate dihalodiphosphine 15 has been obtained from
the reaction of Ph5P5 with 2.5 equiv of I2.15
Derivatives of the phosphino-halophosphonium cation
[12]+ have been previously isolated in conjunction with a
weakly basic anion.1,16-20 In this context, the formation of
phosphino-halophosphonium cations as intermediates in the
halogenation reaction of polyphosphine has been exploited
as a synthetic approach to catena-phosphinophosphonium
cations by sequestering the product halide X- into a complex
anion. This is demonstrated by the reactions of tetracyclo-
hexyl-cyclo-tetraphosphine (CyP)4 with PhICl2, PCl5 or I2,
in the presence of Me3SiOTf or GaX3 (X ) Cl, I), which
provide quantitative formation of salts containing the first
cyclo-2-halo-1,3,4-triphosphino-2-phosphonium cations [17]+
and [19]+, and the first cyclo-2,4-dihalo-1,3-diphosphino-2,4-
diphosphonium dication [20]2+ (Chart 1). The new cyclo-
phosphino-halophosphonium cation [20]2+ can be considered
as a phosphine-phosphenium donor-acceptor complex and
undergoes ligand exchange reactions with PMe3 or 1,2-
bis(dimethylphosphino)ethane (dmpe) to effect dissociation
1
1
2
system, JAM ) -260, JMX ) -140, JAX ) -8 Hz). Chemical
analyses proved to be problematic for [17][GaI4]·1/2 CH2Cl2 owing
to the partial removal of solvents of crystallization upon isolation
(Figure 1).
Reaction of 2 with PhICl2 in the Presence of Me3SiOTf. A
solution of freshly prepared PhICl2 [(i) 75 mg, 0.275 mmol, in 5
mL CH2Cl2; (ii) 137 mg, 0.5 mmol, in 5 mL CH2Cl2] was added
(14) Fild, M.; Hollenberg, I.; Glemser, O. Naturwissenschaften 1967, 54,
89–90.
(15) Hoffmann, H.; Gru¨nwald, R. Chem. Ber. 1961, 94, 186–193. In this
contribution, (PhP)5 was misleadingly assigned as (PhP)4.
(16) Burford, N.; Cameron, T. S.; LeBlanc, D. J.; Losier, P.; Sereda, S.;
Wu, G. Organometallics 1997, 16, 4712–4717.
´
(21) Krassowska-Swiebocka, B.; Prokopenko, G.; Skulski, L. Synlett 1999,
9, 1409–1410.
(22) Henderson, Wm. A.; Epstein, M., Jr.; Seichter, F. S. J. Am. Chem.
Soc. 1963, 85, 2462–2466.
(17) Burford, N.; Ragogna, P. J. Dalton Trans. 2002, 4307–4315.
(18) Burford, N.; Ragogna, P. J.; McDonald, R.; Ferguson, M. J. Am. Chem.
Soc. 2003, 125, 14404–14410.
(23) Budzelaar, P. H. M. gNMR for Windows, 5.0; Cherwell Scientific
Publishing Limited: Oxford, UK, 1997.
(19) Weigand, J. J.; Burford, N.; Lumsden, M. D.; Decken, A. Angew.
Chem., Int. Ed. 2006, 45, 6733–6737.
(24) Finer, E. G.; Harris, R. K. Prog. Nucl. Magn. Reson. Spectrosc. 1970,
6, 61–118.
(25) Forgeron, M. A. M.; Gee, M.; Wasylishen, R. E. J. Phys. Chem. A
2004, 108, 4895–4908.
(20) Weigand, J. J.; Burford, N.; Decken, A. Eur. J. Inorg. Chem. 2008,
4343–4347.
9
17944 J. AM. CHEM. SOC. VOL. 131, NO. 49, 2009

Synthetic Procedures to catena-Phosphorus Cations
A R T I C L E S
dropwise to a stirred solution of 2 (114 mg, 0.25 mmol) and
Me3SiOTf [(i) 45 µL, 0.25 mmol; (ii) 90 µL, 0.5 mmol] in CH2Cl2
(5 mL) at room temperature. The reaction was monitored by of
31P{1H} NMR spectroscopy (Figure 2, i and ii).
(55), 120 (84); 31P{1H} NMR (CD2Cl2, 300 K, [ppm]): δ ) 127.2
(s); elemental analysis for C6H11Cl7GaP (432.02): calcd C 16.7, H
2.6; found: C 16.5, H 2.6.
Preparation of [27][GaCl4]. To a cooled solution (0 °C) of PMe3
(0.52 M in toluene, 1 mL, 0.52 mmol) in CH2Cl2 (5 mL) was added
a solution of [20][Ga2Cl7]2 (169 mg, 0.13 mmol) in CH2Cl2 (2 mL)
within 2 min. After 15 min the reaction mixture was allowed to
warm to room temperature and stirred for a further 24 h. The oily
phase was separated and dissolved in MeCN (1.5 mL). The MeCN
solution was under-layered with CH2Cl2 and stored at -20 °C. After
four days, [27][GaCl4]2 was obtained as block shaped crystals. Data
for [27][GaCl4]2: Yield: 35% (73 mg); 31P{1H} NMR (CD3CN, 300
K, [ppm]): only one diastereomer observed, broad signals, δ )
-33.1 (AA′) and 19.2 (XX′); elemental analysis for C18H40Cl8Ga2P4
(803.48): calcd C 26.9, H 5.0; found: C 27.2, H 5.3.
Preparation of [23][GaCl4]. A solution of GaCl3 (88 mg, 0.5
mmol, in 8 mL CH2Cl2) was added dropwise to a stirred solution
of PCl5 (104 mg, 0.5 mmol) in CH2Cl2 (10 mL). The reaction
mixture was stirred at room temperature for 10 min and stored at
-32 °C. Clear, colorless needles of [23][GaCl4] started to separate
after 1 day. Data for [23][GaCl4]: Yield: 95% (182 mg, 0.48 mmol);
m.p. 308-310 °C; Raman (280 mW, 25 °C, cm-1): 650 (16, ν3(F2),
PCl4+), 455 (100, ν1(A1), PCl4+), 373 (2, ν3(F2), GaCl4-), 347 (61,
ν1(A1), GaCl4-), 250 (74, ν4(F2), PCl4+), 178 (34, ν2(E), PCl4+),
151 (35, ν4(F2), GaCl4-), 121 (39, ν2(E), GaCl4-); 31P{1H} NMR
(CD2Cl2, 300 K, [ppm]): δ ) 85.1 (s).
Preparation of [29][GaCl4]2. A solution of dmpe (41.7 µL, 37.5
mg, 0.25 mmol) in CH2Cl2 (3 mL) was added dropwise within 30
min to a cooled (0 °C) solution of [20][Ga2Cl7]2 (163 mg, 0.125
mmol) in CH2Cl2 (10 mL). After warming to room temperature,
the formed precipitate was separated and washed with hexane (2
× 6 mL). The precipitate was dissolved in MeCN (3 mL), carefully
under-layered with CH2Cl2 (5 mL), and stored at -20 °C. Colorless
crystals of [29][GaCl4]2 were formed within three days. Data for
[29][GaCl4]2: Yield: 85% (146 mg, 0.21 mmol); m.p. 146-148 °C;
Raman (300 mW, 25 °C, cm-1): 2990 (34), 2943 (48), 2924 (49),
2908 (100), 2859 (25), 1444 (20), 1395 (21), 1342 (16), 1300 (17),
1261 (18), 1192 (17), 1022 (18), 997 (17), 845 (19), 804 (20), 770
(21), 743 (22), 729 (23), 651 (33), 453 (34), 421 (33), 369 (-44),
348 (66), 320 (31), 247 (39), 218 (39), 179 (37), 149 (45), 120
(42); 31P{1H} NMR (CD3CN, 300 K, [ppm]): -68.8 (1P, -P-PA-
P-), 50.0 (2P, -PX-P-PX-, AX2 spin system, 1JAX ) -293); elemental
analysis for C12H27Cl8Ga2P3 (687.33): calcd C 21.0, H 4.0; found:
C 21.4, H 4.2.
Formation of a Mixture of [29][GaCl4]2 and [30][GaCl4]2. A
solution of [20][Ga2Cl7]2 (163 mg, 0.125 mmol) in CH2Cl2 (2 mL)
was added all at once at room temperature to a solution of dmpe
(41.7 µL, 37.5 mg, 0.25 mmol) in CH2Cl2 (3 mL). The immediate
formation of an oil was observed. The oily phase was separated
and dissolved in MeCN (3 mL), and the formed precipitate (Cy4P4)
separated. To the clear solution was added CH2Cl2 (5 mL) and an
approximate 1:1 mixture (as shown by 31P{1H} NMR) of compound
[29][GaCl4]2 and [30][GaCl4]2 was obtained as a precipitate. Data
for [29][GaCl4]2 and [30][GaCl4]2: Yield: 125 mg; 31P{1H} NMR
Reaction of 2 with PCl5 in the Presence of GaCl3. A solution
of freshly prepared PCl5 (104 mg, 0.5 mmol, in 4 mL CH2Cl2) was
added dropwise to a stirred solution of 2 (114 mg, 0.25 mmol) and
GaCl3 (176 mg, 1.0 mmol) in CH2Cl2 (5 mL) at room temperature.
The reaction was monitored by 31P{1H} NMR spectroscopy (Figure
3).
Preparation of [19][GaCl4] and [20][Ga2Cl7]2. A solution of
PCl5 [(i) 52 mg, 0.25 mmol, in 5 mL CH2Cl2; (ii) 104 mg, 0.5
mmol, in 8 mL CH2Cl2] was added dropwise to a stirred solution
of (CyP)4 (114 mg, 0.25 mmol) and GaCl3 [(i) 44 mg, 0.25 mmol;
(ii) 176 mg, 1.0 mmol] in CH2Cl2 (8 mL). The reaction mixture
was stirred at room temperature for 10 min, and the formation of
(i) [19]+ or (ii) [20]2+ was confirmed by 31P-NMR spectroscopy.
The solvent was partially removed in vacuo (∼5 mL), and the
solution was layered with pentane (5 mL) and stored at -32 °C.
Colorless crystals of [19][GaCl4] or [20][Ga2Cl7]2 formed after a
few days. Data for [19][GaCl4]: Yield: 60% (106 mg, 0.15 mmol);
m.p. 119-122 °C; Raman (300 mW, 25 °C, cm-1): 2939 (100),
2890 (49), 2850 (80), 1495 (14), 1442 (32), 1344 (20), 1298 (19),
1267 (21), 1190 (16), 1080 (12), 1025 (26), 1000 (17), 849 (22),
816 (18), 734 (22), 572 (20), 461 (24), 423 (30), 367 (28), 344
(43), 291 (25), 166 (37), 150 (37), 121 (44); 31P{1H} NMR (CD2Cl2,
300 K, [ppm]): -54.4 (P, PA), -40.7 (2P, PM), 95.1 (1P, PX, AM2X
spin system, 1JAM ) -285, 1JMX ) -126, 2JAX ) 18 Hz); elemental
analysis for C24H44Cl5GaP4 (703.49): calcd C 41.0, H 6.3; found:
C 41.3, H 6.4. Data for [20][Ga2Cl7]2: Yield: 90% (293 mg, 0.23
mmol); m.p. 106-109 °C; Raman (300 mW, 25 °C, cm-1): 2944
(100), 2900 (360), 2859 (50), 1442 (18), 1342 (13), 1299 (9), 1290
(10), 1266 (12), 1192 (13), 1176 (12), 1106 (5), 1080 (7), 1022
(20), 993 (14), 843 (15), 800 (7), 743 (8), 720 (11), 592 (14), 471
(8), 420 (20), 369 (68), 357 (18), 287 (17), 262 (10), 234 (10), 212
(12), 191 (19), 166 (26), 138 (54); 31P{1H} NMR (CD2Cl2, 300 K,
[ppm]): 9.3 (2P, PA), 83.2 (2P, PX, A2X2 spin system, 1JAX ) -288);
elemental analysis for C24H44Cl16Ga4P4 (1302.64): calcd C 22.1, H
3.4; found: C 22.1, H 3.6.
Preparation of [24][GaCl4]. Method A: A solution of PCl5 (104
mg, 0.50 mmol, in 8 mL CH2Cl2) was added dropwise to a stirred
solution of [20][Ga2Cl7]2 (130 mg, 0.10 mmol) in CH2Cl2 (4 mL).
The reaction mixture was stirred at room temperature for 5 h. The
solvent was partially removed in vacuo (∼5 mL), the solution was
layered with pentane (5 mL) and stored at -32 °C. Method B: To
solution of 2 (91 mg, 0.20 mmol) and GaCl3 (144 mg, 0.80 mmol)
in CH2Cl2 (5 mL) was slowly added a solution PCl5 (332 mg, 1.60
mmol) in CH2Cl2 (6 mL) at room temperature. The solvent was
partially removed in vacuo (∼5 mL), the solution was layered with
pentane (5 mL) and stored at -32 °C. For both cases, colorless
crystals of [24][GaCl4] were formed within two days. Data for
[24][GaCl4]: Yield: 74% (160 mg, 0.37 mmol, method A);
quantitative (method B); m.p. 96-98 °C; Raman (300 mW, 25 °C,
cm-1): 2959 (61), 2908 (25), 2872 (66), 2860 (65), 1515 (14), 1447
(48), 1351 (22), 1328 (17), 1296 (27), 1283 (20), 1268 (24), 1208
(17), 1179 (17), 1079 (17), 1027 (24), 1000 (21), 846 (22), 819
(27), 760 (24), 632 (29), 549 (52), 488 (55), 432 (41), 369 (31),
344 (100), 336 (83), 308 (44), 223 (54), 204 (61), 173 (37), 151
(CH3CN, C6D6 Capillary, 300 K, [ppm]); [29][GaCl4]2: δ ) -68.8
1
(1P, -P-PA-P-), 50.0 (2P, --PX-P-PX-, AX2 spin system, JAX
)
-293); [30][GaCl4]2: δ ) -55.9 (2P, -P-PA-PA-P-), 18.8 (2P, -PX-
P-P-PX-, AA′XX′ spin system, 1JAX ) 1JA′X′ ) -315, 2JAA′ ) 151,
2
3
2JAX′ ) JXA′ ) 18, JXX′ ) -9 Hz).
Crystal Structures. Suitable single crystals for all compounds
were coated with Paratone-N oil, mounted using a glass fibre pin
and frozen in the cold nitrogen stream of the goniometer. X-ray
diffraction data for 226 and [29][GaCl4]2 were collected on a Bruker
AXS APEX CCD diffractometer equipped with a rotation anode
at 153(2) K using graphite-monochromated Mo KR radiation (λ )
0.71073 Å) with a scan width of 0.3° and 7 s for 2, and 5 s for
[29][GaCl4]2 exposure times. In both cases generator settings were
50 kV and 180 mA. Diffraction data were collected over the full
sphere and were corrected for absorption. The data reduction
(SAINT)27 and correction (SADABS)28 was performed with the
Bruker software. X-ray diffraction data for [17][GaI4]·1/2CH2Cl2,
[19][GaCl4], [20][Ga2Cl7]2, [23][GaCl4], [24][GaCl4], and
[27][GaCl4]2 were collected on a Rigaku RAXIS RAPID diffrac-
tometer with a imaging plate area detector (graphite-monochromated
Mo KR radiation, λ ) 0.71073 Å). Crystals were mounted under
fluorolube on the tip of 150 µm micromounts. The data were
(26) Henderson, W. A.; Epstein, M.; Seichter, F. S. J. Am. Chem. Soc.
1963, 85, 2462–2466.
(27) SAINT 7.23A; Bruker AXS, Inc: Madison, WI, 2006.
(28) Sheldrick, G. M. SADABS; Bruker AXS, Inc.: Madison, WI, 2004.
9
J. AM. CHEM. SOC. VOL. 131, NO. 49, 2009 17945

A R T I C L E S
Weigand et al.
Table 1. Crystallographic Data
2
[17][GaI4]·1/2 CH2Cl2
[19][GaCl4]
[20][Ga2Cl7]2
formula
C24H44P4
456.47
C24.5H45ClP4GaI5
1203.22
C24H44Cl5P4Ga
703.49
0.29×0.27×0.21
colorless block
monoclinic
P21/n
18.491(9)
9.143(9)
19.970(5)
90
C24H44Cl16P4Ga4
1302.63
0.27×0.14×0.06
colorless needle
orthorhombic
Pbca
17.8070(4)
17.9537(3)
31.5222(8)
90
Mr [g mol-1
]
dimension [mm3]
color, habit
crystal system
space group
a [Å]
0.16×0.13×0.13
colorless block
tetragonal
0.27×0.19×0.16
yellow pinacoid
triclinic
j
j
P421c
P1
10.1235(2)
10.1235(2)
12.4110(5)
90
90
90
10.5502(3)
13.5437(5)
13.9971(5)
101.395(2)
93.704(1)
99.350(2)
1924.9(1)
2
b [Å]
c [Å]
R [deg]
ꢀ [deg]
104.27(5)
90
3272(5)
4
90
90
γ [deg]
V [Å3]
1271.94(6)
2
10077.7(4)
8
Z
T [K]
153(1)
1.192
496
123(2)
2.076
1130
123(2)
1.428
1456
123(2)
1.717
5152
Fc [g cm-3
F(000)
]
λMoKR [Å]
0.71073
0.306
multi-scan
13577
981
0.0251
955
0.249, -0.123
65
0.71073
4.976
multi-scan
96666
11152
0.026
9830
2.33, -1.74
472
0.71073
1.458
none
79803
6680
0.115
5249
1.12, -0.66
352
0.71073
3.109
multi-scan
86025
36726
0.031
21819
1.42, -0.79
477
µ [mm-1
]
absorption correction
reflections collected
reflections unique
Rint
reflection obs. [F > 3σ(F)]
residual density [e Å-3
parameters
]
GOF
1.112
1.077
1.000
0.970
R1 [I > 2σ(I)]
wR2 (all data)
CCDC
0.0213
0.0583
745539
0.0258
0.0305
745543
0.0590
0.0589
745537
0.0478
0.0593
745538
[23][GaCl4]
[24][GaCl4]
[27][GaCl4]2
[29][GaCl4]2
formula
Cl8GaP
384.32
0.38×0.19×0.17
colorless needle
orthorhombic
Pbcm
6.1146(3)
13.514(1)
13.792(1)
90
C6H11Cl17GaP
432.02
0.25×0.12×0.08
colorless needle
monoclinic
P21/c
8.783(2)
13.740(3)
26.02(1)
90
C18H40Cl8Ga2P4
803.47
0.26×.25×0.22
colorless needle
monoclinic
P21/c
9.740(2)
12.396(3)
28.660(7)
90
90.19(1)
90
C12H27Cl8Ga2P3
687.29
0.14×.11×0.09
colorless block
orthorhombic
Pca21
12.2913(3)
14.9034(5)
14.9881(6)
90
Mr [g mol-1
]
dimension [mm3]
color, habit
crystal system
space group
a [Å]
b [Å]
c [Å]
R [deg]
ꢀ [deg]
90
90
1139.7(1)
4
91.96(2)
90
3137(2)
4
90
90
2727.1(2)
4
γ [deg]
V [Å3]
3460.6(2)
4
Z
T [K]
123(2)
2.240
728
123(2)
1.829
1696
123(2)
1.542
1624
153(1)
1.674
1368
Fc [g cm-3
F(000)
]
λMoKR [Å]
0.71073
4.361
0.71073
3.015
0.71073
2.368
0.71073
2.935
µ [mm-1
]
absorption correction
reflections collected
reflections unique
Rint
multi-scan
8903
1656
multi-scan
17765
7802
multi-scan
48724
7909
multi-scan
12814
3810
0.030
0.040
0.101
0.0328
reflection obs. [F > 3σ(F)]
1397
0.72, -0.97
52
6005
1.22, -0.78
294
6752
1.75, -1.29
290
3512
0.634, -0.533
231
residual density [e Å-3
parameters
]
GOF
1.098
1.114
1.089
1.026
R1 [I > 3σ(I)]
wR2 (all data)
CCDC
0.0338
0.0376
745544
0.0386
0.0427
745541
0.0662
0.1876
745540
0.0259
0.0579
745542
collected using sweeps of ω oscillations. After data reduction,
equivalent reflections were merged. Intensity data were corrected
for Lorentz, absorption and polarization effects. For further crystal
and data collection details, see Table 1. The structures were solved
by direct methods and expanded Fourier techniques. Full matrix
least-squares refinement was carried out with the program
SHELXS9729 against F2 using first isotropic and later anisotropic
thermal parameters for all non-hydrogen atoms. Hydrogen atoms
were generated with idealized geometries and isotropically refined
(29) Sheldrick, G. M. SHELXL-97, Program for crystal structure deter-
mination; University of Go¨ttingen: Germany, 1997.
9
17946 J. AM. CHEM. SOC. VOL. 131, NO. 49, 2009

Synthetic Procedures to catena-Phosphorus Cations
A R T I C L E S
Scheme 5. Preparation of [17][GaI4] and Attempted Preparation of
[18][GaI4]2 (X ) GaI4, OTf) Saltsa
a (i) I2, GaI3, or AgOTf in CH2Cl2; (ii) 2I2, 2GaI3, or 2AgOTf in CH2Cl2.
Table 2. 31P{1H} NMR Parameters for Salts of Cations [17]+, [19]+,
[20]2+, [27]2+, [29]2+, and [30]2+
[17]+
[19]+
[20]2+
[27]2+
[29]2+
[30]2+
spin systema,b A2MX AM2X A2X2 AA′XX′ AX2
AA′XX′
c
δA
-44.2 -54.4 9.3
-31.1 -40.7
-33.1
-68.8 -55.9
δM
δX
34.8
95.1
83.2 19.2
50.0
18.8
d
1JAM
1JMX
2JAX
-260 -285
-140 -126
-8
18
e
e
1JAX, JAA′
-288
-
-
-293 -315, -151
18, -9
1
3
2JA′X, JXX′
a Furthest downfield resonance is denoted by the highest letter in the
alphabet, and the furthest upfield by the lowest letter. By convention the
letter in the spin system is determined by the ratio ∆δ(PiPii)/JP P > 10
(resonance considered to be pseudo-first order and the assigned iiletters
are separated) < 10 (consecutive letters are assigned). b Parameters for
spin systems of higher order are derived by iterative fitting of
i
Figure 1. ORTEP plot of the molecular structure of the cation and anion
in [17][GaCl4]•1/2CH2Cl2. Thermal ellipsoids with 50% probability (hy-
drogen atoms and solvent molecules are omitted for clarity). Selected bond
lengths (Å) and angles (°) are included in Table 2.
experimental data at 300 K. c Absolute signs of the JPP(iso) have been
1
tentatively assigned to be negative. d Chemical shifts (δ) are given in
[ppm] and coupling constants (J) in [Hz]. e Could not be simulated due
to broad signals.
Table 3. Selected Structural Parameters for 2 and Cations [17]+,
[19]+, and [20]2+
2
[17]+ (X ) I)
[19]+ (X ) Cl) [20]2+ (X ) Cl)
using a riding model. For [27][GaCl4]2 the crystal was a twin (twin
law 1 0 0, 0 -1 0, 0 0 -1) with not quite equal components (0.509:
0.491). For compounds [17][GaI4] · 1/2CH2Cl2, [19][GaCl4],
[20][Ga2Cl7]2, [23][GaCl4], [24][GaCl4], and [27][GaCl4]2 the
calculations were performed using the CrystalStructure crystal-
lographic software package.30,31
Bond Lengths [Å]
P1-P2a
P2-P3
P3-P4
P4-P1a
P1-X
2.2224(5)
2.2224(5)
1.868(1)
2.1872(8)
2.2386(7)
2.2400(7)
2.1919(8)
2.4041(5)
2.185(1)
2.2411(8)
2.2478(9)
2.1857(8)
2.011(1)
2.1999(8)
2.2004(8)
2.2077(8)
2.2084(8)
1.9828(9)
1.9832(8)
1.820(2)
1.865(2)
1.791(2)
1.867(2)
P3-X
Results and Discussion
P1-C1
P2-C7
P3-C13
P4-C19
1.838(2)
1.864(2)
1.872(2)
1.863(2)
1.814(2)
1.864(2)
1.873(2)
1.863(2)
The halonium addition reaction that occurs when a phosphine
reacts with a dihalogen has been extrapolated to polyphosphines
to provide a new synthetic approach to phosphinophosphonium
cations. The 31P{1H} NMR spectra of reaction mixtures contain-
ing (CyP)4 (2), I2 and GaI3 in CH2Cl2 solution (Scheme 5) show
three resonances in a first order A2MX spin pattern with relative
intensities of 2:1:1. The data are summarized in Table 2 and
are consistent with the formation of the monocation [17]+ (Chart
1). Chemical shifts at higher field correspond to the phosphine
centers (δA ) -44.2 and δM ) -31.1 ppm) and the low field
shift (δA ) 34.8 ppm) corresponds to the phosphonium center,
in accordance with those for previously reported phosphino-
phosphonium cations.1,17,32 Compound [17][GaI4] was isolated
as extremely air- and moisture-sensitive yellow blocks in
moderate yields (42 %) as a CH2Cl2 solvate.
Bond Angles [deg]
84.03(2)
P1-P2-P3a
P2-P3-P4
P3-P4-P1
P4-P1-P2
P2-P1-C1
P4-P1-C1
P1-P2-C7
P1-P4-C19
P2-P3-C13
P4-P3-C13
P2-P1-X
P4-P1-X
P2-P3-X
P4-P3-X
C1-P1-X
C13-P3-X
85.271(9)
83.71(3)
88.71(3)
83.52(3)
91.79(3)
115.3(1)
115.32(8)
103.97(9)
105.51(8)
98.37(8)
100.35(9)
113.74(4)
113.46(3)
80.55(2)
94.60(3)
80.21(2)
86.97(2)
83.89(2)
89.46(3)
94.59(3)
102.55(5)
102.81(5)
113.29(7)
115.26(7)
105.78(7)
104.73(8)
100.70(7)
100.86(7)
113.79(2)
114.57(2)
110.83(8)
114.21(8)
105.15(8)
106.27(9)
111.47(8)
112.68(8)
113.34(3)
112.41(3)
113.96(3)
112.91(3)
110.64(9)
110.45(9)
The solid state structure of [17]GaI4 ·1/2 CH2Cl2 has been
determined by X-ray crystallography and a view of the cation
and anion in the solid state is shown in Figure 1. Selected
113.79(2)
107.44(9)
a For 2 P1 ) P3, P2 ) Pi, P4 ) Pii, symmetry code: (i) y - 1, -x +
1, -z + 2; (ii) -y + 1, x + 1, -z + 2.
(30) CrystalStructure 3.8: Crystal Structure Analysis Package, Rigaku and
Rigaku/MSC (2000-2006). 9009 New Trails Dr. The Woodlands TX
77381 USA.
(31) CRYSTALS, Issue 11; Carruthers, J. R., Rollett, J. S., Betteridge, P. W.,
Kinna, D., Pearce, L., Larsen, A., Gabe, E., Eds.; Chemical Crystal-
lography Laboratory, Oxford, UK, 1999.
structural parameters are listed in Table 3 along with compara-
tive parameters for the cyclo-tetraphosphine 2. Consistent with
the structural features of [MeCy4P4]+,4 the cyclohexyl substituent
at P1 in [17]+ minimizes the steric interactions by twisting to
enable a gauche conformation of the R-hydrogen atom of C1
and the iodine substituent.4 The P-P bonds at the four-
(32) Burford, N.; Ragogna, Cameron, T. S.; Ragogna, P. J. Am. Chem.
Soc. 2001, 123, 7947–7948.
9
J. AM. CHEM. SOC. VOL. 131, NO. 49, 2009 17947

A R T I C L E S
Weigand et al.
Figure 2. 31P{1H} NMR spectra of the reaction of (CyP)4 with PhICl2 in the presence of Me3SiOTf at RT in CH2Cl2; (i) ∼1.1 equiv of PhICl2; (ii) 2 equiv
of PhICl2.
Scheme 6. Proposed Pathway for Reaction of 2 with PhICl2 in the
Presence of Me3SiOTf
coordinate phosphorus centers are slightly shorter than those
involving the three-coordinate phosphorus centers. Moreover,
the shortest P-C bond occurs at the phosphonium center. The
P4 ring is slightly more puckered than that in [MeCy4P4]+, as
indicated by greater P-P-P-P torsion angles ranging from
23.6-24.2° (vs. 28.9-29.6°). The iodine atom at the phospho-
nium center has a weak interaction with an iodine of the gallate
anion (3.635(3) Å), resulting in an almost linear P1-I1-I3 unit
(168.37(2)°). The P-I bond length (2.4041(5) Å) is typical (2.40
( 0.01 Å),11,12,33 indicating that [17]GaI4 should be considered
as an ionic compound. Attempts to prepare the dication [18]2+
,
by treatment of 2 with 2 equiv of I2 and GaI3 or AgOTf, leads
to the formation of copious amounts of an orange precipitate,
found to be completely insoluble in CH2Cl2, CH3CN, and C6H5F
(Scheme 5). We abstained from a detailed investigation of the
precipitate.
31P{1H} NMR spectra of reaction mixtures containing (CyP)4
(2), PhICl2 and Me3SiOTf in CH2Cl2 are summarized in Figure
2. Reaction mixtures involving an slight excess (1.1 equiv) of
PhICl2 exhibit an AM2X spin system that is assigned to [19]+
(Table 2). The presence of (CyP)4 (δ ) -67.0 ppm)34 and
CyPCl2 (21, δ ) -192.0 ppm)35 in this reaction mixture is
significant as the 31P{1H} NMR spectrum of a reaction of 2
with 2 equiv of PhICl2 in the presence of 2 equiv of Me3SiOTf
(Figure 2(ii)) shows only the presence of [19]+ and CyPCl2 (21).
We interpret these observations according to Scheme 6, which
shows the initial chloronium addition to 2 to give [19]+ followed
by a second addition to give the dication [20]2+. The dication
is not observed implying fast nucleophilic attacks by Cl- at the
phosphonium centers to first displace cation [22]+ and 21. Under
these reaction conditions, we speculate that cation [22]+
undergoes a further and rapid36 nucleophilic attack by Cl- to
give 21 and [CyPdPCy],37 which dimerizes to give 2. The
characteristic A2B pattern corresponding to (CyP)3 was not
observed in the chlorination reactions in contrast to the ring
contraction of [MeCy4P4]+, which is observed on reaction with
PMe3 to yield (CyP)3 and the phosphinophosphonium cation
[Me3P-PMeCy]+.4
Chloronium addition to (CyP)4 is also effected by reaction
with PCl5 and GaCl3 in CH2Cl2. Reaction mixtures of various
stoichiometries have been monitored by 31P{1H} NMR spec-
troscopy at room temperature as summarized in Figure 3. In
the absence of PCl5 (Figure 3, X ) 0 equiv), the two broad
signals (δ ) -43 and -62 ppm) are indicative of a weak adduct
between (CyP)4 and GaCl3 which dissociates in solution.
Introduction of a solution of PCl5 in CH2Cl2 results in the
formation of the tetrachlorophosphonium salt [23][GaCl4], as
shown in Scheme 7a, which reacts with (CyP)4 to give [19]+
(AM2X spin system, Table 2) and PCl3 (δ ) -220.1 ppm; X
38
(33) Cotton, F. A.; Kibala, P. A. J. Am. Chem. Soc. 1987, 109, 3308–
3312.
(34) Albrand, J. P.; Cogne, A.; Robert, J. B. J. Am. Chem. Soc. 1978, 100,
2600–2604.
(37) Diphosphenes (RPdPR) need bulky substituents for kinetic stabili-
zation:Yoshifuji, M.; Shima, I.; Inamoto, K.; Hirotsu, K.; Higushi, T.
J. Am. Chem. Soc. 1981, 103, 4587–4589.
(35) Weferling, N. Z. Anorg. Allg. Chem. 1987, 548, 55–62.
(36) Schoeller, W. W.; Staemmler, V.; Rademacher, P.; Niecke, E. Inorg.
Chem. 1986, 25, 4382–4385.
(38) Baudler, M.; Pinner, C.; Gruner, C.; Hellmann, J.; Schwamborn, M.;
Kloth, B. Z. Naturforsch. B 1977, 32, 1244–1251.
9
17948 J. AM. CHEM. SOC. VOL. 131, NO. 49, 2009

Synthetic Procedures to catena-Phosphorus Cations
A R T I C L E S
Figure 3. 31P{1H} NMR spectra (CH2Cl2, C6D6 capillary, RT) of the stepwise chlorination reaction of 2 with PCl5 in the presence of GaCl3 according to
Scheme 7; X ) 0-3 equiv of PCl5.
Scheme 7. Successive Chlorination of (CyP)4 with [PCl4]+
) 1 equiv).39 A high concentration of PCl5 and GaCl3 in solution
leads to the crystallisation of [23][GaCl4] as colorless needles.
The binary tetrachlorophosphonium cation [23]+ has been
known for some time and was characterized by vibrational40
and 31P NMR41 spectroscopic studies, as well as by crystal
Figure 4. ORTEP plot of the perspective view of the unit cell of
[23][GaCl4] perpendicular to the bc plane. Thermal ellipsoids with 50%
probability at 123(2) K [symmetry code: (i) x, 0.5 - y, -z; (ii) x, y,
0.5 - z].
structure determinations with a large combination of several
counter-anions.42 However, to the best of our knowledge, an
X-ray determination of [23]+ as the tetrachlorogallate salt has
not been reported. Compound [23][GaCl4] crystallizes in the
geometry, whereas the anion is significantly distorted, exhibiting
Cl-E-Cl angles between 108.69(2) and 113.47(2)° ([GaCl4]-)
and between 108.43(5) and 110.38(3)° ([PCl4]+). This trend is
orthorhombic space group Pbca with four molecular units in
the unit cell (Figure 4). The structure is isotypical with
[PCl4][FeCl4].43 The cation displays an almost perfect tetrahedral
9
J. AM. CHEM. SOC. VOL. 131, NO. 49, 2009 17949

A R T I C L E S
Weigand et al.
Figure 5. ORTEP plot of the molecular structure of [19][GaCl4]. Thermal ellipsoids with 50% probability at 123(2) K (hydrogen atoms are omitted for
clarity). Selected bond lengths (Å) and angles (deg) are included in Table 2.
also reflected by the Ga-Cl distances varying from 2.1704(7)
to 2.1867(9)Å, whereas the P-Cl bond lengths are within the
limits and are almost identical (1.9285(8) and 1.9302(9) Å).
The molecular structure of [23][GaCl4] shows short interatomic
Cl· · ·Cl distances in the range of 3.338(2) to 3.470(2) Å between
the [PCl4]+ and [GaCl4]- units, which are shorter than the sum
of the van der Waals radii (3.50 Å),44 indicating weak
cation· · ·anion interactions.
Two triplets, assigned to [20]2+, are observed when the
stoichiometry of PCl4+ exceeds that of (CyP)4 (Table 2; Scheme
7b, Figure 3, X ) 2 equiv). The cations [19]+ and [20]2+ are
resilient in this reaction mixture due to the absence of chloride
anion. Addition of excess PCl5 leads to appearance of two
41
singlets attributed to [23]+ (δ ) 85.1ppm) and [24]+ (δ )
127.2 ppm). Cation [24]+ represents the final chlorination
product of 2 when 8 equiv of PCl5 are added (Scheme 7c).
Equimolar reaction mixtures of (CyP)4, GaCl3, and PCl3 in
CH2Cl2 at room temperature have enabled isolation of
[19][GaCl4]. Similarly, [20][Ga2Cl7]2 has been isolated from the
1:4:2 reaction of (CyP)4, GaCl3, and PCl3 in CH2Cl2 (Scheme
7b). Both compounds were obtained as colorless needles. A view
of the molecular units of [19][GaCl4] and [20][Ga2Cl7]2 is shown
in Figures 5 and 6, respectively, and structural parameters are
listed in Table 3.
The structural features of [19][GaCl4] are comparable with
those discussed for [17]GaI4 ·1/2 CH2Cl2. The solid state
structure of [20][Ga2Cl7]2 contains a symmetric (approximate
C2V) cation [20]2+ consistent with the A2X2 spin system observed
in the solution 31P{1H} NMR spectrum. The P-P bond lengths
in [20]2+ are essentially identical [2.1999(8) to 2.2084(8) Å]
(39) Johnson, S. E.; Knobler, C. B. Phosphorus, Sulfur and Silicon 1996,
115, 227–240.
(40) (a) Shamir, J.; van der Veken, B. J.; Herman, M. A.; Rafaeloff, R. J.
Figure 6. ORTEP plot of the molecular structure of [20][GaCl4]. Thermal
Raman Spectrosc. 1981, 11, 215–220. (b) Finch, A.; Gates, P. N.;
ellipsoids with 50% probability at 123(2) K (hydrogen atoms are omitted
for clarity). Selected bond lengths (Å) and angles (deg) are included in
Table 2.
Muir, A. S. Polyhedron 1986, 5, 1537–1542.
(41) Dillon, K. B.; Nisbet, M. P.; Waddington, T. C. J. Chem. Soc., Dalton
Trans. 1978, 11, 1455–1460.
(42) Aubauer, C.; Kaupp, M.; Klapo¨tke, T. M.; No¨th, H.; Piotrowski, H.;
Schnick, W.; Senker, J.; Suter, M. J. Chem. Soc., Dalton Trans. 2001,
1880–1889, and references therein.
and are only slightly shorter than those in (CyP)4 [2.2224(5)
Å] and in [19]+ [2.1872(8) to 2.2478(9) Å]. The P-Cl bonds
[1.9828(9) and 1.9832(8) Å] in [20]2+ are shorter than that in
[19]+ [2.011(1) Å] as expected due to the higher charge in the
(43) Kistenmacher, T. J.; Stucky, G. D. Inorg. Chem. 1968, 10, 2150–
2155.
(44) Bondi, A. J. Phys. Chem. 1964, 68, 441–451.
9
17950 J. AM. CHEM. SOC. VOL. 131, NO. 49, 2009

Synthetic Procedures to catena-Phosphorus Cations
A R T I C L E S
Figure 7. ORTEP plot of [24][GaCl4]2. Thermal ellipsoids with 50%
probability (hydrogen atoms and counteranions are omitted for clarity) Only
one cation of the asymmetric unit and the interaction of the counteranion
is shown. Selected bond lengths (Å) and angles (deg): P2-Cl12 1.954(1),
P2-Cl13 1.953(1), P2-Cl14 1.954(1), P2-C7 1.792(2), Ga1-Cl1 2.1834(7),
Ga1-C2 2.1932(8), Ga1-Cl3 2.1753(8), Ga1-Cl4 2.1578(8), Cl12-
P2-Cl13 108.36(4), Cl12- P2-Cl14 107.94(5), Cl12-P2-C7 110.57(9),
Cl13-P2-Cl14 107.66(4), Cl13-P2-C7 110.7(1), Cl14-P2-C7
111.52(9).
Figure 8. ORTEP plot of the molecular structure of the cation [27]2+ in
[27][GaCl4]2. Thermal ellipsoids with 50% probability (hydrogen atoms and
counteranions are omitted for clarity). Selected bond lengths (Å), angles
(deg) and dihedral angles: P1-P2 2.186(2), P2-P3 2.227(2), P3-P4
2.198(2), P2-C7 1.874(6), P2-C7 1.879(5); P1-P2-P3 94.98(8),
P2-P3-P4 95.10(8), P1-P2-C7 107.6(2), P3-P2-C7 107.9(2), P2-
P3-C13 107.1(2), P4-P3-C13 107.3(2), Cl12-P2-C7 110.57(9),
Cl13-P2-Cl14 107.66(4), Cl13-P2-C7 110.7(1), Cl14-P2-C7 111.52(9);
P1-P2-P3-P4 132.13(8), C7-P2-P3-C13 -7.6(2), C7-P2-P3-P4-
117.5(2), C13-P3-P2-P1 -118.0(2).
Scheme 8. Formation of acyclic-2,3-Diphosphino-1,4-diphosphonium
Dication [27]2+ via Displacement Reaction of [20]2+ with PMe3 and
Proposed Mechanism
between Cl13 of [24]+ and Cl2 of [GaCl4]- is within the sum
of the van der Waals radii (rCl ) 1.75 Å, 2rCl ) 3.50 Å),44
classifying this as a weak donor-acceptor interaction.
The 31P{1H} NMR spectra of the slow addition of 1 equiv
[20][Ga2Cl7]2 to 4 equiv of PMe3 show mainly two broad signals
(δA ) -33.1, δX ) 19.2 ppm; Table 2) due to fluxional behavior
that in accordance to other observation are assigned to the 2,3-
diphosphino-1,4-diphosphonium dication [27]2+ (Scheme 8). As
shown in Scheme 8, nucleophilic attack of dication [20]2+ by
PMe3 is proposed to give the five-membered monocation I,
which is subsequently attacked by a second equivalent PMe3
to yield monocation II.47 The 31P{1H} NMR spectrum of a test
reaction obtained from the slow addition of 2 equiv PMe3 to
dication [27]2+ is complicated, however, an AMX spin system
with resonances at -40.5 (1PA, dd, JAM ) 293, JAX ) 312
Hz), 17.3 (1PM, dd, 1JAM ) 293, 2JMX ) 47 Hz), and 95.7 (1PX,
dd, 1JAX ) 312, 2JMX ) 47 Hz) ppm indicates the formation of
cation [Me3PMPACyPXCyCl]+ (II) as an intermediate. We
envisage that cation II subsequently undergoes conversion to
dication [20]2+ with addition of PMe3. Colorless crystals of
[27][GaCl4]2 were obtained in low yield (35%), but spectro-
scopic characterization was hampered by dynamic behavior in
solution. The solid state structure of the cation [27]2+ (Figure
8) is consistent with those of other derivatives48,49,47 prepared
by reductive coupling of chlorophosphinophosphonium ions
[12]+ (Scheme 9), and the eclipsed conformation of the central
C-P-P-C framework [torsion angle of 7.7(3)°] is due to a
combination of steric interactions in the terminal and internal
positions.47
dication. The P-C bond lengths at the phosphonium centers in
[19]+ and [20]2+ [1.791(2) to 1.820(2) Å] are significantly
shorter than those at the phosphine centers [1.863(2) to 1.873(2)
Å]. The [GaCl4]- anions in [19][GaCl4] adopt a slightly distorted
tetrahedral geometry with Cl-Ga-Cl bond angles between
107.36(3) and 111.94(4)°. The anion in [20][Ga2Cl7]2, which is
isosteric with Cl2O7,45 contains two distorted tetrahedral gallium
centers associated via a chloride bridge with a mean Ga-Cl-Ga
bond angle of 110.88(4)°. The gauche conformation of the
[Ga2Cl7]- anion can be explained by the minimization of Cl-Cl
interactions.46 The molecular structures of [19][GaCl4] and
[20][Ga2Cl7]2 show no interion Cl · · ·Cl interactions.
In the presence of excess PCl5 and GaCl3 in CH2Cl2, (CyP)4
dissociates to give [24][GaCl4] quantitatively (Scheme 7c),
which crystallizes with two independent, but essentially identical
formula units of [24][Ga2Cl7]2 in the unit cell. A view of one
of the molecular units is depicted in Figure 7. The mean P-Cl
bond lengths (1.954 Å) in the cations are slightly shorter than
those in the monocation [19]+ (2.011(1) Å) and the dication
[20]2+ (1.983(1) Å) due to the inductive effect of the chloro
substituents in [24]+. The Cl-P-Cl and Cl-P-C angles range
from 107.86(4) to 111.60(9)° consistent with the tetrahedral
arrangement of the cation. The Cl · · ·Cl contact (3.281(2) Å)
1
1
The reaction of [20][Ga2Cl7]2 with PMe3 can be considered
as a ligand-induced cyclodissociation, highlighting [27]2+ as a
(47) Carpenter, Y.-Y.; Dyker, C. A.; Burford, N.; Lumsden, M. D.; Decken,
A. J. Am. Chem. Soc. 2008, 130, 15732–15741.
(48) Karaghiosoff, K. Ph.D. Thesis, Ludwig-Maximilians-Universita¨t:
Munich, Germany, 1986.
(45) Simon, A.; Borrmann, H. Angew. Chem., Int. Ed. 1981, 27, 1339–
1341.
(49) Dyker, C. A.; Burford, N.; Lumsden, M. D.; Decken, A. J. Am. Chem.
Soc. 2006, 128, 9632–9633.
(46) Meyer, G.; Blachnik, R. Anorg. Allg. Chem. 1983, 503, 126–132.
9
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A R T I C L E S
Weigand et al.
Scheme 9. Formation of acyclic-2,3-Diphosphino-1,4-diphosphonium
Dications [25]2+ via Reductive Coupling Reactions of a
Chlorophosphoniumphosphine ([12]+) with Phosphines47
Scheme 10. Formation of cyclic-2,3-Diphosphino-1,4-diphosphonium
Dications [28]2+ via Reductive Coupling Reaction According to Dillon
and Co-workers50
Scheme 11. Formation of cyclic-2-Phosphino-1,3-diphosphonium
[29]2+ and 2,3-Diphosphino-1,4-diphosphonium Dications [30]2+ via
Displacement Reaction of [20]2+ with dmpe and Suggested
Reaction Mechanisma
Figure 9. 31P{1H} NMR spectra (CH3CN, C6D6 capillary, RT) of the re-
dissolved precipitate of the reaction mixture of [20][Ga2Cl7]2 with dmpe
according to Scheme 11 (a,ii). Signals assigned to unknown side-products
are labeled with asterisks. Expansions (inset) show the experimental (up)
and fitted23 (down) spectra for cation [20]2+
.
spin systems assigned to cations [29]2+ and [30]2+, respectively
(Table 2). Compound [30][GaCl4]2 could not be isolated, but
the 31P{1H} NMR spectrum has been successfully simulated as
an AA′XX′ spin system in accordance to other cyclo-2,3-
diphosphino-1,4-diphosphonium dications50 (Figure 9).
The reaction of dmpe with dication [20]2+ to form cations
[29]2+ and [30]2+ can be interpreted according to the proposed
mechanisms in Scheme 11. The initial step for both cases is
the ring-opening of [20]2+ by nucleophilic attack of dmpe to
form dication III. The subsequent reaction can now proceed in
one of two ways. The dication III is not observed implying
either fast intermolecular nucleophilic attack by a second dmpe
molecule (conc. [20]2+ < dmpe) to form cation VII or by an
intramolecular attack (conc. [20]2+ > dmpe) to form cation
[29]2+ and triphosphine IV. Intramolecular ring-closure of cation
VII results in the formation of dication [30]2+. Triphosphines
of type IV are known to be highly reactive and we speculate
that the reaction of a second equivalent of dmpe leads to the
formation of cation V. Subsequent intramolecular attack ac-
cording to Scheme 11 results in the formation of the second
equivalent of [29]2+ and [CyPdPCy],37 which dimerizes to give
2. Attempts to identify the intermediates III-VII in various
stoichiometric combinations of dication [20]2+ and dmpe and
under various reaction conditions were unsuccessful. However,
when 2 equiv of dmpe are added slowly to a cooled (0 °C)
solution of [20][Ga2Cl7]2 in CH2Cl2, the 31P{1H} NMR spectrum
of the reaction mixture reveals the stoichiometric formation of
only [29][GaCl4]2 and 2 (Scheme 11). The salt was isolated in
high yield (85 %) as air- and moisture-sensitive colorless blocks.
The solid state structure of [29]2+, shown in Figure 10, exhibits
structural features that are consistent with those of derivatives
previously prepared by the alkylation51 of cyclic triphosphenium
ions to form triphosphonium salts.52,53 The formation of the
mixture of cations [29]2+ and [30]2+ might be explained by these
two competitive reactions, however, dication [29]2+ is the
thermodynamically favored product. The formation of the
kinetically favored dication [30]2+ results from the local
a (i) slow addition of dmpe, CH2Cl2, 0 °C, (ii) fast addition of
[20][Ga2Cl7]2 to dmpe, CH2Cl2, RT.
ligand-stablized diphosphenium dication. In this context, Dillon
and co-workers reported the reductive cycloaddition reaction
of dichlorophosphines with a bidentate diphosphine to form
cyclo-2,3-diphosphino-1,4-diphosphonium dications [28]2+ with
an organic backbone (Scheme 10).50 By analogy, when a
solution of [20][Ga2Cl7]2 in CH2Cl2 is added rapidly to a CH2Cl2
solution containing 2 equiv of dmpe, a oily phase is formed
which has been characterized as an equimolar mixture of the
new salts [29][GaCl4]2 and [30][GaCl4]2 and 2, as illustrated in
Scheme 11. The oil dissolves in acetonitrile accompanied by
precipitation of 2. The clear solution exhibits the 31P{1H} NMR
spectrum depicted in Figure 9, displaying AX2 and AA′XX′
(50) Boyall, A. J.; Dillon, K. B.; Howard, J. A. K.; Monks, P. K.;
(51) Dillon, K. B.; Goeta, A. E.; Howard, J. A. K.; Monks, P. K.; Shepherd,
Thompson, A. L. Dalton Trans. 2007, 1374–1376.
H. J.; Thompson, A. L. Dalton Trans. 2008, 1144–1149.
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Synthetic Procedures to catena-Phosphorus Cations
A R T I C L E S
Scheme 12. Formal Retro [2 + 2] or [1 + 1 + 1′ + 1′] Reaction
Channels for the Degradation of Dication [20]2+
allates. Isolation of the new cations is made possible by the
presence of GaX3, which engages the halide anion and inhibits
the P-P bond cleavage. In contrast to the analogous dications
[28]2+ reported by Dillon and co-workers, the formation of
[30]2+ represents a new approach for the generation of ligand-
stabilized diphosphenium dications. Dication [20]2+ reacts with
Me3P or dmpe and dissociates formally via a retro [2 + 2] or
[1 + 1 + 1′ + 1′] process (Scheme 12) releasing [RP]2+ and
[R2P2]2+ fragments.
Figure 10. ORTEP plot of the molecular structure of the cation [29]2+ in
[29][GaCl4]2. Thermal ellipsoids with 50% probability (hydrogen atoms and
counteranions are omitted for clarity). Selected bond lengths (Å) and angles
(deg): P1-P2 2.191(1), P1-P3 2.214(1), P1-C1 1.873(3), P2-C7 1.806(3),
P2-C9 1.792(4), P2-C10 1.795(4), P3-C8 1.815(3), P3-C11 1.787(3),
P3-C12 1.783(4), C7-C8 1.535(5), P2-P1-P3 90.18(4), P2-P1-C1
104.4(1), P3-P1-C1 108.1(1), C9-P2-C10 110.6(8), C9-P2-C7 110.1(2),
P1-P2-C10 116.4(1), P1-P2-C7 100.2(1), C11-P3-C12 108.6(2),
C8-P3-C11 110.3(2), P1-P3-C12 117.3(1), P1-P3-C11 107.2(1),
P1-P3-C8 104.4(1).
Acknowledgment. We gratefully acknowledge the Alexander
von Humboldt-Foundation (Feodor Lynen Return Fellowship for
J.J.W.), the FCI (Liebig scholarship for J.J.W.), the International
Research Training Group (IRTG 1444, funding for R.J.D.), the
European Phosphorus Science Network (PhoSciNet CM0802), the
Natural Sciences and Engineering Research Council of Canada, the
Killam Foundation and the Canada Research Chairs Program for
funding. We thank Prof. David Emsley (McMaster University) for
valuable discussion. J.J.W. thanks Prof. F. Ekkehardt Hahn (WWU
Mu¨nster) for his generous support and advice.
overconcentration of dmpe, since the dication [20]2+ was slowly
added to the dmpe solution.
Conclusion
Reactions of tetracyclohexyl-cyclo-tetraphosphine (CyP)4 with
a source of halonium cations in the presence of GaX3 (X ) Cl,
I) allows for the isolation of first cyclo-2-halo-1,3,4-triphos-
phino-2-phosphonium cations and cyclo-2,4-dihalo-1,3-diphos-
phino-2,4-diphosphonium dications as their corresponding met-
Supporting Information Available: Crystallographic informa-
tion. This material is available free of charge via the Internet at
http://pubs.acs.org.
(52) Schmidpeter, A.; Lochschmidt, S.; Karaghiosoff, K.; Sheldrick, W. S.
J. Chem. Soc., Chem. Commun. 1985, 1447–1448.
(53) Ellis, B. D.; Macdonald, C. L. B. Coord. Chem. ReV. 2007, 251, 936–
973, and references therein.
JA907693F
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