Formation of [Ph2P5]+, [Ph 4P6]2+, and [Ph6P7] 3+ cationic clusters by consecutive insertions of [Ph 2P]+ into P-P bonds of the P

Article abstract of DOI:10.1002/anie.200804903

Positively phosphorus: A solvent-free melt system (P₄/Ph ₂PCl/GaCl₃) represents a powerful medium for the functionalization of the P₄ tetrahedron to form new cationic phosphorus-rich organophosphorus cage and cl

Full text of DOI:10.1002/anie.200804903

Angewandte
Chemie
DOI: 10.1002/anie.200804903
Cationic Phosphorus Clusters
Formation of [Ph2P5]+, [Ph4P6]2+, and [Ph6P7]3+ Cationic Clusters
+
ꢀ
by Consecutive Insertions of [Ph2P] into P P Bonds of the
P4 Tetrahedron**
Jan J. Weigand,* Michael Holthausen, and Roland Frꢀhlich
Many transition-metal complexes containing a broad variety
of degraded or aggregated Pn units, resulting from P4
activation, have been discovered and described.[1–3] In com-
parison, the functionalization of P4 with main-group frag-
ments represents a new and rapidly developing field.
Recently, Bertrand and co-workers have found that carbenes
react with white phosphorus, with or without inducing its
fragmentation or aggregation[4]. Similarly, heavier carbene-
like main-group-element derivatives containing Al,[5] Ga,[6]
[Ph2PCl!GaCl3] (2), the chloro(diphenylphosphanyl)diphe-
ꢀ
nylphosphonium cation 3, and the counteranions [GanCl3n+1
]
(n = 1, 2, 3) can be readily obtained from the binary Ph2PCl/
GaCl3 system. This melt is a reactive source of the diphenyl-
+
ꢀ
phosphenium cation [Ph2P] , which inserts into P P bonds of
(PhP)5, to give the 2,3,4,5-cyclo-tetraphosphanyl-1,4-diphos-
phonium dication 4.[12,13] As an acceptor for phosphenium
insertion, P4 should be more viable to accommodate multiple
charges and, hence, the formation of larger cationic clusters
than the monocationic species 1 is conceivable. Herein, we
report the targeted preparation of mono- to tricationic
clusters [Ph2P5]+ (5), [Ph4P6]2+ (6a), [Ph6P7]3+ (7a, see
below)[14] by reaction of P4 in the room-temperature molten
medium M with varied stoichiometries and reaction con-
ditions such as temperature and reaction time.
Tl,[7] and Si,[8] insert into the P P bonds of the P4 tetrahe-
ꢀ
dron.[9] Krossing and co-workers have reported the insertion
of in situ-prepared, highly electrophilic, carbene-analogous
[PX2]+ cations (X = Br, I) into one of the P P bonds of P4,
ꢀ
yielding phosphorus-rich binary cage cations [P5X2]+ (1, see
below). Although highly reactive, these cations could be
successfully isolated using non-oxidizing, weakly coordinating
counteranions of type [Al(OR)4]ꢀ (OR = polyfluorinated
aliphatic alkoxide).[10] In contrast to the well-developed
chemistry of oligophosphorus anions,[11] 1 represents the
only structurally characterized cationic homoatomic phos-
phorus cluster reported.
We recently reported that a room-temperature molten
medium M, consisting of the donor–acceptor complex
The reaction of P4 with an excess of Ph2PCl in freshly
prepared molten medium M (P4/Ph2PCl/GaCl3 1:8:5) at 708C
for 7 h gave rise to a clear, pale yellow honey-like melt
(Scheme 1b). The 31P{1H} NMR spectrum (Figure 1a) of the
dissolved melt in CH2Cl2 revealed two new spin systems,
A2MX2 (5: dA = ꢀ292.0, dM = ꢀ5.4, dX = 19.7 ppm, 1J-
(PA,PX) = ꢀ139.7, 1J(PM,PX) = ꢀ212.2, 2J(PA,PM) = 8.3 Hz)
and ABMM’XX’ (6a: dA = ꢀ231.7, dB = ꢀ213.0, dM =
[*] Dr. J. J. Weigand, M. Holthausen
Institut fꢀr Anorganische und Analytische Chemie
Universitꢁt Mꢀnster
Corrensstrasse 30, 48149 Mꢀnster (Germany)
Fax: (+49)251-83-33108
E-mail: jweigand@uni-muenster.de
Dr. R. Frꢂhlich
Organisch-Chemisches Institut, Universitꢁt Mꢀnster (Germany)
[**] We gratefully acknowledge the Alexander von Humboldt-Founda-
tion (Feodor Lynen Return Fellowship for J.J.W.) and the FCI (Liebig
scholarship for J.J.W.). J.J.W. thanks Prof. F. Ekkehardt Hahn
(Mꢀnster) for his generous support and advice. The authors are
indebted to and thank Jꢂrg Stierstorfer (Munich) and Dr. Alexander
Hepp for help with Raman and NMR measurements, respectively,
and Dr. Robert Wolf for helpful discussions.
Scheme 1. Reaction of P4 with GaCl3 and Ph2PCl where a) x=1, y=1;
(608C for 45 min.); b) x=8, y=5 (708C for 7 h); c) x=6, y=3 (608C
for 1 h than 1008C for 12 h).
Supporting Information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200804903.
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295

Communications
system, would be expected for the symmetrical
isomer 6b which may, therefore, only be
present in concentrations below the detection
limit. The P6 cage arrangement proposed for
6a is unprecedented and, to our knowledge,
there are only two related neutral tricyclic
hexaphosphanes, reported by Jutzi and co-
workers.[19]
The
variable
temperature
31P{1H} NMR spectrum of the reaction mixture
(temperature profile down to 200 K) indicated
no dynamic behavior of cations 5 and 6a in
CD2Cl2 solution. The monocation
5 was
formed quantitatively as a tetrachlorogallate
salt by the 1:1:1 reaction of P4, Ph2PCl, and
GaCl3 (Scheme 1a) at 608C within 45 minutes
as a pale yellow, crystalline material (71%
yield).[18] Compound 5[GaCl4] is very air- and
moisture-sensitive but is stable for at least six
months
at
room
temperature.
The
13C{1H} NMR spectrum of 5[GaCl4] in CD2Cl2
1
showed a characteristic, large J(C,P) value of
48.6 Hz with smaller long-range couplings of
J < 13 Hz. The monocation 5 is very stable in
CD2Cl2 solution and, after two weeks, there
were no indications of decomposition or rear-
rangement in the 31P{1H} NMR sample. The
C2v-symmetric P5 cage, as already deduced in
solution from the 31P{1H} NMR spectrum, was
also confirmed in the solid state by single-
crystal X-ray diffraction. A view of the molec-
ular structure of the nearly C2v-symmetric
cation 5 is shown in Figure 2. 5[GaCl4] crystal-
¯
lizes in the triclinic space group P1 with three
Figure 1. a) 31P{1H} NMR spectrum (101.26 MHz) of the reaction mix-
ture according to Scheme 1a) after 7 h at 708C and dissolved in
CH2Cl2. Signals assigned to unknown side-products are labeled with
asterisks; b) 31P{1H} NMR spectrum (161.94 MHz) of the reaction
mixture according to Scheme 1c) after 12 h at 1008C and dissolved in
CH2Cl2. Expansions (inset) show the experimental (up) and fitted[16]
(down) spectra for cation 7a. Signals assigned to decomposition
products and other compounds are labeled according to a).
ꢀ174.4, dX = 80.5 ppm),[15,16] the presence of the phosphanyl–
phosphonium cation 3 (two doublets, d = 75.8, ꢀ0.6 ppm,
1J(P,P) = ꢀ380.1 Hz), and small amounts of the [Ph2PClH]+
cation 8,[17] which is a decomposition product, presumably
resulting from solvent activation.[18]
The proton-coupled 31P NMR spectrum of the reaction
mixture showed only an additional splitting of the downfield
resonance at 41 ppm (1J(P,H) = 581.0 Hz) resulting from the
one-bond coupling of the hydrogen to the phosphorus atom in
8. The resonances for the A2MX2 spin system can be assigned
to the monocation 5 as shown in Figure 1.
The resonances for the ABMM’XX’ spin system with an
approximate ratio of 1:1:2:2 suggest the formation of the
dicationic species 6a, containing four chemically inequivalent
phosphorus atoms. Two second-order resonances with rela-
tive intensities of 1:2, representing an AA’XX’X’’X’’’ spin
Figure 2. ORTEP representation of the molecular structure of the
cation 5 in 5[GaCl4]. Thermal ellipsoids are set at 50% probability.
Hydrogen atoms and counteranions are omitted for clarity. Only one
cation of the asymmetric unit is shown. Selected bond lengths [ꢃ] and
ꢀ
ꢀ
ꢀ
ꢀ
angles [8]: P1 C1 1.792(3), P1 C7 1.789(3), P1 P2 2.182(1), P1
ꢀ
ꢀ
ꢀ
ꢀ
P3 2.186(1), P2 P4 2.244(1), P2 P5 2.239(1), P3 P5 2.249(1), P3
ꢀ
P4 2.245(1), P4 P5 2.179(1); C1-P1-C7 108.4(1), C1-P1-P2 115.5(1),
C7-P1-P3 112.9(1), P2-P1-P3 88.28(4), P1-P2-P4 84.76(4), P1-P3-
P5 86.38(4), P2-P4-P3 85.33(4), P3-P5-P2 85.34(4), P4-P2-P5 58.18(3),
P5-P3-P4 58.01(3).
296
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Chemie
formula units in the unit cell. The three crystallographically
different cations display nearly identical bond lengths and
angles. However, in two of the three cations the phenyl groups
ꢀ
are disordered. The P P bond lengths in 5 (ranging from
2.179(1) to 2.249(1) ꢀ) are very close to the values found in
the [P5Br2]+ ion (ranging from 2.150(7) to 2.262(8) ꢀ).[10] The
bonds between the tri- and tetracoordinated phosphorus
ꢀ
atoms and the P4 P5 bond in cation 5 are approximately 0.07
ꢀ
ꢀ shorter than the remaining P P bonds and are even shorter
ꢀ
than those in P4 (2.220 ꢀ). The P4 P5 bond length is
reminiscent of both the related strained SiP4 cage compound
(2.159(2) ꢀ)[8d] and of bicyclo[1.1.0]tetraphosphanes, R2P4
ꢀ
(R = organyl) which display relatively short P P bridgehead
bonds (2.120 ꢀ).[20] It has been observed in several examples,
ꢀ
that P P distances involving a cationic four-coordinate
phosphorus center are generally slightly shorter.[13,21,22]
Attempts to form dication 6a by a stoichiometric reaction
of P4 and the melt M (P4/Ph2PCl/GaCl3 1:2:2) resulted in
mixtures of 3, 5, 6a, and 8 from which it has not been possible
to isolate cation 6a. Besides the isolation of dication 6a, we
were interested in the possibility of inserting more than two
[Ph2P]+ cations into the P4 framework. However, only
mixtures of 3, 5, and 6a were formed when the GaCl3 mole
fraction was lower than 0.5. In these mixtures, it can be
assumed that gallium is present entirely in the tetrachlor-
ogallate [GaCl4]ꢀ form. Hence, the melt is considered to be a
basic medium in which highly positively charged cations
might not be stable.[23] Subsequently, we increased the amount
of GaCl3 by performing a 1:3:6 reaction of P4, Ph2PCl, and
GaCl3 (Scheme 1c) at 1008C, hence, switching to an acidic
medium. Indeed, a clean reaction occurred, with the forma-
tion of one major product. From this melt, pure, colorless
crystals of the heptachlorodigallate salt 7a[Ga2Cl7]3 were
grown at 1008C within 12 h. The crystals were washed with
small amounts of 1,2-difluorobenzene and pentane, giving
analytically pure 7[Ga2Cl7]3 in moderate yield (40%). Com-
pound 7a[Ga2Cl7]3 is extremely moisture- and air-sensitive
and melts between 85–878C. The compound crystallized in
Figure 3. ORTEP representation of the molecular structure of the
cation 7a in 7a[Ga2Cl7]3. Thermal ellipsoids are set at 50% probability.
Hydrogen atoms and counteranions are omitted for clarity. Selected
ꢀ
ꢀ
ꢀ
bond lengths [ꢃ] and angles [8]: P2 C1 1.784(3), P2 C7 1.791(3), P1
ꢀ
ꢀ
ꢀ
ꢀ
P2 2.223(1), P1 P3 2.218(1), P1 P4 2.219(1), P2 P5 2.27(1), P3
ꢀ
ꢀ
ꢀ
ꢀ
P6 2.224(1), P4 7 2.227(1), P5 P6 2.215(1), P6 P7 2.219(1), P5
P7 2.220(1); C1-P2-C7 109.3(1), C1-P2-P1 113.3(1), C7-P2-P1 106.4(1),
P3-P1-P2 91.89(4), P4-P1-P2 91.49(4), P3-P1-P4 91.61(4), P1-P2-
P5 109.31(4), P2-P5-P6 101.08(4), P2-P5-P7 104.02(4), P6-P5-
P7 60.06(3).
represented by a quartet, indicating only a coupling to the
three bridging phosphorus atoms (1J(B,X) = 1J(B,X’) = 1J-
(B,X’’) = ꢀ306.1 Hz, 2J(B,A) = 2J(B,A’) = 2J(B,A’’) = 0 Hz).
The coupling patterns for the basal phosphorus atoms at
dA = ꢀ163.7 ppm and the bridging phosphonium centers at
dX = 112.6 ppm are complex, owing to second order effects
1
(1J(A,X) = 1J(A’,X’) = 1J(A’’,X’’) = ꢀ397.0 Hz , J(A,A’) = 1J-
(A,A’’) = 1J(A’,A’’) = ꢀ220.4 Hz,
2J(X,X’) = 2J(X,X’’) = 2J-
2J(A,X’) = 2J(A,X’’) = 2J(A’,X’’) =
¯
the triclinic space group P1 with two formula units in the unit
(X’,X’’) = 16.5 Hz,
cell. To our knowledge, the [Ph6P7]3+ cation (7a) represents
the first structurally characterized homoatomic phosphorus
cage with a positive charge greater than one. In the solid state,
trication 7a takes the form of a P7 cage with a typical
nortricyclane (tricyclo[2.2.1.02.6]heptane) skeleton, reminis-
cent of the [P7]3ꢀ trianion or P4S3 (Figure 3).[24,25] However, 7a
incorporates three tetracoordinated phosphonium centers in
the bridging positions. Hence, the molecular structure has
approximate C3 symmetry. The bond lengths and angles
follow a similar trend to that in the monocation 5.
Consistently with the solid state structure, the
31P{1H} NMR spectrum of 7a[Ga2Cl7]3 in CD2Cl2 solution at
room temperature (Figure 1b) features three resonances
which display a complex AA’A’’BXX’X’’ spin pattern with
relative intensities of 3:1:3, resulting from the C3 symmetry of
the cation. There are no indications of the formation of the
asymmetric isomer 7b in the spectrum. Iterative analyses[16] of
the complex spectrum, performed at two external field
strengths, revealed a first order resonance for the tri-
coordinated apical phosphorus atom at dB = ꢀ157.1 ppm
14.2 Hz). Full spectroscopic characterization of 7a[Ga2Cl7]3
was hampered by its limited stability in solution. Elemental
analysis indicated that 7a[Ga2Cl7]3 could be isolated as a pure
compound from the reaction mixture.[18] However, it readily
decomposes as soon as dissolved in CD2Cl2, forming 6a, 5, 3,
and 8 (Figure 1b). A detailed investigation, to understand the
decomposition of trication 7a in solution, is currently under-
way.
In summary, the solvent-free method represents a power-
ful strategy for the functionalization of the P4 tetrahedron to
form new cationic phosphorus-rich organophosphorus cage
and cluster systems, as illustrated by the formation of mono-
to trications 5, 6a, and 7a, by the consecutive insertion of
+
ꢀ
[Ph2P] into P P bonds of the P4 tetrahedron. The trication 7a
was only formed in cases where the reaction was carried out in
acidic media (GaCl3 mole fraction > 0.5), indicating that
insertion of [Ph2P]+ strongly depends on the presence of an
excess of Lewis acid to prevent the detrimental presence of
Clꢀ ions, which decompose 7a by nucleophilic attack. We are
currently investigating the reactivity of various other Lewis
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297

Communications
[12] J. J. Weigand, N. Burford, A. Decken, Eur. J. Inorg. Chem. 2008,
4343.
acid/chloropnictogen systems with P4 and the behavior of the
reaction products in organic solvents.
[13] J. J. Weigand, N. Burford, M. Lumsden, A. Decken, Angew.
Chem. 2006, 118, 6885; Angew. Chem. Int. Ed. 2006, 45, 6733.
[14] Possible isomers, 6a/6b for the dications and 7a/7b for the
trications, assuming that two or more positive phosphonium
centers are not situated adjacent to each other.
[15] The NMR spectrum of 6a could not be simulated owing to its
complexity. For the assignment of the phosphorus nuclei see the
2D 31P–31P COSY NMR spectrum provided in the Supporting
Information.
[16] P. H. M. Budzelaar, gNMR for Windows (5.0.6.0) NMR Simu-
lation Program, IvorySoft 2006.
[17] F. Sh. Shagvaleev, T. V. Zykova, R. I. Tarasova, T. Sh. Sitdikova,
V. V. Moskva, J. Gen. Chem. USSR (Engl. Trans.) 1990, 60, 1585;
Z. Obshch. Khim. 1990, 60, 1775.
Received: October 7, 2008
Published online: December 8, 2008
Keywords: cations · cluster compounds · phosphorus ·
.
solvent-free synthesis · structure elucidation
[1] A. P. Ginsberg, W. E. Lindsell, J. Am. Chem. Soc. 1971, 93, 2082.
[2] M. Peruzzini, L. Gonsalvi, A. Romerosa, Chem. Soc. Rev. 2005,
34, 1038, and references therein.
[3] a) J. S. Figueroa, C. C. Cummins, J. Am. Chem. Soc. 2004, 126,
13916; b) C. C. Cummins, Angew. Chem. 2006, 118, 876; Angew.
Chem. Int. Ed. 2006, 45, 862; c) N. A. Piro, J. S. Figueroa, J. T.
McKellar, C. C. Cummins, Science 2006, 313, 1276.
[4] a) C. A. Dyker, G. Bertrand, Science 2008, 321, 1050; b) J. D.
Masuda, W. W. Schoeller, B. Doonadieu, G. Bertrand, Angew.
Chem. 2007, 119, 7182; Angew. Chem. Int. Ed. 2007, 46, 7052;
c) J. D. Masuda, W. W. Schoeller, B. Doonadieu, G. Bertrand, J.
Am. Chem. Soc. 2007, 129, 14180.
[18] Experimental details, X-ray diffraction data for 5[GaCl4] and
31
31P COSY NMR spectra are provided
ꢀ
P
7a[Ga2Cl7]3, and 2D
in the Supporting Information. CCDC 704598 (5) and 704599
(7a) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
[5] a) C. Dohmeier, H. Schnꢁckel, C. Robl, U. Schneider, R.
Ahlrichs, Angew. Chem. 1994, 106, 225; Angew. Chem. Int. Ed.
Engl. 1994, 33, 199; b) Y. Peng, H. Fan, H. Zhu, H. W. Roesky, J.
Magull, C. E. Hughes, Angew. Chem. 2004, 116, 3525; Angew.
Chem. Int. Ed. 2004, 43, 3443.
[6] a) M. B. Power, A. R. Barron, Angew. Chem. 1991, 103, 1403;
Angew. Chem. Int. Ed. Engl. 1991, 30, 1353; b) W. Uhl, M.
Benter, Chem. Commun. 1999, 771.
[7] A. R. Fox, R. J. Wright, E. Rivard, P. P. Power, Angew. Chem.
2005, 117, 7907; Angew. Chem. Int. Ed. 2005, 44, 7729.
[8] a) N. Wiberg, A. Wꢁrner, K. Karaghiosoff, D. Fenske, Chem.
Ber. 1997, 130, 135; b) H.-W. Lerner, M. Bolte, K. Karaghiosoff,
M. Wagner, Organometallics 2004, 23, 6073; c) W. T. K. Chan, F.
Garcꢂa, A. D. Hopkins, L. C. Martin, M. McPartlin, D. S. Wright,
Angew. Chem. 2007, 119, 3144; Angew. Chem. Int. Ed. 2007, 46,
3084; d) Y. Xiong, S. Yao, M. Brym, M. Driess, Angew. Chem.
2007, 119, 4595; Angew. Chem. Int. Ed. 2007, 46, 4511.
[9] J. M. Lynam, Angew. Chem. 2008, 120, 843; Angew. Chem. Int.
Ed. 2008, 47, 831.
[19] P. Jutzi, R. Kroos, A. Mꢃller, M. Penk, Angew. Chem. 1989, 101,
628; Angew. Chem. Int. Ed. Engl. 1989, 28, 600.
[20] a) E. Niecke, R. Rꢃger, B. Krebs, Angew. Chem. 1982, 94, 553;
Angew. Chem. Int. Ed. Eng. 1982, 21, 544; b) W. W. Schoeller, V.
Staemmler, P. Rademacher, E. Niecke, Inorg. Chem. 1986, 25,
4382.
[21] a) N. Burford, C. A. Dyker, A. Decken, Angew. Chem. 2005, 117,
2416; Angew. Chem. Int. Ed. 2005, 44, 2364; b) N. Burford, C. A.
Dyker, M. Lumsden, A. Decken, Angew. Chem. 2005, 117, 6352;
Angew. Chem. Int. Ed. 2005, 44, 6196.
[22] D. J. Wolstenholme, J. J. Weigand, R. J. Davidson, J. K. Pearson,
T. S. Cameron, J. Phys. Chem. A 2008, 112, 3424.
[23] For related aluminates, see J. A. Boon, J. A. Levisky, J. L. Pflug,
J. S. Wilkes, J. Org. Chem. 1986, 51, 480.
[24] a) M. Baudler, W. Faber, J. Hahn, Z. Anorg. Allg. Chem. 1980,
469, 15; b) G. Fritz, H. Rothmann, E. Matern, Z. Anorg. Allg.
Chem. 1992, 610, 33; c) I. Kovꢄcs, G. Baum, G. Fritz, D. Fenske,
N. Wiberg, H. Schuster, K. Karaghiosoff, Z. Anorg. Allg. Chem.
1993, 619, 453; d) S. Charles, J. C. Fettinger, B. W. Eichhorn, J.
Am. Chem. Soc. 1995, 117, 5303.
[25] a) D. Weber, C. Mujica, H. G. von Schnering, Angew. Chem.
1982, 94, 869; Angew. Chem. Int. Ed. Engl. 1982, 21, 836; b) H.
Hꢁnle, H. G. von Schnering, Angew. Chem. 1986, 98, 370;
Angew. Chem. Int. Ed. Engl. 1986, 25, 352.
[10] a) I. Krossing, I. Raabe, Angew. Chem. 2001, 113, 4544; Angew.
Chem. Int. Ed. 2001, 40, 4406; b) M. Gonsior, I. Krossing, L.
Mꢃller, I. Raabe, M. Jansen, L. van Wuellen, Chem. Eur. J. 2002,
8, 4475.
[11] M. Baudler, K. Glinka, Chem. Rev. 1993, 93, 1623.
298
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