Formation of new larger ring cyclic triphosphenium ions in solution-A 31P NMR study

Article abstract of DOI:10.1016/j.ica.2011.06.044

In a notable extension of previous work, we have shown that several diphosphanes will form larger (7- or 8-membered ring) cyclic triphosphenium ions (CTIs) in solution by reaction with PX₃ (X = Cl, Br or I), sometimes in the presence of SnCl₂ or SnBr₂. We have also formed new CTIs from two ferrocene derivatives. The ions are readily identifiable by ³¹P NMR solution-state spectroscopy, having large ¹J _P-P values between the middle 'bare' phosphorus atom P_A and the outer phosphorus atoms P_B (and P_C where the outer groups are inequivalent). In addition, some data for known CTIs, but with different counter-ions, are presented. Three of the new CTIs have been successfully protonated, two by both AlCl₃/^tBuCl and triflic acid, and one via the triflic acid route only.

Full text of DOI:10.1016/j.ica.2011.06.044

Inorganica Chimica Acta 376 (2011) 325–331
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Formation of new larger ring cyclic triphosphenium ions in solution – A 31P NMR
study
⇑
Rachel Bashforth, Alice J. Boyall, Keith B. Dillon , Philippa K. Monks, Jennifer C. Potts
Chemistry Department, Durham University, South Road, Durham DH1 3LE, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
In a notable extension of previous work, we have shown that several diphosphanes will form larger (7- or
8-membered ring) cyclic triphosphenium ions (CTIs) in solution by reaction with PX3 (X = Cl, Br or I),
sometimes in the presence of SnCl2 or SnBr2. We have also formed new CTIs from two ferrocene deriva-
Received 2 February 2011
Received in revised form 22 June 2011
Accepted 29 June 2011
1
tives. The ions are readily identifiable by 31P NMR solution-state spectroscopy, having large JP–P values
Available online 5 July 2011
between the middle ‘bare’ phosphorus atom PA and the outer phosphorus atoms PB (and PC where the
outer groups are inequivalent). In addition, some data for known CTIs, but with different counter-ions,
are presented. Three of the new CTIs have been successfully protonated, two by both AlCl3/tBuCl and tri-
flic acid, and one via the triflic acid route only.
Keywords:
Cyclic triphosphenium ions
31P NMR spectroscopy
Large rings
Ó 2011 Elsevier B.V. All rights reserved.
1
1. Introduction
er frequency, together with a large JP–P value, generally greater
than 400 Hz.
Cyclic triphosphenium ions (CTIs) are heterocycles with a
hydrocarbon backbone and three linked phosphorus atoms, the
middle one of which is ‘bare’ and nominally in the +1 oxidation
state, Fig. 1; they have an overall charge of +1. The first example
of such an ion was synthesised and structurally characterised by
Schmidpeter et al. [1]; several other CTIs have subsequently
been reported [2–16], notably from work by Macdonald and
co-workers [5–8] and in our research group [10–16]. Ring sizes
from 4 to 7 have been described, and some have been character-
ised by single-crystal X-ray diffraction [1,6,8,10,14]; the P–P
bond lengths are very similar in all cases and lie between 2.11
and 2.15 Å, intermediate between normal phosphorus–phospho-
rus single and double bonds. Most examples, however, are either
5- or 6-membered rings. The literature in the area to 2007 has
been well reviewed by Ellis and Macdonald [7]. These ions
may be useful P(I) sources in solution [5–8]. Synthetic methods
are outlined in Scheme 1.
2. Results and discussion
The diphosphanes used in this study are illustrated in Fig. 2.
2.1. New systems forming 7- or 8-membered rings
2.1.1. Bis-diisopropylphosphinobutane, dippb
This 7-membered ring cyclic triphosphenium ion 1 (Fig. 3) was
prepared in solution by reaction of the diphosphane with PCl3, both
in the absence and presence of SnCl2, (Eqs. (1) and (2)); 31P{1H}
NMR data are presented in Table 1. (In Tables 1–3, the counter-
ion from reactions involving SnX2 is presented as SnX6 for sim-
plicity; this does not preclude the possibility of SnX5 in solution,
or even a mixture of tin(II) and tin(IV) halogeno-anions if oxidation
is incomplete.) In addition, singlet resonances were observed at
116.5 ppm in the presence of PCl3 alone, and at 114.8 ppm with
SnCl2 also present. These may be ascribed to the dichlorinated
dication 2 (Fig. 3), with a slight shift difference due to the change
of anion [17,18]. In the absence of an additional reducing agent
such as SnCl2, the diphosphane itself acts as the reducing agent,
Eq. (1). In the presence of SnCl2, the main reaction will be a redox
one involving this reagent, Eq. (2). Formation of the dichlorodi-
phosphonium salt 2b (Fig. 3) is still probable, however, since ali-
phatic diphosphanes are quite good reducing agents, unlike
aromatic ones.
2ꢀ
ꢀ
It was therefore of considerable interest to try to extend the
range of known CTIs, particularly for larger ring sizes. The ions
may be readily recognised in solution from their 31P NMR prop-
erties, with a large shift difference between the triplet of PA
(Fig. 1) at lower frequency and the doublet of PB (Fig. 1) at high-
⇑
Corresponding author.
E-mail address: k.b.dillon@durham.ac.uk (K.B. Dillon).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.06.044

326
R. Bashforth et al. / Inorganica Chimica Acta 376 (2011) 325–331
2+
+
2Cl-
Cl-
3
+ 2PCl3
2
+
iPr2P
PiPr2
iPr2P
Cl
PiPr2
Cl
iPr2P
PiPr2
P
ð1Þ
+
2-
2
+ 2PCl3
+
2SnCl2
+
SnCl4
SnCl6
iPr2P
PiPr2
iPr2P
PiPr2
P
2
ð2Þ
diphosphane was also reacted with PBr3 and SnBr2, leading to rel-
atively rapid formation of 3b (Table 1). The 31P NMR spectra re-
corded on a spectrometer operating at a lower frequency showed
slight second order effects, with the doublet and triplet both
appearing as doublets of doublets. These effects were reduced, as
expected, when the spectra were recorded on an instrument oper-
ating at a higher frequency. Not surprisingly, no signals were de-
tected for the dihalogenated diphosphonium dication in these
systems.
2.1.2. 2,20-Bis(diphenylphosphino)-1,10-biphenyl, biphep
Seven-membered ring formation was very slow in the absence
of an additional reducing agent. Very weak signals for the CTI were
found after 3 days from reaction of this aromatic diphosphane with
PCl3 only, suggesting that it is a comparatively poor reducing
agent. In the presence of SnCl2, ring formation occurred within
hours; the 31P NMR data for 3a (Fig. 3) are given in Table 1. The
+
2.1.3. 2,20-Bis(dicyclohexylphosphino)-1,10-biphenyl, cybiphep
These reactions were carried out only with the appropriate ti-
n(II) halide present as a reducing agent. Interestingly, in the
chloro-system the cyclic intermediate 4 (Fig. 3) was detected, par-
allel to those observed previously by us when elucidating the
mechanism of formation of cyclic triphosphenium ions [15]. Such
intermediates have only ever been detected with alkyl rather than
aryl substituents on the diphosphane. Compound 4 yielded a dou-
blet and triplet in the initial 31P NMR spectrum, dPD 38.3 ppm, dPC
R2P
PR2
B
B
PA
Fig. 1. The general structure of a CTI.
+
1
ꢀ26.0 ppm, JP–P 393 Hz (Fig. 3). The gradual disappearance of the
PR2 X-
signals associated with 4 and increase in intensity of the reso-
nances from 5a are readily apparent in the stackplot shown in
Fig. 4. The reaction with PBr3 and SnBr2 was carried out success-
fully on more dilute solutions to form 5b (Table 1), but signals from
the cyclic intermediate were not observed in this instance, possibly
because of more rapid CTI formation.
(X = Cl, Br, I)
R2P
B
B
PX3
PA
P
+
PX3 + SnX2
2-
(X = Cl, Br)
SnX6
R2P
R2P
PR2
PR2
R2P
PR2
2
+
PCl3 + AlCl3
-
2.1.4. 1,2-Bis(dicyclopentylphosphinomethyl)benzene, dcppmb
As just a small quantity of the diphosphane was available,
chloro-reactions only were attempted. The 7-membered ring CTI,
6 (Fig. 3) formed both in the absence and presence of SnCl2, Table 1.
A singlet observed in several spectra at 108.5 ppm was assigned to
the dichlorodiphosphonium dication, 7 (Fig. 3).
AlCl4
P
Scheme 1. Synthesis of cyclic triphosphenium ions from a diphosphane.
Table 1
31P NMR data for new CTIs with larger ring sizes.
2.1.5. (ꢀ)2,3-O-Isopropylidene-2,3-dihydroxy-1,4-
1JP–P
(Hz)
bis(diphenylphosphino)butane, diop
Compound
number
Counter-
ion
Ring
size
PB
(ppm)
PA
(ppm)
This diphosphane was reacted with PCl3 in the presence of
SnCl2; the 7-membered ring CTI 8 (Fig. 3) was formed, and its
NMR data are included in Table 1. Attempts to prepare 8 as its
hexabromostannate salt using a PBr3–SnBr2 mixture were unsuc-
cessful. A cloudy solution resulted, eventually leading to an orange
precipitate which suggested the possible formation of polymeric
phosphorus, and no assignable solution spectrum could be ob-
tained. A repeat reaction using more dilute solutions again pro-
duced a cloudy solution.
1a
1b
3a
3b
5a
5b
6a
6b
8
9a
9b
9c
10a
10b
10c
Clꢀ
SnCl6
SnCl6
SnBr6
7
7
7
7
7
7
7
7
7
8
8
8
8
8
8
55.9
55.5
29.9
29.9
30.5
30.5
35.2
36.6
25.1
26.1
26.2
26.1
27.0
27.3
27.1
ꢀ264.8
ꢀ262.5
ꢀ153.5
ꢀ153.9
ꢀ141.7
ꢀ141.8
ꢀ244.5
ꢀ246.5
ꢀ198.2
ꢀ112.2
ꢀ111.6
ꢀ112.2
ꢀ162.7
ꢀ163.7
ꢀ166.4
474
480
431
434
443
444
475
472
467
555
552
553
514
516
521
2ꢀ
2ꢀ
2ꢀ
2ꢀ
SnCl6
2ꢀ
SnBr6
Clꢀ
2ꢀ
SnCl6
2ꢀ
SnCl6
Clꢀ
2ꢀ
SnCl6
Brꢀ
Clꢀ
2.1.6. 9,9-Dimethyl-4,5-bis(diphenylphosphino)xanthene, dppdmx
There was a very slow reaction of this diphosphane with PCl3
only; the 8-membered ring 9 (Fig. 3) was detected after 3 days,
and its signals (Table 1) were still weak after 6 days. Ring forma-
2ꢀ
SnCl6
SnBr6
2ꢀ

R. Bashforth et al. / Inorganica Chimica Acta 376 (2011) 325–331
327
(a) Larger ring systems
Ph2P
Cy2P
iPr2P
PiPr2
PPh2
PCy2
dippb
biphep
cybiphep
O
O
O
Cp2P
PCp2
Ph2P
PPh2
Ph2P
PPh2
dcppmb
diop
dppdmx
O
Ph2P
PPh2
DPEphos
(b) Ferrocene derivatives
PiPr2
PPh2
Fe
Fe
PiPr2
PtBu2
dippf
dppdtbpf
(c) To produce different counter-ions to those in the literature
iPr2P
PiPr2
Cy2P
PCy2
Ph2P
PPh2
Et2P
PEt2
depp
dippp
dppb
dcype
Fig. 2. Diphosphanes used.
tion was faster with SnCl2 present, where the CTI signals were ob-
servable within 90 min of solution mixing, and the reaction went
to completion. Reaction was also faster with PBr3 than with PCl3,
with the ring signals immediately visible in the spectrum. The re-
sults are in good agreement with each other, and are listed in Ta-
ble 1. Second order effects on the spectra were again apparent in
these systems from spectrometers operating at lower frequencies,
with both resonances appearing as doublets of doublets. This is
understandable, as the shift difference between PA and PB is smal-
ler for dppdmx derivatives than for any of the other systems
studied.
resonances was found for the SnBr2 reaction, corresponding to
the hexabromostannate salt 10c.
2.2. New CTIs from ferrocene derivatives
2.2.1. 1,10-Bis(di-isopropylphosphino)ferrocene, dippf
This diphosphane formed the CTI 11 (Fig. 3) readily when re-
acted with PCl3. The 31P NMR data for 11 are listed in Table 2,
and are comparable with those reported previously by us for the
CTI derived from 1,10-bis(diphenylphosphino)ferrocene (dPA
1
ꢀ135.4 ppm, dPB 33.2 ppm, JP–P 497 Hz) [13]. A singlet resonance
at 116.2 ppm was ascribed to the dichlorodiphosphonium dication
12 (Fig. 3).
2.1.7. Bis(2-diphenylphosphinophenyl)ether, DPEphos
Reaction of DPEphos with both PCl3 and PBr3 was very slow, and
only the doublet signal was seen after 3 days. Reaction was there-
fore carried out with SnX2 present, where ring formation was much
faster. Two sets of signals were seen in the SnCl2 reaction, attrib-
uted to different counter-ions 10a, 10b, Table 1 [17,18]. The reac-
tion was repeated with excess SnCl2 to afford the
hexachlorostannate salt, 10b, as the only product. Only one set of
2.2.2. 1-(Diphenylphosphino)-10-(ditertbutylphosphino)ferrocene,
dppdtbpf
Formation of the CTI 13 (Fig. 3) from this unsymmetrical
diphosphane was accomplished using PCl3 alone, PCl3 with SnCl2
and PCl3 with AlCl3; all three signals in each case appeared as dou-
blets of doublets, and the 31P NMR results are collected in Table 2.

328
R. Bashforth et al. / Inorganica Chimica Acta 376 (2011) 325–331
+
2+
+
X-
2X-
2-
1/2 SnX6
iPr2P
PiPr2
iPr2P
PiPr2
Cl
P
Cl
PPh2
Ph2P
P
1a X- = Cl-
2a X- = Cl-
1b X- = 1
/
2 SnCl6
2b X- = 1
/2 SnCl6
2-
2-
3a X- = Cl-
3b X- = Br-
+
2+
+
1/2 SnX6
2-
2-
SnCl6
X-
PPh2
PCy2
Ph2P
Cy2P
P
P
Cp2P
PCp2
P
Cl
5a X- = Cl-
5b X- = Br-
6a X- = Cl-
4
2-
6b X- = 1
/
2 SnCl6
2+
+
+
O
O
2Cl-
1/2 SnCl6
X-
2-
O
P
Cp2P
Cl
PCp2
Cl
Ph2P
PPh2
Ph2P
PPh2
P
8
9a X- = Cl-
7
9b X- = 1
/2 SnCl6
2-
9c X- = Br-
+
+
2+
iPr2
P
PtBu2
PiPr2
Cl
X-
Cl-
2Cl-
Fe
P
P
Fe
Fe
iPr2
P
PiPr2
Cl
PPh2
12a X- = Cl-
11
10
12b X- = 1
/
2 SnCl6
2-
12c X- = AlCl4
-
Fig. 3. New CTIs and related compounds synthesised.
Table 2
31P NMR data for new systems of ferrocene derivatives.
Compound number
Counter-ion
Ring size
PC (ppm)
PB (ppm)
PA (ppm)
1JPA–PC (Hz)
1JPA–PB (Hz)
4JPB–PC (Hz)
11
Clꢀ
6
6
6
6
–
51.9
37.0
37.5
37.2
ꢀ148.7
ꢀ139.4
ꢀ137.9
ꢀ139.3
490
531
525
529
–
–
13a
13b
13c
Clꢀ
65.6
65.8
65.5
549
546
548
37
37
37
2ꢀ
SnCl6ꢀ
AlCl4
2.3. Results for known CTIs with different counter-ions
2.4. Protonation studies
The 31P NMR data for these (mainly) smaller-ring systems are
collected in Table 3; the ions are shown in Fig. 5, numbered from
14 to 17 in order of ring size. Good agreement was obtained in
all instances with the NMR parameters obtained previously for
other counter-ions [10,13,15,16].
Three of the new CTIs, 3a, 5a and 9b, with 7-, 7- and 8-mem-
bered rings, were successfully protonated to give the dications
18, 19 and 20, respectively (Fig. 6) [2,13,16,19]. Protonations of
3a and 9b were carried out by both triflic acid [13,16] and a mix-
t
ture of AlCl3 with BuCl [2,13,19]. Compound 5a was protonated

R. Bashforth et al. / Inorganica Chimica Acta 376 (2011) 325–331
329
Table 3
31P NMR data for CTIs with different counter-ions to those in the literature.
Compound number
Counter-ion
Ring size
PB (ppm)
PA (ppm)
1JP–P (Hz)
Ref.
2ꢀ
14
15
16
17
SnCl6
5
6
6
7
87.2
30.6
44.8
34.1
ꢀ289.0
ꢀ252.1
ꢀ299.4
ꢀ211.0
455
418
457
456
[13]
[15]
[15]
Iꢀ
2ꢀ
SnCl6
Iꢀ
[10,16]
Fig. 4. Stackplot showing the cyclic intermediate 4 in the formation of CTI 5a.
+
3. Conclusions
+
2-
Cy2P
P
PCy2
I-
SnCl6
The results described above show that it is feasible to form 7-
and 8-membered ring cyclic triphosphenium ions from a variety
of diphosphanes in solution, by reaction with PX3 (X = Cl or Br),
sometimes in the presence of SnX2 or AlCl3. For aromatic substitu-
ents on the diphosphane, causing it to be a comparatively poorer
reducing agent, reaction is often slow with PCl3 alone, and may
be accelerated either by adding SnCl2 as a more powerful reducing
agent, or by using PBr3, where the P–X bonds are more easily bro-
ken. When the substituents on the diphosphane are aliphatic or ali-
cyclic, making it a better reducing agent, reaction usually takes
place readily with PCl3 alone. Three of the new CTIs have been pro-
tonated by triflic acid, indicating that the rings are reasonably ro-
bust even in the presence of such a vigorous reagent. The cyclic
intermediate on the way to CTI formation was detected only in
the cybiphep system [15]. Signals readily assignable to the dichlo-
rodiphosphonium dication were sometimes observed, particularly
where the diphosphane itself proved to be a good reducing agent.
Et2P
PEt2
P
2
14
15
+
+
2-
SnCl6
I-
Et2P
P
PEt2
Ph2P
PPh2
P
2
16
17
Fig. 5. CTIs synthesised with different counter-ions.
via the triflic acid route only. The 31P NMR results are given in Ta-
ble 4. One interesting point is that protonation causes inequiva-
lence of the outer phosphorus atoms PB and PC in 19; this also
happens on alkylation of the central phosphorus atom PA of the
cybiphep system [20]. For 18a, 19 and 20b the spectra were re-
4. Experimental
All manipulations, including NMR sample preparation, were
carried out either under an inert atmosphere of dry nitrogen or
in vacuo, using standard Schlenk line or glovebox techniques.
1
corded proton-coupled as well as decoupled, enabling JP–H to be
recorded (Table 4).

330
R. Bashforth et al. / Inorganica Chimica Acta 376 (2011) 325–331
2+
2+
2+
2X-
2X-
2X-
PCy2
PPh2
O
Cy2P
Ph2P
P
P
Ph2P
PPh2
H
H
P
H
19 X- = 1/2 SnCl62-/ CF3SO3
-
20a X- = 1/2 SnCl62-/ CF3SO3
-
-
18a X- = 1/2 SnCl62-/ CF3SO3
20b X- = AlCl4
-
-
18b X- = AlCl4
Fig. 6. Protonated CTIs.
161.91 or 202.3 MHz, respectively; chemical shifts are referenced
to 85% H3PO4, with the high frequency direction taken as positive.
Quantities of reagents used in the syntheses are shown in Table 5.
Table 4
31P NMR data for protonated CTIs.
Compound
dPA (ppm)
dPB (ppm)
dPC (ppm)
1JP–P (Hz)
1JP–H (Hz)
18a
18b
19
20a
20b
ꢀ105.6
ꢀ107.0
ꢀ112.5
ꢀ88.1
18.0
18.1
22.8
19.4
21.2
ꢀ
234
242
248, 247
302
250
NR
243
NR
–
4.1. Example reactions
21.8
–
–
4.1.1. Synthesis of the dippb cyclic triphosphenium ion, 1a
Dippb (0.0286 g, 0.10 mmol) was dissolved in 1.0 mL CDCl3.
PCl3 (0.010 mL, 0.11 mmol) was then added and a 31P{1H} NMR
spectrum recorded soon after mixing.
ꢀ87.5
301
238
NR – not recorded.
Chemicals of the best available commercial grade were used, in
general without further purification. The 31P NMR spectra of all
phosphorus-containing starting materials were recorded, to verify
that no major impurities were present. 31P NMR spectra were ob-
tained on Varian Mercury 200, Varian Unity 300, Mercury 400 or
Inova 500 Fourier-transform spectrometers at 80.96, 121.40,
4.1.2. Synthesis of the dippb cyclic triphosphenium ion 1b using SnCl2
Dippb (0.0235 g, 0.08 mmol) and SnCl2 (0.0152 g, 0.08 mmol)
were dissolved in 1.0 mL CDCl3. PCl3 (0.007 mL, 0.08 mmol) was
then added and a 31P{1H} NMR spectrum recorded soon after
mixing.
Table 5
Quantities of reagents used.
Compound number
Diphosphane
Counter-ion
Quantities used
Diphosphane
PX3
ml
SnX2
g
Triflic acid
AlCl3/tBuCl mix
mmols
g
mmol
mmol
mmol
ml
mmol
1a
1b
3a
3b
5a
5b
6a
6b
8
9a
9b
9c
10a/b
10b
10c
11
13a
13b
13c
14
dippb
dippb
Clꢀ
SnCl6
SnCl6
SnBr6
0.0286
0.0235
0.0200
0.0200
0.0120
0.0093
0.0079
0.0200
0.0115
0.0300
0.0200
0.1400
0.1082
0.1082
0.1082
0.0508
0.0361
0.0140
0.0284
0.0400
0.0419
0.0136
0.079
0.10
0.08
0.010
0.007
0.020
0.020
0.002
0.002
0.010
0.010
0.002
0.030
0.020
0.020
0.020
0.020
0.020
0.010
0.010
0.003
0.007
0.008
0.054a
0.11
0.08
0.23
0.21
0.023
0.021
0.11
0.11
0.023
0.34
0.21
0.23
0.23
0.23
0.23
0.11
0.11
0.034
0.080
0.092
0.13
0.046
0.141
0.46
0.34
0.023
0.23
0.11
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
0.02
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
0.23
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2ꢀ
0.0152
0.030
0.030
0.0044
0.0120
–
0.030
0.0090
–
0.08
0.16
0.11
0.023
0.043
–
0.16
0.047
–
2ꢀ
biphep
biphep
cybiphep
cybiphep
dcppmb
dcppmb
diop
dppdmx
dppdmx
dppdmx
DPEphos
DPEphos
DPEphos
dippf
dppdtbpf
dppdtbpf
dppdtbpf
dcype
depp
dippp
0.038
0.038
0.022
0.017
0.018
0.045
0.023
0.052
0.035
0.24
2ꢀ
2ꢀ
SnCl6
2ꢀ
SnBr6
Clꢀ
2ꢀ
SnCl6
2ꢀ
SnCl6
Clꢀ
Brꢀ
–
–
2ꢀ
SnCl6
0.040
0.0380
0.1000
0.0560
–
0.21
0.20
0.53
0.20
–
Clꢀ/SnCl6
0.20
0.20
0.20
0.12
2ꢀ
2ꢀ
SnCl6
2ꢀ
SnBr6
Clꢀ
Clꢀ
0.070
0.027
0.055
0.095
0.19
0.049
0.19
0.057
0.038
0.025
0.24
–
–
2ꢀ
SnCl6
SnBr6
0.0060
0.0085
0.0180
–
0.0100
–
0.050
0.080
0.0161
0.040
0.030
0.032
0.064
0.095
–
0.053
–
0.27
0.42
0.085
0.21
0.16
2ꢀ
2ꢀ
SnCl6
15
16
17
18a
18b
19
20a
20b
Iꢀ
2ꢀ
SnCl6
0.004
b
dppb
Iꢀ
ꢀ
ꢀ
biphep
biphep
cybiphep
dppdmx
dppdmx
½ SnCl62ꢀ/CF3SO3
0.030
0.020
0.0135
0.140
0.020
0.040
0.030
0.002
0.020
0.010
½ SnCl62ꢀ/AlCl4
0.20
–
–
ꢀ
½ SnCl62ꢀ/CF3SO3ꢀ
0.009
0.02
–
0.10
0.23
–
½ SnCl62ꢀ/CF3SO3
½ SnCl62ꢀ/AlCl4
0.035
0.10
ꢀ
a
Quantity in grams.
b
From 0.4 mL of a standard solution prepared from 6.5418 g PI3 dissolved in 45 mL of dry DCM (concentration of 0.353 mmol/mL).

R. Bashforth et al. / Inorganica Chimica Acta 376 (2011) 325–331
[2] S. Lochschmidt, A. Schmidpeter, Z. Naturforsch. B 40 (1985) 765.
331
4.1.3. Synthesis of the protonated biphep CTI
[3] A. Schmidpeter, S. Lochschmidt, Phosphorus Sulfur 29 (1986) 73.
[4] F.S. Gamper, H. Schmidbaur, Chem. Ber. 126 (1993) 601.
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[6] B.D. Ellis, C.L.B. Macdonald, Inorg. Chem. 45 (2006) 6864.
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Chem. 47 (2008) 1196.
[9] P. Kilian, A.M.Z. Slavin, J.D. Woollins, Dalton Trans. (2006) 2175.
[10] J.A. Boon, H.L. Byers, K.B. Dillon, A.E. Goeta, D.A. Longbottom, Heteroat. Chem.
11 (2000) 226.
[11] R.J. Barnham, R.M.K. Deng, K.B. Dillon, A.E. Goeta, J.A.K. Howard, H.
Puschmann, Heteroat. Chem. 12 (2001) 501.
[12] K.B. Dillon, P.K. Monks, R.J. Olivey, H.H. Karsch, Heteroat. Chem. 15 (2004) 464.
[13] J.D. Burton, R.M.K. Deng, K.B. Dillon, P.K. Monks, R.J. Olivey, Heteroat. Chem. 16
(2005) 447.
[14] R.M.K. Deng, K.B. Dillon, A.E. Goeta, A.L. Thompson, Acta Crystallogr., Sect. E 61
(2005) m296.
[15] K.B. Dillon, P.K. Monks, Dalton Trans. (2007) 1420.
[16] A.J. Boyall, K.B. Dillon, P.K. Monks, J.C. Potts, Heteroat. Chem. 18 (2007) 609.
[17] K.B. Dillon, R.K. Harris, P.N. Gates, A.S. Muir, K. Root, Spectrochim. Acta A 47
(1991) 831.
4.1.3.1. With triflic acid (18a). Biphep (0.03 g, 0.06 mmol) and SnCl2
(0.05 g, 0.3 mmols) were dissolved in 1.0 mL CDCl3. PCl3 (0.04 mL,
0.5 mmol) was then added, and a 31P{1H} NMR spectrum recorded
soon after mixing to check that the cyclic triphosphenium ion had
formed. An excess of triflic acid (0.02 mL, 0.2 mmols) was added,
and both 31P{1H} and 31P NMR spectra were recorded.
t
4.1.3.2. With AlCl3 and BuCl (18b). Biphep (0.02 g, 0.04 mmol) and
SnCl2 (0.08 g, 0.4 mmols) were dissolved in 1.0 mL CDCl3. PCl3
(0.03 mL, 0.3 mmol) was then added, and a 31P{1H} NMR spectrum
recorded soon after mixing to check that the cyclic triphosphenium
ion had formed. AlCl3/tBuCl mixture1 was then added by syringe
(0.2 mL, 0.2 mmols), and a 31P{1H} spectrum recorded.
Acknowledgments
[18] R.K. Harris, P.N. Gates, A. Root, A.S. Muir, Spectrochim. Acta A 48 (1992) 1371.
[19] A. Schmidpeter, S. Lochschmidt, K. Karaghiosoff, W.S. Sheldrick, J. Chem. Soc.,
Chem. Commun. (1985) 1447.
[20] R. Bashforth, A.J. Boyall, K.B. Dillon, A.E. Goeta, J.A.K. Howard, A.M. Kenwright,
P.K. Monks, M.R. Probert, H.J. Shepherd, A.L. Thompson, Dalton Trans,
submitted for publication.
We would like to thank the Maria da Graça Memorial Fund/
Chemistry Department, University of Durham (P.K.M.), for financial
support.
References
[1] A. Schmidpeter, S. Lochschmidt, W.S. Sheldrick, Angew. Chem., Int. Ed. 21
(1982) 63.