A twist on Hellwinkel's salt, [P(2,2′-biphenyl)2]+[P(2,2′-biphenyl)3]-

Article abstract of DOI:10.1139/cjc-2017-0648

Treating PCl₅ with C₁₂H₈Li₂, generated from either C₁₂H₁₀, C₁₂H₈Br₂, or C₁₂H₈I₂, affords three products in different ratios

Full text of DOI:10.1139/cjc-2017-0648

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ARTICLE
A twist on Hellwinkel’s salt, [P(2,2=-biphenyl)2]+[P(2,2=-biphenyl)3]–
Khatera Hazin and Derek P. Gates
Abstract: Treating PCl5 with C12H8Li2, generated from either C12H10, C12H8Br2, or C12H8I2, affords three products in different
ratios depending on the source of the lithiated biphenyl. Hellwinkel’s salt [P(C12H8)2][P(C12H8)3] ([1][2]) and another product
[P(C12H8)(C24H16)][P(C12H8)3] ([1=][2]) were obtained by reacting PCl5 with 2,2=-dilithiobiphenyl [Route A: 2.5 equiv.; obtained from
biphenyl, n-BuLi, and TMEDA; Route B: 3.0 equiv.; obtained from 2,2=-diiodobiphenyl and n-BuLi; Route C: 4.0 equiv.; obtained
from 2,2=-dibromobiphenyl and n-BuLi]. The synthesis, isolation, and characterization of the chiral spiro-compound [1=][2] and
the characterization of the pentavalent phosphorane [P(C12H8)2(C12H9)] (3) are reported. The complex [1=][2] was characterized by
31P{1H} NMR spectroscopy, X-ray crystallography, and mass spectrometry. The pentavalent compound (3) was characterized by
31P{1H} NMR spectroscopy and X-ray crystallography.
Key words: anions, phosphorus heterocycles, weakly coordinating anions, spirocycles.
Résumé : Le traitement du PCl5 par le C12H8Li2 généré a` partir soit de C12H10, de C12H8Br2 ou de C12H8I2 génère trois produits dont
les proportions varient selon la source du biphényle lithié. Nous avons obtenu le sel de Hellwinkel [P(C12H8)2][P(C12H8)3] ([1][2]) et
un autre produit, le [P(C12H8)(C24H16)][P(C12H8)3] ([1=][2]), en faisant réagir le PCl5 avec le 2,2=-dilithiobiphényle [voie A : 2,5 équiv.;
obtenu a` partir du biphényle traité par le n-BuLi et le TMEDA; voie B : 3,0 équiv.; obtenu a` partir du 2,2=-diiodobiphényle traité
par le n-BuLi; voie C : 4,0 équiv.; obtenu a` partir de 2,2=-dibromobiphényle traité par le n-BuLi]. Nous présentons la synthèse,
l’isolation et la caractérisation du composé spiro chiral [1=][2] ainsi que la caractérisation du phosphorane pentavalent
[P(C12H8)2(C12H9)] (3). Nous avons caractérisé le complexe [1=][2] par spectroscopie RMN 31P{1H}, radiocristallographie et spectro-
métrie de masse, et le composé pentavalent (3), par spectroscopie RMN 31P{1H} et radiocristallographie. [Traduit par la Rédaction]
Mots-clés : anions, hétérocycles phosphorés, anions a` coordinance faible, spirocycles.
plications is the lability of the P–O bonds and the donor properties
of the oxygen atoms within the anion.
Introduction
The development of weakly coordinating anions is of particular
interest and plays a critical role in the generation and stabiliza-
tion of highly reactive cations.1–7 Many of the major advance-
ments in this area have involved the elaboration of classical
group 13 element based anions such as [BF4]– and [AlCl4]–. Partic-
ularly noteworthy are the fluorinated anions shown in Chart 1:
[A]–,8–19 [B]–,20–31 and [C]–,3,32–37 each of which has been isolated as
Brønsted acids and must be stored at low temperatures.
As an alternative to the anion [D]–, we sought anions featuring
P–C rather than P–O bonds, analogues of the tetraarylborates.
Because [PPh6]– and [P(ArF)6]– are not known and would be pre-
dicted to have limited stability, the salt [1][2] (Chart 2) featuring
the P–C containing anion [2]– was appealing. This compound,
along with Li[2], was first reported by Hellwinkel in 1965 and was
resolved into optically active enantiomers.42–44 Derivatives of [2]–
with a 4-methyl-biphenyl chelate have also been synthesized.45
Moreover, an ammonium salt, HNMe2Ph[P(C12F8)3], has been
claimed as a protic activator for metallocene catalysts for ethylene
polymerization.46 It should be noted that limited synthetic and
characterization details for this compound were provided. There-
fore, we set out to explore the synthesis of parent [1][2] with the
ultimate goal of accessing new Brønsted acids.
We were inspired by the formal evolution of [BF4]– and [AlCl4]–
to more complex and less donating anions (e.g., [A]––[C]–). As a
result, we have been exploring the weakly coordinating anion
properties of larger derivatives of the classical weakly coordinat-
ing anion, [PF6]–. In particular, the weakly coordinating anion
properties of the fascinating tris(tetrachlorobenzenediolato)phos-
phate (Chart 1, [D]–) are of interest.38 We have shown that Brøn-
sted acids HL2[D] (L = Et2O, THF, CH3CN, DMF) can be isolated as
solids and used as initiators for the cationic polymerization of
olefins.39,40 These initiators compare favorably with the estab-
lished Brønsted acid H(OEt2)2[A] and initiator system H(OEt2)2[C].
Attractive features of HL2[D] include its ease of synthesis (direct
reaction of PCl5 and C6Cl4(OH)2), its moderate stability at ambient
temperature, and its ability to initiate polymerization at higher
Herein, we report our efforts to synthesize and isolate Hellwinkel’s
salt [1][2] and the unexpected discovery of the byproducts [1=][2] and 3.
Both [1=][2] and 3 were structurally characterized by X-ray crystallog-
raphy.
Results and discussion
In an effort to avoid brominated or iodinated biphenyl as a
starting material, biphenyl was directly lithiated with n-BuLi
(2.4 equiv.) in N,N,N=,N=-tetramethylethylenediamine (TMEDA)
(2.4 equiv.) (Scheme 1, Route A). It has been shown previously that
temperatures than are required of typical cationic initiators.41
potential concern with using [D]– in cationic polymerization ap-
A
Received 15 October 2017. Accepted 4 January 2018.
K. Hazin and D.P. Gates. Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC V6T 1Z1, Canada.
Corresponding author: Derek P. Gates (email: dgates@chem.ubc.ca).
This paper is part of a Special Issue to honour Professor Neil Burford.
Dedicated to Professor Neil Burford: inspirational teacher, mentor, and friend.
Copyright remains with the author(s) or their institution(s). Permission for reuse (free in most cases) can be obtained from RightsLink.
Can. J. Chem. 00: 1–8 (0000) dx.doi.org/10.1139/cjc-2017-0648
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Chart 1. Selected examples of boron(III)-, aluminum(III)-, and phosphorus(V)-containing weakly coordinating anions.
the same mass as the anion [2]–, suggesting that this cation had
the formulation [P(C12H8)3]+. This was perplexing because the
bond connectivity necessary to generate a P-centered cation with
this molecular formula was not immediately obvious.
Chart 2. Hellwinkel’s spiro-compound [1][2].
It has previously been reported that treating [1][2] with dilithi-
ated biphenyl (1.0 equiv.) affords Li[2].42 In an effort to simplify
this unexpected product mixture, a portion of the isolated reac-
tion mixture from above (Route A) was suspended in THF and
treated with C12H8Li2 (1 equiv.) in Et2O. The 2,2=-dilithiobiphenyl
was prepared from C12H8Br2 and n-BuLi (2.0 equiv.). Analysis of an
aliquot of the soluble portion of the reaction mixture by 31P{1H}
NMR spectroscopy revealed that the major signals were at 35.2
and –183.3 ppm (see Fig. 1b; major signals assigned to [1=][2]) and a
very small signal (<10% of the intensity of [1=]+) at 27.2 ppm (as-
signed to [1]+ of [1][2]). The aforementioned signal at –86.2 ppm,
observed in the product mixture for Route A, was no longer ob-
served. The reaction mixture was filtered to remove poorly solu-
ble residual salts (e.g., [1][2], Li[2], LiBr, etc.). The filtrate was
collected, and the soluble product was isolated as a solid after
solvent removal. Crystals suitable for X-ray diffraction were ob-
tained by cooling (–30 °C) a solution of the crude product in a
mixture of THF and Et2O (1:1).
The molecular structure of the isolated compound, [1=][2], is
shown in Fig. 2, along with selected metrical parameters. Impor-
tantly, the structure confirms the formulation obtained from
mass spectrometric analysis, [P(C12H8)3][P(C12H8)3], yet the bond
connectivity was totally unexpected. Particularly striking, is the
structure of the cation [1=]+, which contains the twisted 2,2=-bis
(phenyl)biphenyl ligand (Chart 3). Although the neutral compound
2,2=-bis(phenyl)biphenyl is known and has been structurally char-
acterized,49–55 to our knowledge, there are only three mentions of
complexes featuring the 2,2=-bis(phenyl)biphenyl dianionic li-
gand.56–58 It should be noted that in the early reports of Hellwin-
kel, the possible coupling of the biphenyl moieties to form a
byproduct was considered on the basis of IR spectra and melting
point data.42,59 In the present case, the structurally characterized
product [1=][2] was further characterized by 31P NMR spectroscopy
and ESI-MS.
the direct metallation of biphenyl with n-BuLi in the presence of
TMEDA leads to 2,2=-dilithiobiphenyl.47,48 In the present work,
the dilithiation was confirmed by quenching a small aliquot re-
moved from the reaction mixture with Me3SiCl [1H NMR d8-THF:
␦ = 0.43, 6H, Si(CH3)3; 7.24–7.89, 8H, Ar–H]. Subsequently, a solu-
tion of PCl5 in THF/Et2O (40 mL/6 mL) was slowly added to
2,2=-dilithiobiphenyl to afford Hellwinkel’s salt [1][2] as the major
product, as estimated by 31P{1H} NMR spectroscopy (Fig. 1a; ␦ =
25.8 [1]+ and –184.7 ppm [2]–). Surprisingly, the 31P{1H} NMR spec-
trum of the reaction mixture suggested that at least two addi-
tional products were present as evidenced by the presence of a
singlet resonance at 30.6 ppm, close to that of [1]+ and another
,
singlet resonance at –86.2 ppm.
Attempts to isolate [1][2] from the aforementioned mixture
were unsuccessful given the poor solubility of the products in
typical organic solvents (e.g., CHCl3, CH2Cl2, Et2O, THF, acetone,
toluene). Analysis of the crude material by electrospray mass spec-
trometry (ESI-MS; Supplementary Figs. S1 and S2) was particularly
informative. In the negative mode, a single ion was observed that
was assigned to [2]– (m/z = 487.1). Unexpectedly, analysis in the
positive mode revealed two ions, one of which was assigned to [1]+
of Hellwinkel’s salt (m/z = 335.2). The other cation (m/z = 487.2) had
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Hazin and Gates
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Scheme 1. Synthesis of [1][2] via routes A–C.
The salt [1=][2] co-crystallizes with THF and diethyl ether solvent
in the lattice. There are weak interactions between the cation
and the anion in [1=][2] (Supplementary Fig. S5) with weak C···H,
C···C, and H···H contacts, with the closest contacts as follows:
C(21)···H(38) = 2.677(1) Å; C(15)···C(69) = 3.281(2) Å; H(21)···H(38) =
2.361(2) Å. In addition, there are moderate to strong interactions
between the oxygen in the THF solvent and hydrogen atoms of the
[1=]+ cation, namely O(1)···H(29) = 2.531(2) Å and O(2b)···H(28) =
2.553(5). There is also a close contact between the oxygen of
THF and a methyl group of diethyl ether solvate, namely
H(84C)···O(2B) = 1.639(4) Å. For comparison, the sum of the van der
Waals radii for oxygen and hydrogen is 2.72 Å, that for carbon and
hydrogen is 2.90 Å,60 and a typical O–H bond length is 0.96 Å in
water.61
length in the anion of [P(2,2=-biphenyl)2][2] [dP–C = 1.932(2) Å] is
similar to the average P–C bond length observed in [1=][2] [dP–C
=
1.929(4) Å]. The P(2)–C(48) bond length 1.944(1) Å is slightly elon-
gated with respect to the other P–C bonds in the anion of [1=][2].
The C–C bond lengths between the biphenyl moieties in the anion
of [1=][2] [average 1.478(3) Å] are shorter than the C–C bond length
in biphenyl itself [1.506(17) Å].63,64 Within the biphenyl ligands of
[2]–, the angle between the mean planes of the aryl moieties show
only minor deviations from planarity [i.e., ⌰(C49–C54)–(C55–C60)
=
4.4(4)°, ⌰(C37–C42)–(C43–C48) = 7.2(4)° and ⌰(C61–C66)–(C67–C72) = 5.6(5)°].
These angles are similar to those between the mean planes of the
aryl moieties in the salt [1][2] (⌰ = 3.0(6)°, 5.1(5)°, 6.3(5)°).62
With the identity of [1=][2] confirmed, it remained to identify the
species responsible for the signal at –86.2 ppm in the 31P NMR
spectrum of the reaction mixture from Route A (Fig. 1a). Thus, a
second portion of the isolated crude reaction mixture from
Route A was suspended in n-butanol and gravity filtered. Upon
standing of the filtrate at ambient temperature in air atmosphere
for 3 weeks, crystals suitable for X-ray crystallographic analysis
were isolated. The molecular structure of the pentacoordinate
phosphorane 3 is shown in Fig. 3. Interestingly, the phosphorus(V)
centre in 3 adopts a distorted trigonal bipyramidal geometry with
one carbon of each of the chelating biphenyl ligands in the axial
positions, i.e., C(12) and C(24). This leaves the second carbon of
each of the two chelating ligands along with the carbon of the
monodentate biphenyl in the equatorial plane (Chart 4). As ex-
pected, the equatorial P–C bonds [average 1.868(7) Å] are shorter
than the axial P–C bonds [average 1.917(6) Å].
The Cax–P–Ceq bond angles [average 90.0(4)°] are in the range
expected for a trigonal bipyramid with the maximum deviations
being 94.5(2)° and 86.1(2)° for C(1)–P(1)–C(24) and C(12)–P(1)–C(1),
respectively. The C–C bond length connecting the two phenylene
moieties of the monodentate biphenyl [C(31)–C(30) = 1.491(6) Å] is
slightly elongated compared with the other two chelating biphenyl
ligands in 3 [C(6)–C(7) = 1.475(7) Å; C(18)–C(19) = 1.474(5) Å]. This
lengthening is most likely due to disruption of ␲-conjugation
within the twisted monodentate biphenyl ligand. Specifically, the
angle between the mean planes of the phenylene moieties in the
monodentate 2-biphenyl ligand [⌰(C25–C30)–(C31–C36) = 51.5(2)°] are
The unprecedented cation [1=]+ adopts a highly distorted tetra-
hedral geometry at phosphorus. Specifically, the C(1)–P(1)–C(12)
angle of the chelated 2,2=-biphenyl ligand at 94.0(1)° is signifi-
cantly more acute than the C(7)–P(1)–C(36) angle of the 2,2=-
bis(phenyl)biphenyl ligand at 121.5(5)°. In contrast, the bond lengths
in the cation show only minor perturbations from those expected.
For example, the average P–C bond lengths [dP–C = 1.80(3) Å] are
longer than the average P–C bond length in the previously re-
ported [1]+ [dP–C = 1.777(4) Å].62 Interestingly, the C–C bond lengths
connecting the four phenylene moieties of the twisted 2,2=-bis
(phenyl)biphenyl ligand in [1=]+ [average 1.493(3) Å] are slightly longer
than that between the phenylene of the biphenyl in [1=]+ [C(6)–
C(7) = 1.475(2) Å]. This lengthening presumably reflects the de-
creased ␲-conjugation that accompanies the twisting in [1=]+. For
example, angles between the mean planes of the phenylene moi-
eties in the 2,2=-bis(phenyl)biphenyl ligand [⌰(C13–C18)–(C19–C24)
=
80.0(4)°; ⌰(C19–C24)–(C25–C30) = 81.9(4)°; ⌰(C25–C30)–(C31–C36) = 73.9(4)°]
are significantly greater than that for the chelated 2,2=-biphenyl
[⌰(C1–C6)–(C7–C12) = 3.4(5)°]. In comparison, the angle between the
mean planes of the aryl moieties in the uncomplexed 2,2=-(biphenyl)
biphenyl are shorter (⌰ = 47.3°, 50.9°, 43.0°).50
In contrast to the cation [1=]+, the phosphorus(V) center in [2]–
shows only minor perturbation from regular octahedral geometry
displaying metrical parameters similar to those found in the pre-
viously reported salt [1][2].62 For example, the average P–C bond
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Can. J. Chem. Vol. 00, 0000
Fig. 1. 31P{1H} NMR (121 MHz, 25 °C) spectra of the following: (a) the
reaction mixture obtained by reacting PCl5 with 2,2=-lithiobiphenyl
[2.5 equiv.; obtained from biphenyl, n-BuLi (2.0 equiv.) and TMEDA]
in THF/Et2O — Route A in Scheme 1; (b) the reaction mixture
obtained by reacting a portion of isolated reaction mixture from
Route A (above) with 2,2=-dilithiobiphenyl in Et2O; (c) crystals of
isolated [1=][2] dissolved in THF/Et2O solution; and (d) crystals of
isolated 3 dissolved in THF/Et2O.
uted to an unidentified species (␦ = 37.4). Unfortunately, the poor
solubility and limited quantity of 3 obtained thwarted additional
characterization of this product. It should be noted that Hellwin-
kel previously observed 3 and its 4-methyl-biphenyl derivative as
characterized by IR spectroscopy, elemental analysis, and optical
rotation studies.42,43,45
Although Hellwinkel’s earlier reports mentioned the possibility
that [1=][2] was a byproduct in the formation of [1][2] from
2,2=-diiodobiphenyl,42 this was not shown explicitly. Thus, we fol-
lowed the published procedure exactly (Scheme 1, Route B), albeit
on a smaller scale. 2,2=-Dilithiobiphenyl was prepared by treating
2,2=-diiodobenzene with n-BuLi (2.4 equiv.) in diethyl ether. To this
mixture was added PCl5 in diethyl ether, and the “product” was
isolated according to the reported procedure. The “product” was
dissolved in THF/Et2O, and the 31P{1H} NMR spectrum is shown in
Fig. 4a. Remarkably, the major product we observed was [1=][2] (␦ =
29.8 and –183.8) with the minor product being [1][2] (␦ = 26.8 and
–183.8). Interestingly, the intensity of the signal for [2]– was very
small compared with that of [1=]+ or [1]+. This suggests that there
may be significant quantities of the Cl– or I– counterion present.
These results are in contrast to those of Hellwinkel who reported
only the signals attributed to [1][2] (␦ = 26.5 and –186.5 ppm in
DMF-d7); the 31P{1H} NMR spectrum of the “product” we obtained
in DMF-d7 reveals signals at ␦ = 31.9, 27.0 and –183.4 ppm. In our
hands, it appears that insertion product [1=]+ is the major product.
Given the 3:1 stoichiometric ratio of the 2,2=-diiodobiphenyl li-
gand to phosphorus pentachloride, there is insufficient
2,2=-diiodobiphenyl to afford both [1=]+ and [2]– stoichiometrically.
It is for this reason that we believe the main products are [1=]X and
[1]X (X = Cl or Br) with minimal amounts of [1=][2] and [1][2] being
formed.
Given the above results, we became interested to see whether
the ratio of [1]+ to [1=]+ could be influenced by starting with 2,2=-
dibromobiphenyl instead of 2,2=-diiodobiphenyl. In this case
(Scheme 1, Route C), the crude product mixture isolated from the
reaction mixture was dissolved in THF/Et2O and analyzed by
31P{1H} NMR spectroscopy. The spectrum (Fig. 4b) reveals that the
major product contained the cation [1]+ with the minor product
containing [1=]+. Although the relative intensity of the signal as-
cribed to [2]– is greater than that for the iodo-precursor, the spec-
trum still suggests that a significant quantity of halide salt is
formed.
Before closing, a comment on the mechanism of formation for
[1=][2] is warranted. It is remarkable that the coupling of biphenyl
is observed following all three routes. First, the coupling arylene
moieties during the lithiation of aryl halides, i.e., Ar–X + Ar–Li ¡
Ar–Ar + LiX (X = Br or I), is well precedented. In fact, the reaction
of 1,2-diiodobenzene or 1,2-dibromobenzene with n-BuLi (2.4 equiv.)
followed by carboxylation affords low yields of 2,2=-C12H8(COOH)2
(up to 17%).65–67 Thus, it may be inferred that the presumptive
intermediate, 1-halo-2-lithiobenzene, is readily coupled to itself
or to 1,2-dihalobenzene to afford 2-halo,2=-lithiobiphenyl and
2,2=-dihalobiphenyl, respectively. These products may be further
lithiated and (or) coupled to the corresponding tetraphenyl deriv-
atives. Thus, the observed formation of [1=]+ when starting with
2,2=-dihalobiphenyl derivatives (i.e., Routes B or C) can be ratio-
nalized.
It is considerably more difficult to explain the observed cou-
pling of biphenyl to give [1=]+, which is observed following
Route A. In this case, nucleophilic aromatic substitution is not
possible and only an oxidative coupling of Ar–Li moieties is plau-
sible. However, the possible oxidizing agents are limited to the
phosphorus(V) of PCl5, adventitious oxygen, or perhaps solvent.
As the reactions were performed under rigorously anaerobic con-
ditions and the results are entirely reproducible, we consider that
the most likely oxidant is PCl5. That said, we do not observe any
evidence by 31P NMR spectroscopy of the reactions solutions for
the reduced products although it is possible these species are
significantly greater than that for the two chelated 2,2=-biphenyl
ligands [⌰(C1–C6)–(C7–C12) = 4.9(2)°; ⌰(C13–C18)–(C19–C24) = 2.3(2)°].
The crystals of 3 were further characterized by 31P{1H} NMR
spectroscopy in THF/Et2O (Fig. 1d), which displayed a singlet reso-
nance assigned to the product (␦ = –86.2) and a small signal attrib-
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Hazin and Gates
5
Fig. 2. Molecular structure of the salt (S)–[1=]–⌬–[2]·1.73 THF·0.27·Et2O. For clarity, one enantiomer of the cation [1=]+ and one enantiomer of
the anion [2]– are shown. Solvents of crystallization (1.73×THF and 0.27× Et2O) and hydrogen atoms are omitted for clarity. Ellipsoids are
drawn at the 50% probability level. Selected bond lengths (Å): P(1)–C(1) = 1.795(1); P(1)–C(12) = 1.795(1); P(1)–C(36) = 1.807(1); P(1)–C(13) = 1.797(1);
P(2)–C(49) = 1.925(1); P(2)–C(61) = 1.933(1); P(2)–C(72) = 1.926(1). Selected bond angles (°): C(1)–P(1)–C(12) = 94.0(1); C(36)–P(1)–C(13) = 121.1(5); C(12)–
P(1)–C(36) = 109.6(6); C(49)–P(2)–C(72) = 178.2(5); C(60)–P(2)–C(61) = 89.7(5). [Colour online.]
Chart 3. Spiro-compound [P(C12H8)(C24H16)][P(C12H8)3], [1=][2].
Fig. 3. Molecular structure of 3. Ellipsoids are drawn at the 50%
probability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths (Å): P(1)–C(1) = 1.868(4); P(1)–C(12) = 1.925(4); P(1)–C(13) =
1.861(4); P(1)–C(24) = 1.909(4); P(1)–C(25) = 1.874(4). Selected bond
angles (°): C(1)–P(1)–C(12) = 86.1(2); C(1)–P(1)–C(13) = 108.7(1); C(13)–P(1)–
C(24) = 86.7(1); C(13)–P(1)–C(25) = 130.6(1); C(25)–P(2)–C(24) = 90(1).
[Colour online.]
insoluble. The coupling reaction of phosphorus(V) compounds
with lithiated aryl or Grignard reagents (PhMgBr) is favoured. For
example, the reaction of EtP(=O)(OEt)2 with 2PhMgBr in THF at
68 °C gives substituted phosphonates Ph2P(=O)OEt, PhP(=O)(OEt)2,
(EtO)2P(=O)OEt, EtP(=O)(OEt)2, and (EtO)3P(=O),68 as well as the
coupling of ((C6H5)O)POCl2 with PhMgBr to afford (C6H5)3P=O.69
In another instance, (biphenyl)(Ph)P(=N–Ts) reacts with 2,2=-
dilithiated biphenyl to give P(biphenyl)2(Ph).56 The spirophos-
phorane (Ph(C(CF3)2O)2)P–H reacts with RLi (R = Me, n-Bu, t–Bu,
aryl) to yield (Ph(C(CF3)2O)2)P–R.70
Conclusion
We have explored several potential routes to afford Hellwin-
kel’s salt [1][2]. In addition to the desired compound, we have
isolated a novel complex cation incorporating an alternative cat-
ion [1=]+ with the formulation [P(C12H8)3]+ that is formally derived
from the insertion of an additional biphenyl unit into [1]+ and the
phosphorus(V) containing weakly coordinating anion [2]–. This
new “twist” on Hellwinkel’s salt was characterized by means of
mass spectrometry, 31P{1H} NMR spectroscopy, and X-ray crystal-
lography. Additionally, we were able to isolate and characterize
the neutral species 3 by X-ray crystallography and 31P{1H} NMR
spectroscopy.
Scientific) was deoxygenated with nitrogen and dried by passing
through a column containing activated alumina, dried over cal-
cium hydride, distilled, and freeze–pump–thaw (×3) degassed prior
to use and stored over molecular sieves prior to use. THF (Fisher
Scientific) was dried and distilled over benzophenone ketyl prior
to use. Phosphorus pentachloride (Sigma Aldrich) was sublimed
prior to use. 2,2=-Dibromobiphenyl71 was prepared following lit-
erature procedure. 2,2=-Diiodobiphenyl was prepared following
the analogous 2,2=-dibromobiphenyl procedure. Mass spectrometry
Experimental
General procedures
All experiments were performed using standard Schlenk or
glove box techniques under nitrogen atmosphere. Et2O (Fisher
Published by NRC Research Press

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6
Can. J. Chem. Vol. 00, 0000
Chart 4. Penta-coordinated phosphorane 3, P(C12H8)2(C12H9).
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. X-ray crys-
tallography data were collected on a Bruker X8 APEX II diffractom-
eter with graphite-monochromated Mo K␣ radiation. A single
crystal was immersed in oil and mounted on a glass fiber. Data
were collected and integrated using the Bruker SAINT72 software
package and corrected for absorption effect using SADABS.73 All
structures were solved by direct methods and subsequent Fourier
difference techniques. Unless noted, all nonhydrogen atoms were
refined anisotropically, whereas all hydrogen atoms were in-
cluded in calculated positions but not refined. All refinements
were performed using the SHELXL-201474 via the Olex2 inter-
face.75 [1=][2] co-crystallizes with 0.27 diethyl ether and 1.73 THF
solvate molecules.
Synthesis of [P(C12H8)(C24H16)]+ ([1=]+), [P(C12H8)2]+ ([1]+),
[P(C12H8)3]– ([2]–), and [P(C12H8)2(C12H9)] (3)
Route A
To a solution of biphenyl (4.73 g, 30.7 mmol) in TMEDA (11.0 mL,
8.60 g, 74.0 mmol) was added n-BuLi (46 mL, 74.0 mmol, 1.6 mol/L
in n-hexane). The bright orange solution was stirred at ambient
temperature under N2 atmosphere for 3 d. The reaction mixture
was cooled to –20 °C to obtain yellow crystals. The supernatant
was removed by cannula filtration and the residue washed with
THF (20 mL). Subsequently, a solution of PCl5 (2.51 g, 12.0 mmol)
in THF/Et2O (40 mL/6 mL) was slowly added at –78 °C. Upon addi-
tion, a light brown precipitate was obtained and the mixture
stirred overnight. The supernatant was removed via cannula fil-
tration and the precipitate was washed with diethyl ether (30 mL),
filtered, and dried under vacuo. A beige powder was isolated
(2.41 g), which was later shown to contain [1][2], [1=][2], and 3.
31P{1H} NMR (121 MHz, THF/Et2O, 25 °C): ␦ = 30.6, 25.8, –184.7;
HRMS (ESI/TOF, positive mode) m/z = [M]+ Calcd for C24H16P1
335.0990; Found 335.0987 and [M]+ Calcd for C36H24P1 487.1616;
Found 487.1620; LRMS (ESI, negative mode) m/z = 487.1 ([M]–).
Fig. 4. 31P{1H} NMR (121 MHz, 25 °C) spectrum of [1][2] and [1=][2] via
(a) dilithiated 2,2=-diiodobiphenyl recorded in THF/Et2O solution
(Route B) and (b) dilithiated 2,2=-dibromobiphenyl recorded in THF/
Et2O solution (Route C).
Route B
To a solution of 2,2=-diiodobiphenyl (1.01 g, 2.50 mol) in Et2O
(20 mL) was added n-BuLi (3.42 mL, 5.25 mol, 1.53 mol/L in n-hexane)
at 0 °C. The reaction mixture was stirred for 4 h at 0 °C and cooled
down to –78 °C for an additional 1 h, followed by the addition of a
PCl5 (0.17 g, 0.83 mmol) solution in Et2O (17 mL) at –78 °C to afford
a light brown precipitate. The reaction mixture was allowed to
warm up to ambient temperature overnight and extracted with
degassed H2O (7 mL). The precipitate was cannula filtered, washed
with Et2O, and dried under vacuo. A beige powder was isolated
(0.66 g), which contains [1][2] and [1=][2].
31P{1H} NMR (121 MHz, THF/Et2O, 25 °C): ␦ = 29.8, 26.8, –183.8;
((CD3)2NCOD) ␦ = 31.9, 27.0, –183.4; 1H NMR (400 MHz, (CD3)2NCOD,
25 °C): ␦ = 8.69 (m, 1H, Ar-H), 8.22 (m, 1H, Ar-H), 7.99 (m, 2H, Ar-H),
7.88 (m, 1H, Ar-H), 7.81 (m, 1H, Ar-H), 7.74 (m, 1H, Ar-H), 7.66 (m, 1H,
Ar-H), 7.57 (m, 2H, Ar-H), 7.37 (m, 1H, Ar-H), 7.21 (m, 2H, Ar-H), 7.01
(m, 1H, Ar-H), 6.82 (m, 1H, Ar-H), 6.70 (m, 1H, Ar-H).
Route C
and NMR spectra were performed in the facilities of the University of
British Columbia. Low resolution electrospray ionization mass spec-
tra, LRMS (ESI), were recorded on Bruker Esquire LC. High resolution
electrospray ionization mass spectra, HRMS (ESI), were recorded on
Micromass LCT time of flight (TOF) mass spectrometer. 1H, 13C{1H},
and 31P{1H} NMR spectra were recorded on Bruker Avance 400 MHz
spectrometers at ambient temperature. H3PO4 (85%) was used as ex-
ternal standard for 31P NMR spectra with ␦ = 0.0. 1H NMR and 13C{1H}
NMR spectra were referenced to deuterated solvents.
2,2=-Dibromobiphenyl (0.73 g, 2.35 mol) was dissolved in 11 mL
anhydrous Et2O. The colourless mixture was cooled at 0 °C, fol-
lowed by the slow addition of n-BuLi (2.9 mL, 4.70 mol, 1.6 mol/L in
n-hexane). The reaction mixture was stirred for 4 h at 0 °C. PCl5
(0.12 g, 0.59 mol) was added at –78 °C and stirred overnight to
afford a light brown precipitate. The precipitate was extracted
with H2O (20 mL), cannula filtered, and dried under vacuo. A beige
powder was isolated (0.64 g), which contains [1][2] and [1=][2].
31P{1H} NMR (121 MHz, THF/Et2O, 25 °C): ␦ = 32.6, 24.4, –183.8.
X-ray structure determination
Synthesis of [P(C12H8)(C24H16)][P(C12H8)3] ([1=][2])
CCDC-1573489 ([1=][2]) and CCDC-1573488 (3) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
To a stirred solution of 2,2=-dibromobiphenyl (0.57 g, 1.83 mol)
in diethyl ether (20 mL) at 0 °C was slowly added n-BuLi (2.30 mL,
3.70 mol, 1.6 mol/L in n-hexane). The pale yellow solution was
Published by NRC Research Press

Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
Hazin and Gates
7
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stirred for 4 h at 0 °C. To the reaction mixture was added a sus-
pension of the solid from Route A described above (1.00 g,
0.56 mol) in THF (20 mL). Upon addition, an off-yellow precipitate
was obtained. The reaction mixture was stirred overnight at am-
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which contains [1=][2] and minor [1][2]. A concentrated solution of
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31P{1H} NMR (121 MHz, THF/Et2O, 25 °C): ␦ = 35.2, –184.4; HRMS
(ESI/TOF, positive mode) m/z = [M]+ Calcd for C36H24P1 487.1616;
Found 487.1615 and LRMS (ESI, negative mode) m/z = 487.1 ([M]–).
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A portion of the mixture from Route A described above (0.177 g)
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remove insoluble material. Within 3 weeks, colourless crystals
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31P{1H} NMR (121 MHz, THF/Et2O, 25 °C): ␦ = –86.2.
Acknowledgements
The authors are grateful to the Natural Sciences and Engineer-
ing Counsel (NSERC) of Canada for financial support of this work.
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