Synthesis of 1,2-Diphospholides Using a Main Group superbase

Article abstract of DOI:10.1021/acs.organomet.8b00480

The synthesis of a range of 1,2-diphospholides can be achieved by a one-pot procedure involving the reactions of aromatic primary phosphines bearing ortho-CH₂ substituents with the superbase mixture of ⁿBuLi/Sb(NMe₂)₃ in the presence of the Lewis base donor TMEDA (Me₂NCH₂CH₂NMe₂). The synthesis of the parent benzo-1,2-diphospholide and the substituted derivatives 4-methoxybenzo-1,2-diphospholide, 9-methylbenzo-1,2-diphospholide, and naphtho-1,2-diphospholide are reported from readily prepared primary phosphines. Bulk synthesis of the potassium salt of the previously reported 4,6-dimethylbenzo-1,2-diphospholide anion using this route provides a convenient starting material for reactivity studies.

Full text of DOI:10.1021/acs.organomet.8b00480

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Synthesis of 1,2-Diphospholides Using a Main Group “Superbase”
Lily S. H. Dixon,† Schirin Hanf,†,‡ Jessica E. Waters,† Andrew D. Bond,† and Dominic S. Wright*,†
†Chemistry Department, Cambridge University, Lensfield Road, Cambridge CB2 1EW, United Kingdom
‡
̈
̈
̈
Fakultat fur Chemie und Mineralogie, University of Leipzig, Johannisallee 29, D-04103 Leipzig, Germany
S
* Supporting Information
ABSTRACT: The synthesis of a range of 1,2-diphospholides can be achieved by a
one-pot procedure involving the reactions of aromatic primary phosphines bearing
ortho-CH2 substituents with the superbase mixture of nBuLi/Sb(NMe2)3 in the
presence of the Lewis base donor TMEDA (Me2NCH2CH2NMe2). The synthesis of
the parent benzo-1,2-diphospholide and the substituted derivatives 4-methoxybenzo-
1,2-diphospholide, 9-methylbenzo-1,2-diphospholide, and naphtho-1,2-diphospholide
are reported from readily prepared primary phosphines. Bulk synthesis of the potassium salt of the previously reported 4,6-
dimethylbenzo-1,2-diphospholide anion using this route provides a convenient starting material for reactivity studies.
diphospholides had been reported (Scheme 1).7,8 Both routes
INTRODUCTION
■
make use of uncommon and challenging-to-synthesize starting
materials, and require the isolation and purification of
intermediates. Furthermore, the highly specific starting
materials used in each synthesis preclude the possibility of
generating species isoelectronic with the indenyl anion.
The ability to tune phosphorus-based compounds by varying
the electronic and steric properties of the substituents has
made phosphines and related ligands ubiquitous throughout
transition metal chemistry.1 Phosphorus-containing analogues
of classically carbon-based frameworks have played an
invaluable role in this field.2 However, development of a
more comprehensive library of these types of ligands is often
limited by convoluted syntheses as well as a lack of generality
of the synthetic methods employed.3
Recently, the synthesis of the 4,6-dimethyl-substituted
diphospholide anion (1) (Figure 1c) was reported con-
currently by the Hey-Hawkins group9 and us,10 using two
different synthetic approaches. Our approach, which involves
the one-pot reaction of MesPH2 (Mes = 2,4,6-trimethylphen-
yl) with the redox-active superbase mixture nBuLi/Sb(NMe2)3,
involves the in situ generation of the tetraphosphane-1,4-diide
The indenyl ligand (Figure 1a) has had an important role in
various aspects of organometallic chemistry.4 The vast increase
2−
[MesP]4 which then ring-closes by a combination of ortho-
Me deprotonation and oxidation (Scheme 2a). This pathway is
related to the Hey-Hawkins route but with the advantage that
it does not require the availability of the aryl-substituted
tetraphosphane-1,4-diide as a starting material (Scheme 2b), a
factor which is likely to limit the synthetic scope.9
Figure 1. Structures of the indenyl (a), indazolide (b), and 4,6-
dimethylbenzo-1,2-diphospholide (c) anions.
In this paper we explore the generality of our one-pot
approach to 1,2-diphospholides, starting from readily prepared
primary phosphines containing ortho-CH2 functionality. DFT
calculations are used to compare the electronic structures of
the series of new 1,2-diphospholides obtained with the valence-
isoelectronic indenyl anion.
in the rate of ligand substitution for indenyl complexes relative
to cyclopentadienyl complexes has potentially important
implications for transition metal catalysis.5 In contrast, η-
coordination of group 15 analogues of indenyl, such as the
nitrogen ligand N-indazolide (Figure 1b) is rare, and this effect
has not yet been exploited in this area.6 General synthetic
access to phosphorus counterparts of indenyl would allow
investigation of the reactivity of their transition metal
complexes, both in terms of kinetics, and accessible bonding
modes. The inclusion of one or more phosphorus atoms into
the indenyl framework also introduces the possibility of bis-
coordination of the phosphorus atom through the π-system as
well as the lone pair, providing increased functionality relative
to all-carbon analogues.
RESULTS AND DISCUSSION
■
While the synthesis of the anion 1 (Figure 1c) was an
important first step, our primary aim in the current work was
to develop a general method for the synthesis of a range of
benzannulated-1,2-diphospholides which could act as ligands
in organometallic chemistry. By applying the same method-
Special Issue: Organometallic Complexes of Electropositive Ele-
ments for Selective Synthesis
Despite the thorough investigations carried out by many
groups globally, the 1,2-diphospholides remain under-repre-
sented in the literature due to their challenging syntheses.7,8
Indeed, until recently only two synthetic routes to 1,2-
Received: July 10, 2018
© XXXX American Chemical Society
A
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a
Scheme 1. Previously Reported Syntheses 1,2-Diphospholides
a
(a) Mathey (R = Ph, Et)7 and (b) Hey-Hawkins.8
commercially available. However, we have found that the
simple one-pot route developed by Vedejs et al. is particularly
useful in this respect (see Scheme 4 and the Experimental
Section).11
Scheme 2. Previously Reported Syntheses of the (4,6-
Dimethylbenzo)-1,2-diphosphlide Anion (1)
a
a
Scheme 4. General Synthesis for Primary Arylphosphines
a
TMEDA = Me2NCH2CH2NMe2.
a
R = R′ = Me, R′′ = H; R = R′ = R′′ = H; R = OMe, R′ = H, R′′ = H;
R = R′ = H, R′′ = Me. THF solvent. (1) Addition at −78 °C, stirring
at −78 °C for 2 h. (2) Addition of THF solution at −78 °C, stirring at
−78 °C for 3 h. (3) Slow addition of reagent solution to a THF
solution of PCl3 at −78 °C then slow warming to rt overnight with
stirring. Slow addition of reagent solution to a slurry of LiAlH4 at 0 °C
followed by slow warming to rt with stirring.
ology used in the synthesis of 1, we have been able to access
the unsubstituted benzo-1,2-diphospholide (2), the 4-me-
thoxy-substituted analogue (3), and 9-methylbenzo-1,2-
diphospholide (4). The synthesis of compounds 2−4 was
achieved according to Scheme 3 (see the Experimental
Section). Our previous studies of 1, showed that this reaction
involving C−H activation of the o-CH2 groups occurs via a
series of oligo-phosphorus intermediates.10
Combining the ease of access to the phosphine starting
materials with their facile transformation to the corresponding
benzo-1,2-diphospholides provides a simple two-step approach
from commercially available aryl bromides. The primary
phosphine precursors in the current study (Scheme 4) were
selected in order to allow the incorporation of substituents
within the C6- and C3P2-ring units of the benzo-1,2-
diphospholide anions. Since the reactions occur under highly
nucleophilic conditions, the incorporation of highly electro-
philic substituents (such as CO or CN) was not
considered.
One potential drawback of our synthetic approach is the fact
that the primary phosphine starting materials are not
a
Scheme 3. General Synthesis for Benzo-1,2-diphospholides
Anions 2−4 can be isolated as their [Li(TMEDA)2]+ salts as
powders after filtration and washing with n-pentane. All of the
1
isolated products show clean H, 31P, and 13C{1H} NMR
spectra and high-resolution negative-ion mass spectrometry
was able to identify the phospholide anions in the case of 2 and
3 (within 0.0014−0.0037 mass units of the theoretical).
However, satisfactory elemental analysis could not be obtained
on any of the solid salts, as a result of the presence of variable
amounts of finely divided Sb metal and/or Sb Zintl
compounds which proved to be impossible to remove fully.
1
We estimate on the basis of elemental analysis and H NMR
integration that the percentage of impurities in 2−4 range from
ca. 5% to 20%, from batch to batch. Our previous work on the
3−
a
mechanism of formation of anion 1 showed that the Sb7
1: R = R′ = Me, R′′ = H, 2: R = R′ = R′′ = H, 3: R = OMe, R′ = H,
Zintl ion is formed concurrently with the diphospholide.10 The
similar solubilities of the diphospholide salts and the antimony
Zintl compound formed in the reaction (most likely
R′′ = H, 4: R = R′ = H, R′′ = Me. Toluene solvent. (1) Addition at
−78 °C then stirred at rt for 1 h. (2) Addition at −78 °C, warmed to
rt then heated under reflux for 2 h.
B
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Li(TMEDA)2]3{Sb7])3−10 meant that washing and fractional
crystallization were ineffective methods of purification.
As part of our studies, we also explored the effect on the
reaction of changing the alkali metal counterion. This
development is important because the presence of a heavier
alkali metal counterion (e.g., Na+, K+, vs Li+) should provide a
greater driving force for metathesis reactions of the 1,2-
diphospholides with a range of transition and main group
metals. The reaction of MesPH2 with KH in the presence of
the Lewis base donor PMDETA [(Me2CH2CH2)2NMe]
followed by reaction with Sb(NMe2)3 at reflux gave
[K(PMEDTA)][1] in 44% yield. This salt was reported
previously by Hey-Hawkins using the reaction of MesPCl2 with
K metal but only in 20% yield.9
change in chemical shift of the phosphorus atom that formally
bears the negative charge in anion 4 (P1, δ = 117.3 ppm)
relative to the anions with unsubstituted 5-membered rings
(P1, δ = 133.4−147.1 ppm) demonstrates the way in which
substitution of the 5-membered ring influences the properties
of the benzo-1,2-diphospholides.
Further confirmation of the formation of the phospholides
comes from the structural characterization of the salts
[Li(TMEDA)2][2] and [Li(12-crown-4)2][4] by single-crystal
X-ray diffraction (see the Experimental Section). Despite
repeated attempts, no X-ray-quality crystals containing
methoxy-substituted anion 3 could be obtained. The [Li-
(TMEDA)2]+ salt of 2 was crystallized from a mixture of
toluene and THF at room temperature. The structure of
[Li(TMEDA)2][2] is ion separated, with two independent
benzo-1,2-diphospholide anions (2), both being disordered
over two orientations in an approximate 90:10 ratio. The major
orientation of one of the anions is shown in Figure 3.
NMR spectroscopic analysis proved to be a powerful tool for
the identification and characterization of the benzo-1,2-
diphospholides. Figure 2 shows the 1,2-diphospholide region
Figure 3. Ortep drawing of the molecular structure of the anion 2.
Displacement ellipsoids with 40% probability at 180(2) K. [Li-
(TMEDA)2]+ counterion, hydrogen atoms, and molecular disorder
have been omitted for clarity. Selected bond lengths and angles are
listed in Table 2.
The [Li(12-crown-4)2]+ salt of 4 was obtained by using 12-
crown-4 in place of TMEDA in the reaction of Scheme 3.
[Li(12-crown-4)2][4] was crystallized by storage of a THF/
toluene solution at room temperature, allowing the 9-
methylbenzo-1,2-diphospholide (4) to be structurally charac-
terized (Figure 4). Comparison of the structural parameters for
Figure 2. 31P{1H} NMR spectra of the [Li(TMEDA)2] salts of the
anions (from bottom to top) 1−4. THF solvent, 298 K. See Scheme 3
for structural formulas.
of the 31P{1H} NMR spectrum of the [Li(TMEDA)2]+ salts of
1−4. A summary of the 31P chemical shifts and coupling
constants of each of the anions is shown in Table 1.
The downfield shifts witnessed for these compounds
indicate both multiple bond character and delocalization
about the 5-membered ring. Further confirmation of the P−P
1
multiple bond character is provided by the large JPP coupling
Figure 4. Ortep drawing of the molecular structure of the anion 4.
Displacement ellipsoids with 40% probability at 180(2) K. [Li(12-
crown-4)2]+ counterion and hydrogen atoms have been omitted for
clarity. Selected bond lengths and angles are listed in Table 2.
constants in each of the anions (448−457 Hz). The significant
1
Table 1. 31P NMR Chemical Shifts and JPP Coupling
a
Constants for the Anions 1−4
previously reported anion 110 with new anions 2 and 4 shows
that the bond lengths and angles within their five-membered
C3P2 ring units are nearly identical within the crystallographic
errors (Table 2).
The delocalization of the negative charge within the C3P2
ring units of 1, 2, and 4 is evident from the planarity of the
rings as well as from bond length analysis. The phosphorus−
anion
chemical shift (P2, P1, δ ppm)
1JPP (Hz)
1
2
3
4
222.5, 133.4
230.3, 144.3
233.6, 147.1
229.7, 117.3
449
452
457
448
a
Chemical shifts relative to 85% H3PO4 in D2O (298 K).
C
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nBuLi/As(NMe2)3 with MesPH2 gives the arsenic−phosphorus
heterocycle 4,6-dimethylbenzo-1-arsa-2-phospholide, an ar-
senic analogue of antimony heterocycle 6.10 The NMR
spectroscopic characteristics of the [Li(TMEDA)2]+ salt of
the arsenic anion are similar to 6, displaying a singlet resonance
at δ = 175.7 ppm in the 31P NMR spectrum and a singlet at δ =
9.01 in the 1H NMR spectrum, for the C−H of the 5-
membered ring. The proposed mechanism of formation of 6 is
shown in Scheme 6. The observed formation of 6 is likely to
arise from the greater steric congestion around the phosphine
group, allowing competition between intramolecular cycliza-
tion and the formation of the tetraphosphane-1,4-diide (which
is responsible for the formation of the 1,2-phospholide).
Optimized geometries and frontier molecular orbitals of the
anions were calculated using DFT methods.15 The optimized
structures were obtained employing the B3LYP functional14 in
conjunction with a cc-pVTZ basis set (Supporting Informa-
tion, section 2).15 Comparison of the HOMOs and LUMOs
across the series of diphospholides synthesized shows that the
electronic distributions in the indenyl and 1,2-disphospholide
anions are similar (Figure 6). Overall, the results are similar to
the previously reported DFT calculations on 1,9,10 with
substituents on the C6- and C3P2-rings having little effect,
apart from that on the LUMO of 5 in which the electron
density is distributed toward the second C6-ring unit.
Qualitative analysis of the calculated iso-surfaces shows a
larger coefficient at the P1 atoms in the HOMO of the
benzodiphospholides relative to the (corresponding) C1 atom
of the indenyl anion. These data suggest that this series of
benzo-1,2-diphospholides would react with electrophiles at P1.
This is also suggested by natural population analysis, in which
the charges on P1 (i.e., bonded to the arene ring) are all
marginally negative (−0.01−0.05e) and the charges on P2 are
positive (ca. +0.1e). In contrast, all of the corresponding C
atoms of the 5-membered ring in the indenyl anion have
significant negative charges. The HOMO−LUMO gaps,
obtained from single-point calculations, are significantly
smaller in the 1,2-diphospholides compared to those in the
indenyl anion (by ca. 0.5−0.7 eV in 1−5), with the MeO-
substitution in 3 and the Me-substitution in 4 decreasing the
HOMO−LUMO gaps by ca. 0.15 eV compared to those of 1,
2, and 5.
Table 2. Selected Bond Lengths (Å) and Angles (deg) from
the Solid State Structures of Anions 1, 2, and 4
anion 2 (average
anion 1 (average
over three
independent anions)
over two
independent
anions)
anion 4
P1−P2
P2−C1
P1−C3
C1−C2
C3−P1−P2
C1−P2−P1
C2−C1−P2
2.119
1.703
1.792
1.417
93.1
2.106
1.719
1.788
1.393
94.0
2.111(4)
1.754(10)
1.791(9)
1.430(13)
92.4(3)
96.1
118.2
96.3
116.4
98.0(4)
114.1(8)
carbon bond lengths of 1.688(13)−1.800(3) Å and the
phosphorus−phosphorus bond lengths of 2.1029(15)−
2.121(3) Å are shorter than expected for the corresponding
single bonds (ca. 1.85 Å for P−C12 and ca. 2.21 Å for P−P).13
The observed P−C and P−P bond lengths are also similar to
those reported for other aromatic phosphorus-containing
heterocycles (P−C ca. 1.74−1.77 Å and P−P 2.11 Å in
3
−
cyclo-P5 ). Also worth noting is the significant deviation from
the ideal 120° angle expected for sp2 hydridization at the
phosphorus centers. The observed range of 90.1(2)−98.7(4)°
is far closer to the 90° angle expected for an unhybridized
atom, suggesting that the associated nonbonding lone pair of
each phosphorus atom is held in an orbital with high s-
character.
In further synthetic studies, we attempted to extend our
methodology to other polyaromatic backbones. The primary
phosphine 1-phosphino-2-methylnaphthalene was prepared
according to the procedure outlined in Scheme 4 (see the
Experimental Section). Reaction of this phosphine with nBuLi/
Sb(NMe2)3 in the presence of TMEDA (Scheme 5), however,
Scheme 5. Synthesis of the Naphtha-1,2-diphospholide (5)
a
and Naphtha-1-stiba-2-phospholide (6) Anions
CONCLUSIONS
a
The [Li(TMEDA)2]+ counterions are not included. The ratio of 5/6
■
is ca. 1.5:1 from integration of the 31P NMR spectrum. Reaction
conditions: toluene/THF solvent mixture, reflux 2.5 h.
We have shown that a range of new benzo-1,2-diphospholides
can be synthesized directly from readily synthesized aromatic
primary phosphines. Our approach has allowed the synthesis of
parent (unsubstituted) phospholide 2 as well as frameworks
containing substituents on the C6 and C3P2 ring units. One
drawback of our synthetic approach (at least at first sight) is
the presence of antimony metal and/or antimony Zintl ions as
contaminants. However, all of the isolated products show no
phosphorus-, carbon-, or hydrogen-based impurities and
should be useful ligand-transfer reagents for the future
development of organometallic chemistry in this area. The
HOMOs and LUMOs of the 1,2-diphospholide anions are
similar to those of the valence-isoelectronic indenyl anion, but
with smaller HOMO−LUMO gaps. The HOMO−LUMO gap
shows a marked dependence on the presence of electron-
donating groups; strongly electron-donating groups on the C6-
ring unit or electron-donating groups on the C atom of the
C3P2 unit result in decreased HOMO−LUMO separation.
This observation may provide the basis for tuning the donor−
produced a mixture of two products. The 31P NMR spectrum
of the solid product isolated from the reaction showed the
presence of a doublet at δ = 152.1 ppm (1JPP = 455 Hz) and a
double doublet at δ 212.6 ppm (1JPP = 455 Hz, 2JPH = 38 Hz),
confirming the formation of desired phospholide anion 5.
However, a singlet at δ = 218.5 ppm was also observed (Figure
1
5). The downfield shift as well as the absence of any JPP or
2JPH coupling is strongly indicative of the formation of
antimony-containing naphtha-1-stiba-2-phospholide anion 6
(Scheme 4).
1
The identity of 6 is further supported by H NMR and
1H−31P HMBC spectroscopic studies, which show that the
3
proton resonance at δ = 10.30 (d, JPH = 3.5 Hz) can be
assigned to the C−H of the 5-membered ring of 6. In our
previously published work we showed that the reaction of
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Figure 5. 31P NMR spectrum of Li(TMEDA)2 salts of 5 and 6, THF solvent. See Scheme 5 for structural formulas.
Sb(NMe2)3/nBuLi under the same conditions as those used
for 1−5 gives an intractable mixture of products.
Scheme 6. Proposed Mechanism for the Formation of the
Phosphorus−Antimony Heterocycle Anion 6
EXPERIMENTAL SECTION
■
General Experimental Techniques. All reactions were carried
out at room temperature under dry, oxygen-free nitrogen using
standard Schlenk and glovebox techniques and dry and degassed
solvents. All solvents were collected freshly distilled over sodium
wire/benzophenone (THF, diethyl ether), sodium metal (toluene), or
sodium wire (n-hexane, n-pentane); TMEDA and PMDETA were
distilled under nitrogen from CaH2 and stored over 4 Å molecular
sieves under nitrogen. Deuterated NMR solvents were degassed and
dried over 4 Å molecular sieves. All other reagents were used as
received. Ice/water cooling baths were used to obtain a temperature
of 0 °C, ice/acetone baths were used to obtain a temperature of −10
°C, and dry ice/acetone baths were used to obtain a temperature of
−78 °C.
Synthesis of Primary Phosphines. A solution of the appropriate
aryl bromide (50 mmol) in THF (80 mL) was cooled to −78 °C and
acceptor properties of the 1,2-diphospholide anions for metal
coordination.
As a final note to the current study, we have been unable to
extend this work to the synthesis of the corresponding 1,2-
diarsolides, for example, the reaction of MesAsH2 with
n
treated by slow addition with BuLi (1.6 M in hexane, 35 mL, 56
mmol). The resultant white suspension was stirred at −78 °C for 2 h
before being added via cannula to a solution of ZnCl2 (8.2 g, 60
mmol) in THF (100 mL) at −78 °C. After stirring for 2 h at −78 °C
this solution was added to a solution of PCl3 (5.5 mL, 63 mmol) in
Figure 6. Frontier molecular orbitals of the indenyl anion and anions 2−5 at an isovalue of 0.04. B3LYP functional,14 cc-pVTZ15 basis set.
Calculations were performed using the Gaussian 09 suite.16
E
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THF (100 mL) at −78 °C over the course of 2 h. The resultant
colorless solution was allowed to warm to rt overnight. The crude
solution was added dropwise to a slurry of LiAlH4 (3.8 g, 100 mmol)
in diethyl ether (200 mL) at −10 °C. After addition was complete, the
suspension was allowed to warm to rt slowly overnight. The reaction
was cooled to 0 °C and quenched by dropwise addition of
deoxygenated 4 M aqueous HCl (150 mL). The reaction mixture
was allowed to warm to rt and the organic phase was isolated by
cannula transfer. The aqueous layer was extracted with diethyl ether
(3 × 100 mL). The combined organic extracts were dried over
MgSO4, filtered, and freed from solvent, giving the desired product as
a colorless oil which required no further purification.
3. Yield 30% (assuming pure sample). 1H NMR (400.1 MHz,
THF-d8, 25 °C) δ 2.15 (s, 24H, TMEDA, CH3), 2.30 (s, 8H,
3
TMEDA, CH2), 3.71 (s, 3H, OCH3), 6.25 (d, 1H, JHH = 8.5 Hz,
aromatic CH), 7.06 (bs, 1H, aromatic CH), 7.69 (dd, 1H, 3JHH = 8.5
Hz, 6.0 Hz, aromatic CH), 7.70 (d, 2JPH = 39.0 Hz, PCH). 31P NMR
(162.0 MHz, THF-d8, 25 °C) δ 147.1 (d, 1P, 1JPP = 457 Hz, PPCH),
1
2
233.7 (dd, 1P, JPP = 457 Hz, JPH = 39 Hz, PPCH). 13C{1H} NMR
(100.6 MHz, THF-d8, 25 °C) δ 46.2 (s, TMEDA, CH3), 54.9 (s,
3
OCH3), 58.4 (s, TMEDA, CH2), 102.3 (dd, JPC = 9 Hz, aromatic),
3
4
2
106.6 (dd, JPC = 15 Hz, JPC = 2 Hz, aromatic), 129.4 (d, JPC = 26
2
3
Hz, aromatic), 136.1 (dd, JPC = 25.5 Hz, JPC = 4 Hz, aromatic),
138.8 (dd, 1JPC = 58 Hz, 2JPC = 4 Hz, PPCH), 150.9 (dd, 2JPC = 9 Hz,
3JPC = 4 Hz, aromatic), 154.4 (s, aromatic), 155.1 (d, JPC = 58 Hz,
1
1
o-Tolylphosphine. Yield, 40%. H NMR (400.1 MHz, C6D6, 25
°C), δ 2.14 (s, 3H, o-CH3), 3.70 (d, 2H, PH2, 1JPH = 200 Hz), 6.87−
6.92 (m, 2H, aromatic CH), 7.00 (m, 1H, aromatic CH), 7.30 (m,
1H, aromatic CH). 31P NMR (162.0 MHz, C6D6, 25 °C), δ −131.6
aromatic). LR-ESI-MS (negative): m/z 181 (3, 1%), 166 (3 − Me,
20%), 151 (3 − OMe, 100%). HR-ESI-MS (negative): Calcd for
C8H7OP2 (3) m/z = 180.9972. Found m/z = 181.0009.
1
4. Yield 39% (assuming pure sample). 1H NMR (400.1 MHz,
THF-d8, 25 °C) δ 2.15 (s, 24H, TMEDA, CH3), 2.30 (s, 8H,
(t, 1P, PH2, JPH = 200 Hz).
4-Phosphino-3-methylanisole. Yield, 35%. 1H NMR (400.1 MHz,
toluene-d8, 25 °C), δ 2.17 (s, 3H, o-CH3), 3.34 (s, 3H, OCH3), 3.70
TMEDA, CH2), 2.72 (d, 3H, 3JPH = 13 Hz, CH3), 6.52 (t, 1H, 3JHH
=
1
3
7.0 Hz, aromatic CH), 6.73 (dd, 1H, 3JHH = 8.0 Hz, 7.0 Hz, aromatic
(d, 2H, PH2, JPH = 200 Hz), 6.48 (dd, 1H, aromatic CH, JHH = 8
4
3
3
Hz, JPH = 2 Hz), 6.62 (s, 1H, aromatic CH), 7.26 (t, 1H, aromatic
CH), 7.40 (d, 1H, JHH = 8.0 Hz, aromatic CH), 7.80 (t, JHH = 7.0
CH, J = 8 Hz). 31P NMR (162.0 MHz, toluene-d8, 25 °C), δ −135.9
Hz, aromatic CH). 31P NMR (162.0 MHz, THF-d8, 25 °C) δ 117.3
1
(d, 1P, 1JPP = 448 Hz, PPCMe), 222.3 (dq, 1P, 1JPP = 457 Hz, 3JPH
=
(t, 1P, PH2, JPH = 199 Hz).
1
13 Hz, PPCMe). 13C{1H} NMR (100.6 MHz, THF-d8, 25 °C) δ 19.7
1-Phosphino-2-ethylbenzene. Yield, 64%. H NMR (400.1 MHz,
C6D6, 25 °C), δ 1.06 (t, 3H, o-CH2CH3, 3JHH = 7.5 Hz), 2.56 (q, 3H,
(dd, 2JPC = 35 Hz, 3JPC = 32 Hz, CH3), 46.2 (s, TMEDA, CH3), 58.4
o-CH2CH3, 3JHH = 7.5 Hz), 3.77 (d, 2H, PH2, 1JPH = 200 Hz), 6.89 (t,
3
(s, TMEDA, CH2), 114.0 (d, JPC = 16 Hz, aromatic), 117.4 (s,
3
aromatic), 119.0 (d, 2JPC = 10 Hz, aromatic), 129.8 (d, 2JPC = 25 Hz,
1H, aromatic CH, JHH = 7.5 Hz), 6.69 (m, 1H, aromatic CH), 7.06
1
(t, 1H, aromatic CH, J = 8 Hz), 7.31 (t, 1H, aromatic CH), J = 7.5
Hz). 31P NMR (162.0 MHz, C6D6, 25 °C), δ −131.2 (t, 1P, PH2, 1JPH
= 200 Hz).
aromatic), 163.6 (d, JPC = 56 Hz, aromatic). X-ray data, formula
C8H7P2·Li(C8H16O4)2, MW = 524.43, crystal system triclinic, space
̅
group P1, Z = 2, a = 8.4645(4), b = 12.2344(6), c = 14.0658(7) Å, α
1
= 95.494(3), β = 95.576(4), γ = 110.021(3)°, V = 1349.13(12) Å3,
ρcalc = 1.291 Mg m−3, T = 180(2) K, μ(Cu Kα) = 1.835 mm−1, total
reflections 16 339, unique reflections 3241, Rint = 0.082, R1 [I <
2σ(I)] = 0.127, wR2 (all data) = 0.311.
1-Phosphino-2-methylnaphthalene. Yield, 51%. H NMR (400.1
MHz, C6D6, 25 °C), δ 2.31 (s, 3H, o-CH3), 3.86 (d, 2H, PH2, 1JPH
=
3
4
205 Hz), 7.01 (dd, 1H, aromatic CH, JHH = 8.5 Hz, JPH = 2 Hz),
7.22 (m, 1H, aromatic CH), 7.31 (m, 1H, aromatic CH), 7.47 (d, 1H,
3
3
aromatic CH, JHH = 8.5 Hz), 7.59 (d, 1H, aromatic CH, JHH = 8.5
Synthesis of [K(PMDETA)] (1). A suspension of KH (0.126 g, 3.1
mmol) in toluene (18 mL) was treated with PMDETA (0.66 mL, 3.1
mmol) and MesPH2 (0.24 g, 1.6 mmol) at −78 °C. The resulting
mixture was allowed to warm to rt, than heated to reflux for 5 min,
after which a yellow suspension was present. This was allowed to cool
to rt before being cooled to −78 °C and treated with Sb(NMe2)3 (2.0
M solution in toluene, 0.56 mL, 1.1 mmol). After warming to rt, the
reaction was heated under reflux for 3 h. Once at rt, the black
suspension was filtered through glass filter paper, yielding a yellow/
orange solution. This was freed from volatiles under vacuum and
suspended in pentane (10 mL). The resultant yellow precipitate was
isolated by cannula filtration, then washed with pentane (2 × 10 mL)
(0.130 g, 0.33 mmol, 44%). 1H NMR (400 MHz, THF-d8) δ 7.98 (d,
2JPH = 38 Hz, 1H, P(CH)C), 7.38 (s, 1H, C(CH)C), 6.37 (s, 1H,
C(CH)C), 2.63 (s, 3H, CH3), 2.41 (m, 4H, PMDETA CH2), 2.30 (s,
3H, CH3), 2.30 (m, 4H, PMDTA CH2), 2.18 (s, 3H, PMDTA CH3),
2.14 (s, 12H, PMDETA CH3). 31P{1H} NMR (162 MHz, THF-d8) δ
Hz), 8.17 (d, 1H, aromatic CH, JHH = 8.5 Hz). 31P NMR (162.0
3
1
MHz, C6D6, 25 °C), δ −157.6 (t, 1P, PH2, JPH = 205 Hz).
Synthesis of [Li(TMEDA)2] Salts of 2−4. A solution of the
appropriate primary phosphine (0.95 mmol) in toluene (10 mL) was
treated with TMEDA (0.57 mL, 3.8 mmol) and cooled to −78 °C.
n
Treatment with BuLi (1.6 M in hexane, 1.2 mL, 1.9 mmol) and
warming to rt yielded a yellow suspension which was stirred for 1 h.
After cooling again to −78 °C, Sb(NMe2)3 (2.0 M in toluene, 0.24
mL, 0.48 mmol) was added, before allowing the solution to warm to
rt, then heating under reflux for 2 h. The resultant suspension was
allowed to cool to rt before being filtered through glass filter paper.
Solvent was removed from the filtrate, and the residue was vigorously
stirred in n-pentane (10 mL), yielding the desired product as an
impure precipitate.
2. Yield 22% (assuming pure sample). 1H NMR (400.1 MHz,
THF-d8, 25 °C) δ 2.15 (s, 24H, TMEDA, CH3), 2.30 (s, 8H,
TMEDA, CH2), 6.49 (t, 1H, 3JHH = 7.0 Hz, aromatic CH), 6.65 (dd,
1H, 3JHH = 8.0 Hz, 6.5 Hz, aromatic CH), 7.58 (d, 1H, 3JHH = 8.0 Hz,
1
1
223.7 (d, JPP = 447 Hz, 1P, PPCH), 137.7 (d, JPP = 447 Hz, 1P,
PPCH).
3
3
aromatic CH), 7.89 (t, 1H, JHH = 7.0 Hz, JPH = 7.0 Hz, aromatic
Synthesis of [Li(TMEDA)2] Salts of 5 and 6. A solution of 1-
phosphino-2-methylnaphthalene (0.20 g, 1.15 mmol) in toluene (12
mL) and THF (3 mL) was treated with TMEDA (0.69 mL, 4.60
mmol) and cooled to −78 °C. Next, 1.6 M nBuLi in hexane (1.45 mL,
2.30 mmol) was added dropwise to the stirred solution causing the
color to change to bright orange. After stirring for 1 h at rt, the now
deep-red solution was cooled to −78 °C and treated with 2.0 M
Sb(NMe2)3 in toluene (0.30 mL, 0.60 mmol). Once at rt, the brown
solution was heated under reflex for 2.5 h. After cooling to rt, THF (5
mL) was added, and the dark brown solution was filtered through
glass filter paper. The filtrate was freed from volatiles under vacuum,
and the solid residue was stirred with n-pentane (20 mL). Filtration of
this suspension yielded a mixture of the [Li(TMEDA)2] salts of 5 and
6 in a ratio of 2:1 as a brown precipitate.
CH), 7.90 (d, 2JPH = 38.0 Hz, PCH). 31P NMR (162.0 MHz, THF-d8,
25 °C) δ 146.0 (dd, 1P, JPP = 455 Hz, JPH = 7 Hz, PPCH), 222.3
(dd, 1P, 1JPP = 455 Hz, 2JPH = 38 Hz, PPCH). 13C{1H} NMR (100.6
MHz, THF-d8, 25 °C) δ 46.2 (s, TMEDA, CH3), 58.4 (s, TMEDA,
CH2), 114.3 (dd, JPC = 15 Hz, aromatic), 117.9 (d, JPC = 2 Hz,
aromatic), 122.7 (d, JPC = 10.5 Hz, aromatic), 129.3 (d, JPC = 25.5
1
3
3
4
3
2
3
1
2
Hz, JPC = 4 Hz, aromatic), 138.8 (dd, JPC = 57.5 Hz, JPC = 4 Hz,
PPCH), 151.5 (dd, 2JPC = 9 Hz, 3JPC = 4 Hz, aromatic), 162.4 (d, 1JPC
= 60 Hz, aromatic). LR-ESI-MS (negative): m/z 151 (2, 100%). HR-
ESI-MS (negative): Calcd for C7H5P2 (2) m/z = 150.9866. Found m/
z = 150.9852. X-ray data, formula C7H5P2·Li(C6H16N2)2, MW =
390.40, crystal system monoclinic, space group C2/c, Z = 16, a =
32.3894(7), b = 17.6315(4), c = 16.9036(4) Å, β = 103.1995(11)°, V
= 9398.2(4) Å3, ρcalc = 1.104 Mg m−3, T = 180(2) K, μ(Cu Kα) =
1
Spectral Data for [Li(TMEDA)2][5]. H NMR (400.1 MHz, THF-
1.735 mm−1, total reflections 35 584, unique reflections 8792, Rint
0.046, R1 [I < 2σ(I)] = 0.072, wR2 (all data) = 0.218.
=
d8, 25 °C) δ 2.15 (s, 24H, TMEDA CH3), 2.30 (s, 8H, TMEDA,
3
CH2), 6.95 (d, 1H, JHH = 8.5 Hz, aromatic CH), 7.00 (m, 1H,
F
DOI: 10.1021/acs.organomet.8b00480
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
aromatic CH), 7.10 (m, 1H, aromatic CH), 7.48 (d, 1H, JHH = 8.0
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Hz, aromatic CH), 7.62 (d, JHH = 8.5 Hz, aromatic CH), 8.01 (d,
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aromatic CH). 31P NMR (162.0 MHz, THF-d8, 25 °C) δ 152.1 (d,
1
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1
Spectral Data for [Li(TMEDA)2][6]. H NMR (400.1 MHz, THF-
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3
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3
127.3 (d, JPC = 30 Hz, aromatic), 127.7 (s, aromatic), 128.5
(aromatic), 159.3 (aromatic), 162.5 (PSbCH).
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00480.
General experimental techniques, 1H and 31P NMR
spectroscopic characterization, computational details, X-
ray single-crystal analysis of [Li(TMEDA)2][2] and
[Li(18-crown-6)2][4] (DOCX)
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1,2-Diphospholide Ions. Angew. Chem., Int. Ed. Engl. 1995, 34, 590.
Accession Codes
CCDC 1852044−1852045 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
̈
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AUTHOR INFORMATION
Corresponding Author
*E-mail dsw1000@cam.ac.uk.
ORCID
Andrew D. Bond: 0000-0002-1744-0489
Dominic S. Wright: 0000-0002-9952-3877
Funding
The Cambridge Commonwealth European and International
Trust and Gonville and Caius College Cambridge (L.S.H.D.),
the Studienstiftung des deutschen Volkes, Fonds of the
Chemical Industry (S.H.) and Selwyn College Cambridge
(Walters-Kundert Studentship, J.E.W.).
■
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Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
We acknowledge the use of the EPSRC UK National Service
for Computational Chemistry Software (NSCCS) at Imperial
College London and contributions from its staff in carrying out
this work. We dedicate this paper to Prof. Dietmar Stalke on
the occasion of his 60th birthday.
G
DOI: 10.1021/acs.organomet.8b00480
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DOI: 10.1021/acs.organomet.8b00480
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