Reactivity vs. Stability of Cyclopropenium Substituted Phosphonium Salts

Article abstract of DOI:10.1002/ejic.201900867

The stability vs. reactivity of electrophilic 3-(triphenylphosphonio)-cyclopropenium salts towards a neutral nucleophile, such as triphenylphosphane, is reported. Depending on the nature of cyclopropenyl substituents (R), the three-membered cyclic structure is preserved (R = Ph) or evolves by ring opening to the isomeric linear allene (R = Mes). The respective formation of 1,3-bis(triphenylphosphonio)-2,3-diphenylcyclopropene and 3,3-bis(triphenylphosphonio)-1,1-dimesitylallene products is rationalized on the basis of steric and electrostatic constraints.

Full text of DOI:10.1002/ejic.201900867

DOI: 10.1002/ejic.201900867
Full Paper
P-Based Cyclopropenium Cations | Very Important Paper |
Reactivity vs. Stability of Cyclopropenium Substituted
Phosphonium Salts
Rachid Taakili,[a] Carine Duhayon,[a] Noël Lugan,[a] and Yves Canac*[a]
Abstract: The stability vs. reactivity of electrophilic 3-(triphen- opening to the isomeric linear allene (R = Mes). The respective
ylphosphonio)-cyclopropenium salts towards a neutral nucleo- formation of 1,3-bis(triphenylphosphonio)-2,3-diphenylcyclo-
phile, such as triphenylphosphane, is reported. Depending on propene and 3,3-bis(triphenylphosphonio)-1,1-dimesitylallene
the nature of cyclopropenyl substituents (R), the three-mem- products is rationalized on the basis of steric and electrostatic
bered cyclic structure is preserved (R = Ph) or evolves by ring constraints.
Introduction
most stable carbocations.[6] Amino substituents are not only
responsible for the characterization of a wide range of cyclo-
Three-membered cycles are of considerable interest because of propeniums of type A, but they also allowed to stabilize cyclo-
their essential role as intermediates in many chemical transfor- propenylidenes B, the ensuing carbenic species.[7] Among cy-
mations.[1] Their inherent ring strain causes a high reactivity clopropenylidene-phosphorus derivatives, stabilized phosphe-
that could lead to ring-opening[2] or ring-expansion reactions.[3] nium cations of type C were recently prepared for the purpose
Among three-membered cycles, cyclopropenium cations be- of accessing novel α-cationic phosphane ligands.[8] Cycloprope-
long to a category apart due to the delocalization of two π- nium substituted phosphonium salts of type D were briefly in-
electrons over three 3p orbitals which confers higher stability.[4] vestigated with the main objective of designing highly electro-
Beyond aromatic effects, the nature of cyclopropenyl substitu- philic phosphorus cations that can serve as Lewis acid initia-
ents play a determinant role in the stability vs. reactivity of tors.[9] Thanks to the critical effect of π-donating amino substit-
these two π-electron Hückel prototypes.[5] In comparison with uents, a large gamme of unsaturated three membered cycles
cyclopropeniums bearing only carbon substituents, amino A–D, neutral, mono- or dicationic in nature, were thus isolated
groups due to their strong π-donating effect and the electro- (Figure 1).
negativity of nitrogen induce additional stability which has the
Based on this long history of cyclopropenium cations, the
consequence of placing aminocyclopropeniums among the present article aims to evaluate the role of the substitution pat-
Figure 1. (a) Representation of known cyclopropenium type-systems A–D based on π-donating amino substituents. (b) Cyanine-type resonance structures of
cyclopropenium type-systems A–D.
[a] LCC-CNRS, CNRS, Université de Toulouse,
tern in the stability vs. reactivity of cyclopropenium substituted
phosphonium salts of type D, the dicationic representatives of
this fascinating family of two π-electron aromatic systems that
have been poorly studied to date and may be of fundamental
and applied interest.
205 route de Narbonne, 31077 Toulouse Cedex 4, France
E-mail: yves.canac@lcc-toulouse.fr
https://www.lcc-toulouse.fr/article388.html
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.201900867.
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Results and Discussion
According to the recent report of Alcarazo and co-workers, 3-
triphenylphosphonio-1,2-bis(diisopropylamino)cyclopropenium
[2](OTf)2 was smoothly prepared in good yield from related 3-
chlorocyclopropenium salt [1](OTf) and PPh3 in the presence of
NaOTf in THF at 60 °C (Scheme 1, method a).[9] The dicationic
phosphonium [2](OTf)2 was also readily obtained by reacting
cyclopropenium precursor [1](OTf) with the PPh3/Me3SiOTf sys-
tem in CH2Cl2 at room temperature (Scheme 1, method b).[10]
Figure 2. Perspective view of the cationic part of cyclopropenium substituted
phosphonium salt [2](OTf)2 with thermal ellipsoids drawn at the 30 % proba-
bility level (for clarity, the H atoms are omitted). Selected bond lengths [Å]
and angles [°]: C1–P1 1.7776(19), C1–C2 1.384(2), C2–C3 1.424(3), C1–C3
1.389(3), C2–N1 1.299(2), C3–N2 1.291(2), P1–C1–C2 143.93(15), P1–C1–C3
154.26(15), C2–C1–C3 61.80(13), C1–C2–N1 146.91(19).
Scheme 1. Preparation of 3-triphenylphosphonio-1,2-bis(diisopropylamino)-
cyclopropenium [2](OTf)2 from 3-chlorocyclopropenium [1](OTf). a) (1.5 eq.)
PPh3, (1.1 eq.) NaOTf, THF, 60 °C, 95 %; b) (1.1 eq.) PPh3, (1.1 eq.) Me3SiOTf,
CH2Cl2, r.t., 90 %.
whatever the conditions of the reaction (solvent, temperature,
number of equivalents), 31P NMR spectroscopy evidenced only
the resonance of [2](OTf)2 along with free PPh3. The inertness
As observed for the tetrafluoroborate analogue,[9] the 31P of cyclopropenium [2](OTf)2 towards a soft nucleophile such as
NMR spectrum of [2](OTf)2 displayed a single signal shifted PPh3 was reasonably attributed to the dominating contribution
downfield relative to PPh3 (δP = –5.9 ppm) at δP = 9.3 ppm. In of cyanine-type resonance forms in the description of [2](OTf)2
the 13C NMR spectrum, the C–+PPh3 carbon atom was found to due to the strong interaction of the π-donor nitrogen groups
be slightly deshielded (δC = 140.9 ppm, brs) with respect to the with the aromatic system (Figure 1b).
C–Cl carbon atom of precursor [1](OTf) (δC = 133.4 ppm, s) in
agreement with a sp2-type carbon atom.[11] The exact structure
of [2](OTf)2 was established by X-ray diffraction analysis of
single crystals obtained from a CH2Cl2/Et2O mixture at room
temperature (Figure 2).[12] In the solid state, the ring and the
amino substituents are nearly coplanar confirming the interac-
tion of the nitrogen lone pairs with the π-system of the ring. It
is also worth noting the quasi-tetrahedral environment of the
phosphorus atom and the absence of interaction of the two
TfO– counteranions with the cyclopropenium bearing the phos-
phonium moiety.
To overcome the overly stabilizing effect of NiPr2 substitu-
ents on the cyclic structure, 1,2-diarylcyclopropenes were then
selected as alternative precursors.[13] Treatment of 3,3-dichloro-
1,2-diphenylcyclopropene 3 with a stoichiometric amount of
PPh3 in CH2Cl2 at room temperature afforded the correspond-
ing 3-triphenylphosphoniocyclopropene [5]Cl in 90 % yield
(Scheme 2). The 31P NMR spectrum of [5]Cl displayed a singlet
at δP = 29.1 ppm shifted downfield relative to [2](OTf)2 (δP =
9.3 ppm), in the typical range for phosphonium derivatives.[14]
The cyclopropenic structure was indicated by the presence of
the upfield 13C NMR resonance of the cyclic sp3-type carbon
1
Anticipating an exaltation of the electrophilic character for atom with proper multiplicity (δC = 47.2 ppm, (d, JCP
=
cyclopropenium [2](OTf)2 due to its dicationic character, the ad- 111.7 Hz)). The cationic nature of [5]Cl was unambiguously con-
dition of a second equivalent of PPh3 was considered. However, firmed by ESI mass spectroscopy (5+: m/z 487.1).
Scheme 2. Preparation of bis(phosphonium) salts [7–8](OTf)2 from corresponding 3,3-dichloro-1,2-diarylcyclopropene precursors 3–4 via 3-phosphoniocyclo-
propenes [5–6]Cl.
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The same reactivity was observed from related 3,3-dichloro-
A similar reactivity was then expected from related 3-phos-
1,2-dimesitylcyclopropene 4 as illustrated with the quantitative phoniocyclopropene [6]Cl. Addition of an equivalent of PPh3 in
formation of 3-triphenylphosphoniocyclopropene [6]Cl under the presence of Me3SiOTf in CH2Cl2 at room temperature to
the same conditions. As observed for [5]Cl, 31P and 13C NMR [6]Cl resulted in the formation of bis(phosphonium) salt
spectra of [6]Cl confirmed its cationic character as well as the [8](OTf)2 in 86 % isolated yield (Scheme 2). However, surpris-
direct linkage of the phosphonium moiety to the cyclopropene ingly, the 31P NMR spectrum exhibited only the appearance of
1
ring (δP = 30.4 ppm (s); δC = 52.4 ppm, (d, JCP = 109.7 Hz)) a single resonnance (δP = 25.3 ppm), thus precluding the forma-
(Scheme 2). It should be noted that if spectroscopic data of [5– tion of a disymmetrical cyclopropene similar to that observed
6]Cl are here in favor of a cyclopropenic structure, 3-halogeno- in the previous case. Mass spectroscopy (8+: m/z 947.3 [M –
cyclopropenes are known to be more or less displaced to their TfO]+) accounted for the presence of two triphenylphosphonio
cyclopropenium form depending on the ability of the halide moieties in agreement with the expected dicationic nature. The
ion to dissociate from the cation.[15]
fascinating structure of [8](OTf)2 was further assigned on the
basis of its 13C NMR chemical shifts, in particular by the pres-
ence of three triplets attributed to quaternary carbon atoms
with one of them appearing at very low field (δC = 227.6 ppm
(t, JCP = 3.0 Hz); δC = 117.7 ppm (t, JCP = 13.2 Hz); δC = 75.7 ppm
(t, JCP = 74.2 Hz)). The allenic structure deduced from the 13C
NMR spectrum was finally confirmed by X-ray diffraction analy-
sis of colorless crystals obtained from a CH2Cl2/Et2O mixture at
room temperature (Figure 3, right).[12] The solid state analysis
confirms that the central carbon atom is in a quasi linear envi-
ronment (C1–C2–C3 179.991°), as would be anticipated for such
unsaturated derivative with the two allenic C=C bonds not sig-
nificantly different (C1–C2: 1.325(4) Å; C2–C3 1.314(4) Å). By
contrast to cyclopropene [7](OTf)2, the two phosphonio groups
are located on the same carbon atom, which causes the second
carbon atom on the periphery of the allenic structure to be
substituted by two mesityl groups. The angle between
[(PPh3)+2-C=] and [(Mes)2-C=] planes deviates from the orthogo-
nality by about 10.38° certainly for steric and electrostatic con-
straints between the two bulky phosphonio moieties as illus-
trated by the angle value (P1–C1–P1′ 123.33(14)°). The corre-
sponding angle involving the two mesityl rings (C4–C3–C4′
119.9(2)°) is very close to the ideal value (ca. 120.0°).
To further evaluate the role of cyclopropenyl substituents, 3-
phosphoniocyclopropene [5]Cl was treated with a stoichiomet-
ric amount of PPh3 in the presence of two equivalents of
Me3SiOTf in CH2Cl2 at room temperature. 31P NMR monitoring
revealed the disappearance of the signal of [5]Cl with concomi-
tant appearance of a AX-type system (δP = 15.0 ppm (d),
30.3 ppm (d), JPP = 10.5 Hz) giving a first indication about the
nature and the environment of the two phosphorus atoms. In
the latter, isolated with a yield of 96 % and expected to contain
two phosphonio moieties, the preservation of the cyclopropene
ring was evidenced by the presence of the characteristic carbon
atom of sp3-type in the high field region (δC = 39.3 ppm,
1
(d, JCP = 74.4 Hz)) of the 13C NMR spectrum (Scheme 2). The
dicationic character was confirmed from ESI mass spectroscopy
(m/z 863.2 [M – TfO]+). X-ray diffraction analysis of colorless
crystals, deposited from CH2Cl2/Et2O at –20 °C, allowed finally
this dicationic salt to be assigned to the cyclopropene [7](OTf)2
bearing two triphenylphosphonio groups (Figure 3, left).[12]
Compound [7](OTf)2 corresponds in fact to a chiral cyclo-
propene in which the two cationic fragments are connected
to two carbon atoms of different nature, of sp2- and sp3-type,
respectively. The unsaturated three-membered cycle is clearly
indicated by the presence of two single C–C bonds (C1–C2:
The two different structures obtained by modifying only a
1.525(4); C1–C3: 1.540(4) Å) and one double C=C bond (C2–C3: substituent (Ph vs. Mes) on the starting cyclopropene raise
1.307(4) Å). Noteworthy, the related C2 and C3 carbon atoms questions about the mechanism of formation of bis(phospho-
reside in a planar environment while the C1 carbon atom is nium) salts [7–8](OTf)2. Assuming in both series an equilibrium
characterized by a distorted tetrahedral geometry.
between the two covalently bonded cationic chlorocycloprop-
Figure 3. Perspective views of the cationic part of bis(phosphonium) derivatives [7](OTf)2 (left) and [8](OTf)2 (right) with thermal ellipsoids drawn at the 30 %
probability level (for clarity, the H atoms are omitted). Selected bond lengths [Å] and angles [°]: [7](OTf)2: C1–P2 1.853(3), C3–P1 1.765(3), C1–C2 1.525(4), C1–
C3 1.540(4), C2–C3 1.307(4), P1–C3–C1 147.6(2), P1–C3–C2 148.3(2), P2–C1–C2 112.83(18), P2–C1–C3 115.09(19), C2–C1–C3 50.50(17), C1–C2–C3 65.4(2), C1–
C3–C2 64.1(2); [8](OTf)2: C1–P1 1.8357(13), C1–C2 1.325(4), C2–C3 1.314(4), C3–C4 1.511(2), C1–C2–C3 179.991, P1–C1–C2 118.33(7), P1–C1–P1′ 123.33(14),
C2–C3–C4 120.03(11), C4–C3–C4′ 119.9(2).
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enes [5–6]Cl and [5a–6a]Cl via corresponding 3-triphenylphos-
In the case of 1,2-mesityl-substituted cyclopropene [6]Cl, the
phoniocyclopropenium intermediate,[15] the formation of bis- nucleophilic attack of PPh3 would not take place at the C-Mes
(phosphonium) salts [7–8](OTf)2 can be tentatively rationalized carbon atoms for steric reasons, preferring to form the gem(tri-
by the existence of steric and electrostatic constraints.
phenylphosphonio) cyclopropene [6b](OTf)2. As reported for
sterically encumbered cyclopropenes such as tetrakis(trimethyl-
silyl)cyclopropenes,[17] we assume that the electrostatic con-
strained 3,3-bis(phosphonio)cyclopropene [6b](OTf)2 would re-
arrange spontaneously by ring opening to the transient vinyl-
carbene [6c](OTf)2 followed by a 1,2-shift of a mesityl group to
the carbenic center affording finally the experimentally isolated
allene [8](OTf)2 (Scheme 3). Similar rearrangement was also evi-
denced by reacting bulky tris(alkylthio)cyclopropeniums with
phosphanes via the formation of unstable 3-phosphoniocyclo-
propenes.[18]
In the case of 1,2-diphenyl-substituted cyclopropene [5]Cl,
the sterically demanding PPh3 nucleophile would preferentially
react at the C-Ph positions (Scheme 3, pathway a) minimizing
thus the electrostatic repulsion between the two phosphonio
groups, and affording the dicationic cyclopropene [7](OTf)2 in
a single step. Although a priori less likely, we can not exclude
the reaction pathway b that involves the nucleophilic attack of
PPh3 to the carbon atom bearing the phosphonium group. The
corresponding bis(phosphonium) salt [5b](OTf)2 would then
give the cyclopropene [7](OTf)2 via the highly constrained bi-
cyclic intermediate [5c](OTf)2 which formally accounts for the
migration of a phosphonio group.[16]
The mechanism of formation of cyclopropene [7](OTf)2 was
experimentally supported by the slow hydrolysis of 3-phos-
Scheme 3. Proposed mechanisms for the formation of bis(phosphonium) salts [7–8](OTf)2 from corresponding 3-phosphoniocyclopropenes [5–6]Cl. All isolated
products are framed.
Scheme 4. Proposed mechanisms for the formation of vinyl phosphonium [9]Cl and 1,2-dimesitylcyclopropenone 10 from hydrolysis of 3-phosphoniocyclo-
propenes [5–6]Cl.
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phoniocyclopropene [5]Cl to the vinyl phosphonium [9]Cl, the conservation of the cyclic structure to give the 1,3-bis(phos-
latter salt being formed in 75 % yield after one day in wet phonio)cyclopropene [7](OTf)2 if the substituent is a phenyl
CH2Cl2. As for [7](OTf)2, the formation of [9]Cl would probably group or spontaneous ring-opening into the linear 3,3-
involve the cyclopropene isomer [5a]Cl which would undergo bis(phosphonio)allene [8](OTf)2 if the substituent is larger, such
nucleophilic attack of a hydroxide ion at the C-Ph position to as a mesityl group. The mechanism of formation of these two
form the hydroxycyclopropene [5d]Cl followed by ring opening unprecedented bis(phosphonium) salts [7–8](OTf)2 based on an
and hydrogen migration (Scheme 4, right).[19] The vinyl phos- isomeric backbone of general formula [Ar2C3(PPh3)2]2+(OTf)2–
phonium [9]Cl obtained in a fully stereospecific manner was was mainly rationalized by the existence of steric and electro-
characterized by multi-nuclear NMR spectroscopy (δP
=
static constraints. The generalization of this methodology to
15.9 ppm)[20] and subjected to X-ray diffraction analysis from other cyclopropenium salt precursors and phosphane nucleo-
colorless crystals deposited from a CH2Cl2/Et2O mixture at room philes deserves to be investigated, thus opening up prospects
temperature (Figure 4).[12] The Z-configuration of [9]Cl was for the preparation of highly electrophilic species that could act
mainly attributed to attractive P+/O– electrostatic interactions.
as Lewis acid initiators in organocatalysis.
Experimental Section
General Remarks: All manipulations were performed under an
inert atmosphere of dry nitrogen by using standard vacuum line
and Schlenk tube techniques. Dry and oxygen-free organic solvents
(THF, Et2O, CH2Cl2, toluene, pentane) were obtained using a LabSolv
(Innovative Technology) solvent purification system. Acetonitrile
was dried and distilled from CaH2 under argon. All other reagent-
grade chemicals were purchased from commercial sources and
used as received. 1H, 31P, and 13C NMR spectra were obtained on
Bruker Avance 400 and Avance III HD 400 spectrometers. NMR
chemical shifts δ are in ppm, with positive values to high frequency
relative to the tetramethylsilane reference for 1H and 13C and to
H3PO4 for 31P. If necessary, additional information on the carbon
signal attribution was obtained using 13C{1H, 31P}, J-modulated
spin-echo (JMOD) 13C{1H}, 1H–13C HMQC, and/or HMBC experi-
ments. Mass spectra (ESI mode) were obtained using a Xevo G2
QTof (Waters) spectrometer and were performed by the mass spec-
trometry service of the “Institut de Chimie de Toulouse”. 3-chloro-
1,2-bis(diisopropylamino)cyclopropenium salt [1](OTf) was pre-
pared according to a previously described procedure.[11] 3,3-di-
chloro-1,2-diphenylcyclopropene 3, and 3,3-dichloro-1,2-dimesityl-
Figure 4. Perspective view of the cationic part of vinyl phosphonium [9]Cl
with thermal ellipsoids drawn at the 30 % probability level (for clarity, the H
atoms are omitted). Selected bond lengths [Å] and angles [°]: C1–P1 1.788(2),
C1–C2 1.336(3), C2–C3 1.513(3), C3–O1 1.212(3), P1–C1–C2 125.32(18), C1–
C2–C3 123.2(2), C2–C3–O1 119.3(2).
The 3-triphenylphosphoniocyclopropene [6]Cl was found to
be relatively more stable towards hydrolysis. However, after few cyclopropene 4 were prepared according to a previously described
procedure.[13]
days in wet CH2Cl2, the concomitant formation of 1,2-dimesityl-
cyclopropenone 10 and PPh3 was evidenced by 31P and 1H NMR
3-Triphenylphosphonio-1,2-bis(diisopropylamino)cyclopropenium
bis(triflate) [2](OTf)2
spectroscopy (Scheme 4, left).[21] This reactivity is in agreement
with the mechanism proposed for the formation of bis(phos-
phonium) salt [8](OTf)2. The hydroxide nucleophile would not
Method a: Chlorocyclopropenium salt [1](OTf) (0.22 g, 0.52 mmol),
triphenylphosphane (0.20 g, 0.78 mmol) and sodium trifluorometh-
anesulfonate (0.10 g, 0.57 mmol) were dissolved in THF (10 mL),
and the suspension was stirred at 60 °C for 16 hours. The solvent
react indeed at the C-Mes carbon atoms for steric reasons, but
+
at the C-PPh3 position yielding the 3-hydroxycyclopropene
[6d]Cl which would then stabilize by elimination of PPh3 and was evaporated under vacuum, and the solid residue was dissolved
in CH2Cl2 (10 mL) and filtered. After evaporation of the solvent, the
solid was washed with THF (10 mL) affording [2](OTf)2 as a white
microcrystalline solid (0.39 g, 95 %).
formation of 1,2-dimesitylcyclopropenone 10.
Conclusions
Method b: To a solution of chlorocyclopropenium salt [1](OTf)
(0.15 g, 0.36 mmol) in CH2Cl2 (5 mL) was added triphenylphosphane
(0.10 g, 0.39 mmol) and trimethylsilyl trifluoromethanesulfonate
(71 μL, 0.39 mmol) at –40 °C. The solution was then stirred at room
temperature for 2 hours. The solvent was evaporated under vac-
uum, and the solid residue was washed with THF (10 mL) affording
a white microcrystalline solid (0.25 g, 90 %). Recrystallization at
The outcome of the reaction between a neutral nucleophile
such as triphenylphosphane and an electrophilic chlorocyclo-
propenium salt vs. dichlorocyclopropene depends on the na-
ture of cyclopropenyl substituents. While strongly π-donating
amino groups stabilize the cationic cyclopropenium form,
weaker π-donating aryl groups favor the neutral cyclopropenic room temperature from CH2Cl2/Et2O gave [2](OTf)2 as colorless
crystals.
form as demonstrated with the formation of 3-triphenylphos-
phonio-1,2-diarylcyclopropenes [4–5]Cl. When treating with a
second equivalent of nucleophile, aryl substituents of cyclo-
1H NMR (CD3CN, 25 °C): δ = 0.81 (d, JHH = 7.0 Hz, 12H, CH3), δ =
1.45 (d, JHH = 7.0 Hz, 12H, CH3), 3.47 (sept, JHH = 7.0 Hz, 2H, CH),
propenes [4–5]Cl play an additional role, namely either the 4.30 (sept, JHH = 7.0 Hz, 2H, CH), 7.84–7.89 (m, 6H, Har), 7.96–8.03
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(m, 9H, Har). 13C NMR (CD3CN, 25 °C): δ = 20.1 (s, CH3), 21.5 (s, CH3),
56.6 (brs, CH), 83.6 (d, JCP = 105.6 Hz, C), 116.5 (d, JCP = 93.6 Hz, C),
(d, JCP = 94.6 Hz, C), 117.3 (d, JCP = 84.5 Hz, C), 122.1 (q, JCF =
320.9 Hz, CF3SO3), 122.8 (s, C), 130.1 (d, JCP = 4.0 Hz, CHar), 131.0 (s,
122.1 (q, JCF = 321.9 Hz, CF3SO3), 132.1 (d, JCP = 13.1 Hz, CHar), 135.9 CHar), 131.1 (s, CHar), 131.3 (s, CHar), 131.7 (d, JCP = 12.1 Hz, CHar),
(d, JCP = 12.1 Hz, CHar), 137.9 (d, JCP = 3.0 Hz, CHar), 140.9 (brs, C). 132.2 (d, JCP = 13.1 Hz, CHar), 133.4 (s, CHar), 134.7 (d, JCP = 12.1 Hz,
31P NMR (CD3CN, 25 °C): δ = 9.3 ppm. MS (ES+): m/z: 647.2 [M+]. CHar), 135.7 (d, JCP = 10.1 Hz, CHar), 136.9 (s, CHar), 137.0 (d, JCP
=
HRMS (ES+): calcd. for C34H43N2O3SF3P 647.2684, found 647.2677.
3.0 Hz, CHar), 137.7 (d, JCP = 3.0 Hz, CHar), 144.8 (t, JCP = 3.0 Hz, C).
31P NMR (CD3CN, 25 °C): δ = 15.0 (d, JPP = 10.5 Hz), 30.3 (d, JPP
=
3-Chloro-3-triphenylphosphonio-1,2-diphenylcyclopropene chlor-
ide [5]Cl
10.5 Hz) ppm. MS (ES+): m/z: 863.2 [M+]. HRMS (ES+): calcd. for
C52H40O3SF3P2 863.2125, found 863.2109.
To a solution of 3,3-dichloro-1,2-diphenylcyclopropene 3 (0.11 g,
0.42 mmol) in CH2Cl2 (5 mL) was added triphenylphosphane (0.12 g,
0.46 mmol) at room temperature, and the solution was then stirred
for 2 hours. The solvent was evaporated under vacuum, and the
solid residue was washed with THF (10 mL) affording [5]Cl as a
white air sensitive solid (0.20 g, 90 %).
3,3-Bis(triphenylphosphonio)-1,1-dimesitylallene bis(triflate) [8](OTf)2
Method a: To a solution of 3,3-dichloro-1,2-dimesitylcyclopropene 4
(0.29 g, 0.83 mmol) in CH2Cl2 (15 mL) was added triphenylphos-
phane (0.55 g, 2.10 mmol) and trimethylsilyl trifluoromethanesulf-
onate (319 μL, 1.75 mmol) at –40 °C. The solution was then stirred at
room temperature for 12 hours. The solvent was evaporated under
vacuum, and the solid residue was washed with THF (20 mL) afford-
ing a white solid (0.70 g, 75 %). Recrystallization at room tempera-
ture from CH2Cl2/Et2O gave [8](OTf)2 as colorless crystals.
1H NMR (CD3CN, 25 °C): δ = 7.49–7.55 (m, 4H, Har), 7.56–7.63 (m,
6H, Har), 7.69–7.81 (m, 12H, Har), 7.89–7.93 (m, 3H, Har). 13C NMR
(CD3CN, 25 °C): δ = 47.2 (d, JCP = 111.7 Hz, C), 116.0 (s, C), 117.7 (d,
JCP = 86.5 Hz, C), 123.5 (d, JCP = 2.0 Hz, C), 130.7 (s, CHar), 130.8 (s,
Method b: To a solution of 3-phosphoniocyclopropene [6]Cl (0.10 g,
0.16 mmol) in CH2Cl2 (10 mL) was added triphenylphosphane
(0.05 g, 0.18 mmol) and trimethylsilyl trifluoromethanesulfonate
(63 μL, 0.35 mmol) at –40 °C. The resulting solution was then stirred
at room temperature for 3 hours. The solvent was evaporated under
vacuum, and the solid residue was washed with THF (20 mL) afford-
ing [8](OTf)2 as a white solid (0.15 g, 86 %).
CHar), 131.5 (d, JCP = 12.1 Hz, CHar), 133.4 (s, CHar), 135.7 (d, JCP
=
10.1 Hz, CHar), 136.9 (d, JCP = 3.0 Hz, CHar). 31P NMR (CD3CN, 25 °C):
δ = 29.1 ppm. MS (ES+): m/z: 487.1 [M+]. HRMS (ES+): calcd. for
C33H25ClP 487.1382, found 487.1381.
3-Chloro-3-triphenylphosphonio-1,2-dimesitylcyclopropene chlor-
ide [6]Cl
To a solution of 3,3-dichloro-1,2-dimesitylcyclopropene 4 (0.10 g,
0.29 mmol) in CH2Cl2 (5 mL) was added triphenylphosphane
(83 mg, 0.32 mmol) at room temperature, and the solution was then
stirred for 2 hours. The solvent was evaporated under vacuum, and
the solid residue was washed with THF (10 mL) affording [6]Cl as a
white air sensitive solid (0.17 g, 95 %).
1H NMR (CD3CN, 25 °C): δ = 1.37 (s, 12H, CH3), 2.34 (s, 6H, CH3), 6.95
(s, 4H, Har), 7.52–7.56 (m, 12H, Har), 7.61–7.66 (m, 12H, Har), 7.79–
7.83 (m, 6H, Har). 13C NMR (CD3CN, 25 °C): δ = 21.0 (s, CH3), 22.5 (s,
CH3), 75.7 (t, JCP = 74.2 Hz, C), 116.0 (m, C) [This 13C NMR signal
corresponds to the chemical resonance of the Cipso carbon atoms
+
of the PPh3 groups. Since it is a second order system, the corre-
3
2
sponding coupling constants (1JCP = 88.0 Hz, JCP = 0 Hz, JPP
=
1H NMR (CD3CN, 25 °C): δ = 1.78 (s, 12H, CH3), 2.34 (s, 6H, CH3), 7.04
(s, 4H, Har), 7.60–7.70 (m, 12H, Har), 7.89–7.94 (m, 3H, Har). 13C NMR
(CD3CN, 25 °C): δ = 21.3 (s, CH3), 52.4 (d, JCP = 109.7 Hz, C), 117.1
(d, JCP = 87.5 Hz, C), 119.9 (s, C), 121.9 (d, JCP = 3.0 Hz, C), 130.7 (s,
CHar), 131.3 (d, JCP = 12.1 Hz, CHar), 136.4 (d, JCP = 10.1 Hz, CHar),
136.9 (d, JCP = 3.0 Hz, CHar), 140.1 (s, C), 143.4 (s, C). 31P NMR
(CD3CN, 25 °C): δ = 30.4 ppm. MS (ES+): m/z: 571.2 [M+]. HRMS (ES+):
calcd. for C39H37ClP 571.2321, found 571.2316.
42.0 Hz) were determined by simulation using the software Mest
Renova.], 117.7 (t, JCP = 13.2 Hz, C), 122.2 (q, JCF = 320.8 Hz, CF3SO3),
126.6 (t, JCP = 5.0 Hz, C), 131.4 (t, JCP = 6.7 Hz, CHar), 131.9 (s, CHar),
136.7 (t, JCP = 5.0 Hz, CHar), 137.6 (s, CHar), 138.0 (t, JCP = 3.0 Hz, C),
140.9 (s, C), 227.6 (t, JCP = 3.0 Hz, C). 31P NMR (CD3CN, 25 °C): δ =
25.3 ppm. MS (ES+): m/z: 947.3 [M+]. HRMS (ES+): calcd. for
C58H52O3SF3P2 947.3064, found 947.3076.
3-Oxo-1,2-diphenylprop-1-enyl-triphenylphosphonium chloride [9]Cl
1,3-Bis(triphenylphosphonio)-2,3-diphenylcyclopropene bis(triflate)
[7](OTf)2
A solution of [5]Cl (0.10 g, 0.19 mmol) in wet CH2Cl2 (5 mL) was
stirred at room temperature for 1 day. After evaporation of the sol-
vent under vacuum, the solid residue was washed with Et2O (20 mL)
affording a white solid (0.07 g, 75 %). Recrystallization at room tem-
perature from CH2Cl2/Et2O gave [9]Cl as colorless crystals.
Method a: To a solution of 3,3-dichloro-1,2-diphenylcyclopropene 3
(0.17 g, 0.65 mmol) in CH2Cl2 (10 mL) was added triphenylphos-
phane (0.43 g, 1.62 mmol) and trimethylsilyl trifluoromethanesulf-
onate (248 μL, 1.37 mmol) at –40 °C. The resulting solution was
then stirred at room temperature for 12 hours. The solvent was
evaporated under vacuum, and the solid residue was washed with
THF (20 mL) affording a white solid (0.59 g, 89 %). Recrystallization
at –20 °C from CH2Cl2/Et2O gave [7](OTf)2 as colorless crystals.
1H NMR (CD3CN, 25 °C): δ = 7.20–7.24 (m, 2H, Har), 7.35–7.38 (m,
2
2H, Har), 7.43 (d, JHP = 16.7 Hz, 1H, CHP), 7.48–7.56 (m, 10H, Har),
7.62–7.65 (m, 2H, Har), 7.69–7.76 (m, 9H, Har). 13C NMR (CD3CN,
25 °C): δ = 110.1 (d, JCP = 89.5 Hz, CH), 118.9 (d, JCP = 91.5 Hz, C),
128.6 (s, CHar), 129.4 (s, CHar), 130.4 (s, CHar), 130.7 (d, JCP = 13.1 Hz,
Method b: To a solution of 3-phosphoniocyclopropene [5]Cl (0.10 g,
0.19 mmol) in CH2Cl2 (10 mL) was added triphenylphosphane
(0.06 g, 0.21 mmol) and trimethylsilyl trifluoromethanesulfonate
(73 μL, 0.40 mmol) at –40 °C. The resulting solution was then stirred
at room temperature for 3 hours. The solvent was evaporated under
vacuum, and the solid residue was washed with THF (20 mL) afford-
ing [7](OTf)2 as a white solid (0.18 g, 96 %).
CHar), 130.8 (s, CHar), 132.9 (s, CHar), 135.2 (s, C), 135.5 (d, JCP
=
11.1 Hz, CHar), 135.8 (s, CHar), 136.1 (d, JCP = 3.0 Hz, CHar), 166.6 (d,
J
CP = 3.0 Hz, C), 194.9 (d, JCP = 6.0 Hz, CO). 31P NMR (CD3CN, 25 °C):
δ = 15.9 ppm. MS (ES+): m/z: 469.2 [M+]. HRMS (ES+): calcd. for
C33H26OP 469.1721, found 469.1726.
Hydrolysis of 3-chloro-3-triphenylphosphonio-1,2-dimesitylcyclo-
propene chloride [6]Cl
1H NMR (CD3CN, 25 °C): δ = 7.15–7.30 (m, 12H, Har), 7.34–7.45 (m,
10H, Har), 7.50–7.57 (m, 6H, Har), 7.62–7.69 (m, 6H, Har), 7.83–7.89 A solution of [6]Cl (0.10 g, 0.34 mmol) in wet CH2Cl2 (5 mL) was
1
(m, 3H, Har), 7.92–7.98 (m, 3H, Har). 13C NMR (CD3CN, 25 °C): δ =
39.3 (d, JCP = 74.4 Hz, C), 98.8 (dd, JCP = 5.5 and 103.1 Hz, C), 116.4
stirred at room temperature. After 3 days, 31P and H NMR spectro-
scopy indicate the quantitative formation of 1,2-dimesityl cyclo-
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Table 1. Crystallographic data.
[2](OTf)2
[7](OTf)2
[8](OTf)2
[9]Cl
Empirical formula
Formula mass
Crystal system
Space group
T [K]
a [Å]
b [Å]
c [Å]
α [°]
C36H45Cl2F6N2O6PS2
881.76
Triclinic
P –1
C54H42Cl2F6O6P2S2
1097.90
Triclinic
P –1
C59H55F6O7.50P2S2
1124.15
Monoclinic
C 2/c
C33H26ClOP
504.96
Monoclinic
P21/c
100
143
170
150
12.3514(5)
13.0626(5)
14.9092(6)
77.0138(18)
66.5174(18)
71.8820(17)
2082.80(15)
1.406
13.5665(10)
13.9157(7)
15.6326(7)
82.648(4)
69.202(6)
66.429(6)
2528.4(3)
1.442
24.4695(12)
16.6341(7)
17.9893(8)
90
128.615(2)
90
27.04340(4)
10.09730(2)
25.48880(4)
90
111.837(3)
90
ꢀ [°]
γ [°]
V [Å3]
Dc
5721.2(5)
1.302
6460.68(12)
1.038
Z
2
2
4
8
μ[mm–1
]
0.366
3.154
0.220
0.188
λ [Å]
0.71073
106322
10437/0.027
8655, n=3
496
1.54180
25591
0.71073
71847
7123/0.033
5605, n=3
354
0.71073
212055
16139/0.046
11076, n=3
649
Refl. measured
Refl. unique/Rint
Refl. with I > n σ(I)
Nb parameters
Refinement on
R with I > n σ(I)
7555/0.045
7515, n=-3
649
F
F2
0.0564
F
F
0.0499
0.0618
0.0503
R
w with I > n σ(I)
0.0593
0.1167
0.0680
0.0623
GooF
1.024
2.27/–1.03
0.993
0.86/–0.78
0.985
1.19/–0.44
0.999
0.61/–0.54
Δρmax/Δρmin [e Å–3
]
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CCDC 1942815 (for {for [2](OTf)2}), 1942816 (for {for [7](OTf)2}), 1942817
(for {for [8](OTf)2}), and 1942818 (for {for [9]Cl}) contain the supplemen-
tary crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre.
In addition to the Ministère de l'Enseignement Supérieur de la
Recherche et de la Technologie and the Université Paul Sabatier,
the authors thank the Centre National de la Recherche Scientif-
ique (CNRS).
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Keywords: Phosphorus · Ligand effects · Reaction
mechanisms · Electrostatic interactions · Ring strain
Eur. J. Inorg. Chem. 2019, 3982–3989
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Received: August 9, 2019
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