Carbene-stabilized phosphenium oxides and sulfides

Article abstract of DOI:10.1002/chem.201202279

Carbene→chalcogenophosphenium adducts, which correspond to an intermolecular stabilization mode of the so far elusive, free oxo- and thiooxophosphenium species [R₂P⁺=X] (X=O, S) by imidazolylidene (NHC) and diaminocyclopropenylidene (BAC) donors, have been isolated and fully characterized. The dative character of the R ₂C:→P⁺(X)Ph₂ bond was confirmed experimentally by nucleophilic displacement of the carbene donor with a chloride ion and by an exchange reaction of the NHC ligand of the NHC:→P ⁺(O)Ph₂ adduct with an independently prepared BAC ligand, thereby giving the BAC:→P⁺(O)Ph₂ adduct. This dative character was further characterized by the DFT-calculated preference of carbene→chalcogenophosphenium systems for a heterolytic dissociation mode over a homolytic one.

Full text of DOI:10.1002/chem.201202279

FULL PAPER
DOI: 10.1002/chem.201202279
Carbene-Stabilized Phosphenium Oxides and Sulfides
Carine Maaliki,[a, b] Christine Lepetit,[a, b] Carine Duhayon,[a, b] Yves Canac,*[a, b] and
Remi Chauvin*[a, b]
Dedicated to Professor Guy Bertrand on the occasion of his 60th birthday
Abstract: Carbene!chalcogenophos-
phenium adducts, which correspond to
an intermolecular stabilization mode of
the so far elusive, free oxo- and thio-
the R2C:!P+(X)Ph2 bond was con-
firmed experimentally by nucleophilic
displacement of the carbene donor
with a chloride ion and by an exchange
reaction of the NHC ligand of the
NHC:!P+(O)Ph2 adduct with an inde-
pendently prepared BAC ligand, there-
by giving the BAC:!P+(O)Ph2 adduct.
This dative character was further char-
acterized by the DFT-calculated prefer-
ence of carbene!chalcogenophosphe-
nium systems for a heterolytic dissocia-
tion mode over a homolytic one.
ACHTUNGTRENNUNGoxoACHTUNGTRENNUNG
phosphenium species [R2P+ =X]
(X=O, S) by imidazolylidene (NHC)
and diaminocyclopropenylidene (BAC)
donors, have been isolated and fully
characterized. The dative character of
Keywords: carbenes · dative bonds ·
exchange interactions · phospheni-
um compounds · stabilization
1. Introduction
Phosphenium cations [R2P:+] (A, Scheme 1), that is, the “di-
agonal” analogues of carbenes [R2C:] in the singlet spin
state, can either be stabilized internally by donor atoms (N,
P, etc.) on the substituents (R)[1] or externally by the reversi-
ble coordination of a donating ligand (D) to the accepting
phosphenium moiety. This D!
[PR2]+ “dative stabilization
ACHTUNGTRENNUNG
mode”, which results in an increase in the coordination
number of the P atom from s2 to s3, has been exemplified in
intramolecular systems with heteroatomic N, O, and S
donors[2] and in intermolecular systems with phosphane[3] or
carbenic donors.[4] Indeed, amidiniophosphines were shown
to be accurately described as NHC!phosphenium adducts
(Scheme 1).[5] On the other hand, the amphoteric Lewis
character of phosphenium cations was illustrated by the co-
ordination of their lone pair to transition-metal centers.[6] In
this context and in spite of the oxophilic character of low-
valent P atoms, nonmetal acceptors, such as “promoted”
Group 16 atoms, have not yet been addressed.[7] Although
the leading basic properties of PIII centers indeed increase
their propensity to undergo oxidation, the paucity of report-
Scheme 1. Lewis structures of imidazoliophosphines versus NHC–phos-
pheniums (top) and chalcogenoimidazoliophosphines versus NHC–chal-
cogenophospheniums (bottom), which correspond to an intermolecular
stabilization of the free phospheniums (A) and the chalcogenophospheni-
ums (B), respectively.
[a] C. Maaliki, Dr. C. Lepetit, C. Duhayon, Dr. Y. Canac,
Prof. R. Chauvin
CNRS, LCC (Laboratoire de Chimie de Coordination)
205 route de Narbonne, F-31077 Toulouse (France)
Fax : (+33)561-55-30-03
E-mail: yves.canac@lcc-toulouse.fr
chauvin@lcc-toulouse.fr
ed attempts at preparing chalcogenophospheniums is likely
+
ꢀ
ꢀ
related to the P
X polarization of the PPX bond, which
increases when going up Group 16 (O>S>Se).[8] Thus, the
isolation of free chalcogenophosphenium cations [R2P+ =X]
(B) would require very peculiar donating substituents;
indeed, the only characterized example was reported by
Schmidpeter et al. in the less-challenging selenooxophosphe-
nium series, [(Ph3PCPh)2P+ =Se], in which the electrophilic
phosphorus center was stabilized by strongly donating phos-
[b] C. Maaliki, Dr. C. Lepetit, C. Duhayon, Dr. Y. Canac,
Prof. R. Chauvin
Universitꢀ de Toulouse, UPS, INP
LCC, F-31077 Toulouse (France)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201001008. It contains the
1H NMR and 31P NMR spectra of the new compounds.
Chem. Eur. J. 2012, 18, 16153 – 16160
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
16153

phonium ylide substituents.[9]
Similar attempts to isolate
more polarized oxo- and thio-
oxophospheniums were report-
ed to mainly afford four-mem-
bered cyclodimeric species,
[R2PX]22+, but the nature of the
ꢀ
four P X bonds was not ad-
dressed.[10] Likewise, Burford
and co-workers described rele-
vant 4-aminopyridiniothiooxo-
phosphines as DMAP-coordi-
nated thiophosphoniums on the
basis of the observation of a
displacement of DMAP by
PMe3, but theoretical argu-
ments on the exact nature of
Scheme 2. Synthetic routes to chalcogenoimidazoliophosphines 5a,b from phenylimidazole 1 and subsequent
ꢀ
heterolytic cleavage of the C P bond.
ꢀ
the N P bond remain desira-
ble.[11] It should be noted that in all the reported examples,
such species were referred to as oxo-, thioxo-, or selenoxo-
phosphoniums and, more generally, as chalcogenophospho-
niums, by implying a reference to (s3,l4)-phosphonium struc-
tures. The merit of the alternative designations phospheni-
um oxides, phosphenium sulfides, and, more generally, chal-
cogenophospheniums is the implicit reference to their here-
after demonstrated Lewis acidic character.
respectively. Notably, the neutral phosphine oxide (4a)
could also be obtained, albeit in a poorer 25% yield, in a
one-pot procedure by treating compound 1 with 1 equivalent
of nBuLi in the presence of a stoichiometric amount of di-
phenylphosphonyl chloride. Quaternization of the sp2
N atom of the imidazole ring of compounds 4a,b with
MeOTf in CH2Cl2 allowed chalcogenoimidazoliophosphines
5a and 5b to be isolated in 94 and 96% yield, respectively
(Scheme 2, route a). An alternative strategy involved the ox-
idation of amidiniophosphine 3 by m-CPBA in CH2Cl2 or by
S8 in toluene, thereby allowing chalcogenophosphines 5a
and 5b to be isolated in 48 and 72% yield, respectively
(Scheme 2, route b).[14]
Because carbenes are currently considered as stabilizing
agents of reactive electrophilic species, such as unusual cati-
ons[4,12] and low-coordinate main-group atoms,[13] one may
wonder about their possible use in stabilizing chalcogeno-
phospheniums of type B. Having established the R2N2C:!
+
The 31P NMR chemical shifts of chalcogenoamidiniophos-
phines 5a (dp =+18.5 ppm) and 5b (dp =+30.8 ppm) were
found to be similar to those of their respective neutral pre-
cursors (4a: dp =+16.1 ppm, 4b: dp =+29.6 ppm). Their
ionic structure was consistent with their poor solubility in
ꢀ
PR’2 dative character of the C P bond in amidiniophos-
phines,[5] herein, we address the exact nature of the C P
ꢀ
+
ꢀ
bond in P-oxidized analogues, [R2N2C P(=X)R’2] , on the
basis of experimental and theoretical investigations
(Scheme 1).
ꢀ
nonpolar solvents and with the deshielding of the N CH3
signal in their 1H NMR spectra (dH range from 3.7 to
4.1 ppm). The structures of compounds 2, 3, 4a,b, and 5b
were finally confirmed by X-ray-diffraction analysis of color-
less crystals (Table 1, Figure 1).[15]
2. Results and Discussion
Several complementary approaches were envisaged for ac-
cessing chalcogenoimidazoliophosphines 5a,b from the read-
ily available 1-phenylimidazole (1, Scheme 2). The addition
of 1 equivalent of nBuLi in Et2O, followed by a stoichiomet-
ric amount of chlorodiphenylphosphine, afforded mono-
phosphine 2 (dp =ꢀ29.3 ppm) in 55% yield. The reaction of
compound 2 with 1 equivalent
As a general trend, quaternization of the imidazole ring
ꢀ
of imidazoliophosphines results in a lengthening of the C1
P1 bond; herein, such behavior was particularly observed on
going from compound 4b (1.8110(12) ꢂ) to compound 5b
(1.839(3) ꢂ). This result can be attributed to the dative
of MeOTf in CH2Cl2 gave
Table 1. Selected bond lengths [ꢂ] taken from the X-ray-diffraction data of compounds 2, 3, 4a,b, and 5b and
of Ph3P=X (X=O, S) reference compounds.[a]
A
3
(dp =
2
3
4a
4b
5b
Ph3P=S
Ph3P=O
2
ꢀ
C1 P1
1.8307(10)
1.3234(14)
1.3690(16)
–
–
1.8346(14)
1.3433(18)
1.3500(18)
–
–
1.8066(10)
1.3279(13)
1.3698(14)
–
1.8110(12)
1.3222(16)
1.3725(16)
1.9463(4)
–
1.839(3)
1.344(4)
1.354(4)
1.9458(11)
–
–
–
–
–
–
–
was treated with meta-chloro-
perbenzoic acid (m-CPBA) in
CH2Cl2 or with S8 in toluene to
afford their corresponding neu-
tral chalcogenophosphines (4a
ꢀ
C1 N1
ꢀ
C1 N2
–
1.94–1.95
–
P1=S
P1=O
1.4899(7)
1.48–1.49
[a] Data extracted from the Cambridge Crystallographic Database[15] (for atom numbering, see Scheme 2 and
and 4b) in 82 and 88% yield, Figure 1).
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Chem. Eur. J. 2012, 18, 16153 – 16160

Carbene-Stabilized Phosphenium Oxides and Sulfides
FULL PAPER
Figure 1. X-ray crystal structures of compounds 4a (left), 4b (middle), and 5b (right); thermal ellipsoids are set at 30% probability, and the triflate
anions and H atoms are omitted for clarity.
ꢀ
nature of the C P bond in cationic derivatives 3 and 5b or,
equivalently, by saying that compounds 3 and 5b are better
described as NHC–phosphenium and NHC–thioxophosphe-
dene (BAC) is known to be a stronger donor than unsaturat-
ed NHCs,[17] the bis(diisopropylamino)cyclopropeniodi
phen-
ylphosphine (7) was envisaged following a procedure that
was recently reported by Alcarazo et al.[18]
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
+
ꢀ
nium adducts, respectively. Thus, by comparison to P
X
bonds, the expected depolarization of the P2+
bond to
Treatment of compound 7 with m-CPBA in CH2Cl2 or S8
in toluene afforded the corresponding cyclopropeniochalco-
genophosphines (8a and 8b) in 79 and 62% yield, respec-
tively (Scheme 3).[19] The observed 31P NMR chemical shifts
(8a: dp =+14.0 ppm; 8b: dp =+28.4 ppm) are within the typ-
ical range for phosphine oxides and thioxides, and similar to
those of imidazolio analogues 5a,b. The structures of com-
pounds 8a,b were finally confirmed by X-ray-diffraction
analysis of colorless crystals and compared with that of the
precursor (7, Figure 2).[15]
ꢀ
ꢀ
X
P+=X bonds (X=O, S), is balanced by donation from the
carbene ligand. Indeed, the PPX bond lengths are similar to
those reported in Ph3PPX triaryl chalcogenophosphine ref-
erence compounds (Table 1). Notably, attempts to crystal-
lize oxo-analogue 5a only afforded N,N-methyl-
ACHTUNGTRENNUNG(phenyl)imidazolium salt 6, which resulted from the cleav-
[16]
ꢀ
ꢀ
age of the N2C P bond. The weakness of the C P bond
in compounds 5a,b was confirmed by the displacement of
the NHC moiety (which was isolated after protonation as
imidazolium cation 6) from the phosphenium fragment by a
chloride ion (treatment with Et4NCl at room temperature),
which can be regarded as a weak nucleophile towards stand-
ꢀ
ard C P bonds. Similar chemical evidence for the dative
ꢀ
nature of the N2C P bond was recently reported for nonoxi-
dized imidazoliophosphine (PIII) analogues of compound
3[5b] and, thus, the same conclusion applies to the PV chalco-
genoimidazoliophosphines (5a,b).
Scheme 3. Preparation of chalcogenocyclopropeniophosphines 8a,b by
oxidation of the PIII precursor (7) and subsequent heterolytic cleavage of
A carbene donor that is stronger than imidazolylidene is
expected to increase the stability of the chalcogenophosphe-
nium adducts. Because bis(diisopropylamino)cyclopropenyli-
ꢀ
the C P bond.
Figure 2. X-ray crystal structures of compounds 7 (left), 8a (middle), and 8b (right); thermal ellipsoids are set at 30% probability, and the tetrafluorobo-
ꢀ
ꢀ
ꢀ
ꢀ
rate anions and H atoms are omitted for clarity. Selected bond distances [ꢂ] and angles [8]: 7: C1 P1 1.807(2), C1 C2 1.373(3), C2 C3 1.417(3), C2 N1
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ ꢀ
1.309(3); C2 C1 P1 147.86(18). 8a: C1 P1 1.8016(9), C1 C2 1.3812(13), C2 C3 1.4196(13), C2 N1 1.3058(12), P1 O1 1.4843(7); C1 P1 O1 112.25(4),
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
C2 C1 P1 150.66(7). 8b: C1 P1 1.807(3), C1 C2 1.382(5), C2 C3 1.418(4), C2 N1 1.299(5), P1 S1 1.9476(12); C1 P1 S1 113.71(12), C2 C1 P1
147.1(3).
Chem. Eur. J. 2012, 18, 16153 – 16160
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www.chemeurj.org
16155

Y. Canac, R. Chauvin et al.
ꢀ
Table 2. Quantitative variation in the dative character of C···P bonds
over a representative series of carbene!chalcogenophosphenium ad-
ducts.
No significant difference between the C1 P1 bond lengths
was found for the PV derivatives 8a (1.8016(9) ꢂ) and 8b
(1.807(3) ꢂ) and for the PIII precursor 7 (1.807(2) ꢂ). This
result suggests that both systems can be described as donor–
acceptor adducts with similar characters. Moreover, the
[a]
[b]
Donor
BAC
Acceptor
DGhomo
DGhetero
D(DG)[c]
Energy shift[d]
+PPh2
62.7
58.6
69.7
65.8
60.7
71.1
62.5
55.4
61.9
57.4
49.3
55.0
0.2
3.2
7.9
8.4
11.4
16.1
–
+P(S)Ph2
+P(O)Ph2
+PPh2
3.0
4.7
–
3.0
4.7
ꢀ
slight shortening of the P1 O1 bond from 1.4899(7) ꢂ in
neutral oxide 4a to 1.4843(7) ꢂ in cationic oxide 8a tends to
suggest a decrease in the negative charge at the oxygen
center of the latter compound, which corresponds to a depo-
NHC
+P(S)Ph2
+P(O)Ph2
+
ꢀ
[a] Homolytic Gibbs dissociation energy at 298.15 K in kcalmolꢀ1
.
.
ꢀ
larization of the P O $P=O bond; such depolarization is
[b] Heterolytic Gibbs dissociation energy at 298.15 K in kcalmolꢀ1
ꢀ
possibly induced by some dative character of the C1 P1
[c] D(DG)=DGhomoꢀDGhetero
, calculated at the PCM-(U)B3PW91/6-
31G** level in the CH3CN continuum (e=35.688). [d] Difference in
D(DG) values with the upper entry.
bond in compound 8a. As in the case of compounds 5a,b
ꢀ
(Scheme 2), the dative nature of the C P bond in com-
pounds 8a,b was experimentally confirmed by the displace-
ment of the BAC carbene by a chloride ion acting as a
weak, but efficient nucleophile: the addition of Et4NCl to
compound 8a at 608C resulted in the formation of bis(diiso-
propylamino)cyclopropenium salt 9[20] after cleavage of the
purely ionic situation (X:ꢀ, P+), depending on the sign
ꢀ
C
and
C
magnitude
of
D(DG)=DGhomo(X PR2!X +
PR2)ꢀDGhetero(XꢀPR2!Xꢀ++PR2).[21]
[16]
ꢀ
weak C P bond (Scheme 3).
Further evidence for the
For imidazolylidene–phosphenium systems, the D(DG)
value was found to be positive in the range of 8.4–16.1 kcal
molꢀ1, ranking in the following order: +PPh2 <+P(S)Ph2 <
+P(O)Ph2. In the BAC–phosphenium series, the general
trend remained the same with a preference for the hetero-
lytic dissociation mode, albeit with less pronounced D(DG)
values ranging from 0.2 to
donor–acceptor nature of such systems was provided by a
carbene-ligand-exchange reaction. The addition of freshly
prepared BAC carbene[20] to NHC–oxophosphenium 5a in
THF at ꢀ788C resulted in the formation of the correspond-
ing cyclopropenylideneoxophosphenium (8a, Scheme 4).
7.9 kcalmolꢀ1 on going from
+PPh2 to +P(O)Ph2). This result
is consistent with the lower sta-
bility (higher proton affinity) of
the BAC carbene compared to
the NHC-type carbenes. The
+
ꢀ
ꢀ
C P bond of the [BAC PPh2]
system was actually found to be
dissociatively ambivalent, with
equivalent propensity to homo-
lytic and heterolytic dissocia-
tion. These data (Table 2) show
the higher dative character of
Scheme 4. NHC–BAC ligand-exchange reaction from NHC–oxophosphenium 5a to cyclopropenylidene coun-
terpart 8a. Because the reaction was performed in THF, in which compounds 5a and 8a were poorly soluble,
the 31P NMR spectra of the products were recorded in CD2Cl2 after the evaporation of THF and compared
with that of an authentic sample in the same solvent.
ꢀ
the C P(X)Ph2 bond in chalco-
Monitoring the reaction by 31P NMR spectroscopy at ꢀ208C
allowed an intermediate resonance at d=++25.9 ppm to be
identified and tentatively attributed to an adduct (10) that
resulted from the nucleophilic attack of the BAC carbene
on the electrophilic carbon center of compound 5a. As re-
cently demonstrated with chloride ions in the nonoxidized
series,[5b] intermediate 10 would be prone to give cationic
oxide 8a through an a-elimination process. After work-up,
the displaced NHC fragment was recovered in its protonat-
ed form, that is, imidazolium salt 6.
genophosphines (X=O, S) in comparison to the parent non-
oxidized phosphines (X=lone pair). The dative character
increases in the order: X=lone pair<S<O, with strictly
identical shifts of 3.0 and 4.7 kcalmolꢀ1 in both the imida
ACHTUNGTRENNUNGzol-
AHCTUNGTREGyNNNU lidene and BAC series. The calculated values also indicate
that the thiooxophosphenium, +P(S)Ph2, dissociates more
+
easily than the oxophosphenium, P(O)Ph2.
In both series, the calculated values confirmed the “true”
+
dative character of the R2C:!P(X)Ph2 bond. In other
words, chalcogenoimidazolio- and chalcogenocyclopropenio-
phosphines are, thus, definitely more-accurately described as
carbene!chalcogenophosphenium adducts.
ꢀ
The nature of the C P(X)Ph2 bond was further investigat-
ed by performing DFT calculations. Thus, the differences
between the homolytic and heterolytic Gibbs dissociation
energies D(DG) were calculated at 298.15 K in the CH3CN
continuum dielectric medium (polarizable continuum model
(PCM) method) at the (U)B3PW91/6-31G** level (Table 2).
The degree of dative character of a generic X···P bond
3. Conclusion
+
ꢀ
Oxidized carbeniophosphines (R2C Ph2P=X; X=O, S)
have been isolated and fully characterized as stable carbene
ꢀ
varies from the purely covalent situation (X P) to the
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Chem. Eur. J. 2012, 18, 16153 – 16160

Carbene-Stabilized Phosphenium Oxides and Sulfides
FULL PAPER
adducts. The experimental evidence for the R2C:!P+(X)Ph2
dative bond, which was provided by the displacement of the
carbene by a chloride ion acting as a weak but efficient nu-
cleophile was theoretically confirmed and refined by the
preference for a heterolytic dissociation mode over the ho-
molytic one. From the NHC:!P+(O)Ph2 adduct, exchange
of the NHC ligand by the more nucleophilic BAC carbene
afforded the corresponding BAC:!P+(O)Ph2 adduct, thus
providing a further illustration of the relevance of the
donor–acceptor description of the carbene!chalcogeno-
phosphenium systems. Just as for their PIII parent, but in an
even more pronounced manner, PV chalcogenocarbenio-
phosphines must be referred to as carbene!phosphenium
oxide or sulfide adducts. The PIII lone pair of carbeniophos-
phines had previously been demonstrated to remain availa-
ble for coordination to metal fragments[4] and, herein, is re-
ported to remain available for coordination to nonmetallic
Lewis acids, such as promoted Group 16 atoms.[7] A natural
issue for future investigation is the generalization of this
study to Group-14- and Group-15-oxidized phosphenium an-
alogues, namely, methylene–phosphoniums [R2P+ =CR2][22]
134.2 (CHAr), 133.1 (d, J
(C,P)=7.0 Hz; C), 130.8 (CHAr), 130.3 (d, J
(CHAr), 120.5 (q, J ACHTUNGTRENNUNG
(C,F)=320.0 Hz; CF3SO3ꢀ), 41.1 ppm (d, J
ACHTUNGTRENNUNG
U
ACHTUNGTRENNUNG
A
4.5 Hz; CH3); 31P NMR (CDCl3, 258C): d=ꢀ18.2 ppm; MS (ES): m/z:
343.1 [M]+; HRMS (ES): m/z calcd for C22H20N2P: 343.1364; found:
343.1367; elemental analysis calcd (%) for C23H20F3N2O3PS·0.3CH2Cl2:
C 53.82, H 4.00, N 5.38; found: C 53.30, H 4.19, N 5.49.
Neutral phosphine oxide 4a: Route a: m-CPBA (42 mg, 0.02 mmol) was
added to a solution of compound 2 (80 mg, 0.02 mmol) in CH2Cl2 (4 mL)
at RT, and the mixture was stirred for 2 h. After evaporation of the sol-
vent under vacuum, purification by column chromatography on silica gel
(EtOAc/n-pentane) afforded compound 4a as a white solid (68 mg,
82%). Recrystallization at ꢀ208C from CH2Cl2/Et2O gave compound 4a
as colorless crystals. M.p. 160–1618C.
Route b: nBuLi (2.5m in n-hexane, 2.6 mL, 6.94 mmol) was added to a
solution of 1-(1-phenyl)-1H-imidazole (1, 1.0 g, 6.94 mmol) in Et2O
(60 mL) at ꢀ788C. The suspension was warmed to RT and stirred for 4 h.
After the addition of diphenylphosphinic chloride (1.32 mL, 6.94 mmol)
at ꢀ788C, the solution was slowly warmed to RT and stirred for 3 h. The
organic layer was washed with brine, extracted with Et2O (2ꢃ20 mL),
and dried over MgSO4. After evaporation of the solvent, purification by
column chromatography on silica gel (EtOAc/n-pentane) afforded com-
pound 4a as a white solid (602 mg, 25%).
1H NMR (CDCl3, 258C): d=7.77–7.70 (m, 5H; HAr), 7.53–7.25 ppm (m,
12H; HAr); 13C NMR (CDCl3, 258C): d=147.5 (d, J
ACHTUNGTRENNUNG
+
[23]
ꢀ
and iminophosphoniums [R2P =N R].
142.5 (C), 137.4 (d, J
C), 136.9 (d, J
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
(ES): m/z: 345.1 [M+H]+; HRMS (ES): m/z calcd for C21H18N2OP:
345.1157; found: 345.1157; elemental analysis calcd (%) for
C21H17N2OP·0.1CH2Cl2: C 71.48, H 4.90, N 7.89; found: C 71.56, H 5.05,
N 7.79.
Experimental Section
General remarks: THF, Et2O, and toluene were dried and distilled over
sodium/benzophenone; n-pentane, CH2Cl2, and CH3CN were dried and
distilled over P2O5. All other reagents were commercially available and
used as received. All reactions were carried out under an argon atmos-
phere by using Schlenk and vacuum-line techniques. 1H, 13C, and
31P NMR spectroscopy was performed on Bruker DPX 300 and Avance
500 spectrometers. NMR chemical shifts (d) are given in ppm, relative to
tetramethylsilane (1H and 13C) or to H3PO4 (31P); coupling constants (J)
are given in Hz.
Neutral phosphine sulfide 4b: Elemental sulfur (500 mg, 1.95 mmol) was
added to a solution of compound 2 (320 mg, 0.97 mmol) in toluene
(10 mL) at RT, and the mixture was stirred for 2 h at 1108C. After evapo-
ration of the solvent, purification by column chromatography on silica
gel (CH2Cl2) afforded compound 4b as a white solid (309 mg, 88%). Re-
crystallization at ꢀ208C from CH2Cl2/Et2O gave compound 4b as color-
1
less crystals. M.p. 205–2068C; H NMR (CD2Cl2, 258C): d=7.88–7.80 (m,
Neutral phosphine 2: nBuLi (2.5m in n-hexane, 7.8 mL, 19.4 mmol) was
added to a solution of 1-(1-phenyl)-1H-imidazole (1, 2.80 g, 19.4 mmol)
in Et2O (60 mL) at ꢀ788C. The suspension was warmed to RT and stirred
for 4 h. After the addition of chlorodiphenylphosphine (3.6 mL,
19.4 mmol) at ꢀ788C, the solution was slowly warmed to RT and stirred
for 3 h. The organic layer was washed with brine, extracted with Et2O
(2ꢃ20 mL), and dried over MgSO4. After evaporation of the solvent, pu-
rification by column chromatography on silica gel (EtOAc/n-pentane) af-
forded compound 2 as a yellow solid (3.4 g, 55%). Recrystallization at
ꢀ208C from CH2Cl2/Et2O gave compound 2 as colorless crystals. M.p.
126–1278C; 1H NMR (CDCl3, 258C): d=7.75–7.68 (m, 5H; HAr), 7.46–
4H;
13C NMR (CD2Cl2, 258C): d=141.8 (d, J
132.5 (d, (C,P)=11.0 Hz; CHAr), 131.8 (d,
130.1 (d, J(C,P)=16.2 Hz; CHAr), 129.3 (CHAr), 128.5 (CHAr), 127.4
(CHAr), 126.9 (d, J
(C,P)=1.96 Hz; CHAr), 125.6 ppm (CHAr); 31P NMR
H
Ar), 7.53–7.40 (m, 7H; HAr), 7.41–7.12 ppm (m, 6H; HAr);
(C,P)=130.9 Hz; C), 138.1 (C),
(C,P)=3.09 Hz; CHAr),
AHCTUNGTRENNUNG
J
G
JACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
(CD2Cl2, 258C): d=+29.6 ppm; MS (DCI-CH4): m/z: 361.0 [M+H]+;
HRMS (DCI-CH4): m/z calcd for C21H18N2PS: 361.0928; found: 361.0939;
elemental analysis calcd (%) for C21H17N2PS·0.2CH2Cl2: C 66.88, H 4.62,
N 7.34; found: C 66.68, H 4.99, N 7.07.
Cationic phosphine oxide 5a: Route a: Methyl trifluoromethanesulfonate
(80 mL, 0.73 mmol) was added to a solution of compound 4a (250 mg,
0.73 mmol) in CH2Cl2 (10 mL) at RT, and the mixture was stirred for 2 h.
After evaporation of the solvent under vacuum and washing with Et2O
(8 mL), compound 5a was isolated as a yellow solid (347 mg, 94%).
7.22 ppm (m, 12H; HAr); 13C NMR (CDCl3, 258C): d=146.8 (d, J
5.1 Hz; C), 137.9 (C), 135.4 (d, J(C,P)=0.8 Hz; C), 133.9 (d, J
20.7 Hz; CHAr), 131.2 (CHAr), 129.1 (CHAr), 128.6 (CHAr), 128.5 (d, J-
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG(C,P)=7.7 Hz; CHAr), 126.4 (d, JACHTNUGTRENG(NNU C,P)=3.7 Hz; CHAr), 123.8 ppm
(CHAr); 31P NMR (CDCl3, 258C): d=ꢀ29.3 ppm; MS (ES): m/z: 329.1
[M+H]+; HRMS (ES): m/z calcd for C21H18N2P: 329.1208; found:
329.1192; elemental analysis calcd (%) for C21H17N2P: C 76.82, H 5.22,
N 8.53; found: C 76.13, H 5.36, N 8.26.
Route b: m-CPBA (42 mg, 0.24 mmol) was added to a solution of com-
pound 3 (60 mg, 0.12 mmol) in CH2Cl2 (6 mL) at RT, and the mixture
was stirred for 2 h. After evaporation of the solvent under vacuum and
washing with Et2O (8 mL), compound 5a was isolated as a yellow solid
(30 mg, 48%).
Cationic phosphine 3: Methyl trifluoromethanesulfonate (100 mL,
0.91 mmol) was added to a solution of compound 2 (300 mg, 0.91 mmol)
in CH2Cl2 (18 mL) at RT, and the mixture was stirred for 2 h. After evap-
oration of the solvent under vacuum and washing with Et2O (10 mL),
compound 3 was isolated as a yellow solid (418 mg, 93%). 1H NMR
(CDCl3, 258C): d=7.75–7.72 (m, 2H; HAr), 7.56–7.39 (m, 9H; HAr), 7.37–
7.25 (m, 6H; HAr), 3.50 ppm (s, 3H; CH3); 13C NMR (CDCl3, 258C): d=
1H NMR (CD3CN, 258C): d=7.88 (s, 1H; HAr), 7.70–7.45 (m, 12H; HAr),
7.35–7.30 (m, 1H; HAr), 7.17–7.08 (m, 3H; HAr), 4.02 ppm (s, 3H; CH3);
13C NMR (CD3CN, 258C): d=139.0 (d, J
ACHTUNGTRENNUNG
134.1 (d, J
N
ACHTUNGTRENNUNG
JACHTUNGTRENNUNG
J
N
N
ACHTUNGTRENNUNG
147.8 (d, J
C
E
JACHTUNGTRENNUNG
J
A
Chem. Eur. J. 2012, 18, 16153 – 16160
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
16157

Y. Canac, R. Chauvin et al.
Table 3. X-ray crystallographic data and structure-refinement parameters for compounds 2, 3, 4a,b, 5b, 6, 7, and 8a,b.
2
3
4a
4b
5b
formula
C21H17N2P
328.35
monoclinic
P21/c
12.62782(12)
9.78055(7)
14.23772(14)
90
C23H20F3N2O3PS
492.46
monoclinic
P21/c
6.79816(10)
14.20863(19)
23.8075(3)
90
C21H17N2OP
344.35
orthorhombic
Pbca
15.69713(13)
13.42347(11)
16.36596(12)
90
C21H17N2PS
360.42
monoclinic
P21/c
12.55599(13)
9.45061(9)
15.61721(16)
90
C23H20F3N2O3PS2
524.52
monoclinic
P21/c
13.8269(5)
27.9313(7)
12.9384(5)
90
Mw [gmolꢀ1
]
crystal system
space group
a [ꢂ]
b [ꢂ]
c [ꢂ]
a [8]
b [8]
108.8207(11)
90
1664.44(3)
4
90.5547(14)
90
2299.52(6)
4
90
90
15.61721(16)
90
1767.86(3)
4
110.543(4)
90
4679.1(3)
8
g [8]
V [ꢂ3]
Z
3448.47(5)
8
density
1.310
1.472
180
1.422
2.380
100
1.326
0.170
180
1.354
2.510
180
1.489
3.189
100
m [mmꢀ1
T [K]
]
q range [8]
3.7–60.1
Cu (1.54180)
19348
2466
0.022
3.6–60.6
Cu (1.54180)
16801
3444
0.024
3.3–29.4
Mo (0.71073)
100539
4593
3.7–60.7
Cu (1.54180)
10782
2666
0.014
3.4–52.9
Cu (1.54180)
20677
5400
0.035
radiation (l [ꢂ])
total reflns
unique reflns
Rint
0.033
used reflns
refined parameters
refinement on
R [I>ns(I)]
wR [I>ns(I)]
GOF
2336
218
F
0.0272
0.0400 (n=3)
1.012
ꢀ0.25/0.26
3278
298
F
0.0287
0.0321 (n=3)
0.945
ꢀ0.34/0.28
3838
226
F
0.0330 (n=3)
0.0405 (n=3)
1.062
ꢀ0.29/0.35
2570
227
F
0.0262 (n=3)
0.0323 (n=3)
1.030
ꢀ0.21/0.30
5362
613
F2
(n=3)
(n=3)
0.0454 (n=ꢀ3)
0.1209 (n=ꢀ3)
0.966
ꢀ0.48/0.70
D1min/D1max [eꢂꢀ3
]
6
7
8a
8b
formula
C11H11F3N2O3S
C27H38BF4N2O0.12
510.31
monoclinic
P21/n
8.3307(3)
28.0011(5)
12.3730(3)
90
P
C27H38BF4N2OP
524.39
orthorhombic
Pbca
14.9809(2)
16.8997(2)
21.9870(3)
90
C27H38BF4N2PS
540.45
monoclinic
P21/c
10.42668(17)
16.4610(2)
16.7823(2)
90
Mw [gmolꢀ1
]
308.28
orthorhombic
Pbca
9.24800(7)
10.33088(8)
27.2427(2)
90
crystal system
space group
a [ꢂ]
b [ꢂ]
c [ꢂ]
a [8]
b [8]
90
90
103.379(3)
90
2807.90(15)
4
90
90
100.1163(15)
90
2835.62(7)
4
g [8]
V [ꢂ3]
Z
2602.77(4)
8
5566.48(13)
8
density
1.573
2.680
180
1.207
1.246
180
1.251
1.296
100
1.266
0.216
100
m [mmꢀ1
T [K]
]
q range [8]
radiation (l [ꢂ])
total reflns
unique reflns
Rint
3.2–60.7
Cu (1.54180)
29375
1965
0.024
3.2–60.7
Cu (1.54180)
43721
4241
0.029
4.0–71.7
Cu (1.54180)
28409
5430
0.017
3.1–29.4
Mo (0.71073)
61404
7279
0.047
used reflns
1858
4002
5135
5276
refined parameters
refinement on
R [I>ns(I)]
wR [I>ns(I)]
GOF
181
F
0.0284 (n=3)
0.0320 (n=3)
1.049
ꢀ0.27/0.30
325
F
0.0610 (n=3)
0.0674 (n=3)
1.017
ꢀ0.67/0.99
325
F
0.0309 (n=3)
0.0389 (n=3)
1.055
ꢀ0.40/0.37
325
F
0.0879 (n=3)
0.1066 (n=3)
1.164
ꢀ0.85/1.69
D1min/D1max [eꢂꢀ3
]
m/z: 359.1 [M]+; HRMS (ES): m/z calcd for C22H20N2PO: 359.1313;
found: 359.1308.
Route b: Elemental sulfur (42 mg, 0.49 mmol) was added to a solution of
compound 3 (80 mg, 0.49 mmol) in toluene (10 mL) at RT, and the solu-
tion was stirred for 2 h at 1108C. After evaporation of the solvent under
vacuum and washing with Et2O (8 mL), compound 5b was isolated as a
yellow solid (61 mg, 72%).
Cationic phosphine oxide 5b: Route a: Methyl trifluoromethanesulfonate
(50 mL, 0.46 mmol) was added to a solution of compound 4b (165 mg,
0.46 mmol) in CH2Cl2 (5 mL) at RT, and the mixture was stirred for 2 h.
After evaporation of the solvent under vacuum and washing with Et2O
(10 mL), compound 5b was isolated as a yellow solid (231 mg, 96%).
1H NMR (CD2Cl2, 258C): d=8.01–7.97 (m, 3H; HAr), 7.92–7.82 (m, 2H;
H
Ar), 7.69–7.36 (m, 10H; HAr), 7.29–7.11 (m, 2H; HAr), 3.71 ppm (s, 3H;
CH3); 13C NMR (CD2Cl2, 258C): d=139.3 (d, J
AHCTUNGTRENNUNG
16158
www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 16153 – 16160

Carbene-Stabilized Phosphenium Oxides and Sulfides
FULL PAPER
(C), 133.5 (d, J
132.3 (d, (C,P)=11.8 Hz; CHAr), 132.0 (d,
131.4 (d, J(C,P)=10.9 Hz; CHAr), 130.9 (CHAr), 130.6 (CHAr), 129.6
(CHAr), 129.5 (d, J(C,P)=13.7 Hz; CHAr), 129.1 (d, J(C,P)=13.4 Hz;
CHAr), 128.0 (d, J(C,P)=3.3 Hz; CHAr), 127.5 (d, J(C,P)=91.4 Hz; C),
127.4 (d, (C,P)=3.3 Hz; CHAr), 126.7 (CHAr), 122.5 (CHAr), 121.3
(CHAr), 120.8 (q, J
N
G
Cyclopropenium salt 9 was prepared by the addition of diisopropylamine
(9.4 mL, 0.13 mol) at 08C to a stirring solution of tetrachlorocyclopro-
pene (2.7 mL, 0.022 mol) in CH2Cl2 (300 mL). After warming to RT and
stirring for 6 h, a pale-yellow suspension was formed. NaBF4 (2.36 g,
0.022 mmol) was added and the suspension was stirred vigorously over-
night. Triphenylphosphine (5.64 g, 0.021 mol) was added, followed imme-
diately by deionized water (250 mL), and the suspension was stirred at
RT for 8 h. The organic layer was washed with deionized water (4ꢃ
250 mL) to afford a yellow solution, which was dried over MgSO4. The
volatile compounds were removed under vacuum. Compound 9 was puri-
fied by two successive recrystallizations from refluxing THF. M.p. 168–
1698C; 1H NMR (CD3CN, 258C): d=7.21 (s, 1H; HAr), 4.01 (sept,
J
ACHTUNGTRENNUNG
R
JACHTUNGTRENNUNG
E
G
JACHTUNGTRENNUNG
Imidazolium salt 6: A mixture of tetraethylammonium chloride (21 mg,
0.13 mmol) and compound 5a (67 mg, 0.13 mmol) was dissolved in
CD3CN (6.0 mL) and stirred at RT. NMR spectroscopic analysis showed
that compound 5a was slowly and quantitatively converted into imidazo-
lium salt 6, which was characterized by comparison of the multinuclear
NMR data with those of an authentic sample that was prepared as descri-
bed below.
J
J
N
ACHTUNGTNER(NUNG H,H)=6.8 Hz, 2H; CH), 1.34 (t,
97.8 (CH), 57.5 (CH), 48.1 (CH), 19.9 (CH3), 19.7 (CH3); MS (ES): m/z:
237.2 [M]+; HRMS (ES): m/z calcd for C15H29N2: 237.2331; found:
237.2336.
Imidazolium salt 6 was prepared by the addition of methyl trifluoro-
ACHTUNGTRENNUNGmethanesulfonate (569 mL, 0.35 mmol) to 1-(1-phenyl)-1H-imidazole (1,
Computational details: Geometries were fully optimized at the
(U)B3PW91/6–31G** level by using Gaussian 09.[24] Vibrational analysis
was performed at the same level as the geometry optimizations. Solvent
effects were included by using the polarizable continuum model (PCM),
which was implemented in Gaussian 09 for CH3CN (e=35.688). Gibbs
free energies were calculated at 298.15 K.
500 mg, 0.35 mmol) in CH2Cl2 (5.0 mL) at RT. After evaporation of the
solvent under vacuum and washing with Et2O (10.0 mL), compound 6
was isolated as a white solid (1.10 g, 96%). Recrystallization at RT from
CH2Cl2/n-pentane gave compound 6 as colorless crystals. M.p. 83–848C;
1H NMR (CD3CN, 258C): d=8.98 (s, 1H; HAr), 7.79 (s, 1H; HAr), 7.64
(br s, 5H; HAr), 7.58 (s, 1H; HAr), 3.98 ppm (s, CH3); 13C NMR (CD3CN,
258C): d=135.4 (CH), 134.9 (C), 130.3 (CHAr), 130.2 (CHAr), 124.4
(CHAr), 122.4 (CHAr), 121.6 (CHAr), 36.2 ppm (CH3); MS (ES): m/z:
159.1 [M]+; HRMS (ES): m/z calcd for C10H11N2: 159.0922; found:
159.0911; elemental analysis calcd (%) for C11H11F3N2O3S: C 42.86,
H 3.60, N 9.09; found: C 43.84, H 3.84, N 8.33.
Crystal-structure determination of compounds 2, 3, 4a,b, 5b, 6, 7, and
8a,b: (Table 3) Intensity data were collected at low temperatures on a
GEMINI Oxford diffractometer. Structures were solved by using
SIR92[25] or SUPERFLIP[26] and refined by full-matrix least-squares pro-
cedures with the program CRYSTALS.[27] Atomic-scattering factors were
taken from the International Tables for X-ray Crystallography.[28] All
nonhydrogen atoms were refined anisotropically. Hydrogen atoms were
refined by using a riding model. Absorption corrections were introduced
by using the program MULTISCAN.[29] Compound 7 (C27H38BF4N2P)
was crystallized with compound 8a (C27H38BF4N2OP) in the ratio
0.12:0.88.
Cationic phosphine oxide 8a: m-CPBA (74 mg, 0.43 mmol) was added to
a solution of compound 7 (220 mg, 0.43 mmol) in CH2Cl2 (10 mL) at RT,
and the mixture was stirred for 2 h at RT. After evaporation of the sol-
vent under vacuum, recrystallization from CHCl3/n-pentane afforded
compound 8a as colorless crystals (180 mg, 79%). M.p. 110–1128C;
1H NMR (CD3CN, 258C): d=8.02–7.44 (m, 10H; HAr), 4.15 (sept,
J
J
N
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Acknowledgements
U
J
N
ACHTUNGTRENNUNG
Beyond the Ministꢄre de l’Enseignement Supꢀrieur de la Recherche et
de la Technologie and the Universitꢀ Paul-Sabatier, the authors also
thank the Centre National de la Recherche Scientifique and the ANR
program (No. ANR-08-JCJC-0137–01) for a doctoral fellowship to C.M.
The theoretical studies were performed by using HPC resources from
CALMIP (Grant 2011 and 2012 [0851]), and from GENCI-[CINES/
IDRIS] (Grant 2011 and 2012 [085008]).
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
20.3 (CH3), 19.3 ppm (CH3); 31P NMR (CD3CN, 258C): d=+15.2 ppm;
MS (ES): m/z: 437.2 [M]+; HRMS (ES): m/z calcd for C27H38N2OP:
437.2722; found: 437.2722.
Cationic phosphine sulfide 8b: Elemental sulfur (43 mg, 0.17 mmol) was
added to
a solution of compound 7 (57 mg, 0.17 mmol) in toluene
(5.0 mL), and the mixture was stirred for 3 h at 508C. After evaporation
of the solvent, purification by column chromatography on silica gel
(CH2Cl2) afforded compound 8b as a white solid (38 mg, 62%). Recrys-
tallization at RT from CH2Cl2/n-pentane gave compound 8b as colorless
crystals. M.p. 2208C dec.; 1H NMR (CD3CN, 258C): d=7.98–7.90 (m,
[1] a) A. H. Cowley, R. A. Kemp, Chem. Rev. 1985, 85, 367; b) M. San-
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Low Coordination in Phosphorus Chemistry (Eds.: M. Regitz, O.
Scherer), Thieme, Stuttgart, 1990, pp. 129; c) D. Gudat, Coord.
Chem. Rev. 1997, 163, 71.
[2] a) T. Kaukorat, I. Neda, R. Schmutzler, Coord. Chem. Rev. 1994,
137, 53; b) C. Chuit, C. Reyꢀ, Eur. J. Inorg. Chem. 1998, 1847;
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[3] a) N. Burford, T. S. Cameron, P. J. Ragogna, J. Am. Chem. Soc. 2001,
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4H; HAr), 7.77–7.63 (m, 6H; HAr), 4.15 (sept, J
3.61 (sept, J(H,H)=6.9 Hz, 2H; CH), 1.36 (d, J
CH3), 1.00 ppm (d, J
(H,H)=6.9 Hz, 12H; CH3); 13C NMR (CD3CN,
258C): d=136.4 (d, J(C,P)=6.7 Hz; C), 133.5 (d, J(C,P)=3.2 Hz; CHAr),
131.9 (d, J(C,P)=11.6 Hz; CHAr), 130.1 (d, J(C,P)=93.5 Hz; C), 129.5 (d,
(C,P)=13.6 Hz; CHAr), 99.4 (d, J(C,P)=73.4 Hz; C), 54.0 (CH), 53.5
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
J
N
ACHTUNGTRENNUNG
(CH), 20.6 (CH3), 19.8 ppm (CH3); 31P NMR (CD3CN, 258C): d=
+28.4 ppm; MS (ES): m/z: 453.2 [M]+; HRMS (ES): m/z calcd for
C27H38N2PS: 453.2496; found: 453.2493.
Diaminocyclopropenium salt 9: A mixture of tetraethylammonium chlor-
ide (22 mg, 0.13 mmol) and compound 8a (70 mg, 0.13 mmol) was dis-
solved in CD3CN (6 mL) and stirred at 508C. NMR spectroscopic analy-
sis showed that compound 8a was slowly and quantitatively converted
into cyclopropenium salt 9, which was characterized by comparison of
the multinuclear NMR data with those of authentic sample that was pre-
pared as described below.
[4] a) N. Kuhn, J. Fahl, D. Blꢅser, R. Boese, Z. Anorg. Allg. Chem.
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Received: June 27, 2012
Revised: September 2, 2012
Published online: October 18, 2012
16160
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