(Phosphino)(aryl)carbenes: Effect of aryl substituents on their stabilization mode

Article abstract of DOI:10.1021/ja0281986

A broad range of (phosphino)(aryl)carbenes, 1b-d, 10a,b, and 14a,b, were prepared by photolysis of their diazo precursors. The influence of the steric and electronic properties of the aryl ring on the structure and stability of these carbenes was studied

Full text of DOI:10.1021/ja0281986

Published on Web 12/10/2002
(Phosphino)(Aryl)Carbenes: Effect of Aryl Substituents on
Their Stabilization Mode
Emmanuelle Despagnet-Ayoub,† Ste´phane Sole´,† Heinz Gornitzka,†
Alexander B. Rozhenko,‡ Wolfgang W. Schoeller,*,‡ Didier Bourissou,*,† and
Guy Bertrand*,†,§
Contribution from the Laboratoire d’He´te´rochimie Fondamentale et Applique´e du CNRS
(UMR 5069), UniVersite´ Paul Sabatier, 118, route de Narbonne,
F-31062 Toulouse Cedex 04, France, Fakulta¨t fu¨r Chemie der UniVersita¨t, Postfach 10 01 31,
D-33615 Bielefeld, Germany, and UniVersity of California at RiVerside-Centre National de la
Recherche Scientifique Joint Research Chemistry Laboratory (UMR 2282),
Department of Chemistry, UniVersity of California, RiVerside, California 92521-0403
Received August 19, 2002
Abstract: A broad range of (phosphino)(aryl)carbenes, 1b-d, 10a,b, and 14a,b, were prepared by photolysis
of their diazo precursors. The influence of the steric and electronic properties of the aryl ring on the structure
and stability of these carbenes was studied both experimentally and theoretically. Among the different
stabilization modes investigated, those featuring an acceptor as well as a spectator aryl substituent result
in stable or at least persistent carbenes that could be completely characterized by classical spectroscopic
methods. In marked contrast, the new susbtitution pattern featuring a donor aryl ring results in a very
fleeting carbene.
Introduction
In the last 15 years, our understanding of carbene chemistry
has advanced dramatically with the preparation of persistent
triplet di(aryl)carbenes1 and the isolation of singlet carbenes.2
The former are potential building blocks for organic magnets,3
while the latter, when used as ligands for transition metal centers,
afford complexes with enhanced catalytic activity.4
Following the early predictions by Wanzlick,5 the first isolated
singlet carbenes A6 and B7 featured two heteroatomic substit-
Figure 1. Structure of stable singlet carbenes A-C, 1a, and 2a.
uents that both interact with the carbene center (Figure 1);
however, totally different stabilization modes are involved for
A (push-pull) and B (push-push). The range of stable carbenes
was recently expanded to include monoheteroatom-substituted
carbenes, for which the stabilization modes also differ signifi-
cantly one to the another. A “push-pull” stabilization allowed
for the preparation of the (aryl)carbene 1a,8 while for carbenes
2a9 and C,10 a single electron-active substituent is involved and
the aryl substituent remains merely a spectator.
To determine the electronic and steric factors that influence
the stability and structure of these carbenes, we report here a
detailed experimental and computational study of (phosphino)-
(aryl)carbenes bearing different substituents on the aryl ring.
Notably, a new susbtitution pattern featuring a donor aryl ring
has been investigated.
* To whom correspondence should be addressed: e-mail gbertran@
mail.ucr.edu.
† Universite´ Paul Sabatier.
‡ Fakulta¨t fu¨r Chemie der Universita¨t.
§ University of California.
(1) (a) Tomioka, H. Acc. Chem. Res. 1997, 30, 315. (b) Tomioka, H. In
AdVances in Carbene Chemistry; Brinker, U. H., Ed.; JAI Press: Stamford,
CT, 1998; Vol. 2, p 175. (c) Tomioka, H.; Iwamoto, E.; Takura, H.; Hirai,
K. Nature 2001, 412, 626. (d) Tomioka, H.; Watanabe, T.; Hattori,.;
Nomura, N.; Hirai, K. J. Am. Chem. Soc. 2002, 124, 474.
(2) (a) Bourissou, D.; Guerret, O.; Gabba¨ı, F. P.; Bertrand, G. Chem. ReV.
2000, 100, 39. (b) Arduengo, A. J., III Acc. Chem. Res. 1999, 32, 913.
(3) (a) Iwamura, H.; Koga, N. Acc. Chem. Res. 1993, 26, 346. (b) Veciana, J.;
Iwamura, H. MRS Bull. 2000, 25, 41.
(4) (a) Jafarpour, L.; Nolan, S. P. AdV. Organomet. Chem. 2001, 46, 181. (b)
Herrmann, W. A.; Weskamp, T.; Bohm, V. P. W. AdV. Organomet. Chem.
2002, 48, 1. (c) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290.
(5) (a) Wanzlick, H. W.; Kleiner, H. J. Angew. Chem. 1961, 73, 493. (b)
Wanzlick, H. W. Angew. Chem., Int. Ed. Engl. 1962, 1, 75. (c) Wanzlick,
H. W.; Esser, F.; Kleiner, H. J. Chem. Ber. 1963, 96, 1208. (d) Wanzlick,
H. W.; Scho¨nherr, H. J. Liebigs Ann. Chem. 1970, 731, 176. (e) Scho¨nherr,
H. J.; Wanzlick, H. W. Chem. Ber. 1970, 103, 1037. (f) Walentowski, R.;
Wanzlick, H. W. Z. Naturforsch. 1970, 25b, 1421.
(6) (a) Igau, A.; Gru¨tzmacher, H.; Baceiredo, A.; Bertrand, G. J. Am. Chem.
Soc. 1988, 110, 6463. (b) Igau, A.; Baceiredo, A.; Trinquier, G.; Bertrand,
G. Angew. Chem., Int. Ed. Engl. 1989, 28, 621.
(7) Arduengo, A. J., III; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1991,
113, 361.
(8) Buron, C.; Gornitzka, H.; Romanenko V.; Bertrand, B. Science 2000, 288,
834.
(9) Despagnet, E.; Gornitzka, H.; Rozhenko, A. B.; Schoeller, W. W.;
Bourissou, D.; Bertrand, G. Angew. Chem., Int. Ed. 2002, 41, 2835.
(10) (a) Sole´, S.; Gornitzka, H.; Schoeller, W. W.; Bourissou, D.; Bertrand, G.
Science 2001, 292, 1901. (b) Wentrup, C. Science 2001, 292, 1846.
9
124
J. AM. CHEM. SOC. 2003, 125, 124-130
10.1021/ja0281986 CCC: $25.00 © 2003 American Chemical Society

Stabilization Modes of (Phosphino)(Aryl)Carbenes
A R T I C L E S
Scheme 1
level were performed on the model (phosphino)(aryl)carbenes
1*a-f, featuring NH2 groups at phosphorus, and on the
experimentally observed carbene 1a. Surprisingly, the optimized
structures for 1*a-e, summarized in Table 2, are very similar
whatever the position and the number of trifluoromethyl groups
(P-Ccarb ) 1.56-1.58 Å, Ccarb-Cipso ) 1.42-1.44 Å, and
P-Ccarb-Cipso ) 141-146°), and isomeric carbenes 1*a,b and
1*c-e are very close in energy. This suggests that, despite the
strong withdrawing effect of the CF3 group, the CF3-substituted
aryl rings provide only a weak withdrawing effect, which is
further corroborated by comparing the optimized geometries of
1*a-e with that of the related (phenyl)carbene 1*f. A significant
electronic contribution of the aryl substituent was only observed
for 1a featuring di(isopropyl)amino groups at phosphorus.
Indeed, the steric repulsion between the bulky substituents at
Table 1. Selected NMR Data and Thermal Stability of
Phosphinocarbenes R2PCR′
1
compound
R
R′
31P 13C JPC T (°C)
ref
c
1a
1b
1c
1d
2a
10a
N(i-Pr)2
N(i-Pr)2
N(i-Pr)2
N(i-Pr)2
N(i-Pr)2
N(i-Pr)2
o,o′-(CF3)2Ph
o,p-(CF3)2Ph
o-(CF3)Ph
p-(CF3)Ph
o,o′,p-Me3Ph
C6F5
-22 146 271
-19 149 193
-20 149 124
80 8
40 this work
40 this work
-13 160 66 -20 this work
-23 151 65
9 133 58
6
40 9
20 this work
20 this work
-70 this work
10b N(c-Hex)2 C6F5
14a N(i-Pr)2
14b N(i-Pr)2
the phosphorus center and the aryl ring widens the P-Ccarb
-
o-Me-p-(NMe2)Ph -18
Cipso bond angle (155°). As a result, the overlap between the
carbene lone pair and the π-system of the aryl ring increases,
as indicated by the significant shortening of the Ccarb-Cipso bond
length (1.40 Å) observed in this case.
o-MePh -20 156 46
0
this work
Results and Discussion
Although, as mentioned above, numerous decomposition
pathways were observed for 1b and 1d, gentle heating of carbene
1c at 40 °C overnight affords the four-membered heterocycle
5c, which was characterized spectroscopically (Scheme 2). The
presence of an AX system in the 31P NMR spectrum (δ 31P
36.8 and 75.5, JPP ) 52 Hz) suggested a novel two carbene
unit coupling. Indeed, the previously reported CdC dimeriza-
tion8 and [2 + 2]-cycloaddition12 pathways would have lead to
symmetrical structures featuring two magnetically equivalent
phosphorus atoms. The structure of 5c was deduced from the
X-ray diffraction study performed on compound 6c, which was
obtained by treatment of 5c with elemental sulfur (Figure 2,
Table 3). Formally, compound 5c results from the dimerization
of 1c with concomitant elimination of 1 equiv of the imine
Me2CdN(i-Pr).13 Mechanistically, it is likely that initial nu-
cleophilic attack of the carbene on the electrophilic phosphorus
center of another carbene molecule leads to the zwitterionic
structure 7c. The expected ring closure of 7c is probably
impeded by steric constraints, so that elimination of imine occurs
to give the 1λ3,3λ5-diphosphabutadiene 8c; an electrocyclization
finally affords the four-membered diphosphorus-containing
heterocycle 5c.
(Pentafluorophenyl)- and (p-NR2-Substituted-aryl)car-
benes 10a,b and 14a,b. The synthesis of (phosphino)carbenes
1a-d and 2a demonstrates that observable (phosphino)(aryl)-
carbenes can be prepared whatever the steric bulk and the
electronic propertiessacceptor or spectatorsof the aryl ring.
Subsequently, the preparation of (phosphino)carbenes featuring
a donor aryl substituent was investigated. Because fluorine atoms
have potentially a π-donating effect and as C-F bonds are inert
toward insertion of singlet10 and even triplet carbenes,14 the
pentafluorophenyl substituent15 was chosen for initial study.
(CF3-Substituted-aryl)carbenes 1a-1d. The influence of the
electronic and steric effects of electron-withdrawing substituents
on the structure and stability of (phosphino)(aryl)carbenes was
investigated by varying the number and position of CF3 groups
on the aryl ring. Three new diazo precursors 4b-d were
prepared in moderate yields by metalation of the corresponding
aryldiazomethanes 3b-d, followed by reaction with chlorobis-
(diisopropylamino)phosphine (Scheme 1). Photolysis of 4b-d
(312 nm) in deuterated toluene at low temperature allowed
carbenes 1b-d to be characterized by multinuclear NMR
spectroscopy.
Thermal stabilities of 1b-d, as determined qualitatively by
variable-temperature 31P NMR experiments, are very different.
The indicated values Tc correspond to the temperatures above
which degradation occurs within a few hours (Table 1). From
these values, it is clear that steric hindrance plays the key role
in determining the stability of the carbenes. Indeed, Tc signifi-
cantly decreases for o,p-(CF3)2- (1b) compared to o,o′-(CF3)2-
(1a) (by about 40 °C) and for p-CF3- (1d) compared to o-CF3-
substituted arylcarbene (1c) (by about 60 °C); moreover, the
o,p-(CF3)2 derivative (1b) has approximately the same stability
as the o-CF3-substituted arylcarbene (1c). In all cases, the
phosphino group affords the necessary stabilization, even to the
extent that carbene 1d featuring a naked aryl ring can be
characterized spectroscopically at low temperature.
The 31P and 13C NMR spectroscopic data for carbenes 1a-d
are very similar (Table 1), the only noticeable difference being
1
the magnitude of the JPC coupling constant, which decreases
progressively from 1a to 1d. Although these data are difficult
to rationalize (the magnitude of the coupling constants depends
on the influence of orbital, spin-dipolar, Fermi contact, and
higher order quantum mechanical contributions), it is likely to
indicate some modification in the electronic structure of (aryl)-
carbenes.
(12) (a) Svara, J.; Fluck, E.; Riffel, H. Z. Naturforsch. 1985, 40b, 1258. (b)
Neumu¨ller, B.; Fluck, E. Phosphorus Sulfur 1986, 29, 23. (c) Keller, H.;
Maas, G.; Regitz, M. Tetrahedron Lett. 1986, 27, 1903.
(13) The structure of the imine Me2CdN(i-Pr) was deduced by comparison of
its 1H NMR data with those of an authentic sample.
To gain more of an insight into the electronic role of the
aryl substituents,11 ab initio calculations at the B3LYP/6-31g*
(14) (a) Tomioka, H.; Taketsuji, K. J. Chem. Soc., Chem. Commun. 1997, 1745.
(b) Hirai, K.; Tomioka, H. J. Am. Chem. Soc. 1999, 121, 10213.
(15) Fluorine combines σ-acceptor and π-donor properties, as illustrated by Taft
constants (σI ) +0.5, σR ) -0.34 according to Ehrenson, S.; Brownless,
R. T. C.; Taft, R. W. Prog. Phys. Org. Chem. 1973, 10, 1). Accordingly,
the pentafluorophenyl substituent could in principle behave as an acceptor,
a spectator, or even as a donor.
(11) Substituent effects have been studied computationally: (a) For (aryl)-
(hydrogeno)carbenes, Geise, C. M. J. Org. Chem. 2000, 65, 8348. (b) For
(aryl)(carbomethoxy)carbenes: Geise, C. M.; Wang, Y.; Mykhaylova, Frink,
B. T.; Toscano, J. P.; Hadad, C. M. J. Org. Chem. 2002, 67, 3079.
9
J. AM. CHEM. SOC. VOL. 125, NO. 1, 2003 125

A R T I C L E S
Despagnet-Ayoub et al.
Table 2. Optimized Structures (at the B3LYP/6-31g* Level) for (Phosphino)(aryl)carbenesa
compound
R
R′
PC
CC
ipso
PCC
ΣP
PCCipsoC
PCCipsoC
o
Erel (kcal/mol)
ipso
o
1*a
1*b
1*c
1*d
1*e
1*f
NH2
NH2
NH2
NH2
NH2
NH2
N(i-Pr)2
NH2
N(i-Pr)2
NH2
o,o′-(CF3)2
o,p-(CF3)2
o-CF3
p-CF3
m-CF3
H
o,o′-(CF3)2
F5
F5
1.562
1.567
1.568
1.572
1.577
1.582
1.573
1.586
1.593
1.613
1.610
1.422
1.425
1.433
1.434
1.439
1.441
1.403
1.435
1.431
1.431
1.443
146.2
145.5
145.2
143.9
141.2
140.6
155.6
136.1
136.1
140.7
136.9
360.0
359.6
359.8
359.3
359.4
358.8
358.5
358.9
359.8
344.9
359.2
117.8
98.6
-65.7
-85.2
-56.3
-61.6
-48.6
-38.2
-74.8
-12.4
-87.4
-31.0
-4.4
+0.8
0
0
+0.3
+1.0
126.6
121.2
133.8
143.8
109.1
169.5
99.5
1a
10*
10a
14*
14**
p-NH2
p-NH2
151.2
175.6
N(i-Pr)2
a PC and CCipso bond lengths are given in angstroms; PCCipso bond angles and PCCipsoCo and PCCipsoCo′ dihedral angles are expressed in degrees. The
sum of the bond angles around phosphorus is referred to as ΣP. Relative energies Erel are given for the isomeric structures (1*a,b) and (1*c-e). In each
series, the most stable carbene is used as reference (1*a and 1*c, respectively).
Table 3. Crystallographic Data for Compounds 6c and 11a
6c
11a
formula
formula weight
cryst system
space group
a, Å
b, Å
c, Å
R, deg
â, deg
C34H51F6N3P2S
709.78
monoclinic
P21/n
11.422(2)
28.059(5)
11.827(2)
C38H56F10N6P2
848.83
triclinic
P1h
7.8502(4)
10.8228(6)
12.8265(7)
98.102(1)
93.709(1)
105.260(1)
1034.91(10)
1
95.211(3)
γ, deg
V, Å3
3774.8(11)
4
1.249
Z
d
Figure 2. Thermal ellipsoid diagram (50% probability) of 6c. For clarity
the i-Pr and CF3 groups have been simplified. Selected bond lengths (in
angstroms) and angles (in degrees): P(1)-C(1), 1.7619(16); P(1)-C(9),
1.8775(16); P(2)-C(1), 1.7291(16); P(2)-C(9), 1.8614(16); P(1)-C(1)-
P(2), 93.65(8); C(1)-P(2)-C(9), 88.39(7); P(2)-C(9)-P(1), 85.83(7);
C(9)-P(1)-C(1), 86.92(7).
calcd, Mg/m3
1.362
absorp coeff, mm-1
no. of total reflns
no. of unique reflns
R1 [I > 2σ(I)]
0.227
26 846
9350
0.0446
0.1086
0.380, -0.329
0.186
11 619
11 621
0.0866
0.2411
0.538, -0.652
wR2 (all data)
(∆/F)max [e Å-3
]
Scheme 2
Scheme 3
Scheme 4
Diazo compounds 9a,b were prepared in moderate yields (34-
37%) by metalation of the pentafluorophenyldiazomethane,16
followed by coupling with chlorobis(diisopropylamino)phos-
phine (Scheme 3). Photolysis (254 nm) of 9a,b in toluene at
-50 °C affords carbenes 10a,b in good yields (60-67%). The
31P and 13C NMR chemical shifts (10a δ 31P 9.4, δ 13C 133.3,
1JPC ) 58 Hz) are in the range typical for (phosphino)carbenes
(Table 1). Carbenes 10a,b are stable for days in solution at -30
°C and can even be observed by 31P NMR up to room
temperature where decomposition occurs within hours whatever
the solvent (pentane, toluene, diethyl ether, tetrahydrofuran).
It should be noted that carbenes 10a,b react cleanly with their
diazo precursors at room temperature. Indeed, the corresponding
azines 11a,b are obtained in good yields (63-72%) when the
photolytic degradation of the diazo compounds is performed to
half conversion (Scheme 4). The structures of 11a,b were
deduced from multinuclear NMR spectroscopy and confirmed
by an X-ray diffraction study for 11a (Figure 3, Table 3). This
carbene-diazo coupling is a reaction typical of transient
carbenes,17 something that has also recently been observed for
a stable N-heterocyclic carbene.18
(16) Meese, C. O. Liebigs Ann. Chem. 1985, 1711.
9
126 J. AM. CHEM. SOC. VOL. 125, NO. 1, 2003

Stabilization Modes of (Phosphino)(Aryl)Carbenes
A R T I C L E S
Figure 6. Optimized geometries of 14* (left) and 14** (right).
this crystalline sample cannot be discussed in detail, carbene
10b clearly adopts a perpendicular rather than the expected
coplanar structure in the solid state. The rotation of the aryl
ring is probably induced by steric hindrance from the isopropyl
groups. This hypothesis was corroborated by calculations on
the isopropyl-substituted compound 10a itself: the plane of the
aryl ring was predicted to be rotated by 93° with respect to that
of the carbene (Table 2). Due to this rotation of the aryl ring,
carbenes 10a,b adopt a similar structure to that of the (phos-
phino)(mesityl)carbene 2a. The pentafluorophenyl ring merely
behaves as a spectator substituent, thus no unequivocal conclu-
sions can be drawn about (phosphino)carbenes featuring a donor
aryl susbtituent.
Figure 3. Thermal ellipsoid diagram (50% probability) of 11a. Selected
bond lengths (in angstroms) and angles (in degrees): P(1)-C(1), 1.859(4);
C(1)-N(1), 1.292(5); N(1)-N(1A), 1.427(6); P(1)-C(1)-N(1), 119.8(3);
C(1)-N(1)-N(1A), 113.2(3); N(2)-P(1)-N(3), 112.64(15); N(2)-P(1)-
C(1), 105.27(15); N(3)-P(1)-C(1), 100.45(15).
To try to force the aryl ring to behave as a π-donor
substituent, one possibility is to introduce an amino group in
the para position. This hypothesis was initially investigated
theoretically on the model carbene 14* (Figure 6, Table 2).19
Although neither a significant shortening of the Ccarb-Cipso nor
an elongation of the P-Ccarb bond lengths could be observed,
the π-system of the aryl ring was found to lie almost parallel
to the empty 2p orbital of the carbene center. Moreover, a
pyramidalization of the phosphorus atom was predicted, which
clearly indicates a weaker donation of the phosphino group. For
the bis(diisopropylamino)phosphino analogue 14**, calculations
found that the phosphorus center recovers its planar environ-
ment, but in marked contrast with that observed for 10a, the
aryl ring remains almost parallel to the carbene vacant orbital.
On taking into account the major role played by the steric
bulk of the ortho substituents on the stability of (phosphino)-
(aryl)carbenes (vide supra), we chose carbene 14a, featuring
an o-methyl substituent as a second target molecule; substituents
at both ortho positions would certainly prevent the desired
coplanar arrangement, as in the case of 10a,b. The starting
(aryl)diazomethane 12a was prepared in 38% yield by solid-
liquid phase transfer at 35 °C.20 The introduction of the
phosphino group was very tricky and could only be achieved
in 15% yield by addition of chlorobis(diisopropylamino)-
phosphine and lithium diisopropylamide to an ether solution of
12a at room temperature (Scheme 5). Diazo compound 13a was
characterized by multinuclear NMR spectroscopy. Photolysis
of 13a (254 nm) in toluene solution at -70 °C allowed for the
characterization of the corresponding carbene 14a by 31P NMR
spectroscopy (δ 31P -17.9). Any attempts to get 13C NMR data
were prevented by the extreme instability of 14a, which
decomposes within a few hours even at -70 °C. This peculiar
Figure 4. Optimized geometries of 10* (left) and 10a (right).
Figure 5. Thermal ellipsoid diagram (30% probability) of 10b. For clarity
the c-Hex groups have been simplified.
Interestingly, ab initio calculations carried out on the model
(pentafluorophenyl)(phosphino)carbene 10* with NH2 substit-
uents at phosphorus predicted that, in contrast with carbenes
1*a-d and (phenyl)carbene 1*f, the plane of the aryl ring of
10* is rotated by only 11.5° with respect to that of the carbene
(37.2° for 1*f) (Table 2, Figure 4). The almost coplanar
orientation of the aryl ring with the P-Ccarbene bond is likely to
result from a conjugation between the π-system of the aryl ring
(which is enriched by the fluorine atoms) and the carbene vacant
orbital. However, this interaction is probably weak since it is
not visible on examination of the P-Ccarb and Ccarb-Cipso bond
lengths. Experimentally, only poor-quality crystals of 10b could
be obtained from a pentane solution at -50 °C (Figure 5).
Although the geometric parameters resulting from a study of
(19) Carbenes 14 can be considered as phenylogues of the (amino)(phosphino)-
carbenes: (a) Goumri, S.; Leriche, Y.; Gornitzka, H.; Baceiredo, A.;
Bertrand, G. Eur. J. Inorg. Chem. 1998, 1539. (b) Merceron, N.; Miqueu,
K.; Baceiredo, A.; Bertrand, G. J. Am. Chem. Soc. 2002, 124, 6806.
(20) Aggarwal, V. K.; Ford, J. G.; Fonquerna, S.; Adams, H.; Jones, R. V. H.
J. Am. Chem. Soc. 1998, 120, 8328.
(17) (a) Regitz, M.; Maas, G. Diazo Compounds. Properties and Synthesis;
Academic Press: Orlando, FL, 1986; Chapt. 2. (b) Glaser, R.; Chen, G.
S.; Barnes, C. L. J. Org. Chem. 1993, 58, 7446.
(18) Hopkins, J. M.; Bowdridge, M.; Robertson, K. N.; Cameron, T. S.; Jenkins,
H. A.; Clyburne, J. A. C. J. Org. Chem. 2001, 66, 5713.
9
J. AM. CHEM. SOC. VOL. 125, NO. 1, 2003 127

A R T I C L E S
Despagnet-Ayoub et al.
Scheme 5
chemical shifts are reported in parts per million (ppm) relative to Me4-
Si as external standard. 19F NMR chemical shifts are given relative to
an external standard of CF3CO2H. 31P NMR downfield chemical shifts
are expressed with a positive sign, in ppm, relative to external 85%
H3PO4. Infrared spectra were recorded on a Perkin-Elmer FT-IR
spectrometer 1725 X. Mass spectra were obtained on a Ribermag R10
10E instrument. Pentafluorophenyldiazomethane16 and other starting
(aryl)diazomethanes 3b-d and 12a,b25 were prepared by decomposition
of the corresponding tosylhydrazone salts.
instability of 14a is likely to result from the donor group
introduced in the aryl substituent. This hypothesis was confirmed
by preparing the related (phosphino)(aryl)carbene 14b featuring
a methyl group in the ortho position but no amino group in the
para position. Carbene 14b was generated by photolysis (254
nm) of its diazo precursor at -60 °C and characterized
spectroscopically. All the NMR data (Table 1) are very similar
to those of the related (phosphino)(mesityl)carbene 2a. In
contrast to 14a, carbene 14b could be observed by 31P NMR
up to 0 °C, where it decomposes within a few hours.
General Procedure for the Synthesis of Diazo Compounds 4b-
d, 9a,b, and 13b. A diethyl ether solution (4 mL) of the lithium salt of
hexamethyldisilazane (0.27 g, 1.6 mmol) was added dropwise at -100
°C to a diethyl ether solution (20 mL) of the aryldiazomethane (1.6
mmol). After 30 min, a suspension of chlorobis(diisopropylamino)-
phosphine (0.43 g, 1.6 mmol) in diethyl ether (5 mL) was added. The
solution was warmed to room temperature, and the solvent was removed
under vacuum. The crude residue was extracted with pentane (30 mL)
and quickly filtered through neutral activated alumina. Diazo com-
pounds were obtained as deeply orange crystals from acetonitrile
solutions at -30 °C.
Conclusion
4b: mp 66 °C; 31P{1H} NMR (CDCl3) δ 71.0 (s); 19F NMR (CDCl3)
The phosphino group brings enough stabilization to singlet
(aryl)carbenes to allow for their spectroscopic characterization
under standard laboratory conditions. The phosphino group
clearly behaves as a weak π- and σ-donor substituent, while
the role of the aryl substituents strongly depends on both their
electronic and steric properties. The most stable derivative 1a
features a push-pull cumulenic structure, which is imposed by
the bulky withdrawing 2,6-bis(trifluoromethyl)phenyl group.
Despite their electron-withdrawing properties, less sterically
hindered aryl groups behave as spectator substituents, as
observed in 1b-d. Carbenes 10a,b are somewhat peculiar
because steric factors induce the rotation of the potentially
π-donating pentafluorophenyl ring, which finally behaves as
only a spectator substituent. When the aryl substituent is strongly
enriched electronically by an amino group, a push-push system
is obtained. However, the phosphino and aryl π-donor groups
do not have additive effects but rather an overall destabilizing
effect,21 making the resulting carbene 14a extremely reactive.
At the first glance, this is surprising since carbenes featuring
two π-donor amino groups are highly stable. But this is more
understandable if one consider the opposite inductive effects
of phosphino (σ-donor) and amino (σ-acceptor) groups.
This understanding of the effects governing the stability of
phosphinocarbenes will greatly facilitate the preparation of a
variety of new stable or at least persistent carbenes. Having in
hand such species will allow for the discovery of new types of
reactions,22 including those involving carbenes in excited
states,23 which have so far required rather sophisticated tech-
niques.24
δ 14.5 (s), 12.3 (s); 1H NMR (CDCl3) δ 1.04 (d, 12 H, 3JHH ) 6.6 Hz,
3
3
CH3), 1.29 (d, 12 H, JHH ) 6.6 Hz, CH3), 3.46 (septet, 4 H, JHH
)
6.6 Hz, CH), 7.64 (d, 1 H, 3JHH ) 8.5 Hz, Hortho), 7.88 (s, 1 H, Hmeta),
7.99 (d, 1 H, 3JHH ) 8.5 Hz, Hmeta); 13C{1H} NMR (CDCl3) δ 24.5 (d,
3JCP ) 7 Hz, CH3), 25.1 (d, 3JCP ) 6 Hz, CH3), 48.2 (d, 2JCP ) 13 Hz,
CH), 50.8 (d, JCP ) 42 Hz, CN2), 124.1 (q, JCF ) 272 Hz, CF3),
124.1 (q, JCF ) 274 Hz, CF3), 125.8 (q, JCF ) 31 Hz, Cpara), 126.3
1
1
1
2
3
2
4
(qd, JCP ) 3 Hz, JCF ) 33 Hz, Cortho), 127.9 (d, JCP ) 3 Hz, Cmeta),
128.6 (d, JCP ) 27 Hz, Cortho), 129.6 (s, Cmeta), 137.0 (d, JCP ) 24
3
2
Hz, Cipso); IR (diethyl ether) νCN 2046. Anal. Calcd for C21H31F6N4P:
2
C 52.06, H 6.45, N 11.56. Found: C 51.84, H 6.20, N 11.90.
4c: mp 108 °C; 31P{1H} NMR (C6D6) δ 66.8 (s); 19F NMR (C6D6)
1
3
δ 14.4 (s); H NMR (CDCl3) δ 0.97 (d, 12 H, JHP ) 6.6 Hz, CH3),
1.25 (d, 12 H, 3JHH ) 6.6 Hz, CH3), 3.43 (septet, 4 H, 3JHH ) 6.6 Hz,
CH), 7.17 (pt, 1 H, JHH ) 7.6 Hz, Harom), 7.40 (pt, 1 H, JHH ) 7.6
3
3
3
3
Hz, Harom), 7.62 (d, 1 H, JHH ) 7.6 Hz, Harom), 7.83 (pt, 1 H, JHH
)
4JHP ) 7.6 Hz, Harom); 13C{1H} NMR (C6D6) δ 24.4 (d, JCP ) 7 Hz,
CH3), 24.5 (d, 3JCP ) 6 Hz, CH3), 48.0 (d, 2JCP ) 12 Hz, CH), 49.5 (d,
1JCP ) 24 Hz, CN2), 124.8 (d, JCP ) 3 Hz, Carom), 126.4 (q, 2JCF ) 30
Hz, Cortho), 125.3 (q, 1JCF ) 274 Hz, CF3), 127.3 (q, 4JCF ) 6 Hz, Cmeta),
3
3
2
129.0 (d, JPC ) 21 Hz, Cortho), 131.3 (s, Carom), 132.3 (qd, JCP ) 22
Hz, JCF ) 2 Hz, Cipso); IR (tetrahydrofuran) νCN 2042. Anal. Calcd
3
2
for C20H32F3N4P: C 57.68, H 7.74, N 13.46. Found: C 57.45, H 7.34,
N 13.71.
4d: mp 73 °C; 31P{1H} NMR (C7D8) δ 62.6 (s); 19F NMR (C7D8) δ
14.9 (d, 7JFP ) 9 Hz); 1H NMR (C7D8) δ 1.15 (d, 6 H, 3JHH ) 6.6 Hz,
CH3), 1.25 (d, 6 H, 3JHH ) 6.6 Hz, CH3), 3.38 (septet, 4 H, 3JHH ) 6.6
Hz, CH), 7.30 (d, 2 H, 3JHH ) 8.4 Hz, Harom), 7.44 (d, 2 H, 3JHH ) 8.4
2
Hz, Harom); 13C{1H} NMR (C7D8) δ 24.0 (d, JCP ) 7 Hz, CH3), 25.1
(d, 2JCP ) 7 Hz, CH3), 48.2 (d, 1JCP ) 12 Hz, CH), 53.1 (d, 1JCP ) 50
Hz, CN2), 123.4 (d, 3JCP ) 11 Hz, Cortho), 126.1 (q, 2JCF ) 4 Hz, Cmeta),
1
2
125.5 (q, JCF ) 271 Hz, CF3), 125.6 (q, JCF ) 31 Hz, Cpara), 138.3
Experimental Section
2
(d, JCP ) 29 Hz, Cipso); IR (diethyl ether) νCN 2032. Anal. Calcd for
2
All manipulations were performed under an inert atmosphere of
argon by standard Schlenk techniques. Dry, oxygen-free solvents were
employed. 1H, 13C, 19F, and 31P NMR spectra were recorded on Bruker
AC80, AC200, WM250, or AMX400 spectrometers. 1H and 13C
C20H32F3N4P: C 57.68, H 7.74, N 13.46. Found: C 57.99, H 8.12, N
13.14.
9a: mp 63 °C (decomp); 31P{1H} NMR (C6D6) δ 66.0 (t, 4JPF ) 61
3
Hz); 19F NMR (C6D6) δ -87.5 (t, 2 F, JFF ) 22 Hz, Fmeta), -82.6 (t,
1 F, 3JFF ) 22 Hz, Fpara), -62.7 (dd, 2 F, 3JFF ) 22 Hz, 4JFP ) 61 Hz,
(21) Similarly, di(phosphino)carbenes are not sufficiently stable to be character-
ized by NMR spectroscopy: Baceiredo, A.; Igau, A.; Bertrand, G.; Menu,
M. J.; Dartiguenave, Y.; Bonnet, J. J. J. Am. Chem. Soc. 1986, 108, 7868.
(22) The first direct complexation of a phosphinocarbene to a transition metal
carbene has been observed with 1a: Despagnet, E.; Miqueu, K.; Gornitzka,
H.; Dyer, P. W.; Bourissou, D.; Bertrand G. J. Am. Chem. Soc. 2002, 124,
in press.
(23) Excited-state reactions of an isolable silylene have recently been reported:
Kira, M.; Ishida, S.; Iwamoto, T.; Kabuto, C. J. Am. Chem. Soc. 2002,
124, 3930.
(24) (a) Scaiano, J. C. In Kinetics and Spectroscopy of Carbenes and Biradicals;
Platz, M. S., Ed.; Plenum: New York, 1990; p 353. (b) Migirdicyan, E.;
Kozankiewicz, B.; Platz, M. S. In AdVances in Carbene Chemistry; Brinker,
U., Ed.; JAI Press: Stamford, CT, 1998; Vol. 2, p 97. (c) Xu, G.; Chang,
T. M.; Zhou, J.; McKee, M. L.; Shevlin, P. B. J. Am. Chem. Soc. 1999,
121, 7150.
(25) Kaufman, G. M.; Smith, J. A.; Vander Stouw, G. G.; Shechter, H. J. Am.
Chem. Soc. 1965, 87, 935.
9
128 J. AM. CHEM. SOC. VOL. 125, NO. 1, 2003

Stabilization Modes of (Phosphino)(Aryl)Carbenes
A R T I C L E S
2
3
3
F
ortho); 1H NMR (C6D6) δ 1.11 (d, 12 H, 3JHH ) 6.6 Hz, CH3), 1.23 (d,
CHarom), 116.3 (qd, JCF ) 27 Hz, JCP ) 6 Hz, Carom), 123.7 (d, JCP
1
12 H, 3JHH ) 6.6 Hz, CH3), 3.38 (septet d, 4 H, 3JHH ) 6.6 Hz, 3JHP
)
) 26 Hz, CHarom), 125.6 (q, JCF ) 276 Hz, CF3), 126.5 (s, CHarom),
131.5 (s, CHarom), 142.7 (d, JCP ) 6 Hz, Cipso), 148.6 (d, JCP ) 124
11.8 Hz, CH); 13C{1H} NMR (C6D6) δ 24.2 (d, JCP ) 9 Hz, CH3),
24.7 (d, 3JCP ) 7 Hz, CH3), 42.4 (md, 1JCP ) 54 Hz, CP), 48.2 (d, 2JCP
) 13 Hz, CH), 109.2 (md, 2JCP ) 21 Hz, Cipso), 138.3 (md, 1JCF ) 252
Hz, Carom), 139.6 (md, JCF ) 252 Hz, Carom), 144.8 (md, JCF ) 248
Hz, Carom); IR (diethyl ether) νCN ) 2051. Anal. Calcd for
3
2
1
Hz, Ccarbene).
1d (hν 312 nm, 223 K): 31P{1H} NMR (C7D8) δ -12.9 (q, JPF
)
7
1
1
11 Hz); 19F NMR (C6D6) δ 14.9 (d, JFP ) 9 Hz); H NMR (C7D8) δ
1.05 (d, 24 H, 3JHH ) 6.4 Hz, CH3), 3.10 (septet, 4 H, 3JHH ) 6.4 Hz,
CH), 6.84 (d, 2 H, 3JHH ) 8.4 Hz, Harom), 7.46 (d, 2 H, 3JHH ) 8.4 Hz,
7
1
2
C19H28F5N4P: C 52.05, H 6.44, N 12.78. Found: C 52.34, H 6.68, N
12.52.
H
arom); 13C{1H} NMR (C7D8) δ 22.7 (s, CH3), 48.5 (s, CH), 125.7 (q,
2
5
9b: mp 84 °C (decomp); 31P{1H} NMR (C6D6) δ 67.2 (t, 4JPF ) 58
1JCF ) 297 Hz, CF3), 118.9 (qd, JCF ) 32 Hz, JCP ) 8 Hz, Cpara),
3
3
Hz); 19F NMR (C6D6) δ -87.5 (t, 2 F, JFF ) 22 Hz, Fmeta), -82.6 (t,
120.8 (d, JCP ) 28 Hz, CHarom), 131.1 (s, CHarom), 150.8 (s, Cipso),
1
1 F, 3JFF ) 22 Hz, Fpara), -62.4 (dd, 2 F, 3JFF ) 22 Hz, 4JFP ) 58 Hz,
159.7 (d, JCP ) 66 Hz, Ccarbene).
1
10a (hν 254 nm, 223 K): 31P{1H} NMR (C7D8, 193 K) δ 9.4 (q, JPF
F
ortho); H NMR (C6D6) δ 0.95-1.83 (m, 40 H, CH2), 2.93 (m, 4 H,
CH); 13C{1H} NMR (C6D6) δ 25.6 (s, CH2), 25.8 (s, CH2), 26.8 (s,
) 18 Hz); 19F NMR (C7D8) δ -98.8 (ttd, 1 F, 3JFF ) 22 Hz, 4JFF ) 7
CH2), 27.3 (s, CH2), 35.3 (d, 3JCP ) 7 Hz, CH2), 35.8 (d, 3JCP ) 7 Hz,
6
3
Hz, JFP ) 18 Hz, Fpara), -91.6 (t, 2 F, JFF ) 22 Hz, Fmeta), -71.2
2
2
3
4
4
1
CH2), 56.7 (d, JCP ) 11 Hz, CH), 58.0 (d, JCP ) 10 Hz, CH); IR
(pentane) νCN ) 2051. Anal. Calcd for C31H44F5N4P: C 62.19, H 7.41,
N 9.36. Found: C 62.47, H 7.68, N 9.02.
(ddd, 2 F, JFF ) 22 Hz, JFF ) 7 Hz, JFP ) 18 Hz, Fortho); H NMR
(C7D8, 193 K) δ 1.03 (d, 24 H, 3JHH ) 6.5 Hz, CH3), 3.10 (septet d, 4
H, 3JHH ) 6.5 Hz, 3JHP ) 20.1 Hz, CH); 13C{1H} NMR (C7D8, 193 K)
2
2
13b: mp 104 °C; 31P{1H} NMR (C7D8) δ 64.4 (s); 1H NMR (CDCl3)
δ 22.5 (s, CH3), 48.6 (s, CH), 121.2 (t, JCF ) 19 Hz, Cipso), 133.2
(md, 1JCF ) 239 Hz, Carom), 133.3 (d, 1JCP ) 55 Hz, Ccarb), 138.0 (md,
3
3
δ 0.96 (d, 12 H, JHH ) 6.5 Hz, CH3), 1.25 (d, 12 H, JHH ) 6.5 Hz,
CH3), 2.31 (s, 3 H, CH3), 3.42 (septet, 4 H, 3JHH ) 6.5 Hz, CH), 7.11
(br s, 3 H, Harom), 7.63 (br s, 1 H, Harom); 13C{1H} NMR (CDCl3) δ
20.4 (s, CH3), 24.4 (d, 3JCP ) 7 Hz, CH3), 47.8 (d, 2JCP ) 12 Hz, CH),
1JCF ) 250 Hz, Carom), 138.5 (md, JCF ) 239 Hz, Carom).
1
10b (hν 254 nm, 293 K): 31P{1H} NMR (C6D6) δ 5.9 (q, JPF ) 17
Hz).
1
14a (hν 254 nm, 203 K): 31P{1H} NMR (C7D8) δ -17.9 (s).
50.9 (d, JCP ) 17 Hz, CN2), 125.7 (s, CHarom), 125.9 (d, JCP ) 2 Hz,
3
14b (hν 254 nm, 223 K): 31P{1H} NMR (C7D8) δ -19.8 (s); H
1
CHarom), 127.9 (d, JCP ) 14 Hz, CHarom), 130.8 (s, CHarom), 130.9 (d,
2JCP ) 21 Hz, Cipso), 135.9 (s, Carom); IR (diethyl ether) νCN ) 2032.
NMR (C7D8) δ 1.02 (d, 24 H, 3JHH ) 6.0 Hz, CH3), 2.47 (d, 3 H, 5JHP
2
3
Anal. Calcd for C20H35N4P: C 66.27, H 9.73, N 15.46. Found: C 65.94,
H 9.38, N 15.72.
) 3.6 Hz, CH3), 3.25 (septet, 4 H, JHH ) 6.0 Hz, CH), 7.02 (br s, 1
H, Harom), 7.14 (br s, 1 H, Harom), 7.37 (br s, 2 H, Harom); 13C{1H} NMR
5
Synthesis of the Diazo Compound 13a. To a diethyl ether solution
(5 mL) of diazo compound 12a (17 mg, 0.1 mmol) were successively
added at room temperature chlorobis(diisopropylamino)phosphine (27
mg, 0.1 mmol) and a diethyl ether solution (3 mL) of lithium
diisopropylamide (12 mg, 0.11 mmol). The solvent was removed under
vacuum. The crude residue was extracted with pentane (10 mL) and
quickly filtered over neutral activated alumina. Diazo compound 13a
was obtained as deep purple crystals (15% yield) from an acetonitrile
solution at -30 °C: mp 113 °C; 31P{1H} NMR (C6D6) δ 62.90 (s); 1H
(C7D8) δ 23.5 (s, CH3), 23.6 (s, CH3), 44.8 (s, CH), 119.1 (d, JCP
10 Hz, CHarom), 121.8 (d, JCP ) 26 Hz, CHarom), 127.3 (d, JCP ) 23
Hz, Carom), 129.9 (d, JCP ) 4 Hz, Cipso), 130.3 (s, CHarom), 137.5 (s,
CHarom), 156.1 (d, JCP ) 46 Hz, Ccarbene).
)
3
3
2
1
Thermal Rearrangement of Carbene 1c. A toluene solution (1
mL) of carbene 1c (31 mg, 0.07 mmol) was heated at 40 °C overnight.
Compound 5c was characterized spectroscopically without further
purification. Excess elemental sulfur (10 mg, 0.3 mmol) was then added
at room temperature to the toluene solution of 5c. After 2 h, the solvent
was removed under vacuum and the crude residue was purified by
column chromatography (pentane/diethyl ether 95/5, Rf ) 0.2). Deriva-
tive 6c was isolated as yellow crystals (68% yield) from a saturated
diethyl ether solution. 5c: 31P{1H} NMR (CDCl3) δ 75.5 (qd, JPP ) 52
Hz, 5JFP ) 14 Hz), 36.8 (d, JPP ) 52 Hz); 19F NMR (C6D6) δ 18.0 (d,
5JFP ) 14 Hz), 17.9 (s). 6c: mp 188 °C (decomp); 31P{1H} NMR
(CDCl3) δ 63.6 (d, JPP ) 95 Hz), 42.5 (d, JPP ) 95 Hz); 19F NMR
3
NMR (C6D6) δ 1.10 (d, 12 H, JHH ) 6.8 Hz; CH3), 1.25 (d, 12 H,
3JHH ) 6.8 Hz, CH3), 2.40 (s, 3 H, CH3), 2.50 (s, 6 H, CH3N), 3.42
3
(septet, 4 H, JHH ) 6.8 Hz, CH), 6.51 (s, 1 H, Harom), 6.54 (d, 1 H,
3JHH ) 8.0 Hz, Harom), 7.72 (d, 1 H, JHH ) 8.0 Hz, Harom); 13C{1H}
3
3
NMR (C6D6) δ 20.9 (s, CH3), 24.5 (d, JCP ) 2.8 Hz, CH3), 40.2 (s,
CH3N), 48.06 (d, 2JCP ) 12.0 Hz, CH), 49.6 (d, 1JCP ) 15.7 Hz, CN2),
104.7 (s, Cpara), 111.1 (s, Cmeta), 115.0 (s, Cmeta), 128.8 (br s, Carom),
129.3 (br s, Carom), 129.6 (d, JCP ) 9.2 Hz, Cortho); IR (diethyl ether)
νCN ) 2029.
General Procedure for the Synthesis of Carbenes 1b-d, 10a,b,
and 14a,b. A toluene solution (1 mL) of the diazo precursor (20 mg)
was irradiated (254 or 312 nm) at -60 °C. The reaction was controlled
by 31P NMR spectroscopy to ensure completion.
3
1
(C6D6) δ 22.0 (s), 17.5 (s); H NMR (CDCl3) δ 0.31 (s, 6 H, CH3),
0.48 (s, 6 H, CH3), 1.06 (s, 6 H, CH3), 1.24 (s, 6 H, CH3), 1.46 (s, 6
H, CH3), 1.57 (s, 6 H, CH3), 3.61 (br s, 2 H, CH), 4.00 (br s, 2 H,
CH), 4.64 (br s, 2 H, CH), 4.95 (pt, 1 H, 2JHP ) 15.3 Hz, Hcycle), 7.31-
8.85 (br s, 8 H, Harom); 13C{1H} NMR (CDCl3) δ 22.8 (s, CH3), 22.9
(s, CH3), 30.0 (d, 3JCP ) 3 Hz, CH3), 23.4 (d, 3JCP ) 5 Hz, CH3), 24.0
(s, CH3), 24.2 (d, JCP ) 4 Hz, CH3), 25.6 (s, CH3), 46.7 (d, JCP ) 4
Hz, CH), 48.1 (br s, CH), 49.0 (br s, CH), 58.9 (dd, JCP ) 38 Hz, JCP
2
1b (hν 312 nm, 223 K): 31P{1H} NMR (C7D8) δ -19.3 (s); 19F NMR
3
2
7
5
1
(C6D6) δ 14.5 (d, JFP ) 5 Hz, CF3), 11.3 (d, JFP ) 9 Hz, CF3); H
NMR (C7D8) δ 1.50 (d, 24 H,3JHH ) 6.7 Hz, CH3), 3.20 (septet d, 4 H,
3JHH ) 6.7 Hz, 3JHP ) 21 Hz, CH), 6.63 (dd, 1 H, 4JHP ) 3.0 Hz, 3JHH
) 54 Hz, CHcycle), 125.3 (s, CHarom), 125.5 (s, CHarom), 126.9 (q, JCF
)
2 Hz, CHarom), 128.3 (s, CHarom), 130.7 (s, CHarom), 131.2 (s, CHarom),
134.2 (q, JCF ) 4 Hz, CHarom), 141.0 (q, JCF ) 5.2 Hz, CHarom). Anal.
Calcd for C34H51F6N3P2S: C 57.53, H 7.24, N 5.92. Found: C 57.92,
H 7.61, N 5.67.
Reaction of Carbene 10a with Its Diazo Precursor 9a. A pentane
solution (2 mL) of diazo compound 9a (0.10 g, 0.23 mmol) was
irradiated (λ 300 nm) at -50 °C for 8 h. The reaction was monitored
by 31P NMR and the irradiation was continued to half conversion. This
mixture was then held at room temperature for 14 h before the solvent
was removed in vacuo. Yellow crystals of 11a were obtained (0.06 g;
63%) from a saturated diethyl ether/acetonitrile solution at -30 °C:
mp 151 °C (decomp); 31P{1H} NMR (C6D6) δ 56.8 (t, 4JPF ) 49 Hz);
19F NMR (C6D6) δ -88.3 (dd, 4 F, 3JFF ) 20 Hz, 3JFF ) 17 Hz, Fmeta),
3
) 8.5 Hz, Hortho), 7.24 (s, 1 H, Hmeta), 7.30 (d, 1 H, JHH ) 8.5 Hz,
H
meta); 13C{1H} NMR (C7D8) δ 22.3 (s, CH3), 48.9 (s, CH), 115.3 (qd,
3JCF ) 29 Hz, JCP ) 22 Hz, Cortho), 116.9 (qd, JCF ) 33 Hz, JCP
)
3
3
5
1
1
6 Hz, Cpara), 125.9 (q, JCF ) 272 Hz, CF3), 126.0 (q, JCF ) 270 Hz,
CF3), 123.1 (d, 3JCP ) 23 Hz, Cortho), 124.5 (m, Cmeta), 127.8 (s, Cmeta),
2
1
144.4 (d, JCP ) 17 Hz, Cipso), 149.2 (d, JCP ) 193 Hz, Ccarbene).
1c (hν 312 nm, 223 K): 31P{1H} NMR (C7D8) δ -20.1 (s); 19F NMR
(C6D6) δ 12.5 (d, 5JFP ) 10 Hz); 1H NMR (C7D8) δ 1.11 (d, 24 H, 3JHH
) 6.5 Hz, CH3), 3.20 (septet, 4 H, 3JHH ) 6.5 Hz, CH), 6.56 (pt, 1 H,
3JHH ) 7.6 Hz, Harom), 6.96 (d, 1 H, 3JHH ) 7.9 Hz, Harom), 7.15 (pt, 1
H, 3JHH ) 7.6 Hz, Harom), 7.64 (d, 1 H, 3JHH ) 7.9 Hz, Harom); 13C{1H}
5
NMR (C7D8) δ 22.5 (s, CH3), 48.6 (s, CH), 116.7 (d, JCP ) 7 Hz,
9
J. AM. CHEM. SOC. VOL. 125, NO. 1, 2003 129

A R T I C L E S
Despagnet-Ayoub et al.
3
-80.8 (t, 2 F, JFF ) 20 Hz, Fpara), -58.1 (m, 4 F, Fortho); MS (EI,
Computational Details. All calculations were performed with the
Gaussian 98 set of programs.29 The various structures were fully
optimized at the B3LYP level. This density functional is built with
Becke’s three-parameter exchange functional30 and the Lee-Yang-
Parr correlation functional.31 All heavy main-group atoms were
augmented by a single set of polarization functions [basis set 6-31g-
(d)]. The energy optimizations were conducted by analytically deter-
mined nuclear gradients. All of the investigated structures were
characterized by vibrational analysis within the harmonic approximation.
The force constants were derived from analytically computed gradients.
NH3) m/z 849, 231, 132; IR (pentane) νCdN ) 1518. Anal. Calcd for
C38H56F10N6P2: C 53.77, H 6.65, N 9.90. Found: C 53.48, H 6.34, N
10.24.
Reaction of Carbene 10b with Its Diazo Precursor 9b. A diethyl
ether solution (2 mL) of diazo compound 9b (0.10 g, 0.17 mmol) was
irradiated (λ 300 nm) at -50 °C for 8 h. The reaction was monitored
by 31P NMR and the irradiation was continued until half conversion
was achieved. This mixture was then maintained at room temperature
for 14 h before the solvent was removed in vacuo. Yellow crystals of
11b were obtained (0.07 g; 72%) from a saturated diethyl ether solution
at -30 °C: mp 244 °C (decomp); 31P{1H} NMR (CDCl3) δ 70,0 (t,
4JPF ) 32 Hz); 19F NMR (CDCl3) δ -87.2 (t, 2 F, 3JFF ) 23 Hz, Fmeta),
-80.3 (t, 1 F, 3JFF ) 23 Hz, Fpara), -59.3 (d, 2 F, 3JFF ) 23 Hz, Fortho);
1H NMR (CDCl3) δ 1.09-1.73 (m, 40 H, CH2), 2.70 (m, 4 H, CH); IR
(CDCl3) νCdN ) 1516. Anal. Calcd for C62H88F10N6P2: C 63.68, H
7.59, N 7.19. Found: C 64.02, H 7.86, N 6.84.
X-ray Crystallographic Studies of Compounds 6c, 10b, and 11a.
Crystal data for all structures are presented in Table 3. Data were
collected at low temperatures on a Bruker-AXS CCD 1000 diffracto-
meter with Mo KR (λ ) 0.710 73 Å). The structures were solved by
direct methods by means of SHELXS-9726 and refined with all data
on F2 by means of SHELXL-97.27 All non-hydrogen atoms were refined
anisotropically. 11a shows two different orientations of a nonmeroheral
twin in the reciprocal space. By using the program package GEMINI,28
we were able to separate the two domains. The refinement by using
HKLF 5 in SHELXL gave occupancies of about 60 to 40 for the two
orientations.
Acknowledgment. Financial support of this work by the
Centre National de la Recherche Scientifique, the University
Paul Sabatier (France), the University of California at Riverside,
the Deutsche Forschungsgemeinschaft, and the Funds der
Chemischen Industrie is gratefully acknowledged.
Supporting Information Available: X-ray crystallographic
data for compounds 6c, 10b, and 11a (print/PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
JA0281986
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