Generation of α-phosphinocarbene complexes and their evolution: New light on relevant isomerization pathways

Article abstract of DOI:10.1021/om800884v

The η¹-α-phosphinocarbene complex Cp(CO) ₂Mn= CR(PHMes) (R = Ph, Me) is generated by nucleophilic attack of MesPH₂ at the electrophilic center of the cationic Mn-carbyne complex [Cp(CO)₂Mn≡CR]⁺, followed by deprotonation. One of its identified isomerization pathways to η¹-phosphaalkene derivatives is shown to be both base-catalyzed and stereoselective, and to involve a transient phosphidocarbene species engaged in an acid-catalyzed migratory CO-insertion step.

Full text of DOI:10.1021/om800884v

5180
Organometallics 2008, 27, 5180–5183
Generation of r-Phosphinocarbene Complexes and Their Evolution:
New Light on Relevant Isomerization Pathways
Dmitry A. Valyaev,† Noe¨l Lugan,*,‡ Guy Lavigne,‡ and Nikolai A. Ustynyuk†
Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne, 31077 Toulouse
CEDEX 4, France, and A. N. NesmeyanoV Institute of Organoelement Compounds, Russian Academy of
Sciences, 28 VaViloV str., GSP-1, B-334, 119991 Moscow, Russia
ReceiVed September 11, 2008
Summary: The η1-R-phosphinocarbene complex Cp(CO)2Mnd
CR(PHMes) (R ) Ph, Me) is generated by nucleophilic attack
of MesPH2 at the electrophilic center of the cationic Mn-carbyne
complex [Cp(CO)2MntCR]+, followed by deprotonation. One
of its identified isomerization pathways to η1-phosphaalkene
deriVatiVes is shown to be both base-catalyzed and stereose-
lectiVe, and to inVolVe a transient phosphidocarbene species
engaged in an acid-catalyzed migratory CO-insertion step.
Scheme 1
recently, Bertrand et al. proposed a second approach,6 consisting
of the elaboration of a stable R-phosphinocarbene ligand to be
subsequently reacted with a transition-metal complex. The
method was only applied to one ligand, namely, (iPr2N)2P(Ar)C:,
and was illustrated by the synthesis of 2. Clearly, the search
for a simple and general route to η1-R-phosphinocarbene
complexes remains an open area of investigation.
A literature survey reveals that simple tertiary phosphines
are prone to interact with the electrophilic carbon atom of
transition-metal carbyne complexes to give isolable R-phos-
phoniocarbene compounds.7 With these observations in mind,
we became interested in exploring the method disclosed in
Scheme 2, which is somewhat reminiscent of Fischer’s method
and proved to be efficient in the case of amines as nucleophiles
for the preparation of aminocarbene complexes.8 We envisioned
that secondary and even primary phosphines might constitute
ideal incoming nucleophiles NuH (Nu ) PR′R′′, PHR′), offering
a convenient route to η1-R-phosphinocarbene complexes.
Since the seminal finding by Fischer and Maasbo¨l some 40
years ago,1 heteroatom-substituted transition-metal carbene
complexes have received considerable attention in light of their
broad application scope in organic synthesis.2 Though the case
of phosphino-substituted carbenes has been examined in detail,3,4
η1-R-phosphinocarbene complexes remain extremely scarce and
their reactivity virtually unexplored.5,6 Basically, there are only
two known synthetic routes to such complexes. The first one,
originally introduced by Fischer,5 consists of a direct nucleo-
philic attack of a phosphide reagent at the electrophilic carbyne
atom of a carbyne complex. The reaction of K[PMePh] with
[(CO)5WtCNEt2]+ was indeed found to give the carbene
complexes 1 (Scheme 1), albeit only in 3-4% yield. More
* To whom correspondence should be addressed. E-mail: noel.lugan@
lcc-toulouse.fr.
† A. N. Nesmeyanov Institute of Organoelement Compounds.
‡ Laboratoire de Chimie de Coordination.
(1) Fischer, E. O.; Maasbo¨l, A. Angew. Chem., Int. Ed. Engl. 1964, 3,
580–581.
Scheme 2
(2) (a) Do¨rwald, F. Z. Metal Carbenes in Organic Synthesis, Wiley-
VCH: Weinheim, Germany, 1999. (b) Topics in Organometallic Chemistry;
Do¨tz, K. H., Ed.; Wiley: New York, 2004; Vol. 13.
(3) For η2-R-phospinocarbene complexes see: (a) Cotton, F. A.; Falvello,
L. R.; Najjar, R. C. Organometallics 1982, 1, 1640–1644. (b) Fischer, E. O.;
Reitmeier, R.; Ackermann, K. Angew. Chem., Int. Ed. Engl. 1983, 22, 411–
412. (c) Kreissl, F. R.; Wolfgruber, M.; Sieber, W. J. J. Organomet. Chem.
1984, 270, C4–C6. (d) Hovnanian, N.; Hubert-Pfalzgraf, L. G. J. Organomet.
Chem. 1986, 299, C29–C31. (e) Kreissl, F. R.; Wolfgruber, M. Z.
Naturforsch. 1988, 43B, 1307–1310. (f) Anstice, H. M.; Fielding, H. H.;
Gibson, V. C.; Housecroft, C. E.; Kee, T. P. Organometallics 1991, 10,
2183–2191. (g) Kreissl, F. R.; Ostermeier, J.; Ogric, C. Chem. Ber. 1995,
128, 289–292. (h) Lehotkay, Th.; Wurst, K.; Jaitner, P.; Kreissl, F. R. J.
Organomet. Chem. 1996, 523, 105–110. (i) Dovesi, S.; Solari, E.; Scopelliti,
R.; Floriani, C. Angew. Chem., Int. Ed. 1999, 38, 2388–2391. (j) Merceron-
Saffon, N.; Gornitzka, H.; Baceiredo, A.; Bertrand, G. J. Organomet. Chem.
2004, 689, 1431–1435.
(4) For metallacyclic complexes containing MdC-PRR′ fragments, see:
(a) Jamison, G. M.; Saunders, R. S.; Wheeler, D. R.; Alam, T. M.; McClain,
M. D.; Loy, D. A. Organometallics 1996, 15, 3244–3246. (b) Scheer, M.;
Kramkowski, P.; Schuster, K. Organometallics 1999, 18, 2874–2883. (c)
Burrows, A. D.; Carr, N.; Green, M.; Lynam, J. M.; Mahon, M. F.; Murray,
M.; Kiran, B.; Nguyen, M. T.; Jones, C. Organometallics 2002, 21, 3076–
3078.
In a first set of experiments, the cationic carbyne manganese
complex [3a]BPh49 was treated with the secondary phosphines
HPPh2 and HP(NiPr2)2 at low temperature (Scheme 3). This led
to the formation of the green R-phosphoniocarbene adducts [4]+,
whose IR characteristics10 are very similar to those of the closely
related complex [Cp(CO)2MndC(Ph)PMe3]BCl4.7b Complex 4b
(7) (a) Kreissl, F. R.; Stu¨ckler, P. J. Organomet. Chem. 1976, 110, C9–
C11. (b) Kreissl, F. R.; Stu¨ckler, P.; Meineke, E. W. Chem. Ber. 1977,
110, 3040–3045. (c) Filippou, A. C.; Wtissner, D.; Kociok-Ko¨hn, G.; Hinz,
I. J. Organomet. Chem. 1997, 541, 333–343. (d) Romero, P. E.; Piers, W. E.;
McDonald, R. Angew. Chem., Int. Ed. 2004, 43, 6161–6165.
(8) (a) Kreissl, F. R. Carbyne Complexes; VCH: Weinheim, Germany,
1988; p 117. (b) McGeary, M. J.; Tonker, T. L.; Templeton, J. L.
Organometallics 1985, 4, 2102–2106.
(9) (a) Terry, M. R.; Mercado, L. A.; Kelley, C.; Geoffroy, G. L.; Lugan,
N.; Nombel, P.; Mathieu, R.; Haggerty, B. S.; Owens-Waltermire, B. E.;
Rheingold, A. L. Organometallics 1994, 13, 843–865. (b) Ortin, Y.; Lugan,
N.; Mathieu, R. Dalton Trans. 2005, 1620–1636.
(5) Fischer, E. O.; Reitmeier, R. Z. Naturforsch. 1983, 38b, 582–586.
(6) (a) Despagnet, E.; Miqueu, K.; Gornitzka, H.; Dyer, P. W.; Bourissou,
D.; Bertrand, G. J. Am. Chem. Soc. 2002, 124, 11834–11835. (b) Despagnet,
E. Ph.D. Thesis, Universite´ Paul Sabatier, Toulouse, France, 2002 (national
no. 2002TOU30073).
(10) IR (CH2Cl2): for 4a, 2020 (s), 1960 (s) (νCO) cm-1; for 4b, 2018
(s), 1943 (s) (νCO) cm-1; for [Cp(CO)2MndC(Ph)PMe3]BCl4, 2010 (s), 1944
(s) (νCO) cm-1 7b
.
10.1021/om800884v CCC: $40.75
2008 American Chemical Society
Publication on Web 09/26/2008

Communications
Organometallics, Vol. 27, No. 20, 2008 5181
Scheme 3
Figure 1. ORTEP drawing of 6d (ellipsoids set at the 50%
probability level). Selected bond lengths (Å) and angles (deg):
Mn1-C3, 1.859(2); C3-P1, 1.811(2); C3-C4, 1.521(3); P1-C21,
1.837(2); P1-H1, 1.33(3); Mn1-C3-C4, 124.9(2); Mn1-C3-P1,
124.8(1);C4-C3-P1,109.9(2);C3-P1-C21,108.0(1);C3-P1-H1,
101(1); C3-P1-H1, 94(1).
was found to be stable at room temperature and was fully
characterized by NMR, highlighting its carbene nature.11
Addition of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to [4]+
at -80 °C induced the formation of an elusive species, which
appeared to be extremely thermolabile, evolving rapidly into
the η3-phosphinoketene complexes 5.
The structure of 5 was inferred from spectroscopic data and
confirmed by X-ray diffraction (see the Supporting Information).
Here the presence of a π-bound η3-phosphinoketene ligand could
be understood as the result of an intramolecular CO insertion
across the MndC bond12 of the elusive targeted η1-phosphi-
nocarbene complexes, concomitant with a coordination of the
pendant phosphine moiety.
alkoxy- and aminocarbene complexes,15a in a domain one would
actually expect for non-heteroatom Mn complexes.15b This
indicates that the present R-phosphinocarbene ligand prototype
MesHP(R)C: is much less of an electron donor than common
alkoxy- and aminocarbene ligands. Here, the absence of typical
carbene stabilization is due to the lack of conjugation of the
phosphorus lone pair with the carbene moiety, fully consistent
with the occurrence of a pyramidal geometry around the
phosphorus atom (sum of bond angles around P1 303°). It is
noteworthy that the exactly opposite situation was encountered
in the case of Bertrand’s complexes 2, where the NMR and
X-ray data indicated a significant contribution of the betaine
σ-phosphavinyl form L2ClRh--(CAr)dP+(NiPr2)2.16
Very characteristically, the carbene 6c, which is relatively
stable in nonpolar solvents, evolves rapidly in THF, affording
the η3-phosphinoketene 5c17 (Scheme 4) as the main transfor-
mation product after 15 min at 25 °C (>95% by NMR). The
latter further transforms, albeit more slowly (ca. 36 h at 25 °C),
into the η1-(E)-phosphaalkene 7c. The carbene 6d undergoes
similar isomerization in THF solution, but the ketene intermedi-
ate 5d is by far less stable,18 giving 7d within ca. 1.5 h at 25
°C. The η1-phosphaalkene structure of 7 was established by
In further attempts to intercept the η1-phosphinocarbene
complexes, the reaction was extended to a primary phosphine,
namely, MesPH2 (Mes ) 2,4,6-trimethylphenyl). Gratifyingly,
deprotonation of the transient phosphoniocarbene adduct [4c]+
appeared to be spontaneous, leading to the desired η1-phosphi-
nocarbene 6c. The parallel conversion of [4d]+, starting from
[3a]BCl4, into 6d was not spontaneous but could be completed
upon addition of NEt3.
Complexes 6c,d were fully characterized by spectroscopic
means,13 complemented for 6d by an X-ray diffraction study
(see Figure 1).14 The 31P{1H} NMR spectra for 6c,d show
signals at 18.9 and 10.1 ppm, respectively. Typical low-field
13C{1H} NMR resonances are observed for the carbene carbon
atoms (6c, δ 358.2 (d, 1JPC ) 75.5 Hz); 6d, δ 366.5 (d, 1JPC
)
(14) Crystal data for 6d: C18H20MnO2P, Mr ) 354.25, monoclinic, space
group P21/n, a ) 13.045(4) Å, b ) 10.2333(17) Å, c ) 13.172(4) Å, ꢀ )
81 Hz)). The IR νCO stretching bands in 6 appear at frequencies
103.52(3)°, V ) 1709.7(8), Z ) 4, Fcalcd ) 1.376 g cm-3, µ ) 0.869 mm-1
,
much higher than those of the corresponding bands in Mn
2.8° > θ > 26.4°, 12 778 reflections (3488 independent, Rint ) 0.049), 456
parameters, R1 (I > 2σ(I)) ) 0.0467, wR2 (all data) ) 0.1466, ∆Fmax/min 1.07/
-10.36 e Å-3. CCDC-692689 contains full crystallographic data for this paper.
These data can be obtained free of charge from the Cambridge Crystallographic
Data Centre at www.ccdc.cam.ac.uk/data_request/cif.
(11) Selected NMR data for 4b: 31P NMR (CD2Cl2) δ 25.5 (dt, 1JPH
)
1
3
545.7 Hz, JPH ) 14 Hz) ppm; 13C{1H} NMR (CD2Cl2) δ 325.2 (d, JPC
) 24.5 Hz, MndC)) ppm.
(12) For explicit intramolecular insertion of CO across the MdC bond
see: (a) Mitsudo, T.; Watanabe, H.; Sasaki, T.; Takegami, Y.; Watanabe,
Y.; Kafuku, K.; Nakatsu, K. Organometallics 1989, 8, 368–378. (b)
Grotjahn, D. B.; Bikzhanova, G. A.; Collins, L. S. B.; Concolino, T.; Lam,
K.-C.; Rheingold, A. L. J. Am. Chem. Soc. 2000, 122, 5222–5223.
(13) Selected spectroscopic data for 6c: 1H NMR (300.1 MHz, C6D5CD3,
(15) (a) For example, IR (CH2Cl2): for Cp(CO)2MndC(OEt)Me, 1947
(s), 1875 (s) (νCO) cm-1; for Cp(CO)2MndC(NHMe)Me, 1912 (s), 1841
(s) (νCO) cm-1. (b) IR (CH2Cl2): for 6d, 1970 (s), 1906 (s) (νCO) cm-1; for
Cp(CO)2MndCPh2, 1968 (s), 1910 (s) (νCO) cm-1
.
(16) (a) Chemical shifts of carbene CR atoms in L2ClRhdC(Ar)P(NiPr2)2
(δ 114.4 ppm, L2 ) (CO)2; δ 120.6 ppm, L2 ) η4-nbd)6a are very upfield
compared to shifts for the structurally similar (η4-cod)ClRhdC(OEt)R (δ
291.1 ppm)16b and [(η4-cod)(CO)RhdC(OEt)R]+ (δ 281.2-297.4 ppm).16c
Also, the Rh-CR bond distance in (η4-nbd)ClRhdC(Ar)P(NiPr2)2 (2.097
Å6a) is longer than the regular RhdC bond (for example d(Rh-CR) ) 1.994
Å in [(η4-cod)(CO)RhdC(OEt)CHdCHC6H4OMe]+)16c) and the P-CR
bond (1.637 Å) is significantly shorter than a single bond (d(P-C) ) 1.80-
1.82 Å). (b) Go¨ttker-Schnetmann, I.; Aumann, R.; Bergander, K. Organo-
metallics 2001, 20, 3574–3581. (c) Barluenga, J.; Vicente, R.; Lopez, L. A.;
Rubio, E.; Tomas, M.; Alvarez-Rua, C. J. Am. Chem. Soc. 2004, 126, 470–
471.
3
3
298 K) δ 6.99 (t, JHH ) 6.6 Hz, 2H, m-H (Ph)), 6.81 (t, JHH ) 6.6 Hz,
1
1H, p-H (Ph)), 6.80 (d, JPH ) 260.4 Hz, 1H, PHMes), 6.69 (s, 2H, m-H
(Mes)), 6.61 (d, 3JHH ) 7.3 Hz, 2H, o-H (Ph)), 4.49 (s, 5H, C5H5), 2.52 (s,
6H, o-CH3 (Mes)), 2.04 (s, 3H, p-CH3 (Mes)) ppm; 31P NMR (121.5 MHz,
C6D5CD3, 298 K) δ 18.9 (d, 1JPH ) 260.4 Hz) ppm; 13C{1H} NMR (125.8
MHz, C6D5CD3, 240 K) δ 358.2 (d, 1JPC ) 75.5 Hz, MndC-P), 233.0 (br
s, Mn-CO), 118.2-142.9 (Ph and Mes), 90.5 (s, C5H5), 24.1 (br s, o-CH3),
20.9 (s, p-CH3) ppm; IR (CH2Cl2) 1973, 1910 (s) (νCO), 1590 (w), 1570
(w) (νCdC) cm-1. Selected spectroscopic data for 6d: 1H NMR (300.1 MHz,
1
C6D6, 298 K) δ 6.84 (s, 2H, m-H (Mes)), 6.39 (d, JPH ) 261.5 Hz, 1H,
3
PHMes), 4.72 (s, 5H, C5H5), 3.16 (d, JPH ) 14.5 Hz, 3H, MndC-CH3),
(17) Selected spectroscopic data for 5c: 31P NMR (THF-d8, 298 K):
1
2.43 (s, 6H, o-CH3 (Mes)), 2.19 (s, 3H, p-CH3 (Mes)) ppm; 31P NMR (121.5
δ-44.0 (d, JPH ) 403.8 Hz) ppm; 13C{1H} NMR (C6D5CD3, 233 K) δ
1
3
2
2
MHz, C6D6, 298 K) δ 10.15 (dq, JPH ) 261.5 Hz, JPH ) 14.5 Hz) ppm;
239.9 (d, JPC ) 19 Hz, P-CdCdO), 230.4 (d, JPC ) 27.5 Hz, Mn-
13C{1H} NMR (75.45 MHz, C6D6, 298 K) δ 366.5 (d, JPC ) 81.1 Hz,
CO),-28.2 (d, 1JPC ) 31.5 Hz, P-CdCdO) ppm; IR (THF) 1932 (s) (νCO),
1
MndC-P), 232.6 (br s, Mn-CO), 128.4-143.1 (Ph and Mes), 90.4 (s,
1725 (m br) (νCdCdO) cm-1
.
2
3
C5H5), 47.7 (d, JPC ) 11.6 Hz, MndC-CH3), 23.5 (d, JPC ) 11.6 Hz,
o-CH3), 20.9 (s, p-CH3) ppm; IR (CH2Cl2) 1970 (s), 1906 (s) (νCO), 1610
(18) Selected spectroscopic data for 5d: 31P NMR (THF-d8, 298 K) δ-
1
24.9 (d, JPH ) 390 Hz); IR (THF) 1930 (s) (νCO), 1730 (m br) (νCdCdO
)
(w), 1592 (w) (νCdC) cm-1
.
cm-1
.

5182 Organometallics, Vol. 27, No. 20, 2008
Communications
acyl anion (IR (THF): 1888 (s) cm-1 (νCO); 1620 (m) cm-1
(νCdO)) [9c]-, whose structure was unambiguously established
by 13C{1H} NMR spectroscopy, showing signals at δ 233.6 (br
s, MnsCO) and 267.6 (br s, CdO), along with the characteristic
signal of the carbon of the four-membered ring (δ 143.2 (d,
1JPC ) 60 Hz, PdC). Such data are in agreement with those
corresponding to the known neutral iron complex Cp(CO)-
Scheme 4
Fe-C(O)C(R)dP-PR2 (R ) NiPr2), exhibiting the same
metallocyclic structure.22 Further experiments indicated that the
addition of traces of water to [8c]-, even at -80 °C, triggers
its instantaneous and quantitative conversion into [9c]-. On
another hand, parallel attempts to prepare the dicarbonyl anion
n
[8d]- from 6d and BuLi under the same reaction conditions
led only to the quantitative formation of the monocarbonyl
species [9d]-, probably due to intrinsic existence of a proton
source, the relatively acidic methyl group of the carbene
ligand.23
NMR spectroscopy,19 and the E geometry of the PdC bond
was inferred from NOE experiments.
The observation of an acid-catalyzed rearrangement of the
anionic dicarbonyl anions [8]- into the monocarbonyl acyl
derivatives [9]- can be rationalized in terms of the proposed
reaction sequence shown in Scheme 5, involving (i) a proto-
The observed rearrangement of the η1-R-phospinocarbene
ligand of 6 into an η1-phosphaalkene by a formal 1,2-hydrogen
shift is reminiscent of the NiPr2 group migration reported by
Bertrand in the case of complex 2 (L2 ) (CO)2; vide supra),
which was, however, nonstereoselective.6b In this respect, the
occurrence of the phosphinoketenes 5c,d as intermediates on
the stereoselective way to the final η1-phosphaalkene products
7 appeared to be rather puzzling to us. Keeping in mind that
closely related carbene-alkene rearrangements of Fischer-type
alkoxycarbene complexes of group 6 metals are base-cata-
lyzed,20 we examined the influence of a base on the isomer-
ization encountered here.
t
nation of [8]- by a proton sourceswater, BuOH, or complex
6d itselfsgiving the elusive hydrido species 10, (ii) a fast
migratory CO-insertion of the σ-phosphaalkenyl fragment
concomitant with coordination of the phosphorus atom to
produce 11, and (iii) deprotonation of 11 by the remaining [8]-
to give [9]-.
Scheme 5
As shown below, such experiments led us to the tantalizing
observation of apparently adVerse effects of different bases on
the course of the reaction and the nature of intermediates.
In our first experiments, addition of a catalytic amount of
Et3N (ca. 15%) to a solution of 6c in CH2Cl2 at 25 °C resulted
in its faster and spectroscopically quantitative conversion into
5c, now within 2-3 min, whereas subsequent isomerization
into 7c required 3-4 h. This second step could be even more
efficiently accelerated upon addition of an excess of Et3N
(ca. 5 equiv, 5 min reaction time). In contrast, Et3N did not
affect the transformation of 6d under the same reaction
conditions. A stronger base, namely DBU, effectively led to
the immediate and quantitative isomerization of both 6c and
6d in CH2Cl2, affording the η1-phosphaalkene species 7 with
>99% E selectiVity.
The ease of the isomerization of 10 into 11 is understood in
terms of the enhanced electrophilicity of its carbonyl groups
resulting from a reduction of the negative charge on the metal
center upon protonation. This is reminiscent of earlier observa-
tions on the oxidative activation of the anionic acyl complex
[Cp′(CO)2Mn-C(O)Tol]- 24 or neutral σ-alkyl25 and σ-alkenyl26
transition-metal complexes toward migratory CO insertion.
To establish the origin of the high stereoselectivity of the
isomerization process and the unexpected role of CO insertion
in its course, we studied in detail the deprotonation of carbenes
6c,d. It was found that the reaction of 6c with nBuLi in THF at
-80 °C leads smoothly to the formation of a deep red anionic
species, [8c]-, which appeared to be stable at room temperature
for several hours. Its IR spectrum displays the three-band pattern
(IR (THF): 1882 (vs), 1811 (s), 1772 (s) cm-1 (νCO)) typical
for a dicarbonyl species of the type [Cp(CO)2M(L)]Li.21 Quite
surprisingly, the deprotonation of 6c with another base, tBuOLi,
led to the quantitative formation of the orange monocarbonyl
(21) The occurrence of three-band patterns in such anionic complexes
is ascribed to an interaction of lithium cations with the oxygen atom of a
CO group: (a) Ulmer, S. W.; Scarstad, P. M.; Burlitch, J. M.; Hughes, R. E.
J. Am. Chem. Soc. 1973, 95, 4469–4471. (b) Darensbourg, M. J.; Burns,
D. Inorg. Chem. 1974, 13, 2970–2973. (c) Darensbourg, M. J.; Darensbourg,
D. J.; Burns, D.; Drew, D. A. J. Am. Chem. Soc. 1976, 98, 3127–3136. (d)
Sentets, S.; Serres, R.; Ortin, Y.; Lugan, N.; Lavigne, G. Organometallics
2008, 27, 2078–2091.
(22) Kato, T.; Polishchuk, O.; Gornitzka, H.; Baceiredo, A.; Bertrand,
G. J. Organomet. Chem. 2000, 613, 33–36.
(23) (a) Casey, C. P.; Anderson, R. L. J. Am. Chem. Soc. 1974, 96,
1230–1231. (b) Bernasconi, C. F.; Sun, W. Organometallics 1995, 14, 5615–
5621. (c) Bernasconi, C. F.; Ruddat, V. J. Am. Chem. Soc. 2002, 124, 14968–
14976.
(24) (a) Sheridan, J. B.; Johnson, J. R.; Handwerker, B. M.; Geoffroy,
G. L. Organometallics 1988, 7, 2404–2411. (b) Bassner, S. L.; Sheridan,
J. B.; Kelley, C.; Geoffroy, G. L. Organometallics 1989, 8, 2121–2126.
(25) (a) Magnuson, R. H.; Meirowitz, R.; Zulu, S.; Giering, W. P. J. Am.
Chem. Soc. 1982, 104, 5790–5791. (b) Skagestad, V.; Tilset, M. Organo-
metallics 1992, 11, 3293–3301.
(26) (a) Reger, D. L.; Mintz, E. Organometallics 1984, 3, 1759–1761.
(b) Reger, D. L.; Mintz, E.; Lebioda, L. J. Am. Chem. Soc. 1986, 108,
1940–1949. (c) Reger, D. L.; Klaeren, S. A.; Babin, J. E.; Adams, R. D.
Organometallics 1988, 7, 181–189.
(19) Selected data for 7c: 31P NMR (C6D6, 298 K) δ 281.6 (br s) ppm;
1
13C{1H} NMR (C6D6, 298 K) δ 166.9 (d, JPC ) 47 Hz, PdC) ppm.
Selected data for 7d: 31P NMR (C6D6, 298 K) δ 278.8 (br s) ppm; 13C{1H}
1
NMR (C6D6, 298 K) δ 161.2 (d, JPC ) 54.5 Hz, PdC). These data are
very similar to those of (η1-P(Mes)dCPh2) transition-metal complexes:
Eshtiagh-Hosseini, H.; Kroto, H. W.; Nixon, J. F.; Maah, M. J.; Taylor,
M. J. J. Chem. Soc., Chem. Commun. 1981, 199–200.
(20) (a) Fischer, E. O.; Plabst, D. Chem. Ber. 1974, 107, 3326–3331.
(b) Casey, C. P.; Brunsvold, W. R. Inorg. Chem. 1977, 16, 391–396.

Communications
Organometallics, Vol. 27, No. 20, 2008 5183
The protonation of [9]- by [Et3NH]Cl27 or NH4Claq leads to
the E-selective formation of 7, bearing evidence for the key
role of the monocarbonyl acyl anion [9]- in the base-catalyzed
isomerization. The observed E stereoselectivity may be attributed
to an external electrophilic attack of the outcoming proton at
the carbon of the phosphaalkene moiety with concomitant
deinsertion of the acyl. Let us remind the reader that the base-
catalyzed rearrangement of Fischer-type alkoxycarbene com-
plexes, for which the postulated mechanism naturally does not
involve CO insertion, shows a preferred Z selectivity for the
alkene.20 The results obtained for 6 indicate that the CO insertion
in the hydride 10 is kinetically preferred over reductive
elimination, which would induce the opposite selectivity.
In summary, we have developed a simple and efficient method
for the synthesis of transition-metal η1-R-phosphinocarbene
complexes by nucleophilic attack of primary or secondary
phosphines at an electrophilic carbyne center, followed by
deprotonation of the intermediate η1-R-phosphoniocarbene. This
led us to isolate the new species Cp(CO)2MndC(R)PHMes (R
) Me, Ph), representing the archetype of a η1-R-phosphinocar-
bene complex, and to trace precisely the elementary steps of
its subsequent stereoselective isomerization into η1-phosphaalk-
ene derivatives. Though such a transformation might have been
regarded as predictable, evidence was provided that its intimate
mechanism is not trivial and includes an acid-catalyzed migra-
tory CO insertion as the key C-C bond forming step. Beyond
the scope of the present work, we are convinced that such a
mechanistic pathway is of fundamental relevance and will be
possibly applicable to other types of anionic transition-metal
σ-complexes.
Acknowledgment. Financial support of the Centre Na-
tional de la Recherche Scientifique (France) and the Russian
Foundation for Basic Research (Grant No. 08-03-00846) is
gratefully acknowledged. D.A.V. also thanks the INTAS for
the Young Scientist Fellowship No. 05-109-4753 and the
University Paul Sabatier (Toulouse, France) for a travel grant.
Supporting Information Available: Text and tables giving
details of the synthesis and spectroscopic characterization of
[3a]BPh4, 5a,b, 4b, 6c,d, 7c,d, 8c[Li], and 9c,d, details on the NMR
monitoring of the isomerization of 6c,d, and details on the X-ray
diffraction studies of complexes 5a,b and 6d. This material is
available free of charge via the Internet at http://pubs.acs.org.
(27) The mixture of ketene (5c or 5d) and phosphaalkene (7c or 7d)
complexes was observed during the reaction course, giving finally 7c or
7d in more than 97% E selectivity.
OM800884V