Coordination chemistry of inversely polarized phosphaalkenes toward group 10 metal centers

Article abstract of DOI:10.1021/om0502943

A series of palladium and platinum complexes containing inversely polarized phosphaalkenes (Me₂N)(R)C=PR′ (R = H, R′ = Mes*, 2; R = Me, R′ = Mes*, 3; R = H, R′ = Mes, 4), exhibiting different steric and electronic environments, have been synthesized. Ligand 2 coordinates in n¹-P fashion to either palladium (PdCl ₂(n¹-P)₂, 5) or platinum (cis-Pt(Cl)2(n ¹P)₂, 6; trans-Pt(Cl)₂(n¹-P) ₂, 7). The equimolar reaction of 3 with Pd(COD)Cl₂ afforded a mixture in 3/1 ratio of cyclopalladated dimeric complexes [PdCl(k²-P,C-CH₂N(Me)CH= PMes*)]2, 9 (eis isomer) and 9′ (trans isomer). The latter was characterized by X-ray diffraction. The less hindered ligand 4 acts as bridging phosphido-like ligand with both palladium (μ-P-[PdCl₂(MesP=CH(NMe₂))]₂,11) and platinium (μ-P-[PtCl₂(MesP=CH(NMe₂))]2, 12). In the platinum case, the reaction of two or more equivalents of the ligand 4 gave a mixture of the complex containing 2 ligands/Pt and the cationic complex with 3 ligands/Pt, 13. This complex was isolated from the reaction of 3.5 equiv of 4 with the Pt precursor.

Full text of DOI:10.1021/om0502943

3856
Organometallics 2005, 24, 3856-3863
Coordination Chemistry of Inversely Polarized
Phosphaalkenes toward Group 10 Metal Centers
Le¨ıla Boubekeur, Louis Ricard, Pascal Le Floch, and Nicolas Me´zailles*
Laboratoire “He´te´roe´le´ments et Coordination”, UMR CNRS 7653 (DCPH), De´partement de
Chimie, Ecole Polytechnique, 91128 Palaiseau Ce´dex, France
Received April 18, 2005
A series of palladium and platinum complexes containing inversely polarized phospha-
alkenes (Me2N)(R)CdPR′ (R ) H, R′ ) Mes*, 2; R ) Me, R′ ) Mes*, 3; R ) H, R′ ) Mes, 4),
exhibiting different steric and electronic environments, have been synthesized. Ligand 2
coordinates in η1-P fashion to either palladium (PdCl2(η1-P)2, 5) or platinum (cis-Pt(Cl)2(η1-
P)2, 6; trans-Pt(Cl)2(η1-P)2, 7). The equimolar reaction of 3 with Pd(COD)Cl2 afforded a
mixture in 3/1 ratio of cyclopalladated dimeric complexes [PdCl(κ2-P,C-CH2N(Me)CHd
PMes*)]2, 9 (cis isomer) and 9′ (trans isomer). The latter was characterized by X-ray
diffraction. The less hindered ligand 4 acts as bridging phosphido-like ligand with both
palladium (µ-P-[PdCl2(MesPdCH(NMe2))]2, 11) and platinium (µ-P-[PtCl2(MesPdCH(NMe2))]2,
12). In the platinum case, the reaction of two or more equivalents of the ligand 4 gave a
mixture of the complex containing 2 ligands/Pt and the cationic complex with 3 ligands/Pt,
13. This complex was isolated from the reaction of 3.5 equiv of 4 with the Pt precursor.
Scheme 1
Introduction
Among low-coordinated phosphorus compounds, phos-
phaalkenes have been studied in depth and were shown
to be versatile ligands in transition metal chemistry.
Many modes of coordination are known, involving either
the lone pair at phosphorus or the PdC bond, or both.
In rare instances, these ligands acted as bridging
ligands between two metal centers (Scheme 1).
Once the coordination chemistry was well understood,
some applications in catalysis could be envisioned.
Recently, Yoshifuji et al. have developed several metal-
catalyzed processes with kinetically stabilized bis-
phosphaalkenes (mostly with Pd(II) centers) as ligands.1
In general, phosphaalkenes R1PdCR2R3 feature an
electron distribution P(δ+)dC(δ-) consistent with the
difference in electronegativity of the respective elements
(P (2.1), C (2.5) according to the Pauling scale). More
recently, phosphaalkenes with inverse electron distribu-
tion have been synthesized, but their coordination
chemistry has been studied only in a few instances so
far. In particular, Weber et al. currently are developing
the coordination of ferriophosphaalkene ligands.2 In
addition to the coordination modes accessible to phos-
phaalkenes, these ligands may be viewed as possessing
two lone pairs at phosphorus because of the resonance
structure in which the doublet at nitrogen participates
Scheme 2
in the delocalization. Accordingly, Cowley, Arduengo,
et al. reported the synthesis of a bis-borane adduct in
1997.3 Also, the η1-P Cr(0) complexes of derivative 1
dismutate in organic solvents to binuclear species with
a bridging phosphorus atom and a free ligand (Scheme
2).4,5
* To whom correspondence should be addressed. Tel: +33 1 69 33
45 70. Fax: +33 1 69 33 39 90. E-mail: mezaille@poly.polytechnique.fr.
(1) Ozawa, F.; Ishiyama, T.; Yamamoto, S.; Kawagishi, S.; Mu-
rakami, H.; Yoshifuji, M. Organometallics 2004, 23, 1698. Ozawa, F.;
Kawagishi, S.; Ishiyama, T.; Yoshifuji, M. Organometallics 2004, 23,
1325. Ozawa, F.; Okamoto, H.; Kawagishi, S.; Yamamoto, S.; Minami,
T.; Yoshifuji, M. J. Am. Chem. Soc. 2002, 124, 10968. Liang, H. Z.;
Ito, S.; Yoshifuji, M. Org. Lett. 2004, 6, 425. Gajare, A. S.; Toyota, K.;
Yoshifuji, M.; Ozawa, F. J. Org. Chem. 2004, 69, 6504.
(2) Weber, L.; Kleinebekel, S.; Pumpenmeier, L.; Stammler, H. G.;
Neumann, B. Organometallics 2002, 21, 1998. Weber, L.; Scheffer, M.
H.; Stammler, H. G.; Neumann, B.; Schoeller, W. W.; Sundermann,
A. Organometallics 1999, 18, 4216.
(3) Arduengo, A. J.; Calabrese, J. C.; Cowley, A. H.; Dias, H. V. R.;
Goerlich, J. R.; Marshall, W. J.; Riegel, B. Inorg. Chem. 1997, 36, 2151.
Arduengo, A. J.; Carmalt, C. J.; Clyburne, J. A. C.; Cowley, A. H.; Pyati,
R. Chem. Commun. 1997, 981.
(4) Grobe, D.; Le Van, J.; Nientiedt, B.; Krebs, M. Chem. Ber. 1988,
121, 655.
10.1021/om0502943 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 07/01/2005

Inversely Polarized Phosphaalkenes
Organometallics, Vol. 24, No. 16, 2005 3857
Scheme 3
The ligand/metal stoichiometry of 2/1 was confirmed by
both the elemental analysis and the 1H NMR spectrum.
Indeed, the signal of the phosphaolefinic proton is
characterized by a deceptively simple virtual triplet
(simplified AA′XX′ spin system, ∑JH-P ) 19.5 Hz) at
8.2 ppm. In the 13C NMR spectrum, the signal of the
phosphalkene carbon atom (AXX′ spin system) should
have allowed us to discriminate between cis and trans
geometries. Indeed, the magnitude of the 2JP-P coupling
constant is indicative of the geometry. However, it
appears as an unresolved broad peak, precluding the
extraction of the coupling constants. Complex 5 ap-
peared to be sensitive to hydrolysis. Because of the lack
of X-ray structure, the cis or trans geometry, drawn
above, could not be ascertained on the basis of NMR
spectroscopy alone. To obtain this geometrical informa-
tion, an IR spectrum in the near-infrared region was
recorded. Indeed it is well known that trans complexes
give rise to one intense band and cis give two bands in
In this instance, inversely polarized phosphaalkenes
do resemble phosphido ligands which display richer
coordination chemistry. For example, binuclear Ni,6
Pd,7,8 and Pt9 complexes with bis-bridging phosphido
ligands have found interesting developments. Both the
lack of general knowledge on the coordination chemistry
of inversely polarized phosphaalkenes and their poten-
tial resemblance to phosphide ligands prompted us to
study their behavior toward metal centers with catalytic
relevance (Pd(II) and Pt(II)). We wish to present here
our first investigations in this area.
Results and Discussion
the region between 300 and 350 cm-1 10
. For complex 5,
a broad, intense band was observed at 335 cm-1, clearly
proving the trans relation between the two phospha-
alkene moieties. The comparison with an analogous Pt
center was then envisaged. The same reaction was thus
carried out with [(COD)PtCl2] in THF. In this case, an
additional piece of information should be accessible
Three different ligands, 2-4, were selected, allowing
the modification of both steric and electronic environ-
ment (Scheme 3).
Reactivity of 2. The stoichiometric reaction of ligand
2 with [(COD)PdCl2] in THF led rapidly to the formation
of a dark red solution. The 31P NMR spectrum of the
crude mixture showed the presence of a single complex,
5, characterized by a singlet at +32 ppm. The change
in the chemical shift by -50 ppm strongly suggested
1
because of the existence of a nuclear spin (I ) /2) of
one of the two Pt isotopes. Indeed, it is well known that
the magnitude of the 1JPt-P coupling constant in [(R3P)2-
PtCl2] complexes strongly depends on the cis or trans
relation between the two phosphines ligands.11 Quite
surprisingly, 2 did not displace the COD ligand from
the Pt center, even under heating conditions in THF.
We then turned our attention to a precursor whose
ligands would be more easily replaced, such as the
propionitrile in [(C2H5CN)2PtCl2], or to a chloro-bridged
Pt dimer which is typically cleaved by two electron
donors, [PtCl2(PMe3)]2. When the reaction was carried
out with the nitrile derivative, the initially pale yellow
solution (in CH2Cl2) turned slowly darker, and the
formation of the two isomers in a 0.7/1 ratio, 6 and 7,
was observed. The reaction is very slow and requires
48 h to be complete, as indicated by 31P NMR (eq 2).
the formation of an η1 complex. A H NMR spectrum
1
recorded from an aliquot of this solution showed that
half of the starting [(COD)PdCl2] had not reacted. This
was later confirmed by the reaction between 2 equiv of
2 and [(COD)PdCl2] in THF (eq 1). The dark violet crude
mixture showed the formation of the same complex, 5.
This complex was fully characterized by usual NMR
techniques, as well as elemental analyses. Unfortu-
nately, X-ray quality crystals of 5 could not be obtained.
(5) Weber, L. Eur. J. Inorg. Chem. 2000, 2425.
(6) Jones, R. A.; Stuart, A. L.; Atwood, J. L.; Hunter, W. E.; Rogers,
R. D. Organometallics 1982, 1, 1721. Jones, R. A.; Stuart, A. L.; Atwood,
J. L.; Hunter, W. E. Organometallics 1983, 2, 874.
(7) Zhuravel, M. A.; Moncarz, J. R.; Glueck, D. S.; Lam, K. C.;
Rheingold, A. L. Organometallics 2000, 19, 3447; Mizuta, T.; Aoki, S.;
Nakayama, K.; Miyoshi, K. Inorg. Chem. 1999, 38, 4361.
(8) Zhuravel, M. A.; Grewal, N. S.; Glueck, D. S.; Lam, K. C.;
Rheingold, A. L. Organometallics 2000, 19, 2882. Alonso, E.; Casas, J.
M.; Cotton, F. A.; Feng, X. J.; Fornies, J.; Fortuno, C.; Tomas, M. Inorg.
Chem. 1999, 38, 5034.
(9) Cristofani, S.; Leoni, P.; Pasquali, M.; Eisentraeger, F.; Albinati,
A. Organometallics 2000, 19, 4589. Itazaki, M.; Nishihara, Y.; Osakada,
K., Organometallics 2004, 23, 1610. Leoni, P.; Chiaradonna, G.;
Pasquali, M.; Marchetti, F. Inorg. Chem. 1999, 38, 253. Leoni, P.;
Pasquali, M.; Fortunelli, A.; Germano, G.; Albinati, A. J. Am. Chem.
Soc. 1998, 120, 9564.
Complex 6 is characterized by a singlet at -3.6 ppm
with Pt satellites (1JPt-P ) 3888 Hz), and complex 7 is
characterized by a singlet at 15.4 ppm with Pt satellites
(10) Minghetti, G.; Stoccoro, S.; Cinellu, M. A.; Zucca, A.; Manassero,
M.; Sansoni, M. J. Chem. Soc., Dalton Trans. 1998, 4119. Bandyo-
padhyay, P.; Bandyopadhyay, D.; Chakravorty, A.; Cotton, F. A.;
Falvello, L. R.; Han, S. J. Am. Chem. Soc. 1983, 105, 6327.
(11) Kroto, H. W.; Nixon, J. F.; Taylor, M. J.; Frew, A. A.; Muir, K.
W. Polyhedron 1982, 1, 89.

3858 Organometallics, Vol. 24, No. 16, 2005
Boubekeur et al.
(1JPt-P ) 2855 Hz) in the 31P NMR spectrum. This
ated for the two complexes, at δ 3.05 (major species) and
δ 3.08 ppm (minor species) and at δ 7.42 ppm (minor)
and δ 7.48 ppm (major), clearly showing the similarity
between the complexes 9 and 9′. The strongest evidence
for the formation of a single Pd-CH2 bond is given by
a doublet at δ 4.21 ppm, which integrates for two
hydrogen atoms. This signal is quite downfield shifted
from the N-CH3 signal (broadened doublet at 3.05/3.08
ppm), which integrates as expected for three hydrogens.
In the 13C{1H} NMR spectrum, the phosphaalkene
carbon resonates at 186.2 ppm, in the usual range for
such compounds.5 As in the 1H spectrum, the signal for
the CH2-Pd appears at low field (57.1 ppm) compared
to the N-CH3 (40.7 ppm) (eq 4).
assignment was done exclusively on the basis of the
1
magnitude of the JPt-P coupling constants, which are
not ambiguous in this case (cis having a larger coupling
constant than trans), as the mixture of the isomers could
1
not be separated. In the H NMR of the mixture, the
phosphaolefinic proton appears for 6 as a doublet, with
2JH-P ) 14.5 Hz and 3JH-P ) 0 Hz at 8.35 ppm, and as
a pseudotriplet for 7 (AA′XX′ spin system) with ∑JH-P
) 19.5 Hz at 8.22 ppm. These complexes are however
sensitive to hydrolysis and partly decomposed during
13C NMR acquisition.
In the case of the Pt dimer precursor, mixing the two
reactants in THF or CH2Cl2 at room temperature led
to a yellow solution. The 31P NMR spectrum of the crude
mixture after few minutes showed the formation of a
new complex, [8], characterized by two sets of doublets
2
centered at 31.0 ppm (1JPt-P ) 2583 Hz, JP-P ) 590
Hz, phosphaalkene) and -17.6 ppm (1JPt-P ) 3026 Hz,
2JP-P ) 590 Hz, PMe3) respectively (eq 3).
Definitive evidence for the formation of a dimeric
species was provided by X-ray crystal analysis. Yellow
crystals were obtained by a two-step sequence: first,
microcrystals deposited from the C6D6 solution used for
NMR characterization. These were then dissolved in
acetone, which was allowed to slowly evaporate to yield
orange polycrystalline material and dark yellow/orange
crystals. The latter were hand picked and the structure
was solved. The ORTEP plot is presented in Figure 1
together with significant bond distances and angles. The
structure corresponds to isomer 9′. One clearly sees the
formation of a single bond between the Pd center and a
former CH3 moiety of the dimethyl-amino group. The
bond distances N(1)-C(3) and N(1)-C(2) at 1.486(3) and
1.457(2) Å, respectively, are consistent with single
bonds. On the other hand, the N(1)-C(1) bond distance
The magnitude of both of these coupling constants,
2
1JPt-P and JP-P, clearly indicate the formation of the
trans complex. Unfortunately, an equilibrium is rapidly
established as starting ligand 2 and Pt precursor
[Pt2Cl4(PMe3)2] remain in the spectrum with constant
concentration (even after 24 h), and the complex [8]
could therefore not be isolated pure from the crude
mixture.
Reactivity of 3. We then focused our attention on
the closely related, in terms of steric requirements at
the phosphorus center, ligand 3. As expected from the
synthesis of the above-mentioned complexes, 3 was
reacted with 2 equiv of [(COD)PdCl2]. The solution
turned green very fast, then slowly yellow, and a white
precipitate appeared overnight. The yellow solution is
characterized by two singlets at 70.9 and 71.4 ppm in
the 31P NMR spectrum, in a 3/1 ratio. The change in
the chemical shift from 3 is only around -22 ppm
(compared to -50 ppm from 2 to 5). Moreover, an aliquot
of this yellow solution revealed that only half of the
starting [(COD)PdCl2] had been consumed. The reaction
was thus carried out with only 1 equiv of palladium
precursor and led to the same mixture of complexes, 9
and 9′. The two complexes possess very similar solubili-
ties and were obtained as a mixture in 68% yield. They
are very soluble in THF, less so in acetone, soluble in
warm benzene or toluene, and not soluble in hexanes
or diethyl ether. The complexes are very robust, as they
are not decomposed by either water or air. The elemen-
tal analysis was performed on the mixture of the two
complexes and confirmed that these are isomers as
shown in eq 4. The spectroscopic analysis was also
carried out on the mixture of the isomers. 1H NMR
spectroscopy verifies the 3/1 ratio observed in the 31P
NMR spectrum, which allowed us to clearly assign the
various signals. Only two sets of signals are differenti-
Figure 1. Molecular structure of complex 9′. Thermal
ellipsoids are drawn to the 30% probability level. Hydrogen
atoms were omitted for clarity. Selected bond distances (Å)
and bond angles (deg): Pd(1)-C(2) 2.018(2); Pd(1)-P(1)
2.2177(5); Pd(1)-Cl(1) 2.4293(5); Pd(1)-Cl(1)# 2.4591(5);
C(1)-P(1) 1.746(2); C(5)-P(1) 1.852(2); C(1)-N(1) 1.331(2);
N(1)-C(3) 1.486(3); N(1)-C(2) 1.457(2). C(1)-P(1)-C(5)
102.2(1);C(1)-P(1)-Pd(1)104.07(7);P(1)-C(1)-N(1)113.9(1);
C(1)-N(1)-C(2) 117.8(2); C(1)-N(1)-C(3) 123.7(2); C(2)-
N(1)-C(3) 118.4(2); P(1)-C(1)-C(4) 125.6(2); N(1)-C(1)-
C(4) 120.1(2).

Inversely Polarized Phosphaalkenes
Organometallics, Vol. 24, No. 16, 2005 3859
Scheme 4
(1.331(2) Å) lies between a single and a double bond.
The same situation is found for the P(1)-C(1) bond
distance (1.746(2) Å: double bond), which is clearly
shorter than the P(1)-C(5) bond to the Mes* group
(1.852(2) Å: single bond). The acute C(1)-P(1)-Pd(1)
and C(1)-P(1)-C(5) bond angles at 104.07(7)° and
102.2(1)°, respectively, are typical of low-coordinated
phosphorus species (weak hybridization at P). However,
the geometry at P(1) is strongly pyramidalized (∑angles
at P(1) ) 320.17°), which suggests a partial loss of the
P-C double bond character. Both the C(1) and N(1) are
planar (sum of the angles at N(1) ) 359.9° and at C(1)
) 359.6°), pointing toward a delocalized structure
(Scheme 4) en route to the zwitterionic structure. This
is corroborated by the dihedral angle C(4)-C(1)-P(1)-
C(Ph) of 32.6°.
Figure 2. Molecular structure of complex 10. Thermal
ellipsoids are drawn to the 30% probability level. Hydrogen
atoms were omitted for clarity. Selected bond distances (Å)
and bond angles (deg): Pd(1)-P(2) 2.251(2); Pd(1)-P(1)
2.279(2); Pd(2)-P(2) 2.272(2); Pd(2)-P(1) 2.246(2); Pd(1)-
Cl(1) 2.363(2); Pd(1)-Cl(2) 2.372(2). C(1)-P(1) 1.811(6);
C(13)-P(2) 1.804(8); C(1)-N(1) 1.269(8); C(13)-N(2) 1.22(1);
C(4)-P(1) 1.823(6); C(16)-P(2) 1.814(6); Pd(2)‚‚‚Pd(1)
3.1896(6); C(1)-P(1)-Pd(1) 105.6(2); C(13)-P(2)-Pd(1)
104.6(3); C(1)-P(1)-Pd(2) 105.2(2); C(13)-P(2)-Pd(2)
106.1(3);C(1)-P(1)-C(4)112.5(3);C(13)-P(2)-C(16)113.1(4);
P(1)-C(1)-N(1) 133.6(5); P(2)-C(13)-N(2) 135.7(8); C(1)-
N(1)-C(2) 127.8(6); C(1)-N(1)-C(3) 119.5(7).
In this case, the very bulky nature of the phosphorus
substituant (Mes*) prevents the formation of bimetallic
species with a bridging (phosphido-like) ligand. Dimin-
ishing the size of the substituent should favor such a
coordination mode (vide supra).
Reactivity of 4. In a last modification of the elec-
tronic and steric requirements of the inverse polarized
phosphaalkenes, we studied the reactivity of ligand 4
with the same precursors. As in the case of 3, carrying
out the reaction with 1, 2, or more equivalents of 4 with
[(COD)PdCl2] led only to the formation of a complex with
1/1 stoichiometry. This complex, 10, is characterized by
a very strong upfield shift from the starting ligand 4 (δ
) -115 ppm, ∆δ ) -170 ppm) in the 31P NMR
spectrum. The violet complex was obtained in 90% yield
after precipitation with hexanes, filtration, and drying.
It was then fully characterized by usual NMR spectros-
copy and elemental analysis. Elemental analysis con-
firmed the stoichiometry but did not allow to differen-
ciate between monomeric and dimeric structure. A first
strong indication of the dimeric structure is given by
X-ray quality crystals were obtained by slow diffusion
of hexanes into a CH2Cl2 solution of 10. The ORTEP
plot is presented in Figure 2 together with significant
bond distances and angles.
The X-ray structure confirmed the formation of a
dimer. Most interestingly, the ligand can now be viewed
as a pseudozwitterionic moiety (P-∼N+), which is fully
consistent with the strong upfield shift observed in the
31P NMR spectrum. Indeed, the nitrogen atom is planar
(∑angles ) 359.9°) and the C-N bond distance of
1.269(8) Å is consistent with a double bond. On the other
hand, the P-C bond distance is now clearly a single
bond: 1.811(6) Å (it is similar to the P-C bond distance
with the mesityl group: 1.823(6) Å). This indicates a
phosphide type structure (R2P-). Overall in this com-
plex, the extreme case of inversely polarized phos-
phaalkenes is observed. The dimer is slightly disym-
metrical, as shown by two “longer” Pd-P at ca. 2.275 Å
(average) and two “shorter” Pd-P at ca. 2.248 Å
(average). The distance between the two Pd centers is
long, 3.1896(6) Å, and clearly shows the absence of a
real Pd‚‚‚Pd bond. The C(1)-P(1)-C(4) bond angle,
112.5°, is much wider than usually observed for free or
coordinated phosphaalkene ligands, again showing the
phosphido-like structure. The second view of the com-
plex reveals the stacking between the two mesityl
moieties (distance C(4)‚‚‚C(16): 3.72 Å)). Overall this
structure is quite similar to the several reported dimers
with bridging phosphido ligands.7,8 Among these, a
search in the Cambridge database allowed us to observe
two different groups of structures: with or without a
Pd-Pd single bond. For the complexes in which there
is a metal-metal bond, the distance is short (between
1
the H NMR spectrum, which shows a virtual triplet-
like signal for the phosphaalkene hydrogen atom (cou-
pling with two phosphorus atoms, simplified AA′XX′
spin system, ∑JH-P ) 13.4 Hz) at 8.95 ppm. The ortho
(2.90 ppm) and para (2.15 ppm) methyl groups of the
Mes substituent are quite downfield shifted, clearly
indicating a lower electron density. The two methyl
groups of the dimethylamino also experience a downfield
shift (from 3.0 in 4 to 3.7 and 4.2 in 10). Altogether,
the data points toward the formation of a dimer in which
the ligand is bridging (eq 5).

3860 Organometallics, Vol. 24, No. 16, 2005
Boubekeur et al.
2
2.57 and 2.62 Å)12 and the P-Pd-P bond angle is wide
(between 112.7° and 113.0°). On the other hand, the
distribution of complexes without Pd-Pd single bonds
is larger: distance between 3.20 and 3.64 Å, and
P-Pd-P bond angle between 68.5° and 81.4°.7,13 In our
complex, the distance between the two Pd centers is
marginally shorter (3.1896(6) Å) than the shortest
reported structure without a Pd-Pd bond. The P(1)-
Pd(1)-P(2) and P(1)-Pd(2)-P(2) bond angles are mea-
sured at 75.53° and 75.77°, respectively. Together, these
data clearly indicate the absence of a Pd‚‚‚Pd single
bond.
Hz, JP-P ) 25.5 Hz, 2P) and a triplet at -16.5 ppm
(1JPt-P ) 3433.6 Hz, JP-P ) 25.5 Hz, 1P).
2
The analogous Pt dimeric complex, 11, was obtained
by the stoichiometric reaction between 4 and [(COD)-
PtCl2]. Again, the phosphorus chemical shift resonates
at high field: -148.9 ppm. Coupling with two equivalent
Pt centers is obvious, as the signal appears as a
pseudopentet: singlet with satellites of one and/or two
195Pt atoms (1JPt-P ) 2600.1 Hz). Apart from this typical
feature, the other 1H and 13C NMR spectra are similar
to those of complex 10 (eq 6).
In the 1H NMR spectrum, the signals of the phospha-
alkene protons appear at 7.50 ppm as the expected
doublet of triplets (1H, AXY2 spin system) and at 8.78
ppm as a second-order virtual triplet (2H, AA′XX′Y spin
system). The same type of second-order figure of cou-
pling is observed in the 13C NMR spectrum. Indeed a
virtual doublet of triplets is seen at 186 ppm (usual
range for inversely polarized phosphaalkene). Finally,
adding more starting material did not lead to the
formation of the homoleptic dicationic species, most
probably for steric reasons.
Conclusion
Through few examples, using three different inversely
polarized phosphaalkenes, we have observed several of
the possible coordination modes that are accessible to
these ligands: (a) η1 coordination via the lone pair of
phosphorus as “regular” phosphaalkenes; (b) bridging
phosphido-like ligand, via the two lone pairs of the
formally zwitterionic structure; (c) bidentate ligation,
via η1 coordination of the lone pair of phosphorus and
Pd-C bond formation via insertion into the C-H bond
of the N-CH3 moiety.
Nevertheless, the reactivity of 4 with a platinium
center appeared to be richer. Unlike what was observed
for the palladium derivatives, variation of the ratio 4/Pt
center from 1/1 to 3.5/1 led to the formation of mixtures
of several complexes that are not in equilibrium (eq 7).
Indeed, adding 2 equiv of 4 to a CH2Cl2 solution of
[(COD)PtCl2] led to a mixture of complex 11 (about
40%), the expected complex [12] (about 20%, cis or
trans), characterized by a singlet with Pt satellites at
-14.3 ppm (1JPt-P ) 3037.5 Hz) and the complex 13
characterized by a doublet and a triplet both with Pt
satellites (about 40%). With 3 equiv of 3, complex 13
becomes the major species (about 90%). The remaining
products are the starting material and complex [12] (5%
according to 31P NMR spectroscopy). With 3.5 equiv,
only 4 and 13 are observed by 31P NMR. Thus, complex
13 could be obtained pure in 85% yield (based on the
Pt precursor) after extraction of remaining starting
material (and COD) in diethyl ether. It was fully
characterized by NMR techniques as well as elemental
analyses. In the 31P NMR spectrum, complex 13 is
characterized by a doublet at -0.4 ppm (1JPt-P ) 1780.0
It appeared that ligand 2 is quite a weak ligand of
the Pd(II) center (complex 5 was easily hydrolyzed) and
Pt(II) center (unable to break quantitatively a chloro-
bridged dimer). Ligand 3 gave an unprecedented biden-
tate ligation after a formal Pd insertion into a N-CH3
bond. Finally, ligand 4, being much less sterically
demanding, can either bridge two centers or act as
monodentate ligand. We have also observed with these
ligands a very significant difference in reactivity toward
Pd(II) and analogous Pt(II) centers. In short, the
combination of only three ligands with two metal centers
led to a very rich coordination chemistry. We are
currently studying the mechanism of the formation of
complexes 9 and 9′ as well as their use in catalytic
processes. Indeed, preliminary experiments show that
the bridge is easily cleaved to form monomeric com-
plexes, which are currently under investigation. The
behavior of these inversely polarized phosphaalkene
ligands toward other metal centers is also being inves-
tigated, and results will be presented in due course.
(12) Arif, A. M.; Heaton, D. E.; Jones, R. A.; Nunn, C. M. Inorg.
Chem. 1987, 26, 4228. Sommovigo, M.; Pasquali, M.; Leoni, P.; Englert,
U. Inorg. Chem. 1994, 33, 2686. Leoni, P.; Sommovigo, M.; Pasquali,
M.; Sabatino, P.; Braga, D. J. Organomet. Chem. 1992, 423, 263.
Englert, U.; Matern, E.; Olkowska-Oetzel, J.; Pikies, J. Acta Crystal-
logr. Sect. E.: Struct. Rep. Online 2003, 59, M376.
(13) Heyn, R. H.; Gorbitz, C. H. Organometallics 2002, 21, 2781.
Gebauer, T.; Frenzen, G.; Dehnicke, K. Z. Naturforsch. (B) 1992, 47,
1505. Brunner, H.; Dormeier, S.; Grau, I.; Zabel, M. Eur. J. Inorg.
Chem. 2002, 2603. Mizuta, T.; Nakayama, K.; Aoki, S.; Miyoshi, K.
Bull. Chem. Soc. Jpn. 2002, 75, 1547. Bekiaris, G.; Roschenthaler, G.
V.; Behrens, U. Z. Anorg. Allg. Chem. 1992, 618, 153. Wong, W. K.;
Liang, H. Z.; Yung, M. Y.; Guo, H. P.; Yung, K. F.; Wong, W. T.;
Edwards, P. G. Inorg. Chem. Commun. 2004, 7, 737.

Inversely Polarized Phosphaalkenes
Organometallics, Vol. 24, No. 16, 2005 3861
Table 1. 31P NMR Data for Complexes 4, 6, 7, 9, 9′,
10, 11, and 13
2
compound
δP in ppm
1JPPt in Hz JPP in Hz δH in ppm
4
32.0
8.20
8.35
8.22
6
-3.6
3888
2855
7
15.4
70.9 (major)
71.4 (minor)
9 or 9′
10
11
13
-114.8
-148.9
-0.4
8.85
9.03
7.50
2600
1780
25.5
placed under nitrogen. THF (10 mL) was then added and the
mixture stirred at room temperature overnight. The volume
of the purple solution was reduced to 1/3, and hexanes (7 mL)
were added, resulting in the precipitation of a purple solid. It
was filtered, washed with diethyl ether, and then dried under
Figure 3. Molecular structure of complex 10: side view.
Thermal ellipsoids are drawn to the 30% probability level.
Hydrogen atoms are omitted for clarity.
1
vacuum. Yield: 90% (253 mg). 31P{1H} (THF-d8): δ 31.2. H
(THF-d8) δ 1.15 (s, 9H, tBu), 1.75 (s, 18H, 2×tBu), 2.5 (bs, 6H,
NMe2), 7.43 (vt, 2H, ∑JHP ) 3.0 Hz, H of Mes*), 8.20 (vt, 1H,
∑JHP ) 19.5 Hz, HCd). 13C{1H} (THF-d8): δ 31.4 (s, C10), 35.7
Experimental Section
(s, C9), 35.1 (s, C8), 40.4 (s, C2), 40.6 (s, C7), 123.5 (vt, ∑JC-P
)
All experiments were performed under an atmosphere of
dry nitrogen or argon using standard Schlenk and glovebox
techniques. Solvents were freshly distilled under argon from
Na/benzophenone (THF, diethyl ether, hexanes) or from P2O5
(dichloromethane, CDCl3). Ligands 2,14 3,15 and 416 and
complexes [Pd(COD)Cl2],17 [Pt(COD)Cl2],18 [Pt(C2H5CN)2Cl2],19
and [Pt2Cl4(PMe3)2]20 were prepared according to literature
procedures.
8.1 Hz, C5), 125.6 (m, C3), 152.2 (s C6), 157.8 (vt, ∑JC-P ) 5.4
Hz, C4), 165.5 (m, C1). IR (KBr): 335 cm-1, broad, intense.
Anal. Calcd for C42H72Cl2N2P2Pd: C, 59.75; H, 8.60. Found:
C, 60.10; H, 8.92.
Nuclear magnetic resonance spectra were recorded on a
Bruker Avance 300 spectrometer operating at 300 MHz for
1H, 75.5 MHz for 13C, and 121.5 MHz for 31P. 1H and 13C
chemical shifts are reported in ppm relative to Me4Si as
external standard. 31P are relative to a 85% H3PO4 external
reference. Coupling constants are expressed in hertz. The
following abbreviations are used: b, broad; s, singlet; d,
doublet; dd, doublet of doublet; t, triplet; m, multiplet; v,
virtual. Elemental analyses were performed by the “Service
d’Analyses du CNRS, Gif/Yvette”.
Crystallography. Yellow plates of complex 9′ were ob-
tained by slow evaporation of an acetone/C6D6 solution of the
complex at room temperature. Magenta plates of complex 10
were obtained by slow diffusion of hexanes into a solution of
the complex in CDCl3 at RT. Data were collected on a Nonius
Kappa CCD diffractometer using a Mo KR (λ ) 0.71073 Å)
X-ray source and a graphite monochromator. Experimental
details are described in Table 1. The crystal structure was
solved using SIR 97 and SHELXL-97. Molecular drawings
were made using ORTEP III for Windows, then POV-Ray.
CCDC-268892 and 268893 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free
of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax: (international) +44-1223/336-
033; e-mail: deposit@ccdc.cam.ac.uk].
Synthesis of Complexes 6 and 7. 2 (100 mg, 0.3 mmol)
and [Pt(C2H5CN)2Cl2] (60 mg, 0.15 mmol) were weighed in air
and then placed under nitrogen. CH2Cl2 (7 mL) was then added
and the solution stirred at 35 °C overnight. The volume of the
orange solution was reduced to 1/3, and hexanes (7 mL) were
added, resulting in the precipitation of an orange solid. It was
filtered, washed with diethyl ether, and then dried under
vacuum. Yield: 89% (124 mg).
1
1
6: 31P{1H} (CD2Cl2): δ -3.6 ppm (s, JP-Pt ) 3888 Hz). H
(CD2Cl2): δ 1.21 (s, 9H, tBu), 1.80 (s, 18H, 2×tBu), 2.71 (m,
3H, NMe), 3.45 (bs, 3H, NMe), 7.55 (s, 2H, H of Mes*), 8.35
2
(d, 1H, JH-P ) 14.5 Hz, HCd).
1
1
7: 31P{1H} (CD2Cl2): δ 15.4 ppm (s, JP-Pt ) 2855 Hz). H
(CD2Cl2): δ 1.21 (s, 9H, tBu), 1.80 (s, 18H, 2×tBu), 2.65 (bs,
3H, NMe), 3.15 (bs, 3H, NMe), 7.50 (s, 2H, H of Mes*), 8.22
(vt, 1H, ∑JH-P ) 19.5 Hz, HCd). Anal. Calcd for C42H72-
Cl2N2P2Pt: C, 54.07; H, 7.78. Found: C, 54.30; H, 7.97.
Synthesis of Complexes 9 and 9′. 3 (300 mg, 0.86 mmol)
and [Pd(COD)Cl2] (245 mg, 0.86 mmol) were weighed in air
and then placed under nitrogen. THF (20 mL) was then added
and the mixture stirred at room temperature overnight, during
which time a white precipitate formed. The yellow solution
was filtered and reduced to about 3 mL. Hexanes (20 mL) were
added, which resulted in the precipitation of a yellow solid,
which was filtered. The solid was crystallized from warm
benzene. Yield: 68% (287 mg). Anal. Calcd for C44H74-
Cl2N2P2Pd2: C, 54.10; H, 7.64. Found: C, 54.00; H, 7.39.
9 or 9′: major species: 31P{1H} (THF-d8): δ 70.9 ppm (s).
1H (THF-d8): δ 1.33 (s, 3H, CH3), 1.37 (s, 9H, tBu para of
Synthesis of Complex 5. 2 (200 mg, 0.6 mmol) and
[Pd(COD)Cl2] (85 mg, 0.3 mmol) were weighed in air, then
(14) Mackewitz, T. W.; Peters, C.; Bergstra¨sser, U.; Leininger, S.;
Regitz, M. J. Org. Chem. 1997, 62, 7605. Becker, G.; Mundt, O.;
Ro¨ssler, M.; Schneider, E. Z. Chem. 1978, 21, 407.
(15) Oehme, H.; Leissring, E.; Meyer, H. Tetrahedron Lett. 1980,
21, 1141; Oehme, H.; Leissring, E.; Meyer, H. Z. Anorg. Allg. Chem.
1981, 21, 41.
(16) Becker, G.; Uhl, W.; Wessely, H. J. Z. Anorg. Allg. Chem. 1981,
479, 41.
(17) Drew, D.; Doyle, J. R. Inorg. Synth. 1990, 28, 348.
(18) McDermott, J. X.; White, J. F.; Whitesides, J. F. J. Am. Chem.
Soc. 1976, 98, 6521.
3
Mes*), 1.73 (s, 18H, tBu ortho of Mes*), 3.05 (d, JHP ) 11.8
3
Hz, 3H, NMe), 4.21 (d, JHP ) 9.9 Hz, 2H, NCH2Pd), 7.48 (s,
(19) Elding, L. I.; Oskarsson, A.; Kukushkin, V. Y. Inorg. Synth.
1997, 31, 280.
2
2H, CH arom). 13C{1H} (THF-d8): δ 17.9 (d, JCP ) 5.0 Hz,
CH3, C2), 31.5 (s, C10), 34.2 (d, 2JCP ) 5.0 Hz, C12), 35.7 (s, C9),
39.5 (s, C11), 40.7 (s, CH3-N, C4), 57.1 (m, CH2-N, C3), 122.0
(20) Smithies, A. C.; Rycheck, M.; Orchin, M. J. Organomet. Chem.
1968, 12, 199.

3862 Organometallics, Vol. 24, No. 16, 2005
Table 2. Crystal Data and Structural Refinement Details for 9′ and 10
Boubekeur et al.
9′
10a
formula
Mr
T [K]
C
44H74Cl2N2P2Pd2,2(C6D6)
C24H36Cl4N2P2Pd2,3.5(CHCl3)
1144.97
1186.88
150.0(1)
150.0(1)
cryst syst
space group
a [Å]
monoclinic
C2/c
36.0050(10)
9.8830(10)
17.7840(10)
90.00
117.5200(10)
90.00
5612.2(7)
4
monoclinic
P21/n
12.1510(10)
16.8030(10)
22.6970(10)
90.00
100.8900(10)
90.00
4550.7(5)
4
b [Å]
c [Å]
R [deg]
â [deg]
γ [deg]
V [Å3]
Z
F [g cm-3
]
1.355
0.829
1.723
1.736
µ [cm-1
]
cryst size [mm]
F(000)
index ranges
scan type
0.20 × 0.18 × 0.12
0.18 × 0.12 × 0.12
2368
2348
-50 50; -13 13; -25 24
phi and omega scans
30.03/I > 2σI
332; 19
-12 15; -21 19; -29 22
phi and omega scans
27.48/I > 2σI
426; 18
2θmax[deg]/criterion
no. of params refined;data/param
no. of reflns collected
no. of indep reflns
no. of reflns used
wR2
15 209
40 629
8167
10 412
6368
7767
0.0912
0.1970
R1
0.0334
0.0650
goodness of fit
1.061
1.070
largest diff peak/hole [e Å-3
]
1.018(0.080)/-0.794(0.080)
4.927(0.206)/-1.775(0.206)
a Note for structure 10: Poorly resolved structure due to large mosaicity. Unresolved disorder is apparent. Large unexplained residue
near C15. A chloroform molecule located near a symmetry center was incompletely resolved and accounted for using the Platon SQUEEZE
function.
3
2
(d, JCP ) 5.0 Hz, C7), 152.1 (s, C8), 159.0 (d, JCP ) 7.0 Hz,
C6), 186.2 (m, P-C-N, C1). Note: C5 is not observed.
9′ or 9: minor species: 31P{1H} (THF-d8): δ 71.4 ppm (s).
1H (THF-d8) δ 1.33 (s, 3H, CH3), 1.37 (s, 9H, tBu para of Mes*),
Synthesis of Complex 11. 4 (52 mg, 0.25 mmol) and
[Pt(COD)Cl2] (94 mg, 0.25 mmol) were weighed in air and then
placed under nitrogen. CH2Cl2 (10 mL) was then added and
the mixture stirred at room temperature overnight. The
volume of the orange solution was reduced to 1/3, and hexanes
(10 mL) were added, resulting in the precipitation of an orange
solid. It was filtered, washed with diethyl ether, and then dried
under vacuum. The title complex was obtained in 87% yield
3
1.73 (s, 18H, tBu ortho of Mes*), 3.08 (d, JHP ) 11.8 Hz, 3H,
3
NMe), 4.21 (d, JHP ) 9.9 Hz, 2H, NCH2Pd), 7.42 (s, 2H, CH
meta).
1
(103 mg). 31P{1H} (CDCl3): δ -148.9 ppm (s, JPt-P ) 2600.1
1
Hz). H (CDCl3): δ 2.25 (s, 3H, H5), 2.90 (s, 6H, 2x H6), 3.85
(s, 3H, H8), 4.40 (bs, 3H, H8), 6.75 (s, 2H, H3), 9.03 (b, 1H, H7,
AA′XX′). 13C{1H} (CDCl3): δ 21.7 (s, C5), 27.8 (s, C6), 32.1 (s,
C8), 37.4 (s, C8), 129.3 (s, C1), 131.2 (bs, C3), 142.1 (s, C4), 144.7
(m, C2), 163.3 (bs, C5). Anal. Calcd for C24H36Cl4N2P2Pt2: C,
30.46; H, 3.83. Found: C, 30.76; H, 4.05.
Synthesis of Complex 13. 4 (100 mg, 0.48 mmol) was
weighed in a drybox and dissolved in CH2Cl2 (5 mL). [Pt(COD)-
Cl2] (52 mg, 0.14 mmol) was added solid to the solution, which
turned instantaneously red. The mixture was stirred at room
temperature for 2 h, and then the solvent was removed under
vacuum, leaving an oily residue. Diethyl ether was added (5
mL) and the mixture stirred for 15 min, which resulted in the
precipitation of an orange solid. It was filtrated, washed with
diethyl ether (2 × 2 mL), and dried under vacuum to yield
the title complex in 85% yield (based on Pt, 105 mg). 31P{1H}
Synthesis of Complex 10. 4 (103 mg, 0.5 mmol) and
[Pd(COD)Cl2] (141 mg, 0.5 mmol) were weighed in air and then
placed under nitrogen. THF (10 mL) was then added and the
mixture stirred at room temperature overnight. The volume
of the purple solution was reduced to 1/3, and hexanes (7 mL)
were added, resulting in the precipitation of a purple solid. It
was filtered, washed with diethyl ether, and then dried under
vacuum. The title complex was obtained as a purple solid in
92% yield (176 mg). Anal. Calcd for C24H36Cl4N2P2Pd2: C,
37.48; H, 4.72. Found: C, 37.16; H, 4.65. 31P{1H} (CDCl3): δ
2
(CD2Cl2): δ -0.4 ppm (1JPt-P ) 1780.0 Hz, JP-P ) 25.5 Hz,
2
1
2P), -16.5 ppm (1JPt-P ) 3433.6 Hz, JP-P ) 25.5 Hz, 1P). H
(CD2Cl2): δ 2.10 (s, 6H, CH3 para of Mes), 2.22 (s, 3H, CH3
para of Mes), 2.28 (s, 6H, 2×CH3 ortho of Mes), 2.48 (s, 6H,
4×CH3 ortho of Mes), 2.92 (bs, 12H, NMe2), 3.28 (bs, 6H,
1
-114.8 ppm (s). H (CDCl3): δ 2.18 (s, 3H, H5), 2.90 (s, 6H,
2×H6), 3.70 (s, 3H, H8), 4.15 (bs, 3H, H8), 6.65 (s, 2H, H3), 8.85
(vt, 1H, ∑JH-P ) 13.4 Hz, H7, AA′XX′). 13C{1H} (CDCl3): δ 21.7
(s, C5), 28.1 (s, C6), 33.3 (s, C8), 38.5 (s, C8), 129.3 (s, C1), 130.8
(bs, C3), 143.1 (s, C4), 145.7 (vt, ∑JC-P ) 2.0 Hz, C2), 164.2 (bs,
C5).
4
NMe2), 6.65 (d, 2H, JH-P ) 3.0 Hz, H of Mes), 6.85 (s, 4H, H
of Mes), 7.50 (dt, 1H, 2JH-P ) 16.7 Hz, 4JH-P ) 13.6 Hz, HCd,
AXY2), 8.78 (vt, 2H, ∑JH-P ) 9.1 Hz, 2×HCd, AA′XX′Y).
13C{1H} (CD2Cl2): δ 20.8 (s, CH3 of Mes), 20.8 (s, C6 of Mes),
20.8 (s, CH3 of Mes), 24.0 (d, ∑JC-P ) 10.8 Hz, C7 of Mes),
25.1 (pt, ∑JC-P ) 11.1 Hz, C6 of Mes), 41.8 (bs, C8 9), 50.1
or
(bs, C9 or 8), 128.2 (vt, ∑JC-P ) 8.7 Hz, C3′), 128.4 (s, C3), 140.2
(s, C4), 140.9 (d, ∑JC-P ) 2.6 Hz, C1), 142.4 (d, JC-P ) 7.5 Hz,
C1′ or 4′), 144.1 (d, 2JC-P ) 9.7 Hz, C2′), 144.6 (vt, ∑JC-P ) 11.6

Inversely Polarized Phosphaalkenes
Organometallics, Vol. 24, No. 16, 2005 3863
Hz, C2), 173.4 (d, C5′), 186.4 (vdt, ∑JC-P ) 23.1 Hz, C5). Anal.
Calcd for C36H54Cl2N3P3Pt: C, 48.71; H, 6.13. Found: C, 49.02;
H, 6.25.
Acknowledgment. This work was supported by the
CNRS and the Ecole Polytechnique.
Supporting Information Available: CIF files and tables
giving crystallographic data for 9′ and 10, including atomic
coordinates, bond lengths and angles, and anisotropic dis-
placement parameters. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM0502943