η2-palladium and platinum(II) complexes of a λ4-phosphinine anion: Syntheses, X-ray crystal structures, and DFT calculations

Article abstract of DOI:10.1021/om049871y

A 1-methyl-2,6-bis(trimethylsilyl)-3,5-diphenylphosphinine anion (2) reacts with [MCl₂-(PPh₃)₂] (M = Pd, Pt) to afford the corresponding n²-platinum (3) and platinum (4) complexes in which coordination of the ligand to the [MCl(PPh₃)] fragments occurs through the P-C bond. Complexes 3 and 4 were structurally characterized. Both complexes adopt the same stereochemistry, the Cl ligand lying cis to the carbon atom of the P-C bond. Variable-temperature NMR experiments demonstrate that in 3 and 4 the [MCl(PPh₃)] fragment rapidly exchanges between the two P-C bonds in solution. DFT calculations on model complexes were performed to determine the structure of the transition state in the case of the palladium complex 3. The value of the calculated ΔG^? is discussed regarding the experimental values obtained by NMR studies. IMOMM (DFT-MM3, QM/MM hybrid method) calculations were also carried out on the real systems to rationalize the stereochemistry of both complexes.

Full text of DOI:10.1021/om049871y

2870
Organometallics 2004, 23, 2870-2875
η2-P a lla d iu m a n d P la tin u m (II) Com p lexes of a
λ4-P h osp h in in e An ion : Syn th eses, X-r a y Cr ysta l
Str u ctu r es, a n d DF T Ca lcu la tion s
Audrey Moores, Nicolas Me´zailles, Louis Ricard, Yves J ean, and Pascal le Floch*
Laboratoire “He´te´roe´le´ments et Coordination”, UMR CNRS 7653, Ecole Polytechnique,
91128 Palaiseau Cedex, France
Received February 23, 2004
A 1-methyl-2,6-bis(trimethylsilyl)-3,5-diphenylphosphinine anion (2) reacts with [MCl2-
(PPh3)2] (M ) Pd, Pt) to afford the corresponding η2-palladium (3) and platinum (4) complexes
in which coordination of the ligand to the [MCl(PPh3)] fragments occurs through the P-C
bond. Complexes 3 and 4 were structurally characterized. Both complexes adopt the same
stereochemistry, the Cl ligand lying cis to the carbon atom of the P-C bond. Variable-
temperature NMR experiments demonstrate that in 3 and 4 the [MCl(PPh3)] fragment
rapidly exchanges between the two P-C bonds in solution. DFT calculations on model
complexes were performed to determine the structure of the transition state in the case of
the palladium complex 3. The value of the calculated ∆Gq is discussed regarding the
experimental values obtained by NMR studies. IMOMM (DFT-MM3, QM/MM hybrid method)
calculations were also carried out on the real systems to rationalize the stereochemistry of
both complexes.
Sch em e 1
In tr od u ction
It is now well established that phosphinines are
suitable precursors of 1-R phosphahexadienyl anions
through reaction of their electrophilic phosphorus atom
with nucleophiles. This reactivity has been widely
exploited in the synthesis of numerous λ3-1,2- and λ3-
1,4-dihydrophosphinine and 1,1-λ5-phosphinine deriva-
tives (Scheme 1).1
Sch em e 2
However, only little attention has been paid to their
reactivity toward metal fragments. Some authors have
shown that these anions can coordinate transition
metals through the carbocyclic part of the ring in an
η5-fashion, and two bis(1-R-2,4,6-trisubstituted phos-
phinine) iron complexes were structurally character-
ized.2 Recently, with the aim to develop the use of these
anionic ligands in coordination chemistry and catalysis,
we reinvestigated their synthesis and their electronic
structure through DFT calculations.3 During this study,
some η5-lithium complexes of λ4-phosphinine anions
were synthesized and structurally characterized. Un-
doubtedly, the most significant feature of these λ4-
phosphinine anions is their ambidentate character that
allows coordination through the anionic π-system (η5)
or through the lone pair (η1) at phosphorus. However,
some recent studies have shown that η1-coordination at
phosphorus is limited and exclusively occurs when
ancillary ligands are present at the periphery of the ring
to encapsulate the metal center. Thus a series of group
94 and group 105 complexes of SPS pincer ligands have
recently been discovered and have found interesting
applications in coordination chemistry and catalysis
(Scheme 2).6 To gain a better understanding of the
factors that govern the coordination behavior of these
anions (η5-coordination versus η1-coordination), we de-
cided to investigate their reactivity toward metallic
fragments that usually favor η1-coordination. Therefore,
we focused this study on Pd(II) and Pt(II) complexes.
As will be seen, this investigation led us to discover a
new bonding mode of these anions. Herein we report
on these results.
(1) (a) Ashe, A. J . I.; Smith, T. W. Tetrahedron Lett. 1977, 407-
410. (b) Ma¨rkl, G.; Merz, A. Tetrahedron Lett. 1968, 3611-3614. (c)
Ma¨rkl, G.; Merz, A. Tetrahedron Lett. 1971, 1215-1218. (d) Ma¨rkl,
G.; Martin, C.; Weber, W. Tetrahedron Lett. 1981, 22, 1207-1210. (e)
Dimroth, K. Acc. Chem. Res. 1982, 15, 58-64.
(2) (a) Markl, G.; Martin, C. Angew. Chem., Int. Ed. Engl. 1974,
13, 408-409. (b) Dave, T.; Berger, S.; Bilger, E.; Kaletsch, H.; Pebler,
J .; Knecht, J .; Dimroth, K. Organometallics 1985, 4, 1565-1572. (c)
Baum, G.; Massa, W. Organometallics 1985, 4, 1572-1574. (d) Nief,
F.; Fischer, J . Organometallics 1986, 5, 877-883.
(3) Moores, A.; Ricard, L.; Le Floch, P.; Me´zailles, N. Organometal-
lics 2003, 22, 1960-1966.
(4) Doux, M.; Me´zailles, N.; Ricard, L.; Le Floch, P. Organometallics
2003, 22, 4624-4626.
(5) (a) Doux, M.; Bouet, C.; Me´zailles, N.; Ricard, L.; Le Floch, P.
Organometallics 2002, 21, 2785-2788. (b) Doux, M.; Me´zailles, N.;
Ricard, L.; Le Floch, P. Eur. J . Inorg. Chem. 2003, 3878-3894.
(6) Doux, M.; Me´zailles, N.; Melaimi, M.; Ricard, L.; Le Floch, P.
Chem. Commun. 2002, 1566-1567.
10.1021/om049871y CCC: $27.50 © 2004 American Chemical Society
Publication on Web 05/06/2004

η2-Pd and Pt(II) Complexes of λ4-Phosphinine Anion
Organometallics, Vol. 23, No. 12, 2004 2871
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r a l Refin em en t Deta ils for Str u ctu r es of Com p ou n d s 3 a n d 4
3
4
cryst size [mm]
empirical formula
molecular mass
cryst syst
space group
a [Å]
0.20 × 0.18 × 0.16
0.18 × 0.08 × 0.06
C
42H47ClP2PdSi2
C42H47ClP2PtSi2
811.77
monoclinic
P21/c
12.7040(10)
900.46
monoclinic
P21/c
12.6760(10)
b [Å]
18.8580(10)
18.9290(10)
c [Å]
17.2190(10)
17.2060(10)
R [deg]
90.00
106.4700(10)
90.00
3955.9(4)
90.00
106.4520(10)
90.00
3959.4(4)
â [deg]
γ [deg]
V [Å]3
Z
4
4
calcd density [g‚cm-3
]
1.363
0.707
30.03
1680
1.511
3.781
30.03
1808
abs. coeff [cm-1
2θmax [deg]
F(000)
]
index ranges
-17 17; -23 26; -24 24
-17 17; -26 24; -24 24
no. of reflns collected/indep
no. of reflns used
Rint
18 799/11 507
20 690/11 539
8837
0.0221
8329
0.0340
abs corr
0.8716 min., 0.8953 max.
0.5493 min., 0.8049 max.
no. of params refined
refln/param
440
20
0.0397/0.1148
1.063
440
18
0.0360/0.0734
0.981
final R1a/wR2 [I > 2σ(I)]b
goodness-of-fit on F2
diff peak/hole [e‚Å-3
]
1.386(0.093)/-1.254(0.093)
2.547(0.137)/-1.959(0.137)
a
b
2
2 2
2
R1 ) ∑|Fo| - |Fc||/∑|Fo|. wR2 ) (∑w||Fo| - |Fc| | /∑w|Fo| )1/2
.
Resu lts a n d Discu ssion
All our experiments were conducted with the 2,6-bis-
(trimethylsilyl)phosphinine 1, a ligand that was already
used in the synthesis of η5-lithium complexes. Phosphi-
nine 1 was chosen because of its availability and for the
steric bulk provided by the two SiMe3 groups that
enhances kinetic stability.
Synthesis of anion 2 was carried out following a
classical procedure that involves the reaction of a
stoichiometric amount of MeLi at -78 °C in THF. The
complete formation of 2 was checked by 31P NMR.
Addition of [Pd(PPh3)2Cl2] at low temperature followed
by a very slow warming overnight to room temperature
afforded complex 3. Interestingly, the 31P NMR spec-
trum of the crude mixture revealed the presence of free
triphenylphosphine, indicating that an exchange of
ligand had taken place. However, the formulation of 3
could not be unambiguously established by examination
of its NMR data. Indeed, its 31P NMR spectrum exhibits
2
an AB system (12.35 ppm, 25.30 ppm, J PP ) 31.7 Hz),
F igu r e 1. ORTEP view of one molecule of complex 3.
Ellipsoids are scaled to enclose 50% of the electron density.
The numbering is arbitrary and different from that used
in the assignment of NMR spectra. Relevant distances (Å)
and bond angles (deg): Pd1-P1, 2.2014(6); Pd1-Cl1,
2.3930(6); Pd1-C1, 2.238(2); Pd1-P2, 2.3106(6); P1-C1,
1.775(2); P1-C5, 1.767(2); P1-C6, 1.824(2); C1-C2,
1.451(3); C2-C3, 1.377(3); C3-C4, 1.428(3); C4-C5,
1.386(3); P1-Pd1-C1, 47.12(6); P1-Pd1-P2, 111.09(2);
C1-Pd1-Cl1, 104.10(6), P2-Pd1-Cl1, 97.75(2); C5-P1-
C1, 112.3(1); C5-P1-C6, 109.5(1); C1-P1-C6, 116.2(1);
C2-C1-P1, 113.4(2); C3-C2-C1, 124.5(2); C2-C3-C4,
127.9(2); C5-C4-C3, 124.5(2); C4-C5-P1, 115.4(2).
and its 1H and 13C NMR spectra (recorded at 25 °C)
suggest that 3 adopts a symmetrical structure, the two
trimethylsilyl groups being magnetically equivalent.
Fortunately single crystals of 3 could be grown and an
X-ray crystallographic study was undertaken. An ORTEP
plot of one molecule of 3 is presented in Figure 1, and
the most significant distances and angles are listed in
Table 1. Contrary to the structure expected from the
1H and 13C NMR data, complex 3 is not symmetrical
and features one [PdCl(PPh3)] fragment coordinated in
an η2-fashion onto one P-C bond of anion 2. Note that
this geometry is in good agreement with the 31P NMR
1
spectrum but disagrees with H and 13C NMR data. This
toward the less congested region of the molecule. It must
be noted that no trace of the second isomer (P1 and P2
in a trans arrangement) could be detected during our
experiments. Examination of bond distances and bond
angles within the ring shows that the geometry of the
quite unusual structure deserves further comment.
First, the overall geometry around palladium is square
planar, the Cl1 ligand and the C1 carbon being fixed in
a cis-arrangement. The triphenylphosphine ligand points

2872 Organometallics, Vol. 23, No. 12, 2004
Moores et al.
Sch em e 3
Sch em e 4
ring has been significantly modified upon coordination.
Thus the two P-C bonds of the ring are shortened (P1-
C1 ) 1.775(2) Å, P1-C5 ) 1.767(2) Å) by comparison
with values recorded in the free anionic ligand [2][Li-
(THF)4] (average 1.807 Å). The electronic delocalization
that occurs in the carbocyclic part of the ring in the
anionic ligand has been totally disrupted, and there is
a clear alternation between short and long C-C bonds.
Thus, whereas the C1-C2 (1.451(3) Å) and C3-C4
(1.428(3) Å) bond lengths are quite long, the C2-C3
(1.377(3) Å) and C4-C5 (1.386(3) Å) bond lengths are
short. Interestingly, the pyramidality at phosphorus
(sum of the C-P-C angles) is significantly reduced from
302.1° in [2][Li(THF)]4 to 338.0° in complex 3. There is
a close structural analogy between the metallacycle in
complex 3 (P-C bond distances and pyramidality at
phosphorus) and those in observed phosphinomethanide
complexes [(η2-R2P-CH2)M] (M ) Zr,7 Pd,8 Mo9] reported
by Karsch, Bickelhaupt, and Cowley.
To complete this study, syntheses of analogous Ni and
Pt complexes were also attempted. Various nickel(II)
complexes ([Ni(PPh3)2Cl2], [NiBr2(DME)] + PPh3 in a
1:1 ratio) were tested, but each experiment led to a
mixture of compounds whose structures could not be
established on the exclusive basis of 31P NMR data.
More satisfactory results were obtained by reacting
anion 2 with the [Pt(PPh3)2Cl2] complex (Scheme 4).
Suitable microcrystals of 4 could be obtained, and a
X-ray crystallographic study was carried out. A view of
one molecule of 4 is presented in Figure 2, and the most
significant bond lengths and bond angles are listed in
Table 1. As can be seen, the overall structure of 4 closely
resembles that of complex 3. The stereochemistry of the
complex is the same, the C1 carbon atom and the Cl1
ligand being fixed in a cis-arrangement. Apart from the
metal ligand bond distances, all metric parameters
within the ring are close to those recorded in complex
3.
F igu r e 2. ORTEP view of one molecule of complex 4.
Ellipsoids are scaled to enclose 50% of the electron density.
The numbering is arbitrary and different from that used
in the assignment of NMR spectra. Relevant distances (Å)
and bond angles (deg): Pt1-P1, 2.1915(8); Pt1-Cl1,
2.3803(8); Pt1-C1, 2.234(3); Pt1-P2, 2.2561(8); P1-C1,
1.794(3); P1-C5, 1.774(3); P1-C6, 1.821(3); C1-C2,
1.460(4); C2-C3, 1.382(4); C3-C4, 1.437(4); C4-C5,
1.373(4); P1-Pt1-C1, 47.8(1); P1-Pt1-P2, 111.99(3); C1-
Pt1-Cl1, 102.6(1); P2-Pt1-Cl1, 97.64(3); C5-P1-C1,
112.5(2); C5-P1-C6, 108.7(2); C1-P1-C6, 116.3(1); C2-
C1-P1, 112.7(2); C3-C2-C1, 124.7(3); C2-C3-C4,
128.3(3); C5-C4-C3, 124.3(3); C4-C5-P1, 115.9(2).
Interestingly, the lack of symmetry is not reflected
1
in the H and 13C NMR spectra, which exhibit a broad
single signal for the trimethylsilyl group as well as for
the carbon atoms and substituents (13C). Suspecting
that 3 and 4 exist in solution as two enantiomeric
complexes involved in a rapid equilibrium, a variable-
temperature 1H NMR study was undertaken. This
experiment was carried out on complexes 3 and 4 (in
CD2Cl2 for 3, THF-d8 for 4). As expected, cooling
solutions of 3 or 4 revealed that a dynamic process takes
place. At -20 °C, for complex 3, the signal of the
trimethylsilyl groups significantly broadens and coa-
lescence was observed at -48 °C. Below this tempera-
ture, two distincts signals could be observed. At -65
°C, signals (-0.555 and -0.048 ppm) are fine enough
to calculate a free energy of 43.7 kJ ‚mol-1 for the
exchange. For the platinum complex 4, the coalescence
temperature is -8 °C and the difference of frequency
between the two signals was measured at -40 °C
(-0.421 and -0.006 ppm), indicating a ∆Gq value of 55.5
kJ ‚mol-1 (Scheme 5, Figure 3).10
To shed some light on this mechanism as well as on
the stereochemistry of 3 and 4, DFT-B3LYP calculations
(see Theoretical Methods) were first carried out on four
model structures, Ia ,b and IIa ,b, a and b referring to
two different stereochemical arrangements around the
metal atom, Pd (I) or Pt (II) (Scheme 6). To save
computation time, the triphenylphosphine ligand was
replaced by a PH3 ligand, the phenyl groups at the
(7) (a) Karsch, H. H.; Grauvogl, G.; Kawecki, M.; Bissinger, P.;
Kumberger, O.; Schier, A.; Muller, G. Organometallics 1994, 13, 610-
618. (b) Karsch, H. H.; Grauvogl, G.; Deubelly, B.; Muller, G. Organo-
metallics 1992, 11, 4238-4245.
(8) van der Sluis, M.; Beverwijk, V.; Termaten, A.; Bickelhaupt, F.;
Kooijman, H.; Spek, A. L. Organometallics 1999, 18, 1402-1407.
(9) Carrano, C. J .; Cowley, A. H.; Nunn, C. M.; Pakulski, M.;
Quashie, S. J . Chem. Soc., Chem. Commun. 1988, 170-171.
(10) For ∆Gq formula see Supporting Information and Gu¨nther, H.
NMR Spectroscopy; Wiley: New York, 1980.

η2-Pd and Pt(II) Complexes of λ4-Phosphinine Anion
Organometallics, Vol. 23, No. 12, 2004 2873
F igu r e 3. Variable-temperature NMR spectra (in ppm) of compound 4 in d8-THF.
Sch em e 5
Sch em e 6
F igu r e 4. Transition state Ia TS of the interconversion
between the two enantiomeric Pd complexes Ia and Ia ′.
Sch em e 7
Ta ble 2. Dista n ces a n d An gles w ith in th e DF T
Op tim ized Str u ctu r es Ia , Ib, IIa , IIb, a n d Ia TS
Ia
Ib
IIa
IIb
Ia TS
(M ) Pd) (M ) Pd) (M ) Pt) (M ) Pt) (M ) Pd)
M-P(1)
2.264
2.435
2.240
2.347
1.787
1.775
1.840
1.440
1.378
1.425
1.382
109.1
116.4
111.0
46.73
2.256
2.408
2.259
2.421
1.790
1.772
1.836
1.442
1.376
1.426
1.381
109.2
118.1
111.6
46.71
2.248
2.443
2.245
2.294
1.798
1.781
1.838
1.450
1.372
1.431
1.379
109.2
117.4
110.4
47.17
2.268
2.423
2.218
2.345
1.806
1.784
1.837
1.456
1.368
1.435
1.374
109.2
118.2
110.5
47.47
2.253
2.401
M-Cl(1)
M-C(1)
M-P(2)
2.297
1.765
1.765
1.843
1.401
1.400
1.400
1.401
107.2
112.6
112.6
P(1)-C(1)
P(1)-C(5)
P(1)-C(6)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(1)-P(1)-C(5)
C(1)-P(1)-C(6)
C(5)-P(1)-C(6)
P(1)-M-C(1)
fragment as an axial substituent. The metal, chloride,
and the phosphorus (PH3) atoms are in the symmetry
plane of the phosphinine ring, the chloride ligand being
located below the ring plane. The environment around
the metal is T-shaped with a large P1-Pd1-Cl1 angle,
which is consistent with a d8-ML3 complex. C-C bond
lengths within the phosphinine ring are now essentially
identical (between 1.400 and 1.401 Å), whereas P-C
distances have decreased from 1.787 and 1.775 Å in Ia
structure to 1.765 Å; this accounts for a delocalization
of the negative charge held by the ligand in Ia TS. This
interconversion process thus involves a change in the
coordination mode of the ligand (from η2 to η1 and back
to η2) accompanied by a rotation of the whole [PdPH3-
Cl] fragment around the P1-Pd1 bond. The agreement
between the ∆Gq theoretical value (30.2 kJ ‚mol-1) and
the experimental one (43.7 kJ ‚mol-1) seems reasonable
taking into account that these calculations were per-
formed on a simplified model.
â-position were replaced by H atoms, and the trimeth-
ylsilyl groups were replaced by SiH3 groups.
The theoretical parameters for Ia and IIa were found
to be in good agreement with the experimental values
in 3 and 4 (see Table 2). More precisely, bond lengths
and bond angles within the ring are nicely reproduced,
while the metal-ligand distances are overestimated at
most by 0.06 Å. The structure of Ia TS, the transition
state for the interconversion between the two enantio-
meric Pd complexes Ia and Ia ′ (image of Ia with respect
to the symmetry plane of the phosphinine ring, Scheme
7), is presented in Figure 4, and bond lengths and bond
angles are given in Table 2. In this structure, the
palladium fragment is bound in an η1-fashion to the
phosphorus atom of the phosphinine, so that this ligand
can be described as a λ5-phosphinine with the metal
A series of calculations were also performed to ratio-
nalize the absence of the isomer of 3 adopting a trans
arrangement between the two phosphorus centers. For
the unsubstituted model complexes Ia (cis) and Ib
(trans), the calculated DFT-B3LYP energy difference of

2874 Organometallics, Vol. 23, No. 12, 2004
Moores et al.
for 13C, and 121.5 MHz for 31P. Solvent peaks are used as
internal reference relative to Me4Si for 1H and 13C chemical
shifts (ppm); 31P chemical shifts are relative to a 85% H3PO4
external reference. Coupling constants are given in hertz. The
following abbreviations are used: s, singlet; d, doublet; t,
triplet; m, multiplet. Methyllithium in ether solution was
purchased from Fluka. Phosphinine 1 was prepared following
procedures described in the literature.13 Elemental analyses
were performed by the “Service d’analyses du CNRS” at Gif
sur Yvette.
6.3 kJ ‚mol-1 (∆G ) 2.6 kJ ‚mol-1) in favor of Ia is
actually too small to rationalize the absence of the trans
isomer. However, complexes Ia and Ib are only models,
and as trimethylsilyl and triphenylphosphine substit-
uents are replaced by SiH3 and PH3, respectively, steric
congestion cannot be reproduced reasonably. The cis
(III) and trans (IV) isomers with the experimental
substituents were thus studied by means of QM/MM
calculations using the IMOMM program.11 In these
calculations, the QM part was made of the model
systems (namely, complex Ia for III and Ib for IV), the
remaining part of the molecule (the phenyl groups and
the methyl groups of trimethylsilyl substituents) being
described at the MM3 level (substituents drawn in bold
in Scheme 6). Surprisingly, the energy difference falls
down to 3.8 kJ ‚mol-1, a result that makes unlikely the
hypothesis about steric interactions at work in the trans
isomer IV. Finally, single-point energy calculations were
performed at the DFT-B3LYP level using the IMOMM
geometries. The cis isomer was now found to be more
stable by 14.6 kJ ‚mol-1, a value large enough to account
for the experimental absence of the trans isomer (less
than 1% according to the theoretical value). These sets
of results show that a clear preference for the cis isomer
is reproduced only if the actual substituents are intro-
duced and calculated at the QM level. The failure of QM/
MM calculations to give a significant energy difference
between the two isomers might be due to the pure MM
description of the phenyl groups. On the other hand,
these calculations do not take into account solvation
effect which might change the relative energies of the
two isomers. However recent DFT studies on [M(PMe3)2-
X2] complexes (M ) Pd, Pt; X ) Cl, Br, I) showed that
polar solvents always tend to favor the cis isomer versus
the trans one, due to the smaller dipole moment of the
latter.12
Syn th esis of 3. A solution of phosphinine 1 (50 mg, 0.13
mmol) in THF (2 mL) was prepared. A solution of MeLi in
ether (80 µL, 0.13 mmol, 1.6 M) was added at -78 °C. The
solution turned from colorless to red. The solution was warmed
to room temperature, and completion of the reaction was
checked by 31P NMR. [PdCl2(PPh3)2] (89 mg, 0.13 mmol) was
then added at -78 °C. The solution was stirred at this
temperature for 6 h. The solution was further left, allowing
the cold bath to warm to room temperature over a period of
14 h. The solution was then orange. Lithium salts were
removed by CH2Cl2 extraction (3 × 5 mL). After solvent
removal, the orange solid was washed with ether (3 × 5 mL).
The product was recovered as a yellow powder (87 mg, 84%
yield), decomposition > 220 °C. Anal. Calcd for C42H47ClP2-
1
PdSi2: C, 62.14; H, 5.84. Found: C, 62.30; H, 5.91. H NMR
2
(CDCl3): -1.15 (s, 18 H, Si-(CH3)3), 1.82 (d, J HP ) 12.3 Hz,
4
3 H, P-CH3), 6.34 (d, J HP ) 5.9 Hz, 1 H, Hpara), 7.33-7.74
(m, 25 H, CH of phenyls). 13C{1H} NMR (CDCl3): 3.23 (s, Si-
1
3
(CH3)3), 11.5 (dd, J PC ) 40.6 Hz, J PC ) 11.1 Hz, P-CH3),
3
4
124.33 (dd, J PC ) 29.2 Hz, J PC ) 9.7 Hz, CparaH), 127.59,
130.61 (2 s, CH of phenyls), 128.16 (s, CH of PPh3), 128.30,
134.64 (2 d, J PC ) 10.1, 13.6 Hz, CH of PPh3), 129.68 (t, ∑J PC
) 24.7 Hz, Cortho-TMS), 130.23 (d, J PC ) 1.7 Hz, CH of
1
phenyls), 133.47 (d, J PC ) 36.1 Hz, Cipso of PPh3), 145.27 (d,
3
4
2J PC ) 14.9 Hz, Cmeta-Ph), 158.17 (dd, J PC ) 8.3 Hz, J PC
)
3.8 Hz, Cipso of phosphinine phenyls). 31P{1H} NMR (CDCl3):
2
2
12.35 (d, J PP ) 31.7 Hz, P of phosphinine), 25.30 (d, J PP
31.7 Hz, P of PPh3).
)
Syn th esis of 4. To a solution of phosphinine 1 (50 mg, 0.13
mmol) in THF (2 mL) was added a solution of MeLi in ether
(80 µL, 0.13 mmol, 1.6 M) at -78 °C. The solution turned from
colorless to red. The solution was warmed to room tempera-
ture, and completion of the reaction was checked by 31P NMR.
[PtCl2(PPh3)2] (100 mg, 0.13 mmol) was then added at -78
°C. The solution was stirred at this temperature for 6 h. The
solution was further left, allowing the cold bath to warm to
room temperature over a period of 14 h. The solution was then
brown. Lithium salts were removed by CH2Cl2 extraction (3
× 5 mL). After solvent removal, the brown solid was washed
with hexanes (3 × 5 mL) and ether (3 × 5 mL). The product
was recovered as a pale green powder (93 mg, 81% yield),
decomposition > 220 °C. Anal. Calcd for C42H47ClP2PtSi2: C,
56.02; H, 5.26. Found: C, 55.76; H, 5.53. 1H NMR (THF-d8,
Con clu sion
We synthesized the first Pd and Pt(II) complexes
where a 1-methyl-phosphacyclohexadienyl anion is co-
ordinated in an η2-fashion to the metal. A rapid ex-
change of the metal fragment between the two P-C
bonds of the ring was evidenced by variable-temperature
NMR experiments, and the structure of the transition
state was determined by DFT calculations. We believe
that this new coordination mode of phosphacyclohexa-
dienyl anions can be extended to other metal fragments.
Studies aimed at determining factors that favor η2-
coordination versus η5-coordination through the car-
bocyclic π-system of the ring are currently underway
in our laboratories.
2
60 °C): -1.12 (s, 18 H, Si-(CH3)3), 1.93 (dd, J HP ) 12.3 Hz,
4J HP ) 0.95 Hz, 3 H, P-CH3), 6.03 (d, 4J HP ) 4.8 Hz, 1 H, Hpara),
7.19-7.81 (m, 25 H, CH of phenyls). 13C{1H} NMR (THF-d8,
1
3
20 °C): 4.84 (bs, Si-(CH3)3), 13.29 (dd, J PC ) 42.0 Hz, J PC
)
3
4
5.6 Hz, P-CH3), 124.99 (dd, J P-C ) 26.5 Hz, J P-C ) 7.4 Hz,
C
paraH), 127.92-137.45 (m, CH of phenyls and Cortho-TMS),
Exp er im en ta l Section
142.00 (bs, Cmeta-Ph), 147.97 (bs, Cipso of phenyls). 31P{1H}
1
All reactions were routinely performed under an inert
atmosphere of argon or nitrogen by using Schlenk and glovebox
techniques and dry deoxygenated solvents. Dry THF, ether,
and hexanes were obtained by distillation from Na/benzophe-
none. Dry dichloromethane was distilled over P2O5. Nuclear
magnetic resonance spectra were recorded on a Bruker AC-
NMR (THF-d8, 20 °C): -18.07 (d with satellites, J PPt
)
2792.98 Hz, 2J PP ) 24.1 Hz, P of phosphinine), 26.73 (td, 1J PPt
2
) 4752.21 Hz, J PP ) 24.1 Hz, P of PPh3).
Th eor etica l Meth od s. Geometry optimizations and single-
point energy-only calculations were carried out using the
density functional theory (DFT)14,15 by means of a pure
1
200 SY spectrometer operating at 300.0 MHz for H, 75.5 MHz
(13) (a) Avarvari, N.; LeFloch, P.; Mathey, F. J . Am. Chem. Soc.
1996, 118, 11978-11979. (b) Avarvari, N.; LeFloch, P.; Ricard, L.;
Mathey, F. Organometallics 1997, 16, 4089-4098.
(14) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and
Molecules; Oxford University Press: Oxford, U.K., 1989.
(11) Maseras, F.; Morokuma, K. J . Comput. Chem. 1995, 16, 1170-
1179.
(12) Harvey, J . N.; Heslop, K. M.; Orpen, A. G.; Pringle, P. G. Chem.
Commun. 2003, 278-279.

η2-Pd and Pt(II) Complexes of λ4-Phosphinine Anion
Organometallics, Vol. 23, No. 12, 2004 2875
gradient-corrected exchange functional and the Lee-Yang-
Parr nonlocal correlation functional BLYP16 as implemented
in the Gaussian 98 program.17 A quasi-relativistic effective core
potential operator was used to represent the electron core of
the palladium and the platinium atom. The basis set for the
metal was that associated with the pseudopotential with a
standard double-ú LANL2DZ contraction.18 6-31G* basis set
was used for C, Si, P, and Cl atoms and the 6-31G basis set
for H atoms.19 The stationary points (minima, transition
states) located at the DFT-B3LYP level were characterized by
frequency calculations. The IMOMM set of programs (QM/MM
calculation) was also used to optimize full size complexes, the
QM part being described at the DFT-B3LYP level with the
basis set detailed above and the MM part by the MM3 force
field.11
X-r a y Str u ctu r a l Deter m in a tion . Pale yellow plates of
complex 3 crystallized by diffusing hexanes into a dichloro-
methane solution of the complex 3. Yellow needles of isomor-
phous complex 4 were obtained by slow evaporation of a THF
solution of complex 4. Data were collected on a Nonius Kappa
CCD diffractometer using a Mo KR (λ ) 0.71070 Å) X-ray
source and a graphite monochromator at 150 K. Experimental
details are described in Tables 1 and 2. The crystal structures
were solved using SIR 9720 and SHELXL-97.21 ORTEP draw-
ings were made using ORTEP III for Windows.22 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:
(internat.) +44-1223/336-033; e-mail:
deposit@
ccdc.cam.ac.uk].
Ack n ow led gm en t. The authors thank Agusti Lle-
dos for fruitful discussions. Feliu Maseras is also
acknowledged for providing the IMOMM set of pro-
grams. The CNRS and the Ecole Polytechnique are
thanked for supporting this work. The use of computa-
tional facilities of the French Institute IDRIS is grate-
fully acknowledged. This research was partially sup-
ported by the Improving Human Potential Programme,
Access to Research Infrastructures under contract HPRI-
1999-00071, “Access to CESCA and CEPBA Large-Scale
Facilities” established between the European Com-
munity and CESCA-CEPBA. The Spanish “Direccio´n
General de Investigacio´n” (Project BQU2002-04110-
CO2-02) is also acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordinates and equivalent isotropic displacement
parameters, bond lengths and bond angles, anisotropic dis-
placement parameters, and hydrogen coordinates, ORTEP
view of one molecule of compounds 3 and 4; details on variable-
temperature NMR; a listing of coordinates for calculated
structures Ia ,b, IIa ,b, Ia TS, and IMOMM optimized III and
IV; optimized energies for structures Ia ,b, IIa ,b, Ia TS, III,
and IV. This material is available free of charge via the
Internet at http://pubs.acs.org.
(15) Ziegler, T. Chem. Rev. 1991, 91, 651-667.
(16) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098-3108. (b) Perdew,
J . P. Phys. Rev. B 1986, 33, 8822-8832.
(17) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . J .
A.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Baboul, A. G.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.;
Martin, R. L.; Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; J ohnson, B.; Chen,
W.; Wong, M. W.; Andres, J . L.; Gonzalez, C.; Head-Gordon, M.;
Replogle, E. S.; Pople, J . A. In Gaussian 98, revision A-11; Gaussian,
Inc.: Pittsburgh, PA, 1998.
(18) Hay, P. J .; Wadt, W. R. J . Chem. Phys. 1985, 82, 299-310.
(19) (a) Hehre, W. J .; Ditchfield, R.; Pople, J . A. J . Chem. Phys. 1972,
56, 2257. (b) Harihara, P.; Pople, J . A. Theor. Chim. Acta 1973, 28,
213-222. (c) Francl, M. M.; Pietro, W. J .; Hehre, W. J .; Binkley, J . S.;
Gordon, M. S.; DeFrees, D. J .; Pople, J . A. J . Chem. Phys. 1982, 77,
3654-3665.
OM049871Y
(20) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R.
SIR97, an integrated package of computer programs for the solution
and refinement of crystal structures using single-crystal data.
(21) Sheldrick, G. M. SHELXL-97; Universita¨t Go¨ttingen: Go¨ttin-
gen, Germany, 1997.
(22) Farrugia, L. J . ORTEP-3; Department of Chemistry: University
of Glasgow.