Versatility of iminophosphoranes and noninnocent behavior of the 1,5-cyclooctadiene ligand in palladium(II) complexes. Synthesis of σ-allyl derivatives

Article abstract of DOI:10.1021/om700707j

The treatment of PdCl₂(NCPh)₂ with Ph ₃P=NPh (1) gives the expected complex trans-PdCl₂[N(Ph)- PPh₃]₂ (3). However, the reaction of PdCl₂(COD) (COD = 1,5-cyclooctadiene) with 1 or Ph₃P=N-1-Np (2) (Np = naphthyl) occurs through nucleophilic attack of 1 or 2 on one olefinic bond of the COD ligand followed by proton abstraction on the adjacent methylene group, giving the η¹-allyl complexes [Ph₃P(R)NH...Cl ₂Pd(C₈H₁₁)] (R = Ph, 4; Np, 5). The X-ray structure of 4 has been determined and shows two interesting facts: (i) the η¹-η²-bonded cyclooctadienyl ligand, containing a η¹-allyl fragment, and (ii) the presence of a strong H bond between one of the Cl ligands and the proton of the NH group. This H bond persists in solution, as shown by NMR and molar conductance measurements. The abstraction of a chloride on 4 by reaction with AgClO₄ cleaves the H bond and gives a mixture of the salt [Ph₃PN-(H)Ph](ClO₄) (6) and the neutral η¹-η²-cyclooctadienyl complex [Pd(μ-Cl)(C₈H₁₁)]₂ (7). Complex 7 is an adequate precursor for the synthesis of other stable η¹-allyl complexes, and no η¹-η² allyl interconversion has been observed.

Full text of DOI:10.1021/om700707j

Organometallics 2007, 26, 6397-6402
6397
Versatility of Iminophosphoranes and Noninnocent Behavior of the
1,5-Cyclooctadiene Ligand in Palladium(II) Complexes. Synthesis of
σ-Allyl Derivatives
David Aguilar, Francisco Azna´rez, Raquel Bielsa, Larry R. Falvello, Rafael Navarro, and
Esteban P. Urriolabeitia*
Departamento de Compuestos Organometa´licos, Instituto de Ciencia de Materiales de Arago´n, CSIC,
UniVersidad de Zaragoza, 50009 Zaragoza, Spain
ReceiVed July 16, 2007
The treatment of PdCl2(NCPh)2 with Ph3PdNPh (1) gives the expected complex trans-PdCl2[N(Ph)-
PPh3]2 (3). However, the reaction of PdCl2(COD) (COD ) 1,5-cyclooctadiene) with 1 or Ph3PdN-1-Np
(2) (Np ) naphthyl) occurs through nucleophilic attack of 1 or 2 on one olefinic bond of the COD ligand
followed by proton abstraction on the adjacent methylene group, giving the η1-allyl complexes
[Ph3P(R)NH‚‚‚Cl2Pd(C8H11)] (R ) Ph, 4; Np, 5). The X-ray structure of 4 has been determined and
shows two interesting facts: (i) the η1-η2-bonded cyclooctadienyl ligand, containing a η1-allyl fragment,
and (ii) the presence of a strong H bond between one of the Cl ligands and the proton of the NH group.
This H bond persists in solution, as shown by NMR and molar conductance measurements. The abstraction
of a chloride on 4 by reaction with AgClO4 cleaves the H bond and gives a mixture of the salt [Ph3PN-
(H)Ph](ClO4) (6) and the neutral η1-η2-cyclooctadienyl complex [Pd(µ-Cl)(C8H11)]2 (7). Complex 7 is
an adequate precursor for the synthesis of other stable η1-allyl complexes, and no η1-η3 allyl
interconversion has been observed.
modulate their reactivity depending on whether they are
coordinated or not to the metal, for instance in species such as
RCH2CN.5b Phosphorus ylides are also able to react with bonded
nitriles, and some notable results have been reported.6
Introduction
Reactions that form C-C and C-X bonds (X ) heteroatom)
through nucleophilic attack on a CdC or a CtN bond, activated
by bonding to a transition metal, are versatile and powerful
synthetic tools.1 Nucleophilic addition to Pd-coordinated alk-
enes2 is a very well-known reaction with important implications
in industrial processes. Among the different olefins and diolefins,
1,5-cyclooctadiene (COD) has been one of the most studied
systems, due to its versatility and due also to the wide variety
of bonding modes obtained.3 Stabilized phosphorus ylides are
a particular class of nucleophiles, and they have shown a clear
reactivity toward alkenes bonded to Pd(II) and Pt(II) centers,4a,b
as a result of which the corresponding σ-alkyl complexes have
been formed. This reactivity has been recently applied to other
substrates as nucleophiles.4c Coordinated nitriles are also
adequate precursors for C-C and C-X couplings, and a wide
reactivity is being developed at the present time.5 For instance,
1,3-diazadienes,5a imines,5c and 1,2,4-oxadiazolines5e can be
obtained by reaction of the appropriate precursor with Pd(II)-
or Pt(II)-bonded nitriles. In addition, it is also possible to
In line with these results, a recent contribution shows that
iminophosphoranes are also able to react with Pt-bonded
nitriles.7 Iminophosphoranes are species of general structure
R3PdNR′ (R, R′ ) alkyl, aryl, etc.), which show a very rich
coordination chemistry.8,9 Aiming to expand the scope of the
use of iminophosphoranes as nucleophiles in C-N bond forming
reactions, we have probed the reactivity of Ph3PdNPh (1) and
Ph3PdNNp (2) (Np ) naphthyl) toward Pd(II) precursors, such
as PdCl2(NCR)2 (R ) Me, Ph) and PdCl2(COD). This reactivity
could in principle be more complicated than anticipated, since
it has been reported that the reactivity of 1 with simple Pd(II)
complexes such as Li2[PdCl4]10 or Pd(OAc)2
gives the
11,12
(5) (a) Guschin, P. V.; Bokach, N. A.; Luzyanin, K. V.; Nazarov, A. A.;
Haukka, M.; Kukushkin, V. Y. Inorg. Chem. 2007, 46, 1684. (b) Lasri, J.;
Januario Charmier, M. A.; Haukka, M.; Pombeiro, A. J. L. J. Org. Chem.
2007, 72, 750. (c) Lasri, J.; Januario Charmier, M. A.; Guedes da Silva,
M. F. C.; Pombeiro, A. J. L. Dalton Trans. 2006, 5062. (d) Khripun, A.
V.; Kukushkin, V. Y.; Selivanov, S. I.; Haukka, M.; Pombeiro, A. J. L.
Inorg. Chem. 2006, 45, 5073. (e) Bokach, N. A.; Krokhin, A. A.; Nazarov,
A. A.; Kukushkin, V. Y.; Haukka, M.; Frau´sto da Silva, J. J. R.; Pombeiro,
A. J. L. Eur. J. Inorg. Chem. 2005, 3042. (f) Garnovskii, D. A.; Bokach,
N. A.; Pombeiro, A. J. L.; Haukka, M.; Frau´sto da Silva, J. J. R.; Kukushkin,
V. Y. Eur. J. Inorg. Chem. 2005, 3467.
(6) (a) Vicente, J.; Chicote, M. T.; Ferna´ndez-Baeza, J.; Lahoz, F. J.;
Lo´pez, J. A. Inorg. Chem. 1991, 30, 3617. (b) Vicente, J.; Chicote, M. T.;
Beswick, M. A.; Ram´ırez de Arellano, M. C. Inorg. Chem. 1996, 35, 6592.
(7) Bokach, N. A.; Kukushkin, V. Y.; Kelly, P. F.; Haukka, M.;
Pombeiro, A. J. L. Dalton Trans. 2005, 1354.
* Corresponding author. Fax: (+34) 976761187. E-mail: esteban@
unizar.es.
(1) (a) Crabtree, R. H. In The Organometallic Chemistry of the Transition
Metals, 4th ed.; Wiley-Interscience: John Wiley & Sons: New Jersey, 2005;
Chapter 8, pp 207 and ff. (b) Elsenbroich, C.; Salzer, A. In Organometallics,
A Concise Introduction, 2nd ed.; VCH: Weinheim, Germany, 1992; Chapter
15, pp 293 and ff.
(2) Maitilis, P. M.; Espinet, P.; Russell, M. J. H. In ComprehensiVe
Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W.,
Eds.; Pergamon Press: Oxford, U.K., 1982; Vol. 6, pp 315 and ff.
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2003, 22, 5406.
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Bautista, D. Organometallics 1998, 18, 2677. (b) Vicente, J.; Chicote, M.
T.; MacBeath, C.; Jones, P. G. Organometallics 2003, 22, 1843. (c) Fantasia,
S.; Jacobsen, H.; Cavallo, L.; Nolan, S. P. Organometallics 2007, 26, 3286.
(8) (a) Steiner, A.; Zacchini, S.; Richards, P. I. Coord. Chem. ReV. 2002,
227, 193. (b) Fei, Z.; Dyson, P. J. Coord. Chem. ReV. 2005, 249, 2056. (c)
Dehnicke, K.; Krieger, M.; Massa, W. Coord. Chem. ReV. 1999, 182, 19.
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(10) Alper, H. J. Organomet. Chem. 1977, 127, 385.
10.1021/om700707j CCC: $37.00 © 2007 American Chemical Society
Publication on Web 11/01/2007

6398 Organometallics, Vol. 26, No. 25, 2007
Scheme 1. Synthesis and Reactivity of Iminophosphoranes 1 and 2
Aguilar et al.
cyclopalladated derivative [Pd(µ-Cl){C6H4(PPh2dNPh)-2}]2
through a C-H bond activation reaction.
C1A to C8A for one of the congeners in Figure 2; see SI for
the other congener), meaning that the initial cyclooctadiene
ligand has been deprotonated at a methylene group adjacent to
an olefinic CdC bond. The organic fragment is an amino-
phosphonium cation, showing that the initial iminophosphorane
1 has been protonated at the iminic atom N(1). The two
fragments are in close contact, joined by a hydrogen bond
between the NH group and the chlorine atom Cl(1).
Results and Discussion
The starting iminophosphoranes Ph3PdNR (R ) Ph, 1; Np,
2) were prepared following published methods.13 The reaction
of phenylazide or 1-naphthylazide with PPh3 (1:1 molar ratio)
in dry CH2Cl2 gives 1 or 2, respectively, isolated as white solids.
Compound 1 reacts with PdCl2(NCPh)2 (2:1 molar ratio) in
acetone to give 3 (Scheme 1), with two bonded iminophospho-
ranes 1, according to its analytical and spectroscopic data. Thus,
a simple ligand exchange reaction has occurred, instead of a
nucleophilic attack on the nitrile ligand.7 The IR spectrum of 3
shows the νPN stretch at 1313 cm-1, shifted to low energy with
respect to the free ligand 1 (1345 cm-1) and strongly suggesting
the N-bonding of 1, while the trans arrangement of the chloride
ligands can be inferred from the observation of a single band
at 317 cm-1. The 31P{1H} NMR spectrum of 3 shows a single
peak at δ ) 30.06 ppm, strongly deshielded with respect to the
free ligand (δ ) 3.38 ppm) and also in good agreement with
the N-coordination of 1.
A quite different process has been observed in the reactivity
of 1 or 2 with another Pd precursor. The reaction of PdCl2-
(COD) with 1 or 2 (1:1 molar ratio) in CH2Cl2 at 25 °C results
in the clean synthesis of complex 4 or 5, respectively (Scheme
1). The X-ray crystal structure of complex 4 has been determined
by diffraction methods. Parameters concerning data collection
and refinement are presented in Table 1, and selected bond
lengths and angles are given in Table 2. The structure of 4
(Figure 1) shows that the complex possesses an anionic
organometallic part (Figure 2) and a cationic organic part. The
anionic organometallic part shows a Pd atom in a distorted
square-planar environment, bonded to two cis chlorine ligands,
Cl(1) and Cl(2), and to a disordered cyclooctadienyl ligand (ring
The hydrogen bond is characterized by the intermolecular
distances Cl(1)‚‚‚H(1N) [2.3800 Å] and N(1)‚‚‚Cl(1) [3.131(3)
Å] and the angle N(1)-H(1N)‚‚‚Cl(1) [143°]. These values fall
at the low end of the usual range of distances found in the
literature for similar hydrogen bonds.14 Moreover, it must be
taken into account that this type of hydrogen bonds has been
described as robust and useful as structure-directing tools.14c
In fact, the presence of this hydrogen bond in 4seven in
solutionsis remarkable and has important consequences for its
chemical behavior.
Concerning the cationic organic fragment, the P(1)-N(1)
bond distance [1.624(3) Å] suggests a high degree of single-
bond character since it is identical, within experimental error,
to those found in [Ph3PN(H)Ph](BF4) [1.621(4) and 1.635(4)
Å],15a and it is longer than that found in the free iminophos-
phorane Ph3PdNPh [1.603(3) Å].15b On the other hand, the
anionic organometallic fragment shows the Pd atom in a very
distorted environment. The disordered cyclooctadienyl ligand
is σ-bonded through the carbon atom C(5AB); there is a
nonbonded olefinic group [C(6AB)-C(7A) in the congener
shown in Figure 2] and a bonded olefinic fragment [C(1A)-
C(2AB)]. The different Pd-C bond distances are almost
identical, within experimental error, to those reported previously
(14) (a) Bergamini, P.; Bertolasi, V.; Milani, F. Eur. J. Inorg. Chem.
2004, 1277. (b) Adams, C. J.; Angeloni, A.; Orpen, A. G.; Podesta, T. J.;
Shore, B. Cryst. Growth Des. 2006, 6, 411. (c) Kumar, D. K.; Das, A.;
Dastidar, P. Cryst. Growth Des. 2006, 6, 216.
(11) Vicente, J.; Abad, J. A.; Clemente, R.; Lo´pez-Serrano, J.; Ram´ırez
de Arellano, M.C.; Jones, P. G.; Bautista, D. Organometallics 2003, 22,
4248.
(12) Bielsa, R.; Larrea, A.; Navarro, R.; Soler, T.; Urriolabeitia, E. P.
Eur. J. Inorg. Chem. 2005, 1734.
(15) (a) Llamas-Saiz, A. L.; Foces-Foces, C.; Elguero, J.; Molina, P.;
Alajar´ın, M.; Vidal, A. Acta Crystallogr., Sect. C 1992, 48, 1940. (b) Bo¨hm,
E.; Dehnicke, K.; Beck, J.; Hiller, W.; Stra¨hle, J.; Maurer, A.; Fenske, D.
Z. Naturforsch., B 1988, 43, 138. (c) Orpen, A. G.; Brammer, L.; Allen, F.
H.; Kennard, O.; Watson, D. G. J. Chem. Soc., Dalton Trans. 1989, S1 -
S83.
(13) Staudinger, H.; Meyer, J. HelV. Chim. Acta 1919, 2, 635.

Versatility of Iminophosphoranes
Organometallics, Vol. 26, No. 25, 2007 6399
Table 1. Crystal Data and Structure Refinement for
Compound 4‚CH2Cl2
empirical formula
fw
C33H34Cl4NPPd
723.80
temp (K)
radiation (λ, Å)
cryst syst
space group
a (Å)
150(1)
0.71073
monoclinic
I2/a
19.369(4)
b (Å)
12.150(2)
c (Å)
27.890(6)
â (deg)
103.74(3)
6376(2)
V (Å3)
Z
D
8
calc (Mg/m3)
1.508
0.992
µ (mm-1
)
cryst size (mm3)
0.12 × 0.27 × 0.32
no. of reflns collected
no. of indep reflns
25 791
7078 (Rint ) 0.0316)
7078/20/407
1.064
R1 ) 0.0403, wR2 ) 0.1088
R1 ) 0.0609, wR2 ) 0.1149
0.878 and -1.259
Figure 1. Thermal ellipsoid drawing of 4‚CH2Cl2 showing the
hydrogen bond between cation and anion. Ellipsoids representing
non-H atoms are drawn at 50% probability level.
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak, hole (e‚Å-3
)
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Compound 4‚CH2Cl2
Pd(1)-C(5AB)
Pd(1)-C(2AB)
Pd(1)-Cl(1)
2.029(4)
2.160(4)
2.4847(11) Pd(1)-Cl(2)
1.497(6)
Pd(1)-C(1A)
Pd(1)-C(2B)
2.171(9)
2.25(2)
2.3548(10)
1.292(9)
1.419(12)
1.605(9)
1.529(13)
1.418(4)
C(5AB)-C(6AB)
C(7A)-C(8A)
C(1A)-C(2AB)
C(3A)-C(4A)
P(1)-N(1)
C(6AB)-C(7A)
1.519(10) C(8A)-C(1A)
1.327(10) C(2AB)-C(3A)
1.550(15) C(4A)-C(5AB)
1.624(3)
N(1)-C(9)
C(5AB)-Pd(1)-C(2AB) 84.08(19)
C(5AB)-Pd(1)-C(1A) 91.5(3)
C(5AB)-Pd(1)-Cl(2) 90.21(14) C(1A)-Pd(1)-Cl(2)
C(2AB)-Pd(1)-Cl(2) 160.43(16) C(5AB)-Pd(1)-Cl(1)
163.7(2)
176.32(16)
92.56(13)
126.1(2)
C(1A)-Pd(1)-Cl(1)
Cl(2)-Pd(1)-Cl(1)
86.1(5)
93.38(4)
C(2AB)-Pd(1)-Cl(1)
C(9)-N(1)-P(1)
Figure 2. Thermal ellipsoid plot of one disordered anionic
organometallic congener of 4‚CH2Cl2. Ellipsoids representing non-H
atoms are drawn at 50% probability level.
for the η1-η2-cyclooctadienyl ligand in a dinuclear complex.16
The Pd(1)-Cl(1) bond distance [2.4847(11) Å] is longer than
the Pd(1)-Cl(2) bond distance [2.3548(10) Å], reflecting the
higher trans influence of the σ-allyl carbon atom, and both
distances are in the usual range for this type of bond.15c
The characterization of 4 and 5 in solution provides additional
information. The 31P{1H} NMR spectra of 4 and 5 show a single
peak in each case in good agreement with the presence of a
ligand is η1-σ bonded. The clear shielding of the coordinated
CdC olefinic bond with respect to the free olefin and the
appearance of the metalated PdCH signal in the alkylic region
are strong evidence for the η1-allyl-η2-olefin bonding mode
of the cyclooctadienyl ligand.16
Additional evidence for the presence of the hydrogen bond
in solution is provided by the measurement of the molar
conductance ΛM of 4 in acetone.17 It must be noted that the
NMR spectra in acetone-d6 show the same features as those
obtained in CDCl3 or CD2Cl2. The experimental value is ΛM
) 31.1 Ω-1 cm2 mol-1. Typical values of molar conductance
for 1:1 electrolytes appear in the range 100-120 Ω-1 cm2
1
phosphonium unit. The H NMR spectra of 4 and 5 show 10
well-defined peaks, spread in the 1-6 ppm region and assigned
to the 11 protons of the cyclooctadienyl ligand. The well-
resolved line shapes of these peaks are temperature independent
and suggest a static behavior of the ligand on the NMR time
scale. The most rermarkable feature of each spectrum is a wide
peak at 10.78 ppm (4) or 11.16 ppm (5), assigned to the NH
proton. The shift of this peak to very low field suggests that
the intermolecular hydrogen bond observed in the X-ray crystal
structure of 4 is retained in solution. The 13C{1H} NMR spectra
of 4 and 5 show all expected peaks for the structures shown in
mol-1 17
, so this result means that 4 is not completely dissociated
and that the hydrogen bond is present to a significant extent in
solution. However, the nonzero value of ΛM also means that
an equilibrium between the dissociated (ionic) and associated
(neutral) forms must be operative in solution. This equilibrium
seems to be shifted mainly to the associated neutral form due
to the hydrogen bond and has to be very fast with respect to
the NMR time scale since only one species is observed in
solution.
The other singular fact about 4 and 5 is the generation of the
cyclooctadienyl ligand from the coordinated 1,5-cyclooctadiene
by deprotonation with an external base.16 A plausible mechanism
for this process is presented in Scheme 2 and could involve the
exo nucleophilic attack of the iminophosphorane (through the
iminic N atom) on one olefinic CdC bond, giving a σ-alkyl
1
Scheme 1, and assignment of all signals in the H and 13C
spectra was carried out with the help of homo- and heteronuclear
correlation 2D spectra and selective 1D NOESY and ROESY.
While 31P NMR data clearly show the presence of the
aminophosphonium unit in solution, and 1H NMR data suggest
the perseverance of the hydrogen bond, also in solution, 13C
NMR data indicate that the allyl unit on the cyclooctadienyl
(16) (a) Agami, C.; Levisalles, J.; Rose-Munch, F. J. Organomet. Chem.
1972, 35, C59. (b) Dahan, F.; Agami, C.; Levisalles, J.; Rose-Munch, F. J.
Chem. Soc., Chem. Commun. 1974, 505. (c) Dahan, F. Acta Crystallogr.,
Sect. B 1976, 32, 1941.
(17) Geary, W. J. Coord. Chem. ReV. 1971, 7, 81.

6400 Organometallics, Vol. 26, No. 25, 2007
Scheme 2. Proposed Mechanism for Synthesis of 4 and 5
Aguilar et al.
intermediate similar to those reported with phosphorus ylides.4a,b
Once the C-N coupling has taken place, this intermediate could
undergo intramolecular deprotonation on the methylene adjacent
to the attack position, giving the amino-phosphonium unit and
the dichloro η1-η2-cyclooctadienyl Pd(II) derivative. The forma-
tion of the intermolecular H bond could be the final step. This
process is rather sensitive to the type of base. It has been
reported16 that the treatment of PdCl2(COD) with NEt3 gives
complex 7; that is, there is no interaction between the am-
monium salt [HNEt3]+ and the cyclooctadienyl anionic complex,
while reaction of PdCl2(COD) with DBU (1,8-diazabicyclo-
[5.4.0]undec-7-ene) results in the recovery of the starting
compounds.
The reaction of 8 with dppe (1:1 molar ratio) in CH2Cl2 gives
9 (Scheme 1). The 31P{1H} NMR spectrum shows a low-field
AB spin system (50.78 and 49.31 ppm, JPP ) 37 Hz), due to
the two P atoms of the dppe ligand bonded as a P,P′-chelate.
Thus, 8 and 9 again present the cyclooctadienyl ligand with
the η1-η2-bonding mode.
2
Complex 7 reacts with PPh3 in CH2Cl2 (Scheme 1) to give
10 as a 1:1 mixture of geometric isomers after cleavage of the
chlorine bridging system. Complex 10 has been characterized
by the usual analytic and spectroscopic means (see Experimental
Section), which confirm that the η1-allyl coordination persists.
Chloride abstraction on 10, promoted by silver salts, in solvents
with low bonding ability, might reasonably be expected to
promote the η1-η3 interconversion of the allyl fragment.
However, treatment of a solution of 10 in THF with AgClO4
(1:1 molar ratio) gives a mixture of several products, as is clear
from the 31P{1H} NMR spectrum of the crude solid. From this
mixture one main component (ca. 50%) could be identified, the
bis-phosphino derivative 11 (Scheme 1). Complex 11 can be
independently prepared in pure form by reaction of 10 with
AgClO4 and PPh3 (1:1:1 molar ratio), as shown in Scheme 1
and as described in the Experimental Section, and it is easily
characterized due to the observation of an AB spin system (23.39
and 22.89 ppm, 2JPP ) 43 Hz) in the 31P{1H} NMR spectrum,
assigned to the two cis P atoms. We have not been able to
determine the nature of the other species, although it seems that
the presence of complex 11 in the mixture suggests that the
hypothetical monophosphino-(η1,η3-cyclooctadienyl) complex
is not stable and evolves with transfer of one PPh3 ligand. All
of these results, and especially the syntheses of 8-11, indicate
that the η1-η3 interconversion of the allyl fragment is not a
favored process in this case and that the stable bonding form
of the cyclooctadienyl ligand is the η1-η2 form, that is, acting
as a three-electron donor ligand.
η1-σ-Allyl ligands are very scarce, and the stability of this
bonding mode in 4 and 5 is noteworthy.18 We have probed the
reactivity of 4 in order to test this stability and the possible
interconversion into the more usual η3-allyl bonding mode. First,
we have transformed 4 (or 5) into a more useful starting product.
The reaction of 4 with AgClO4 (1:1 molar ratio) in MeOH
gives the mixture of the amino-phosphonium salt 6, the known
organometallic 7,16 and AgCl. All components of this mixture
could be isolated in pure form by adequate choice of solvents
(see Experimental Section). Thus, the hydrogen bond in 4 is
cleaved by the chloride abstraction and subsequent dimerization.
1
The H NMR spectrum shows the peak assigned to the NH
proton at 8.06 ppm, upfield shifted from the starting product 4
(10.78 ppm) and as expected for the disappearance of the
hydrogen bond. Complex 7 has already been reported,16 and
the method described here could be considered as a synthetic
alternative. Moreover, 7 is a good starting compound for
preparing other η1-η2-cyclooctadienyl complexes and also for
checking the interconversion between the η1- and η3-bonding
modes of the allyl fragment of the cyclooctadienyl ligand. In
principle, the creation of empty coordination sites should provide
a reasonable pathway to the η1 to η3 conversion.
Complex 7 reacts with AgClO4 in NCMe to give the bis-
solvate 8 (Scheme 1). The characterization of 8 shows that the
cyclooctadienyl ligand retains its η1-η2-bonding mode. The IR
spectrum, the elemental CHN analyses, and the 1H NMR
spectrum of 8 confirm the coordination of two molecules of
NCMe to the Pd center. Attempts to use less coordinating
ligands such as THF did not yield the final complexes as solids
due to extensive decomposition. The NCMe ligands in 8 can
be removed by reaction with other more coordinating groups.
Conclusion
The reactivity of the iminophosphoranes Ph3PdNPh and
Ph3PdN-1-Np (Ph ) phenyl, Np ) naphthyl) toward different
palladium substrates gives different types of products. When
PdCl2(COD) is used as substrate, the iminophosphorane attacks
one olefinic bond and the expected C-N coupling is produced,
followed by deprotonation and formation of an organopalladium
compound with the cyclooctadienyl ligand. The iminophospho-
rane is thus transformed into an amino-phosphonium salt,
which forms a strong hydrogen bond [N-H‚‚‚Cl-Pd] with a
coordinated chlorine ligand. The cyclooctadienyl ligand is η1-
(18) Braunstein, P.; Zhang, J.; Welter, R. Dalton Trans. 2003, 507, and
references therein.

Versatility of Iminophosphoranes
Organometallics, Vol. 26, No. 25, 2007 6401
3
3
η2 bonded, and the η1 fragment belongs to an allylic group.
This η1 coordination of the allyl group has proved to be very
stable, and all attempts to promote an η1-η3 interconversion
of the allyl fragment were unsuccessful.
dCH, C8H11, JHH ) 8.7), 5.66 (t, 1H, bonded dCH, C8H11, JHH
) 7.7), 5.78 (m, 1H, H3, free dCH, C8H11), 6.32 (m, 1H, bonded
3
dCH, C8H11), 6.90 (t, 1H, Hp, NPh, JHH ) 7.5), 7.01 (t, 2H, Hm,
NPh, 3JHH ) 7.5), 7.10 (d, 2H, Ho, NPh), 7.56 (m, 6H, Hm, PPh3),
7.68 (m, 3H, Hp, PPh3), 7.78 (m, 6H, Ho, PPh3), 10.78 (s, 1H, NH).
13C{1H} NMR (CDCl3): δ 24.34 (CH2, C8H11), 28.94 (CH2, C8H11),
39.96 (CH2, C8H11), 57.30 (C1, PdCH, C8H11), 100.08 (bonded d
CH, C8H11), 114.23 (bonded dCH, C8H11), 121.04 (d, Ci, PPh3,
Experimental Section
Safety Note: Caution! Perchlorate salts of metal complexes with
organic ligands are potentially explosive. Only small amounts of
these materials should be prepared, and they should be handled
with great caution. See: J. Chem. Educ. 1973, 50, A335-A337.
General Methods. Solvents were dried and distilled under argon
using standard procedures before use. Elemental analyses were
carried out on a Perkin-Elmer 2400-B microanalyzer. Infrared
spectra (4000-200 cm-1) were recorded on a Perkin-Elmer 883
infrared spectrophotometer from Nujol mulls between polyethylene
sheets. The 1H, 13C{1H}, and 31P{1H} NMR spectra were recorded
in CDCl3, CD2Cl2, or acetone-d6 solutions at 25 °C (other
temperatures were specified) on Bruker AvanceII-300, Avance-
1JPC ) 93.8), 122.97 (d, Co, NPh, JPC ) 6.7), 123.91 (Cp, NPh),
3
129.02 (Cm, NPh), 129.83 (d, Cm, PPh3, 3JPC ) 13.4), 132.12 (C2,
free dCH, C8H11), 132.98 (C3, free dCH, C8H11), 133.87 (d, Co,
PPh3, 2JPC ) 11.1), 134.84 (d, Cp, PPh3, 4JPC ) 2.9), 138.52 (d, Ci,
2
NPh, JPC ) 2.5).
Synthesis of 5. Complex 5 was prepared following the same
procedure as that reported for 4. Thus, PdCl2(COD) (0.200 g, 0.70
mmol) was reacted with 2 (0.282 g, 0.70 mmol) in CH2Cl2 (30
mL) to give 5 as a yellow solid. Obtained: 0.29 g (60%). Anal.
Calc for C36H34Cl2NPPd (688.96): C, 62.76; H, 4.97; N, 2.03.
Found: C, 62.90; H, 5.35; N, 2.10. MS (MALDI+): m/z 404
[C10H7N(H)dPPh3]+. IR (ν, cm-1): 1306 (νPN), 325, 297 (νPdCl).
1
400, and Avance-500 spectrometers (δ, ppm; J, Hz); H and 13C-
{1H} were referenced using the solvent signal as internal standard,
31P{1H} NMR (CDCl3): δ 36.34. H NMR (CDCl3): δ 1.09 (m,
1
1
while 31P{1H} was referenced to H3PO4 (85%). The H SELNO-
1H, CH2, C8H11), 1.48 (m, 1H, CH2, C8H11), 1.77-1.81 (m, 2H,
CH2, C8H11), 2.30 (m, 1H, CH2, C8H11), 2.70 (m, 1H, CH2, C8H11),
3.77 (m, 1H, H1, PdCH, C8H11), 4.95 (m, 1H, H2, free dCH, C8H11,
3JHH ) 8.5), 5.63 (t, 1H, bonded dCH, C8H11, JHH ) 7.8), 5.75
(m, 1H, H3, free dCH, C8H11), 6.27 (m, 1H, bonded dCH, C8H11),
7.05-7.09 (m, 2H, H2 + H3, C10H7), 7.24-7.32 (m, 2H, H4 + H6,
C10H7), 7.46 (m, 6H, Hm, PPh3), 7.53 (d, 1H, H5, C10H7, JHH
1D, SELRO-1D, and NOESY-2D NMR experiments were per-
formed with optimized mixing times (D8/P15), depending of the
irradiated signal. ESI/APCI mass spectra were recorded using an
Esquire 3000 ion-trap mass spectrometer (Bruker Daltonic GmbH,
Bremen, Germany) equipped with a standard ESI/APCI source.
Samples were introduced by direct infusion with a syringe pump.
Nitrogen served both as the nebulizer gas and the dry gas. Helium
served as a cooling gas for the ion trap and collision gas for MSn
experiments. Other mass spectra (positive ion FAB) were recorded
from CH2Cl2 solutions on a V. G. Autospec spectrometer. Molar
conductance measurements were carried out in acetone solutions
(c ) 5 × 10-4 M) on a Philips PW-9509 digital conductivity meter.
The starting compounds Ph3PdNPh (1) and Ph3PdN-1-Np (2) were
prepared according to the Staudinger method by reaction of the
corresponding azides with PPh3.13 Complexes PdCl2(NCPh)219 and
PdCl2(COD)20 were also prepared by reported procedures.
Synthesis of 3. To a suspension of PdCl2(NCPh)2 (0.100 g, 0.26
mmol) in acetone (20 mL) was added 1 (0.184 g, 0.52 mmol). The
resulting mixture was stirred at room temperature for 7 h. During
the reaction time, the initial suspension gradually dissolved, giving
a clear yellow solution. This solution was evaporated to small
volume (2 mL) and treated with 20 mL of Et2O, giving 3 as a yellow
solid. Obtained: 0.12 g (52%). Anal. Calc for C48H40Cl2N2P2Pd
(884.12): C, 65.21; H, 4.56; N, 3.17. Found: C, 64.90; H, 4.47;
N, 3.10. MS (MALDI+): m/z 849 (100%) [M - Cl]+. IR (ν, cm-1):
1313 (νPN), 317 (νPdCl). 31P{1H} NMR (CDCl3): δ 30.06. 1H NMR
(CDCl3): δ 6.62-6.67 (m, 3H, Ho + Hp, NPh), 7.00 (d, 2H, Hm,
NPh, 3JHH ) 7.1), 7.29 (m, 6H, Hm, PPh3), 7.42 (m, 3H, Hp, PPh3),
7.82 (m, 6H, Ho, PPh3).
Synthesis of 4. A solution of PdCl2(COD) (0.200 g, 0.70 mmol)
in 20 mL of CH2Cl2 was added dropwise to a solution of 1 (0.247
g, 0.70 mmol) in 10 mL of CH2Cl2. The resulting yellow solution
was stirred at 25 °C for 2 h. The solvent was then evaporated to
dryness, and the residue was treated with 20 mL of Et2O to give 4
as a yellow solid, which was filtered, washed with additional Et2O
(10 mL), and air-dried. Obtained: 0.273 g (61%). Anal. Calc for
C32H32Cl2NPPd (638.9): C, 60.16; H, 5.05; N, 2.19. Found: C
60.18; H 5.03; N 2.31. MS (MALDI+): m/z 354 (100%) [PhN-
(H)dPPh3]+. IR (ν, cm-1): 1304 (νPN), 341, 321 (νPdCl). 31P{1H}
NMR (CDCl3): δ 32.31. 1H NMR (CDCl3): δ 1.09 (m, 1H, CH2,
C8H11), 1.50 (m, 1H, CH2, C8H11), 1.80-1.86 (m, 2H, CH2, C8H11),
2.35 (m, 1H, CH2, C8H11), 2.70 (td, 1H, CH2, C8H11, 2JHH ) 19.9,
3JHH ) 5.7), 3.79 (m, 1H, H1 (PdCH), C8H11), 4.99 (t, 1H, H2, free
3
3
)
7.7), 7.58-7.64 (m, 4H, H7, C10H7 + Hp, PPh3), 7.75 (m, 6H, Ho,
3
PPh3), 8.15 (d, 1H, H8, C10H7, JHH ) 7.9), 11.16 (s, 1H, NH).
13C{1H} NMR (CDCl3): δ 24.07 (CH2, C8H11), 28.85 (CH2, C8H11),
39.83 (CH2, C8H11), 57.77 (C1, PdCH, C8H11), 99.83 (bonded d
CH, C8H11), 101.30 (s, C3, C8H11), 114.16 (bonded dCH, C8H11),
1
4
121.72 (d, Ci, PPh3, JPC ) 105.2), 123.69 (d, C8, C10H7, JPC
)
0.7), 124.92 (d, C3, C10H7, 4JPC ) 2.2), 125.28 (d, C2, C10H7, 3JPC
) 8.1), 126.27-126.48 (C4, C6, C10H7), 126.48 (C5, C10H7), 127.72
(C7, C10H7), 129.58 (d, Cm, PPh3, 3JPC ) 13.2), 130.66 (C2, C8H11),
131.57 (C9, C10H7), 131.63 (C10, C10H7), 133.97 (d, Co, PPh3, 2JPC
2
4
) 11.02), 134.26 (d, C1, JPC ) 0.7), 134.58 (d, Cp, PPh3, JPC
)
2.9).
Synthesis of 6 and 7. To a suspension of 4 (0.154 g, 0.24 mmol)
in MeOH (15 mL) was added AgClO4 (0.055 g, 0.26 mmol). The
resulting mixture was stirred at 25 °C for 20 min with exclusion of
light. After the reaction time, the gray suspension (which contains
AgCl and complex 7) was filtered through a Celite pad. (i) The
resulting yellow solution was evaporated to small volume (∼2 mL).
By Et2O addition (15 mL) and further stirring 6 was obtained as a
white solid. Obtained: 0.083 g (76%). (ii) The gray precipitate was
suspended in 20 mL of CH2Cl2, extracted during 20 min at 25 °C
and then filtered through a Celite pad. The resulting yellow solution
was evaporated to dryness to obtain 7 as a yellow solid. Obtained:
0.025 g (21%). Complex 7 has been previously reported.16
Characterization of 6. Anal. Calc for C24H21ClNO4P·0.8H2O
(468.3): C, 61.56; H, 4.86; N, 3.00. Found: C, 61.23; H, 4.70; N,
3.10. MS (MALDI+): m/z 354 (100) [PhN(H)dPPh3]+. IR (ν,
cm-1): 1303 (νPN), 3147 (νNH). 31P{1H} NMR (CDCl3): δ ) 32.96.
1H NMR (CDCl3): δ 7.00 (d, 2H, Ho, NPh, JHH ) 7.8), 7.03 (t,
3
1H, Hp, NPh, 3JHH ) 7.8), 7.15 (t, 2H, Hm, NPh), 7.68 (m, 6H, Hm,
2
PPh3), 7.80-7.84 (m, 9H, Hp + Ho, PPh3), 8.06 (d, 1H, NH, JPH
) 9.3).
Synthesis of 8. AgClO4 (0.245 g, 1.18 mmol) was added to a
suspension of 7 (0.270 g, 0.54 mmol) in NCMe (10 mL), and the
resulting mixture was stirred at room temperature for 20 min with
exclusion of light. The gray suspension was then filtered through
a Celite pad, and the resulting yellow solution was evaporated to
small volume (∼1 mL). By Et2O addition (20 mL) and further
stirring, 8 was obtained as a yellow solid. Obtained: 0.214 g (67%).
(19) Anderson, G. K.; Lin, M. Inorg. Synth. 1990, 28, 60.
(20) Drew, D.; Doyle, J. R.; Shaver, A. G. Inorg. Synth. 1972, 13, 47.

6402 Organometallics, Vol. 26, No. 25, 2007
Aguilar et al.
Anal. Calc for C12H17ClN2O4Pd (395.15): C, 36.47; H, 4.34; N,
7.09. Found: C, 36.29; H, 4.04; N, 6.91. MS (MALDI+): m/z
396 [M + H]+. IR (ν, cm-1): 2350, 2319 (νCN). 1H NMR
(CDCl3): δ 1.48 (m, 1H, CH2, C8H11), 1.67 (m, 1H, CH2, C8H11),
1.95-2.08 (m, 2H, CH2, C8H11), 2.24 (s, br, 6H, NCMe), 2.27 (m,
Crystal Structure Determination and Data Collection for 4‚
CH2Cl2. Crystals of 4‚CH2Cl2 of adequate quality for X-ray
measurements were grown by vapor diffusion of Et2O into a CH2-
Cl2 solution of 4 at -5 °C. A single crystal was mounted at the
end of a quartz fiber in a random orientation, covered with
perfluorinated oil, and placed under a cold stream of nitrogen gas.
Data collection was performed at 150 K on an Oxford Diffraction
Xcalibur2 diffractometer using graphite-monocromated Mo KR
radiation (λ ) 0.71073 Å). A hemisphere of data was collected
based on ω-scan and φ-scan series. The frames were integrated
using the program CrysAlis RED,21 and the integrated intensities
were corrected for absorption with SADABS.22
2
3
1H, CH2, C8H11), 2.78 (td, 1H, CH2, C8H11, JHH ) 18.7, JHH
)
6.3), 4.22 (m, 1H, H1, PdCH, C8H11), 4.96 (t, 1H, H2, free dCH,
3
C8H11, JHH ) 8.3), 5.72 (m, 1H, bonded dCH, C8H11), 5.84 (td,
3
4
1H, H3, free dCH, C8H11, JHH ) 8.2, JHH ) 3.8), 6.36 (m, 1H,
bonded dCH, C8H11).
Synthesis of 9. 1,2-Bis(diphenylphosphino)ethane (0.198 g, 0.50
mmol) was added to a solution of 8 (0.196 g, 0.50 mmol) in CH2-
Cl2 (20 mL), and the resulting mixture was stirred for 1 h at 25 °C
and then filtered through Celite. The obtained yellow solution was
evaporated to dryness, and the residue treated with Et2O (15 mL).
Further stirring gave 9 as a white solid. Obtained: 0.201 g (56%).
Complex 11 was recrystallized from CH2Cl2/hexane, giving color-
less crystals of 11‚0.4CH2Cl2, which were used for analytic and
spectroscopic purposes. The amount of CH2Cl2 was quoted by
Structure Solution and Refinement. The structure was solved
and developed by Patterson and Fourier methods.23 All non-
hydrogen atoms were refined with anisotropic displacement pa-
rameters. The hydrogen atoms were placed at idealized positions
and treated as riding atoms. Each hydrogen atom was assigned an
isotropic displacement parameter equal to 1.2 times the equivalent
isotropic displacement parameter of its parent atom. The structures
1
integration of the corresponding peak on the H NMR spectrum.
Anal. Calc for C34H35ClO4P2Pd·0.4CH2Cl2 (745.4): C, 55.43; H,
4.84. Found: C, 55.83; H, 5.05; MS (MALDI+): m/z 611 [M -
ClO4]+. 31P{1H} NMR (CDCl3): δ 49.31, 50.78 (AB spin system,
2
were refined to Fo , and all reflections were used in the least-squares
calculations.24 The anionic complex centered on Pd1 has two major
groups for one disorder assembly: the organic ligand. The olefin
is η2 bonded to Pd1 and the allyl function is η1 ligated. The ring
runs in opposite directions in the two disorder groups (see SI). The
two disorder groups are labeled “A” and “B”, and the atoms
common to the two are labeled “AB”. The atomic sites for the first
disordered congener, “A”, beginning with the olefinic group, are
[olefinic:] C1A, C2AB, [methylene:] C3A, C4A, [allyl:] C5AB,
C6AB, C7A, [methylene:] C8A. The second congener, in the same
order of chemical entities as that used for the first disorder
group, consists of [olefinic:] C2AB, C2B, [methylene:] C3B, C6AB,
[allyl:] C5AB, C6B, C7B, [methylene:] C8B we report the structure
in space group I2/a. The structure can also be set on a monoclinic
C-centered lattice, with space group C2/c. This would require the
use of a nonreduced net in the ac-plane. In order to reduce
correlations in the refinement, we used the “most reduced” cell,
the one with the shortest available axes, which is also the least
oblique cell choice, which in this case corresponds to I2/a. The
dimensions of the C-centered cell are a ) 30.053 Å, b ) 12.150
Å, c ) 19.369 Å, â ) 115.23°.
2
2PPh2, JPP ) 37.0). 1H NMR (CDCl3): δ 1.62 (m, 1H, CH2,
C8H11), 1.90 (m, 2H, CH2, C8H11), 2.35 (m, 3H, CH2, C8H11), 2.54
(m, 2H, CH2, dppe), 2.96 (m, 2H, CH2, dppe), 4.95 (m, 1H, H1,
PdCH, C8H11), 5.18 (t, 1H, H2, free dCH, C8H11, 3JHH ) 9.3), 5.27
(m, 1H, bonded dCH, C8H11), 5.54 (m, 1H, H3, free dCH, C8H11),
5.72 (m, 1H, bonded dCH, C8H11), 7.44-7.59 (m, 20H, PPh2,
dppe).
Synthesis of 10. To a solution of 7 (0.220 g, 0.44 mmol) in
CH2Cl2 (20 mL) was added PPh3 (0.230 g, 0.88 mmol). The
resulting solution was stirred at room temperature for 30 min, then
evaporated to dryness. The oily residue was treated with Et2O (15
mL), giving 10 as a yellow solid. Obtained: 0.170 g (75%).
Complex 10 was characterized as a equimolecular mixture of cis
and trans isomers. Complex 10 was recrystallized from CH2Cl2/
Et2O, giving yellow crystals of 10‚0.5CH2Cl2, which were used
for analytic and spectroscopic purposes. Anal. Calc for C26H26-
ClPPd‚0.5 CH2Cl2 (553.8): C, 57.47; H, 4.91. Found: C, 57.01;
H, 4.85. MS (MALDI+): m/z 476 [M - Cl]+. 31P{1H} NMR
(CDCl3): δ 23.52 (s, PPh3), 24.81(s, PPh3) (cis/trans mixture). 1H
NMR (CDCl3): δ 1.51 (m, CH2, C8H11), 1.59 (m, CH2, C8H11),
1.64 (m, CH2, C8H11), 1.71 (m, CH2, C8H11) 1.83-2.30 (m, CH2,
C8H11), 2.55-2.73 (m, 2H, CH2, C8H11), 2.81 (m, CH2, C8H11),
3.09 (m, CH2, C8H11), 3.80 (m, PdCH, C8H11), 4.15 (m, PdCH,
C8H11), 5.05-5.17 (m, H2, free dCH, C8H11, both isomers), 5.43
(t, bonded dCH, C8H11, 3JHH ) 7.5), 5.50 (t, bonded dCH, C8H11,
3JHH ) 6.0), 5.57 (m, H3, free dCH, C8H11), 5.67 (m, H3, free
dCH, C8H11), 5.78 (m, bonded dCH, C8H11), 6.05 (m, bonded
dCH, C8H11), 7.40-7.43 (m, Hm + Hp, PPh3, both isomers), 7.62-
7.71 (m, Ho, PPh3, both isomers).
Acknowledgment. Funding by the Ministerio de Educacio´n
y Ciencia (MEC) (Spain, Projects CTQ2005-01037 and
CTQ2005-03141) is gratefully acknowledged. R.B. and D.A.
thank Ministerio de Educacio´n y Ciencia (Spain) and Diputacio´n
General de Arago´n (Spain) for respective research grants.
Supporting Information Available: Tables giving complete
data collection parameters, atomic coordinates, bond distances and
angles, and thermal parameters for 4·CH2Cl2. This material is
available free of charge via the Internet at http://pubs.acs.org
Synthesis of 11. To a solution of 10 (0.076 g, 0.15 mmol) in
THF (20 mL) were added AgClO4 (0.031 g, 0.15 mmol) and PPh3
(0.039 g, 0.15 mmol). The resulting mixture was stirred at room
temperature for 20 min with exclusion of light. After the reaction
time, the gray suspension was filtered through a Celite pad, and
the resulting solution was evaporated to small volume (∼2 mL).
By Et2O addition (15 mL) and stirring 11 was obtained as a yellow
solid. Obtained: 0.070 g (56%). Anal. Calc for C44H41ClO4P2Pd
(837.6): C, 63.09; H, 4.93. Found: C, 62.98; H, 5.00. 31P{1H}
NMR (CDCl3): δ 23.39, 22.89 (AB spin system, 2JPP ) 43.0). 1H
NMR (CDCl3): δ 1.25-1.38 (m, 2H, CH2, C8H11), 1.84-2.04 (m,
3H, CH2, C8H11), 2.16 (m, 1H, CH2, C8H11), 5.16-5.27 (m, 2H,
H3 + H2, free dCH, C8H11), 5.31-5.34 (m, 2H, PdCH + bonded
dCH, C8H11), 5.87 (t, 1H, bonded dCH, C8H11, 3JHH ) 8.7), 7.24-
7.42 (m, 30H, PPh3).
OM700707J
(21) CrysAlis RED, Oxford Diffraction Ltd., Version 1.171.27p8; 2005.
(22) Sheldrick, G. M. SADABS, Program for absorption and other
corrections; Go¨ttingen University, 1996.
(23) Sheldrick, G. M. SHELXS-86. Acta Crystallogr. 1990, A46, 467.
(24) Sheldrick, G. M. SHELXL-97: FORTRAN program for the refine-
ment of crystal structures from diffraction data; Go¨ttingen University, 1997.
Molecular graphics were done using the commercial package: SHELXTL-
PLUS, Release 5.05/V; Siemens Analytical X-ray Instruments, Inc.:
Madison, WI, 1996.