Coordination of olefins and N-donor ligands at the fragment [2,6-bis((diphenylphosphino)methyl)pyridine]-palladium(II). Synthesis, structure, and amination of the new dicationic complexes [Pd(PNP)(CH2=CHR)](BF4)2 (R = H, P

Article abstract of DOI:10.1021/om970699q

Dicationic complexes of palladium(II) containing the tridentate ligand 2,6-bis((diphenylphosphino)methyl)pyridine (PNP) of the general formula [Pd(PNP)L](BF₄)₂ (L = MeCN, pyridine, C₂H₄, CH₂=CHPh) hav

Full text of DOI:10.1021/om970699q

2060
Organometallics 1998, 17, 2060-2066
Coor d in a tion of Olefin s a n d N-Don or Liga n d s a t th e
F r a gm en t [2,6-Bis((d ip h en ylp h osp h in o)m eth yl)p yr id in e]-
p a lla d iu m (II). Syn th esis, Str u ctu r e, a n d Am in a tion of
th e New Dica tion ic Com p lexes
[P d (P NP )(CH2dCHR)](BF 4)2 (R ) H, P h )
Christine Hahn,† Aldo Vitagliano,‡ Federico Giordano,‡ and Rudolf Taube*,§
Institut fu¨r Anorganische Chemie, Universita¨t Wu¨rzburg, Am Hubland, D-97074 Wu¨rzburg,
Germany, Dipartimento di Chimica, Universita` di Napoli “Federico II”, via Mezzocannone 4,
I-80134 Napoli, Italy, and Anorganisch-Chemisches Institut, Technische Universita¨t Mu¨nchen,
Lichtenbergstrasse 4, D-85747 Garching, Germany
Received August 11, 1997
Dicationic complexes of palladium(II) containing the tridentate ligand 2,6-bis((diphen-
ylphosphino)methyl)pyridine (PNP) of the general formula [Pd(PNP)L](BF4)2 (L ) MeCN,
pyridine, C2H4, CH2dCHPh) have been prepared from Pd(PNP)Cl2 by addition of 2 equiv of
AgBF4 in the presence of an excess of the respective ligand L in CH2Cl2. The corresponding
amine complex (L ) NHMe2) was obtained by substitution of the acetonitrile from [Pd-
1
(PNP)(MeCN)](BF4)2 by NHMe2 at 0 °C. The complexes were characterized by H, 13C, and
31P NMR spectroscopy, and the molecular structure of the styrene complex was determined
by X-ray diffraction analysis. The spectral and structural parameters of the complexes are
discussed in comparison to those of the recently prepared Rh(I) analogues. Nucleophilic
attack of secondary amines on the coordinated olefins gave the corresponding â-aminoethyl
complexes from which, upon reductive degradation, the respective ethylamines were obtained,
showing selective anti-Markovnikov addition in the case of the styrene complex.
In tr od u ction
of related complexes in which the complete ligand
sphere is maintained and only the metal ion is changed
from rhodium(I) to palladium(II). In this way direct
evidence may be obtained about the influence of the
central ion on the structural parameters and on the
electrophilic character of the coordinated olefin. We
report in this paper the synthesis and characterization
of the dicationic palladium(II) N-donor ligand complexes
[Pd(PNP)L](BF4)2 (L ) MeCN, pyridine, NHMe2). We
also report the synthesis of the complexes [Pd(PNP)-
(CH2dCHR)](BF4)2 (R ) H, Ph), which appear to be the
first dicationic monoolefin Pd(II) complexes to be iso-
lated, and the crystal structure of the styrene complex,
as well as their reactivity toward secondary amines.
The only reported catalytic addition of secondary
amines to a simple olefin under mild conditions was
obtained, although with a low turnover, with the cat-
ionic rhodium(I) ethylene complex [Rh(C2H4)(PPh3)2(Me2-
CO)]PF6.1
To study the mechanism of this reaction in detail, the
structure and reactivity of model complexes containing
the [2,6-bis((diphenylphosphino)methyl)pyridine]rhodium-
(I) fragment [Rh(PNP)]+ as a stable structural unit were
investigated.2,3 Although the nucleophilic attack of the
amine on the π-coordinated olefin is reputably the
crucial step in the rhodium-catalyzed hydroamination
reaction,4 this failed in the case of the [Rh(PNP)(olefin)]+
model complexes, which reacted by substitution of the
coordinated olefin, giving the corresponding amine
complexes.2
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Dica tion ic
P a lla d iu m (II) N-Don or Liga n d Com p lexes. To
On the other hand, it is well-known that the stoichio-
metric olefin amination can be carried out by nucleo-
philic attack of an amine on palladium(II)5 and platinum-
(II)6 complexes. It seemed therefore interesting for the
model studies to compare the structure and reactivity
(4) A stepwise catalytic cycle, involving N-H activation rather than
nucleophilic attack, was obtained in the Ir-promoted amination of
norbornene. See: Casalnuovo, A. L.; Calabrese, J . C.; Milstein, D. J .
Am. Chem. Soc. 1988, 110, 6738.
(5) (a) Panunzi, A.; De Renzi, A.; Palumbo, R.; Paiaro, G. J . Am.
Chem. Soc. 1969, 91, 3879. (b) Panunzi, A.; De Renzi, A.; Paiaro, G. J .
Am. Chem. Soc. 1970, 92, 3488. (c) Gasc, M.; Lattes, A.; Perie, J . J .
Tetrahedron 1983, 39, 703-731. (d) Young, G. B. In Comprehensive
Organometallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson,
G., Eds.; Pergamon Press: London, 1995; Vol. 9, pp 533-588.
(6) (a) A° kermark, B.; Ba¨ckvall, J .-E.; Hegedus, L. S.; Zetterberg, K.;
Siirala-Hanse´n, K.; Sjo¨berg, K. J . Organomet. Chem. 1974, 72, 127.
(b) A° kermark, B.; Ba¨ckvall, J .-E.; Siirala-Hanse´n, K.; Sjo¨berg, K.;
Zetterberg, K. Tetrahedron Lett. 1974, 1363. (c) A° kermark, B.; Ba¨ck-
vall, J .-E.; Zetterberg, K. Acta Chem. Scand. 1982, B36, 577-585. (d)
Davies, J . A. in Comprehensive Organometallic Chemistry II; Abel, E.
W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: London,
1995; Vol. 9, pp 293-316.
†
Universita¨t Wu¨ rzburg. E-mail:
christine.hahn@mail.uni-
wuerzburg.de.
‡ Universita` di Napoli.
§ Technische Universita¨t Mu¨nchen.
(1) (a) Krukowka, E.; Taube, R.; Steinborn, D. Ger. Offen. 296 909
A5 (10.11.88), 1991; Chem. Abstr. 1992, 116, 213993b. (b) Taube, R.
In Applied Homogeneous Catalysis with Organometallic Compounds;
Cornils, B.., Herrmann, W. A., Eds.; Verlag Chemie: Weinheim,
Germany, 1996; Vol. 1, p 507.
(2) Hahn, C.; Sieler, J .; Taube, R. Chem. Ber. 1997, 130, 939.
(3) Hahn, C.; Sieler, J .; Taube, R. Polyhedron 1998, in press.
S0276-7333(97)00699-7 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 04/17/1998

New Dicationic Complexes of Palladium
Organometallics, Vol. 17, No. 10, 1998 2061
investigate an appropriate synthetic route for dicationic
PNP-palladium(II) complexes as well as their general
properties, first complexes with different N-donor ligands
(N(sp) f N(sp2) f N(sp3)) were prepared. The synthesis
of the acetonitrile complex [Pd(PNP)(MeCN)](BF4)2 was
already described by DuBois and co-workers,7 where,
however, a mixture of the acetonitrile complex and the
dinuclear complex [Pd2(PNP)3](BF4)4 was obtained by
the reaction of the PNP ligand with [Pd(MeCN)4](BF4)2
in acetonitrile. In our case the pure acetonitrile and
pyridine complexes [Pd(PNP)L](BF4)2 (L ) MeCN (1),
acetonitrile.9 The coordination of the PNP ligand in
complexes 1-3 is suggested by the two bands10 at about
1568 and 1603 cm-1 and the noncoordination of the
-
BF4 anions by the strong band at 1058 cm-1 11
.
The N-donor ligand complexes were further charac-
1
terized by 31P and H NMR spectroscopy. The 13C NMR
spectra are also available, except for the amine complex
3, due to its relatively fast decomposition in solution.
When the NMR data are compared to those of the
corresponding Rh(I) complexes,2,3 relevant systematic
differences are found only for the 31P resonances and
for the proton resonances of the methylene groups
bound to phosphorus, while the other signals are not
significantly displaced. In the 31P NMR spectrum a
singlet appears at δ 36.1 for 1 (in CD2Cl2), at δ 38.3 for
2 (in acetone-d6), and at δ 37.3 for 3 (acetone-d6). The
signals are shifted downfield compared to those of the
analogous rhodium(I) complexes [Rh(PNP)L]BF4, whose
signals are at δ 31.7 (L ) MeCN), δ 30.9 (L ) pyridine),
and δ 34.3 (L ) NHMe2), respectively, in acetone-d6..2,3
Also, a rather downfield shift of the virtual triplet of
the methylene protons of the PNP ligand is observed
which appears in the 1H NMR spectra at δ 4.66 (in
CD2Cl2, 1), δ 5.14 (in acetone-d6, 2), and δ 4.68 (in
CDCl3, 3) in comparison to those for the respective
rhodium(I) analogues at δ 4.29 (L ) MeCN), δ 4.36 (L
) pyridine), and δ 4.22 (L ) NHMe2) in acetone-d6.2,3
The observed trend reflects the greater positive charge
of the Pd2+ compared to the Rh+ cation, whose effect
on chemical shifts is reasonably expected to be greater
on directly bonded ligand atoms, especially when they
have a soft character, as do the phosphine P atoms and
the π-bonded CdC double bond.
8
pyridine (2)) could be synthesized from Pd(PNP)Cl2
with 2 equiv of AgBF4 and an excess of the ligand L in
dichloromethane at room temperature according to
eq 1.
L/CH2Cl2
Pd(PNP)Cl2 + 2AgBF4
8
[Pd(PNP)L](BF4)2 + 2AgCl (1)
1, L ) CH3CN
2, L ) pyridine
Complexes 1 and 2 were obtained in good yields as
crystalline solids which are soluble in dichloromethane,
chloroform, acetone, acetonitrile, and methanol and
insoluble in diethyl ether and hydrocarbons such as
toluene and hexane. In the solid state, the acetonitrile
complex 1 decomposes in moist air while the pyridine
complex 2 is moderately stable. The corresponding
amine complex [Pd(PNP)(NHMe2)](BF4)2 (3) could not
be prepared from Pd(PNP)Cl2 and silver salt in the
presence of NHMe2 in CH2Cl2 or acetone, since decom-
position occurred at room temperature as well as at 0
°C. However, the amine complex could be obtained via
displacement of the acetonitrile ligand from [Pd(PNP)-
(MeCN)](BF4)2 by dimethylamine at 0 °C (cf. eq 2).
Syn th esis a n d Str u ctu r e of Dica tion ic P a lla -
d iu m (II) Olefin Com p lexes. The dicationic palla-
dium(II) olefin complexes [Pd(PNP)(CH2dCHR)](BF4)2
(R ) H (4), Ph (5)) could be obtained in good yields in
the same manner as described for the complexes 1 and
2 from Pd(PNP)Cl2 and 2 equiv of silver tetrafluorobo-
rate in the presence of an excess of the free olefin,
according to eq 3.
The amine complex 3, which precipitated as a beige
crystalline solid upon dropping diethyl ether into the
concentrated reaction solution, is less stable than the
acetonitrile complex 1. Even at room temperature
complex 3 releases dimethylamine and changes color to
brown. The dissolution of the complex 3 in chloroform,
dichloromethane, acetone, or methanol is accompanied
by precipitation of a dark oil.
The ethylene complex 4 precipitated as an ivory-
colored crystalline solid by dropping diethyl ether into
the solution. The yellow styrene complex 5 crystallized
upon concentration of the solution. Both olefin com-
plexes decompose in moist air as solids and are mod-
erately stable in solution only in the presence of an
excess of the corresponding free olefin. To the best of
our knowledge, these are the first dicationic palladium-
(II) monoolefin complexes that have been isolated. To
In the IR spectrum of complex 1 the two characteristic
bands at 2305 and 2340 cm-1 indicate the coordinated
(7) Steffey, B. D.; Miedaner, A.; Maciejewski-Farmer, M. L.; Ber-
natis, P. R.; Herring, A. M.; Allured, V. S.; Carperos, V.; DuBois, D. L.
Organometallics 1994, 13, 4844.
(8) Vasapollo, G.; Nobile, C. F.; Sacco, A. J . Organomet. Chem. 1985,
296, 435-441.
(9) Storhoff, B. N.; Lewis, H. C. Coord. Chem. Rev. 1977, 23, 1.
(10) Dahlhoff, W. V.; Nelson, S. M. J . Chem. Soc. (A) 1971, 2184.
(11) Beck, W.; Su¨nkel, K. Chem. Rev. 1988, 88, 1405.

2062 Organometallics, Vol. 17, No. 10, 1998
Hahn et al.
Ta ble 1. 13C a n d 1H NMR Ch em ica l Sh ifts (δ) of
th e F r ee a n d Coor d in a ted Olefin s in
[P d (P NP )(olefin )](BF 4)2 a n d [Rh (P NP )(olefin )]BF 4
2
compd
C(1)
C(2) H(1z) H(1e) H(2)
CH2dCH2
123.3
88.0
59.5
5.30
4.49
3.54
5.74 6.72
5.16 6.56
3.87 4.96
[Pd(PNP)(CH2dCH2)]2+ a
[Rh(PNP)(CH2dCH2)]+ b
PhCHdCH2
112.0 135.5 5.24
77.2 120.2 4.46
[Pd(PNP)(PhCHdCH2)]2+ a
[Rh(PNP)(PhCHdCH2)]+ b
51.5
75.8 3.72
a
In CD2Cl2. bIn acetone-d6.
avoid displacement and/or nucleophilic attack on the
coordinated olefin, it proved important to perform the
reaction in the absence of other potential donors, and
the anhydrous silver salt was thus added as a solid,
which could dissolve in CH2Cl2 because of transient
complexation by the excess olefin.
F igu r e 1. ORTEP view of the complex dication of 5.
Thermal ellipsoids are drawn at the 50% probability
level.
The isolated complexes were characterized by IR and
1
31P, H, and 13C NMR spectroscopy. The two IR bands
corresponding Rh(I) complexes, although they still ap-
pear at substantially higher field compared to the free
olefin. Furthermore, while in the case of the Rh(I)
styrene complex the shift difference between the ter-
minal carbon C(1) and the methyne carbon C(2) is
essentially the same as for the free olefin, this difference
almost doubles in the case of the Pd(II) complex 5 (that
is, the methyne carbon C(2) undergoes a much larger
downfield shift than the terminal carbon C(1) on going
from Rh+ to Pd2+). The proton signals follow the same
trend. Even if the 13C chemical shifts of π-bonded ole-
fins can be only partly correlated with the extent of σ
and π contributions to the metal-olefin bond,12 these
downfield shifts are consistent with the increased posi-
tive charge of the central ion and with the consequent
strong decrease in π back-donation that is expected,
all the coordination environments being the same. In
the styrene complex 5, the larger downfield shift ob-
served for the methyne carbon C(2) suggests a larger
fractional positive charge on this atom than in the free
olefin (and in the Rh+ complex). This suggests some
unsymmetrical bonding of the olefin, where the methyne
carbon is farther away from the metal and is positively
charged,12,13 as is indeed confirmed by the X-ray struc-
tural analysis of complex 5.
at about 1560 and 1600 cm-1 in the spectra of 4 and 5
indicate the coordination of the PNP ligand,10 and as
-
also found for complexes 1-3, the fact that both BF4
anions are not coordinated is suggested by the bands
at 1052 and 1060 cm-1 which were observed for 4 and
5, respectively.11
In the 31P NMR spectra a singlet appears at δ 51.3
for 4 and at δ 47.0 for 5. These signals are shifted
downfield compared to those for the corresponding
Rh(I) complexes (δ 38.2 and δ 41.7, respectively), in
agreement with the higher positive charge on the metal
ion. They are also shifted by about 10 ppm downfield
compared to those for the N-donor ligand complexes
1-3, most likely as a consequence of the weaker donor
character of the olefinic double bond compared to that
of nitrogen. This is consistent with the feature found
for the corresponding PNP rhodium(I) complexes.2
While in the 1H NMR spectrum of the ethylene
complex 4 the characteristic virtual triplet for the
methylene protons of the PNP ligand is found at δ 4.91,
the typical signal pattern of an AA′BB′XX′ spin system
is observed for these protons of the complex 5 which
consists of two doublets of virtual triplets at δ 4.79 and
4.91 with a coupling constant of J H -H ) 17.0 Hz. Since
a
b
The 13C NMR signals of the olefinic carbons of styrene
are also strongly downfield shifted in comparison to
those found for the cationic palladium(II) complex [Pd-
(C5H5){P(n-C4H9)3}(CH2dCHPh)]ClO4 (δ 56.2 and 92.1).12
It is worth noting that for the latter complex not only
the lower positive charge but also the coordinative satu-
ration12 contributes to the lower values of the 13C δ’s.
Molecu la r Str u ctu r e of [P d (P NP )(CH2dCHP h )]-
(BF 4)2 (5). Single crystals of the title compound, suit-
able for X-ray analysis, were obtained from a concen-
trated solution in dichloromethane containing an excess
of styrene after standing at -20 °C for a few days. An
ORTEP view of the complex dication is shown in Figure
1. Selected bond lengths and angles are collected in
Table 2. The molecule displays the usual square-planar
coordination around the palladium center (apart from
the two bite angles P-Pd-N (81.2°), which are con-
in the 13C and 31P spectra only one signal is observed
for corresponding nuclei in the symmetry-related halves
of the PNP ligand, this indicates the collapse of the C2v
symmetry of the [Pd(PNP)]2+ fragment to a C2 sym-
metry. This in turn indicates that, under the conditions
of the spectral runs (25 °C, anhydrous CD2Cl2), the
coordinated styrene molecule rotates freely around the
Pd-double-bond axis but does not undergo (on the NMR
frequency scale) rapid exchange with the free ligand,
whose traces are indeed observable in the spectrum. The
last observation seems to be uncommon for 16 e- olefin
complexes of Pd(II), which in most cases give averaged
resonances even at low temperature,11 and indicates a
lower than usual lability of the coordinated olefin,
1
probably arising from steric reasons (see later). The H
and 13C shifts of the olefinic protons and carbons in the
two complexes 4 and 5 are listed in Table 1, in
comparison to those of the corresponding Rh(I) com-
plexes and to those of the free olefins. As seen from
Table 1, the olefin signals of complexes 4 and 5 are
strongly shifted downfield compared to those for the
(12) Kurosawa, H.; Majima, T.; Asada, N. J . Am. Chem. Soc. 1980,
102, 6996 and references therein.
(13) Albright, T. A.; Hoffmann, R.; Thibeault, J . C.; Thorn, D. L. J .
Am. Chem. Soc. 1979, 101, 3801.

New Dicationic Complexes of Palladium
Organometallics, Vol. 17, No. 10, 1998 2063
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles (d eg) for [P d (P NP )(CH2dCHR)](BF 4)2 (5)
Pd-P(1)
Pd-C(1)
P(1)-C(1)
2.314(1)
2.165(7)
1.832(6)
Pd-P(2)
Pd-C(2)
P(2)-C(15)
2.330(2)
2.273(7)
1.840(5)
Pd-N
C(1)-C(2)
2.058(4)
1.292(10)
P(1)-Pd-P(2)
N-Pd-C(1)
C(1)-C(2)-C(3)
162.4(1)
159.3(4)
128.1(11)
P(1)-Pd-N
N-Pd-C(2)
Pd-C(2)-C(3)
81.2(2)
166.5(4)
111.5(8)
P(2)-Pd-N
C(1)-Pd-C(2)
81.2(2)
33.7(4)
strained to be smaller than 90°), and its overall geom-
etry is quite similar to that of the corresponding Rh(I)
complex,2 indicating that the steric constraints imposed
by (and acting on) the coordinated PNP ligand largely
dominate the effects of packing forces. Thus, the
pyridine ring forms an angle of 21° (20° in the Rh(I)
complex) with the coordination plane defined by P(1),
N, P(2), and Pd, and the styrene double bond is tilted
by 15° from the normal to the coordination plane (16°
in the Rh(I) complex). The tilting of the double bond
appears to arise in both cases from the need to avoid a
close steric contact between the styrene phenyl ring and
the equatorial phenyl group on P(2).
The C(1)-C(2) double-bond distance (1.29(1) Å) is the
shortest ever reported for Pd(II) and Pt(II) styrene
complexes, perhaps too short to be realistic. Neverthe-
less, even allowing in this case for an error 3-4 times
larger than the standard deviation of 0.01 Å (formal
standard deviations are notoriously fairly optimistic),
the CdC double bond is not longer than expected for
the free olefin and definitely is much shorter than in
the corresponding Rh+ complex (1.383(7) Å). Again, this
is consistent with a much lower (if any) metal to olefin
π-back-donation expected for the Pd2+ complex.
Rea ctivity of th e P a lla d iu m (II) Olefin Com -
p lexes 4 a n d 5 tow a r d Secon d a r y Am in es. The
nucleophilic addition of amines to a simple monoolefin
coordinated to Pt(II) or Pd(II) in 16 e- complexes is well-
known.5,6 However, while in the case of Pt(II) a broad
range of complexes has been found to be reactive,5,16,17
not many examples of such a reaction have been
reported in the case of Pd(II).6 Indeed, Pd(II) olefin
complexes are less stable and more labile than corre-
sponding Pt(II) complexes, and therefore an amine is
likely to give in most cases a substitution reaction rather
than a nucleophilic addition.
Theoretical18 and experimental17 studies indicate that
cationic species are more reactive toward nucleophilic
attack than neutral complexes. Accordingly, the dica-
tionic complexes 4 and 5 would be expected to be very
reactive. On the other hand, the high positive charge
of dicationic complexes is also expected to favor a
substitution reaction, both thermodynamically and ki-
netically, and therefore the outcome of the reactions of
4 and 5 with secondary amines is not easily predictable
in advance.
It is particularly interesting to compare the metal-
ligand bond distances with those of the corresponding
Rh(I) complex,2 because the two molecules are isoelec-
tronic and isostructural (when packing is not consid-
ered). The comparison shows small but significant
differences appearing in a clear and consistent pattern.
The Pd-N distance (2.058(4) Å) is shorter than the
Rh-N distance by 0.04 Å, while the average Pd-P
distance (2.32 Å) is longer than the average Rh-P
distance by 0.03 Å. The Pd-C(1) and Pd-C(2) distances
(2.165(7) and 2.273(7) Å, respectively) are longer than
the corresponding Rh-C distances by 0.03 and 0.07 Å,
respectively. Thus, the increase of the central ion
charge increases the bond strength with the almost
purely donor pyridine nitrogen but reduces the bond
strength with ligands having π-acceptor ability (the
phosphine and, especially, the CdC double bond). The
greater elongation (relative to the Rh(I) complex) ob-
served for Pd-C(2) bond compared to the Pd-C(1) is
consistent with the larger downfield shift observed for
the C(2) carbon. Thus, increasing the charge of the cen-
tral ion causes the olefin to slip toward a less sym-
metrical bonding, with an increased difference between
the two Pd-C bond lengths. Such slipping was also ob-
served in Pd(II)14 and Pt(II)15 complexes of para-sub-
stituted styrenes, as the result of the presence of elec-
tron-releasing substituents. Apparently, the asymmetry
in the styrene bonding to the metal can be increased
by all the factors which are expected to increase the
relative importance of the σ-donor component of the
olefin-metal bond compared to the π-back-donation.
The bonding parameters of the [Pd(PNP)]2+ fragment
in the styrene complex 5 are approximately identical
with those found in the analogous triethylphosphine
complex [Pd(PNP)(PEt3)](BF4)2.7 Only the Pd-N dis-
tance is significantly shorter in the complex 5 (2.058(4)
Å) than that observed in the triethylphosphine complex
(2.107(4) Å). This may be explained by the weaker
σ-donor ability of the CdC double bond in comparison
to the phosphine donor.
The ethylene complex 4 does indeed react with a
4-fold excess of piperidine in dichloromethane at -78
°C, giving the corresponding palladium(II) â-aminoethyl
complex 6 (cf. Scheme 1). This addition product, which
was isolated as a beige solid, could not be purified by
recrystallization. However, the 1H NMR spectrum of
the crude product is quite consistent with the expected
structure of 6 (see Experimental Section). A solution
of 6 upon standing for 4 days at room temperature was
analyzed by gas chromatography, which showed no â-H-
elimination product. Upon reductive degradation of the
complex 6 with NaBH4 in THF ethylpiperidine was
1
obtained in a yield of 78%, which was detected by H
NMR and GC analysis. Other products could not be
detected.
The nucleophilic attack of dimethylamine on the
styrene complex 5 also occurred. However, even at -78
°C the substitution reaction could not be suppressed
completely (cf. Scheme 2). The 1H NMR spectrum of
(16) Green, M.; Sarhan, J . K. K.; Al-Najjar, I. M. J . Chem. Soc.,
Dalton Trans. 1981, 1565.
(17) Annibale, G.; Maresca, L.; Natile, G.; Tiripicchio, A.; Tiripicchio
Camellini, M. J . Chem. Soc., Dalton Trans. 1982, 1587.
(18) Sakaki, S.; Maruta, K.; Ohkubo, K. Inorg. Chem. 1987, 26, 2499.
(14) Miki, K.; Shiotani, O.; Kai, Y.; Kasai, N.; Kanatani, H.;
Kurosawa, H. Organometallics 1983, 2, 585.
(15) Nyburg, S. C.; Simpson, K.; Wong-Ng, W. J . Chem. Soc., Dalton
Trans. 1976, 1865.

2064 Organometallics, Vol. 17, No. 10, 1998
Hahn et al.
Sch em e 1
what unexpected, not only because it is in contrast to
what is observed in the case of Pt(II) but also because
the 13C shift data suggest a fractional positive charge
on the methyne carbon C(2) relative to C(1). It should
be kept in mind, however, that the regiochemical results
of amine addition to unsaturated ligands have to be
taken with some caution, since reversibility and thus
equilibration of the product mixture are possible.20
Nevertheless, under the hypothesis of a kinetic control
of the recaction, its regiochemistry can be reasonably
explained on steric grounds, by considering the opti-
mized geometry of the transition state for the nucleo-
philic addition.18 It is seen that in the case of attack at
C(2) the styrene phenyl ring would be pushed toward
the metal, thus interacting sterically with the proximal
phenyl group on the phosphine ligand and raising the
energy of the transition state. On the other hand, in
the case of attack at C(1) the styrene phenyl ring is
pushed away from the metal, and no additional barrier
is added to the reaction, which would explain the
observed regiochemistry.
Sch em e 2
Con clu sion
The results reported in this paper show that dicat-
ionic palladium(II) complexes of the type [Pd(PNP)L]-
(BF4)2 can be obtained both with N-donor ligands (L )
CH3CN, pyridine, Me2NH) and with olefins (L ) C2H4,
PhCHdCH2), by removing the chloride ions from Pd-
(PNP)Cl2 with 2 equiv of silver salt under appropriate
conditions. The comparison of their NMR and X-ray
diffraction data with those of the isoelectronic and
isostructural Rh(I) complexes2,3 shows a number of
consistent differences resulting from the increased
nuclear charge. Among these, large downfield 13C shifts
of the olefinic carbons, significantly longer metal-olefin
bond distances, and a significantly shorter CdC distance
in the π-coordinated styrene were found, reflecting a
somewhat weaker bond and a strongly decreased back-
donation in the dicationic palladium(II) complex. In
addition, in comparison to their rhodium(I) analogues,
complexes 1-5 are less stable both in air as solids and
in solution, consistent with the expected higher ten-
dency to undergo hydrolysis. If it is considered that
complexes 4 and 5 are the first dicationic monoolefin
palladium(II) complexes to be described, their very
existence as isolable species suggests that the PNP
the isolated solid exhibits the typical AA′BB′XX′ signal
pattern at δ 4.23 and 4.48 (J H -H ) 16.8 Hz) for the
a
b
nonequivalent methyl protons of the PNP ligand and a
singlet at δ 2.27 for the dimethylamino group which can
be assigned to the addition product 7; in addition, the
signals of the amine complex 3 were observed in a ratio
of ca. 4:1 (7:3). Also, no indication for a â-H elimination
could be observed when a solution of the resulting solid
in CH2Cl2 was stored over 4 days at room temperature.
The mixture of the complexes was used directly for
the reductive degradation with LiBEt3H in THF. In the
ether extract not only PhCH2CH2NMe2 (in a yield of
21%) but also the corresponding quaternary ammonium
ligand might have a role in their stabilization.
A
stabilizing factor could possibly be a steric protection
against substitution reactions exerted by the proximal
P-phenyl groups protruding on each side of the coordi-
nated olefin. Indeed, no fast exchange was observed
with the free olefin in the NMR spectra at room
temperature, an uncommon feature for 16 e- Pd(II)
olefin complexes. Since coordination at the Pd(PNP)2+
fragment strongly increases the electrophilic character
of the olefin compared to that of the corresponding Rh-
(PNP)+ species, they are susceptible to nucleophilic
attack by secondary amines, probably with the help of
the above-mentioned moderate inertness to substitution.
Unfortunately, as long as the target is a catalytic
hydroamination, the palladium(II) species are not fa-
salt (PhCH2CH2)2NMe2 was detected by 1H NMR
+
spectroscopy in about 30% molar ratio. Obviously a
nucleophilic attack of complex 7 at the π-coordinated
styrene in 5 is responsible for the formation of the
ammonium salt. Such multiple addition was also
observed in the case of the platinum(II) â-aminoethyl
complexes.19 The regiochemistry of the products indi-
cates an anti-Markovnikov attack on the coordinated
styrene, which is opposite to what observed for a neutral
Pt(II) complex.16 The anti-Markovnikov attack is some-
(20) (a) Ba¨ckvall, J .-E.; Bjo¨rkman, E. E. Acta Chem. Scand. 1984,
B38, 91. (b) A° kermark, B.; Vitagliano, A. Organometallics 1985, 4,
1275.
(19) De Renzi, A.; Paiaro, G.; Panunzi, A.; Paolillo, L. Gazz. Chim.
Ital. 1972, 102, 281.

New Dicationic Complexes of Palladium
Organometallics, Vol. 17, No. 10, 1998 2065
Ta ble 3. Cr ysta l Da ta , Da ta Collection
Con d ition s, a n d Solu tion a n d Refin em en t Deta ils
for [P d (P NP )(CH2dCHP h )](BF 4)2 (5)
vored, since the Pd-C σ-bond in the â-aminoethyl
complexes is too stable to be cleaved protolytically under
the reaction conditions and can only undergo reductive
cleavage with irreversible destruction of the complex.
Nevertheless, the present study shows the possibility
of isolating dicationic monoolefin complexes of palla-
dium(II), opening the way to further investigations on
the synthesis and properties of a class of compounds
which are expected to be highly reactive.
cryst size/mm
formula
fw
0.10 × 0.20 × 0.30
PdP2F8NC39B2H35
859.7
cryst syst
space group
monoclinic
P21/c
a/Å
b/Å
c/Å
13.930(5)
12.040(4)
22.665(5)
94.85(2)
3788(3)
4
â/deg
V/Å3
Exp er im en ta l Section
Z
F(000)
1736
1.50
1.51
1.540 56
72
54.6
7454
4715
478
Gen er a l Com m en ts. All reactions were carried out under
dry argon or ethylene. All solvents were dried, degassed, and
distilled before using. Acetone, piperidine, CD2Cl2, CDCl3, and
acetone-d6 were refluxed over 4 Å molecular sieves and
degassed by bubbling argon. Styrene was distilled under
reduced pressure before use. Diethyl ether and THF were
refluxed over Na/benzophenone. AgBF4 and NHMe2 were
obtained from Fluka and used without further purification.
Dm/g cm-3
Dc/g cm-3
λ(Cu KR)/Å
θmax (deg)
µ/cm-1
no. of indep rflns
no. of rflns above 3σ(I)
no. of refined params
goodness of fit
R
0.800
0.046
0.050
Infrared spectra were recorded in Nujol on
a Philips
1
Analytical PU9600 FTIR spectrometer. The H NMR spectra
were recorded at 200 MHz on a Varian XL-200, at 270 MHz
on a Bruker AC-270, or at 300 MHz on a Varian Gemini 300
NMR spectrometer. The 31P{1H} NMR spectra were recorded
at 121 MHz and the 13C{1H} NMR spectra at 75 MHz on a
Varian Gemini 300 NMR spectrometer. The 1H NMR shifts
were referenced to the resonance of the residual protons of
the solvents. The 31P NMR shifts were referenced to external
85% H3PO4. A Chrompack CP 9000 gas chromatograph was
used for the identification of liquid organic compounds.
Elemental analyses of C, H, and N were carried out on a LECO
CHN 932 analyzer.
Rw
Syn th eses. Pd(PNP)Cl2 was prepared according to the
procedure described in the literature.8
[P d (P NP )(MeCN)](BF 4)2 (1) a n d [P d (P NP )(p y)](BF 4)2
(2). To a suspension of 100 mg (0.153 mmol) of Pd(PNP)Cl2
in 3 mL of CH2Cl2 and 0.5 mL of acetonitrile (1) or pyridine
(2) was added 60 mg (0.31 mmol) of AgBF4. After the
dissolution of the starting complex, silver chloride precipitated.
The silver chloride was filtered off, and the volume of the
solution was reduced to 1.5 mL. The acetonitrile complex 1
crystallized as a pale yellow solid upon dropwise addition of 1
mL of diethyl ether and standing for 2-3 h at -20 °C. The
pyridine complex 2 precipitated as an ivory-colored crystalline
solid when 8 mL of diethyl ether was added slowly to the
filtrate. The products were filtered off, washed two times with
diethyl ether, and dried under vacuum.
X-r a y Da ta Collection a n d Red u ction . X-ray data were
collected from a prismatic crystal covered with glue at room
temperature on an Enraf-Nonius CAD4-F automatic diffrac-
tometer using Cu KR graphite-monochromated radiation and
operating in the ω/θ scan mode. The unit cell parameters were
obtained by a least-squares fitting of the setting values of 25
strong reflections in the θ range 24 e θ e 29°. Three
monitoring reflections, measured every 500 reflections, showed
insignificant intensity fluctuations. The structure was solved
by the heavy-atom method. At the end of the isotropic
refinement a correction for absorption effects was applied
according to Walker and Stuart21 by using the computer
program DIFABS (maximum and minimum values of the
absorption correction were 1.20 and 0.65). The full-matrix
least-squares refinement minimized the quantity ∑w(∆F)2 with
w-1 ) [σ2(Fo) + (0.02Fo)2 + 0.8], where σ is derived from
counting statistics. All non-hydrogen atoms were refined
anisotropically. H atoms, placed in calculated positions, were
assigned the isotropic equivalent thermal parameters of the
carrier atoms and included in the final refinement as riding
atoms. The final Fourier difference map showed no peaks
greater than 0.76 e Å-3. The largest shift-to-esd ratio in the
final cycle was 0.02.
All calculations, carried out on a Vax 750 at the Centro
Interdipartimentale di Metodologie Chimico-fisiche of the
University of Naples, were performed by using the Enraf-
Nonius (SDP) set of programs.22
Final atomic coordinates, full lists of bond distances and
angles, hydrogen atom parameters, and anisotropic thermal
parameters of the non-hydrogen atoms have been deposited
as Supporting Information. Crystal data, data collection
conditions, and solution and refinement details are given in
Table 3.
1: yield 93 mg (0.115 mmol, 76%); dec pt 140-150 °C. Anal.
Calcd for C33H30B2F8N2P2Pd: C, 49.76; H, 3.80; N, 3.52.
Found: C, 49.77; H, 4.36; N, 3.40. 31P NMR (CD2Cl2): δ 36.1
(s). 1H NMR (CD2Cl2): δ 2.25 (s, 3H, CH3), 4.66 (vt, J P-H
+
2
4J P-H ) 5.3 Hz, 4H, CH2), 7.67 (m, 12H, Ph), 7.74 (d, 2H, J H-H
2
)7.8 Hz, py), 7.96-8.03 (m, 8H, Ph), 8.26 (t, 1H, J H-H ) 7.8
Hz, py). 13C NMR (75 MHz, CD2Cl2): δ 3.8 (s, CH3), 42.4 (vt,
3
1
3
1J P-C + J P-C ) 14.3 Hz, CH2), 124.4 (vt, J P-C + J P-C ) 7.5
1
3
Hz, py-3,5), 129.4 (br, CN), 130.4 (vt, J P-C + J P-C ) 5.5 Hz,
Phm), 133.2 (vt, J P-C + J P-C ) 7.1 Hz, Pho), 133.7 (s, Php),
1
3
1
143.2 (s, py-4), 162.9 (vt, J P-C
(Nujol): ν(py), 1576 and 1603; ν(BF4), 1058; ν(CN), 2305 and
2340 cm-1
+
3J P-C < 3 Hz, py-2,6). IR
.
2: yield 128 mg (0.153 mmol, 100%); dec pt 132 °C. Anal.
Calcd for C36H32B2F8N2P2Pd: C, 51.81; H, 3.86; N, 3.36.
Found: C, 51.42; H, 3.87; N, 3.36. 31P NMR (acetone-d6): δ
38.3 (s). 1H NMR (acetone-d6): δ 5.14 (vt, 4H, J P-H + J P-H
) 5.2 Hz, CH2), 7.52-7.57 (m, 12H, Ph), 7.63-7.78 (m, 8H,
Ph, py), 7.95 (d, 2H, J ) 7.7 Hz, py), 8.05 (t, 1H, J ) 7.7 Hz,
py), 8.24 (t, 1H, J ) 7.8 Hz, py[PNP]), 8.82 (d, 2H, J H-H ) 5.2
2
4
Hz, py). 13C NMR (CD2Cl2): δ 41.8 (vt, J P-C + J P-C ) 13.3
1
3
Hz, CH2), 124.2 (vt, 1J P-C + 3J P-C ) 6.7 Hz, py-3,5[PNP]), 127.3
1
3
(s, py-3,5), 130.1 (vt, J P-C + J P-C ) 5.4 Hz, Phm), 132.8 (s,
Php), 133.2 (vt, J P-C + J P-C ) 7.1 Hz, Pho), 139.8 (s, py-4),
1
3
1
3
143.4 (s, py-4), 151.8 (s, py-2.6), 162.0 (vt, J P-C + J P-C ) 3
Hz, py-2,6[PNP]). IR (Nujol): ν(py), 1566 and 1603; ν(BF4),
1057 cm-1
.
[P d (P NP )(NHMe2)](BF 4)2 (3). To a solution of 317 mg
(0.398 mmol) of [Pd(PNP)(CH3CN)](BF4)2 in 4 mL of CH2Cl2
was added 5 mL of a ca. 1 M solution of dimethylamine in
CH2Cl2 at -78 °C. The solution was stirred for 10 min and
(21) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158.
(22) Enraf-Nonius CAD-4 Software, Version 5.0; Enraf-Nonius,
Delft, The Netherlands, 1989.

2066 Organometallics, Vol. 17, No. 10, 1998
Hahn et al.
warmed to 0 °C. At this temperature the volume of the
solution was reduced to 1.5 mL. A beige solid precipitated
upon addition of diethyl ether. The solid was filtered off,
washed with diethyl ether, and dried under vacuum. The
product could not be purified by recrystallization due to its
poor stability in solution.
(m, PdCH2CH2), 4.44 (vt, 2J P-H + 4J P-H ) 4.1 Hz, PCH2), 7.48-
7.61 (m, Ph, py), 7.63-7.76 (m, Ph).
Red u ctive Degr a d a tion of 6. A 205 mg amount of [Pd-
(PNP)(CH2CH2NC5H10)]BF4 (6) (0.26 mmol) was suspended in
5 mL of THF. A 40 mg (1.06 mmol) portion of NaBH4 was
added to the suspension at -78 °C. The mixture was warmed
to room temperature and stirred for 1 h. A 4 mL amount of
diethyl ether and 2 mL of 2 M HCl were added at 0 °C. After
the mixture was stirred for 1 h, the aqueous layer was
separated and NaOH added. The basic aqueous phase was
extracted two times with 4 mL of diethyl ether and dried over
Na2SO4. The solvent was removed from the ether extract
under reduced pressure. A 26 mg amount of a pale yellow oil
was obtained, which was identified as ca. 90% pure ethylpi-
Yield: 175 mg (0.218 mmol, 55%). Dec pt 116 °C. 1H NMR
3
(CDCl3): δ 2.44 (d, 3H, J H-H ) 5.6 Hz, NCH3), 3.9 (br, 1H,
HN), 4.68 (vt, 4H, 2J P-H + 4J P-H ) 5.0 Hz, CH2), 7.63 (m, Ph),
7.97 (m, Ph) (the d and t of pyridine overlapped by a broad
signal of an impurity as well as by Ph multiplets). IR
(Nujol): ν(py), 1568 and 1610; ν(BF4), 1058 cm-1
.
[P d (P NP )(C2H4)](BF 4)2 (4). A suspension of 1.01 g of Pd-
(PNP)Cl2 (1.55 mmol) and 602 mg of AgBF4 (3.10 mmol, 2
equiv) in 20 mL of CH2Cl2 was cooled to -78 °C and stirred
for 5 min under ethylene. Upon warming, the mixture was
stirred for 10 min at room temperature. The precipitated AgCl
was filtered off, and the ivory-colored product crystallized by
slow dropping of ca. 70 mL of diethyl ether with stirring of
the solution. The product was filtered off, washed with diethyl
ether, and dried under vacuum.
1
peridine by H NMR and GC analysis (yield 78%).
Rea ction of 5 w ith NHMe2 a n d Red u ctive Degr a d a -
tion . A 300 mg amount of [Pd(PNP)(CH2dCHPh)](BF4)2 (0.35
mmol) was dissolved in 3 mL of CH2Cl2, and this solution was
cooled to -78 °C. A 2 mL portion of a solution of NHMe2 in
CH2Cl2 (ca. 1 M, 5-6 equiv, ca. 1.9 mmol, also cooled to -78
°C) was added. The reaction mixture changed color to pale
brown and was stirred for 30 min at -78 °C. The solvent was
removed under vacuum at the same temperature, leaving a
beige microcrystalline solid. The crude product could not be
purified by recrystallization. The solid was characterized as
Yield: 1.0 g (1.28 mmol, 83%). Dec pt: 134-138 °C. Anal.
Calcd for
C33H31B2F8NP2Pd: C, 50.58; H, 3.99; N, 1.79.
Found: C, 50.49; H, 4.36; N, 1.77. 31P NMR (CD2Cl2): δ 51.3
(s). 1H NMR (CD2Cl2): δ 4.49 (s, 4H, C2H4), 4.91 (vt, 4H, 2J P-H
+ 4J P-H ) 5.4 Hz, CH2), 7.62-7.73 (m, 14H, Ph and py), 7.79-
7.86 (m, 8H, Ph), 7.92 (t, 1H, J H-H ) 7.6 Hz, py). 13C NMR
1
such by H NMR spectroscopy (CDCl3): δ 2.27 (s, NMe2), 3.26
2
(m, PdCHPhCH2), 3.78 (m, PdCHPhCH2), 4.23 (dvt, J P-H
+
1
3
4J P-H ) 4.7 Hz, J H-H ) 16.8 Hz, PCHa), 4.48 (dvt, 2J P-H + 4J P-H
) 3.1 Hz, J H-H ) 16.8 Hz, PCHb), 6.28 (d, J ) 15.0 Hz,
PdCHPh), 6.85 (m, PdCHPh), 7.29-7.68 (m, Ph, py), 7.93 (m,
Ph). In addition, the signals of 3 appear in this spectrum. For
the reductive degradation this solid was used directly.
(CD2Cl2): δ 44.5 (vt, J P-C + J P-C ) 13.6 Hz), 88.0 (s, C2H4),
1
3
1
123.9 (vt, J P-C + J P-C ) 7.0 Hz, py-3,5), 130.4 (vt, J P-C
+
3J P-C ) 6.0 Hz, Phm), 133.6 (vt, J P-C + J P-C ) 6.6 Hz, Pho),
1
3
134.0 (s, Php), 143.4 (s, py-4), 160.1 (vt, J P-C + 3J P-C ) 3 Hz,
1
py-2,6). IR (Nujol): ν(py), 1564 and 1622; ν(BF4), 1052 cm-1
.
[P d (P NP )(CH2dCHP h )](BF 4)2 (5). To a suspension of 300
mg (0.459 mmol) of Pd(PNP)Cl2 in 10 mL of CH2Cl2 and 1 mL
of styrene was added 180 mg (0.925 mmol) of AgBF4. The
mixture was stirred for 10 min. The precipitated silver
chloride was filtered off, and the volume of the solution was
reduced to 1.5 mL. The solution was stored for 30 min at -20
°C. The yellow crystalline product was filtered off, washed
three times with diethyl ether and dried under vacuum.
Yield: 320 mg (0.372 mmol, 81%). Dec pt: 140-150 °C.
Anal. Calcd for C39H35B2F8NP2Pd: C, 54.49; H, 4.10; N, 1.63.
Found: C, 54.63; H, 4.18; N, 1.61. 31P NMR (CD2Cl2): δ 47.0
The crude product (containing ca. 0.93 mmol of palladium)
was suspended in 5 mL of THF and the suspension cooled to
-45 °C. Upon addition of 1 mL of a solution of 1.0 M LiBEt3H
in THF to the suspension the mixture changed color im-
mediately to brown and was stirred for 30 min at -45 °C. The
mixture was warmed to room temperature and stirred for 30
min. A 10 mL amount of diethyl ether and 5 mL of 2 M HCl
were added at 0 °C. After the mixture was stirred for 1 h, the
aqueous layer was separated and NaOH added. The basic
aqueous phase was extracted two times with 4 mL of diethyl
ether and dried over Na2SO4. The diethyl ether of the extract
was removed under vacuum, leaving a brown-yellow oil which
was identified by 1H NMR spectroscopy as a mixture of PhCH2-
(s). 1H NMR (CD2Cl2): δ 4.46 (m, 1H, styrene), 4.79 (dvt, 2H,
2
2J H
) 17.0 Hz, J P-H
+
4J P-H ) 4.9 Hz, PCHa), 4.91 (vt,
-H
a
b
2H, 2J H b ) 17.0 Hz, 2J P-H + 4J P-H ) 5.4 Hz, PCHb), 5.16 (d,
+
-H
a
CH2NMe2 and (PhCH2CH2)2NMe2 (in a ratio of about 2:1).
1H, J H-H ) 8.6 Hz, styrene), 6.56 (m, styrene), 6.79 (d, J H-H
) 7.6 Hz, PPho, styrene), 7.15 (t, J H-H ) 7.7 Hz, PPhm,
styrene), 7.33 (t, J H-H ) 7.5 Hz, PPhp, styrene), 7.51-7.88 (m,
The yield of PhCH2CH2NMe2 was 21%, as found by GC
analysis. Other isomers were not detected. The chemical
shifts and retention time were compared to those of authentic
samples prepared according to the procedure in ref 23.
1
3
PPh and py). 13C NMR (CD2Cl2): δ 44.4 (vt, J P-C + J P-C
)
1
13.2 Hz), 77.2 (s, styrene), 120.2 (s, styrene), 123.9 (vt, J P-C
+ 3J P-C ) 5.8 Hz, py-3,5), 128.6 (s, styrene), 130.4 (vt, 1J P-C
+
Ack n ow led gm en t. An ERASMUS visiting scholar-
ship for C.H. at the University of Napoli, May-J uly
1996, is acknowledged. We thank the Deutsche For-
schungsgemeinschaft (Sonderforschungsbereich 347 of
the University of Wu¨rzburg) and the Italian National
Research Council (CNR) for financial support.
3J P-C ) 5.3 Hz, Phm), 130.5 (vt, J P-C + 3J P-C ) 5.2 Hz, Phm′),
1
133.3 (s, styrene), 133.9 (vt, 1J P-C + 3J P-C ) 6.4 Hz, Pho), 134.0
1
3
(vt, J P-C + J P-C ) 6.5 Hz, Pho′), 134.1 (s, Php), 143.4 (s, py-
4), 159.9 (vt, J P-C + 3J P-C < 3 Hz, py-2,6). IR (Nujol): ν(py),
1
1560 and 1600; ν(BF4), 1060 cm-1
.
R ea ct ion of 4 w it h P ip er id in e. A 345 mg amount of
[Pd(PNP)(C2H4)](BF4)2 (0.440 mmol) was dissolved in 3 mL of
CH2Cl2; this solution was cooled to -78 °C, and 175 µL of
piperidine (ca. 4 equiv) was added. The reaction mixture
changed color immediately to brown. After the mixture was
stirred for 1 h at -78 °C, the solvent was removed under
vacuum while cold. A beige solid was obtained, which was
recrystallized two times from CH2Cl2/diethyl ether. However,
after the second recrystallization some brown impurities
maintained (205 mg, 60% yield). The isolated product was
identified by 1H NMR spectroscopy (CDCl3) as [Pd(PNP)-
(CH2CH2NC5H10)]BF4 (6): δ 1.35-1.62 (m’s, Hâ,γ of piperidine
ring), 1.89 (m, PdCH2CH2), 2.36 (m, HR of piperidine ring), 2.75
Su p p or tin g In for m a tion Ava ila ble: Tables of the com-
plete set of crystallographic data, atomic coordinates and
equivalent isotropic displacement parameters, all bond lengths
and angles, anisotropic displacement parameters, and hydro-
gen coordinates and isotropic displacement parameters (7
pages). Ordering information is given on any current mast-
head page.
OM970699Q
(23) von Braun, J . Chem. Ber. 1910, 43, 3209.