Olefins coordinated at a highly electrophilic site - Dicationic palladium(II) complexes and their equilibrium reactions with nucleophiles

Article abstract of DOI:10.1002/1099-0682(200102)2001:2<419::AID-EJIC419>3.0.CO;2-2

Dicationic olefin palladium(II) complexes [Pd(PNP)(olefin)] (BF₄)₂ [olefin = ethylene, propene, styrene, (Z)-2-butene, (E)-2-butene, norbornene; PNP = 2,6-bis(diphenylphosphanylmethyl)pyridine] have been prepared and characterized by ¹H, ¹³C, and ³¹p NMR spectroscopy. The coordinated double bond in these complexes is strongly electrophilic, and easily adds a variety of nucleophiles NuH (H₂O, MeOH, aliphatic and aromatic amines). This reaction competes with olefin displacement in a rapidly reversible equilibrium process, as a result of which the addition products can also be obtained starting from the substituted compounds [Pd(PNP)(NuH)](BF₄)₂ and the appropriate olefin. Equilibrium constants for the addition and substitution reactions have been determined in a number of cases. Proton abstraction from [Pd(PNP)(CHRCHR′NuH)]²⁺ by NaHCO₃ quantitatively drives the equilibrium to β-functionalized alkyl complexes of the general formula [Pd(PNP)(CHRCHR′Nu)](BF₄), which are unusually stable to β-H elimination.

Full text of DOI:10.1002/1099-0682(200102)2001:2<419::AID-EJIC419>3.0.CO;2-2

FULL PAPER
Olefins Coordinated at a Highly Electrophilic Site ؊ Dicationic Palladium(II)
Complexes and Their Equilibrium Reactions with Nucleophiles
Christine Hahn,[a] Pasquale Morvillo,[a] and Aldo Vitagliano*[a]
Dedicated to Professor Paolo Corradini on the occasion of his 70th birthday
Keywords: Palladium / Alkene complexes / Nucleophilic additions / Tridentate ligands / Aminations
Dicationic olefin palladium(II) complexes [Pd(PNP)(olef-
in)](BF4)2 [olefin = ethylene, propene, styrene, (Z)-2-butene, starting
(E)-2-butene, norbornene; PNP = 2,6-bis(diphenylphosphan- [Pd(PNP)(NuH)](BF4)2 and the appropriate olefin. Equilib-
ylmethyl)pyridine] have been prepared and characterized by rium constants for the addition and substitution reactions
result of which the addition products can also be obtained
from the substituted compounds
1H, 13C, and 31P NMR spectroscopy. The coordinated double
bond in these complexes is strongly electrophilic, and easily
adds a variety of nucleophiles NuH (H2O, MeOH, aliphatic
and aromatic amines). This reaction competes with olefin dis-
have been determined in a number of cases. Proton abstrac-
tion from [Pd(PNP)(CHRCHRЈNuH)]2+ by NaHCO3 quantit-
atively drives the equilibrium to β-functionalized alkyl com-
plexes of the general formula [Pd(PNP)(CHRCHRЈNu)](BF4),
placement in a rapidly reversible equilibrium process, as a which are unusually stable to β-H elimination.
Introduction
secondary aliphatic amines. A number of questions arose
from the above study, e.g. concerning the range of accessible
(ϩ2) charged complexes, their reactivity with nucleophiles
weaker than aliphatic amines, and the nature (kinetic or
thermodynamic) and extent of the competition between nu-
cleophilic addition and displacement. In the present paper,
we address these issues, presenting some quantitative evid-
ence for the high electrophilicity of the olefin and for the
interplay between addition and substitution reactions in
these species. We also report the generation of a rare class
of non-chelating β-functionalized (alkyl)PdII derivatives
that are thermally stable and do not undergo β-H
elimination.[10Ϫ13]
(Olefin)palladium(II) complexes are important interme-
diates in organic syntheses and catalytic processes,[1] where
the addition of nucleophiles to the CϭC double bond is
the crucial step. This offers numerous possibilities for the
functionalization of simple olefins.[2] Among these, the hy-
droamination process, which was first investigated in the
early 1970s, has recently attracted renewed attention.[3] The
electrophilic character of the coordinated olefin is enhanced
by an increase in the positive charge on the metal center,[4]
as also shown by the ability of cationic PdII complexes to
promote olefin polymerization[5] and copolymerization[6] re-
actions. Accordingly, very high reactivity would, in prin-
ciple, be expected for complexes where the metal center be-
ars a net (ϩ2) charge, thus making such species appealing
targets for investigation. On the other hand, a net (ϩ2)
charge would also enhance the electrophilic character and
hardness of the metal center, and in such species the soft
olefinic ligand can be expected to be readily displaceable,
even by weak ligands and/or nucleophiles. Consequently, di-
cationic alkene complexes are expected to be accessible only
within a rather narrow range of conditions and their react-
ivity is not readily predictable in advance. In line with the
above considerations, no dicationic PdII complex of a
simple monoolefin had been described in the literature[7]
until we reported[8] the synthesis and characterization of
two compounds of the formula [Pd(PNP)(CH2ϭ
CHR)](BF4)2 [PNP ϭ 2,6-bis(diphenylphosphanylmethyl)-
pyridine;[9] R ϭ H, Ph], together with their reactions with
Results and Discussion
Synthesis and Characterization of [Pd(PNP)(olefin)]2؉
Complexes
The
dicationic
(olefin)palladium(II)
complexes
[Pd(PNP)(olefin)](BF4)2 [olefin: CH2ϭCH2 (1), CH2ϭ
CHMe (2), CH2ϭCHPh (3), (Z)-MeCHϭCHMe (4), (E)-
(1)
[a]
`
Dipartimento di Chimica, Universita di Napoli ‘‘Federico II’’,
Via Mezzocannone 4, 80134 Napoli, Italy
Fax: (internat.) ϩ 39-081/674199
E-mail: alvitagl@unina.it
Eur. J. Inorg. Chem. 2001, 419Ϫ429
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/0202Ϫ0419 $ 17.50ϩ.50/0
419

C. Hahn, P. Morvillo, A. Vitagliano
MeCHϭCHMe (5), norbornene (6)] were prepared by reac- Table 1. 13C NMR chemical shifts of the coordinated olefins in
FULL PAPER
tion of the chloro complex [Pd(PNP)Cl]Cl[14] with two
equivalents of silver tetrafluoroborate in the presence of an
excess of the olefin according to Equation (1). The prepara-
tion of complexes 1 and 3 by the same procedure has been
described previously.[8] In an alternative synthetic route,
the norbornene complex 6 could be prepared by displace-
1Ϫ6 (∆δ ϭ δcoord Ϫ δfree
)
Olefin
δ(ϭCH2) ∆δ(ϭCH2) δ(ϭCH) ∆δ(ϭCH)
[8]
CH2ϭCH2
88.0
86.4
77.2
Ϫ35.3
Ϫ29.6
Ϫ34.8
MeCHϭCH2[8]
118.1
120.2
110.9
107.8
105.2
Ϫ16.5
Ϫ15.3
Ϫ14.4
Ϫ17.6
Ϫ30.5
PhCHϭCH2
(Z)-MeCHϭCHMe
ment of ethylene with an excess of norbornene [Equa- (E)-MeCHϭCHMe
Norbornene
tion (2)] and was obtained in high yield in an analytically
pure state.
NMR time scale, which seems to be a rather unusual feature
for coordinatively unsaturated PdII complexes.[17] However,
the exchange is fast on the laboratory time scale, as shown
by an experiment in which free ethylene was added to an
NMR sample of the propene complex 2 at room temper-
ature. The 1H NMR spectrum of the mixture, recorded
within 3 min of mixing, showed the presence of both species
1 and 2, the relative abundances of which remained un-
changed with time, indicating a rapid equilibration of the
olefin complexes. The equilibrium constant for the ex-
change [Equation (3)] of ethylene for propene was estimated
as K ϭ 1.4 by integration of the NMR signals of the four
species involved. Similar experiments were performed on
complexes 3؊5, allowing estimation of the respective equi-
librium constants [Equation (3)].
(2)
The complexes 2 and 4؊6 were characterized by 31P, 1H,
and 13C NMR spectroscopy. They were found to be moder-
ately stable in dichloromethane and nitromethane solution
at room temperature and may be stored for months under
a dry atmosphere. They slowly decompose in moist air, as
was also observed for the ethylene and styrene complexes 1
and 3.[8] The H and 31P NMR spectra of the complexes
1
(see Experimental Section) indicate an averaged C2 sym-
metry for the propene complex 2 and an averaged C2v sym-
metry for the complexes 4 and 6 and hence a fast rotation
of the olefin about the PdϪdouble bond axis in each case.
The spectrum of the propene complex 2 does not show sub-
stantial changes on cooling down to 203 K, indicating that
at this temperature olefin rotation is still fast on the NMR
time scale. The pattern observed for the propene complex 2
also indicates that at room temperature the exchange
(dissociationϪreassociation) of the olefin is slow on the
NMR time scale. This was confirmed for all the complexes
examined by the appearance of well-separated signals for
the protons of free and coordinated olefin when a small
amount of free olefin was added to each sample.
(3)
The relative stabilities of the olefin complexes seem to be
determined essentially by steric factors. It is worth noting
that (E)-2-butene gives a more stable complex than (Z)-2-
butene, in contrast to the sequence typically found for (2-
butene)metal complexes.[16,18] This most likely arises from
the C2 symmetry of the ‘‘pocket’’ created by the PNP li-
gand, which is better suited for hosting the (E)- as com-
pared to the (Z)-olefin. The substantially lower stability of
the styrene complex 3 can be ascribed to a steric interaction
between the phenyl groups, which was revealed by its X-
ray structure.[8]
As anticipated in the introduction, the olefin in com-
plexes 1؊6 is easily displaced, even by ligands that are usu-
ally weakly coordinative towards d8 ions. Dissolution in
acetone led to loss of the olefin from all of the complexes,
while saturation of dichloromethane solutions of 1, 2, or 3
with water followed by evaporation of the solvent furnished
the aqua complex 7 [Equation (4)]. The displacement of
ethylene by acetonitrile, giving complex 8, proved to be even
The 13C chemical shifts of the olefinic carbon atoms in
the complexes 1؊6 are listed in Table 1, together with the
corresponding coordination-induced shifts ∆δ. A rather
uniform albeit modest upfield shift is observed: The average
∆δ is Ϫ15 ppm for the methine carbon atoms (except in the
case of norbornene) and Ϫ33 ppm for the methylene carbon
atoms, confirming previous observations for complexes 1
and 3.[8] As pointed out previously,[8] the small values of ∆δ
are consistent with the high positive charge present on the
central ion (as compared with the isoelectronic RhI com-
plexes[15]) and with a consequent presumably low contribu-
tion of π-back-donation to the metalϪolefin bond.[16]
Olefin Displacement
As mentioned in the previous section, in complexes 1؊6 more favorable. In the latter two cases, the equilibrium con-
at room temperature the olefin exchange is slow on the stants for the exchange [Equation (4)] were determined by
420
Eur. J. Inorg. Chem. 2001, 419Ϫ429

Dicationic Palladium(II) Complexes
FULL PAPER
1H NMR measurements in CD2Cl2/CD3NO2 (4:1) and were of ethylene and a drop of water (resulting in a biphasic mix-
found to be K ϭ 5·10Ϫ2 and K ϭ 9·102 for 7 and 8, respect- ture), signals appeared in the spectrum indicative of a par-
ively.
tial conversion of 1 to addition products (see below). These
addition products were almost undetectable in the absence
of an excess of heterogeneous water. This qualitatively in-
dicated the occurrence of an overall equilibrium, in which
the nucleophilic attack on the coordinated olefin was fol-
lowed by proton transfer to the water phase (see Scheme 1).
Indeed, when the reaction was performed in the presence of
solid NaHCO3 (ca. 2 equiv.), the equilibrium was seen to be
quantitatively shifted towards the addition products, which
could be isolated as a solid mixture and were assigned the
mono- and dialkylated structures 9 and 10 (Scheme 1). In
(4)
1
the H NMR spectrum of the mixture, two sets of signals
are seen for the [PdCH2CH2O] moiety at δ ϭ 2.02 and 3.44
for 9 and at δ ϭ 1.79 and 2.79 for 10. Integration of these
signals reveals a ratio of ca. 1:3. Correspondingly, two dif-
ferent signals are observed for the PCH2 group of the co-
ordinated PNP ligand, at δ ϭ 4.38 and δ ϭ 4.44, respect-
ively, in the same 1:3 ratio. Reductive degradation of the
product mixture with NaBH4 in [D8]THF gave a solution
Reactions with Nucleophiles
Complexes 1؊6 were treated with a number of nucleo-
philes, including water, methanol, and aliphatic and aro-
matic amines. In many cases, the reaction mixtures were
1
directly analyzed by H NMR, which revealed details that
would have remained undetected in normal preparative ex-
periments and hence provided a quantitative estimation of
the factors controlling the behaviour of the system.
1
in which the H NMR signals of ethanol and diethyl ether
were found in the same 1:3 ratio as observed for 9 and 10
(corresponding to a molar ratio of 1:1.5), thus independ-
ently confirming the above assignments.
Reactions with H2O
As mentioned above, treatment of the ethylene complex
1 with an excess of H2O resulted in the displacement of the
Both the substitution reaction and the nucleophilic at-
olefin with production of the aqua complex tack were found to be readily reversible. Indeed, addition
[Pd(PNP)(H2O)](BF4)2 (7) [Equation (4)], which was isol- of 5 equiv. of concentrated HBF4 to a sample of the alkyl
1
ated and characterized by H NMR. However, when the derivatives 9 and 10 in the presence of free ethylene resulted
reaction was performed in an NMR tube using an excess in the formation of 1. Also, treatment of the aqua complex
Scheme 1
Eur. J. Inorg. Chem. 2001, 419Ϫ429
421

C. Hahn, P. Morvillo, A. Vitagliano
FULL PAPER
7 with NaHCO3 in dichloromethane saturated with ethylene
likewise produced the same mixture of alkyl derivatives 9
and 10. The formation of 10 was also performed in a step-
wise manner, i.e. by first abstracting a proton from the co-
ordinated water in 7 with an excess of NaHCO3, giving the
hydroxo complex [Pd(PNP)(OH)]BF4 (11), and then treat-
ing the isolated complex 11 with ethylene. The latter reac-
(6)
1
tion was monitored by H NMR, which revealed the initial
formation of the monoalkylated species 9 followed by par-
tial conversion to 10.
A similar set of equilibria were revealed in the case of the
propene complex 2. The major observed addition product
(80% based on Pd) was the mononuclear primary alkyl de-
rivative 12, corresponding to a Markovnikov addition. Two
pertinent differences from the ethylene case were qualitat-
ively apparent. Firstly, the addition products were barely
detectable in the absence of added NaHCO3, indicating that
the addition reaction is appreciably less favored than in the
case of ethylene. Secondly, the binuclear species 13 was only
produced as a minor product (20% based on Pd), probably
reflecting the steric repulsion between two secondary car-
bon atoms linked to the same oxygen atom.
2-butenes, giving a relative measure of the stabilities of the
(β-methoxyalkyl)palladium species compared with the re-
spective free olefins.
(7)
Reactions with MeOH
In the case of the ethylene complex 1, the equilibrium
represented by Equation (7) also results in a site exchange
of the α- and β-protons of the alkyl chain. This exchange
Dissolution of the ethylene complex 1 in CD3OD pro-
duced a strongly acidic solution, the H NMR spectrum of
1
1
was actually revealed at room temperature by a H NMR
which revealed the presence of the addition product [D3]14,
a substitution product [D3]15, and free ethylene in a molar
ratio of 1:1:1. In the case of the propene complex 2, the
addition product [D3]16 was formed to a lesser extent (cor-
responding ratio 1:4:4), while for the styrene complex 3,
only the substitution product [D3]15 and free styrene were
detectable in solution. Small amounts of the addition prod-
ucts were also detectable in the case of the 2-butene com-
plexes 4 and 5. Addition of an excess of free olefin to the
solutions of 1 and 2 led to an increase in the relative
amounts of the corresponding addition products 14 and 16,
respectively. These results indicate that in methanol solution
two fast equilibrium reactions are operative [Equation (5)
and Equation (6)].
saturation transfer experiment, in which irradiation of
either of the CH2 groups caused a partial transfer of mag-
netization to the other CH2 unit as well as to the free CH2ϭ
CH2 molecules, indicating that the overall exchange [Equa-
tion (7)] takes place at a rate comparable to the relaxation
rates (1Ϫ10 sϪ1).
In line with our expectations, when the complexes 1؊5
were treated with 2 equiv. of NaHCO3 in methanol in the
presence of an excess of free olefin, the equilibrium repres-
ented by Equation (7) was driven to completion leading to
quantitative formation of the corresponding β-methoxyal-
kyl complexes 14 and 16؊18, which could be isolated. In
the case of the ethylene complex 1, the nucleophilic attack
was also performed in a CH2Cl2 solution using 4 equiv. of
MeOH, which led to the same result. High regioselectivity
was achieved in the reactions of the propene and styrene
complexes 2 and 3, which gave 16 and 17, respectively, in
better than 97% abundances.[19] The structures of 16 and 17
were independently confirmed by reductive cleavage of the
complexes with NaBH4 in CD3OD, which gave
CH3CH(Me)OMe and CH3CH(Ph)OMe, respectively. Ad-
dition of methanol to the (Z)- and (E)-2-butene complexes
4 and 5 furnished the diastereomers 18a and 18b, respect-
ively, which could be distinguished by virtue of the slight
(5)
The equilibrium constants for the overall reaction [Equa- but significant differences in their 1H NMR spectra (see
tion (7)] were estimated for ethylene, propene, and the two Experimental Section). The structures of 18a and 18b were
422
Eur. J. Inorg. Chem. 2001, 419Ϫ429

Dicationic Palladium(II) Complexes
FULL PAPER
assigned assuming trans attack on the respective olefin com- tion (0.007 mol LϪ1) of the isolated dimethylamine complex
plexes 4 and 5. Although at present we are unable to pro- 19,[8] an equilibrium was attained within about 1 h at
vide any direct evidence for this assumption,[20] the alternat- 283 K. The final solution contained the addition product
ive possibility of a cis addition (i.e. a true migratory inser- 20ϪHϩ together with very small but measurable amounts
tion) seems unlikely in the light of previous knowledge on of the starting complex 19. The ratio 20ϪHϩ/19 was found
the stereochemistry of nucleophilic addition.[21] However, to be proportional to the concentration of free ethylene,
circumstantial evidence regarding this matter comes from confirming the existence of the equilibrium and allowing
the fact that although cationic (alkyl)(olefin) complexes of estimation of the equilibrium constant for the formal ‘‘in-
palladium(II) with bidentate ligands undergo rather fast in- sertion’’[23] reaction represented by Equation (9) (K ϭ 3·104
sertion,[5]
the
isolated
methyl
derivative L molϪ1).
[Pd(PNP)(CH3)]BF4 is totally unreactive towards ethyl-
ene.[22]
(9)
The obtained β-methoxyalkyl complexes are quite stable
as solids and in solution, both when the σ-bonded carbon
atom is primary (as in 14, 16, and 17) and when it is second-
ary (as in 18a,b). No interconversion between the two dias-
tereomers 18a and 18b was observed in dichloromethane
solution over a period of one week.
In spite of the commonly encountered high reactivity of
norbornene, no addition product of methanol could be ob-
tained from complex 6, possibly because of steric instability
of the σ-alkyl derivative that would be produced by the nu-
cleophilic attack, or (as suggested by a referee) because of
inertness of exo-η2-norbornene towards trans addition.
In an attempt to cleave the PdϪC σ-bond protolytically,
the β-methoxyalkyl complexes were treated with gaseous
HCl in CD2Cl2 solution, allowing direct monitoring of the
reaction by NMR. However, this led to an immediate rever-
sion of the nucleophilic addition through heterolytic frag-
mentation. The respective olefin was liberated, along with
MeOH and [Pd(PNP)Cl]BF4.
Similar experiments were performed using propene and
styrene as the olefins. In the case of propene, the addition
product 21ϪHϩ was formed in an equilibrium reaction, the
estimated constant for which was K ϭ 102 L molϪ1. In the
case of styrene, no addition product could be detected.
However, when the reaction was performed starting from
the styrene complex 3 and an excess (4 equiv.) of Me2NH
was added, the primary alkyl derivative 22 was formed im-
mediately and completely isomerized within 1 h to the sec-
ondary (anti-Markovnikov) alkyl derivative 23 (Scheme 2).
The same reaction with excess Me2NH was also performed
with the propene complex 2, resulting in a mixture of 21
(82%) and the anti-Markovnikov product 24 (18%). The re-
giochemical assignments of the products 21؊24 were con-
firmed by in situ reduction with sodium borohydride and
1H NMR identification of the resulting amines. The higher
stability of the secondary (anti-Markovnikov) alkyl derivat-
ive 23 compared to 22 is in contrast to the common trend
shown by alkylmetal complexes (primary Ͼ secondary ϾϾ
tertiary), but seems to reflect a common outcome in amin-
ation reactions of styrene.[3a]
(8)
For the complexes 18a and 18b, the reversion of the addi-
tion led almost exclusively to the formation of (Z)- and (E)-
2-butene, respectively, which provides evidence for the mi-
croscopic reversibility of this reaction.
Experiments similar to those described above were per-
formed using aniline as a nucleophile. Starting from a solu-
tion (0.015 mol LϪ1) of the isolated aniline complex 25 con-
taining 0.1 mol LϪ1 of free ethylene, an equilibrium distri-
Reactions with Amines
The reactions of the secondary alkylamines piperidine bution of 10:1 between the starting complex and the addi-
and dimethylamine with the ethylene and styrene complexes tion product 26ϪHϩ was attained within a few minutes.
1 and 3 were recently reported from a purely preparative The estimated equilibrium constant for the formal ‘‘inser-
point of view.[8] We have now investigated the process in tion’’[23] reaction [Equation (10)] is K ϭ 1 L molϪ1. Upon
more detail and have extended the studies to less basic aro- addition of NaHCO3 (2 equiv.), the equilibrium was quant-
matic amines. After adding an excess of ethylene to a solu- itatively driven towards the addition product 26, which was
Eur. J. Inorg. Chem. 2001, 419Ϫ429
423

C. Hahn, P. Morvillo, A. Vitagliano
FULL PAPER
Scheme 2
formed together with small amounts of the dialkylated
By combining these values with that for the ethylene dis-
placement by acetonitrile [K ϭ 9·102, see Equation (4)], the
equilibrium constants for the substitution (Ksub) and addi-
tion (Kadd) reactions with aniline and dimethylamine were
estimated. The values are reported in Table 2, together with
the corresponding values for the propene complex 2.
product 27.[24]
(10)
(12)
Table 2. Approximate values of the equilibrium constants for the
addition (Kadd), substitution (Ksub), and ‘‘insertion’’ (see ref.[23]
(Kins ϭ Kadd/Ksub) reactions of 1 and 2 with amines
)
In the above experiments, the equilibrium concentration
of the ethylene complex 1 was below the limit of detection,
hence the equilibrium constants for the substitution and ad-
dition reactions could not be directly evaluated. In order to
estimate their individual values, the equilibrium constants
of two auxiliary substitution reactions [Equation (11) and
1
Equation (12)] were determined by H NMR.
((Scan 19))
Amine
Me2NH
PhNH2
Olefin
Kins
Kadd
Ksub Kins
Kadd
Ksub
(11)
[L·molϪ1] [L·molϪ1
]
[L·molϪ1] [L·molϪ1
]
CH2ϭCH2 3·104
CH2ϭCHMe 1·102
1013
1011
6·108 1
1·109 5·10Ϫ2
2·105
2·105
3·105
1.5·104
424
Eur. J. Inorg. Chem. 2001, 419Ϫ429

Dicationic Palladium(II) Complexes
FULL PAPER
The Kadd values given in Table 2 show that nucleophilic Conclusions
attack on the coordinated olefin is a quite favorable process
in the dicationic complex, even when the nucleophile is a
poorly basic aromatic amine. Moreover, the acidic β-am-
monioalkyl derivative generated in the reaction can be fur-
ther converted into the more stable β-aminoalkyl species
through proton abstraction by an auxiliary base. When the
basicity of the amine decreases, the nucleophilic attack is
less favored, but at the same time the β-ammonioalkyl de-
rivative is more acidic, and a successive proton abstraction
becomes more favored. Therefore, the overall reaction in
the presence of an auxiliary base is expected to be driven
to a similar extent towards the (β-aminoalkyl)palladium de-
rivative. In view of these considerations, we treated com-
plexes 1 and 2 with primary aromatic amines of varying
basicity (ranging from 4-methoxyaniline, pKa ϭ 5.3 to 2-
chloroaniline, pKa ϭ 2.6) and NaHCO3 (2 equiv.) in the
presence of an excess of the respective gaseous olefins. The
(β-aminoethyl)PdII compounds 26 and 28؊34 were indeed
obtained in good yields (Scheme 3) as cream-colored solids
The use of the tridentate ‘‘pincer’’ ligand PNP has al-
lowed the unprecedented isolation of stable dicationic (ol-
efin)PdII complexes, and the subject of nucleophilic addi-
tion to PdII-coordinated olefins has been re-examined using
these dicationic complexes as substrates. The σ-alkyl deriv-
atives resulting from the nucleophilic attack are remarkably
stable towards β-H elimination, as a consequence of the un-
availability of the adjacent coordination sites. Since side-
reactions arising from β-H elimination do not take place,
for the first time approximate equilibrium data could be
obtained for the nucleophilic addition and for the competit-
ive substitution reaction. The results indicate that in a dicat-
ionic PdII complex the olefin is highly activated towards
nucleophilic addition (much more so than in neutral spe-
cies[25]), both kinetically and thermodynamically. It is relev-
ant to note in this respect that in monocationic complexes
containing a ligand isoelectronic and isostructural with
PNP (i.e. PCP), no nucleophilic attack on a coordinated
olefin is observed.[26] The coordinated double bond actually
acts as a strong electrophile, as indicated by its ability to
capture a lone pair from methanol and to successively pro-
tonate a base as weak as methanol itself. Viewed from an-
other perspective, the σ-alkyl derivatives resulting from the
nucleophilic attack are strongly stabilized by the residual
positive charge on the metal ion, and it appears that the
CϪPd σ-bond is more stabilized by the positive charge than
the PdϪN bond of a coordinated amine. Thus, the formal
‘‘insertion’’[23] of the olefin into the PdϪN bond is thermo-
dynamically favored (Table 2), while it was found to be dis-
favored in the case of neutral species.[27] This finding could
be relevant for the development of synthetically useful hy-
droaminations, because olefin displacement, which is con-
sidered to be a serious obstacle to achieving such process-
es,[3a] might become a minor concern or even be of no con-
sequence in the case of dicationic species.
1
and were characterized by H NMR.
Scheme 3
Experimental Section
The structures of the propene derivatives 28, 33, and 34
were assigned essentially as in the case of the water and
methanol adducts, and indicated selective attack at the sec-
ondary carbon atom (Markovnikov addition). As in the
case of the corresponding β-methoxyalkyl species 14 and
16؊18, the complexes 26 and 28؊34 can be stored indefin-
itely as solids and are also stable in solution; no evidence
for β-H elimination was observed after a week in dichloro-
General: All reactions were carried out under dry nitrogen. CH2Cl2
was refluxed with CaH2, MeOH with Mg/Mg(OMe)2, and diethyl
ether with Na/benzophenone. The solvents were distilled prior to
˚
use. CD2Cl2, CD3NO3, and CDCl3 were dried with 4-A molecular
sieves. AgBF4 was obtained from ABCR and was used without
further purification. The aromatic amines RNH2 were obtained
from Aldrich and were distilled prior to use. Ϫ NMR spectra were
recorded with Varian Gemini 200, Bruker AC-200, Bruker AC-250,
1
methane. This stability towards β-H elimination is quite ex- and Bruker WH-400 instruments. H NMR shifts were referenced
to the resonances of the residual protons in the solvents and the
13C NMR shifts to the solvent resonances (δ ϭ 53.8, CD2Cl2; δ ϭ
62.8, CD3NO2). For the 31P NMR spectra, H3PO4 (85%) was used
as an external standard.
ceptional in (alkyl)Pd species that are not stabilized by four-
or five-membered ring formation.[11] It most likely arises
from the impossibility of the putative hydride ligand to ac-
cess either of the cis positions, both of them being firmly
bound by the two phosphane ‘‘arms’’ of the PNP ligand. It
is noteworthy in this respect that the only β-functionalized
open-chain alkyl PdII derivatives hitherto isolated are trans-
[Pd(PMe3)2(CH2CH2Y)Br] (Y ϭ CO2Me, CN).[13]
Syntheses: The complexes [Pd(PNP)Cl]Cl,[14] [Pd(PNP)(CH2ϭ
CHR)](BF4)2 [R ϭ H (1), Ph (3)], and [Pd(PNP)(L)](BF4)2 [L ϭ
MeCN (8), Me2NH (19), pyridine (35)][8] were prepared according
to previously described procedures.
Eur. J. Inorg. Chem. 2001, 419Ϫ429
425

C. Hahn, P. Morvillo, A. Vitagliano
JHP ϭ 4.2 Hz, 2 H, ϭCH, norbornene), 4.95 (pseudo t, NHP
FULL PAPER
[Pd(PNP)(olefin)](BF4)2 (2, 4؊6). ؊ General Procedure: A mixture
ϭ
of [Pd(PNP)Cl]Cl (200 mg, 0.306 mmol) and AgBF4 (121 mg, 5.0 Hz, 4 H, PCH2), 7.57 (d, JHH ϭ 7.4 Hz, 2 H, py-3,5), 7.69Ϫ7.73
0.620 mmol) in CH2Cl2 (10 mL) was saturated with the appropriate
gaseous olefin (in the case of norbornene 10 equiv. of the olefin
was added). After stirring the mixture for 10 min, the precipitate
was filtered off. In the case of 2-butenes and norbornene, the pre-
cipitate (containing the product) was washed with nitromethane (1
mL, free from any nitrile!). The product was precipitated from the
solution by the dropwise addition of diethyl ether. The solid was
collected by filtration, washed with diethyl ether, and dried in va-
cuo.
(m, 12 H, Ph), 7.86Ϫ7.98 (m, 9 H, Ph, py). Ϫ 13C NMR (50 MHz,
CD3NO2): δ ϭ 23.6 (s, norbornene), 43.9 (s, norbornene), 46.0
(pseudo t, NCP ϭ 14.6 Hz), 54.5 (s, norbornene), 105.2 (s, ϭCH,
norbornene), 124.6 (pseudo t, NCP ϭ 5.6 Hz, py-3,5), 125.4 (pseudo
t, NCP ϭ 27.3 Hz, Phi), 130.7 (pseudo t, NCP ϭ 5.6 Hz, Phm), 134.1
(pseudo t, NCP ϭ 7.4 Hz, Pho), 134.7 (s, Php), 144.2 (s, py-4), 159.9
(s, py-2,6). Ϫ 31P NMR (81 MHz, CH2Cl2): δ ϭ 50.4 (s).
[Pd(PNP)(H2O)](BF4)2 (7): To
a solution of 1 (100 mg,
0.127 mmol) in CH2Cl2 (6 mL) was added ca. 50 equiv. of H2O
(100 µL). After stirring for a few minutes, a yellow crystalline solid
precipitated, which was collected by filtration, washed several times
with diethyl ether, and dried in vacuo. Yield 90%. Ϫ 1H NMR
(200 MHz, CD2Cl2): δ ϭ 3.0 (v br, H2O), 4.45 (br, 4 H, PCH2),
7.54Ϫ8.05 (m, 23 H, Ph, py).
2: Yield 191 mg (0.243 mmol, 78%); ivory-colored solid; m.p. 181
°C (dec.). Ϫ C34H33B2F8NP2Pd (797.62): calcd. C 51.20, H 4.17,
N 1.76; found C 50.91, H 4.21, N 1.69. Ϫ 1H NMR (200 MHz,
CD2Cl2): δ ϭ 1.51 (d, JHH ϭ 6.2 Hz, 3 H, CH3), 4.56 (d pseudo t,
JHH ϭ 17.2 Hz, NHP ϭ 5.4 Hz, 2 H, PCHaHb), 4.66 (d, JHH
ϭ
14.8 Hz, 1 H, ϭCH2), 4.70 (d, JHH ϭ 7.8 Hz, 1 H, ϭCH2), 5.21 (d
pseudo t, JHH ϭ 17.2 Hz, NHP ϭ 5.0 Hz, 2 H, PCHaHb), 6.00 (br,
1 H, ϭCH), 7.59Ϫ8.02 (m, 23 H, Ph, py). Ϫ 13C NMR (50 MHz,
CD2Cl2): δ ϭ 21.5 (s, CH3), 44.9 (pseudo t, NCP ϭ 12.8 Hz, PCH2),
86.3 (s, ϭCH2), 118.1 (s, ϭCH), 124.5 (pseudo t, NCP ϭ 25.5 Hz,
Phi), 124.5 (br, py-3,5), 125.5 (pseudo t, NCP ϭ 27.3 Hz, PhiЈ),
131.2Ϫ131.3 (br, Phm), 133.8 (pseudo t, NCP ϭ 5.7 Hz, Pho), 134.9
(s, Php), 135.1 (pseudo t, NCP ϭ 7.7 Hz, PhoЈ), 144.1 (s, py-4), 161.1
(br, py-2,6). Ϫ 31P NMR (CH2Cl2, 81 MHz): δ ϭ 46.9 (s).
Reactions of 1 and 2 with H2O: To a solution of 1 or 2 (100 mg) in
CH2Cl2 (6 mL), saturated with ethylene or propene, respectively, 2
equiv. of NaHCO3 and 50 equiv. of H2O were added. The mixture
was then stirred for 3 h, the solid was filtered off, and the solvent
was removed under reduced pressure. A solid was obtained, which
was recrystallized from CH2Cl2/diethyl ether.
9/10: Yield 87 mg (97% based on Pd); pale-yellow solid. Ϫ 1H
NMR (200 MHz, CDCl3): 9: δ ϭ 2.02 (m, 2 H, PdCH2), 3.44 (m,
2 H, CH2), 4.44 (pseudo t, NHP ϭ 4.6 Hz, 4 H, PCH2), 7.35Ϫ7.73
(m, 23 H, Ph, py). Ϫ 10: δ ϭ 1.79 (m, 2 H, PdCH2), 2.78 (m, 2 H,
CH2), 4.38 (pseudo t, NHP ϭ 4.6 Hz, 4 H, PCH2), 7.35Ϫ7.73 (m,
23 H, Ph, py). Ϫ 31P NMR (81 MHz, CH2Cl2): 9/10: δ ϭ 24.1 (s).
4: Yield 196 mg (0.242 mmol, 79%); pale-yellow solid; m.p. 205 °C
(dec.). Ϫ C35H35B2F8NP2Pd (811.64): calcd. C 51.79, H 4.35, N
1.73; found C 51.56, H 4.20, N 1.63. Ϫ 1H NMR (200 MHz,
CD2Cl2): δ ϭ 1.69 (br. d, JHH ϭ 3.6 Hz, 6 H, CH3), 4.83 (pseudo
t, NHP ϭ 5.2 Hz, 4 H, CH2), 5.97 (br. q, 2 H, ϭCH), 7.50 (d, JHH ϭ
1
12/13: Yield 82 mg (92% based on Pd); orange-yellow solid. Ϫ H
7.8 Hz, 2 H, py-3,5), 7.71 (m, 12 H, Ph), 7.83Ϫ8.03 (m, 9 H, py, NMR (200 MHz, CDCl3): 12: δ ϭ 0.81 (d, JHH ϭ 6.0 Hz, 3 H,
Ph). Ϫ 13C NMR (50 MHz, CD2Cl2): δ ϭ 17.5 (s, CH3), 44.2 CH3), 2.01 (m, 2 H, PdCH2), 3.66 (m, 1 H, CH), 4.44 (pseudo t,
(pseudo t, NCP ϭ 14.8 Hz, PCH2), 110.8 (s, ϭCH), 124.8 (br, py-
NHP ϭ 4.6 Hz, 4 H, PCH2), 7.15Ϫ7.75 (m, 23 H, Ph, py). Ϫ 13:
3,5), 131.2 (pseudo t, NCP ϭ 5.6 Hz, Phm), 134.7 (s, Php), 134.9 δ ϭ 1.17 (d, JHH ϭ 4 Hz, 3 H, CH3), 2.01 (m, 2 H, PdCH2), 3.65
(pseudo t, NCP ϭ 7.5 Hz, Pho), 144.2 (s, py-4), 160.4 (br, py-2,6).
31P NMR (CH2Cl2, 81 MHz): δ ϭ 45.3 (s).
(m, 1 H, CH), 4.44 (pseudo t, NHP ϭ 4.6 Hz, 4 H, PCH2),
7.15Ϫ7.75 (m, 23 H, Ph, py). Ϫ 31P NMR (81 MHz, CH2Cl2): 12/
13: δ ϭ 22.3 (s), 23.7 (s).
Ϫ
5: Yield 211 mg (0.260 mmol, 85%); pale-yellow solid.
Ϫ
Reductive Degradation with NaBH4: To a suspension of 20 mg of
the appropriate product mixture (9/10 or 12/13) in [D8]THF (0.7
mL), cooled in an ice-bath, was added excess NaBH4. After stirring
for 1 h at room temperature, the dark-brown solution was filtered
C35H35B2F8NP2Pd (811.64): calcd. C 51.79, H 4.35, N 1.73; found
C 51.50, H 4.16, N 1.60. Ϫ 1H NMR (400 MHz, CD2Cl2): δ ϭ
1.47 (br. d, JHH ϭ 3.6 Hz, 6 H, CH3), 4.76 (d pseudo t, NHP
5.6 Hz, JHH ϭ 17.4 Hz, 2 H, PCHaHb), 5.14 (d pseudo t, NHP
ϭ
ϭ
1
and the filtrate was analyzed by H NMR spectroscopy.
4.6 Hz, JHH ϭ 17.4 Hz, 2 H, PCHaHb), 5.86 (br. m, 2 H, ϭCH),
7.67Ϫ8.00 (m, 22 H, Ph, py), 8.11 (t, JHH ϭ 8.0 Hz, 1 H, py-4). Ϫ
13C NMR (100 MHz, CD2Cl2): δ ϭ 19.1 (s, CH3), 43.7 (pseudo t,
[Pd(PNP)(OH)]BF4 (11): A mixture of 7 (100 mg, 0.129 mmol) and
2 equiv. of NaHCO3 in CH2Cl2 (5 mL) was stirred for 1.5 h. The
mixture was then filtered and the product was precipitated from
the filtrate by the dropwise addition of diethyl ether. The orange-
yellow solid was collected by filtration, washed with diethyl ether,
and dried in vacuo. Yield 85 mg (124 mmol, 96%). Ϫ 1H NMR
(200 MHz, CD2Cl2): δ ϭ 4.21 (pseudo t, NHP ϭ 4.4 Hz, 4 H,
PCH2), 7.15Ϫ7.75 (m, 23 H, Ph, py). Ϫ 31P NMR (81 MHz,
CH2Cl2): δ ϭ 22.3 (s).
NCP ϭ 14.1 Hz, PCH2), 107.8 (s, ϭCH), 124.6 (pseudo t, NCP
ϭ
5.3 Hz, py-3,5), 124.7 (pseudo t, NCP ϭ 27.1 Hz, Phi), 125.5
(pseudo t, NCP ϭ 26.1 Hz, PhiЈ), 130.5 (br, Phm), 133.1 (pseudo t,
NCP ϭ 5.3 Hz, Pho), 134.3 (s, Php), 134.3 (PhoЈ), 134.4 (s, PhpЈ),
144.2 (s, py-4), 160.3 (br, py-2,6). Ϫ 31P NMR (CH2Cl2, 81 MHz):
δ ϭ 45.5 (s).
6. ؊ Method A: According to the general procedure: yield 235 mg
(0.251 mmol, 82%), ivory-colored solid. Ϫ Method B: To a solution
of 1 (150 mg, 0.191 mmol) in CH2Cl2 (5 mL) was added ca. 10
equiv. of norbornene (2 mmol). After stirring the mixture for 1 h,
the product was precipitated by the dropwise addition of diethyl
ether. The solid was filtered off, washed three times with diethyl
ether, and dried in vacuo. Yield 175 mg (0.187 mmol, 98%). Ϫ
C38H37B2F8NP2Pd·CH2Cl2 (934.63): calcd. C 50.12, H 4.21, N
1.50; found C 49.80, H 4.03, N 1.39. Ϫ 1H NMR (200 MHz,
CD2Cl2): δ ϭ 0.77 (m, 1 H, norbornene), 1.34 (m, 1 H, norbor-
Reactions of [Pd(PNP)(CHRCHRЈ)](BF4)2 (1؊5) with MeOH. ؊
General Procedure: To a solution of 1؊5 (100 mg) in MeOH (2
mL) cooled to 0 °C were added an excess of the appropriate olefin
and 2 equiv. of NaHCO3. The mixture was stirred for 3 h, the
precipitate was filtered off, and the solvent was removed under re-
duced pressure. A beige solid was obtained in each case, which was
recrystallized from CH2Cl2/diethyl ether.
[Pd(PNP)(CH2CH2OMe)]BF4
(14):
Yield
85%.
Ϫ
nene), 1.55 (br, 4 H, norbornene), 1.94 (br, norbornene), 4.92 (t, C34H34BF4NOP2Pd (727.82): calcd. C 56.11, H 4.71, N 1.93; found
426 Eur. J. Inorg. Chem. 2001, 419Ϫ429

Dicationic Palladium(II) Complexes
FULL PAPER
C 55.73, H 4.73, N 1.82. Ϫ 1H NMR (200 MHz, CD2Cl2): δ ϭ
Reaction of 3 with Me2NH: Two NMR tubes were prepared, each
2.00 (m, 2 H, PdCH2), 2.85 (s, 3 H, OCH3), 3.10 (m, 2 H, CH2), containing a solution of 3 (8 mg) in CD2Cl2 (0.6 mL) with 4 equiv.
1
4.43 (pseudo t, NHP ϭ 4.6 Hz, 4 H, PCH2), 7.48Ϫ7.94 (m, 23 H, of gaseous Me2NH. A H NMR spectrum was recorded immedi-
Ph, py). Ϫ 31P NMR (81 MHz, CH2Cl2): δ ϭ 24.4 (s).
ately after the addition of the amine.
[Pd(PNP){CH2CH(Me)OMe}]BF4
(16):
Yield
86%.
Ϫ
[(PNP)PdCH2CH(Ph)NMe2]؉ (22): NMR: δ ϭ 1.68 [s, 6 H,
N(CH3)2], 2.28 (m, 1 H, PdCH2), 2.48 (m, 1 H, PdCH2), 3.44 (m,
1 H, CH), 4.37 (pseudo t, 4 H, NHP ϭ 4.4 Hz, PCH2), 6.55 (d, 2
C35H36BF4NOP2Pd · CH2Cl2 (826.73): calcd. C 52.30, H 4.63, N
1.69; found C 51.26, H 4.46, N 1.62. Ϫ 1H NMR (400 MHz,
CD2Cl2): δ ϭ 0.68 (d, JHH ϭ 5.9 Hz, 3 H, CH3), 1.67 (m, 1 H, H, JHH ϭ 8.2 Hz, Ph), 7.06 (m, 3 H, Ph), 7.53Ϫ7.98 (m, 23 H,
PdCH2), 2.20 (m, 1 H, PdCH2), 2.74 (s, 3 H, OCH3), 3.05 (m, 1 PPh, py). Ϫ For the reductive degradation, an excess of NaBH4
H, CH), 4.28Ϫ4.40 (m, 4 H, PCH2), 7.50Ϫ7.68 (m, 22 H, Ph, py), (dissolved in a drop of CD3OD) was added instantly to one of the
1
7.91 (t, JHH ϭ 7.8 Hz, 1 H, py-4).
two solutions. After 20 min, its H NMR spectrum was recorded
again, which now featured signals due to CH3CH(Ph)NMe2. Ϫ The
second sample was again analyzed by H NMR after 1 h.
[Pd(PNP){CH2CH(Ph)OMe}]BF4 (17): Yield 80%. Ϫ 1H NMR
(200 MHz, CD2Cl2): δ ϭ 2.00 (m, 1 H, PCH2), 2.19 (m, 1 H,
1
PdCH2), 2.65 (s, 3 H, OCH3), 3.78 (m, 1 H, CH), 4.41 (m, PCH2), [(PNP)PdCH(Ph)CH2NMe2]؉ (23): NMR: δ ϭ 1.89 [s, 6 H,
6.84 (m, 2 H, CPh), 7.12 (m, 3 H, CPh), 7.49Ϫ7.95 (m, 23 H, PPh, N(CH3)2], 2.48 (m, 1 H, NCH2), 2.68 (m, 1 H, PdCH), 3.98 (m, 1
py). Ϫ 31P NMR (81 MHz, CH2Cl2): δ ϭ 24.7 (s).
H, NCH2), 4.26 (d pseudo t, NHP ϭ 4.6 Hz, JHH ϭ 17 Hz, 2 H,
PCHaHb), 4.40 (d pseudo t, NHP ϭ 4.4 Hz, JHH ϭ 17 Hz, 2 H,
PCHaHb), 6.41 (d, JHH ϭ 7 Hz, 2 H, Ph), 6.87 (m, 3 H, Ph),
7.50Ϫ7.92 (m, 23 H, PPh, py). Ϫ After treatment of the solution
with NaBH4 (CD3OD) as described above, the signals of
PhCH2CH2NMe2 were detectable.
[Pd(PNP){CH(Me)CH(Me)OMe}]BF4 [18a, obtained from (Z)-2-
1
butene]: Yield 83%. Ϫ H NMR (200 MHz, CD2Cl2): δ ϭ 0.82 (d,
JHH ϭ 5.6 Hz, 3 H, CH3), 0.92 (m, 3 H, CH3), 2.74 (m, 2 H,
CHϪCH), 2.92 (s, 3 H, OCH3), 4.31 (pseudo t, NHP ϭ 4.2 Hz, 4
H, PCH2), 7.44Ϫ7.95 (m, 23 H, Ph, py). Ϫ 31P NMR (81 MHz,
CH2Cl2): δ ϭ 21.8 (s).
Reaction of 2 with 4 Equiv. of Me2NH: The reaction was carried
out in an NMR tube in a similar manner as described for the reac-
tion of 3 with Me2NH.
[Pd(PNP){CH(Me)CH(Me)OMe}]BF4 [18b, obtained from (E)-2-
1
butene]: Yield 81%. Ϫ H NMR (200 MHz, CD2Cl2): δ ϭ 0.93 (d,
J
HH ϭ 5.4 Hz, 3 H, CH3), 1.04 (m, 3 H, CH3), 2.72 (s, 3 H, OCH3), [(PNP)PdCH2CH(Me)NMe2]؉ (21): 1H NMR (200 MHz,
2.74 (m, 2 H, CHϪCH), 4.35 (m, 4 H, PCH2), 7.45Ϫ7.93 (m, 23
H, Ph, py).
CD2Cl2): δ ϭ 0.70 (d, JHH ϭ 6.2 Hz, 3 H, CH3), 1.85 (m, 1 H,
PdCH2), 1.97 (s, 6 H, NCH3), 2.05 (m, 1 H, PdCH2), 2.62 (m, 1
H, CH), 4.48 (pseudo t, NHP ϭ 4.6 Hz, 4 H, PCH2), 7.57Ϫ7.98 (m,
23 H, Ph, py).
Reductive Degradation of 16 and 17 with NaBH4: To a solution of
20 mg of compound 16 or 17 in CD3OD (0.7 mL), cooled in an
ice-bath, was added excess NaBH4. After stirring for 1 h at room
temperature, the dark-brown solution was filtered and the filtrate
[(PNP)PdCH(Me)CH2NMe2]؉ (24): 1H NMR (200 MHz,
CD2Cl2): δ ϭ 1.02 (d pseudo t, JHH ϭ 7.0 Hz, NHP ϭ 3 Hz, 3 H,
was analyzed by 1H NMR spectroscopy. Ϫ 1H NMR: CH3CH(Me)- CH3), 1.84 (s, 6 H, NCH3), 4.36 (pseudo t, NHP ϭ 4.4 Hz, 4 H,
OCD3: δ ϭ 1.14 (d, JHH ϭ 6.2 Hz, 6 H, CH3), 3.50 (sept, JHH
6.2 Hz, 1 H, CH).; CH3CH(Ph)OCD3: δ ϭ 1.41 (d, JHH ϭ 6.1 Hz,
3 H, CH3), 4.34 (q, JHH ϭ 6.1 Hz, 1 H, CH), 7.28 (m, 5 H, Ph).
ϭ
PCH2), 7.55Ϫ8.02 (m, 23 H, Ph, py). The remaining signals for
CH and CH2 are overlapped with the signals due to 21.
[Pd(PNP)(PhNH2)](BF4)2 (25): To a solution of 1 (100 mg) in
CH2Cl2 (3 mL) was added aniline (0.5 mL). After stirring for a few
minutes, an ivory-colored solid crystallized, which was collected by
filtration, washed three times with diethyl ether, and dried in vacuo.
Yield 85%. Ϫ C37H34B2F8N2P2Pd·0.75CH2Cl2 (912.27): calcd. C
49.70, H 3.92, N 3.07; found C 49.79, H 3.91, N 3.14. Ϫ 1H NMR
(200 MHz, CD2Cl2): δ ϭ 4.59 (pseudo t, NHP ϭ 4.8 Hz, 4 H,
PCH2), 5.70 (br, 2 H, NH2), 6.67 (d, JHH ϭ 7.6 Hz, 2 H, NPh),
Treatment of 14, 16؊18a,b with HCl: Gaseous HCl was bubbled
through solutions of 14, 16؊18a,b in CD2Cl2, which led to a color
change from orange to yellow. The H NMR spectra of these solu-
1
tions were found to feature signals attributable to both the free
olefin and [Pd(PNP)Cl]ϩ.
[Pd(PNP)(MeOH)](BF4)2 (15): Compound 1 (100 mg) was dis-
solved in MeOH (5 mL) and the solvent was removed under re-
duced pressure. This procedure was repeated twice more. Finally,
the yellow solid was washed with diethyl ether and dried in vacuo.
Yield 95%. Ϫ 1H NMR (200 MHz, CD2Cl2): δ ϭ 3.17 (br, 1 H,
6.89 (m, 3 H, NPh), 7.55Ϫ7.80 (m, 22 H, Ph, py), 7.88 (t, JHH
ϭ
7.6 Hz, 1 H, py-4).
Reactions of 25 with Ethylene and Propene: A solution of 24 (8
OH), 3.38 (s, 3 H, CH3), 4.49 (pseudo t, NHP ϭ 4.6 Hz, 4 H, PCH2), mg) in CD2Cl2/CD3NO2 (6:1) (0.6 mL) was saturated with either
7.48Ϫ8.01 (m, 23 H, Ph, py).
ethylene or propene. Since the signals of the addition products ap-
pear in the spectra at relatively low intensity and are partly over-
lapped by the signals of 25, the full set of signals could not be de-
tected.
Reactions of 19 with Ethylene and Propene: Solutions of 19 (3 mg)
in CD2Cl2 (0.6 mL) were saturated with ethylene and propene, re-
spectively.
[(PNP)PdCH2CH2NH2Ph]2؉ (25؊H؉): NMR: δ ϭ 2.12 (m, 1 H,
PdCH2), 3.28 (m, 1 H, NCH2), 4.47 (pseudo t, NHP ϭ 4.8 Hz, 4
H, PCH2).
[(PNP)PdCH2CH2NHMe2]2؉ (20؊H؉): NMR: δ ϭ 1.82 (m, 2 H,
PdCH2), 2.28 (s, 6 H, NMe2), 2.79 (m, 2 H, NCH2), 4.52 (pseudo
t, NHP ϭ 5.0 Hz, 4 H, PCH2), 7.48Ϫ8.02 (m, 23 H, Ph, py).
[(PNP)PdCH2CH(Me)NH2Ph]2؉ (26؊H؉): NMR: δ ϭ 0.92 (d,
JHH ϭ 6.0 Hz, 3 H, CH3).
[(PNP)PdCH2CH(Me)NHMe2]2؉ (21؊H؉): NMR: δ ϭ 0.82 (d,
JHH ϭ 6.2 Hz, 3 H, CH3), 1.79 (m, 1 H, PdCH2), 1.92 (m, 1 H,
PdCH2), 2.15 (s, 3 H, NCH3), 2.22 (s, 3 H, NCH3), 2.89 (m, 1 H, Preparation of [Pd(PNP)(CH2CHRNHAr)](BF4)2 (26, 28؊34) ؊
CH), 4.56 (pseudo t, NHP ϭ 4.6 Hz, 4 H, PCH2), 7.55Ϫ8.02 (m, 23
H, Ph, py).
General Procedure: A solution of 1 or 2 (100 mg) in CH2Cl2 (2 mL)
was cooled to 0 °C and saturated with the appropriate olefin; 2
Eur. J. Inorg. Chem. 2001, 419Ϫ429
427

C. Hahn, P. Morvillo, A. Vitagliano
FULL PAPER
equiv. of NaHCO3 and 4 equiv. of ArNH2 were then added. After
stirring the mixture for 3 h, the precipitate was filtered off and the
filtrate was concentrated to dryness under reduced pressure. A
beige solid was obtained, which was recrystallized from CH2Cl2/
diethyl ether.
7.0 Hz, 1 H, NC6H4Cl), 6.73 (t, JHH ϭ 7.8 Hz, 1 H, NC6H4Cl),
7.09 (d, JHH ϭ 8 Hz, 1 H, NC6H4Cl), 7.44Ϫ7.85 (m, 23 H, PPh,
py).
Reaction of 26 with 1: To a solution of 26 (7 mg) in CD2Cl2 (0.6
mL) saturated with ethylene, 1 (8 mg) was added, which led to a
color change to reddish. An excess of NaHCO3 was added and the
mixture was stirred overnight, after which it had become yellow.
[Pd(PNP)(CH2CH2NHPh)]BF4
(26):
Yield
87%.
Ϫ
C39H37BF4N2P2Pd·0.5CH2Cl2 (831.31): calcd. C 57.07, H 4.60, N
3.37; found C 56.72, H 4.58, N 3.26. Ϫ 1H NMR (200 MHz,
CD2Cl2): δ ϭ 2.09 (m, 2 H, PdCH2), 2.93 (br, 2 H, CH2N), 3.41
(br, 1 H, NHPh), 4.43 (pseudo t, NHP ϭ 4.6 Hz, 4 H, PCH2), 5.98
(d, JHH ϭ 7.6 Hz, 2 H, NPho), 6.54 (t, JHH ϭ 7.4 Hz, 1 H, NPhp),
6.92 (t, JHH ϭ 7.4 Hz, 2 H, NPhm), 7.53Ϫ7.88 (m, 22 H, Ph, py),
7.94 (t, JHH ϭ 7.2 Hz, 1 H, py-4). Ϫ 31P NMR (81 MHz, CH2Cl2):
δ ϭ 23.8 (s).
27: 1H NMR (200 MHz): δ ϭ 1.74 (m, 4 H, PdCH2), 2.78 (t br,
J ϭ 7.8 Hz, 4 H, CH2N), 4.35 (pseudo-t, NHP ϭ 4.8 Hz, 8 H,
PCH2), 5.73 (d, JHH ϭ 8.0 Hz, 2 H, NPho), 6.33 (t, JHH ϭ 7.2 Hz,
1 H, NPhp), 6.62 (t, JHH ϭ 7.2 Hz, 1 H, NPhm), 7.41Ϫ7.96 (m, 46
H, Ph, py).
Equilibrium Constant Determinations: The equilibrium constants
for the exchange and addition reactions were determined by 1H
NMR analysis of equilibrium mixtures at 298 K (methanol addi-
tion reactions) or 283 K (all other cases) in CD2Cl2 or CD2Cl2/
CD3NO2 (4:1) solution (c ϭ 7Ϫ15 m). With one exception (addi-
tion of Me2NH to propene complex 2), the reported values are the
average result of three measurements run at different olefin or li-
gand concentrations. Very unbalanced exchange equilibria [e.g.
Equation (11)] were handled by treating a solution of the most
stable complex with a large excess of the exchanging ligand. The
amine addition equilibria (olefin ‘‘insertion’’[23]) were handled by
treating a solution of the pure [Pd(PNP)(amine)](BF4)2 complex
(19 or 25) with an excess of the olefin. In this approach, the amount
of free amine in the solution was made negligible and hence the
simultaneous occurrence of proton-transfer equilibria to the free
base could also be neglected. For the ligand-exchange reactions
solutions (0.015 ) of 2؊5 [Equation (3)], 1 [Equation (4), L ϭ
H2O], and 25 [Equation (11]) were prepared and treated with an
excess of the appropriate substituting ligand. In the case of the
ethylene/MeCN exchange [Equation (4)], a solution of 8 was
treated with a large excess of ethylene. The equilibrium constant
for the PhNH2/Me2NH exchange [Equation (12)] could not be de-
termined directly because of an overlapping of all the relevant sig-
nals of the four species. Therefore, the constants of two further
auxiliary equilibria were measured, involving the exchanges pyrid-
ine/Me2NH (K ϭ 1 in CD2Cl2) and PhNH2/pyridine (K ϭ 4·10Ϫ4
in CD2Cl2/CD3NO2).
[Pd(PNP)(CH2CH2NHC6H4OMe-p)]BF4 (29): Yield 80%. Ϫ 1H
NMR (200 MHz, CDCl3): δ ϭ 2.05 (m, 2 H, PdCH2), 2.86 (br, 2
H, NCH2), 3.07 (br, 1 H, NH), 3.68 (s, 3 H, CH3) 4.45 (pseudo t,
NHP ϭ 4.8 Hz, 4 H, PCH2), 5.95 (d, JHH ϭ 9.2 Hz, 2 H, NC6H4),
6.54 (d, JHH ϭ 9.2 Hz, 2 H, NC6H4), 7.50Ϫ7.82 (m, 23 H, Ph, py).
Ϫ
31P NMR (81 MHz, CH2Cl2): δ ϭ 23.6 (s).
[Pd(PNP)(CH2CH2NHC6H4Me-p)]BF4 (30): Yield 84%. Ϫ 1H
NMR (200 MHz, CDCl3): δ ϭ 2.05 (m, 2 H, PdCH2), 2.15 (s, 3 H,
CH3), 2.89 (br, 2 H, NCH2), 3.19 (br, 1 H, NH), 4.44 (pseudo t,
NHP ϭ 4.6 Hz, 4 H, PCH2), 5.80 (d, JHH ϭ 8.2 Hz, 2 H, NC6H4),
6.73 (d, JHH ϭ 8.2 Hz, 2 H, NC6H4), 7.49Ϫ7.74 (m, 23 H, Ph, py).
Ϫ
31P NMR (81 MHz, CH2Cl2): δ ϭ 23.6 (s).
[Pd(PNP)(CH2CH2NHC6H4Cl-m)]BF4 (31): Yield 81%. Ϫ 1H
NMR (200 MHz, CDCl3): δ ϭ 2.03 (m, 2 H, PdCH2), 2.79 (br, 2
H, CH2N), 3.50 (br, 1 H, NH), 4.45 (pseudo t, NHP ϭ 4.2 Hz, 4
H, PCH2), 5.88 (m, 2 H, NC6H4Cl), 6.48 (d, JHH ϭ 8.2 Hz, 1 H,
NC6H4Cl), 6.81 (t, JHH ϭ 8.4 Hz, 1 H, NC6H4Cl), 7.52Ϫ7.72 (m,
23 H, Ph, py). Ϫ 31P NMR (81 MHz, CH2Cl2): δ ϭ 23.6 (s).
[Pd(PNP)(CH2CH2NHC6H4Cl-o)]BF4 (32): Yield 81%.
Ϫ
C39H36BF4N2P2Pd · 1.5 CH2Cl2 (950.68): calcd. C 51.11, H 4.13,
N 2.94; found C 50.76, H 4.01, N 2.86. Ϫ 1H NMR (200 MHz,
CDCl3): δ ϭ 2.09 (m, 2 H, PdCH2), 2.94 (br, 2 H, CH2N), 4.03 (br
t, JHH ϭ 5.0 Hz, 1 H, NH), 4.46 (pseudo t, NHP ϭ 4.8 Hz, 4 H,
PCH2), 5.78 (d, JHH ϭ 8.0 Hz, 1 H, NC6H4Cl), 6.48 (d, JHH
ϭ
7.8 Hz, 1 H, NC6H4Cl), 6.78 (t, JHH ϭ 8.0 Hz, 1 H, NC6H4Cl),
7.11 (d, JHH ϭ 7.8 Hz, 1 H, NC6H4Cl), 7.46Ϫ7.83 (m, 23 H, Ph,
py).
Acknowledgments
[Pd(PNP){CH2CH(Me)NHPh}]BF4 (28): Yield 83%. Ϫ 1H NMR
(250 MHz, CD2Cl2): δ ϭ 0.84 (d, JHH ϭ 6.3 Hz, 3 H, CH3), 1.94
(m, 1 H, CH2), 2.20 (m, 1 H, CH2), 3.12 (d, JHH ϭ 9.1 Hz, 1 H,
NH), 3.27 (m, 1 H, CH), 4.39 (pseudo t, NHP ϭ 4.7 Hz, 4 H,
PCH2), 5.87 (d, JHH ϭ 7.8 Hz, 2 H, NPh), 6.53 (t, JHH ϭ 7.5 Hz,
1 H, NPh), 6.87 (t, JHH ϭ 7.8 Hz, 2 H, NPh), 7.48Ϫ7.75 (m, 22
H, PPh, py-3,5), 7.95 (t, 1 H, py-4).
We thank the Deutsche Akademie der Naturforscher Leopoldina
(BMBF-LPD 9801-4) (C. H.) and the MURST (PRIN
9803243241) for financial support. We also thank the CIMCF, Un-
`
iversita di Napoli ‘‘Federico II’’ for providing access to NMR facil-
ities. We are grateful to Prof. D. Steinborn for helpful discussions.
[1] [1a]
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1
[Pd(PNP){CH2CH(Me)NHC6H4Me-p}]BF4 (33): Yield 86%. Ϫ H
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NMR (200 MHz, CD2Cl3): δ ϭ 0.83 (d, JHH ϭ 7.0 Hz, 3 H, CH3),
1.92 (m, 1 H, CH2), 2.15 (s, 3 H, CH3) 2.20 (m, 1 H, CH2), 2.96
(d, JHH ϭ 9.0 Hz, 1 H, NH), 3.24 (m, 1 H, CH), 4.38 (pseudo-t,
NHP ϭ 4.5 Hz, 4 H, PCH2), 5.82 (d, JHH ϭ 7.1 Hz, 2 H, NC6H4),
6.71 (d, JHH ϭ 7.1 Hz, 2 H, NC6H4), 7.50Ϫ7.95 (m, 23 H, PPh, py).
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1.89 (m, 1 H, CH2), 2.21 (m, 1 H, CH2), 3.27 (m, 1 H, CH), 3.93
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ϭ
428
Eur. J. Inorg. Chem. 2001, 419Ϫ429

Dicationic Palladium(II) Complexes
FULL PAPER
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The 1H NMR spectrum of 16 shows three multiplets (1 H each)
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which can be assigned to the ϪCH2CH(Me)Ϫ fragment, the
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the CHPh fragment to which the methoxy group is bound.
The best way of establishing the stereochemistry of the addition
would be an X-ray structure determination of either 18a or
18b, but as yet we have been unable to obtain suitable crystals
of the complexes. The methine HϪH coupling constants (7.1
and 9.1 Hz, respectively, in CD3OD) could also be useful for
this purpose, but only in conjunction with a detailed theoretical
study aimed at establishing the conformational distribution of
the species. To be reliable, such a QM/MM investigation should
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Dicationic PdII complexes of the chelating olefin 1,5-cyclo-
[7a]
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R. Roulet, R. Vouillamoz,
[7b]
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A. J. Canty, in: Comprehensive Organometallic Chemistry II
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[23]
[11]
C. Hahn, A. Vitagliano, unpublished results.
The term ‘‘insertion’’ refers only to the formal outcome of the
reaction and does not have any mechanistic implication. It is
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[13]
[14]
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M. Herberhold, in: Metal π-Complexes, Elsevier Science
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429