Palladium(0)-olefin complexes with potentially terdentate nitrogen-sulfur ligands. the role of the chelate in the olefin exchange path

Article abstract of DOI:10.1016/S0022-328X(00)00870-6

The synthesis and the reactivity of Pd(0) olefin complexes [Pd(η²-olefin)(SNS)] and [Pd(η²-olefin)(NSN)] containing potentially terdentate nitrogen-sulfur ligands were studied. The presence of a potentially coordinating atom in the environment of the metal, influences strongly the fluxional behavior in solution but not the overall reactivity with respect to olefin exchange and thermodynamic stability which is very close to that of the corresponding bidentate nitrogen-sulfur complexes. The intimate mechanism of olefin exchange also involves a path promoted by the third dangling coordinating atom which induces olefin dissociation and stabilizes the ensuing Pd(0) three-coordinated species.

Full text of DOI:10.1016/S0022-328X(00)00870-6

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 622 (2001) 155–165
Palladium(0)–olefin complexes with potentially terdentate
nitrogen–sulfur ligands. The role of the chelate in the olefin
exchange path
Luciano Canovese *, Fabiano Visentin, Gavino Chessa, Graziano Gardenal,
Paolo Uguagliati
Dipartimento di Chimica, Uni6ersita’ di Venezia, Calle Larga Santa Marta 2137-30123 Venezia, Italy
Received 22 September 2000; accepted 7 November 2000
Abstract
The synthesis and the reactivity of Pd(0) olefin complexes [Pd(h2-olefin)(SNS)] and [Pd(h2-olefin)(NSN)] containing potentially
terdentate nitrogen–sulfur ligands were studied. The presence of a potentially coordinating atom in the environment of the metal,
influences strongly the fluxional behavior in solution but not the overall reactivity with respect to olefin exchange and
thermodynamic stability which is very close to that of the corresponding bidentate nitrogen–sulfur complexes. The intimate
mechanism of olefin exchange also involves a path promoted by the third dangling coordinating atom which induces olefin
dissociation and stabilizes the ensuing Pd(0) three-coordinated species. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Pallidium(0)–olefin complexes; Terdentate nitrogen–sulfur ligands; Olefin exchange path
1. Introduction
(tmetc) was involved [6]. Based on these and other
investigations [7] we concluded that comparatively sta-
ble species, while lending themselves to structural and
reactivity studies, are less useful as catalytic agents. In
searching for a reasonable compromise between stabil-
ity and reactivity, we devised to study palladium(0)
complexes of electron-deficient olefins and potentially
terdentate SꢀNꢀS or NꢀSꢀN pyridin-thioether ligands.
Indeed, these chelating agents are known to behave as
bidentate ligands imparting a degree of stability simi-
lar to that of analogous complexes with related, truly
bidentate chelating moieties [5g], while the dangling
uncoordinated arm induces a general fluxionality in
solution, liable to promote dissociation of the olefin
fragment and stabilization of the ensuing three-coordi-
nated palladium(0) species. Similar goals were sought
by other authors using different PꢀNꢀN hemilabile
ligands [8]. To the best of our knowledge, no sulphur–
nitrogen donor ligands have been studied so far to this
purpose. The complexes investigated and the olefins
employed are shown in Scheme 1 and Table 1.
Zero valent palladium complexes are assumed to be
intermediates in a number of stoicheiometric and cata-
lytic processes involving CꢀC or CꢀN bond formation,
such as cross-coupling [1], Heck [2], allyl alkylation [3]
and amination [4]. In spite of their great importance,
there is a paucity of studies on these species. As a part
of our systematic investigations on attacks on palla-
dium–allyl complexes by a variety of nucleophiles, we
often examined Pd(0) substrates containing different
ancillary ligands and electron poor olefins [4a,b,5]. In
this context, we determined the equilibrium constants
of olefin exchange between various metal substrates
and the rates of such exchange processes when the
hindered olefin tetramethylethylenetetracarboxylate
* Corresponding author. Tel.: +39-41-5298567/5298568; fax: +
39-41-5298517.
E-mail address: Cano@unive.it (L. Canovese).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00870-6

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L. Cano6ese et al. / Journal of Organometallic Chemistry 622 (2001) 155–165
with tmetc in CHCl3. The course of the reaction was
followed by UV–Vis spectrophotometric techniques in
the range 600–330 nm in the presence of a constant
excess of tmetc over the metal substrate ([Pd]0=1×
10−4 mol dm−3) in order to ensure pseudo-first order
conditions and to minimize the contribution of the
reverse reaction to the overall spectral changes. Under
these conditions the absorbance Dt obeys the mono-ex-
ponential rate law Dt=Dꢀ+(Do−Dꢀ)exp(−kobst)
where Do, Dꢀ and kobs are the initial, final absorbances
and the observed rate constants, respectively. The kobs
values, determined by non-linear regression where Do,
Dꢀ and kobs are the parameters to be optimized, fit the
expression
kobs=k1+k2[tmetc]
(1)
in the case of complexes [Pd(h2-nq)(SNS(R))] (R=i-Pr,
t-Bu,Ph) (Fig. 1).
In the case of [Pd(h2-nq)(SNS(Et))] and [Pd(h2-
nq)(NSN)] the expression which would fit better the
kobs values is:
kobs=k2[tmetc]
(2)
the intercept being statistically insignificant. With the
complex [Pd(h2-nq)(SNS(Me))] a general decomposi-
tion taking place in the reacting mixture prevents any
measurements.
Scheme 1.
2. Results and discussion
A suitable mechanism for fitting these results is
shown in Scheme 2, which also involves rate determin-
ing first-order formation of an olefin-free Pd(0) inter-
mediate I which subsequently reacts rapidly with tmetc
to yield the final olefin exchange product [Pd(h2-
tmetc)(SNS(R))]. Under the kinetic conditions pertain-
ing to data in Table 2, Scheme 2 reduces to Scheme 3
and will yield rate law Eq. (1). As for the nature of
intermediate I, we have no evidence to rule out the
presence of a solvent molecule in the coordination
sphere of the metal along with the terdentate ligand
SNS(R), even though a coordinatively unsaturated, sol-
vent-free three-coordinated species is not without prece-
dent [8].
2.1. Olefin exchange rates
The rates of olefin exchange in Pd(0) systems are in
general comparatively high and correspond to associa-
tive mechanisms. Thus, the reactions are sensitive to
steric hindrance, so that use of a sterically demanding
olefin such as tmetc will slow down the process to rate
values measured easily by customary spectrophotomet-
ric techniques. We have already exploited these features
to gain intimate mechanistic information on related
bidentate complexes [6]. We have now extended this
study to complexes containing the present potentially
terdentate ligands (see Scheme 1).
The occurrence of a first-order path k1, when observ-
able (Table 2), can be traced back to the capability of
the dangling arm bearing a coordinating atom in the
potentially terdentate ligands SNS(R) to stabilize an
The complexes [Pd(h2-nq)(SNS(R))] (R=Me, Et, i-
Pr, t-Bu, Ph) and [Pd(h2-nq)(NSN)] containing the
chromophoric olefin 1,4-naphthoquinone were reacted
Table 1
Complexes under study
[Pd(h2-ma)(SNS(Me))]
[Pd(h2-ma)(SNS(Et))]
[Pd(h2-ma)(SNS(i-Pr))]
[Pd(h2-ma)(SNS(t-Bu))]
[Pd(h2-ma)(SNS(Ph))]
[Pd(h2-ma)(NSN)]
[Pd(h2-nq)(SNS(Me))]
[Pd(h2-nq)(SNS(Et))]
[Pd(h2-nq)(SNS(i-Pr))]
[Pd(h2-nq)(SNS(t-Bu))]
[Pd(h2-nq)(SNS(Ph))]
[Pd(h2-nq)(NSN)]
[Pd(h2-fn)(SNS(Me))]
[Pd(h2-tmetc)(SNS(Et))]
[Pd(h2-tmetc)(SNS(i-Pr))]
[Pd(h2-tmetc)(SNS(t-Bu))]
[Pd(h2-tmetc)(SNS(Ph))]
[Pd(h2-tmetc)(NSN)]
[Pd(h2-fn)(SNS(Et))]
[Pd(h2-fn)(SNS(t-Bu))]
[Pd(h2-fn)(NSN)]
a
a Complex obtained from amination reaction of the corresponding allyl species (see text).

L. Cano6ese et al. / Journal of Organometallic Chemistry 622 (2001) 155–165
157
Fig. 1. Fit of kobs values to added tmetc concentration for the reaction [Pd(h2-nq)(SNS(R))]+tmetc=[Pd(h2-tmetc)(SNS(R))]+nq (R=i-Pr,
t-Bu, Ph) (Eq. (1)).
substituent on the SNS(R) ligand, which has proved
useful in analyzing analogous associative olefin ex-
changes. The k2 value for R=Ph arises apparently
from a balance of steric and favorable electronic effects
which renders this group comparable to the i-Pr sub-
olefin-free Pd(0) species [Pd(SNS(R))], possibly also
containing a coordinated solvent molecule. Consis-
tently, no independent k1 paths have been observed in
earlier works in which Pd(0) complexes with bidentate
NS ligands were examined [6].
The fact that the k1 term appears to be virtually
insensitive to the R substituent in the chelating ligand
might be taken as an indication that the k1 pathway is
dissociative in nature. However, the k1 term in rate law
Eq. (1) could not be detected for SNS(R) (R=Me, Et)
and NSN complexes. In the case of R=Me, extensive
decomposition prevents any measurement. In the case
of R=Et, the determination is plagued by a high
uncertainty due to decomposition side reactions. The
lack of a reliably measurable k1 term for the NSN
complex may be ascribed to the low tendency of this
ligand to behave as terdentate due to the unfavorable
position of the dangling pyridine nitrogen caused by the
tetrahedral sulfur hybridization. On the other hand the
k2 values in Table 2 parallel those obtained under
similar conditions in analogous reactions involving the
mentioned bidentate ligands as far as both the magni-
tude and the adverse effect of the steric demands of the
R group are concerned. The latter confirms the associa-
tive nature of the direct olefin exchange pathway (k2)
under study. A reasonable value for k2 in the case of
[Pd(h2-nq)(SNS(Me))] reacting with tmetc can be de-
duced by extrapolating the LFER plot of log k2 versus
the Beckhaus front strain parameter [9] for the R
Scheme 2.
Table 2
First and second order rate constants for olefin exchange reactions
with tmetc in CHCl3 at 25°C
Complex
k1 (s−1
)
k2 (dm3 mol−1 s−1
)
[Pd(h2-nq)(SNS(Me))]
[Pd(h2-nq)(SNS(Et))]
33 a
992
[Pd(h2-nq)(SNS(i-Pr))] 3.8×10−494×10−5 0.6890.01
[Pd(h2-nq)(SNS(t-Bu))] 4.1×10−493×10−5 0.07490.004
[Pd(h2-nq)(SNS(Ph))] 1.2×10−391×10−3 0.990.1
[Pd(h2-nq)(NSN)]
15.390.4
a Extrapolated value from the linear regression of log k2 versus S
(Beckhaus Front Strain parameter) see text.

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L. Cano6ese et al. / Journal of Organometallic Chemistry 622 (2001) 155–165
by the use of an excess of both reacting olefins, tmetc
and nq, where upon the equilibria involving the olefin-
free intermediate I are suppressed ([Pd]0=1×10−4
,
[tmetc]=1.04×10−3–4.04×10−3, [nq]0=1.3×10−3
mol dm−3, u=410 nm). Under these conditions the
pseudo first-order rate constants kobs fit the linear rela-
tionship (Fig. 3)
k
obs=k−2[nq]0+k2[tmetc]
(4)
Scheme 3.
The k2 and k−2 values obtained by linear regression
according to Eq. (4) are 0.7190.04 and 1.61 90.02
mol−1 dm3 s−1, respectively. The resulting k2 parame-
ter is in very good agreement with the value reported in
Table 2 which was determined from Eq. (1). The ratio
k2/k−2=Kequil (0.4490.03) is close to unity, similar to
those measured in the analogous way for bidentate
NS(R) ligands [6b]. This confirms earlier views that the
two Pd(0)–olefin complexes involved in the exchange
stituent. Fig. 2 shows the LFER plot of log k2 versus
the front strain parameter of R for SNS(R) ligands [6b].
We have also studied kinetically the approach to
equilibrium for the reaction
[Pd(h2−nq)(SNS(i−Pr))]
k
2
+tmetc X [Pd(h2−tmetc)(SNS(i−Pr))]+nq
(3)
k
−2
Fig. 2. LFER between log k2 for alkyl-substituted ancillary ligand complexes and Beckhaus front strain parameter of R alkyl substituent.
Fig. 3. Fit of kobs to added tmetc concentration under pseudo-first order conditions for both direct and reverse paths of reaction (3).

L. Cano6ese et al. / Journal of Organometallic Chemistry 622 (2001) 155–165
159
Fig. 4. Non-linear fit of absorbance to entering olefin concentration for KE determination for reaction (5) in acetone at 298 K (R=i-Pr).
have similar stability as far as this is governed by the
electron-withdrawing ability of the olefin substituents,
with the bidentate or terdentate ligand hardly affecting
this feature.
[nq]+[ol]=[nq]0+[ol]0
[nq]=[nq]0+[2]
Dl=m1[1]+m2[2]
The parameters to be optimized were KE and m2.The
latter was either held constant at the experimentally
accessible value (from the spectrum of complex 2 inde-
pendently prepared) or allowed to float during the
iterative process. In the latter case, the final optimized
value turned out to coincide with that determined di-
rectly (Fig. 4). The KE values are also listed in Table 3.
As can be seen, the KE values in both solvents cover
a narrow range, spanning at most one order of magni-
tude. The complexes in acetone appear to be somewhat
leveled off. The complexes with ma are in general more
stable (KE\1) than those of nq, thanks to the higher
electron-withdrawing ability of the former olefin. This
behavior is in agreement with our previous findings
2.2. Olefin substitution equilibrium constants
Equilibrium constants for the reactions
K
E
[Pd(h2−nq)(LL%L)]+ol X [Pd(h2−ol)(LL%L)]+nq
1
2
where LL%L=SNS(R), ol=ma or NSN, ol=ma, fn
(5)
in CHCl3 or acetone were determined by recording
spectral changes in the range 300–600 nm of mixtures
obtained by adding appropriate microaliquots of solu-
tions of ol to a solution of 1 ([Pd]0 ca. 1×10−4 mol
dm−3) in the thermostatted cell compartment of the
spectrophotometer. Acetone was also chosen as the
solvent since in CHCl3 decomposition takes place in
some cases. The equilibria were rapidly established.
Absorbance data were analyzed at 410 nm in the case
of SNS(R) derivatives and at 400 nm in the case of
[Pd(h2-nq)(SNS)] complex where the change in ab-
sorbance was the largest and the olefins ol and nq do
not absorb appreciably.
Table 3
Equilibrium constant (KE) for the reaction (5) at 25°C in CHCl3
a
a
Complex
KE in
KE in CHCl3
CH3COCH3
[Pd(h2-nq)(SNS(Me))]
[Pd(h2-nq)(SNS(Et))]
[Pd(h2-nq)(SNS(i-Pr))]
[Pd(h2-nq)(SNS(t-Bu))]
[Pd(h2-nq)(SNS(Ph))]
4.990.2
5.290.3
13.190.5
1491
Decomposition
11.590.6
2293
5392
Decomposition
Under these conditions abstract factor analysis [10]
of the observed spectral changes indicated that at most
two independently absorbing species were present, i.e.
complexes 1 and 2.The absorbance data Dl were fitted
by non-linear least squares according to the model
7.290.2
Entering olefin
[Pd(h2-nq)(NSN)]
ma
fn
1192
3.590.5
KE=[2][nq]/[1][ol]
[Pd]tot=[1]+[2]
a Entering olefin: ma.

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L. Cano6ese et al. / Journal of Organometallic Chemistry 622 (2001) 155–165
Fig. 5. 1H-NMR spectra of [Pd(h2-tmetc)(NSN)] at 178 (5a) and 298 K (5b) in CDCl3.
about olefin exchange in Pd(0) complexes with a-di-
imines and pyridinthioethers. The equilibrium constants
for terdentate ligand complexes are fairly close to those
for exchange of the same olefins in analogous bidentate
systems, indicating that the governing factor affecting
the thermodynamic stability of these Pd(0) olefin com-
plexes is the relative electron-withdrawing properties of
the olefins involved, the nature and potential behavior
of the chelating ancillary ligands playing only a minor
role.
These findings were confirmed also in the case of the
[Pd(h2-nq)(NSN)] complex. The olefin exchange equi-
libria were determined in this case only in CHCl3,
thanks to the stability of the substrate, using ma and fn
as entering olefins (Table 3). The values of KE confirm
that maleic anhydride is the more stabilizing olefin.
tions could be better explained by invoking a fluxional
behavior in which the symmetry arises from fast (on the
NMR time scale) alternating ‘windscreen wipe’ motion
of the two wings bearing the peripheral nucleophiles.
This phenomenon has already been observed in Pd(II)
h3-allyl complexes in which potentially terdentate lig-
ands display similar behavior [5g]. This hypothesis is
confirmed by the analysis of variable temperature spec-
tra of the most diagnostic complex [Pd(h2-
tmetc)(NSN)]. The spectrum at 178 K shows an
asymmetry, which can only be ascribed to a bidentate
NS species with a dangling pyridine arm. In fact, the
spectrum at this temperature displays four singlets
(3.72, 3.66, 3.58, 3.55 ppm), a multiplet at 4.22 ppm,
and seven signal groups in the aromatic range (Fig.
5(a)). The latter are easily interpreted as eight signals
ascribable pair wise to the four protons of the coordi-
nated pyridine (lower field) and to those of the uncoor-
dinated pyridine (higher field). The 4.22 ppm multiplet
is made up of two partially overlapping AB quartets
ascribed to the thiomethyl CH2ꢀS protons belonging to
the two arms differently engaged in the coordination to
the metal (i.e. coordinated and uncoordinated wing).
The presence of two AB systems also implies the freez-
ing of pyramidal sulfur inversion [6b]. The asymmetry
in the complex brings about a difference in the chemical
environments of olefin substituents which place them-
selves at the right and the left of a plane perpendicular
to the main coordination plane and above and below
the coordination plane with respect to the substituent
3. NMR studies
3.1. Characterization of complexes and fluxional
beha6ior
Selected 1H- and 13C-NMR spectral data for the
complexes under study are reported in the Section 4.
1
The room temperature H-NMR spectra of the com-
plexes display features typical of symmetric species,
which are inconsistent with the presence of a terdentate
species acting as a bidentate ‘ arm off ’ ligand and an
olefin in a square-planar environment. These observa-

L. Cano6ese et al. / Journal of Organometallic Chemistry 622 (2001) 155–165
161
moiety (ꢀCH2ꢀpyridine) of the frozen sp3 sulfur. This
will explain the presence of the four singlets ascribable
to the olefinic carbomethoxy protons. On increasing the
temperature, rapid flipping involving both pyridine-
bearing arms induces an increasing generalized symme-
rate of olefin exchange is slow on the NMR time scale.
In fact, the H-NMR spectrum of the reaction mixture
1
displays signals ascribable to all four species involved.
Apparently, the less efficient tmetc is ideally suited for
this type of experiment. As expected, the same equi-
librium composition can be attained by mixing equimo-
lar amounts of the final exchange products. Analogous
results were obtained with those other complexes that
display a dissociative term in the rate law (Eq. (1)).
Needless to say, the merit of this experiment rests on
the absence of other causes of exchange, such as direct
binuclear bimolecular olefin or polydentate ligand ex-
change or sufficient decomposition to allow a signifi-
cant concentration of free olefin in the mixture (i.e. no
formation of metallic palladium was observed). The
most we can say is that the latter occurrence can be
safely ruled out. A similar crossover experiment was
devised by Elsevier et al. to provide evidence for an
olefin dissociative mechanism in Pd(0) olefin complexes
containing rigid bidentate ligands [7a]. The possibility
of a binuclear second-order path was in that case ruled
out on steric grounds.
1
try, as can be seen from the 298 K H-NMR spectrum
(Fig. 5(b)). In fact, the four high field carbomethoxy
singlets collapse into a singlet (3.68 ppm). Meanwhile
simplification of the two AB systems ascribable to the
ꢀCH2ꢀpyridine protons into a singlet (4.24 ppm) and
formation of a unique pyridine ABXY system in the
aromatic region occurs (Fig. 5(b)).
This observed fluxional behavior does not necessarily
involve either sulfur inversion or olefin propeller-like
rotation. In fact, rotation of the bulky olefin tmetc
seems to be severely hindered in related bidentate NS
complexes [11].
The complexes [Pd(h2-tmetc)(SNS)(R)] display
analogous fluxional features arising from the fast alter-
nating flipping of the sulfur-bearing arms, although
analysis of the variable temperature spectra is not as
diagnostic as that of the NSN analog [Pd(h2-
tmetc)(NSN)] due to the much lower, unattainable
freezing temperature. This can be explained by the
better ability of sulfur as compared to nitrogen as a
nucleophile and/or by the lesser strain required by the
SNS ligand to act as terdentate. However in the case of
the complex [Pd(h2-tmetc)(SNS(Ph))], the fluxional
movement is clearly depressed at low temperature. In
fact, at 178 K the presence of a singlet due to the
CH2ꢀS protons of uncoordinated arm (4.56 ppm) su-
perimposed to a broad AB system due to the CH2ꢀS
protons of the coordinated one is observed. Moreover
the high field spectrum displays a broad signal due to
the olefin carbomethoxy protons in which two sepa-
rated singlets (3.57 ppm, 3H; 3.31ppm, 3H) and an
unresolved one (3.61 ppm, 6H) are identified. The ‘
wind-screen ’ movement is readily restored on slightly
increasing the temperature (183 K), as can be deduced
from the collapse of the signals.
3.3. Allyl complexes
Since it was not possible to prepare some Pd(0)
species by direct exchange reactions of the appropriate
ligand and olefin with Pd2(dba)3·CHCl3 (see Table 1),
we devised to synthesize the fn derivative [Pd(h2-
fn)(SNS(t-Bu))] by amination of [Pd(h3-allyl)(SNS(t-
Bu))]SO3CF3 with piperidine in the presence of fn
([4a,b] and Refs. therein).
The fluxional behavior of the parent h3-allyl complex
is similar to that of its SNS(Me) analogs containing
either h3-C3H5 or h3-1,1-Me2C3H3, in which the alter-
nating flipping movement of the arms induces a h3–h1
allyl isomerization [5f,g]. It is worth noting that the
NSN analog [Pd(h3-allyl)(NSN)]+, while undergoing
the fast flipping movement of the potentially terdentate
ligand, does not induce any h3–h1 rearrangement of
the allyl fragment, probably owing to the lower coordi-
nating ability of the nitrogen relative to sulfur com-
bined with a higher strain involved in the chelate rings
when NSN acts as terdentate (vide supra).
3.2. Olefin exchange reactions between palladium(0)
complexes
We sought to confirm the hypothesis of an olefin
dissociative pathway in the olefin exchange reactions
studied kinetically (Eq. (1)) by carrying out a crossover
experiment involving an equimolar mixture ([Pd]0=
2×10−2 mol dm−3) of [Pd(h2-tmetc)(SNS (Et))] and
[Pd(h2-ma)(SNS(i-Pr))] in CDCl3 at 25°C. The ability
of at least one of these complexes to release its coordi-
nated olefin by a dissociative path should lead to the
establishment of an equilibrium involving the presence
of all four species, i.e. the starting substrates and the
olefin exchange products [Pd(h2-tmetc)(SNS(i-Pr))] and
[Pd(h2-ma)(SNS(Et))] which can only be detected if the
The amination of the complex [Pd(h3-allyl)(SNS(t-
Bu))]+ by piperidine was followed at 25°C in CDCl3
either in the presence or in the absence of fn ([Pd]0=
0.05, [fn]0=0.05, [pip]0=0.25 mol dm−3). The reaction
in the presence of fn is easily interpreted on the basis of
the characteristic spectral features of [Pd(h2-fn)(SNS(t-
Bu))] and the allylamine C5H10NꢀCH2CHꢁCH2 (see
Section 4). In the absence of fn, the reaction takes place
with formation of allylamine but is accompanied by
extensive decomposition, as indicated by the presence
of free polydentate ligand. However, there is spectral
evidence at low fields in the pyridine protons range for

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L. Cano6ese et al. / Journal of Organometallic Chemistry 622 (2001) 155–165
formation of a Pd(0) species which is most likely iden-
tified as the terdentate olefin-free [Pd(SNS(t-Bu))]. This
observation, coupled to the kinetic findings discussed
above, lends support to the view that sufficient Pd(0)
stabilization by SNS ligands may occur even in the
absence of a stabilizing p-accepting olefin.
atmosphere (N2). The resulting solution was stirred in
the dark for 4 h. To the filtered solution (glass-fiber
filter) 0.141 g (0.497 mmol) of 2,6-bis-(t-butylth-
iomethyl)pyridine (SNS(t-Bu)) was added. The solution
was stirred for 1 h, treated with activated charcoal for
15 min and filtered on celite filter. Addition of di-
ethylether to the concentrated solution yields 0.229 g
(0.395 mmol, yield 83%) of the title complex as a white
precipitate. Anal. Found: C, 39.46; H, 5.17; N, 2.36.
C19H30NO3S3F3Pd requires: C, 39.34; H, 5.21; N,
2.41%. The following numbering scheme was used for
the allylic fragment:
4. Experimental
4.1. Preparation of ligands
4.1.1. 2[(2-Pyridylmethylthio)methyl)]pyridine (NSN)
The title compound was prepared as in Ref. [5g].
4.1.2. 2,6-bis(Methylthiomethyl)pyridine (SNS(Me))
The title compound was prepared as in Ref. [12].
4.1.3. 2,6-bis(Arylthiomethyl)pyridine (SNS(R))
These compounds were prepared in a way similar to
(SNS(Me)) using the suitable thiolate RS−K+ (R=Et,
i-Pr, t-Bu, Ph).
IR (in KBr, cm−1): wC N 1598 (m); wS O 1269 (s).
ꢁ
ꢁ
1H-NMR (in CDCl3, RT), l (ppm): H4 7.89 (t, 1H,
J=7.7 Hz); H3,5 7.64 (d, 2H, J=7.7 Hz); CH2ꢀS 4.40
(s, 4H); SC(CH3)3 1.38 (s, 18H); H1%,3% 4.05 (s, 4H, br);
H2% 5.79 (qn, 1H, J=10.0 Hz). 13C{1H}-NMR (in
CDCl3, RT), l (ppm): C2,6 159.6; C4 140.1; C3,5 123.1;
C2% 120.9; C1%,3% 65.8; CH2ꢀS 40.5; SꢀC(CH3)3 48.8;
SꢀC(CH3)3 30.4.
1
4.1.3.1. SNS(Et). Yield 74%. H-NMR (in CDCl3, RT),
l (ppm): H4 7.62 (t, 1H, J=7.7 Hz); H3,5 7.26 (d, 2H,
J=7.7 Hz); CH2ꢀS 3.83 (s, 4H); SꢀCH2ꢀCH3 2.50 (q,
4H, J=7.5 Hz); SCH2CH3 1.24 (t, 6H, J=7.5 Hz).
13C-NMR (in CDCl3, RT), l (ppm): C4 137.2; C3,5
158.5; C2,6 120.9; CH2ꢀS 37.7; SꢀCH2CH3 25.6;
SCH2CH3 14.4.
4.1.3.2. SNS(i-Pr). Yield 99%. 1H-NMR (in CDCl3,
RT), l (ppm): H4 7.56 (t, 1H, J=7.7 Hz); H3,5 7.23 (d,
2H, J=7.7 Hz); CH2ꢀS 3.81 (s, 4H); SꢀCH(CH3)2 2.84
(sept, 2H, J=6.7 Hz); SꢀCH(CH3)2 1.19 (d, 12H, J=
6.7 Hz). 13C-NMR (in CDCl3, RT), l (ppm): C4 137.1;
C3,5 158.5; C2,6 120.9; CH2ꢀS 37.0; SꢀCH 34.6;
SꢀCH(CH3)2 23.2.
4.3. Preparation of Pd(0) complexes
4.3.1. Pd2(dba)3·CHCl3
The title complex was obtained according to Ref.
[13].
4.3.2. [Pd(p2-ol)(LL%L)]
The published complexes [Pd(h2-fn)(SNS(Me))],
[Pd(h2-fn)(NSN)] and the following reported species
were obtained according to Ref. [5g].
4.1.3.3. SNS(t-Bu). Yield 94%. 1H-NMR (in CDCl3,
RT), l (ppm): H4 7.58 (t, 1H, J=7.7 Hz); H3,5 7.32 (d,
2H, J=7.7 Hz); CH2ꢀS 3.91 (s, 4H); SꢀC(CH3)3 1.34
(s, 18H). 13C-NMR (in CDCl3, RT), l (ppm): C4 136.9;
C3,5 158.5; C2,6 121.2; CH2ꢀS 43.1; SꢀC(CH3)3 35.5;
SC(CH3)3 31.0.
The following numbering scheme was adopted:
4.1.3.4. SNS(Ph). Yield 67%. 1H-NMR (in CDCl3, RT),
l (ppm): H4 7.51 (t, 1H, J=7.7 Hz); CH2ꢀS 4.26 (s,
4H); H3,5 Phenyl protons 7.25 (m, 12H). 13C-NMR (in
CDCl3, RT), l (ppm): C4 137.2; C3,5 157.3; C2,6 121.2;
Ca 135.8; Cb 129.5; Cc 120.9; Cd 126.3; CH2ꢀS 40.3.
4.2. Preparation of [Pd(p3-C3H5)(SNS(t-Bu))]SO3CF3
To a solution of 0.087 g (0.238 mmol) of [Pd(h3-
C3H5)Cl]2 in 10 ml of freshly distilled CHCl3, 0.124 g
(0.483 mmol) of Ag SO3CF3 were added under inert

L. Cano6ese et al. / Journal of Organometallic Chemistry 622 (2001) 155–165
163
4.3.3. [Pd(p2-ma)(SNS(Me))]
4.3.8. [Pd(p2-ma)(NSN)]
Yield 87% (yellow microcrystals). Found: C, 38.64;
H, 3.81; N, 3.51. C13H15NO3S2Pd requires: C, 38.71; H,
Yield 95% (yellow microcrystals). Found: C, 45.58;
H, 3.38; N, 6.69. C16H14N2O3SPd requires: C, 45.72; H,
3.75; N, 3.48%. IR (in KBr, cm−1): wC O 1788 (s), 1713
3.36; N, 6.67%. IR (in KBr, cm−1): wC O 1792 (s), 1724
ꢁ
ꢁ
1
1
(s); wC N 1593 (m). H-NMR (in CDCl3, RT), l (ppm):
(s); wC N 1592 (m). H-NMR (in CDCl3, RT), l (ppm):
ꢁ
ꢁ
H4 7.80 (t, 1H, J=7.7 Hz); H3,5 7.42 (d, 2H, J=7.7
Hz); CH2ꢀS and HCꢁCH 4.16 (s, 6H); SꢀCH3 2.24 (s,
6H). 13C{1H}-NMR (in CD2Cl2, RT), l (ppm): C4
137.8; C3,5 122.1; C2,6 158.3; CꢁO 170.8; CH2ꢀS 43.6;
SꢀCH3 16.6; HCꢁCH 44.5.
H6 8.30 (d, 1H, J=5.2 Hz); H4 7.70 (td, 1H, J=7.7,
1.6 Hz); H3 7.46 (d, 1H, J=7.7 Hz); H5 7.09 (dd, 1H,
J=7.7, 5.2 Hz); CH2ꢀS 4.16 (s, 4H); HCꢁCH 4.16 (s,
2H). 13C-NMR (in CDCl3, RT), l (ppm):CꢁO 171.6; C2
156.8; C6 150.3; C4 137.5; C5 123.6; C3 122.8; CꢁC 46.0;
CH2ꢀS 41.9.
4.3.4. [Pd(p2-ma)(SNS(Et))]
4.3.9. [Pd(p2-nq)(SNS(Me))]
Yield 88% (yellow microcrystals). IR (in KBr, cm−1):
wC O 1794 (s), 1715 (s); wC N 1593 (m). 1H-NMR (in
Yield 74% (brown–orange microcrystals). Found: C,
49.11; H, 4.12; N, 3.01. C19H19NO2S2Pd requires: C,
ꢁ
ꢁ
CDCl3, RT), l (ppm): H4 7.78 (t, 1H, J=7.7 Hz); H3,5
7.41 (d, 2H, J=7.7 Hz); CH2ꢀS and HCꢁCH 4.19 (s,
6H); SꢀCH2CH3 2.67 (q, 4H, J=7.4 Hz); SCH2CH3
1.31 (t, 6H, J=7.4 Hz). 13C{1H}-NMR (in CD2Cl2,
RT), l (ppm): C4 137.7; C3,5 121.8; C2,6 158.7; CꢁO
170.9; CH2ꢀS 41.5; SꢀCH2CH3 27.6; SCH2CH3 13.4;
HCꢁCH 44.3.
49.19; H, 4.13; N, 3.02%. IR (in KBr, cm−1): wC O
ꢁ
1626;wC N 1587 (m). 1H-NMR (in CDCl3, RT), l (ppm):
ꢁ
H4 7.64 (t, 1H, J=7.6 Hz); H3,5 7.21 (d, 2H, J=7.6
Hz); CH2ꢀS 4.04 (s, 4H); SꢀCH3 2.27 (s, 6H); HCꢁCH
4.65 (s, 2H, br); He 7.97 (m, 2H); Hf 7.52 (m, 2H).
13C{1H}-NMR (in CDCl3, RT), l (ppm): C4 138.0; C3,5
123.1; C2,6 160.0; C1ꢁO 183.2; Ce 124.9; Cf 131.5; Cg
135.1; HCꢁCH 63.9; CH2ꢀS 44.6; SꢀCH3 17.5.
4.3.5. [Pd(p2-ma)(SNS(i-Pr))]
Yield 87% (yellow microcrystals). IR (in KBr, cm−1):
wC O 1795 (s), 1724 (s); wC N 1597 (m). 1H-NMR (in
4.3.10. [Pd(p2-nq)(SNS(Et))]
Yield 61% (brown–orange microcrystals). IR (in
ꢁ
ꢁ
CDCl3, RT), l (ppm): H4 7.76 (t, 1H, J=7.7 Hz); H3,5
7.42 (d, 2H, J=7.7 Hz); CH2ꢀS and HCꢁCH 4.20 (s,
6H); SꢀCH(CH3)2 3.00 (sept, 2H, J=6.7 Hz);
SCH(CH3)2 1.34 (d, 12H, J=6.7 Hz). 13C{1H}-NMR
(in CD2Cl2, RT), l (ppm): C4 137.7; C3,5 121.7; C2,6
159.0; CꢁO 171.0; CH2ꢀS 40.5; SꢀCH(CH3)2 37.0;
SCH(CH3)2 22.1; HCꢁCH 44.2.
KBr, cm−1): wC O 1624 (s); wC N 1587 (m). H-NMR (in
1
ꢁ
ꢁ
CDCl3, RT), l (ppm): H4 7.66 (t, 1H, J=7.7 Hz); H3,5
7.31 (d, 2H, J=7.7 Hz); CH2ꢀS 4.09 (s, 4H);
SꢀCH2CH3 2.62 (q, 4H, J=7.3 Hz); SCH2CH3 1.22 (t,
6H, J=7.3 Hz); HCꢁCH 4.87 (s, 2H, br); He 8.00 (m,
2H); Hf 7.54 (m, 2H). 13C{1H}-NMR (in CDCl3, RT),
l (ppm): C4 137.9; C3,5 122.8; C2,6 158.5; CꢁO 183.9; Ce
125.0; Cf 131.5; Cg 134.9; CꢁC 63.2; CH2ꢀS 41.7;
SꢀCH2CH3 28.3; SꢀCH2CH3 14.0.
4.3.6. [Pd(p2-ma)(SNS(t-Bu))]
Yield 70% (yellow microcrystals). Found: C, 46.77;
H, 5.61; N, 2.91. C19H27NO3S2Pd requires: C, 46.81; H,
4.3.11. [Pd(p2-nq)(SNS(i-Pr))]
Yield 79% (orange microcrystals). Found: C, 53.18;
H, 5.10; N, 2.81. C23H27NO2S2Pd requires: C, 53.13; H,
5.59; N, 2.88%. IR (in KBr, cm−1): wC O 1795 (s), 1724
ꢁ
1
(s); wC N 1597 (m). H-NMR (in CDCl3, RT), l (ppm):
ꢁ
5.23; N, 2.69%. IR (in KBr, cm−1): wC O 1641 (s), 1616
ꢁ
H4 7.75 (t, 1H, J=7.7 Hz); H3,5 7.46 (d, 2H, J=7.7
Hz); CH2ꢀS e HCꢁCH 4.22 (s, 6H); SC(CH3)3 1.42 (s,
18H). 13C{1H}-NMR (in CD2Cl2, RT), l (ppm): C4
138.1; C3,5 122.2; C2,6 159.8; CꢁO 171.7; CH2ꢀS 39.2;
SꢀC(CH3)3 46.0; SC(CH3)3 30.5; HCꢁCH 45.2.
1
(s); wC N 1589 (m). H-NMR (in CDCl3, RT), l (ppm):
ꢁ
H4 7.66 (t, 1H, J=7.7 Hz); H3,5 7.31 (d, 2H, J=7.7
Hz); CH2ꢀS 4.07 (s, 4H); SꢀCH(CH3)2 2.90 (sept, 2H,
J=6.6 Hz); SCH(CH3)2 1.27 (d, 12H, J=6.7 Hz);
HCꢁCH 4.89 (s, 2H, br); He 8.02 (m, 2H); Hf 7.48 (m,
2H). 13C{1H}-NMR (in CDCl3, RT), l (ppm): C4
137.7; C3,5 121.9; C2,6 159.6; CꢁO 185.0; Ce 125.0; Cf
131.1; Cg 135.3; HCꢁCH 60.7; CH2ꢀS 39.9;
SꢀCH(CH3)2 37.0; SꢀCH(CH3)2 22.8.
4.3.7. [Pd(p2-ma)(SNS(Ph))]
Yield 95% (yellow microcrystals). Found: C, 52.42;
H, 3.58; N, 2.69. C23H19NO3S2Pd requires: C, 52.37; H,
3.63; N, 2.66%. IR (in KBr, cm−1): wC O 1796 (s), 1724
ꢁ
1
(s); wC N 1593 (m). H-NMR (in CDCl3, RT), l (ppm):
4.3.12. [Pd(p2-nq)(SNS(t-Bu))]
ꢁ
H4 7.58 (t, 1H, J=7.7 Hz); CH2ꢀS 4.49 (s, 4H);
HCꢁCH 4.27 (s, 2H); H3,5, Hb, Hc, Hd, 7.25 (m, 12H).
13C{1H}-NMR (in CDCl3, RT), l (ppm): C4 138.0; C3,5
122.5; C2,6 158.3; CꢁO 171.5; Ca 132.6; Cb 131.5; Cc
129.0; Cd 128.1; CH2ꢀS 46.1.
Yield 60% (orange microcrystals). IR (in KBr,
cm−1): wC O 1627 (s); wC N 1591 (m). 1H-NMR (in
ꢁ
ꢁ
CDCl3, RT), l (ppm): H4 7.64 (t, 1H, J=7.7 Hz); H3,5
7.35 (d, 2H, J=7.7 Hz); CH2ꢀS 4.14 (s, 4H); SC(CH3)3
1.38 (s, 18H); HCꢁCH 4.88 (s, 2H); He 8.00 (m, 2H); Hf

164
L. Cano6ese et al. / Journal of Organometallic Chemistry 622 (2001) 155–165
7.47 (m, 2H). 13C{1H}-NMR (in CDCl3, RT), l (ppm):
C4 137.7; C3,5 121.9; C2,6 160.1; CꢁO 185.7;Ce 125.0; Cf
131.0; Cg 135.5; HCꢁCH 60.7; CH2ꢀS 38.6; SꢀC(CH3)3
45.8; SꢀC(CH3)3 30.5.
5.74; N, 2.15%. IR (in KBr, cm−1): wC O 1740 (s), 1720
ꢁ
1
(s), 1697 (s); wC N 1598 (m). H-NMR (in CDCl3, RT),
ꢁ
l (ppm): H4 7.73 (t, 1H, J=7.7 Hz); H3,5 7.61 (d, 2H,
J=7.7 Hz); CH2ꢀS 4.25 (s, 4H); OꢀCH3 3.72 (s, 12H);
SC(CH3)3 1.42 (s, 18H). 13C{1H}-NMR (in CD2Cl2,
RT), l (ppm): C4 137.6; C3,5 121.5; C2,6 160.2; CꢁO
169.5; OꢀCH3 51.9; CH2ꢀS 38.8; SꢀC(CH3)3 45.6;
SC(CH3)3 30.8; CꢁC not observed.
4.3.13. [Pd(p2-nq)(SNS(Ph))]
Yield 92% (brown–orange microcrystals). Found: C,
59.28; H, 3.89; N, 2.35. C29H23NO2S2Pd requires: C,
59.23; H, 3.94; N, 2.38%. IR (in KBr, cm−1): wC O 1643
ꢁ
1
(s), 1620 (s); wC N 1591 (m). H-NMR (in CDCl3, RT),
4.3.18. [Pd(p2-tmetc)(SNS(Ph))]
ꢁ
l (ppm): H3,5 7.04 (d, 2H, J=7.7 Hz); CH2ꢀS 4.36 (s,
4H); HCꢁCH 4.96 (s, 2H); H4, Hb, Hc, Hd, He, Hf 7.6
(m, 15H). 13C{1H}-NMR (in CDCl3, RT), l (ppm): C4
137.6; C3,5 122.4; C2,6 158.5; CꢁO 185.1; Ca 132.8; Cb
128.8; Cc 131.5; Cd 127.8; Ce 125.1; Cf 131.3; Cg 135.2;
HCꢁCH 61.7; CH2ꢀS 45.3.
Yield 79% (yellow microcrystals). Found: C, 50.51;
H, 4.21; N, 2.05. C29H29NO8S2Pd requires: C, 50.47; H,
4.24; N, 2.03%. IR (in KBr, cm−1): wC O 1720 (s), 1711
ꢁ
1
(s), 1680 (s); wC N 1597 (m). H-NMR (in CDCl3, RT),
ꢁ
l (ppm): H4 7.54 (t, 1H, J=7.7 Hz); CH2ꢀS 4.62 (s,
4H); OꢀCH3 3.66 (s, 12H); H3,5, Hb, Hc, Hd 7.32 (m,
12H). 13C{1H}-NMR (in CDCl3, RT), l (ppm): C4
137.9; C3,5 121.9; C2,6 158.5; CꢁO 169.2; Ca 133.1; Cb
130.5; Cc 128.8; Cd 127.3; OꢀCH3 52.1; CH2ꢀS 44.5;
CꢁC not observed.
4.3.14. [Pd(p2-nq)(NSN)]
Yield 83% (dark orange microcrystals). Found: C,
55.01; H, 3.81; N, 5.81. C22H18N2O2SPd requires: C,
54.95; H, 3.77; N, 5.83%. IR (in KBr, cm−1): wC O 1626
ꢁ
1
(s); wC N 1583 (m). H-NMR (in CDCl3, RT), l (ppm):
4.3.19. [Pd(p2-tmetc)(NSN)]
ꢁ
H6, He 8.10 (m, 4H); Hf 7.55 (m, 2H); H4 7.34 (td, 2H,
J=7.7, 1.6 Hz); H3, H5 7.00 (m, 4H); HCꢁCH 4.95 (s,
2H); CH2ꢀS 3.98 (s, 4H). 13C{1H}-NMR (in CDCl3,
RT), l (ppm): C2 156.9; C3 122.6; C4 136.9; C5 123.2;
C6 148.8; CꢁO 181.5; Ce 125.0; Cf 131.2; Cg 135.8;
HCꢁCH 64.7; CH2ꢀS 40.8.
Yield 85% (yellow microcrystals). Found: C, 45.41;
H, 4.11; N, 4.85. C22H24N2O8SPd requires: C, 45.33; H,
4.15; N, 4.81%. IR (in KBr, cm−1): wC O 1728 (s), 1695
ꢁ
1
(s); wC N 1590 (m). H-NMR (in CDCl3, RT), l (ppm):
ꢁ
H6 8.40 (d, 2H, J=5.0 Hz); H4, H3 7.52 (m, 4H); H5
6.96 (ddd, 2H, J=7.7, 5.0, 1.8 Hz); CH2ꢀS 4.26 (s, 4H);
OꢀCH3 3.76 (s, 12H). 13C{1H}-NMR (in CDCl3, RT), l
(ppm): C2 157.4; C3 122.3; C4 136.8; C5 124.0; C6 150.2;
CꢁO 169.3; CH2ꢀS 41.0; OꢀCH3 52.0; CꢁC not
observed.
4.3.15. [Pd(p2-tmetc)(SNS(Et))]
Yield 76% (yellow microcrystals). Found: C, 42.52;
H, 4.89; N, 2.25. C21H29NO8S2Pd requires: C, 42.46; H,
4.92; N, 2.36%. IR (in KBr, cm−1): wC O 1732 (s), 1689
ꢁ
1
(s); wC N 1591 (m). H-NMR (in CDCl3, RT), l (ppm):
4.3.20. [Pd(p2-fn)(SNS(Et))]
ꢁ
H4 7.76 (t, 1H, J=7.7 Hz); H3,5 7.52 (d, 2H, J=7.7
Hz); CH2ꢀS 4.27 (s, 4H); OꢀCH3 3.73 (s, 12H);
SꢀCH2CH3 2.65 (q, 4H, J=7.4 Hz); SCH2CH3 1.27 (t,
6H, J=7.4 Hz). 13C{1H}-NMR (in CD2Cl2, RT), l
(ppm): C4 140.3; C3,5 124.1; C2,6 161.6; CꢁO 171.3;
OꢀCH3 53.9; CH2ꢀS 43.6; SꢀCH2CH3 30.0; SCH2CH3
16.1; CꢁC not observed.
Yield 40% (white microcrystals) IR (in KBr, cm−1):
wCN 2202.6 (s), wC N 1599 (m). 1H-NMR (in CDCl3,
ꢁ
RT), l (ppm): H4 7.83 (t, 1H, J=7.7 Hz); H3,5 7.48 (d,
2H, J=7.7Hz); CH2ꢀS 4.28 (s, 4H); SꢀCH2ꢀCH3 2.73
(q, 4H, J=7.4Hz); SꢀCH2ꢀCH3 1.35 (t, 6H, J=
7.4Hz); HCꢁCH 3.12 (s, 2H).
4.3.21. [Pd(p2-fn)(SNS(t-Bu))]
4.3.16. [Pd(p2-tmetc)(SNS(i-Pr))]
The title complex was obtained in an NMR tube as
the product of the amination reaction of [Pd(h3-
C3H5)(SNS(t-Bu))]SO3CF3 with piperidine (Pip) in the
presence of fumaronitrile (fn) and was not separated.
Yield 77% (yellow microcrystals). IR (in KBr, cm−1):
1
wC O 1724 (s), 1695 (s), 1674 (s); wC N 1597 (m). H-
ꢁ
ꢁ
NMR (in CDCl3, RT), l (ppm): H4 7.75 (t, 1H, J=7.7
Hz); H3,5 7.52 (d, 2H, J=7.7 Hz);CH2ꢀS 4.27 (s, 4H);
OꢀCH3 3.72 (s, 12H); SꢀCH(CH3)2 2.90 (sept, 2H,
J=6.7 Hz); SCH(CH3)2 1.30 (d, 12H, J=6.7 Hz).
13C{1H}-NMR (in CDCl3, RT), l (ppm): C4 137.8; C3,5
121.6; C2,6 159.7; CꢁO 169.4; OꢀCH3 52.0; CH2ꢀS 40.1;
SꢀCH(CH3)2 37.1; SCH(CH3)2 22.8; CꢁC not observed.
In
C3H5)(SNS(t-Bu))]SO3CF3, piperidine,and fumaroni-
trile ([Pd]0=[fn]0=5.10−2; [Pip]0=0.25 mol dm−3
a
typical experiment the complex [Pd(h3-
)
were dissolved in 0.6 ml of CDCl3. The reaction went to
1
completion in a few minutes and the H-NMR spec-
trum displays the signals ascribable to allylpiperidine
(C3H5ꢀNC5H10) [14] and to [Pd(h2-fn)(SNS(t-Bu))]
species.
4.3.17. [Pd(p2-tmetc)(SNS(t-Bu))]
Yield 79% (yellow microcrystals). Found: C, 46.12;
H, 5.81; N, 2.15. C25H37NO8S2Pd requires: C, 46.19; H,
1H-NMR (in CDCl3, RT), l (ppm): H4 7.76 (t, 1H,
J=7.7Hz); H3,5 7.48 (d, 2H, J=7.7Hz); CH2ꢀS 4.19,

L. Cano6ese et al. / Journal of Organometallic Chemistry 622 (2001) 155–165
165
[4] (a) L. Canovese, F. Visentin, P. Uguagliati, G. Chessa, A. Pesce,
J. Organomet. Chem. 566 (1998) 61. (b) B. Crociani, S. Antonar-
oli, G. Bandoli, L. Canovese, F. Visentin, P. Uguagliati,
Organometallics 18 (1999) 1137. (c) K. Selvakumar, M. Valen-
tini, M. Wo¨rle, P.S. Pregosin, A. Albinati, Organometallics 18
(1999)1207.
4.33 (AB, 2H, J=15Hz); HCꢁCH 3.12 (s, 2H);
SꢀC(CH3)3 1.40, (s, 18H).
4.4. IR and NMR measurements
The IR, 1H, and 13C{1H}-NMR spectra were
recorded on a Nicolet Magna™ 750 spectrophotometer
and on a Bruker AC™ 200 spectrometer, respectively.
The temperature dependent 1H-NMR spectra were
analyzed using the SWAN program [15].
[5] (a) B. Crociani, F. Di Bianca, P. Uguagliati. L. Canovese, A.
Berton, J. Chem. Soc. Dalton Trans. (1991) 71. (b) B. Crociani,
S. Antonaroli, F. Di Bianca, L. Canovese, F. Visentin, P.
Uguagliati, J. Chem. Soc. Dalton Trans. (1994) 1145. (c) L.
Canovese, F. Visentin, P. Uguagliati, F. Di Bianca, S. Antonar-
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Lucchini, G. Bandoli, Inorg. Chim. Acta 275 (1998) 385. (g) L.
Canovese, F. Visentin, G. Chessa, A. Niero, P. Uguagliati,
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L. Canovese, F. Visentin, P. Uguagliati, Inorg. Chim. Acta
submitted.
4.5. Kinetic and equilibrium measurements
The kinetics of olefin substitution were studied by
addition of known aliquots of tmetc solutions to solu-
tions of the complex under study in CHCl3 ([Pd]0:
10−4mol dm−3) in the thermostatted cell compartment
of a Lambda 40 Perkin–Elmer™ spectrophotometer at
the designed temperature. The reactions were followed
by recording spectral changes in the wavelength range
of 300–540 nm or at a suitable fixed wavelength.
Equilibrium studies were performed by addition of
microaliquots of a solution of the designed olefin (or
ligand) to a solution of the complex under study at
controlled temperature (25°C). The spectral features of
the resulting mixtures were recorded by means of a
Lambda 40 Perkin–Elmer spectrophotometer. Mathe-
matical and statistical data analysis was carried out on
a personal computer equipped with a locally adapted
version of Marquardt’s algorithm [16] written in Tur-
bobasic™ (Borland).
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