Insertion of 1,1-Me2propadiene across the Pd-C bond of pyridylthioether methyl complexes. A mechanistic study

Article abstract of DOI:10.1016/S0020-1693(02)01432-9

Novel neutral and cationic palladium methyl complexes containing pyridylthioethers (R′N-SR) as ancillary ligands and different leaving groups were synthesised and characterised by spectroscopic methods and elemental analysis. The reactivity of these complexes toward allene (allene=DMA=1,1-Me₂propadiene) insertion across the Pd-C bond was studied under different conditions. The influence of steric and electronic parameters, solvents and leaving groups was explored and an overall mechanistic picture is proposed. The distortion promoted by the ancillary ligand geometry together with the nature of the leaving group proved to be of primary importance in determining the reactivity of the complexes under study. The observed rate constants span several orders of magnitude. On the contrary, only a modest effect is observed when solvents with increasing dielectric constants are employed. The complex [Pd(PPh₃)(Me)(MeN-S^tBu)]⁺ shows a reactivity modulated by the presence of the phosphine which imparts to the substrate a peculiar reactivity owing to the scarce tendency of the phosphine itself to act as a leaving group.

Full text of DOI:10.1016/S0020-1693(02)01432-9

Inorganica Chimica Acta 346 (2003) 158ꢀ168
/
www.elsevier.com/locate/ica
Insertion of 1,1-Me2propadiene across the Pdꢀ
/
C bond of pyridylꢀ
/
thioether methyl complexes. A mechanistic study
Luciano Canovese *, Gavino Chessa, Claudio Santo, Fabiano Visentin,
Paolo Uguagliati
Dipartimento di Chimica, Universita` Ca’ Foscari di Venezia, Dorsoduro 2137, I-30123 Venice, Italy
Received 13 August 2002; accepted 14 September 2002
Abstract
Novel neutral and cationic palladium methyl complexes containing pyridylthioethers (R?Nꢀ
leaving groups were synthesised and characterised by spectroscopic methods and elemental analysis. The reactivity of these
complexes toward allene (alleneꢁDMAꢁ1,1-Me2propadiene) insertion across the PdꢀC bond was studied under different
/SR) as ancillary ligands and different
/
/
/
conditions. The influence of steric and electronic parameters, solvents and leaving groups was explored and an overall mechanistic
picture is proposed. The distortion promoted by the ancillary ligand geometry together with the nature of the leaving group proved
to be of primary importance in determining the reactivity of the complexes under study. The observed rate constants span several
orders of magnitude. On the contrary, only a modest effect is observed when solvents with increasing dielectric constants are
employed. The complex [Pd(PPh3)(Me)(MeNꢀ
StBu)]ꢂ shows a reactivity modulated by the presence of the phosphine which
imparts to the substrate a peculiar reactivity owing to the scarce tendency of the phosphine itself to act as a leaving group.
/
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Palladium methyl complexes; Ancillary ligands; A mechanistic study
1. Introduction
remarkable enhancement of the rate of insertion of
substituted allenes into the PdꢀMe bond. Among
/
The reaction of insertion of unsaturated molecules
different interpretations involving the bite angle, the
rigidity and the hemilability of the bidentate ancillary
ligand [4] we suggested that the enhanced reactivity
observed would arise from destabilisation of the sub-
strate. This would be due to the balanced interplay
among the distortion induced by the pyridine substitu-
ent, the peculiar characteristics of the flexible wing
bearing the thioether function (which prevents decom-
position), and the electronic properties of the ligand
itself. As a matter of fact, to the best of our knowledge
into the metalꢀcarbon bond is of increasing importance
/
in a large number of catalytic processes [1]. Interest
about this reaction arises from both theoretical and
practical aspects, due to its potential versatility in a wide
number of synthetic paths toward CꢀC bond formation
/
and possible subsequent polymerisation reactions [2].
We have been recently involved in a study aiming at
elucidating the intimate mechanism of allene insertion
into the Pdꢀ
/
C bond producing palladiumꢀallyl species
/
the complex [Pd Cl(Me)(ClNꢀ
/
SPh)] (ClNꢀ
/
SPhꢁ6-
/
since, in our opinion, no straightforward interpretations
on such a mechanism were available at the time [3]. We
chloro-2-phenylthiomethylpyridine) proves to be the
most efficient substrate with respect to allene insertion
of all complexes studied so far. Apparently, the distor-
tion of the ligand backbone coupled with the lowered
nucleophilic power of the coordinating atoms N and S
(due to the decreased basicity of pyridine nitrogen)
induce the greatest accelerating effect observed until
now [3b]. Eventually, this behaviour was traced back to
the customary mechanism of nucleophilic substitution
clearly demonstrated that a distortion of the pyridylꢀ
/
thioether ancillary ligand backbone induced by a sub-
stituent in position six of the pyridine ring causes a
* Corresponding author. Tel.: ꢂ
8517.
E-mail address: cano@unive.it (L. Canovese).
/
39-41-257-8571; fax: ꢂ39-41-257-
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(02)01432-9

L. Canovese et al. / Inorganica Chimica Acta 346 (2003) 158ꢀ
/
168
159
via an asynchronous associative path in which the
entering group, the leaving group and the group trans
to the leaving group lie in the trigonal plane of the
pentacoordinated intermediate arranged in a trigonal
bipyramidal geometry in which destabilisation of the
ground state structure would favour the reaction [5].
However, some aspects of the problem, i.e., the role of
the halogen and that of the solvent, are yet to be
clarified. In fact the formation of the final allyl species
requires the removal of the halogen ion which otherwise
would remain in the environment of the metal centre
presumably forming a zwitterion or a pentacoordinated
species. The identification of the most efficient leaving
group and of the most suitable solvent represents a non-
trivial problem in an attempt to reveal the intimate
reaction mechanism with respect to polymerisation
reactions. For these reasons we decided to extend our
mechanistic study on allene insertion to palladium
methyl complexes bearing pyridylthioether ligands in
different solvents and with different halide groups.
Moreover, the study was expanded to pyridylthioether
palladium methyl triphenylphosphine and solvento
species, the latter being by far the most reactive
substrate. This paper reports the results of this investi-
gation and establishes the most likely mechanism of
allene insertion on palladium methyl complexes bearing
pyridylthioethers as ancillary ligands, which the ensuing
comprehensive summary reported in Table 1 allowing a
prompt comparison among all the feasible effects
operating in these reactions.
complex [PdCl(Me)(R?Nꢀ
/
SR)] [3]. The synthesis of the
complexes [PdX(Me)(R?Nꢀ
[PdL(Me)(R?Nꢀ CH3CN, PPh3) was accom-
SR)]ꢂ (Lꢁ
plished starting from the chloro-species
[PdCl(Me)(R?NꢀSR)] by metathetic exchange with an
excess of KBr or NaI (XꢁBr, I) in acetone/CH2Cl2 or
CH2Cl2 respectively and by dechloridation of the same
starting substrate by AgOTf in CH3CN (LꢁCH3CN)
or in THF followed by addition of a stoichiometric
amount of PPh3 (LꢁPPh3). The corresponding allyl
/
SR)] (Xꢁ/Br, I,) or
/
/
/
/
/
/
derivatives were synthesised according to the customary
procedure starting from the corresponding allyl dimers
by addition of the appropriate ancillary ligand or by
reacting the methyl derivatives with DMA (dimethylal-
lene). The studied complexes, the related ligands and the
allyl insertion products are summarised in Scheme 1 in
which the reported formulas must be considered topo-
logical representations of all the [PdX(Me)(R?Nꢀ
/
SR)]
SR] isomeric species.
and [Pd(h3-1,1,2-Me3C3H2)(R?Nꢀ
/
As a matter of fact we showed that almost all the
methyl complexes synthesised are present in solution
and in the solid as a unique isomer in which the methyl
group coordinated to the palladium centre occupies the
cis position with respect to the thioetheric sulphur, the
geometry of complexes being apparently governed by
the trans-influence of the groups [3]. Significant excep-
tions are represented by the complexes bearing the 6-
chloro substituted pyridylthioether ligand as described
elsewhere
[Pd(PPh3)(Me)(MeNꢀ
[3b]
and
by
the
complex
/
StBu)]ꢂ synthesised in the pre-
sent work for the first time. In the latter case both the
diasteroisomers are present in solution with the marked
predominance of the species with the methyl group trans
2. Results and discussion
1
to thioetheric sulphur, as can be deduced from H and
31P NMR evidence (see below). The trans-influence of
the phosphine clearly overwhelms that of the sulphur
and the ratio between isomers determined from low
temperature 1H NMR signals could be taken as a direct
measure of such a phenomenon.
2.1. Synthesis and characterisation of the complexes
Addition under inert atmosphere (N2) of the appro-
priate ligand (R?Nꢀ
/
SR) to
a
[PdCl(Me)(COD)] in toluene yields the corresponding
solution of
Table 1
Second-order rate constants, k2 (molꢃ1 dm3 sꢃ1) for the insertion of 1,1-dimethylpropadiene into the Pdꢀ
Me bond in CH2Cl2 at 25 8C
/
Complex
R
Me
Et
6.53ꢄ
iPr
4.08ꢄ
tBu
2.33ꢄ
Ph
[PdCl(Me)(HNꢀ
[PdCl(Me)(MeNꢀ
[PdBr(Me)(MeNꢀ
[PdI(Me)(MeNꢀSR)]
[PdCl(Me)(ClNꢀSR)]
[Pd(NCMe)(Me)(HNꢀ
[Pd(NCMe)(Me)(MeNꢀ
[Pd(PPh3)(Me)(MeNꢀ
SR)]ꢂ
/
SR)]
SR)]
SR)]
8.17ꢄ
2.42
/
10ꢃ4 a
/
10ꢃ4 a
/
10ꢃ4 a
/
10ꢃ4 b
4.0ꢄ
23
/
10ꢃ2 b
b
/
3.3ꢄ
/
10ꢃ1 b
/
1.16
/
1.28
a
30
a
/
164
c
c
c
/
SR)]ꢂ
SR)]ꢂ
2000
2100
3200
7.2ꢄ
/
/
/
10ꢃ3 d
a
b
c
From Ref. [3b].
From Ref. [3a].
Determined under second-order conditions.
See text.
d

160
L. Canovese et al. / Inorganica Chimica Acta 346 (2003) 158ꢀ168
/
The electron withdrawal due to electronegativity of
the halide enhances the coordinative capability of the
sulphur to palladium as can be deduced from the
decrease in the sulphur inversion rate. Consistently,
the signal of the thioetheric protons of the complex
[Pd(CH3CN)(Me)(MeNꢀ
singlet at room temperature indicating the weakness of
the CH3CNꢀPd bond.
The case of [Pd(PPh3)(Me)(MeNꢀ
/
StBu)]ꢂ appears as a sharp
/
/
StBu)]ꢂ deserves a
detailed discussion since the electronic properties of
PPh3 impart to the substrate a peculiar behaviour in
solution and an unusual reactivity which will be
discussed further on. As for the rearrangement in
solution, it is noteworthy that the complex appears as
a pair of diasteroisomers which rapidly interconvert, as
can be deduced from the 1H and 31P NMR spectra
(Scheme 2).
The low temperature (223 K, 200 MHz) and the room
temperature 31P NMR spectra (298 K, 300 MHz) in
CDCl3 display two distinct singlets (dꢁ34.07, 39.07
/
ppm) with relative intensity of 1:10, respectively. On
increasing the temperature collapse of the singlets is
readily reached (298 K, 200 MHz) and eventually a
single sharp signal is observed. The low temperature 1H
NMR (200 MHz) and room temperature (300 MHz)
spectra confirm the hypothesis of the presence of two
diasteroisomers. On the basis of the shielding properties
of phenyl cones linked to phosphorus (which causes the
highest field shift to the signal of the adjacent protons)
we tentatively assign the trans configuration to the more
abundant isomer with respect to the mutual position of
Me and sulphur: (hereafter trans, see Experimental
section). The high trans influence of phosphine would
destabilise the cis isomer to a higher extent than the
trans one, inducing a generalised fast rearrangement at
Scheme 1.
2.2. Solution behaviour
2.2.1. Methyl complexes
The most prominent phenomenon that can be in-
1
vestigated by H NMR technique in these substrates is
the inversion of absolute configuration of sulphur since
no other fluxional rearrangements could usually be
observed owing to the existence of only one diasteroi-
somer. Such behaviour was deeply investigated in
previous papers and there is no merit in analysing it
again, even if novel species are involved [3]. It should be
sufficient to remind that this phenomenon is concentra-
tion-independent and will bring about, when operative,
the collapse of the AB quartet ascribable to the
diasterotopic CH2S endocyclic protons. The collapsing
temperature in the case of the new complex
room temperature via the breaking of Pdꢀ
/
N or PdꢀS
/
bonds. Moreover, it is evident that the presence of
groups with high trans influence will induce loss of
diasterotopicity of the CH2S protons whose NMR
signal at room temperature will turn into a sharp singlet.
2.2.2. Allyl complexes
As already stated elsewhere, the insertion of allenes
into the PdꢀMe bond might represent an alternative
/
route to sterically hindered allyl complexes [3]. The
substrates studied in this work are however synthesised
either via the customary reaction of the specific ancillary
ligand with the allyl dimer [Pd (m-Cl)(h3-1,1,2-
[PdCl(Me)(MeNꢀ
found in analogous systems [3]. In the case of the
complexes [PdX(Me)(MeNꢀ Cl, Br, I) the
StBu)], (Xꢁ
/SMe)] is 328 K and is close to that
/
/
Me3C3H2)]2 or via allene insertion into the Pdꢀ
/
Me
collapsing temperatures depend somewhat on the elec-
tronegativity of the halide trans to sulphur. Thus, at the
selected temperature of 298 K the NMR spectra of the
bond. NMR and UVꢀVis spectra of the insertion
/
products were in any case superposable to those of
authentic samples independently synthesised and char-
acterised. As for the fluxional rearrangement, it should
be sufficient to state that the behaviour of the species
involved is similar to that of analogous species described
in depth in several papers published so far [6]. The
endocyclic protons CH2ꢀS of the complexes display
/
different behaviour on going from the well resolved AB
quartet of the chloride derivative to the broad singlet of
[PdI(Me)(MeNꢀ
StBu)] (Fig. 1).
/

L. Canovese et al. / Inorganica Chimica Acta 346 (2003) 158ꢀ
/
168
161
Fig. 1. Selected zone of 1H NMR spectra of [PdX(Me)(MeNꢀ
/
StBu)] (Xꢁ
Cl, Br, I) complexes recorded at 298 K in CDCl3.
/
Scheme 2.
The slower reactions were studied under pseudo-first-
order conditions ([Allene]0]10ꢄ[Pd]0, [Pd]0:1ꢄ
presence of the four available diasteroisomers could
never be detected since inversion of absolute configura-
tion of the sulphur is generally operative at any
attainable low temperature. At 298 K the apparent allyl
rotation that usually occurs by a mechanism analogous
to that proposed in the case of isomerisation of the
/
/
/
/
10ꢃ4 mol dmꢃ3) whereas the faster ones were examined
under second-order conditions. The kobs or the k2 values
were determined by the customary non-linear fit of
absorbance versus time data for first-order or second-
order integrated rate laws, respectively. The k2 values in
the case of the slower reactions were determined as the
slopes of plots of pseudo-first-order kobs versus [A]0
[Pd(PPh3)(Me)(MeNꢀ
/
StBu)] substrate is observed (i.e.
S bond and recombination).
breaking of PdꢀN or Pdꢀ
/
/
However, it is noteworthy that this kind of isomerism
could take place via an associative path promoted by the
lone pair at sulphur [7]. Eventually in the temperature
range dictated by the nature of the solvent (CDCl3 or
CD2Cl2) no hints of h3-h1-h3 isomerism are gained since
the signals ascribable to syn and anti moieties (CH3 and
H) never collapse.
(Aꢁ/1,1-dimethylpropadiene) according to the rate law
kobs ꢁk2[A]0
(1)
No statistically significant intercept could be detected
in these systems. This finding is in accord with previous
results which have been discussed in a preceding paper
dealing with analogous systems [3]. For the sake of
completeness and clarity we collected all the results
obtained so far in Table 1, so that the most important
information emerging from these systems can be easily
gathered. Analysis of the data in Table 1 suggests some
primary conclusions that can be summarised as follows:
2.2.3. Kinetics of allene insertion
The reaction of allene insertion (reaction (1)) was
1
studied by means of H NMR and UVꢀ
/
Vis techniques
in CD2Cl2 or in CH2Cl2 solution at 25 8C (unless
otherwise stated) and the results are summarised in
Table 1.
i) The effects induced by the substituents R (to
sulphur) and R? (in position six of pyridine ring)

162
L. Canovese et al. / Inorganica Chimica Acta 346 (2003) 158ꢀ168
/
have been confirmed; in particular the rate of
insertion on going from the bulkiest (Rꢁt
Bu) to
the least hindered (RꢁMe) sulphur substituent
accordingly increases to some extent. Moreover, if
the more electron-accepting phenyl group is com-
i
pared to the sterically similar Pr the rate of allene
insertion increases by two orders of magnitude.
Eventually, the remarkable increase in the rate of
insertion is definitely established when distortion of
the coordination main plane of complexes is in-
duced by the pyridine ring substituent, Cl being
more efficient than Me in this respect.
undissociated chloride in non protic solvents leading to
more reactive species cannot be ruled out.
/
/
The associative character of the rate-determining step
clearly emerges from these findings and from the
activation parameters obtained from the Eyring plot
[8] of reaction rates carried out in THF at different
temperatures (DH#ꢁ
/
109
/
0.2 Kcal molꢃ1
;
DS#ꢁ
/
ꢃ
/
219
/
1 cal molꢃ1 Kꢃ1). THF was chosen in order to
expand the temperature range safely attainable. Asso-
ciative attack of allene to the substrate S presumably
takes place through a penta-coordinated trigonal bi-
pyramidal transition state leading to the tetra-coordi-
nated species I. Under these circumstances the X group
acts as the leaving group, thereby explaining the strong
dependence of the reaction rate on the nature of X. As
can be seen in Table 1, the complexes [Pd(NCMe)(Me)-
ii) The influence of the substituent cis to Me (X) was
carefully determined. The reaction rate was found
to strongly depend on the nature of X and the
reactivity order Cl5
/
Br:
/
IꢀCH3CN proved to be
/
operative.
(HNꢀ
(MeNꢀ
so far, irrespective of the pyridine substituent (the
complexes [Pd(NCMe)(Me)(HNꢀ and
SPh)]ꢂ
[Pd(NCMe)(Me)(MeNꢀ
SPh)]ꢂ are too reactive to be
/
SR)]ꢂ (Rꢁ
/
Me, tBu) and [Pd(NCMe)(Me)-
/
StBu)]ꢂ display the highest reactivity observed
Based on these experimental findings we propose the
following mechanistic Scheme 3:
Under the steady-state assumption, the overall rate
law is:
/
/
studied). Apparently, some sort of levelling off effect
takes place in the case of acetonitrile complexes. In the
kꢅꢁkf [A]km=(kr[Xꢃ]ꢂkm)
(2)
case of complexes [PdX(Me)(MeNꢀ
/
StBu)] (Xꢁ
Cl, Br,
/
which is a time-dependent function since [Xꢃ] changes
with time. However, since the apparent kobs or k2 values
appear to be time-independent, we advance the hypoth-
esis that kr is negligible with respect to km. Thus, under
I) the reactivity trend agrees with the decreasing
electronegativity of the halide; however, no outstanding
effects are observed, probably due to the non protic
nature of the solvent employed. Under these circum-
stances the nucleophilic power of the halides will be
considerably enhanced and their ‘lability’ will be de-
pressed, giving rise to a levelling-off in reactivity. At
variance, in protic solvents the nucleophilic capability of
the halides spans almost three orders of magnitude and
a reverse leaving group effect is observed [5]. The
subsequent fast Me migration will not influence the
observed overall rate. In this respect one might interpret
the complete reaction profile as an asynchronous
mechanism occurring in at least two steps, the first
being the more energetically disfavoured. At variance
with our previous conclusions derived from the use of
complexes with only one leaving group (Cl) [3], the
influence of the leaving group, while confirming our
mechanistic picture, prompts us to advance a different
hypothesis about the structure of the pentacoordinated
transition state. According to the well-established and
widely accepted mechanism of nucleophilic substitution
in planar tetracoordinated complexes, we suggest that
the trigonal plane contains the entering allene, the
leaving group (X), and the substituent trans to the
leaving group (sulphur).
the limiting condition kmꢁ
mining step is the attack of allene to the substrate with
displacement of Xꢃ), rate law 2 reduces to k*ꢁ
kf[A]0
with k2ꢁkf (Eq. (1)) or to kfꢁk2 under second-order
/
kr[Xꢃ] (i.e. the rate deter-
/
/
/
conditions. In order to clarify the role of the halide ion
we made some determinations in the presence of an
excess of Ph(nBu)3NꢂClꢃ ([Clꢃ]0]
/
10ꢄ[Pd]0). How-
/
ever, the results were hardly interpretable since, instead
of the expected decrease in the reactivity a modest
increase (20%) in the observed rate was observed. A
similar result was found by other authors [4g] and no
unambiguous conclusion was reached from such a
finding. We advance herein the plausible explanation
that a change in dielectric constant will increase to some
extent the reaction rate according to the trend observed
when solvents with increasing dielectric constants were
employed (see further). However, alternative mechan-
isms involving attack to the metal centre by the almost
An alternative mechanism which is consistent with the
experimental evidence involves formation of a five-
coordinate intermediate followed by the rate-determin-
ing methyl migration with concomitant breaking of the
palladiumꢀ/halide bond (Scheme 4). (However, in this
Scheme 3.
case the activation parameters would be hard to

L. Canovese et al. / Inorganica Chimica Acta 346 (2003) 158ꢀ
/
168
163
Scheme 4.
interpret owing to their composite nature, since now the
rate law would be k*ꢁkf[A]km/kr).
The influence of the nature of the solvent was also
investigated for [PdCl(Me)(MeNꢀSMe)] and the results
are collected in Table 2. As can be seen, on going from
CH2Cl2 to CH3CN the reaction rates only double.
Clearly the dielectric characteristics of the solvent are
not of prime importance, as expected of the similar,
neutral transition states involved.
/
/
Scheme 5.
30 ppm as a broad singlet (due to the pair of fast
interchanging isomers) which increases at first with time
and subsequently disappears slowly.
Thus, concentration vs time data for the species S and
P2 were obtained from the relevant 31P NMR signals
(Section 3) and simultaneously fitted to the differential
equation model of Scheme 5 via a multiresponse non
linear regression algorithm based on Marquardt’s
method [9] in the MATLABTM [10] computing environ-
2.2.4. Kinetics of allene insertion on
[Pd(PPh3)(Me)(MeNꢀ
StBu)]ꢂ
/
The 1H and 31P NMR spectra of the mixture obtained
at the end of the reaction between allene and
[Pd(PPh3)(Me)(MeNꢀ
StBu)]ꢂ show the presence of
three different products. These species were identified
/
ment, which provided the fitted values of kfkm/(krꢂ
km):kfꢁk2ꢁ(7.290.1)ꢄ and k2Iꢁ(3.39
10ꢃ3
0.3)ꢄ
10ꢃ1 molꢃ1 dm3 sꢃ1. Fig. 4 shows the model
/
/
/
/
/
/
/
/
in solution as [Pd(h3-1,1,2-Me3C3H2)(PPh3)2]ꢂ, [Pd(h3-
/
1,1,2-Me3C3H2)(MeNꢀ
/
StBu)]ꢂ and the free ligand
concentration profiles for S and P2 along with their
respective experimental data sets (standard error of
MeNꢀ
/
StBu by comparison with the spectra of the
10ꢃ4
;
parameter correlation coefficientꢁ
/
authentic samples independently synthesised. The 1H
NMR spectrum of the reaction mixture together with
those of the pure samples are reported in Fig. 2 whereas
selected signals of the species involved are reported in
Section 3.
fitꢁ
0.44).
The k2 value could be obtained separately by fitting
/
4ꢄ
/
ꢃ
/
the concentration of S to time according to the
customary integrated form of the rate law for second-
order reactions [11] ([S]0ꢁ
/
0.03, [A]0ꢁ0.146 mol
/
The probable reaction course yielding these products
is represented in Scheme 5, which can be easily
monitored by 31P NMR (298 K, 300 MHz) as can be
seen in Fig. 3 where the substrate S shows a time-
decaying pair of broad singlets at 34 and 39 ppm
ascribable to the two cis and trans diasteroisomers,
respectively (see earlier), whereas the bis-phosphine allyl
dmꢃ3). The resulting value was virtually identical to
that derived from the simultaneous multi-response
fitting procedure.1
As can be seen from the ensuing k2 value, the presence
of PPh3 group strongly depresses the reactivity of
species P2 displays a time-increasing AB system (dꢁ
27.0 and 25.3 ppm, Jꢁ40.3 Hz). The intermediate I,
which we identify as a tetracoordinated allyl complex
bearing an S (or N)-bound pyridylꢀthioether ligand
(MeNꢀ
StBu) with a dangling N (or S)-arm, resonates at
/
1
Owing to the presence of the fast equilibrium between the rapidly
/
interchanging trans ꢀ
speaking the k2 constant determined experimentally should be given
by the expression k2ꢁ(k2trans k2cis KE)/(1ꢂKE). However, we may
assume that k2:k2trans based on the hypothesis that the cis-isomer is
either unreactive or at most as reactive as the trans-isomer since the
distorted pyridine nitrogen should be a better leaving group than
sulphur. In other words, second-order conversion of the substrate S to
intermediate I will proceed predominantly via the k2trans pathway.
Moreover, it is noteworthy that also the intermediate I is probably
/
cis isomers (trans X
/
cis, KE:
/
0.1), strictly
/
/
ꢂ/
/
/
/
Table 2
Second-order rate constants, k2 (molꢃ1 dm3 sꢃ1) for the insertion of
1,1-dimethylpropadiene into the PdꢀMe bond of the complex
/
[PdCl(Me)(MeNꢀ
/
SMe)] in different solvents at 25 8C
present as two pairs of isomers bearing the NꢀS ligand S- or N-bound
/
to palladium and with the substituted allyl terminus pseudo-cis or
pseudo-trans to phosphine. The presence of a dangling arm would
however promote a fast interchange among all the possible species,
giving rise to the observed room temperature broad singlet [12]. At low
Complex
Solvent
CH2Cl2
2.42
THF
4.3
MeCN
5.1
[PdCl(Me)(MeNꢀSMe)]
/
temperature (223 K) the signal splits into two distinct singlets (dꢁ
/
23.3, 30.5 ppm) displaying different population (1:10).

164
L. Canovese et al. / Inorganica Chimica Acta 346 (2003) 158ꢀ168
/
Fig. 2. Selected zones of 1H NMR spectra recorded at 298 K in CDCl3 of: (1) MeNꢀ
(3) [Pd(h3-1,1,2-Me3C3H2)(MeNꢀStBu)]ꢂClO4ꢃ; (4) reaction mixture (Scheme 5).
/
StBu (free ligand); (2) [Pd(h3-1,1,2-Me3C3H2)(PPh3)2]ꢂClO4
;
ꢃ
/
[Pd(PPh3)(Me)(MeNꢀ
/
StBu)]ꢂ owing to the low ten-
minced ice were then added. The product was extracted
with Et2O (150 ml), treated with anhydrous MgSO4 for
12 h, filtered and dried under vacuum. 1.65 g (10.7
mmol) of the crude compound as a yellowish oil was
obtained. The product was considered to be reasonably
pure and therefore used in the reported synthesis (vide
infra) without further purification.
dency of the nitrogen (or, less likely, the sulphur) of the
thioether ligand to act as the leaving group attributable
to the chelating effect [13].
Quite interestingly, two molecules of I will further
react with each other giving rise to the products ([Pd-
(h3-1,1,2-Me3C3H2)(MeNꢀ
/
StBu)]ꢂ, [Pd(h3-1,1,2-Me3-
C3H2)(PPh3)2)]ꢂ and MeNꢀ
/
StBu), probably through
Yield 70.4%. Anal. Found: C, 62.46; H, 7.07; N, 9.28.
Calc. for C8H11NS: C, 62.70; H, 7.24; N, 9.14%. IR:
the interplay of mutual trans-influence and electronic
factors of the fragments involved in the multicentre
intermediate that is likely to be formed.
1
nCꢀN 1591.5 cmꢃ1 (NaCl). H NMR (CDCl3, Tꢁ
/
298
7.16
7.02 (1H, H5Pyr, d, Jꢁ
7.7
CH2ꢀS, s), dꢁ2.54 (3H, Pyrꢀ
2.07 (3H, Sꢀ
CH3, s). 13C NMR (CDCl3,
298 K, dꢁppm); dꢁ
(C2Pyr), dꢁ136.56 (CP4yr), dꢁ
(C5Pyr), dꢁ
39.87 (PyrꢀCH2ꢀS), dꢁ
dꢁ14.94 (SꢀCH3).
K, dꢁ
(1H, H3Pyr, d, Jꢁ
Hz), dꢁ3.77 (2H, Pyrꢀ
CH3, s), dꢁ
Tꢁ
/
ppm); dꢁ
/
7.54 (1H, H4Pyr, t, Jꢁ
7.7 Hz), dꢁ
/
7.7 Hz), dꢁ
/
/
/
/
/
/
/
/
/
/
/
3. Experimental
/
/
/
157.72 (C6Pyr), dꢁ
121.15 (C3Pyr), dꢁ
/157.49
/
/
/119.54
3.1. Synthesis of ligands
/
/
/
/
24.21 (PyrꢀCH3)
/
/
/
3.1.1. 6-Methyl-2-methylthiomethylpyridine (MeSꢀ
NMe)
To a suspension of 5 g (89.3 mmol) KOH in 50 ml of
/
DMSO, 2.13 g (30.4 mmol) of CH3SꢃNaꢂ and 2.16 g
(15.2 mmol) of 6-methyl-2-chloromethylpyridine [14]
were added. The resulting suspension was stirred for
1.5 h at room temperature (r.t.). Water (100 ml) and
3.1.2. R?Nꢀ
/
SR (R?ꢁ
/
H; Rꢁ
/
Me, t-Bu: R?ꢁ
/
Me; Rꢁt-
/
Bu)
The synthesis of the title ligands was carried out
according to published procedures [15].

L. Canovese et al. / Inorganica Chimica Acta 346 (2003) 158ꢀ
/
168
165
Fig. 3. Selected zones recorded at 298 K in CD2Cl2 of the time dependent 31P NMR signals of the species involved in the reaction reported in Scheme
5.
3.2. Synthesis of methyl complexes
3.2.1. [PdCl(Me)(MeNꢀSMe)]
/
To 255.2 mg (0.96 mmol) of the complex
[PdCl(Me)(COD)] [16] dissolved in 30 ml of freshly
distilled toluene, 162.4 mg (1.06 mmol) of MeNꢀSMe
/
ligand was added under inert atmosphere (N2). The
resulting solution was stirred at r.t. for 4 h and then
dried under reduced pressure. The residue was dissolved
in CH2Cl2, treated with activated charcoal and filtered
on celite filter. Reduction to small volume and pre-
cipitation with Et2O at r.t. yields 234.4 mg (0.76 mmol)
of the title complex as pale-yellow microcrystals.
Yield 79%. Anal. Found: C, 35.01; H, 4.35; N, 4.48.
Calc. for C9H14ClNPdS: C, 34.85; H, 4.55; N, 4.52%.
1
IR: nCꢀN 1600.8 cmꢃ1 (KBr). H NMR (CDCl3, Tꢁ
/
298 K, dꢁ
7.21 (1H, H5Pyr, d, Jꢁ
7.7Hz), dꢁ4.56, 4.18 (2H, Pyrꢀ
15.3), dꢁ3.07 (3H, PyrꢀCH3, s), dꢁ
s), dꢁ1.08 (3H, Pdꢀ
CH3, s). 13C NMR (in CDCl3, Tꢁ
298 K), (ppm) dꢁ
163.78 (C2Pyr), dꢁ154.62 (C6Pyr), dꢁ
138.40 (C4Pyr), dꢁ125.39 (C3Pyr), dꢁ121.09 (C5Pyr), dꢁ
/
ppm) dꢁ
/
7.64 (1H, H4Pyr, t, Jꢁ
7.7Hz), dꢁ
7.19 (1H, H3Pyr, d, Jꢁ
CH2ꢀS, ab system, Jꢁ
2.28 (3H, SꢀCH3,
/
7.7 Hz), dꢁ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
Fig. 4. Fit of concentrations (Y, mol dmꢃ3) to time (t, min) for
/
/
/
reaction in Scheme 5 according to the proposed mechanism (see text).
/
/
/

166
L. Canovese et al. / Inorganica Chimica Acta 346 (2003) 158ꢀ168
/
46.21 (Sꢀ
/
CH2ꢀ
/
Pyr), dꢁ
/
20.09 (Sꢀ
/
CH3), dꢁ
/
26.97
3.2.6. [Pd(NCMe)(Me)(MeNꢀ
StBu)]ꢂOTfꢃ
/
(PyrꢀCH3), dꢁ
/
/
ꢃ
/
4.97 (Pdꢀ
/
CH3).
Yellow solid. Yield 91%. Anal. Found: C, 35.67; H,
4.59; N, 5.76. Calc. for C15H23F3N2O3PdS2: C, 35.54; H,
4.57; N, 5.53%. IR: nCꢀN 1600.8 cmꢃ1, nCꢀF 1263.3
t
3.2.2. [PdCl(Me)(R?Nꢀ
/
SR)] (R?ꢁ
/
H; RꢁMe, Bu:
/
1
cmꢃ1, nSꢀO 1031.9 cmꢃ1 (KBr). H NMR (in CDCl3,
t
R?ꢁ
/
Me; RꢁMe, Bu)
/
Tꢁ
dꢁ
7.52 (1H, H3Pyr, d, Jꢁ
Jꢁ5.5 Hz), dꢁ4.58, 4.40 (2H, Pyrꢀ
Jꢁ17.2 Hz), dꢁ2.75 (3H, NꢁCꢀCH3, s), dꢁ
PyrꢀCH3, s), dꢁ1.27 (9H, SꢀC(CH3)3, s), dꢁ
Pdꢀ
CH3, s). 13C NMR (in CDCl3, Tꢁ
dꢁ
160.70 (C2Pyr), dꢁ156.48 (C6Pyr), dꢁ
dꢁ 121.46 (Nꢁ
125.38 (C3Pyr), dꢁ121.15 (C5Pyr), dꢁ
CH3), dꢁ118.98 (CF3SO3), dꢁ52.33 (SꢀC(CH3)3),
dꢁ42.68 (SꢀCH2ꢀPyr), dꢁ30.83 (SꢀC(CH3)3), dꢁ
26.48 (PyrꢀCH3), dꢁ3.60 (NꢁCꢀCH3), dꢁ 3.81
(PdꢀCH3).
/
298 K), (ppm) dꢁ
/
7.76 (1H, H4Pyr, t, Jꢁ
/
7.7 Hz),
7.22 (1H, H5Pyr, d,
CH2ꢀS, ab system,
These complexes were synthesised according to pub-
lished procedures ([3b] and references therein).
/
/
7.7 Hz), dꢁ
/
/
/
/
/
/
/
/
/
/
2.44 (3H,
3.2.3. [Pd(NCMe)(Me)(HNꢀ
To 150.0 mg (0.51 mmol) of [PdCl(Me)(HNꢀ
/
SMe)]ꢂOTfꢃ
/
/
/
/
1.03 (3H,
/
SMe)]
/
/
298 K), (ppm)
139.89 (C4Pyr),
C ꢀ
dissolved in 20 ml of CH2Cl2, 131.6 mg (0.51 mmol) of
AgCF3SO3 (AgOTf) dissolved in 4.5 ml of MeCN were
added. The reaction mixture was stirred in the dark for 3
hours and then filtered on millipore. The clear solution
was concentrated at r.t. under reduced pressure and the
residue dissolved in 1 ml of CH2Cl2 was eventually
precipitated by addition of Et2O. 199.3 mg (0.44 mmol)
of the title compound as a whitish solid were obtained.
Yield 87%. Anal. Found: C, 29.23; H, 3.63; N, 6.49.
Calc. for C11H15F3N2O3PdS2: C, 29.31; H, 3.35; N,
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
ꢃ
/
/
3.2.7. [Pd(NCMe)(Me)(MeNꢀ
SPh)]ꢂOTfꢃ
/
Whitish solid. Yield 87%. Anal. Found: C, 38.99; H,
3.57; N, 5.12. Calc. for C17H19F3N2O3PdS2: C, 38.75; H,
3.63; N, 5.32%. IR: nCꢀN 1602.8 cmꢃ1, nC-F 1255.6
6.21%. IR: nCꢀN 1600.8 cmꢃ1, nCꢀF 1249.8 cmꢃ1, nSꢀO
1039.6 cmꢃ1 (KBr). H NMR (CDCl3, Tꢁ
/
298K, dꢁ
/
1
1
cmꢃ1, nSꢀO 1029.9 cmꢃ1 (KBr). H NMR (in CDCl3,
ppm) dꢁ
H4Pyr, t, Jꢁ
Hz), dꢁ4.53, 4.26 (2H, Pyrꢀ
16.4 Hz), dꢁ2.51 (6H, SꢀCH3, Nꢂ
0.88 (3H, PdꢀCH3, s).
The following substrates were prepared using proce-
dures analogous to that of [Pd(NCMe)(Me)(HNꢀ
SMe)]ꢂOTfꢃ.
/
8.80 (1H, H6Pyr, bd, Jꢁ
7.3 Hz), dꢁ
7.63 (1H, H3Pyr HP5yr, d, Jꢁ
CH2ꢀ
/
4.8 Hz), dꢁ7.90 (1H,
/
Tꢁ
7.33 (5H, H3Pyr, H5Pyr, Hortho, Hpara, m), dꢁ
PyrꢀCH2ꢀS, bs), dꢁ2.81 (3H, NꢂCꢀCH3, s), dꢁ
2.43 (3H, PyrꢀCH3, s), dꢁ1.06 (3H, Pdꢀ
NMR (in CDCl3, Tꢁ298 K), (ppm) dꢁ
dꢁ
154.82 (C6Pyr), dꢁ139.72 (C4Pyr), dꢁ
dꢁ 133.10 (Cmeta), dꢁ
121.95 (C5Pyr), dꢁ
dꢁ130.45 (Cortho), dꢁ128.45 (C ꢀS), dꢁ
C ꢀCH3), dꢁ50.24 (SꢀCH2ꢀPyr), dꢁ
CH3), dꢁ3.50 (NꢁCꢀCH3), dꢁ 2.02(Pdꢀ
/
298, dꢁ
/
ppm) dꢁ
/
7.67 (3H, H4Pyr, Hmeta, m), dꢁ
/
/
/
/7.3
/4.76 (2H,
/
/
/
S, ab system, Jꢁ
CꢀCH3, s), dꢁ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
CH3, s). 13C
/
/
/
161.16 (C2Pyr),
125.63 (C3Pyr),
/
/
/
/
/
/
/
131.49 (Cpara),
121.21 (Nꢂ
/
/
/
/
/
/
/
/
/
/
26.58 (Pyrꢀ
/
3.2.4. [Pd(NCMe)(Me)(HNꢀ
StBu)]ꢂOTfꢃ
/
/
/
/
/
ꢃ
/
/CH3).
Whitish solid. Yield 78%. Anal. Found: C, 33.87; H,
4.41; N, 5.72. Calc. for C14H21F3N2O3PdS2: C, 34.12; H,
4.29; N, 5.68%. IR: nCꢀN 1602.8 cmꢃ1, nCꢀF 1259.5
3.2.8. [Pd(PPh3)(Me)(MeNꢀ
/
StBu)]ꢂOTfꢃ
To 100.0 mg (0.28 mmol) of [PdCl(Me)(MeNꢀ
/
StBu)]
cmꢃ1, nSꢀO 1031.9 cmꢃ1 (KBr). 1H NMR (CDCl3, Tꢁ
/
dissolved in 20 ml of THF, 71.9 mg (0.28 mmol) of
AgCF3SO3 (AgOTf) dissolved in 3 ml of MeCN were
added. The reaction mixture was stirred in the dark for 3
h and then the AgCl was filtered off by millipore. To the
clear solution 75.4 mg (0.28 mmol) of PPh3 were added
and the resulting mixture was concentrated at r.t. under
reduced pressure. Addition of Et2O induces precipita-
tion of a yellowish oil which crystallises under stirring at
0 8C. 171.4 g (0.23 mmol) of the title complex as a
whitish solid was obtained by filtration and drying
under vacuum.
295 K, dꢁ
7.88 (1H, H4Pyr, t, Jꢁ
7.8 Hz), dꢁ
7.56 (1H, H5Pyr, d, Jꢁ
PyrꢀCH2ꢀS, b AB system Jꢁ15.2 Hz,), dꢁ
NꢂCꢀCH3, s), dꢁ1.35 (9H, SꢀC(CH3)3, s), dꢁ
(3H, PdꢀCH3, s)
/
ppm) dꢁ
/
8.73 (1H, H6Pyr, d, Jꢁ
7.8 Hz), dꢁ
7.66 (1H, H3Pyr, d, Jꢁ
7.8 Hz), dꢁ4.40 (2H,
2.56 (3H,
0.88
/
5.1 Hz) dꢁ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
3.2.5. [Pd(NCMe)(Me)(HNꢀ
SPh)]ꢂOTfꢃ
/
Pale orange solid. Yield 72%. Anal. Found: C, 37.20;
H, 3.61; N, 5.67. Calc. for C16H17F3N2O3PdS2: C, 37.47;
H, 3.34; N, 5.46%. IR: nCꢀN 1600.8 cmꢃ1, nCꢀF 1249.8
Yield 82%. Anal. Found: C, 51.01; H, 4.63; N, 1.89.
Calc. for C31H35F3NO3PPdS2: C, 51.13; H, 4.84; N,
1.92%. IR: nCH 3055.1 cmꢃ1, nCꢀN 1604.7 cmꢃ1, nCF
cmꢃ1, nSꢀO 1039.6 cmꢃ1 (KBr). H NMR (in CDCl3,
1
Tꢁ
dꢁ
7.85 (1H, H4Pyr, td, Jꢁ
(1H, H3Pyr, dd, Jꢁ
7.7 Hz, Jꢁ
H5Pyr, bd, Jꢁ
5.9 Hz), dꢁ7.45 (5H, Sꢀ
4.81, dꢁ4.44 (2H, PyrꢀCH2ꢀS, ab system, Jꢁ
Hz), dꢁ2.52 (3H, NꢂCꢀCH3, s), dꢁ0.89 (3H, Pdꢀ
CH3, s).
/
298 K, dꢁ
/
ppm) dꢁ
/
8.90 (1H, H6Pyr, d, Jꢁ
/
5.9 Hz),
1.7 Hz), dꢁ7.74
1.7 Hz), dꢁ7.67 (1H,
C6H5, m), dꢁ
14.5
1
/
/
7.7 Hz, Jꢁ
/
/
1271.0 cmꢃ1, nSꢀO 1031.9 cmꢃ1 (KBr). H NMR (in
/
/
/
CDCl3, Tꢁ
15Hphenyl, m), dꢁ
(3H, PyrꢀCH3, bs), dꢁ
0.79 (3H, Pdꢀ
CH3, s). 31P NMR (in CDCl3, Tꢁ
dꢁppm) dꢁ37.71 (PPh3, bs).
/
298 K, dꢁ
4.68 (2H, Pyrꢀ
0.89 (9H, Sꢀ
/
ppm) dꢁ
/
7.3ꢀ
CH2ꢀ
C(CH3)3, s), dꢁ
298 K,
/
8.0 (18H, 3HPyr
,
/
/
/
/
/
/
/
S, s), dꢁ2.73
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/

L. Canovese et al. / Inorganica Chimica Acta 346 (2003) 158ꢀ
/
168
167
StBu)]
3.3.2. [Pd(h3-1,1,2-Me3C3H2)(MeNꢀSMe)]ꢂClO4
/
ꢃ
3.2.9. [PdBr(Me)(MeNꢀ
/
To 100.0 mg (0.28 mmol) of [PdCl(Me)(MeNꢀ
/
Stꢀ
/
To a solution of 85.4 mg (0.189 mmol) of the dimer
[Pd(m-Cl)(h3-1,1,2-Me3C3H2)]2 in CH2Cl2 (5 ml), 59.7
Bu)] dissolved in 60 ml of CH2Cl2 and 40 ml of acetone,
172.8 mg (1.45 mmol) of finely grounded KBr were
added. The resulting yellow suspension was stirred till its
colour turned to brown (2h) and eventually dried under
reduced pressure. The residue was treated with 20 ml of
CH2Cl2, filtered, and the resulting clear solution was
eventually collected. Concentration under reduced pres-
sure and addition of Et2O yields 70.9 mg (0.21 mmol) of
the title complex as a brown solid.
mg (0.387 mmol) of the ligand MeNꢀSMe dissolved in 4
/
ml of CH2Cl2 and 111.5 mg (0.794 mmol) of Na-
ClO.4H2O in 4 ml of MeOH were added. The resulting
suspension was stirred for 1 h and dried under reduced
pressure. The residue was dissolved in CH2Cl2, treated
with activated charcoal and filtered on celite filter.
Reduction to small volume and addition of Et2O yield
157.4 mg (0.356 mmol) of the title product as a yellow
solid.
Yield 75%. Anal. Found: C, 36.61; H, 4.91; N, 3.46.
Calc. for C12H20BrNPdS: C, 36.33; H, 5.08; N, 3.53%.
Yield 94%. Anal. Found: C, 37.92; H, 5.17; N, 3.20.
Calc. for C14H22ClNO4PdS: C, 38.02; H, 5.01; N,
3.17%.I.R.: nCꢀN 1602.8 cmꢃ1, nClO 1089.7 cmꢃ1, dClO
IR: nCꢀN 1598.9 cmꢃ1 (KBr). 1H NMR (in CDCl3, Tꢁ
/
298 K, dꢁ
7.19 (1H, H5Pyr, d, Jꢁ
Jꢁ8.4 Hz), dꢁ4.62, 4.18 (2H, Pyrꢀ
Jꢁ14.6), dꢁ3.11(3H, PyrꢀCH3, s), dꢁ
C(CH3)3, s), dꢁ1.15 (3H, Pdꢀ
CH3, s). 13C NMR (in
CDCl3, Tꢁ298 K, dꢁppm) dꢁ
162.86 (C2Pyr), dꢁ
156.55 (C6Pyr), dꢁ138.50 (C4Pyr), dꢁ124.97 (C3Pyr), dꢁ
119.75 (C5Pyr), dꢁ
50.51(SꢀC(Me)3), dꢁ42.45 (Sꢀ
CH2ꢀPyr), dꢁ30.74 (SꢀC(CH3)3), dꢁ28.66 (Pyrꢀ
CH3), dꢁ 7.29 (PdꢀCH3).
/
ppm) dꢁ
/
7.61 (1H, H4Pyr, t, Jꢁ
8.0 Hz), dꢁ
7.15 (1H, H3Pyr, d,
CH2ꢀS, ab system,
1.25 (9H, Sꢀ
/
7.7 Hz), dꢁ
/
626.8 cmꢃ1 (KBr). 1H NMR (in CDCl3, Tꢁ
/
298 K, dꢁ
7.7 Hz), dꢁ7.55 (1H,
7.38 (H3Pyr, d, Jꢁ
7.9 Hz), dꢁ
S, Hsyn, s), dꢁ3.74 (1H, Hanti, s),
CH3, s), dꢁ2.31 (3H, SꢀCH3, s),
2.14 (3H, CH3central, s), dꢁ
1.44 (3H, CH3anti, s)
/
/
/
ppm) dꢁ
H5Pyr, d, Jꢁ
4.42 (3H, Pyrꢀ
dꢁ2.75 (3H, Pyrꢀ
dꢁ
dꢁ
/
7.81 (1H, H4Pyr, t, Jꢁ
7.9 Hz), dꢁ
CH2ꢀ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
1.71 (3H, CH3syn, s),
/
/
/
/
/
/
/
/
/
/
/
ꢃ
/
/
3.3.3. [Pd(h3-1,1,2-Me3C3H2)(PPh3)2]ꢂClO4
ꢃ
3.2.10. [PdI(Me)(MeNꢀ
To 100.0 mg (0.28 mmol) of [PdCl(Me)(MeNꢀ
/
StBu)]
The cream-white title complex was prepared in
the same way as [Pd(h3-1,1,2-Me3C3H2)(MeNꢀ
/
StBu)]
dissolved in 10 ml of CH2Cl2, 254.8 mg (1.70 mmol) of
finely grounded anhydrous NaI were added. The result-
/
ꢃ
SMe)]ꢂClO4 using 2 equiv. of PPh3 as ancillary
ligand.
ing cloudy pinkꢀorange suspension was stirred for 1 h
/
Yield 94%. Anal. Found: C, 61.85; H, 4.93. Calc. for
C42H41ClO4P2Pd: C, 62.00; H, 5.08%. IR: nCH 3051.3
cmꢃ1, nClO 1091.7 cmꢃ1, dClO 623.0 cmꢃ1 (KBr). H
and washed in a separatory funnel with two aliquots of
10 ml each of distilled water. The organic residue was
treated with CaCl2 and the resulting red-brick filtered
anhydrous solution was concentrated under reduced
pressure. Addition of Et2O yields the precipitation of
92.5 mg (0.21 mmol) of the title complex as a red-brick
solid.
1
NMR (in CDCl3, Tꢁ
P(C6H5)3, m), dꢁ3.55 (1H, Hsyn, bd, Jꢁ
3.30 (1H, Hanti, dd, Jꢁ9.5 Hz, Jꢁ2.2Hz) dꢁ
CH3central, s), dꢁ1.38 (3H, CH3syn, pseudo t, Jꢁ
Hz), dꢁ0.96 (3H, CH3anti, d, Jꢁ10.2 Hz, Jꢁ6.6 Hz).
31P NMR (in CDCl3, Tꢁ
298 K, dꢁppm) dꢁ27.07,
dꢁ25.29 (2P, AB system, Jꢁ40.3 Hz)
The complexes
[Pd(h3-1,1,2-Me3C3H2)(R?Nꢀ
SR)]ꢂClO4 (R?ꢁ Me, tBu, Ph: R?ꢁ
H; Rꢁ Me;
Rꢁt
Bu, Ph) were synthesised according to published
/
298 K, dꢁ
/
ppm) dꢁ
4.4 Hz) dꢁ
1.99 (3H,
6.5
/
7.32 (30H,
/
/
/
/
/
/
/
/
/
/
/
Yield 75%. Anal. Found: C, 32.50; H, 4.38; N, 3.26.
Calc. for C12H20INPdS: C, 32.48; H, 4.54; N, 3.16%. IR:
/
/
/
n
CꢀN 1595.1 cmꢃ1 (KBr). 1H NMR (in CDCl3, Tꢁ
/
298
7.19
7.15 (1H, H5Pyr, d, Jꢁ
7.7
CH2ꢀS, bs) dꢁ3.15(3H, Pyrꢀ
1.24 (9H, SꢀC(CH3)3, s), dꢁ1.18 (3H, Pdꢀ
CH3, s) 13C NMR (in CDCl3, Tꢁ
298 K, dꢁppm) dꢁ
162.37 (C2Pyr), dꢁ156.95 (C6Pyr), dꢁ138.61 (C4Pyr), dꢁ
124.80 (C3Pyr), dꢁ119.98 (C5Pyr), dꢁ
50.59 (SꢀC(CH3)3),
dꢁ42.27 (SꢀCH2ꢀPyr), dꢁ30.83 (SꢀC(CH3)3), dꢁ
31.47 (PyrꢀCH3), dꢁ 11.94 (PdꢀCH3).
/
/
7.60 (1H, H4Pyr, t, Jꢁ
6.9 Hz), dꢁ
/
7.7 Hz), dꢁ
/
/
K, dꢁ
(1H, H5Pyr, d, Jꢁ
Hz), dꢁ4.41 (2H, Pyrꢀ
CH3, s), dꢁ
/
ppm) dꢁ
/
ꢃ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
procedures [3b]
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
4. Solvents and reagents
/
/
ꢃ
/
/
THF and CH2Cl2 were distilled under inert atmos-
phere on Na/benzophenone and on CaH2, respectively.
MeCN was degassed by N2 and stored on molecular
3.3. Allyl complexes
3.3.1. [Pd(m-Cl)(h3-1,1,2-Me3C3H2)]2
˚
sieves (4 A). Acetone was distilled under inert atmos-
˚
phere on molecular sieves (3 A). All other chemicals
were commercially available grade products.
The title complex was obtained according to a
published procedure [4d].

168
L. Canovese et al. / Inorganica Chimica Acta 346 (2003) 158ꢀ
/
168
(1987) 513;
5. IR, NMR and UV
/
Vis measurements
ꢀ
(i) B. Cazes, Pure Appl. Chem. 62 (1990) 1867;
(j) J.G.P. Delis, P.G. Aubel, K. Vrieze, P.W.N.M. van Leeuwen,
Organometallics 16 (1997) 2948;
The IR spectra were recorded on a Nicolet MagnaTM
750 spectrophotometer. The 1H and 13C{1H} NMR
spectra were recorded on a Bruker AC 200 or Avance
(k) S. Mecking, Coord. Chem. Rev. 203 (2000) 325 (and references
therein);
(l) R. Zimmer, C.U. Dinesh, E. Nandanan, F.A. Khan, Chem.
Rev. 100 (2000) 3067 (and references therein);
(m) T. Yagyu, M. Hamada, K. Osakada, T. Yamamoto,
Organometallics 20 (2001) 1087.
300 spectrometers. UVꢀ
surements were performed on a Perkinꢀ
40 spectrophotometer equipped with a Perkinꢀ
/
Vis spectra and kinetic mea-
Elmer Lambda
Elmer
/
/
PTP 6 (Peltier temperature programmer) apparatus.
[2] (a) S. Kacker, A. Sen, J. Am. Chem. Soc. 119 (1997) 1028;
(b) W. Liu, J.M. Malinoski, M. Brookhart, Organometallics 21
(2002) 2836.
[3] (a) L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, G.
Bandoli, Organometallics 19 (2000) 1461;
6. Kinetics measurements
(b) L. Canovese, F. Visentin, G. Chessa, C. Santo, P. Uguagliati,
G. Bandoli, J. Organomet. Chem. 650 (2002) 43.
[4] (a) P. Dierkes, P.W.N.M. van Leeuwen, J. Chem. Soc., Dalton
Trans. (1999) 1519;
The kinetics of allene insertions were studied by
addition of known aliquots of allene solutions to
solutions of the complex under study in CH2Cl2
([Pd]0:
10ꢃ4 mol dmꢃ3) in the thermostatted cell
compartment of the spectrophotometer or by addition
of known amounts of allene solutions to solutions of the
/
(b) P.G.C.M. Dekker, C.J. Elsevier, K. Vrieze, P.W.N.M. van
Leeuwen, Organometallics 11 (1992) 1598;
(c) R. van Asselt, E.E.C.G. Gielens, R.E. Rulke, K. Vrieze, C.J.
¨
Elsevier, J. Am. Chem. Soc. 116 (1994) 977;
(d) H.A. Ankersmit, N. Veldman, A.L. Spek, K. Eriksen, K.
Goubitz, K. Vrieze, G. van Koten, Inorg. Chim. Acta 252 (1996)
203;
complex under study in CD2Cl2 ([Pd]0:
/
5ꢄ
10ꢃ2 mol
/
dmꢃ3) into a 5-mm NMR tube. The reactions were
followed by recording spectral changes in the wave-
length range 250/350 nm and at a fixed suitable
(e) R.E. Rulke, J.G.P. Delis, A.M. Groot, C.J. Elsevier,
¨
P.W.N.M. van Leeuwen, K. Vrieze, K. Goubitz, H. Schenk, J.
Organomet. Chem. 508 (1996) 109;
wavelength in the case of UVꢀ/Vis technique or follow-
ing the disappearance of the Pdꢀ
/
CH3 signal (d :1 ppm)
/
(f) J.H. Groen, C.J. Elsevier, K. Vrieze, W.J.J. Smeets, A.L. Spek,
Organometallics 15 (1996) 3445;
1
in the case of H NMR studies. Kinetic measurements
were performed under either pseudo-first or second-
order conditions; mathematical and statistical data
analysis was carried out on a personal computer
equipped with a locally adapted version of Marquardt’s
algorithm [9a] written in TURBOBASICTM. The reaction of
(g) J.G.P. Delis, J.H. Groen, K. Vrieze, P.W.N.M. van Leeuwen,
N. Veldman, A.L. Spek, Organometallics 16 (1997) 551;
(h) R.E. Rulke, V.E. Kaasjager, D. Kliphuis, C.J. Elsevier,
¨
P.W.N.M. van Leeuwen, K. Vrieze, K. Goubitz, Organometallics
15 (1996) 668;
(i) J.H. Groen, J.G.P. Delis, P.W.N.M. van Leeuwen, K. Vrieze,
Organometallics 16 (1997) 68.
[Pd(PPh3)(Me)(MeNꢀ
StBu)]ꢂ with allene was studied
/
[5] M.L. Tobe, J. Burgess, Inorganic Reactions Mechanisms, Ch. 3,
Addison Wesley, New York, 1999.
following the concentration of the species by integration
of 31P NMR signals referred to a constant internal
standard (H3PO4 in a coassial tube). The concentrations
of the involved species were independently determined
and their internal consistency was assured by the
relevant mass balance equations.
[6] L. Canovese, F. Visentin, C. Santo, G. Chessa, P. Uguagliati,
Polyhedron 20 (2001) 3171 (and references therein).
[7] L. Canovese, V. Lucchini, C. Santo, F. Visentin, A. Zambon, J.
Organomet. Chem. 642 (2002) 58.
[8] P. Uguagliati, R.A. Michelin, U. Belluco, R. Ros, J. Organomet.
Chem. 169 (1979) 115.
[9] (a) D.W. Marquardt, J. Appl. Math. 11 (1963) 431;
(b) A. Costantinides, N. Mastoufi, Numerical Methods for
Chemical Engineers with MATLAB Applications, Ch. 7, Interna-
tional Series in the Phys. and Chem. Engineering Sciences,
Prentice Hall, New York, 1999.
References
[1] (a) P.W.N.M. van Leeuwen, G. van Koten, in: J.A. Mouljin,
P.W.N.M. van Leeuwen, P.A. van Santen (Eds.), Catalysis: An
Integrated Approach to Omogeneous, Heterogeneous and In-
dustrial Catalysis (and references therein), Elsevier Science,
Amsterdam, 1993;
[10] MATLAB, The Mathworks Inc., Natick, MA.
[11] J.H. Espenson, Chemical Kinetics and Reaction Mechanisms, Ch.
2, 2nd ed., McGraw-Hill, New York, 1995.
[12] L. Canovese, F. Visentin, G. Chessa, A. Niero, P. Uguagliati,
Inorg. Chim. Acta 293 (1999) 44.
(b) A. Yamamoto, J. Chem. Soc., Dalton Trans. (1999) 1027;
(c) L. Besson, J. Gore`, B. Cazes, Tetrahedron Lett. 36 (1995)
3853;
[13] M.J. Carter, J.K. Beattie, Inorg. Chem.
1233.
[14] K.C. Lee, D.Y. Chi, J. Org. Chem. 64 (1999) 8576.
9
(1970)
(d) R. Grigg, M. Monteith, V. Sridharan, C. Terrier, Tetrahedron
54 (1998) 3885;
[15] (a) L. Canovese, F. Visentin, P. Uguagliati, G. Chessa, A. Pesce,
J. Organomet. Chem. 566 (1998) 61;
(e) J.M. Zenner, R.C. Larock, J. Org. Chem. 64 (1999) 7312;
(f) I. Shimuzu, J. Tsuji, J. Chem. Lett. (1984) 203;
(g) M. Ahmar, B. Caszes, J. Gore´, Tetrahedron Lett. 25 (1984)
4505;
(b) L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, A.
Dolmella, J. Organomet. Chem. 601 (2000) 1.
[16] R.E. Rulke, J.M. Ernsting, A.L. Spek, C.J. Elsevier, P.W.N.M.
¨
(h) M. Ahmar, B. Caszes, J.J. Barieux, J. Gore´, Tetrahedron 43
van Leeuwen, K. Vrieze, Inorg. Chem. 32 (1993) 5769.