The marked influence of steric and electronic properties of ancillary pyridylthioether ligands on the rate of allene insertion into the palladium-carbon bond

Article abstract of DOI:10.1016/S0022-328X(02)01145-2

Neutral methyl-and acyl-palladium chloro complexes containing pyridylthioether ancillary ligands (R'N-SR) (R = H, Me, Cl: R = Me, Et, i-P,t-Bu, Ph) have been synthesised and characterised by elemental analysis and spectroscopic methods. The reactivity of these complexes toward allene (allene = DMA = 1,1,-dimethylpropadiene; TMA = 1,1,3,3-tetramethylprodadiene) insertion into the palladium-carbon bond has been studied by ¹H-NMR and UV-vis techniques. The rate of reaction appears to be strongly influenced by the steric and electronic properties of the ancillary ligand. The distortion induced by the substituents R' in position 6 of the pyridine ring on the main coordination plane of the substrate (allowed by sulphur sp³ hybridisation) renders the substrate itself more prone to nucleophilic attack by the allene. The rate of allene insertion can further be enhanced by lowering the basicity of the chelating atoms in the N-S moiety which results in an increase of electrophilicity of the palladium core so that the rate constants measured in the case of the complexes containing the ligand 6-chloro-2-phenylthiomethylpyridine (CIN-SPh) are by far the greatest observed so far for similar reactions. Furthermore, on the basis of the indication emerging from the exhaustive study on the behaviour of all the rdylthioether methyl complexes, an associative asynchronous bond making mechanism for the rate determining nucleophilic attack by allene is proposed.

Full text of DOI:10.1016/S0022-328X(02)01145-2

Journal of Organometallic Chemistry 650 (2002) 43–56
www.elsevier.com/locate/jorganchem
The marked influence of steric and electronic properties of
ancillary pyridylthioether ligands on the rate of allene insertion
into the palladium–carbon bond
Luciano Canovese a,*, Fabiano Visentin a, Gavino Chessa a, Claudio Santo a,
Paolo Uguagliati a, Giuliano Bandoli b
a Dipartimento di Chimica, Calle Larga Santa Marta, Uni6ersita` degli Studi di Venezia, 2137-30123 Venice, Italy
b Dipartimento di Scienze Farmaceutiche, Uni6ersita` di Pado6a, Padua, Italy
Received 7 September 2001; accepted 7 January 2002
Abstract
Neutral methyl- and acyl-palladium chloro complexes containing pyridylthioether ancillary ligands (R%NꢀSR) (R%=H, Me, Cl;
R=Me, Et, i-Pr, t-Bu, Ph) have been synthesised and characterised by elemental analysis and spectroscopic methods. The
reactivity of these complexes toward allene (allene=DMA=1,1-dimethylpropadiene; TMA=1,1,3,3-tetramethylpropadiene)
1
insertion into the palladium–carbon bond has been studied by H-NMR and UV–vis techniques. The rate of reaction appears
to be strongly influenced by the steric and electronic properties of the ancillary ligand. The distortion induced by the substituent
R% in position 6 of the pyridine ring on the main coordination plane of the substrate (allowed by sulphur sp3 hybridisation) renders
the substrate itself more prone to nucleophilic attack by the allene. The rate of allene insertion can further be enhanced by
lowering the basicity of the chelating atoms in the NꢀS moiety which results in an increase of electrophilicity of the palladium
core, so that the rate constants measured in the case of the complexes containing the ligand 6-chloro-2-phenylthiomethylpyridine
(ClNꢀSPh) are by far the greatest observed so far for similar reactions. Furthermore, on the basis of the indications emerging from
the exhaustive study on the behaviour of all the related pyridylthioether methyl complexes, an associative asynchronous bond
making mechanism for the rate determining nucleophilic attack by allene is proposed. © 2002 Elsevier Science B.V. All rights
reserved.
Keywords: Allene; Pyridylthioether; Palladium–carbon bond; Insertion mechanism
into the metal–alkyl and metal–aryl bonds in chelate
complexes and its catalytic implications [3]. These reac-
tions appear to be affected by the steric, electronic, and
structural properties of the chelating ligand, although a
variety of features may emerge, depending on the bite
angle and rigidity of such ligand and its hemilability [4].
We have observed a remarkable rate enhancement of
allene insertion induced by distortion of the coordina-
tion environment caused by the presence of a sub-
stituent in position six of the pyridine ring of the
bidentate ligand R%NꢀSR [1]. As a matter of fact, such
distortion will render the requisite preliminary step of
these insertion reactions, i.e. prior coordination of the
allene, much easier [3f, 4e,f]. Our work also hinted that
the highest rate of allene insertion can be achieved by a
combination of main coordination plane distortion and
lowered basicity of coordinating atoms (N and/or S) in
1. Introduction
We are currently studying the mechanism of allene
insertion into the palladium–carbon bond in pyridylth-
ioether methyl complexes of type [PdCl(Me)(R%NꢀSR)]
(R%NꢀSR=6-R%-C5H3N-2-CH2SR) to give [Pd(h3-2-
methylallyl)(R%NꢀSR)]+ [1].
The interaction of organopalladium compounds with
allenes is particularly important since, under catalytic
conditions, assembly of allenes, carbon monoxide, and
nucleophiles leads to allylamines, methacrylates, or het-
erocycles [2]. This is a particular issue of the more
general field of the insertion of unsaturated molecules
* Corresponding author. Tel.: +39-41-5298567/68; fax: +39-41-
5298517.
E-mail address: cano@unive.it (L. Canovese).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(02)01145-2

44
L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
the chelating ligand. In fact, when the electron-with-
drawing phenyl group is bound to sulphur, the highest
second-order rate constant for allene insertion is ob-
tained [1]. Thus, in our search for the most efficient
factors enhancing the rate of allene insertion in these
systems, we have conceived the idea of decreasing the
basicity of both the pyridine nitrogen and of the sul-
phur in our pyridylthioether ligands while maintaining
the distortion of the coordination plane and providing
for sufficient stability of the metal–polydentate ring, as
ensured by the high flexibility of the S-donor chelate
ligand. To this aim, we have synthesised the ligands and
the complexes in Scheme 1, where the methyl group
bound to palladium is trans to the pyridine nitrogen
(see further). We have also carried out a kinetic investi-
gation of the reaction in order to confirm our hypothe-
sis and to provide a comprehensive overview of the
factors governing the mechanism of allene insertion.
(1)
2. Results and discussion
2.1. Synthesis, characterisation and X-ray structure
Addition, under inert atmosphere (N2), of the appro-
priate ligand (R%NꢀSR) to a toluene solution of [Pd-
Cl(Me)(COD)] yields the corresponding complexes
[PdCl(Me)(R%NꢀSR)]. Reaction of a CHCl3 solution of
these complexes with carbon monoxide yields almost
instantaneously the related acyl species [Pd-
Cl(COMe)(R%NꢀSR)]. The methyl and the acyl com-
plexes react in CH2Cl2 with allenes DMA or TMA to
give the allyl derivatives as reported in Scheme 1. All
the new unpublished complexes were characterised by
elemental analysis, IR spectroscopy and NMR spec-
trometry (see Section 3). In order to assess the relative
positions of the palladium-bound methyl group and the
pyridine nitrogen, we have carried out an X-ray struc-
ture determination of the complex [PdCl(Me)-
(HNꢀSMe)]. The structure motif of the complex is
given by the juxtaposition in the unit cell of two
monomeric units (Fig. 1), which are virtually identical,
the r.m.s. deviation of their superimposition being 0.05
Scheme 1.
,
,
A, with the largest deviation (0.10 A) shown by the
C(8) methyl atom. The coordination around palladium
is square-planar with the chloride and the sulphur of
the pyridylthioether ligand trans to one another, the cis
Fig. 1. ORTEP drawing of the asymmetric unit showing the atom
numbering scheme and 50% displacement ellipsoids. Hydrogen atoms
have been omitted for clarity.

L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
45
Table 1
the contrary, the PdꢀN separation lengthens from
,
Selected bond lengths (A) and bond angles (°)
,
2.091(7) to 2.16 (1) A, the SꢀPdꢀN bite angle remaining
virtually unchanged at ca. 83.5°.
Bond lengths
Other metrical parameters compare favourably with
the expected values, as can be seen by looking at the
data retrieved in version 5.19 (April 2000) of Cam-
bridge Structural Database (CSD) [6]. In particular the
mean value for the PdꢀCl lengths observed in this
Pd(1)ꢀS(1)
Pd(1)ꢀCl(1)
Pd(1)ꢀN(1)
Pd(1)ꢀC(8)
S(1)ꢀC(6)
2.257(5)
2.315(6)
2.16(1)
2.01(1)
1.81(1)
1.79(2)
Pd(2)ꢀS(1%)
Pd(2)ꢀCl(1%)
Pd(2)ꢀN(1%)
Pd(2)ꢀC(8%)
S(1%)ꢀC(6%)
S(1%)ꢀC(7%)
2.255(6)
2.340(6)
2.17(1)
2.00(1)
1.79(1)
1.81(2)
S(1)ꢀC(7)
,
,
complex (2.328(6) A) parallels that of 2.335 A encoun-
Bond angles
tered in other 1512 PdꢀCl entries whereas the PdꢀC(8)
S(1)ꢀPd(1)ꢀN(1)
S(1)ꢀPd(1)ꢀC(8)
Cl(1)ꢀPd(1)ꢀN(1)
Cl(1)ꢀPd(1)ꢀC(8)
S(1)ꢀPd(1)ꢀCl(1)
N(1)ꢀPd(1)ꢀC(8)
Pd(1)ꢀS(1)ꢀC(6)
Pd(1)ꢀS(1)ꢀC(7)
C(6)ꢀS(1)ꢀC(7)
S(1)ꢀC(6)ꢀC(5)
84.1(4)
88.8(6)
95.3(4)
91.6(6)
177.6(2)
172.3(7)
99.3(6)
104.4(7)
100.6(9)
112(1)
S(1%)ꢀPd(2)ꢀN(1%)
S(1%)ꢀPd(2)ꢀC(8%)
Cl(1%)ꢀPd(2)ꢀN(1%)
Cl(1%)ꢀPd(2)ꢀC(8%)
S(1%)ꢀPd(2)ꢀCl(1%)
N(1%)ꢀPd(2)ꢀC(8%)
Pd(2)ꢀS(1%)ꢀC(6%)
Pd(2)ꢀS(1%)ꢀC(7%)
C(6%)ꢀS(1%)ꢀC(7%)
S(1%)ꢀC(6%)ꢀC(5%)
83.8(4)
89.6(6)
95.7(4)
90.7(6)
176.2(2)
173.2(7)
99.3(5)
102.0(7)
99.9(8)
113(1)
,
separation of 2.01(1) A is slightly shorter than the mean
,
value (2.037 A) observed in sixty PdꢀCmethyl
determinations.
In the unit cell the minimum Pd···Pd separation is
,
3.769 A and the only, somewhat, short interactions (in
,
the range 2.71–2.78 A) involve the chloride ligands
with the phenyl hydrogens at C(4) and C(6).
2.2. Solution beha6iour
2.2.1. Methyl complexes
The NMR investigations on the methyl derivatives
[PdCl(Me)(R%NꢀSR)] (R%=H, Me) indicate the pres-
ence of one single isomer, in which the pyridylthioether
ligand acts as a bidentate since only one PdꢀCH3
protons signal is observed, among other pieces of evi-
dence. The complete characterisation of these com-
plexes requires low temperature studies since all these
species undergo fluxional rearrangement at room tem-
perature. From theoretical considerations based on the
mutual trans influence between the methyl group and
the sulphur atom [4d,7] and the available structural
determinations reported in this paper and elsewhere, [1]
we conceive the hypothesis that the most likely isomer
is the species in which the palladium coordinated
methyl group lies trans to the pyridine nitrogen. The
observed fluxional behaviour of these substrates can be
easily traced back to the pyramidal sulphur inversion
[8]; in fact on increasing temperature the observable AB
quartet due to diastereotopic CH2S protons disappears
yielding a broad singlet. Apparently the chirogenic
nature of sulphur is lost upon inversion of its absolute
configuration and such a phenomenon appears to be
independent of substrate concentration in conformity
with the intramolecular sulphur rearrangement which is
known to be of widespread occurrence in both Pd(0)
and Pd(II) complexes [5,9]. Moreover, detailed investi-
gations by dynamic NMR on some substrates support
this conclusion since the calculated activation parame-
ters are in agreement with this mechanistic picture [10].
Fig. 2. A perspective view of the complex showing the C(6) atom
,
,
below (by 0.50 A) and the C(7) atom above (by 1.73 A) the mean
coordination plane.
bond angles ranging from 83.8 to 95.7° and the trans
angles between 172.3 and 177.6° (Table 1). In both
units the palladium atom is out of the mean coordina-
,
,
tion plane by 0.05 A, the N···S bite distance is 2.96 A
and the NꢀPdꢀS bite angle is equal within error [84.1
(4) and 83.8 (4)°], while the values for the dihedral
angles between the mean coordination plane and the
six-membered ring are slightly different [13.3(5) and
10.4(6)°] as well as the PdꢀS(1)ꢀC(7) angles [104.4(7)
and 102.0(7)°].
In the five-membered ring the C(6) atom is out by
, ,
A (0.47 A in the other unit) from the
0.49
PdꢀN(1)ꢀC(5)ꢀS(1) mean plane (Fig. 2) and the two
bond angles at sulphur, PdꢀS(1)ꢀC(6) and
C(7)ꢀS(1)ꢀC(6), approach 100° [99.3(6)–100.6(9)° and
99.3(5)–99.9(8)°, respectively].
1
The room temperature H-NMR spectra of the com-
A comparison with the previously reported palla-
dium(0) complex containing the same pyridylthioether
bidentate ligand, i.e. [Pd(h2-tcne)(HNꢀSMe)] [5] shows
that, on going from the oxidation number 0 to II, the
plexes [PdCl(Me)(ClNꢀSR)] display quite different fea-
tures since the observed fluxional behaviour cannot be
traced back only to sulphur inversion. As a matter of
fact the room temperature spectrum of the complex
[PdCl(Me)(ClNꢀStBu)] exhibits a collapsing AB system
,
,
PdꢀS distance of 2.352(3) A shortens to 2.256 A and on

46
L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
(CH2S protons) and an incipient broadening of the
signals ascribable to t-Bu methyl groups (l=1.31
ppm), to PdꢀCH3 protons (l=1.16 ppm) and to the
partially obscured pyridine H5 (l$7.5 ppm). These
pieces of evidence suggest the presence of a fast sulphur
inversion coupled with a process involving a fast rear-
rangement between isomers. As a matter of fact either
decreasing or increasing the temperature lead to a
spectrum simplification. The low temperature spectrum
is in accord with a ‘frozen’ situation in which only the
predominant NꢀMe trans isomer (hereafter trans) is
observable. The high temperature spectrum suggests a
very rapid interchange between the species as indicated
in the following scheme. The resulting average spectrum
takes into account the presence of the NꢀMe cis isomer
(hereafter cis) in small concentration, as can be seen
from the tell-tale chemical shift and shape of the pyri-
dine H5 which happens to be markedly affected by the
trans influence of the group trans to pyridine.
plain the absence of the ancillary ligand rotation even
in the 6-chloropyridine acyl complexes, owing to the
increased electrophilicity of the metal core which would
render the Pd–nitrogen bond more stable.
2.2.3. Allyl complexes
The complete characterisation of allyl complexes was
achieved by studying authentic samples obtained via
direct synthesis in CH2Cl2 between the suitable
pyridylthioether R%NꢀSR ligand and the appropriate
allyl dimer [Pd(h3-allyl)Cl]2. However, the addition of
DMA or TMA to a solution of [PdCl(Me)(R%NꢀSR)] or
[PdCl(COMe)(R%NꢀSR)] substrates yields, upon addi-
tion of NaClO4, the same allyl complexes. Therefore
this path might represent a valid alternative route to the
sterically hindered allyl species, [1,17] thereby overcom-
ing the difficulties usually encountered when employing
allene insertion methods [18]. The solution behaviour of
1
the allyl complexes is conveniently studied by H-NMR
technique since similar species had been investigated in
depth and the resulting spectral features are well known
[9c]. It would be useful to differentiate the studied allyl
complexes on the basis of the allyl fragment symmetry.
The complexes bearing the unsymmetrical allyl moiety
would give rise to four diastereoisomers (together with
their enantiomers which are undetectable under our
experimental conditions). A topological representation
of the diastereoisomers and the fluxional rearrange-
ments involved at room temperature are given in the
following scheme:
Thus, at variance with the complexes bearing
R%NꢀSR (R%=H, Me) ligands the 6-chloro substituted
pyridylthioeter complexes undergo fast interchange be-
tween trans and cis isomers probably owing to the low
basicity of the pyridine nitrogen [14] and the high trans
influence of the methyl group. However, thermody-
namic parameters for the above cis–trans equilibrium
could not be determined owing to the very large differ-
ence in population between isomers.
Other interpretations involving adventitious nucle-
ophiles (water, impurities, etc.) promoting species with
an uncoordinated dangling arm were ruled out since the
rate of interconversion between isomers displays no
concentration dependence and therefore the rearrange-
ment seems to be intramolecular in nature.
1
2.2.2. Acyl complexes
In fact in the room temperature H-NMR spectra of
The 1H-NMR spectra of acyl complexes [Pd-
Cl(COMe)(R%NꢀSR)] are characterised by a down-field
shift of the signal ascribed to COCH3 protons (Dl:1.5
ppm with respect to methyl analogs). This evidence
coupled with an intense IR signal at :1700 cm−1
testifies the CO insertion into the PdꢀC bond [4d,15,16].
Since CO insertion takes place with retention of
configuration [4d,15] we postulate that the acyl com-
plexes would display the customary NꢀCOMe trans
configuration (vide supra). The reduced basicity of the
acyl with respect to the methyl group indeed will ex-
these complexes the presence of a sharp singlet ascrib-
able to CH2S protons and of two couples of singlets
attributed to syn and anti allyl CH3 groups and pro-
tons, respectively, indicates the concomitant occurrence
of both fluxional rearrangements (i.e. sulphur inversion
and apparent rotation). No hints of syn–anti isomerism
(h3-h1-h3 rearrangement) are detectable at room tem-
perature except for the cases of allyl–acyl complexes in
which the collapse of the signals due to the allyl pro-
tons only suggests an operative and selective syn–anti
isomerism. On decreasing the temperature the apparent

L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
47
rotation is suddenly ‘frozen’ but the sulphur inversion
phenomenon results still operative, albeit being by far
the less energetic process [9c]. Only in the case of the
−90 °C CD2Cl2 spectrum of the complex [Pd(h3-1,1,2-
Me3C3H2)(ClNꢀSMe)]ClO4 together with the slightly
broadened signals indicating the presence of two iso-
mers (at different concentration) does a hint of only
one AB quartet due to thioetheric protons of the less
concentrated isomer become visible in the 4.1–4.5 ppm
interval.
The 1H-NMR spectra of the complexes bearing a
symmetric allyl moiety are trivial and can be traced
back to the customary features discussed elsewhere [19].
Again, no traces of h3-h1-h3 isomerism due to steric
hindrance of the allyl fragment are detected at room
temperature.
2.3. Kinetics of allene insertion
The course of insertion of DMA (reaction 1) was
1
monitored by H-NMR by following the disappearance
of PdꢀCH3 proton signals at ꢀ1 ppm in CD2Cl2 for
the complexes [PdCl(Me)(HNꢀSR)] (R=Me, Et, i-Pr,
t-Bu). The analogous insertion of TMA was too slow
to measure due to product decomposition. The k2 con-
stants were computed from the resulting first half-lives
under second-order conditions {[Pd]0=5×10−2
,
[DMA]0=0.25 mol dm−3; k2=ln((2[DMA]0−[Pd]0)/
[DMA]0)/t1/2([DMA]0−[Pd]0)}.
The faster reactions were followed by UV–vis tech-
nique at 25 °C in CH2Cl2 under pseudo-first order
conditions
([A]0]10×[Pd]0),
[Pd]0:1×10−4
mol dm−3) or second-order conditions for the fastest
ones. For the former, the k2 values were determined as
the slopes of plots of pseudo-first order rate constants,
kobs, versus [A]0, according to rate law (2) (A=allene)
(Fig. 3):
Fig. 3. Plot of kobs vs. [TMA] for the reaction of insertion of
1,1,3,3-tetramethylpropadiene (TMA) into the PdꢀMe bond of the
complex [PdCl(Me)(ClN-SMe)] in CH2Cl2 at 25 °C.
k
obs=k2[A]0
(2)
The kobs values were determined by non-linear fitting of
absorbance data (D) to time according to the first-order
monoexponential law Dt=D8 +(D0−D8) exp(−
kobst).
In no case could a statistically significant intercept be
detected, corresponding to an allene-independent path,
at variance with what was observed previously for the
insertion of norbornadiene and allene into the palla-
dium–carbon bond of complexes containing bidentate
nitrogen ligands [4e,g,i].
Table 2
Second-order rate constants, k2 (mol−1 dm3 s−1) for the insertion of
1,1-dimethylpropadiene (DMA) and 1,1,3,3-tetramethylpropadiene
(TMA) across the PdꢀMe and PdꢀCOMe bonds according to Eq. (2)
in CD2Cl2 or CH2Cl2 at 25 °C
Complexes
DMA
TMA
d
d
d
d
d
[PdCl(Me)(HNꢀSMe)]
[PdCl(Me)(HNꢀSEt)]
[PdCl(Me)(HNꢀSiPr)]
[PdCl(Me)(HNꢀStBu)]
[PdCl(Me)(HNꢀSPh)]
8.17×10−4 a
6.53×10−4 a
4.08×10−4 a
2.33×10−4 a,cb
(4.090.3)
×10−2 b,c
(3.390.1)
×10−1 b,c
2391 b,c
For the faster reactions under second-order condi-
tions ([Pd]0:1×10−4, [A]0:1–5×10−4 mol dm−3
)
the k2 constants were directly determined by non-linear
regression of absorbance data to the customary second-
order integrated rate law.
As can be seen from the data in Table 2, the follow-
ing effects on the rate can be assessed:
(i) Steric hindrance at the allene moiety depresses
dramatically the rate of insertion to the extent
that the more hindered TMA does not lend itself
to a kinetic study with complexes bearing HNꢀSR
(R=Me, Et, i-Pr, t-Bu, Ph) as ancillary ligands.
(ii) Increasing steric hindrance at the sulphur sub-
stituent R depresses the rate to some extent (less
than one order of magnitude); a phenyl group,
which displays steric properties similar to those of
i-Pr, imparts a marked rate increase (two orders
of magnitude).
[PdCl(Me)(MeNꢀStBu)]
(1.0790.05)
×10−2 b,c
[PdCl(Me)(MeNꢀSPh)]
[PdCl(Me)(ClNꢀSMe)]
[PdCl(Me)(ClNꢀStBu)]
[PdCl(Me)(ClNꢀSPh)]
(4.690.1)×10−1 b,c
1.1890.07 c
0.27890.005 c
3.2690.06 c
–
117925 e
3091 c
16497 e
[PdCl(COMe)(HNꢀStBu)] (1.3790.07)
×10−2 c
[PdCl(COMe)(MeNꢀStBu)] 1.2790.07 c
[PdCl(COMe)(ClNꢀStBu)] 160910 e
(8.790.3)×10−3 c
1.9390.09 c
a Measured by 1H-NMR technique in CD2Cl2 (see Section 2).
b Ref. [1].
c Measured by UV–vis technique in CH2Cl2 under pseudo-first
order conditions.
d Too slow to measure.
e Measured by UV–vis technique in CH2Cl2 under second-order
conditions.

48
L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
(iii) The presence of a substituent in the position 6 of
reactivity of metal solvento-species compared to neutral
ones toward insertion of small unsaturated molecules
[3e]). Since there is no merit in invoking more compli-
cated mechanisms than those required by the experi-
mental evidence, we are reluctant to entertain other
possible mechanistic hypotheses involving the role of
solvento-species or intermediate isomerisation steps
[4c,4g,15] on the basis of the rate law (2) found experi-
mentally in our system.
As a matter of fact, the rate of bimolecular associa-
tion, kf, is expected to be depressed by increased steric
hindrance at both the entering allene (TMA vs. DMA)
and the sulphur substituent R, the effect being, how-
ever, overwhelmed if R is an electron-accepting group
such as Ph which will increase the electrophilic charac-
ter of the metallic center and will render it more prone
to allene association. Moreover, steric hindrance will
also increase the rate of intermediate reversal to start-
ing reactants, thereby producing the observed overall
decrease in reactivity.
the pyridine ring (R%=Me, Cl) causes a striking
increase in rate. The highest effect is reached
when both R% and R are good electron-attracting
groups (R%=Cl; R=Ph).
(iv) Other things being equal, acyl–palladium com-
plexes react much faster with DMA than their
methyl–palladium analogs.
(v) These reactivity trends are also effective in the
reactions involving TMA, albeit with much lower
rates.
These findings are in agreement with a simple stepwise
mechanism involving formation of an intermediate ad-
duct containing the starting metal substrate and the
coordinated allene (I), followed by migration of the X
group to yield the allene insertion product 2 according
to the following scheme:
Furthermore, substitution at the 6-position of the
pyridine ring, which has been shown to provoke severe
distortion of the substrate’s main coordination plane,
[1] will cause a remarkable rate enhancement due to
destabilisation of the ground state and a concomitant
increase in the kf constant.
The presence of a 6-methyl substituent in the pyri-
dine ring of a pyridyl–phosphine ligand bound to
Pd(II) has been shown to enhance markedly the rate
and the selectivity of methoxy carbonylation of
propyne catalysed by such palladium(II) complexes
[22]. Substituents adjacent to the nitrogen donor atom
in bidentate a-diimine methylpalladium(II) complexes
also were shown to strongly accelerate carbon monox-
ide insertion into the PdꢀMe bond [4e]. These effects
can be attributed to the ensuing distortion from planar-
ity of the coordination environment (vide supra), caus-
In this mechanistic framework, under the assumption
of steady-state conditions for [I] the second-order rate
constant in Eq. (2) is to be read as
k2=kfkm/(kr+km)
(3)
where kf is the second-order rate constant for bimolecu-
lar associative formation of I, kr is the first-order rate
constant for monomolecular dissociation of I back to
starting reactants, km is the first-order rate constant for
monomolecular migration of X to the allene moiety.
We can only provide a stoichiometric indication of
the nature of intermediate I as a five-coordinate adduct
since it could never be detected. Alternative formula-
tions might involve either a four-coordinate species
containing a monodentate R%NꢀSR ligand with a dan-
gling uncoordinated arm or a cationic chelate form of
the type [Pd(h2-allene)(X)(R%NꢀSR)]+Cl−. However,
the view of intermediate I as a five-coordinate species,
while providing the simplest mechanistic picture based
on the available experimental evidence, fits well in the
well-established wealth of knowledge gathered so far in
the field of nucleophilic substitution on square-planar
d8 metal complexes. As a matter of fact, formation of I
is just a case of associative asynchronous bond making
between the metal substrate and the allene as the
nucleophile, with the migrating X group playing the
role of the ‘leaving group’ [20]. In this picture, the
allene, the X group, and the group trans to X will lie on
the same plane (the equatorial positions of a trigonal
bipyramid), thereby providing an easy route to inser-
tion [21] (incidentally this would explain the higher
ing
a
greater tendency to form five-coordinate
complexes with unsaturated species [23]. However, the
acceleration effects by pyridine 6-substituents that we
have found here (Table 3) are by far the greatest
obser6ed since all these precedents, indicating that the
flexible structure of our S-donor chelate R%NꢀSR lig-
ands is particularly suited to exploit these effects, since
it will allow severe distortion while imparting sufficient
stability to the metal–polydentate ligand framework,
thereby preventing decomposition of the substrate in
the course of allene insertion. The effect is, expectedly,
magnified by increased electron-withdrawing properties
of the 6-substituent (e.g. Cl), which will make the metal
center even more electrophilic toward allene associa-
tion. This would also hold true if intermediate I is a
four-coordinate species with a dangling N-arm, since
the electronegative 6-chloride would depress the coordi-
nating capability of the pyridine nitrogen and labilise
the bidentate R%NꢀSR ligand.

L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
49
Table 3
1H- and 13C-NMR data for the complexes at 25 °C in CDCl3

50
L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
Table 3 (Continued)

L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
51
Table 3 (Continued)

52
L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
Table 3 (Continued)
The fact that the acyl complexes react faster than
their methyl analogs (Table 2) has already been ob-
served with bidentate nitrogen ligands [4g], and is likely
to stem from faster allene association to the metal, due
to the lower basicity of COMe relative to Me which
should favour formation of the electron-rich species I,
although this factor would be expected to disfavour the
migratory insertion step. Apparently, the balance of
these contrasting effects results in a much faster overall
rate. The rate increase on going from X=Me to X=
COMe is much less marked with substituted 6-pyridine
ring ligands (R%=Me, Cl), owing to a levelling-off
effect on the reactivity of the starting substrates. With
the sterically hindered allene TMA the reactivities of
the methyl and acetyl complexes are of the same order
of magnitude, suggesting that steric hindrance to allene
association leads to limiting values in the rates.
pyridin-2-yl)-methanol [24], which was obtained from
the commercially available 2-chloro-6-methylpyridine
following the method reported by Chi and co-workers
[25].
3.1.2. 6-Chloro-2-methylthiomethylpyridine (ClNꢀSMe)
To a solution of 2.77 g (49.38 mmol) of KOH in 20
ml of DMSO, 0.865 g (12.34 mmol) of CH3S−Na+ and
1.0 g (6.17 mmol) of 6-chloro-2-chloromethylpyridine
were added. The resulting solution was stirred for 1.5 h
at room temperature (r.t.) 60 ml of water was then
added. The product was extracted with Et2O (120 ml)
and the resulting solution was treated with anhydrous
Na2SO4 (12 h), filtered and dried under vacuum. The
crude yellowish oil was purified by flash-chromatogra-
phy (SiO2) using n-hexane–Et2O 9:1 v/v as eluent.
0.482 g (2.78 mmol) of the title product was obtained.
In this case the attack of excess CH3S− at the aromatic
ring yields 6-thiomethyl-2-methylthiomethylpyridine in
1
3. Experimental
large quantity (yield 40%; identified from its H-NMR
spectrum:
l
(ppm) 2.65 (SꢀCH3, s, 3H); 3.75
3.1. Synthesis of ligands
(CH2ꢀSꢀCH3, s, 2H); 2.11 (CH2ꢀSꢀCH3, s, 3H); 7.03
(H3(pyr), d, J=8.0 Hz, 1H); 7.05 (H(5pyr), d, J=8.0 Hz,
1H); 7.47 (H4(pyr), t, J=8.0 Hz, 1H)).
3.1.1. 6-Chloro-2-chloromethylpyridine
The title compound was prepared according to pub-
lished procedure by reacting SOCl2 with (6-chloro-
Yield: 45%. Found: C, 48.52; H, 4.61; N, 7.98.
C7H8NSCl requires: C, 48.41; H, 4.64; N, 8.07%. IR

L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
53
1
(KBr, cm−1) wCꢁN 1582(s). H-NMR (CDCl3): l (ppm)
tion with n-hexane at 0 °C yields 215.5 mg (0.6519
mmol) of the title complex as pale-yellow microcrystals.
Yield: 87%. Found: C, 29.12; H, 3.31; N, 4.21.
C8H11NSCl2Pd requires: C, 29.07; H, 3.35; N, 4.24%.
IR (KBr, cm−1): wCꢁN 1581.6(s).
The following complexes were prepared in the same
way as [PdCl(Me)(ClNꢀSMe)] using the appropriate
ligand.
2.08 (SꢀCH3, s, 3H); 3.76 (CH2ꢀS, s, 2H); 7.22 (H(5pyr)
,
d, J=7.7 Hz, 1H); 7.32 (H3(pyr), d, J=7.7 Hz, 1H); 7.64
(H4(pyr), t, J=7.7 Hz, 1H). 13C-NMR (CDCl3): l(ppm)
15.2 (SꢀCH3); 39.4 (SꢀCH2); 121.3 (C3(pyr)); 121.4
(C5(pyr)); 139.2 (C(4pyr)); 150.6 (C(6pyr)); 159.7 (C2(pyr)).
The following compounds were prepared similarly to
the above described ClNꢀSMe ligand using the appro-
priate thiolate species.
3.2.3. [PdCl(Me)(ClNꢀStBu)] (pale-yellow microcrys-
tals)
Yield: 89%. Found: C, 34.51; H, 4.58; N, 3.81.
C11H17NSCl2Pd requires: C, 35.46; H, 4.60; N, 3.76%.
IR (KBr, cm−1): wCꢁN 1583.5(s).
3.1.3. 6-Chloro-2-tert-butylthiomethylpyridine (ClNꢀ
SꢀtBu)
Yield: 94%. Found: C, C, 55.58; H, 6.60; N, 6.48.
C10H14NSCl requires: C, 55.67; H, 6.54; N, 6.49%. IR
(KBr, cm−1) wCꢁN 1583.5(s). 1H-NMR (CDCl3): l
(ppm) 1.32 (CꢀCH3, s, 9H); 3.87 (CH2ꢀS, s, 2H); 6.96
(H5(pyr), d, J=7.7 Hz, 1H); 7.21 (H(3pyr), d, J=7.7 Hz,
1H); 7.49 (H4(pyr), t, J=7.7 Hz, 1H). 13C-NMR
(CDCl3): l (ppm) 30.7 (C(CH3)3); 34.8 (SꢀCH2); 43.1
(C(CH3)3); 121.5 (C3(pyr)); 121.9 (C5(pyr)); 138.8 (C(4pyr));
150.1 (C6(pyr)); 160.3 (C2(pyr)).
3.2.4. [PdCl(Me)(ClNꢀSPh)] (pale-yellow microcrystals)
Yield: 83%. Found: C, 39.82; H, 3.34; N, 3.60.
C14H15NSCl2Pd requires: C, 39.77; H, 3.34; N, 3.57%.
IR (KBr, cm−1): wCꢁN 1589.3(s).
3.2.5. [PdCl(Me)(HNꢀSMe)] (yellow microcrystals)
Yield: 87%. Found: C, 32.41; H, 4.11; N, 4.71.
C8H12NSClPd requires: C, 32.45; H, 4.08; N, 4.73%. IR
(KBr, cm−1): wCꢁN 1601(s).
3.1.4. 6-Chloro-2-phenylthiomethylpyridine (ClNꢀSPh)
Yield: 90%. Found: C, 61.18; H, 4.31; N, 6.01.
C12H10NSCl requires: C, 61.14; H, 4.28; N, 5.94%. IR
(KBr, cm−1): wCꢁN 1584.6(s). 1H-NMR (CDCl3): l
(ppm) 4.23 (CH2ꢀS, s, 2H); 7.26 (H3(p,5yr)+H(phen), m,
7H); 7.56 (H4(pyr), t, J=7.7 Hz, 1H). 13C-NMR
(CDCl3): l (ppm) 39.7 (SꢀCH2); 121.0 (C3(pyr)); 122.3
(C(5pyr)); 126.3 (C(pphen)); 128.7 (Co(phen)); 129.5 (C(mphen));
135.0 (SꢀC); 138.9 (C4(pyr)); 150.4 (C6(pyr)); 158.5 (C(2pyr)).
3.2.6. [PdCl(Me)(HNꢀSEt)] (yellow microcrystals)
Yield: 89%. Found: C, 34.90; H, 4.51; N, 4.53.
C9H14NSClPd requires: C, 34.86; H, 4.55; N, 4.52%. IR
(KBr, cm−1): wCꢁN 1601(s).
3.2.7. [PdCl(Me)(HNꢀSꢀiPr)] (pale-yellow microcrys-
tals)
3.1.5. R%NꢀSR (R%=H; R=Me, Et, i-Pr, t-Bu, Ph:
R%=Me; R=t-Bu, Ph)
These pyridylthioether ligands were synthesised ac-
cording to published procedures [5,9c].
Yield: 85%. Found: C, 36.97; H, 5.01; N, 4.20.
C9H16NSClPd requires: C, 37.05; H, 4.97; N, 4.23%. IR
(KBr, cm−1): wCꢁN 1601(s).
The following complexes were prepared according to
published procedure [1]. The used methods were, how-
ever, similar to those described above.
[PdCl(Me)(HNꢀSꢀt-Bu)] (yellow microcrystals);
[PdCl(Me)(HNꢀSPh)] (bright-yellow microcrystals);
[PdCl(Me)(MeNꢀSꢀt-Bu)] (pale-yellow microcrystals);
and
3.2. Synthesis of complexes
3.2.1. [PdCl(Me)(COD)]
The title complex was obtained according to pub-
lished procedure [26] by adding Sn(Me)4 to a CH2Cl2
solution of [PdCl2COD] [27] under inert atmosphere
(N2).
[PdCl(Me)(MeNꢀSPh)] (pale-yellow microcrystals).
1H- and 13C-NMR data for the new complexes re-
ported in this section are summarised in Table 3.
3.2.8. [PdCl(COMe)(HNꢀSꢀtBu)]
Gaseous carbon monoxide (CO) was bubbled
through a stirred solution of 101.8 mg (0.301 mmol) of
[PdCl(Me)(HNꢀSꢀtBu)] dissolved in 30 ml of freshly
distilled CH2Cl2 for 1 h. The resulting solution was
treated with activated charcoal filtered on celite filter
and concentrated under reduced pressure. Addition of
diethylether yields 93.2 mg (0.254 mmol) of the acyl
complex as a pale-yellow solid.
3.2.2. [PdCl(Me)(ClNꢀSMe)]
To 198.1 mg (0.7475 mmol) of the complex [Pd-
Cl(Me)(COD)] dissolved in 30 ml of freshly distilled
toluene, 142.8 mg (0.8223 mmol) of ClNꢀSMe ligand
was added under inert atmosphere (N2). The resulting
solution was stirred at r.t. for 4 h and eventually dried
under reduced pressure. The residue was dissolved in
CH2Cl2, treated with activated charcoal and filtered on
celite filter. Reduction to small volume and precipita-
Yield: 84%. Found: C, 39.37; H, 5.01; N, 3.92.
C12H18NOSClPd requires: C, 39.36; H, 4.95; N, 3.82%.
IR (KBr, cm−1): wCꢁN 1601(s); wCꢁO 1693(s).

54
L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
The following complexes were prepared in the same
3.2.14. [Pd(p3-1,1,2,3,3-Me5C3)(ClNꢀSMe)]ClO4
(pale-yellow microcrystals)
Yield: 60%. Found: C, 36.67; H, 4.74; N, 2.82.
C15H23NO4SCl2Pd requires: C, 36.71; H, 4.72; N,
2.85%. IR (KBr, cm−1): wCꢁN 1581.6(s).
way as [PdCl(COMe)(HNꢀSꢀtBu)] using the appropri-
ate starting substrates.
3.2.9. [PdCl(COMe)(MeNꢀSꢀtBu)] (pale-yellow
microcrystals)
Yield: 87%. Found: C, 40.97; H, 5.31; N, 3.72.
C13H20NOSClPd requires: C, 41.07; H, 5.30; N, 3.68%.
IR (KBr, cm−1): wCꢁN 1590(s); wCꢁO 1709(s).
3.2.15. [Pd(p3-1,1,2,3,3-Me5C3)(ClNꢀSꢀtBu)]ClO4
(pale-yellow microcrystals)
Yield: 80%. Found: C, 43.51; H, 4.57; N, 2.51.
C18H29NO4SCl2Pd requires: C, 43.46; H, 4.56; N,
2.53%. IR (KBr, cm−1): wCꢁN 1583.5(s).
3.2.10. [PdCl(COMe)(ClNꢀSꢀtBu)] (whitish
microcrystals, 79.0% yield)
Yield: 84%. Found: C, 35.97; H, 4.25; N, 3.48.
C12H17NOSCl2Pd requires: C, 35.98; H, 4.28; N, 3.50%.
IR (KBr, cm−1): wCꢁN 1585(s); wCꢁO 1715(s).
The following complexes were synthesised according
to published procedures [4d].
3.2.16. [Pd(p3-1,1,2,3,3-Me5C3)(ClNꢀSPh)]ClO4
(pale-yellow microcrystals)
Yield: 60%. Found: C, 43.48; H, 4.54; N, 2.55.
C20H25NO4SCl2Pd requires: C, 43.46; H, 4.56; N,
2.53%. IR (KBr, cm−1): wCꢁN 1581.6(s).
[Pd2(m-Cl)2(h3-1,1,2-Me3C3H2)2]
(pale-yellow
3.2.17. [Pd(p3-1,1-Me2CC(COMe)CH2)(ClNꢀSꢀtBu)]-
ClO4 (pale-yellow microcrystals)
Yield: 66%. Found: C, 36.03; H, 4.24; N, 3.48.
C17H25NO5SCl2Pd requires: C, 35.98; H, 4.28; N,
3.50%. IR (KBr, cm−1): wCꢁN 1585.4(s); wCꢁO 1714.6(s).
microcrystals);
[Pd2(m-Cl)2(h3-1,1,2,3,3-Me5C3)2] (pale-yellow micro-
crystals); and
[Pd2(m-Cl)2(h3-1,1-Me2CC(COMe)CH2)2] (pale-yel-
low microcrystals).
3.2.18. [Pd(p3-1,1-Me2CC(COMe)CH2)(HNꢀSꢀtBu)]-
ClO4 (pale-yellow microcrystals)
Yield: 56%. Found: C, 39.33; H, 4.97; N, 3.78.
C17H26NO5SClPd requires: C, 39.36; H, 4.95; N, 3.82%.
IR (KBr, cm−1): wCꢁN 1601(s); wCꢁO 1693(s).
3.2.11. [Pd(p3-1,1,2-Me3C3H2)(ClNꢀSꢀtBu)]ClO4
To a solution of 73.5 mg (0.163 mmol) of the dimer
[Pd2(m-Cl)2(h3-1,1,2-Me3C3H2)2] in CH2Cl2 (2 ml), 74.6
mg (0.346 mmol) of the ligand ClNꢀSꢀtBu dissolved in
5 ml of CH2Cl2 and 94 mg (0.67 mmol) of NaClO4·H2O
in 4 ml of MeOH were added. The cloudy solution was
stirred at r.t. for 1 h and then dried under reduced
pressure. The residue was dissolved in CH2Cl2, treated
with activated charcoal and filtered on celite filter. The
resulting solution was concentrated and treated with
diethyl-ether. The allyl complex precipitated as a pale-
yellow compound (155.6 mg, 0.308).
Yield: 94%. Found: C, 38.03; H, 4.96; N, 2.81.
C16H25NO4SCl2Pd requires: C, 38.07; H, 4.99; N,
2.78%. IR (KBr, cm−1): wCꢁN 1585.5(s).
The following complexes were synthesised in the
same way as [Pd(h3-1,1,2-Me3C3H2)(ClNꢀSꢀtBu)]ClO4
using the appropriate starting substrates and ligands.
3.2.19. [Pd(p3-1,1-Me2CC(COMe)CH2)(MeNꢀSꢀtBu)]-
ClO4 (pale-yellow microcrystals)
Yield: 59%. Found: C, 41.11; H, 5.28; N, 3.72.
C18H28NO5SClPd requires: C, 41.07; H, 5.30; N, 3.68%.
IR (KBr, cm−1): wC=N 1590(s); wCꢁO 1709(s).
3.2.20. [Pd(p3-1,1,2-Me3C3H2)(HNꢀSMe)]ClO4 (whitish
microcrystals)
Yield: 81%. Found: C, 36.43; H, 4.74; N, 3.25.
C13H20NO4SClPd requires: C, 36.46; H, 4.71; N, 3.27%.
IR (KBr, cm−1): wCꢁN 1590(s).
3.2.21. [Pd(p3-1,1,2-Me3C3H2)(HNꢀSEt)]ClO4 (whitish
microcrystals)
Yield: 93%. Found: C, 38.01; H, 4.97; N, 3.20.
C14H22NO4SClPd requires: C, 38.02; H, 5.01; N, 3.17%.
IR (KBr, cm−1): wCꢁN 1601(s).
3.2.12. [Pd(p3-1,1,2-Me3C3H2)(ClNꢀSMe)]ClO4
(pale-yellow microcrystals)
Yield: 91%. Found: C, 33.81; H, 4.16; N, 3.08.
C13H19NO4SCl2Pd requires: C, 33.75; H, 4.14; N,
3.03%. IR (KBr, cm−1): wCꢁN 1584.6(s).
3.2.22. [Pd(p3-1,1,2-Me3C3H2)(HNꢀSꢀiPr)]ClO4
(pale-yellow microcrystals)
Yield: 99%. Found: C, 39.53; H, 5.34; N, 3.12.
C15H24NO4SClPd requires: C, 39.49; H, 5.30; N, 3.07%.
IR (KBr, cm−1): wCꢁN 1603(s).
3.2.13. [Pd(p3-1,1,2-Me3C3H2)(ClNꢀSPh)]ClO4
(pale-yellow microcrystals)
Yield: 92%. Found: C, 41.17; H, 4.06; N, 2.72.
C18H21NO4SCl2Pd requires: C, 41.20; H, 4.03; N,
2.67%. IR (KBr, cm−1): wCꢁN 1581.6(s).
The following complexes were synthesised according
to published procedures [1].

L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
55
Table 4
scan method (maximum and minimum transmission
factor of 0.92 and 0.48). The structure was solved by
the heavy-atom method starting from three-dimen-
sional Patterson map and refinement on F2 was first
done isotropically and subsequently with application
of anisotropy only to the heavy and nitrogen atoms.
The structure solution was based on the observed
reflections, while the refinement was based on all
reflections. The hydrogen atoms were placed in ide-
alised positions and constrained to ride on the carbon
atoms to which they are bonded. Their contributions
were added to the structure factor calculations but
their positions were not refined. The final difference
map showed no unusual feature. Structure determina-
tion and refinement were performed with the
SHELXTL NT program package [28].
Crystal data and structure refinement parameters
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
C8H12ClNPdS
296.1
orthorhombic
Pna21 (No. 33)
,
a (A)
18.999(9)
8.389(4)
13.260(8)
2113(2)
8
1.861
0.71073
21.5
2.1–22.5
1390
1273
1390/137
0.052, 0.129
0.057, 0.135
1.083
,
b (A)
,
c (A)
3
,
V (A )
Z
Dcalc (Mg m−3
)
,
Wavelength (A)
v(Mo–Ka) (cm−1
[ range (°)
)
Reflections collected
Reflections observed (I\2|(I))
Data/parameters
R1 a, wR2 b (I\2|(I))
R1 a, wR2 b (all data)
Goodness-of-fit on F2
3.4. IR, NMR and UV–6is measurements
The IR, 1H- and 13C{1H}-NMR spectra were
recorded on a Nicolet Magna™ 750 spectrophotome-
ter and on a Bruker AC™ 200 or on a Varian
400™Unity, respectively. UV–vis spectra and kinetic
measurements were performed on a Perkin–Elmer
Lambda 40™ spectrophotometer equipped with a
Perkin–Elmer PTP 6™ (Peltier Temperature Pro-
grammer) apparatus.
a R1=ꢀꢁF0ꢂ−ꢂFcꢁ/ꢀꢂF0ꢂ.
b wR2={ꢀ[w(F02−Fc2)2]/ꢀ[w(F20)2]}1/2
.
[Pd(h3-1,1,2-Me3C3H2)(HNꢀSꢀtBu)]ClO4 (pale-yel-
low microcrystals);
[Pd(h3-1,1,2-Me3C3H2)(HNꢀSPh)]ClO4
(whitish
microcrystals);
[Pd(h3-1,1,2-Me3C3H2)(MeNꢀSꢀtBu)]ClO4 (pale-yel-
3.5. Kinetics measurements
low microcrystals);
[Pd(h3-1,1,2-Me3C3H2)(MeNꢀSPh)]ClO4
(whitish
The kinetics of allene insertions were studied by
addition of known aliquots of allene solutions to so-
lutions of the complex under study in CH2Cl2
([Pd]0:10−4 mol dm−3) in the thermostatted cell
compartment of the spectrophotometer or by addition
of known amounts of allene solutions to solutions of
the complex under study in CD2Cl2 ([Pd]0:5×10−2
mol dm−3) into a 5 mm NMR tube. The reactions
were followed by recording spectral changes in the
wavelength range 250–350 nm and at a fixed suitable
wavelength in the case of UV–vis technique or fol-
lowing the disappearance of PdꢀCH3 signal (l:1
ppm) in the case of 1H-NMR studies. Kinetic mea-
surements were performed either under 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 Mar-
microcrystals);
[Pd(h3-1,1,2,3,3-Me5C3)(MeNꢀSꢀtBu)]ClO4 (pale-yel-
low microcrystals); and
[Pd(h3-1,1,2,3,3-Me5C3)(MeNꢀSPh)]ClO4 (pale-yel-
low microcrystals).
3.3. Sol6ents and reagents
Toluene and CH2Cl2 were distilled under inert at-
mosphere on Na/benzophenone and on CaH2, respec-
tively. All other chemicals were commercially
available grade products.
3.3.1. X-ray data collection and structure refinement of
[PdCl(Me)(HNꢀSMe)]
Crystal data, summary of data collection and struc-
ture refinement details are collected in Table 4. Dif-
fraction data were collected at r.t. on a single-crystal
STOE four-circle diffractometer, using a yellow thin
plane of dimension 0.30×0.15×0.05 mm. Since the
diffracting ability of the sample fell off rapidly with
increasing Bragg angle, data collection was restricted
to 2[=45°. The structure amplitudes were obtained
after the usual Lorentz and polarisation correction
and data were corrected for absorption using the psi-
quardt’s algorithm [29] written in TURBOBASIC™
.
4. Supplementary material
Final non-H atoms positional coordinates, bond
distances and angles, anisotropic thermal parameters
and atomic coordinates for hydrogens are available
with the author on request.

56
L. Cano6ese et al. / Journal of Organometallic Chemistry 650 (2002) 43–56
(b) M. Tschoerner, G. Trabesinger, A. Albinati, P.S. Pregosin,
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