Mechanism of the reaction of allyl amination of Pd(II) allyl complexes containing chelating pyridine-chalcogen ligands. A surprisingly low influence of the chalcogen atom

Article abstract of DOI:10.1016/S0277-5387(01)00922-6

The rates of amine nucleophilic attack on the allyl ligand (k₂) and the equilibrium constants (K_E) for the displacement of bidentate ligands in Pd(II) allyl complexes of chelating pyridine-chalcogen ethers [Pd(η³-allyl)(RN-XPh)]⁺ (R = H, Me; X = S, Se) are shown to depend strongly on the steric and electronic requirements of the reactants but are hardly affected by the nature of the chalcogen. Results about the reactivity and solution behaviour of these systems help build up a fairly complete mechanistic picture for this important class of reactions involving coordinated allyl species. In particular the reactivity of the complexes bearing pyridine-thioether ligands is close to that of their pyridine-selenoether analogues, probably owing to a balance of σ and π capabilities of the chalcogen atom. The associative nature of the ligand displacement is markedly affected by steric requirements which depend on the allyl bulkiness. The complexes bearing the ligands with methyl substituted pyridine are the more reactive, due to the destabilisation of the complex ground state induced by the distortion of the starting substrate. We also describe the fluxional behaviour of these species in terms of inversion of the chalcogen absolute configuration and apparent rotation of the allyl ligand.

Full text of DOI:10.1016/S0277-5387(01)00922-6

Polyhedron 20 (2001) 3171–3181
www.elsevier.com/locate/poly
Mechanism of the reaction of allyl amination of Pd(II) allyl
complexes containing chelating pyridine–chalcogen ligands.
A surprisingly low influence of the chalcogen atom
Luciano Canovese *, Fabiano Visentin, Claudio Santo, Gavino Chessa,
Paolo Uguagliati
Dipartimento di Chimica, Uni6ersita´ di Venezia, Calle Larga Santa Marta 2137-30123 Venice, Italy
Received 19 June 2001; accepted 28 August 2001
Abstract
The rates of amine nucleophilic attack on the allyl ligand (k2) and the equilibrium constants (KE) for the displacement of
bidentate ligands in Pd(II) allyl complexes of chelating pyridine–chalcogen ethers [Pd(h3-allyl)(RNꢀXPh)]+ (R=H, Me; X=S,
Se) are shown to depend strongly on the steric and electronic requirements of the reactants but are hardly affected by the nature
of the chalcogen. Results about the reactivity and solution behaviour of these systems help build up a fairly complete mechanistic
picture for this important class of reactions involving coordinated allyl species. In particular the reactivity of the complexes
bearing pyridine–thioether ligands is close to that of their pyridine–selenoether analogues, probably owing to a balance of s and
p capabilities of the chalcogen atom. The associative nature of the ligand displacement is markedly affected by steric requirements
which depend on the allyl bulkiness. The complexes bearing the ligands with methyl substituted pyridine are the more reactive,
due to the destabilisation of the complex ground state induced by the distortion of the starting substrate. We also describe the
fluxional behaviour of these species in terms of inversion of the chalcogen absolute configuration and apparent rotation of the allyl
ligand. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Allylpalladium; Bidentate ligands; Pyridine–chalcogen ethers; Allyl amination mechanism; Solution behaviour
1. Introduction
ied were either labile, as in the case of a-diimine
(L–L%=NꢀN%) [3b,4] and pyridine–thioethers (L–L%=
NꢀS) [5], or hemilabile such as imino-phosphine species
[6]. The terdentate ligands were similar in nature since
the same nucleophilic atoms were used, thus potentially
three-coordinating labile pyridine–dithioether (L–L%–
L=SꢀNꢀS), dipyridine–thioether (L–L%–L=NꢀSꢀN)
and dipyridine–amine (L–L%–L=NꢀNꢀN) or hemi-
As a part of the extensive study being currently
carried out on the reactivity of Pd(II) allyl complexes
[1] (which are still a promising source of synthetic
applications) [2], we have undertaken a systematic in-
vestigation on the mechanism of nucleophilic attack by
amines on the allyl ligand. This has been shown previ-
ously to occur on a terminal carbon atom of the
h3-bound allyl fragment on the face opposite with
respect to the metal centre [3]. The ancillary ligands we
considered were bidentate (L–L%) or terdentate (L–L%–
L¦) species and the reactions were always carried out in
the presence of an activated olefin which leads to a
stable Pd(0) olefin complex. The bidentate ligands stud-
labile
pyridine–amino–phosphine
ligands were synthesised
(L–L%–L¦=
and the
PꢀNꢀN)
corresponding Pd(II) allyl complexes were studied [7].
The reactivity and the solution behaviour of Pd(0)
olefin complexes, which are the products of the amina-
tion reaction, were also widely studied [8]. Moreover it
was possible to obtain the Pd(II) allyl complexes by
allene insertion into the metal–carbon bond of palla-
dium–alkyl species [9]. We showed that the flexibility
and the distortion of the chelate ring of the ancillary
* Corresponding author. Tel.: +39-041-257-8571; fax: +39-041-
257-8517.
E-mail address: cano@unive.it (L. Canovese).
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)00922-6

3172
L. Cano6ese et al. / Polyhedron 20 (2001) 3171–3181
ligand are of paramount importance in affecting the
allene insertion rate [10].
The preparation of the pyridine–selenoether ligands
follows a similar method to that used for their pyri-
dine–thioether analogues [5]. In the case of the sele-
nium derivatives, the yields were lower than those
observed for the sulfur containing ligands owing to the
tendency of selenium to give diselenide compounds. As
can be seen in Scheme 1, the complexes under study can
be divided into three different groups on the basis of
symmetry, and consequently the number of possible
isomers.
A schematic representation of isomeric distribution
for all the species studied is reported in Scheme 2.
Complexes 1a and 1b with an unsubstituted allyl
ligand can give rise to two rotational isomers due to the
relative orientation of the central allyl proton and of
chalcogen substituent (it should be recalled that the
allyl ligand binds side-on with respect to the main
coordination plane). In contrast, complexes 2a, 2b and
2b% (dimethyl substituted allyl fragment) yield four po-
tential rotameric forms on the basis of the arrange-
ments possible for the central allyl proton and the
chalcogen substituent and of the position of the
dimethyl substituted allyl terminus which can be cis or
trans to sulfur atom as shown in Scheme 2. The com-
We therefore decided to extend our investigation to
palladium complexes containing pyridine–selenium lig-
ands in order to assess the versatility of these new
species. In this paper we describe their reactivity and
also report on the synthesis and reactivity of new Pd(II)
complexes with novel pyridine–thioether ligands. The
electronic and steric factors influencing the mechanism
of nucleophilic attack on allyl complexes bearing pyri-
dine–chalcogen ligands are discussed in the light of
these results.
2. Results and discussion
2.1. Synthesis and NMR characterisation of ligands
and complexes
The synthesised ligands and complexes, with their
numbering scheme (which implies no isomeric prefer-
ence and only indicates atom locations), are reported in
Scheme 1.
Scheme 1.

L. Cano6ese et al. / Polyhedron 20 (2001) 3171–3181
3173
which are present in different populations, are clearly
detectable. In particular, the aliphatic zone of such
spectra contains particularly diagnostic groups of sig-
nals. The four sets of resonances, each with doublet
multiplicity, between 3.10 and 3.96 ppm are ascribable
to the four allyl anti protons (J=12.7 Hz) (two for
each rotamer) which differ by their position with re-
spect to the nitrogen atom. The occurrence of two
rotameric forms is further supported by the observation
of two singlets, corresponding to the methyl sub-
stituents in the pyridine ring at 2.71 and 2.74 ppm,
respectively. On increasing the temperature several flux-
ional processes take place, and the ensuing room tem-
perature (r.t.) spectrum shows loss of CH2ꢀSe
diastereotopicity, syn–syn, anti–anti isomerism and re-
duction to one singlet of the pyridine-methyl signals.
This suggests concomitant chalcogen inversion [11] and
apparent allyl fragment rotation [1e,2d] (no syn–anti or
h3–h1–h3 isomerism is observed at r.t.).
In the case of complexes 2a and 2b (1,1-Me2allyl), as
already stated, four isomers are expected and this is
indeed the case for complex 2a (unsubstituted pyridine
ring) which displays in the low temperature spectrum
two sets of doublets (one for each rotamer) in the
region 3.00–4.10 ppm. These signals are ascribable to
the anti protons which can be alternatively pseudo-cis
or pseudo-trans to the chalcogen or nitrogen atom of
the ancillary ligand. In the 188 K spectrum of complex
2b (Fig. 1(b)) only the couple of doublets between 3.60
and 3.85 ppm is detectable, suggesting the presence of
only the couple of rotamers in which the dimethyl
substituted allyl terminus lies, for steric reasons,
pseudo-trans to the pyridine nitrogen. The low tempera-
ture 2D NOESY confirms this hypothesis since no
selective NOE signals from the methyl substituent of
the pyridine ring to the methyl substituents of the allyl
terminus can be observed.
Scheme 2.
plexes 3a, 3a% and 3b, 3b% (phenyl substituted allyl
fragment) could produce eight isomers owing to: (i) the
position of the central allyl proton and the chalcogen
substituent, (ii) the cis or trans position of the substi-
tuted allyl terminus, and (iii) the position of phenyl
group which can be syn or anti within the allyl fragment
and consequently with respect to the metal core. How-
ever, as already observed for analogous species [6b], no
evidence for a phenyl group in anti position could be
detected since the magnitude of J(Hcentral–Hanti Ph) cou-
pling constant (14–12 Hz) observed at low temperature
strongly suggests the syn position for this group. There-
fore, the exclusion of such an isomeric choice (probably
due to steric reasons) halves the number of isomers.
The Pd(0) fumaronitrile complexes 4a and 4b give two
diastereoisomers on the basis of the olefin face coordi-
nated to the metal centre, namely Re and Si species.
In Fig. 1(a), selected resonances obtained in the low
temperature 1H NMR spectrum of complex 1b are
reported. As can be seen, the two expected rotamers,
At variance, positive NOE signals from the methyl
substituent of the pyridine ring to both the syn and anti
allyl protons are clearly detectable, except for the case
of anti allyl protons of the less-populated rotamer
which displays an intensity of the crosspeak near the
background noise. This fact is probably due to the low
concentration of the isomer and/or to the unfavourable
position of the proton. Thus the signals in the interval
3.0–3.5 can be assigned to the protons pseudo-trans to
the pyridine nitrogen; moreover the methyl group on
pyridine ring, according to Pregosin’s suggestion, can
be considered a non-selective but useful ‘reporter ’ [1e].
1
The low temperature H NMR spectra of complexes 3a
and 3b (1-phenyl-allyl) display the presence of all the
four expected isomers. The isomers distribution is easily
determined on the basis of the characteristic features of
1H NMR spectra of the complexes bearing this peculiar
allyl fragment. The pair of rotamers bearing the phenyl
substituent in the allyl terminus pseudo-cis to pyridine

3174
L. Cano6ese et al. / Polyhedron 20 (2001) 3171–3181
other associative mechanisms [12] could not be ruled
out. The spectra of complexes 4a and 4b differ accord-
ing to the presence of a singlet (l=2.93 ppm; r.t.) due
to the methyl substituent on pyridine ring in the case of
4b complex which also displays a residual coupling
nitrogen displays a marked up-field shift (:7 ppm) of
the pyridine 6-H proton caused by the shielding due to
phenyl ring currents [6b]. On the other hand, the 6-H
pyridine proton of the remaining pair resonates at 8.74
(unresolved doublet). It is possible to establish, there-
fore, that the more abundant pair of rotamers for
complex 3a place the substituted allyl terminus pseudo-
cis to pyridine nitrogen. At variance, complex 3b dis-
plays a different situation and the more abundant pair
of rotamers contains phenyl substituents that are
pseudo-trans to the pyridine nitrogen, this phenomenon
arising due to steric reasons. These spectra also exhibit
a distribution of the anti protons in the usual intervals
(3.15–3.40 and 3.80–4.10 ppm), thereby confirming the
position of the anti protons pseudo-trans to the pyridine
between CH6 2
ꢀSe protons and 77Se (2JH–Se=13.7 Hz).
This kind of fluxional behaviour was studied in detail in
the case of pyridine–thioether Pd(0) fumaronitrile com-
plexes [8a,b] and no particular differences could be
1
detected with respect to these species. The H NMR
spectrum at 188 K of 4b complex shows the presence of
both Re and Si isomers as clearly indicated by the
couple of singlets due to methyl substituent on the
pyridine ring at 2.81 and 2.83 ppm (isomeric ratio
1:2.3), respectively, by the two (one of which not com-
pletely resolved) AB systems ascribable to endocyclic
CH6 2ꢀSe protons (bs 4.45, AB sys lA=4.43, lB=4.53
ppm, JAB=14.2 Hz), and by the two AB systems
ascribable to the olefin protons (lA=3.13, lB=3.21
1
ring (3.00–3.50 ppm). The low temperature H NMR
signals ascribable to the diagnostic anti allyl protons
are reported in Table 1.
Palladium(0) fumaronitrile complexes do not deserve
detailed comments owing to their customary features
and behaviour. As a matter of fact, the 1H NMR
spectra of the synthesised Pd(0) complexes (see Section
3) are superimposable to those obtained in the amina-
tion reaction in the presence of fumaronitrile. The r.t.
spectra show a generalised fluxionality ascribable to
selenium inversion [11] and olefin rotation, although
ppm, JAB=9.8 Hz; lA%=3.13, lB%=3.18 ppm, JA%,B%
=
9.8 Hz).
2.2. Reacti6ity
The following allyl amination reactions (Scheme 3)
1
were studied by UV–Vis spectroscopy and H NMR
spectrometry in CDCl3 at r.t.
Fig. 1. Aliphatic region of the low temperature 1H NMR spectra of complexes 1b (a) and 2b (b) (200 MHz, CD2Cl2, 188 K).

L. Cano6ese et al. / Polyhedron 20 (2001) 3171–3181
3175
Table 1
1H NMR data for allyl anti protons and pyridine-substituent methyl protons of selected complexes recorded at 188 K in CD2Cl2
Complex
Rotamer (%Major, M; %minor, m)
HaSnti (pseudo-cis to S)
HaNnti (pseudo-cis to N)
C5H4NꢀCH3
RIII+RIV
RI+RII
1a
1b
2a
M 60%
m 40%
M 60%
m 40%
50%
3.10 d
3.27 d
3.16 d
3.35 d
4.07 d
4.07 d
3.83 d
3.91 d
3.90 d
3.89 d
100%
100%
70%
2.74 s
2.71 s
3.21 d
3.31 d
50%
50%
30%
100%
2b
3a
3.66 d
3.77 d
4.14 d
2.73 s
2.70 s
a
a
b
b
90%
4.14 d
b
M 60%
m 40%
M 55%
3.15 d
10%
10%
80%
b
3.45 d
b
3b
3.92 d
2.74 s
2.66 s
2.50 bs
2.50 bs
b
m 45%
4.04 d
a
b
3.25 bd
3.25 d
20%
a
b
a Not separated signals.
b Obscured by solvent signal.
Moreover the complex [Pd(h3-allyl)(Pip)2]+ is not in-
volved in the isomerisation reaction since in a further
experiment no reaction between bispiperidino complex
and I2 (independently synthesised) was observed. This
isomerisation phenomenon is easily detected thanks to
In any case the formation of the Pd(0) fumaronitrile
complexes together with the corresponding allyl-amines
was detected. When the reacting complexes bear unsub-
stituted allyl, and 1-phenyl-allyl fragments only one
allyl-amine isomer was observed. The peculiar reactivity
of the complexes bearing the mono-substituted allyl
species [PhCHꢀCHꢀCH2]− which only leads to the
formation of the linear amino-olefin PhCHꢁCHꢀ
CH2NC5H10 is not without precedent [6b,13] and prob-
ably originates from the extremely low rate of nucle-
ophilic attack by piperidine on the phenyl-substituted
allyl terminus which depends on steric and electronic
factors. The predominant formation of the linear allyl-
amine PhCHꢁCHCH2NC5H10 could indeed be traced
back to its stabilisation via double bond conjugation.
As a matter of fact, similar results were also obtained in
the palladium catalysed alkylation of 1-arylprop-2-enyl
acetates with enolates (Nu) which leads to linear olefins
(E)-ArCHꢁCHCH2Nu [14].
The reaction of complexes 2 with piperidine in the
presence of fumaronitrile leads to the formation of the
usual Pd(0) fumaronitrile complexes and to a mixture
of the two allyl-amine isomers (Me2CꢁCHCH2NC5H10
(I1) and CH2ꢁCHCMe2NC5H10 (I2)). Surprisingly the
isomer ratio I1/I2 depends upon the nature of the
ancillary ligand. The observed ratio is 5 in the case of
complex 2a (L–L%=HNꢀSePh) and 30 (or more) with
2b and 2b% complexes (L–L%=MeNꢀXPh). In this latter
case significant immediate formation of the inert (with
respect to allyl-amination reaction) [Pd(h3-allyl)(Pip)2]+
complex and a slow isomerisation reaction are ob-
served, so that the 30:1 isomeric ratio is slowly reached.
1
the characteristic feature of the H NMR spectra of the
two allyl-amine isomers [5b]. It is noteworthy that
,
similar findings were described by Akermark et al. in
the case of the allyl amination of labile ligand com-
plexes by aliphatic amines [15]. We are not able, at the
moment, to propose a mechanism in order to explain
such an experimental result but we are still studying
this problem and work is still in progress in our labora-
tory in order to interpret these findings.
2.3. Kinetics and mechanism
The h3-allyl complexes [Pd(h3-allyl)(RNꢀXPh)]+ (al-
lyl=C3H5, 1,1-Me2ꢀC3H3, 1-PhꢀC3H4; R=H, Me;
X=Se, S) ([Pd]0:10−4 mol dm−3) react smoothly
with a variable excess of piperidine (Pip) ([Pip]0=1×
10−3–1.2×10−2 mol dm−3) in CHCl3 at 25 °C in the
Scheme 3.

3176
L. Cano6ese et al. / Polyhedron 20 (2001) 3171–3181
Fig. 2. Fit of kobs to [pip] for the reaction of complex 1a with piperidine at 25 °C according to Eq. (2).
presence of fumaronitrile (fn) ([fn]0=2×10−4–4×
10−4 mol dm−3) and of pyridine–chalcogenether lig-
and (RNꢀXPh) ([RNꢀXPh]0=10−3 mol dm−3) to give
the Pd(0) olefin complexes [Pd(h2-fn)(RNꢀXPh)] and
the allylammine C5H10NꢀC3H3R1R2.
The reaction course, which was confirmed by NMR
spectrometry (vide supra), was followed by monitoring
UV–Vis spectral changes in the wavelength range 280–
400 nm as a function of reaction time. Under these
conditions the reactions reached completion as indi-
cated by comparison of solution spectra at the end of
the reactions with those of the final products indepen-
dently prepared. The conversion of the reactants into
products with time appeared to obey the mono-expo-
nential relationship At=Aꢀ+(A0−Aꢀ) exp(−kobst)
which corresponds to a pseudo-first order process
can be proposed based on the above experimental
evidence. This mechanism was also confirmed by NMR
experiments carried out either in CDCl3 or CD2Cl2.
According to this mechanistic picture the h3-allyl
substrate S is in fast pre-equilibrium (KE) with the inert
bisamino species B via the displacement of the biden-
tate ligand RNꢀXPh. The substrate undergoes con-
comitant rate-determining bimolecular attack by the
amine (k2 step) to give a labile Pd(0) intermediate
species I bearing an h2-bound allyl cation which is
displaced rapidly and quantitatively by the activated
olefin fumaronitrile (fn) to give the final products P1
and P2 (therefore the fn concentration will not influ-
ence the overall rate constant). Accordingly, the
pseudo-first order rate constant kobs is given by Eq. (3):
k
obs= k2[Pip]/(1+KE[Pip]2/[RN−XPh])
(3)
−d[[Pd(h3-allyl)(RN−XPh)]+]/dt
Consequently, the h and i parameters in the ob-
=kobs[[Pd(h3-allyl)(RN−XPh)]+]
(1)
served rate law 2 can be identified as the second-order
rate constant k2 and the equilibrium constant KE, re-
spectively (Table 2).
The inertness of the bisamino species B towards
nucleophilic attack of amines on the allyl group is a
common feature of this class of reactions and was
confirmed by independent reactivity measurements on
the authentic isolated species [4,5].
The kobs values, determined by non-linear regression
analysis of At (absorbance at time t) versus t (time)
data display a bivariate dependence (Eq. (2)) on [Pip]
and [RNꢀXPh] which are considered to be constant
with time, being in excess over the metal substrate
concentration:
obs=h[Pip]/(1+i[Pip]2/[RN−XPh])
(2)
This can be rationalised by the essentially s-donating
ability of the amines (compared with the better p-ac-
cepting ability of the bidentate ligands examined),
which increases the electron density on the central
metal, thereby decreasing the electrophilic character of
the allyl ligand.
As can be seen in Table 2 the reactivity of the
complexes bearing the pyridine–thioether ligands is
very similar to that of the analogous pyridine–sele-
k
The parameter values h and i were determined by
non-linear regression of rate constants to Eq. (2) (Fig.
2).
In line with the wealth of our previous findings
relating to the analogous reactions of Pd(II) h3-allyl
substrates containing labile or hemilabile chelating lig-
ands [4,5], the stepwise mechanism shown in Scheme 4

L. Cano6ese et al. / Polyhedron 20 (2001) 3171–3181
3177
Scheme 4.
noether species, the k2 and KE values being virtually
\[Pd(h3-1,1-Me2allyl)(HNꢀXPh)]+
[Pd(h3-allyl)(MeNꢀXPh)]+
$[Pd(h3-1-phenylallyl)(MeNꢀXPh)]+
\[Pd(h3-1,1-Me2allyl)(MeNꢀXPh)]+
The complexes bearing the ligands with the methyl
substituted pyridine still come out as more reactive.
superimposable. This surprising result probably derives
from a balance of s and p capabilities of the chalcogen
atoms. Apparently, the slightly higher p ability of the
larger selenium atom as compared to sulfur offsets its
lower basicity [16]; this characteristic feature could be
very important if Pd(0) derivatives are involved.
Within homologous series (same RNꢀXPh) the KE
values increase in the order:
Table 2
Second-order rate constants and equilibrium constants for reactions
of allyl complexes with piperidine in CHCl3 at 25 °C
[Pd(h3-allyl)(HNꢀXPh)]+
\[Pd(h3-1-phenylallyl)(HNꢀXPh)]+
$[Pd(h3-1,1-Me2allyl)(HNꢀXPh)]+
[Pd(h3-allyl)(MeNꢀXPh)]+
Complex
k2
KE
(mol−1 dm3 s−1
)
[Pd(h3-C3H5)(HNꢀSePh)]ClO4
(1a)
4.0790.06
10793
$[Pd(h3-1-phenylallyl)(MeNꢀXPh)]+
\[Pd(h3-1,1-Me2allyl)(MeNꢀXPh)]+
[Pd(h3-C3H5)(HNꢀSPh)]ClO4
[Pd(h3-C3H5)(MeNꢀSePh)]ClO4
(1b)
3.990.3 a
14.390.9
204960 a
24009200
In the latter case, the KE values are approximately
one order of magnitude higher than in the case of
complexes bearing HNꢀXR ligands.
The associative mechanism of the ligand displace-
ment is strongly influenced by steric requirements which
clearly depend on the allyl bulkiness within each ho-
mologous series. Moreover the pyridine methyl sub-
stituent imparts an instability to the whole molecule
which is pointed out by the generalised increase and
levelling off of KE values.
[Pd(h3-C3H5)(MeNꢀSPh)]ClO4
[Pd(h3-1,1-Me2C3H3)(HNꢀ
SePh)]ClO4 (2a)
10.090.6 a
0.15490.005
21009200 a
12.790.6
[Pd(h3-1,1-Me2C3H3)(HNꢀ
SPh)]ClO4
0.16390.002 a
0.5790.01
0.53390.009
0.8790.02
0.8790.03
8.590.3
1891 a
360910
400910
2291
[Pd(h3ꢀ1,1-Me2C3H3)-
(MeNꢀSePh)]ClO4 (2b)
[Pd(h3-1,1-Me2C3H3)-
(MeNꢀSPh)]ClO4 (2b%)
[Pd(h3-1-Ph-C3H4)-
(HNꢀSePh)]ClO4
[Pd(h3-1-Ph-C3H4)-
(HNꢀSPh)]ClO4 (3a)
[Pd(h3-1-Ph-C3H4)-
(MeNꢀSePh)]ClO4 (3b)
[Pd(h3-1-Ph-C3H4)-
(MeNꢀSPh)]ClO4 (3b%)
2491
As for the k2 values, again no influence by the
chalcogen atom can be detected. It is convenient to
discuss the reactivity of the substrates on the basis of
the following reactivity orders:
1870990
27009300
9.690.8
[Pd(h3-allyl)(HNꢀXPh)]+
\[Pd(h3-1-phenylallyl)(HNꢀXPh)]+
a Data from Ref. [5b].

3178
L. Cano6ese et al. / Polyhedron 20 (2001) 3171–3181
Apparently the destabilisation of the complex ground
state also influences the amination reaction. However,
the decrease in reactivity within the same series is easily
traced back to the influence of steric bulkiness on the
rates of bimolecular associative reactions. On the other
hand, molecular activation induced by distortion of the
starting substrate reflects the increase in k2 (on going
from the first to the second reactivity order) and the
levelling off of the reactivity between [Pd(h3-allyl)-
(MeNꢀXPh)]+ and [Pd(h3-1-phenylallyl)(MeNꢀXPh)]+
, the latter being slightly less reactive. This phenomenon
probably depends on the ground state activation cou-
pled with the electron withdrawing capability of the
phenyl group which activates the allyl moiety towards
nucleophilic attack, thereby overcoming the steric bulk-
iness and rendering the complex as reactive as its
unsubstituted allyl analogue (if the statistical factor due
to the halving of the number of attack sites is taken
into account).
resulting solution was stirred for 4 h at 55 °C. The
reaction mixture was dried under reduced pressure and
the residue was treated with an ice/water mixture and
neutralised with Na2CO3. The crude product was ex-
tracted with CH2Cl2 and dried with Na2SO4 for 12 h.
The filtered solution was dried under reduced pressure
by means of a high vacuum line; the oily product (3.76
g, 26.5 mmol, yield 65.3%) was used without further
purification.
1H NMR (CDCl3, r.t., ppm): l=2.57 (CH3, s, 3H),
4.65 (CH2ꢀCl, s, 2H), 7.10 (H3, d, J=7.7 Hz, 1H), 7.29
(H5, d, J=7.7 Hz, 1H), 7.61 (H4, t, J=7.7 Hz, 1H).
3.1.3. 2-(Phenyl-selenomethyl)-6-methyl-pyridine
(MeNꢀSePh)
The title compound was synthesised in a way similar
to that employed in the case of HNꢀSePh ligand start-
ing from 0.71
g
(5.0 mmol) of 2-chloro-6-
methylpyridine and 1.57 g (10 mmol) of seleno-phenol
in the presence of 2.25 g (40 mmol) KOH in DMSO.
The ligand was obtained as a yellowish oil (1.15 g, 4.39
mmol, yield 87.7%).
3. Experimental
Anal. Found: C, 59.52; H, 4.96; N, 5.30. Calc. for
C13H13NSe: C, 59.56; H, 5.00; N, 5.34%. IR (NaCl,
cm−1): wCꢁN 1591. 1H NMR (CDCl3, r.t., ppm): se-
lenomethyl protons l=4.21 (CH2ꢀSe, s, J2H–Se=12.1
Hz, 2H); pyridine protons l=6.92 (H3, d, J=7.7 Hz,
1H), 7.43 (H4, t, J=7.7 Hz, 1H), 6.97 (H5, d, J=7.7
Hz, 1H); l=2.52 (C5H3N-6-CH3, s, 3H); l=7.20–7.31
(HoꢀHp, m, 3H); l=7.45–7.56 (Hm, m, 2H). 13C{1H}
NMR (CDCl3, r.t., ppm): selenomethyl carbons l=
3.1. Preparation of ligands
3.1.1. 2-(Phenyl-selenomethyl)-pyridine (HNꢀSePh)
To a 10 ml solution of 2.25 g (40.0 mmol) of KOH
and 0.943 g (6.00 mmol) of seleno-phenol (HSeꢀPh) in
DMSO, 0.820 g (5 mmol) of 2-chloromethylpyridine
hydrochloride was added and the resulting solution was
stirred vigorously for 1 h; 50 ml of water was then
added. The organic phase was extracted with diethyl
ether (2×30 ml) and treated with anhydrous Na2SO4
for 12 h. The solution was filtered and concentrated to
dryness under reduced pressure and the oily product
was flash-chromatographed by eluting with CH2Cl2/
Et2O on SiO2 column. A yellowish oil (0.73 g, 2.98
mmol) was obtained. Yield 59.6%.
1
33.7 (CH2ꢀSe, JC–Se=62.2 Hz); pyridine carbons l=
157.8 (C6), 121.0 (C5), 136.3 (C4), 119.6 (C3), 157.7 (C2);
phenyl carbons l=129.9 (SeꢀC), 133.3 (Co, J2C–Se=10
Hz), 128.7 (Cm), 127.0 (Cp); C5H3N-6-CH3 l=24.2.
77Se{1H} NMR (CDCl3, r.t., ppm): l=358. 77Se NMR
(CDCl3, r.t., ppm): l=358 (t, JSe–H=12.1 Hz).
Anal. Found: C, 58.12; H, 4.38; N, 5.60. Calc. for
C12H11NSe: C, 58.09; H, 4.47; N, 5.65%. IR (NaCl,
3.2. Preparation of Pd(II) complexes
cm−1): wCꢁN 1590. H NMR (CDCl3, r.t., ppm): seleno-
3.2.1. [Pd(p3-C3H5)(HNꢀSePh)]ClO4 (1a)
1
methyl protons l=4.23 (CH2ꢀSe, s, J2H–Se=12.4 Hz,
2H); pyridine protons l=7.53 (H4, td, J=7.6, 1.8 Hz,
1H), 8.51 (H6, dd, J=5.4, 1.8 Hz, 1H); l=7.06–7.28
(H3ꢀH5ꢀHoꢀHmꢀHp, m, 7H). 13C{1H} NMR (CDCl3,
r.t., ppm): seleno-methyl carbons l=33.8 (CH2ꢀSe,
J1C–Se=60.2 Hz); pyridine carbons l=158.7 (C2), 123.0
(C3), 136.4 (C4), 121.7 (C5), 149.5 (C6); phenyl carbons
l=129.9 (SeꢀC), 133.6 (Co), 129.0 (Cm), 127.3 (Cp).
77Se{1H} NMR (CDCl3, r.t., ppm): l=359. 77Se NMR
(CDCl3, r.t., ppm): l=359 (tt, JSe–H=12.4, 3.6 Hz).
To a solution of 0.126 g (0.308 mmol) of [Pd(h3-
C3H5)Cl]2 [17a] in 20 ml of CH2Cl2, 0.16 g (0.646
mmol) of HNꢀSePh and 0.173 g (1.23 mmol) of
NaClO4·H2O were added. The solution was stirred for
30 min and concentrated under reduced pressure. The
solid was dissolved in CH2Cl2, treated with activated
charcoal and filtered on celite. The resulting yellow
solution was concentrated and the title complex was
obtained as an off-white solid (0.298 g, 0.60 mmol,
yield 97.6%) by addition of diethyl ether.
Anal. Found: C, 36.51; H, 3.28; N, 2.89. Calc. for
C15H16ClNO4SePd: C, 36.39; H, 3.26; N, 2.83%. IR
3.1.2. 2-Chloro-6-methylpyridine
1
To a 5.0 g (40.6 mmol) of 2-hydroxymethyl-6-
methylpyridine in a 250 ml flask placed into an ice
bath, 40 ml of thionyl chloride was slowly added; the
(KBr, cm−1): wCꢁN 1599, wClO 1090, lClO 623. H NMR
(CDCl3, r.t., ppm): selenomethyl protons l=4.77
(CH2ꢀSe, s, 2H); allyl protons l=4.60 (Hsyn, br s, 2H),

L. Cano6ese et al. / Polyhedron 20 (2001) 3171–3181
3179
l=3.76 (Hanti, br s, 2H), l=5.98 (Hcentral, q, J=10.1
Hz, 1H); pyridine protons l=7.85 (H4, td, J=7.8, 1.6
Hz, 1H), 8.92 (H6, d, J=5.5 Hz, 1H); pyridine and
phenyl protons l=7.29–7.66 (H3ꢀH5ꢀHoꢀHmꢀHp, m,
7H). 13C{1H} NMR (CDCl3, r.t., ppm): selenomethyl
carbons l=40.8 (CH2ꢀSe, 1JC–Se=56 Hz); pyridine
carbons l=159.3 (C2), 124.9 (C3), 140.0 (C4), 125.3
(C5), 155.2 (C6); phenyl carbons l=126.0 (SeꢀC),
130.3 (Co), 133.6 (Cm), 130.4 (Cp); allyl carbons l=
58.2 (C1, br), 120.3 (C2), 75.8 (C3, br).
l=7.24–7.35 (H3ꢀH5ꢀHoꢀHp, m, 5H). 13C{1H} NMR
(CDCl3, r.t., ppm): selenomethyl carbons l=39.8
(CH2ꢀSe, 1JC–Se=52.2 Hz); C5H3N-6-CH3 l=28.9;
pyridine carbons l=160.0 (C2), 121.1 (C3), 139.2 (C4),
123.7 (C5), 157.9 (C6); phenyl carbons l=124.3
(SeꢀC), 129.3 (Co), 133.0 (Cm), 129.6 (Cp); allyl carbons
l=59.5 (CA1, b), 116.9 (CA2), 74.1 (CA3, br).
3.2.5. [Pd(p3-1,1-Me2C3H3)(MeNꢀSePh)]ClO4 (2b)
Yield 91.0% (pale yellow microcrystals).
Anal. Found: C, 40.31; H, 4.21; N, 2.58. Calc. for
C18H22ClNO4SePd: C, 40.25; H, 4.13; N, 2.61%. IR
Complexes 2a, 3a, 1b–3b and 3a%, 2b%, 3b% were
synthesised similarly to complex 1a using the appropri-
ate Pd(II) dimer [17b] and ligand.
1
(KBr, cm−1): wCꢁN 1601, wClO 1082, lClO 624. H NMR
(CDCl3, r.t., ppm): selenomethyl protons l=4.78
(CH2ꢀSe, br d, 2H); allyl protons l=5.64 (Hcentral, dd,
J=13.7, 7.7 Hz, 1H), l=4.69 (Hsyn, d, J=7.7 Hz,
1H), l=3.77 (Hanti, d, J=13.3 Hz, 1H); allyl methyls
l=1.85 (Mesyn, s, 3H), 1.48 (Meanti, s, 3H); pyridine
protons l=7.63 (H4, t, J=7.7 Hz, 1H); C5H3N-6-CH3
l=2.78 (CH3, s, 3H); phenyl protons l=7.46–7.54
(Hm, m, 2H); l=7.20–7.35 (H3ꢀH5ꢀHoꢀHp, m, 5H).
13C{1H} NMR (CDCl3, r.t., ppm): selenomethyl car-
bons l=39.7 (CH2ꢀSe, 1JC–Se=53.3 Hz); C5H3N-6-
CH3 l=22.3; pyridine carbons l=160.0 (C2), 122.5
(C3), 139.3 (C4), 124.1 (C5), 159.0 (C6); phenyl carbons
l=124.7 (SeꢀC), 129.9 (Co), 133.3 (Cm), 129.9 (Cp);
allyl carbons l=96.3 (C1, br), 111.6 (C2), 64.1 (C3, br),
29.6 (Csyn), 22.3 (Canti).
3.2.2. [Pd(p3-1,1-Me2C3H3)(HNꢀSePh)]ClO4 (2a)
Yield 94.7% (pale yellow microcrystals).
Anal. Found: C, 38.95; H, 3.88; N, 2.90. Calc. for
C17H20ClNO4SePd: C, 39.03; H, 3.85; N, 2.88%. IR
1
(KBr, cm−1): wCꢁN 1605, wClO 1076, lClO 622. H NMR
(CDCl3, r.t., ppm): selenomethyl protons l=4.71
(CH2ꢀSe, br s, 2H); allyl protons l=5.63 (Hcentral, bt,
1H), l=4.45 (Hsyn, br s, 1H), l=4.01 (Hanti, bs, 1H);
allyl methyls l=1.80 (Mesyn, s, 3H), 1.44 (Meanti, s,
3H); pyridine protons l=7.85 (H4, t, J=7.7 Hz, 1H),
8.85 (H6, br s, 1H); l=7.20–7.65 (H3ꢀH5ꢀHoꢀHmꢀHp,
m, 7H). 13C{1H} NMR (CDCl3, r.t., ppm): se-
lenomethyl carbons l=39.9 (CH2ꢀSe, 1JC–Se=55.5
Hz); pyridine carbons l=159.1 (C2), 124.7 (C3), 139.5
(C4), 125.1 (C5), 154.1 (C6, br); phenyl carbons l=
125.6 (SeꢀC), 130.1 (Co), 133.2 (Cm), 130.1 (Cp); allyl
carbons l=obscured (C1), 114.1 (C2), 66.4 (C3, br),
27.79 (Csyn, br), 21.9 (Canti).
3.2.6. [Pd(p3-1-PhC3H4)(MeNꢀSePh)]ClO4 (3b)
Yield 96.0% (yellow microcrystals).
Anal. Found: C, 45.09; H, 3.78; N, 2.41. Calc. for
C22H22ClNO4SePd: C, 45.16; H, 3.79; N, 2.39%. IR
(KBr, cm−1):wCꢁN 1604, wClO 1087.8, lClO 624.9. 1H
NMR (CDCl3, r.t., ppm): selenomethyl protons l=
3.2.3. [Pd(p3-1-PhC3H4)(HNꢀSePh)]ClO4 (3a)
Yield 94.0% (Yellow microcrystals).
4.76 (CH2ꢀSe, br s, 2H); allyl protons l=6.31 (Hcentral
,
Anal. Found: C, 44.22; H, 3.58; N, 2.50. Calc. for
C21H20ClNO4SePd: C, 44.16; H, 3.53; N 2.45%. IR
br s, 1H), l=4.08 (Hsyn, br s, 1H), l=3.93 (Hanti H, br
s, 1H), l=5.42 (Hanti Ph, br s, 1H); C5H3N-6-CH3 l=
2.63 (CH3, br s, 3H); pyridine and phenyl protons
l=7.09–7.62 (HoꢀHmꢀHpꢀH3ꢀH4ꢀH5, m, 8H).
(KBr, cm−1): wCꢁN 1599, wClO 1091.7, lClO 623.0. H
1
NMR (CDCl3, r.t., ppm): selenomethyl protons l=
4.66 (CH2ꢀSe, br s, 2H); pyridine protons l=6.93 (H6,
br, 1H); allyl protons l=6.35 (Hcentral, br s, 1H),
l=4.40 (Hsyn, br s, 1H), l=3.42 (Hanti H, br s, 1H),
l=5.59 (Hanti Ph, br s, 1H); pyridine and phenyl pro-
tons l=7.17–7.89 (HoꢀHmꢀHpꢀH3ꢀH4ꢀH5, m, 8H).
3.2.7. [Pd(p3-1-PhC3H4)(HNꢀSPh)]ClO4 (3a%)
Yield 95.3% (yellow microcrystals).
Anal. Found: C, 48.16; H, 3.88; N, 2.71. Calc. for
C21H20ClNO4SPd: C, 48.11; H, 3.84; N, 2.67%. IR
1
(KBr, cm−1): wCꢁN 1601, wClO 1093.6, lClO 624.9. H
3.2.4. [Pd(p3-C3H5)(MeNꢀSePh)]ClO4 (1b)
Yield 96.2% (pale yellow microcrystals).
NMR (CDCl3, r.t., ppm): thiomethyl protons l=4.80
(CH2ꢀS, br AB system, 2H); allyl protons l=6.36
(Hcentral, br s, 1H), l=4.32 (Hsyn, br s, 1H), l=3.49
(Hanti H, br s, 1H), l=5.57 (Hanti Ph, br s, 1H); pyridine
and phenyl protons l=6.85–7.88 (HoꢀHmꢀHpꢀ
H3ꢀH4ꢀH5ꢀH6, m, 9H).
Anal. Found: C, 37.69; H, 3.61; N, 2.87. Calc. for
C16H18ClNO4SePd: C, 37.75; H, 3.56; N, 2.85%. IR
1
(KBr, cm−1):wCꢁN 1601, wClO 1090, lClO 624. H NMR
(CDCl3, r.t., ppm): selenomethyl protons l=4.85
(CH2ꢀSe, s, 2H); pyridine protons l=7.66 (H4, t,
J=7.7 Hz, 1H); allyl protons l=4.76 (Hsyn, br s, 2H),
l=5.91 (Hcentral, tt, J=12.8; 7.2 Hz, 1H), l=3.70
(Hanti, br s, 2H); C5H3N-6-CH3 l=2.78 (3H, s, CH3);
phenyl and pyridine protons l=7.56 (Hm, m, 2H);
3.2.8. [Pd(p3-1,1-Me2C3H3)(MeNꢀSPh)]ClO4 (2b%)
Yield 97.3% (pale yellow microcrystals).
Anal. Found: C, 44.14; H, 4.55; N, 2.81. Calc. for
C18H22ClNO4SPd: C, 44.10; H, 4.52; N, 2.86%. IR

3180
L. Cano6ese et al. / Polyhedron 20 (2001) 3171–3181
(KBr, cm−1):wCꢁN 1602.8, wClO 1082.0, lClO 623.0. H
NMR (CDCl3, r.t., ppm): thiomethyl protons lA=
4.74, lB=4.81 (CH2ꢀS, AB system, JAB=16 Hz, 2H);
allyl protons l=5.61 (Hcentral, dd, J=13.4, 7.7 Hz,
Se=13.7 Hz, 2H); olefin protons (fumaronitrile) l=
3.19 (Hol, s, 2H); pyridine protons l=7.16 (H5, d,
J=7.6 Hz, 1H); C5H3N-6-CH3 l=2.93 (CH3, s, 3H);
1
pyridine
and
methyl
protons
l=7.24–7.32
1H), l=4.68 (Hsyn, d, J=7.7 Hz, 1H), l=3.7 (Hanti
,
(HoꢀHpꢀH3, m, 4H); l=7.56–7.63 (HmꢀH4, m, 3H).
d, J=13.4 Hz, 1H); allyl methyls l=1.75 (Mesyn, s,
3H), 1.43 (Meanti, s, 3H); pyridine protons l=7.71 (H4,
t, J=7.7 Hz, 1H); C5H3N-6-CH3 l=2.80 (CH3, s,
3H); pyridine and phenyl protons l=7.48–7.53 (Hm,
m, 2H); l=7.31–7.39 (HoꢀHpꢀH3ꢀH5, m, 5H).
3.4. IR and NMR measurements
The IR, 1H, and 13C{1H} NMR spectra were
recorded in a Nicolet Magna™ 750 spectrophotometer
and in a Bruker™ AC 200 or a Varian ™ 400 Unity
3.2.9. [Pd(p3-1-PhC3H4)(MeNꢀSPh)]ClO4 (3b%)
Yield 95.0% (yellow microcrystals).
spectrometers, respectively. The H 2D NOESY experi-
1
ments were performed at 188 K in CD2Cl2 by means of
a Varian™ 400 Unity spectrometer (400 MHz) using a
standard three pulse sequence. The mixing time for
complex 2b was 1.8 s. The temperature dependent H
NMR spectra were analysed using the SWAN program
Anal. Found: C, 49.15; H, 4.12; N, 2.58. Calc. for
C22H22ClNO4SPd: C, 49.09; H, 4.12; N 2.60%. IR
(KBr, cm−1):wCꢁN 1607, wClO 1087.8, lClO 624.9. 1H
NMR (CDCl3, r.t., ppm): thiomethyl protons lA=
4.63, lB=5.04 (CH2ꢀS, AB system, JAB=16.8 Hz,
2H); pyridine protons l=7.71 (H4, t, J=7.7 Hz, 1H);
allyl protons l=6.35 (Hcentral, br m, 1H), l=4.85
(Hsyn, br s, 1H), l=4.07 (Hanti H, br s, 1H), l=5.37
(Hanti Ph, br s, 1H); C5H3N-6-CH3 l=2.70 (CH3, br s,
3H); pyridine and phenyl protons l=7.14–7.54
(HoꢀHmꢀHpꢀH3ꢀH5, m, 7H).
1
[18].
3.5. Kinetic and equilibrium measurements
The kinetics of allyl amination were studied by the
addition of known aliquots of piperidine solutions to
solutions of the complex under study in CHCl3 ([Pd]0:
10−4mol dm−3
) in the presence of fumaronitrile(
3.3. Preparation of Pd(0) complexes
[fn]0:2–4×10−4 mol dm−3) and pyridine–chalcogen
ether ([RNꢀXPh]0:10−3 mol dm−3) in the ther-
mostated cell compartment of a Lambda 40 Perkin–
3.3.1. [Pd(p2-fn)(HNꢀSePh)] (4a)
To 0.0746 g (0.30 mmol) of HNꢀSePh dissolved in 15
Elmer™
spectrophotometer
at
the
designed
ml of anhydrous acetone 0.0246 g (0.315 mmol) of
temperature. The reactions were followed by recording
spectral changes in the wavelength range of 280–400
nm or at a suitable fixed wavelength.
Mathematical and statistical data analysis was car-
ried out in a personal computer equipped with a locally
adapted version of Marquardt’s algorithm [19] written
in TURBOBASIC™.
fumaronitrile and 0.148
g
(0.143 mmol) of
Pd2DBA3·CHCl3 were added under inert atmosphere
(N2). The solution was stirred for 30 min. Activated
charcoal was added and the mixture was filtered on
celite.
Reduction to small volume by reduced pressure and
addition of diethyl ether yielded 0.102 g (0.236 mmol;
yield 82.4%) of the title compound as off-white
microcrystals.
Acknowledgements
Anal. Found: C, 44.50; H, 3.06; N, 9.78. Calc. for
C16H13N3SePd: C, 44.42; H, 3.03; N, 9.71%. IR (KBr,
cm−1): wCꢂN 2198.7, wCꢁN 1595.1. 1H NMR (CDCl3, r.t.,
ppm): selenomethyl protons l=4.43 (CH2ꢀSe, br s,
2H); olefin protons (fumaronitrile) l=3.24 (Hol, s,
2H); pyridine protons l=7.72 (H4, td, J=7.7, 1.7 Hz,
1H), 8.89 (H6, d, J=5.2 Hz, 1H); pyridine and phenyl
protons l=7.69 (Hm, m, 2H); l=7.26–7.42
(HoꢀHpꢀH3ꢀH5, m, 5H).
We thank Dr. A. Zambon for low temperature
NOESY experiments.
References
[1] (a) P.E. Blo¨chl, A. Togni, Organometallics 15 (1996) 4125;
,
(b) J.D. Oslob, B. Akermark, P. Helquist, P.O. Norrby,
Organometallics 16 (1997) 3015;
(c) A. Togni, U. Burckhardt, V. Gramlich, P.S. Pregosin, R.
Salzmann, J. Am. Chem. Soc. 118 (1996) 1031;
(d) K. Nordstro¨m, E. Macedo, C. Moberg, J. Org. Chem. 62
(1997) 1604;
(e) A. Albinati, R.W. Kunz, C.J. Ammann, P.S. Pregosin,
Organometallics 10 (1991) 1800.
3.3.2. [Pd(p2-fn)(MeNꢀSePh)] (4b)
The title complex was prepared in the same way as
the 4a complex. Yield 75.8% (yellow microcrystals).
Anal. Found: C, 35.71; H, 3.32; N, 9.35. Calc. for
C17H15N3SePd: C, 45.72; H, 3.39; N. 9.41%. IR (KBr,
[2] (a) B.M. Trost, T.R. Verhoeven, in: G. Wilkinson, F.G.A. Stone,
E.W. Abel (Eds.), Comprehensive Organometallic Chemistry,
vol. 8, Pergamon, Oxford, 1982 (chap. 57 and references therein);
1
cm−1): wCꢂN 2198.7, wCꢁN 1600. H NMR (CDCl3, r.t.,
ppm): selenomethyl protons l=4.45 (CH2ꢀSe, s, JH–

L. Cano6ese et al. / Polyhedron 20 (2001) 3171–3181
3181
(b) C.G. Frost, J. Howarth, J.M.J. Williams, Tetrahedron Asym-
metry 3 (1992) 1089 (and references therein);
(c) L. Canovese, F. Visentin, P. Uguagliati, B. Crociani, J.
Chem. Soc., Dalton Trans. (1996) 1921;
(c) J. Tsuji, in: Palladium Reagents and Catalysis, Wiley,
Chichester, 1995, p. 4 (chap. 2);
(d) R. Van Asselt, C.J. Elsevier, W.J.J. Smeets, A.L. Speck,
Inorg. Chem. 33 (1994) 1521.
(d) B.M. Trost, D.L. van Vranken, Chem. Rev. 96 (1996) 395.
[9] (a) R. Grigg, M. Monteith, V. Sridharan, C. Terrier, Tetrahe-
dron 54 (1998) 3885;
(b) J.M. Zenner, R.C. Larock, J. Org. Chem. 64 (1999) 7312
(and references therein).
[10] L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, G. Bandoli,
Organometallics 19 (2000) 1461.
,
[3] (a) J.E. Ba¨ckvall, R.E. Nordberg, K. Zetterberg, B. Akermark,
Organometallics 2 (1983) 1625;
(b) B. Crociani, S. Antonaroli, F. Di Bianca, L. Canovese, F.
Visentin, P. Uguagliati, J. Chem. Soc., Dalton Trans. (1994)
1145.
[4] (a) L. Canovese, F. Visentin, P. Uguagliati, F. Di Bianca, S.
Antonaroli, B. Crociani, J. Chem. Soc. (1994) 3113;
(b) L. Canovese, F. Visentin, P. Uguagliati, B. Crociani, F. Di
Bianca, Inorg. Chim. Acta 235 (1995) 45;
(c) L. Canovese, F. Visentin, P. Uguagliati, F. Di Bianca, A.
Fontana, B. Crociani, J. Organomet. Chem. 508 (1996) 101.
[5] (a) L. Canovese, F. Visentin, P. Uguagliati, G. Chessa, V.
Lucchini, G. Bandoli, Inorg. Chim. Acta 275 (1998) 385;
(b) L. Canovese, F. Visentin, P. Uguagliati, G. Chessa, A. Pesce,
J. Organomet. Chem. 566 (1998) 61.
[6] (a) B. Crociani, S. Antonaroli, G. Bandoli, L. Canovese, F.
Visentin, P. Uguagliati, Organometallics 18 (1999) 1137;
(b) B. Crociani, S. Antonaroli, L. Canovese, F. Visentin, P.
Uguagliati, Inorg. Chim. Acta 315 (2001) 172.
[7] L. Canovese, F. Visentin, G. Chessa, A. Niero, P. Uguagliati,
Inorg. Chim. Acta 293 (1999) 44.
[11] (a) R.J. Cross, T.H. Green, R. Keat, J. Chem. Soc., Dalton
Trans. (1976) 1150;
(b) R.J. Cross, T.H. Green, R. Keat, J.F. Paterson, J. Chem.
Soc., Dalton Trans. (1976) 1486.
[12] L. Canovese, V. Lucchini, unpublished results.
[13] O. Kuhn, H. Mayr, Angew. Chem., Int. Ed. Engl. 38 (1999) 343.
[14] M. Kawatsura, Y. Uozumi, T. Hayashi, Chem. Commun. (1998)
217.
[15] B. Akermark, K. Zetterberg, S. Hansson, B. Krakenberger, A.
Vitagliano, J. Organomet. Chem. 335 (1987) 133.
[16] (a) S.G. Murray, F.R. Hartley, Chem. Rev. 81 (1981) 365;
(b) L. Linford, H.G. Raubenheimer, Adv. Organomet. Chem. 32
(1991) 1.
[17] (a) F.R. Hartley, S.R. Jones, J. Organomet. Chem. 66 (1974)
465;
(b) P.R. Auburn, P.B. Mackenzie, B. Bosnich, J. Am. Chem.
Soc. 107 (1985) 2033.
[8] (a) L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, A.
Dolmella, J. Organomet. Chem. 601 (2000) 1;
[18] G. Balacco, J. Chem. Inf. Comput. Sci. 34 (1994) 1235.
[19] D.W. Marquardt, SIAM J. Appl. Math. 11 (1963) 431.
(b) L. Canovese, F. Visentin, G. Chessa, G. Gardenal, P.
Uguagliati, J. Organomet. Chem. 622 (2001) 155;