Transmetalation reactions. The role of the stabilizing olefin in determining the overall reaction rate

Article abstract of DOI:10.1016/j.jorganchem.2008.07.028

A systematic study concerning the transmetalation reaction between the palladium butadienyl complexes [PdCl((ZC{double bond, long}CZ)₂Me)(L-L′)] (Z = COOMe; L-L′ = MeN-SPh (1A), N-SPh (1B), DPPQ-Me (1C), BiPy (1D), DPPE (1E)) and tributyl-phenylethynyl-stannane in the presence of some stabilizing olefins (ma, fn, nq, dmfu, and tmetc) was undertaken. The dependence of the reaction rate on the nature of the ancillary ligand was discussed in terms of the donor capability and steric characteristics of the ligand. It has been noticed that, other things being equal, the joined distorted MeN-SPh ligand imparts the highest reactivity to its derivative (complex 1A). The most surprising issue was however represented by the olefin which seems to affect heavily the reactivity of the starting substrate thereby increasing the overall reaction rate. The most active olefins were ma and fn. In the case of the reaction between the complex 1A and tributyl-phenylethynyl-stannane in the presence of fn an exhaustive kinetic study was carried out and a mechanistic hypothesis was advanced.

Full text of DOI:10.1016/j.jorganchem.2008.07.028

Journal of Organometallic Chemistry 693 (2008) 3324–3330
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Transmetalation reactions. The role of the stabilizing olefin
in determining the overall reaction rate
*
Luciano Canovese , Fabiano Visentin, Carlo Levi, Claudio Santo
Dipartimento di Chimica, Università Ca’ Foscari, Calle Larga S. Marta 2137, 30123 Venezia, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 June 2008
Received in revised form 10 July 2008
Accepted 11 July 2008
Available online 29 July 2008
A systematic study concerning the transmetalation reaction between the palladium butadienyl com-
plexes [PdCl((ZC@CZ)2Me)(L-L0)] (Z = COOMe; L-L0 = MeN-SPh (1A), N-SPh (1B), DPPQ-Me (1C), BiPy
(1D), DPPE (1E)) and tributyl-phenylethynyl-stannane in the presence of some stabilizing olefins (ma,
fn, nq, dmfu, and tmetc) was undertaken. The dependence of the reaction rate on the nature of the ancil-
lary ligand was discussed in terms of the donor capability and steric characteristics of the ligand. It has
been noticed that, other things being equal, the joined distorted MeN-SPh ligand imparts the highest
reactivity to its derivative (complex 1A). The most surprising issue was however represented by the olefin
which seems to affect heavily the reactivity of the starting substrate thereby increasing the overall reac-
tion rate. The most active olefins were ma and fn. In the case of the reaction between the complex 1A and
tributyl-phenylethynyl-stannane in the presence of fn an exhaustive kinetic study was carried out and a
mechanistic hypothesis was advanced.
Keywords:
Transmetalation reaction
Stille coupling
Palladium(II) butadyenyl complexes
Kinetic study
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
constant and strongly coordinating ligands favour the SE2 cyclic
step whereas the SE2 open path is preferred when the solvents dis-
The Stille reaction consisting in the palladium catalyzed cross
coupling between carbon electrophiles and organo-stannanes is
an important and attractive method in modern synthetic organic
chemistry [1]. It is usually represented by a catalytic cycle in which
the Pd(0) catalyst is firstly oxidized by the organic electrophile to
the corresponding Pd(II) derivative which undergoes the trans-
metalation reaction followed by the reductive elimination of the
coupled organic derivative and the subsequent restoration of the
Pd(0) catalyst [1f,2]. The complexity of the entire mechanism is
testified by the number of papers dealing with the different steps
of the cycle and by the fact that the nature of the solvent, the elec-
tronic and steric properties of the ancillary ligand, the stannane
and the organic electrophile heavily affect the reactivity of every
single step [3a]. The rate-determining step of the whole process
can be therefore represented by the oxidative addition, by the
transmetalation and even by the reductive elimination [1a,1i,2,4].
However, the transmetalation reaction seems to be the most
complex and therefore the less granted process even though its
associative character (apart from few exceptions [4g]) is recog-
nized on the basis of the work of Espinet [3a–c and refs. therein].
In particular, two different associative pathways which are
strongly dependent on the nature of the solvent and the reactant
are possible. Thus, poorly coordinating solvents with low dielectric
play remarkable polarity and coordinating capability and the li-
gands are weak as coordinating and bridging species [5].
Consequently, the general catalytic cycle for the Stille reaction
can be represented by Scheme 1.
In order to optimize the efficiency of the transmetalation step
two different approaches are available i.e. the enhancement of
the nucleophilic character of the organo-stannanes and the
enhancement of the electrophilic character of the palladium com-
plex. The former can be achieved by the use of suitable additives as
fluoride [6] and hydroxide ions [7] whereas the electrophilicity of
the palladium complex can be generally obtained by decreasing
the basicity of the ancillary ligands (i.e. arsine complexes are more
reactive than their phosphine analogues [1e,4e,4f] and the reactiv-
ity order induced by coordinated halide is I < Br < Cl [3a, p. 4720]).
In this respect, it is well known that coordinated electron-poor ole-
fins are effective in removing electron density from the metal cen-
tre. Such an effect was widely utilized to facilitate reductive
elimination in palladium(II) substrates [8], and for that reason
when the reductive elimination step becomes the rate determining
step in a palladium catalyzed C–C coupling the addition of an exog-
enous olefin was particularly advantageous. Thus, Schwartz and
co-workers have shown that the coupling of allyl halides with allyl
tin [9a] reagents (and with other allyl organometallic substrates
[9b,9c]) does not proceed unless an electron-withdrawing olefin
such as maleic anhydride was added. This is confirmed by the de-
tailed kinetics and theoretical studies of Kurosawa et al. on allyl
* Corresponding author. Tel.: +39 041 2348655; fax: +39 041 2348517.
E-mail address: cano@unive.it (L. Canovese).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.07.028

L. Canovese et al. / Journal of Organometallic Chemistry 693 (2008) 3324–3330
3325
2. Results and discussion
2.1. Synthesis of palladium butadienyl and palladium(0) olefin
derivatives
The complex [PdCl((MeOOC–C@C–COOMe)2Me)(MeN-SPh)]
(1A) was obtained by reacting an excess of dmbd (dimethyl-2-
butynedioate) with the complex [PdCl(Me)(MeN-SPh)] (dmbd:
complex = 3:1) for 22 h in CH2Cl2 at RT [14a]. The palladiumbutadie-
nyl derivatives [PdCl((ZC@CZ)2Me)(L-L0)] (Z = COOMe; L-L0 = N-SPh
(1B), DPPQ-Me (1C), BiPy (1D), DPPE (1E)) were obtained according
to published methods [14] by adding an equimolar amount of the
appropriate ligand (B, C, D, E) to a solution of the complex (1A) in
freshly distilled anhydrous CH2Cl2. All the complexes bearing mixed
chelating ligands (N–S or N–P) display the butadienyl group in trans
position to the pyridine nitrogen atom [14a].
Scheme 1.
The organic poly-unsaturated products 3 were easily separated
from the dried mixture of the transmetalation reaction (1) by
extraction with diethyl ether. The solid residue yields the com-
plexes [Pd(g2-ol)(L-L0)] (L-L0 = A, B, C, D, E; ol = a, b, c, d, e). As a
check of consistency we also prepared the complexes indepen-
dently by reacting Pd2DBA3 ꢀ CHCl3 with the corresponding ligand
L-L0 and olefin ol in anhydrous acetone under inert atmosphere
(N2) according to published procedures [15,16]. The complex 2Cb
was obtained through direct olefin exchange by reacting the sub-
strate 2Cd with fumaronitrile.
aryl palladium complex which showed that the reductive elimina-
tion occurs from an
nated olefin [10].
g
3-allyl palladium complexes with a coordi-
In a preliminary study concerning the synthesis of some poly-
unsaturated compounds by transmetalation we noticed that the
nature and the concentration of the olefin employed heavily
interferes with the overall rate of the stoichiometric reaction,
thereby showing that its role was not simply confined to the sta-
bilisation of the palladium(0) reaction product [11]. Moreover, in
this case the rate determining step was better represented by
the transmetalation step than by of the reductive elimination
which was proved to be fast [12]. Since the mechanism govern-
ing the palladium catalyzed synthesis of poly-unsaturated com-
pounds is a widely investigated topics [13] and therefore its
2.2. Kinetic and mechanistic study
The reactions between the type 1 complexes and tributyl-phen-
ylethynyl-stannane yielding (2Z,4Z)-tetramethyl-7-phenylhepta-
2,4-dien-6-yne-2,3,4,5-tetracarboxylate (3a) and the palladium(0)
olefin derivatives 2 went smoothly to completion and were fol-
lowed by 1H NMR technique in CDCl3 at RT and studied in detail
by UV–Vis spectrophotometric technique in CHCl3 at RT.
comprehension would represent
a very important task, we
decided to undertake an exhaustive study of the kinetics of the
reactions between some butadienyl palladium(II) complexes
bearing differently designed bidentate ancillary ligands (prepared
according to published methods [14]) and tributyl-phenyleth-
ynyl-stannane.
2.3. The role of the olefin
The reaction and the compounds involved in the present paper
are reported in Scheme 2.
The most surprising result arising from this study is represented
by the role of the olefin in determining the rate of reaction (1). As a
Scheme 2.

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L. Canovese et al. / Journal of Organometallic Chemistry 693 (2008) 3324–3330
matter of fact, addition of maleic anhydride to the slowly reacting
equimolar solution of complex 1A and tributyl-phenylethynyl-
stannane drives the reaction to completion in few minutes. Thus,
we decided to study the dependence on the olefin in the case of
complex 1A (which displays the highest reactivity among all the
other complexes synthesized) and 1C. We therefore determined a
qualitative order of reactivity when reaction (1) was carried out
using different olefins but maintaining constant the temperature
(298 K), the solvent (CDCl3), the concentration of the complex,
stannane and the concentration of the olefin under study by means
of 1H NMR technique.
ciency of the stannane attack on intermediate I (k2[R0Sn(n-Bu3)]).
[21] As can be deduced from Table 1, it is apparent that ma is
the most effective promoter, probably because it combines a high
electron-withdrawing character with a modest Z-symmetry modu-
lated steric demand which would drive the attack through the
unsubstituted side of the olefin [15].
Path 2 represents the process occurring without added olefin
and takes place by
p pre-coordination of the alkynyl stannane [22].
The observed rate constant for the reaction in Scheme 3 is de-
scribed by the following expression (5) when the steady state
approximation is applied to the monodentate intermediate species
*
The efficiency of the olefin in promoting the reaction (1) is sum-
marized in the following reactivity order and in Table 1 [17]:
I and I in path 1 and 2, respectively:
ma > fn ꢁ nq > dmfu > tmetc
In order to shed light on the overall mechanism we undertook
an exhaustive investigation on the reactivity of complex 1A as a
function of the concentration of stannane and fumaronitrile [18]
in CHCl3 at 298 K using the UV–Vis spectrophotometric technique
which allows higher and therefore favourable concentration ratios
among reactants and the complex under study.
Each kinetic run, carried out in the presence of an excess of
stannane and fumaronitrile (i.e. pseudo-first order conditions with
respect to the complex concentration, [Stannane]0 P 10 ꢀ [1A]0;
[fn]0 P 10 ꢀ [1A]0), went smoothly to completion according to the
mono-exponential rate law
obsꢃt
Dt ¼ D1 þ ðD0 ꢂ D Þeꢂk
ð2Þ
1
where D0, D and kobs (parameters to be optimized) represent the
1
initial, the final absorbance and the observed rate constant. Each
set of rate constants obtained at various stannane concentrations
and at fixed fn concentration fits the expression:
Fig. 1. Plot of kobs vs. [Stannane] with the corresponding best-fits for the reaction of
complex 1A with tributyl-phenylethynyl-stannane in CHCl3 at 298 K. For the sake of
clarity kobs values are reported for only three different concentrations of fn.
½R0Snðn-Bu3Þꢄ
kobs ¼ d
ð3Þ
ð1 þ
c
½R0Snðn-Bu3ÞꢄÞ
From the analysis of the whole set of kinetic data it appears that the
concentration of fn determines the asymptotic value of each curve
(see Fig. 1).
Therefore, the following expression will appropriately describe
the family of curves:
Table 2
Kinetic parameters d and
out at each fumaronitrile concentration
c determined from non linear regression of Eq. (3) carried
[fn] (mol dmꢂ3
)
d (molꢂ1 dm3 sꢂ1
)
c
(molꢂ1 dm3)
0.97 ꢅ 10ꢂ3
1.29 ꢅ 10ꢂ3
1.58 ꢅ 10ꢂ3
2.03 ꢅ 10ꢂ3
2.51 ꢅ 10ꢂ3
0.171 0.009
0.174 0.010
0.189 0.002
0.220 0.020
0.232 0.003
248 18
249 20
ð
a
ð1 þ
þ b½fnꢄÞ½R0Snðn-Bu3Þꢄ
kobs
¼
ð4Þ
c
½R0Snðn-Bu3ÞꢄÞ
247
8
246 31
247 11
The values for d and
are listed in Table 2.
From the linear regression of d vs. [fn] reported in Fig. 2 we ob-
tained the following values:
= 0.12 0.01 molꢂ1 dm3 sꢂ1
b = 44 5 molꢂ2 dm6 sꢂ1
c
for each kobs set at different fn concentrations
a
;
.
In analogy with the observations of other authors, we also no-
ticed that addition of free bidentate ligand L-L0 to the reaction mix-
ture markedly slowed down the reaction rate. Therefore a plausible
reaction scheme which takes into account the kinetic evidence
might be the following Scheme 3 [19]:
Path 1 represents the preferred process since the electrophilic
character of the metal centre is significantly enhanced by coordina-
tion of the electron-withdrawing olefin which favours the effi-
Table 1
Reaction time (95% conversion) in minutes for complexes 1A and 1C reacting with
tributyl-phenylethynyl-stannane in the presence of different olefins
Complex
ma
fn
nq
dmfu
No olefin
1A
1C
<7a
<7a
15
60
40
60
90
240
150
Daysb
a
Time required for recording the NMR spectrum.
With decomposition.
b
Fig. 2. Linear fit of d vs. [fn].

L. Canovese et al. / Journal of Organometallic Chemistry 693 (2008) 3324–3330
3327
ꢃ
ꢃ
ꢃ
ꢃ ꢃ
k2k1ðkꢃ þ k Þ½fnꢄ½R0Snðn-Bu3Þꢄ þ kꢂ1k k ½R0Snðn-Bu3Þꢄ þ k2k k ½R0Snðn-Bu3Þꢄ
2
ꢂ1
2
1
2
1 2
kobs
¼
ð5Þ
ðkꢃꢂ1 þ kꢃ Þkꢂ1 þ ðkꢃ þ kꢃ Þk2½R0Snðn-Bu3Þꢄ
2
ꢂ1
2
Eq. (5) reduces to Eq. (6) uponꢃsome rearrangement and under the
hypothesis that the term k2k1ꢃ k2[R0Sn(n-Bu3)]2 is negligible with re-
spect to the other addends.
Lewis basicity of the chelating atom (from N, S to P) and in the
rigidity of the ancillary ligand itself disfavours the reactivity of
the related complexes owing to the enhanced electronic density
of the palladium and to the lack of necessary flexibility of the ancil-
lary ligand in forming the substrate with an uncoordinated wing.
The difference in reactivity between the distorted complex 1C
and the complex 1D again emphasizes that the most important
role in this sort of reactions is played by the distortion and the con-
sequent ligand emilability. As a matter of fact, substrate 1C is more
reactive than 1D despite the fact that the better donor ability of the
phosphorus atom in 1C would decrease its nucleophilicity. Eventu-
ally, the low reactivity of complex 1E can directly be traced back to
the coordinating capability of the phosphine which probably ren-
ders the ring opening pathway negligible.
ꢀ
ꢁ
kꢃ1kꢃ2
½R0Snðn-Bu3Þ ꢄ
k1k2
½fnꢄ þ k
ꢃ
3
k
þkꢃ2
ꢂ1
ꢂ1
kobs
¼
ð6Þ
1 þ k ½R0Snðn-Bu3Þꢄ
k2
ꢂ1
Eq. (4) and Eq. (6) are coincident with
k1k2=k and
¼ k2=k
a
¼ k1ꢃ k2ꢃ =ðkꢃꢂ1 þ k2ꢃ Þ; b ¼
c
.
ꢂ1
ꢂ1
Owing to the complexity of Eq. (6), only some qualitative
considerations can be made. As matter of fact the ratio
a
k2/kꢂ1 = 247 30 suggests that the attack of the stannane to the
monodentate species I is very efficient even when compared with
the entropically favoured ring closure since the coordinated olefin
would enhance the electrophilicity of the metal centre. The k1 va-
lue is given by the ratio b/c = 0.18 0.03 and can presumably be
2.5. Activation of a less reactive stannane
traced back to the entering of the olefin into a complex which dis-
plays a high tendency to ring opening; according to the steady
state approximation, it is remarkably smaller than the rate con-
The most obvious extension of the enhanced overall reactivity of
the coupling processes promoted by the presence of the olefin in ex-
cess is the transmetalation reaction with poorly reactive stannanes.
We therefore tested the reaction between the complex 1A and trib-
utyl-vinyl-stannane (CH2@CH–Sn(n-Bu)3) which is less prone to
electrophilic attack than tributyl-phenylethynyl-stannane. As a
matter of fact, the presence of a slight excess of maleic anhydride
in the reaction between the complex 1A and the vinyl stannane
stants consuming the intermediate I. The value of
a = 0.12 0.01
which is related to Path 2 is not easily interpreted.ꢃIt probably re-
flects the high value of the entropically favoured kꢂ1 with respect
to the other rate constants when Path 2 is taken into account.
2.4. The role of the ancillary ligand
([1A]:[vinyl stannane]:[ma] = 1:1.1:1.2; [1A] ꢁ 3 ꢅ 10ꢂ2 mol dmꢂ3
)
in CDCl3 at 298 K drives the reaction to completion in ꢆ1200 with the
formation of the (2Z,4Z)-tetramethylhepta-2,4,6-triene-2,3,4,5-tet-
racarboxylate derivative (CH2@CH(MeOOCC@CCOOMe)2Me) (3b).
The same reaction carried out in the absence of maleic anhydride
takes more than several days.
The soundness of Scheme 3 strongly relies on the lability of the
pyridine nitrogen of the chelating MeN-SPh ligand (A) which is
well documented in several papers [15]. As a matter of fact, the dis-
tortion of the MeN-SPh ligand coupled with the marked trans influ-
ence of the butadienyl group in complex 1A induces a remarkable
emilability of the pyridine nitrogen and therefore a marked fluxio-
nality of the ligand, thereby favouring the attack of even adventi-
tious nucleophiles at the metal centre. Thus, the overall reaction
rate would slow down when a complex bearing ligands with lower
lability is employed. Such hypothesis was clearly confirmed by
comparison of the reactivity data of all the complexes reported
in Scheme 2. The ensuing reactivity order for the complexes, deter-
mined in CDCl3 at RT using fumaronitrile (or maleic anhydride) as
stabilizing olefin, is the following [23]:
3. Conclusions
From the experimental results of the present work it is possible
to conclude that:
(a) The olefin heavily interferes in the mechanism of transmeta-
lation step in the C–C coupling between the palladium-buta-
dienyl complexes and alkynyl-stannane and its nature is of
primary importance in determining the overall reaction rate.
(b) The most efficient olefin is maleic anhydride, probably
thanks to its high electron-withdrawing character and
reduced steric requirements which favour its pre-
coordination.
1A > 1B >> 1C >> 1D >> 1E
This order is governed by the electrophilicity of the palla-
dium(II) centre which in turn is modulated by the donor capability
and by the steric characteristics of the ligands. An increase in the
Scheme 3.

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L. Canovese et al. / Journal of Organometallic Chemistry 693 (2008) 3324–3330
(c) In the reaction between the complex 1A and tributyl-phen-
tributyl-phenylethynyl-stannane and fumaronitrile at adequate
concentrations were added and the absorbance changes were
monitored in the 250–400 nm wavelength interval or at fixed
wavelength (320 nm).
ylethynyl-stannane in the presence of fumaronitrile, the
kinetics indicate a mechanism involving an associative
attack of both stannane and olefin on the starting complex.
(d) The reaction rate of the transmetalation reactions of buta-
dienyl chloro palladium complexes bearing bidentate
ligands is influenced by the ligand emilability which
depends on the ground state distortion of the complex itself
and on the mutual trans labilization of the butadienyl frag-
ment and the opposite atom.
(e) Maleic anhydride displays its efficiency in promoting the
transmetalation reaction also when the less activated
vinyl-stannanes are used.
(f) In the possible application of the results described in the
present paper to a catalytic approach to the Stille reaction,
it might be anticipated that the use of dmfu as olefin could
be useful since it could display its accelerating effect on
the transmetalation reaction while allowing a sufficient
reactivity to the ensuing palladium(0) dmfu derivative
which can be quite easily oxidized by the organic halide [4k].
4.6. Synthesis of the butadienyl complexes
[PdCl((MeOOCC@CCOOMe)2Me)(HN-SPh)] (1B)
To a suspension of 0.64 g (0.0975 mmol) of 1A in 6 ml of freshly
distilled anhydrous CH2Cl2 0.0604 g (0.3 mmol) of the ligand HN-
SPh (B) was added and the reaction mixture was stirred for
60 min. The solution was concentrated under reduced pressure
and the complex was precipitated as pale creamy solid by addition
of diethyl ether. The product was filtered off, washed with small
aliquots of diethyl ether and dried under vacuum (0.576 g, yield
92%).
1H NMR (300 MHz, CDCl3, T = 298 K, ppm) d: 9.21 (d, 1H, H6,
J = 5.3 Hz), 7.65 (t, 1H, H4, J = 7.7 Hz), 7.62–7.69 (m, 2H, phenyl
Hortho), 7.39–7.28 (m, 5H, H3, H5, phenyl Hmeta, Hpara), 5.11 (d, 2H,
J = 16.5 Hz Pyr–CH2–S), 4.19 (d, 2H, J = 16.5 Hz Pyr–CH2–S), 3.81,
(s, 3H, COOCH3), 3.77, (bs, 3H, COOCH3), 3.67, (s, 3H, COOCH3),
3.64 (bs, 3H, COOCH3), 2.19 (s, 3H, @CCH3).
4. Experimental
13C{1H} NMR (CDCl3, T = 298 K, ppm), d: 171.3 (CO, COOCH3),
170.3 (CO, COOCH3), 168.1 (broad CO, COOCH3), 161.0 (CO,
COOCH3), 157.2 (C, C2), 150.7 (CH, C6), 139.0 (CH, C4), 132.0 (CH,
phenyl Cmeta), 130.4 (CH, phenyl Cpara), 129.7 (C, phenyl Cipso),
129.6 (CH, phenyl Cortho), 123.9 (CH, C5), 122.8 (CH, C3), 52.4,
52.2, 52.0, 51.6 (CH3, COOCH3), 49.1 (broad CH2, CH2–S), 26.4
(CH3, Pyr–CH3), 19.0 (CH3, @CCH3).
4.1. Solvents and reagents
Acetone and CH2Cl2 were distilled over 4 Å molecular sieves and
CaH2, respectively. CHCl3 was distilled over silver foil under inert
atmosphere. All the other chemicals were commercially available
grade products and were used as purchased.
IR (KBr pellet):
m
= 1711 cmꢂl (C@0), 1602.6 cmꢂl (C@N).
Anal. Calc. for C25H26ClNO8PPdS: C, 46.74; H, 4.08; N, 2.18.
4.2. Data analysis
Found: C, 46.82; H, 4.12; N, 2.27%.
The complexes 1A, 1C, 1D, 1E were prepared according to pub-
lished procedures [14a].
Mathematical and statistical analysis of data was carried out by
locally adapted non linear regression algorithms written under
SCIENTISTTM environment.
4.7. [Pd(g
2-dmfu)(MeN-SPh)] (2Ad)
4.3. IR, NMR, and UV–Vis measurements
Owing to solubility reasons and to its intrinsic instability the ti-
tle complex is hardly separable in pure form from Pd2DBA3 ꢀ CHCl3
which represents the most useful starting substrate for obtaining
[Pd(g2-ol)(L-L0)] derivatives. Therefore, we have identified it di-
rectly from the NMR tube as the product of the reaction of complex
1B with stannane in the presence of dmfu by comparison with the
spectra of analogous species. No further purification was carried
out.
The IR and the 1H and 13C NMR spectra were recorded on a Per-
kin–Elmer Spectrum One spectrophotometer and on a Bruker 300
Avance spectrometer, respectively. UV–Vis spectra were taken on
a Perkin–Elmer Lambda 40 spectrophotometer equipped with a
Perkin–Elmer PTP6 (Peltier temperature programmer) apparatus.
4.4. GC-MS spectrometry measurements
1H NMR (300 MHz, CDCl3, T = 298 K, ppm) d: 7.56 (t, 1H, H4,
J = 7.7 Hz), 7.47–7.44 (m, 2H, phenyl Hortho), 7.29–7.25 (m, 4H,
H3, phenyl Hmeta, Hpara), 7.13 (d, 1H, H5, J = 7.7 Hz); 4.38 (bs, 2H,
Pyr–CH2–S), 3.08 (bs, 2H, CH@CH); 2.84 (bs, 3H, Pyr–CH3).
The GC–MS spectra were recorded on a Thermo Quest Finnigan
Trace 2000 Series gas chromatograph-mass spectrometer using a
Mega Fused Silica capillary column (stationary phase: SE52,
30 m ꢅ 0.25 mm i.d.).
4.8. Synthesis of the Pd(0) olefin complexes [Pd(g
2-nq)(DPPQ-Me)]
(2Cc)
4.5. Preliminary studies and kinetic measurements
To a solution of 0.1035 g (0.1 mmol) of Pd2DBA3 ꢀ CHCl3 in 10 ml
of freshly distilled anhydrous acetone, 0.072 g (0.22 mmol) of
DPPQ-Me (C) and 0.791 g (0.5 mmol) of naphthoquinone (nq) were
added. The solution was stirred under inert atmosphere (Ar) for 3 h
at RT. The solvent was removed under reduced pressure and the
dry residue was dissolved in CH2Cl2. The resulting solution was fil-
tered on a celite filter, concentrated and the complex was precipi-
tated as an orange solid by addition of diethyl ether. The complex
was filtered off, washed with small aliquots of diethyl ether and
dried under vacuum (0.077 g, yield 65%).
All the transmetalation reactions were preliminarily studied by
1H NMR technique by dissolving the complex under study in 0.6 ml
of CDCl3 ([Complex]0 1–3 ꢅ 10ꢂ2 mol dmꢂ3) and adding microa-
liquots of a concentrated CDCl3 solution of tributyl-phenyleth-
ynyl-stannane (or tributyl-vinyl-stannane) and olefin. The
reaction progress was followed by monitoring the signal for the
disappearance of the starting complex and the contemporary
appearance of the final products 2 and 3.
The UV–Vis preliminary study was carried out by placing 3 ml
of freshly prepared solution of the complex 1A ([1A]0 = 1 ꢅ 10ꢂ4
mol dmꢂ3) in a thermostatted (298 K) cell compartment of the
UV–Vis spectrophotometer. Microaliquots of solution containing
1H NMR (300 MHz, CDCl3, T = 298 K, ppm) d: 8.19 (d; 1H,
J = 8.4 Hz; H4); 8.04 (d; 1H, J = 7.7 Hz; Ha); 7.90 (d; H, J = 7.9 Hz;
H5); 7.79 (t; 1H, JHP = JHH 7.7 Hz; H7); 7.69 (d; 1H, J = 7.7 Hz;

L. Canovese et al. / Journal of Organometallic Chemistry 693 (2008) 3324–3330
3329
Ha); 7.58–7.62 (m, 2H, PPh2); 7.51–7.56 (m; 2H; H6, H3); 7.38–
7.47 (m; 6H; Hb, PPh2); 7.29–7.35 (m; 2H; PPh2); 7.06–7.13 (m,
2H, PPh2); 5.01 (m, 2H, CH@CH); 3.14 (s, 3H, quinoline-CH3);
13C{1H} NMR (CDCl3, T = 298 K, ppm) d: 185.1 (CO, CO trans-P);
184.0 (d, CO, JCP = 6.2 Hz CO trans-N); 165.6 (C, C2); 151.5 (C,
C10); 151.2 (C, C9); 138.3 (CH, C4); 137.8 (CH, C7); 134.3 (d, C,
JCP = 35.1 Hz, C8); 131.2 (CH, Cb); 131.0 (CH, C5); 130.5 (CH, Cb);
126.3 (d, CH, JCP = 4.8 Hz, C6); 125.4 (CH, Ca); 125.0 (CH, Ca);
123.8 (CH, C3); 66.2 (d, CH, JCP = 21.0 Hz CH@CH trans-P); 62.6
(CH, CH@CH trans-N); 30.2 (CH3, quinoline-CH3). 31P{1H} NMR
52.8 (CH3, COOCH3); 52.6 (CH3, COOCH3); 52.5 (CH3, COOCH3);
18.7 (CH3, @CCH3);
MS (m/z, %): 400 (29) [M+], 368 (39), 341 (100), 336 (43), 309
(28), 165 (28), 152 (29), 105 (64), 77 (39), 59 (42).
4.12. (2Z,4Z)-Tetramethyl hepta-2,4,6-triene-2,3,4,5-tetracarboxylate
(3b)
1H NMR (300 MHz, CDCl3, T = 298 K, ppm) d: 6.42 (dd, 1H, J =
17.6, 11.7 Hz, Hc); 5.66 (d, 1H, J = 11.7, Ha); 5.61 (d, 1H, J = 17.6,
Hb); 3.93 (s, 3H, COOCH3); 3.87 (s, 3H, COOCH3); 3.76 (s, 3H,
COOCH3); 3.73 (s, 3H, COOCH3); 1.93 (s, 3H, CH3).
(CDCl3, T = 298 K, ppm) d: 25.3. IR(KBr pellet)
1622 cmꢂ1 (C@O); 1588 cmꢂ1 (C@N). Anal. Calc. for
32H24NO2PPd: C, 64.93; H, 4.09; N, 2.37. Found: C, 64.64; H,
m = 1636,
C
13C{1H} NMR (CDCl3, T = 298 K, ppm) d: 169.5 (CO); 167.4 (CO);
164.9 (CO); 164.8 (CO); 145.3 (C, C@C); 144.7 (C, C@C); 130.0 (CH2;
CH2@CH); 125.9 (C, C@C); 125.8 (CH; CH2@CH); 124.2 (C, C@C);
52.7 (CH3, COOCH3); 52.6 (2CH3, COOCH3); 52.5 (CH3, COOCH3);
18.1 (CH3, @CCH3).
4.27; N, 2.39%.
The complexes 2Aa, 2Ab, 2Ac, 2Ae, 2Bb [16a], 2Ca [16b], 2Cd
[24], 2Db, 2Eb [25], 2Ea [26] were prepared according to published
procedures.
MS (m/z, %): 326 (11) [M+], 267 (37), 235 (91), 336 (43), 309
(28), 165 (28), 152 (29), 105 (64), 77 (39), 59 (42).
4.9. [Pd(
g
2-fn)(DPPQ-Me)] (2Cb)
To a solution of 0.10 g (0.17 mmol) of [Pd(
g
2-dmfu)(DPPQ-Me)]
Appendix A. Supplementary material
(2Cd) in 20 ml of freshly distilled CH2Cl2, 0.0162 g (0.21 mmol) of
fumaronitrile was added. The reaction mixture was stirred under
inert atmosphere for 30 min. The solvent was removed under re-
duced pressure and the creamy residue was washed several times
with diethyl ether. The suspension was eventually filtered off and
dried under vacuum (0.0829 g, yield 93.6%).
Summary of the observed rate constants at different concentra-
tions of fumaronitrile and stannane. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.07.028.
1H NMR (300 MHz, CDCl3, T = 298 K, ppm) d: 8.30 (d; 1H,
J = 8.4 Hz; H4); 8.00 (d; H, J = 7.8 Hz; H5); 7.84 (t; 1H, JHP = JHH
7.4 Hz; H7); 7.64 (t; 1H, J = 7.4 Hz; H6); 7.63 (d; 1H; J = 8.4 Hz;
H3); 7.58–7.43 (m; 10H; PPh2); 3.45 (dd, 1H, JHH = 9.5 Hz,
JPH = 3.2 Hz, CH@CH trans-N); 3.24 (s, 3H, quinoline-CH3); 2.96 (t,
1H, JHH = JPH = 9.5 Hz, CH@CH trans-P).
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m
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steady state were consistent with the shape of Eq. (4). However, in the pre-
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not consistent with the fact that no monosubstituted monodentate species
were ever detected by 1H NMR technique under our experimental conditions.
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free ligand strongly competes with the stannane and the olefin in solution
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SE2 open mechanism could be operative on the basis of the olefin nature which
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[17] The reactions of complexes 1A and 1C with tributyl-phenylethynyl-stannane
[23] Reactions (1) carried out under equal experimental conditions
([Complex]0:[Stannane]0:[ol]0 = 1:1.1:1.2; [Complex]0 ꢁ 3 ꢅ 10ꢂ2 mol dmꢂ3
)
in CDCl3 at 298 K were over in: (fn) 1A: <7 min; 1B: 60 min; 1C: 105 min;
1D: 480 min; 1E: 5 days (82%); (ma) 1A: <7 min; 1C: 10 min; 1E: <1 day.
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were
carried
out
under
equal
experimental
conditions
([Complex]0:[Stannane]0:[ol]0 = 1:1.1:1.2; [Complex]0 ꢁ 3 ꢅ 10ꢂ2 mol dmꢂ3
)
in CDCl3 at 298 K. In the case of complex 1A we have also studied the
reaction in the presence of but-2-ynedioic acid dimethyl ester (dma) yielding
the palladacyclopentadiene derivative. The reactivity induced by dma lies
between those of nq and dmfu.
[26] R.J. Cross, D.M.P. Mingos, in: Organometallic Compounds of Nickel, Palladium
and Platinum, Chapman & Hall, London–New York, 1985, p. 144.