Palladium(II) and palladium(0) complexes of pyridylthioether-based metallodendrimers. Synthesis, characterization, and mechanistic study of the influence of wedge size on allyl amination

Article abstract of DOI:10.1021/om020391l

Pd(II) allyl and Pd(0) fumaronitrile complexes bearing pyridyl-dithioether-based dendrimers as ancillary ligands have been synthesized and fully characterized by means of NMR spectrometry, elemental analysis, and MALDI-TOF technique. The fluxional behavior of the species was investigated by studying the ¹H NMR spectra recorded in CD₂Cl₂ at variable temperature and interpreted on the basis of a windshield-wiper motion of the dendritic wings which alternatively coordinate at the metal core. The reactivity of piperidine on the Pd(II) allyl substrates to give the allylamine derivative and the corresponding Pd(0) fumaronitrile species was also studied. The second-order rate constants k₂ and the equilibrium constants K_E relating to piperidine attack on the allyl fragment and to the concomitant displacement of the dendrimer ligand by piperidine, respectively, were determined and discussed taking into account the increasing dendritic size. Surprisingly, no macroscopic effects are observed on going from the model molecule to the second-generation dendritic substrates, and only with the third generation dendritic wedge complex are remarkable variations in the rate and equilibrium constants observed. We therefore advance the hypothesis that a sudden rearrangement at this stage occurs in solution. Such a rearrangement would induce an increase of steric hindrance at the allyl fragment and a concomitant distortion of the ligand in the environment of the metal core, thereby justifying the decrease of k₂ and the increase of K_E values.

Full text of DOI:10.1021/om020391l

4342
Organometallics 2002, 21, 4342-4349
P a lla d iu m (II) a n d P a lla d iu m (0) Com p lexes of
P yr id ylth ioeth er -Ba sed Meta llod en d r im er s. Syn th esis,
Ch a r a cter iza tion , a n d Mech a n istic Stu d y of th e
In flu en ce of Wed ge Size on Allyl Am in a tion
Luciano Canovese,* Gavino Chessa,* Claudio Santo, Fabiano Visentin, and
Paolo Uguagliati
Dipartimento di Chimica, Universita` Ca’ Foscari di Venezia, Dorsoduro 2137,
I-30123, Venezia, Italy
Received May 14, 2002
Pd(II) allyl and Pd(0) fumaronitrile complexes bearing pyridyl-dithioether-based dendrim-
ers as ancillary ligands have been synthesized and fully characterized by means of NMR
spectrometry, elemental analysis, and MALDI-TOF technique. The fluxional behavior of the
1
species was investigated by studying the H NMR spectra recorded in CD2Cl2 at variable
temperature and interpreted on the basis of a windshield-wiper motion of the dendritic wings
which alternatively coordinate at the metal core. The reactivity of piperidine on the Pd(II)
allyl substrates to give the allylamine derivative and the corresponding Pd(0) fumaronitrile
species was also studied. The second-order rate constants k2 and the equilibrium constants
KE relating to piperidine attack on the allyl fragment and to the concomitant displacement
of the dendrimer ligand by piperidine, respectively, were determined and discussed taking
into account the increasing dendritic size. Surprisingly, no macroscopic effects are observed
on going from the model molecule to the second-generation dendritic substrates, and only
with the third generation dendritic wedge complex are remarkable variations in the rate
and equilibrium constants observed. We therefore advance the hypothesis that a sudden
rearrangement at this stage occurs in solution. Such a rearrangement would induce an
increase of steric hindrance at the allyl fragment and a concomitant distortion of the ligand
in the environment of the metal core, thereby justifying the decrease of k2 and the increase
of KE values.
In tr od u ction
Extension of this concept to more elaborated struc-
tures6-9 provided significant insight into structure-
activity effects. For example, Chow and Mak7 performed
a detailed mechanistic study of the copper-catalyzed
Diels-Alder reaction. Their results led to the conclusion
that steric hindrance of the dendritic shell is a key
factor. As a matter of fact, on going from the second to
the third generation, the catalytic activity dropped while
the selectivity increased slightly.
A similar effect was also observed by Seebach9 on
studying the Ti-catalyzed enantioselective nucleophilic
addition of Et2Zn to benzaldehyde using dendrimers
with TADDOL cores. Consequently, to optimize the
properties of the catalyst, the dendritic systems should
contain tailored microenvironments and even structural
features promoting interactions between the active site
and the reactants. However, the conformational behav-
ior of dendrimers and its connection with the site
present in the core is still a source of intriguing dispute,7
and further studies ought to be carried out in order to
elucidate the influence of branched units on the reactiv-
ity of the metal core.10
Metallodendrimers are emerging as efficient and
recyclable catalysts in many chemical reactions.1,2 Gen-
erally, metal centers involved in chemical reactions are
placed either at the periphery or within the dendrimers.
Numerous studies in this area indicate that the
dendritic framework exerts a considerable influence on
the properties of the metal center. In particular, when
the active site is located at the core, the dendritic
superstructure around it can provide a shielding which
generates a microenvironment reminiscent of those
found in biological systems.3,4
Among the functional dendrimers bearing catalytic
pockets that mimic enzymes the “dendrizymes” reported
by Brunner are noteworthy.5 Catalytic studies carried
out on those systems showed a modest but favorable
effect of the dendritic branching on the properties of the
active site.
* Corresponding authors. E-mail: cano@unive.it and chessa@unive.it.
(1) (a) Astruc, D.; Chardac, F. Chem. Rev. 2001, 101, 2991. (b)
Twyman, L. J .; King, A. S. H.; Martin, I. K. Chem. Soc. Rev. 2002, 31,
69.
(2) Oosterom G. E.; Reek J . N. H.; Kamer P. C. J .; van Leeuwen P.
W. N. M. Angew. Chem., Int. Ed. 2001, 40, 1828.
(3) Smith, D. K.; Diederich, F. Chem. Eur. J . 1998, 4, 1353.
(4) Hetch, S.; Fre´chet, J . M. J . Angew. Chem., Int. Ed. 2001, 40, 74.
(5) Brunner, H. J . Organomet. Chem. 1995, 500, 39.
(6) Bolm, C.; Derrien, N.; Sarger, A. Synlett. 1966, 387.
(7) Chow, H. F.; Mak, C. C. J . Org. Chem. 1997, 62, 5116.
(8) Yamago, S.; Furukuwa, M.; Azuma, A.; Yoshida, J . I. Tetrahedron
Lett. 1998, 39, 3783.
(9) Rheiner, P. B.; Seebach, D. Chem Eur. J . 1999, 5, 3221.
10.1021/om020391l CCC: $22.00 © 2002 American Chemical Society
Publication on Web 09/14/2002

Pyridylthioether-Based Metallodendrimers
Organometallics, Vol. 21, No. 21, 2002 4343
Sch em e 1a
In this respect we chose to investigate the reactivity
and the solution behavior of palladium(II) allyl com-
plexes bearing dendritic wedges as ancillary ligands. Pd-
(II) allyl complexes have been systematically investi-
gated as substrates in the reaction involving the
nucleophilic attack by amines at the coordinated allyl
ligand. In particular we investigated in depth the allylic
amination of palladium allyl complexes bearing pyridyl-
imines and pyridyl-thioethers as ancillary ligands. The
ensuing wealth of available information allows a useful
comparison with the results of the present work.11
Moreover, since the accepted reaction mechanism of
allyl amination in these systems consists of a fast
equilibrium displacement of the ancillary ligand by the
reacting amine parallel to nucleophilic attack of the
amine itself to the coordinated allyl fragment (vide
infra), information on both thermodynamic and kinetic
issues could be gathered. In other words, the magnitude
of the displacement equilibrium constants and of the
bimolecular rate constants can be analyzed as a function
of the increasing bulkiness of the dendritic wedges,
thereby providing clear-cut information on the acces-
sibility and on the consequent reactivity of the metal
core.
a
Reagents and conditions: (i) K2CO3, 18-crown-6, DMF,
45 °C, 24 h; (ii) SOCl2, 50 °C, 4 h.
Sch em e 2a
Recently12 we reported on the synthesis of a series of
dendritic pyridyl ligands, 7-9, and the corresponding
Pd(II) complexes. We report herein on mechanistic
studies on the reactivity of the η3-allyl complexes
containing such ligands toward amination with piperi-
dine.
Resu lts a n d Discu ssion
Syn th esis of Den d r itic Liga n d s. The dendritic
ligands used in this study were designed for the
incorporation of palladium into a specific binding site
within the dendrimeric structure.12
The synthetic strategy leading to dendritic wedges
7-9 consists of preparing the building block 3 (Scheme
1) and coupling it with the known pyridine-based
dendritic fragments 4-62 (Scheme 2) to form ether
linkages. The key intermediate 3 was synthesized from
4-benzyloxy-2,6-bis(chloromethyl)pyridine, 1,13,14 as de-
picted in Scheme 1.
The introduction of the thioether functions was ac-
complished in 84% yield by reacting the dichloride 1
with 4-mercaptobenzyl alcohol15 in DMF in the presence
a
Reagents and conditions: (i) K2CO3, DMF, 70 °C, 24 h;
(ii) K2CO3, DMF, 60 °C, 48 h.
of K2CO3 and 18-crown-6 at 45 °C. The dihydroxymethyl
derivative 2 was then converted to the corresponding
dichloride 3 by treatment with SOCl2 at 50 °C. After
chromatographic purification, the building block 3 was
obtained in 82% yield. Combination of 2 equiv of diethyl
chelidamate 4 with the pyridylthioether-type ligand 3
under Williamson etherification conditions using K2CO3
as the base and DMF as the solvent gave the dendritic
wedge SNS(1) (7) in 92% yield.
(10) Bosman, A. W.; J ansenn, H. M.; Meijer, E. W. Chem. Rev. 1999,
99, 1665.
(11) (a) Crociani, B.; Antonaroli, S.; Di Bianca, F.; Canovese, L.;
Visentin, F.; Uguagliati, P. J . Chem. Soc., Dalton Trans. 1994, 1145.
(b) Canovese, L.; Visentin, F.; Uguagliati, P.; Di Bianca, F.; Antonaroli,
S.; Crociani, B. J . Chem. Soc., Dalton Trans. 1994, 3113. (c) Canovese,
L.; Uguagliati, P.; Visentin, F.; Crociani, B.; Di Bianca. F. Inorg. Chim.
Acta 1995, 235, 45. (d) Crociani, B.; Antonaroli, S.; Paci, M.; Di Bianca,
F.; Canovese L. Organometallics 1997, 16, 384. (e) Canovese, L.;
Visentin, F.; Uguagliati, P.; Chessa, G.; Lucchini, L.; Bandoli, G. Inorg.
Chim. Acta 1998, 275-276, 385. (f) Canovese, L.; Visentin, F.;
Uguagliati, P.; Bandoli, G. Inorg. Chim. Acta 1998, 277, 247-252. (g)
Canovese, L.; Visentin, F.; Uguagliati, P.; Chessa, G.; Pesce, A. J .
Organomet. Chem. 1998, 566, 61. (h) Canovese, L.; Visentin, F.; Chessa,
G.; Niero, A.; Uguagliati, P. Inorg. Chim. Acta 1999, 293, 44. (i)
Canovese, L.; Visentin, F.; Santo, C.; Chessa, G.; Uguagliati, P.
Polyhedron 2001, 20. (j) Canovese, L.; Visentin, F.; Chessa, G.;
Gardenal, G.; Uguagliati, P. J . Organomet. Chem. 2001, 622, 155.
(12) Chessa, G.; Scrivanti, A.; Canovese, L.; Visentin, F.; Uguagliati,
P. Chem. Commun. 1999, 959.
Similarly, coupling of the higher generation polypy-
ridine dendritic fragments 5 and 6 with 3 provided the
dendritic wedges SNS(2) (8) and SNS(3) (9) in 85% and
82%, respectively.
Dendritic wedges 7-9 were fully characterized by IR,
1H and 13C NMR spectroscopy, MALDI-TOF mass
spectrometry, and elemental analysis.
In general, the 1H NMR spectra of the dendritic
ligands 7-9 show signals attributable to aliphatic
methylene, benzylic, and aromatic protons introduced
(13) Chessa, G.; Scrivanti, A. J . Chem. Soc., Perkin Trans. 1 1996,
307.
(14) Chessa G.; Scrivanti, A. J . Heterocycl. Chem. 1997, 1851.
(15) Gricen R.; L. N. Owen, J . Chem. Soc. 1963, 1947.

4344 Organometallics, Vol. 21, No. 21, 2002
Canovese et al.
Sch em e 3
by the pyridylthioether ligand in addition to the ex-
pected patterns arising from the pyridyl fragments
4-6.13
Also MALDI-TOF analysis of compounds 7-9 gave
mass spectra, characterized by the presence of [M + H]+,
[M + Na]+, and [M + K]+ ions for all the samples under
study. The m/z values of the observed ions are in
agreement with related theoretical average masses
(percent error of measured mass < 0.5%).
Syn th esis of P a lla d iu m (II) Allyl Com p lexes. Ad-
dition at RT of 2,6-bis(phenylthiomethylpyridine) (SNS-
(0))11j as reference compound and of the appropriate
dendritic ligand SNS(1), SNS(2), and SNS(3) to the
dimeric species [Pd2(µ-Cl)2(η3-C3H5)2]16 or [Pd2(µ-Cl)2-
(η3-1,1-(CH3)2C3H3)2]17 in CH2Cl2 yields the required
allyl complex upon chloride abstraction with a stoichio-
metric amount of AgSO3CF3.
The complexes were obtained in 76%, 75%, 59%, and
86% yield in the cases of [Pd(η3-C3H5)SNS(0)]SO3CF3,
[Pd(η3-C3H5)SNS(1)]SO3CF3, [Pd(η3-C3H5)SNS(2)]SO3-
CF3, and [Pd(η3-C3H5)SNS(3)]SO3CF3 and 73%, 73%,
72%, and 88% yield in the cases of [Pd(η3-1,1-(CH3)2-
C3H3)SNS(0)]SO3CF3, [Pd(η3-1,1-(CH3)2C3H3)SNS(1)]-
SO3CF3, [Pd(η3-1,1-(CH3)2C3H3)SNS(2)]SO3CF3, and [Pd-
(η3-1,1-(CH3)2C3H3)SNS(3)], respectively.
1H NMR spectrometry provides a timely check on the
complex formation since coordinated allyl proton signals
are easily detectable and selected significant signals of
the free ligand shift downfield upon coordination. The
complexes were also characterized by elemental analysis
and MALDI-TOF technique. In the latter case the mass
spectra are characterized by the presence of ions cor-
responding to [SNS Pd]+ and [SNS Pd allyl]+ ionic
species.
protons give rise to slightly broadened AX4 or AX2
structures in the case of unsubstituted or substituted
allyl fragment, respectively. Owing to the most favorable
signal ratio, we will discuss in this section only the
solution behavior of [Pd(η3-C3H5)SNS(0)]SO3CF3 and
[Pd(η3-1,1-(CH3)2C3H3)SNS(0)]SO3CF3 since the observ-
able features for all the other allyl species described in
this paper can be traced back to an analogous behavior.
In the RT 1H NMR spectrum of [Pd(η3-C3H5)SNS-
(0)]SO3CF3 in CDCl3 a doublet (δ ) 4.20 ppm) and a
quintet (δ ) 5.98 ppm) ascribable to the allyl terminus
and the central proton, respectively, are detectable (AX4
system). The signals attributable to the SNS ligand shift
downfield upon coordination, so that thiomethyl protons
CH2-S resonate as a singlet at δ ) 4.62 ppm, the
pyridine protons H3,5 are detectable as a multiplet
together with the phenyl protons at δ ) 7.30, and the
pyridine H4 resonates at δ ) 7.66 ppm as a triplet.
This behavior, which is not unprecedented,11f,h was
interpreted on the basis of a windshield-wiper move-
ment of the dentritic arms which alternatively coordi-
nate, inducing a sulfur absolute configuration inversion
together with η3-η1-η3 allyl isomerization.11f,h This rear-
rangement, at variance with other observed fluxional
phenomena,18 is concentration independent and can be
interpreted on the basis of the intramolecular mecha-
nistic path represented in Scheme 3 (intermediate IIa ).
Solu tion Beh a vior of P a lla d iu m (II) Allyl Com -
p lexes. Selected 1H and 13C NMR data for the new
complexes are reported in the Experimental Section.
It has been shown11f that in the solid state palladium-
(II) allyl complexes bearing potentially terdentate py-
ridyl-dithioether SNS ligands are tetracoordinated spe-
cies with the allyl fragment η3-coordinated and the SNS
moiety acting as bidentate; consequently the complexes
[Pd(η3-C3H5)SNS(0)]SO3CF3, [Pd(η3-C3H5)SNS(1)]SO3-
CF3, [Pd(η3-C3H5)SNS(2)]SO3CF3, and [Pd(η3-C3H5)SNS-
(3)]SO3CF3 are expected to exist as couples of diaste-
reoisomers deriving from the mutual position of the allyl
H2 and the coordinated sulfur substituent R, which may
be on the same or on the opposite side of the main
coordination plane. In the case of the complexes [Pd-
(η3-1,1-(CH3)2C3H3)SNS(0)]SO3CF3, [Pd(η3-1,1-(CH3)2-
C3H3)SNS(1)]SO3CF3, [Pd(η3-1,1-(CH3)2C3H3)SNS(2)]SO3-
CF3, and [Pd(η3-1,1-(CH3)2C3H3)SNS(3)]SO3CF3 four
distinct isomers should be present since, besides the
above-mentioned species, the substituted allyl terminal
carbon can be either cis or trans to the central coordi-
nating pyridyl nitrogen atom (the existing enantiomers
go undetected under our experimental conditions).
However, the RT 1H NMR spectral data strongly suggest
the presence in solution of symmetric structures in
which no differences between coordinated and uncoor-
dinated SNS branches can be detected and the allyl
1
Analogously the RT H NMR spectrum of [Pd (η3-1,1-
(CH3)2C3H3)SNS(0)]SO3CF3 is easily interpreted on the
basis of similar behavior. Thus, the phenyl and the
isochronous H3,5 pyridine protons resonate at δ ) 7.31
ppm, and the triplet ascribable to pyridine H4 and the
thiomethyl CH2-S protons are detected at δ ) 7.63 and
4.58 ppm, respectively. The allyl protons display an AX2
system where the H2 proton is detected as a triplet at
(16) Harley, F. R.; J ones, S. R. J . Organomet. Chem. 1974, 66, 472.
(17) Auburn, P. R.; Mackenzie, P. B.; Bosnich, B. J . Am. Chem. Soc.
1985, 107, 2033.
(18) Canovese, L.; Lucchini, V.; Santo, C.; Visentin, F.; Zambon, A.
J . Organomet. Chem. 2002, 642, 58.

Pyridylthioether-Based Metallodendrimers
Organometallics, Vol. 21, No. 21, 2002 4345
5.67 ppm and the CH2 -CH-C(CH3)2 as a doublet at 4.18
ppm. The methyl protons of the allyl fragment CH2-CH-
C(CH3)2 resonate as distinct singlets at δ ) 1.51 (anti)
and 1.82 (syn) ppm.
This behavior also can be interpreted on the basis of
Scheme 3. The two possible η1-allyl species are not
isoergodic, and only on increasing the temperature does
the more crowded species become accessible as an
intermediate in the fluxional process, as is apparent in
the spectrum at T ) 323 K, in which the two CH3-
singlets collapse, indicating that the η3-η1-η3 isomer-
ism via the sterically hindered ΙΙb intermediate becomes
operative.
characterized by a singlet at δ ) 3.21 ppm (olefinic
protons), a broad AB system at δ ) 4.54 ppm (CH2-S),
a multiplet at δ ) 7.33 ppm (H3,5 and phenyl protons),
pyr
and a triplet at δ ) 7.61 ppm (H4pyr). The solution
behavior of palladium(0) species is interpreted on the
basis of a fluxional rearrangement which takes into
account the apparent symmetry of the substrate de-
scribed by the above-mentioned spectrum. This feature
is in fact inconsistent with a structure bearing a
terdentate ligand which can only act as a bidentate arm-
off species in a square planar environment shared with
an η2-coordinated olefin. Again the “windshield-wiper”
motion of the two branches induces a generalized
symmetry that can be traced back to the formation of
an intermediate species with two peripheral partially
bound sulfur atoms. The fumaronitrile remains tightly
η2-coordinated, as can be deduced from the residual AB
system at δ ) 4.54 ppm (CH2-S) determined by the
presence of chiral palladium, which does not change its
absolute configuration as dictated by the olefin face
coordinated to the metal. Obviously, under these cir-
cumstances the AB system could not stem from the
chirality of the sulfur, which rapidly inverts its absolute
configuration through the fast “windshield-wiper” mo-
tion. Again, no particular differences among the 1H
NMR spectra describing the fluxional rearrangement of
the complexes bearing different dendritic wedges can
be observed; the detected behaviors seem independent
of the size of ancillary ligands also with the palladium-
(0) substrates.
The observed phenomena could not be considered
unusual in the case of SNS derivatives which, with
respect to their coordinating capability and steric de-
mand, are very close to those of analogous potentially
terdentate S-N-S ligands.11h,f However, on increasing
the size of the dendritic branch, no hints of unusual
behavior can be observed since the spectral features of
all the studied species are very similar independently
of the concentration of the complexes, the steric demand,
and electronic characteristics of the macrocones. As a
1
matter of fact the H NMR spectra of [Pd(η3-C3H5)SNS-
(3)]SO3CF3 and [Pd(η3-1,1-(CH3)2C3H3)SNS(3)]SO3CF3
are superimposable to those of the corresponding SNS
derivatives, apart from the relative signal intensity of
the protons of the coordinating site and of the allyl
protons (which are almost annihilated within the skel-
eton signals). Apparently some sort of fluxional rear-
rangement is still operative without relationship to the
size of the ligands.
Allyl Am in a tion Rea ction s. The allyl amination
reactions were monitored both by 1H NMR spectrometry
and by UV-vis spectroscopy (vide infra). Formation of
the corresponding [Pd(η2-fn)(S-N-S)] species and the
piperidine-allyl derivatives was confirmed by compari-
son of the ensuing 1H NMR spectra with those of
authentic samples independently synthesized.
Syn th esis of P a lla d iu m (0) F u m a r on itr ile Com -
p lexes. The palladium(0) fumaronitrile complexes were
obtained by addition of the specific dendritic ligand
S-N-S to a solution containing a stoichiometric amount
19
of Pd2(DBA)3CHCl3 in the presence of a slight excess
Kin etics a n d Mech a n ism of th e Allyl Am in a tion
Rea ction . The complexes [Pd(η3-allyl)(SNS)] react at
25 °C in CHCl3 with piperidine in the presence of
fumaronitrile (fn) to give the corresponding palladium-
(0) fumaronitrile complexes and allylpiperidine.
All the reactions were followed by monitoring UV-
vis absorbance changes in the wavelength range 500-
280 nm (or at selected wavelengths) of CHCl3 solutions
of the allyl complexes A ([Pd]0 = 1 × 10-4 mol dm-3) in
the presence of fn ((2-8) × 10-4 mol dm-3) and an excess
of terdentate S-N-S ligand (g1 × 10-3 mol dm-3).
Under these conditions the reactions went smoothly to
completion, as can be seen by comparison of the final
spectra obtained after seven (or eight) half-lives with
those of the authentic final products independently
synthesized. The conversion of A into B with time
appeared to obey the monoexponential relationship At
) A∞ + (A0 - A∞) exp(-kobst), corresponding to a pseudo-
first-order process:
of fumaronitrile in acetone at RT under inert atmo-
sphere (N2).
The complexes [Pd(η2-fn)SNS(0)], [Pd(η2-fn)SNS(1)],
[Pd(η2-fn)SNS(2)], and [Pd (η2-fn)SNS(3)] were obtained
1
in 44%, 84%, 71%, and 90% yield, respectively. The H
NMR spectra provide an easy identification of the
samples, which were however fully characterized by
elemental analysis, 13C NMR, and MALDI-TOF tech-
nique. In particular MALDI-TOF mass spectra show the
presence of ions corresponding to [SNS Pd]+ ionic
species for all Pd(0) dendritic compounds. Ions at lower
m/z values are also detected due to the dendritic
fragmentation already observed under MALDI condi-
tions for pyridine-based dendrimers.20
Solu tion Beh a vior of P a lla d iu m (0) F u m a r on i-
tr ile Com p lexes. Also in the case of the palladium(0)
substrates it is convenient to discuss the spectral
features of the SNS(0) derivative because of the more
favorable signal ratio and the similarity of behavior. The
1
most significant H NMR data for the Pd(0) fumaroni-
-d[A]/dt ) kobs[A]
(1)
trile complexes are those ascribable to olefinic protons,
to CH2-S thiomethyl protons, and the signals in the
aromatic region. Thus the complex [Pd(η2-fn)SNS(0)] is
The kobs values, calculated by nonlinear regression
analysis of At (absorbance at time t) versus t (time),
show a bivariate dependence on entering piperidine HY
and added SNS ligand concentration (both considered
as constant, being in large excess over the metal),
whereas the fumaronitrile concentration does not affect
(19) Ukai, T.; Kawazura, H.; Ishii, Y.; Bonnet, J . J .; Ibers, J . A. J .
Organomet. Chem. 1974, 65, 253.
(20) Chessa, G.; Scrivanti, A.; Seraglia, R.; Traldi, P. Rapid Com-
mun. Mass Spectrom. 1998, 12, 1533.

4346 Organometallics, Vol. 21, No. 21, 2002
Canovese et al.
Sch em e 4
2
F igu r e 1. Dependence of kobs/[PIP]0 on [PIP]0 /[SNS(0)]0
for reaction of [Pd(η3-allyl)SNS(0)] with piperidine in CHCl3
at 25 °C.
Ta ble 1. Secon d -Or d er Ra te Con sta n ts (k2) a n d
Equ ilibr iu m Con sta n ts (KE) for Rea ction s of
P a lla d iu m Allyl Com p lexes w ith P ip er id in e a t 25
°C in CHCl3
can be easily explained on the basis of the increased
steric hindrance of the denditric branches influencing
the rate of associative attack of piperidine on the
coordinated allyl fragment. In this respect the decreas-
ing k2 value on going from first to third dendrimer
generation is not surprising even if the k2 value seems
to be slightly affected up to the second generation, since
the reactivity appears to be hardly modulated by the
substantial increase in the steric demand of the branches.
Rearrangement in solution would leave the allyl frag-
ment equally prone to the piperidine attack until no
rearrangement could compensate for the ensuing steric
hindrance of the third-generation dendrimeric complex.
The drop in reaction rate (1 order of magnitude) bears
witness to this very fact.
complex
k2 (mol-1‚dm3‚s-1
)
KE
[Pd(η3-C3H5)SNS(0)]+
[Pd(η3-C3H5)SNS(1)]+
[Pd(η3-C3H5)SNS(2)]+
[Pd(η3-C3H5)SNS(3)]+
13.6 ( 0.4
13.9 ( 0.3
6.7 ( 0.3
0.7 ( 0.4
5335 ( 263
8677 ( 403
9728 ( 945
42000 ( 20000
the observed rate constants. Such dependence can be
described by eq 2:
kobs ) k2[HY]/(1+ KE[HY]2/[SNS])
which can be rewritten as
(2)
k
obs/[HY] ) k2/(1+ KEF)
(3)
On the other hand, the degree of displacement of the
ligand by the incoming piperidine as testified by the
value of the thermodynamic parameter KE parallels the
observed reaction rate trend. Again the value of the
equilibrium constant suddenly increases when the third-
generation complex [Pd(η3-C3H5)(SNS(3))] is investi-
gated. The magnitude of KE was shown to increase with
the decreasing nucleophilic capability of pyridyl nitrogen
and thioetheric sulfur but also with the release of steric
strain,11g-i which becomes very important in the case
of the sterically hindered [Pd(η3-C3H5)(SNS(3))] com-
plex. Apparently, the electrostatic interaction between
the dendritic branches induces severe distortion of the
complex coordination plane and concomitant destabili-
zation of the whole structure. The change in reactivity
as a consequence of the increasing size of the ligand
molecules involved can be thus traced back to a confor-
mational change in the substrates. Chow and co-workers
demonstrated that the Diels-Alder reaction catalyzed
by copper complexes bearing bis(oxazoline) dendrimers
as chelating agents can be strongly reduced on going
from the second to the third ligand generation7 and that
such behavior is attributable to a folding-back of the
dendritic structure, which determines an increased
steric hindrance at the copper reactive site.
where F ) [HY]2/[SNS].
The parameters k2 and KE were determined by
nonlinear regression of rate constants to eq 3 (Figure
1), while the values of k2 and KE are listed in Table 1.
Such a dependence was interpreted on the basis of
the stepwise mechanism of Scheme 4. This mechanism
appears to be common to the whole class of reactions
involving allyl amination of allyl palladium complexes
with both bi- or terdentate pyridylmethanimine, py-
ridylthioether, or pyridylselenoether ligands,11 irrespec-
tively of their nucleophilic capabilities, electronic char-
acteristics, and steric requirements. The role of these
properties may become of paramount importance in
relation to the size and complexity of the dentritic cone
containing the metal-allyl species since it is possible to
distinguish between the slow attack on the allyl frag-
ment (k2) and the fast and concomitant displacement
of the palladium-coordinated ancillary ligand (KE),
thereby gathering information on the accessibility of
both the reaction centers. In any case, the accessibility
of the metal center seems warranted irrespectively of
the dendritic size (vide infra). However, as can be seen
in Table 1, the size of the dentritic cone becomes
relevant only starting from the [Pd(η3-C3H5)SNS(3)]
complex. Apparently, some sort of structural phenom-
enon abruptly occurs on going from the second- to the
third-generation dendrimeric complex. The trend of k2
Thus, in the present work the observed discontinuity
in the thermodynamic and kinetic parameters on going
from second- to third-generation metal dendrimers may
correspond to the transition from extended to globular

Pyridylthioether-Based Metallodendrimers
Organometallics, Vol. 21, No. 21, 2002 4347
MS) using a reflex time-of-flight instrument (Bruker-Franzen
Analytik) equipped with a “Scout” ion source operating in
positive linear mode (instrumental conditions: nitrogen laser
λ ) 337 nm; laser energy ) 50 µJ ; acceleration voltage ) 25
kV). Dithranol was used as matrix laid down in solution with
the sample (solvent: chloroform).
configuration of the dendritic branches, as dictated by
their steric and electronic interaction, which would
increase both the steric hindrance and distortion at the
reactive metal core. Therefore, the concomitant changes
in k2 and KE are easily understood. However, since no
particular differences among different generation metal
Syn th esis of Liga n d s. 4-Ben zyloxy-2,6-bis(4-h yd r oxy-
m eth ylp h en ylth iom eth yl)p yr id in e, 2. A suspension of K2-
CO3 (995 mg, 7.2 mmol) and thiol (845 mg, 6.03 mmol) in dry
DMF (30 mL) was stirred at room temperature under reduced
pressure for 30 min, after which 4-benzyloxy-2,6-bis(chlorom-
ethyl)pyridine (810 mg, 2.87 mmol) and 18-crown-6 (152 mg,
0.574 mmol) were added, and the reaction mixture was heated
at 45 °C for 24 h under an atmosphere of argon. After
evaporation of the solvent the organic product was extracted
with CH2Cl2 (150 mL). The organic extract was washed with
brine (2 × 75 mL), dried (Na2SO4), and evaporated under
reduced pressure. The crude product was purified by flash
chromatography eluting with 10% EtOAc in CH2Cl2, gradually
increasing to 60%, to give 2 as a white solid (1.18 g, 84%).
Mp: 106-107 °C. 1H NMR (CDCl3): δ 2.42 (bs, 2H, OH), 4.20
(s, 4H, CH2S), 4.61 (s, 4H, CH2OH), 5.00 (s, 2H, PhCH2O), 6.87
(s, 2H, pyr-H3,5), 7.23 (m, 8H, Ph-H), 7.37 (5H, m Ph-H). 13C
NMR (CDCl3): δ 39.8 (CH2S), 64.5 (CH2OH), 69.9 (CH2O),
108.2 (pyr-C3,5), 127.4, 127.5, 128.3, 128.6, 129.3, 134.7, 135.4,
and 139.1 (Ph-C), 158.8 (pyr-C2,6), 166.2 (pyr-C4). IR (cm-1):
3290 (br, OH). Anal. Calcd for C28H27NO3S2: C, 68.69; H, 5.56;
N, 2.86. Found: C, 68.59; H, 5.34; N, 2.86.
4-Ben zyloxy-2,6-bis(4-ch lor om eth ylph en ylth iom eth yl)-
p yr id in e, 3. A solution of dialcohol 2 (1.156 g, 2.38 mmol) in
SOCl2 (15 mL) was heated at 50 °C for 4 h, after which the
excess of SOCl2 was evaporated and the residue was neutral-
ized with 10% aqueous Na2CO3. The aqueous phase was
extracted with CH2Cl2 (150 mL). The organic extract was
washed with water, dried (Na2SO4), and evaporated under
reduced pressure. Purification by flash chromatography elut-
ing sequentially with CH2Cl2 and 2% Et2O in CH2Cl2 gave the
chloride 3 (1.025 g, 82%). Mp: 133-133.5 °C. 1H NMR
(CDCl3): δ 4.23 (s, 4H, CH2S), 4.54 (s, 4H, CH2Cl), 4.99 (s,
2H, PhCH2O), 6.84 (s, 2H, pyr-H3,5), 7.28 (m, 8H, Ph-H), 7.36
(m 5H, Ph-H). 13C NMR (CDCl3): δ 39.7 (CH2S), 45.8 (CH2-
Cl), 69.9 (CH2O), 108.2 (pyr-C3,5), 127.6, 128.4, 128.7, 129.1,
129.2, 135.3, 135.4, and 136.5 (Ph-C), 158.6 (pyr-C2,6), 166.2
(pyr-C4). IR (cm-1): 1263 (CH2Cl). Anal. Calcd for C28H25Cl2-
NOS2: C, 63.87; H, 4.79; N, 2.66. Found: C, 63.71; H, 4.62;
N, 2.59.
1
dendrimers can be gathered from analysis of the RT H
NMR spectra with respect to the fluxional phenomena
(which would be strongly influenced by the size of the
wedges), one may postulate an alternative explanation
to the accepted windshield-wiper motion of the dendritic
wings. Thus, we tentatively entertain the intriguing
hypothesis that it is the metal itself that migrates
within the potentially terdentate coordinative site,
thereby inducing the observed fluxional rearrangement.
Work is in progress in our laboratory in order to confirm
this view and gather more information about this
phenomenon.
Con clu sion
A series of pyridyl-dithioether-based Pd(II) and Pd-
(0) metallodendrimers were successfully synthesized
and characterized by NMR, elemental analysis, and
MALDI-TOF determinations. The reactivity of the Pd-
(II) allyl complexes was also studied with respect to the
allyl amination by piperidine, and the results obtained
were compared and discussed in terms of increasing
wedge size. The kinetic and thermodynamic behavior
of the species is hardly influenced by the dendrimer
generation. Only the SNS(3) allyl palladium derivative
shows markedly different values in both allyl amination
rate and ligand displacement constant, and this finding
was traced back to the configuration assumed in solu-
tion upon the electronic and steric interaction of the
third-generation SNS moiety. Such a configuration
would increase the steric hindrance on the allyl frag-
ment and the distortion of the main coordination plane
around the metal, thereby imparting the observed
reactivity to the system.
Exp er im en ta l Section
SNS(1), 7. A mixture of diethyl 4-hydroxypyridine-2,6-
dicarboxylate, 4 (421 mg, 1.76 mmol), and anhydrous K2CO3
(243 mg, 1.76 mmol) in dry DMF (10 mL) was stirred at 25 °C
under reduced pressure for 30 min, then 4-benzyloxy-2,6-bis-
(4-chloromethylphenylthiomethyl)pyridine, 3 (421 mg, 0.8
mmol), was added and the reaction mixture was allowed to
react at 70 °C for 24 h under a nitrogen atmosphere. After
removal of the solvent from the reaction mixture the resulting
residue was extracted with CH2Cl2 (100 mL). The organic
extract was washed with brine, dried (Na2SO4), and finally
evaporated. The crude product was purified by flash chroma-
tography eluting with 2% MeOH in CH2Cl2 to give 7 as a glassy
solid (690 mg, 92%). 1H NMR (CDCl3): δ 1.46 (t, 12H, J ) 7.1
Hz, CH2CH3), 4.23(s, 4H, CH2S), 4.47 (q, 8H, J ) 7.1 Hz, CH2-
CH3), 5.01 (s, 2H, PhCH2O), 5.15 (s, 4H, CH2Opyr), 6.87 (s,
2H, pyr-H3,5), 7.35 (m, 13H, Ph-H), 7.84 (s, 4H, pyr-H3,5). 13C
NMR (CDCl3): δ 13.9 (CH3CH2), 39.7 (CH2S), 62.1 (CH3CH2),
69.6 and 70.0 (CH2O), 107.9 and 114.2 (pyr-C3,5), 127.3, 128.0
128.1, 128.4, 128.9, 132.2, 135.2, and 136.9 (Ph-C), 150.0 and
158.4 (pyr-C2,6), 164.4 (CdO), 165.8 and 166.2 (pyr-C4). IR
(cm-1): 1744 and 1719 (CdO). MALDI-MS: m/z 955 ([M +
Na]+). Anal. Calcd for C50H49N3O11S2: C, 64.43; H, 5.30; N,
4.51. Found: C, 63.64; H, 5.19; N, 4.46.
Gen er a l Com m en ts. 2,6-Bis(phenylthiomethyl)pyridine
(SNS),20 4-mercaptobenzyl alcohol,15 4-benzyloxy-2,6-bis(chlo-
romethyl)pyridine,13,14 diethyl 4-hydroxypyridine-2,6-dicar-
boxylate, and second- and third-generation dendritic fragments
(EtO2C)4-[Py]3-OH and (EtO2C)8-[Py]7-OH were prepared ac-
cording to literature procedures.13
Tetrahydrofuran (THF) was distilled from Na-benzophenone
immediately before use. Dimethyl sulfoxide (DMSO) and
acetone were dried and stored over 3 Å and 4 Å molecular
sieves, respectively. N,N-Dimethylformamide (DMF) was puri-
fied by distillation from CaH2 and stored over 4 Å molecular
sieves in a dark bottle. Dichloromethane was freshly distilled
from CaH2. Other solvents and reagents were generally used
without further purification. Column chromathography was
performed using silica gel (SiO2, Macherey Nagel, 0.04-0.063
mm, 230-400 mesh).
1H and 13C NMR spectra were obtained on a Bruker AC 200
or on a Bruker Avance 300 spectrometer using the solvent
signal as internal standard. The infrared spectra were recorded
on a Nicolet Magna-IR 750 spectrometer as KBr pellets.
Melting points were taken in capillary tubes with a Buchi 535
apparatus and are uncorrected.
Mass spectra of dendrimers were obtained by matrix-
assisted laser desorption ionization mass spectrometry (MALDI-
SNS(2), 8. Compound 8 was prepared by the same synthetic
procedure as described for 7 starting from the dendritic

4348 Organometallics, Vol. 21, No. 21, 2002
Canovese et al.
tetraester HO-[Py]3-(CO2Et)4 5 (944 mg, 1.58 mmol), anhy-
drous K2CO3 (260 mg, 1.88 mmol), and 4-benzyloxy-2,6-bis(4-
chloromethylphenylthiomethyl)pyridine, 3 (395 mg, 0.75 mmol),
in dry DMF (20 mL). Purification by flash chromatography
eluting with 3% MeOH in CH2Cl2 gave 8 as a glassy solid (1.05
g, 85%). 1H NMR (CDCl3): δ 1.45 (t, 24H, J ) 7.1 Hz, CH2CH3),
4.23 (s, 4H, CH2S), 4.47 (q, 16H, J ) 7.1 Hz, CH2CH3), 5.00
(s, 2H, PhCH2O), 5.07 (s, 4H, CH2Opyr), 5.29 (s, 8H, pyrCH2-
Opyr), 6.88 (s, 2H, pyr-H3,5), 7.03 (s, 4H, pyr-H3,5), 7.32 (m 13
H, Ph-H), 7.89 (s, 8H, pyr-H3,5). 13C NMR (CDCl3): δ 13.9 (CH3-
CH2), 39.6 (CH2S), 62.2 (CH3CH2), 69.6 and 70.5 (CH2O), 107.4,
107.9, and 114.3 (pyr-C3,5), 127.3, 128.0, 128.1, 128.4, 128.8,
132.6, 135.2, and 136.7 (Ph-C), 150.1, 156.4, and 158.4 (pyr-
([SNS(1)PdC3H6]+). Anal. Calcd for C54H55F3N3O14PdS3C: C,
52.75; H, 4.51; N, 3.42. Found: C, 52.70; H, 4.68; N, 3.26.
[P d (η3-C3H5)SNS(2)]SO3CF 3. The title compound was
obtained as the [Pd(η3-C3H5)(SNS)]SO3CF3 complex using SNS-
1
(2) as ligand. Yield: 59% (whitish powder). H NMR (CDCl3):
δ 1.45 (t, 12H, CH2CH3, J ) 7.1 Hz), 3.97 (bs, 4H, all-CH2),
4.45 (q, 8H, J ) 7.1 Hz, CH2CH3,), 4.49 (s, 4H, CH2S), 5.07 (s,
2H, PhCH2O), 5.10 (s, 4H, CH2Opyr), 5.30 (s, 8H, pyrCH2-
Opyr), 5.74 (bq, 1H, all-CH), 7.02 (bs, 6H, pyr-H3,5), 7.24-7.47
(m, 13H, Ph-H), 7.89 (s, 8H, pyr-H3,5). 13C NMR (CDCl3): δ
14.6 (CH3CH2), 44.9 (CH2S), 62.9 (CH3CH2), 66.1 (all-CH2), 69.9
and 71.2 (CH2O), 108.0, 110.6, and 115.0 (pyr-C3,5), 116.8 (all-
CH), 128.1, 128.9, 129.0, 129.2, 130.9, 135.1, and 135.5 (Ph-
C), 150.8, 157.3, and 159.8 (pyr-C2,6), 164.9 (CdO), 166.6, 166.9,
and 167.3 (pyr-C4). MALDI-MS: m/z 1758 ([SNS(2)Pd]+), 1799
([SNS(2)PdC3H6]+). IR (cm-1): 1742 and 1724 (CdO). Anal.
Calcd for C90H91F3N7O26PdS3: C, 55.54; H, 4.71; N, 5.04.
Found: C, 55.66; H, 4.58; N, 4.79
C
2,6), 164.2 (CdO), 165.8, 165.9, and 166.3 (pyr-C4). IR (cm-1):
1745 and 1720 (CdO). MALDI-MS: m/z 1673 ([M + Na]+).
Anal. Calcd for C86H85N7O23S2: C, 62.65; H, 5.20; N, 5.95.
Found: C, 61.31; H, 4.99; N, 5.79.
SNS(3), 9. Compound 9 was prepared as described for 7
starting from the dendron (CO2Et)8-[Py]7-OH 6 (1.2 g, 0.91
mmol), anhydrous K2CO3 (0.133 g, 0.96 mmol), 18-crown-6 (24
mg, 0.09 mmol), and 4-benzyloxy-2,6-bis(4-chloromethylphe-
nylthiomethyl)pyridine, 3 (0.226 g, 0.43 mmol), in dry DMF
(20 mL) at 50 °C for 48 h. The crude product was purified by
flash chromatography eluting with 3% MeOH in CH2Cl2 and
finally recrystallized from CH2Cl2/EtOH (1:2, 15 mL) to give
9 as an amorphous white solid (1.101 g, 82%). 1H NMR
(CDCl3): δ 1.44 (t, 48H, J ) 7.1 Hz, CH2CH3), 4.21 (s, 4H,
CH2S), 4.46 (q, 32H, J ) 7.1 Hz, CH2CH3), 4.99 (s, 2H,
PhCH2O), 5.06 (s, 4H, CH2Opyr), 5.21 (s, 8H, pyrCH2Opyr),
5.32 (s, 16H, pyrCH2Opyr), 6.86 (s, 2H, pyr-H3,5), 7.00 (s, 4H,
pyr-H3,5), 7.09 (s, 8H, pyr-H3,5), 7.31 (m 13 H, Ph-H), and 7.90
(s, 16H, pyr-H3,5). 13C NMR (CDCl3): δ 13.9 (CH3CH2), 39.7
(CH2S), 62.2 (CH3CH2), 69.6, 70.2, and 70.5 (CH2O), 107.2,
107.3, 107.9, and 114.3 (pyr-C3,5), 127.3, 128.0, 128.4, 128.6,
132.6, 135.2, and 136.8 (Ph-C), 150.1, 156.7, 156.8, and 158.3
(pyr-C2,6), 164.2 (CdO), 165.8, 165.9, 166.0, and 166.3 (pyr-
C4). IR (cm-1): 1745 and 1720 (CdO). MALDI-MS: m/z 3106
([M + Na]+). Anal. Calcd for C158H157N15O47S2‚H2O‚CHCl3: C,
59.32; H, 5.01; N, 6.53. Found: C, 60.57; H, 4.76; N, 6.55.
Syn th esis of P a lla d iu m (II) Com p lexes. [P d (η3-C3H5)-
SNS(0)]SO3CF 3. To a solution of 87.1 mg (0.238 mmol) of [Pd2-
(µ-Cl)2(η3-C3H5)2] in freshly distilled CH2Cl2 (10 mL) was added
123.3 mg (0.479 mmol) of AgSO3CF3 under inert atmosphere
(N2). The solution, magnetically stirred, was reacted in the
dark for 4 h. To the filtered solution was added 161.8 mg (0.5
mmol) of 2,6-bis(phenylthiomethyl)pyridine (SNS) ligand. The
resulting mixture was stirred for 30 min and finally treated
with activated charcoal for 10 min and filtered on Celite filter.
Addition of Et2O to the cooled (ice bath) and concentrated
solution yields 235.6 mg (0.38 mmol 76%) of the title complex
[P d (η3-C3H5)SNS(3)]SO3CF 3. The title compound was
obtained as the [Pd(η3-C3H5)(SNS)]SO3CF3 complex using SNS-
1
(3) as ligand. Yield: 86% (whitish powder). H NMR (CDCl3):
δ 1.43 (t, 48H, J ) 7.1 Hz, CH2CH3), 4.09 (bd, 2H, all-CH2),
4.43 (q, 32H, J ) 7.1 Hz, CH2CH3), 4.59 (bs, 4H, CH2S), 5.09
(bs, 6H, CH2Opyr and PhCH2O), 5.20 (s, 8H, pyrCH2Opyr) 5.31
(s, 16H, pyrCH2Opyr), 7.01 (s, 6H, pyr-H3,5), 7.09 (s, 8H, pyr-
H
3,5) 7.31-7.52 (m 13 H, Ph-H), and 7.89 (s, 16H, pyr-H3,5).
13C NMR (CDCl3): δ 13.9 (CH3CH2), 46.0 (CH2S), 62.2
(CH3CH2), 66.9 (all-CH2), 69.0, 70.2, 70.5, and 70.9 (CH2O),
107.1, 107.4, 110.6, and 114.3 (pyr-C3,5), 117.5 (all-CH), 127.5,
128.0, 128.5, 128.6, 131.0, 131.4, 134.0, and 136.1 (Ph-C),
150.1, 156.6, 156.9, and 159.4 (pyr-C2,6), 164.2 (CdO), 165.9,
166.0, and 167.0 (pyr-C4). IR (cm-1): 1743 and 1721 (CdO).
MALDI-MS: m/z 3190 ([SNS(3)Pd]+), 3231 ([SNS(3)PdC3H6]+).
Anal. Calcd for C162H163F3N15O50PdS3: C, 57.57; H, 4.86; N,
6.22. Found: C, 57.44; H, 4.80; N, 6.21.
[P d (η3-1,1-(CH 3)2C3H 3)SNS(0)]SO3CF 3. The title com-
pound was obtained following the usual synthetic scheme
using [Pd2(µ-Cl)2(η3-1,1-(CH3)2C3H3)2] as starting material and
SNS(0) as ligand. Yield: 73% (whitish powder). 1H NMR
(CDCl3): δ 1.51 (s, 3H, all-CH3 anti), 1.82 (s, 3H, all-CH3 syn),
4.18 (d, 2H, J ) 10.4 Hz, all-CH2), 5.58 (s, 4H, CH2S), 5.67 (t,
1H, J ) 10.4 Hz, all-CH), 7.16-7.45 (m, 2H, pyr-H3,5 and Ph-
H), 7.63 (t, 1H, J ) 7.7 Hz, pyr-H4). 13C NMR (CDCl3): δ 23.3
(all-CH3 anti), 29.3 (all-CH3 syn), 46.8 (CH2S), 62.5 (all-CH2), 99.3
(all-C(CH3)2), 112.4 (all-CH), 124.7 (pyr-C3,5), 129.7, 130.2,
131.1, and 132.2 (Ph-C), 140.3 (pyr-C4), 159.5 (pyr-C2,6). Anal.
Calcd for
C25H27F3NO3PdS3: C, 46.26; H, 4.19; N, 2.16.
Found: C, 46.06; H, 4.02; N, 2.11.
[P d (η3-1,1-(CH 3)2C3H 3)SNS(1)]SO3CF 3. The title com-
pound was obtained as the [Pd(η3-1,1-(CH3)2C3H3)SNS(0)]SO3-
CF3 complex using SNS(1) as ligand. Yield: 73% (whitish
powder). 1H NMR (CDCl3): δ 1.44 (t, 12H, J ) 7.1 Hz,
CH2CH3), 1.48 (bs, 3H, all-CH3 anti), 1.80 (s, 3H, all-CH3 syn),
4.11 (d, 2H, J ) 10.5 Hz, all-CH2), 4.45 (q, 8H, J ) 7.1 Hz,
CH2CH3), 4.52 (s, 4H, CH2S), 5.10 (s, 2H, PhCH2O), 5.20 (s,
4H, CH2Opyr), 5.56 (t, 1H, all-CH, J ) 10.5 Hz), 6.97 (s, 2H,
1
as a whitish precipitate. H NMR (CDCl3): δ 4.20 (d, 4H, J )
9.8 Hz, all-CH2), 4.62 (s, 4H, CH2S), 5.98 (q, 1H, J ) 9.8 Hz,
all-CH), 7.19-7.43 (m, 12H, pyr-H3,5 and Ph-H), 7.66 (t, 1H, J
) 7.8 Hz, pyr-H4). 13C NMR (CDCl3): δ 47.1 (CH2S), 67.4 (all-
CH2), 118.8 (all-CH), 124.5 (pyr-C3,5), 129.6, 130.1, 131.3, and
132.2 (Ph-C), 140.4 (pyr-C4), 159.4 (pyr-C2,6). Anal. Calcd for
pyr-H3,5), 7.31-7.58 (m, 13H, Ph-H), 7.83 (s, 4H, pyr-H3,5). 13
C
C
23H23F3NO3PdS3: C, 44.48; H, 3.73; N, 2.26. Found: C, 44.32;
H, 3.98; N, 2.51.
NMR (CDCl3): δ 14.6 (CH3CH2), 23.2 (all-CH3 anti), 29.3 (all-
CH3 syn), 46.7 (CH2S), 62.5 (all-CH2), 62.9 (CH3CH2), 70.1 and
71.6 (CH2O), 99.8 (all-C(CH3)2), 111.9 (all-CH), 111.5 and 114.9
(pyr-C3,5), 128.2, 129.0, 129.1, 129.2, 132.0, 132.4, 134.9, and
136.6 (Ph-C), 150.8 and 160.6 (pyr-C2,6), 165.0 (CdO), 166.7
and 167.5 (pyr-C4). IR (cm-1): 1744 and 1720 (CdO). MALDI-
MS: m/z 1041 ([SNS(1)Pd]+), 1110 ([SNS(1)PdC5H10]+). Anal.
Calcd for C56H58F3N3O14PdS3: C, 53.52; H, 4.65; N, 3.34.
Found: C, 53.45; H, 4.71; N, 3.36
[P d (η3-C3H5)SNS(1)]SO3CF 3. The title compound was
obtained as the [Pd(η3-C3H5)(SNS)]SO3CF3 complex using SNS-
1
(1) as ligand. Yield: 75% (whitish powder). H NMR (CDCl3):
δ 1.45 (t, 12H, J ) 7.1 Hz, CH2CH3), 3.99 (bs, 4H, all-CH2),
4.45 (q, 8H, J ) 7.1 Hz, CH2CH3), 4.56 (s, 4H, CH2S), 5.08 (s,
2H, PhCH2O), 5.18 (s, 4H, CH2Opyr), 5.79 (bq, 1H, all-CH, J
) 9.9 Hz), 6.97 (s, 2H, pyr-H3,5), 7.32-7.51 (m, 13H, Ph-H),
7.82 (s, 4H, pyr-H3,5). 13C NMR (CDCl3): δ 14.6 (CH3CH2), 45.3
(CH2S), 62.9 (CH3CH2), 66.3 (all-CH2), 70.3 and 71.4 (CH2O),
110.9 and 114.9 (pyr-C3,5), 117.2 (all-CH), 128.1, 129.1, 129.2
131.7, 133.3, 135.0, and 135.7 (Ph-C), 150.7 and 160.0 (pyr-
[P d (η3-1,1-(CH 3)2C3H 3)SNS(2)]SO3CF 3. The title com-
pound was obtained as the [Pd(η3-1,1-(CH3)2C3H3)SNS(0)]SO3-
CF3 complex using SNS(2) as ligand. Yield: 73% (whitish
1
C
2,6), 165.0 (CdO), 166.7 and 167.4 (pyr-C4). IR (cm-1): 1744
and 1720 (CdO). MALDI-MS: m/z 1042 ([SNS(1)Pd]+), 1082
powder). H NMR (CDCl3): δ 1.36 (s, 3H, all-CH3 anti), 1.44 (t,
24H, J ) 7.1 Hz, CH2CH3), 1.66 (s, 3H, all-CH3 syn), 3.86 (bs,

Pyridylthioether-Based Metallodendrimers
Organometallics, Vol. 21, No. 21, 2002 4349
2H, all-CH2), 4.45 (q, 16H, J ) 7.1 Hz CH2CH3), 4.47 (bs, 4H,
CH2S), 5.05 (s, 2H, PhCH2O), 5.09 (s, 4H, CH2Opyr), 5.29 (s,
8H, pyrCH2Opyr), 5.64 (bt, 1H, all-CH), 6.97 (s, 2H, pyr-H3,5),
7.03 (s, 4H, pyr-H3,5), 7.28-7.49 (m, 13H, Ph-H), 7.89 (s, 8H,
pyr-H3,5). 13C NMR (CDCl3): δ 14.6 (CH3CH2), 22.7 (all-CH3
anti), 28.4 (all-CH3 syn), 44.9 (CH2S), 62.9 (CH3CH2 and all-CH2),
70.0 and 71.2 (CH2O), 97.7 (all-C(CH3)2), 110.4 (all-CH and
pyr-C3,5), 108.0, and 115.0 (pyr-C3,5), 128.1, 128.9, 129.1, 130.6,
135.3, and 135.5 (Ph-C), 150.8, 157.2, and 159.7 (pyr-C2,6),
164.9 (CdO), 166.6, 166.9, and 167.0 (pyr-C4). IR (cm-1): 1743
and 1724 (CdO). MALDI-MS: m/z 1758 ([SNS(2)Pd]+), 1826
([SNS(2)PdC5H10]+). Anal. Calcd for C92H94F3N7O26PdS3: C,
55.99; H, 4.80; N, 4.97. Found: C, 55.85; H, 4.63; N, 4.72.
[P d (η3-1,1-(CH 3)2C3H 3)SNS(3)]SO3CF 3. The title com-
pound was obtained as the [Pd(η3-1,1-(CH3)2C3H3)SNS(0)]SO3-
CF3 complex using SNS(3) as ligand. Yield: 88% (whitish
powder). 1H NMR (CDCl3): δ 1.43 (t, 51H, J ) 7.1 Hz, CH2CH3
and all-CH3 anti), 1.69 (s, 3H, all-CH3 syn), 4.06 (bd, 2H, all-CH2),
4.45 (q, 32H, J ) 7.1 Hz, CH2CH3), 4.54 (bs, 4H, CH2S), 5.10
(bs, 6H, CH2Opyr and PhCH2O), 5.20 (s, 8H, pyrCH2Opyr) 5.30
(s, 16H, pyrCH2Opyr), 5.50 (bt, 1H, all-CH), 7.01 (s, 6H, pyr-
δ 14.6 (CH3CH2), 23.9 (fn-CH), 46.5 (CH2S), 62.9 (CH3CH2),
70.4 and 71.1 (CH2O), 110.0 and 114.9 (pyr-C3,5), 122.5 (CN),
127.9, 129.0, 129.2 129.3, 132.0, 134.1, 134.8, and 135.5 (Ph-
C), 150.7 and 160.0 (pyr-C2,6), 165.0 (CdO), 166.7 (pyr-C4). IR
(cm-1): 2207 (CtN), 1741 and 1720 (CdO). MALDI-MS: m/z
1041 ([SNS(1)Pd]+). Anal. Calcd for C54H51N5O11PdS2: C,
58.09; H, 4.60; N, 6.27. Found: C, 58.23; H, 4.31; N, 6.21.
[P d (η2-fn )SNS(2)]: whitish powder, 71% yield. 1H NMR
(CDCl3): δ 1.45 (m, 24H, CH2CH3), 3.11 (s, 2H, fn-CH), 4.46
(q, 12H, J ) 7.1 Hz, CH2CH3, and bs, CH2S), 5.07 (s, 2H,
PhCH2O), 5.11 (s, 4H, CH2Opyr), 5.30 (s, 8H, pyrCH2Opyr),
6.98 (s, 2H, pyr-H3,5), 7.02 (s, 4H, pyr-H3,5) 7.28-7.52 (m, 13H,
Ph-H), 7.89 (s, 8H, pyr-H3,5). 13C NMR (CDCl3): δ 14.6 (CH3-
CH2), 23.9 (fn-CH), 46.2 (CH2S), 62.9 (CH3CH2), 69.9 and 71.2
(CH2O), 108.0, 110.2, and 115.0 (pyr-C3,5), 122.5 (all-CN), 128.0,
128.9, 129.2, 129.3, 131.4, 134.1, 134.8, and 135.7 (Ph-C),
150.8, 157.3, and 159.9 (pyr-C2,6), 164.9 (CdO), 166.6, 166.8,
and 166.9 (pyr-C4). IR (cm-1): 2204 (CtN), 1740 and 1718 (Cd
O). MALDI-MS: m/z 1758 ([SNS(2)Pd]+). Anal. Calcd for
C
90H87N9O23PdS2: C, 58.96; H, 4.78; N, 6.88. Found: C, 59.23;
H, 4.66; N, 6.93.
H
3,5), 7.09 (s, 8H, pyr-H3,5) 7.30-7.50 (m, 13H, Ph-H), and 7.88
[P d (η2-fn )SNS(3)]: whitish powder, 90% yield. 1H NMR
(CDCl3): δ 1.43 (t, 48H, J ) 7.1 Hz, CH2CH3), 3.08 (s, 2H,
fn-CH), 4.46 (q, 36H, J ) 7.1 Hz, CH2CH3 and CH2S), 5.06 (s,
2H, PhCH2O), 5.10 (s, 4H, CH2Opyr), 5.21 (s, 8H, pyrCH2-
Opyr), 5.32 (s, 16H, pyrCH2Opyr), 6.97 (s, 2H, pyr-H3,5), 7.01
(s, 4H, pyr-H3,5), 7.10 (s, 8H, pyr-H3,5), 7.33-7.52 (m, 13H, Ph-
H), and 7.90 (s, 16H, pyr-H3,5). 13C NMR (CDCl3): δ 14.6 (CH3-
CH2), 24.0 (fn-CH), 46.3 (CH2S), 62.8 (CH3CH2), 69.9, 70.9, and
71.2 (CH2O), 107.8, 108.0, 110.1, and 114.9 (pyr-C3,5), 122.4
(all-CN), 127.9, 129.1 129.3, 131.4, 134.1, 134.8, and 135.8 (Ph-
C), 150.8, 157.3, 157.5, and 159.9 (pyr-C2,6), 164.9 (CdO), 166.6,
166.7, and 166.8 (pyr-C4). IR (cm-1): 2210 (CtN), 1744 and
1719 (CdO). MALDI-MS: m/z 3192 ([SNS(3)Pd]+). Anal. Calcd
for C162H159N17O47PdS2: C, 59.56; H, 4.91; N, 7.29. Found: C,
59.66; H, 4.74; N, 7.04.
(s, 16H, pyr-H3,5). 13C NMR (CDCl3): δ 14.6 (CH3CH2), 22.9
(all-CH3 ), 29.0 (all-CH3 syn), 46.7 (CH2S), 62.9 (all-CH2), 62.8
anti
(CH3CH2), 69.7, 70.9, 71.2, and 71.6 (CH2O), 99.1 (all-C(CH3)2),
107.8, 108.1, 111.5, and 114.9 (pyr-C3,5), 112.2 (all-CH), 128.2,
128.7, 129.1, 129.5, 131.8, 132.5, 134.8, and 137.0 (Ph-C),
150.8, 157.3, 157.6, and 160.4 (pyr-C2,6), 164.9 (CdO), 166.6,
166.7, and 167.6 (pyr-C4). IR (cm-1): 1744 and 1720 (CdO).
MALDI-MS: m/z 3189 ([SNS(3)Pd]+), 3257 ([SNS(3)PdC5H10]+).
Anal. Calcd for C164H166F3N15O50PdS3: C, 57.82; H, 4.91; N,
6.17. Found: C, 57.57; H, 4.71; N, 6.08.
Syn th esis of P a lla d iu m (0) Com p lexes. [P d (η2-fn )SNS-
(0)]. A 23.8 mg (0.305 mmol) sample of fumaronitrile and 94.4
mg (0.292 mmol) of 2,6-diphenylthiomethylpyridine (SNS(0))
were dissolved in 15 mL of freshly distilled acetone under inert
atmosphere (N2). A 150 mg (0.145 mmol) sample of Pd2DBA3‚
CHCl3 was added, and the resulting solution was reacted
under magnetic stirring for 1 h. The initial violet-colored
mixture turned into an orange solution, which was treated
with activated charcoal for several minutes and filtered on a
Celite filter. Concentration under reduced pressure of the
filtered solution and addition of Et2O yielded 66 mg (44% yield)
NMR Mea su r em en ts. The temperature-dependent 1H
NMR spectra were analyzed using the SWAN program.20
UV-Vis, Kin etic Mea su r em en ts, a n d Da ta An a lysis.
The kinetics of allyl amination of complexes [Pd(η3-allyl)SNS]-
SO3CF3 were studied by adding known aliquots of piperidine
solution to a solution of [Pd(η3-allyl)SNS]SO3CF3, fn, and the
appropriate ligand SNS in the thermostated cell compartment
of a PE Lambda 40 spectrophotometer. The reactants were in
constant excess over the metal ([Pd]0 ≈ 1 × 10-4 mol dm-3),
and the progress of the reaction was monitored by recording
absorbance changes in the range 500-280 nm or at fixed
wavelength with time. Mathematical and statistical data
analysis was carried out on a personal computer by means of
a locally adapted version of Marquardt’s algorithm.21
1
of the title complex as a whitish powder. H NMR (CDCl3): δ
3.21 (s, 2H, fn-CH), 4.40-4.68 (bm, 4H, CH2S), 7.17-7.49 (m,
12H, pyr-H3,5 and Ph-H), 7.61 (t, 1H, J ) 7.7 Hz, pyr-H4). 13C
NMR (CDCl3): δ 23.9 (fn-CH), 46.5 (CH2S), 122.6 (CN), 123.2
(pyr-C3,5), 128.8, 129.8, 132.1, and 133.2 (Ph-C), 138.7 (pyr-
C4), 158.8 (pyr-C2,6). IR (cm-1): 2201 (CtN). Anal. Calcd for
C
23H19N3PdS2: C, 54.38; H, 3.77; N, 8.27. Found: C, 54.53;
H, 3.58; N, 8.37.
The complexes [Pd(η2-fn)SNS(1)], [Pd(η2-fn)SNS(2)], and
[Pd(η2-fn)SNS(3)] were synthesized in the same way as [Pd-
(η2-fn)SNS(0)] using the appropriate SNS ligand.
[P d (η2-fn )SNS(1)]: whitish powder, 84% yield. 1H NMR
(CDCl3): δ 1.46 (m, 12H, CH2CH3), 3.16 (s, 2H, fn-CH), 4.47
(q, 12H, J ) 7.1 Hz, CH2CH3 and bs, CH2S), 5.03 (s, 2H,
PhCH2O), 5.19 (s, 4H, CH2Opyr), 6.88 (s, 2H, pyr-H3,5), 7.29-
7.58 (m, 13H, Ph-H), 7.84 (s, 4H, pyr-H3,5). 13C NMR (CDCl3):
Ack n ow led gm en t. We wish to thank Dr. R. Sera-
glia (CNR Padua) for the MALDI-TOF spectra and the
Italian Ministero dell’Universita` e della Ricerca Scien-
tifica for financial support (40%).
OM020391L
(21) Balacco, G. J . Chem. Inf. Comput. Sci. 1994, 34, 1235.
(22) Marquardt, D. W. SIAM J . App. Math. 1963, 11, 431.