Attack of substituted alkynes on olefin palladium(O) derivatives of pyridylthioethers. The first kinetic study on the mechanism of formation of palladacyclopentadiene complexes

Article abstract of DOI:10.1021/om058036t

The formation of metallacyclopentadienyl derivatives was studied under controlled conditions, and the kinetics and mechanism of reactions between pyridylthioether olefin Pd(0) substrates and substituted alkynes of the type ZC=CZ (Z = COOMe, COOEt, COOt-Bu) leading to the corresponding palladacyclopentadienyl species were systematically investigated. In the case of less hindered ancillary ligands the attack of the alkyne forming a reactive monoalkyne intermediate was found to be the rate-determining step. In this respect the rates of reaction were discussed in terms of the substituent-induced basicity-of sulfur and nitrogen of the ancillary ligands. The associative nature of the attack was unequivocally established, and the formation of a transition state bearing a monodentate ancillary ligand was proposed. In the case of more hindered ancillary ligands a partially stabilized monoalkyne intermediate is formed irrespective of the olefin in the starting complex, and this species strongly influences the reaction progress. Formation of hexamethylmellitate under mild conditions is also observed.

Full text of DOI:10.1021/om058036t

Organometallics 2005, 24, 5537-5548
5537
Attack of Substituted Alkynes on Olefin Palladium(0)
Derivatives of Pyridylthioethers. The First Kinetic Study
on the Mechanism of Formation of
Palladacyclopentadiene Complexes
Luciano Canovese,*,† Fabiano Visentin,† Gavino Chessa,† Paolo Uguagliati,†
Carlo Levi,† and Alessandro Dolmella§
Dipartimento di Chimica, Universita` Ca’ Foscari, Calle Larga S. Marta 2137,
30123 Venezia, Italy, and Dipartimento di Scienze Farmaceutiche, Universita` di Padova,
Via F. Marzolo 5, 35131 Padova, Italy
Received June 21, 2005
The formation of metallacyclopentadienyl derivatives was studied under controlled
conditions, and the kinetics and mechanism of reactions between pyridylthioether olefin
Pd(0) substrates and substituted alkynes of the type ZCtCZ (Z ) COOMe, COOEt, COOt-
Bu) leading to the corresponding palladacyclopentadienyl species were systematically
investigated. In the case of less hindered ancillary ligands the attack of the alkyne forming
a reactive monoalkyne intermediate was found to be the rate-determining step. In this respect
the rates of reaction were discussed in terms of the substituent-induced basicity of sulfur
and nitrogen of the ancillary ligands. The associative nature of the attack was unequivocally
established, and the formation of a transition state bearing a monodentate ancillary ligand
was proposed. In the case of more hindered ancillary ligands a partially stabilized monoalkyne
intermediate is formed irrespective of the olefin in the starting complex, and this species
strongly influences the reaction progress. Formation of hexamethylmellitate under mild
conditions is also observed.
Introduction
cyclopentadienes by addition of the appropriate reac-
tants.4 It was soon noticed that reactions of Pd2DBA3
with DMA carried out in the presence of an ancillary
ligand (L) lead to the formation of palladacyclopenta-
diene complexes of the type [PdL2(CCOOMe)4]. How-
ever, the electronic features of ancillary ligands were
important; thus, in the presence of phosphines or
phosphites the derivatives containing π-coordinated
DMA were separated, but only the phosphine sub-
strate could add one further DMA molecule to give the
palladacyclopentadiene species, the complex [Pd(η2-
DMA)L2] (L ) phosphites) being unreactive. The influ-
ence of the π-acidity of ancillary ligands was apparent,
and cyclopalladate species only could be obtained when
essentially dative ancillary ligands were employed.5
Ishii and co-workers also demonstrated that the
complex [Pd(η2-ma)(bipy)] (ma ) maleic anhydride, bipy
) 2,2′-bipyridyl) can easily add two DMA molecules,
giving rise to the expected palladacyclopentadienyl
species,5 but, to the best of our knowledge, no other
Pd(0) substrates bearing different olefins or ancillary
ligands were studied in order to assess whether the
electronic and steric features of the chemical environ-
ment could influence the cyclometalation reaction path.
Palladium-catalyzed reactions involving unsaturated
molecules are well documented by the wealth of papers
that have appeared in recent years. For instance,
several annulation reactions1 and the synthesis of
conjugated dienes2 represent two important and widely
studied topics in which palladium substrates and alkynes
react through the key intermediacy of metallacyclic
complexes of palladium(II). The central role of these
compounds is well recognized, and the chemistry of
group 10 metallacycles was recently reviewed.3 How-
ever, despite their importance, no detailed mechanistic
studies on the formation of these substrates are avail-
able in the literature since they were first synthesized
by Maitlis in the 1970s by reacting Pd2DBA3 with
dimethylacetylene dicarboxylate (DMA) in a variety of
solvents to give the polymeric substrate [Pd(CCOOMe)4]n.
The latter can be converted into several different
derivatives including dienes, mellitates, and pallada-
* To whom correspondence should be addressed. E-mail: cano@
unive.it.
† Universita` Ca’ Foscari.
§ Universita` di Padova.
(1) (a) Schore, N. E. Chem. Rev. 1988, 88, 1081. (b) Cacchi, S. J.
Organomet. Chem. 1999, 576, 42. (c) Rubin, M.; Sromek, A. W.;
Gevorgyan V. Synlett. 2003, 15, 2265.
(4) (a) Moseley, K.; Maitlis, P. M. Chem. Commun. 1971, 1604. (b)
Roe, D. M.; Bailey, P. M.; Moseley, K.; Maitlis, P. M. J. Chem. Soc.,
Chem. Commun. 1972, 1273. (c) Moseley, K.; Maitlis, P. M. J. Chem.
Soc. Dalton Trans. 1974, 169. (d) Roe. D. M.; Calvo, C.; Krishnamachari
N.; Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1975, 125.
(5) (a) Ito, T. S.; Hasegawa, S.; Takahashi, Y.; Ishii, Y. J. Organomet.
Chem. 1974, 73, 401. (b) Susuki, H.; Itoh, K. Ishii, Y.; Simon, K.; Ibers
J. A. J. Am. Chem. Soc. 1976, 26, 8494.
(2) (a) van Belzen, R.; Hoffman, H.; Elsevier, C. J. Angew. Chem.,
Int. Ed. Engl. 1997, 36,1743. (b) van Belzen, R.; Klein, R. A.; Kooijman,
H.; Veldman, N.; Spek, A. L.; Elsevier, C. J. Organometallics 1998,
17, 1812. (c) van Belzen, R.; Elsevier, C. J.; Dedieu, A.; Veldman, N.;
Spek, A. L. Organometallics 2003, 22, 722.
(3) Campora, J.; Palma, P.; Carmona, E. Coord. Chem. Rev. 1999,
193-195, 207.
10.1021/om058036t CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/12/2005

5538 Organometallics, Vol. 24, No. 23, 2005
Canovese et al.
Scheme 1
On the basis of the well-established experience ac-
quired in our laboratory about the steric and electronic
characteristics of Pd(0) substrates carefully tuned by
variously substituted bi- and terdentate pyridylthio-
ethers and bearing different olefins6 we decided to
undertake a detailed study on the reactivity of the
complexes reported in Scheme 1 with respect to the
cyclometalation induced by DMA according to reaction
1, with the awareness that no previous kinetic studies
were carried out nor have mixed donor ligands been
hitherto employed:
with Pd(0) olefin complexes bearing phospho- and
thioquinolines as mixed donor bidentate ligands.
Results and Discussion
General Considerations. Among all the Pd(0) olefin
complexes studied in the present paper, only the DPPQ-
Me and TMQ-Me derivatives represent novel substrates
that have never been synthesized and described here-
tofore. Therefore, only the solution rearrangements of
these species will be discussed, the characterization and
the fluxional behavior of all other Pd(0) derivatives
being widely dealt with elsewhere.6,7
Pd(0) Olefin Complexes. The complexes [Pd(η2-ol)-
(DPPQ-Me)] (ol ) tmetc, ma) and [Pd(η2-tmetc)(TMQ-
Me)] were obtained by addition of the ancillary ligand
(DPPQ-Me, TMQ-Me) and of the appropriate olefin
to an anhydrous acetone solution of the precursor
Pd2DBA3‚CHCl3 under inert atmosphere (Ar). The
formation of the complexes was monitored by means of
1H and 13C NMR since the signals of the olefin and of
the ancillary ligands shift upfield and downfield respec-
tively upon coordination. In any case these complexes
[Pd(η2-ol)(L-L′)] + 2 ZOOCCtCCOOZ f
[Pd(C4(COOZ)4)(L-L′)] + ol (1)
With the aim of clarifying the intimate mechanism
governing this reaction and possibly establishing the
conditions that allow the accumulation of a π-coordi-
nated alkyne intermediate, we also studied reaction 1
(6) (a) Canovese, L.; Visentin, F.; Uguagliati, P.; Crociani, B. J. Chem
Soc., Dalton Trans. 1996, 1921. (b) Chessa, G.; Canovese, L.; Visentin,
F.; Uguagliati, P. Inorg. Chem. Commun. 1999, 2, 607. (c) Canovese,
L.; Visentin, F.; Chessa, G.; Uguagliati, P.; Dolmella, A. J. Organomet.
Chem. 2000, 601, 1. (d) Canovese, L.; Visentin, F.; Chessa, G.;
Gardenal, G.; Uguagliati, P. J. Organomet. Chem. 2001, 622, 155. (e)
Canovese, L.; Chessa, G.; Santo, C.; Visentin, F.; Uguagliati, P.
Organometallics 2002, 21, 4342.
(7) Canovese, L.; Lucchini, V.; Santo, C.; Visentin, F.; Zambon, A.
J. Organomet. Chem. 2002, 642, 58.

Formation of Palladacyclopentadiene Complexes
Organometallics, Vol. 24, No. 23, 2005 5539
behave differently in solution than their pyridylthio-
ether analogues. The enhanced rigidity of the DPPQ-
Me and TMQ-Me ancillary ligand skeleton with respect
to the flexibly joined structure of pyridylthioethers
hampers the apparent olefin rotation that is usually
observed in the case of complexes bearing the latter as
ancillary ligand. It is well known, in fact, that such a
movement is principally due to rearrangement of the
ancillary ligand (Pd-N or Pd-S cleavage and subse-
quent recombination) rather than to an effective olefin
rotation, especially in the case of the tmtc moiety.6,7 The
1H NMR analysis of the planar DPPQ-Me derivatives
in the presence of an apparent olefin rotation would give
rise to a symmetric spectrum for the olefin protons. At
variance, the spectra clearly indicate the existence of a
tightly coordinated olefin in an unsymmetrical environ-
ment. This situation may arise only from the presence
of olefin protons (or substituents) lying cis or trans to
phosphorus, as can be further deduced from the P-H
and H-H coupling constants (see Experimental Sec-
tion). The case of the complex [Pd(η2-tmetc)(TMQ-Me)]
differs from those of the DPPQ-Me substrates. This
complex, in fact, undergoes a fluxional rearrangement
that could be interpreted on the basis of sulfur absolute
configuration inversion. The olefin COOCH3 protons
yield a couple of singlets (3.73, 3.75 ppm) which do not
collapse even at 183 K. In our experience this behavior
can be traced back to the low-energy sulfur inversion
process that is often operative even at the lowest
temperature usually achievable.6,7
Palladacyclopentadienyl Complexes. The pallada-
cyclopentadienyl complexes were obtained under con-
trolled atmosphere (Ar) by adding a slight excess of the
polymeric precursor [Pd(C4(COOZ)4)]n (Z ) Me, Et, t-Bu)
to a solution of the ligand L-L′ in anhydrous acetone
(see Scheme 1); the complexes [Pd(C4(COOZ)4)]n (Z )
Et, t-Bu) represent novel species that have never been
synthesized so far. The same substrates could otherwise
be obtained by reacting the Pd(0) olefin complex bearing
the appropriate ancillary ligand L-L′ with the activated
alkyne ZCtCZ (Z ) Me, Et, t-Bu) in anhydrous CH2Cl2.
In both cases the products were coincident, as shown
by the superimposition of the 1H, 13C NMR and IR
spectra of the cyclopalladate species independently
synthesized.
The palladacyclopentadienyl complexes, like their
Pd(0) olefin precursors, undergo two coexisting different
fluxional rearrangements, i.e., ancillary ligand rotation
and sulfur absolute configuration inversion. The latter
phenomenon, which represents the mechanism requir-
ing less energy, can be easily revealed in the case of
the pyridylthioether derivatives by means of the 1H
DNMR technique. As a matter of fact, the diastereotopic
CH2S protons at low temperature upon “freezing” of the
sulfur inversion movement produce an AB system in the
interval 3.5-4.5 ppm. The substituents R at sulfur and
R′ in position 6 of the pyridine ring play an important
role in this respect. The R′ group (R′ ) Me, Cl) induces
distortion of the Pd-N bond with concomitant weaken-
ing of the bond itself, disfavoring sulfur inversion since
the strengthening of the Pd-S bond as a synergic
response occurs with consequent lowering of the sulfur
inversion rate. An additional effect is generated by the
R substituent at sulfur. As a matter of fact the stereo-
electronic characteristics of these groups influence the
Pd-S bond, which can be strengthened when an electron-
donor group increases the basicity of sulfur. Thus the
rate of sulfur inversion as a function of the stereoelec-
tronic characteristics of the substituent R follows the
order Ph > Me > t-Bu independently of the nature of
R′.
In the case of the complex [Pd(C4(COOZ)4)(TMQ-Me)],
owing to the planarity of the metallacycle and the lack
of an internal probe such as the methylene protons, no
sulfur absolute configuration inversion is detected. This
species however undergoes Pd-N (or Pd-S) bond cleav-
age and recombination analogously to its Pd(0) olefin
complexes (vide supra). The rearrangement is clearly
indicated by the appearance in the low-temperature
1
(233 K) H NMR spectrum of four distinct singlets in
the interval 3.25-4.00 ppm ascribable to the COOCH3
protons “frozen” to the right or to the left side and in
near or in far position with respect to the palladium
atom. At RT the two surviving observed singlets were
assigned to the COOCH3 protons lying near (broad
singlet) or far (sharp singlet) from palladium (see
Experimental Section). Similar behavior is noticed in
the case of all the pyridylthioether derivatives that
undergo similar fluxional rearrangements. The main
difference among these substrates comes again from the
presence of a substituent in position 6 of the pyridine
ring (R′ ) Me, Cl). The already observed weakening of
the Pd-N bond, in the case of the corresponding Pd(0)
complexes, induces a considerable increase in the ligand
fluxionality, thereby confirming the mechanistic picture
proposed.6,7 In this case, presumably, the strengthened
Pd-S bond acts as a pivot in the rearrangement process.
Again, the sulfur substituents R play a secondary but
noticeable role in the complexes bearing unsubstituted
pyridine (R′ ) H); thus, an induced increase of sulfur
basicity slows down the fluxional rearrangement.
The formation of complexes of the type [Pd(C4(COOZ)4)-
(DPPQ-Me)] (Z ) Me, Et, t-Bu) is duly confirmed by the
1H and 31P NMR spectra since marked downfield shifts
of the phosphorus (∆δ g 38 ppm) and quinoline-CH3 (∆δ
g 0.32 ppm) signals are detected upon coordination. At
variance with the other Pd(II) cyclometalated complexes
described above, no fluxional rearrangements at RT are
observed for these substrates in their corresponding 1H
NMR spectra; thus, Z protons (Z ) Me, Et, t-Bu) give
rise to four distinguishable groups of signals in any case.
The palladacyclopentadienyl complexes bearing the
potentially terdentate ligands S-N-S(R) (R ) Me, t-Bu,
Ph) were synthesized analogously to the other previ-
ously described species and identified by NMR tech-
nique. The RT 1H NMR spectra of these substrates
display only one broad singlet attributable to the CH2-S
protons (the signal of the S-N-S(t-Bu) derivatives being
more broadened than those of the phenyl and methyl
species). Moreover, the signals pertaining to the two
sulfur substituents R are coincident irrespectively of
their nature. The COOCH3 protons resonate as two
singlets attributable to the protons belonging to the
groups near to or far from the palladium center,
respectively. This strongly indicates the alternating
coordination of the sulfur atoms lying on both wings of
the potentially terdentate ligand. This rearrangement
represents a quite usual phenomenon when terdentate

5540 Organometallics, Vol. 24, No. 23, 2005
Canovese et al.
pyridylthioeter ligands are used in palladium complexes
bearing two coordination sites already occupied by
nucleophiles.6e,8
On decreasing the temperature, the signals attribut-
able to COOCH3 protons differentiate, showing in the
case of the complex [Pd(C4(COOMe)4)(SNS(t-Bu))] at 213
K four separated singlets at 3.21, 3.58, 3.59, and 3.66
ppm, but only one S-C(CH3)3 signal at 1.22 ppm and
only one AB system ascribable to endocyclic CH2-S
protons (integrating 4H) at 3.95 and 4.43 ppm (J ) 14.6
Hz). No singlets (or other signals) belonging to the
CH2-S protons of the uncoordinated wing are detectable.
Moreover, all the palladacyclopentadienyl SNS(R) com-
plexes behave similarly since only small differences in
temperature separate the phenomena in the case of
differently substituted complexes. This behavior is not
unprecedented, and in the case of the [PdCl(Me)(SNS-
(t-Bu))] derivative an analogous fluxionality was ob-
served.8b In this case, however, we suggest a rearrange-
ment that takes into account a nitrogen-centered T-
shaped intermediate.9 The pyridine nitrogen acting as
a pivot in a roundabout movement allows the fast
alternate coordination of the sulfur atoms. The cyclo-
pentadienyl carbon trans to nitrogen never changes its
position. Neither does the carbon trans to sulfur, the
two interchanging rings being equivalent. The sulfur
absolute configuration inversion does not happen since
some sort of residual coordination is probably operative.
An alternative explanation would take into account the
formation of a symmetric pentacoordinate species bear-
ing both sulfur substituents on the same side with
respect to the complex main coordination plane and the
cyclopentadienyl moiety perpendicular to the plane
itself, which however evolves into an open structure
upon precipitation at low temperature (vide post).
X-ray Crystal Structures. The molecular structures
of the neutral complexes 1 ((2,6-bis((tert-butylthio)-
methyl)pyridine)(1,2,3,4-tetrakis(methoxycarbonyl)-
buta-1,3-diene-1,4-diyl)palladium) ([Pd(C4(COOMe)4)-
(SNS(t-Bu))]) and 2 ((2-((tert-butylthio)methyl)pyridine)-
(1,2,3,4-tetrakis(methoxycarbonyl)buta-1,3-diene-1,4-
diyl)palladium) ([Pd(C4(COOMe)4)(HNSt-Bu)]), together
with the numbering scheme used, are shown as ORTEP10
drawings in Figures 1 and 2, respectively. Both com-
plexes show the metal at the center of a distorted square
planar environment. The distortion is toward a tetra-
hedral arrangement. However, for simplicity we will
refer to the Pd main coordination plane as the basal or
equatorial plane, although this is somewhat inadequate.
In 1, the atoms in the basal plane, other than Pd, are
N, S(1), C(16), and C(19), and they deviate from the
plane by 0.23, -0.22, 0.26, and -0.27 Å, respectively.
In 2, the set is made up by the atoms N, S, C(11), and
C(14); they deviate from the equatorial plane by 0.16,
-0.15, -0.18, and 0.17 Å, respectively. Also the Pd
atoms lie off the main coordination plane, by 0.20 in 1
and 0.15 Å in 2.
Figure 1. Molecular structure of complex 1. Thermal
ellipsoids are at the 40% probability level; hydrogen atoms
have been omitted for clarity.
Figure 2. Molecular structure of complex 2. The figure
settings are as for 1.
The above data indicate that 1 is more tetrahedrally
distorted than 2. The idea is confirmed by looking at
the dihedral angle made by the triangles N-Pd-S(1)
and C(16)-Pd-C(19) in 1 (24.8°) and by the triangles
N-Pd-S and C(11)-Pd-C(14) in 2 (17.1°). Other
indications are given by the departure of the angles
S(1)-Pd-C(19) in 1 (156.0(1)°) and S-Pd-C(11) in 2
(163.0(1)°) from the ideal 180°, as well as by the
deviation of the bite angles N-Pd-S(1) and C(16)-Pd-
C(19) (81.9(1)° and 78.7(1)°) in 1 and N-Pd-S and
C(11)-Pd-C(14) (82.9(1)° and 79.4(2)°) in 2 from the
expected value of 90° for a regular square planar
geometry.
The chelate ligands form, upon coordination, two five-
membered rings in both 1 and 2, whose overall main
features are similar. In 1, the atoms participating in
the chelate pyridine ring, other than Pd, are N, C(1),
C(6), and S(1); in 2, the corresponding atoms are N, C(5),
C(6), and S. In both complexes this ring assumes a twist-
envelope (half-chair, C2) arrangement, with the sulfur
atom “at the flap”, outside the mean plane defined by
the remaining four atoms. In 1, the atoms in this plane
(8) (a) Canovese, L.; Visentin, F.; Uguagliati, P.; Lucchini, V.;
Bandoli, G. Inorg. Chim. Acta 1998, 277, 247. (b) Canovese, L.;
Visentin, F.; Chessa, G.; Uguagliati, P.; Santo, C.; Bandoli, G.; Maini,
L. Organometallics 2003, 22, 3230.
(9) (a) Thorn, D. L.; Hoffmann, R. J. Am. Chem. Soc. 1978, 100,
2079. (b) Gogoll, A.; O¨ rnebro, J.; Grennberg, H.; Ba¨ckwall, J. J. Am.
Chem. Soc. 1994, 116, 3632. (c) Albinati, A.; Kunz, R. W.; Ammann,
C. J.; Pregosin, P. S. Organometallics 1991, 10, 1800.
(10) Johnson, C. K. ORTEP, Report ORNL-5138; Oak Ridge Na-
tional Laboratory: Oak Ridge, TN, 1976.

Formation of Palladacyclopentadiene Complexes
Organometallics, Vol. 24, No. 23, 2005 5541
Scheme 2
deviate up to 0.07 Å, with the sulfur off by 1.00 Å; in 2,
the atoms deviate up to 0.02 Å, with the sulfur off by
0.86 Å. The five-membered ring planes Pd-N-C(1)-
C(6)-S(1) (in 1) and Pd-N-C(5)-C(6)-S (in 2) make
dihedral angles of 26.9° and 20.5°, respectively, with the
main coordination plane. As for the ring formed by the
butadienyl ligand, the atoms participating in it, besides
the metal center, are C(16), C(17), C(18), C(19) and
C(11), C(12), C(13), C(14) in 1 and 2, respectively. In
both complexes these rings are virtually planar, with
deviations from the mean ring plane limited to 0.03 Å
in 1 and 0.05 Å in 2. In complex 1, the plane of this
ring makes dihedral angles of 14.7° and 39.1° with the
basal plane and the Pd-N-C(1)-C(6)-S(1) plane,
respectively. In complex 2, the corresponding angles are
11.4° and 31.1°.
examples of mononuclear neutral square planar Pd(II)
complexes showing the Npyr-S-C-C donor set.
Data indicate that the Pd-S bond distances in 1 and
2 are the longest in this group of molecules. This is due,
in our opinion, to the stronger trans influence of the
negatively charged C σ-bonded ligand over the sulfur
atom. In fact, in the other molecules examined the sulfur
donor is faced either by a pyridine nitrogen12-14 or by a
chloride,15-17 both of them softer bases. In 1 and 2 also
the pyridine nitrogen atom is faced by a negatively
charged σ-bonded C ligand. Thus, the Pd-N distances
are longer than those found in the complexes where the
nitrogen is trans to sulfur (a softer base),12-14 yet shorter
than those found in the other known complexes where
the nitrogen is trans to a negatively charged C atom.16,17
The Pd-C distances (see above) show a dual behavior.
In fact, the shortest Pd-C distances in 1 and 2 are
similar to those found in the other complexes where the
σ-bonded C ligand belongs to an olefin moiety,12-14,17
whereas the longest Pd-C bonds are similar to those
found in the complexes where the C donor atom belongs
to a methide group.15,16
The orientation of the four C-C(dO)-OCH3 residues
in the butadienyl ligand of the two complexes also
deserves some comments. In 1, the residues I-IV
branch from C(16), C(17), C(18), and C(19), respectively,
and define angles of 91.4°, 14.3°, 99.8°, and 31.0°,
respectively, with the main coordination plane. The
reciprocal orientation of the residues is such that the
mean plane of residue II is nearly orthogonal to those
of residue I (89.5°) and III (87.9°). In 2, the residues
I-IV branch from C(11), C(12), C(13), and C(14),
respectively, and define angles of 74.7°, 37.2°, 26.1°, and
72.8°, respectively, with the basal plane. As for their
reciprocal orientation, the mean plane of residue IV is
roughly perpendicular to that of residue II (71.9°) and
almost coplanar to that of residue I (18.1°).
With respect to bond distances, they look similar
overall in 1 and 2. The Pd-S distance in 1 (2.394(1) Å)
is ca. 0.02 Å longer than in 2 (2.369(1) Å), whereas the
Pd-N distances are alike (2.126(2) and 2.126(4) Å in 1
and 2, respectively). On the contrary, both molecules
show one Pd-C distance shorter than the other (1.997(3),
2.040(2) Å in 1 and 2.013(4), 2.042(4) Å in 2). The
shortest distance is always the one where the σ-bonded
carbon is trans to nitrogen; besides, the shortest Pd-C
distance in 1 is also ca. 0.02 Å shorter than the shortest
Pd-C distance in 2.
Kinetic and Mechanistic Study. The oxidative
coupling of DMA promoted by the [Pd(η2-ol)(RN-SR′)]
derivatives (ol ) ma, tmetc; R ) H, Cl; R′ ) Me, Ph,
1
t-Bu) was studied by H NMR technique or by UV/vis
spectrophotometry under pseudo-first-order conditions.
In this respect, to 3 mL of prethermostated solution of
the complex under study ([Pd]0 )10-4 mol dm-3 in
freshly distilled CHCl3) was added a microaliquot of
DMA solution ([DMA]0 g 20[Pd]0). In the literature,
some qualitative studies were carried out using ma
derivatives;5a unfortunately in our case the ma com-
plexes upon DMA addition give rise to a very fast
reaction leading to the cyclopalladate species. Con-
versely, when tmetc derivatives are studied, the ab-
sorbance change associated with the reaction in Scheme
2 is generally described by the following monoexponen-
tial expression:
To compare our data with those already published,
we performed a search in the Cambridge Crystal-
lographic Database11 looking for mononuclear, neutral
square planar Pd(II) complexes showing the Npyr-S-
C-C/Cl donor set (Npyr ) pyridine nitrogen). The search
returned seven structures.12-16
A comparison with the present results as well as with
other results from our group is feasible.17 To the best
of our knowledge, 1 and 2 are the first reported
obst
At ) A∞ + (A0 - A∞)e-k
(2)
(11) Allen, F. H. Acta Crystallogr. 2002, B58, 380; Cambridge
Structural Database (Version 5.25 of November 2003 + 3 updates).
(12) Spencer, J.; Pfeffer, M.; DeCian, A.; Fischer, J. J. Org. Chem.
1995, 60, 1005 (entry code SUPMIZ).
(13) Spencer, J.; Pfeffer, M.; Kyritsakas, N.; Fischer, J. Organo-
metallics 1995, 14, 2214 (entry codes ZAFCUE, ZAFDEP).
(14) Dupont, J.; Basso, N. R.; Meneghetti, M. R.; Konrath, R. A.;
Burrow, R.; Horner, M. Organometallics 1997, 16, 2386 (entry code
RUQVOO).
(15) Canovese, L.; Visentin, F.; Chessa, G.; Uguagliati, P.; Bandoli,
G. Organometallics 2000, 19, 1461 (entry codes XEKVAK, XEKVEO).
(16) Canovese, L.; Visentin, F.; Chessa, G.; Santo, C.; Uguagliati,
P.; Bandoli, G. J. Organomet. Chem. 2002, 650, 43 (entry code
HUGGAR).
(17) Canovese, L.; Visentin, F.; Chessa, G.; Uguagliati, P.; Santo,
C.; Dolmella, A. Organometallics 2005, 24, 3297.
where At, A , and A0 represent the absorbance of the
reaction mixture at time t, at the end, and at the
beginning of the reaction, kobs being the observed
pseudo-first-order rate constant. In this respect the use
of this home-synthesized bulky olefin slows the reaction
rate, allowing a detailed study of the oxidative DMA
coupling on Pd(0) substrates. Linear regression of the
ensuing kobs vs alkyne concentration for each complex
gives rise to the second-order rate constants listed in
Table 1.

5542 Organometallics, Vol. 24, No. 23, 2005
Canovese et al.
Table 1. Second-Order Rate Constants (mol-1 dm3
s-1) for the Reaction of the Complexes [
Pd(η2-tmetc)(RN-SR′)] with DMA in CHCl3 at 25 °C
R ) H
R ) Me
R ) Cl
R′ ) Me
R′ ) Ph
R′ ) t-Bu
0.20 ( 0.02
0.137 ( 0.005
0.015 ( 0.001
0.09 ( 0.02
0.114 ( 0.005
10.5 ( 0.5
10.8 ( 0.5
2.59 ( 0.05
Table 2. Second-Order Rate Constants (mol-1 dm3
s-1) for the Reaction of the Complex
[Pd(η2-tmetc)(HN-SMe)] with ZCtCZ in CHCl3
at 25 °C
Z ) COOMe
Z ) COOEt
Z ) COOt-Bu
0.006 ( 0.001
0.199 ( 0.002
0.088 ( 0.002
The monoexponential absorbance change, the failure
to observe any intermediate (1H NMR check), and the
linear dependence of kobs on the concentration of the
alkyne suggest a steady state mechanism in which a
reactive Pd(0) monoalkyne intermediate species reacts
immediately to give the reaction product. In this respect,
the second-order rate constants experimentally deter-
mined are referred to the first alkyne-dependent rate-
determining stage (Scheme 2). This reaction profile is
also maintained if the bulkiness of the ester group Z on
the alkyne moiety is increased. In Table 2 the second-
order rate constants as a function of the alkyne sub-
stituent Z group are reported in the case of the complex
[Pd(η2-tmetc)(HN-SMe)].
The associative nature of the first alkyne attack is
confirmed by the correlation of log k2 vs the front strain
steric parameter S18 (Figure 3) and by the activation
parameters determined by the reparametrized Eyring
plot19 for the same complex reacting with DMA in the
temperature range 288-313 K. The ensuing activation
parameters are ∆Hq ) 13 ( 2 kJ mol-1 and ∆Sq ) -19
( 7 J mol-1 K-1. These values are in line with those
found in associative olefin exchange reactions among
Pd(0) derivatives bearing pyridylthioether ligands.6
From the data in Tables 1 and 2, the lowering of the
rate constants on increasing the steric demand of the
ancillary ligand and entering alkyne is evident. How-
ever, it might be noticed that the substituents R on the
pyridine ring affect the reaction rates to a different
extent, and thus the ensuing reactivity cannot be easily
traced back to the substituent bulkiness. As a matter
of fact, the reactivity hardly changes on going from
complexes bearing R′ ) H to those with R′ ) Me (a
similar conclusion is drawn when the Pd(0) pyridyl-
thioether olefin substrates are compared in olefin
exchange reactions, since also in these reactions the
pyridine substituent (H vs Me) hardly affects the overall
reactivity6c-e). Conversely, it has been shown15-17 that
distortion due to the pyridine substituent (R′ ) Me, Cl)
strongly influences the reactivity toward insertion of
unsaturated molecules in Pd(II) pyridylthioether de-
rivatives, chlorine being the most effective for electronic
reasons. In the present case, as can be seen in Table 1,
the presence of a chlorine group in position 6 of the
pyridine ring, having a hindrance analogous to that of
the methyl group, imparts a reactivity enhanced by
about 2 orders of magnitude to the corresponding
Figure 3. Plot of log k2 vs front strain parameters (ref
17).
derivatives. This remarkable behavior is probably the
net result between an unfavorable steric hindrance and
an overwhelming tendency to chelate ring opening due
to a lowered basicity of the chlorine-substituted pyri-
dine. This will provide for an easier entry of the first
alkyne into the coordination sphere of the transition
state carrying the bulky leaving olefin and the incoming
alkyne simultaneously bound to palladium.
For the sake of completeness the reactivity of sub-
strates bearing a rigid ancillary ligand was investigated,
and in this respect [Pd(η2-tmetc)(TMQ-Me)] reacts
slowly with DMA (rate constant ) 0.052 ( 0.001 mol-1
dm3 s-1). Since the complex [Pd(η2-tmetc)(TMQ-Me)] is
moderately less reactive than [Pd(η2-tmetc)(MeN-SMe)],
one might advance the hypothesis that rigidity of the
TMQ-Me ligand skeleton disfavors the crowded transi-
tion state determined by the incoming DMA. It is
moreover noteworthy that the exchange of a sulfur
donor with phosphorus renders the corresponding [Pd(η2-
tmetc)(DPPQ-Me)] complex almost unreactive.
A further indication about the associative nature of
the first alkyne attack is represented by the high
reaction rates found in the case of complexes bearing
scarcely hindered olefins. The complexes [Pd(η2-ma)-
(R′N-SR)] (R′ ) H, Me, Cl; R ) Me, Ph) indeed react
immediately with DMA, and in this respect the associa-
tive alkyne attack is in line with previous findings on
olefin exchange reactions that were extensively studied
so far.6
Complexes with MeN-St-Bu as Ancillary Ligand.
Apparently the monoalkyne intermediate is a very
reactive species. It is however known that similar
monoalkyne species could be stabilized and obtained by
5a
increasing the π-acidity and/or the bulkiness of the
ancillary ligand.20 In this respect we chose to study the
kinetics of addition of DMA to the complex [Pd(η2-
tmetc)(MeN-St-Bu)] in the hope of isolating the mono-
alkyne intermediate or alternatively to gain further
information on its mechanistic behavior. As expected,
the spectral absorbance changes detected by UV/vis
technique do not obey a monoexponential law, the trend
rather suggesting a buildup of an intermediate. Accord-
ingly, analysis of the related 1H NMR spectra (see
Figure 4) shows the accumulation of an intermediate
(18) Beckhaus, H.-D. Angew. Chem., Int. Ed. Engl. 1978, 17, 593.
(19) Uguagliati, P.; Michelin, R. A.; Belluco, U.; Ros, R. J. Organo-
met. Chem. 1979, 169, 115.
(20) tom Dieck, H.; Munz, C.; Mu¨ller, C. J. Organomet. Chem. 1990,
384, 243.

Formation of Palladacyclopentadiene Complexes
Organometallics, Vol. 24, No. 23, 2005 5543
Figure 4. Time-dependent 1H NMR spectra for the reaction between [Pd(η2-tmetc)(MeN-St-Bu)] and DMA: (a) spectrum
of an authentic sample of [Pd(η2-tmetc)(MeN-St-Bu)], t ) 0; (b) t ) 8 min after DMA addition; t ) 26 min after DMA
#
addition; (d) spectrum of an authentic sample of [Pd(C4(COOMe)4)(MeN-St-Bu)]. ) [Pd(η2-DMA)(MeN-St-Bu)].
species characterized by the signals pertaining to a
pyridine ring very near to those of the starting substrate
in the interval 7.15-7.75 ppm. Signals ascribable to
CH2-S, Pyr-CH3, and C(CH3)3 were also detected as one
broad and two sharp singlets at 4.22, 2.87, and 1.41
ppm, respectively. The time-dependent concentration of
this species can be described by the unsymmetrical bell-
shaped profile typical of an intermediate species. More-
over the amount of free tmetc olefin matches with the
sum of the concentrations of the intermediate and the
final compounds. No coordinated DMA is however
detected since its signal falls in a very crowded spectral
region, and moreover, similarly to the analogous Pd(0)
olefin derivatives, this complex undergoes fast exchange
between the coordinated and the uncoordinated unsat-
urated moiety.
tion changes of the starting, the intermediate, and the
final cyclopalladate product. On the other hand, the
plausible model involving two slow equilibria was ruled
out because the cyclopalladate complex is unreactive
even in the presence of a large excess of tmetc. Careful
analysis of the spectra suggests that the monoalkyne
compound represents in this case the quite stable
product of an alternative route rather than a reactive
intermediate. As a matter of fact, its accumulation is
favored by the steric hindrance of the ancillary ligand,
which prevents to some extent the attack of the free
alkyne. Thus, the cyclopalladate becomes the result of
the multistep mechanism shown in Scheme 3, in which
a simplified reaction path used as a mechanistic model
is reported. The undetected reactive intermediate I is
likely to be a mixed olefin-alkyne Pd(0) species.
The analysis of concentration profiles does not allow
a simple interpretation. The simple model based on a
slow equilibrium reaction giving rise to a monoalkyne
intermediate followed by an irreversible reaction does
not fit the 1H NMR experimentally detected concentra-
The fit of the time-dependent concentrations recorded
1
from H NMR data to time according to the proposed
mechanism is shown in the Figure 5. The fit of the
concentration profiles for this complex system, while
being fairly good, is affected by high parameter correla-

5544 Organometallics, Vol. 24, No. 23, 2005
Canovese et al.
Scheme 3
tion coefficients, which are reflected by high standard
errors of estimates for the fitted parameters. Neverthe-
less, it is noteworthy that the fitted kF value (0.024 (
0.001 mol-1 dm3 s-1), which is the most accurately
determined parameter, is in substantial accord with the
second-order rate constants reported in Table 1.
Figure 5. Fit of NMR-determined concentration profiles
The reaction between the complex [Pd(η2-ma)(MeN-
StBu)] and DMA would induce the accumulation of the
monoalkyne intermediate irrespectively of the leaving
olefin, since only the bulkiness of the MeN-StBu ligand
forces the reaction toward the production of such
derivative. The 1H NMR experiment unequivocally
shows indirectly the accumulation of the intermediate.
As a matter of fact, the free ma, which is detected as a
broad singlet at ≈7 ppm, originated by displacement
from the [Pd(η2-ma)(MeN-StBu)] complex by the alkyne
attack at the beginning of the reaction, is in large excess
with respect to the final cyclopalladate product, which
is present in traces. This is a strong indication of the
fast accumulation of an intermediate which subse-
quently reacts slowly to give the product. The interme-
diate is not detected since free ma exchanges rapidly
with the alkyne of the monocoordinated alkyne inter-
mediate. The free ma also exchanges with the coordi-
nated olefin of the starting complex, as can be seen by
the small shifts and the general broadening of all the
signals. The equilibrium constant KE related to the
displacement of ma by DMA was estimated by NMR and
confirmed by spectrophotometric titration (KE ) 0.0140
( 0.003). Figure 6 reports the absorbance data vs the
concentration of the titrant DMA and the corresponding
fit. Pd(0) gives rise with ma to more stable complexes
than those bearing tmetc. However, owing to its reduced
steric hindrance, ma itself is rapidly displaced by the
entering unsaturated moiety. This result parallels those
found in the former studies dealing with olefin ex-
changes in Pd(0) olefin derivatives.6
according to the mechanism in Scheme 3.
Figure 6. Spectrophotometric determination of equilib-
rium constant KE for the reaction of [Pd(η2-ma)(MeN-StBu)]
with DMA in CHCl3 at 25 °C. Fit of absorbance vs [DMA]
at λ ) 287 nm.
at 3.87 ppm in CDCl3, separated after complete pre-
cipitation of the cyclometalate complexes from the
mother liquor by HPLC and characterized by mass
spectrometry. Its mechanism of formation appears to
be rather complicated, since, contrary to our expectation,
the stable cyclopalladate substrate does not react with
one further alkyne molecule to give the mellitate under
mild conditions.
The fast formation of the intermediate does not allow
fast formation of the cyclopalladate product since the
rate of reaction is lowered by the formation of the same
scarcely reactive monoalkyne derivative obtained in the
case of [Pd(η2-tmetc)(MeN-St-Bu)]. Moreover, the very
small absorbance change associated with product for-
mation hampers any attempt at precise determination
of the kinetic constants by spectrophotometric technique
under pre-equilibrium conditions.
Formation of Hexamethylmellitate. The NMR
spectra obtained under mild experimental conditions
and at low DMA/complex ratios show the formation of
hexamethylmellitate as a side product of the quantita-
tive production of cyclopalladate. Such a symmetric
compound was identified from its characteristic singlet
Moreover, preliminary investigation shows that mel-
litate production is not monotonically dependent on
alkyne concentration. Since the palladium-mediated
synthesis of this species usually requires long time, high
temperature, and high alkyne excess,4c we intend to
investigate exhaustively its mechanism of formation in
a forthcoming study.
Experimental Section
Solvents and Reagents. Acetone and CH2Cl2 were distilled
over CaH2 and 4 Å molecular sieves, respectively, under inert
atmosphere (Ar). Chloroform was distilled and stored over
silver foil. All the other chemicals were commercially available
grade products unless otherwise stated.

Formation of Palladacyclopentadiene Complexes
Organometallics, Vol. 24, No. 23, 2005 5545
1
IR, NMR, and UV-Vis Measurements. The IR and H
and 13C{lH} NMR spectra were recorded on a Perkin-Elmer
Spectrum One spectrophotometer and on a Bruker 300 Avance
spectrometer, respectively. The proton and carbon assign-
ment was performed by 1H-13C-HMQC and -HMBC experi-
ments. UV-vis spectra were taken on a Perkin-Elmer Lambda
40 spectrophotometer equipped with a Perkin-Elmer PTP6
(Peltier temperature programmer) apparatus.
X-ray Diffraction Analysis. Crystals of 1 and 2 suitable
for X-ray analysis were mounted on the top of a glass fiber,
coated with epoxy resin, and placed on the goniometer head
of a STADI 4 CCD diffractometer. Data were collected at room
temperature using graphite-monochromated Mo KR radiation
(λ ) 0.71073 Å) and corrected for Lorentz and polarization
effects as well as for absorption.
Water (50 mL) was then added, and the reaction products were
extracted by Et2O (50 mL). The organic solution was dried over
MgSO4 (6 h), filtered, and dried under vacuum. The purifica-
tion of the crude product was achieved by flash chromatogra-
phy through a silica column with CH2Cl2 as eluent. Concen-
tration under vacuum of the eluate yields 1.005 g (5.3 mmol)
of the pale yellow compound. Yield: 59% IR (KBr pellet): νCd
N 1564.9 cm-1. 1H NMR (CDCl3, T ) 298 K, ppm): thiomethyl
protons, δ, 2.58 (s, 3H, S-CH3), methyl protons 2.79 (s, 3H,
Qui-CH3), quinoline protons 7.32 (d, 1H, H3qui, J ) 8.4 Hz),
7.37 (dd, 1H, H7qui, J ) 7.3; 1.5 Hz), 7.44 (t, 1H, H6qui, J ) 7.6
Hz), 7.53 (dd, 1H, H5qui, J ) 7.9; 1.5 Hz), 8.02 (d, 1H, H4qui, J
) 8.4 Hz). 13C NMR (CDCl3, T ) 298 K, ppm): quinoline
carbons, δ, 158.6 (C2qui), 122.9 (C3qui), 136.6 (C4qui), 126.3 (C5qui),
126.1 (C6qui), 123.0 (C7qui), 139.5 (C8qui), 145.4 (C9qui), 126.5
(C10qui), thiomethyl carbons 14.6 (qui-S-CH3), methyl carbons
25.8 (qui-CH3).
The two structures were solved by the heavy-atom methods
using the SHELXTL NT21 computer program and refined on
F2 by standard full-matrix least-squares with SHELXL-97.22
All non-hydrogen atoms were refined anisotropically; the
hydrogen atoms were placed in calculated positions and refined
as a riding model. A summary of crystal and refinement data
is reported in Table 1Si; Table 2Si lists selected bond distances
and angles of the two complexes.
Preliminary Studies and Kinetic Measurements. All
the cycloaddition reactions were preliminarily analyzed by 1H
NMR technique by dissolving the complex under study in 0.6
mL of CDCl3 ([complex]0 ≈ 2 × 10-2 mol dm-3). An appropriate
aliquot of alkyne was added ([alkyne]0 ≈ 4.1 × 10-2 mol dm-3),
and the reaction was followed to completion by monitoring the
signals for the disappearance of the starting complex and the
contemporary appearance of the cyclopalladate species.
A UV-vis preliminary investigation was also performed
with the aim of determining a suitable wavelength. For this
purpose, 3 mL of freshly distilled CHCl3 solution of the complex
under study ([complex]0 ≈ 1 × 10-4 mol dm-3) was placed in a
thermostated (25 °C) cell compartment of the UV-vis spec-
trophotometer, and microaliquots of a concentrated solution
of the alkyne were added. The absorbance change was moni-
tored in the 245-500 nm wavelength interval.
Synthesis of the Bidentate and Terdentate Ligands.
The synthesis of the ligands 6-chloro-2-tert-butylthiomethyl-
pyridine (ClN-St-Bu), 6-chloro-2-phenylthiomethylpyridine (ClN-
SPh), 6-chloro-2-methylthiomethylpyridine (ClN-SMe),15 6-
methyl-2-phenylthiomethylpyridine (MeN-SPh), 6-methyl-2-
tert-butylthiomethylpyridine (MeN-St-Bu), 2-phenylthio-
methylpyridine (HN-SPh), 2-tert-butylthiomethylpyridine (HN-
St-Bu),23 2-methylthiomethylpyridine (HN-SMe),6c 6-methyl-
2-methylthiomethy1pyridine (MeN-SMe),24 2,6-bis(phenyl-
thiomethyl)pyridine (S-N-S(Ph)), 2,6-bis(tert-butylthiomethyl)-
pyridine (S-N-S(t-Bu)),6d 2,6-bis(methylthiomethyl)pyridine (S-
N-S(Me)),25 and 8-diphenylphosphanyl-2-methylquinoline
(DPPQ-Me)16 was carried out according to published proce-
dures. All other chemicals were commercial grade and were
purified or dried by standard methods where required.26
2-Methyl-8-thiomethylquinoline (TMQ-Me). To 1.01 g
(18.1 mmol) of KOH in 20 mL of anhydrous DMSO were added
3.156 g (45.03 mmol) of CH3SNa and 2 g (9 mmol) of
8-bromoquinoline. The resulting mixture was stirred under
inert atmosphere (N2) for 5 h at RT and overnight at 80 °C.
Synthesis of Pd(0) Olefin Complexes Bearing Biden-
tate Ligands. [Pd(η2-tmetc)(TMQ-Me)]. 2-Methylthio-
methylquinoline (TMQ-Me, 0.058 g, 0.345 mmol), 0.0792 g
(0.345 mmol) of tmetc, and 0.150 g (0.145 mmol) of Pd2DBA3‚
CHCl3 were dissolved under inert atmosphere (N2) in 15 mL
of anhydrous acetone. The resulting solution was stirred for 1
h, treated with activated charcoal, and eventually filtered off
on a Celite filter. Concentration under reduced pressure and
addition of Et2O yields 0.142 g (0.25 mmol) of the title product
as pale yellow microcrystals. Yield: 88%. IR (KBr pellet): νCd
1703.1, νCdN 1564.9 cm-1 1H NMR (CDCl3, T ) 298 K,
.
O
ppm): thiomethyl protons,δ, 2.90 (s, 3H, S-CH3), methyl
protons 3.14 (s, 3H, CH3-qui), ester protons 3.73 (s, 6H,
COOCH3), 3.75 (s, 6H, COOCH3), quinoline protons 7.53 (d,
1H, H3qui, J ) 8.5 Hz), 7.57 (t, 1H, H6qui, J ) 7.3 Hz), 7.83 (dd,
1H, H5qui, J ) 8.0; 1.2 Hz), δ 7.99 (dd, 1H, H7qui, J ) 7.3; 1.4
Hz), δ 8.2 (d, 1H, H4qui, J ) 8.5 Hz). 13C NMR (CDCl3, T ) 298
K, ppm): quinoline carbons, δ, 165.26 (C2qui), 124.29 (C3qui),
138.96 (C4qui), 129.68 (C5qui), 126.77 (C6qui), 135.33 (C7qui), 134.84
(C8qui), 148.26 (C9qui), 128.45 (C10qui), thiomethyl carbons 25.88
(qui-S-CH3), methyl carbons 31.00 (qui-CH3), 52.54-52.77
(OCH3), vinyl carbons 89.02-89.96 (CdC), carbonyl carbons
170.19-170.40 (CdO). Anal. Calcd for C23H29NO8PdS:
47.14, H 4.99, N 2.39. Found: C 47.31, H 4.92, N 2.42.
C
The following complexes were synthesized in an analogous
way using the appropriate ligand and olefin.
[Pd(η2-tmetc)(ClN-SPh)]. Yield: 83% (pale yellow micro-
1
crystals). IR (KBr pellet): νCdO 1703.1, νCdN 1564.9 cm-1. H
NMR (CDCl3, T ) 298 K, ppm): methyl ester protons, δ, 3.64
(s,12H, COOCH3), thiomethyl protons 4.51 (s, 2H, Pyr-CH2S),
pyridine protons 7.20 (d, 1H, H5Pyr, J ) 7.6 Hz), 7.41 (d,1H,
H3Pyr, J ) 7.6 Hz), 7.64 (t, 1H, H4Pyr, J ) 7.7 Hz), phenyl
protons 7.26-7.39 (bm, 3H, Hortho, Hpara), 7.43 (bm, 2H, 2Hmeta).
13C NMR (CDCl3, T ) 298 K, ppm): pyridine carbons, δ, 158.73
(C2Pyr), 121.97 (C3Pyr), 140.04 (C4Pyr), 124.85 (C5Pyr), thiomethyl
carbon 47.44 (Pyr-CH2S), methyl carbons 47.44 (COOCH3),
phenyl carbons 129.76 (Cortho), 132.90 (Cmeta), 129.41 (Cpara),
carbonyl carbons 169.89 (CdO). Anal. Calcd for C22H22ClNO8-
PdS: C 43.87, H 3.68, N 2.33. Found: C 43.69, H 3.73, N 2.31.
[Pd(η2-tmetc)(ClN-SMe)]. Yield: 72% (pale yellow micro-
1
crystals). IR (KBr pellet): νCdO 1703.1, νCdN 1564.9 cm-1. H
NMR (CDCl3, T ) 298 K, ppm): thiomethyl protons, δ, 2.38
(s, 3H, S-CH3), methyl ester protons 3.71 (s, 12H, COOCH3),
thiomethyl protons 4.13 (s, 2H, Pyr-CH2S), pyridine protons
7.40 (d, 1H, H5Pyr, J ) 7.8 Hz), 7.35 (d, 1H, H3Pyr, J ) 7.8 Hz),
7.70 (t, 1H, H4Pyr, J ) 7.7 Hz). 13C NMR (CDCl3, T ) 298 K,
ppm): pyridine carbons, δ, 159.11 (C2Pyr), 122.32 (C3Pyr), 139.97
(C4Pyr), 124.38 (C5Pyr), thiomethyl carbons 43.35 (Pyr-CH2S),
19.15 (S-CH3), methyl carbons 52.64 (COOCH3), carbonyl
carbons 169.97 (CdO). Anal. Calcd for C17H20ClNO8PdS: C
37.79, H 3.73, N 2.59. Found: C 37.74, H 3.81, N 2.55.
[Pd(η2-tmetc)(ClN-St-Bu)]. Yield: 81% (pale yellow mi-
(21) Sheldrick, G. M. SHELXTL NT, Version 5.10; Bruker AXS
Inc.: Madison, WI, 1999.
(22) Sheldrick, G. M. SHELXL-97, Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Go¨ttingen, Germany,
1997.
(23) Canovese, L.; Visentin, F.; Uguagliati, P.; Chessa, G.; Pesce,
A. J. Organomet. Chem. 1998, 566, 61.
(24) Canovese, L.; Chessa, G.; Santo, C.; Visentin, F.; Uguagliati,
P. Inorg. Chim. Acta 2003, 346, 158.
(25) Canovese, L.; Chessa, G.; Marangoni, G.; Pitteri, B.; Uguagliati,
P.; Visentin, F. Inorg. Chim. Acta 1991, 186, 79.
(26) Armarego, W. L. F.; Perrin., D. D. In Purification of Laboratory
Chemicals, 3rd ed.; Pergamon: New York, 1988.
crocrystals). IR (KBr pellet): νCdO 1703.1, νCdN 1564.9 cm-1
1H NMR (CDCl3, T ) 298 K, ppm): tert-butyl protons, δ, 1.41
.

5546 Organometallics, Vol. 24, No. 23, 2005
Canovese et al.
(s, 9H, S-C(CH3)3), methyl ester protons 3.70 (s, 12H, COOCH3),
thiomethyl protons 4.24 (s, 2H, Pyr-CH2S), pyridine protons
7.42 (dd, 1H, H5Pyr, J ) 7.9; 1.13 Hz), 7.33 (dd, 1H, H3Pyr, J )
7.6; 0.9 Hz), 7.70 (t, 1H, H4Pyr, J ) 7.7 Hz). 13C NMR (CDCl3,
T ) 298 K, ppm): pyridine carbons, δ, 159.98 (C2Pyr), 155.10
(C6Pyr), 121.42 (C3Pyr), 140.04 (C4Pyr), 124.77 (C5Pyr), thiomethyl
carbon 40.10 (Pyr-CH2S), tert-butyl carbons 30.76 (C(CH3)3),
quaternary t-butyl carbon 48.47 (S-C(CH3)3), methyl carbons
52.51 (COOCH3). Anal. Calcd for C20H26ClNO8PdS: C 41.25,
H 4.50, N 2.41. Found: C 41.35, H 4.46, N 2.35.
atmosphere. The resulting solution was stirred for 2 h at RT
and concentrated under vacuum. Addition of diethyl ether (20
mL) yields 0.2101 g (0.38 mmol) of the title substrate as pale
yellow microcrystals. The complex was filtered, washed with
diethyl ether, and dried in a desiccator. Yield: 94%. IR (KBr
pellet): νCdO 1722.9, 1689.9, νCdN 1611.0, νC-H 2953.6 cm-1
.
1H NMR (CDCl3, T ) 298 K, ppm): methyl protons, δ, 2.24 (s,
3H, S-CH3), methyl ester protons, 3.65 (s, 3H, COOCHR3), 3.70
(s, 3H, COOCHR3), 3.72 (s, 6H, COOCHâ ); thiomethyl protons
3
4.11 (s, 2H, pyr-CH2S), pyridine protons 7.41 (td, 1H, H5
,
pyr
Jortho5-4 ) 7.5 Hz, Jmeta5-3 ) 1.4 Hz), 7.5 (d, 1H, 3pyr, Jortho3-4
)
[Pd(η2-tmetc)(MeN-SMe)]. Yield: 88% (pale yellow micro-
crystals). IR (KBr pellet): νCdO 1736.0, 1722.9, νCdN 1611.0
cm-1. 1H NMR (CDCl3, T ) 298, ppm): thiomethyl protons, δ,
4.17 (s, 2H, CH2-S), methyl protons, 2.43 (s, 3H, S-CH3), 2.86
(s, 3H, C-CH3), methyl ester protons 3.72 (s, 12H, COOCH3),
pyridine protons 7.64 (t, 1H, H4pyr, J ) 7.7 Hz), 7.26 (d, 1H,
H3pyr, J ) 7.7 Hz), 7.21 (d, 1H, H5pyr, J ) 7.7 Hz). Anal. Calcd
for C18H23NO8PdS: C 41.59, H 4.46, N 2.69. Found: C 41.67,
H 4.40, N 2.58.
7.7 Hz), 7.88 (td, 1H, H4pyr, Jmeta4-6 ) 1.7 Hz), 8.65 (dd, 1H,
H6pyr, Jortho6-5 ) 5.6 Hz). 13C NMR (CDCl3, T ) 298 K, ppm):
methyl carbon, δ, 18.59 (S-CH3), thiomethyl carbons 43.42 (pyr-
CH2-S), methyl carbons 51.51, 51.76 (COOCRH3), 51.91
(COOCâH3), pyridine carbons 124.67 (C5pyr), 124.97 (C3pyr),
139.67 (C4pyr), 152.46 (C6pyr), 159.95 (C2pyr), cyclo-butadienyl
carbons 144.36, 149.02 (CâdC), 158.14, 169.23 (CRdC), car-
bonyl carbons 164.14, 165.30 (CâOOCH3), 173.66, 173.94
(CROOCH3). Anal. Calcd for C19H21NO8PdS: C 43.07, H 3.99,
N 2.64. Found: C 42.98, H 3.96, N 2.59.
[Pd(η2-tmetc)(MeN-St-Bu)]. Yield: 78% (pale yellow micro-
crystals). IR (KBr pellet): νCdO, 1736.0, 1696.5, νCdN, 1604.4
cm-1. 1H NMR (CDCl3, T ) 298, ppm): thiomethyl protons, δ,
4.21 (s, 2H, CH2-S), tert-butyl protons, 1.37 (s, 9H, S-C(CH3)3),
methyl protons, 2.84 (s, 3H, C-CH3); methyl ester protons, 3.71,
The following complexes were prepared in an analogous way
using the appropriate ligands.
[PdC4(COOMe)4(HN-SPh)]. Yield: 93% (pale yellow micro-
crystals). IR (KBr pellet): νCdO 1722.9, 1689.9, νCdN 1611.0,
νC-H 2953.6 cm-1. 1H NMR (CDCl3, T ) 298 K, ppm): methyl
ester protons, δ, 3.38 (s, 3H, COOCHR ), 3.65 (s, 3H, COOCHR ),
3.69 (s, 12H, COOCH3), pyridine protons, 7.62 (t, 1H, H4
J
pyr
) 7.7 Hz), 7.21 (d, 2H H3pyr, H5pyr J ) 7.7 Hz). Anal. Calcd for
C21H29NO8PdS: C 44.88, H 5.20, N 2.49. Found: C 44.83, H
5.27, N 2.39.
3
3
3.71 (s, 6H, COOCHâ ); thiomethyl protons, 4.42 (s, 2H, pyr-
3
[Pd(η2-tmetc)(DPPQ-Me)]. Yield: 72% (ochre microcrys-
CH2S), phenyl protons, 7.3 (m, 5H, S-Ph), pyridine protons 7.64
(m, 1H, H5pyr, Jortho5-4 ) 7.5 Hz, Jmeta5-3 ) 1.4 Hz), 7.67 (m,
1H, H3pyr, Jortho3-4 ) 7.7 Hz), 7.75 (td, 1H, H4pyr, Jmeta4-6 ) 1.7
Hz), 8.63 (dd, 1H, H6pyr, Jortho6-5 ) 5.5 Hz). 13C NMR (CDCl3,
T ) 298 K, ppm): thiomethyl carbons, δ, 47.53 (pyr-CH2-S),
methyl carbons 51.49 (COOCRH3), 51.94 (COOCâH3), pyridine
carbons 124.32 (C5pyr), 124.54 (C3pyr), 139.49 (C4pyr), 152.15
(C6pyr), 159.36 (C2pyr), phenyl carbons 129.83, 130.02, 130.54,
133.58 (S-C6H5) cyclobutadienyl carbons 144.69, 149.02 (CâdC),
164.17, 165.35 (CRdC), carbonyl carbons 159.42, 168.70
(CâOOCH3), 173.02, 173.72 (CROOCH3). Anal. Calcd for C24H23-
NO8PdS: C 48.70, H 3.92, N 2.37. Found: C 48.76, H 3.89, N
2.40.
tals). IR (KBr pellet): νCdO, 1742.6, 1716.3, νCdN, 1617.6 cm-
.
1
1H NMR (CDCl3, T ) 298, ppm): methyl protons, δ, 3.22 (s,
3H, C-CH3); methyl ester protons, 3.71, 3.26 (s, 12H, COOCH3);
phenyl, H5quin, H7
protons, 7.54-7.69 (m, 6H); phenyl
quin
protons, 7.41 (m, 6H); quinoline protons,7.87 (t, 1H, H6quin, J
) 7.7 Hz), 7.93 (d, 1H, H3quin, J ) 9 Hz), 8.22 (d, 1H, H4quin, J
) 9 Hz). 31P{1H} (CDCl3, T ) 298, ppm): δ, 25.53. Anal. Calcd
for C32H30NO8PPd: C 55.38, H 4.36, N 2.02. Found: C 55.43,
H 4.28, N 2.09.
[Pd(η2-ma)(DPPQ-Me)]. Yield: 86% (pale green micro-
crystals). IR (KBr pellet): νCdO, 1772.5.6, 1812.4, νCdN, 1617.6
cm-1. 1H NMR (CDCl3, T ) 298, ppm): methyl protons, δ, 3.19
(s, 3H, C-CH3); olefin protons, 4.15 (dd, 1H CHdCH trans to
P, JPH ) 10.7, JHH ) 4.0 Hz), 4.44 (dd, 1H, CHdCH cis to P,
JPH ) JHH ) 4.0 Hz); phenyl protons, 7.44 (m, 10H); quinoline
protons, 7.63 (d, 1H, H3qui, J ) 8.4),7.65 (d, 1H, H7qui, J ) 7.7
Hz), 7.83 (t, 1H, H6qui, J ) 0 7.7 Hz), 7.99 (d, 1H, H5qui, J ) 7.7
Hz), 8.29 (d, 1H, H4qui, J ) 8.4 Hz). 31P{1H} (CDCl3, T ) 298,
ppm) δ, 23.01. Anal. Calcd for C26H20NO3PPd: C 58.72, H 3.79,
N 2.63. Found: C 58.81, H 3.70, N 2.59.
[PdC4(COOMe)4(HN-St-Bu)]. Yield: 91% (pale yellow
microcrystals). IR (KBr pellet): νCdO 1722.9, 1689.9, νCdN
1
1611.0, νC-H 2953.6 cm-1. H NMR (CDCl3, T ) 298 K, ppm):
methyl protons, δ, 1.18 (s, 9H, S-(CH3)3), methyl ester protons,
3.60 (s, 3H, COOCHR3), 3.68 (s, 3H, COOCHR3), 3.69 (s, 3H,
COOCHâ ), 3.72 (s, 3H, COOCHâ ), thiomethyl protons 4.27
3
3
(s, 2H, pyr-CH2S), pyridine protons 7.38 (t, 1H, H5pyr, Jortho5-4
) 7.7 Hz), 7.5 (d, 1H, H3pyr, Jortho3-4 ) 7.7 Hz), 7.87 (td, 1H,
H4pyr, Jortho4-3 ) 7.7 Hz, Jmeta4-6 ) 1.7 Hz), 8.60 (d, 1H, H6
,
pyr
Synthesis of the Polymeric Precursors. [PdC4(COO-
Me)4]n. The complex was prepared according to the published
procedure4a by reacting under inert atmosphere (Ar) 0.414 g
(0.4 mmol) of Pd2DBA3‚CHCl3 suspended in 20 mL of anhy-
drous acetone with 0.3068 mL (1.25 mmol) of DMA added
dropwise. The initially dark suspension was stirred for 1 h at
RT, and the resulting yellow solution was treated with
activated charcoal. Filtration on a Celite filter, concentration
under vacuum, and addition of diethyl ether yields 0.282 g
(0.72 mmol) of the title complex as yellow microcrystals.
Yield: 90%. IR (KBr pellet): νCdO 1730.0, 1700.0, νC-H, 2960.0
Jortho6-5 ) 5.5 Hz). 13C NMR (CDCl3, T ) 298 K, ppm): methyl
carbons, δ, 31.19 (S-C(CH3)3), thiomethyl carbons 40.49 (pyr-
CH2-S), tert-butyl carbon 40.49 (S-C(CH3)3), methyl carbons
51.44 (COOCâH3), 51.78 (COOCRH3), pyridine carbons 123.66
(C3pyr), 124.37 (C5pyr), 139.83 (C4pyr), 151.88 (C6pyr), 161.34
(C2pyr), cyclobutadienyl carbons 144.96, 145.73 (CâdC), 163.02,
165.26 (CRdC), carbonyl carbons 164.36, 164.69 (CâOOCH3),
173.75, 173.27 (CROOCH3). Anal. Calcd for C22H27NO8PdS: C
46.20, H 4.76, N 2.45. Found: C 46.19, H 4.66, N 2.51.
[PdC4(COOMe)4(MeN-SMe)]. Yield: 91% (pale yellow
microcrystals). IR (KBr pellet): νCdO 1703.1, νCdN 1611.0, νC-H
cm-1
.
2953.6 cm-1 1H NMR (CDCl3, T ) 298 K, ppm): methyl
.
The following complexes were prepared in an analogous way
using the appropriate alkynes.
protons, δ, 2.15 (s, 3H, S-CH3), methyl protons, 2.80 (s, 3H,
pyr-CH3), methyl ester protons, 3.55 (s, 6H, COOCHR3), 3.71
[PdC4(COOEt)4]n. Yield: 96% (yellow microcrystals). IR
(KBr pellet): νCdO 1716.0, 1690.0, νC-H 2986.0 cm-1
.
(s, 6H, COOCHâ ), thiomethyl protons 4.28 (s, 2H, pyr-CH2S),
3
pyridine protons 7.26 (s, 2H, H5pyr,), 7.5 (d, 1H, H3pyr, H4pyr),
7.72 (t, 1H, Jortho ) 9 Hz). 13C NMR (CDCl3, T ) 298 K, ppm):
methyl carbon, δ, 17.59 (S-CH3), methyl carbon 27.88 (pyr-
CH3), thiomethyl carbons 43.42 (pyr-CH2-S), methyl carbons
51.50 (COOCRH3), 51.98, (COOCâH3), pyridine carbons 121.60
(C5pyr), 124.57 (C3pyr), 139.10 (C4pyr), 157.12 (C6pyr), 162.58
[PdC4(COOt-Bu)4]n. Yield: 91% (yellow microcrystals). IR
(KBr pellet): νCdO 1709.0, 1678.0, νC-H 2986.5 cm-1
.
Synthesis of the Palladacyclopentadienyl Derivatives.
[PdC4(COOMe)4(HN-SMe)]. To 0.0685 g (0.46 mmol) of the
ligand HN-SMe dissolved in 15 mL of anhydrous acetone was
added 0.164 g (0.41 mmol) of [PdC4(COOMe)4]n under inert

Formation of Palladacyclopentadiene Complexes
Organometallics, Vol. 24, No. 23, 2005 5547
(C2pyr), cyclobutadienyl carbons 148 (CâdC), 165 (CdC), car-
bonyl carbons 165.10 (CâOOCH3), 173.39 (CROOCH3). Anal.
Calcd for C20H23NO8PdS: C 44.17, H 4.26, N 2.58. Found: C
44.24, H 4.22, N 2.63.
8.5 Hz), 7.58 (t, 1H, H6qui, J ) 7.6 Hz), 7.80-8.00 (bm, 2H,
H5qui, H7qui), 8.25 (d, 1H, H4qui, J ) 7.7). Anal. Calcd for C23H23-
NO8PdS: C 47.64, H 4.00, N 2.42. Found: C 47.66, H 4.05, N
2.38.
[PdC4(COOMe)4(MeN-SPh)]. Yield: 66% (pale yellow
[PdC4(COOMe)4(DPPQ-Me)]. Yield: 87% (orange micro-
crystals). IR (KBr pellet): νCdO 1729.4, 1696.5, νCdN 1611.0 cm
-1. 1H NMR (CDCl3, T ) 298 K, ppm): methyl protons, δ, 3.39
(s, 3H, C-CH3), methyl ester protons 3.68 (s, 3H, Pd-CdC-
COOCH3), 3.64 (s, 3H, Pd-C-COOCH3), 2.89 (s, 3H, Pd-C-
COOCH3), 2.86 (s, 3H, Pd-C-COOCH3); quinoline protons 7.89
(d, 1H, H3qui, d, J ) 9 Hz), 8.18 (d, 1H, H4qui, J ) 9 Hz); phenyl
protons 7.42 (m, 10H). 31P{1H} (CDCl3, T ) 298, ppm) δ, 30.16.
Anal. Calcd for C34H30NO8PPd: C 56.88, H 4.21, N 1.95.
Found: C 56.94, H 4.15, N 2.01.
microcrystals). IR (KBr pellet): νCdO 1703.1, νCdN 1611.0, νC-H
2953.6 cm-1 1H NMR (CDCl3, T ) 298 K, ppm): methyl
.
protons, δ, 2.81 (s, 3H, pyr-CH3), methyl ester protons 3.43 (s,
6H, COOCHR3), 3.72 (s, 6H, COOCHâ ); thiomethyl protons,
3
4.61 (s, 2H, pyr-CH2S), phenyl protons, 7.26 (m, 3H, S-Ph),
7.57 (m, 2H, S-Ph), pyridine protons 7.64 (d, 1H, H5pyr, Jortho5-4
) 7.6 Hz), 7.08 (d, 1H, H3pyr, Jortho3-4 ) 7.6 Hz), 7.60 (m, 1H,
H4pyr). 13C NMR (CDCl3, T ) 298 K, ppm): methyl carbons, δ,
27.42 (pyr-CH3), thiomethyl carbons, 46.89 (pyr-CH2-S), methyl
carbons 51.47 (COOCRH3), 51.98 (COOCâH3), pyridine carbons
121.19 (C3pyr), 124.26 (C5pyr), 138.89 (C4pyr), 156.92 (C2pyr),
161.93 (C2pyr), phenyl carbons 129.84, 132.62, (S-C6H5), cyclo-
butadienyl carbons 147.31 (CâdC), 167.06 (CRdC), carbonyl
carbons 164.91 (CâOOCH3), 173.44 (CROOCH3). Anal. Calcd
for C25H25NO8PdS: C 49.55, H 4.16, N 2.31. Found: C 49.61,
H 4.17, N 2.35.
[PdC4(COOEt)4(DPPQ-Me)]. Yield: 47% (red-orange mi-
crocrystals). IR (KBr pellet): νCdO 1722.9, 1696.5, νCdN 1611.0
1
cm -1. H NMR (CDCl3, T ) 298 K, ppm): methyl protons, δ,
2.91 (s, 3H, C-CH3); ethyl ester protons 1.23 (t, 3H, Pd-CdC-
COOCH2CH3), 1.22 (t, 3H, Pd-C-COOCH2CH3), 1.00 (t, 3H, Pd-
C-COOCH2CH3), 0.85 (t, 3H, Pd-C-COOCH2CH3), 4.11 (bm,
4H, Pd-C-COOCH2CH3), 3.77 (bm, 3H, Pd-C-COOCH2CH3);
quinoline protons, 7.87 (d, 1H, H3qui, d, J ) 9 Hz), 8.17 (d, 1H,
H4qui, J ) 9 Hz); phenyl protons 7.42 (m, 10H). 31P{1H} (CDCl3,
T ) 298, ppm) δ, 30.31. Anal. Calcd for C38H28NO8PPd: C
59.74, H 3.69, N 1.83. Found: C 59.83, H 3.59, N 1.78.
[PdC4(COOMe)4(MeN-St-Bu)]. Yield: 91% (pale yellow
microcrystals). IR (in KBr) (cm-1): νCdO 1703.1, νCdN 1611.0,
νC-H 2947.0 cm-1. 1H NMR (CDCl3, T ) 298 K, ppm): methyl
protons, δ, 1.13 (s, 9H, S-(CH3)3), methyl protons 2.79 (s, 3H,
pyr-CH3), methyl ester protons, 3.31 (s, 3H, COOCHR3), 3.74
[PdC4(COOt-Bu)4(DPPQ-Me)]. Yield: 86% (yellow micro-
crystals). IR (KBr pellet): νCdO 1702.9, 1683.7, νCdN 1611.0 cm
-1. 1H NMR (CDCl3, T ) 298 K, ppm): methyl protons, δ, 3.11
(s, 3H, C-CH3), tert-butyl protons, 1.51 (s, 9H, C(CH3)3), 1.50
(s, 9H, C(CH3)3), 1.04 (s, 9H, C(CH3)3), 0.97 (s, 9H, C(CH3)3);
quinoline protons 7.83 (d, 1H, H3qui, d, J ) 9 Hz), 8.11 (d, 1H,
H4qui, J ) 9 Hz); phenyl protons 7.53-7.33 (m, 10H). 31P{1H}
(CDCl3, T ) 298, ppm): δ, 25.79. Anal. Calcd for C46H54NO8-
PPd: C 62.34, H 6.14, N 1.58. Found: C 62.41, H 6.15, N 1.64.
[PdC4(COOMe)4(SNS(Me))]. Yield: 58% (yellow micro-
crystals). IR (KBr pellet): νCdO 1703.1, 1676.8, νCdN 1611.0,
νC-H 2953.6 cm-1. 1H NMR (CDCl3, T ) 298 K, ppm): methyl
protons, δ, 2.17 (s, 6H, S-CH3), methyl ester protons, 3.54 (s,
(s, 3H, COOCHR3), 3.70 (s, 6H, COOCHâ ), thiomethyl protons
3
4.41 (s, 2H, pyr-CH2S), pyridine protons 7.24, 7.26 (2d, 2H,
H5pyr, H3pyr, Jmeta ) 4.15 Hz), 7.71 (t, 1H, H4pyr, Jortho ) 7.7 Hz).
13C NMR (CDCl3, T ) 298 K, ppm): methyl carbon, δ, 27.47
(pyr-CH3), 31.27 (S-C(CH3)3), thiomethyl carbons 41.36 (pyr-
CH2-S), tert-butyl carbon 49.71 (S-C(CH3)3), methyl carbons
51.17, 51.52 (COOCRH3), 51.90 (COOCâH3), pyridine carbons
120.24 (C5pyr), 124.29 (C3pyr), 139.30 (C4pyr), 158.62 (C6pyr),
161.94 (C2pyr), cyclo-butadienyl carbons 155.13 (CâdC), 163.20,
171.07 (CRdC), carbonyl carbons 166.62 (CâOOCH3), 172.13,
174.96 (CROOCH3). Anal. Calcd for C23H29NO8PdS: C 47.17,
H 4.99, N 2.39. Found: C 47.12, H 4.90, N 2.33.
6H, COOCHR3), 3.72 (s, 6H, COOCHâ ); thiomethyl protons
[PdC4(COOMe)4(ClN-SMe)]. Yield: 91% (pale yellow micro-
3
1
crystals). IR (KBr pellet): νCdO 1703.1, νCdN 1584.6 cm -1. H
4.21 (s, 4H, pyr-CH2S), pyridine protons 7.39 (d, 2H, H5
,
pyr
H3pyr), 7.82 (t, 1H, H4pyr, Jortho)7.7 Hz). 13C NMR (CDCl3, T )
298 K, ppm): methyl carbon, δ, 16.98 (S-CH3), thiomethyl
carbons 43.50 (pyr-CH2-S), methyl carbons 51.56 (COOCRH3),
51.98 (COOCâH3), pyridine carbons 123.26 (C5pyr, C3pyr), 160.12
(C2pyr, C6pyr), cyclo-butadienyl carbons 148.00 (CâdC), 163.20
(CRdC), carbonyl carbons 165.04 (CâOOCH3), 173.08 (CROOCH3).
Anal. Calcd for C21H25NO8PdS2: C 42.75, H 4.27, N 2.37.
Found: C 42.79, H 4.23, N 2.31.
NMR (CDCl3, T ) 298 K, ppm): methyl protons, δ, 2.17 (s,
3H, CH3-S), methyl ester protons 3.60 (bs, 6H, Pd-CdC-
COOCH3), 3.72 (s, 6H, Pd-C-COOCH3), thiomethyl protons
4.32 (s, 2H, pyr-CH2S), pyridine protons 7.43 (d, 1H, H3pyr, J
) 7.7 Hz), 7.43 (d, 1H, H5pyr, J ) 7.7 Hz), 7.80 (t, 1H, H4pyr, J
) 7.7 Hz). Anal. Calcd for C19H20ClNO8PdS: C 40.44, H 3.57,
N 2.48. Found: C 40.39, H 3.62, N 2.43.
[PdC4(COOMe)4(ClN-SPh)]. Yield: 80% (pale yellow mi-
crocrystals). IR (KBr pellet): νCdO, 1703.1; νCdN, 1584.6 cm-1
.
[PdC4(COOMe)4(SNS(Ph))]. Yield: 79% (pale yellow mi-
crocrystals). IR (KBr pellet): νCdO 1716.3, 1736, 1676.8, νCdN
1611.0, νC-H, 2960.1 cm-1. 1H NMR (CDCl3, T ) 298 K, ppm):
methyl ester protons, δ, 3.39 (s, 6H, COOCHR3), 3.74 (s, 6H,
1H NMR (CDCl3, T ) 298 K, ppm): methyl ester protons, δ,
3.49 (s, 6H, Pd-CdC-COOCH3), 3.72 (s, 6H, Pd-C-COOCH3),
thiomethylene protons 4.63 (bs, 2H, pyr-CH2S), aromatic
protons 7.25-7.35 (m, 4H, 2Hortho, 1Hpara, H5pyr), 7.21 (d, 1H,
H3pyr, J ) 7.7 Hz), 7.63 (t, 1H, H4pyr, J ) 7.7 Hz), 7.55-7.65
(m, 2H, 2Hmeta). Anal. Calcd for C24H22ClNO8PdS: C 46.02, H
3.54, N 2.24. Found: C 46.09, H 3.58, N 2.19.
COOCHâ ); thiomethyl protons 4.55 (s, 4H, pyr-CH2S), phenyl
3
protons 7.35 (m, 10H, S-Ph), pyridine protons 7.10 (d, 2H, H5
,
pyr
H3pyr), 7.56 (t, 1H, H4pyr, Jortho ) 7.7 Hz). Anal. Calcd for C31H29-
NO8PdS2: C 52.14, H 4.09, N 1.96. Found: C 52.23, H 4.12, N
2.02.
[PdC4(COOMe)4(ClN-St-Bu)]. Yield: 90% (pale yellow
microcrystals). IR (KBr pellet): νCdO 1703.1, νCdN, 1564.9 cm
[PdC4(COOMe)4(SNS(t-Bu))]. Yield: 75% (pale yellow
microcrystals). IR (KBr pellet): νCdO 1722.1, 1607, νCdN 1611.0,
νC-H, 2976.2 cm-1. 1H NMR (CDCl3, T ) 298 K, ppm): methyl
protons, δ, 1.33 (s, 12H, S-C(CH3)3), methyl ester protons 3.30
1
-1. H NMR (CDCl3, T ) 298 K, ppm): tert-butyl protons, δ,
1.17 (s, 9H, S-C(CH3)3), methyl ester protons 3.59 (bs, 6H, Pd-
CdC-COOCH3), 3.71 (s, 6H, Pd-C-COOCH3), thiomethylene
protons 4.46 (s, 2H, pyr-CH2S), pyridine protons 7.41 (d, 1H,
H5pyr, J ) 7.7 Hz), 7.42 (d, 1H, H3pyr, J ) 7.7 Hz), 7.80 (t, 1H,
H4pyr, J ) 7.8 Hz). Anal. Calcd for C22H26ClNO8PdS: C 43.58,
H 4.32, N 2.31. Found: C 43.62, H 4.35, N 2.28.
(s, 6H, COOCHR3), 3.73 (s, 6H, COOCHâ ); thiomethyl protons
3
4.34 (s, 4H, pyr-CH2S), pyridine protons 7.36 (d, 2H, H5
,
pyr
H3pyr), 7.75 (t, 1H, H4pyr, Jortho ) 7.7 Hz). Anal. Calcd for C26H33-
NO8PdS2: C 47.45, H 5.05, N 2.13. Found: C 47.50, H 5.00, N
2.15.
[PdC4(COOMe)4(TMQ-Me)]. Yield: 86% (pale yellow mi-
-1
crocrystals). IR (KBr pellet): νCdO 1703.1, νCdN 1564.9 cm
.
[PdC4(COOEt)4(HN-SMe)]. In the synthesis of the title
complex n-hexane instead of diethyl ether is used as precipi-
tant. Yield: 77% (yellow microcrystals). IR (KBr pellet): νCdO
1H NMR (CDCl3, T ) 298 K, ppm): thiomethyl protons, δ, 2.73
(s, 3H, S-CH3), methyl protons, 2.97 (s, 3H, qui-CH3), methyl
ester protons, 3.60 (bs, 6H, Pd-CdC-COOCH3), 3.72 (s, 6H,
Pd-C-COOCH3), quinoline protons 7.49 (d, 1H, H3qui, d, J )
1
1709.7, νCdN 1611.0, νC-H 2953.6 cm-1. H NMR (CDCl3, T )
298 K, ppm): methyl protons, δ, 1.25 (m, 12 H, COO-CH2-

5548 Organometallics, Vol. 24, No. 23, 2005
Canovese et al.
CH3), methyl protons 2.23 (s, 3H, S-CH3), methylene protons
4.15 (m, 10H, pyr-CH2S, COO-CH2-CH3), pyridine protons 7.39
7.35 (t, 1H, H5pyr, Jortho4-5 ) 7.7 Hz), 7.47 (d, 1H, H3pyr, Jortho3-4
) 7.7 Hz), 7.84 (td, 1H, H4pyr, Jmeta4-6 ) 1.6 Hz), 8.95 (d, 1H,
H6pyr, Jortho6-5 ) 5.3 Hz). Anal. Calcd for C31H45NO8PdS: C
53.33, H 6.50, N 2.01. Found: C 53.27, H 6.45, N 2.12.
(t, 1H, H5pyr, Jortho4-5 ) 7.7 Hz), 7.49 (d, 1H, H3pyr, Jortho3-4
)
7.7 Hz), 7.87 (td, 1H, H4pyr, Jmeta4-6 ) 1.5 Hz), 8.62 (d, 1H, H6
,
pyr
Jortho6-5 ) 4.9 Hz). Anal. Calcd for C23H29NO8PdS: C 47.17, H
4.99, N 2.39. Found: 47.20, H 5.03, N 2.34.
Supporting Information Available: Table 1 Si (sum-
mary of crystal and refinement data) and Table 2 Si (selected
bond distances and angles of the two complexes). Equilibrium
constant determination, nonlinear regression analysis, and
simulation details. This material is available free of charge
via the Internet at http://pubs.acs.org.
[PdC4(COOt-Bu)4(HN-SMe)]. In the synthesis of the title
complex n-hexane instead of diethyl ether is used as precipi-
tant. Yield: 49% (dark yellow oily product). IR (KBr pellet):
1
νCdO 1709.7, νCdN 1611.0, νC-H 2953.6 cm-1. H NMR (CDCl3,
T ) 298 K, ppm): methyl protons, δ, 1.38, 1.50, 1.51, 1.52 (4s,
36 H, COO-C(CH3)3), methyl protons 2.16 (s, 3H, S-CH3),
thiomethyl protons 4.24 (s, 2H, pyr-CH2S), pyridine protons
OM058036T