Chloride-modulated insertion reactions of dimethylallene across the Pd-C bond in palladium methyl complexes bearing potentially terdentate pyridylthioether ligands

Article abstract of DOI:10.1021/om030293f

Palladium methyl complexes with potentially terdentate pyridylthioether (S-N-S(R) = 2,6-bis(R-thiomethyl)pyridine, R = Me, t-Bu, Ph; N-S-N = 2[(2-pyridylmethylthio)methyl]pyridine) ligands have been prepared and characterized. Both the bidentate chloride [Pd(Me)(S-N-S(R))]Cl and the terdentate chloride-free [Pd(Me)(S-N-S(R))]⁺ species are present in solution and display a substantially different reactivity toward allene insertion across the Pd-C bond. The structures of the complexes [Pd(Me)(S-N-S(t-Bu))]OTf and [Pd(Me)(S-N-S(t-Bu))]Cl were determined by X-ray diffraction. The chloride methyl substrates [Pd(Me)(S-N-S(R))]Cl display an enhanced reactivity in solution with respect to the allene insertion, and this reactivity was traced back to the distortion of the main coordination plane induced by the presence of an uncoordinated -CH₂-S-R group in position 6 of the coordinating pyridine. The equilibrium position between the terdentate and the bidentate species can be modulated by addition of chloride ion, which therefore controls the overall reactivity of the system.

Full text of DOI:10.1021/om030293f

3230
Organometallics 2003, 22, 3230-3238
Ch lor id e-Mod u la ted In ser tion Rea ction s of
Dim eth yla llen e a cr oss th e P d -C Bon d in P a lla d iu m
Meth yl Com p lexes Bea r in g P oten tia lly Ter d en ta te
P yr id ylth ioeth er Liga n d s
Luciano Canovese,*,† Fabiano Visentin,† Gavino Chessa,† Paolo Uguagliati,†
Claudio Santo,† Giuliano Bandoli,‡ and Lucia Maini§
Dipartimento di Chimica, Universita` Ca’ Foscari, Calle Larga S. Marta 2137,
30123 Venezia, Italy, Dipartimento di Scienze Farmaceutiche, Universita` di Padova,
Via F. Marzolo 5, 35131 Padova, Italy, and Dipartimento di Chimica “G. Ciamician”,
Universita` di Bologna, Via Selmi 2, 40126 Bologna, Italy
Received April 22, 2003
Palladium methyl complexes with potentially terdentate pyridylthioether (S-N-S(R) )
2,6-bis(R-thiomethyl)pyridine, R ) Me, t-Bu, Ph; N-S-N ) 2[(2-pyridylmethylthio)methyl]-
pyridine) ligands have been prepared and characterized. Both the bidentate chloride
[Pd(Me)(S-N-S(R))]Cl and the terdentate chloride-free [Pd(Me)(S-N-S(R))]+ species are
present in solution and display a substantially different reactivity toward allene insertion
across the Pd-C bond. The structures of the complexes [Pd(Me)(S-N-S(t-Bu))]OTf and
[Pd(Me)(S-N-S(t-Bu))]Cl were determined by X-ray diffraction. The chloride methyl
substrates [Pd(Me)(S-N-S(R))]Cl display an enhanced reactivity in solution with respect
to the allene insertion, and this reactivity was traced back to the distortion of the main
coordination plane induced by the presence of an uncoordinated -CH2-S-R group in position
6 of the coordinating pyridine. The equilibrium position between the terdentate and the
bidentate species can be modulated by addition of chloride ion, which therefore controls the
overall reactivity of the system.
In tr od u ction
under study. In this respect we have recently demon-
strated that distortion of the flexible backbone of the
ancillary ligands may induce a considerable increase in
the rate of allene (1,1′-dimethylallene, DMA; 1,1′, 3,3′-
tetramethylallene, TMA) insertion into the palladium-
carbon bond in pyridylthioether halide methyl palla-
dium complexes ([PdX(Me)(RN-SR′)], X ) Cl, Br, I; R
) H, Me, Cl; R′ ) Me, t-Bu, Ph) to give the correspond-
ing allyl complexes.3 We decided to extend our mecha-
nistic study to systems bearing potentially terdentate
pyridylthioether species as ancillary ligands (S-N-
S(R), N-S-N) since these ligands may impart a pecu-
liar reactivity to their complexes. The complexes under
study, the corresponding allyl species, and the atom-
numbering scheme (which implies no isomeric prefer-
ences but indicates only atom location) are reported in
Scheme 1.
In this respect several investigations were made by
us and other authors,4 and some interesting results
were obtained. Thus, the palladium allyl derivatives of
terdentate ligands display a facile room-temperature
η3-η1-η3 isomerism of the allyl fragment,4c,d and the
Pd(0) olefin derivatives show a reactivity consistent with
the capability of the terdentate ligand to stabilize Pd(0)
three-coordinate species, thereby inducing a dissociative
path parallel to the associative one in olefin exchange
The insertion reactions of unsaturated molecules into
metal-carbon bonds are of widespread importance in
numerous synthetic paths to C-C bond formation.1 In
particular palladium complexes are largely used in
catalyzed copolymerization reactions leading to carbon
monoxide, alkene, alkyne, and allene copolymers.2
Moreover, the choice of the organometallic catalysts is
of paramount importance in determining the reactivity
and the regio-stereochemical features of the system
* Corresponding author. E-mail: cano@unive.it.
† Universita` Ca’ Foscari.
‡ Universita` di Padova.
§ Universita` di Bologna.
(1) (a) Shimuzu, I.; Tsuji, J . Chem. Lett. 1984, 203. (b) Ahmar, M.;
Caszes, B.; Gore´, J . Tetrahedron Lett. 1984, 25, 4505. (c) Ahmar, M.;
Caszes, B.; Barieux, J . J .; Gore´, J . Tetrahedron 1987, 43, 513. (d) Cazes,
B. Pure Appl. Chem. 1990, 62, 1867. (e) van Leeuwen, P. W. N. M.;
van Koten, G. In Catalysis: An Integrated Approach to Homogeneous,
Heterogeneous and Industrial Catalysis; Mouljin, J . A., et al., Eds.;
Elsevier Science: Amsterdam, 1993 (and references therein). (f)
Besson, L.; Gore`, J .; Cazes, B. Tetrahedron Lett. 1995, 36, 3853 and
3857. (g) Delis, J . G. P.; Aubel, P. G.; Vrieze, K.; van Leeuwen, P. W.
N. M. Organometallics 1997, 16, 2948. (h) Kacker, S.; Sen, A. J . Am.
Chem. Soc. 1997, 119, 1028. (i) Grigg, R.; Monteith, M.; Sridharan,
V.; Terrier, C. Tetrahedron 1998, 54, 3885. (j) Zenner, J . M.; Larock,
R. C.; J . Org. Chem. 1999, 64, 7312. (k) Yamamoto, A. J . Chem. Soc.,
Dalton Trans. 1999, 1027. (l) Mecking, S. Coord. Chem. Rev. 2000,
203, 325 (and references therein). (m) Zimmer, R.; Dinesh, C. U.;
Nandanan, E.; Khan, F. A. Chem. Rev. 2000, 100, 3067 (and references
therein). (n) Yagyu, T.; Hamada, M.; Osakada, K.; Yamamoto, T.
Organometallics 2001, 20, 1087. (o) Liu, W.; Malinoski, J . M.;
Brookhart, M. Organometallics 2002, 21, 2836.
(3) (a) Canovese, L.; Visentin, F.; Chessa, G.; Uguagliati, P.; Bandoli,
G. Organometallics 2000, 19, 1461. (b) Canovese, L.; Visentin, F.;
Chessa, G.; Santo, C.; Uguagliati, P.; Bandoli, G. J . Organomet. Chem.
2002, 650, 43. (c) Canovese, L.; Chessa, G.; Santo, C.; Visentin, F.;
Uguagliati, P. Inorg. Chim. Acta 2003, 346, 158.
(2) Groen, J . H.; Elsevier, C. J .; Vrieze, K.; Smeets, W. J . J .; Spek,
A. L. Organometallics 1996, 15, 3445 (and references therein)
10.1021/om030293f CCC: $25.00 © 2003 American Chemical Society
Publication on Web 06/24/2003

Chloride-Modulated Insertion Reactions
Organometallics, Vol. 22, No. 16, 2003 3231
Sch em e 1
Sch em e 2
the ligand act as a truly tris-chelating one, in any case
influencing the stability of the ensuing allyl complex.
Therefore, it appears that the presence of chloride ion
could modulate the reaction rate of allene insertion by
modifying the equilibrium position in Scheme 2,
where the tris-chelate complex I would display a
decreased reactivity with respect to the bis-chelate II
since the latter should resemble the most reactive
6-substituted species.3 Thus, we decided to synthesize
and study the complexes reported in Scheme 1, to assess
their behavior in solution and their reactivity with
respect to DMA insertion into the Pd-C bond in the
presence (or in the absence) of free chloride ion. The
results of such an investigation are reported in the
present paper.
Resu lt a n d Discu ssion
Syn th esis of P a lla d iu m Com p lexes. Addition un-
der inert atmosphere (N2) of the potentially terdentate
ligand L-L′-L (L-L′-L ) S-N-S(R), N-S-N) to a
solution of [PdCl(Me)(COD)] in THF yields the pyridyl-
thioether methyl complex [Pd(Me)(L-L′-L)]Cl as air-
stable yellow microcrystals.. These substrates were
obtained in quantitative yields and are easily character-
1
ized by comparison of their H NMR spectra with those
1
of the corresponding free ligand. In fact the H NMR
spectra of the coordinated ligands display a generalized
downfield shift of characteristic signals (i.e., ∆δCH2S(SNS)
) 0.8-1, ∆δCH2S(NSN) ) 0.4 ppm). Dechloridation of these
species by AgOTf in CH2Cl2 and addition of diethyl ether
to the filtered and concentrated reaction mixture yield
the corresponding whitish ionic complexes [Pd(Me)(L-
L′-L)]+OTf-. These substrates are air-stable micro-
crystalline species, and their solution behavior and
1
consequently their H NMR spectra are well differenti-
ated from the corresponding chloride species (vide infra).
The allyl derivatives were synthesized by the usual
procedure starting from the corresponding allyl dimers
4d
by addition of the appropriate L-L′-L ligand
or by
reacting the chloro methyl palladium complexes with
DMA.
Cr yst a l St r u ct u r e Det er m in a t ion . The ORTEP5
drawing of the complex [Pd(Me)(S-N-S(t-Bu))]OTf is
(4) (a) Wehman, P.; Ru¨lke, R. E.; Kaasjager, V. E.; Kamer, P. C. J .;
Kooijman, H.; Spek, A. L.; Elsevier, C. J .; Vrieze, K.; van Leeuwen, P.
W. N. M. J . Chem. Soc., Chem. Commun. 1995, 331. (b) Ru¨lke, R. E.;
Kaasjager, V. E.; Wehman, P.; Elsevier, C. J .; van Leeuwen, P. W. N.
M.; Vrieze, K.; Fraanje, J .; Goubitz, K.; Spek, A. L. Organometallics
1996, 15, 3022. (c) Canovese, L.; Visentin, F.; Uguagliati, P.; Chessa,
G.; Lucchini, V.; Bandoli, G. Inorg. Chim. Acta 1998, 275, 385. (d)
Canovese, L.; Visentin, F.; Chessa, G.; Niero, A.; Uguagliati P. Inorg.
Chim. Acta 1999, 293, 44. (e) Canovese, L.; Visentin, F.; Chessa, G.;
Gardenal, G.; Uguagliati, P. J . Organomet. Chem. 2001, 622, 155.
(5) J ohnson, C. K. ORTEP, report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.
reactions;4e both these phenomena are promoted by the
alternating attack of the third coordinating atom of the
dangling wing of the ligand. In the case of methyl
complexes, the presence of a potentially coordinating
arm in position 6 of the pyridine ring of the ancillary
ligand may induce distortion if uncoordinated or make

3232 Organometallics, Vol. 22, No. 16, 2003
Canovese et al.
Ta ble 2. Selected Bon d Len gth s (Å), An gles (d eg),
a n d Geom etr y of th e P ossible Wea k Hyd r ogen
Bon d s for th e Com p lex [P d (Me)(S-N-S(t-Bu ))]Cl
Bond Lengths
Pd(1)-C(16)
Pd(1)-N(1)
C(6)-S(1)
2.034(6)
2.074(4)
1.822(5)
1.864(5)
Pd(1-S(1)
Pd(1)-S(2)
C(11)-S(2)
C(12)-S(2)
2.2911(11)
2.3029(12)
1.792(6)
C(7)-S(1)
1.859(5)
Bond Angles
N(1)-Pd(1)-S(1)
C(16)-Pd(1)-S(1)
S(1)-Pd(1)-S(2)
C(6)-S(1)-Pd(1)
C(5)-C(6)-S(1)
N(1)-C(5)-C(6)
85.63(10) N(1)-Pd(1)-S(2)
85.70(10)
95.24(18)
93.36(18) C(16)-Pd(1)-S(2)
170.46(5)
C(16)-Pd(1)-N(1) 178.6(2)
96.82(14) C(11)-S(2)-Pd(1)
115.0(3)
116.1(4)
98.14(17)
117.6(4)
117.8(5)
C(1)-C(11)-S(2)
N(1)-C(1)-C(11)
F igu r e 1. Drawing of the complex [Pd(Me)(S-N-S(t-
Bu))]OTf (2b) with the numbering scheme. Ellipsoids are
at the 40% level.
Hydrogen Bonds
H- - -A (Å) D- - -A (Å) D-H- - -A (Å)
D-H- - -A
Ta ble 1. Selected Bon d Len gth s (Å), An gles (d eg),
a n d Geom etr y of th e P ossible Wea k Hyd r ogen
Bon d s for th e Com p lex [P d (Me)(S-N-S(t-Bu ))]OTf
C(20)-H(20A)- - -Cl(2)
C(21)-H(21A)- - -Cl(2)a
C(21)-H(21B)- - -Cl(2)b
2.66
2.60
2.60
3.608(6)
3.536(4)
3.536(4)
166
163
163
a
b
Bond Lengths
Refers to the atom in the position -x, -y, -1-z. Refers to
the atom in the position x, -y, 1/2+z.
Pd-S(1)
Pd-N
S(1)-C(2)
S(1)-C(9)
2.281(6)
2.078(6)
1.74(1)
1.90(2)
Pd-S(2)
2.315(6)
2.079(8)
1.92(2)
1.85(1)
Pd-C(1)
S(2)-C(8)
S(2)-C(10)
Bond Angles
S(1)-Pd-N
83.5(6)
S(2)-Pd-N
88.6(6)
97.6(8)
173.6(9)
93.3(6)
119(1)
S(1)-Pd-C(1)
S(1)-Pd-S(2)
Pd-S(1)-C(2)
S(1)-C(2)-C(3)
C(2)-C(3)-N
90.3(8)
170.7(1)
100.7(5)
114.2(9)
118(1)
S(2)-Pd-C(1)
N-Pd-C(1)
Pd-S(2)-C(8)
S(2)-C(8)-C(7)
C(8)-C(7)-N
117(1)
Hydrogen Bonds
H- - -A (Å) D- - -A (Å) D-H- - -A (Å)
D-H- - -A
C(2)-H(2a)- - -F(2)
2.61
2.65
2.64
3.45
3.52
3.35
145
151
130
C(8)-H(8a)- - -O (3A)a
C(8)-H(8b)- - -F (3A)a
a
Refers to the atom in the position x, 1+y, z.
F igu r e 2. Drawing of the complex [Pd(Me)(S-N-S(t-
Bu))]Cl (1b) with the numbering scheme. Ellipsoids are at
the 40% level.
shown in Figure 1, together with the numbering scheme
used, while relevant bond lengths and angles are
reported in Tables 1and 2. As can be seen in Figure 1,
the “inner core” of the cation is roughly planar with S(1),
S(2), C(9), and C(10) atoms above the average coordina-
tion plane (by 0.08, 0.15, 1.84, and 1.94 Å, respectively)
and the C(2) and C(8) atoms below this plane (by 1.14
and 0.25 Å, respectively). The five-membered ring Pd-
S(1)-C(2)-C(3)-N adopts a slightly envelope confor-
mation with Pd, C(2), C(3), and N coplanar, whereas
S(1) lies off by 0.20 Å. On the contrary, the Pd-S(2)-
C(8)-C(7)-N ring shows a more pronounced envelope
conformation with the C(8) atom out (by 0.38 Å) from
the mean plane defined by Pd, S(2), C(7), and N atoms.
The Pd-S(1), Pd-S(2), and Pd-N distances (2.281(6),
2.315(6), and 2.078(6) Å, respectively) are in good
agreement with the average values, retrieved from the
Cambridge Structural Database,6 in 39 mononuclear
Pd(II) complexes for Pd-S distances (mean value: 2.306
Å) and in 23 cationic complexes containing Pd(II)-N
(pyridine-type) bonds (mean value: 2.057 Å). Inciden-
tally, the Pd(II)-N distance in neutral pyridine com-
plexes rises to 2.162(5) Å, as can be noticed in numerous
examples.3a,b,7 No effective hydrogen bonds occur, and
the complex is built up by juxtaposition at van der
Waals distances of well-separated Pd(II) cations and
sulfonate counteranions, although the separations in-
volving the methylene hydrogens (Table 1a) seem to be
of some significance.
We have also carried out the X-ray structure deter-
mination of the complex [Pd(Me)(S-N-S(t-Bu))]Cl,
which apparently separates due to solubility factors
from a CH2Cl2/hexane solution in which both species
[PdCl(Me)(S-N-S(t-Bu))] and [Pd(Me)(S-N-S(t-Bu))]Cl
are present in equilibrium. The ORTEP5 drawing of the
latter is shown in Figure 2, together with the numbering
scheme used, while relevant bond lengths and angles
are reported in Table 2.
[Pd(Me)(S-N-S(t-Bu))]Cl proved to be the RS iso-
meric form (the tert-butyl groups are located over and
under the plane formed by the metal and the coordinat-
ing atoms). The coordination around the Pd(II) is
analogous to the previously described complexes with
(7) (a) Kay, Y.; Yasuoka, N.; Kasay, N. Bull. Chem. Soc. J pn. 1979,
52, 737. (b) Okeya, S.; Kawakita, Y.; Matsumoto. S.; Nakamura, Y.;
Kawaguchi, S.; Kanehisa, N.; Miki, K.; Kasay, N. Bull. Chem. Soc. J pn.
1981, 55, 2134. (c) Newkome, G. R.; Kiefer, G. E.; Frere, Y. A.; Onishi,
M.; Gupta, V. K.; Fronczek, F. R. Organometallics 1986, 5, 348.
(6) Allen, F. H.; Davies, J . E.; Gralloy, J . J .; J ohnson, O.; Kennard,
O.; Macrae, C. F.; Mitchell, E. M.; Mitchell, G. F.; Smith, J . M.; Watson,
D. G. J . Chem. Inf. Comput. Sci. 1991, 31, 187; Cambridge Crystal-
lographic Database (Version 5.22 of October 2001).

Chloride-Modulated Insertion Reactions
Organometallics, Vol. 22, No. 16, 2003 3233
1
F igu r e 4. Low-temperature (188 K) H NMR spectrum
of the complex [PdCl(Me)(S-N-S(t-Bu))] (1b) in CD2Cl2.
1
F igu r e 3. Low-temperature (203 K) H NMR spectrum
of the complex [PdCl(Me)(N-S-N)] (4) in CD2Cl2.
Pd(1)-S(1), Pd(1)-S(2), Pd(1)-N(1), and Pd(1)-C(16)
distances of 2.2911(11), 2.3029(12), 2.074(4), and 2.034(6)
Å, respectively. Both five-membered rings Pd(1)-S(1)-
C(6)-C(5)-N(1) and Pd(1)-S(2)-C(11)-C(1)-N(1) adopt
an envelope conformation with S(1) and S(2) placed at
-0.46 and 0.24 Å with respect to the mean plane defined
by Pd, C, and N atoms. One-half water molecule is
present per formula unit; the water molecule forms two
hydrogen bonds with the chloride atom (O- - -Cl- dis-
tances 3.151(9) and 2.857(9) Å). The chloride atom
interacts with the hydrogen atoms to form weak hydro-
gen bonds (Table 2).
1
F igu r e 5. Low-temperature (223 K) H NMR spectrum
Solu tion Beh a vior . [P d (Me)(S-N-S(R))]Cl. The
chloride methyl complexes (1) bearing the 2-bis(thio-
methyl)pyridine derivatives S-N-S(R) as ancillary
ligands behave differently from the corresponding
N-S-N complex (4). The low-temperature 1H NMR
spectrum of the latter can be interpreted as arising from
a truly arm-off species in which only two of the three
potentially coordinating nucleophiles are coordinated to
palladium. In fact, as can be seen in Figure 3, the
presence of two different groups of signals in the
aromatic zone and the two AB systems (at 4-4.5 ppm)
ascribable to the diastereotopic CH2-S-CH2 protons
contiguous to the chiral coordinated sulfur clearly
support this hypothesis.
of the complex [Pd(Me)(S-N-S(Me))]OTf (2a ) in CD2Cl2.
species promoted by the enhanced nucleophilicity of the
t-Bu-substituted sulfur atoms should explain the ob-
served behavior.
As an alternative explanation one should take into
account a fast alternating coordination of the ligand
wings without concomitant inversion of the sulfur
absolute configuration. In other words, this movement
is sterically controlled since the bulkiness of the t-Bu
groups governs the enantiospecificity of the exchanging
movement, with the configuration of sulfur lying on the
incoming wing being somehow predetermined by that
of the coordinated one.
Apparently, the sp3 sulfur hybridization disfavors the
concomitant formation of two strained chelating rings.
On the contrary, when the S-N-S derivatives 1 are
studied, a general fluxionality ascribable to the alter-
nating ligand wings movement is detectable at any
attainable temperature. The thioetheric sulfurs of the
S-N-S moiety can evidently act as efficient nucleo-
philes thanks to the flexibility of the backbone structure
of the ligand itself and to the presence of two sp3-
hybridized sulfur atoms. Thus, the incoming sulfur
linked to the joined uncoordinated wing can easily
attack the metal center, thereby promoting the subse-
quent release of its symmetric counterpart. Under these
circumstances the absolute sulfur configuration would
rapidly interconvert and no diastereotopic protons would
be detected. However, the case of the complex [Pd(Me)-
(S-N-S(t-Bu))]Cl (1b) is peculiar in some respect. The
low-temperature (188 K) 1H NMR spectrum of the
sample in CD2Cl2 (Figure 4) displays signals indicating
the presence of one single species and one single well-
resolved AB system at ca. 5 ppm ascribable to CH2S
protons. The formation of a symmetric pentacoordinate
[P d (Me)(S-N-S(R))]OTf. The chloride-free com-
plexes of S-N-S ligands (2) display a solution behavior
typical of tercoordinated chelating ligands. The room-
temperature NMR spectra display symmetric structures
in which the rapid inversion of the absolute sulfur
configuration is the only observable fluxionality. At low
1
temperature the sulfur inversion is frozen and the H
NMR spectra display the presence of a pair of dia-
stereoisomers (meso and RS) in different populations
together with the AB systems of the endocyclic CH2S
protons. The low-temperature spectrum (208 K) of the
complex [Pd(Me)(S-N-S(t-Bu))]+ (2b ) displays the
presence of almost only one isomer (∼90%), the isomeric
distribution at 223 K for the other complexes being
∼60% (R ) Me (2a )) (Figure 5), ∼70% (R ) Ph (2c)).
The room-temperature 1H NMR spectrum of [Pd(Me)-
(N-S-N)]+ (5) exhibits signals that clearly belong to a
truly tercoordinate species. However, several broad
signals observed in the spectrum suggest the presence
of oligo- or polymeric structures. These oligomers,
probably due to the distorted third arm of the ligand

3234 Organometallics, Vol. 22, No. 16, 2003
Canovese et al.
Sch em e 3
Sch em e 4
the low temperature. However, since only one species
is detectable, we may conclude either that more likely
the sulfur freezes into only one preferential configura-
tion (only one diastereoisomer and its undetected enan-
tiomer) or that the two diastereoismers are isochronous.
These processes are clearly attributable to the peculiar
configuration of the N-S-N ligand, which disfavors
concomitant formation of two strained rings, which in
turn should induce the η3-η1-η3 allyl isomerism.
Kin etics a n d Mech a n ism of th e Allen e In ser tion
Rea ction . From NMR data it appears that in the case
of S-N-S derivatives the chloride complexes (II) react
considerably faster than their chloride-free counterparts
(I). In fact the chloride derivatives react almost instan-
taneously, whereas the reaction involving the chloride-
free substrates takes several hours under NMR experi-
mental conditions (vide infra).
interfering with adjacent molecules, behave as the
monomeric species when reacting with DMA, giving rise
quantitatively to the expected allyl complex (6).
As for the allyl complexes, they do not deserve a
detailed description since their solution behavior is quite
similar to that of analogous species described by us
elsewhere.4d,8 It should be sufficient to recall that
complexes bearing asymmetric allyl fragments and a
potentially tercoordinate ligands (although they should
exist as four diastereoisomers owing to the presence of
the asymmetric uncoordinated wing) rapidly intercon-
vert at room temperature. The fast fluxional rearrange-
ment observed is due to the η3-η1-η3 isomerism of the
allyl fragment induced by the nucleophilic attack of the
uncoordinated sulfur on the dangling wing. Under these
circumstances the sulfur absolute configuration inver-
sion remains obviously operative. On the contrary, the
N-S-N ligand, although undergoing the fast alternat-
ing coordination movement, never induces η3-η1-η3
However both I and II species react with allene; thus
the chloride concentration is time dependent and there-
fore it can modulate the equilibrium position and
consequently the observed rate constant in such a way
as to make its determination not straightforward
(Scheme 4).
The kinetic Scheme 4 could in principle be easily
integrated numerically as a function of the parameters
kI, kII, and KE. These can be determined by UV/vis
spectrophotometry via nonlinear regression of absorb-
ance to time data. However, owing to the high param-
eter correlation, the close proximity of extinction coef-
ficients of I and II, and the high difference between kI
and kII (vide infra), we preferred to dissect the overall
kinetic study into partial, separate sections correspond-
ing to (i) direct determination of KE, (ii) independent
determination of kI (from the chloride-free species I in
the absence of added Cl-), and (iii) independent deter-
mination of kII starting from II in the presence of an
excess of Cl-. The resulting data are reported in Table
3.
1
isomerism, and the low-temperature (223 K) H NMR
spectrum shows the presence of a substrate in which
the ligand acts like a bidentate (Scheme 3).
Sulfur inversion is “frozen” in this case, and a pair of
AB systems ascribable to H2C-S-CH2 protons are
observed which arise from the position of the substituted
allyl terminus with respect to the uncoordinated or to
the coordinated wing.4d However, only one species
among the four possible diastereoisomers is detectable
under our experimental conditions, which should origi-
nate from an asymmetric ligand (bidentate N-S-N)
coupled with an asymmetric allyl fragment. In this case,
the less energetic process is probably the alternating
attack of the dangling pyridines, which goes on despite
The equilibrium constants KE were determined by 1H
NMR technique by adding successive aliquots of tri-
ethylbenzylammonium chloride (TEBA) to a CD2Cl2
solution of substrate I ([Pd]0 ≈ 10-2 mol dm-3; the ionic
strength was not controlled) and recording the resulting
spectrum at 298 K (see Experimental Section and
Figure 6).
(8) Canovese, L.; Visentin, F.; Uguagliati, P.; Lucchini, V.; Bandoli,
G. Inorg. Chim. Acta 1998, 277, 247.

Chloride-Modulated Insertion Reactions
Organometallics, Vol. 22, No. 16, 2003 3235
stituent. Thus, since the electron-withdrawing capabil-
ity of the CH2-Py group lies between those of Me and
Cl- groups, the ensuing reactivity of the bis-chelate
chloride substrates (II) appears reasonable since it is
intermediate between those of the bidentate pyridyl-
thioether substrates bearing chloride and a methyl
group in position 6 of the pyridine ring.
Curiously both the complexes derived from the N-S-N
ligand (chloride and chloride-free) behave differently
from the corresponding S-N-S species. When DMA is
added to a CD2Cl2 solution of the chloride-free substrate,
an immediate reaction is observed. The typical 1H NMR
spectrum of the corresponding allyl derivative quanti-
tatively formed suggests that the substrate reacts
irrespectively of its mono- or oligomeric form and that
the reaction is fast, analogously to those where biden-
tate solvento substrates are involved;3c on the other
hand, the reactivity of the chloride species is inde-
pendent of added chloride. Apparently the poorly coor-
dinating pyridine nitrogen of the arm-off wing (vide
supra) does not displace the chloride ion, thereby
imparting to the N-S-N derivatives a low reactivity
analogous to that of an authentic bis-chelate chloride
species. As a matter of fact, since the structure of the
latter in solution is not distorted (the coordinated
pyridine ring is not substituted in position 6), its
reactivity lies between those of the bidentate HN-SPh
and HN-SMe chloro-methyl derivatives (Table 3).
F igu r e 6. 1H NMR chemical shift changes (298 K) upon
addition of triethylbenzylammonium chloride to a CD2Cl2
solution of [Pd(Me)(S-N-S(Me))]OTf (2a ). Solid line is the
best-fitting curve according to the model (see Experimental
Section).
The final 1H NMR spectrum ([Cl-]0 ≈ [Pd]0) was
virtually superposable to that of an authentic sample
of chloride species II. The equilibrium constants (Table
3) reflect the nucleophilic capability of the R-substituted
sulfur (the S-N-S(Ph) ligand being the less coordinat-
ing species and the S-N-S(t-Bu) the more coordinating
one). Despite the high nucleophilic strength of Cl- in
nonprotic solvents, no hints of complete displacement
of the ligands were observed. Apparently, the chelating
effect of the terdentate species is overwhelmed by the
chloride only when the mutual trans-influence of the
trans-coordinated chalcogen atoms is operative.
Exp er im en ta l Section
Ter d en t a t e Liga n d s. 2-[(2-Pyridylmethylthio)methyl]-
pyridine (N-S-N) and 2,6-bis(R-thiomethyl)pyridine (S-N-
S(R); R) Me, t-Bu, Ph) were synthesized according to pub-
lished procedures.4c-e All solvents were purified and distilled
by standard methods before use, while all other analytical
grade reagents were used as received.
The chloride-free complexes I react slowly with DMA,
whose insertion into the Pd-Me bond was directly
[P d Cl(Me)(COD)]. The title complex was obtained from
1
[Pd(COD)Cl2]9 following the published procedure.10
determined by H NMR technique under second-order
conditions (following the methyl signal disappearance)
only in the case of the species [Pd(Me)(S-N-S(Ph))]+
(2c). The substrates [Pd(Me)(S-N-S(R))]+ (2a , 2b) are
much less reactive, and in both cases the rate constant
was deduced from the half-life of the reaction (Table 2).
According to all the previous findings,3 the associative
attack of allene on the metal center is disfavored by
increasing basicity of the sulfur and by increasing steric
requirements of the substituent R of the sulfur itself.
However, the most noticeable result is the difference
between the rate constants of the chloride-free (I) and
the chloride (II) substrates (Table 2), which span several
orders of magnitude. The chloride species II behave
similarly to the bidentate pyridylthioether chloro methyl
complexes bearing a substituent group (Me, Cl) in
position 6 of the pyridine ring. Since the high reactivity
of the latter species was traced back to the distortion of
the chelate ring with respect to the main coordination
plane,3 we therefore advance the hypothesis that the
uncoordinated wing would induce an analogous effect.
Thus the chloride ion can modulate the overall rate of
allene insertion by simply modifying the position of
equilibrium between the closed (I) and the partially
open (II) species. Moreover, it was demonstrated3b,c that
the reactivity in this type of reaction depends strongly
on the basicity of the pyridine nitrogen, which can be
varied by changing the electronegativity of the 6-sub-
[P d (Me)(S-N-S(Me))]Cl (1a ). To a solution of 226.3 mg
(1.14 mmol) of 2,6-bis(mehtylthiomethyl)pyridine (S-N-
S(Me)) in 20 mL of THF was added 273.6 mg (1.03 mmol) of
[PdCl(Me)(COD)]. The solution was stirred for 4 h, although
the reaction product starts precipitating after 1 h owing to its
low solubility in THF. The reaction mixture was dried under
reduced pressure and dissolved in 15 mL of CH2Cl2, treated
with activated charcoal, filtered on Celite filter, and reduced
to a small volume. Addition of diethyl ether yields a yellowish
oily product, which was crystallized by stirring at 0 °C. The
yellow microcrystals were filtered off, washed with 20 mL of
diethyl ether, and dried under vacuum (334.8 mg, 91%). 1H
NMR (CDCl3, T ) 298 K, ppm): pyridine protons δ 7.93 (m,
3H, H3Pyr, H4Pyr, H5Pyr,), thiomethyl protons δ 5.04 (s, 4H,
Pyr(CH2-S)2), methyl protons δ 2.75 (s, 6H, S-CH3), methyl
protons δ 0.63 (s, 3H, Pd-CH3). IR: νCdN 1595.1 cm-1 (KBr).
Anal. Calcd for C10H16ClNPdS2: C, 33.71; H, 4.53; N, 3.93.
Found: C, 33.50; H, 4.64; N, 3.68.
The following complexes were synthesized in the same way
as [Pd(Me)(S-N-S(Me))]Cl using the appropriate ligand.
[P d (Me)(S-N-S(t-Bu ))]Cl (1b). Yield: 92% (yellow micro-
crystals). 1H NMR (CDCl3, 295 K, ppm): pyridine protons δ
8.09 (2H, H3Pyr,H5Pyr, d, J ) 7.7 Hz), 7.92 (t, 1H, H4Pyr, J ) 7.1
Hz), thiomethyl protons δ 4.99 (s, 4H, Pyr-CH2-S), tert-butyl
protons δ 1.49 (s, 18H, S-C(Me)3), methyl protons δ 0.74 (s,
(9) Chatt, J .; Vallarino, L. M.; Venanzi, L. M. J . Chem Soc. 1957,
3413.
(10) Ru¨lke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.

3236 Organometallics, Vol. 22, No. 16, 2003
Canovese et al.
3H, Pd-CH3). IR: νCdN 1597.0 cm-1 (KBr). Anal. Calcd for
8.41 (d, 2H, H6Pyr, J ) 4.6 Hz), 7.96 (td, 2H, H4Pyr, J ) 7.6 Hz,
C
16H28ClNPdS2: C, 43.64; H, 6.41; N, 3.18. Found: C, 43.88;
J ) 1.5 Hz), 7.58 (d, 2H, H3Pyr, J ) 7.9 Hz), 7.48 (t, 2H, H5
,
Pyr
H, 6.25; N, 3.32.
J ) 6.4 Hz), thiomethyl protons δ 5.18, δ ) 4.69 (AB system,
4H, Pyr-CH2-S, J ) 14.9 Hz), methyl protons δ 1.36 (s, 3H,
Pd-CH3). IR: νCdN 1602.8, νC-F 1259.5, νSdO 1029.9 cm-1
(KBr). Anal. Calcd for C14H15F3N2O3PdS2: C, 34.44; H, 3.05;
N, 5.90. Found: C, 34.44; H, 3.05; N, 5.90.
[P d (Me)(S-N-S(P h ))]Cl (1c). Yield: 94% (yellow micro-
crystals). 1H NMR (CDCl3, 298 K, ppm): pyridine and phenyl
protons δ 7.75-7.47 (m, 5H, H4Pyr, Hmeta), δ 7.30, (m, 8H, H5
,
Pyr
H3Pyr, Hortho, Hpara), thiomethyl protons δ 5.03 (s, 4H, Pyr-
CH2-S), methyl protons δ 1.10 (s, 3H, Pd-CH3). 13C NMR (in
CDCl3, 298 K, ppm): pyridine carbons δ 157.45 (C2Pyr, C6Pyr),
138.38 (C4Pyr), 122.88 (C3Pyr, C5Pyr), phenyl carbons δ 131.73,
129.21, 128.90, thiomethyl carbons δ 47.57 (S-CH2-Pyr),
methyl carbons δ -5.32 (Pd-CH3). IR: νCdN 1597.0 cm-1 (KBr).
Anal. Calcd for C20H28ClNPdS2: C, 50.00; H, 4.20; N, 2.92.
Found: C, 49.74; H, 4.28; N, 2.93.
The allyl complexes 3 and 6 were prepared analogously to
the similar species whose synthetic procedure was published
elsewhere.4d,8
[P d(η3-1,1,2-(Me)3C3H2)(S-N-S(Me))]OTf (3a). Yield: 90%
1
(cream-colored microcrystals). H NMR (CDCl3, 298 K, ppm):
pyridine protons δ 7.89 (t, 1H, H4pyr, J ) 7.7 Hz), 7.56 (d, 2H,
H5pyr, H3pyr, J ) 7.7 Hz), thiomethyl protons δ 4.20 (s, 4H, Pyr-
CH2-S), allyl protons δ 3.97 (s, 2H, Hsyn, Hanti), thiomethyl
protons δ 2.15 (s, 6H, S-CH3), allyl methyl δ 2.14 (s, 3H, C2-
CH3), 1.69 (bs, 3H, C1-CH3syn), 1.50 (bs, 3H, C1-CH3anti). IR
[P d Cl(Me)(N-S-N))] (4). Yield: 91% (red-brown micro-
crystals). 1H NMR (CDCl3, 298 K, ppm): pyridine protons δ
8.74 (bs, 2H, H6Pyr) 7.69 (Td, 2H, H4 J ) 7.7 Hz, J ) 1.5
Pyr
Hz), 7.47 (d, 2H, H3Pyr, J ) 7.3 Hz), 7.21 (t, 1H, H5Pyr, J ) 6.4
Hz), thiomethyl protons δ 4.22 (bs, 4H, S(CH2-Pyr)2), methyl
protons δ 0.90 (s, 3H, Pd-CH3). IR: νCdN coordinated 1589.3, νCdN
ν
CdN: 1597.0 cm-1 (KBr). Anal. Calcd for C16H24F3NO3PdS3:
C, 35.72; H, 4.50; N, 2.60. Found: C, 35.72; H, 4.68; N, 2.83.
[P d (η3-1,1,2-(Me)3C3H2)(S-N-S(t-Bu ))]OTf (3b). Yield:
1602.7 cm-1 (KBr). Anal. Calcd for C13H15ClN2PdS:
1
uncoordinated
87.4% (yellow microcrystals). H NMR (CDCl3, 298 K, ppm):
pyridine protons δ 7.87 (t, 1H, H4pyr, J ) 7.8 Hz), 7.61 (d, 2H,
H5pyr, H3pyr, J ) 7.8 Hz), thiomethyl protons δ 4.24 (s, 4H, Pyr-
CH2-S), allyl protons δ 4.10 (bs, 2H, Hsyn, Hanti), allyl methyl
δ 2.16 (s, 3H, C2-CH3), 1.74 (s, 3H, C1-CH3syn), 1.51 (s, 3H,
C1-CH3anti), tert-butyl protons δ 1.32 (s, 18H, S-C(CH3)3). IR
C, 41.84; H, 4.05; N, 7.51. Found: C, 42.08; H, 3.79; N, 7.78.
[P d (Me)(S-N-S(Me))]OTf (2a ). To a solution of 150 mg
(0.42 mmol) of [Pd(Me)(S-N-S(Me))]Cl in CH2Cl2 (20 mL) was
added 113.6 mg (0.44 mmol) of AgOTf. The resulting suspen-
sion was stirred in the dark for 3 h and filtered on a Millipore
filter. The clear solution obtained was treated with activated
charcoal and filtered on Celite filter. Reduction under reduced
pressure and addition of diethyl ether yielded the title
compound as a whitish solid, which was recrystallized from
CH2Cl2/diethyl ether and dried under vacuum. A total of 0.28
ν
CdN: 1602.8 cm-1 (KBr). Anal. Calcd for C22H36F3NO3PdS3:
C, 42.47; H, 5.83; N, 2.25. Found: C, 42.65; H, 5.86; N, 2.47.
[P d (η3-1,1,2-(Me)3C3H 2)(S-N-S(P h ))]OTf (3c). Yield:
1
73.2% (whitish microcrystals). H NMR (CDCl3, 298 K, ppm):
pyridine and phenyl protons δ 7.55 (t, 1H, H4pyr, J ) 7.7 Hz),
7.22 (m, 12H, H5pyr, H3pyr, S-C6H5), thiomethyl protons δ 4.15
(s, 4H, Pyr-CH2-S), allyl protons δ 4.13 (bs, 2H, Hsyn, Hanti),
allyl methyl δ 2.17 (s, 3H, C2-CH3), 1.68 (s, 3H, C1-CH3syn),
1.46 (s, 3H, C1-CH3anti). IR νCdN: 1603.0 cm-1 (KBr). Anal.
1
mmol of the product were obtained (129.3 mg, 67%). H NMR
(CDCl3, 298 K, ppm): pyridine protons δ 7.92 (t, 1H, H4Pyr, J
) 7.9 Hz), 7.66 (d, 2H, H3Pyr, H5Pyr, J ) 7.9 Hz), thiomethyl
protons δ 4.83 (bs, 4H, Pyr-CH2-S), methyl protons δ 2.72
(s, 6H, S-CH3), 0.62 (s, 3H, Pd-CH3). 13C NMR (CDCl3, 298
K, ppm): pyridine carbons δ 156.31 (C2Pyr, C6Pyr), 140.80 (C4Pyr),
123.33 (C3Pyr, C5Pyr), thiomethyl carbons δ 49.98 (S-CH2-Pyr),
methyl carbons δ -8.92 (Pd-CH3). IR: νCdN 1597.0, νC-F
1257.5, νSdO 1029.9 cm-1 (KBr). Anal. Calcd for C11H16F3NO3-
PdS3: C, 28.12; H, 3.43; N, 2.98. Found: C, 28.06; H, 3.50; N,
2.73.
Calcd for
C26H28F3NO3PdS3: C, 47.16; H, 4.26; N, 2.12.
Found: C, 47.34; H, 3.96; N, 1.84.
[P d (η3-1,1,2-(Me)3C3H2)(N-S-N)]ClO4 (6). Yield: 54.8%
(red-orange microcrystals). 1H NMR (CDCl3, 298 K, ppm):
pyridine protons δ 8.44 (d, 2H, H6pyr, J ) 4.2 Hz), 7.66 (td,
2H, H4pyr, J ) 7.5 Hz, J ) 1.7 Hz), 7.21(d, 2H, H3pyr, J ) 6.22
Hz), 7.19 (t, 2H, H5pyr, J ) 6.2), thiomethyl protons δ 4.37 (s,
4H, Pyr-CH2-Ss), allyl protons δ 4.08 (s, 1H, Hsyn), 3.71 (s,
1H, Hanti), allyl methyl δ 2.17 (s, 3H, C2-CH3), 1.70 (s, 3H,
C1-CH3syn), 1.46 (s, 3H, C1-CH3anti). IR νCdN: 1602.8 cm-1
(KBr). Anal. Calcd for C18H23ClN2O4PdS: C, 42.78; H, 4.59;
N, 5.54. Found: C, 42.74; H, 4.72; N, 5.33.
The following complexes were synthesized in the same way
as [Pd(Me)(S-N-S(Me))]OTf using the appropriate starting
substrate.
[P d (Me)(S-N-S(t-Bu ))]OTf (2b). Yield: 88% (whitish
microcrystals). 1H NMR (CDCl3, 298 K, ppm): pyridine protons
δ 7.92 (t, 1H, H4Pyr, J ) 7.9 Hz), 7.82 (d, 2H, H3Pyr, H5Pyr, J )
7.5 Hz), thiomethyl protons δ 4.77 (s, 4H, Pyr-CH2-S), tert-
butyl protons δ 1.49 (s, 18H, S-C(CH3)3), methyl protons δ
0.77 (s, 3H, Pd-CH3). 13C NMR (CDCl3, 298 K, ppm): pyridine
X-r a y An a lysis. The X-ray data collection of [Pd(Me)(S-
N-S(t-Bu))]OTf (2b) was performed at room temperature with
a STADI 4 CCD STOE area detector diffractometer on single
crystal mounted in a thin-walled glass capillary with graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å). Systematic
absences could not unambiguously identify the space group;
solution was therefore carried out in C2, Cm, and C2/ m. Close
scrutiny of the possible monoclinic space group with mirror
planes yielded no viable solutions, while a satisfactory refine-
ment was achieved in the first space group. However, solution
in C2 of the structures performed with the SHELXTL/PC11
was rather difficult due to the pseudo mirror plane bisecting
the cationic complex. The metal and the two sulfur atoms were
located from a Patterson synthesis, while the sulfonato group
and most of the non hydrogen atoms were identified from a
subsequent Fourier synthesis. After some cycles of refinement,
performed with the SHEXL-93 program,12 the SO3 group
appeared disordered, two distinct sites for oxygen atoms being
identified, and these were refined satisfactorily with occupan-
carbons δ 157.35 (C2Pyr, C6Pyr), 140.57 (C4Pyr), 122.62 (C3
,
Pyr
C5Pyr), thioether carbons δ 54.06 (S-C(CH3)3), 44.79 (S-CH2-
Pyr), tert-butyl carbons δ 31.04 (S-C(CH3)3), methyl carbon δ
-8.98 (Pd-CH3). IR: νCdN 1595.1, νC-F 1263.3, νSdO 1028.0
cm-1 (KBr). Anal. Calcd for C17H28F3NO3PdS3: C, 36.81; H,
4.98; N, 2.28. Found: C, 36.81; H, 4.98; N, 2.28.
[P d(Me)(S-N-S(P h ))]OTf (2c). Yield: 89% (whitish micro-
crystals). 1H NMR (CDCl3, 298 K, ppm): pyridine and phenyl
protons δ 7.94 (d, 1H, H4Pyr, J ) 7.7 Hz), 7.77 (m, 4H, Hmeta),
7.69 (d, 2H, H3Pyr, H5Pyr, J ) 7.7 Hz), 7.46 (m, 6H, Hortho, Hpara),
thiomethyl protons δ 5.17 (bs, 4H, Pyr-CH2-S), methyl
protons δ 0.67 (s, 3H, Pd-CH3). 13C NMR (CDCl3, 298 K,
ppm): pyridine carbons δ 156.17 (C2Pyr, C6Pyr), 140.58 (C4Pyr),
123.19 (C3Pyr, C5Pyr), phenyl carbons δ 132.56, 131.40, 130.78,
130.28, thiomethyl carbons δ 53.98 (S-CH2-Pyr), methyl
carbon δ -5.63 (Pd-CH3). IR: νCdN 1597.0, νC-F 1271.0, νSdO
1029.9 cm-1 (KBr). Anal. Calcd for C21H20F3NO3PdS3: C, 42.46;
H, 3.39; N, 2.36. Found: C, 42.56; H, 3.68; N, 2.51.
(11) Sheldrick, G. M. SHELXTL/ PC, Version 5.03; Siemens Ana-
lytical X-ray Instruments Inc.: Madison, WI, 1994.
(12) Sheldrick, G. M. SHELXL-93, Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Germany, 1993.
[P d (Me)(N-S-N)]OTf (5). Yield: 97% (pale orange micro-
crystals). 1H NMR (CDCl3, 298 K, ppm): pyridine protons δ

Chloride-Modulated Insertion Reactions
Organometallics, Vol. 22, No. 16, 2003 3237
Ta ble 3. Equ ilibr iu m Con sta n ts (KE) for th e
Ad d ition of Ch lor id e to Com p lexes I (Sch em e 2) in
CD2Cl2 a t 298 K a n d Secon d -Or d er Ra te Con sta n ts
Ta ble 4. Cr ysta llogr a p h ic Da ta
formula
space group
fw
a, Å
b, Å
c, Å
C17H28F3NO3PdS3 C17.5H32Cl4N1O0.5Pd1S2
C2 (No. 5)
553.98
Pbcn (No. 60)
576.76
kI
a
(mol-1 dm3 s-1
)
21.541(4)
12.051(2)
8.919(2)
97.15(3)
2297(1)
4
28.332(1)
9.5796(4)
18.3486(8)
complex I
KE
[Pd(Me)(S-N-S(Ph))]+
[Pd(Me)(S-N-S(Me))]+
[Pd(Me)(S-N-S(t-Bu))]+
[Pd(Me)(N-S-N)]+
780 ( 140
53 ( 7
71 ( 14
(4.35 ( 0.09) × 10-4 b
∼ 8 × 10-6 c
∼ 1 × 10-6 c
fast
â, deg
V, Å3
4979.9(4)
8
Z
λ Å; µ(Mo KR),
0.71073; 1.12
0.71073; 1.348
kII
k2
mm-1
d
complex II
(mol-1 dm3 s-1
)
(mol-1 dm3 s-1
)
f(calcd), g cm-3
no. of indep reflns 3417
1.602
1.539
6617
4058
[PdCl(Me)(S-N-S(Ph))]
[PdCl(Me)(S-N-S(Me))]
80 ( 2
36 ( 1
23-164e
2.42-117e
0.33 - 30e
no. of reflns with
I>2σ(I)
2221
[PdCl(Me)(S-N-S(t-Bu))] 0.4 ( 0.2
[PdCl(Me)(N-S-N)]
(4.3 ( 0.2) × 10-3 8.17 × 10-4 to
no. of variables
171
0.048
0.100
240
4.0 × 10-2 f
Ra
wR2
0.048
0.092
0.79
b
a
b
Determined by 1HNMR technique. Determined by 1H NMR
technique under second-order conditions. c Determined from t1/2
data according to the relationship kI ) ln((2[DMA]0 - [complex]0)/
largest difference 0.60
peak (e Å-3
)
d
[DMA]0)/(([DMA]0 - [complex]0)t1/2). Determined by UV/vis tech-
R ) ∑||Fo| - |Fc|| /∑|Fo|. bwR2 ) [∑w(Fo - Fc2)2 /∑w(Fo2)2]1/2
.
a
2
nique from experiments under pseudo-first-order conditions. e k2
values for insertion of DMA into the Pd-Me bond of the complexes
[PdCl(Me)(R′N-SR)] (R′N-SR bidentate pyridylthioether ligand
bearing an R′ substituent in position 6 of pyridine ring; R′ ) Me
(lower limit), R′ ) Cl (upper limit)). From refs 1a,b. f k2 values for
insertion reaction of DMA into the Pd-Me bond of the complexes
[PdCl(Me)(HN-SR)] (HN-SR bidentate pyridylthioether ligand
without a substituent in the pyridine ring; R ) Me (lower limit),
R′ ) Ph (upper limit)). From refs 1a,b. Second-order rate constants
for the reaction of allene (DMA) insertion into the Pd-Me bond
of complexes I (kI, in CD2Cl2) and II (kII, in CH2Cl2) (Scheme 4)
at 298 K along with second-order rate constants (k2) for the
reactions of allene (DMA) insertion into the Pd-Me bond of related
bidentate systems (see Results and Discussion).
750 spectrophotometer and on a Bruker 300 Avance spectrom-
eter, respectively. UV-vis spectra and kinetic measurements
were performed on a Perkin-Elmer Lambda 40 spectropho-
tometer equipped with a Perkin-Elmer PTP 6 (Peltier Tem-
perature Programmer) apparatus.
Equ ilibr iu m a n d Kin etic Mea su r em en ts. The determi-
nation of equilibrium constants (Scheme 2) was achieved by
adding preweighed aliquots of TEBA chloride (triethylbutyl-
ammonium chloride) to a solution in CD2Cl2 of the complex
under study ([Pd(Me)(S-N-S(R))]OTf, R ) Me, t-Bu, Ph; [Pd]0
≈ 5 × 10-2 mol dm-3) into a 5 mm NMR tube at 298 K. The
resulting 1H NMR spectra were recorded and analyzed by a
nonlinear least-squares procedure according to the following
model:
cies 2/3 and 1/3. On the contrary, although a final difference
Fourier synthesis had shown rather extended regions of
electron density at the sites of F atoms, it did not prove
possible to resolve them into separate components. In the
refinement procedure, based on F2, only the non-hydrogen
atoms of the “inner core”, together with the S(3) of the anion,
were assigned anisotropic displacement parameters.
As expected, significant matrix correlations (up to 0.89) were
observed between thermal motion parameters of the atoms
related by the pseudo-mirror (for example, S(1)/S(2), C(2)/C(8),
C(3)/C(7), ..., for which x, y, z coordinates correspond with
values very close to x, -y, z).
[Pd]0 ) [I] + [II]
[Cl-]0 ) [II] + [Cl-]
KE ) [II]/[I][Cl-]
and minimizing the sum of squares
Crystal data, summary of data collection, and structure
refinement are collected in Table 4.
Because of pseudosymmetry, which caused problems in
refinement, some caution is required in considering the bond
lengths and angles.
The X-ray data collection of [Pd(Me)(S-N-S(t-Bu))]Cl (1b)
was performed at 183 K with a Bruker Smart CCD diffrac-
tometer on single crystal mounted on a thin-walled glass
capillary with graphite-monochromated Mo KR radiation. All
non-H atoms were refined anisotropically. H atoms bound to
C atoms were added in calculated positions. The water
molecules was refined with site occupancy 0.5. The computer
program SHELXTL11 was used for structure solution and
refinement.
2
Φ )
(νobs - νcalc)
∑
where νobs is the observed chemical shift upon addition of Cl-
and νcalc ) νI(1 - [II]/[Pd]0) + νII[II]/[Pd]0 is the chemical shift
calculated at the current values of the parameters being
optimized (KE and νII). νI and νII are the chemical shifts relating
to Pd-CH3 (R ) Ph) or CH2-S (R ) Me, t-Bu) in I and II,
respectively. During each iterative cycle νII can be held
1
constant at the value experimentally determined from the H
NMR spectrum of species II taken in the presence of excess
Cl-.
The kinetics of DMA insertion were carried out under
pseudo-first-order conditions ([Pd]0 ≈ 10-4, [Cl-]0 ≈ 10-3
,
Crystal data, summary of data collection, and structure
refinement are also collected in Table 4.
[DMA] > 10-3 mol dm-3) in CH2Cl2 at 25 °C by adding
appropriate aliquots of DMA solutions to solutions of the
palladium substrates II and TEBA chloride in the pre-
thermostated cell of the spectrophotometer. The kinetics
obeyed the monoexponential rate law At ) A∞ + (A0 - A∞)
exp(-kobst), where kobs is given by the expression
Solven ts a n d Rea gen ts. Unless otherwise stated, all the
reactions were performed under inert atmosphere (N2) by
Schlenk technique at room temperature. THF and CH2Cl2 were
dried and distilled on Na/benzophenone and on CaH2, respec-
tively. Acetone and CH3CN were stored over molecular sieves
and distilled under N2 immediately before use. All other
chemicals were commercially available grade products.
IR, NMR, a n d UV-Vis Mea su r em en ts. The IR and 1H
and 13C{1H} NMR spectra were recorded on a Nicolet Magna
kobs ) [DMA]0(kII[Cl-]0 + kI/KE)/(1/KE + [Cl-]0)
according to Scheme 4.

3238 Organometallics, Vol. 22, No. 16, 2003
Canovese et al.
Since kI/KE , kII[Cl-]0 under our experimental condition (see
Table 3), kobs reduces to
0.15 mol dm-3) and computing the ensuing kI constants from
the customary second-order rate law or from the estimated
half-life time as kI ≈ ln((2[DMA]0 - [Pd]0)/[DMA]0)/(([DMA]0
- [Pd]0)t1/2).
kobs ) [DMA]0kII[Cl-]0/(1/KE + [Cl-]0)
Su p p or tin g In for m a tion Ava ila ble: Text giving details
of the X-ray crystal structure studies and table of crystal
structure determination data, atomic coordinates, anisotropic
thermal parameters, and bond lengths and angles (CIF files)
is available free of charge via the Internet at http://pubs.acs.org.
from which the second-order rate constant kII can be deter-
mined from the slope of kobs versus [DMA]0 at the known values
of [Cl-]0 and KE.
Owing to the small values of kI, these constants were
determined by 1H NMR experiments by reacting the chloride-
free species I ([I]0 ≈ 3 × 10-2 mol dm-3) with DMA ([DMA]0 ≈
OM030293F