Synthesis and reactivity of new methylallylpalladium(II) complexes with bidentate 2-(methylthio-N-benzylidene)anilines

Article abstract of DOI:10.1016/j.jorganchem.2003.10.028

This work describes the synthesis, characterisation and reactivity of new methylallyl Pd(II) complexes that contain bidentate 2-(methylthio-N-benzylidene)anilines as ligands. The reaction of the binuclear complex [(η³-Me-allyl)Pd(μ-Cl)₂] with AgBF₄ causes the total abstraction of the chloride bridges, with the subsequent formation of an intermediary fragment of Pd(II). This fragment in turn reacts with neutral bidentate 2-(methylthio- N -benzylidene)anilines to give cationic complexes of Pd(II) of general formula [(η³-Me-allyl)Pd(η ²-S,N-MeSC₆H₄N=CHC₆ H₄(X)Y)]BF₄ [X=H, Y=H (1); X=F, Y=H (2); X=Me, Y=H (3); X=H, Y=Cl (4); X=H, Y=Me₂N (5); X=H, Y=NO₂ (6)]. The new complexes were characterised by means of elemental analysis, IR, NMR [¹H, ¹⁹F {¹H}, ¹³C{¹H}, ³¹ P{¹H}, Dept, ¹H-H-COSY, HSQC, HMBC] and mass spectroscopies. The reaction of the Pd(II) complexes with nucleophiles such as NaI, (EtO)₂PS₂K, KCN, KSCN or NaH lead to the deco-ordination of the bidentate ligands to give dimeric or polymeric complexes of Pd(II). The reactivity pattern observed is discussed by a theoretical analysis based on Fukui functions.

Full text of DOI:10.1016/j.jorganchem.2003.10.028

Journal of Organometallic Chemistry 689 (2004) 395–404
www.elsevier.com/locate/jorganchem
Synthesis and reactivity of new methylallylpalladium(II)
complexes with bidentate 2-(methylthio-N-benzylidene)anilines
*
ꢀ
ꢀ
Raul Contreras , Barbara Loeb, Mauricio Valderrama, Mario Lagos,
ꢀ
Francisco Burgos, Paola Ramırez, Javier Concepcion
ꢀ
Departamento de Quꢀımica Inorgꢀanica, Facultad de Quꢀımica, Pontificia Universidad Catꢀolica de Chile, Av. Vicu~na Mackenna 4860,
Casilla 306, Santiago-22, Chile
Received 27 June 2003; accepted 22 October 2003
Abstract
This work describes the synthesis, characterisation and reactivity of new methylallyl Pd(II) complexes that contain bidentate 2-
(methylthio-N-benzylidene)anilines as ligands. The reaction of the binuclear complex [(g3-Me-allyl)Pd(l-Cl)2] with AgBF4 causes
the total abstraction of the chloride bridges, with the subsequent formation of an intermediary fragment of Pd(II). This fragment in
turn reacts with neutral bidentate 2-(methylthio-N-benzylidene)anilines to give cationic complexes of Pd(II) of general formula [(g3-
Me-allyl)Pd(g2-S,N-MeSC6H4N@CHC6H4(X)Y)]BF4 [X ¼ H, Y ¼ H (1); X ¼ F, Y ¼ H (2); X ¼ Me, Y ¼ H (3); X ¼ H, Y ¼ Cl (4);
X ¼ H, Y ¼ Me2N (5); X ¼ H, Y ¼ NO2 (6)]. The new complexes were characterised by means of elemental analysis, IR, NMR [1H,
1
19F{1H}, 13C{1H}, 31P{1H}, Dept, H–1H-COSY, HSQC, HMBC] and mass spectroscopies. The reaction of the Pd(II) complexes
with nucleophiles such as NaI, (EtO)2PS2K, KCN, KSCN or NaH lead to the deco-ordination of the bidentate ligands to give
dimeric or polymeric complexes of Pd(II). The reactivity pattern observed is discussed by a theoretical analysis based on Fukui
functions.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Palladium; 2-(Methylthio-N-benzylidene)anilines complexes; Schiff base complexes; Methylallylpalladium complexes; NMR spectra
1. Introduction
benzylideneanilines, of class [p-XC6H4CH@NC6H4(2-
SMe)] (X ¼ H, Me, OMe, Cl, NO2). These ligands react
with palladium(II) acetate to produce a cyclopalladation
reaction. In this sense, Schiff bases are suitable ligands
for cyclopalladation or mercuration reactions [5].
In this work, we report the synthesis and characteri-
sation of new mononuclear cationic complexes of palla-
dium(II) of the type [(g3-Me-allyl)Pd(g2-S,N-MeSC6
H4N@CHC6H4(X)Y)]BF4 where X ¼ H, Y ¼ H (1);
X ¼ F, Y ¼ H (2); X ¼ Me, Y ¼ H (3); X ¼ H, Y ¼ Cl (4);
X ¼ H, Y ¼ Me2N (5) and X ¼ H, Y ¼ NO2 (6)]. The re-
activity of the S–C bond of the thioether group of the
Schiff base toward nucleophilic attack is discussed.
Theoretically, by analysing the corresponding Fukui
functions [6–8], the reactivity of the different sites of the
molecule with regard to nucleophilic, electrophilic or free
radical attack is analyzed. The latter study sheds light on
the reactivity behaviour of the palladium(II) cationic
complexes reported in the present work.
Transition metal complexes containing heterodi-
functional bidentate ligands that present hard and soft
donor sites are expected to be efficient in some catalytic
transformations [1]. In particular, complexes containing
thioether derivatives with N,S-; As,S- or P,S-donor sets
as ligands have been extensively studied. Due to the
thioether function the ligand is expected to be more la-
bile, permitting the formation of a vacant site at the
metal centre [2]. These complexes also show the ability
to transfer the alkyl group from the thioether to suitable
nucleophiles, and be converted into thiolate complexes
[3].
In 1995, Basuli et al. [4] studied the co-ordination
properties of Schiff bases derived from substituted
* Corresponding author. Tel.: +5626864415; fax: +5626864744.
E-mail address: rcontrer@puc.cl (R. Contreras).
0022-328X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.10.028

396
R. Contreras et al. / Journal of Organometallic Chemistry 689 (2004) 395–404
2. Experimental
2.1. General
3.07 [s, 2H, Hanti], 3.90 [s, 2H, Hsyn], 7.46 [dt, 1H, H4,
3J(H4–H5) ¼ 3J(H4–H3) ¼ 7.45 Hz, 4J(H4–H6) ¼ 1.3 Hz],
7.52 [dt, 1H, H5, 3J(H5–H4) ¼ 3J(H5–H6) ¼ 7.45 Hz,
3
4J(H5–H3) ¼ 1.4 Hz], 7.60 [pt, 2H, H9, H11, J(H9–H8)
3
3
All reactions were carried out under purified nitrogen
by using Schlenk-tube techniques. The solvents used in
the reactions were of analytical grade and, in some cases
of reagent grade, and were dried by a reported proce-
dure [9]. The 2-(methylthio)-N-substituted-benzylidene)
anilines were synthesised according to standard proce-
dures by condensing equimolar amounts of 2-(methyl-
thio)aniline and the respective substituted benzaldehyde,
under continuous stirring for 2 h, in the presence of
magnesium sulfate [10]. The compounds [(g3-Me-al-
lyl)Pd(l-X)]2 (X ¼ Cl, I) [11,12] and [(EtO)2PS2K] [13]
were prepared following literature methods.
NMR spectra were recorded on Bruker AC-200P and
Avance-400 spectrometers. Chemical shifts are reported
in ppm relative to Me4Si (1H) and 85% H3PO4
(31P{1H}, positive shifts downfield). The IR spectra in
the range 4000–250 cmꢀ1 were recorded in KBr pellets
on a model Vector-22 FT-IR Bruker spectrophotometer.
Elemental analyses (C, H, N, S) were made with a Fi-
sons model EA-1108 microanalyser. FAB mass spectral
analyses were performed in a VG Autospec spectrome-
ter with 3-nitrobenzylalcohol as a matrix. Conductivity
measurements were carried out in solution, using a
WTW LF-521 conductimeter with a cell of constant
1.07.
ꢁ
3J(H9–H11) ꢁ J(H11–H10) ꢁ J(H11–H12) ¼ 7.5 Hz],
7.74–7.65 [m, 3H, H10, H6, H3], 8.06 [d, 2H, H8, H12,
3
3J(H8–H12) ꢁ J(H12–H11) ¼ 7.3 Hz], 9.09 [s, 1H, CH7@
N]. FT-IR (KBr, cmꢀ1): m(CN), 1610 vs, m(BF4), 1057 vs,
521 m. MS (FABþ) m/z 388 (Mþ–BF4).
2: Yield: 198 mg (79%). Anal. Found: C, 43.9; H, 4.1;
S, 6.3; N, 2.6. Calc. for C18H19BF5NPdS: C, 43.8; H,
3.8; S, 6.5; N, 2.8%. KM ¼ 112.8 Xꢀ1 molꢀ1 cm2. H
1
NMR in CD3CN; d 2.04 [s, 3H, C(allyl)–Me], 2.83 [s,
3H, S–Me], 3.07 [s, 2H, Hanti], 3.96 [s, 2H, Hsyn], 7.34
[dd, 1H, H11, 3J(H11–H10) ¼ 9.3 Hz, 4J(H11–H9) ¼ 1.6
Hz] 7.43 [dd, 1H, H8, 3J(H8–H9) ¼ 7.4 Hz, 4J(H11–
H9) ¼ 1.9 Hz], 7.50 [m, 2H, H3, H4], 7.64 [m, 2H, H5,
3
H6], 7.74 [dpt, 1H, H10, 3J(H10–H11) ꢁ J(H10–H9) ꢁ 7.4
Hz, 4J(H10–H8) ¼ 1.9 Hz], 8.21 [dt, 1H, H9, 3J(H9–
3
H8) ꢁ J(H9H10) ¼ 7.5 Hz], 9.18 [s, 1H, CH7@N].19F
NMR in CD3CN: d )115.8 [s, F-ring]. FT-IR (KBr,
cmꢀ1): m(CN), 1621 vs, m(BF4), 1060 vs, 521 m. MS
(FABþ) m/z 406 (Mþ–BF4).
3: Yield: 168 mg (65%). Anal. Found: C, 46.4; H, 4.7;
S, 6.3; N, 3.1. Calc.for C19H22 BF4NPdS: C, 46.6; H,
4.5; S, 6.5; N, 2.9%. 1H NMR in CD3CN: d 2.02 [s, 3H,
C(allyl)–Me], 2.57 [s, 3H, C–Me], 2.91 [s, 3H,S–Me],
2.02 [s, 2H, Hanti], 3.85 [s, 2H, Hsyn], 7.41 [d, 1H, H11,
3J(H11–H10) ¼ 8.2 Hz], 7.43 [pt, 1H, H9, 3J(H9–
3
H8) ꢁ J(H9–H10) ¼ 8.1 Hz], 7.56 [m, 3H, H4, H5, H10],
4
2.2. Synthesis of complexes
7.75 [dd, 1H H3, 3J(H3–H4) ¼ 7.5 Hz, J(H3–H5) ¼ 1.5
Hz], 7.78 [dd, 1H, H6, 3J(H6–H5) ¼ 7.5 Hz, 4J(H6–
H4) ¼ 1.3 Hz], 7.95 [d, 1H, H8, 3J(H8–H9) ¼ 7.6 Hz],
9.37 [s, 1H, CH7@N]. FT-IR (KBr, cmꢀ1): m(CN), 1610
vs, m(BF4), 1056 vs, 521 m. MS (FABþ) m/z 402 (Mþ–
BF4).
2.2.1. [(g3-Me-allyl)Pd(g2-S,N-MeSC6H4N@CHC6H4
(X)Y)]BF4 [X ¼ H, Y ¼ H (1); X ¼ F, Y ¼ H (2);
X ¼ Me, Y ¼ H (3); X ¼ H, Y ¼ Cl (4); X ¼ H,
Y ¼ Me2N (5); X ¼ H, Y ¼ NO2 (6)]
A solution of [(g3-Me-allyl)Pd(l-Cl)]2 (0.25 mmol,
100 mg) in THF (20 cm3) was treated with AgBF4 (0.51
mmol, 100 mg). The mixture was stirred at room tem-
perature for 2 h and the AgCl formed was filtered off
through Kieselguhr. To the resulting solution was added
a stoichiometric amount of the corresponding bidentate
ligand [L1: 0.50 mmol, MeSC6H4N@CHC6H5 (113.5
mg); MeSC6H4N@CHC6H4F (122.5 mg); MeSC6H4N@
CHC6H4Me (120.5 mg); MeSC6H4N@CHC6H4Cl
(130.8 mg); MeSC6H4N@CHC6H4NMe2 (135 mg);
MeSC6H4N@CHC6H4NO2 (136 mg)], and the mixture
stirred at room temperature. The solution was concen-
trated to a small volume and the complexes were pre-
cipitated by the addition of Et2O. The solid product was
collected by filtration, washed with cold THF and Et2O,
and dried under vacuum.
4: Yield: 168 mg (65%). Anal. Found: C, 41.3; H, 3.6;
S, 6.2; N, 2.7. Calc. for C18H19BClF4NPdS: C, 41.1; H,
3.6; S, 6.1; N, 2.6%. 1H NMR in CD3CN; d 2.08 [s, 3H,
C(allyl)–Me], 2.88 [s, 3H, S–Me], 3.11 [s, 2H, Hanti], 3.97
3
[s, 2H, Hsyn], 7.49 [dt, 1H, H4, 3J(H4–H3) ꢁ J(H4–
H5) ¼ 7.5 Hz; 4J(H4–H6) ¼ 1.3 Hz], 7.54 [dt, 1H, H5,
3
4
3J(H5–H4) ꢁ J(H5–H6) ¼ 7.6 Hz, J(H5–H3) ¼ 1.5 Hz],
7.63 [d, 2H, 0 Hb,Hb0, AA0BB0 system: 3J(Ha–
Hb) ¼ 3J(Ha0-Hb ) ¼ 8.5 Hz], 7.69 [dd, 1H, H3, J(H3–
3
H4) ¼ 7.6 Hz, 4J(H3–H5) ¼ 1.5 Hz], 7.74 [dd, 1H, H6,
3J(H6–H5) ¼ 7.6 Hz, J(H6–H4) ¼ 1.2 Hz], 8.07 [d, 2H,
4
Ha, Ha0, AA0BB0 system: 3J(HaHb) ¼ 3J(Ha0–Hb0) ¼ 8.5
Hz], 9.07 [s, 1H, CH7@N]. FT-IR (KBr, cmꢀ1): m(CN),
1612 vs, m(BF4), 1060 vs, 521 m.
5: Yield: 253 mg (96%). Anal. Found: C, 46.2; H, 4.8;
S, 6.3; N, 5.4. Calc. for C20H25BF4N2PdS: C, 46.3; H,
4.9; S, 6.2; N, 5.4%. 1H NMR in CD3CN: d 2.21 [s, 3H,
C(allyl)–Me], 2.86 [s, 3H, S–Me], 3.13 [s, 6H, NMe2],
3.18 [s, 2H, Hanti], 4.07 [s, 2H, Hsyn], 6.85 [d, 2H, Hb,Hb0,
AA0BB0 system: 3J(Ha–Hb) ¼ 3J(Ha0–Hb0) ¼ 9.0 Hz],
1: Yield: 200 mg (83%). Anal. Found: C, 45.7; H, 4.3;
S, 6.5; N, 2.5. Calc. for C18H20BF4NPdS: C, 45.5; H, 4.2;
S, 6.7; N, 2.9%. KM ¼ 200 Xꢀ1 molꢀ1cm2. H NMR in
1
CD3CN: d 2.07 [s, 3H, C(allyl)–Me], 2.85 [s, 3H, S–Me],

R. Contreras et al. / Journal of Organometallic Chemistry 689 (2004) 395–404
397
3
7.40 [dt, 1H, H4, 3J(H4–H3) ꢁ J(H4–H5) ¼ 7.7 Hz;
formed were collected by filtration, washed with cold
Et2O, and dried under vacuum. The NMR data of the
crystals correspond to the free ligands. The filtrate was
evaporated to dryness to give a brown–orange solid
residue, which was characterised as [(g3-Me-al-
lyl)Pd{g2-S2P(OEt)2}] by comparison with an authentic
sample.
4J(H4–H6) ¼ 1.1 Hz], 7.51 [dt, 1H, H5, 3J(H5–
H6) ꢁ J(H5–H4) ¼ 8.0 Hz, 4J(H5–H3) ¼ 1.2 Hz], 7.67
3
3
4
[dd, 1H, H3, J(H3–H4) ¼ 7.7 Hz, J(H3–H5) ¼ 1.2 Hz],
3
7.68 [d, 1H, H6, J(H6–H5) ¼ 8.0 Hz], 8.02 [d, 2H, Ha,
Ha0, AA0BB0 system: 3J(HaHb) ¼ 3J(Ha0–Hb0) ¼ 9.0
Hz], 8.83 [s, 1H, CH7@N]. FT-IR (KBr, cmꢀ1): m(CN),
1591 vs, m(BF4), 1051 vs, 521 m. MS (FABþ) m/z 431
(Mþ–BF4).
Preparation of [(g3-Me-allyl)Pd{g2-S2P(OEt)2}]. To
a solution of the binuclear complex [(g3-Me-allyl)
PdCl]2{ 0.50 mmol, 200 mg} in Me2CO (30 cm3),
[(EtO)2PS2K] (1.01 mmol, 228 mg) was added. The
mixture was stirred at room temperature for 5 h and the
KCl formed filtered off through Kieselguhr. The solu-
tion was evaporated to dryness under reduced pressure.
The brown orange residue formed was washed with cold
Et2O. This product was dissolved in the minimal
amount of CHCl3 and crystallised at room temperature.
The product formed was washed with cold Et2O, and
dried under vacuum. Anal. Found: C, 27.3; H, 5.1; S,
1.7. Calc. for C8H17O2PPdS2: C, 27.7; H, 4.9; S, 1.9%.
1H NMR in CDCl3: d 1.36 [t, br, 6H, Me], 1.94 [s, 3H,
C(allyl)–Me], 2.76 [s, 2H, Hanti], 3.97 [s, 2H, Hsyn], 4.13
[m, 4H, CH2–R]. 31P{1H} NMR in CDCl3: d 103.4 [s,
S2PEt2].
6: Yield: 131 mg (65%). Anal. Found: C, 45.3; H, 3.6;
S, 5.8; N, 5.1. Calc. for C18H19BF4N2O2PdS: C, 41.5; H,
3.7; S, 6.2; N, 5.4%. 1H NMR in CD3CN: d 2.08 [s, 3H,
C(allyl)–Me], 2.7 [s, 3H, S–Me], 3.10 [s, 2H, Hanti], 4.03
[s, 2H, Hsyn], 7.45 [m, 2H, H3, H4], 7.52 [m, 1H, H6],
7.58 [m, 1H, H5], 8.22 [d, 2H, Ha, Ha0, AA0BB0 system:
3J(Ha–Hb) ¼ 3J(Ha0–Hb0) ¼ 8.8 Hz], 8.39 [d, 2H, Hb,
Hb0, AA0BB0 system: 3J(Ha–Hb) ¼ 3J(Ha0–Hb0) ¼ 8.8
Hz], 8.98 [s, 1H, CH7@N]. FT-IR (KBr, cmꢀ1): m(CN),
1616 vs, m(BF4), 1060 vs, 521 m. MS (FABþ) m/z 433
(Mþ–BF4).
2.3. Reactivity studies
2.3.1. Reaction of complexes 1–6 with NaI
To a solution of the cationic complexes [(g3-Me-allyl)
Pd(g2-S,N-MeSC6H4N@CHC6H4R0)]BF4 [0.50 mmol:
R0 ¼ H (1; 237.7 mg); F (2; 246.7 mg); Me (3; 244.8 mg);
Cl (4; 255 mg); NMe2 (5; 259.2 mg); NO2 (6; 260.2 mg)]
in Me2CO (20 cm3), a stoichiometric amount of NaI
(0.50 mmol, 75 mg) was added, and the mixture stirred at
room temperature for 24 h. The solvent was evaporated
under reduced pressure and the solid dissolved in the
minimum amount of Et2O. The resulting solution was
allowed to stand at )25 °C for 72 h. Two type of crystals
were formed (yellow and orange) which were collected by
filtration, washed with cold Et2O, and dried under vac-
2.3.3. Reaction of complexes 1–6 with KA (A ¼ CNꢀ,
SCNꢀ)
To a solution of the cationic complex [(g3-Me-al-
lyl)Pd(g2-S,N-MeSC6H4N@CHC6H4R0)]BF4 [0.50 mmol:
R0 ¼ H (1; 237.7 mg); F (2; 246.7 mg); Me (3; 244.8 mg);
Cl (4; 255 mg); NMe2 (5; 259.2 mg); NO2 (6; 260.2 mg)]
in Me2CO (20 cm3), it was added a stoichiome-
tric amount of KA (0.50 mmol, A ¼ CNꢀ: 33 mg, A ¼
SCNꢀ: 48.6 mg), and the mixture stirred at room tem-
perature for 5 h. The solution was concentrated under
reduced pressure and the white solid formed was elimi-
nated by filtration through Kieselguhr. The resulting
solution was allowed to stand at )25 °C. Orange crystals
were formed, which were collected by filtration, washed
with cold Et2O, and dried under vacuum. The 1H NMR
spectroscopic data of the orange crystals correspond to
the free ligand (MeSC6H4N@ CHC6H4R0). The insolu-
ble white solid was analysed by IR spectroscopy; it
corresponds to a polymer of general formula [(g3-Me-
allyl)Pd(g1-A)x]n (m(CN) ¼ 2116 and m(SCN) ¼ 2141
cmꢀ1).
1
uum. The H NMR spectroscopic data of the orange
crystals correspond to the free ligand (MeSC6H4N@
CHC6H4R0) while the yellow crystals correspond to the
neutral complex [(g3-Me-allyl)Pd(l-I)]2 [1H NMR in
CDCl3; d 1.94 (s, 3H,C(allyl)–Me), 4.13 (s, 2H, Hsym),
3.06 (s, 2H, Hanti). FAB mass spectrum: {(3-Me-al-
lyl)Pd(l-I]}þ2 , m/z 578 (Mþ), 451 (Mþ–I) [11].
2.3.2. Reaction of complexes 1–6 with [(EtO)2PS2K]
To a solution of complex [(g3-Me-allyl)Pd(g2-S,N-
MeSC6H4N@CHC6H4R0)] BF4 [0.50 mmol, R0 ¼ H (1;
237.7 mg); F (2; 246.7 mg); Me (3; 244.8 mg); Cl (4; 255
mg); NMe2 (5; 259.2 mg); NO2 (6; 260.2 mg)] in Me2CO
(20 cm3) was added a stoichiometric amount of [(EtO)2
PS2K] (0.50 mmol, 114 mg). The mixture was stirred at
room temperature for 5 h and filtered through Kies-
elguhr. The solvent was evaporated under reduced
pressure to dryness and the residue dissolved in a min-
imum amount of Et2O. The resulting solution was al-
lowed to stand at )25 °C for 72 h. The crystals that
2.3.4. Reaction of complexes 1–6 with NaH
To a solution of complex [(g3-Me-allyl)Pd(g2-S,N-
MeSC6H4N@CHC6H4R0)] BF4 [0.50 mmol: R0 ¼ H (1;
237.7 mg); F (2; 246.7 mg); Me (3; 244.8 mg); Cl (4;
255.0 mg); NMe2 (5; 259.2 mg); NO2 (6; 260.2 mg)] in
MeCN (30 cm3), a stoichiometric amount of NaH (0.50
mmol, 12.0 mg) was added under inert atmosphere and
in an ice bath. The mixture was stirred at room tem-
perature for 15 min. The dark solution was concentrated

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R. Contreras et al. / Journal of Organometallic Chemistry 689 (2004) 395–404
under reduced pressure and the black solid formed re-
moved by filtration through Kieselguhr. The resulting
solution was evaporated to dryness and a red solid res-
idue was formed. The 1H NMR spectroscopic data
showed that the residue corresponds to a mixture of
products: methyl-allylchloride, free ligand, benzalde-
hyde and 2-(methylthio)aniline. The insoluble black
solid corresponds to metallic palladium.
3. Results and discussion
The
2-(methylthio)-N-substituted-benzylidene)ani-
lines ligands were synthesised according to a general
procedure. Typically, a condensation of equimolar
amounts of 2-(methylthio)aniline and the respective
substituted benzaldehyde was performed under contin-
uous stirring, in the presence of magnesium sulphate.
The overall reaction for all the ligands is represented in
Scheme 1.
2.4. Theoretical and computational details
The ligands were characterised by IR and NMR
spectroscopies. The infrared spectra show an intense
band in the 1600–1680 cmꢀ1 range corresponding to the
mC@N stretching vibrations. The 1H NMR spectra show
a signal at low field (d 8.28–8.77 ppm) attributed to the
iminic proton. A singlet signal is also observed in the d
2.44–2.48 ppm range, assigned to protons of the meth-
ylthioether group [18], together with the characteristic
signals of the substituents of the benzylidene group. In
the 19F NMR spectrum, the fluorinated derivative
shows one singlet signal at )47.7 ppm assigned to the
fluorine atom. The 13C NMR spectra of the ligands
exhibit the singlet signal corresponding to the carbon of
the SMe group in the d 14.3–14.9 ppm range and a
singlet signal of the iminic carbon at d 156.8–160.4 ppm
[18].
The binuclear complex [(g3-Me-allyl)Pd(l-Cl)]2 re-
acted in tetrahydrofuran with silver tetrafluoroborate in
a 1:2 molar ratio, forming the probably solvated inter-
mediate species [(g3-Me-allyl)Pd(THF)x]þ. This which
reacted further with the different bidentate Schiff bases to
give the corresponding palladium(II) cationic complexes
[(g3-Me-allyl)Pd(g2-S,N-MeSC6H4N ¼ CHC6H4(X)Y)]
BF4 where X ¼ H, Y ¼ H (1); X ¼ F, Y ¼ H (2); X ¼ Me,
Y ¼ H (3); X ¼ H, Y ¼ Cl (4); X ¼ H, Y ¼ Me2N (5) and
X ¼ H, Y ¼ NO2 (6)]. This is illustrated in Scheme 2.
Complexes 1–6 were isolated as stable orange solids
and characterised by elemental analyses, conductivity
measurements, IR, NMR and mass spectroscopies.
Complexes behave as 1:1 electrolytes in acetonitrile,
with conductivity values in the 113–200 Xꢀ1 cm2 molꢀ1
range. Their FT-IR spectra in KBr pellets show the
presence of the uncoordinated anion, m(BF4) ca. 1060
and 521 cmꢀ1, together with the absorption band cor-
responding to the C@N group at the 1610–1621 cmꢀ1
range.
All calculations were performed with the Gaussian 98
package [14]. density functional theory (DFT) was em-
ployed with the three-parameter hybrid exchange func-
tional of Becke [15] and the Lee et al. [16] correlation
functional (B3LYP). Relativistic effective core potentials
(ECPs) for palladium were employed in all B3LYP
calculations. The basis set was the standard LANL2DZ
included in Gaussian. The geometries were obtained by
full geometry optimisation at the B3LYP level. Graph-
ical pictures were obtained with the MOLEKEL
program [17].
In the frame of Frontier molecular orbital theory [8c],
an electrophilic attack can be explained by the sharing
of electrons from the HOMO with the electrophile,
while a nucleophilic attack can be seen as the accepting
of the nucleophile electrons by the LUMO. Most of the
frontier-electron theory of chemical reactivity can be
rationalized from DFT. Parr and Yang derived an ex-
pression that quantifies the previously described con-
cepts (for a detailed theoretical discussion see [8a–8d]
and references therein), by means of the Fukui function,
that is defined as follows [8b,8d]:
ꢀ
ꢁ
ꢀ
ꢁ
ol
om
oq
oN
f ðrÞ ¼
or f ðrÞ ¼
:
ð1Þ
N
m
With q the electronic density, l the chemical potential, m
the external potential and N is the number of electrons
of the system.
Using the finite-difference approximation for the
Fukui function, it is possible to rewrite f ðrÞ as a func-
tion of measurable quantities, and separate it in three
parts: f ðrÞꢀ. Fukui function for the most probable
electrophilic attack sites, f ðrÞþ, Fukui function for the
most probably nucleophilic attack sites and f ðrÞ°, Fukui
function for probable radical attack sites. The expres-
sions that define these indexes are the following:
Selected 1H NMR data of complexes 1–6 are
summarised in Table 1. The spectra show three singlet
resonances at the ranges d 2.00–2.21, 3.06–3.18 and
3.85–4.14 ppm, attributed to the methyl group, and the
methylenic protons Hanti and Hsyn of the co-ordinated
methylallyl ligand, respectively [19].
Variable-temperature experiments (295–353 K) show
that at high temperature (353 K) occurs a slight
broadening of the resonance assigned to the methylene
protons of the methylallyl group, probably due to a
f ðrÞꢀ ¼ ½qðrÞN ꢀ qðrÞNꢀ1ꢂ ꢁ qðrÞ
f ðrÞþ ¼ ½qðrÞNþ1 ꢀ qðrÞN ꢂ ꢁ qðrÞ
:
ð2Þ
ð3Þ
HOMO
:
LUMO
f ðrÞþ þ f ðrÞꢀ qNþ1 ꢀ qNꢀ1
0
f ðrÞ ¼
¼
2
2
qHOMO þ qLUMO
ꢁ
:
ð4Þ
2

R. Contreras et al. / Journal of Organometallic Chemistry 689 (2004) 395–404
399
H
X
C
NH2
S
N
CHO
+ H2O
+
S
Y
Me
Scheme 1. X ¼ H; Y ¼ H, Cl, NMe2. NO2, Y ¼ H; X ¼ F, Me.
H3
C
H1
C
H4
Me
S-B
AgBF4
THF
[(η3-Me-allyl)Pd(THF)2]BF4
H2
1/2 [(η3-Me-allyl)Pd(µ-Cl)]2
Pd
BF4
S
N
H
C
X
Scheme 2. X ¼ H; Y ¼ H (1); X ¼ F, Y ¼ H (2); X ¼ Me, Y ¼ H (3); X ¼ H, Y ¼ Cl (4), X ¼ H, Y ¼ Me2N (5); X ¼ H, Y ¼ NO2 (6).
Table 1
1H NMR data in CD3CN for complexes 1–6
Assignment
(1)
(2)
(3)a
(4)
(5)b
(6)
Me-allyl(H1)
Hanti
Hsyn
2.06
3.06
3.89
2.80
9.10
2.04
3.07
3.96
2.80
9.20
2.00
3.02
3.85
2.90
9.4
2.08
3.11
3.97
2.88
9.07
2.21
3.18
4.07
2.90
8.80
2.08
3.10
4.03
2.70
9.00
S–Me(H2)
–N@C–H7
a ortho-Me(H12): d 2.57 ppm.
b p-NMe2(H8): d 3.13 ppm.
rapid p–r interconversion of the ligand. This behaviour
has been observed for analogous compounds [19d].
Moreover, the complexes show two singlet signal at
the ranges d 2.7–2.9 and 8.8–9.4 ppm, assigned to the
methyl protons of the thioether group and an iminic
proton, respectively.
two or three bonds was observed. Moreover, the spec-
0
trum shows a strong correlation between C14, C14 , C15,
0
0
0
C15 carbons with the Ha, Ha and Hb,Hb protons, with
0
constants coupling values of 1J(C14–Ha) ¼ 1J(C14
–
1
1
0
0
0
Ha ) ¼ 157 Hz and J(C15–Hb) ¼ J(C15 –Hb ) ¼ 160.7 Hz,
respectively. Fig. 2 shows the assignment of carbons C4,
C5, C17, C1 and C3 at high field with their respective 1J(C–
H) coupling constants (Table 3).
1
The H and 13C chemical shifts were assigned with
the aid of 1H–1H COSY, DEPT, 1H–13C COSY, HSQC
and HMBC experiments. The 13C NMR data and the
1J(C–H) coupling values are listed in Tables 2 and 3,
respectively. The protons and carbon numbering scheme
are indicated in Fig. 1.
Both figures show the C–H interactions at two- and
three-bonds (Table 2). For all complexes these interac-
3
tions generally show J(C–H) coupling constants values
2
higher than J(C–H). A similar behaviour was observed
The 13C assignments were achieved by 1H–13C COSY
spectra using HMBC conditions for short or longer range
(one-, two- or three-bond correlation). As an example,
in trimethylplatinum (IV) complexes [20].
In general, the 19F NMR spectrum of the cationic
complexes, show a signal appearing at )150 ppm corre-
sponding to the tetrafluoroborate anion (BFꢀ4 ). Complex
(2) shows an additional signal at )115 ppm, assigned to
the fluorine atom of the substituted Schiff base.
1
the H–13C HMBC spectrum for complex 5 is shown in
Fig. 2. The low field signal correlation clearly shows the
assignation of the iminic carbon (C12) at d 168.4 ppm with
the corresponding coupling with the iminic proton
[1J(C12–H7) ¼ 164 Hz]. A strong interaction between C14,
Finally, the mass spectra of the complexes (FABþ
mode) show peaks at m=z ¼ 388 (1), 406(2), 402(3),
431(5) and 433(6) (highest relative abundance values of
0
14 , C13 and C11 carbons with the iminic proton H7 at
C

400
R. Contreras et al. / Journal of Organometallic Chemistry 689 (2004) 395–404
Table 2
13C NMR data in CD3CN for complexes 1–6
Assignment
(1)
66.4
(2)
64.5
(3)g
65.4
(4)
66.0
(5)h
65.7
(6)
65.2
C1,C3(allyl)
C2(allyl)
C4(Me-allyl)
C5(S–Me)
C6
132.4
22.9
23.6
134.9
21.7
135.6
22.4
23.8
135.8
22.4
23.1
135.4
22.4
23.5
136.0
22.3
19.5
21.1
131.3
132.1
130.5
131.2
131.0
120.7
152.1
170.3
136.7
130.5
129.9
134.2
–
130.3
130.8
132.9
139.2
120.5
151.3
170.2
136.2
131.9
126.7
144.5
128.8
131.1
131.4
130.7
130.5
130.1
120.2
151.2
168.4
134.6
131.6
129.5
139.2
–
130.8
128.5
130.2
130.5
119.8
152.6
168.4
121.3
133.0
111.7
154.4
–
132.8
129.4
128.4
128.7
119.2
149.8
163.6
141.9
130.4
124.3
150.4
–
C7
C8
130.4
132.6
C9
C10
129.2
119.2
150.2
C11
C12(–N@C–)
C13
C14, 140
C15, 150
C16
161.5
123.7(d)a
124.6(d)b
129.1(d)c
134.8(d)d
115.9(d)e
161.8(d)f
C17
C18
–
–
–
–
a
2JCF ¼ 10.9 Hz.
3JCF ¼ 3.5 Hz.
4JCF ¼ 32.5 Hz.
3JCF ¼ 8.9 Hz.
2JCF ¼ 20.6 Hz.
1JCF ¼ 253.5 Hz.
b
c
d
e
f
g 18.9 ppm ortho-Me.
h 39.8 ppm p-NMe2.
Table 3
Coupling constants (1JCH in Hz) for complexes 1–6 determined from 2D-NMR (HMBC) spectra
Assignment
(1)
(2)a
(3)b
(4)
(5)
(6)
1J(C1-Hanti)c
1J(C1-Hsyn)d
1J(C4–H1)
155
162
129
136
174
164
144
161
169
158
154
158
154
133
146
174
163
167
152
172
163
159
158
161
131
142
172
165
146
169
171
163
166
161
164
130
158
162
130
139
175
164
147
164
164
157f
161g
159
162
127
140
164
162
160
156
168
162f
168g
1J(C5–H2)
142
e
1J(C7–H3)
1J(C8–H4)
165
161
158
168
161f
164g
1J(C9–H5)
1J(C10–H6)
1J(C12–H7)
1J{C14–H8(Ha,a0)}
1J({C15–H9(Hb,b0)}
a
1J(C16–H10) ¼ 164 Hz; 1J(C17–H11) ¼ 165 Hz.
1J(C16–H10) ¼ 111 Hz; 1J(C17–H11) ¼ 163 Hz.
1J(C1-Hanti) ¼ 1J(C3-Hanti).
b
c
d
1J(C1-Hsyn) ¼ 1J(C3-Hsyn).
e Not resolved.
f
1J(C14–Ha) ¼ 1J(C14 –Ha ).
0
0
g
1J(C15–Hb) ¼ 1J(C15 –Hb ).
0
0
90–100%), with an isotopic distribution that matched
that calculated for a m=e relationship corresponding to
[Mþ–BF4].
thioether to suitable nucleophiles [3,21]. These proper-
ties were analysed for complexes 1–6, in order to com-
pare their behaviour with previously studied
compounds. These were treated with different nucleo-
philes such as NaI, (EtO)2PS2K, KCN, KSCN and
NaH. The products obtained by these reactions are
collected in Scheme 3.
3.1. Reactivity of complexes 1–6 with nucleophiles
As mentioned in the introduction, transition metal
complexes that contain ligands with a thioether group
show the ability to transfer the methyl group from the
Thus, the reaction with NaI in acetonitrile gives the
corresponding free ligand and the binuclear complex

R. Contreras et al. / Journal of Organometallic Chemistry 689 (2004) 395–404
401
formula. The 31P{1H} NMR spectrum shows a signal at
d 103.4 ppm corresponding to the phosphorus atom [22].
The reactions of complexes 1–6 with KCN or KSCN
in methanol solution show similar results. In both cases
we observed the formation of a very insoluble white
precipitate. The IR of the solids showed strong bands at
2116 and 2141 cmꢀ1, respectively, which correspond to
the asymmetric stretching frequency of the CN group.
These bands agreed with the values found in literature
for the polymeric compounds [(g3-Me-allyl)Pd(A)x]n
[A ¼ CNꢀ, SCNꢀ] [23]. Moreover, the respective free
ligands were recovered from the filtrate.
+
Me(H1;C )
4
H3
C7
Me(H2;C5)
Hsyn
Hsyn
C2
H4
C1
Hanti
S
C3
Hanti
C6
C8
C9
Pd
C11
N
H5
C10
H6
H7
C12
Ha'
C14
C13
'
Ha
C14
C15
'
Finally, a complete decomposition of the complexes
with NaH in acetonitrile solutions was observed. We
detected the reduction of the metal to Pd°, a partial
decomposition of the ligand and the formation of 3-
methyl-1-propene.
Hb'
C15
C16
Hb
Fig. 1. Proton and carbon atoms numbering for complex 5.
These results indicate that the 2-(methylthio)-N-
subtituted-benzylidene)anilines ligands bonded to the
organometallic fragment [(g3-Me-allyl)Pd] show that
the thioether group of the Schiff base is not accessible
for a cleavage of the C–S bond. In all cases the nucle-
ophilic attack produced the deco-ordination of the Schiff
base, and no demethylation reaction was observed.
These results are different to those with complexes of the
type [Cl2M(L2)] (where M ¼ Pd(II) or Pt(II) and L2 is o-
(diphenylphophino) thioanisole. In these cases the re-
action with nucleophiles such as thiocynate, iodide or
benzylamine, produces the cleavage of the C–S bond of
the coordinated ligand transforming the methylthioether
group into a thiolate group [3d,3e,3f].
[(g3-Me-allyl)Pd(l-I)]2. These compounds were charac-
terised by NMR and mass spectroscopy. On the other
hand, the reactions of the complexes with (EtO)2PS2K
in acetone afford a brown–orange solid which was
characterised as the neutral complex [(g3-Me-al-
lyl)Pd{g2-S2P(OEt)2], demonstrating the displacement
of the N,S-donor ligand. The neutral complex was
characterised by comparison with a sample prepared by
the reaction of the complex [(g3-Me-allyl)Pd(l-I)]2 with
[(EtO)2PS2K] in acetone. The brown–orange crystals
1
obtained exhibit the expected signals in the H NMR
spectrum in the required proportions of the proposed
H2
H8
H
1
Ha-H
a'
6 3
H -H
H
anti
b
H -Hb'
H
syn
H
7
H
5
4
H
ppm
110
120
130
140
150
160
170
ppm
20
4-1
15,15'-b,b'
5-2
15,15'-a,a'
4
4-anti
15,15'
5
4-syn
10-6
13-7
17
10-4
10
40
13-b,b'
13
9-5
17-8
7-5
1,3-1
8
60
9,6,7
3,1
14,14'
2
1,3-syn
1,3-anti
14,14'-7
11-7
8-4
7-3
80
14-14'-a,a'
11-6
100
120
140
160
11
15,15'
16
11-5
10
13
6-2
16-a,a'
8
2-1
12-7
9,6,7
14,14'
2
12
16-8
12-a,a'
Low Field
High Field
16
9.0
8.5
8.0
7.5
7.0
6.5
4.0
3.5
3.0
2.5
2.0
ppm
Fig. 2. 1H–13C COSY (HMBC) NMR spectrum of complex 5 in CD3CN showing low and high field C–H correlation signals.

402
R. Contreras et al. / Journal of Organometallic Chemistry 689 (2004) 395–404
H
C
NaI
[(η3-Meallyl)Pd(µ-I)]2
N
+
- NaBF4
S
Me
X
C
Y
H
[(EtO)2PS2K]
[(η3-Meallyl)Pd(S2P(OEt)2)]
N
+
- KBF4
Me
H3
S
Me
C
H1
C
H4
Me
S
H2
Pd
BF4
N
H
C
X
Y
H
X
C
KCN, KSCN
- KBF4
[(η3-Meallyl)Pd(µ-A)x]n
N
+
Y
A = CN, SCN
S
Me
X
NH2
CHO
+ Me2C=CH2
Y
+
+
S
Me
Y
NaH
X
- NaBF4
H
C
N
Pd˚
+
S
Scheme 3. Reactions of complexes 1–6 with nucleophiles.
Moreover, the attempts to exchange the bidentate
attack. For this purpose a charge density analysis (nat-
ural charge analysis as defined in Gaussian 98 program)
was performed. This was made for the atoms involved in
the experimental target, i.e. the Me–S cleavage; the at-
oms that showed a high Fukui function toward a nu-
cleophile, high f ðrÞþ, were also included. They
corresponded to the iminic N and C atoms. The results
obtained are summarised in Table 4. The three com-
plexes show a very similar charge distribution for the
selected atoms. Moreover, the S–C(Me) bond distances
are also very close, and are slightly longer compared
with these distances in the free ligand.
ligand with a similar more basic ligand (i.e. reaction of
complex 6 with the ligand MeSC6H4N@CHC6H4NMe2)
were unsuccessful. In all cases the 1H NMR spectra
show no variations respect to the starting complex. This
experiment discards the possibility of the formation of a
vacant site by deco-ordination of one end of the bid-
entate Schiff base ligand.
As a complement to the experimental reactivity re-
actions, theoretical calculations for complexes 1, 5 and 6
were performed. The main goal was to explain the lack
of reactivity of the Me–S group toward a nucleophilic

R. Contreras et al. / Journal of Organometallic Chemistry 689 (2004) 395–404
403
Table 4
Complex
Charge density (fukui function f ðrÞþ)
ꢁ
Bond distance (A)
C12
N
S
Me(C5)
S–Mea
S–Meb
1
5
6
)0.2724 (0.339)
)0.2937 (0.074)
)0.2782 (0.159)
)0.2783 (0.214)
)0.3018 (0.087)
)0.2653 (0.152)
0.3028 (0.019)
0.3018 (0.122)
0.3041 (0.006)
)0.7773 (0.002)
)0.7791 (0.011)
)0.7767 (0.001)
1.8955
1.8951
1.8958
1.8829
1.8833
1.8829
a Complex.
b Free ligand.
A study of nucleophilic f ðrÞþ and electrophilic f ðrÞꢀ
Fukui functions was performed. A graphical represen-
tation of the results for the f ðrÞþ function of complexes
1, 5 and 6 is displayed in Fig. 3.
ligand; and (iii) in these systems, the S–C(Me) bond is
not weak enough to transfer the methyl group to the
incoming nucleophile.
The theoretical results analysed above are in agree-
ment with the experimental behaviour, and support the
reactivity routes proposed.
It can be seen that the suitable sites for nucleophilic
attack, f ðrÞþ, are located on the Pd center, the N atom
and the C–H iminic bonds, while the S–Me moiety
shows no electronic contribution in all complexes.
Therefore, a nucleophile should attack the regions with
high f ðrÞþ function and not the S–Me bond, as would
be expected in a demethylation reaction. Probably, in a
first stage, the nucleophile attacks the iminic moiety
or the metal center, and in a subsequent step the de-
coordination of the ligand takes place, yielding finally a
polynuclear species.
Acknowledgements
ꢀ
We thank ‘‘Fondo de Desarrollo Cientıfico y Tec-
nologico (FONDECYT)’’, Chile (Grant 8980007 and
ꢀ
ꢀ
1030520) and ‘‘Direccion de Investigacion, Pontificia
Universidad Catolica de Chile (DIPUC)’’, (Grant 234/
ꢀ
ꢀ
2002) for financial support.
On the basis of these results, and specially considering
the fact that the Fukui functions do not present a dis-
tribution on the S–C(Me) fragment, the following can be
concluded: (i) all three complexes should show a similar
chemical reactivity toward nucleophilic attack, as ob-
served in the experimental results; (ii) from a theoretical
point of view, a nucleophilic attack should only occur
on the metal or on the iminic moiety of the co-ordinated
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