Syntheses of palladated aryldithioacetals. Unexpected rearrangement involving C-S and C-Pd bonds

Article abstract of DOI:10.1021/om0008981

The reaction of C₆HI(OMe)₃-2,3,4- CH(STo)₂-6 (1) (To = 4-tolyl) with [Pd(dba)₂] (dba = dibezylideneacetone) at room temperature gives [Pd₂{κ²-C,S-CH(STo)(C₆H(STo-2) (OMe)₃-3,4,5)₂ (μ-I)₂] (3) or, in the presence of Tl(OTf) (OTf = CF₃SO₃) and bpy (2,2′-bipyridine), the cationic cyclopalladated complex [Pd{κ²-C,S-C₆H(OMe)₃-2,3,4- CH(STo)₂-6}(bpy)]OTf (2). 3 reacts with Tl(OTf) and (i) RNC (1:2:4) to give cis-[Pd{κ²-C,S-CH(STo){C₆H(STo-2) (OMe)₃-3,4,5}}-CNR)₂]OTf [R = 2,6-dimethylphenyl (4), ^tBu (4′)] or (ii) bpy to give an isometric form of 2, cis-[Pd{κ²-C,S-CH(STo){C₆H(STo-2)(OMe)₃- 3,4,5}}(bpy)]OTf (5). The last reaction can be reversed by reacting 5 with NaI. The compound 2 reacts with NaI to give [Pd(C₆H(OMe)₃- 2,3,4-(CH(STo)₂-6)I(bpy)] (6), which can be also prepared by reaction of 1 with [Pd(dba)₂] in the presence of bpy. Complex 2 isomerizes to 5 when refluxed in 1,2-dichloroethane. The crystal structures of 2 and 4 have been determined by X-ray diffraction studies.

Full text of DOI:10.1021/om0008981

Organometallics 2001, 20, 1109-1114
1109
Syn th eses of P a lla d a ted Ar yld ith ioa ceta ls. Un exp ected
Rea r r a n gem en t In volvin g C-S a n d C-P d Bon d s†
J ose´ Vicente,*,‡ J ose´-Antonio Abad,*,| and Francisco S. Herna´ndez-Mata
Grupo de Quı´mica Organometa´lica, Departamento de Quı´mica Inorga´nica,
Facultad de Quı´mica, Universidad de Murcia, Aptdo. 4021, E-30071 Murcia, Spain
Peter G. J ones*,§
Institut fu¨r Anorganische und Analytische Chemie, Technische Universita¨t Braunschweig,
Postfach 3329, 38023 Braunschweig, Germany
Received October 20, 2000
The reaction of C6HI(OMe)3-2,3,4-CH(STo)2-6 (1) (To ) 4-tolyl) with [Pd(dba)2] (dba )
dibezylideneacetone) at room temperature gives [Pd2{κ2-C,S-CH(STo)(C6H(STo-2)(OMe)3-
3,4,5)2(µ-I)2] (3) or, in the presence of Tl(OTf) (OTf ) CF3SO3) and bpy (2,2′-bipyridine), the
cationic cyclopalladated complex [Pd{κ2-C,S-C6H(OMe)3-2,3,4-CH(STo)2-6}(bpy)]OTf (2). 3
reacts with Tl(OTf) and (i) RNC (1:2:4) to give cis-[Pd{κ2-C,S-CH(STo){C6H(STo-2)(OMe)3-
3,4,5}}(CNR)2]OTf [R ) 2,6-dimethylphenyl (4), tBu (4′)] or (ii) bpy to give an isomeric form
of 2, cis-[Pd{κ2-C,S-CH(STo){C6H(STo-2)(OMe)3-3,4,5}}(bpy)]OTf (5). The last reaction can
be reversed by reacting 5 with NaI. The compound 2 reacts with NaI to give [Pd(C6H(OMe)3-
2,3,4-CH(STo)2-6)I(bpy)] (6), which can be also prepared by reaction of 1 with [Pd(dba)2] in
the presence of bpy. Complex 2 isomerizes to 5 when refluxed in 1,2-dichloroethane. The
crystal structures of 2 and 4 have been determined by X-ray diffraction studies.
In tr od u ction
CO plus O2 gave benzoate palladium complexes.8 We
have also shown that some ortho-formyl palladium
complexes undergo a rare rearrangement involving a
positional exchange between the formyl group and the
palladium moiety with breaking and reforming of C-C
and C-Pd bonds (see [a] in Scheme 1).1,2 The mecha-
nism of this process is not clear. We proposed a pathway
through an oxallyl species,1,2,9 although other possibili-
ties such as the participation of a palladium benzyne
species cannot be discarded.9 A rearrangement process
involving orthometalated aryl iridium complexes is also
known;13 in these cases breaking and re-forming of C-H
and C-Ir bonds takes place (see [b] in Scheme 1). The
authors demonstrate a mechanism involving the oxida-
tive addition of one of the NMe C-H bonds, followed
by a sequence of C-H bond-breaking and bond-re-
forming steps. In the present paper, we describe the first
ortho-palladated aryldithioacetals and a new type of
rearrangement involving the cleavage of alkyl-S and
aryl-Pd bonds and formation of aryl-S and alkyl-Pd
bonds (see [c] in Scheme 1). We propose two possible
reaction pathways for this transformation.
One of our topics of interest is the synthesis and study
of arylpalladium complexes containing reactive ortho
substituents. We have achieved their synthesis through
different routes, and thus, the use of arylmercurials as
transmetalating agents has permitted us to obtain aryl-
palladium complexes having CHO,1-3 C(O)Me,2 C(O)-
NHtBu,4 CH2OEt,5 or NO26 groups at the ortho position.
We have also prepared 2-aminoarylpalladium complexes
by oxidative addition to Pd(0) of the corresponding
bromo- or iodoarenes.7,8 Many of these compounds show
interesting properties.9 Thus for example, reactions with
(i) alkynes gave different organic products, such as
indenones, indenols,10 spirocyclic compounds,4,5,11 or
alkenyl-4,5 or indenylpalladium12 complexes, those with
(ii) isocyanides gave ketenimines,4 and those with (iii)
† Dedicated to Professor Rafael Uso´n on the occasion of his 75th
birthday.
‡ E-mail: jvs@um.es. www: http://www.scc.um.es/gi/gqo/.
| E-mail: jaab@um.es.
§ E-mail: p.jones@tu-bs.de.
(1) Vicente, J .; Abad, J . A.; J ones, P. G. Organometallics 1992, 11,
3512.
(2) Vicente, J .; Abad, J . A.; Gil-Rubio, J .; J ones, P. G.; Bembenek,
E. Organometallics 1993, 12, 4151.
Exp er im en ta l Section
(3) Vicente, J .; Abad, J . A.; Rink, B.; Herna´ndez, F.-S.; Ram´ırez de
Arellano, M. C. Organometallics 1997, 16, 5269.
(4) Vicente, J .; Abad, J . A.; Shaw, K. F.; Gil-Rubio, J .; Ram´ırez de
Arellano, M. C.; J ones, P. G. Organometallics 1997, 16, 4557.
(5) Vicente, J .; Abad, J . A.; Ferna´ndez-de-Bobadilla, R.; J ones, P.
G.; Ram´ırez de Arellano, M. C. Organometallics 1996, 15, 24.
(6) Vicente, J .; Arcas, A.; Blasco, M. A.; Lozano, J .; Ram´ırez de
Arellano, M. C. Organometallics 1998, 17, 5374.
(7) Vicente, J .; Abad, J . A.; Sa´nchez, J . A. J . Organomet. Chem. 1988,
352, 257.
The NMR spectra, elemental analyses, conductivity mea-
surements in acetone, and melting point determinations
(10) Vicente, J .; Abad, J . A.; Gil-Rubio, J . Organometallics 1996,
15, 3509.
(11) Vicente, J .; Abad, J . A.; Gil-Rubio, J .; J ones, P. G. Organome-
tallics 1995, 14, 2677.
(12) Vicente, J .; Abad, J . A.; Bergs, R.; J ones, P. G.; Ram´ırez de
Arellano, M. C. Organometallics 1996, 15, 1422.
(13) Van der Zeijden, A. A. H.; van Koten, G.; Luijk, R.; Nordemann,
R. A.; Spek, A. L. Organometallics 1988, 7, 1549.
(8) Vicente, J .; Abad, J . A.; Frankland, A. D.; Ram´ırez de Arellano,
M. C. Chem. Eur. J . 1999, 5, 3066.
(9) Abad, J . A. Gazz. Chim. Ital. 1997, 127, 119.
10.1021/om0008981 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 02/13/2001

1110 Organometallics, Vol. 20, No. 6, 2001
Vicente et al.
filtered off, washed with Et2O, air-dried, and further heated
Sch em e 1
in an oven at 70 °C to give 2 as a yellow solid. Yield: 210 mg,
1
78%; mp 184 °C (dec). ΛM ) 136 Ω-1 cm2 mol-1. H NMR (300
MHz, d6-acetone, TMS, 20 °C): δ 8.9-6.7 (several m, 17H, bpy
+ C6H4Me-4 + C6H), 6.17 [s, 1H, CH(STo)2], 3.82 (s, 3H, MeO),
3.81 (s, 6H, 2MeO), 2.28, 1.98 (s, C6H4Me-4). At -60 °C the
MeO signals are separated (3.77, 3.74, 3.73 ppm). Anal. Calcd
for C35H33F3N2O6PdS3: C, 50.20; H, 3.98; N, 3.35; S, 11.49.
Found: C, 49.90; H, 4.05; N, 3.62; S, 11.34. Single crystals
were grown by slow diffusion of n-hexane into CH2Cl2 solutions
of 2.
Syn th esis of [P d 2{K2-C,S-CH(STo)(C6H(STo-2)(OMe)3-
3,4,5)2(µ-I)2] (3). Meth od A. This complex was prepared as 2
from [Pd(dba)2] (663 mg, 1.14 mmol) and 1 (763 mg, 1.38 mmol)
to give 3 as an orange solid. Yield: 574 mg, 76%.
Meth od B. Complex 5 (100 mg, 0.12 mmol) was reacted
with NaI (18 mg, 0.12 mmol) in acetone (10 cm3) for 24 h. The
mixture was evaporated to dryness and the residue recrystal-
lized from CH2Cl2/Et2O. Yield: 63 mg, 80%. The sample
contained traces of a compound having bpy, which were easily
removed by a further recrystallization. Mp: 181 °C (dec). ΛM
1
) 1 Ω-1 cm2 mol-1. H NMR (200 MHz, CDCl3, TMS): δ 7.81,
3
7.50, 7.24 (d, J (HH) ) 7.7 Hz, 2 H; C6H4Me-4); 7.14 (b m, 3
H; C6H4Me-4 and C6H); 5.57 (s, 1 H; CHPd); 3.78, 3.63, 3.27
(s, 3 H; MeO); 2.34, 2.32 (s, 3 H; C6H4Me-4). 13C{1H} NMR (75
MHz, CDCl3,): δ 155.0, 152.7, 144.1, 141.8, 140.3, 140.2 (C);
134.0 (CH); 131.2(C), 131.0, 130.2, 129.8 (CH); 129.2, 122.0
(C); 107.5 (CH); 60.8, 60.7 (MeO); 56.4 (CHPd); 55.2 (MeO);
21.3 (2xMe). Anal. Calcd for C48H50I2O6Pd2S4: C, 43.74; H,
3.83; S, 9.73. Found: C, 43.63; H, 3.77; S, 9.89.
Complex 3 (150 mg, 0.11 mmol) in CH2Cl2 (10 cm3) was
reacted with an aqueous solution of HCl (17 cm3, 4%) for 23
h. The organic phase was washed twice with aqueous NaOH
solution (1 g/100 cm3) and once with water (80 cm3). The
resulting organic phase was stirred with MgSO4, filtered over
MgSO4, and evaporated to dryness. The residue was stirred
with Et2O (30 cm3) and filtered over Celite, and the filtrate
was evaporated to dryness to give an orange solid with the
were carried out as described earlier.14 The compounds
“Pd(dba)2”15,16 ([Pd2(dba)3]‚dba, dba ) dibenzylideneacetone)
and 2-iodo-3,4,5-trimethoxybenzaldahyde17 were prepared as
described previously.
1
same IR and H NMR data as that obtained by reacting 5 with
PhICl2 (see below).
Syn th esis of cis-[P d{K2-C,S-CH(STo){C6H(STo-2)(OMe)3-
3,4,5}}(CNXy)2]OTf (4). Complex 3 (100 mg, 0.075 mmol) was
reacted with Tl(OTf) (54 mg, 0.15 mmol) in CH2Cl2 (20 cm3)
for 15 min, then XyNC (Xy ) 2,6-dimethylphenyl, 40 mg, 0.30
mmol) was added and the mixture stirred for 2 h. The
suspension was filtered over Celite, the filtrate was concen-
trated to ca. 1 cm3, and Et2O (6 cm3) was added. The resulting
suspension was filtered, and the solid was washed with Et2O
and dried, first with air, then in an oven at 70 °C for 3 h, and
finally for 3 days in a vacuum desiccator over phosphorus
pentoxide to give 4 as a yellow solid. Yield: 124 mg, 86%; mp
160 °C. ΛM ) 119 Ω-1 cm2 mol-1 (dec). IR (cm-1): ν(CtN) 2184.
1H NMR (300 MHz, CDCl3, TMS, -60 °C): δ 7.6-7.9 (several
m, 15 H, aromatic H's), 5.59 (s, 1 H, CHPd), 3.97, 3.86, 3.59
(s, 3H, MeO), 2.41, 1.97 (s, 3 H; C6H4Me-4), 2.37, 2.26 (s, 6H,
C6H3Me2-2,6). 3C{1H} NMR (75 MHz, CDCl3,): δ 156.5, 152.8,
144.3, 142.1, 139.7, 139.5, 135.3, 135.2 (C); 133.2 (CH); 130.8,
130.5 (C); 130.1, 130.0 (CH); 129.4 (C); 129.1, 128.2, 128.1
(CH); 116.1 (C); 108.2 (CH, C6H); 65.5 (CHPd); 62.9, 60.7, 56.3
(OMe); 20.9, 20.7 (Me, STo); 18.3 (4xMe, 2xCNC6H3Me2-2,6).
Anal. Calcd for C43H43F3N2O6PdS3: C, 54.73; H, 4.60; N, 2.97;
S, 10.19. Found: C, 54.95; H, 4.75; N, 3.10; S, 9.84. Single
crystals were grown by slow diffusion of n-pentane into
solutions of 4 in CH2Cl2.
Syn t h esis of C6H I(OMe)3-2,3,4-CH (STo)2-6 (1) (To )
4-tolyl). 4-Thiocresol (2.31 g, 18.6 mmol) was added to a
solution of 2-iodo-3,4,5-trimethoxybenzaldehyde (3.00 g, 9.30
mmol) and 4-toluenesulfonic acid (two small crystals) in 1,2-
dichloroethane. The solution was refluxed in the presence of
anhydrous MgSO4 for 10 h and, then, filtered over anhydrous
MgSO4. The solvent was evaporated in vacuo and the residue
treated with n-pentane (4 cm3) at 0 °C. The white solid formed
was filtered, washed with cold n-pentane, and air-dried.
1
Yield: 4.49 g, 87%. H NMR (200 MHz, CDCl3, TMS): δ 7.26,
3
(d, J HH ) 8 Hz 4 H, C6H4Me-4), 7.05 (s, 1 H, C6H), 7.04 (d,
3J HH ) 8 Hz 4 H, C6H4Me-4), 5.92 [s, 1H, CH(STo)2], 3.84, 3.83,
3.76 (s, 3H, 2MeO); 2.28, 1.98 (s, C6H4Me-4).
Syn th esis of [P d {K2-C,S-C6H(OMe)3-2,3,4-CH(STo)2-6}-
(bp y)]OTf (2). [Pd(dba)2] (180 mg, 0.32 mmol) and bpy (2,2′-
bipyridine) (52 mg, 0.34 mmol) were mixed under nitrogen in
toluene (20 cm3). The iodoarene 1 (192 mg, 0,34 mmol) and
Tl(OTf) (122 mg, 0.34 mmol) were added to the resulting
solution, and the mixture was stirred at room temperature
under nitrogen for 20 h. The solvent was evaporated in vacuo,
CH2Cl2 (35 cm3) was added, and the resulting suspension was
filtered over Celite. The filtrate was concentrated (ca. 2 cm3),
and Et2O (15 cm3) was added. A solid precipitated and was
Syn th esis of cis-[P d{K2-C,S-CH(STo){C6H(STo-2)(OMe)3-
3,4,5}}(CNtBu )2]OTf (4′). This was prepared as described for
4 from 3 (100 mg, 0.08 mmol), Tl(TfO) (54 mg, 0.15 mmol),
(14) Vicente, J .; Chicote, M. T.; Gonza´lez-Herrero, P.; J ones, P. G.
Inorg. Chem. 1997, 36, 5735.
(15) Takahashi, Y.; Ito, S.; Sakai, S.; Ishii, Y. J . Chem. Soc., Chem.
Commun. 1970, 1065.
(16) Heck, R. F. Palladium Reagents in Organic Synthesis; Academic
Press: New York, 1985.
(17) J anssen, D. E.; Wilson, C. V. In Organic Syntheses; Leonard,
N. J ., Ed.; Wiley-Sons: New York, 1956; Vol. 36, p 46.
t
and BuNC (35 µL, 0.30 mmol). Yield: 118 mg, 92%; mp 80
°C. ΛM ) 133 Ω-1 cm2 mol-1. IR (cm-1): ν(CtN) 2210. 1H NMR
(300 MHz, CDCl3, TMS): δ 7.5-7.0 (m, 8 H,2×C6H4Me-4), 6.56
(s, 1 H, C6H), 5.30 (s, 1 H, CHPd), 3.78, 3.77, 3.54 (s, 3H, MeO),

Palladated Aryldithioacetals
Organometallics, Vol. 20, No. 6, 2001 1111
t
2.36, 2.35 (s, 3 H; C6H4Me-4), 1.53, 1.44 (s, 9H, Bu). 13C{1H}
NMR (75 MHz, CDCl3,): δ 156.6, 152.0, 147.1, 141.7, 140.4,
138.9, 132.4, 130.8, 129.5, 127.8, 116.1 (C); 133.9, 130.3, 130.0,
129.7 (CH, o- and m-C6H4); 107.5 (CH, C6); 60.8, 60.7, 56.0
Ta ble 1. Cr ysta l Da ta for Com p lexes 2 a n d 4
2‚1/2CH2Cl2
4
formula
Mr
C35.5H34ClF3N2O6PdS3 C43H43F3N2O6PdS3
879.68
943.37
t
t
(OMe); 59.4, 58.9 (C, Bu); 55.9 (CHPd); 29.8, 29.7 (Me, Bu);
cryst size (mm)
cryst syst
space group
cell constants
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
0.36 × 0.22 × 0.10
monoclinic
P21/n
30 × 0.25 × 0.13
triclinic
P1h
20.9, 20.7 (Me, STo); 21.2 (2×C6H4Me-4). Anal. Calcd for
C
35H43F3N2O6PdS3: C, 49.61; H, 5.13; N, 3.31; S, 11.35.
Found: C, 49.28; H, 5.12; N, 3.32; S, 11.65.
Syn t h esis of [P d {K2-C,S-CH (STo){C6H (STo-2)(OMe)3-
3,4,5}}(bp y)]OTf (5). Meth od A. A solution of 2 (100 mg, 0.12
mmol) in 1,2-dichloroethane (5 cm3) was refluxed for 8 h. The
solution was concentrated and Et2O (10 cm3) was added, giving
5 as a yellow solid. Yield: 85 mg, 85%.
10.751(1)
21.613(2)
15.528(2)
90
93.187(3)
90
11.426(1)
14.429(1)
14.591(1)
79.347(3)
73.791(3)
67.750(3)
2129.3(3)
2
Meth od B. Tl(OTf) (162 mg, 0.46 mmol) and complex 3 (100
mg, 0.23 mmol) were stirred in CH2Cl2 (20 cm3) for 15 min.
Then bpy (72 mg, 0.46 mmol) was added, and the mixture was
stirred for 8 h and then filtered over Celite. The filtrate was
concentrated (ca. 1 cm3) and Et2O added, causing the precipi-
tation of yellow 4, which was filtered, washed with Et2O, and
dried in an oven for 2 h (70 °C) and over phosphorus pentoxide
for 2 days. Yield: 334 mg, 87%; mp 215 °C (dec). ΛM ) 133
3602.7(7)
4
Z
λ (Å)
0.71073
1.622
0.827
0.980-0.739
1788
0.71073
1.471
0.645
0.928-0.738
968
D
calc (Mg m-3
)
µ (mm-1
transmissions
F(000)
)
T (K)
143(2)
173(2)
no. of rflns
measd
indep
Ω-1 cm2 mol-1. H NMR (300 MHz, CDCl3, TMS): δ 8.93 (d,
1
23 115
7370
0.066
544
45 910
12 429
0.043
532
3J (HH) ) 5.5 Hz, 1 H), 8.56 (t, 3J (HH) ) 7.5 Hz, 2 H), 8.20 (d,
3J (HH) ) 6.5 Hz, 2 H), 8.05 (t, 3J (HH) ) 7.5 Hz, 1 H), 7.85 (d,
Rint
3J (HH) ) 7.5 Hz, 2 H), 7.71 (t, J (HH) ) 6.5 Hz, 1 H), 7.51 (t,
3
no. of params
no. of restraints
R1a
3J (HH) ) 6.5 Hz, 1 H), 7.4-7.0 (m, 6 H), 6.27 (s, 1 H, C6H),
4.71 (s, 1 H, CHPd), 3.79, 3.63, 3.55 (s, 3 H, MeO), 2.32 (s, 6
H, 2×C6H4Me-4). Anal. Calcd for C35H33F3N2O6PdS3: C, 50.20;
H, 3.98; N, 3.35; S, 11.49. Found: C, 49.95; H, 4.12; N, 3.51;
S, 11.54.
603
0
0.048
0.126
0.948
0.8
0.030
0.079
1.043
0.7
wR2b
S(F2)
max. ∆F (e Å-3
)
a
b
Complex 5 (125 mg, 0.15 mmol) in CH2Cl2 (10 cm3) was
reacted with PhICl2 (41 mg. 0.15 mmol). After 1 h stirring,
the suspension was filtered to give a yellow solid (mainly
[PdCl2(bpy)] in accord with its IR spectrum) and a solution,
which was concentrated to dryness. The residue was extracted
with Et2O (8 cm3) and filtered over Celite, the filtrate was
concentrated (ca. 1 cm3), and n-hexane (5 cm3) was added to
give a solid, which was filtered, washed with n-hexane, and
dried in the air to give an orange solid that shows an IR band
at 1688 (vs) cm-1, assignable to ν(CdO), and 1H NMR
resonances (300 MHz, CDCl3) at δ 10.59 (s, CHO, 1 H), 7.37
(s, C6H, 1 H), 7.03 (s, br, C6H4Me-4, 4 H), 3.95 (s, 2 OMe, 6
H), 3.76 (s, OMe, 3 H), 2.27 (s, C6H4Me-4, 3 H), suggesting it
to be C6H(OMe)3-4,5,6-(CHO)-2-(SC6H4Me-4)-1 (23 mg, 48%
yield).
Syn th esis of [P d (C6H(OMe)3-2,3,4-CH(STo)2-6)I(bp y)]
(6). Meth od A. [Pd(dba)2] (90 mg, 0.16 mmol) and bpy (27
mg, 0.17 mmol) were mixed under nitrogen in toluene (20 cm3).
Iodoarene 1 (96 mg, 0,17 mmol) was added to the resulting
mixture, which was stirred at room temperature under
nitrogen for 20 h. The solvent was evaporated in vacuo and
the residue extracted with CH2Cl2 (20 cm3), the extract being
filtered over Celite. The resulting solution was evaporated (ca.
2 cm3) and Et2O (15 cm3) added, causing the precipitation of a
solid that was filtered, washed with Et2O, and air-dried, giving
yellow 6. Yield: 97 mg, 74%.
R1 ) ∑||Fo| - |Fc||/∑|Fo| for reflections with I > 2σI. wR2 )
2
[∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]0.5 for all reflections; w-1 ) σ2(F2) +
2
(aP)2 + bP, where P ) (2Fc + Fo2)/3 and a and b are constants
set by the program.
(2xC6H4Me-4). Anal. Calcd for C34H33N2IO3PdS2: C, 50.10; H,
4.09; N, 3.44; S, 7.87. Found: C, 49.88; H, 4.15; N, 3.60; S,
7.76.
X-r ay Str u ctu r e Deter m in ation s. Com pou n d 2‚1/2CH2Cl2:
Data were collected to 2θmax 52.7° on a Bruker SMART 1000
CCD diffractometer using Mo KR radiation. The structure was
refined anisotropically on F2 using the program SHELXL-97
(G. M. Sheldrick, University of Go¨ttingen). H atoms were
included using a riding model or as rigid methyl groups. The
anion, the methoxy carbon C8, and the solvent molecule are
all disordered over two positions.
Com p ou n d 4: Data were collected to 2θmax 60° as above.
The structure was refined as above.
Crystallographic data (excluding structure factors) for both
compounds have been deposited with the Cambridge Crystal-
lographic Data Centre under the numbers CCDC-146289 (2)
and -146290 (4). Copies may be obtained without charge
from: CCDC, Union Road, Cambridge CB2 1EZ, UK [fax:
internat. + 44-1223/336-033; e-mail: deposit@ccdc.cam.ac.uk].
Resu lts a n d Discu ssion
Meth od B. NaI (18 mg, 0.12 mmol) was added to a solution
of 5 (100 mg, 0.12 mmol) in acetone (12 cm3). The resulting
mixture was stirred for 1 h. The solvent was evaporated and
the residue extracted with CH2Cl2 (20 cm3). The extract was
filtered over Celite, giving a yellow solution that was evapo-
rated (ca. 1 cm3). Addition of Et2O (10 cm3) caused the
precipitation of 6, which was filtered, washed with Et2O, and
air-dried. Yield: 65 mg, 67%; mp 95 °C (dec). ΛM ) 13 Ω-1
The reaction of the 2-iodoarene 1 with [Pd(dba)2] (dba
) dibenzylideneacetone) in the presence of Tl(OTf) (OTf
) CF3SO3) and bpy (2,2-bipyridine) results in the
formation of the cationic cyclopalladated complex 2
(Scheme 2), whose structure has been confirmed by
X-ray studies (see below). To the best of our knowledge,
this is the first synthesis of a palladated dithioacetal
complex. We have attempted the synthesis of complexes
of this type by direct palladation of thiocresol- and
ethylenedithiol-dithioacetal derivatives of terephthal-
aldehyde with Pd(OAc)2 in refluxing toluene. However,
such reactions result in the formation of metallic pal-
cm2 mol-1 1H NMR (300 MHz, CDCl3, TMS, -60 °C, see
.
discussion): δ 9.7-6.2 (several m, 18 H, aromatic protons and
CH(STo)2); 3.96, 3.88, 3.79 (s, 3 H, MeO); 2.24, 2.00 (s, 3 H,
C6H4Me-4). 13C{1H} NMR (50 MHz, CDCl3,): δ 155.2, 153.8,
153.7, 150.9, 141.4, 138.8, 131.3, 126.1, 121.9 (C); 152.0, 150.3,
138.7, 138.5, 133.2, 131.6, 129.1, 128.8, 126.3, 125.7 (CH);
106.4 (CH, C5); 66.8, 60.6, 59.9, 55.7 (OMe, CH(STo)2; 20.9

1112 Organometallics, Vol. 20, No. 6, 2001
Vicente et al.
Sch em e 2
group is displaced by a iodo ligand (Scheme 2), while
treatment of the later with NaI results in the displace-
ment of the bpy ligand, regenerating 3; this fact could
indicate that the chelate ligand is more strongly bonded
to the palladium atom in 5 than in 2. Complex 6 can be
obtained directly from 1 by reacting it with [Pd(dba)2]
and bpy.
Summarizing the reactivity of 1, it is possible to
observe two groups of interconnected complexes: the
first one includes complexes 2 and 6, while 3, 4, 4′, and
5 are included in the second one. We only have been
able to get single crystals of 2 and 4, but it is reasonable
to propose that 6 contains the same aryl ligand as 2
because both complexes can be interconverted, while 3,
4′, and 5 have the new isomerized alkyl ligand present
in 4 because 3 and 5 can be interconverted and both
give the same complex 4. However, with these data only,
the possibility that 3 had the dithioacetal ligand and
that the rearrangement took place after reacting it with
RNC or with bpy and Tl(OTf) to give 4 or 5, respectively,
could not be discarded. To solve this problem, we treated
complex 3 with aqueous hydrochloric acid and complex
5 with PhICl2 in the presence of moisture. Both gave
the same organic compound, proving that both have the
proposed formulation shown in Scheme 2. In accordance
1
with its IR and H NMR spectra this compound could
be C6H(OMe)3-2,3,4-(CHO)-6-(SC6H4Me-4)-1.
We have also observed a connection between both
families of complexes. Thus, when complex 2 is refluxed
in 1,2-dichloroethane, it is converted into its isomer 5.
In fact, even freshly prepared samples of 2 show in their
1H NMR spectra weak signals due to the presence of
traces of complex 5, and after a week the ratio 5:2 is 9.
These observations indicate that the isomerized alkyl-
palladium complexes are thermodynamically more stable
than the non-isomerized aryl complexes and that the
formation of non-isomerized 2 is under kinetic control.
A possible reaction pathway for the rearrangement
process leading to complex 3 is proposed in Scheme 3.
The oxidative addition of 1 to Pd(0) would form the
expected cyclopalladated dithioacetal A. The C-S bond
cleavage, probably induced by the steric hindrance
between the iodo ligand and the ortho methoxy group,
would lead to an iodothiolate complex B containing a
sulfur ylide aryl ligand. Such cleavage of one C-S bond
in thioacetals has been reported, but requires the use
of Ca/NH3 or Na/NH3,18 lithium alkyls,19 or (Me3Si)3SiH
under free radical conditions.20 A C-S reductive cou-
pling process would give a thioether, and the resulting
Pd(0) could be trapped, forming an anionic three-
coordinated complex C using the CdS π electron density
of the sulfur ylide. Such a C-S coupling process is well
documented21,22 and constitutes an important step in
palladium-catalyzed C-S bond formation.23-25 Finally,
ladium; when these reactions were carried out at room
temperature, palladium thiolates seem to be formed.
When 1 is reacted at room temperature with [Pd-
(dba)2], complex 3 is obtained. We supposed that this
compound was an iodine-bridging dimer having the C-S
chelate ligand present in 2. However, this compound
reacts with Tl(OTf) and XyNC (Xy ) 2,6-dimethylphen-
yl) to give 4, whose structure has been determined by
X-ray diffraction studies (see below), showing that an
unexpected rearrangement has taken place. This rear-
rangement involves the cleavage of the HC-S(Pd) and
aryl-Pd bonds and the formation of aryl-S and HC-
Pd bonds (Scheme 2). The analogous complex 4′ is
(18) Page, P. C. B.; Wilkes, R. D.; Reynolds, D. In Comprehensive
Organic Functional Group Transformations; Katritzky, A. R., Meth-
Cohn, O., Rees, C. W., Ley, S. V., Eds.; Pergamon: Oxford, 1995; Vol.
2, p 128.
(19) Krief, A.; Kenda, B.; Barbeaux, P. Tetrahedron Lett. 1991, 32,
2509.
(20) Aria, P.; Lesage, M.; Wayner, D. D. M. Tetrahedron Lett. 1991,
32, 2853.
(21) Mann, G.; Baranano, D.; Hartwig, J . F.; Rheingold, A. L.; Guzei,
I. A. J . Am. Chem. Soc. 1998, 120, 9205.
t
similarly prepared using BuNC.
Complex 3 reacts with Tl(TfO) and bpy to give com-
plex 5, which is an isomer of 2. Complex 5 reacts with
XyNC (1:2) in CH2Cl2 to give 4 quantitatively. The
compounds 2 and 5 show a different reactivity toward
iodide. Thus, the former reacts with NaI, giving complex
6 in which the donor sulfur atom of the dithioacetal
(22) Hartwig, J . F. Acc. Chem. Res. 1998, 31, 852.
(23) Murahashi, S.-I.; Yamamura, M.; Yanagisawa, K.-i.; Mita, N.;
Kondo, K. J . Org. Chem. 1979, 44, 2408.

Palladated Aryldithioacetals
Sch em e 3
Organometallics, Vol. 20, No. 6, 2001 1113
F igu r e 1. Thermal ellipsoid plot of the cation of 2 (20%
probability levels) with the labeling scheme. Selected bond
lengths (Å) and angles (deg): Pd-C(1) 1.986(4), Pd-N(31)
2.063(3), Pd-N(41) 2.104(3), Pd-S(1) 2.2743(10); C(1)-
Pd-N(31) 97.97(14), N(31)-Pd-N(41) 79.01(13), C(1)-Pd-
S(1) 82.51(11), N(41)-Pd-S(1) 101.87(9), C(11)-S(1)-
C(10) 102.60(19), C(11)-S(1)-Pd 110.45(13), C(10)-S(1)-
Pd 96.48(13), C(21)-S(2)-C(10) 104.8(2).
bpy by iodide. The last reaction has been proved
independently. The different result of the reaction
between 1 and Pd(dba)2 when performed in the presence
or without bpy and Tl(OTf) can be understood if the
intermediate A rapidly reacts with Tl(OTf) and bpy to
give 2, which rearranges to give 5 more slowly than A
does to give 3. A similar argument can be invoked in
the case of the synthesis of complex 6 from Pd(dba)2.
1
NMR Sp ectr a . The H resonances due to the dithio-
acetal carbon CH(STo)2 appear at 6.17 ppm for complex
2. In the case of 6 it cannot be assigned. The corre-
sponding signal of the starting iodoarene 1 appears at
5.92 ppm. In the case of the isomerized species 3-5 the
CH-Pd signals appear within the range 6.2-4.7. In
consequence, the positions of these signals are not
diagnostic for discerning if a given complex is an ortho-
palladated dithioacetalarene or an isomerized alkylpal-
ladium derivative. This happens similarly with the 13C
NMR spectra.
the nucleophilic Pd(0) should attack the CH carbon atom
to give the final Pd(II) complex 3. An alternative
pathway, suggested by one referee, could involve two
[1,3] sigmatropic rearrangements. Thus, the cleavage
of the S-Pd bond from A could give a tricoordinate
complex D, which could undergo a [1,3] sigmatropic
rearrangement to give E, which would evolve easily to
3 through a new [1,3] sigmatropic rearrangement
involving the migration of the PdI group. The rear-
rangement leading to 5 from 2 could be explained
similarly. When 6 was heated in solution of dichloro-
ethane (6 or 22 h) or toluene (16 h), a mixture mainly
containing 6 and 3 was obtained. Because 6 shows a
slight conductivity in acetone (ΛM ) 13 Ω-1 cm2 mol-1),
the partial rearrangement of 6 to give 3 can be under-
stood if 6 is in equilibrium with the iodide of the cation
of 2 (in fact, 2 reacts with iodide to give 6; see Scheme
2) and that this salt is transformed into the iodide salt
of the cation of 5 that evolves to 3 by displacement of
At room temperature, complex 4 exhibits fluxional
behavior because both isonitrile ligands appear as
equivalent in the 1H and 13C NMR spectra. Such
equivalence disappears on cooling to -60 °C. Interest-
ingly, on cooling, the other signals broaden slightly; this
could be due to the decreasing of the sulfur inversion
rate. Usually such rates are high, but fluxionality due
to a sulfur inversion has been observed in cyclopalla-
dated thioethers.26 Surprisingly the analogous complex
t
4′ does not show the same behavior and both BuNC
ligands are nonequivalent at room temperature in the
1H and 13C NMR spectra.
1
In the H NMR spectra of 6, at room or low (-60 °C)
temperatures, the signal corresponding to the hydrogen
of the CH(STo)2 group was not observed and the methyls
of both To groups appear as two broad signals. This
could be due to a restricted rotation about the C-Pd
bond.5,27
(24) Carpita, A.; Rossi, R.; Scamuzzi, B. Tetrahedron Lett. 1989, 30,
2699.
(25) Ishiyama, T.; Mori, M.; Suzuki, A.; Miyaura, N. J . Organomet.
Chem. 1996, 525, 225.
(26) Dupont, J .; Beydoun, N.; Pfeffer, M. J . Chem. Soc., Dalton
Trans. 1989, 1715.

1114 Organometallics, Vol. 20, No. 6, 2001
Vicente et al.
contacts Pd‚‚‚C21 3.33, Pd‚‚‚C22 3.67, and Pd‚‚‚C26 3.48
Å. The hydrogen atom H10 at the chiral carbon C10 is
trans to the ring C21-26 (torsion angle H10-C10-S2-
C21 176°; the corresponding angle to S1-C11 is 40°).
The different Pd-N distances [Pd-N41, 2.104(3); Pd-
N31, 2.063(3) Å] may indicate a greater trans influence
exerted by the aryl carbon donor ligand with respect to
the sulfur donor, although the severe distortion shown
by this complex may also influence these distances.
The structure of 4 (Figure 2, Table 1) shows the
coordination at palladium to be nonplanar, with S1 lying
0.70 Å out of the plane through Pd, C4, C5, and C30;
there is no obvious cause for this. The triflate oxygen
atoms are involved in four C-H‚‚‚O hydrogen bonds, of
which the shortest is H25‚‚‚O5 2.44 Å. The bond
distances between Pd and the isocyanide carbons are
significantly different [Pd-C4, 2.0573(16); Pd-C5,
1.9941(16)], suggesting again a greater trans influence
of the carbon donor ligand (in this case an alkyl group)
than of the sulfur donor (a thioether ligand).
Con clu sion s. The synthesis and characterization of
the first palladated dithioacetal complex are reported.
An unexpected and previously unreported rearrange-
ment process is also described. This involves the trans-
formation of a dithioacetal aryl ligand into a dithioether
alkyl ligand through the cleavage of HC-S and aryl-
Pd bonds and formation of aryl-S and HC-Pd bonds.
We believe that such transformation takes place with
the active participation of the palladium atom, which
promotes a carbon-sulfur bond coupling related to that
found in palladium-catalyzed arylations of thiols.
F igu r e 2. Thermal ellipsoid plot of the cation of 4 (30%
probability levels) with the labeling scheme. Selected bond
lengths (Å) and angles (deg): Pd-C(4) 1.9941(16), Pd-C(5)
2.0573(16), Pd-C(30) 2.0588(15), Pd-S(1) 2.3357(4), N(4)-
C(4) 1.149(2), N(5)-C(5) 1.145(2); C(4)-Pd-C(5) 95.96(6),
C(4)-Pd-C(30) 88.58(6), C(5)-Pd-S(1) 91.34(4), C(30)-
Pd-S(1) 85.90(4), C(21)-S(1)-C(11) 106.70(7), C(21)-
S(1)-Pd 99.66(5), C(11)-S(1)-Pd 110.07(5), C(31)-S(2)-
C(30) 106.51(7).
X-r a y Str u ctu r es. The solid state structure of 2 has
been determined by X-ray diffraction methods (Figure
1, Table 1). The coordination at the palladium atom is
significantly nonplanar; the atom N31 lies 0.59 Å out
of the best plane through Pd, S1, C1, and N41 (mean
deviation 0.03 Å). The interplanar angle of the bpy
ligand is 14°. Steric crowding between the methoxy
group at O1 and the bpy ligand may be responsible for
these features; nonbonded distances are C36‚‚‚O1 2.91
and H36‚‚‚O1 2.54 Å. The ring C21-26 adopts an
unusual position above the Pd atom, with nonbonded
Ack n ow led gm en t. This work was supported by
Direccio´n General de Investigacio´n Cient´ıfica y Te´cnica
(PB97-1047), INTAS (97-0166), and the Fonds der
Chemischen Industrie. F.S.H.M. is grateful to Funda-
cio´n Se´neca, Comunidad Auto´noma de la Regio´n de
Murcia (Spain), for a grant.
Su p p or tin g In for m a tion Ava ila ble: Atomic positional
parameters, bond lengths and interbond angles, atomic dis-
placement parameters, and hydrogen atom parameters. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(27) Brown, J . M.; Perez-Torrente, J . J .; Alcock, N. W.; Clase, H. J .
Organometallics 1995, 14, 207.
OM0008981