Unexpected formation of an ortho-palladated diphenylthioether

Article abstract of DOI:10.1021/om0496683

The reaction of [Ph₄P][BrC₆H₄S-2] with [Pd₂(dba)₃]-dba (dba = dibenzylideneacetone) in the presence of PPh₃ gives trans-tPd(C₆H ₄Ph-2)Br(PPh₃₂]. A sequence of reactions consisting of oxidative addition of the tetraphenylphosphonium cation to palladium(O), reductive C-S coupling to give BrC₆H₄Ph-2, and, again, an oxidative addition of the latter to palladium-(0) seems to constitute the pathway for the formation of the final palladium complex. Some experimental evidence supporting this pathway is provided. The crystal structure of trans-[Pd(C₆H₄Ph-2)Br(PPh₃) ₂] has been solved by an X-ray.

Full text of DOI:10.1021/om0496683

Organometallics 2004, 23, 4325-4327
4325
Notes
Un exp ected F or m a tion of a n or th o-P a lla d a ted
Dip h en ylth ioeth er
J ose´ Vicente,*,† J ose´-Antonio Abad,* and Rosa-Mar´ıa Lo´pez-Nicola´s
Grupo de Qu´ımica Organometa´lica, Departamento de Quı´mica Inorga´nica,
Facultad de Qu´ımica, Universidad de Murcia, Apartado 4021, E-30071 Murcia, Spain
Peter G. J ones*,‡
Institut fu¨r Anorganische und Analytische Chemie der Technischen Universita¨t,
Postfach 3329, 38023 Braunschweig, Germany
Received May 12, 2004
Sch em e 1
Summary: The reaction of [Ph4P][BrC6H4S-2] with
[Pd2(dba)3]‚dba (dba ) dibenzylideneacetone) in the
presence of PPh3 gives trans-[Pd(C6H4SPh-2)Br(PPh3)2].
A sequence of reactions consisting of oxidative addition
of the tetraphenylphosphonium cation to palladium(0),
reductive C-S coupling to give BrC6H4SPh-2, and,
again, an oxidative addition of the latter to palladium-
(0) seems to constitute the pathway for the formation of
the final palladium complex. Some experimental evi-
dence supporting this pathway is provided. The crystal
structure of trans-[Pd(C6H4SPh-2)Br(PPh3)2] has been
solved by an X-ray diffraction study.
In tr od u ction
One of our research interests involves the synthesis
of ortho-functionalized arylpalladium complexes1-4 and
the study of their reactivity toward CO,4-6 isoni-
triles,4,5,7,8 or alkynes.4,9,10 In this context, we prepared
the tetraphenylphosphonium salt of the 2-bromoben-
zenethiolate anion, [PPh4][BrC6H4S] (1), with the pur-
pose of reacting it with Pd(dba)2 and obtaining the first
arylpalladium complexes having a negatively charged
sulfur atom at the ortho position. We report here the
unexpected results of this reaction and a proposal of the
mechanism.
Resu lts a n d Discu ssion
The salt [PPh4][BrC6H4S] (1) precipitated in water
when 2-bromobenzenethiol was reacted with NaOH and
[PPh4]Cl in 1:5.5:1 molar ratios (Scheme 1). The elec-
trospray mass spectroscopy in the negative and positive
modes, the molar conductivity in acetone, and NMR
spectroscopic data of 1 prove the above formulation.
However, the reaction of 1 with Pd(dba)2 ([Pd2(dba)3]‚dba)
and PPh3 (1:2) in boiling toluene (2.5 h) did not give
the expected complex trans-[PPh4][Pd(C6H4S-2)Br(PPh3)2]
but instead trans-[Pd(C6H4SPh-2)Br(PPh3)2] (2; Scheme
1). A possible explanation of this result would be that,
under the reaction conditions, the salt 1 decomposes to
give PPh3 and BrC6H4SPh-2 (3) and the latter adds to
Pd(dba)2 to give 2; in such a case only 1 equiv of PPh3
would be needed. However, although the reaction goes
well using 1 equiv of added PPh3, when 1 was refluxed
in toluene for 2.5 h, it was recovered unaltered in
virtually quantitative yield.
† E-mail: jvs@um.es. http://www.scc.um.es/gi/gqo/.
‡ E-mail: p.jones@tu-bs.de.
(1) Vicente, J .; Abad, J . A.; Mart´ınez-Viviente, E.; Ram´ırez de
Arellano, M. C.; J ones, P. G. Organometallics 2000, 19, 752.
(2) Vicente, J .; Abad, J . A.; Hernandez-Mata, F. S.; J ones, P. G. J .
Am. Chem. Soc. 2002, 124, 3848.
(3) Vicente, J .; Abad, J . A.; Lo´pez-Serrano, J .; Clemente, R.; Ram´ırez
de Arellano, M. C.; J ones, P. G.; Bautista, D. Organometallics 2003,
22, 4248.
(4) Vicente, J .; Saura-Llamas, I.; Turp´ın, J .; Ram´ırez de Arellano,
M. C.; J ones, P. G. Organometallics 1999, 18, 2683.
(5) Vicente, J .; Abad, J . A.; Fo¨rtsch, W.; J ones, P. G.; Fischer, A. K.
Organometallics 2001, 20, 2704.
(6) Vicente, J .; Abad, J . A.; Frankland, A. D.; Ram´ırez de Arellano,
M. C. Chem. Eur. J . 1999, 5, 3066.
(7) Vicente, J .; Abad, J . A.; Martinez-Viviente, E.; J ones, P. G.
Organometallics 2002, 21, 4454.
(8) Vicente, J .; Saura-Llamas, I.; Gru¨nwald, C.; Alcaraz, C.; J ones,
P. G.; Bautista, D. Organometallics 2002, 21, 3587.
(9) Vicente, J .; Abad, J . A.; Ferna´ndez-de-Bobadilla, R.; J ones, P.
G.; Ram´ırez de Arellano, M. C. Organometallics 1996, 15, 24.
(10) Vicente, J .; Abad, J . A.; Lopez-Pelaez, B.; Martinez-Viviente,
E. Organometallics 2002, 21, 58.
We propose the following sequence of reactions to
explain the formation of 2 (Scheme 2). First, the Ph4P+
cation oxidatively adds to Pd(0) to give a phenyl Pd(II)
10.1021/om0496683 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 07/28/2004

4326 Organometallics, Vol. 23, No. 18, 2004
Notes
Sch em e 2
F igu r e 1. Molecular structure of complex 2, with thermal
ellipsoids at the 30% probability level. Selected bond
lengths (Å) and angles (deg): Pd-C(11) 2.016(3), Pd-P(2)
2.3337(7), Pd-P(1) 2.3366(7), Pd-Br 2.5296(3), S-C(12)
1.776(3), S-C(21) 1.780(3), C(11)-Pd-P(2) 88.21(7), C(11)-
Pd-P(1) 89.47(7), P(2)-Pd-P(1) 174.75(3), C(11)-Pd-Br
177.29(8), P(2)-Pd-Br 91.633(19), P(1)-Pd-Br 90.909(19),
C(12)-S-C(21) 103.87(13).
We have also reproduced the last step in the forma-
tion of 2. Thus, we have prepared 3 by a palladium-
catalyzed coupling of 2-bromobenzenethiol and iodoben-
zene in the presence of KOtBu (1:1.4:1), using a mixture
of Pd(dba)2 and 1,1′-diphenylphosphinoferrocene as the
catalyst. The refluxing in toluene of a mixture of 3,
Pd(dba)2, and PPh3 (1.2:1:2) gave complex 2.
The crystal and molecular structure of 2 has been
determined by X-ray diffraction studies (Figure 1). The
palladium atom is in a square-planar coordination with
the phosphine ligands in trans position.
derivative that reacts with the 2-bromobenzenethiolate
anion to give a phenyl(2-bromophenylthiolate)Pd(II)
complex, A. This intermediate undergoes a C-S reduc-
tive coupling to give 3 and [Pd(PPh3)2]. An oxidative
addition process between these reagents gives 2. This
pathway also assumes the formation of 3 but through
a palladium-mediated reaction.
Oxidative addition reactions of quaternary phospho-
nium salts to Pd(0) complexes to give organopalladium-
(II) complexes have been reported.11 Such reactions are
involved in aryl-aryl exchange between arylpalladium
complexes and arylphosphine ligands1,12-17 and consti-
tute a key step in some new palladium-catalyzed
syntheses of phosphines.18-20 In fact, we have modeled
this step in carrying out the reaction of [Ph4P]Cl with
Pd(dba)2 and PPh3 (molar ratio 1:0.5:1), which results
in the formation of trans-[PdPhCl(PPh3)2].13
Con clu sion s
Although oxidative addition and reductive elimination
reactions in palladium chemistry are very well-known
processes, we describe here (i) one of the few examples
in which a phosphonium cation is oxidatively added to
Pd(0) and (ii) the first example in which two reagents
are able to react through a sequence of reactions
consisting of three steps: an oxidative addition giving
a Pd(II) complex that suffers a reductive C-S coupling,
giving a product that is able to add oxidatively to the
intermediate palladium(0) complex, giving a palladated
thioether. We have proposed a mechanism and modeled
most of the proposed steps.
The proposed C-S reductive coupling process of the
complex A to give 3 is an important step in the
palladium-catalyzed synthesis of diarylthioethers from
thiolates with aryl halides or triflates.21-30
(11) Sakamoto, M.; Shimizu, I.; Yamamoto, A. Chem. Lett. 1995,
1101.
(12) Kong, K. C.; Cheng, C. H. J . Am. Chem. Soc. 1991, 113, 6313.
(13) Herrmann, W. A.; Brossmer, C.; Priermeier, T.; Ofele, K. J .
Organomet. Chem. 1994, 481, 97.
Exp er im en ta l Section
(14) Goodson, F. E.; Wallow, T. I.; Novak, B. M. J . Am. Chem. Soc.
1997, 119, 12441.
(15) Grushin, V. V. Organometallics 2000, 19, 1888.
(16) de la Torre, G.; Gouloumis, A.; Vazquez, P.; Torres, T. Angew.
Chem., Int. Ed. 2001, 40, 2895.
(17) Segelstein, B. E.; Butler, T. W.; Chenard, B. L. J . Org. Chem.
1995, 60, 12.
(18) Kwong, F. Y.; Chan, K. S. Organometallics 2000, 19, 2058.
(19) Kwong, F. Y.; Chan, K. S. Chem. Commun. 2000, 1069.
(20) Kwong, F. Y.; Lai, C. W.; Tian, Y.; Chan, K. S. Tetrahedron
Lett. 2000, 41, 10285.
Syn th esis of [P P h 4][Br C6H4S] (1). A solution of NaOH
(551 mg, 13.8 mmol) in water (40 mL) was slowly added to a
mixture of BrC6H4SH-2 (470 mg, 2.49 mmol) and water (40
mL). The resulting mixture was stirred under nitrogen for 15
min, and [Ph4P]Cl (933 mg, 2.49 mmol) was added. The
resulting suspension was stirred for 15 min and filtered, and
the solid was washed with water (3 × 5 mL) and Et2O (3 × 5
mL) and dried, giving 1 as a pale yellow solid. Yield: 1.19 g,
(21) Kosugi, M.; Ogata, T.; Terada, M.; Sano, H.; Migita, T. Bull.
Chem. Soc. J pn. 1985, 58, 3657.
(22) Ciattini, P. G.; Morera, E.; Ortar, G. Tetrahedron Lett. 1995,
36, 4133.
(23) Baran˜ano, D.; Hartwig, J . F. J . Am. Chem. Soc. 1995, 117, 2937.
(24) Ishiyama, T.; Mori, M.; Suzuki, A.; Miyaura, N. J . Organomet.
Chem. 1996, 525, 225.
(26) Pinchart, A.; Dallaire, C.; Gingras, M. Tetrahedron Lett. 1998,
39, 543.
(27) Kondo, T.; Mitsudo, T. Chem. Rev. 2000, 100, 3205.
(28) Schopfer, U.; Schlapbach, A. Tetrahedron 2001, 57, 3069.
(29) Li, G. Y.; Zheng, G.; Noonan, A. F. J . Org. Chem. 2001, 66,
8677.
(25) Zheng, N.; McWilliams, J . C.; Fleitz, F. J .; Armstrong, J . D.;
Volante, R. P. J . Org. Chem. 1998, 63, 9606.
(30) Mann, G.; Baran˜ano, D.; Hartwig, J . F.; Rheingold, A. L.; Guzei,
I. A. J . Am. Chem. Soc. 1998, 120, 9205.

Notes
Organometallics, Vol. 23, No. 18, 2004 4327
1
87%. ΛM ) 126 Ω-1 mol-1 cm2. H NMR (200 MHz, CDCl3): δ
ferrocene (15 mg, 0.026 mmol), and Pd(dba)2 (16 mg, 0.026
mmol) were added, and the resulting mixture was stirred at
50 °C for 3 days. After this time it was not necessary to work
under nitrogen. The solvent was removed in vacuo, the residue
was extracted with Et2O (3 × 5 mL), and the extracts were
filtered over Celite. The red filtrate was concentrated (ca. 3
mL) and purified by TLC chromatography (dichloromethane/
n-hexane, 1:4). The band containing the product (Rf ) 0.52)
was collected and extracted with acetone. This solution was
concentrated to dryness, and the residue was redissolved in
Et2O and dried with anhydrous magnesium sulfate. The
suspension was filtered and the filtrate concentrated to
dryness, giving 3 as a colorless oil. Yield: 660 mg, 97%. 1H
7.82-7.51 (several m, 20 H PPh4 + 1 H C6H4), 7.14 (dd, 1 H,
3
4
H2 or H5 C6H4, J H,H ) 8 Hz, J H,H ) 2 Hz), 6.61 (td, 1 H, H3
3
4
or H4 C6H4, J H,H ) 8 Hz, J H,H ) 2 Hz), 6.27 (td, 1 H, H3 or
H4 C6H4, 3J H,H ) 8 Hz, 4J H,H ) 2 Hz). 13C{1H} NMR (100 MHz,
+
CDCl3): δ 135.80 (CH, C6H4), 135.71 (d, CH, para CH’s PPh4
,
J P,C ) 2.6 Hz), 134.26 (d, CH, meta CH’s PPh4+, J P,C ) 10.2
Hz), 130.75 (CH, C6H4), 130.71 (d, CH, ortho CH’s PPh4+, J P,C
) 12.8 Hz), 125.10 (CH, C6H4), 118.59 (CH, C6H4), 117.26 (d,
C, CP, J P,C ) 88.7 Hz). 31P{1H} NMR (121 MHz, CDCl3): δ
24.3 (s, PPh4). ESMS (MeCN) + (m/z): 339.1 (PPh4+). ESMS
(MeCN) - (m/z): 188.6 (100), 187.3 (69) (BrC6H4S-).
Syn t h esis of tr a n s-[P d (C6H 4SP h -2)Br (P P h 3)2] (2).
Meth od A. Pd(dba)2 (1.09 g, 1.90 mmol) and PPh3 (1.00 g, 3.81
mmol) were mixed in toluene (10 mL) under nitrogen and
stirred for 15 min. 1 (1.00 g, 1.90 mmol) was added, and the
resulting mixture was refluxed under nitrogen for 2.5 h. Some
palladium formed. The solvent was evaporated, the residue
was extracted in the air with CH2Cl2 (4 × 5 mL), and the
extracts were filtered over Celite. The red filtrate was con-
centrated to dryness and the residue triturated with Et2O (20
mL), giving a solid that was separated by filtration, washed
with Et2O (3 × 5 mL), and air-dried, giving pale yellow 2.
Yield: 1.13 g, 67%.
3
NMR (300 MHz, CDCl3): δ 7.55 (dd, 1 H, H3 or H6 C6H4 J H,H
4
) 8 Hz, J H,H ) 2 Hz), 7.48-7.43 (several m, 5 H, C6H5), 7.14
3
4
(td, 1 H, H4 or H5 C6H4 J H,H ) 8 Hz, J H,H ) 2 Hz), 7.02 (td,
1 H, H4 or H5 C6H4 J H,H ) 8 Hz, 4J H,H ) 2 Hz), 6.90 (dd, 1 H,
3
H3 or H6 C6H4 J H,H ) 8 Hz, J H,H ) 2 Hz). 13C{1H} NMR (50
MHz, CDCl3): δ 138.8 (C), 133.5 (CH), 133.0 (CH), 132.8 (C),
129.7 (CH), 129.6 (CH), 128.5 (CH), 127.8 (CH), 127.2 (CH),
123.00 (C). FAB-MS: m/z 266 (M+, 100%).
3
4
X-r a y Cr ysta l Str u ctu r e of 2‚Et2O. A single crystal,
obtained by slow diffusion of Et2O into a CH2Cl2 solution of 2,
was mounted in inert oil and transferred to the cold gas stream
of the diffractometer (Bruker SMART 1000 CCD). Crystal data
for 2‚Et2O: C52H49BrOP2PdS, M ) 970.22, monoclinic, a )
17.8954(12) Å, b ) 12.4133(8) Å, c ) 20.4354(14) Å, â )
101.376(3)°, U ) 4450.4(5) Å3, T ) 143 K, space group P21/c,
Z ) 4, µ(Mo KR) ) 1.472 mm-1, 84 493 reflections measured,
11 047 unique (Rint ) 0.083), which were used in all calcula-
tions. Refinement using the program SHELXL-97 (G. M.
Sheldrick, University of Go¨ttingen) proceeded to a final wR(F2)
of 0.091 (all data), R(F) 0.035 for 523 parameters; max. ∆F
0.53 e Å-3. CCDC number 228878.
Meth od B. Pd(dba)2 (217 mg, 0.38 mmol) and PPh3 (200
mg, 0.76 mmol) were dissolved in toluene (15 mL) under
nitrogen and stirred for 5 min. Compound 3 (120 mg, 0.46
mmol) was added and the resulting mixture refluxed under
nitrogen for 2 h. Working up as described for 1 renders 2.
Yield: 260 mg, 76%. Dec pt: 178 °C. 1H NMR (200 MHz,
CDCl3): δ 7.6-7.5 (m, 12 H), 7.35-7.18 (several m, 21 H), 6.96
3
4
(m, 1 H), 6.70 (dd, 2 H, C6H5 J H,H ) 8 Hz, J H,H ) 1.7 Hz),
6.31 (m, 2 H), 5.58 (m, 1 H, C6H4). 13C{1H} NMR (50 MHz,
CDCl3): δ 152.40 (t, CS, C6H4, J P,C ) 3.62 Hz), 144.99 (t, CPd,
2
4
J P,C ) 3.77 Hz), 135.00 (t, CH, ortho CH’s PPh3 | J P,C + J P,C
|
5
) 12.6 Hz), 134.86 (CH, C6H5), 133.17 (t, C, CS C6H5, J P,C
)
1
3
Ack n ow led gm en t. We thank Ministerio de Ciencia
y Tecnolog´ıa and FEDER (BQU2001-0133). R.M.L.N.
thanks Ministerio de Educacio´n, Cultura y Deporte
(Spain), for a grant.
1.1 Hz), 131.45 (t, CH, ipso CH’s PPh3 | J P,C + J P,C| ) 45.7
Hz), 129.75 (CH, para CH’s PPh3), 128.86 (CH), 128.06 (CH),
3
127.72 (t, CH, meta CH’s PPh3 | J P,C + 5J P,C| ) 10.2 Hz), 124.77
(CH, C6H4), 123.48 (CH), 123.19 (CH). 31P{1H} NMR (121 MHz,
CDCl3): δ 24.58 (s, 2 PPh3). Anal. Calcd for C48H39BrP2PdS:
C, 64.33; H, 4.39; S, 3.58. Found: C, 63.98; H, 4.53; S, 3.41.
Syn th esis of Br C6H4SP h -2 (3). 2-Bromobenzenethiol (0.31
mL, 488 mg, 2.57 mmol) and KOtBu (306 mg, 2.57 mmol) were
mixed in toluene under nitrogen and stirred for 15 min. Then,
iodobenzene (0.40 mL, 3.54 mmol), 1,1′-diphenylphosphino-
Su p p or tin g In for m a tion Ava ila ble: CIF file for complex
2‚Et2O. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM0496683