Insertion of alkenyl sulfides into a palladium-aryl bond. 2. Stabilization of σ-yl-κS chelates and decomposition reactions through C-S cleavage

Article abstract of DOI:10.1021/om9604076

The reaction of [Pd(C₆F₅)Br(NCMe)₂] with the allylic sulfides R¹SCH₂CH=CH₂ (R¹ = -CH₂-CH=CH₂, Me), n-BuSCHMeCH=CH₂, and n-BuSCH₂CH=CHMe results in insertion of the double bond into the Pd-C₆F₅ bond and β-SR elimination (C-S cleavage) to give the corresponding (pentafluorophenyl)alkenes and a palladium thiolate. With alkenyl sulfides of longer carbon chains RS(CH₂)_nCH=CH₂ (R = n-Bu, Ph; n = 2, 3) five-membered (n = 2, 13, 14) or six-membered (n = 3, 16, 17) σ-yl-τS-palladacycles were obtained. The six-membered derivatives isomerize to the corresponding five-membered palladacycles (18, 19) by one-step Pd-migration (Pd-H elimination-readdition). Inversion of the coordinated sulfur is observed in these derivatives, and the dynamic process has been studied for the monomeric complexes [(σ-κS-(Rthio)alkyl)Pd(acac)] (13b, 14b, 18b, 19b). ΔG?_Tc values show that the S-inversion is easier for the Ph-substituted than for the n-Bu-substituted complexes. The decomposition of the σ-yl-κS palladacycles occurs through Pd-migration and, when Pd and S are placed three bonds apart in the chain, β-SR elimination; this is the same process observed in the reaction of [Pd(C₆F₅)Br(NCMe)₂] with allylic sulfides. Double bond isomerization of the (pentaflurophenyl)alkene products formed in the decomposition reactions is observed, catalyzed by Pd-H intermediates. Double pentafluorophenyl arylation is also observed in some cases.

Full text of DOI:10.1021/om9604076

5010
Organometallics 1996, 15, 5010-5017
In ser tion of Alk en yl Su lfid es in to a P a lla d iu m -Ar yl
Bon d . 2. Sta biliza tion of σ-yl-KS Ch ela tes a n d
Decom p osition Rea ction s th r ou gh C-S Clea va ge
Ana C. Albe´niz, Pablo Espinet,* and Yong-Shou Lin
Departamento de Quı´mica Inorga´nica, Facultad de Ciencias, Universidad de Valladolid,
47005 Valladolid, Spain
Received May 24, 1996X
The reaction of [Pd(C6F5)Br(NCMe)2] with the allylic sulfides R1SCH2CHdCH2 (R1 ) -CH2-
CHdCH2, Me), n-BuSCHMeCHdCH2, and n-BuSCH2CHdCHMe results in insertion of the
double bond into the Pd-C6F5 bond and â-SR elimination (C-S cleavage) to give the
corresponding (pentafluorophenyl)alkenes and a palladium thiolate. With alkenyl sulfides
of longer carbon chains RS(CH2)nCHdCH2 (R ) n-Bu, Ph; n ) 2, 3) five-membered (n ) 2,
13, 14) or six-membered (n ) 3, 16, 17) σ-yl-κS-palladacycles were obtained. The
six-membered derivatives isomerize to the corresponding five-membered palladacycles (18,
19) by one-step Pd-migration (Pd-H elimination-readdition). Inversion of the coordinated
sulfur is observed in these derivatives, and the dynamic process has been studied for the
monomeric complexes [(σ-κS-(Rthio)alkyl)Pd(acac)] (13b, 14b, 18b, 19b). ∆GqTc values show
that the S-inversion is easier for the Ph-substituted than for the n-Bu-substituted complexes.
The decomposition of the σ-yl-κS palladacycles occurs through Pd-migration and, when Pd
and S are placed three bonds apart in the chain, â-SR elimination; this is the same process
observed in the reaction of [Pd(C6F5)Br(NCMe)2] with allylic sulfides. Double bond
isomerization of the (pentaflurophenyl)alkene products formed in the decomposition reactions
is observed, catalyzed by “Pd-H” intermediates. Double pentafluorophenyl arylation is also
observed in some cases.
In tr od u ction
membered palladacycles with η2-ene-κS butenyl sulfides
as ligands have been prepared.7-10 Three-membered11-13
or five-membered14-18 σ-yl-κS (alkylthio)alkylpalladium
derivatives are also known. Thus, alkenyl sulfides are
suitable substrates to study the Heck reaction in detail,
and since S is a good donor atom for Pd, after insertion
of the double bond into the Pd-R bond the stabilization
of intermediates through S-coordination may be pos-
sible.
In this work, the stable arylating reagent [Pd-
(C6F5)Br(NCMe)2] is reacted with RS(CH2)nCHdCH2 (R
) n-Bu, Ph, -CH2CHdCH2; n ) 1-3). As already
described, the simplicity of the 19F NMR spectral
pattern of the pentafluorophenyl group makes of this
technique a convenient tool to investigate the fate of the
intermediates formed after insertion of the double bond
Alkenyl sulfides have been used as substrates in
Heck-type reactions to give substituted unsaturated
derivatives.1-6 C-S bond cleavage has been observed
in the reaction of vinyl and allylic sulfides with Grignard
or organomercuric reagents catalyzed by Ni(II),1,4,6 Pd-
(II),1,5 and Cu(I)2,3 compounds. In some cases, both the
terminal olefin and the C-S bond of allylic sulfides have
been directly attacked by alkyl or aryl groups from the
Grignard reagents, and a mixture of organic compounds
were obtained (eq 1).1-3 However, the selective attack
to either the terminal double bond3 or C-S bond3,4-6 in
allyl and vinyl sulfides has also been reported.
(7) McCrindle, R.; Alyea, E. C.; Ferguson, G.; Dias, S. A.; McAlees,
A. J .; Parvez, M. J . Chem. Soc., Dalton Trans. 1980, 137.
(8) Abel, E. W.; Evans, D. G.; Koe, J . R.; Sik, V.; Bates, P. A.;
Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1989, 985.
(9) McCrindle, R.; Alyea, E. C.; Dias, S. A.; McAlees, A. J . J . Chem.
Soc., Dalton Trans. 1979, 640.
(10) Goodall, D. C. J . Chem. Soc. A 1968, 887.
(11) Yoshida, G.; Kurosawa, H.; Okawara, R. J . Organomet. Chem.
1976, 113, 85.
(12) (a) Miki, K.; Kai, Y.; Yasuoka, N.; Kasai, N. J . Organomet.
Chem. 1977, 135, 53. (b) Miki, K.; Kai, Y.; Yasuoka, N.; Kasai, N. Bull.
Chem. Soc. J pn. 1981, 54, 3639.
(13) Albe´niz, A. C.; Espinet, P.; Lin, Y.-S.; Mart´ın, A.; Orpen, A. G.
Organometallics 1996, 15, 5003.
(14) Takahashi, Y.; Tokuda, A.; Sakai, S.; Ishii, Y. J . Organomet.
Chem. 1972, 35, 415.
(15) Holton, R. A.; Kjonaas, R. A. J . Am. Chem. Soc. 1977, 99, 4177.
(16) Holton, R. A.; Zoeller, J . R. J . Am. Chem. Soc. 1985, 107, 2124.
(17) Holton, R. A.; Kjonaas, R. A. J . Organomet. Chem. 1977, 142,
C15.
On the other hand, alkenyl sulfides are potential
chelating ligands toward palladium. Five and a half-
* To whom correspondence should be addressed. E-mail: espinet
@cpd.uva.es.
X Abstract published in Advance ACS Abstracts, September 15, 1996.
(1) Okamura, H.; Takei, H. Tetrahedron Lett. 1979, 36, 3425.
(2) Gendreau, Y.; Normant, J . F.; Villieras, J . J . Organomet. Chem.
1977, 142, 1.
(3) Barsanti, P.; Calo`, V.; Lopez, L.; Marchese, G.; Naso, F.; Pesce,
G. J . Chem. Soc., Chem. Commun. 1978, 1085.
(4) Okamura, H.; Miura, M.; Takei, H. Tetrahedron Lett. 1979, 1,
43.
(18) Canty, A. J . in Comprehensive Organometallic Chemistry:
A
(5) Trost, B. M.; Tanigawa, Y. J . Am. Chem. Soc. 1979, 101, 4743.
(6) Trost, B. M.; Ornstein, P. L. Tetrahedron Lett. 1981, 22(36), 3463.
Review of the Literature 1982-1994; Abel, E. W., Stone, F. G. A.,
Wilkinson, G., Eds.; Pergamon Press: New York, 1995; Vol. 9, p 225.
S0276-7333(96)00407-4 CCC: $12.00 © 1996 American Chemical Society

Insertion of Alkenyl Sulfides into a Pd-Aryl Bond
Organometallics, Vol. 15, No. 23, 1996 5011
Ta ble 1. Rea ction s of [P d (C6F 5)Br (NCMe)2] w ith Allylic Su lfid es
entry
sulfide
Pd(C6F5)Br/sulfide
organic products (molar ratio)
palladium products
1
2
3
diallyl sulfide
diallyl sulfide
allyl methylsulfide
1/1
2/1
1/1
2 (33), 4 (9), 5 (1)
2 (9), 4 (7.5), 5 (1)
2 (2.5), 4 (2.6), 5 (1)
3, 6, PdBr2, PdS, Pd
PdBr2, PdS, Pd
[MeSPdBr]n, PdBr2, PdS, Pd
Sch em e 1
into the Pd-C6F5 bond.19 Six- and five-membered σ-yl-
κS chelating complexes are detected or isolated and
their isomerization and final decomposition is analyzed,
thus gaining insight into the mechanism of C-S bond
cleavage.
Sch em e 2
Resu lts
Rea ction s w ith Allyl Su lfid es. The reactions of
diallyl sulfide or allyl methyl sulfide with [Pd(C6F5)Br-
(NCMe)2] give products resulting from C-S bond cleav-
age (Scheme 1). The reactions proceed through coordi-
nation of the unsaturated substrate to Pd(II) followed
by insertion of the double bond into the PdC6F5 moiety
and then â-elimination of a Pd thiolate. The experi-
ments were carried out with different reactant ratios,
and the results are given in Table 1. The organic
1
products were identified by 19F and H NMR and GC-
MS and also, when solids, by elemental analysis. All
these data are given in the Experimental Section.
When equimolar amounts of [Pd(C6F5)Br(NCMe)2] (1)
and allyl sulfide are mixed in CH2Cl2 (Scheme 1), allyl
pentafluorobenzene (2) and [BrPdSCH2CHdCH2]n (3)
are formed as major compounds. Part of 2 undergoes
further arylation by “Pd(C6F5)Br” to give 1,3-bis(pen-
tafluorophenyl)-1-propene (4), which was isolated as a
white solid. A small amount of trans-1-(pentafluoro-
phenyl)-1-propene (5) was found. It was formed by
isomerization of 2 catalyzed by Pd-H generated under
the reaction conditions (the final step in the forma-
tion of the bisaryl derivative 4 is Pd-H elimination).
Bis(allenethiolato)palladium (6) was obtained as orange
crystals, and its formation can be explained by exchange
between molecules of compound 3 to give 6 and PdBr2.
As shown in Table 1, when the Pd:allyl-moiety ratio
increases the amount of compound 4 formed clearly rises
(4 amounts to 43% of organic products in entry 2 and
43% in entry 3 versus 21% in entry 1). Moreover, the
allyl-containing palladium complexes 3 and 6 disappear
as a result of total reaction with “Pd(C6F5)Br”. Com-
pounds 3 and [MeSPdBr]n are very insoluble, and it was
not possible to separate them from PdS, PdBr2, and Pd
1
also formed in the reactions; their H NMR spectra were
recorded in DMSO-d6 as solvent, where they are soluble.
The observed C-S bond cleavage could occur either
by PdC6F5 addition to the double bond and subsequent
â-elimination of Pd-S or by direct attack of the C6F5
group to the C-S bond (Scheme 2). In order to clarify
the mechanism of this process, the reactions with
n-butyl 1-buten-3-yl sulfide and n-butyl but-2-enyl
sulfide were studied since the final products obtained
will depend on the reaction mechanism. The reactions
of these organic sulfides with equimolar amounts of [Pd-
(C6F5)Br(NCMe)2] were carried out in CDCl3 in NMR
tubes.
With n-butyl 1-buten-3-yl sulfide (Scheme 3) 50%
conversion was observed after 3 h, and the elimination
products (E)-1-(pentafluorophenyl)-2-butene (7) and (Z)-
1-(pentafluorophenyl)-2-butene (8) were found in a ratio
7:8 ) 4:1 by 19F NMR analyses. After 1 day the reaction
(19) (a) Albe´niz, A. C.; Espinet, P.; Foces-Foces, C.; Cano, F. H.
Organometallics 1990, 9, 1079. (b) Albe´niz, A. C.; Espinet, P.; J eannin,
Y.; Philoche-Levisalles, M.; Mann, B. E. J . Am. Chem. Soc. 1990, 112,
6594. (c) Albe´niz A. C.; Espinet, P. Organometallics 1991, 10, 2987-
2988. (d) Albe´niz, A. C.; Espinet. P.; Lin, Y.-S. Organometallics 1995,
14, 2977-2986.

5012 Organometallics, Vol. 15, No. 23, 1996
Albe´niz et al.
Sch em e 3
Sch em e 4
was complete, and a mixture of organic compounds 7,
8, (E)-3-methyl-1,3-bis(pentafluorophenyl)-1-propene (9),
and (E)-1,4-bis(pentafluorophenyl)-1-butene (10) was
obtained (ratio: 7:1.6:3.3:1). The formation of bis-
(pentafluorophenyl) compounds is due to reaction of 7
or the putative 4-(pentafluorophenyl)-1-butene (11,
formed from isomerization of 7) with “Pd(C6F5)Br”
synthons.
These results support mechanism a in Scheme 2 for
the cleavage of the carbon-sulfur bond in the reaction
of allylic sulfides with “Pd(C6F5)Br” synthons: insertion
of the olefin double bond into the Pd-C6F5 bond to give
an unstable alkyl palladium complex followed by elimi-
nation of the Pd-SR group at the â-position. The
insertion-SR elimination mechanism has been found
in the reaction of allylic aryl sulfides with RhH(PPh3)4.20
The â-SR elimination promoted by nickel has also been
reported.21
The reaction of n-butyl but-2-enyl sulfide with [Pd-
(C6F5)Br(NCMe)2] (Scheme 4) showed 10% conversion
after 3 h and gave only 3-methyl-3-(pentafluorophenyl)-
1-propene (12), derived from olefin insertion into the
Pd-C6F5 bond and subsequent â-SR elimination. After
24 h, compounds 7, 8, 9, 10, and 12 had been formed
(ratio: 3:1:14:3:1). Since the reaction is slow and there
is a large amount of unreacted “Pd(C6F5)Br” synthons,
most of 12 was easily pentafluoroarylated to afford 9.
The final step in this reaction, Pd-H elimination to give
the alkene, generates significant amounts of “PdHBr”
species, which probably react with the starting n-Bu-
SCH2CHdCHCH3 and add to the double bond with
subsequent cleavage of the C-S bond to generate CH3-
CH2CHdCH2; this product can react with “Pd(C6F5)-
Br” species and lead to the formation of 7, 8, and 10.
The reaction is slower than the corresponding of n-butyl
1-buten-3-yl sulfide, probably due to the higher substi-
tution of the double bond, and secondary reactions such
as the Pd-H addition described become important.
Rea ction s w ith Bu t-3-en yl Su lfid es. Complexes
13a and 14a are easily prepared in good yields by
reaction of [Pd(C6F5)Br(NCMe)2] with the corresponding
butenyl sulfides, as shown in Scheme 5.
To clarify some features of the NMR spectra of these
two derivatives (see below), their corresponding mono-
meric acetylacetonato complexes 13b and 14b were
obtained by treatment of the dimers with Tl(acac).
Tables 2 and 3 collect the 19F and 1H NMR data of
complexes 13a , 13b, 14a , 14b, and other derivatives
prepared from other alkenyl sulfides, which will be
discussed in the following sections. The 1H NMR
1
spectra were assigned with the help of homonuclear H
COSY and decoupling experiments when necessary.
(20) Osakada, K.; Matsumoto, K.; Yamamoto, T.; Yamamoto, A.
Organometallics 1985, 4, 857.
(21) Shiu, L.-L.; Yu, C.-C.; Wong, K.-T.; Chen, B.-L.; Cheng, W.-L.;
Yuan, T.-M.; Luh, T.-Y. Organometallics 1993, 12, 1018.

Insertion of Alkenyl Sulfides into a Pd-Aryl Bond
Organometallics, Vol. 15, No. 23, 1996 5013
19F and 1H NMR spectra at room temperature. In 1
week, 12% of complex 14a had decomposed to the
organic compounds 7, 8, 11, and 1-(pentafluorophenyl)-
1-butene (15); in addition, a dark brown solid, [PhSPd-
Br]n, was obtained. However, only 2% of 13a had
decomposed to 11 after 1 week. When solutions of either
complex in CHCl3 were refluxed for 12 h, 87% of 14a or
13% of 13a decomposed. The resulting organic products
and their ratios (in parentheses) are summarized in eq
2. Thus, the n-butyl substituted sulfide derivative is
Sch em e 5
15
clearly more stable than the corresponding phenyl one.
This is consistent with the results found for similar
palladium complexes with σ-yl-κS chelating ligands.14
4-(Pentafluorophenyl)-1-butene (11) is the only or-
ganic compound observed in the decomposition of 13a ,
but a large number of isomeric (pentafluorophenyl)-
butenes are formed when 14a decomposes. However it
seems that, in this latter case, 11 is again the product
immediately formed when 14a decomposes, and the
other olefins come from the isomerization of 11 pro-
moted by the starting Pd complex 14a . To test this
hypothesis, a 2-fold molar amount of allyl pentafluo-
robenzene (2) was added to 13a in CDCl3 solution. The
Ta ble 2. 19F NMR Da ta for P a lla d iu m Com p lexesa
b
complex
Fmeta
Fpara
Fortho
13a
13b
14a
14b
16
-163.2 (b)
-164.0 (b)
-163.1 (b)
-163.9 (m)
-163.8 (b)
-163.5 (b)
-163.6 (b)
-158.3 (b)
-159.7 (b)
-158.1 (b)
-159.5 (t)
-159.0 (b)
-158.7 (b)
-158.9 (b)
-143.2 (b)
-143.9 (b)
-143.0 (b)
-143.8 (m)
-142.6 (b)
-142.4 (b)
-144.7 (b)
17c
18a
18bd
19a
19b
-164.3/-164.3 (b) -159.7/-160.0 (b) -144.4/-144.8 (b)
-163.5 (b)
-164.1 (m)
-158.8 (b)
-159.6 (t)
-144.6 (b)
-144.7 (b)
1
19F and H NMR spectra showed that 50% of 2 isomer-
a
δ, measured on a Bruker AC-300 spectrometer at 293 K using
ized to 5 after 1 week, yet the decomposition of 13a was
not accelerated.
CDCl3 as solvent (except when otherwise noted), downfield from
CFCl3 as reference.
observed as two broad signals in a ratio of 1.4:1 for 18b.
b 3
d
J
) 20-21 Hz. c 273 K. Isomers are
F-F
Rea ction s w ith P en t-4-en yl Su lfid es. Complexes
16 and 17 are formed via reaction between [Pd(C6F5)-
Br(NCMe)2] and the corresponding pent-4-enyl sulfide
at 293 K for 0.5 h, or at 273 K for 1 h, as shown in
Scheme 6. Purification of these complexes was unsuc-
cessful since they isomerize by one-step Pd migration
to the more stable five-membered palladacyclic com-
plexes 18a and 19a . The processes were followed by
19F NMR at room temperature, and after 1 h 70% of 17
had isomerized to 19a , but only 10% of 16 had converted
into 18a . The isomerization rate was studied for
complex 17. The process is first order on the Pd complex
with a rate constant k ) (2.31 ( 0.08) × 10-4 s-1. From
the Eyring equation the activation free energy for
Fluxional behavior was observed for 13b and 14b, and
the process was studied by 19F NMR at variable tem-
perature. At low temperature (243 K), each complex
shows two sets of 19F resonances corresponding to two
diastereoisomers resulting from the fact that the two
coordinated atoms in the palladacycle are chiral. The
effect is clearly observed in the Fpara region for 13b (two
triplets in 1:1.3 ratio) and the Fortho resonances of 14b
(two signals in 1:1.3 ratio). Upon heating the spectra
of 13b and 14b coalesce to one set of signals (Tc ) 293
K for 13b and Tc ) 268 K for 14b at 282 MHz). This
effect is attributed to inversion at the coordinated sulfur
atom of the ligand, which interconverts both distereo-
isomers. The activation free energy ∆Gq, at the coales-
isomerization of 17 is ∆Gq
) 92.1 ( 0.2 kJ mol-1
.
293K
Thus, it seems that the attainment of an adequate ring
size, and so a more stable situation, promotes the
isomerization of these and other palladium complexes,
such as the derivatives with η2-ene-κS ligands PdCl2-
[MeSCH2C(Me)2CH2CHdCH2] and PdCl2[MeS(CH2)3-
CHdCH2].7,8
Complexes 18a and 19a react with Tl(acac) to give
monomeric acetylacetonato derivatives 18b and 19b,
respectively. The structures of 18a and 19a can be
further supported by the analyses of the 1H NMR
spectra of 18b and 19b. The spectral data of all these
complexes are given in Tables 2 and 3.
cence temperature, for the inversion process is ∆Gq
293K
) 61.37 ( 0.19 kJ /mol for 13b and ∆Gq
) 53.99 (
268K
0.18 kJ /mol for 14b. These values are consistent with
the values reported for the inversion of thioethers
coordinated to Pd.22
Complexes 13a and 14a are stable as solids. In
CDCl3 solution 13a is fairly stable too. However,
compound 14a slowly decomposes. The stability of 13a
and 14a was studied looking at the evolution of their
(22) Abel, E. W.; Bhargava, S. K.; Orrell, K. G. Prog. Inorg. Chem.
1984, 32, 1.

5014 Organometallics, Vol. 15, No. 23, 1996
Ta ble 3. 1H NMR Da ta for th e P a lla d iu m Com p lexesa ,b
Albe´niz et al.
compd
H1
H2
H3
H4
H5
H6
R
other
13a
2.98 b (2H) 1.80 b (1H)
0.96 b (1H)
2.92 b (2H) 1.48 b (2H)
3.33 b (1H)
3.33 b (1H) 2.74 b (2H), 1.80 b (2H),
2.74 b (1H) 1.46 m (2H), 0.96 b (3H)
2.92 b (1H) 2.73 b (2H), 1.78 m (2H),
2.73 b (1H) 1.48 m (2H), 0.95 t (7.4, 3H)
3.43 b (1H) 8.0 b (2H), 7.4 b (3H)
2.79 b (1H)
2.89 b (1H) 7.9 m (2H), 7.4 m (3H)
2.78 b (1H)
2.92 b (1H) 2.70 m (2H), 1.74 m (2H),
13b
14a
14b
16
3.38 b m (1H)
3.43 b (1H)
3.37 b (1H)
5.26 s (1H), 1.94 s
(3H), 1.88 s (3H)
3.04 b (2H) 1.86 b (1H)
0.90 b (1H)
3.10 b (1H) 1.44 b (1H)
2.89 b (1H) 1.20 b (1H)
3.05 b (1H) 2.10 b (1H) 1.42 b (1H) 3.56 b (1H)
2.84 b (1H) 1.89 b (1H) 0.69 b (1H)
5.30 s (1H), 1.98 s
(3H), 1.87 s (3H)
2.10 b (1H)
1.42 m (2H), 0.93 t (7.4, 3H)
17
3.25 b (1H) 2.15 b (1H) 1.41 b (1H) 3.54 b (1H)
2.78 b (1H) 1.95 b (1H) 0.60 b (1H)
3.01 b (1H) 7.9 b (2H), 7.4 m (3H)
2.15 b (1H)
18a
18b
2.93 b (2H) 1.79 b (1H)
1.24 b (1H)
3.31 b (1H)
1.98 b (1H) 2.78 b (2H) 2.60 b (2H), 1.79 b (2H)
1.70 b (1H)
1.9 b (1H)
1.43 m (2H), 0.94 t (7.4, 3H)
2.76 m (2H), 1.77 m (2H),
2.7-3.0 b
1.4-1.55 b
(2H)
2.7-3.0 b
(1H)
2.7-3.0 b
(1H)
5.21s (1H), 1.91s
(3H), 1.85 s (3H)
(2H)
1.4-1.55 b 2.6 b (1H)
(1H)
1.48 m (2H), 0.94 t (7.4, 3H)
19a
19b
2.99 b (2H) 1.91 b (1H)
1.24 b (1H)
3.47 b (1H)
3.1 b (1H)
2.03 b (1H) 2.82 b (2H) 8.0 m (2H), 7.4 m (3H)
1.68 b (1H)
2.7-2.95 b 1.4-1.7 m
1.9 m (1H) 2.7-2.95 b 7.9 m (2H), 7.4 m (3H)
5.25 s (1H), 1.94 s
(3H), 1.84 s (3H)
(2H)
(2H)
(2H)
1.4-1.7 m
(1H)
a
b
δ mult J values (Hz) are given in parentheses. CDCl3 used as solvent. The temperature used is 293 K for each complex except 17
at 273 K.
Sch em e 6
yl)pentene are obtained: (E)-5-(pentafluorophenyl)-2-
pentene (20), (Z)-5-(pentafluorophenyl)-2-pentene (21),
5-(pentafluorophenyl)-1-pentene (22), (E)-1-(pentafluo-
rophenyl)-2-pentene (23), and (E)-1-(pentafluorophenyl)-
1-pentene (24). They are depicted in eq 3 along with
their relative ratios in parentheses; the corresponding
brown insoluble palladium thiolate is also obtained.
The high number of isomeric (pentafluorophenyl)-
pentenes is again due to double bond isomerization in
5-(pentafluorophenyl)-1-pentene (22) catalyzed by the
starting Pd complex. In fact, complex 19a is capable of
effecting the isomerization of allylpentafluorobenzene
(2) to (E)-1-(pentafluorophenyl)-1-propene (5), as de-
scribed for complex 13a . Figure 1 shows the change in
organic product distribution with time for the decom-
The inversion of the sulfur atom in complexes 18b
and 19b was studied by 19F NMR at different temper-
atures. Two signals for the Fortho atoms were observed
at 243 K for each complex, and the coalescence temper-
atures at 282 MHz are 305 K (18b) and 280 K (19b),
1
position of 19a , monitored by 19F and H NMR. Com-
corresponding to ∆Gq
) 60.10 ( 0.16 kJ mol-1 for
pound 22 is the only organic product formed when the
decomposition process starts; as the reaction time
increases the percentage of 22 in the mixture decreases,
as it is isomerized into 21, 23, 24, and especially 20
(100% is taken each time as the total amount of organic
compounds, which constantly increases as the decom-
position proceeds).
305K
18b and ∆Gq
) 54.36 ( 0.16 kJ mol-1 for 19b.
280K
The decompositions of 18a and 19a in CDCl3 solutions
were analyzed by 1H and 19F NMR. After 7 days at
room temperature 53% of the starting 18a had decom-
posed, whereas 79% of 19a had decomposed under the
same conditions. Several isomers of (pentafluorophen-

Insertion of Alkenyl Sulfides into a Pd-Aryl Bond
Organometallics, Vol. 15, No. 23, 1996 5015
Sch em e 7
F igu r e 1.
Discu ssion
Alkenyl sulfides are potential chelating alkene-
thioether ligands provided that the S-atom and the
olefin are sufficiently spaced to give a stable metalla-
cycle. However, we have not detected the formation of
η2-κS palladium complexes in the reactions between [Pd-
(C6F5)Br(NCMe)2] and any of the alkenyl sulfides tried,
not even at low temperature. The coordination of the
sulfur atom is more favorable, and most probably it
occurs first, but as soon as the olefin coordinates
(whether as a chelate or with previous decoordination
of the S we cannot say) insertion into the Pd-C6F5 bond
occurs.
Different alkenyl chain lengths have been tried: RS-
(CH2)nCHdCH2 (n ) 1-3), and this has a decisive
influence on the fate of the intermediate formed after
insertion. When the organometallic moiety bears S and
Pd three bonds apart, â-SR elimination takes place, as
shown by the behavior of the allyl sulfides tried and in
the decomposition process of complexes 13a , 14a , 18a ,
and 19a (see below). For longer (n ) 2, 3) chain lengths
formation of σ-yl-κS palladium complexes is observed.
The five-membered palladacycles are the most stable
rings found, and the six-membered complexes easily
isomerize to five-membered palladium derivatives. The
analogous reaction with a vinyl sulfide (n ) 0) was
described in the previous paper in this issue and also
gives a stable three-membered σ-yl-κS palladacycle.13
The five-membered complexes decompose in solution
very slowly at room temperature or faster when strong
conditions are used. According to the results of these
decomposition experiments, the stabilities of the com-
plexes follow the order 13a > 14a > 18a > 19a . The
decomposition of these derivatives arises from 1, 2
hydrogen shift (Pd-H elimination-readdition) and
elimination of Pd and the â-SR group to give a terminal
C6F5-substituted monoolefin; the olefin can then isomer-
ize to several positional isomers under catalysis by the
starting palladium complex, as shown by the rate of
formation of the different isomers in Figure 1. This
catalytical process is supported by the isomerization of
allylpentafluorobenzene in the presence of complexes
13a or 19a .
readdition with the opposite regiochemistry. This rota-
tion is restricted in the S-η2-olefin palladacycle. Con-
sequently, decoordination of the sulfur atom is expected
for the process of double bond insertion into the Pd-H
bond to occur. In fact, the higher unstability of the
complexes with phenyl-substituted sulfides, 14a and
19a , can be understood as a consequence of the aromatic
Ph ring weakening the coordinating ability of the sulfur
atom and easing its decoordination. The higher donor
ability of the n-Bu-substituted sulfide makes the Pd-S
bond stronger, and consequently complexes 13a and 18a
are more stable. A similar stability trend has been
found for n-Bu- and Ph-sulfur-substituted σ-yl-κS pal-
ladium complexes reported in the literature.14 On the
other hand, the CH2 (position 5 in Table 3) in complexes
18a and 19a is less sterically hindered by the C6F5 ring
and the â-H elimination is probably easier than for the
but-4-enyl sulfide complexes 13a and 14a . Hence, the
stability order found is as follows: 13a , 14a > 18a , 19a .
The rates for the isomerization of complexes 16 and
17 parallel the stabilities of 18a and 19a , respectively;
that is, the isomerization of 16 to 18a is slower than
that of 17 to 19a in CDCl3 solution. The mechanism of
the isomerization is a one-step Pd-migration (1,2-
hydrogen shift) most probably controlled by the deco-
ordination of the sulfur atom, which, as discussed
above, is more favorable for 17 than for 16.
Finally, the fluxionality of the complexes 13b, 14b,
18b, and 19b is attributed to the existence of pyramidal
inversion of the configuration of the sulfur atom. Ac-
cording to the free energy of activation values found,
∆GqTc, the ease of the process is 13b ≈ 18b < 14b ≈
19b; that is, the inversion of the sulfur atom in
complexes with ligand-containing n-Bu sulfides is more
difficult than in those containing Ph sulfides. The
The proposed mechanism of the decomposition and
catalytical activity toward olefin isomerization is de-
picted in Scheme 7. According to this mechanism, once
PdH elimination has occurred, rotation around the Pd-
olefin bond is needed in intermediate 25 for PdH

5016 Organometallics, Vol. 15, No. 23, 1996
Albe´niz et al.
equimolar amounts of the reactants were employed, the final
products were a mixture of organic compounds 2, 4, and 5
(ratio 2.5:2.6:1) and a dark brown solid (mixture of [MeSPd-
Br]n, PdBr2, PdS, and Pd).
probable reason of this trend is that the inversion occurs
through a planar transition state, which is stabilized
by (3p-2p)π conjugation between the S lone pair and
the phenyl aromatic ring in the complex involving a PhS
moiety.23,24
[MeSPdBr]n: 1H NMR (DMSO-d6, δ, 300 MHz) 2.1 (s, Me).
Rea ction s of [P d (C6F 5)Br (NCMe)2] w ith n -Bu tyl 1-
Bu ten -3-yl Su lfid e a n d w ith n -Bu tyl Bu t-2-en yl Su lfid e.
Two NMR tubes were charged with [Pd(C6F5)Br(NCMe)2]
(0.025 g, 0.0574 mmol) and n-butyl 2-methylallyl sulfide
(0.0105 mL, 0.0574 mmol) or [Pd(C6F5)Br(NCMe)2] (0.025 g,
0.0574 mmol) and n-butyl but-2-enyl sulfide (0.0096 mL,
0.0574 mmol) in CDCl3 (0.6 mL), respectively. The reactions
were monitored by 1H and 19F NMR for 24 h. The final
products were analyzed.
7: 19F NMR (CDCl3, δ, 282 MHz), -163.5 (m, Fmeta), -158.4
(t, Fpara), -144.7 (m, Fortho); 1H NMR (CDCl3, δ, 300 MHz), 5.5
(m, 2H, H2, H3), 3.37 (dd, J ) 5.3, 1.5 Hz, 2H, H1), 1.64 (dd, J
) 5.9, 1.2 Hz, 3H, H4); MS (El) m/z (relative intensity) 222
(M+, 67), 207 (71), 194 (25), 187 (45), 181 (100), 161 (15), 93
(14), 41 (14).
8: 19F NMR (CDCl3, δ, 282 MHz) -164.0 (m, Fmeta), -158.5
(t, Fpara), -144.3 (m, Fortho); 1H NMR (CDCl3, δ, 300 MHz) 5.5-
5.6 (m, 2H, H2, H3), 3.44 (d, J ) 7.4 Hz, 2H, H1), 1.74 (d, J )
6.8 Hz, 3H, H4); MS (El) m/z (relative intensity) 222 (M+, 82),
207 (75), 187 (55), 181 (100), 93 (24), 69 (32), 41 (98).
9: 19F NMR (CDCl3, δ, 282 MHz) -162.4, 163.3 (m, Fmeta),
-156.5, 157.0 (t, Fpara), -143.1, 143.4 (m, Fortho); 1H NMR
(CDCl3, δ, 300 MHz) 6.76 (dd, J ) 16.3, 7.5 Hz, 1H, H2), 6.38
(d, J ) 16.3 Hz, 1H, H1), 4.10 (qui, J ) 7.3 Hz, 1H, H3), 1.55
(d, J ) 7.3 Hz, 3H, Me); MS (El) m/z (relative intensity) 388
(M+, 13), 373 (25), 187 (7), 181 (100), 161 (9), 143 (9), 13 (8),
93 (8).
10: 19F NMR (CDCl3, δ, 282 MHz) -162.9, 163.4 (m, Fmeta),
-157.2, 157.4 (t, Fpara), -143.9, 144.3 (m, Fortho); 1H NMR
(CDCl3, δ, 300 MHz) 6.50 (dt, J ) 16.0, 6.9 Hz, 1H, H2), 6.26
(d, J ) 16.0 Hz, 1H, H1), 2.91 (t, J ) 7.3 Hz, 2H, H4), 2.56 (q,
J ) 7.3 Hz, 2H, H3); MS (El) m/z (relative intensity) 388 (M+,
14), 207 (100), 187 (52), 181 (77), 161 (16), 93 (8).
Exp er im en ta l Section
Gen er a l Con sid er a tion s. 19F, 1H, 13C, and 31P NMR
spectra were recorded on Bruker AC-300 and ARX-300 instru-
ments. Chemical shifts are reported in δ units (parts per
million, ppm) downfield from Me4Si for 1H and 13C, CFCl3 for
19F, and H3PO4 (85% aqueous solution, external reference) for
31P. Carbon and hydrogen microanalyses were carried out on
a Perkin-Elmer 2400 CHN elemental analyzer.
All solvents were dried and distilled before use by standard
methods. RSCH2CH2CHdCH2, RSCH2CH2CH2CHdCH2 (R )
n-Bu and Ph), n-BuSCH(CH3)CHdCH2, and n-BuSCH2-
CHdCHCH3 were synthesized as reported in the literature.10
Diallyl sulfide and allyl methyl sulfide were commercially
available (Aldrich). [Pd(C6F5)Br(NCMe)2] was prepared as
previously reported.19a
NOTE: Some of the organic products obtained are rather
volatile and can be lost if evaporation is carried out under high
vacuum. Thus, the use of a low vacuum water pump is
recommended and when necessary it will be noted in the
preparations below.
Rea ction of [P d (C6F 5)Br (NCMe)2] w ith Dia llyl Su lfid e.
To a solution of [Pd(C6F5)Br(NCMe)2] (0.400 g, 0.918 mmol)
in CH2Cl2 (20 mL) was added diallyl sulfide (0.118 mL, 0.918
mmol). After 8 h of stirring a dark brown precipitate was
filtered (mixture of 3, PdBr2, PdS, and Pd). The filtrate was
evaporated to dryness carefully using a water pump. The
orange residue was chromatographed through a silica gel
column eluting with n-hexane and then diethyl ether.
A
colorless oily residue formed after careful evaporation of the
solvent of the first fraction, which was a mixture of 2, 4, and
1
5 (ratio 33:9:1) by analyses of its H and 19F NMR spectra and
12: 19F NMR (CDCl3, δ, 282 MHz) -163.1 (m, Fmeta), -158.2
(t, Fpara), -143.3 (m, Fortho); 1H NMR (CDCl3, δ, 300 MHz) 5.9
(m, 1H, H2), 5.0 (m, 2H, H1), 3.82 (qui, J ) 6.9 Hz, 1H, H3),
1.5 (d, J ) 6.9 Hz, Me); MS (El) m/z (relative intensity) 222
(M+, 94), 207 (100), 187 (84), 181 (72).
P r ep a r a tion of 13a . n-Butyl but-3-enyl sulfide (0.079 mL,
0.459 mmol) was added to a solution of [Pd(C6F5)Br(NCMe)2]
(0.200 g, 0.459 mmol) in CH2Cl2 (5 mL) at room temperature.
After 2 h of stirring, the solution was evaporated to dryness.
On addition of ether (2 mL) and then n-hexane (3 mL) and
cooling a yellow precipitate formed, which was filtered, washed
with ether/n-hexane (2:3), and air-dried to give a yellow solid
13a (85% yield).
GC-MS. The white solid 4 can be isolated by evaporating off
(oil pump) the more volatile compounds 2 and 5. The second
fraction (ether used as eluent) afforded orange crystals, 6, after
concentration of the solution to 1 mL, addition of n-hexane (3
mL), and cooling (yield: 15% based on Pd).
3: 1H NMR (DMSO-d6, δ, 300 MHz) 5.8 (m, 1H), 5.1 (m,
2H), 3.1 (m, 2H).
4: 19F NMR (CDCl3, δ, 282 MHz) -162.4/-163.2 (m, Fmeta),
-156.3/-156.5 (t, Fpara), -143.4/-143.9 (m, Fortho); 1H NMR
(CDCl3, δ, 300 MHz) 6.56 (dt, J ) 16.4, 6.6 Hz, 1H, H2), 6.40
(d, J ) 16.4 Hz, 1H, H1), 3.66 (d, J ) 6.6 Hz, 2H, H3). Anal.
Calcd for C15H4F10: C, 48.15; H, 1.08. Found: C, 48.26; H,
1.12.
5: 19F NMR (CDCl3, δ, 282 MHz) -163.9 (m, Fmeta), -158.5
(t, Fpara), -144.5 (m, Fortho); 1H NMR (CDCl3, δ, 300 MHz) 6.56
(dq, J ) 16.2, 6.5 Hz, 1H, H2), 6.27 (dq, J ) 16.2, 1.6 Hz, 1H,
H1), 1.94 (dd, J ) 6.5, 1.6 Hz, 3H, H3); MS (El) m/z (relative
intensity) 208 (M+, 100), 189 (22), 187 (28), 181 (79), 169 (14),
158 (15).
6: 1H NMR (CDCl3, δ, 300 MHz) 5.98 (m, 2H, H2), 5.35 (m,
4H, H1), 3.62 (d, J ) 6.9 Hz, 4H, H3); MS (EI) m/z (relative
intensity) 252 (M+, 71), 250 (100), 248 (53), 215 (21), 108 (25).
Anal. Calcd for C6H10PdS2: C, 28.52; H, 3.99. Found: C,
28.55; H, 3.95.
When [Pd(C6F5)Br(NCMe)2] (1 mol) and diallyl sulfide (0.5
mol) were mixed in CH2Cl2, the same procedure as above was
used. A mixture of organic compounds 2, 4, and 5 in a ratio
9:7.5:1 and a black solid mixture of PdBr2, PdS, and Pd were
obtained.
13a : Anal. Calcd for C28H32Br2F10Pd2S2: C, 33.79; H, 3.24.
Found: C, 33.91; H, 3.27.
P r ep a r a tion of 14a . Complex 14a was prepared from
phenyl but-3-enyl sulfide following the same procedure used
to prepare 13a . A yellow solid, 14a , was obtained (88% yield).
1
14a : 13C{1H} NMR (CDCl3, δ, 75.4 MHz) 144.9 (bd, J CF
)
1
244.1 Hz, C6F5), 139.5 (bd, J CF ) 240.4 Hz, C6F5), 137.3 (bd,
1J CF ) 251.0 Hz, C6F5), 132.8 (Ph), 132.2 (C1Ph), 129.9 (Ph),
129.5 (Ph), 112.8 (b, C6F5), 52.0 (C3), 41.3 (C1), 38.0 (C2), 27.9
(C4). Anal. Calcd for C32H24Br2F10Pd2S2: C, 37.12; H, 2.34.
Found: C, 37.07; H, 2.39.
P r ep a r a tion of 18a . Complex 18a was prepared from
n-butyl pent-4-enyl sulfide by the same procedure used to
prepare 13a , but changing the reaction time to 30 h. The
preparation afforded a yellow solid 18a (68% yield).
18a : Anal. Calcd for C30H36Br2F10Pd2S2: C, 35.21; H, 3.55.
Found: C, 35.46; H, 3.59.
P r ep a r a tion of 19a . Complex 19a was prepared from
phenyl pent-4-enyl sulfide by the same procedure used to
prepare 13a , but changing the reaction time to 4 h. A yellow
solid 19a was obtained (77% yield).
R ea ct ion of [P d (C6F 5)Br (NCMe)2] w it h Allyl Met h yl
Su lfid e. The same procedure as above was used. When the
(23) Murray, S. G.; Hartley, F. R. Chem. Rev. 1981, 81, 365-414.
(24) Abel, E. W.; Bhargava, S. K.; Orrell, K. G.; Sik, V.; Williams,
B. L. Tetrahedron 1982, 1(3), 289.

Insertion of Alkenyl Sulfides into a Pd-Aryl Bond
Organometallics, Vol. 15, No. 23, 1996 5017
19a : Anal. Calcd for C34H28Br2F10Pd2S2: C, 38.40; H, 2.63.
Found: C, 38.36; H, 2.68.
22: 19F NMR (CDCl3, δ, 282 MHz) -163.5 (m, Fmeta), -158.6
(t, Fpara), -144.8 (m, Fortho); 1H NMR (CDCl3, δ, 300 MHz) 5.8
(m, J ) 16.9, 10.2, 6.2 Hz, 1H, H2), 4.95-5.1 (m, J ) 16.9,
10.2 Hz, 2H, H1), 2.7-2.8 (m, 2H, H5)*, 2.2-2.3 (m, 2H, H3)*,
1.68 (qui, J ) 7.3 Hz, 2H, H4); MS (El) m/z (relative intensity)
236 (M+).
P r ep a r a tion of 13b. To a solution of 13a (0.060 g, 0.06
mmol) in CH2Cl2 (10 mL) was added Tl(acac) (0.037 g, 0.12
mmol). After 1 h, the white precipitate formed was filtered
off. The light yellow filtrate was evaporated to dryness. The
residue was triturated with ether (2 mL) and n-hexane (2 mL).
A light yellow solid 13b formed (69% yield).
13b. Anal. Calcd for C19H23F5O2PdS: C, 44.15; H, 4.45.
Found: C, 44.09; H, 4.38.
The synthesis of 14b, 18b, and 19b was accomplished by
the same method described above for 13b, starting from 14a ,
18a , and 19a respectively.
*: overlapped with other signals of compounds.
23: 19F NMR (CDCl3, δ, 282 MHz) -163.5 (m, Fmeta), -158.3
(t, Fpara), -144.3 (m, Fortho); 1H NMR (CDCl3, δ, 300 MHz) 5.3-
5.45 (m, 2H, H2, H3)*, 3.36 (d, J ) 6.6 Hz, 2H, H1), 2.0 (qui, J
) 7.2 Hz, 2H, H4), 0.95 (t, J ) 7.2 Hz, 3H, H5); MS (El) m/z
(relative intensity) 236 (M+, 22), 207 (20), 194 (100), 187 (29),
181 (34), 55 (37), 41 (13).
14b: yellow solid (67% yield). Anal. Calcd for C21H19F5O2-
SPd: C, 46.98; H, 3.57. Found: C, 46.34; H, 3.60.
18b: obtained as a yellow oily residue (75% yield).
19b: yellow oily residue (79% yield).
*: overlapped with other of other compounds.
24: 19F NMR (CDCl3, δ, 282 MHz) -163.3 (m, Fmeta), -158.2
(t, Fpara), -144.8 (m, Fortho); 1H NMR (CDCl3, δ, 300 MHz) 6.55
(dt, J ) 14.0, 7.0 Hz, 1H, H2), 6.27 (dt, J ) 14.0 Hz, 4J HF ) 1.4
Hz, 1H, H1), 2.11 (qui, J ) 7.2 Hz, 2H, H3), 1.2 (m, 2H, H4),
0.96 (t, J ) 7.2 Hz, 3H, H5); MS (El) m/z (relative intensity)
236 (M+, 1), 194 (4), 170 (7), 85 (22), 71 (35), 57 (80), 55 (32),
43 (100), 41 (75).
All monomeric complexes were analyzed by 1H and 19F
NMR. The inversion of the sulfur atom in each monomer was
studied at different temperatures by 19F NMR. Rate constants
were determined at the coalescence temperature using the
equation k ) (π/21/2)‚δν.25 Uncertainties in the rate constant
were calculated assuming a δν variation of ( 0.35 Hz. The
rate constants are given as follows: k ) 69.3 ( 1.5 s-1 for 13b;
k ) 165.4 ( 1.5 s-1 for 14b; k ) 320.9 ( 1.5 s-1 for 18b; k )
416.8 ( 1.5 s-1 for 19b. Free energies of activation were
Isom er iza tion of Allylp en ta flu or oben zen e Ca ta lyzed
by 13a . An NMR tube was charged with 13a (0.020 g, 0.02
mmol), CDCl3 (0.6 mL), and allylpentafluorobenzene (0.0062
1
mL, 0.04 mmol). The analysis of H and 19F NMR indicated
that 50% of allylpentafluorobenzene had isomerized to 5 after
7 days.
calculated using the Eyring equation in the form ∆Gq
)
-2.3RT log(KBT/hkobs). Error was calculated using the above-
mentioned uncertainty in kobs and a temperature variation of
(0.4 K.25
The isomerization of allylpentafluorobenzene was also
performed in the presence of complex 19a by the same
procedure described above. Twenty-two percent of 2 was
isomerized to 5 after 8 h at room temperature. However, 19a
began to decompose at this point.
F or m a tion a n d Isom er iza tion of 16. An NMR tube was
charged with [Pd(C6F5)Br(NCMe)2] (0.025 g, 0.0574 mmol),
CDCl3 (0.6 mL), and n-butyl pent-4-enyl sulfide (0.0107 mL,
0.0574 mmol) at room temperature. The arylation of the
alkenyl sulfide was complete after 30 min and complex 16
formed; it was identified by 1H and 19F NMR. Eighty-three
percent of 16 had isomerized to 18a after 1 day.
Decom p osition of 13a . An NMR tube was charged with
13a (0.030 g, 0.03 mmol) and CDCl3 (0.6 mL). Analysis of the
1H and 19F NMR spectra showed that 2% of 13a decomposed
to 4-(pentafluorophenyl)-1-butene (11) after 7 days at room
temperature. However, the rate of the decomposition in-
creased to 13% when 13a (0.060 g, 0.06 mmol) in CHCl3 (15
mL) was refluxed for 12 h.
11: 19F NMR (CDCl3, δ, 282 MHz) -163.5 (m, Fmeta), -158.3
(t, Fpara), -144.5 (m, Fortho); 1H NMR (CDCl3, δ, 300 MHz) 5.8
4
(m, 1H, H2), 5.0 (m, 2H, H1), 2.80 (tt, J ) 7.3 Hz, J HF ) 1.6
Hz, 2H, H4), 2.34 (q, J ) 7.3 Hz, 2H, H3); MS (El) m/z (relative
intensity) 222 (M+, 26), 181 (100), 161 (10), 93 (8), 41 (58).
The same procedure was used to study of the decomposition
of 14a , 18a , and 19a . All organic products were identified by
1H and 19F NMR and GC-MS. In the case of 14a and 19a , a
brown solid [PhSPdBr]n was isolated.
F or m a tion a n d Isom er iza tion of 17. To a solution of [Pd-
(C6F5)Br(NCMe)2] (0.04 g, 0.0918 mmol) in CDCl3 (0.6 mL) in
an NMR tube was added phenyl pent-4-enyl sulfide (0.0166
mL, 0.0918 mmol) at 273 K. 17 formed after 1 h and was
1
identified by H and 19F NMR. The solution was warmed to
293 K, and isomerization of 17 to 19a was observed. After 3
h at this temperature 95% of 17 had been converted.
[PhSPdBr]n: 1H NMR (DMSO-d6, δ, 300 MHz), 8.1 (b, 2H,
Ph), 7.3 (b, 3H, Ph). Anal. Calcd for C6H5BrSPd: C, 24.39;
H, 1.71. Found: C, 25.05; H, 1.70.
The rate constant was measured by recording 19F NMR
spectra every 10 min at 293 K (relaxation delays of at least
5T1’s were used). A plot of ln[signal integral] versus time gave
the first-order rate constant. The reported uncertainty in the
isomerization rate corresponds to one standard deviation in
the slope of the best fit line multiplied by the Student’s factor
15: 19F NMR (CDCl3, δ, 282 MHz) -163.2 (m, Fmeta), -158.0
(t, Fpara), -144.0 (m, Fortho); 1H NMR (CDCl3, δ, 300 MHz) 6.60
(dt, J ) 16.3, 6.5 Hz, 1H, H2), 6.26 (dt, J ) 16.3 Hz, 4J HF ) 1.6
Hz, 1H, H1), 2.3 (m, 2H, H3)*, 1.11 (t, J ) 7.5 Hz, 3H, H4); MS
(El) m/z (relative intensity) 222 (M+, 2), 181 (100), 161 (3), 142
(8), 85 (17), 71 (26), 57 (77), 43 (100), 41 (66).
t
1-R(f).26 The free energy of activation was calculated using
the Eyring equation in the form ∆Gq ) -2.3RT log(KBT/hkobs).
Error was calculated using the above-mentioned uncertainty
in kobs and a temperature variation of (0.4 K.25
*: overlapped with signals of other compounds.
20: 19F NMR (CDCl3, δ, 282 MHz) -163.7 (m, Fmeta), -158.5
(t, Fpara), -144.6 (m, Fortho); 1H NMR (CDCl3, δ, 300 MHz) 5.4
4
(m, 2H, H2, H3), 2.74 (tt, J ) 7.0 Hz, J HF ) 1.5 Hz, 2H, H5),
2.25 (m, 2H, H4), 1.62 (dd, J ) 3.5, 1.2 Hz, 3H, H1); MS (El)
m/z (relative intensity) 236 (M+, 9), 181 (12), 161 (4), 93 (2),
55 (100), 43 (2), 41 (5).
Ack n ow led gm en t. We are grateful to the Direccio´n
General de Investigacio´n Cient´ıfica y Te´cnica (Project
PB93-0222), and the Commission of the European
Communities (Network “Selective Processes and Ca-
talysis Involving Small Molecules” CHRX-CT93-0147)
for financial support. We also thank the Ministerio de
Educacio´n y Ciencia and the AECI/Universidad de
Valladolid for fellowships to Y.-S.L.
21: 19F NMR (CDCl3, δ, 282 MHz) -163.5 (m, Fmeta), -158.4
(t, Fpara), -144.6 (m, Fortho); 1H NMR (CDCl3, δ, 300 MHz) 5.5
(m, 2H, H2, H3), 2.7-2.8 (m, 2H, H5)*, 2.34 (q, J ) 7.4, 2H,
H4), 1.53 (dm, J ) 6.7 Hz, 3H, H1); MS (El) m/z (relative
intensity) 236 (M+, 7), 194 (20), 181 (12), 71 (9), 57 (23), 55
(100), 43 (22), 41 (20).
OM9604076
*: overlapped with signals of other compounds.
(25) Sandstro¨m, J . Dynamic NMR Spectroscopy; Academic Press:
New York, 1982.
(26) Eckschlager, K. Errors, Measurement and Results in Chemical
Analysis; Van Nostrand Reinhold: London, 1961.