Study of the evolution of η1-η2-enylpalladium complexes when the palladium-migration process is blocked

Article abstract of DOI:10.1021/om9707228

η¹-η²-Enylpalladium complexes have been detected and/or isolated in the reaction of [PdPfBr(NCMe)₂] (Pf = C₆F₅) with the dienes R-CH=CH-(CH₂)_n-Y-(CH₂)_m-CH=CH ₂ (R = H, Me; n, m = 0, 1; Y = CCl₂, C(COOMe)₂, CO₂, O, SiMe₂, SO₂). Insertion of one double bond into the Pd-aryl bond and coordination of the remaining double bond gives the above-mentioned organometallic derivatives. The dienes tested have a non-hydrogen-containing link (Y), so Pd migration to give η³-allyl derivatives is blocked. The evolution and decomposition processes observed for the η¹-η²-enyls reveal that β-X elimination is the main operating pathway for Y = CCl₂ (X = Cl) or Y = OCO, O, SiMe₂ (X = YR′). When Y = C(COOMe)₂ or SO₂, C-X cleavage is not observed and intramolecular insertion to give cyclic products or Pd-H elimination to generate a substituted diene predominates, respectively. From these results, a trend in C-X cleavage easiness in the presence of palladium can be estimated: C-C ? C-SO₂ < C-Cl < C-O (ether) < C-O (ester) ≈ C-Si.

Full text of DOI:10.1021/om9707228

5964
Organometallics 1997, 16, 5964-5973
Stu d y of th e Evolu tion of η1-η2-En ylp a lla d iu m Com p lexes
Wh en th e P a lla d iu m -Migr a tion P r ocess Is Block ed
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 August 14, 1997X
η1-η2-Enylpalladium complexes have been detected and/or isolated in the reaction of
[PdPfBr(NCMe)2] (Pf ) C6F5) with the dienes R-CHdCH-(CH2)n-Y-(CH2)m-CHdCH2 (R
) H, Me; n, m ) 0, 1; Y ) CCl2, C(COOMe)2, CO2, O, SiMe2, SO2). Insertion of one double
bond into the Pd-aryl bond and coordination of the remaining double bond gives the above-
mentioned organometallic derivatives. The dienes tested have a non-hydrogen-containing
link (Y), so Pd migration to give η3-allyl derivatives is blocked. The evolution and
decomposition processes observed for the η1-η2-enyls reveal that â-X elimination is the main
operating pathway for Y ) CCl2 (X ) Cl) or Y ) OCO, O, SiMe2 (X ) YR′). When Y )
C(COOMe)2 or SO2, C-X cleavage is not observed and intramolecular insertion to give cyclic
products or Pd-H elimination to generate a substituted diene predominates, respectively.
From these results, a trend in C-X cleavage easiness in the presence of palladium can be
estimated: C-C , C-SO2 < C-Cl < C-O (ether) < C-O (ester) ≈ C-Si.
In tr od u ction
intermediate A (Scheme 1) and may divert it to path-
ways b and c (Scheme 1) or to new reaction pathways.
Different processes can follow the insertion of a double
bond into the Pd-R bond to give the final organic or
organometallic product (Scheme 1). When a nonconju-
gated diene is used, Pd migration to give η3-allylpalla-
dium complexes is probably the most common route and
operates efficiently in the absence of excess diene (a,
Scheme 1).1-3 These functionalized palladium allyls can
be converted into substituted alkenes by attack of a
nucleophile or carbonylation,4,5 in what could be de-
scribed as a distant addition of R and Nu to the diene
(Scheme 1).
To explore this idea, the following dienes were
tested: R-CHdCH-(CH2)n-Y-(CH2)m-CHdCH2 (R )
H, n ) 0, m ) 1, Y ) CCl2; R ) Me, n ) m ) 0, Y )
CO2; R ) H, n ) m ) 0, Y ) SO2; R ) H, n ) m ) 1, Y
) C(COOMe)2, O, SiMe2, SO2). Their reactions with
[PdPfBr(NCMe)2] (Pf ) C6F5) give several η1-η2-enylpal-
ladium intermediates, which were identified and then
decomposed to study the occurrence of alternative
pathways to Pd migration.
Resu lts a n d Discu ssion
Pd migration can be aborted by decoordination of the
new olefin to generate R-substituted dienes (Scheme 1,
b). This is promoted by the presence of any alkene that
is a better ligand than the R diene (i.e., a less-
substituted one) and coordinates preferentially.1,2,6 Cy-
clization (Scheme 1, c) is also an important alternative
to Pd migration and gives access to new types of organic
cyclic derivatives.7
Different stabilities were found for the organometallic
complexes detected in the reactions of [PdPfBr(NCMe)2]
(Pf ) C6F5) with allyl-vinyl, divinyl, or diallyl dienes
bearing a link lacking hydrogen in the hydrocarbon
chain. For this reason, the reactions of the divinyl or
allyl-vinyl dienes, which give rise to stable η1-η2-
enylpalladium complexes, are discussed first, followed
by the reactions of the diallyl diolefins, which lead to
less stable organometallic derivatives. 1H NMR data
for the η1-η2-enylpalladium derivatives formed in these
reactions are collected in Table 1.
Another way of aborting Pd migration is to introduce
a non-hydrogen-containing link in the carbon chain
between both double bonds of the diene. Since Pd
migration operates through Pd-H elimination-read-
ditions, the link suppresses this route of evolution for
Rea ction w ith 3,3-Dich lor o-1,5-h exa d ien e. The
reaction of [PdPfBr(NCMe)2] with 3,3-dichloro-1,5-hexa-
diene at room temperature gives the η1-η2-enylpalla-
dium compound 1a as a colorless precipitate that is
quite insoluble in common organic solvents (Scheme 2).
After separation of 1a , a small amount of (Z)-3-chloro-
6-pentafluorophenyl-1,3-hexadiene (2) was found in the
mother liquors. The cis configuration of the trisubsti-
tuted double bond was confirmed by NOE experiments
(NOE H2-H4, 4.7%). Treatment of 1a with Tl(acac)
(acac ) acetylacetonate) in CH2Cl2 leads to the mono-
X Abstract published in Advance ACS Abstracts, December 1, 1997.
(1) Albe´niz, A. C.; Espinet, P.; Lin, Y.-S. Organometallics 1997, 16,
4138.
(2) Larock, R. C.; Takagi, K. J . Org. Chem. 1984, 49, 2701.
(3) Larock, R. C.; Takagi, K. Tetrahedron Lett. 1983, 24 (33), 3457.
(4) Tsuji, J . Palladium Reagents and Catalysis; Wiley: Chichester,
1995; p 61.
(5) Ba¨ckvall, J .-E. Adv. Met.-Org. Chem. 1989, 1, 135.
(6) Albe´niz, A. C.; Espinet, P; Lin, Y.-S. Organometallics 1995, 14,
2977.
(7) Recent rewievs: (a) Negishi, E.; Cope´ret, C.; Ma, S.; Liou, S.-Y.;
Liu, F. Chem Rev. 1996, 96, 365. (b) Trost, B. M. Angew. Chem., Int.
Ed. Engl. 1995, 34, 259. (c) De Meijere, A.; Meyer, F. E. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 2379.
S0276-7333(97)00722-X CCC: $14.00 © 1997 American Chemical Society

Evolution of η1-η2-Enylpalladium Complexes
Organometallics, Vol. 16, No. 26, 1997 5965
Sch em e 1
Sch em e 2
meric complex 1b, which is soluble in most organic
solvents and could be studied better by NMR (eq 1).
The insertion reaction was monitored by 19F NMR.
The reactants were mixed, and 1,3,5-trichloro-2,4,6-
trifluorobenzene was added as an internal standard.
When all of the starting material had been consumed,
1a was found to account for 99% of the Pf present (less
than 1% left in solution); in addition, 2 (1%) was
observed. According to these data, insertion of the less-
hindered allylic double bond into the Pd-Pf bond is
preferred to form a stable 5.5-membered η1-η2 pallada-
cycle (1a ).8 The formation of a small amount of 2 can
be interpreted via Pd-H elimination-readdition fol-
lowed by â-Cl elimination (Scheme 2).
When a suspension of 1a in CHCl3 was refluxed for
20 h, decomposition was observed and (E,Z)-4-chloro-
1-(pentafluorophenyl)-1,4-hexadiene (3), 1-chloro-3-
((pentafluorophenyl)methyl)-1-cyclopentene (4), and 2
in a ratio of 3:2:1, plus palladium halides, were formed
(Scheme 2). The geometrical assignment of 3 was
confirmed by NOE experiments (NOE H3-H5, 4.8%).
The proposed mechanism for the decomposition is
depicted in Scheme 2. Again, Pd-H elimination-
readdition continues until â-Cl elimination occurs to
give 2 and 3. Thus, the process of Pd migration along
the carbon chain to form an η3-allylpalladium complex
is interrupted by the CCl2 link. Pd-Cl readdition,
required for Pd-allyl formation, is not observed in the
reaction in this case, even though the addition of Pd-
Cl to olefin is possible.9,10 â-Cl elimination has been
previously observed in some palladium-mediated
reactions11-13 or proposed to explain the formation of
some products or several isomerization processes in η1-
η2 palladium complexes.9,14 Cyclization from a putative
6.5-membered palladacycle followed by Pd migration
and Pd-Cl elimination is also observed to give the
cyclopentene derivative 4.
Rea ction w ith Vin yl Cr oton a te. A mixture of
complexes 5a and 6a (5a :6a ) 7:1) can be isolated from
the reaction of [PdPfBr(NCMe)2] with vinyl crotonate
at room temperature (Scheme 3). In addition, products
resulting from the cleavage of the ester C-O bond were
found in the mother liquors (see below). Attempts to
separate 5a from 6a failed. Inspection of the spectral
data of the mixture indicated that the carbonyl oxygen
(8) The size of the η1-η2-enyl palladacycles is referred to as n.5-
membered, n being the number of atoms in the cycle and adding 0.5
to account for the π-coordination of the double bond to the metal (see,
for example: Omae, I. Angew. Chem., Int. Ed. Engl. 1982, 21, 889).
(9) Parra-Hake, M.; Rettig, M. F.; Williams, J . L.; Wing, R. M.
Organometallics 1986, 5, 1032.
(12) Kaneda, K.; Uchiyama, T.; Fujiwara, Y.; Imanaka, T.; Teranishi,
S. J . Org. Chem. 1979, 44, 55.
(10) Wiger, G.; Albelo, G.; Rettig, M. F. J . Chem. Soc., Dalton Trans.
1974, 2242.
(11) Zhu, G.; Lu, X. Organometallics 1995, 14, 4899.
(13) Larock, R. C.; Bernhardt, J . C.; Driggs, R. J . J . Organomet.
Chem. 1978, 156, 45.
(14) Albelo, G.; Rettig, M. F. J . Organomet. Chem. 1972, 42, 183.

5966 Organometallics, Vol. 16, No. 26, 1997
Albe´niz et al.

Evolution of η1-η2-Enylpalladium Complexes
Organometallics, Vol. 16, No. 26, 1997 5967
Sch em e 3
acts as a donor atom in complex 5a , but the propenyl
double bond coordinates to palladium in 6a . The IR
spectrum (Nujol mull) shows one very intense absorp-
and 6c display high-field shifts compared to the free
ligand, as observed for 6a .
tion at 1655 cm-1 and a small one around 1740 cm-1
.
The former can be assigned to ν(CO) of the major
derivative 5a and the latter to 6a . A decrease in ν(CO)
is expected upon coordination, compared with the 1741
cm-1 absorption for vinyl crotonate (CH2Cl2 solution).
The 1H NMR spectrum of the mixture shows the
resonances of the olefinic protons H1 and H2 for the
major compound 5a at δ 7.12 and 5.87, respectively,
very close to the corresponding resonances for free vinyl
crotonate (δ 7.05 and 5.82). A broad signal at δ 5.69
1
appears in the H NMR spectrum of the minor deriva-
tive 6a , which was assigned to the H1 and H2 protons
(Table 1). The large difference in chemical shifts
between the olefinic protons in the propenyl moiety for
free vinyl crotonate and 6a suggests the coordination
of the double bond to palladium. The appearance of
1
broad signals in the H and 19F NMR of 5a and 6a is
The reaction of [PdPfBr(NCMe)2] with vinyl crotonate
was monitored at low temperature by NMR (Scheme 3).
probably due to exchange of the two coordination modes
and the presence of different arrangements of two chiral
moieties in the dimer which gives rise to diastereoiso-
mers.
Insertion of one double bond into the Pd-Pf bond was
19
evident at -10 °C, and after 30 min, two broad
F
ortho
signals (ratio of 8:3, δ values characteristic of C-Pf)
appeared. With the help of H NMR, the main signal
1
To avoid the presence of diastereoisomers derived
from the dimeric structures of 5a and 6a and help to
characterize the structures of both complexes in more
detail, monomeric derivatives were obtained (5b, 6b,
and 6c in a ratio of 5:4:1) by treating 5a and 6a with
Tl(acac) (eq 2). It is interesting that almost half of 5a
changed the coordination mode from oxygen to the
propenyl double bond after treatment with Tl(acac). Two
isomers 6b and 6c, most likely arising from the presence
of a chiral carbon and a coordinated prochiral double
bond, are clearly observed in the 19F and 1H NMR
can be assigned to the overlapping Fortho resonances of
5a and 6a , derived from insertion of the terminal vinylic
19
double bond. The minor
F
signal corresponds to
ortho
1
a compound that has two small broad signals in the H
NMR spectrum (δ 3.50 and 6.08 ppm) in a ratio of 2:1,
which probably correspond to the PdCH2 and PfCH
moieties in complex 7, i.e., a product of insertion with
the opposite regiochemistry of the terminal vinylic
double bond, the Pf group adding to the more substi-
tuted carbon. As the temperature was raised 7 decom-
posed, and its disappearance was complete at 20 °C.
1
spectra. The H resonances of all olefinic protons in 6b

5968 Organometallics, Vol. 16, No. 26, 1997
Albe´niz et al.
Sch em e 4
tially. The reaction was also monitored at low temper-
ature. Only 12 was formed after 3 h at 0 °C, and as
the reaction time increased, 13 slowly appeared. After
all of the starting materials were consumed, the amount
of 13 continued to raise according to integration of the
19F NMR signals, which confirms that complex 13 is
produced by isomerization of 12 (Scheme 4).
13 is a mixture of two isomers in a 1.7:1 ratio from
integration of the 19F NMR signals. The 1H NMR
spectrum of 13 in acetone-d6 shows two pairs of ABX
systems (one pair per isomer in the ratio found in the
19F NMR spectrum), which can be assigned to PfCH2-
CH and PdCH2CH moieties, respectively. The two
diastereoisomers observed are derived from the two
asymmetric carbons present in the complex which are
formed in a slightly stereoselective cyclization step, as
the ratio of the isomers implies. 13 is a rare example
of an organometallic derivative containing a complexed
episulfone. The latter is an important intermediate in
the Ramberg-Ba¨cklund transformation of halosul-
fones.20 Other palladacycles containing a SO2 unit are
also uncommon. A four-membered ring palladacycle has
been reported;21 a 4.5-membered cyclic allyl sulphinato
complex was detected at low temperature.22
After 8 h at room temperature, a mixture of 5a (63%),
6a (9%), vinylpentafluorobenzene (8, 21%), trans-1,2-
bis(pentafluorophenyl)ethylene (9, 7%), and crotonic
acid (28%) was obtained. 8 and crotonic acid come from
C-O cleavage of the â-ester moiety.15 The bis(Pf)
derivative results from arylation of 8 by residual [Pd-
PfBr(NCMe)2], followed by Pd-H elimination.
On the other hand, when 5a and 6a were dissolved
in CDCl3 and warmed at 50 °C for 1 day, they decom-
posed to vinylpentafluorobenzene (8), (E,E)-(pentafluo-
rophenyl)vinyl crotonate (10a), (E,Z)-(pentafluorophenyl)-
vinyl crotonate (10b), 2-(pentafluorophenyl)aldehyde
(11), and crotonic acid in a ratio of 10:3:1:1:10 (Scheme
3). 10a and 10b are formed by Pd-H elimination.
However, the dominant process is the â-elimination of
a crotonato group after Pd migration to the Pf-substi-
tuted carbon, which produces 8 and crotonic acid.11 The
same type of C-O(CO) cleavage is observed in the
decomposition of 7. â-acetoxy elimination has been
observed in the Pd-mediated synthesis of certain bu-
tyrolactones.11 The small amount of product 11 ob-
served is the result of the cleavage of the crotonate
C(O)-O bond.
Only insertion of the terminal vinylic double bond is
observed, but the addition of the Pd-Pf moiety can occur
in either direction. The preference for the less-substi-
tuted one is clear, as shown by the ratio, (5a + 6a ):7 )
8:3. Accordingly, the arylation on the terminal carbon
is predominant, although a preference for the more
substituted end of the olefin has been found for some
heteroatom-substituted alkenes.16,17 The results ob-
tained are coincident with the arylation of enol esters
reported by Heck18 and the phenyl functionalization of
enol acetates via tin enolates catalyzed by palladium.19
Rea ction w ith Divin yl Su lfon e. [PdPfBr(NCMe)2]
reacted with divinyl sulfone for 10 h at room tempera-
ture to form 12 and a second product with spectral data
(see below) that are compatible with structure 13 (12:
13 ) 5:1, Scheme 4). 12 was isolated as a yellow solid
(61% yield). However, all attempts at isolation of 13
failed due to its instability when kept in solution and
the lower solubility of 12, which crystallizes preferen-
Rea ction w ith Dia llyl Su bstr a tes. The reactions
of [PdPfBr(NCMe)2] with the diallyl substrates
CH2dCH-(CH2)-Y-(CH2)-CHdCH2 gave, at low tem-
perature, the corresponding 6.5-membered η1-η2-enyl
derivatives (Scheme 5, Y ) SO2, 14, T ) 263 K; Y ) O,
15, T ) 243 K; Y) SiMe2, 16, T ) 243 K; Y )
C(COOMe)2, 17, T ) 253 K).23 When the temperature
was raised, decomposition of these derivatives was
observed as well as isomerization to the 5.5-membered
η1-η2-enyl complexes 18 (Y ) SO2), 19 (Y ) O), and 20
(Y) SiMe2). The decomposition process is faster than
isomerization for 17, and the corresponding 5.5-mem-
bered enyl complex was not observed. The organome-
tallic derivatives detected follow several routes of
decomposition, often operating simultaneously. How-
ever, a main pathway can be identified in each case,
which depends on the nature of Y. The pathways are
as follows (Scheme 5 and Table 2):
(i) Cycliza tion . This was observed in the decompo-
sition of 17 (Y ) C(COOMe)2); cyclization, Pd migration,
and, finally, Pd-H elimination gives the endocyclic
cyclopentene derivative 21.24 The PdHBr species gener-
ated in the final Pd-H elimination just described is
responsible for two side reactions. First, efficient H-
transfer to the σ-alkylpalladium derivative formed after
cyclization occurs, and it gives the saturated derivative
22 (mixture of two diasteroisomers in a 1:1 ratio, by 19
F
(20) March, J . Advanced Organic Chemistry; Wiley: New York,
1992; p 1030.
(21) (a) Henderson, W.; Kemmitt, R. D. W.; Prouse, L. J . S.; Russell,
D. R. J . Chem. Soc., Dalton Trans. 1989, 259. (b) Chiu, K. W.; Fawcett,
J .; Henderson, W.; Kemmitt, R. D. W. J . Chem. Soc., Dalton Trans.
1987, 733.
(15) C-O cleavage of the â-ester moiety in compound 7 gives 8 and
a crotonato group. This group can be converted into crotonic acid by
the HBr formed in the decomposition of the “HPdBr” species generated
in the formation of 9 and probably by the small amount of HCl present
in the CDCl3 used as solvent, since the quantity of the compounds
handled in the monitored experiments, and so the amount of crotonato
formed, is very small.
(22) O’Brien, S. J . Chem. Soc. A 1970, 9.
(23) Diastereoisomers were observed as two broad signals in the 19
F
NMR spectrum of 14 and 17, probably as a result of the prochiral
nature of the double bond and the dimeric nature of the complexes.
The diastereomeric ratios are 1:0.6 (14) and 1:0.8 (17).
(16) Heck, R. F. Palladium Reagents in Organic Syntheses; Academic
Press: London, 1985; p 268.
(17) Daves, G. D., J r.; Hallberg, A. Chem. Rev. 1989, 89, 1433.
(18) Heck, R. F. J . Am. Chem. Soc. 1968, 90, 5535.
(19) Kosugi, M.; Hagiwara, I.; Sumiya, T.; Migita, T. J . Chem. Soc.,
Chem. Commun. 1983, 344.
(24) The cyclization reactions of dimethyl diallylmalonate have been
studied, see: (a) Hegedus, L. S. In Organometallics in Synthesis;
Schlosser, M., Ed.; Wiley: Chichester, 1994; Chapter 5. (b) Larock, R.
C. Adv. Met.-Org. Chem. 1994, 3, 97. (c) Oppolzer, W. Angew. Chem.,
Int. Ed. Engl. 1989, 28, 38. (d) Grigg, R.; Mitchell, T. R. B.; Ramasubbu,
A. J . Chem. Soc., Chem. Commun. 1979, 669.

Evolution of η1-η2-Enylpalladium Complexes
Organometallics, Vol. 16, No. 26, 1997 5969
Sch em e 5
NMR, eq 3).25,26 Second, dimethyl diallylmalonate
(ii) P d -H Elim in a tion . This was observed in the
decomposition of complexes 14 and 18 (Y ) SO2), which
afford 24 as the main product. 24 undergoes further
transformations under the decomposition conditions to
give 25 through double-bond isomerization and 26 by
hydrogenation of the terminal double bond (both pro-
cesses produced by Pd-H species generated in the
formation of 24)25 and 27 by arylation of 24 by “PdPfBr”
species (Scheme 6 and Table 2). The amount of com-
pound 24 and its derivatives 25-27 accounts for 79%
of the reaction products, which reveals Pd-H elimina-
tion as the preferred decomposition route. The regio-
chemistry of 27 was inequivocally assigned by a 1H-
19F heteronuclear NOE experiment: 4.1% NOE was
found between the ortho fluorines of the Pf group and
H1 of the (pentafluorophenyl)allyl group. The coinci-
dence of the chemical shifts of its olefinic protons and
the alkene signals for 24, 25, and 26 leads to the
regiochemistry shown in the schemes. Other processes
starting material inserts into the Pd-H bond to yield,
through the same route just described for 21, the Pf-
free cyclopentene 23 (eq 4). H-transfer to the starting
“PdPfBr” species is also observed, and some PfH is
formed.25
(26) The absence of olefinic protons in the 1H NMR spectrum and
GC-MS support this proposal, even though the 1H NMR spectrum of
22 was difficult to assign because of heavy overlapping of its signals
with other compounds.
(25) Albe´niz, A. C.; Espinet, P.; Lin, Y.-S. Organometallics 1997,
16, 4030.

5970 Organometallics, Vol. 16, No. 26, 1997
Ta ble 2. P r od u cts Obta in ed in th e Decom p osition of η1:η2-En yl Der iva tives 14-20a
Albe´niz et al.
c
Y ) SO2
28 (7%)
Y ) Ob
Y ) SiMe2
Y ) C(COOMe)2
cyclization
40 (11%)
21 (56%)
22 (13%)
23 (31%)
Pd-H elimination
24 (16%)
25 (32%)
26 (19%)
27 (12%)
32 (4%)
30 (5%)
31 (5%)
â-X elimination
29 (10%)
31 (3%)
35 (29%)
38 (28%)
propanal (7%)
29 (60%)
30 (15%)
31 (4%)
37 (15%)
39 (6%)
a
b
See Scheme 5 for compound structure; percentages are given in parentheses. 19 (5%) and 7% of unidentified compounds were also
found in the final mixture. c Only Pf-containing products are given.
to give the η3-propenylpalladium complex 38, which can
be crystallized from the reaction mixture.30,31
Sch em e 6
â-X elimination is the only decomposition pathway
observed for diallyldimethylsilane and the main route
for diallyl ether. However, a small amount of cyclic
derivative 40 (as a mixture of two diastereoisomers) is
observed for the latter diene (about 11% of the decom-
position products). Cyclization, Pd migration, and
reductive elimination of alkyl and Br explains the
formation of 40. The actual mutual arrangement of H2
and H3 could not be determined since the values of the
vicinal coupling constants between them (4.7 and 3.1
Hz for each isomer) are not unequivocal.32 However,
oxidative addition of RX (R ) allyl) to Pd(0) under
similar reaction conditions to those used here proceeds
with retention of configuration at the C center.33 Thus,
the reverse reaction, reductive elimination of RBr,
should also occur with retention of configuration, giving
40 with the configuration depicted in Scheme 5. The
two diastereoisomers observed arise from the nonfixed
configuration at the third chiral carbon in the cycle.
are also observed, i.e., cyclization of 14 to give 28
(Scheme 5) and C-S cleavage (â-X elimination) to form
29. 29 can also evolve to 30 and 31 through the same
processes depicted in Scheme 6.27
(iii) C-X Clea va ge (â-X Elim in a tion ).28 This is the
main decomposition pathway for derivatives 15 and 19
(Y ) O) and for 16 and 20 (Y ) SiMe2). â-X elimination
in 15 or 16 gives 29 (and/or its derivatives 30 and 31,
Table 2) and the corresponding “PdBrX” species that
react to give propanal (Y ) O, X ) OCH2CHdCH2) or,
by hydrolysis-polymerization and cleavage of the Si-
allyl bond, dimethylpolysiloxanes and propene (Y )
SiMe2, X ) Si(Me)2CH2CHdCH2).29
Alternatively, C-X cleavage can occur from the
undetected η1-η2-enyl derivatives 34 (Scheme 5) that
arise from double-bond switch in a 1,5-diene-hydri-
dopalladium intermediate (33) generated in turn by
Pd-H elimination from 15 or 16.1 The process gives
propene and the corresponding “PdBr(PfX)” species that
react to give the 3-(pentafluorophenyl)propanal species
35 (Y ) O) or dimethyl(3-(pentafluorophenyl)propenyl)-
bromosilane species 36. 36 reacts further by hydrolysis
and dimerization to yield 1,1,3,3-tetramethylbis((E)-3-
(pentafluorophenyl)propenyl)disiloxane 37 (Y ) SiMe2)
as the final product observed. For diallyl ether (Y )
O), the propene produced in this process reacts further
Con clu sion s
η1-η2-Enylpalladium derivatives are obtained either
by direct coordination of the unattacked double bond to
palladium or by one-step Pd migration and then coor-
dination of the second double bond. 6.5-, 5.5-, and 4.5-
membered η1-η2-enylpalladacycles are observed, and
although the actual stability of these derivatives de-
pends on the particular complex, the 6.5-membered
complexes are clearly the least stable.
Since the Pd-migration mechanism is blocked for the
unsaturated substrates used, the formation of η3-allyl
derivatives is prevented unless other mechanisms trans-
port the Pd atom past the block to reach the second
double bond. No η3-allylpalladium complexes were
found, indicating that Pd migration is the only efficient
mechanism to form these complexes.
(27) A small amount of starting diallyl sulfone is catalytically
isomerized to 2,3-dihydro-3,4-dimethylthiophene-1,1-dioxide (32, 4%)
by “PdHBr” through insertion into Pd-H bonds and cyclization.
(28) For other examples of palladium â-X elimination, see ref 10
and for X ) Cl, refs 11 and 12. X ) OR: b) Nguefack, J .-F.; Bolitt, V.;
Sinou, D. J . Chem. Soc., Chem. Commun. 1995, 1893. (c) Duan J .-P.;
Cheng, C.-H. Tetrahedron Lett. 1993, 34, 4019. X ) OH: (d) Hosokawa,
T.; Sugafuji, T.; Yamanaka, T.; Murahashi, S. J . Organomet. Chem.
1994, 470, 253. X ) SiR3: (e) Ikenaga, K.; Kikukawa, K.; Matsuda, T.
J . Org. Chem. 1987, 52, 1276. (f) Karabelas, K.; Hallberg, A. J . Org.
Chem. 1986, 51, 5286. (g) Ikenaga, K.; Kikukawa, K.; Matsuda, T. J .
Chem. Soc. Perkin Trans. 1986, 1959.
(30) The reaction of [PdCl4]2- with allyl ether to form palladium-
(II)-allyl complex 38 and propenal has also been reported, see:
Pietropaolo, R.; Faraone, F.; Sergi, S.; Pietropaolo, D. J . Organomet.
Chem. 1972, 42, 177.
(31) A small amount of 2-(pentafluorophenyl)propene (39) was found
in the reaction with diallyldimethylsilane (Y ) SiMe2), which probably
comes from insertion of the allylic double bond into the Pd-C6F5 bond
with opposite regiochemistry, that is, C6F5 binds to the more substi-
tuted double bond; subsequent Pd migration of one carbon and â-SiR3
elimination gives 39 and allyl(dimethyl)bromosilane.
(32) Tedder, J . M.; Nechvatal, A.; Murray, A. W.; Carnduff, J . Basic
Organic Chemistry; Wiley: Chichester, 1970; p 181.
(33) Kurosawa, H.; Ogoshi, S.; Kawasaki, Y.; Murai, S.; Miyoshi,
M.; Ikeda, I. J . Am. Chem. Soc. 1990, 112, 2813.
(29) (a) Kliegman, J . M. J . Organomet. Chem. 1971, 29, 73. (b)
Sommer, L. H.; Tyler, L. J .; Whitmore, F. C. J . Am. Chem. Soc. 1948,
70, 2872.

Evolution of η1-η2-Enylpalladium Complexes
Organometallics, Vol. 16, No. 26, 1997 5971
P r ep a r a tion of (Acetyla ceton a to){η1-η2-3,3-d ich lor o-6-
(p en ta flu or op h en yl)-1-h exen -5-yl}p a lla d iu m (II) (1b). Tl-
(acac) (0.026 g, 0.086 mmol) was added to a suspension of 1a
(0.041 g, 0.043 mmol) in CH2Cl2 (15 mL). After 1 h of stirring,
the white precipitate (TlBr) was filtered. The filtrate was
evaporated to dryness, and diethyl ether (2 mL) was added.
The mixture was cooled down, and a white solid, 1b, was
obtained (72% yield).
â-X elimination (C-X cleavage, X * C, H) occurs for
most of the substrates employed either as the main
decomposition route or as a side reaction. Pd-X read-
dition (X * H) does not take place in any case. The ease
of â-X elimination follows the order C-C , C-SO2 <
C-Cl < C-O (ether) < C-O (ester) ≈ C-Si.
1b. Anal. Calcd for C17H15Cl2F5O2Pd: C, 38.99; H, 2.88.
Found: C, 38.66; H, 2.84. 19F NMR (CDCl3, δ, 282 MHz);
-162.9 (m, Fmeta), -157.8 (t, Fpara), -143.3 (m, Fortho).
Decom p osition of 1a . A suspension of 1a (0.030 g, 0.030
mmol) in CHCl3 (15 mL) was refluxed for 20 h. The brown
precipitate (PdBrCl) was filtered off. Upon evaporation of the
solvent, a colorless residue formed, which was a mixture of 3,
4, and 2 in a ratio of 3:2:1.
3. 19F NMR (CDCl3, δ, 282 MHz): -163.5 (m, Fmeta), -157.2
(t, Fpara), -143.6 (m, Fortho). 1H NMR (CDCl3, δ, 300 MHz):
6.56 (dt, J ) 16.3, 6.7 Hz, 1H, H2), 6.37 (dt, J ) 16.3, 1.4 Hz,
1H, H1), 5.65 (qt, J ) 6.6, 1.1 Hz, 1H, H5), 3.25 (db, J ) 6.7
Hz, 2H, H3), 1.76 (dt, J ) 6.6, 1.2 Hz, 3H, H6). MS (EI) m/ z
(relative intensity): 282 (M+, 0.2), 181 (6), 103 (32), 101 (100),
65 (88), 51 (5).
4. 19F NMR (CDCl3, δ, 282 MHz): -162.8 (m, Fmeta), -157.4
(t, Fpara), -143.3 (m, Fortho). 1H NMR (CDCl3, δ, 300 MHz):
5.56 (m, 1H, H2), 3.03 (m, 1H, H3), 2.78-2.73 (m, 2H, CH2Pf),
2.54 (m, 2H, H5), 2.15 (m, 1H, H4), 1.68 (m, 1H, H4′). MS (EI)
m/z (relative intensity): 282 (M+, 41), 247 (45), 231 (13), 187
(16), 181 (100), 123 (11), 101 (11), 77 (15), 65 (22), 53 (13), 51
(10).
Rea ction w ith Vin yl Cr oton a te. Vinyl crotonate (0.055
mL, 0.459 mmol) was added to [Pd(C6F5)Br(NCMe)2] (0.200 g,
0.459 mmol) dissolved in CH2Cl2 (10 mL). After 8 h of stirring,
activated carbon was added and the suspension filtered. The
solvent was evaporated, and the residue was chromatographed
through a silica gel column. The first batch obtained using
n-hexane as the eluent gave, after evaporation of the solvent,
a colorless oily residue; it was a mixture of 8 and 9. A small
amount of white solid 9 separated after removal of 8 by suction.
A second batch was obtained with diethyl ether as the eluent.
Concentration of the solution to ca. 2 mL afforded a yellow
solid, 5a mixed with 12% of 6a (total yield 44%). An aqueous
KOH solution (1 M) was added to the mother liquors, and the
mixture was vigorously stirred. The aqueous phase was
neutralized with aqueous HCl solution (1 M) and then ex-
tracted with diethyl ether. The organic phase was dried with
MgSO4, and the solvent was evaporated. A white residue,
crotonic acid, was found.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. [Pd(C6F5)Br(NCMe)2]34 and the
dienes 3,3-dichloro-1,5-hexadiene,35 diallyl ether,36 and diallyl
sulfone37 were prepared by literature methods. Other ligands
were purchased from Aldrich and Lancaster Chemical Co. and
used without further purification. Solvents were dried em-
ploying the usual desiccants and distilled before use. 1H and
19F NMR spectra were obtained on Bruker AC-300 and ARX-
300 spectrometers at 293 K unless otherwise noted. 1H and
13C chemical shifts were referenced to TMS and 19F chemical
shifts to CFCl3. Infrared spectra (Nujol mulls) were recorded
on a Perkin-Elmer 883 spectrometer. Elemental analyses were
performed on a Perkin-Elmer 240 microanalyzer. Organic
products were analyzed using an HP-5890 gas chromatograph
connected to an HP-5988 mass spectrometer at an ionizing
voltage of 70 eV and a quadrupole analyzer; chemical ioniza-
tion using methane at 230 eV was also used. Evaporation of
solvents was carried out using a water pump to avoid evapora-
tion of low-boiling organic derivatives of interest.
Mon itor in g Rea ction of [P d (C6F 5)Br (NCMe)2] w ith
Dien es a t Low Tem p er a tu r e by NMR (Gen er a l Meth od ).
[Pd(C6F5)Br(NCMe)2] (0.025 g, 0.0574 mmol) in CDCl3 (0.6 mL)
was charged in an NMR tube and cooled down, and the diolefin
(0.0574 mmol) was added. The reaction was monitored by
alternatively taking 1H and 19F NMR spectra on a Bruker AC-
300 spectrometer with a thermostated multinuclear QNP
probe head operating in the FT mode. The temperature was
slowly increased (10 °C at a time) to observe the reaction
course. 1H homonuclear correlation experiments were carried
out at low temperature for the assignment of some derivatives
when necessary. The final products were analyzed by 1H and
19F NMR and GC-MS. The yields for the products were
determined by integration of the 1H and 19F NMR signals.
Rea ction w ith 3,3-Dich lor o-1,5-Hexa d ien e. To a solu-
tion of [Pd(C6F5)Br(NCMe)2] (0.089 g, 0.20 mmol) in CH2Cl2
(2 mL) was added 3,3-dichloro-1,5-hexadiene (0.034 mL, 0.20
mmol). After 1 h of stirring, the white precipitate, 1a , was
filtered, washed with CH2Cl2, and air dried (71% yield). The
mother liquors were evaporated to dryness and extracted with
n-hexane, and the insoluble residue “PdBrCl” was filtered off.
After evaporation of the solvent, a colorless oily residue, 2,
was obtained.
5a mixed with 12% of 6a . Anal. Calcd for C24H16Br2F10O4-
Pd2: C, 30.96; H, 1.72. Found: C, 30.98; H, 1.70. 19F NMR
(CDCl3, δ, 282 MHz): 5a -162.8 (b, Fmeta), -156.5 (b, Fpara),
-142.8 (b, Fortho); 6a -162.3 (b, Fmeta), -155.8 (b, Fpara), -142.8
(b, Fortho).
1a . Anal. Calcd for C24H16Br2Cl4F10Pd2: C, 28.58; H, 1.60.
Found: C, 28.80; H, 1.61. IR (cm-1, Nujol mull, C6F5): 1659,
The reaction was examined by NMR at low temperature
(-10 °C), and complex 7 was detected; the final products are
5a (63%), 6a (9%), 8 (21%), 9 (7%) and crotonic acid (yields
1522, 1503, 1119, 1030, 949 cm-1
.
19F NMR (CDCl3, δ, 282
MHz, 253 K): -161.5 (b, Fmeta), -155.7 (b, Fpara), -142.2 (b,
F
ortho).
1
were determined by integration of the H or 19F NMR signals
2. 19F NMR (CDCl3, δ, 282 MHz): -163.1 (m, Fmeta), -157.6
and based on vinyl crotonate).
7. 19F NMR (CDCl3, δ, 282 MHz, 263 K): -162.7 (b, Fmeta),
-156.2 (b, Fpara), -141.3 (b, Fortho).
(t, Fpara), -144.4 (m, Fortho). 1H NMR (CDCl3, δ, 300 MHz):
6.35 (dd, J ) 16.5, 10.5 Hz, 1H, H2), 5.75 (t, J ) 7.4 Hz, 1H,
H4), 5.57 (d, J ) 16.5 Hz, 1H, H1), 5.20 (d, J ) 10.5 Hz, 1H,
H1′), 2.84 (t, J ) 7.3 Hz, 2H, H6), 2.62 (q, J ) 7.3 Hz, 1H, H5);
MS (EI) m/z (relative intensity): 282 (M+, 10), 181 (14), 103
(21), 101 (65), 65 (100), 51 (6).
Rea ction of 5a a n d 6a w ith Tl(a ca c). To a mixture of
5a and 6a (0.040 g, 0.042 mmol) in CHCl3 (5 mL) was added
Tl(acac) (0.026 g, 0.084 mmol). A white precipitate (TlBr) was
formed immediately, and it was filtered after 30 min. By
evaporation of the solvent, a light yellow oily residue was
obtained, which was a mixture of 5b, 6b, and 6c with a ratio
of 5:4:1. 19F NMR (CDCl3, δ, 282 MHz): 5b -163.4 (m, Fmeta),
-157.9 (t, Fpara), -143.2 (m, Fortho); 6b -163.2 (m, Fmeta), -157.3
(t, Fpara), -143.4 (m, Fortho); 6c -163.1 (m, Fmeta), -157.6 (t,
(34) Albe´niz, A. C.; Espinet, P.; Foces-Foces, C.; Cano, F. H.
Organometallics 1990, 9, 1079.
(35) Seyferth, D.; Murphy, G. J .; Mauze´, B. J . Am. Chem. Soc. 1977,
99, 5317.
(36) Olson, W. T.; Hipsher, H. F.; Buess, C. M.; Goodman, I. A.; Hart,
I.; Lamneck, J . H., J r.; Gibbons, L. C. J . Am. Chem. Soc. 1947, 69,
2451.
(37) Hirano, M.; Tomaru, J .-I.; Morimoto, T. Bull. Chem. Soc. J pn.
1991, 64, 3752.
F
para), -143.2 (m, Fortho).
Decom p osition of 5a a n d 6a . The mixture of 5a and 6a
(0.030 g, 0.032 mmol) in CHCl3 (2 mL) was warmed at 55 °C

5972 Organometallics, Vol. 16, No. 26, 1997
Albe´niz et al.
for 1 day. After the black precipitate was filtered and the
solvent evaporated, a colorless residue was obtained, which
contained 8, 10a , 10b, and 11 in a ratio of 10:3:1:1, and
crotonic acid.
14. 19F NMR (CDCl3, δ, 282 MHz, 243 K): -161.4/-163.0
(b, Fmeta), -155.5/-157/6 (b, Fpara), -143.2/-142.2 (b, Fortho).21
18. 19F NMR (CDCl3, δ, 282 MHz, 273 K): -162.9 (b, Fmeta),
-157.9 (b, Fpara), -138.3 (b, Fortho).
10a . 19F NMR (CDCl3, δ, 282 MHz): -163.1 (m, Fmeta),
-157.2 (t, Fpara), -141.6 (m, Fortho). 1H NMR (CDCl3, δ, 300
MHz): 8.18 (d, J ) 13.0 Hz, 1H, Pf-CHdCH), 7.20 (m, J )
15.6, 7.1 Hz, 1H, Me-CHdCH), 6.35 (d, J ) 13.0 Hz, 1H, Pf-
CHdCH), 5.95 (dq, J ) 15.6, 1.6 Hz, 1H, Me-CHdCH), 1.97
(dd, J ) 7.1, 1.6 Hz, 3H, Me-CHdCH). MS (EI) m/ z (relative
intensity): 278 (M+, 2), 181 (6), 161 (3), 69 (100), 41 (18).
10b. 19F NMR (CDCl3, δ, 282 MHz): -162.3 (m, Fmeta),
-156.1 (t, Fpara), -138.4 (m, Fortho). 1H NMR (CDCl3, δ, 300
MHz): 7.57 (d, J ) 7.0 Hz, 1H, Pf-CHdCH), 7.15 (m, 1H,
Me-CHdCH), 5.90 (m, 1H, Me-CHdCH), 5.63 (dt, J ) 7.0,
4J F-H ) 1.2 Hz, 1H, Pf-CHdCH), 1.95 (m, 3H, Me-CHdCH).
MS (EI) m/ z (relative intensity): 278 (M+, 0.8), 181 (5), 161
(3), 69 (100), 41 (16).
11. 19F NMR (CDCl3, δ, 282 MHz): -162.3 (m, Fmeta),
-154.9 (t, Fpara), -142.4 (m, Fortho). 1H NMR (CDCl3, δ, 300
MHz): 9.77 (b, 1H, CHO), 3.88 (b, 2H, Pf-CH2). MS (EI) m/ z
(relative intensity): 210 (M+, 31), 181 (100), 161 (24), 132 (19),
93 (17).
Rea ction w ith Divin yl Su lfon e. To a solution of [Pd-
(C6F5)Br(NCMe)2] (0.200 g, 0.459 mmol) in CH2Cl2 (10 mL)
was added divinyl sulfone (0.046 mL, 0.459 mmol). After 10
h at room temperature, a mixture of 12 and 13 had formed in
a ratio of 5:1, as shown by the 19F NMR spectrum in CH2Cl2
(a capillary tube with acetone-d6 was used as external lock
solvent). The solvent was reduced to ca. 0.5 mL and n-hexane
was added (2 mL). A yellow solid, 12, was obtained (61% yield).
12. Anal. Calcd for C20H12Br2F10O4Pd2S2: C, 25.47; H, 1.28.
Found: C, 25.32; H, 1.29. IR (SO2): 1303 (s), 1128 (s), 991-
24. 19F NMR (CDCl3, δ, 282 MHz): -162.6 (m, Fmeta),
-154.2 (t, Fpara), -142.4 (m, Fortho). 1H NMR (CDCl3, δ, 300
MHz): 6.63 (d, J ) 16.3 Hz, 1H PfCHdCHCH2-), 6.57 (dd, J
) 16.3, 6.0 Hz, 1H, PfCHdCHCH2-), 5.95 (m, J ) 17.1, 10.0,
7.4 Hz, 1H, CH2dCHCH2-), 5.56-5.43 (m, J ) 17.1, 10.0 Hz,
2H, CH2dCHCH2-), 3.90 (d, J ) 6.0 Hz, 2H, PfCHdCHCH2-),
3.75 (d, J ) 7.4 Hz, 2H, CH2dCHCH2-). MS (EI) m/ z
(relative intensity): 312 (M+, 3), 207 (100), 187 (43), 181 (41),
138 (6), 41 (46).
25. 19F NMR (CDCl3, δ, 282 MHz): -162.5 (m, Fmeta),
-154.5 (t, Fpara), -142.6 (m, Fortho). 1H NMR (CDCl3, δ, 300
MHz): 6.92 (dq, J ) 15.1, 7.0 Hz, 1H, MeCH dCH-), 6.56 (d,
J ) 16.3 Hz, 1H, PfCHdCHCH2-), 6.48 (dd, J ) 16.3, 6.7 Hz,
1H, PfCHdCHCH2-), 6.32 (dq, J ) 15.1, 1.5 Hz, 1H,
MeCHdCH-), 3.88 (d, J ) 6.7 Hz, 2H, PfCHdCHCH2-), 1.97
(dd, J ) 7.0, 1.5 Hz, 3H, MeCHdCH-). MS (EI) m/ z (relative
intensity): 312 (M+, 2), 207 (100), 187 (43), 181 (30), 41 (12).
26. 19F NMR (CDCl3, δ, 282 MHz): -162.6 (m, Fmeta),
-154.3 (t, Fpara), -142.5(m, Fortho). 1H NMR (CDCl3, δ, 300
MHz): 6.64 (d, J ) 16.2 Hz, 1H, PfCHdCHCH2-), 6.58 (dd, J
) 16.2, 6.0 Hz, 1H, PfCHdCHCH2-), 3.91 (d, J ) 6.0 Hz, 2H,
PfCHdCHCH2-), 2.98 (m, 2H, -CH2CH2Me), 1.90 (m, J ) 7.4
Hz, 2H, -CH2CH2Me), 1.08 (t, J ) 7.4 Hz, 3H, -CH2CH2Me).
MS (EI) m/z (relative intensity): 314 (M+, 1), 312 (22), 247
(8), 233 (9), 220 (7), 181 (100), 41 (10).
27. Anal. Calcd for
C18H8F10O2S: C, 45.20; H, 1.67.
Found: C, 44.82; H, 1.68. 19F NMR (CDCl3, δ, 282 MHz):
-162.3 (m, Fmeta), -153.9 (t, Fpara), -142.4 (m, Fortho). 1H NMR
(CDCl3, δ, 300 MHz): 6.67 (d, J ) 16.2 Hz, 1H, PfCHdCH-
CH2-), 6.60 (dd, J ) 16.2, 6.0 Hz, 1H, PfCHdCHCH2-), 3.96
(d, J ) 6.0 Hz, 2H, PfCHdCHCH2-). MS (EI) m/ z (relative
intensity): 478 (M+, 0.7), 207 (100), 187 (35), 181 (29), 138
(5).
966 (sb) cm-1
.
19F NMR (acetone-d6, δ, 282 MHz): -163.9 (b,
F
meta), -157.7 (b, Fpara), -141.4 (b, Fortho).
131. 19F NMR (acetone-d6, δ, 282 MHz): -164.9 (m, Fmeta),
-160.6 (t, Fpara), -142.2 (m, Fortho). 1H NMR (acetone-d6, δ,
300 MHz): 3.05 (m, 2H, Pf-CHH′CH), 2.56 (b, 1H, Pf-
CHH′CH), 2.15 (b, 1H, Pd-CHH′CH), 1.8-2.0 (m, 2H, Pd-
CHH′CH).
28. 19F NMR (CDCl3, δ, 282 MHz): -161.1 (m, Fmeta),
-154.7 (t, Fpara), -142.8 (m, Fortho). 1H NMR (CDCl3, δ, 300
5
MHz): 6.43 (m, J H
) 1.3 Hz, 1H, H5), 3.31 (dd, J ) 12.5,
-Me
7.8 Hz, 1H, H2), 3.28 (m, J 3-PfCHH′ ) 9.1, J 3-2′ ) 1.5 Hz, 1H,
H3), 3.18 (d, J ) 14.5 Hz, 1H, PfCHH′-), 3.03 (dd, J ) 12.5,
1.5 Hz, 1H, H2′), 2.93 (dd, J ) 14.5, 9.1 Hz, 1H, PfCHH′-),
2.10 (d, J ) 1.3 Hz, 3H, Me). MS (EI) m/ z (relative inten-
sity): 312 (M+, 26), 233 (13), 181 (100), 161 (6), 67 (7), 65 (7),
41 (13).
132. 19F NMR (acetone-d6, δ, 282 MHz), -164.9 (m, Fmeta),
-160.6 (t, Fpara), -142.2 (m, Fortho). 1H NMR (acetone-d6, δ,
300 MHz), 3.1 (m, 2H, Pf-CHH′CH), 2.47 (b, 1H, Pf-
CHH′CH), 2.3 (b, 1H, Pd-CHH′CH), 1.8-2.0 (m, 2H, Pd-
CHH′CH).
Rea ction w ith Dia llyl Su lfon e. [Pd(C6F5)Br(NCMe)2]
(0.030 g, 0.0689 mmol) and diallyl sulfone (0.0087 mL, 0.0689
mmol) were mixed at -30 °C in CDCl3 (0.6 mL), and the
reaction was monitored by 1H and 19F NMR. Complexes 14
and 18 were detected and identified. After 2 days at room
temperature, a black precipitate had formed, which was
filtered, and the products contained in the filtrate were
analyzed: 24 (32%), 25 (16%), 26 (19%), 27 (12%), 28 (7%), 32
(4%), 30 (5%), and 31 (5%) (the yields are based on diallyl
sulfone).
The compounds in the above-mentioned mixture could be
separated in several batches when the reaction was carried
out using higher amounts of the starting materials. To [Pd-
(C6F5)Br(NCMe)2] (0.200 g, 0.459 mmol) in CH2Cl2 (10 mL)
was added allyl sulfone (0.058 mL, 0.459 mmol). After 2 days
of stirring, a palladium mirror appeared on the flask wall.
Activated carbon was added to the black suspension, it was
filtered, and the filtrate was evaporated to dryness. The resi-
due was triturated with n-hexane and separated by column
chromatography (silica gel). A first batch, eluting with n-
hexane, afforded a colorless oily residue, which was 31 mixed
with 30. The use of diethyl ether as the eluent afforded a
second batch. Evaporation of the solvent to ca. 2 mL and
cooling led to a white solid (27, 11% yield). After the separa-
tion of 27, its mother liquors were subjected to preparative
TLC using diethyl ether as the eluent. Two batches were ob-
tained, with Rf ) 0.90 (24, 25, and 26) and 0.75 (28 and 32).
30. 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 (EI)
m/ z (relative intensity): 208 (M+, 100), 189 (22), 187 (28), 181
(79), 169 (14), 158 (15).
31. 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). MS
(EI) m/ z (relative intensity): 374 (M+, 53), 355 (17), 205 (16),
193 (27), 187 (34), 181 (100), 163 (25), 161 (17), 143 (18).
32. 1H NMR (CDCl3, δ, 300 MHz): 6.30 (m, J H
) 1.6
5
4
-Me
Hz, 1H, H5), 3.50 (dd, J ) 13.3, 8.0 Hz, 1H, H2), 3.00 (m, J )
8.0, 7.1, 4.0 Hz, 1H, H3), 2.95 (dd, J ) 13.3, 4.0 Hz, 1H, H2′),
1.99 (d, J ) 1.6 Hz, 3H, Me4), 1.32 (d, J ) 7.1 Hz, 3H, Me3).
MS (EI) m/ z: 146 (M+).
Rea ction w ith Dia llyl Eth er . An NMR tube charged with
[Pd(C6F5)Br(NCMe)2] (0.030 g, 0.0689 mmol) and CDCl3 (0.6
mL) was cooled to -30 °C, and diallyl ether (0.0084 mL, 0.0689
mmol) was added. The behavior of the reaction at low
temperature was monitored by NMR, and complexes 15 and
19 were identified. Finally, the temperature was increased
to 20 °C, and after 1 day, the mixture of products formed was
shown to be 19 (5%), 29 (10%), 31 (3%), 35 (29%), 38 (28%),
40 (11%), propanal (7%), and an unknown component (7%).

Evolution of η1-η2-Enylpalladium Complexes
Organometallics, Vol. 16, No. 26, 1997 5973
15. 19F NMR (CDCl3, δ, 282 MHz, 243 K): -162.4/-163.2
(m, Fmeta), -156.3/-156.5 (t, Fpara), -143.4/-143.9 (m, Fortho).
19. 19F NMR (CDCl3, δ, 282 MHz, 273 K): -162.4(b, Fmeta),
-157.2 (b, Fpara), -142.6 (b, Fortho).
39, and silicone polymers. By removing the more volatile
compounds by suction, 37 mixed with 31 were obtained.
Diethyl ether was employed as the second eluent, and it
afforded a small amount of 38.
36. 19F NMR (CDCl3, 263 K, δ, 282 MHz): -162.3 (m, Fmeta),
-156.7 (t, Fpara), -143.6 (m, Fortho). 1H NMR (CDCl3, 263 K,
δ, 300 MHz): 6.27 (dt, J ) 15.1, 5.0 Hz, 1H, PfCH2CHdCH-),
5.72 (d, J ) 15.1 Hz, 1H, PfCH2CHdCH-), 3.55 (d, J ) 5.0
Hz, 2H, PfCH2CHdCH-), 0.60 (s, 6H, Me).
To separate and identify the products, the reaction was
repeated using a higher amount of reactants. To [Pd(C6F5)-
Br(NCMe)2] (0.086 g, 0.20 mmol) in CH2Cl2 (10 mL) was added
diallyl ether (0.024 mL, 0.20 mmol). After 1 day of stirring,
activated carbon was added and the suspension filtered. The
yellow filtrate was evaporated to dryness, and diethyl ether
(5 mL) was added; after cooling down the mixture, a yellow
solid bis(µ-bromo)-bis(η3-propenyl)dipalladium(II) (38) ap-
peared (23%). The mother liquors were evaporated to dryness
and chromatographed on a silica gel column. With n-hexane,
a mixture of 31 and 29 was obtained. When diethyl ether was
used as the eluent, two more batches were obtained, which
were formed by 35 and 40, mixed with some unidentified
compounds, the first one, and a small amount of 15, 38, and
19, the second one. Finally, CH2Cl2 was used as the eluent,
and a small amount of 38 was obtained again.
29. 19F NMR (CDCl3, δ, 282 MHz): -163.5 (m, Fmeta),
-158.1 (t, Fpara), -144.7 (m, Fortho). 1H NMR (CDCl3, δ, 300
MHz): 5.87 (m, 1H, H2), 5.1 (m, 2H, H1), 3.43 (d, J ) 6.2 Hz,
2H, H3). MS (EI) m/ z (relative intensity): 208 (M+, 97), 189
(24), 187 (38), 181 (100), 169 (24), 161 (22), 158 (18).
35. 19F NMR (CDCl3, δ, 282 MHz): -162.7 (m, Fmeta),
-157.2 (t, Fpara), -144.0 (m, Fortho). 1H NMR (CDCl3, δ, 300
MHz): 9.81 (b, 1H, -CHO), 3.02 (t, J ) 7.9 Hz, 2H, PfCH2-
CH2-), 2.79 (dd, J ) 7.9, 0.7 Hz, 2H, PfCH2CH2-). MS (EI)
m/ z (relative intensity): 224 (M+, 46), 181 (100), 168 (35), 163
(54), 99 (25), 75 (22), 56 (60).
38. Anal. Calcd for C6H10Br2Pd2: C, 15.85; H, 2.22. Found:
C, 16.03; H, 2.19. 1H NMR (CDCl3, δ, 300 MHz), 5.45 (m, 1H,
H2), 4.23 (d, J ) 6.9 Hz, 2H, H-syn), 3.11 (d, J ) 12.3 Hz, 2H,
H-anti).
401. 19F NMR (CDCl3, δ, 282 MHz): -162.5 (m, Fmeta),
-157.1(t, Fpara), -143.5 (m, Fortho). 1H NMR (CDCl3, δ, 300
MHz): 5.18 (d, J ) 4.7 Hz, 1H, H2), 3.97 (t, J ) 7.6 Hz, 1H,
H5), 3.57 (dd, J ) 8.8, 7.6 Hz, 1H, H5′), 2.95-2.80 (m, J ) 13.9
Hz, 1H, PfCHH′-), 2.68 (dd, J ) 13.9, 8.5 Hz, 1H, PfCHH′-),
2.25 (m, 1H, H4), 1.90 (m, 1H, H3), 0.94 (d, J ) 6.7 Hz, 3H,
Me). MS (EI) m/ z (relative intensity): 265 (M+ - Br, 14), 194
(28), 181 (94), 84 (25), 55 (100), 43 (33), 41 (64).
37. 19F NMR (CDCl3, 293 K, δ, 282 MHz): -163.2 (m, Fmeta),
-157.7 (t, Fpara), -144.2 (m, Fortho). 1H NMR (CDCl3, 293 K,
δ, 300 MHz): 6.07 (dt, J ) 18.4, 5.7 Hz, 1H, PfCH2CHdCH-),
5.60 (dt, J ) 18.4, 1.5 Hz, 1H, PfCH2CHdCH-), 3.48 (dd, J )
5.7, 1.5 Hz, 2H, PfCH2CHdCH-), 0.09 (s, 6H, Me). MS (EI)
m/ z (relative intensity): 546 (M+, 5), 531 (12), 365 (20), 181
(42), 169 (40), 155 (100), 151 (80), 137 (21), 77 (17).
39. 19F NMR (CDCl3, 293 K, δ, 282 MHz): -163.2 (m, Fmeta),
-157.1 (t, Fpara), -142.6 (m, Fortho). 1H NMR (CDCl3, 293 K,
δ, 300 MHz): 5.50 (s, 1H, H1), 5.16 (s, 1H, H1′), 2.08 (s, 3H,
Me). MS (EI) m/ z (relative intensity): 208 (M+, 100), 195 (40),
193 (42), 181 (64), 143 (51), 123 (33), 86 (35), 84 (46).
-(Si(Me2)-O)n -. MS (EI) m/ z (relative intensity): n ) 4,
281 (M+ - Me, 100), 265 (8), 249 (6), 193 (7), 73 (6); n ) 5, 355
(M+ - Me, 93), 267 (49), 251 (7), 73 (100), 45 (8); n ) 6, 429
(M+ - Me, 5), 341 (14), 325 (5), 147 (13), 73 (100), 45 (6).
Rea ction w ith Dim eth yl Dia llylm a lon a te. [Pd(C6F5)-
Br(NCMe)2] (0.030 g, 0.0689 mmol), dimethyl diallylmalonate
(0.014 mL, 0.0689 mmol), and CDCl3 (0.6 mL) were mixed in
an NMR tube at -20 °C. The reaction was monitored, and
complex 17 was identified. After 1 h at room temperature, a
mixture of organic derivatives was obtained which contained
21 (56% or 47%), 23 (31% or 26%), and 22 (13% or 11%) (the
yields in parentheses were determined by integration of the
1H and 19F NMR signals and are based on dimethyl diallyl-
malonate or C6F5, respectively). In addition, pentafluoroben-
zene (16%) (based on C6F5) was found in the solution.
17. 19F NMR (CDCl3, δ, 282 MHz, 253 K): -162.4/-163.0
(b, Fmeta), -157.1/-157.5 (b, Fpara), -142.3/-143.2 (b, Fortho).21
21. 19F NMR (CDCl3, δ, 282 MHz): -162.8 (m, Fmeta),
-157.4 (t, Fpara), -143.3 (m, Fortho). 1H NMR (CDCl3, δ, 300
1
2
MHz): 5.56 (m, J H
) 1.0 Hz, 1H, H2), 3.74 (s, 3H,
-Me
-COOMe), 3.69 (s, 3H, -COOMe ′), 2.95 (m, 2H, H4, PfCHH′-),
2.56 (m, 1H, PfCHH′-), 2.55 (dd, J ) 13.7, 7.9 Hz, 1H, H5),
2.03 (dd, J ) 13.7, 5.6 Hz, 1H, H5′), 1.83 (d, J ) 1.0 Hz, 3H,
Me3). 13C NMR (CDCl3, δ, 75 MHz): 124.1 (C2), 52.7 (COOCH3),
47.3 (C4), 37.4 (C5), 26.3 (PfCH2-), 14.5 (Me3). MS (EI) m/ z
(relative intensity): 378 (M+, 22), 318 (82), 259 (76), 181 (100),
165 (86), 137 (45), 79 (67), 77 (80), 59 (72).
402. 19F NMR (CDCl3, δ, 282 MHz): -162.5 (m, Fmeta),
-157.2(t, Fpara), -143.6 (m, Fortho). 1H NMR (CDCl3, δ, 300
MHz): 4.87 (d, J ) 3.1 Hz, 1H, H2), 4.00 (dd, J ) 8.3, 7.8 Hz,
1H, H5), 3.76 (dd, J ) 8.3, 7.5 Hz, 1H, H5′), 2.95-2.80 (m, 2H,
-CH2 Pf)*, 2.06 (m, 1H, H4), 1.90 (m, 1H, H3)*, 1.01 (d, J ) 7.3
Hz, 3H, Me) (asterisk indicates signals overlapped with those
of 401). MS: coincident with MS for 401.
23. 1H NMR (CDCl3, δ, 300 MHz): 5.41 (m, J H
) 1.1
1
2
-Me
Hz, 1H, H2), 3.72 (s, 3H, -COOMe), 3.70 (s, 3H, -COOMe′),
2.78 (m, 2H, H4, H5), 1.92 (dd, J ) 14.8, 5.6 Hz, 1H, H5′), 1.72
(d, J ) 1.1 Hz, 3H, Me3), 1.05 (d, J ) 6.8 Hz, 3H, Me4). 13C
NMR (CDCl3, δ, 75 MHz): 121.8 (C2), 52.6 (-COOCH3), 41.9
(C4), 40.5 (C5), 18.9 (Me3), 14.6 (Me4). MS (EI) m/ z (relative
intensity): 212 (M+, 5), 153 (29), 152 (41), 93 (100), 77 (30),
59 (20).
Rea ction w ith Dia llyld im eth ylsila n e. The reaction was
carried out at -30 °C in an NMR tube which was charged with
[Pd(C6F5)Br(NCMe)2] (0.030 g, 0.0689 mmol), CDCl3 (0.6 mL),
and diallyldimethylsilane (0.0126 mL, 0.0689 mmol). The
temperature was slowly increased, and complexes 16 and 20
were identified. After 10 h at room temperature, the black
precipitate was filtered through Celite and the final mixture
contained 29 (60%), 30 (15%), 31 (4%), 37 (15%), 39 (6%),
propene and -(Me2Si)n-O (n ) 4, 5, and 6) (yields are based
on C6F5).
22. 19F NMR (CDCl3, δ, 282 MHz): -163.0 (m, Fmeta),
-157.8/-157.7* (t, Fpara), -143.5/-143.6* (m, Fortho) (asterisk
indicates two signals corresponding to both diastereoisomers).
MS (EI) m/ z (relative intensity): 380 (M+, 20), 261 (45), 221
(48), 181 (100), 139 (76), 107 (45), 79 (77), 59 (94).
16. 19F NMR (CDCl3, δ, 282 MHz, 243 K): -161.9 (b, Fmeta),
-156.8 (b, Fpara), -143.4 (b, Fortho).
Ack n ow led gm en t. This work was supported by the
Direccio´n General de Investigacio´n Cient´ıfica y Te´cnica
(Spain) (Project No. PB96-0363), the Commission of the
European Communities (Network “Selective Processes
and Catalysis Involving Small Molecules”, Grant No.
CHRX-CT93-0147), and the J unta de Castilla y Leo´n
(Project No. VA 40-96). Y.-S.L. thanks the Spanish
Ministerio de Educacio´n y Ciencia and the AECI/ICD-
Universidad de Valladolid for fellowships.
20. 19F NMR (CDCl3, δ, 282 MHz, 263 K): -162.8 (b, Fmeta),
-157.8 (b, Fpara), -143.5 (b, Fortho).
Higher amounts of [Pd(C6F5)Br(NCMe)2] (0.180 g, 0.413
mmol) and diallyldimethylsilane (0.076 mL, 0.413 mmol) in
CH2Cl2 (5 mL) were used to carry out the reaction at room
temperature. After 10 h, the palladium metal formed was
filtered off and the filtrate was evaporated to dryness. The
residue was separated by silica gel column chromatography.
Elution with n-hexane and evaporation of the solvent gave a
colorless oily residue, which was a mixture of 29, 30, 31, 37,
OM9707228