Palladium(0)-catalyzed cis-trans alkene isomerizations

Article abstract of DOI:10.1021/om800305h

The cis-trans isomerization of some olefins bearing strong electron-withdrawing substituents (dmma and E-tse) is catalyzed by their mere coordination to a suitable Pd(O) fragment without any external reagents. The choice of spectator ligand is fundamental to the efficiency of the process, and the phosphanyl-quinolines dppq and dppq-Me have proven to be particularly effective. The mechanism of the rearrangement is discussed, and the presence of electron-withdrawing and conjugated substituents on the olefins appears to be an essential prerequisite for the isomerization.

Full text of DOI:10.1021/om800305h

Organometallics 2008, 27, 3577–3581
3577
Palladium(0)-Catalyzed Cis-Trans Alkene Isomerizations
Luciano Canovese, Claudio Santo, and Fabiano Visentin*
Dipartimento di Chimica, UniVersita` Ca′ Foscari, Calle Larga S. Marta 2137, 30123 Venezia, Italy
ReceiVed April 4, 2008
The cis-trans isomerization of some olefins bearing strong electron-withdrawing substituents (dmma
and E-tse) is catalyzed by their mere coordination to a suitable Pd(0) fragment without any external
reagents. The choice of spectator ligand is fundamental to the efficiency of the process, and the phosphanyl-
quinolines dppq and dppq-Me have proven to be particularly effective. The mechanism of the rearrangement
is discussed, and the presence of electron-withdrawing and conjugated substituents on the olefins appears
to be an essential prerequisite for the isomerization.
Scheme 1
The amazing number of research articles related to the
cis-trans isomerization of olefins reflects the great importance
of such a process in organic1 and inorganic chemistry2 as well
as in biology.3 In general (Z)- and (E)-olefins do not interconvert
spontaneously at room temperature in the absence of an
appropriate external promoter. The fundamental role of this
agent is to support the formal breaking of the double bond via
either a homolytic or a heterolytic process with consequent
reduction in the energy barrier to rotation. The homolytic
breaking of the π system has been basically observed in the
case of direct photoisomerization,3,4 of isomerization initiated
by radical generators or paramagnetic molecules (atomic
bromine or iodine, oxygen, nitrogen oxide, etc.),5 and of
electrochemical6 or thermal isomerization.7 The heterolytic
breaking involves a reactive nucleophilic8 or electrophlic1b
counterpart, and the rupture of the double bond is greatly favored
in an ethylene system where there are electron-withdrawing
groups bound to one carbon and electron-donating substituents
on the other. In this respect, groups conjugated to the double
bond are particularly functional.
Geometric olefin isomerizations may also be obtained by
resorting to transition-metal assistance. Thus, it is noteworthy
that many tungsten- or molybdenum-based catalysts exhibit a
high efficiency both in metathesis and in isomerization of
internal acyclic olefins as a consequence of the so-called “metal-
alkylidene chain” mechanism.9a–c An efficient isomerization of
cis-alkenes can also be achieved by Pd(II) catalysts, via a
mechanism involving a carbocation.9e On the other hand, an
extensive olefin isomerization is observed during the reduction
of cis-alkenes or semihydrogenation of alkynes under dihydro-
gen atmosphere. Pd0,10 Ni0,11 RhI,10,12 and IrI 13 catalysts are
typically employed, and the mechanism seems to proceed via
an equilibrium between a metal dihydrido olefin complex and
a metal monohydrido alkyl complex.
In particular, Spencer and co-workers10c have found that
during the palladium-catalyzed reduction of cis-olefins with
deuterium, some trans-alkenes containing one deuterium atom
are obtained (Scheme 1). This proves that deuterium is directly
involved in the isomerization; furthermore, the same authors
have shown that polarization of the metal-hydrogen bond
determines the site of attack (from B to C) at the most
electronically favored end of the double bond. However, a
question is left unanswered: previous works14 had established
that the production of trans-alkene via ꢀ-elimination (from D
to E) occurs with cis geometry and consequently, according to
* To whom correspondence should be addressed. E-mail: fvise@unive.it.
(1) (a) Larock, R. C. In ComprehensiVe Organic Transformations; VCH:
New York, 1989; pp 109-119, and references therein. (b) Mackenzie, K.
In The Chemistry of Alkenes; Patai, S., Ed.; Wiley: New York, 1964; pp
338-413.
(2) Barton, D. ; Ollis, D. In ComprehensiVe Organic Chemistry,; Jones,
D. N., Ed.; Pergamon Press: Oxford, U.K., 1979; Vol. 3, pp 1201-1207.
(3) Dugave, C.; Demange, L. Chem. ReV. 2003, 103, 2475–2532.
(4) (a) Benali, O.; Miranda, M. A.; Termos, R. Eur. J. Org. Chem. 2002,
14, 2317–2322. (b) Goez, M.; Eckert, G. J. Am. Chem. Soc. 1996, 118,
140–154. (c) Ebbsen, T. B.; Tokumaru, K.; Sumitani, M.; Yoshihara, K. J.
Phys. Chem. 1989, 93, 5453–5457.
(5) (a) Sykes, P. In A Guidebook to Mechanism in Organic Chemistry;
Longman Scientific and Technical: Singapore, 1986; pp 315-316. (b)
Hepperle, S. S.; Li, Q.; East, A. L. L. J. Phys. Chem. 2005, 93, 10975–
10981. (c) Gibson, T. W.; Strassburger, P. J. Org. Chem. 1976, 41, 791–
793.
(6) Doherty, A. P.; Scott, K. J. Electroanal. Chem. Interfacial Electro-
chem. 1988, 442, 35–40.
(10) (a) Kluwer, A. M.; Koblenz, T. S.; Jonischkeit, T.; Woelk, K.;
Elsevier, C. J. J. Am. Chem. Soc. 2005, 127, 15470–15480. (b) Dunne,
J. O.; Duckett, S. B.; Konya, D.; Len˜ero, K. Q.; Drent, E. J. Am. Chem.
Soc. 2004, 126, 5257–5258. (c) Yu, J.; Spencer, J. B. J. Am. Chem. Soc.
1997, 119, 5257–5258.
(11) Druliner, J. D. Organometallics 1984, 2, 205–208.
(12) (a) Musolino, M. G.; Apa, G.; Donato, A.; Pietropaolo, R. Catal.
Today 2005, 100, 467–471. (b) Brown, J.; Parker, D. J. Chem. Soc., Chem.
Commun. 1980, 342–344.
(7) Golub, M. A.; Lee, W. M. J. Polym. Sci., Polym. Lett. Ed. 1983,
21, 867–874.
(8) (a) Larpent, C.; Meignan, G. Tetrahedron Lett. 1993, 27, 4331–
4334. (b) Roundhill, D. M.; Ganguly, S. J. Chem. Soc. Chem. Commun.
1991, 639–640.
(9) (a) Tlenkopatchev, M.; Fomine, S. J. Organomet. Chem. 2001, 630,
157–168. (b) Leconte, M. J.; Basset, M. J. Am. Chem. Soc. 1979, 101, 7296–
7302. (c) Bilhou, J. L.; Basset, J. M.; Mutin, R.; Grydon, W. F. J. Am.
Chem. Soc. 1977, 99, 4083–4090. (d) Yu, J.; Gaunt, J.; Spencer, J. B. J.
Org. Chem. 2002, 67, 4627–4629. (e) Sen, A.; Lai, T.-W. Inorg. Chem.
1981, 20, 4036–4038.
(13) (a) Matsumoto, T.; Yoshida, H. Catal. Lett. 2001, 72, 1–2. (b)
Kovacs, J.; Todd, T. D.; Reibenspies, J. H.; Joo, F.; Darensbourgh, D. J.
Organometallics 2000, 19, 3963–3969.
(14) (a) Evans, J.; Scwartz, J.; Urquhart, P. W. J. Organomet. Chem.
1974, 81, C37–C-39. (b) McCarthy, T. J.; Nuzzo, R. G.; Whiteside, G. M.
J. Am. Chem. Soc. 1981, 103, 3396–3403.
10.1021/om800305h CCC: $40.75
2008 American Chemical Society
Publication on Web 06/17/2008

3578 Organometallics, Vol. 27, No. 14, 2008
CanoVese et al.
Scheme 2
Scheme 3
Table 1a
entry
cat. (amt (mol %))
t (h)
conversn (%)
1
2
3
4
5
6
6
7
1b (5)
1b (5)
1b (5)
1a (5)
1a (5)
1a (5)
1b (1)
1b (1)
6
24
48
6
24
48
24
48
56
95
99
56
86
97
28
43
nylphosphine)ethane), [Pd(neoc)(η2-dmfu)]16 (1d; neoc ) 2,9-
dimethyl-1,10-phenanthroline), and [Pd(NSPh)(η2-dmfu)]15 (1e;
NSPh ) 2-(phenylthiomethyl)pyridine) were virtually ineffective
under the same mild operating conditions.
a All reactions were run using the substrate dmfu at a concentration
of 0.3 mol/dm-3, in 0.8 mL of CDCl3 at 298 K under an argon
atmosphere.
These findings led us to verify the applicability of this
catalytic system to other olefinic substrates. Our attention was
therefore focused on the disulfonic derivative Z-tse (Z-tse )
(Z)-1,2-bis[(4-methylphenyl)sulfonyl]ethene),17 which electroni-
cally resembles dmfu. When a 3-fold excess of this olefin was
added to complexes 1a,b in CDCl3, we could observe the
immediate and complete displacement of dimethyl fumarate to
produce respectively the new complexes 2a,b; this result clearly
showed the better efficiency of Z-tse in stabilizing the pal-
ladium(0) substrate.18 Also in this case the complexes 2a,b
slowly turned into 3a,b (∼12 h) through the cis-trans isomer-
ization of coordinated olefin (Scheme 3). Interestingly, the
excess Z-tse continued its conversion to E-tse17 even after the
complete formation of complexes 3a,b, which thus displayed
catalytic properties. Once again the course of the reactions could
be easily deduced by the changes detected in the 1H and 31P{1H}
Scheme 1, it would lead to 100% incorporation of deuterium
into the final olefins. The experimental level of incorporated
deuterium is not complete, and so, a competing mechanism may
be possible. The simplest option is to assume that the metal
adds first to the double bond of the cis-alkene and then
isomerization could occur without the mediation of deuterium
(directly from A to E).
Results and Discussion
In the present paper we report a direct and exhaustive proof
of an olefin isomerization mechanism promoted by a pal-
ladium(0) substrate without any other external mediation.
Our first observation involved the ability of the novel
zerovalent palladium complexes [Pd(dppq)(η2-dmfu)] (1a) and
[Pd(dppq-Me)(η2-dmfu)] (1b) (dmfu ) dimethyl fumarate; dppq
) 8-(diphenylphosphino)quinoline; dppq-Me ) 8-(diphenylphos-
phino)-2-methylquinoline) to promote the complete isomeriza-
tion of dimethyl maleate to its respective trans species dimethyl
fumarate (Scheme 2). This catalytic transformation could be
obtained in a CDCl3 solution at room temperature (Table 1).
The simplest hypothesis of the mechanism for this catalysis
entails a fast equilibrium displacement of the coordinated
dimethyl fumarate by excess of dimethyl maleate to yield
[Pd(dppq)(η2-dmma)] (dmma ) dimethyl maleate), followed
by the slow cis-trans isomerization of the coordinated olefin.
This suggestion is directly supported by the appearance of a
small peak in the 31P{1H} NMR spectrum of the catalytic
mixture after the addition of dimetyl maleate. This peak, with
a chemical shift very near to that belonging to the catalytic
species [Pd(dppq)(η2-dmfu)], may be attributed to the complex
[Pd(dppq)(η2-dmma)]. The strong difference in intensity be-
tween the two peaks suggests that the displacement equilibrium
is definitely favorable to 1a. The minor peak consistently
disappears at the end of the reaction when all dimethyl maleate
has been converted into dimethyl fumarate.
(16) Canovese, L.; Visentin, F.; Santo, P. J. Organomet. Chem. 2007,
692, 4187–4192.
(17) Brown, A. C.; Carpino, L. A. J. Org. Chem. 1985, 50, 1749–1750.
(18) The complete displacement of dmfu by Z-tse is attested by
determination of the equilibrium constant KE3
:
[Pd(dppq)(η2-dmfu)] + Z-tse 7KE38 [Pd(dppq)(η2-Z-tse)] +
dmfu
Its value was not directly accessible, as it was too high, but it could be
indirectly estimated by spectrophotometric determinations of the olefin
substitution equilibrium constants KE1 and KE2 concerning the reactions:
[Pd(dppq)(η2-dmfu)] + fn 7KE18 [Pd(dppq)(η2-fn)] + dmfu
[Pd(dppq)(η2-fn)] + Z-tse 7KE28 [Pd(dppq)(η2-Z-tse)] + fn
with dmfu ) dimethyl fumarate and fn ) fumaronitrile. The values obtained
were KE1) 4600 ( 600 and KE2 ) 270 ( 50. From these findings the
value of KE3, given by the product of KE1 and KE2, was (1.2 ( 0.3) × 106.
For a detailed description of the method see the Supporting Information
and: Canovese, L.; Visentin, F.; Uguagliati, P.; Crociani, B. J. Chem. Soc.,
Dalton Trans. 1996, 1921–1926.
The fundamental importance of the phosphanyl-quinoline
ancillary ligands was immediately evident: the corresponding
complexes [Pd(dppe)(η2-dmfu)]15 (1c; dppe ) 1,2-bis(diphe-
(15) Canovese, L.; Visentin, F.; Chessa, G.; Uguagliati, P.; Santo, C.;
Maini, L. J. Organomet. Chem. 2007, 692, 2342–2345.

Pd(0)-Catalyzed Cis–Trans Alkene Isomerizations
Organometallics, Vol. 27, No. 14, 2008 3579
Figure 2. Gibbs free energy values (kcal/mol) for the different
reaction paths computed at the B3PW91 level.
Scheme 4
Figure 1. Fit of concentration of starting complex 2b to time
according to eq 1 in CDCl3 at 25 °C (c0 ) 1.5 × 10-2 mol dm-3).
NMR spectra. It is noteworthy that this system offers the
feasibility to isolate the intermediates complexes 2a,b with the
coordinated olefin in a cis arrangement; their precipitates could
be simply obtained by treating with diethyl ether a CH2Cl2
solution of starting compounds 1a,b kept at low temperature
(-15 °C) immediately after the addition of Z-tse. In contrast, a
long reaction time (several hours at room temperature) ensured
the complete conversion of 2a,b into the thermodynamically
more stable species 3a,b.19
again the complete replacement of dimethyl fumarate by the
more effective olefin added, with the consequent formation of
the new species 2c-e, but no or only a weak tendency to the
subsequent cis-trans isomerization of the coordinated olefin.
In particular, the complexes 2d,e (with neoc and NSPh as
ancillary ligands, respectively), were substantially unreactive,
while the conversion of the diphosphino complex 2c into the
species 3c containing E-tse required some weeks.
In light of the above findings it is reasonable to suppose that
the promotion of this unprecedented olefin rearrangement must
fundamentally stems from a cooperative and subtle influence
of the two coordinating groups of the spectator ligand on the
Pd-alkene bond. In an attempt to gain information concerning
this point, the reaction mechanism was investigated employing
density functional theory (DFT) calculations. The simulated
system concerned the isomerization of the complex [Pd-
(dmpq)(η2-dmma)] (dmpq ) 8-(dimethylphosphino)quinoline)
into the corresponding [Pd(dmpq)(η2-dmfu)]. Replacing the two
phenyl phosphorus substituents of the experimentally tested dppq
ligand with two methyl groups makes the process less compu-
tationally intensive.
Both of these products were isolated as yellow crystalline
solids, which are stable at room temperature for months in a
closed vessel without any tendency of the cis species to turn
into the corresponding trans isomer. The elemental analyses of
2a,b were the same as those of 3a,b, respectively, and resulted
in good agreement with the expected composition. In contrast,
1
the H, 31P{1H}, and 13C{1H} NMR spectra revealed some
appreciable differences which allowed us to distinguish easily
the cis from the trans products.
All these circumstances represented very favorable conditions
for a kinetic study focused on the isomerization process. Indeed,
in CDCl3 solution at 298 K the complexes 2a,b rearranged at a
rate for which monitoring by NMR spectroscopy is feasible. In
particular, for the species 2b a set of concentration vs time data
could be obtained with high precision from relevant signals of
1H NMR spectra (Figure 1). In this case we could observe that
the consumption of starting material followed a first-order rate
law according to eq 1.
Schematic energy profiles (∆G values) are shown in Figure 2.
It is apparent that the reaction can proceed following two
similar but distinct pathways.
For both pathways we detected a high-energy PdII-cyclo-
metalated intermediate (C1 or C2), produced by a sort of
nucleophilic attack of the electron-rich palladium(0) fragment
to the R,ꢀ-unsaturated coordinated olefin. The addition was
conjugate (1,4) with consequent formation of two new Pd-C
and Pd-O σ bonds and the shift of the olefinic double bond
from the 2,3- to the 3,4-position (Scheme 4).
ct ) c0 exp(-k1t)
(1)
The analysis yielded the rate constant k1 ) (1.27 ( 0.01) ×
10-4 s-1
.
This kinetic evidence supports strongly our hypothesis of a
unimolecular rearrangement for the coordinated olefin isomeriza-
tion.
The strategic role of phosphanyl-quinoline ligands in this
process is once again highlighted by comparison with the
behavior of analogous palladium(0) complexes 1c-e bearing
different ancillary ligands. As a matter of fact, after their
treatment with an equimolar amount of Z-tse we could observe
Both intermediates were connected to the reactants and to
the products by two transition states (B1 or B2 and D1 or D2) in
which the olefinic double bond is partially twisted and elongated
and the carbonyl oxygen is partially bonded to palladium.
Pathway 1 was significantly favored by the low energy profile,
determined by the strong trans effect/influence of the phosphorus
which weakens the Pd-C(3) bond in the starting complex A,
and by the higher stability of the intermediate C1 which has
phosphorus and carbon in cis and not in trans reciprocal
(19) The complexes 3a,b could also be obtained by direct exchange of
dmfu in the starting compounds 1a,b with E-tse (E-tse ) (E)-1,2-bis[(4-
methylphenyl)sulfonyl]ethane). This olefin was synthesized according to
the procedure described in ref 17.

3580 Organometallics, Vol. 27, No. 14, 2008
CanoVese et al.
NMR (CDCl3, T ) 298 K, ppm) δ 20.8; 13C{1H} NMR (CDCl3,
T ) 298 K, ppm) δ 48.8 (CH3, OCH3, trans-P); 49.5 (d, CH, JCP
) 28.6 Hz, CHdCH trans-P), 50.5 (CH3, OCH3, trans-N), 50.7
(CH, CHdCH trans-N), 122.8 (CH, C3), 127.3 (d, CH, JCP ) 4.3
Hz, C6), 130.7 (CH, C5), 136.6 (d, C, JCP ) 31.3 Hz, C8), 137.7
(d, CH, JCP ) 2.5 Hz, C7), 137.9 (CH, C4), 151.1 (C, C9), 151.4
(C, C10), 155.4 (CH, C2), 173.0 (d, CO, JCP ) 5.8 Hz, CO trans-
N), 174.3 (CO, CO trans-P); IR (KBr pellet) ν 1632 cm-1 (CdO).
Anal. Calcd for C27H24NO4PPd: C, 57.51; H, 4.29; N, 2.48. Found:
C, 57.65; H, 4.39; N, 2.44.
positions (as for the C2 species). The activation energy of the
low-energy path (20.7 kcal/mol) is quite compatible with our
experimental findings.
Eventually these results explained the decisive and peculiar
role of phosphanyl-quinoline in promoting the olefin rearrange-
ment: on one side the presence of the strong trans-labilizing
phosphine group favors activation of the initial compound, and
on the other the weak trans-labilizing quinoline group provides
sufficient stability to the key intermediate C1. Moreover, the
calculations emphasized the crucial role exercised by the
conjugate CdO group for the outcome of the whole process.
This evidence seems to reduce significantly the spectrum of
olefins fit for this mechanism of rearrangement. Among the
functional groups able to perform the same role of carbonyl,
we could experimentally verify the appreciable ability of the
sulfonyl unit.
In conclusion, we have shown both experimentally and
theoretically an original mechanism for the cis-trans isomer-
ization of alkenes promoted exclusively by a palladium(0)
fragment. Further work is currently under way to define precisely
the range of substituents on the olefin and the range of ancillary
ligands of palladium(0) complexes required to ensure good
efficiency to the process.
1
Selected data for 1b: H NMR (300 MHz, CDCl3, T ) 298 K,
ppm) δ 3.16 (s, 3H, quinoline-CH3); 3.21 (s, 3H, OCH3 trans-P),
3.64 (s, 3H, OCH3 trans-N), 3.96 (t, 1H, JCHdCH ) 10.5 Hz, JPH
10.5 Hz, CHdCH trans-P); 4.50 (dd, 1H, JCHdCH ) 9.2 Hz, JPH
)
)
2.4 Hz, CHdCH trans-N), 7.31-7.45 (m, 8H, PPh2), 7.56 (d, H, J
) 8.4 Hz; H3), 7.58 (t, 1H, J ) 7.7 Hz, H6), 7.70-7.76 (m, 2H,
PPh2), 7.85 (t, 1H, JHH ) JHP ) 7.7 Hz, H7), 7.92 (d, H, J ) 7.7
Hz, H5), 8.21 (d, 1H, J ) 8.4 Hz, H4); 31P{1H} NMR (CDCl3, T
) 298 K, ppm) δ 20.6; 13C{1H} NMR (CDCl3, T ) 298 K, ppm)
δ 31.8 (CH3, quinoline-CH3), 48.1 (d, CH, JCP ) 31.8 Hz, CHdCH
trans-P), 49.1 (CH, CHdCH trans-N), 50.4 (CH3, OCH3, trans-P),
50.5 (CH3, OCH3, trans-N), 123.3 (CH, C3), 126.1 (d, CH, JCP
)
4.4 Hz, C6), 130.7 (CH, C5), 135.2 (d, C, JCP ) 31.3 Hz, C8), 137.5
(CH, C7), 138.1 (CH, C4), 151.5 (C, C9), 151.8 (C, C10), 164.0 (C,
C2), 174.0 (CO, CO trans-P), 174.3 (d, CO, JCP ) 5.5 Hz, CO
trans-N); IR (KBr pellet) ν 1697, 1677 cm-1 (CdO). Anal. Calcd
for C28H26NO4PPd: C, 58.19; H, 4.53; N, 2.42. Found: C, 58.36;
H, 4.64; N, 2.39.
Experimental Section
Materials. Unless otherwise stated, all manipulations were
carried out under an argon atmosphere using standard Schlenk
techniques. All solvents were purified by standard procedures and
distilled under argon immediately prior to use.
Synthesis of Complexes 2a,b. A solution of complex 1a or 1b
(0.2 mmol) in dry dichloromethane was cooled to -15 °C, and
solid Z-tse (0.0673 g, 0.2 mmol) was quickly added under an inert
atmosphere (argon). The reaction mixture was stirred for 5 min
and then dried under reduced pressure. The pale yellow solid
obtained was washed with several aliquots of diethyl ether to
remove the free dmfu (0.1295 g, yield 92.3% for 2a; 0.1358 g,
yield 88.2% for 2b). Analytically pure complexes were obtained
by recrystallization from CH2Cl2/Et2O.
dppq,20 dppq-Me,20 Pd2DBA3 · CHCl3,21 [Pd(dppe)(η2-dmfu)]15
(1c), [Pd(neoc)(η2-dmfu)]16 (1d), and [Pd(NSPh)(η2-dmfu)]15 (1e)
were prepared by following literature procedures. All other
chemicals were commercial grade and were used without further
purification.
1D and 2D NMR spectra were recorded using a Bruker DPX300
or Bruker DPX500 spectrometer. Chemical shifts (ppm) are given
relative to TMS (1H and 13C NMR) and 85% H3PO4 (31P NMR).
Peaks are labeled as singlet (s), doublet (d), triplet (t), quartet (q),
multiplet (m), and broad (br). The proton and carbon assignment
was performed by 1H-2D COSY, 1H 2D NOESY, 1H-13C HMQC,
and HMBC experiments.
Selected data for 2a: 1H NMR (CDCl3, T ) 298 K, ppm) δ 2.32
(s, 3H, CH3), 2.40 (s, 3H, CH3), 3.95 (dd, 1H, JCHdCH ) 9.3 Hz,
JPH ) 8.0 Hz, CHdCH trans-P), 4.24 (dd, 1H, JCHdCH ) 9.3 Hz,
JPH ) 2.5 Hz, CHdCH trans-N); 6.91 (d, 2H, J ) 8.1 Hz, Hc),
7.15 (d; 2H, J ) 8.1 Hz, Hc), 7.29-7.46 (m, 10H, PPh2, Hb), 7.64
(dd, 1H, J ) 8.3 and 4.8 Hz, H3), 7.7 (dd, 1H, J ) 8.0 Hz, JPH
)
Synthesis of [Pd(dppq)(η2-dmfu)] (1a) and [Pd(dppq-Me)(η2-
dmfu)] (1b). To a solution of dmfu (0.0640 g, 0.44 mmol) and the
appropriate bidentate ligands (0.405 mmol) in dry acetone (15 mL)
was added solid Pd2DBA3 · CHCl3 (0.200 g, 0.193 mmol) under
an inert atmosphere (argon). The reaction mixture was stirred for
1 h at room temperature, and the initial dark suspension turned to
an orange-yellow solution. This resulting solution was dried under
reduced pressure, and the residue was redissolved in dichlo-
romethane. Addition of charcoal and filtration on Celite removed
the traces of metallic palladium, yielding a clear solution. Reduction
to small volume (3-4 mL) and addition of diethyl ether gave the
products as microcrystalline yellow solids after cooling to 0 °C
(0.1764 g, yield 80.1% for 1a; 0.1802 g, yield 80.7% for 1b).
8.0, H7), 7.83-7.92 (m, 4H, PPh2), 7.96 (t, 1H, J ) 8.0 Hz, H6),
8.02 (d, 1H, J ) 8.0 Hz, H5), 8.40 (d, 1H, J ) 8.3 Hz, H4), 10.28
(d, 1H, 4.8 Hz, H2); 31P{1H} NMR (CDCl3, T ) 298 K, ppm) δ
22.7; IR (KBr pellet) ν 1297, 1128 cm-1 (SdO). Anal. Calcd for
C37H32NO4PPdS2: C, 58.77; H, 4.27; N, 1.85. Found: C, 58.65; H,
4.22; N, 1.82.
Selected data for 2b: 1H NMR (CDCl3, T ) 298 K, ppm) δ
2.08 (s, 3H, CH3), 2.36 (s, 3H, CH3), 3.32 (s, 3H, CH3 quinoline),
4.13 (dd, 1H, JCHdCH ) 9.3 Hz, JPH ) 8.0 Hz, CHdCH trans-P),
4.22 (dd, 1H, JCHdCH ) 9.3 Hz, JPH ) 2.5 Hz, CHdCH trans-N),
6.77 (d, 2H, J ) 7.9 Hz, Hc), 7.08 (d, 2H, J ) 7.9 Hz, Hc),
7.34-7.63 (m, 15H, PPh2, H7, H3, H6, Hb), 7.90 (d, 2H, J ) 7.9
Hz, Hb), 7.96 (d, 1H, J ) 7.9 Hz, H5), 8.26 (d, 1H, J ) 8.5 Hz,
H4); 31P{1H} NMR (CDCl3, T ) 298 K, ppm) δ 24.9; IR (KBr
pellet) ν 1298, 1128 cm-1 (SdO). Anal. Calcd for C37H32NO4-
PPdS2: C, 58.77; H, 4.27; N, 1.85. Found: C, 58.62; H, 4.18; N,
1.82.
Synthesis of Complexes 3a,b. To a solution of complex 1a or
1b (0.2 mmol) in dry dichloromethane was added solid Z-tse
(0.0673 g, 0.2 mmol) under an inert atmosphere (argon). The
reaction mixture was stirred for 24 h, treated with activated charcoal,
and filtered off on a Celite layer. The clear solution was concen-
trated to a small volume under reduced pressure and diluted with
1
Selected data for 1a: H NMR (300 MHz, CDCl3, T ) 298 K,
ppm) δ 3.37 (s, 3H, OCH3 trans-P), 3.70 (s, 3H, OCH3 trans-N),
4.11 (t, 1H, JCHdCH ) 10.5 Hz, JPH ) 10.5 Hz, CHdCH trans-P),
4.52 (dd, 1H, JCHdCH ) 9.2 Hz, JPH ) 2.2 Hz, CHdCH trans-N),
7.33-7.48 (m, 8H, PPh2), 7.56 (dd; H, J ) 8.3 Hz; J ) 4.7 Hz,
H3), 7.63-7.70 (m, 2H, PPh2, H6), 7.96-8.01 (m, 2H, H5, H7),
8.37 (d, 1H, J ) 8.3 Hz, H4), 9.43 (d, 1H, J ) 4.7 Hz, H2); 31P{1H}
(20) Canovese, L.; Visentin, F.; Chessa, G.; Uguagliati, P.; Santo, C.;
Dolmella, A. Organometallics 2005, 24, 3297–3308.
(21) Ukai, T.; Kawazura, H.; Ishii, Y.; Bonnet, J. J.; Ibers, J. A. J.
Organomet. Chem. 1974, 65, 253–266.

Pd(0)-Catalyzed Cis–Trans Alkene Isomerizations
Organometallics, Vol. 27, No. 14, 2008 3581
diethyl ether to precipitate the title products as cream-colored
microcrystals (0.1240 g, yield 82.0% for 3a; 0.1215 g, yield 78.9%
for 3b).
C3), 125.5 (CH, C5), 127.0 (CH, Cb), 127.2 (C, C6), 128.4 (CH,
Cc), 137.1 (C, C4,7), 132.8 (CH, C9), 138.0 (CH, C4); 141.2 (C,
Ca), 141.6 (C, Cd), 145.6 (C, C7), 162.3 (C, C2); IR (KBr pellet) ν
1286, 1131 cm-1 (SdO). Anal. Calcd for C30H28N2O4PdS2: C,
55.34; H, 4.33; N, 4.30. Found: C, 55.22; H, 4.26; N, 4.39.
Selected data for 2e: 1H NMR (CDCl3, T ) 298 K, ppm) δ 2.29
(s, 3H, CH3), 2.42 (s, 3H, CH3), 4.01 (d, 1H, J ) 9.2 Hz, CHdC,
trans-N), 4.11 (d, 1H, J ) 9.2 Hz, CHdCH, trans-S), 4.36, 4.42
(AB system, 2H, J ) 16.1 Hz, CH2S), 7.01 (d, 2H, J ) 8.1 Hz,
Hc), 7.23 (d, 2H, J ) 8.1 Hz, Hc), 7.26-7.34 (m, 5H, H3, H5, H10,
H8), 7.63-7.68 (m, 4H, Hb, H9), 7.74 (d, 1H, J ) 7.7 Hz, H4),
7.94 (d, 2H, J ) 8.1 Hz), 9.67 (d, 1H, J ) 4.4 Hz, H6); 13C{1H}
NMR (CDCl3, T ) 298 K, ppm) δ 21.4 (CH3, PhCH3), 21.5 (CH3,
PhCH3), 47.5 (CH2, CH2S), 60.6 (CH, CHdCH, trans-S), 61.5 (CH,
CHdCH trans-N), 123.0 (CH, C3), 124.1 (CH, C5), 127.4 (CH,
Cb), 127.5 (CH, Cb), 128.7 (CH, Cc), 129.0 (CH, Cc), 129.2
(CH, C10), 129.3 (CH, C8), 131.9 (C, C7), 132.8 (CH, C9), 138.0
(CH, C4), 140.7 (C, Ca), 140.8 (C, Ca), 142.2 (C, Cd), 142.4 (C,
Cd), 155.2 (CH, C2), 156.9 (C, C6); IR (KBr pellet) ν 1293, 1136
cm-1 (SdO). Anal. Calcd for: C28H27NO4PdS3: C, 52.21; H, 4.22;
N, 2.17. Found: C, 52.27; H, 4.29; N, 2.26.
Selected data for 3a: 1H NMR (CDCl3, T ) 298 K, ppm) δ 2.37
(s, 3H, CH3), 2.39 (s, 3H, CH3), 4.18 (dd, 1H, JCHdCH ) 9.2 Hz,
JPH ) 9.2 Hz, CHdCH trans-P); 4.65 (dd, 1H, JCHdCH ) 9.2 Hz,
JPH ) 1.6 Hz, CHdCH trans-N), 6.94 (d, 2H, J ) 8.6 Hz, Hc),
6.97 (d, 2H, J ) 8.6 Hz, Hc), 7.39-7.44 (m, 10H, PPh2, Hb), 7.64
(dd, 1H, J ) 8.6 and 4.6 Hz, H3), 7.68-7.84 (m, 5H, PPh2, H7),
8.00-8.04 (m, 2H, H5, H6), 8.40 (d, 1H, J ) 8.6 Hz, H4), 10.22
(d, 1H, J ) 4.6 Hz, H2); 31P{1H} NMR (CDCl3, T ) 298 K, ppm)
δ 23.7; 13C{1H} NMR (CDCl3, T ) 298 K, ppm) δ 21.4 (CH3,
PhCH3, trans-P and trans-N), 60.5 (d, CH, JCP ) 50.5 Hz, CHdCH
trans-P), 64.6 (CH, CHdCH trans-N), 123.1 (CH, C3), 126.0 (CH,
Cb), 126.6 (CH, Cb), 127.4 (d, CH, JCP ) 4.3 Hz, H7), 129.0 (CH,
Cc), 129.1 (CH, Cc), 131.1 (CH, C5), 136.0 (d, C, JCP ) 32.9 Hz,
C8), 137.8 (CH, C6), 138.2 (CH, C4), 139.4 (C, Ca), 140.8 (C, Ca),
141.4 (C, Cd), 141.7 (C, Cd), 151.2 (C, C10), 151.5 (C, C9), 159.5
(CH, C6); IR (KBr pellet) ν 1295, 1141 cm-1 (SdO). Anal. Calcd
for C37H32NO4PPdS2: C, 58.77; H, 4.27; N, 1.85. Found: C, 58.88;
H, 4.38; N, 1.88.
Selected data for 3b: 1H NMR (CDCl3, T ) 298 K, ppm) δ
2.36 (s, 3H, CH3), 2.37 (s, 3H, CH3), 3.42 (s, 3H, CH3 quinoline),
4.13 (dd, 1H, JCHdCH ) 9.1 Hz, JPH ) 9.1 Hz, CHdCH trans-P),
4.50 (dd, 1H, JCHdCH ) 9.2 Hz, JPH ) 2.3 Hz, CHdCH trans-N),
6.91 (d, 2H, J ) 8.6 Hz, Hc), 6.94 (d, 2H, J ) 8.6 Hz, Hc),
7.37-7.47 (m, 10H, PPh2, Hb), 7.57-7.79 (m, 7H, PPh2, H3, H7,
H6), 7.96 (d, 1H, J ) 8.0 Hz, H5), 8.25 (d, 1H, J ) 8.5 Hz, H4);
31P{1H} NMR (CDCl3, T ) 298 K, ppm) δ 23.7; IR (KBr pellet)
ν 1297, 1136 cm-1 (SdO). Anal. Calcd for C37H32NO4PPdS2: C,
58.77; H, 4.27; N, 1.85. Found: C, 58.94; H, 4.36; N, 1.89.
Synthesis of Complexes 2c-e. Z-tse (0.0673 g, 0.2 mmol) was
added to a solution prepared by dissolving 0.2 mmol of complex
1c15 (or 1d16 or 1e15) in dry dichloromethane (15 mL). The reaction
mixture was stirred for 30 min and then evaporated to dryness in
vacuo. The resulting white solids were carefully washed first with
dry diethyl ether (3 × 5 mL) and then n-pentane (2 × 5 mL) (0.1635
g, yield 97.2% for 2c; 0.1226 g, yield 94.2% for 2d; 0.1190 g,
yield 92.4% for 2e).
Computational Details. The calculations were performed with
the Gaussian03 package22 at the B3PW91 level23 using Ahlrichs’s
def2-SVP24 basis set. The geometry optimizations were performed
without any symmetry constraint, followed by analytical frequency
calculations to confirm that a minimum or a transition state had
been reached. Cartesian coordinates and energies of stationary points
are reported in the Supporting Information.
Acknowledgment. We thank Profs. O. De Lucchi, F.
Fabris, and S. Cossu for helpful suggestions about the syn-
thesis of sulfones.
Supporting Information Available: Tables giving Cartesian
coordinates and energies of stationary points and figures giving
nonlinear regression fits. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM800305H
Selected data for 2c: 1H NMR (CDCl3, T ) 298 K, ppm) δ
2.12-2.59 (m, 4H, CH2P), 2.33 (s, 3H, CH3), 4.20 (m, AA′XX′
system, CHdCH, 2H), 6.96 (d, 4H, J ) 8.1 Hz, Hc), 7.40 (m, Ho
and Hp, 12H), 7.55 (d, 4H, J ) 8.2 Hz, Hb), 7.84 (m, Hm, 8H);
31P{1H} NMR (CDCl3, T ) 298 K, ppm) δ 41.8; 13C{1H} NMR
(CDCl3, T ) 298 K, ppm) δ 21.4 (CH3, PhCH3), 27.5 (m, AXX′
system, CH2, CH2P), 65.8 (d, CH, JCP ) 45.7 Hz, CHdCH), 126.8
(CH, Cb), 129.7 (CH, Cc), 141.4 (C, Ca), 141.5 (C, Cd); IR (KBr
pellet) ν 1292, 1138 cm-1 (SdO). Anal. Calcd for C42H40O4P2PdS2:
C, 59.96; H, 4.79%.. Found: C, 59.80; H, 4.74.
(22) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.;, Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,
C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.;
Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision
C.02; Gaussian, Inc., Wallingford, CT, 2004.
1
Selected data for 2d: H NMR (CDCl3, T ) 298 K, ppm): δ
2.30 (s, 6H, PhCH3), 3.25 (s, 6H, neoc-CH3), 4.31 (s, 2H, CHdCH),
6.96 (d, 4H, J ) 8.1 Hz, Hc), 7.60 (d, 2H, J ) 8.3 Hz, H3), 7.64
(d, 4H, J ) 8.1 Hz, Hb), 7.81 (s, 2H, H5), 8.23 (d, 2H, J ) 8.1 Hz,
H4); 13C{1H} NMR (CDCl3, T ) 298 K, ppm) δ 21.4 (CH3,
PhCH3), 29.9 (CH3, neoc-CH3), 55.2 (CH, CHdCH), 124.9 (CH,
(23) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(24) Weigenda, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, 3297.